publicationDate,title,abstract,id
2018-09-23,Ferromagnetic resonance in thin ferromagnetic film with surface anisotropy,"The ferromagnetic resonance frequencies are obtained for a thin ferromagnetic
film with surface anisotropy for the cases when the external magnetic field is
applied perpendicularly or parallel to the film surface, and for various
combinations of boundary conditions on the film surface. It is shown that in
the presence of surface anisotropy the ferromagnetic resonance frequency
essentially depends both on the film thickness and on the value of the surface
anisotropy constant. The results obtained provide a basis for the correct
interpretation of experimental data obtained by means of broadband
ferromagnetic resonance in thin film structures.",1809.08644v1
2010-10-06,Ferromagnetic Resonance in Spinor Dipolar Bose--Einstein Condensates,"We used the Gross--Pitaevskii equations to investigate ferromagnetic
resonance in spin-1 Bose--Einstein condensates with a magnetic dipole-dipole
interaction. By introducing the dipole interaction, we obtained equations
similar to the Kittel equations used to represent ferromagnetic resonance in
condensed matter physics. These equations indicated that the ferromagnetic
resonance originated from dipolar interaction, and that the resonance frequency
depended upon the shape of the condensate. Furthermore, spin currents driven by
spin diffusions are characteristic of this system.",1010.1075v1
2006-07-05,Theory of the spin-torque-driven ferromagnetic resonance in a ferromagnet/normal-metal/ferromagnet structure,"We present a theoretical analysis of current driven ferromagnetic resonance
in a ferromagnet/normal-metal/ferromagnet tri-layer. This method of driving
ferromagnetic resonance was recently realized experimentally by Tulapurkar et
al. [Nature 438, 339 (2005)] and Sankey et al. [Phys. Rev. Lett. 96, 227601
(2006)]. The precessing magnetization rectifies the alternating current applied
to drive the ferromagnetic resonance and leads to the generation of a dc
voltage. Our analysis shows that a second mechanism to generate a dc voltage,
rectification of spin currents emitted by the precessing magnetization, has a
contribution to the dc voltage that is of approximately equal size for the thin
ferromagnetic films used in the experiment.",0607145v2
2020-09-04,Detection of Ferromagnetic Resonance from 1 nm-thick Co,"To explore the further possibilities of nanometer-thick ferromagnetic films
(ultrathin ferromagnetic films), we investigated the ferromagnetic resonance
(FMR) of 1 nm-thick Co film. Whilst an FMR signal was not observed for the Co
film grown on a SiO2 substrate, the insertion of a 3 nm-thick amorphous Ta
buffer layer beneath the Co enabled the detection of a salient FMR signal,
which was attributed to the smooth surface of the amorphous Ta. This result
implies the excitation of FMR in an ultrathin ferromagnetic film, which can
pave the way to controlling magnons in ultrathin ferromagnetic films.",2009.01977v1
2011-08-05,Thermoelectric detection of ferromagnetic resonance of a nanoscale ferromagnet,"We present thermoelectric measurements of the heat dissipated due to
ferromagnetic resonance of a Permalloy strip. A microwave magnetic field,
produced by an on-chip coplanar strip waveguide, is used to drive the
magnetization precession. The generated heat is detected via Seebeck
measurements on a thermocouple connected to the ferromagnet. The observed
resonance peak shape is in agreement with the Landau-Lifshitz-Gilbert equation
and is compared with thermoelectric finite element modeling. Unlike other
methods, this technique is not restricted to electrically conductive media and
is therefore also applicable to for instance ferromagnetic insulators.",1108.1286v1
2011-12-03,Microwave-induced DC Signal in a Permalloy Thin Strip at Low Applied Magnetic Field,"We investigated the ferromagnetic resonance signals in a polycrystalline
permalloy thin strip under in-plane low static magnetic field. A series of DC
voltages, which contain ferromagnetic resonance or spin wave resonance signals,
were measured by inducing microwave frequencies greater than 10 gigahertz. The
resonant signals measured in low magnetic field show different properties from
those detected in high field condition. Based on the theory of DC effects in
ferromagnetic resonance and the experimental data of anisotropic
magnetoresistance, a quantitative model was proposed. We found that the shape
anisotropy significantly affects magnetization, and distorts the resonant
signals in low field condition.",1112.0610v1
2005-02-18,Resonances in Ferromagnetic Gratings Detected by Microwave Photoconductivity,"We investigate the impact of microwave excited spin excitations on the DC
charge transport in a ferromagnetic (FM) grating. We observe both resonant and
nonresonant microwave photoresistance. Resonant features are identified as the
ferromagnetic resonance (FMR) and ferromagnetic antiresonance (FMAR). A
macroscopic model based on Maxwell and Landau-Lifschitz equations reveals the
macroscopic nature of the FMAR. The experimental approach and results provide
new insight in the interplay between photonic, spintronic, and charge effects
in FM microstructures.",0502442v1
2018-08-12,Resonant Driving induced Ferromagnetism in the Fermi Hubbard Model,"In this letter we consider quantum phases and the phase diagram of a Fermi
Hubbard model under periodic driving that has been realized in recent cold atom
experiments, in particular, when the driving frequency is resonant with the
interaction energy. Due to the resonant driving, the effective Hamiltonian
contains a correlated hopping term where the density occupation strongly
modifies the hopping strength. Focusing on half filling, in addition to the
charge and spin density wave phases, large regions of ferromagnetic phase and
phase separation are discovered in the weakly interacting regime. The mechanism
of this ferromagnetism is attributed to the correlated hopping because the
hopping strength within a ferromagnetic domain is normalized to a larger value
than the hopping strength across the domain. Thus, the kinetic energy favors a
large ferromagnetic domain and consequently drives the system into a
ferromagnetic phase. We note that this is a different mechanism in contrast to
the well-known Stoner mechanism for ferromagnetism where the ferromagnetism is
driven by interaction energy.",1808.03966v2
2016-11-09,Theoretical study of the stripline ferromagnetic resonance response of metallic ferromagnetic films based on an analytical model,"We develop an advanced analytical model for calculating the broadband
stripline ferromagnetic resonance (FMR) response for metallic ferromagnetic
films, taking into account the exchange interaction as well as the exchange
boundary conditions at the film surface. This approach leads to simple
analytical expressions in the Fourier space. As a result, a numerical code
which implements inverse Fourier transform of these equations is very quick.
This allows us to explore a wide space of parameters as numerical examples of
application of this theory. In particular, we investigate the joint effect of
microwave eddy current shielding and magnetisation pinning at the ferromagnetic
film surfaces on the shape of the stripline FMR response of the film.",1611.02834v1
2018-08-03,Definition of the interlayer interaction type in magnetic multilayers analyzing the shape of the ferromagnetic resonance peaks,"We present theoretical study of ferromagnetic resonance in a system of two
coupled magnetic layers. We show that an interaction between the layers leads
to the occurrence of the so-called Fano resonance. The Fano resonance changes
the shape of the ferromagnetic resonance peak. It introduces a peak asymmetry.
The asymmetry type is defined by the sign of the interaction between the
magnetic layers. Therefore, studying the shape of the ferromagnetic resonance
peaks one can define the type of the interlayer coupling (ferromagnetic or
antiferromagnetic). We show that using numerical simulations one can estimate a
magnitude of the interaction by fitting the asymmetric resonance peaks.",1808.01296v1
2009-07-14,Localized ferromagnetic resonance force microscopy in permalloy-cobalt films,"We report Ferromagnetic Resonance Force Microscopy (FMRFM) experiments on a
justaposed continuous films of permalloy and cobalt. Our studies demonstrate
the capability of FMRFM to perform local spectroscopy of different
ferromagnetic materials. Theoretical analysis of the uniform resonance mode
near the edge of the film agrees quantitatively with experimental data. Our
experiments demonstrate the micron scale lateral resolution in determining
local magnetic properties in continuous ferromagnetic samples.",0907.2415v1
2009-10-13,Resonant coupling of coplanar waveguides with ferromagnetic tubes,"Resonant coupling of coplanar waveguides is explored by wrapping proximate
shorted ends of the waveguides with micron size ferromagnetic Co90Ta5Zr5 tubes.
Ferromagnetic resonance and up to 7 outer surface modes are identified.
Experimental results for these contorted rectangular tubes are in good
agreement with micromagnetic simulations and model calculations of
magnetostatic modes for an elliptical ferromagnetic tube. These results
indicate that the modes are largely determined by tube topology and dimensions
but less so by the detailed shape.",0910.2442v1
2010-12-10,Spin-orbit driven ferromagnetic resonance: A nanoscale magnetic characterisation technique,"We demonstrate a scalable new ferromagnetic resonance (FMR) technique based
on the spin-orbit interaction. An alternating current drives FMR in uniform
ferromagnetic structures patterned from the dilute magnetic semiconductors
(Ga,Mn)As and (Ga,Mn)(As,P). This allows the direct measurement of magnetic
anisotropy coefficients and damping parameters for individual nano-bars. By
analysing the ferromagnetic resonance lineshape, we perform vector magnetometry
on the current-induced driving field, observing contributions with symmetries
of both the Dresselhaus and Rashba spin-orbit interactions.",1012.2397v1
2015-02-17,Direct Observation of Ferromagnetic State in Gold Nanorods Probed using Electron Spin Resonance Spectroscopy,"X-band electron spin resonance (ESR) spectroscopy has been performed for gold
nanorods (AuNRs) of four different sizes covered with a diamagnetic stabilizing
component, cetyltrimethylammmonium bromide. The ESR spectra show ferromagnetic
features such as hysteresis and resonance field shift, depending on the size of
the AuNRs. In addition, the ferromagnetic transition is indicated by an abrupt
change in the spectra of the two smallest AuNRs studied. A large g-value in the
paramagnetic region suggests that the ferromagnetism in the AuNRs originates
from strong spin-orbit interaction.",1502.04934v1
2006-09-05,Electrical detection of spin pumping due to the precessing magnetization of a single ferromagnet,"We report direct electrical detection of spin pumping, using a lateral normal
metal/ferromagnet/normal metal device, where a single ferromagnet in
ferromagnetic resonance pumps spin polarized electrons into the normal metal,
resulting in spin accumulation. The resulting backflow of spin current into the
ferromagnet generates a d.c. voltage due to the spin dependent conductivities
of the ferromagnet. By comparing different contact materials (Al and /or Pt),
we find, in agreement with theory, that the spin related properties of the
normal metal dictate the magnitude of the d.c. voltage.",0609089v1
2020-08-08,Two-magnon frequency-pulling effect in ferromagnetic resonance,"We report the experimental observation in thin films of the hybridization of
the uniform ferromagnetic resonance mode with nonuniform magnons as a result of
the two-magnon scattering mechanism, leading to a frequency-pulling effect on
the ferromagnetic resonance. This effect, when not properly accounted for,
leads to a discrepancy in the dependence of the ferromagnetic resonance field
on frequency for different field orientations. The frequency-pulling effect is
the complement of the broadening of the ferromagnetic resonance lineshape by
two-magnon scattering and can be calculated using the same parameters. By
accounting for the two-magnon frequency shifts through these means, consistency
is achieved in fitting data from in-plane and perpendicular-to-plane resonance
conditions.",2008.03423v2
2022-04-04,Voltage-driven exchange resonance achieving 100\% mechanical efficiency,"Magnetic resonances driven by current-induced torques are crucial tools to
study magnetic materials but are very limited in frequency and mechanical
efficiency. We propose an alternative mechanism, voltage-induced torque, to
realize high efficiency in generating high-frequency magnetization dynamics.
When a ferromagnet-topological insulator-ferromagnet trilayer heterostructure
is operated as an adiabatic quantum motor, voltage-induced torque arises from
the adiabatic motion of gapped topological electrons on the two interfaces and
act oppositely on the two ferromagnetic layers, which can excite the exchange
mode where the two ferromagnetic layers precess with a $\pi$-phase difference.
The exchange mode resonance, bearing a much higher frequency than the
ferromagnetic resonance, is accompanied by topological charge pumping, leading
to a sharp peak in electrical admittance at the resonance point. Because the
output current is purely adiabatic while dissipative current vanishes
identically, the proposed voltage-driven exchange resonance entails a
remarkably high mechanical efficiency close to unity, which is impossible in
any current-driven systems.",2204.03534v2
1995-05-26,Stochastic resonance in a system of ferromagnetic particles,"We show that a dispersion of monodomain ferromagnetic particles in a solid
phase exhibits stochastic resonance when a driven linearly polarized magnetic
field is applied. By using an adiabatic approach, we calculate the power
spectrum, the distribution of residence times and the mean first passage time.
The behavior of these quantities is similar to their corresponding ones in
other systems in which stochastic resonance has also been observed.",9505136v1
2002-07-19,Cyclotron Resonance of Itinerant Holes in Ferromagnetic InMnAs/GaSb Heterostructures,"We report the first observation of hole cyclotron resonance (CR) in
ferromagnetic InMnAs/GaSb heterostructures both in the high-temperature
paramagnetic phase and the low-temperature ferromagnetic phase. We clearly
resolve two resonances that exhibit strong temperature dependence in position,
linewidth, and intensity. We attribute the two resonances to the so-called
fundamental CR transitions expected for delocalized holes in the valence band
in the magnetic quantum limit, demonstrating the existence of $p$-like
itinerant holes that are describable within the Luttinger-Kohn effective mass
theory.",0207485v1
2010-09-21,Electron Spin Resonance of the ferromagnetic Kondo lattice CeRuPO,"The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated
by Electron Spin Resonance (ESR) at microwave frequencies of 1, 9.4, and
34~GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+
resonance in a metallic Ce compound and can be followed below the ferromagnetic
transition temperature Tc=14 K. At T>Tc the interplay between the RKKY-exchange
interaction and the crystal electric field anisotropy determines the ESR
parameters. Near Tc the spin relaxation rate is influenced by the critical
fluctuations of the order parameter.",1009.4108v1
2021-03-15,Ferromagnetic Resonance in Permalloy Metasurfaces,"Permalloy films with one-dimensional (1D) profile modulation of submicron
periodicity are fabricated based on commercially available DVD-R discs and
studied using ferromagnetic resonance (FMR) method and micromagnetic numerical
simulations. The main resonance position shows in-plane angular dependence
which is strongly reminiscent of that in ferromagnetic films with uniaxial
magnetic anisotropy. The main signal and additional low field lines are
attributed to multiple standing spin wave resonances defined by the grating
period. The results may present interest in magnetic metamaterials and
magnonics applications.",2103.08704v1
2022-01-26,Local ferromagnetic resonance measurements of mesoscopically patterned ferromagnets using deterministically placed nanodiamonds,"Nitrogen-vacancy centers in diamond have recently been established as
effective sensors of the magnetization dynamics in vicinal ferromagnetic
materials. We demonstrate sub-100 nm placement accuracy of
nitrogen-vacancy-containing nanodiamonds and use these as local sensors that
probe optically detected ferromagnetic resonance in mesoscopically patterned
Permalloy islands. These measurements reveal variations in the ferromagnetic
resonance signal at different sites on these structures with distinct behavior
in the edge and the bulk of patterned features. These test measurements
establish an easily implemented approach for spatially targeted measurements of
spin dynamics in mesoscale ferromagnets. In principle, the methodology can also
be extended to local studies of nanoscale ferromagnets such as single magnetic
nanowires and nanoparticles.",2201.10722v1
2022-06-12,Interference phenomena in Josephson junctions with ferromagnetic bilayers: Spin-triplet correlations and resonances,"We study the Josephson effect in planar $SF_1F_2S$ junctions that consist of
conventional $s$-wave superconductors ($S$) connected by two metallic
monodomain ferromagnets ($F_1$ and $F_2$) with arbitrary transparency of
interfaces. We solve the scattering problem in the clean limit based on the
Bogoliubov-de Gennes equation for both spin-singlet and odd in frequency
spin-triplet pairing correlations. We calculate numerically the Josephson
current-phase relation $I(\phi)$. While the first harmonic of $I(\phi)$ is
completely generated by spin-singlet and short-range spin-triplet
superconducting correlations, for noncollinear magnetizations of ferromagnetic
layers the second harmonic has an additional long-range spin-triplet component.
Therefore, for strong ferromagnetic influence, the long-range spin-triplet
contribution to the second harmonic dominates. We find an exception due to the
geometric resonance for equal ferromagnetic layers when the first harmonic is
strongly enhanced. Both first and second harmonic amplitudes oscillate with
ferromagnetic layer thicknesses due to $0-\pi$ transitions. We study the
influence of interface transparencies and find additional resonances for finite
transparency of interface between ferromagnetic layers.",2206.05770v3
2020-05-30,Magnetization dynamics in proximity-coupled superconductor/ferromagnet/superconductor multilayers,"In this work, magnetization dynamics is studied in
superconductor/ferromagnet/superconductor three-layered films in a wide
frequency, field, and temperature ranges using the broad-band ferromagnetic
resonance measurement technique. It is shown that in presence of both
superconducting layers and of superconducting proximity at both
superconductor/ferromagnet interfaces a massive shift of the ferromagnetic
resonance to higher frequencies emerges. The phenomenon is robust and
essentially long-range: it has been observed for a set of samples with the
thickness of ferromagnetic layer in the range from tens up to hundreds of
nanometers. The resonance frequency shift is characterized by proximity-induced
magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the
drop of magnetization. The shift and the corresponding uniaxial anisotropy grow
with the thickness of the ferromagnetic layer. For instance, the anisotropy
reaches 0.27~T in experiment for a sample with 350~nm thick ferromagnetic
layer, and about 0.4~T in predictions, which makes it a ferromagnetic film
structure with the highest anisotropy and the highest natural resonance
frequency ever reported. Various scenarios for the superconductivity-induced
magnetic anisotropy are discussed. As a result, the origin of the phenomenon
remains unclear. Application of the proximity-induced anisotropies in
superconducting magnonics is proposed as a way for manipulations with a
spin-wave spectrum.",2006.00348v1
2019-12-03,Nanoscale Tantalum Layer Controlling the Magnetic Coupling between Two Ferromagnetic Electrodes via Insulator of a Magnetic Tunnel Junction,"Ability to tailor the nature of the magnetic coupling between two
ferromagnetic electrodes can enable the realization of new spintronics device
systems. This paper discusses our finding that deposition of an ultrathin
tantalum (Ta) on the NiFe top electrode reversed the nature of
inter-ferromagnetic electrode coupling. We observed that the deposition of ~ 5
nm Ta on the top of a magnetic tunnel junction with Ta( 2 nm)/Co(5 nm)/NiFe (5
nm)/AlOx( 2 nm)/NiFe (10-15 nm) configuration changed the magnetic coupling
between two ferromagnetic electrodes from antiferromagnetic to ferromagnetic.
We investigated Ta effect using multiple magnetic characterizations like
ferromagnetic resonance, magnetometry, and polarized neutron reflectometry.
Ferromagnetic resonance characterization was very sensitive for detecting the
changes in magnetic coupling via the insulating spacer. This simple approach of
adding Ta film to alter the magnetic coupling can impact the other burgeoning
areas like molecular spintronics. We found that preexisting magnetic coupling
between two ferromagnetic electrodes impacted the resultant magnetic properties
of magnetic tunnel junctions based molecular spintronics devices.",1912.01331v1
2007-01-14,Sr1.5Ba0.5Zn2Fe12O22 Hexaferrites Ferromagnetic Resonance and Nonlinear Excitation for Magneto-Electric Devices,"A magneto electric (ME) effect was reported [1] for the insulator material of
helimagnetic hexaferrite of Sr1.5Ba0.5Zn2Fe12O22. In this study we are
interested in investigating this materials ferromagnetic resonance to define
its internal anisotropy fields. By using a vibrating sample magnetometer (VSM)
and ferromagnetic resonance (FMR) analysis we realized that this helical
hexaferrite has about -0.5 kOe exchange anisotropy field of HE. Also, by using
an alternative free energy model we derived this materials Polder tensor and
its ferromagnetic resonance condition. Meanwhile, we were able to show a
potential magneto electric coupling by nonlinear excitation of planar helical
hexaferrite, in which a magnetic nonlinear excitation is integrated into
dielectric permittivity.
  Index Terms, Ferrites, ferromagnetic resonances, and magnetic nonlinear
excitations.",0701309v2
2023-07-31,Gating ferromagnetic resonance of magnetic insulators by superconductors via modulating electric-field radiation,"We predict that ferromagnetic resonance in insulating magnetic film with
inplane magnetization radiates electric fields polarized along the
magnetization with opposite amplitudes at two sides of the magnetic insulator,
which can be modulated strongly by adjacent superconductors. With a single
superconductor adjacent to the magnetic insulator this radiated electric field
is totally reflected with a $\pi$-phase shift, which thereby vanishes at the
superconductor side and causes no influence on the ferromagnetic resonance.
When the magnetic insulator is sandwiched by two superconductors, this
reflection becomes back and forth, so the electric field exists at both
superconductors that drives the Meissner supercurrent, which in turn shifts
efficiently the ferromagnetic resonance. We predict an ultrastrong coupling
between magnons in the yttrium iron garnet and Cooper pairs in NbN with the
frequency shift achieving tens of percent of the bare ferromagnetic resonance.",2307.16472v2
2015-09-16,Fano resonance in a normal metal/ferromagnet-quantum dot-superconductor device,"We investigate theoretically the Andreev transport through a quantum dot
strongly coupled with a normal metal/ferromagnet and a superconductor
(N/F-QD-S), in which the interplay between the Kondo resonance and the Andreev
bound states (ABSs) has not been clearly clarified yet. Here we show that the
interference between the Kondo resonance and the ABSs modifies seriously the
lineshape of the Kondo resonance, which manifests as a Fano resonance. The
ferromagnetic lead with spin-polarization induces an effective field, which
leads to splitting both of the Kondo resonance and the ABSs. The
spin-polarization together with the magnetic field applied provides an
alternative way to tune the lineshape of the Kondo resonances, which is
dependent of the relative positions of the Kondo resonance and of the ABSs.
These results indicate that the interplay between the Kondo resonance and the
ABSs can significantly affect the Andreev transport, which could be tested by
experiments.",1509.04801v1
2022-04-18,Influence of the presence of multiple resonances on material parameter determination using broadband ferromagnetic resonance spectroscopy,"The influence of the presence of multiple resonances in ferromagnetic
resonance spectra on extracted material parameters is investigated using
numerical simulations. Our results show that the systematic error of assuming
an incorrect number of resonances for a material can lead to the extraction of
material parameters that significantly deviate from any of the true material
parameters. When noise is present in experimental ferromagnetic resonance
spectra increasing the frequency range of the broadband characterization can
significantly reduce the error-margins when the data is analyzed assuming the
correct number of resonances present in the material. For the cases
investigated in this study it was found that analyzing the data using a single
resonance results in extracted gyromagnetic ratios and effective magnetization
parameters that are consistent with the weighted average of the true material
parameters. We further provide a cautionary example regarding the extraction of
the inhomogeneous linewidth broadening and damping parameters of materials that
contain an unknown number of resonances.",2204.08500v1
1999-01-26,Resonant transmission of normal electrons through Andreev states in ferromagnets,"Giant oscillations of the conductance of a superconductor - ferromagnet -
superconductor Andreev interferometer are predicted. The effect is due to the
resonant transmission of normal electrons through Andreev levels when the
voltage $V$ applied to the ferromagnet is close to $2h_0/e$ ($h_0$ is the
spin-dependant part of the electron energy). The effect of bias voltage and
phase difference between the superconductors on the current and the
differential conductance is presented. These efects allow a direct spectroscopy
of Andreev levels in the ferromagnet.",9901278v1
2006-08-01,Voltage generation by ferromagnetic resonance,"A ferromagnet can resonantly absorbs rf radiation to sustain a steady
precession of the magnetization around an internal or applied magnetic field.
We show that under these ferromagnetic resonance (FMR) conditions, a dc voltage
is generated at a normal-metal electric contact to a ferromagnet with spin-flip
scattering. This mechanism allows an easy electric detection of magnetization
dyamics.",0608022v1
2013-12-23,Magnetic states and ferromagnetic resonance in geometrically frustrated arrays of multilayer ferromagnetic nanoparticles ordered on triangular lattices,"We present a theoretical investigation of magnetostatic interaction effects
in geometrically frustrated arrays of anisotropic multilayer ferromagnetic
nanoparticles arranged in different spatially configured systems with
triangular symmetry. We show that the interlayer magnetostatic interaction
significantly expands the opportunities to create magnetically frustrated
systems. The effects of the magnetostatic interaction in magnetization reversal
processes and the possibility to control the ferromagnetic resonance spectrum
in such systems are discussed.",1312.6478v2
2016-10-21,Electromotive forces generated in 3d-transition ferromagnetic metal films themselves under their ferromagnetic resonance,"We report the electromotive force (EMF) properties generated in 3d-transition
ferromagnetic metal (FM = Fe, Co, and Ni80Fe20) films themselves under their
ferromagnetic resonance (FMR). For Fe and Co films, the EMF due to the
anomalous-Hall effect is dominantly generated under their FMR. Meanwhile, for a
Ni80Fe20 film, the EMF due to the inverse spin-Hall effect in the Ni80Fe20 film
itself under the FMR is mainly generated. This tendency is qualitatively
explained with differences of the spin polarization, the spin Hall
conductivity, the anomalous Hall conductivity, the magnetization saturation,
and the resistivity of the FM films.",1610.06695v2
2021-04-24,Theory of magnetic inertial dynamics in two-sublattice ferromagnets,"The magnetic inertial dynamics have been investigated for one sublattice
ferromagnets. Here, we develop the magnetization dynamics in two-sublattice
ferromagnets including the intra- and inter-sublattice inertial dynamics.
First, we derive the magnetic susceptibility of such a ferromagnet. Next, by
finding the poles of the susceptibility, we calculate the precession and
nutation resonance frequencies. Our results suggest that while the resonance
frequencies show decreasing behavior with the increasing intra-sublattice
relaxation time, the effect of inter-sublattice inertial dynamics is
contrasting.",2104.11878v2
2022-01-16,Ferromagnetic resonance modulation in $d$-wave superconductor/ferromagnetic insulator bilayer systems,"We investigate ferromagnetic resonance (FMR) modulation in $d$-wave
superconductor (SC)/ferromagnetic insulator (FI) bilayer systems theoretically.
The modulation of the Gilbert damping in these systems reflects the existence
of nodes in the $d$-wave SC and shows power-law decay characteristics within
the low-temperature and low-frequency limit. Our results indicate the
effectiveness of use of spin pumping as a probe technique to determine the
symmetry of unconventional SCs with high sensitivity for nanoscale thin films.",2201.06060v2
2003-04-04,Dynamic exchange coupling and Gilbert damping in magnetic multilayers,"We theoretically study dynamic properties of thin ferromagnetic films in
contact with normal metals. Moving magnetizations cause a flow of spins into
adjacent conductors, which relax by spin flip, scatter back into the
ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins
outside the moving magnetization enhances the overall damping of the
magnetization dynamics in accordance with the Gilbert phenomenology. Transfer
of spins between different ferromagnets by these nonequilibrium spin currents
leads to a long-ranged dynamic exchange interaction and novel collective
excitation modes. Our predictions agree well with recent
ferromagnetic-resonance experiments on ultrathin magnetic films.",0304116v1
2012-11-12,Spin polarization and magnetoresistance through a ferromagnetic barrier in bilayer graphene,"We study spin dependent transport through a magnetic bilayer graphene
nanojunction configured as two dimensional normal/ferromagnetic/normal
structure where the gate-voltage is applied on the layers of ferromagnetic
graphene. Based on the fourband Hamiltonian, conductance is calculated by using
Landauer Butikker formula at zero temperature. For parallel configuration of
the ferromagnetic layers of bilayer graphene, the energy band structure is
metallic and spin polarization reaches to its maximum value close to the
resonant states, while for antiparallel configuration, the nanojunction behaves
as a semiconductor and there is no spin filtering. As a result, a huge
magnetoresistance is achievable by altering the configurations of ferromagnetic
graphene especially around the band gap.",1211.2701v1
2003-04-18,Elementary Excitations of Ferromagnetic Metal Nanoparticles,"We present a theory of the elementary spin excitations in transition metal
ferromagnet nanoparticles which achieves a unified and consistent quantum
description of both collective and quasiparticle physics. The theory starts by
recognizing the essential role played by spin-orbit interactions in determining
the energies of ferromagnetic resonances in the collective excitation spectrum
and the strength of their coupling to low-energy particle-hole excitations. We
argue that a crossover between Landau-damped ferromagnetic resonance and
pure-state collective magnetic excitations occurs as the number of atoms in
typical transition metal ferromagnet nanoparticles drops below approximately
$10^4$, approximately where the single-particle level spacing, $\delta$,
becomes larger than, $\sqrt{\alpha} E_{\rm res}$, where $E_{\rm res}$ is the
ferromagnetic resonance frequency and $\alpha$ is the Gilbert damping
parameter. We illustrate our ideas by studying the properties of semi-realistic
model Hamiltonians, which we solve numerically for nanoparticles containing
several hundred atoms. For small nanoparticles, we find one isolated
ferromagnetic resonance collective mode below the lowest particle-hole
excitation energy, at $E_{\rm res} \approx 0.1$ meV. The spectral weight of
this pure excitation nearly exhausts the transverse dynamical susceptibility
spectral weight. As $\delta$ approaches $\sqrt{\alpha} E_{\rm res}$, the
ferromagnetic collective excitation is more likely to couple strongly with
discrete particle-hole excitations. In this regime the distinction between the
two types of excitations blurs. We discuss the significance of this picture for
the interpretation of recent single-electron tunneling experiments.",0304427v1
2020-05-28,Spin-Pumping-Induced Non-Linear Electric Current on the Surface of a Ferromagnetic Topological Insulator,"We investigate the spin-pumping-induced electric current on the surface of a
three-dimensional topological insulator hybridized with a ferromagnet, namely,
ferromagnetic topological insulator. In order to do this, we establish the
microscopic formalism and construct the perturbation theory using a Keldysh
Green's function approach. We analyze how this electric current is generated by
an exchange interaction and an external ac magnetic field, which is the driving
force of ferromagnetic resonance as well as the spin pumping. The mechanism is
as follows. First, the ferromagnetic resonance is driven and a zero-momentum
magnon emerges. It is the fluctuation from the saturation magnetization
pointing parallel to the precession axis of the ferromagnetic resonance. After
then, the spin pumping is generated with the zero-momentum magnon being the
carrier of spin. The zero-momentum magnon and the topological insulator surface
state couples through the exchange interaction and the spin carried by the
magnon is transferred to it. Owing to the spin-momentum locking, the
transferred spin is converted into the momentum of topological insulator
surface state leading to the generation of electric current flowing
perpendicular to the precession axis of the ferromagnetic resonance. It is
quadratic in the amplitude of external ac magnetic field whereas it is linear
to the strength of the exchange interaction. The associated electric voltage is
described by the spectrum of zero-momentum magnon. The non-linearity of
spin-pumping-induced electric current in the ac magnetic field as well as the
linearity in the exchange-interaction strength reflects that the surface of
ferromagnetic topological insulator has a high-performing functionality of
generating the electric charge current by magnetic controlling.",2005.13850v1
2010-09-19,Effect of spin transfer torque on the magnetic domain wall ferromagnetic resonance frequency in the nanowires,"We investigate the influence of the domain wall ferromagnetic resonance
frequency on the spin transfer torque in a ferromagnetic nanowire. By employing
micromagnetic simulations with the spin transfer torque, we find that the
domain wall resonance frequency decreases with increasing spin polarized
current density, when there is no change in the resonance frequency of the
domain itself. Surprisingly, the variation of the resonance frequency is
remarkable (> 1.6 GHz) with the spin transfer torque even though the domain
wall is pinned. Since the presented domain wall ferromagnetic resonance study
has been performed for the pinned domain wall, the contributions of extrinsic
defects are excluded. It is strong advantages of the present study, since the
effects of extrinsic pinning sites are inevitable in the imaging or transport
measurements.",1009.3618v1
1993-12-03,Dynamic Domains Above the Ferromagnetic Resonance Instability,"A simplified model is introduced and analysed to show, that for the
Landau-Lifshitz equation stable, steady state solutions of domain type exist in
ferromagnetic systems, strongly driven by external transverse fields. These
dynamic domain states are able to describe the drastic reduction of the power
absorption found experimentally above the instability of the homogeneous
magnetisation. The excitations of the domain states are presented and the
relevance of the model for real ferromagnets is discussed.",9312015v1
2001-09-17,Ferromagnetic resonance in periodic particle arrays,"We report measurements of the ferromagnetic resonance (FMR) spectra of arrays
of submicron size periodic particle arrays of permalloy produced by
electron-beam lithography. In contrast to plane ferromagnetic films, the
spectra of the arrays show a number of additional resonance peaks, whose
position depends strongly on the orientation of the external magnetic field and
the interparticle interaction. Time-dependent micromagnetic simulation of the
ac response show that these peaks are associated with coupled exchange and
dipolar spin wave modes",0109307v1
2003-07-21,Nuclear Magnetic Resonance in a Ferromagnet-Semiconductor Heterostructure,"We report the observation of nuclear magnetic resonance (NMR) in a
ferromagnet-semiconductor heterostructure in the presence of a spin-polarized
current. Spin-polarized electrons injected from a metallic ferromagnet generate
a large nuclear spin population in a GaAs quantum well by dynamic polarization.
The characteristic time for the polarization process is approximately 20 sec,
and the nuclear polarization can persist for several minutes after the current
is turned off. Resonant depolarization is observed in the presence of an AC
magnetic field or when the injection current is modulated at the NMR frequency.",0307512v1
2004-09-05,Bias voltage controlled magnetization switch in ferromagnetic semiconductor resonant tunneling diodes,"We predict that the Curie temperature of a ferromagnetic resonant tunneling
diode will decrease abruptly, by approximately a factor of two, when the
downstream chemical potential falls below the quantum well resonance energy.
This property follows from elementary quantum transport theory notions combined
with a mean field description of diluted magnetic semiconductor ferromagnetism.
We illustrate this effect by solving coupled non-equilibrium Green's function,
magnetic mean-field, and electrostatic Poisson equations self-consistently to
predict the bias voltage and temperature dependence of the magnetization of a
model system.",0409106v2
2006-02-04,Spin-transfer-driven ferromagnetic resonance of individual nanomagnets,"We demonstrate a technique that enables ferromagnetic resonance (FMR)
measurements of the normal modes for magnetic excitations in individual
nanoscale ferromagnets, smaller in volume by a factor of 1000 than can be
probed by other methods. The measured peak shapes indicate two regimes of
response: simple FMR and phase locking. Studies of the resonance frequencies,
amplitudes, and linewidths as a function of microwave power, DC current, and
magnetic field provide detailed new information about the exchange, damping,
and spin-transfer torques that govern the dynamics in magnetic nanostructures.",0602105v1
2006-07-03,On-chip detection of ferromagnetic resonance of a single submicron permalloy strip,"We measured ferromagnetic resonance of a single submicron ferromagnetic
strip, embedded in an on-chip microwave transmission line device. The method
used is based on detection of the oscillating magnetic flux due to the
magnetization dynamics, with an inductive pick-up loop. The dependence of the
resonance frequency on applied static magnetic field agrees very well with the
Kittel formula, demonstrating that the uniform magnetization precession mode is
being driven.",0607036v1
2009-04-11,Coupled Superconducting Phase and Ferromagnetic Order Parameter Dynamics,"Via a direct coupling between the magnetic order parameter and the singlet
Josephson supercurrent, we detect spin-wave resonances, and their dispersion,
in ferromagnetic Josephson junctions in which the usual insulating or metallic
barrier is replaced with a weak ferromagnet. The coupling arises within the
Fraunhofer interferential description of the Josephson effect, because the
magnetic layer acts as a time dependent phase plate. A spin-wave resonance at a
frequency ws implies a dissipation that is reflected as a depression in the
current-voltage curve of the Josephson junction when hbar ws = 2eV. We have
thereby performed a resonance experiment on only 10^7 Ni atoms.",0904.1780v1
2012-03-01,Current-induced resonance in a ferromagnet - antiferromagnet junction,"We calculate the response of a ferromagnet - antiferromagnet junction to a
high-frequency magnetic field as a function of the spin-polarized current
through the junction. Conditions are choused under which the response is zero
in absence of such a current. It is shown that increasing in the current
density leads to proportional increase in the resonance frequency and resonant
absorption. A principal possibility is indicated of using ferromagnet -
antiferromagnet junction as a terahertz radiation detector.",1203.0114v1
2015-03-12,Chirp spectroscopy applied to the characterization of Ferromagnetic Resonance in Magnetic Tunnel Junctions,"Magnetic Tunnel Junction devices find use in several applications based on
the exploitation of the Spin-Transfer Torque phenomenon. The Ferromagnetic
Resonance curve is a key characteristic of any Magnetic Tunnel Junctions. It is
usually characterized both experimentally and numerically by performing a lot
of measurements of the magnetic response to a sinusoidal field or current. Here
we propose the use of a chirp signal as excitation signal to reconstruct the
Ferromagnetic resonance curve with a single measurement/simulation. A
micromagnetic comparison of the proposed method with the traditional one is
shown.",1503.03719v1
2016-07-20,A microwave interferometer of the Michelson-type to improve the dynamic range of broadband ferromagnetic resonance measurements,"We present a Michelson-type microwave interferometer for use in ferromagnetic
resonance experiments. The interferometer is capable of broadband operation
without manual adjustment of phase delay or amplitude attenuation. A prototype
of the design shows significant improvement of the signal-to-noise ratio when
compared to non-interferometric ferromagnetic resonance experiments. We
demonstrate that this increase in sensitivity can lead to a drastic increase in
the data acquisition rate for hard-to-measure thin films that otherwise would
require long integration times.",1607.06137v2
2019-07-06,Angle-resolved broadband ferromagnetic resonance apparatus enabled through a spring-loaded sample mounting manipulator,"Broadband ferromagnetic resonance is a useful technique to determine the
magnetic anisotropy and study the magnetization dynamics of magnetic thin
films. We report a spring-loaded sample loading manipulator for reliable sample
mounting and rotation. The manipulator enables maximum signal, enhances system
stability and is particularly useful for fully automated in-plane-field
angle-resolved measurements. This angle-resolved broadband ferromagnetic
resonance apparatus provides a viable method to study anisotropic damping and
weak magnetic anisotropies, both vital for fundamental research and
applications.",1907.03097v1
2017-11-07,Dzyaloshinskii-Moriya interaction induced extrinsic linewidth broadening of ferromagnetic resonance,"For a thin ferromagnetic film with the Dzyaloshinskii-Moriya interaction
(DMI), we derive an expression of the extrinsic ferromagnetic resonance (FMR)
linewidth in a quantum mechanical way, taking into account scatterings from
structural inhomogeneity. In the presence of the DMI, the magnon dispersion
exhibits rich resonant states, especially in small external magnetic fields and
strong DMI strength. It is found that the FMR linewidth shows several
characteristic features such as a finite linewidth at zero frequency and peaks
in the low frequency range.",1711.02263v1
2020-08-27,Nutation Resonance in Ferromagnets,"The inertial dynamics of magnetization in a ferromagnet is investigated
theoretically. The analytically derived dynamic response upon microwave
excitation shows two peaks: ferromagnetic and nutation resonances. The exact
analytical expressions of frequency and linewidth of the magnetic nutation
resonance are deduced from the frequency dependent susceptibility determined by
the inertial Landau-Lifshitz-Gilbert equation. The study shows that the
dependence of nutation linewidth on the Gilbert precession damping has a
minimum, which becomes more expressive with increase of the applied magnetic
field.",2008.12221v3
2014-08-07,Ferromagnetic resonance of a magnetic dimer with dipolar coupling,"We develop a general formalism for analyzing the ferromagnetic resonance
characteristics of a magnetic dimer consisting of two magnetic elements (in a
horizontal or vertical configuration) coupled by dipolar interaction, taking
account of their finite-size and aspect ratio. We study the effect on the
resonance frequency and resonance field of the applied magnetic field (in
amplitude and direction), the inter-element coupling, and the uniaxial
anisotropy in various configurations. We obtain analytical expressions for the
resonance frequency in various regimes of the interlayer coupling. We
(numerically) investigate the behavior of the resonance field in the
corresponding regimes. The critical value of the applied magnetic field at
which the resonance frequency vanishes may be an increasing or a decreasing
function of the dimer's coupling, depending on the anisotropy configuration. It
is also a function of the nanomagnets aspect ratio in the case of in-plane
anisotropy. This and several other results of this work, when compared with
experiments using the standard ferromagnetic resonance with fixed frequency, or
the network analyzer with varying frequency and applied magnetic field, provide
a useful means for characterizing the effective anisotropy and coupling within
systems of stacked or assembled nanomagnets.",1408.1594v1
2018-08-25,Resonance spin transfer torque in ferromagnetic/normal/ferromagnetic spin-valve structure of topological insulators,"We theoretically study the spin current and spin-transfer torque generation
in a conventional spin- valve hybrid structure of type ferromagnetic/normal
metal/ferromagnetic (FM/NM/FM) made of the topological insulator (TI), in which
a gate voltage is attached to the normal layer. We demonstrate the penetration
of the spin-transfer torque into the right ferromagnetic layer and show that,
unlike graphene spin-valve junction, the spin-transfer torque in TI is very
sensitive to the chemical potential of the NM region. As an important result,
by changing the chemical potential of the NM spacer and magnetization
directions, one can control all components of the STT. Interestingly, both the
resonance spin current and the resonance spin-transfer torque appear for
energies determined from a resonance equation. By increasing the chemical
potential of the NM spacer, the amplitude of the STTs decreases while at large
chemical potentials of $\mu_N$ there are intervals of chemical potential in
which both the spin current and the spin-transfer torque become zero. These
findings could open new perspectives for applications in spin-transfer torque
magnetic random access memory (STT-MRAM) devices based on TI.",1808.08379v1
1995-05-06,Stochastic Resonance in 3D Ising Ferromagnets,"Finite 3D Ising ferromagnets are studied in periodic magnetic fields both by
computer simulations and mean-field theoretical approaches. The phenomenon of
stochastic resonance is revealed. The characteristic peak obtained for the
correlation function between the external oscillating magnetic field and
magnetization versus the temperature of the system, is studied for various
external fields and lattice sizes. Excellent agreement between simulation and
theoretical results are obtained.",9505025v1
2001-02-13,Resonant electron transmission through a finite quantum spin chain,"Electron transport in a finite one dimensional quantum spin chain (with
ferromagnetic exchange) is studied within an $s-d$ exchange Hamiltonian. Spin
transfer coefficients strongly depend on the sign of the $s-d$ exchange
constant. For a ferromagnetic coupling, they exhibit a novel resonant pattern,
reflecting the salient features of the combined electron-spin system. Spin-flip
processes are inelastic and feasible at finite voltage or at finite
temperature.",0102236v1
2006-04-21,Dual-frequency ferromagnetic resonance,"We describe a new experimental technique to investigate coupling effects
between different layers or modes in ferromagnetic resonance (FMR). Dual FMR
frequencies are excited (2-8 GHz) simultaneously and detected selectively in a
broadband RF circuit, using lock-in amplifier detection at separate modulation
frequencies.",0604519v1
2018-01-29,Antiferromagnetic rare region effect in $Pr_{0.5}Ca_{0.5}MnO_3$,"We present evidence of coexistence of electron paramagnetic resonance signal
and anti-ferromagnetic resonance signals above the anti-ferromagnetic (AFM)
transition ($T_N$) in $Pr_{0.5}Ca_{0.5}MnO_3$. We identify the latter with AFM
rare regions within the Griffiths-like phase scenario with the associated
temperature scale $T^\ast$ extending above room temperature.",1801.09437v1
2016-08-03,Evolution of magnetic fluctuations through the Fe-induced paramagnetic to ferromagnetic transition in Cr$_2$B,"In itinerant ferromagnets, the quenched disorder is predicted to dramatically
affect the ferromagnetic to paramagnetic quantum phase transition driven by
external control parameters at zero temperature. Here we report a study on
Fe-doped Cr$_2$B, which, starting from the paramagnetic parent, orders
ferromagnetically for Fe-doping concentrations $x$ larger than $x_{\rm
c}=2.5$\%. In parent Cr$_2$B, $^{11}$B nuclear magnetic resonance data reveal
the presence of both ferromagnetic and antiferromagnetic fluctuations. The
latter are suppressed with Fe-doping, before the ferromagnetic ones finally
prevail for $x>x_{\rm c}$. Indications for non-Fermi liquid behavior, usually
associated with the proximity of a quantum critical point, were found for all
samples, including undoped Cr$_2$B. The sharpness of the ferromagnetic-like
transition changes on moving away from $x_{\rm c}$, indicating significant
changes in the nature of the magnetic transitions in the vicinity of the
quantum critical point. Our data provide constraints for understanding quantum
phase transitions in itinerant ferromagnets in the limit of weak quenched
disorder.",1608.01136v1
2019-09-09,Ferromagnetic resonance assisted optomechanical magnetometer,"The resonant enhancement of mechanical and optical interaction in
optomechanical cavities enables their use as extremely sensitive displacement
and force detectors. In this work we demonstrate a hybrid magnetometer that
exploits the coupling between the resonant excitation of spin waves in a
ferromagnetic insulator and the resonant excitation of the breathing mechanical
modes of a glass microsphere deposited on top. The interaction is mediated by
magnetostriction in the ferromagnetic material and the consequent mechanical
driving of the microsphere. The magnetometer response thus relies on the
spectral overlap between the ferromagnetic resonance and the mechanical modes
of the sphere, leading to a peak sensitivity better than 900 pT Hz$^{-1/2}$ at
206 MHz when the overlap is maximized. By externally tuning the ferromagnetic
resonance frequency with a static magnetic field we demonstrate sensitivity
values at resonance around a few nT Hz$^{-1/2}$ up to the GHz range. Our
results show that our hybrid system can be used to build high-speed sensor of
oscillating magnetic fields.",1909.03924v4
2003-09-24,Anomalous behavior of spin wave resonances in Ga_{1-x}Mn_{x}As thin films,"We report ferromagnetic and spin wave resonance absorption measurements on
high quality epitaxially grown Ga_{1-x}Mn_{x}As thin films. We find that these
films exhibit robust ferromagnetic long-range order, based on the fact that up
to seven resonances are detected at low temperatures, and the resonance
structure survives to temperatures close to the ferromagnetic transition. On
the other hand, we observe a spin wave dispersion which is linear in mode
number, in qualitative contrast with the quadratic dispersion expected for
homogeneous samples. We perform a detailed numerical analysis of the
experimental data and provide analytical calculations to demonstrate that such
a linear dispersion is incompatible with uniform magnetic parameters. Our
theoretical analysis of the ferromagnetic resonance data, combined with the
knowledge that strain-induced anisotropy is definitely present in these films,
suggests that a spatially dependent magnetic anisotropy is the most likely
reason behind the anomalous behavior observed.",0309566v2
2009-03-12,Observation of localized ferromagnetic resonance in a continuous ferromagnetic film via magnetic resonance force microscopy,"We present Magnetic Resonance Force Microscopy (MRFM) measurements of
Ferromagnetic Resonance (FMR) in a 50 nm thick permalloy film, tilted with
respect to the direction of the external magnetic field. At small probe-sample
distances the MRFM spectrum breaks up into multiple modes, which we identify as
local ferromagnetic resonances confined by the magnetic field of the MRFM tip.
Micromagnetic simulations support this identification of the modes and show
they are stabilized in the region where the dipolar tip field has a component
anti-parallel to the applied field.",0903.2285v1
2015-01-06,Sensing magnetic nanoparticles using nano-confined ferromagnetic resonances in a magnonic crystal,"We demonstrate the use of the magnetic-field-dependence of highly spatially
confined, GHz-frequency ferromagnetic resonances in a ferromagnetic
nanostructure for the detection of adsorbed magnetic nanoparticles. This is
achieved in a large area magnonic crystal consisting of a thin ferromagnetic
film containing a periodic array of closely spaced, nano-scale anti-dots. Stray
fields from nanoparticles within the anti-dots modify resonant dynamic
magnetisation modes in the surrounding magnonic crystal, generating easily
measurable resonance peak shifts. The shifts are comparable to the resonance
linewidths for high anti-dot filling fractions with their signs and magnitudes
dependent upon the modes' localisations (in agreement with micromagnetic
simulation results). This is a highly encouraging result for the development of
frequency-based nanoparticle detectors for high speed nano-scale biosensing.",1501.01171v1
2021-09-20,"Electron Spin Resonance of the itinerant ferromagnets LaCrGe3, CeCrGe3 and PrCrGe3","We report Electron Spin Resonance of the itinerant ferromagnets LaCrGe3,
CeCrGe3, and PrCrGe3. These compounds show well defined and very similar
spectra of itinerant Cr 3d spins in the paramagnetic temperature region. Upon
cooling and crossing the Cr-ferromagnetic ordering (below around 90 K) strong
spectral structures start to dominate the resonance spectra in a quite
different manner in the three compounds. In the Ce- and Pr-compounds the
resonance is only visible in the paramagnetic region whereas in the La-compound
the resonance can be followed far below the ferromagnetic ordering temperature.
This behavior will be discussed in terms of the specific interplay between the
4f and 3d magnetism which appears quite remarkable since CeCrGe3 displays heavy
fermion behavior even in the magnetically ordered state.",2109.09341v1
2021-10-04,Anomalous temperature dependence of phonon pumping by ferromagnetic resonance in Co/Pd multilayers with perpendicular anisotropy,"We demonstrate the pumping of phonons by ferromagnetic resonance in a series
of [Co(0.8 nm)/Pd(1.5 nm)]$_n$ multilayers ($n =$ 6, 11, 15, and 20) with large
magnetostriction and perpendicular magnetic anisotropy. The effect is shown
using broadband ferromagnetic resonance over a range of temperatures (10 to 300
K), where a resonant damping enhancement is observed at frequencies
corresponding to standing wave phonons across the multilayer. The strength of
this effect is enhanced by approximately a factor of 4 at 10 K compared to room
temperature, which is anomalous in the sense that the temperature dependence of
the magnetostriction predicts an enhancement that is less than a factor of 2.
Lastly, we demonstrate that the damping enhancement is correlated with a shift
in the ferromagnetic resonance field as predicted quantitatively from linear
response theory.",2110.01714v1
2016-07-25,Optically Detected Ferromagnetic Resonance in Metallic Ferromagnets via Nitrogen Vacancy Centers in Diamond,"We report quantitative measurements of optically detected ferromagnetic
resonance (ODFMR) of ferromagnetic thin films that use nitrogen-vacancy (NV)
centers in diamonds to transduce FMR into a fluorescence intensity variation.
To uncover the mechanism responsible for these signals, we study ODFMR as we 1)
vary the separation of the NV centers from the ferromagnet (FM), 2) record the
NV center longitudinal relaxation time $T_1$ during FMR, and 3) vary the
material properties of the FM. Based on the results, we propose the following
mechanism for ODFMR. Decay and scattering of the driven, uniform FMR mode
results in spinwaves that produce fluctuating dipolar fields in a spectrum of
frequencies. When the spinwave spectrum overlaps the NV center ground-state
spin resonance frequencies, the dipolar fields from these resonant spinwaves
relax the NV center spins, resulting in an ODFMR signal. These results lay the
foundation for an approach to NV center spin relaxometry to study FM dynamics
without the constraint of directly matching the NV center spin-transition
frequency to the magnetic system of interest, thus enabling an alternate
modality for scanned-probe magnetic microscopy that can sense ferromagnetic
resonance with nanoscale resolution.",1607.07485v1
2016-03-02,Ferromagnetic resonance in submicron permalloy stripes,"We present the results of systematic experimental investigations and
micromagnetic simulations for the ferromagnetic resonance in rectangular
permalloy microstripes. It is shown that the resonant magnetization
oscillations have a complex spatial structure including a quasi-homogeneous
precession, lateral spin-wave resonances and localized edge modes, which
strongly depend on sample orientation in an external magnetic field.",1603.00694v1
2002-10-18,Effect of Impurities and Effective Masses on Spin-Dependent Electrical Transport in Ferromagnet-Normal Metal-Ferromagnet Hybrid Junctions,"The effect of nonmagnetic impurities and the effective masses on the
spin-dependent transport in a ferromagnet-normal metal-ferromagnet junction is
investigated on the basis of a two-band model. Our results show that impurities
and the effective masses of electrons in two ferromagnetic electrodes have
remarkable effects on the behaviors of the conductance, namely, both affect the
oscillating amplitudes, periods, as well as the positions of the resonant peaks
of the conductance considerably. The impurity tends to suppress the amplitudes
of the conductance, and makes the spin-valve effect less obvious, but under
certain conditions the phenomenon of the so-called impurity-induced resonant
tunneling is clearly observed. The impurity and the effective mass both can
lead to nonmonotonous oscillation of the junction magnetoresistance (JMR) with
the incident energy and the thickness of the normal metal. It is also observed
that a smaller difference of the effective masses of electrons in two
ferromagnetic electrodes would give rise to a larger amplitude of the JMR.",0210392v1
2018-02-28,Single ferromagnetic fluctuations in UCoGe revealed by 73Ge- and 59Co-NMR studies,"$^{73}$Ge and $^{59}$Co nuclear magnetic resonance (NMR) and nuclear
quadrupole resonance (NQR) measurements have been performed on a
$^{73}$Ge-enriched single-crystalline sample of the ferromagnetic
superconductor UCoGe in the paramagnetic state. The $^{73}$Ge NQR parameters
deduced from NQR and NMR are close to those of another isostructural
ferromagnetic superconductor URhGe. The Knight shifts of the Ge and Co sites
are well scaled to each other when the magnetic field is parallel to the $b$ or
$c$ axis. The hyperfine coupling constants of Ge are estimated to be close to
those of Co. The large difference of spin susceptibilities between the $a$ and
$b$ axes could lead to the different response of the superconductivity and
ferromagnetism with the field parallel to these directions. The temperature
dependence of the nuclear spin-lattice relaxation rates $1/T_1$ at the two
sites is similar to each other above 5 K. These results indicate that the
itinerant U-$5f$ electrons are responsible for the ferromagnetism in this
compound, consistent with previous studies. The similarities and differences in
the three ferromagnetic superconductors are discussed.",1802.10221v1
2022-07-21,Influence of nonuniform magnetization reorientation on spin-orbit torque measurements,"Measurements of spin-orbit torques in a ferromagnetic/nonmagnetic multilayer
are typically based on an assumption that the entire ferromagnetic layer
uniformly responds to the spin-orbit torque. This assumption breaks down when
the thickness of the ferromagnetic layer is comparable to the dynamic exchange
coupling length, which can be as short as a few nanometers in certain
measurement geometries. The nonuniform magnetization reorientation coupled with
nonuniform contribution of each magnetic sublayer to the magnetoresistance or
the Kerr effect may impact the accuracy in the extrapolation of spin-orbit
torque, particularly if a thick ferromagnetic layer is used. In this paper, we
use numerical models to investigate such an impact in three different
techniques: the magneto-optic-Kerr-effect method, the second-harmonic method
and the spin torque ferromagnetic resonance method. We show that the
second-harmonic and magneto-optic-Kerr-effect methods are prone to be
influenced by the nonuniform magnetization reorientation, while the spin torque
ferromagnetic resonance method is much less impacted.",2207.10349v1
2014-12-02,A rigorous two-dimensional model for the stripline ferromagnetic resonance response of metallic ferromagnetic films,"In this work we constructed a two-dimensional numerical model for calculation
of the stripline ferromagnetic resonance (FMR) response of metallic
ferromagnetic films. We also conducted numerical calculations by using this
software. The calculations demonstrated that the eddy current contribution to
the FMR response decreases with a decrease in the stripline width. The most
important manifestations of the conductivity (eddy current) effect are
excitation of the higher-order standing spin waves across the film thickness in
the materials for which the standing spin wave peaks would be absent in cavity
FMR measurements and strong dependence of the off-resonance series conductance
of the stripline on the stripline width. Whereas the contribution of the eddy
currents to the stripline FMR response can be very significant, because wide
striplines (100nm+) are conventionally used for the FMR measurements, it is
negligible in the case of excitation of spin waves, just because very narrow
stripline transducers (0.5-5micron wide) are required in order to excite spin
waves in metallic ferromagnetic films in a noticeable frequency/applied field
range.",1412.0777v1
2015-11-04,Coupling of microwave magnetic dynamics in thin ferromagnetic films to stripline transducers in the geometry of the broadband stripline ferromagnetic resonance,"We constructed a quasi-analytical self-consistent model of the
stripline-based broadband ferromagnetic resonance (FMR) measurements of
ferromagnetic films. Exchange-free description of magnetization dynamics in the
films allowed us to obtain simple analytical expressions. They enable quick and
efficient numerical simulations of the dynamics. With this model we studied the
contribution of radiation losses to the ferromagnetic resonance linewidth, as
measured with the stripline FMR. We found that for films with large
conductivity of metals the radiation losses are significantly smaller than for
magneto-insulating films. Excitation of microwave eddy currents in these
materials contributes to the total microwave impedance of the system. This
leads to impedance mismatch with the film environment resulting in decoupling
of the film from the environment and, ultimately, to smaller radiation losses.
We also show that the radiation losses drop with an increase in the stripline
width and when the sample is lifted up from the stripline surface. Hence, in
order to eliminate this measurement artifact one needs to use wide striplines
and introduce a spacer between the film and the sample surface. The radiation
losses contribution is larger for thicker films.",1511.01201v1
2016-07-15,Theory of spin-coherent transport through a defect spin state in a metal/ferromagnet tunnel junction during ferromagnetic resonance,"We describe the coherent interaction between a defect spin at the interface
of a ferromagnet and a non-magnetic material, under bias and when the
magnetization of the ferromagnetic contact precesses during ferromagnetic
resonance. The magnet filters charge carriers by preferentially allowing in
parallel spins, which leads to a dynamic spin accumulation on the defect. Local
effective fields acting on the defect spin site modify the defect spin's
precession, which also modifies the charge current through the defect. This new
form of current-detected spin resonance reveals the local environment of the
defect, and thus can yield the defect identity.",1607.04535v2
2000-07-06,Detecting Gapless Excitations above Ferromagnetic Domain Walls,"In a two or three dimensional ferromagnetic XXZ model, a low energy
excitation mode above a magnetic domain wall is gapless, whereas all of the
usual spin wave excitations moving around the whole crystal are gapful.
Although this surprising fact was already proved in a mathematically rigorous
manner, the gapless excitations have not yet been detected experimentally. For
this issue, we show theoretically that the gapless excitations appear as the
dynamical fluctuations of the experimental observable, magnetoresistance, in a
ferromagnetic wire. We also discuss other methods (e.g., ferromagnetic
resonance and neutron scattering) to detect the gapless excitations
experimentally.",0007099v1
2004-04-24,Spin and Charge Pumping by Ferromagnetic-Superconductor Order Parameters,"We study transport in ferromagnetic-superconductor/normal-metal systems. It
is shown that charge and spin currents are pumped from ferromagnetic
superconductors into adjacent normal metals by adiabatic changes in the order
parameters induced by external electromagnetic fields. Spin and charge pumping
identify the symmetry of the superconducting order parameter, e.g., singlet
pairing or triplet pairing with opposite or equal spin pairing. Consequences
for ferromagnetic-resonance experiments are discussed.",0404591v2
2008-02-25,Tunnel barrier enhanced voltage signals generated by magnetization precession of a single ferromagnetic layer,"We report the electrical detection of magnetization dynamics in an
Al/AlOx/Ni80Fe20/Cu tunnel junction, where a Ni80Fe20 ferromagnetic layer is
brought into precession under the ferromagnetic resonance (FMR) conditions. The
dc voltage generated across the junction by the precessing ferromagnet is
enhanced about an order of magnitude compared to the voltage signal observed
when the contacts in this type of multilayered structure are ohmic. We discuss
the relation of this phenomenon to magnetic spin pumping and speculate on other
possible underlying mechanisms responsible for the enhanced electrical signal.",0802.3646v1
2014-01-15,Structural and magnetic properties of irradiated SiC,"We present a comprehensive structural characterization of ferromagnetic SiC
single crystals induced by Ne ion irradiation. The ferromagnetism has been
confirmed by electron spin resonance and possible transition metal impurities
can be excluded to be the origin of the observed ferromagnetism. Using X-ray
diffraction and Rutherford backscattering/channeling spectroscopy, we estimate
the damage to the crystallinity of SiC which mutually influences the
ferromagnetism in SiC.",1401.3543v1
2018-10-03,Selective Activation of an Isolated Magnetic Skyrmion in a Ferromagnet with Microwave Electric Fields,"We theoretically reveal that pure eigenmodes of an isolated magnetic skyrmion
embedded in a ferromagnetic environment can be selectively activated using
microwave electric fields without exciting gigantic ferromagnetic resonances,
in contrast to conventional methods using microwave magnetic fields. We also
demonstrate that this selective activation of a skyrmion can efficiently drive
its translational motion in a ferromagnetic nanotrack under application of an
external magnetic field inclined from the normal direction. We find that a mode
with combined breathing and rotational oscillations induces much faster
skyrmion propagation than the breathing mode studied previously by Wang et al.
[Phys. Rev. B 92, 020403(R) (2015)].",1810.01606v1
2019-09-17,Microwave induced tunable subharmonic steps in superconductor-ferromagnet-superconductor Josephson junction,"We investigate the coupling between ferromagnet and superconducting phase
dynamics in superconductor-ferromagnet-superconductor Josephson junction. The
current-voltage characteristics of the junction demonstrate a pattern of
subharmonic current steps which forms a devil's staircase structure. We show
that a width of the steps becomes maximal at ferromagnetic resonance. Moreover,
we demonstrate that the structure of the steps and their widths can be tuned by
changing the frequency of the external magnetic field, ratio of Josephson to
magnetic energy, Gilbert damping and the junction size.",1909.08004v1
2023-01-26,Anisotropic spin-current spectroscopy of ferromagnetic superconducting gap symmetries,"We develop a microscopic theory of tunneling spin transport at the magnetic
interface between a ferromagnetic insulator and a ferromagnetic superconductor
(FSC) driven by ferromagnetic resonance. We show that the spin susceptibilities
of the FSC can be extracted from the spin currents by tuning the easy axis of
the FSC, and thus the spin currents can be a probe for the symmetries of the
spin-triplet Cooper pairing. Our results will offer a route to exploiting the
synergy of magnetism and superconductivities for spin devices.",2301.11027v3
2002-02-11,Radiation Induced Landau-Lifshitz-Gilbert Damping in Ferromagnets,"The Landau-Lifshitz-Gilbert damping coefficient employed in the analysis of
spin wave ferromagnetic resonance is related to the electrical conductivity of
the sample. The changing magnetization (with time) radiates electromagnetic
fields. The electromagnetic energy is then absorbed by the sample and the
resulting heating effect describes magnetic dissipative damping. The
ferromagnetic resonance relaxation rate theoretically depends on the geometry
(shape and size) of the sample as well as temperature in agreement with
experiment.",0202181v1
2002-05-02,Spin battery operated by ferromagnetic resonance,"Precessing ferromagnets are predicted to inject a spin current into adjacent
conductors via Ohmic contacts, irrespective of a conductance mismatch with, for
example, doped semiconductors. This opens the way to create a pure spin source
spin battery by the ferromagnetic resonance. We estimate the spin current and
spin bias for different material combinations.",0205028v2
2005-05-04,Intrinsic Curie temperature bistability in ferromagnetic semiconductor resonant tunneling diodes,"We predict bistability in the Curie temperature-voltage characteristic of
double barrier resonant-tunneling structures with dilute ferromagnetic
semiconductor quantum wells. Our conclusions are based on simulations of
electrostatics and ballistic quantum transport combined with a mean-field
theory description of ferromagnetism in dilute magnetic semiconductors.",0505101v2
2008-05-27,Self-sustained magnetoelectric oscillations in magnetic resonant tunneling structures,"The dynamic interplay of transport, electrostatic, and magnetic effects in
the resonant tunneling through ferromagnetic quantum wells is theoretically
investigated. It is shown that the carrier-mediated magnetic order in the
ferromagnetic region not only induces, but also takes part in intrinsic,
robust, and sustainable high-frequency current oscillations over a large window
of nominally steady bias voltages. This phenomenon could spawn a new class of
quantum electronic devices based on ferromagnetic semiconductors.",0805.4068v1
2008-06-24,Spin dynamics in point contacts to single ferromagnetic films,"Excitation of magnons or spin-waves driven by nominally unpolarized transport
currents in point contacts of normal and ferromagnetic metals is probed by
irradiating the contacts with microwaves. Two characteristic dynamic effects
are observed: a rectification of off-resonance microwave current by spin-wave
nonlinearities in the point contact conductance, and a resonant stimulation of
spin-wave modes in the nano-contact core by the microwave field. These
observations provide a direct evidence that the magnetoconductance effects
observed are due to GHz spin dynamics at the ferromagnetic interface driven by
the spin transfer torque effect of the transport current.",0806.3805v1
2009-02-13,Charge pumping and the colored thermal voltage noise in spin valves,"Spin pumping by a moving magnetization gives rise to an electric voltage over
a spin valve. Thermal fluctuations of the magnetization manifest themselves as
increased thermal voltage noise with absorption lines at the ferromagnetic
resonance frequency and/or zero frequency. The effect depends on the
magnetization configuration and can be of the same order of magnitude as the
Johnson-Nyquist thermal noise. Measuring colored voltage noise is an
alternative to ferromagnetic resonance experiments for nano-scale ferromagnetic
circuits.",0902.2389v2
2010-11-11,Spin Torque Ferromagnetic Resonance Induced by the Spin Hall Effect,"We demonstrate that the spin Hall effect in a thin film with strong
spin-orbit scattering can excite magnetic precession in an adjacent
ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer
generates an oscillating transverse spin current in the Pt, and the resultant
transfer of spin angular momentum to the NiFe induces ferromagnetic resonance
(FMR) dynamics. The Oersted field from the current also generates an FMR signal
but with a different symmetry. The ratio of these two signals allows a
quantitative determination of the spin current and the spin Hall angle.",1011.2788v1
2013-10-23,Magnetization Characteristic of Ferromagnetic Thin Strip by Measuring Anisotropic Magnetoresistance and Ferromagnetic Resonance,"The magnetization characteristic in a permalloy thin strip is investigated by
electrically measuring the anisotropic magnetoresistance and ferromagnetic
resonance in in-plane and out-of-plane configurations. Our results indicate
that the magnetization vector can rotate in the film plane as well as out of
the film plane by changing the intensity of external magnetic field of certain
direction. The magnetization characteristic can be explained by considering
demagnetization and magnetic anisotropy. Our method can be used to obtain the
demagnetization factor, saturated magnetic moment and the magnetic anisotropy.",1310.6117v1
2015-12-04,Itinerant ferromagnetism in 1D two-component Fermi gases,"We study a one-dimensional two-component atomic Fermi gas with an infinite
intercomponent contact repulsion. It is found that adding an attractive
resonant odd-wave interaction breaking the rotational symmetry one can make the
ground state ferromagnetic. A promising system for the observation of this
itinerant ferromagnetic state is a 1D gas of $^{40}$K atoms, where 3D $s$-wave
and $p$-wave Feshbach resonances are very close to each other and the 1D
confinement significantly reduces the inelastic decay.",1512.01392v1
2021-03-10,Anisotropic superconducting spin transport at magnetic interfaces,"We present a theoretical investigation of anisotropic superconducting spin
transport at a magnetic interface between a p-wave superconductor and a
ferromagnetic insulator. Our formulation describes the ferromagnetic resonance
modulations due to spin current generation depending on spin-triplet Cooper
pair, including the frequency shift and enhanced Gilbert damping, in a unified
manner. We find that the Cooper pair symmetry is detectable from the
qualitative behavior of the ferromagnetic resonance modulation. Our theory
paves the way toward anisotropic superconducting spintronics.",2103.05871v3
2010-02-25,Ferromagnetic Resonance of Co/Gd and Co/Tb Multilayers,"The in-plane dynamics of ferrimagnetic Co/Gd multilayers are investigated by
means of ferromagnetic resonance, magneto-optical Kerr effect and SQUID
magnetometry. The power absorbed from these multilayers is strongly temperature
dependent. For example, the resonant peak for a (Co 40 A /Gd 40 A)8 multilayer
vanishes approximately 50 K below room temperature. We have further
investigated Gd/Co/Gd and Tb/Co/Tb trilayers with different thicknesses of Gd
(5-7 A), Tb (1-7 A) and Co (30-40 A). At room temperature, these Co-based
trilayers show a shift of approximately 600 Oe at 24 GHz in the uniform
ferromagnetic resonance field, compared to pure Co film, indicating the
exchange coupling between the Co and Gd. The shift in the field for the
resonance increases as the temperature is decreased. Furthermore the resonance
linewidth increases as the temperature is decreased. The experimental results
are in good agreement with our theoretical calculations.",1002.4889v1
2014-10-14,Spin precession mapping at ferromagnetic resonance via nuclear resonant scattering,"We probe the spin dynamics in a thin magnetic film at ferromagnetic resonance
by nuclear resonant scattering of synchrotron radiation at the 14.4 keV
resonance of $^{57}$Fe. The precession of the magnetization leads to an
apparent reduction of the magnetic hyperfine field acting at the $^{57}$Fe
nuclei. The spin dynamics is described in a stochastic relaxation model adapted
to the ferromagnetic resonance theory by Smit and Beljers to model the decay of
the excited nuclear state. From the fits of the measured data the shape of the
precession cone of the spins is determined. Our results open a new perspective
to determine magnetization dynamics in layered structures with very high depth
resolution by employing ultrathin isotopic probe layers.",1410.3689v1
2007-05-21,Evidence for ferromagnetic spin-pairing superconductivity in UGe$_2$: A $^{73}$Ge-NQR study under pressure,"We report that a novel type of superconducting order parameter has been
realized in the ferromagnetic states in UGe$_2$ via $^{73}$Ge
nuclear-quadrupole-resonance (NQR) experiments performed under pressure ($P$).
Measurements of the nuclear spin-lattice relaxation rate $(1/T_1)$ have
revealed an unconventional nature of superconductivity such that the up-spin
band is gapped with line nodes, but the down-spin band remains gapless at the
Fermi level. This result is consistent with that of a ferromagnetic
spin-pairing model in which Cooper pairs are formed among ferromagnetically
polarized electrons. The present experiment has shed new light on a possible
origin of ferromagnetic superconductivity, which is mediated by ferromagnetic
spin-density fluctuations relevant to the first-order transition inside the
ferromagnetic states.",0705.2944v1
2014-11-19,Dynamical spin injection at a quasi-one-dimensional ferromagnet-graphene interface,"We present a study of dynamical spin injection from a three-dimensional
ferromagnet into two-dimensional single-layer graphene. Comparative
ferromagnetic resonance (FMR) studies of ferromagnet/graphene strips buried
underneath the central line of a coplanar waveguide show that the FMR linewidth
broadening is the largest when the graphene layer protrudes laterally away from
the ferromagnetic strip, indicating that the spin current is injected into the
graphene areas away from the area directly underneath the ferromagnet being
excited. Our results confirm that the observed damping is indeed a signature of
dynamical spin injection, wherein a pure spin current is pumped into the
single-layer graphene from the precessing magnetization of the ferromagnet. The
observed spin pumping efficiency is difficult to reconcile with the expected
backflow of spins according to the standard spin pumping theory and the
characteristics of graphene, and constitutes an enigma for spin pumping in
two-dimensional structures.",1411.5339v2
2013-11-29,Magnon radiation by moving Abrikosov vortices in ferromagnetic superconductors and superconductor-ferromagnet multilayers,"In systems combining type-II superconductivity and magnetism the
non-stationary magnetic field of moving Abrikosov vortices may excite spin
waves, or magnons. This effect leads to the appearance of an additional damping
force acting on the vortices. By solving the London and Landau-Lifshitz-Gilbert
equations we calculate the magnetic moment induced force acting on vortices in
ferromagnetic superconductors and superconductor/ferromagnet superlattices. If
the vortices are driven by a dc force, magnon generation due to the Cherenkov
resonance starts as the vortex velocity exceeds some threshold value. For an
ideal vortex lattice this leads to an anisotropic contribution to the
resistivity and to the appearance of resonance peaks on the current voltage
characteristics. For a disordered vortex array the current will exhibit a
step-like increase at some critical voltage. If the vortices are driven by an
ac force with a frequency \omega, the interaction with magnetic moments will
lead to a frequency-dependent magnetic contribution \eta_M to the vortex
viscosity. If \omega is below the ferromagnetic resonance frequency \omega_F,
vortices acquire additional inertia. For \omega > \omega_F dissipation is
enhanced due to magnon generation. The viscosity \eta_M can be extracted from
the surface impedance of the ferromagnetic superconductor. Estimates of the
magnetic force acting on vortices for the U-based ferromagnetic superconductors
and cuprate/manganite superlattices are given.",1311.7620v1
2010-06-02,Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance,"The broadband microstrip ferromagnetic resonance technique has been applied
for detection and characterization of a magnetic inhomogeneity in a film
sample. In the case of a 100nm thick Permalloy film an additional magnetically
depleted top sub-layer, practically unidentifiable by the conventional
ferromagnetic resonance setup, has been detected and characterized. These
results have been confirmed by Brillouin light scattering spectroscopy
revealing the fact that the optical properties of the additional sub-layer do
not differ much from those of the bulk of the film. Subsequent characterization
of a large number of other presumably single-layer films with thicknesses in
the range 30-100nm using the same ferromagnetic resonance technique also
revealed the same effect.",1006.0331v1
2013-10-23,Exchange-dominated Standing Spin Wave Excitations under microwave irradiation in Ni80Fe20 Thin Films,"We investigated the microwave-assisted DC voltages of ferromagnetic
resonances and exchangedominated standing spin wave excitations in two
different in-plane magnetized permalloy thin films via homodyne detection. The
line shapes of ferromagnetic resonance spectra and the dispersion curves of
ferromagnetic resonance and standing spin wave are in agreement of previous
studies, while further investigations of DC voltage spectra for these two
excitations reveal that 1. unlike ferromagnetic resonance signals, the
anti-symmetrical line shapes of standing spin wave excitations are not depend
on the electromagnetic relative phase of assisted microwave, and 2. linewidths
of their DC voltage spectra are distinct. The complicated spin dynamics of
standing spin wave is consequently discussed by applying
Landau-Lifshitz-Gilbert equation in term of exchange interaction.",1310.6108v1
2015-01-30,Microscopic properties of degradation-free capped GdN thin films studied by Electron Spin Resonance,"The microscopic magnetic properties of high-quality GdN thin films have been
investigated by electron spin resonance (ESR) and ferromagnetic resonance (FMR)
measurements. Detailed temperature dependence ESR measurements have shown the
existence of two ferromagnetic components at lower temperatures which was not
clear from the previous magnetization measurements. The temperature, where the
resonance shift occurs for the major ferromagnetic component, seems to be
consistent with the Curie temperature obtained from the previous magnetization
measurement. On the other hand, the divergence of line width is observed around
57 K for the minor ferromagnetic component. The magnetic anisotropies of GdN
thin films have been obtained by the analysis of FMR angular dependence
observed at 4.2 K. Combining the X-ray diffraction results, the correlation
between the magnetic anisotropies and the lattice constants is discussed.",1501.07672v1
2017-05-26,Static and Dynamic Magnetic Properties of FeMn/Pt Multilayers,"Recently we have demonstrated the presence of spin-orbit toque in FeMn/Pt
multilayers which, in combination with the anisotropy field, is able to rotate
its magnetization consecutively from 0o to 360o without any external field.
Here, we report on an investigation of static and dynamic magnetic properties
of FeMn/Pt multilayers using combined techniques of magnetometry, ferromagnetic
resonance, inverse spin Hall effect and spin Hall magnetoresistance
measurements. The FeMn/Pt multilayer was found to exhibit ferromagnetic
properties, and its temperature dependence of saturation magnetization can be
fitted well using a phenomenological model by including a finite distribution
in Curie temperature due to subtle thickness variations across the multilayer
samples. The non-uniformity in static magnetic properties is also manifested in
the ferromagnetic resonance spectra, which typically exhibit a broad resonance
peak. A damping parameter of around 0.106 is derived from the frequency
dependence of ferromagnetic resonance linewidth, which is comparable to the
reported values for other types of Pt-based multilayers. Clear inverse spin
Hall signals and spin Hall magnetoresistance have been observed in all samples
below the Curie temperature, which corroborate the strong spin-orbit torque
effect observed previously.",1705.09423v1
2022-10-01,Nonlinear features of the superconductor--ferromagnet--superconductor $\varphi_0$ Josephson junction in ferromagnetic resonance region,"We demonstrate the manifestations of the nonlinear features in magnetic
dynamics and IV-characteristics of the $\varphi_0$ Josephson junction in the
ferromagnetic resonance region. We show that at small values of system
parameters, namely, damping, spin-orbit interaction, and Josephson to magnetic
energy ratio, the magnetic dynamics is reduced to the dynamics of the scalar
Duffing oscillator, driven by the Josephson oscillations. The role of
increasing superconducting current in the resonance region is clarified.
Shifting of the ferromagnetic resonant frequency and the reversal of its
damping dependence due to nonlinearity are demonstrated by the full
Landau-Lifshitz-Gilbert-Josephson system of equations, and in its different
approximations. Finally, we demonstrate the negative differential resistance in
the IV--characteristics, and its correlation with the foldover effect.",2210.00366v1
2004-02-18,Interface-Localized Mode In Bilayer Film Ferromagnetic Resonance Spectrum,"Ferromagnetic resonance (FMR) in exchange-coupled bilayer films has been the
subject of intensive studies in recent years. From the experimental viewpoint,
a characteristic feature of this FMR is that some specimens show single
resonance, whereas others show double resonance. Moreover, double resonance can
exhibit a regular pattern, in which the high-field (HF) line intensity
surpasses that of the low-field (LF) line, or it can exhibit an inverted
pattern with the HF line less intense than the LF line. There is a general
belief that the inverted FMR pattern occurs when the HF line is an ""optic
mode"", i.e. an out-of-phase composition of individual sublayer modes, and the
LF line is an ""acoustic mode"", or an in-phase mode composition. The existing
theoretical explanations of bilayer ferromagnetic resonance are, as a rule,
based on phenomenological equation of motion of the magnetization vector. In
this paper, we propose a theory of FMR in ultrathin bilayers based on an
entirely microscopic approach, using the Heisenberg model of localized spins
and assuming that the two ferromagnetic sublayers are exchange-coupled through
their interface. This rigorous microscopic FMR theory does explain the inverted
pattern of the bilayer FMR spectrum by assuming the HF line to correspond to an
in-phase mode, but of interface-localized nature; this gives a possibility to
explore the HF resonance line corresponding to the interface-localized mode as
a potential source of information concerning the bilayer interface.",0402475v1
2013-06-16,Zero-Field Fiske Resonance Coupled with Spin-waves in Ferromagnetic Josephson Junctions,"AC Josephson current density in a Josephson junction with DC bias is
spatially modulated by an external magnetic field, and induces an
electromagnetic (EM) field inside the junction. The current-voltage ($I$-$V$)
curve exhibits peaks due to the resonance between the EM field and the
spatially modulated AC Josephson current density. This is called {\it Fiske
resonance}. Such a spatially modulated Josephson current density can be also
induced by a non-uniform insulating barrier and the Fiske resonance appears
without external magnetic field. This is called zero-field Fiske resonance
(ZFFR). In this paper, we theoretically study the ZFFR coupled with spin-waves
in a superconductor/ferromagnetic insulator/superconductor junction
(ferromagnetic Josephson junction) with a non-uniform ferromagnetic insulating
barrier. The resonant mode coupled with spin-waves can be induced without
external magnetic field. We find that the $I$-$V$ curve shows resonant peaks
associated with composite excitations of spin-waves and the EM field in the
junction. The voltage at the resonance is obtained as a function of the normal
modes of EM field. The ZFFRs coupled with spin-waves are found as peak
structures in the DC Josephson current density as a function of bias voltage.",1306.3652v2
2020-05-29,Electron spin resonance and ferromagnetic resonance spectroscopy in the high-field phase of the van der Waals magnet CrCl$_3$,"We report a comprehensive high-field/high-frequency electron spin resonance
(ESR) study on single crystals of the van der Waals magnet CrCl$_3$. This
material, although being known for quite a while, has received recent
significant attention in a context of the use of van der Waals magnets in novel
spintronic devices. Temperature-dependent measurements of the resonance fields
were performed between 4 and 175 K and with the external magnetic field applied
parallel and perpendicular to the honeycomb planes of the crystal structure.
These investigations reveal that the resonance line shifts from the
paramagnetic resonance position already at temperatures well above the
transition into a magnetically ordered state. Thereby the existence of
ferromagnetic short-range correlations above the transition is established and
the intrinsically two-dimensional nature of the magnetism in the title compound
is proven. To study details of the magnetic anisotropies in the field-induced
effectively ferromagnetic state at low temperatures, frequency-dependent
ferromagnetic resonance (FMR) measurements were conducted at 4 K. The observed
anisotropy between the two magnetic-field orientations is analyzed by means of
numerical simulations based on a phenomenological theory of FMR. These
simulations are in excellent agreement with measured data if the shape
anisotropy of the studied crystal is taken into account, while the
magnetocrystalline anisotropy is found to be negligible in CrCl$_3$. The
absence of a significant intrinsic anisotropy thus renders this material as a
practically ideal isotropic Heisenberg magnet.",2005.14559v1
2010-05-04,Effect of disorder studied with ferromagnetic resonance for arrays of tangentially magnetized sub-micron Permalloy discs fabricated by nanosphere lithography,"Tangentially magnetized trigonal arrays of sub-micron Permalloy discs are
characterized with ferromagnetic resonance to determine the possible
contributions to frequency and linewidth from array disorder. Each array is
fabricated by a water-surface self-assembly lithographic technique, and
consists of a large trigonal array of 700 nm diameter magnetic discs. Each
array is characterized by a different degree of ordering. Two modes are present
in the ferromagnetic resonance spectra: a large amplitude, `fundamental' mode
and a lower amplitude mode at higher field. Angular dependence of the resonance
field in a very well ordered array is found to be negligible for both modes.
The relationship between resonance frequency and applied magnetic field is
found to be uncorrelated with array disorder. Linewidth is found to increase
with increasing array disorder.",1005.0452v3
2005-10-25,Resonant proximity effect in normal metal / diffusive ferromagnet / superconductor junctions,"Resonant proximity effect in the normal metal / insulator / diffusive
ferromagnet / insulator / $s$- and d-wave superconductor (N/I/DF/I/S) junctions
is studied for various regimes by solving the Usadel equation with the
generalized boundary conditions. It is shown that the resonant proximity effect
originating from the exchange field in DF layer strongly modifies the tunneling
conductance and density of states.",0510665v1
2006-02-10,Low-frequency vortex dynamic susceptibility and relaxation in mesoscopic ferromagnetic dots,"Vortex dynamics in a restricted geometry is considered for a magnetic system
consisting of ferromagnetic cylindrical dots. To describe the vortex dynamic
susceptibility and relaxation the equation of motion for the vortex center
position is applied. The dependencies of the vortex dynamic susceptibility and
resonance linewidth on geometrical parameters are calculated. A new method of
extracting damping parameter from the vortex low-frequency resonance peaks is
proposed and applied for interpretation of resonance data on FeNi circular
dots.",0602279v1
2006-04-26,Time-domain measurement of driven ferromagnetic resonance,"We present a time-resolved measurement of magnetization dynamics during
ferromagnetic resonance (FMR) in a single layer of Ni81Fe19. Small-angle (<1
deg.) precession of elemental Ni, Fe moments could be measured directly and
quantitatively using time-resolved x-ray magnetic circular dichroism (XMCD) in
transmission. The high temporal and rotational sensitivity of of this technique
has allowed characterization of the phase and amplitude of driven FMR motion at
2.3 GHz, verifying basic expectations for a driven resonance.",0604610v1
2008-01-15,Broadband ferromagnetic resonance of Ni81Fe19 wires using a rectifying effect,"The broadband ferromagnetic resonance measurement using the rectifying effect
of Ni81Fe19 wire has been investigated. One wire is deposited on the center
strip line of the coplanar waveguide (CPW) and the other one deposited between
two strip lines of CPW. The method is based on the detection of the
magnetoresistance oscillation due to the magnetization dynamics induced by the
radio frequency field. The magnetic field dependences of the resonance
frequency and the rectification spectrum are presented and analytically
interpreted on the standpoint of a uniform magnetization precession model.",0801.2203v1
2009-05-14,A compact apparatus for studies of element and phase-resolved ferromagnetic resonance,"We present a compact sample holder equipped with electromagnets and high
frequency transmission lines; the sample holder is intended for combined x-ray
magnetic circular dichroism (XMCD) and ferromagnetic resonance measurements
(FMR). Time-resolved measurements of resonant x-ray detected FMR during forced
precession are enabled by use of a rf excitation that is phase-locked to the
storage ring bunch clock. Several applications of the combined XMCD + FMR
technique are presented, demonstrating the flexibility of the experimental
design.",0905.2353v1
2011-02-10,Circularly Polarized Resonant Rayleigh Scattering and Skyrmions in the $ν$ = 1 Quantum Hall Ferromagnet,"We use the circularly polarized resonant Rayleigh scattering (RRS) to study
the quantum Hall ferromagnet at $\nu$ = 1. At this filling factor we observe a
right handed copolarized RRS which probes the Skyrmion spin texture of the
electrons in the photoexcited grounds state. The resonant scattering is not
present in the left handed copolarization, and this can be related to the
correlation between Skymionic effects, screening and spin wave excitations.
These results evidence that RRS is a valid method for the study of the spin
texture of the quantum Hall states.",1102.2185v2
2015-06-18,Dispersive read-out of ferromagnetic resonance for strongly coupled magnons and microwave photons,"We demonstrate the dispersive measurement of ferromagnetic resonance in a
yttrium iron garnet sphere embedded within a microwave cavity. The reduction in
the longitudinal magnetization at resonance is measured as a frequency shift in
the cavity mode coupled to the sphere. This measurement is a result of the
intrinsic non-linearity in magnetization dynamics, indicating a promising route
towards experiments in magnon cavity quantum electro-dynamics.",1506.05631v1
2015-06-19,Coherent manipulation of a Majorana qubit by a mechanical resonator,"We propose a hybrid system composed of a Majorana qubit and a nanomechanical
resonator, implemented by a spin-orbit-coupled superconducting nanowire, using
a set of static and oscillating ferromagnetic gates. The ferromagnetic gates
induce Majorana bound states in the nanowire, which hybridize and constitute a
Majorana qubit. Due to the oscillation of one of these gates, the Majorana
qubit can be coherently rotated. By tuning the gate voltage to modulate the
local spin-orbit coupling, it is possible to reach the resonance of the
qubit-oscillator system for relatively strong couplings.",1506.05879v2
2018-09-07,Nuclear spin pumping by pulling effect,"The nuclear-to-electron spin angular momentum conversion via hyperfine
coupling in a normal metal (NM)/ferromagnet (FM) bilayer system is
theoretically investigated by using the nonequilibrium Green's function method.
The spin current generated by the nuclear magnetic resonance (NMR) is found to
be enhanced by the pulling effect in the FM when the temperature is lower than
NMR resonance frequency. In a Co/Pt bilayer system, we show that the spin
current by NMR becomes larger than that of the ferromagnetic resonance (FMR).",1809.02272v1
2021-01-07,Microwave directional dichroism resonant with spin excitations in the polar ferromagnet GaV$_4$S$_8$,"We have investigated the directional dichroism of magnetic resonance spectra
in the polar ferromagnet GaV$_4$S$_8$. While four types of structural domains
are energetically degenerated under zero field, the magnetic resonance for each
domain is well separated by applying magnetic fields due to uniaxial magnetic
anisotropy. Consequently, the directional dichroism as large as 20 % is clearly
observed without domain cancellation. The present observation therefore
demonstrates that not only magnetoelectric mono-domain crystals but also
magnetoelectric multi-domain specimens can be used to realize microwave
(optical) diodes owing to the lack of inversion domains.",2101.02411v1
2006-12-01,Theory of digital magneto resistance in ferromagnetic resonant tunneling diodes,"We propose a ferromagnetic spintronic system, which consists of two serial
connected resonant tunneling diodes. One diode is nonmagnetic whereas the other
comprises a ferromagnetic emitter and quantum well. Using a selfconsistent
coherent transport model we show that the current-voltage characteristic of the
ferromagnetic diode can be strongly modulated by changing the relative
orientation of the magnetizations in the emitter and quantum well,
respectively. By a continuous change of the relative magnetization angle the
total resistance exhibits a discrete jump realizing digital magneto resistance.
The interplay between the emitter's Fermi energy level and the relative
magnetization orientations allows to tailor the current voltage characteristics
of the ferromagnetic diode from ohmic to negative differential resistance
regime at low voltages.",0612025v1
2007-02-20,Spin dynamics in a superconductor / ferromagnet proximity system,"The ferromagnetic resonance of thin sputtered Ni80Fe20 films grown on Nb is
measured. By varying the temperature and thickness of the Nb the role of the
superconductivity on the whole ferromagnetic layer in these heterostructures is
explored. The change in the spin transport properties below the superconducting
transition of the Nb is found to manifest itself in the Ni80Fe20 layer by a
sharpening in the resonance of the ferromagnet, or a decrease in the effective
Gilbert damping co-efficient. This dynamic proximity effect is in contrast to
low frequency studies in these systems, where the effect of the superconductor
is confined to a small region in the ferromagnet. We interpret this in terms of
the spin pumping model.",0702461v1
2007-08-27,Determination of Penetration Depth of Transverse Spin Current in Ferromagnetic Metals by Spin Pumping,"Spin pumping in nonmagnetic/ferromagnetic metal multilayers is studied both
theoretically and experimentally. We show that the line widths of the
ferromagnetic resonance (FMR) spectrum depend on the thickness of the
ferromagnetic metal layers, which must not be in resonance with the oscillating
magnetic field. We also show that the penetration depths of the transverse spin
current in ferromagnetic metals can be determined by analyzing the line widths
of their FMR spectra. The obtained penetration depths in NiFe, CoFe and CoFeB
were 3.7 [nm], 2.5 [nm] and 12.0 [nm], respectively.",0708.3528v3
2011-10-05,Molecule Induced Strong Exchange Coupling between Ferromagnetic Electrodes of a Magnetic Tunnel Junction,"Multilayer edge molecular spintronics device (MEMSD) approach can produce
novel logic and memory units for the computers. MEMSD are produced by bridging
the molecular channels across the insulator, in the exposed edge region(s) of a
magnetic tunnel junction (MTJ). The bridged molecular channels start serving as
the dominant exchange coupling medium between the two ferromagnetic electrodes
of a MTJ. Present study focus on the effect of molecule enhanced exchange
coupling on the magnetic properties of the MTJ. This paper shows that
organometallic molecular clusters (OMCs) strongly increased the magnetic
coupling between the two ferromagnetic electrodes. SQUID magnetometer showed
that OMCs transformed the typical hysteresis magnetization curve of a
Co/NiFe/AlOx/NiFe MTJ into linear one. Ferromagnetic resonance studies showed
that OMC bridges affected the two fundamental resonance peaks of the
Co/NiFe/AlOx/NiFe MTJ. According to magnetic force microscopy, OMCs caused the
disappearance of magnetic contrast from the Co/NiFe/AlOx/NiFe tunnel junction
area. These three independent and complimentary experiments, suggested the
development of extremely strong interlayer exchange coupling. This work
delineated a practical route to control the exchange coupling between
ferromagnetic electrodes. Ability to tailor magnetic coupling can lead to the
development of molecule based quantum computation device architecture.",1110.0885v1
2015-09-10,Ferromagnetic resonance and magnetoresistive measurements evidencing magnetic vortex crystal in nickel thin film with patterned antidot array,"Ferromagnetic vortices deliver robust out-of-plane magnetization at extremely
small scales. Their handling and creation therefore has high potential to
become a necessary ingredient for future data storage technologies in order to
keep up with the pace of growing information density demands. In this study we
show that by using one step nanolithography method, we are able to create
ferromagnetic vortex lattices in thin nickel films. The necessary control of
the magnetic stray field at the domain edges was achieved by actively modifying
the ferromagnetic thin film anisotropic properties at nanometer scale. We
present experimental evidence using ferromagnetic resonance and
magnetoresistance measurements supporting simulations based on the theoretical
prediction of the proclaimed vortex structures.",1509.03344v1
2018-04-18,Ferromagnetic resonance linewidth in coupled layers with easy-plane and perpendicular magnetic anisotropies,"Magnetic bilayers with different magnetic anisotropy directions are
interesting for spintronic appli- cations as they offer the possibility to
engineer tilted remnant magnetization states. We investigate the ferromagnetic
resonance (FMR) linewidth of modes associated with two interlayer exchange-
coupled ferromagnetic layers, the first a CoNi multilayer with a perpendicular
magnetic anisotropy, and the second a CoFeB layer with an easy-plane
anisotropy. For antiferromagnetic interlayer ex- change coupling, elevated FMR
linewidths are observed below a characteristic field. This is in contrast to
what is found in uncoupled, ferromagnetically coupled and single ferromagnetic
layers in which the FMR linewidth increases monotonically with field. We show
that the characteristic field at which there is a dramatic increase in FMR
linewidth can be understood using a macrospin model with Heisenberg-type
exchange coupling between the layers.",1804.06796v1
2021-03-09,Self-induced spin-orbit torques in metallic ferromagnets,"We present a phenomenological theory of spin-orbit torques in a metallic
ferromagnet with spin-relaxing boundaries. The model is rooted in the coupled
diffusion of charge and spin in the bulk of the ferromagnet, where we account
for the anomalous Hall effects as well as the anisotropic magnetoresistance in
the corresponding constitutive relations for both charge and spin sectors. The
diffusion equations are supplemented with suitable boundary conditions
reflecting the spin-sink capacity of the environment. In inversion-asymmetric
heterostructures, the uncompensated spin accumulation exerts a dissipative
torque on the order parameter, giving rise to a current-dependent linewidth in
the ferromagnetic resonance with a characteristic angular dependence. We
compare our model to recent spin-torque ferromagnetic resonance measurements,
illustrating how rich self-induced spin-torque phenomenology can arise even in
simple magnetic structures.",2103.05743v2
2022-01-26,Instability of the ferromagnetic quantum critical point in strongly interacting 2D and 3D electron gases with arbitrary spin-orbit splitting,"In this work we revisit itinerant ferromagnetism in 2D and 3D electron gases
with arbitrary spin-orbit splitting and strong electron-electron interaction.
We identify the resonant scattering processes close to the Fermi surface that
are responsible for the instability of the ferromagnetic quantum critical point
at low temperatures. In contrast to previous theoretical studies, we show that
such processes cannot be fully suppressed even in presence of arbitrary
spin-orbit splitting. A fully self-consistent non-perturbative treatment of the
electron-electron interaction close to the phase transition shows that these
resonant processes always destabilize the ferromagnetic quantum critical point
and lead to a first-order phase transition. Characteristic signatures of these
processes can be measured via the non-analytic dependence of the spin
susceptibility on magnetic field both far away or close to the phase
transition.",2201.10995v1
2016-03-17,Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations,"Nowadays, micromagnetic simulations are a common tool for studying a wide
range of different magnetic phenomena, including the ferromagnetic resonance. A
technique for evaluating reliability and validity of different micromagnetic
simulation tools is the simulation of proposed standard problems. We propose a
new standard problem by providing a detailed specification and analysis of a
sufficiently simple problem. By analyzing the magnetization dynamics in a thin
permalloy square sample, triggered by a well defined excitation, we obtain the
ferromagnetic resonance spectrum and identify the resonance modes via Fourier
transform. Simulations are performed using both finite difference and finite
element numerical methods, with \textsf{OOMMF} and \textsf{Nmag} simulators,
respectively. We report the effects of initial conditions and simulation
parameters on the character of the observed resonance modes for this standard
problem. We provide detailed instructions and code to assist in using the
results for evaluation of new simulator tools, and to help with numerical
calculation of ferromagnetic resonance spectra and modes in general.",1603.05419v1
2014-10-11,Spin wave free spectrum and magnetic field gradient of nanopatterned planes of ferromagnetic cobalt nanoparticles: key properties for magnetic resonance based quantum computing,"We present a study by ferromagnetic resonance at microwave Q band of two
sheets of cobalt nanoparticles obtained by annealing SiO2 layers implanted with
cobalt ions. This ex- perimental study is performed as a function of the
applied magnetic field orientation, tempera- ture, and dose of implanted cobalt
ions. We demonstrate that each of those magnetic sheet of cobalt nanoparticles
can be well modelled by a nearly two dimensional ferromagnetic sheet hav- ing a
reduced effective saturation magnetization, compared to a regular thin film of
cobalt. The nanoparticles are found superparamagnetic above around 210 K and
ferromagnetic below this blocking temperature. Magnetostatic calculations show
that a strong magnetic field gradient of around 0.1 G/nm could be produced by a
ferromagnetic nanostripe patterned in such magnetic sheet of cobalt
nanoparticles. Such a strong magnetic field gradient combined with electron
para- magnetic resonance may be relevant for implementing an intermediate scale
quantum computer based on arrays of coupled electron spins, as previously
reported (Eur. Phys. J. B (2014) 87, 183). However, this new approach only
works if no additional spin decoherence is introduced by the spin waves
exitations of the ferromagnetic nanostructure. We thus suggest theoretically
some possible magnetic anisotropy engineering of cobalt nanoparticles that
could allow to suppress the spin qubit decoherence induced by the unwanted
collective excitation of their spins.",1410.3005v1
2015-08-09,Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance,"A distinguishing feature of spin accumulation in ferromagnet-semiconductor
devices is precession of the non-equilibrium spin population of the
semiconductor in a magnetic field. This is the basis for detection techniques
such as the Hanle effect, but these approaches become less effective as the
spin lifetime in the semiconductor decreases. For this reason, no electrical
Hanle measurement has been demonstrated in GaAs at room temperature. We show
here that by forcing the magnetization in the ferromagnet (the spin injector
and detector) to precess at the ferromagnetic resonance frequency, an
electrically generated spin accumulation can be detected from 30 to 300 K. At
low temperatures, the distinct Larmor precession of the spin accumulation in
the semiconductor can be detected by ferromagnetic resonance in an oblique
field. We verify the effectiveness of this new spin detection technique by
comparing the injection bias and temperature dependence of the measured spin
signal to the results obtained using traditional methods. We further show that
this new approach enables a measurement of short spin lifetimes (< 100 psec), a
regime that is not accessible in semiconductors using traditional Hanle
techniques.",1508.02093v1
2007-12-10,Ferromagnetic Quantum Critical Fluctuations and Anomalous Coexistence of Ferromagnetism and Superconductivity in UCoGe Revealed by Co-NMR and NQR Studies,"Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)
studies were performed in the recently discovered UCoGe, in which the
ferromagnetic and superconducting (SC) transitions were reported to occur at
$T_{\rm Curie} \sim 3$ K and $T_S \sim 0.8$ K (N. T. Huy {\it et al.}, Phys.
Rev. Lett. {\bf 99} (2007) 067006), in order to investigate the coexistence of
ferromagnetism and superconductivity as well as the normal-state and SC
properties from a microscopic point of view. From the nuclear spin-lattice
relaxation rate $1/T_1$ and Knight-shift measurements, we confirmed that
ferromagnetic fluctuations which possess a quantum critical character are
present above $T_{\rm Curie}$ and the occurrence of ferromagnetic transition at
2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal
state show that UCoGe is an itinerant ferromagnet similar to ZrZn$_2$ and
YCo$_2$. The onset SC transition was identified at $T_S \sim 0.7$ K, below
which $1/T_1$ of 30 % of the volume fraction starts to decrease due to the
opening of the SC gap. This component of $1/T_1$, which follows a $T^3$
dependence in the temperature range of $0.3 - 0.1$ K, coexists with the
magnetic components of $1/T_1$ showing a $\sqrt{T}$ dependence below $T_S$.
  From the NQR measurements in the SC state, we suggest that the self-induced
vortex state is realized in UCoGe.",0712.1403v2
2020-06-24,Ferromagnetic induced Kondo effect in graphene with a magnetic impurity,"We investigate the many-body effects of a magnetic adatom in ferromagnetic
graphene by using the numerical renormalization group method. The nontrivial
band dispersion of ferromagnetic graphene gives rise to interesting Kondo
physics different from that in conventional ferromagnetic materials. For a
half-filled impurity in undoped graphene, the presence of ferromagnetism can
bring forth Kondo correlations, yielding two kink structures in the local
spectral function near the Fermi energy. When the spin splitting of local
occupations is compensated by an external magnetic field, the two Kondo kinks
merge into a full Kondo resonance characterizing the fully screened ground
state. Strikingly, we find the resulting Kondo temperature monotonically
increases with the spin polarization of Dirac electrons, which violates the
common sense that ferromagnetic bands are usually detrimental to Kondo
correlations. Doped ferromagnetic graphene can behave as half metals, where its
density of states at the Fermi energy linearly vanishes for one spin direction
but keeps finite for the opposite direction. In this regime, we demonstrate an
abnormal Kondo resonance that occurs in the first spin direction, while
completely absent in the other one.",2006.13582v1
2005-09-01,Ferromagnetic resonance study of polycrystalline Cobalt ultrathin films,"We present room temperature ferromagnetic resonance (FMR) studies of
polycrystalline ||Pt/10 nm Cu/t Co/10 nm Cu/Pt|| films as a function of Co
layer thickness (1 < t < 10 nm) grown by evaporation and magnetron sputtering.
FMR was studied with a high frequency broadband coplanar waveguide (up to 25
GHz) using a flip-chip method. The resonance field and the linewidth were
measured as a function of the ferromagnetic layer thickness. The evaporated
films exhibit a lower magnetization density (Ms = 1131 emu/cm^3) compared to
the sputtered films (Ms= 1333 emu/cm^3), with practically equal perpendicular
surface anisotropy (Ks ~ -0.5 erg/cm^2). For both series of films, a strong
increase of the linewidth was observed for Co layer thickness below 3 nm. For
films with a ferromagnetic layer thinner than 4 nm, the damping of the
sputtered films is larger than that of the evaporated films. The thickness
dependence of the linewidth can be understood in term of the spin pumping
effect, from which the interface spin mixing conductance
g^{\uparrow\downarrow}S^{-1} is deduced.",0509036v1
2003-05-20,Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes,"We introduce the concept of computerized tomographic microscopy in magnetic
resonance imaging using the magnetic fields and field gradients from a
ferromagnetic probe. We investigate a configuration where a two-dimensional
sample is under the influence of a large static polarizing field, a small
perpendicular radio-frequency field, and a magnetic field from a ferromagnetic
sphere. We demonstrate that, despite the non-uniform and non-linear nature of
the fields from a microscopic magnetic sphere, the concepts of computerized
tomography can be applied to obtain proper image reconstruction from the
original spectral data by sequentially varying the relative sample-sphere
angular orientation. The analysis shows that the recent proposal for atomic
resolution magnetic resonance imaging of discrete periodic crystal lattice
planes using ferromagnetic probes can also be extended to two-dimensional
imaging of non-crystalline samples with resolution ranging from micrometer to
Angstrom scales.",0305084v1
2008-10-22,Strong asymmetry of microwave absorption by bi-layer conducting ferromagnetic films in the microstrip-line based broadband ferromagnetic resonance,"Peculiarities of ferromagnetic resonance response of conducting magnetic
bi-layer films of nanometric thicknesses excited by microstrip microwave
transducers have been studied theoretically. Strong asymmetry of the response
has been found. Depending on the order of layers with respect to the transducer
either the first higher-order standing spin wave mode, or the fundamental mode
shows the largest response.
  Film conductivity and lowered symmetry of microwave fields of such
transducers are responsible for this behavior. Amplitude of which mode is
larger also depends on the driving frequency. This effect is explained as
shielding of the asymmetric transducer field by eddy currents in the films.
This shielding remains very efficient for films with thicknesses well below the
microwave skin depth. This effect may be useful for studying buried magnetic
interfaces and should be accounted for in future development of broadband
inductive ferromagnetic resonance methods.",0810.4020v1
2011-02-28,Ferromagnetic resonance in epitaxial films: Effects of lattice strains and voltage control via ferroelectric substrate,"The phenomenon of ferromagnetic resonance (FMR) provides fundamental
information on the physics of magnetic materials and lies at the heart of a
variety of signal processing microwave devices. Here we demonstrate
theoretically that substrate-induced lattice strains may change the FMR
frequency of an epitaxial ferromagnetic film dramatically, leading to ultralow
and ultrahigh resonance frequencies at room temperature. Remarkably, the FMR
frequency varies with the epitaxial strain nonmonotonically, reaching minimum
at a critical strain corresponding to the strain-induced spin reorientation
transition. Furthermore, by coupling the ferromagnetic film to a ferroelectric
substrate, it becomes possible to achieve an efficient voltage control of FMR
parameters. In contrast to previous studies, we found that the tunability of
FMR frequency varies with the applied electric field and strongly increases at
critical field intensity. The revealed features open up wide opportunities for
the development of advanced tunable magnetoelectric devices based on strained
nanomagnets.",1102.5722v1
2012-07-18,Interface Ferromagnetism in a SrMnO3/LaMnO3 Superlattice,"Resonant soft x-ray absorption measurements at the O K edge on a
SrMnO3/LaMnO3 superlattice show a shoulder at the energy of doped holes, which
corresponds to the main peak of resonant scattering from the modulation in the
doped hole density. Scattering line shape at the Mn L3,2 edges has a strong
variation below the ferromagnetic transition temperature. This variation has a
period equal to half the superlattice superperiod and follows the development
of the ferromagnetic moment, pointing to a ferromagnetic phase developing at
the interfaces. It occurs at the resonant energies for Mn3+ and Mn4+ valences.
A model for these observations is presented, which includes a double-exchange
two-site orbital and the variation with temperature of the hopping frequency
tij between the two sites.",1207.4522v1
2014-09-18,Interference effects induced by Andreev bound states in a hybrid nanostructure composed by a quantum dot coupled to ferromagnetic and superconductor leads,"In this work, it is considered a nanostructure composed by a quantum dot
coupled to two ferromagnets and a superconductor. The transport properties of
this system are studied within a generalized mean-field approximation taking
into account proximity effects and spin-flip correlations within the quantum
dot. It is shown that the zero-bias transmittance for the co-tunneling between
the ferromagnetic leads presents a dip whose height depends on the relative
orientation of the magnetizations. When the superconductor is coupled to the
system, electron-hole correlations between different spin states leads to a
resonance in the place of the dip appearing in the transmittance. Such an
effect is accompanied by two anti-resonances explained by a leakage of
conduction channels from the co-tunneling to the Andreev transport. In the
non-equilibrium regime, correlations within the quantum dot introduce a
dependence of the resonance condition on the finite bias applied to the
ferromagnetic leads. However, it is still possible to observe signatures of the
same interference effect in the electrical current.",1409.5390v1
2015-03-29,Low-non-linearity spin-torque oscillations driven by ferromagnetic nanocontacts,"Spin-torque oscillators are strong candidates as nano-scale microwave
generators and detectors. However, because of large amplitude-phase coupling
(non-linearity), phase noise is enhanced over other linear auto-oscillators.
One way to reduce nonlinearity is to use ferromagnetic layers as a resonator
and excite them at localized spots, making a resonator-excitor pair. We
investigated the excitation of oscillations in dipole-coupled ferromagnetic
layers, driven by localized current at ferromagnetic nano-contacts.
Oscillations possessed properties of optical-mode spin-waves and at low field
($\approx$200 Oe) had high frequency (15 GHz), a moderate precession amplitude
(2--3$^\circ$), and a narrow spectral linewidth ($<$3 MHz) due to localized
excitation at nano-contacts. Micromagnetic simulation showed emission of
resonator's characteristic optical-mode spin-waves from disturbances generated
by domain-wall oscillations at nano-contacts.",1503.08408v2
2015-05-05,Spin pumping from a ferromagnet into a hopping insulator: the role of resonant absorption of magnons,"Motivated by recent experiments on spin pumping from a ferromagnet into
organic materials in which the charge transport is due to hopping, we study
theoretically the generation and propagation of spin current in a hopping
insulator. Unlike metals, the spin polarization at the boundary with
ferromagnet is created as a result of magnon absorption within pairs of
localized states and it spreads following the current-currying resistor network
(although the charge current is absent). We consider a classic resonant
mechanism of the ac absorption in insulators and adapt it to the absorption of
magnons. A strong enhancement of pumping efficiency is predicted when the
Zeeman splitting of the localized states in external magnetic field is equal to
the frequency of ferromagnetic resonance. Under this condition the absorption
of a magnon takes place within individual sites.",1505.01211v1
2015-06-09,Spin dynamics in a Curie-switch,"Ferromagnetic resonance properties of F$_1$/f/F$_2$/AF multilayers, where
weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic
layers F$_1$ and F$_2$, with F$_1$ being magnetically soft and F$_2$ -
magnetically hard due to exchange pinning to antiferromagnetic layer AF, are
investigated. Spacer-mediated exchange coupling is shown to strongly affect the
resonance fields of both F$_1$ and F$_2$ layers. Our theoretical calculations
as well as measurements show that the key magnetic parameters of the spacer,
which govern the ferromagnetic resonance in F$_1$/f/F$_2$/AF, are the magnetic
exchange length ($\Lambda$), effective saturation magnetization at $T=0$
$(m_0)$, and effective Curie temperature ($T_{\text{C}}^{\text{eff}}$). The
values of these key parameters are deduced from the experimental data for
multilayers with f = Ni$_x$Cu$_{100-x}$, for the key ranges in Ni-concentration
($x=54\div70$ at. %) and spacer thickness ($d=3\div 6$ nm). The results
obtained provide a deeper insight into thermally-controlled spin precession and
switching in magnetic nanostructures, with potential applications in spin-based
oscillators and memory devices.",1506.02928v1
2020-07-07,Current Fluctuations Driven by Ferromagnetic and Antiferromagnetic Resonance,"We consider electron transport in ferromagnets or antiferromagnets sandwiched
between metals. When spins in the magnetic materials precess, they emit
currents into the surrounding conductors. Generally, adiabatic pumping in
mesoscopic systems also enhances current fluctuations. We generalize the
description of current fluctuations driven by spin dynamics in three ways using
scattering theory. First, our theory describes a general junction with any
given electron scattering properties. Second, we consider antiferromagnets as
well as ferromagnets. Third, we treat multiterminal devices. Using shot
noise-induced current fluctuations to reveal antiferromagnetic resonance
appears to be easier than using them to reveal ferromagnetic resonance. The
origin of this result is that the associated energies are much higher as
compared to the thermal energy. The thermal energy governs the Johnson-Nyquist
that is independent of the spin dynamics. We give results for various
junctions, such as ballistic and disordered contacts. Finally, we discuss
experimental consequences.",2007.03257v2
2023-01-09,X-ray detected ferromagnetic resonance techniques for the study of magnetization dynamics,"Element-specific spectroscopies using synchrotron-radiation can provide
unique insights into materials properties. The recently developed technique of
X-ray detected ferromagnetic resonance (XFMR) allows studying the magnetization
dynamics of magnetic spin structures. Magnetic sensitivity in XFMR is obtained
from the X-ray magnetic circular dichroism (XMCD) effect, where the phase of
the magnetization precession of each magnetic layer with respect to the
exciting radio frequency is obtained using stroboscopic probing of the spin
precession. Measurement of both amplitude and phase response in the magnetic
layers as a function of bias field can give a clear signature of spin-transfer
torque (STT) coupling between ferromagnetic layers due to spin pumping. Over
the last few years, there have been new developments utilizing X-ray scattering
techniques to reveal the precessional magnetization dynamics of ordered spin
structures in the GHz frequency range. The techniques of diffraction and
reflectometry ferromagnetic resonance (DFMR and RFMR) provide novel ways for
the probing of the dynamics of chiral and multilayered magnetic materials,
thereby opening up new pathways for the development of high-density and
low-energy consumption data processing solutions.",2301.03256v1
2014-03-17,Spin resonance without spin splitting,"We predict that a single-level quantum dot without discernible splitting of
its spin states develops a spin-precession resonance in charge transport when
embedded into a spin valve. The resonance occurs in the generic situation of
Coulomb blockaded transport with ferromagnetic leads whose polarizations
deviate from perfect antiparallel alignment. The resonance appears when
electrically tuning the interaction-induced exchange field perpendicular to one
of the polarizations -- a simple condition relying on vectors in contrast to
usual resonance conditions associated with energy splittings. The spin
resonance can be detected by stationary dI/dV spectroscopy and by oscillations
in the time-averaged current using a gate-pulsing scheme. The generic
noncollinearity of the ferromagnets and junction asymmetry allow for an
all-electric determination of the spin-injection asymmetry, the anisotropy of
spin relaxation, and the magnitude of the exchange field. We also investigate
the impact of a nearby superconductor on the resonance position. Our simplistic
model turns out to be generic for a broad class of coherent few-level quantum
systems.",1403.4002v2
2008-01-07,Magnetization reversal driven by spin-injection : a mesoscopic spin-transfer effect,"A mesoscopic description of spin-transfer effect is proposed, based on the
spin-injection mechanism occurring at the junction with a ferromagnet. The
effect of spin-injection is to modify locally, in the ferromagnetic
configuration space, the density of magnetic moments. The corresponding
gradient leads to a current-dependent diffusion process of the magnetization.
In order to describe this effect, the dynamics of the magnetization of a
ferromagnetic single domain is reconsidered in the framework of the
thermokinetic theory of mesoscopic systems. Assuming an Onsager
cross-coefficient that couples the currents, it is shown that spin-dependent
electric transport leads to a correction of the Landau-Lifshitz-Gilbert
equation of the ferromagnetic order parameter with supplementary diffusion
terms. The consequence of spin-injection in terms of activation process of the
ferromagnet is deduced, and the expressions of the effective energy barrier and
of the critical current are derived. Magnetic fluctuations are calculated: the
correction to the fluctuations is similar to that predicted for the activation.
These predictions are consistent with the measurements of spin-transfer
obtained in the activation regime and for ferromagnetic resonance under
spin-injection.",0801.1019v1
2008-09-23,Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact,"We describe electrical detection of spin pumping in metallic nanostructures.
In the spin pumping effect, a precessing ferromagnet attached to a normal-metal
acts as a pump of spin-polarized current, giving rise to a spin accumulation.
The resulting spin accumulation induces a backflow of spin current into the
ferromagnet and generates a dc voltage due to the spin dependent conductivities
of the ferromagnet. The magnitude of such voltage is proportional to the
spin-relaxation properties of the normal-metal. By using platinum as a contact
material we observe, in agreement with theory, that the voltage is
significantly reduced as compared to the case when aluminum was used.
Furtheremore, the effects of rectification between the circulating rf currents
and the magnetization precession of the ferromagnet are examined. Most
significantly, we show that using an improved layout device geometry these
effects can be minimized.",0809.3859v1
2015-02-13,Antiferromagnet-Mediated Spin Transfer Between Metal and Ferromagnet,"We develop a theory for spin transported by coherent Neel dynamics through an
antiferromagnetic insulator coupled to a ferromagnetic insulator on one side
and a current-carrying normal metal with strong spin-orbit coupling on the
other. The ferromagnet is considered within the mono-domain limit and we assume
its coupling to the local antiferromagnet Neel order at the
ferromagnet|antiferromagnet interface through exchange coupling. Coupling
between the charge current and the local Neel order at the other interface is
described using spin Hall phenomenology. Spin transport through the
antiferromagnet, assumed to possess an easy-axis magnetic anisotropy, is solved
within the adiabatic approximation and the effect of spin current flowing into
the ferromagnet on its resonance linewidth is evaluated. Onsager reciprocity is
used to evaluate the inverse spin Hall voltage generated across the metal by a
dynamic ferromagnet as a function the antiferromagnet thickness.",1502.04128v1
2019-06-01,Magnetic fluctuations in the itinerant ferromagnet LaCrGe3 studied by 139La NMR,"LaCrGe$_3$ is an itinerant ferromagnet with a Curie temperature of $T_{\rm
c}$ = 85 K and exhibits an avoided ferromagnetic quantum critical point under
pressure through a modulated antiferromagnetic phase as well as tri-critical
wing structure in its temperature-pressure-magnetic field ($T$-$p$-$H$) phase
diagram. In order to understand the static and dynamical magnetic properties of
LaCrGe$_3$, we carried out $^{139}$La nuclear magnetic resonance (NMR)
measurements. Based on the analysis of NMR data, using the
self-consistent-renomalization (SCR) theory, the spin fluctuations in the
paramagnetic state are revealed to be isotropic ferromagnetic and three
dimensional (3D) in nature. Moreover, the system is found to follow the
generalized Rhodes-Wohfarth relation which is expected in 3D itinerant
ferromagnetic systems. As compared to other similar itinerant ferromagnets, the
Cr 3$d$ electrons and their spin fluctuations are characterized to have a
relatively high degree of localization in real space.",1906.00249v1
2021-09-14,Quantum magnetism of ferromagnetic spin dimers in $α$-KVOPO$_4$,"Magnetism of the spin-$\frac12$ $\alpha$-KVOPO$_4$ is studied by
thermodynamic measurements, $^{31}$P nuclear magnetic resonance (NMR), neutron
diffraction, and density-functional band-structure calculations. Ferromagnetic
Curie-Weiss temperature of $\theta_{\rm CW}\simeq 15.9$ K and the saturation
field of $\mu_0H_s\simeq 11.3$ T suggest the predominant ferromagnetic coupling
augmented by a weaker antiferromagnetic exchange that leads to a short-range
order below 5 K and the long-range antiferromagnetic order below $T_{\rm
N}\simeq 2.7$ K in zero field. Magnetic structure with the propagation vector
$\mathbf k=(0,\frac12,0)$ and the ordered magnetic moment of 0.58 $\mu_B$ at
1.5 K exposes a non-trivial spin lattice where strong ferromagnetic dimers are
coupled antiferromagnetically. The reduction in the ordered magnetic moment
with respect to the classical value (1 $\mu_{\rm B}$) indicates sizable quantum
fluctuations in this setting, despite the predominance of ferromagnetic
exchange. We interpret this tendency toward ferromagnetism as arising from the
effective orbital order in the folded chains of the VO$_6$ octahedra.",2109.06840v1
2008-06-20,Penetration Depth of Transverse Spin Current in Ferromagnetic Metals,"The line width of the ferromagnetic resonance (FMR) spectrum of
Cu/CoFeB/Cu/Co/Cu is studied. Analyzing the FMR spectrum by the theory of spin
pumping, we determined the penetration depth of the transverse spin current in
the Co layer. The obtained penetration depth of Co is 1.7 nm.",0806.3315v1
2014-02-14,Extremely high-resolution measurements of microwave magnetisation dynamics in magnetic thin films and nanostructures,"In this work we discuss the use of interferometric measurement technique to
study microwave magnetization dynamics on ferromagnetic nanostructures. We
demonstrate that in this way one can resolve features which are impossible to
resolve with broadband ferromagnetic resonance and traveling spin wave
spectroscopy otherwise.",1402.3459v1
2022-11-15,Experimental Observation of a Magnetic Interfacial Effect,"We observed a magnetic interfacial effect due to the coupling between two
interfaces of different materials. The interface is compoust of an
antiferromagnetic and other quasi-ferromagnetic material. This effect we
measured through the ferromagnetic resonance technique without and with
electric current.",2211.08130v1
2005-01-19,Ferromagnetic Resonance in selected nanostructural materials designed for technological applications,"During the past ten years nanostructures have been subject of active
research. Fabrication of such systems follows well developed methods. The
increase in the number of materials available for research and applications
requires that the methods of their characterization be even more precise then
before. Thin film structures have many advantages for technological
applications because of compatibility with integrated circuit design. The
magnetoimpedance, MI (change of impedance of a ferromagnet on application of a
field) in 3-layered structures consisting of two magnetic layers separated by a
non-magnetic conductive layer has been predicted to show high MI. In many cases
the experimental values of MI effect are smaller than the theoretical
predictions. Therefore, more careful characterization of the samples is a must.
Accordingly, the first part of the present research deals with a ferromagnetic
resonance, FMR, study of thin films and multilayers containing Fe20Ni80 layered
nanocomponents. The second system proposed for ferromagnetic resonance study
consists of Co/GdCo multilayers prepared by rf-sputtering. It was chosen as a
model system both for convenience and in view of possible applications. The
third group of magnetic materials for FMR characterization consists of powders:
commercial polystyrene beads (Dynabeads-480) and CoNi powders with nanoscale
particle dimensions. These particles have many biomedical applications. FMR and
microwave absorption in micron size powders have been studied previously. More
recently new methods of small particle fabrication have been developed.
Therefore their characterization by microwave methods is highly desirable.",0501449v1
2022-07-08,Measuring the magnon-photon coupling in shaped ferromagnets: tuning of the resonance frequency,"Cavity photons and ferromagnetic spins excitations can exchange information
coherently in hybrid architectures, at speeds set by their mutual coupling
strength. Speed enhancement is usually achieved by optimizing the geometry of
the electromagnetic cavity. Here we show that the geometry of the ferromagnet
plays also an important role, by setting the fundamental frequency of the
magnonic resonator. Using focused ion beam patterning, we vary the aspect ratio
of different Permalloy samples reaching operation frequencies above 10 GHz
while working at low external magnetic fields. Additionally, we perform broad
band ferromagnetic resonance measurements and cavity experiments that
demonstrate that the magnon-photon coupling strength can be estimated using
either open transmission lines or resonant cavities, yielding very good
agreement. Finally, we describe a simple theoretical framework based on
electromagnetic and micromagnetic simulations that successfully accounts for
the experimental results. This approach can be used to design hybrid quantum
systems exploiting whatsoever magnetostatic mode excited in ferromagnets of
arbitrary size and shape and to tune their operation conditions.",2207.03829v3
2008-10-27,Hybrid resonant phenomenon in a metamaterial structure with integrated resonant magnetic material,"We explore the hybridization of fundamental material resonances with the
artificial resonances of metamaterials. A hybrid structure is presented in the
waveguide environment that consists of a resonant magnetic material with a
characteristic tuneable gyromagnetic response that is integrated into a
complementary split ring resonator (CSRR) metamaterial structure. The combined
structure exhibits a distinct hybrid resonance in which each natural resonance
of the CSRR is split into a lower and upper resonance that straddle the
frequency for which the magnetic material's permeability is zero. We provide an
analytical understanding of this hybrid resonance and define an effective
medium theory for the combined structure that demonstrates good agreement with
numerical electromagnetic simulations. The designed structure demonstrates the
potential for using a ferrimagnetic or ferromagnetic material as a means of
creating a tunable metamaterial structure.",0810.4871v1
2000-10-11,"The frequency, temperature, and magnetic field dependence of ferromagnetic resonance and anti-resonance in La$_{0.8}$Sr$_{0.2}$MnO$_3$","Employing a broadband microwave reflection configuration, we have measured
the complex surface impedance, $Z_S(\omega,T,H)$, of single crystal
La$_{0.8}$Sr$_{0.2}$MnO$_3$, as a function of frequency (0.045-45 GHz),
temperature (250-325 K), and magnetic field (0-1.9 kOe). The microwave surface
impedance depends not only on the resistivity of the material, but also on the
magnetic permeability, $\hat\mu(\omega,T,H)$, which gives rise to ferromagnetic
resonance (FMR) and ferromagnetic anti-resonance (FMAR). The broadband nature
of this experiment allows us to follow the FMR to low frequency and to deduce
the behavior of both the local internal fields and the local magnetization in
the sample.",0010172v1
2003-07-03,"Cyclotron Resonance in Ferromagnetic InMnAs/(Al,Ga)Sb Heterostructures","We report the observation of hole cyclotron resonance (CR) in
InMnAs/(Al,Ga)Sb heterostructures in a wide temperature range covering both the
paramagnetic and ferromagnetic phases. We observed two pronounced resonances
that exhibit drastic changes in position, linewidth, and intensity at a
temperature higher than the Curie temperature, indicating possible local
magnetic ordering or clustering. We attribute the two resonances to the
fundamental CR transitions expected for delocalized valence-band holes in the
quantum limt. Using an 8-band {\bf k$\cdot$p} model, which incorporates
ferromagnetism within a mean-field approximation, we show that the
temperature-dependent CR peak shift is a direct measure of the carrier-Mn
exchange interaction. Significant line narrowing was observed at low
temperatures, which we interpret as the suppression of localized spin
fluctuations.",0307087v1
2006-04-27,Weakly Coupled Motion of Individual Layers in Ferromagnetic Resonance,"We demonstrate a layer- and time-resolved measurement of ferromagnetic
resonance (FMR) in a Ni81Fe19 / Cu / Co93Zr7 trilayer structure. Time-resolved
x-ray magnetic circular dichroism has been developed in transmission, with
resonant field excitation at a FMR frequency of 2.3 GHz. Small-angle (to 0.2
degree), time-domain magnetization precession could be observed directly, and
resolved to individual layers through elemental contrast at Ni, Fe, and Co
edges. The phase sensitivity allowed direct measurement of relative phase lags
in the precession oscillations of individual elements and layers. A weak
ferromagnetic coupling, difficult to ascertain in conventional FMR
measurements, is revealed in the phase and amplitude response of individual
layers across resonance.",0604635v1
2014-07-04,Temperature Dependent Ferromagnetic Resonance via the Landau-Lifshitz-Bloch Equation: Application to FePt,"Using the Landau-Lifshitz-Bloch (LLB) equation for ferromagnetic materials,
we derive analytic expressions for temperature dependent absorption spectra as
probed by ferromagnetic resonance (FMR). By analysing the resulting
expressions, we can predict the variation of the resonance frequency and
damping with temperature and coupling to the thermal bath. We base our
calculations on the technologically relevant L1$_0$ FePt, parameterised from
atomistic spin dynamics simulations, with the Hamiltonian mapped from ab-initio
parameters. By constructing a multi-macrospin model based on the LLB equation
and exploiting GPU acceleration we extend the study to investigate the effects
on the damping and resonance frequency in ${\mu}$m sized structures.",1407.1174v1
2014-09-23,Combining ferromagnetic resonator and digital image correlation to study the strain induced resonance tunability in magnetoelectric heterostructures,"This paper reports the development of a methodology combining microstrip
ferromagnetic resonance (MS-FMR) and digital image correlation (DIC) in order
to silmuteanously measure the voltage-induced strains and the magnetic
resonance in artificial magnetoelectric heterostructures (magnetic
films/piezoelectric substrate? or magnetic films/flexible
substrate/piezoelectric actuator ?). The overall principle of the technique and
the related analytical modelling are described. It is powerful to estimate the
magnetostriction coefficient of ferromagnetic thin films and can be used to
determine the effective magnetoelectric coefficient of the whole
heterostructures in addition to the piezoelectric coefficient related to the
in-plane voltage-induced strains. This methodology can be applied to system for
which the strains are well transmitted at the different interfaces.",1409.6641v1
2015-06-17,Continuous wave approach for simulating Ferromagnetic Resonance in nanosized elements,"We present a numerical approach to simulate the Ferromagnetic Resonance (FMR)
of micron and nanosized magnetic elements by a micromagnetic finite difference
method. In addition to a static magnetic field a linearly polarized oscillating
magnetic field is utilized to excite and analyze the spin wave excitations
observed by Ferromagnetic Resonance in the space- and time-domain. Our
continuous wave approach (CW) provides an alternative to the common simulation
method, which uses a pulsed excitation of the magnetic system. It directly
models conventional FMR-experiments and permits the determination of the real
and imaginary part of the complex dynamic susceptibility without the need of
post-processing. Furthermore not only the resonance fields, but also
linewidths, ellipticity, phase relations and relative intensities of the
excited spin wave modes in a spectrum can be determined and compared to
experimental data. The magnetic responses can be plotted as a function of
spatial dimensions yielding a detailed visualization of the spin wave modes and
their localization as a function of external magnetic field and frequency. This
is illustrated for the case of a magnetic micron sized stripe.",1506.05292v1
2020-04-08,Charge-to-spin conversion efficiency in ferromagnetic nanowires by spin torque ferromagnetic resonance: Reconciling lineshape and linewidth analysis methods,"Spin orbit torques are of great interest for switching the magnetization
direction in nanostructures, moving skyrmions and exciting spin waves. The
standard method of determining their efficiency is by spin torque ferromagnetic
resonance (ST-FMR), a technique that involves analyzing the resonance linewidth
or lineshape. On microstuctures these two analysis methods are quite
consistent. Here we present ST-FMR results on permalloy (Ni$_{80}$Fe$_{20}$)
nanowires -- with widths varying from $150$ to 800 nm -- that show that the
standard model used to analyze the resonance linewidth and lineshape give
different results; the efficiency appears greatly enhanced in nanowires when
the lineshape method is used. A ST-FMR model that properly accounts for the
sample shape is presented and shows much better consistency between the two
methods. Micromagnetic simulations are used to verify the model. These results
and the more accurate nanowire model presented are of importance for
characterizing and optimizing charge-to-spin conversion efficiencies in
nanostructures.",2004.03784v1
2019-01-04,How to accurately determine a saturation magnetization of the sample in a ferromagnetic resonance experiment?,"The phenomenon of ferromagnetic resonance (FMR) is still being exploited for
determining the magnetocrystalline anisotropy constants of magnetic materials.
We show that one can also determine accurately the saturation magnetization of
the sample using results of FMR experiments after taking into account the
relationship between resonance frequency and curvature of the spatial
distribution of free energy at resonance. Specifically, three examples are
given of calculating saturation magnetization from FMR data: we use historical
Bickford's measurements from 1950 for bulk magnetite, Liu's measurements from
2007 for a 500 mn thin film of a weak ferromagnet (Ga, Mn)As, and Wang's
measurements from 2014 for an ultrathin film of YIG. In all three cases, the
magnetization values we have determined are consistent with the results of
measurements.",1901.01207v1
2021-11-15,Nonstanding spin waves in a single rectangular permalloy microstrip under uniform magnetic excitation,"Ferromagnetic resonance modes in a single rectangular Ni$_{80}$Fe$_{20}$
microstrip were directly imaged using time-resolved scanning transmission x-ray
microscopy combined with a phase-locked ferromagnetic resonance excitation
scheme and the findings were corroborated by micromagnetic simulations.
Although under uniform excitation in a single confined microstructure typically
standing spin waves are expected, all imaged spin waves showed a nonstanding
character both, at and off resonance, the latter being additionally detected
with microantenna-based ferromagnetic resonance. The effect of the edge quality
on the spin waves was observed in micromagnetic simulations.",2111.07773v3
2023-03-09,Antiferromagnetic resonances in superconductor-ferromagnet multilayers,"In this work, we study magnetization dynamics in superconductor-ferromagnet
(S-F) thin-film multilayer. Theoretical considerations supported by the
broad-band ferromagnetic resonance spectroscopy reveal development of acoustic
and optic resonance modes in S-F multilayers at significantly higher
frequencies in comparison to the Kittel mode of individual F-layers. These
modes are formed due to antiferromagnetic-like interaction between F-layers via
shared circulating superconducting currents in S-layers. The gap between
resonance modes is determined by the thickness and superconducting penetration
depth in S-layers. Overall, rich spectrum of S-F multilayers and its tunability
opens wide prospects for application of these multialyers in magnonics as well
as in various superconducting hybrid systems.",2303.05175v2
2018-11-13,Ferromagnetic resonance and magnetic precessions in $\varphi_0$ junction,"The Josephson $\varphi_0$ junctions with the current-phase relation $I = I_c
\sin (\varphi-\varphi_0)$, where the phase shift $\varphi_0$ is proportional to
the magnetic moment perpendicular to the gradient of the asymmetric spin-orbit
potential, demonstrate a number of unique features important for
superconducting spintronics and modern informational technologies. Here we show
that a current sweep along IV-characteristic of the $\varphi_0$ junction may
lead to regular magnetization dynamics with a series of specific phase
trajectories. The origin of these trajectories is related to a direct coupling
between the magnetic moment and the Josephson oscillations in these junctions,
and ferromagnetic resonance when Josephson frequency coincides with the
ferromagnetic one. We demonstrate that an external electromagnetic field can
control the dynamics of magnetic moment within a current interval corresponding
to a Shapiro step and produce topological transformation of specific precession
trajectories. We demonstrate the appearance of the DC component of
superconducting current and clarify its role in the transformation of
IV-characteristics in the resonance region. Good agreement between numerical
and analytical results has been found in the ferromagnetic resonance region.
The presented results might be used for developing novel resonance methods of
determination of the spin-orbit coupling parameter in the non-centrosymmetric
materials. We discuss experiments which can test our results.",1811.05282v2
2021-05-19,"Determination of the spin Hall angle by the inverse spin Hall effect, device level ferromagnetic resonance, and spin torque ferromagnetic resonance: a comparison of methods","The spin torque ferromagnetic resonance (STFMR) is one of the popular methods
for measurement of the spin Hall angle (SHA). However, in order to accurately
determine SHA from STFMR measurements, the acquired data must be carefully
analyzed: The resonance linewidth should be determined to an accuracy of a
fraction of an Oe, while the dynamical interaction leading to the measured
response consists of the conventional field-induced ferromagnetic resonance
(FMR), spin-torque induced FMR, and of the inverse spin Hall effect (ISHE).
Additionally, the signal often deteriorates when DC current is passed through
the device. In this work we compare the STFMR method with two other FMR-based
methods that are used to extract SHA. The first is a device-level FMR and the
second is based on the ISHE. We identify artefacts that are caused by the noise
floor of the instrumentation that make the measurement of SHA illusive even
when the signal to noise ratio seems to be reasonable. Additionally, we
estimate a 10% error in SHA that results from neglecting the magnetic
anisotropies as in conventional measurements. Overall, we find the STFMR to be
the most robust of the three methods despite the complexity of the interaction
taking place therein. The conclusions of our work lead to a more accurate
determination of SHA and will assist in the search of novel materials for
energy efficient spin-based applications.",2105.09023v1
2007-11-02,Spin-torque driven ferromagnetic resonance of Co/Ni synthetic layers in spin valves,"Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thin
Co/Ni synthetic layers with perpendicular anisotropy confined in spin-valve
based nanojunctions. Field swept ST-FMR measurements were conducted with a
magnetic field applied perpendicular to the layer surface. The resonance lines
were measured under low amplitude rf excitation, from 1 to 20 GHz. These
results are compared with those obtained using conventional rf field driven FMR
on extended films with the same Co/Ni layer structure. The layers confined in
spin valves have a lower resonance field, a narrower resonance linewidth and
approximately the same linewidth vs frequency slope, implying the same damping
parameter. The critical current for magnetic excitations is determined from
measurements of the resonance linewidth vs dc current and is in accord with the
one determined from I-V measurements.",0711.0405v2
2017-10-14,Repulsive polarons in alkaline-earth(-like) atoms across an orbital Feshbach resonance,"We characterize properties of the so-called repulsive polaron across the
recently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms.
Being a metastable quasiparticle excitation at the positive energy, the
repulsive polaron is induced by the interaction between an impurity atom and a
Fermi sea. By analyzing in detail the energy, the polaron residue, the
effective mass, and the decay rate of the repulsive polaron, we reveal
interesting features that are intimately related to the two-channel nature of
the orbital Feshbach resonance. In particular, we find that the life time of
the repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the
two channels, and has a maximum on the BEC-side of the resonance. Further, by
considering the stability of a mixture of the impurity and the majority atoms
against phase separation, we show that the itin- erant ferromagnetism may exist
near the orbital Feshbach resonance at appropriate densities. Our results can
be readily probed experimentally, and have interesting implications for the
observation of itinerant ferromagnetism near an orbital Feshbach resonance.",1710.05166v1
1995-08-25,Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets,"The spin-lattice relaxation time $\tau_{SL}$ is a key quantity both for the
dynamical response of ferromagnets excited by laser pulses and as the speed
limit of magneto-optical recording. Extending the theory for the electron
paramagnetic resonance of magnetic impurities to spin-lattice relaxation in
ferromagnetic rare earths we calculate $\tau_{SL}$ for Gd and find a value of
48 ps in very good agreement with time-resolved spin-polarized photoemission
experiments. We argue that the time scale for $\tau_{SL}$ in metals is
essentially given by the spin-orbit induced magnetocrystalline anisotropy
energy.",9508120v1
1998-06-30,Spin Flip Torsion Balance,"The spin flip of the conduction electrons at the interface of a ferromagnetic
and a nonmagnetic part of a metallic wire, suspended between two electrodes, is
shown to tort the wire when a current is driven through it.
  In order to enhance the effect it is suggested to use an alternating current
in resonance with the torsional oscillations.
  Thereby the magnetic polarization of the conduction electrons in the
ferromagnet can be measured directly, and compared to the total magnetization.
  This may yield new information on the transport properties of the narrow band
electrons in itinerant ferromagnets.",9806370v1
1999-10-11,Anomalous spin susceptibility and magnetic polaron formation in the double exchange systems,"The magnetic susceptibility and spin-spin correlation of the double-exchange
model for doped manganites are investigated through the Monte Carlo
calculations on the three-dimensional lattice model. Deviations of the
susceptibility from the Curie-Weiss behavior above the ferromagnetic ordering
temperature $T_c$ seem to indicate a formation of local ferromagnetic clusters
in the vicinity of $T_c$, which is consistent with recent electron paramagnetic
resonance experiments for La$_{2/3}$Ca$_{1/3}$MnO$_3$. A further analysis of
the spin-spin correlations show the ferromagnetic cluster size to be
three-to-four lattice spacings, suggesting that the charge carriers may form
magnetic polarons.",9910153v1
2001-07-12,Superconducting proximity effect in clean ferromagnetic layers,"We investigate superconducting proximity effect in clean ferromagnetic layers
with rough boundaries. The subgap density of states is formed by Andreev bound
states at energies which depend on trajectory length and the ferromagnetic
exchange field. At energies above the gap, the spectrum is governed by resonant
scattering states. The resulting density of states, measurable by tunneling
spectroscopy, exhibits a rich structure, which allows to connect the
theoretical parameters from experiments.",0107252v1
2003-04-22,Optical spin transfer in ferromagnetic semiconductors,"Circularly polarized laser pulses that excite electron-hole pairs across the
band gap of (III,Mn)V ferromagnetic semiconductors can be used to manipulate
and to study collective magnetization dynamics. The initial spin orientation of
a photocarrier in a (III,V) semiconductors is determined by the polarization
state of the laser. We show that the photocarrier spin can be irreversibly
transferred to the collective magnetization, whose dynamics can consequently be
flexibly controlled by suitably chosen laser pulses. As illustrations we
demonstrate the feasibility of all optical ferromagnetic resonance and optical
magnetization reorientation.",0304492v2
2003-07-12,"Magnetic and microwave properties of (Ni,Co)Fe2O4-ferroelectric and (La,Ca,Sr)MnO3-ferroelectric multilayer structures","Structural, magnetic and ferromagnetic resonance characterization studies
have been performed on lay-ered ferromagnetic-ferroelectric oxides that show
strong magnetoelectric coupling. The samples contained thick films of ferrites
or substituted lanthanum manganites for the ferromagnetic phase and lead
zirconate titanate for the ferroelectric phase, and were sintered high
temperatures. Results indicate defect free ferrites, but deterioration of
manganite parameters due to diffusion at the interface and accounts for poor
magnetoelectric coupling in manganite-PZT samples.",0307302v1
2003-10-16,Spin Torque and its Relation to Spin Filtering,"The spin torque exerted on a magnetic moment is a reaction to spin filtering
when spin-polarized electrons interact with a thin ferromagnetic film. We show
that, for certain conditions, a spin transmission resonance (STR) gives rise to
a failure of spin filtering. As a consequence, no spin is transfered to the
ferromagnet. The condition for STR depends on the incoming energy of electrons
and the thickness of the film. For a simple model we find that when the STR
condition is satisfied, the ferromagnetic film is transparent to the incoming
electrons.",0310392v1
2004-01-30,Non-quasiparticle states in the core level spectra of ferromagnetic semiconductors and half-metallic ferromagnets,"The Green's functions that determine x-ray spectra are calculated in the s-d
exchange model of a saturated conducting ferromagnet in the presence of the
core hole. A possibility to observe non-quasiparticle (NQP) states in the core
level (x-ray absorption, emission and photoelectron) spectroscopy is
demonstrated. It is shown that NQP contributions to resonant x-ray scattering
spectra can be considerably enhanced by core hole effects in comparison with
those to the density of states.",0401625v2
2004-07-14,Quantum Mechanics of Spin Transfer in Ferromagnetic Multilayers,"We use a quantum mechanical treatment of a ballistic spin current to describe
novel aspects of spin transfer to a ferromagnetic multilayer. We demonstrate
quantum phenomena from spin transmission resonance (STR) to magnetoelectric
spin echo (MESE), depending on the coupling between the magnetic moments in the
ferromagnetic thin films. Our calculation reveals new channels through which
the zero spin transfer occurs in multilayers: the STR and MESE. We also
illustrate that counter-intuitively, a negative spin torque can act initially
on the second moment in a bilayer system.",0407365v1
2005-12-02,Exchange enhanced anisotropy in ferromagnetic/antiferromagnetic multilayers: dynamic consequences,"The phenomena of exchange anisotropy is well known in terms of static
magnetization properties such as enhanced coercivity and magnetization loop
shifts. These effects are primarily associated with effective anisotropies
introduced into the ferromagnet by exchange coupling with a strongly
anisotropic antiferromagnet. These effective anisotropies can be understood as
manifestations of a more fundamental exchange induced susceptibility. We show
that a consequence of this view is that a class of unusual dynamic effects
associated with the exchange susceptibility should also exist. The effects
become apparent near the ordering temperature of the antiferromagnet and affect
domain wall velocities, domain wall resonances, and precessional switching of
the ferromagnet.",0512034v1
2006-03-09,Spin Current and Current-Induced Spin Transfer Torque in Ferromagnet-Quantum Dot-Ferromagnet Coupled Systems,"Based on Keldysh's nonequilibrium Green function method, the spin-dependent
transport properties in a ferromagnet-quantum dot (QD)-ferromagnet coupled
system are investigated. It is shown the spin current shows quite different
characteristics from its electrical counterpart, and by changing the relative
orientation of both magnetizations, it can change its magnitude even sign. The
current-induced spin transfer torque (CISTT) is uncovered to be greatly
enhanced when the bias voltage meets with the discrete levels of the QD at
resonant positions. The relationship between the CISTT, the electrical current
and the spin current is also addressed.",0603235v1
2006-07-27,A possible model to high TC ferromagnetism in Gallium Manganese Nitrides based on resonation properties of impurities in semiconductors,"The high TC ferromagnetism in (Ga,Mn)N were observed and almost all results
are approximately similar to the experimental results in (Ga,Mn)As except the
value of TC. Though all standard experiments on magnetism clearly support the
results, the value is unexpectedly high. This work present and discuss the
possibility of high TC ferromagnetism, after brief review of the experimental
results. The key speculation to Bosonization method in three dimensions is
resembled with the problems in Anderson localization.",0607708v1
2007-06-12,Temperature dependence of magnetic anisotropy in bulk and nanoparticles of Pr_0.5Sr_0.5MnO_3,"Nanoparticles (size 20, 40 and 60 nm) of Pr_0.5Sr_0.5MnO_3 are prepared by
sol-gel technique and their magnetic properties are studied using ferromagnetic
resonance and magnetization measurements. A comparison with the properties of
the bulk material shows that the ferromagnetic transition at 265 K remains
unaffected but the anti-ferromagnetic transition at T_N = 150 K disappears in
the nanoparticles. Further, the temperature dependence of magnetic anisotropy
shows a complex behavior, being higher in the nanoparticles at high
temperatures and lower at lower temperatures in comparison with the bulk.",0706.1662v1
2007-06-12,Magnetic fingerprint in a ferromagnetic wire: Spin torque diode effect and induction of the DC voltage spectrum inherent in the wire under application for RF current,"We report the rectifying effect of a constant-wave radio frequency (RF)
current by a magnetic domain wall (DW) on a single-layered ferromagnetic wire.
A direct-current (DC) voltage is generated by the spin torque diode effect,
which is a consequence of magnetoresistance oscillation due to the resonant
spin wave excitation induced by the spin-polarized RF current. The DC voltage
spectrum strongly depends on the internal spin structure in the DW, which
corresponds to the magnetic fingerprint of the spin structure in the
ferromagnetic wire.",0706.1733v1
2008-02-13,FMR induced Josephson Current in a Superconductor/Ferromagnet/Superconductor Junction,"We propose the phase dynamics induced by spin waves in a
superconductor/ferromagnet/superconductor (SC/FM/SC) Josephson junction. The
resistively shunted junction (RSJ) model, which describes the dynamics of
superconducting phase difference, is extended to include the spin wave
excitation by ferromagnetic resonance (FMR) using the gauge invariant phase
difference between two s-wave superconductors. The current-voltage
characteristics show step structures when the magnetization in FM is driven by
tuning the microwave frequency to FMR in the SC/FM/SC junction. The result
presents a new route to observe the spin wave excitation using the Josephson
effect.",0802.1755v2
2008-04-07,Ferromagnetic Josephson junction with precessing magnetization,"The Josephson current in a diffusive
superconductor/ferromagnet/superconductor junction with precessing
magnetization is calculated within the quasiclassical theory of
superconductivity. When the junction is phase-biased, a stationary current
(without a.c. component) can flow through it despite the non-equilibrium
condition. A large critical current is predicted due to a dynamically induced
long range triplet proximity effect. Such effect could be observed in a
conventional hybrid device close to the ferromagnetic resonance.",0804.1050v1
2008-06-10,Geometrical control of the magnetization direction in high aspect-ratio PdNi ferromagnetic nano-electrodes,"We present a study of electron-beam evaporated Pd0.4Ni0.6 alloy thin films by
means of ferromagnetic resonance measurements on extended films of varying
thickness and anisotropic magnetoresistance measurements of lithographically
patterned high aspect-ratio ferromagnetic electrodes, respectively. The results
reveal that the direction of the magnetization strongly depends on the
electrode lateral dimensions, transitioning from in-plane magnetization for
extended films to out-of-the-plane magnetization for electrode widths below 2-3
microns, reaching 58 degrees off-plane for 100 nm-wide nanoelectrodes.",0806.1744v1
2008-09-16,Stochastic dynamics of magnetization in a ferromagnetic nanoparticle out of equilibrium,"We consider a small metallic particle (quantum dot) where ferromagnetism
arises as a consequence of Stoner instability. When the particle is connected
to electrodes, exchange of electrons between the particle and the electrodes
leads to a temperature- and bias-driven Brownian motion of the direction of the
particle magnetization. Under certain conditions this Brownian motion is
described by the stochastic Landau-Lifshitz-Gilbert equation. As an example of
its application, we calculate the frequency-dependent magnetic susceptibility
of the particle in a constant external magnetic field, which is relevant for
ferromagnetic resonance measurements.",0809.2611v1
2013-06-26,"Actuation, propagation, and detection of transverse magnetoelastic waves in ferromagnets","We study propagation of ultrasonic waves through a ferromagnetic medium with
special attention to the boundary conditions at the interface with an
ultrasonic actuator. In analogy to charge and spin transport in conductors, we
formulate the energy transport through the system as a scattering problem. We
find that the magneto-elastic coupling leads to a non-vanishing magnetic
(elastic) energy accompanying the acoustic (spin) waves with a resonantly
enhanced effect around the dispersion relation anti-crossing point. We
demonstrate the physics of excitation of magnetization dynamics via acoustic
waves injection around the ferromagnetic resonance frequency.",1306.6268v2
2015-09-09,Inertial terms to magnetization dynamics in ferromagnetic thin films,"Inertial magnetization dynamics have been predicted at ultrahigh speeds, or
frequencies approaching the energy relaxation scale of electrons, in
ferromagnetic metals. Here we identify inertial terms to magnetization dynamics
in thin Ni$_{79}$Fe$_{21}$ and Co films near room temperature. Effective
magnetic fields measured in high-frequency ferromagnetic resonance (115-345
GHz) show an additional stiffening term which is quadratic in frequency and
$\sim$ 80 mT at the high frequency limit of our experiment. Our results extend
understanding of magnetization dynamics at sub-picosecond time scales.",1509.02836v1
2010-05-12,Proposal for a ferromagnetic multiwell spin oscillator,"The highly nonlinear coupling of transport and magnetic properties in a
multiwell heterostructure, which comprises ferromagnetic quantum wells made of
diluted magnetic semiconductors, is theoretically investigated. The interplay
of resonant tunneling and carrier-mediated ferromagnetism in the magnetic wells
induces very robust, self-sustained current and magnetization oscillations.
Over a large window of steady bias voltages the spin polarization of the
collector current is oscillating between positive and negative values,
realizing a spin oscillator device.",1005.2087v1
2012-01-31,Exchange-induced phase separation in Ni-Cu films,"Magneto-structural properties of films of diluted ferromagnetic alloys
Ni$_x$Cu$_{1-x}$ in the concentration range $0.7 < x < 1.0$ are studied
experimentally. Films deposited by magnetron sputtering show partial phase
separation, as evidenced by structural analysis and ferromagnetic resonance
measurements. The phase diagram of the Ni$_x$Cu$_{1-x}$ bulk system is obtained
using numerical theoretical analysis of the electronic structure, taking into
account the inter-atomic exchange interactions. The results confirm the
experimentally found partial phase separation, explain it as magnetic in
origin, and indicate an additional metastable region connected with the
ferromagnetic transition in the system.",1201.6493v1
2012-04-11,Magnetostatic spin waves and magnetic-wave chaos in ferromagnetic films. II. Numerical simulations of non-linear waves,"A method and some results of numeric simulations of magnetostatic spin waves
in ferromagnetic films are exponded, in comparison with the theory earlier
presented in arXiv preprint 1204.0200. In particular, roles of films finiteness
(edges) and defects in formation of linear and non-linear magnetostatic wave
patterns, excitation and evolution of two-dimensional solitons, and chaotic
non-linear ferromagnetic resonance are considered.",1204.2423v1
2019-06-06,Current noise geometrically generated by a driven magnet,"We consider a non-equilibrium cross-response phenomenon, whereby a driven
magnetization gives rise to electric shot noise (but no d.c. current). This
effect is realized on a nano-scale, with a small metallic ferromagnet which is
tunnel-coupled to two normal metal leads. The driving gives rise to a
precessing magnetization. The geometrically generated noise is related to a
non-equilibrium distribution in the ferromagnet. Our protocol provides a new
channel for detecting and characterizing ferromagnetic resonance.",1906.02730v2
2018-03-13,Ultrafast light switching of ferromagnetism in EuSe,"We demonstrate that light resonant with the bandgap forces the
antiferromagnetic semiconducor EuSe to enter ferromagnetic alignment in the
picosecond time scale. A photon generates an electron-hole pair, whose electron
forms a supergiant spin polaron of magnetic moment of nearly 6,000 Bohr
magnetons. By increasing the light intensity, the whole of the sample can be
fully magnetized. The key to the novel large photoinduced magnetization
mechanism is the huge enhancement of the magnetic susceptibility when both
antiferromagnetic and ferromagnetic interactions are present in the material,
and are of nearly equal magnitude, as is the case in EuSe.",1803.05038v1
2024-03-21,Efecto Hall de espin inverso en peliculas de Nb Mo y Bi por bombeo de espin,"The inverse spin Hall effect used for detection of spin currents was observed
by voltage measurements in bilayers of normal metal (NM)/ferromagnetic metal
(FM), using Nb, Mo and Bi as normal metal and Permalloy (Py,
Ni$_{81}$Fe$_{19}$) as ferromagnetic metal. The spin current was generated by
the spin pumping effect with ferromagnetic resonance. The samples were
deposited by dc magnetron sputtering at room temperature on Si (001)
substrates. The three bilayers of Nb/Py, Mo/Py and Bi/Py had a spin-orbit
coupling large enough to observe the voltage generation by spin Hall effect",2403.17976v1
2004-07-20,Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films,"We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots
and the preparation of room-temperature ferromagnetic nanocrystalline thin
films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation
reaction in DMSO under atmospheric conditions. Synthesis was monitored by
electronic absorption and electron paramagnetic resonance (EPR) spectroscopies.
Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the
synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from
the surfaces of as-prepared nanocrystals using dodecylamine to yield
high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and
uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and
Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic
susceptibilities, confirmed that the manganese is substitutionally incorporated
into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing
from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was
observed in spin-coated thin films of the nanocrystals, with 300 K saturation
moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct
ferromagnetic resonance signal was observed in the EPR spectra of the
ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its
dependence on synthetic variables are discussed in the context of these and
previous theoretical and experimental results.",0407500v1
2023-03-13,Experimental investigation of the effect of topological insulator on the magnetization dynamics of ferromagnetic metal: $BiSbTe_{1.5}Se_{1.5}$ and $Ni_{80}Fe_{20}$ heterostructure,"We have studied ferromagnetic metal/topological insulator bilayer system to
understand magnetization dynamics of ferromagnetic metal (FM) in contact with a
topological insulator (TI). At magnetic resonance condition, the precessing
magnetization in the metallic ferromagnet ($Ni_{80}Fe_{20}$) injects spin
current into the topological insulator ($BiSbTe_{1.5}Se_{1.5}$), a phenomenon
known as spin-pumping. Due to the spin pumping effect, fast relaxation in the
ferromagnet results in the broadening of ferromagnetic resonance linewidth
($\Delta H$). We evaluated the parameters like effective Gilbert damping
coefficient ($\alpha_{eff}$), spin-mixing conductance ($g_{eff}^{\uparrow
\downarrow}$) and spin current density ($j_S^0$) to confirm a successful spin
injection due to spin-pumping into the $BiSbTe_{1.5}Se_{1.5}$ layer. TIs embody
a spin-momentum locked surface state that span the bulk band-gap. It can act
differently to the FM magnetization than the other normal metals. To probe the
effect of topological surface state, a systematic low temperature study is
crucial as surface state of TI dominates at lower temperatures. The exponential
growth of $\Delta H$ for all different thickness combination of FM/TI bilayers
and effective Gilbert damping coefficient ($\alpha_{eff}$) with lowering
temperature confirms the prediction that spin chemical bias generated from
spin-pumping induces surface current in TI due to spin-momentum locking. The
hump-like feature of magnetic anisotropy field ($H_K$)of the bilayer around 60K
suggests that the decrease of interfacial in-plane magnetic anisotropy can
result from exchange coupling between the TI surface state and the local
moments of FM layer.",2303.07025v2
2004-09-12,Stochastic Resonance and Nonequilibrium Dynamic Phase Transition of Ising Spin System Driven by a Joint External Field,"We studied the dynamic response and stochastic resonance of kinetic Ising
spin system (ISS), subject to the joint external field of weak sinusoidal
modulation and stochastic white-noise, through solving the mean-field equation
of motion based on Glauber dynamics. The periodically driven stochastic ISS
shows the occurrence of characteristic stochastic resonance as well as
nonequilibrium dynamic phase transition (NDPT) when the frequency and amplitude
h0 of driving field, the temperature t of the system and noise intensity D
attain a specific accordance in quantity. There exist in the system two typical
dynamic phases, referred to as dynamic disordered paramagnetic and ordered
ferromagnetic phases respectively, corresponding to zero and unit dynamic order
parameter. We also figured out the NDPT boundary surface of the system which
separates the dynamic paramagnetic and dynamic ferromagnetic phase in the 3D
parameter space of h0~t~D. An intriguing dynamical ferromagnetic phase with an
intermediate order parameter at 0.66 was revealed for the first time in the ISS
subject to the perturbation of a joint determinant and stochastic field. Our
primary result indicates that the intermediate order dynamical ferromagnetic
phase is dynamic metastable in nature and owns a peculiar characteristic in its
stability and response to external driving field when compared with fully order
dynamic ferromagnetic phase.",0409306v1
2011-07-22,Interaction of Josephson and magnetic oscillations in Josephson tunnel junctions with a ferromagnetic layer,"We study the dynamics of Josephson junctions with a thin ferromagnetic layer
F [superconductor-ferromagnet-insulator-ferromagnet-superconductor (SFIFS)
junctions]. In such junctions, the phase difference $\phi$ of the
superconductors and magnetization $M$ in the F layer are two dynamic parameters
coupled to each other. We derive equations describing the dynamics of these two
parameters and formulate the conditions of validity. The coupled Josephson
plasma waves and oscillations of the magnetization $M$ affect the form of the
current-voltage ($I$-$V$) characteristics in the presence of a weak magnetic
field (Fiske steps). We calculate the modified Fiske steps and show that the
magnetic degree of freedom not only changes the form of the Fiske steps but
also the overall view of the $I$-$V$ curve (new peaks related to the magnetic
resonance appear). The $I$-$V$ characteristics are shown for different lengths
of the junction including those which correspond to the current experimental
situation. We also calculate the power $P$ absorbed in the system if a
microwave radiation with an ac in-plane magnetic field is applied (magnetic
resonance). The derived formula for the power $P$ essentially differs from the
one which describes the power absorption in an isolated ferromagnetic film. In
particular, this formula describes the peaks related to the excitation of
standing plasma waves as well as the peak associated with the magnetic
resonance.",1107.4493v2
2014-01-09,FMR Study of Co/Ti Bilayer Thin Films,". We focused on the interaction between two ferromagnetic cobalt layers
through a non-magnetic titanium layer. The magnetic properties of the structure
were characterized by ferromagnetic resonance technique (FMR). The data were
collected as a function of non-magnetic titanium layer thickness. Co/Ti
multilayer (Ti (50 {\AA})/Co(45 {\AA})/Ti(2-40 {\AA})/Co(40 {\AA})/Ti(100
{\AA}))films were grown onto naturally oxidized p-type single crystal Si (100)
substrate at UHV condition with magnetron sputtering system at room
temperature. The thickness of Ti spacer layer ranges from 2 to 40 {\AA} with 2
{\AA} steps. We did not observe usual optic and acoustic modes; instead we had
two broad overlapped peaks for the films ranged from 6 {\AA} to 40 {\AA}. One
interesting result was the high anisotropic resonance field values for these
films. Exchange coupling between ferromagnetic layers causes shift on resonance
field values but these shifts in our samples were much larger than expected.
This large anisotropic behavior is not clear at the moment. Our theoretical
model was not able to determine a value for the exchange coupling parameter.
One reason can be the close thickness values for Co sublayers. The other reason
can be the Ti non-magnetic layer. If titanium did not grow layer by layer on
cobalt, the cobalt ferromagnetic layers may behave as a single layer. As a
result one cannot observe exchange interaction between ferromagnetic layers
through non-magnetic spacer.",1401.1924v1
2002-09-24,Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd_0.8Pb_0.2MnO_3 above the transition temperature,"Single crystals of Nd_{1-x}Pb_{x}MnO_{3} with x=0.2 are grown by high
temperature solution growth technique using PbO-PbF_{2} flux. Magnetization
studies on the samples show a transition to a ferromagnetic state below T_c ~
125 K and the resistivity measurements show it to be an insulator throughout
the temperature range 50 - 300 K. Electron Paramagnetic Resonance studies have
been performed for T > T_{C} with a view to comparing the results with those on
metallic ferromagnetic manganites. The temperature dependence of various
parameters like g-value, linewidth and intensity has been studied in the
temperature range 150 - 300 K. It is found that they behave in a manner similar
to that exhibited by metallic ferromagnetic manganites.",0209546v1
2008-01-08,Relevance of ferromagnetic correlations for the Electron Spin Resonance in Kondo lattice systems,"Electron Spin Resonance (ESR) measurements of the ferromagnetic Kondo lattice
system CeRuPO show a well defined ESR signal which is related to the magnetic
properties of the Ce3+ moment. In contrast, no ESR signal could be observed in
the antiferromagnetic homologue CeOsPO. Additionally, we detect an ESR signal
in a further ferromagnetic Yb compound, YbRh, while it was absent in a number
of Ce or Yb intermetallic compounds with dominant antiferromagnetic exchange,
independently of the presence of a strong Kondo interaction or the proximity to
a (quantum) critical point. Thus, the observation of an ESR signal in a Kondo
lattice is neither specific to Yb nor to the proximity of a quantum critical
point, but seems to be connected to the presence of ferromagnetic fluctuations.
These conclusions not only provide a basic concept to understand the ESR in
Kondo lattice systems even well below the Kondo temperature as observed in the
heavy fermion metal YbRh2Si2 but point out ESR as a prime method to investigate
directly the spin dynamics of the Kondo ion.",0801.1191v1
2010-07-21,Exchange anisotropy pinning of a standing spin wave mode,"Standing spin waves in a thin film are used as sensitive probes of interface
pinning induced by an antiferromagnet through exchange anisotropy. Using
coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin
wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was
studied for a range of IrMn thicknesses. We show that pinning of the standing
mode can be used to amplify, relative to the fundamental resonance, frequency
shifts associated with exchange bias. The shifts provide a unique `fingerprint'
of the exchange bias and can be interpreted in terms of an effective
ferromagnetic film thickness and ferromagnet/antiferromagnet interface
anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic
Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in
the pinning fields. The pinning strength magnitude is found to grow with
cooling of the sample, while the effective ferromagnetic film thickness
simultaneously decreases. These results suggest that exchange bias involves
some deformation of magnetic order in the interface region.",1007.3577v1
2014-08-25,Electrical detection of ferromagnetic resonance in ferromagnet/n-GaAs heterostructures by tunneling anisotropic magnetoresistance,"We observe a dc voltage peak at ferromagnetic resonance (FMR) in samples
consisting of a single ferromagnetic (FM) layer grown epitaxially on the
$\mathit{n-}$GaAs (001) surface. The FMR peak is detected as an interfacial
voltage with a symmetric line shape and is present in samples based on various
FM/$n$-GaAs hetrostructures, including Co$_{2}$MnSi/$n$-GaAs,
Co$_{2}$FeSi/$n$-GaAs and Fe/$n$-GaAs. We show that the interface bias voltage
dependence of the FMR signal is identical to that of the tunneling anisotropic
magnetoresistance (TAMR) over most of the bias range. Furthermore, we show how
the precessing magnetization yields a dc FMR signal through the TAMR effect and
how the TAMR phenomenon can be used to predict the angular dependence of the
FMR signal. This TAMR-induced FMR peak can be observed under conditions where
no spin accumulation is present and no spin-polarized current flows in the
semiconductor.",1408.5842v1
2014-12-03,"Eddy current interactions in a Ferromagnet-Normal metal bilayer structure, and its impact on ferromagnetic resonance lineshapes","We investigate the effect of eddy currents on ferromagnetic resonance (FMR)
in ferromagnet-normal metal (FM/NM) bilayer structures. Eddy-current effects
are usually neglected for NM layer thicknesses below the microwave (MW) skin
depth (approx. 800 nm for Au at 10 GHz). However, we show that in much thinner
NM layers (10-100 nm of Au or Cu) they induce a phase shift in the FMR
excitation when the MW driving field has a component perpendicular to the
sample plane. This results in a strong asymmetry of the measured absorption
lines. In contrast to typical eddy-current effects, the asymmetry is larger for
thinner NM layers and is tunable through changing the sample geometry and the
NM layer thickness.",1412.1385v3
2015-09-06,Study of spin dynamics and damping on the magnetic nanowire arrays with various nanowire widths,"We investigate the spin dynamics including Gilbert damping in the
ferromagnetic nanowire arrays. We have measured the ferromagnetic resonance of
ferromagnetic nanowire arrays using vector-network analyzer ferromagnetic
resonance (VNA-FMR) and analyzed the results with the micromagnetic
simulations. We find excellent agreement between the experimental VNA-FMR
spectra and micromagnetic simulations result for various applied magnetic
fields. We find that the demagnetization factor for longitudinal conditions, Nz
(Ny) increases (decreases) as decreasing the nanowire width in the
micromagnetic simulations. For the transverse magnetic field, Nz (Ny) increases
(decreases) as increasing the nanowire width. We also find that the Gilbert
damping constant increases from 0.018 to 0.051 as the increasing nanowire width
for the transverse case, while it is almost constant as 0.021 for the
longitudinal case.",1509.01807v1
2016-04-21,Ferromagnetic resonance of exchange-coupled perpendicularly magnetized bilayers,"Strong ferromagnetic interlayer exchange couplings $J$ in perpendicularly
magnetized systems are becoming increasingly desirable for applications. We
study whether ferromagnetic interlayer exchange couplings can be measured by a
combination of broadband ferromagnetic resonance methods and magnetometry
hysteresis loops. For this we model the switching and the eigenexcitations in
bilayer systems comprising a soft layer coupled to a thicker harder layer that
possesses higher perpendicular magnetic anisotropy. For large $J >0$ the
switching fields are essentially independent of $J$ but the frequency of the
optical eigenmode of the bilayer and the linewidth of the acoustical and
optical eigenmode are directly sensitive to the coupling. We derive a corpus of
compact analytical expressions to analyze these frequencies, their linewidth
and discuss the meaning thereof. We illustrate this corpus on a system
mimicking the fixed layers of a magnetic tunnel junction meant for spin torque
applications.",1604.06332v1
2016-07-13,Surface state dominated spin-charge current conversion in topological insulator/ferromagnetic insulator heterostructures,"We report the observation of ferromagnetic resonance-driven spin pumping
signals at room temperature in three-dimensional topological insulator thin
films -- Bi2Se3 and (Bi,Sb)2Te3 -- deposited by molecular beam epitaxy on
yttrium iron garnet thin films. By systematically varying the Bi2Se3 film
thickness, we show that the spin-charge conversion efficiency, characterized by
the inverse Rashba-Edelstein effect length (lambda_IREE), increases
dramatically as the film thickness is increased from 2 quintuple layers,
saturating above 6 quintuple layers. This suggests a dominant role of surface
states in spin and charge interconversion in topological insulator/ferromagnet
heterostructures. Our conclusion is further corroborated by studying a series
of YIG/(BiSb)2Te3 heterostructures. Finally, we use the ferromagnetic resonance
linewidth broadening and the inverse Rashba-Edelstein signals to determine the
effective interfacial spin mixing conductance and lambda_IREE.",1607.03872v1
2016-10-21,Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance,"Thin films of perovskite oxides offer the possibility of combining emerging
concepts of strongly correlated electron phenomena and spin current in magnetic
devices. However, spin transport and magnetization dynamics in these complex
oxide materials are not well understood. Here, we experimentally quantify spin
transport parameters and magnetization damping in epitaxial perovskite
ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$
(LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO
thickness dependence of Gilbert damping, we estimate a short spin diffusion
length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance
comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find
that anisotropic non-Gilbert damping due to two-magnon scattering also
increases with the addition of SRO. Our results demonstrate LSMO/SRO as a
spin-source/spin-sink system that may be a foundation for examining
spin-current transport in various perovskite heterostructures.",1610.06661v1
2018-04-17,Ultrasensitive multi-mode ESR probed ferromagnetic two-level system of $Mn^{4+}$ impurity ion in the insulated $MnO_6$ complex of $SrLaAlO_4$ at $20~mK$,"Ultrasnsitive multi-mode electron spin resonance spectroscopy in the
$SrLaAlO_4$ dielectric resonator at $20~mK$ reveals ferromagnetic states of
$Mn^{4+}$ impurity ion. The formation of ferromagnetic states in the $MnO_6$
complex implies to oxygen deficiency of this multi-valence $Mn^{4+}$ ion.
Experiment results supports that an intricate electronic hybridization in
$MnO_6$ structural instability is related to Pseudo Jahn-Teller effect.
Measured dipolar hyperfine structure parameter of nucleus is
$P_{\scriptscriptstyle\parallel} =-3.7\times 10^{-4}~cm^{-1}$. Mean inverse
third power of the electron distance is $\langle r_q^{-3}\rangle=3.325~a.u.$
assuming nuclear electric quadruple moment $Q=+0.33(1)~barn$. In such a state,
giant g-factor is observed due to magneto (ferromagnetic) impedance taking in
to account a two-level system on the adiabatic-potential-energy-surface. The
spins exhibited parity is opposite in the interaction of
highest-occupied-molecular-orbital and lowest-unoccupied-molecular-orbital
coupling.",1804.06320v1
2016-11-09,Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/ nonmagnetic metal/ ferromagnet multilayered stacks,"In this work we focus on magnetic relaxation in Mn$_{80}$Ir$_{20}$(12 nm)/
Cu(6 nm)/ Py($d_\mathrm{F}$) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM)
multilayers with different thickness of the ferromagnetic permalloy layer. An
effective FM-AFM interaction mediated via the conduction electrons in the
nonmagnetic Cu spacer -- the spin-pumping effect -- is detected as an increase
in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of
the resonant magnetic field. We further find experimentally that the
spin-pumping-induced contribution to the linewidth is inversely proportional to
the thickness of the Py layer. We show that this thickness dependence likely
originates from the dissipative dynamics of the free and localized spins in the
AFM layer. The results obtained could be used for tailoring the dissipative
properties of spintronic devices incorporating antiferromagnetic layers.",1611.02865v1
2012-04-06,Andreev current induced by ferromagnetic resonance,"We study charge transport through a metallic dot coupled to a superconducting
and a ferromagnetic lead with a precessing magnetization due to ferromagnetic
resonance. Using the quasiclassical theory, we find that the magnetization
precession induces a dc current in the subgap regime even in the absence of a
bias voltage. This effect is due to the rectification of the ac spin currents
at the interface with the ferromagnet; it exists in the absence of spin current
in the superconductor. When the dot is strongly coupled to the superconductor,
we find a strong enhancement in a wide range of parameters as compared to the
induced current in the normal state.",1204.1491v1
2019-06-27,Magnetic proximity effect induced FMR frequency enhancement in {Py/FeMn} bilayers,"Ferromagnetic resonance (FMR) in exchange-coupled ferromagnet-antiferromagnet
(FM/AFM) bilayers commonly shows a moderate increase in the resonance frequency
owing to the induced unidirectional anisotropy. Here we report a large FMR
frequency enhancement toward the sub-THz range observed in Py/FeMn with
ultrathin AFM FeMn. The effect is connected with a sizable induced magnetic
moment in FeMn caused by the magnetic proximity effect from the Py layer. The
observed FMR properties are explained as due to the competing intrinsic
antiferromagnetic order and the ferromagnetic proximity effect in nanometer
thin FeMn. Our results show that combining materials with strong and weak
anti/ferromagnetic ordering can potentially close the notoriously difficult
GHz-THz gap important for high-speed spintronic applications.",1906.11688v2
2021-02-21,Direct and inverse spin-orbit torques in antiferromagnetic and ferromagnetic FeRh/W(001),"We use \textit{ab-initio} calculations to investigate spin-orbit torques
(SOTs) in FeRh(001) deposited on W(100). Since FeRh undergoes a
ferromagnetic-antiferromagnetic phase transition close to room temperature, we
consider both phases of FeRh. In the antiferromagnetic case we find that the
effective magnetic field of the even torque is staggered and therefore ideal to
induce magnetization dynamics or to switch the antiferromagnet (AFM). At the
antiferromagnetic resonance the inverse SOT induces a current density, which
can be determined from the SOT. In the ferromagnetic case our calculations
predict both even and odd components of the SOT, which can also be used to
describe the ac and dc currents induced at the ferromagnetic resonance. For
comparison we compute the SOTs in the c($2\times 2$) AFM state of Fe/W(001).",2102.10598v1
2022-04-22,A short-circuited coplanar waveguide for low-temperature single-port ferromagnetic resonance spectroscopy set-up to probe the magnetic properties of ferromagnetic thin films,"A coplanar waveguide shorted in one end is proposed, designed, and
implemented successfully to measure the properties of magnetic thin films as a
part of the vector network analyzer ferromagnetic resonance (VNA-FMR)
spectroscopy set-up. Its simple structure, potential applications and easy
installation inside the cryostat chamber made it advantageous especially for
low-temperature measurements. It provides a wide band of frequencies in the
gigahertz range essential for FMR measurements. Our spectroscopy set-up with
short-circuited coplanar waveguide has been used to extract Gilbert damping
coefficient and effective magnetization values for standard ferromagnetic thin
films like Py and Co. The thickness and temperature dependent studies of those
magnetic parameters have also been done here for the afore mentioned magnetic
samples.",2204.10596v2
2001-05-26,Time-resolved ferromagnetic resonance in epitaxial Fe1-xCox films,"Magnetodynamics in epitaxial Fe1-xCox films on GaAs (100) are studied using
time-resolved ferromagnetic resonance, in which the free precession of the
magnetization after an impulsive excitation is measured using the polar Kerr
effect. The sample is rotated with respect to the static and pulsed field
directions, providing a complete mapping of the free energy surface and
characteristic relaxation times. The magnetic response can be simulated with a
simple coherent rotation model except in the immediate vicinity of switching
fields. Bulk and surface anisotropies are identified, and unusual dynamics
associated with the coexistence of cubic and uniaxial anisotropies are
observed.",0105513v1
2002-10-26,Dynamic exchange coupling in magnetic bilayers,"A long-ranged dynamic interaction between ferromagnetic films separated by
normal-metal spacers is reported, which is communicated by nonequilibrium spin
currents. It is measured by ferromagnetic resonance (FMR) and explained by an
adiabatic spin-pump theory. In FMR the spin-pump mechanism of spatially
separated magnetic moments leads to an appreciable increase in the FMR line
width when the resonance fields are well apart, and results in a dramatic
line-width narrowing when the FMR fields approach each other.",0210588v2
2006-08-16,Quantum-size effect and tunneling magnetoresistance in ferromagnetic-semiconductor quantum heterostructures,"We report on the resonant tunneling effect and the increase of tunneling
magnetoresistance (TMR) induced by it in ferromagnetic-semiconductor GaMnAs
quantum-well heterostructures. The observed quantum levels of the GaMnAs
quantum well were successfully explained by the valence-band kp model with the
p-d exchange interaction. It was also found that the Fermi level of the
electrode injecting carriers is important to observe resonant tunneling in this
system.",0608357v1
2007-06-12,Theory of the Pseudospin Resonance in Semiconductor Bilayers,"The pseudospin degree of freedom in a semiconductor bilayer gives rise to a
collective mode analogous to the ferromagnetic resonance mode of a ferromagnet.
We present a theory of the dependence of the energy and the damping of this
mode on layer separation $d$. Based on these results, we discuss the
possibility of realizing transport-current driven pseudospin-transfer
oscillators in semiconductors.",0706.1702v1
2007-10-15,Ferromagnetic resonance study of polycrystalline Fe_{1-x}V_x alloy thin films,"Ferromagnetic resonance has been used to study the magnetic properties and
magnetization dynamics of polycrystalline Fe$_{1-x}$V$_{x}$ alloy films with
$0\leq x < 0.7$. Films were produced by co-sputtering from separate Fe and V
targets, leading to a composition gradient across a Si substrate. FMR studies
were conducted at room temperature with a broadband coplanar waveguide at
frequencies up to 50 GHz using the flip-chip method. The effective
demagnetization field $4 \pi M_{\mathrm{eff}}$ and the Gilbert damping
parameter $\alpha$ have been determined as a function of V concentration. The
results are compared to those of epitaxial FeV films.",0710.2826v2
2008-12-03,Observation of ferromagnetic resonance in strontium ruthenate (SrRuO3),"We report the observation of ferromagnetic resonance (FMR) in SrRuO3 using
the time-resolved magneto-optical Kerr effect. The FMR oscillations in the
time-domain appear in response to a sudden, optically induced change in the
direction of easy-axis anistropy. The high FMR frequency, 250 GHz, and large
Gilbert damping parameter, alpha ~ 1, are consistent with strong spin-orbit
coupling. We find that the parameters associated with the magnetization
dynamics, including alpha, have a non-monotonic temperature dependence,
suggestive of a link to the anomalous Hall effect.",0812.0832v1
2009-06-26,Conductance oscillation due to the geometrical resonance in FNS double junctions,"We theoretically analyzed the Andreev reflection in ferromagnetic
metal/nonmagnetic metal/superconductor double junctions with special attention
to the electron interference effect in the nonmagnetic metal layer. We showed
that the conductance oscillates as a function of the bias voltage due to the
geometrical resonance. We found that the exchange field, and therefore the spin
polarization of the ferromagnetic metal can be determined from the period of
the conductance oscillation, which is proportional to the square root of the
exchange field.",0906.4863v1
2010-03-28,Giant magnetic broadening of ferromagnetic resonance in a GMR Co/Ag/Co/Gd quadlayer,"Both magnetic-resonance damping and the giant magnetoresistance effect have
been predicted to be strongly affected by the local density of states in thin
ferromagnetic films. We employ the antiferromagnetic coupling between Co and Gd
to provide a spontaneous change from parallel to antiparallel alignment of two
Co films. A sharp increase in magnetic damping accompanies the change from
parallel to antiparallel alignment, analogous to resistivity changes in giant
magnetoresistance.",1003.5344v1
2010-04-15,Ferromagnetism in repulsive Fermi gases: upper branch of Feshbach resonance versus hard spheres,"We use quantum Monte Carlo, including backflow corrections, to investigate a
two-component Fermi gas on the upper branch of a Feshbach resonance and
contrast it with the hard sphere gas. We find that, in both cases, the Fermi
liquid becomes unstable to ferromagnetism at a $k_F a$ smaller than the mean
field result, where $k_F$ is the Fermi wavevector and $a$ the scattering
length. Even though the total energies $E(k_F a)$ are similar in the two cases,
their pair correlations and kinetic energies are completely different,
reflecting the underlying potentials. We discuss the extent to which our
calculations shed light on recent experiments.",1004.2680v1
2010-10-19,Ferromagnetic resonance with a magnetic Josephson junction,"We show experimentally and theoretically that there is a coupling via the
Aharonov-Bohm phase between the order parameter of a ferromagnet and a singlet,
s-wave, Josephson supercurrent. We have investigated the possibility of
measuring the dispersion of such spin waves by varying the magnetic field
applied in the plane of the junction and demonstrated the electromagnetic
nature of the coupling by the observation of magnetic resonance side-bands to
microwave induced Shapiro steps.",1010.3858v1
2010-12-06,Local electrical characterization of resonant magnetization motion in a single ferromagnetic sub-micrometer particle in lateral geometry,"In this article a detailed characterization of a magnetization motion in a
single sub-micrometer and multi-terminal ferromagnetic structure in lateral
geometry is performed in a GHz regime using direct DC characterization
technique. We have shown applicability of the Stoner-Wohlfarth model to the
magnetic nano-structure with large length to with ratio. Applying the model to
experimental data we are able to extract relevant magnetization motion
parameters and show a correlation between high frequency inductive currents and
local magnetization. Additionally, DC voltage generated over the structure at
the resonance, with external magnetic field under an angle to the shape
anisotropy axis, is explained by the model.",1012.1266v1
2011-04-28,Temperature dependent anisotropy and elastic effects in ferromagnetic nanowire arrays,"Temperature dependent Ferromagnetic Resonance measurements performed as a
function of diameter on Nickel nanowire arrays reveal several interesting
features in these systems. With diameter decrease from 100 nm to 15 nm, a
transition induced by surface anisotropy increase is observed at 50 nm in easy
axis orientation from parallel to perpendicular with respect to individual
nanowire geometric axis. Analysis of resonance field $H_{res}$ temperature
variation (between liquid Helium and room temperature) reveals underlying
strong magneto-elastic effects in small and large diameter nanowire arrays with
potential applications in recording and spintronics.",1104.5348v3
2011-05-16,On the line shape of the electrically detected ferromagnetic resonance,"This work reviews and examines two particular issues related with the new
technique of electrical detection of ferromagnetic resonance (FMR). This
powerful technique has been broadly applied for studying magnetization and spin
dynamics over the past few years. The first issue is the relation and
distinction between different mechanisms that give rise to a photovoltage via
FMR in composite magnetic structures, and the second is the proper analysis of
the FMR line shape, which remains the ""Achilles heel"" in interpreting
experimental results, especially for either studying the spin pumping effect or
quantifying the spin Hall angles via the electrically detected FMR.",1105.3236v1
2013-07-03,Large Spin Pumping from Epitaxial Y3Fe5O12 Thin Films to Pt and W Layers,"Epitaxial Y3Fe5O12 thin films have been deposited by off-axis sputtering,
which exhibit excellent crystalline quality, enabling observation of large spin
pumping signals in Pt/Y3Fe5O12 and W/Y3Fe5O12 bilayers driven by cavity
ferromagnetic resonance. The inverse spin Hall voltages reach 2.10 mV and -5.26
mV in 5-mm long Pt/Y3Fe5O12 and W/Y3Fe5O12 bilayers, respectively, excited by a
radio-frequency magnetic field of 0.3 Oe. From the ferromagnetic resonance
linewidth broadening, the interfacial spin mixing conductance of 4.56E14
{\Omega}-1m-2 and 2.30E14 {\Omega}-1m-2 are obtained for Pt/Y3Fe5O12 and
W/Y3Fe5O12 bilayers, respectively.",1307.1172v1
2013-10-30,Spin torque ferromagnetic resonance with magnetic field modulation,"We demonstrate a technique of broadband spin torque ferromagnetic resonance
(ST-FMR) with magnetic field modulation for measurements of spin wave
properties in magnetic nanostructures. This technique gives great improvement
in sensitivity over the conventional ST-FMR measurements, and application of
this technique to nanoscale magnetic tunnel junctions (MTJs) reveals a rich
spectrum of standing spin wave eigenmodes. Comparison of the ST-FMR
measurements with micromagnetic simulations of the spin wave spectrum allows us
to explain the character of low-frequency magnetic excitations in nanoscale
MTJs.",1310.7996v1
2013-12-12,Microwave manipulation of electrically injected spin polarized electrons in silicon,"We demonstrate microwave manipulation of the spin states of electrically
injected spin-polarized electrons in silicon. Although the silicon channel is
bounded by ferromagnetic metal films, we show that moderate microwave power can
be applied to the devices without altering the device operation significantly.
Resonant microwave irradiation is used to induce spin rotation of
spin-polarized electrons as they travel across a silicon channel, and the
resultant spin polarization is subsequently detected by a ferromagnetic
Schottky barrier spin detector. These results demonstrate the potential for
combining advanced electron spin resonance techniques to complement the study
of semiconductor spintronic devices beyond standard magnetotransport
measurements.",1312.3663v1
2016-02-26,Tuning the magnetocrystalline anisotropy in $R$CoPO by means of $R$ substitution: a ferromagnetic resonance study,"We report on broad-band electron spin resonance measurements performed within
the itinerant ferromagnetic phase of $R$CoPO ($R$ = La, Pr, Nd and Sm). We
reveal that the $R$ substitution is highly effective in gradually introducing a
sizeable easy-plane magnetocrystalline anisotropy within the Co sublattice. We
explain our results in terms of a subtle interplay of structural effects and of
indirect interactions between the $f$ and $d$ orbitals from $R$ and Co,
respectively.",1602.08377v1
2010-05-13,Competition between pairing and ferromagnetic instabilities in ultracold Fermi gases near Feshbach resonances,"We study the quench dynamics of a two-component ultracold Fermi gas from the
weak into the strong interaction regime, where the short time dynamics are
governed by the exponential growth rate of unstable collective modes. We obtain
an effective interaction that takes into account both Pauli blocking and the
energy dependence of the scattering amplitude near a Feshbach resonance. Using
this interaction we analyze the competing instabilities towards Stoner
ferromagnetism and pairing.",1005.2366v1
2013-08-06,Broadband ferromagnetic resonance characterization of GaMnAs thin films,"The precessional magnetization dynamics of GaMnAs thin films are
characterized by broadband network analyzer ferromagnetic resonance (FMR) in a
coplanar geometry at cryogenic temperatures. The FMR frequencies are
characterized as function of in-plane field angle and field amplitude. Using an
extended Kittel model of the FMR dispersion the magnetic film parameters such
as saturation magnetization and anisotropies are derived. The modification of
the FMR behavior and of the magnetic parameters of the thin film upon annealing
is analyzed.",1308.1232v1
2008-07-28,Magnetoelectric bistabilities in ferromagnetic resonant tunneling structures,"The conditions for the occurrence of pronounced magnetoelectric bistabilities
in the resonant tunneling through a ferromagnetic quantum well are
theoretically investigated. The bistability appears due to the mutual feedback
of the carriers Coulomb interaction and the carriers exchange coupling with
magnetic impurities in the well. It is shown that the well Curie temperature
depends strongly on the relative alignment of the quantum well level and the
reservoirs chemical potentials, which can be modified electrically. Switching
between a ""current-on/magnetism-off"" and a ""current-off/magnetism-on"" mode
becomes possible, if the well temperature lies in-between the bistable values
of the well Curie temperature.",0807.4445v1
2014-06-10,Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance,"We show by vector network analyzer ferromagnetic resonance measurements that
low Gilbert damping {\alpha} down to 0.006 can be achieved in perpendicularly
magnetized MgO/CoFeB/MgO thin films with ultra-thin insertions of Ta in the
CoFeB layer. While increasing the number of Ta insertions allows thicker CoFeB
layers to remain perpendicular, the effective areal magnetic anisotropy does
not improve with more insertions, and also comes with an increase in {\alpha}.",1406.2491v2
2016-12-19,Thickness dependence study of current-driven ferromagnetic resonance in Y3Fe5O12/heavy metal bilayers,"We use ferromagnetic resonance to study the current-induced torques in
YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80
nm, with Pt or Ta thin film on top, are measured by applying a microwave
current into the heavy metals and measuring the longitudinal DC voltage
generated by both spin rectification and spin pumping. From a symmetry analysis
of the FMR lineshape and its dependence on YIG thickness, we deduce that the
Oersted field dominates over spin-transfer torque in driving magnetization
dynamics.",1612.06111v1
2017-05-05,Light-induced anisotropic skyrmion and stripe phases in a Rashba ferromagnet,"An external off-resonant pumping is proposed as a tool to control the
Dzyaloshinskii-Moriya interaction (DMI) in ferromagnetic layers with strong
spin-orbit coupling. Combining theoretical analysis with numerical simulations
for an $s$-$d$-like model we demonstrate that linearly polarized off-resonant
light may help stabilizing novel noncollinear magnetic phases by inducing a
strong anisotropy of the DMI. We also investigate how with the application of
electromagnetic pumping one can control the stability, shape and size of
individual skyrmions to make them suitable for potential applications.",1705.02261v2
2015-02-10,Disentangling relativistic spin torques in a ferromagnet/semiconductor bilayer,"Recently discovered relativistic spin torques induced by a lateral current at
a ferromagnet/paramagnet interface are a candidate spintronic technology for a
new generation of electrically-controlled magnetic memory devices.
Phenomenologically, the torques have field-like and antidamping-like components
with distinct symmetries. Microscopically, they are considered to have two
possible origins. In one picture, a spin-current generated in the paramagnet
via the relativistic spin Hall effect (SHE) is absorbed in the ferromagnet and
induces the spin transfer torque (STT). In the other picture, a non-equilibrium
spin-density is generated via the relativistic inverse spin galvanic effect
(ISGE) and induces the spin-orbit torque (SOT) in the ferromagnet. From the
early observations in paramagnetic semiconductors, SHE and ISGE are known as
companion phenomena that can both allow for electrically aligning spins in the
same structure. It is essential for our basic physical understanding of the
spin torques at the ferromagnet/paramagnet interface to experimentally
disentangle the SHE and ISGE contributions. To achieve this we prepared an
epitaxial transition-metal-ferromagnet/semiconductor-paramagnet single-crystal
structure and performed a room-temperature vector analysis of the relativistic
spin torques by means of the all-electrical ferromagnetic resonance (FMR)
technique. By design, the field-like torque is governed by the ISGE-based
mechanism in our structure while the antidamping-like torque is due to the
SHE-based mechanism",1502.02870v1
2016-05-25,Exploring the ferromagnetic behaviour of a repulsive Fermi gas via spin dynamics,"Ferromagnetism is a manifestation of strong repulsive interactions between
itinerant fermions in condensed matter. Whether short-ranged repulsion alone is
sufficient to stabilize ferromagnetic correlations in the absence of other
effects, like peculiar band dispersions or orbital couplings, is however
unclear. Here, we investigate ferromagnetism in the minimal framework of an
ultracold Fermi gas with short-range repulsive interactions tuned via a
Feshbach resonance. While fermion pairing characterises the ground state, our
experiments provide signatures suggestive of a metastable Stoner-like
ferromagnetic phase supported by strong repulsion in excited scattering states.
We probe the collective spin response of a two-spin mixture engineered in a
magnetic domain-wall-like configuration, and reveal a substantial increase of
spin susceptibility while approaching a critical repulsion strength. Beyond
this value, we observe the emergence of a time-window of domain immiscibility,
indicating the metastability of the initial ferromagnetic state. Our findings
establish an important connection between dynamical and equilibrium properties
of strongly-correlated Fermi gases, pointing to the existence of a
ferromagnetic instability.",1605.07850v2
2017-10-04,Possible evidence for spin-transfer torque induced by spin-triplet supercurrent,"Cooper pairs in superconductors are normally spin singlet. Nevertheless,
recent studies suggest that spin-triplet Cooper pairs can be created at
carefully engineered superconductor-ferromagnet interfaces. If Cooper pairs are
spin-polarized they would transport not only charge but also a net spin
component, but without dissipation, and therefore minimize the heating effects
associated with spintronic devices. Although it is now established that triplet
supercurrents exist, their most interesting property - spin - is only inferred
indirectly from transport measurements. In conventional spintronics, it is well
known that spin currents generate spin-transfer torques that alter
magnetization dynamics and switch magnetic moments. The observation of similar
effects due to spin-triplet supercurrents would not only confirm the net spin
of triplet pairs but also pave the way for applications of superconducting
spintronics. Here, we present a possible evidence for spin-transfer torques
induced by triplet supercurrents in superconductor/ferromagnet/superconductor
(S/F/S) Josephson junctions. Below the superconducting transition temperature
T_c, the ferromagnetic resonance (FMR) field at X-band (~ 9.0 GHz) shifts
rapidly to a lower field with decreasing temperature due to the spin-transfer
torques induced by triplet supercurrents. In contrast, this phenomenon is
absent in ferromagnet/superconductor (F/S) bilayers and
superconductor/insulator/ferromagnet/superconductor (S/I/F/S) multilayers where
no supercurrents pass through the ferromagnetic layer. These experimental
observations are discussed with theoretical predictions for ferromagnetic
Josephson junctions with precessing magnetization.",1710.01534v1
1994-10-06,Andreev Reflection In Ferromagnet-Superconductor Junctions,"The transport properties of a ferromagnet-superconductor (FS) junction are
studied in a scattering formulation. Andreev reflection at the FS interface is
strongly affected by the exchange interaction in the ferromagnet. The
conductance G_FS of a ballistic point contact between F and S can be both
larger or smaller than the value G_FN with the superconductor in the normal
state, depending on the ratio of the exchange and Fermi energies. If the
ferromagnet contains a tunnel barrier (I), the conductance G_FIFS exhibits
resonances which do not vanish in linear response -- in contrast to the Tomasch
oscillations for non-ferromagnetic materials.",9410014v2
2000-04-05,Linear response conductance and magneto-resistance of ferromagnetic single-electron transistors,"The current through ferromagnetic single-electron transistors (SET's) is
considered. Using path integrals the linear response conductance is formulated
as a function of the tunnel conductance vs. quantum conductance and the
temperature vs. Coulomb charging energy. The magneto-resistance of
ferromagnet-normal metal-ferromagnet (F-N-F) SET's is almost independent of the
Coulomb charging energy and is only reduced when the transport dwell time is
longer than the spin-flip relaxation time. In all-ferromagnetic (F-F-F) SET's
with negligible spin-flip relaxation time the magneto-resistance is calculated
analytically at high temperatures and numerically at low temperatures. The
F-F-F magneto-resistance is enhanced by higher order tunneling processes at low
temperatures in the 'off' state when the induced charges vanishes. In contrast,
in the 'on' state near resonance the magneto-resistance ratio is a
non-monotonic function of the inverse temperature.",0004082v3
2013-01-16,Dynamics of localized modes in a composite multiferroic chain,"In a coupled ferroelectric/ferromagnetic system, i.e. a composite
multiferroic, the propagation of magnetic or ferroelectric excitations across
the whole structure is a key issue for applications. Of a special interest is
the dynamics of localized magnetic or ferroelectric modes (LM) across the
ferroelectric-ferromagnetic interface, particularly when the LM's carrier
frequency is in the band of the ferroelectric and in the band gap of the
ferromagnet. For a proper choice of the system's parameters, we find that there
is a threshold amplitude above which the interface becomes transparent and a
band gap ferroelectric LM penetrates the ferromagnetic array. Below that
threshold, the LM is fully reflected. Slightly below this transmission
threshold, the addition of noise may lead to energy transmission, provided that
the noise level is not too low nor too high, an effect that resembles
stochastic resonance. These findings represent an important step towards the
application of ferroelectric and/or ferromagnetic LM-based logic.",1301.3802v2
2013-07-09,Strain-controlled nonvolatile magnetization switching,"We investigate different approaches towards a nonvolatile switching of the
remanent magnetization in single-crystalline ferromagnets at room temperature
via elastic strain using ferromagnetic thin film/piezoelectric actuator
hybrids. The piezoelectric actuator induces a voltage-controllable strain along
different crystalline directions of the ferromagnetic thin film, resulting in
modifications of its magnetization by converse magnetoelastic effects. We
quantify the magnetization changes in the hybrids via ferromagnetic resonance
spectroscopy and superconducting quantum interference device magnetometry.
These measurements demonstrate a significant strain-induced change of the
magnetization, limited by an inefficient strain transfer and domain formation
in the particular system studied. To overcome these obstacles, we address
practicable engineering concepts and use a model to demonstrate that a
strain-controlled, nonvolatile magnetization switching should be possible in
appropriately engineered ferromagnetic/piezoelectric actuator hybrids.",1307.2433v1
2013-10-17,Electrical Detection of Direct and Alternating Spin Current Injected from a Ferromagnetic Insulator into a Ferromagnetic Metal,"We report room temperature electrical detection of spin injection from a
ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py).
Non-equilibrium spins with both static and precessional spin polarizations are
dynamically generated by the ferromagnetic resonance of YIG magnetization, and
electrically detected by Py as dc and ac spin currents, respectively. The dc
spin current is electrically detected via the inverse spin Hall effect of Py,
while the ac spin current is converted to a dc voltage via the spin
rectification effect of Py which is resonantly enhanced by dynamic exchange
interaction between the ac spin current and the Py magnetization. Our results
reveal a new path for developing insulator spintronics, which is distinct from
the prevalent but controversial approach of using Pt as the spin current
detector.",1310.4840v1
2014-07-11,Persistent ferromagnetism and topological phase transition at the interface of a superconductor and a topological insulator,"At the interface of an s-wave superconductor and a three-dimensional
topological insulator, Ma- jorana zero modes and Majorana helical states have
been proposed to exist respectively around magnetic vortices and geometrical
edges. Here we first show that a single magnetic impurity at such an interface
splits each resonance state of a given spin channel outside the superconducting
gap, and also induces two new symmetric impurity states inside the gap. Next we
find that an increase in the superconducting gap suppresses both the
oscillation magnitude and period of the RKKY inter- action between two
interface magnetic impurities mediated by BCS quasi-particles. Within a mean
field approximation, the ferromagnetic Curie temperature is found to be
essentially independent of the superconducting gap, an intriguing phenomenon
due to a compensation effect between the short-range ferromagnetic and
long-range anti-ferromagnetic interactions. The existence of persis- tent
ferromagnetism at the interface allows realization of a novel topological phase
transition from a non-chiral to a chiral superconducting state at sufficiently
low temperatures, providing a new platform for topological quantum computation.",1407.3029v1
2015-01-04,Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridate Y2Ir2O7,"Pyrochlore iridates have recently attracted growing interest in condensed
matter physics because of their potential for realizing new topological states.
In order to achieve such quantum states, it is essential to understand
themagnetic properties of these compounds, as their electronic structures are
strongly coupled with theirmagnetic ground states. In this work, we report a
systematic study of the magnetic properties of pyrochlore Y2Ir2O7 and its
hole-doped compounds by performing magnetic, electron spin resonance,
electrical transport, and x-ray photoelectron spectroscopy (XPS) measurements.
We demonstrate the existence of weak ferromagnetism on top of a large
antiferromagnetic background in the undoped compound. Hole doping by calcium
was found to enhance both the ferromagnetism and the electrical conductivity.
The XPS characterization shows the coexistence of Ir4+ and Ir5+ in the undoped
compound, and the amount of Ir5+ increases with Ca doping, which highlights the
possible origins of the weak ferromagnetism associated with the formation of
Ir5+.We also observe a vertical shift in the M-H curves after field cooling,
which may arise from a strong coupling between the ferromagnetic phase and the
antiferromagnetic background.",1501.00615v1
2017-02-17,Charge Transport and Entropy Production Rate in Magnetically Active Molecular Dimer,"We consider charge and thermal transport properties of magnetically active
paramagnetic molecular dimer. Generic properties for both transport quantities
are reduced currents in the ferro- and anti-ferromagnetic regimes compared to
the paramagnetic and efficient current blockade in the anti-ferromagnetic
regime. In contrast, while the charge current is about an order of magnitude
larger in the ferromagnetic regime, compared to the anti-ferromagnetic, the
thermal current is efficiently blockaded there as well. This disparate behavior
of the thermal current is attributed to current resonances in the ferromagnetic
regime which counteract the thermal flow. The temperature difference strongly
reduces the exchange interaction and tends to destroy the magnetic control of
the transport properties. The weakened exchange interaction opens up a
possibility to tune the system into thermal rectification, for both the charge
and thermal currents.",1702.05389v2
2008-07-29,Dose dependence of ferromagnetism in Co-implanted ZnO,"We have studied the structural, magnetic and electronic properties of
Co-implanted ZnO (0001) films grown on Al2O3 (1120) substrates for different
implantation doses and over a wide temperature range. Strong room temperature
ferromagnetism is observed with magnetic parameters depending on the cobalt
implantation dose. A detailed analysis of the structural and magnetic
properties indicates that there are two magnetic phases in Co-implanted ZnO
films. One is a ferromagnetic phase due to the formation of long range
ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer,
the second one is a superparamagnetic phase, which occurs due to the formation
of metallic cobalt clusters in the Al2O3 substrate. Using x-ray resonant
magnetic scattering, the element specific magnetization of cobalt, oxygen and
Zn was investigated. Magnetic dichroism was observed at the Co L2,3 edges as
well as at the O K edge. In addition, the anomalous Hall effect is also
observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO
films.",0807.4711v1
2018-06-11,Competing magnetic correlations across the ferromagnetic quantum critical point in the Kondo system CeTi$_{1-x}$V$_x$Ge$_3$: $^{51}$V NMR as a local probe,"$^{51}$V nuclear magnetic resonance (NMR) and magnetization studies on
CeTi$_{1-x}$V$_x$Ge$_3$ have been performed to explore the evolution from the
ferromagnetic ($x = 0.113$) to the antiferromagnetic Kondo lattice state ($x =
1$), with focus on the emergence of a possible ferromagnetic quantum critical
point (FMQCP) at $x_c \approx 0.4$. From the temperature dependence of the
nuclear spin-lattice relaxation rate, $1/T_1T$, and the Knight shift,
\textit{K}, for $x=0.113$ and $x=1$ a considerable competition between ferro-
and antiferromagnetic correlations is found. Around the critical concentration
($x = 0.35, 0.405$) quantum-critical spin fluctuations entail weak
antiferromagnetic spin fluctuations admixed with ferromagnetic spin
fluctuations. The FMQCP in CeTi$_{1-x}$V$_x$Ge$_3$ therefore is not purely
ferromagnetic in nature.",1806.04111v3
2018-07-31,Spin absorption at ferromagnetic-metal/platinum-oxide interface,"We investigate the absorption of a spin current at a
ferromagnetic-metal/Pt-oxide interface by measuring current-induced
ferromagnetic resonance. The spin absorption was characterized by the magnetic
damping of the heterostructure. We show that the magnetic damping of a
Ni$_{81}$Fe$_{19}$ film is clearly enhanced by attaching Pt-oxide on the
Ni$_{81}$Fe$_{19}$ film. The damping enhancement is disappeared by inserting an
ultrathin Cu layer between the Ni$_{81}$Fe$_{19}$ and Pt-oxide layers. These
results demonstrate an essential role of the direct contact between the
Ni$_{81}$Fe$_{19}$ and Pt-oxide to induce sizable interface spin-orbit
coupling. Furthermore, the spin-absorption parameter of the
Ni$_{81}$Fe$_{19}$/Pt-oxide interface is comparable to that of intensively
studied heterostructures with strong spin-orbit coupling, such as an oxide
interface, topological insulators, metallic junctions with Rashba spin-orbit
coupling. This result illustrates strong spin-orbit coupling at the
ferromagnetic-metal/Pt-oxide interface, providing an important piece of
information for quantitative understanding the spin absorption and spin-charge
conversion at the ferromagnetic-metal/metallic-oxide interface.",1807.11806v1
2019-02-22,A highly sensitive magnetic sensor using a 2D van der Waals ferromagnetic material,"Two-dimensional (2D) van der Waals ferromagnetic materials are emerging as
promising candidates for applications in ultra-compact spintronic nanodevices,
nanosensors, and information storage. Our recent discovery of the strong room
temperature ferromagnetism in single layers of VSe2 grown on graphite or MoS2
substrate has opened new opportunities to explore these ultrathin magnets for
such applications. In this paper, we present a new type of magnetic sensor that
utilizes the single layer VSe2 film as a highly sensitive magnetic core. The
sensor relies in changes in resonance frequency of the LC circuit composed of a
soft ferromagnetic microwire coil that contains the ferromagnetic VSe2 film
subject to applied DC magnetic fields. The sensitivity of the sensor reaches an
extremely high value of 16x10^6 Hz/Oe, making it an excellent candidate for a
wide range of magnetic sensing applications.",1902.08365v1
2019-12-03,Large Resistance Change on Magnetic Tunnel Junction based Molecular Spintronics Devices,"Molecular bridges covalently bonded to two ferromagnetic electrodes can
transform ferromagnetic materials and produce intriguing spin transport
characteristics. This paper discusses the impact of molecule induced strong
coupling on spin transport. To study the molecular coupling effect
organometallic molecular complex (OMC) was bridged between two ferromagnetic
electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the
exposed side edges. OMCs induced strong iter-ferromagnetic electrode coupling
to yield drastic changes in transport properties of the magnetic tunnel
junction testbed at the room temperature. These OMCs also transformed the
magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic
resonance studies provided insightful data to explain transport studies on the
magnetic tunnel junction based molecular spintronics devices.",1912.01305v1
2020-08-11,Itinerant ferromagnetism in the repulsive Hubbard chain with anisotropic odd-wave attraction,"The ground-state properties of the Hubbard chain with on-site repulsion and
anisotropic nearest-neighbor attraction are investigated by means of density
matrix renormalization group calculations. The non-local attraction acts
between fermions of one spin component only, mimicking the effect of p-wave
Feshbach resonances in cold-atom systems. We analyze the onset of itinerant
ferromagnetism, pinpointing the critical attraction strength where partially
and fully ferromagnetic states occur. In the cold-atom setup, where the two
(pseudo) spin populations are separately conserved, ferromagnetism occurs with
the nucleation of a fully imbalanced band-insulating domain hosting the
attractive component only. The size of this domain grows with the attraction
strength, therefore increasing the (opposite) imbalance of the other domain,
until the two spin components are fully separated. In the presence of a
harmonic trap, the ferromagnetic state hosts a partially imbalanced domain in
the center with an excess of the attractive component and filling lower than
one. This central region is surrounded by fully imbalanced domains, located in
the trap tails, hosting only fermions belonging to the other component.",2008.04588v1
2020-08-12,Accelerating the laser-induced demagnetization of a ferromagnetic film by antiferromagnetic order in an adjacent layer,"We study the ultrafast demagnetization of Ni/NiMn and Co/NiMn
ferromagnetic/antiferromagnetic bilayer systems after excitation by a laser
pulse. We probe the ferromagnetic order of Ni and Co using magnetic circular
dichroism in time-resolved pump--probe resonant X-ray reflectivity. Tuning the
sample temperature across the antiferromagnetic ordering temperature of the
NiMn layer allows to investigate effects induced by the magnetic order of the
latter. The presence of antiferromagnetic order in NiMn speeds up the
demagnetization of the ferromagnetic layer, which is attributed to
bidirectional laser-induced superdiffusive spin currents between the
ferromagnetic and the antiferromagnetic layer.",2008.05268v1
2021-05-07,Magnetic properties of the itinerant ferromagnet LaCrGe3 under pressure studied by 139La NMR,"$^{139}$La nuclear magnetic resonance (NMR) measurements under pressure ($p =
0-2.64$ GPa) have been carried out to investigate the static and dynamic
magnetic properties of the itinerant ferromagnet LaCrGe$_3$. $^{139}$La-NMR
spectra for all measured pressures in the ferromagnetically ordered state show
a large shift due to the internal field induction $|$$B_{\rm int}$$|$ $\sim$ 4
T at the La site produced by Cr ordered moments. The change in $B_{\rm int}$ by
less than 5\% with $p$ up to 2.64~GPa indicates that the Cr 3$d$ moments are
robust under pressure. The temperature dependence of NMR shift and $B_{\rm
int}$ suggest that the ferromagnetic order develops below $\sim$ 50~K under
higher pressures in a magnetic field of $\sim$ 7.2 T. Based on the analysis of
NMR data using the self-consistent-renormalization (SCR) theory, the spin
fluctuations in the paramagnetic state well above $T_{\rm C}$ are revealed to
be three dimensional ferromagnetic throughout the measured $p$ region.",2105.03479v1
2021-06-26,Spin current injection via equal-spin Cooper pairs in ferromagnet/superconductor heterostructures,"Equal-spin Cooper pairs are pivotal building blocks for superconducting
spintronics devices. In recent experiments, unusual behavior was observed in
ferromagnet/ferromagnet/superconductor devices when a precession of the
magnetization was induced by ferromagnetic resonance. By using a
non-equilibrium Usadel Green function formalism, we study spin transport for
such a setup. We solve for spin-resolved distribution functions and demonstrate
that the spin injection process in superconductors is governed by the inverse
proximity effect in the superconducting layer. We find that equal-spin Cooper
pairs, which are produced by the two misaligned ferromagnetic layers, transport
spin inside the S layer. This then results in an increase of the injected spin
current below the superconducting critical temperature. Our calculations
provide the first evidence of the essential role of equal-spin Cooper pairs on
spin-transport properties of S/F devices and pave new avenues for the design of
superconducting spintronics devices.",2106.13988v3
2022-07-14,Magnetization dynamics in proximity-coupled superconductor-ferromagnet-superconductor multilayers. Part II,"In this work, we study magnetization dynamics in
superconductor-ferromagnet-superconductor thin-film structures. Results of the
broad-band ferromagnetic resonance spectroscopy are reported for a large set of
samples with varied thickness of both superconducting and ferromagnetic layers
in a wide frequency, field, and temperature ranges. Experimentally the
one-dimensional anisotropic action of superconducting torque on magnetization
dynamics is established; its dependence on thickness of layers is revealed. It
is demonstrated that experimental findings support the recently-proposed
mechanism of the superconducting torque formation via the interplay between the
superconducting kinetic inductance and magnetization precession at
superconductor-ferromagnet interfaces.",2207.06751v2
2002-04-04,Spin dynamics in La_{1-x}Sr_{x}MnO_{3} (x \le 0.175) investigated by high-field ESR spectroscopy,"High-field electron spin resonance (ESR) experiments have been carried out in
single crystals of La_{1-x}Sr_xMnO_3 in the concentration range 0 \le x \le
0.175. Different quasioptical arrangements have been utilized in the frequency
range 40 < \nu < 700GHz and for magnetic fields B \le 12T. A splitting of the
antiferromagnetic resonance (AFMR) mode is observed in the magnetic field for
the parent compound LaMnO_3 in agreement with the antiferromagnetic structure
of this material. Abrupt changes in the AFMR frequencies have been observed
around x = 0.025 and attributed to the possible transition between
antiferromagnetic and canted state. For increasing Sr-doping the observed AFMR
modes are splitted even in zero field, which can be naturally explained using a
concept of a canted magnetic structure for x<0.1. In La_{0.825}Sr_{0.175}MnO_3
the ESR spectra are consistent with the ferromagnetic and metallic state. The
lines of ferromagnetic resonance and ferromagnetic antiresonance can be clearly
seen in the spectra. For intermediate concentrations 0.1 \le x \le 0.15 a
complicated set of ESR spectra has been observed, which can be well explained
by a single ferromagnetic resonance mode and taking into account electrodynamic
effects.",0204112v1
2009-06-17,The Kondo effect in ferromagnetic atomic contacts,"Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk,
electronic conduction in these materials takes place mainly through the $s$ and
$p$ electrons, whereas the magnetic moments are mostly in the narrow
$d$-electron bands, where they tend to align. This general picture may change
at the nanoscale because electrons at the surfaces of materials experience
interactions that differ from those in the bulk. Here we show direct evidence
for such changes: electronic transport in atomic-scale contacts of pure
ferromagnets (iron, cobalt and nickel), despite their strong bulk
ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of
local magnetic moments by the conduction electrons below a characteristic
temperature. The Kondo effect creates a sharp resonance at the Fermi energy,
affecting the electrical properties of the system;this appears as a Fano-Kondo
resonance in the conductance characteristics as observed in other artificial
nanostructures. The study of hundreds of contacts shows material-dependent
lognormal distributions of the resonance width that arise naturally from Kondo
theory. These resonances broaden and disappear with increasing temperature,
also as in standard Kondo systems. Our observations, supported by calculations,
imply that coordination changes can significantly modify magnetism at the
nanoscale. Therefore, in addition to standard micromagnetic physics, strong
electronic correlations along with atomic-scale geometry need to be considered
when investigating the magnetic properties of magnetic nanostructures.",0906.3135v1
2013-06-19,"Asymmetric Ferromagnetic Resonance, Universal Walker Breakdown, and Counterflow Domain Wall Motion in the Presence of Multiple Spin-Orbit Torques","We study the motion of several types of domain wall profiles in spin-orbit
coupled magnetic nanowires and also the influence of spin-orbit interaction on
the ferromagnetic resonance of uniform magnetic films. We extend previous
studies by fully considering not only the field-like contribution from the
spin-orbit torque, but also the recently derived Slonczewski-like spin-orbit
torque. We show that the latter interaction affects both the domain wall
velocity and the Walker breakdown threshold non-trivially, which suggests that
it should be accounted in experimental data analysis. We find that the presence
of multiple spin-orbit torques may render the Walker breakdown to be universal
in the sense that the threshold is completely independent on the
material-dependent Gilbert damping, non-adiabaticity, and the chirality of the
domain wall. We also find that domain wall motion against the current injection
is sustained in the presence of multiple spin-orbit torques and that the wall
profile will determine the qualitative influence of these different types of
torques (e.g. field-like and Slonczewski-like). In addition, we consider a
uniform ferromagnetic layer under a current bias, and find that the resonance
frequency becomes asymmetric against the current direction in the presence of
Slonczewski-like spin-orbit coupling. This is in contrast with those cases
where such an interaction is absent, where the frequency is found to be
symmetric with respect to the current direction. This finding shows that
spin-orbit interactions may offer additional control over pumped and absorbed
energy in a ferromagnetic resonance setup by manipulating the injected current
direction.",1306.4680v1
2003-09-05,Reduction of Magnetic Noise in Magnetic Resonance Force Microscopy,"We study the opportunity to reduce a magnetic noise produced by a uniform
cantilever with a ferromagnetic particle in magnetic resonance force microscopy
(MRFM) applications. We demonstrate theoretically a significant reduction of
magnetic noise and the corresponding increase of the MRFM relaxation time using
a nonuniform cantilever.",0309158v1
2014-03-06,Influence of the Dzyaloshinskii-Moriya interaction on the spin-torque diode effect,"This paper predicts the effect of the Dzyaloshinskii-Moriya interaction (DMI)
and spin Hall effect in the spin-torque diode response of a Magnetic Tunnel
Junction built over a Tantalum strip. Our results indicate that, for a
microwave current large enough, the DMI can change qualitatively the resonant
response by splitting the ferromagnetic resonance peak. We also find out that
the two modes have a non-uniform spatial distribution.",1403.1485v1
2017-09-28,Electromagnon on the Surface of Magnetic Topological Insulator,"We investigate theoretically the electromagnon on the surfaces of the
magnetic topological insulator thin films. It is found that when the magnetic
asymmetry between the top and bottom surfaces is there, the ferromagnetic
resonance is driven by the electric field which is two orders of magnitude more
efficient compared with that by the magnetic field. The resonant frequency of
the electromagnon is also estimated.",1709.09830v1
1997-03-26,Stochastic Resonance in Chaotic Spin-Wave Dynamics,"We report the first experimental observation of noise-free stochastic
resonance by utilizing the intrinsic chaotic dynamics of the system. To this
end we have investigated the effect of an external periodic modulation on
intermittent signals observed by high power ferromagnetic resonance in yttrium
iron garnet spheres. Both the signal-to-noise ratio and the residence time
distributions show the characteristic features of stochastic resonance. The
phenomena can be explained by means of a one-dimensional intermittent map. We
present analytical results as well as computer simulations.",9703018v1
2001-04-16,Enhancement of Nuclear Spin Superradiance by Electron Resonator,"Superradiance of nuclear spins is considered, when the nuclei interact via
hyperfine forces with electrons of a ferromagnet. The consideration is based on
a microscopic model. If the sample, coupled with a resonant electric circuit,
possesses electronic magnetization, then the electron subsystem plays the role
of an additional effective resonator, by enhancing the coupling between nuclear
spins and the resonant circuit. Radiation power can be increased by three
orders, while the radiation time of a superradiance burst can become three
times shorter. In the presence of dynamic nuclear polarization, the regime of
pulsing superradiance can occur.",0104276v1
2003-03-10,Energy Spectra of Magnetostatic Oscillations in Ferrite Disk Resonators,"Ferromagnetic resonators with short-wavelength, so-called magnetostatic (MS),
oscillations can be considered in microwaves as point (with respect to the
external electromagnetic fields) particles. It was shown recently [E. O.
Kamenetskii, Phys. Rev. E, 63, 066612 (2001)] that MS oscillations in a small
ferrite disk resonator can be characterized by a discrete spectrum of energy
levels. This fact allows analyzing the MS oscillations similarly to quantum
mechanical problems. In this paper we give the results of energy spectrum
calculations for MS oscillations in a ferrite disk resonator.",0303164v2
2006-04-05,Current-driven resonant excitation of magnetic vortex,"A magnetic vortex core in a ferromagnetic circular nanodot has a resonance
frequency originating from the confinement of the vortex core. By the
micromagnetic simulation including the spin-transfer torque, we show that the
vortex core can be resonantly excited by an AC (spin-polarized) current through
the dot and that the resonance frequency can be tuned by the dot shape. The
resistance measurement under the AC current successfully detects the resonance
at the frequency consistent with the simulation.",0604123v1
2013-08-14,Electrical Detection of Spin Wave Resonance in a Permalloy Thin Strip,"We investigated the microwave-induced DC response of spin wave resonance
(SWR) in a permalloy thin strip via electrical detection. Our experimental
results obtained by sweeping the external field reveal that: 1. the amplitude
of SWR signals depend on the direction of external field and, 2. unlike the DC
response of ferromagnetic resonance, SWR spectra are always anti-symmetrical.
The spin dynamics are discussed based on these unusual signals in resonant
condition.",1308.3069v1
2006-02-16,Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies,"We develop a model for ferromagnetic resonance in systems with competing
uniaxial and cubic anisotropies. This model applies to (i) magnetic materials
with both uniaxial and cubic anisotropies, and (ii) magnetic nanoparticles with
effective core and surface anisotropies; We numerically compute the resonance
frequency as a function of the field and the resonance field as a function of
the direction of the applied field for an arbitrary ratio of cubic-to-uniaxial
anisotropy. We also provide some approximate analytical expressions in the case
of weak cubic anisotropy. We propose a method that uses these expressions for
estimating the uniaxial and cubic anisotropy constants, and for determining the
relative orientation of the cubic anisotropy axes with respect to the crystal
principle axes. This method is applicable to the analysis of experimental data
of resonance type measurements for which we give a worked example of an iron
thin film with mixed anisotropy.",0602369v3
2007-11-09,A Digital Switch and Femto-Tesla Magnetic Field Sensor Based on Fano Resonance in a Spin Field Effect Transistor,"We show that a Spin Field Effect Transistor, realized with a semiconductor
quantum wire channel sandwiched between half-metallic ferromagnetic contacts,
can have Fano resonances in the transmission spectrum. These resonances appear
because the ferromagnets are half-metallic, so that the Fermi level can be
placed above the majority but below the minority spin band. In that case, the
majority spins will be propagating, but the minority spins will be evanescent.
At low temperatures, the Fano resonances can be exploited to implement a
digital binary switch that can be turned on or off with a very small gate
voltage swing of few tens of microvolts, leading to extremely small dynamic
power dissipation during switching. An array of 500,000 x 500,000 such
transistors can detect ultrasmall changes in a magnetic field with a
sensitivity of 1 femto-Tesla/sqrt{Hz}, if each transistor is biased near a Fano
resonance.",0711.1475v1
2007-12-03,Finite size effects on spin-torque driven ferromagnetic resonance in spin-valves with a Co/Ni synthetic free layer,"Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study magnetic
excitations in Co/Ni synthetic layers confined in nanojunctions. Field swept
ST-FMR measurements were conducted with a magnetic field applied perpendicular
to the layer surface. The resonance lines were measured under low amplitude
excitation in a linear response regime. The resulting resonance fields were
compared with those obtained using conventional rf field driven FMR on extended
films with the same Co/Ni layer structure. A lower resonance field is found in
confined structures. The effect of both dipolar fields acting on the Co/Ni
layer emanating from other magnetic layers in the device and finite size
effects on the spin wave spectrum are discussed.",0712.0404v2
2017-10-09,Weak magnetic anisotropy in GdRh$_2$Si$_2$ studied by magnetic resonance,"The antiferromagnetically (AFM) ordered state of GdRh$_{2}$Si$_{2}$ which
consists of AFM-stacked ferromagnetic layers is investigated by magnetic
resonance spectroscopy. The almost isotropic Gd$^{3+}$ paramagnetic resonance
becomes anisotropic in the AFM ordered region below 107 K. The emerging
internal anisotropic exchange-fields are still small enough to allow an
investigation of their magnetization dynamics by using a standard
microwave-frequency magnetic resonance technique. We could characterize this
anisotropy in detail in the ferromagnetic layers of the excitation at 9 and 34
GHz. We derived a resonance condition for the AFM ordered phase to describe the
weak in-plane anisotropic behaviour in combination with a mean-field analysis.",1710.03079v1
2021-07-16,Influence of inter-sublattice coupling on the terahertz nutation spin dynamics in antiferromagnets,"Spin nutation resonance has been well-explored in one-sublattice
ferromagnets. Here, we investigate the spin nutation in two-sublattice
antiferromagnets as well as, for comparison, ferrimagnets with inter-and
intra-sublattice nutation coupling. In particular, we derive the susceptibility
of the two-sublattice magnetic system in response to an applied external
magnetic field. To this end, the antiferromagnetic and ferrimagnetic (sub-THz)
precession and THz nutation resonance frequencies are calculated. Our results
show that the precession resonance frequencies and effective damping decrease
with intra-sublattice nutation coupling, while they increase with inter
-sublattice nutation in an antiferromagnet. However, we find that the THz
nutation resonance frequencies decrease with both the intra-and
inter-sublattice nutation couplings. For ferrimagnets, conversely, we calculate
two nutation modes with distinct frequencies, unlike antiferromagnets. The
exchange-like precession resonance frequency of ferrimagnets decreases with
intra-sublattice nutation coupling and increases with inter-sublattice nutation
coupling, like antiferromagnets, but the ferromagnetic-like precession
frequency of ferrimagnets is practically invariant to the intra and
inter-sublattice nutation couplings.",2107.07939v2
2021-08-24,Higher-order ferromagnetic resonances in periodic arrays of synthetic-antiferromagnet nanodiscs,"We investigate spin dynamics in nanodisc arrays of synthetic-antiferromagnets
(SAF) made of Py/NiCu/Py trilayers, where the NiCu spacer undergoes a Curie
transition at about 200 K. The observed ferromagnetic resonance spectra have
three distinct resonance modes at room temperature, which are fully recreated
in our micromagnetic simulations showing also how the intra-SAF asymmetry can
be used to create and control the higher-order resonances in the structure.
Below the Curie temperature of the spacer, the system effectively transitions
into a single-layer nanodisc array with only two resonance modes. Our results
show how multi-layering of nano-arrays can add tunable GHz functionality
relevant for such rapidly developing fields as magnetic meta-materials,
magnonic crystals, arrays of spin-torque oscillators and neuromorphic
junctions.",2108.10581v1
2023-03-28,Exploring terahertz-scale exchange resonances in synthetic ferrimagnets with ultrashort optically induced spin currents,"Using spin currents generated by fs laser pulses, we demonstrate excitation
of GHz ferromagnetic resonance and THz ferrimagnetic exchange resonances in
Co/Gd/Co/Gd multilayers by time-resolved magneto-optic Kerr effect
measurements. Varying the Gd layer thickness allows for a tuning of the
resonance spectrum by manipulating the total angular momentum and strength of
effective exchange fields between the antiferromagnetically coupled layers.
Close to the compensation point of angular momentum, a minimum in the frequency
of the exchange-dominated mode and a maximum in the frequency of the
ferromagnetic resonance mode is observed. Finally, to gain better understanding
of the excitation mechanism, we analyze the anomalous variation in the measured
exchange mode amplitude as a function of its frequency. A peak in this
amplitude in the vicinity of the compensation point of angular momentum is
explained using a macrospin model, taking nonlinear effects at finite
precession amplitudes into account.",2303.15985v2
2001-10-17,Nonequilibrium excitations in Ferromagnetic Nanoparticles,"In recent measurements of tunneling transport through individual
ferromagnetic Co nanograins, Deshmukh, Gu\'eron, Ralph et al.
\cite{mandar,gueron} (DGR) observed a tunneling spectrum with discrete
resonances, whose spacing was much smaller than what one would expect from
naive independent-electron estimates. In a previous publication,
\cite{prl_kleff} we had suggested that this was a consequence of nonequilibrium
excitations, and had proposed a ``minimal model'' for ferromagnetism in
nanograins with a discrete excitation spectrum as a framework for analyzing the
experimental data. In the present paper, we provide a detailed analysis of the
properties of this model: We delineate which many-body electron states must be
considered when constructing the tunneling spectrum, discuss various
nonequilibrium scenarios and compare their results with the experimental data
of Refs. \cite{mandar,gueron}. We show that a combination of nonequilibrium
spin- and single-particle excitations can account for most of the observed
features, in particular the abundance of resonances, the resonance spacing and
the absence of Zeeman splitting.",0110348v1
2002-12-11,Ferromagnetic resonant tunneling diodes as spin polarimeters and polarizers,"A method for measuring the degree of spin polarization of magnetic materials
based on spin-dependent resonant tunneling is proposed. The device we consider
is a ballistic double-barrier resonant structure consisting of a ferromagnetic
layer embedded between two insulating barriers. A simple procedure, based on a
detailed analysis of the differential conductance, allows to accurately
determine the polarization of the ferromagnet. The spin-filtering character of
such a system is furthermore addressed. We show that a 100% spin selectivity
can be achieved under appropriate conditions. This approach is believed to be
well suited for the investigation of diluted magnetic semiconductor
heterostructures.",0212242v1
2005-04-23,Residual Kondo effect in quantum dot coupled to half-metallic ferromagnets,"We study the Kondo effect in a quantum dot coupled to half-metallic
ferromagnetic electrodes in the regime of strong on-dot correlations. Using the
equation of motion technique for nonequilibrium Green functions in the slave
boson representation we show that the Kondo effect is not completely suppressed
for anti-parallel leads magnetization. In the parallel configuration there is
no Kondo effect but there is an effect associated with elastic cotunneling
which in turn leads to similar behavior of the local (on-dot) density of states
(LDOS) as the usual Kondo effect. Namely, the LDOS shows the temperature
dependent resonance at the Fermi energy which splits with the bias voltage and
the magnetic field. Moreover, unlike for non-magnetic or not fully polarized
ferromagnetic leads the only minority spin electrons can form such resonance in
the density of states. However, this resonance cannot be observed directly in
the transport measurements and we give some clues how to identify the effect in
such systems.",0504604v2
2006-03-05,Stray Field Magnetic Resonance Tomography using Ferromagnetic Spheres,"The methodology for obtaining two- and three-dimensional magnetic resonance
images by using azimuthally symmetric dipolar magnetic fields from
ferromagnetic spheres is described. We utilize the symmetric property of a
geometric sphere in the presence of a large externally applied magnetic field
to demonstrate that a complete two- or three-dimensional structured rendering
of a sample can be obtained without the motion of the sample relative to the
sphere. Sequential positioning of the integrated sample-sphere system in an
external magnetic field at various angular orientations provides all the
required imaging slices for successful computerized tomographic image
reconstruction. The elimination of the requirement to scan the sample relative
to the ferromagnetic tip in this imaging protocol is a potentially valuable
simplification compared to previous scanning probe magnetic resonance imaging
proposals.",0603034v1
2007-04-19,Ferromagnetic resonance force microscopy on a thin permalloy film,"Ferromagnetic Resonance Force Microscopy (FMRFM) offers a means of performing
local ferromagnetic resonance. We have studied the evolution of the FMRFM force
spectra in a continuous 50 nm thick permalloy film as a function of probe-film
distance and performed numerical simulations of the intensity of the FMRFM
probe-film interaction force, accounting for the presence of the localized
strongly nonuniform magnetic field of the FMRFM probe magnet. Excellent
agreement between the experimental data and the simulation results provides
insight into the mechanism of FMR mode excitation in an FMRFM experiment.",0704.2442v1
2011-08-10,Bias-induced destruction of ferromagnetism and disorder effects in GaMnAs heterostructures,"The magneto-electric properties of resonant tunneling double barrier
structures using GaMnAs for the quantum well is investigated within a
self-consistent Green's function approach and a tight-binding electronic
structure model. The magnetic state of the well is determined self-consistently
by the tunneling current which controls the hole spin density and, hence, the
degree of exchange splitting of the subbands inside the well. Prompted by
recent experiments we compare model systems of increasing defect concentration
(substitutional disorder) regarding their I-V curve, magnetic state, and spin
polarization. We predict that, near resonance, the ferromagnetic order which
may be present at zero bias in the GaMnAs well tends to be destroyed. Resonance
peaks are found to be more sensitive to disorder than ferromagnetic ordering
and spin polarization of the steady-state current.",1108.2108v1
2015-02-02,Resonant magneto-tunneling between normal and ferromagnetic electrodes in relation to the three-terminal spin transport,"The recently suggested mechanism [Y. Song and H. Dery, Phys. Rev. Lett. 113,
047205 (2014)] of the three-terminal spin transport is based on the resonant
tunneling of electrons between ferromagnetic and normal electrodes via an
impurity. The sensitivity of current to a weak external magnetic field stems
from a spin blockade, which, in turn, is enabled by strong on-site repulsion.
We demonstrate that this sensitivity exists even in the absence of repulsion
when a single-particle description applies. Within this description, we
calculate exactly the resonant-tunneling current between the electrodes. The
mechanism of magnetoresistance, completely different from the spin blocking,
has its origin in the interference of virtual tunneling amplitudes. Spin
imbalance in ferromagnetic electrode is responsible for this interference and
the resulting coupling of the Zeeman levels. This coupling also affects the
current in the correlated regime.",1502.00350v1
2015-08-06,Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between non-magnetic materials,"The Rashba-Edelstein effect stems from the interaction between the electron's
spin and its momentum induced by spin-orbit interaction at an interface or a
surface. It was shown that the inverse Rashba-Edelstein effect can be used to
convert a spin- into a charge current. Here, we demonstrate that a Bi/Ag Rashba
interface can even drive an adjacent ferromagnet to resonance. We employ a
spin-torque ferromagnetic resonance excitation/detection scheme which was
developed originally for a bulk spin-orbital effect, the spin Hall effect. In
our experiment, the direct Rashba-Edelstein effect generates an oscillating
spin current from an alternating charge current driving the magnetization
precession in a neighboring permalloy (Py, Ni80Fe20) layer. Electrical
detection of the magnetization dynamics is achieved by a rectification
mechanism of the time dependent multilayer resistance arising from the
anisotropic magnetoresistance.",1508.01410v1
2015-10-20,Evaluation of Spin Waves and Ferromagnetic Resonance Contribution to the Spin Pumping in Ta/CoFeB Structure,"The spin waves and ferromagnetic resonance (FMR) contribution to the spin
pumping signal is studied in the Ta/CoFeB interface under different excitation
bias fields. Ferromagnetic resonance is excited utilizing a coplanar waveguide
and a microwave generator. Using a narrow waveguide of about 3 {\mu}m,
magnetostatic surface spin waves with large wavevector (k) of about 0.81
{\mu}m^-1 are excited. A large k value results in dissociation of spin waves
and FMR frequencies according to the surface spin wave dispersion relation.
Spin waves and FMR contribution to the spin pumping are calculated based on the
area under the Lorentzian curve fitting over experimental results. It is found
that the FMR over spin waves contribution is about 1 at large bias fields in
Ta/CoFeB structure. Based on our spin pumping results, we propose a method to
characterize the spin wave decay constant which is found to be about 5.5 {\mu}m
in the Ta/CoFeB structure at a bias field of 600 Oe.",1510.05745v1
2015-11-25,Ferromagnetic resonance phase imaging in spin Hall multilayers,"We experimentally image the magnetic precession phase of patterned spin Hall
multilayer samples to study the rf driving field vector using time-resolved
anomalous Nernst effect (TRANE) microscopy. Our ferromagnetic resonance (FMR)
measurements quantify the phase and amplitude for both the magnetic precession
and the electric current, which allows us to establish the total driving field
orientation and the strength of spin Hall effect. In a channel of uniform
width, we observe spatial variation of the FMR phase laterally across the
channel. We interpret our findings in the context of electrical measurement
using the spin-transfer torque ferromagnetic resonance technique and show that
observed phase variation introduces a systematic correction into the spin Hall
angle if spatial phase and amplitude variations are not taken into account.",1511.08126v1
2015-11-27,Resonance spin-charge phenomena and mechanism of magnetoresistance anisotropy in manganite/metal bilayer structures,"The dc voltage generated under ferromagnetic resonance has been studied in
bilayer structures based on manganite thin epitaxial films La0.67Sr0.33MnO3
(LSMO) and non-magnetic metals (Au, Pt, and SrRuO3) in the temperature range up
to the Curie point. The effect is shown to be caused by two different
phenomena: (1) the resonance dc electromotive force related to anisotropic
magnetoresistance (AMR) in the manganite film and (2) pure spin current (spin
pumping) registered by means of the inverse spin Hall effect in normal metal.
The two phenomena were separated using the angular dependence of the effect,
the external magnetic field H0 being rotated in the film plane. It was found
that the AMR mechanism in the manganite films differs substantially from that
in traditional ferromagnetic metals being governed by the colossal
magnetoresistance together with the in-plane magnetic anisotropy. The spin
pumping effect registered in the bilayers was found to be much lower than that
reported for common ferromagnets; possible reasons are discussed.",1511.08664v1
2017-03-30,Study of spin pumping in Co thin film vis-a-vis seed and capping layer using ferromagnetic resonance spectroscopy,"We investigated the dependence of the seed [Ta/Pt, Ta/Au] and capping [Pt/Ta,
Au/Ta] layers on spin pumping effect in the ferromagnetic 3 nm thick Co thin
film using ferromagnetic resonance spectroscopy. The data is fitted with Kittel
equation to evaluate damping constant and g-factor. A strong dependence of seed
and capping layers on spin pumping has been discussed. The value of damping
constant {alpha} is found to be relatively large i.e. 0.0326 for the
Ta{3}/Pt{3}/Co{3}/Pt{3}/Ta{3} {nm} multi-layer structure, while it is 0.0104
for Ta{3}/Co{3}/Ta{3} {nm}. Increase in {alpha} is observed due to Pt layer
that works as a good sink for spins due to high spin orbit coupling. In
addition, we measured the effective spin conductance = 2.0e18 m-2 for the
trilayer structure Pt{3}/Co{3}/Pt{3} {nm} as a result of the enhancement in
{alpha} relative to its bulk value. We observed that the evaluated g-factor
decreases as effective demagnetizing magnetic field increases in all the
studied samples. The azimuthal dependence of magnetic resonance field and line
width showed relatively high anisotropy in the trilayer Ta{3}/Co{3}/Ta{3} {nm}
structure.",1703.10630v1
2019-05-02,Negligible thermal contributions to the spin pumping signal in ferromagnetic metal-Platinum bilayers,"Spin pumping by ferromagnetic resonance is one of the most common technique
to determine spin hall angles, Edelstein lengths or spin diffusion lengths of a
large variety of materials. In recent years, rising concerns have appeared
regarding the interpretation of these experiments, underlining that the signal
could arise purely from thermoelectric effects, rather than from coherent spin
pumping. Here, we propose a method to evaluate the presence or absence of
thermal effects in spin pumping signals, by combining bolometry and spin
pumping by ferromagnetic resonance measurements, and comparing their timescale.
Using a cavity to perform the experiments on Pt\Permalloy and La0.7Sr0.3MnO3\Pt
samples, we conclude on the absence of any measurable thermoelectric
contribution such as the spin Seebeck and anomalous Nernst effects at resonance",1905.00771v2
2014-03-04,Off-Resonant Manipulation of Spins in Diamond via Precessing Magnetization of a Proximal Ferromagnet,"We report the manipulation of nitrogen vacancy (NV) spins in diamond when
nearby ferrimagnetic insulator, yttrium iron garnet, is driven into precession.
The change in NV spin polarization, as measured by changes in
photoluminescence, is comparable in magnitude to that from conventional
optically detected magnetic resonance, but relies on a distinct mechanism as it
occurs at a microwave frequency far removed from the magnetic resonance
frequency of the NV spin. This observation presents a new approach to
transferring ferromagnetic spin information into a paramagnet and then
transducing the response into a robust optical signal. It also opens new
avenues for studying ferromagnetism and spin transport at the nanoscale.",1403.0656v1
2012-04-24,Nonlocal feedback in ferromagnetic resonance,"Ferromagnetic resonance in thin films is analyzed under the influence of
spatiotemporal feedback effects. The equation of motion for the magnetization
dynamics is nonlocal in both space and time and includes isotropic, anisotropic
and dipolar energy contributions as well as the conserved Gilbert- and the
non-conserved Bloch-damping. We derive an analytical expression for the
peak-to-peak linewidth. It consists of four separate parts originated by
Gilbert damping, Bloch-damping, a mixed Gilbert-Bloch component and a
contribution arising from retardation. In an intermediate frequency regime the
results are comparable with the commonly used Landau-Lifshitz-Gilbert theory
combined with two-magnon processes. Retardation effects together with Gilbert
damping lead to a linewidth the frequency dependence of which becomes strongly
nonlinear. The relevance and the applicability of our approach to ferromagnetic
resonance experiments is discussed.",1204.5342v1
2020-01-27,Acoustic ferromagnetic resonance and spin pumping induced by surface acoustic waves,"Voltage induced magnetization dynamics of magnetic thin films is a valuable
tool to study anisotropic fields, exchange couplings, magnetization damping and
spin pumping mechanism. A particularly well established technique is the
ferromagnetic resonance (FMR) generated by the coupling of microwave photons
and magnetization eigenmodes in the GHz range. Here we review the basic
concepts of the so-called acoustic ferromagnetic resonance technique (a-FMR)
induced by the coupling of surface acoustic waves (SAW) and magnetization of
thin films. Interestingly, additional to the benefits of the microwave excited
FMR technique, the coupling between SAW and magnetization also offers fertile
ground to study magnon-phonon and spin rotation couplings. We describe the
in-plane magnetic field angle dependence of the a-FMR by measuring the
absorption / transmission of SAW and the attenuation of SAW in the presence of
rotational motion of the lattice, and show the consequent generation of spin
current by acoustic spin pumping.",2001.09581v1
2019-02-07,Unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling,"We report strong unidirectional anisotropy in bulk polycrystalline B20 FeGe
measured by ferromagnetic resonance spectroscopy. Bulk and micron-sized samples
were produced and analytically characterized. FeGe is a B20 compound with
inherent Dzyaloshinskii-Moriya interaction. Lorenz microscopy confirms a
skyrmion lattice at $190 \; \text{K}$ in a magnetic field of 150 mT.
Ferromagnetic resonance was measured at $276 \; \text{K} \pm 1 \; \text{K}$,
near the Curie temperature. Two resonance modes were observed, both exhibit a
unidirectional anisotropy of $K=1153 \; \text{J/m}^3 \pm 10 \; \text{J/m}^3$ in
the primary, and $K=28 \; \text{J/m}^3 \pm 2 \; \text{J/m}^3$ in the secondary
mode, previously unknown in bulk ferromagnets. Additionally, about 25 standing
spin wave modes are observed inside a micron-sized FeGe wedge, measured at room
temperature ($\sim \; 293$ K). These modes also exhibit unidirectional
anisotropy.",1902.02665v2
2020-11-03,Symmetry breaking induced magnon-magnon coupling in synthetic antiferromagnets,"We propose a general theory of microwave absorption spectroscopy for
symmetry-breaking synthetic antiferromagnets (SAFs). Generally, inhomogeneity
or different thickness of the two ferromagnetic sublayers of a SAF results in
the intrinsic symmetry breaking, while out-of-plane components of dc magnetic
fields lead to the extrinsic one. The broken symmetry of SAFs excludes the
original symmetry-protected crossing between pure in-phase and out-of-phase
resonance modes with opposite parity. Alternatively, new frequency branches
become hybridization of original bare modes in terms of
symmetry-breaking-induced magnon-magnon coupling, which results in an indirect
gap in ferromagnetic resonance frequencies. Also, the dependence of gap width
on the degree of symmetry breaking for several typical cases are presented and
compared with existing experiments. Our theory provides a simple but physical
understanding on the rich structure of ferromagnetic resonance spectra for
asymmetric SAFs.",2011.01583v1
2021-05-23,Multifunctional operation of the double-layer ferromagnetic structure coupled by a rectangular nanoresonator,"The use of spin waves as a signal carrier requires developing the functional
elements allowing for multiplexing and demultiplexing information coded at
different wavelengths. For this purpose, we propose a system of thin
ferromagnetic layers dynamically coupled by a rectangular ferromagnetic
resonator. We show that a single and double, clockwise and counter-clockwise,
circulating modes of the resonator offer a wide possibility of control of
propagating waves. Particularly, at frequency related to the double-clockwise
circulating spin-wave mode of the resonator, the spin wave excited in one layer
is transferred to the second one where it propagates in the backward direction.
Interestingly, the wave excited in the second layer propagates in the forward
direction only in that layer. This demonstrates add-drop filtering, as well as
circulator functionality. Thus, the proposed system can become an important
part of future magnonic technology for signal routing.",2105.10875v1
2021-06-21,Resonant Measurement of Non-Reorientable Spin-Orbit Torque from a Ferromagnetic Source Layer Accounting for Dynamic Spin Pumping,"Using a multilayer structure containing (cobalt detector layer)/(copper
spacer)/(Permalloy source layer), we show experimentally how the
non-reorientable spin-orbit torque generated by the Permalloy source layer (the
component of spin-orbit torque that does not change when the Permalloy
magnetization is rotated) can be measured using spin-torque ferromagnetic
resonance (ST-FMR) with lineshape analysis. We find that dynamic spin pumping
between the magnetic layers exerts torques on the magnetic layers as large or
larger than the spin-orbit torques, so that if dynamic spin pumping is
neglected the result would be a large overestimate of the spin-orbit torque.
Nevertheless, the two effects can be separated by performing ST-FMR as a
function of frequency. We measure a non-reorientable spin torque ratio
$\xi_{\text{Py}} = 0.04 \pm 0.01$ for spin current flow from Permalloy through
an 8 nm Cu spacer to the Co, and a strength of dynamic spin pumping that is
consistent with previous measurements by conventional ferromagnetic resonance.",2106.11127v1
2021-08-20,Probing anisotropy in epitaxial Fe/Pt bilayers by spin-orbit torque ferromagnetic resonance,"We report the generation and detection of spin-orbit torque ferromagnetic
resonance (STFMR) in micropatterned epitaxial Fe/Pt bilayers grown by molecular
beam epitaxy. The magnetic field dependent measurements at an in-plane magnetic
field angle of 45 degrees with respect to the microwave-current direction
reveal the presence of two distinct voltage peaks indicative of a strong
magnetic anisotropy. We show that STFMR can be employed to probe the underlying
magnetic properties including the anisotropies in the Fe layer. We compare our
STFMR results with broadband ferromagnetic resonance spectroscopy of the
unpatterned bilayer thin films. The experimental STFMR measurements are
interpreted using an analytical formalism and further confirmed using
micromagnetic modeling, which shed light on the field-dependent magnetization
alignment in the microstructures responsible for the STFMR rectification. Our
results demonstrate a simple and efficient method for determining magnetic
anisotropies in microstructures by means of rf spectroscopy.",2108.09132v1
2022-04-23,Theory of inertial spin dynamics in anisotropic ferromagnets,"Recent experimental observation of inertial spin dynamics calls upon holistic
reevaluation of the theoretical framework of magnetic resonance in
ferromagnets. Here, we derive the secular equation of an inertial spin system
in analogy to the ubiquitous Smit-Beljers formalism. We find that the frequency
of precessional ferromagnetic resonances is decreased as compared to
non-inertial case. We also find that the frequency of nutational resonances is
generally increased due to the presence of magnetic anisotropy and applied
magnetic field. We obtain exact solutions of the secular equation and
approximations that employ the terminology of non-inertial theory and thus
allow for convenient estimates of the inertial effects.",2204.11057v2
2013-02-24,Electron spin resonance in a dilute magnon gas as a probe of magnon scattering resonances,"We study the electron spin resonance in a dilute magnon gas that is realized
in a ferromagnetic spin system at low temperature. A quantum cluster expansion
is developed to show that the frequency shift of the single-magnon peak changes
its sign and the linewidth reaches its maximum across a scattering resonance
between magnons. Such characteristic behaviors are universal and can be used to
experimentally locate the two-magnon resonance when an external parameter such
as pressure is varied. Future achievement of the two-magnon resonance may have
an impact comparable to the Feshbach resonance in ultracold atoms and will open
up a rich variety of strongly correlated physics such as the recently proposed
Efimov effect in quantum magnets. We also suggest how the emergence of an
Efimov state of three magnons and its binding energy may be observed with the
electron spin resonance.",1302.5908v2
2020-07-06,Transverse and Longitudinal Spin-Torque Ferromagnetic Resonance for Improved Measurements of Spin-Orbit Torques,"Spin-torque ferromagnetic resonance (ST-FMR) is a common method used to
measure spin-orbit torques (SOTs) in heavy metal/ferromagnet bilayer
structures. In the course of a measurement, other resonant processes such as
spin pumping (SP) and heating can cause spin current or heat flows between the
layers, inducing additional resonant voltage signals via the inverse spin Hall
effect (ISHE) and Nernst effects (NE). In the standard ST-FMR geometry, these
extra artifacts exhibit a dependence on the angle of an in-plane magnetic field
that is identical to the rectification signal from the SOTs. We show
experimentally that the rectification and artifact voltages can be quantified
separately by measuring the ST-FMR signal transverse to the applied current
(i.e., in a Hall geometry) in addition to the usual longitudinal geometry. We
find that in Pt (6 nm)/CoFeB samples the contribution from the artifacts is
small compared to the SOT rectification signal for CoFeB layers thinner than 6
nm, but can be significant for thicker magnetic layers. We observe a sign
change in the artifact voltage as a function of CoFeB thickness that we suggest
may be due to a competition between a resonant heating effect and the SP/ISHE
contribution.",2007.02850v1
2008-10-02,Voltage controlled inversion of magnetic anisotropy in a ferromagnetic thin film at room temperature,"The control of magnetic properties by means of an electric field is an
important aspect in magnetism and magnetoelectronics. We here utilize
magnetoelastic coupling in ferromagnetic/piezoelectric hybrids to realize a
voltage control of magnetization orientation at room temperature. The samples
consist of polycrystalline nickel thin films evaporated onto piezoelectric
actuators. The magnetic properties of these multifunctional hybrids are
investigated at room temperature as a function of the voltage controlled stress
exerted by the actuator on the Ni film. Ferromagnetic resonance spectroscopy
shows that the magnetic easy axis in the Ni film plane is rotated by 90 degree
upon changing the polarity of the voltage Vp applied to the actuator. In other
words, the in-plane uniaxial magnetic anisotropy of the Ni film can be inverted
via the application of an appropriate voltage Vp. Using SQUID magnetometry, the
evolution of the magnetization vector is recorded as a function of Vp and of
the external magnetic field. Changing Vp allows to reversibly adjust the
magnetization orientation in the Ni film plane within a range of approximately
70 degree. All magnetometry data can be quantitatively understood in terms of
the magnetic free energy determined from the ferromagnetic resonance
experiments. These results demonstrate that magnetoelastic coupling in hybrid
structures indeed is a viable option to control magnetization orientation in
technologically relevant ferromagnetic thin films at room temperature.",0810.0389v1
2014-10-14,Coherent coupling between ferromagnetic magnon and superconducting qubit,"Rigidity of an ordered phase in condensed matter results in collective
excitation modes spatially extending in macroscopic dimensions. Magnon is a
quantum of an elementary excitation in the ordered spin system, such as
ferromagnet. Being low dissipative, dynamics of magnons in ferromagnetic
insulators has been extensively studied and widely applied for decades in the
contexts of ferromagnetic resonance, and more recently of Bose-Einstein
condensation as well as spintronics. Moreover, towards hybrid systems for
quantum memories and transducers, coupling of magnons and microwave photons in
a resonator have been investigated. However, quantum-state manipulation at the
single-magnon level has remained elusive because of the lack of anharmonic
element in the system. Here we demonstrate coherent coupling between a magnon
excitation in a millimetre-sized ferromagnetic sphere and a superconducting
qubit, where the interaction is mediated by the virtual photon excitation in a
microwave cavity. We obtain the coupling strength far exceeding the damping
rates, thus bringing the hybrid system into the strong coupling regime.
Furthermore, we find a tunable magnon-qubit coupling scheme utilising a
parametric drive with a microwave. Our approach provides a versatile tool for
quantum control and measurement of the magnon excitations and thus opens a new
discipline of quantum magnonics.",1410.3781v1
2020-02-02,Broadband Magnetoresistance in Ferromagnetic and Paramagnetic Samples of La0.7Ca0.3-xSrxMnO3,"We have studied the room-temperature magnetoimpedance of paramagnetic (x =
0.06) and ferromagnetic (x = 0.1) samples in La0.7Ca0.3-xSrxMnO3 series using a
radio-frequency impedance analyzer and also microwave power absorption using a
network analyzer. In both measurements, samples were enclosed tightly inside a
copper stripcoil and impedance or reflection coefficient of this copper
stripcoil was measured as a function of the applied magnetic field for
different frequencies of current (f = 0.1 to 2.5 GHz). The direction of the
applied magnetic field was perpendicular to the alternating magnetic field
produced by the coil. In the ferromagnetic sample (x = 0.1), magnetoresistance
shows a peak around zero field for lower frequencies but a peak appears at H
away from the origin at higher frequencies. The position of the peak shifts
towards higher fields with increasing frequency. A similar trend is also found
for the paramagnetic sample (x = 0.06) but the peak occurs at a higher field
compared to the ferromagnetic sample for the same frequency. Microwave power
absorption also shows features similar to magnetoresistance. Line shape
analysis of the data was performed by fitting the data to a Lorentzian
function. It is concluded that the observed features are imprints of
ferromagnetic resonance in x = 0.1 and paramagnetic resonance in x = 0.06
samples.",2002.00356v1
2022-01-26,Coexisting Kondo hybridization and itinerant f-electron ferromagnetism in UGe2,"Kondo hybridization in partially filled f-electron systems conveys
significant amount of electronic states sharply near the Fermi energy leading
to various instabilities from superconductivity to exotic electronic orders.
UGe2 is a 5f heavy fermion system, where the Kondo hybridization is interrupted
by the formation of two ferromagnetic phases below a 2nd order transition Tc ~
52 K and a crossover transition Tx ~ 32 K. These two ferromagnetic phases are
concomitantly related to a spin-triplet superconductivity that only emerges and
persists inside the magnetically ordered phase at high pressure. The origin of
the two ferromagnetic phases and how they form within a Kondo-lattice remain
ambiguous. Using scanning tunneling microscopy and spectroscopy, we probe the
spatial electronic states in the UGe2 as a function of temperature. We find a
Kondo resonance and sharp 5f-electron states near the chemical potential that
form at high temperatures above Tc in accordance with our density functional
theory (DFT) + Gutzwiller calculations. As temperature is lowered below Tc, the
resonance narrows and eventually splits below Tx dumping itinerant f-electron
spectral weight right at the Fermi energy. Our findings suggest a Stoner
mechanism forming the highly polarized ferromagnetic phase below Tx that itself
sets the stage for the emergence of unconventional superconductivity at high
pressure.",2201.11189v2
2020-07-03,Light-controlled room temperature ferromagnetism in vanadium-doped tungsten diselenide semiconducting monolayers,"Atomically thin transition metal dichalcogenide (TMD) semiconductors hold
enormous potential for modern optoelectronic devices and quantum computing
applications. By inducing long-range ferromagnetism (FM) in these
semiconductors through the introduction of small amounts of a magnetic dopant,
it is possible to extend their potential in emerging spintronic applications.
Here, we demonstrate light-mediated, room temperature (RT) FM, in V-doped WS2
(V-WS2) monolayers. We probe this effect using the principle of magnetic LC
resonance, which employs a soft ferromagnetic Co-based microwire coil driven
near its resonance in the radio frequency (RF) regime. The combination of LC
resonance with an extraordinary giant magneto-impedance effect, renders the
coil highly sensitive to changes in the magnetic flux through its core. We then
place the V-WS2 monolayer at the core of the coil where it is excited with a
laser while its change in magnetic permeability is measured. Notably, the
magnetic permeability of the monolayer is found to depend on the laser
intensity, thus confirming light control of RT magnetism in this
two-dimensional (2D) material. Guided by density functional calculations, we
attribute this phenomenon to the presence of excess holes in the conduction and
valence bands, as well as carriers trapped in the magnetic doping states, which
in turn mediates the magnetization of the V-WS2 monolayer. These findings
provide a unique route to exploit light-controlled ferromagnetism in low
powered 2D spintronic devices capable of operating at RT.",2007.01505v1
2012-04-19,Ferromagnetism in graphene nanoribbons: split versus oxidative unzipped ribbons,"Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons
(GNRs), and (b) oxidative unzipped and chemically converted graphene
nanoribbons (CCGNRs) were investigated for their magnetic properties using the
combination of static magnetization and electron spin resonance measurements.
The two types of ribbons possess remarkably different magnetic properties.
While the low temperature ferromagnet-like feature is observed in both types of
ribbons, such room temperature feature persists only in potassium-split
ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a
'positive exchange bias'. Electron spin resonance measurements infer that the
carbon related defects may responsible for the observed magnetic behaviour in
both types of ribbons. Furthermore, proton hyperfine coupling strength has been
obtained from hyperfine sublevel correlation experiments performed on the GNRs.
Electron spin resonance provides no indications for the presence of potassium
(cluster) related signals, emphasizing the intrinsic magnetic nature of the
ribbons. Our combined experimental results may infer the coexistence of
ferromagnetic clusters with anti-ferromagnetic regions leading to disordered
magnetic phase. We discuss the origin of the observed contrast in the magnetic
behaviours of these two types of ribbons.",1204.4401v1
2021-02-28,Spin and charge interconversion in Dirac semimetal thin films,"We report spin-to-charge and charge-to-spin conversion at room temperature in
heterostructure devices that interface an archetypal Dirac semimetal, Cd3As2,
with a metallic ferromagnet, Ni0.80Fe0.20 (permalloy). The spin-charge
interconversion is detected by both spin torque ferromagnetic resonance and
ferromagnetic resonance driven spin pumping. Analysis of the symmetric and
anti-symmetric components of the mixing voltage in spin torque ferromagnetic
resonance and the frequency and power dependence of the spin pumping signal
show that the behavior of these processes is consistent with previously
reported spin-charge interconversion mechanisms in heavy metals, topological
insulators, and Weyl semimetals. We find that the efficiency of spin-charge
interconversion in Cd3As2/permalloy bilayers can be comparable to that in heavy
metals. We discuss the underlying mechanisms by comparing our results with
first principles calculations.",2103.00653v1
2022-01-11,Resonant Precession of Magnetization and Precession -- Induced DC voltages in FeGaB Thin Films,"Measurements of frequency dependent ferromagnetic resonance (FMR) and spin
pumping driven dc voltage (V_{dc}) are reported for amorphous films of
Fe_{78}Ga_{13}B_{9} (FeGaB) alloy to address the phenomenon of self-induced
inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets. The
V_{dc} signal, which is antisymmetric on field reversal, comprises of symmetric
and asymmetric Lorentzians centered around the resonance field. Dominant role
of thin film size effects is seen in setting the magnitude of static
magnetization, V_{dc} and dynamics of magnetization precession in thinner films
(\leq 8 nm). The film thickness dependence of magnetization parameters
indicates the presence of a magnetically disordered region at the
film-substrate interface, which may promote preferential flow of spins
generated by the precessing magnetization towards the substrate. However, the
V_{dc} signal also draws contributions from rectification effects of a \approx
0.4 \% anisotropic magnetoresistance and a large (\approx 54 n\Omega.m)
anomalous Hall resistivity (AHR) of these films which ride over the effect of
spin-orbit coupling driven spin-to-charge conversion near the film-substrate
interface. We have addressed these data in the framework of the existing
theories of electrodynamics of a ferromagnetic film subjected to
radio-frequency field in a coplanar waveguide geometry. Our estimation of the
self-induced ISHE for the sample with 54 n\Omega.m AHR shows that it may
contribute significantly (\approx 90\%) to the measured symmetric voltage. This
study is expected to be very useful for fully understanding the spin pumping
induced dc voltages in metallic ferromagnets with disordered interfaces and
large anomalous Hall effect.",2201.03739v1
2023-08-07,"Buzdin, Shapiro and Chimera Steps in $\varphi_0$ Josephson Junctions","The unique resonance and locking phenomena in the
superconductor-ferromagnet-superconductor $\varphi_0$ Josephson junction under
external electromagnetic radiation are demonstrated when not just the electric
but also the magnetic component of external radiation is taken into account.
Due to the coupling of superconductivity and magnetism in this system, the
magnetic moment precession of the ferromagnetic layer caused by the magnetic
component of external radiation can lock the Josephson oscillations, which
results in the appearance of a particular type of steps in the current-voltage
characteristics, completely different from the well-known Shapiro steps. We
call these steps the Buzdin steps in the case when the system is driven only by
the magnetic component and the Chimera steps in the case when both magnetic and
electric components are present. Unlike the Shapiro steps where the
magnetization remains constant along the step, here it changes though the
system is locked. The spin-orbit coupling substantially contributes to the
amplitude, i.e., the size of these steps. Dramatic changes in their amplitudes
are also observed at frequencies near the ferromagnetic resonance. Combinations
of the Josephson and Kittel ferromagnetic resonances together with different
types of locking pronounced in dynamics and current-voltage characteristics
make the physics of this system very interesting and open up a series of new
applications.",2308.03701v2
2005-03-27,Magnetic Vortex Resonance in Patterned Ferromagnetic Dots,"We report a high-resolution experimental detection of the resonant behavior
of magnetic vortices confined in small disk-shaped ferromagnetic dots. The
samples are magnetically soft Fe-Ni disks of diameter 1.1 and 2.2 um, and
thickness 20 and 40 nm patterned via electron beam lithography onto microwave
co-planar waveguides. The vortex excitation spectra were probed by a vector
network analyzer operating in reflection mode, which records the derivative of
the real and the imaginary impedance as a function of frequency. The spectra
show well-defined resonance peaks in magnetic fields smaller than the
characteristic vortex annihilation field. Resonances at 162 and 272 MHz were
detected for 2.2 and 1.1 um disks with thickness 40 nm, respectively. A
resonance peak at 83 MHz was detected for 20-nm thick, 2-um diameter disks. The
resonance frequencies exhibit weak field dependence, and scale as a function of
the dot geometrical aspect ratio. The measured frequencies are well described
by micromagnetic and analytical calculations that rely only on known properties
of the dots (such as the dot diameter, thickness, saturation magnetization, and
exchange stiffness constant) without any adjustable parameters. We find that
the observed resonance originates from the translational motion of the magnetic
vortex core.",0503632v1
2014-09-16,Contact potential instability in the path-integral description of itinerant ferromagnetism,"It has long been predicted that a two-component non-localized Fermi gas will
exhibit spontaneous polarization for sufficiently strong repulsive
interactions, a phenomenon which is called itinerant ferromagnetism. Recent
experiments with ultracold atomic gases have reached the interaction strength
for which theoretical models have predicted the occurrence of the
normal-to-itinerant-ferromagnetic phase transition, but so far this transition
has not been observed. The instability of the repulsive branch of the Feshbach
resonance prevents the formation of the itinerant ferromagnetic state, but it
is not clear whether this is the only instability impeding its experimental
realization. In this article, we use the path-integral formalism with density
fields in the Hubbard-Stratonovich transformation to study the stability of a
homogeneous two-component Fermi gas with contact interactions. Within the
saddle-point approximation we show that none of the extrema of the action are
minima, meaning all extrema are unstable to small density fluctuations. This
implies a more general mechanical instability of the polarized (itinerant
ferromagnetic) and normal states of the system in the path-integral formalism.
We find that it is important to consider the stability of the system when
studying itinerant ferromagnetism. Since (mechanical) stability may be
influenced by the details of the interaction potential, we suggest the use of a
more realistic potential than the contact potential in future theoretical
descriptions.",1409.4630v2
2014-05-20,Interaction energy and itinerant ferromagnetism in a strongly interacting Fermi gas in the absence of molecule formation,"We investigate the interaction energy and the possibility of itinerant
ferromagnetism in a strongly interacting Fermi gas at zero temperature in the
absence of molecule formation. The interaction energy is obtained by summing
the perturbative contributions of Galitskii-Feynman type to all orders in the
gas parameter. It can be expressed by a simple phase space integral of an
in-medium scattering phase shift. In both three and two dimensions (3D and 2D),
the interaction energy shows a maximum before reaching the resonance from the
Bose-Einstein condensate side, which provides a possible explanation of the
experimental measurements of the interaction energy. This phenomenon can be
theoretically explained by the qualitative change of the nature of the binary
interaction in the medium. The appearance of an energy maximum has significant
effects on the itinerant ferromagnetism. In 3D, the ferromagnetic transition is
reentrant and itinerant ferromagnetism exists in a narrow window around the
energy maximum. In 2D, the present theoretical approach suggests that itinerant
ferromagnetism does not exist, which reflects the fact that the energy maximum
becomes much lower than the energy of the fully polarized state.",1405.5242v6
2023-05-08,Large magnetocaloric effect in the kagome ferromagnet Li$_9$Cr$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$,"Single-crystal growth, magnetic properties, and magnetocaloric effect of the
$S = 3/2$ kagome ferromagnet Li$_9$Cr$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$
(trigonal, space group: $P\bar{3}c1$) are reported. Magnetization data suggest
dominant ferromagnetic intra-plane coupling with a weak anisotropy and the
onset of ferromagnetic ordering at $T_{\rm C} \simeq 2.6$ K. Microscopic
analysis reveals a very small ratio of interlayer to intralayer ferromagnetic
couplings ($J_{\perp}/J \simeq 0.02$). Electron spin resonance data suggest the
presence of short-range correlations above $T_{\rm C}$ and confirms
quasi-two-dimensional character of the spin system. A large magnetocaloric
effect characterized by isothermal entropy change of $-\Delta S_{\rm m}\simeq
31$ J kg$^{-1}$ K$^{-1}$ and adiabatic temperature change of $-\Delta T_{\rm
ad}\simeq 9$ K upon a field sweep of 7 T is observed around $T_{\rm C}$. This
leads to a large relative cooling power of $RCP \simeq 284$ J kg$^{-1}$. The
large magnetocaloric effect, together with negligible hysteresis render
Li$_9$Cr$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$ a promising material for magnetic
refrigeration at low temperatures. The magnetocrystalline anisotropy constant
$K \simeq -7.42 \times 10^4$ erg cm$^{-3}$ implies that the compound is an
easy-plane type ferromagnet with the hard axis normal to the $ab$-plane,
consistent with the magnetization data.",2305.04744v1
2005-01-09,Nonequilibrium Kondo Effect in a Quantum Dot Coupled to Ferromagnetic Leads,"We study the Kondo effect in the electron transport through a quantum dot
coupled to ferromagnetic leads, using a real-time diagrammatic technique which
provides a systematic description of the nonequilibrium dynamics of a system
with strong local electron correlations. We evaluate the theory in an extension
of the `resonant tunneling approximation', introduced earlier, by introducing
the self-energy of the off-diagonal component of the reduced propagator in spin
space. In this way we develop a charge and spin conserving approximation that
accounts not only for Kondo correlations but also for the spin splitting and
spin accumulation out of equilibrium. We show that the Kondo resonances, split
by the applied bias voltage, may be spin polarized. A left-right asymmetry in
the coupling strength and/or spin polarization of the electrodes significantly
affects both the spin accumulation and the weight of the split Kondo resonances
out of equilibrium. The effects are observable in the nonlinear differential
conductance. We also discuss the influence of decoherence on the Kondo
resonance in the frame of the real-time formulation.",0501172v1
2007-07-11,Soft X-ray Circular Reflectivity from Ferromagnetic Transition-Metal Films Near the Brewster's Angle: Theoretical and Numerical X-ray Resonant Magnetic Scattering Study,"We first report a novel phenomenon that manifests itself in a colossal
difference in soft x-ray reflectivity from ferromagnetic transition-metal films
between the left- and right-handed circular polarization (LCP and RCP) modes at
a resonance near normal Brewster's angle. Theoretical and numerical studies of
sft x-ray resonant magnetic scattering using the circular-polarization-mode
basis reveal that this effect arises from a totally destructive interference of
photons scattered individually from chargem orbital, and spin degrees of
freedom in magnetized thin films that selectively occurs only for one helicity
of the opposite circular modes when the required criteria are fulfilled. Across
the normal Brewster's angle. the polarization state of scattered soft x-ray is
continuously variable from the RCP to the LCP mode (or vice versa) through the
linear s polarization mode by changing the incidence angle of linear
p-polarized x rays at the resonance.",0707.1627v1
2009-05-28,Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires,"We use spin torque ferromagnetic resonance to measure the spectral properties
of dipole-exchange spin waves in permalloy nanowires. Our measurements reveal
that geometric confinement has a profound effect on the damping of spin waves
in the nanowire geometry. The damping parameter of the lowest-energy quantized
spin wave mode depends on applied magnetic field in a resonant way and exhibits
a maximum at a field that increases with decreasing nanowire width. This
enhancement of damping originates from a nonlinear resonant three-magnon
confluence process allowed at a particular bias field value determined by
quantization of the spin wave spectrum in the nanowire geometry.",0905.4699v2
2009-10-24,Spin-torque driven ferromagnetic resonance in a nonlinear regime,"Spin-valve based nanojunctions incorporating Co|Ni multilayers with
perpendicular anisotropy were used to study spin-torque driven ferromagnetic
resonance (ST-FMR) in a nonlinear regime. Perpendicular field swept resonance
lines were measured under a large amplitude microwave current excitation, which
produces a large angle precession of the Co|Ni layer magnetization. With
increasing rf power the resonance lines broaden and become asymmetric, with
their peak shifting to lower applied field. A nonhysteretic step jump in ST-FMR
voltage signal was also observed at high powers. The results are analyzed in in
terms of the foldover effect of a forced nonlinear oscillator and compared to
macrospin simulations. The ST-FMR nonhysteretic step response may have
applications in frequency and amplitude tunable nanoscale field sensors.",0910.4678v1
2011-04-21,^{59}Co-Nuclear Quadrupole Resonance and Nuclear Magnetic Resonance studies on YCoGe --- Comparison between YCoGe and UCoGe ---,"We have performed ^{59}Co-nuclear quadrupole resonance (NQR) and nuclear
magnetic resonance (NMR) studies on YCoGe, which is a reference compound of
ferromagnetic superconductor UCoGe, in order to investigate the magnetic
properties at the Co site. Magnetic and superconducting transitions were not
observed down to 0.3 K, but a conventional metallic behavior was found in
YCoGe, although its crystal structure is similar to that of UCoGe. From the
comparison between experimental results of two compounds, the ferromagnetism
and superconductivity observed in UCoGe originate from the U-5f electrons.",1104.4246v1
2012-10-09,Micromagnetic theory of spin relaxation and ferromagnetic resonance in multilayered metallic films,"Spin relaxation in the ultrathin metallic films of stacked microelectronic
devices is investigated on the basis of a modified Landau-Lifshitz equation of
micromagnetic dynamics in which the damping torque is treated as originating
from the coupling between precessing magnetization-vector and the introduced
stress-tensors of intrinsic and extrinsic magnetic anisotropy. Particular
attention is given to the time of exponential relaxation and ferromagnetic
resonance linewidth which are derived in analytic form from the equation of
magnetization energy loss and Gabor uncertainty relation between the
full-width-at-half-maximum in resonance-shaped line and lifetime of resonance
excitation. The potential of developed theory is briefly discussed in the
context of recent measurements.",1210.2609v3
2014-07-02,Element-Specific Depth Profile of Magnetism and Stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 Interface,"Depth-sensitive magnetic, structural and chemical characterization is
important in the understanding and optimization of novel physical phenomena
emerging at interfaces of transition metal oxide heterostructures. In a
simultaneous approach we have used polarized neutron and resonant X-ray
reflectometry to determine the magnetic profile across atomically sharp
interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers
with sub-nanometer resolution. In particular, the X-ray resonant magnetic
reflectivity measurements at the Fe and Mn resonance edges allowed us to
determine the element specific depth profile of the ferromagnetic moments in
both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a
magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in
contrast to previous observations on inversely deposited layers. Additional
resonant X-ray reflection measurements indicate a region of an altered Mn- and
O-content at the interface, with a thickness matching that of the magnetic
diluted layer, as origin of the reduction of the magnetic moment.",1407.0737v1
2015-02-06,Resonant indirect exchange via remote 2D channel,"We apply the previously developed theory of the resonant indirect exchange
interaction to explain the ferromagnetic properties of the hybrid
heterostructure consisting of a InGaAs-based quantum well (QW) sandwiched
between GaAs barriers with a remote Mn delta-layer. The experimentally obtained
dependence of the Curie temperature on the QW depth exhibits a maximum related
to the region of resonant indirect exchange. We suggest the theoretical
explanantion and a fit to this dependence as a result of the two contributions
to ferromagnetism - the intralayer contribution and the resonant exchange
contribution provided by the QW.",1502.01816v1
2015-05-07,Resonant driving of magnetization precession in a ferromagnetic layer by coherent monochromatic phonons,"We realize resonant driving of the magnetization precession by monochromatic
phonons in a thin ferromagnetic layer embedded into a phononic Fabry-Perot
resonator. A femtosecond laser pulse excites resonant phonon modes of the
structure in the 10-40 GHz frequency range. By applying an external magnetic
field, we tune the precession frequency relative to the frequency of the
phonons localized in the cavity and observe the enormous increase in the
amplitude of the magnetization precession when the frequencies of free
magnetization precession and phonons localized in the cavity are equal.",1505.01729v1
2015-05-11,An electromechanical Ising machine,"Solving intractable mathematical problems in simulators composed of atoms,
ions, photons or electrons has recently emerged as a subject of intense
interest. Here we extend this concept to phonons that are localised in
spectrally pure resonances in an electromechanical system which enables their
interactions to be exquisitely fashioned via electrical means. We harness this
platform to emulate the Ising Hamiltonian whose spin 1/2 particles are
replicated by the phase bistable vibrations from a parametric resonance where
multiple resonances play the role of a spin bath. The coupling between the
mechanical pseudo spins is created by generating thermomechanical two-mode
squeezed states which impart correlations between resonances that can imitate a
ferromagnetic, random or an anti-ferromagnetic state on demand. These results
suggest an electromechanical simulator for the Ising Hamiltonian could be built
with a large number of spins with multiple degrees of coupling, a task that
would overwhelm a conventional computer.",1505.02467v1
2018-09-19,Occurrence of Mixed Phase in Bi0.5Sr0.5Mn0.9Cr0.1O3 bulk sample: Electron Paramagnetic Resonance and Magnetization Studies,"We study the effects of 10% Cr substitution in Mn sites of Bi0.5Sr0.5MnO3 on
the antiferromagnetic (AFM) (TN ~ 110 K) transition using structural, magnetic
and electron paramagnetic resonance (EPR) techniques. Field cooled (FC) and
zero field cooled (ZFC) magnetization measurements done from 400 K down to 4 K
show that the compound is in the paramagnetic (PM) phase till 50 K where it
undergoes a transition to a short range ferromagnetic phase (FM). Electron
paramagnetic resonance measurements performed in the temperature range 300 K
till 80 K conform with the magnetization measurements as symmetric signals are
observed owing to the paramagnetic phase. Below 80 K, signals become
asymmetric. Electron paramagnetic resonance intensity peaks at ~ 110 K, the
decreasing intensity below this temperature confirming the presence of
antiferromagnetism. We conclude that below 50 K the magnetization and EPR
results are consistent with a cluster glass phase of BSMCO, where ferromagnetic
clusters coexist with an antiferromagnetic background.",1809.07302v2
2019-09-18,Ferromagnetic resonance with magnetic phase selectivity by means of resonant elastic x-ray scattering on a chiral magnet,"Cubic chiral magnets, such as Cu$_{2}$OSeO$_{3}$, exhibit a variety of
non-collinear spin textures, including a trigonal lattice of spin whirls,
so-called skyrmions. Using magnetic resonant elastic x-ray scattering (REXS) on
a crystalline Bragg peak and its magnetic satellites while exciting the sample
with magnetic fields at GHz frequencies, we probe the ferromagnetic resonance
modes of these spin textures by means of the scattered intensity. Most notably,
the three eigenmodes of the skyrmion lattice are detected with large
sensitivity. As this novel technique, which we label REXS-FMR, is carried out
at distinct positions in reciprocal space, it allows to distinguish
contributions originating from different magnetic states, providing information
on the precise character, weight and mode mixing as a prerequisite of tailored
excitations for applications.",1909.08293v2
2019-10-17,Phonon Transport Controlled by Ferromagnetic Resonance,"The resonant coupling of phonons and magnons is important for the
interconversion of phononic and spin degrees of freedom. We studied the phonon
transmission in LiNbO3 manipulated by the dynamic magnetization in a Ni thin
film. It was observed that the phonons could be absorbed strongly through
resonant magnon-phonon coupling, which was realized by optimizing the
interfacial coupling between Ni and LiNbO3. The line shapes of phonon
transmission were further investigated considering the magnon-phonon
interconversion in the elastically driven ferromagnetic resonance process. The
results promote unique routes for phonon manipulation and detection in the
presence of magnetization dynamics.",1910.08148v1
2020-12-04,Nutation in antiferromagnetic resonance,"The effect of inertial spin dynamics is compared between ferromagnetic,
antiferromagnetic and ferrimagnetic systems. The linear response to an
oscillating external magnetic field is calculated within the framework of the
inertial Landau--Lifshitz--Gilbert equation using analytical theory and
computer simulations. Precession and nutation resonance peaks are identified,
and it is demonstrated that the precession frequencies are reduced by the spin
inertia, while the lifetime of the excitations is enhanced. The interplay
between precession and nutation is found to be the most prominent in
antiferromagnets, where the timescale of the exchange-driven sublattice
dynamics is comparable to inertial relaxation times. Consequently,
antiferromagnetic resonance techniques should be better suited for the search
for intrinsical inertial spin dynamics on ultrafast timescales than
ferromagnetic resonance.",2012.02790v3
2018-06-25,Wideband and on-chip excitation for dynamical spin injection into graphene,"Graphene is an ideal material for spin transport as very long spin relaxation
times and lengths can be achieved even at room temperature. However, electrical
spin injection is challenging due to the conductivity mismatch problem. Spin
pumping driven by ferromagnetic resonance is a neat way to circumvent this
problem as it produces a pure spin current in the absence of a charge current.
Here, we show spin pumping into single layer graphene in micron scale devices.
A broadband on-chip RF current line is used to bring micron scale permalloy
(Ni$_{80}$Fe$_{20}$) pads to ferromagnetic resonance with a magnetic field
tunable resonance condition. At resonance, a spin current is emitted into
graphene, which is detected by the inverse spin hall voltage in a close-by
platinum electrode. Clear spin current signals are detected down to a power of
a few milliwatts over a frequency range of 2 GHz to 8 GHz. This compact device
scheme paves the way for more complex device structures and allows the
investigation of novel materials.",1806.09356v1
2020-09-09,Superconductivity-enhanced spin pumping: Role of Andreev resonances,"We describe a simple hybrid superconductor$|$ferromagnetic-insulator
structure manifesting spin-resolved Andreev bound states in which dynamic
magnetization is employed to probe spin related physics. We show that, at low
bias and below $T_c$, the transfer of spin angular momentum pumped by an
externally driven ferromagnetic insulator is greatly affected by the formation
of spin-resolved Andreev bound states. Our results indicate that these bound
states capture the essential physics of condensate-facilitated spin flow. For
finite thicknesses of the superconducting layer, comparable to the coherence
length, resonant Andreev bound states render highly transmitting subgap spin
transport channels. We point out that the resonant enhancement of the subgap
transport channels establishes a prototype Fabry-P\'erot resonator for spin
pumping.",2009.04423v4
2021-08-09,Antiferromagnetic resonances in twinned EuFe2As2 single crystal,"In this work, we report ferromagnetic resonance spectroscopy of EuFe2As2
single crystals. We observe ferromagnetic resonance responses, which are
attributed to antiferromagnetic resonances of Eu sub-lattice with orthorhombic
crystal structure and with different orientations of twin domains relative to
the external field. We confirm validity of the recently-proposed spin
Hamiltonian with anisotropic Eu-Eu exchange interaction and biquadratic Eu-Fe
exchange interaction.",2108.03847v3
2023-03-30,Angular dependence of the electrically driven and detected ferromagnetic resonance in Ni$_{36}$Fe$_{64}$ wires,"We study the angular dependence of ferromagnetic resonance (FMR) in
Ni$_{36}$Fe$_{64}$ wires using both traditional microwave-absorption and
electrical-detection techniques. In our experiments we apply a static magnetic
field at an angle $\theta$ with respect to the wire, while the microwave
current, which is responsible for driving FMR, is always flowing along the
wire. For different $\theta$s we find a very similar behavior for both
microwave-absorption and electrically-detected FMR -- the resonance magnetic
field follows a simple ""$1/\cos(\theta)$"" dependence. This simple behavior
highlights the importance of the relative orientation between the driving
current and magnetic field. We also investigated the dependence of the
electrically detected FMR on dc and rf (microwave) current magnitudes. As
expected, the resonance signal increases linearly with both the applied dc
current and the microwave power.",2303.17363v1
2024-02-09,Resonances involving integer magnons and spin-1/2 excitations in a magnetism modulated two-dimensional electron gas,"We conduct an experimental study of high-mobility two-dimensional electron
gas (2DEG) in GaAs/AlGaAs quantum wells modulated by strong magnetism at an
in-plane magnetic field ($B$). The modulated $B$-fields are performed via the
single stripe and gratings which are made of the heavy rare earth metal Terbium
(Tb) thin films on the sample surface. The robust ferromagnetic resonances
(FMRs) persist to the temperature of 50-70 K in both the stripe and grating
samples, for the ferromagnetism (FM) phase of Tb exists at above 100 K. The
high-order (with integer numbers of $j \equiv \hbar\omega/g\mu_{B}B = 1,
2,$...) magnetic resonances can also be observed in the stripe structure via
the microwave (MW) photovoltaic detection and magnetoresistance under microwave
irradiation. In addition, the resonance features around $j = 1/2$ are robust in
the single-stripe modulated sample, which suggests the spinons with spin-1/2
collective excitations in a 1D Heisenberg model.",2402.06792v1
2007-04-24,Element-resolved x-ray ferrimagnetic and ferromagnetic resonance spectroscopy,"We report on the measurement of element-specific magnetic resonance spectra
at gigahertz frequencies using x-ray magnetic circular dichroism (XMCD). We
investigate the ferrimagnetic precession of Gd and Fe ions in Gd-substituted
Yttrium Iron Garnet, showing that the resonant field and linewidth of Gd
precisely coincide with Fe up to the nonlinear regime of parametric
excitations. The opposite sign of the Gd x-ray magnetic resonance signal with
respect to Fe is consistent with dynamic antiferromagnetic alignment of the two
ionic species. Further, we investigate a bilayer metal film,
Ni$_{80}$Fe$_{20}$(5 nm)/Ni(50 nm), where the coupled resonance modes of Ni and
Ni$_{80}$Fe$_{20}$ are separately resolved, revealing shifts in the resonance
fields of individual layers but no mutual driving effects. Energy-dependent
dynamic XMCD measurements are introduced, combining x-ray absorption and
magnetic resonance spectroscopies.",0704.3139v2
2010-08-12,Rotational Doppler Effect in Magnetic Resonance,"We compute the shift in the frequency of the spin resonance in a solid that
rotates in the field of a circularly polarized electromagnetic wave. Electron
spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are
considered. We show that contrary to the case of the rotating LC circuit, the
shift in the frequency of the spin resonance has strong dependence on the
symmetry of the receiver. The shift due to rotation occurs only when rotational
symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape
of the body, or by magnetocrystalline anisotropy. General expressions for the
resonance frequency and power absorption are derived and implications for
experiment are discussed.",1008.2142v1
2021-10-11,Spin pumping at terahertz nutation resonances,"We investigate spin pumping current injected by the nutation resonances of a
ferromagnet or an antiferromagnet into an adjacent metal. Comparing the dc spin
pumping current between the normal precession and nutation resonances, we find
that the ratio of spin pumping current at the nutation resonance to the
precession resonance is more pronounced in antiferromagnets. We further show
that the spin pumping current injected by the nutation resonance is opposite in
sign as compared to the normal precession mode. This could offer a useful
experimental signature for identifying such nutation resonances. Analyzing the
nature of the nutational eigenmodes, we show that the sign change in spin
current is rooted in a reversal of the precession sense for the nutation
mode(s). Furthermore, the nutational modes in antiferromagnets are found to be
dominated by precession of one of the two sublattices only.",2110.05136v2
2014-10-17,Ferromagnetic resonance in $ε$-Co magnetic composites,"We investigate the electromagnetic properties of assemblies of nanoscale
$\epsilon$-cobalt crystals with size range between 5 nm to 35 nm, embedded in a
polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate
the samples by transmission electron microscopy (TEM) imaging, demonstrating
that the particles aggregate and form chains and clusters. By using a broadband
coaxial-line method, we extract the magnetic permeability in the frequency
range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance
with respect to an externally applied magnetic field. We find that the
zero-magnetic field ferromagnetic resonant peak shifts towards higher
frequencies at finite magnetic fields, and the magnitude of complex
permeability is reduced. At fields larger than 2.5 kOe the resonant frequency
changes linearly with the applied magnetic field, demonstrating the transition
to a state in which the nanoparticles become dynamically decoupled. In this
regime, the particles inside clusters can be treated as non-interacting, and
the peak position can be predicted from Kittel's ferromagnetic resonance theory
for non-interacting uniaxial spherical particles combined with the
Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields
this magnetic order breaks down and the resonant frequency in zero magnetic
field reaches a saturation value reflecting the interparticle interactions as
resulting from aggregation. Our results show that the electromagnetic
properties of these composite materials can be tuned by external magnetic
fields and by changes in the aggregation structure.",1410.4789v2
1999-08-04,Nonlinear Dynamics of Nuclear-Electronic Spin Processes in Ferromagnets,"Spin dynamics is considered in ferromagnets consisting of electron and
nuclear subsystems interacting with each other through hyperfine forces. In
addition, the ferromagnetic sample is coupled with a resonance electric
circuit. Under these conditions, spin relaxation from a strongly nonequilibrium
initial state displays several peculiarities absent for the standard set-up in
studying spin relaxation. The main feature of the nonlinear spin dynamics
considered in this communication is the appearance of ultrafast coherent
relaxation, with characteristic relaxation times several orders shorter than
the transverse relaxation time $T_2$. This type of coherent spin relaxation can
be used for extracting additional information on the intrinsic properties of
ferromagnetic materials and also can be employed for different technical
applications.",9908072v1
2001-08-19,Optical Pumping in Ferromagnet-Semiconductor Heterostructures: Magneto-optics and Spin Transport,"Epitaxial ferromagnetic metal - semiconductor heterostructures are
investigated using polarization-dependent electroabsorption measurements on
GaAs p-type and n-type Schottky diodes with embedded In1-xGaxAs quantum wells.
We have conducted studies as a function of photon energy, bias voltage,
magnetic field, and excitation geometry. For optical pumping with circularly
polarized light at energies above the band edge of GaAs, photocurrents with
spin polarizations on the order of 1 % flow from the semiconductor to the
ferromagnet under reverse bias. For optical pumping at normal incidence, this
polarization may be enhanced significantly by resonant excitation at the
quantum well ground-state. Measurements in a side-pumping geometry, in which
the ferromagnet can be saturated in very low magnetic fields, show hysteresis
that is also consistent with spin-dependent transport. Magneto-optical effects
that influence these measurements are discussed.",0108292v1
2005-04-01,Coherent effects in double-barrier ferromagnet/superconductor/ferromagnet junctions,"Coherent quantum transport in ferromagnet/superconductor/ferromagnet (FSF)
double-barrier junctions is studied. Analytic expressions for charge and spin
conductance spectra are derived for the general case of insulating interfaces
(from metallic to tunnel limit), the Fermi velocity mismatch, and for parallel
(P) and antiparallel (AP) alignment of the electrode magnetizations. We focus
on two characteristic features of finite size and coherency: subgap electronic
transport, and oscillations of the differential conductance. Periodic vanishing
of the Andreev reflection at the energies of geometrical resonances above the
superconducting gap is a striking consequence of the quasiparticle
interference. In contrast with the case of incoherent transport, a non-trivial
spin-polarization without the excess spin accumulation is found for the AP
alignment.",0504029v1
2005-04-27,The effect of stripe domain structure on dynamic permeability of thin ferromagnetic films with out-of-plane uniaxial anisotropy,"The permeability is calculated for a thin ferromagnetic film with the stripe
domain structure and out-of-plane uniaxial magnetic anisotropy. Analytical
expressions for the frequency dependence of components of permeability tensor
are derived with the use of the Smit-Beljers method, with the thickness of
domain walls and the domain wall motion being neglected. The effect of the
domain width and the angle between the anisotropy axis and the film plane on
the frequency dependence of the permeability is analyzed. General equations
relating the static permeability components and the ferromagnetic resonance
frequencies are found. The results of the approach are applied to the
derivation of the constraint for the microwave permeability of thin
ferromagnetic films. The analysis of the constraint as a function of the axis
deviation angle, the domain aspect ratio and the damping parameter allows the
conditions to be found for maximal microwave permeability. The results obtained
may be useful in connection with the problem of developing high-permeable
microwave magnetic materials.",0504710v1
2005-08-30,Cooperative Phenomenon of Ferromagnetism and Unconventional Superconductivity in UGe$_2$: A ^73^Ge-NQR Study under Pressure,"We report on a cooperative phenomenon of ferromagnetism and unconventional
superconductivity (SC) in UGe$_2$ through the measurements of $^{73}$Ge
nuclear-quadrupole-resonance (NQR) under pressure ($P$). The NQR spectra
evidenced phase separation into ferromagnetic and paramagnetic phases in the
vicinity of $P_c\sim 1.5$ GPa, pointing to a first-order transition. The
measurements of nuclear-spin-lattice-relaxation-rate $1/T_1$ revealed that SC
emerges under the background of ferromagnetism, but not of the paramagnetic
phase.",0508731v1
2005-10-28,Negative Refraction in Ferromagnet/Superconductor Superlattices,"Negative refraction, which reverses many fundamental aspects of classical
optics, can be obtained in systems with negative magnetic permeability and
negative dielectric permittivity. This Letter documents an experimental
realization of negative refraction at millimeter waves, finite magnetic fields
and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and
superconducting thin films. In the present case the superconducting
YBa_2Cu_3O_7 layers provide negative permittivity while negative permeability
is achieved via ferromagnetic (La:Sr)MnO_3 layers for frequencies and magnetic
fields close to the ferromagnetic resonance. In these superlattices the
refractive index can be switched between positive and negative regions using
external magnetic field as tuning parameter.",0510777v1
2006-03-13,Experimental evidence for competition of antiferromagnetic and ferromagnetic correlations in HgCr2S4,"A detailed study of poly- and single crystalline samples of the normal spinel
HgCr2S4 is reported. The structural refinement reveals enhanced values of the
atomic displacements suggesting closeness to a structural instability.
Magnetization, electron-spin resonance and specific-heat studies document
strong ferromagnetic fluctuations close to 50 K and the occurrence of complex
antiferromagnetic order at TN = 22 K. We found highly unconventional behavior
resembling properties of a non-collinear antiferromagnet and soft ferromagnet
dependent on temperature and magnetic field. Even weak external magnetic fields
disturb the antiferromagnetic order and strongly enhance the ferromagnetic
correlations. The conductivity shows an insulating character with
non-monotonous temperature behavior and a metal-to-insulator like transition at
80 K well above the magnetic transition. The observed anomalies are related to
bond frustration due to competing magnetic exchange interactions between the Cr
ions.",0603348v1
2006-07-26,"Angle-dependent magnetotransport in cubic and tetragonal ferromagnets: Application to (001)- and (113)A-oriented (Ga,Mn)As","General expressions for the longitudinal and transverse resistivities of
single-crystalline cubic and tetragonal ferromagnets are derived from a series
expansion of the resistivity tensor with respect to the magnetization
orientation. They are applied to strained (Ga,Mn)As films, grown on (001)- and
(113)A-oriented GaAs substrates, where the resistivities are theoretically and
experimentally studied for magnetic fields rotated within various planes
parallel and perpendicular to the sample surface. We are able to model the
measured angular dependences of the resistivities within the framework of a
single ferromagnetic domain, calculating the field-dependent orientation of the
magnetization by numerically minimizing the free-enthalpy density.
Angle-dependent magnetotransport measurements are shown to be a powerful tool
for probing both anisotropic magnetoresistance and magnetic anisotropy. The
anisotropy parameters of the (Ga,Mn)As films inferred from the magnetotransport
measurements agree with those obtained by ferromagnetic resonance measurements
within a factor of two.",0607679v1
2007-07-04,Detection of the magneto-structural phase coexistence in MnAs epilayers at a very early stage,"We report on the appearance of magnetic stripes in MnAs/GaAs(100) epilayers
at temperatures well below the ferromagnetic transition of the system. The
study has been performed by ferromagnetic resonance experiments (FMR) on MnAs
epilayers grown on (100) and (111) GaAs substrates. The FMR spectra of the
MnAs/GaAs(100) samples at 180 K reveal the appearance of zones of different
magnetic behavior with respect to the low-temperature homogeneous ferromagnetic
phase. The angular and the temperature dependence of the spectra serve us to
detect the inter-growth of the non-magnetic phase into the ferromagnetic phase
at a very early stage of the process. The experimental data show that the new
phase nucleates in a self-arranged array of stripes in MnAs/GaAs(100) thin
films while it grows randomly in the same films grown on GaAs(111).",0707.0703v1
2007-10-10,Microwave photovoltage and photoresistance effects in ferromagnetic microstrips,"We investigate the dc electric response induced by ferromagnetic resonance in
ferromagnetic Permalloy (Ni80Fe20) microstrips. The resulting magnetization
precession alters the angle of the magnetization with respect to both dc and rf
current. Consequently the time averaged anisotropic magnetoresistance (AMR)
changes (photoresistance). At the same time the time-dependent AMR oscillation
rectifies a part of the rf current and induces a dc voltage (photovoltage). A
phenomenological approach to magnetoresistance is used to describe the distinct
characteristics of the photoresistance and photovoltage with a consistent
formalism, which is found in excellent agreement with experiments performed on
in-plane magnetized ferromagnetic microstrips. Application of the microwave
photovoltage effect for rf magnetic field sensing is discussed.",0710.1974v3
2008-06-27,Field-dependent AC susceptibility of itinerant ferromagnets,"Whereas dc measurements of magnetic susceptibility, $\chi$, fail to
distinguish between local and weak itinerant ferromagnets, radio-frequency (rf)
measurements of $\chi$ in the ferromagnetic state show dramatic differences
between the two. We present sensitive tunnel-diode resonator measurements of
$\chi$ in the weak itinerant ferromagnet ZrZn$_2$ at a frequency of 23 MHz.
Below Curie temperature, $T_C \approx 26$ K, the susceptibility is seen to
increase and pass through a broad maximum at approximately 15 K in zero applied
dc magnetic field. Application of a magnetic field reduces the amplitude of the
maximum and shifts it to lower temperatures. The existence and evolution this
maximum with applied field is not predicted by either the Stoner or
self-consistent renormalized (SCR) spin fluctuations theories. For temperatures
below $T_C$ both theories derive a zero-field limit expression for $\chi$. We
propose a semi-phenomenological model that considers the effect of the internal
field from the polarized fraction of the conduction band on the remaining,
unpolarized conduction band electrons. The developed model accurate describes
the experimental data.",0806.4612v1
2011-03-01,Two-orbital Kondo effect in quantum dot coupled to ferromagnetic leads,"We study the Kondo effect of a two-orbital vertical quantum dot (QD) coupled
to two ferromagnetic leads by employing an equation of motion method. When the
ferromagnetic leads are coupled with parallel spin polarization, we find three
peaks in the single-particle excitation spectra. The middle one is the Kondo
resonance caused by the orbital degrees of freedom. In magnetic fields, the
Kondo effect vanishes. However, at a certain magnetic field new two-fold
degenerate states arise and the Kondo effect emerges there. In contrast, when
the ferromagnetic leads are coupled with antiparallel spin polarization, the
Kondo effect caused by the spin (orbital) degrees of freedom survives (is
suppressed) in magnetic fields. We investigate the field dependence of the
conductance in the parallel and antiparallel spin polarizations of the leads
and find that the conductance changes noticeably in magnetic fields.",1103.0304v2
2012-08-02,Anomalous Fermi level behavior in GaMnAs at the onset of ferromagnetism,"We present the systematic study of the resonant tunneling spectroscopy on a
series of ferromagnetic-semiconductor Ga1-xMnxAs with the Mn content x from
~0.01 to 3.2%. The Fermi level of Ga1-xMnxAs exists in the band gap in the
whole x region. The Fermi level is closest to the valence band (VB) at x=1.0%
corresponding to the onset of ferromagnetism near the metal-insulator
transition (MIT), but it moves away from the VB as x increasing or decreasing
from 1.0%. This anomalous behavior of the Fermi level indicates that the
ferromagnetism and MIT emerge in the Mn-derived impurity band.",1208.0575v2
2014-01-22,Coexistence of Superconductivity and Ferromagnetism in P-doped EuFe2As2,"The magnetic structure of the Eu2+ moments in the superconducting
EuFe2(As1-xPx)2 sample with x = 0.15 has been determined using element specific
x-ray resonant magnetic scattering. Combining magnetic, thermodynamic and
scattering measurements, we conclude that the long range ferromagnetic order of
the Eu2+ moments aligned primarily along the c axis coexists with the bulk
superconductivity at zero field. At an applied magnetic field >= 0.6 T,
superconductivity still coexists with the ferromagnetic Eu2+ moments which are
polarized along the field direction. We propose a spontaneous vortex state for
the coexistence of superconductivity and ferromagnetism in EuFe2(As0.85P0.15)2.",1401.5463v1
2015-02-16,Electrical manipulation of a ferromagnet by an antiferromagnet,"We demonstrate that an antiferromagnet can be employed for a highly efficient
electrical manipulation of a ferromagnet. In our study we use an electrical
detection technique of the ferromagnetic resonance driven by an in-plane
ac-current in a NiFe/IrMn bilayer. At room temperature, we observe
antidamping-like spin torque acting on the NiFe ferromagnet, generated by the
in-plane current driven through the IrMn antiferromagnet. A large enhancement
of the torque, characterized by an effective spin-Hall angle exceeding most
heavy transition metals, correlates with the presence of the exchange-bias
field at the NiFe/IrMn interface. It highlights that, in addition to strong
spin-orbit coupling, the antiferromagnetic order in IrMn governs the observed
phenomenon.",1502.04570v2
2015-04-09,Spin-transfer torque effects in the dynamic forced response of the magnetization of nanoscale ferromagnets in superimposed ac and dc bias fields in the presence of thermal agitation,"Spin-transfer torque (STT) effects on the stationary forced response of
nanoscale ferromagnets subject to thermal fluctuations and driven by an ac
magnetic field of arbitrary strength and direction are investigated via a
generic nanopillar model of a spin-torque device comprising two ferromagnetic
strata representing the free and fixed layers and a nonmagnetic conducting
spacer all sandwiched between two ohmic contacts. The STT effects are treated
via the Brown magnetic Langevin equation generalized to include the Slonczewski
STT term thereby extending the statistical moment method [Y. P. Kalmykov et
al., Phys. Rev. B 88, 144406 (2013)] to the forced response of the most general
version of the nanopillar model. The dynamic susceptibility, nonlinear
frequency-dependent dc magnetization, dynamic magnetic hysteresis loops, etc.
are then evaluated highlighting STT effects on both the low-frequency thermal
relaxation processes and the high-frequency ferromagnetic resonance, etc.,
demonstrating a pronounced dependence of these on the spin polarization current
and facilitating interpretation of STT experiments.",1504.02319v2
2009-12-07,High temperature ferromagnetism of Li-doped vanadium oxide nanotubes,"The nature of a puzzling high temperature ferromagnetism of doped
mixed-valent vanadium oxide nanotubes reported earlier by Krusin-Elbaum et al.,
Nature 431 (2004) 672, has been addressed by static magnetization, muon spin
relaxation, nuclear magnetic and electron spin resonance spectroscopy
techniques. A precise control of the charge doping was achieved by
electrochemical Li intercalation. We find that it provides excess electrons,
thereby increasing the number of interacting magnetic vanadium sites, and, at a
certain doping level, yields a ferromagnetic-like response persisting up to
room temperature. Thus we confirm the surprising previous results on the
samples prepared by a completely different intercalation method. Moreover our
spectroscopic data provide first ample evidence for the bulk nature of the
effect. In particular, they enable a conclusion that the Li nucleates
superparamagnetic nanosize spin clusters around the intercalation site which
are responsible for the unusual high temperature ferromagnetism of vanadium
oxide nanotubes.",0912.1237v1
2009-12-23,Microscopic Coexistence of Ferromagnetism and Superconductivity in Single-Crystal UCoGe,"Unambiguous evidence for the microscopic coexistence of ferromagnetism and
superconductivity in UCoGe ($T_{\rm Curie} \sim 2.5$ K and $T_{\rm SC}$ $\sim$
0.6 K) is reported from $^{59}$Co nuclear quadrupole resonance (NQR). The
$^{59}$Co-NQR signal below 1 K indicates ferromagnetism throughout the sample
volume, while nuclear spin-lattice relaxation rate $1/T_1$ in the ferromagnetic
(FM) phase decreases below $T_{\rm SC}$ due to the opening of the
superconducting(SC) gap. The SC state was found to be inhomogeneous, suggestive
of a self-induced vortex state, potentially realizable in a FM superconductor.
In addition, the $^{59}$Co-NQR spectrum around $T_{\rm Curie}$ show that the FM
transition in UCoGe possesses a first-order character, which is consistent with
the theoretical prediction that the low-temperature FM transition in itinerant
magnets is generically of first-order.",0912.4545v1
2011-12-31,"Ferromagnetic Ordering in Carbon Nanotubes, Incorporated in Diamond Single Crystals","The physical origin of the mechanism of the formation of ferromagnetic
ordering in carbon nanotubes (NTs), produced by high energy ion beam
modification of diamond single crystals in $\langle{110}\rangle$ and
$\langle{111}\rangle$ directions has been found. It is concluded from analysis
of experimental results on ferromagnetic spin wave resonance observed, that the
only $\pi$-electronic subsystem of given NTs is responsible for the appearance
of ferromagnetism. It is determined by asymmetry in spin density distribution
in Su-Schrieffer-Heeger (SSH) topological soliton lattice. The formation of SSH
topological soliton lattice is considered in the frames of generalized
SSH-model of organic conductors, in which $\pi$-electronic subsystem is
represented being to be 1D quantum Fermi liquid.
  The phenomenon of formation of uncompensated antiferromagnetic ordering
coexisting with superconductivity at room temperature in carbon nanotubes,
produced by high energy ion beam modification of diamond single crystals in
$\langle{100}\rangle$ direction is argued.",1201.0285v3
2012-04-10,Complex itinerant ferromagnetism in noncentrosymmetric Cr11Ge19,"The noncentrosymmetric ferromagnet Cr11Ge19 has been investigated by
electrical transport, AC and DC magnetization, heat capacity, x-ray
diffraction, resonant ultrasound spectroscopy, and first principles electronic
structure calculations. Complex itinerant ferromagnetism in this material is
indicated by nonlinearity in conventional Arrott plots, unusual behavior of AC
susceptibility, and a weak heat capacity anomaly near the Curie temperature (88
K). The inclusion of spin wave excitations was found to be important in
modeling the low temperature heat capacity. The temperature dependence of the
elastic moduli and lattice constants, including negative thermal expansion
along the c axis at low temperatures, indicate strong magneto-elastic coupling
in this system. Calculations show strong evidence for itinerant ferromagnetism
and suggest a noncollinear ground state may be expected.",1204.2254v2
2020-02-26,Control of spin dynamics in artificial honeycomb spin-ice-based nanodisks,"We report the experimental and theoretical characterization of the
angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged
on a honeycomb lattice. The magnetic field and microwave frequency dependence,
measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes
that is strongly affected by the microstate of the network. Based on symmetry
arguments with respect to the external field, we show that certain parts of the
ferromagnetic network contribute to the detected signal. A comparison of the
experimental data with micromagnetic simulations reveals that different
subsections of the lattice predominantly contribute to the high-frequency
response of the array. This is confirmed by optical characterizations using
microfocused Brillouin light scattering. Furthermore, we find indications that
nucleation and annihilation of vortex-like magnetization configurations in the
low-field range affect the dynamics, which is different from clusters of
ferromagnetic nanoellipses. Our work opens up new perspectives for designing
magnonic devices that combine geometric frustration in gyrotropic vortex
crystals at low frequencies with magnonic crystals at high frequencies.",2002.11694v1
2018-03-29,Giant resonant nonlinear damping in nanoscale ferromagnets,"Magnetic damping is a key metric for emerging technologies based on magnetic
nanoparticles, such as spin torque memory and high-resolution biomagnetic
imaging. Despite its importance, understanding of magnetic dissipation in
nanoscale ferromagnets remains elusive, and the damping is often treated as a
phenomenological constant. Here we report the discovery of a giant
frequency-dependent nonlinear damping that strongly alters the response of a
nanoscale ferromagnet to spin torque and microwave magnetic field. This novel
damping mechanism originates from three-magnon scattering that is strongly
enhanced by geometric confinement of magnons in the nanomagnet. We show that
the giant nonlinear damping can invert the effect of spin torque on a
nanomagnet leading to a surprising current-induced enhancement of damping by an
antidamping torque. Our work advances understanding of magnetic dynamics in
nanoscale ferromagnets and spin torque devices.",1803.10925v1
2020-06-29,Ultrafast optically induced ferromagnetic state in an elemental antiferromagnet,"We present evidence for an ultrafast optically induced ferromagnetic
alignment of antiferromagnetic Mn in Co/Mn multilayers. We observe the
transient ferromagnetic signal at the arrival of the pump pulse at the Mn L$_3$
resonance using x-ray magnetic circular dichroism in reflectivity. The
timescale of the effect is comparable to the duration of the excitation and
occurs before the magnetization in Co is quenched. Theoretical calculations
point to the imbalanced population of Mn unoccupied states caused by the Co
interface for the emergence of this transient ferromagnetic state.",2006.16061v4
2021-10-04,Lumped circuit model for inductive antenna spin-wave transducers,"We derive a lumped circuit model for inductive antenna spin-wave transducers
in the vicinity of a ferromagnetic medium. The model considers the antenna's
Ohmic resistance, its inductance, as well as the additional inductance due to
the excitation of ferromagnetic resonance or spin waves in the ferromagnetic
medium. As an example, the additional inductance is discussed for a wire
antenna on top of a ferromagnetic waveguide, a structure that is characteristic
for many magnonic devices and experiments. The model is used to assess the
scaling properties and the energy efficiency of inductive antennas. Issues
related to scaling antenna transducers to the nanoscale and possible solutions
are also addressed.",2110.01318v3
2023-12-12,Interacting Floquet topological magnons in laser-irradiated Heisenberg honeycomb ferromagnets,"When a Heisenberg honeycomb ferromagnet is irradiated by high frequency
circularly polarized light, the underlying uncharged magnons acquire a time
dependent Aharonov Casher phase, which makes it a Floquet topological magnon
insulator. In this context, we investigate the many body interaction effects of
Floquet magnons in laser irradiated Heisenberg honeycomb ferromagnets with
ocontaining Dzyaloshinskii Moriya interaction under the application of
circularly polarized off resonant light. We demonstrate that the quantum
ferromagnet systems periodically laser driven exhibits temperature driven
topological phase transitions due to Floquet magnon magnon interactions. The
thermal Hall effect of Floquet magnons serves as a prominent signature for
detecting these many body effects near the critical point, enabling
experimental investigation into this phenomenon. Our study complements the lack
of previous theoretical works that the topological phase transition of the
Floquet magnon under the linear spin wave approximation is only tunable by the
light field. Our study presents a novel approach for constructing Floquet
topological phases in periodically driven quantum magnet systems that goes
beyond the limitations of the linear spin wave theory. We provide numerical
results based on the well known van der Waals quantum magnet CrX3 (X=F, Cl, Br,
and I), calling for experimental implementation.",2312.06929v1
2024-02-02,Mechanism of ferromagnetism enhancement in a La$_{2/3}$ Sr$_{1/3}$ MnO$_3$ membrane released from epitaxial strain,"Recent studies have shown that the magnetic properties of the ferromagnetic
perovskite oxide La$_{2/3}$ Sr$_{1/3}$ MnO$_3$ (LSMO) grown on an SrTiO3 (STO)
substrate, such as its magnetic moment and Curie temperature, can be improved
by releasing the film from the substrate. However, the microscopic origin of
this enhancement is not yet well understood. In this study, we use synchrotron
radiation measurements to investigate the mechanism of ferromagnetism
enhancement in an LSMO membrane released from an STO substrate by dissolving a
water-soluble Sr$_4$Al$_2$O$_7$ buffer layer. Using resonant photoemission
spectroscopy on the as-grown LSMO film and LSMO membrane, we elucidate that the
strain release from the STO substrate enhances the itineracy of the Mn-3d
electrons via p-d hybridization, and this strengthens the double-exchange
interaction. The reinforcement of the double-exchange interaction, in turn,
improves the ferromagnetism of LSMO.",2402.01179v1
2024-03-19,Acoustoelectric non-local spin wave power detector for studying magnon-phonon coupling,"We have developed a simple detection scheme to study spin waves excited by
surface acoustic wave (SAW) in ferromagnetic thin films. Metallic antennas made
of Ta and a ferromagnetic element are placed along the SAW propagation path.
The SAW excites spin waves in the ferromagnetic element and induces
acoustoelectric current in the antennas, which are detected as a DC voltage.
The DC voltage takes an extremum at the spin wave resonance condition, which
demonstrates that the antenna acts as a non-local spin wave detector. The
antennas placed before and after the ferromagnetic element along the SAW
propagation path can probe spin wave excitation from reflected and transmitted
SAWs, respectively. Interestingly, we find characteristics of spin wave
excitations that are different for the reflected and transmitted SAWs: the
former excites spin waves with larger frequency with broader linewidth compared
to the latter. The results show that the antennas act as a non-local spin wave
power detector and can be used to map out the spin wave spectra in a unique
way, providing insights into the magnon-phonon coupling in magnetic
nanostructures fabricated on phononic SAW devices.",2403.12745v1
1995-09-22,Critical Dynamics of Magnets,"We review our current understanding of the critical dynamics of magnets above
and below the transition temperature with focus on the effects due to the
dipole--dipole interaction present in all real magnets. Significant progress in
our understanding of real ferromagnets in the vicinity of the critical point
has been made in the last decade through improved experimental techniques and
theoretical advances in taking into account realistic spin-spin interactions.
We start our review with a discussion of the theoretical results for the
critical dynamics based on recent renormalization group, mode coupling and spin
wave theories. A detailed comparison is made of the theory with experimental
results obtained by different measuring techniques, such as neutron scattering,
hyperfine interaction, muon--spin--resonance, electron--spin--resonance, and
magnetic relaxation, in various materials. Furthermore we discuss the effects
of dipolar interaction on the critical dynamics of three--dimensional isotropic
antiferromagnets and uniaxial ferromagnets. Special attention is also paid to a
discussion of the consequences of dipolar anisotropies on the existence of
magnetic order and the spin--wave spectrum in two--dimensional ferromagnets and
antiferromagnets. We close our review with a formulation of critical dynamics
in terms of nonlinear Langevin equations.",9509141v1
2004-01-30,Magnetoelectric Effects in Ferromagnetic Metal-Piezoelectric Oxide Layered Structures,"Frequency dependence of magnetoelectric (ME) coupling is investigated in
trilayers of ferromagnetic alloy and piezoelectric lead zirconate titanate
(PZT). The ferromagnetic phases studied include permendur, a soft magnet with
high magnetostriction, iron, nickel, and cobalt. Low frequency data on ME
voltage coefficient versus bias magnetic field indicate strong coupling only
for trilayers with permendure or Ni. Measurements of frequency dependence of ME
voltage reveal a giant ME coupling at electromechanical resonance. The ME
interactions for transverse fields is an order of magnitude stronger than for
longitudinal fields. The maximum voltage coefficient of 90 V/cm Oe at resonance
is measured for samples with nickel or permendure and is three orders of
magnitude higher than low-frequency values.",0401648v1
2005-05-19,Soft X-ray Resonant Magnetic Scattering Studies on Fe/CoO Exchange Bias System,"We have used soft X-ray Resonant Magnetic Scattering (XRMS) to search for the
presence of an effective ferromagnetic moment belonging to the
antiferromagnetic (AF) layer which is in close contact with a ferromagnetic (F)
layer. Taking advantage of the element specificity of the XRMS technique, we
have measured hysteresis loops of both Fe and CoO layers of a CoO(40
\AA)/Fe(150 \AA) exchange bias bilayer. From these measurements we have
concluded that the proximity of the F layer induces a magnetic moment in the AF
layer. The F moment of the AF layer has two components: one is frozen and does
not follow the applied magnetic field and the other one follows in phase the
ferromagnetic magnetization of the F layer. The temperature dependence of the F
components belonging to the AF layer is shown and discussed.",0505482v1
2006-07-25,Non-perturbative $J_{pd}$ model and ferromagnetism in dilute magnets,"We calculate magnetic couplings in the $J_{pd}$ model for dilute magnets, in
order both to identify the relevant parameters which control ferromagnetism and
also to bridge the gap between first principle calculations and model
approaches. The magnetic exchange interactions are calculated
non-perturbatively and disorder in the configuration of impurities is treated
exacly, allowing us to test the validity of effective medium theories.
  Results differ qualitatively from those of weak coupling. In contrast to mean
field theory, increasing $J_{pd}$ may not favor high Curie temperatures: $T_C$
scales primarily with the bandwidth. High temperature ferromagnetism at small
dilutions is associated with resonant structure in the p-band. Comparison to
diluted magnetic semiconductors indicate that Ga(Mn)As has such a resonant
structure and thus this material is already close to optimality.",0607640v1
2006-09-11,"Current-driven ferromagnetic resonance, mechanical torques and rotary motion in magnetic nanostructures","We study theoretically the detection and possible utilization of electric
current-induced mechanical torques in ferromagnetic-normal metal
heterostructures that are generated by spin-flip scattering or the absorption
of transverse spin currents by a ferromagnet. To this end, we analyze the DC
voltage signals over a spin valve that is driven by an AC current. In agreement
with recent studies, this ""rectification"", measured as a function of AC
frequency and applied magnetic field, contains important information on the
magnetostatics and --dynamics. Subsequently, we show that the vibrations
excited by spin-transfer to the lattice can be detected as a splitting of the
DC voltage resonance. Finally, we propose a concept for a spin-transfer-driven
electric nanomotor based on integrating metallic nanowires with carbon
nanotubes, in which the current-induced torques generate a rotary motion.",0609258v2
2006-06-27,Periodic structure of spin-transfer current in ferromagnetic multilayers,"We show that the drift-diffusion mechanism in a normal-metal layer in
combination with the resonance electron-magnon interactions at
ferromagnet-normal interface of F-N-F heterostucture creates spatial
instability modes and, out of these modes, a quasi-stable periodic structure of
spin-transfer d.c. current can arise with certain channel step and
step-to-radius ratio. The ferromagnetic resonance conditions determine
spin-transfer current density. Independent nano-oscillators creating
intersecting arrays of channels can phase-lock on sub-micrometer distance,
which depends on multilayer geometry and applied fields. By decreasing the
layer thickness, the number of channels affected by each independent
d.c.-current source and their radius may be diminished. Phase-locking of
multiple independent nano-oscillators can be used for enhancement of output
power.",0606064v1
2008-06-25,Experimental Observation of the Inverse Proximity Effect in Superconductor/Ferromagnet Layered Structures,"We have studied the nuclear magnetic resonance (NMR) of 51V nuclei in the
superconductor/ferromagnet thin film heterostructures Ni/V/Ni and
Pd{1-x}Fe{x}/V/Pd{1-x}Fe{x} in the normaland superconducting state. Whereas the
position and shape of the NMR line in the normal state for the trilayers is
identical to that observed in a single V-layer, in the superconducting state
the line shape definitely changes, developing a systematic distortion of the
high-field wing of the resonance line. We consider this as the first
experimental evidence for the penetration of ferromagnetism into the
superconducting layer, a phenomenon which has been theoretically predicted
recently and dubbed the inverse proximity effect.",0806.4104v1
2009-05-29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
magnitude larger than soft magnetic materials, such as pure iron (Fe) and
permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
FMR linewidth depends linearly on frequency for perpendicular applied fields
and increases significantly when the magnetization is rotated into the film
plane. Irradiation of the film with Helium ions decreases the PMA and the
distribution of PMA parameters. This leads to a great reduction of the FMR
linewidth for in-plane magnetization. These results suggest that fluctuations
in PMA lead to a large two magnon scattering contribution to the linewidth for
in-plane magnetization and establish that the Gilbert damping is enhanced in
such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
pure Fe).",0905.4779v2
2010-07-07,"Three attractively interacting fermions in a harmonic trap: Exact solution, ferromagnetism, and high-temperature thermodynamics","Three fermions with strongly repulsive interactions in a spherical harmonic
trap, constitute the simplest nontrivial system that can exhibit the onset of
itinerant ferromagnetism. Here, we present exact solutions for three trapped,
attractively interacting fermions near a Feshbach resonance. We analyze energy
levels on the upper branch of the resonance where the atomic interaction is
effectively repulsive. When the s-wave scattering length a is sufficiently
positive, three fully polarized fermions are energetically stable against a
single spin-flip, indicating the possibility of itinerant ferromagnetism, as
inferred in the recent experiment. We also investigate the high-temperature
thermodynamics of a strongly repulsive or attractive Fermi gas using a quantum
virial expansion. The second and third virial coefficients are calculated. The
resulting equations of state can be tested in future quantitative experimental
measurements at high temperatures and can provide a useful benchmark for
quantum Monte Carlo simulations.",1007.1041v1
2010-09-29,Acoustically driven ferromagnetic resonance,"Surface acoustic waves (SAW) in the GHz frequency range are exploited for the
all-elastic excitation and detection of ferromagnetic resonance (FMR) in a
ferromagnetic/ferroelectric (nickel/lithium niobate) hybrid device. We measure
the SAW magneto-transmission at room temperature as a function of frequency,
external magnetic field magnitude, and orientation. Our data are well described
by a modified Landau-Lifshitz-Gilbert approach, in which a virtual,
strain-induced tickle field drives the magnetization precession. This causes a
distinct magnetic field orientation dependence of elastically driven FMR that
we observe in both model and experiment.",1009.5798v2
2011-05-27,Resonances in a dilute gas of magnons and metamagnetism of isotropic frustrated ferromagnetic spin chains,"We show that spin-S chains with SU(2)-symmetric, ferromagnetic
nearest-neighbor and frustrating antiferromagnetic next-nearest-neighbor
exchange interactions exhibit metamagnetic behavior under the influence of an
external magnetic field for small S, in the form of a first-order transition to
the fully polarized state. The corresponding magnetization jump increases
gradually starting from an S-dependent critical value of exchange couplings and
takes a maximum in the vicinity of a ferromagnetic Lifshitz point. The
metamagnetism results from resonances in the dilute magnon gas caused by an
interplay between quantum fluctuations and frustration.",1105.5626v2
2012-12-23,Magnetoelectric coupling in a ferroelectric/ferromagnetic chain revealed by ferromagnetic resonance,"Understanding the multiferroic coupling is one of the key issues in the feld
of multiferroics. As shown here theoretically, the ferromagnetic resonance
(FMR) renders possible an access to the magnetoelectric coupling coefficient in
composite multiferroics. This we evidence by a detailed analysis and numerical
calculations of FMR in an unstrained chain of BaTiO3 in the tetragonal phase in
contact with Fe, including the effect of depolarizing field. The spectra of the
absorbed power in FMR are found to be sensitive to the orientation of the
interface electric polarization and to an applied static electric field. Here
we propose a method for measuring the magnetoelectric coupling coefficient by
means of FMR.",1212.5794v1
2013-01-28,Spin filter effect at room temperature in GaN/GaMnN ferromagnetic resonant tunneling diode,"We have investigated the spin current polarization without the external
magnetic field in the resonant tunneling diode with the emitter and quantum
well layers made from the ferromagnetic GaMnN. For this purpose we have applied
the self-consistent Wigner-Poisson method and studied the spin-polarizing
effect of the parallel and antiparallel alignment of the magnetization in the
ferromagnetic layers. The results of our calculations show that the
antiparallel magnetization is much more advantageous for the spin filter
operation and leads to the full spin current polarization at low temperatures
and 35 % spin polarization of the current at room temperature.",1301.6544v1
2013-12-05,Strong impact of the eddy-current shielding on ferromagnetic resonance response of sub-skin-depth-thick conducting magnetic multilayers,"Exchange-coupled nonmagnetic (NM) and ferromagnetic (FM) conducting
multilayers are crucial for microwave spintronic devices of the future. We
demonstrate, experimentally and theoretically, that in broadband measurements
of ferromagnetic resonance (FMR) 10-70 nm-thick permalloy (Py) layers are
shielded from the dynamic magnetic field of the microstrip line by eddy
currents circulating in the NM capping layers, which strongly diminishes the
amplitude of magnetisation precession in the FM material. Our findings have
direct implications for designing broadband FMR and measurements of spin
current injection through interfaces realised by placing a conducting
multilayer above a microwave microstrip line. We show that the eddy-current
shielding is very strong at high microwave frequencies (30 GHz) even when the
thickness of the NM capping layer is <5 nm, which is well below the microwave
skin depth for Au, Cu, Ta, Pd, Pt and other NM metals technologically important
for spintronics.",1312.1404v2
2014-02-24,Coplanar waveguide based ferromagnetic resonance in ultrathin film magnetic nanostructures: impact of conducting layers,"We report broadband ferromagnetic resonance (FMR) measurements based on a
coplanar waveguide (CPW) of ultrathin magnetic film structures that comprise
in-plane/out-of-plane decoupled layers deposited on nonmagnetic buffer layers
of various thickness or other buffer structures with a diverse sheet
resistance. We show that the excitation of the fundamental mode can be
substantially (up to 10 times) enhanced in the structures deposited on buffer
layers with a low sheet resistance in comparison to the structures deposited on
thin or weakly conducting buffer layers. The results are analyzed in terms of
shielding of the electromagnetic field of CPW by the conducting buffer layers.
The effect of enhancement of FMR absorption can be attractive for applications
in spintronic devices that utilize magnetization dynamics of ultrathin
ferromagnetic layers.",1402.5844v2
2014-08-25,Spin-Scattering Rates in Metallic Thin Films Measured by Ferromagnetic Resonance Damping Enhanced by Spin-Pumping,"We determined the spin-transport properties of Pd and Pt thin films by
measuring the increase in ferromagnetic resonance damping due to spin-pumping
in ferromagnetic (FM)-nonferromagnetic metal (NM) multilayers with varying NM
thicknesses. The increase in damping with NM thickness depends strongly on both
the spin- and charge-transport properties of the NM, as modeled by diffusion
equations that include both momentum- and spin-scattering parameters. We use
the analytical solution to the spin-diffusion equations to obtain
spin-diffusion lengths for Pt and Pd. By measuring the dependence of
conductivity on NM thickness, we correlate the charge- and spin-transport
parameters, and validate the applicability of various models for
momentum-scattering and spin-scattering rates in these systems: constant,
inverse-proportional (Dyakanov-Perel), and linear-proportional (Elliot-Yafet).
We confirm previous reports that the spin-scattering time can be shorter than
the momentum scattering time in Pt, and the Dyakanov-Perel-like model is the
best fit to the data.",1408.5921v2
2016-09-26,Ferromagnetic resonance study of composite Co/Ni - FeCoB free layers with perpendicular anisotropy,"We study the properties of composite free layers with perpendicular
anisotropy. The free layers are made of a soft FeCoB layer ferromagnetically
coupled by a variable spacer (Ta, W, Mo) to a very anisotropic [Co/Ni]
multilayer embodied in a magnetic tunnel junction meant for spin torque memory
applications. For this we use broadband ferromagnetic resonance to follow the
field dependence of the acoustical and optical excitation of the composite free
layer in both in-plane and out-of-plane applied fields. The modeling provides
the interlayer exchange coupling, the anisotropies and the damping factors. The
popular Ta spacer are outperformed by W and even more by Mo, which combines the
strongest interlayer exchange coupling without sacrificing anisotropies,
damping factors and transport properties.",1609.07863v1
2019-05-22,Floquet Second-Order Topological Superconductor Driven via Ferromagnetic Resonance,"We consider a Floquet triple-layer setup composed of a two-dimensional
electron gas with spin-orbit interactions, proximity coupled to an s-wave
superconductor and to a ferromagnet driven at resonance. The ferromagnetic
layer generates a time-oscillating Zeeman field which competes with the induced
superconducting gap and leads to a topological phase transition. The resulting
Floquet states support a second-order topological superconducting phase with a
pair of localized zero-energy Floquet Majorana corner states. Moreover, the
phase diagram comprises a Floquet helical topological superconductor, hosting a
Kramers pair of Majorana edge modes protected by an effective time-reversal
symmetry, as well as a gapless Floquet Weyl phase. The topological phases are
stable against disorder and parameter variations and are within experimental
reach.",1905.09241v1
2008-07-12,Micromagnetic simulations of small arrays of submicron ferromagnetic particles,"We report the results of a set of simulations of small arrays of submicron
ferromagnetic particles. The actions of dipolar and exchange interactions were
qualitatively investigated by analysing the ferromagnetic resonance spectra at
9.37 GHz resulting from the magnetization response of con- nected and
unconnected particles in the array as a function of the applied dc magnetic
field. We find that the magnetization precession movement (at resonance)
observed in individual particles in the array presents a distinctive behaviour
(an amplitude mismatch) in comparison to isolated, one-particle reference
simulations, a result that we attribute to the action of interparticle dipolar
couplings. Exchange interactions appear to have an important role in modifying
the spectra of connected particles, even through a small contact surface.",0807.1978v1
2011-11-16,Adiabatic quantum pumping through surface states in 3D topological insulators,"We investigate adiabatic quantum pumping of Dirac fermions on the surface of
a strong 3D topological insulator. Two different geometries are studied in
detail, a normal metal -- ferromagnetic -- normal metal (NFN) junction and a
ferromagnetic -- normal metal -- ferromagnetic (FNF) junction. Using a
scattering matrix approach, we first calculate the tunneling conductance and
then the adiabatically pumped current using different pumping mechanisms for
both types of junctions. We explain the oscillatory behavior of the conductance
by studying the condition for resonant transmission in the junctions and find
that each time a new resonant mode appears in the transport window, the pumped
current diverges. We also predict an experimentally distinguishable difference
between the pumped current and the rectified current.",1111.3927v1
2016-12-20,Ferromagnetic resonance and interlayer exchange coupling in magnetic multilayers with compositional gradients,"Ferromagnetic resonance (FMR) in magnetic multilayers of type F1/f/F2, where
two strongly ferromagnetic layers F1 and F2 are separated by a weakly magnetic
spacer f with a compositional gradient along its thickness, is investigated.
The method allows to detect the weak signal from the spacer in additional to
the more pronounced and readily measured signal from the outer
strongly-magnetic layers, and thereby study the properties of the spacer as
well as the interlayer exchange interaction it mediates. Variable temperature
FMR measurements, especially near the relevant Curie points, reveal a rich set
of properties of the exchange interactions in the system. The obtained results
are useful for designing and optimizing nanostructures with
thermally-controlled magnetic properties.",1612.06785v1
2017-10-28,High frequency dynamics modulated by collective magnetization reversal in artificial spin ice,"Spin-torque ferromagnetic resonance (ST-FMR) arises in heavy
metal/ferromagnet heterostructures when an alternating charge current is passed
through the bilayer stack. The methodology to detect the resonance is based on
the anisotropic magnetoresistance, which is the change in the electrical
resistance due to different orientations of the magnetization. In connected
networks of ferromagnetic nanowires, known as artificial spin ice, the
magnetoresistance is rather complex owing to the underlying collective behavior
of the geometrically frustrated magnetic domain structure. Here, we demonstrate
ST-FMR investigations in a square artificial spin-ice system and correlate our
observations to magnetotransport measurements. The experimental findings are
described using a simulation approach that highlights the importance of the
correlated dynamics response of the magnetic system. Our results open the
possibility of designing reconfigurable microwave oscillators and
magnetoresistive devices based on connected networks of nanomagnets.",1710.10534v1
2018-03-05,Off-resonant all-optical switching dynamics in a ferromagnetic model system,"We present a theoretical study of the the effects of off-resonant polarized
optical fields on a ferromagnetic model system. We determine the light-induced
dynamics of itinerant carriers in a system that includes magnetism at the
mean-field level and spin-orbit coupling. We investigate an all-optical
switching process for ferromagnets, which is close to the one proposed by
Qaiumzadeh et al. [Phys. Rev. B 88, 064416] for the inverse Faraday effect. By
computing the optically driven coherent dynamics together with incoherent
scattering mechanisms we go beyond a perturbation expansion in powers of the
optical field. We find an important contribution of a dynamic Stark effect
coupling of the Raman type between the magnetic bands, which leads to a
polarization-dependent effect on the magnetization that may support or oppose
switching, but also contributes to demagnetization via an increase in
electronic energy.",1803.01924v1
2018-08-03,Ferromagnetic resonance in thin films - cross-validation analysis of numerical solutions of Smit-Beljers equation. Application to GaMnAs,"(Dated: August 3, 2018) The new method of numerical analysis of experimental
ferromagnetic resonance (FMR) spectra in thin films is developed and applied to
(Ga,Mn)As thin films. Specifically, it starts with the finding of numerical
solutions of Smit-Beljers (SB) equation and continues with their subsequent
statistical analysis within the cross-validation (CV) approach taken from
machine learning techniques. As a result of this treatment, we are able to
reinterpret the available FMR experimental results in diluted ferromagnetic
semiconductor (Ga,Mn)As thin films with the resulting determination of
magnetocrystalline anisotropy constants. The outcome of CV analysis points out
that it is necessary to take into account terms describing the bulk cubic
anisotropy up to the fourth order to reproduce FMR experimental results for
(Ga,Mn)As correctly. This finding contradicts the wide-spread conviction in the
literature that only first order cubic anisotropy term is important in this
material. We also provide numerical values of these higher order cubic
anisotropy constants for (Ga,Mn)As thin films resulting from SB-CV approach.",1808.01347v1
2020-09-02,Effect of the Optical Pumping and Magnetic Field on the States of Phase Separation Domains in Eu_{0.8}Cr_{0.2}Mn_2O_5,"The effect of optical pumping and applied magnetic field on the
characteristics of ferromagnetic layers in one-dimensional superlattices is
studied. At low enough temperatures, these layers correspond to phase
separation domains in RMn_2O_5 and R_{0.8}Ce_{0.2}Mn_2O_5 multiferroics. The
formation of such domains occurs owing to the charge ordering of Mn^{3+} and
Mn^{4+} ions and to the finite probability for e_g electrons to tunnel between
these pairs of ions. The volume occupied by such superlattices is rather small,
and they can be treated as isolated ferromagnetic semiconductor
heterostructures, spontaneously formed in the host crystal. The sequences of
ferromagnetic resonances related to the superlattice layers in
Eu_{0.8}Ce_{0.2}Mn_2O_5 are studied. The characteristics of these resonances
give information on the properties of such layers. For the first time, it is
demonstrated that the optical pumping gives rise to a new metastable state of
superlattices, which can be recovered by the magnetic field cycling to the
state existing before the optical pumping. It is found that the superlattices
recovered by the magnetic field exist up to temperatures higher than those in
as-grown crystals.",2009.01057v1
2021-05-14,An energy harvesting technology controlled by ferromagnetic resonance,"We have successfully demonstrated electrical charging using the electromotive
force (EMF) generated in a ferromagnetic metal (FM) film under ferromagnetic
resonance (FMR). In the case of Ni80Fe20 films, electrical charge due to the
EMF generated under FMR can be accumulated in a capacitor; however, the amount
of charge is saturated well below the charging limit of the capacitor.
Meanwhile in the case of Co50Fe50, electrical charge generated under FMR can be
accumulated in a capacitor and the amount of charge increases linearly with the
FMR duration time. The difference between the Ni80Fe20 and Co50Fe50 films is
due to the respective magnetic field ranges for the FMR excitation. When the FM
films were in equivalent thermal states during FMR experiments, Co50Fe50 films
could maintain FMR in a detuned condition, while Ni80Fe20 films were outside
the FMR excitation range. The EMF generation phenomenon in an FM film under FMR
can be used an energy harvesting technology by appropriately controlling the
thermal conditions of the FM film.",2105.06606v1
2023-07-23,Unconventional spin polarization at Argon ion milled SrTiO3 Interfaces,"Interfacial two-dimensional electron gas (2DEG) formed at the perovskite-type
oxide, such as SrTiO3, has attracted significant attention due to its
properties of ferromagnetism, superconductivity, and its potential application
in oxide-based low-power consumption electronics. Recent studies have
investigated spin-to-charge conversion at the STO interface with different
materials, which could affect the efficiency of this 2DEG interface. In this
report, we presented an Ar^+ ion milling method to create a 2DEG at STO
directly by inducing oxygen vacancies. To quantify the spin-to-charge
conversion of this interface, we measured the angular-dependent spin-torque
ferromagnetic resonance (ST-FMR) spectra, revealing an unconventional spin
polarization at the interface of Argon ion-milled STO and NiFe. Furthermore, a
micromagnetic simulation for angular-dependent spin-torque ferromagnetic
resonance (ST-FMR) has been performed, confirming the large unconventional spin
polarization at the interface.",2307.12390v1
2024-03-25,Detection of spin pumping free of rectification and thermal artefacts in molecular-based ferromagnetic insulator V[TCNE]x~2,"The molecular-based ferrimagnetic insulator V(TCNE)x has gained recent
interest for efficient spin-wave excitation due to its low Gilbert damping
ratio a=4E-5, and narrow ferromagnetic resonance linewidth f=1Oe. Here we
report a clean spin pumping signal detected on V(TCNE)x/metal bilayer
structures, free from spin rectification or thermal artifacts. On-chip coupling
of microwave power is achieved via a coplanar waveguide to measure the in-plane
angle-dependence of the inverse spin-Hall effect under ferromagnetic resonance
conditions with respect to a constant external magnetic field. A signature of
pure spin current from V(TCNE)x is observed in both platinum and permalloy
metal layers, demonstrating the utility of V(TCNE)x for magnon spintronics
studies in molecule/solid-state heterostructures.",2403.16429v2
2002-01-18,Electron Paramagnetic Resonance Study of Phase Segregation in Nd$_{0.5}$Sr$_{0.5}$MnO$_3$,"We present results of an electron paramagnetic resonance (EPR) study of
Nd$_{1-x}$Sr$_x$MnO$_3$ with x = 0.5 across the paramagnetic to ferromagnetic,
insulator to metal transition at 260 K (T$_c$) and the antiferromagnetic,
charge ordering transition (T$_N$ = T$_{co}$) at 150 K. The results are
compared with those on Nd$_{0.45}$Sr$_{0.55}$MnO$_3$ which undergoes a
transition to a homogeneous A-type antiferromagnetic phase at T$_N$ = 230 K and
on La$_{0.77}$Ca$_{0.23}$MnO$_3$ which undergoes a transition to coexisting
ferromagnetic metallic and ferromagnetic insulating phases. For x = 0.5, the
EPR signals below T$_c$ consist of two Lorentzian components attributable to
the coexistence of two phases. From the analysis of the temperature dependence
of the resonant fields and intensities, we conclude that in the mixed phase
ferromagnetic and A-type antiferromagnetic (AFM) phases coexist. The x = 0.55
compound shows a single Lorentzian throughout the temperature range. The signal
persists for a few degrees below T_N. The behaviour of the A-type AFM phase is
contrasted with that of the two ferromagnetic phases present in
La$_{0.77}$Ca$_{0.23}$MnO$_3$. The comparison of behaviour of A-type AFM signal
observed in both Nd$_{0.5}$Sr$_{0.5}$MnO$_3$and
Nd$_{0.45}$Sr$_{0.55}$MnO$_3with the two FM phases of
La$_{0.77}$Ca$_{0.23}$MnO$_3$, vis-a-vis the shift of resonances with respect
to the paramagnetic phases and the behaviour of EPR intensity as a function of
temperature conclusively prove that the Nd$_{0.5}$Sr$_{0.5}$MnO$_3$undergoes
phase separation into A-type AFM and FM phases.",0201336v2
2017-07-27,Electron spin resonance for the detection of long-range spin nematic order,"In this paper we propose that electron spin resonance (ESR) measurements
enable us to detect the long-range spin nematic order. We show that the
frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by
the ferroquadrupolar order parameter together with other quantities. The
ferroquadrupolar order parameter is extractable from the angular dependence of
the frequency shift. In contrast, the antiferroquadrupolar order parameter is
usually invisible in the frequency shift. Instead, the long-range
antiferroquadrupolar order yields a characteristic resonance peak in the ESR
spectrum, which we call a magnon-pair resonance peak. This resonance
corresponds to the excitation of the bound magnon pair at the wave vector $\bm
k={\bm 0}$. Reflecting the condensation of bound magnon pairs, the field
dependence of the magnon-pair resonance frequency shows a singular upturn at
the saturation field. Moreover, the intensity of the magnon-pair resonance peak
shows a characteristic angular dependence and it vanishes when the magnetic
field is parallel to one of the axes that diagonalize the weak anisotropic
interactions. We confirm these general properties of the magnon-pair resonance
peak in the spin nematic phase by studying an $S=1$ bilinear-biquadratic model
on the square lattice in the linear flavor-wave approximation. In addition, we
argue applications to the $S=1/2$ frustrated ferromagnets and also the $S=1/2$
orthogonal dimer spin system SrCu$_2$(BO$_3$)$_2$, both of which are candidate
materials of spin nematics. Our theory for the antiferroquadrupolar ordered
phase is consistent with many features of the magnon-pair resonance peak
experimentally observed in the low-magnetization regime of
SrCu$_2$(BO$_3$)$_2$.",1707.08784v2
2004-07-16,"A Theoretical Study on Spin-Dependent Transport of ""Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet"" Junctions with 4-Valued Conductances","As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically
investigate multiple-valued (or multi-level) cell property, which is in
principle realized by sensing conductances of four states recorded with
magnetization configurations of two FMs; (up,up), (up,down), (down,up),
(down,down). In order to sense all the states, 4-valued conductances
corresponding to the respective states are necessary. We previously proposed
that 4-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2
junctions, where FM1 and FM2 have different spin polarizations, and the spacer
depends on spin [J. Phys.: Condens. Matter 15, 8797 (2003)]. In this paper, an
ideal SPS is considered as a single-wall armchair carbon nanotube encapsulating
magnetic atoms, where the nanotube shows on-resonance or off-resonance at the
Fermi level according to its length. The magnitude of the obtained 4-valued
conductances has an opposite order between the on-resonant nanotube and the
off-resonant one, and this property can be understood by considering electronic
states of the nanotube. Also, the magnetoresistance ratio between (up,up) and
(down,down) can be larger than the conventional one between parallel and
anti-parallel configurations.",0407439v1
2016-03-03,"Cantilever detected ferromagnetic resonance in thin Fe$_{50}$Ni$_{50}$, Co$_2$FeAl$_{0.5}$Si$_{0.5}$ and Sr$_2$FeMoO$_6$ films using a double modulation technique","In this work we introduce a new method of a ferromagnetic resonance (FMR)
detection from thin, nm-size, films. Our setup is based on the commercial
piezo-cantilever, used for atomic force microscopy. It has an option to rotate
the sample in the magnetic field and it operates up to the high microwave
frequencies of 160 GHz. Using our cantilever based FMR spectrometer we have
investigated a set of samples, namely quasi-bulk and 84 nm film
Co$_2$FeAl$_{0.5}$Si$_{0.5}$ samples, 16 nm Fe$_{50}$Ni$_{50}$ film and 150 nm
Sr$_2$FeMoO$_6$ film. The high frequency ferromagnetic resonance (FMR) response
from an extremely thin Fe$_{50}$Ni$_{50}$ film we have fitted with the
conventional model for the magnetization dynamics. The cantilever detected FMR
experiments on Sr$_2$FeMoO$_6$ film reveal an inability of the conventional
model to fit frequency and angular dependences with the same set of parameters,
which suggests that one has to take into account much more complicated nature
of the magnetization precession in the Sr$_2$FeMoO$_6$ at low temperatures and
high frequencies. Moreover, the complicated dynamics of the magnetization
apparent in all investigated samples is suggested by a drastic increase of the
linewidths with increasing microwave frequency, and by an emergence of the
second line with an opposite angular dependence.",1603.01142v1
2016-04-20,Resonance-based Detection of Magnetic Nanoparticles and Microbeads Using Nanopatterned Ferromagnets,"Biosensing with ferromagnet-based magnetoresistive devices has been dominated
by electrical detection of particle-induced changes to the devices' static
magnetic configuration. There are however potential advantages to be gained
from using field dependent, high frequency magnetization dynamics for magnetic
particle detection. Here we demonstrate the use of nano-confined ferromagnetic
resonances in periodically patterned magnetic films for the detection of
adsorbed magnetic particles with diameters ranging from 6 nm to 4 $\mu$m. The
nanopatterned films contain arrays of holes which can act as preferential
adsorption sites for small particles. Hole-localized particles act in unison to
shift the resonant frequencies of the various modes of the patterned layer with
shift polarities determined by the localization of each mode within the
nanopattern's repeating unit cell. The same polarity shifts are observed for a
large range of coverages, even when hole-localized particles are covered by
quasi-continuous particle sheets. For large particles however, preferential
adsorption no longer occurs, leading to resonance shifts with polarities which
are independent of the mode localization. Analogous shifts are seen in
continuous layers where, for small particles, the shift of the layer's
fundamental mode is typically about 10 times less than in patterned systems and
induced by relatively weak fields emanating beyond the particle in the
direction of the static applied field. This highlights the importance of having
confined modes consistently positioned with respect to nearby particles.",1604.05835v1
2020-01-27,Resonant thermal energy transfer to magnons in a ferromagnetic nanolayer,"Energy harvesting is a modern concept which makes dissipated heat useful by
transferring thermal energy to other excitations. Most of the existing
principles for energy harvesting are realized in systems which are heated
continuously, for example generating DC voltage in thermoelectric devices. Here
we present the concept of high-frequency energy harvesting where the dissipated
heat in a sample excites resonant magnons in a 5-nm thick ferromagnetic metal
layer. The sample is excited by femtosecond laser pulses with a repetition rate
of 10 GHz which results in temperature modulation at the same frequency with
amplitude ~0.1 K. The alternating temperature excites magnons in the
ferromagnetic nanolayer which are detected by measuring the net magnetization
precession. When the magnon frequency is brought onto resonance with the
optical excitation, a 12-fold increase of the amplitude of precession indicates
efficient resonant heat transfer from the lattice to coherent magnons. The
demonstrated principle may be used for energy harvesting in various nanodevices
operating at GHz and sub-THz frequency ranges.",2001.09732v2
2019-04-30,Tunable ferromagnetic resonance in coupled trilayers with crossed in-plane and perpendicular magnetic anisotropies,"A novel approach to tune the ferromagnetic resonance frequency of a soft
magnetic Ni$_{80}$Fe$_{20}$ (Permalloy = Py) film with in-plane magnetic
anisotropy (IMA) based on the controlled coupling to a hard magnetic
NdCo$_\text{x}$ film with perpendicular magnetic anisotropy (PMA) through a
non-magnetic Al spacer is studied. Using transverse magneto-optical Kerr effect
(TMOKE), alternating gradient magnetometry (AGM) as well as vector network
analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both
Co concentration and Al spacer thickness on the static and dynamic magnetic
properties of the coupled IMA/PMA system is investigated. Compared to a single
Py film, two striking effects of the coupling between IMA and PMA layers can be
observed in their FMR spectra. First, there is a significant increase in the
zero-field resonance frequency from 1.3 GHz up to 6.6 GHz, and second, an
additional frequency hysteresis occurs at low magnetic fields applied along the
hard axis. The maximum frequency difference between the frequency branches for
increasing and decreasing magnetic field is as high as 1 GHz, corresponding to
a tunability of about 20% at external fields of typically less than $\pm$70 mT.
The origin of the observed features in the FMR spectra is discussed by means of
magnetization reversal curves.",1904.13275v1
2002-09-11,Magnetic Anisotropy in La_0.8Sr_0.2MnO_3: Electron Spin Resonance,"We report on Ferromagnetic-Resonance experiments in a single crystal of
La_0.8Sr_0.2MnO_3 in the temperature range from 4 to 300 K. The observed
anisotropy of the resonance line changes on crossing the transition from the
orthorhombic O-phase to the rhombohedral R-phase at T~100 K and indicates a
reorientation of the spins at about 130 K.",0209257v1
2004-01-22,Spin fluctuations in the quasi-two dimensional Heisenberg ferromagnet GdI_2 studied by Electron Spin Resonance,"The spin dynamics of GdI_2 have been investigated by ESR spectroscopy. The
temperature dependences of the resonance field and ESR intensity are well
described by the model for the spin susceptibility proposed by Eremin et al.
[Phys. Rev. B 64, 064425 (2001)]. The temperature dependence of the resonance
linewidth shows a maximum similar to the electrical resistance and is discussed
in terms of scattering processes between conduction electrons and localized
spins.",0401415v1
2004-10-19,Zero-field splitting of Kondo resonances in a carbon nanotube quantum dot,"We present low-temperature electron transport measurements on a single-wall
carbon nanotube quantum dot exhibiting Kondo resonances at low temperature.
Contrary to the usual behavior for the spin-1/2 Kondo effect we find that the
temperature dependence of the zero bias conductance is nonmonotonic. In
nonlinear transport measurements low-energy splittings of the Kondo resonances
are observed at zero magnetic field. We suggest that these anomalies reflect
interactions between the nanotube and a magnetic (catalyst) particle. The
nanotube device may effectively act as a ferromagnetically contacted Kondo dot.",0410467v2
2007-09-20,Spin wave resonances in La_{0.7}Sr_{0.3}MnO_{3} films: measurement of spin wave stiffness and anisotropy field,"We studied magnetic field dependent microwave absorption in epitaxial
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films using an X-band Bruker ESR spectrometer. By
analyzing angular and temperature dependence of the ferromagnetic and spin-wave
resonances we determine spin-wave stiffness and anisotropy field. The spin-wave
stiffness as found from the spectrum of the standing spin-wave resonances in
thin films is in fair agreement with the results of inelastic neutron
scattering studies on a single crystal of the same composition [Vasiliu-Doloc
et al., J. Appl. Phys. \textbf{83}, 7343 (1998)].",0709.3204v2
2009-06-22,Kondo resonance narrowing in d- and f-electron systems,"By developing a simple scaling theory for the effect of Hund's interactions
on the Kondo effect, we show how an exponential narrowing of the Kondo
resonance develops in magnetic ions with large Hund's interaction. Our theory
predicts an exponential reduction of the Kondo temperature with spin S of the
Hund's coupled moment, a little-known effect first observed in d-electron
alloys in the 1960's, and more recently encountered in numerical calculations
on multi-band Hubbard models with Hund's interactions. We discuss the
consequences of Kondo resonance narrowing for the Mott transition in d-band
materials, particularly iron pnictides, and the narrow ESR linewidth recently
observed in ferromagnetically correlated f-electron materials.",0906.4107v1
2009-07-10,Measurement of Conduction Electron Polarization Via the Pairing Resonance,"We show that the pairing resonance in the Pauli-limited normal state of
ultra-thin superconducting Al films provides a spin-resolved probe of
conduction electron polarization in thin magnetic films. A
superconductor-insulator-ferromagnet tunneling junction is used to measure the
density of states in supercritical parallel magnetic fields that are well
beyond the Clogston-Chandresekhar limit, thus greatly extending the field range
of the tunneling density of states technique. The applicability and limitations
of using the pairing resonance as a spin probe are discussed.",0907.1800v1
2011-04-12,Interactions and magnetic moments near vacancies and resonant impurities in graphene,"The effect of electronic interactions in graphene with vacancies or resonant
scatterers is investigated. We apply dynamical mean-field theory in combination
with quantum Monte Carlo simulations, which allow us to treat
non-perturbatively quantum fluctuations beyond Hartree-Fock approximations. The
interactions narrow the width of the resonance and induce a Curie magnetic
susceptibility, signaling the formation of local moments. The absence of
saturation of the susceptibility at low temperatures suggests that the coupling
between the local moment and the conduction electrons is ferromagnetic.",1104.2207v1
2012-10-30,Microwave assisted resonant domain wall nucleation in permalloy nanowires,"We have designed a system to study microwave assisted domain wall nucleation
in permalloy nanowires. We find a substantial decrease in the nucleation field
when microwave fields are applied, in comparison to pulse fields. A clear
resonance peak is observed in the frequency dependence of the nucleation field,
which coincides with the uniform mode ferromagnetic resonance frequency. Owing
to the well-defined nucleation process, the switching field distribution is
small in contrast to previous reports. Our results show that localized
microwave field provides an efficient tool for injecting domain walls into
magnetic nanowires.",1210.7875v1
2015-07-16,Antiferromagentic resonance detected by DC voltages in MnF$_2$/Pt bilayers,"We performed coplanar waveguide-based broadband ferromagnetic resonance
experiments on the antiferromagnetic insulator MnF$_2$, while simultaneously
recording the DC voltage arising in a thin platinum film deposited onto the
MnF$_2$. The antiferromagnetic resonance is clearly reflected in both the
transmission through the waveguide as well as the DC voltage in the Pt strip.
The DC voltage remains largely unaffected by field reversal and thus presumably
stems from microwave rectification and/or heating effects. However, we identify
a small magnetic field orientation dependent contribution, compatible with
antiferromagnetic spin pumping theory.",1507.04490v1
2020-08-22,Pseudospin resonances reveal synthetic spin-orbit interaction,"We investigate a spin-full double quantum dot (DQD) coupled to the leads in a
pseudospin valve configuration. The interplay of interaction and interference
produces in the stability diagram a rich variety of resonances, modulated by
the system parameters. In presence of ferromagnetic leads and pseudospin
anisotropy, those resonances split, turn into dips and acquire a Fano shape
thus revealing a synthetic spin-orbit coupling induced on the DQD. A set of
rate equations derived for a minimal model captures those features. The model
accurately matches the numerical results obtained for the full system in the
framework of a generalized master equation and calculated within the
cotunneling approximation.",2008.09857v1
2019-05-16,Element-specific visualization of dynamic magnetic coupling in a Co/Py bilayer microstructure,"We present the element-specific and time resolved visualization of uniform
ferromagnetic resonance excitations of a Permalloy (Py) disk - Cobalt (Co)
stripe bilayer microstructure. The transverse high frequency component of the
resonantly excited magnetization is sampled in the ps regime by a combination
of ferromagnetic resonance (FMR) and scanning transmission X-ray microscopy
(STXM- FMR) recording snapshots of the local magnetization precession of Py and
Co with nanometer spatial resolution. The approach allows us to individually
image the resonant dynamic response of each element, and we find that angular
momentum is transferred from the Py disk to the Co stripe and vice versa at
their respective resonances. The integral (cavity) FMR spectrum of our sample
shows an unexpected additional third resonance. This resonance is observed in
the STXM-FMR experiments as well and our microscopic findings suggest that it
is governed by magnetic exchange between Py and Co, showing for the Co stripe a
difference in relative phase of the magnetization due to stray field influence.",1905.06772v6
2024-02-07,Anatomy of localized edge modes in laterally coupled waveguides,"We present a systematic micromagnetic study of standing spin-wave modes in
infinitely long Permalloy strips with rectangular cross-section. Using a
finite-element dynamic-matrix method, we first calculate the eigenfrequencies
and the corresponding eigenvectors (mode profiles), as a function of the
in-plane magnetic field applied across the strip. The ferromagnetic resonance
spectra is computed from the mode profiles, assuming a homogeneous
radio-frequency excitation, equivalently to an experimental ferromagnetic
resonance measurement. The investigation of the field-dependent mode profiles
enables for the classification of the observed resonances, here focusing mostly
on the true edge mode localized at the vicinity of strip edges. Furthermore, we
study the mode localization in pairs of 50-nm-thick Permalloy strips as a
function of the strip width and their lateral separation. For closely spaced
strips, the spatial profile of the quasi-uniform mode is substantially modified
due to a significant hybridization with the edge-localized standing spin-wave
modes of the neighbouring strip. We show that a wide-range-tunability of the
localized edge-mode resonances can be achieved with a precise control of the
magnetostatic coupling between the strips. Extreme sensitivity of the edge mode
frequency on the bias field demonstrates a potential of the edge resonances for
field sensing. Furthermore, for narrow strips (~100 nm in width), due to the
reduced number of the allowed confined modes, a field-controllable switching
between the resonances localized either in the strip center or at the edges of
the strips can be achieved.",2402.04715v1
2014-01-08,Dynamic exchange via spin currents in acoustic and optical modes of ferromagnetic resonance in spin-valve structures,"Two ferromagnetic layers magnetically decoupled by a thick normal metal
spacer layer can be, nevertheless, dynamically coupled via spin currents
emitted by the spin-pump and absorbed through the spin-torque effects at the
neighboring interfaces. A decrease of damping in both layers due to a partial
compensation of the angular momentum leakage in each layer was previously
observed at the coincidence of the two ferromagnetic resonances. In case of
non-zero magnetic coupling, such a dynamic exchange will depend on the mutual
precession of the magnetic moments in the layers. A difference in the linewidth
of the resonance peaks is expected for the acoustic and optical regimes of
precession. However, the interlayer coupling hybridizes the resonance responses
of the layers and therefore can also change their linewidths. The interplay
between the two mechanisms has never been considered before. In the present
work, the joint influence of the hybridization and non-local damping on the
linewidth has been studied in weakly coupled NiFe/CoFe/Cu/CoFe/MnIr spin-valve
multilayers. It has been found that the dynamic exchange by spin currents is
different in the optical and acoustic modes, and this difference is dependent
on the interlayer coupling strength. In contrast to the acoustic precession
mode, the dynamic exchange in the optical mode works as an additional damping
source. A simulation in the framework of the Landau-Lifshitz-Gilbert formalism
for two ferromagnetic layers coupled magnetically and by spin currents has been
done to separate the effects of the non-local damping from the resonance modes
hybridization. In our samples both mechanisms bring about linewidth changes of
the same order of magnitude, but lead to a distinctly different angular
behavior. The obtained results are relevant for a broad class of coupled
magnetic multilayers with ballistic regime of the spin transport.",1401.1672v1
1999-04-17,Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles,"We measure electron tunneling via discrete energy levels in ferromagnetic
cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. Due
to magnetic anisotropy, the energy of each tunneling resonance shifts as an
applied magnetic field rotates the particle's magnetic moment. We see both
spin-increasing and decreasing tunneling transitions, but we do not observe the
spin degeneracy at small magnetic fields seen previously in non-magnetic
materials. The tunneling spectrum is denser than predicted for independent
electrons, possibly due to spin-wave excitations.",9904248v2
1999-08-26,Percolative phase separation induced by nonuniformly distributed excess oxygens,"The zero-field $^{139}$La and $^{55}$Mn nuclear magnetic resonances were
studied in $\rm La_{0.8}Ca_{0.2}MnO_{3+\delta}$ with different oxygen
stoichiometry $\delta$. The signal intensity, peak frequency and line
broadening of the $^{139}$La NMR spectrum show that excess oxygens have a
tendency to concentrate and establish local ferromagnetic ordering around
themselves. These connect the previously existed ferromagnetic clusters
embedded in the antiferromagnetic host, resulting in percolative conduction
paths. This phase separation is not a charge segregation type, but a
electroneutral type. The magnetoresistance peak at the temperature where
percolative paths start to form provides a direct evidence that phase
separation is one source of colossal magnetoresistance effect.",9908371v1
2000-05-27,Complex orbital state in manganites,"The $e_g$-orbital states with complex coefficients of the linear combination
of $x^2-y^2$ and $3z^2-r^2$ are studied for the ferromagnetic state in doped
manganites. Especially the focus is put on the competition among uniform
complex, staggered complex, and real orbital states. As the hole-doping $x$
increases, the real, the canted complex, and the staggered complex orbital
states appears successively. Uniform complex state analoguous to Nagaoka
ferromagnet does not appear. These complex states can be expressed as a
resonating state among the planer orbitals as the orbital liquid, accompanied
by no Jahn-Teller distortion.",0005482v1
2002-04-16,Spin accumulation in ferromagnetic single-electron transistors in the cotunneling regime,"We propose a new method of direct detection of spin accumulation, which
overcomes problems of previous measurement schemes. A spin dependent current in
a single-electron transistor with ferromagnetic electrodes leads to spin
accumulation on the metallic island. The resulting spin-splitting of the
electrochemical potentials of the island, because of an additional shift by the
charging energy, can be detected from the spacing between two resonances in the
current-voltage characteristics. The results were obtained in the framework of
a real-time diagrammatic approach which allows to study higher order
(co-)tunneling processes in the strong nonequlibrium situation.",0204354v1
2004-03-18,Low Losses Left Handed Materials Using Metallic Magnetic Cylinders,"We discuss materials based on arrays of metallic magnetic cylindrical
structures near ferromagnetic resonance with applied magnetic fields at
microwave frequencies. We have found that the materials have a negative
refraction index when the appropriate structure is chosen. Numerical FDTD
simulations were performed, after a very large number of geometries were swept.
The simulations reveal that only ferromagnetic cylinders, with diameters of 0.1
cm and 0.5 cm apart, and with periodic or random configurations, are
left-handed materials with very small losses; i.e. with transmitivity
practically unity or no losses.",0403479v1
2004-06-21,Spin-Polarized Transprot through Double Quantum Dots,"We investigate spin-polarized transport phenomena through double quantum dots
coupled to ferromagnetic leads in series. By means of the slave-boson
mean-field approximation, we calculate the conductance in the Kondo regime for
two different configurations of the leads: spin-polarization of two
ferromagnetic leads is parallel or anti-parallel. It is found that transport
shows some remarkable properties depending on the tunneling strength between
two dots. These properties are explained in terms of the Kondo resonances in
the local density of states.",0406490v1
2005-01-19,Maximal entanglement of two spinor Bose-Einstein condensates,"Starting with two weakly-coupled anti-ferromagnetic spinor condensates, we
show that by changing the sign of the coefficient of the spin interaction,
$U_{2}$, via an optically-induced Feshbach resonance one can create an
entangled state consisting of two anti-correlated ferromagnetic condensates.
This state is maximally entangled and a generalization of the Bell state from
two anti-correlated spin-1/2 particles to two anti-correlated spin$-N/2$ atomic
samples, where $N$ is the total number of atoms.",0501471v1
2005-07-15,Tunnel magnetoresistance of quantum dots coupled to ferromagnetic leads in the sequential and cotunneling regimes,"We study electronic transport through quantum dots weakly coupled to
ferromagnetic leads with collinear magnetization directions. Tunneling
contributions of first and second order in the tunnel-coupling strength are
taken into account. We analyze the tunnel magnetoresistance (TMR) for all
combinations of linear and nonlinear response, at or off resonance, with an
even or odd dot-electron number. Different mechanisms for transport and spin
accumulation the various regimes give rise to different TMR behavior.",0507357v1
2005-10-25,Resonant peak in the density of states in the normal metal / diffusive ferromagnet / superconductor junctions,"The conditions for the formation of zero-energy peak in the density of states
(DOS) in the normal metal / insulator / diffusive ferromagnet / insulator /
s-wave superconductor (N/I/DF/I/S) junctions are studied by solving the Usadel
equations. The DOS of the DF is calculated in various regimes for different
magnitudes of the resistance, Thouless energy and the exchange field of the DF,
as well as for various resistances of the insulating barriers. The conditions
for the DOS peak are formulated for the cases of weak proximity effect (large
resistance of the DF/S interface) and strong proximity effect (small resistance
of the DF/S interface).",0510657v1
2006-02-03,Low Ghz loss in sputtered epitaxial Fe,"We show that sputtered, pure epitaxial iron films can have high-frequency
loss as low as, or lower than, any known metallic ferromagnetic
heterostructure. Minimum 34 Ghz ferromagnetic resonance (FMR) linewidths of 41
Oe are demonstrated, some ~ 5-10 % lower than the previous minimum reported for
molecular beam epitaxially (MBE) deposited Fe. Intrinsic and extrinsic damping
have been separated over 0-40 Ghz, giving a lower bound for intrinsic LL(G)
relaxation rates of lambda or G = 85 MHz (alpha = 0.0027) and extrinsic 50 Mhz.
Swept frequency measurements indicate the potential for integrated frequency
domain devices with Q>100 at 30-40 Ghz.",0602094v1
2006-09-06,"Magnitude and crystalline anisotropy of hole magnetization in (Ga,Mn)As","Theory of hole magnetization Mc in zinc-blende diluted ferromagnetic
semiconductors is developed relaxing the spherical approximation of earlier
approaches. The theory is employed to determine Mc for (Ga,Mn)As over a wide
range of hole concentrations and a number of crystallographic orientations of
Mn magnetization. It is found that anisotropy of Mc is practically negligible
but the obtained magnitude of Mc is significantly greater than that determined
in the spherical approximation. Its sign and value compares favorably with the
results of available magnetization measurements and ferromagnetic resonance
studies.",0609128v1
2006-10-06,Significant enhancement of room temperature ferromagnetism in surfactant coated polycrystalline Mn doped ZnO particles,"We report a surfactant assisted synthesis of Mn doped ZnO polycrystalline
samples showing robust room temperature ferromagnetism as characterized by
X-ray diffraction analysis, Transmission Electron Microscopy, Electron
Paramagnetic Resonance and DC magnetization mearurements. This surfactant
assisted synthesis method, developed by us, is found to be highly reproducible.
Further, it can also be extended to the synthesis of other transition metal
doped ZnO.",0610170v1
2003-08-14,Dynamic Domains in Strongly Driven Ferromagnetic Films,"The spatiotemporal structure formation problem is investigated in the region
far above the transverse ferromagnetic resonance instability. The
investigations are based on the dissipative Landau-Lifshitz equation and have
been performed on a model which takes external fields, isotropic exchange
fields, anisotropy fields and the demagnetizing part of the dipolar field into
consideration. The numerical simulations for these models exhibit stationary
domain structure in the rotating frame. Employing analytical methods and
simplifying the model, certain features, such as the magnetization within the
domains and the proportion of the system in each domain, are described
analytically.",0308017v1
2007-10-11,Direct current voltage induced by microwave signal in a ferromagnetic wire,"Experimental results of rectification of a constant wave radio frequency (RF)
current flowing in a single-layered ferromagnetic wire are presented. We show
that a detailed external magnetic field dependence of the RF current induced a
direct-current voltage spectrum. The mechanism of the rectification is
discussed in a term of the spin transfer torque, and the rectification is
closely related to resonant spin wave excitation with the assistant of the
spin-polarized RF current. The micromagnetic simulation taking into account the
spin transfer torque provides strong evidence which supports the generation of
spin wave excitation by the RF current.",0710.2172v1
2007-12-17,Proximity effect-assisted absorption of spin currents in superconductors,"The injection of pure spin current into superconductors by the dynamics of a
ferromagnetic contact is studied theoretically. Taking into account suppression
of the order parameter at the interfaces (inverse proximity effect) and the
energy-dependence of spin-flip scattering, we determine the
temperature-dependent ferromagnetic resonance linewidth broadening. Our results
agree with recent experiments in Nb|permalloy bilayers [C. Bell et al.,
arXiv:cond-mat/0702461].",0712.2814v1
2008-01-18,Selective Spin Injection Controlled by Electrical way in Ferromagnet/Quantum Dot/Semiconductor system,"Selective and large polarization of current injected into semiconductor (SC)
is predicted in Ferromagnet (FM)/Quantum Dot (QD)/SC system by varying the gate
voltage above the Kondo temperature. In addition, spin-dependent Kondo effect
is also revealed below Kondo temperature. It is found that Kondo resonances for
up spin state is suppressed with increasing of the polarization P of the FM
lead. While the down one is enhanced. The Kondo peak for up spin is disappear
at P=1.",0801.2922v1
2008-10-23,Magnetic moment manipulation by a Josephson current,"We consider a Josephson junction where the weak-link is formed by a
non-centrosymmetric ferromagnet. In such a junction, the superconducting
current acts as a direct driving force on the magnetic moment. We show that the
a.c. Josephson effect generates a magnetic precession providing then a feedback
to the current. Magnetic dynamics result in several anomalies of current-phase
relations (second harmonic, dissipative current) which are strongly enhanced
near the ferromagnetic resonance frequency.",0810.4286v3
2009-03-23,Multi-terminal spin-dependent transport in ballistic carbon nanotubes,"We study theoretically nonlocal spin transport in a ballistic carbon nanotube
contacted to two ferromagnetic leads and two normal-metal leads. When the
magnetizations of the two ferromagnets are changed from a parallel to an
antiparallel configuration, the circuit shows a hysteretic behavior which is
specific to the few-channel regime. In the coherent limit, the amplitude of the
magnetic signals is strongly enhanced due to resonance effects occurring inside
the nanotube. Our calculations pave the way for experiments on low-dimensional
nonlocal spin transport, which should give results remarkably different from
the experiments realized so far in the multichannel diffusive incoherent
regime.",0903.3813v1
2010-03-19,Dynamics of magnetization on the topological surface,"We investigate theoretically the dynamics of magnetization coupled to the
surface Dirac fermions of a three dimensional topological insulator, by
deriving the Landau-Lifshitz-Gilbert (LLG) equation in the presence of charge
current. Both the inverse spin-Galvanic effect and the Gilbert damping
coefficient $\alpha$ are related to the two-dimensional diagonal conductivity
$\sigma_{xx}$ of the Dirac fermion, while the Berry phase of the ferromagnetic
moment to the Hall conductivity $\sigma_{xy}$. The spin transfer torque and the
so-called $\beta$-terms are shown to be negligibly small. Anomalous behaviors
in various phenomena including the ferromagnetic resonance are predicted in
terms of this LLG equation.",1003.3769v1
2010-09-08,The temperature-dependent magnetization profile across an epitaxial bilayer of ferromagnetic La2/3Ca1/3MnO3 and superconducting YBa2Cu3O7-d,"Epitaxial bilayers of ferromagnetic La2/3Ca1/3MnO3 (LCMO) and superconducting
YBa2Cu3O7-d (YBCO) have been grown on single-crystalline SrTiO3 (STO)
substrates by pulsed laser deposition. The Manganese magnetization profile
across the FM layer has been determined with high spatial resolution at low
temperatures by X-ray resonant magnetic reflectivity (XRMR). It is found that
not only the adjacent superconductor but also the substrate underneath
influences the magnetization of the LCMO film at the interfaces at low
temperatures. Both effects can be investigated individually by XRMR.",1009.1553v1
2010-09-29,AC Josephson Effect Induced by Spin Injection,"Pure spin currents can be injected and detected in conductors via
ferromagnetic contacts. We consider the case when the conductors become
superconducting. A DC pure spin current flowing in one superconducting wire
towards another superconductor via a ferromagnet contact induces AC voltage
oscillations caused by Josephson tunneling of condensate electrons.
Quasiparticles simultaneously counterflow resulting in zero total electric
current through the contact. The Josephson oscillations can be accompanied by
Carlson-Goldman collective modes leading to a resonance in the voltage
oscillation amplitude.",1009.5790v1
2010-11-16,Negative refraction in natural ferromagnetic metals,"It is generally believed that Veselago's criterion for negative refraction
cannot be fulfilled in natural materials. However, considering imaginary parts
of the permittivity ({\epsilon}) and permeability ({\mu}) and for metals at not
too high frequencies the general condition for negative refraction becomes
extremely simple: Re({\mu}) < 0 --> Re(n) < 0. Here we demonstrate
experimentally that in such natural metals as pure Co and FeCo alloy the
negative values of the refractive index are achieved close to the frequency of
the ferromagnetic resonance. Large values of the negative refraction can be
obtained at room temperature and they can easily be tuned in moderate magnetic
fields.",1011.3663v1
2011-01-11,Magnon Pumping by a Time-Dependent Transverse Magnetic Field in Ferromagnetic Insulators,"The magnon pumping effect in ferromagnetic insulators under an external
time-dependent transverse magnetic field is theoretically studied. Generation
of a magnon current is discussed by calculating the magnon source term in the
spin continuity equation. This term represents the non-conservation of magnons
arising from an applied transverse magnetic field. The magnon source term has a
resonance structure as a function of the angular frequency of the transverse
field, and this fact is useful to enhance the pumping effect.",1101.2137v2
2011-06-17,Current effect on magnetization oscillations in a ferromagnet - antiferromagnet junction,"Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
junction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration.",1106.3519v1
2012-07-13,Magnetic relaxation in bilayers of yttrium iron garnet/platinum due to the dynamic coupling at the interface,"We show that in ferromagnetic (FM)/normal metal (NM) bilayers the dynamic
coupling at the interface transfers an additional magnetic relaxation from the
heavily damped motion of the conduction electron spins in the NM layer to the
FM spins. While the FM relaxation rates due to two-magnon scattering and spin
pumping decrease rapidly with increasing FM film thickness, the damping due to
the dynamic coupling does not depend on the FM film thickness. The proposed
mechanism explains the very large broadening of ferromagnetic resonance lines
in thick films of yttrium iron garnet after deposition of a Pt layer.",1207.3330v1
2012-07-13,Surface-induced Magnetism Fluctuations in Single Crystal of NiBi3 Superconductor,"We report anistropy in superconducting and normal state of NiBi3 single
crystals with Tc = 4.06 K. The magnetoresistance results indicate the absence
of scattering usually associated with ferromagnetic metals, suggesting the
absence of bulk long range magnetic order below 300 K. However, the electron
spin resonance results demonstrate that ferromagnetism fluctuations exist on
the surface of the crystal below 150K.",1207.3345v1
2012-08-10,Phase Separation in Mixtures of Repulsive Fermi Gases Driven by Mass Difference,"We show that phase separation must occur in a mixture of fermions with
repulsive interaction if their mass difference is sufficiently large. This
phenomenon is highly dimension-dependent. Consequently, the density profiles of
phase separated 3d mixtures are very different from those in 1d. Noting that
the ferromagnetic transition of a spin-1/2 repulsive Fermi gas is the equal
mass limit of the phase separation in mixtures, we show from the Bethe Ansatz
solution that a ferromagnetic transition will take place in the scattering
states when the repulsive interaction passes through resonance and becomes
attractive.",1208.2211v2
2012-08-31,On the interpretation of the angular dependence of the FMR spectrum in heterogeneous ferromagnetic thin films,"We demonstrate that a multi-peak FMR spectrum, with lines corresponding to
resonance in different ferromagnetic regions of a heterogeneous thin-film
sample, can collapse to a single-peak spectrum if there exists a particular
field configuration, or the configuration of the external magnetic field with
respect to the film surface, in which $dH_{\text{res}}/dM_{\text{eff}}=0$
within the region magnetically dominating in the sample.",1208.6573v1
2012-10-18,Enhanced Inverse Spin-Hall Effect in Ultrathin Ferromagnetic/Normal Metal Bilayers,"We measure electrically detected ferromagnetic resonance in microdevices
patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification
voltages are observed and distinguished via their angular dependence. The
spin-pumping voltage shows an unexpected increase as the cobalt thickness is
reduced below 2 nm. This enhancement allows more efficient conversion of spin
to charge current and motivates a theory modelling the dependence of impurity
scattering on surface roughness.",1210.5230v1
2015-07-13,Effective 90-degree magnetization rotation in Co2FeAl thin film/Piezoelectric system probed by microstripline ferromagnetic,"Microstripline ferromagnetic resonance technique has been used to study the
indirect magnetoelectric coupling occurring in an artificial magnetoelectric
heterostructure consisting of a magnetostrictive thin film cemented onto a
piezoelectric actuator. Two different modes (sweep-field and sweep-frequency
modes) of this technique have been employed to quantitatively probe the
indirect magnetoelectric coupling and to observe a voltage induced
magnetization rotation (of 90 degree). This latter has been validated by the
experimental frequency variation of the uniform mode and by the amplitude of
the sweep-frequency spectra.",1507.03308v1
2016-03-10,Resonant excitation of the spin-wave current in hybrid nanostructures,"Using the non-equilibrium statistical operator method (NSO), we have
investigated the spin transport through the interface in a
semiconductor/ferromagnetic insulator hybrid structure. We have analyzed the
approximation of effective parameters, when each of the considered subsystems
(conduction electrons, magnons, and phonons) is characterized by its effective
temperature. We have constructed the macroscopic equations, describing the
spin-wave current caused by both resonantly excited spin system of conduction
electrons and by an inhomogeneous thermal field in the ferromagnetic insulator.",1603.03207v1
2016-10-15,Spin excitations in an all-organic double quantum dot molecule,"We realize a strongly coupled double quantum dot in a single all-organic
molecule by introducing a non-conjugated bridge in between two identical
conjugated moieties. Spin-1/2 Kondo and Kondo enhanced low-energy excitations
for respectively the odd and even electron occupation are observed in
off-resonant transport. The ground state in the even occupation can be the
singlet or the triplet state varying between samples. This observation suggests
that both anti-ferromagnetic and ferromagnetic interactions between spins are
of the same order of magnitude.",1610.04715v1
2016-11-14,Low-temperature evolution of the spectral weight of a spin-up carrier moving in a ferromagnetic background,"We derive the lowest-temperature correction to the self-energy of a spin-up
particle injected in a ferromagnetic background. The background is modeled with
both Heisenberg and Ising Hamiltonians so that differences due to gapless vs.
gapped magnons can be understood. Beside the expected thermal broadening of the
quasiparticle peak as it becomes a resonance inside a continuum, we also find
that spectral weight is transferred to regions lying outside this continuum. We
explain the origin of this spectral weight transfer and its low-temperature
evolution.",1611.04575v1
2009-12-17,Quantum-level control in a III-V-based ferromagnetic-semiconductor heterostructure with a GaMnAs quantum well and double barriers,"We investigate the spin-dependent tunneling properties in a three-terminal
III-V-based ferromagnetic-semiconductor heterostructure with a 2.5-nm-thick
GaMnAs quantum well (QW) and double barriers. We successfully control the
quantum levels and modulate the spin-dependent current with varying the voltage
of the electrode connected to the GaMnAs QW. Our results will open up a new
possibility for realizing three-terminal spin resonant-tunneling devices.",0912.3409v1
2013-09-10,Spin rectification induced by dynamical Hanle effect,"Dynamic response of spin accumulation to a time-dependent magnetic field has
been investigated in a ferromagnetic/nonmagnetic bilayer under ferromagnetic
resonance. In this system, magnetization precession driven by a microwave
generates direct-current (dc) and alternate-current (ac) spin accumulation in
the nonmagnetic layer by the spin pumping. The ac spin accumulation is coupled
with the microwave magnetic field through a dynamical Hanle spin precession,
giving rise to rectified spin accumulation comparable with the dc spin
accumulation directly generated by the spin pumping.",1309.2365v1
2019-12-05,Spin pumping into a spin glass material,"Spin pumping is a recently established means for generating a pure spin
current, whereby spins are pumped from a magnet into the adjacent target
material under the ferromagnetic resonance condition. We theoretically
investigate the spin pumping from an insulating ferromagnet into spin glass
materials. Combining a dynamic theory of spin glasses with the linear-response
formulation of the spin pumping, we calculate temperature dependence of the
spin pumping near the spin glass transition. The analysis predicts that a
characteristic peak appears in the spin pumping signal, reflecting that the
spin fluctuations slow down upon the onset of spin freezing.",1912.02337v2
2021-08-13,Coupling the Higgs mode and ferromagnetic resonance in spin-split superconductors with Rashba spin-orbit coupling,"We consider the Higgs mode at nonzero momentum in superconductors and
demonstrate that in the presence of Rashba spin-orbit coupling, it couples
linearly with an external exchange field. The Higgs-spin coupling dramatically
modifies the spin susceptibility near the superconducting critical temperature
and consequently enhances the spin pumping effect in a ferromagnetic
insulator/superconductor bilayer system. We show that this effect can be
detected by measuring the magnon-induced voltage generated by the inverse spin
Hall effect.",2108.06202v2
2022-02-05,Gyromagnetic bifurcation in a levitated ferromagnetic particle,"We examine the mechanical rotation of a levitated magnetic particle that is
induced by ferromagnetic resonance under microwave irradiation. We show that
two stable solutions appear in a certain range of parameters by bifurcation
when the rotation frequency is comparable to the microwave frequency. This
phenomenon originates from the coexistence of the Barnett and the Einstein-de
Haas effects. We also reveal that this measurement is sensitive to the strength
of the spin-rotation coupling. Our work provides a platform for accessing a
microscopic relaxation process from spin to macroscopic rotation.",2202.02461v2
2022-11-09,Giant efficiency of long-range orbital torque in Co/Nb bilayers,"We report unambiguously experimental evidence of a strong orbital current in
Nb films with weak spin-orbit coupling via the spin-torque ferromagnetic
resonance (ST-FMR) spectrum for Fe/Nb and Co/Nb bilayers. The sign change of
the damping-like torque in Co/Nb demonstrates a large spin-orbit correlation
and thus great efficiency of orbital torque in Co/Nb. By studying the
efficiency as a function of the thickness of Nb sublayer, we reveal a long
orbital diffusion length (~3.1 nm) of Nb. Further planar Hall resistance (PHE)
measurements at positive and negative applying current confirm the nonlocal
orbital transport in ferromagnetic-metal/Nb heterostructures.",2211.04809v1
2023-03-02,Spin Pumping into Carbon Nanotubes,"We theoretically study spin pumping from a ferromagnetic insulator (FI) into
a carbon nanotube (CNT). By employing the bosonization method, we formulate the
Gilbert damping induced by the FI/CNT junction, which can be measured by
ferromagnetic resonance. We show that the increase in the Gilbert damping has a
temperature dependence characteristic of a Luttinger liquid and is highly
sensitive to the Luttinger parameter of the spin sector for a clean interface.
We also discuss the experimental relevance of our findings based on numerical
estimates, using realistic parameters.",2303.01343v2
2023-08-23,Parallel simulation of the magnetic moment reversal within the $φ_0$-Josephson junction model,"Periodic structure of the magnetization reversal (MR) domains is studied
within the superconductor-ferromagnetic-superconductor $\phi_0$-junction model.
The model is described by the Cauchy problem for the system of nonlinear
ordinary equations which is numerically solved by means of the 2-step
Gauss-Legendre method. Two versions of parallel implementation on the basis of
MPI and OpenMP techniques have been developed. Efficiency of both versions is
confirmed by test calculations. An effect of frequency of ferromagnetic
resonance on the configuration of MR domains has been investigated.",2308.11996v1
2023-11-10,Observation of the out-of-plane orbital antidamping-like torque,"The out-of-plane antidamping-like orbital torque fosters great hope for
high-efficiency spintronic devices. Here we report experimentally the
observation of out-of-plane antidamping-like torque that could be generated by
z-polarized orbital current in ferromagnetic-metal/oxidized Cu bilayers, which
is presented unambiguously by the magnetic field angle dependence of
spin-torque ferromagnetic resonance signal. The oxidized Cu thickness
dependence of orbital torque ratios highlights the interfacial effect would be
responsible for the generation of orbital current. Besides that, the oxidized
Cu thickness dependence of damping parameter further proves the observation of
antidamping-like torque. This result contributes to enriching the
orbital-related theory of the generation mechanism of the orbital torque.",2311.05868v1
2023-10-13,Electronic structure of CrO$_2$ probed by NMR and DFT,"Electronic structure of ferromagnetic half-metal CrO$_2$ was studied by means
of 53Cr nuclear magnetic resonance (NMR) spectroscopy and density functional
theory (DFT). The measured NMR spectrum consists of three distinct spectral
lines and is interpreted as a triplet arising due to electric quadrupole
interaction. The observed NMR parameters agree well with those obtained from
electronic structure calculations, corresponding to the presence of Cr$^{4+}$
with fully occupied localized dxy singlet and partially occupied degenerated
dxz and dyz states, as required by ferromagnetic double exchange mechanism.
With high accuracy the orbital occupations and valence states of all Cr atoms
within the CrO$_2$ structure are found uniform.",2311.12846v1
2012-12-21,Shot noise of spin current and spin transfer torque,"We report the theoretical investigation of noise spectrum of spin current and
spin transfer torque for non-colinear spin polarized transport in a spin-valve
device which consists of normal scattering region connected by two
ferromagnetic electrodes. Our theory was developed using non-equilibrium
Green's function method and general non-linear $S^\sigma-V$ and $S^\tau-V$
relations were derived as a function of angle $\theta$ between magnetization of
two leads. We have applied our theory to a quantum dot system with a resonant
level coupled with two ferromagnetic electrodes. It was found that for the MNM
system, the auto-correlation of spin current is enough to characterize the
fluctuation of spin current. For a system with three ferromagnetic layers,
however, both auto-correlation and cross-correlation of spin current are needed
to characterize the noise spectrum of spin current. Furthermore, the spin
transfer torque and the torque noise were studied for the MNM system. For a
quantum dot with a resonant level, the derivative of spin torque with respect
to bias voltage is proportional to $\sin\theta$ when the system is far away
from the resonance. When the system is near the resonance, the spin transfer
torque becomes non-sinusoidal function of $\theta$. The derivative of noise
spectrum of spin transfer torque with respect to the bias voltage $N_\tau$
behaves differently when the system is near or far away from the resonance.
Specifically, the differential shot noise of spin transfer torque $N_\tau$ is a
concave function of $\theta$ near the resonance while it becomes convex
function of $\theta$ far away from resonance. For certain bias voltages, the
period $N_\tau(\theta)$ becomes $\pi$ instead of $2\pi$. For small $\theta$, it
was found that the differential shot noise of spin transfer torque is very
sensitive to the bias voltage and the other system parameters.",1212.5474v1
2008-08-06,Electron spin resonance in Kondo systems,"We calculate the dynamical spin response of Kondo impurity and Kondo lattice
systems within a semiphenomenological Fermi liquid description, at low
temperatures $T<T_K$, the Kondo temperature, and low magnetic fields $B \ll k_B
T_K/g\mu_B$. Fermi liquid parameters are determined by comparison (i) with
microscopic theory (numerical renormalization group) for the impurity model and
(ii) with experiment for the lattice model. We find in the impurity case that
the true impurity spin resonance has a width of the order of $T_K$ and
disappears altogether if the $g$-factors of impurity spin and conduction
electron spin are equal. However, there is an impurity-induced resonance
contribution at the conduction electron resonance. The latter is broadened by
spin lattice relaxation and is usually unobservable. In contrast, for the
Anderson lattice in the Kondo regime we find a \textit{sharp} ESR resonance
line only slightly shifted from the local resonance and broadened by spin
lattice relaxation, the latter significantly reduced by both the effects of
heavy fermion physics and ferromagnetic fluctuations. We conjecture that our
findings explain the sharp ESR-lines recently observed in several heavy fermion
compounds.",0808.0892v2
2016-07-11,Triple-resonant Brillouin light scattering in magneto-optical cavities,"An enhancement in Brillouin light scattering of optical photons with magnons
is demonstrated in magneto-optical whispering gallery mode resonators tuned to
a triple resonance point. This occurs when both the input and output optical
modes are resonant with those of the whispering gallery resonator, with a
separation given by the ferromagnetic resonance (FMR) frequency. The
identification and excitation of specific optical modes allows us to gain a
clear understanding of the mode-matching conditions. A selection rule due to
wavevector matching leads to an intrinsic single-sideband excitation. Strong
suppression of one sideband is essential for one-to-one frequency mapping in
coherent optical-to-microwave conversion.",1607.02985v2
2023-04-04,Experimental Evidence of Amplitude-Dependent Surface Wave Dispersion via Nonlinear Contact Resonances,"In this letter, we provide an experimental demonstration of
amplitude-dependent dispersion tuning of surface acoustic waves interacting
with nonlinear resonators. Leveraging the similarity between the dispersion
properties of plate edge waves and surface waves propagating in a semi-infinite
medium, we use a setup consisting of a plate with a periodic arrangement of
bead-magnet resonators along one of its edges. Nonlinear contact between the
ferromagnetic beads and magnets is exploited to realize nonlinear local
resonance effects. First, we experimentally demonstrate the nonlinear softening
nature and amplitude-dependent dynamics of a single bead-magnet resonator on
both rigid and compliant substrates. Next, the dispersion properties of the
system in the linear regime are investigated. Finally, we demonstrate how the
interplay of nonlinear local resonances with plate edge waves gives rise to
amplitude-dependent dispersion properties. The findings will inform the design
of more versatile surface acoustic wave devices that can passively adapt to
loading conditions.",2304.01494v2
2017-08-08,Spin-orbit-torque driven magnetoimpedance in Pt-layer/magnetic-ribbon heterostructures,"When a flow of electron passes through a paramagnetic layer with strong
spin-orbit-coupling such as platinum (Pt), a net spin current is produced via
spin Hall effect (SHE). This spin current can exert a torque on the
magnetization of an adjacent ferromagnetic layer which can be probed via
magnetization dynamic response, e.g. spin-torque ferromagnetic resonance
(ST-FMR). Nevertheless, that effect in lower frequency magnetization dynamic
regime (MHz) where skin effect occurs in high permeability ferromagnetic
conductors namely the magneto-impedance (MI) effect can be fundamentally
important which has not been studied so far. Here, by utilizing the MI effect
in magnetic-ribbon/Pt heterostructure with high magnetic permeability that
allows the ac current effectively confined at the skin depth of ~100 nm
thickness, the effect of spin-orbit-torque (SOT) induced by the SHE probed via
MI measurement is investigated. We observed a systematic MI frequency shift
that increases by increasing the applied current amplitude and thickness of the
Pt layer (varying from 0 nm to 20 nm). In addition, the role of Pt layer in
ribbon/Pt heterostructure is evaluated with ferromagnetic resonance (FMR)
effect representing standard Gilbert damping increase as the result of presence
of the SHE. Our results unveil the role of SOT in dynamic control of the
transverse magnetic permeability probed with impedance spectroscopy as useful
and valuable technique for detection of future SHE devices.",1708.02402v2
2018-11-19,"Electronic structure of the novel high-$T_{\rm C}$ ferromagnetic semiconductor (Ga,Fe)Sb: x-ray magnetic circular dichroism and resonance photoemission spectroscopy studies","The electronic structure and the magnetism of the novel ferromagnetic
semiconductor (Ga,Fe)Sb, whose Curie temperature $T_{\rm C}$ can exceed room
temperature, were investigated by means of x-ray absorption spectroscopy (XAS),
x-ray magnetic circular dichroism (XMCD), and resonance photoemission
spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra
suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic
moments deduced using XMCD sum rules were found to be large, indicating that
there is a considerable amount of 3$d^{6}$ contribution to the ground state of
Fe. From RPES, we observed a strong dispersive Auger peak and non-dispersive
resonantly enhanced peaks in the valence-band spectra. The latter is a
fingerprint of the correlated nature of Fe 3$d$ electrons, whereas the former
indicates their itinerant nature. It was also found that the Fe 3$d$ states
have finite contribution to the DOS at the Fermi energy. These states
presumably consisting of majority-spin $p$-$d$ hybridized states or
minority-spin $e$ states would be responsible for the ferromagnetic order in
this material.",1811.07467v1
2016-11-17,Inductive detection of field-like and damping-like AC inverse spin-orbit torques in ferromagnet/normal metal bilayers,"Functional spintronic devices rely on spin-charge interconversion effects,
such as the reciprocal processes of electric field-driven spin torque and
magnetization dynamics-driven spin and charge flow. Both damping-like and
field-like spin-orbit torques have been observed in the forward process of
current-driven spin torque and damping-like inverse spin-orbit torque has been
well-studied via spin pumping into heavy metal layers. Here we demonstrate that
established microwave transmission spectroscopy of ferromagnet/normal metal
bilayers under ferromagnetic resonance can be used to inductively detect the AC
charge currents driven by the inverse spin-charge conversion processes. This
technique relies on vector network analyzer ferromagnetic resonance (VNA-FMR)
measurements. We show that in addition to the commonly-extracted spectroscopic
information, VNA-FMR measurements can be used to quantify the magnitude and
phase of all AC charge currents in the sample, including those due to spin
pumping and spin-charge conversion. Our findings reveal that
Ni$_{80}$Fe$_{20}$/Pt bilayers exhibit both damping-like and field-like inverse
spin-orbit torques. While the magnitudes of both the damping-like and
field-like inverse spin-orbit torque are of comparable scale to prior reported
values for similar material systems, we observed a significant dependence of
the damping-like magnitude on the order of deposition. This suggests interface
quality plays an important role in the overall strength of the damping-like
spin-to-charge conversion.",1611.05798v2
2018-05-22,FMR-related phenomena in spintronic devices,"Spintronic devices, such as non-volatile magnetic random access memories and
logic devices, have attracted considerable attention as potential candidates
for future high efficient data storage and computing technology. In a heavy
metal or other emerging material with strong spin-orbit coupling (SOC), the
charge currents induce spin currents or spin accumulations via SOC. The
generated spin currents can exert spin-orbit torques (SOTs) on an adjacent
ferromagnet, which opens up a new way to realize magnetization dynamics and
switching of the ferromagnetic layer for spintronic devices. In the SOT scheme,
the charge-to-spin interconversion efficiency (SOT efficiency) is an important
figure of merit for applications. For the effective characterization of this
efficiency, the ferromagnetic resonance (FMR) based methods, such as the spin
transfer torque ferromagnetic resonance (ST-FMR) and the spin pumping, are
common utilized in addition to low frequency harmonic or dc measurements. In
this review, we focus on the ST-FMR measurements for the evaluation of the SOT
efficiency. We provide a brief summary of the different ST-FMR setups and data
analysis methods. We then discuss ST-FMR and SOT studies in various materials,
including heavy metals and alloys, topological insulators, two dimensional (2D)
materials, interfaces with strong Rashba effect, antiferromagnetic materials,
two dimensional electron gas (2DEG) in oxide materials and oxidized nonmagnetic
materials.",1805.08496v1
2024-03-06,Tracing Dirac points of topological surface states by ferromagnetic resonance,"Ferromagnetic resonance is used to reveal features of the buried electronic
band structure at interfaces between ferromagnetic metals and topological
insulators. By monitoring the evolution of magnetic damping, the application of
this method to a hybrid structure consisting of a ferromagnetic layer and a 3D
topological insulator reveals a clear fingerprint of the Dirac point and
exhibits additional features of the interfacial band structure not otherwise
observable. The underlying spin-pumping mechanism is discussed in the framework
of dissipation of angular momentum by topological surface states (TSSs). Tuning
of the Fermi level within the TSS was verified both by varying the
stoichiometry of the topological insulator layer and by electrostatic
backgating and the damping values obtained in both cases show a remarkable
agreement. The high energy resolution of this method additionally allows us to
resolve the energetic shift of the local Dirac points generated by local
variations of the electrostatic potential. Calculations based on the chiral
tunneling process naturally occurring in TSS agree well with the experimental
results.",2403.03518v2
2005-12-21,Why RKKY exchange integrals are inappropriate to describe ferromagnetism in diluted magnetic semiconductors,"We calculate Curie temperatures and study the stability of ferromagnetism in
diluted magnetic materials, taking as a model for the exchange between magnetic
impurities a damped Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and a shor
t range term representing the effects of superexchange. To properly include
effects of spin and thermal fluctuations as well as geometric disorder, we
solve the effective Heisenberg Hamiltonian by means of a recently developed
semi-analytical approach. This approach, ``self-consistent local Random Phase
Approximation (SC-L RPA)'', is explained. We show that previous mean-field
treatments, which have been widely used in the literature, largely overestimate
both the Curie temperatures and the stability of ferromagnetism as a function
of carrier density. The discr epancy when compared to the current approach was
that effects of frustration in RKKY oscillations had been strongly
underestimated by such simple mea n-field theories. We argue that the use, as
is frequent, of a weakly-disordered RKKY exchange to model ferromagnetism in
diluted III-V systems is inconsistent with the observation of ferromagnetism
over a wide region of itinerant carrier densities. This may be puzzling when
compared to the apparent success of calculations based on {\it ab-initio}
estimates of the coupling; we propose a resolution to this issue by taking
RKKY-like interactions between resonant states close to the Fermi level.",0512540v1
2008-04-21,Local electronic structure of Cr in the II-VI diluted ferromagnetic semiconductor Zn$_{1-x}$Cr$_x$Te,"The electronic structure of the Cr ions in the diluted ferromagnetic
semiconductor Zn$_{1-x}$Cr$_x$Te ($x=0.03$ and 0.15) thin films has been
investigated using x-ray magnetic circular dichroism (XMCD) and photoemission
spectroscopy (PES). Magnetic-field ($H$) and temperature ($T$) dependences of
the Cr $2p$ XMCD spectra well correspond to the magnetization measured by a
SQUID magnetometer. The line shape of the Cr $2p$ XMCD spectra is independent
of $H$, $T$, and $x$, indicating that the ferromagnetism is originated from the
same electronic states of the Cr ion. Cluster-model analysis indicates that
although there are two or more kinds of Cr ions in the Zn$_{1-x}$Cr$_x$Te
samples, the ferromagnetic XMCD signal is originated from Cr ions substituted
for the Zn site. The Cr 3d partial density of states extracted using Cr $2p \to
3d$ resonant PES shows a broad feature near the top of the valence band,
suggesting strong $s$,$p$-$d$ hybridization. No density of states is detected
at the Fermi level, consistent with their insulating behavior. Based on these
findings, we conclude that double exchange mechanism cannot explain the
ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te.",0804.3272v1
2014-07-02,Spin Waves in Ferromagnetic Insulators Coupled via a Normal Metal,"Herein, we study the spin-wave dispersion and dissipation in a ferromagnetic
insulator--normal metal--ferromagnetic insulator system. Long-range dynamic
coupling because of spin pumping and spin transfer lead to collective magnetic
excitations in the two thin-film ferromagnets. In addition, the dynamic dipolar
field contributes to the interlayer coupling. By solving the
Landau-Lifshitz-Gilbert-Slonczewski equation for macrospin excitations and the
exchange-dipole volume as well as surface spin waves, we compute the effect of
the dynamic coupling on the resonance frequencies and linewidths of the various
modes. The long-wavelength modes may couple acoustically or optically. In the
absence of spin-memory loss in the normal metal, the spin-pumping-induced
Gilbert damping enhancement of the acoustic mode vanishes, whereas the optical
mode acquires a significant Gilbert damping enhancement, comparable to that of
a system attached to a perfect spin sink. The dynamic coupling is reduced for
short-wavelength spin waves, and there is no synchronization. For intermediate
wavelengths, the coupling can be increased by the dipolar field such that the
modes in the two ferromagnetic insulators can couple despite possible small
frequency asymmetries. The surface waves induced by an easy-axis surface
anisotropy exhibit much greater Gilbert damping enhancement. These modes also
may acoustically or optically couple, but they are unaffected by thickness
asymmetries.",1407.0635v1
2015-01-13,Strain-Induced Extrinsic High-Temperature Ferromagnetism in the Fe-Doped Hexagonal Barium Titanate,"Diluted magnetic semiconductors possessing intrinsic static magnetism at high
temperatures represent a promising class of multifunctional materials with high
application potential in spintronics and magneto-optics. In the hexagonal
Fe-doped diluted magnetic oxide, 6H-BaTiO$_{3-\delta}$, room-temperature
ferromagnetism has been previously reported. Ferromagnetism is broadly accepted
as an intrinsic property of this material, despite its unusual dependence on
doping concentration and processing conditions. However, the here reported
combination of bulk magnetization and complementary in-depth local-probe
electron spin resonance and muon spin relaxation measurements, challenges this
conjecture. While a ferromagnetic transition occurs around 700 K, it does so
only in additionally annealed samples and is accompanied by an extremely small
average value of the ordered magnetic moment. Furthermore, several additional
magnetic instabilities are detected at lower temperatures. These coincide with
electronic instabilities of the Fe-doped 3C-BaTiO$_{3-\delta}$ pseudocubic
polymorph. Moreover, the distribution of iron dopants with frozen magnetic
moments is found to be non-uniform. Our results demonstrate that the intricate
static magnetism of the hexagonal phase is not intrinsic, but rather stems from
sparse strain-induced pseudocubic regions. We point out the vital role of
internal strain in establishing defect ferromagnetism in systems with competing
structural phases.",1501.02938v1
2015-04-08,Selective interlayer ferromagnetic coupling between the Cu spins in YBa$_2$ Cu$_3$ O$_{7-x}$ grown on top of La$_{0.7}$ Ca$_{0.3}$ MnO$_3$,"Studies to date on ferromagnet/d-wave superconductor heterostructures focus
mainly on the effects at or near the interfaces while the response of bulk
properties to heterostructuring is overlooked. Here we use resonant soft x-ray
scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between
the in-plane Cu spins in YBa$_2$ Cu$_3$ O$_{7-x}$ (YBCO) superconductor when it
is grown on top of ferromagnetic La$_{0.7}$ Ca$_{0.3}$ MnO$_3$ (LCMO) manganite
layer. This coupling, present in both normal and superconducting states of
YBCO, is sensitive to the interfacial termination such that it is only observed
in bilayers with MnO_2but not with La$_{0.7}$ Ca$_{0.3}$ interfacial
termination. Such contrasting behaviors, we propose, are due to distinct
energetic of CuO chain and CuO$_2$ plane at the La$_{0.7}$ Ca$_{0.3}$ and
MnO$_2$ terminated interfaces respectively, therefore influencing the transfer
of spin-polarized electrons from manganite to cuprate differently. Our findings
suggest that the superconducting/ferromagnetic bilayers with proper interfacial
engineering can be good candidates for searching the theorized
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the
competing quantum orders in highly correlated electron systems.",1504.01820v2
2018-11-23,Broadening Frequency Range of a Ferromagnetic Axion Haloscope with Strongly Coupled Cavity-Magnon Polaritons,"With the axion being a prime candidate for dark matter, there has been some
recent interest in direct detection through a so called `Ferromagnetic
haloscope.' Such devices exploit the coupling between axions and electrons in
the form of collective spin excitations of magnetic materials with the readout
through a microwave cavity. Here, we present a new, general, theoretical
treatment of such experiments in a Hamiltonian formulation for strongly coupled
magnons and photons, which hybridise as cavity-magnon polaritons. Such strongly
coupled systems have an extended measurable dispersive regime. Thus, we extend
the analysis and operation of such experiments into the dispersive regime,
which allows any ferromagnetic haloscope to achieve improved bandwidth with
respect to the axion mass parameter space. This experiment was implemented in a
cryogenic setup, and initial search results are presented setting laboratory
limits on the axion-electron coupling strength of $g_{aee}>3.7\times10^{-9}$ in
the range $33.79~\mu$eV$< m_a<33.94~\mu$eV with $95\%$ confidence. The
potential bandwidth of the Ferromagnetic haloscope was calculated to be in two
bands, the first of about $1$GHz around $8.24$GHz (or $4.1~\mu$eV mass range
around $34.1~\mu$eV) and the second of about $1.6$GHz around $10$GHz
($6.6~\mu$eV mass range around $41.4~\mu$eV). Frequency tuning may also be
easily achieved via an external magnetic field which changes the ferromagnetic
resonant frequency with respect to the cavity frequency. The requirements
necessary for future improvements to reach the DFSZ axion model band are
discussed in the paper.",1811.09348v3
2008-07-09,High temperature ferromagnetism in Co-implanted TiO2 rutile,"We report on structural, magnetic and electronic properties of Co-implanted
TiO2 rutile single crystals for different implantation doses. Strong
ferromagnetism at room temperature and above is observed in TiO2 rutile plates
after cobalt ion implantation, with magnetic parameters depending on the cobalt
implantation dose. While the structural data indicate the presence of metallic
cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra
gives clear evidence for a substitutional Co 2+ state. The detailed analysis of
the structural and magnetic properties indicates that there are two magnetic
phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the
formation of long range ferromagnetic ordering between implanted magnetic
cobalt ions in the rutile phase, and the second one is a superparamagnetic
phase originates from the formation of metallic cobalt clusters in the
implanted region. Using x-ray resonant magnetic scattering, the element
specific magnetization of cobalt, oxygen and titanium in Co-implanted TiO2
single crystals are investigated. Magnetic dichroism was observed at the Co L
edges as well as at the O K edge. The interaction mechanism, which leads to
ferromagnetic ordering of substituted cobalt ions in the host matrix, is also
discussed.",0807.1555v1
2016-05-10,Photoenhanced spin/valley polarization and tunneling magnetoresistance in ferromagnetic-normal-ferromagnetic silicene junction,"We theoretically demonstrate a simple way to significantly enhance the
spin/valley polarizations and tunnel- ing magnetoresistnace (TMR) in a
ferromagnetic-normal-ferromagnetic (FNF) silicene junction by applying a
circularly polarized light in off-resonant regime to the second ferromagnetic
(FM) region. We show that the fully spin-polarized current can be realized in
certain ranges of light intensity. Increasing the incident energy in the
presence of light will induce a transition of perfect spin polarization from
positive to negative or vice versa depending on magnetic configuration
(parallel or anti-parallel) of FNF junction. Additionally, under a circularly
polarized light, valley polarization is very sensitive to electric field and
the perfect valley polarization can be achieved even when staggered electric
field is much smaller than exchange field. The most important result we would
like to emphasize in this paper is that the perfect spin polarization and 100%
TMR induced by a circularly polarized light are completely independent of
barrier height in normal region. Furthermore, the sign reversal of TMR can be
observed when the polarized direction of light is changed. A condition for
observing the 100% TMR is also reported. Our results are expected to be
informative for real applications of FNF silicene junction, especially in
spintronics.",1605.02829v1
2020-01-09,"Hybridization between the ligand $p$ band and Fe-3$d$ orbitals in the p-type ferromagnetic semiconductor (Ga,Fe)Sb","(Ga,Fe)Sb is a promising ferromagnetic semiconductor for practical spintronic
device applications because its Curie temperature ($T_{\rm C}$) is above room
temperature. However, the origin of ferromagnetism with high $T_{\rm C}$
remains to be elucidated. Here, we use soft x-ray angle-resolved photoemission
spectroscopy (SX-ARPES) to investigate the valence-band (VB) structure of
(Ga$_{0.95}$,Fe$_{0.05}$)Sb including the Fe-3$d$ impurity band (IB), to unveil
the mechanism of ferromagnetism in (Ga,Fe)Sb. We find that the VB dispersion in
(Ga$_{0.95}$,Fe$_{0.05}$)Sb observed by SX-ARPES is similar to that of GaSb,
indicating that the doped Fe atoms hardly affect the band dispersion. The
Fe-3$d$ resonant ARPES spectra demonstrate that the Fe-3$d$ IB crosses the
Fermi level ($E_{\rm F}$) and hybridizes with the VB of GaSb. These
observations indicate that the VB structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb is
consistent with that of the IB model which is based on double-exchange
interaction between the localized 3$d$ electrons of the magnetic impurities.
The results indicate that the ferromagnetism in (Ga,Fe)Sb is formed by the
hybridization of the Fe-3$d$ IB with the ligand $p$ band of GaSb.",2001.02895v1
2019-01-31,Fundamental Spin Interactions Underlying the Magnetic Anisotropy in the Kitaev Ferromagnet CrI$_3$,"We lay the foundation for determining the microscopic spin interactions in
two-dimensional (2D) ferromagnets by combining angle-dependent ferromagnetic
resonance (FMR) experiments on high quality CrI$_3$ single crystals with
theoretical modeling based on symmetries. We discover that the Kitaev
interaction is the strongest in this material with $K \sim -5.2$ meV, 25 times
larger than the Heisenberg exchange $J \sim -0.2$ meV, and responsible for
opening the $\sim$5 meV gap at the Dirac points in the spin-wave dispersion.
Furthermore, we find that the symmetric off-diagonal anisotropy $\Gamma \sim
-67.5$ $\mu$eV, though small, is crucial for opening a $\sim$0.3 meV gap in the
magnon spectrum at the zone center and stabilizing ferromagnetism in the 2D
limit. The high resolution of the FMR data further reveals a $\mu$eV-scale
quadrupolar contribution to the $S=3/2$ magnetism. Our identification of the
underlying exchange anisotropies opens paths toward 2D ferromagnets with higher
$T_\text{C}$ as well as magnetically frustrated quantum spin liquids based on
Kitaev physics.",1902.00077v2
2019-12-10,Josephson current through a ferromagnetic bilayer: Beyond the quasiclassical approximation,"Based on the Bogoliubov-de Gennes equations, we provide an exact numerical
solution for the critical current of Josephson junctions with a composite
ferromagnetic bilayer. We demonstrate that for the antiparallel orientation of
the magnetic moments of the bilayer, the presence of a potential barrier at the
bilayer interface results in large oscillations of the critical current as a
function of ferromagnet thickness and/or exchange field. Because of this, and
remarkably, in the range of small exchange field and thicknesses, the magnetism
leads to the increase of the critical current. This effect is well pronounced
at low temperature but disappears near $T_c$. If the potential barrier is
replaced by a spin-active barrier at the bilayer interface the conventional
0-$\pi$ transition, similar to the case of an uniform ferromagnetic Josephson
junction, is observed. Strikingly, for a parallel orientation of the magnetic
moments of the bilayer, the presence of the spin-active barrier restores the
anomalous behavior---potential barrier in the antiparallel case. These
behaviors result from the resonant tunneling of Cooper pairs across the
composite barrier---an effect related to the spin-dependent Fermi vector in the
presence of the ferromagnets' exchange field.",1912.04447v2
2020-09-07,Spin pumping in d-wave superconductor/ferromagnet hybrids,"Spin-pumping across ferromagnet/superconductor (F/S) interfaces has attracted
much attention lately. Yet the focus has been mainly on s-wave
superconductors-based systems whereas (high-temperature) d-wave superconductors
such as YBa2Cu3O7-d (YBCO) have received scarce attention despite their
fundamental and technological interest. Here we use wideband ferromagnetic
resonance to study spin-pumping effects in bilayers that combine a soft
metallic Ni80Fe20 (Py) ferromagnet and YBCO. We evaluate the spin conductance
in YBCO by analyzing the magnetization dynamics in Py. We find that the Gilbert
damping exhibits a drastic drop as the heterostructures are cooled across the
normal-superconducting transition and then, depending on the S/F interface
morphology, either stays constant or shows a strong upturn. This unique
behavior is explained considering quasiparticle density of states at the YBCO
surface, and is a direct consequence of zero-gap nodes for particular
directions in the momentum space. Besides showing the fingerprint of d-wave
superconductivity in spin-pumping, our results demonstrate the potential of
high-temperature superconductors for fine tuning of the magnetization dynamics
in ferromagnets using k-space degrees of freedom of d-wave/F interfaces.",2009.03196v3
2023-06-13,Circuit QED detection of induced two-fold anisotropic pairing in a hybrid superconductor-ferromagnet bilayer,"Hybrid systems represent one of the frontiers in the study of unconventional
superconductivity and are a promising platform to realize topological
superconducting states. Owing to their mesoscopic dimensions, these materials
are challenging to probe using many conventional measurement techniques, and
require new experimental probes to successfully characterize. In this work, we
develop a probe that enables us to measure the superfluid density of
micron-size superconductors using microwave techniques drawn from circuit
quantum electrodynamics (cQED). We apply this technique to a paradigmatic
hybrid system, the superconductor/ferromagnet bilayer, and find that the
proximity-induced superfluid density is two-fold anisotropic within the plane
of the sample and exhibits power law temperature-scaling which is indicative of
a nodal superconducting state. These experimental results are consistent with
the theoretically predicted signatures of induced triplet pairing with a nodal
$p$-wave order parameter. Moreover, we unexpectedly observe drastic
modifications to the microwave response at frequencies near the ferromagnetic
resonance, suggesting a coupling between the spin dynamics and induced
superconducting order in the ferromagnetic layer. Our results offer new
insights into the unconventional superconducting states induced in
superconductor/ferromagnet heterostructures and simultaneously establish a new
avenue for the study of fragile unconventional superconductivity in
low-dimensional materials such as van der Waals heterostructures.",2306.08043v1
1998-08-28,Ferromagnetic resonance force microscopy on microscopic cobalt single layer films,"We report mechanical detection of ferromagnetic resonance signals from
microscopic Co single layer thin films using a magnetic resonance force
microscope (MRFM). Variations in the magnetic anisotropy field and the
inhomogeneity of were clearly observed in the FMR spectra of microscopic Co
thin films 500 and 1000 angstrom thick and 40 X 200 micron^2 in lateral extent.
This demonstrates the important potential that MRFM detection of FMR holds for
microscopic characterization of spatial distribution of magnetic properties in
magnetic layered materials and devices.",9808326v1
2005-08-30,Large angle magnetization dynamics measured by time-resolved ferromagnetic resonance,"A time-resolved ferromagnetic resonance technique was used to investigate the
magnetization dynamics of a 10 nm thin Permalloy film. The experiment consisted
of a sequence of magnetic field pulses at a repetition rate equal to the
magnetic systems resonance frequency. We compared data obtained by this
technique with conventional pulsed inductive microwave magnetometry. The
results for damping and frequency response obtained by these two different
methods coincide in the limit of a small angle excitation. However, when
applying large amplitude field pulses, the magnetization had a non-linear
response. We speculate that one possible cause of the nonlinearity is related
to self-amplification of incoherence, known as the Suhl instabilities.",0508708v1
2008-12-29,Temperature dependent dynamic and static magnetic response in magnetic tunnel junctions with Permalloy layers,"Ferromagnetic resonance and static magnetic properties of CoFe/Al2O3/CoFe/Py
and CoFe/Al2O3/CoFeB/Py magnetic tunnel junctions and of 25nm thick
single-layer Permalloy(Py) films have been studied as a function of temperature
down to 2K. The temperature dependence of the ferromagnetic resonance excited
in the Py layers in magnetic tunnel junctions shows knee-like enhancement of
the resonance frequency accompanied by an anomaly in the magnetization near
60K. We attribute the anomalous static and dynamic magnetic response at low
temperatures to interface stress induced magnetic reorientation transition at
the Py interface which could be influenced by dipolar soft-hard layer coupling
through the Al2O3 barrier.",0812.4953v1
2010-06-30,Micromagnetic analysis of magnetic noise in ferromagnetic nanowires,"We investigate the magnetic thermal noise in magnetic nanowires with and
without a domain wall by employing micromagnetic simulations. The magnetic
thermal noise due to random thermal fluctuation fields gives important physical
quantities related with the magnetic susceptibility. We find that the resonance
frequency of a domain wall is distinguishable from one of a magnetic domain
itself. For the single domain without a domain wall, the resonance frequency is
well described by the Kittel's formula considering a ferromagnetic specimen as
a simple ellipsoid with demagnetizing factors for various wire widths and
thicknesses. However, additional resonance frequencies from the magnetic domain
wall show the different dependences of the wire width and thickness. It implies
that the spins inside the domain wall have different effective fields and the
spin dynamics.",1006.5763v1
2010-09-18,Composite excitation of Josephson phase and spin waves in Josephson junctions with ferromagnetic insulator,"Coupling of Josephson-phase and spin-waves is theoretically studied in a
superconductor/ferromagnetic insulator/superconductor (S/FI/S) junction.
Electromagnetic (EM) field inside the junction and the Josephson current
coupled with spin-waves in FI are calculated by combining Maxwell and
Landau-Lifshitz-Gilbert equations. In the S/FI/S junction, it is found that the
current-voltage (I-V) characteristic shows two resonant peaks. Voltages at the
resonant peaks are obtained as a function of the normal modes of EM field,
which indicates a composite excitation of the EM field and spin-waves in the
S/FI/S junction. We also examine another type of junction, in which a
nonmagnetic insulator (I) is located at one of interfaces between S and FI. In
such a S/I/FI/S junction, three resonant peaks appear in the I-V curve, since
the Josephson-phase couples to the EM field in the I layer.",1009.3551v3
2011-02-09,Enhancement of the response of non-uniform resonance modes of a nanostructure in the Picoprobe microwave-current injection ferromagnetic resonance,"The non-uniform standing spin-wave modes in thin magnetic films and
nanostructures provide important information about surfaces and buried
interfaces. Very often they are lacking in the recorded ferromagnetic resonance
spectra for symmetry reasons. In this work we experimentally demonstrate that
by direct injection of microwave currents into an array of Permalloy
nanostripes using a microscopic microwave coaxial to coplanar adaptor one can
efficiently excite non-uniform standing spin wave modes with odd symmetry. The
proposed method is quick and allows easy spatial mapping of magnetic properties
with the resolution down to 100 microns. We have validated this method using an
example from a periodical array of nanostripes. The results from direct current
injection are compared to that of microstrip-based FMR measurements.",1102.1805v2
2012-06-14,Low-field microwave absorption in epitaxial La-Sr-Mn-O films resulting from the angle-tuned ferromagnetic resonance in the multidomain state,"We studied magnetic-field induced microwave absorption in 100-200 nm thick
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films on SrTiO$_{3}$ substrate and found a
low-field absorption with a very peculiar angular dependence: it appears only
in the oblique field and is absent both in the parallel and in the
perpendicular orientations. We demonstrate that this low-field absorption
results from the ferromagnetic resonance in the multidomain state (domain-mode
resonance). Its unusual angular dependence arises from the interplay between
the parallel component of the magnetic field that drives the film into
multidomain state and the perpendicular field component that controls the
domain width through its effect on domain wall energy. The low-field microwave
absorption in the multidomain state can be a tool to probe domain structure in
magnetic films with in-plane magnetization.",1206.3041v1
2012-07-20,Measurement of the dynamical dipolar coupling in a pair of magnetic nano-disks using a Ferromagnetic Resonance Force Microscope,"We perform an extensive experimental spectroscopic study of the collective
spin-wave dynamics occurring in a pair of magnetic nano-disks coupled by the
magneto-dipolar interaction. For this, we take advantage of the stray field
gradient produced by the magnetic tip of a ferromagnetic resonance force
microscope (f-MRFM) to continuously tune and detune the relative resonance
frequencies between two adjacent nano-objects. This reveals the anti-crossing
and hybridization of the spin-wave modes in the pair of disks. At the exact
tuning, the measured frequency splitting between the binding and anti-binding
modes precisely corresponds to the strength of the dynamical dipolar coupling
$\Omega$. This accurate f-MRFM determination of $\Omega$ is measured as a
function of the separation between the nano-disks. It agrees quantitatively
with calculations of the expected dynamical magneto-dipolar interaction in our
sample.",1207.4919v1
2012-08-14,"Disorder effects on resonant tunneling transport in GaAs/(Ga,Mn)As heterostructures","Recent experiments on resonant tunneling structures comprising (Ga,Mn)As
quantum wells [Ohya et al., Nature Physics 7, 342 (2011)] have evoked a strong
debate regarding their interpretation as resonant tunneling features and the
near absences of ferromagnetic order observed in these structures. Here, we
present a related theoretical study of a GaAs/(Ga,Mn)As double barrier
structure based on a Green's function approach, studying the self-consistent
interplay between ferromagnetic order, structural defects (disorder), and the
hole tunnel current under conditions similar to those in experiment. We show
that disorder has a strong influence on the current-voltage characteristics in
efficiently reducing or even washing out negative differential conductance,
offering an explanation for the experimental results. We find that for the Be
lead doping levels used in experiment the resulting spin density polarization
in the quantum well is too small to produce a sizable exchange splitting.",1208.2802v1
2013-01-30,Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions,"Spin-transfer ferromagnetic resonance (ST-FMR) in symmetric magnetic tunnel
junctions (MTJs) with a varied thickness of the MgO tunnel barrier (0.75 nm <
$t_{MgO}$ < 1.05 nm) is studied using the spin-torque diode effect. The
application of an RF current into nanosized MTJs generates a DC mixing voltage
across the device when the frequency is in resonance with the resistance
oscillations arising from the spin transfer torque. Magnetization precession in
the free and reference layers of the MTJs is analyzed by comparing ST-FMR
signals with macrospin and micromagnetic simulations. From ST-FMR spectra at
different DC bias voltage, the in-plane and perpendicular torkances are
derived. The experiments and free-electron model calculations show that the
absolute torque values are independent of tunnel barrier thickness. The
influence of coupling between the free and reference layer of the MTJs on the
ST-FMR signals and the derived torkances are discussed.",1301.7186v1
2013-06-04,Interlayer coupling in spin valves studied by broadband ferromagnetic resonance,"Magnetization dynamic response of coupled and uncoupled spin valves with
structure NiFe(20 nm)/Cu(t_Cu)/NiFe(20 nm)/IrMn(10nm) were probed using
broadband ferromagnetic resonance absorption measurements. By varying the Cu
thickness t_Cu we were able to tailor the coupling intensity between the free
and pinned layers. Broadband spectra show two resonant modes for each measured
field. It is noticed that the coupling among NiFe layers modifies the amplitude
of the absorption peaks and, moreover, the dispersion relations of the modes,
which are distorted specially at the anti-parallel state. A numerical model is
proposed and applied to address the underlying physics and the observed
properties of these systems.",1306.0915v1
2013-07-10,RF amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance,"The radio-frequency (RF) voltage amplification property of a tunnel
magnetoresistance device driven by an RF external-magnetic-field-induced
ferromagnetic resonance was studied. The proposed device consists of a magnetic
tunnel junction (MTJ) and an electrically isolated coplanar waveguide. The
input RF voltage applied to the waveguide can excite the resonant dynamics in
the free layer magnetization, leading to the generation of an output RF voltage
under a DC bias current. The dependences of the RF voltage gain on the static
external magnetic field strength and angle were systematically investigated.
The design principles for the enhancement of the gain factor are also
discussed.",1307.2745v1
2013-11-22,"Spin-Wave Resonance Model of Surface Pinning in Ferromagnetic Semiconductor (Ga,Mn)As Thin Films","The source of spin-wave resonance (SWR) in thin films of the ferromagnetic
semiconductor (Ga,Mn)As is still under debate: does SWR stem from the
\emph{surface} anisotropy (in which case the surface inhomogeneity (SI) model
would apply), or does it originate in the \emph{bulk} inhomogeneity of the
magnetic structure of the sample (and thus requires the use of the volume
inhomogeneity (VI) model)? This paper outlines the ground on which the
controversy arose and shows why in different conditions a resonance sample may
meet the assumptions of either the SI or the VI model. In our considerations we
refer to the SWR spectra measured by Furdyna's team [X. Liu \textit{et al.},
Physical Review B \textbf{75}, 195220 (2007)] in (Ga,Mn)As thin films in
different configurations of the static magnetic field $\vec{H}$ with respect to
the surface. We demonstrate that the observed configuration dependence of the
SWR spectrum of the studied material can be described with the use of the
surface pinning parameter.",1311.5767v2
2014-09-09,Micro-strip ferromagnetic resonance study of strain-induced anisotropy in amorphous FeCuNbSiB film on flexible substrate,"The magnetic anisotropy of a FeCuNbSiB (Finemet) film deposited on Kapton has
been studied by micro-strip ferromagnetic resonance technique. We have shown
that the flexibility of the substrate allows a good transmission of elastic
strains generated by a piezoelectric actuator. Following the resonance field
angular dependence, we also demonstrate the possibility of controlling the
magnetic anisotropy of the film by applying relatively small voltages to the
actuator. Moreover, a suitable model taking into account the effective elastic
strains measured by digital image correlation and the effective elastic
coefficients measured by Brillouin light scattering, allowed to deduce the
magnetostrictive coefficient. This latter was found to be positive
$(\lambda=16\times10^{-6}$) and consistent with the usually reported values for
bulk amorphous FeCuNbSiB.",1409.2845v1
2015-05-28,Driving and detecting ferromagnetic resonance in insulators with the spin Hall effect,"We demonstrate the generation and detection of spin-torque ferromagnetic
resonance in Pt/YIG bilayers. A unique attribute of this system is that the
spin Hall effect lies at the heart of both the generation and detection
processes and no charge current is passing through the insulating magnetic
layer. When the YIG undergoes resonance, a dc voltage is detected
longitudinally along the Pt that can be described by two components. One is the
mixing of the spin Hall magnetoresistance with the microwave current. The other
results from spin pumping into the Pt being converted to a dc current through
the inverse spin Hall effect. The voltage is measured with applied magnetic
field directions that range in-plane to nearly perpendicular. We find that for
magnetic fields that are mostly out-of-plane, an imaginary component of the
spin mixing conductance is required to model our data.",1505.07791v1
2016-01-08,Current Control of Magnetic Anisotropy via Stress in a Ferromagnetic Metal Waveguide,"We demonstrate that in-plane charge current can effectively control the spin
precession resonance in an Al2O3/CoFeB/Ta heterostructure. Brillouin Light
Scattering (BLS) was used to detect the ferromagnetic resonance field under
microwave excitation of spin waves at fixed frequencies. The current control of
spin precession resonance originates from modification of the in-plane uniaxial
magnetic anisotropy field H_k, which changes symmetrically with respect to the
current direction. Numerical simulation suggests that the anisotropic stress
introduced by Joule heating plays an important role in controlling H_k. These
results provide new insights into current manipulation of magnetic properties
and have broad implications for spintronic devices.",1601.02048v1
2016-01-13,Spin Vortex Resonance in Non-planar Ferromagnetic Dots,"In planar structures, the vortex resonance frequency changes little as a
function of an in-plane magnetic field as long as the vortex state persists.
Altering the topography of the element leads to a vastly different dynamic
response that arises due to the local vortex core confinement effect. In this
work, we studied the magnetic excitations in non-planar ferromagnetic dots
using a broadband microwave spectroscopy technique. Two distinct resonance
frequency ranges were observed depending on the position of the vortex core
controllable by applying a relatively small magnetic field. The micromagnetic
simulations are in qualitative agreement with the. experimental results.",1601.03133v1
2015-11-17,Fingerprints of entangled spin and orbital physics in itinerant ferromagnets via angle resolved $resonant$ photoemission,"A novel method for mapping the local spin and orbital nature of the ground
state of a system via corresponding flip excitations in both sectors is
proposed based on angle resolved resonant photoemission and related diffraction
patterns, presented here for the first time via an ab-initio modified one-step
theory of photoemission. The analysis is done on the paradigmatic weak
itinerant ferromagnet bcc Fe, whose magnetism, seen as a correlation phenomenon
given by the coexistence of localized moments and itinerant electrons, and the
non-Fermi liquid behaviour at ambient and extreme conditions both remain
unclear. The results offer a real space imaging of local pure spin flip and
entangled spin flip-orbital flip excitations (even at energies where spin flip
transitions are hidden in quasiparticle peaks) and of chiral, vortex-like
wavefronts of excited electrons, depending on the orbital character of the
bands and the direction of the local magnetic moment. Such effects, mediated by
the hole polarization, make resonant photoemission a promising tool to perform
a full tomography of the local magnetic properties of a system with a high
sensitivity to localization/correlation, even in itinerant or macroscopically
non magnetic systems.",1604.07767v1
2016-07-01,Probing strongly hybrid nuclear-electronic states in a model quantum ferromagnet,"We present direct local-probe evidence for strongly hybridized
nuclear-electronic spin states of an Ising ferromagnet LiHoF$_4$ in a
transverse magnetic field. The nuclear-electronic states are addressed via a
magnetic resonance in the GHz frequency range using coplanar resonators and a
vector network analyzer. The magnetic resonance spectrum is successfully traced
over the entire field-temperature phase diagram, which is remarkably well
reproduced by mean-field calculations. Our method can be directly applied to a
broad class of materials containing rare-earth ions for probing the
substantially mixed nature of the nuclear and electronic moments.",1607.00124v3
2016-10-04,Magnetomechanical coupling and ferromagnetic resonance in magnetic nanoparticles,"We address the theory of the coupled lattice and magnetization dynamics of
freely suspended single-domain nanoparticles. Magnetic anisotropy generates
low-frequency satellite peaks in the microwave absorption spectrum and a
blueshift of the ferromagnetic resonance (FMR) frequency. The low-frequency
resonances are very sharp with maxima exceeding that of the FMR, because their
magnetic and mechanical precessions are locked, thereby suppressing Gilbert
damping. Magnetic nanoparticles can operate as nearly ideal motors that convert
electromagnetic into mechanical energy. The Barnett/Einstein-de Haas effect is
significant even in the absence of a net rotation.",1610.01072v2
2018-11-03,Ferromagnetic resonance in the complex permeability of an Fe$_3$O$_4$ nanosuspension at radio and microwave frequencies,"The complex permeability of an iron-oxide nanosuspension has been measured as
a function of magnetic field strength at RF and microwave frequencies using a
loop-gap resonator. The particles were suspended in water and had an 8-nm
diameter Fe$_3$O$_4$ core that was coated by Dextran. The real part of the
permeability increased sharply beyond a frequency-dependent threshold value of
the static magnetic field before saturating. Just beyond this threshold field,
there was a peak in the imaginary part of the permeability. The permeability
measurements, which exhibited features associated with ferromagnetic resonance,
were used to determine the dependence of the microwave absorption on static
magnetic field strength. Using the absorption data, the $g$-factor of the
nanosuspension was found to be $1.86\pm 0.07$.",1811.01168v1
2020-07-30,Resonant subwavelength control of the phase of spin waves reflected from a ferromagnetic film edge,"Using frequency-domain finite element calculations cross-checked with
micromagnetic simulations, we demonstrate that the phase of spin waves
reflected from an interface between a permalloy film and a bilayer can be
controlled by changing dimensions of the bilayer. Treating the bilayer formed
by the permalloy film and a ferromagnetic stripe as a segment of a multi-mode
waveguide, we show that spin-wave Fabry-Perot resonances of one of its modes
are responsible for the high sensitivity of the phase of reflected waves to
stripe width and the stripe-film separation. Thus, the system is a unique
realization of a fully magnonic Gires-Tournois interferometer based on a
two-modes resonator, which can be treated as a magnonic counterpart of a
metasurface, since it enables manipulation of the phase of spin waves at
subwavelength distances. Knowledge gained from these calculations might be used
to design magnonic devices such as flat lenses or magnetic particle detectors.",2007.15226v5
2012-03-30,Network analyzer measurements of spin transfer torques in magnetic tunnel junctions,"We demonstrate a simple network-analyzer technique to make quantitative
measurements of the bias dependence of spin torque in a magnetic tunnel
junction. We apply a microwave current to exert an oscillating spin torque near
the ferromagnetic resonance frequency of the tunnel junction's free layer. This
produces an oscillating resistance that, together with an applied direct
current, generates a microwave signal that we measure with the network
analyzer. An analysis of the resonant response yields the strength and
direction of the spin torque at non-zero bias. We compare to measurements of
the spin torque vector by time-domain spin-torque ferromagnetic resonance.",1204.0038v2
2018-09-12,Anomalous increasing of the intensity of field dependence optical mode ferromagnetic resonance in the exchange coupled bilayer system,"Acoustic and optical ferromagnetic resonance (FMR) in the interlayer exchange
coupled Fe$_{20}$Ni$_{80}$/Co bilayer have been investigated. In the optical
mode, unexpected increasing tendencies of peak value at the resonance frequency
has been observed under an increasing magnetic field. We presented analytical
calculations with which the exchange coupling between Co and Fe$_{20}$Ni$_{80}$
layers, the magnetization and the in-plane uniaxial anisotropy are taken into
account, to interpret the increasing of the maximum values of the optical
permeability. Both experimental measurements and theoretical calculation show
that such tendencies are dependent on the layer thickness t, and that there is
a critical field above which the optical peak value begins to decrease. These
results might help us to understand the mechanism of interlayer exchange
coupling induced optical FMR and might enlighten us to find new possibility of
high frequency applications of magnetic materials.",1809.04372v2
2018-09-18,Local manipulation of quantum magnetism in 1D ultracold Fermi gases across narrow resonances,"Effective range is a quantity to characterize the energy dependence in
two-body scattering strength, and is widely used in cold atomic systems
especially across narrow resonances. Here we show that the effective range can
significantly modify the magnetic property of one-dimensional (1D) spin-$1/2$
fermions in the strongly repulsive regime. In particular, the effective range
breaks the large spin degeneracy in the hard-core limit, and induces a
Heisenberg exchange term in the spin chain that is much more sensitive to the
local density than that induced by the bare coupling. With an external harmonic
trap, this leads to a very rich magnetic pattern where the anti-ferromagnetic
(AFM) and ferromagnetic (FM) correlations can coexist and distribute in highly
tunable regions across the trap. Finally, we propose to detect the
range-induced magnetic order in the tunneling experiment. Our results can be
directly tested in 1D Fermi gases across narrow resonance, and suggest a
convenient route towards the local manipulation of quantum magnetism in cold
atoms.",1809.06836v2
2019-07-02,Bias-free reconfigurable magnonic phase shifter based on a spin-current controlled ferromagnetic resonator,"Controllable phase modulation plays a pivotal role in the researches of
magnonic logic gates. Here we propose a reconfigurable spin-current controlled
magnonic phase shifter based on a ferromagnetic resonator. The proposed phase
shifter requires no magnetic bias field during operation. The device is
directly configured over the waveguide while keeping the original structure of
the waveguide unaffected. Numerical micromagnetic simulations show that the
phase shifter could yield either a {\pi}-phase or no shift depending on the
magnetization status of the resonator, which can be controlled by a current
pulse. Moreover, the phase-shifting operation could be affected by spin
current. At different input current density, the device could be either used as
a dynamic controlled phase shifter or a spin-wave valve. Finally, a XNOR
magnonic logic gate is demonstrated using the proposed phase shifter. Our work
can be a beneficial step to enhance the functionality and compatibility of the
magnonic logic circuits.",1907.01303v1
2019-09-05,"Detection of magnetic nanoparticles (MNPs) using spin current nano-oscillator (SCNO) biosensor: A frequency-based rapid, ultra-sensitive, magnetic bioassay","This Letter is a micromagnetic simulation-based study on the GHz-frequency
ferromagnetic resonances for the detection of magnetic nanoparticles (MNPs)
using spin current nano-oscillator (SCNO) operating in precession mode as a
spintronic biosensor. The magnetic stray fields from the MNPs in an
antibody-antigen-MNP complex on the SCNO surface modify the ferromagnetic
resonance peaks and generate measurable resonance peak shifts. Moreover, our
results strongly indicate the position-sensitive behavior of the SCNO biosensor
and ways to eradicate this effect to facilitate better bio-sensing performance.
Additionally, a study has been made on how nanoparticles with different sizes
can alter the SCNO device performance. This simulation-based study on the SCNO
device shows a promise of frequency-based nano-biosensor with a sensitivity of
detecting even a single MNP, even in presence of thermal noise.",1909.02204v2
2021-01-07,Abnormal Critical Fluctuations Revealed by Magnetic Resonance in the Two-Dimensional Ferromagnetic Insulators,"Phase transitions and critical phenomena, which are dominated by fluctuations
and correlations, are one of the fields replete with physical paradigms and
unexpected discoveries. Especially for two-dimensional magnetism, the
limitation of the Ginzburg criterion leads to enhanced fluctuations breaking
down the mean-field theory near a critical point. Here, by means of magnetic
resonance, we investigate the behavior of critical fluctuations in the
two-dimensional ferromagnetic insulators $\rm CrXTe_3 (X=Si, Ge)$. After
deriving the classical and quantum models of magnetic resonance, we deem the
dramatic anisotropic shift of the measured $g$ factor to originate from
fluctuations with anisotropic interactions. The deduction of the $g$ factor
behind the fluctuations is consistent with the spin-only state (${g\approx}$
2.050(10) for $\rm CrSiTe_3$ and 2.039(10) for $\rm CrGeTe_3$). Furthermore,
the abnormal enhancement of $g$ shift, supplemented by specific heat and
magnetometry measurements, suggests that $\rm CrSiTe_3$ exhibits a more typical
two-dimensional nature than $\rm CrGeTe_3$ and may be closer to the quantum
critical point.",2101.02440v1
2019-01-29,Low-impedance superconducting microwave resonators for strong coupling to small magnetic mode volumes,"Recent experiments on strongly coupled microwave and ferromagnetic resonance
modes have focused on large volume bulk crystals such as yttrium iron garnet,
typically of millimeter-scale dimensions. We extend these experiments to lower
volumes of magnetic material by exploiting low-impedance lumped-element
microwave resonators. The low impedance equates to a smaller magnetic mode
volume, which allows us to couple to a smaller number of spins in the
ferromagnet. Compared to previous experiments, we reduce the number of
participating spins by two orders of magnitude, while maintaining the strength
of the coupling rate. Strongly coupled devices with small volumes of magnetic
material may allow the use of spin orbit torques, which require high current
densities incompatible with existing structures.",1901.10395v1
2020-09-18,Nontrivial temperature dependence of ferromagnetic resonance frequency for spin reorientation transitions,"We find unusual temperature dependence of the ferromagnetic resonance (FMR)
frequency $f_{\rm R}$ for the spin-reorientation (SR) transition, in which the
easy axis changes depending on temperature, observed in the Nd permanent
magnet, Nd$_2$Fe$_{14}$B: $f_{\rm R} \sim 0$ below the SR transition
temperature ($T_{\rm R}$), drastic increase of $f_{\rm R}$ around $T_{\rm R}$,
and decrease from a peak at higher temperatures. It is nontrivial that the SR
transition causes the unusual behavior of the FMR frequency in a wide
temperature region. We show the mechanism of the temperature dependence by
theoretical and computational analyses. We derive a general relation between
$f_{\rm R}$ and magnetizations to help the understanding of the mechanism, and
clarify that the fluctuation of the transverse magnetization is a key
ingredient for the resonance in all temperature regions.",2009.08581v1
2021-02-01,Strong coupling of Fe-Co alloy with ultralow damping to superconducting co-planar waveguide resonators,"We report on the strong coupling between a metallic ferromagnetic Fe75Co25
thin film patterned element and a range of superconducting Nb half-wavelength
co-planar waveguide (CPW) resonators. By varying the volume of the ferromagnet
we demonstrate that the coupling rate scales linearly with the square root of
the number of spins and achieve a coupling rate over 700 MHz, approaching the
ultrastrong coupling regime. Experiments varying the center conductor width
while maintaining constant magnetic volume verify that decreasing the center
conductor width increases coupling and cooperativity. Our results show that the
frequency dependence of the coupling rate is linear with the fundamental and
higher order odd harmonics of the CPW, but with differing efficiencies. The
results show promise for scaling planar superconducting resonator/magnetic
hybrid systems to smaller dimensions.",2102.01129v1
2021-07-02,Anomalous Gilbert Damping and Duffing Features of the SFS {\boldmath $\varphi_0$} Josephson Junction,"We demonstrate unusual features of phase dynamics, IV-characteristics and
magnetization dynamics of the $\varphi_0$ Josephson junction at small values of
spin-orbit interaction, ratio of Josephson to magnetic energy and Gilbert
damping. In particular, an anomalous shift of the ferromagnetic resonance
frequency with an increase of Gilbert damping is found. The ferromagnetic
resonance curves show the Duffing oscillator behaviour, reflecting the
nonlinear nature of Landau-Lifshitz-Gilbert (LLG) equation. Based on the
numerical analysis of each term in LLG equation we obtained an approximated
equation demonstrated both damping effect and Duffing oscillator features. The
resulting Duffing equation incorporates the Gilbert damping in a special way
across the dissipative term and the restoring force. A resonance method for the
determination of spin-orbit interaction in noncentrosymmetric materials which
play the role of barrier in $\varphi_0$ junctions is proposed.",2107.00982v3
2021-11-24,Bifurcation structure and chaos in nanomagnet coupled to Josephson junction,"Recently an irregular easy axis reorientation demonstrating the Kapitza
pendulum features were observed in numerical simulations of nanomagnet coupled
to the Josephson junction. To explain its origin we study the magnetization
bifurcations and chaos which appear in this system due to interplay of
superconductivity and magnetism. The bifurcation structure of the magnetization
under the variation of Josephson to magnetic energy ratio as a control
parameter demonstrates several precessional motions. They are related to
chaotic behavior, bistability, and multiperiodic orbits in the ferromagnetic
resonance region. Effect of external periodic drive on the bifurcation
structure is investigated. The results demonstrate high-frequency modes of
periodic motion and chaotic response near resonance. Far from the ferromagnetic
resonance we observe a quasiperiodic behavior.",2111.12659v1
2021-12-19,Engineering spin wave spectra in thick Ni$_{80}$Fe$_{20}$ rings by using competition between exchange and dipolar fields,"Control of the spin wave dynamics in nanomagnetic elements is very important
for the realization of a broad range of novel magnonic devices. Here we study
experimentally the spin wave resonance in thick ferromagnetic rings (100 nm)
using perpendicular ferromagnetic resonance spectroscopy. Different from what
was observed for the continuous film of the same thickness, or from ring with
similar lateral dimensions but with lower thicknesses, the spectra of thick
patterned rings show a non-monotonic dependence of the mode intensity on the
resonance field for a fixed frequency. To explain this effect, the theoretical
approach by considering the dependence of the mode profiles on both the radial
and axial coordinates was developed. It was demonstrated that such unusual
behavior is a result of the competition between exchange and dipolar fields
acting at the spin excitations in the structure under study. The calculations
are in a good agreement with the experimental results.",2112.13657v1
2022-01-12,Locking of magnetization and Josephson oscillations at ferromagnetic resonance in $\varphi_0$ junction under external radiation,"We demonstrate the locking by external electromagnetic radiation of magnetic
precession in the $ \varphi_0 $ Josephson junction through Josephson
oscillations in the region of ferromagnetic resonance. This leads to a step in
the dependence of the magnetization on the bias current, the position of which
is determined by the radiation frequency and the shape of the resonance curve.
In junctions with a strong spin-orbit coupling, states with negative
differential resistance appear on the IV-characteristic, resulting in an
additional locking step. A detailed study of the time dependence of voltage and
magnetization and their Fourier transforms shows that the corresponding
oscillations have the same frequency as the oscillations at the first step, but
they have a different amplitude and different dependence on the radiation
frequency. This makes it possible to control not only the frequency, but also
the amplitude of the magnetic precession in the locking region. It opens up
unique perspectives for the control and manipulation of magnetic moment in
hybrid systems such as anomalous Josephson junctions.",2201.04524v1
2023-05-31,The Ferris ferromagnetic resonance technique: principles and applications,"Measurements of ferromagnetic resonance (FMR) are pivotal to modern magnetism
and spintronics. Recently, we reported on the Ferris FMR technique, which
relies on large-amplitude modulation of the externally applied magnetic field.
It was shown to benefit from high sensitivity while being broadband. The Ferris
FMR also expanded the resonance linewidth such that the sensitivity to spin
currents was enhanced as well. Eventually, the spin Hall angle ({\theta}_SH)
was measurable even in wafer-level measurements that require low current
densities to reduce the Joule heating. Despite the various advantages, analysis
of the Ferris FMR response is limited to numerical modeling where the linewidth
depends on multiple factors such as the field modulation profile and the
magnetization saturation. Here, we describe in detail the basic principles of
operation of the Ferris FMR and discuss its applicability and engineering
considerations. We demonstrated these principles in a measurement of the
orbital Hall effect taking place in Cu, using an Au layer as the orbital to
spin current converter. This illustrates the potential of the Ferris FMR for
the future development of spintronics technology.",2306.01783v1
2018-07-04,Phase Boundary Exchange Coupling in the Mixed Magnetic Phase Regime of a Pd-doped FeRh Epilayer,"Spin-wave resonance measurements were performed in the mixed magnetic phase
regime of a Pd-doped FeRh epilayer that appears as the first-order
ferromagnetic-antiferromagnetic phase transition takes place. It is seen that
the measured value of the exchange stiffness is suppressed throughout the
measurement range when compared to the expected value of the fully
ferromagnetic regime, extracted via the independent means of a measurement of
the Curie point, for only slight changes in the ferromagnetic volume fraction.
This behavior is attributed to the influence of the antiferromagnetic phase:
inspired by previous experiments that show ferromagnetism to be most persistent
at the surfaces and interfaces of FeRh thin films, we modelled the
antiferromagnetic phase as forming a thin layer in the middle of the epilayer
through which the two ferromagnetic layers are coupled up to a certain critical
thickness. The development of this exchange stiffness is then consistent with
that expected from the development of an exchange coupling across the magnetic
phase boundary, as a consequence of a thickness dependent phase transition
taking place in the antiferromagnetic regions and is supported by complimentary
computer simulations of atomistic spin-dynamics. The development of the Gilbert
damping parameter extracted from the ferromagnetic resonance investigations is
consistent with this picture.",1807.01615v6
2016-03-01,Magnetic field dependence of the neutron spin resonance in CeB6,"In zero magnetic field, the famous neutron spin resonance in the f-electron
superconductor CeCoIn5 is similar to the recently discovered exciton peak in
the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5
into two components, indicating that it is a doublet. Here we employ inelastic
neutron scattering (INS) to scrutinize the field dependence of spin
fluctuations in CeB6. The exciton shows a markedly different behavior without
any field splitting. Instead, we observe a second field-induced magnon whose
energy increases with field. At the ferromagnetic zone center, however, we find
only a single mode with a non-monotonic field dependence. At low fields, it is
initially suppressed to zero together with the antiferromagnetic order
parameter, but then reappears at higher fields inside the hidden-order phase,
following the energy of an electron spin resonance (ESR). This is a unique
example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR
and INS consistently over a broad range of magnetic fields.",1603.00383v2
2018-11-20,Topological Fermi-arc surface resonances in bcc iron,"The topological classification of matter has been extended to include
semimetallic phases characterized by the presence of topologically protected
band degeneracies. In Weyl semimetals, the foundational gapless topological
phase, chiral degeneracies are isolated near the Fermi level and give rise to
the Fermi-arc surface states. However, it is now recognized that chiral
degeneracies are ubiquitous in the band structures of systems with broken
spatial inversion ($\mathcal{P}$) or time-reversal ($\mathcal{T}$) symmetry.
This leads to a broadly defined notion of topological metals, which implies the
presence of disconnected Fermi surface sheets characterized by non-zero Chern
numbers inherited from the enclosed chiral degeneracies. Here, we address the
possibility of experimentally observing surface-related signatures of chiral
degeneracies in metals. As a representative system we choose bcc iron, a
well-studied archetypal ferromagnetic metal with two nontrivial electron
pockets. We find that the (110) surface presents arc-like resonances attached
to the topologically nontrivial electron pockets. These Fermi-arc resonances
are due to two different chiral degeneracies, a type-I elementary Weyl point
and a type-II composite (Chern numbers $\pm 2$) Weyl point, located at slightly
different energies close to the Fermi level. We further show that these surface
resonances can be controlled by changing the orientation of magnetization,
eventually being eliminated following a topological phase transition. Our study
thus shows that the intricate Fermi-arc features can be observed in materials
as simple as ferromagnetic iron, and are possibly very common in polar and
magnetic materials broadly speaking. Our study also provides methodological
guidelines to identifying Fermi-arc surface states and resonances, establishing
their topological origin and designing control protocols.",1811.08178v1
2004-05-26,Microwave Magnetoelectric Effects in Single Crystal Bilayers of Yttrium Iron Garnet and Lead Magnesium Niobate-Lead Titanate,"The first observation of microwave magnetoelectric (ME) interactions through
ferromagnetic resonance (FMR) in bilayers of single crystal
ferromagnetic-piezoelectric oxides and a theoretical model for the effect are
presented. An electric field E produces a mechanical deformation in the
piezoelectric phase, resulting in a shift dHE in the resonance field for the
ferromagnet. The strength of ME coupling is obtained from data on dHE vs E.
Studies were performed at 9.3 GHz on bilayers of (111) yttrium iron garnet
(YIG) films and (001) lead magnesium niobate-lead titanate (PMN-PT). The
samples were positioned outside a TE102-reflection type cavity. Resonance
profiles were obtained for E = 0-8 kV/cm for both in-plane and out-of-plane
magnetic fields H. Important results are as follows. (i) The ME coupling in the
bilayers is an order of magnitude stronger than in polycrystalline composites
and is in the range 1-5.4 Oe cm/kOe, depending on the YIG film thickness. (ii)
The coupling strength is dependent on the magnetic field orientation and is
higher for out-of-plane H than for in-plane H. (iii) Estimated ME constant and
its dependence on volume ratio for the two phases are in good agreement with
the data.",0405622v1
2007-06-27,Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study,"We systematically study the influence of ferromagnetic leads on the Kondo
resonance in a quantum dot tuned to the local moment regime. We employ Wilson's
numerical renormalization group method, extended to handle leads with a spin
asymmetric density of states, to identify the effects of (i) a finite spin
polarization in the leads (at the Fermi-surface), (ii) a Stoner splitting in
the bands (governed by the band edges) and (iii) an arbitrary shape of the
leads density of states. For a generic lead density of states the quantum dot
favors being occupied by a particular spin-species due to exchange interaction
with ferromagnetic leads leading to a suppression and splitting of the Kondo
resonance. The application of a magnetic field can compensate this asymmetry
restoring the Kondo effect. We study both the gate-voltage dependence (for a
fixed band structure in the leads) and the spin polarization dependence (for
fixed gate voltage) of this compensation field for various types of bands.
Interestingly, we find that the full recovery of the Kondo resonance of a
quantum dot in presence of leads with an energy dependent density of states is
not only possible by an appropriately tuned external magnetic field but also
via an appropriately tuned gate voltage. For flat bands simple formulas for the
splitting of the local level as a function of the spin polarization and gate
voltage are given.",0706.3997v1
2008-11-04,"Perspectives in spintronics: magnetic resonant tunneling, spin-orbit coupling, and GaMnAs","Spintronics has attracted wide attention by promising novel functionalities
derived from both the electron charge and spin. While branching into new areas
and creating new themes over the past years, the principal goals remain the
spin and magnetic control of the electrical properties, essentially the I-V
characteristics, and vice versa. There are great challenges ahead to meet these
goals. One challenge is to find niche applications for ferromagnetic
semiconductors, such as GaMnAs. Another is to develop further the science of
hybrid ferromagnetic metal/semiconductor heterostructures, as alternatives to
all-semiconductor room temperature spintronics. Here we present our
representative recent efiorts to address such challenges. We show how to make a
digital magnetoresistor by combining two magnetic resonant diodes, or how
introducing ferromagnetic semiconductors as active regions in resonant
tunneling diodes leads to novel efiects of digital magnetoresistance and of
magnetoelectric current oscillations. We also discuss the phenomenon of
tunneling anisotropic magnetoresistance in Fe/GaAs junctions by introducing the
concept of the spin-orbit coupling field, as an analog of such fields in
all-semiconductor junctions. Finally, we look at fundamental electronic and
optical properties of GaMnAs by employing reasonable tight-binding models to
study disorder efiects.",0811.0500v1
2012-07-31,Surface Acoustic Wave-Driven Ferromagnetic Resonance in Nickel Thin Films: Theory and Experiment,"We present an extensive experimental and theoretical study of surface
acoustic wave-driven ferromagnetic resonance. In a first modeling approach
based on the Landau-Lifshitz-Gilbert equation, we derive expressions for the
magnetization dynamics upon magnetoelastic driving that are used to calculate
the absorbed microwave power upon magnetic resonance as well as the spin
current density generated by the precessing magnetization in the vicinity of a
ferromagnet/normal metal interface. In a second modeling approach, we deal with
the backaction of the magnetization dynamics on the elastic wave by solving the
elastic wave equation and the Landau-Lifshitz-Gilbert equation
selfconsistently, obtaining analytical solutions for the acoustic wave phase
shift and attenuation. We compare both modeling approaches with the complex
forward transmission of a LiNbO$_3$/Ni surface acoustic wave hybrid device
recorded experimentally as a function of the external magnetic field
orientation and magnitude, rotating the field within three different planes and
employing three different surface acoustic wave frequencies. We find
quantitative agreement of the experimentally observed power absorption and
surface acoustic wave phase shift with our modeling predictions using one set
of parameters for all field configurations and frequencies.",1208.0001v1
2014-12-07,Stoner ferromagnetism of a strongly interacting Fermi gas in the quasirepulsive regime,"Recent advances in rapidly quenched ultracold atomic Fermi gases near a
Feshbach resonance have brought about a number of interesting problems, in the
context of observing the long-sought Stoner ferromagnetic phase transition. The
possibility of experimentally obtaining a ""quasirepulsive"" regime in the upper
branch of the energy spectrum due to the rapid quench is currently being
debated, and the Stoner transition has mainly been investigated theoretically
by using perturbation theory or at high polarization, due to the limited
theoretical approaches in the strongly repulsive regime. In this work, we
present a nonperturbative theoretical approach to the quasirepulsive upper
branch of a Fermi gas near a broad Feshbach resonance, and we determine the
finite-temperature phase diagram for the Stoner instability. Our results agree
well with the known quantum Monte-Carlo simulations at zero temperature, and we
recover the known virial expansion prediction at high temperature for arbitrary
interaction strengths. At resonance, we find that the Stoner transition
temperature becomes of the order of the Fermi temperature, around which the
molecule formation rate becomes vanishingly small. This suggests a feasible way
to observe Stoner ferromagnetism in the nondegenerate temperature regime.",1412.2412v3
2019-03-13,Nutation spectroscopy of a nanomagnet driven into deeply nonlinear ferromagnetic resonance,"Strongly out-of-equilibrium regimes in magnetic nanostructures exhibit novel
properties, linked to the nonlinear nature of magnetization dynamics, which are
of great fundamental and practical interest. Here, we demonstrate that
field-driven ferromagnetic resonance can occur with substantial spatial
coherency at unprecedented large angle of magnetization precessions, which is
normally prevented by the onset of spin-wave instabilities and magnetization
turbulent dynamics. Our results show that this limitation can be overcome in
nanomagnets, where the geometric confinement drastically reduces the density of
spin-wave modes. The obtained deeply nonlinear ferromagnetic resonance regime
is probed by a new spectroscopic technique based on the application of a second
excitation field. This enables to resonantly drive slow coherent magnetization
nutations around the large angle periodic trajectory. Our experimental findings
are well accounted for by an analytical model derived for systems with uniaxial
symmetry. They also provide new means for controlling highly nonlinear
magnetization dynamics in nanostructures, which open interesting applicative
opportunities in the context of magnetic nanotechnologies.",1903.05411v1
2022-05-19,Resonant phonon-magnon interactions in free-standing metal-ferromagnet multilayer structures,"We analyze resonant magneto-elastic interactions between standing
perpendicular spin wave modes (exchange magnons) and longitudinal acoustic
phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer
structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all
metal layers control the frequencies and eigenmodes of acoustic vibrations. The
here proposed design allows for achieving and tuning the spectral and spatial
modes overlap between phonons and magnons that results in their strong resonant
interaction. Realistic simulations for gold-nickel multilayers show that
sweeping the external magnetic field should allow for observing resonantly
enhanced interactions between individual magnon and phonon modes in a broad
range of frequencies spanning from tens of GHz up to several hundreds of GHz,
which can be finely tuned through the multilayer design. Our results would
enable the systematic study and the deep understanding of resonantly enhanced
magneto-elastic coupling between individual phonon and magnon modes up to
frequencies of great contemporary fundamental and applied interest.",2205.09805v1
2018-12-23,Voltage control of the long-range p-d exchange coupling in a ferromagnet-semiconductor quantum well hybrid structure,"Voltage control of ferromagnetism on the nanometer scale is highly appealing
for the development of novel electronic devices. Here a key challenge is to
implement and combine low power consumption, high operation speed, reliable
reversibility and compatibility with semiconductor technology. Hybrid
structures based on the assembly of ferromagnetic and semiconducting building
blocks are attractive candidates in that respect as such systems bring together
the properties of the isolated constituents: They are expected to show magnetic
order as a ferromagnet and to be electrically tunable as a semiconductor. Here
we demonstrate the electrical control of the exchange coupling in a hybrid
consisting of a ferromagnetic Co layer and a semiconductor CdTe quantum well,
separated by a thin non-magnetic (Cd,Mg)Te barrier. The effective magnetic
field of the exchange interaction reaches up to 2.5 Tesla and can be turned on
and off by application of 1 V bias across the heterostructure. The mechanism of
this electric field control is essentially different from the conventional
concept, in which wavefunctions are spatially redistributed to vary the
exchange interaction, requiring high field strengths. Here we address instead
control of the novel exchange mechanism that is mediated by elliptically
polarized phonons emitted from the ferromagnet, i.e. the phononic ac Stark
effect. An essential parameter of this coupling is the splitting between heavy
and light hole states in the quantum well which can be varied by the electric
field induced band bending. Thereby the splitting can be tuned with respect to
the magnon-phonon resonance energy in the ferromagnet, leading to maximum
coupling for flat band conditions. Our results demonstrate the feasibility of
electrically controlled exchange coupling in hybrid semiconductor
nanostructures at quite moderate electric field strengths.",1812.09680v1
2003-03-06,Magnetovibrational coupling in small cantilevers,"A nano-magnetomechanical system consisting of a cantilever and a thin
magnetic film is predicted to display magnetovibrational modes, which should
enable applications for sensors and actuators. The {}``polaritonic{}'' modes
can be detected by line splittings in ferromagnetic resonance spectra.",0303114v2
2004-09-25,Nano-mechanical magnetization reversal,"The dynamics of the ferromagnetic order parameter in thin magnetic films is
strongly affected by the magnetomechanical coupling at certain resonance
frequencies. By solving the equation of motion of the coupled mechanical and
magnetic degrees of freedom we show that the magnetic-field induced
magnetization switching can be strongly accelerated by the lattice and
illustrate the possibility of magnetization reversal by mechanical actuation.",0409681v1
2009-10-28,Preparation of Cobalt Thin Films by Sputtering Systems and Its Magnetic Characterization,"Different thicknesses of cobalt thin films were growth by magnetron
sputtering deposition techniques. The films thicknesses were determinated with
X ray Photoelectron Spectroscopy (XPS) and Quartz Crystal Monitoring (QCM). XPS
is also used to determinate the films quality. The films magnetic properties
were determinated by Ferromagnetic Resonance (FMR) technique.",0910.5452v1
2018-03-19,Internal spin resistance of spin batteries,"For spin batteries we introduce the concept of internal spin resistance which
quantifies the amount of backflow from the load to the battery. It allows to
relate through a Thevenin-Norton relation, spin current sources to spin
accumulation sources. The value of the internal spin resistance is derived
explicitly for several spin batteries based on spin injection, ferromagnetic
resonance or spin Hall effect.",1803.07101v1
2023-11-28,Temperature dependence of the magnon-phonon interaction in high overtone bulk acoustic resonator-ferromagnetic thin film hybrids,"Tailored magnon-phonon hybrid systems, where high overtone bulk acoustic
resonators couple resonantly to the magnonic mode of a ferromagnetic thin film,
are considered optimal for the creation of acoustic phonons with a defined
circular polarization. This class of devices is therefore ideal for the
investigation of phonon propagation properties and assessing their capacity to
transport angular momentum in the classical and potentially even in the quantum
regime. Here, we study the coupling between the magnons in a ferromagnetic
\ch{Co25Fe75} thin film and the transverse acoustic phonons in a bulk acoustic
wave resonators formed by the sapphire substrate onto which the film is
deposited. Using broadband ferromagnetic resonance experiments as a function of
temperature, we investigate the strength of the coherent magnon-phonon
interaction and the individual damping rates of the magnons and phonons
participating in the process. This demonstrates that this coupled magnon-phonon
system can reach a cooperativity $C\approx 1$ at cryogenic temperatures. Our
experiments also showcase the potential of strongly coupled magnon-phonon
systems for strain sensing applications.",2311.16725v1
2021-03-26,Microwave resonances of magnetic skyrmions in thin film multilayers,"Non-collinear magnets exhibit a rich array of dynamic properties at microwave
frequencies. They can host nanometre-scale topological textures known as
skyrmions, whose spin resonances are expected to be highly sensitive to their
local magnetic environment. Here, we report a magnetic resonance study of an
[Ir/Fe/Co/Pt] multilayer hosting N\'eel skyrmions at room temperature.
Experiments reveal two distinct resonances of the skyrmion phase during
in-plane ac excitation, with frequencies between 6-12 GHz. Complementary
micromagnetic simulations indicate that the net magnetic dipole moment rotates
counterclockwise (CCW) during both resonances. The magnon probability
distribution for the lower-frequency resonance is localised within isolated
skyrmions, unlike the higher-frequency mode which principally originates from
areas between skyrmions. However, the properties of both modes depend
sensitively on the out-of-plane dipolar coupling, which is controlled via the
ferromagnetic layer spacing in our heterostructures. The gyrations of stable
isolated skyrmions reported in this room temperature study encourage the
development of new material platforms and applications based on skyrmion
resonances. Moreover, our material architecture enables the resonance spectra
to be tuned, thus extending the functionality of such applications over a
broadband frequency range.",2103.14524v1
2012-10-04,THz spectroscopy in the pseudo-Kagome system Cu3Bi(SeO3)2O2Br,"Terahertz (THz) transmission spectra have been measured as function of
temperature and magnetic field on single crystals of Cu3Bi(SeO3)2O2Br. In the
time-domain THz spectra without magnetic field, two resonance absorptions are
observed below the magnetic ordering temperature T_N~27.4 K. The corresponding
resonance frequencies increase with decreasing temperature and reach energies
of 1.28 and 1.23 meV at 3.5 K. Multi-frequency electron spin resonance
transmission spectra as a function of applied magnetic field show the field
dependence of four magnetic resonance modes, which can be modeled as a
ferromagnetic resonance including demagnetization and anisotropy effects.",1210.1343v2
2013-02-28,First-principles calculations of spin and angle-resolved resonant photoemission spectra of Cr(110) surfaces at the 2$p$ - 3$d$ resonance,"A first principles approach for spin and angle resolved resonant
photoemission is developed within multiple scattering theory and applied to a
Cr(110) surface at the 2$p$-3$d$ resonance. The resonant photocurrent from this
non ferromagnetic system is found to be strongly spin polarized by circularly
polarized light, in agreement with experiments on antiferromagnetic and
magnetically disordered systems. By comparing the antiferromagnetic and
Pauli-paramagnetic phases of Cr, we explicitly show that the spin polarization
of the photocurrent is independent of the existence of local magnetic moments,
solving a long-standing debate on the origin of such polarization. New spin
polarization effects are predicted for the paramagnetic phase even with
unpolarized light, opening new directions for full mapping of spin interactions
in macroscopically non magnetic or nanostructured systems.",1302.7160v1
2014-12-11,Deviation From the Landau-Lifshitz-Gilbert equation in the Inertial regime of the Magnetization,"We investigate in details the inertial dynamics of a uniform magnetization in
the ferromagnetic resonance (FMR) context. Analytical predictions and numerical
simulations of the complete equations within the Inertial
Landau-Lifshitz-Gilbert (ILLG) model are presented. In addition to the usual
precession resonance, the inertial model gives a second resonance peak
associated to the nutation dynamics provided that the damping is not too large.
The analytical resolution of the equations of motion yields both the precession
and nutation angular frequencies. They are function of the inertial dynamics
characteristic time $\tau$, the dimensionless damping $\alpha$ and the static
magnetic field $H$. A scaling function with respect to $\alpha\tau\gamma H$ is
found for the nutation angular frequency, also valid for the precession angular
frequency when $\alpha\tau\gamma H\gg 1$. Beyond the direct measurement of the
nutation resonance peak, we show that the inertial dynamics of the
magnetization has measurable effects on both the width and the angular
frequency of the precession resonance peak when varying the applied static
field. These predictions could be used to experimentally identify the inertial
dynamics of the magnetization proposed in the ILLG model.",1412.3783v1
2019-06-28,Ground-state cooling of an magnomechanical resonator induced by magnetic damping,"Quantum manipulation of mechanical resonators has been widely applied in
fundamental physics and quantum information processing. Among them, cooling the
mechanical system to its quantum ground state is regarded as a key step. In
this work, we propose a scheme which one can realize ground-state cooling of
resonator in a cavity magnomechanical system. The system consists of a
microwave cavity and a small ferromagnetic sphere, in which phonon-magnon
coupling and cavity photon-magnon coupling can be achieved via magnetostrictive
interaction and magnetic dipole interaction, respectively. After adiabatically
eliminating the cavity mode, an effective Hamiltonian which consists of magnon
and mechanical modes is obtained. Within experimentally feasible parameters, we
demonstrate that the ground-state cooling of the magnomechanical resonator can
be achieved by extra magnetic damping. Unlike optomechanical cooling,
magnomechanical interaction is utilized to realize the cooling of resonators.
We further illustrate the ground-state cooling can be effectively controlled by
the external magnetic field.",1906.12081v1
2019-11-26,Ultrastrong coupling between a microwave resonator and antiferromagnetic resonances of rare earth ion spins,"Quantum magnonics is a new and active research field, leveraging the strong
collective coupling between microwaves and magnetically ordered spin systems.
To date work in quantum magnonics has focused on transition metals and almost
entirely on ferromagnetic resonances in yttrium iron garnet (YIG).
Antiferromagnetic systems have gained interest as they produce no stray field,
and are therefore robust to magnetic perturbations and have narrow, shape
independent resonant linewidths. Here we show the first experimental evidence
of ultrastrong-coupling between a microwave cavity and collective
antiferromagnetic resonances (magnons) in a rare earth crystal. The combination
of the unique optical and spin properties of the rare earths and collective
antiferromagnetic order paves the way for novel quantum magnonic applications.",1911.11311v1
2000-04-20,Spin accumulation in the semi classical and quantum regimes,"We consider spin accumulation at a ferromagnet--normal metal interface in the
presence of magnetic scattering in the normal metal. In the classical regime,
we discuss the inverse Drude scaling of the conductance as a function of the
interface transparencies. We present a treatment based on an exact solution of
the Boltzmann equation. In the quantum regime, we solve a single impurity
``spin-flip Fabry Perot interferometer'' for quantum coherent multiple
scatterings, in which we find a resonance in the spin flip channels. This
resonance appears to be the quantum analog of the semi classical inverse Drude
scaling of the conductance.",0004355v2
2002-01-23,Mechanical detection of FMR spectrum in a normally magnetized YIG disk,"The ferromagnetic resonance spectrum of a normally magnetized YIG disk, with
thickness of 4.75$\mu$m and radius of 80$\mu$m, is measured at room temperature
both by magnetic resonance force microscopy and by standard detection of the
microwave susceptibility. The comparison indicates that MRFM represents one of
the most potent means of obtaining the \emph{complete} FMR spectra of
micron-size samples. In the weak coupling regime, the measured data can be
quantitatively understood within the framework of the Damon and Eshbach model.",0201409v1
2004-01-05,Resonance magneto-resistance in double barrier structure with spin-valve,"The conductance and tunnel magneto-resistance (TMR) of the double barrier
magnetic tunnel junction with spin-valve sandwich (F/P/F) inserted between two
insulating barrier, are theoretically investigated. It is shown, that resonant
tunnelling, due to the quantum well states of the electron confined between two
barriers, sharply depends on the mutual orientation of the magnetizations of
ferromagnetic layers F. The calculated optimistic value of TMR exceeds 2000% .",0401006v2
2004-01-29,Driving mechanisms behind the various phases in manganese perovskites revealed by Mn 2p resonance photoemission,"Unusual temperature and doping dependence of the Mn 3d spectral functions of
manganese perovskites Nd1-xSrxMnO3 has been revealed by the high-resolution Mn
2p-3d resonance photoemission. The temperature-dependent spectra cannot be
explained by any theoretical model currently under debate, while showing
evidence for a microscopic and dynamic phase segregation. The experimental
results strongly suggest that the competition of both the dynamical and static
Jahn-Teller effects with ferromagnetic ordering at high and low temperatures,
respectively, is responsible for the actual electronic states.",0401601v1
2004-08-21,Fermion Superfluids of Non-Zero Orbital Angular Momentum near Resonance,"We study the pairing of Fermi gases near the scattering resonance of the
$\ell\neq 0$ partial wave. Using a model potential which reproduces the actual
two-body low energy scattering amplitude, we have obtained an analytic solution
of the gap equation. We show that the ground state of $\ell=1$ and $\ell=3$
superfluid are orbital ferromagnets with pairing wavefunctions $Y_{11}$ and
$Y_{32}$ respectively. For $\ell=2$, there is a degeneracy between $Y_{22}$ and
a ""cyclic state"". Dipole energy will orient the angular momentum axis. The gap
function can be determined by the angular dependence of the momentum
distribution of the fermions.",0408468v1
2005-03-08,The temperature dependence of interlayer exchange coupling - spin waves vs. spacer effects,"There are different mechanisms proposed to be responsible for the temperature
dependence of the interlayer exchange coupling (IEC), namely a smearing out of
the spacer or interface Fermi surface and excitations and interactions of spin
waves. We propose a possibility to separate both effects by calculating the
excitation spectrum of an extended Heisenberg model and connecting the results
with ferromagnetic resonance (FMR) experiments. To solve the Heisenberg model
we use an approximation that was shown to yield excellent results. In this
paper the main idea of this procedure is explained and a detailed investigation
of the spin wave contribution to the temperature dependence of FMR resonance
frequencies and fields is carried out.",0503178v1
2005-03-15,System size resonance in an attractor neural network,"We study the response of an attractor neural network, in the ferromagnetic
phase, to an external, time-dependent stimulus, which drives the system
periodically two different attractors. We demonstrate a non-trivial dependance
of the system via a system size resonance, by showing a signal amplification
maximum at a certain finite size.",0503374v1
2006-05-23,Suppression of telegraph noise in a CPP spin valve by an oscillating spin torque: Numerical study,"The phenomenon of stochastic resonance (SR) has been mainly studied in
one-dimensional systems with additive noise. We show that in higher dimensional
systems and in the presence of multiplicative noise, a non-linear magnetic
system with a strongly periodic current can show behavior similar to that of SR
but only for frequencies below the ferromagnetic resonance (FMR) frequency of
the system. Such a phenomena can provide an effective way to suppress low
frequency noise in spin valve magnetic sensors.",0605585v1
1996-06-04,Direct Hopf Bifurcation in Parametric Resonance of Hybridized Waves,"We study parametric resonance of interacting waves having the same wave
vector and frequency. In addition to the well-known period-doubling instability
we show that under certain conditions the instability is caused by a Hopf
bifurcation leading to quasiperiodic traveling waves. It occurs, for example,
if the group velocities of both waves have different signs and the damping is
weak. The dynamics above the threshold is briefly discussed. Examples
concerning ferromagnetic spin waves and surface waves of ferro fluids are
discussed.",9605006v1
2000-04-11,Theory of acoustic analog of magneto-optic Kerr effect under magnon-phonon resonance,"Theory of the acoustic analog of the polar Kerr effect is developed for an
inclined incidence of the p-type wave on the interface between isotropic
non-magnetic medium and ferromagnetic cubic crystal. Magnetic field dependences
of ellipticity and rotation of the polarization plane of the reflected wave
under magnon-phonon resonance are analysed in a weak-coupling approximation for
interaction of magnetic and elastic subsystems.",0004017v1
2008-01-15,A Resonant soft x-ray powder diffraction study to determine the orbital ordering in A-site ordered SmBaMn2O6,"Soft X-ray resonant powder diffraction has been performed at the Mn L2,3
edges of A-site ordered SmBaMn2O6. The energy and polarization dependence of
the (1/2 1/2 0) reflection provide direct evidence for a (x2-z2)/(y2-z2) type
orbital ordering in contrast to the single layer manganite. The temperature
dependence of the reflection indicates an orbital reorientation transition at
210 K, below which the charge and orbital ordered MnO2 sheets show AAAA type of
stacking. The concurring reduction of the ferromagnetic super exchange
correlations leads to further charge localization.",0801.2235v1
2008-02-06,Self-organized plane arrays of metallic magnetic elements,"We studied the dynamic magnetic properties of plane periodical arrays of
circular permalloy nano-dots fabricated using a self-organized mask formed by
polysterene nanospheres on the surface of a Permalloy film. Conventional
(microwave cavity) and broadband coplanar-line ferromagnetic resonance setups
were used for the measurements. We found several well resolved resonance peaks.
This result shows that the self-organized mask fabrication technique is able to
produce high-quality samples with small dispersion of geometrical and magnetic
parameters.",0802.0731v1
2008-09-14,Coherent and incoherent metamaterials and the order-disorder transitions,"We demonstrate a new class of ""coherent"" metamaterials, where a regular
ensemble of meta-molecules shows a collective, i.e. coherent, narrow band
resonant response, while disordering the ensemble leads to broadening and
eventually disappearance of the resonance. We draw parallels between the
observed collective behavior of meta-molecules and the Mossbauer effect and
notice certain remarkable similarities with the phase transitions of
ferromagnetic systems.",0809.2361v1
2008-11-18,Cyclotron resonance of a magnetic quantum dot,"The energy spectrum of a one-electron quantum dot doped with a single
magnetic ion is studied in the presence of an external magnetic field. The
allowed cyclotron resonance (CR) transitions are obtained together with their
oscillator strength (OS) as function of the magnetic field, the position of the
magnetic ion, and the quantum dot confinement strength. With increasing
magnetic field a ferromagnetic - antiferromagnetic transition is found that
results in clear signatures in the CR absorption. It leads to discontinuities
in the transition energies and the oscillator strengths and an increase of the
number of allowed transitions.",0811.2954v1
2008-12-30,Magnetically tunable rf wave absorption in polycrystalline La0.67Ba0.33MnO3,"We investigated temperature and magnetic field dependent radio-frequency
electromagnetic absorption in La0.67Ba0.33MnO3 by monitoring changes in
resonance frequency (fr) and current (II) through a LC resonant circuit powered
by an integrated chip oscillator. The ferromagnetic to paramagnetic transition
at Tc in zero external magnetic field is accompanied by an abrupt increase in
fr and I and they are tunable by small external magnetic field. We observed
fractional changes as much as 46% in delfr/fr and 23% in delI/I around Tc under
H = 0.1 T that can be exploited for low magnetic field sensors and other
applications.",0812.5000v1
2010-12-20,Probing La(0.7)Sr(0.3)MnO3 multilayers via spin wave resonances,"La(0.7)Sr(0.3)MnO3/BiFeO3 and La(0.7)Sr(0.3)MnO3/PbZr20Ti80O3 epitaxial
heterostructures have been grown on SrTiO3 substrates. Spin wave resonances are
used to study interface properties of the ferromagnetic La(0.7)Sr(0.3)MnO3. We
find that the addition of the BiFeO3 or PbZr20Ti80O3 causes out-of-plane
surface pinning of the La(0.7)Sr(0.3)MnO3. We are able to place new limits on
the exchange constant D of La(0.7)Sr(0.3)MnO3 grown on these substrates and
confirm the presence of uniaxial and biaxial anisotropies caused by the SrTiO3
substrate.",1012.4273v1
2011-08-12,Magnetic noise induced by dc current in a micron-size magnetic wire,"The magnetic noise spectra induced by direct-current (dc) current flowing
through a micron-scale ferromagnetic wire have been investigated. We have
observed the noise spectra with a resonance frequency. Under the application of
the magnetic field in the plane, the magnetic field dependences of the
resonance frequency and amplitude were well interpreted by the analytical
calculation based on the stochastic model. The noise spectra are attributable
to the resistance oscillation reflecting the uniform magnetization precession
which is produced by the Joule heating due to the dc current.",1108.2548v1
2013-01-07,Metallic spintronic nanofilm as a hydrogen sensor,"We investigate the response of palladium-cobalt bi-layer thin films to
hydrogen charging at atmospheric pressure for spintronic applications. We find
that hydrogen absorption by the palladium layer results in the narrowing and
shifting of the ferromagnetic resonance line for the material. We explain the
observed phenomena as originating from reduction in spin pumping effect and
from variation in the magnetic anisotropy of the cobalt film through an
interface effect. The shift of the resonance frequency or field is the easiest
to detect. We utilize it to demonstrate functionality of the bi-layer films as
a hydrogen sensor.",1301.1106v2
2014-04-09,Current-induced spin torque resonance of magnetic insulators,"We formulate a theory of the AC spin Hall magnetoresistance (SMR) in a
bilayer system consisting of a magnetic insulator such as yttrium iron garnet
(YIG) and a heavy metal such as platinum (Pt). We derive expressions for the DC
voltage generation based on the drift-diffusion spin model and quantum
mechanical boundary condition at the interface that reveal a spin torque
ferromagnetic resonance (ST-FMR). We predict that ST-FMR experiments will
reveal valuable information on the current-induced magnetization dynamics of
magnetic insulators and AC spin Hall effect.",1404.2360v2
2015-10-22,Magneto-optical coupling in whispering gallery mode resonators,"We demonstrate that yttrium iron garnet microspheres support optical
whispering gallery modes similar to those in non-magnetic dielectric materials.
The direction of the ferromagnetic moment tunes both the resonant frequency via
the Voigt effect as well as the degree of polarization rotation via the Faraday
effect. An understanding of the magneto-optical coupling in whispering gallery
modes, where the propagation direction rotates with respect to the
magnetization, is fundamental to the emerging field of cavity optomagnonics.",1510.06661v2
2016-03-10,Localized NMR Mediated by Electrical-Field-Induced Domain Wall Oscillation in Quantum-Hall-Ferromagnet Nanowire,"We present fractional quantum Hall domain walls confined in a gate-defined
wire structure. Our experiments utilize spatial oscillation of domain walls
driven by radio frequency electric fields to cause nuclear magnetic resonance.
The resulting spectra are discussed in terms of both large quadrupole fields
created around the wire and hyperfine fields associated with the oscillating
domain walls. This provides the experimental fact that the domain walls survive
near the confined geometry despite of potential deformation, by which a
localized magnetic resonance is allowed in electrical means.",1603.03167v1
2016-04-15,Electron magnetic resonance in magnetic nanoparticles: dependence on the particle size and applicability of the modified giant spin model,"Superparamagnetic nanoparticles containing hundreds and thousands of coupled
electron spins are on the boundary between classical and quantum behavior, and
demonstrate features which are typical for paramagnetic spins and absent in
macroscopic ferromagnetic systems. In order to better understand the evolution
of magnetization dynamics from quantum to classical behavior with the increase
in the system size, we study the electron magnetic resonance signal in
suspensions of iron oxide nanoparticles as the function of the particle size.
The experimental data are compared with numerical simulations based on the
giant spin approach.",1604.04594v2
2016-09-08,Kondo resonance of a Co atom exchange coupled to a ferromagnetic tip,"The Kondo effect of a Co atom on Cu(100) was investigated with a
low-temperature scanning tunneling microscope using a monoatomically sharp
nickel tip. Upon a tip-Co contact, the differential conductance spectra exhibit
a spin-split asymmetric Kondo resonance. The computed ab initio value of the
exchange coupling is too small to suppress the Kondo effect, but sufficiently
large to produce the splitting observed. A quantitative analysis of the line
shape using the numerical renormalization group technique indicates that the
junction spin polarization is weak.",1609.02363v1
2016-09-26,Transverse Magneto-Optical Kerr Effect in Active Magneto-Plasmonic Structures,"We propose a novel method to enhance the transverse magneto-optical Kerr
effect (TMOKE) in the magneto-plasmonic (MP) nanostructures by means of the
active dielectric layer. We report the theoretical analysis of the
magnetoplasmonic structure with a ferromagnetic dielectric doped with
rear-earth ions (Nd3+) as the example of a gain layer. The enhancement takes
place near the surface plasmon polariton (SPP) resonances of the
nanostructures. The stimulated emission of the dopants in the field of SPP wave
partially compensates its losses. It is shown that due to a decrease of SPP
damping a Q-factor of the MP resonance increases and the TMOKE is increased in
comparison with the passive nanostructure.",1609.07883v1
2012-01-26,Inhomogeneous spin diffusion in traps with cold atoms,"The spin diffusion and damped oscillations are studied in the collision of
two spin polarized clouds of cold atoms with resonant interactions. The strong
density dependence of the diffusion coefficient leads to inhomogeneous spin
diffusion that changes from central to surface spin flow as the temperature
increases. The inhomogeneity and the smaller finite trap size significantly
reduce the spin diffusion rate at low temperatures. The resulting spin
diffusion rates, spin drag and initial damped oscillations are compatible with
measurements at low to high temperatures for resonant attractive interactions
but are incompatible with a metastable ferromagnetic phase.",1201.5526v2
2018-09-26,Resonant magnetic induction tomography of a magnetized sphere,"We demonstrate the structural imaging of magnetostatic spin-wave modes hosted
in a millimeter-sized ferromagnetic sphere. Unlike for low-dimensional magnetic
materials, there is no prior technique to image these modes in bulk magnetized
solid of revolution. Based on resonant magnetic induction tomography in the
microwave range, our approach ensures the robust identification of these
non-trivial spin-wave modes by establishing their azimuthal and polar
dependences, starting point of magnonic fundamental studies and hybrid systems
with complex spin textures well beyond the uniform precession mode.",1809.09785v2
2020-04-01,Interaction-induced current asymmetries in resonant transport through interacting quantum-dot spin valves revealed by iterative summation of path integrals,"Resonant tunneling of electrons between two ferromagnets and a quantum dot in
the presence of an externally applied magnetic field reveals a strong gate
dependence in the linear and nonlinear bias regime. This gate dependence
originates from the interplay between Coulomb interactions and spin-dependent
hybridization between the quantum dot and the leads. To take into account
Coulomb interaction strengths of the same order of magnitude as the external
magnetic field and the hybridization strength we adopt the numerically exact
iterative summation of path integrals (ISPI).",2004.00432v1
2018-06-20,Large Scale Finite-Element Simulation of Micromagnetic Thermal Noise,"An efficient method for the calculation of ferromagnetic resonant modes of
magnetic structures is presented. Finite-element discretization allows flexible
geometries and location dependent material parameters. The resonant modes can
be used for a semi-analytical calculation of the power spectral density of the
thermal white-noise, which is relevant for many sensor applications. The
proposed method is validated by comparing the noise spectrum of a nano-disk
with time-domain simulations.",1806.07683v1
2020-11-13,Non-symmetric spin-pumping in a multiferroic heterostructure,"We present spin pumping experiments in Co/Pt bilayers grown on Al2O3(0001)
and on ferroelectric Y-cut LiNbO3 substrates. Spin pumping is triggered by
resonant ferromagnetic resonance induced by surface acoustic waves. We observe
that spin pumping efficiency varies when both the magnetization vector and the
acoustic wave vector are reversed in Pt/Co/LiNbO3. This phenomenon is not
observed in Pt/Co/Al2O3. We propose that the in-plane electric polarization of
LiNbO3 is at the origin of the observed phenomenon. These observations open up
the perspective of an electric field control of spin pumping efficiency.",2011.06872v1
2022-06-01,Dynamic Fingerprints of Synthetic Antiferromagnet Nanostructures with Interfacial Dzyaloshinskii-Moriya Interaction,"Synthetic antiferromagnet (SAF) nanostructures with interfacial
Dzyaloshinskii-Moriya interaction can host topologically distinct spin textures
such as skyrmions and thus are regarded as promising candidates for both
spintronics and magnonics applications. Here, we present comprehensive
micromagnetic simulations of such material systems and discuss the rich phase
diagrams that contain various types of magnetic configurations. Aside from the
static properties, we further discuss the resonant excitations of the
calculated magnetic states which include individual skyrmions and skyrmioniums.
Finally, the internal modes of SAF skyrmion clusters are studied and discussed
in the context of magnetic sensing applications based on the dynamic
fingerprint in broadband ferromagnetic resonance measurements.",2206.00554v2
2022-07-19,Exact Hole-induced Resonating-Valence-Bond Ground State in Certain $U=\infty$ Hubbard Models,"We prove that the motion of a single hole induces the nearest-neighbor
resonating-valence-bond ground state in the $U=\infty$ Hubbard model on a
triangular cactus - a tree-like variant of a kagome lattice. The result can be
easily generalized to $t-J$ models with antiferromagnetic interactions $J\geq
0$ on the same graphs. This is a weak converse of Nagaoka's theorem of
ferromagnetism on a bipartite lattice.",2207.09498v2
2022-11-28,Dynamical susceptibility of Skyrmion crystal,"Using stereographic projection approach we develop a theory for calculation
of dynamical susceptibility tensor of Skyrmion crystals (SkX), formed in thin
ferromagnetic films with Dzyaloshinskii-Moriya interaction and in the external
magnetic field. Staying whenever possible within analytical framework, we
employ the model anzats for static SkX configuration and discuss small
fluctuations around it. The obtained formulas are numerically analyzed in the
important case of uniform susceptibility, accessible in magnetic resonance (MR)
experiments. We show that, in addition to three characteristic MR frequencies
discussed earlier both theoretically and experimentally, one should also expect
several resonances of smaller amplitude at somewhat higher frequencies.",2211.15740v1
2024-03-11,Magnetic vortex polarity reversal induced gyrotropic motion spectrum splitting in a ferromagnetic disk,"We investigate the gyrotropic motion of the magnetic vortex core in a chain
of a few micron-sized Permalloy disks by electrical resistance measurement with
amplitude-modulated magnetic field. We observe a distinctive splitting of the
resistance peak due to the resonant vortex-core motion under heightened radio
frequency (RF) magnetic field excitation. Our micromagnetic simulation
identifies the splitting of the resonant peak as an outcome of vortex polarity
reversal under substantial RF amplitudes. This study enhances our understanding
of nonlinear magnetic vortex dynamics amidst large RF amplitudes and proposes a
potential pathway for spintronic neural computing thanks to their unique and
controllable magnetization dynamics.",2403.06491v1
1998-06-30,Effects of doping on spin correlations in the periodic Anderson model,"We studied the effects of hole doping on spin correlations in the periodic
Anderson model, mainly at the full and three-quarters-full lower bands cases.
In the full lower band case, strong anti-ferromagnetic correlations develop
when the on-site repulsive interaction strength $U$ becomes comparable to the
quasi-particle band width. In the three-quarters full case, a novel kind of
spin correlation develops that is consistent with the resonance between a
$(\pi,0)$ and a $(0,\pi)$ spin-density wave. In this state the spins on
different sublattices appear uncorrelated. Hole doping away from the completely
full case rapidly destroys the long-range anti-ferromagnetic correlations, in a
manner reminiscent of the destruction of anti-ferromagnetism in the Hubbard
model. In contrast to the Hubbard model, the doping does not shift the peak in
the magnetic structure factor from the $(\pi,\pi)$ position. At dopings
intermediate to the full and three-quarters full cases, only weak spin
correlations exist.",9806374v1
1999-01-16,Transition between two ferromagnetic states driven by orbital ordering in La_{0.88}Sr_{0.12}MnO_3,"A lightly doped perovskite mangantite La_{0.88}Sr_{0.12}MnO_3 exhibits a
phase transition at T_{OO}=145 K from a ferromagnetic metal (T_C=172 K) to a
novel ferromagnetic insulator.We identify that the key parameter in the
transition is the orbital degree of freedom in e_g electrons. By utilizing the
resonant x-ray scattering technique, orbital ordering is directly detected
below T_{OO}, in spite of a significant diminution of the cooperative
Jahn-Teller distortion. The new experimental features are well described by a
theory treating the orbital degree of freedom under strong electron
correlation. The present experimental and theoretical studies uncover a crucial
role of the orbital degree in the metal-insulator transition in lightly doped
manganites.",9901148v1
2001-10-26,Charge current in ferromagnet - triplet superconductor junctions,"We calculate the tunneling conductance spectra of a ferromagnetic metal /
insulator / triplet superconductor from the reflection amplitudes using the
Blonder-Tinkham-Klapwijk (BTK) formula. For the triplet superconductor, we
assume one special $p$-wave order parameter, having line nodes, and two two
dimensional $f$-wave order parameters with line nodes, breaking the time
reversal symmetry. Also we examine nodeless pairing potentials. The evolution
of the spectra with the exchange potential depends solely on the topology of
the gap. The weak Andreev reflection within the ferromagnet results in the
suppression of the tunneling conductance and eliminates the resonances due to
the anisotropy of the pairing potential. The tunneling spectra splits
asymmetrically with respect to $E=0$ under the influence of an external
magnetic field. The results can be used to distinguish between the possible
candidate pairing states of the superconductor Sr$_2$RuO$_4$.",0110544v1
2002-01-14,Temperature dependence of the spin and orbital magnetization density in $Sm_{1-x}Gd_{x} Al_{2}$ around the spin-orbital compensation point,"Non-resonant ferromagnetic x-ray diffraction has been used to separate the
spin and orbital contribution to the magnetization density of the proposed
zero-moment ferromagnet $Sm_{0.982}Gd_{0.018} Al_{2}$. The alignment of the
spin and orbital moments relative to the net magnetization shows a sign
reversal at 84K, the compensation temperature. Below this temperature the
orbital moment is larger than the spin moment, and vice versa above it. This
result implies that the compensation mechanism is driven by the different
temperature dependencies of the $4f$ spin and orbital moments. Specific heat
data indicate that the system remains ferromagnetically ordered throughout.",0201211v2
2002-04-03,Josephson Plasma in RuSr2GdCu2O8,"Josephson plasma in RuSr$_{2}$GdCu$_{2}$O$_{8}$,
Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), and
RuSr$_{2}$Eu$_{2-x}$Ce$_{x}$Cu$_{2}$O$_{10}$ (x = 0.5) compounds is
investigated by the sphere resonance method. The Josephson plasma is observed
in a low-frequency region (around 8.5 cm$^{-1}$ at T $\ll$ $T_{c}$) for
ferromagnetic RuSr$_{2}$GdCu$_{2}$O$_{8}$, while it increases to 35 cm$^{-1}$
for non-ferromagnetic Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), which
represents a large reduction in the Josephson coupling at ferromagnetic
RuO$_{2}$ block layers. The temperature dependence of the plasma does not shift
to zero frequency ({\it i.e.} $j_{c}$ = 0) at low temperatures, indicating that
there is no transition from the 0-phase to the $\pi$-phase in these compounds.
The temperature dependence and the oscillator strength of the peak are
different from those of other non-magnetic cuprates, and the origins of these
anomalies are discussed.",0204070v1
2002-07-16,Spin-polarized currents in superconducting films,"We present a microscopic theory of coherent quantum transport through a
superconducting film between two ferromagnetic electrodes. The scattering
problem is solved for the general case of
ferromagnet/superconductor/ferromagnet (FSF) double-barrier junction, including
the interface transparency from metallic to tunnel limit, and the Fermi
velocity mismatch. Charge and spin conductance spectra of FSF junctions are
calculated for parallel (P) and antiparallel (AP) alignment of the electrode
magnetization. Limiting cases of nonmagnetic normal-metal electrodes (NSN) and
of incoherent transport are also presented. We focus on two characteristic
features of finite size and coherency: subgap tunneling of electrons, and
oscillations of the differential conductance. Periodic vanishing of the Andreev
reflection at the energies of geometrical resonances above the superconducting
gap is a striking consequence of the quasiparticle interference. Also, the
non-trivial spin-polarization of the current is found for FSF junctions in AP
alignment. This is in contrast with the incoherent transport, where the
unpolarized current is accompanied by excess spin accumulation and destruction
of superconductivity. Application to spectroscopic measurements of the
superconducting gap and the Fermi velocity is also discussed.",0207375v1
2003-01-14,Writing Spin in a Quantum Dot with Ferromagnetic and Superconducting Electrodes,"We propose an efficient mechanism for the operation of writing spin in a
quantum dot, which is an ideal candidate for qubit. The idea is based on the
Andreev reflection induced spin polarization (ARISP) in a ferromagnetic /
quantum-dot / superconductor system. We find that on the resonance of Andreev
reflection, the spin polarization of quantum dot strongly denpends on the
magnetization of ferromagnetic electrode, and the sign of the spin polarization
is controllable by bias voltage. In the presence of intradot Coulomb
interaction, we show that ARISP effect can still survive as long as the
charging energy is comparable to the superconducting gap. Detailed conditions
and properties of ARISP are also discussed.",0301213v1
2003-04-16,NRG study of the Kondo effect in the presence of itinerant-electron ferromagnetism,"The Kondo effect in quantum dots (QDs) - artificial magnetic impurities -
attached to ferromagnetic leads is studied with the numerical renormalization
group (NRG) method. It is shown that the QD level is spin-split due to presence
of ferromagnetic electrodes, leading to a suppression of the Kondo effect. We
find that the Kondo effect can be restored by compensating this splitting with
a magnetic field. Although the resulting Kondo resonance then has an unusual
spin asymmetry with a reduced Kondo temperature, the ground state is still a
locally-screened state, describable by Fermi liquid theory and a generalized
Friedel sum rule, and transport in the unitary limit is not spin dependent.",0304385v2
2003-05-19,Josephson effect in double-barrier superconductor-ferromagnet junctions,"We study the Josephson effect in ballistic double-barrier SIFIS planar
junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet
(F), and insulating interfaces (I). We solve the scattering problem based on
the Bogoliubov--de Gennes equations and derive a general expression for the dc
Josephson current, valid for arbitrary interfacial transparency and Fermi wave
vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle
transmission resonances contribute significantly to the Andreev process. The
Josephson current is calculated for various parameters of the junction, and the
influence of both interfacial transparency and FWVM is analyzed. For thin
layers of strong ferromagnet and finite interfacial transparency, we find that
coherent (geometrical) oscillations of the maximum Josephson current are
superimposed on the oscillations related to the crossover between 0 and $\pi$
states. For the same case we find that the temperature-induced $0-\pi$
transition occurs if the junction is very close to the crossovers at zero
temperature.",0305437v2
2003-08-19,"Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors","We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5}
{\rm A cm}^{-2}$.",0308386v3
2004-06-07,"Electronic self-doping of Mo-states in A2FeMoO6 (A=Ca, Sr and Ba) half-metallic ferromagnets - a Nuclear Magnetic Resonance study","A systematic study of (A,A')2FeMoO6 (A,A'=Ca, Sr, Ba) ferromagnetic oxides
with double perovskite structure has been performed using 95,97Mo and 57Fe NMR
spectroscopy. These oxides are isoelectronic but have substantially different
Curie temperatures. The NMR analysis provides clear evidence that the magnetic
moment at Mo sites is not constant but varies sensitively with the ionic size
of the alkaline ions. The 95,97Mo frequency, and thus the electronic charge at
Mo ions, is found to be smaller in Ba and Ca than in Sr-based oxides. The
charge release from Mo sites is accompanied by an uptake at Fe sites, and thus
a self-doping Fe-Mo process is observed. This process is controlled by relevant
structural parameters: the Fe-O-Mo bond length and bending. A clear
relationship between the Curie temperature and the magnetic moment and thus
electron density at Mo sites has been disclosed. The relevance of these
findings for the understanding of ferromagnetic coupling in double perovskites
is discussed.",0406161v1
2005-04-14,High Temperature Molecular Magnetism Caused by pi-electrons: Copper Phthalocyanine Doped with Alkaline Metals,"Electron spin resonance spectra of copper phthalocyanine doped with alkaline
metals (AxCuPc) have been investigated. The temperature dependence of ESR
spectra indicates the ferromagnetic behavior. The Curie-Weiss temperature
varies from 30K to 115K depending on the stoichiometry x of samples. Some
particles of polycrystalline samples were attracted to a weak magnet at
temperature slightly higher than 77K. The observed magnetism is caused by
unpaired pi-electrons of phthalocyanine anions on the Eg doubly degenerated
molecular orbital. The observed ferromagnetism can be understood within the
framework of the McConnell-2 model proposed for organic ferromagnetic
charge-transfer complexes. The high-temperature magnetism in AxCuPc is
considered to be a result of the Zener mechanism of double exchange between
phthalocyanine molecular anions of different valence.",0504354v1
2005-10-07,Theory of orbital state and spin interactions in ferromagnetic titanates,"A spin-orbital superexchange Hamiltonian in a Mott insulator with $t_{2g}$
orbital degeneracy is investigated. More specifically, we focus on a spin
ferromagnetic state of the model and study a collective behavior of orbital
angular momentum. Orbital order in the model occurs in a nontrivial way -- it
is stabilized exclusively by quantum effects through the order-from-disorder
mechanism. Several energetically equivalent orbital orderings are identified.
Some of them are specified by a quadrupole ordering and have no unquenched
angular momentum at low energy. Other states correspond to a noncollinear
ordering of the orbital angular momentum and show the magnetic Bragg peaks at
specific positions. Order parameters are unusually small because of strong
quantum fluctuations. Orbital contribution to the resonant x-ray scattering is
discussed. The dynamical magnetic structure factor in different ordered states
is calculated. Predictions made should help to observe elementary excitations
of orbitals and also to identify the type of the orbital order in ferromagnetic
titanates. Including further a relativistic spin-orbital coupling, we derive an
effective low-energy spin Hamiltonian and calculate a spin-wave spectrum, which
is in good agreement with recent experimental observations in YTiO$_3$.",0510175v1
2006-09-19,Optical response to magnetic ordering in PrMnO_3: the relevance of the double exchange interaction,"The optical conductivity of the undoped PrMnO$_3$ manganite has been
investigated in details at various temperatures between 300 and 4 K. Its low
energy spectrum exhibits an optical gap, and is characterized by a single broad
peak centered at $\sim$ 2 eV. This peak is interpreted in terms of an indirect
interband transition between the split bands $e_\text{g}$ caused by a strong
electron Jahn-Teller phonon coupling. The spectral weight of this transition is
found to be related to the magnetic ordering, which consists of ferromagnetic
planes coupled antiferromagnetically. We show that such a 2D ferromagnetism
plays, via the double exchange interaction, an essential role in the electronic
properties of PrMnO$_3$, which is a 3D antiferromagnetic compound. Finally, an
excess of optical spectral weight is found above the N\'eel temperature, and is
attributed to ferromagnetic fluctuations. A signature of such fluctuations is
equally found from electron spin resonance experiments.",0609451v1
2005-01-01,Equatorial and related non-equilibrium states in magnetization dynamics of ferromagnets: Generalization of Suhl's spin-wave instabilities,"We investigate the nonlinear dynamics underlying the evolution of a 2-D
nanoscale ferromagnetic film with uniaxial anisotropy in the presence of
perpendicular pumping. Considering the associated Landau-Lifshitz spin
evolution equation with Gilbert damping together with Maxwell equation for the
demagnetization field, we study the dynamics in terms of the stereographic
variable. We identify several new fixed points for suitable choice of external
field in a rotating frame of reference. In particular, we identify explicit
equatorial and related fixed points of the spin vector in the plane transverse
to the anisotropy axis when the pumping frequency coincides with the amplitude
of the static parallel field. We then study the linear stability of these novel
fixed points under homogeneous and spin wave perturbations and obtain a
generalized Suhl's instability criterion, giving the condition for exponential
growth of P-modes under spin wave perturbations. Two parameter phase diagrams
(in terms of amplitudes of static parallel and oscillatory perpendicular
magnetic fields) for stability are obtained, which differ qualitatively from
those for the conventional ferromagnetic resonance near thermal equilibrium and
are amenable to experimental tests.",0501002v2
2007-07-26,Spin transport in proximity induced ferromagnetic graphene,"Magnetic gates in close proximity to graphene can induce ferromagnetic
correlations. We study the effect of such induced magnetization dependent
Zeeman splittings on the graphene transport properties. We estimate that
induced spin splittings of the order of \Delta ~ 5 meV could be achieved with
the use of magnetic insulator gates, e.g. EuO-gates, deposited on top of
graphene. We demonstrate that such splittings in proximity induced
ferromagnetic graphene could be determined directly from the tunneling
resonances in the linear response conductance, as the top gate creates also a
tunable barrier in the graphene layer. We show how such splittings could also
be determined independently by magnetoresistance measurements in a spin-valve
geometry. Because the spin polarization of the current near the Dirac point
increases with the length of the barrier, long magnetic gates are desirable for
determining \Delta experimentally.",0707.3976v2
2007-11-14,Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes,"Using a laterally-fabricated quantum-dot (QD) spin-valve device, we
experimentally study the Kondo effect in the electron transport through a
semiconductor QD with an odd number of electrons (N). In a parallel magnetic
configuration of the ferromagnetic electrodes, the Kondo resonance at N = 3
splits clearly without external magnetic fields. With applying magnetic fields
(B), the splitting is gradually reduced, and then the Kondo effect is almost
restored at B = 1.2 T. This means that, in the Kondo regime, an inverse
effective magnetic field of B ~ 1.2 T can be applied to the QD in the parallel
magnetic configuration of the ferromagnetic electrodes.",0711.2124v2
2008-05-20,Proposed realization of itinerant ferromagnetism in optical lattices,"We propose to realize the itinerant ferromagnetism of two-component cold
fermionic atoms in the $p$-orbital bands in optical lattices. The band flatness
in the two-dimensional honeycomb lattice dramatically amplifies the interaction
effect driving the ferromagnetic transition even with a relatively weak
repulsive interaction. This scheme has the advantage that the stability of the
system can be maintained without suffering decaying to the molecular state as
one approaches the Feshbach resonance from the side with positive scattering
length. Experimental signatures and detections are also discussed.",0805.3031v7
2008-06-16,Interplay of Local-Moment Ferromagnetism and Superconductivity in ErRh$_4$B$_4$ Single Crystals,"Tunnel-diode resonator technique was used to study crystals of ferromagnetic
re-entrant superconductor, ErRh$_{4}$B$_{4}$. At the boundary between
ferromagnetism (FM) and superconductivity (SC), dynamic magnetic
susceptibility, $\chi(T,H)$, exhibits highly asymmetric behavior upon warming
and cooling as well as enhanced diamagnetism on the SC side. SC phase nucleates
upon warming in a cascade of discontinuous jumps in magnetic susceptibility
$\chi(T,H)$, whereas FM phase develops gradually as reported in detail in
\cite{prozorov2008}. Here we further investigate enhanced diamagnetism. We find
that when a magnetic field is applied along the magnetic easy axes, a region of
enhanced diamagnetic screening is smaller than in the perpendicular
orientation. A discussion of possible causes of this effect is provided.",0806.2479v1
2009-07-21,A repulsive atomic gas in a harmonic trap on the border of itinerant ferromagnetism,"Alongside superfluidity, itinerant (Stoner) ferromagnetism remains one of the
most well-characterized phases of correlated Fermi systems. A recent experiment
has reported the first evidence for novel phase behavior on the repulsive side
of the Feshbach resonance in a two-component ultracold Fermi gas. By adapting
recent theoretical studies to the atomic trap geometry, we show that an
adiabatic ferromagnetic transition would take place at a weaker interaction
strength than is observed in experiment. This discrepancy motivates a simple
non-equilibrium theory that takes account of the dynamics of magnetic defects
and three-body losses. The formalism developed displays good quantitative
agreement with experiment.",0907.3725v2
2009-10-16,Ferromagnetic proximity effect in F-QDot-S device,"Ferromagnetic proximity effect is studied in InAs nanowire (NW) based quantum
dots (QD) strongly coupled to a ferromagnetic (F) and a superconducting (S)
lead. The influence of the F lead is detected through the splitting of the
spin-1/2 Kondo resonance. We show that the F lead induces a local exchange
field on the QD, which has varying amplitude and a sign depending on the charge
states. The interplay of the F and S correlations generates an exchange field
related supgap feature. This novel mini-gap allows now the visualization of the
exchange field also in even charge states",0910.3237v2
2010-01-28,Stability of a Fully Magnetized Ferromagnetic state in Repulsively Interacting Ultracold Fermi Gases,"We construct a variational wave function to study whether a fully polarized
Fermi sea is energetically stable against a single spin flip. Our variational
wave function contains sufficient short-range correlation at least to the same
level as Gutzwiller's projected wave function. For Hubbard lattice model and
continuum model with pure repulsive interaction, we show a fully polarized
Fermi sea is generally unstable even when the repulsive strength becomes
infinite. While for a resonance model, ferromagnetic state is possible if the
s-wave scattering length is positive and sufficiently large, and the system is
prepared in scattering state orthogonal to molecular bound state. However, we
can not rule out the possibility that more exotic correlation can destabilize
the ferromagnetic state.",1001.5139v2
2010-08-11,Nanoscale Dichotomy of Ti 3d Carriers Mediating the Ferromagnetism in Co:TiO2 Anatase Thin Films,"We study the surface and bulk electronic structure of the room-temperature
ferromagnet Co:TiO2 anatase films using soft and hard x-ray photoemission
spectroscopy with probe sensitivities of ~1 nm and ~10 nm, respectively. We
obtain direct evidence of metallic Ti$^{3+}$ states in the bulk, which get
suppressed to give a surface semiconductor, thus indicating a surface-bulk
dichotomy. X-ray absorption and high-sensitivity resonant photoemission
spectroscopy reveal Ti$^{3+}$ electrons at the Fermi level (E$_F$) and
high-spin Co$^{2+}$ electrons occurring away from E$_F$. The results show the
importance of the charge neutrality condition: Co$^{2+}$ + V$_{O}$$^{2-}$ +
2Ti$^{4+}$ $\leftrightarrow$ Co$^{2+}$ + 2Ti$^{3+}$ (V$_O$ is oxygen vacancy),
which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the
Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals.",1008.1908v1
2010-09-12,Universal valence-band picture of the ferromagnetic semiconductor GaMnAs,"The origin of ferromagnetism in the prototype ferromagnetic semiconductor
GaMnAs is still controversial due to the insufficient understanding of its band
structure and Fermi level position. Here, we show the universal valence-band
(VB) picture of GaMnAs obtained by resonant tunneling spectroscopy for a
variety of surface GaMnAs layers with the Mn concentrations from 6 to 15% and
the Curie temperatures from 71 to 154 K. We find that the Fermi level exists in
the bandgap, and that the VB structure of GaAs is almost perfectly maintained
in all the GaMnAs samples, i.e. VB is not merged with the impurity band.
Furthermore, the p-d exchange splitting of VB is found to be quite small (only
several meV) even in GaMnAs with a high Curie temperature (154 K). These
results indicate that the VB structure of GaMnAs is quite insensitive to the Mn
doping.",1009.2235v1
2010-12-11,Magnetism in C or N-doped MgO and ZnO: density-functional study of impurity pairs,"It is shown that substitution of C or N for O recently proposed as a way to
create ferromagnetism in otherwise nonmagnetic oxide insulators is curtailed by
formation of impurity pairs, and the resultant C2 spin=1 dimers as well as the
isoelectronic N2^{2+} interact antiferromagneticallly in p-type MgO. For
C-doped ZnO, however, we demonstrate using the HSE hybrid functional that a
resonance of the spin-polarized C2 pp\pi* states with the host conduction band
results in a long-range ferromagnetic interaction. Magnetism of open-shell
impurity molecules is proposed as a possible route to d0-ferromagnetism in
oxide spintronic materials.",1012.2439v1
2011-02-01,One-dimentional magnonic crystal as a medium with magnetically tunable disorder on a periodical lattice,"We show that periodic magnetic nanostructures (magnonic crystals) represent
an ideal system for studying excitations on disordered periodical lattices
because of the possibility of controlled variation of the degree of disorder by
varying the applied magnetic field. Ferromagnetic resonance (FMR) data
collected inside minor hysteresis loops for a periodic array of Permalloy
nanowires of alternating width and magnetic force microscopy images of the
array taken after running each of these loops were used to establish convincing
evidence that there is a strong correlation between the type of FMR response
and the degree of disorder of the magnetic ground state. We found two types of
dynamic responses: anti-ferromagnetic (AFM) and ferromagnetic (FM), which
represent collective spin wave modes or collective magnonic states. Depending
on the history of sample magnetization either AFM or FM state is either the
fundamental FMR mode or represents a state of a magnetic defect on the
artificial crystal. A fundamental state can be transformed into a defect one
and vice versa by controlled magnetization of the sample.",1102.0069v1
2011-02-12,Electrical control of ferromagnetism in Mn-doped semiconductor heterostructures,"The interplay of tunneling transport and carrier-mediated ferromagnetism in
narrow semiconductor multi-quantum well structures containing layers of GaMnAs
is investigated within a self-consistent Green's function approach, accounting
for disorder in the Mn--doped regions and unwanted spin-flips at
heterointerfaces on phenomenological ground. We find that the magnetization in
GaMnAs layers can be controlled by an external electric bias. The underlying
mechanism is identified as spin-selective hole tunneling in and out of the
Mn-doped quantum wells, whereby the applied bias determines both hole
population and spin polarization in these layers. In particular we predict
that, near resonance, ferromagnetic order in the Mn doped quantum wells is
destroyed. The interplay of both magnetic and transport properties combined
with structural design potentially leads to several interrelated physical
phenomena, such as dynamic spin filtering, electrical control of magnetization
in individual magnetic layers, and, under specific bias conditions, to
self-sustained current and magnetization oscillations
(magneticmulti-stability). Relevance to recent experimental results is
discussed.",1102.2507v2
2011-04-05,"Ferromagnetic Enhancement of CE-type Spin Ordering in (Pr,Ca)MnO$_3$","We present resonant soft X-ray scattering (RSXS) results from small band
width manganites (Pr,Ca)MnO$_3$, which show that the CE-type spin ordering (SO)
at the phase boundary is stabilized only below the canted antiferromagnetic
transition temperature and enhanced by ferromagnetism in the macroscopically
insulating state (FM-I). Our results reveal the fragility of the CE-type
ordering that underpins the colossal magnetoresistance (CMR) effect in this
system, as well as an unexpected cooperative interplay between FM-I and CE-type
SO which is in contrast to the competitive interplay between the ferromagnetic
metallic (FM-M) state and CE-type ordering.",1104.0757v1
2011-07-04,Continuous Generation of Spinmotive Force in a Patterned Ferromagnetic Film,"We study, both experimentally and theoretically, the generation of a dc
spinmotive force. By exciting a ferromagnetic resonance of a comb-shaped
ferromagnetic thin film, a continuous spinmotive force is generated.
Experimental results are well reproduced by theoretical calculations, offering
a quantitative and microscopic understanding of this spinmotive force.",1107.0549v4
2011-10-25,"Magnetoresistance of individual ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires","We investigate, angle dependent, the magnetoresistance (MR) of individual
self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic
temperatures. The shape of the MR traces and the observed strong anisotropies
in transport can be ascribed to the interplay of the negative magnetoresistance
effect and a strong uniaxial anisotropy with the magnetic easy direction
pointing along the wire axis. The magnetoresistance can be well described by a
quantitative analysis based on the concept of the effective magnetic field,
usually used to describe ferromagnetic resonance phenomena. The nanowires we
investigate exhibit a uniaxial anisotropy which is approximately 5 times larger
than the strain induced anisotropy observed in lithographically prepared
(Ga,Mn)As stripes.",1110.5507v1
2011-12-09,Interfacial coupling across a modified interface studied with ferromagnetic resonance,"Using spin waves we directly probe the interface of an exchange biased
Ni$_{80}$Fe$_{20}$/Ir$_{25}$Mn$_{75}$ film which has been modified by the
presence of an Au dusting layer. Combining this experimental data with a
discretised simulation model, parameters relating to interface exchange
coupling and modification of interface magnetisation are determined. Exchange
coupling is found to be relatively uniform as gold thickness is increased, and
undergoes a sudden drop at 1.5$\textrm{\AA}$ of gold. Interface magnetisation
decreases as a function of the gold dusting thickness. Antiparallel alignment
of the ferromagnet and antiferromagnet supress the interface magnetisation
compared to when they are in parallel alignment. These findings imply that the
interface region has specific magnetisation states which depend on the
ferromagnet orientation.",1112.2045v1
2012-06-07,"Hybridization of electromagnetic, spin and acoustic waves in magnetic having conical spiral ferromagnetic order","The spectrum of hybrid electromagnetic-spin-acoustic waves for magnetic
having conical spiral ferromagnetic structure defined by heterogeneous exchange
and relativistic interactions have been received. The possibility of resonant
interaction of spin, electromagnetic and acoustic waves has been shown. The
electromagnetic waves reflectance from the half-infinity layer of magnetic
having conical spiral ferromagnetic order has been calculated for different
values of external magnetic field (angle of spiral). The acoustic Faradey
effect has been considered.",1206.1421v2
2013-01-10,"Magnetization precession induced by quasi-transverse picosecond strain pulses in (311) ferromagnetic (Ga,Mn)As","Quasi-longitudinal and quasi-transverse picosecond strain pulses injected
into a ferromagnetic (311) (Ga,Mn)As film induce dynamical shear strain in the
film, thereby modulating the magnetic anisotropy and inducing resonant
precession of the magnetization at a frequency ~10 GHz. The modulation of the
out-of-plane magnetization component by the quasitransverse strain reaches
amplitudes as large as 10% of the equilibrium magnetization. Our theoretical
analysis is in good agreement with the observed results, thus providing a
strategy for ultrafast magnetization control in ferromagnetic films by strain
pulses.",1301.2188v1
2013-02-07,Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3d-5d Transition-Metal Compound Sr3CuIrO6,"We report a combined experimental and theoretical study of the unusual
ferromagnetism in the one-dimensional copper-iridium oxide Sr$_3$CuIrO$_6$.
Utilizing Ir $L_3$ edge resonant inelastic x-ray scattering, we reveal a large
gap magnetic excitation spectrum. We find that it is caused by an unusual
exchange anisotropy generating mechanism, namely, strong ferromagnetic
anisotropy arising from antiferromagnetic superexchange, driven by the
alternating strong and weak spin-orbit coupling on the $5d$ Ir and 3d Cu
magnetic ions, respectively. From symmetry consideration, this novel mechanism
is generally present in systems with edge-sharing Cu$^{2+}$O$_4$ plaquettes and
Ir$^{4+}$O$_6$ octahedra. Our results point to unusual magnetic behavior to be
expected in mixed 3d-5d transition-metal compounds via exchange pathways that
are absent in pure 3d or 5d compounds.",1302.1818v2
2013-05-28,Ground-State Ferromagnetic Transition in Strongly Repulsive One-Dimensional Fermi Gases,"We prove that as a one-dimensional Fermi gas is brought across the resonance
adiabatically from large repulsion to large attraction, the singlet ground
state will give way to the maximum spin state, which is the lowest energy state
among the states accessible to the system in this process. In the presence of
tiny symmetry breaking fields that destroy spin conservation, the singlet
ground state can evolve to the ferromagnetic state or a spin segregated state.
We have demonstrated these effects by exact calculations on fermion cluster
relevant to current experiments, and have worked out the quantum mechanical
wavefunction that exhibits phase separation.",1305.6361v3
2013-06-10,Angular Preisach analysis of Hysteresis loops and FMR lineshapes of ferromagnetic nanowire arrays,"Preisach analysis is applied to the study of hysteresis loops measured for
different angles between the applied magnetic field and the common axis of
ferromagnetic Nickel nanowire arrays. When extended to Ferromagnetic Resonance
(FMR) lineshapes, with same set of parameters extracted from the corresponding
hysteresis loops, Preisach analysis shows that a different distribution of
interactions or coercivities ought to be used in order to explain experimental
results. Inspecting the behavior of hysteresis loops and FMR linewidth versus
field angle, we infer that angular dependence might be exploited in angle
sensing devices that could compete with Anisotropic (AMR) or Giant
Magnetoresistive (GMR) based devices.",1306.2216v2
2013-07-06,Probing the Spin Pumping Mechanism: Exchange Coupling with Exponential Decay in Y3Fe5O12/barrier/Pt Heterostructures,"Ferromagnetic resonance driven spin pumping of pure spin currents from a
ferromagnet into a nonmagnetic material promises new spin-functional devices
with low energy consumption. The mechanism of spin pumping is under intense
investigation and it is widely believed that exchange interaction between the
ferromagnet and nonmagnetic material is responsible for this phenomenon. We
observe a thousand-fold exponential decay of the spin pumping from 20-nm thick
Y3Fe5O12 films to platinum across insulating barriers, from which the
exponential decay lengths of 0.16 and 0.23 nm are extracted for oxide barriers
with band gaps of 4.93 eV and 2.36 eV, respectively. This prototypical
signature of quantum tunneling through a barrier underscores the importance of
exchange coupling for spin pumping and reveals its dependence on the
characteristics of the barrier material.",1307.1816v2
2014-01-24,Wavenumber-dependent Gilbert damping in metallic ferromagnets,"New terms to the dynamical equation of magnetization motion, associated with
spin transport, have been reported over the past several years. Each newly
identified term is thought to possess both a real and an imaginary effective
field leading to fieldlike and dampinglike torques on magnetization. Here we
show that three metallic ferromagnets possess an imaginary effective-field term
which mirrors the well-known real effective-field term associated with exchange
in spin waves. Using perpendicular standing spin wave resonance between 2-26
GHz, we evaluate the magnitude of the finite-wavenumber ($k$) dependent Gilbert
damping $\alpha$ in three typical device ferromagnets, Ni$_{79}$Fe$_{21}$, Co,
and Co$_{40}$Fe$_{40}$B$_{20}$, and demonstrate for the first time the presence
of a $k^2$ term as $\Delta\alpha=\Delta\alpha_0+A_{k}\cdot k^2$ in all three
metals. We interpret the new term as the continuum analog of spin pumping,
predicted recently, and show that its magnitude, $A_{k}$=0.07-0.1 nm$^2$, is
consistent with transverse spin relaxation lengths as measured by conventional
(interlayer) spin pumping.",1401.6467v2
2014-04-09,Proximity effect on spin-dependent conductance and thermopower of correlated quantum dots,"We study the electric and thermoelectric transport properties of correlated
quantum dots coupled to two ferromagnetic leads and one superconducting
electrode. Transport through such hybrid devices depends on the interplay of
ferromagnetic-contact induced exchange field, superconducting proximity effect
and correlations leading to the Kondo effect. We consider the limit of large
superconducting gap. The system can be then modeled by an effective Hamiltonian
with a particle-non-conserving term describing the creation and annihilation of
Cooper pairs. By means of the full density-matrix numerical renormalization
group method, we analyze the behavior of electrical and thermal conductances,
as well as the Seebeck coefficient as a function of temperature, dot level
position and the strength of the coupling to the superconductor. We show that
the exchange field may be considerably affected by the superconducting
proximity effect and is generally a function of Andreev bound state energies.
Increasing the coupling to the superconductor may raise the Kondo temperature
and partially restore the exchange-field-split Kondo resonance. The competition
between ferromagnetic and superconducting proximity effects is reflected in the
corresponding temperature and dot level dependence of both the linear
conductance and the (spin) thermopower.",1404.2615v2
2014-07-30,Room Temperature Spin Pumping in Topological Insulator Bi2Se3,"Three-dimensional (3D) topological insulators are known for their strong
spin-orbit coupling and the existence of spin-textured topological surface
states which could be potentially exploited for spintronics. Here, we
investigate spin pumping from a metallic ferromagnet (CoFeB) into a 3D
topological insulator (Bi2Se3) and demonstrate successful spin injection from
CoFeB into Bi2Se3 and the direct detection of the electromotive force generated
by the inverse spin Hal effect (ISHE) at room temperature. The spin pumping,
driven by the magnetization dynamics of the metallic ferromagnet, introduces a
spin current into the topological insulator layer, resulting in a broadening of
the ferromagnetic resonance (FMR) linewidth. We find that the FMR linewidth
more than quintuples, the spin mixing conductance can be as large as
3.4*10^20m^-2 and the spin Hall angle can be as large as 0.23 in the Bi2Se3
layer.",1407.7940v1
2014-11-04,Magnetoimpedance effect at the high frequency range for the thin film geometry: Numerical calculation and experiment,"The magnetoimpedance effect is a versatile tool to investigate ferromagnetic
materials, revealing aspects on the fundamental physics associated to
magnetization dynamics, broadband magnetic properties, important issues for
current and emerging technological applications for magnetic sensors, as well
as insights on ferromagnetic resonance effect at non-saturated magnetic states.
Here, we perform a theoretical and experimental investigation of the
magnetoimpedance effect for the thin film geometry in a wide frequency range.
We calculate the longitudinal magnetoimpedance for single layered, multilayered
or exchange biased systems from an approach that considers a magnetic
permeability model for planar geometry and the appropriate magnetic free energy
density for each structure. From numerical calculations and experimental
results found in literature, we analyze the magnetoimpedance behavior, and
discuss the main features and advantages of each structure. To test the
robustness of the approach, we directly compare theoretical results with
experimental magnetoimpedance measurements obtained in a wide range of
frequencies for an exchange biased multilayered film. Thus, we provide
experimental evidence to confirm the validity of the theoretical approach
employed to describe the magnetoimpedance in ferromagnetic films, revealed by
the good agreement between numerical calculations and experimental results.",1411.0971v1
2014-11-12,Dependence of the Efficiency of Spin Hall Torque on the Transparency of Pt-Ferromagnetic Layer Interfaces,"We report that spin current transport across Pt-ferromagnet (FM) interfaces
is strongly dependent on the type and the thickness of the FM layer and on
post-deposition processing protocols. By employing both harmonic voltage
measurements and spin-torque ferromagnetic resonance measurements, we find that
the efficiency of the Pt spin Hall effect in exerting a damping-like spin
torque on the FM ranges from < 0.05 to > 0.10 under different interfacial
conditions. We also show that the temperature dependence of the spin torque
efficiencies for both the damping-like torque and field-like torque is
dependent upon the details of the Pt-FM interface. The ""internal"" spin Hall
angle of the Pt thin films used in this study, after taking the interfacial
spin transmission factor into account, is estimated to be ~ 0.20. This suggests
that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque
efficiency of Pt-based spintronic devices.",1411.3379v1
2015-02-06,Transport across a carbon nanotube quantum dot contacted with ferromagnetic leads: experiment and non-perturbative modeling,"We present measurements of tunneling magneto-resistance (TMR) in single-wall
carbon nanotubes attached to ferromagnetic contacts in the Coulomb blockade
regime. Strong variations of the TMR with gate voltage over a range of four
conductance resonances, including a peculiar double-dip signature, are
observed. The data is compared to calculations in the ""dressed second order""
(DSO) framework. In this non-perturbative theory, conductance peak positions
and linewidths are affected by charge fluctuations incorporating the properties
of the carbon nanotube quantum dot and the ferromagnetic leads. The theory is
able to qualitatively reproduce the experimental data.",1502.02005v3
2015-08-02,Magnetism and electronic structure of YTiO$_3$ thin films,"High-quality (001)-oriented (pseudo-cubic notation) ferromagnetic YTiO$_3$
thin films were epitaxially synthesized in a layer-by-layer way by pulsed laser
deposition. Structural, magnetic and electronic properties were characterized
by reflection-high-energy-electron-diffraction, X-ray diffraction, vibrating
sample magnetometry, and element-resolved resonant soft X-ray absorption
spectroscopy. To reveal ferromagnetism of the constituent titanium ions, X-ray
magnetic circular dichroism spectroscopy was carried out using four detection
modes probing complimentary spatial scale, which overcomes a challenge of
probing ferromagnetic titanium with pure Ti3+(3d$^1$). Our work provides a
pathway to distinguish between the roles of titanium and A-site magnetic
rare-earth cations in determining the magnetism in rare-earth titanates thin
films and heterostructures.",1508.00198v2
2015-09-15,Dynamical current-induced ferromagnetic and antiferromagnetic resonances,"We demonstrate that ferromagnetic and antiferromagnetic excitations can be
triggered by the dynamical spin accumulations induced by the bulk and surface
contributions of the spin Hall effect. Due to the spin-orbit interaction, a
time-dependent spin density is generated by an oscillatory electric field
applied parallel to the atomic planes of Fe/W(110) multilayers. For symmetric
trilayers of Fe/W/Fe in which the Fe layers are ferromagnetically coupled, we
demonstrate that only the collective out-of-phase precession mode is excited,
while the uniform (in-phase) mode remains silent. When they are
antiferromagnetically coupled, the oscillatory electric field sets the Fe
magnetizations into elliptical precession motions with opposite angular
velocities. The manipulation of different collective spin-wave dynamical modes
through the engineering of the multilayers and their thicknesses may be used to
develop ultrafast spintronics devices. Our work provides a general framework
that probes the realistic responses of materials in the time or frequency
domain.",1509.04599v2
2015-10-16,Adjacent Fe-Vacancy Interactions as the Origin of Room Temperature Ferromagnetism in (In$_{1-x}$Fe$_x$)$_2$O$_3$,"Dilute magnetic semiconductors (DMSs) show great promise for applications in
spin-based electronics, but in most cases continue to elude explanations of
their magnetic behavior. Here, we combine quantitative x-ray spectroscopy and
Anderson impurity model calculations to study ferromagnetic Fe-substituted
In$_2$O$_3$ films, and we identify a subset of Fe atoms adjacent to oxygen
vacancies in the crystal lattice which are responsible for the observed room
temperature ferromagnetism. Using resonant inelastic x-ray scattering, we map
out the near gap electronic structure and provide further support for this
conclusion. Serving as a concrete verification of recent theoretical results
and indirect experimental evidence, these results solidify the role of
impurity-vacancy coupling in oxide-based DMSs.",1510.05030v1
2015-11-30,Engineering quantum magnetism in one-dimensional trapped Fermi gases with p-wave interactions,"The highly controllable ultracold atoms in a one-dimensional (1D) trap
provide a new platform for the ultimate simulation of quantum magnetism. In
this regard, the Neel-antiferromagnetism and the itinerant ferromagnetism are
of central importance and great interest. Here we show that these magnetic
orders can be achieved in the strongly interacting spin-1/2 trapped Fermi gases
with additional p-wave interactions. In this strong coupling limit, the 1D
trapped Fermi gas exhibit an effective Heisenberg spin XXZ chain in the
anisotropic p-wave scattering channels. For a particular p-wave attraction or
repulsion within the same species of fermionic atoms, the system displays
ferromagnetic domains with full spin segregation or the anti-ferromagnetic spin
configuration in the ground state. Such engineered magnetisms are likely to be
probed in a quasi-1D trapped Fermi gas of $^{40}$ K atoms with very close
s-wave and p-wave Feshbach resonances.",1511.09377v4
2016-10-13,Spin-wave spectra in periodically surface-modulated ferromagnetic thin films,"This article presents theoretical results for the dynamic response of
periodically surface-modulated ferromagnetic thin films. For such system, the
role of the periodic dipolar field induced by the modulation is addressed by
using the plane-wave method. By controlling the geometry of the modulated
volumes within the film, the frequency modes and spatial profiles of spin waves
can be manipulated. The angular dependence of the frequency band-gaps unveils
the influence of both dynamic and static magnetic charges, which reside in the
edges of the etching periodic zones, and it is stablished that band-gap widths
created by static magnetic charges are broader than the one created by dynamic
magnetic charges. To corroborate the validity of the model, the theoretical
results are compared with ferromagnetic resonance simulations, where a very
good agreement is achieved between both methods. The theoretical model allows
for a detailed understanding of the physics underlying these kind of systems,
thereby providing an outlook to potential applications associated with magnonic
crystals-based devices.",1610.04176v1
2016-10-18,Spin- and valley-dependent Goos-Hanchen effect in silicene and gapped graphene structures,"We investigate the Goos-H\""anchen shift for ballistic electrons (i) reflected
from a step-like inhomogeneity of the potential energy and (or) effective mass,
and (ii) transmitted through a ferromagnetic barrier region in monolayer
silicene or gapped graphene. For the electrons reflected from a single
interface we found that the Goos-H\""anchen shift is valley-polarized for gapped
graphene structure, and valley- and spin-polarized for silicene due to the
spin-valley coupling. Incontrast, for example, to gapless graphene the lateral
beam shift in gapped structures occurs not only in the case of total, but also
of partial, reflection, i.e. at the angles smaller than the critical angle of
total reflection. We have also demonstrated that the valley- and spin-polarized
displacement of the electron beam, transmitted through a ferromagnetic silicene
barrier, resonantly depends on the barrier width. The resonant values of the
displacement can be controlled by adjusting the electric potential, the
external perpendicular electric field, and the exchange field induced by an
insulating ferromagnetic substrate.",1610.05491v1
2017-07-31,Perfect spin filter by periodic drive of a ferromagnetic quantum barrier,"We consider the problem of particle tunneling through a periodically driven
ferromagnetic quantum barrier connected to two leads. The barrier is modeled by
an impurity site representing a ferromagnetic layer or quantum dot in a
tight-binding Hamiltonian with a local magnetic field and an AC-driven
potential, which is solved using the Floquet formalism. The repulsive
interactions in the quantum barrier are also taken into account. Our results
show that the time-periodic potential causes sharp resonances of perfect
transmission and reflection, which can be tuned by the frequency, the driving
strength, and the magnetic field. We demonstrate that a device based on this
configuration could act as a highly-tunable spin valve for spintronic
applications.",1708.00004v1
2018-02-17,Potential and spin-exchange interaction between Anderson impurities in graphene,"The effective interaction between resonant magnetic Anderson impurities in
graphene, mediated by conduction electrons, is studied as a function of the
strength of the onsite energy level of the impurities and the amplitude of
coupling to conduction electrons. The sign and character of the interaction
depend on whether the impurities reside on the same or opposite sublattices.
For the same (opposite) sublattice, the potential interaction is attractive
(repulsive) in the weak coupling limit with $1/R^3$ dependence on the distance;
the interaction reverses sign and becomes repulsive (attractive) in the strong
coupling limit and displays $1/R$ behavior. The spin-exchange coupling is
ferromagnetic (antiferromagnetic) at both large and small distances, but
reverses sign and becomes anti-ferromagnetic (ferromagnetic) for intermediate
distances. For opposite sublattices, the effective spin exchange coupling is
resonantly enhanced at distances where the energy levels cross the Dirac
points.",1802.06171v1
2018-02-26,Devil's Staircases in SFS Josephson Junctions,"We study the effect of coupling between the superconducting current and
magnetization in the superconductor/ferromagnet/superconductor Josephson
junction under an applied circularly polarized magnetic field. Manifestation of
ferromagnetic resonance in the frequency dependence of the amplitude of the
magnetization and the average critical current density is demonstrated
numerically. The IV-characteristics show subharmonic steps that form devil's
staircases, following a continued fraction algorithm. The origin of the found
steps is related to the effect of the magnetization dynamics on the phase
difference in the Josephson junction. The dynamics of our system is described
by a generalized RCSJ model coupled to the Landau-Lifshitz-Gilbert equation. In
the suplement we justify analytically the appearance of the fractional steps in
IV-characteristics of the superconductor/ferromagnet/superconductor Josephson
junction.",1802.09212v2
2017-04-11,Role of polar compensation in interfacial ferromagnetism of LaNiO$_3$/CaMnO$_3$ superlattices,"Polar compensation can play an important role in the determination of
interfacial electronic and magnetic properties in oxide heterostructures. Using
x-ray absorption spectroscopy, x-ray magnetic circular dichroism, bulk
magnetometry, and transport measurements, we find that interfacial charge
redistribution via polar compensation is essential for explaining the evolution
of interfacial ferromagnetism in LaNiO$_3$/CaMnO$_3$ superlattices as a
function of LaNiO$_3$ layer thickness. In insulating superlattices (4 unit
cells or less of LaNiO$_3$), magnetism is dominated by Ni-Mn superexchange,
while itinerant electron-based Mn-Mn double-exchange plays a role in thicker
metallic superlattices. X-ray magnetic circular dichroism and resonant x-ray
scattering show that Ni-Mn superexchange contributes to the magnetization even
in metallic superlattices. This Ni-Mn superexchange interaction can be
explained in terms of polar compensation at the LaNiO$_3$-CaMnO$_3$ interface.
These results highlight the different mechanisms responsible for interfacial
ferromagnetism and the importance of understanding compensation due to polar
mismatch at oxide-based interfaces when engineering magnetic properties.",1704.03163v1
2014-05-08,Enhancement of Spin Pumping in $\mathrm{Y_3Fe_5O_{12}/Pt/Ni_{81}Fe_{19}}$ Trilayer Film,"We study spin pumping in a
$\mathrm{Y_3Fe_5O_{12}(YIG)/Pt/Ni_{81}Fe_{19}(Py)}$ trilayer film by means of
the inverse spin Hall effect (ISHE). When the ferromagnets are not excited
simultaneously by a microwave, ISHE-induced voltage is of the opposite sign at
each ferromagnetic resonance (FMR). The opposite sign is consistent with spin
pumping of bilayer films. On the other hand, the voltage is of the same sign at
each FMR when both the ferromagnets are excited simultaneously. Futhermore, the
voltage greatly increases in magnitude. The observed voltage is unconventional;
neither its sign nor magnitude can be expected from spin pumping of bilayer
films. Control experiments show that the unconventional voltage is dominantly
induced by spin pumping at the Py/Pt interface. Interaction between YIG and Py
layers is a possible origin of the unconventional voltage.",1405.1929v1
2014-06-04,Hyperfine magnetic field in ferromagnetic graphite,"Information on atomic-scale features is required for a better understanding
of the mechanisms leading to magnetism in non-metallic, carbon-based materials.
This work reports a direct evaluation of the hyperfine magnetic field produced
at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR).
The experimental investigation was made possible by the results of
first-principles calculations carried out in model systems, including graphene
sheets with atomic vacancies and graphite nanoribbons with edge sites partially
passivated by oxygen. A similar range of maximum hyperfine magnetic field
values (18-21T) was found for all systems, setting the frequency span to be
investigated in the NMR experiments; accordingly, a significant 13C NMR signal
was detected close to this range without any external applied magnetic field in
ferromagnetic graphite.",1406.1119v1
2015-12-04,Magnetic proximity effect at interface between a cuprate superconductor and an oxide spin valve,"Heterostructures consisting of a cuprate superconductor YBa2Cu3O7x and a
ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve have been studied by
SQUID magnetometry, ferromagnetic resonances and neutron reflectometry. It was
shown that due to the influence of magnetic proximity effect a magnetic moment
is induced in the superconducting part of heterostructure and at the same time
the magnetic moment is suppressed in the ferromagnetic spin valve. The
experimental value of magnetization induced in the superconductor has the same
order of magnitude with the calculations based on the induced magnetic moment
of Cu atoms due to orbital reconstruction at the superconductor-ferromagnetic
interface. It corresponds also to the model that takes into account the change
in the density of states at a distance of order of the coherence length in the
superconductor. The experimentally obtained characteristic length of
penetration of the magnetic moment into superconductor exceeds the coherence
length for cuprate superconductor. This fact points on the dominance of the
mechanism of the induced magnetic moment of Cu atoms due to orbital
reconstruction.",1512.01336v1
2016-05-12,Classical limit of Rabi nutations in spins of ferromagnets,"Rabi oscillations describe the interaction of a two-level system with a
rotating electromagnetic field. As such, they serve as the principle method for
manipulating quantum bits. By using a combination of femtosecond laser pulses
and microwave excitations, we have observed the classical form of Rabi
nutations in a ferromagnetic system whose equations of motion mirror the case
of a precessing quantum two-level system. Key to our experiments is the
selection of a subset of spins that is in resonance with the microwave
excitation and whose coherence time is thereby extended. Taking advantage of
Gilbert damping, the relaxation times are further increased such that
mode-locking takes place. The observation of such Rabi nutations is the first
step towards potential applications based on phase-coherent spin manipulation
in ferromagnets.",1605.03996v1
2016-08-02,Spin dynamics and magnetic interactions of Mn dopants in the topological insulator Bi$_2$Te$_3$,"The magnetic and electronic properties of the magnetically doped topological
insulator Bi$_{\rm 2-x}$Mn$_{\rm x}$Te$_3$ were studied using electron spin
resonance (ESR) and measurements of static magnetization and electrical
transport. The investigated high quality single crystals of Bi$_{\rm
2-x}$Mn$_{\rm x}$Te$_3$ show a ferromagnetic phase transition for $x\geq 0.04$
at $T_{C}\approx 12$ K. The Hall measurements reveal a p-type finite
charge-carrier density. Measurements of the temperature dependence of the ESR
signal of Mn dopants for different orientations of the external magnetic field
give evidence that the localized Mn moments interact with the mobile charge
carriers leading to a Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling
between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a
low-dimensional character of magnetic correlations that persist far above the
ferromagnetic ordering temperature.",1608.00827v2
2017-10-18,Magnetic Dynamics of Phase Separation Domains in GdMn2O5 and Gd0.8Ce0.2Mn2O5 Multiferroics,"Specific features of the magnetic properties and magnetic dynamics of
isolated phase separation domains in GdMn2O5 and Gd0.8Ce0.2Mn2O5 have been
investigated. These domains represent 1D superlattices consisting of dielectric
and conducting layers with the ferromagnetic orientation of their spins. A set
of ferromagnetic resonances of separate superlattice layers has been studied.
The properties of the 1D superlattices in GdMn2O5 and Gd0.8Ce0.2Mn2O5 are
compared with the properties of the previously investigated RMn2O5 (R = Eu, Tb,
Er, and Bi) series. The similarity of the properties for all the RMn2O5
compounds with different R ion types is established. Based on the concepts of
the magnetic dynamics of ferromagnetic multilayers and properties of
semiconductor superlattices, a 1D model of the superlattices in RMn2O5 is
built.",1710.06695v1
2018-01-01,Optical Control of Exchange Interaction and Kondo Temperature in cold Atom Gas,"The relevance of magnetic impurity problems in cold atom systems depends
crucially on the nature of exchange interaction between itinerant fermionic
atoms and a localized impurity atom. In particular, Kondo physics occurs only
if the exchange interaction is anti-ferromagnetic, and strong enough to yield
high enough Kondo temperature ($T_K/T_F \ge 0.1$). Focusing, as an example, on
the experimentally accessible system of ultra-cold $^{173}$Yb atoms, it is
shown that the sign and strength of an exchange interaction between an
itinerant Yb($^{1}$S$_{0}$) atom and a trapped Yb($^{3}$P$_{0}$) atom can be
optically controlled. Explicitly, as the light intensity increases (from zero),
the exchange interaction changes from ferromagnetic to anti-ferromagnetic. When
the light intensity is just below a singlet Feshbach resonance, the singlet
scattering length $a_S$ is large and negative, and the Kondo temperature
increases sharply.",1801.00482v3
2019-06-07,Angle resolved relaxation of spin currents by antiferromagnets in spin valves,"We observe and analyze tunable relaxation of a pure spin current by an
antiferromagnet in spin-valves. This is achieved by carefully controlling the
angle between a resonantly excited ferromagnetic layer pumping the spin current
and the N\'eel vector of the antiferromagnetic layer. The effect is observed as
an angle-dependent spin-pumping contribution to the ferromagnetic resonance
linewidth. An interplay between spin-mixing conductance and, often disregarded,
longitudinal spin conductance is found to underlie our observations, which is
in agreement with a recent prediction for related ferromagnetic spin valves.",1906.03124v3
2019-06-19,Correlation between the Dzyaloshinskii-Moriya interaction and the orbital angular momentum at an oxide / ferromagnet interface,"We report on the Dzyaloshinskii-Moriya (DMI) interaction at the interface
between a ferromagnet and an oxide. We demonstrate experimentally that oxides
can give rise to DMI. By comparison of systems comprised of Pt/Co90Fe10/Oxide
and Cu/Co90Fe10/Oxide, we also show how oxidation of one interface can enhance
and add to the total DMI of that generated by the Pt interface. This is due to
the fact that the DMI on both interfaces promotes left-handed chirality.
Finally, by use of ferromagnetic resonance spectroscopy, we show that the DMI
and the spectroscopic splitting factor, which is a measure of the orbital
momentum, are correlated. This indicates the importance of hybridization and
charge transfer at the oxide interface for the DMI.",1906.08395v1
2020-02-10,Spontaneous ferromagnetism and finite surface energy gap in the topological insulator Bi$_2$Se$_3$ from surface Bi$_\rm{Se}$ antisite defects,"We perform ab-initio calculations on Bi$_\mathrm{{Se}}$ antisite defects in
the surface of Bi$_2$Se$_3$, finding strong low-energy defect resonances with a
spontaneous ferromagnetism, fixed to an out-of-plane orientation due to an
exceptional large magnetic anisotropy energy. For antisite defects in the
surface layer, we find semi-itinerant ferromagnetism and strong hybridization
with the Dirac surface state, generating a finite energy gap. For deeper lying
defects, such hybridization is largely absent, the magnetic moments becomes
more localized, and no energy gap is present.",2002.03962v2
2000-06-28,Theory of interlayer tunneling in bi-layer quantum Hall ferromagnets,"Spielman et al. have recently observed a large zero-bias peak in the tunnel
conductance of a bi-layer system in a quantum Hall ferromagnet state. We argue
that disorder-induced topological defects in the pseudospin order parameter
limit the peak size and destroy the predicted Josephson effect. We predict that
the peak would be split and shifted by an in-plane magnetic field in a way that
maps the dispersion relation of the ferromagnet's Goldstone mode. We also
predict resonant structures in the DC I-V characteristic under bias by an {\em
ac} electric field.",0006457v1
2017-05-25,"High-temperature intrinsic ferromagnetism in the (In,Fe)Sb semiconductor","The (In,Fe)Sb layers with the Fe content up to 13 at. % have been grown on
(001) GaAs substrates using the pulsed laser deposition. The TEM investigations
show that the (In,Fe)Sb layers are epitaxial and free of the inclusions of a
second phase. The observation of the hysteretic magnetoresistance curves at
temperatures up to 300 K reveals that the Curie point is above room
temperature. The resonant character of magnetic circular dichroism confirms the
intrinsic ferromagnetism in the (In,Fe)Sb layers. We suggest that the
ferromagnetism of the (In,Fe)Sb matrix is not carrier-mediated and apparently
is determined by the mechanism of superexchange interaction between Fe atoms
(This work was presented at the XXI Symposium Nanophysics and Nanoelectronics,
Nizhny Novgorod, March, 13-16, 2017 (book of proceedings v.1, p. 195),
http://nanosymp.ru/UserFiles/Symp/2017_v1.pdf).",1705.09318v3
2018-07-24,Impact of magnetic moment and anisotropy of Co$_\textrm{1-x}$Fe$_\textrm{x}$ thin films on the magnetic proximity effect of Pt,"We present a systematic study of the magnetic proximity effect in Pt,
depending on the magnetic moment and anisotropy of adjacent metallic
ferromagnets. Element-selective x-ray resonant magnetic reflectivity
measurements at the Pt absorption edge (11565$\,$eV) are carried out to
investigate the spin polarization of Pt in Pt/Co$_\textrm{1-x}$Fe$_\textrm{x}$
bilayers. We observe the largest magnetic moment of (0.72$\,\pm\,$0.03)$\,
\mu_\textrm{B}$ per spin polarized Pt atom in
Pt/Co$_\textrm{33}$Fe$_\textrm{67}$, following the Slater-Pauling curve of
magnetic moments in Co-Fe alloys. In general, a clear linear dependence is
observed between the Pt moment and the moment of the adjacent ferromagnet.
Further, we study the magnetic anisotropy of the magnetized Pt which clearly
adopts the magnetic anisotropy of the ferromagnet below. This is depicted for
Pt on Fe(001) and on Co$_\textrm{50}$Fe$_\textrm{50}$(001), which have a
45$^{\circ}$ relative rotation of the fourfold magnetocrystalline anisotropy.",1807.09032v2
2018-08-28,An Intrinsic Spin Orbit Torque Nano-Oscillator,"Spin torque and spin Hall effect nanooscillators generate high intensity spin
wave auto oscillations on the nanoscale enabling novel microwave applications
in spintronics, magnonics, and neuromorphic computing. For their operation,
these devices require externally generated spin currents either from an
additional ferromagnetic layer or a material with a high spin Hall angle. Here
we demonstrate highly coherent field and current tunable microwave signals from
nanoconstrictions in single 15 and 20 nm thick permalloy layers. Using a
combination of spin torque ferromagnetic resonance measurements, scanning
microBrillouin light scattering microscopy, and micromagnetic simulations, we
identify the autooscillations as emanating from a localized edge mode of the
nanoconstriction driven by spin orbit torques. Our results pave the way for
greatly simplified designs of auto oscillating nanomagnetic systems only
requiring a single ferromagnetic layer.",1808.09330v1
2019-11-07,Quantum Oscillations of Gilbert Damping in Ferromagnetic/Graphene Bilayer Systems,"We study the spin dynamics of a ferromagnetic insulator on which graphene is
placed. We show that the Gilbert damping is enhanced by the proximity exchange
coupling at the interface. The modulation of the Gilbert damping constant is
proportional to the product of the spin-up and spin-down densities of states of
graphene. Consequently, the Gilbert damping constant in a strong magnetic field
oscillates as a function of the external magnetic field that originates from
the Landau level structure of graphene. We find that a measurement of the
oscillation period enables the strength of the exchange coupling constant to be
determined. The results demonstrate in theory that the ferromagnetic resonance
measurements may be used to detect the spin resolved electronic structure of
the adjacent materials, which is critically important for future spin device
evaluations.",1911.02775v2
2020-05-21,Surface lattice resonance based magneto-plasmonic switch in NiFe patterned nano-structure,"In this work, a 2D magneto-plasmonic grating structure combining materials
with ferromagnetic and plasmonic properties is demonstrated. NiFe composite
ferromagnetic material, as an active medium with tunable physical properties,
and Au metal, as a plasmonic excitation layer, were the materials of choice.
Here, we have experimentally investigated the active control of the plasmonic
characteristics in Au/NiFe bilayer by the action of an external magnetic field,
as well as the switching effect of the system. The active plasmonic control,
can be achieved by the magnetization switching of the ferromagnetic material,
opening a new path in the development of active plasmonic devices. To our best
knowledge, this is the first demonstration of such a magneto-optical plasmonic
switch based on the coupling of plasmons with magneto-optical active materials,
in which the response time was estimated to be in the range of microseconds.",2005.10913v1
2020-06-11,Observation of a strongly ferromagnetic spinor Bose-Einstein condensate,"We report the observation of strongly ferromagnetic $F=1$ spinor
Bose-Einstein condensates of $^7$Li atoms. The condensates are generated in an
optical dipole trap without using magnetic Feshbach resonances, so that the
condensates have internal spin degrees of freedom. Studying the non-equilibrium
spin dynamics, we have measured the ferromagnetic spin interaction energy and
determined the $s$-wave scattering length difference among total spin $f$
channels to be $a_{f=2}-a_{f=0} =-18(3)$ Bohr radius. This strong
collision-channel dependence leads to a large variation in the condensate size
with different spin composition. We were able to excite a radial monopole mode
after a spin-flip transition between the $|m_F=0\rangle$ and $|m_F=1\rangle$
spin states. From the experiments, we estimated the scattering length ratio
$a_{f=2}/a_{f=0}=0.27(6)$, and determined $a_{f=2}$ = 7(2) and $a_{f=0}$ =
25(5) Bohr radii, respectively. The results indicate the spin-dependent
interaction energy of our system is as large as 46$\%$ of the condensate
chemical potential.",2006.06228v1
2020-06-22,Absence of Spin Hall Magnetoresistance in Pt/(CoNi)n multilayers,"We systematically studied the magnetoresistance effect in a Pt/(CoNi)n
multilayer system with perpendicular magnetic anisotropy and the fcc (111)
texture. The angular dependence of magnetoresistance, including high-order
cosine terms, was observed in a plane perpendicular to the electrical current;
this was attributed to the geometrical-size effects caused by crystal symmetry,
the ordered arrangement of grains, and the anisotropic interface
magnetoresistance effect caused by the breaking of the symmetry at interfaces.
Based on the accuracy of our experimental results, the magnitude of spin Hall
magnetoresistance (SMR) in Pt/(CoNi)n was expected to be below
$1\times10^{-4}$. However, on evaluating the spin Hall angle of $\geq$ 0.07 for
Pt using spin-torque ferromagnetic resonance measurements, the theoretical
magnitude of SMR in our samples was estimated to exceed $7\times10^{-4}$. This
absence of SMR in the experimental results can be explained by the
Elliott-Yafet spin relaxation of itinerant electrons in the ferromagnetic
metal, which indicates that the boundary conditions of the spin current in the
heavy metal/ferromagnetic insulator may not be applicable to all-metallic
heterostructures.",2006.12029v1
2020-06-22,Spin-orbit torque induced magnetisation dynamics and switching in CoFeB/Ta/CoFeB system with mixed magnetic anisotropy,"Spin-orbit torque (SOT) induced magnetisation switching in CoFeB/Ta/CoFeB
trilayer with two CoFeB layers exhibiting in-plane magnetic anisotropy (IPMA)
and perpendicular magnetic anisotropy (PMA) is investigated. Interlayer
exchange coupling (IEC), measured using ferromagnetic resonance technique is
modified by varying thickness of Ta spacer. The evolution of the IEC leads to
different orientation of the magnetic anisotropy axes of two CoFeB layers: for
thicker Ta layer where magnetisation prefers antiferromagnetic ordering and for
thinner Ta layer where ferromagnetic coupling exists. Magnetisation state of
the CoFeB layer exhibiting PMA is controlled by the spin-polarized current
originating from SOT in $\mu m$ sized Hall bars. The evolution of the critical
SOT current density with Ta thickness is presented, showing an increase with
decreasing $t_\mathrm{Ta}$, which coincides with the coercive field dependence.
In a narrow range of $t_\mathrm{Ta}$ corresponding to the ferromagnetic IEC,
the field-free SOT-induced switching is achieved.",2006.12068v1
2021-07-21,Dynamics of two ferromagnetic insulators coupled by superconducting spin current,"A conventional superconductor sandwiched between two ferromagnets can
maintain coherent equilibrium spin current. This spin supercurrent results from
the rotation of odd-frequency spin correlations induced in the superconductor
by the magnetic proximity effect. In the absence of intrinsic magnetization,
the superconductor cannot maintain multiple rotations of the triplet component
but instead provides a Josephson type weak link for the spin supercurrent. We
determine the analogue of the current-phase relation in various circumstances
and show how it can be accessed in experiments on dynamic magnetization. In
particular, concentrating on the magnetic hysteresis and the ferromagnetic
resonance response, we show how the spin supercurrent affects the
nonequilibrium dynamics of magnetization which depends on a competition between
spin supercurrent mediated static exchange contribution and a dynamic spin
pumping contribution. Depending on the outcome of this competition, a mode
crossing in the system can either be an avoided crossing or mode locking.",2107.09959v2
2021-08-03,Atomic scale control of spin current transmission at interfaces,"Spin transmission at ferromagnet/heavy metal interfaces is of vital
importance for many spintronic devices. Usually the spin current transmission
is limited by the spin mixing conductance and loss mechanisms such as spin
memory loss. In order to understand these effects, we study the interface
transmission when an insulating interlayer is inserted between the ferromagnet
and the heavy metal. For this we measure the inverse spin Hall voltage
generated from optically injected spin current pulses as well as the magnitude
of the spin pumping using ferromagnetic resonance. From our results we conclude
that significant spin memory loss only occurs for 5d metals with less than half
filled d-shell.",2108.01770v1
2021-11-16,Ultrathin ferrimagnetic GdFeCo films with very low damping,"Ferromagnetic materials dominate as the magnetically active element in
spintronic devices, but come with drawbacks such as large stray fields, and low
operational frequencies. Compensated ferrimagnets provide an alternative as
they combine the ultrafast magnetization dynamics of antiferromagnets with a
ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets
in spintronic devices their advantageous properties must be retained also in
ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x
thin films in the thickness range t = 2-20 nm were grown on high resistance
Si(100) substrates and studied using broadband ferromagnetic resonance
measurements at room temperature. By tuning their stoichiometry, a nearly
compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1-x ultrathin films
for the first time, with an effective magnetization of Meff = 0.02 T and a low
effective Gilbert damping constant of {\alpha} = 0.0078, comparable to the
lowest values reported so far in 30 nm films. These results show great promise
for the development of ultrafast and energy efficient ferrimagnetic spintronic
devices.",2111.08768v1
2022-03-07,Ultrafast optical observation of spin-pumping induced dynamic exchange coupling in ferromagnetic semiconductor/metal bilayer,"Spin angular momentum transfer in magnetic bilayers offers the possibility of
ultrafast and low-loss operation for next-generation spintronic devices. We
report the field- and temperature- dependent measurements on the magnetization
precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr
effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift
indicates a clear signature of an enhanced dynamic exchange coupling between
the two ferromagnetic (FM) layers due to the reinforced spin pumping at
resonance. The temperature dependence of the dynamic exchange-coupling reveals
a primary contribution from the ferromagnetism in (Ga,Mn)As.",2203.03225v2
2022-06-01,"A hybrid ferromagnetic transmon qubit: circuit design, feasibility and detection protocols for magnetic fluctuations","We propose to exploit currently available tunnel ferromagnetic Josephson
junctions to realize a hybrid superconducting qubit. We show that the
characteristic hysteretic behavior of the ferromagnetic barrier provides an
alternative and intrinsically digital tuning of the qubit frequency by means of
magnetic field pulses. To illustrate functionalities and limitation of the
device, we discuss the coupling to a read-out resonator and the effect of
magnetic fluctuations. The possibility to use the qubit as a noise detector and
its relevance to investigate the subtle interplay of magnetism and
superconductivity is envisaged.",2206.00715v1
2022-07-26,Anderson-Higgs mass of magnons in superconductor/ferromagnet/superconductor systems,"Anderson-Higgs mechanism of mass generation is a generic concept in
high-energy and condensed matter physics. It shows up through the Meissner
effect providing the expulsion of static and low-frequency magnetic fields from
superconductors. However, it does not affect propagating electromagnetic waves
with a spectrum gap determined by the plasma frequency, which is too large to
be sensitive to the superconducting transition. Here we demonstrate the
spectroscopic manifestation of the Anderson-Higgs mass, showing that it
determines the spectrum gap of magnons in
superconductor/ferromagnet/superconductor multilayers. Moreover, we show that
this effect has been observed in recent experiments as a spontaneous
ferromagnetic resonance frequency shift in such systems. Our theory explains
many unusual experimental features and suggests effective controls over the
magnon spectrum with tunable spectral gap and group-velocity reversal. These
findings pave the way to a wide range of advanced functionalities for possible
applications in magnonics.",2207.13201v2
2022-08-10,Efficient spin-to-charge interconversion in Weyl semimetal TaP at room temperature,"In this paper we present spin-to-charge current conversion properties in the
Weyl semimetal TaP by means of the inverse Rashba-Edelstein effect (IREE) with
the integration of this quantum material with the ferromagnetic metal Permalloy
$(Py=Ni_{81}Fe_{19})$. The spin currents are generated in the Py layer by the
spin pumping effect (SPE) from microwave-driven ferromagnetic resonance and are
detected by a dc voltage along the TaP crystal, at room temperature. We observe
a field-symmetric voltage signal without the contamination of asymmetrical
lines due to spin rectification effects observed in studies using metallic
ferromagnets. The observed voltage is attributed to spin-to-charge current
conversion based on the IREE, made possible by the spin-orbit coupling induced
intrinsically by the bulk band structure of Weyl semimetals. The measured IREE
coefficient ${\lambda}_{IREE}=(0.30 \pm{0.01})$ nm is two orders of magnitude
larger than in graphene and is comparable to or larger than the values reported
for some metallic interfaces and for several topological insulators.",2208.05151v1
2022-08-10,Spin-carrier coupling induced ferromagnetism and giant resistivity peak in EuCd$_2$P$_2$,"EuCd$_2$P$_2$ is notable for its unconventional transport: upon cooling the
metallic resistivity changes slope and begins to increase, ultimately 100-fold,
before returning to its metallic value. Surprisingly, this giant peak occurs at
18K, well above the N\'{e}el temperature ($T_N$) of 11.5K. Using a suite of
sensitive probes of magnetism, including resonant x-ray scattering and
magneto-optical polarimetry, we have discovered that ferromagnetic order onsets
above $T_N$ in the temperature range of the resistivity peak. The observation
of inverted hysteresis in this regime shows that ferromagnetism is promoted by
coupling of localized spins and itinerant carriers. The resulting carrier
localization is confirmed by optical conductivity measurements.",2208.05499v1
2022-11-16,Strongly coupled magnon-plasmon polaritons in graphene- 2D ferromagnet heterostructures,"Magnons and plasmons are two very different types of collective modes, acting
on the spin and charge degrees of freedom, respectively. At first sight, the
formation of hybrid plasmon-magnon polaritons in heterostructures of plasmonic
and magnetic systems would face two challenges, the small mutual interaction,
via Zeeman coupling of the electromagnetic field of the plasmon with the spins,
and the energy mismatch, as in most systems plasmons have energies in the eV
range, orders of magnitude larger than magnons. Here we show that graphene
plasmons form polaritons with the magnons of two-dimensional ferrromagnetic
insulators, placed up to to half a micron apart, with Rabi couplings in the
range of 100 GHz (dramatically larger than cavity QED magnonics). This strong
coupling is facilitated both by the small energy of graphene plasmons and the
cooperative super-radiant nature of the plasmon-magnon coupling afforded by
phase matching. We show that the Rabi coupling can be modulated both
electrically and mechanically and we propose a attenuated total internal
reflection experiment to implement ferromagnetic resonance experiments on 2D
ferromagnets driven by plasmon excitation.",2211.08949v1
2022-11-19,Anomalous sign inversion of spin-orbit torque in ferromagnetic/nonmagnetic bilayer systems due to self-induced spin-orbit torque,"Self-induced spin-orbit torques (SI-SOTs) in ferromagnetic (FM) layers have
been overlooked when estimating the spin Hall angle (SHA) of adjacent
nonmagnetic (NM) layers. In this work, we observe anomalous sign inversion of
the total SOT in the spin-torque ferromagnetic resonance due to the enhanced
SI-SOT, and successfully rationalize the sign inversion through a theoretical
calculation considering the SHE in both the NM and FM layers. The findings show
that using an FM layer whose SHA sign is the same as that of the NM achieves
efficient SOT-magnetization switching with the assistance of the SI-SOT. The
contribution of the SI-SOT becomes salient for a weakly conductive NM layer,
and conventional analyses that do not consider the SI-SOT can overestimate the
SHA of the NM layer by a factor of more than 150.",2211.10692v1
2023-01-06,Interfacial magnetic anisotropy controlled spin pumping in Co60Fe20B20/Pt stack,"Controlled spin transport in magnetic stacks is required to realize pure spin
current-driven logic and memory devices. The control over the generation and
detection of the pure spin current is achieved by tuning the spin to charge
conversion efficiency of the heavy metal interfacing with ferromagnets. Here,
we demonstrate the direct tunability of spin angular momentum transfer and
thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy.
The ultra-low thickness of CoFeB thin film tilts the magnetic easy axis from
in-plane to out-of-plane due to surface anisotropy. The Ferromagnetic resonance
measurements are performed to investigate the magnetic anisotropy and spin
pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in
the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density,
with varying ferromagnetic layer thickness, is found to increase from 0.11 to
0.24 MA/m2, with increasing in-plane anisotropy field. Such interfacial
anisotropy-controlled generation of pure spin current can potentially lead to
next-generation anisotropic spin current-controlled spintronic devices.",2301.02370v1
2023-07-05,Theoretical determination of Ising-type transition by using the Self-Consistent Harmonic Approximation,"Over the years, the Self-Consistent Harmonic Approximation (SCHA) has been
successfully utilized to determine the transition temperature of many different
magnetic models, particularly the Berezinskii-Thouless-Kosterlitz transition in
two-dimensional ferromagnets. More recently, the SCHA has found application in
describing ferromagnetic samples in spintronic experiments. In such a case, the
SCHA has proven to be an efficient formalism for representing the coherent
state in the ferromagnetic resonance state. One of the main advantages of using
the SCHA is the quadratic Hamiltonian, which incorporates thermal spin
fluctuations through renormalization parameters, keeping the description simple
while providing excellent agreement with experimental data. In this article, we
investigate the SCHA application in easy-axis magnetic models, a subject that
has not been adequately explored to date. We obtain both semiclassical and
quantum approaches of the SCHA for a general anisotropic magnetic model and
employ them to determine various quantities such as the transition temperature,
spin-wave energy spectrum, magnetization, and critical exponents. To verify the
accuracy of the method, we compare the SCHA results with experimental and Monte
Carlo simulation data for many distinct well-known magnetic materials.",2307.02596v2
2023-10-31,Microwave Spin-Pumping from an Antiferromagnet FeBO3,"Recently, canted antiferromagnets offer great potential for fundamental
research and applications due to their unique properties. The presence of the
Dzyaloshinskii-Moriya interaction leads to the existence of a weak
ferromagnetic moment at room temperature. We study both theoretically and
experimentally microwave spin pumping by the quasi-ferromagnetic mode from a
canted easy plane antiferromagnet with weak ferromagnetism FeBO3. The
conversion of a microwave signal into the constant voltage is realized using
the inverse spin Hall effect in an iron borate/heavy metal heterostructure. We
use an additional bias magnetic field to selectively tune the resonance
frequency of such a microwave detector over a wide range up to 43.5 GHz with
potential sensitivity near 2.5 microV/W. We confirm the pure spin current
nature by changing polarity of the detected via inverse spin Hall effect
voltage by switching the direction of the bias magnetic field. We believe that
our results will be useful for the development of highly tunable, portable and
sensitive microwave antiferromagnet-based functional devices.",2310.20422v1
2018-10-05,Magnetic anisotropy and spin-polarized two-dimensional electron gas in the van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$,"We report a comprehensive experimental investigation on the magnetic
anisotropy in bulk single crystals of Cr$_2$Ge$_2$Te$_6$, a
quasi-two-dimensional ferromagnet belonging to the family of magnetic layered
transition metal trichalcogenides that have attracted recently a big deal of
interest with regard to the fundamental and applied aspects of two-dimensional
magnetism. For this purpose electron spin resonance (ESR) and ferromagnetic
resonance (FMR) measurements have been carried out over a wide frequency and
temperature range. A gradual change in the angular dependence of the ESR
linewidth at temperatures above the ferromagnetic transition temperature
$T_{\rm c}$ reveals the development of two-dimensional spin correlations in the
vicinity of $T_{\rm c}$ thereby proving the intrinsically low-dimensional
character of spin dynamics in Cr$_2$Ge$_2$Te$_6$. Angular and frequency
dependent measurements in the ferromagnetic phase clearly show an easy-axis
type anisotropy of this compound. Furthermore, these experiments are compared
with simulations based on a phenomenological approach, which takes into account
results of static magnetization measurements as well as high temperature $g$
factors obtained from ESR spectroscopy in the paramagnetic phase. As a result
the determined magnetocrystalline anisotropy energy density (MAE) $K_U$ is
$(0.48 \pm 0.02) \times10^6$ erg/cm$^3$. This analysis is complemented by
density functional calculations which yield the experimental MAE value for a
particular value of the electronic correlation strength $U$. The analysis of
the electronic structure reveals that the low-lying conduction band carries
almost completely spin-polarized, quasi-homogeneous, two-dimensional states.",1810.02560v3
2016-04-05,Homodyne-detected ferromagnetic resonance of in-plane magnetized nano-contacts: composite spin wave resonances and their excitation mechanism,"This work provides a detailed investigation of the measured in-plane
field-swept homodyne-detected ferromagnetic resonance (FMR) spectra of an
extended Co/Cu/NiFe pseudo spin valve stack using a nanocontact (NC) geometry.
The magnetodynamics are generated by a pulse-modulated microwave current and
the resulting rectified dc mixing voltage, which appears across the NC at
resonance, is detected using a lock-in amplifier. Most notably, we find that
the measured spectra of the NiFe layer are composite in nature and highly
asymmetric, consistent with the broadband excitation of multiple modes.
Additionally, the data must be fit with two Lorentzian functions in order to
extract a reasonable value for the Gilbert damping of the NiFe. Aided by
micromagnetic simulations, we conclude that (i) for in-plane fields the rf
Oersted field in the vicinity of the NC plays the dominant role in generating
the observed spectra, (ii) in addition to the FMR mode, exchange dominated spin
waves are also generated, and (iii) the NC diameter sets the mean wavevector of
the exchange dominated spin wave, in good agreement with the dispersion
relation.",1604.01389v1
2016-06-23,FMR studies of exchange-coupled multiferroic polycrystalline Pt/BiFeO$_3$/Ni$_{81}$Fe$_{19}$/Pt heterostructures,"An experimental study of the in-plane azimuthal behaviour and frequency
dependence of the ferromagnetic resonance field and the resonance linewidth as
a function of BiFeO$_3$ thickness is carried out in a polycrystalline
exchange-biased BiFeO$_3$/Ni$_{81}$Fe$_{19}$ system. The magnetization decrease
of the Pt/BiFeO$_3$/Ni$_{81}$Fe$_{19}$/Pt heterostructures with BiFeO$_3$
thickness deduced from static measurements has been confirmed by dynamic
investigations. Ferromagnetic resonance measurements have shown lower
gyromagnetic ratio in a perpendicular geometry compared with that of a parallel
geometry. The monotonous decrease of gyromagnetic ratio in a perpendicular
geometry as a function of the BiFeO$_3$ film thickness seems to be related to
the spin-orbit interactions due to the neighbouring Pt film at its interface
with Ni$_{81}$Fe$_{19}$ film. The in-plane azimuthal shape of the total
linewidth of the uniform mode shows isotropic behaviour that increases with
BiFeO$_3$ thickness. The study of the frequency dependence of the resonance
linewidth in a broad band of 3 to 35 GHz has allowed the determination of
intrinsic and extrinsic contributions to the relaxation as function of
BiFeO$_3$ thickness in perpendicular geometries. In our system the magnetic
relaxation is dominated by the spin-pumping mechanism due to the presence of
Pt. The insertion of BiFeO$_3$ between Pt and Ni$_{81}$Fe$_{19}$ attenuates the
spin-pumping damping at one interface.",1606.07296v1
2019-05-20,Injection locking at fractional frequencies of magnetic tunnel junction (MTJ)-based read sensors' ferromagnetic resonance modes,"Being nonlinear dynamic systems, magnetic read sensors should respond to an
excitation signal of a frequency considerably different from their natural
ferromagnetic resonance (FMR) frequencies. Because of the magnetization
dynamics' inherent nonlinear nature, the sensors' response should be measured
at the DC, excitation frequency, and its multiples (harmonics). In this paper,
we present results of such measurements, accomplished using a one-port
nonlinear vector network analyzer (NVNA), which show distinct resonances at
fractional frequencies of the free layer (FL) FMR mode. Identification of these
resonances, resulting from the nonlinear nature of the spin-torque (ST)-induced
magnetization dynamics, was performed using micromagnetic modeling. In
particular, we show that the measured DC response at the above-mentioned
fractional frequencies can be explained by a low-order nonlinearity and strong
magnetodipolar feedback between magnetic layers adjacent to an MgO barrier.
Additionally, we determined that the simulated harmonic response is strongly
enhanced by the mutual ST effect between these layers. Finally, we demonstrate
that the read sensors' nonlinear magnetization dynamics and, by extension,
their harmonic response are highly sensitive to various magnetic and ST
parameters. Thus, this study shows that using NVNA measurements in conjunction
with micromagnetic modeling can clarify the uncertainty in the definition of
these parameters.",1905.08183v2
2016-06-29,Double resonance response of a superconducting quantum metamaterial: manifestation of non-classical states of photons,"We report a theoretical study of ac response of superconducting quantum
metamaterials (SQMs), i.e. an array of qubits (two-levels system) embedded in
the low-dissipative resonator. By making use of a particular example of SQM,
namely the array of charge qubits capacitively coupled to the resonator, we
obtain a second-order phase transition between an incoherent (the
high-temperature phase) and coherent (the low-temperatures phase) states of
photons. This phase transition in many aspects resembles the
paramagnetic-ferromagnetic phase transition. The critical temperature of the
phase transition, $T^\star$, is determined by the energy splitting of two-level
systems $\delta$, number of qubits in the array $N$, and the strength of the
interaction $\eta$ between qubits and photons in the cavity. We obtain that the
photon states manifest themselves by resonant drops in the frequency dependent
transmission $D(\omega)$ of electromagnetic waves propagating through a
transmission line weakly coupled to the SQM. At high temperatures the
$D(\omega)$ displays a single resonant drop, and at low temperatures a peculiar
\emph{double resonance response} has to be observed. The physical origin of
such a resonant splitting is the quantum oscillations between two coherent
states of photons of different polarizations.",1606.09078v1
2021-05-08,Coupling microwave photons to topological spin-textures in Cu$_2$OSeO$_3$,"Topologically protected nanoscale spin textures, known as magnetic skyrmions,
possess particle-like properties and feature emergent magnetism effects. In
bulk cubic heli-magnets, distinct skyrmion resonant modes are already
identified using a technique like ferromagnetic resonance in spintronics.
However, direct light-matter coupling between microwave photons and skyrmion
resonance modes has not been demonstrated yet. Utilising two distinct cavity
systems, we realise to observe a direct interaction between the cavity resonant
mode and two resonant skyrmion modes, the counter-clockwise gyration and
breathing modes, in bulk Cu$_2$OSeO$_3$. For both resonant modes, we find the
largest coupling strength at 57 K indicated by an enhancement of the cavity
linewidth at the degeneracy point. We study the effective coupling strength as
a function of temperature within the expected skyrmion phase. We attribute the
maximum in effective coupling strength to the presence of a large number of
skyrmions, and correspondingly to a completely stable skyrmion lattice. Our
experimental findings indicate that the coupling between photons and resonant
modes of magnetic skyrmions depends on the relative density of these
topological particles instead of the pure spin number in the system.",2105.03719v1
2004-04-28,Field and stress tunable microwave composite materials based on ferromagnetic microwires,"New types of tunable composite materials are considered, the effective
microwave permittivity of which may depend on an external dc magnetic field or
tensile stress. The composites consist of short pieces of conductive
ferromagnetic microwires embedded into a dielectric matrix. The short wire
inclusions play a role of the elementary scatterers, when the electromagnetic
wave irradiates the composite and induces a longitudinal current distribution
and electrical dipole moment in each inclusion. These induced dipole moments
form the dipole response, which can be characterized by some complex effective
permittivity. The later may have a resonance or relaxation dispersion caused by
the strong current distribution along a wire, which depends on the wire high
frequency surface impedance. In the vicinity of the resonance frequency any
variations in the wire surface impedance result in a large change of the
current distribution, and hence in the dipole moment of each inclusion and the
effective permittivity on the whole. For a ferromagnetic conductive microwire,
the surface impedance may depend not only on its conductivity but also on the
dc external magnetic field and tension through the so-called magneto-impedance
effect (MI). Therefore, the dispersion of the effective permittivity can be
tuned from a resonance type to a relaxation type, when a sufficient magnetic
field or tensile stress is applied to the composite sample. A number of
applications can be proposed, including the stress-sensitive media for remote
non-destructive health monitoring of different structures, and selective
microwave coatings with field-dependent reflection/transmission coefficients.",0404679v6
2017-07-04,Local moment formation and magnetic coupling of Mn guest atoms in Bi$_2$Se$_3$: a low-temperature ferromagnetic resonance study,"We compare the magnetic and electronic configuration of single Mn atoms in
molecular beam epitaxy (MBE) grown Bi$_2$Se$_3$ thin films, focusing on
electron paramagnetic (ferromagnetic) resonance (EPR and FMR, respectively) and
superconducting quantum interference device (SQUID) techniques. X-ray
diffraction (XRD) and electron backscatter diffraction (EBSD) reveal the
expected increase of disorder with increasing concentration of magnetic guest
atoms, however, Kikuchi patterns show that disorder consists majorly of
mum-scale 60deg twin domains in the hexagonal Bi$_2$Se$_3$ structure, which are
promoted by the presence of single unclustered Mn impurities. Ferromagnetism
below T$_C$ ~ (5.4 +/- 0.3) K can be well described by critical scaling laws
M(T) ~ (1-T/T$_C$)$^\beta$ with a critical exponent $\beta$ = (0.34 +/- 0.2)),
suggesting 3D Heisenberg class magnetism instead of e.g. 2D-type coupling
between Mn-spins in van der Waals gap sites. From EPR hyperfine structure data
we determine a Mn$^{2+}$ (d$^5$, S = 5/2) electronic configuration with a
g-factor of 2.002 for -1/2 --> +1/2 transitions. In addition, from the strong
dependence of the low temperature FMR fields and linewidth on the field
strength and orientation with respect to the Bi$_2$Se$_3$ (0001) plane, we
derive magnetic anisotropy energies of up to K1 = -3720 erg/cm3 in MBE-grown
Mn-doped Bi$_2$Se$_3$, reflecting the first order magneto-crystalline
anisotropy of an in-plane magnetic easy plane in a hexagonal (0001) crystal
symmetry. Across the ferromagnetic-paramagnetic transition the FMR intensity is
suppressed and resonance fields converge the paramagnetic limit of a Mn$^{2+}$
(d$^5$, S = 5/2).",1707.00975v1
2011-06-07,Nonperturbative Effects on the Ferromagnetic Transition in Repulsive Fermi Gases,"It is generally believed that a dilute spin-1/2 Fermi gas with repulsive
interactions can undergo a ferromagnetic phase transition to a spin-polarized
state at a critical gas parameter $(k_{\rm F}a)_c$. Previous theoretical
predictions of the ferromagnetic phase transition have been based on the
perturbation theory, which treats the gas parameter as a small number. On the
other hand, Belitz, Kirkpatrick, and Vojta (BKV) have argued that the phase
transition in clean itinerant ferromagnets is generically of first order at low
temperatures, due to the correlation effects that lead to a nonanalytic term in
the free energy. The second-order perturbation theory predicts a first-order
phase transition at $(k_{\rm F}a)_c=1.054$, consistent with the BKV argument.
However, since the critical gas parameter is expected to be of order O(1),
perturbative predictions may be unreliable. In this paper we study the
nonperturbative effects on the ferromagnetic phase transition by summing the
particle-particle ladder diagrams to all orders in the gas parameter. We
consider a universal repulsive Fermi gas where the effective range effects can
be neglected, which can be realized in a two-component Fermi gas of $^6$Li
atoms by using a nonadiabatic field switch to the upper branch of a Feshbach
resonance with a positive s-wave scattering length. Our theory predicts a
second-order phase transition, which indicates that ferromagnetic transition in
dilute Fermi gases is possibly a counterexample to the BKV argument. The
predicted critical gas parameter $(k_{\rm F}a)_c=0.858$ is in good agreement
with the recent quantum Monte Carlo result $(k_{\rm F}a)_c=0.86$ for a nearly
zero-range potential [S. Pilati, \emph{et al}., Phys. Rev. Lett. {\bf 105},
030405 (2010)]. We also compare the spin susceptibility with the quantum Monte
Carlo result and find good agreement.",1106.1345v4
2012-12-05,Depth profile of the ferromagnetic order in a YBa$_2$Cu$_3$O$_7$ / La$_{2/3}$Ca$_{1/3}$MnO$_3$ superlattice on a LSAT substrate: a polarized neutron reflectometry study,"Using polarized neutron reflectometry (PNR) we have investigated a
YBa2Cu3O7(10nm)/La2/3Ca1/3MnO3(9nm)]10 (YBCO/LCMO) superlattice grown by pulsed
laser deposition on a La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrate. Due to the
high structural quality of the superlattice and the substrate, the specular
reflectivity signal extends with a high signal-to-background ratio beyond the
fourth order superlattice Bragg peak. This allows us to obtain more detailed
and reliable information about the magnetic depth profile than in previous PNR
studies on similar superlattices that were partially impeded by problems
related to the low temperature structural transitions of the SrTiO3 substrates.
In agreement with the previous reports, our PNR data reveal a strong magnetic
proximity effect showing that the depth profile of the magnetic potential
differs significantly from the one of the nuclear potential that is given by
the YBCO and LCMO layer thickness. We present fits of the PNR data using
different simple block-like models for which either a ferromagnetic moment is
induced on the YBCO side of the interfaces or the ferromagnetic order is
suppressed on the LCMO side. We show that a good agreement with the PNR data
and with the average magnetization as obtained from dc magnetization data can
only be obtained with the latter model where a so-called depleted layer with a
strongly suppressed ferromagnetic moment develops on the LCMO side of the
interfaces. The models with an induced ferromagnetic moment on the YBCO side
fail to reproduce the details of the higher order superlattice Bragg peaks and
yield a wrong magnitude of the average magnetization. We also show that the PNR
data are still consistent with the small, ferromagnetic Cu moment of 0.25muB
that was previously identified with x-ray magnetic circular dichroism and x-ray
resonant magnetic reflectometry measurements on the same superlattice.",1212.0986v1
1999-07-13,Nonlinear Spin Dynamics in Ferromagnets with Electron-Nuclear Coupling,"Nonlinear spin motion in ferromagnets is considered with nonlinearity due to
three factors: (i) the sample is prepared in a strongly nonequilibrium state,
so that evolution equations cannot be linearized as would be admissible for
spin motion not too far from equilibrium, (ii) the system considered consists
of interacting electron and nuclear spins coupled with each other via hyperfine
forces, and (iii) the sample is inserted into a coil of a resonant electric
circuit producing a resonator feedback field. Due to these nonlinearities,
coherent motion of spins can develop, resulting in their ultrafast relaxation.
A complete analysis of mechanisms triggering such a coherent motion is
presented. This type of ultrafast coherent relaxation can be used for studying
intrinsic properties of magnetic materials.",9907188v1
2001-05-04,Coexistence of Paramagnetic-Charge-Ordered and Ferromagnetic-Metallic Phases in La0.5Ca0.5MnO3 evidenced by ESR,"Throughout a complete Electron Spin Resonance (ESR) and magnetization study
of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated
state established in this compound below T~210 K. Between TN<T<TC, the ESR
spectra shows two lines characteristic of two different magnetic phases. From
the resonance field (Hr) derived for each line we argue that the
incommensurate-charge-ordering phase (ICO) which coexists with
ferromagnetic-metallic (FMM) clusters in this temperature interval, is mainly
paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a
relatively small field, which suggests that the internal energy associated with
those phases is very similar. Below TN, there is an appreciable FM contribution
to the magnetization and the ESR spectra indicates the presence of FM clusters
in an antiferromagnetic matrix (canted). Our results show that ESR could be a
very useful tool to investigate the nature of the phase-separated state now
believed to play a fundamental role in the physics of mixed valent manganites.",0105088v1
2001-10-08,Influence of Nd on the magnetic properties of Nd1-xCaxMnO3,"The role played by the Nd ions in the magnetic properties of Nd0.5Ca0.5MnO3
and Nd0.7Ca0.3MnO3 is studied using static magnetization, neutron diffraction
and high frequency (9.4-475GHz) Electron Spin Resonance. We show that the Nd
ions are weakly coupled to the Mn ions via ferromagnetic exchange and are
responsible for the peculiar ferromagnetic resonance observed in the FM phase
of both compounds (ground state below 120K for x=0.3, high field state for
x=0.5). We then use ESR to look for magnetic phase separation in the low field,
CO phase of Nd0.5Ca0.5MnO3. We show that there is no trace of the FM phase
imbedded in the CO phase, contrary to what is observed in La0.5Ca0.5MnO3 or
Pr0.5Sr0.5MnO3.",0110139v1
2003-06-03,Phase separation effects in charge-ordered Pr0.5Ca0.5MnO3 thin film,"Compressed Pr0.5Ca0.5MnO3 films (250nm) deposited on LaAlO3 have been studied
by Electron Spin Resonance technique under high frequency and high magnetic
field. We show evidences for the presence of a ferromagnetic phase (FM)
embedded in the charge-order phase (CO), in form of thin layers which size
depends on the strength and orientation of the magnetic field (parallel or
perpendicular to the substrate plane). This FM phase presents an easy plane
magnetic anisotropy with an anisotropy constant 100 times bigger than typical
bulk values. When the magnetic field is applied perpendicular to the substrate
plane, the FM phase is strongly coupled to the CO phase whereas for the
parallel orientation it keeps an independent ferromagnetic resonance even when
the CO phase becomes antiferromagnetic.",0306075v1
2003-07-04,Soft Magnetorotons and Broken-Symmetry States in Bilayer Quantum Hall Ferromagnets,"The recent report on the observation of soft magnetorotons in the dispersion
of charge-density excitations across the tunneling gap in coupled bilayers at
total Landau level filling factor $\nu_T=1$ is reviewed. The inelastic light
scattering experiments take advantage of the breakdown of wave-vector
conservation that occurs under resonant excitation. The results offer evidence
that in the quantum Hall state there is a roton that softens and sharpens
markedly when the phase boundary for transitions to highly-correlated
compressible states is approached. These findings are interpreted with
Hartree-Fock evaluations of the dynamic structure factor. The model includes
the effect of disorder in the breakdown of wave-vector conservation and
resonance enhancement profiles within a phenomenological approach. These
results link the softening of magnetorotons to enhanced excitonic Coulomb
interactions in the ferromagnetic bilayers.",0307108v1
2003-07-09,Frequency Dependence of Magnetoelectric Interactions in Layered Structures of Ferromagnetic Alloys and Piezoelectric Oxides,"Magnetoelectric (ME) interactions in layered structures of magnetostrictive
and piezoelectric phases are mediated by mechanical deformation. Here we
discuss the frequency dependence of ME coupling in bilayers and trilayers of
Permendur, a ferromagnetic alloy, and lead zirconate titanate. Data on ME
voltage coefficient versus frequency profiles reveal a giant ME coupling at
electromechanical resonance. The maximum voltage coefficient of 90 V/cm Oe is
three orders of magnitude higher than low-frequency values. The ME interactions
for transverse fields is an order of magnitude stronger than for longitudinal
fields. These results are in agreement with theory. The resonance ME effect,
therefore, is a novel tool for enhancing the magnetic-to-electric field
conversion efficiency in the composites.",0307208v1
2003-11-10,Resonant excitation of the domain wall oscillations by a parallel current under spin injection,"A possibility is discussed of observing spin injection effect on the
ferromagnet domain structure by means of resonant excitation of the domain wall
oscillations by a spin-polarized ac injection current. The natural frequency of
the domain wall oscillations in a thin ferromagnetic film with parallel
anisotropy is calculated. Amplitude of the domain wall forced oscillations
excited by the spin-polarized ac current is determined. Then effect of such
oscillations on the current is considered and appearance of nonlinear phenomena
such as rectification of the ac current and second harmonic generation is
predicted.",0311204v1
2004-07-14,Ferromagnetic resonance study of free hole contribution to magnetization and magnetic anisotropy in modulation-doped Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As:Be,"Ferromagnetic resonance (FMR) is used to study magnetic anisotropy of GaMnAs
in a series of Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As heterostructures
modulation-doped by Be. The FMR experiments provide a direct measure of cubic
and uniaxial magnetic anisotropy fields, and their dependence on the doping
level. It is found that the increase in doping -- in addition to rising the
Curie temperature of the Ga$_{1 - x}$Mn$_{x}$As layers -- also leads to a very
significant increase of their uniaxial anisotropy field. The FMR measurements
further show that the effective $g$-factor of Ga$_{1 - x}$Mn$_{x}$As is also
strongly affected by the doping. This in turn provides a direct measure of the
contribution from the free hole magnetization to the magnetization of Ga$_{1 -
x}$Mn$_{x}$As system as a whole.",0407371v1
2005-04-21,Charge order suppression and antiferromagnetic to ferromagnetic switch over in Pr_0.5Ca_0.5MnO_3 nanowires,"We have prepared crystalline nanowires (diameter ~ 50 nm, length ~ a few
microns) of the charge ordering manganite Pr_0.5Ca_0.5Mn_O3 using a low
reaction temperature hydrothermal method and characterized them using X-ray
diffraction, transmission electron microscopy, SQUID magnetometry and electron
magnetic resonance measurements. While the bulk sample shows a charge ordering
transition at 245 K and an antiferromagnetic transition at 175 K, SQUID
magnetometry and electron magnetic resonance experiments reveal that in the
nanowires phase, a ferromagnetic transition occurs at ~ 105 K. Further, the
antiferromagnetic transition disappears and the charge ordering transition is
suppressed. This result is particularly significant since the charge order in
Pr_0.5Ca_0.5MnO_3 is known to be very robust, magnetic fields as high as 27 T
being needed to melt it.",0504550v1
2006-09-09,Ground-state Competition of Two-Component Bosons in Optical Lattice near a Feshbach Resonance,"We investigate the ground state properties of an equal mixture of two species
of bosons in its Mott-insulator phase at a filling factor two per site. We
identify one type of spin triplet-singlet transition through the competition of
ground state. When the on-site interaction is weak ($U<U_c$) the two particles
prefer to stay in the lowest band and with weak tunnelling between neighboring
sites the system is mapped into an effective spin-1 ferromagnetic exchange
Hamiltonian. When the interaction is tuned by a Feshbach resonance to be large
enough ($U>U_c$), higher band will be populated. Due to the orbital coupling
term $S^+S^-$ in the Hamiltonian, the two atoms in different orbits on a site
would form an on-site singlet. For a non-SU(2)-symmetric model, easy-axis or
easy-plane ferromagnetic spin exchange models may be realized corresponding to
phase separation or counter-flow superfluidity, respectively.",0609219v3
2007-03-22,Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets,"We measure the magnetic damping parameter a in thin film CoFeB and permalloy
(Py) nanomagnets at room temperature using ferromagnetic resonance driven by
microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm
0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for
extended thin films, but significantly less than the effective damping
determined previously for similar nanomagnets by fits to time-domain studies of
large-angle magnetic excitations and magnetic reversal. The greater damping
found for the large amplitude nanomagnet dynamics is attributed to the
nonlinear excitation of non-uniform magnetic modes.",0703577v1
2007-05-29,Resonant scattering of spin waves from a region of inhomogeneous magnetic field in a ferromagnetic film,"The transmission of a dipole-dominated spin wave in a ferromagnetic film
through a localised inhomogeneity in the form of a magnetic field produced by a
dc current through a wire placed on the film surface was studied experimentally
and theoretically. It was shown that the amplitude and phase of the transmitted
wave can be simultaneously affected by the current induced field, a feature
that will be relevant for logic based on spin wave transport.
  The direction of the current creates either a barrier or well for spin wave
transmission. The main observation is that the current dependence of the
amplitude of the spin wave transmitted through the well inhomogeneity is
non-monotonic. The dependence has a minimum and an additional maximum. A theory
was constructed to clarify the nature of the maximum. It shows that the
transmission of spin waves through the inhomogeneity can be considered as a
scattering process and that the additional maximum is a scattering resonance.",0705.4191v1
2007-06-12,Complex ferromagnetic state and magnetocaloric effect in single crystalline Nd_{0.7}Sr_{0.3}MnO_{3},"The magnetocaloric effect in single crystalline Nd_{0.7}Sr_{0.3}MnO_{3} is
investigated by measuring the field-induced adiabatic change in temperature
which reveals a single negative peak around 130 K well below the Curie
temperature (T_C=203 K). In order to understand this unusual magnetocaloric
effect, we invoke the reported {55}^Mn spin-echo nuclear magnetic resonance,
electron magnetic resonance and polarized Raman scattering measurements on
Nd_{0.7}Sr_{0.3}MnO_{3}. We show that this effect is a manifestation of a
competition between the double exchange mechanism and correlations arising from
coupled spin and lattice degrees of freedom which results in a complex
ferromagnetic state. The critical behavior of Nd_{0.7}Sr_{0.3}MnO_{3} near
Curie temperature is investigated to study the influence of the coupled degrees
of freedom. We find a complicated behavior at low fields in which the order of
the transition could not be fixed and a second-order-like behavior at high
fields.",0706.1610v1
2008-02-22,Conductance and current noise of a superconductor/ferromagnet quantum point contact,"We study the conductance and current noise of a superconductor/ferromagnet
(S/F) single channel Quantum Point Contact (QPC) as a function of the QPC bias
voltage, using a scattering approach. We show that the Spin-Dependence of
Interfacial Phase Shifts (SDIPS) acquired by electrons upon scattering by the
QPC can strongly modify these signals. For a weakly transparent contact, the
SDIPS induces sub-gap resonances in the conductance and differential Fano
factor curves of the QPC. For high transparencies, these resonances are
smoothed, but the shape of the signals remain extremely sensitive to the SDIPS.
We show that noise measurements could help to gain more information on the
device, e.g. in cases where the SDIPS modifies qualitatively the differential
Fano factor of the QPC but not the conductance.",0802.3269v1
2008-02-26,A Nuclear Magnetic Resonance Study on Rubrene-cobalt Nano-composites,"We implemented a nuclear magnetic resonance (NMR) study on rubrene(C42H28)-Co
nano-composites that exhibit an enhanced magnetoresistance (MR) ratio of 80%.
The 59Co NMR spin echo experiment enabled clarification of the hyperfine field
of Co at the interface between the ferromagnet and the molecules, which has not
been investigated for molecular spintronics. An enhanced hyperfine field of the
Co was observed in the rubrene-Co nano-composites, which may be related to the
enhancement of the MR ratio. This study demonstrates the importance of
microscopic investigation of the interface between molecules and ferromagnets
that governs spin-dependent transport in molecular spin devices.",0802.3728v1
2008-08-01,Field-Driven Domain-Wall Dynamics in GaMnAs Films with Perpendicular Anisotropy,"We combine magneto-optical imaging and a magnetic field pulse technique to
study domain wall dynamics in a ferromagnetic (Ga,Mn)As layer with
perpendicular easy axis. Contrary to ultrathin metallic layers, the depinning
field is found to be smaller than the Walker field, thereby allowing for the
observation of the steady and precessional flow regimes. The domain wall width
and damping parameters are determined self-consistently. The damping, 30 times
larger than the one deduced from ferromagnetic resonance, is shown to
essentially originate from the non-conservation of the magnetization modulus.
An unpredicted damping resonance and a dissipation regime associated with the
existence of horizontal Bloch lines are also revealed.",0808.0119v1
2009-01-27,Broadband Ferromagnetic Resonance Linewidth Measurement of Magnetic Tunnel Junction Multilayers,"The broadband ferromagnetic resonance (FMR) linewidth of the free layer of
magnetic tunnel junctions is used as a simple diagnostic of the quality of the
magnetic structure. The FMR linewidth increases near the field regions of free
layer reversal and pinned layer reversal, and this increase correlates with an
increase in magnetic hysteresis in unpatterned films, low frequency noise in
patterned devices, and previous observations of magnetic domain ripple by use
of Lorentz microscopy. Postannealing changes the free layer FMR linewidth
indicating that considerable magnetic disorder, originating in the
exchange-biased pinned layer, is transferred to the free layer.",0901.4196v1
2009-08-15,Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions,"Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to
measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel
junctions (MTJs). For this purpose, T-FMR measurements were conducted with an
external magnetic field up to 14 kOe applied perpendicular to the film surface
of MgO-based MTJs under a dc bias. The observed frequency-field relationship
suggests that a 20 A CoFeB free layer has an effective demagnetization field
much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/-
0.3) kOe. This value is consistent with the saturation field obtained from
magnetometry measurements on extended films of the same CoFeB thickness.
In-plane T-FMR on the other hand shows less consistent results for the
effective demagnetization field, presumably due to excitations of more complex
modes. These experiments suggest that the perpendicular T-FMR is preferred for
quantitative magnetic characterization of nanoscale MTJs.",0908.2164v1
2009-10-08,Proposal for Efficient Generation of Spin-Polarized Current in Silicon,"We propose a spin-dependent resonant tunneling structure to efficiently
inject spin-polarized current into silicon (Si). By means of a heavily doped
polycrystalline Si (Poly-Si) between the ferromagnetic metal (FM) and Si to
reduce the Schottky barrier resistance, we estimated raising the tunneling
current density up to $10^8$Am$^{-2}$. The small Fermi sea of the charge
carriers in Si focuses the tunneling electrons to the resonant spin states
within a small region of transverse momentum in the ferromagnet which creates
the spin polarization of the current. Because of the large exchange splitting
between the spin up and down bands, the decay of the spin current is explained
in terms of scattering out of the focused beam. The spin polarization in the
current survives only if the thickness of the FM-layer is smaller than the
spin-diffusion length estimated from that cause.",0910.1611v2
2010-01-17,"Feasibility of study magnetic proximity effects in bilayer ""superconductor/ferromagnet"" using waveguide-enhanced Polarized Neutron Reflectometry","A resonant enhancement of the neutron standing waves is proposed to use in
order to increase the magnetic neutron scattering from a
""superconductor/ferromagnet""(S/F) bilayer. The model calculations show that
usage of this effect allows to increase the magnetic scattering intensity by
factor of hundreds. Aspects related to the growth procedure (order of
deposition, roughness of the layers etc) as well as experimental conditions
(resolution, polarization of the neutron beam, background etc) are also
discussed.
  Collected experimental data for the S/F heterostructure
Cu(32nm)/V(40nm)/Fe(1nm)/MgO confirmed the presence of a resonant 60-fold
amplification of the magnetic scattering.",1001.2895v2
2010-02-04,Polarization transformations by a magneto-photonic layered structure in vicinity of ferromagnetic resonance,"The polarization properties of a magnetophotonic crystal at the frequencies
located in the vicinity of ferromagnetic resonance are studied. The
investigations are curried out taking into consideration the fact that the
magnitude of material losses in ferrite layers at this frequency band is
significant. The method is based on obtaining a system of ordinary differential
equations and further analyzing the stability of solutions of this system. The
electromagnetic properties of the structure under study are found out via the
analysis of the eigenvalues of the transfer matrix of the structure period. On
this basis the boundaries of the stopbands and passbands of the eigenwaves are
determined. The frequency and angular dependences of the reflection and
transmission coefficients are given. The angle of the rotation of the
polarization plane and the ellipticity of the reflected and transmitted fields
are obtained.",1002.1087v2
2010-02-16,Dynamic Nuclear Polarization and Nuclear Magnetic Resonance in the Simplest Pseudospin Quantum Hall Ferromagnet,"We present dynamic nuclear polarization (DNP) in the simplest pseudospin
quantum Hall ferromagnet (QHF) of an InSb two-dimensional electron gas with a
large g factor using tilted magnetic fields. The DNP-induced amplitude change
of a resistance spike of the QHF at large current enables observation of the
resistively detected nuclear magnetic resonance of the high nuclear spin
isotope 115In with nine quadrupole splittings. Our results demonstrate the
importance of domain structures in the DNP process. The nuclear spin relaxation
time T1 in this QHF was relatively short (~ 120 s), and almost temperature
independent.",1002.3087v3
2010-06-29,Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study,"Microstrip ferromagnetic resonance and Brillouin scattering are used to
provide a comparative determination of the magnetic parameters of thin
permalloy layers interfaced with a non-magnetic (Al2O3) or with an
antiferromagnetic oxide (NiO). It is shown that the perpendicular anisotropy is
monitored by an interfacial surface energy term which is practically
independent of the nature of the interface. In the investigated interval of
thicknesses (5-25 nm) the saturation magnetisation does not significantly
differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy
and exchange-bias anisotropy are also derived from this study of the dynamic
magnetic excitations and compared to our independent evaluations using
conventional magnetometry",1006.5598v1
2010-10-01,Ferromagnetic resonance study of Co/Pd/Co/Ni multilayers with perpendicular anisotropy irradiated with Helium ions,"We present a ferromagnetic resonance (FMR) study of the effect of Helium ion
irradiation on the magnetic anisotropy, the linewidth and the Gilbert damping
of a Co/Ni multilayer coupled to Co/Pd bilayers. The perpendicular magnetic
anisotropy decreases linearly with He ion fluence, leading to a transition to
in-plane magnetization at a critical fluence of 5x10^{14} ions/cm^2. We find
that the damping is nearly independent of fluence but the FMR linewidth at
fixed frequency has a maximum near the critical fluence, indicating that the
inhomogeneous broadening of the FMR line is a non-monotonic function of the He
ion fluence. Based on an analysis of the angular dependence of the FMR
linewidth, the inhomogeneous broadening is associated with spatial variations
in the magnitude of the perpendicular magnetic anisotropy. These results
demonstrate that ion irradiation may be used to systematically modify the
magnetic anisotropy and distribution of magnetic anisotropy parameters of
Co/Pd/Co/Ni multilayers for applications and basic physics studies.",1010.0268v2
2010-11-09,Strain-mediated magnetoelectric coupling in magnetostrictive/piezoelectric heterostructures and resulting high frequency effects,"Magnetoelectric coupling terms are derived in piezoelectric/magnetostrictive
(multiferroic) thin film heterostructures using Landau-Ginzburg free energy
expansions in terms of strain and by considering strain boundary conditions
between the two materials. Then, a general effective medium method for solving
for the complete electromagnetic susceptibility tensor of such heterostructures
is used to calculate the ferromagnetic resonance frequency in a
BaTiO$_3$/NiFe$_2$O$_4$ superlattice. This method differs from existing methods
for treating magnetoelectric heterostructures since the magnetic and electric
dipolar fields are not assumed constant but vary from one film to another. The
ferromagnetic resonance frequency shift is calculated as a function of applied
electric field and is compared to some experimental results.",1011.2016v2
2012-07-24,'Kondo state' and Kondo resonance in a two-dimensional electron gas,"The delicate balance of spin-screening and spin-aligning interactions
determines many of the peculiar properties of dilute magnetic systems. We study
a surface-supported all-organic multi-impurity Kondo spin system at the atomic
scale by low-temperature scanning tunnelling microscopy and -spectroscopy. The
model system consists of spin-1/2 radicals that are aligned in one-dimensional
chains and interact via a ferromagnetic RKKY interaction mediated by the 2DEG
of the supporting substrate. Due to the RKKY-induced enhanced depopulation of
one spin-subband in the 2DEG, we finally succeeded to detect the so far
unobserved 'Kondo state' as opposed to the well-established Kondo resonance.
Its cloud of screening electrons, that are virtually bound to the radicals
below the Kondo temperature, represents the extended exchange hole of the
ferromagnetically polarized spin chain imaged here in real space.",1207.5613v1
2012-10-09,Spectral Characteristics of the Microwave Emission by the Spin Hall Nano-Oscillator,"We utilized microwave spectroscopy to study the magnetization oscillations
locally induced in a Permalloy film by a pure spin current, which is generated
due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency
is lower than the ferromagnetic resonance of Permalloy, indicating that the
oscillation forms a self-localized nonpropagating spin-wave soliton. At
cryogenic temperatures, the spectral characteristics are remarkably similar to
the traditional spin-torque nano-oscillators driven by spin-polarized currents.
However, the linewidth of the oscillation increases exponentially with
temperature and an additional peak appears in the spectrum below the
ferromagnetic resonance, suggesting that the spectral characteristics are
determined by interplay between two localized dynamical states.",1210.2758v2
2012-12-31,Effects of lateral device size and material properties on the ferromagnetic resonance response of spinwave eigen-modes in magnetic devices,"We analyze the effects of lateral device size and magnetic material
parameters on the ferromagnetic resonance (FMR) response. Results presented are
directly relevant to widely used FMR experimental techniques for extracting
magnetic parameters from thin films, the results of which are often assumed to
carry over to corresponding nanometer-sized patterned devices. We show that
there can be significant variation in the FMR response with device size, and
that the extent of the variation depends on the magnetic material properties.
This explains, for example, why different experiments along these lines have
yielded different size-dependent trends from damping measurements. Observed
trends with increasing size and different material parameters are explained
through the evolution of three distinct eigen-modes, demonstrating the
respective roles of demagnetization and exchange. It is also shown that there
is a crossover of dominant eigen-modes in the response signal, accompanied by
conjugating edge-type modes, leading to evident effects in measured linewidth
and damping. Among the sizes considered, in higher saturation magnetization, we
observe as much as a 40% increase in apparent damping, due solely to device
size variation.",1212.6835v1
2013-02-20,Magnetostrictive thin films for microwave spintronics,"Multiferroic composite materials, consisting of coupled ferromagnetic and
piezoelectric phases, are of great importance in the drive towards creating
faster, smaller and more energy efficient devices for information and
communications technologies. Such devices require thin ferromagnetic films with
large magnetostriction and narrow microwave resonance linewidths. Both
properties are often degraded, compared to bulk materials, due to structural
imperfections and interface effects in the thin films. We report the
development of single crystal thin films of Galfenol (Fe81Ga19) with
magnetostriction as large as the best reported values for bulk material. This
allows the magnetic anisotropy and microwave resonant frequency to be tuned by
voltage-induced strain, with a larger magnetoelectric response and a narrower
linewidth than any previously reported Galfenol thin films. The combination of
these properties make the single crystal thin films excellent candidates for
developing tunable devices for magnetic information storage, processing and
microwave communications.",1302.5097v1
2013-05-30,Evolution of ferromagnetic and spin-wave resonances with crystalline order in thin films of full-Heusler alloy Co2MnSi,"We report the evolution of magnetic moment as well as magnetic anisotropy
with crystalline order in Co$_2$MnSi thin films grown on $(100)$ MgO by pulsed
laser deposition. The films become more ordered as the annealing temperature
($T_A$) increases from 400 to 600 $^0$C. The extent of \emph{L}$2_1$ ordering
in the films annealed at 600 $^0$C is $\approx 96%$. The static magnetization
measurements by vibrating sample magnetometry shows a maximum moment of 4.95
$\mu_B$ per formula unit with low coercivity ($H_C$ $\approx$ 65 Oe) in the
films annealed at 600 $^0$C. A rigorous analysis of the azimuthal and polar
angle dependent ferromagnetic resonance (FMR) measured at several temperatures
allows determination of various anisotropy fields relevant to our system as a
function of $T_A$. Finally, we have evaluated the exchange stiffness constant
down to 100 K using spin wave modes in FMR spectra. We have also estimated the
exchange energies as well as stiffness constant by varying the lattice
parameter \emph{ab-initio} using the Korringa-Kohn-Rostoker method.",1305.7048v1
2013-11-06,Magnetization dynamics of cobalt grown on graphene,"Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which
has demonstrated promising results in a variety of material systems. This
technique utilizes the resonant precession of magnetization in a ferromagnet to
inject spin into an adjacent non-magnetic material. Spin pumping into graphene
is attractive on account of its exceptional spin transport properties. This
article reports on FMR characterization of cobalt grown on CVD graphene and
examines the validity of linewidth broadening as an indicator of spin pumping.
In comparison to cobalt samples without graphene, direct contact
cobalt-on-graphene exhibits increased FMR linewidth--an often used signature of
spin pumping. Similar results are obtained in Co/MgO/graphene structures, where
a 1nm MgO layer acts as a tunnel barrier. However, SQUID, MFM, and Kerr
microscopy measurements demonstrate increased magnetic disorder in cobalt grown
on graphene, perhaps due to changes in the growth process and an increase in
defects. This magnetic disorder may account for the observed linewidth
enhancement due to effects such as two-magnon scattering or mosaicity. As such,
it is not possible to conclude successful spin injection into graphene from FMR
linewidth measurements alone.",1311.1441v1
2014-01-29,Magnetic-Field-Modulated Resonant Tunneling in Ferromagnetic-Insulator-Nonmagnetic junctions,"We present a theory for resonance-tunneling magnetoresistance (MR) in
Ferromagnetic-Insulator-Nonmagnetic junctions. The theory sheds light on many
of the recent electrical spin injection experiments, suggesting that this MR
effect rather than spin accumulation in the nonmagnetic channel corresponds to
the electrically detected signal. We quantify the dependence of the tunnel
current on the magnetic field by quantum rate equations derived from the
Anderson impurity model, with important addition of impurity spin interactions.
Considering the on-site Coulomb correlation, the MR effect is caused by
competition between the field, spin interactions and coupling to the magnetic
lead. By extending the theory, we present a basis for operation of novel
nm-size memories.",1401.7649v2
2014-04-08,Ferromagnetic resonance spin pumping in CoFeB with highly resistive non-magnetic electrodes,"The relative contribution of spin pumping and spin rectification from the
ferromagnetic resonance of CoFeB/non-magnetic bilayers was investigated as a
function of non-magnetic electrode resistance. Samples with highly resistive
electrodes of Ta or Ti exhibit a stronger spin rectification signal, which may
result in over-(or under-)estimation of the spin Hall angle of the materials,
while those with low resistive electrodes of Pt or Pd show the domination of
the inverse spin Hall effect from spin pumping. By comparison with samples of
single FM layer and an inverted structure, we provide a proper analysis method
to extract spin pumping contribution.",1404.1993v1
2014-07-01,Dipole-dipole interaction in arrays of Fe/Fe$_x$O$_y$ core/shell nanocubes probed by ferromagnetic resonance,"This paper represents a detailed theoretical study of the role of the
longrange magnetic dipole-dipole interaction evidenced by the ferromagnetic
resonance (FMR) spectra for the ordered arrays of cubic nanoparticles. We show
that the size of the array essentially controls the stability of the system,
allowing to suppress the intermittent low-field excitations starting from the
arrays formed by 6x6 nanoparticles. Our numerical simulations allow to
determine the threshold inter-particle distance (around 80 {\div} 100 nm),
after which the dipole-dipole interaction becomes negligible so that the FMR
spectrum of the nanoparticle arrays becomes the same as the spectrum featured
by a single nanoparticle. We also compare our simulations with experimental
FMR-spectra of 24 Fe/Fe$_x$O$_y$-nanocubes irregularly placed on a substrate.",1407.0148v1
2014-09-04,High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry,"We demonstrate theoretically that by placing a ferromagnetic particle between
a nitrogen-vacancy (NV) magnetometer and a target spin, the magnetometer
sensitivity is increased dramatically. Specifically, using materials and
techniques already experimentally available, we find that by taking advantage
of the ferromagnetic resonance the minimum magnetic moment that can be measured
is smaller by four orders of magnitude in comparison to current
state-of-the-art magnetometers. As such, our proposed setup is sensitive enough
to detect a single nuclear spin at a distance of $30$~nm from the surface
within less than one second of data acquisition at room temperature. Our
proposal opens the door for nanoscale NMR on biological material under ambient
conditions.",1409.1497v1
2014-10-02,Investigation of the temperature-dependence of ferromagnetic resonance and spin waves in Co2FeAl0.5Si0.5,"Co2FeAl0.5Si0.5 (CFAS) is a Heusler compound that is of interest for
spintronics applications, due to its high spin polarization and relatively low
Gilbert damping constant. In this study, the behavior of ferromagnetic
resonance as a function of temperature was investigated in CFAS, yielding a
decreasing trend of damping constant as the temperature was increased from 13
to 300 K. Furthermore, we studied spin waves in CFAS using both frequency
domain and time domain techniques, obtaining group velocities and attenuation
lengths as high as 26 km/s and 23.3 um, respectively, at room temperature.",1410.0439v1
2014-10-07,Y3Fe5O12 Spin Pumping for Quantitative Understanding of Pure Spin Transport and Spin Hall Effect in a Broad Range of Materials,"Using Y3Fe5O12 (YIG) thin films grown by our sputtering technique, we study
dynamic spin transport in nonmagnetic (NM), ferromagnetic (FM) and
antiferromagnetic (AF) materials by ferromagnetic resonance (FMR) spin pumping.
From both inverse spin Hall effect (ISHE) and damping enhancement, we determine
the spin mixing conductance and spin Hall angle in many metals. Surprisingly,
we observe robust spin conduction in AF insulators excited by an adjacent YIG
at resonance. This demonstrates that YIG spin pumping is a powerful and
versatile tool for understanding spin Hall physics, spin-orbit coupling (SOC),
and magnetization dynamics in a broad range of materials.",1410.1597v1
2014-12-01,Stabilization of helical magnetic structures in thin multilayers,"Based on micromagnetic simulations, we report on a novel helical magnetic
structure in a soft magnetic film that is sandwiched between and
exchange-coupled to two hard magnetic layers. Confined between antiparallel
hard magnetic moments, a helix with a turn of 180$^{\circ}$ is stable without
the presence of an external magnetic field. The magnetic stability is
determined by the energy minimization and is a result of an internal field
created by exchange interaction and anisotropy. Since the internal field stores
magnetic energy, the helix can serve as an energy-storing element in spin-based
nanodevices. Due to the significantly different magnetic resonance frequencies,
the ferromagnetic and helical ground states are easy to distinguish in a
broadband ferromagnetic resonance experiment.",1412.1379v1
2015-02-12,Anti-damping spin transfer torque through epitaxial Nickel oxide,"We prepare the high quality epitaxial
MgO(001)[100]/Pt(001)[100]/NiO(001)[100]/FeNi/SiO2 films to investigate the
spin transport in the NiO antiferromagnetic insulator. The ferromagnetic
resonance measurements of the FeNi under a spin current injection from the Pt
by the spin Hall effect revealed the change of the ferromagnetic resonance
linewidth depending on the amount of the spin current injection. The results
can be interpreted that there is an angular momentum transfer through the NiO.
A high efficient angular momentum transfer we observed in the epitaxial NiO can
be attributed to the well-defined orientation of the antiferromagnetic moments
and the spin quantization axis of the injected spin current.",1502.03855v1
2015-02-18,Ferromagnetic Critical Behavior in U(Co$_{1-x}$Fe$_x$)Al ($0 \leq x \leq 0.02$) Studied by $^{59}$Co Nuclear Quadrupole Resonance Measurement,"In order to investigate physical properties around a ferromagnetic (FM)
quantum transition point and a tricritical point (TCP) in the
itinerant-electron metamagnetic compound UCoAl, we have performed the $^{59}$Co
nuclear quadrupole resonance (NQR) measurement for the Fe-substituted
U(Co$_{1-x}$Fe$_x$)Al ($x$ = 0, 0.5, 1, and 2%) in zero external magnetic
field. The Fe concentration dependence of $^{59}$Co-NQR spectra at low
temperatures indicates that the first-order FM transition occurs at least above
$x$ = 1%. The magnetic fluctuations along the $c$ axis detected by the nuclear
spin-spin relaxation rate $1/T_2$ exhibit an anomaly at $T_\mathrm{max}$ $\sim$
20 K and enhance with increasing $x$. These results are in good agreement with
theoretical predictions and indicate the presence of prominent critical
fluctuations at the TCP in this system.",1502.05155v1
2015-03-26,Magnetic ordering of nitrogen-vacancy centers in diamond via resonator-mediated coupling,"Nitrogen-vacancy centers in diamond, being a promising candidate for quantum
information processing, may also be an ideal platform for simulating many-body
physics. However, it is difficult to realize interactions between
nitrogen-vacancy centers strong enough to form a macroscopically ordered phase
under realistic temperatures. Here we propose a scheme to realize long-range
ferromagnetic Ising interactions between distant nitrogen-vacancy centers by
using a mechanical resonator as a medium. Since the critical temperature in the
long-range Ising model is proportional to the number of spins, a ferromagnetic
order can be formed at a temperature of tens of millikelvin for a sample with
$\sim10^4$ nitrogen-vacancy centers. This method may provide a new platform for
studying many-body physics using qubit systems.",1503.07625v1
2015-07-08,Phase-sensitive imaging of ferromagnetic resonance using ultrafast heat pulses,"Measuring local magnetization dynamics and its spatial variation is essential
for advancements in spintronics and relevant applications. Here we demonstrate
a phase-sensitive imaging technique for studying patterned magnetic structures
based on picosecond laser heating. With the time-resolved anomalous Nernst
effect (TRANE) and extensions, we simultaneously image the dynamic
magnetization and RF driving current density. The stroboscopic detection
implemented in TRANE microscopy provides access to both amplitude and phase
information of ferromagnetic resonance (FMR) and RF current. Using this
approach, we measure the spatial variation of the Oersted driving field angle
across a uniform channel. In a spatially nonuniform sample with a cross shape,
a strong spatial variation for the RF current as well as FMR precession is
observed. We find that both the amplitude and the phase of local FMR precession
are closely related to those of the RF current.",1507.02303v1
2015-07-22,Magnetic anisotropy induced by crystal distortion in Ge1-xMn xTe/PbTe//KCl (001) ferromagnetic semiconductor layers,"Ferromagnetic resonance (FMR) study of magnetic anisotropy is presented for
thin layers of IV-VI diluted magnetic semiconductor Ge1-xMn xTe with x=0.14
grown by molecular beam epitaxy (MBE) on KCl (001) substrate with a thin PbTe
buffer. Analysis of the angular dependence of the FMR resonant field reveals
that an easy magnetization axis is located near to the normal to the layer
plane and is controlled by two crystal distortions present in these
rhombohedral Ge1-xMnxTe layers: the ferroelectric distortion with the relative
shift of cation and anion sub-lattices along the [111] crystal direction and
the biaxial in-plane, compressive strain due to thermal mismatch.",1507.06124v1
2015-08-03,Static magnetic proximity effect in Pt/Ni$_{1-x}$Fe$_x$ bilayers investigated by x-ray resonant magnetic reflectivity,"We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive
tool to detect proximity induced interface spin polarization in Pt/Fe,
Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers.
We demonstrate that a detailed analysis of the reflected x-ray intensity gives
insight in the spatial distribution of the spin polarization of a non-magnetic
metal across the interface to a ferromagnetic layer. The evaluation of the
experimental results with simulations based on optical data from ab initio
calculations provides the induced magnetic moment per Pt atom in the spin
polarized volume adjacent to the ferromagnet. We find the largest spin
polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni.
Additional XRMR experiments with varying photon energy are in good agreement
with the theoretical predictions for the energy dependence of the magnetooptic
parameters and allow identifying the optical dispersion $\delta$ and absorption
$\beta$ across the Pt L3-absorption edge.",1508.00379v1
2015-08-05,Ferromagnetic Spin Fluctuation and Unconventional Superconductivity in Rb$_{2}$Cr$_{3}$As$_{3}$ revealed by $^{75}$As NMR and NQR,"We report $^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) studies on the superconductor Rb$_{2}$Cr$_{3}$As$_{3}$ with a
quasi one-dimensional crystal structure. Below $T\sim$ 100 K, the spin-lattice
relaxation rate (1/$T_{1}$) divided by temperature, 1/$T_{1}T$, increases upon
cooling down to $T_{\rm c}$ = 4.8 K, showing a Curie-Weiss-like temperature
dependence. The Knight shift also increases with decreasing temperature. These
results suggest ferromagnetic spin fluctuation. In the superconducting state,
1/$T_{1}$ decreases rapidly below $T_{\text{c}}$ without a Hebel-Slichter peak,
and follows a $T^5$ variation below $T\sim$ 3 K, which point to unconventional
superconductivity with point nodes in the gap function.",1508.01012v1
2015-11-24,Inverse Spin Hall Effect from pulsed Spin Current in Organic Semiconductors with Tunable Spin-Orbit Coupling,"Exploration of spin-currents in organic semiconductors (OSECs) induced by
resonant microwave absorption in ferromagnetic substrates has been of great
interest for potential spintronics applications. Due to the inherently weak
spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE)
response is very subtle; limited by the microwave power applicable under
continuous-wave (cw) excitation. Here we introduce a novel approach for
generating significant ISHE signals using pulsed ferromagnetic resonance, where
the ISHE is ~2-3 orders of magnitude larger compared to cw excitation. This
strong ISHE enables us to investigate a variety of OSECs ranging from
pi-conjugated polymers with strong SOC that contain intrachain platinum atoms,
to weak SOC polymers, to C60 films, where the SOC is predominantly caused by
the molecule surface curvature. The pulsed-ISHE technique offers a robust route
for efficient injection and detection schemes of spin-currents at room
temperature, and paves the way for spin-orbitronics in plastic materials.",1511.07848v1
2016-03-01,Ferromagnetic resonance and magnetic damping in C-doped Mn5Ge3,"Ferromagnetic resonance (FMR) was used to investigate the static and dynamic
magnetic properties of carbon-doped Mn5Ge3 (C$_{0.1}$ and C$_{0.2}$) thin films
grown on Ge(111). The temperature dependence of magnetic anisotropy shows an
increased perpendicular magneto-crystalline contribution at 80K with an
in-plane easy axis due to the large shape contribution. We find that our
samples show a small FMR linewidth (corresponding to an intrinsic magnetic
damping parameter $\alpha$=0.005), which is a measure of the spin relaxation
and directly related with the magnetic and structural quality of the material.
In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at
around 200K for all the samples, which seems to be not correlated to the
C-doping. The magnetic relaxation parameters have been determined and indicate
the two-magnon scattering as the main extrinsic contribution. We observe a
change in the main contribution from scattering centres in Mn5Ge3C0.2 at low
temperatures, which could be related to the minimum in linewidth.",1603.00190v1
2016-04-16,A broadband Ferromagnetic Resonance dipper probe for magnetic damping measurements from 4.2 K to 300 K,"A dipper probe for broadband Ferromagnetic Resonance (FMR) operating from 4.2
K to room temperature is described. The apparatus is based on a 2-port
transmitted microwave signal measurement with a grounded coplanar waveguide.
The waveguide generates a microwave field and records the sample response. A
3-stage dipper design is adopted for fast and stable temperature control. The
temperature variation due to FMR is in the milli-Kelvin range at liquid helium
temperature. We also designed a novel FMR probe head with a spring-loaded
sample holder. Improved signal-to-noise ratio and stability compared to a
common FMR head are achieved. Using a superconducting vector magnet we
demonstrate Gilbert damping measurements on two thin film samples using a
vector network analyzer with frequency up to 26 GHz: 1) A Permalloy film of 5
nm thickness and 2) a CoFeB film of 1.5 nm thickness. Experiments were
performed with the applied magnetic field parallel and perpendicular to the
film plane.",1604.04688v1
2016-04-24,Who pumps spin current into nonmagnetic-metal (NM) layer in YIG/NM multilayers at ferromagnetic resonance?,"Spin pumping in Yttrium-iron-garnet (YIG)/nonmagnetic-metal (NM) layer
systems under ferromagnetic resonance (FMR) conditions is a popular method of
generating spin current in the NM layer. A good understanding of the spin
current source is essential in extracting spin Hall angle of the NM and in
potential spintronics applications. It is widely believed that spin current is
pumped from precessing YIG magnetization into NM layer. Here, by combining
microwave absorption and DC-voltage measurements on YIG/Pt and YIG/NM1/NM2
(NM1=Cu or Al, NM2=Pt or Ta), we unambiguously showed that spin current in NM
came from the magnetized NM surface (in contact with YIG) due to the magnetic
proximity effect (MPE), rather than the precessing YIG magnetization. This
conclusion is reached through our unique detecting method where the FMR
microwave absorption of the magnetized NM surface, hardly observed in the
conventional FMR experiments, was greatly amplified when the electrical
detection circuit was switched on.",1604.07025v1
2016-06-10,Indirect Coupling between Two Cavity Photon Systems via Ferromagnetic Resonance,"We experimentally realize indirect coupling between two cavity modes via
strong coupling with the ferromagnetic resonance in Yttrium Iron Garnet (YIG).
We find that some indirectly coupled modes of our system can have a higher
microwave transmission than the individual uncoupled modes. Using a coupled
harmonic oscillator model, the influence of the oscillation phase difference
between the two cavity modes on the nature of the indirect coupling is
revealed. These indirectly coupled microwave modes can be controlled using an
external magnetic field or by tuning the cavity height. This work has potential
for use in controllable optical devices and information processing
technologies.",1606.03469v1
2017-08-06,Asymmetric Andreev resonant state with a magnetic exchange field in spin-triplet superconducting monolayer $MoS_2$,"Featuring spin-valley degree of freedom by a magnetic exchange
field-induction to gain transport of charge carriers through a junction based
on superconducting subgap tunneling can provide a new scenario for future
electronics. Transmission of low-energy Dirac-like electron (hole)
quasiparticles through a ferromagnet/superconductor (F/S) interface can be of
noticeable importance due to strong spin-orbit coupling in the valence band of
monolayer $MoS_2$ (ML-MDS). The magnetic exchange field (MEF) of a
ferromagnetic section on top of ML-MDS may affect the electron (hole)
excitations for spin-up and spin-down electrons, differently. Tuning the MEF
enables one to control either electrical properties (such as band gap, SOC and
etc.) or spin-polarized transport. We study the influence of MEF on the
chirality of Andreev resonant state (ARS) appearing at the relating F/S
interface, in which the induced pairing order parameter is chiral $p$-wave
symmetry. The resulting normal conductance is found to be more sensitive to the
magnitude of MEF and doping regime of F region. Unconventional spin-triplet
$p$-wave symmetry features the zero-bias conductance, which strongly depends on
$p$-doping level of F region in the relating NFS junction.",1708.01863v1
2013-08-19,A Universal Method for Separating Spin Pumping from Spin Rectification Voltage of Ferromagnetic Resonance,"We develop a method for universally resolving the important issue of
separating spin pumping (SP) from spin rectification (SR) signals in bilayer
spintronics devices. This method is based on the characteristic distinction of
SP and SR, as revealed in their different angular and field symmetries. It
applies generally for analyzing charge voltages in bilayers induced by the
ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves
the outstanding problem that device specific microwave properties restrict the
universal quantification of the spin Hall angle in bilayer devices via FMR
experiments. Furthermore, it paves the way for directly measuring the nonlinear
evolution of spin current generated by spin pumping. The spin Hall angle in a
Py/Pt bilayer is thereby directly measured as 0.021$\pm$0.015 up to a large
precession cone angle of about 20$^{\circ}$.",1308.4041v3
2017-01-10,Size-dependent frequency bands in the ferromagnetic resonance of a Fe-nanocube,"Using full micromagnetic simulations we calculate the spectra of
ferromagnetic resonance (FMR) for an iron (core-shell) nanocube and show that
the FMR characteristics are strongly size dependent. For instance, for a
$40~$nm it is found that, in contrast to a macrospin picture, the spectrum of
the iron nanocube possesses two bands centered around $0.4~$T and $\approx
0.1~$T. The peaks originate from the surface anisotropy induced by the strong
demagnetizing fields (DMFs) of iron. Further simulations reveal that for
$\approx 20~$nm nanocubes the macrospin model becomes viable. Above $40~$nm we
find a broad band for FMR absorption. Our results point to possible
interpretations of existing FMR experimental observations for the system
studied here.",1701.02503v1
2017-04-24,Spin injection into silicon detected by broadband ferromagnetic resonance spectroscopy,"We studied the spin injection in a NiFe(Py)/Si system using broadband
ferromagnetic resonance spectroscopy. The Gilbert damping parameter of the Py
layer on top of the Si channel was determined as a function of the Si doping
concentration and Py layer thickness. For fixed Py thickness we observed an
increase of the Gilbert damping parameter with decreasing resistivity of the Si
channel. For a fixed Si doping concentration we measured an increasing Gilbert
damping parameter for decreasing Py layer thickness. No increase of the Gilbert
damping parameter was found Py/Si samples with an insulating interlayer. We
attribute our observations to an enhanced spin injection into the
low-resistivity Si by spin pumping.",1704.07006v1
2014-03-30,Dual-band metacomposites containing hybrid Fe and Co-based ferromagnetic microwires,"We investigated the microwave properties of polymer based metacomposites
containing hybridized parallel Fe- and Co-based microwire arrays. A dual-band
left-handed feature was observed in the frequency bands of 1.5 to 5.5 GHz and 9
to 17 GHz, indicated by two transmission windows associated with ferromagnetic
resonance of Fe-based microwires and long range dipolar resonance between the
wire arrays. The plasma frequency after hybridization is significantly
increased due to the enhanced effective diameter through the wire-wire
interactions between the Fe- and Co- microwire couples. These results offer
essential perspectives in designing the multi-band metamaterial for microwave
applications such as sensors and cloaking devices.",1405.0479v1
2014-05-05,Planar array of self-assembled Ga$_{x}$Fe$_{4-x}$N nanocrystals in GaN: Magnetic anisotropy determined via ferromagnetic resonance,"The magnetic anisotropy of a planar array of Ga$_{x}$Fe$_{4-x}$N nanocrystals
(NCs) embedded in a GaN host is studied by ferromagnetic resonance. X-ray
diffraction and transmission electron microscopy are employed to determine the
phase and distribution of the nanocrystals. The magnetic anisotropy is found to
be primarily uniaxial with the hard axis normal to the NCs plane and to have a
comparably weak in-plane hexagonal symmetry. The origin of the magnetic
anisotropy is discussed taking into consideration the morphology of the
nanocrystals, the epitaxial relations, strain effects and magnetic coupling
between the NCs.",1405.0906v2
2016-08-21,Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe1-xCox)2As2 revealed by 75As nuclear magnetic resonance,"Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence
of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations
in both the hole- and electron-doped BaFe$_2$As$_2$ families of iron-pnictide
superconductors by a Korringa ratio analysis. Motivated by the NMR work, we
investigate the possible existence of FM fluctuations in another iron pnictide
superconducting family, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$. We re-analyzed our
previously reported data in terms of the Korringa ratio and found clear
evidence for the coexistence of stripe-type AFM and FM spin correlations in the
electron-doped CaFe$_2$As$_2$ system. These NMR data indicate that FM
fluctuations exist in general in iron-pnictide superconducting families and
thus must be included to capture the phenomenology of the iron pnictides.",1608.05952v1
2017-10-13,Spin dynamics of FeGa$_{3-x}$Ge$_x$ studied by Electron Spin Resonance,"The intermetallic semiconductor FeGa$_{3}$ acquires itinerant ferromagnetism
upon electron doping by a partial replacement of Ga with Ge. We studied the
electron spin resonance (ESR) of high-quality single crystals of
FeGa$_{3-x}$Ge$_x$ for $x$ from 0 up to 0.162 where ferromagnetic order is
observed. For $x = 0$ we observed a well-defined ESR signal, indicating the
presence of pre-formed magnetic moments in the semiconducting phase. Upon Ge
doping the occurrence of itinerant magnetism clearly affects the ESR properties
below $\approx 40$~K whereas at higher temperatures an ESR signal as seen in
FeGa$_{3}$ prevails independent on the Ge-content. The present results show
that the ESR of FeGa$_{3-x}$Ge$_x$ is an appropriate and direct tool to
investigate the evolution of 3d-based itinerant magnetism.",1710.04891v1
2018-01-25,Sensitivity of ferromagnetic resonance in PdCo alloyed films to hydrogen gas,"In this work we studied the ferromagnetic resonance response of Co(x)Pd(1-x)
alloy samples with different cobalt contents (x = 0.65, 0.39, 0.24 & 0.14). We
found significant differences in the response of the samples to the presence of
hydrogen gas in the samples' environment. Two particular films (with x=0.39 and
0.24) demonstrated behaviour which is promising for application in hydrogen gas
sensing. Using the Co(39)Pd(61) alloy thin film, we were able to measure
hydrogen gas concentration in a very broad range (from <0.1% to 100%) at a
fixed value of the external magnetic field. Finally, we demonstrate that the
Co(24)Pd(76) alloy thin film is sensitive to ultra-low hydrogen gas
concentrations - from 10 to 10000 ppm.",1801.08324v1
2018-09-25,"Theory of damping in magnetization dynamics, dispelling a myth and pointing a way forward","There is a widely-held belief amongst theoreticians that the Gilbert damping
parameter {\alpha} in magnetization dynamics is infinite for a pure metal at
T=0. The basic error leading to this belief is pointed out explicitly and the
various methods of calculation used are viewed in a unified way based on the
Lorentzian lineshape of ferromagnetic resonance spectra. A general torque
formula for {\alpha} is proposed as a good starting-point for treating
inhomogeneous materials such as alloys, compounds and layered structures. Local
spin density functional theory provides a simple physical picture, in terms of
a non-uniform precessional cone angle in ferromagnetic resonance, of how such
inhomogeneity contributes to the damping. In a complementary many-body theory
this contribution is given by a vertex correction to the torque-torque response
function.",1809.09429v1
2019-06-04,High frequency voltage-induced ferromagnetic resonance in magnetic tunnel junctions,"Voltage-induced ferromagnetic resonance (V-FMR) in magnetic tunnel junctions
(MTJs) with a W buffer is investigated. Perpendicular magnetic anisotropy (PMA)
energy is controlled by both thickness of a CoFeB free layer deposited directly
on the W buffer and a post-annealing process at different temperatures. The PMA
energy as well as the magnetization damping are determined by analysing
field-dependent FMR signals in different field geometries. An optimized MTJ
structure enabled excitation of V-FMR at frequencies exceeding 30 GHz. The
macrospin modelling is used to analyse the field- and angular-dependence of the
V-FMR signal and to support experimental magnetization damping extraction.",1906.01301v1
2019-07-25,Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator,"We use micromagnetic simulation to demonstrate layer-selective detection of
magnetization directions from magnetic dots having two recording layers by
using a spin-torque oscillator (STO) as a read device. This method is based on
ferromagnetic resonance (FMR) excitation of recording-layer magnetizations by
the microwave field from the STO. The FMR excitation affects the oscillation of
the STO, which is utilized to sense the magnetization states in a recording
layer. The recording layers are designed to have different FMR frequencies so
that the FMR excitation is selectively induced by tuning the oscillation
frequency of the STO. Since all magnetic layers interact with each other
through dipolar fields, unnecessary interlayer interferences can occur, which
are suppressed by designing magnetic properties of the layers. We move the STO
over the magnetic dots, which models a read head moving over recording media,
and show that changes in the STO oscillation occur on the one-nanosecond
timescale.",1907.10877v2
2019-09-06,The interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films,"We report on broadband ferromagnetic resonance linewidth measurements
performed on epitaxial Heusler thin films. A large and anisotropic two-magnon
scattering linewidth broadening is observed for measurements with the
magnetization lying in the film plane, while linewidth measurements with the
magnetization saturated perpendicular to the sample plane reveal low Gilbert
damping constants of $(1.5\pm0.1)\times 10^{-3}$, $(1.8\pm0.2)\times 10^{-3}$,
and $<8\times 10^{-4}$ for Co$_2$MnSi/MgO, Co$_2$MnAl/MgO, and Co$_2$FeAl/MgO,
respectively. The in-plane measurements are fit to a model combining Gilbert
and two-magnon scattering contributions to the linewidth, revealing a
characteristic disorder lengthscale of 10-100 nm.",1909.02738v2
2020-04-28,Enhancement of acoustic spin pumping by acoustic distributed Bragg reflector cavity,"Surface acoustic waves (SAWs) in the GHz frequency range can inject spin
currents dynamically into adjacent nonmagnetic layers via spin pumping effect
associated with ferromagnetic resonance. Here, we demonstrate an enhancement of
acoustic ferromagnetic resonance and spin current generation by a pair of SAW
reflector gratings, which form an acoustic analogue of the distributed Bragg
reflector cavity. In the experiment, we confirmed 2.04 $\pm$ 0.02 times larger
SAW power absorption in a device with cavity than in case of no acoustic
cavity. We confirmed up to 2.96 $\pm$ 0.02 times larger spin current generation
by measuring electric voltages generated by the inverse Edelstein effect (IEE)
at the interface between Cu and Bi$_2$O$_3$. The results suggest that acoustic
cavities would be useful to enhance the conversion efficiency in SAW driven
coupled magnon-phonon dynamics.",2004.13885v3
2020-12-25,Spin-circuit representation of spin-torque ferromagnetic resonance,"Spin-torque ferromagnetic resonance (ST-FMR) particularly using magnetic
insulators and heavy metals possessing a giant spin Hall effect (SHE) has
gotten a lot of attention for the development of spintronic devices. To devise
complex functional devices, it is necessary to construct the equivalent
spin-circuit representations of different phenomena. Such representation is
useful to translate physical equations into circuit elements, benchmarking
experiments, and then proposing creative and efficient designs. We utilize the
superposition principle in circuit theory to separate the spin Hall
magnetoresistance and spin pumping contributions in the ST-FMR experiments. We
show that the proposed spin-circuit representation reproduces the standard
results in literature. We further consider multilayers like a spin-valve
structure with an SHE layer sandwiched by two magnetic layers and show how the
corresponding spin-circuit representation can be constructed by simply writing
a vector netlist and solved using circuit theory.",2012.13591v1
2021-01-20,Spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions,"Heterostructures composed of ferromagnetic layers that are mutually
interacting through a nonmagnetic spacer are at the core of magnetic sensor and
memory devices. In the present study, layer-resolved ferromagnetic resonance
was used to investigate the coupling between the magnetic layers of a
Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were
observed for both magnetic layers, as probed at the Co and Ni L3 x-ray
absorption edges, showing a strong interlayer interaction through the
insulating MgO barrier. A theoretical model based on the
Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange
coupling and spin pumping between the magnetic layers. Fits to the experimental
data were carried out, both with and without a spin pumping term, and the
goodness of the fit was compared using a likelihood ratio test. This rigorous
statistical approach provides an unambiguous proof of the existence of
interlayer coupling mediated by spin pumping.",2101.08157v1
2012-05-13,Voltage-Induced Ferromagnetic Resonance in Magnetic Tunnel Junctions,"We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB
magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled
magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements
reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have
similar magnitudes, and thus that both torques are equally important for
understanding high-frequency voltage-driven magnetization dynamics in MTJs. As
an example, we show that VCMA can increase the sensitivity of an MTJ-based
microwave signal detector to the sensitivity level of semiconductor Schottky
diodes.",1205.2835v2
2017-05-16,"Note: Derivative divide, a method for the analysis of broadband ferromagnetic resonance in the frequency domain","Broadband ferromagnetic resonance (bbFMR) spectroscopy is an established
experimental tool to quantify magnetic properties. Due to frequency-dependent
transmission of the microwave setup, bbFMR measurements in the frequency domain
require a suitable background removal method. Here, we present a measurement
and data analysis protocol that allows to perform quantitative frequency-swept
bbFMR measurements without the need for a calibration of the microwave setup.
The method, its limitations and advantages are described in detail. Finally the
method is applied to evaluate FMR spectra of a permalloy thin film. The
extracted material parameters are in very good agreement with those obtained
using a conventional analysis in field-space.",1705.05694v2
2017-05-22,Hydrogen-modified inverse Spin Hall Effect in palladium-cobalt bi-layer films,"The influence of hydrogen gas absorption by the Pd layer of bi-layered films
containing Pd and Co layers on the inverse Spin Hall Effect (iSHE) in the
material is measured. iSHE is driven by ferromagnetic resonance in the cobalt
layer. In these conditions, the iSHE is seen as a d.c. voltage across the Pd
layer. In the presence of hydrogen gas the iSHE peak shifts downwards in the
applied field together with the ferromagnetic resonance absorption peak for the
material. In parallel, an increase in the iSHE peak height and in its width is
observed. Our analysis suggests that these observations can potentially be
explained as a reduction in the spin Hall angle for the Palladium layer in the
presence of hydrogen gas.",1705.07547v2
2018-07-13,Gilbert damping of high anisotropy Co/Pt multilayers,"Using broadband ferromagnetic resonance, we measure the damping parameter of
[Co(5 \r{A})/Pt(3 \r{A})]${\times 6}$ multilayers whose growth was optimized to
maximize the perpendicular anisotropy. Structural characterizations indicate
abrupt interfaces essentially free of intermixing despite the miscible
character of Co and Pt. Gilbert damping parameters as low as 0.021 can be
obtained despite a magneto-crystalline anisotropy as large as
$10^6~\textrm{J/m}^3$. The inhomogeneous broadening accounts for part of the
ferromagnetic resonance linewidth, indicating some structural disorder leading
to a equivalent 20 mT of inhomogenity of the effective field. The unexpectedly
relatively low damping factor indicates that the presence of the Pt heavy metal
within the multilayer may not be detrimental to the damping provided that
intermixing is avoided at the Co/Pt interfaces.",1807.04977v1
2019-01-07,Simultaneous Optical and Electrical Spin-Torque Magnetometry with Stroboscopic Detection of Spin-Precession Phase,"Spin-based coherent information processing and encoding utilize the
precession phase of spins in magnetic materials. However, the detection and
manipulation of spin precession phases remain a major challenge for advanced
spintronic functionalities. By using simultaneous electrical and optical
detection, we demonstrate the direct measurement of the precession phase of
Permalloy ferromagnetic resonance driven by the spin-orbit torques from
adjacent heavy metals. The spin Hall angle of the heavy metals can be
independently determined from concurrent electrical and optical signals. The
stroboscopic optical detection also allows spatially measuring local
spin-torque parameters and the induced ferromagnetic resonance with
comprehensive amplitude and phase information. Our study offers a route towards
future advanced characterizations of spin-torque oscillators, magnonic
circuits, and tunnelling junctions, where measuring the current-induced spin
dynamics of individual nanomagnets are required.",1901.01923v1
2019-02-01,Collective magnetization dynamics in nano-arrays of thin FePd discs,"We report on the magnetization dynamics of a square array of mesoscopic
discs, fabricated from an iron palladium alloy film. The dynamics properties
were explored using ferromagnetic resonance measurements and micromagnetic
simulations. The obtained spectra exhibit features resulting from the
interactions between the discs, with a clear dependence on both temperature and
the direction of the externally applied field. We demonstrate a qualitative
agreement between the measured and calculated spectra. Furthermore, we
calculated the mode profiles of the standing spin waves excited during a
time-dependent magnetic field excitations. The resulting maps confirm that the
features appearing in the ferromagnetic resonance absorption spectra originate
from the temperature and directional dependent inter-disc interactions.",1902.00403v1
2019-03-28,Magnetic-Resonance-Induced Pseudo-electric Field and Giant Current Response in Axion Insulators,"A quantized version of the magnetoelectric effect, known as the topological
magnetoelectric effect, can exist in a time-reversal invariant topological
insulator with all its surface states gapped out by magnetism. This topological
phase, called the axion insulator phase, has been theoretically proposed but is
still lack of conclusive experimental evidence due to the small signal of
topological magnetoelectric effect. In this work, we propose that the dynamical
in-plane magnetization in an axion insulator can generate a ""pseudo-electric
field"", which acts on the surface state of topological insulator films and
leads to the non-zero response current. Strikingly, we find that the current at
magnetic resonance (either ferromagnetic or anti-ferromagnetic) is larger than
that of topological magnetoelectric effect by several orders of magnitude, and
thereby serves as a feasible smoking gun to confirm the axion insulator phase
in the candidate materials.",1903.12068v2
2019-04-09,Ferromagnetic Resonance Studies of Strain tuned Bi:YIG Films,"Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large
Magneto-optical activity with low losses still needs to get probed for its
magnetization dynamics. We demonstrate a controlled tuning of
magnetocrystalline anisotropy in Bi-doped Y_3 Fe_5 O_12 (Bi:YIG) films of high
crystalline quality using growth induced epitaxial strain on [111]-oriented
Gd_3 Ga_5 O_12 (GGG) substrate. We optimize a growth protocol to get thick
highly-strained epitaxial films showing large magneto-crystalline anisotropy,
compare to thin films prepared using a different protocol. Ferromagnetic
resonance measurements establish a linear dependence of the out-of-plane
uniaxial anisotropy on the strain induced rhombohedral distortion of Bi:YIG
lattice. Interestingly, the enhancement in the magnetoelastic constant due to
an optimum substitution of Bi^(3+) ions with strong spin orbit coupling does
not strongly affect the precessional damping (~2x10^(-3) ). Large
magneto-optical activity, reasonably low damping, large magnetocrystalline
anisotropy and large magnetoelastic coupling in BiYIG are the properties that
may help BiYIG emerge as a possible material for photo-magnonics and other
spintronics applications.",1904.04800v2
2019-11-03,Magnetic damping modulation in $IrMn_{3}/Ni_{80}Fe_{20}$ via the magnetic spin Hall effect,"Non-collinear antiferromagnets can have additional spin Hall effects due to
the net chirality of their magnetic spin structure, which provides for more
complex spin-transport phenomena compared to ordinary non-magnetic materials.
Here we investigated how ferromagnetic resonance of permalloy
($Ni_{80}Fe_{20}$) is modulated by spin Hall effects in adjacent epitaxial
$IrMn_{3}$ films. We observe a large dc modulation of the ferromagnetic
resonance linewidth for currents applied along the [001] $IrMn_{3}$ direction.
This very strong angular dependence of spin-orbit torques from dc currents
through the bilayers can be explained by the magnetic spin Hall effect where
$IrMn_{3}$ provides novel pathways for modulating magnetization dynamics
electrically.",1911.00943v1
2019-12-05,Quasiparticle conductance in Spin Valve Josephson Structures,"We study the quasiparticle current in clean ferromagnetic Josephson
structures of the form $S_1/F_1/N/F_2/S_2$, where $S$, $F$, and $N$ denote
superconducting, ferromagnetic or normal layers respectively. Our focus is on
the structure of the conductance $G$ as a function of bias $V$, emphasizing the
subgap region. We use a fully self consistent numerical method, coupled to a
transfer matrix procedure to extract $G(V)$. We choose material parameters
appropriate to experimentally realized Co Cu Nb structures. We find a resonance
peak structure as a function of the intermediate layer thickness and of the
misalignement angle $\phi$ between $F$ layers. To understand this resonance
structure, we develop an approximate analytic method. For experimentally
relevant thicknesses, the conductance has multiple subgap peaks which oscillate
in position between low and critical bias positions. These oscillations occur
in both $\phi$ and the layer thicknesses. We compare our results with those
obtained for the spin valve structures $(F_1/N/F_2/S_2)$ and discuss the
implications of our results for the fabrication of spin Josephson devices.",1912.02715v1
2020-06-23,Magnetization dynamics in synthetic antiferromagnets: Role of dynamical energy and mutual spin pumping,"We investigate magnetization dynamics in asymmetric interlayer exchange
coupled Py/Ru/Py trilayers using both vector network analyzer-based and
electrically detected ferromagnetic resonance techniques. Two different
ferromagnetic resonance modes, in-phase and out-of-phase, are observed across
all three regimes of the static magnetization configurations, through
antiparallel alignment at low fields, the spin-flop transition at intermediate
fields, and parallel alignment at high fields. The nonmonotonic behavior of the
modes as a function of the external field is explained in detail by analyzing
the interlayer exchange and Zeeman energies and is found to be solely governed
by the interplay of their dynamical components. In addition, the linewidths of
both modes were determined across the three regimes and the different behaviors
of the linewidths versus external magnetic field are attributed to mutual spin
pumping induced in the samples. Interestingly, the difference between the
linewidths of the out-of-phase and in-phase modes decreases at the spin-flop
transition and is reversed between the antiparallel and parallel aligned
magnetization states.",2006.13031v1
2020-08-21,Integration and characterization of micron-sized YIG structures with very low Gilbert damping on arbitrary substrates,"We present a novel process that allows the transfer of monocrystalline
yttrium-iron-garnet microstructures onto virtually any kind of substrate. The
process is based on a recently developed method that allows the fabrication of
freestanding monocrystalline YIG bridges on gadolinium-gallium-garnet. Here the
bridges' spans are detached from the substrate by a dry etching process and
immersed in a watery solution. Using drop casting the immersed YIG platelets
can be transferred onto the substrate of choice, where the structures finally
can be reattached and thus be integrated into complex devices or experimental
geometries. Using time resolved scanning Kerr microscopy and inductively
measured ferromagnetic resonance we can demonstrate that the structures retain
their excellent magnetic quality. At room temperature we find a ferromagnetic
resonance linewidth of $\mu_0\Delta H_{HWHM}\approx 195\,\mu T$ and we were
even able to inductively measure magnon spectra on a single micron-sized
yttrium-iron-garnet platelet at a temperature of 5 K. The process is flexible
in terms of substrate material and shape of the structure. In the future this
approach will allow for new types of spin dynamics experiments up to now
unthinkable.",2008.09390v1
2020-10-18,Quantifying power flow processes mediated by spin currents,"The power flow process mediated by spin current in the bilayer device
consisting of ferromagnetic metal (FM) and non-magnetic metal (NM) layers is
examined by realizing experimental evaluations for each process from the
microwave absorption to electromotive force (EMF) output. The absorption power
by ferromagnetic resonance (FMR) of the thin FM layer during the EMF output is
directly measured in operando using an antenna probe system. The transfer
efficiency of the absorption power into the NM layer by spin pumping is
estimated from strict linewidth evaluation of EMF spectra. The maximum transfer
efficiency of the spin pumping power to the external load via the inverse spin
Hall effect is determined to be 4.2X10^(-8) under 160mW microwave irradiation
using an analysis model assuming a parallel circuit. The main factors reducing
the efficiency are found to be low resistivity of the NM layer and the
interface loss. These quantifications are important as a first step to consider
the efficient transfer of spin energy mediated by spin currents.",2010.08997v3
2020-11-26,Optically-induced frequency up-conversion of the ferromagnetic resonance in an ultrathin garnet,"We perform ultrafast pump-probe measurements on a nanometer-thick crystalline
Bi-doped yttrium iron garnet film with perpendicular magnetic anisotropy.
Tuning the photon energy of the pump laser pulses above and below the
material's bandgap, we trigger ultrafast optical and spin dynamics via both
one- and two-photon absorption. Contrary to the common scenario, the
optically-induced heating of the system induces an increase up to 20% of the
ferromagnetic resonance frequency. We explain this unexpected result in terms
of a photo-induced modification of the magnetic anisotropy, i.e. of the
effective field, identifying the necessary conditions to observe this effect.
Our results disclose the possibility to optically increase the magnetic
eigenfrequency in nanometer-thick magnets.",2011.13403v1
2021-03-06,Resolving Discrepancies in Spin-Torque Ferromagnetic Resonance Measurements: Lineshape vs. Linewidth Analyses,"When spin-orbit torques are measured using spin-torque ferromagnetic
resonance (ST-FMR), two alternative ways of analyzing the results to extract
the torque efficiencies -- lineshape analysis and analysis of the change in
linewidth versus DC current -- often give inconsistent results. We identify a
source for these inconsistencies. We show that fits of ST-FMR data to the
standard analysis framework leave significant residuals that we identify as due
to (i) current-induced excitations of a small volume of magnetic material with
magnetic damping much larger than the bulk of the magnetic layer, that we
speculate is associated with the heavy-metal/magnet interface and (ii)
oscillations of the sample magnetization at the modulation frequency due to
heating. The dependence of the residual signals on DC current can interfere
with an accurate extraction of spin-torque efficiencies by the linewidth
method. We show that the discrepancies between the two types of analysis can be
largely eliminated by extrapolating the window of magnetic fields used in the
linewidth fits to small values so as to minimize the influence of the residual
signals.",2103.04172v1
2021-05-24,Spin pumping of two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interactions,"We theoretically consider spin pumping in a junction between a ferromagnetic
insulator (FI) and a two-dimensional electron gas (2DEG) in which the Rashba
and Dresselhaus spin-orbit interactions coexist. Using second-order
perturbation theory, we derive an increase in linewidth in the case of an
interfacial exchange coupling in a ferromagnetic resonance (FMR) experiment. We
clarify how the enhancement of Gilbert damping depends on the resonant
frequency and spin orientation of the FI. We show that this setup of an FMR
experiment can provide information on the spin texture of 2DEG at the Fermi
surface.",2105.11193v3
2021-08-07,Strong Momentum-Dependent Electron-Magnon Renormalization of a Surface Resonance on Iron,"The coupling of fermionic quasiparticles to magnons is essential for a wide
range of processes, from ultrafast magnetization dynamics in ferromagnets to
Cooper pairing in superconductors. Although magnon energies are generally much
larger than phonon energies, up to now their electronic band renormalization
effect in ferromagnetic metals suggests a significantly weaker quasiparticle
interaction. Here, using spin- and angle-resolved photoemission, we show an
extraordinarily strong renormalization leading to replica-band formation of an
iron surface resonance at ~200 meV. Its strong magnetic linear dichroism
unveils the magnetic nature and momentum dependence of the energy
renormalization. By determining the frequency- and momentum-dependent
self-energy due to generic electron-boson interaction to compute the resultant
electron spectral function, we show that the surface-state replica formation is
consistent with strong coupling to an optical spin wave in a Fe thin film.",2108.03421v1
2021-10-31,Thermally induced all-optical ferromagnetic resonance in thin YIG films,"All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
damping or spin stiffness. In this work we demonstrate that the AO-FMR method
can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
layer (Au, Pt) is deposited on top of the film. Magnetization precession is
triggered by heating of the metallic layer with femtosecond laser pulses. The
heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
the quasi-equilibrium orientation of magnetization, which results in
precessional magnetization dynamics. The laser-induced magnetization precession
corresponds to a uniform (Kittel) magnon mode, with the precession frequency
determined by the magnetic anisotropy of the material as well as the external
magnetic field, and the damping time set by a Gilbert damping parameter. The
AO-FMR method thus enables measuring local magnetic properties, with spatial
resolution given only by the laser spot size.",2111.00586v1
2021-11-30,First and second order magnetic anisotropy and damping of europium iron garnet under high strain,"Understanding and tailoring static and dynamic properties of magnetic
insulator thin films is important for spintronic device applications. Here, we
grow atomically flat epitaxial europium iron garnet (EuIG) thin films by pulsed
laser deposition on (111)-oriented garnet substrates with a range of lattice
parameters. By controlling the lattice mismatch between EuIG and the
substrates, we tune the strain in EuIG films from compressive to tensile
regime, which is characterized by X-ray diffraction. Using ferromagnetic
resonance, we find that in addition to the first-order perpendicular magnetic
anisotropy which depends linearly on the strain, there is a significant
second-order one that has a quadratic strain dependence. Inhomogeneous
linewidth of the ferromagnetic resonance increases notably with increasing
strain, while the Gilbert damping parameter remains nearly constant (~
2x10^-2). These results provide valuable insight into the spin dynamics in
ferrimagnetic insulators and useful guidance for material synthesis and
engineering of next-generation spintronics applications.",2111.15142v1
2022-03-04,Simultaneous optical trapping and magnetic micromanipulation of ferromagnetic iron-doped upconversion microparticles in six degrees of freedom,"Optical trapping of magnetic Fe-oxide particles is notoriously difficult due
to their high refractive indices, not to mention high absorptivity at the
trapping infra-red wavelengths. We synthesize Fe co-doped NaYF4:Yb,Er
ferromagnetic upconversion particles that not only have refractive indices
conducive for optical trapping, but also heat less than Haematite particles at
off-resonant wavelengths. These particles are hexagonal shaped with dimensions
of the order of 3 micrometer and also bear high coercivity of 20 mT and
saturation magnetisation of 1 Am^2/kg. This enables simultaneous use of optical
trapping and magnetic forces to generate micro-manipulation in all the six
degrees of freedom of a rigid body. We also show that these particles heat
significantly when illuminated on absorption resonance at 975 nm while emitting
visible light with possible implications for fluorescence microscopy and
photothermal therapy of cancer cells.",2203.02152v2
2022-04-25,Oscillations and confluence in three-magnon scattering of ferromagnetic resonance,"We have performed a time-resolved and phase-sensitive investigation of
three-magnon scattering of ferromagnetic resonance (FMR) over several orders of
magnitude in excitation power. We observe a regime that hosts transient
oscillations of the FMR magnon population, despite higher-order magnon
interactions at large powers. Also at high powers, the scattering generates
$180^\circ$ phase shifts of the FMR magnons. These phase shifts correspond to
reversals in the three-magnon scattering direction, between splitting and
confluence. These scattering reversals are most directly observed after
removing the microwave excitation, generating coherent oscillations of the FMR
magnon population much larger than its steady-state value during the
excitation. Our model is in strong agreement with these findings. These
findings reveal the transient behavior of this three-magnon scattering process,
and the nontrivial interplay between three-magnon scattering and the magnons'
phases.",2204.11969v4
2022-09-30,Hybrid magnetization dynamics in $\text{Cu}_\text{2}\text{OSeO}_\text{3}$/$\mathrm{NiFe}$ heterostructures,"We investigate the coupled magnetization dynamics in heterostructures of a
single crystal of the chiral magnet $\mathrm{Cu_2OSeO_3}$ (CSO) and a
polycrystalline ferromagnet $\mathrm{NiFe}$ (Py) thin film using broadband
ferromagnetic resonance (FMR) at cryogenic temperatures. We observe the
excitation of a hybrid mode (HM) below the helimagnetic transition temperature
of CSO. This HM is attributed to the spin dynamics at the CSO/Py interface. We
study the HM by measuring its resonance frequencies for in plane rotations of
the external magnetic field. We find that the HM exhibits dominantly four-fold
anisotropy, in contrast to the FMR of CSO and Py.",2210.00897v1
2022-11-30,Tensor network study of the spin-1/2 Heisenberg anti-ferromagnet on the Shuriken lattice,"We investigate the ground state of the spin $S=1/2$ Heisenberg
anti-ferromagnet on the Shuriken lattice, also in the presence of an external
magnetic field. To this end, we employ two-dimensional tensor network
techniques based on infinite projected entangled pair and simplex states
considering states with different sizes of the unit cells. We show that a
valence bond crystal with resonances over length six loops emerges as the
ground state (at any given finite bond dimension) yielding the lowest reported
estimate of the ground state energy $E_0/J = -0.4410 \pm 0.0001$ for this
model, estimated in the thermodynamic limit. We also study the model in the
presence of an external magnetic field and find the emergence of $0$, $1/3$ and
$2/3$ magnetization plateaus with states respecting translation and point group
symmetries that feature loop-four plaquette resonances instead.",2211.16932v2
2023-01-01,Spin Hall Induced Magnetization Dynamics in Multiferroic Tunnel Junction,"The combination of spin-orbit coupling driven effects and multiferroic
tunneling properties was explored experimentally in thin Pt/Co/BTO/LSMO
multilayers. The presence of a Pt heavy metal allows for the spin
current-induced magnetization precession of Co upon radio-frequency charge
current injection. The utilization of a BTO ferroelectric tunnel barrier
separating the Co and LSMO ferromagnetic electrodes gives rise to both
tunneling-magnetoresistance and electroresistance. Using the spin-orbit torque
ferromagnetic resonance, the maganetization dynamics of the Co/Pt bilayers was
studied at room temperature. Unexpectedly the magnetization dynamics study in
the same geometry performed at low temperature reveals the existence of both Co
and LSMO resonance peaks indicating efficient spin current generation both
using the spin Hall effect in Pt and spin pumping in LSMO that tunnel via the
BTO barrier.",2301.00459v1
2023-05-08,Observation of Enhanced Dynamic ΔG effect near Ferromagnetic Resonance Frequency,"The field-dependence elastic modulus of magnetostrictive films, also called
{\Delta}E or {\Delta}G effect, is crucial for ultrasensitive magnetic field
sensors based on surface acoustic waves (SAWs). In spite of a lot of successful
demonstrations, rare attention was paid to the frequency-dependence of
{\Delta}E or {\Delta}G effect. In current work, shear horizontal-type SAW delay
lines coated with a thin FeCoSiB layer have been studied at various frequencies
upon applying magnetic fields. The change of shear modulus of FeCoSiB has been
extracted by measuring the field-dependent phase shift of SAWs. It is found
that the {\Delta}G effect is significantly enhanced at high-order harmonic
frequencies close to the ferromagnetic resonance frequency, increasing by ~82%
compared to that at the first SAW mode (128 MHz). In addition, the smaller the
effective damping factor of magnetostrictive layer, the more pronounced
{\Delta}G effect can be obtained, which is explained by our proposed dynamic
magnetoelastic coupling model.",2305.04473v1
2023-05-24,Competing Uniaxial Anisotropies in Epitaxial Fe Thin Films Grown on InAs(001),"We report on the interplay of two uniaxial magnetic anisotropies in epitaxial
Fe thin films of varying thickness grown on InAs(001) as observed in
ferromagnetic resonance experiments. One anisotropy originates from the Fe/InAs
interface while the other originates from in-plane shear strain resulting from
the anisotropic relaxation of the Fe film. X-ray diffraction was used to
measure the in-plane lattice constants of the Fe films, confirming the
correlation between the onset of film relaxation and the corresponding shear
strain inferred from ferromagnetic resonance data. These results are relevant
for ongoing efforts to develop spintronic and quantum devices utilizing large
spin-orbit coupling in III-V semiconductors.",2305.14648v1
2023-06-27,Off-Resonant Detection of Domain Wall Oscillations Using Deterministically Placed Nanodiamonds,"Nitrogen-vacancy (NV) centers in diamond offer a sensitive method of
measuring the spatially localized dynamics of magnetization and associated spin
textures in ferromagnetic materials. We use NV centers in a deterministically
positioned nanodiamond to demonstrate off-resonant detection of GHz-scale
microwave field driven oscillations of a single domain wall (DW). The technique
exploits the enhanced relaxation of NV center spins due to the broadband stray
fields generated by an oscillating DW pinned at an engineered defect in a
lithographically patterned ferromagnetic nanowire. Discrepancies between the
observed DW oscillation frequency and predictions from micromagnetic
simulations suggest extreme sensitivity of DW dynamics to patterning
imperfections such as edge roughness. These experiments and simulations
identify potential pathways toward quantum spintronic devices that exploit
current driven DWs as nanoscale microwave generators for qubit control, greatly
increasing the driving field at an NV center and thus drastically reducing the
{\pi} pulse time.",2306.15493v1
2023-09-07,Gænice: a general model for magnon band structure of artificial spin ices,"Arrays of artificial spin ices exhibit reconfigurable ferromagnetic resonance
frequencies that can be leveraged and designed for potential
applications.However, analytical and numerical studies of the frequency
response of artificial spin ices have remained somewhat limited due to the need
of take into account nonlocal dipole fields in theoretical calculations or by
long computation times in micromagnetic simulations. Here, we introduce
Gaenice, a framework to compute magnon dispersion relations of arbitrary
artificial spin ice configurations. Gaenice makes use of a tight-binding
approach to compute the magnon bands. It also provides the user complete
control of the interaction terms included, e.g., external field, anisotropy,
exchange, and dipole, making it useful also to compute ferromagnetic resonances
for a variety of structures, such as multilayers and ensembles of weakly or
non-interacting nanoparticles. Because it relies on a semi-analytical model,
Gaenice is computationally inexpensive and efficient, making it an attractive
tool for the exploration of large parameter spaces.",2309.03826v2
2023-11-14,Temperature Dependence of Spin Pumping in Ni81Fe19/NbN Bilayer Thin Films,"We present a comprehensive study of broadband spin pumping utilizing the
inverse spin Hall effect phenomena in bilayer samples comprising Ni81Fe19 (15
nm) and NbN (with NbN thickness varying from 20 nm to 140 nm), conducted over a
temperature and frequency range spanning from 300 K to 4 K and 2 GHz to 12 GHz,
respectively. Our investigations reveal a systematic shift in ferromagnetic
resonance fields, amplitude, and line widths as functions of both frequency and
temperature. Notably, we observed a temperature-dependent increase in the spin
Hall angle value, surpassing previously reported values. Furthermore, our
results demonstrate a pronounced temperature dependence in the inverse spin
Hall effect voltage, exhibiting a significant reduction below the Tc. This
reduction in inverse spin Hall effect voltage is accompanied by an increase in
the linewidth of the ferromagnetic resonance mode.",2311.08257v1
2024-02-19,Broadband ferromagnetic resonance in Mn-doped Li ferrite nanoparticles,"Lithium ferrites are well known materials due to their numerous technological
applications especially in microwave devices. Mn-doped lithium ferrite
nanoparticles were prepared by sol-gel technique by means of Pechini method,
and then annealed at different temperatures in 250 to 1000 {\deg}C range. XRD
confirms spinel formation with particle size in the 15 to 200 nm range, with
increased size with annealing temperature. Microwave magnetoabsorption data of
annealed lithium ferrite nanoparticles, obtained with a broadband system based
on a network analyzer operating up to 8.5 GHz are presented. At fields up to
200 mT we can observe a broad absorption peak that shifts to higher frequencies
with magnetic field according to ferromagnetic resonance theory. The amplitude
of absorption, up to 85%, together with the frequency width of about 4.5 GHz
makes this material suitable as wave absorber. Samples annealed at higher
temperatures show a behaviour similar to polycrystalline samples, thus
suggesting their multidomain character",2402.12096v1
2006-07-21,Spin splitting and Kondo effect in quantum dots coupled to noncollinear ferromagnetic leads,"We study the Kondo effect in a quantum dot coupled to two noncollinear
ferromagnetic leads. First, we study the spin splitting
$\delta\epsilon=\epsilon_{\downarrow}-\epsilon_{\uparrow}$ of an energy level
in the quantum dot by tunnel couplings to the ferromagnetic leads, using the
Poor man's scaling method. The spin splitting takes place in an intermediate
direction between magnetic moments in the two leads. $\delta\epsilon \propto
p\sqrt{\cos^2(\theta/2)+v^2\sin^2(\theta/2)}$, where $p$ is the spin
polarization in the leads, $\theta$ is the angle between the magnetic moments,
and $v$ is an asymmetric factor of tunnel barriers ($-1<v<1$). Hence the spin
splitting is always maximal in the parallel alignment of two ferromagnets
($\theta=0$) and minimal in the antiparallel alignment ($\theta=\pi$). Second,
we calculate the Kondo temperature $T_{\mathrm{K}}$. The scaling calculation
yields an analytical expression of $T_{\mathrm{K}}$ as a function of $\theta$
and $p$, $T_{\mathrm{K}}(\theta, p)$, when $\delta\epsilon \ll T_{\mathrm{K}}$.
$T_{\mathrm{K}}(\theta, p)$ is a decreasing function with respect to
$p\sqrt{\cos^2(\theta/2)+v^2\sin^2(\theta/2)}$. When $\delta\epsilon$ is
relevant, we evaluate $T_{\mathrm{K}}(\delta\epsilon, \theta, p)$ using the
slave-boson mean-field theory. The Kondo resonance is split into two by finite
$\delta\epsilon$, which results in the spin accumulation in the quantum dot and
suppression of the Kondo effect.",0607548v2
2006-12-07,"Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N - relation between structural, electronic, and magnetic properties","We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and
(Ga,Fe)N layers on c-sapphire substrates and their thorough characterization
via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy
(TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS),
secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect,
electron-paramagnetic resonance (EPR), and magnetometry employing a
superconducting quantum interference device (SQUID). A combination of TEM and
EDS reveals the presence of coherent nanocrystals presumably FexN with the
composition and lattice parameter imposed by the host. From both TEM and SIMS
studies, it is stated that the density of nanocrystals and, thus the Fe
concentration increases towards the surface. In layers with iron content x<0.4%
the presence of ferromagnetic signatures, such as magnetization hysteresis and
spontaneous magnetization, have been detected. We link the presence of
ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced
by TEM and EDS studies. This interpretation is supported by magnetization
measurements after cooling in- and without an external magnetic field, pointing
to superparamagnetic properties of the system. It is argued that the high
temperature ferromagnetic response due to spinodal decomposition into regions
with small and large concentration of the magnetic component is a generic
property of diluted magnetic semiconductors and diluted magnetic oxides showing
high apparent Curie temperature.",0612200v2
2009-06-08,SU(2) slave-boson formulation of spin nematic states in S=1/2 frustrated ferromagnets,"An SU(2) slave boson formulation of bond-type spin nematic orders is
developed in frustrated ferromagnets, where the spin nematic states are
described as the resonating spin-triplet valence bond (RVB) states. The
d-vectors of spin-triplet pairing ansatzes play the role of the directors in
the bond-type spin quadrupolar states. The low-energy excitations around such
spin-triplet RVB ansatzes generally comprise the (potentially massless) gauge
bosons, massless Goldstone bosons, and spinon individual excitations. Extending
the projective symmetry group argument to the spin-triplet ansatzes, we show
how to identify the number of massless gauge bosons efficiently. Applying this
formulation, we next (i) enumerate possible mean field solutions for the S=1/2
ferromagnetic J1-J2 Heisenberg model on the square lattice, with ferromagnetic
nearest neighbor J1 and competing antiferromagnetic next-nearest neighbor J2,
and (ii) argue their stability against small gauge fluctuations. As a result,
two stable spin-triplet RVB ansatzes are found in the intermediate coupling
regime around J1:J2 \simeq 1:0.4. One is the Z_2 Balian-Werthamer (BW) state
stabilized by the Higgs mechanism and the other is the SU(2) chiral p-wave
(Anderson-Brinkman-Morel) state stabilized by the Chern-Simon mechanism. The
former Z_2 BW state in fact shows the same bond-type spin quadrupolar order as
found in the previous exact diagonalization study [N. Shannon et al., Phys.
Rev. Lett. 96, 027213 (2006)].",0906.1248v3
2014-01-15,Characterization of the Spin-1/2 Linear-Chain Ferromagnet CuAs$_2$O$_4$,"The magnetic and lattice properties of the $S$=1/2 quantum-spin-chain
ferromagnet, CuAs$_2$O$_4$, mineral name trippkeite, were investigated. The
crystal structure of CuAs$_2$O$_4$ is characterized by the presence of
corrugated CuO$_2$ ribbon chains. Measurements of the magnetic susceptibility,
heat capacity, electron paramagnetic resonance and Raman spectroscopy were
performed. Our experiments conclusively show that a ferromagnetic transition
occurs at $\sim$7.4 K. $\textit{Ab initio}$ DFT calculations reveal dominant
ferromagnetic nearest-neighbor and weaker antiferromagnetic next-
nearest-neighbor spin exchange interactions along the ribbon chains. The ratio
of $J_{\rm nn}$/$J_{\rm nnn}$ is near -4, placing CuAs$_2$O$_4$ in close
proximity to a quantum critical point in the $J_{\rm nn}$ - $J_{\rm nnn}$ phase
diagram. TMRG simulations used to analyze the magnetic susceptibility confirm
this ratio. Single-crystal magnetization measurements indicate that a magnetic
anisotropy forces the Cu$^{2+}$ spins to lie in an easy plane perpendicular to
the $c$-axis. An analysis of the field and temperature dependent magnetization
by modified Arrott plots reveals a 3d-XY critical behavior. Lattice
perturbations induced by quasi-hydrostatic pressure and temperature were mapped
via magnetization and Raman spectroscopy.",1401.3400v1
2015-02-13,Magnon transport through microwave pumping,"We present a microscopic theory of magnon transport in ferromagnetic
insulators (FIs). Using magnon injection through microwave pumping, we propose
a way to generate magnon dc currents and show how to enhance their amplitudes
in hybrid ferromagnetic insulating junctions. To this end focusing on a single
FI, we first revisit microwave pumping at finite (room) temperature from the
microscopic viewpoint of magnon injection. Next, we apply it to two kinds of
hybrid ferromagnetic insulating junctions. The first is the junction between a
quasi-equilibrium magnon condensate and magnons being pumped by microwave,
while the second is the junction between such pumped magnons and noncondensed
magnons. We show that quasi-equilibrium magnon condensates generate ac and dc
magnon currents, while noncondensed magnons produce essentially a dc magnon
current. The ferromagnetic resonance (FMR) drastically increases the density of
the pumped magnons and enhances such magnon currents. Lastly, using microwave
pumping in a single FI, we discuss the possibility that a magnon current
through an Aharonov-Casher phase flows persistently even at finite temperature.
We show that such a magnon current arises even at finite temperature in the
presence of magnon-magnon interactions. Due to FMR, its amplitude becomes much
larger than the condensed magnon current.",1502.03865v2
2015-04-29,Role of transparency of platinum-ferromagnet interface in determining intrinsic magnitude of spin Hall effect,"The spin Hall effect (SHE) converts charge current to pure spin currents in
orthogonal directions in materials that have significant spin-orbit
coupling.The efficiency of the conversion is described by the spin Hall Angle
(SHA). The SHA can most readily be inferred by using the generated spin
currents to excite or rotate the magnetization of ferromagnetic films or
nano-elements via spin-transfer torques.Some of the largest spin torque derived
spin Hall angles (ST-SHA) have been reported in platinum. Here we show, using
spin torque ferromagnetic resonance (ST-FMR) measurements, that the
transparency of the Pt-ferromagnet interface to the spin current plays a
central role in determining the magnitude of the ST-SHA. We measure a much
larger ST-SHA in Pt/cobalt (~0.11) compared to Pt/permalloy (~0.05) bilayers
when the interfaces are assumed to be completely transparent. Taking into
account the transparency of these interfaces, as derived from spin-mixing
conductances, we find that the intrinsic SHA in platinum has a much higher
value of 0.19 +- 0.04 as compared to the ST-SHA. The importance of the
interface transparency is further exemplified by the insertion of atomically
thin magnetic layers at the Pt/permalloy interface that we show strongly
modulates the magnitude of the ST-SHA.",1504.07929v1
2016-02-01,Facet-dependent giant spin orbit torque in single crystalline antiferromagnetic Ir-Mn / ferromagnetic permalloy bilayers,"There has been considerable interest in spin-orbit torques for the purpose of
manipulating the magnetization of ferromagnetic (FM) films or nano-elements for
spintronic technologies. Spin-orbit torques are derived from spin currents
created from charge currents in materials with significant spin-orbit coupling
that diffuse into an adjacent FM material. There have been intensive efforts to
search for candidate materials that exhibit large spin Hall angles, i.e.
efficient charge to spin current conversion. Here we report, using spin torque
ferromagnetic resonance, the observation of a giant spin Hall angle of up to
~0.35 in (100) oriented single crystalline antiferromagnetic (AF) IrMn3 thin
films, coupled to ferromagnetic permalloy layers, and a spin Hall angle that is
about three times smaller in (111) oriented films. For the (100) oriented
samples we show that the magnitude of the spin Hall angle can be significantly
changed by manipulating the populations of the various AF domains through field
annealing. Using ab-initio calculations we show that the triangular AF
structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity
that is three times larger for the (100) than for the (111) orientations,
consistent with our experimental findings.",1602.00670v1
2016-07-06,"Impurity states in the magnetic topological insulator V:(Bi,Sb)$_2$Te$_3$","The ferromagnetic topological insulator V:(Bi,Sb)$_2$Te$_3$ has been recently
reported as a quantum anomalous Hall (QAH) system. Yet the microscopic origins
of the QAH effect and the ferromagnetism remain unclear. One key aspect is the
contribution of the V atoms to the electronic structure. Here the valence band
of V:(Bi,Sb)$_2$Te$_3$ thin films was probed in an element-specific way by
resonant photoemission spectroscopy. The signature of the V $3d$ impurity band
was extracted, and exhibits a high density of states near Fermi level.
First-principles calculations support the experimental results and indicate the
coexistence of ferromagnetic superexchange and double exchange interactions.
The observed impurity band is thus expected to contribute to the ferromagnetism
via the interplay of different mechanisms.",1607.01662v2
2017-03-22,Fast domain wall motion induced by antiferromagnetic spin dynamics at the angular momentum compensation temperature of ferrimagnets,"Antiferromagnetic spintronics is an emerging research field which aims to
utilize antiferromagnets as core elements in spintronic devices. A central
motivation toward this direction is that antiferromagnetic spin dynamics is
expected to be much faster than ferromagnetic counterpart because
antiferromagnets have higher resonance frequencies than ferromagnets. Recent
theories indeed predicted faster dynamics of antiferromagnetic domain walls
(DWs) than ferromagnetic DWs. However, experimental investigations of
antiferromagnetic spin dynamics have remained unexplored mainly because of the
immunity of antiferromagnets to magnetic fields. Furthermore, this immunity
makes field-driven antiferromagnetic DW motion impossible despite rich physics
of field-driven DW dynamics as proven in ferromagnetic DW studies. Here we show
that fast field-driven antiferromagnetic spin dynamics is realized in
ferrimagnets at the angular momentum compensation point TA. Using rare-earth
3d-transition metal ferrimagnetic compounds where net magnetic moment is
nonzero at TA, the field-driven DW mobility remarkably enhances up to 20 km/sT.
The collective coordinate approach generalized for ferrimagnets and atomistic
spin model simulations show that this remarkable enhancement is a consequence
of antiferromagnetic spin dynamics at TA. Our finding allows us to investigate
the physics of antiferromagnetic spin dynamics and highlights the importance of
tuning of the angular momentum compensation point of ferrimagnets, which could
be a key towards ferrimagnetic spintronics.",1703.07515v1
2018-03-02,Response and phase transition of a Kitaev spin liquid in a local magnetic field,"We study the response of the Kitaev spin liquid (KSL) to a local magnetic
field perpendicular to the Kitaev honeycomb lattice. The local magnetic field
induces a dynamical excitation of a flux pair in the spin liquid and the system
can be described by a generally particle-hole asymmetric interacting resonant
level model. The dynamical excitation of the flux pair closes the flux gap in
the spectrum of the spin correlation function locally for the gapless KSL even
from the perturbative response to a weak magnetic field. Beyond the
perturbative regime, the p-h asymmetry competes with the magnetic field and
results in a rich phase diagram. Moreover, the magnetic field breaks the gauge
equivalence of the ferromagnetic and anti-ferromagnetic Kitaev couplings of the
ground state and leads to very different behaviors for the two cases. The
anti-ferromagnetic case experiences a first order phase transition to the
polarized state during magnetization whereas the ferromagnetic case does not.
This study can be generalized to the Kitaev model in a uniform magnetic field
and may help understand issues in recent experiments on KSL candidates.",1803.01011v4
2018-12-02,Direct detection of induced magnetic moment and efficient spin-to-charge conversion in graphene/ferromagnetic structures,"This article shows that the spin-to-charge current conversion in single-layer
graphene (SLG) by means of the inverse Rashba-Edelstein effect (IREE) is made
possible with the integration of this remarkable 2D-material with the unique
ferrimagnetic insulator yttrium iron garnet (YIG = $Y_{3}Fe_{5}O_{12}$) as well
as with the ferromagnetic metal permalloy (Py = $Ni_{81}Sb_{19}$). By means of
X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)
techniques, we show that the carbon atoms of the SLG acquires an induced
magnetic moment due to the proximity effect with the magnetic layer. The spin
currents are generated in the magnetic layer by spin pumping from microwave
driven ferromagnetic resonance and are detected by a dc voltage along the
graphene layer, at room temperature. The spin-to-charge current conversion,
occurring at the graphene layer, is explained by the extrinsic spin-orbit
interaction (SOI) induced by the proximity effect with the ferromagnetic layer.
The results obtained for the SLG/YIG and SLG/Py systems confirm very similar
values for the IREE parameter, which are larger than the values reported in
previous studies for SLG. We also report systematic investigations of the
electronic and magnetic properties of the SLG/YIG by means of scanning
tunneling microscopy (STM).",1812.00455v1
2019-12-26,Orbitally-resolved ferromagnetism of monolayer CrI$_3$,"Few-layer CrI$_3$ is the most known example among two-dimensional (2D)
ferromagnets, which have attracted growing interest in recent years. Despite
considerable efforts and progress in understanding the properties of 2D magnets
both from theory and experiment, the mechanism behind the formation of in-plane
magnetic ordering in chromium halides is still under debate. Here, we propose a
microscopic orbitally-resolved description of ferromagnetism in monolayer
CrI$_3$. Starting from first-principles calculations, we construct a low-energy
model for the isotropic Heisenberg exchange interactions. We find that there
are two competing contributions to the long-range magnetic ordering in CrI$_3$:
(i) Antiferromagnetic Anderson's superexchange between half-filled $t_{2g}$
orbitals of Cr atoms; and (ii) Ferromagnetic exchange governed by the
Kugel-Khomskii mechanism, involving the transitions between half-filled
$t_{2g}$ and empty $e_g$ orbitals. Using numerical calculations, we estimate
the exchange interactions in momentum-space, which allows us to restore the
spin-wave spectrum, as well as estimate the Curie temperature. Contrary to the
nearest-neighbor effective models, our calculations suggest the presence of
sharp resonances in the spin-wave spectrum at 5--7 meV, depending on the
vertical bias voltage. Our estimation of the Curie temperature in monolayer
CrI$_3$ yields 55--65 K, which is in good agreement with experimental data.",1912.11828v1
2020-08-05,Proximate ferromagnetic state in the Kitaev model material $α$-RuCl$_{3}$,"$\alpha$-RuCl$_{3}$ is a major candidate for the realization of the Kitaev
quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures
indicates deviations from the Kitaev model. We have quantified the spin
Hamiltonian of $\alpha$-RuCl$_{3}$ by a resonant inelastic x-ray scattering
study at the Ru $L_{3}$ absorption edge. In the paramagnetic state, the
quasi-elastic intensity of magnetic excitations has a broad maximum around the
zone center without any local maxima at the zigzag magnetic Bragg wavevectors.
This finding implies that the zigzag order is fragile and readily destabilized
by competing ferromagnetic correlations. The classical ground state of the
experimentally determined Hamiltonian is actually ferromagnetic. The zigzag
state is stabilized via a quantum ""order by disorder"" mechanism, leaving
ferromagnetism -- along with the Kitaev spin liquid -- as energetically
proximate metastable states. The three closely competing states and their
collective excitations hold the key to the theoretical understanding of the
unusual properties of $\alpha$-RuCl$_{3}$ in magnetic fields.",2008.02037v2
2022-03-16,Effect of hydrogen gas on magnetic properties of alloys of ferromagnetic metals with Pd and its application in hydrogen gas sensing,"The mass-production of fuel-cell vehicles and the eventual transition to the
hydrogen economy will require safe, inexpensive and reliable sensors capable of
simultaneously detecting low concentrations of leaking hydrogen and measuring
broad ranges of hydrogen concentration in storage and energy generating
systems. Although several competing sensor technologies can potentially be used
in this role, just a few of them have thus far demonstrated a combination of
all desirable characteristics. This group of devices also includes
magneto-electronic sensors that can detect the presence of hydrogen gas in a
range of hydrogen concentrations from zero to 100% at atmospheric pressure with
the response time approaching the industry standard of one second. The hydrogen
gas sensing mechanism underpinning the operation of magneto-electronic sensors
is based on the physical processes of ferromagnetic resonance, magneto-optical
Kerr effect and anomalous Hall effect that enable one to measure
hydrogen-induced changes in the magnetic properties of structures combining Pd
with one or several ferromagnetic metals such as Co, Fe or Ni. In this chapter,
we overview the physical foundations of emergent ferromagnetic Pd-alloy-based
magneto-electronic hydrogen sensors and compare their characteristics with
those of high-performing multilayer thin film-based counterparts that have
already demonstrated a potential to find commercial applications.",2203.08575v1
2022-04-28,Multi-wavelength magnetic coding of helical luminescence in ferromagnetic 2D layered CrI3,"Two-dimensional (2D) van der Waals (vdW) ferromagnets have opened new avenues
for manipulating spin at the limits of single or few atomic layers, and for
creating unique magneto-exciton devices through the coupling of long-range
ferromagnetic (FM) orders and excitons. However, 2D vdW ferromagnets explored
so far have rarely possessed exciton behaviors; to date, FM CrI3 have been
recently revealed to show ligand-field photoluminescence correlated with FM
ordering, but typically with a broad emission peak. Alternatively, many-body
excitons have been observed in antiferromagnetic (AFM) NiPS3, but the coupling
of excitons with AFM orders is exponentially more difficult, owing to extremely
high coercivity. Here, we report a straightforward approach to realize strong
coupling of narrow helical emission and FM orders at a low magnetic field in
CrI3 through a relatively simple microsphere cavity. We show that the resonant
whispering-gallery-modes (WGM) of SiO2 microspheres give rising to a series of
strong oscillation helical emissions with a full width at half-maximum (FWHM)
of ~5 nm under continuous wave excitation. Reversible magnetic control and
coding of helical luminescence with multiwavelength is realized in the range of
950-1100 nm. This work enables plenty of opportunities for creating magnetic
encoding lasing for photonic integrated chips.",2204.13318v1
2023-03-16,Antiferromagnet-mediated interlayer exchange: hybridization versus proximity effect,"We investigate the interlayer coupling between two thin ferromagnetic (F)
films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and
show how it transitions between different regimes on changing the AF thickness.
Employing layer-selective Kerr magnetometry and ferromagnetic-resonance
techniques in a complementary manner enables us to distinguish between three
functionally distinct regimes of such ferromagnetic interlayer coupling. The F
layers are found to be individually and independently exchange-biased for thick
FeMn spacers - the first regime of no interlayer F-F* coupling. F-F* coupling
appears on decreasing the FeMn thickness below 9 nm. In this second regime
found in structures with 6.0-9.0 nm thick FeMn spacers, the interlayer coupling
exists only in a finite temperature interval just below the effective N\'eel
temperature of the spacer, which is due to magnon-mediated exchange through the
thermally softened antiferromagnetic spacer, vanishing at lower temperatures.
The third regime, with FeMn thinner than 4 nm, is characterized by a much
stronger interlayer coupling in the entire temperature interval, which is
attributed to a magnetic-proximity induced ferromagnetic exchange. These
experimental results, spanning the key geometrical parameters and thermal
regimes of the F*/AF/F nanostructure, complemented by a comprehensive
theoretical analysis, should broaden the understanding of the interlayer
exchange in magnetic multilayers and potentially be useful for applications in
spin-thermionics.",2303.09301v2
2023-04-01,High-quality NiFe thin films on oxide/non-oxide platforms via pulsed laser deposition at room temperature,"Soft ferromagnetic NiFe thin films are promising for applications in
spintronic devices because of their constituent electrical and magnetic
properties. Electron beam evaporation and sputtering techniques have been used
to deposit NiFe thin films. For in-situ stacking of NiFe with functional
complex oxides, the pulsed laser deposition (PLD) method is highly desirable.
However, the growth of high-quality NiFe (and non-oxide thin films in general)
by PLD remains a formidable task. Here, we report high-quality NiFe thin films
of various thicknesses on oxide/non-oxide substrates with desirable magnetic
properties by PLD at room temperature. The magnetic properties are found to be
strongly dependent on the laser fluence of the deposition process. The laser
fluence of 4 Joule/cm$^2$ produces the highest magnetization of ~547 emu/cc.
The small coercivity (few Oersted) and sharp ferromagnetic switching behaviour
indicate uniaxial anisotropy with an easy axis along the in-plane direction. In
addition, thickness-dependent magnetodynamics characterizations are studied via
ferromagnetic resonance. Our findings indicate the ferromagnetic
characteristics are sensitive to the quality of the oxide/non-oxide substrate
surface. These results offer significant insight into the PLD-based development
of thin metal magnetic films.",2304.00357v1
2023-11-17,Enhancement of spin to charge conversion efficiency at the topological surface state by inserting normal metal spacer layer in the topological insulator based heterostructure,"We report efficient spin to charge conversion (SCC) in the topological
insulator (TI) based heterostructure ($BiSbTe_{1.5}Se_{1.5}/Cu/Ni_{80}Fe_{20}$)
by using spin-pumping technique where $BiSbTe_{1.5}Se_{1.5}$ is the TI and
$Ni_{80}Fe_{20}$ is the ferromagnetic layer. The SCC, characterized by inverse
Edelstein effect length ($\lambda_{IEE}$) in the TI material gets altered with
an intervening Copper (Cu) layer and it depends on the interlayer thickness.
The introduction of Cu layer at the interface of TI and ferromagnetic metal
(FM) provides a new degree of freedom for tuning the SCC efficiency of the
topological surface states. The significant enhancement of the measured
spin-pumping voltage and the linewidth of ferromagnetic resonance (FMR)
absorption spectra due to the insertion of Cu layer at the interface indicates
a reduction in spin memory loss at the interface that resulted from the
presence of exchange coupling between the surface states of TI and the local
moments of ferromagnetic metal. The temperature dependence (from 8K to 300K) of
the evaluated $\lambda_{IEE}$ data for all the trilayer systems, TI/Cu/FM with
different Cu thickness confirms the effect of exchange coupling between the TI
and FM layer on the spin to charge conversion efficiency of the topological
surface state.",2311.10460v1
2024-02-06,Ultrafast terahertz field control of the emergent magnetic and electronic interactions at oxide interfaces,"Ultrafast electric-field control of emergent electronic and magnetic states
at oxide interfaces offers exciting prospects for the development of new
generations of energy-efficient devices. Here, we demonstrate that the
electronic structure and emergent ferromagnetic interfacial state in epitaxial
LaNiO3/CaMnO3 superlattices can be effectively controlled using intense
single-cycle THz electric-field pulses. We employ a combination of
polarization-dependent X-ray absorption spectroscopy with magnetic circular
dichroism and X-ray resonant magnetic reflectivity to measure a detailed
magneto-optical profile and thickness of the ferromagnetic interfacial layer.
Then, we use time-resolved and temperature-dependent magneto-optical Kerr
effect, along with transient optical reflectivity and transmissivity
measurements, to disentangle multiple correlated electronic and magnetic
processes driven by ultrafast high-field (~1 MV/cm) THz pulses. These processes
include an initial sub-picosecond electronic response, consistent with
non-equilibrium Joule heating; a rapid (~270 fs) demagnetization of the
ferromagnetic interfacial layer, driven by THz-field-induced nonequilibrium
spin-polarized currents; and subsequent multi-picosecond dynamics, possibly
indicative of a change in the magnetic state of the superlattice due to the
transfer of spin angular momentum to the lattice. Our findings shed light on
the intricate interplay of electronic and magnetic phenomena in this strongly
correlated material system, suggesting a promising avenue for efficient control
of two-dimensional ferromagnetic states at oxide interfaces using ultrafast
electric-field pulses.",2402.04302v1
2024-03-05,Unraveling spin texture and spin-orbit coupling contributions in spin triplet superconductivity,"Over the past decade, it has been proposed theoretically and confirmed
experimentally that long-range spin triplet (LRT) superconductivity can be
generated in ferromagnet-superconductor hybrids either by the presence of spin
textures (ST-LRT) or thanks to spin-orbit coupling (SOC-LRT). Nevertheless,
there has been no theoretical or experimental investigation to date suggesting
that both contributions could simultaneously exist within an experimental
system. To disentangle these contributions, we present a comprehensive study of
superconducting quasiparticle interference effects taking place inside a
ferromagnetic layer interfacing a superconductor, through the investigation of
above-gap conductance anomalies (CAs) related to MacMillan-Rowell resonances.
The bias dependence of the CAs has been studied under a wide range of in-plane
(IP) and out-of-plane (OOP) magnetic fields in two types of epitaxial,
V/MgO/Fe-based ferromagnet-superconductor junctions with interfacial spin-orbit
coupling. We observe an anisotropy of the CAs amplitude under small IP and OOP
magnetic fields while remaining weakly affected by high fields, and implement
micromagnetic simulations to help us distinguish between the ST-LRT and SOC-LRT
contributions. Our findings suggest that further exploration of Fabry-P\'erot
type interference effects in electron transport could yield valuable insights
into the hybridization between superconductors and ferromagnets induced by
spin-orbit coupling and spin textures.",2403.02819v2
2005-10-28,Electron magnetic resonance studies of nanomanganite Nd0.67Sr0.33MnO3,"Nd_0.67Sr_0.33MnO_3 nanoparticles with the grain size of about 30 nm are
prepared by sol-gel method.These nanopowders are annealed at four different
temperatures viz. 800 oC, 900 oC, 1000 oC and 1100 oC to study the effect of
particle size on magnetic, transport and electron magnetic resonance (EMR)
spectral parameters. The samples are characterized by XRD, SEM, EDAX and TEM.
The ac susceptibility experiments show that as the particle size increases the
ferromagnetic to paramagnetic transition temperature (Tc) decreases. The
metal-insulator transition temperature also changes with the particle size as
revealed by resistivity measurements. EMR spectra of the nanopowders are
recorded from room temperature down to 4K using an X-band EPR spectrometer. the
spectra could be fitted using two broad-Gaussian lineshapes below Tc and
suggested the ferromagnetic nature of the samples. Above Tc a single Lorenzian
fits the signals as expetced for paramagnetic samples. The EMR spectral
parameters are found to be different from the bulk (polycrystalline)sample
data. The spectral parameters show variation with the particle size. The
presence of the two signals in the ferromagnetic phase is attributed to core
and shell regions in the nanoparticles. We could estimate the shell thickness
from the EMR intensity data as 0.7 - 1 nm which agrees with other measurements.",0510780v1
2005-12-15,Ferromagnetic Resonance Linewidths in Ultrathin Structures: Theoretical Studies of Spin Pumping,"We present theoretical studies of the spin pumping contribution to the
ferromagnetic resonance linewidth for various ultrathin film ferromagnetic
structures. We consider the isolated film on a substrate, with Fe on Au(100)
and Fe on W(110) as examples. We explore as well the linewidth from this
mechanism for the optical and acoustical collective modes of FM/Cu$_{\rm
N}$/FM/Cu(100) structures. The calculations employ a realistic electronic
structure, with self consistent ground states generated from the empirical
tight binding method, with nine bands for each material in the structure. The
spin excitations are generated through use of the random phase approximation
applied to the system, including the semi infinite substrate on which the
structure is grown. We calculate the frequency response of the system directly
by examining the spectral density associated with collective modes whose wave
vector parallel to the surface is zero. Linewidths with origin in leakage of
spin angular momentum from the adsorbed structure to the semi infinite
substrate may be extracted from these results. We discuss a number of issues,
including the relationship between the interfilm coupling calculated
adiabatically for trilayers, and that extracted from the (dynamical) spin wave
spectrum. We obtain excellent agreement with experimental data, within the
framework of calculations with no adjustable parameters.",0512333v1
2006-05-15,Magnetic reconfiguration of MnAs/GaAs(001) observed by Magnetic Force Microscopy and Resonant Soft X-ray Scattering,"We investigated the thermal evolution of the magnetic properties of MnAs
epitaxial films grown on GaAs(001) during the coexistence of
hexagonal/orthorhombic phases using polarized resonant (magnetic) soft X-ray
scattering and magnetic force microscopy. The results of the diffuse satellite
X-ray peaks were compared to those obtained by magnetic force microscopy and
suggest a reorientation of ferromagnetic terraces as temperature rises. By
measuring hysteresis loops at these peaks we show that this reorientation is
common to all ferromagnetic terraces. The reorientation is explained by a
simple model based on the shape anisotropy energy. Demagnetizing factors were
calculated for different configurations suggested by the magnetic images. We
noted that the magnetic moments flip from an in-plane mono-domain orientation
at lower temperatures to a three-domain out-of-plane configuration at higher
temperatures. The transition was observed when the ferromagnetic stripe width L
is equal to 2.9 times the film thickness d. This is in good agreement with the
expected theoretical value of L = 2.6d.",0605356v1
2008-05-15,Thickness dependent magnetic anisotropy of ultrathin LCMO epitaxial thin films,"The magnetic properties of La0.7Ca0.3MnO3 (LCMO) manganite thin films were
studied with magnetometry and ferromagnetic resonance as a function of film
thickness. They maintain the colossal magnetoresistance behavior with a
pronounced metal-insulator transition around 150-200 K, except for the very
thinnest films studied (3 nm). Nevertheless, LCMO films as thin as 3 nm remain
ferromagnetic, without a decrease in saturation magnetization, indicating an
absence of dead-layers, although below approx. 6 nm the films remain insulating
at low temperature. Magnetization hysteresis loops reveal that the magnetic
easy axes lie in the plane of the film for thicknesses in the range of 4-15 nm.
Ferromagnetic resonance studies confirm that the easy axes are in-plane, and
find a biaxial symmetry in-plane with two, perpendicular easy axes. The
directions of the easy axes with respect to the crystallographic directions of
the cubic SrTiO3 substrate differ by 45 degrees in 4 nm and 15 nm thick LCMO
films.",0805.2336v1
2014-12-01,Experimental and Numerical Understanding of Localized Spin Wave Mode Behavior in Broadly Tunable Spatially Complex Magnetic Configurations,"Spin wave modes confined in a ferromagnetic film by the spatially
inhomogeneous magnetic field generated by a scanned micromagnetic tip of a
ferromagnetic resonance force microscope (FMRFM) enable microscopic imaging of
the internal fields and spin dynamics in nanoscale magnetic devices. Here we
report a detailed study of spin wave modes in a thin ferromagnetic film
localized by magnetic field configurations frequently encountered in FMRFM
experiments, including geometries in which the probe magnetic moment is both
parallel and antiparallel to the applied uniform magnetic field. We demonstrate
that characteristics of the localized modes, such as resonance field and
confinement radius, can be broadly tuned by controlling the orientation of the
applied field relative to the film plane. Micromagnetic simulations accurately
reproduce our FMRFM spectra allowing quantitative understanding of the
localized modes. Our results reveal a general method of generating tightly
confined spin wave modes in various geometries with excellent spatial
resolution that significantly facilitates the broad application of FMRFM. This
paves the way to imaging of magnetic properties and spin wave dynamics in a
variety of contexts for uncovering new physics of nanoscale spin excitations.",1412.0726v1
2015-03-24,Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure,"Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key
factors for the free layer magnetization switching by spin transfer torque
technique in magnetic tunnel junction devices. The magnetization precessional
dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure
was explored in broad band frequency range by employing micro-strip
ferromagnetic resonance technique. The polar angular variation of resonance
field and linewidth at different frequencies have been analyzed numerically
using Landau-Lifshitz-Gilbert equation by taking into account the total free
energy density of the film. The numerically estimated parameters Land\'{e}
$g$-factor, PMA constant, and effective magnetization are found to be 2.1,
2$\times10^{5}$ erg/cm$^{3}$ and 7145 Oe, respectively. The frequency
dependence of Gilbert damping parameter ($\alpha$) is evaluated by considering
both intrinsic and extrinsic effects into the total linewidth analysis. The
value of $\alpha$ is found to be 0.006 at 10 GHz and it increases with
decreasing precessional frequency.",1503.07043v5
2016-01-14,Sensitivity Enhancement of Pd/Co Bi-layer Film for Hydrogen Gas Sensing using Perpendicular-to-Plane Ferromagnetic Resonance Configuration,"Previously, it has been shown that the strength of the perpendicular magnetic
anisotropy (PMA) of thin Palladium-Cobalt bi-layer films can be modified when
hydrogen gas is absorbed by the Palladium (Pd) layer. In our recent work we
showed that the ferromagnetic resonance (FMR) response of this material is
sensitive to changes in PMA upon exposure of Pd to hydrogen gas. As such, a
simple, compact and contactless hydrogen gas sensor could exploit FMR-based
detection, of the reversible hydrogen-gas-induced changes in PMA. The magnitude
of the FMR peak shift is critical in determining the sensor's sensitivity: the
higher the FMR peak shift at a given hydrogen gas concentration, the higher the
sensitivity. In the present work we demonstrate that the detection sensitivity
is enhanced when the static magnetic field is applied perpendicular to the film
plane. A factor of eight times improvement is observed with respect to the
in-plane FMR configuration studied previously. An analysis based on the Kittel
equation for FMR frequencies of a ferromagnetic film is carried out in order to
understand the mechanism of sensitivity enhancement. The result is important
for optimizing Pd/Co bi-layered thin films for use in novel platforms for
hydrogen gas sensing.",1601.03500v1
2016-02-24,Eddy-current effects on ferromagnetic resonance: Spin wave excitations and microwave screening effects,"We investigate how controlling induced eddy currents in thin film
ferromagnet-normal metal (FM/NM) structures can be used to tailor the local
microwave (MW) fields in ferromagnetic resonance (FMR) experiments. The MW
fields produced by eddy currents will in general have a relative phase shift
with respect to the applied MW field which depends on the sample geometry. The
induced fields can thus partially compensate the applied MW field, effectively
screening the FM in selected parts of the sample. The highly localized fields
produced by eddy currents enable the excitation of spin wave modes with
non-zero wave vectors, in contrast to the uniform k = 0 mode normally excited
in FMR experiments. We find that the orientation of the applied MW field is one
of the key parameters controlling the eddy-current effects. The induced
currents are maximized when the applied MW field is oriented perpendicular to
the sample plane. Increasing the magnitude of the eddy currents results in a
stronger induced MW field, enabling a more effective screening of the applied
MW field as well as an enhanced excitation of spin wave modes. This
investigation underlines that eddy currents can be used to control the
magnitude and phase of the local MW fields in thin film structures.",1602.07463v2
2018-11-02,Anatomy of electrical signals and dc-voltage lineshape in spin torque ferromagnetic resonance,"The electrical detection of spin torque ferromagnetic resonance (st-FMR) is
becoming a popular method for measuring the spin-Hall angle of heavy metals
(HM). However, various sensible analysis on the same material with either the
same or different experimental setups yielded different spin-Hall angles with
large discrepancy, indicating some missing ingredients in our current
understanding of st-FMR. Here we carry out a careful analysis of electrical
signals of the st-FMR in a HM/ferromagnet (HM/FM) bilayer with an arbitrary
magnetic anisotropy. The FM magnetization is driven by two radio-frequency (rf)
forces: the rf Oersted field generated by an applied rf electric current and
the so called rf spin-orbit torque from the spin current flowing
perpendicularly from the HM to the FM due to the spin-Hall effect. By using the
universal form of the dynamic susceptibility matrix of magnetic materials at
the st-FMR, the electrical signals originated from the anisotropic
magnetoresistance, anomalous Hall effect and inverse spin-Hall effect are
analysed and dc-voltage lineshape near the st-FMR are obtained.
Angle-dependence of dc-voltage is given for two setups. A way of experimentally
extracting the spin-Hall angle of a HM is proposed.",1811.00810v1
2014-05-19,"Comparison of micromagnetic parameters of ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As","We report on the determination of micromagnetic parameters of epilayers of
the ferromagnetic semiconductor (Ga,Mn)As, which has easy axis in the sample
plane, and (Ga,Mn)(As,P) which has easy axis perpendicular to the sample plane.
We use an optical analog of ferromagnetic resonance where the
laser-pulse-induced precession of magnetization is measured directly in the
time domain. By the analysis of a single set of pump-and-probe magneto-optical
data we determined the magnetic anisotropy fields, the spin stiffness and the
Gilbert damping constant in these two materials. We show that incorporation of
10% of phosphorus in (Ga,Mn)As with 6% of manganese leads not only to the
expected sign change of the perpendicular to plane anisotropy field but also to
an increase of the Gilbert damping and to a reduction of the spin stiffness.
The observed changes in the micromagnetic parameters upon incorporating P in
(Ga,Mn)As are consistent with the reduced hole density, conductivity, and Curie
temperature of the (Ga,Mn)(As,P) material. We report that the magnetization
precession damping is stronger for the n = 1 spin wave resonance mode than for
the n = 0 uniform magnetization precession mode.",1405.4677v1
2018-10-18,Ferromagnetic spin fluctuations in the filled skutterudite SrFe4As12 revealed by 75As NMR-NQR measurements,"$^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance
(NQR) measurements have been carried out to investigate the magnetic and
electronic properties of the filled skutterudite metallic compound
SrFe$_4$As$_{12}$. The temperature dependence of Knight shift $K$ determined by
the NQR spectrum under a small magnetic field ($\le$ 0.5 T) shows the similar
temperature dependence of the magnetic susceptibility $\chi$ which exhibits a
broad maximum at $T^\ast$ $\sim$ 50 K. The nuclear spin-lattice relaxation rate
divided by temperature, 1/$T_1T$, increases with decreasing temperature and
exhibits a broad maximum at $T$ $\sim$ 70 K, similar to the case of $\chi$. The
temperature dependence of $K$ and $1/T_1T$ is reasonably explained by a simple
model where we assume a concave-shaped band structure near the Fermi energy.
Based on a Korringa ratio analysis using the $T_1$ and $K$ data, ferromagnetic
spin fluctuations are found to exist in SrFe$_4$As$_{12}$. These results
indicate that SrFe$_4$As$_{12}$ can be characterized to be a metal with
ferromagnetic correlations and also the peculiar band structure responsible for
the suppression of $1/T_1T$ and $K$ at low temperatures.",1810.08302v1
2018-03-26,Domain-wall-assisted giant magnetoimpedance of thin-wall ferromagnetic nanotubes,"We study the effciency of the magnetoimpedance (MI) of thin-wall
circumferentially ordered nanotubes in sub-GHz and GHz frequency regimes using
micromagnetic simulations. We consider empty ferromagnetic tubes as well as
tubes filled with non-magnetic conductors of circular cross-section (nanowire
coverings) focusing on the low-field regime of MI (below the characteristic
field of the low-frequency ferromagnetic resonance). In this field area, the
effcient mechanism of MI is related to oscillations of the positions of
(perpendicular to the tube axis) domain walls (DWs). Two mechanisms of driving
the DW motion by the ac current are taken into account; the driving via the
Oersted field and via the spintransfer torque. The simulations are performed
for Co nanotubes of the diameter of 300nm. Achievable low-field MI exceeds
100%, while the field region of a high sensitivity of that DW-based giant MI is
of the width of tens of kA/m. The later is widely adjustable with changing the
density of the driving ac current, its frequency, and the nanotube length. Of
particular interest is the resonant motion of DW due to the interaction with
the nanotube ends the conditions of whom are discussed.",1803.09512v2
2019-02-18,Stacking order-dependent sign-change of microwave phase due to eddy currents in nanometer-scale NiFe/Cu heterostructures,"In the field of spintronics, ferromagnetic/non-magnetic metallic multilayers
are core building blocks for emerging technologies. Resonance experiments using
stripline transducers are commonly used to characterize and engineer these
stacks for applications. Up to now in these experiments, the influence of eddy
currents on the excitation of the dynamics of ferromagnetic magnetization below
the skin-depth limit was most often neglected. Here, using a coplanar stripline
transducer, we experimentally investigated the broadband ferromagnetic
resonance response of NiFe/Cu bilayers a few nanometers thick in the
sub-skin-depth regime. Asymmetry in the absorption spectrum gradually built up
as the excitation frequency and Cu-layer thickness increased. Most
significantly, the sign of the asymmetry depended on the stacking order.
Experimental data were consistent with a quantitative analysis considering eddy
currents generated in the Cu layers and the subsequent phaseshift of the
feedback magnetic field generated by the eddy currents. These results extend
our understanding of the impact of eddy currents below the microwave magnetic
skin-depth and explain the lineshape asymmetry and phase lags reported in
stripline experiments.",1902.06501v3
2019-08-20,Suppression of ferromagnetic spin fluctuations in the filled skutterudite superconductor SrOs4As12 revealed by 75As NMR-NQR measurements,"Motivated by the recent observation of ferromagnetic spin correlations in the
filled skutterudite SrFe$_4$As$_{12}$ [Ding et al., Phys. Rev. B 98, 155149
(2018)], we have carried out $^{75}$As nuclear magnetic resonance (NMR) and
nuclear quadrupole resonance (NQR) measurements to investigate the role of
magnetic fluctuations in a newly discovered isostructural superconductor
SrOs$_4$As$_{12}$ with a superconducting transition temperature of $T_{\rm c}$
$\sim$ 4.8 K. Knight shift $K$ determined by the NQR spectrum under a small
magnetic field ($\le$ 0.5 T) is nearly independent of temperature, consistent
with the temperature dependence of the magnetic susceptibility. The nuclear
spin-lattice relaxation rate divided by temperature, 1/$T_1T$, is nearly
independent of temperature above $\sim$ 50 K and increases slightly with
decreasing temperature below the temperature. The temperature dependence is
reasonably explained by a simple model where a flat band structure with a small
ledge near the Fermi energy is assumed. By comparing the present NMR data with
those in SrFe$_4$As$_{12}$, we found that the values of $|K|$ and $1/T_1T$ in
SrOs$_4$As$_{12}$ are smaller than those in SrFe$_4$As$_{12}$, indicating no
obvious ferromagnetic spin correlations in SrOs$_4$As$_{12}$. From the
temperature dependence of 1/$T_1$ in the superconducting state, an $s$-wave
superconductivity is realized.",1908.07923v1
2020-08-30,From Ising model to Kitaev Chain -- An introduction to topological phase transitions,"In this general article, we map the one-dimensional transverse field quantum
Ising model of ferromagnetism to Kitaev's one-dimensional p-wave
superconductor, which has its application in fault-tolerant topological quantum
computing. Mapping Pauli's spin operators of transverse Ising chain to spinless
fermionic creation and annihilation operators by Inverse Jordan-Wigner
transformation leads to a Hamiltonian form closely related to Kitaev Chain,
which exhibits topological phase transition where phases are characterized by
different topological invariant that changes discontinuously at the transition
point. Kitaev Chain supports two Majorana zero modes (MZMs) in the non-trivial
topological phase, while none is in the trivial phase. The doubly degenerate
ground state of the transverse Ising in ferromagnetic phase corresponds to
non-local free fermion degree made from MZMs. The quasi-particle excitations of
Ising chain, viz., domain wall formation in the ferromagnetic phase and
spin-flip in paramagnetic phase maps to Bogoliubon excitations. The mapping
suggests that a non-local order parameter can be defined for Kitaev Chain to
work with the usual paradigm of Landau's theory.",2009.01078v6
2002-05-29,Stochastic resonance in the driven Ising model on small-world networks,"We investigate the stochastic resonance phenomena in the field-driven Ising
model on small-world networks. The response of the magnetization to an
oscillating magnetic field is examined by means of Monte Carlo dynamic
simulations, with the rewiring probability varied. At any finite value of the
rewiring probability, the system is found to undergo a dynamic phase transition
at a finite temperature, giving rise to double resonance peaks. While the peak
in the ferromagnetic phase grows with the rewiring probability, that in the
paramagnetic phase tends to reduce, indicating opposite effects of the
long-range interactions on the resonance in the two phases.",0205608v1
2008-11-13,Template nanowires for spintronics applications: nanomagnet microwave resonators functioning in zero applied magnetic field,"Low-cost spintronic devices functioning in zero applied magnetic field are
required for bringing the idea of spin-based electronics into the real-world
industrial applications. Here we present first microwave measurements performed
on nanomagnet devices fabricated by electrodeposition inside porous membranes.
In the paper, we discuss in details a microwave resonator consisting of three
nanomagnets, which functions in zero external magnetic field. By applying a
microwave signal at a particular frequency, the magnetization of the middle
nanomagnet experiences the ferromagnetic resonance (FMR), and the device
outputs a measurable direct current (spin-torque diode effect). Alternatively,
the nanodevice can be used as a microwave oscillator functioning in zero field.
In order to test the resonators at microwave frequencies, we developed a simple
measurement set-up.",0811.2241v1
2011-01-12,Unequal Layer Densities in Bilayer Wigner Crystal at High Magnetic Field,"We report studies of pinning mode resonances of magnetic field induced
bilayer Wigner crystals of bilayer hole samples with negligible interlayer
tunneling and different interlayer separations d, in states with varying layer
densities, including unequal layer densities. With unequal layer densities,
samples with large d relative to the in-plane carrier-carrier spacing a, two
pinning resonances are present, one for each layer. For small d/a samples, a
single resonance is observed even with significant density imbalance. These
samples, at balance, were shown to exhibit an enhanced pinning mode frequency
[Zhihai Wang et al., Phys. Rev. Lett. 136804 (2007)], which was ascribed to a
one-component, pseudospin ferromagnetic Wigner solid. The evolution of the
resonance frequency and line width indicates the quantum interlayer coherence
survives at moderate density imbalance, but disappears when imbalance is
sufficiently large.",1101.2436v1
2014-02-27,Sensitive Magnetic Force Detection with a Carbon Nanotube Resonator,"We propose a technique for sensitive magnetic point force detection using a
suspended carbon nanotube (CNT) mechanical resonator combined with a magnetic
field gradient generated by a ferromagnetic gate electrode. Numerical
calculations of the mechanical resonance frequency show that single Bohr
magneton changes in the magnetic state of an individual magnetic molecule
grafted to the CNT can translate to detectable frequency shifts, on the order
of a few kHz. The dependences of the resonator response to device parameters
such as length, tension, CNT diameter, and gate voltage are explored and
optimal operating conditions are identified. A signal-to-noise analysis shows
that in principle, magnetic switching at the level of a single Bohr magneton
can be read out in a single shot on timescales as short as 10 microseconds.
This force sensor should enable new studies of spin dynamics in isolated single
molecule magnets, free from the crystalline or ensemble settings typically
studied.",1402.6780v1
2014-04-02,Ground-state cooling of a carbon nanomechanical resonator by spin-polarized current,"We study the nonequilibrium steady state of a mechanical resonator in the
quantum regime realized by a suspended carbon nanotube quantum dot contacted by
two ferromagnets. Because of the spin-orbit interaction and/or an external
magnetic field gradient, the spin on the dot couples directly to the flexural
eigenmodes. Accordingly, the nanomechanical motion induces inelastic spin flips
of the tunneling electrons. A spin-polarized current at finite bias voltage
causes either heating or active cooling of the mechanical modes. We show that
maximal cooling is achieved at resonant transport when the energy splitting
between two dot levels of opposite spin equals the vibrational frequency. Even
for weak electron-resonator coupling and moderate polarizations we can achieve
ground-state cooling with a temperature of the leads, for instance, of
$T=10\omega$.",1404.0485v3
2014-11-22,Quantification of the spin-Hall anti-damping torque with a resonance spectrometer,"We present a simple technique using a cavity-based resonance spectrometer to
quantify the anti-damping torque due to the spin Hall effect. Modification of
ferromagnetic resonance is observed as a function of small DC current in
sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and
strong spin-Hall metal Ta. From the detected current-induced linewidth change,
we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic
layer thickness. Our results demonstrate that a sensitive resonance
spectrometer can be a general tool to investigate spin Hall effects in various
material systems, even those with vanishingly low conductivity and
magnetoresistance.",1411.6166v1
2016-07-08,Control of magnon-photon coupling strength in a planar resonator/YIG thin film configuration,"A systematic study of the coupling at room temperature between ferromagnetic
resonance (FMR) and a planar resonator is presented. The chosen magnetic
material is a ferrimagnetic insulator (Yttrium Iron Garnet: YIG) which is
positioned on top of a stop band (notch) filter based on a stub line
capacitively coupled to a 50 $\Omega$ microstrip line resonating at 4.731 GHz.
Control of the magnon-photon coupling strength is discussed in terms of the
microwave excitation configuration and the YIG thickness from 0.2 to 41 $\mu$m.
From the latter dependence, we extract a single spin-photon coupling of
g$_{0}$/2$\pi$=162$\pm$6 mHz and a maximum of an effective coupling of 290 MHz.",1607.02358v3
2018-11-11,Reconstruction of the DOS at the end of a S/F bilayer,"Influence of a nonmagnetic surface on the density of states in a spin-split
superconductor, which is realized on the basis of a S/F bilayer, is
investigated. It is demonstrated that if the ferromagnet magnetization has a
defect in the form of a domain wall in the vicinity of the surface, the
superconducting density of states is reconstructed manifesting the spin-split
Andreev resonances. Formation of these resonances is not connected to any
superconducting order parameter inhomogeneities. Andreev reflection processes
forming the resonances occur at the inhomogeneity of the spin-split gap
generated by the domain wall. These resonances can be used as a spectroscopic
probe of a domain wall presence and motion.",1811.04373v2
2013-09-11,Fano resonances of microwave structures with embedded magneto-dipolar quantum dots,"Long range dipole-dipole correlation in a ferromagnetic sample can be treated
in terms of collective excitations of the system as a whole. Ferrite samples
with linear dimensions smaller than the dephasing length, but still much larger
than the exchange-interaction scales are mesoscopic structures. Recently, it
was shown that mesoscopic quasi-2D ferrite disks, distinguishing by
multiresonance magneto-dipolar-mode (MDM) spectra, demonstrate unique
properties of artificial atomic structures: energy eigenstates, eigen
power-flow vortices and eigen helicity parameters. Because of these properties,
MDMs in a ferrite disk enable the confinement of microwave radiation to
subwavelength scales. In microwave structures with embedded MDM ferrite
samples, one can observe quantized fields with topologically distinctive
characteristics. The use of a quasi-2D ferrite-disk scatterer with internal MDM
resonance spectra along the channel propagation direction could change the
transmission dramatically. In this paper, we show that interaction of the MDM
ferrite particle with its environment has a deep analogy with the
Fano-resonance interference observed in natural and artificial atomic
structures. We characterize the observed effect as Fano-resonance interference
in MDM quantum dots.",1309.2792v1
2018-09-29,Transport Spectroscopy of Sublattice-Resolved Resonant Scattering in Hydrogen-Doped Bilayer Graphene,"We report the experimental observation of sublattice-resolved resonant
scattering in bilayer graphene by performing simultaneous cryogenic atomic
hydrogen doping and electron transport measurements in ultrahigh vacuum. This
allows us to monitor the hydrogen adsorption on the different sublattices of
bilayer graphene without atomic-scale microscopy. Specifically, we detect two
distinct resonant scattering peaks in the gate-dependent resistance, which
evolve as a function of atomic hydrogen dosage. Theoretical calculations show
that one of the peaks originates from resonant scattering by hydrogen adatoms
on the {\alpha}-sublattice (dimer site) while the other originates from
hydrogen adatoms on the \b{eta}-sublattice (non-dimer site), thereby enabling a
method for characterizing the relative sublattice occupancy via transport
measurements. Utilizing this new capability, we investigate the adsorption and
thermal desorption of hydrogen adatoms via controlled annealing and conclude
that hydrogen adsorption on the \b{eta}-sublattice is energetically favored.
Through site-selective desorption from the {\alpha}-sublattice, we realize
hydrogen doping with adatoms primarily on a single sublattice, which is highly
desired for generating ferromagnetism.",1810.00259v1
2018-10-27,Microwave control of thermal magnon spin transport,"We observe that an rf microwave field strongly influences the transport of
incoherent thermal magnons in yttrium iron garnet. Ferromagnetic resonance in
the nonlinear regime suppresses thermal magnon transport by 95%. The transport
is also modulated at non-resonant conditions in two cases, both related to the
magnon band minimum. Firstly, a strong enhancement of the nonlocal signal
appears at a static magnetic field below the resonance condition. This increase
only occurs at one field polarity and can be as large as 800%. We attribute
this effect to magnon kinetic processes, which give rise to band-minimum
magnons and high-energy chiral surface modes. Secondly, the signal increases at
a static field above the resonance condition, where the rf frequency coincides
with the magnon band minimum. Our study gives insight into the interplay
between coherent and incoherent spin dynamics: The rf field modifies the
occupation of relevant magnon states and, via kinetic processes, the magnon
spin transport.",1810.11667v1
2019-07-09,Magnetic dipole ordering in resonant dielectric metasurfaces,"Artificial magnetism at optical frequencies can be realized in metamaterials
composed of periodic arrays of subwavelength elements, also called
""meta-atoms"". Optically-induced magnetic moments can be arranged in both
unstaggered structures, naturally associated with ferromagnetic (FM) order, or
staggered structures, linked correspondingly to antiferromagnetic (AFM) order.
Here we demonstrate that such magnetic dipole orders of the lattices of
meta-atoms can appear in low-symmetry Mie-resonant metasurfaces where each
asymmetric dielectric (non-magnetic) meta-atom supports a localized trapped
mode. We reveal that these all-dielectric resonant metasurfaces possess not
only strong optical magnetic response but also they demonstrate a significant
polarization rotation of the propagating electromagnetic waves at both FM and
AFM resonances. We confirm these findings experimentally by measuring directly
the spectral characteristics of different modes excited in all-dielectric
metasurfaces, and mapping near-field patterns of the electromagnetic fields at
the microwave frequencies.",1907.04187v2
2019-07-10,Temperature dependence of magnetic resonance in ferrimagnetic GdFeCo alloys,"We provide a macroscopic theory and experimental results for magnetic
resonances of antiferromagnetically-coupled ferrimagnets. Our theory, which
interpolates the dynamics of antiferromagnets and ferromagnets smoothly, can
describe ferrimagnetic resonances across the angular momentum compensation
point. We also present experimental results for spin-torque induced
ferrimagnetic resonance at several temperatures. The spectral analysis based on
our theory reveals that the Gilbert damping parameter, which has been
considered to be strongly temperature dependent, is insensitive to temperature.
We envision that our work will facilitate further investigation of
ferrimagnetic dynamics by providing a theoretical framework suitable for a
broad range of temperatures.",1907.04540v1
2020-02-03,Thermal relaxation of magnons and phonons near resonance points in magnetic insulators,"We theoretically investigate the energy relaxation rate of magnons and
phonons near the resonance points to clarify the underlying mechanism of heat
transport in ferromagnetic materials. We find that the simple two-temperature
model is valid for the one-phonon/one-magnon process, as the rate of energy
exchange between magnons and phonons is proportional to the temperature
difference between them, and it is independent of temperature in the high
temperature limit. We found that the magnon-phonon relaxation time due to the
one-phonon/one-magnon interaction could be reduced to 1.48 $\mu s$ at the
resonance point by applying an external magnetic field. It means that the
resonance effect plays a significant role in enhancing the total magnon-phonon
energy exchange rate, apart from the higher order interaction processes.",2002.00547v1
2021-01-08,Compact tunable YIG-based RF resonators,"We report on the design, fabrication, and characterization of compact tunable
yttrium iron garnet (YIG) based RF resonators based on $\mu$m-sized spin-wave
cavities. Inductive antennas with both ladder and meander configurations were
used as transducers between spin waves and RF signals. The excitation of
ferromagnetic resonance and standing spin waves in the YIG cavities led to
sharp resonances with quality factors up to 350. The observed spectra were in
excellent agreement with a model based on the spin-wave dispersion relations in
YIG, showing a high magnetic field tunability of about 29 MHz/mT.",2101.02909v4
2012-05-10,Dipolar broadening of nuclear spin resonance under dynamical pumping,"We study the polarisation dependence of the homogeneously broadened nuclear
spin resonance in a crystal. We employ a combinatorial method to restrict the
nuclear states to a fixed polarisation and show that the centre of the
resonance is shifted linearly with the nuclear polarisation by up to the zero
polarisation line width. The width shrinks from its maximum value at zero
polarisation to zero at full polarisation. This suggests to use the line shape
as a direct measure of nuclear polarisation reached under dynamical pumping. In
the limit of single quantum of excitation above the fully ferromagnetic state,
we provide an explicit solution to the problem of nuclear spin dynamics which
links a bound on the fastest decay rate to the observable width of the
resonance line.",1205.2189v1
2018-03-05,Theory of magnetoelastic resonance in a mono-axial chiral helimagnet,"We study magnetoelastic resonance phenomena in a mono-axial chiral helimagnet
belonging to hexagonal crystal class. By computing the spectrum of coupled
elastic wave and spin wave, it is demonstrated how hybridization occurs
depending on their chirality. Specific features of the magnetoelastic resonance
are discussed for the conical phase and the soliton lattice phase stabilized in
the mono-axial chiral helimagnet. The former phase exhibits appreciable
non-reciprocity of the spectrum, the latter is characterized by a
multi-resonance behavior. We propose that the non-reciprocal spin wave around
the forced-ferromagnetic state has potential capability to convert the linearly
polarized elastic wave to circularly polarized one with the chirality opposite
to the spin wave chirality.",1803.01691v2
2020-08-26,Direct Imaging of Resonant Phonon-Magnon Coupling,"Direct detection of phonons is important for the investigation of information
interconversion between the resonantly coupled magnons and phonons. Here we
report resonant coupling of magnons and phonons, which can be directly
visualized by using micro focused Brillouin light scattering in Ni/LiNbO3
hybrid heterostructures. The patterns of surface acoustic wave phonons,
originating from the interference between the original wave {\psi}0(A_0,k) and
reflected wave {\psi}1(A_1,-k), can be modulated by magnetic field due to the
magnon-phonon coupling. By analyzing the information of phonons obtained from
Brillouin spectroscopy, the properties of the magnon system (Ni film), e.g.,
ferromagnetic resonance field and resonance linewidth can be determined. The
results provide spatially resolved information about phonon manipulation and
detection in a coupled magnon-phonon system.",2008.11391v2
2020-09-14,Ground state cooling of magnomechanical resonator in PT-symmetric cavity magnomechanical system at room temperature,"We propose to realize the ground state cooling of magnomechanical resonator
in a parity-time (PT)-symmetric cavity magnomechanical system composed of a
loss ferromagnetic sphere and a gain microwave cavity. In the scheme, the
magnomechanical resonator can be cooled close to its ground state via the
magnomechanical interaction, and it is found that the cooling effect in
PT-symmetric system is much higher than that in non-PT-symmetric system.
Resorting to the magnetic force noise spectrum, we investigate the final mean
phonon number with experimentally feasible parameters and find surprisingly
that the ground state cooling of magnomechanical resonator can be directly
achieved at room temperature. Furthermore, we also illustrate that the ground
state cooling can be flexibly controlled via the external magnetic field.",2009.06293v1
2022-04-01,Magnetic resonances in EuSn$_2$As$_2$ single crystal,"In this work, we report the broad-band ferromagnetic resonance spectroscopy
of EuSn$_2$As$_2$ single crystals at different temperatures in combination with
magnetization measurements and structural characterization. We observe
conventional collective acoustic resonance mode of the A-type antiferromagnetic
spin-flop phase in the Eu sub-lattice, and its transition to the paramagnetic
resonance above the ordering temperature. Furthermore, we observe reproducibly
additional well-defined spectral line. The origin of the additional line
remains unclear. However, its temperature dependence attributes it to magnetism
in the Eu sub-lattice.",2204.00389v1
2022-12-15,Resonant and off-resonant magnetoacoustic waves in epitaxial Fe$_3$Si/GaAs hybrid structures,"Surface acoustic waves (SAWs) provide an efficient dynamical coupling between
strain and magnetization in micro/nano-metric devices. Using a hybrid device
composed of a piezoelectric, GaAs, and a ferromagnetic Heusler alloy thin film,
Fe$_3$Si, we are able to quantify the amplitude of magnetoacoustic waves
generated with SAWs via magnetic imaging in an X-ray photoelectron microscope.
The cubic anisotropy of the sample together with a low damping coefficient
allows for the observation of resonant and non-resonant magnetoelastic
coupling. Additionally, via micromagnetic simulation, we verify the
experimental behavior and quantify the magnetoelastic shear strain component in
Fe$_3$Si that appears to be very large ($b_2=14\times 10^6$ J/m$^3$), much
larger than the one found in Nickel.",2212.07994v1
2023-06-07,Gain assisted controllable fast light generation in cavity magnomechanics,"We study the controllable output field generation from a cavity
magnomechanical resonator system that consists of two coupled microwave
resonators. The first cavity interacts with a ferromagnetic yttrium iron garnet
(YIG) sphere providing the magnon-photon coupling. Under passive cavities
configuration, the system displays high absorption, prohibiting output
transmission even though the dispersive response is anamolous. We replace the
second passive cavity with an active one to overcome high absorption, producing
an effective gain in the system. We show that the deformation of the YIG sphere
retains the anomalous dispersion. Further, tuning the exchange interaction
strength between the two resonators leads to the system's effective gain and
dispersive response. As a result, the advancement associated with the
amplification of the probe pulse can be controlled in the close vicinity of the
magnomechanical resonance. Furthermore, we find the existence of an upper bound
for the intensity amplification and the advancement of the probe pulse that
comes from the stability condition. These findings may find potential
applications for controlling light propagation in cavity magnomechanics.",2306.04390v1
2024-02-28,Coherent control of terahertz-scale spin resonances using optical spin-orbit torques,"Using optically generated spin-orbit torques generated by the heavy metal Pt
we demonstrate coherent control of GHz ferromagnetic resonances in Pt/Co/Pt
multilayers as well as sub-THz exchange resonances in [Gd/Co]$_2$ multilayers.
Employing a double-pump setup, we show that depending on the helicities of the
pump pulses, spin resonances can either be coherently amplified or suppressed
if the time delay between the arrival of the pump beams is chosen
appropriately. Furthermore, investigating phase and amplitude of the
exchange-driven modes, we identify features that challenge the current
understanding of optically generated spin-orbit torques, and we discuss
possible explanations.",2402.18671v1
2002-08-01,Field dependent permittivity of composite materials containing ferromagnetic wires,"The effective permittivity of composites containing ferromagnetic microwires
has been analysed within a one-particle approximation, by considering a wire
piece as an independent scatterer and solving the scattering problem with the
impedance boundary condition. A new integro-differential equation for the
current distribution in a wire is obtained, which is valid for the surface
impedance matrix of a general form. In the vicinity of the antenna resonance,
the dispersion behaviour of the effective permittivity can depend strongly on a
dc external magnetic field applied to the whole composite sample, experiencing
a transformation from a resonant spectrum to a relaxation one. If the
resonance-like dispersion behaviour is realised, the real part of the effective
permittivity can be made negative past the resonance for sufficiently small
wire-inclusion concentrations (well below the percolation threshold). Applying
a dc external magnetic field, the negative peak of the real part of effective
permittivity continuously decreases as the dispersion tends to become of a
relaxation type. The magnetic field required to cause these changes in the
effective permittivity is of the order of the anisotropy field, that is, in the
range of few Oe for Co-based microwires. The field dependence of the effective
permittivity arises from a high sensitivity of the ac surface impedance of a
ferromagnetic wire to a magnetic field (known as the magneto-impedance (MI)
effect). This work demonstrates a possibility of using the MI effect to design
field-controlled composites and band-gap structures. Another range of
applications is related to tuneable waveguides where the composite material is
used as an additional field-dependent cover.",0208026v4
2020-10-29,2D correlations in the van der Waals ferromagnet CrBr$_{3}$ using high frequency electron spin resonance spectroscopy,"Broadening the knowledge and understanding on the magnetic correlations in
van der Waals layered magnets is critical in realizing their potential
next-generation applications. In this study, we employ high frequency (240 GHz)
electron spin resonance (ESR) spectroscopy on plate-like CrBr$_{3}$ to gain
insight into the magnetic interactions as a function of temperature (200 - 4 K)
and the angle of rotation ${\theta}$. We find that the temperature dependence
of the ESR linewidth is well described by the Ginzberg-Landau critical model as
well as Berezinskii-Kosterlitz-Thouless (BKT) transition model, indicative of
the presence of two-dimensional (2D) correlations. This suggests that the
three-dimensional ferromagnet CrBr$_{3}$, which has been described as an Ising
or Heisenberg ferromagnet, could present 2D magnetic correlations and BKT-like
behavior even in its bulk form; an observation that, to the best of our
knowledge, has not been reported in the literature. Furthermore, our findings
show that the resonance field follows a $(3cos^2{\theta} - 1)$-like angular
dependence, while the linewidth follows a $(3cos^2{\theta} - 1)^2$-like angular
dependence. This observed angular dependence of the resonance field and
linewidth further confirm an unanticipated 2D magnetic behavior in CrBr$_{3}$.
This behavior is likely due to the interaction of the external magnetic field
applied during the ESR experiment that allows for the mediation of long-range
vortex-like correlations between the spin clusters that may have formed due to
magnetic phase separation. This study demonstrates the significance of
employing spin sensitive techniques such as ESR to better understand the
magnetic correlations in similar van der Waals magnets.",2010.15342v1
2016-04-25,Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc,"Using finite element micromagnetic simulations, we study how resonant
magnetisation dynamics in thin magnetic discs with perpendicular anisotropy are
influenced by magnetostatic coupling to a magnetic nanoparticle. We identify
resonant modes within the disc using direct magnetic eigenmode calculations and
study how their frequencies and profiles are changed by the nanoparticle's
stray magnetic field. We demonstrate that particles can generate shifts in the
resonant frequency of the disc's fundamental mode which exceed resonance
linewidths in recently studied spin torque oscillator devices. Importantly, it
is shown that the simulated shifts can be maintained over large field ranges
(here up to 1T). This is because the resonant dynamics (the basis of
nanoparticle detection here) respond directly to the nanoparticle stray field,
i.e. detection does not rely on nanoparticle-induced changes to the magnetic
ground state of the disk. A consequence of this is that in the case of small
disc-particle separations, sensitivities to the particle are highly mode- and
particle-position-dependent, with frequency shifts being maximised when the
intense stray field localised directly beneath the particle can act on a large
proportion of the disc's spins that are undergoing high amplitude precession.",1604.07277v2
2021-12-16,Parametric resonance of spin waves in ferromagnetic nanowires tuned by spin Hall torque,"We present a joint experimental and theoretical study of parametric resonance
of spin wave eigenmodes in Ni$_{80}$Fe$_{20}$/Pt bilayer nanowires. Using
electrically detected magnetic resonance, we measure the spectrum of spin wave
eigenmodes in transversely magnetized nanowires and study parametric excitation
of these eigenmodes by a microwave magnetic field. We also develop an
analytical theory of spin wave eigenmodes and their parametric excitation in
the nanowire geometry that takes into account magnetic dilution at the nanowire
edges. We measure tuning of the parametric resonance threshold by antidamping
spin Hall torque from a direct current for the edge and bulk eigenmodes, which
allows us to independently evaluate frequency, damping and ellipticity of the
modes. We find good agreement between theory and experiment for parametric
resonance of the bulk eigenmodes but significant discrepancies arise for the
edge modes. The data reveals that ellipticity of the edge modes is
significantly lower than expected, which can be attributed to strong
modification of magnetism at the nanowire edges. Our work demonstrates that
parametric resonance of spin wave eigenmodes is a sensitive probe of magnetic
properties at edges of thin-film nanomagnets.",2112.09222v1
2006-11-01,Ferromagnetic resonance study of sputtered Co|Ni multilayers,"We report on room temperature ferromagnetic resonance (FMR) studies of [$t$
Co$|2t$ Ni]$\times$N sputtered films, where $0.1 \leq t \leq 0.6$ nm. Two
series of films were investigated: films with same number of Co$|$Ni bilayer
repeats (N=12), and samples in which the overall magnetic layer thickness is
kept constant at 3.6 nm (N=1.2/$t$). The FMR measurements were conducted with a
high frequency broadband coplanar waveguide up to 50 GHz using a flip-chip
method. The resonance field and the full width at half maximum were measured as
a function of frequency for the field in-plane and field normal to the plane,
and as a function of angle to the plane for several frequencies. For both sets
of films, we find evidence for the presence of first and second order
anisotropy constants, $K_1$ and $K_2$. The anisotropy constants are strongly
dependent on the thickness $t$, and to a lesser extent on the total thickness
of the magnetic multilayer. The Land\'e g-factor increases with decreasing $t$
and is practically independent of the multilayer thickness. The magnetic
damping parameter $\alpha$, estimated from the linear dependence of the
linewidth, $\triangle H$, on frequency, in the field in-plane geometry,
increases with decreasing $t$. This behaviour is attributed to an enhancement
of spin-orbit interactions with $t$ decreasing and in thinner films, to a
spin-pumping contribution to the damping.",0611027v2
2008-06-26,Ferromagnetic resonance force spectroscopy of individual sub-micron size samples,"We review how a magnetic resonance force microscope (MRFM) can be applied to
perform ferromagnetic resonance (FMR) spectroscopy of \emph{individual}
sub-micron size samples. We restrict our attention to a thorough study of the
spin-wave eigen-modes excited in permalloy (Py) disks patterned out of the same
43.3 nm thin film. The disks have a diameter of either 1.0 or $0.5 \mu$m and
are quasi-saturated by a perpendicularly applied magnetic field. It is shown
that \emph{quantitative} spectroscopic information can be extracted from the
MRFM measurements. In particular, the data are extensively compared with
complementary approximate models of the dynamical susceptibility: i) a 2D
analytical model, which assumes an homogeneous magnetization dynamics along the
thickness and ii) a full 3D micromagnetic simulation, which assumes an
homogeneous magnetization dynamics below a characteristic length scale $c$ and
which approximates the cylindrical sample volume by a discretized
representation with regular cubic mesh of lateral size $c=3.9$ nm. In our
analysis, the distortions due to a breaking of the axial symmetry are taken
into account, both models incorporating the possibility of a small misalignment
between the applied field and the normal of the disks.",0806.4244v1
2009-09-27,Space-time symmetry violation of the fields in quasi-2D ferrite particles with magnetic-dipolar-mode oscillations,"In magnetic systems with reduced dimensionality, the effects of dipolar
interactions allow the existence of long-range ordered phases. Long-range
magnetic-dipolar interactions are at the heart of the explanation of many
peculiar phenomena observed in nuclear magnetic resonance, ferromagnetic
resonance, and Bose-Einstein-condensate structures. In this paper we show that
magnetic-dipolar-modes (MDMs) in quasi-2D ferrite disks are characterized by
symmetry breaking effects. Our analysis is based on postulates about a physical
meaning of the magnetostatic-potential function as a complex scalar wave
function, which presumes the long-range phase correlations. An important
feature of the MDM oscillations in a ferrite disk concerns the fact that a
structure with symmetric parameters and symmetric basic equations goes into
eigenstates that are not space-time symmetric. The proper solutions are found
based on an analysis of magnetostatic-wave propagation in a helical coordinate
system. For a ferrite disk, we show that while a composition of two helical
waves may acquire a geometrical phase over-running of during a period, every
separate helical wave has a dynamical phase over-running of and so behaves as a
double-valued function. We demonstrate that unique topological structures of
the fields in a ferrite disk are intimately related to the symmetry breaking
properties of MDM oscillations. The solutions give the MDM power-flow-density
vortices with cores at the disk center and azimuthally running waves of
magnetization. One can expect that the proposed models of long-range ordered
phases and space-time violation properties of magnetic-dipolar interactions can
be used in other magnetic structures, different from the
ferromagnetic-resonance system with reduced dimensionality.",0909.4920v1
2013-10-28,Precise determination of the spectroscopic g-factor using broadband ferromagnetic resonance spectroscopy,"We demonstrate that the spectroscopic g-factor can be determined with high
precision and accuracy by broadband ferromagnetic resonance measurements and
applying an asymptotic analysis to the data. Spectroscopic data used to
determine the g-factor is always obtained over a finite range of frequencies,
which can result in significant errors in the fitted values of the
spectroscopic g-factor. We show that by applying an asymptotic analysis to
broadband datasets, precise values of the intrinsic g-factor can be determined
with errors well below 1 %, even when the exact form of the Kittel equation
(which describes the relationship between the frequency and resonance field) is
unknown. We demonstrate this methodology with measured data obtained for
sputtered Ni80Fe20 (""Permalloy"") thin films of varied thicknesses, where we
determine the bulk g-factor value to be 2.109 +/- 0.003. Such an approach is
further validated by application to simulated data that includes both noise and
an anisotropy that is not included in the Kittel equation that was used in the
analysis. Finally, we show a correlation of thickness and interface structure
to the magnitude of the asymptotic behavior, which provide insight into
additional mechanisms that may induce deviations from the Kittel equation.",1310.7515v1
2014-07-15,Magnetic nanoparticle traveling in external magnetic field,"A set of equations describing the motion of a free magnetic nanoparticle in
an external magnetic field in a vacuum, or in a medium with negligibly small
friction forces is postulated. The conservation of the total particle momentum,
i.e. the sum of the mechanical and the total spin momentum of the nanoparticle
is taken into account explicitly. It is shown that for the motion of a
nanoparticle in uniform magnetic field there are three different modes of
precession of the unit magnetization vector and the director that is parallel
the particle easy anisotropy axis. These modes differ significantly in the
precession frequency. For the high-frequency mode the director points
approximately along the external magnetic field, whereas the frequency and the
characteristic relaxation time of the precession of the unit magnetization
vector are close to the corresponding values for conventional ferromagnetic
resonance. On the other hand, for the low-frequency modes the unit
magnetization vector and the director are nearly parallel and rotate in unison
around the external magnetic field. The characteristic relaxation time for the
low-frequency modes is remarkably long. This means that in a rare assembly of
magnetic nanoparticles there is a possibility of additional resonant absorption
of the energy of alternating magnetic field at a frequency that is much smaller
compared to conventional ferromagnetic resonance frequency. The scattering of a
beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic
field is also considered taking into account the precession of the unit
magnetization vector and director.",1407.3964v1
2015-03-25,Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers,"We demonstrate theoretically a strong local enhancement of the intensity of
the in-plane microwave magnetic field in multilayered structures made from a
magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two
non-magnetic layers with a high dielectric constant matching that of YIG. The
enhancement is predicted for the excitation regime when the microwave magnetic
field is induced inside the multilayer by the transducer of a stripline
Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous
numerical solution of the Landau-Lifshitz-Gilbert equation consistently with
the Maxwell's equations, we investigate the magnetisation dynamics in the
multilayer. We reveal a strong photon-magnon coupling, which manifests itself
as anti-crossing of the ferromagnetic resonance (FMR) magnon mode supported by
the YIG layer and the electromagnetic resonance mode supported by the whole
multilayered structure. The frequency of the magnon mode depends on the
external static magnetic field, which in our case is applied tangentially to
the multilayer in the direction perpendicular to the microwave magnetic field
induced by the stripline of the BFMR setup. The frequency of the
electromagnetic mode is independent of the static magnetic field. Consequently,
the predicted photon-magnon coupling is sensitive to the applied magnetic field
and thus can be used in magnetically tuneable metamaterials based on
simultaneously negative permittivity and permeability achievable thanks to the
YIG layer. We also suggest that the predicted photon-magnon coupling may find
applications in microwave quantum information systems.",1503.07282v1
2015-06-25,Hybridized magnetic microwire metacomposites towards microwave cloaking and barcoding applications,"The microwave behavior of polymer metacomposites containing parallel Fe-based
and continuous/short-cut Co-based microwire arrays has been investigated. A
magnetic field-tunable metacomposite feature has been identified in the dense
continuous hybrid composite confirmed by the transmission windows in the
frequency band of 1 to 3.5 GHz. The complex magnetically tuned
redshift-blueshift evolution of the transmission window is reasoned to result
from the competition between the dynamic wire-wire interaction and the
ferromagnetic resonance of Fe-based wires. Increasing Co-based inter-wire
spacing to 10 mm in the continuous hybrid composites, a remarkable dual-band
transmission window in the 1.5-3.5 GHz and 9-17 GHz is respectively induced by
the ferromagnetic resonance of Fe-based wires and the magnetic resonance
arising between Fe-Co wire couples. The hybridization of parallel Fe-based and
short-cut Co-based wires in the polymer composite leads to a significant
enhancement of the transmission window in the frequency band of 1 to 6 GHz due
to the band-stop nature of Co-based wires. The advanced hybridized microwire
metacomposites are arguably demonstrated to be particularly attractive for
microwave cloaking and radio frequency barcoding applications.",1506.07745v1
2019-11-03,Ferromagnetic dynamics detected via one- and two-magnon NV relaxometry,"The NV center in diamond has proven to be a powerful tool for locally
characterizing the magnetic response of microwave excited ferromagnets. To
date, this has been limited by the requirement that the FMR excitation
frequency be less than the NV spin resonance frequency. Here we report NV
relaxometry based on a two-magnon Raman-like process, enabling detection of FMR
at frequencies higher than the NV frequency. For high microwave drive powers,
we observe an unexpected field-shift of the NV response relative to a
simultaneous microwave absorption signal from a low damping ferrite film. We
show that the field-shifted NV response is due to a second order Suhl
instability. The instability creates a large population of non-equilibrium
magnons which relax the NV spin, even when the uniform mode FMR frequency
exceeds that of the NV spin resonance frequency, hence ruling out the
possibility that the NV is relaxed by a single NV-resonant magnon. We argue
that at high frequencies the NV response is due to a two-magnon relaxation
process in which the difference frequency of two magnons matches the NV
frequency, and at low frequencies we evaluate the lineshape of the one-magnon
NV relaxometry response using spinwave instability theory.",1911.00829v1
2021-04-16,Strong magnon-photon coupling with chip-integrated YIG in the zero-temperature limit,"The cross-integration of spin-wave and superconducting technologies is a
promising method for creating novel hybrid devices for future information
processing technologies to store, manipulate, or convert data in both classical
and quantum regimes. Hybrid magnon-polariton systems have been widely studied
using bulk Yttrium Iron Garnet (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) and
three-dimensional microwave photon cavities. However, limitations in YIG growth
have thus far prevented its incorporation into CMOS compatible technology such
as high quality factor superconducting quantum technology. To overcome this
impediment, we have used Plasma Focused Ion Beam (PFIB) technology -- taking
advantage of precision placement down to the micron-scale -- to integrate YIG
with superconducting microwave devices. Ferromagnetic resonance has been
measured at millikelvin temperatures on PFIB-processed YIG samples using planar
microwave circuits. Furthermore, we demonstrate strong coupling between
superconducting resonator and YIG ferromagnetic resonance modes by maintaining
reasonably low loss while reducing the system down to the micron scale. This
achievement of strong coupling on-chip is a crucial step toward fabrication of
functional hybrid quantum devices that advantage from spin-wave and
superconducting components.",2104.08068v3
2021-10-04,Separation of Artifacts from Spin-Torque Ferromagnetic Resonance Measurements of Spin-Orbit Torque for the Low-Symmetry van der Waals Semi-Metal ZrTe$_\textbf{3}$,"We measure spin-orbit torque generated by exfoliated layers of the
low-symmetry semi-metal ZrTe$_3$ using the spin-torque ferromagnetic resonance
(ST-FMR) technique. When the ZrTe$_3$ has a thickness greater than about 10 nm,
artifacts due to spin pumping and/or resonant heating can cause the standard
ST-FMR analysis to overestimate the true magnitude of the torque efficiency by
as much as a factor of 30, and to indicate incorrectly that the spin-orbit
torque depends strongly on the ZrTe$_3$ layer thickness. Artifact-free
measurements can still be achieved over a substantial thickness range by the
method developed recently to detect ST-FMR signals in the Hall geometry as well
as the longitudinal geometry. ZrTe$_3$/Permalloy samples generate a
conventional in-plane anti-damping spin torque efficiency
$\xi_{||}^{\text{DL}}$ = 0.014 $\pm$ 0.004, and an unconventional in-plane
field-like torque efficiency $|\xi_{||}^{\text{FL}}|$ = 0.003 $\pm$ 0.001. The
out-of-plane anti-damping torque is negligible. We suggest that artifacts
similarly interfere with the standard ST-FMR analysis for other van der Waals
samples thicker than about 10 nm.",2110.01720v2
2022-04-25,Reduced effective magnetization and damping by slowly-relaxing impurities in strained $γ$-$\mathrm{Fe_2O_3}$ thin films,"We study the static and dynamic magnetic properties of epitaxially strained
$\gamma$-$\mathrm{Fe_2O_3}$ (maghemite) thin films grown via pulsed-laser
deposition on MgO substrates by SQUID magnetometry and cryogenic broadband
ferromagnetic resonance experiments. SQUID magnetometry measurements reveal
hysteretic magnetization curves for magnetic fields applied both in- and out of
the sample plane. From the magnetization dynamics of our thin films, we find a
small negative effective magnetization in agreement with a strain induced
perpendicular magnetic anisotropy. Moreover, we observe a non-linear evolution
of the ferromagnetic resonance-linewidth as function of the microwave frequency
and explain this finding with a model based on slowly relaxing impurities, the
so-called slow relaxor model. By investigating the magnetization dynamics in
our maghemite thin films as a function of frequency and temperature, we can
isolate the temperature dependent contribution of the slowly relaxing
impurities to the resonance linewidth and, in particular, observe a sign change
in the effective magnetization. This finding provides evidence for a transition
of the magnetic anisotropy from a perpendicular easy axis to an easy in-plane
anisotropy for reduced temperatures.",2204.11498v1
2022-07-04,Long-distance coupling of spin qubits via topological magnons,"We consider two distant spin qubits in quantum dots, both coupled to a
two-dimensional topological ferromagnet hosting chiral magnon edge states at
the boundary. The chiral magnon is used to mediate entanglement between the
spin qubits, realizing a fundamental building block of scalable quantum
computing architectures: a long-distance two-qubit gate. Previous proposals for
long-distance coupling with magnons involved off-resonant coupling, where the
detuning of the spin-qubit frequency from the magnonic band edge provides
protection against spontaneous relaxation. The topological magnon mode, on the
other hand, lies in-between two magnonic bands far away from any bulk magnon
resonances, facilitating strong and highly tuneable coupling between the two
spin qubits. Even though the coupling between the qubit and the chiral magnon
is resonant for a wide range of qubit splittings, we find that the
magnon-induced qubit relaxation is vastly suppressed if the coupling between
the qubit and the ferromagnet is antiferromagnetic. A fast and high-fidelity
long-distance coupling protocol is presented capable of achieving spin-qubit
entanglement over micrometer distances with $1\,$MHz gate speed and up to
$99.9\%$ fidelities. The resulting spin-qubit entanglement may be used as a
probe for the long-sought detection of topological edge magnons.",2207.01264v1
2022-09-27,Tailoring crosstalk between localized 1D spin-wave nanochannels using focused ion beams,"1D spin-wave conduits are envisioned as nanoscale components of
magnonics-based logic and computing schemes for future generation electronics.
`A-la-carte methods of versatile control of the local magnetization dynamics in
such nanochannels are highly desired for efficient steering of the spin waves
in magnonic devices. Here, we present a study of localized dynamical modes in
1-$\mu$m-wide Permalloy conduits probed by microresonator ferromagnetic
resonance technique. We clearly observe the lowest-energy edge mode in the
microstrip after its edges were finely trimmed by means of focused Ne$^+$ ion
irradiation. Furthermore, after milling the microstrip along its long axis by
focused ion beams, creating consecutively $\sim$50 and $\sim$100 nm gaps,
additional resonances emerge and are attributed to modes localized at the inner
edges of the separated strips. To visualize the mode distribution, spatially
resolved Brillouin light scattering microscopy was used showing an excellent
agreement with the ferromagnetic resonance data and confirming the mode
localization at the outer/inner edges of the strips depending on the magnitude
of the applied magnetic field. Micromagnetic simulations confirm that the
lowest-energy modes are localized within $\sim$15-nm-wide regions at the edges
of the strips and their frequencies can be tuned in a wide range (up to 5 GHz)
by changing the magnetostatic coupling (i.e. spatial separation) between the
microstrips.",2209.13180v2
2022-11-09,Time-resolved measurement of spin excitations in Cu$_2$OSeO$_3$,"Magnetic diffraction in combination with x-ray detected ferromagnetic
resonance (DFMR) is a powerful technique for performing time-resolved
measurements on individual spin textures. Here, we study the ferromagnetic
resonance (FMR) modes of both the conical and field-polarized phases in the
chiral magnet Cu$_2$OSeO$_3$. Following the identification of the FMR modes at
different temperatures using broadband vector network analyzer FMR, we use DFMR
on the crystalline (001) Bragg peak to reveal the time-dependent spin
configurations of the selected FMR modes. By being able to measure both the
amplitude and phase response of the spin system across the resonance, a
continuous phase advance (of 180$^\circ$) in the conical mode, and a phase lag
(of 180$^\circ$) in the field-polarized mode is found. By performing dynamic
measurements in the conical phase as a function of the linear polarization
angle of the x-rays, i.e., successively probing the dynamics of the moments, we
find an inversion of the dynamics along the conical axis upon inverting the
applied field direction. By allowing for time-resolved measurements of the
phase and amplitude of individual magnetic phases, DFMR opens up new
opportunities for obtaining a deeper understanding of the complex dynamics of
chiral magnets.",2211.05195v1
2023-02-15,Coupling of ferromagnetic and antiferromagnetic spin dynamics in Mn$_{2}$Au/NiFe thin-film bilayers,"We investigate magnetization dynamics of Mn$_{2}$Au/Py (Ni$_{80}$Fe$_{20}$)
thin film bilayers using broadband ferromagnetic resonance (FMR) and Brillouin
light scattering spectroscopy. Our bilayers exhibit two resonant modes with
zero-field frequencies up to almost 40 GHz, far above the single-layer Py FMR.
Our model calculations attribute these modes to the coupling of the Py FMR and
the two antiferromagnetic resonance (AFMR) modes of Mn2Au. The
coupling-strength is in the order of 1.6 T$\cdot$nm at room temperature for
nm-thick Py. Our model reveals the dependence of the hybrid modes on the AFMR
frequencies and interfacial coupling as well as the evanescent character of the
spin waves that extend across the Mn$_{2}$Au/Py interface",2302.07915v1
2007-11-02,Electric-field controlled spin reversal in a quantum dot with ferromagnetic contacts,"Manipulation of the spin-states of a quantum dot by purely electrical means
is a highly desirable property of fundamental importance for the development of
spintronic devices such as spin-filters, spin-transistors and single-spin
memory as well as for solid-state qubits. An electrically gated quantum dot in
the Coulomb blockade regime can be tuned to hold a single unpaired spin-1/2,
which is routinely spin-polarized by an applied magnetic field. Using
ferromagnetic electrodes, however, the properties of the quantum dot become
directly spin-dependent and it has been demonstrated that the ferromagnetic
electrodes induce a local exchange-field which polarizes the localized spin in
the absence of any external fields. Here we report on the experimental
realization of this tunneling-induced spin-splitting in a carbon nanotube
quantum dot coupled to ferromagnetic nickel-electrodes. We study the
intermediate coupling regime in which single-electron states remain well
defined, but with sufficiently good tunnel-contacts to give rise to a sizable
exchange-field. Since charge transport in this regime is dominated by the
Kondo-effect, we can utilize this sharp many-body resonance to read off the
local spin-polarization from the measured bias-spectroscopy. We show that the
exchange-field can be compensated by an external magnetic field, thus restoring
a zero-bias Kondo-resonance, and we demonstrate that the exchange-field itself,
and hence the local spin-polarization, can be tuned and reversed merely by
tuning the gate-voltage. This demonstrates a very direct electrical control
over the spin-state of a quantum dot which, in contrast to an applied magnetic
field, allows for rapid spin-reversal with a very localized addressing.",0711.0320v1
2021-08-19,"Development of magnetism in Fe-doped magnetic semiconductors: Resonant photoemission and x-ray magnetic circular dichroism studies of (Ga,Fe)As","Fe-doped III-V ferromagnetic semiconductors (FMSs) such as (In,Fe)As,
(Ga,Fe)Sb, (In,Fe)Sb, and (Al,Fe)Sb are promising materials for spintronic
device applications because of the availability of both n- and p-type materials
and the high Curie temperatures. On the other hand, (Ga,Fe)As, which has the
same zinc-blende crystal structure as the Fe-doped III-V FMSs, shows
paramagnetism. The origin of the different magnetic properties in the Fe-doped
III-V semiconductors remains to be elucidated. To address this issue, we use
resonant photoemission spectroscopy (RPES) and x-ray magnetic circular
dichroism (XMCD) to investigate the electronic and magnetic properties of the
Fe ions in a paramagnetic (Ga$_{0.95}$,Fe$_{0.05}$)As thin film. The observed
Fe 2$p$-3$d$ RPES spectra show that the Fe 3$d$ states are similar to those of
ferromagnetic (Ga,Fe)Sb. The estimated Fermi level is located in the middle of
the band gap in (Ga,Fe)As. The Fe $L_{2,3}$ XMCD spectra of
(Ga$_{0.95}$,Fe$_{0.05}$)As show pre-edge structures, which are not observed in
the Fe-doped FMSs, indicating that the minority-spin ($\downarrow$)
$e_\downarrow$ states are vacant in (Ga$_{0.95}$,Fe$_{0.05}$)As. The XMCD
results suggest that the carrier-induced ferromagnetic interaction in
(Ga$_{0.95}$,Fe$_{0.05}$)As is short-ranged and weaker than that in the
Fe-doped FMSs. The experimental findings suggest that the electron occupancy of
the $e_\downarrow$ states contributes to the appearance of ferromagnetism in
the Fe-doped III-V semiconductors, for p-type as well as n-type compounds.",2108.08598v1
2014-05-14,Finite range and upper branch effects on itinerant ferromagnetism in repulsive Fermi gases: Bethe-Goldstone ladder resummation approach,"We investigate the ferromagnetic transition in repulsive Fermi gases at zero
temperature with upper branch and effective range effects. Based on a general
effective Lagrangian that reproduces precisely the two-body $s$-wave scattering
phase shift, we obtain a nonperturbative expression of the energy density as a
function of the polarization by using the Bethe-Goldstone ladder resummation.
For hard sphere potential, the predicted critical gas parameter $k_{\rm
F}a=0.816$ and the spin susceptibility agree well with the results from
fixed-node diffusion Monte Carlo calculations. In general, positive and
negative effective ranges have opposite effects on the critical gas parameter
$k_{\rm F}a$: While a positive effective range reduces the critical gas
parameter, a negative effective range increases it. For attractive potential or
Feshbach resonance model, the many-body upper branch exhibits an energy maximum
at $k_{\rm F}a=\alpha$ with $\alpha=1.34$ from the Bethe-Goldstone ladder
resummation, which is qualitatively consistent with experimental results. The
many-body T-matrix has a positive-energy pole for $k_{\rm F}a>\alpha$ and it
becomes impossible to distinguish the bound state and the scattering state.
These positive-energy bound states become occupied and therefore the upper
branch reaches an energy maximum at $k_{\rm F}a=\alpha$. In the zero range
limit, there exists a narrow window ($0.86<k_{\rm F}a<1.56$) for the
ferromagnetic phase. At sufficiently large negative effective range, the
ferromagnetic phase disappears. On the other hand, the appearance of
positive-energy bound state resonantly enhances the two-body decay rate around
$k_{\rm F}a=\alpha$ and may prevent the study of equilibrium phases and
ferromagnetism of the upper branch Fermi gas.",1405.3338v4
2020-12-09,Pressure control of the magnetic anisotropy of the quasi-two-dimensional van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$,"We report the results of the pressure-dependent measurements of the static
magnetization and of the ferromagnetic resonance (FMR) of Cr$_2$Ge$_2$Te$_6$ to
address the properties of the ferromagnetic phase of this quasi-two-dimensional
van der Waals magnet. The static magnetic data at hydrostatic pressures up to
3.4 GPa reveal a gradual suppression of ferromagnetism in terms of a reduction
of the critical transition temperature, a broadening of the transition width
and an increase of the field necessary to fully saturate the magnetization
$M_{\rm s}$. The value of $M_{\rm s} \simeq 3\mu_{\rm B}$/Cr remains constant
within the error bars up to a pressure of 2.8 GPa. The anisotropy of the FMR
signal continuously diminishes in the studied hydrostatic pressure range up to
2.39 GPa suggesting a reduction of the easy-axis type magnetocrystalline
anisotropy energy (MAE). A quantitative analysis of the FMR data gives evidence
that up to this pressure the MAE constant $K_{\rm U}$, although getting
significantly smaller, still remains finite and positive, i.e. of the easy-axis
type. Therefore, a recently discussed possibility of switching the sign of the
magnetocrystalline anisotropy in Cr$_2$Ge$_2$Te$_6$ could only be expected at
still higher pressures, if possible at all due to the observed weakening of the
ferromagnetism under pressure. This circumstance may be of relevance for the
design of strain-engineered functional heterostructures containing layers of
Cr$_2$Ge$_2$Te$_6$.",2012.05193v2
2022-08-10,Enhancement of Spin-Charge Conversion Efficiency for Co$_{3}$Sn$_{2}$S$_{2}$ across Transition from Paramagnetic to Ferromagnetic Phase,"Co$_{3}$Sn$_{2}$S$_{2}$ (CSS) is one of the shandite compounds and becomes a
magnetic Weyl semimetal candidate below the ferromagnetic phase transition
temperature ($\textit{T}_\textrm{C}$). In this paper, we investigate the
temperature ($\textit{T}$) dependence of conversion between charge current and
spin current for the CSS thin film by measuring the spin-torque ferromagnetic
resonance (ST-FMR) for the trilayer consisting of CSS / Cu / CoFeB. Above
$\textit{T}_\textrm{C}$ ~ 170 K, the CSS / Cu / CoFeB trilayer exhibits the
clear ST-FMR signal coming from the spin Hall effect in the paramagnetic CSS
and the anisotropic magnetoresistance (AMR) of CoFeB. Below
$\textit{T}_\textrm{C}$, on the other hand, it is found that the ST-FMR signal
involves the dc voltages ($\textit{V}_\textrm{dc}$) not only through the AMR
but also through the giant magnetoresistance (GMR). Thus, the resistance
changes coming from both AMR and GMR should be taken into account to correctly
understand the characteristic field angular dependence of
$\textit{V}_\textrm{dc}$. The spin Hall torque generated from the ferromagnetic
CSS, which possesses the same symmetry as that for spin Hall effect, dominantly
acts on the magnetization of CoFeB. A definite increase in the spin-charge
conversion efficiency ($\xi$) is observed at $\textit{T}$ <
$\textit{T}_\textrm{C}$, indicating that the phase transition to the
ferromagnetic CSS promotes the highly efficient spin-charge conversion. In
addition, our theoretical calculation shows the increase in spin Hall
conductivity with the emergence of magnetic moment at $\textit{T}$ <
$\textit{T}_\textrm{C}$, which is consistent with the experimental observation.",2208.05394v1
2023-12-27,"CdTe and HgTe doped with V, Cr, and Mn -- prospects for the quantum anomalous Hall effect","Using first principle calculations we examine properties of (Cd,V)Te,
(Cd,Cr)Te, (Hg,V)Te, and (Hg,Cr)Te relevant to the quantum anomalous Hall
effect (QAHE), such as the position of V- and Cr- derived energy levels and the
exchange interactions between magnetic ions. We consider CdTe and HgTe,
containing 12.5% of cation-substitutional V or Cr ions in comparison to the
well-known case of (Cd,Mn)Te and (Hg,Mn)Te, and examine their suitability for
the fabrication of ferromagnetic barriers or ferromagnetic topological quantum
wells, respectively. To account for the strong correlation of transition metal
d electrons we employ hybrid functionals with different mixing parameters aHSE
focusing on aHSE = 0.32, which better reproduces the experimental band gaps in
HgTe, CdTe, Hg0.875Mn0.125Te, and Cd0.875Mn0.125Te. We find that Cr, like Mn,
acts as an isoelectronic dopant but V can be an in-gap donor in CdTe and a
resonant donor in HgTe, similar to the case of Fe in HgSe. From the magnetic
point of view, Cr-doping results in a ferromagnetic phase within the general
gradient approximation (GGA) but interactions become antiferromagnetic within
hybrid functionals. However, (Hg,V)Te is a ferromagnet within both
exchange-correlation functionals in a stark contrast to (Hg,Mn)Te for which
robust antiferromagnetic coupling is found theoretically and experimentally.
Furthermore, we establish that the Jahn-Teller effect is relevant only in the
case of Cr-doping. Considering lower defect concentrations in HgTe-based
quantum wells compared to (Bi,Sb)3Te2 layers, our results imply that HgTe
quantum wells or (Cd,Hg)Te barriers containing either V or Cr show advantages
over (Bi,Sb,Cr,V)3Te2-based QAHE systems but whether (i) ferromagnetic coupling
will dominate in the Cr case and (ii) V will not introduce too many electrons
to the quantum well is to be checked experimentally",2312.16732v1
2021-07-21,Magnetic field tuning of the spin dynamics in the magnetic topological insulators (MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$,"We report a high frequency/high magnetic field electron spin resonance
(HF-ESR) spectroscopy study in the sub-THz frequency domain of the two
representatives of the family of magnetic topological insulators
(MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$ with $n = 0$ and 1. The HF-ESR
measurements in the magnetically ordered state at a low temperature of $T = 4$
K combined with the calculations of the resonance modes showed that the spin
dynamics in MnBi$_{\text{4}}$Te$_{\text{7}}$ is typical for an anisotropic
easy-axis type ferromagnet (FM) whereas MnBi$_{\text{2}}$Te$_{\text{4}}$
demonstrates excitations of an anisotropic easy-axis type antiferromagnet
(AFM). However, by applying the field stronger than a threshold value $\sim 6$
T we observed in MnBi$_{\text{2}}$Te$_{\text{4}}$ a crossover from the AFM
resonance modes to the FM modes which properties are very similar to the
ferromagnetic response of MnBi$_{\text{4}}$Te$_{\text{7}}$. We attribute this
remarkably unusual effect unexpected for a canonical easy-axis AFM, which,
additionally, can be accurately reproduced by numerical calculations of the
excitation modes, to the closeness of the strength of the AFM exchange and
magnetic anisotropy energies which appears to be a very specific feature of
this compound. Our experimental data evidences that the spin dynamics of the
magnetic building blocks of these compounds, the Mn-based septuple layers
(SLs), is inherently ferromagnetic featuring persisting short-range FM
correlations far above the magnetic ordering temperature as soon as the SLs get
decoupled either by introducing a nonmagnetic quintuple interlayer, as in
MnBi$_{\text{4}}$Te$_{\text{7}}$, or by applying a moderate magnetic field, as
in MnBi$_{\text{2}}$Te$_{\text{4}}$, which may have an effect on the surface
topological band structure of these compounds.",2107.09929v1
2002-12-04,Spin-resolved off-specular neutron scattering from magnetic domain walls using the polarized $^3He$ gas spin filter,"We report on the use of the polarized $^3$He gas filter and neutron resonant
enhancement techniques for the measurement of spin-polarized diffuse neutron
scattering due to ferromagnetic domains. A CoO/Co exchange biased bilayer was
grown on a Ti/Cu/$Al_2O_3$ neutron resonator template. The system is cooled in
an applied magnetic field of $H_a=2000$ Oe through the N\'{e}el temperature of
the antiferromagnet to 10 K where the applied magnetic field is swept as to
measure the magnetic hysteresis loop. After the second magnetization reversal
at the coercive field $H_{c2}=+ 230$ Oe, the system is supposed to approach the
original magnetic configuration. In order to prove that this is not the case
for our exchange biased bilayer, we have measured four off-specular maps I++,
I+-, I-+, I-- at $H_a \approx + 370$ Oe, where the Co magnetic spins were
mostly reversed. They show a striking behavior in the total reflection region:
while the nonspin-flip scattering exhibits no diffuse reflectivity, the
spin-flip scattering shows strong diffuse scattering at incident angles which
satisfy the resonance conditions. Moreover the spin-flip off-specular part of
the reflectivity is asymmetric. The I-+ intensity occurs at higher exit angles
than the specularly reflected neutrons, and the I+- intensity is shifted to
lower angles. Their intensities are noticeably different and there is a
splitting of the resonance positions for the up and down neutron spins
($\alpha_{n} ^{+} \ne \alpha_{n} ^{-}$) . Additionally, a strong influence of
the stray fields from magnetic domains to the resonance splitting is observed.",0212092v1
2004-06-09,Time-Dependent Spin-Polarized Transport Through a Resonant Tunneling Structure with Multi-Terminal,"The spin-dependent transport of the electrons tunneling through a resonant
tunneling structure with ferromagnetic multi-terminal under dc and ac fields is
explored by means of the nonequilibrium Green function technique. A general
formulation for the time-dependent current and the time-averaged current is
established. As its application the systems with two and three terminals in
noncollinear configurations of the magnetizations under dc and ac biases are
investigated, respectively. The asymmetric factor of the relaxation times for
the electrons with different spin in the central region is uncovered to bring
about various behaviours of the TMR. The present three-terminal device is
different from that discussed in literature, which is coined as a spin
transistor with source. The current-amplification effect is found. In addition,
the time-dependent spin transport for the two-terminal device is studied. It is
found that the photonic sidebands provide new channels for the electrons
tunneling through the barriers, and give rise to new resonances of the TMR,
which is called as the photon-asisted spin-dependent tunneling. The asymmetric
factor of the relaxation times is observed to lead to additional resonant peaks
besides the photon-asisted resonances.",0406221v1
2014-06-25,"Surface acoustic wave driven ferromagnetic resonance in (Ga,Mn)(As,P) epilayers","Interdigitated transducers were used to generate and detect surface acoustic
waves on a thin layer of (Ga,Mn)(As,P). The out-of-plane uniaxial magnetic
anisotropy of this dilute magnetic semiconductor is very sensitive to the
strain of the layer, making it an ideal test material for the dynamic control
of magnetization via magneto-striction. The time-domain measurement of the
amplitude and phase of the transmitted SAW during magnetic field sweeps
indicated a clear resonant behavior at a field close to the one calculated to
give a precession frequency equal to the SAW frequency. A resonance was
observed from 5K to 85K, just below the Curie temperature of the layer. A full
analytical treatment of the coupled magnetization/acoustic dynamics showed that
the magneto-strictive coupling modifies the elastic constants of the material
and accordingly the wave-vector solution to the elastic wave equation. The
shape and position of the resonance were well reproduced by the calculations,
in particular the fact that velocity (phase) variations resonated at lower
fields than the acoustic attenuation variations.",1406.6483v1
2021-06-04,Resonant optical topological Hall conductivity from skyrmions,"We study the high frequency Hall conductivity in a two-dimensional (2D) model
of conduction electrons coupled to a background magnetic skyrmion texture via
an effective Hund's coupling term. For an ordered skyrmion crystal, a Kubo
formula calculation using the basis of skyrmion crystal Chern bands reveals a
resonant Hall response at a frequency set by the Hund's coupling:
$\hbar\omega_{\text{res}} \approx J_H$. A complementary real-space Kubo formula
calculation for an isolated skyrmion in a box reveals a similar resonant Hall
response. A linear relation between the area under the Hall resonant curve and
the skyrmion density is discovered numerically and is further elucidated using
a gradient expansion which is valid for smooth textures and a local
approximation based on a spin-trimer calculation. We point out the issue of
distinguishing this skyrmion contribution from a similar feature arising from
spin-orbit interactions, as demonstrated in a model for Rashba spin-orbit
coupled electrons in a collinear ferromagnet, which is analogous to the
difficulty of unambiguously separating the d.c. topological Hall effect from
the anomalous Hall effect. The resonant feature in the high frequency
topological Hall effect is proposed to provide a potentially useful local
optical signature of skyrmions via probes such as scanning magneto-optical Kerr
microscopy.",2106.02641v2
1998-01-20,Coherent Resonant Tunneling Through an Artificial Molecule,"Coherent resonant tunneling through an artificial molecule of quantum dots in
an inhomogeneous magnetic field is investigated using an extended Hubbard
model. Both the multiterminal conductance of an array of quantum dots and the
persistent current of a quantum dot molecule embedded in an Aharanov-Bohm ring
are calculated. The conductance and persistent current are calculated
analytically for the case of a double quantum dot and numerically for larger
arrays using a multi-terminal Breit-Wigner type formula, which allows for the
explicit inclusion of inelastic processes. Cotunneling corrections to the
persistent current are also investigated, and it is shown that the sign of the
persistent current on resonance may be used to determine the spin quantum
numbers of the ground state and low-lying excited states of an artificial
molecule. An inhomogeneous magnetic field is found to strongly suppress
transport due to pinning of the spin-density-wave ground state of the system,
and giant magnetoresistance is predicted to result from the ferromagnetic
transition induced by a uniform external magnetic field.",9801201v1
2006-11-12,Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks,"Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic
resonance spectra of individual micron-size disks with identical diameter, 1
$m$m, but different layer structures. For a disk composed of a single 43.3 nm
thick permalloy (Py) layer, the lowest energy mode in the perpendicular
configuration is the uniform precession. The higher energy modes are standing
spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30)
nm multilayer structure, it has been interpreted that the lowest energy mode
becomes a precession localized at the Cu/Py interfaces. When the multilayer is
changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is
coupled to the precession of the thin layer.",0611307v3
2002-08-21,Interval methods for FMR spectra simulation,"The aim of this presentation is to promote the use of interval methods in the
so called 'hard science', like physics or materials science. The example
problem, simulation of ferromagnetic resonance spectra in amorphous wire,
serves as an evidence of their power, even in their simplest, easy to
understand, forms. The spectra, simulated for realistic values of anisotropy
constants, show amazingly rich variety of their forms, probably never suspected
by experimentalists. The method delivers guaranteed values of resonance fields
for any orientation of the sample in the external magnetic field, not just for
specific, 'highly symmetric', analytical cases; no resonance field is ever
missed. The experimental data, to be published elsewhere, are in excellent
concordance with numerical findings.",0208029v1
2009-04-20,Relaxation in the 3D ordered CoTAC spin chain by quantum nucleation of 0D domain walls,"We have shown that resonant quantum tunnelling of the magnetisation (QTM),
until now observed only in 0D cluster systems (SMMs), occurs in the molecular
Ising spin chain, CoTAC ([(CH_3)_3NH]CoCl_3 - 2H_2O) which orders as a canted
3D-antiferromagnet at T_C=4.15 K. This effect was observed around a resonant
like field value of 1025 Oe. We present here measurements of the relaxation of
the magnetisation as a function of time, from the zero field cooled (ZFC)
antiferromagnet state and from the saturated ferromagnet state. We show that,
at the resonant field, the relaxation from the saturated state occurs in a
complicated process, whereas, surprisingly, in the case of the ZFC state, the
relaxation is exponential.",0904.2984v1
2011-07-20,Competing instabilities in quench experiments with ultracold Fermi gases near a Feshbach resonance,"Tunability of effective two body interactions near Feshbach resonances is a
powerful experimental tool in systems of ultracold atoms. It has been used to
explore a variety of intriguing phenomena in recent experiments. However not
all of the many-body properties of such systems can be understood in terms of
effective models with contact interaction given by the scattering length of the
two particles in vacuum. For example, when a two component Fermi mixture is
quenched to the BEC side of the Feshbach resonance, a positive scattering
length suggests that interactions are repulsive and thus collective dynamics
should be dominated by the Stoner instability toward a spin polarized
ferromagnetic state. On the other hand, existence of low energy two particle
bound states suggests a competing instability driven by molecule formation.
Compe- tition between spontaneous magnetization and pair formation is
determined by the the interplay of two-particle and many-body phenomena. In
these lecture notes we summarize our recent theoretical results, which analyzed
this competition from the point of view of unstable collective modes. We also
comment on the relevance of this theoretical analysis to recent experiments
reported in Ref. (Jo, Lee, Choi, Christensen, Kim, Thywissen, Pritchard and
Ketterle, 2009).",1107.3930v1
2011-10-06,Spin pumping with coherent elastic waves,"We show that the resonant coupling of phonons and magnons can be exploited to
generate spin currents at room temperature. Surface acoustic wave (SAW) pulses
with a frequency of 1.55 GHz and duration of 300 ns provide coherent elastic
waves in a ferromagnetic thin film/normal metal (Co/Pt) bilayer. We use the
inverse spin Hall voltage in the Pt as a measure for the spin current and
record its evolution as a function of time and external magnetic field
magnitude and orientation. Our experiments show that a spin current is
generated in the exclusive presence of a resonant elastic excitation. This
establishes acoustic spin pumping as a resonant analogue to the spin Seebeck
effect.",1110.1187v2
2013-01-24,Soliton dynamics of an atomic spinor condensate on a Ring Lattice,"We study the dynamics of macroscopically-coherent matter waves of an
ultra-cold atomic spin-one or spinor condensate on a ring lattice of six sites
and demonstrate a novel type of spatio-temporal internal Josephson effect.
Using a discrete solitary mode of uncoupled spin components as an initial
condition, the time evolution of this many-body system is found to be
characterized by two dominant frequencies leading to quasiperiodic dynamics at
various sites. The dynamics of spatially-averaged and spin-averaged degrees of
freedom, however, is periodic enabling an unique identification of the two
frequencies. By increasing the spin-dependent atom-atom interaction strength we
observe a resonance state, where the ratio of the two frequencies is a
characteristic integer multiple and the spin-and-spatial degrees of freedom
oscillate in ""unison"". Crucially, this resonant state is found to signal the
onset to chaotic dynamics characterized by a broad band spectrum. In a
ferromagnetic spinor condensate with attractive spin-dependent interactions,
the resonance is accompanied by a transition from oscillatory- to
rotational-type dynamics as the time evolution of the relative phase of the
matter wave of the individual spin projections changes from bounded to
unbounded.",1301.5851v1
2014-09-29,Localization and magnetism of the resonant impurity states in Ti doped PbTe,"The problem of localization of the resonant impurity states is discussed for
an illustrative example of Titanium doped Lead Telluride. Electronic structure
of PbTe:Ti is studied using first principles methods, densities of states and
Bloch spectral functions are analyzed. We show that Ti creates resonant states
in the conduction band of PbTe, however, spectral functions of the system
strongly suggest localization of these states and show poor hybridization with
PbTe electronic structure. The contrast between results presented here and
previously reported spectral functions for PbTe:Tl correlate very well with the
different effect of those impurities on thermopower (S) of PbTe, which is large
increase is S for PbTe:Tl and almost no effect on S for PbTe:Ti. Moreover,
magnetic properties of the system are studied and formation of magnetic moments
on Ti atoms is found, both for ordered (ferromagnetic) and disordered
(paramagnetic-like) phases, showing that PbTe:Ti can be a magnetic
semiconductor.",1409.8089v1
2014-11-17,"Resonant translational, breathing and twisting modes of pinned transverse magnetic domain walls","We study translational, breathing and twisting resonant modes of transverse
magnetic domain walls pinned at notches in ferromagnetic nanostrips. We
demonstrate that a mode's sensitivity to notches depends strongly on the
characteristics of that particular resonance. For example, the frequencies of
modes involving lateral motion of the wall are the ones which are most
sensitive to changes in the notch intrusion depth (especially at the narrower,
more strongly confined end of the domain wall). In contrast, the breathing
mode, whose dynamics are concentrated away from the notches is relatively
insensitive to changes in the notches' sizes. We also demonstrate a sharp drop
in the translational mode's frequency towards zero when approaching depinning
which is found, using a harmonic oscillator model, to be consistent with a
reduction in the local slope of the notch-induced confining potential at its
edge.",1411.4502v2
2014-12-25,Normal-mode splitting in the coupled system of hybridized nuclear magnons and microwave photons,"In the weak ferromagnetic MnCO$_3$ system, a low-frequency collective spin
excitation (magnon) is the hybridized oscillation of nuclear and electron spins
coupled through the hyperfine interaction. By using a split-ring resonator, we
performed transmission spectroscopy measurements of MnCO$_3$ system and
observed, for the first time, avoiding crossing between the hybridized
nuclear-electron magnon mode and the resonator mode in the NMR-frequency range.
The splitting strength is quite large due to the large spin density of
$^{55}$Mn, and the cooperativity value $C=0.2$ (magnon-photon coupling
parameter) is close to the conditions of strong coupling. The results reveal a
new class of spin systems, in which the coupling between nuclear spins and
photons is mediated by electron spins via the hyperfine interaction, and in
which the similar normal-mode splitting of the hybridized nuclear magnon mode
and the resonator mode can be observed.",1412.7799v3
2015-08-21,Radiative damping in wave guide based FMR measured via analysis of perpendicular standing spin waves in sputtered Permalloy films,"The damping $\alpha$ of the spinwave resonances in 75 nm, 120 nm, and 200nm
-thick Permalloy films is measured via vector-network-analyzer
ferromagnetic-resonance (VNA-FMR) in the out-of-plane geometry. Inductive
coupling between the sample and the waveguide leads to an additional radiative
damping term. The radiative contribution to the over-all damping is determined
by measuring perpendicular standing spin waves (PSSWs) in the Permalloy films,
and the results are compared to a simple analytical model. The damping of the
PSSWs can be fully explained by three contributions to the damping: The
intrinsic damping, the eddy-current damping, and the radiative damping. No
other contributions were observed. Furthermore, a method to determine the
radiative damping in FMR measurements with a single resonance is suggested.",1508.05265v1
2015-10-05,Ferromagnetic resonance of coupled shifted chains of nano-elements,"We investigate the FMR characteristics of a magnetic dimer composed of two
chains of iron nanoparticles coupled by dipolar interactions. The latter are
treated beyond the point-dipole approximation taking into account the finite
size and arbitrary shape of the nano-elements. The resonance frequency is
calculated as a function of the amplitude of the applied magnetic field and the
resonance field is computed as a function of the direction of the applied
field, varied both in the plane of the two chains and perpendicular to it. We
highlight a critical value of the magnetic field which marks a state transition
that should be important in magnetic recording media.",1510.01075v2
2015-11-05,Perpendicular standing spin wave and magnetic anisotropic study on amorphous FeTaC films,"Magnetic anisotropy, spin wave (SW) excitation and exchange stiffness
constant of amorphous FeTaC ($d$ = 20-200 nm) films were studied as a function
of thickness using micro-strip ferromagnetic resonance (MS-FMR) technique. The
MS-FMR spectra for in-plane applied magnetic field show the presence of uniform
precessional mode ($n$ = 0) along with first perpendicular standing spin wave
(PSSW) mode ($n$ = 1) especially for $d$ = 50, 100 and 200 nm films. The
angular ($\varphi_{H}$) dependence of resonance field ($H_{r}$) and magnetic
field dependence of resonance frequencies ($f_{r}$) in planar configuration for
the uniform and PSSW modes were modeled successfully by using dispersion
relation which arises from a combination of exchange and dipolar interactions.
The relevant parameters such as saturation magnetization ($4\pi M_{S}$),
uniaxial anisotropic constant ($K_{u}$), $g$-factor, and exchange stiffness
constants ($A_{ex}$) are estimated for different FeTaC film thickness. $A_{ex}$
is found to increase from 1.52(4)$\times$10$^{-7}$ to 5.0(5)$\times$10$^{-6}$
erg/cm as the thickness of film increases from 50 to 200 nm, possibly due to
surface pinning effect or significant inhomogeneity especially at higher
thickness films.",1511.01722v2
2015-11-24,Ferromagnetic Resonance of a YIG film in the Low Frequency Regime,"An improved method for characterizing the magnetic anisotropy of films with
cubic symmetry is described and is applied to an yttrium iron garnet (111)
film. Analysis of the FMR spectra performed both in-plane and out-of-plane from
0.7 to 8 GHz yielded the magnetic anisotropy constants as well as the
saturation magnetization. The field at which FMR is observed turns out to be
quite sensitive to anisotropy constants (by more than a factor ten) in the low
frequency (< 2 GHz) regime and when the orientation of the magnetic field is
nearly normal to the sample plane; the restoring force on the magnetization
arising from the magnetocrystalline anisotropy fields is then comparable to
that from the external field, thereby allowing the anisotropy constants to be
determined with greater accuracy. In this region, unusual dynamical behaviors
are observed such as multiple resonances and a switching of FMR resonance with
only a 1 degree change in field orientation at 0.7 GHz.",1511.07892v1
2016-09-11,Angular dependence of electron spin resonance for detecting quadrupolar liquid state of frustrated spin chains,"Spin nematic phase is a phase of frustrated quantum magnets with a
quadrupolar order of electron spins. Since the spin nematic order is usually
masked in experimentally accessible quantities, it is important to develop a
methodology for detecting the spin nematic order experimentally. In this paper
we propose a convenient method for detecting quasi-long-range spin nematic
correlations of a quadrupolar Tomonaga-Luttinger liquid state of $S=1/2$
frustrated ferromagnetic spin chain compounds, using electron spin resonance
(ESR). We focus on linewidth of a so-called paramagnetic resonance peak in ESR
absorption spectrum. We show that a characteristic angular dependence of the
linewidth on the direction of magnetic field arises in the spin nematic phase.
Measurments of the angular dependence give a signature of the quadrupolar
Tomonaga-Luttinger liquid state. In our method we change only the direction of
the magnetic field, keeping the magnitude of the magnetic field and the
temperature. Therefore, our method is advantageous for investigating the
one-dimensional quadrupolar liquid phase that usually occupies only a narrow
region of the phase diagram.",1609.03114v2
2018-04-24,$\text{Co}_{25}\text{Fe}_{75}$ Thin Films with Ultralow Total Damping,"We measure the dynamic properties of $\text{Co}_{25}\text{Fe}_{75}$ thin
films grown by dc magnetron sputtering. Using ferromagnetic resonance
spectroscopy, we demonstrate an ultralow total damping parameter in the
out-of-plane configuration of < 0.0013, whereas for the in-plane configuration
we find a minimum total damping of < 0.0020. In both cases, we observe low
inhomogeneous linewidth broadening in macroscopic films. We observe a minimum
full-width half-maximum linewidth of 1 mT at 10 GHz resonance frequency for a
12 nm thick film. We characterize the morphology and structure of these films
as a function of seed layer combinations and find large variation of the
qualitative behavior of the in-plane linewidth vs. resonance frequency.
Finally, we use wavevector-dependent Brillouin light scattering spectroscopy to
characterize the spin-wave dispersion at wave vectors up to 23 $\mu
\text{m}^{-1}$.",1804.08786v1
2009-12-18,Stochastic resonance of a nanomagnet excited by spin transfer torque,"Spin transfer torque from spin-polarized electrical current can excite
large-amplitude magnetization dynamics in metallic ferromagnets of nanoscale
dimensions. Since magnetic anisotropy energies of nanomagnets are comparable to
the thermal energy scale, temperature can have a profound effect on the
dynamics of a nanomagnet driven by spin transfer torque. Here we report the
observation of unusual types of microwave-frequency nonlinear magnetization
dynamics co-excited by alternating spin transfer torque and thermal
fluctuations. In these dynamics, temperature amplifies the amplitude of
GHz-range precession of magnetization and enables excitation of highly
nonlinear dynamical states of magnetization by weak alternating spin transfer
torque. We explain these thermally activated dynamics in terms of non-adiabatic
stochastic resonance of magnetization driven by spin transfer torque. This type
of magnetic stochastic resonance may find use in sensitive nanometer-scale
microwave signal detectors.",0912.3842v1
2014-06-16,Anisotropic Uniaxial Pressure Response in UCoAl Studied by Nuclear Magnetic Resonance Measurement,"We have performed nuclear quadrupole resonance and nuclear magnetic resonance
measurements on UCoAl with strong Ising-type anisotropy under $b$- and $c$-axes
uniaxial pressure. In the $b$-axis uniaxial pressure ($P_{\parallel b}$)
measurement, we observed an increase in the metamagnetic transition field with
increasing $P_{\parallel b}$. In the $c$-axis uniaxial pressure ($P_{\parallel
c}$) measurement, on the other hand, we observed a ferromagnetic transition in
zero magnetic field along the $c$-axis above $P_{\parallel c}$ = 0.08 GPa. The
anomaly of the nuclear spin-lattice relaxation rate divided by the temperature
$\left[ (T_1 T)^{-1} \right]$ at $T$ = 20 K is suppressed by $P_{\parallel b}$
and slightly enhanced by $P_{\parallel c}$. The anisotropic uniaxial pressure
response indicates that uniaxial pressure is a good parameter for tuning the
Ising magnetism in UCoAl.",1406.3920v1
2017-07-29,Magnetic Actuation and Feedback Cooling of a Cavity Optomechanical Torque Sensor,"We demonstrate the integration of a mesoscopic ferromagnetic needle with a
cavity optomechanical torsional resonator, and its use for quantitative
determination of the needle's magnetic properties, as well as amplification and
cooling of the resonator motion. With this system we measure torques as small
as 32 zNm, corresponding to sensing an external magnetic field of 0.12 A/m (150
nT). Furthermore, we are able to extract the magnetization (1710 kA/m) of the
magnetic sample, not known a priori, demonstrating this system's potential for
studies of nanomagnetism. Finally, we show that we can magnetically drive the
torsional resonator into regenerative oscillations, and dampen its mechanical
mode temperature from room temperature to 11.6 K, without sacrificing torque
sensitivity.",1707.09471v1
2018-10-24,Strong Coupling of Magnons to Microwave Photons in Three-Dimensional Printed Resonators,"We report on ferromagnetic resonant mode hybridization in re-entrant cavities
made with a commercial three-dimensional (3D) printer, followed by conventional
3D metalization with copper and tin. The cavity volume was only 7% that of a
standard cavity resonating at the same frequency, while maintaining a high
quality factor. Simulations were in very good agreement. We obtained an
effective coupling of about 40 MHz in two cavities at room temperature. These
experimental results demonstrate the utility of tunable filters based on
complex 3D printed cavities.",1810.10305v3
2020-01-29,Microwave magnetoabsorption in R0.6Sr0.4MnO3 (R = Pr and Nd),"We report microwave magnetoabsorption (P) at room temperature in
R0.6Sr0.4MnO3 (R = Pr and Nd) samples. P as a function of dc magnetic field
(-2.5 kOe to +2.5 kOe) was measured for a broad frequency range (f = 0.1 - 4
GHz) of microwave magnetic field using a vector network analyzer and a copper
strip coil which encloses one of the above samples. As the external dc magnetic
field decreased from the maximum field, P initially increases and shows a
maximum for a critical field and then decreases as the field approaches zero.
The critical field increases with increasing frequency of the microwave signal.
Line shape analysis of the obtained spectra suggests that the observed features
in P are caused by ferromagnetic resonance (FMR) in R = Pr and electron
paramagnetic resonance (ESR) in R = Nd samples, which were confirmed using a
coplanar waveguide-based broadband magnetic resonance spectrometer.",2001.10778v1
2021-01-22,Opportunities for long-range magnon-mediated entanglement of spin qubits via on- and off-resonant coupling,"The ability to manipulate entanglement between multiple spatially-separated
qubits is essential for quantum information processing. Although
nitrogen-vacancy (NV) centers in diamond provide a promising qubit platform,
developing scalable two-qubit gates remains a well-known challenge. To this
end, magnon-mediated entanglement proposals have attracted attention due to
their long-range spin-coherent propagation. Optimal device geometries and gate
protocols of such schemes, however, have yet to be determined. Here we predict
strong long-distance ($>\mu$m) NV-NV coupling via magnon modes with
cooperativities exceeding unity in ferromagnetic bar and waveguide structures.
Moreover, we explore and compare on-resonant transduction and off-resonant
virtual-magnon exchange protocols, and discuss their suitability for generating
or manipulating entangled states at low temperatures ($T\lesssim 150$ mK) under
realistic experimental conditions. This work will guide future experiments that
aim to entangle spin qubits in solids with magnon excitations.",2101.09220v2
2018-06-12,Resonant spin wave excitation in magnetoplasmonic bilayers by short laser pulses,"In magnetically ordered solids a static magnetic field can be generated by
virtue of the transverse magneto-optical Kerr effect (TMOKE). Moreover, the
latter was shown to be dramatically enhanced due to the optical excitation of
surface plasmons in nanostructures with relatively small optical losses. In
this paper we suggest a new method of resonant optical excitations in a
prototypical bilayer composed of noble metal (Au) with grating and a
ferromagnet thin film of yttrium iron garnet (YIG) via frequency comb. Based on
magnetization dynamics simulations we show that for the frequency comb with the
parameters, chosen in resonant with spin-wave excitations of YIG, TMOKE is
drastically enhanced, hinting towards possible technological applications in
the optical control of spintronics systems.",1806.04764v1
2018-07-24,Excitation and control of large amplitude standing magnetization waves,"A robust approach to excitation and control of large amplitude standing
magnetization waves in an easy axis ferromagnetic by starting from a ground
state and passage through resonances with chirped frequency microwave or spin
torque drives is proposed. The formation of these waves involves two stages,
where in the first stage, a spatially uniform, precessing magnetization is
created via passage through a resonance followed by a self-phase-locking
(autoresonance) with a constant amplitude drive. In the second stage, the
passage trough an additional resonance with a spatial modulation of the driving
amplitude yields transformation of the uniform solution into a doubly
phase-locked standing wave, whose amplitude is controlled by the variation of
the driving frequency. The stability of this excitation process is analyzed
both numerically and via Whitham's averaged variational principle.",1807.09033v1
2018-08-25,Twisted magnetization states and inhomogeneous resonance modes in a Fe/Gd ferrimagnetic multilayer,"Static and dynamic magnetic properties of a ferrimagnetic
[Fe(35A)/Gd(50A)]x12 superlattice were investigated in a wide 4-300 K
temperature range using magneto-optical Kerr effect (MOKE) and ferromagnetic
resonance (FMR) techniques. The multilayer structure was sputtered on a
transparent glass substrate which made it possible to perform MOKE measurements
on both Fe and Gd terminated sides of the superlattice. These experiments
allowed us to detect a transition between field-aligned and canted magnetic
states on both sides of the film and to distinguish between the bulk and
surface twisted phases of the superlattice. As a result, the experimental H-T
magnetic phase diagram of the system was obtained. FMR studies at frequencies
7-36 GHz demonstrated a complex evolution of absorption spectra as temperature
decreased from room down to 4 K. Two spectral branches were detected in the
sample. Theoretical simulations show that the observed spectral branches
correspond to different types of inhomogeneous resonance modes in the
multilayer with non-uniform magnetization precession inside Gd layers.",1808.08466v1
2019-02-06,Observation of Low Temperature Magneto-Mechanic Effects in Crystalline Resonant Phonon Cavities,"We observe magnetic effects in ultra-high quality factor crystalline quartz
Bulk Acoustic Wave resonators at milli-Kelvin temperature. The study reveals
existence of hysteresis loops, jumps and memory effects of acoustical resonance
frequencies. These loops arise as a response to the external magnetic field and
span over few Hertz range for modes with linewidths of about $25$mHz, which
constitute a frequency shift of order 60 linewidths. The effects are broadband
but get stronger towards higher frequencies where both nonlinear effects and
losses are limited by two level systems. This suggests that the observed
effects are due to ferromagnet-like phase of a spin ensemble coupled to
mechanical modes. The observed coupling between mechanical and spin degrees of
freedom in the ultra low loss regime brings new possibilities for the emerging
class of quantum hybrid systems.",1902.02001v2
2019-02-26,Strong magnon-photon coupling in ferromagnet-superconducting resonator thin-film devices,"We demonstrate strong magnon-photon coupling of a thin-film permalloy device
fabricated on a coplanar superconducting resonator. A coupling strength of
0.152 GHz and a cooperativity of 68 are found for a 30-nm-thick permalloy
stripe. The coupling strength is tunable by rotating the biasing magnetic field
or changing the volume of permalloy. We also observe an enhancement of
magnon-photon coupling in the nonlinear regime of the superconducting
resonator, which is mediated by the nucleation of dynamic flux vortices. Our
results demonstrate a critical step towards future integrated hybrid systems
for quantum magnonics and on-chip coherent information transfer.",1902.09715v1
2019-03-28,Surface resonance of the Heusler half metal Co2MnSi probed by SX-ARPES,"Heusler compounds are promising materials for spintronics with adjustable
electronic properties including 100% spin polarization at the Fermi energy. We
investigate the electronic states of AlOx capped epitaxial thin films of the
ferromagnetic half metal Co2MnSi ex-situ by soft X-ray angular resolved
photoemission spectroscopy (SX-ARPES). Good agreement between the experimental
SX- ARPES results and photoemission calculations including surface effects was
obtained. In particular, we observed in line with our calculations a large
photoemission intensity at the center of the Brillouin zone, which does not
originate from bulk states, but from a surface resonance. This provides strong
evidence for the validity of the previously proposed model based on this
resonance, which was applied to explain the huge spin polarization of Co2MnSi
observed by angular-integrating UV-photoemission spectroscopy.",1903.11840v1
2019-11-19,Magnetic and electronic phase transitions probed by nanomechanical resonance,"Two-dimensional (2D) materials enable new types of magnetic and electronic
phases mediated by their reduced dimensionality like magic-angle induced phase
transitions, 2D Ising antiferromagnets and ferromagnetism in 2D atomic layers
and heterostructures. However, only a few methods are available to study these
phase transitions, which for example is particularly challenging for
antiferromagnetic materials. Here, we demonstrate that these phases can be
probed by the mechanical motion: the temperature dependent resonance frequency
and quality factor of multilayer 2D material membranes show clear anomalies
near the phase transition temperature, which are correlated to anomalies in the
specific heat of the materials. The observed coupling of mechanical degrees of
freedom to magnetic and electronic order is attributed to thermodynamic
relations that are not restricted to van der Waals materials. Nanomechanical
resonators, therefore, offer the potential to characterize phase transitions in
a wide variety of materials, including those that are antiferromagnetic,
insulating or so thin that conventional bulk characterization methods become
unsuitable.",1911.08537v1
2020-05-28,Giant Magneto-refractive Effect in Second Harmonic Generation from Plasmonic Antennas in the Mid-infrared,"Metallic nanostructures exhibit strong nonlinear-optical response at surface
plasmon resonances, where the light-matter coupling efficiency is enhanced. An
active modulation of this response can be realized by means of an external
magnetic field. Here we utilize a nonlinear magneto-refractive effect in
spintronic multilayer antennas to achieve a resonant 20\% modulation in second
harmonic generation (SHG) in the mid-infrared. We discuss mechanisms of this
modulation and show that it cannot be explained by an unequal enhancement of
the electromagnetic field in the two spin states of the multilayer. Instead, we
propose a novel contribution to the nonlinear susceptibility, which relies on
the spin-dependent electron mean free path in metals. In contrast to
magneto-optics in ferromagnets, our approach results in no shift of the
resonance and thus ensures that the largest SHG and its strongest modulation
are simultaneously observed.",2005.13889v1
2020-09-01,Mapping the stray fields of a nanomagnet using spin qubits in SiC,"We report the use of optically addressable spin qubits in SiC to probe the
magnetic stray fields generated by a ferromagnetic microstructure
lithographically patterned on the surface of a SiC crystal. The stray fields
cause shifts in the resonance frequency of the spin centers. The spin resonance
is driven by a micrometer-sized microwave antenna patterned adjacent to the
magnetic element. The patterning of the antenna is done to ensure that the
driving microwave fields are delivered locally and more efficiently compared to
conventional, millimeter-sized circuits. A clear difference in the resonance
frequency of the spin centers in SiC is observed at various distances to the
magnetic element, for two different magnetic states. Our results offer a
wafer-scale platform to develop hybrid magnon-quantum applications by deploying
local microwave fields and the stray field landscape at the micrometer
lengthscale.",2009.00347v1
2020-11-03,Gravito-magnetic resonance in the field of a gravitational wave,"Using the construction of the Fermi frame, the field of a gravitational wave
can be described in terms of gravito-electromagnetic fields that are transverse
to the propagation direction and orthogonal to each other. In particular, the
gravito-magnetic field acts on spinning particles and we show that, due to the
action of the gravitational wave field, a new phenomenon, that we call
gravito-magnetic resonance, may appear. We give both a classical and a quantum
description of this phenomenon and suggest that it can be used as the basis for
a new type of gravitational wave detectors. Our results highlight the
effectiveness of collective spin excitations, e.g. spin waves in magnetized
materials, in detecting high frequency gravitational waves. Here we suggest
that, when gravitational waves induce a precession of the electron spin, power
is released in the ferromagnetic resonant mode endowed with quadrupole symmetry
of a magnetized sphere. This offers a possible path to the detection of the
gravito-magnetic effects of a gravitational wave.",2011.01663v1
2021-04-05,Spin Pumping of an Easy-Plane Antiferromagnet Enhanced by Dzyaloshinskii-Moriya Interaction,"Recently, antiferromagnets have received revived interest due to their
significant potential for developing next-generation ultrafast magnetic
storage. Here we report dc spin pumping by the acoustic resonant mode in a
canted easy-plane antiferromagnet {\alpha}-Fe2O3 enabled by the
Dzyaloshinskii-Moriya interaction. Systematic angle and frequency dependent
measurements demonstrate that the observed spin pumping signals arise from
resonance-induced spin injection and inverse spin Hall effect in
{\alpha}-Fe2O3/metal heterostructures, mimicking the behavior of spin pumping
in conventional ferromagnet/nonmagnet systems. The pure spin current nature is
further corroborated by reversal of the polarity of spin pumping signals when
the spin detector is switched from platinum to tungsten which has an opposite
sign of the spin Hall angle. Our results highlight the potential opportunities
offered by the low-frequency acoustic resonant mode in canted easy-plane
antiferromagnets for developing next-generation, functional spintronic devices.",2104.01796v2
2021-06-28,Fully Resonant Magneto-elastic Spin-wave Excitation by Surface Acoustic Waves under Conservation of Energy and Linear Momentum,"We report on the resonant excitation of spin waves in micro-structured
magnetic thin films by surface acoustic waves (SAWs). The spin waves as well as
the acoustic waves are studied by micro-focused Brillouin light scattering
spectroscopy. Besides the excitation of the ferromagnetic resonance, a process
which does not fulfill momentum conservation, also the excitation of
finite-wavelength spin waves can be observed at low magnetic fields. Using
micromagnetic simulations, we verify that during this excitation both energy
and linear momentum are conserved and fully transferred from the SAW to the
spin wave.",2106.14705v3
2021-07-28,Ultrastrong tunable coupler between superconducting LC resonators,"We investigate the ultrastrong tunable coupler for coupling of
superconducting resonators. Obtained coupling constant exceeds 1 GHz, and the
wide range tunability is achieved both antiferromagnetics and ferromagnetics
from $-1086$ MHz to 604 MHz. The ultrastrong coupler is composed of rf-SQUID
and dc-SQUID as tunable junctions, which connected to resonators via shared
aluminum thin film meander lines enabling such a huge coupling constant. The
spectrum of the coupler obviously shows the breaking of the rotating wave
approximation, and our circuit model treating the Josephson junction as a
tunable inductance reproduces the experimental results well. The ultrastrong
coupler is expected to be utilized in quantum annealing circuits and/or NISQ
devices with dense connections between qubits.",2107.13175v3
2021-08-13,Optical signatures of the coupled spin-mechanics of a levitated magnetic microparticle,"We propose a platform that combines the fields of cavity optomagnonics and
levitated optomechanics in order to control and probe the coupled
spin-mechanics of magnetic dielectric particles. We theoretically study the
dynamics of a levitated Faraday-active dielectric microsphere serving as an
optomagnonic cavity, placed in an external magnetic field and driven by an
external laser. We find that the optically driven magnetization dynamics
induces angular oscillations of the particle with low associated damping.
Further, we show that the magnetization and angular motion dynamics can be
probed via the power spectrum of the outgoing light. Namely, the characteristic
frequencies attributed to the angular oscillations and the spin dynamics are
imprinted in the light spectrum by two main resonance peaks. Additionally, we
demonstrate that a ferromagnetic resonance setup with an oscillatory
perpendicular magnetic field can enhance the resonance peak corresponding to
the spin oscillations and induce fast rotations of the particle around its
anisotropy axis.",2108.06214v1
2021-09-08,Triplet resonating valence bond theory and transition metal chalcogenides,"We develop a quantum spin liquid theory for quantum magnets with easy-plane
ferromagnetic exchange. These strongly entangled quantum states are obtained by
dimer coverings of 2D lattices with triplet $S = 1, m_z = 0$ bonds, forming a
triplet resonating valence bond (tRVB) state. We discuss the conditions and the
procedure to transfer well-known results from conventional singlet resonating
valence bond theory to tRVB. Additionally, we present mean field theories of
Abrikosov fermions on 2D triangular and square lattices, which can be
controlled in an appropriate large $N$ limit. We also incorporate the effect of
charge doping which stabilizes $p+ip$-wave superconductivity. Beyond the pure
theoretical interest, our study may help to resolve contradictory statements on
certain transition metal chalcogenides, including 1T-TaS$_2$, as a potential
tRVB spin-liquid.",2109.03851v1
2021-12-29,Multiorbital spin-triplet pairing and spin resonance in the heavy-fermion superconductor $\mathrm{UTe_2}$,"The heavy-fermion system $\mathrm{UTe_2}$ is a candidate for spin-triplet
superconductivity, which is of considerable interest to quantum engineering.
Among the outstanding issues is the nature of the pairing state. A recent
surprising discovery is the observation of a resonance in the spin excitation
spectrum at an antiferromagnetic wavevector [C. Duan {\it et al.}, Nature
\textbf{600}, 636 (2021)], which stands in apparent contrast to the
ferromagnetic nature of the interactions expected in this system. We show how
the puzzle can be resolved by a multiorbital spin-triplet pairing constructed
from local degrees of freedom. Because it does not commute with the kinetic
part of the Hamiltonian, the pairing contains both intra- and inter-band terms
in the band basis. We demonstrate that the intraband pairing component
naturally yields a spin resonance at the antiferromagnetic wavevector. Our work
illustrates how orbital degrees of freedom can enrich the nature and properties
of spin-triplet superconductivity of strongly-correlated quantum materials.",2112.14750v1
2022-01-08,Spin to charge conversion at Rashba-split SrTiO$_3$ interfaces from resonant tunneling,"Spin-charge interconversion is a very active direction in spintronics. Yet,
the complex behaviour of some of the most promising systems such as SrTiO$_3$
(STO) interfaces is not fully understood. Here, on the basis of a 6-band
$\boldsymbol{k.p}$ method combined with spin-resolved scattering theory, we
give a theoretical demonstration of transverse spin-charge interconversion
physics in STO Rashba interfaces. Calculations involve injection of spin
current from a ferromagnetic contact by resonant tunneling into the native
Rashba-split resonant levels of the STO triangular quantum well. We compute an
asymmetric tunneling electronic transmission yielding a transverse charge
current flowing in plane, with a dependence with gate voltage in a very good
agreement with existing experimental data.",2201.02898v1
2022-01-21,Cavity Ferromagnetic Resonance Study of Acoustic and Optic excitations in Ru/Cr/Co and Ru/Co multilayers,"Two series of [Ru10/Cox)]12 and [Ru6/Cr3/Cox)]12 x=16-60 easy-plane
anisotropy multilayers (all thicknesses in {\AA}), prepared by sputter
deposition, are studied by cavity FMR. The acoustic modes are excited by
setting the RF field perpendicular to the saturating in-plane field. Their
resonance fields are in good agreement with the values predicted for acoustic
modes by macrospin models, using the interlayer RKKY exchange and anisotropy
fields derived by the magnetic measurements. The resonance fields of the modes
excited by setting the RF field parallel to the saturating field, are lower
than those expected for optical modes. This and could attributed to the
existence of hybridized mixed modes, according to results of micromagnetic
simulations which also show that the mode mixing is related to the
inhomogeneous magnetization profile along the multilayer thickness.",2201.08630v1
2022-02-02,Antiferromagnetic parametric resonance driven by voltage-controlled magnetic anisotropy,"Voltage controlled magnetic anisotropy (VCMA) is a low-energy alternative to
manipulate the ferromagnetic state, which has been recently considered also in
antiferromagnets (AFMs). Here, we theoretically demonstrate that VCMA can be
used to excite linear and parametric resonant modes in easy-axis AFMs with
perpendicular anisotropy, thus opening the way for an efficient electrical
control of the Neel vector, and for detection of high-frequency dynamics. Our
work leads to two key results: (i) VCMA parametric pumping experiences the
so-called exchange enhancement of the coupling efficiency and, thus, is 1-2
orders of magnitude more efficient than microwave magnetic fields or
spin-orbit-torques, and (ii) it also allows for zero-field parametric
resonance, which cannot be achieved by other parametric pumping mechanisms in
AFMs with out-of-plane easy axis. Therefore, we demonstrate that the VCMA
parametric pumping is the most promising method for coherent excitation and
manipulation of AFM order in perpendicular easy-axis AFMs.",2202.01156v1
2022-02-07,Magnetization dynamics affected by phonon pumping,"""Pumping"" of phonons by a dynamic magnetization promises to extend the range
and functionality of magnonic devices. We explore the impact of phonon pumping
on room-temperature ferromagnetic resonance (FMR) spectra of bilayers of thin
yttrium iron garnet (YIG) films on thick gadolinium gallium garnet substrates
over a wide frequency range. At low frequencies the Kittel mode hybridizes
coherently with standing ultrasound waves of a bulk acoustic resonator to form
magnon polarons that induce rapid oscillations of the magnetic susceptibility,
as reported before. At higher frequencies, the phonon resonances overlap,
merging into a conventional FMR line, but with an increased line width. The
frequency dependence of the increased line broadening follows the predictions
from phonon pumping theory in the thick substrate limit. In addition, we find
substantial magnon-phonon coupling of a perpendicular standing spin wave (PSSW)
mode. This evidences the importance of the mode overlap between the acoustic
and magnetic modes, and provides a route towards engineering the magnetoelastic
mode coupling.",2202.03331v1
2022-06-09,Nanomechanical Characterization of an Antiferromagnetic Topological Insulator,"The antiferromagnetic topological insulator MnBi2Te4 (MBT) exhibits an ideal
platform to study exotic topological phenomena and magnetic properties. The
transport signatures of magnetic phase transitions in the MBT family materials
have been well-studied. However, their mechanical properties and
magneto-mechanical coupling have not been well-explored. We use
nanoelectromechanical systems to study the intrinsic magnetism in MBT thin
flakes via their magnetostrictive coupling. We investigate mechanical resonance
signatures of magnetic phase transitions from antiferromagnetic (AFM) to canted
antiferromagnetic (cAFM) to ferromagnetic (FM) phases versus magnetic field at
different temperatures. The spin-flop transitions in MBT are revealed by
frequency shifts of mechanical resonance. With temperatures going above TN, the
transitions disappear in the resonance frequency map, consistent with transport
measurements. We use a magnetostrictive model to correlate the frequency shifts
with the spin-canting states. Our work demonstrates a technique to study
magnetic phase transitions, magnetization and magnetoelastic properties of the
magnetic topological insulator.",2206.04786v1
2022-09-03,Steady off-diagonal long-range order state in a half-filled dimerized Hubbard chain induced by a resonant pulsed field,"We show that a resonant pulsed field can induce a steady superconducting
state even in the deep Mott insulating phase of the dimerized Hubbard model.
The superconductivity found here in the non-equilibrium steady state is due to
the $\eta $-pairing mechanism, characterized by the existence of the
off-diagonal long-range order (ODLRO), and is absent in the ground-state phase
diagram. The key of the scheme lies in the generation of the field-induced
charge density wave (CDW) state that is from the valence bond solid. The
dynamics of this state resides in the highly-excited subspace of dimerized
Hubbard model and is dominated by a $\eta $-spin ferromagnetic model. The decay
of such long-living excitation is suppressed because of energy conservation. We
also develop a dynamical method to detect the ODLRO of the non-equilibrium
steady state. Our finding demonstrates that the non-equilibrium many-body
dynamics induced by the interplay between the resonant external field and
electron-electron interaction is an alternative pathway to access a new exotic
quantum state, and also provides an alternative mechanism for enhancing
superconductivity.",2209.01298v1
2022-09-09,Steady helix states in a resonant XXZ Heisenberg model with Dzyaloshinskii-Moriya interaction,"We systematically investigate possible helix states in XXZ Heisenberg model
with Dzyaloshinskii-Moriya (DM) interaction. Exact solutions show that a set of
precession helix states can be constructed by deliberate superposition of
degenerate eigenstates of the Hamiltonian under the resonant condition. When a
non-Hermitian balance boundary term is imposed as a quenching action, the
quench dynamics shows that a steady helix state emerges from some easily
prepared initial states, including saturate and maximally mixed ferromagnetic
states, according to the analysis of perturbation method. The corresponding
dynamics for near resonant cases is also investigated numerically, indicating
the robustness of the scheme. Our findings highlight the cooperation of
non-Hermiticity and the DM interaction in quantum spin system, suggesting a way
for preparing steady helix state in non-Hermitian quantum spin system.",2209.04102v1
2022-09-21,Interactive Entanglement in Hybrid Opto-magno-mechanics System,"We present a novel cavity opto-magno-mechanical hybrid system to generate
entanglements among multiple quantum carriers, such as magnons, mechanical
resonators, and cavity photons in both the optical and microwave domains. Two
Yttrium iron garnet (YIG) spheres are embedded in two separate microwave
cavities which are joined by a communal mechanical resonator. Because the
microwave cavities are separate, the ferromagnetic resonate frequencies of two
YIG spheres can be tuned independently, as well as the cavity frequencies. We
show that entanglement can be achieved with experimentally reachable
parameters. The entanglement is robust against environmental thermal noise,
owing to the mechanical cooling process achieved by the optical cavity. The
maximum entanglement among different carriers is achieved by optimizing the
parameters of the system. The individual tunability of the separated cavities
allows us to independently control the entanglement properties of different
subsystems and establish quantum channels with different entanglement
properties in one system. This work could provide promising applications in
quantum metrology and quantum information tasks.",2209.10120v2
2023-03-03,Spin-wave Resonance in Arrays of Nanoscale Synthetic-antiferromagnets,"The study concerns dynamics of standing spin waves in arrays of sub-100 nm
elliptic synthetic-antiferromagnet (SAF) nanodisks. We performed a detailed
ferromagnetic resonance analysis in conjunction with micromagnetic modeling to
find out several prominent traits of such systems. One broad line is shown to
be the sole resonant response for a SAF of the considered sizes. We demonstrate
that this mode is degenerated, and its excitation map resembles a superposition
of in-center and edge-type oscillations. We also show how this hybrid
excitation leads to almost twofold enhancement in the shape-induced anisotropy
of the mode.",2303.01919v1
2023-04-30,Specific features of g $\approx$ 4.3 EPR line behavior in magnetic nanogranular composites,"Films of metal-insulator nanogranular composites M$_x$D$_{100-x}$ with
different composition and percentage of metal and dielectric phases (M = Fe,
Co, CoFeB; D = Al$_2$O$_3$, SiO$_2$, LiNbO$_3$; x $\approx$ 15-70 at.%) are
investigated by magnetic resonance in a wide range of frequencies (f = 7-37
GHz) and temperatures (T = 4.2-360 K). In addition to the usual ferromagnetic
resonance signal from an array of nanogranules, the experimental spectra
contain an additional absorption peak, which we associate with the electron
paramagnetic resonance (EPR) of Fe and Co ions dispersed in the insulating
space between the granules. In contrast to the traditional EPR of Fe and Co
ions in weakly doped non-magnetic matrices, the observed peak demonstrates a
number of unusual properties, which we explain by the presence of magnetic
interactions between ions and granules.",2305.00551v1
2024-02-05,Controlling magnon-photon coupling in a planar geometry,"The tunability of magnons enables their interaction with various other
quantum excitations, including photons, paving the route for novel hybrid
quantum systems. Here, we study magnon-photon coupling using a high-quality
factor split-ring resonator and single-crystal yttrium iron garnet (YIG)
spheres at room temperature. We investigate the dependence of the coupling
strength on the size of the sphere and find that the coupling is stronger for
spheres with a larger diameter as predicted by theory. Furthermore, we
demonstrate strong magnon-photon coupling by varying the position of the YIG
sphere within the resonator. Our experimental results reveal the expected
correlation between the coupling strength and the rf magnetic field. These
findings demonstrate the control of coherent magnon-photon coupling through the
theoretically predicted square-root dependence on the spin density in the
ferromagnetic medium and the magnetic dipolar interaction in a planar
resonator.",2402.03071v1
2002-05-09,Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagnetic Sr2FeMoO6,"Magnetic dc susceptibility ($\chi$) and electron spin resonance (ESR)
measurements in the paramagnetic regime, are presented. We found a Curie-Weiss
(CW) behavior for $\chi$(T) with a ferromagnetic $\Theta = 446(5)$ K and
$\mu_{eff} = 4.72(9) \mu_{B}/f.u.$, this being lower than that expected for
either $Fe^{3+}(5.9\mu_{B})$ or $Fe^{2+}(4.9\mu_{B})$ ions. The ESR g-factor $g
= 2.01(2)$, is associated with $Fe^{3+}$. We obtained an excellent description
of the experiments in terms of two interacting sublattices: the localized
$Fe^{3+}$ ($3d^{5}$) cores and the delocalized electrons. The coupled equations
were solved in a mean-field approximation, assuming for the itinerant electrons
a bare susceptibility independent on $T$. We obtained $\chi_{e}^{0} = 3.7$
$10^{-4}$ emu/mol. We show that the reduction of $\mu_{eff}$ for $Fe^{3+}$
arises from the strong antiferromagnetic (AFM) interaction between the two
sublattices. At variance with classical ferrimagnets, we found that $\Theta$ is
ferromagnetic. Within the same model, we show that the ESR spectrum can be
described by Bloch-Hasegawa type equations. Bottleneck is evidenced by the
absence of a $g$-shift. Surprisingly, as observed in CMR manganites, no
narrowing effects of the ESR linewidth is detected in spite of the presence of
the strong magnetic coupling. These results provide evidence that the magnetic
order in $Sr_{2}FeMoO_{6}$ does not originates in superexchange interactions,
but from a novel mechanism recently proposed for double perovskites.",0205187v1
2003-07-16,Ferromagnetic zigzag chains and properties of the charge ordered perovskite manganites,"The low-temperature properties of the so-called ''charge ordered'' state in
50% doped perovskite manganites are described from the viewpoint of the
magnetic spin ordering. In these systems, the zigzag antiferromagnetic
ordering, combined with the double-exchange physics, effectively divides the
whole sample into the one-dimensional ferromagnetic zigzag chains and results
in the anisotropy of electronic properties. The electronic structure of one
such chain is described by an effective 3$\times$3 Hamiltonian in the basis of
Mn($3de_g$) orbitals. We treat this problem analytically and consider the
following properties: (i) the nearest-neighbor magnetic interactions; (ii) the
distribution of the Mn($3de_g$) and Mn($4p$) states near the Fermi level, and
their contribution to the optical conductivity and the resonant x-ray
scattering near the Mn $K$-absorption edge. We argue that the anisotropy of
magnetic interactions in the double-exchange limit, combined with the isotropic
superexchange interactions, readily explains both the local and the global
stability of the zigzag antiferromagnetic state. The two-fold degeneracy of
$e_g$ levels plays a very important role in the problem and explains the
insulating behavior of the zigzag chain, as well as the appearance of the
orbital ordering in the double-exchange model. Importantly, however, the charge
ordering itself is expected to play only a minor role and is incompatible with
the ferromagnetic coupling within the chain. We also discuss possible effects
of the Jahn-Teller distortion and compare the tight-binding picture with
results of band structure calculations in the local-spin-density approximation.",0307382v1
2004-03-28,Fully polarized states and decoherence,"The aim of this review is to show how ``ferromagnetic'' states, that is,
states having a fully polarization, can produce intrinsic decoherence by
unitary evolution. This effect can give an understanding of recent experiments
on mesoscopic devices as quantum point contacts showing the 0.7 conductance
anomaly and the wide number of data about saturation of dephasing time observed
at very low temperatures, as a fully polarized two dimensional electron gas.
But similar effects can be seen in different area of physics as for example the
Dicke model describing the interaction of two-level systems with a radiation
mode. In this case one can show that decoherence is intrinsic and remove a
Schr\""odinger cat state leaving a single coherent state, collapsing the wave
function in the thermodynamic limit. So, saturation of dephasing time at low
temperatures in mesoscopic devices can be understood by a fully polarized two
dimensional electron gas that, by an exchange model, can be reduced to a
generalized form of the Dicke Hamiltonian and where the quasiparticles are spin
excitations interacting with magnons. In this way, one can see that several
experiments on nanowires and quantum dots can be satisfactorily explained. The
existence of intrinsic decoherence in the thermodynamic limit could have deep
implications in fundamental problems like quantum measurement and
irreversibility. Recent experiments with cavities with a large number of
photons and with nuclear magnetic resonance in organic molecular crystals give
a first strong support to this view.",0403678v1
2005-09-07,Magnetization Reversal and Nanoscopic Magnetic Phase Separation in Doped La1-xSrxCoO3,"The doped perovskite cobaltite La1-xSrxCoO3 (LSCO) has been advanced as a
model system for studying intrinsic magnetic phase separation. We have employed
a first-order reversal curve (FORC) method to probe the amount of irreversible
switching in bulk polycrystalline LSCO as a function of Sr doping, field
cooling procedure, and temperature. The value of the FORC distribution, rho, is
used as a measure of the extent of irreversible switching. For x < 0.18, the
small values of rho and its ridge-like distribution along local coercivity (Hc)
and zero bias (Hb), are characteristic of non-interacting single domain
particles. This is consistent with the formation of an array of isolated
nanoscopic ferromagnetic clusters, as observed in previous work. For x >= 0.18,
the much larger values of rho, the tilting of its distribution towards negative
bias field, and the emergence of regions with negative rho, are consistent with
increased long-range ferromagnetic ordering. The FORC distributions display
little dependence on the cooling procedure. With increasing temperature, the
fraction of irreversible switching determined from the FORC distribution
follows closely the ferromagnetic phase fraction measured by La nuclear
magnetic resonance. Our results furthermore demonstrate that the FORC method is
a valuable first-pass characterization tool for magnetic phase separation.",0509190v1
2006-02-27,Ferromagnetic Wires Composite Media with Tunable Scattering Spectra at Microwaves,"We demonstrate composite media with ferromagnetic wires that exhibit a
frequency region at the microwave regime with scattering spectra strongly
dependent on an external magnetic field or stress. These tunable composite
materials have recently been proposed theoretically; however, no direct
experimental verification has been reported. We used composite materials with
predominantly oriented CoFeCrSiB glass-coated amorphous wires having large
magnetoimpedance at GHz frequencies. The free space measurements of reflection
and transmission coefficients were conducted in the frequency range 1-8 GHz in
the presence of an external static magnetic field or stress applied to the
whole sample. In general, the transmission spectra show greater changes in the
range of 10dB for a relatively small magnetic field of few Oe or stress of 0.1
MPa. The obtained results are quantitatively consistent with the analytical
expressions predicted by the effective medium arguments. The incident
electromagnetic wave induces an electrical dipole moment in each wire, the
aggregate of which forms the effective dipole response of the whole composite
structure in the radiative near or far field region. The field and stress
dependences of the effective response arise from a field or tensile stress
sensitivity of the ac surface impedance of a ferromagnetic wire. In the
vicinity of the antenna resonance the variations in the magneto-impedance of
the wire inclusions result in large changes of the total effective response. A
number of applications of proposed materials is discussed including the field
tunable microwave surfaces and the self-sensing media for the remote
non-destructive evaluation of structural materials.",0602644v2
2006-06-05,Phenomenological theory of current driven exchange switching in ferromagnetic nanojunctions,"Phenomenological approach is developed in the theory of spin-valve type
ferromagnetic junctions to describe exchange switching by current flowing
perpendicular to interfaces. Forward and backward current switching effects are
described and they may be principally different in nature. Mobile electron
spins are considered as being free in all the contacting ferromagnetic layers.
Joint action of the following two current effects is investigated: the
nonequilibrium longitudinal spin-injection effective field and the transverse
spin-transfer surface torque. Dispersion relation for fluctuations is derived
and solved for a junction model having spatially localized spin transfer
torque: depth of the torque penetration into the free layer is assumed much
smaller than the total free layer thickness. Some critical value of the well
known Gilbert damping constant is established for the first time. Spin transfer
torque dominates in the instability threshold determination for small enough
damping constants, while the spin-injection effective field dominates for high
damping. Fine interplay between spin transfer torque and spin injection is
necessary to provide a hysteretic behavior of the resistance versus current
dependence. The state diagram building up shows the possibility of
non-stationary (time dependent) nonlinear states arising due to instability
development. Calculations lead to the instability rise time values of the order
of 0.1 ns. Spin wave resonance frequency spectrum softening occurs under the
current growing to the instability threshold. Magnetization fluctuations above
the threshold rise oscillating with time for low damping, but rise
aperiodically and much more rapid for high damping.",0606102v2
2006-10-24,31P-NMR and muSR Studies of Filled Skutterudite Compound SmFe4P12: Evidence for Heavy Fermion Behavior with Ferromagnetic Ground State,"The 31P-NMR (nuclear magnetic resonance) and muSR (muon spin relaxation)
measurements on the filled skutterudite system SmFe4P12 have been carried out.
The temperature T dependence of the 31P-NMR spectra indicates the existence of
the crystalline electric field effect splitting of the Sm3+$ (J = 5/2)
multiplet into a ground state and an excited state of about 70 K. The
spin-lattice relaxation rate 1/T1 shows the typical behavior of the Kondo
system, i.e., 1/T1 is nearly T independent above 30 K, and varies in proportion
to T (the Korringa behavior, 1/T1 \propto T) between 7.5 K and 30 K. The T
dependence deviated from the Korringa behavior below 7 K, which is independent
of T in the applied magnetic field of 1 kOe, and suppressed strongly in higher
fields. The behavior is explained as 1/T1is determined by ferromagnetic
fluctuations of the uncovered Sm3+ magnetic moments by conduction electrons.
The muSR measurements in zero field show the appearance of a static internal
field associated with the ferromagnetic order below 1.6 K.",0610648v1
2009-04-14,Spin and charge pumping in magnetic tunnel junctions with precessing magnetization: A nonequilibrium Green function approach,"We study spin and charge currents pumped by precessing magnetization of a
single ferromagnetic layer within F|I|N or F|I|F (F-ferromagnet; I-insulator;
N-normal-metal) multilayers of nanoscale thickness attached to two normal metal
electrodes with no applied bias voltage between them. Both simple
one-dimensional model, consisting of a single precessing spin and a potential
barrier as the ""sample,"" and realistic three-dimensional devices are
investigated. In the rotating reference frame, where the magnetization appears
to be static, these junctions are mapped onto a four-terminal dc circuit whose
effectively half-metallic ferromagnetic electrodes are biased by the frequency
$\hbar \omega/e$ of microwave radiation driving magnetization precession at the
ferromagnetic resonance (FMR) conditions. We show that pumped spin current in
F|I|F junctions, diminished behind the tunnel barrier and increased in the
opposite direction, is filtered into charge current by the second $F$ layer to
generate dc pumping voltage of the order of $\sim 1$ $\mu$V (at FMR frequency
$\sim 10$ GHz) in an open circuit. In F|I|N devices, several orders of
magnitude smaller charge current and the corresponding dc voltage appear
concomitantly with the pumped spin current due to barrier induced asymmetry in
the transmission coefficients connecting the four electrodes in the rotating
frame picture of pumping.",0904.2198v1
2011-04-11,Writing electronic ferromagnetic states in a high-temperature paramagnetic nuclear spin system,"In this paper we use the Nuclear Magnetic Resonance (NMR) to write eletronic
states of a ferromagnetic system into a high-temperature paramagnetic nuclear
spins. Through the control of phase and duration of radiofrequency pulses we
set the NMR density matrix populations, and apply the technique of quantum
state tomography to experimentally obtain the matrix elements of the system,
from which we calculate the temperature dependence of magnetization for
different magnetic fields. The effects of the variation of temperature and
magnetic field over the populations can be mapped in the angles of spins
rotations, carried out by the RF pulses. The experimental results are compared
to the Brillouin functions of ferromagnetic ordered systems in the mean field
approximation for two cases: the mean field is given by (i) $B=B_0+\lambda M$
and (ii) $B=B_0+\lambda M + \lambda^\prime M^3$, where $B_0$ is the external
magnetic field, and $\lambda, \lambda^\prime$ are mean field parameters. The
first case exhibits second order transition, whereas the second case has first
order transition with temperature hysteresis. The NMR simulations are in good
agreement with the magnetic predictions.",1104.1953v2
2012-03-05,Magnetic behavior of Ba_{3}Cu_{3}Sc_{4}O_{12},"The chain-like system Ba_{3}Cu_{3}Sc_4O_{12} has potentially interesting
magnetic properties due to the presence of Cu^{2+} and a structure-suggested
low-dimensionality. We present magnetization M versus magnetic field H and
temperature T, T- and H-dependent heat-capacity C_{p}, ^{45}Sc nuclear magnetic
resonance (NMR), muon spin rotation ({\mu}SR), neutron diffraction measurements
and electronic structure calculations for Ba_{3}Cu_{3}Sc_{4}O_{12}. The onset
of magnetic long-range antiferromagnetic order at T_{N} ~16 K is consistently
evidenced from the whole gamut of our data. A significant sensitivity of T_{N}
to the applied magnetic field H (T_{N}~0 K for H=70 kOe) is also reported.
Coupled with a ferromagnetic Curie-Weiss temperature ({\theta}_{CW}~65 K) in
the susceptibility (from a 100 K-300 K fit), it is indicative of competing
ferromagnetic and antiferromagnetic interactions. These indications are
corroborated by our density functional theory based electronic structure
calculations where we find the presence of significant ferromagnetic couplings
between some copper ions whereas AF couplings were present between some others.
Our experimental data, backed by our theoretical calculations, rule out
one-dimensional magnetic behaviour suggested by the structure and the observed
long-range order is due to the presence of non-negligible magnetic interactions
between adjacent as well as next-nearest chains.",1203.0826v2
2014-11-15,Spin-transfer-torque through antiferromagnetic IrMn,"Spin-transfer-torque, a transfer of angular momentum between the electron
spin and the local magnetic moments, is a promising and key mechanism to
control ferromagnetic materials in modern spintronic devices . However, much
less attention has been paid to the same effect in antiferromagnets. For the
sake of investigating how the spin current interacts with the magnetic moments
in antiferromagnets, we perform spin-torque ferromagnetic resonance
measurements on Co20Fe60B20 4nm/Ir25Mn75 tIrMn nm/Pt 4 nm multilayers under a
spin Hall effect of Pt. The effective magnetic damping in Co20Fe60B20 is
modified by the spin current injected from the Pt layer via the IrMn layer. The
results indicate that the spin current interacts with IrMn magnetic moments and
exerts the anti-damping torque on the magnetic moments of Co20Fe60B20 through
the IrMn. It is also found that the reduction of the exchange bias in the
IrMn/Pt interface degrades the anti-damping torque exerted on the Co20Fe60B20
layer, suggesting the transmission of the spin torque becomes less efficient as
the interface exchange coupling degrades. Our work infers that the magnetic
moments in IrMn can be manipulated by spin torque similarly to the one in a
ferromagnetic layer.",1411.4100v4
2015-10-09,Magnetic anisotropy of polycrystalline high-temperature ferromagnetic Mn$_x$Si$_{1-x}$ ($x\approx0.5$) alloy films,"A set of thin film Mn$_x$Si$_{1-x}$ alloy samples with different manganese
concentration x = 0.44 - 0.63 grown by the pulsed laser deposition (PLD) method
onto the Al$_2$O$_3$(0001) substrate was investigated in the temperature range
4 - 300 K using ferromagnetic resonance (FMR) measurements in the wide range of
frequencies (f = 7 - 60 GHz) and magnetic fields (H = 0 - 30 kOe). For samples
with x = 0.52 - 0.55, FMR data show clear evidence of ferromagnetism with high
Curie temperatures T$_\text{C}$ ~ 300 K. These samples demonstrate complex and
unusual character of magnetic anisotropy described in the frame of
phenomenological model as a combination of the essential second order easy
plane anisotropy contribution and the additional forth order uniaxial
anisotropy contribution with easy direction normal to the film plane. We
explain the obtained results by a polycrystalline (mosaic) structure of the
films caused by the film-substrate lattice mismatch. The existence of extra
strains at the crystallite boundaries leads to an essential inhomogeneous
magnetic anisotropy in the film plane.",1510.02634v1
2016-04-18,Anisotropic magnetization relaxation in ferromagnetic multilayers with variable interlayer exchange coupling,"The FMR linewidth and its anisotropy in F$_1$/f/F$_2$/AF multilayers, where
spacer f has a low Curie point compared to the strongly ferromagnetic F$_1$ and
F$_2$, is investigated. The role of the interlayer exchange coupling in
magnetization relaxation is determined experimentally by varying the thickness
of the spacer. It is shown that stronger interlayer coupling via thinner
spacers enhances the microwave energy exchange between the outer ferromagnetic
layers, with the magnetization of F$_2$ exchange-dragged by the resonance
precession in F$_1$. A weaker mirror effect is also observed: the magnetization
of F$_1$ can be exchange-dragged by the precession in F$_2$, which leads to
anti-damping and narrower FMR linewidths. A theory is developed to model the
measured data, which allows separating various contributions to the magnetic
relaxation in the system. Key physical parameters, such as the interlayer
coupling constant, in-plane anisotropy of the FMR linewidth, dispersion of the
magnetic anisotropy fields are quantified. These results should be useful for
designing high-speed magnetic nanodevices based on thermally-assisted
switching.",1604.05145v1
2013-08-21,Intense low-energy ferromagnetic fluctuations in the antiferromagnetic heavy-fermion metal CeB6,"Heavy-fermion metals exhibit a plethora of low-temperature ordering
phenomena, among them the so-called hidden-order phases that in contrast to
conventional magnetic order are invisible to standard neutron diffraction. One
of the oldest and structurally simplest hidden-order compounds, CeB6, became
famous for an elusive phase that was attributed to the antiferroquadrupolar
ordering of cerium-4f moments. In its ground state, CeB6 also develops a more
usual antiferromagnetic (AFM) order. Hence, its essential low-temperature
physics was always considered to be solely governed by AFM interactions between
the dipolar and multipolar Ce moments. Here we overturn this established
perspective by uncovering an intense ferromagnetic (FM) low-energy collective
mode that dominates the magnetic excitation spectrum of CeB6. Our inelastic
neutron-scattering data reveal that the intensity of this FM excitation by far
exceeds that of conventional spin-wave magnons emanating from the AFM wave
vectors, thus placing CeB6 much closer to a FM instability than could be
anticipated. This propensity of CeB6 to ferromagnetism may account for much of
its unexplained behavior, such as the existence of a pronounced electron spin
resonance, and should lead to a substantial revision of existing theories that
have so far largely neglected the role of FM interactions.",1308.4491v1
2018-05-07,Electrically controlled long-distance spin transport through an antiferromagnetic insulator,"Spintronics uses spins, the intrinsic angular momentum of electrons, as an
alternative for the electron charge. Its long-term goal is in the development
of beyond-Moore low dissipation technology devices. Recent progress
demonstrated the long-distance transport of spin signals across ferromagnetic
insulators. Antiferromagnetically ordered materials are however the most common
class of magnetic materials with several crucial advantages over ferromagnetic
systems. In contrast to the latter, antiferromagnets exhibit no net magnetic
moment, which renders them stable and impervious to external fields. In
addition, they can be operated at THz frequencies. While fundamentally their
properties bode well for spin transport, previous indirect observations
indicate that spin transmission through antiferromagnets is limited to short
distances of a few nanometers. Here we demonstrate the long-distance, over tens
of micrometers, propagation of spin currents through hematite (\alpha-Fe2O3),
the most common antiferromagnetic iron oxide, exploiting the spin Hall effect
for spin injection. We control the spin current flow by the interfacial
spin-bias and by tuning the antiferromagnetic resonance frequency with an
external magnetic field. This simple antiferromagnetic insulator is shown to
convey spin information parallel to the compensated moment (N\'eel order) over
distances exceeding tens of micrometers. This newly-discovered mechanism
transports spin as efficiently as the net magnetic moments in the best-suited
complex ferromagnets. Our results pave the way to ultra-fast, low-power
antiferromagnet-insulator-based spin-logic devices that operate at room
temperature and in the absence of magnetic fields.",1805.02451v1
2018-05-31,Investigation into the role of the orbital moment in a series of isostructural weak ferromagnets,"The orbital contribution to the magnetic moment of the transition metal ion
in the isostructural weak ferromagnets ACO$_3$ (A=Mn,Co,Ni) and FeBO$_3$ was
investigated by a combination of first-principles calculations, non-resonant
x-ray magnetic scattering and x-ray magnetic circular dichroism. A non-trivial
evolution of the orbital moment as a function of the $3d$ orbitals filling is
revealed, with an anomalously large value found in the Co member of the family.
Here, the coupling between magnetic and lattice degrees of freedom produced by
the spin-orbit interaction results in a large single-ion anisotropy and a
peculiar magnetic-moment-induced electron cloud distortion, evidenced by the
appearance of a subtle scattering amplitude at space group-forbidden
reflections and significant magnetostrictive effects. Our results, which
complement a previous investigation on the sign of the Dzyaloshinskii$-$Moriya
interaction across the series, highlight the importance of spin-orbit coupling
in the physics of weak ferromagnets and prove the ability of modern
first-principles calculations to predict the properties of materials where the
Dzyaloshinskii$-$Moriya interaction is a fundamental ingredient of the magnetic
Hamiltonian.",1805.12423v2
2015-12-03,Cavity quantum electrodynamics with ferromagnetic magnons in a small yttrium-iron-garnet sphere,"Hybridizing collective spin excitations and a cavity with high cooperativity
provides a new research subject in the field of cavity quantum electrodynamics
and can also have potential applications to quantum information. Here we report
an experimental study of cavity quantum electrodynamics with ferromagnetic
magnons in a small yttrium-iron-garnet (YIG) sphere at both cryogenic and room
temperatures. We observe for the first time a strong coupling of the same
cavity mode to both a ferromagnetic-resonance (FMR) mode and a magnetostatic
(MS) mode near FMR in the quantum limit. This is achieved at a temperature ~ 22
mK, where the average microwave photon number in the cavity is less than one.
At room temperature, we also observe strong coupling of the cavity mode to the
FMR mode in the same YIG sphere and find a slight increase of the damping rate
of the FMR mode. These observations reveal the extraordinary robustness of the
FMR mode against temperature. However, the MS mode becomes unobservable at room
temperature in the measured transmission spectrum of the microwave cavity
containing the YIG sphere. Our numerical simulations show that this is due to a
drastic increase of the damping rate of the MS mode.",1512.00983v1
2016-05-02,Electrical Detection of Magnetization Dynamics via Spin Rectification Effects,"The purpose of this article is to review the current status of a frontier in
dynamic spintronics and contemporary magnetism, in which much progress has been
made in the past decade, based on the creation of a variety of micro- and
nano-structured devices that enable electrical detection of magnetization
dynamics. The primary focus is on the physics of spin rectification effects,
which are well suited for studying magnetization dynamics and spin transport in
a variety of magnetic materials and spintronic devices. Intended to be
intelligible to a broad audience, the paper begins with a pedagogical
introduction, comparing the methods of electrical detection of charge and spin
dynamics in semiconductors and magnetic materials respectively. After that it
provides a comprehensive account of the theoretical study of both the angular
dependence and line shape of electrically detected ferromagnetic resonance
(FMR), which is summarized in a handbook formate easy to be used for analyzing
experimental data. We then review and examine the similarity and differences of
various spin rectification effects found in ferromagnetic films, magnetic
bilayers and magnetic tunnel junctions, including a discussion of how to
properly distinguish spin rectification from the spin pumping/inverse spin Hall
effect generated voltage. After this we review the broad applications of
rectification effects for studying spin waves, nonlinear dynamics, domain wall
dynamics, spin current, and microwave imaging. We also discuss spin
rectification in ferromagnetic semiconductors. The paper concludes with both
historical and future perspectives, by summarizing and comparing three
generations of FMR spectroscopy which have been developed for studying
magnetization dynamics.",1605.00710v2
2016-08-25,Magnetoresistence engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates,"We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot
device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The
wire segment can be electrically tuned to a single dot or to a double dot
regime using the FSGs and a backgate. In both regimes we find a strong MR and a
sharp MR switching of up to 25\% at the field at which the magnetizations of
the FSGs are inverted by the external field. The sign and amplitude of the MR
and the MR switching can both be tuned electrically by the FSGs. In a double
dot regime close to pinch-off we find {\it two} sharp transitions in the
conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic
contacts, with one transition near zero and one at the FSG switching fields.
These surprisingly rich characteristics we explain in several simple resonant
tunneling models. For example, the TMR-like MR can be understood as a
stray-field controlled transition between singlet and a triplet double dot
states. Such local magnetic fields are the key elements in various proposals to
engineer novel states of matter and may be used for testing electron spin-based
Bell inequalities.",1608.07143v1
2017-06-22,Observation of anomalous spin-torque generated by a ferromagnet,"In this work we report observation of in-plane current induced out-of-plane
magnetic field driven torque in spin valve structure. Since ferromagnet has
high spin orbit coupling it is expected to be the source of spin-orbit-torque
as it possesses anomalous-Hall-effect (AHE: equivalent to spin Hall effect in
heavy metal). So we have carried out spin-torque ferromagnetic resonance
(ST-FMR) experiment in a spin valve (consists of a fixed magnet and a free
magnet which are separated by Cu spacer), passing in-plane radio frequency
current and measuring DC voltage. Our experimental results eventually indicate
that spin torque exerted on the free magnet is not caused due to the spin
current injection by the fixed magnet owing to its AHE, but it is originated
from in-plane current driven out-of plane effective magnetic field. This is new
class of spin torque which is completely different from Slonczewski-spin
transfer torque and Rashba like field like torque. The effective out-of plane
magnetic field depends on the direction of current (in-plane) and magnetization
(in-plane) of the pinned layer. One possible mechanism behind this
unconventional torque could be intefacial spin-scattering which is also origin
of current in-plane GMR effect. Most importantly this effective out-of plane
torque can be useful to switch out-of plane magnetic bits in spintronic memory
application.",1706.07245v1
2018-01-16,Spin-orbit-torque and magnetic damping in tailored ferromagnetic bilayers,"We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in
ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched
between Pt and MgO layers. We find that the FM layer in contact with the Pt
layers dominantly determines that spin Hall angle, which is consistent with the
spin-transparency model. By contrast, the FMR linewidths are considerably
influenced not only by the spin-pumping effect across the Pt|FM in terface but
also by the spin relaxation such as two-magnon scattering at the FMMgO
interface.The CoMgO interface leads to notably increased FMR linewidths, while
the Py|MgO interface has less effect. This different contribution of each
interface to the spin Hall angel and dissipation parameter suggests that the
stack configuration of Pt|Co|Py|MgO requires less writing energy than
Pt|Py|Co|MgO in spin-orbit-torque-driven magnetic switching. Our approach
offers a promising method to optimize material parameters by engineering either
interfaces in contact with the heavy-metal or the oxide layer.",1801.05131v2
2019-06-03,Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide $β$-MoTe$_2$,"Single-crystal materials with sufficiently low crystal symmetry and strong
spin-orbit interactions can be used to generate novel forms of spin-orbit
torques on adjacent ferromagnets, such as the out-of-plane antidamping torque
previously observed in WTe$_2$/ferromagnet heterostructures. Here, we present
measurements of spin-orbit torques produced by the low-symmetry material
$\beta$-MoTe$_2$, which unlike WTe$_2$ retains bulk inversion symmetry. We
measure spin-orbit torques on $\beta$-MoTe$_2$/Permalloy heterostructures using
spin-torque ferromagnetic resonance as a function of crystallographic alignment
and MoTe$_2$ thickness down to the monolayer limit. We observe an out-of-plane
antidamping torque with a spin torque conductivity as strong as 1/3 of that of
WTe$_2$, demonstrating that the breaking of bulk inversion symmetry in the
spin-generation material is not a necessary requirement for producing an
out-of-plane antidamping torque. We also measure an unexpected dependence on
the thickness of the $\beta$-MoTe$_2$ -- the out-of-plane antidamping torque is
present in MoTe$_2$/Permalloy heterostructures when the $\beta$-MoTe$_2$ is a
monolayer or trilayer thick, but goes to zero for devices with bilayer
$\beta$-MoTe$_2$.",1906.01068v1
2019-07-02,"In-plane to perpendicular magnetic anisotropy switching in heavily-Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature","We report switching of magnetic anisotropy (MA) from in-plane to
perpendicular with increasing the thickness d of a (001)-oriented
ferromagnetic-semiconductor (FMS) (Ga0.7,Fe0.3)Sb layer with a high Curie
temperature (Tc > 320 K), using ferromagnetic resonance at room temperature. We
show that the total MA energy (E) along the [001] direction changes its sign
from positive (in-plane) to negative (perpendicular) with increasing d above an
effective critical value \mathrm{d}_\mathrm{C}^\mathrm{*}\ ~ 42 nm. We reveal
that (Ga,Fe)Sb has two-fold symmetry in the film plane. Meanwhile, in the plane
perpendicular to the film including the in-plane [110] axis, the two-fold
symmetry with the easy magnetization axis along [110] changes to four-fold
symmetry with easy magnetization axis along <001> with increasing d. This
peculiar behavior is different from that of (Ga,Mn)As, in which only the
in-plane MA depends on the film thickness and has four-fold symmetry due to its
dominant cubic anisotropy along the <100> axes. This work provides an important
guide for controlling the easy magnetization axis of high-Tc FMS (Ga,Fe)Sb for
room-temperature device applications.",1907.01188v1
2020-01-23,Magnetism at iridate/manganite interface: influence of strong spin-orbit interaction,"The complex investigation of dc transport and magnetic properties of the
epitaxial manganite/iridate heterostructure was carried out by mean of X-ray
(XRD), dc resistance measurements, ferromagnetic resonance (FMR) and polarized
neutron reflectivity (PNR). Epitaxial growth of the heterostructure proceeded
according to the cube-to-cube mechanism with the small lattice turn. The dc
measurement indicates the presence of a conduction channel at the
iridate/manganite interface due to the charge leakage from iridate that makes
it hole doped, while the manganite side becomes electron doped. This is
confirmed by the first principles calculations based on density functional
theory [Sayantika Bhowal, and Sashi Satpathy AIP Conference Proceedings 2005,
020007 (2018)] that show the charge transfer at the interface from the
half-filled spin-orbit entangled Jeff = 1/2 state of the iridate to the empty e
states of manganite. The neutron scattering data show the turn of magnetization
vector of the heterostructure (mainly manganite) on 26 degree closer to the
external field with reducing temperature down to 10K. Additional ferromagnetic
state appearing at T<100K indicate on emergence of ferromagnetism in the thin
(10 nm) paramagnetic SIO film close to the interface. We have measured the dc
voltage aroused on the SIO film caused by spin pumping and the anisotropic
magnetoresistance in the heterostructure.",2001.08403v1
2020-04-21,Role of interfacial oxidation in generation of spin-orbit torques,"We report that current-induced spin-orbit torques (SOTs) in
heavy-metal/ferromagnetic-metal bilayers are strongly altered by the oxidation
of the ferromagnetic layer near the interface. We measured damping-like (DL)
and field-like (FL) SOTs for Pt/Co and Pt/Ni$_{81}$Fe$_{19}$ (Pt/Py) films
using spin-torque ferromagnetic resonance. In the Pt/Co film, we found that the
oxidation of the Co layer near the interface enhances both DL and FL SOTs in
spite of the insulating nature of the CoO$_x$ layer. The enhancement of the
SOTs disappears by inserting a thin Ti layer at the Pt/CoO$_x$ interface,
indicating that the dominant source of the SOTs in the Pt/CoO$_x$/Co film is
the spin-orbit coupling at the Pt/CoO$_x$ interface. In contrast to the
Pt/CoO$_x$/Co film, the SOTs in the Pt/PyO$_x$/Py film are dominated by the
bulk spin-orbit coupling. Our result shows that the interfacial oxidation of
the Pt/Py film suppresses the DL-SOT and reverses the sign of the FL-SOT. The
change of the SOTs can be attributed to the change of the real and imaginary
parts of the spin mixing conductance induced by the insertion of the insulating
PyO$_x$ layer. These results show that the interfacial oxidation provides an
effective way to manipulate the strength and sign of the SOTs.",2004.09837v1
2018-08-02,Generation of pure superconducting spin current in magnetic heterostructures via non-locally induced magnetism due to Landau Fermi-liquid effects,"We propose a mechanism for the generation of pure superconducting
spin-current carried by equal-spin triplet Cooper pairs in a superconductor (S)
sandwiched between a ferromagnet (F) and a normal metal (N$_{\rm so}$) with
intrinsic spin-orbit coupling. We show that in the presence of Landau
Fermi-liquid interactions the superconducting proximity effect can induce
non-locally a ferromagnetic exchange field in the normal layer, which
disappears above the superconducting transition temperature of the structure.
The internal Landau Fermi-liquid exchange field leads to the onset of a spin
supercurrent associated with the generation of long-range spin-triplet
superconducting correlations in the trilayer. We demonstrate that the magnitude
of the spin supercurrent as well as the induced magnetic order in the N$_{\rm
so}$ layer depends critically on the superconducting proximity effect between
the S layer and the F and N$_{\rm so}$ layers and the magnitude of the relevant
Landau Fermi-liquid interaction parameter. We investigate the effect of spin
flip processes on this mechanism. Our results demonstrate the crucial role of
Landau Fermi-liquid interaction in combination with spin-orbit coupling for the
creation of spin supercurrent in superconducting spintronics, and give a
possible explanation of a recent experiment utilizing spin-pumping via
ferromagnetic resonance [Jeon $\it{ et}$ $\it{al.}$, Nat. Mat. ${\bf 17}$, 499
(2018)].",1808.01045v1
2019-02-10,Evidence of Pure Spin-Current Generated by Spin Pumping in Interface Localized States in Hybrid Metal-Silicon-Metal Vertical Structures,"Due to the difficulty to grow high quality semiconductors on ferromagnetic
metals, the study of spin diffusion transport in Si was only limited to lateral
geometry devices. In this work, by using ultra-high vacuum wafer-bonding
technique, we have successfully fabricated metal semiconductor metal
CoFeB/MgO/Si/Pt vertical structures. We hereby demonstrate pure spin-current
injection and transport in the perpendicular current flow geometry over a
distance larger than 2\mu m in n-type Si at room temperature. In those
experiments, a pure propagating spin-current is generated via ferromagnetic
resonance spin-pumping and converted into a measurable voltage by using the
inverse spin-Hall effect occurring in the top Pt layer. A systematic study by
varying both Si and MgO thicknesses reveals the important role played by the
localized states at the MgO/Si interface for the spin-current generation.
Proximity effects involving indirect exchange interactions between the
ferromagnet and the MgO/Si interface states appears to be a prerequisite to
establish the necessary out-of-equilibrium spin-population in Si under the
spin-pumping action.",1902.03652v1
2019-02-12,Magnetoelectric effect in band insulator-ferromagnet heterostructures,"We theoretically study magnetoelectric effects in a heterostructure of a
generic band insulator and a ferromagnet. In contrast to the kinetic
magnetoelectric effect in metals, referred to as the Edelstein effect or the
inverse spin galvanic effect, our mechanism relies on virtual interband
transitions between the valence and conduction bands and therefore immune to
disorder or impurity scattering. By calculating electric field-induced
magnetization by the linear response theory, we reveal that the magnetoelectric
effect shows up without specific parameter choices. The magnetoelectric effect
qualitatively varies by changing the direction of the magnetic moment in the
ferromagnet: the response is diagonal for the out-of-plane moment, whereas it
is off-diagonal for the inplane moment. We also find out that in optical
frequencies, the magnetoelectric signal can be drastically enhanced via
interband resonant excitations. Finally, we estimate the magnitude of the
magnetoelectric effect for a hybrid halide perovskite semiconductor as an
example of the band insulator and compare it with other magnetoelectric
materials. We underscore that our mechanism is quite general and widely
expectable, only requiring the Rashba spin-orbit coupling and exchange
coupling. Our result could potentially offer a promising method of Joule
heating-free electric manipulation of magnetic moments in spintronic devices.",1902.04204v1
2019-04-25,High Spin-Wave Propagation Length Consistent with Low Damping in a Metallic Ferromagnet,"We report ultra-low intrinsic magnetic damping in
Co$_{\text{25}}$Fe$_{\text{75}}$ heterostructures, reaching the low $10^{-4}$
regime at room temperature. By using a broadband ferromagnetic resonance
technique, we extracted the dynamic magnetic properties of several
Co$_{\text{25}}$Fe$_{\text{75}}$-based heterostructures with varying
ferromagnetic layer thickness. By estimating the eddy current contribution to
damping, measuring radiative damping and spin pumping effects, we found the
intrinsic damping of a 26\,nm thick sample to be $$\alpha_{\mathrm{0}} \lesssim
3.18\times10^{-4}$. Furthermore, using Brillouin light scattering microscopy we
measured spin-wave propagation lengths of up to $(21\pm1)\,\mathrm{\mu m}$ in a
26 nm thick Co$_{\text{25}}$Fe$_{\text{75}}$ heterostructure at room
temperature, which is in excellent agreement with the measured damping.",1904.11321v3
2019-11-25,Large non-reciprocal propagation of surface acoustic waves in epitaxial ferromagnetic/semiconductor hybrid structures,"Non-reciprocal propagation of sound, that is, the different transmission of
acoustic waves traveling along opposite directions, is a challenging
requirement for the realization of devices like acoustic isolators and
circulators. Here, we demonstrate the efficient non-reciprocal transmission of
surface acoustic waves (SAWs) propagating along opposite directions of a GaAs
substrate coated with an epitaxial Fe$_3$Si film. The non-reciprocity arises
from the acoustic attenuation induced by the magneto-elastic (ME) interaction
between the SAW strain field and spin waves in the ferromagnetic film, which
depends on the SAW propagation direction and can be controlled via the
amplitude and orientation of an external magnetic field. The acoustic
transmission non-reciprocity, defined as the difference between the transmitted
acoustic power for forward and backward propagation under ME resonance, reaches
values of up to 20%, which are, to our knowledge, the largest non-reciprocity
reported for SAWs traveling along a semiconducting piezoelectric substrate
covered by a ferromagnetic film. The experimental results are well accounted
for by a model for ME interaction, which also shows that non-reciprocity can be
further enhanced by optimization of the sample design. These results make
Fe$_3$Si/GaAs a promising platform for the realization of efficient
non-reciprocal SAW devices.",1911.11072v3
2020-08-29,Unveiling the polarity of the spin-to-charge current conversion in $Bi_2Se_3$,"We report an investigation of the spin- to charge-current conversion in
sputter-deposited films of topological insulator $Bi_2Se_{3}$ onto single
crystalline layers of YIG $(Y_{3}Fe_{5}O_{12})$ and polycrystalline films of
Permalloy $(Py = Ni_{81}Fe_{19})$. Pure spin current was injected into the
$Bi_{2}Se_{3}$ layer by means of the spin pumping process in which the spin
precession is obtained by exciting the ferromagnetic resonance of the
ferromagnetic film. The spin-current to charge-current conversion, occurring at
the $Bi_{2}Se_{3}/$ferromagnet interface, was attribute to the inverse
Rashba-Edelstein effect (IREE). By analyzing the data as a function of the
$Bi_{2}Se_{3}$ thickness we calculated the IREE length used to characterize the
efficiency of the conversion process and found that 1.2 pm
$\leq|{\lambda}_{IREE}|\leq$ 2.2 pm. These results support the fact that the
surface states of $Bi_{2}Se_{3}$ have a dominant role in the spin-charge
conversion process, and the mechanism based on the spin diffusion process plays
a secondary role. We also discovered that the spin- to charge-current mechanism
in $Bi_{2}Se_{3}$ has the same polarity as the one in Ta, which is the opposite
to the one in Pt. The combination of the magnetic properties of YIG and Py,
with strong spin-orbit coupling and dissipationless surface states
topologically protected of $Bi_{2}Se_{3}$ might lead to spintronic devices with
fast and efficient spin-charge conversion.",2008.12900v1
2020-09-01,Spin coherence on the ferromagnetic spherical surface,"Spintronics on flat surfaces has been studied over the years, and the
scenario is relatively well-known; however, there is a lack of information when
we consider non-flat surfaces. In this paper, we are concerned about the spin
dynamics of the ferromagnetic model on the spherical surface. We use the
Schwinger bosonic formalism for describing the thermodynamics of spin operators
in terms of spinon operators. Opposite to the flat two-dimensional model, which
is disordered at finite temperature, the curvature of the spherical surface
provides non-zero critical temperature for Schwinger boson condensation, which
characterizes order at finite temperature even in the absence of external
magnetic fields. The thermodynamics is then analyzed in the low-temperature
regime. In addition, we consider the presence of both static and oscillating
magnetic fields, the necessary condition for inducing the ferromagnetic
resonance, and we show systematically that the studied model is well-described
by $SU(2)$ coherent states, which provides the correct dynamics of the
magnetization. The archived results can be applied for describing a diversity
of experiments such as spin superfluidity, angular momentum injection by spin
pumping and spin-transfer torque in non-conventional junctions, magnon
dissipation, and magnetoelectronics on the spherical surface.",2009.00636v2
2021-03-05,Ferromagnetic Composite Self-Arrangement in Iron-Implanted Epitaxial Palladium Thin Films,"We report on the formation of the dilute $Pd_{1-x}Fe_x$ compositions with
tunable magnetic properties under an ion-beam implantation of epitaxial Pd thin
films. Binary $Pd_{1-x}Fe_x$ alloys with a mean iron content $x$ of $0.025$,
$0.035$ or $0.075$ were obtained by the implantation of $40 keV$ $Fe^+$ ions
into the palladium films on MgO (001) substrate to the doses of
$0.5\cdot10^{16}, 1.0\cdot10^{16}$ and $3.0\cdot10^{16}$ $ions/cm^2$,
respectively. Structural and magnetic studies have shown that iron atoms occupy
regular fcc-lattice Pd-sites without the formation of any secondary
crystallographic phase. All the iron implanted Pd films reveal ferromagnetism
at low temperatures (below $200 K$) with both the Curie temperature and
saturation magnetization determined by the implanted iron dose. In contrast to
the magnetic properties of the molecular beam epitaxy grown $Pd_{1-x}Fe_x$
alloy films with the similar iron contents, the Fe-implanted Pd films possess
weaker in-plane magnetocrystalline anisotropy, and, accordingly, a lower
coercivity. The observed multiple ferromagnetic resonances in the implanted
$Pd_{1-x}Fe_x$ films indicate a formation of a magnetically inhomogeneous state
due to spinodal decomposition into regions, presumably layers, with identical
crystal symmetry but different iron contents. The multiphase magnetic structure
is robust with respect to the vacuum annealing at $770 K$, though develops
towards well-defined local $Pd-Fe$ compositions.",2103.03562v1
2021-08-03,Possibility to detect the bound state of the Heisenberg ferromagnetic chain at intermediate temperature,"Motivated by the lack of direct evidence with inelastic neutron scattering of
the well documented bound state of Heisenberg ferromagnets, we use the
time-dependent Thermal Density Matrix Renormalization Group algorithm to study
the temperature dependence of the dynamical spin structure factor of Heisenberg
ferromagnetic spin chains. For spin-1/2, we show that the bound state appears
as a well defined excitation with significant spectral weight in the
temperature range $J/12 \lesssim T \lesssim J/3$, pointing to the possibility
of detecting it with inelastic neutron scattering near $k=\pi$ provided the
temperature is neither too low nor too high - at low temperature, the spectral
weight only grows as $T^{3/2}$, and at high temperature the bound state peak
merges with the two-magnon continuum. For spin-1, the situation is more subtle
because the bound state with two neighboring spin flips competes with an
anti-bound state with two spin-flips on the same site. As a consequence, the
relative spectral weight of the bound state is smaller than for spin-1/2, and a
weak resonance due to the anti-bound state appears in the continuum. A clearer
signature of the bound state (resp. anti-bound state) can be obtained if a
negative (resp. positive) biquadratic interaction is present.",2108.01401v3
2021-08-12,Optically controllable magnetism in atomically thin semiconductors,"Electronic states in two-dimensional layered materials can exhibit a
remarkable variety of correlated phases including Wigner-crystals, Mott
insulators, charge density waves, and superconductivity. Recent experimental
and theoretical research has indicated that ferromagnetic phases can exist in
electronically-doped transition metal dichalcogenide (TMD) semiconductors, but
a stable magnetic state at zero magnetic field has eluded detection. Here, we
experimentally demonstrate that mesoscopic ferromagnetic order can be generated
and controlled by local optical pumping in monolayer WSe2 at zero applied
magnetic field. In a spatially resolved pump-probe experiment, we use
polarization-resolved reflectivity from excitonic states as a probe of
charge-carrier spin polarization. When the sample is electron-doped at density
$n_e = 10^{12} cm^{-2}$, we observe that a local, circularly-polarized,
microwatt-power optical pump breaks the symmetry between equivalent
ferromagnetic spin configurations and creates magnetic order which extends over
mesoscopic regions as large as 8 um x 5 um, bounded by sample edges and folds
in the 2D semiconductor. The experimental signature of magnetic order is
circular dichroism (CD) in reflectivity from the excitonic states, with
magnitude exceeding 20% at resonant wavelengths. The helicity of the pump
determines the orientation of the magnetic state, which can be aligned along
the two principle out-of-plane axes. In contrast to previous studies in 2D
materials that have required non-local, slowly varying magnetic fields to
manipulate magnetic phases, the demonstrated capability to control long-range
magnetism and corresponding strong CD with local and tunable optical pumps is
highly versatile. This discovery will unlock new TMD-based spin and optical
technologies and enable sophisticated control of correlated electron phases in
two-dimensional electron gases (2DEGs).",2108.05931v1
2021-12-19,Optical signatures of periodic magnetization: the moiré Zeeman effect,"Detecting magnetic order at the nanoscale is of central interest for the
study of quantum magnetism in general, and the emerging field of moir\'e
magnets in particular. Here, we analyze the exciton band structure that arises
from a periodic modulation of the valley Zeeman effect. Despite long-range
electron-hole exchange interactions, we find a sizable splitting in the energy
of the bright circularly-polarized exciton Umklapp resonances, which serves as
a direct optical probe of magnetic order. We first analyze quantum moir\'e
magnets realized by periodic ordering of electron spins in Mott-Wigner states
of transition metal dichalcogenide (TMD) monolayers or twisted bilayers: we
show that spin-valley dependent exciton-electron interactions allow for probing
the spin-valley order of electrons and demonstrate that it is possible to
observe unique signatures of ferromagnetic order in a triangular lattice and
both ferromagnetic and N\'eel order in a honeycomb lattice. We then focus on
semiclassical moir\'e magnets realized in twisted bilayers of ferromagnetic
materials: we propose a detection scheme for moir\'e magnetism which is based
on inter-layer exchange coupling between spins in a moir\'e magnet and excitons
in a TMD monolayer.",2112.10276v2
2022-02-22,Giant spin torque efficiency in naturally oxidized polycrystalline TaAs thin films,"We report the measurement of efficient charge-to-spin conversion at room
temperature in Weyl semimetal/ferromagnet heterostructures with both oxidized
and pristine interfaces. Polycrystalline films of the Weyl semimetal, TaAs, are
grown by molecular beam epitaxy on (001) GaAs and interfaced with a metallic
ferromagnet (Ni$_{0.8}$Fe$_{0.2}$). Spin torque ferromagnetic resonance
(ST-FMR) measurements in samples with an oxidized interface yield a spin torque
efficiency as large as $\xi_{\mathrm{FMR}}=0.45\pm 0.25$ for a 8 nm
Ni$_{0.8}$Fe$_{0.2}$ layer thickness. By studying ST-FMR in these samples with
varying Ni$_{0.8}$Fe$_{0.2}$ layer thickness, we extract a damping-like torque
efficiency as high as $\xi_{\mathrm{DL}}=1.36\pm 0.66$. In samples with a
pristine (unoxidized) interface, the spin torque efficiency has opposite sign
to that observed in oxidized samples ($\xi_{\mathrm{FMR}}=-0.27\pm 0.14$ for a
5 nm Ni$_{0.8}$Fe$_{0.2}$ layer thickness). We also find a lower bound on the
spin Hall conductivity ($424 \pm 110 \frac{\hbar}{e}$ S/cm) which is
surprisingly consistent with theoretical predictions for the single crystal
Weyl semimetal state of TaAs.",2202.10656v1
2022-09-21,Dynamics of photo-induced ferromagnetism in oxides with orbital degeneracy,"By using intense coherent electromagnetic radiation, it may be possible to
manipulate the properties of quantum materials very quickly, or even induce new
and potentially useful phases that are absent in equilibrium. For instance,
ultrafast control of magnetic dynamics is crucial for a number of proposed
spintronic devices and can also shed light on the possible dynamics of
correlated phases out of equilibrium. Inspired by recent experiments on
spin-orbital ferromagnet YTiO$_3$ we consider the nonequilibrium dynamics of
Heisenberg ferromagnetic insulator with low-lying orbital excitations. We model
the dynamics of the magnon excitations in this system following an optical
pulse which resonantly excites infrared-active phonon modes. As the phonons
ring down they can dynamically couple the orbitals with the low-lying magnons,
leading to a dramatically modified effective bath for the magnons. We show this
transient coupling can lead to a dynamical acceleration of the magnetization
dynamics, which is otherwise bottlenecked by small anisotropy. Exploring the
parameter space more we find that the magnon dynamics can also even completely
reverse, leading to a negative relaxation rate when the pump is blue-detuned
with respect to the orbital bath resonance. We therefore show that by using
specially targeted optical pulses, one can exert a much greater degree of
control over the magnetization dynamics, allowing one to optically steer
magnetic order in this system. We conclude by discussing interesting parallels
between the magnetization dynamics we find here and recent experiments on
photo-induced superconductivity, where it is similarly observed that depending
on the initial pump frequency, an apparent metastable superconducting phase
emerges.",2209.10567v1
2023-04-11,Emergence of flat bands via orbital-selective electron correlations in Mn-based kagome metal,"Kagome lattice has been actively studied for the possible realization of
frustration-induced two-dimensional flat bands and a number of
correlation-induced phases. Currently, the search for kagome systems with a
nearly dispersionless flat band close to the Fermi level is ongoing. Here, by
combining theoretical and experimental tools, we present
Sc$_3$Mn$_3$Al$_7$Si$_5$ as a novel realization of correlation-induced
almost-flat bands in the kagome lattice in the vicinity of the Fermi level. Our
magnetic susceptibility, $^{27}$Al nuclear magnetic resonance, transport, and
optical conductivity measurements provide signatures of a correlated metallic
phase with tantalizing ferromagnetic instability. Our dynamical mean-field
calculations suggest that such ferromagnetic instability observed originates
from the formation of nearly flat dispersions close to the Fermi level, where
electron correlations induce strong orbital-selective renormalization and
manifestation of the kagome-frustrated bands. In addition, a significant
negative magnetoresistance signal is observed, which can be attributed to the
suppression of flat-band-induced ferromagnetic fluctuation, which further
supports the formation of flat bands in this compound. These findings broaden a
new prospect to harness correlated topological phases via multiorbital
correlations in 3$d$-based kagome systems.",2304.04928v1
2024-02-15,Standing spin waves in Permalloy-NiO bilayers as a probe of the interfacial exchange coupling,"Ferromagnetic/Antiferromagnetic (FM/AFM) bilayers dynamics have been a recent
topic of interest due to the interaction occurring at the interface, where the
magnetic moments of the AFM can be imprinted into the FM, and the exchange bias
field can affect these dynamics. Here, we investigate Permalloy (Py) and NiO
(Py/NiO) hybrids and for comparison single Py films in the broad Py thickness
range varied from few nm to 200 nm by using static (Kerr effect) and dynamic
(spin waves) measurements along with micromagnetic simulations. We observe
hybrid modes between uniform (ferromagnetic resonance FMR, n=0) and
perpendicular standing spin waves (PSSWs, n=1, 2) and a clear enhancement of
the PSSWs modes frequencies upon interfacing Py with NiO both from experiments
and simulations. This enhancement becomes less pronounced as the thickness of
the film increases, demonstrating its interfacial origin rooted in the exchange
coupling between the FM and AFM layers. Besides, through micromagnetic
simulations, we investigate and correlate changes in spatial profiles of the
PSSWs with the interfacial exchange coupling. As the thickness is increased, we
see that the n=1 and n=2 modes begin to couple with the fundamental FMR mode,
resulting in asymmetric (with respect the Py layer center) modes. Our results
suggest that PSSWs detection in a ferromagnet offers a means of probing the
interfacial exchange coupling with the adjacent AFM layer. Furthermore, the
controlled spatial symmetry breaking by the AFM layer enables engineering of
PSSWs with different spatial profiles in the FM.",2402.10292v1
1995-01-10,Formation of Dynamic Domains in Strongly Driven Ferromagnets,"Based on the dissipative Landau-Lifshitz equation, the spatiotemporal
structure formation problem is investigated in the region far above the
transverse ferromagnetic resonance instability. Apart from the external fields,
the model contains an isotropic exchange field, a shape demagnetisation field
and an anisotropy field. Numerical simulations exhibit in the rotating frame a
stationary domain structure with a precessing motion in the walls regimes.
Employing analytical methods, characteristic elements of this structure are
explained. This driven dissipative system shows similarities to equilibrium
systems of coexisting phases and organises itself in such a way that the local
dynamics tends to become hamiltonian.",9501006v2
1998-02-13,The Matrix Product Approach to Quantum Spin Ladders,"We present a manifestly rotational invariant formulation of the matrix
product method valid for spin chains and ladders. We apply it to 2 legged spin
ladders with spins 1/2, 1 and 3/2 and different magnetic structures labelled by
the exchange coupling constants, which can be ferromagnetic or
antiferromagnetic along the legs and the rungs of the ladder We compute ground
state energy densities, correlation lengths and string order parameters. We
present numerical evidence of the duality properties of the 3 different non
ferromagnetic spin 1/2 ladders. We show that the long range topological order
characteristic of isolated spin 1 chains is broken by the interchain coupling.
The string order correlation function decays exponentially with a finite
correlation length that we compute. A physical picture of the spin 1 ladder is
given in terms of a collection of resonating spin 1 chains. Finally for ladders
with spin equal or greater than 3/2 we define a class of AKLT states whose
matrix product coefficients are given by 9-j symbols.",9802150v1
1998-11-24,Microwave surface impedance of proximity-coupled superconducting (Nb) / spin-glass (CuMn) bilayers,"The surface impedance of Nb/CuMn (superconducting/spin-glass) bilayers has
been measured at 10 GHz with the parallel plate resonator technique to obtain
information about the exotic behavior of the order parameter in
superconducting/magnetic proximity systems. The data strongly differs from the
superconducting/normal-metal case, showing the magnetic nature of the CuMn
layer, which acts as a weak ferromagnet. The results are described in the
framework of two models for the electrodynamics of
superconducting/ferromagnetic (S/M) bilayers characterized by a
proximity-coupling length scale which is independent of temperature.",9811347v1
1999-08-02,Skyrmion Dynamics and NMR Line Shapes in QHE Ferromagnets,"The low energy charged excitations in quantum Hall ferromagnets are
topological defects in the spin orientation known as skyrmions. Recent
experimental studies on nuclear magnetic resonance spectral line shapes in
quantum well heterostructures show a transition from a motionally narrowed to a
broader `frozen' line shape as the temperature is lowered at fixed filling
factor. We present a skyrmion diffusion model that describes the experimental
observations qualitatively and shows a time scale of $\sim 50 \mu{\rm sec}$ for
the transport relaxation time of the skyrmions. The transition is characterized
by an intermediate time regime that we demonstrate is weakly sensitive to the
dynamics of the charged spin texture excitations and the sub-band electronic
wave functions within our model. We also show that the spectral line shape is
very sensitive to the nuclear polarization profile along the z-axis obtained
through the optical pumping technique.",9908029v2
2001-11-06,Discrete Breathers in Anisotropic Ferromagnetic Spin Chains,"We prove the existence of discrete breathers (time-periodic, spatially
localized solutions) in weakly coupled ferromagnetic spin chains with easy-axis
anisotropy. Using numerical methods we then investigate the continuation of
discrete breather solutions as the intersite coupling is increased. We find a
band of frequencies for which the 1-site breather continues all the way to the
soliton solution in the continuum. There is a second band, which abuts the
first, in which the 1-site breather does not continue to the soliton solution,
but a certain multi-site breather does. This banded structure continues, so
that in each band there is a particular multi-site breather which continues to
the soliton solution. A detailed analysis is presented, including an exposition
of how the bifurcation pattern changes as a band is crossed. The linear
stability of breathers is analyzed. It is proved that 1-site breathers are
stable at small coupling, provided a non-resonance condition holds, and an
extensive numerical stability analysis of 1-site and multisite breathers is
performed. The results show alternating bands of stability and instability as
the coupling increases.",0111085v1
2002-06-05,Many-Body Approch to Spin-Dependent Transport in Quantum Dot Systems,"By means of a diagram technique for Hubbard operators we show the existence
of a spin-dependent renormalization of the localized levels in an interacting
region, e.g. quantum dot, modeled by the Anderson Hamiltonian with two
conduction bands. It is shown that the renormalization of the levels with a
given spin direction is due to kinematic interactions with the conduction
sub-bands of the opposite spin. The consequence of this dressing of the
localized levels is a drastically decreased tunneling current for
ferromagnetically ordered leads compared to that of paramagnetically ordered
leads. Furthermore, the studied system shows a spin-dependent resonant
tunneling behaviour for ferromagnetically ordered leads.",0206048v1
2002-07-01,The polymer phase of the TDAE-C$_{60}$ organic ferromagnet,"The high-pressure Electron Spin Resonance (ESR) measurements were preformed
on TDAE-C$_{60}$ single crystals and stability of the polymeric phase was
established in the $P - T$ parameter space. At 7 kbar the system undergoes a
ferromagnetic to paramagnetic phase transition due to the pressure-induced
polymerization. The polymeric phase remains stable after the pressure release.
The depolymerization of the pressure-induced phase was observed at the
temperature of 520 K. Below room temperature, the polymeric phase behaves as a
simple Curie-type insulator with one unpaired electron spin per chemical
formula. The TDAE$^+$ donor-related unpaired electron spins, formerly
ESR-silent, become active above the temperature of 320 K and the Curie-Weiss
behavior is re-established.",0207034v1
2003-01-15,Electronic Transport in Hybrid Mesoscopic Structures: A Nonequilibrium Green Function Approach,"We present a unified transport theory of hybrid structures, in which a
confined normal state ($N$) sample is sandwiched between two leads each of
which can be either a ferromagnet ($F$) or a superconductor ($S$) via tunnel
barriers. By introducing a four-dimensional Nambu-spinor space, a general
current formula is derived within the Keldysh nonequilibrium Green function
formalism, which can be applied to various kinds of hybrid mesoscopic systems
with strong correlations even in the nonequilibrium situation. Such a formula
is gauge invariant. We also demonstrate analytically for some quantities, such
as the difference between chemical potentials, superconductor order parameter
phases and ferromagnetic magnetization orientations, that only their relative
value appears explicitly in the current expression. When applied to specific
structures, the formula becomes of the Meir-Wingreen-type favoring strong
correlation effects, and reduces to the Landauer-B\""uttiker-type in
noninteracting systems such as the double-barrier resonant structures, which we
study in detail beyond the wide-band approximation.",0301264v3
2003-06-19,Exchange anisotropy and the dynamic phase transition in thin ferromagnetic Heisenberg films,"Monte Carlo simulations have been performed to investigate the dependence of
the dynamic phase behavior on the bilinear exchange anisotropy of a classical
Heisenberg spin system. The system under consideration is a planar thin
ferromagnetic film with competing surface fields subject to a pulsed
oscillatory external field. The results show that the films exhibit a single
discontinuous dynamic phase transition (DPT) as a function of the anisotropy of
the bilinear exchange interaction in the Hamiltonian. Furthermore there is no
evidence of stochastic resonance (SR) associated with the DPT. These results
are in marked contrast to the continuous DPT observed in the same system as a
function of temperature and applied field strength for a fixed bilinear
exchange anisotropy.",0306502v1
2003-06-25,EPR and ferromagnetism in diluted magnetic semiconductor quantum wells,"Motivated by recent measurements of electron paramagnetic resonance (EPR)
spectra in modulation-doped CdMnTe quantum wells, [F.J. Teran {\it et al.},
Phys. Rev. Lett. {\bf 91}, 077201 (2003)], we develop a theory of collective
spin excitations in quasi-two-dimensional diluted magnetic semiconductors
(DMSs). Our theory explains the anomalously large Knight shift found in these
experiments as a consequence of collective coupling between Mn-ion local
moments and itinerant-electron spins. We use this theory to discuss the physics
of ferromagnetism in (II,Mn)VI quantum wells, and to speculate on the
temperature at which it is likely to be observed in n-type modulation doped
systems.",0306635v2
2003-07-13,"Structural and magnetoelectric properties of MFe2O4-PZT (M=Ni,Co) and (La)x(Ca,Sr)1-x - PZT multilayers","Thick film layered magnetoelectric composites consisting of ferromagnetic and
ferroelectric phases have been synthesized with nickel ferrite (NFO), cobalt
ferrite (CFO), La0.7Sr0.3MnO3 (LSMO), or La0.7Ca0.3MnO3 (LCMO) and lead
zirconate titanate (PZT). Structural, magnetic and ferromagnetic resonance
characterization shows evidence for defect free ferrites, but deterioration of
manganite parameters. The resistivity and dielectric constants are smaller than
expected values. The magnetoelectric effect (ME) is stronger in ferrite-PZT
than in manganite-PZT. The ME voltage coefficient aE at room temperature is the
highest in NFO-PZT and the smallest for LCMO-PZT. The transverse ME effect is
an order of magnitude stronger than the longitudinal effect. The magnitude of
aE correlates well with magnetic permeability for the ferrites.",0307309v1
2004-04-01,Phonon-Metamorphosis in Ferromagnetic Manganite Films: Probing the Evolution of an Inhomogeneous State,"The analysis of phonon anomalies provides valuable information about the
cooperative dynamics of lattice, spin and charge degrees of freedom.
Significant is the anomalous temperature dependence of the external modes
observed in La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) films. The two external modes
merge close to the ferromagnetic to paramagnetic transition at $T_C$ and,
moreover, two new modes evolve in this temperature range with strong resonances
at slightly higher frequencies. We propose that this observed phonon
metamorphosis probes the inhomogeneous Jahn-Teller distortion, manifest on the
temperature scale $T_C$. The analysis is based on the first observation of all
eight phonon modes in the metallic phase of LSMO and on susceptibility
measurements which identify a Griffiths-like phase.",0404023v1
2004-07-05,Prediction of Ferromagnetic Correlations in Coupled Double-Level Quantum Dots,"Numerical results are presented for transport properties of two coupled
double-level quantum dots. The results strongly suggest that under appropriate
circumstances the dots can develop a novel ferromagnetic (FM) correlation at
quarter-filling (one electron per dot). In the strong coupling regime (Coulomb
repulsion larger than electron hopping) and with the inter-dot tunneling larger
than the tunneling to the leads, an S=1 Kondo resonance develops in the density
of states, leading to a peak in the conductance. A qualitative 'phase diagram',
incorporating the new FM phase, is presented. It is also shown that the
conditions necessary for the FM regime are less restrictive than naively
believed, leading to its possible experimental observation in real quantum
dots.",0407109v2
2004-07-08,Magnetic Fluctuations in the Metallic State of Na$_{0.7}$CoO$_2$ Revealed by $^{23}$Na NMR,"Nuclear-magnetic-resonance (NMR) studies were performed in Na$_{0.7}$CoO$_2$
to investigate its magnetic properties from the microscopic point of view.
Na$_{0.7}$CoO$_2$ is a starting compound of the recently discovered
superconductor Na$_{0.35}$CoO$_2$$\cdot 1.3$H$_2$O, in which Co atoms form a
triangular structure. Although $^{23}$Na-NMR results show no magnetic anomaly
down to 1.5 K, Knight shift ($^{23}K$) and $^{23}(1/T_1T)$ of $^{23}$Na
continue to increase, suggestive of the vicinity of the magnetic phase. From
the relation between $^{23}K$ and $^{23}(1/T_1T)$, it is shown that
ferromagnetic fluctuations are dominant below 100 K. In addition to the
ferromagnetic correlations, antiferromagnetic fluctuations are also developed
in a low temperature region below 4 K. Magnetic fluctuations suggested by our
experiment are discussed.",0407195v1
2004-08-10,Coherent optical control of spin-spin interaction in doped semiconductors,"We provide a theory of laser-induced interaction between spins localized by
impurity centers in a semiconductor host. By solving exactly the problem of two
localized spins interacting with one itinerant exciton, an analytical
expression for the induced spin-spin interaction is given as a function of the
spin separation, laser energy, and intensity. We apply the theory to shallow
neutral donors (Si) and deep rare-earth magnetic impurities (Yb) in III-V
semiconductors. When the photon energy approaches a resonance related to
excitons bound to the impurities, the coupling between the localized spins
increases, and may change from ferromagnetic to anti-ferromagnetic. This
light-controlled spin interaction provides a mechanism for the quantum control
of spins in semiconductors for quantum information processing; it suggests the
realization of spin systems whose magnetic properties can be controlled by
changing the strength and the sign of the spin-spin interaction.",0408216v1
2004-09-05,"Error threshold in optimal coding, numerical criteria and classes of universalities for complexity","The free energy of the Random Energy Model at the transition point between
ferromagnetic and spin glass phases is calculated. At this point, equivalent to
the decoding error threshold in optimal codes, free energy has finite size
corrections proportional to the square root of the number of degrees. The
response of the magnetization to the ferromagnetic couplings is maximal at the
values of magnetization equal to half. We give several criteria of complexity
and define different universality classes. According to our classification, at
the lowest class of complexity are random graph, Markov Models and Hidden
Markov Models. At the next level is Sherrington-Kirkpatrick spin glass,
connected with neuron-network models. On a higher level are critical theories,
spin glass phase of Random Energy Model, percolation, self organized
criticality (SOC). The top level class involves HOT design, error threshold in
optimal coding, language, and, maybe, financial market. Alive systems are also
related with the last class. A concept of anti-resonance is suggested for the
complex systems.",0409107v1
2004-09-08,Spin-dependent Andreev reflection tunneling through a quantum dot with intradot spin-flip scattering,"We study Andreev reflection (AR) tunneling through a quantum dot (QD)
connected to a ferromagnet and a superconductor, in which the intradot
spin-flip interaction is included. By using the nonequibrium-Green-function
method, the formula of the linear AR conductance is derived at zero
temperature. It is found that competition between the intradot spin-flip
scattering and the tunneling coupling to the leads dominantes resonant
behaviours of the AR conductance versus the gate voltage.A weak spin-flip
scattering leads to a single peak resonance.However, with the spin-flip
scattering strength increasing, the AR conductance will develop into a double
peak resonannce implying a novel structure in the tunneling spectrum of the AR
conductance. Besides, the effect of the spin-dependent tunneling couplings, the
matching of Fermi velocity, and the spin polarization of the ferromagnet on the
AR conductance is eximined in detail.",0409180v1
2004-12-20,Current induced spin injection and surface torque in ferromagnetic metallic junctions,"Joint influence of two effects, namely, nonequilibrium spin injection by
current, and current induced surface torque, on spin-valve type ferromagnetic
metallic junctions is considered theoretically. The CPP configuration is
assumed. The consideration is based on solving a coupled set of equations of
motion for the mobile electron and lattice magnetizations. Boundary conditions
are derived from the total magnetization flux continuity condition. A
dispersion relation is derived for current dependent spin-wave fluctuations.
The fluctuations become unstable under current density exceeding some threshold
value. Joint action of the longitudinal spin injection and the torque lowers
the instability threshold. The spin injection softens spin wave frequency near
the threshold and can pin magnetization at the injecting contact. The pinning
rises under the current increasing, so that the appearance of new spin-wave
resonance lines can be observed.",0412523v1
2005-02-11,Angular Conductance Resonances of Quantum Dots Non-Collinearly Coupled to Ferromagnetic Leads,"The zero bias conductance of quantum dots coupled to ferromagnetic leads is
investigated. In the strong coupling regime, it is found that the conductance
is a non-monotonic function of the angle between the magnetisation directions
in the two contacts. This behaviour is an effect of the presence of the leads
which induces an angle dependent spin split of the quantum dot states, and spin
flip transitions between the quantum dot states whenever the magnetisation
directions of the leads are non-collinear which enhances the current density at
the chemical potential. In the weak coupling regime, the system reverts to
normal spin valve character.",0502288v2
2005-04-22,Perturbation of magnetostatic modes observed by FMRFM,"Magnetostatic modes of Yttrium Iron Garnet (YIG) films are investigated by
ferromagnetic resonance force microscopy (FMRFM). A thin film ``probe'' magnet
at the tip of a compliant cantilever introduces a local inhomogeneity in the
internal field of the YIG sample. This influences the shape of the sample's
magnetostatic modes, thereby measurably perturbing the strength of the force
coupled to the cantilever. We present a theoretical model that explains these
observations; it shows that tip-induced variation of the internal field creates
either a local ``potential barrier'' or ``potential well'' for the
magnetostatic waves. The data and model together indicate that local magnetic
imaging of ferromagnets is possible, even in the presence of long-range spin
coupling, through the induction of localized magnetostatic modes predicted to
arise from sufficiently strong tip fields.",0504598v1
2005-05-12,Dynamics of magnetization coupled to a thermal bath of elastic modes,"We study the dynamics of magnetization coupled to a thermal bath of elastic
modes using a system plus reservoir approach with realistic magnetoelastic
coupling. After integrating out the elastic modes we obtain a self-contained
equation for the dynamics of the magnetization.
  We find explicit expressions for the memory friction kernel and hence, {\em
via} the Fluctuation-Dissipation
  Theorem, for the spectral density of the magnetization thermal fluctuations.
  For magnetic samples in which the single domain approximation is valid, we
derive an equation for the dynamics of the uniform mode.
  Finally we apply this equation to study the dynamics of the uniform
magnetization mode in insulating ferromagnetic thin films.
  As experimental consequences we find that the fluctuation correlation time is
of the order of the ratio between the film thickness, $h$, and the speed of
sound in the magnet and that the line-width of the ferromagnetic resonance peak
should scale as $B_1^2h$ where $B_1$ is the magnetoelastic coupling constant.",0505331v3
2005-05-17,Magneto-transport characteristics of La1.4Ca1.6Mn2O7 thin film deposited by spray pyrolysis,"Polycrystalline thin films of double layer manganite La_1.4Ca_1.6Mn_2O_7
(DLCMO) have been deposited by nebulized spray pyrolysis on single crystal
LaAlO_3 substrates. These single phase films having grain size in the range
70-100 nm exhibit ferromagnetic transition at T_C ~ 107K. The short range
ferromagnetic ordering due to in plane spin coherence is evidenced to occur at
a higher temperature around 225 K. Insulator/semiconductor to metal transition
occurs at a lower temperature T_P ~ 55K. The transport mechanism above T_C is
of Mott`s variable range hopping type. Below T_C the current-voltage
characteristics show non-linear behaviour that becomes stronger with decreasing
temperature. At low temperatures below T_CA ~ 30K a magnetically frustrated
spin canted state is observed. The DLCMO films exhibit resonable low field
magnetoresistance and at 77K the magnetoresistance ratio is ~ 5% at 0.6 kOe and
\~ 13% at 3 kOe.",0505407v1
2005-05-31,Distinct order of Gd 4f and Fe 3d moments coexisting in GdFe4Al8,"Single crystals of flux-grown tetragonal GdFe4Al8 were characterized by
thermodynamic, transport, and x-ray resonant magnetic scattering measurements.
In addition to antiferromagnetic order at TN ~ 155 K, two low-temperature
transitions at T1 ~ 21 K and T2 ~ 27 K were identified. The Fe moments order at
TN with an incommensurate propagation vector (tau,tau,0) with tau varying
between 0.06 and 0.14 as a function of temperature, and maintain this order
over the entire T<TN range. The Gd 4f moments order below T2 with a
ferromagnetic component mainly out of plane. Below T1, the ferromagnetic
components are confined to the crystallographic plane. Remarkably, at low
temperatures the Fe moments maintain the same modulation as at high
temperatures, but the Gd 4f moments apparently do not follow this modulation.
The magnetic phase diagrams for fields applied in [110] and [001] direction are
presented and possible magnetic structures are discussed.",0506007v2
2005-10-01,Spin-polarized proximity effect in superconducting junctions,"We study spin dependent phonomena in superconducting junctions in both
ballistic and diffusive regimes. For ballistic junctions we study both
ferromagnet / $s$- and d-wave superconductor junctions and two dimensional
electron gas / s-wave superconductor junctions with Rashba spin-orbit coupling.
It is shown that the exchange field alway suppresses the conductance while the
Rashba spin-orbit coupling can enhance it. In the latter part of the article we
study the diffusive ferromagnet / insulator / $s$- and d-wave superconductor
junctions, where the proximity effect can be enhanced by the exchange field in
contrast to common belief. It is shown that the resonant proximity effect
originating from the exchange field strongly influences the tunneling
conductance and density of states.",0510008v2
2005-11-22,Magnetomechanical Torques in Small Magnetic Cantilevers,"We study the dnamics of small magnetic cantilevers, either made from Si
covered by a magnetic film or entirely ferromagnetic ones. The
magnetomechanical torques are found to cause line splittings in ferromagnetic
resonance spectra and magnetization reversal facilitated by mechanical degrees
of freedom. We show that the magnetomechanical torques can extend the limits of
detecting and exciting motion at the nanoscale. A ""nanomotor"" described here
effectively transforms rf magnetic fields into mechanical oscillations. We
furthermore propose to integrate mechanical oscillators into magnetoelectronic
devices that make use of current-induced spin-transfer torques. This opens new
possibilities for electric transducers of nanomechanical motion.",0511548v1
2005-12-08,Controlling spin in an electronic interferometer with spin-active interfaces,"We consider electronic current transport through a ballistic one-dimensional
quantum wire connected to two ferromagnetic leads. We study the effects of the
spin-dependence of interfacial phase shifts (SDIPS) acquired by electrons upon
scattering at the boundaries of the wire. The SDIPS produces a spin splitting
of the wire resonant energies which is tunable with the gate voltage and the
angle between the ferromagnetic polarizations. This property could be used for
manipulating spins. In particular, it leads to a giant magnetoresistance effect
with a sign tunable with the gate voltage and the magnetic field applied to the
wire.",0512176v2
2006-02-19,Origin of four-fold anisotropy in square lattices of circular ferromagnetic dots,"We discuss the four-fold anisotropy of in-plane ferromagnetic resonance (FMR)
field $H_r$, found in a square lattice of circular Permalloy dots when the
interdot distance $a$ gets comparable to the dot diameter $d$. The minimum
$H_r$, along the lattice $<11>$ axes, and the maximum, along the $<10>$ axes,
differ by $\sim$ 50 Oe at $a/d$ = 1.1. This anisotropy, not expected in
uniformly magnetized dots, is explained by a non-uniform magnetization
$\bm(\br)$ in a dot in response to dipolar forces in the patterned magnetic
structure. It is well described by an iterative solution of a continuous
variational procedure.",0602447v4
2006-02-22,Soliton pair dynamics in patterned ferromagnetic ellipses,"Confinement alters the energy landscape of nanoscale magnets, leading to the
appearance of unusual magnetic states, such as vortices, for example. Many
basic questions concerning dynamical and interaction effects remain unanswered,
and nanomagnets are convenient model systems for studying these fundamental
physical phenomena. A single vortex in restricted geometry, also known as a
non-localized soliton, possesses a characteristic translational excitation mode
that corresponds to spiral-like motion of the vortex core around its
equilibrium position. Here, we investigate, by a microwave reflection
technique, the dynamics of magnetic soliton pairs confined in lithographically
defined, ferromagnetic Permalloy ellipses. Through a comparison with
micromagnetic simulations, the observed strong resonances in the subgigahertz
frequency range can be assigned to the translational modes of vortex pairs with
parallel or antiparallel core polarizations. Vortex polarizations play a
negligible role in the static interaction between two vortices, but their
effect dominates the dynamics.",0602509v1
2006-07-31,Colossal magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4,"A detailed investigation of ZnCr2Se4 is presented which is dominated by
strong ferromagnetic exchange but orders antiferromagnetically at T_N = 21 K.
Specific heat C and thermal expansion Delta L/L exhibit sharp first-order
anomalies at the antiferromagnetic transition. T_N is strongly reduced and
shifted to lower temperatures by external magnetic fields and finally is fully
suppressed suggesting a field induced quantum critical behavior close to 60
kOe. Delta L/L(T) is unusually large and exhibits negative thermal expansion
below 75 K down to T_N indicating strong frustration of the lattice.
Magnetostriction Delta L/L(H) reveals colossal values (0.5x10^{-3}) comparable
to giant magnetostriction materials. Electron-spin resonance, however, shows
negligible spin-orbital coupling excluding orbitally induced Jahn-Teller
distortions. The obtained results point to a spin-driven origin of the
structural instability at T_N explained in terms of competing ferromagnetic and
antiferromagnetic exchange interactions yielding strong bond frustration.",0607811v1
2006-09-04,Half-Metallic Ferromagnetism and the spin polarization in CrO$_2$,"We present electronic structure calculations in combination with local and
non-local many-body correlation effects for the half-metallic ferromagnet
CrO$_2$. Finite-temperature Dynamical Mean Field Theory results show the
existence of non-quasiparticle states, which were recently observed as almost
currentless minority spin states near the Fermi energy in resonant scattering
experients. At zero temperatures, Variational Cluster Approach calculations
support the half-metallic nature of CrO$_2$ as seen in superconducting point
contact spectroscopy. The combination of these two techniques allowed us to
qualitatively describe the spin-polarization in CrO$_2$.",0609060v3
2006-12-06,Low-T_c Josephson junctions with tailored barrier,"Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb based
superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson tunnel
junctions with a thickness step in the metallic ferromagnetic
\Ni_{0.6}\Cu_{0.4} interlayer were fabricated. The step was defined by optical
lithography and controlled etching. The step height is on the scale of a few
angstroms. Experimentally determined junction parameters by current-voltage
characteristics and Fraunhofer pattern indicate an uniform F-layer thickness
and the same interface transparencies for etched and non-etched F-layers. This
technique could be used to tailor low-T_c Josephson junctions having controlled
critical current densities at defined parts of the junction area, as needed for
tunable resonators, magnetic-field driven electronics or phase modulated
devices.",0612164v2
2007-01-17,Beta-NMR of Isolated Lithium in Nearly Ferromagnetic Palladium,"The temperature dependence of the frequency shift and spin-lattice relaxation
rate of isolated, nonmagnetic Li-8 impurities implanted in a nearly
ferromagnetic host (Pd) are measured by means of beta-detected nuclear magnetic
resonance (b-NMR). The shift is negative, very large and increases
monotonically with decreasing T in proportion to the bulk susceptibility of Pd
for T > T*~ 100 K. Below T*, an additional shift occurs which we attribute to
the response of Pd to the defect. The relaxation rate is much slower than
expected for the large shift and is linear with T below T*, showing no sign of
additional relaxation mechanisms associated with the defect.",0701394v1
2007-01-25,Shape-induced phenomena in the finite size antiferromagnets,"It is of common knowledge that the direction of easy axis in the finite-size
ferromagnetic sample is controlled by its shape. In the present paper we show
that a similar phenomenon should be observed in the compensated
antiferromagnets with strong magnetoelastic coupling. Destressing energy which
originates from the long-range magnetoelastic forces is analogous to
demagnetization energy in ferromagnetic materials and is responsible for the
formation of equilibrium domain structure and anisotropy of macroscopic
magnetic properties. In particular, crystal shape may be a source of additional
uniaxial magnetic anisotropy which removes degeneracy of antiferromagnetic
vector or artificial 4th order anisotropy in the case of a square cross-section
sample. In a special case of antiferromagnetic nanopillars shape-induced
anisotropy can be substantially enhanced due to lattice mismatch with the
substrate. These effects can be detected by the magnetic rotational torque and
antiferromagnetic resonance measurements.",0701631v2
2007-10-02,"Determination of the micromagnetic parameters in (Ga,Mn)As using domain theory","The magnetic domain structure and magnetic properties of a ferromagnetic
(Ga,Mn)As epilayer with perpendicular magnetic easy-axis are investigated. We
show that, despite strong hysteresis, domain theory at thermodynamical
equilibrium can be used to determine the micromagnetic parameters. Combining
magneto-optical Kerr microscopy, magnetometry and ferromagnetic resonance
measurements, we obtain the characteristic parameter for magnetic domains
$\lambda_c$, the domain wall width and specific energy, and the spin stiffness
constant as a function of temperature. The nucleation barrier for magnetization
reversal and the Walker breakdown velocity for field-driven domain wall
propagation are also estimated.",0710.0479v1
2008-01-11,Charge pumping in magnetic tunnel junctions: Scattering theory,"We study theoretically the charge transport pumped by magnetization dynamics
through epitaxial FIF and FNIF magnetic tunnel junctions (F: Ferromagnet, I:
Insulator, N: Normal metal). We predict a small but measurable DC pumping
voltage under ferromagnetic resonance conditions for collinear magnetization
configurations, which may change sign as function of barrier parameters. A much
larger AC pumping voltage is expected when the magnetizations are at right
angles. Quantum size effects are predicted for an FNIF structure as a function
of the normal layer thickness.",0801.1779v3
2008-01-21,"Static and dynamic properties of 0, pi, and 0-pi ferromagnetic tunnel Josephson Junctions","We present experimental studies of static and dynamic properties of 0, pi and
0-pi superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson
junctions of small and intermediate length. In the underdamped limit these
junctions exhibit a rich dynamical behavior such as resonant steps on the
current-voltage characteristics. Varying the experimental conditions, zero
field steps, Fiske steps and Shapiro steps are observed with a high resolution.
A strong signature of the 0-pi Josephson junction is demonstrated by measuring
the critical current as a function of two components (B_x, B_y) of an in-plane
magnetic field. The experimental observation of a half-integer zero field step
in 0-pi SIFS junctions is presented.",0801.3229v1
2008-06-04,"Broadband electrical detection of spin excitations in (Ga,Mn)As using a photovoltage technique","We report on microwave photovoltage and simultaneous magnetotransport
measurements in a (Ga,Mn)As film oriented normal to the magnetic field. We
detect the ferromagnetic resonance over a broad frequency range of 2 GHz to
18.5 GHz and determine the spectroscopic g-factor and separate the Gilbert from
the inhomogeneous contribution to magnetization relaxation. Temperature
dependent measurements below the saturation magnetization indicate that the
photovoltage signal can serve as a sensitive tool to study the crystal
anisotropy. We demonstrate that the combination of spin dynamics with charge
transport is a promising tool to study microstructured ferromagnetic
semiconductor samples.",0806.0785v1
2008-09-18,Coexistence of Long-Range Magnetic Order and Superconductivity from Campbell Penetration Depth Measurements,"Application of a tunnel-diode resonator (TDR) technique for studies of the
vortex response in magnetic superconductors is described. Operating at very
small excitation fields and sufficiently high frequency, TDR was used to probe
small-amplitude linear AC response in several types of single crystals where
long-range magnetic order coexists with bulk superconductivity. Full local -
moment ferromagnetism destroys superconductivity and can coexist with it only
in a narrow temperature range ($\sim 0.3$ K). In contrast, weak ferromagnetic
as well as antiferromagnetic orders can coexist with bulk superconductivity and
may even lead to enhancements of vortex pinning. By analyzing the Campbell
penetration depth we find sharp increase of the true critical current in the
vicinity of the magnetic phase transitions. We conclude that critical magnetic
fluctuations are responsible for this enhancement.",0809.3154v1
2008-09-26,Damping and magnetic anisotropy of ferromagnetic GaMnAs thin films,"The magnetic properties of annealed, epitaxial Ga0.93Mn0.07As layers under
tensile and compressive stress have been investigated by X-band (9GHz) and
Q-band (35GHz) ferromagnetic resonance (FMR) spectroscopy. From the analysis of
the linewidths of the uniform mode spectra the FMR Gilbert damping factor
""alpha"" has been determined. At T=4K we obtain a minimum damping factor of
""alpha"" = 0.003 for the compressively stressed layer. Its value is not
isotropic. It has a minimum value for the easy axes orientations of the
magnetic field and increases with the measuring temperature. Its average value
is for both type of films of the order of 0.01 in spite of strong differences
in the inhomogeneous linewidth which vary between 20 Oe and 600 Oe for the
layers grown on GaAs and GaInAs substrates respectively.",0809.4644v2
2009-04-02,Fano-Kondo Spin Filter,"We study spin-dependent conductance in a system composed of a ferromagnetic
(FM) Scanning Tunneling Microscope (STM) tip coupled to a metallic host surface
with an adatom. The Kondo resonance is taken into account via the
Doniach-Sunjic spectral function. For short lateral tip-adatom distances and
due to the interplay between Kondo physics, quantum interfering effects and the
ferromagnetism of the tip, a spin-splitting of the Fano-Kondo line shape arises
in the conductance. A strong enhancement of the Fano-Kondo profile for the
majority spin component of the FM tip is observed. When the tip is placed on
the adatom, this gives a conductance 100 % polarized for a particular range of
bias voltage. The system thus can be used as a powerful generator of spin
polarized currents.",0904.0482v1
2009-04-06,Probing Quantum Hall Pseudospin Ferromagnet by Resistively Detected NMR,"Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to
investigate a two-subband electron system in a regime where quantum Hall
pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals
that the easy-axis QHPF state around the total filling factor $\nu =4 $ can be
detected by the RD-NMR measurement. Approaching one of the Landau level (LL)
crossing points, the RD-NMR signal strength and the nuclear spin relaxation
rate $1/T_{1}$ enhance significantly, a signature of low energy spin
excitations. However, the RD-NMR signal at another identical LL crossing point
is surprisingly missing which presents a puzzle.",0904.0917v1
2009-11-13,Quantifying spin Hall angles from spin pumping: Experiments and Theory,"Spin Hall effects intermix spin and charge currents even in nonmagnetic
materials and, therefore, ultimately may allow the use of spin transport
without the need for ferromagnets. We show how spin Hall effects can be
quantified by integrating permalloy/normal metal (N) bilayers into a coplanar
waveguide. A dc spin current in N can be generated by spin pumping in a
controllable way by ferromagnetic resonance. The transverse dc voltage detected
along the permalloy/N has contributions from both the anisotropic
magnetoresistance (AMR) and the spin Hall effect, which can be distinguished by
their symmetries. We developed a theory that accounts for both. In this way, we
determine the spin Hall angle quantitatively for Pt, Au and Mo. This approach
can readily be adapted to any conducting material with even very small spin
Hall angles.",0911.2725v2
2009-11-21,Spectroscopic Study of $^{75}$As and $^{139}$La NMR on Layered Structure Ferromagnet LaCoAsO,"$^{75}$As and $^{139}$La field-swept NMR spectra were obtained for the novel
weakly itinerant ferromagnet LaCoAsO with 2D layered structure above the Curie
temperature of 55 K. By analyzing NMR spectra, temperature dependences of
Knight shift $K$ and nuclear quadrupole resonance frequency $\nu_Q$ were
obtained successfully for each nucleus. We confirmed from the so-called
$K$-$\chi$ plots that the macroscopic magnetization of our {LaCoAsO} powder
sample is intrinsic and does not contain the contribution from impurity phases.
We estimated hyperfine coupling constants from the slope of $K$-$\chi$ plots
and compared to that of iron-arsenide superconductor.",0911.4166v2
2010-04-24,Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001),"Magnetic anisotropies of Co-implanted ZnO (0001) films grown on
single-crystalline Al2O3 (11-20) substrates have been studied by ferromagnetic
resonance (FMR) technique for different cobalt implantation doses. The FMR data
show that the easy and hard axes have a periodicity of 60 degrees in the film
plane, in agreement with the hexagonal structure of the ZnO films. This
six-fold in-plane magnetic anisotropy, which is observed for the first time in
ZnO-based diluted magnetic semiconductors, is attributed to the substitution of
cobalt on Zn sites in the ZnO structure, and a clear indication for long range
ferromagnetic ordering between substitutional cobalt ions in the
single-crystalline ZnO films.",1004.4291v1
2010-06-03,Minimization of Ohmic losses for domain wall motion in a ferromagnetic nanowire,"We study current-induced domain-wall motion in a narrow ferromagnetic wire.
We propose a way to move domain walls with a resonant time-dependent current
which dramatically decreases the Ohmic losses in the wire and allows to drive
the domain wall with higher speed without burning the wire. For any domain wall
velocity we find the time-dependence of the current needed to minimize the
Ohmic losses. Below a critical domain-wall velocity specified by the parameters
of the wire the minimal Ohmic losses are achieved by dc current. Furthermore,
we identify the wire parameters for which the losses reduction from its dc
value is the most dramatic.",1006.0725v1
2010-10-07,Power optimization for domain wall motion in ferromagnetic nanowires,"The current mediated domain-wall dynamics in a thin ferromagnetic wire is
investigated. We derive the effective equations of motion of the domain wall.
They are used to study the possibility to optimize the power supplied by
electric current for the motion of domain walls in a nanowire. We show that a
certain resonant time-dependent current moving a domain wall can significantly
reduce the Joule heating in the wire, and thus it can lead to a novel proposal
for the most energy efficient memory devices. We discuss how Gilbert damping,
non-adiabatic spin transfer torque, and the presence of Dzyaloshinskii-Moriya
interaction can effect this power optimization.",1010.1537v1
2011-04-29,Universality of the Kondo effect in quantum dots with ferromagnetic leads,"We investigate quantum dots in clean single-wall carbon nanotubes with
ferromagnetic PdNi-leads in the Kondo regime. In most odd Coulomb valleys the
Kondo resonance exhibits a pronounced splitting, which depends on the tunnel
coupling to the leads and an external magnetic field $B$, and only weakly on
gate voltage. Using numerical renormalization group calculations, we
demonstrate that all salient features of the data can be understood using a
simple model for the magnetic properties of the leads. The magnetoconductance
at zero bias and low temperature depends in a universal way on $g \mu_B (B-B_c)
/ k_B T_K$, where $T_K$ is the Kondo temperature and $B_c$ the external field
compensating the splitting.",1104.5699v1
2011-07-01,"High frequency magnetic behavior through the magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered ferromagnetic thin films","We studied the dynamics of magnetization through an investigation of the
magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered thin films grown by
magnetron sputtering. Impedance measurements were analyzed in terms of the
mechanisms responsible for their variations at different frequency intervals
and the magnetic and structural properties of the multilayers. Analysis of the
mechanisms responsible for magnetoimpedance according to frequency and external
magnetic field showed that for the CoFeB/Cu multilayer, ferromagnetic resonance
(FMR) contributes significantly to the magnetoimpedance effect at frequencies
close to 470 MHz. This frequency is low when compared to the results obtained
for CoFeB/Ta and CoFeB/Ag multilayers and is a result of the anisotropy
distribution and non-formation of regular bilayers in this sample. The MImax
values occurred at different frequencies according to the used non-magnetic
metal. Variations between 25% and 30% were seen for a localized frequency band,
as in the case of CoFeB/Ta and CoFeB/Ag, as well as for a wide frequency range,
in the case of CoFeB/Cu.",1107.0204v1
2011-07-05,Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of $La_{1.9}Sr_{0.1}CuO_4$ - $La_{0.67}Ca_{0.33}MnO_3$ - $La_{1.9}Sr_{0.1}CuO_4$,"Transport and Conductance spectra measurements of ramp-type junctions made of
cuprate superconducting $La_{1.9}Sr_{0.1}CuO_4$ electrodes and a manganite
ferromagnetic $La_{0.67}Ca_{0.33}MnO_3$ barrier are reported. At low
temperatures below $T_c$, the conductance spectra show Andreev-like broad peaks
superposed on a tunneling-like background, and sometimes also sub-gap Andreev
resonances. The energy gap values $\Delta$ found from fits of the data ranged
mostly between 7-10 mV. As usual, the gap features were suppressed under
magnetic fields but revealed the tunneling-like conductance background. After
field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always
higher than under zero field cooling, reflecting the negative magnetoresistance
of the manganite barrier. A signature of superparamagnetism was found in the
conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed
critical currents with barrier thickness of 12 nm or more, were shown to be an
artifact due to incomplete milling of one of the superconducting electrodes.",1107.0806v1
2011-10-26,Tunable Kondo effect in double quantum dots coupled to ferromagnetic contacts,"We investigate the effects induced by spin polarization in the contacts
attached to a serial double quantum dot. The polarization generates effective
magnetic fields and suppresses the Kondo effect in each dot. The super-exchange
interaction ($J_{\mathrm{AFM}}$), tuned by the inter-dot tunnelling rate $t$,
can be used to compensate the effective fields and restore the Kondo resonance
when the contact polarizations are aligned. As a consequence, the direction of
the spin conductance can be controlled and even reversed using electrostatic
gates alone. Furthermore, we study the associated two-impurity Kondo model and
show that a ferromagnetic exchange coupling ($J_{\mathrm{FM}}$) leads to an
effective spin-1 exchange-anisotropic Kondo model which exhibits a quantum
phase transition in the presence of partially polarized contacts.",1110.5819v2
2011-12-11,Spin-polarized current effect on antiferromagnet magnetization in a ferromagnet - antiferromagnet nanojunction: Theory and simulation,"Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
nanojunction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration. Numerical simulation
is carried out of the magnetization dynamics of the antiferromagnetic layer in
the nanojunction with spin-polarized current. Outside the instability range,
the simulation results coincide completely with analytical calculations using
linear approximation. In the instability range, undamped oscillations occur of
the longitudinal and transverse magnetization components.",1112.2362v1
2012-03-08,Ferromagnetic insulating state in tensile-strained LaCoO$_3$ thin films,"With local density approximation + Hubbard $U$ (LDA+$U$) calculations, we
show that the ferromagnetic (FM) insulating state observed in tensile-strained
LaCoO$_3$ epitaxial thin films is most likely a mixture of low-spin (LS) and
high-spin (HS) Co, namely, a HS/LS mixture state. Compared with other FM
states, including the intermediate-spin (IS) state (\textit{metallic} within
LDA+$U$), which consists of IS Co only, and the insulating IS/LS mixture state,
the HS/LS state is the most favorable one. The FM order in HS/LS state is
stabilized via the superexchange interactions between adjacent LS and HS Co. We
also show that Co spin state can be identified by measuring the electric field
gradient (EFG) at Co nucleus via nuclear magnetic resonance (NMR) spectroscopy.",1203.1861v1
2012-06-29,Ferromagnetism and superconductivity in P-doped CeFeAsO,"We report on superconductivity in CeFeAs1-xPxO and the possible coexistence
with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with
ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering
temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K
and does not shift to lower temperatures with further increase of the P
concentration. Therefore, a quantum-critical-point scenario with T^N_Fe -> 0K
which is widely discussed for the iron based superconductors can be excluded
for this alloy series. Surprisingly, thermal expansion and X-ray powder
diffraction indicate the absence of an orthorhombic distortion despite clear
evidence for short range AFM Fe-ordering from muon-spin-rotation measurements.
Furthermore, we discovered the formation of a sharp electron spin resonance
signal unambiguously connected with the emergence of FM ordering.",1206.7088v2
2012-07-05,Negative differential magneto-resistance in ferromagnetic wires with domain walls,"A domain wall in a ferromagnetic one-dimensional nanowire experiences current
induced motion due to its coupling with the conduction electrons. When the
current is not sufficient to drive the domain wall through the wire, or it is
confined to a perpendicular layer, it nonetheless experiences oscillatory
motion. In turn, this oscillatory motion of the domain wall can couple
resonantly with the electrons in the system affecting the transport properties
further. We investigate the effect of the coupling between these domain wall
modes and the current electrons on the transport properties of the system and
show that such a system demonstrates negative differential magnetoresistance
due to the resonant coupling with the low-lying modes of the domain wall
motion.",1207.1210v1
2012-10-18,Single-domain shape anisotropy in near-macroscopic Ni$_{80}$Fe$_{20}$ thin-film rectangles,"Shape anisotropy provides a simple mechanism to adjust the local bias field
in patterned structures. It is well known that for ellipsoidal particles $<1$
$\mu$m in size, a quasi-single domain state can be realized with uniform
anisotropy field. For larger patterned ferromagnetic thin-film elements, domain
formation is thought to limit the effectiveness of shape anisotropy. In our
work we show that very soft lithographically patterned Ni$_{80}$Fe$_{20}$ films
with control of induced magnetic anisotropy can exhibit shape anisotropy fields
in agreement with single-domain models, for both hysteresis loop measurements
at low field and ferromagnetic resonance measurements at high field. We show
the superiority of the fluxmetric form over the magnetometric form of
anisotropy estimate for thin films with control dimensions from 10 $\mu$m to
150 $\mu$m and in-plane aspect ratios above 10.",1210.5251v3
2013-01-18,Asymmetry-induced effects in Kondo quantum dots coupled to ferromagnetic leads,"We study the spin-resolved transport through single-level quantum dots
strongly coupled to ferromagnetic leads in the Kondo regime, with a focus on
contact and material asymmetry-related effects. By using the numerical
renormalization group method, we analyze the dependence of relevant spectral
functions, linear conductance and tunnel magnetoresistance on the system
asymmetry parameters. In the parallel magnetic configuration of the device the
Kondo effect is generally suppressed due to the presence of exchange field,
irrespective of system's asymmetry. In the antiparallel configuration, on the
other hand, the Kondo effect can develop if the system is symmetric. We show
that even relatively weak asymmetry may lead to the suppression of the Kondo
resonance in the antiparallel configuration and thus give rise to nontrivial
behavior of the tunnel magnetoresistance. In addition, by using the
second-order perturbation theory we derive general formulas for the exchange
field in both magnetic configurations of the system.",1301.4512v1
2013-01-24,Spin transport parameters in metallic multilayers determined by ferromagnetic resonance measurements of spin pumping,"We measured spin transport in nonferromagnetic (NM) metallic multilayers from
the contribution to damping due to spin pumping from a ferromagnetic Co90Fe10
thin film. The multilayer stack consisted of NM1/NM2/Co90Fe10(2 nm)/NM2/NM3
with varying NM materials and thicknesses. Using conventional theory for one
dimensional diffusive spin transport in metals, we show that the effective
damping due to spin pumping can be strongly affected by the spin transport
properties of each NM in the multilayer, which permits the use of damping
measurements to accurately determine the spin transport properties of the
various NM layers in the full five-layer stack. We find that due to its high
electrical resistivity, amorphous Ta is a poor spin conductor, in spite of a
short spin-diffusion length of 1.0 nm, and that Pt is an excellent spin
conductor by virtue of its low electrical resistivity and a spin diffusion
length of only 0.5 nm. Spin Hall effect measurements may have underestimated
the spin Hall angle in Pt by assuming a much longer spin diffusion length.",1301.5861v1
2013-03-11,Exotic Ising dynamics in a Bose-Hubbard model,"We explore the dynamical properties of a one-dimensional Bose-Hubbard model,
where two bosonic species interact via Feshbach resonance. We focus on the
region in the phase diagram which is described by an effective, low-energy
ferromagnetic Ising model in both transverse and longitudinal fields. In this
regime, we numerically calculate the dynamical structure factor of the
Bose-Hubbard model using the time-evolving block decimation method. In the
ferromagnetic phase, we observe both the continuum of excitations and the bound
states in the presence of a longitudinal field. Near the Ising critical point,
we observe the celebrated E8 mass spectrum in the excited states. We also point
out possible measurements which could be used to detect these excitations in an
optical lattice experiment.",1303.2408v2
2013-04-01,Phase competitions in epitaxial Pr$_{0.5}$Ca$_{0.5}$MnO$_3$/La$_{0.5}$Sr$_{0.5}$MnO$_3$ superlattices,"We studied the charge-orbital ordering in the superlattice of charge-ordered
insulating Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ and ferromagnetic metallic
La$_{0.5}$Sr$_{0.5}$MnO$_3$ by resonant soft x-ray diffraction. A
temperature-dependent incommensurability is found in the orbital order. In
addition, a large hysteresis is observed that is caused by phase competition
between insulating charge ordered and metallic ferromagnetic states. No
magnetic phase transitions are observed in contrast to bulk, confirming the
unique character of the superlattice. The deviation from the commensurate
orbital order can be directly related to the decrease of ordered-layer
thickness that leads to a decoupling of the orbital-ordered planes along the c
axis.",1304.0337v1
2013-04-09,Tuning the Ultrafast Spin Dynamics in Carrier-Density-Controlled Ferromagnets,"Ultrafast strengthening or quenching of the ferromagnetic order of
semiconducting Eu1-xGdxO was achieved by resonant photoexcitation. The
modification of the magnetic order is established within 3 ps as revealed by
optical second harmonic generation. A theoretical analysis shows that the
response is determined by the interplay of chemically and optically generated
carriers in a nonequilibrium scenario beyond the three-temperature model.
General criteria for the design of spintronics materials with tunable ultrafast
spin dynamics are given.",1304.2509v2
2013-05-03,Dependence of spin pumping spin Hall effect measurements on layer thicknesses and stacking order,"Voltages generated from inverse spin Hall and anisotropic magneto-resistance
effects via spin pumping in ferromagnetic (F)/non-magnetic (N) bilayers are
investigated by means of a broadband ferromagnetic resonance approach. Varying
the non-magnetic layer thickness enables the determination of the spin
diffusion length in Pd of 5.5 +/- 0.5 nm. We also observe a systematic change
of the voltage lineshape when reversing the stacking order of the F/N bilayer,
which is qualitatively consistent with expectations from spin Hall effects.
However, even after independent calibration of the precession angle, systematic
quantitative discrepancies in analyzing the data with spin Hall effects remain.",1305.0745v2
2013-05-07,Micromagnetic modelling of anisotropic damping in ferromagnet,"We report a numerical implementation of the Landau-Lifshitz-Baryakhtar
theory, which dictates that the micromagnetic relaxation term obeys the
symmetry of the magnetic crystal, i. e. replacing the single intrinsic damping
constant with a tensor of corresponding symmetry. The effect of anisotropic
relaxation is studied in thin saturated ferromagnetic disk and ellipse with and
without uniaxial magneto-crystalline anisotropy. We investigate the angular
dependency of the linewidth of magnonic resonances with respect to the given
structure of the relaxation tensor. The simulations suggest that the anisotropy
of the magnonic linewidth is determined by only two factors: the projection of
the relaxation tensor onto the plane of precession and the ellipticity of the
later.",1305.1641v2
2013-06-29,Coexistence of Half-Metallic Itinerant Ferromagnetism with Local-Moment Antiferromagnetism in Ba{0.60}K{0.40}Mn2As2,"Magnetization, nuclear magnetic resonance, high-resolution x-ray diffraction
and magnetic field-dependent neutron diffraction measurements reveal a novel
magnetic ground state of Ba{0.60}K{0.40}Mn2As2 in which itinerant
ferromagnetism (FM) below a Curie temperature TC = 100 K arising from the doped
conduction holes coexists with collinear antiferromagnetism (AFM) of the Mn
local moments that order below a Neel temperature TN = 480 K. The FM ordered
moments are aligned in the tetragonal ab-plane and are orthogonal to the
AFM-ordered Mn moments that are aligned along the c-axis. The magnitude and
nature of the low-T FM ordered moment correspond to complete polarization of
the doped-hole spins (half-metallic itinerant FM) as deduced from magnetization
and ab-plane electrical resistivity measurements.",1307.0091v2
2013-07-10,"Scaling of spin Hall angle in 3d, 4d and 5d metals from Y3Fe5O12/metal spin pumping","Pure spin currents generated by spin pumping in ferromagnet/nonmagnet (FM/NM)
bilayers produce inverse spin Hall effect (ISHE) voltages in the NM, from which
spin pumping and transport characteristics of the NM can be extracted. Due to
its exceptionally low damping, Y3Fe5O12 (YIG) is an important and widely used
FM for microwave devices and ferromagnetic resonance (FMR) spin pumping. Here
we report systematic investigation of spin pumping from 20-nm thick YIG thin
films to a series of 3d, 4d and 5d normal metals (Cu, Ag, Ta, W, Pt and Au)
with various spin-orbit coupling strengths. From enhanced Gilbert damping
obtained from the frequency dependence of FMR linewidths and ISHE signals, the
spin Hall angles and YIG/NM interfacial spin mixing conductances are
quantitatively determined for these metals. The spin Hall angles largely vary
as the fourth power of the atomic number, corroborating the dominant role of
spin-orbit coupling across a broad range in the inverse spin Hall effect.",1307.2648v2
2013-07-10,Inverse Spin Hall Effect in NiFe / Normal Metal Bilayers,"Spin pumping in ferromagnets provides a source of pure spin currents. Via the
inverse spin Hall effect a spin current is converted into a charge current and
a corresponding detectable DC-voltage. The ratio of injected spin current to
resulting charge current is given by the spin Hall angle. However, the number
of experiments more or less equals the number of different values for spin Hall
angles, even for the most studied normal metal platinum. This publication
provides a full study of inverse spin Hall effect and anisotropic
magnetoresistance for different NiFe(Py) / normal metal bilayers using a
coplanar waveguide structure. Angle and frequency dependent measurements
strongly suggest that spin pumping and inverse spin Hall effect can be used to
quantify spin Hall angles only if certain conditions are met. Ruling out the
anisotropic magnetoresistance as a parasitic voltage generating effect
measurements of the inverse spin Hall effect in Py/Pt and Py/Au yield spin Hall
angles of 0.09 and 0.008 respectively. Furthermore, DC-voltages at
ferromagnetic resonance for Py/Pt are studied as a function of temperature and
the results are compared to theoretical models.",1307.2947v1
2013-07-18,Non-equilibrium spin-current detection with a single Kondo impurity,"We present a theoretical study based on the Anderson model of the transport
properties of a Kondo impurity (atom or quantum dot) connected to ferromagnetic
leads, which can sustain a non-equilibrium spin current. We analyze the case
where the spin current is injected by an external source and when it is
generated by the voltage bias. Due to the presence of ferromagnetic contacts, a
static exchange field is produced that eventually destroys the Kondo
correlations. We find that such a field can be compensated by an appropriated
combination of the spin-dependent chemical potentials leading to the
restoration of the Kondo resonance. In this respect, a Kondo impurity may be
regarded as a very sensitive sensor for non-equilibrium spin phenomena.",1307.4970v2
2013-11-05,Spin accumulation detection of FMR driven spin pumping in silicon-based metal-oxide-semiconductor heterostructures,"The use of the spin Hall effect and its inverse to electrically detect and
manipulate dynamic spin currents generated via ferromagnetic resonance (FMR)
driven spin pumping has enabled the investigation of these dynamically injected
currents across a wide variety of ferromagnetic materials. However, while this
approach has proven to be an invaluable diagnostic for exploring the spin
pumping process it requires strong spin-orbit coupling, thus substantially
limiting the materials basis available for the detector/channel material
(primarily Pt, W and Ta). Here, we report FMR driven spin pumping into a weak
spin-orbit channel through the measurement of a spin accumulation voltage in a
Si-based metal-oxide-semiconductor (MOS) heterostructure. This alternate
experimental approach enables the investigation of dynamic spin pumping in a
broad class of materials with weak spin-orbit coupling and long spin lifetime
while providing additional information regarding the phase evolution of the
injected spin ensemble via Hanle-based measurements of the effective spin
lifetime.",1311.0965v1
2013-11-28,Dynamic Spin Fluctuations at $T\rightarrow 0$ in a Spin-1/2 Ferromagnetic Kagome Lattice,"We report magnetization, electron spin resonance (ESR), and muon spin
relaxation ($\mu $SR) measurements on single crystals of the $S=1/2$ (Cu$%
^{+2}$) kagom\'{e} compound Cu(1,3-benzendicarboxylate). The $\mu $SR is
carried to temperatures as low as 45 mK. The spin Hamiltonian parameters are
determined from the analysis of the magnetization and ESR data. We find that
this compound has anisotropic ferromagnetic interactions. Nevertheless, no spin
freezing is observed even at temperatures two orders of magnitude lower than
the coupling constants. In light of this finding, the relation between
persistent spin dynamics and spin liquid are reexamined.",1311.7411v1
2013-12-09,Spectroscopic study of the magnetic ground state of Nb$_{1-y}$Fe$_{2+y}$,"We have investigated single crystals and polycrystals from the series
Nb$_{1-y}$Fe$_{2+y}$, $-0.004 \leq y \leq 0.018$ by electron spin resonance,
muon spin relaxation and M\""ossbauer spectroscopy. Our data establish that at
lowest temperatures all samples exhibit bulk magnetic order. Slight Fe-excess
induces low-moment ferromagnetism, consistent with bulk magnetometry ($\simeq
0.06 ~\mu_B/{\rm Fe}$), Nb--rich and stoichiometric NbFe$_2$ display spin
density wave order with small magnetic moment amplitudes of the order $\sim
0.001 - 0.01 ~\mu_B/{\rm Fe}$. This provides microscopic evidence for a
modulated magnetic state on the border of ferromagnetism in NbFe$_2$.",1312.2357v4
2013-12-10,Spin Pumping and Inverse Spin Hall Effect in Platinum: The Essential Role of Spin-Memory Loss at Metallic Interfaces,"Through combined ferromagnetic resonance, spin-pumping and inverse spin Hall
effect experiments in Co|Pt bilayers and Co|Cu|Pt trilayers, we demonstrate
consistent values of spin diffusion length $\ell_{\rm sf}^{\rm Pt}=3.4\pm0.4$
nm and of spin Hall angle $\theta_{\rm SHE}^{\rm Pt}=0.051\pm0.004$ for Pt. Our
data and model emphasize on the partial depolarization of the spin current at
each interface due to spin-memory loss. Our model reconciles the previously
published spin Hall angle values and explains the different scaling lengths for
the ferromagnetic damping and the spin Hall effect induced voltage.",1312.2717v2
2013-12-17,Control of the in-plane anisotropy in off-stoichiometric NiMnSb,"NiMnSb is a ferromagnetic half-metal which, because of its rich anisotropy
and very low Gilbert damping, is a promising candidate for applications in
information technologies. We have investigated the in-plane anisotropy
properties of thin, MBE-grown NiMnSb films as a function of their Mn
concentration. Using ferromagnetic resonance (FMR) to determine the uniaxial
and four-fold anisotropy fields, 2KU/Ms and 2K1/Ms, we find that a small
variation in composition is sufficient to change the film from primarily
four-fold to primarily uniaxial behavior, allowing for continuous tuning of the
anisotropy. This provides valuable flexibility in designing new device
geometries.",1312.4781v2
2015-01-27,An experimental demonstration of room-temperature spin transport in n-type Germanium epilayers,"We report the first experimental demonstration of room-temperature spin
transport in n-type Ge epilayers grown on a Si(001) substrate. By utilizing
spin pumping under ferromagnetic resonance, which inherently endows a spin
battery function for semiconductors connected with the ferromagnet, a pure spin
current is generated in the n-Ge at room temperature. The pure spin current is
detected by using the inverse spin Hall effect of either Pt or Pd electrode on
the n-Ge. A theoretical model including a geometrical contribution allows to
estimate a spin diffusion length in n-Ge at room temperature to be 660 nm. The
temperature dependence of the spin relaxation time provides evidence for
Elliott-Yafet spin relaxation mechanism.",1501.06691v1
2015-03-04,Unusual ferromagnetic critical behavior owing to short-range antiferromagnetic correlations in antiperovskite Cu1-xNMn3+x(0.1<x<0.4),"For ferromagnets, varying from simple metals to strongly correlated
oxides,the critical behaviors near the Curie temperature (TC) can be grouped
into several universal classes. In this paper, we report an unusual critical
behavior in manganese nitrides Cu1-xNMn3+x(0.1<x<0.4). Although the critical
behavior below TC can be well described by mean field (MF) theory, robust
critical fluctuations beyond the expectations of any universal classes are
observed above TC in x=0.1. The critical fluctuations become weaker when x
increases, and the MF-like critical behavior is finally restored at x=0.4. In
addition, the paramagnetic susceptibility of all the samples deviates from the
Curie-Weiss (CW) law just above TC. This deviation is gradually smeared as x
increases. The short-range antiferromagnetic ordering above TC revealed by our
electron spin resonance measurement explains both the unusual critical behavior
and the breakdown of the CW law.",1503.01196v1
2015-04-21,Tailoring the magnetodynamic properties of nanomagnets using magnetocrystalline and shape anisotropies,"Magnetodynamical properties of nanomagnets are affected by the demagnetizing
fields created by the same nanoelements. In addition, magnetocrystalline
anisotropy produces an effective field that also contributes to the spin
dynamics. In this article we show how the dimensions of magnetic elements can
be used to balance crystalline and shape anisotropies, and that this can be
used to tailor the magnetodynamic properties. We study ferromagnetic ellipses
patterned from a 10 nm thick epitaxial Fe film with dimensions ranging from 50
x 150 nm to 150 x 450 nm. The study combines ferromagnetic resonance (FMR)
spectroscopy with analytical calculations and micromagnetic simulations, and
proves that the dynamical properties can be effectively controlled by changing
the size of the nanomagnets. We also show how edge defects in the samples
influence the magnetization dynamics. Dynamical edge modes localized along the
sample edges are strongly influenced by edge defects, and this needs to be
taken into account in understanding the full FMR spectrum",1504.05404v2
2015-04-23,Tunneling spectroscopy and Josephson current of superconductor-ferromagnet hybrids on the surface of a 3D TI,"We investigate the charge transport property of superconductor (S) /normal
metal (N) / ferromagnet insulator (FI) /(normal metal) N' and S/N/FI/N'/S
Josephson junctions on a three-dimensional topological insulator surface. We
find asymmetric local density of states (LDOSs) in a S/N/FI/N' junction and
show that the finite length of the N interlayer gives rise to subgap resonant
spikes in the differential conductance and LDOSs. In a S/N/FI/N'/S junction,
the Josephson current shows a non-sinusoidal current-phase relation and the N
(or N') interlayer decreases the magnitude of the critical current
monotonically.",1504.06208v2
2015-05-29,Strain behavior and lattice dynamics in Ni50Mn35In15,"The lattice dynamics in the polycrystalline shape-memory Heusler alloy
Ni$_{50}$Mn$_{35}$In$_{15}$ has been studied by means of resonant ultrasound
spectroscopy (RUS). RUS spectra were collected in a frequency range $100-1200$
kHz between 10 and 350 K. Ni$_{50}$Mn$_{35}$In$_{15}$ exhibits a ferromagnetic
transition at 313 K in the austenite and a martensitic transition at 248 K
accompanied by a change of the magnetic state. Furthermore it displays a
antiferromagnetic to ferromagnetic transition within the martensitic phase. We
determined the temperature dependence of the shear modulus and the acoustic
attenuation of Ni$_{50}$Mn$_{35}$In$_{15}$ and compared it with magnetization
data. Following the structural softening, which accompanies the martensitic
transition as a pretransitional phenomenon, a strong stiffening of the lattice
is observed at the martensitic magneto-structural transition. Only a weak
magnetoelastic coupling is evidenced at the Curie temperatures both in
austenite and martensite phase. The large acoustic damping in the martensitic
phase compared with the austenitic phase reflects the motion of the twin walls,
which freezes out in the low temperature region.",1505.08090v1
2015-06-02,Coexistence of antiferromagnetic and ferromagnetic spin correlations in SrCo2As2 revealed by 59Co and 75As NMR,"In nonsuperconducting, metallic paramagnetic SrCo2As2, inelastic neutron
scattering measurements have revealed strong stripe-type $\chi$(q) = ($\pi$,0)
antiferromagnetic (AFM) spin correlations. Here, using nuclear magnetic
resonance (NMR) measurements on 59Co and 75As nuclei, we demonstrate that
stronger ferromagnetic (FM) spin correlations coexist in SrCo2As2. Our NMR data
are consistent with density functional theory (DFT) calculations which show
enhancements at both q = ($\pi$,0) and the in-plane FM q = 0 wavevectors in
static magnetic susceptibility $\chi$(q). We suggest that the strong FM
fluctuations prevent superconductivity in SrCo2As2, despite the presence of
stripe-type AFM fluctuations. Furthermore, since DFT calculations have
consistently revealed similar enhancements of the $\chi$(q) at both q =
($\pi$,0) and q = 0 in the iron-based superconductors and parent compounds, our
observation of FM correlations in SrCo2As2 calls for detailed studies of FM
correlations in the iron-based superconductors.",1506.00994v2
2015-06-14,Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films,"We report the first experimental realization of orbital two-channel Kondo
(2CK) effect from two-level systems (TLSs) in epitaxial L10-MnAl films with
giant perpendicular magnetic anisotropy. The resistivity exhibits a
low-temperature (T) upturn with a clear transition from a lnT-dependence to
T1/2-dependence and deviation from it in three distinct T regimes, which are
independent of applied magnetic fields. The magnitudes of Kondo temperature and
energy splitting of the TLSs are greatly enhanced in comparison to those in
other systems exhibiting orbital 2CK, suggesting strong coupling between the
tunneling centers with conduction electrons via resonant scattering. These
results point to a considerable robustness of the orbital 2CK effect even in
the presence of ferromagnetic ordering and significant spin polarization of the
conduction electrons.",1506.04360v2
2015-08-31,All electrical manipulation of magnetization dynamics in a ferromagnet by antiferromagnets with anisotropic spin Hall effects,"We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets
using spin-torque ferromagnetic resonance tuned by a dc-bias current. The
observed spin torques predominantly arise from diffusive transport of spin
current generated by the spin Hall effect. We find a growth-orientation
dependence of the spin torques by studying epitaxial samples, which may be
correlated to the anisotropy of the spin Hall effect. The observed anisotropy
is consistent with first-principles calculations on the intrinsic spin Hall
effect. Our work demonstrates large tunable spin-orbit effects in
magnetically-ordered materials.",1508.07906v2
2015-09-03,All-Optical Vector Measurement of Spin-Orbit-Induced Torques Using Both Polar and Quadratic Magneto-Optic Kerr Effects,"We demonstrate that the magneto-optic-Kerr effect with normal light incidence
can be used to obtain quantitative optical measurements of both components of
spin-orbit-induced torque (both the antidamping and effective-field components)
in heavy-metal/ferromagnet bilayers. This is achieved by analyzing the
quadratic Kerr effect as well as the polar Kerr effect. The two effects can be
distinguished by properly selecting the polarization of the incident light. We
use this all-optical technique to determine the spin-orbit torques generated by
a series of Pt/Permalloy samples, finding values in excellent agreement with
spin-torque ferromagnetic resonance measurements.",1509.01266v1
2015-09-13,Effects of Cr substitution on the magnetic and transport properties and electronic states of SrRuO3 epitaxial thin films,"The effect of Cr substitution in a SrRuO3 epitaxial thin film on SrTiO3
substrate was investigated by measuring the magnetic and transport properties
and the electronic states. The ferromagnetic transition temperature of the
SrRu0.9Cr0.1O3 film (166 K) was higher than that of the SrRuO3 film (147 K).
Resonant photoemission spectroscopy experimentally revealed that the Cr 3dt2g
orbital is hybridized with the Ru 4dt2g orbital in the SrRu0.9Cr0.1O3 film,
supporting the assumption that the enhancement of the ferromagnetic transition
temperature through Cr substitution stems from the widening of energy bands due
to the hybridization of Cr 3dt2g and Ru 4dt2g orbitals. Furthermore, we found
that the Hall resistivity of the SrRu0.9Cr0.1O3 film at low temperature is not
a linear function of magnetic field in the high-field region where the
out-of-plane magnetization was saturated; this result suggests that the
SrRu0.9Cr0.1O3 film undergoes a structural transition at low temperature
accompanied with the modulation of the Fermi surface.",1509.03804v1
2015-10-06,"Interplay between Spin-Orbit Coupling and Strong Correlation Effects: Comparison of Three Osmate Double Perovskites: Ba$_{2}A$OsO$_{6}$ ($A=$Na, Ca, Y)","High formal valence Os-based double perovskites are a focus of current
interest because they display strong interplay of large spin orbit coupling and
strong electronic correlation. Here we present the electronic and magnetic
characteristics of a sequence of three cubic Os based double perovskites
Ba$_{2}$$A$OsO$_{6}$, ($A=$Na, Ca, Y), with formal valences (charge states) of
Os$^{+7}~(d^{1})$, Os$^{+6}(d^{2})$, Os$^{+5}(d^{3})$. For these first
principles based calculations we apply an ``exact exchange for correlated
electrons'' functional, with exact exchange applied in a hybrid fashion solely
to the Os($5d$) states. While Ba$_{2}$NaOsO$_{6}$ is a ferromagnetic Dirac-Mott
insulator studied previously, the other two show antiferromagnetic ordering
while all retain the cubic (undistorted) structure. For comparison purposes we
have investigated only the ferromagnetic ordered phase. A metal-insulator
transition is predicted to occur upon rotating the direction of magnetization
in all three materials, reflecting the central role of spin orbit coupling in
these small gap osmates. Surprises arising from comparing formal charge states
with the radial charge densities are discussed. Chemical shielding factors and
orbital susceptibilities are provided for comparison with future nuclear
magnetic resonance data.",1510.01719v1
2015-11-11,Photoinduced demagnetization and insulator-to-metal transition in ferromagnetic insulating BaFeO$_3$ thin films,"We studied the electronic and magnetic dynamics of ferromagnetic insulating
BaFeO3 thin films by using pump-probe time-resolved resonant x-ray reflectivity
at the Fe 2p edge. By changing the excitation density, we found two distinctly
different types of demagnetization with a clear threshold behavior. We assigned
the demagnetization change from slow (~ 150 ps) to fast (< 70 ps) to a
transition into a metallic state induced by laser excitation. These results
provide a novel approach for locally tuning magnetic dynamics. In analogy to
heat assisted magnetic recording, metallization can locally tune the
susceptibility for magnetic manipulation, allowing to spatially encode magnetic
information.",1511.03365v1
2016-02-23,Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films,"The Gilbert damping of ferromagnetic materials is arguably the most important
but least understood phenomenological parameter that dictates real-time
magnetization dynamics. Understanding the physical origin of the Gilbert
damping is highly relevant to developing future fast switching spintronics
devices such as magnetic sensors and magnetic random access memory. Here, we
report an experimental study of temperature-dependent Gilbert damping in
permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance.
From the thickness dependence, two independent contributions to the Gilbert
damping are identified, namely bulk damping and surface damping. Of particular
interest, bulk damping decreases monotonically as the temperature decreases,
while surface damping shows an enhancement peak at the temperature of ~50 K.
These results provide an important insight to the physical origin of the
Gilbert damping in ultrathin magnetic films.",1602.07325v1
2016-03-09,Evolution of perpendicular magnetized tunnel junctions upon annealing,"We study the evolution of perpendicularly magnetized tunnel junctions under
300 to 400 $^{\circ}$C annealing. The hysteresis loops do not evolve much
during annealing and they are not informative of the underlying structural
evolutions. These evolutions are better revealed by the frequencies of the
ferromagnetic resonance eigenmodes of the tunnel junction. Their modeling
provides the exchange couplings and the layers' anisotropies within the stack
which can serve as a diagnosis of the tunnel junction state after each
annealing step. The anisotropies of the two CoFeB-based parts and the two
Co/Pt-based parts of the tunnel junction decay at different rates during
annealing. The ferromagnet exchange coupling through the texture-breaking Ta
layer fails above 375$^{\circ}$C. The Ru spacer meant to promote a synthetic
antiferromagnet behavior is also insufficiently robust to annealing. Based on
these evolutions we propose optimization routes for the next generation tunnel
junctions.",1603.02824v1
2016-06-22,Induced magnetization and power loss for a periodically driven system of ferromagnetic nanoparticles with randomly oriented easy axes,"We study the effect of an elliptically polarized magnetic field on a system
of non-interacting, single-domain ferromagnetic nanoparticles characterized by
a uniform distribution of easy axis directions. Our main goal is to determine
the average magnetization of this system and the power loss in it. In order to
calculate these quantities analytically, we develop a general perturbation
theory for the Landau-Lifshitz-Gilbert (LLG) equation and find its steady-state
solution for small magnetic field amplitudes. On this basis, we derive the
second-order expressions for the average magnetization and power loss,
investigate their dependence on the magnetic field frequency, and analyze the
role of subharmonic resonances resulting from the nonlinear nature of the LLG
equation. For arbitrary amplitudes, the frequency dependence of these
quantities is obtained from the numerical solution of this equation. The impact
of transitions between different regimes of regular and chaotic dynamics of
magnetization, which can be induced in nanoparticles by changing the magnetic
field frequency, is examined in detail.",1606.07131v1
2016-06-27,Stability of a skyrmion and interaction of magnons,"The stability of a single Belavin-Polyakov (BP) skyrmion in isotropic
Heisenberg ferromagnet is studied. Such skyrmion is higher in energy than the
uniform ferromagnetic state and is thus metastable. Starting from the lattice
model in two spatial dimensions and using Maleyev-Dyson representation for spin
operators, we examine the effects of magnon-magnon interaction for two
quantities at $T=0$. First we discuss the self-energy corrections to magnon
energy. Second we analyze the two-particle Green's function and possible bound
states of two magnons. The simplicity of the model makes possible full analytic
treatment of all relevant processes. We found that the magnons remain
well-defined quasiparticles with a finite lifetime. The bound states of two
magnons are suppressed near the skyrmion, although they are not excluded far
away from it. A resonance for the magnons of dilational mode in the vicinity of
BP skyrmion is also found, which leads to a redistribution of the spectral
weight. We conclude that the BP skyrmion as the classical topological object is
not destroyed by quantum fluctuations.",1606.08308v2
2016-08-21,The Unusual Nature of Confined Modes in a Chiral System,"Nonreciprocity of spin wave propagation is a well-known consequence of
antisymmetric exchange contributions possible in magnetic spin systems that
lack inversion symmetry. In this case, it is possible for the energy of a state
to depend on the sign of its momentum as {\omega}(k) ${\neq}$ {\omega}(-k). We
discuss here the consequences of this nonreciprocity on counterpropagating
travelling spin wave states. In a confined geometry we find states with
well-defined nodes but with amplitudes that are modulated such that inversion
symmetry of the mode profile is lost. This feature leads to the suggestion that
additional features may become visible in, for example, ferromagnetic resonance
studies of ferromagnetic micro-elements with DMI, allowing a quantification of
the amplitude and direction of the DMI. Moreover, this interference between
nonreciprocal modes forms the basis for a generalized concept of mode
confinement.",1609.03417v1
2016-10-08,Perpendicularly magnetized CoFeB multilayers with tunable interlayer exchange for synthetic ferrimagnets,"A study of the multilayer system MgO/CoFeB(1.1nm)/Ta($t$)/CoFeB(0.8nm)/MgO is
presented, where the two CoFeB layers are separated by a Ta interlayer of
varying thickness $t$. The magnetization properties deduced from complementary
techniques such as superconducting quantum interference magnetometry,
ferromagnetic resonance frequency measurements and Brillouin light scattering
spectroscopy can be tuned by changing the Ta thickness between $t$=0.25 nm, 0.5
nm and 0.75 nm. For $t$=0.5 nm, a ferromagnetic coupling is observed, whereas
for t=0.75 nm, the antiferromagnetic coupling needed to construct a synthetic
ferrimagnet is realized. In the later case, the shape of magnetic domain walls
between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic
alignment is very different. This behavior can be interpreted as a result of
the change in dipolar as well as interlayer exchange energy and domain wall
pinning, which is an important conclusion for the realization of data storage
devices based on synthetic ferri- and antiferromagnets.",1610.02550v1
2016-10-22,Enhanced spin-orbit torque via modulation of spin current absorption,"The magnitude of spin-orbit torque (SOT), exerted to a ferromagnet (FM) from
an adjacent heavy metal (HM), strongly depends on the amount of spin currents
absorbed in the FM. We exploit the large spin absorption at the Ru interface to
manipulate the SOTs in HM/FM/Ru multilayers. While the FM thickness is smaller
than its spin dephasing length of 1.2 nm, the top Ru layer largely boosts the
absorption of spin currents into the FM layer and substantially enhances the
strength of SOT acting on the FM. Spin-pumping experiments induced by
ferromagnetic resonance support our conclusions that the observed increase in
the SOT efficiency can be attributed to an enhancement of the spin-current
absorption. A theoretical model that considers both reflected and transmitted
mixing conductances at the two interfaces of FM is developed to explain the
results.",1610.06989v1
2018-04-10,Conductance resonances and crossing of the edge channels in the quantum Hall ferromagnet state of Cd(Mn)Te microstructures,"In this paper we report on the observation of very high and narrow
magnetoconductance peaks which we attribute to the transition to quantum Hall
ferromagnet (QHFM) state occurring at the edges of the sample. We show that the
expected spatial degeneracy of chiral edge channels is spontaneously lifted in
agreement with theoretical studies performed within the Hartree-Fock
approximation. We indicate also that separated edge currents which flow in
parallel, may nevertheless cross at certain points, giving rise to the
formation of topological defects or one-dimensional magnetic domains.
Furthermore, we find that such local crossing of chiral channels can be induced
on demand by coupling spin states of a Landau level to different current
terminals and applying a DC source-drain voltage.",1804.03386v3
2018-04-23,Thermoelectric radiation detector based on a superconductor-ferromagnet junction: calorimetric regime,"We study the use of a thermoelectric junction as a thermal radiation detector
in the calorimetric regime, where single radiation bursts can be separated in
time domain. We focus especially on the case of a large thermoelectric figure
of merit $ZT$ affecting significantly for example the relevant thermal time
scales. This work is motivated by the use of hybrid superconductor/ferromagnet
systems in creating an unprecedentedly high low-temperature $ZT$ even exceeding
unity. Besides constructing a very general noise model which takes into account
cross correlations between charge and heat noise, we show how the detector
signal can be efficiently multiplexed by the use of resonant LC circuits giving
a fingerprint to each pixel. We show that for realistic detectors operating at
temperatures around 100 to 200 mK, the energy resolution can be as low as 1
meV. This allows for a broadband single-photon resolution at photon frequencies
of the order or below 1 THz.",1804.08319v1
2018-11-25,Spin current cross-correlations as a probe of magnon coherence,"Motivated by the important role of the normalized second order coherence
function, often called $g^{(2)}$, in the field of quantum optics, we propose a
method to determine magnon coherence in solid-state devices. Namely, we show
that the cross-correlations of pure spin-currents injected by a ferromagnet
into two metal leads, normalized by their dc value, replicate the behavior of
$g^{(2)}$ when magnons are driven far from equilibrium. We consider two
scenarios: driving by ferromagnetic resonance, which leads to the coherent
occupation of a single mode, and driving by heating of the magnons, which leads
to an excess of incoherent magnons. We find an enhanced normalized
cross-correlation in the latter case, thereby demonstrating bunching of
nonequilibrium thermal magnons due to their bosonic statistics. Our results
contribute to the burgeoning field of quantum magnonics, which seeks to explore
and exploit the quantum nature of magnons.",1811.10001v1
2020-07-17,Unraveling nanoscale magnetic ordering in Fe3O4 nanoparticle assemblies via x-rays,": Understanding the correlations between magnetic nanoparticles is important
for nanotechnologies, such as high-density magnetic recording and biomedical
applications, where functionalized magnetic particles are used as contrast
agents and for drug delivery. The ability to control the magnetic state of
individual particles depends on the good knowledge of magnetic correlations
between particles when assembled. Inaccessible via standard magnetometry
techniques, nanoscale magnetic ordering in self-assemblies of Fe3O4
nanoparticles is here unveiled via x-ray resonant magnetic scattering (XRMS).
Measured throughout the magnetization process, the XRMS signal reveals
size-dependent inter-particle magnetic correlations. Smaller (5 nm) particles
show little magnetic correlation, even when tightly close-packed, yielding to
mostly magnetic disorder in the absence of external field, which is
characteristic of superparamagnetic behavior. In contrast, larger (11 nm)
particles tend to be strongly correlated, yielding a mix of magnetic orders
including ferromagnetic and anti-ferromagnetic orders. These strong magnetic
correlations are present even when the particles are sparsely distributed.",2007.09226v1
2020-07-29,Tuning Spin Current Injection at Ferromagnet/Non-Magnet Interfaces by Molecular Design,"There is a growing interest in utilizing the distinctive material properties
of organic semiconductors for spintronic applications. Here, we explore
injection of pure spin current from Permalloy into a small molecule system
based on dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) at ferromagnetic
resonance. The unique tunability of organic materials by molecular design
allows us to study the impact of interfacial properties on the spin injection
efficiency systematically. We show that both, spin injection efficiency at the
interface as well as the spin diffusion length can be tuned sensitively by the
interfacial molecular structure and side chain substitution of the molecule.",2007.16068v1
2010-05-10,"Exchange constant and domain wall width in (Ga,Mn)(As,P) films with self-organization of magnetic domains","The incorporation of Phosphorus into (Ga,Mn)As epilayers allows for the
tuning of the magnetic easy axis from in-plane to perpendicular-to-plane
without the need for a (Ga,In)As template. For perpendicular easy axis, using
magneto-optical imaging a self-organized pattern of up- and down-magnetized
domains is observed for the first time in a diluted magnetic semiconductor.
Combining Kerr microscopy, magnetometry and ferromagnetic resonance
spectroscopy, the exchange constant and the domain wall width parameter are
obtained as a function of temperature. The former quantifies the effective
Mn-Mn ferromagnetic interaction. The latter is a key parameter for domain wall
dynamics. The comparison with results obtained for (Ga,Mn)As/(Ga,In)As reveals
the improved quality of the (Ga,Mn)As$_{1-y}$P$_y$ layers regarding domain wall
pinning, an increase of the domain wall width parameter and of the effective
Mn-Mn spin coupling. However, at constant Mn doping, no significant increase of
this coupling is found with increasing P concentration in the investigated
range.",1005.1494v1
2013-08-05,"Ferromagnetic response of a ""high-temperature"" quantum antiferromagnet","We study the finite temperature antiferromagnetic phase of the ionic Hubbard
model in the strongly interacting limit using quantum Monte Carlo based
dynamical mean field theory. We find that the ionic potential plays a dual role
in determining the antiferromagnetic order. A small ionic potential (compared
to Hubbard repulsion) increases the super-exchange coupling in the projected
sector of the model, leading to an increase in the Neel temperature of the
system. A large ionic potential leads to resonance between projected
antiferromagnetically ordered configurations and density ordered configurations
with double occupancies, thereby killing antiferromagnetism in the system. This
novel way of degrading antiferromagnetism leads to spin polarization of the low
energy single particle density of states. The dynamic response of the system
thus mimics ferromagnetic behaviour, although the system is still an
antiferromagnet in terms of the static spin order.",1308.1091v2
2017-01-19,Spin-filtering in superconducting junction with the manganite interlayer,"We report on the electronic transport and the impact of spin-filtering in
mesa-structures made of epitaxial thin films of cuprate superconductor
YBa2Cu3Ox(YBCO) and the manganite LaMnO3 (LMO) interlayer with the Au/Nb
counterelectrode. Ferromagnetic resonance measurements of heterostructure
Au/LMO/YBCO shows ferromagnetic state at temperatures below 150 K as in the
case of reference LMO film grown on the neodymium gallate substrate. The
heights of the tunneling barrier evaluated from resistive characteristics of
mesa-structures at different thickness of interlayer showed an exponential
decrease from 30 mV down to 5 mV with the increase of manganite interlayer
thickness. Temperature dependence of the conductivity of mesa-structures could
be described taking into account the d-wave superconductivity in YBCO and a
spin filtering of the electron transport. Spin filtering is supported also by
measurements of magneto-resistance and the high sensitivity of mesa-structure
conductivity to weak magnetic fields.",1701.05364v1
2017-01-27,A unified description of collective magnetic excitations,"In this work, we define a set of analytic tools to describe the dynamic
response of the magnetization to small perturbations, which can be used on its
own or in combination with micromagnetic simulations and does not require
saturation. We present a general analytic description of the ferromagnetic high
frequency susceptibility tensor to describe angular as well as frequency
dependent ferromagnetic resonance spectra and account for asymmetries in the
line shape. Furthermore, we expand this model to reciprocal space and show how
it describes the magnon dispersion. Finally we suggest a trajectory dependent
solving tool to describe the equilibrium states of the magnetization.",1701.09078v2
2017-04-01,Band filling control of the Dzyaloshinskii-Moriya interaction in weakly ferromagnetic insulators,"We observe and explain theoretically a dramatic evolution of the
Dzyaloshinskii-Moriya interaction in the series of isostructural weak
ferromagnets, MnCO$_3$, FeBO$_3$, CoCO$_3$ and NiCO$_3$. The sign of the
interaction is encoded in the phase of x-ray magnetic diffraction amplitude,
observed through interference with resonant quadrupole scattering. We find very
good quantitative agreement with first-principles electronic structure
calculations, reproducing both sign and magnitude through the series, and
propose a simplified `toy model' to explain the change in sign with 3 d shell
filling. The model gives a clue for qualitative understanding of the evolution
of the DMI in Mott and charge transfer insulators.",1704.00161v2
2011-11-24,Magnetic proximity effect in $\mathbf{YBa_2Cu_3O_7/La_{2/3}Ca_{1/3}MnO_3}$ and $\mathbf{YBa_2Cu_3O_7/LaMnO_{3+δ}}$ superlattices,"Using neutron reflectometry and resonant x-ray techniques we studied the
magnetic proximity effect (MPE) in superlattices composed of superconducting
YBa$_2$Cu$_3$O$_7$ (YBCO) and ferromagnetic-metallic (FM-M)
La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) or ferromagnetic-insulating (FM-I)
LaMnO$_{3+\delta}$ (LMO). We find that the MPE strongly depends on the
electronic state of the manganite layers, being pronounced for the FM-M LCMO
and almost absent for FM-I LMO. We also detail the change of the magnetic depth
profile due to the MPE and provide evidence for its intrinsic nature.",1111.5772v2
2011-11-30,Theory of the ac spin-valve effect,"The spin-valve complex magnetoimpedance of symmetric ferromagnet/normal
metal/ferromagnet junctions is investigated within the drift-diffusion
(standard) model of spin injection. The ac magnetoresistance---the real part
difference of the impedances of the parallel and antiparallel magnetization
configurations---exhibits an overall damped oscillatory behavior, as an
interplay of the diffusion and spin relaxation times. In wide junctions the ac
magnetoresistance oscillates between positive and negative values, reflecting
resonant amplification and depletion of the spin accumulation, while the line
shape for thin tunnel junctions is predicted to be purely Lorentzian. The ac
spin-valve effect could be a technique to extract spin transport and spin
relaxation parameters in the absence of a magnetic field and for a fixed sample
size.",1111.7244v1
2011-12-28,Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism,"We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin
films using x-ray magnetic circular dichroism (XMCD) and
resonance-photoemission spectroscopy. From the Mn 2$p$$\rightarrow3d$ XMCD
results, it is shown that, while XMCD signals only due to paramagnetic
Mn$^{2+}$ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic and
ferromagnetic Mn$^{2+}$ ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N
revealed that the localized Mn$^{2+}$ ground state and Mn$^{2+}$ state
hybridized with ligand hole coexisted, implying $p$-$d$ exchange coupling. In
the valence-band spectra, spectral weight near the Fermi level was suppressed,
suggesting that interaction between magnetic moments in ZnO:Mn,N has localized
nature.",1201.0006v1
2012-01-12,Influence of a transverse static magnetic field on the magnetic hyperthermia properties and high-frequency hysteresis loops of ferromagnetic FeCo nanoparticles,"The influence of a transverse static magnetic field on the magnetic
hyperthermia properties is studied on a system of large-losses ferromagnetic
FeCo nanoparticles. The simultaneous measurement of the high-frequency
hysteresis loops and of the temperature rise provides an interesting insight
into the losses and heating mechanisms. A static magnetic field of only 40 mT
is enough to cancel the heating properties of the nanoparticles, a result
reproduced using numerical simulations of hysteresis loops. These results cast
doubt on the possibility to perform someday magnetic hyperthermia inside a
magnetic resonance imaging setup.",1201.2536v1
2016-08-03,"Nearly ferromagnetic metal state in the collapsed tetragonal phase of YFe$_2$(Ge,Si)$_2$","The surprising discovery of tripling the superconducting critical temperature
of KFe$_2$As$_2$ at high pressures issued an intriguing question of how the
superconductivity in the collapsed tetragonal phase differs from that in the
non-collapsed phases of Fe-based superconductors. Here we report $^{89}$Y
nuclear magnetic resonance study of YFe$_2$Ge$_{x}$Si$_{2-x}$ compounds whose
electronic structure is similar to that of iron-pnictide collapsed tetragonal
phases already at ambient pressure. Fe(Ge,Si) layers show strong ferromagnetic
spin fluctuations whereas layers are coupled antiferromagnetically -- both
positioning the studied family close to a quantum critical point. Next,
localized moments attributed either to Fe interstitial or antisite defects may
account for magnetic impurity pair-breaking effects thus explaining the
substantial variation of superconductivity among different YFe$_2$Ge$_2$
samples.",1608.01130v1
2016-12-29,Spin-Pairing Correlations and Spin Polarization of Majorana Bound States in Two-Dimensional Topological Insulator Systems,"We demonstrate that zero-energy Majorana bound state, in the ferromagnetic
insulator (FI)-superconductor (SC) junction formed on the edge of
two-dimensional topological insulator, exhibits three types of spin-triplet
pairing correlations and its spin polarization direction is position
independent in ferromagnetic insulator. When an electron is injected with a
spin (anti-)parallel to this direction, equal-spin Andreev reflection exhibits
the widest (narrowest) resonance peak. Similar behaviour is found when the
coupling between two Majorana bound states in a FI-SC-FI junction is invoked,
though an additional weak spin-singlet pairing correlation is generated. These
signatures can readily facilitate the experimental detection of spin-triplet
correlations and spin polarization of Majorana bound states.",1612.09127v1
2017-06-05,Terahertz-driven magnetism dynamics in the orthoferrite DyFeO3,"Terahertz driven magnetization dynamics are explored in the orthoferrite
DyFeO3. A high-field, single cycle THz pulse is used to excite magnon modes in
the crystal together with other resonances. Both quasi-ferromagnetic and
quasi-antiferromagnetic magnon modes are excited and appear in time-resolved
measurements of the Faraday rotation. Other modes are also observed in the
measurements of the time-resolved linear birefringence. Analysis of the
excitation process reveals that despite larger than expected electro-optical
susceptibility it is mainly the THz magnetic field that couples to the
quasi-ferromagnetic and quasi-antiferromagnetic magnon branches.",1706.01545v1
2017-07-25,3D MOKE spin-orbit torque magnetometer,"We demonstrate simultaneous detection of current driven antidamping-like and
field-like spin-orbit torques in heavy metal/ferromagnetic metal bilayers by
measuring all three magnetization components m_(x,) m_y, and m_z using the
vector magneto-optic Kerr effect. We have also implemented a self-calibration
method to accurately determine the effective fields of spin-orbit torques. With
this technique, we investigate the magnitude and direction of spin-orbit
torques in a series of platinum/permalloy samples. The values found are in
excellent agreement with results obtained via quadratic magneto-optic Kerr
effect, planar Hall effect, and spin transfer ferromagnetic resonance
measurements.",1707.08565v1
2017-10-25,Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation,"The possibility to generate short spin waves is of great interest in the
field of magnonics nowadays. We present an effective and technically affordable
way of conversion of long spin waves, which may be generated by conventional
microwave antenna, to the short, sub-micrometer waves. It is achieved by
grating-assisted resonant dynamic dipolar interaction between two ferromagnetic
layers separated by some distance. We analyze criteria for the optimal
conversion giving a semi-analytical approach for the coupling coefficient. We
show by the numerical calculations the efficient energy transfer between layers
which may be either of co-directional or contra-directional type. Such a system
may operate either as a short spin wave generator or a frequency filter, moving
foreward possible application of magnonics.",1710.09138v1
2019-06-14,Mechanisms of FMR line broadening in CoFeB-LiNbO$_3$ granular films in the vicinity of metal-insulator transition,"Metal-insulator (CoFeB)$_x$(LiNbO$_3$)$_{100-x}$ nanocomposite films with
different content of the ferromagnetic (FM) phase $x$ are investigated by
ferromagnetic resonance (FMR) technique. A strong change of the FMR line shape
is observed in the vicinity of metal-insulator transition (MIT) of the film,
where the hopping-type conductivity $\sigma$ modifies to the regime of a strong
intergranular tunnelling, characterized by a logarithmic dependence $\sigma(T)$
at high temperatures. It is shown that below MIT, the FMR linewidth is mainly
determined by the inhomogeneous distribution of the local anisotropy axes in
the film plane. Above MIT, the contribution of this inhomogeneity to the line
broadening decreases. At the same time, two-magnon magnetic relaxation
processes begin to play a significant role in the formation of the linewidth.
The observed behaviour indicates the critical role of interparticle exchange in
the tunnelling regime above MIT of the nanocomposite.",1906.06320v2
2019-06-18,Anomalous spin-orbit field via Rashba-Edelstein effect at W/Pt interface,"We have studied spin-orbit (SO) field in Ni$_{80}$Fe$_{20}$(Py)/W/Pt trilayer
by means of spin-torque ferromagnetic resonance, and demonstrated that the W/Pt
interface generates an extra SO field acting on the Py layer. This
unprecedented field originates from the following three processes, 1) spin
accumulation at W/Pt interface via the Rashba-Edelstein effect, 2) diffusive
spin transport in the W layer, and 3) spin absorption into the Py layer through
accumulation at the Py/W interface. Our result means that we can create extra
SO field away from the ferromagnet/ metal interface and control its strength by
a combination of two different metals.",1906.07314v2
2019-06-24,Large Spin Anomalous Hall Effect in L1$\rm_{0}$-FePt: Symmetry and Magnetization Switching,"We quantitatively evaluate a spin anomalous Hall effect (SAHE), generating
spin angular momentum flow (spin current, $J_{\rm s}$), in an L1$\rm_{0}$-FePt
ferromagnet by exploiting giant magnetoresistance devices with L1$\rm_{0}$-FePt
/ Cu / Ni$\rm_{81}$Fe$\rm_{19}$ . From the ferromagnetic resonance linewidth
modulated by the charge current ($J_{\rm c}$) injection, the spin anomalous
Hall angle ($ \alpha_{\rm SAH} $) is obtained to be 0.25 $ \pm $ 0.03. The
evaluation of $ \alpha_{\rm SAH} $ at different configurations between $J_{\rm
c}$ and magnetization enables us to discuss the symmetry of SAHE and gives the
unambiguous evidence that SAHE is the source of $J_{\rm s}$. Thanks to the
large $ \alpha_{\rm SAH} $, we demonstrate the SAHE-induced magnetization
switching.",1906.09730v1
2019-09-29,Charge and spin textures of Ising quantum Hall ferromagnet domain walls,"We investigate the charge and spin structures associated with arbitrary
smooth polarization textures in Ising (integer) quantum Hall ferromagnets. We
consider the case where the two polarizations (denoted ""pseudospin"" up and
down) correspond to states with opposite physical spin and different Landau
level indices, $n\uparrow$ and $m\downarrow$. We derive analytic expressions
for the charge and spin densities, as functions of the underlying pseudospin
texture, and use these results to investigate different types of linear domain
walls, both analytically and numerically. We find that any smooth domain wall
between two oppositely polarized domains carries a universal quantized charge
dipole density proportional to the difference of Landau level indices, $n-m$.
Additionally, non-uniformities in the domain wall may give rise to excess net
charge localized at the domain wall. Interestingly, the physical spin density
associated with the domain wall generally exhibits a much more complex
multipolar structure than that of the pseudospin texture. These results should
for example help to elucidate the mechanisms underlying nuclear electric
resonance and nuclear polarization oscillations in Ising quantum Hall systems.",1909.13249v1
2019-10-17,Planar Hall driven torque in a FM/NM/FM system,"An important goal of spintronics is to covert a charge current into a spin
current with a controlled spin polarization that can exert torques on an
adjacent magnetic layer. Here we demonstrate such torques in a two ferromagnet
system. A CoNi multilayer is used as a spin current source in a sample with
structure CoNi/Au/CoFeB. Spin torque ferromagnetic resonance is used to measure
the torque on the CoFeB layer. The response as a function of the applied field
angle and current is consistent with the symmetry expected for a torques
produced by the planar Hall effect originating in CoNi. We find the strength of
this effect to be comparable to that of the spin Hall effect in platinum,
indicating that the planar Hall effect holds potential as a spin current source
with a controllable polarization direction.",1910.08039v1
2019-10-23,Superconductivity at the Pressure-Induced Ferromagnetic Critical Region in UCoGe,"The phase separation of the ferromagnetic (FM) and paramagnetic (PM) phases
in the superconducting (SC) state of UCoGe at the FM critical region was
investigated using $^{59}$Co nuclear quadrupole resonance (NQR) technique by
taking advantage of its site-selective feature. The NQR measurements revealed
that the first-order quantum phase transition occurs between the FM and the PM
states. The nuclear spin-lattice relaxation rate $1/T_1$ exhibited a clear drop
at the SC state in the PM phase, whereas it was not detected in the FM phase,
which indicates that the superconductivity in the FM phase becomes weaker at
the FM critical region due to the presence of the PM SC state. This result
suggests that the SC condensation energy of the PM SC state is equal or larger
than that of the FM SC state in this region. The pressure-temperature phase
diagram of UCoGe was modified by taking the results from this study into
account.",1910.10396v1
2020-02-07,Model of damping and anisotropy at elevated temperatures: application to granular FePt films,"Understanding the damping mechanism in finite size systems and its dependence
on temperature is a critical step in the development of magnetic
nanotechnologies. In this work, nano-sized materials are modeled via atomistic
spin dynamics, the damping parameter being extracted from Ferromagnetic
Resonance (FMR) simulations applied for FePt systems, generally used for
heat-assisted magnetic recording media (HAMR). We find that the damping
increases rapidly close to Tc and the effect is enhanced with decreasing system
size, which is ascribed to scattering at the grain boundaries. Additionally,
FMR methods provide the temperature dependence of both damping and the
anisotropy, important for the development of HAMR. Semi-analytical calculations
show that, in the presence of a grain size distribution, the FMR linewidth can
decrease close to the Curie temperature due to a loss of inhomogeneous line
broadening. Although FePt has been used in this study, the results presented in
the current work are general and valid for any ferromagnetic material.",2002.02865v1
2020-12-02,Electric field control of interaction between magnons and quantum spin defects,"Hybrid systems coupling quantum spin defects (QSD) and magnons can enable
unique spintronic device functionalities and probes for magnetism. Here, we add
electric field control of magnon-QSD coupling to such systems by integrating
ferromagnet-ferroelectric multiferroic with nitrogen-vacancy (NV) center spins.
Combining quantum relaxometry with ferromagnetic resonance measurements and
analytical modeling, we reveal that the observed electric-field tuning results
from ferroelectric polarization control of the magnon-generated fields at the
NV. Exploiting the demonstrated control, we also propose magnon-enhanced hybrid
electric field sensors with improved sensitivity.",2012.01497v2
2020-12-08,Dissipation-induced antiferromagnetic-like frustration in coupled photonic resonators,"We propose a photonic quantum simulator for anti-ferromagnetic spin systems
based on reservoir engineering. We consider a scheme where quadratically driven
dissipative Kerr cavities are indirectly coupled via lossy ancillary cavities.
We show that the ancillary cavities can produce an effective dissipative and
Hamiltonian anti-ferromagnetic-like coupling between the cavities. By solving
the master equation for a triangular cavity configuration, we demonstrate that
the non-equilibrium steady state of the system bears full analogy with the
ground state of an antiferromagnetic Ising model, exhibiting key signatures of
frustration. We show that when the effective photon hopping amplitude is zero,
the engineered non-local dissipation alone is capable of inducing
antiferromagnetic interaction and frustration. This simple scheme can be
generalised to arbitrary lattice geometries, providing a fully controllable
recipe for simulating antiferromagnetism and frustration on a controlled
quantum optical platform.",2012.04502v1
2020-12-22,Dirac magnons pairing via pumping,"We study pumping of magnons to the Dirac points of magnon's Brillouin zone of
a ferromagnet on a honeycomb lattice. In particular, we consider second-order
Suhl process, when due to interaction between magnons, a pair of magnons is
created due to absorption of two electromagnetic wave quanta. We introduce a
bosonic analog of the Cooper ladder for the magnon pair, which is shown to
enhance the pairing of magnons at the Dirac points. As a result of pairing of
the Dirac magnons, the system becomes unstable towards formation of a magnetic
state with zero or reduced magnetization - the Dirac magnon paired state. In
this case the resonant frequency of the pump equals to that of energy of the
Dirac points. Our estimates suggest that the Dirac magnon paired state can be
found in the CrBr$_{3}$ or CrCl$_{3}$ ferromagnet below in vicinity of the
Curie temperature.",2012.12051v4
2018-06-07,Magnetic domain walls as broadband spin wave and elastic magnetisation wave emitters,"We report on the direct observation of spin wave and elastic wave emission
from magnetic domain walls in ferromagnetic thin films. Driven by alternating
homogeneous magnetic fields the magnetic domain walls act as coherent
magnetisation wave sources. Directional and low damped elastic waves below and
above the ferromagnetic resonance are excited. The wave vector of the
magnetoelastically induced acoustic shear waves is linearly tuned by varying
the excitation frequency. Domain wall emitted magnetostatic surface spin waves
occur at higher frequencies, which characteristics are confirmed by
micromagnetic simulations. The distinct modes of magnetisation wave excitation
from micromagnetic objects are a general physical phenomenon relevant for
dynamic magnetisation processes in structured magnetic films. Magnetic domain
walls can act as reconfigurable antennas for spin wave and elastic wave
generation with control of the wave orientation.",1806.02646v1
2018-07-03,Large spin current generation by the spin Hall effect in mixed crystalline phase Ta thin films,"Manipulation of the magnetization in heavy-metal/ferromagnetic bilayers via
the spin-orbit torque requires high spin Hall conductivity of the heavy metal.
We measure inverse spin Hall voltage using a co-planar wave-guide based
broadband ferromagnetic resonance set-up in Py/Ta system with varying
crystalline phase of Ta. We demonstrate a strong correlation between the
measured spin mixing conductance and spin Hall conductivity with the
crystalline phase of Ta thin films. We found a large spin Hall conductivity of
$-2439~(\hbar/e)~\Omega^{-1}$cm$^{-1}$ for low-resistivity (68 $\mu\Omega-$cm)
Ta film having mixed crystalline phase, which we attribute to an extrinsic
mechanism of the spin Hall effect.",1807.01127v1
2019-01-07,Giant anisotropy of Gilbert damping in epitaxial CoFe films,"Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the
central interests in spintronics applications. Here we report a giant Gilbert
damping anisotropy in epitaxial Co$_{50}$Fe$_{50}$ thin film with a
maximum-minimum damping ratio of 400 \%, determined by broadband spin-torque as
well as inductive ferromagnetic resonance. We conclude that the origin of this
damping anisotropy is the variation of the spin orbit coupling for different
magnetization orientations in the cubic lattice, which is further corroborate
from the magnitude of the anisotropic magnetoresistance in Co$_{50}$Fe$_{50}$.",1901.01941v1
2019-01-25,Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe,"A $^{59}$Co nuclear quadrupole resonance (NQR) was performed on a
single-crystalline ferromagnetic (FM) superconductor UCoGe under pressure. The
FM phase vanished at a critical pressure $P_c$, and the NQR spectrum just below
$P_c$ showed phase separation of the FM and paramagnetic (PM) phases below
Curie temperature $T_{\textrm{Curie}}$, suggesting first-order FM quantum phase
transition (QPT). We found that the internal field was absent above $P_c$, but
the superconductivity is almost unchanged. This result suggests the existence
of the nonunitary to unitary transition of the superconductivity around $P_c$.
Nuclear spin-lattice relaxation rate $1/T_1$ showed the FM critical
fluctuations around $P_c$, which persist above $P_c$ and are clearly related to
superconductivity in the PM phase. This FM QPT is understood to be a weak first
order with critical fluctuations. $1/T_1$ sharply decreased in the
superconducting (SC) state above $P_c$ with a single component, in contrast to
the two-component $1/T_1$ in the FM SC state, indicating that the inhomogeneous
SC state is a characteristic feature of the FM SC state in UCoGe.",1901.08699v1
2019-01-29,Lasing in Ferromagnetic Plasmonic Arrays,"We report on lasing at visible wavelengths in arrays of ferromagnetic Ni
nanodisks overlaid with an organic gain medium. We demonstrate that by placing
an organic gain material within the mode volume of the plasmonic nanoparticles
both the radiative and, in particular, the high ohmic losses of Ni nanodisk
resonances can be compensated. Under increasing pump fluence, the systems
exhibit a transition from lattice-modified spontaneous emission to lasing, the
latter being characterized by highly directional and sub-nanometer linewidth
emission. By breaking the symmetry of the array, we observe tunable multimode
lasing at two wavelengths corresponding to the particle periodicity along the
two principal directions of the lattice. Our results pave the way for
loss-compensated magnetoplasmonic devices and topological photonics.",1901.10358v1
2019-03-08,Field-free spin-orbit torque switching in Co/Pt/Co multilayer with mixed magnetic anisotropies,"Spin-orbit-torque (SOT) induced magnetization switching in Co/Pt/Co trilayer,
with two Co layers exhibiting magnetization easy axes orthogonal to each other
is investigated. Pt layer is used as a source of spin-polarized current as it
is characterized by relatively high spin-orbit coupling. The spin Hall angle of
Pt, $\theta = 0.08$ is quantitatively determined using spin-orbit torque
ferromagnetic resonance technique. In addition, Pt serves as a spacer between
two Co layers and depending on it's thickness, different interlayer exchange
coupling (IEC) energy between ferromagnets is induced. Intermediate IEC
energies, resulting in a top Co magnetization tilted from the perpendicular
direction, allows for SOT-induced feld-free switching of the top Co layer. The
switching process is discussed in more detail, showing the potential of the
system for neuromorphic applications.",1903.03368v1
2019-04-16,Large tunneling magnetoresistance in VSe2/MoS2 magnetic tunnel junction,"Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of
realizing heterostructures with coveted properties. Here, we report a
theoretical investigation of the vdW magnetic tunnel junction (MTJ) based on
VSe2/MoS2 heterojunction, where the VSe2 monolayer acts as the ferromagnet with
the room-temperature ferromagnetism. We propose the concept of spin-orbit
torque (SOT) vdW MTJ with reliable reading and efficient writing operations.
The non-equilibrium study reveals a large tunneling magnetoresistance (TMR) of
846 % at 300 Kelvin, identifying significantly its parallel and anti-parallel
states. Thanks to the strong spin Hall conductivity of MoS2, SOT is promising
for the magnetization switching of VSe2 free layer. Quantum-well states come
into being and resonances appear in MTJ, suggesting that the voltage control
can adjust transport properties effectively. The SOT vdW MTJ based on VSe2/MoS2
provides desirable performance and experimental feasibility, offering new
opportunities for 2D spintronics.",1904.07499v1
2019-11-19,Imaging non-standing spin-waves in confined micron-sized ferromagnetic structures under uniform excitation,"A non-standing character of directly imaged spin-waves in confined
micron-sized ultrathin permalloy (Ni\textsubscript{80}Fe\textsubscript{20})
structures is reported along with evidence of the possibility to alter the
observed state by modifications to the sample geometry. Using micromagnetic
simulations the presence of the spin-wave modes excited in the permalloy
stripes along with the quasi-uniform modes were calculated. The predicted
spin-waves were imaged in direct space using time resolved scanning
transmission X-ray microscopy, combined with a ferromagnetic resonance
excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing
character of the spin-waves. Also it was shown by micromagnetic simulations and
confirmed with STXM-FMR results that the observed character of the spin-waves
can be influenced by the local magnetic fields in different sample geometries.",1911.08281v1
2019-12-03,Magnetic Force Microscopy Revealing Molecule Impact on Magnetic Tunnel Junction Based Molecular Devices at Room Temperature,"Commercially successful magnetic tunnel junction can harness the unmatched
capabilities of molecular device elements by solving decade-old fabrication
issues. Utilization of magnetic tunnel junction as a testbed for molecules also
enables unprecedented magnetic studies of molecular spintronics devices. This
paper utilizes magnetic force microscopy (MFM) to vividly show that
organometallic molecules when bridged between two ferromagnetic electrodes
along the magnetic tunnel junction edges, transformed the magnetic electrodes
itself. Molecules impacted several hundred-micron areas of ferromagnetic
electrodes at room temperature. Complementary, magnetic resonance and
magnetometer studies supported the dramatic MFM results. Molecule induced
changes in the magnetic electrodes impacted the transport of the magnetic
tunnel junction and stabilized as much as six orders smaller current at room
temperature. Magnetic tunnel junction based molecular devices can be a gateway
to a vast range of commercially viable futuristic logic and memory devices that
are controlled by the molecular quantum states near room temperature.",1912.01316v1
2019-12-13,Epitaxial growth and antiferromagnetism of Sn-substituted perovskite iridate SrIr$_{0.8}$Sn$_{0.2}$O$_3$,"5d iridates have shown vast emergent phenomena due to a strong interplay
among its lattice, charge and spin degrees of freedom, because of which the
potential in spintronic application of the thin-film form is highly leveraged.
Here we have epitaxially stabilized perovskite SrIr$_{0.8}$Sn$_{0.2}$O$_3$ on
[001] SrTiO$_3$ substrates through pulsed laser deposition and systematically
characterized the structural, electronic and magnetic properties. Physical
properties measurements unravel an insulating ground state with a weak
ferromagnetism in the compressively strained epitaxial film. The octahedral
rotation pattern is identified by synchrotron x-ray diffraction, resolving a
mix of $a^+b^-c^-$ and $a^-b^+c^-$ domains. X-ray magnetic resonant scattering
directly demonstrates a G-type antiferromagnetic structure of the magnetic
order and the spin canting nature of the weak ferromagnetism.",1912.06735v1
2020-06-14,Spin-orbit torque generated by amorphous Fe$_{x}$Si$_{1-x}$,"While tremendous work has gone into spin-orbit torque and spin current
generation, charge-to-spin conversion efficiency remains weak in silicon to
date, generally stemming from the low spin-orbit coupling (low atomic number,
Z) and lack of bulk lattice inversion symmetry breaking. Here we report the
observation of spin-orbit torque in an amorphous, non-ferromagnetic
Fe$_{x}$Si$_{1-x}$ / cobalt bilayer at room temperature, using spin torque
ferromagnetic resonance and harmonic Hall measurements. Both techniques provide
a minimum spin torque efficiency of about 3 %, comparable to prototypical heavy
metals such as Pt or Ta. According to the conventional theory of the spin Hall
effect, a spin current in an amorphous material is not expected to have any
substantial contribution from the electronic bandstructure. This, combined with
the fact that Fe$_{x}$Si$_{1-x}$ does not contain any high-Z element, paves a
new avenue for understanding the underlying physics of spin-orbit interaction
and opens up a new class of material systems - silicides - that is directly
compatible with complementary metal-oxide-semiconductor (CMOS) processes for
integrated spintronics applications.",2006.07786v1
2020-08-07,Spin wave excitations in exchange biased IrMn/CoFe bilayers,"Using an atomistic spin model, we have simulated spin wave injection and
propagation into antiferromagnetic IrMn from an exchange coupled CoFe layer.
The spectral characteristics of the exited spin waves have a complex beating
behavior arising from the non-collinear nature of the antiferromagnetic order.
We find that the frequency response of the system depends strongly on the
strength and frequency of oscillating field excitations. We also find that the
strength of excited spin waves strongly decays away from the interfacial layer
with a frequency dependent attenuation. Our findings suggest that spin waves
generated by coupled ferromagnets are too weak to reverse IrMn in their
entirety even with resonant excitation of a coupled ferromagnet. However,
efficient spin wave injection into the antiferromagnet is possible due to the
non-collinear nature of the IrMn spin ordering.",2008.03036v1
2020-09-09,Effect of dipolar interactions on cavity magnon-polaritons,"The strong photon-magnon coupling between an electromagnetic cavity and two
yttrium iron garnet (YIG) spheres has been investigated in the context of a
strong mutual dipolar interaction between the spheres. A decrease in the
coupling strength between the YIG spheres and the electromagnetic cavity is
observed, along with an increase of the total magnetic losses, as the distance
between the spheres is decreased. A model of inhomogeneous broadening of the
ferromagnetic resonance linewidth, partly mitigated by the dipolar narrowing
effect, reproduces the reduction in the coupling strength observed
experimentally. These findings have important implications for the
understanding of strongly coupled photon-magnon system involving densely packed
magnetic objects, such as ferromagnetic nanowires arrays, in which the total
coupling strength with an electromagnetic cavity might become limited due to
mutual dipolar interactions.",2009.04557v1
2020-10-06,Emergent spin dynamics enabled by lattice interactions in a bicomponent artificial spin ice,"Artificial spin ice (ASI) are arrays on nanoscaled magnets that can serve
both as models for frustration in atomic spin ice as well as for exploring new
spin-wave-based strategies to transmit, process, and store information. Here,
we exploit the intricate interplay of the magnetization dynamics of two
dissimilar ferromagnetic metals arranged on complimentary lattice sites in a
square ASI to effectively modulate the spin-wave properties. We show that the
interaction between the two sublattices results in unique spectra attributed to
each sublattice and we observe inter- and intra-lattice dynamics facilitated by
the distinct magnetization properties of the two materials. The dynamic
properties are systematically studied by angular-dependent broadband
ferromagnetic resonance and confirmed by micromagnetic simulations. We show
that the combination of materials with dissimilar magnetic properties enables
the realization of a wide range of two-dimensional structures potentially
opening the door to new concepts in nanomagnonics.",2010.03008v1
2020-10-09,Inplane spin orbit torque magnetization switching and its detection using the spin rectification effect at sub-GHz frequencies,"Inplane magnetization reversal of a permalloy/platinum bilayer was detected
using the spin rectification effect. Using a sub GHz microwave frequency to
excite spin torque ferromagnetic resonance (ST FMR) in the bilayer induces two
discrete DC voltages around an external static magnetic field of 0 mT. These
discrete voltages depend on the magnetization directions of the permalloy and
enable detection of the inplane magnetization reversal. The threshold current
density for the magnetization reversal is from 10 to 20 MA/cm^2, the same order
as for known spin orbit torque (SOT) switching with in-plane magnetization
materials. The magnitude of the signal is the same or larger than that of the
typical ST FMR signal; that is, detection of magnetization switching is highly
sensitive in spite of deviation from the optimal ST-FMR condition. The proposed
method is applicable to a simple device structure even for a small
ferromagnetic electrode with a width of 100 nm.",2010.04435v1
2020-11-17,Orbital Rashba effect in surface oxidized Cu film,"Recent experimental observation of unexpectedly large current-induced
spin-orbit torque in surface oxidized Cu on top of a ferromagnet suggested a
possible role of the orbital Rashba effect (ORE). With this motivation, we
investigate the ORE from first principles by considering an oxygen monolayer on
top of a Cu(111) film. We show that surface oxidization of Cu film leads to
gigantic enhancement of the ORE for states near the Fermi surface. The
resulting chiral orbital texture in the momentum space is exceptionally strong,
reaching $\sim 0.5\hbar$ in magnitude. We find that resonant hybridization
between O $p$-states and Cu $d$-states is responsible for the emergence of the
ORE. We demonstrate that application of an external electric field generates
huge orbital Hall current, which is an order of magnitude larger than the spin
Hall current found in heavy metals. This implies that ""orbital torque""
mechanism may be significant in surface oxidized Cu/ferromagnet structures. It
also encourages experimental verification of the orbital texture in surface
oxidized Cu through optical measurements such as angle-resolved photoemission
spectroscopy.",2011.08601v1
2021-02-16,"Spin injection into vanadium dioxide films from a typical ferromagnetic metal, across the metal-insulator transition of the vanadium dioxide films","A vanadium dioxide VO2 film shows metal-insulator transition (MIT) induced by
changing environmental temperature. We report the temperature dependence of
electromotive force properties generated in VO2/Ni80Fe20 bilayer junctions
under the ferromagnetic resonance (FMR) of the Ni80Fe20 layer. An electromotive
force generated in a VO2/Ni80Fe20 bilayer junction under the FMR showed a small
change across the MIT temperature of the VO2 film, while the VO2 film
resistance drastically changed. This behavior was not only explained with the
temperature dependence of the electromotive force property generated in the
Ni80Fe20 film itself under the FMR, but also with the generated electromotive
forces due to the inverse spin-Hall effect (ISHE) in the VO2 film under the FMR
of the Ni80Fe20 film. That is, we successfully demonstrated the spin injection
from a Ni80Fe20 film into a VO2 film across the MIT temperature of the VO2
film.",2102.07998v1
2021-03-09,Strong Magnon-Magnon Coupling in Synthetic Antiferromagnets,"Synthetic antiferromagnet, comprised of two ferromagnetic layers separated by
a non-magnetic layer, possesses two uniform precession resonance modes:
in-phase acoustic mode and out-of-phase optic mode. In this work, we
theoretically and numerically demonstrated the strong coupling between acoustic
and optic magnon modes. The strong coupling is attributed to the symmetry
breaking of the system, which can be realized by tilting the bias field or
constructing an asymmetrical synthetic antiferromagnet. It is found that the
coupling strength can be highly adjusted by tuning the tilting angle of bias
field, the magnitude of antiferromagnetic interlayer exchange coupling, and the
thicknesses of ferromagnetic layers. Furthermore, the coupling between acoustic
and optic magnon modes can even reach the ultrastrong coupling regime. Our
findings show high promise for investigating quantum phenomenon with a magnonic
platform.",2103.05153v1
2021-03-24,Monolayer 1T-NbSe2 as a 2D correlated magnetic insulator,"Monolayer group-V transition metal dichalcogenides in their 1T phase have
recently emerged as a platform to investigate rich phases of matter, such as
spin liquid and ferromagnetism, resulting from strong electron correlations.
Although 1T phase NbSe2 does not occur naturally in bulk form, it has been
discovered that the 1T and 1H phases can coexist when monolayer NbSe2 is grown
via molecular beam epitaxy (MBE). This discovery has inspired theoretical
investigations predicting collective phenomena such as ferromagnetism in two
dimensions. Here, by controlling the MBE growth parameters, we demonstrate the
successful growth of single-phase 1T-NbSe2. By combining scanning tunneling
microscopy/spectroscopy and ab initio calculations, we show that this system is
a charge-transfer insulator, with the upper Hubbard band located above the
valence band maximum. Furthermore, by creating a vertical 1T/2H NbSe2
heterostructure, we find evidence of exchange interactions between the
localized magnetic moments in 1T phase and the metallic/superconducting phase,
as manifested by Kondo resonances and Yu-Shiba-Rusinov bound states.",2103.12948v1
2021-05-21,Photo-induced Antiferromagnetic-ferromagnetic Transition and Electronic Structure Modulation in GdBaCo$_2$O$_{5.5}$ Thin Film,"We investigate both the ferromagnetic (FM) and antiferromagnetic (AFM)
ultrafast dynamics of a strongly correlated oxide system, GdBaCo$_2$O$_{5.5}$
thin film, by time-resolved x-ray magnetic circular dichroism in reflectivity
(XMCDR) and resonant magnetic x-ray diffraction (RMXD). A photo-induced AFM-FM
transition characterized by an increase of the transient XMCDR beyond the
unpumped value and a decay of RMXD was observed. The photon-energy dependence
of the transient XMCDR and reflectivity can likely be interpreted as a
concomitant photo-induced spinstate transition.",2105.10083v1
2021-06-30,Confined Magnons,"Magnetic structures are known to possess magnon excitations confined to their
surfaces and interfaces, but these spatially localized modes are often not
resolved in spectroscopy experiments. We develop a theory to calculate the
confined magnon spectra and its associated spin scattering function, which is
the physical observable in neutron and electron scattering, and a proxy for
photon spectroscopy based on X-ray, Raman and THz sources. We show that extra
anisotropy at the surface or interface plays a key role in magnon confinement.
We obtain analytical expressions for the confinement length scale, and show
that it is qualitatively similar for ferromagnets and antiferromagnets in
dimension d>=2. For d=1 we find remarkable differences between ferromagnetic
and antiferromagnetic models. The theory indicates the presence of several
confined magnon resonances in addition to the usual magnons thought to explain
the excitations of magnetic nanostructures. Detecting these modes may elucidate
the impact of the interface on spin anisotropy and magnetic order.",2106.15771v2
2021-08-11,Enhancement of in-plane anisotropy in MoS2/CoFeB bilayers,"Transition metal dichalcogenides (TMD) possess novel properties which makes
them potential candidates for various spintronic applications. Heterostructures
of TMD with magnetic thin film have been extensively considered for
spin-orbital torque, enhancement of perpendicular magnetic anisotropy etc.
However, the effect of TMD on magnetic anisotropy in heterostructures of
in-plane magnetization has not been studied so far. Further the effect of the
TMD on the domain structure and magnetization reversal of the ferromagnetic
system is another important aspect to be understood. In this context we study
the effect of MoS2, a well-studied TMD material, on magnetic properties of
CoFeB in MoS2/CoFeB heterostructures. The reference CoFeB film possess a weak
in-plane anisotropy. However, when the CoFeB is deposited on MoS2 the in-plane
anisotropy is enhanced as observed from magneto optic Kerr effect (MOKE)
microscopy as well as ferromagnetic resonance (FMR). Magnetic domain structure
and magnetization reversal have also been significantly modified for the
MoS2/CoFeB bilayer as compared to the reference CoFeB layer. Frequency and
angle dependent FMR measurement show that the magnetic anisotropy of CoFeB
increases with increase in thickness of MoS2 in the MoS2/CoFeB
heterostructures.",2108.05130v1
2021-09-11,Giant demagnetization effects induced by superconducting films,"We show that a ferromagnetic (F) slab with the in-plane magnetization
sandwiched between two superconducting (S) films experiences strong
demagnetization effect due to the Meissner screening of the stray magnetic
field by the superconductors. In the extreme case the transition of the S films
from normal to the superconducting state can switch the demagnetization factor
from 0 to 1 which is in a sharp contrast with the S/F bilayers where such
transition affects the magnetic field inside the F film only slightly. The
giant demagnetization effect is shown to be qualitatively robust against the
decreasing of the superconducting film thickness and may provide a hint towards
the explanation of the anomalously large ferromagnetic resonance frequency
shift recently observed for the S/F/S structures [I. A. Golovchanskiy, N. N.
Abramov, V. S. Stolyarov, V. I. Chichkov, M. Silaev, I. V. Shchetinin, A. A.
Golubov, V. V. Ryazanov, A. V. Ustinov, and M. Yu. Kuprianov, Phys. Rev. Appl.
14, 024086 (2020)].",2109.05258v1
2021-10-05,Collective magnetic and plasma excitations in Josephson $ψ$ junctions,"We show that Josephson $\psi$ junctions with the half-metallic (HM) weak link
coupled to the superconducting (S) electrodes through the ferromagnetic (F)
layers host collective excitations of magnetic moment and the Josephson phase.
This results in the shift of the ferromagnetic resonance frequency, anomalies
in the current-voltage characteristics and the appearance of additional
magnetic anisotropy in the F layers. In contrast to the previously studied
S/F/S junctions, the coupling between magnetic and plasma modes emerges even in
the long-wavelength limit. Such coupling is shown to enable the controllable
magnetization reversal in the F layer governed by the d.c. current pulse which
provides the effective mechanism for magnetic moment manipulation in the
devices of superconducting spintronics.",2110.02087v1
2021-11-22,Excitation and reception of magnetostatic surface spin waves in thin conducting ferromagnetic films by coplanar microwave antennas. Part II: Experiment,"We report on propagating spin-wave spectroscopy measurements carried out on
coplanar nano-antenna devices made from a Si/SiO$_2$/Ru(5nm)/Co(20)/Pt(5nm)
film. The measurements were analyzed in detail by employing newly developed
theoretical modeling and de-embedding procedures. The magnetic parameters of
the film were determined by complementary Brillouin light scattering and
ferromagnetic resonance measurements. The propagating spin wave signals could
be accounted for quantitatively for the range of externally applied magnetic
fields investigated in this study: 130-1500 Oe.",2111.11111v3
2022-01-11,Building instructions for a ferromagnetic axion haloscope,"A ferromagnetic haloscope is a rf spin-magnetometer used for searching Dark
Matter in the form of axions. A magnetic material is monitored searching for
anomalous magnetization oscillations which can be induced by dark matter
axions. To properly devise such instrument one first needs to understand the
features of the searched-for signal, namely the effective rf field of dark
matter axions $B_a$ acting on electronic spins. Once the properties of $B_a$
are defined, the design and test of the apparatus may start. The optimal sample
is a narrow linewidth and high spin-density material such as Yttrium Iron
Garnet (YIG), coupled to a microwave cavity with almost matched linewidth to
collect the signal. The power in the resonator is collected with an antenna and
amplified with a Josephson Parametric amplifier, a quantum-limited device
which, however, adds most of the setup noise. The signal is further amplified
with low noise HEMT and down-converted for storage with an heterodyne receiver.
This work describes how to build such apparatus, with all the experimental
details, the main issues one might face, and some solutions.",2201.04081v1
2022-01-12,Microscopic probe of magnetic polarons in antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$,"Colossal magnetoresistance (CMR) emerges from intertwined spin and charge
degrees of freedom in the form of ferromagnetic clusters also known as trapped
magnetic polarons. As a result, CMR is rarely observed in antiferromagnetic
materials. Here we use electron spin resonance (ESR) to reveal microscopic
evidence for the formation of magnetic polarons in antiferromagnetic
Eu$_{5}$In$_{2}$Sb$_{6}$. First, we observe a reduction of the Eu$^{2+}$ ESR
linewidth as a function of the applied magnetic field consistent with
ferromagnetic clusters that are antiferromagnetically coupled. Additionally,
the Eu$^{2+}$ lineshape changes markedly below T' ~ 200 K, a temperature scale
that coincides with the onset of CMR. The combination of these two effects
provide strong evidence that magnetic polarons grow in size below T' and start
influencing the macroscopic properties of the system.",2201.04464v1
2022-01-27,Simultaneous measurement of the exchange parameter and saturation magnetization using propagating spin waves,"The exchange interaction in ferromagnetic ultra-thin films is a critical
parameter in magnetization-based storage and logic devices, yet the accurate
measurement of it remains a challenge. While a variety of approaches are
currently used to determine the exchange parameter, each has its limitations,
and good agreement among them has not been achieved. To date, neutron
scattering, magnetometry, Brillouin light scattering, spin-torque ferromagnetic
resonance spectroscopy, and Kerr microscopy have all been used to determine the
exchange parameter. Here we present a novel method that exploits the wavevector
selectivity of Brillouin light scattering to measure the spin wave dispersion
in both the backward volume and Damon-Eshbach orientations. The exchange,
saturation magnetization, and magnetic thickness are then determined by a
simultaneous fit of both dispersion branches with general spin wave theory
without any prior knowledge of the thickness of a magnetic ""dead layer"". In
this work, we demonstrate the strength of this technique for ultrathin metallic
films, typical of those commonly used in industrial applications for magnetic
random-access memory.",2201.11270v1
2022-02-04,A Magnetoelectric Memory Device Based on Pseudo-Magnetization,"We propose a new type of magnetoelectric memory device that stores magnetic
easy-axis information or pseudo-magnetization, rather than a definite
magnetization direction, in piezoelectric/ferromagnetic (PE/FM)
heterostructures. Theoretically, we show how a PE/FM combination can lead to
non-volatility in pseudo-magnetization exhibiting ferroelectric-like behavior.
The pseudo-magnetization can be manipulated by extremely low voltages
especially when the FM is a low-barrier nanomagnet. Using a circuit model
benchmarked against experiments, we determine the switching energy, delay,
switching probability and retention time of the envisioned 1T/1C memory device
in terms of magnetic and circuit parameters and discuss its thermal stability
in terms of a key parameter called back-voltage vm which is an electrical
measure of the strain-induced magnetic field. Taking advantage of ferromagnetic
resonance (FMR) measurements, we experimentally extract values for vm in CoFeB
films and circular nano-magnets deposited on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT)
which agree well with the theoretical values. Our experimental findings indeed
indicate the feasibility of the proposed novel device and confirm the assumed
parameters in our modeling effort.",2202.02203v2
2022-03-09,Exchange spin waves in thin films with gradient composition,"We report investigation of ferromagnetic resonance phenomenon in
ferromagnetic thin films with essentially non-uniform composition. Epitaxial
Pd-Fe thin film with linear distribution of Fe content across the thickness is
used as the model material. Anomalous perpendicular standing spin waves are
observed and quantified using the collective dynamic equation. Numerical
analysis yields the exchange stiffness constant for diluted Pd-Fe alloy
$D=2A/\mu_0M_s=15$~T$\cdot$nm$^2$ and the ratio of the effective magnetization
to the saturation magnetization $M_{eff}/M_s=1.16$. It is demonstrated that,
overall, engineering of thin films with non-uniform composition across the
thickness can be used for high-frequency or low-field magnonic operations using
exchange spin waves.",2203.05014v1
2022-05-09,Direct and alternating magnon spin currents across a junction interface irradiated by linearly polarized laser,"The developments in the field of quantum optics raise expectations that
laser-matter coupling is a promising building block for magnonics. Here, we
propose a method for the generation of direct and alternating spin currents of
magnons across the junction interface irradiated by linearly polarized laser.
In a junction of ferromagnetic insulators with a large electronic gap, the spin
angular momentum is exchanged during the tunneling process of magnons across
the junction interface. The advanced technology in the field of plasmonics and
metamaterials realizes that spins irradiated by the laser field interact only
with the magnetic component of the laser through the Zeeman coupling. Using an
analytic perturbation theory, we provide a general formula for magnon transport
induced by the inversion symmetry breaking across the junction interface. Then,
we show that those spin currents are enhanced by the ferromagnetic resonance,
and the period of the ac spin current is one-half of that of the laser magnetic
field. Finally, we estimate the magnitude of the spin current, and find that it
will be within experimental reach.",2205.04572v1
2022-05-23,Theoretical analysis of FMR-driven spin pumping current and its properties via Self-Consistent Harmonic Approximation,"We applied the Self-Consistent Harmonic Approximation (SCHA), combined with
coherent states formalism, to study the ferromagnetic resonance (FMR) in a
ferromagentic/normal metal junction. Due to the interface interaction, the
FMR-generated spin current is injected from the magnetic insulator to the
normal metal, the so-called spin pumping. Ordinarily, ferromagnetic models are
described by bosonic representation or phenomenological theories; however, in a
coherent magnetization state, the SCHA is the more natural choice to treat FMR
problems. Over the years, the SCHA has successfully applied to investigate
ferro and antiferromagnetism in a wide range of scenarios. The main point of
the SCHA formalism involves the adoption of a quadratic model for which
corrections are included through temperature-dependent renormalization
parameters. Therefore, the SCHA is an efficient method for determining the
properties of magnetically ordered phases. Using the SCHA, we obtained the
temperature dependence of FMR-driven spin pumping. In addition, we found the
spin-mix conductance, the additional damping from the angular momentum
injection into the normal metal side, and the magnetic susceptibility. The SCHA
outcomes are in remarkable agreement with the results of the literature.",2205.11615v2
2022-06-14,Possible Coexistence of Antiferromagnetic and Ferromagnetic Spin Fluctuations in the Spin-triplet Superconductor UTe2 Revealed by 125Te NMR under Pressure,"A spin-triplet superconducting state mediated by ferromagnetic (FM) spin
fluctuations has been suggested to occur in the newly discovered heavy-fermion
superconductor UTe$_2$. However, the recent neutron scattering measurements
revealed the presence of antiferromagnetic (AFM) spin fluctuations in UTe$_2$.
Here, we report the $^{125}$Te nuclear magnetic resonance (NMR) studies of a
single-crystal UTe$_2$, suggesting the coexistence of FM and AFM spin
fluctuations in UTe$_2$. Owing to the two different Te sites in the compound,
we conclude that the FM spin fluctuations are dominant within ladders and the
AFM spin fluctuations originate from the inter-ladder magnetic coupling.
Although AFM spin fluctuations exist in the system, the FM spin fluctuations in
the ladders may play an important role in the appearance of the spin-triplet
superconducting state of UTe$_2$.",2206.06893v1
2022-11-04,Rotationally invariant formulation of spin-lattice coupling in multi-scale modeling,"In the spirit of multi-scale modeling, we develop a theoretical framework for
spin-lattice coupling that connects, on the one hand, to ab initio calculations
of spin-lattice coupling parameters and, on the other hand, to the
magneto-elastic continuum theory. The derived Hamiltonian describes a closed
system of spin and lattice degrees of freedom and explicitly conserves the
total momentum, angular momentum and energy. Using a new numerical
implementation that corrects earlier Suzuki-Trotter decompositions we perform
simulations on the basis of the resulting equations of motion to investigate
the combined magnetic and mechanical motion of a ferromagnetic nanoparticle,
thereby validating our developed method. In addition to the ferromagnetic
resonance mode of the spin system we find another low-frequency mechanical
response and a rotation of the particle according to the Einstein-de-Haas
effect. The framework developed herein will enable the use of multi-scale
modeling for investigating and understanding a broad range of
magneto-mechanical phenomena from slow to ultrafast time scales.",2211.02382v1
2023-01-02,Topological Kondo Superconductors,"Spin-triplet $p$-wave superconductors are promising candidates for
topological superconductors. They have been proposed in various
heterostructures where a material with strong spin-orbit interaction is coupled
to a conventional $s$-wave superconductor by proximity effect. However,
topological superconductors existing in nature and driven purely by strong
electron correlations are yet to be studied. Here we propose a realization of
such a system in a class of Kondo lattice materials in the absence of
spin-orbit coupling and proximity effect. Therein, the odd-parity Kondo
hybridization mediates ferromagnetic spin-spin coupling and leads to
spin-triplet resonant-valence-bond ($t$-RVB) pairing between local moments.
Spin-triplet $p\pm i p^\prime$-wave topological superconductivity is reached
when Kondo effect co-exists with $t$-RVB. We identify the topological nature by
the non-trivial topological invariant and the Majorana fermions at edges. Our
results offer a comprehensive understanding of experimental observations on
UTe$_2$, a U-based ferromagnetic heavy-electron superconductor.",2301.00538v1
2023-02-06,Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide,"Many technologically useful magnetic oxides are ferrimagnetic insulators,
which consist of chemically distinct cations. Here, we examine the spin
dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite
(Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave
excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance
to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice
sites. Our results show that the precessing cation moments retain a rigid,
collinear configuration to within $\approx$2$^\circ$. Moreover, the effective
spin relaxation is identical to within $<$10% for all magnetic cations in the
ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in
resonantly driven ferrimagnetic oxides, where the magnetic moments from
different cations precess as a coherent, collective magnetization.",2302.03100v1
2023-03-22,Twisted bilayer graphene reveals its flat bands under spin pumping,"The salient property of the electronic band structure of twisted bilayer
graphene (TBG), at the so-called magic angle (MA), is the emergence of flat
bands around the charge neutrality point. These bands are associated with the
observed superconducting phases and the correlated insulating states. Scanning
tunneling microscopy combined with angle resolved photoemission spectroscopy
are usually used to visualize the flatness of the band structure of TBG at the
MA. Here, we theoretically argue that spin pumping (SP) provides a direct probe
of the flat bands of TBG and an accurate determination of the MA. We consider a
junction separating a ferromagnetic insulator and a heterostructure of TBG
adjacent to a monolayer of a transition metal dichalcogenide. We show that the
Gilbert damping of the ferromagnetic resonance experiment, through this
junction, depends on the twist angle of TBG, and exhibits a sharp drop at the
MA. We discuss the experimental realization of our results which open the way
to a twist switchable spintronics in twisted van der Waals heterostructures.",2303.12380v2
2023-05-03,Kinetic Magnetism in Triangular Moiré Materials,"Magnetic properties of materials ranging from conventional ferromagnetic
metals to strongly correlated materials such as cuprates originate from Coulomb
exchange interactions. The existence of alternate mechanisms for magnetism that
could naturally facilitate electrical control have been discussed theoretically
but an experimental demonstration in an extended system has been missing. Here,
we investigate MoSe$_2$/WS$_2$ van der Waals heterostructures in the vicinity
of Mott insulator states of electrons forming a frustrated triangular lattice
and observe direct evidence for magnetic correlations originating from a
kinetic mechanism. By directly measuring electronic magnetization through the
strength of the polarization-selective attractive polaron resonance, we find
that when the Mott state is electron doped the system exhibits ferromagnetic
correlations in agreement with the Nagaoka mechanism.",2305.02150v2
2023-05-07,Lectures on spintronics and magnonincs,"In this series of lectures, we discuss the basic theoretical concepts of
magnonics and spintronics. We first briefly recall the relevant topics from
quantum mechanics, electrodynamics of continuous media, and basic theory of
magnetism. We then discuss the classical theory of magnetic dynamics:
ferromagnetic and antiferromagnetic resonance, dynamic susceptibilities, and
spin waves. We open the main discussion with phenomena of spin and exchange
spin currents, spin torques, the spin Hall effect, and the spin Hall and Hanle
magnetoresistance. Special emphasis is given to the effects of spin transfer
torque and spin pumping, where we follow the celebrated derivation utilizing
Landauer quantum multi-channel scattering matrix approach. Finally, we outline
the most important features distinguishing antiferromagnetic dynamics from
ferromagnetic one, which make antiferromagnets particularly promising material
candidates for spintronics and magnonics.",2305.04385v1
2023-05-23,Theory of inverse Rashba-Edelstein effect induced by spin pumping into a two-dimensional electron gas,"The inverse Rashba-Edelstein effect (IREE) in a two-dimensional electron gas
(2DEG) induced by spin pumping from an adjacent ferromagnetic insulator (FI) is
investigated theoretically. In particular, spin and current densities in the
2DEG in which both Rashba and Dresselhaus spin-orbit interactions coexist are
formulated, and their dependencies on ferromagnetic resonance frequency and
orientation of the spin in the FI are clarified. It is shown that spin density
diverges when the ratio between the Rashba and Dresselhaus spin-orbit
interactions approaches unity, while current density stays finite there. These
results can be applied for evaluating spin splitting on the Fermi surface in a
2DEG and designing spintronic devices using IREE.",2305.13953v3
2023-08-04,Spin pumping effect in non-Fermi liquid metals,"We propose that the spin pumping effect is a valuable probe to non-Fermi
liquid (NFL) metals in correlated electron systems. In a bilayer structure
composed of a NFL metal and a ferromagnetic insulator subjected to ac magnetic
field, the precessing spins in the FI inject spin current into the NFL metal,
which modulates the ferromagnetic resonance (FMR) as a backaction. For NFL
metals in the vicinity of a quantum critical point, the FMR modulation shows
power-law scaling with the frequency and the temperature, which is closely
related to the quantum critical behavior and reflects the non-quasiparticle
nature of spin relaxation in NFL metals.",2308.02189v1
2023-08-17,Interfacial Fe segregation and its influence on magnetic properties of CoFeB/MgFeO multilayers,"We investigated the effect of Fe segregated from partially Fe-substituted MgO
(MgFeO) on the magnetic properties of CoFeB/MgFeO multilayers. X-ray
photoelectron spectroscopy (XPS) as well as magnetic measurements revealed that
the segregated Fe was reduced to metal and exhibited ferromagnetism at the
CoFeB/MgFeO interface. The CoFeB/MgFeO multilayer showed more than 2-fold
enhancement in perpendicular magnetic anisotropy (PMA) energy density compared
with a standard CoFeB/MgO multilayer. The PMA energy density was further
enhanced by inserting an ultrathin MgO layer in between CoFeB and MgFeO layers.
Ferromagnetic resonance measurement also revealed a remarkable reduction of
magnetic damping in the CoFeB/MgFeO multilayers.",2308.08876v1
2023-12-28,A new double-layered kagome antiferromagnet ScFe$_6$Ge$_4$,"ScFe$_6$Ge$_4$ with the LiFe$_6$Ge$_4$-type structure (space group
$R{\bar{3}}m$), which has a double-layered kagome lattice (18$h$ site) of Fe
crystallographically equivalent to that of a well-known topological ferromagnet
Fe$_3$Sn$_2$, is newly found to be antiferromagnetic (AFM) with a high N\'eel
temperature of $T_{\rm{N}} \approx 650$ K, in contrast to the ferromagnetic
(FM) ground state previously proposed in a literature. $^{45}$Sc nuclear
magnetic resonance experiment revealed the absence of a hyperfine field at the
Sc site, providing microscopic evidence for the AFM state and indicating AFM
coupling between the bilayer kagome blocks. The stability of the AFM structure
under the assumption of FM intra-bilayer coupling is verified by DFT
calculations.",2312.17069v1
1998-09-03,ESR Modes in CsCuCl3 in Pulsed Magnetic Fields,"We present ESR results for 35-134GHz in the antiferromagnet CsCuCl3 at
T=1.5K. The external field is applied perpendicular to the hexagonal c-axis.
With our pulsed field facility we reach 50T an unprecedented field for low
temperature ESR. We observe strong resonances up to fields close to the
ferromagnetic region of ~30T. These results are discussed in a model for
antiferromagnetic modes in a two-dimensional frustrated triangular spin system.",9809073v1
2000-01-25,Phase interference of spin tunneling in an arbitrarily directed magnetic field,"We present an exact analytic study on the topological phase interference
effect in resonant quantum tunneling of the magnetization between degenerate
excited levels for biaxial ferromagnets in an arbitrarily directed magnetic
field. We show that the topological phase interference effect depends on the
orientation of the field distinctly. The transition from classical to quantum
behavior is also discussed.",0001355v2
2001-08-29,Theoretical investigation on the possibility of preparing left-handed materials in metallic magnetic granular composites,"We investigate the possibility of preparing left-handed materials in metallic
magnetic granular composites. Based on the effective medium approximation, we
show that by incorporating metallic magnetic nanoparticles into an appropriate
insulating matrix and controlling the directions of magnetization of metallic
magnetic components and their volume fraction, it may be possible to prepare a
composite medium of low eddy current loss which is left-handed for
electromagnetic waves propagating in some special direction and polarization in
a frequency region near the ferromagnetic resonance frequency. This composite
may be easier to make on an industrial scale. In addition, its physical
properties may be easily tuned by rotating the magnetization locally.",0108503v1
2001-09-13,Ferromagnetism of magnetic semiconductors--Zhang-Rice limit,"It is suggested that p-d hybridization contributes significantly to the hole
binding energy E_b of Mn acceptors in III-V compounds, leading in an extreme
case to the formation of Zhang-Rice-like small magnetic polarons. The model
explains both strong increase of E_b and evolution of Mn spin-resonance
spectrum with the magnitude of valence-band offsets. For such a structure of Mn
impurity in III-V materials, possible models accounting for the recently
determined Curie temperature of about 940 K in a compensated Ga(0.91)Mn(0.09)N
are discussed.",0109245v1
2001-10-11,Interaction between Kondo impurities in a quantum corral,"We calculate the spectral densities for two impurities inside an elliptical
quantum corral using exact diagonalization in the relevant Hilbert subspace and
embedding into the rest of the system. For one impurity, the space and energy
dependence of the change in differential conductance $\Delta = dI/dV$ observed
in the quantum mirage experiment is reproduced. In presence of another
impurity, $\Delta = dI/dV$ is very sensitive to the hybridization between
impurity and bulk. The impurities are correlated ferromagnetically between
them. A hopping $\gtrsim 0.15$ eV between impurities destroy the Kondo
resonance.",0110227v1
2003-04-08,Novel surface anisotropy term in the FMR spectra of amorphous microwires,"Some recent publications on ferromagnetic resonance in amorphous wires
mention presumably new kind of anisotropy, called there circumferential
anisotropy, as an explanation of various spectral features. In this paper we
argue that there is no special reason to speak of the new kind of anisotropy,
since the observed spectra can be well described in terms of more traditional
uniaxial and surface anisotropies alone.",0304195v1
2003-10-29,Imaging of spinor gases,"We explore the dielectric properties of spinor condensates. Gases with vector
(nematic) order, such as spin-1 condensates with ferromagnetic
(antiferromagnetic) interactions, display optical activity (birefringence).
This optical activity/birefringence is respectively seen for light detuned from
resonance by a frequency which is not too large compared with the
fine/hyperfine structure. Careful tuning of the light frequency can isolate
either of these two effects. These features can be used to image spin textures
in clouds of spin 1 bosons, and to discern states showing different types of
spin order.",0310687v2
2003-11-14,Magnetization reversal and spin dynamics exchange in biased F/AF bilayers probed with complex permeability spectra,"The spin dynamics of the ferromagnetic pinned layer of
ferro-antiferromagnetic coupled NiFe/MnNi bilayers is investigated in a broad
frequency range (30 MHz-6 GHz). A phenomenological model based on the
Landau-Lifshitz equation for the complex permeability of the F/AF bilayer is
proposed. The experimental results are compared to theoretical predictions. We
show that the resonance frequencies, measured during the magnetization, are
likewise hysteretic.",0311338v1
2003-12-01,Transitions at avoided level crossing with interaction and disorder,"We investigate the influence of interaction between tunneling particles and
disorder on their avoided-level-crossing transitions in the fast-sweep limit.
Whereas the results confirm expectations based on the mean-field arguments that
ferromagnetic/antiferromagnetic couplings suppress/enhance transitions, we
found large deviations from the mean-field behavior for dipole-dipole
interactions (DDI) in molecular magnets Mn-12 and Fe-8. For ideal crystals of
the needle, spherical, and disc shapes DDI tends to enhance transitions. This
tendency is inverted for the needle shape in the presence of even small
disorder in the resonance fields of individual particles, however.",0312030v1
2004-01-28,Microscopic mechanisms of magnetization reversal,"Two principal scenarios of magnetization reversal are considered. In the
first scenario all spins perform coherent motion and an excess of magnetic
energy directly goes to a nonmagnetic thermal bath. A general dynamic equation
is derived which includes a tensor damping term similar to the
Bloch-Bloembergen form but the magnetization magnitude remains constant for any
deviation from equilibrium. In the second reversal scenario, the absolute value
of the averaged sample magnetization is decreased by a rapid excitation of
nonlinear spin-wave resonances by uniform magnetization precession. We have
developed an analytic k-space micromagnetic approach that describes this entire
reversal process in an ultra-thin soft ferromagnetic film for up to 90^{o}
deviation from equilibrium. Conditions for the occurrence of the two scenarios
are discussed.",0401590v1
2004-05-13,Magnetization reduction induced by nonlinear effects,"This letter reports the first detailed measurement of $M_z$, the component
parallel to the effective field direction, when ferromagnets are excited by
microwave fields at high power levels. It is found that $M_z$ drops
dramatically at the saturation of the main resonance. Simultaneous measurements
of $M_z$ and absorption power show that this drop corresponds to a diminution
of the spin-lattice relaxation rate. These changes are interpreted as
reflecting the properties of longitudinal spinwaves excited above Suhl's
instability. Similar behavior should be expected in spinwave emission by
currents.",0405301v3
2005-06-30,Magnon transport and spin current switching through quantum dots,"We study the nonequilibrium spin current through a quantum dot consisting of
two localized spin-1/2 coupled to two ferromagnetic insulators. The influence
of an intra-dot magnetic field and exchange coupling, different dot-reservoir
coupling configurations, and the influence of magnon chemical potential
differences vs. magnetic field gradients onto the spin current are examined. We
discuss various spin switching mechanisms and find that, in contrast to
electronic transport, the spin current is very sensitive to the specific
coupling configuration and band edges. In particular, we identify 1- and
2-magnon transport processes which can lead to resonances and antiresonances
for the spin current.",0506806v1
2005-08-02,Orbital polaron lattice formation in lightly doped La1-xSrxMnO3,"By resonant x-ray scattering at the Mn K-edge on La7/8Sr1/8MnO3, we show that
an orbital polaron lattice (OPL) develops at the metal-insulator transition of
this compound. This orbital reordering explains consistently the unexpected
coexistence of ferromagnetic and insulating properties at low temperatures, the
quadrupling of the lattice structure parallel to the MnO2-planes, and the
observed polarization and azimuthal dependencies. The OPL is a clear
manifestation of strong orbital-hole interactions, which play a crucial role
for the colossal magnetoresistance effect and the doped manganites in general.",0508064v2
2005-11-21,Micromagnetic simulations of absoption spectra,"Further development of a previously introduced method for numerically
simulating magnetic spin waves is presented. Together with significant
improvements in speed, the method now allows one to calculate the energy
absorbed by the various modes excited by a position- and time-dependent H1
field in a ferromagnetic body of arbitrary shape in the presence of a (uniform
or non uniform) static H0 field as well as the internal exchange and anisotropy
fields. The method is applied to the case of the single vortex state in a thin
disc, a ring, and various square slabs, for which the absorption spectra are
calculated and the most strongly excited resonance modes are identified.",0511499v1
2006-03-01,Orbital ordering and enhanced magnetic frustration of strained BiMnO3 thin films,"Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on
SrTiO3 substrates, and orbital ordering and magnetic properties of the thin
films were investigated. The ordering of the Mn^{3+} e_g orbitals at a wave
vector (1/4 1/4 1/4) was detected by Mn K-edge resonant x-ray scattering. This
peculiar orbital order inherently contains magnetic frustration. While bulk
BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by
in-plane compressive strains in the films brings about cluster-glass-like
properties.",0603020v1
2006-03-13,Magnetization of nanoparticle systems in a rotating magnetic field,"The investigation of a sizable thermal enhancement of magnetization is put
forward for uniaxial ferromagnetic nanoparticles that are placed in a rotating
magnetic field. We elucidate the nature of this phenomenon and evaluate the
resonant frequency dependence of the induced magnetization. Moreover, we reveal
the role of magnetic dipolar interactions, point out potential applications and
reason the feasibility of an experimental observation of this effect.",0603338v3
2006-06-13,Rectification of radio frequency current in ferromagnetic nanowire,"We report the rectification of a constant wave radio frequency (RF) current
by using a single-layer magnetic nanowire; a direct-current voltage is
resonantly generated when the RF current flows through the nanowire. The
mechanism of the rectification is discussed in terms of the spin torque diode
effect reported for magnetic tunnel junction devices and the rectification is
shown to be direct attributable to resonant spin wave excitation by the RF
current.",0606305v2
2006-10-25,NMR Probing Spin Excitations in the Ring-Like Structure of a Two-Subband System,"Resistively detected nuclear magnetic resonance (NMR) is observed inside the
ring-like structure, with a quantized Hall conductance of 6e^2/h, in the phase
diagram of a two subband electron system. The NMR signal persists up to 400 mK
and is absent in other states with the same quantized Hall conductance. The
nuclear spin-lattice relaxation time, T1, is found to decrease rapidly towards
the ring center. These observations are consistent with the assertion of the
ring-like region being a ferromagnetic state that is accompanied by collective
spin excitations.",0610706v1
2006-11-23,Ab-initio GMR and current-induced torques in Au/Cr multilayers,"We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and
current-induced-torques (CITs) in Cr/Au multilayers that is based on
non-equilibrium Green's functions and spin density functional theory. We find
substantial GMR due primarily to a spin-dependent resonance centered at the
Cr/Au interface and predict that the CITs are strong enough to switch the
antiferromagnetic order parameter at current-densities $\sim 100$ times smaller
than typical ferromagnetic metal circuit switching densities.",0611599v1
2006-12-21,Spin wave excitations: The main source of the temperature dependence of Interlayer exchange coupling in nanostructures,"Quantum mechanical calculations based on an extended Heisenberg model are
compared with ferromagnetic resonance (FMR) experiments on prototype trilayer
systems Ni_7/Cu_n/Co_2/Cu(001) in order to determine and separate for the first
time quantitatively the sources of the temperature dependence of interlayer
exchange coupling. Magnon excitations are responsible for about 75% of the
reduction of the coupling strength from zero to room temperature. The remaining
25% are due to temperature effects in the effective quantum well and the
spacer/magnet interfaces.",0612568v1
2007-01-12,Spectroscopy of the parametric magnons excited by 4-wave process,"Using a Magnetic Resonace Force Microscope, we have performed ferromagnetic
resonance (FMR) spectroscopy on parametric magnons created by 4-wave process.
This is achieved by measuring the differential response to a small source
modulation superimposed to a constant excitation power that drives the dynamics
in the saturation regime of the transverse component. By sweeping the applied
field, we observe abrupt readjustement of the total number of magnons each time
the excitation coincides with a parametric mode. This gives rise to
ultra-narrow peaks whose linewith is lower than $5~10^{-6}$ of the applied
field.",0701287v1
2004-09-17,On the physical origins of the negative index of refraction,"The physical origins of negative refractive index are derived from a dilute
microscopic model, producing a result that is generalized to the dense
condensed phase limit. In particular, scattering from a thin sheet of electric
and magnetic dipoles driven above resonance is used to form a fundamental
description for negative refraction. Of practical significance, loss and
dispersion are implicit in the microscopic model. While naturally occurring
negative index materials are unavailable, ferromagnetic and ferroelectric
materials provide device design opportunities.",0409083v1
2007-05-14,"Identification of the dominant precession damping mechanism in Fe, Co, and Ni by first-principles calculations","The Landau-Lifshitz equation reliably describes magnetization dynamics using
a phenomenological treatment of damping. This paper presents first-principles
calculations of the damping parameters for Fe, Co, and Ni that quantitatively
agree with existing ferromagnetic resonance measurements. This agreement
establishes the dominant damping mechanism for these systems and takes a
significant step toward predicting and tailoring the damping constants of new
materials.",0705.1990v1
2007-05-15,The Nuclear Spin Nanomagnet,"Linearly polarized light tuned slightly below the optical transition of the
negatively charged exciton (trion) in a single quantum dot causes the
spontaneous nuclear spin polarization (self-polarization) at a level close to
100%. The effective magnetic field of spin-polarized nuclei brings the optical
transition energy into resonance with photon energy. The resonantly enhanced
Overhauser effect sustains the stability of the nuclear self-polarization even
in the absence of spin polarization of the quantum dot electron. As a result
the optically selected single quantum dot represents a tiny magnet with the
ferromagnetic ordering of nuclear spins - the nuclear spin nanomagnet.",0705.2167v2
2007-06-04,Electric-field control of tunneling magnetoresistance effect in a Ni/InAs/Ni quantum-dot spin valve,"We demonstrate an electric-field control of tunneling magnetoresistance (TMR)
effect in a semiconductor quantum-dot (QD) spin-valve device. By using
ferromagnetic Ni nano-gap electrodes, we observe the Coulomb blockade
oscillations at a small bias voltage. In the vicinity of the Coulomb blockade
peak, the TMR effect is significantly modulated and even its sign is switched
by changing the gate voltage, where the sign of the TMR value changes at the
resonant condition.",0706.0373v2
2007-11-22,Dicke-like effect in spin-polarized transport through coupled quantum dots,"Spin-dependent electronic transport through a quantum dot side-coupled to two
quantum dots and attached to ferromagnetic leads with collinear (parallel and
antiparallel) magnetizations is analyzed theoretically. The intra-dot Coulomb
correlations are taken into account, whereas the inter-dot ones are neglected.
Transport characteristics, i.e. conductance and tunnel magnetoresistance
associated with the magnetization rotation from parallel to antiparallel
configurations, are calculated by the noneqiulibrium Green function technique.
The Green functions are derived by the equation of motion method in the
Hartree-Fock approximation. The conductance spectra are shown to reveal
features similar to the Dicke resonance in atomic physics.",0711.3611v2
2008-03-05,Fano-Rashba effect in quantum dots,"We consider the electronic transport through a Rashba quantum dot coupled to
ferromagnetic leads. We show that the interference of localized electron states
with resonant electron states leads to the appearance of the Fano-Rashba
effect. This effect occurs due to the interference of bound levels of
spin-polarized electrons with the continuum of electronic states with an
opposite spin polarization. We investigate this Fano-Rashba effect as a
function of the applied magnetic field and Rashba spin-orbit coupling.",0803.0671v1
2008-05-05,Visualizing the spin of individual molecules,"Low-temperature spin-polarized scanning tunneling microscopy is employed to
study spin transport across single Cobalt-Phathalocyanine molecules adsorbed on
well characterized magnetic nanoleads. A spin-polarized electronic resonance is
identified over the center of the molecule and exploited to spatially resolve
stationary spin states. These states reflect two molecular spin orientations
and, as established by density functional calculations, originate from a
ferromagnetic molecule-lead superexchange interaction mediated by the organic
ligands.",0805.0485v1
2008-11-11,Current and Shot Noise Measurements in a Carbon Nanotube-Based Spin Diode,"Low-temperature measurements of asymmetric carbon nanotube (CNT) quantum dots
are reported. The CNTs are end-contacted with one ferromagnetic and one
normal-metal electrode. The measurements show a spin-dependent rectification of
the current caused by the asymmetry of the device. This rectification occurs
for gate voltages for which the normal-metal lead is resonant with a level of
the quantum dot. At the gate voltages at which the current is at the maximum
current, a significant decrease in the current shot noise is observed.",0811.1757v1
2009-02-12,Origin of magnetic moments in defective TiO2 single crystals,"In this paper we show that ferromagnetism can be induced in pure TiO2 single
crystals by oxygen ion irradiation. By combining x-ray diffraction,
Raman-scattering, and electron spin resonance spectroscopy, a defect complex,
\emph{i.e.} Ti$^{3+}$ ions on the substitutional sites accompanied by oxygen
vacancies, has been identified in irradiated TiO2. This kind of defect complex
results in a local (TiO$_{6-x}$) stretching Raman mode. We elucidate that
Ti$^{3+}$ ions with one unpaired 3d electron provide the local magnetic
moments.",0902.2092v1
2009-06-03,Microwave assisted magnetization reversal in single domain nanoelements,"We studied the microwave assisted magnetic reversal of 65 nm by 71 nm
elliptical Ni80Fe20 nanomagnets. Hysteresis curves were measured by
magneto-optical Kerr effect for a range of microwave frequencies and
amplitudes. The coercive field Hc was reduced by 26% for an rf field of 0.08Hc
when the microwave frequency coincided with the minimum of the experimentally
determined ferromagnetic resonance frequency with varying dc field. The
experimental results for the fractional reduction in Hc with rf field amplitude
are in good agreement with numerical simulations for an array of interacting
macrospins with a physically realistic shape anisotropy distribution",0906.0626v1
2009-06-20,Wavevector-dependent spin filtering and spin transport through magnetic barriers in graphene,"We study the spin-resolved transport through magnetic nanostructures in
monolayer and bilayer graphene. We take into account both the orbital effect of
the inhomogeneous perpendicular magnetic field as well as the in-plane spin
splitting due to the Zeeman interaction and to the exchange coupling possibly
induced by the proximity of a ferromagnetic insulator. We find that a single
barrier exhibits a wavevector-dependent spin filtering effect at energies close
to the transmission threshold. This effect is significantly enhanced in a
resonant double barrier configuration, where the spin polarization of the
outgoing current can be increased up to 100% by increasing the distance between
the barriers.",0906.3809v1
2009-06-26,Relaxation Mechanism for Ordered Magnetic Materials,"We have formulated a relaxation mechanism for ferrites and ferromagnetic
metals whereby the coupling between the magnetic motion and lattice is based
purely on continuum arguments concerning magnetostriction. This theoretical
approach contrasts with previous mechanisms based on microscopic formulations
of spin-phonon interactions employing a discrete lattice. Our model explains
for the first time the scaling of the intrinsic FMR linewidth with frequency,
and 1/M temperature dependence and the anisotropic nature of magnetic
relaxation in ordered magnetic materials, where M is the magnetization. Without
introducing adjustable parameters our model is in reasonable quantitative
agreement with experimental measurements of the intrinsic magnetic resonance
linewidths of important class of ordered magnetic materials, insulator or
metals.",0906.4979v1
2009-08-14,Spin-wave interference in three-dimensional rolled-up ferromagnetic microtubes,"We have investigated spin-wave excitations in rolled-up Permalloy microtubes
using microwave absorption spectroscopy. We find a series of quantized
azimuthal modes which arise from the constructive interference of Damon-Eshbach
type spin waves propagating around the circumference of the microtubes, forming
a spin-wave resonator. The mode spectrum can be tailored by the tube's radius
and number of rolled-up layers.",0908.2082v1
2009-08-31,Microwave screening by conduction currents in thin magnetic films: application in stripline broadband FMR,"Ferromagnetic resonance in conducting magnetic bilayers was studied using
microstrip transducers. It was found that excitation or suppression of standing
spin waves could be achieved through enhanced inhomogeneity of eddy currents in
the bilayer caused by finite thickness. This effect is observable in films with
thicknesses below the magnetic skin depth and can be used to study standing
spin wave modes in heterostructures.",0908.4443v2
2009-09-09,Rapid Domain Wall Motion in Permalloy Nanowires Excited by Spin-Polarized Current Applied Perpendicular to the Nanowire,"We study domain wall (DW) dynamics in permalloy nanowires excited by
alternating spin-polarized current applied perpendicular to the nanowire. Spin
torque ferromagnetic resonance measurements reveal that DW oscillations at a
pinning site in the nanowire can be excited with velocities as high as 800 m/s
at current densities below 10$^7$ A/cm$^2$.",0909.1822v4
2009-11-16,Exchange coupling in transition-metal nano-clusters on Cu(001) and Cu(111) surfaces,"We present results of density-functional calculations on the magnetic
properties of Cr, Mn, Fe and Co nano-clusters (1 to 9 atoms large) supported on
Cu(001) and Cu(111). The inter-atomic exchange coupling is found to depend on
competing mechanisms, namely ferromagnetic double exchange and
antiferromagnetic kinetic exchange. Hybridization-induced broadening of the
resonances is shown to be important for the coupling strength. The cluster
shape is found to weaken the coupling via a mechanism that comprises the
different orientation of the atomic d-orbitals and the strength of
nearest-neighbour hopping. Especially in Fe clusters, a correlation of binding
energy and exchange coupling is also revealed.",0911.3004v1
2009-11-17,Polaronic distortion and vacancy-induced magnetism in MgO,"The electronic structure of the neutral and singly charged Mg vacancy in MgO
is investigated using density functional theory. For both defects, semilocal
exchange correlation functionals such as the local spin density approximation
incorrectly predict a delocalized degenerate ground state. In contrast
functionals that take strong correlation effects into account predict a
localized solution, in agreement with spin resonance experiments. Our results,
obtained with the HSE hybrid, atomic self-interaction corrected and LDA+U
functionals, provide a number of constraints to the possibility of
ferromagnetism in hole doped MgO.",0911.3372v1
2010-01-07,Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate,"We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein
condensate by a temporal modulation of spin exchange interaction, which is
tunable with optical Feshbach resonance. Adopting techniques from coherent
control, we demonstrate the localization/freezing of spin mixing dynamics, and
the suppression of the intrinsic dynamic instability and spontaneous spin
domain formation in a ferromagnetically interacting condensate of $^{87}$Rb
atoms. This work points to a promising scheme for investigating the weak
magnetic spin dipole interaction, which is usually masked by the more dominant
spin exchange interaction.",1001.1035v2
2010-01-16,Resonance Damping in Ferromagnets and Ferroelectrics,"The phenomenological equations of motion for the relaxation of ordered phases
of magnetized and polarized crystal phases can be developed in close analogy
with one another. For the case of magnetized systems, the driving magnetic
field intensity toward relaxation was developed by Gilbert. For the case of
polarized systems, the driving electric field intensity toward relaxation was
developed by Khalatnikov. The transport times for relaxation into thermal
equilibrium can be attributed to viscous sound wave damping via
magnetostriction for the magnetic case and electrostriction for the
polarization case.",1001.2845v1
2010-03-10,Circuit QED and sudden phase switching in a superconducting qubit array,"Superconducting qubits connected in an array can form quantum many-body
systems such as the quantum Ising model. By coupling the qubits to a
superconducting resonator, the combined system forms a circuit QED system.
Here, we study the nonlinear behavior in the many-body state of the qubit array
using a semiclassical approach. We show that sudden switchings as well as a
bistable regime between the ferromagnetic phase and the paramagnetic phase can
be observed in the qubit array. A superconducting circuit to implement this
system is presented with realistic parameters .",1003.2006v1
2010-06-24,ESR evidence for disordered magnetic phase from ultra-small carbon nanotubes embedded in zeolite nanochannels,"A multi-frequency electron spin resonance (ESR) study provides evidence for
the occurrence of low temperature ferromagnetic/spin-glass behavior in aligned
arrays of sub-nanometer single walled carbon nanotubes confined in zeolite
nano-channels, owing to sp2-type non-bonding carbon associated localized states
with density of ~3 x 1019 /g. Features related to the much anticipated
conduction ESR are not detected. In the paramagnetic phase, the ESR linewidth
is found to be weakly dependent on microwave frequency.",1006.4841v1
2010-06-24,Circularly polarized modes in magnetized spin plasmas,"The influence of the intrinsic spin of electrons on the propagation of
circularly polarized waves in a magnetized plasma is considered. New eigenmodes
are identified, one of which propagates below the electron cyclotron frequency,
one above the spin-precession frequency, and another close to the
spin-precession frequency.\ The latter corresponds to the spin modes in
ferromagnets under certain conditions. In the nonrelativistic motion of
electrons, the spin effects become noticeable even when the external magnetic
field $B_{0}$ is below the quantum critical\ magnetic field strength, i.e.,
$B_{0}<$ $B_{Q} =4.4138\times10^{9}\, \mathrm{T}$ and the electron density
satisfies $n_{0} \gg n_{c}\simeq10^{32}$m$^{-3}$. The importance of electron
spin (paramagnetic) resonance (ESR) for plasma diagnostics is discussed.",1006.4878v1
2010-07-23,Super-Atom Representation of High-TC Superconductivity,"A resonating valence bond RVB approach is taken to demonstrate formation of
real-space Cooper pairs and High-TC superconductivity HTS. Non-adiabatic
coupling between holes aggregates (super-atoms) and undoped anti-ferromagnet
cause virtual excitations in either system due to inter-system coupling. HTS is
said to reflect cooperative co-existence of two Bose-Einstein condensates in
terms of one real-space Cooper pair condensate, and a second magnon condensate,
which form at the same critical temperature. TC is formulated in terms of the
super-exchange interaction. Connection is made to an equivalent real-space BCS
formulation of HTS. Novel perspectives on the HTS in the electron-doped
Sr1-xLaxCuO2 and Nd2-xCexCuO4 emerge.",1007.4115v1
2010-08-18,Dzyaloshinskii--Moriya interaction: How to measure its sign in weak ferromagnetics?,"Three experimental techniques sensitive to the sign of the
Dzyaloshinskii--Moriya interaction are discussed: neutron diffraction,
Moessbauer gamma-ray diffraction, and resonant x-ray scattering. Classical
examples of hematite (alpha-Fe2O3) and MnCO3 crystals are considered in detail",1008.3092v1
2011-02-25,"First-principles calculations of magnetization relaxation in pure Fe, Co, and Ni with frozen thermal lattice disorder","The effect of the electron-phonon interaction on magnetization relaxation is
studied within the framework of first-principles scattering theory for Fe, Co,
and Ni by displacing atoms in the scattering region randomly with a thermal
distribution. This ""frozen thermal lattice disorder"" approach reproduces the
non-monotonic damping behaviour observed in ferromagnetic resonance
measurements and yields reasonable quantitative agreement between calculated
and experimental values. It can be readily applied to alloys and easily
extended by determining the atomic displacements from ab initio phonon spectra.",1102.5305v2
2011-07-04,Minimization of the Switching Time of a Synthetic Free Layer in Thermally Assisted Spin Torque Switching,"We theoretically studied the thermally assisted spin torque switching of a
synthetic free layer and showed that the switching time is minimized if the
condition H_J=|H_s|/(2 alpha) is satisfied, where H_J, H_s and alpha are the
coupling field of two ferromagnetic layers, the amplitude of the spin torque,
and the Gilbert damping constant. We also showed that the coupling field of the
synthetic free layer can be determined from the resonance frequencies of the
spin-torque diode effect.",1107.0753v2
2011-09-22,Probing the spin states of three interacting electrons in quantum dots,"We observe a low-lying sharp spin mode of three interacting electrons in an
array of nanofabricated AlGaAs/GaAs quantum dots by means of resonant inelastic
light scattering. The finding is enabled by a suppression of the inhomogeneous
contribution to the excitation spectra obtained by reducing the number of
optically-probed quantum dots. Supported by configuration-interaction
calculations we argue that the observed spin mode offers a direct probe of
Stoner ferromagnetism in the simplest case of three interacting spin one-half
fermions.",1109.4758v1
2011-12-03,Inverse Transverse Magneto-Optical Kerr Effect,"It is demonstrated that a static in-plane magnetic field is generated in a
ferromagnetic film by p-polarised light obliquely incident on the film. This
phenomenon can be called inverse transverse magneto-optical Kerr effect. The
femtosecond laser pulse of peak intensity of 500 W/{\mu}m2 generates in nickel
an effective magnetic field of about 100 Oe. The value of the effective
magnetic field can be increased by more than an order of magnitude at the
surface plasmon polariton resonance excited in smooth metal dielectric
structures or in plasmonic crystals.",1112.0681v1
2012-08-02,Stimulated emission of radiation using spin-population inversion in metals: a spin-laser,"Arrays of 10 nm-diameter point contacts of exchange-coupled
spin-majority/spin-minority ferromagnetic metals, integrated into
infrared-terahertz range photon resonators, are fabricated and measured
electrically and optically. Giant, threshold-type electronic excitations under
high-current pumping of the devices are observed as abrupt but reversible steps
in device resistance, in many cases in access of 100%, which correlate with
optical emission from the devices. The results are interpreted as due to
stimulated spin-flip electron-photon relaxation in the system.",1208.0550v2
2013-01-15,Manipulation of Ferromagnets via the Spin-Selective Optical Stark Effect,"We investigate the non-resonant all-optical switching of magnetization. We
treat the inverse Faraday effect (IFE) theoretically in terms of the
spin-selective optical Stark effect for linearly or circularly polarized light.
In the dilute magnetic semiconductors (Ga,Mn)As, strong laser pulses below the
band gap induce effective magnetic fields of several teslas in a direction
which depends on the magnetization and light wave vectors. Our theory
demonstrates that the polarized light catalyzes the angular momentum transfer
between lattice and the magnetization.",1301.3481v2
2013-05-10,Noise and fluctuation relations of a spin diode,"We consider fluctuation relations between the transport coefficients of a
spintronic system where magnetic interactions play a crucial role. We
investigate a prototypical spintronic device (a spin-diode) which consists of
an interacting resonant level coupled to two ferromagnetic electrodes. We
thereby obtain the cumulant generating function for the spin transport in the
sequential tunnelling regime. We demonstrate the fulfilment of the nonlinear
fluctuation relations when up and down spin currents are correlated in the
presence of both spin-flip processes and external magnetic fields.",1305.2346v1
2013-07-12,Observation of Longitudinal Spin Seebeck Effect with Various Transition Metal Films,"We evaluated the thermoelectric properties of longitudinal spin Seebeck
devices by using ten different transition metals (TMs). Both the intensity and
sign of spin Seebeck coefficients were noticeably dependent on the degree of
the inverse spin Hall effect and the resistivity of each TM film. Spin
dependent behaviors were also observed under ferromagnetic resonance. These
results indicate that the output of the spin Seebeck devices originates in the
spin current.",1307.3320v1
2013-11-01,Strain-Tunable Magnetocrystalline Anisotropy in Epitaxial Y3Fe5O12 Thin Films,"We demonstrate strain-tuning of magnetocrystalline anisotropy over a range of
more than one thousand Gauss in epitaxial Y3Fe5O12 films of excellent
crystalline quality grown on lattice-mismatched Y3Al5O12 substrates.
Ferromagnetic resonance (FMR) measurements reveal a linear dependence of both
out-of-plane and in-plane uniaxial anisotropy on the strain-induced tetragonal
distortion of Y3Fe5O12. Importantly, we find the spin mixing conductance G_r
determined from inverse spin Hall effect and FMR linewidth broadening remains
large: G_r = 3.33 x 10^14 Ohm^-1m^-2 in Pt/Y3Fe5O12/Y3Al5O12 heterostructures,
quite comparable to the value found in Pt/Y3Fe5O12 grown on lattice-matched
Gd3Ga5O12 substrates.",1311.0238v1
2013-12-09,Spin-orbit torque opposing the Oersted torque in ultrathin Co/Pt bilayers,"Current-induced torques in ultrathin Co/Pt bilayers were investigated using
an electrically driven FMR technique. The angle dependence of the resonances,
detected by a rectification effect as a voltage, were analysed to determine the
symmetries and relative magnitudes of the spin-orbit torques. Both anti-damping
(Slonczewski) and field-like torques were observed. As the ferromagnet
thickness was reduced from 3 to 1 nm, the sign of the field-like torque
reversed. This observation is consistent with the emergence of a Rashba spin
orbit torque in ultra-thin bilayers.",1312.2409v1
2013-12-31,Tuning Magnetic Properties Polycrystalline of PtCo Alloys Films with Pt,"We experimentally investigated disordered PtxCo1-x (here x: 0.4, 0.5 and 0.6)
alloy thin films magnetic properties which depended on Pt content. The magnetic
properties of PtCo films were described with two effects, one of them is the
hybridization between Co 3d and Pt 5d energy levels and it causes Pt magnetic
polarization. The second one is the high spin orbit coupling constant of Pt
which increases the ratio of magnetic orbital moment to spin moment. We
investigated magnetic properties considering these effects by vibrating sample
magnetometer (VSM) and ferromagnetic resonance (FMR) techniques.",1401.0227v2
2014-10-07,Determination of intrinsic spin Hall angle in Pt,"The spin Hall angle in Pt is evaluated in Pt/NiFe bilayers by spin torque
ferromagnetic resonance (ST-FMR) measurements, and is found to increase with
increasing the NiFe thickness. To extract the intrinsic spin Hall angle in Pt
by estimating the total spin current injected into NiFe from Pt, the NiFe
thickness dependent measurements are performed and the spin diffusion in the
NiFe layer is taken into account. The intrinsic spin Hall angle of Pt is
determined to be 0.068 at room temperature, and is found to be almost constant
in the temperature range 13 - 300 K.",1410.1601v1
2014-11-06,Non-reciprocity of spin wave propagation induced by the interface Dzyaloshinskii-Moriya interaction in Py/Pt film structures,"Results of a comprehensive study by means of Brillouin spectroscopy,
complemented by Ferromagnetic Resonance characterization, of spin waves (SW)
propagating in Py/Pt bi-layers, characterized by pronounced interface
Dzyaloshinskii-Moriya interactions (IDMI) are reported. Non-conventional wave
behavior of SW travelling in opposite directions, characterized by
non-reciprocity with respect to the inversion of the sign of the SW
wave-number, has been revealed. The value of the effective IDMI constant D has
been estimated.",1411.1684v1
2015-02-23,Filling of magnetic-impurity-induced gap in topological insulators by potential scattering,"We show that the energy gap induced by ferromagnetically aligned magnetic
impurities on the surface of a topological insulator can be filled, due to
scattering off the non-magnetic potential of the impurities. In both a
continuum surface model and a three-dimensional tight-binding lattice model, we
find that the energy gap disappears already at weak potential scattering as
impurity resonances add spectral weight at the Dirac point. This can help
explain seemingly contradictory experimental results as to the existence of a
gap.",1502.06403v2
2015-02-24,Spin rectification for collinear and non-collinear magnetization and external magnetic field configurations,"Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically
detected for collinear and non-collinear magnetization and external magnetic
field configurations. The line shape, line width and signal polarity are
analysed. The spin rectication theory has been much extended by taking the
magneto-crystalline anisotropy and shape anisotropy into account, which
explained non-collinear resonances and agrees very well with experimental data.
Thus, a comprehensive understanding of spin rectification in ferromagnetic
metal was demonstrated in this work.",1502.06859v1
2015-03-31,Two integrable differential-difference equations derived from NLS-type equation,"Two integrable differential-difference equations are derived from a
(2+1)-dimensional modified Heisenberg ferromagnetic equation and a resonant
nonlinear Schr\""oinger equation respectively. Multi-soliton solutions of the
resulted semi-discrete systems are given through Hirota's bilinear method.
Elastic and inelastic interaction behavior between two solitons are studied
through the asymptotic analysis. Dynamics of two-soliton solutions are shown
with graphs.",1503.09073v3
2015-04-08,Electron spin polarization by isospin ordering in correlated two-layer quantum Hall systems,"Enhancement of the electron spin polarization in a correlated two-layer
two-dimensional electron system at a total Landau level filling factor of one
is reported. Using resistively detected nuclear magnetic resonance, we
demonstrate that the electron spin polarization of two closely-spaced
two-dimensional electron systems becomes maximized when inter-layer Coulomb
correlations establish spontaneous isospin ferromagnetic order. This
correlation-driven polarization dominates over the spin polarizations of
competing single-layer fractional Quantum Hall states under electron density
imbalances.",1504.02007v1
2016-10-10,Parametric frequency mixing in the magneto-elastically driven FMR-oscillator,"We demonstrate the nonlinear frequency conversion of ferromagnetic resonance
(FMR) frequency by optically excited elastic waves in a thin metallic film on
dielectric substrates. Time-resolved probing of the magnetization directly
witnesses magneto-elastically driven second harmonic generation, sum- and
difference frequency mixing from two distinct frequencies, as well as
parametric downconversion of each individual drive frequency. Starting from the
Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an
elastically driven nonlinear parametric oscillator and show that frequency
mixing is dominated by the parametric modulation of FMR frequency.",1610.02926v1
2018-04-04,Independence of spin-orbit torques from the exchange bias direction in Ni$_{81}$Fe$_{19}$/IrMn bilayers,"We investigated a possible correlation between spin Hall angles and exchange
bias in Ni$_{81}$Fe$_{19}$/IrMn samples by performing spin torque ferromagnetic
resonance measurements. This correlation is probed by patterning of
Ni$_{81}$Fe$_{19}$/IrMn bilayers in different relative orientations with
respect to the exchange bias direction. The measured voltage spectra allow a
quantitative determination of spin Hall angles, which are independent of the
orientation around 2.8\pm0.3%.",1804.01612v1
2019-05-28,Spontaneous topological transitions in a honeycomb lattice of exciton-polariton condensates due to spin bifurcations,"We theoretically explore nonresonantly pumped polaritonic graphene, a system
consisting of a honeycomb lattice of micropillars in the regime of strong
light-matter coupling. We demonstrate that, depending on the parameters of the
structure, such as intensity of the pump and coupling strength between the
pillars, the system shows rich variety of macroscopic ordering, including
analogs of ferromagnetic, antiferromagnetic, and resonant valence bond phases.
Transitions between these phases are associated with dramatic reshaping of the
spectrum of the system connected with spontaneous appearance of topological
order.",1905.12137v2
2017-01-04,Undulator radiation in the THz range,"The experimental device for generation of undulator radiation in terahertz
wavelength region by use of undulator on ferromagnets is created. The device is
based on a beam of a microtrone with the energy 7.5 MeV. The radiation
wavelength is 200 micron. Registered spontaneous radiation has a power of 10
microwatt at a current of a beam 2 mA in a pulse. With the optical resonator,
in a mode, the amplification of 6 percent is received, that in some times is
more than expected value. This effect is explained as a result of partial
coherence of radiation.",1701.00916v1
2013-09-28,High-efficiency GHz frequency doubling without power threshold in thin-film Ni81Fe19,"We demonstrate efficient second-harmonic generation at moderate input power
for thin film Ni81Fe19 undergoing ferromagnetic resonance (FMR). Powers of the
generated second-harmonic are shown to be quadratic in input power, with an
upconversion ratio three orders of magnitude higher than that demonstrated in
ferrite. The second harmonic signal generated exhibits a significantly lower
linewidth than that predicted by low-power Gilbert damping, and is excited
without threshold. Results are in good agreement with an analytic, approximate
expansion of the Landau-Lifshitz-Gilbert (LLG) equation.",1309.7483v1
2014-06-18,Axial Current driven by Magnetization Dynamics in Weyl Semimetals,"We theoretically study the axial current $\bm{j}_5$ (defined as the
difference between the charge current with opposite chirality) in doped Weyl
semimetal using a Green's function technique. We show that the axial current is
controlled by the magnetization dynamics in a magnetic insulator attached to a
Weyl semimetal. We find that the induced axial current can be detected by using
ferromagnetic resonance or the inverse spin Hall effect and can be converted
into charge current with no accompanying energy loss. These properties make
Weyl semimetal advantageous for application to low-consumption electronics with
new functionality.",1406.4636v1
2016-05-20,Interlayer interaction in multilayer CoPt/Co structures,"We report a study of interlayer exchange interaction in multilayer CoPt/Co
structures consisting of periodic CoPt multilayer film with an ""easy axis""
anisotropy and thick Co layer with an ""easy plane"" anisotropy separated by Pt
spacer with variable thickness. The magnetooptical Kerr effect (MOKE) and
ferromagnetic resonance (FMR) measurements show up the essentially
non-collinear state of magnetic moments of the layers and strong exchange
coupling between CoPt and Co subsystems. The estimation of effective anisotropy
and exchange coupling in a simple model based on the Landau-Lifshitz-Gilbert
equation describing magnetization dynamics was performed.",1605.06468v1
2016-05-25,Probing Strong Correlations with Light Scattering: the Example of the Quantum Ising model,"In this paper we calculate the nonlinear susceptibility and the resonant
Raman cross section for the paramagnetic phase of the ferromagnetic Quantum
Ising model in one dimension. In this region the spectrum of the Ising model
has a gap $m$. The Raman cross section has a strong singularity when the energy
of the outgoing photon is at the spectral gap $\omega_{f} \approx m$ and a
square root threshold when the frequency difference between the incident and
outgoing photons $\omega_{i} -\omega_{f} \approx 2m$. The latter feature
reflects the fermionic nature of the Ising model excitations.",1605.07693v1
2017-12-27,Finite temperature magnon spectra in yttrium iron garnet from mean field approach in tight-binding model,"We study magnon spectra at finite temperature in yttrium iron garnet from
tight-binding model with nearest neighboring exchange interaction. The spin
reduction due to thermal magnon excitation are taken into account via the mean
field approximation to the local spin and found to be different at two sets of
iron atoms. The resulting temperature dependence of the spin wave gap shows
good agreement with experiment. We find only two magnon modes are relevant to
ferromagnetic resonance.",1712.09512v1
2019-07-05,Single-particle versus collective effects in assemblies of nanomagnets: screening,"We discuss experimentally realizable situations in which surface effects may
""screen out"" the dipolar interactions in an assembly of nanomagnets, which then
behaves as a noninteracting system. We consider three examples of physical
observables, equilibrium magnetization, ac susceptibility and ferromagnetic
resonance spectrum, to illustrate this screening effect. For this purpose, we
summarize the formalism that accounts for both the intrinsic features of the
nanomagnets and their collective effects within an assembly the condition for
screening.",1907.02720v1
2019-10-09,Scattering of exchange spin waves from regions of modulated magnetization,"We investigate the reflection coefficient of spin waves propagating in an
ultra-thin ferromagnetic film with regions where saturation magnetization is
modulated. We find analytically and using micromagnetic simulations that there
are transmission resonances that depend on the width of the regions and on the
energy of excitation. Our results resemble the quantum mechanical
Ramsauer-Townsend effect in which an electron with certain energies can
propagate above a potential field without scattering. Our findings are useful
for reconfigurable magnonic devices where the saturation magnetization can be
dynamically controlled via a thermal landscape.",1910.04303v1
2020-01-19,Chiral Coupling to Magnetodipolar Radiation,"We review and extend the theory of chiral pumping of spin waves by
magnetodipolar stray fields that generate unidirectional spin currents and
asymmetric magnon densities. We illustrate the physical principles by two kinds
of chiral excitations of magnetic films, i.e., by the evanescent Oersted field
of a narrow metallic stripline with an AC current bias and a magnetic nanowire
under ferromagnetic resonance.",2001.06821v2
2012-05-02,Switching off the magnetic exchange coupling by quantum resonances,"We clarify the role of quantum-well states in magnetic trilayer systems from
majority carrier in the ferromagnetic and all carriers in the antiferromagnetic
configurations. In addition to numerical and analytic calculations, heuristic
pictures are provided to explain effects of a capping layer and side-layer
modulation in recent experiments. This immediately offers answers to two
unexplained subtle findings in experiments and band-structure calculations,
individually. Furthermore, it allows a more flexible tuning of or even turning
off the interlayer exchange coupling.",1205.0365v2
2017-09-05,Voltage control of interface rare-earth magnetic moments,"The large spin orbit interaction in rare earth atoms implies a strong
coupling between their charge and spin degrees of freedom. We formulate the
coupling between voltage and the local magnetic moments of rare earth atoms
with partially filled 4f shell at the interface between an insulator and a
metal. The rare earth-mediated torques allow power-efficient control of
spintronic devices by electric field-induced ferromagnetic resonance and
magnetization switching.",1709.01271v1
2019-04-03,Spurious Ferromagnetic Remanence Detected by Hybrid Magnetometer,"Nuclear magnetic resonance detection in ultra low field regime enables the
measurement of different components of a spurious remanence in the polymeric
material constituting the sample container. A differential atomic magnetometer
detects simultaneously the static field generated by the container and the
time-dependent signal from the precessing nuclei. The nuclear precession
responds with frequency shifts and decay rate variations to the container
magnetization. Two components of the latter act independently on the atomic
sensor and on the nuclear sample. A model of the measured signal allows a
detailed interpretation, on the basis of the interaction geometry.",1904.01901v1
2019-08-24,Chiral Pumping of Spin Waves,"We report a theory for the coherent and incoherent chiral pumping of spin
waves into thin magnetic films through the dipolar coupling with a local
magnetic transducer, such as a nanowire. The ferromagnetic resonance of the
nanowire is broadened by the injection of unidirectional spin waves that
generate a non-equilibrium magnetization in only half of the film. A
temperature gradient between the local magnet and film leads to a
unidirectional flow of incoherent magnons, i.e., a chiral spin Seebeck effect.",1908.09141v2
2019-12-24,Large spin Hall angle and spin mixing conductance in highly resistive antiferromagnetic Mn2Au,"Antiferromagnetic (AFM) materials recently have shown interest in the
research in spintronics due to its zero stray magnetic field, high anisotropy,
and spin orbit coupling. In this context, the bi-metallic AFM Mn2Au has drawn
attention because it exhibits unique properties and its Neel temperature is
very high. Here, we report spin pumping and inverse spin Hall effect
investigations in Mn2Au and CoFeB bilayer system using ferromagnetic resonance.
We found large spin Hall angle {\theta}_SH = 0.22",1912.11522v2
2020-08-17,Bosonic Hofstadter butterflies in synthetic antiferromagnetic patterns,"The emergence of Hofstadter butterflies for bosons in synthetic-gauge-field
antiferromagnetic patterns is theoretically studied. We report on a specific
tight-binding model of artificial antiferromagnetic structures incorporating
both nearest and next-to-nearest neighbour tunnelings and allowing for the
formation of the fractal spectra even with the vanishing gauge field flux
through the lattice. The model is applied to square and honeycomb lattices.
Possible experimental realization is suggested for the lattices of microring
resonators connected by waveguides. Finally, the structure of the butterflies
is analyzed for different points in the magnetic Brillouin zone for both the
ferromagnetic and antiferromagnetic patterns.",2008.08447v1
2021-04-13,Dynamic Magnetoelastic Boundary Conditions and the Pumping of Phonons,"We derive boundary conditions at the interfaces of magnetoelastic
heterostructures under ferromagnetic resonance for arbitrary magnetization
directions and interface shapes. We apply our formalism to
magnet$\vert$nonmagnet bilayers and magnetic grains embedded in a nonmagnetic
thin film, revealing a nontrivial magnetization angle dependence of acoustic
phonon pumping.",2104.05992v2
2021-06-08,Resonant excitation of twisted spin waves in magnetic vortices using rotating magnetic fields,"Twisted spin waves attracted research attentions lately and the orbital
angular momentum they carry may be utilized in communication and computing
technologies. In this work, we manifest by micromagnetic simulations that
twisted spin wave modes naturally exist in thick ferromagnetic disks. The
twisted spin waves can be readily stimulated using rotating magnetic field when
it is tuned to the eigenfrequency of corresponding modes. We analytically
derive dispersion relation of the twisted spin waves and the results agree well
with the numerical studies. Lastly, we demonstrate that the topological charge
of twisted spin waves can be controlled by the exciting field.",2106.04214v1
2021-06-23,Quantum critical phenomena in a spin-1/2 frustrated square lattice with spatial anisotropy,"We present a model compound with a spin-1/2 spatially anisotropic frustrated
square lattice, in which three antiferromagnetic interactions and one
ferromagnetic interaction are competing. We observe an unconventional gradual
increase in the low-temperature magnetization curve reminiscent of the quantum
critical behavior between gapped and gapless phases. In addition, the specific
heat and electron spin resonance signals indicate one-dimensional
characteristics. These results demonstrate quantum critical behavior associated
with one dimensionalization caused by frustrated interactions in the spin-1/2
spatially anisotropic square lattice.",2106.12126v1
2022-07-23,A comprehensive simulation package for analysis of multilayer spintronic devices,"We present cmtj - a comprehensive simulation package that allows large-scale
macrospin simulations for a variety of multilayer spintronics devices. Apart
from conventional static simulations, such as magnetoresistance and
magnetisation hysteresis loops, cmtj implements a mathematical model of dynamic
experimental techniques commonly used for spintronics devices characterisation,
for instance: spin diode ferromagnetic resonance, pulse-induced microwave
magnetometry, or harmonic Hall voltage measurements. We demonstrate the
accuracy of the macrospin simulations on a variety of examples, accompanied by
some experimental results.",2207.11606v1
2022-12-30,Excitations of Ising Strings on a Lattice,"The 3d Ising model in the low temperature (ferromagnetic) phase describes
dynamics of two-dimensional surfaces -- domain walls between clusters of
parallel spins. The Kramers--Wannier duality maps these surfaces into
worldsheets of confining strings in the Wegner's ${\mathbb Z}_2$ gauge theory.
We study the excitation spectrum of long Ising strings by simulating the
${\mathbb Z}_2$ gauge theory on a lattice. We observe a strong mixing between
string excitations and the lightest glueball state and do not find indications
for light massive resonances on the string worldsheet.",2301.00034v2
2023-03-03,Theory of the low- and high-field superconducting phases of UTe$_2$,"Recent nuclear magnetic resonance (NMR) and calorimetric experiments have
observed that UTe$_2$ exhibits a transition between two distinct
superconducting phases as a function of magnetic field strength for a field
applied along the crystalline $b$-axis. To determine the nature of these
phases, we employ a microscopic two-band minimal Hamiltonian with the essential
crystal symmetries and structural details. We also adopt anisotropic
ferromagnetic exchange terms. We study the resulting pairing symmetries and
properties of these low- and high-field phases in mean field theory.",2303.02152v2
2023-04-01,All-optical magnetization control in CrI$_3$ monolayers: a microscopic theory,"Bright excitons in ferromagnetic monolayers CrI$_3$ efficiently interact with
lattice magnetization, which makes possible all-optical resonant magnetization
control in this material. Using the combination of ab-initio simulations within
Bethe-Salpeter approach, semiconductor Bloch equations and Landau-Lifshitz
equations, we construct a microscopic theory of this effect. Solving
numerically the resulting system of the coupled equations describing the
dynamics of atomic spins and spins of the excitons, we demonstrate the
possibility of a tunable control of macroscopic magnetization of a sample.",2304.00331v2
2023-11-17,Magnon topological transition in skyrmion crystal,"We study the magnon spectrum in skyrmion crystal formed in thin ferromagnetic
films with Dzyalosinskii-Moria interaction in presence of magnetic field.
Focusing on two low-lying observable magnon modes and employing stereographic
projection method, we develop a theory demonstrating a topological transition
in the spectrum. Upon the increase of magnetic field, the gap between two
magnon bands closes, with the ensuing change in the topological character of
both bands. This phenomenon of gap closing, if confirmed in magnetic resonance
experiments, may deserve further investigation by thermal Hall conductivity
experiments.",2311.10622v1
2023-11-22,Nonrelaxational FMR peak broadening in spatially inhomogeneous films,"The modification of magnetic properties in spatially inhomogeneous epitaxial
films of magnetic shape memory alloys in martensitic state with the temperature
variation has been studied. The proposed theoretical model is based on Landau
theory of martensitic transformation and statistical model of martensitic
state. It was shown that that spatial inhomogeneity of the material leads to
the dispersion of local martensitic transformation temperatures resulting in
the variation of local magnetic anisotropy values. This model allows describing
the dramatic ferromagnetic resonance line broadening observed in the
experiments in epitaxial films of magnetic shape memory alloys at low
temperatures.",2311.13733v1
2023-11-30,Antiferromagnetic droplet soliton driven by spin current,"We demonstrate that a spin current flowing through a nano-contact into a
uniaxial antiferromagnet with first- and second-order anisotropy can excite a
self-localized dynamic magnetic soliton, known as a spin-wave droplet in
ferromagnets. The droplet nucleates at a certain threshold current with the
frequency of the N\'eel vector precession laying below the antiferromagnetic
resonance. The frequency exhibits nonlinear behavior with the increasing of
applied current. At the high value of applied torque, the soliton mode
transforms, and the oscillator emits spin waves propagating in the
antiferromagnetic layer.",2311.18583v1
2023-12-15,Nonlinear enhancement of coherent magnetization dynamics,"Magnets are interesting materials for classical and quantum information
technologies. However, the short decoherence and dephasing times that determine
the scale and speed of information networks, severely limit the appeal of
employing the ferromagnetic resonance. Here we show that the lifetime and
coherence of the uniform Kittel mode can be enhanced by 3-magnon
interaction-induced mixing with the long-lived magnons at the minima of the
dispersion relation. Analytical and numerical calculations based on this model
explain recent experimental results and predict experimental signatures of
quantum coherence.",2312.09856v1
2024-01-26,FeCuNbSiB thin films with sub-Oersted coercivity,"Nanocrystalline FeCuNbSiB thin films were fabricated through magnetron
sputtering followed by heat treatment, resulting in samples characterized by
low coercivity and high effective magnetization. Comprehensive microstructural
analysis, employing X-ray diffraction and transmission electron microscopy
techniques such as selected area electron diffraction, high-resolution imaging,
and Fourier transform, was conducted. Magnetic properties were investigated
using an alternating gradient field magnetometer and broadband ferromagnetic
resonance. The structural analysis revealed a well-defined microstructure of
nanograins within an amorphous matrix in all of our films. However, the
coercivity of the 80 nm films did not exhibit as low values as observed for the
160 nm films",2401.15176v1
1997-12-02,Stochastic Hysteresis and Resonance in a Kinetic Ising System,"We study hysteresis for a two-dimensional, spin-1/2, nearest-neighbor,
kinetic Ising ferromagnet in an oscillating field, using Monte Carlo
simulations and analytical theory. Attention is focused on small systems and
weak field amplitudes at a temperature below $T_{c}$. For these restricted
parameters, the magnetization switches through random nucleation of a single
droplet of spins aligned with the applied field. We analyze the stochastic
hysteresis observed in this parameter regime, using time-dependent nucleation
theory and the theory of variable-rate Markov processes. The theory enables us
to accurately predict the results of extensive Monte Carlo simulations, without
the use of any adjustable parameters. The stochastic response is qualitatively
different from what is observed, either in mean-field models or in simulations
of larger spatially extended systems. We consider the frequency dependence of
the probability density for the hysteresis-loop area and show that its average
slowly crosses over to a logarithmic decay with frequency and amplitude for
asymptotically low frequencies. Both the average loop area and the
residence-time distributions for the magnetization show evidence of stochastic
resonance. We also demonstrate a connection between the residence-time
distributions and the power spectral densities of the magnetization time
series. In addition to their significance for the interpretation of recent
experiments in condensed-matter physics, including studies of switching in
ferromagnetic and ferroelectric nanoparticles and ultrathin films, our results
are relevant to the general theory of periodically driven arrays of coupled,
bistable systems with stochastic noise.",9712021v2
2001-06-27,Different Gd3+ sites in CaB6: an ESR study,"The local environment of Gd3+ (4f7 S=7/2) ions in single crystals of
Ca1-xGdxB6 (0.0001 < x < 0.01) is studied by means of Electron Spin Resonance
(ESR). The spectra for low concentration samples (x < 0.001) show a split
spectrum due to cubic crystal field effects(CFE). The lineshape of each fine
structure line is lorentzian, indicating an insulating environment for the Gd3+
ions. For higher concentrations (0.003 < x < 0.01), the spectra show a single
resonance (g=1.992(4), DH1/2 ~ 30-60 Oe) with no CFE and dysonian lineshape
indicating metallic environment for the Gd3+ ions. For intermediate
concentrations, a coexistence of spectra corresponding to insulating and
metallic regions is observed. Most of the measured samples show the weak
ferromagnetism (WF) as reported for Ca1-xLaxB6 (x ~ 0.005), but, surprisingly,
this WF has no effect in our ESR spectra either for metallic or insulating
environments. This result suggests that the ferromagnetism in these systems
might be isolated in clusters (defect-rich regions) and its relationship with
metallicity is nontrivial.",0106550v3
2005-10-12,"Electronic states and cyclotron resonance in p-type InMnAs and InMnAs/(Al,Ga)Sb at ultrahigh magnetic fields","We present a theoretical and experimental study on electronic and
magneto-optical properties of p-type paramagnetic InMnAs dilute magnetic
semiconductor alloys and ferromagnetic p-type InMnAs/(Al,Ga)Sb thin films in
ultrahigh (> 100 T) external magnetic fields \textbf{B}. We use an 8 band
Pidgeon-Brown model generalized to include the wavevector dependence of the
electronic states along B as well as s-d and p-d exchange interactions with
localized Mn d-electrons. In paramagnetic p-InMnAs alloys, we compute the
spin-dependent electronic structure as a function of Mn doping and examine how
the valence band structure depends on parameters such as the sp-d exchange
interaction strength and effective masses. The cyclotron resonance (CR) and
magneto-optical properties of InMnAs are computed using Fermi's golden rule. In
addition to finding strong CR for hole-active polarization in p-type InMnAs, we
also find strong CR for electron-active polarization. The electron-active CR in
the valence bands results from transitions between light and heavy hole Landau
levels and is seen in experiments. In ferromagnetic p-InMnAs/(Al,Ga)Sb, two
strong CR peaks are observed which shift with position and increase in strength
as the Curie temperature is approached from above. This transition takes place
well above the Curie temperature and can be attributed to the increase in
magnetic ordering at low temperatures.",0510323v1
2007-03-23,Magnetocrystalline anisotropy and magnetization reversal in GaMnP synthesized by ion implantation and pulsed-laser melting,"We report the observation of ferromagnetic resonance (FMR) and the
determination of the magnetocrystalline anisotropy in (100)-oriented
single-crystalline thin film samples of GaMnP with x=0.042. The contributions
to the magnetic anisotropy were determined by measuring the angular- and the
temperature-dependencies of the FMR resonance fields and by superconducting
quantum interference device magnetometry. The largest contribution to the
anisotropy is a uniaxial component perpendicular to the film plane; however, a
negative contribution from cubic anisotropy is also found. Additional in-plane
uniaxial components are observed at low temperatures, which lift the degeneracy
between the in-plane [011] and [01-1] directions as well as between the
in-plane [010] and [001] directions. Near T=5K, the easy magnetization axis is
close to the in-plane [01-1] direction. All anisotropy parameters decrease with
increasing temperature and disappear above the Curie temperature T_C. A
consistent picture of the magnetic anisotropy of ferromagnetic GaMnP emerges
from the FMR and magnetometry data. The latter can be successfully modeled when
both coherent magnetization rotation and magnetic domain nucleation are
considered.",0703625v1
2010-06-08,Kinetic phenomena in metallic multilayers,"A series of kinetic phenomena in metallic multilayers has been considered.
The kinetic properties of multilayers differ essentially from the properties of
both massive metals and thin films. One of the main reasons of that is the
influence of electron interaction of electrons with interfaces between layers.
From one hand, this interaction leads to the additional electron scattering and
conductivity of multilayer may be noticeably less than specific conductivities
of composing metals. From the other hand, the electron reflection from
interfaces in a strong magnetic field may results in considerable increasing of
conducting properties in consequence of the static skin effect. Due to changing
of electron trajectories after collisions with interfaces new types of periodic
motion in the magnetic field and therefore new size and resonance phenomena in
high frequency fields appear. In thin normal layers on the superconducting
substrate, changing of trajectories is due to Andreev reflection and resonance
effects, which do not exist in normal multilayers, films, and bulk
monocrystals, take place. In multilayers consisting of ferromagnetic and
nonmagnetic metals, the internal magnetic field in ferromagnetic layers must be
taken into account, if the Larmor radius in this field is comparable with the
layer thickness. Because of the mutual diffusion of metals, the kinetic
coefficients of multilayers are changed in time. The investigation of this
changing may be used for determination of diffusion coefficient for the bulk
and grain-boundary diffusion. The effects, which have been analyzed
theoretically in this review, can be used for the obtaining information on the
electron interaction with interfaces in conducting multilayers.",1006.1499v1
2012-08-14,Valence-band structure of ferromagnetic semiconductor (InGaMn)As,"To clarify the whole picture of the valence-band structures of prototype
ferromagnetic semiconductors (III,Mn)As (III: In and Ga), we perform systematic
experiments of the resonant tunneling spectroscopy on [(In_0.53Ga_0.47)_1-x
Mn_x]As (x=0.06-0.15) and In_0.87Mn_0.13As grown on AlAs/ In_0.53Ga_0.47As:Be/
p+InP(001). We show that the valence band of InGaMnAs almost remains unchanged
from that of the host semiconductor InGaAs, that the Fermi level exists in the
band gap, and that the p-d exchange splitting in the valence band is negligibly
small in (InGaMn)As. In the In0.87Mn0.13As sample, although the resonant peaks
are very weak due to the large strain induced by the lattice mismatch between
InP and InMnAs, our results also indicate that the Fermi level exists in the
band gap and that the p-d exchange splitting in the valence band is negligibly
small. These results are quite similar to those of GaMnAs obtained by the same
method, meaning that there are no holes in the valence band, and that the
impurity-band holes dominate the transport and magnetism both in the InGaMnAs
and In_0.87Mn_0.13As films. This band picture of (III,Mn)As is remarkably
different from that of II-VI-based diluted magnetic semiconductors.",1208.2928v1
2014-01-10,Investigation of the strongly correlated one-dimensional magnetic behavior of NiTa2O6,"The magnetic properties of NiTa$_2$O$_6$ were investigated by magnetic
susceptibility, specific heat, electron paramagnetic resonance, neutron powder
diffraction and pulse field magnetization measurements. Accompanying \textit{ab
initio} DFT calculations of the spin-exchange constants complemented and
supported our experimental findings that NiTa$_2$O$_6$ must be described as a
quasi-1D Heisenberg $S$ = 1 spin chain system with a nearest-neighbor only
anti-ferromagnetic spin-exchange interaction of 18.92(2) K. Inter-chain
coupling is by about two orders of magnitude smaller. Electron paramagnetic
resonance measurements on Mg$_{1-x}$Ni$_x$Ta$_2$O$_6$ ($x \approx$ $1\%$)
polycrystalline samples enabled us to estimate the single-ion zero-field
splitting of the $S$ = 1 states which amounts to less than $4\%$ of the
nearest-neighbor spin-exchange interaction. At 0 T NiTa$_2$O$_6$ undergoes
long-range anti-ferromagnetic ordering at 10.3(1) K evidenced by a
$\lambda$-type anomaly in the specific heat capacity. On application of a
magnetic field the specific heat anomaly is smeared out. We confirmed the
magnetic structure by neutron powder diffraction measurements and at 2.00(1) K
refined a magnetic moment of 1.93(5) $\mu_{\rm{B}}$ per Ni$^{2+}$ ion.
Additionally, we followed the magnetic order parameter as a function of
temperature. Lastly we found saturation of the magnetic moment at 55.5(5) T
with a $g$-factor of 2.14(1), with an additional high field phase above 12.8(1)
T. The onset of the new high field phase is not greatly effected by
temperature, but rather smears out as one approaches the long-range ordering
temperature.",1401.2401v1
2016-01-23,Spatial dispersion of magnetic-edge magnetoplasmons: Effect of semi-infinite gate,"Magnetic-edge magnetoplasmons (MEMPs) are obtained for a two-dimensional
electron system (2DES) with atop semi-infinite metallic gate, at a distance
$d$, and atop semi-infinite ferromagnetic film at a strong perpendicular
magnetic field. For two most fast MEMPs, one with positive chirality and other
with negative chirality, a strong spatial dispersion, due to effect of metallic
half-plane gate, is obtained; some slower MEMPs manifest spatial dispersion
too. Present MEMPs are localized at the magnetic-edge that is close to the
wedge of metallic half-plane gate; the metallic wedge enhances localization of
MEMPs at magnetic-edge. Obtained spatial dispersion has unconventional form. In
particular, for two most fast MEMPs the phase velocities, $\omega/k_{x}$, are
the linear polynomials on the wave vector $k_{x}$ in the long-wavelength
region, $k_{x}d \ll 1$. Strong effect of the ferromagnetic film hysteresis on
the MEMPs phase velocities and their anti-crossings are obtained for $0<k_{x}d
\leq1$. Two MEMPs of opposite chirality, especially two most fast MEMPs, at
some resonance frequency can create a resonance circuit, with closed wave path
along a fraction of the magnetic edge perimeter, with a total change of the
wave phase given by an integer of $2\pi$.",1601.06217v2
2020-07-02,Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study,"We study the tunnel magnetoresistance (TMR) effect and magnetocrystalline
anisotropy in a series of magnetic tunnel junctions (MTJs) with $L1_1$-ordered
fcc ferromagnetic alloys and MgO barrier along the [111] direction. Considering
the (111)-oriented MTJs with different $L1_1$ alloys, we calculate their TMR
ratios and magnetocrystalline anisotropies on the basis of the first-principles
calculations. The analysis shows that the MTJs with Co-based alloys (CoNi,
CoPt, and CoPd) have high TMR ratios over 2000$\%$. These MTJs have
energetically favored Co-O interfaces where interfacial antibonding between Co
$d$ and O $p$ states is formed around the Fermi level. We find that the
resonant tunneling of the antibonding states, called the interface resonant
tunneling, is the origin of the obtained high TMR ratios. Our calculation of
the magnetocrystalline anisotropy shows that many $L1_1$ alloys have large
perpendicular magnetic anisotropy (PMA). In particular, CoPt has the largest
value of anisotropy energy $K_{\rm u} \approx 10\,{\rm MJ/m^3}$. We further
conduct a perturbation analysis of the PMA with respect to the spin-orbit
interaction and reveal that the large PMA in CoPt and CoNi mainly originates
from spin-conserving perturbation processes around the Fermi level.",2007.01068v2
2010-05-05,Magnetic proximity effects in V/Fe superconductor/ferromagnet single bilayer revealed by waveguide-enhanced polarized neutron reflectometry,"Polarized neutron reflectometry is used to study the magnetic proximity
effect in a superconductor/ferromagnet (SC/FM) system of composition
Cu(32nm)/V(40nm)/Fe(1nm)/MgO. In contrast to previous studies, here a single
SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary
signal enhancement is achieved by waveguide resonance, i.e. preparing the
V(40nm)/Fe(1nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate
and Cu top layer, respectively . A new magnetic state of the system was
observed at temperatures below 0.7 TC. manifested in a systematic change in the
height and width of the waveguide resonance peak. Upon increasing the
temperature from 0.7 TC to TC, a gradual decay of this state is observed,
accompanied by a 5% growth of the diffuse scattering. According to theoretical
studies, such behavior is the result of the magnetic proximity effect. Due to
the presence of the thin FM layer the superconducting electrons are polarized
and, as a result, near the SC/FM interface an additional magnetic layer appears
in the SC with thickness comparable to ksi, the coherence length of the
superconductor.",1005.0685v1
2012-01-24,Electron Spin Resonance of the Yb 4f moment in Yb(Rh1-xCox)2Si2,"[published in Phys. Rev. B 85, 035119 (2012)] The evolution of spin dynamics
from the quantum critical system YbRh2Si2 to the stable trivalent Yb system
YbCo2Si2 was investigated by Electron Spin Resonance (ESR) spectroscopy. While
the Kondo temperature changes by one order of magnitude, all compositions of
the single crystalline series Yb(Rh1-xCox)2Si2 show well defined ESR spectra
with a clear Yb3+ character for temperatures below \approx 20 K. With
increasing Co-content the ESR g-factor along the c-direction strongly increases
indicating a continuous change of the ground state wave function and, thus, a
continuous change of the crystal electric field. The linewidth presents a
complex dependence on the Co-content and is discussed in terms of the Co-doping
dependence of the Kondo interaction, the magnetic anisotropy and the influence
of ferromagnetic correlations between the 4f states. The results provide
evidence that, for low Co-doping, the Kondo interaction allows narrow ESR
spectra despite the presence of a large magnetic anisotropy, whereas at high
Co-concentrations, the linewidth is controlled by ferromagnetic correlations. A
pronounced broadening due to critical correlations at low temperatures is only
observed at the highest Co-content. This might be related to the presence of
incommensurate magnetic fluctuations.",1201.5022v1
2016-08-29,Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses,"Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG)
films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have
been grown as a basic material for spin-wave propagation experiments in
microstructured waveguides. The continuously strained films exhibit nearly
perfect crystallinity without significant mosaicity and with effective lattice
misfits of delta a(perpendicular)/a(substrate) ~10-4 and below. The
film/substrate interface is extremely sharp without broad interdiffusion layer
formation. All LPE films exhibit a nearly bulk-like saturation magnetization of
(1800+-20) Gs and an `easy cone' anisotropy type with extremely small in-plane
coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy
with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No
significant out-of-plane anisotropy is observed, but a weak dependence of the
effective magnetization on the lattice misfit is detected. The narrowest
ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is
the lowest value reported so far for YIG films of 100 nm thicknesses and below.
The Gilbert damping coefficient for investigated LPE films is estimated to be
close to 1 x 10-4.",1608.08043v1
2017-10-20,Ferromagnetic resonance of a two-dimensional array of nanomagnets: Effects of surface anisotropy and dipolar interactions,"We develop an analytical approach for studying the FMR frequency shift due to
dipolar interactions and surface effects in two-dimensional arrays of
nanomagnets with (effective) uniaxial anisotropy along the magnetic field. For
this we build a general formalism on the basis of perturbation theory that
applies to dilute assemblies but which goes beyond the point-dipole
approximation as it takes account of the size and shape of the nano-elements,
in addition to their separation and spatial arrangement. The contribution to
the frequency shift due to the shape and size of the nano-elements has been
obtained in terms of their aspect ratio, their separation and the lattice
geometry. We have also varied the size of the array itself and compared the
results with a semi-analytical model and reached an agreement that improves as
the size of the array increases. We find that the red-shift of the
ferromagnetic resonance due to dipolar interactions decreases for smaller
arrays. Surface effects may induce either a blue-shift or a red-shift of the
FMR frequency, depending on the crystal and magnetic properties of the
nano-elements themselves. In particular, some configurations of the
nano-elements assemblies may lead to a full compensation between surface
effects and dipole interactions.",1710.07452v2
2017-12-27,Effect of Cr spacer on structural and magnetic properties of Fe/Gd multilayers,"In this work we analyse the role of a thin Cr spacer between Fe and Gd layers
on structure and magnetic properties of a [Fe(35A)/Cr(tCr)/Gd(50A)/Cr(tCr)]x12
superlattice. Samples without the Cr spacer (tCr=0) and with a thin tCr=4A are
investigated using X-ray diffraction, polarized neutron and resonance X-ray
magnetic reflectometry, SQUID magnetometery, magneto-optical Kerr effect and
ferromagnetic resonance techniques. Magnetic properties are studied
experimentally in a wide temperature range 4-300K and analysed theoretically
using numerical simulation on the basis of the mean-field model. We show that a
reasonable agreement with the experimental data can be obtained considering
temperature dependence of the effective field parameter in gadolinium layers.
The analysis of the experimental data shows that besides a strong reduction of
the antiferromagnetic coupling between Fe and Gd, the introduction of Cr
spacers into Fe/Gd superlattice leads to modification of both structural and
magnetic characteristics of the ferromagnetic layers.",1712.09628v2
2018-10-19,Effect of Meissner screening and trapped magnetic flux on magnetization dynamics in thick Nb/Ni80Fe20/Nb trilayers,"We investigate the influence of Meissner screening and trapped magnetic flux
on magnetization dynamics for a Ni80Fe20 film sandwiched between two thick Nb
layers (100 nm) using broadband (5-20 GHz) ferromagnetic resonance (FMR)
spectroscopy. Below the superconducting transition Tc of Nb, significant
zero-frequency line broadening (5-6 mT) and DC resonance field shift (50 mT) to
a low field are both observed if the Nb thickness is comparable to the London
penetration depth of Nb films (>= 100 nm). We attribute the observed peculiar
behaviors to the increased incoherent precession near the Ni80Fe20/Nb interface
and the effectively focused magnetic flux in the middle Ni80Fe20 caused by
strong Meissner screening and (defect-)trapped flux of the thick adjacent Nb
layers. This explanation is supported by static magnetic properties of the
samples and comparison with FMR data on thick Nb/Ni80Fe20 bilayers. Great care
should therefore be taken in the analysis of FMR response in ferromagnetic
Josephson structures with thick superconductors, a fundamental property for
high-frequency device applications of spin-polarized supercurrents.",1810.08443v2
2017-05-03,Current driven second harmonic domain wall resonance in ferromagnetic metal/ nonmagnetic metal bilayer: a field-free method for spin Hall angle measurements,"We study the ac current-driven domain wall motion in bilayer ferromagnetic
metal (FM)/nonmagnetic metal (NM) nanowire. The solution of the modified
Landau-Lifshitz-Gilbert equation including all the spin transfer torques is
used to describe motion of the domain wall in presence of the spin Hall effect.
We show that the domain wall center has second harmonic frequency response in
addition to the known first harmonic excitation. In contrast to the
experimentally observed second harmonic response in harmonic Hall measurements
of spin-orbit torque in magnetic thin films, this second harmonic response
directly originates from spin-orbit torque driven domain wall dynamics. Based
on the spin current generated by domain wall dynamics, the longitudinal spin
motive force generated voltage across the length of the nanowire is determined.
The second harmonic response introduces additionally a new practical field-free
and all-electrical method to probe the effective spin Hall angle for FM/NM
bilayer structures that could be applied in experiments. Our results also
demonstrate the capability of utilizing FM/NM bilayer structure in domain wall
based spin torque signal generators and resonators.",1705.01355v5
2018-06-15,Magnetoelastic coupling and ferromagnetic-type in-gap spin excitations in multiferroic $α$-Cu$_2$V$_2$O$_7$,"We investigate magnetoelectric coupling and low-energy magnetic excitations
in multiferroic $\alpha$-Cu$_2$V$_2$O$_7$ by detailed thermal expansion,
magnetostriction, specific heat and magnetization measurements in magnetic
fields up to 15~T and by high-field/high-frequency electron spin resonance
studies. Our data show negative thermal expansion in the temperature range
$\leq 200$~K under study. Well-developed anomalies associated with the onset of
multiferroic order (canted antiferromagnetism with a significant magnetic
moment and ferroelectricity) imply pronounced coupling to the structure. We
detect anomalous entropy changes in the temperature regime up to $\sim 80$~K
which significantly exceed the spin entropy. Failure of Gr\""uneisen scaling
further confirms that several dominant ordering phenomena are concomitantly
driving the multiferroic order. By applying external magnetic fields, anomalies
in the thermal expansion and in the magnetization are separated. Noteworthy,
the data clearly imply the development of a canted magnetic moment at
temperatures above the structural anomaly. Low-field magnetostriction supports
the scenario of exchange-striction driven multiferroicity. We observe
low-energy magnetic excitations well below the antiferromagnetic gap, i.e., a
ferromagnetic-type resonance branch associated with the canted magnetic moment
arising from Dzyaloshinsii-Moriya interactions. The anisotropy parameter
$\tilde{D}=1.6(1)$~meV indicates a sizeable ratio of DM- and isotropic magnetic
exchange.",1806.05862v1
2019-01-31,Do topology and ferromagnetism cooperate at the EuS/Bi$_2$Se$_3$ interface?,"We probe the local magnetic properties of interfaces between the insulating
ferromagnet EuS and the topological insulator Bi$_2$Se$_3$ using low energy
muon spin rotation (LE-$\mu$SR). We compare these to the interface between EuS
and the topologically trivial metal, titanium. Below the magnetic transition of
EuS, we detect strong local magnetic fields which extend several nm into the
adjacent layer and cause a complete depolarization of the muons. However, in
both Bi$_2$Se$_3$ and titanium we measure similar local magnetic fields,
implying that their origin is mostly independent of the topological properties
of the interface electronic states. In addition, we use resonant soft X-ray
angle resolved photoemission spectroscopy (SX-ARPES) to probe the electronic
band structure at the interface between EuS and Bi$_2$Se$_3$. By tuning the
photon energy to the Eu anti-resonance at the Eu $M_5$ pre-edge we are able to
detect the Bi$_2$Se$_3$ conduction band, through a protective Al$_2$O$_3$
capping layer and the EuS layer. Moreover, we observe a signature of an
interface-induced modification of the buried Bi$_2$Se$_3$ wave functions and/or
the presence of interface states.",1901.11347v1
2019-12-10,Magnetic properties of thin epitaxial Pd$_{1-x}$Fe$_x$ alloy films,"In the paper we present the results of extensive studies of palladium-rich
Pd1-xFex alloy films epitaxially grown on MgO single-crystal substrate. In a
composition range of x = 0.01-0.07 these materials are soft ferromagnets, the
saturation magnetization and magnetic anisotropy of which can be tuned by its
composition. Vibrating sample magnetometry was used to study temperature
dependences of spontaneous magnetic moment and to establish the temperature of
magnetic ordering (Curie temperature). Ferromagnetic resonance (FMR)
measurements at low temperatures in the in-plane and out-of-plane geometries
revealed the four-fold in-plane magnetic anisotropy with the easy directions
along the <110> axes of the substrate. The modelling of the angular dependence
of the field for resonance allowed to extract the cubic and tetragonal
contributions to the magnetic anisotropy of the films and establish their
dependence on the concentration of iron in the alloy. Experimental data are
discussed in the framework of existing theories of dilute magnetic alloys.
Using the anisotropy constants established from FMR, the magnetic hysteresis
loops are reproduced utilizing the Stoner-Wohlfarth model thus indicating the
predominant coherent magnetic moment rotation at low temperatures. The obtained
results compile a database of magnetic properties of a palladium-iron alloy
considered as a material for superconducting spintronics.",1912.04852v1
2020-03-28,Acoustic Wave Induced FMR Assisted Spin-Torque Switching of Perpendicular MTJs with Anisotropy Variation,"We have investigated Surface Acoustic Wave (SAW) induced ferromagnetic
resonance (FMR) assisted Spin Transfer Torque (STT) switching of perpendicular
MTJ (p-MTJ) with inhomogeneities using micromagnetic simulations that include
the effect of thermal noise. With suitable frequency excitation, the SAW can
induce ferromagnetic resonance in magnetostrictive materials, and the
magnetization can precesses in a cone with high deflection from the
perpendicular direction. With incorporation of inhomogeneity via lateral
anisotropy variation as well as room temperature thermal noise, the
magnetization precession in different gains can be significantly incoherent.
Interestingly, the precession in different grains are found to be in phase,
even though the precession amplitude (angle of deflection from the
perpendicular direction) vary across grains of different anisotropy.
Nevertheless, the high mean deflection angle can complement the STT switching
by reducing the STT current significantly; even though the applied stress
induced change in anisotropy is much lower than the total anisotropy barrier.
This work indicates that SAW assisted switching can improve energy efficiency
while being scalable to very small dimensions, which is technologically
important for STT-RAM and elucidates the physical mechanism for the potential
robustness of this paradigm in realistic scenarios with thermal noise and
material inhomogeneity",2003.12903v1
2020-08-05,"Light Induced Electron Spin Resonance Properties of van der Waals CrX3 (X = Cl, I) Crystals","The research on layered van der Waals (vdW) magnets is rapidly progressing
owing to exciting fundamental science and potential applications. In bulk
crystal form, CrCl3 is a vdW antiferromagnet with in-plane ferromagnetic
ordering below 17 K, and CrI3 is a vdW ferromagnet below 61 K. Here, we report
on the electron spin resonance (ESR) properties of CrCl3 and CrI3 single
crystals upon photo-excitation in the visible range. We noticed remarkable
changes in the ESR spectra upon illumination. In the case of CrCl3, at 10 K,
the ESR signal is shifted from g = 1.492 (dark) to 1.661 (light), line width
increased from 376 to 506 Oe, and the signal intensity is reduced by 1.5 times.
Most interestingly, the observed change in the signal intensity is reversible
when the light is cycled on/off. We observed almost no change in the ESR
spectral parameters in the paramagnetic phase (>20 K) upon illumination. Upon
photo-excitation of CrI3, the ESR signal intensity is reduced by 1.9 times; the
g-value increased from 1.956 to 1.990; the linewidth increased from 1170 to
1260 Oe at 60 K. These findings are discussed by taking into account the skin
depth, the slow relaxation mechanism and the appearance of low-symmetry fields
at the photo-generated Cr2+ Jahn-Teller centers. Such an increase in the
g-value as a result of photo-generated Cr2+ ions is further supported by our
many-body wavefunction calculations. This work has the potential to extend to
monolayer vdWs magnets by combining ESR spectroscopy with optical excitation
and detection.",2008.02208v1
2021-03-17,Spin injection efficiency at metallic interfaces probed by THz emission spectroscopy,"Terahertz (THz) spin-to-charge conversion has become an increasingly
important process for THz pulse generation and as a tool to probe ultrafast
spin interactions at magnetic interfaces. However, its relation to traditional,
steady state, ferromagnetic resonance techniques is poorly understood. Here we
investigate nanometric trilayers of Co/X/Pt (X=Ti, Au or Au0:85W0:15) as a
function of the 'X' layer thickness, where THz emission generated by the
inverse spin Hall effect is compared to the Gilbert damping of the
ferromagnetic resonance. Through the insertion of the 'X' layer we show that
the ultrafast spin current injected in the non-magnetic layer defines a direct
spin conductance, whereas the Gilbert damping leads to an effective spin
mixing-conductance of the trilayer. Importantly, we show that these two
parameters are connected to each other and that spin-memory losses can be
modeled via an effective Hamiltonian with Rashba fields. This work highlights
that magneto-circuits concepts can be successfully extended to ultrafast
spintronic devices, as well as enhancing the understanding of spin-to-charge
conversion processes through the complementarity between ultrafast THz
spectroscopy and steady state techniques.",2103.09557v1
2021-07-14,Frequency fluctuations of ferromagnetic resonances at milliKelvin temperatures,"Unwanted fluctuations over time, in short, noise, are detrimental to device
performance, especially for quantum coherent circuits. Recent efforts have
demonstrated routes to utilizing magnon systems for quantum technologies, which
are based on interfacing single magnons to superconducting qubits. However, the
coupling of several components often introduces additional noise to the system,
degrading its coherence. Researching the temporal behavior can help to identify
the underlying noise sources, which is a vital step in increasing coherence
times and the hybrid device performance. Yet, the frequency noise of the
ferromagnetic resonance (FMR) has so far been unexplored. Here, we investigate
such FMR frequency fluctuations of a YIG sphere down to mK-temperatures, and
find them independent of temperature and drive power. This suggests that the
measured frequency noise in YIG is dominated by so far undetermined noise
sources, which properties are not consistent with the conventional model of
two-level systems, despite their effect on the sample linewidth. Moreover, the
functional form of the FMR frequency noise power spectral density (PSD) cannot
be described by a simple power law. By employing time-series analysis, we find
a closed function for the PSD that fits our observations. Our results underline
the necessity of coherence improvements to magnon systems for useful
applications in quantum magnonics.",2107.06531v1
2021-12-14,Magneto-electronic hydrogen gas sensors: a critical review,"Devices enabling early detection of low concentrations of leaking hydrogen
and precision measurements in a wide range of hydrogen concentrations in
hydrogen storage systems are essential for the mass-production of fuel-cell
vehicles and, more broadly, for the transition to the hydrogen economy. Whereas
several competing sensor technologies are potentially suitable for this role,
ultra-low fire-hazard, contactless and technically simple magneto-electronic
sensors stand apart because they have been able to detect the presence of
hydrogen gas in a range of hydrogen concentrations from 0.06% to 100% at
atmospheric pressure with the response time approaching the industry gold
standard of one second. This new kind of hydrogen sensors is the subject of
this review article, where we inform the academic physics, chemistry, material
science and engineering communities as well as industry researchers about the
recent developments in the field of magneto-electronic hydrogen sensors,
including those based on magneto-optical Kerr effect, anomalous Hall effect and
Ferromagnetic Resonance with a special focus on Ferromagnetic Resonance (FMR)
based devices. In particular, we present the physical foundations of
magneto-electronic hydrogen sensors and we critically overview their advantages
and disadvantages for applications in the vital areas of the safety of
hydrogen-powered cars and hydrogen fuelling stations as well as hydrogen
concentration meters, including those operating directly inside
hydrogen-fuelled fuel cells. We believe that this review will be of interest to
a broad readership, also facilitating the translation of research results into
policy and practice.",2112.07296v1
2022-07-28,Spin-polarized supercurrent through the van der Waals Kondo lattice ferromagnet Fe$_3$GeTe$_2$,"In the new van der Waals Kondo-lattice Fe$_3$GeTe$_2$, itinerant
ferromagnetism and heavy fermionic behaviour coexist. Both the key properties
of such a system namely a spin-polarized Fermi surface and a low Fermi momentum
are expected to significantly alter Andreev reflection dominated transport at a
contact with a superconducting electrode, and display unconventional
proximity-induced superconductivity. We observed interplay between Andreev
reflection and Kondo resonance at mesoscopic interfaces between superconducting
Nb and Fe$_3$GeTe$_2$. Above the critical temperature ($T_c$) of Nb, the
recorded differential conductance ($dI/dV$) spectra display a robust zero-bias
anomaly which is described well by a characteristic Fano line shape arising
from Kondo resonance. Below $T_c$, the Fano line mixes with Andreev reflection
dominated $dI/dV$ leading to a dramatic, unconventional suppression of
conductance at zero bias. As a consequence, an analysis of the Andreev
reflection spectra within a spin-polarized model yields an anomalously large
spin-polarization which is not explained by the density of states of the
spin-split bands at the Fermi surface alone. The results open up the
possibilities of fascinating interplay between various quantum phenomena that
may potentially emerge at the mesoscopic superconducting interfaces involving
Kondo lattice systems hosting spin-polarized conduction electrons.",2207.14050v1
2022-08-17,The quantum dynamic range of room temperature spin imaging,"Magnetic resonance imaging of spin systems combines scientific applications
in medicine, chemistry and physics. Here, we investigate the pixel-wise
coherent quantum dynamics of spins consisting of a 40 by 40 micron sized region
of interest implanted with nitrogen vacancy centers (NV) coupled to a
nano-magnetic flake of $\mathrm{CrTe_2}$. $\mathrm{CrTe_2}$ is an in-plane van
der Waals ferromagnet, which we can probe quantitatively by the NV electron's
spin signal even at room temperature. First, we combine the nano-scale sample
shapes measured by atomic force microscope with the magnetic resonance imaging
data. We then map out the coherent dynamics of the colour centers coupled to
the van der Waals ferromagnet using pixel-wise coherent Rabi and Ramsey imaging
of the NV sensor layer. Next, we fit the pixel-wise solution of the Hamiltonian
to the quantum sensor data. Combining data and model, we can explore the
detuning range of the spin oscillation with a quantum dynamic range of over
$\left|\Delta_{max}\right|= 60 { }\mathrm{MHz} $ in the Ramsey interferometry
mode. Finally, we show the effect of the $\mathrm{CrTe_2}$ van der Waals magnet
on the coherence of the NV sensor layer and measure a 70 times increase in the
maximum frequency of the quantum oscillation going from the Rabi to the Ramsey
imaging mode.",2208.08146v1
2022-08-21,Efficient generation of spin currents by the Orbital Hall effect in pure Cu and Al and their measurement by a Ferris-wheel ferromagnetic resonance technique at the wafer level,"We present a new ferromagnetic resonance (FMR) method that we term the Ferris
FMR. It is wideband, has significantly higher sensitivity as compared to
conventional FMR systems, and measures the absorption line rather than its
derivative. It is based on large-amplitude modulation of the externally applied
magnetic field that effectively magnifies signatures of the spin-transfer
torque making its measurement possible even at the wafer-level. Using the
Ferris FMR, we report on the generation of spin currents from the orbital Hall
effect taking place in pure Cu and Al. To this end, we use the spin-orbit
coupling of a thin Pt layer introduced at the interface that converts the
orbital current to a measurable spin current. While Cu reveals a large
effective spin Hall angle exceeding that of Pt, Al possesses an orbital Hall
effect of opposite polarity in agreement with the theoretical predictions. Our
results demonstrate additional spin- and orbit- functionality for two important
metals in the semiconductor industry beyond their primary use as interconnects
with all the advantages in power, scaling, and cost.",2208.09802v1
2022-09-06,Temperature- and field angular-dependent helical spin period characterized by magnetic dynamics in a chiral helimagnet $MnNb_3S_6$,"The chiral magnets with topological spin textures provide a rare platform to
explore topology and magnetism for potential application implementation. Here,
we study the magnetic dynamics of several spin configurations on the monoaxial
chiral magnetic crystal $MnNb_3S_6$ via broadband ferromagnetic resonance (FMR)
technique at cryogenic temperature. In the high-field forced ferromagnetic
state (FFM) regime, the obtained frequency f vs. resonance field Hres
dispersion curve follows the well-known Kittel formula for a single FFM, while
in the low-field chiral magnetic soliton lattice (CSL) regime, the dependence
of Hres on magnetic field angle can be well-described by our modified Kittel
formula including the mixture of a helical spin segment and the FFM phase.
Furthermore, compared to the sophisticated Lorentz micrograph technique, the
observed magnetic dynamics corresponding to different spin configurations allow
us to obtain temperature- and field-dependent proportion of helical spin
texture and helical spin period ratio L(H)/L(0) via our modified Kittel
formula. Our results demonstrated that field- and temperature-dependent
nontrivial magnetic structures and corresponding distinct spin dynamics in
chiral magnets can be an alternative and efficient approach to uncovering and
controlling nontrivial topological magnetic dynamics.",2209.02266v1
2023-02-01,Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning,"Thin garnet films are becoming central for magnon-spintronics and
spin-orbitronics devices as they show versatile magnetic properties together
with low magnetic losses. These fields would benefit from materials in which
heat does not affect the magnetization dynamics, an effect known as the
non-linear thermal frequency shift. In this study, low damping Bi substituted
Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser
Deposition. Through a fine tuning of the growth parameters, the precise control
of the perpendicular magnetic anisotropy allows to achieve a full compensation
of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are
optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as
the only tuning parameter induces the easy-axis to go from out-of-plane to
in-plane. For films that are close to the dipolar compensation, Ferromagnetic
Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$
that has almost no temperature dependence over a large temperature range (260 K
to 400 K) resulting in an anisotropy temperature exponent of 2. These findings
put Bi:YIG system among the very few materials in which the temperature
dependence of the magnetic anisotropy varies at the same rate than the
saturation magnetization. This interesting behavior is ascribed
phenomenologically to the sizable orbital moment of $Bi^{3+}$.",2302.00585v1
2023-12-01,Large enhancement of spin-orbit torques under a MHz modulation due to phonon-magnon coupling,"The discovery of spin-orbit torques (SOTs) generated through the spin Hall or
Rashba effects provides an alternative write approach for magnetic
random-access memory (MRAM), igniting the development of spin-orbitronics in
recent years. Quantitative characterization of SOTs highly relies on the
SOT-driven ferromagnetic resonance (ST-FMR), where a modulated microwave
current is used to generate ac SOTs and the modulation-frequency is usually
less than 100 kHz (the limit of conventional lock-in amplifiers). Here we have
investigated the SOT of typical SOT material/ferromagnet bilayers in an
extended modulation-frequency range, up to MHz, by developing the ST-FMR
measurement. Remarkably, we found that the measured SOTs are enhanced about
three times in the MHz range, which cannot be explained according to present
SOT theory. We attribute the enhancement of SOT to additional magnon
excitations due to phonon-magnon coupling, which is also reflected in the
slight changes of resonant field and linewidth in the acquired ST-FMR spectra,
corresponding to the modifications of effective magnetization and damping
constant, respectively. Our results indicate that the write current of SOT-MRAM
may be reduced with the assistant of phonon-magnon coupling.",2401.02967v1
2024-02-01,"Element-specific and high-bandwidth ferromagnetic resonance spectroscopy with a coherent, extreme ultraviolet (EUV) source","We developed and applied a tabletop, ultrafast, high-harmonic generation
(HHG) source to measure the element-specific ferromagnetic resonance (FMR) in
ultra-thin magnetic alloys and multilayers on an opaque Si substrate. We
demonstrate a continuous wave bandwidth of 62 GHz, with promise to extend to
100 GHz or higher. This laboratory-scale instrument detects the FMR using
ultrafast, extreme ultraviolet (EUV) light, with photon energies spanning the
M-edges of most relevant magnetic elements. An RF frequency comb generator is
used to produce a microwave excitation that is intrinsically synchronized to
the EUV pulses with a timing jitter of 1.4 ps or better. We apply this system
to measure the dynamics in a multilayer system as well as Ni-Fe and Co-Fe
alloys. Since this instrument operates in reflection-mode, it is a milestone
toward measuring and imaging the dynamics of the magnetic state and spin
transport of active devices on arbitrary and opaque substrates. The higher
bandwidth also enables measurements of materials with high magnetic anisotropy,
as well as ferrimagnets, antiferromagnets, and short-wavelength (high
wavevector) spinwaves in nanostructures or nanodevices. Furthermore, the
coherence and short wavelength of the EUV will enable extending these studies
using dynamic nanoscale lensless imaging techniques such as coherent
diffractive imaging, ptychography, and holography.",2402.00783v1
2013-11-21,Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloy as magnetic electrodes,"HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning
spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance
(FMR) techniques are used in view of comparing (static and dynamic) magnetic
and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel
magnetic junctions (TMJ), deposited on various single crystalline substrates
(a-plane sapphire, MgO(100) and Si(111)). They allow for providing a
correlation between these magnetic properties and the fine structure
investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and
contains a large concentration of Co atoms, which, however, is significantly
reduced when using a sapphire substrate. The Co layer is polycrystalline and
shows larger grains for films grown on a sapphire substrate. The VSM
investigation reveals in-plane anisotropy only for samples grown on a sapphire
substrate. The FMR spectra of the TMJs are compared to the obtained ones with a
single Co and Co2MnGe films of identical thickness deposited on a sapphire
substrate. As expected, two distinct modes are detected in the TMJs while only
one mode is observed in each single film. For the TMJ grown on a sapphire
substrate the FMR behavior does not significantly differ from the superposition
of the individual spectra of the single films, allowing for concluding that the
exchange coupling between the two magnetic layers is too small to give rise to
observable shifts. For TMJs grown on a Si or on a MgO substrate the resonance
spectra reveal one mode which is nearly identical to the obtained one in the
single Co film, while the other observed resonance shows a considerably smaller
intensity and cannot be described using the magnetic parameters appropriate to
the single Co2MnGe film.",1311.5589v1
2015-12-07,Dynamic magnetic susceptibility and electrical detection of ferromagnetic resonance,"The dynamic magnetic susceptibility of magnetic materials near ferromagnetic
resonance (FMR) is very important in interpreting dc-voltage in electrical
detection of FMR. Based on the causality principle and the assumption that the
usual microwave absorption lineshape around FMR is Lorentzian, general forms of
dynamic susceptibility of an arbitrary sample and the corresponding dc-voltage
lineshape are obtained. Our main findings are: 1) The dynamic susceptibility is
not a Polder tensor for material with arbitrary anisotropy. Two off-diagonal
elements are not in general opposite to each other. However, the linear
response coefficient of magnetization to total rf field is a Polder tensor.
This may explain why two off-diagonal elements are always assumed to be
opposite to each other in analyses. 2) The frequency dependence of dynamic
susceptibility near FMR is fully characterized by six numbers while its field
dependence is fully characterized by seven numbers. 3) A recipe of how to
determine these numbers by standard microwave absorption measurements for an
arbitrary sample is proposed. Our results allow one to unambiguously separate
the contribution of the anisotropic magnetoresistance to dc-voltage from that
of the anomalous Hall effect. With these results, one can reliably extract the
information of spin pumping and the inverse spin Hall effect, and determine the
spin-Hall angle. 4) The field-dependence of susceptibility matrix at a fixed
frequency may have several peaks when the effective field is not monotonic of
the applied field. In contrast, the frequency-dependence of susceptibility
matrix at a fixed field has only one peak. Furthermore, in the case that
resonance frequency is not sensitive to the applied field, the field dependence
of susceptibility matrix, as well as dc-voltage, may have another non-resonance
broad peak. Thus, one should be careful in interpreting observed peaks.",1512.01913v1
2023-08-07,$\textit{In situ}$ electric-field control of ferromagnetic resonance in the low-loss organic-based ferrimagnet V[TCNE]$_{x\sim 2}$,"We demonstrate indirect electric-field control of ferromagnetic resonance
(FMR) in devices that integrate the low-loss, molecule-based, room-temperature
ferrimagnet vanadium tetracyanoethylene (V[TCNE]$_{x \sim 2}$) mechanically
coupled to PMN-PT piezoelectric transducers. Upon straining the V[TCNE]$_x$
films, the FMR frequency is tuned by more than 6 times the resonant linewidth
with no change in Gilbert damping for samples with $\alpha = 6.5 \times
10^{-5}$. We show this tuning effect is due to a strain-dependent magnetic
anisotropy in the films and find the magnetoelastic coefficient $|\lambda_S|
\sim (1 - 4.4)$ ppm, backed by theoretical predictions from DFT calculations
and magnetoelastic theory. Noting the rapidly expanding application space for
strain-tuned FMR, we define a new metric for magnetostrictive materials,
$\textit{magnetostrictive agility}$, given by the ratio of the magnetoelastic
coefficient to the FMR linewidth. This agility allows for a direct comparison
between magnetostrictive materials in terms of their comparative efficacy for
magnetoelectric applications requiring ultra-low loss magnetic resonance
modulated by strain. With this metric, we show V[TCNE]$_x$ is competitive with
other magnetostrictive materials including YIG and Terfenol-D. This combination
of ultra-narrow linewidth and magnetostriction in a system that can be directly
integrated into functional devices without requiring heterogeneous integration
in a thin-film geometry promises unprecedented functionality for electric-field
tuned microwave devices ranging from low-power, compact filters and circulators
to emerging applications in quantum information science and technology.",2308.03353v1
2020-02-07,Scattering of Dirac electrons from a skyrmion: emergence of robust skew scattering,"We study electron scattering from a closed magnetic structure embedded in the
top surface of a topological insulator (TI). Outside the structure there is a
uniform layer of ferromagnetic insulator (FMI), leading to a positive effective
mass for the Dirac electrons. The mass inside can be engineered to be negative,
leading to a skyrmion structure. The geometric shape of the structure can be
circular or deformed, leading to integrable or chaotic dynamics, respectively,
in the classical limit. For a circular structure, the relativistic quantum
scattering characteristics can be calculated analytically. For a deformed
structure, we develop an efficient numerical method, the multiple multipole
method, to solve the scattering wavefunctions. We find that anomalous Hall
effect as characterized by strong skew scattering can arise, which is robust
against structural deformation due to the resonant modes. In the short (long)
wavelength regime, the resonant modes manifest themselves as confined vortices
(excited edge states). The origin of the resonant states is the spin phase
factor of massive Dirac electrons at the skyrmion boundary. Further, in the
short wavelength regime, for a circular skyrmion, a large number of angular
momentum channels contribute to the resonant modes. In this regime, in
principle, classical dynamics are relevant, but we find that geometric
deformations, even those as severe as leading to fully developed chaos, have
little effect on the resonant modes. The vortex structure of the resonant
states makes it possible to electrically ``charge'' the skyrmion, rendering
feasible to manipulate its motion electrically. In the long wavelength regime,
only the lowest angular momentum channels contribute to the resonant modes,
making the skew scattering sharply directional. These phenomena may find
applications for information storage and in Hall devices based on dynamic
skyrmion.",2002.02944v1
2000-04-12,Resonant Spin-Dependent Tunneling in Spin-Valve Junctions in the Presence of Paramagnetic Impurities,"The tunnel magnetoresistance (TMR) of F/O/F magnetic junctions, (F's are
ferromagnetic layers and O is an oxide spacer) in the presence of magnetic
impurities within the barrier, is investigated. We assume that magnetic
couplings exist both between the spin of impurity and the bulk magnetization of
the neighboring magnetic electrode, and between the spin of impurity and the
spin of tunneling electron. Consequently, the resonance levels of the system
formed by a tunneling electron and a paramagnetic impurity with spin S=1, are a
sextet. As a result the resonant tunneling depends on the direction of the
tunneling electron spin. At low temperatures and zero bias voltage the TMR of
the considered system may be larger than TMR of the same structure without
paramagnetic impurities. It is calculated that an increase in temperature leads
to a decrease in the TMR amplitude due to excitation of spin-flip processes
resulting in mixing of spin up and down channels. It is also shown that
asymmetry in the location of the impurities within the barrier can lead to
asymmetry in $I(V)$ characteristics of impurity assisted current and two
mechanisms responsible for the origin of this effect are established. The first
one is due to the excitation of spin-flip processes at low voltages and the
second one arises from the shift of resonant levels inside the insulator layer
under high applied voltages.",0004198v2
1999-05-25,Finite Temperature Resonant Tunneling in False Vacuum Decay and the Lee-Yang Theorem,"We consider the cosmological model of a self-interacting $\phi^4 - \phi^2$
quantum scalar field and extend our previous results, [3], on resonant
tunneling and consequent particle production, to the case of finite
temperature. Using the mathematical equivalence between, the Euclidean path
integral of a $\phi^4 - \phi^2$ quantum field theory (in the saddle point
approximation), on one hand, and the partition function of a 4-dimensional
ferromagnet (in the Ising model approximation), on the other, we derive the
following results. Tunneling is a first order phase transition. The creation of
metastable bound states of instanton-antinstanton pairs under the barrier
,(i.e. resonant tunneling), is the seed that gives rise to particle production.
Through the application of the Lee-Yang theorem for phase transitions, (as well
as demonstrating the underlying connection this has with the poles of the
S-matrix element in the quantum scattering theory), we show that the
fluctuations around the dominant escape paths of instantons (i.e. fluctuations
of the bubble wall) with momenta comparable to the scale curvature of the
bubble, drive the mechanism for resonant tunneling in false vacuum decay. We
also identify the temperature dependence of the parameters in the potential
term, (or equivalently, of the instanton bubbles), for a wide range of
temperatures Finally, we show that the picture of a dilute instanton
gas,remains valid even at finite temperatures, as this gas becomes more and
more dilute with the increase of the temperature. This suppression continues
until we reach the critical temperature, at which point there is only one
instanton left, with an infinitely thick wall.",9905095v2
2014-11-26,Fine structure of spectra in the antiferromagnetic phase of the Kondo lattice model,"We study the antiferromagnetic phase of the Kondo lattice model on bipartite
lattices at half-filling using the dynamical mean-field theory with numerical
renormalization group as the impurity solver, focusing on the detailed
structure of the spectral function, self-energy, and optical conductivity. We
discuss the deviations from the simple hybridization picture, which adequately
describes the overall band structure of the system (four quasiparticle branches
in the reduced Brillouin zone), but neglects all effects of the
inelastic-scattering processes. These lead to additional structure inside the
bands, in particular asymmetric resonances or dips that become more pronounced
in the strong-coupling regime close to the antiferromagnet-paramagnetic Kondo
insulator quantum phase transition. These features, which we name ""spin
resonances"", appear generically in all models where the $f$-orbital electrons
are itinerant (large Fermi surface) and there is N\'eel antiferromagnetic order
(staggered magnetization), such as periodic Anderson model and Kondo lattice
model with antiferromagneitc Kondo coupling, but are absent in
antiferromagnetic phases with localized $f$-orbital electrons (small Fermi
surface), such as the Kondo lattice model with ferromagnetic Kondo coupling. We
show that with increasing temperature and external magnetic-field the spin
resonances become suppressed at the same time as the staggered magnetization is
reduced. Optical conductivity $\sigma(\Omega)$ has a threshold associated with
the indirect gap, followed by a plateau of low conductivity and the main peak
associated with the direct gap, while the spin resonances are reflected as a
secondary peak or a hump close to the main optical peak. This work demonstrates
the utility of high-spectral-resolution impurity solvers to study the dynamical
properties of strongly correlated fermion systems.",1411.7227v1
2015-03-05,Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy,"The magnitude of the spin polarization at the Fermi level of ferromagnetic
materials at room temperature is a key property for spintronics. Investigating
the Heusler compound Co$_2$MnSi a value of 93$\%$ for the spin polarization has
been observed at room temperature, where the high spin polarization is related
to a stable surface resonance in the majority band extending deep into the
bulk. In particular, we identified in our spectroscopical analysis that this
surface resonance is embedded in the bulk continuum with a strong coupling to
the majority bulk states. The resonance behaves very bulk-like, as it extends
over the first six atomic layers of the corresponding (001)-surface. Our study
includes experimental investigations, where the bulk electronic structure as
well as surface-related features have been investigated using spin-resolved
photoelectron spectroscopy (SR-UPS) and for a larger probing depth
spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The
results are interpreted in comparison with first-principles band structure and
photoemission calculations which consider all relativistic, surface and
high-energy effects properly.",1503.01573v1
2015-09-09,Current-modulation annealing to control microwave permittivity in composites with melt-extracted microwires,"We investigate the microwave properties of epoxy-based composite containing
melt-extracted CoFeBSiNb microwires fabricated by a combined current-modulation
annealing (CCMA) technique. We observe a shift of the resonance peak in the
effective permittivity spectra of the composite sample containing annealed 25
mm Nb-doped microwires as an applied magnetic field is increased. This
observation is consistent with the absorption-dominated impedance for thick
microwires and the ferromagnetic resonance phenomenon. It is shown that CCMA is
an appropriate technique to release internal residual stresses. Hence, for
samples containing small amounts of Nb, we observe that CCMA allows us to
suppress the high frequency resonance peak observed in samples containing
as-cast wires. However, for samples containing a high amount of Nb, the high
frequency peak remains despite the CCMA treatment. In this case, the
observation of a two-peak feature in the permittivity spectra is attributed to
the coexistence of the amorphous phase and a small amount of nanocrystallites
distributed at the wire surface. However, due to large magnetostatic energy of
long (35 mm) and short (15 mm) as-cast wires and imperfect wire-epoxy bonding
no shift of the resonance peak and the characteristic double peak of the
permittivity spectrum can be detected. Overall, CCMA emerges as a promising
strategy to control microwave permittivity in composites with melt-extracted
microwires.",1509.02623v1
2017-02-15,Resonant properties of dipole skyrmions in amorphous Fe/Gd multilayers,"The dynamic response of dipole skyrmions in Fe/Gd multilayer films is
investigated by ferromagnetic resonance measurements and compared to
micromagnetic simulations. We detail thickness and temperature dependent
studies of the observed modes as well as the effects of magnetic field history
on the resonant spectra. Correlation between the modes and the magnetic phase
maps constructed from real-space imaging and scattering patterns allows us to
conclude the resonant modes arise from local topological features such as
dipole skyrmions but does not depend on the collective response of a closed
packed lattice of these chiral textures. Using, micromagnetic modeling, we are
able to quantitatively reproduce our experimental observations which suggests
the existence of localized spin-wave modes that are dependent on the helicity
of the dipole skyrmion. We identify four localized spin wave excitations for
the skyrmions that are excited under either in-plane or out-of-plane r.f.
fields. Lastly we show that dipole skyrmions and non-chiral bubble domains
exhibit qualitatively different localized spin wave modes.",1702.04691v2
2020-11-15,A tunable magneto-acoustic oscillator with low phase noise,"A frequency-tunable low phase noise magneto-acoustic resonator is developed
on the base of a parallel-plate straight-edge bilayer consisting of a
yttrium-iron garnet (YIG) layer grown on a substrate of a gallium-gadolinium
garnet(GGG). When a YIG/GGG sample forms an ideal parallel plate, it supports a
series of high-quality-factor acoustic modes standing along the plate
thickness. Due to the magnetostriction of the YIG layer the ferromagnetic
resonance (FMR) mode of the YIG layer can strongly interact with the acoustic
thickness modes of the YIG/GGG structure, when the modes' frequencies match. A
particular acoustic thickness mode used for the resonance excitations of the
hybrid magneto-acoustic oscillations in a YIG/GGG bilayer is chosen by the YIG
layer FMR frequency, which can be tuned by the variation of the external bias
magnetic field. A composite magneto-acoustic oscillator, which includes an
FMR-based resonance pre-selector, is developed to guarantee satisfaction of the
Barkhausen criteria for a single-acoustic-mode oscillation regime. The
developed low phase noise composite magneto-acoustic oscillator can be tuned
from 0.84 GHz to 1 GHz with an increment of about 4.8 MHz (frequency distance
between the adjacent acoustic thickness modes in a YIG/GGG parallel plate), and
demonstrates the phase noise of -116 dBc/Hz at the offset frequency of 10 kHz.",2011.07648v1
2022-06-26,Nonequilibrium spintronic transport through Kondo impurities,"In this work we analyze the nonequilibrium transport through a quantum
impurity (quantum dot or molecule) attached to ferromagnetic leads by using a
hybrid numerical renormalization group-time-dependent density matrix
renormalization group thermofield quench approach.For this, we study the bias
dependence of the differential conductance through the system, which shows a
finite zero-bias peak, characteristic of the Kondo resonance and reminiscent of
the equilibrium local density of states. In the non-equilibrium settings, the
resonance in the differential conductance is also found to decrease with
increasing the lead spin polarization. The latter induces an effective exchange
field that lifts the spin degeneracy of the dot level. Therefore as we
demonstrate, the Kondo resonance can be restored by counteracting the exchange
field with a finite external magnetic field applied to the system. Finally, we
investigate the influence of temperature on the nonequilibrium conductance,
focusing on the split Kondo resonance. Our work thus provides an accurate
quantitative description of the spin-resolved transport properties relevant for
quantum dots and molecules embedded in magnetic tunnel junctions.",2206.12841v2
2022-11-22,Magnetic resonance study of rare-earth titanates,"We present a nuclear magnetic resonance (NMR) and electron spin resonance
(ESR) study of rare-earth titanates derived from the spin-1/2 Mott insulator
YTiO$_3$. Measurements of single-crystalline samples of (Y,Ca,La)TiO$_3$ in a
wide range of isovalent substitution (La) and hole doping (Ca) reveal several
unusual features in the paramagnetic state of these materials. $^{89}$Y NMR
demonstrates a clear discrepancy between the static and dynamic local magnetic
susceptibilities, with deviations from Curie-Weiss behavior far above the Curie
temperature $T_C$. No significant changes are observed close to $T_C$, but a
suppression of fluctuations is detected in the NMR spin-lattice relaxation time
at temperatures of about $3\times T_C$. Additionally, the nuclear spin-spin
relaxation rate shows an unusual peak in dependence on temperature for all
samples. ESR of the unpaired Ti electron shows broad resonance lines at all
temperatures and substitution/doping levels, which we find to be caused by
short electronic spin-lattice relaxation times. We model the relaxation as an
Orbach process that involves a low-lying electronic excited state, which
enables the determination of the excited-state gap from the temperature
dependence of the ESR linewidths. We ascribe the small gap to Jahn-Teller
splitting of the two lower Ti $t_{2g}$ orbitals. The value of the gap closely
follows $T_C$ and is consistent with the temperatures at which deviations from
Curie-Weiss fluctuations are observed in NMR. These results provide insight
into the interplay between orbital and spin degrees of freedom in rare-earth
titanates and indicate that full orbital degeneracy lifting is associated with
ferromagnetic order.",2211.12387v2
2023-12-20,Resonant Raman Scattering of Few Layers CrBr$_3$,"We investigate the vibrational and magnetic properties of thin layers of
chromium tribromide (CrBr$_3$) with a thickness ranging from three to twenty
layers (3~L to 20~L) revealed by the Raman scattering (RS) technique.
Systematic dependence of the RS process efficiency on the energy of the laser
excitation is explored for four different excitation energies: 1.96 eV, 2.21
eV, 2.41 eV, and 3.06 eV. Our characterization demonstrates that for 12 L
CrBr$_3$, 3.06~eV excitation could be considered resonant with interband
electronic transitions due to the enhanced intensity of the Raman-active
scattering resonances and the qualitative change in the Raman spectra.
Polarization-resolved RS measurements for 12 L CrBr$_3$ and first-principles
calculations allow us to identify five observable phonon modes characterized by
distinct symmetries, classified as the A$_\textrm{g}$ and E$_\textrm{g}$ modes.
The evolution of phonon modes with temperature for a 20 L CrBr$_3$ encapsulated
in hexagonal boron nitride flakes demonstrates alterations of phonon energies
and/or linewidths of resonances indicative of a transition between the
paramagnetic and ferromagnetic state at Curie temperature ($T_\textrm{C}
\approx 50$ K). The exploration of the effects of thickness on the phonon
energies demonstrated small variations pronounces exclusively for the thinnest
layers in the vicinity of 3 - 5 L. This observation is attributed to strong
localization in the real space of interband electronic excitations, limiting
the effects of confinement for resonantly excited Raman modes to atomically
thin layers.",2312.13088v1
2002-07-26,Spin injection and spin accumulation in all-metal mesoscopic spin valves,"We study the electrical injection and detection of spin accumulation in
lateral ferromagnetic metal-nonmagnetic metal-ferromagnetic metal (F/N/F) spin
valve devices with transparent interfaces. Different ferromagnetic metals,
permalloy (Py), cobalt (Co) and nickel (Ni), are used as electrical spin
injectors and detectors. For the nonmagnetic metal both aluminium (Al) and
copper (Cu) are used. Our multi-terminal geometry allows us to experimentally
separate the spin valve effect from other magneto resistance signals such as
the anomalous magneto resistance (AMR) and Hall effects. We find that the AMR
contribution of the ferromagnetic contacts can dominate the amplitude of the
spin valve effect, making it impossible to observe the spin valve effect in a
'conventional' measurement geometry. In a 'non local' spin valve measurement we
are able to completely isolate the spin valve signal and observe clear spin
accumulation signals at T=4.2 K as well as at room temperature (RT). For
aluminum we obtain spin relaxation lengths (lambda_{sf}) of 1.2 mu m and 600 nm
at T=4.2 K and RT respectively, whereas for copper we obtain 1.0 mu m and 350
nm. The spin relaxation times tau_{sf} in Al and Cu are compared with theory
and results obtained from giant magneto resistance (GMR), conduction electron
spin resonance (CESR), anti-weak localization and superconducting tunneling
experiments. The spin valve signals generated by the Py electrodes (alpha_F
lambda_F=0.5 [1.2] nm at RT [T=4.2 K]) are larger than the Co electrodes
(alpha_F lambda_F=0.3 [0.7] nm at RT [T=4.2 K]), whereas for Ni (alpha_F
lambda_F<0.3 nm at RT and T=4.2 K) no spin signal is observed. These values are
compared to the results obtained from GMR experiments.",0207641v1
2002-12-18,Nuclear Magnetic Resonance and Magnetization Studies of the Ferromagnetic Ordering Temperature Suppression in Ru Deficient SrRuO3,"The synthesis of SrRuO3 under high-pressure oxygen produces a
nonstoichiometric form with randomly distributed vacancies on the Ru-sites,
along with a significantly reduced ferromagnetic ordering temperature. In order
to gain additional insight into the suppression of the ferromagnetism, local
studies utilizing 99,101 Ru zero-field spin-echo NMR, and Ru K-edge XAFS, along
with complimentary magnetization and x-ray diffraction measurements, have been
carried out on samples of SrRuO3 annealed at both (""ambient"") atmospheric
pressure and ""high-pressure"" oxygen (600 atm). Consistent with previous work,
the NMR spectrum for ""ambient"" SrRuO3 consists of two well-defined peaks at
64.4 MHz and 72.2 MHz corresponding to the 99Ru and 101Ru isotopes,
respectively, and a hyperfine field of 329 kG. Although the magnetization
measurements show a lower ferromagnetic ordering temperature for the
""high-pressure"" oxygen sample (90 K compared to 160 K for the ""ambient""
sample), the NMR spectrum shows no significant shift in the two peak
frequencies. However, the two peaks exhibit considerable broadening, along with
structure on both the low and high frequency sides which is believed to be
quadrupolar in origin. Analysis of the Ru K-edge XAFS reveals more disorder in
the Ru-O bond for the ""high-pressure"" oxygen sample compared to the ""ambient""
sample. Furthermore, XANES of Ru K-edge analysis indicates no difference in the
valence of Ru between the two samples. The magnetic behavior indicates the
existence of some vacancies on the Ru sites for the ""high-pressure"" oxygen
sample.",0212435v2
2014-08-18,Tunneling Conductance and Spin Transport in Clean Ferromagnet-Ferromagnet-Superconductor Heterostructures,"We present a transfer matrix approach that combines the
Blonder-Tinkham-Klapwijk (BTK) formalism and self-consistent solutions to the
Bogolibuov-de Gennes (BdG) equations and use it to study the tunneling
conductance and spin transport in ferromagnet (${\rm F}$)-superconductor (${\rm
S}$) trilayers (${\rm F_1F_2 S}$) as functions of bias voltage. The
self-consistency ensures that the spin and charge conservation laws are
properly satisfied. We consider forward and angularly averaged conductances
over a broad range of the strength of the exchange fields and ${\rm F}$
thicknesses, as the relative in-plane magnetization angle, $\phi$, between the
two ferromagnets varies. The $\phi$-dependence of the self-consistent
conductance curves in the trilayers can differ substantially from that obtained
via a non-self-consistent approach. The zero bias forward conductance peak
exhibits, as $\phi$ varies, resonance effects intricately associated with
particular combinations of the geometrical and material parameters. We find,
when the magnetizations are non-collinear, signatures of the anomalous Andreev
reflections in the subgap regions of the angularly averaged conductances. When
${\rm F_1}$ is half-metallic, the angularly averaged subgap conductance chiefly
arises from anomalous Andreev reflection. The in-plane components of the spin
current are strongly bias dependent, while the out-of-plane spin current
component is only weakly dependent upon voltage. The components of the spin
current aligned with the local exchange field of one of the F layers are
conserved in that layer and in the S region, while they oscillate in the other
layer. We compute the spin transfer torques, in connection with the oscillatory
behavior of spin currents, and verify that the spin continuity equation is
strictly obeyed in our method.",1408.4172v2
2019-07-24,Strange metal behavior in a pure ferromagnetic Kondo lattice,"The strange metal phases found to develop in a wide range of materials near a
quantum critical point (QCP), have posed a long-standing mystery. The frequent
association of strange metals with unconventional superconductivity and
antiferromagnetic QCPs has led to a belief that they are highly entangled
quantum states. Ferromagnets, by contrast are regarded as an unlikely setting
for strange metals, for they are weakly entangled and their QCPs are often
interrupted by competing phases or first order phase transitions. Here, we
provide compelling evidence that the stoichiometric heavy fermion ferromagnet
CeRh$_6$Ge$_4$ becomes a strange metal at a pressure-induced QCP: specific heat
and resistivity measurements demonstrate that the FM transition is continuously
suppressed to zero temperature revealing a strange metal phase. We argue that
strong magnetic anisotropy plays a key role in this process,injecting
entanglement, in the form of triplet resonating valence bonds (tRVBs) into the
ordered ferromagnet. We show that the singular transformation from tRVBs into
Kondo singlets that occurs at the QCP causes a jump in the Fermi surface
volume: a key driver of strange metallic behavior. Our results open up a new
direction for research into FM quantum criticality, while also establishing an
important new setting for the strange metal problem. Most importantly, strange
metallic behavior at a FM quantum critical point suggests that it is quantum
entanglement rather than the destruction of antiferromagnetism that is the
common driver of the many varied examples of strange metallic behavior.",1907.10470v2
2020-09-10,Origin of magnetic moments and ferromagnetic properties of potassium clusters in zeolite A,"K clusters arrayed in zeolite A are investigated in detail. K clusters are
generated in regular alpha-cages of zeolite A by the loading of guest K metal
at a loading density of K atoms per alpha-cage, $n$. The value of $n$ was
changed from 0 to 7.2. It is known that this system shows ferromagnetic
properties for $n > 2$, where the Curie temperature increases with $n$, has a
peak of approx,8 K at $n approx 3.6$, and decreases to 0 K at $n = 7.2$. The
negative Weiss temperature is estimated from the Curie-Weiss law for $n > 2$. A
spherical quantum-well (SQW) model for the K cluster with 1$s$, 1$p$, and 1$d$
quantum states has previously been proposed, and the ferromagnetic properties
were explained as being due to $s$-electrons in 1$p$ states. A spin-cant model
of Mott-insulator antiferromagnetism in a K cluster array has been proposed for
the origin of the ferromagnetic properties. However, the SQW model cannot
explain either the $n$-dependence of the Curie temperature or that of the Curie
constant. In the present study, detailed measurements were made of the optical
reflection, magnetic properties, electron spin resonance, and electrical
resistivities. An optical reflection band at 0.7 eV is clearly observed for $2
< n < 6$ at low temperatures, and is assigned to the excitation of the
sigma-bonding state between 1$p$-states in adjoining alpha-cages. The
electrical resistivity indicates an insulating state continuously for $n$. We
propose an advanced SQW model with consideration for sigma-bonding, the orbital
orthogonality of 1$p$-hole states, and also the superlattice structure. We
explain the observed electronic properties using this model based on a
correlated polaron system. We propose an enhancement effect of the
Dzyaloshinsky-Moriya (DM) interaction between adjoining $1p$ orbitals by the
extension of the Rashba mechanism of spin-orbit interaction.",2009.04828v1
2021-08-31,Systemic Consequences of Disorder in Magnetically Self-Organized Topological MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ Superlattices,"MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ materials system has recently
generated strong interest as a natural platform for realization of the quantum
anomalous Hall (QAH) state. The system is magnetically much better ordered than
substitutionally doped materials, however, the detrimental effects of certain
disorders are becoming increasingly acknowledged. Here, from compiling
structural, compositional, and magnetic metrics of disorder in ferromagnetic
MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ it is found that migration of Mn
between MnBi$_{2}$T$e_{4}$ septuple layers (SLs) and otherwise non-magnetic
Bi$_{2}$Te$_{3}$ quintuple layers (QLs) has systemic consequences - it induces
ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in
ferromagnetic resonance as an acoustic and optical resonance mode of the two
coupled spin subsystems. Even for a large SL separation (n $\gtrsim$ 4 QLs) the
structure cannot be considered as a stack of uncoupled two-dimensional layers.
Angle-resolved photoemission spectroscopy and density functional theory studies
show that Mn disorder within an SL causes delocalization of electron
wavefunctions and a change of the surface bandstructure as compared to the
ideal MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$. These findings highlight the
critical importance of inter- and intra-SL disorder towards achieving new QAH
platforms as well as exploring novel axion physics in intrinsic topological
magnets.",2109.00044v3
1996-09-09,Kinetic Ising System in an Oscillating External Field: Stochastic Resonance and Residence-Time Distributions,"Experimental, analytical, and numerical results suggest that the mechanism by
which a uniaxial single-domain ferromagnet switches after sudden field reversal
depends on the field magnitude and the system size. Here we report new results
on how these distinct decay mechanisms influence hysteresis in a
two-dimensional nearest-neighbor kinetic Ising model. We present theoretical
predictions supported by numerical simulations for the frequency dependence of
the probability distributions for the hysteresis-loop area and the
period-averaged magnetization, and for the residence-time distributions. The
latter suggest evidence of stochastic resonance for small systems in moderately
weak oscillating fields.",9609086v2
1999-12-14,Resonant quantum coherence of magnetization at excited states in nanospin systems with different crystal symmetries,"The quantum interference effects induced by the Wess-Zumino term, or Berry
phase are studied theoretically in resonant quantum coherence of magnetization
vector between degenerate excited states in nanometer-scale single-domain
ferromagnets in the absence of an external magnetic field. By applying the
periodic instanton method in the spin-coherent-state path integral, we evaluate
the low-lying tunnel splittings between degenerate excited states of
neighboring wells. And the low-lying energy level spectrum of m-th excited
states are obtained with the help of the Bloch theorem in one-dimensional
periodic potential.",9912231v2
2001-06-12,Evidence for internal field in graphite: A conduction electron spin resonance study,"We report conduction electron spin resonance measurements performed on highly
oriented pyrolitic graphite samples between 10 K and 300 K using S (f = 4 GHz),
X (f = 9.4 GHz), and Q (f = 34.4 GHz) microwave bands for the external
dc-magnetic field applied parallel (H || c) and perpendicular (H perp c) to the
sample hexagonal c-axis. The results obtained in the H || c geometry are
interpreted in terms of the presence of an effective internal
ferromagnetic-like field Heff-int(T,H) that increases as the temperature
decreases and the applied dc-magnetic field increases. We associate the
occurrence of the Heff-int(T,H) with the field-induced metal-insulator
transition in graphite and discuss its origin in the light of relevant
theoretical models.",0106232v1
2001-08-09,Oxygen Nuclear Magnetic Resonance Study of RuSr2EuCu2O8,"We report the results from a 17O Nuclear Magnetic Resonance (NMR) study of
the high temperature superconducting cuprate (HTSC), RuSr2EuCu2O8. This
compound has recently been found to exhibit the coexistence of magnetic order
and superconductivity. At 9 T, the magnetic order in the RuO2 layers is
predominately ferromagnetic. We measured the 17O NMR spectra from 10 K to 330 K
and find the occurrence of an increasing 17O NMR shift with increasing
temperature for temperatures above ~200 K, providing direct evidence that
RuSr2RCu2O8 is similar to a very underdoped HTSC. The analysis of the NMR shift
and spectral width of the 17O NMR line gives a small but measurable hyperfine
field of ~9 mT from the Ru moment at the oxygen site in the copper oxygen
planes. We show that the 17O NMR linewidth is governed by dipolar contributions
from the Ru moment.",0108157v1
2001-11-14,"Magnetic Ordering, Orbital Ordering and Resonant X-ray Scattering in Perovskite Titanates","The effective Hamiltonian for perovskite titanates is derived by taking into
account the three-fold degeneracy of $t_{2g}$ orbitals and the strong
electron-electron interactions. The magnetic and orbital ordered phases are
studied in the mean-field approximation applied to the effective Hamiltonian. A
large degeneracy of the orbital states in the ferromagnetic phase is found in
contrast to the case of the doubly degenerate $e_g$ orbitals. Lifting of this
orbital degeneracy due to lattice distortions and spin-orbit coupling is
examined. A general form for the scattering cross section of the resonant x-ray
scattering is derived and is applied to the recent experimental results in
YTiO$_3$. The spin wave dispersion relation in the orbital ordered YTiO$_3$ is
also studied.",0111249v1
2002-11-03,"Resonant photoemission spectroscopy study of insulator-to-metal transition in Cr- and Ru-doped Nd_{1/2}A_{1/2}Mn_{1-y} O_{3} (A=Ca, Sr)","Electronic structures of very dilute Cr- or Ru-doped Nd_{1/2}A_{1/2}MnO_{3}
(NAMO; A=Ca, Sr) manganites have been investigated using the Mn and Cr 2p -> 3d
resonant photoemission spectroscopy (PES). All the Cr- and Ru-doped NAMO
systems exhibit the clear metallic Fermi edges in the Mn e_g spectra near E_F,
consistent with their metallic ground states. The Cr 3d states with t^3_{2g}
configuration are at ~ 1.3 eV below E_F, and the Cr e_{g} states do not
participate in the formation of the band near E_F. Cr- and Ru-induced
ferromagnetism and insulator-to-metal transitions can be understood with their
measured electronic structures.",0211041v1
2003-07-25,Determining carrier densities in InMnAs by cyclotron resonance,"Accurate determination of carrier densities in ferromagnetic semiconductors
by Hall measurements is hindered by the anomalous Hall effect, and thus
alternative methods are being sought. Here, we propose that cyclotron resonance
(CR) is an excellent method for carrier density determination for InMnAs-based
magnetic structures. We develop a theory for electronic and magneto-optical
properties in narrow gap InMnAs films and superlattices in ultrahigh magnetic
fields oriented along [001]. In n-type InMnAs films and superlattices, we find
that the e-active CR peak field is pinned at low electron densities and then
begins to shift rapidly to higher fields above a critical electron
concentration allowing the electron density to be accurately calibrated. In
p-type InMnAs, we observe two h-active CR peaks due to heavy and light holes.
The lineshapes depend on temperature and line broadening. The light hole CR
requires higher hole densities and fields. Analyzing CR lineshapes in p-films
and superlattices can help determine hole densities.",0307653v1
2004-01-06,The Role of Multiferroics in the Negative Index of Refraction,"We explore the possibility of realizing intrinsic far infrared negative index
materials (NIM) in multiferroic crystals (crystals simultaneously possessing a
ferroelectric and ferromagnetic phase) possessing electric and magnetic dipole
resonances with nearby resonance frequencies, or overlapping regions of
negative permittivity and permeability. We demonstrate the functionality of
such a material using finite difference time domain simulations. In order to
motivate the connection between multiferroics and negative index materials, we
discuss the negative index of refraction in the polariton picture.",0401046v1
2004-02-17,The fate of Kondo resonances in certain Kondo lattices: a ``poor woman's'' scaling analysis,"We present an effective field theory for the Kondo lattice, which can
exhibit, in a certain range of parameters, a non Fermi liquid paramagnetic
phase at the brink of a zero temperature Anti Ferromagnetic (AF) transition.
The model is derived in a natural way from the bosonic Kondo-Heisenberg model,
in which the Kondo resonances are treated as true (but damped) Grassmann
fields. One loop Renormalization Group (RG) treatment of this model gives a
phase diagram for the Kondo lattice as a function of $ J_K $ where, for $ J_K<
J_c$ the system shows AF order, for $J_K> J_1$ one has the heavy electron phase
and for $ J_c < J_K < J_1$ the formation of the Kondo singlets is incomplete,
leading to the breakdown of the Landau Fermi liquid theory.",0402447v1
2004-04-22,Self-interaction corrected relativistic theory of magnetic scattering of x rays: Application to praseodymium,"A first-principles theory of resonant magnetic scattering of x rays is
presented. The scattering amplitudes are calculated using a standard
time-dependent perturbation theory to second order in the electron-photon
interaction vertex. In order to calculate the cross section reliably an
accurate description of the electronic states in the material under
investigation is required and this is provided by the density functional theory
(DFT) employing the Local Spin Density Approximation combined with the
self-interaction corrections (SIC-LSD). The magnetic x-ray resonant scattering
(MXRS) theory has been implemented in the framework of the relativistic
spin-polarized LMTO-ASA band structure calculation method. The theory is
illustrated with an application to ferromagnetic praseodymium. It is shown that
the theory quantitatively reproduces the dependence on the spin and orbital
magnetic moments originally predicted qualitatively (Blume, J. Appl. Phys, {\bf
57}, 3615 (1985)) and yields results that can be compared directly with
experiment.",0404543v3
2004-06-08,Magnetism and electron spin resonance in single crystalline beta-AgNpO2(SeO3),"We report magnetization, susceptibility, electrical transport, and electron
spin resonance (ESR) studies of single crystals of beta-AgNpO2(SeO3). Here the
valence of the Np sites is expected to be Np(V). We observe a magnetic
transition below 8 K, where the transition temperature is dependent on the
effective magnetic moment. Although the transition appears to be ferromagnetic,
no hysteresis is seen in the magnetization, and the saturation moment above 0.1
T is found to be about 60% of the free NpO2 ion moment. The decrease in the Np
moments determined experimentally is thought to arise from crystal field and
spin-orbit effects. Although Np(V) is expected to be ESR silent, we observe
temperature dependent ESR spectra at ~44 GHz (for fields above the saturation
field) that show slight shifts in the g-factor and line width at low
temperatures. Our results provide evidence that both Np(V) and Np(IV) valences
are present, where the latter may be a minority population. The crystals,
although dark in appearance, are electrically insulating (rho > 10^10 Ohm-cm)
at room temperature.",0406194v1
2004-12-06,Non-collinear magnetoconductance of a quantum dot,"We study theoretically the linear conductance of a quantum dot connected to
ferromagnetic leads. The dot level is split due to a non-collinear magnetic
field or intrinsic magnetization. The system is studied in the non-interacting
approximation, where an exact solution is given, and, furthermore, with Coulomb
correlations in the weak tunneling limit. For the non-interacting case, we find
an anti-resonance for a particular direction of the applied field,
non-collinear to the parallel magnetization directions of the leads. The
anti-resonance is destroyed by the correlations, giving rise to an interaction
induced enhancement of the conductance. The angular dependence of the
conductance is thus distinctly different for the interacting and
non-interacting cases when the magnetizations of the leads are parallel.
However, for anti-parallel lead magnetizations the interactions do not alter
the angle dependence significantly.",0412145v2
2004-12-14,Nuclear Magnetic Resonance as a probe of nanometre-size orbital textures in magnetic transition metal oxides,"The study of strong electron correlations in transition metal oxides with
modern microscopy and diffraction techniques unveiled a fascinating world of
nanosize textures in the spin, charge, and crystal structure. Examples range
from high $T_c$ superconducting cuprates and nickelates, to hole doped
manganites and cobaltites. However, in many cases the appearance of these
textures is accompanied with ""glassiness"" and multiscale/multiphase effects,
which complicate significantly their experimental verification. Here, we
demonstrate how nuclear magnetic resonance may be uniquely used to probe
nanosize orbital textures in magnetic transition metal oxides. As a convincing
example we show for the first time the detection of nanoscale orbital phase
separation in the ground state of the ferromagnetic insulator
La$_{0.875}$Sr$_{0.125}$MnO$_3$.",0412371v1
2006-02-06,Switching the sign of photon induced exchange interactions in semiconductor microcavities with finite quality factors,"We investigate coupling of localized spins in a semiconductor quantum dot
embedded in a microcavity with a finite quality factor. The lowest cavity mode
and the quantum dot exciton are coupled forming a polariton, whereas excitons
interact with localized spins via exchange. The finite quality of the cavity Q
is incorporated in the model Hamiltonian by adding an imaginary part to the
photon frequency. The Hamiltonian, which treats photons, spins and excitons
quantum mechanically, is solved exactly. Results for a single polariton clearly
demonstrate the existence of a resonance, sharper as the temperature decreases,
that shows up as an abrupt change between ferromagnetic and antiferromagnetic
indirect anisotropic exchange interaction between localized spins. The origin
of this spin-switching finite-quality-factor effect is discussed in detail
remarking on its dependence on model parameters, i.e., light-matter coupling,
exchange interaction between impurities, detuning and quality factor. For
parameters corresponding to the case of a (Cd,Mn)Te quantum dot, the resonance
shows up for Q around 70 and detuning around 10 meV. In addition, we show that,
for such a quantum dot, and the best cavities actually available (quality
factors better than 200) the exchange interaction is scarcely affected.",0602122v1
2006-11-28,Exchange interaction between single magnetic adatoms,"The magnetic coupling between single Co atoms adsorbed on a copper surface is
determined by probing the Kondo resonance using low-temperature scanning
tunneling spectroscopy. The Kondo resonance, which is due to magnetic
correlation effects between the spin of a magnetic adatom and the conduction
electrons of the substrate, is modified in a characteristic way by the coupling
of the neighbouring adatom spins. Increasing the interatomic distance of a
Cobalt dimer from 2.56A to 8.1A we follow the oscillatory transition from
ferromagnetic to antiferromagnetic coupling. Adding a third atom to the
antiferromagnetically coupled dimer results in the formation of a collective
correlated state.",0611716v2
2007-03-28,Spin transport across carbon nanotube quantum dots,"We investigate linear and nonlinear transport in interacting single wall
carbon nanotubes (SWCNTs) that are weakly attached to ferromagnetic leads. For
the reduced density matrix of a SWCNT quantum dot, equations of motion which
account for an arbitrarily vectored polarisation of the contacts are derived.
We focus on the case of large diameter nanotubes where exchange effects
emerging from short-ranged processes can be excluded and the four-electron
periodicity at low bias can be observed. This yields in principle four distinct
resonant tunnelling regimes, but due to symmetries in the involved
groundstates, each two possess a mirror-symmetry. With a non-collinear
configuration, we recover at the 4N <-> 4N+1 / 4N+3 <-> 4N resonances the
analytical results known for the angular dependence of the conductance of a
single level quantum dot or a metallic island. The two other cases are treated
numerically and show on the first glance similar, yet not analytically
describable dependences. In the nonlinear regime, negative differential
conductance features occur for non-collinear lead magnetisations.",0703756v2
2007-05-07,Stability of spinor Fermi gases in tight waveguides,"The two and three-body correlation functions of the ground state of an
optically trapped ultracold spin-1/2 Fermi gas (SFG) in a tight waveguide (1D
regime) are calculated in the plane of even and odd-wave coupling constants,
assuming a 1D attractive zero-range odd-wave interaction induced by a 3D p-wave
Feshbach resonance, as well as the usual repulsive zero-range even-wave
interaction stemming from 3D s-wave scattering. The calculations are based on
the exact mapping from the SFG to a ``Lieb-Liniger-Heisenberg'' model with
delta-function repulsions depending on isotropic Heisenberg spin-spin
interactions, and indicate that the SFG should be stable against three-body
recombination in a large region of the coupling constant plane encompassing
parts of both the ferromagnetic and antiferromagnetic phases. However, the
limiting case of the fermionic Tonks-Girardeau gas (FTG), a spin-aligned 1D
Fermi gas with infinitely attractive p-wave interactions, is unstable in this
sense. Effects due to the dipolar interaction and a Zeeman term due to a
resonance-generating magnetic field do not lead to shrinkage of the region of
stability of the SFG.",0705.0937v1
2007-07-09,"Effective chiral magnetic currents, topological magnetic charges, and microwave vortices in a cavity with an enclosed ferrite disk","In microwaves, a TE-polarized rectangular-waveguide resonator with an
inserted thin ferrite disk gives an example of a nonintegrable system. The
interplay of reflection and transmission at the disk interfaces together with
the material gyrotropy effect gives rise to whirlpool-like electromagnetic
vortices in the proximity of the ferromagnetic resonance. Based on numerical
simulation, we show that a character of microwave vortices in a cavity can be
analyzed by means of consideration of equivalent magnetic currents. Maxwell
equations allows introduction of a magnetic current as a source of the
electromagnetic field. Specifically, we found that in such nonintegrable
structures, magnetic gyrotropy and geometrical factors leads to the effect of
symmetry breaking resulting in effective chiral magnetic currents and
topological magnetic charges. As an intriguing fact, one can observe precessing
behavior of the electric-dipole polarization inside a ferrite disk.",0707.1216v1
2007-07-09,Microwave whirlpools in a rectangular-waveguide cavity with a thin ferrite disk,"We study a three dimensional system of a rectangular-waveguide resonator with
an inserted thin ferrite disk. The interplay of reflection and transmission at
the disk interfaces together with material gyrotropy effect, gives rise to a
rich variety of wave phenomena. We analyze the wave propagation based on full
Maxwell-equation numerical solutions of the problem. We show that the
power-flow lines of the microwave-cavity field interacting with a ferrite disk,
in the proximity of its ferromagnetic resonance, form whirlpool-like
electromagnetic vortices. Such vortices are characterized by the dynamical
symmetry breaking. The role of ohmic losses in waveguide walls and dielectric
and magnetic losses in a disk is a subject of our investigations.",0707.1236v1
2008-01-03,Resonant Inelastic X-ray Scattering (RIXS) Spectra for Ladder Cuprates,"The ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ is of interest both as a
quasi-one-dimensional analog of the superconducting cuprates and as a
superconductor in its own right when Sr is substituted by Ca. In order to model
resonant inelastic x-ray scattering (RIXS) spectra for this compound, we
investigate the simpler SrCu$_{2}$O$_{3}$ system in which the crystal structure
contains very similar ladder planes. We approximate the LDA dispersion of
SrCu$_{2}$O$_{3}$ by a Cu only two-band tight-binding model. Strong correlation
effects are incorporated by assuming an anti-ferromagnetic ground state. The
available angle-resolved photoemission (ARPES) and RIXS data on the ladder
compound are found to be in reasonable accord with our theoretical predictions.",0801.0604v1
2008-03-19,Resonant Spin-Transfer-Driven Switching of Magnetic Devices Assisted by Microwave Current Pulses,"The torque generated by the transfer of spin angular momentum from a
spin-polarized current to a nanoscale ferromagnet can switch the orientation of
the nanomagnet much more efficiently than a current-generated magnetic field,
and is therefore in development for use in next-generation magnetic random
access memory (MRAM). Up to now, only DC currents and square-wave current
pulses have been investigated in spin-torque switching experiments. Here we
present measurements showing that spin transfer from a microwave-frequency
pulse can produce a resonant excitation of a nanomagnet and lead to improved
switching characteristics in combination with a square current pulse. With the
assistance of a microwave-frequency pulse, the switching time is reduced and
achieves a narrower distribution than when driven by a square current pulse
alone, and this can permit significant reductions in the integrated power
required for switching. Resonantly excited switching may also enable
alternative, more compact MRAM circuit architectures.",0803.2880v1
2008-05-08,Electrically driven single electron spin resonance in a slanting Zeeman field,"The rapidly rising fields of spintronics and quantum information science have
led to a strong interest in developing the ability to coherently manipulate
electron spins. Electron spin resonance (ESR) is a powerful technique to
manipulate spins that is commonly achieved by applying an oscillating magnetic
field. However, the technique has proven very challenging when addressing
individual spins. In contrast, by mixing the spin and charge degrees of freedom
in a controlled way through engineered non-uniform magnetic fields, electron
spin can be manipulated electrically without the need of high-frequency
magnetic fields. Here we realize electrically-driven addressable spin rotations
on two individual electrons by integrating a micron-size ferromagnet to a
double quantum dot device. We find that the electrical control and spin
selectivity is enabled by the micro-magnet's stray magnetic field which can be
tailored to multi-dots architecture. Our results demonstrate the feasibility of
manipulating electron spins electrically in a scalable way.",0805.1083v1
2008-12-12,"Spin diffusion and magnetic eigenoscillations confined to single molecular layers in the organic conductors kappa-(BEDT-TTF)_2Cu[N(CN)_2X (X=Cl, Br)","The layered organic compounds, kappa-(BEDT-TTF)_2Cu[N(CN)_2X (X=Cl, Br) are
metals at ambient temperatures. At low temperatures, the Cl compound is a
weakly ferromagnetic Mott insulator while the isostructural Br compound is a
superconductor. We find by conduction electron spin resonance (CESR) and
antiferromagnetic resonance (AFMR) an extreme anisotropy of spin transport and
magnetic interactions in these materials. In the metallic state spin diffusion
is confined to single molecular layers within the spin lifetime of 10^-9 s.
Electrons diffuse several hundreds of nm without hopping to the next molecular
layer. In the magnetically ordered insulating phase of the Cl compound we
observe and calculate the four AFMR modes of the weakly coupled single
molecular layers. The inter-plane exchange field is comparable or less than the
typically 1 mT dipolar field and almost 10^6 times less than the intra-layer
exchange field.",0812.2383v1
2009-02-05,Magnetic ordering in EuRh2As2 studied by x-ray resonant magnetic scattering,"Element-specific x-ray resonant magnetic scattering investigations were
performed to determine the magnetic structure of Eu in EuRh2As2. In the
temperature range from 46 K down to 6 K, an incommensurate antiferromagnetic
(ICM)structure with a temperature dependent propagation vector (0 0 0.9)
coexists with a commensurate antiferromagnetic (CM) structure.
Angular-dependent measurements of the magnetic intensity indicate that the
magnetic moments lie in the tetragonal basal plane and are ferromagnetically
aligned within the a-b plane for both magnetic structures. The ICM structure is
a spiral-like magnetic structure with a turn angle of 162 deg between adjacent
Eu planes. In the CM structure, this angle is 180 deg. These results are
consistent with band-structure calculations which indicate a strong sensitivity
of the magnetic configuration on the Eu valence.",0902.0975v2
2009-07-12,Why could Electron Spin Resonance be observed in a heavy fermion Kondo lattice?,"We develop a theoretical basis for understanding the spin relaxation
processes in Kondo lattice systems with heavy fermions as experimentally
observed by electron spin resonance (ESR). The Kondo effect leads to a common
energy scale that regulates a logarithmic divergence of different spin kinetic
coefficients and supports a collective spin motion of the Kondo ions with
conduction electrons. We find that the relaxation rate of a collective spin
mode is greatly reduced due to a mutual cancelation of all the divergent
contributions even in the case of the strongly anisotropic Kondo interaction.
The contribution to the ESR linewidth caused by the local magnetic field
distribution is subject to motional narrowing supported by ferromagnetic
correlations. The developed theoretical model successfully explains the ESR
data of YbRh2Si2 in terms of their dependence on temperature and magnetic
field.",0907.2074v2
2009-09-19,Phenomenology of ESR in heavy fermion systems: Fermi liquid and non-Fermi liquid regime,"We extend and apply a recent theory of the dynamical spin response of
Anderson lattice systems to interpret ESR data on YbRh2Si2. Starting within a
semiphenomenological Fermi liquid description at low temperatures T < Tx (a
crossover temperature) and low magnetic fields B << Bx, we extend the
description to the non-Fermi liquid regime by adopting a quasiparticle picture
with effective mass and spin susceptibility varying logarithmically with
energy/temperature, as observed in experiment. We find a sharp ESR resonance
line slightly shifted from the local f-level resonance and broadened by
quasiparticle scattering (taking unequal g-factors of conduction and f
electrons) and by spin-lattice relaxation, both significantly reduced by the
effect of ferromagnetic fluctuations. A detailed comparison of our theory with
the data shows excellent agreement in the Fermi liquid regime. In the non-Fermi
liquid regime we find a close relation of the T-dependence of the specific
heat/spin susceptibility with the observed T-dependence of line shift and
linewidth.",0909.3552v1
2009-09-25,Theory of Raman and Resonant Inelastic X-ray Scattering from Collective Orbital Excitations in YTiO$_3$,"We present two different theories for Raman scattering and Resonant Inelastic
X-ray Scattering (RIXS) in the low temperature ferromagnetic phase of YTiO$_3$
and compare this to the available experimental data. For description of the
orbital ground-state and orbital excitations, we consider two models
corresponding to two theoretical limits: one where the $t_{2g}$ orbitals are
degenerate, and the other where strong lattice distortions split them. In the
former model the orbitals interact through superexchange. The resulting
superexchange Hamiltonian yields an orbitally ordered ground state with
collective orbital excitations on top of it - the orbitons. In the
orbital-lattice model, on the other hand, distortions lead to local
dd-transitions between crystal field levels. Correspondingly, the orbital
response functions that determine Raman and RIXS lineshapes and intensities are
of cooperative or single-ion character. We find that the superexchange model
yields theoretical Raman and RIXS spectra that fit very well to the
experimental data.",0909.4656v2
2010-07-14,d-d Excitations in Bilayer Manganites Probed by Resonant Inelastic X-ray Scattering,"We report a high resolution resonant inelastic x-ray scattering investigation
of the bilayer manganites La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ with $x = 0.36$ and
$0.5$. The momentum dependence along the crystallographic $(110)$ direction for
energy losses $1\,\rm{eV} \leq \Delta E \leq 15\,\rm{eV}$ has been measured in
detail with the data analysis focusing on the energy loss region $1\,\rm{eV}
\leq \Delta E \leq 5\,\rm{eV}$, which includes a strong peak located at $\Delta
E \approx 2\,\rm{eV}$. We observe a clear dispersion of up to $0.5\,\rm{eV}$ in
the measured $\textbf{q}$ range, which is direct evidence of the non-local
character of this excitation. Further, we found that the intensity in this low
energy region strongly depends on both the reduced wave vector $\textbf{q} =
(h, h, 0)$, $h = 0.1 - 0.5$, and temperature, i.e. different ordered phases.
Results can be explained via an intersite $d-d$ charge transfer excitation,
proposed for pseudo-cubic manganites, where the hopping rate is strongly
increased (decreased) by ferromagnetic (antiferromagnetic) alignment of
neighboring in-plane Mn ion core spins.",1007.2283v1
2010-07-19,Standing spin-wave mode structure and linewidth in partially disordered perpendicularly magnetized sub-micron Permalloy disc arrays,"Standing spin wave mode frequencies and linewidths in partially disordered
perpendicular magnetized arrays of sub-micron Permalloy discs are measured
using broadband ferromagnetic resonance and compared to analytical results from
a single, isolated disc. The measured mode structure qualitatively reproduces
the structure expected from the theory. Fitted demagnetizing parameters
decrease with increasing array disorder. The frequency difference between the
first and second radial modes is found to be higher in the measured array
systems than predicted by theory for an isolated disc. The relative frequencies
between successive spin wave modes are unaffected by reduction of the
long-range ordering of discs in the array. An increase in standing spin wave
resonance linewidth at low applied magnetic fields is observed and grows more
severe with increased array disorder.",1007.3062v5
2010-10-08,Time-resolved detection of spin-transfer-driven ferromagnetic resonance and spin torque measurement in magnetic tunnel junctions,"Several experimental techniques have been introduced in recent years in
attempts to measure spin transfer torque in magnetic tunnel junctions (MTJs).
The dependence of spin torque on bias is important for understanding
fundamental spin physics in magnetic devices and for applications. However,
previous techniques have provided only indirect measures of the torque and
their results to date for the bias dependence are qualitatively and
quantitatively inconsistent. Here we demonstrate that spin torque in MTJs can
be measured directly by using time-domain techniques to detect resonant
magnetic precession in response to an oscillating spin torque. The technique is
accurate in the high-bias regime relevant for applications, and because it
detects directly small-angle linear-response magnetic dynamics caused by spin
torque it is relatively immune to artifacts affecting competing techniques. At
high bias we find that the spin torque vector differs markedly from the simple
lowest-order Taylor series approximations commonly assumed.",1010.1777v1
2010-12-17,Structural and magnetic properties of Co2MnSi thin films,"Co2MnSi (CMS) films of different thicknesses (20, 50 and 100 nm) were grown
by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays
diffraction study shows that, in all the samples, the cubic <110> CSM axis is
normal to the substrate and that there exist well defined preferential in-plane
orientations. Static and dynamic magnetic properties were investigated using
vibrating sample magnetometry (VSM) and micro-strip line ferromagnetic
resonance (MS-FMR), respectively. From the resonance measurements versus the
direction and the amplitude of an applied magnetic field we derive most of the
magnetic parameters: magnetization, gyromagnetic factor, exchange stiffness
coefficient and magnetic anisotropy terms. The in-plane anisotropy can be
described as resulting from the superposition of two terms showing a two-fold
and a four-fold symmetry without necessarily identical principal axes. The
observed behavior of the hysteresis loops is in agreement with this complex
form of the in-plane anisotropy",1012.3837v2
2011-02-10,Stimulated emission and absorption of photons in magnetic point contacts: toward metal-based spin-lasers,"Point contacts between high anisotropy ferromagnetic SmCo5 and normal metal
Cu are used to achieve a strong spin-population inversion in the contact core.
Subjected to microwave irradiation in resonance with the Zeeman splitting in
Cu, the inverted spin-population relaxes through stimulated spin-flip photon
emission, detected as peaks in the point contact resistance. Resonant spin-flip
photon absorption is detected as resistance minima, corresponding to sourcing
the photon field energy into the electrical circuit. These results demonstrate
fundamental mechanisms that are potentially useful for designing metallic
spin-based lasers.",1102.2167v1
2011-04-11,Resistively detected nuclear magnetic resonance via a single InSb two-dimensional electron gas at high temperature,"We report on the demonstration of the resistively detected nuclear magnetic
resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at
elevated temperatures up to 4 K. The RDNMR signal of 115In in the simplest
pseudospin quantum Hall ferromagnet triggered by a large direct current shows a
peak-dip line shape, where the nuclear relaxation time T1 at the peak and the
dip is different but almost temperature independent. The large Zeeman,
cyclotron, and exchange energy scales of the InSb 2DEG contribute to the
persistence of the RDNMR signal at high temperatures.",1104.1826v1
2011-06-03,Graded Orbital Occupation near Interfaces in a La2NiO4 - La2CuO4 Superlattice,"X-ray absorption spectroscopy and resonant soft x-ray reflectivity show a
non-uniform distribution of oxygen holes in a La2NiO4 - La2CuO4 (LNO-LCO)
superlattice, with excess holes concentrated in the LNO layers. Weak
ferromagnetism with Tc = 160 K suggests a coordinated tilting of NiO6
octahedra, similar to that of bulk LNO. Ni d3z2-r2 orbitals within the LNO
layers have a spatially variable occupation. This variation of the Ni valence
near LNO-LCO interfaces is observed with resonant soft x-ray reflectivity at
the Ni L edge, at a reflection suppressed by the symmetry of the structure, and
is possible through graded doping with holes, due to oxygen interstitials taken
up preferentially by inner LNO layers. Since the density of oxygen atoms in the
structure can be smoothly varied with standard procedures, this orbital
occupation, robust up to at least 280 K, is tunable.",1106.0634v2
2011-10-01,Electrical measurement of antivortex wall eigenfrequency,"The dynamics of a ferromagnetic antivortex wall has been experimentally
studied in a magnetic nanostructure. Two different techniques have been used to
independently measure the eigenfrequency of an antivortex wall such as the
resonance excitation by sinusoidal microwave and the damped resonance
excitation induced by short voltage pulses. Direct observation of antivortex
wall nucleation has been measured in the frequency domain for the first time.
Electrical measurements of the antivortex dynamics in frequency domain reveal
the existence of multi-eigenmodes as well as nonlinear behaviors for large
excitation amplitudes. The time resolved measurements of the antivortex wall
show that the frequency of the damped gyration is similar to that of frequency
domain and coexistence of spin wave excitations.",1110.0113v1
2011-10-20,Core-Core Dynamics in Spin Vortex Pairs,"We investigate magnetic nano-pillars, in which two thin ferromagnetic
nanoparticles are separated by a nanometer thin nonmagnetic spacer and can be
set into stable spin vortex-pair configurations. The 16 ground states of the
vortex-pair system are characterized by parallel or antiparallel chirality and
parallel or antiparallel core-core alignment. We detect and differentiate these
individual vortex-pair states experimentally and analyze their dynamics
analytically and numerically. Of particular interest is the limit of strong
core-core coupling, which we find can dominate the spin dynamics in the system.
We observe that the 0.2 GHz gyrational resonance modes of the individual
vortices are replaced with 2-6 GHz range collective rotational and vibrational
core-core resonances in the configurations where the cores form a bound pair.
These results demonstrate new opportunities in producing and manipulating spin
states on the nanoscale and may prove useful for new types of ultra-dense
storage devices where the information is stored as multiple vortex-core
configurations.",1110.4430v1
2011-12-21,Vortex motion in Nb/PdNi/Nb trilayers: new aspects in the flux flow state,"We study the dynamics of vortex lines in
Supercondutor/Ferromagnet/Superconductor (SFS) heterostructures at microwave
frequencies. We have employed swept-frequency, Corbino-disk and resonant,
dielectric-resonator techniques to obtain the field and temperature dependence
of the vortex-state parameters. We concentrate here on the genuine flux-flow
resistivity $\rho_{ff}$, that we access at subcritical currents using a
sufficiently high driving frequency. We find that $\rho_{ff}$ does not follow
the well-known Bardeen-Stephen model. Instead, it is well described by a full
time-dependent Ginzburg-Landau expression at very thin F layer thickness, but
changes to a previously unreported field-dependence when the F layer exceeds a
few nm.",1112.5077v1
2012-03-15,Resonance Measurement of Nonlocal Spin Torque in a Three-Terminal Magnetic Device,"A pure spin current generated within a nonlocal spin valve can exert a spin
transfer torque on a nanomagnet. This nonlocal torque enables new design
schemes for magnetic memory devices that do not require the application of
large voltages across tunnel barriers that can suffer electrical breakdown.
Here we report a quantitative measurement of this nonlocal spin torque using
spin-torque-driven ferromagnetic resonance. Our measurement agrees well with
the prediction of an effective circuit model for spin transport. Based on this
model, we suggest strategies for optimizing the strength of nonlocal torque.",1203.3266v2
2012-07-12,Electron correlations in Mn$_x$Ga$_{1-x}$As as seen by resonant electron spectroscopy and dynamical mean field theory,"After two decades from the discovery of ferromagnetism in Mn-doped GaAs, its
origin is still debated, and many doubts are related to the electronic
structure. Here we report an experimental and theoretical study of the valence
electron spectrum of Mn-doped GaAs. The experimental data are obtained through
the differences between off- and on-resonance photo-emission data. The
theoretical spectrum is calculated by means of a combination of
density-functional theory in the local density approximation and dynamical
mean-field theory (LDA+DMFT), using exact diagonalisation as impurity solver.
Theory is found to accurately reproduce measured data, and illustrates the
importance of correlation effects. Our results demonstrate that the Mn states
extend over a broad range of energy, including the top of the valence band, and
that no impurity band splits off from the valence band edge, while the induced
holes seem located primarily around the Mn impurity.",1207.2887v2
2012-07-18,From incommensurate correlations to mesoscopic spin resonance in YbRh2Si2,"Spin fluctuations are reported near the magnetic field driven quantum
critical point in YbRh2Si2. On cooling, ferromagnetic fluctuations evolve into
incommensurate correlations located at q0=+/- (delta,delta) with delta=0.14 +/-
0.04 r.l.u. At low temperatures, an in plane magnetic field induces a sharp
intra doublet resonant excitation at an energy E0=g muB mu0 H with g=3.8 +/-
0.2. The intensity is localized at the zone center indicating precession of
spin density extending xi=6 +/- 2 A beyond the 4f site.",1207.4411v1
2013-01-31,Effects of Transverse Magnetic Anisotropy on Current-Induced Spin Switching,"Spin-polarized transport through bistable magnetic adatoms or single-molecule
magnets (SMMs), which exhibit both uniaxial and transverse magnetic anisotropy,
is considered theoretically. The main focus is on the impact of transverse
anisotropy on transport characteristics and the adatom's/SMM's spin. In
particular, we analyze the role of quantum tunneling of magnetization (QTM) in
the mechanism of the current-induced spin switching, and show that the QTM
phenomenon becomes revealed as resonant peaks in the average values of the
molecule's spin and in the charge current. These features appear at some
resonant fields and are observable when at least one of the electrodes is
ferromagnetic. We also show that the conductance generally depends on the
relative orientation of the average adatom's/SMM's spin and electrode's
magnetic moment. This spin-valve like magnetoresistance effect can be used to
control spin switching of the adatom's/SMM's spin.",1302.1074v1
2013-03-21,Optical reflectivity and magnetoelectric effects on resonant plasmon modes in composite metal-multiferroic systems,"The r\^{o}le of the magnetoelectric effect upon optical reflectivity is
studied by adapting an electrodynamic-based model for a system composed by a 2D
metallic film in contact with an extended multiferroic material exhibiting weak
ferromagnetism. The well-known \emph{Nakayama's} boundary condition is
reformulated by taking into account the magnetoelectric coupling as well as an
externally applied magnetic field $\mathbf{B}$ in an arbitrary direction. It is
found that the reflectance shows strong fluctuations for incident radiation
close to the characteristic antiferromagnetic resonance frequency associated
with the multiferroic material in the THz regime. These results were verified
for a 10 nm metallic foil by using a finite element method (FEM) and the
Rouard's approach, for a wide range of wavelengths (0.1 - 5 mm), showing good
agreement with respect to Nakayama's outcome, for the particular material
BaMnF$_4$.",1303.5296v3
2013-10-24,Towards wafer scale inductive determination of magnetostatic and dynamic parameters of magnetic thin films and multilayers,"We investigate an inductive probe head suitable for non-invasive
characterization of the magnetostatic and dynamic parameters of magnetic thin
films and multilayers on the wafer scale. The probe is based on a planar
waveguide with rearward high frequency connectors that can be brought in close
contact to the wafer surface. Inductive characterization of the magnetic
material is carried out by vector network analyzer ferromagnetic resonance.
Analysis of the field dispersion of the resonance allows the determination of
key material parameters such as the saturation magnetization MS or the
effective damping parameter Meff. Three waveguide designs are tested. The
broadband frequency response is characterized and the suitability for inductive
determination of MS and Meff is compared. Integration of such probes in a wafer
prober could in the future allow wafer scale in-line testing of magnetostatic
and dynamic key material parameters of magnetic thin films and multilayers.",1310.6578v1
2014-09-30,Current-induced spin torque resonance of magnetic insulators affected by field-like spin-orbit torques and out-of-plane magnetizations,"The spin-torque ferromagnetic resonance (ST-FMR) in a bilayer system
consisting of a magnetic insulator such as Y3Fe5O12 and a normal metal with
spin-orbit interaction such as Pt is addressed theoretically. We model the
ST-FMR for all magnetization directions and in the presence of field-like
spin-orbit torques based on the drift-diffusion spin model and quantum
mechanical boundary conditions. ST-FMR experiments may expose crucial
information about the spin-orbit coupling between currents and magnetization in
the bilayers.",1409.8406v2
2014-11-06,Giant magnetodielectric metamaterial,"Dielectric materials with tunable permittivity are highly desirable for
wireless communication, radar technology. However, the tunability of dielectric
properties in the microwave frequency range and higher is an immense challenge
for conventional materials. Here, we demonstrate a giant magnetodielectric
effect in the GHz region in a metamaterial based on ferrite unit cells. The
effect is derived from the coupling of the ferromagnetic resonance and the Mie
resonance in the ferrite unit cells. Both the simulated and experimental
results indicate that the effective permittivity of the metamaterial can be
tuned by modifying the applied magnetic field, and a giant magnetodielectric
effect, [{\epsilon}'(H) - {\epsilon}'(0)]/{\epsilon}'(0) = 15000 % at 11.284
GHz, is obtained. This mechanism offers a promising means of constructing
microwave dielectrics with large tunable ranges and considerable potential for
tailoring via a metamaterial route.",1411.1470v1
2014-12-18,Exchange Magnon-Polaritons in Microwave Cavities,"We formulate a scattering theory to study magnetic films in microwave
cavities beyond the independent-spin and rotating wave approximations of the
Tavis-Cummings model. We demonstrate that strong coupling can be realized not
only for the ferromagnetic resonance (FMR) mode, but also for spin wave
resonances (SWRs); the coupling strengths are mode dependent and decrease with
increasing mode index. The strong coupling regime can be also accessed
electrically by spin pumping into a metal contact.",1412.5809v3
2014-12-22,Numerical Investigation of Symmetry Breaking and Critical Behavior of the Acoustic Streaming Field in High-Intensity Discharge Lamps,"For energy efficiency and material cost reduction it is preferred to drive
high-intensity discharge lamps at frequencies of approximately 300 kHz.
However, operating lamps at these high frequencies bears the risk of
stimulating acoustic resonances inside the arc tube, which can result in low
frequency light flicker and even lamp destruction. The acoustic streaming
effect has been identified as the link between high frequency resonances and
low frequency flicker. A highly coupled 3D multiphysics model has been set up
to calculate the acoustic streaming velocity field inside the arc tube of
high-intensity discharge lamps. It has been found that the velocity field
suffers a phase transition to an asymmetrical state at a critical acoustic
streaming force. The system behaves similar to a ferromagnet near the Curie
point. Furthermore, it is discussed how the model allows to investigate the
light flicker phenomenon. Concerning computer resources the procedure is
considerably less demanding than a direct approach with a transient model.",1412.7032v4
2015-04-06,Quantifying the complex permittivity and permeability of magnetic nanoparticles,"The complex permittivity and permeability of superparamagnetic iron-oxide
nanoparticles has been quantified using a circular waveguide assembly with a
static magnetic field to align the nanoparticle's magnetization. The high
sensitivity of the measurement provides the precise resonant feature of
nanoparticles. The complex permeability in the vicinity of ferromagnetic
resonance (FMR) is in agreement with the nanoparticle's measured magnetization
via conventional magnetometry. A rigorous and self-consistent measure of
complex permittivities and permeabilities of nanoparticles is crucial to
ascertain accurately the dielectric behaviour as well as the frequency response
of nanoparticle magnetization, necessary ingredients when designing and
optimizing magnetic nanoparticles for biomedical applications.",1504.01404v1
2015-04-14,High sensitivity microwave detection using a magnetic tunnel junction in the absence of an external applied magnetic field,"In the absence of any external applied magnetic field, we have found that a
magnetic tunnel junction (MTJ) can produce a significant output direct voltage
under microwave radiation at frequencies, which are far from the ferromagnetic
resonance condition, and this voltage signal can be increase by at least an
order of magnitude by applying a direct current bias. The enhancement of the
microwave detection can be explained by the nonlinear resistance/conductance of
the MTJs. Our estimation suggests that optimized MTJs should achieve
sensitivities for non-resonant broadband microwave detection of about 5,000
mV/mW.",1504.03596v1
2015-04-16,Quantum simulations made easy plane,"Ever since Heisenberg's proposal of a quantum-mechanical origin of
ferromagnetism in 1928, the spin model named after him has been central to
advances in magnetism, featuring in proposals of novel many-body states such as
antiferromagnets, emergent gauge fields in their confined (valence bond
crystal) and deconfined (resonating valence bond spin liquids) versions.
Between them, these cover much of our understanding of modern magnetism
specifically and topological states of matter in general. Many exciting
phenomena predicted theoretically still await experimental realisation, and
cold atomic systems hold the promise of acting as analogue 'quantum simulators'
of the relevant theoretical models, for which ingenious and intricate set-ups
have been proposed. Here, we identify a new class of particularly simple
quantum simulators exhibiting many such phenomena but obviating the need for
fine-tuning and for amplifying perturbatively weak superexchange or
longer-range interactions. Instead they require only moderate on-site
interactions on top of uncorrelated, one-body hopping--ingredients already
available with present experimental technology. Between them, they realise some
of the most interesting phenomena, such as emergent synthetic gauge fields,
resonating valence bond phases, and even the celebrated yet enigmatic spin
liquid phase of the kagome lattice.",1504.04380v1
2015-06-16,Current characteristics of a one-dimensional Hubbard chain: The role of correlation and dissipation,"We study the electronic transport in an infinite one-dimensional Hubbard
chain, driven by a homogeneous electric field. The physical chain is coupled to
fermion bath chains, in order to account for dissipation and to prevent the
occurrence of Bloch Oscillations. The steady state current is computed in the
frame of Keldysh Green's functions in Cluster Perturbation Theory. The current
characteristics are dominated by resonant-tunneling-like structures, which can
be traced back to Wannier-Stark resonances due to anti-ferromagnetic
correlations. The same current characteristic occurs in a non-interacting
Wannier-Stark model with alternating on-site energies. Non-local effects of the
self energy can be accounted for the observed physical behaviour.",1506.04957v1
2015-07-29,Observation of droplet soliton drift resonances in a spin-transfer-torque nanocontact to a ferromagnetic thin film,"Magnetic droplet solitons are non-linear dynamical modes that can be excited
in a thin film with perpendicular magnetic anisotropy with a
spin-transfer-torque. Although droplet solitons have been proved to be stable
with a hysteretic response to applied currents and magnetic fields at low
temperature, measurements at room temperature indicate less stability and
reduced hysteresis width. Here, we report evidence of droplet soliton drift
instabilities, leading to drift resonances, at room temperature that explains
their lower stability. Micromagnetic simulations show that the drift
instability is produced by an effective field asymmetry in the nanocontact
region that can have different origins.",1507.08218v1
2016-01-06,Dynamic response of an artificial square spin ice,"Magnetization dynamics in an artificial square spin-ice lattice made of
Ni80Fe20 with magnetic field applied in the lattice plane is investigated by
broadband ferromagnetic resonance spectroscopy. The experimentally observed
dispersion shows a rich spectrum of modes corresponding to different
magnetization states. These magnetization states are determined by exchange and
dipolar interaction between individual islands, as is confirmed by a
semianalytical model. In the low field regime below 400 Oe a hysteretic
behavior in the mode spectrum is found. Micromagnetic simulations reveal that
the origin of the observed spectra is due to the initialization of different
magnetization states of individual nanomagnets. Our results indicate that it
might be possible to determine the spin-ice state by resonance experiments and
are a first step towards the understanding of artificial geometrically
frustrated magnetic systems in the high-frequency regime.",1601.01219v1
2016-01-06,All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect,"The understanding of spin dynamics in laterally confined structures on
sub-micron length scales has become a significant aspect of the development of
novel magnetic storage technologies. Numerous ferromagnetic resonance
measurements, optical characterization by Kerr microscopy and Brillouin light
scattering spectroscopy and x-ray studies were carried out to detect the
dynamics in patterned magnetic antidot lattices. Here, we investigate
Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices
with different lattice parameters by electrical means and compare them to
micromagnetic simulations. When the system is driven to resonance, a dc voltage
across the length of the sample is detected that changes its sign upon field
reversal, which is in agreement with a rectification mechanism based on the
inverse spin Hall effect. Furthermore, we show that the voltage output scales
linearly with the applied microwave drive in the investigated range of powers.
Our findings have direct implications on the development of engineered
magnonics applications and devices.",1601.01221v1
2016-02-11,Probing ultrafast spin dynamics in the antiferromagnetic multiferroic HoMnO$_3$ through a magnon resonance,"We demonstrate a new approach for directly measuring the ultrafast energy
transfer between elec- trons and magnons, enabling us to track spin dynamics in
an antiferromagnet (AFM). In multiferroic HoMnO3, optical photoexcitation
creates hot electrons, after which changes in the spin order are probed with a
THz pulse tuned to a magnon resonance. This reveals a photoinduced
transparency, which builds up over several picoseconds as the spins heat up due
to energy transfer from hot elec- trons via phonons. This spin-lattice
thermalization time is ?10 times faster than that of typical ferromagnetic (FM)
manganites. We qualitatively explain the fundamental differences in
spin-lattice thermalization between FM and AFM systems and apply a Boltzmann
equation model for treating AFMs. Our work gives new insight into spin-lattice
thermalization in AFMs and demonstrates a new approach for directly monitoring
the ultrafast dynamics of spin order in these systems.",1602.03872v2
2016-03-09,Electric dipole spin resonance in systems with a valley dependent g-factor,"In this theoretical study we qualitatively and quantitatively investigate the
electric dipole spin resonance (EDSR) in a single Si/SiGe quantum dot in the
presence of a magnetic field gradient, e.g., produced by a ferromagnet. We
model a situation in which the control of electron spin states is achieved by
applying an oscillatory electric field, inducing real-space oscillations of the
electron inside the quantum dot. One of the goals of our study is to present a
microscopic theory of valley dependent $g$-factors in Si/SiGe quantum dots and
investigate how valley relaxation combined with a valley dependent $g$-factor
leads to a novel electron spin dephasing mechanism. Furthermore, we discuss the
interplay of spin and valley relaxations in Si/SiGe quantum dots. Our findings
suggest that the electron spin dephases due to valley relaxation, and are in
agreement with recent experimental studies [Nature Nanotechnology 9, 666-670
(2014)].",1603.02829v1
2016-03-25,Large spin pumping effect in antisymmetric precession of Ni$_{79}$Fe$_{21}$/Ru/Ni$_{79}$Fe$_{21}$,"In magnetic trilayer structures, a contribution to the Gilbert damping of
ferromagnetic resonance arises from spin currents pumped from one layer to
another. This contribution has been demonstrated for layers with weakly
coupled, separated resonances, where magnetization dynamics are excited
predominantly in one layer and the other layer acts as a spin sink. Here we
show that trilayer structures in which magnetizations are excited
simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as
large. The antisymmetric (optical) mode of antiferromagnetically coupled
Ni$_{79}$Fe$_{21}$(8nm)/Ru/Ni$_{79}$Fe$_{21}$(8nm) trilayers shows a Gilbert
damping constant greater than that of the symmetric (acoustic) mode by an
amount as large as the intrinsic damping of Py ($\Delta
\alpha\simeq\textrm{0.006}$). The effect is shown equally in field-normal and
field-parallel to film plane geometries over 3-25 GHz. The results confirm a
prediction of the spin pumping model and have implications for the use of
synthetic antiferromagnets (SAF)-structures in GHz devices.",1603.07977v1
2016-04-08,"Chiral Magnetism in an Itinerant Helical Magnet, MnSi - An Extended 29Si NMR Study -","The microscopic magnetism in the helical, the conical and the
ferro-magnetically polarized phases in an itinerant helical magnet, MnSi, has
been studied by an extended 29Si NMR at zero field and under external magnetic
fields. The temperature dependence of staggered moment, M_Q(T), determined by
the 29Si NMR frequency, nu(T), and nuclear relaxation rate, 1/T_1(T) is in
general accord with the SCR theory for weak itinerant ferromagnetic metals and
its extension. The external field dependence of resonance frequency, nu(H),
follows a vector sum of the contributions from atomic hyperfine and macroscopic
fields with a field induced moment characteristic to the itinerant magnets. A
discontinuous jump of the resonance frequency at the critical field, H_c,
between the conical and the polarized phases has also been found that suggests
a first order like change of the electronic states at H_c.",1604.02226v1
2016-04-26,Tuning the resonant frequencies of a drop by a magnetic field,"We report an experimental study of a magnetic liquid drop deposited on a
superhydrophobic substrate and subjected to vertical vibrations in presence of
a static magnetic field. It is well-known that a flattened drop of usual liquid
displays oscillating lobes at its periphery when vibrated. By adding
ferromagnetic nanoparticles to a water drop and varying the strength of the
magnetic field, we are experimentally able to efficiently tune the resonant
frequencies of the drop. By using conservation energy arguments, we show that
the magnetic field contribution is equivalent to adding an effective negative
surface tension to the drop. Our model is found in good agreement with the
experiments with no fitting parameter.",1604.07686v1
2016-07-16,Measurement of spin pumping voltage separated from extrinsic microwave effects,"Conversions between spin and charge currents are core technologies in recent
spintronics. In this article, we provide methods for estimating inverse spin
Hall effects (ISHEs) induced by using microwave-driven spin pumping (SP) as a
spin-current generator. ISHE and SP induce an electromotive force at the
ferromagnetic or spin-wave resonance, which offers a valuable electric way to
study spin physics in materials. At the resonance, a microwave for exciting the
magnetization dynamics induces an additional electromotive force via rf-current
rectification and thermoelectric effects. We discuss methods to separate the
signals generated from such extrinsic microwave effects by controlling sample
structures and configurations. These methods are helpful in performing accurate
measurements on ISHE induced by SP, enabling quantitative studies on the
conversion between spin and charge currents on various kinds of materials.",1607.04716v1
2016-09-24,Superconducting order parameter $π$-phase shift in magnetic impurity wires,"It has previously been found that a magnetic impurity in a conventional
$s$-wave superconductor can give rise to a local $\pi$-phase shift of the
superconducting order parameter. By studying a finite wire of ferromagnetic
impurities, we are able to trace the origin of the $\pi$-phase shift to a
resonance condition for the Bogoliubov-de Gennes quasiparticle states. When
non-resonating states localized at the impurity sites are pulled into the
condensate for increasing magnetic strength, the superconducting order
parameter is reduced in discrete steps, eventually resulting in a $\pi$-phase
shift. We also show that for a finite spin-orbit coupling, the $\pi$-phase
shift is preserved and occurs in a large portion of the topologically
non-trivial phase.",1609.07626v1
2016-10-05,Discrete intrinsic localized modes in a microelectromechanical resonator,"Intrinsic Localized Modes (ILMs) or Discrete Breathers (DBs) are produced
through a non-linear vibration localization phenomenon. While Anderson
localization is due to lattice defects, the nonlinearity of lattices provides
the basis for ILM excitation. Over the past two decades, these ILMs have been
realized in a wide range of physical systems including photonic crystals,
nonlinear atomic lattices, anti-ferromagnets, coupled Josephson junction arrays
and coupled cantilevers. This paper brings out the feasibility of exciting ILMs
in a standalone mechanical resonator. Through piezoelectric driving and optical
visualization, various intriguing features of ILMs have been recorded. The ILMs
in our system are observed as spectral bushes and their frequencies are much
lower than that of the drive frequency. The excitation of ILMs is mediated
through large amplitude instability following autoparametric excitation of a
sub-harmonic mode. The spatial prevalence of discrete ILM excitations is at
antinodes of the sub-harmonic mode. Further, the ILMs have been observed to be
time-variant and various events including attraction-repulsion (or
splitting-merging) of ILMs and hopping occur during the time evolution of ILMs.",1610.01370v2
2016-10-14,Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: experiment and micromagnetic simulations,"We present a comprehensive theoretical and experimental study of
voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe
multiferroic heterostructures patterned into microstrips. A spin-diode
technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in
NiFe strip mechanically coupled with a piezoelectric substrate. Application of
an electric field to a PMNPT creates a strain in permalloy and thus shifts the
FMR and SSWR fields due to the magnetostriction effect. The experimental
results are compared with micromagnetic simulations and a good agreement
between them is found for dynamics of FMR and SSWR with and without electric
field. Moreover, micromagnetic simulations enable us to discuss the amplitude
and phase spatial distributions of FMR and SSWR modes, which are not directly
observable by means of spin diode detection technique.",1610.04500v1
2017-02-13,Spin Pumping and Inverse Spin Hall Voltages from Dynamical Antiferromagnets,"Dynamical antiferromagnets pump spins efficiently into adjacent conductors as
ferromagnets. The high antiferromagnetic resonance frequencies represent a
challenge for experimental detection, but magnetic fields can reduce these
resonance frequencies. We compute the inverse spin Hall voltages resulting from
dynamical spin excitations as a function of a magnetic field along the easy
axis and the polarization of the driving AC magnetic field perpendicular to the
easy axis. We consider the insulating antiferromagnets MnF$_2$, FeF$_2$, and
NiO. Near the spin-flop transition, there is a significant enhancement of the
DC spin pumping and inverse spin Hall voltage for the uniaxial antiferromagnets
MnF$_2$ and FeF$_2$. In the biaxial NiO, the voltages are much weaker, and
there is no spin-flop enhancement of the DC component.",1702.03779v1
2017-02-23,Synchronized spin-photon coupling in a microwave cavity,"We study spin-photon coupling in cavity in the presence of relative phase
shift between two ferromagnetic resonance driving forces. We show that the
anticrossing gap can be manipulated by varying the relative phase. Increasing
the phase difference leads to narrowing the anticrossing gap of hybridized
modes and eventually to phase locked coupling at the value of relative phase of
{\pi}: The FMR and cavity modes become phase locked and oscillate at the same
frequency near the resonance frequency. Characteristic linewidth drop and
transmission amplitude enhancement are demonstrated. The phase resolved
spin-photon coupling can be used both for phase imaging and controlling
coupling parameters.",1702.07110v4
2017-03-24,Nuclear resonant surface diffraction,"Nuclear resonant x-ray diffraction in grazing incidence geometry is used to
determine the lateral magnetic configuration in a one-dimensional lattice of
ferromagnetic nanostripes. During magnetic reversal, strong nuclear
superstructure diffraction peaks appear in addition to the electronic ones due
to an antiferromagnetic order in the nanostripe lattice. We show that the
analysis of the angular distribution of the resonantly diffracted x-rays
together with the time-dependence of the coherently diffracted nuclear signal
reveals surface spin structures with very high sensitivity. This novel
scattering technique provides a unique access to laterally correlated spin
configurations in magnetically ordered nanostructures and, in perspective, also
to their dynamics.",1703.08584v1
2017-08-14,Magnetization dynamics of weak stripe domains in Fe-N thin films: a multi-technique complementary approach,"The resonant eigenmodes of a nitrogen-implanted iron {\alpha}'-FeN
characterized by weak stripe domains are investigated by Brillouin light
scattering and broadband ferromagnetic resonance experiments, assisted by
micromagnetic simulations. The spectrum of the dynamic eigenmodes in the
presence of the weak stripes is very rich and two different families of modes
can be selectively detected using different techniques or different
experimental configurations. Attention is paid to the evolution of the mode
frequencies and spatial profiles under the application of an external magnetic
field, of variable intensity, in the direction parallel or transverse to the
stripes. The different evolution of the modes with the external magnetic field
is accompanied by a distinctive spatial localization in specific regions, such
as the closure domains at the surface of the stripes and the bulk domains
localized in the inner part of the stripes. The complementarity of BLS and FMR
techniques, based on different selection rules, is found to be a fruitful tool
for the study of the wealth of localized mag-netic excitations generally found
in nanostructures.",1708.04178v1
2013-08-15,Detection of the microwave spin pumping using the inverse spin Hall effect,"We report electrical detection of the dynamical part of the spin pumping
current emitted during ferromagnetic resonance (FMR) using the inverse Spin
Hall Effect (ISHE). The experiment is performed on a YIG$|$Pt bilayer. The
choice of YIG, a magnetic insulator, ensures that no charge current flows
between the two layers and only pure spin current produced by the magnetization
dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin
pumping. To avoid measuring the parasitic eddy currents induced at the
frequency of the microwave source, a resonance at half the frequency is induced
using parametric excitation in the parallel geometry. Triggering this nonlinear
effect allows to directly detect on a spectrum analyzer the microwave component
of the ISHE voltage. Signals as large as 30 $\mu$V are measured for precession
angles of a couple of degrees. This direct detection provides a novel efficient
means to study magnetization dynamics on a very wide frequency range with great
sensitivity.",1308.3433v2
2013-08-16,Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering,"How coherent quasiparticles emerge by doping quantum antiferromagnets is a
key question in correlated electron systems, whose resolution is needed to
elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray
scattering (RIXS) experiments in hole-doped cuprates have purported to measure
high-energy collective spin excitations that persist well into the overdoped
regime and bear a striking resemblance to those found in the parent compound,
challenging the perception that spin excitations should weaken with doping and
have a diminishing effect on superconductivity. Here we show that RIXS at the
Cu L3-edge indeed provides access to the spin dynamical structure factor once
one considers the full influence of light polarization. Further we demonstrate
that high-energy spin excitations do not correlate with the doping dependence
of Tc, while low-energy excitations depend sensitively on doping and show
ferromagnetic correlations. This suggests that high-energy spin excitations are
marginal to pairing in cuprate superconductors.",1308.3717v2
2016-11-02,Surface effects on ferromagnetic resonance in magnetic nanocubes,"We study the effect of surface anisotropy on the spectrum of spin-wave
excitations in a magnetic nanocluster and compute the corresponding absorbed
power. For this, we develop a general numerical method based on the (undamped)
Landau-Lifshitz equation, either linearized around the equilibrium state
leading to an eigenvalue problem or solved using a symplectic technique. For
box-shaped clusters, the numerical results are favorably compared to those of
the finite-size linear spin-wave theory. Our numerical method allows us to
disentangle the contributions of the core and surface spins to the spectral
weight and absorbed power. In regard to the recent developments in synthesis
and characterization of assemblies of well defined nano-elements, we study the
effects of free boundaries and surface anisotropy on the spin-wave spectrum in
iron nanocubes and give orders of magnitude of the expected spin-wave
resonances. For an 8 nm iron nanocube, we show that the absorbed power spectrum
should exhibit a low-energy peak around 10 GHz, typical of the uniform mode,
followed by other low-energy features that couple to the uniform mode but with
a stronger contribution from the surface. There are also high-frequency
exchange-mode peaks around 60 GHz.",1611.00614v1
2016-11-15,Spin-Valley Beam Splitter in Graphene,"The fourfold spin-valley degenerate degrees of freedom in bulk graphene can
support rich physics and novel applications associated with multicomponent
quantum Hall effects and linear conductance filtering. In this work, we study
how to break the spin-valley degeneracy of electron beams spatially. We propose
a spin-valley beam splitter in a gated ferromagnetic/pristine/strained graphene
structure. We demonstrate that, in a full resonant tunneling regime for all
spin-valley beam components, the formation of quasi-standing waves can lead
four giant lateral Goos-H\""{a}nchen shifts as large as the transverse beam
width, while the interplay of the two modulated regions can lead difference of
resonant angles or energies for the four spin-valley flavors, manifesting an
effective spin-valley beam splitting effect. The beam splitting effect is found
to be controllable by the gating and strain.",1611.04722v1
2017-04-28,Thermal Control of the Magnon-Photon Coupling in a Notch Filter coupled to a Yttrium-Iron-Garnet/Platinum System,"We report thermal control of mode hybridization between the ferromagnetic
resonance (FMR) and a planar resonator (notch filter) working at 4.74 GHz. The
chosen magnetic material is a ferrimagnetic insulator (Yttrium Iron Garnet:
YIG) covered by 6 nm of platinum (Pt). A current induced heating method has
been used in order to enhance the temperature of the YIG/Pt system. The device
permits us to control the transmission spectra and the magnon-photon coupling
strength at room temperature. These experimental findings reveal potentially
applicable tunable microwave filtering function.",1704.08896v3
2013-09-05,Voltage-induced strain control of the magnetic anisotropy in a Ni thin film on flexible substrate,"Voltage-induced magnetic anisotropy has been quantitatively studied in
polycrystalline Ni thin film deposited on flexible substrate using microstrip
ferromagnetic resonance. This anisotropy is induced by a piezoelectric actuator
on which the film/substrate system was glued. In our work, the control of the
anisotropy through the applied elastic strains is facilitated by the compliant
elastic behavior of the substrate. The in-plane strains in the film induced by
the piezoelectric actuation have been measured by the digital image correlation
technique. Non-linear variation of the resonance field as function of the
applied voltage is found and well reproduced by taking into account the non
linear and hysteretic variations of the induced in-plane strains as function of
the applied voltage. Moreover, we show that initial uniaxial anisotropy
attributed to compliant substrate curvature is fully compensated by the voltage
induced anisotropy.",1309.1417v1
2014-05-28,Electronic control of the spin-wave damping in a magnetic insulator,"It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, $I_\text{dc}$, in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of $I_\text{dc}$ in a 5~$\mu$m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of $\sim 3 \cdot 10^{11}\text{A.m}^{-2}$, in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime.",1405.7415v1
2014-06-26,Spin-torque diode radio-frequency detector with voltage tuned resonance,"We report on a voltage tunable radio-frequency (RF) detector based on a
magnetic tunnel junction (MTJ). The spin-torque diode effect is used to excite
and/or detect RF oscillations in the magnetic free layer of the MTJ. In order
to reduce the overall in-plane magnetic anisotropy of the free layer, we take
advantage of the perpendicular magnetic anisotropy at the interface between
ferromagnetic and insulating layers. The applied bias voltage is shown to have
a significant influence on the magnetic anisotropy, and thus on the resonance
frequency of the device. This influence also depends on the voltage polarity.
The obtained results are accounted for in terms of the interplay of
spin-transfer-torque and voltage-controlled magnetic anisotropy effects.",1406.6935v1
2017-06-04,Field- and temperature-modulated spin-diode effect in a GMR nanowire with dipolar coupling,"An analytical model of the spin-diode effect induced by resonant
spin-transfer torque in a ferromagnetic bilayer with strong dipolar coupling
provides the resonance frequencies and the lineshapes of the magnetic field
spectra obtained under field or laser-light modulation. The effect of laser
irradiation is accounted for by introducing the temperature dependence of the
saturation magnetization and anisotropy, as well as thermal spin-transfer
torques. The predictions of the model are compared with experimental data
obtained with single Co/Cu/Co spin valves, embedded in nanowires and produced
by electrodeposition. Temperature modulation provides excellent signal-to-noise
ratio. High temperature-modulation frequency is possible because these
nanostructures have a very small heat capacity and are only weakly heat-sunk.
The two forms of modulation give rise to qualitative differences in the spectra
that are accounted for by the model.",1706.01036v1
2017-06-20,Tuning an effective spin chain of three strongly interacting one-dimensional fermions with the transversal confinement,"Strongly interacting one-dimensional fermions form an effective spin chain in
the absence of an external lattice potential. We show that the exchange
coefficients of such a chain may be locally tuned by properly tailoring the
transversal confinement. In particular, in the vicinity of a
confinement-induced resonance (CIR) the exchange coefficients may have
simultaneously opposite ferromagnetic and antiferromagnetic characters at
different locations along the trap axis. Moreover, the local exchanges may be
engineered to induce avoided crossings between spin states at the CIR, and
hence a ramp across the resonance may be employed to create different spin
states and to induce spin dynamics in the chain. We show that such unusual spin
chains have already been realized in the experiment of Murmann et al. [Phys.
Rev. Lett. 115, 215301 (2015)].",1706.06513v2
2017-12-07,Spin waves in coupled YIG/Co heterostructures,"We investigate yttrium iron garnet (YIG)/cobalt (Co) heterostructures using
broadband ferromagnetic resonance (FMR). We observe an efficient excitation of
perpendicular standing spin waves (PSSWs) in the YIG layer when the resonance
frequencies of the YIG PSSWs and the Co FMR line coincide. Avoided crossings of
YIG PSSWs and the Co FMR line are found and modeled using mutual spin pumping
and exchange torques. The excitation of PSSWs is suppressed by a thin aluminum
oxide (AlOx) interlayer but persists with a copper (Cu) interlayer, in
agreement with the proposed model.",1712.02561v1
2018-10-13,Spin-torque resonance due to diffusive dynamics at a surface of topological insulator,"We investigate spin-orbit torques on magnetization in an insulating
ferromagnetic (FM) layer that is brought into a close proximity to a
topological insulator (TI). In addition to the well-known field-like spin-orbit
torque, we identify an anisotropic anti-damping-like spin-orbit torque that
originates in a diffusive motion of conduction electrons. This diffusive torque
is vanishing in the limit of zero momentum (i. e. for spatially homogeneous
electric field or current), but may, nevertheless, have a strong effect on
spin-torque resonance at finite frequency provided external field is neither
parallel nor perpendicular to the TI surface. The required electric field
configuration can be created by a grated top gate.",1810.05828v3
2019-09-16,Spin current pumped by resonant skyrmion,"Spin pumping is a widely recognized method to generate the spin current in
the spintronics, which is acknowledged as a fundamentally dynamic process
equivalent to the spin-transfer torque. In this work, we theoretically verify
that the oscillating spin current can be pumped from the microwave-motivated
breathing skyrmion. The skyrmion spin pumping can be excited by a relatively
low frequency compared with the ferromagnetic resonance (FMR) and the current
density is larger than the ordinary FMR spin pumping. Based on the skyrmion
spin pumping, we build a high reading-speed racetrack memory model whose
reading speed is an order of magnitude higher than the SOT (spin-orbit torque)
/STT (spin-transfer torque) skyrmion racetrack. Our work explored the spin
pumping phenomenon in the skyrmion, and it may contribute to the applications
of the skyrmion-based device.",1909.07077v1
2019-10-03,Element-selective tracking ultrafast demagnetization process in Co/Pt multilayer thin films by the resonant magneto-optical Kerr effect,"We examined the photo-induced dynamics of ferromagnetic Co/Pt thin films
demonstrating perpendicular magnetic anisotropy with element specificity using
resonant polar magneto-optical Kerr effect measurements at Pt~N${}_{6,7}$ and
Co~M${}_{2,3}$ edges with an x-ray free electron laser. The obtained results
showed a clear element dependence of photo-induced demagnetization time scales:
$\tau_\textrm{demag.}^\textrm{Co}=80\pm60~\textrm{fs}$ and
$\tau_\textrm{demag.}^\textrm{Pt}=640\pm140~\textrm{fs}$. This dependence is
explained by the induced moment of the Pt atom by current flow from the Co
layer through the interfaces. The observed magnetization dynamics of Co and Pt
can be attributed to the characteristics of photo-induced Co/Pt thin film
phenomena including all-optical switching.",1910.01556v1
2019-10-08,The Triplet Resonating Valence Bond State and Superconductivity in Hund's Metals,"A central idea in strongly correlated systems is that doping a Mott insulator
leads to a superconductor by transforming the resonating valence bonds (RVBs)
into spin-singlet Cooper pairs. Here, we argue that a spin-triplet RVB (tRVB)
state, driven by spatially, or orbitally anisotropic ferromagnetic interactions
can provide the parent state for triplet superconductivity. We apply this idea
to the iron-based superconductors, arguing that strong onsite Hund's
interactions develop intra-atomic tRVBs between the t$_{2g}$ orbitals. On
doping, the presence of two iron atoms per unit cell allows these inter-orbital
triplets to coherently delocalize onto the Fermi surface, forming a fully
gapped triplet superconductor. This mechanism gives rise to a unique staggered
structure of onsite pair correlations, detectable as an alternating $\pi$ phase
shift in a scanning tunnelling Josephson microscope.",1910.03168v2
2020-01-04,Observation of spin-motive force in ferrimagnetic GdFeCo alloy films,"Non-uniform magnetic structures produce emergent electromagnetic phenomena
such as the topological Hall effect and the spin-motive force (SMF). The
experimental reports on the SMF, however, are very few and the relationship
between the SMF and material parameters is still unclear. In this study, we
investigated the SMF in ferrimagnetic GdFeCo alloy films using the
spin-torque-induced ferromagnetic resonance method and clarified the
relationship. The amplitude of the detected SMF becomes larger than that of the
transition metal alloy FeCo by the Gd doping and reaches the maximum near a Gd
composition of the boundary between in-plane and perpendicularly magnetized
films. According to the analytical calculation, the enhancement is related to
the trajectory of the magnetization precession. Moreover, we find that the SMF
induced by the magnetic resonance is inversely proportional to the square of
the damping constant.",2001.01042v2
2020-02-03,Giant magnetoresistance in antiferromagnetic Mn$_2$Au-based tunnel junction,"Recent studies on the electrical switching of tetragonal antiferromagnet
(AFM) via N{\'e}el spin-orbit torque have paved the way for the economic use of
antiferromagnetic materials. The most difficult obstacle that presently limits
the application of antiferromagnetic materials in spintronics, especially in
memory storage applications, could be the small and fragile magnetoresistance
(MR) in the AFM-based nanostructure. In this study, we investigated the spin
transports in Mn$_2$Au-based tunnel junctions based onthe first-principle
scattering theory. Giant MRs more than $1000\%$ are predicted in some
Fe/MgO/Ag/Mn$_2$Au/Ta junctions that are about the same order as that in an
MgO-based ferromagnetic tunnel junction with same barrier thickness. The
interplay of the spin filtering effect, the quantum well resonant states, and
the interfacial resonant states could be responsible for the unusual giant and
robust MRs observed in these Mn$_2$Au-based junctions.",2002.00621v1
2020-12-29,Twist-induced Near-field Thermal Switch Using Nonreciprocal Surface Magnon-Polaritons,"We explore that two ferromagnetic insulator slabs host a strong twist-induced
near-field radiative heat transfer in the presence of twisted magnetic fields.
Using the formalism of fluctuational electrodynamics, we find the existence of
large twist-induced thermal switch ratio in large damping condition and
nonmonotonic twist manipulation for heat transfer in small damping condition,
associated with the different twist-induced effects of nonreciprocal elliptic
surface magnon-polaritons, hyperbolic surface magnon-polaritons, and
twist-non-resonant surface magnon-polaritons. Moreover, the near-field
radiative heat transfer can be significantly enhanced by the twist-non-resonant
surface magnon-polaritons in the ultra-small damping condition. Such
twist-induced effect is applicable for other kinds of anisotropic slabs with
timereversal symmetry breaking. Our findings provide a way to twisted and
magnetic control in nanoscale thermal management and improve it with
twistronics concepts.",2012.14733v1
2020-12-29,Nonreciprocal Multi-mode and Indirect Couplings in Cavity Magnonics,"We investigate the magnon-photon couplings by employing a small magnet within
an irregular resonant cavity, which leads to a desirable nonreciprocity with a
big isolation ratio. Moreover, the higher-order couplings between the spin wave
modes with the polarized photon modes also exhibit the nonreciprocity. These
couplings between polarized photon and spin waves could be regarded as an
indirect multi-modes coupling between the ferromagnetic resonance (FMR) mode
and spin wave mode magnons mediated by the cavity mode photons. We also derive
a coupling matrix to predict the characteristics of this kind of indirect
coupling. The existence of the indirect couplings broaden the field range of
the nonreciprocity of the system. The achieved nonreciprocal multi-mode
magnon-photon couplings in a single system offer a feasible method to improve
the signal transmission quality.",2012.14765v2
2021-01-06,Spin-transport in an organic semiconductor without free charge carrier involvement,"We have experimentally tested the hypothesis of free charge carrier mediated
spin-transport in the small molecule organic semiconductor Alq3 at room
temperature. A spin current was pumped into this material by pulsed
ferromagnetic resonance of an adjacent NiFe layer, while a charge current
resulting from this spin current via the inverse spin-Hall effect (ISHE) was
detected in a Pt layer adjacent on the other side of the Alq3 layer, confirming
a pure spin current through the Alq3 layer. Charge carrier spin states in Alq3,
were then randomized by simultaneous application of electron paramagnetic
resonance (EPR). No influence of the EPR excitation on the ISHE current was
found, implying that spin-transport is not mediated by free charge-carriers in
Alq3.",2101.02140v1
2000-06-05,An electron paramagnetic resonance study of Pr_{0.6}Ca_{0.4}MnO_{3} across the charge ordering transition,"We report the first electron paramagnetic resonance studies of single
crystals and powders of Pr_{0.6}Ca_{0.4}MnO_{3} in the 300-4.2 K range,
covering the charge ordering transition at ~ 240 K and antiferromagnetic
transition (T_N) at ~ 170 K. The asymmetry parameter for the Dysonian single
crystal spectra shows anomalous increase at T_{co}. Below T_{co} the g-value
increases continuously, suggesting a gradual strengthening of orbital ordering.
The linewidth undergoes a sudden increase at T_{co} and continues to increase
down to T_N. The intensity increases as the temperature is decreased till
T_{co} due to the renormalization of magnetic susceptibility arising from the
build up of ferromagnetic correlations. The value of the exchange constant, J,
is estimated to be 154 K.",0006073v1
2012-05-18,"CaIrO3 post-perovskite, a j = 1/2 quasi-one-dimensional antiferromagnet","The 5d5 iridate CaIrO3 is isostructural with the post-perovskite phase of
MgSiO3, recently shown to occur under extreme pressure in the lower Earth's
mantle. It therefore serves as an analogue of post-perovskite MgSiO3 for a wide
variety of measurements at ambient conditions or achievable with conventional
multianvile pressure modules. By multireference configuration-interaction
calculations we here provide essential information on the chemical bonding and
magnetic interactions in CaIrO3. We predict a large antiferromagnetic
superexchange of 120 meV along the c axis, the same size with the interactions
in the cuprate superconductors, and ferromagnetic couplings smaller by an order
of magnitude along a. CaIrO3 can thus be regarded as a j = 1/2
quasi-one-dimensional antiferromagnet. While this qualitatively agrees with the
stripy magnetic structure proposed by resonant x-ray diffraction, the detailed
microscopic picture emerging from our study, in particular, the highly uneven
admixture of t2g components, provides a clear prediction for resonant inelastic
x-ray scattering experiments.",1205.4226v2
2017-09-07,Tunable spin pumping in exchange coupled magnetic trilayers,"Magnetic thin films at ferromagnetic resonance (FMR) leak angular momentum,
which may be absorbed by adjacent layers. This phenomenon, known as spin
pumping, is manifested by an increase in the resonance linewidth ($\Delta H$),
and the closely related Gilbert damping. Another effect of this transfer of
spin currents is a dynamical and long-range coupling that can drive two
magnetic layers into a collective precession when their FMR frequencies
coincide. A collective behavior is also found in magnetic trilayers with
interlayer exchange coupling (IEC). In this study we investigate the interplay
between IEC and spin pumping, using Co/Cu/Py pseudo-spin values. We employ
broadband FMR spectroscopy to explore both the frequency and coupling-strength
dependence of $\Delta H$. Our observations show that there exists a cut-off
frequency, set by the IEC strength, below which the precession is truly
collective and the spin pumping is suppressed. These results demonstrate that
it is possible to control the spin pumping efficiency by varying the frequency
or the interlayer exchange coupling.",1709.02295v1
2018-06-12,Emergent c-axis magnetic helix in manganite-nickelate superlattices,"The nature of the magnetic order in (La2/3Sr1/3MnO3)9/(LaNiO3)3 superlattices
is investigated using x-ray resonant magnetic reflectometry. We observe a new
c-axis magnetic helix state in the (LaNiO3)3 layers that had never been
reported in nickelates, and which mediates the ~130deg magnetic coupling
between the ferromagnetic (La2/3Sr1/3MnO3)9 layers, illustrating the power of
x-rays for discovering the magnetic state of complex oxide interfaces. Resonant
inelastic x-ray scattering and x-ray absorption spectroscopy show that Ni-O
ligand hole states from bulk LaNiO3 are mostly filled due to interfacial
electron transfer from Mn, driving the Ni orbitals closer to an atomic-like 3d8
configuration. We discuss the constraints imposed by this electronic
configuration to the microscopic origin of the observed magnetic structure. The
presence of a magnetic helix in (La2/3Sr1/3MnO3)9/(LaNiO3)3 is crucial for
modeling the potential spintronic functionality of this system and may be
important for designing emergent magnetism in novel devices in general.",1806.04775v1
2018-06-27,Site-selective Probe of Magnetic Excitations in Rare-earth Nickelates using Resonant Inelastic X-ray Scattering,"We have used high-resolution resonant inelastic x-ray scattering (RIXS) to
study a thin film of NdNiO$_3$, a compound whose unusual spin- and bond-ordered
electronic ground state has been of long-standing interest. Below the magnetic
ordering temperature, we observe well-defined collective magnon excitations
along different high-symmetry directions in momentum space. The magnetic
spectra depend strongly on the incident photon energy, which we attribute to
RIXS coupling to different local electronic configurations of the expanded and
compressed NiO$_6$ octahedra in the bond-ordered state. Both the noncollinear
magnetic ground state and the observed site-dependent magnon excitations are
well described by a model that assumes strong competition between the
antiferromagnetic superexchange and ferromagnetic double-exchange interactions.
Our study provides direct insight into the magnetic dynamics and exchange
interactions of the rare-earth nickelates, and demonstrates that RIXS can serve
as a site-selective probe of magnetism in these and other materials.",1806.10499v1
2018-08-13,Gilbert damping phenomenology for two-sublattice magnets,"We present a systematic phenomenological description of Gilbert damping in
two-sublattice magnets. Our theory covers the full range of materials from
ferro- via ferri- to antiferromagnets. Following a Rayleigh dissipation
functional approach within a Lagrangian classical field formulation, the theory
captures intra- as well as cross-sublattice terms in the Gilbert damping,
parameterized by a 2$\times$2 matrix. When spin-pumping into an adjacent
conductor causes dissipation, we obtain the corresponding Gilbert damping
matrix in terms of the interfacial spin-mixing conductances. Our model
reproduces the experimentally observed enhancement of the ferromagnetic
resonance linewidth in a ferrimagnet close to its compensation temperature
without requiring an increased Gilbert parameter. It also predicts new
contributions to damping in an antiferromagnet and suggests the resonance
linewidths as a direct probe of the sublattice asymmetry, which may stem from
boundary or bulk.",1808.04385v2
2018-08-14,Dynamical multistability in a quantum-dot laser,"We study the dynamical multistability of a solid-state single-atom laser
implemented in a quantum-dot spin valve. The system is formed by a resonator
that interacts with a two-level system in a dot in contact with two
ferromagnetic leads of antiparallel polarization. We show that a spin-polarized
current provides high-efficiency pumping leading to regimes of multistable
lasing, in which the Fock distribution of the oscillator displays a
multi-peaked distribution. The emergence of multistable lasing follows from the
breakdown of the usual rotating-wave approximation for the coherent
spin-resonator interaction which occurs at relatively weak couplings. The
multistability manifests itself directly in the charge current flowing through
the dot, switching between distinct current levels corresponding to the
different states of oscillation.",1808.04884v2
2019-02-11,Abrikosov vortex nucleation and its detrimental effect on superconducting spin pumping in Pt/Nb/Ni80Fe20/Nb/Pt proximity structures,"We report Abrikosov vortex nucleation in Pt/Nb/Ni80Fe20/Nb/Pt
proximity-coupled structures under oblique ferromagnetic resonance (FMR) that
turns out to be detrimental to superconducting spin pumping. By measuring an
out-of-plane field-angle {\theta}H dependence and comparison with Pt-absent
control samples, we show that as {\theta}H increases, the degree of enhancement
(suppression) of spin pumping efficiency in the superconducting state for the
Pt-present (Pt-absent) sample diminishes and it reverts to the normal state
value at {\theta}H = 90{\deg}. This can be explained in terms of a substantial
out-of-plane component of the resonance field for the Ni80Fe20 layer (with
in-plane magnetization anisotropy and high aspect ratio) that approaches the
upper critical field of the Nb, turning a large fraction of the singlet
superconductor volume into the normal state.",1902.03862v2
2019-02-20,Photoinduced Floquet topological magnons in Kitaev magnets,"We study periodically driven pure Kitaev model and ferromagnetic phase of the
Kitaev-Heisenberg model on the honeycomb lattice by off-resonant linearly and
circularly-polarized lights at zero magnetic field. Using a combination of
linear spin wave and Floquet theories, we show that the effective
time-independent Hamiltonians in the off-resonant regime map onto the
corresponding anisotropic static spin model, plus a tunable photoinduced
magnetic field along the $[111]$ direction, which precipitates Floquet
topological magnons and chiral magnon edge modes. They are tunable by the light
amplitude and polarization. Similarly, we show that the thermal Hall effect
induced by the Berry curvature of the Floquet topological magnons can also be
tuned by the laser field. Our results pave the way for ultrafast manipulation
of topological magnons in irradiated Kitaev magnets, and could play a pivotal
role in the investigation of ultrafast magnon spin current generation in Kitaev
materials.",1902.07716v2
2019-03-05,Strong Coupling between Microwave Photons and Nanomagnet Magnons,"Coupled microwave photon-magnon hybrid systems offer promising applications
by harnessing various magnon physics. At present, in order to realize high
coupling strength between the two subsystems, bulky ferromagnets with large
spin numbers are utilized, which limits their potential applications for
scalable quantum information processing. In this paper, by enhancing single
spin coupling strength using lithographically defined superconducting
resonators, we report high cooperativities between a resonator mode and a
Kittel mode in nanometer thick Permalloy wires. The on-chip, lithographically
scalable, and superconducting quantum circuit compatible design provides a
direct route towards realizing hybrid quantum systems with nanomagnets, whose
coupling strength can be precisely engineered and dynamic properties can be
controlled by various mechanisms derived from spintronic studies.",1903.01887v3
2019-03-12,Probing GHz Gravitational Waves with Graviton-magnon Resonance,"A novel method for extending frequency frontier in gravitational wave
observations is proposed. It is shown that gravitational waves can excite a
magnon. Thus, gravitational waves can be probed by a graviton-magnon detector
which measures resonance fluorescence of magnons. Searching for gravitational
waves with a wave length $\lambda$ by using a ferromagnetic sample with a
dimension $l$, the sensitivity of the graviton-magnon detector reaches spectral
densities, around $5.4 \times 10^{-22} \times (\frac{l}{\lambda /2\pi})^{-2} \
[{\rm Hz}^{-1/2}]$ at 14 GHz and $8.6 \times 10^{-21} \times (\frac{l}{\lambda
/2\pi})^{-2} \ [{\rm Hz}^{-1/2}]$ at 8.2 GHz, respectively.",1903.04843v4
2020-03-08,Field-induced spin reorientation in the antiferromagnetic Dirac material EuMnBi$_2$ revealed by neutron and resonant x-ray diffraction,"Field-dependent magnetic structure of a layered Dirac material EuMnBi$_2$ was
investigated in detail by the single crystal neutron diffraction and the
resonant x-ray magnetic diffraction techniques. On the basis of the reflection
conditions in the antiferromagnetic phase at zero field, the Eu moments were
found to be ordered ferromagnetically within the $ab$ plane and stacked
antiferromagnetically along the $c$ axis in the sequence of up-up-down-down.
Upon the spin-flop transition under the magnetic field parallel to the $c$
axis, the Eu moments are reoriented from the $c$ to the $a$ or $b$ directions
forming two kinds of spin-flop domains, whereas the antiferromagnetic structure
of the Mn sublattice remains intact as revealed by the quantitative analysis of
the change in the neutron diffraction intensities. The present study provides a
concrete basis to discuss the dominant role of the Eu sublattice on the
enhanced two-dimensionality of the Dirac fermion transport in EuMnBi$_2$.",2003.03719v1
2020-03-11,Highly tunable magnetic coupling in ultrathin topological insulator films due to impurity resonances,"We theoretically investigate the exchange interaction between magnetic
impurities in ultrathin Bi$_2$Se$_3$ topological insulator films by taking into
account the low-energy states produced by the impurities. We find that the
locally induced impurity resonances strongly influence the exchange interaction
between magnetic moments. In particular, we find a non-collinear alignment
being more favorable than the collinear ferromagnetic alignment preferred when
impurity states are ignored and only the pristine topological insulator band
structure is considered. Moreover, we show that by applying of an electric
field perpendicular to the ultrathin film, the exchange interaction can be
drastically enhanced. This opens for the possibility of highly tunable
magnetism by electric field.",2003.05539v1
2020-03-12,"Tunable multiwindow magnomechanically induced transparency, Fano resonances, and slow-to-fast light conversion","We investigate the absorption and transmission properties of a weak probe
field under the influence of a strong control field in a hybrid cavity
magnomechanical system in the microwave regime. This hybrid system consists of
two ferromagnetic material yttrium iron garnet (YIG) spheres strongly coupled
to a single cavity mode. In addition to two magnon-induced transparency (MIT)
that arise due to strong photon-magnon interactions, we observe a
magnomechanically induced transparency (MMIT) due to the presence of nonlinear
phonon-magnon interaction. In addition, we discuss the emergence and tunability
of the multiple Fano resonances in our system. We find that due to strong
photon-magnon coupling the group delay of the probe field can be enhanced
significantly. The subluminal or superluminal propagation depends on the
frequency of the magnons, which can be easily tuned by an external bias
magnetic field. Besides, the group delay of the transmitted field can also be
controlled with the control field power.",2003.13760v4
2020-05-11,Resonant X-ray scattering study of diffuse magnetic scattering from the topological semimetals EuCd$_2$As$_2$ and EuCd$_2$Sb$_2$,"We have investigated the magnetic correlations in the candidate Weyl
semimetals EuCd$_2Pn_2$, ($Pn$=As, Sb) by resonant elastic X-ray scattering
(REXS) at the Eu$^{2+}$ $M_5$ edge. The temperature and field dependence of the
diffuse scattering of EuCd$_2$As$_2$ provide direct evidence that the Eu
moments exhibit slow ferromagnetic correlations well above the N\'{e}el
temperature. By contrast, the diffuse scattering in the paramagnetic phase of
isostructural EuCd$_2$Sb$_2$ is at least an order of magnitude weaker. The FM
correlations present in the paramagnetic phase of EuCd$_2$As$_2$ could create
short-lived Weyl nodes.",2005.04952v1
2020-10-27,Vertex Dependent Dynamic Response of a Connected Kagome Artificial Spin Ice,"We present the dynamic response of a connected Kagome artificial spin ice
with emphasis on the effect of the vertex magnetization configuration on the
mode characteristics. We use broadband ferromagnetic resonance (FMR)
spectroscopy and micromagnetic simulations to identify and characterize
resonant modes. We find the mode frequencies of elongated, single-domain film
segments not only depend on the orientation of their easy-axis with respect to
the applied magnetic field, but also depend on the vertex magnetization
configuration, which suggests control over the FMR mode can be accomplished by
altering the vertex magnetization. Moreover, we study differences between the
vertex center mode (VCM) and the localized domain wall (LDW) mode. We show that
the LDW mode acts as a signature of the domain wall (DW) nucleation process and
the DW dynamics active during segment reversal events. The results show the VCM
and LDW modes can be controlled using a field protocol, which has important
implications for applications in magnonic and spintronic devices.",2010.13965v1
2021-06-03,"Relationship between A-site Cation and Magnetic Structure in 3d-5d-4f Double Perovskite Iridates Ln2NiIrO6 (Ln=La, Pr, Nd)","We report a comprehensive investigation of Ln2NiIrO6 (Ln = La, Pr, Nd) using
thermodynamic and transport properties, neutron powder diffraction, resonant
inelastic x-ray scattering, and density functional theory (DFT) calculations to
investigate the role of A-site cations on the magnetic interactions in this
family of hybrid 3d-5d-4f compositions. Magnetic structure determination using
neutron diffraction reveals antiferromagnetism for La2NiIrO6, a collinear
ferrimagnetic Ni/Ir state that is driven to long range antiferromagnetism upon
the onset of Nd ordering in Nd2NiIrO6, and a non-collinear ferrimagnetic Ni/Ir
sublattice interpenetrated by a ferromagnetic Pr lattice for Pr2NiIrO6. For
Pr2NiIrO6 heat capacity results reveal the presence of two independent magnetic
sublattices and transport resistivity indicates insulating behavior and a
conduction pathway that is thermally mediated. First principles DFT calculation
elucidates the existence of the two independent magnetic sublattices within
Pr2NiIrO6 and offers insight into the behavior in La2NiIrO6 and Nd2NiIrO6.
Resonant inelastic x-ray scattering is consistent with spin-orbit coupling
splitting the t2g manifold of octahedral Ir4+ into a Jeff = 1/2 and Jeff = 3/2
state for all members of the series considered.",2106.02025v1
2021-09-24,Damping in yttrium iron garnet film with an interface,"We report strong damping enhancement in a 200 nm thick yttrium iron garnet
(YIG) film due to spin inhomogeneity at the interface. The growth-induced thin
interfacial gadolinium iron garnet (GdIG) layer antiferromagnetically (AFM)
exchange couples with the rest of the YIG layer. The out-of-plane angular
variation of ferromagnetic resonance (FMR) linewidth $\Delta H$ reflects a
large inhomogeneous distribution of effective magnetization $\Delta 4 \pi
M_{eff}$ due to the presence of an exchange springlike moments arrangement in
YIG. We probe the spin inhomogeneity at the YIG-GdIG interface by performing an
in-plane angular variation of resonance field $H_{r}$, leading to a
unidirectional feature. The large extrinsic $\Delta 4\pi M_{eff}$ contribution,
apart from the inherent intrinsic Gilbert contribution, manifests enhanced
precessional damping in YIG film.",2109.12071v1
2021-10-05,Probing modified gravity with magnetically levitated resonators,"We present an experimental procedure, based on Meissner effect levitation of
neodymium ferromagnets, as a method of measuring the gravitational interactions
between mg masses. The scheme consists of two superconducting lead traps, with
a magnet levitating in each trap. The levitating magnets behave as harmonic
oscillators, and by carefully driving the motion of one magnet on resonance
with the other, we find that it should be easily possible to measure the
gravitational field produced by a 4~mg sphere, with the gravitational
attraction from masses as small as 30~$\mu$g predicted to be measurable within
realistic a realistic measurement time frame. We apply this acceleration
sensitivity to one concrete example and show the ability of testing models of
modified Newtonian dynamics.",2110.02263v1
2021-11-04,Control of the phase of reflected spin-waves from magnonic Gires-Tournois interferometer of subwavelength width,"The phase is one of the fundamental properties of a wave that allows to
control interference effects and can be used to efficiently encode information.
We examine numerically a magnonic resonator of the Gires-Tournois
interferometer type, which enables the control of the phase of spin waves
reflected from the edges of the ferromagnetic film. The considered
interferometer consists of a Py thin film and a thin, narrow Py stripe placed
above its edge, both coupled magnetostatically. We show that the resonances and
the phase of the reflected spin waves are sensitive for a variation of the
geometrical parameters of this bi-layerd part of the system. The high
sensitivity to film, stripe, and non-magnetic spacer thicknesses, offers a
prospect for developing magnonic metasurfaces and sensors.",2111.02678v1
2021-12-23,Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping,"The structural and magnetic properties of Zn/Al doped nickel ferrite thin
films can be adjusted by changing the Zn and Al content. The films are
epitaxially grown by reactive magnetron sputtering using a triple cluster
system to sputter simultaneously from three different targets. Upon the
variation of the Zn content the films remain fully strained with similar
structural properties, while the magnetic properties are strongly affected. The
saturation magnetization and coercivity as well as resonance position and
linewidth from ferromagnetic resonance (FMR) measurements are altered depending
on the Zn content in the material. The reason for these changes can be
elucidated by investigation of the x-ray magnetic circular dichroism spectra to
gain site and valence specific information with elemental specificity.
Additionally, from a detailed investigation by broadband FMR a minimum in
g-factor and linewidth could be found as a function of film thickness.
Furthermore, the results from a variation of the Al content using the same set
of measurement techniques is given. Other than for Zn, the variation of Al
affects the strain and even more pronounced changes to the magnetic properties
are apparent.",2112.12456v1
2022-01-26,Nonlinear magnon polaritons,"We experimentally and theoretically demonstrate that nonlinear spin-wave
interactions suppress the hybrid magnon-photon quasiparticle or ""magnon
polariton"" in microwave spectra of an yttrium iron garnet film detected by an
on-chip split-ring resonator. We observe a strong coupling between the Kittel
and microwave cavity modes in terms of an avoided crossing as a function of
magnetic fields at low microwave input powers, but a complete closing of the
gap at high powers. The experimental results are well explained by a
theoretical model including the three-magnon decay of the Kittel magnon into
spin waves. The gap closure originates from the saturation of the ferromagnetic
resonance above the Suhl instability threshold by a coherent back reaction from
the spin waves.",2201.10889v2
2022-02-01,Numerical Model Of Harmonic Hall Voltage Detection For Spintronic Devices,"We present a numerical macrospin model for harmonic voltage detection in
multilayer spintronic devices. The core of the computational backend is based
on the Landau-Lifshitz-Gilbert-Slonczewski equation, which combines high
performance with satisfactory, for large-scale applications, agreement with the
experimental results. We compare the simulations with the experimental findings
in Ta/CoFeB bilayer system for angular- and magnetic field-dependent resistance
measurements, electrically detected magnetisation dynamics, and harmonic Hall
voltage detection. Using simulated scans of the selected system parameters such
as the polar angle $\theta$, magnetisation saturation
($\mu_\textrm{0}M_\textrm{s}$) or uniaxial magnetic anisotropy ($K_\textrm{u}$)
we show the resultant changes in the harmonic Hall voltage, demonstrating the
dominating influence of the $\mu_\textrm{0}M_\textrm{s}$ on the first and
second harmonics. In the spin-diode ferromagnetic resonance (SD-FMR) technique
resonance method the ($\mu_\textrm{0}M_\textrm{s}$, $K_\textrm{u}$) parameter
space may be optimised numerically to obtain a set of viable curves that fit
the experimental data.",2202.00364v1
2022-02-24,Magnetic resonance probing of ferroelectricity and magnetism in metal-organic frameworks,"We employ electron paramagnetic resonance (EPR) of the spin probe Mn2+ to
study the paraelectric ferroelectric transition in DMAMnF and Mn2 doped DMZnF,
which are considered to be model metal organic frameworks (MOF) with a Pb free
perovskite architecture. In DMAMnF, we study the variation of the Mn2+ EPR line
shape and intensity at the X-band (9.4 GHz) and over 80 to 300 K, and we show
the absence of magnetoelectric coupling at the ferroelectric transition. At the
antiferromagnetic transition in DMMnF, we detect a magnetoelectric coupling
caused by weak ferromagnetism in the AFM phase. In DMZnF, the combination of
EPR of the Mn2+ probe and DFT show that the crystal field is predominantly
determined by the DMA+ cations.",2202.11992v1
2022-03-30,Hybrid magnonics for short-wavelength spin waves facilitated by a magnetic heterostructure,"Recent research on hybrid magnonics has been restricted by the long magnon
wavelengths of the ferromagnetic resonance modes. We present an experiment on
the hybridization of 250-nm wavelength magnons with microwave photons in a
multimode magnonic system consists of a planar cavity and a magnetic bilayer.
The coupling between magnon modes in the two magnetic layers, i.e., the uniform
mode in Permalloy (Py) and the perpendicular standing spin waves (PSSWs) in
YIG, serves as an effective means for exciting short-wavelength PSSWs, which is
further hybridized with the photon mode of the microwave resonator. The
demonstrated magnon-photon coupling approaches the superstrong coupling regime,
and can even be achieved near zero bias field.",2203.16310v1
2022-08-25,Spin mixing conductance and spin magnetoresistance of iridate/manganite interface,"We present results on experimental studies of spin current, measured under
spin pumping at ferromag-netic resonance in wide frequency band 2-20 GHz for
SrIrO3/La0.7Sr0.3MnO3 heterostructures fabricated by RF magnetron sputtering at
high temperature. The epitaxial growth of the thin film in heterostructure by a
cube-on-cube mechanism was confirmed by XRD and TEM analysis. Taking into
account the con-tribution of anisotropic magnetoresistance the spin current was
estimated as 1/3 of the total response. We show that both real and imaginary
parts of spin mixing conductance are valuable for heterostructures with strong
spin-orbit interaction in SrIrO3. Imaginary part of spin mixing conductance was
estimated by means of shift of ferromagnetic resonance field of La0.7Sr0.3MnO3
layer in heterostructure. The spin mag-netoresistance was evaluated from
angular dependencies of magnetoresistance measured in planar Hall
configuration. In order to extract the influence of anisotropic
magnetoresistance a La0.7Sr0.3MnO3 film was measured as well. The spin Hall
angle for heterostructure was found higher than for interface Pt/
La0.7Sr0.3MnO3.",2208.12163v1
2022-11-23,The fractional Landau-Lifshitz-Gilbert equation,"The dynamics of a magnetic moment or spin are of high interest to
applications in technology. Dissipation in these systems is therefore of
importance for improvement of efficiency of devices, such as the ones proposed
in spintronics. A large spin in a magnetic field is widely assumed to be
described by the Landau-Lifshitz-Gilbert (LLG) equation, which includes a
phenomenological Gilbert damping. Here, we couple a large spin to a bath and
derive a generic (non-)Ohmic damping term for the low-frequency range using a
Caldeira-Leggett model. This leads to a fractional LLG equation, where the
first-order derivative Gilbert damping is replaced by a fractional derivative
of order $s \ge 0$. We show that the parameter $s$ can be determined from a
ferromagnetic resonance experiment, where the resonance frequency and linewidth
no longer scale linearly with the effective field strength.",2211.12889v1
2023-03-21,Ultra-sensitive voltage-controlled skyrmion-based spintronic diode,"We have designed a passive spintronic diode based on a single skyrmion
stabilized in a magnetic tunnel junction and studied its dynamics induced by
voltage-controlled anisotropy (VCMA) and Dzyaloshinskii-Moriya interaction
(VDMI). We have demonstrated that the sensitivity (rectified voltage over input
microwave power) with realistic physical parameters and geometry can be larger
than 10 kV/W which is one order of magnitude better than diodes employing a
uniform ferromagnetic state. Our numerical and analytical results on the VCMA
and VDMI-driven resonant excitation of skyrmions beyond the linear regime
reveal a frequency dependence on the amplitude and no efficient parametric
resonance. Skyrmions with a smaller radius produced higher sensitivities,
demonstrating the efficient scalability of skyrmion-based spintronic diodes.
These results pave the way for designing passive ultra-sensitive and energy
efficient skyrmion-based microwave detectors.",2303.11838v2
2023-04-20,Magnon peak lineshape in the transverse dynamical structure factor of a magnetically polarized easy-axis $XXZ$ chain at low temperatures,"The ferromagnetically polarized gapped XXZ spin chain is studied at low
temperatures. Utilizing only the one- and two-magnon spectrums and focusing on
the magnon-creation contribution to the transverse dynamical susceptibility, we
represent the latter in the form of the Dyson equation. Then, following the
well known correspondence between the imaginary part of magnetic susceptibility
and dynamical structure factor, we get the low-temperature formula for the
magnon-peak lineshape. The suggested approach is effective only if the
processes related to magnon creations and to transitions from magnons to
coupled magnon pairs are energetically separated. As it is shown in the paper,
such separation is inherent in the easy-axis chains with rather strong
anisotropy. We present several plots and discuss their lineshapes. As the
supplemental result we obtain integral representations for the
temperature-dependent magnon resonance shift and the parameter which is usually
associated with the decay rate. The low-temperature behavior of the resonance
shift is studied in details. All calculations are performed up to {\it
controllable} error $o({\rm e}^{-\beta E_{gap}})$.",2304.10645v2
2023-05-10,Symmetry and nonlinearity of spin wave resonance excited by focused surface acoustic waves,"The use of a complex ferromagnetic system to manipulate GHz surface acoustic
waves is a rich current topic under investigation, but the high-power nonlinear
regime is under-explored. We introduce focused surface acoustic waves, which
provide a way to access this regime with modest equipment. Symmetry of the
magneto-acoustic interaction can be tuned by interdigitated transducer design
which can introduce additional strain components. Here, we compare the impact
of focused acoustic waves versus standard unidirectional acoustic waves in
significantly enhancing the magnon-phonon coupling behavior. Analytical
simulation results based on modified Landau-Lifshitz-Gilbert theory show good
agreement with experimental findings. We also report nonlinear input power
dependence of the transmission through the device. This experimental
observation is supported by the micromagnetic simulation using mumax3 to model
the nonlinear dependence. These results pave the way for extending the
understanding and design of acoustic wave devices for exploration of
acoustically driven spin wave resonance physics.",2305.06259v1
2023-07-18,Optical Tellegen metamaterial with spontaneous magnetization,"The nonreciprocal magnetoelectric effect, also known as the Tellegen effect,
promises a number of groundbreaking phenomena connected to fundamental (e.g.,
electrodynamics of axion and relativistic matter) and applied physics (e.g.,
magnetless isolators). We propose a three-dimensional metamaterial with an
isotropic and resonant Tellegen response in the visible frequency range. The
metamaterial is formed by randomly oriented bi-material nanocylinders in a host
medium. Each nanocylinder consists of a ferromagnet in a single-domain magnetic
state and a high-permittivity dielectric operating near the magnetic Mie-type
resonance. The proposed metamaterial requires no external magnetic bias and
operates on the spontaneous magnetization of the nanocylinders. By leveraging
the emerging magnetic Weyl semimetals, we further show how a giant bulk
effective magnetoelectric effect can be achieved in a proposed metamaterial,
exceeding that of natural materials by almost four orders of magnitude.",2307.09275v1
2023-07-27,Interfacial Resonance States-Induced Negative Tunneling Magneto-resistance in Orthogonally-Magnetized CoFeB/MgO/CoFeB,"Magnetic tunneling junctions (MTJs) are essential for non-volatile
magneto-resistive random access memory (MRAM) applications. Here, we report the
observation of a large negative tunneling magneto-resistance (TMR) in the
CoFeB/MgO/CoFeB system with an orthogonally-magnetized configuration. Through
the thickness modulation of the MgO barrier, the negative TMR component can be
enhanced up to 20% under a negative voltage bias. Moreover, the tunnel
anisotropic magneto-resistance measurements unveil that the negative TMR
component likely arises from the interfacial resonance states (IRS) in the
minority band of the bottom ferromagnetic layer. Complementary first principle
calculations further quantify the IRS location and strength with respect to the
Fermi level position. Our work not only confirm the vital role of IRS in the
electrical transport of MTJ, but also provide valuable insights for the design
of new-generation voltage-controlled MRAM and related spintronic applications.",2307.14807v1
2024-02-09,"Small-angle X-ray resonant magnetic scattering at the Co M$_{2,3}$ and L$_3$ edges observed with photoemission electron microscopy","X-ray magnetic circular dichroism is an efficient contrast mechanism allowing
for a direct sensitivity to magnetization. Combined with an imaging technique
such as photoemission electron microscopy, it has been successfully applied to
high-resolution investigations of ferromagnetic thin films but also of
three-dimensional systems thanks to the transmission-type contrast in their
shadow. Our focus in this work is the wave-optics scattering pattern that can
be observed near such a shadow's rim. Taking advantage of non-uniform magnetic
states present in near-micron-size Co$_{1-x}$Gd$_x$ beads, we first show how
X-ray resonant magnetic scattering affects the Fresnel diffraction at the Co
L$_3$ edge. In order to confirm this observation, we then turn to the Co
M$_{2,3}$ edges. There, we measure magnetic scattering patterns with a
significantly increased spatial extent (due to the larger wavelength), despite
the signal's weakness. The patterns' origin is supported by a comparison
between our experimental data and a simple analytical model, then numerical
simulations.",2402.06115v1
2024-04-05,Evidence for charge mediated coupling in Fe-Ga/PMN-PT composite multiferroic,"We present an experimental study of the magnetoelectric coupling (MEC) in the
Fe-Ga/PMN-PT thin film multiferroic composite by means of x-ray magnetic
circular dichroism (XMCD) and ferromagnetic resonance (FMR). Our measurements
show evidence for a charge mediated coupling mechanism, suggested by the
asymmetric magnetic remanence (M$_{rem}$) behaviour under opposite electric
fields ($\pm$ E) and the asymmetric resonance field (H$_r$) in the FMR
measurements. Also, the FMR measurements reveal a perpendicular magnetic
anisotropy (PMA), that can be related to an interface charge effect. and it is
tunable by E field. Ab initio calculations support the existence of a charge
mediated coupling at the Fe-Ga/PMN-PT interface.",2404.04383v1
2023-03-15,Chiral phonons and phononic birefringence in ferromagnetic metal - bulk acoustic resonator hybrids,"Magnomechanical devices, in which magnetic excitations couple to mechanical
vibrations, have been discussed as efficient and broadband microwave signal
transducers in the classical and quantum limit. We experimentally investigate
the magnetoelastic coupling between the ferromagnetic resonance (FMR) modes in
a metallic Co$_{25}$Fe$_{75}$ thin film, featuring ultra-low magnetic damping
as well as sizable magnetostriction, and standing transverse elastic phonon
modes in sapphire, silicon and gadolinium gallium garnet by performing
broadband FMR spectroscopy at cryogenic temperatures. For all these substrate
materials, we observe an interaction between the resonant acoustic and magnetic
modes, which can be tailored by the propagation direction of the acoustic mode
with respect to the crystallographic axes. We identify these phonon modes as
transverse shear waves propagating with slightly different velocities with
relative magnitudes of $\Delta v/v\simeq10^{-5}$, i.e., all substrates show
phononic birefringence. Upon appropriately choosing the phononic mode, the
hybrid magnomechanical system enters the Purcell enhanced coupling regime.",2303.08429v1
2001-08-30,"Magnetization, Structural and Nuclear Quadrupole Resonance Study of RuSr2EuCeCu2O10+d","We present the results from a magnetization, structural, and nuclear
quadrupole resonance study of the ruthenate-cuprate, RuSr2R2-xCexCu2O10+d with
x=1 and R=Eu. This compound is a superconductor for Ce doping in the range
0.4<=x<=0.8 and displays ferromagnetic order for 0.4<=x<=1.0. We show that the
tilting and rotation of the RuO6 octahedra are essentially the same for x=1,
x=0.6 and the superconducting antiferromagnet, RuSr2GdCu2O8. However, the
moment per Ru in RuSr2EuCeCu2O10+d is comparable to that observed in
RuSr2EuCu2O8. These results indicate that it is unlikely that the different
magnetic order found in RuSr2R2-xCexCu2O10+d and RuSr2RCu2O8 (R=Y,Gd,Eu) is due
to changes in structurally induced distortions of the RuO6 octahedra as found
in the ruthenate compounds (e.g. Sr1-xCaxRuO3). We show that the Cu nuclear
quadrupole resonance (NQR) data are similar to those observed in the single
CuO2 layer superconductor, La1-xSrxCuO4, where the Cu spin-lattice relaxation
rate is dominated by hyperfine coupling within the CuO2 layers and any
additional hyperfine coupling from spin fluctuations in the RuO2 layers is
small.",0108521v2
2005-01-10,Resonant tunneling in short Josephson SFS junctions,"Josephson effect in short ballistic SINIS and SIFIS double-tunnel junctions,
consisting of clean superconductors (S), a normal metal (N) or metallic
ferromagnet (F), and insulating interfaces (I) is studied. For SINIS
double-tunnel junctions, sharp peaks in the critical Josephson current as a
function of the junction width result from the resonant amplification of the
Andreev process when the quasi-bound states enter the superconducting gap. For
SIFIS double-tunnel junctions spin split quasi-bound states partially amplify
the supercurrent and trigger the transitions between 0 and $\pi$ states of the
junction. Instead of the critical current reaching a peak value (which happens
when the Andreev states cross the Fermi surface in SINIS junctions), a narrow
dip opens up exactly at the peak due to the compensation of partial currents
flowing in opposite directions. This is related to the spin polarization of
Andreev states and explains the coexistence of stable and metastable 0 and
$\pi$ states in the vicinity of the transition. With increased barrier
transparency, the described mechanism of $0-\pi$ transitions is modified by the
broadening and overlapping of quasi-bound states (transmission resonances).
Temperature-induced transitions both from 0 to $\pi$ and from $\pi$ to 0 states
are studied by computing the phase diagram (temperature vs. junction width) for
different interfacial transparencies varying from metallic (transparent) to the
tunnel limit.",0501179v2
2014-09-19,Study of strong photon-magnon coupling in a YIG-film split-ring resonant system,"By using the stripline Microwave Vector Network Analyzer Ferromagnetic
Resonance and Pulsed Inductive Microwave Magnetometry spectroscopy techniques,
we study a strong coupling regime of magnons to microwave photons in the planar
geometry of a lithographically formed split-ring resonator (SRR) loaded by a
single-crystal epitaxial yttrium-iron garnet (YIG) film. Strong anti-crossing
of the photon modes of SRR and of the magnon modes of the YIG film is observed
in the applied-magnetic-field resolved measurements. The coupling strength
extracted from the experimental data reaches 9 percent at 3 GHz.
  Theoretically, we propose an equivalent circuit model of an SRR loaded by a
magnetic film. This model follows from the results of our numerical simulations
of the microwave field structure of the SRR and of the magnetization dynamics
in the YIG film driven by the microwave currents in the SRR. The equivalent
circuit model is in good agreement with the experiment. It provides a simple
physical explanation of the process of mode anti-crossing.
  Our findings are important for future applications in microwave quantum
photonic devices as well as in magnetically tunable metamaterials exploiting
the strong coupling of magnons to microwave photons.",1409.5499v1
2018-02-09,A T-shaped double quantum dot system as a Fano interferometer: interplay of coherence and correlation upon spin currents,"Based on Keldysh non-equilibrium Green function method, we have investigated
spin current production in a hybrid T-shaped device, consisting of a central
quantum dot connected to the leads and a side dot which only couples to the
central dot. The topology of this structure allows for quantum interference of
the different paths that go across the device, yielding Fano resonances in the
spin dependent transport properties. Correlation effects are taken into account
at the central dot and handled within a mean field approximation. Its interplay
with the Fano effect is analyzed in the strong coupling regime. Non-vanishing
spin currents are only obtained when the leads are ferromagnetic, the current
being strongly dependent on the relative orientation of the lead polarizations.
We calculate the conductance (spin and charge) by numerically differentiating
the current, and a rich structure is obtained as a manifestation of quantum
coherence and correlation effects. Increase of the Coulomb interaction produces
localization of states at the side dot, largely suppressing Fano resonances.
The interaction is also responsible for the negative values of the spin
conductance in some regions of the voltage near resonances, effect which is the
spin analog of the Esaki tunnel diode. We also analyze control of the currents
via gate voltages applied to the dots, possibility which is interesting for
practical operations.",1802.03439v1
2018-04-11,NMR and the antiferromagnetic crystal phase regions in rapidly quenched ribbons and in alloys of the type $Cu-Mn-Al$,"It was shown that anomalous resistivity behavior of the $Cu-Mn-Al$ ribbons is
explained by the s-d interaction between conduction electrons and the clustered
Mn atoms. While nuclear magnetic resonance measurements show the
antiferromagnetic and ferromagnetic clusters of Mn atom coexisting without
long-range order, it is an interesting problem to study magnetic resonance
properties also for the antiferromagnetic crystal phase regions (which have
long-range order for larger regions) and which may also occur in these ribbons.
The Heusler Type $Cu-Mn-Al$ Alloy has a composition half way between
$Cu_{2}MnAl$ and $Cu_{3}Al$. Electron microscopy of the premartensitic $\beta
Cu-Zn-Al$ alloy has shown that the $\beta Cu-Zn-Al$ alloy quenched from high
temperature has the electron diffraction patterns of this alloy well explained
by the model with the existence of small particles with an orthorhombic
structure. It was noted that an important aspect of improvement in the material
properties is to create a nanostructured state in matrix, which has significant
advantages in magnetic and mechanical characteristics in contrast to the bulk
materials in crystalline or amorphous state. It is an interesting problem to
study magnetic resonance properties not only for the Mn atoms and clusters
without long-range order but also for the antiferromagnetic crystal phase
regions (which have long-range order for larger regions) which may also occur
in ribbons. This is the aim of our paper.",1804.04196v1
2013-09-24,Linear temperature dependence of electron spin resonance linewidths in La0.7Ca0.3MnO3 and YBaMn2O6,"We analyze recent electron spin resonance (ESR) experiments in La0.7Ca0.3MnO3
and YBaMn2O6 focusing on the behavior of the linewidth at high temperatures
where it is a linear function of the temperature. Noting that the g-factors of
the resonances are characteristic of the Mn4+ ion in a cubic environment, we
make the assumption that the linewidth involves the static susceptibility of
the Mn4+ spins which we analyze in the molecular field approximation. We
conclude that the linear dependence on temperature is associated with the
susceptibility having a Curie or Curie-Weiss form while the
temperature-dependent relaxation mechanism has a microscopic rate proportional
to the temperature. In La0.7Ca0.3MnO3, the Mn4+ susceptibility has the
ferromagnetic Curie-Weiss form, and the static contribution to the linewidth
arising from distortions of the oxygen octahedra is absent due to motional
narrowing brought on by the rapid hopping of the eg polarons. In YBaMn2O6
either of two scenarios is possible. The Mn4+ susceptibility above 520 K is
Curie-like and the static term is present, or the susceptibility has the
antiferromagnetic Curie-Weiss form and the static term is absent due to
motional narrowing. It is concluded that the Curie model, with offsetting
double exchange and and superexchange Curie-Weiss parameters, is the more
likely scenario. It is suggested that the linear-T variation of the linewidth
in both materials arises from either a Korringa-like mechanism involving
interactions with mobile carriers or from a spin-phonon process coming from
interactions between the Mn4+ ions and the lattice vibrations.",1309.6353v1
2019-06-13,Electrodynamic improvements to the theory of magnetostatic modes in ferrimagnetic spheres and their applications to saturation magnetization measurements,"Electrodynamic theory applied to the analysis of TEn0p mode resonances in
ferromagnetic spheres placed either in metallic cavities or in the free space
is compared with Walker-Fletcher's theory of so-called magnetostatic modes. The
influence of the diameter of the sample, its permittivity and the permittivity
of the surrounding media on the resonance frequencies of a few modes is
analyzed. It is shown that the dominant resonances are essentially related
either to negative values of the diagonal component of the permeability tensor
or, for clockwise circularly polarized magnetic fields, to negative effective
permeability. The electrodynamic theory is used to determine the saturation
magnetization (Ms) from measured TEn01 frequency differences. Measurements on
different samples confirmed that Ms can be determined using an electrodynamic
approach with uncertainties of the order of 2% regardless of sample sizes,
metal enclosures or static magnetic field values.",1906.05559v1
2018-12-27,All-dielectric metasurfaces with trapped modes: group-theoretical description,"An all-dielectric metasurface featuring resonant conditions of the trapped
mode excitation is considered. It is composed of a lattice of subwavelength
particles which are made of a high-refractive-index dielectric material
structured in the form of disks. Each particle within the lattice behaves as an
individual dielectric resonator supporting a set of electric and magnetic
(Mie-type) modes. In order to access a trapped mode (which is the TE01 mode of
the resonator), a round eccentric penetrating hole is made in the disk. In the
lattice, the disks are arranged into clusters (unit super-cells) consisting of
four particles. Different orientations of holes in the super-cell correspond to
different symmetry groups producing different electromagnetic response of the
overall metasurface when it is irradiated by the linearly polarized waves with
normal incidence. We perform a systematic analysis of the electromagnetic
response of the metasurface as well as conditions of the trapped mode
excitation involving the group-theoretical description, representation theory
and microwave circuit theory. Both polarization-sensitive and
polarization-insensitive arrangements of particles and conditions for dynamic
ferromagnetic and antiferromagnetic order are derived. Finally, we observe the
trapped mode manifestation in the microwave experiment.",1812.10817v1
2021-06-28,Resonance from antiferromagnetic spin fluctuations for superconductivity in UTe$_2$,"Superconductivity originates from the formation of bound (Cooper) pairs of
electrons that can move through the lattice without resistance below the
superconducting transition temperature $T_c$. Electron Cooper pairs in most
superconductors form anti-parallel spin singlets with total spin $S=0$,
although they can also form parallel spin-triplet Cooper pairs with $S=1$ and
an odd parity wavefunction. Spin-triplet pairing is important because it can
host topological states and Majorana fermions relevant for quantum computation.
Because spin-triplet pairing is usually mediated by ferromagnetic (FM) spin
fluctuations, uranium based materials near an FM instability are considered to
be ideal candidates for realizing spin-triplet superconductivity. Indeed,
UTe$_2$, which has a $T_c\approx 1.6$ K, has been identified as a candidate for
a chiral spin-triplet topological superconductor near an FM instability,
although it also has antiferromagnetic (AF) spin fluctuations. Here we use
inelastic neutron scattering (INS) to show that superconductivity in UTe$_2$ is
coupled to a sharp magnetic excitation, termed resonance, at the Brillouin zone
boundary near AF order. Because the resonance has only been found in
spin-singlet unconventional superconductors near an AF instability, its
observation in UTe$_2$ suggests that AF spin fluctuations may also induce
spin-triplet pairing or that electron pairing in UTe$_2$ has a spin-singlet
component.",2106.14424v2
2021-08-30,Bright and dark states of two distant macrospins strongly coupled by phonons,"We study the collective dynamics of two distant magnets coherently coupled by
acoustic phonons that are transmitted through an intercalated crystal. By
tuning the ferromagnetic resonances of the two magnets to an acoustic resonance
of the crystal, we control a coherent three levels system. We show that the
parity of the phonon mode governs the nature of the indirect coupling between
the magnets: the resonances with odd / even phonon modes correspond to
out-of-phase / in-phase lattice displacements at the magnets, leading to bright
/ dark states in response to uniform microwave magnetic fields, respectively.
The sample is a tri-layer garnet consisting of two thin magnetic layers
epitaxially grown on both sides of a half-millimeter thick non-magnetic single
crystal. In spite of the relatively weak magneto-elastic interaction, the long
lifetimes of the magnon and phonon modes in the sample are the key to unveil
this long range strong coupling. This demonstrates that garnets are a great
platform to study multi-partite hybridization process between magnon and
phonons at microwave frequencies.",2108.13272v2
2021-11-23,Resonant dynamics of skyrmion lattices in thin film multilayers: Localised modes and spin wave emission,"The spectral signatures of magnetic skyrmions under microwave field
excitation are of fundamental interest and can be an asset for high frequency
applications. These topological solitons can be tailored in multilayered thin
films, but the experimental observation of their spin wave dynamics remains
elusive, in particular due to large damping. Here, we study Pt/FeCoB/AlO$_x$
multilayers hosting dense and robust skyrmion lattices at room temperature with
Gilbert damping of $\sim 0.02$. We use magnetic force microscopy to
characterise their static magnetic phases and broadband ferromagnetic resonance
to probe their high frequency response. Micromagnetic simulations reproduce the
experiments with accuracy and allow us to identify distinct resonant modes
detected in the skyrmion lattice phase. Low ($<$ 2 GHz) and intermediate
frequency ($2-8$ GHz) modes involve excitations localised to skyrmion edges in
conjunction with precession of the uniform background magnetisation, while a
high frequency ($>$ 12 GHz) mode corresponds to in-phase skyrmion core
precession emitting spin waves into uniform background with wavelengths in the
50--80 nm range commensurate with the lattice structure. These findings could
be instrumental in the investigation of room temperature wave scattering and
the implementation of novel microwave processing schemes in reconfigurable
arrays of solitons.",2111.11797v2
2023-01-18,Ion-Implanted $^8$Li Nuclear Magnetic Resonance in Highly Oriented Pyrolytic Graphite,"We report $\beta$-detected nuclear magnetic resonance of ultra-dilute
$^{8}$Li$^{+}$ implanted in highly oriented pyrolytic graphite (HOPG). The
absence of motional narrowing and diffusional spin-lattice relaxation implies
Li$^+$ is not appreciably mobile up to 400 K, in sharp contrast to the highly
lithiated stage compounds. However, the relaxation is remarkably fast and
persists down to cryogenic temperatures. Ruling out extrinsic paramagnetic
impurities and intrinsic ferromagnetism, we conclude the relaxation is due to
paramagnetic centers correlated with implantation. While the resulting effects
are not consistent with a Kondo impurity, they also differ from free
paramagnetic centers, and we suggest that a resonant scattering approach may
account for much of the observed phenomenology.",2301.07821v4
2023-07-03,"Continuously Red-Shift and Blue-Shift Wavelength-Tuneable, Narrowband, High Harmonics in the EUV - X-ray Regime for Resonance Imaging and Spectroscopies","We demonstrate a novel technique for producing high-order harmonics with
designer spectral combs in the extreme ultraviolet-soft X-ray range for
resonance applications using spectrally controlled visible lasers. Our approach
enables continuous tunability of the harmonic peaks while maintaining superb
laser-like features such as coherence, narrow bandwidth, and brightness. The
harmonics are conveniently shifted towards lower or higher energies by varying
the infrared pulse parameters, second harmonic generation phase-matching
conditions, and gas density inside a spectral-broadening waveguide. In the time
domain, the X-rays are estimated to emerge as a train of sub-300 attosecond
pulses, making this source ideal for studying dynamic processes in
ferromagnetic nanostructures and other materials through resonant
multidimensional coherent diffractive imaging or other X-ray absorption
spectroscopy techniques. Moreover, the visible driving laser beams exhibit an
ultrashort sub-10 fs pulse dues to nonlinear self-compression with a more than
30-fold enhancement in peak intensity that also extends the tunability of the
linewidth of the harmonic combs.",2307.01182v1
2023-12-05,Infrared spectroscopy of phase transitions in the lowest Landau levels of bilayer graphene,"We perform infrared magneto-spectroscopy of Landau level (LL) transitions in
dual-gated bilayer graphene. At $\nu=4$ when the zeroth LL (octet) is filled,
two resonances are observed indicating the opening of a gap. At $\nu=0$ when
the octet is half-filled, multiple resonances are found to disperse
non-monotonically with increasing displacement field, $D$, perpendicular to the
sheet, showing a phase transition at modest displacement fields to the
layer-polarized state with a gap that opens linearly in $D$. When $D=0$ and
$\nu$ is varied, resonances at $\pm\nu$ show an electron-hole asymmetry with
multiple line splittings as the octet is progressively filled. Broadly these
data show good agreement with predictions from a mean-field Hartree-Fock
calculation, but only by accounting for multiple tight-binding terms in a
four-band model of bilayer graphene that also incorporates valley interaction
anisotropy. Our results are consistent with the presence of a canted
anti-ferromagnet (CAFM) ground state at $\nu=0$, and imply the existence of
intermediate phases in the transition from the CAFM to the layer-polarized
regime.",2312.02489v1
2024-01-17,Effects of Vanadium Doping on the Optical Response and Electronic Structure of WS$_{2}$ Monolayers,"Two-dimensional dilute magnetic semiconductors has been recently reported in
semiconducting transition metal dichalcogenides by the introduction of
spin-polarized transition metal atoms as dopants. This is the case of
vanadium-doped WS$_2$ and WSe$_2$ monolayers, which exhibits a ferromagnetic
ordering even above room temperature. However, a broadband characterization of
their electronic band structure and its dependence on vanadium concentration is
still lacking. Therefore, here we perform power-dependent photoluminescence,
resonant four-wave mixing, and differential reflectance spectroscopy to study
the optical transitions close to the A exciton energy of vanadium-doped WS$_2$
monolayers with distinct concentrations. Instead of a single A exciton peak,
vanadium-doped samples exhibit two photoluminescence peaks associated with
transitions to occupied and unoccupied bands. Moreover, resonant Raman
spectroscopy and resonant second-harmonic generation measurements revealed a
blueshift in the B exciton but no energy change in the C exciton as vanadium is
introduced in the monolayers. Density functional theory calculations showed
that the band structure is sensitive to the Hubbard \(U\) correction for
vanadium and several scenarios are proposed to explain the two
photoluminescence peaks around the A exciton energy region. Our work provides
the first broadband optical characterization of these two-dimensional dilute
magnetic semiconductors, shedding light on the novel electronic features of
WS$_{2}$ monolayers which are tunable by the vanadium concentration.",2401.09402v1
2017-08-04,"Identification of spin wave resonances and crystal field transitions in simple chromites RCrO3 (R=Pr, Sm, Er) at ultralow temperatures in the THz spectral region","We report on THz absorption spectroscopy combined with high magnetic fields
of polycrystalline RCrO3 (R= Pr, Sm, Er) aiming understanding spin wave
resonances at their low temperature magnetic phases. Our measurements show that
the temperature, and the implicit anisotropies at which the Cr3+ spin
reorientation at TSR takes place, are determinant on the ferromagnetic-like
(FM) and the antiferromagnetic-like (AFM) spin modes being optically active. It
is found that they are dependent on Rare Earth 4f moment and ion size. We also
studied temperature and field dependence of crystal field levels in the same
spectroscopic region. Pr3+ non-Kramers emerges at 100 K and Zeeman splits. An
observed absence of spin wave resonances in PrCrO3 is attributed to Pr3+
remaining paramagnetic. In SmCrO3 near cancelation of the spin and orbital
moments is proposed as the possible reason for not detecting Sm3+ ground state
transitions. Here, the FM and AFM resonant modes harden when the temperature
decreases and split linearly on applied fields at 5 K and below. In ErCrO3 the
Er3+ Kramers doublet becomes active at about the TSR onset. Each line further
experiences Zeeman splitting under magnetic fields while an spin reversal
induced by a 2.5 T field, back to the Gamma4 (Fz) from the Gamma1 phase at 2 K,
produces a secondary splitting. The 5 K AFM and FM excitations in ErCrO3 have a
concerted frequency-intensity temperature dependence and a shoulder pointing to
the Er3+ smaller ion size also disrupting the two magnetic sublattice
approximation . Both resonances reduce to one when the temperature is lowered
to 2 K in the Gamma1 representation.",1708.01497v1
2018-04-22,Spontaneous spinning of a rattleback placed on vibrating platform,"The spontaneous spinning of a rattleback placed on a vibrating platform is
investigated. The rattleback is a toy with some curious properties. When placed
on a surface with reasonable friction, the rattleback has a preferred direction
of spin. If rotated anti to it, longitudinal vibrations are set up and spin
direction is reversed.
  In this paper, the dynamics of a rattleback placed on a sinusoidally
vibrating platform are simulated. We can expect base vibrations to excite the
pitch motion of the rattleback, which, because of the coupling between pitch
and spin motion, should cause the rattleback to spin. Results are presented
which show that this indeed is the case- the rattleback has a mono-peak spin
resonance with respect to base vibrations. The rattleback, thus, transduces
translating vibrations into continuous rotary motion and, therefore, is ideal
for applications in Energy harvesting and Vibration sensing.
  The dynamic response of the rattleback was found to be composed of two
principal frequencies that appeared in the pitch and rolling motions. One of
the frequencies was found to have a large coupling with the spin of the
rattleback. Spin resonance was found to occur when the base oscillatory
frequency was twice the value of the coupled frequency. A linearized model is
developed which can predict the values of the two frequencies accurately and
analytical expressions for the same in terms of the parameters of the
rattleback have been derived. The analysis, thus, forms an effective and easy
method for obtaining the spin resonant frequency of a given rattleback.
  Novel ideas for applications utilizing the phenomenon of spin resonance, for
example, an energy harvester composed of a magnetized rattleback surrounded by
ferromagnetic walls and a small scale vibration sensor comprising an array of
several magnetized rattlebacks, are included.",1804.08163v1
2005-05-12,"Perpendicular magnetization reversal, magnetic anisotropy, multi-step spin switching, and domain nucleation and expansion in Ga1-xMnxAs films","We present a comprehensive study of the reversal process of perpendicular
magnetization in thin layers of the ferromagnetic semiconductor Ga1-xMnxAs. For
this investigation we have purposely chosen Ga1-xMnxAs with a low Mn
concentration (x ~ 0.02), since in such specimens contributions of cubic and
uniaxial anisotropy parameters are comparable, allowing us to identify the role
of both types of anisotropy in the magnetic reversal process. As a first step
we have systematically mapped out the angular dependence of ferromagnetic
resonance in thin Ga1-xMnxAs layers, which is a highly effective tool for
obtaining the magnetic anisotropy parameters of the material. The process of
perpendicular magnetization reversal was then studied by magneto-transport
(i.e., Hall effect and planar Hall effect measurements). These measurements
enable us to observe coherent spin rotation and non-coherent spin switching
between the (100) and (010) planes. A model is proposed to explain the observed
multi-step spin switching. The agreement of the model with experiment indicates
that it can be reliably used for determining magnetic anisotropy parameters
from magneto-transport data. An interesting characteristic of perpendicular
magnetization reversal in Ga1-xMnxAs with low x is the appearance of a double
hysteresis loops in the magnetization data. This double-loop behavior can be
understood by generalizing the proposed model to include the processes of
domain nucleation and expansion.",0505322v1
2005-11-03,Electric Field Control of Spin Transport,"Spintronics is an approach to electronics in which the spin of the electrons
is exploited to control the electric resistance R of devices. One basic
building block is the spin-valve, which is formed if two ferromagnetic
electrodes are separated by a thin tunneling barrier. In such devices, R
depends on the orientation of the magnetisation of the electrodes. It is
usually larger in the antiparallel than in the parallel configuration. The
relative difference of R, the so-called magneto-resistance (MR), is then
positive. Common devices, such as the giant magneto-resistance sensor used in
reading heads of hard disks, are based on this phenomenon. The MR may become
anomalous (negative), if the transmission probability of electrons through the
device is spin or energy dependent. This offers a route to the realisation of
gate-tunable MR devices, because transmission probabilities can readily be
tuned in many devices with an electrical gate signal. Such devices have,
however, been elusive so far. We report here on a pronounced gate-field
controlled MR in devices made from carbon nanotubes with ferromagnetic
contacts. Both the amplitude and the sign of the MR are tunable with the gate
voltage in a predictable manner. We emphasise that this spin-field effect is
not restricted to carbon nanotubes but constitutes a generic effect which can
in principle be exploited in all resonant tunneling devices.",0511078v1
2005-12-07,Nanoscale Suppression of Magnetization at Atomically Assembled Manganite Interfaces,"Using polarized X-rays, we compare the electronic and magnetic properties of
a La(2/3)Sr(1/3)MnO(3)(LSMO)/SrTiO(3)(STO) and a modified
LSMO/LaMnO(3)(LMO)/STO interface. Using the technique of X-ray resonant
magnetic scattering (XRMS), we can probe the interfaces of complicated layered
structures and quantitatively model depth-dependent magnetic profiles as a
function of distance from the interface. Comparisons of the average electronic
and magnetic properties at the interface are made independently using X-ray
absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The
XAS and the XMCD demonstrate that the electronic and magnetic structure of the
LMO layer at the modified interface is qualitatively equivalent to the
underlying LSMO film. From the temperature dependence of the XMCD, it is found
that the near surface magnetization for both interfaces falls off faster than
the bulk. For all temperatures in the range of 50K - 300K, the magnetic
profiles for both systems always show a ferromagnetic component at the
interface with a significantly suppressed magnetization that evolves to the
bulk value over a length scale of ~1.6 - 2.4 nm. The LSMO/LMO/STO interface
shows a larger ferromagnetic (FM) moment than the LSMO/STO interface, however
the difference is only substantial at low temperature.",0512158v2
2006-04-21,Spin Precession and Real Time Dynamics in the Kondo Model: A Time-Dependent Numerical Renormalization-Group Study,"A detailed derivation of the recently proposed time-dependent numerical
renormalization-group (TD-NRG) approach to nonequilibrium dynamics in quantum
impurity systems is presented. We demonstrate that the method is suitable for
fermionic as well as bosonic baths. A comparison with exact analytical results
for the charge relaxation in the resonant-level model and for dephasing in the
spin-boson model establishes the accuracy of the method. The real-time dynamics
of a single spin coupled to both types of baths is investigated. We use the
TD-NRG to calculate the spin relaxation and spin precession of a single Kondo
impurity. The short- and long-time dynamics is studied as a function of
temperature in the ferromagnetic and antiferromagnetic regimes. The short-time
dynamics agrees very well with analytical results obtained at second order in
the exchange coupling $J$. In the ferromagnetic regime, the long-time spin
decay is described by the scaling variable $x = 2\rho_F J(T) T t$. In the
antiferromagnetic regime it is governed for $T < T_K$ by the Kondo time scale
$1/T_K$. Here $\rho_F$ is the conduction-electron density of states and $T_K$
is the Kondo temperature. Results for spin precession are obtained by rotating
the external magnetic field from the x axis to the z axis.",0604517v1
2006-04-25,Complete melting of charge order in hydrothermally grown Pr_0.57 Ca_0.41 Ba_0.02 MnO_3 nanowires,"Nanowires of Pr_0.57 Ca_0.41 Ba_0.02 MnO_3 (PCBM) (diameter ~ 80-90 nm and
length ~ 3.5 mm) were synthesized by a low reaction temperature hydrothermal
method. Single-phase nature of the sample was confirmed by XRD experiments.
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM)
were used to characterize the morphology and microstructures of the nanowires.
While the bulk PCBM is known to exhibit charge order (CO) below 230 K along
with a ferromagnetic transition at 110 K, SQUID measurements on the nanowires
of PCBM show that the charge order is completely absent and a ferromagnetic
transition occurs at 115 K. However, the magnetization in the nanowires is
observed to be less compared to that in the bulk. This observation of the
complete melting of the charge order in the PCBM nanowires is particularly
significant in view of the observation of only a weakening of the CO in the
nanowires of Pr_0.5 Ca_0.5 MnO_3. Electron paramagnetic resonance experiments
were also carried out on the PCBM nanowires using an X-band EPR spectrometer.
Characteristic differences were observed in the line width of nanowires when
compared with that of the bulk.",0604567v1
2008-09-20,Anomalous low-temperature magnetoelastic properties of nanogranular (CoFeB)$_{x}$-(SiO$_{2}$)$_{1-x}$,"We report magnetostatic measurements for granulated films
(CoFeB)$_{x}$-(SiO$_{2}$)$_{1-x}$ with fabrication induced intraplanar
anisotropy. The measurements have been performed in the film plane in the wide
temperature interval 4.5$\div$300 K. They demonstrate that above films have
low-temperature anomaly below the percolation threshold for conductivity. The
essence of the above peculiarity is that below 100 K the temperature dependence
of coercive field for magnetization along easy direction deviates strongly from
Neel-Brown law. At temperature lowering, the sharp increase of coercivity is
observed, accompanied by the appearance of coercive field for magnetization
along hard direction in the film plane. We establish that observed effect is
related to the properties of individual ferromagnetic granules. The effect
weakens as granules merge into conglomerates at $x$ higher then percolation
threshold and disappears completely at $x>1$. We explain the above effect as a
consequence of the difference in thermal expansion coefficients of granule and
cover material. At temperature lowering this difference weakens the envelopment
of an individual granule by the cover matrix material, thus permitting to
realize the spontaneous magnetostriction of a granule. The latter induces an
additional anisotropy with new easy axis of a granule magnetization along the
external magnetic field direction. Our explanation is tested and corroborated
by the ferromagnetic resonance measurements in the films at $T$ = 300 K and $T$
= 77 K.",0809.3499v1
2008-11-03,Compensation-dependent in-plane magnetization reversal processes in Ga1-xMnxP1-ySy,"We report the effect of dilute alloying of the anion sublattice with S on the
in-plane uniaxial magnetic anisotropy and magnetization reversal process in
Ga1-xMnxP as measured by both ferromagnetic resonance (FMR) and superconducting
quantum interference device (SQUID) magnetometry. At T=5K, raising the S
concentration increases the uniaxial magnetic anisotropy between in-plane <011>
directions while decreasing the magnitude of the (negative) cubic anisotropy
field. Simulation of the SQUID magnetometry indicates that the energy required
for the nucleation and growth of domain walls decreases with increasing y.
These combined effects have a marked influence on the shape of the
field-dependent magnetization curves; while the direction remains the easy axis
in the plane of the film, the field dependence of the magnetization develops
double hysteresis loops in the [011] direction as the S concentration increases
similar to those observed for perpendicular magnetization reversal in lightly
doped Ga1-xMnxAs. The incidence of double hysteresis loops is explained with a
simple model whereby magnetization reversal occurs by a combination of coherent
spin rotation and noncoherent spin switching, which is consistent with both FMR
and magnetometry experiments. The evolution of magnetic properties with S
concentration is attributed to compensation of Mn acceptors by S donors, which
results in a lowering of the concentration of holes that mediate
ferromagnetism.",0811.0385v1
2009-04-12,Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nano-particles,"We have studied the electronic structure of Zn$_{0.9}$Fe$_{0.1}$O
nano-particles, which have been reported to show ferromagnetism at room
temperature, by x-ray photoemission spectroscopy (XPS), resonant photoemission
spectroscopy (RPES), x-ray absorption spectroscopy (XAS) and x-ray magnetic
circular dichroism (XMCD). From the experimental and cluster-model calculation
results, we find that Fe atoms are predominantly in the Fe$^{3+}$ ionic state
with mixture of a small amount of Fe$^{2+}$ and that Fe$^{3+}$ ions are
dominant in the surface region of the nano-particles. It is shown that the room
temperature ferromagnetism in the Zn$_{0.9}$Fe$_{0.1}$O nano-particles is
primarily originated from the antiferromagnetic coupling between unequal
amounts of Fe$^{3+}$ ions occupying two sets of nonequivalent positions in the
region of the XMCD probing depth of $\sim$ 2-3 nm.",0904.1838v1
2010-08-12,"Experimental probing of exchange interactions between localized spins in the dilute magnetic insulator (Ga,Mn)N","The sign, magnitude, and range of the exchange couplings between pairs of Mn
ions is determined for (Ga,Mn)N and (Ga,Mn)N:Si with x < 3%. The samples have
been grown by metalorganic vapor phase epitaxy and characterized by
secondary-ion mass spectroscopy; high-resolution transmission electron
microscopy with capabilities allowing for chemical analysis, including the
annular dark-field mode and electron energy loss spectroscopy; high-resolution
and synchrotron x-ray diffraction; synchrotron extended x-ray absorption
fine-structure; synchrotron x-ray absorption near-edge structure; infra-red
optics and electron spin resonance. The results of high resolution magnetic
measurements and their quantitative interpretation have allowed to verify a
series of ab initio predictions on the possibility of ferromagnetism in dilute
magnetic insulators and to demonstrate that the interaction changes from
ferromagnetic to antiferromagnetic when the charge state of the Mn ions is
reduced from 3+ to 2+.",1008.2083v2
2012-03-01,Magnetic properties of carbon nanodisk and nanocone powders,"We have investigated the magnetic properties of carbon powders which consist
of nanodisks, nanocones, and a small fraction of carbon-black particles.
Magnetization measurements were carried out using a superconducting quantum
interference device in magnetic fields $-5<\mu_{0}H<5\:\mathrm{T}$ for
temperatures in the range $2\leq T<350\:\mathrm{K}$. Measurements of the
magnetization $M$ versus temperature $T$ and magnetic field $\mu_{0}H$ for
these carbon samples show diamagnetism and paramagetism with an additional
ferromagnetic contribution. The ferromagnetic magnetization is in agreement
with the calculated magnetization from Fe impurities as determined by the
particle-induced x-ray emission method ($<75\:\mu\mathrm{g/g}$). Magnetization
measurements in weak magnetic fields show thermal hysteresis, and for strong
fields the magnetization $M$ decreases as $M\sim aT^{-\alpha}$ with $\alpha<1$,
which is slower than the Curie law ($\alpha=1$), when the temperature
increases. The magnetization $M$ versus magnetic field $\mu_{0}H$ shows
paramagnetic free-spin $S=\frac{1}{2}$ and $\frac{3}{2}$ behaviors for
temperatures $T=2\:\mathrm{K}$ and $15\leq T\leq50\:\mathrm{K}$, respectively.
A tendency for localization of electrons was found by electron spin resonance
when the temperature $T$ decreases ($2<T<40\:\mathrm{K}$). The magnetic
properties in these carbon cone and disk powder samples are more complex than a
free-spin model predicts, which is apparently valid only for the temperature
$T=2\:\mathrm{K}$.",1203.0284v3
2012-10-08,Magnetic anisotropy in strained manganite films and bicrystal junctions,"Transport and magnetic properties of LSMO manganite thin films and bicrystal
junctions were investigated. Manganite films were epitaxially grown on STO,
LAO, NGO and LSAT substrates and their magnetic anisotropy were determined by
two techniques of magnetic resonance spectroscopy. Compare with cubic
substrates a small (about 0.3 persentage), the anisotropy of the orthorhombic
NGO substrate leads to a uniaxial anisotropy of the magnetic properties of the
films in the plane of the substrate. Samples with different tilt of
crystallographic basal planes of manganite as well as bicrystal junctions with
rotation of the crystallographic axes (RB - junction) and with tilting of basal
planes (TB - junction) were investigated. It was found that on vicinal NGO
substrates the value of magnetic anisotropy could be varied by changing the
substrate inclination angle from 0 to 25 degrees. Measurement of magnetic
anisotropy of manganite bicrystal junction demonstrated the presence of two
ferromagnetically ordered spin subsystems for both types of bicrystal
boundaries RB and TB. The magnitude of the magnetoresistance for TB - junctions
increased with decreasing temperature and with the misorientation angle even
misorientation of easy axes in the parts of junction does not change. Analysis
of the voltage dependencies of bicrystal junction conductivity show that the
low value of the magnetoresistance for the LSMO bicrystal junctions can be
caused by two scattering mechanisms with the spin- flip of spin - polarized
carriers due to the strong electron - electron interactions in a disordered
layer at the bicrystal boundary at low temperatures and the spin-flip by anti
ferromagnetic magnons at high temperatures.",1210.2261v1
2013-04-01,Oxygen-Vacancy-Induced Antiferromagnetism to Ferromagnetism Transformation in Multiferroic Thin Films,"Oxygen vacancies (VOs) effects on magnetic ordering in
Eu0.5Ba0.5TiO3-{\delta} (EBTO3-{\delta}) thin films have been investigated
using a combination of experimental measurements and first-principles
density-functional calculations. Two kinds of EBTO3-{\delta}thin films with
different oxygen deficiency have been fabricated. A nuclear resonance
backscattering spectrometry technique has been used to quantitatively measure
contents of the VOs. Eu0.5Ba0.5TiO3 ceramics have been known to exhibit
ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a
ferromagnetic (FM) behavior with a Curie temperature of 1.85 K has been found
in the EBTO3-{\delta} thin films. Spin-polarized Ti3+ ions, which originated
from the VOs, has been proven to mediate a FM coupling between the local Eu 4f
spins and were believed to be responsible for the great change of the magnetic
ordering. Our work opens up a new avenue for developing FM-FE materials by
manipulating the oxygen deficiency in AFM-FE multiferroics.",1304.0300v2
2013-05-14,Long-range FMR driven spin pumping through a nonmagnetic insulator,"Ferromagnetic resonance (FMR) driven spin pumping is an emerging technique
for injection of a pure spin current from a ferromagnet (FM) into a
non-magnetic (NM) material without an accompanying charge current. It is widely
believed that this pumping proceeds exclusively via a short-range exchange
interaction at the FM/NM interface. Here we report robust, long-range spin
pumping from the ferrimagnetic double perovskite Sr2FeMoO6 (SFMO) into Pt
across an insulating barrier up to 200 nm thick, and systematically rule out
all known spurious effects. This result demonstrates dynamic spin injection
over a distance far beyond the coupling range of the exchange interaction,
exposing the need to consider other coupling mechanisms. The characteristic
length scale for magnetic textures in Sr2FeMoO6 is approximately 150 nm,
resulting from structural antiphase boundaries, thus raising the possibility
that magnetic dipole coupling underlies the observed long range spin transfer.
This discovery reveals a route to dynamic angular momentum transfer between a
FM and a NM in the absence of mediation by itinerant electrons and promises new
spin-functional devices employing long-range spin pumping.",1305.3016v2
2013-06-06,Ferromagnetism and infrared electrodynamics of Ga$_{1-x}$Mn$_{x}$As},"We report on the magnetic and the electronic properties of the prototype
dilute magnetic semiconductor Ga$_{1-x}$Mn$_x$As using infrared (IR)
spectroscopy. Trends in the ferromagnetic transition temperature $T_C$ with
respect to the IR spectral weight are examined using a sum-rule analysis of IR
conductivity spectra. We find non-monotonic behavior of trends in $T_C$ with
the spectral weight to effective Mn ratio, which suggest a strong
double-exchange component to the FM mechanism, and highlights the important
role of impurity states and localization at the Fermi level. Spectroscopic
features of the IR conductivity are tracked as they evolve with temperature,
doping, annealing, As-antisite compensation, and are found only to be
consistent with an Mn-induced IB scenario. Furthermore, our detailed
exploration of these spectral features demonstrates that seemingly conflicting
trends reported in the literature regarding a broad mid-IR resonance with
respect to carrier density in Ga$_{1-x}$Mn$_x$As are in fact not contradictory.
Our study thus provides a consistent experimental picture of the magnetic and
electronic properties of Ga$_{1-x}$Mn$_x$As.",1306.1566v1
2013-07-23,Study of the flux effect on nuclear pressure vessel steel by measurement of magnetic properties,"Since Reactor Pressure Vessel steels are ferromagnetic, they provide a
convenient means to monitor changes in the mechanical properties of the
material upon irradiation with high energy particles, by measuring their
magnetic properties. Here, we discuss the correlation between these two
properties (i.e. mechanical and magnetic properties) and microstructure, by
studying the flux effect on the nuclear pressure vessel steel used in reactors
currently under construction in Argentina. Charpy-V notched specimens of this
steel were irradiated in the RA1 experimental reactor at 275{\deg}C with two
lead factors (LFs), 93 and 183. The magnetic properties were studied by means
of DC magnetometry and ferromagnetic resonance. The results show that the
coercive field and magnetic anisotropy spatial distribution are sensitive to
the LF and can be explained by taking into account the evolution of the
microstructure with this parameter. The saturation magnetization shows a
dominant dependence on the accumulated damage. Consequently, the mentioned
techniques are suitable to estimate the degradation of the reactor vessel
steel.",1307.6124v2
2014-10-09,Photoemission and X-ray Absorption Studies of the Diluted Magnetic Semiconductor Ba$_{1-y}$K$_{y}$(Zn$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ Isostructural to Fe-based Superconductors,"The electronic and magnetic properties of a new diluted magnetic
semiconductor (DMS) Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$, which
is isostructural to so-called 122-type Fe-based superconductors, are
investigated by x-ray absorption spectroscopy (XAS) and resonance photoemission
spectroscopy (RPES). Mn $L_{2,3}$-edge XAS indicates that the doped Mn atoms
have the valence 2+ and strongly hybridize with the $4p$ orbitals of the
tetrahedrally coordinating As ligands. The Mn $3d$ partial density of states
(PDOS) obtained by RPES shows a peak around 4 eV and relatively high between
0-2 eV below the Fermi level ($E_{F}$) with little contribution at $E_{F}$,
similar to that of the archetypal DMS Ga$_{1-x}$Mn$_{x}$As. This energy level
creates $d^{5}$ electron configuration with $S=5/2$ local magnetic moments at
the Mn atoms. Hole carriers induced by K substitution for Ba atoms go into the
top of the As $4p$ valence band and are weakly bound to the Mn local spins. The
ferromagnetic correlation between the local spins mediated by the hole carriers
induces ferromagnetism in Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$",1410.2409v2
2014-12-24,Probing the magnetic phases in the Ni-V alloy close to the disordered ferromagnetic quantum critical point with muSR,"Zero (ZF) and longitudinal field (LF) muon spin relaxation data of the {\it
d}-metal alloy Ni$_{1-x}$V$_{x}$ are presented at several vanadium
concentrations $x$ below and above the critical $x_c \approx 11$% where
long-range ferromagnetic (FM) order is suppressed. The clear single precession
frequency observed for Ni, as expected for a homogeneous FM, changes to rather
damped oscillation with small V substitution at $x=4$%, confirming magnetic
inhomogeneities caused by the less magnetic V environments in the magnetic Ni
matrix. Furthermore, local fields and spatial field distributions can be
estimated to characterize different inhomogeneous regimes developing with $x$
in the FM phase of Ni$_{1-x}$V$_{x}$. In the regime of $x=7-10$% a Kubo Toyabe
function well describes the low temperature ZF and LF asymmetry data supporting
a static Gaussian field distribution. Closer to the quantum critical
concentration a single scale static Kubo Toyabe function with one field
distribution is not sufficient to describe the muon relaxation. These data
indicate that further changes in spatial distributions and dynamics are
evolving as expected within the critical regime of a disordered quantum
critical point.",1412.7671v1
2015-04-28,Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5-10 GHz frequency range,"We present a scanning transmission x-ray microscopy setup combined with a
novel microwave synchronization scheme in order to study high frequency
magnetization dynamics at synchrotron light sources. The sensitivity necessary
to detect small changes of the magnetization on short time scales and nanometer
spatial dimensions is achieved by combination of the developed excitation
mechanism with a single photon counting electronics that is locked to the
synchrotron operation frequency. The required mechanical stability is achieved
by a compact design of the microscope. Our instrument is capable of creating
direct images of dynamical phenomena in the 5-10 GHz range, with 35 nm
resolution. When used together with circularly polarized x-rays, the above
capabilities can be combined to study magnetic phenomena at microwave
frequencies, such as ferromagnetic resonance (FMR) and spin waves. We
demonstrate the capabilities of our technique by presenting phase resolved
images of a 6 GHz nanoscale spin wave generated by a spin torque oscillator, as
well as the uniform ferromagnetic precession with ~0.1 deg amplitude at 9 GHz
in a micrometer-sized cobalt strip.",1504.07561v1
2015-05-08,Electronic structures of ferromagnetic superconductors $\mathrm{UGe}_2$ and $\mathrm{UCoGe}$ studied by angle-resolved photoelectron spectroscopy,"The electronic structures of the ferromagnetic superconductors
$\mathrm{UGe}_2$ and $\mathrm{UCoGe}$ in the paramagnetic phase were studied by
angle-resolved photoelectron spectroscopy using soft X-rays ($h\nu =400-500$).
The quasi-particle bands with large contributions from $\mathrm{U}~5f$ states
were observed in the vicinity of $E_\mathrm{F}$, suggesting that the
$\mathrm{U}~5f$ electrons of these compounds have an itinerant character. Their
overall band structures were explained by the band-structure calculations
treating all the $\mathrm{U}~5f$ electrons as being itinerant. Meanwhile, the
states in the vicinity of $E_\mathrm{F}$ show considerable deviations from the
results of band-structure calculations, suggesting that the shapes of Fermi
surface of these compounds are qualitatively different from the calculations,
possibly caused by electron correlation effect in the complicated band
structures of the low-symmetry crystals. Strong hybridization between
$\mathrm{U}~5f$ and $\mathrm{Co}~3d$ states in $\mathrm{UCoGe}$ were found by
the $\mathrm{Co}~2p-3d$ resonant photoemission experiment, suggesting that
$\mathrm{Co}~3d$ states have finite contributions to the magnetic, transport,
and superconducting properties.",1505.01898v1
2015-10-09,Enhanced and Tunable Spin-Orbit Coupling in Tetragonally Strained Fe-Co-B Films,"We have synthesized 20 nm thick films of tetragonally strained interstitial
Fe-Co-B alloys epitaxially grown on Au55Cu45 buffer layer. The strained axis is
perpendicular to the film plane and the corresponding lattice constant c is
enlarged with respect to the in-plane lattice parameter a. By adding the
interstitial boron with different concentrations 0, 4, and 10 at.% we were able
to stabilize the tetragonal strain in 20 nm Fe-Co films with different c/a
ratios of 1.013, 1.034 and 1.02, respectively. Using ferromagnetic resonance
(FMR) and x-ray magnetic circular dichroism (XMCD) we found that the orbital
magnetic moment increases with increasing the c/a ratio, pointing towards the
enhancement of spin-orbit coupling (SOC) at larger strain. Our results show
that careful doping of ferromagnetic films allows to control the SOC by
stabilizing anisotropic strain states. These findings are applicable in
material design for spintronics applications. We also discuss the influence of
B doping on the Fe-Co film microstructure, its magnetic properties and magnetic
relaxation.",1510.02624v1
2015-11-11,Magnetization switching by current and microwaves,"We propose a theoretical model of magnetization switching in a ferromagnetic
multilayer by both electric current and microwaves. The electric current gives
a spin transfer torque on the magnetization, while the microwaves induce a
precession of the magnetization around the initial state. Based on numerical
simulation of the Landau-Lifshitz-Gilbert (LLG) equation, it is found that the
switching current is significantly reduced compared with the switching caused
solely by the spin transfer torque when the microwave frequency is in a certain
range. We develop a theory of switching from the LLG equation averaged over a
constant energy curve. It was found that the switching current should be
classified into four regions, depending on the values of the microwave
frequency. Based on the analysis, we derive an analytical formula of the
optimized frequency minimizing the switching current, which is smaller than the
ferromagnetic resonance frequency. We also derive an analytical formula of the
minimized switching current. Both the optimized frequency and the minimized
switching current decrease with increasing the amplitude of the microwave
field. The results will be useful to achieve high thermal stability and low
switching current in spin torque systems simultaneously.",1511.03366v2
2016-09-08,"Electronic Structures of Ferromagnetic CeAgSb$_2$:Soft X-ray Absorption, Magnetic Circular Dichroism and Angle-Resolved Photoemission Spectroscopies","We report a combined study for the electronic structures of ferromagnetic
CeAgSb$_2$ using soft X-ray absorption (XAS), magnetic circular dichroism
(XMCD), and angle-resolved photoemission (ARPES) spectroscopies. The Ce $M_{4,
5}$ XAS spectra show very small satellite structures, reflecting a strongly
localized character of the Ce $4f$ electrons. The linear dichroism effects in
the Ce $M_{4, 5}$ XAS spectra demonstrate the ground state Ce $4f$ symmetry of
$\Gamma{_6}$, the spatial distribution of which is directed along the $c$-axis.
The XMCD results give support to the picture of local-moment magnetism in
CeAgSb$_2$. Moreover it is also found that the theoretical band dispersions for
LaAgSb$_2$ provides better description of the ARPES band structures than those
for CeAgSb$_2$. Nevertheless, ARPES spectra at the Ce $3d$-$4f$ resonance show
the momentum dependence for the intensity ratio between Ce $4f^{1}_{5/2}$ and
$4f^{1}_{7/2}$ peaks in a part of the Brillouin zone, suggesting the
non-negligible momentum dependent hybridization effect between the Ce $4f$ and
the conduction electrons. This is associated with the moderate mass enhancement
in CeAgSb$_2$.",1609.02387v1
2018-01-31,"Cubic anisotropy in high homogeneity thin (Ga,Mn)As layers","Historically, comprehensive studies of dilute ferromagnetic semiconductors,
e.g., $p$-type (Cd,Mn)Te and (Ga,Mn)As, paved the way for a quantitative
theoretical description of effects associated with spin-orbit interactions in
solids, such as crystalline magnetic anisotropy. In particular, the theory was
successful in explaining {\em uniaxial} magnetic anisotropies associated with
biaxial strain and non-random formation of magnetic dimers in epitaxial
(Ga,Mn)As layers. However, the situation appears much less settled in the case
of the {\em cubic} term: the theory predicts switchings of the easy axis
between in-plane $\langle 100\rangle$ and $\langle 110\rangle$ directions as a
function of the hole concentration, whereas only the $\langle 100\rangle$
orientation has been found experimentally. Here, we report on the observation
of such switchings by magnetization and ferromagnetic resonance studies on a
series of high-crystalline quality (Ga,Mn)As films. We describe our findings by
the mean-field $p$-$d$ Zener model augmented with three new ingredients. The
first one is a scattering broadening of the hole density of states, which
reduces significantly the amplitude of the alternating carrier-induced
contribution. This opens the way for the two other ingredients, namely the
so-far disregarded single-ion magnetic anisotropy and disorder-driven
non-uniformities of the carrier density, both favoring the $\langle 100\rangle$
direction of the apparent easy axis. However, according to our results, when
the disorder gets reduced a switching to the $\langle 110\rangle$ orientation
is possible in a certain temperature and hole concentration range.",1802.00076v2
2018-11-09,Magnetic properties of the itinerant A-type antiferromagnet CaCo2P2 studied by 59Co and 31P NMR,"$^{59}$Co and $^{31}$P nuclear magnetic resonance (NMR) measurements in
external magnetic and zero magnetic fields have been performed to investigate
the magnetic properties of the A-type antiferromagnetic (AFM) CaCo$_2$P$_2$.
NMR data, especially, the nuclear spin lattice relaxation rates 1/$T_1$
exhibiting a clear peak, provide clear evidence for the AFM transition at a
N\'eel temperature of $T_{\rm N}\sim$110~K. The magnetic fluctuations in the
paramagnetic state were found to be three-dimensional ferromagnetic, suggesting
ferromagnetic interaction between Co spins in the ${\it ab}$ plane characterize
the spin correlations in the paramagnetic state. In the AFM state below $T_{\rm
N}$, we have observed $^{59}$Co and $^{31}$P NMR signals under zero magnetic
field. From $^{59}$Co NMR data, the ordered magnetic moments of Co are found to
be in $ab$ plane and are estimated to be 0.35 $\mu_{\rm B}$ at 4.2 K.
Furthermore, the external field dependence of $^{59}$Co NMR spectrum in the AFM
state suggests a very weak magnetic anisotropy of the Co ions and also provides
microscopic evidence of canting the Co ordered moments along the external
magnetic field directions. The magnetic state of the Co ions in CaCo$_2$P$_2$
is well explained by the local moment picture in the AFM state, although the
system is metallic as seen by $1/T_1T$ = constant behavior.",1811.03719v1
2019-05-15,Tuning the distance to a possible ferromagnetic quantum critical point in A2Cr3As3,"Although superconductivity in the vicinity of antiferromagnetic (AFM)
instability has been extensively explored in the last three decades or so,
superconductivity in compounds with a background of ferromagnetic (FM) spin
fluctuations is still rare. We report 75As nuclear quadrupole resonance
measurements on the A2Cr3As3 family, which is the first group of Cr-based
superconductors at ambient pressure, with A being alkali elements. From the
temperature dependence of the spin-lattice relaxation rate (1/T1), we find that
by changing A in the order of A=Na, Na0.75K0.25, K, and Rb, the system is tuned
to approach a FM quantum critical point (QCP). This may be ascribed to the
Cr2-As2-Cr2 bond angle that decreases towards 90 degrees, which enhances the FM
interaction via the Cr2-As2-Cr2 path. Upon moving away from the QCP, the
superconducting transition temperature Tsc increases progressively up to 8.0 K
in Na2Cr3As3, which is in sharp contrast to the AFM case where Tsc usually
shows a maximum around a QCP. The 1/T1 decreases rapidly below Tsc with no
Hebel-Slichter peak, and ubiquitously follows a T5 variation below a
characteristic temperature T*=0.6 Tsc, which indicates the existence of point
nodes in the superconducting gap function commonly in the family. These results
suggest that the A2Cr3As3 family is a possible solid-state analog of superfluid
3He.",1905.06055v2
2019-05-27,Influence of nonmagnetic dielectric spacers on the spin wave response of one-dimensional planar magnonic crystals,"The one-dimensional planar magnonic crystals are usually fabricated as a
sequence of stripes intentionally or accidentally separated by non-magnetic
spacers. The influence of spacers on shaping the spin wave spectra is complex
and still not completely clarified. We performed the detailed numerical studies
of the one-dimensional single- and bi-component magnonic crystals comprised of
a periodic array of thin ferromagnetic stripes separated by non-magnetic
spacers. We showed that the dynamic dipolar interactions between the stripes
mediated by non-magnetic spacer, even ultra-narrow, significantly shift up the
frequency of the ferromagnetic resonance and simultaneously reduce the spin
wave group velocity, which is manifested by the flattening of the magnonic
band. We attributed these changes in the spectra to the modifications of
dipolar pinning and shape anisotropy both dependent on the width of the spacers
and the thickness of the stripes, as well as to the dynamical magnetic volume
charges formed due to inhomogeneous spin wave amplitude.",1905.11016v4
2020-07-30,Temperature-dependent spin-transport and current-induced torques in superconductor/ferromagnet heterostructures,"We investigate the injection of quasiparticle spin currents into a
superconductor via spin pumping from an adjacent FM layer.$\;$To this end, we
use NbN/\ch{Ni80Fe20}(Py)-heterostructures with a Pt spin sink layer and excite
ferromagnetic resonance in the Py-layer by placing the samples onto a coplanar
waveguide (CPW). A phase sensitive detection of the microwave transmission
signal is used to quantitatively extract the inductive coupling strength
between sample and CPW, interpreted in terms of inverse current-induced
torques, in our heterostructures as a function of temperature. Below the
superconducting transition temperature $T_{\mathrm{c}}$, we observe a
suppression of the damping-like torque generated in the Pt layer by the inverse
spin Hall effect (iSHE), which can be understood by the changes in spin current
transport in the superconducting NbN-layer. Moreover, below $T_{\mathrm{c}}$ we
find a large field-like current-induced torque.",2007.15569v1
2013-08-30,Electron microscopy and diffraction study of high-temperature diamond-like Si-based ferromagnetic with self-organized super-lattice distribution of Mn impurity,"New structure data for the high-temperature diluted magnetic semiconductor
Si:Mn, synthesized by laser method are presented. The higher resolution
transmission electron microscopy and diffraction was applied in two crystal
directions of epitaxial layers of DMS Si:Mn with elimination of the
contribution from GaAs substrate and interface. It is established, that the DMS
Si:Mn can be represent as compound with variable composition Si2+xMn1-x (0 <x
<1), single-phase diamond like structure, high crystal perfection and the
self-organized formation of the super-lattice structures with the period equal
to triple the distance between the nearest (110) atomic layers and interval
between (110) layers which are doped by Mn atoms and orientated along the
direction of Si:Mn film growth. The Si with 15 percent of Mn (or Si2.5Mn0.5)
films consist of blocks with the 15-50 nm sizes and with mutually perpendicular
orientations of the super-lattice modulations. Atoms of manganese in the (110)
layers, doped by these impurity, settle down in the form of strips of an
one-atom thickness. These manganese strips in the given (110) layer alternate
occupy about half of area of the layer (110) in the full consent with the
spectral X-ray analysis and ferromagnetic resonance data.",1308.6664v1
2017-04-19,Exploring a proximity-coupled Co chain on Pb(110) as a possible Majorana platform,"Linear, suspended chains of magnetic atoms proximity coupled to an s-wave
superconductor are predicted to host Majorana zero modes at the chain ends in
the presence of strong spin-orbit coupling. Specifically, iron (Fe) chains on
Pb(110) have been explored as a possible system to exhibit topological
superconductivity and host Majorana zero-modes [Nadj-Perge, et al., Science
346, 602 (2014)]. Here, we study chains of the transition metal cobalt (Co) on
Pb(110) and check for topological signatures. Using spin-polarized scanning
tunneling spectroscopy, we resolve ferromagnetic order in the $d$ bands of the
chains. Interestingly, also the subgap Yu-Shiba-Rusinov (YSR) bands carry a
spin polarization as was predicted decades ago. Superconducting tips allow us
to resolve further details of the YSR bands and in particular resonances at
zero energy. We map the spatial distribution of the zero-energy signal and find
it delocalized along the chain. Hence, despite of the ferromagnetic coupling
within the chains and the strong-spin orbit coupling in the superconductor, we
do not find clear evidence of Majorana modes. Simple tight-binding calculations
suggest that the spin-orbit-split bands may cross the Fermi level four times
which suppresses the zero-energy modes.",1704.05756v1
2017-04-25,Unified Treatment of Spin Torques using a Coupled Magnetisation Dynamics and Three-Dimensional Spin Current Solver,"A three-dimensional spin current solver based on a generalised spin
drift-diffusion description, including the spin Hall effect, is integrated with
a magnetisation dynamics solver. The resulting model is shown to simultaneously
reproduce the spin-orbit torques generated using the spin Hall effect, spin
pumping torques generated by magnetisation dynamics in multilayers, as well as
the spin transfer torques acting on magnetisation regions with spatial
gradients, whilst field-like and spin-like torques are reproduced in a spin
valve geometry. Two approaches to modelling interfaces are analysed, one based
on the spin mixing conductance and the other based on continuity of spin
currents where the spin dephasing length governs the absorption of transverse
spin components. In both cases analytical formulas are derived for the
spin-orbit torques in a heavy metal / ferromagnet bilayer geometry, showing in
general both field-like and damping-like torques are generated. The limitations
of the analytical approach are discussed, showing that even in a simple bilayer
geometry, due to the non-uniformity of the spin currents, a full
three-dimensional treatment is required. Finally the model is applied to the
quantitative analysis of the spin Hall angle in Pt by reproducing published
experimental data on the ferromagnetic resonance linewidth in the bilayer
geometry.",1704.07758v2
2015-12-30,Magnetization dynamics and spin pumping induced by standing elastic waves,"The magnetization dynamics induced by standing elastic waves excited in a
thin ferromagnetic film is described with the aid of micromagnetic simulations
taking into account the magnetoelastic coupling between spins and lattice
strains. The simulations have been performed for the 2 nm thick Fe81Ga19 film
dynamically strained by longitudinal and transverse standing waves with various
frequencies, which span a wide range around the resonance frequency nu_res of
coherent magnetization precession in unstrained Fe81Ga19 film. It is found that
standing elastic waves give rise to complex local magnetization dynamics and
spatially inhomogeneous dynamic magnetic patterns. The spatio-temporal
distributions of the magnetization oscillations in standing elastic waves have
the form of standing spin waves with the same wavelength. Remarkably, the
amplitude of magnetization precession does not go to zero at the nodes of these
spin waves, which cannot be precisely described by simple analytical formulae.
In the steady-state regime, the magnetization oscillates with the frequency of
elastic wave, except for the case of longitudinal waves with frequencies well
below nu_res, where the magnetization precesses with a variable frequency
strongly exceeding the wave frequency. The precession amplitude at the
antinodes of standing spin waves strongly increases when the frequency of
elastic wave becomes close to nu_res. The results obtained for the
magnetization dynamics driven by elastic waves are used to calculate the spin
current pumped from the dynamically strained ferromagnet into adjacent
paramagnetic metal. Importantly, the transverse charge current created by the
spin current via the inverse spin Hall effect is high enough to be measured
experimentally.",1512.09051v1
2017-07-21,"Direct Evidence for the Source of Reported Magnetic Behavior in ""CoTe""","In order to unambiguously identify the source of magnetism reported in recent
studies of the Co-Te system, two sets of high-quality, epitaxial CoTe$_x$ films
(thickness $\simeq$ 300 nm) were prepared by pulse laser deposition (PLD).
X-ray diffraction (XRD) shows that all of the films are epitaxial along the
[001] direction and have the hexagonal NiAs structure. There is no indication
of any second phase metallic Co peaks (either $fcc$ or $hcp$) in the XRD
patterns. The two sets of CoTe$_x$ films were grown on various substrates with
PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the
measured lattice parameters $c = 5.396 \AA$ for the former and $c = 5.402\AA$
for the latter, the compositions CoTe$_{1.71}$ (63.1% Te) and CoTe$_{1.76}$
(63.8% Te), respectively, are assigned to the principal phase. Although XRD
shows no trace of metallic Co second phase, the magnetic measurements do show a
ferromagnetic contribution for both sets of films with the saturation
magnetization values for the CoTe$_{1.71}$ films being approximately four times
the values for the CoTe$_{1.76}$ films. $^{59}$Co spin-echo nuclear magnetic
resonance (NMR) clearly shows the existence of metallic Co inclusions in the
films. The source of weak ferromagnetism reported in several recent studies is
due to the presence of metallic Co, since the stoichiometric composition ""CoTe""
does not exist.",1707.06963v2
2019-10-29,Perpendicular magnetic anisotropy in Pt/Co-based full Heusler alloy/MgO thin films structures,"Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a
key ingredient for the development of electrically controlled spintronic
devices. Due to their relatively large spin-polarization, high Curie
temperature and low Gilbert damping the Co-based full Heusler alloys are of
special importance from a scientific and applications point of view. Here, we
study the mechanisms responsible for the PMA in Pt/Co-based full Heusler
alloy/MgO thin films structures. We show that the ultrathin Heusler films
exhibit strong PMA even in the absence of magnetic annealing. By means of
ferromagnetic resonance experiments, we demonstrate that the effective
magnetization shows a two-regime behavior depending on the thickness of the
Heusler layers. Using Auger spectroscopy measurements, we evidence
interdiffusion at the underlayer/Heusler interface and the formation of an
interfacial CoFe-rich layer which causes the two-regime behavior. In the case
of the ultrathin films, the interfacial CoFe-rich layer promotes the strong PMA
through the electronic hybridization of the metal alloy and oxygen orbitals
across the ferromagnet/MgO interface. In addition, the interfacial CoFe-rich
layer it is also generating an increase of the Gilbert damping for the
ultrathin films beyond the spin-pumping effect. Our results illustrate that the
strong PMA is not an intrinsic property of the Heusler/MgO interface but it is
actively influenced by the interdiffusion, which can be tuned by a proper
choice of the underlayer material, as we show for the case of the Pt, Ta and Cr
underlayers.",1910.13107v1
2019-10-29,Ferromagnetic Kitaev interaction and the origin of large magnetic anisotropy in $α$-RuCl$_3$,"$\alpha$-RuCl$_3$ is drawing much attention as a promising candidate Kitaev
quantum spin liquid. However, despite intensive research efforts, controversy
remains about the form of the basic interactions governing the physics of this
material. Even the sign of the Kitaev interaction (the bond-dependent
anisotropic interaction responsible for Kitaev physics) is still under debate,
with conflicting results from theoretical and experimental studies. The
significance of the symmetric off-diagonal exchange interaction (referred to as
the $\Gamma$ term) is another contentious question. Here, we present resonant
elastic x-ray scattering data that provides unambiguous experimental
constraints to the two leading terms in the magnetic interaction Hamiltonian.
We show that the Kitaev interaction ($K$) is ferromagnetic, and that the
$\Gamma$ term is antiferromagnetic and comparable in size to the Kitaev
interaction. Our findings also provide a natural explanation for the large
anisotropy of the magnetic susceptibility in $\alpha$-RuCl$_3$ as arising from
the large $\Gamma$ term. We therefore provide a crucial foundation for
understanding the interactions underpinning the exotic magnetic behaviours
observed in $\alpha$-RuCl$_3$.",1910.13390v1
2017-05-08,Insight into the temperature dependent properties of the ferromagnetic Kondo lattice YbNiSn,"Analyzing temperature dependent photoemission (PE) data of the ferromagnetic
Kondo-lattice (KL) system YbNiSn in the light of the Periodic Anderson model
(PAM) we show that the KL behavior is not limited to temperatures below a
temperature T_K, defined empirically from resistivity and specificic heat
measurements. As characteristic for weakly hybridized Ce and Yb systems, the PE
spectra reveal a 4f-derived Fermi level peak, which reflects contributions from
the Kondo resonance and its crystal electric field (CEF) satellites. In YbNiSn
this peak has an unusual temperature dependence: With decreasing temperature a
steady linear increase of intensity is observed which extends over a large
interval ranging from 100 K down to 1 K without showing any peculiarities in
the region of T_K ~ TC= 5.6 K. In the light of the single-impurity Anderson
model (SIAM) this intensity variation reflects a linear increase of 4f
occupancy with decreasing temperature, indicating an onset of Kondo screening
at temperatures above 100 K. Within the PAM this phenomenon could be described
by a non-Fermi liquid like T- linear damping of the self-energy which accounts
phenomenologically for the feedback from the closely spaced CEF-states.",1705.02763v1
2017-05-18,Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy,"Studies of magnetization dynamics have incessantly facilitated the discovery
of fundamentally novel physical phenomena, making steady headway in the
development of magnetic and spintronics devices. The dynamics can be induced
and detected electrically, offering new functionalities in advanced electronics
at the nanoscale. However, its scattering mechanism is still disputed.
Understanding the mechanism in thin films is especially important, because most
spintronics devices are made from stacks of multilayers with nanometer
thickness. The stacks are known to possess interfacial magnetic anisotropy, a
central property for applications, whose influence on the dynamics remains
unknown. Here, we investigate the impact of interfacial anisotropy by adopting
CoFeB/MgO as a model system. Through systematic and complementary measurements
of ferromagnetic resonance (FMR), on a series of thin films, we identify
narrower FMR linewidths at higher temperatures. We explicitly rule out the
temperature dependence of intrinsic damping as a possible cause, and it is also
not expected from existing extrinsic scattering mechanisms for ferromagnets. We
ascribe this observation to motional narrowing, an old concept so far neglected
in the analyses of FMR spectra. The effect is confirmed to originate from
interfacial anisotropy, impacting the practical technology of spin-based
nanodevices up to room temperature.",1705.06624v1
2017-09-03,Giant tunnel magnetoresistance with a single magnetic phase-transition electrode,"Magnetic phase transition tunnel magnetoresistance (MPT-TMR) effect with a
single magnetic electrode has been investigated by first-principles
calculations. The calculations show that the MPT-TMR of FeRh/MgO/Cu tunnel
junction can be as high as hundreds of percent when the magnetic structure of
FeRh changes from G-type antiferromagnetic (GAFM) to ferromagnetic order. This
new type of MPT-TMR may be superior to the tunnel anisotropic magnetoresistance
because of its huge magneto-resistance effect and similar structural
simplicity. The main mechanism for the giant MPT-TMR can be attributed to the
formation of interface resonant states at GAFM-FeRh/MgO interface. A direct
FeRh/MgO interface is found to be necessary for achieving high MPT-TMR
experimentally. Moreover, we find the FeRh/MgO interface with FeRh in
ferromagnetic phase has nearly full spin-polarization due to the negligible
majority transmission and significantly different Fermi surface of two spin
channels. Thus, it may act as a highly efficient and tunable spin-injector. In
addition, electric field driven MPT of FeRh-based hetero-magnetic
nanostructures can be utilized to design various energy efficient tunnel
junction structures and the corresponding lower power consumption devices. Our
results will stimulate further experimental investigations of MPT-TMR and other
fascinating phenomenon of FeRh-based tunnel junctions that may be promising in
antiferromagnetic spintronics.",1709.00687v2
2017-11-20,Spin Pumping in Ion-beam Sputtered Co_{2}FeAl/Mo Bilayers:Interfacial Gilbert Damping,"The spin pumping mechanism and associated interfacial Gilbert damping are
demonstrated in ion-beam sputtered Co2FeAl (CFA) /Mo bilayer thin films
employing ferromagnetic resonance spectroscopy. The dependence of the net spin
current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement
of the net effective Gilbert damping are reported. The experimental data has
been analyzed using spin pumping theory in terms of spin current pumped through
the ferromagnet /nonmagnetic metal interface to deduce the effective spin
mixing conductance and the spin-diffusion length, which are estimated to be
1.16(0.19)x10^19 m^-2 and 3.50(0.35)nm, respectively. The damping constant is
found to be 8.4(0.3)x10^-3 in the Mo(3.5nm) capped CFA(8nm) sample
corresponding to a ~42% enhancement of the original Gilbert damping
(6.0(0.3)x10^-3) in the uncapped CFA layer. This is further confirmed by
inserting a Cu dusting layer which reduces the spin transport across the CFA
/Mo interface. The Mo layer thickness dependent net spin current density is
found to lie in the range of 1-3 MAm^-2, which also provides additional
quantitative evidence of spin pumping in this bilayer thin film system.",1711.07455v1
2018-03-10,Band-offset-induced lateral shift of valley electrons in ferromagnetic MoS$_2$/WS$_2$ planar heterojunctions,"Low-energy coherent transport and Goos-H\""{a}nchen (GH) lateral shift of
valley electrons in planar heterojunctions composed of normal MoS$_2$ and
ferromagnetic WS$_2$ monolayers are theoretically investigated. Two types of
heterojunctions in the forms of WS$_2$/MoS$_2$/WS$_2$ (type-A) and
MoS$_2$/WS$_2$/MoS$_2$ (type-B) with incident electrons in MoS$_2$ region are
considered in which the lateral shift of electrons is induced by band
alignments of the two constituent semiconductors. It is shown that the type-A
heterojunction can act as an electron waveguide due to electron confinement
between the two WS$_2$/MoS$_2$ interfaces which cause the incident electrons
with an appropriate incidence angle to propagate along the interfaces. In this
case the spin- and valley-dependent GH shifts of totally reflected electrons
from the interface lead to separated electrons with distinct spin-valley
indexes after traveling a sufficiently long distance. In type-B heterojunction,
however, transmission resonances occur for incident electron beams passing
through the structure, and large spin- and valley-dependent lateral shift
values in propagating states can be achieved. Consequently, the transmitted
electrons are spatially well-separated into electrons with distinct spin-valley
indexes. Our findings reveal that the planar heterojunctions of transition
metal dichalcogenides can be utilized as spin-valley beam filter and/or
splitter without external gating.",1803.03811v1
2018-06-01,"Operation of a ferromagnetic axion haloscope at $m_a=58\,μ$eV","Axions, originally proposed to solve the strong CP problem of quantum
chromodynamics, emerge now as leading candidates of WISP dark matter. The rich
phenomenology associated to the light and stable QCD axion can be described as
an effective magnetic field that can be experimentally investigated. For the
QUAX experiment, dark matter axions are searched by means of their resonant
interactions with electronic spins in a magnetized sample. In principle,
axion-induced magnetization changes can be detected by embedding a sample in an
rf cavity in a static magnetic field. In this work we describe the operation of
a prototype ferromagnetic haloscope, with a sensitivity limited by thermal
fluctuations and receiver noise. With a preliminary dark matter search, we are
able to set an upper limit on the coupling constant of DFSZ axions to electrons
$g_{aee}<4.9\times10^{-10}$ at 95\% C.L. for a mass of $58\,\mu$eV (i.\,e.
14\,GHz). This is the first experimental result with an apparatus exploiting
the coupling between cosmological axions and electrons.",1806.00310v2
2018-12-13,Experimental Evidence of Non-Negligible Imaginary Part of Spin Mixing Conductance and Its Impact on Magnetization Dynamics in Heavy-Metal|Ferromagnet Bilayers,"The paper concerns experimental verification of the magnitude of imaginary
part of spin mixing conductance in bilayers comprising heavy metals. We present
results of broadband ferromagnetic resonance studies on heterostructures
consisting of Finemet thin films covered by Pt and Ta wedge layers with the aim
to observe spin pumping effects and to evaluate both the real and imaginary
parts of the spin mixing conductance. The experimental results are analyzed in
the framework of a recent microscopic theory which allows us to estimate the
value of the interfacial spin-orbit interaction and confirm its important role.
In particular, we show that the imaginary part of spin mixing conductance
cannot be regarded as negligible and we discuss its influence on magnetization
dynamics. For Finemet|Ta bilayers, the ratio
$\mathrm{Re}[g_{eff}^{\uparrow\downarrow}]/\mathrm{Im}[g_{eff}^{\uparrow\downarrow}]=$
0.38, that is, the field-like torque dominates over the damping-like torque in
such system. Consequently, relatively small enhancement of precession damping
with respect to significant total torque exerted on the magnetization in
Finemet|Ta system offers an attractive perspective for an application in the
next-generation magnetic random-access memory cells.",1812.05235v2
2018-12-21,Active Control of Mode Crossover and Mode Hopping of Spin Waves in a Ferromagnetic Antidot Lattice,"Active control of spin-wave dynamics is demonstrated using broadband
ferromagnetic resonance in two-dimensional Ni80Fe20 antidot lattices arranged
in hexagonal lattice with fixed lattice constant but varying antidot diameter.
A strong modification in the spin-wave spectra is obtained with the variation
in the antidot diameter as well as with the strength and orientation of the
bias magnetic field. A broad band of modes is observed for the lattice with
higher antidot diameter which decreases systematically as the antidot diameter
is reduced. A crossover between the higher frequency branches is achieved in
lattices with higher antidot diameter. In addition, the spin-wave modes in all
lattices show a strong six-fold anisotropic behaviour due to the variation of
internal field distribution as a function of the bias-field orientation. A mode
hopping-like behavior is observed in the angular dispersions of spin-wave
spectra for samples having intermediate hole diameters. Micromagnetic
simulations qualitatively reproduce the experimentally observed spin-wave modes
and the simulated mode profiles reveal the presence of extended and quantized
standing spin-wave modes in these lattices. These observations are significant
for large tunability and anisotropic propagation of spin waves in GHz frequency
magnetic devices.",1812.08929v1
2019-03-11,Giant spin-orbit torque in a single ferrimagnetic metal layer,"Antiferromagnets and compensated ferrimagnets offer opportunities to
investigate spin dynamics in the 'terahertz gap' because their resonance modes
lie in the 0.3 THz to 3 THz range. Despite some inherent advantages when
compared to ferromagnets, these materials have not been extensively studied due
to difficulties in exciting and detecting the high-frequency spin dynamics,
especially in thin films. Here we show that spin-obit torque in a single layer
of the highly spin-polarized compensated ferrimagnet Mn2RuxGa is remarkably
efficient at generating spin-orbit fields \mu_0H_eff, which approach 0.1x10-10
T m2/A in the low-current density limit -- almost a thousand times the Oersted
field, and one to two orders of magnitude greater than the effective fields in
heavy metal/ferromagnet bilayers. From an analysis of the harmonic Hall effect
which takes account of the thermal contributions from the anomalous Nernst
effect, we show that the antidamping component of the spin-orbit torque is
sufficient to sustain self-oscillation. Our study demonstrates that spin
electronics has the potential to underpin energy-frugal, chip-based solutions
to the problem of ultra high-speed information transfer.",1903.04432v3
2019-03-22,Order and Disorder in the Magnetisation of the Chiral Crystal CrNb$_3$S$_6$,"Competing magnetic anisotropies in chiral crystals with Dzyaloshinskii Moriya
exchange interactions can give rise to non-trivial chiral topological
magnetisation configurations with new and interesting properties. One such
configuration is the magnetic soliton, where the moment continuously rotates
about an axis. This magnetic system can be considered to be one dimensional
and, because of this, it supports a macroscale coherent magnetisation, giving
rise to a tunable chiral soliton lattice (CSL) that is of potential use in a
number of applications in nanomagnetism and spintronics. In this work we
characterise the transitions between the forced-ferromagnetic (F-FM) phase and
the CSL one in CrNb$_3$S$_6$ using differential phase contrast imaging in a
scanning transmission electron microscope, conventional Fresnel imaging,
ferromagnetic resonance spectroscopy, and mean-field modelling. We find that
the formation and movement of dislocations mediate the formation of CSL and
F-FM regions and that these strongly influence the highly hysteretic static and
dynamic properties of the system. Sample size and morphology can be used to
tailor the properties of the system and, with the application of magnetic
field, to locate and stabalise normally unstable dislocations and modify their
dimensions and magnetic configurations in ways beyond that predicted to occur
in uniform films.",1903.09519v1
2019-03-26,Engineering of spin mixing conductance in Ru/FeCo/Ru interfaces: Effect of Re Doping,"We have deposited polycrystalline Re doped $(Fe_{65}Co_{35})_{100-x}Re_{x}$
(0 $\leq$ x $\leq$ 12.6 at\%) thin films grown under identical conditions and
sandwiched between thin layers of Ru in order to study the phenomenon of spin
pumping as a function of Re concentration. In-plane and out-of-plane
ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert
damping with an increase in Re doping. We found evidence of an increase in the
real part of effective spin mixing conductance
[Re($g^{\uparrow\downarrow}_{eff}$)] with the increase in Re doping of 6.6
at\%, while a decrease is evident at higher Re doping. The increase in
Re($g^{\uparrow\downarrow}_{eff}$) can be linked to the Re doping induced
change of the interface electronic structure in the non-magnetic Ru layer and
the effect interfacial spin-orbit coupling has on the effective spin-mixing
conductance. The lowest and highest values of
Re($g^{\uparrow\downarrow}_{eff}$) are found to be 9.883(02) $nm^{-2}$ and
19.697(02) $nm^{-2}$ for 0 at\% and 6.6 at\% Re doping, respectively. The
saturation magnetization decreases with increasing Re doping, from 2.362(13) T
for the undoped film to 1.740(03) T for 12.6 at\% Re doping. This study opens a
new direction of tuning the spin-mixing conductance in magnetic
heterostructures by doping of the ferromagnetic layerr, which is essential for
the realization of energy efficient operation of spintronic devices.",1903.10966v2
2019-04-02,Spin pumping and spin torque in interfacial tailored Co2FeAl/\b{eta}-Ta layers,"The Heusler ferromagnetic (FM) compound Co2FeAl interfaced with a high-spin
orbit coupling non-magnetic (NM) layer is a promising candidate for energy
efficient spin logic circuits. The circuit potential depends on the strength of
angular momentum transfer across the FM/NM interface; hence, requiring low spin
memory loss and high spin-mixing conductance. To highlight this issue, spin
pumping and spin-transfer torque ferromagnetic resonance measurements have been
performed on Co_2FeAl/\beta-Ta heterostructures tailored with Cu interfacial
layers. The interface tailored structure yields an enhancement of the effective
spin-mixing conductance. The interface transparency and spin memory loss
corrected values of the spin-mixing conductance, spin Hall angle and spin
diffusion length are found to be 3.40 \pm 0.01 \times 10^{19} m^{-2}, 0.029 \pm
0.003, and 2.3 \pm 0.5 nm, respectively. Furthermore, a high current modulation
of the effective damping of around 2.1 % has been achieved at an applied
current density of 1 \times 10^9 A/m^2 , which clearly indicates the potential
of using this heterostructure for energy efficient control in spin devices",1904.01506v3
2019-12-11,Coherent transfer of spin angular momentum by evanescent spin waves within antiferromagnetic NiO,"Insulating antiferromagnets are efficient and robust conductors of spin
current. To realise the full potential of these materials within spintronics,
the outstanding challenges are to demonstrate scalability down to nanometric
lengthscales and the transmission of coherent spin currents. Here, we report
the coherent transfer of spin angular momentum by excitation of evanescent spin
waves of GHz frequency within antiferromagnetic NiO at room temperature. Using
element-specific and phase-resolved x-ray ferromagnetic resonance, we probe the
injection and transmission of ac spin current, and demonstrate that insertion
of a few nanometre thick epitaxial NiO(001) layer between a ferromagnet and
non-magnet can even enhance the flow of spin current. Our results pave the way
towards coherent control of the phase and amplitude of spin currents at the
nanoscale, and enable the realization of spin-logic devices and spin current
amplifiers that operate at GHz and THz frequencies.",1912.05621v1
2019-12-10,F+ Center Exchange Mechanism and Magneto Crystalline Anisotropy in Ni doped 3C-SiC,"We report the experimental evidence in support of room temperature
ferromagnetism in Ni doped 3C-SiC. Curie temperature is found to be > 350 K.
Temperature dependent Electron paramagnetic resonance (EPR) study reveals that
the valence state of Ni is 2+ and its environmental symmetry. A clear shift in
both XRD and Raman peak confirms the incorporation of Ni in the host lattice.
The variation in number of vacancies $V_{\mathrm{Si}}$, $V_{\mathrm{C}}$ and
the number of free electron due to doping is consistent with the change in
magnetization of the system. A direct correlation of ferromagnetic order (FM)
with F+ centers exchange mechanism is established. The temperature variation of
the anisotropic constant was determined using Law of Approach to Saturation
(LAS). It was found that effective magnetic anisotropic constant decreases with
increase in temperature. The EPR line width of the annealed sample increases
with decrease in temperature, whereas the integrated intensity decreases with
decrease in temperature. This could be due to incomplete quenching of orbital
angular momentum in Si$_{x}$Ni$_{1-x}$C. In addition to this, the orbital
degeneracy of fast relaxing impurity such as Ni in the cubic crystal field is
not completely removed. This results in the line width decrease with increase
in temperature.",1912.05921v2
2019-12-16,Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures,"Spin currents offer a way to control static and dynamic magnetic properties,
and therefore they are crucial for next-generation MRAM devices or spin-torque
oscillators. Manipulating the dynamics is especially interesting within the
context of photo-magnonics. In typical $3d$ transition metal ferromagnets like
CoFeB, the lifetime of light-induced magnetization dynamics is restricted to
about 1 ns, which e.g. strongly limits the opportunities to exploit the wave
nature in a magnonic crystal filtering device. Here, we investigate the
potential of spin-currents to increase the spin wave lifetime in a functional
bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum
(Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer
generates a transverse spin current when a lateral charge current passes
through the strip. Using time-resolved all-optical pump-probe spectroscopy, we
investigate how this spin current affects the magnetization dynamics in the
adjacent CoFeB layer. We observed a linear spin current manipulation of the
effective Gilbert damping parameter for the Kittel mode from which we were able
to determine the system's spin Hall angles. Furthermore, we measured a strong
influence of the spin current on a high-frequency mode. We interpret this mode
an an exchange dominated higher order spin-wave resonance. Thus we infer a
strong dependence of the exchange constant on the spin current.",1912.07728v1
2019-12-20,Picosecond spin-orbit torque switching of ferrimagnets,"Spintronics provides an efficient platform for realizing non-volatile memory
and logic devices. In these systems, data is stored in the magnetization of
magnetic materials, and magnetization is switched in the writing process. In
conventional spintronic devices, ferromagnetic materials are used which have a
magnetization dynamics timescale of around the nanoseconds, setting a limit for
the switching speed. Increasing the magnetization switching speed has been one
of the challenges in spintronic research. In this work we take advantage of the
ultrafast magnetization dynamics in ferrimagnetic materials instead of
ferromagnets, and we use femtosecond laser pulses and a photoconductive Auston
switch to create picosecond current pulses for switching the ferrimagnet. By
anomalous Hall and magneto-optic Kerr (MOKE) measurement, we demonstrate the
robust picosecond SOT driven magnetization switching of ferrimagnetic GdFeCo.
The time-resolved MOKE shows more than 50 GHz magnetic resonance frequency of
GdFeCo, indicating faster than 20 ps spin dynamics and tens of picosecond SOT
switching speed. Our work provides a promising route to realize picosecond
operation speed for non-volatile magnetic memory and logic applications.",1912.10129v1
2020-08-17,Enhancement of spin Hall conductivity in W-Ta alloy,"Generating pure spin currents via the spin Hall effect in heavy metals has
been an active topic of research in the last decade. In order to reduce the
energy required to efficiently switch neighbouring ferromagnetic layers for
applications, one should not only increase the charge- to-spin conversion
efficiency but also decrease the longitudinal resistivity of the heavy metal.
In this work, we investigate the spin Hall conductivity in W_{1-x}Ta_{x} /
CoFeB / MgO (x = 0 - 0.2) using spin torque ferromagnetic resonance
measurements. Alloying W with Ta leads to a factor of two change in both the
damping-like effective spin Hall angle (from - 0.15 to - 0.3) and longitudinal
resistivity (60 - 120 {\mu}W cm). At 11% Ta concentration, a remarkably high
spin Hall angle value of - 0.3 is achieved with a low longitudinal resistivity
100 {\mu}W cm, which could lead to a very low power consumption for this
W-based alloy. This work demonstrates sputter-deposited W-Ta alloys could be a
promising material for power-efficient spin current generation.",2008.07572v1
2020-08-18,"Evolution of the Fe-3$d$ impurity band state as the origin of high Curie temperature in p-type ferromagnetic semiconductor (Ga,Fe)Sb","(Ga$_{1-x}$,Fe$_x$)Sb is one of the promising ferromagnetic semiconductors
for spintronic device applications because its Curie temperature ($T_{\rm C}$)
is above 300 K when the Fe concentration $x$ is equal to or higher than ~0.20.
However, the origin of the high $T_{\rm C}$ in (Ga,Fe)Sb remains to be
elucidated. To address this issue, we use resonant photoemission spectroscopy
(RPES) and first-principles calculations to investigate the $x$ dependence of
the Fe 3$d$ states in (Ga$_{1-x}$,Fe$_x$)Sb ($x$ = 0.05, 0.15, and 0.25) thin
films. The observed Fe 2$p$-3$d$ RPES spectra reveal that the Fe-3$d$ impurity
band (IB) crossing the Fermi level becomes broader with increasing $x$, which
is qualitatively consistent with the picture of double-exchange interaction.
Comparison between the obtained Fe-3$d$ partial density of states and the
first-principles calculations suggests that the Fe-3$d$ IB originates from the
minority-spin ($\downarrow$) $e$ states. The results indicate that enhancement
of the interaction between $e_\downarrow$ electrons with increasing $x$ is the
origin of the high $T_{\rm C}$ in (Ga,Fe)Sb.",2008.07744v1
2020-09-17,Control of spin-orbit torques by interface engineering in topological insulator heterostructures,"(Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ topological insulators (TIs) are gathering
increasing attention owing to their large charge-to-spin conversion efficiency
and the ensuing spin-orbit torques (SOTs) that can be used to manipulate the
magnetization of a ferromagnet (FM). The origin of the torques, however,
remains elusive, while the implications of hybridized states and the strong
material intermixing at the TI/FM interface are essentially unexplored. By
combining interface chemical analysis and spin-transfer ferromagnetic resonance
(ST-FMR) measurements, we demonstrate that intermixing plays a critical role in
the generation of SOTs. By inserting a suitable normal metal spacer, material
intermixing is reduced and the TI properties at the interface are largely
improved, resulting in strong variations in the nature of the SOTs. A dramatic
enhancement of a field-like torque, opposing and surpassing the Oersted-field
torque, is observed, which can be attributed to the non-equilibrium spin
density in Rashba-split surface bands and to the suppression of spin memory
loss.",2009.08215v1
2020-10-07,High-throughput techniques for measuring the spin Hall effect,"The spin Hall effect in heavy-metal thin films is routinely employed to
convert charge currents into transverse spin currents and can be used to exert
torque on adjacent ferromagnets. Conversely, the inverse spin Hall effect is
frequently used to detect spin currents by charge currents in spintronic
devices up to the terahertz frequency range. Numerous techniques to measure the
spin Hall effect or its inverse were introduced, most of which require
extensive sample preparation by multi-step lithography. To enable rapid
screening of materials in terms of charge-to-spin conversion, suitable
high-throughput methods for measuring the spin Hall angle are required. Here,
we compare two lithography-free techniques, terahertz emission spectroscopy and
broadband ferromagnetic resonance, to standard harmonic Hall measurements and
theoretical predictions using the binary-alloy series Au$_x$Pt$_{1-x}$ as
benchmark system. Despite being highly complementary, we find that all three
techniques yield a spin Hall angle with approximately the same $x$~dependence,
which is also consistent with first-principles calculations. Quantitative
discrepancies are discussed in terms of magnetization orientation and
interfacial spin-memory loss.",2010.03543v1
2021-02-26,Gapless Spin Wave Transport through a Quantum Canted-Antiferromagnet,"In the Landau levels of a two-dimensional electron system or when flat bands
are present, e.g. in twisted van der Waals bilayers, strong electron-electron
interaction gives rise to quantum Hall ferromagnetism with spontaneously broken
symmetries in the spin and isospin sectors. Quantum Hall ferromagnets support a
rich variety of low-energy collective excitations that are instrumental to
understand the nature of the magnetic ground states and are also potentially
useful as carriers of quantum information. Probing such collective excitations,
especially their dispersion {\omega}(k), has been experimentally challenging
due to small sample size and measurement constraints. In this work, we
demonstrate an all-electrical approach that integrates a Fabry-P\'erot cavity
with non-equilibrium transport to achieve the excitation, wave vector selection
and detection of spin waves in graphene heterostructures. Our experiments
reveal gapless, linearly dispersed spin wave excitations in the E = 0 Landau
level of bilayer graphene, thus providing direct experimental evidence for a
predicted canted antiferromagnetic order. We show that the gapless spin wave
mode propagates with a high group velocity of several tens of km/s and
maintains phase coherence over a distance of many micrometers. Its dependence
on the magnetic field and temperature agree well with the hydrodynamic theory
of spin waves. These results lay the foundation for the quest of spin
superfluidity in this high-quality material. The resonant cavity technique we
developed offers a powerful and timely method to explore the collective
excitation of many spin and isospin-ordered many-body ground states in van der
Waals heterostructures and open the possibility of engineering magnonic
devices.",2103.00018v1
2021-06-12,Spin pumping and inverse spin Hall effect in CoFeB/C$_{60}$ bilayers,"Pure spin current based research is mostly focused on ferromagnet (FM)/heavy
metal (HM) system. Because of the high spin orbit coupling (SOC) these HMs
exhibit short spin diffusion length and therefore possess challenges for device
application. Low SOC (elements of light weight) and large spin diffusion length
make the organic semiconductors (OSCs) suitable for future spintronic
applications. From theoretical model it is explained that, due to $\pi$ -
$\sigma$ hybridization the curvature of the C$_{60}$ molecules may increase the
SOC strength. Here, we have investigated spin pumping and inverse spin hall
effect (ISHE) in CoFeB/C$_{60}$ bilayer system using coplanar wave guide based
ferromagnetic resonance (CPW-FMR) set-up. We have performed angle dependent
ISHE measurement to disentangle the spin rectification effects for example
anisotropic magnetoresistance, anomalous Hall effect etc. Further, effective
spin mixing conductance (g$_{eff}^{\uparrow\downarrow}$) and spin Hall angle
($\theta_{SH}$) for C$_{60}$ have been reported here. The evaluated value for
$\theta_{SH}$ is 0.055.",2106.06829v2
2021-07-07,A hole-Cr$^{+}$ nano-magnet in a semiconductor quantum dot,"We study a new diluted magnetic semiconductor system based on the spin of the
ionized acceptor Cr$^+$. We show that the negatively charged Cr$^+$ ion, an
excited state of the Cr in II-VI semiconductor, can be stable when inserted in
a CdTe quantum dot (QD). The Cr$^+$ attracts a heavy-hole in the QD and form a
stable hole-Cr$^+$ complex. Optical probing of this system reveals a
ferromagnetic coupling between heavy-holes and Cr$^+$ spins. At low
temperature, the thermalization on the ground state of the hole-Cr$^+$ system
with parallel spins prevents the optical recombination of the excess electron
on the 3$d$ shell of the atom. We study the dynamics of the nano-magnet formed
by the hole-Cr$^+$ exchange interaction. The ferromagnetic ground states with
M$_z$=$\pm$4 can be controlled by resonant optical pumping and a spin
relaxation time in the 20 $\mu$s range is obtained at T=4.2 K. This spin memory
at zero magnetic field is limited by the interaction with phonons.",2107.03192v2
2021-09-13,Effect of seed layer thickness on Ta crystalline phase and spin Hall angle,"Heavy metal-ferromagnet bilayer structures have attracted great research
interest for charge-to-spin interconversion. In this work, we have investigated
the effect of the permalloy seed layer on the Ta polycrystalline phase and its
spin Hall angle. Interestingly, for the same deposition rates the crystalline
phase of Ta deposited on Py seed layer strongly depends on the thickness of the
seed layer. We have observed a phase transition from $\alpha$-Ta to
($\alpha$+$\beta$)-Ta while increasing the Py seed layer thickness. The
observed phase transition is attributed to the strain at interface between Py
and Ta layers. Ferromagnetic resonance-based spin pumping studies reveal that
the spin-mixing conductance in the to ($\alpha$+$\beta$)-Ta is relatively
higher as compared to the to $\alpha$-Ta. Spin Hall angles of to $\alpha$-Ta
and to ($\alpha$+$\beta$)-Ta are extracted from inverse spin Hall effect (ISHE)
measurements. Spin Hall angle of the to ($\alpha$+$\beta$)-Ta is estimated to
be $\theta$_SH=-0.15 which is relatively higher than that of to $\alpha$-Ta.
Our systematic results connecting the phase of the Ta with seed layer and its
effect on the efficiency of spin to charge conversion might resolve ambiguities
across various literature and open up new functionalities based on the growth
process for the emerging spintronic devices.",2109.06113v2
2021-10-11,Boosting room temperature tunnel magnetoresistance in hybrid magnetic tunnel junctions under electric bias,"Spin-resolved electron symmetry filtering is a key mechanism behind giant
tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel
junctions (MTJs), providing room temperature functionality in modern spin
electronics. However, the core process of the electron symmetry filtering
breaks down under applied bias, dramatically reducing the TMR above 0.5 V. This
strongly hampers the application range of MTJs. To circumvent the problem,
resonant tunneling between ferromagnetic electrodes through quantum well states
in thin layers has been used so far. This mechanism, however, is mainly
effective at low temperatures. Here, a fundamentally different approach is
demonstrated, providing a strong TMR boost under applied bias in
V/MgO/Fe/MgO/Fe/Co hybrids. This pathway uses spin orbit coupling (SOC)
controlled interfacial states in vanadium, which contrary to the V(001) bulk
states are allowed to tunnel to Fe(001) at low biases. The experimentally
observed strong increase of TMR with bias is modelled using two nonlinear
resistances in series, with the low bias conductance of the first (V/MgO/Fe)
element being boosted by the SOC-controlled interfacial states, while the
conductance of the second (Fe/MgO/Fe) junctions controlled by the relative
alignment of the two ferromagnetic layers. These results pave a way to
unexplored and fundamentally different spintronic device schemes, with
tunneling magnetoresistance uplifted under applied electric bias.",2110.05061v1
2021-10-20,"Manifestations of Spinodal Decomposition into Dilute Pd$_{1-x}$Fe$_{x}$ ""Phases"" in Iron-Implanted Palladium Films: FMR Study","Palladium-iron alloys produced by high-dose implantation of iron ions into
epitaxial palladium films were investigated with the ferromagnetic resonance
(FMR) and vibrating sample magnetometry (VSM) techniques. The samples reveal
distinct multiple FMR responses depending on the dose of iron ion implantation.
The post-implantation annealing at 770 K does not bring the implanted films to
a homogeneous solid solution state, as might be expected from the Pd-Fe phase
diagram. On the contrary, the system approaches a stable state composed of
several magnetic phases. FMR spectra exhibit an angular behavior specific for a
stack of interacting magnetic layers. This observation, correlated with the
magnetometry data, indicates that the palladium-iron binary alloy has a
previously unknown tendency towards spinodal decomposition into isostructural
phases with well-defined iron concentrations and, accordingly, with different
temperatures of ferromagnetic ordering and saturation magnetizations.",2110.10397v1
2021-12-23,Stress-tailoring magnetic anisotropy of V$_2$O$_3$/Ni bilayers,"We report on a temperature-driven reversible change of the in-plane magnetic
anisotropy of V$_2$O$_3$/Ni bilayers. This is caused by the rhombohedral to
monoclinic structural phase transition of V$_2$O$_3$ at $T_C$ = 160 K. The
in-plane magnetic anisotropy is uniaxial above $T_C$, but as the bilayer is
cooled through the structural phase transition, a secondary magnetic easy axis
emerges. Ferromagnetic resonance measurements show that this change in magnetic
anisotropy is reversible with temperature. We identify two structural
properties of the V$_2$O$_3$/Ni bilayers affecting the in-plane magnetic
anisotropy: (1) a growth-induced uniaxial magnetic anisotropy associated with
step-like terraces in the bilayer microstructure and (2) a low-temperature
strain-induced biaxial anisotropy associated with the V$_2$O$_3$ structural
phase transition. Magnetoresistance measurements corroborate the change in
magnetic anisotropy across the structural transition and suggest that the
negative magnetostriction of Ni leads to the emergence of a strain-induced
easy-axis. This shows that a temperature-dependent structural transition in
V$_2$O$_3$ may be used to tune the magnetic anisotropy in an adjacent
ferromagnetic thin film.",2112.12826v1
2022-01-12,Light and microwave driven spin pumping across FeGaB-BiSb interface,"3-D topological insulators (TI) with large spin Hall conductivity have
emerged as potential candidates for spintronic applications. Here, we report
spin to charge conversion in bilayers of amorphous ferromagnet (FM)
Fe_{78}Ga_{13}B_{9} (FeGaB) and 3-D TI Bi_{85}Sb_{15} (BiSb) activated by two
complementary techniques: spin pumping and ultrafast spin-current injection. DC
magnetization measurements establish the soft magnetic character of FeGaB
films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband
ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing
magnetization and large value of spin mixing conductance (5.03 x 10^{19}
m^{-2}) as the spin angular momentum leaks into the TI layer. Magnetic field
controlled bipolar dc voltage generated across the TI layer by inverse spin
Hall effect is analyzed to extract the values of spin Hall angle and spin
diffusion length of BiSb. The spin pumping parameters derived from the
measurements of the femtosecond light-pulse-induced terahertz emission are
consistent with the result of FMR. Kubo-Bastin formula and tight-binding model
calculations shed light on the thickness-dependent spin-Hall conductivity of
the TI films, with predictions that are in remarkable agreement with the
experimental data. Our results suggest that room temperature deposited
amorphous and polycrystalline heterostructures provide a promising platform for
creating novel spin orbit torque devices.",2201.04686v1
2022-01-18,Laser-induced charge and spin photocurrents at BiAg$_2$ surface: a first principles benchmark,"Here, we report first principles calculations and analysis of laser-induced
photocurrents at the surface of a prototype Rashba system. By referring to
Keldysh non-equilibrium formalism combined with the Wannier interpolation
scheme we perform first-principles electronic structure calculations of a
prototype BiAg$_2$ surface alloy, which is a well-known material realization of
the Rashba model. In addition to non-magnetic ground state situation we also
study the case of in-plane magnetized BiAg$_2$. We calculate the laser-induced
charge photocurrents for the ferromagnetic case and the laser-induced spin
photocurrents for both the non-magnetic and the ferromagnetic cases. Our
results confirm the emergence of very large in-plane photocurrents as predicted
by the Rashba model. The resulting photocurrents satisfy all the symmetry
restrictions with respect to the light helicity and the magnetization
direction. We provide microscopic insights into the symmetry and magnitude of
the computed currents based on the ab-initio multi-band electronic structure of
the system, and scrutinize the importance of resonant two-band and three-band
transitions for driven currents, thereby establishing a benchmark picture of
photocurrents at Rashba-like surfaces and interfaces. Our work contributes to
the study of the role of the interfacial Rashba spin-orbit interaction as a
mechanism for the generation of in-plane photocurrents, which are of great
interest in the field of ultrafast and terahertz spintronics.",2201.07122v1
2022-02-03,Controlling spin pumping into superconducting Nb by proximity-induced spin-triplet Cooper pairs,"Proximity-induced long-range spin-triplet supercurrents, important for the
field of superconducting spintronics, are generated in
superconducting/ferromagnetic heterostructures when interfacial magnetic
inhomogeneities responsible for spin mixing and spin flip scattering are
present. The multilayer stack Nb/Cr/Fe/Cr/Nb has been shown to support such
exotic currents when fabricated into Josephson junction devices. However,
creating pure spin currents controllably in superconductors outside of the
Josephson junction architecture is a bottleneck to progress. Recently,
ferromagnetic resonance was proposed as a possible direction, the signature of
pure supercurrent creation being an enhancement of the Gilbert damping below
the superconducting critical temperature, but the necessary conditions are
still poorly established. Consistent with theoretical prediction, we
demonstrate conclusively that pumping pure spin currents into a superconductor
is only possible when conditions supporting proximity-induced spin-triplet
effects are satisfied. Our study is an important step forward for
superconducting pure spin current creation and manipulation, considerably
advancing the field of superconducting spintronics.",2202.01520v1
2022-05-13,Large-Area Intercalated 2D-Pb/Graphene Heterostructure as a Platform for Generating Spin-Orbit Torque,"A scalable platform to synthesize ultrathin heavy metals may enable high
efficiency charge-to-spin conversion for next-generation spintronics. Here we
report centimeter-scale synthesis of air-stable, epitaxially registered
monolayer Pb underneath bilayer graphene on SiC (0001) by confinement
heteroepitaxy (CHet). Diffraction, spectroscopy, and microscopy reveal
CHet-based Pb intercalation predominantly exhibits a mottled hexagonal
superstructure due to an ordered network of Frenkel-Kontorova-like domain
walls. The system's air stability enables ex-situ spin torque ferromagnetic
resonance (ST-FMR) measurements that demonstrate charge-to-spin conversion in
graphene/Pb/ferromagnet heterostructures with a 1.5x increase in the effective
field ratio compared to control samples.",2205.06859v3
2022-06-23,Bridging quantum many-body scar and quantum integrability in Ising chains with transverse and longitudinal fields,"Quantum many-body scar (QMBS) and quantum integrability(QI) have been
recognized as two distinct mechanisms for the breakdown of eigenstate
thermalization hypothesis(ETH) in an isolated system. In this work, we reveal a
smooth route to connect these two ETH-breaking mechanisms in the Ising chain
with transverse and longitudinal fields. Specifically, starting from an initial
Ising anti-ferromagnetic state, we find that the dynamical system undergoes a
smooth non-thermal crossover from QMBS to QI by changing the Ising
coupling($J$) and longitudinal field($h$) simultaneously while keeping their
ratio fixed, which corresponds to the Rydberg Hamiltonian with an arbitrary
nearest-neighbor repulsion. Deviating from this ratio, we further identify a
continuous thermalization trajectory in ($h,J$) plane that is exactly given by
the Ising transition line, signifying an intimate relation between
thermalization and quantum critical point. Finally, we map out a completely
different dynamical phase diagram starting from an initial ferromagnetic state,
where the thermalization is shown to be equally facilitated by the resonant
spin-flip at special ratios of $J$ and $h$. By bridging QMBS and QI in Ising
chains, our results demonstrate the breakdown of ETH in much broader physical
settings, which also suggest an alternative way to characterize quantum phase
transition via thermalization in non-equilibrium dynamics.",2206.11463v3
2022-07-02,Robust magnetic order upon ultrafast excitation of an antiferromagnet,"The ultrafast manipulation of magnetic order due to optical excitation is
governed by the intricate flow of energy and momentum between the electron,
lattice and spin subsystems. While various models are commonly employed to
describe these dynamics, a prominent example being the microscopic three
temperature model (M3TM), systematic, quantitative comparisons to both the
dynamics of energy flow and magnetic order are scarce. Here, we apply a M3TM to
the ultrafast magnetic order dynamics of the layered antiferromagnet
GdRh$_2$Si$_2$. The femtosecond dynamics of electronic temperature, surface
ferromagnetic order, and bulk antiferromagnetic order were explored at various
pump fluences employing time- and angle-resolved photoemission spectroscopy and
time-resolved resonant magnetic soft x-ray diffraction, respectively. After
optical excitation, both the surface ferromagnetic order and the bulk
antiferromagnetic order dynamics exhibit two-step demagnetization behaviors
with two similar timescales (<1 ps, ~10 ps), indicating a strong exchange
coupling between localized 4f and itinerant conduction electrons. Despite a
good qualitative agreement, the M3TM predicts larger demagnetization than our
experimental observation, which can be phenomenologically described by a
transient, fluence-dependent increased N\'eel temperature. Our results indicate
that effects beyond a mean-field description have to be considered for a
quantitative description of ultrafast magnetic order dynamics.",2207.00789v1
2022-11-01,Fermi level dependence of magnetism and magnetotransport in the magnetic topological insulators Bi$_{2}$Te$_{3}$ and BiSbTe$_{3}$ containing self-organized MnBi$_{2}$Te$_{4}$ septuple layers,"The magnetic coupling mechanisms underlying ferromagnetism and
magnetotransport phenomena in magnetically doped topological insulators have
been a central issue to gain controlled access to the magneto-topological
phenomena such as quantum anomalous Hall effect and topological axion
insulating state. Here, we focus on the role of bulk carriers in magnetism of
the family of magnetic topological insulators, in which the host material is
either Bi$_{2}$Te$_{3}$ or BiSbTe$_{3}$, containing Mn self-organized in
MnBi$_{2}$Te$_{4}$ septuple layers. We tune the Fermi level using the electron
irradiation technique and study how magnetic properties vary through the change
in carrier density, the role of the irradiation defects is also discussed.
Ferromagnetic resonance spectroscopy and magnetotransport measurements show no
effect of the Fermi level position on the magnetic anisotropy field and the
Curie temperature, respectively, excluding bulk magnetism based on a
carrier-mediated process. Furthermore, the magnetotransport measurements show
that the anomalous Hall effect is dominated by the intrinsic and
dissipationless Berry-phase driven mechanism, with the Hall resistivity
enhanced near the bottom/top of the conduction/valence band, due to the Berry
curvature which is concentrated near the avoided band crossings. These results
demonstrate that the anomalous Hall effect can be effectively managed,
maximized, or turned off, by adjusting the Fermi level.",2211.00546v5
2022-11-22,Generation of out-of-plane polarized spin current by spin swapping,"The generation of spin currents and their application to the manipulation of
magnetic states is fundamental to spintronics. Of particular interest are
chiral antiferromagnets that exhibit properties typical of ferromagnetic
materials even though they have negligible magnetization. Here, we report the
generation of a robust spin current with both in-plane and out-of-plane spin
polarization in epitaxial thin films of the chiral antiferromagnet Mn3Sn in
proximity to permalloy thin layers. By employing temperature-dependent
spin-torque ferromagnetic resonance, we find that the chiral antiferromagnetic
structure of Mn3Sn is responsible for an in-plane polarized spin current that
is generated from the interior of the Mn3Sn layer and whose temperature
dependence follows that of this layer's antiferromagnetic order. On the other
hand, the out-of-plane spin polarized spin current is unrelated to the chiral
antiferromagnetic structure and is instead the result of scattering from the
Mn3Sn/permalloy interface. We substantiate the later conclusion by performing
studies with several other non-magnetic metals all of which are found to
exhibit out-of-plane polarized spin currents arising from the spin swapping
effect.",2211.12398v1
2022-11-28,Orbital selective coupling in CeRh$_3$B$_2$: co-existence of high Curie and high Kondo temperature,"We investigated the electronic structure of the enigmatic CeRh$_3$B$_2$ using
resonant inelastic scattering and x-ray absorption spectroscopy in combination
with $ab$ $initio$ density functional calculations. We find that the Rh 4$d$
states are irrelevant for the high-temperature ferromagnetism and the Kondo
effect. We also find that the Ce 4$f$ crystal-field strength is too small to
explain the strong reduction of the Ce magnetic moment. The data reveal instead
the presence of two different active Ce 4$f$ orbitals, with each coupling
selectively to different bands in CeRh$_3$B$_2$. The inter-site hybridization
of the |J=5/2,Jz=+/-1/2> crystal-field state and Ce 5$d$ band combined with the
intra-site Ce 4$f$-5$d$ exchange creates the strong ferromagnetism, while
hybridization between the |J=5/2,Jz=+/-5/2> and the B $sp$ in the $ab$-plane
contributes to the Kondo interaction which causes the moment reduction. This
orbital selective coupling explains the unique and seemingly contradictory
properties of CeRh$_3$B$_2$.",2211.15264v2
2022-11-28,Correlation driven near-flat band Stoner excitations in a Kagome magnet,"Among condensed matter systems, Mott insulators exhibit diverse properties
that emerge from electronic correlations. In itinerant metals, correlations are
usually weak, but can also be enhanced via geometrical confinement of
electrons, that manifest as `flat' dispersionless electronic bands. In the fast
developing field of topological materials, which includes Dirac and Weyl
semimetals, flat bands are one of the important components that can result in
unusual magnetic and transport behaviour. To date, characterisation of flat
bands and their magnetism is scarce, hindering the design of novel materials.
Here, we investigate the ferromagnetic Kagom\'{e} semimetal Co$_3$Sn$_2$S$_2$
using resonant inelastic X-ray scattering. Remarkably, nearly non-dispersive
Stoner spin excitation peaks are observed, sharply contrasting with the
featureless Stoner continuum expected in conventional ferromagnetic metals. Our
band structure and dynamic spin susceptibility calculations, and thermal
evolution of the excitations, confirm the nearly non-dispersive Stoner
excitations as unique signatures of correlations and spin-polarized electronic
flat bands in Co$_3$Sn$_2$S$_2$. These observations serve as a cornerstone for
further exploration of band-induced symmetry-breaking orders in topological
materials.",2211.15292v1
2022-12-21,Charge transfer and disorder-induced spin relaxation in La2NiMnO6 crystallites,"Investigation of the electronic and spin structure in double perovskites is
recently attracting significant attention, mainly driven by their unique
multifunctional properties and other underlying charge and spin dynamics.
Herein, using X-ray photoelectron spectroscopy (XPS), we explore the influence
of variable fractions of Mn3+/Mn4+ cation in different crystallite sizes of
La2NiMnO6 that control the various completing exchange interactions of Ni/Mn
cations responsible for multiple magnetic transitions. The enhanced itinerant
electron due to Mn4+ + Ni2+ to Mn3+ + Ni3+ charge transfer emerged as a
shoulder like characteristics at the low binding energy in the Mn-2P core-level
spectrum. The various approaches such as difference in saturation
magnetization, presence of multiple charge valance, and magnetic entropy
calculations confirm the presence of antisites disorder and it varies as a
function of milling. As milling provides excess energy that helps with
nucleation or cation ordering. Competing magnetic interactions driven by mixed
valences and disorder were established across a cluster glassy phase in the
crystallites. Electron spin resonance spectroscopy (ESR) was utilized to probe
the temperature-driven ferromagnetic-cluster spin-glass transition with
modified g-factor ranging from 2.050 to 2.037. The line width of the ESR
signals increases across the ferromagnetic to cluster-glass phase transition
due to spin freezing. This phase transition is further characterized by
temperature-dependent ac-magnetic susceptibility measurements. Argand diagram
for the ac-susceptibility of the interacting crystallites suggests a collective
magnetization relaxation dynamic in the proximity of spin-glass freezing
temperature of La2NiMnO6.",2212.10845v2
2023-01-16,Crystal orientation dependent spin pumping in Bi0.1Y2.9Fe5O12/Pt interface,"Ferromagnetic resonance (FMR) based spin pumping is a versatile tool to
quantify the spin mixing conductance and spin to charge conversion (S2CC)
efficiency of ferromagnet/normal metal (FM/NM) heterostructure. The spin mixing
conductance of FM/NM interface can also be tuned by the crystal orientation
symmetry of epitaxial FM. In this work, we study the S2CC in epitaxial Bismuth
substituted Yttrium Iron Garnet (Bi0.1Y2.9Fe5O12) thin films Bi-YIG (100 nm)
interfaced with heavy metal platinum (Pt (8 nm)) deposited by pulsed laser
deposition process on different crystal orientation Gd3Ga5O12 (GGG) substrates
i.e. [100] and [111]. The crystal structure and surface roughness characterized
by X-Ray diffraction and atomic force microscopy measurements establish
epitaxial Bi-YIG[100], Bi-YIG[111] orientations and atomically flat surfaces
respectively. The S2CC quantification has been realized by two complimentary
techniques, (i) FMR-based spin pumping and inverse spin Hall effect (ISHE) at
GHz frequency and (ii) temperature dependent spin Seebeck measurements.
FMR-ISHE results demonstrate that the [111] oriented Bi-YIG/Pt sample shows
significantly higher values of spin mixing conductance ((2.31+-0.23)x10^18
m^-2) and spin Hall angle (0.01+-0.001) as compared to the [100] oriented
Bi-YIG/Pt. A longitudinal spin Seebeck measurement reveals that the [111]
oriented sample has higher spin Seebeck coefficient (106.40+-10 nV mm-1 K-1).
This anisotropic nature of spin mixing conductance and spin Seebeck coefficient
in [111] and [100] orientation has been discussed using the magnetic
environment elongation along the surface normal or parallel to the growth
direction. Our results aid in understanding the role of crystal orientation
symmetry in S2CC based spintronics devices.",2301.06477v1
2023-03-01,Proton-fluence dependent magnetic properties of exfoliable quasi-2D van der Waals Cr2Si2Te6 magnet,"The discovery of long-range magnetic ordering in atomically thin materials
catapulted the van der Waals (vdW) family of compounds into an unprecedented
popularity. In particular, with a current push in space exploration, it is
beneficial to study how the properties of such materials evolve under proton
irradiation. Owing to their robust intra-layer stability and sensitivity to
external perturbations, these materials provide excellent opportunities for
studying proton irradiation as a non-destructive tool for controlling their
magnetic properties. Specifically, the exfoliable Cr2Si2Te6 (CST) is a
ferromagnetic semiconductor with the Curie temperature (TC) of ~32 K. Here, we
have investigated the magnetic properties of CST upon proton irradiation as a
function of fluence (1 x 1015, 5 x 1015, 1 x 1016, 5 x 1016, and 1 x 1018
H+/cm2) by employing variable-temperature, variable-field magnetization
measurements coupled with electron paramagnetic resonance (EPR) spectroscopy
and detail how the magnetization, magnetic anisotropy and EPR spectral
parameters vary as a function of proton fluence across the magnetic phase
transition. While the TC remains constant as a function of proton fluence, we
observed that the saturation magnetization and magnetic anisotropy diverge at
the proton fluence of 5 x 1016 H+/cm2, which is prominent in the ferromagnetic
phase, in particular. This work demonstrates that proton irradiation is a
feasible method for modifying the magnetic properties and local magnetic
interactions of vdWs crystals, which represents a significant step forward in
the design of future spintronic and magneto-electronic applications.",2303.00824v1
2023-05-15,Scattering of magnetostatic surface modes of ferromagnetic films by geometric defects,"Magnonics, an emerging field of Magnetism, studies spin waves (SWs) in
nano-structures, with an aim towards possible applications. As information may
be eventually transmitted with efficiency stored in the phase and amplitude of
spin waves, a topic of interest within Magnonics is the propagation of SW
modes. Thus, understanding mechanisms that may influence SW propagation is of
interest. Here the effect of localized surface geometric defects on
magnetostatic surface modes propagation is studied in ferromagnetic films and
semi-infinite media. Theoretical results are developed that allow to calculate
the scattering of these surface or Damon-Eshbach (DE) modes. A Green-Extinction
theorem is used to determine the scattering of incident surface modes, through
the determination of phase shifts of associated modes that are symmetric and
anti-symmetric under inversion in the same geometry with geometric defects.
Choosing localized symmetric depressions as geometric defects, scattering
transmission coefficients are determined that show perfect transmission at
specific frequencies or wave-lengths, that we associate with resonances in the
system. Interestingly the system shows the appearance of localized modes in the
depression regions, with associated discrete frequencies immersed in the
continuum spectrum of these surface DE modes. These localized modes have a
short wave-length content, and appear similarly in semi-infinite surfaces with
depressions. The latter indicates that these types of scattering effects should
appear in all surfaces with roughness or more pronounced geometric defects.",2305.08749v1
2023-08-28,External magnetic fields enhance capture of magnetic nanoparticles flowing through molded microfluidic channels by ferromagnetic nanostructures,"Magnetic nanoparticles (MNPs) have many applications which require MNPs to be
captured and immobilized for their manipulation and sensing. For example, MNP
sensors based on detecting changes to the ferromagnetic resonances of an
antidot nanostructure exhibit better performance when the nanoparticles are
captured within the antidot inclusions. This study investigates the influence
of microfluidics upon the capture of MNPs by four geometries of antidot array
nanostructures hollowed into 30 nm-thick Permalloy films. The nanostructures
were exposed to a dispersion of 130 nm MNP clusters which passed through PDMS
microfluidic channels with a 400 {\mu}m circular cross-section fabricated from
wire molds. With the microfluidic flow of MNPs, the capture efficiency - the
ratio between the number of nanoparticles captured inside of the antidot
inclusions to the number outside the inclusions - decreased for all four
geometries compared to previous results introducing the particles via droplets
on the film surface. This indicates that most MNPs were passing over the
nanostructures, since there were no significant magnetophoretic forces acting
upon the particles. However, when a static magnetic field is applied, the
magnetophoretic forces generated by the nanostructure are stronger and the
capture efficiencies are significantly higher than those obtained using
droplets. In particular, circular antidots demonstrated the highest capture
efficiency among the four geometries of almost 83.1% when the magnetic field is
parallel to the film plane. In a magnetic field perpendicular to the film, the
circle antidots again show the highest capture efficiency of about 77%. These
results suggest that the proportion of nanoparticles captured inside antidot
inclusions is highest under a parallel magnetic field. Clearly, the geometry of
the nanostructure has a strong influence on the capture of MNPs.",2308.14543v1
2023-09-27,Correlation of Blocking and Néel Temperatures in Ultra-thin Metallic Antiferromagnets,"Nonvolatile spintronics-based devices that utilize electron spin both to
store and transport information face a great challenge when scaled to nano
dimensions due to loss of thermal stability and stray field induced disturbance
in closely packed magnetic bits. The potential replacement of ferromagnetic
materials with antiferromagnets may overcome some of these issues owing to the
superior robustness of sublattice spin orientations to magnetic field
disturbance as long as theyare kept well below the N\'eel temperature, which is
hard to measure with conventional methods, especially in the ultrathin limit.
In this work, we have employed spin pumping from a soft ferromagnetic NiFe
layer into widely used ultrathin metallic antiferromagnet Ir20Mn80, FeMn, PtMn,
PdMn or NiMn with thicknesses in the 0.7-3 nm range, as a probe to detect
damping enhancement during magnetic phase transitions. Independent measurements
of the blocking temperature with magnetometry reveal that temperature dependent
shifts in the resonance peaks can also be used to measure the blocking
temperature, allowing the analysis of the correlation between the N\'eel and
blocking temperatures in trilayers with permalloy and antiferromagnetic layer
separated by a 3 nm thick spacer layer. The thickness dependent
characterization of thermal stability in antiferromagnets provides a key
element for scalable and ultrafast antiferromagnetic spintronics.",2309.15545v1
2023-11-20,Absence of metallicity and bias-dependent resistivity in low-carrier-density EuCd2As2,"EuCd2As2 was theoretically predicted to be a minimal model of Weyl semimetals
with a single pair of Weyl points in the ferromagnet state. However, the
heavily p-doped EuCd2As2 crystals in previous experiments prevent direct
identification of the semimetal hypothesis. Here we present a comprehensive
magneto-transport study of high-quality EuCd2As2 crystals with ultralow bulk
carrier density (10^13 cm-3). In contrast to the general expectation of a Weyl
semimetal phase, EuCd2As2 shows insulating behavior in both antiferromagnetic
and ferromagnetic states as well as surface-dominated conduction from band
bending. Moreover, the application of a dc bias current can dramatically
modulate the resistance by over one order of magnitude, and induce a periodic
resistance oscillation due to the geometric resonance. Such nonlinear transport
results from the highly nonequilibrium state induced by electrical field near
the band edge. Our results suggest an insulating phase in EuCd2As2 and put a
strong constraint on the underlying mechanism of anomalous transport properties
in this system.",2311.11515v1
2023-11-20,Spin Hall conductivity in Bi$_{1-x}$Sb$_x$ as an experimental test of bulk-boundary correspondence,"Bulk-boundary correspondence is a foundational principle underlying the
electronic band structure and physical behavior of topological quantum
materials. Although it has been rigorously tested in topological systems where
the physical properties involve charge currents, it remains unclear whether
bulk-boundary correspondence should also hold for non-conserved spin currents.
We study charge-to-spin conversion in a canonical topological insulator,
Bi$_{1-x}$Sb$_x$, to address this fundamentally unresolved question. We use
spin-torque ferromagnetic resonance measurements to accurately probe the
charge-to-spin conversion efficiency in epitaxial Bi$_{1-x}$Sb$_x$~thin films
of high structural quality spanning the entire range of composition, including
both trivial and topological band structures, as verified using {\it in vacuo}
angle-resolved photoemission spectroscopy. From these measurements, we deduce
the effective spin Hall conductivity (SHC) and find excellent agreement with
the values predicted by tight-binding calculations for the intrinsic SHC of the
bulk bands. These results provide strong evidence that the strong spin-orbit
entanglement of bulk states well below the Fermi energy connects directly to
the SHC in epitaxial Bi$_{1-x}$Sb$_x$~films interfaced with a metallic
ferromagnet. The excellent agreement between theory and experiment points to
the generic value of analyses focused entirely on bulk properties, even for
topological systems involving non-conserved spin currents.",2311.11933v1
2024-02-06,Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure,"Spin pumping has significant implications for spintronics, providing a
mechanism to manipulate and transport spins for information processing.
Understanding and harnessing spin currents through spin pumping is critical for
the development of efficient spintronic devices. The use of a magnetic
insulator with low damping, enhances the signal-to-noise ratio in crucial
experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping.
A magnetic insulator coupled with a heavy metal or quantum material offers a
more straight forward model system, especially when investigating spin-charge
interconversion processes to greater accuracy. This simplicity arises from the
absence of unwanted effects caused by conduction electrons unlike in
ferromagnetic metals. Here, we investigate the spin pumping in coupled
ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with
heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that
magnon transmission occurs at both of the FiMs FMR positions. The enhancement
of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed
to the strong interfacial exchange coupling between FiMs. The modulation of Vsp
is achieved by tuning the bilayer structure. Further, the spin mixing
conductance for these coupled systems is found to be 10^18 m^-2. Our findings
describe a novel coupled FiM system for the investigation of magnon coupling
providing new prospects for magnonic devices.",2402.03734v1
2015-10-12,Room-temperature spin-orbit torque in NiMnSb,"Materials that crystalize in diamond-related lattices, with Si and GaAs as
their prime examples, are at the foundation of modern electronics.
Simultaneoulsy, the two atomic sites in the unit cell of these crystals form
inversion partners which gives rise to relativistic non-equilibrium spin
phenomena highly relevant for magnetic memories and other spintronic devices.
When the inversion-partner sites are occupied by the same atomic species,
electrical current can generate local spin polarization with the same magnitude
and opposite sign on the two inversion-partner sites. In CuMnAs, which shares
this specific crystal symmetry of the Si lattice, the effect led to the
demonstration of electrical switching in an antiferromagnetic memory at room
temperature. When the inversion-partner sites are occupied by different atoms,
a non-zero global spin-polarization is generated by the applied current which
can switch a ferromagnet, as reported at low temperatures in the diluted
magnetic semiconductor (Ga,Mn)As. Here we demonstrate the effect of the global
current-induced spin polarization in a counterpart crystal-symmetry material
NiMnSb which is a member of the broad family of magnetic Heusler compounds. It
is an ordered high-temperature ferromagnetic metal whose other favorable
characteristics include high spin-polarization and low damping of magnetization
dynamics. Our experiments are performed on strained single-crystal epilayers of
NiMnSb grown on InGaAs. By performing all-electrical ferromagnetic resonance
measurements in microbars patterned along different crystal axes we detect
room-temperature spin-orbit torques generated by effective fields of the
Dresselhaus symmetry. The measured magnitude and symmetry of the
current-induced torques are consistent with our relativistic density-functional
theory calculations.",1510.03356v1
2017-07-26,Fluctuations in a model ferromagnetic film driven by a slowly oscillating field with a constant bias,"We present a numerical and theoretical study that supports and explains
recent experimental results on anomalous magnetization fluctuations of a
uniaxial ferromagnetic film in its low-temperature phase, which is forced by an
oscillating field above the critical period of the associated dynamic phase
transition (DPT) [P. Riego, P. Vavassori, A. Berger, Phys. Rev. Lett. 118,
117202 (2017)]. For this purpose, we perform kinetic Monte Carlo simulations of
a two-dimensional Ising model with nearest-neighbor ferromagnetic interactions
in the presence of a sinusoidally oscillating field, to which is added a
constant bias field. We study a large range of system sizes and supercritical
periods and analyze the data using a droplet-theoretical description of
magnetization switching. We find that the period-averaged magnetization, which
plays the role of the order parameter for the DPT, presents large fluctuations
that give rise to well-defined peaks in its scaled variance and its
susceptibility with respect to the bias field. The peaks are symmetric with
respect to zero bias and located at values of the bias field that increase
toward the field amplitude as an inverse logarithm of the field oscillation
period. Our results indicate that this effect is independent of the system size
for large systems, ruling out critical behavior associated with a phase
transition. Rather, it is a stochastic-resonance phenomenon that has no
counterpart in the corresponding thermodynamic phase transition, providing a
reminder that the equivalence of the DPT to an equilibrium phase transition is
limited to the critical region near the critical period and zero bias.",1707.08614v2
2020-12-12,Ultrafast spin-currents and charge conversion at 3d-5d interfaces probed by time-domain terahertz spectroscopy,"Spintronic structures are extensively investigated for their spin orbit
torque properties, required for magnetic commutation functionalities. Current
progress in these materials is dependent on the interface engineering for the
optimization of spin transmission. Here, we advance the analysis of ultrafast
spin-charge conversion phenomena at ferromagnetic-transition metal interfaces
due to their inverse spin-Hall effect properties. In particular the intrinsic
inverse spin Hall effect of Pt-based systems and extrinsic inverse spin-Hall
effect of Au:W and Au:Ta in NiFe/Au:(W,Ta) bilayers are investigated. The
spin-charge conversion is probed by complementary techniques -- ultrafast THz
time domain spectroscopy in the dynamic regime for THz pulse emission and
ferromagnetic resonance spin-pumping measurements in the GHz regime in the
steady state -- to determine the role played by the material properties,
resistivities, spin transmission at metallic interfaces and spin-flip rates.
These measurements show the correspondence between the THz time domain
spectroscopy and ferromagnetic spin-pumping for the different set of samples in
term of the spin mixing conductance. The latter quantity is a critical
parameter, determining the strength of the THz emission from spintronic
interfaces. This is further supported by ab-initio calculations, simulations
and analysis of the spin-diffusion and spin relaxation of carriers within the
multilayers in the time domain, permitting to determine the main trends and the
role of spin transmission at interfaces. This work illustrates that time domain
spectroscopy for spin-based THz emission is a powerful technique to probe
spin-dynamics at active spintronic interfaces and to extract key material
properties for spin-charge conversion.",2012.06900v1
2020-12-17,Energy-efficient spin injector into semiconductors driven by elastic waves,"Generation of spin imbalance in nonmagnetic semiconductors is crucial for the
functioning of many spintronic devices. An attractive design of spin injectors
into semiconductors is based on a spin pumping from a precessing ferromagnet,
typically excited by a microwave magnetic field leading to a high power
consumption of the device. Here we describe theoretically a spin injector with
greatly reduced energy losses, in which the magnetic dynamics is excited by an
elastic wave injected into a ferromagnet-semiconductor heterostructure. To
demonstrate the efficient functioning of such an injector, we perform
micromagnetoelastic simulations of the coupled elastic and magnetic dynamics in
Ni films and Ni/GaAs bilayers. For thick Ni films, it is shown that a
monochromatic acoustic wave generates a spin wave with the same frequency and
wavelength, which propagates over distances of several micrometers at the
excitation frequencies close to the frequency of ferromagnetic resonance. The
simulations of Ni/GaAs bilayers with Ni thicknesses comparable to the
wavelength of the injected acoustic wave demonstrate the development of a
steady-state magnetization precession at the Ni/GaAs interface. The amplitude
of such a precession has a maximum at Ni thickness amounting to three quarters
of the wavelength of the elastic wave, which is explained by an analytical
model. Using simulation data obtained for the magnetization precession at the
Ni/GaAs interface, we evaluate the spin current pumped into GaAs and calculate
the spin accumulation in it by solving the spin diffusion equation. Then the
electrical signals resulting from the spin flow and the inverse spin Hall
effect are determined via the numerical solution of the Laplace's equation. It
is shown that amplitudes of these ac signals are large enough for experimental
measurement, which indicates an efficient acoustically driven spin pumping into
GaAs.",2012.09531v1
2022-03-14,Light-Induced Ferromagnetism in Moiré Superlattices,"Many-body interactions between carriers lie at the heart of correlated
physics. The ability to tune such interactions would open the possibility to
access and control complex electronic phase diagrams on demand. Recently,
moir\'e superlattices formed by two-dimensional materials have emerged as a
promising platform for quantum engineering such phenomena. The power of the
moir\'e system lies in the high tunability of its physical parameters by
tweaking layer twist angle, electrical field, moir\'e carrier filling, and
interlayer coupling. Here, we report that optical excitation can drastically
tune the spin-spin interactions between moir\'e trapped carriers, resulting in
ferromagnetic order in WS2/WSe2 moir\'e superlattices over a small range of
doping at elevated temperatures. Near the filling factor v = -1/3 (i.e., one
hole per three moir\'e unit cells), as the excitation power at the exciton
resonance increases, a well-developed hysteresis loop emerges in the reflective
magnetic circular dichroism (RMCD) signal as a function of magnetic field, a
hallmark of ferromagnetism. The hysteresis loop persists down to charge
neutrality, and its shape evolves as the moir\'e superlattice is gradually
filled, indicating changes of magnetic ground state properties. The observed
phenomenon points to a mechanism in which itinerant photo-excited excitons
mediate exchange coupling between moir\'e trapped holes. This exciton-mediated
interaction can be of longer range than direct coupling between moir\'e trapped
holes, and thus magnetic order can arise even in the dilute hole regime under
optical excitation. This discovery adds a new and dynamic tuning knob to the
rich many-body Hamiltonian of moir\'e quantum matter.",2203.07161v1
2022-09-30,Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl,"Half-metallic ferromagnets (HMF) are on one of the most promising materials
in the field of spintronics due to their unique band structure consisting of
one spin sub-band having metallic characteristics along with another sub-band
with semiconductor-like behavior. In this work, we report the synthesis of a
novel quaternary Heusler alloy FeMnVAl and have studied the structural,
magnetic, transport, and electronic properties complemented with
first-principles calculations. Among different possible structurally ordered
arrangements, the optimal structure is identified by theoretical energy
minimization. The corresponding spin-polarized band structure calculations
indicates the presence of a half-metallic ferromagnetic ground state. A
detailed and careful investigation of the x-ray diffraction data, M\""{o}ssbauer
and nuclear magnetic resonance spectra suggest the presence of site-disorder
between the Fe and Mn atoms in the stable ordered structure of the system. The
magnetic susceptibility measurement clearly establishes a ferromagnetic-like
transition below $\sim$213 K. The ${^{57}}$Fe M\""{o}ssbauer spectrometry
measurements suggest only the Mn-spins could be responsible for the magnetic
order, which is consistent with our theoretical calculation. Surprisingly, the
density-functional-theory calculations reveal that the spin-polarization value
is almost immunized (92.4\% ${\rightarrow}$ 90.4\%) from the Mn-Fe structural
disorder, even when nonmagnetic Fe and moment carrying Mn sites are entangled
inseparably. Robustness of spin polarization and half metallicity in the
studied FeMnVAl compound comprising structural disorder is thus quite
interesting and could provide a new direction to investigate and understand the
exact role of disorders on spin polarization in these class of materials, over
the available knowledge.",2209.15243v1
2014-01-05,Hybrid paramagnetic-ferromagnetic quantum computer design based on electron spin arrays and a ferromagnetic nanostripe,"General design for the practical implementation of hybrid
paramagnetic-ferromagnetic quantum computer.",1401.0878v1
2013-03-01,Dispersive Casimir Pressure Effect from Surface Plasmon Quanta by Quasi 1D Metal Wires in Ferrite Disks and The Josephson Frequencies and Currents,"Ferrites are distinct material for electromagnetic applications due to its
unique spin precession. In this paper, Casimir pressure effect by deploying
magnetically tunable surface plasmon quanta in stratified structure of using
ferrite and metal wires is presented. Previously, oscillating surface plasmon
quanta were successfully included to modify first reflection and first
transmission characteristics. The oscillating surface plasmon quanta in the
modified reflection in such a system, not only does resolve in a typical matter
in metamaterial, but also provide new applications such as creating Casimir
pressure effects through the metamaterial composite shown in this paper. The
Casimir pressure flips from attractive state to repulsive state is referred to
cause mechanism of radiation from surface plasmon quanta. Both Casimir force
analysis and the measured data of radiations indicate us the system develops
quantized states by electric flux induced by ferromagnetic resonance. Quantum
analysis is used to understand the discrete radiations spectra for our
experimental measurement. The discrete radiations are reproduced by using time
dependent Schr\""odinger representation. As a result, we find the Josephson
frequency and Josephson current representations at room temperature and we used
them for extrapolating voltage induced in excited ferrites. Josephson frequency
at X-band is able to differentiate micron volt differences and it allows us to
report the data for voltage induced by ferromagnetic resonance in ferrite at
room temperature. It is understood that the radiation intensity depends on
density of final states and excitation probability when we come to think the
energy matter. It seems possible to create as high as 20mW microwave power
inside waveguide at X-band.",1303.0205v2
2015-11-16,Determination of intrinsic damping of perpendicularly magnetized ultrathin films from time resolved precessional magnetization measurements,"Magnetization dynamics are strongly influenced by damping. An effective
damping constant {\alpha}eff is often determined experimentally from the
spectral linewidth of the free induction decay of the magnetization after the
system is excited to its non-equilibrium state. Such an {\alpha}eff, however,
reflects both intrinsic damping as well as inhomogeneous broadening. In this
paper we compare measurements of the magnetization dynamics in ultrathin
non-epitaxial films having perpendicular magnetic anisotropy using two
different techniques, time-resolved magneto optical Kerr effect (TRMOKE) and
hybrid optical-electrical ferromagnetic resonance (OFMR). By using an external
magnetic field that is applied at very small angles to the film plane in the
TRMOKE studies, we develop an explicit closed-form analytical expression for
the TRMOKE spectral linewidth and show how this can be used to reliably extract
the intrinsic Gilbert damping constant. The damping constant determined in this
way is in excellent agreement with that determined from the OFMR method on the
same samples. Our studies indicate that the asymptotic high-field approach that
is often used in the TRMOKE method to distinguish the intrinsic damping from
the effective damping may result in significant error, because such high
external magnetic fields are required to make this approach valid that they are
out of reach. The error becomes larger the lower is the intrinsic damping
constant, and thus may account for the anomalously high damping constants that
are often reported in TRMOKE studies. In conventional ferromagnetic resonance
(FMR) studies, inhomogeneous contributions can be readily distinguished from
intrinsic damping contributions from the magnetic field dependence of the FMR
linewidth. Using the analogous approach, we show how reliable values of the
intrinsic damping can be extracted from TRMOKE.",1511.04802v1
2018-02-27,Depth-resolved resonant inelastic x-ray scattering at a superconductor/half-metallic ferromagnet interface through standing-wave excitation,"We demonstrate that combining standing-wave (SW) excitation with resonant
inelastic x-ray scattering (RIXS) can lead to depth resolution and interface
sensitivity for studying orbital and magnetic excitations in correlated oxide
heterostructures. SW-RIXS has been applied to multilayer heterostructures
consisting of a superconductor La$_{1.85}$Sr$_{0.15}$CuO$_{4}$(LSCO) and a
half-metallic ferromagnet La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO). Easily
observable SW effects on the RIXS excitations were found in these LSCO/LSMO
multilayers. In addition, we observe different depth distribution of the RIXS
excitations. The magnetic excitations are found to arise from the LSCO/LSMO
interfaces, and there is also a suggestion that one of the dd excitations comes
from the interfaces. SW-RIXS measurements of correlated-oxide and other
multilayer heterostructures should provide unique layer-resolved insights
concerning their orbital and magnetic excitations, as well as a challenge for
RIXS theory to specifically deal with interface effects.",1802.09743v5
2017-12-05,Parton theory of magnetic polarons: Mesonic resonances and signatures in dynamics,"When a mobile hole is moving in an anti-ferromagnet it distorts the
surrounding Neel order and forms a magnetic polaron. Such interplay between
hole motion and anti-ferromagnetism is believed to be at the heart of high-Tc
superconductivity in cuprates. We study a single hole described by the t-Jz
model with Ising interactions between the spins in 2D. This situation can be
experimentally realized in quantum gas microscopes. When the hole hopping is
much larger than couplings between the spins, we find strong evidence that
magnetic polarons can be understood as bound states of two partons, a spinon
and a holon carrying spin and charge quantum numbers respectively. We introduce
a microscopic parton description which is benchmarked by comparison with
results from advanced numerical simulations. Using this parton theory, we
predict a series of excited states that are invisible in the spectral function
and correspond to rotational excitations of the spinon-holon pair. This is
reminiscent of mesonic resonances observed in high-energy physics, which can be
understood as rotating quark antiquark pairs. We also apply the strong coupling
parton theory to study far-from equilibrium dynamics of magnetic polarons
observable in current experiments with ultracold atoms. Our work supports
earlier ideas that partons in a confining phase of matter represent a useful
paradigm in condensed-matter physics and in the context of high-Tc
superconductivity. While direct observations of spinons and holons in real
space are impossible in traditional solid-state experiments, quantum gas
microscopes provide a new experimental toolbox. We show that, using this
platform, direct observations of partons in and out-of equilibrium are
possible. Extensions of our approach to the t-J model are also discussed. Our
predictions in this case are relevant to current experiments with quantum gas
microscopes for ultracold atoms.",1712.01874v1
2021-05-12,Asymptotic entanglement sudden death in two atoms with dipole-dipole and Ising interactions coupled to a radiation field at non-zero detuning,"We investigate the time evolution and asymptotic behavior of a system of two
two-level atoms (qubits) interacting off-resonance with a single mode radiation
field. The two atoms are coupled to each other through dipole-dipole as well as
Ising interactions. An exact analytic solution for the system dynamics that
spans the entire phase space is provided. We focus on initial states that cause
the system to evolve to entanglement sudden death (ESD) between the two atoms.
We find that combining the Ising and dipole-dipole interactions is very
powerful in controlling the entanglement dynamics and ESD compared with either
one of them separately. Their effects on eliminating ESD may add up
constructively or destructively depending on the type of Ising interaction
(Ferromagnetic or anti-Ferromagnetic), the detuning parameter value, and the
initial state of the system. The asymptotic behavior of the ESD is found to
depend substantially on the initial state of the system, where ESD can be
entirely eliminated by tuning the system parameters except in the case of an
initial correlated Bell state. Interestingly, the entanglement, atomic
population and quantum correlation between the two atoms and the field
synchronize and reach asymptotically quasi-steady dynamic states. Each one of
them ends up as a continuous irregular oscillation, where the collapse periods
vanish, with a limited amplitude and an approximately constant mean value that
depend on the initial state and the system parameters choice. This indicates an
asymptotic continuous exchange of energy (and strong quantum correlation)
between the atoms and the field takes place, accompanied by diminished ESD for
these chosen setups of the system. This system can be realized in spin states
of quantum dots or Rydberg atoms in optical cavities, and superconducting or
hybrid qubits in linear resonators.",2105.05694v1
2021-08-24,Full-Spin-Wave-Scaled Finite Element Stochastic Micromagnetism: Mesh-Independent FUSSS LLG Simulations of Ferromagnetic Resonance and Reversal,"In this paper, we address the problem that standard stochastic
Landau-Lifshitz-Gilbert (sLLG) simulations typically produce results that show
unphysical mesh-size dependence. The root cause of this problem is that the
effects of spin wave fluctuations are ignored in sLLG. We propose to represent
the effect of these fluctuations by a ""FUll-Spinwave-Scaled Stochastic LLG"", or
FUSSS LLG method. In FUSSS LLG, the intrinsic parameters of the sLLG
simulations are first scaled by scaling factors that integrate out the spin
wave fluctuations up to the mesh size, and the sLLG simulation is then
performed with these scaled parameters. We developed FUSSS LLG by studying the
Ferromagnetic Resonance (FMR) in Nd$_2$Fe$_{14}$B cubes. The nominal scaling
greatly reduced the mesh size dependence relative to sLLG. We further
discovered that adjusting one scaling exponent by less than 10% delivered fully
mesh-size-independent results for the FMR peak. We then performed three tests
and validations of our FUSSS LLG with this modified scaling. 1) We studied the
same FMR but with magnetostatic fields included. 2) We simulated the total
magnetization of the Nd$_2$Fe$_{14}$B cube. 3) We studied the effective,
temperature- and sweeping rate-dependent coercive field of the cubes. In all
three cases we found that FUSSS LLG delivered essentially mesh-size-independent
results, which tracked the theoretical expectations better than unscaled sLLG.
Motivated by these successful validations, we propose that FUSSS LLG provides
marked, qualitative progress towards accurate, high precision modeling of
micromagnetics in hard, permanent magnets.",2108.10582v1
2021-12-29,High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin-orbit coupling,"One of the cornerstone effects in spintronics is spin pumping by dynamical
magnetization that is steadily precessing (around, e.g., the $z$-axis) with
frequency $\omega_0$, due to absorption of low-power microwaves of frequency
$\omega_0$ under the resonance conditions and in the absence of any applied
bias voltage. The two-decades-old ""standard model"" of this effect, based on the
scattering theory of adiabatic quantum pumping, predicts that component
$I^{S_z}$ of spin current vector $\big( I^{S_x}(t),I^{S_y}(t),I^{S_z} \big)
\propto \omega_0$ is time-independent while $I^{S_x}(t)$ and $I^{S_y}(t)$
oscillate harmonically in time with a single frequency $\omega_0$; whereas
pumped charge current is zero $I \equiv 0$ in the same adiabatic $\propto
\omega_0$ limit. Here we employ more general than ""standard model"" approaches,
time-dependent nonequilibrium Green's function (NEGF) and Floquet-NEGF, to
predict unforeseen features of spin pumping -- precessing localized magnetic
moments within ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose
conduction electrons are exposed to spin-orbit coupling (SOC) of either
intrinsic or proximity origin, will pump both spin $I^{S_\alpha}(t)$ and charge
$I(t)$ currents. All four of these functions harmonically oscillate in time at
both even an odd integer multiples $N\omega_0$ of the driving frequency
$\omega_0$. The cutoff order of such high-harmonics increases with SOC
strength, reaching $N_\mathrm{max} \simeq 11$ in the chosen-for-demonstration
one-dimensional FM or AFM models. Higher cutoff $N_\mathrm{max} \simeq 25$ can
be achieved in realistic two-dimensional (2D) FM models defined on the
honeycomb lattice, where we provide prescription on how to realize them using
2D magnets and their heterostructures.",2112.14685v3
2022-11-06,Interpretation of spin-wave modes in Co/Ag nanodot arrays probed by broadband ferromagnetic resonance,"We present a detailed investigation of the magnetization dynamics in Co/Ag
nanodots, which due to their size can support standing spin-wave (SSW) modes
with complex spectral responses. To interpret the experimentally measured
broadband vector network analyzer ferromagnetic resonance data, we compare the
spectra of the nanoarray structure with those of the unpatterned Co/Ag film of
identical thickness, which serves as a baseline for obtaining the general
magnetic parameters of the system. Using a novel frequency domain, matrix-free
simulation method of the dynamic response, we identify the nature of the
excitation modes, which allows us to assess the boundary conditions for the
nanodots. We find an excellent agreement between the calculated and
experimental values for the frequencies of the fundamental (uniform-like) (011)
mode. The existence of an edge-localized mode in the experiment has been
confirmed and fits very well with theory and micromagnetic simulations, having
the form of a flapping mode at the extrema of the nanodot in one of the
in-plane directions. Its frequency is below the fundamental mode's frequency
and has been shown to be a consequence of the imaginary wave vector for such
localized SSW modes. Higher order SSW modes can be generated from the theory,
which allows us to find a probable mode number for the second bulk SSW (201 or
221 or 131), which lies at frequencies above the fundamental mode.",2211.03042v5
2023-01-27,Morphology and Magnetic vortex chiral symmetry of 2D arrays of magnetic trilayer disks with magnetostatic interlayer coupling determined by X ray resonant magnetic scattering,"X ray resonant magnetic scattering (XRMS) was used to characterize the
magnetization of 2D arrays of trilayer submicron magnets. The interpretation of
the data required the understanding of the morphology of the magnets which was
also deduced from the scattered intensity. The magnets consisted of two
magnetostatically coupled ferromagnetic layers separated by a non-magnetic
spacer. The scattered intensity from the disks resulted to be dependent on the
disks surface curvature. This made the collected intensity at each Bragg
reflection (BR) to be correlated to the reflected light from locations of the
disk with the same angle of curvature. Due to this, quantitative information
was obtained, averaged over the disks illuminated by x rays, of the variations
in thickness and magnetization across the entire area of the disks. This
averaged magnetization mapping of the disks served to study their vortex
configuration in each of their magnetic layers, determining the average
location of the vortex, the chiral symmetry of its magnetic circulation, and
the specific locations where the vortex nucleation starts within the disks.
Chiral asymmetry appeared in the disks when the field was oriented at an
oblique angle with respect to the easy axis of the array. The local magnetic
sensitivity of the technique allowed to identify a non-centrosymmetric
distribution of the magnetization of the disks that explains the observed
chiral asymmetry. Unexpectedly, the magnetic circulation sense of the vortex
was the same in both ferromagnetic layers. In addition, the magnetization of
the buried layer was different in the descent branch than in the ascent branch
of its hysteresis loops.",2301.11851v1
2021-04-15,Active Magnetoplasmonics with Transparent Conductive Oxide Nanocrystals,"Magnetoplasmonics is highly promising to devise active optical elements:
modulating the plasmon resonance condition with magnetic field can boost the
performance of refractometric sensors and nanophotonic optical devices.
Nevertheless, real life applications are hampered by the magnetoplasmonic
trilemma: 1) a good plasmonic metal has sharp optical resonances but low
magneto-optical response; 2) a magnetic metal has strong magneto-optical
response but a very broad plasmonic resonance; 3) mixing the two components
degrades the quality of both features. To overcome the trilemma, we use a
different class of materials, transparent conductive oxide nanocrystals (NCs)
with plasmonic response in the near infrared. Although non-magnetic, they
combine a large cyclotron frequency (due to small electron effective mass) with
sharp plasmonic resonances. We benchmark the concept with F- and In- doped CdO
(FICO) and Sn-doped In2O3 (ITO) NCs to boost the magneto-optical Faraday
rotation and ellipticity, reaching the highest magneto-optical response for a
non-magnetic plasmonic material, and exceeding the performance of
state-of-the-art ferromagnetic nanostructures. The magnetoplasmonic response of
these NCs was rationalized with analytical model based on the excitation of
circular magnetoplasmonic modes. Finally, proof of concept experiments
demonstrated the superior performance of FICO NCs with respect to current state
of the art in magnetoplasmonic refractometric sensing, approaching the
sensitivity of leading localized plasmon refractometric methods with the
advantage of not requiring complex curve fitting.",2104.07772v1
2002-12-02,Theoretical description of the ferromagnetic $π$-junctions near the critical temperature,"The theory of ferromagnetic Pi-junction near the critical temperature is
presented. It is demonstrated that in the dirty limit the modified Usadel
equation adequately describes the proximity effect in ferromagnets. To provide
the description of an experimentally relevant situation, oscillations of the
Josephson critical current are calculated as a function of ferromagnetic layer
thickness for different transparencies of the superconductor-ferromagnet
interfaces.",0212031v1
2004-10-14,Spin dependent transport in ferromagnetic/superconductor/ferromagnetic single electron transistor,"Ferromagnetic single electron transistors with Al islands and orthogonal
ferromagnetic leads (Co) are fabricated using ebeam lithography followed by
shadow evaporation techniques. I-V characteristics exhibit typical single
electron tunneling effects. Transport measurements performed in external
magnetic field show that, when the two ferromagnetic leads are in antiparallel
configuration, spin imbalance leads to a suppression of superconductivity.",0410351v1
1997-12-18,From Nagaoka's ferromagnetism to flat-band ferromagnetism and beyond: An introduction to ferromagnetism in the Hubbard model,"This is a self-contained review about ferromagnetism in the Hubbard model,
which should be accessible to readers with various backgrounds who are new to
the field.
  We describe Nagaoka's ferromagnetism and flat-band ferromagnetism in detail,
giving all necessary backgrounds as well as complete (but elementary)
mathematical proofs. By studying an intermediate model called long-range
hopping model, we also demonstrate that there is indeed a deep relation between
these two seemingly different approaches to ferromagnetism.
  We further discuss some attempts to go beyond these approaches. We briefly
discuss recent rigorous example of ferromagnetism in the Hubbard model which
has neither infinitely large parameters nor completely flat bands. We give
preliminary discussions about possible experimental realizations of the
(nearly-)flat-band ferromagnetism. Finally we focus on some theoretical
attempts to understand metallic ferromagnetism. We discuss three artificial
one-dimensional models in which the existence of metallic ferromagnetism can be
easily proved.",9712219v3
2010-12-01,The second order dense ferromagnetic-ferromagnetic phase transition,"The fcc spin-1 Ising (BEG) model has a dense ferromagnetic ($df$) ground
state instead of the ferromagnetic ground state at low temperature region and
exhibits the dense ferromagnetic ($df$) - ferromagnetic ($F$) phase transition
for $d=D/J=2.9$, $k=K/J=-0.5$, $\ell =L/J=0$ and $h=H/J=0$. The critical
behavior of the dense ferromagnetic ($df$) - ferromagnetic ($F$) phase
transition has been investigated using the cellular automaton cooling and
heating algorithms. The universality class and the type of the dense
ferromagnetic ($df$) - ferromagnetic ($F$) phase transition have been
researched within the framework of the finite - size scaling, the power law
relations and the probability distribution. The results show that the dense
ferromagnetic- ferromagnetic phase transition is of the second order and the
model shows universal second order Ising critical behavior at $d=2.9$ parameter
value through $k=-0.5$ line.",1012.0195v1
1997-12-15,Spin Tunneling in Conducting Oxides,"Direct tunneling in ferromagnetic junctions is compared with
impurity-assisted, surface state assisted, and inelastic contributions to a
tunneling magnetoresistance (TMR). Theoretically calculated direct tunneling in
iron group systems leads to about a 30% change in resistance, which is close to
experimentally observed values. It is shown that the larger observed values of
the TMR might be a result of tunneling involving surface polarized states. We
find that tunneling via resonant defect states in the barrier radically
decreases the TMR (down to 4% with Fe-based electrodes), and a resonant tunnel
diode structure would give a TMR of about 8%. With regards to inelastic
tunneling, magnons and phonons exhibit opposite effects: one-magnon emission
generally results in spin mixing and, consequently, reduces the TMR, whereas
phonons are shown to enhance the TMR. The inclusion of both magnons and phonons
reasonably explains an unusual bias dependence of the TMR.
  The model presented here is applied qualitatively to half-metallics with 100%
spin polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO$_2$/TiO$_2$ and CrO$_2$/RuO$_2$, and an account of their peculiar band
structures is presented. The implications and relation of these systems to CMR
materials which are nearly half-metallic, are discussed.",9712170v2
2000-04-26,Many-polaron system confined to a quantum dot: ground-state energy and optical absorption,"We find for the first time the ground state energy and the optical absorption
spectra for N electrons (holes) interacting with each other and with the
longitudinal optical (LO) phonons at an arbitrary electron-phonon coupling
strength $\alpha$ in a parabolic confinement potential. A recently developed
path integral formalism for identical particles is used in order to account for
the fermion statistics. The approach is applicable to closed and open shells.
Using an extension of the Jensen-Feynman variational principle, the ground
state energy of the N-polarons system in a parabolic confinement potential is
analyzed as a function of N and $\alpha$. A ferromagnetic-to-nonmagnetic
transition is shown to occur between states with different total spin of the
system in the case of strong electron-phonon interaction. This transition is
manifested through the optical absorption spectra and should be experimentally
observable. Strong mixing between zero-phonon and one-phonon states is revealed
in the optical absorption spectrum, when the confinement frequency parameter is
in resonance with the LO phonon frequency (""confinement-phonon resonance"").
Moments of the optical absorption spectra are calculated for a N-polaron system
in a parabolic quantum dot.",0004450v1
2002-07-10,Absence of First-order Transition and Tri-critical Point in the Dynamic Phase Diagram of a Spatially Extended Bistable System in an Oscillating Field,"It has been well established that spatially extended, bistable systems that
are driven by an oscillating field exhibit a nonequilibrium dynamic phase
transition (DPT). The DPT occurs when the field frequency is on the order of
the inverse of an intrinsic lifetime associated with the transitions between
the two stable states in a static field of the same magnitude as the amplitude
of the oscillating field. The DPT is continuous and belongs to the same
universality class as the equilibrium phase transition of the Ising model in
zero field [G. Korniss et al., Phys. Rev. E 63, 016120 (2001); H. Fujisaka et
al., Phys. Rev. E 63, 036109 (2001)]. However, it has previously been claimed
that the DPT becomes discontinuous at temperatures below a tricritical point
[M. Acharyya, Phys. Rev. E 59, 218 (1999)]. This claim was based on
observations in dynamic Monte Carlo simulations of a multipeaked probability
density for the dynamic order parameter and negative values of the fourth-order
cumulant ratio. Both phenomena can be characteristic of discontinuous phase
transitions. Here we use classical nucleation theory for the decay of
metastable phases, together with data from large-scale dynamic Monte Carlo
simulations of a two-dimensional kinetic Ising ferromagnet, to show that these
observations in this case are merely finite-size effects. For sufficiently
small systems and low temperatures, the continuous DPT is replaced, not by a
discontinuous phase transition, but by a crossover to stochastic resonance. In
the infinite-system limit the stochastic-resonance regime vanishes, and the
continuous DPT should persist for all nonzero temperatures.",0207275v1
2003-04-18,Electronic States and Cyclotron Resonance in n-type InMnAs,"We present a theory for electronic and magneto-optical properties of n-type
In(1-x)Mn(x)As magnetic alloy semiconductors in a high magnetic field, B. We
use an 8-band Pidgeon-Brown model generalized to include the wavevector (Kz)
dependence of the electronic states as well as s-d and p-d exchange
interactions with localized Mn d-electrons. Calculated conduction-band Landau
levels exhibit effective masses and g factors that are strongly dependent on
temperature, magnetic field, Mn concentration (x), and Kz. Cyclotron resonance
(CR) spectra are computed using Fermi's golden rule and compared with
ultrahigh-magnetic-field (> 50 T) CR experiments, which show that the electron
CR peak position is sensitive to x. Detailed comparison between theory and
experiment allowed us to extract s-d and p-d exchange parameters, alpha and
beta. we find that not only alpha but also beta affects the electron mass
because of the strong interband coupling in this narrow gap semiconductor. In
addition, we derive analytical expressions for the effective masses and g
facors within the 8-band model. Results indicate that (alpha - beta) is the
crucial parameter that determines the exchange interaction correction to the
cyclotron masses. These findings sould be useful for designing novel devices
based on ferromagnetic semiconductors.",0304434v3
2004-03-18,"Three-terminal transport through a quantum dot in the Kondo regime: Conductance, dephasing, and current-current correlations","We investigate the nonequilibrium transport properties of a three-terminal
quantum dot in the strongly interacting limit. At low temperatures, a Kondo
resonance arises from the antiferromagnetic coupling between the localized
electron in the quantum dot and the conduction electrons in source and drain
leads. It is known that the local density of states is accessible through the
differential conductance measured at the (weakly coupled) third lead. Here, we
consider the multiterminal current-current correlations (shot noise and cross
correlations measured at two different terminals). We discuss the dependence of
the current correlations on a number of external parameters: bias voltage,
magnetic field and magnetization of the leads. When the Kondo resonance is
split by fixing the voltage bias between two leads, the shot noise shows a
nontrivial dependence on the voltage applied to the third lead. We show that
the cross correlations of the current are more sensitive than the conductance
to the appearance of an external magnetic field. When the leads are
ferromagnetic and their magnetizations point along opposite directions, we find
a reduction of the cross correlations. Moreover, we report on the effect of
dephasing in the Kondo state for a two-terminal geometry when the third lead
plays the role of a fictitious voltage probe.",0403485v2
2006-02-09,Magnetization damping in polycrystalline Co ultra-thin films: Evidence for non-local effects,"The magnetic properties and magnetization dynamics of polycrystalline
ultra-thin Co layers were investigated using a broadband ferromagnetic
resonance (FMR) technique at room temperature. A variable thickness (1 nm $\leq
t \leq$ 10 nm) Co layer is sandwiched between 10 nm thick Cu layers (10 nm Cu|
t Co|10 nm Cu), while materials in contact with the Cu outer interfaces are
varied to determine their influence on the magnetization damping. The resonance
field and the linewidth were studied for in-plane magnetic fields in field
swept experiments at a fixed frequency, from 4 to 25 GHz. The Co layers have a
lower magnetization density than the bulk, and an interface contribution to the
magnetic anisotropy normal to the film plane. The Gilbert damping, as
determined from the frequency dependence of the linewidth, increases with
decreasing Co layer thickness for films with outer Pt layers. This enhancement
is not observed in structures without Pt layers. The result can be understood
in terms of a non-local contribution to the damping due to spin pumping from Co
through the Cu layer and spin relaxation in Pt layers. Pt layers just 1.5 nm
thick are found to be sufficient to enhance the damping and thus act as
efficient ""spin-sinks"". In structures with Pt outer layers, this non-local
contribution to the damping becomes predominant when the Co layer is thinner
than 4 nm.",0602243v2
2006-10-25,Ballistic spin field-effect transistors: Multichannel effects,"We study a ballistic spin field-effect transistor (SFET) with special
attention to the issue of multi-channel effects. The conductance modulation of
the SFET as a function of the Rashba spin-orbit coupling strength is
numerically examined for the number of channels ranging from a few to close to
100. Even with the ideal spin injector and collector, the conductance
modulation ratio, defined as the ratio between the maximum and minimum
conductances, decays rapidly and approaches one with the increase of the
channel number. It turns out that the decay is considerably faster when the
Rashba spin-orbit coupling is larger. Effects of the electronic coherence are
also examined in the multi-channel regime and it is found that the coherent
Fabry-Perot-like interference in the multi-channel regime gives rise to a
nested peak structure. For a nonideal spin injector/collector structure, which
consists of a conventional metallic ferromagnet-thin insulator-2DEG
heterostructure, the Rashba-coupling-induced conductance modulation is strongly
affected by large resonance peaks that arise from the electron confinement
effect of the insulators. Finally scattering effects are briefly addressed and
it is found that in the weakly diffusive regime, the positions of the resonance
peaks fluctuate, making the conductance modulation signal sample-dependent.",0610685v2
2007-02-26,Electrical switching of vortex core in a magnetic disk,"A magnetic vortex is a curling magnetic structure realized in a ferromagnetic
disk, which is a promising candidate of a memory cell for future nonvolatile
data storage devices. Thus, understanding of the stability and dynamical
behaviour of the magnetic vortex is a major requirement for developing magnetic
data storage technology. Since the experimental proof of the existence of a
nanometre-scale core with out-of-plane magnetisation in the magnetic vortex,
the dynamics of a vortex has been investigated intensively. However, the way to
electrically control the core magnetisation, which is a key for constructing a
vortex core memory, has been lacking. Here, we demonstrate the electrical
switching of the core magnetisation by utilizing the current-driven resonant
dynamics of the vortex; the core switching is triggered by a strong dynamic
field which is produced locally by a rotational core motion at a high speed of
several hundred m/s. Efficient switching of the vortex core without magnetic
field application is achieved thanks to resonance. This opens up the
potentiality of a simple magnetic disk as a building block for spintronic
devices like a memory cell where the bit data is stored as the direction of the
nanometre-scale core magnetisation.",0702589v1
2009-09-28,Magnetic properties and spin dynamics in single molecule paramagnets Cu6Fe and Cu6Co,"The magnetic properties and the spin dynamics of two molecular magnets have
been investigated by magnetization and d.c. susceptibility measurements,
Electron Paramagnetic Resonance (EPR) and proton Nuclear Magnetic Resonance
(NMR) over a wide range of temperature (1.6-300K) at applied magnetic fields,
H=0.5 and 1.5 Tesla. The two molecular magnets consist of
CuII(saldmen)(H2O)}6{FeIII(CN)6}](ClO4)38H2O in short Cu6Fe and the analog
compound with cobalt, Cu6Co. It is found that in Cu6Fe whose magnetic core is
constituted by six Cu2+ ions and one Fe3+ ion all with s=1/2, a weak
ferromagnetic interaction between Cu2+ moments through the central Fe3+ ion
with J = 0.14 K is present, while in Cu6Co the Co3+ ion is diamagnetic and the
weak interaction is antiferromagnetic with J = -1.12 K. The NMR spectra show
the presence of non equivalent groups of protons with a measurable contact
hyperfine interaction consistent with a small admixture of s-wave function with
the d-function of the magnetic ion. The NMR relaxation results are explained in
terms of a single ion (Cu2+, Fe3+, Co3+) uncorrelated spin dynamics with an
almost temperature independent correlation time due to the weak magnetic
exchange interaction. We conclude that the two molecular magnets studied here
behave as single molecule paramagnets with a very weak intramolecular
interaction, almost of the order of the dipolar intermolecular interaction.
Thus they represent a new class of molecular magnets which differ from the
single molecule magnets investigated up to now, where the intramolecular
interaction is much larger than the intermolecular one.",0909.5063v1
2011-01-04,Universal Spin Transport in a Strongly Interacting Fermi Gas,"Transport of fermions is central in many fields of physics. Electron
transport runs modern technology, defining states of matter such as
superconductors and insulators, and electron spin, rather than charge, is being
explored as a new carrier of information [1]. Neutrino transport energizes
supernova explosions following the collapse of a dying star [2], and
hydrodynamic transport of the quark-gluon plasma governed the expansion of the
early Universe [3]. However, our understanding of non-equilibrium dynamics in
such strongly interacting fermionic matter is still limited. Ultracold gases of
fermionic atoms realize a pristine model for such systems and can be studied in
real time with the precision of atomic physics [4, 5]. It has been established
that even above the superfluid transition such gases flow as an almost perfect
fluid with very low viscosity [3, 6] when interactions are tuned to a
scattering resonance. However, here we show that spin currents, as opposed to
mass currents, are maximally damped, and that interactions can be strong enough
to reverse spin currents, with opposite spin components reflecting off each
other. We determine the spin drag coeffcient, the spin diffusivity, and the
spin susceptibility, as a function of temperature on resonance and show that
they obey universal laws at high temperatures. At low temperatures, the spin
diffusivity approaches a minimum value set by the ratio of the reduced Planck's
constant to the atomic mass. For repulsive interactions, our measurements
appear to exclude a metastable ferromagnetic state [7-9].",1101.0780v1
2011-03-09,Kramers polarization in strongly correlated carbon nanotube quantum dots,"Ferromagnetic contacts put in proximity with carbon nanotubes induce spin and
orbital polarizations. These polarizations affect dramatically the Kondo
correlations occurring in quantum dots formed in a carbon nanotube, inducing
effective fields in both spin and orbital sectors. As a consequence, the carbon
nanotube quantum dot spectral density shows a four-fold split SU(4) Kondo
resonance. Furthermore, the presence of spin-orbit interactions leads to the
occurrence of an additional polarization among time-reversal electronic states
(polarization in the time-reversal symmetry or Kramers sector). Here, we
estimate the magnitude for the Kramer polarization in realistic carbon nanotube
samples and find that its contribution is comparable to the spin and orbital
polarizations. The Kramers polarization generates a new type of effective field
that affects only the time-reversal electronic states. We report new splittings
of the Kondo resonance in the dot spectral density which can be understood only
if Kramers polarization is taken into account. Importantly, we predict that the
existence of Kramers polarization can be experimentally detected by performing
nonlinear differential conductance measurements. We also find that, due to the
high symmetry required to build SU(4) Kondo correlations, its restoration by
applying an external field is not possible in contrast to the compensated SU(2)
Kondo state observed in conventional quantum dots.",1103.1836v1
2012-06-05,"Underscreened Kondo effect in S=1 magnetic quantum dots: Exchange, anisotropy and temperature effects","We present a theoretical analysis of the effects of uniaxial magnetic
anisotropy and contact-induced exchange field on the underscreened Kondo effect
in S=1 magnetic quantum dots coupled to ferromagnetic leads. First, by using
the second-order perturbation theory we show that the coupling to
spin-polarized electrode results in an effective exchange field $B_{\rm eff}$
and an effective magnetic anisotropy $D_{\rm eff}$. Second, we confirm these
findings by using the numerical renormalization group method, which is employed
to study the dependence of the quantum dot spectral functions, as well as
quantum dot spin, on various parameters of the system. We show that the
underscreened Kondo effect is generally suppressed due to the presence of
effective exchange field and can be restored by tuning the anisotropy constant,
when $|D_{\rm eff}| = |B_{\rm eff}|$. The Kondo effect can also be restored by
sweeping an external magnetic field, and the restoration occurs twice in a
single sweep. From the distance between the restored Kondo resonances one can
extract the information about both the exchange field and the effective
anisotropy. Finally, we calculate the temperature dependence of linear
conductance for the parameters where the Kondo effect is restored and show that
the restored Kondo resonances display a universal scaling of $S=1/2$ Kondo
effect.",1206.1034v2
2013-04-10,Magnetization and spin dynamics of the spin S=1/2 hourglass nanomagnet Cu5(OH)2(NIPA)4*10H2O,"We report a combined experimental and theoretical study of the spin S=1/2
nanomagnet Cu5(OH)2(NIPA)4*10H2O (Cu5-NIPA). Using thermodynamic, electron spin
resonance and 1H nuclear magnetic resonance measurements on one hand, and ab
initio density-functional band-structure calculations, exact diagonalizations
and a strong coupling theory on the other, we derive a microscopic magnetic
model of Cu5-NIPA and characterize the spin dynamics of this system. The
elementary five-fold Cu2+ unit features an hourglass structure of two
corner-sharing scalene triangles related by inversion symmetry. Our microscopic
Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange
couplings in each triangle, stabilizing a single spin S=1/2 doublet ground
state (GS), with an exactly vanishing zero-field splitting (by Kramer's
theorem), and a very large excitation gap of \Delta~68 K. Thus, Cu5-NIPA is a
good candidate for achieving long electronic spin relaxation (T1) and coherence
(T2) times at low temperatures, in analogy to other nanomagnets with low-spin
GS's. Of particular interest is the strongly inhomogeneous distribution of the
GS magnetic moment over the five Cu2+ spins. This is a purely
quantum-mechanical effect since, despite the non-frustrated nature of the
magnetic couplings, the GS is far from the classical collinear ferrimagnetic
configuration. Finally, Cu5-NIPA is a rare example of a S=1/2 nanomagnet
showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at
intermediate temperatures.",1304.2826v1
2013-05-12,Spin Pumping and Inverse Spin Hall Effect in Germanium,"We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room
temperature. The spin current in germanium was generated by spin pumping from a
CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch
issue. A clear electromotive force was measured in Ge at the ferromagnetic
resonance of CoFeB. The same study was then carried out on several test
samples, in particular we have investigated the influence of the MgO tunnel
barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO
bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to
anisotropic magnetoresistance and anomalous Hall effect which is dominated by
an asymmetric contribution with respect to the resonance field. We also found
that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample
annealing systematically lead to an increase of the signal. We propose a
theoretical model based on the presence of localized states at the interface
between the MgO tunnel barrier and Ge to account for these observations.
Finally, all of our results are fully consistent with the observation of ISHE
in heavily doped $n$-Ge and we could estimate the spin Hall angle at room
temperature to be $\approx$0.001.",1305.2602v1
2014-02-15,Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt,"We report on an experimental study on the spin-waves relaxation rate in two
series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of
two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser
deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance
force microscope, we measure precisely the ferromagnetic resonance linewidth of
each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth
in the nanostructure is sensibly smaller than the one measured in the extended
film. Analysis of the frequency dependence of the spectral linewidth indicates
that the improvement is principally due to the suppression of the inhomogeneous
part of the broadening due to geometrical confinement, suggesting that only the
homogeneous broadening contributes to the linewidth of the nanostructure. For
the bare YIG nano-disks, the broadening is associated to a damping constant
$\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for
the series with Pt cap layer, attributed to the spin pumping effect. The
measured enhancement allows to extract the spin mixing conductance found to be
$G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our
YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the
design of YIG based nanostructures with optimized magnetic losses.",1402.3630v1
2015-08-13,Observation by resonant angle-resolved photoemission of a critical thickness for 2-dimensional electron gas formation in SrTiO$_3$ embedded in GdTiO$_3$,"For certain conditions of layer thickness, the interface between GdTiO$_3$
(GTO) and SrTiO$_3$ (STO) in multilayer samples has been found to form a
two-dimensional electron gas (2DEG) with very interesting properties including
high mobilities and ferromagnetism. We have here studied two trilayer samples
of the form [2 nm GTO/1.0 or 1.5 unit cells STO/10 nm GTO] as grown on (001)
(LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ (LSAT), with the STO layer
thicknesses being at what has been suggested is the critical thickness for 2DEG
formation. We have studied these with Ti-resonant angle-resolved (ARPES) and
angle-integrated photoemission and find that the spectral feature in the
spectra associated with the 2DEG is present in the 1.5 unit cell sample, but
not in the 1.0 unit cell sample. We also observe through core-level spectra
additional states in Ti and Sr, with the strength of a low-binding-energy state
for Sr being associated with the appearance of the 2DEG, and we suggest it to
have an origin in final-state core-hole screening.",1508.03324v3
2015-08-26,Thermodynamics and dynamics of atomic self-organization in an optical cavity,"Pattern formation of atoms in high-finesse optical resonators results from
the mechanical forces of light associated with superradiant scattering into the
cavity mode. It occurs when the laser intensity exceeds a threshold value, such
that the pumping processes counteract the losses. We consider atoms driven by a
laser and coupling with a mode of a standing-wave cavity and describe their
dynamics with a Fokker-Planck equation, in which the atomic motion is
semiclassical but the cavity field is a full quantum variable. The asymptotic
state of the atoms is a thermal state, whose temperature is solely controlled
by the detuning between the laser and the cavity frequency and by the cavity
loss rate. From this result we derive the free energy and show that in the
thermodynamic limit selforganization is a second-order phase transition. The
order parameter is the field inside the resonator, to which one can associate a
magnetization in analogy to ferromagnetism, the control field is the laser
intensity, however the steady state is intrinsically out-of-equilibrium. In the
symmetry-broken phase quantum noise induces jumps of the spatial density
between two ordered patterns: We characterize the statistical properties of
this temporal behaviour at steady state and show that the thermodynamic
properties of the system can be extracted by detecting the light at the cavity
output. The results of our analysis are in full agreement with previous
studies, extend them by deriving a self-consistent theory which is valid also
when the cavity field is in the shot-noise limit, and elucidate the nature of
the selforganization transition.",1508.06606v2
2016-03-09,Nonmagnetic band gap at the Dirac point of the magnetic topological insulator (Bi$_{1-x}$Mn$_x)_2$Se$_3$,"Magnetic doping is expected to open a band gap at the Dirac point of
topological insulators by breaking time-reversal symmetry and to enable novel
topological phases. Epitaxial (Bi$_{1-x}$Mn$_{x}$)$_{2}$Se$_{3}$ is a
prototypical magnetic topological insulator with a pronounced surface band gap
of $\sim100$ meV. We show that this gap is neither due to ferromagnetic order
in the bulk or at the surface nor to the local magnetic moment of the Mn,
making the system unsuitable for realizing the novel phases. We further show
that Mn doping does not affect the inverted bulk band gap and the system
remains topologically nontrivial. We suggest that strong resonant scattering
processes cause the gap at the Dirac point and support this by the observation
of in-gap states using resonant photoemission. Our findings establish a novel
mechanism for gap opening in topological surface states which challenges the
currently known conditions for topological protection.",1603.02881v1
2016-04-07,Localized and mixed valence state of Ce $4f$ in superconducting and ferromagnetic CeO$_{1-x}$F$_{x}$BiS$_{2}$ revealed by x-ray absorption and photoemission spectroscopy,"We have performed Ce $L_3$-edge x-ray absorption spectroscopy (XAS) and Ce
$4d$-$4f$ resonant photoemission spectroscopy (PES) on single crystals of
CeO$_{1-x}$F$_x$BiS$_2$ for $x=0.0$ and 0.5 in order to investigate the Ce $4f$
electronic states. In the Ce $L_3$-edge XAS, mixed valence of Ce was found in
the $x=0.0$ sample and the F-doping suppresses it, which is consistent with the
results on polycrystalline samples. As for the resonant PES, we found that the
Ce $4f$ electrons in both $x=0.0$ and $0.5$ systems respectively form a flat
band at 1.0 eV and 1.4 eV below the Fermi level and there is no contribution to
the Fermi surfaces. Interestingly, Ce valence in CeOBiS$_2$ deviates from
Ce$^{3+}$ even though Ce $4f$ electrons are localized, indicating the Ce
valence is not in a typical valence fluctuation regime. We assume that
localized Ce $4f$ in CeOBiS$_2$ is mixed with the unoccupied Bi $6p_z$, which
is consistent with the previous local structural study. Based on the analysis
of the Ce $L_3$-edge XAS spectra using Anderson's impurity model calculation,
we found that the transfer integral becomes smaller increasing the number of Ce
$4f$ electrons upon the F substitution for O.",1604.01880v3
2016-10-28,Insulating nanomagnets driven by spin torque,"Magnetic insulators, such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$), are
ideal materials for ultra-low power spintronics applications due to their low
energy dissipation and efficient spin current generation and transmission.
Recently, it has been realized that spin dynamics can be driven very
effectively in micrometer-sized Y$_3$Fe$_5$O$_{12}$/Pt heterostructures by
spin-Hall effects. We demonstrate here the excitation and detection of spin
dynamics in Y$_3$Fe$_5$O$_{12}$/Pt nanowires by spin-torque ferromagnetic
resonance. The nanowires defined via electron-beam lithography are fabricated
by conventional room temperature sputtering deposition on Gd$_3$Ga$_5$O$_{12 }$
substrates and lift-off. We observe field-like and anti-damping-like torques
acting on the magnetization precession, which are due to simultaneous
excitation by Oersted fields and spin-Hall torques. The Y$_3$Fe$_5$O$_{12}$/Pt
nanowires are thoroughly examined over a wide frequency and power range. We
observe a large change in the resonance field at high microwave powers, which
is attributed to a decreasing effective magnetization due to microwave
absorption. These heating effects are much more pronounced in the investigated
nanostructures than in comparable micron-sized samples. By comparing different
nanowire widths, the importance of geometrical confinements for magnetization
dynamics becomes evident: quantized spin-wave modes across the width of the
wires are observed in the spectra. Our results are the first stepping stones
toward the realization of integrated magnonic logic devices based on
insulators, where nanomagnets play an essential role.",1610.09360v1
2017-02-06,Evidence for a Field-induced Quantum Spin Liquid in $α$-RuCl$_3$,"We report a $^{35}$Cl nuclear magnetic resonance study in the honeycomb
lattice, $\alpha$-RuCl$_3$, a material that has been suggested to potentially
realize a Kitaev quantum spin liquid (QSL) ground state. Our results provide
direct evidence that $\alpha$-RuCl$_3$ exhibits a magnetic field-induced QSL.
For fields larger than $\sim 10$ T a spin-gap opens up while resonance lines
remain sharp, evidencing that spins are quantum disordered and locally
fluctuating. The spin gap increases linearly with increasing magnetic field,
reaching $\sim50$ K at 15 T, and is nearly isotropic with respect to the field
direction. The unusual rapid increase of the spin gap with increasing field and
its isotropic nature are incompatible with conventional magnetic ordering and
in particular exclude that the ground state is a fully polarized ferromagnet.
The presence of such a field-induced, gapped QSL phase has indeed been
predicted in the Kitaev model.",1702.01671v3
2017-01-09,Spin-Wave Modes in Transition from a Thin Film to a Full Magnonic Crystal,"Spin-wave modes are studied under the gradual transition from a flat thin
film to a 'full' (one-dimensional) magnonic crystal. For this purpose, the
surface of a pre-patterned 36.8 nm thin permalloy film was sequentially ion
milled resulting in magnonic hybrid structures, referred to as
surface-modulated magnonic crystals, with increasing modulation depth. After
each etching step, ferromagnetic resonance measurements were performed yielding
the spin-wave resonance modes in backward-volume and Damon-Eshbach geometry.
The spin-wave spectra of these hybrid systems reveal an even larger variety of
spin-wave states compared to the 'full' magnonic crystal. The measurements are
corroborated by quasi-analytical theory and micromagnetic simulations in order
to study the changing spin-wave mode character employing spin-wave mode
profiles. In backward-volume geometry, a gradual transition from the uniform
mode in the film limit to a fundamental mode in the thin part of the magnonic
crystal was observed. Equivalently, the first and the second film modes are
transform into a center and an edge mode of the thick part of the magnonic
crystal. Simple transition rules from the $n^{\mathrm{th}}$ film mode to the
$m^{\mathrm{th}}$ mode in the 'full' magnonic crystal are formulated unraveling
the complex mode structure particularly in the backward-volume geometry. An
analogous analysis was performed in the Damon-Eshbach geometry.",1702.05675v3
2017-02-27,Magnetic properties of strained multiferroic CoCr2O4: a soft X-ray study,"Using resonant soft X-ray techniques we follow the magnetic behavior of a
strained epitaxial film of CoCr2O4, a type-II multiferroic. The film is
[110]-oriented, such that both the ferroelectric and ferromagnetic moments can
coexist in plane. X-ray magnetic circular dichroism (XMCD) is used in
scattering and in transmission modes to probe the magnetization of Co and Cr
separately. The transmission measurements utilized X-ray excited optical
luminescence from the substrate. Resonant soft X-ray diffraction (RSXD) was
used to study the magnetic order of the low temperature phase. The XMCD signals
of Co and Cr appear at the same ordering temperature Tc~90K, and are always
opposite in sign. The coercive field of the Co and of Cr moments is the same,
and is approximately two orders of magnitude higher than in bulk. Through sum
rules analysis an enlarged Co2+ orbital moment (m_L) is found, which can
explain this hardening. The RSXD signal of the (q q 0) reflection appears below
Ts, the same ordering temperature as the conical magnetic structure in bulk,
indicating that this phase remains multiferroic under strain. To describe the
azimuthal dependence of this reflection, a slight modification is required to
the spin model proposed by the conventional Lyons-Kaplan-Dwight-Menyuk theory
for magnetic spinels. Lastly, a slight increase in reflected intensity is
observed below Ts=27K when measuring at the Cr edge (but not at the Co edge).",1702.08541v1
2017-08-21,Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering,"We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30
multilayer with ultrathin Fe layers and nominal thickness of the chromium
spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation.
The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has
been detected at zero external field. The joint fit of the reflectivity curves
and Mossbauer spectra of reflectivity measured near the critical angle and at
the ""magnetic"" peak reveals that the magnetic structure of the multilayer is
formed by two spirals, one in the odd and another one in the even iron layers,
with the opposite signs of rotation. The double-spiral structure starts from
the surface with the almost antiferromagnetic alignment of the adjacent Fe
layers. The rotation of the two spirals leads to nearly ferromagnetic alignment
of the two magnetic subsystems at some depth, where the sudden turn of the
magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to
rotate in opposite directions. The observation of this unusual double-spiral
magnetic structure suggests that the unique properties of giant
magneto-resistance devices can be further tailored using ultrathin magnetic
layers.",1708.06269v1
2018-04-17,Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy,"Resonant ultrasound spectroscopy and magnetic susceptibility experiments have
been used to characterize strain coupling phenomena associated with structural
and magnetic properties of the shape-memory Heusler alloy series
Ni$_{50+x}$Mn$_{25-x}$Ga$_{25}$ ($x=0$, 2.5, 5.0, and 7.5). All samples exhibit
a martensitic transformation at temperature $T_M$ and ferromagnetic ordering at
temperature $T_C$, while the pure end member ($x=0$) also has a premartensitic
transition at $T_{PM}$, giving four different scenarios: $T_C>T_{PM}>T_M$,
$T_C>T_M$ without premartensitic transition, $T_C\approx T_M$, and $T_C<T_M$.
Fundamental differences in elastic properties i.e., stiffening versus
softening, are explained in terms of coupling of shear strains with three
discrete order parameters relating to magnetic ordering, a soft mode and the
electronic instability responsible for the large strains typical of martensitic
transitions. Linear-quadratic or biquadratic coupling between these order
parameters, either directly or indirectly via the common strains, is then used
to explain the stabilities of the different structures. Acoustic losses are
attributed to critical slowing down at the premartensite transition, to the
mobility of interphases between coexisting phases at the martensitic transition
and to mobility of some aspect of the twin walls under applied stress down to
the lowest temperatures at which measurements were made.",1804.06183v1
2020-07-06,Ferrimagnetism in EuFe4As12 revealed by 153Eu NMR and 75As NQR measurements,"Filled skutterudite compound EuFe$_4$As$_{12}$ shows the highest magnetic
ordering temperature of $T_{\rm C}$ = 154 K among Eu-based skutterudite
compounds, but its magnetic ground state has not been determined yet. Here, we
performed $^{153}$Eu nuclear magnetic resonance (NMR) and $^{75}$As nuclear
quadrupole resonance (NQR) measurements on EuFe$_4$As$_{12}$ to reveal its
magnetic ground state as well as the physical properties from a microscopic
point of view. From the temperature and magnetic field dependence of $^{153}$Eu
NMR spectrum in the magnetically ordered state, we found that the Eu ions are
in Eu$^{2+}$ state with a nearly 7 $\mu_{\rm B}$ corresponding to $S$ = 7/2
spins. Combined with the magnetization measurements which show the reduced
saturation moments of 4.5 $\mu_{\rm B}$/f.u., we determined the ground magnetic
structure in EuFe$_4$As$_{12}$ to be ferrimagnetic where the Eu$^{2+}$ 4$f$ and
the Fe 3$d$ ordered moments are ferromagnetically aligned in each sublattice
but the moments between the sublattices are antiferromagnetically aligned. We
also found the local distortion at the Eu site from the cubic symmetry in the
magnetically ordered state. The relationship between the rattling motion of Eu
atoms and the local symmetry of the Eu ions is discussed. From the $^{75}$As
NQR nuclear spin-lattice relaxation time measurements as well as $^{153}$Eu NMR
measurements, we found that the 4$f$ electrons of the Eu ions are well
described by the local moment picture in both the magnetic and paramagnetic
metallic states.",2007.02983v1
2010-05-25,"Structural, static and dynamic magnetic properties of CoMnGe thin films on a sapphire a-plane substrate","Magnetic properties of CoMnGe thin films of different thicknesses (13, 34,
55, 83, 100 and 200 nm), grown by RF sputtering at 400{\deg}C on single crystal
sapphire substrates, were studied using vibrating sample magnetometry (VSM) and
conventional or micro-strip line (MS) ferromagnetic resonance (FMR). Their
behavior is described assuming a magnetic energy density showing twofold and
fourfold in-plane anisotropies with some misalignment between their principal
directions. For all the samples, the easy axis of the fourfold anisotropy is
parallel to the c-axis of the substrate while the direction of the twofold
anisotropy easy axis varies from sample to sample and seems to be strongly
influenced by the growth conditions. Its direction is most probably monitored
by the slight unavoidable angle of miscut the Al2O3 substrate. The twofold
in-plane anisotropy field is almost temperature independent, in contrast with
the fourfold field which is a decreasing function of the temperature. Finally,
we study the frequency dependence of the observed line-width of the resonant
mode and we conclude to a typical Gilbert damping constant of 0.0065 for the
55-nm-thick film.",1005.4595v3
2013-08-29,Slaving of the magnetic moment canting to the correlated oxygen rotation in Sr2IrO4 revealed by X-ray resonant scattering,"Sr2IrO4 is a prototype of the class of Mott insulators in the strong
spin-orbit interaction (SOI) limit described by a $J_{\mathrm{eff}}=1/2$ ground
state. In Sr2IrO4, the strong SOI is predicted to manifest itself in the
slaving of the canting of the magnetic moments to the correlated rotation by
11.8(1)$^{\circ}$ of the oxygen octahedra that characterizes its distorted
layered perovskite structure. Using X-ray resonant scattering at the Ir $L_3$
edge we have measured accurately the intensities of Bragg peaks arising from
different components of the magnetic structure. From a careful comparison of
integrated intensities of peaks due to basal-plane antiferromagnetism, with
those due to b-axis ferromagnetism, we deduce a canting of the magnetic moments
of 12.2(8)$^{\circ}$. We thus confirm that in Sr2IrO4 the magnetic moments
rigidly follow the rotation of the oxygen octahedra, indicating that, even in
the presence of significant non-cubic structural distortions, it is a close
realization of the $J_{\mathrm{eff}}=1/2$ state",1308.6460v2
2016-11-23,X-ray imaging of spin currents and magnetisation dynamics at the nanoscale,"Understanding how spins move in time and space is the aim of both fundamental
and applied research in modern magnetism. Over the past three decades, research
in this field has led to technological advances that have had a major impact on
our society, while improving the understanding of the fundamentals of spin
physics. However, important questions still remain unanswered, because it is
experimentally challenging to directly observe spins and their motion with a
combined high spatial and temporal resolution. In this article, we present an
overview of the recent advances in X-ray microscopy that allow researchers to
directly watch spins move in time and space at the microscopically relevant
scales. We discuss scanning X-ray transmission microscopy (STXM) at resonant
soft X-ray edges, which is available at most modern synchrotron light sources.
This technique measures magnetic contrast through the X-ray magnetic circular
dichroism (XMCD) effect at the resonant absorption edges, while focusing the
X-ray radiation at the nanometre scale, and using the intrinsic pulsed
structure of synchrotron-generated X-rays to create time-resolved images of
magnetism at the nanoscale. In particular, we discuss how the presence of spin
currents can be detected by imaging spin accumulation, and how the
magnetisation dynamics in thin ferromagnetic films can be directly imaged. We
discuss how a direct look at the phenomena allows for a deeper understanding of
the the physics at play, that is not accessible to other, more indirect
techniques. Finally, we present an overview of the exciting opportunities that
lie ahead to further understand the fundamentals of novel spin physics,
opportunities offered by the appearance of diffraction limited storage rings
and free electron lasers.",1611.07691v2
2011-11-15,Spin waves in nanosized magnetic films,"We have studied spin excitations in nanosized magnetic films in the
Heisenberg model with magnetic dipole and exchange interactions by the spin
operator diagram technique. Dispersion relations of spin waves in thin magnetic
films (in two-dimensional magnetic monolayers and in two-layer magnetic films)
and the spin-wave resonance spectrum in N-layer structures are found. For thick
magnetic films generalized Landau-Lifshitz equations are derived from first
principles. Landau-Lifshitz equations have the integral (pseudodifferential)
form, but not differential one. Spin excitations are determined by simultaneous
solution of the Landau-Lifshitz equations and the equation for the
magnetostatic potential. For normal magnetized ferromagnetic films the spin
wave damping has been calculated in the one-loop approximation for a diagram
expansion of the Green functions at low temperature. In thick magnetic films
the magnetic dipole interaction makes a major contribution to the relaxation of
long-wavelength spin waves. Thin films have a region of low relaxation of
long-wavelength spin waves. In thin magnetic films four-spin-wave processes
take place and the exchange interaction makes a major contribution to the
damping. It is found that the damping of spin waves propagating in magnetic
monolayer is proportional to the quadratic dependence on the temperature and is
very low for spin waves with small wavevectors. Spin-wave devices on the base
of nanosized magnetic films are proposed -- tunable narrow-band spin-wave
filters with high quality at the microwave frequency range and field-effect
transistor (FET) structures contained nanosized magnetic films under the gate
electrode. Spin-wave resonances in nanosized magnetic films can be used to
construct FET structures operating in Gigahertz and Terahertz frequency bands.",1111.3532v1
2011-11-22,Microstructural magnetic phases in superconducting FeTe0.65Se0.35,"In this paper, we address a number of outstanding issues concerning the
nature and the role of magnetic inhomogenities in the iron chalcogenide system
FeTe1-xSex and their correlation with superconductivity in this system. We
report morphology of superconducting single crystals of FeTe0.65Se0.35 studied
with transmission electron microscopy, high angle annular dark field scanning
transmission electron microscopy and their magnetic and superconducting
properties characterized with magnetization, specific heat and magnetic
resonance spectroscopy. Our data demonstrate a presence of nanometre scale
hexagonal regions coexisting with tetragonal host lattice, a chemical disorder
demonstrating non homogeneous distribution of host atoms in the crystal
lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From
magnetic data and ferromagnetic resonance temperature dependence, we attribute
magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry
nanometre scale regions with structure of Fe7Se8 type. Our results suggest that
nonhomogeneous distribution of host atoms might be an intrinsic feature of
superconducting Fe-Te-Se chalcogenides and we find a surprising correlation
indicating that faster grown crystal of inferior crystallographic properties is
a better superconductor.",1111.5176v2
2012-01-13,"Interval identification of FMR parameters for spin reorientation transition in (Ga,Mn)As","In this work we report results of ferromagnetic resonance studies of a 6% 15
nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were
performed with in-plane oriented magnetic field, in the temperature range
between 5K and 120K. We observe a temperature induced reorientation of the
effective in-plane easy axis from [-110] to [110] direction close to the Curie
temperature. The behavior of magnetization is described by anisotropy fields,
H_{eff} (= 4\piM -H_{2\perp}), H_{2\parallel}, and H_{4\parallel}. In order to
precisely investigate this reorientation, numerical values of anisotropy fields
have been determined using powerful - but still largely unknown - interval
calculations. In simulation mode this approach makes possible to find all the
resonance fields for arbitrarily oriented sample, which is generally
intractable analytically. In 'fitting' mode we effectively utilize full
experimental information, not only those measurements performed in special,
distinguished directions, to reliably estimate the values of important physical
parameters as well as their uncertainties and correlations.",1201.2836v1
2016-08-02,RESPECT: Neutron Resonance Spin-Echo Spectrometer for Extreme Studies,"We propose the design of a Resonance SPin-echo spECtrometer for exTreme
studies, RESPECT, that is ideally suited for the exploration of non-dispersive
processes such as diffusion, crystallization, slow dynamics, tunneling
processes, crystal electric field excitations, and spin fluctuations. It is a
variant of the conventional neutron spin-echo technique (NSE) by i) replacing
the long precession coils by pairs of longitudinal neutron spin-echo coils
combined with RF-spin flippers and ii) by stabilizing the neutron polarization
with small longitudinal guide fields that can in addition be used as field
subtraction coils thus allowing to adjust the field integrals over a range of 8
orders of magnitude. Therefore, the dynamic range of RESPECT can in principle
be varied over 8 orders of magnitude in time, if neutrons with the required
energy are made available. Similarly as for existing NSE-spectrometers, spin
echo times of up to approximately 1 microsecond can be reached if the
divergence and the correction elements are properly adjusted. Thanks to the
optional use of neutron guides and the fact that the currents for the
correction coils are much smaller than in standard NSE, intensity gains of at
least one order of magnitude are expected , making the concept of RESPECT also
competitive for operation at medium flux neutron sources. RESPECT can also be
operated in a MIEZE configuration allowing the investigation of relaxation
processes in depolarizing environments as they occur when magnetic fields are
applied at the sample position, i.e. for the investigation of the dynamics of
flux lines in superconductors, magnetic fluctuations in ferromagnetic
materials, and samples containing hydrogen.",1608.00836v1
2017-07-10,Magnetic criticality-enhanced hybrid nanodiamond-thermometer under ambient conditions,"Nitrogen vacancy (NV) centres in diamond are attractive as quantum sensors
owing to their superb coherence under ambient conditions. However, the NV
centre spin resonances are relatively insensitive to some important parameters
such as temperature. Here we design and experimentally demonstrate a hybrid
nano-thermometer composed of NV centres and a magnetic nanoparticle (MNP), in
which the temperature sensitivity is enhanced by the critical magnetization of
the MNP near the ferromagnetic-paramagnetic transition temperature. The
temperature susceptibility of the NV center spin resonance reached 14 MHz/K,
enhanced from the value without the MNP by two orders of magnitude. The
sensitivity of a hybrid nano-thermometer composed of a Cu_{1-x}Ni_{x} MNP and a
nanodiamond was measured to be 11 mK/Hz^{1/2} under ambient conditions. With
such high-sensitivity, we monitored nanometer-scale temperature variation of
0.3 degree with a time resolution of 60 msec. This hybrid nano-thermometer
provides a novel approach to studying a broad range of thermal processes at
nanoscales such as nano-plasmonics, sub-cellular heat-stimulated processes,
thermodynamics of nanostructures, and thermal remanent magnetization of
nanoparticles.",1707.02885v1
2018-10-03,Magnetoresistance in Co-hBN-NiFe tunnel junctions enhanced by resonant tunneling through single defects in ultrathin hBN barriers,"Hexagonal boron nitride (hBN) is a prototypical high-quality two-dimensional
insulator and an ideal material to study tunneling phenomena, as it can be
easily integrated in vertical van der Waals devices. For spintronic devices,
its potential has been demonstrated both for efficient spin injection in
lateral spin valves and as a barrier in magnetic tunnel junctions (MTJs). Here
we reveal the effect of point defects inevitably present in mechanically
exfoliated hBN on the tunnel magnetoresistance of Co-hBN-NiFe MTJs. We observe
a clear enhancement of both the conductance and magnetoresistance of the
junction at well-defined bias voltages, indicating resonant tunneling through
magnetic (spin-polarized) defect states. The spin polarization of the defect
states is attributed to exchange coupling of a paramagnetic impurity in the
few-atomic-layer thick hBN to the ferromagnetic electrodes. This is confirmed
by excellent agreement with theoretical modelling. Our findings should be taken
into account in analyzing tunneling processes in hBN-based magnetic devices.
More generally, our study shows the potential of using atomically thin hBN
barriers with defects to engineer the magnetoresistance of MTJs and to achieve
spin filtering, opening the door towards exploiting the spin degree of freedom
in current studies of point defects as quantum emitters.",1810.01757v1
2018-10-16,Spin-wave-induced lateral temperature gradient in a YIG thin film/GGG system excited in an ESR cavity,"Lateral thermal gradient of an yttrium iron garnet (YIG) film under the
microwave application in the cavity of the electron spin resonance system (ESR)
was measured at room temperature by fabricating a Cu/Sb thermocouple onto it.
To date, thermal transport in YIG films caused by the Damon-Eshbach mode (DEM)
- the unidirectional spin-wave heat conveyer effect - was demonstrated only by
the excitation using coplanar waveguides. Here we show that effect exists even
under YIG excitation using the ESR cavity - tool often employed to realize spin
pumping. The temperature difference observed around the ferromagnetic resonance
(FMR) field under the 4 mW microwave power peaked at 13 mK. The observed
thermoelectric signal indicates the imbalance of the population between the
DEMs that propagate near the top and bottom surfaces of the YIG film. We
attribute the DEM population imbalance to the different magnetic damping near
the top and bottom YIG surfaces. Additionally, the spin wave dynamics of the
system were investigated using the micromagnetic simulations. The micromagnetic
simulations confirmed the existence of the DEM imbalance in the system with the
increased Gilbert damping at one of the YIG interfaces. The reported results
are indispensable for the quantitative estimation of the electromotive force in
the spin-charge conversion experiments using ESR cavities.",1810.06875v1
2018-10-16,Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor,"Coherent, self-sustained oscillation of magnetization in spin-torque
oscillators (STOs) is a promising source for on-chip, nanoscale generation of
microwave magnetic fields. Such fields could be used for local excitation of
spin-wave resonances, control of spin qubits, and studies of paramagnetic
resonance. However, local characterization of fields emitted by an STO has
remained an outstanding challenge. Here, we use the spin of a single
nitrogen-vacancy (NV) defect in diamond to probe the magnetic fields generated
by an STO in a microbar of ferromagnetic insulator yttrium-iron-garnet (YIG).
The combined spectral resolution and sensitivity of the NV sensor allows us to
resolve multiple spin-wave modes and characterize their damping. When damping
is decreased sufficiently via spin injection, the modes auto-oscillate, as
indicated by a strongly reduced linewidth, a diverging magnetic power spectral
density, and synchronization of the STO frequency to an external microwave
source. These results open the way for quantitative, nanoscale mapping of the
microwave signals generated by STOs, as well as harnessing STOs as local probes
of mesoscopic spin systems.",1810.07306v1
2019-10-19,Anomalies in the switching dynamics of C-type antiferromagnets and antiferromagnetic nanowires,"Antiferromagnets (AFMs) are widely believed to be superior than ferromagnets
in spintronics because of their high stability due to the vanishingly small
stray field. It is thus expected that the order parameter of AFM should always
align along the easy-axis of the crystalline anisotropy. In contrast to this
conventional wisdom, we find that the AFM order parameter switches away from
the easy-axis below a critical anisotropy strength when an AFM is properly
tailored into a nano-structure. The switching time first decreases and then
increases with the damping. Above the critical anisotropy, the AFM order
parameter is stable and precesses under a microwave excitation. However, the
absorption peak is not at resonance frequency even for magnetic damping as low
as 0.01. To resolve these anomalies, we first ascertain the hidden role of
dipolar interaction that reconstructs the energy landscape of the nano-system
and propose a model of damped non-linear pendulum to explain the switching
behavior. In this framework, the second anomaly appears when an AFM is close to
the boundary between underdamped and overdamped phases, where the observed
absorption lineshape has small quality factor and thus is not reliable any
longer. Our results should be significant to extract the magnetic parameters
through resonance techniques.",1910.08668v1
2020-01-19,Impact of the magnetic proximity effect in Pt on the total magnetic moment of Pt/Co/Ta trilayers studied by x-ray resonant magnetic reflectivity,"In this work, we study the influence of the magnetic proximity effect (MPE)
in Pt on the total magnetic moment of thin film trilayer systems consisting of
the ferromagnet (FM) Co adjacent to the heavy metals (HMs) Pt and Ta. We
investigate the trilayer systems HM1/FM/HM2 with different stacking order as
well as a reference bilayer without any MPE. X-ray resonant magnetic
reflectivity (XRMR) is a powerful tool to probe induced magnetism, especially
when buried at interfaces in a multilayer. By using XRMR, we are able to obtain
magnetic depth profiles of the structural, optical and magnetic parameters. By
fitting the experimental data with a Gaussian-like magnetooptic profile taking
the structural roughness at the interface into account, we can extract the
magnetic moment of the spin-polarized layer. Comparing the obtained moments to
the measured total moment of the sample, we can determine the impact of the MPE
on the total magnetic moment of the system. Such information can be critical
for analyzing spin transport experiments, including spin-orbit torque and spin
Hall angle measurements, where the saturation magnetization $M_s$ has to be
taken into account. Therefore, by combining magnetization measurements and XRMR
methods we were able to get a complete picture of the magnetic moment
distribution in these trilayer systems containing spin-polarized Pt.",2001.06857v1
2021-01-14,Magnetic Constitution of Topologically Trivial Thermoelectric PbTe:Cr,"In this paper we report on detailed temperature and magnetic field dependence
of m agnetization of IV-VI semiconductor PbTe doped with mixed valence
transition metal Cr$^{2+/3+}$. The material is studied solely by an integral
superconducting quantum interference device magnetometer in order to
quantitatively determine the contribution of single substitutional Cr$^{3+}$ as
well as of various Cr-Te magnetic nanocrystals, including their identification.
The applied experimental procedure reveals the presence of about
$10^{19}$~cm$^{-3}$ paramagnetic Cr$^{3+}$ ions formed via self-ionization of
Cr$^{2+}$ resonant donors. These are known to improve the thermoelectric figure
of merit parameter zT of this semiconductor. The magnetic finding excellently
agrees with previous Hall effect studies thus providing a new experimental
support for the proposed electronic structure model of PbTe:Cr system with
resonant Cr$^{2+/3+}$ state located (at low temperatures) about 100 meV above
the bottom of the conduction band. Below room temperature a ferromagnetic-like
signal points to the presence of Cr-rich nanocrystalline precipitates. Two most
likely candidates, namely: Cr$_2$Te$_3$ and Cr$_5$Te$_8$ are identified upon
dedicated temperature cycling of the sample at the remnant state. As an
ensemble, the nanocrystals exhibits (blocked) superparamagnetic properties. The
magnetic susceptibility of both n- and p-type PbTe in the temperature range
$100 < T < 400$~K has been established. These magnitudes are essential in
proper accounting for the high temperature magnetic susceptibility of PbTe:Cr.",2101.05705v2
2017-08-22,A pico-Tesla magnetic sensor with PZT bimorph and permanent magnet proof mass,"Ferromagnetic-ferroelectric composites have attracted interests in recent
years for use as magnetic field sensors. The sensing is based on
magneto-electric (ME) coupling between the electric and magnetic subsystems and
is mediated by mechanical strain. Such sensors for AC magnetic fields require a
bias magnetic field to achieve pT-sensitivity. Here we discuss measurements and
theory for a novel passive, AC magnetic sensor that does not require a bias
magnetic field and is based on a PZT bimorph with a permanent magnet proof
mass. Mechanical strain on the PZT bimorph in this case is produced by
interaction between the applied AC magnetic field and remnant magnetization of
the permanent magnet, resulting in an induced voltage across PZT. Our studies
have been performed on sensors with a bimorph of oppositely poled PZT platelets
and a NdFeB permanent magnet proof mass. Magnetic floor noise N on the order of
100 pT per sqrHz and 10 nT per sqrHz are measured at 1 Hz and 10 Hz,
respectively. When the AC magnetic field is applied at the bending resonance of
40 Hz for the bimorph, the measured N 700 pT per sqrHz. We also discuss a
theory for the magneto-electro-mechanical coupling at low frequency and bending
resonance in the sensor and theoretical estimates of ME voltage coefficients
are in very good agreement with the data.",1709.01794v1
2018-07-19,Magnetization nutation induced by surface effects in nanomagnets,"We investigate the magnetization dynamics of ferromagnetic nanoparticles in
the atomistic approach taking account of surface anisotropy and the spin
misalignment it causes. We demonstrate that such inhomogeneous spin
configurations induce nutation in the dynamics of the particle's magnetization.
More precisely, in addition to the ordinary precessional motion with frequency
$f_{p}\sim10\,{\rm GHz}$, we find that the dynamics of the net magnetic moment
exhibits two more resonance peaks with frequencies $f_{c}$ and $f_{n}$ which
are higher than the frequency $f_{p} : f_{c}=4\times f_{p}\sim40\,{\rm GHz}$ is
related with the oscillations of the particle's magnetic moment between the
minima of the effective potential induced by weak surface anisotropy. On the
other hand, the much higher frequency $f_{n}\sim1\,{\rm THz}$ is attributed to
the magnetization fluctuations at the atomic level driven by exchange
interaction. We have compared our results on nutation induced by surface
effects with those rendered by the macroscopic approach based on the
Landau-Lifshitz-Gilbert equation augmented by an inertial term (proportional to
the second-order time derivative of the macroscopic moment) with a
phenomenological coefficient. The good agreement between the two models have
allowed us to estimate the latter coefficient in terms of the atomistic
parameters such as the surface anisotropy constant. We have thus proposed a new
origin for the magnetization nutations as being induced by surface effects and
have interpreted the corresponding resonance peaks and their frequencies.",1807.07392v1
2018-12-31,"Growth, Characterization and High Field Magneto-Conductivity of Co0.1Bi2Se3 Topological Insulator","We report the crystal growth as well as transport properties of Co added
Bi2Se3 single crystals. The values of the lattice parameters a and b for Co
added sample were observed to increase as compared to the pure Bi2Se3. The
Raman spectroscopy displayed higher Raman shift of corresponding vibrational
modes for Co0.1Bi2Se3, and the resistivity curves with and without applied
magnetic field shows a metallic behaviour. Both the crystals were subjected to
magneto-resistance (MR) measurements under applied fields of 14Tesla. The value
of MR is found to decrease from about 380 (5K, 14 Tesla) for Bi2Se3 to 200
degree for Co0.1Bi2Se3. To elaborate the transport properties of pure and Co
added Bi2Se3 crystals, the magneto-conductivity is fitted to the HLN (Hikami
Larkin Nagaoka) equation and it is found that the charge conduction is mainly
dominated by surface driven WAL (weak anti-localization) with negligible bulk
WL (weak localization) contribution in both crystals alike. The MH curves of
Co0.1Bi2Se3 crystal at different temperatures displayed a combination of both
ferromagnetic and diamagnetic behaviour. On the other hand, the Electron
Paramagnetic Resonance (EPR) revealed that pure Bi2Se3 is diamagnetic whereas,
Co orders ferro-magnetically with resonating field around 3422Oe at room
temperature.",1812.11713v1
2019-01-14,Helical Ordering of Spin Trimers in a Distorted Kagome Lattice of Gd$_3$Ru$_4$Al$_{12}$ Studied by Resonant X-ray Diffraction,"Successive magnetic phase transitions at $T_1$=17.5 K and $T_2$=18.5 K in
Gd$_3$Ru$_4$Al$_{12}$, with a distorted kagome lattice of Gd ions, is studied
using resonant X-ray diffraction with polarization analysis. It has been
suggested that in this compound the $S=7/2$ spins on the nearest-neighbor
Gd-triangle form a ferromagnetic trimer and the Gd lattice can be effectively
considered as an antiferromagnetic triangular lattice of $S=21/2$ spin trimers
[S. Nakamura et al., Phys. Rev. B 98, 054410 (2018)]. We show that the magnetic
order in this system is described by an incommensurate wave vector $q$~(0.27,
0, 0), which varies slightly with temperature. In the low temperature phase
below $T_1$, the experimental results are well explained by considering that
the spin trimers form a helical order with both the $c$-axis and $c$-plane
components. In the intermediate phase above $T_1$, the $c$-axis component
vanishes, resulting in a sinusoical structure within the $c$-plane. The
sinusoidal-helical transition at $T_1$ can be regarded as an ordering of chiral
degree of freedom, which is degenerate in the intermediate phase.",1901.04231v1
2019-03-02,"A spin dynamics study in layered van der Waals single crystal, Cr$_2$Ge$_2$Te$_6$","We study the magnetisation dynamics of a bulk single crystal
Cr$_2$Ge$_2$Te$_6$ (CGT), by means of broadband ferromagnetic resonance (FMR),
for temperatures from 60 K down to 2 K. We determine the Kittel relations of
the fundamental FMR mode as a function of frequency and static magnetic field
for the magnetocrystalline easy - and hard - axis. The uniaxial
magnetocrystalline anisotropy constant is extracted and compared with the
saturation magnetisation, when normalised with their low temperature values.
The ratios show a clear temperature dependence when plotted in the logarithmic
scale, which departs from the predicted Callen-Callen power law fit of a
straight line, where the scaling exponent \textit{n}, $K_{u}(T) \propto
[M_s(T)/M_s(2$ K$)]^n$, contradicts the expected value of 3 for uniaxial
anisotropy. Additionally, the spectroscopic g-factor for both the magnetic easy
- and hard - axis exhibits a temperature dependence, with an inversion between
20 K and 30 K, suggesting an influence by orbital angular momentum. Finally, we
qualitatively discuss the observation of multi-domain resonance phenomena in
the FMR spectras, at magnetic fields below the saturation magnetisation.",1903.00584v2
2019-03-27,Theory of standing spin waves in finite-size chiral spin soliton lattice,"We present a theory of standing spin wave (SSW) in a monoaxial chiral
helimagnet. Motivated by experimental findings on the magnetic field-dependence
of the resonance frequency in thin films of Cr${}$Nb$_{3} $S${}_{6}$[Goncalves
et al., Phys. Rev. B95, 104415 (2017)], we examine the SSW over a chiral
soliton lattice (CSL) excited by an ac magnetic field applied parallel and
perpendicular to the chiral axis. For this purpose, we generalize Kittel-Pincus
theories of the SSW in ferromagnetic thin films to the case of non-collinear
helimagnet with the surface end spins which are softly pinned by an anisotropy
field. Consequently, we found there appear two types of modes. One is a Pincus
mode which is composed of a long-period Bloch wave and a short-period ripple
originated from the periodic structure of the CSL. Another is a short-period
Kittel ripple excited by space-periodic perturbation which exists only in the
case where the ac field is applied perpendicular the chiral axis. We
demonstrate that the existence of the Pincus mode and the Kittel ripple is
consistent with experimentally found double resonance profile.",1903.11675v1
2020-03-21,"Improving MRI's slice selectivity in the presence of strong, metal-derived inhomogeneities","Purpose: To develop schemes that deliver faithful 2D slices near field
heterogeneities of the kind arising from non-ferromagnetic metal implants, with
reduced artifacts and shorter scan times.
  Methods: An excitation scheme relying on cross-term spatio-temporal encoding
(xSPEN) was used as basis for developing the new inhomogeneity-insensitive,
slice-selective pulse scheme. The resulting Fully refOCUSED cross-term
SPatiotemporal ENcoding (FOCUSED-xSPEN) approach involved four adiabatic
sweeps. The method was evaluated in silico, in vitro and in vivo using mice
models, and compared against a number of existing and of novel alternatives
based on both conventional and swept RF pulses, including an analogous method
based on LASER's selectivity spatial selectivity.
  Results: Calculations and experiments confirmed that multi-sweep derivatives
of xSPEN and LASER can deliver localized excitation profiles, centered at the
intended positions and endowed with enhanced immunity to B0 and B1 distortions.
This, however, is achieved at the expense of higher SAR than non-swept
counterparts. Furthermore, single-shot FOCUSED-xSPEN and LASER profiles covered
limited off-resonance ranges. This could be extended to bands covering
arbitrary off-resonance values with uniform slice widths, by looping the
experiments over a number of scans possessing suitable transmission and
reception offsets.
  Conclusions: A series of novel approaches were introduced to select slices
near metals, delivering robustness against Bo and B1+ field inhomogeneities.",2003.09733v1
2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
great interest to spintronic technology as they can be used to carry, transport
and process information. Garnet films with PMA present labyrinth domain
magnetic structures that enrich the magnetization dynamics, and could be
employed in more efficient wave-based logic and memory computing devices. In
MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
switching by lowering the needed current and rendering the process faster,
crucial for developing magnetic random-access memories (SOT-MRAM). In this
work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
films with PMA via ferromagnetic resonance measurements, followed by the
excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
by microwaves and heat currents. TIG films presented a Gilbert damping constant
{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
high interfacial spin transparency.",2009.10299v1
2020-10-10,Controlling the anisotropy of a van der Waals antiferromagnet with light,"Magnetic van der Waals materials provide an ideal playground for exploring
the fundamentals of low-dimensional magnetism and open new opportunities for
ultrathin spin processing devices. The Mermin-Wagner theorem dictates that as
in reduced dimensions isotropic spin interactions cannot retain long-range
correlations; the order is stabilized by magnetic anisotropy. Here, using
ultrashort pulses of light, we demonstrate all-optical control of magnetic
anisotropy in the two-dimensional van der Waals antiferromagnet NiPS$_3$.
Tuning the photon energy in resonance with an orbital transition between
crystal-field split levels of the nickel ions, we demonstrate the selective
activation of a sub-THz two-dimensional magnon mode. The pump polarization
control of the magnon amplitude confirms that the activation is governed by the
instantaneous magnetic anisotropy axis emergent in response to photoexcitation
of orbital states with a lowered symmetry. Our results establish pumping of
orbital resonances as a universal route for manipulating magnetic order in
low-dimensional (anti)ferromagnets.",2010.05062v1
2021-02-25,Unidirectional magnetoresistance and spin-orbit torque in NiMnSb,"Spin-dependent transport phenomena due to relativistic spin-orbit coupling
and broken space-inversion symmetry are often difficult to interpret
microscopically, in particular when occurring at surfaces or interfaces. Here
we present a theoretical and experimental study of spin-orbit torque and
unidirectional magnetoresistance in a model room-temperature ferromagnet NiMnSb
with inversion asymmetry in the bulk of this half-heusler crystal. Besides the
angular dependence on magnetization, the competition of Rashba and
Dresselhaus-like spin-orbit couplings results in the dependence of these
effects on the crystal direction of the applied electric field. The
phenomenology that we observe highlights potential inapplicability of commonly
considered approaches for interpreting experiments. We point out that, in
general, there is no direct link between the current-induced non-equilibrium
spin polarization inferred from the measured spin-orbit torque and the
unidirectional magnetiresistance. We also emphasize that the unidirectional
magnetoresistance has not only longitudinal but also transverse components in
the electric field -- current indices which complicates its separation from the
thermoelectric contributions to the detected signals in common experimental
techniques. We use the theoretical results to analyze our measurements of the
on-resonance and off-resonance mixing signals in microbar devices fabricated
from an epitaxial NiMnSb film along different crystal directions. Based on the
analysis we extract an experimental estimate of the unidirectional
magnetoresistance in NiMnSb.",2102.12838v1
2021-03-30,Photoinduced Transient States of Antiferromagnetic Orderings in La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ and SrFeO${}_{3}$ Thin Films Observed through Time-resolved Resonant Soft X-ray Scattering,"The relationship between the magnetic interaction and photoinduced dynamics
in antiferromagnetic perovskites is investigated in this study. In
La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ thin films, commensurate spin ordering is
accompanied by charge disproportionation, whereas SrFeO${}_{3}$ thin films show
incommensurate helical antiferromagnetic spin ordering due to increased
ferromagnetic coupling compared to La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$. To
understand the photoinduced spin dynamics in these materials, we investigate
the spin ordering through time-resolved resonant soft X-ray scattering. In
La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$, ultrafast quenching of the magnetic
ordering within 130 fs through a nonthermal process is observed, triggered by
charge transfer between the Fe atoms. We compare this to the photoinduced
dynamics of the helical magnetic ordering of SrFeO${}_{3}$. We find that the
change in the magnetic coupling through optically induced charge transfer can
offer an even more efficient channel for spin-order manipulation.",2103.16038v1
2021-05-10,Chiral spin spiral in synthetic antiferromagnets probed by circular dichroism in x-ray resonant magnetic scattering,"Noncollinear chiral spin textures in ferromagnetic multilayers are at the
forefront of recent research in nano-magnetism with the promise for fast and
energy-efficient devices. The recently demonstrated possibilities to stabilize
such chiral structures in synthetic antiferromagnets (SAF) has raised interests
as they are immune to dipolar field, hence favoring the stabilization of ultra
small textures, improve mobility and avoid the transverse deflections of moving
skyrmions limiting the efficiency in some foreseen applications. However, such
systems with zero net magnetization are hence difficult to characterize by most
of the standard techniques. Here, we report that the relevant parameters of a
magnetic SAF texture, those being its period, its type (N\'eel or Bloch) and
its chirality (clockwise or counterclockwise), can be directly determined using
the circular dichroism in x-ray resonant scattering (CD-XRMS) at half integer
multilayer Bragg peaks in reciprocal space. The analysis of the dependence in
temperature down to 40K allows us moreover to address the question of the
temperature stability of a spin spiral in a SAF sample and of the temperature
scaling of the symmetric and antisymmetric exchange interactions.",2105.04420v1
2021-09-13,Control of magnetization dynamics by substrate orientation in YIG thin films,"Yttrium Iron Garnet (YIG) and bismuth (Bi) substituted YIG (Bi0.1Y2.9Fe5O12,
BYG) films are grown in-situ on single crystalline Gadolinium Gallium Garnet
(GGG) substrates [with (100) and (111) orientations] using pulsed laser
deposition (PLD) technique. As the orientation of the Bi-YIG film changes from
(100) to (111), the lattice constant is enhanced from 12.384 {\AA} to 12.401
{\AA} due to orientation dependent distribution of Bi3+ ions at dodecahedral
sites in the lattice cell. Atomic force microscopy (AFM) images show smooth
film surfaces with roughness 0.308 nm in Bi-YIG (111). The change in substrate
orientation leads to the modification of Gilbert damping which, in turn, gives
rise to the enhancement of ferromagnetic resonance (FMR) line width. The best
values of Gilbert damping are found to be (0.54)*10-4, for YIG (100) and
(6.27)*10-4, for Bi-YIG (111) oriented films. Angle variation measurements of
the Hr are also performed, that shows a four-fold symmetry for the resonance
field in the (100) grown film. In addition, the value of effective
magnetization (4{\pi}Meff) and extrinsic linewidth ({\Delta}H0) are observed to
be dependent on substrate orientation. Hence PLD growth can assist
single-crystalline YIG and BYG films with a perfect interface that can be used
for spintronics and related device applications.",2109.05901v1
2022-07-28,Antiferromagnetic order in Co-doped Fe$_5$GeTe$_2$ probed by resonant magnetic x-ray scattering,"The quasi-two-dimensional van der Waals magnet Fe$_{5-\delta}$GeTe$_2$ has
emerged as a promising platform for electronic and spintronic functionalities
at room temperature, owing to its large ferromagnetic ordering temperature
$T_{\text{C}}$ $\sim$ 315 K. Interestingly, by cobalt (Co) substitution of iron
in F5GT, $i.e.$ $({\text{Fe}}_{1-x}{\text{Co}}_x)_{5-\delta}{\text{GeTe}}_2$
(Co-F5GT), not only can its magnetic transition temperature be further
enhanced, but the magnetic and structural ground states can also be tuned.
Specifically, an antiferromagnetic (AFM) order is induced beyond the Co doping
level $x \ge 0.4$. Here, we investigate the magnetic properties of a Co-F5GT
single crystal at $x = 0.45(1)$, by utilizing the element specific, resonant
magnetic x-ray scattering technique. Our study reveals an A-type, Ising-like
AFM ground state, with a transition temperature $T_{\text{N}}$ $\sim$ 340 K. In
addition, our work unveils an important contribution from Co magnetic moments
to the magnetic order. The application of the in-plane magnetic fields
gradually polarize the spin moments along the field direction, but without
inducing incommensurate spin texture(s).",2207.14412v1
2022-11-03,Static magnetic and ESR spectroscopic properties of the dimer-chain antiferromagnet BiCoPO$_5$,"We report a comprehensive study of the static susceptibility, high-field
magnetization and high-frequency/high-magnetic field electron spin resonance
(HF-ESR) spectroscopy of polycrystalline samples of the bismuth cobalt
oxy-phosphate BiCoPO$_5$. This compound features a peculiar spin system that
can be considered as antiferromagnetic (AFM) chains built of pairs of
ferromagnetically coupled Co spins and interconnected in all three spatial
directions. It was previously shown that BiCoPO$_5$ orders
antiferromagnetically at $T_{\rm N} \approx 10$ K and this order can be
continuously suppressed by magnetic field towards the critical value
$\mu_0H_{\rm c} \approx 15$ T. In our experiments we find strongly enhanced
magnetic moments and spectroscopic $g$ factors as compared to the expected
spin-only values, suggesting a strong contribution of orbital magnetism for the
Co$^{2+}$ ions. This is quantitatively confirmed by ab initio quantum chemical
calculations. Within the AFM ordered phase, we observe a distinct field-induced
magnetic phase transition. Its critical field rises to $\sim 6$ T at $T \ll
T_{\rm N}$. The HF-ESR spectra recorded at $T\ll T_{\rm N}$ are very rich
comprising up to six resonance modes possibly of the multimagnonic nature that
soften towards the critical region around 6 T. Interestingly, we find that the
Co moments are not yet fully polarized at $H_{\rm c}$ which supports a
theoretical proposal identifying $H_{\rm c}$ as the quantum critical point for
the transition of the spin system in BiCoPO$_5$ to the quantum disordered state
at stronger fields.",2211.01663v1
2022-11-07,Room temperature charge-to-spin conversion from q-2DEG at SrTiO3-based interfaces,"Interfacial two-dimensional electron gas (2DEG), especially the SrTiO3-based
ones at the unexpected interface of insulators, have emerged to be a promising
candidate for efficient charge-spin current interconversion. In this article,
to gain insight into the mechanism of the charge-spin current interconversion
at the oxide-based 2DEG, we focused on conducting interfaces between insulating
SrTiO3 and two types of aluminium-based amorphous insulators, namely SrTiO3/AlN
and SrTiO3/Al2O3, and estimated their charge-spin conversion efficiency,
{\theta}_cs. The two types of amorphous insulators were selected to explicitly
probe the overlooked contribution of oxygen vacancy to the {\theta}_cs. We
proposed a mechanism to explain results of spin-torque ferromagnetic resonance
(ST-FMR) measurements and developed an analysis protocol to reliably estimate
the {\theta}_cs of the oxide based 2DEG. The resultant {\theta}_cs/t, where t
is the thickness of the 2DEG, were estimated to be 0.244 nm-1 and 0.101 nm-1
for the SrTiO3/AlN and SrTiO3/Al2O3, respectively, and they are strikingly
comparable to their crystalline counterparts. Furthermore, we also observe a
large direct current modulation of resonance linewidth in SrTiO3/AlN samples,
confirming its high {\theta}_cs and attesting an oxygen-vacancy-enabled
charge-spin conversion. Our findings emphasize the defects' contribution to the
charge-spin interconversion, especially in the oxide-based low dimensional
systems, and provide a way to create and enhance charge-spin interconversion
via defect engineering.",2211.03383v1
2023-05-09,Axial and polar magnetism in hexagonal YMnO3,"Newly published diffraction data on hexagonal YMnO3 at a temperature of 10 K
are shown to be consistent with a trusted expression of the magnetic symmetry,
although the data alone are not definitive [M. Ramakrishnan et al., Phys. Rev.
Research 5, 013203 (2023)]. Howard et al. conclude from an exhaustive review of
experimental data that the symmetry of the antiferromagnetic motif of Mn ions
is most likely P63'cm' [C. J. Howard et al., Acta Crystallogr. B 69, 534
(2013)]. The data reported by Ramakrishnan et al. does not eliminate symmetry
P63' from our calculated diffraction patterns, because the studied reflection
vector is parallel to the common chiral vector associated with each triangle of
Mn axial dipole moments. Proposed diffraction patterns will give decisive
statements about the magnetic symmetry in future investigations using resonant
x-ray and magnetic neutron diffraction. To this end, both axial and polar
magnetism in the multiferroic are essential in the analysis of diffraction
patterns. The account by Ramakrishnan et al. of polar magnetism in resonant
x-ray diffraction uses a magnetic symmetry of hexagonal YMnO3 not yet
justified, e.g., ferromagnetism and a linear magnetoelectric effect allowed by
their chosen symmetry have not been observed. We study polar magnetism in
symmetry P63'cm' using Dirac multipoles, including Mn anapoles. They also
feature in amplitudes for magnetic neutron diffraction together with Dirac
quadrupoles, previously shown to account for diffraction by pseudo-gap phases
of cuprate superconductors.",2305.05254v1
2023-07-27,Singlet magnetism in intermetallic UGa$_2$ unveiled by inelastic x-ray scattering,"Using high resolution tender-x-ray resonant inelastic scattering and
hard-x-ray non-resonant inelastic scattering beyond the dipole limit we were
able to detect electronic excitations in intermetallic UGa$_2$ that are highly
atomic in nature. Analysis of the spectral lineshape reveals that the local
$5f^2$ configuration characterizes the correlated nature of this ferromagnet.
The orientation and directional dependence of the spectra indicate that the
ground state is made of the $\Gamma_1$ singlet and/or $\Gamma_6$ doublet
symmetry. With the ordered moment in the $ab$ plane, we infer that the
magnetism originates from the higher lying $\Gamma_6$ doublet being mixed with
the $\Gamma_1$ singlet due to inter-site exchange, qualifying UGa$_2$ to be a
true quantum magnet. The ability to observe atomic excitations is crucial to
resolve the on-going debate about the degree of localization versus itineracy
in U intermetallics.",2307.15100v1
2023-11-09,Skyrmion-Excited Spin Wave Fractal Network,"Magnetic skyrmions exhibit unique, technologically relevant pseudo-particle
behaviors which arise from their topological protection, including
well-defined, three-dimensional dynamic modes that occur at microwave
frequencies. During dynamic excitation, spin waves are ejected into the
interstitial regions between skyrmions, creating the magnetic equivalent of a
turbulent sea. However, since the spin waves in these systems have a
well-defined length scale, and the skyrmions are on an ordered lattice, ordered
structures from spin wave interference can precipitate from the chaos. This
work uses small angle neutron scattering (SANS) to capture the dynamics in
hybrid skyrmions and investigate the spin wave structure. Performing
simultaneous ferromagnetic resonance and SANS, the diffraction pattern shows a
large increase in low-angle scattering intensity which is present only in the
resonance condition. This scattering pattern is best fit using a mass fractal
model, which suggests the spin waves form a long-range fractal network. The
fractal structure is constructed of fundamental units with a size that encodes
the spin wave emissions and are constrained by the skyrmion lattice. These
results offer critical insights into the nanoscale dynamics of skyrmions,
identify a new dynamic spin wave fractal structure, and demonstrates SANS as a
unique tool to probe high-speed dynamics.",2311.05469v1
2024-01-08,Microwave-assisted synthesis of LaMnO3+d: Tuning physical properties with microwave power,"Synthesis of transition metal oxides by microwave irradiation is a faster and
energy-saving method compared to conventional heating in an electrical furnace
because microwave energy is directly converted into heat within precursors.
However, not much is known about how the physical properties are modified by
the power of microwaves. We synthesized LaMnO3+d by irradiating oxide
precursors with microwaves and studied the impact of microwave power (P = 1000
W, 1200 W, 1400 W and 1600 W) on magnetism, resistivity, magnetoresistance,
thermopower, magnetic entropy change, magnetostriction, and electron spin
resonance. It is found that paramagnetic to ferromagnetic transition becomes
sharper, saturation magnetization increases, and electrical resistivity at low
temperatures dramatically decreases as P increases. While the resistivity of
samples irradiated with MW power of P less than or equal to 1400 W show
insulating-like behavior down to 50 K, an insulator-metal transition occurs in
the sample exposed to P = 1600 W and this sample also shows a maximum
magnetoresistance (= -55%), magneto-thermopower (=-87%), magnetostriction (-180
x10-6) for H = 50 kOe and magnetic entropy change of 4.78 J/kg. K for H = 30
kOe around the Curie temperature. The intensity of electron spin resonance
spectra at 300 K increases with P. We postulate that the much enhanced physical
properties observed for the P = 1600 W sample arise from the creation of higher
hole density, chemical homogeneity, and increased grain size. Our study shows
that microwave power can be used as a knob to tune magnetism and other physical
properties to our advantage.",2401.04087v1
2024-03-08,Lattice-commensurate skyrmion texture in a centrosymmetric breathing kagome magnet,"Skyrmion lattices (SkL) in centrosymmetric materials typically have a
magnetic period on the nanometer-scale, so that the coupling between magnetic
superstructures and the underlying crystal lattice cannot be neglected. Here,
we reveal the commensurate locking of a SkL to the atomic lattice in
Gd$_3$Ru$_4$Al$_{12}$ via high-resolution resonant elastic x-ray scattering
(REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination
of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a
site of the atomic lattice. Under these conditions, a commensurate SkL, locked
to the crystal lattice, is stable at finite temperatures -- but gives way to a
competing incommensurate ground state upon cooling. We discuss the role of
Umklapp-terms in the Hamiltonian for the formation of this lattice-locked
state, its magnetic space group, the role of slight discommensurations, or
(line) defects in the magnetic texture, and contrast our findings with the case
of SkLs in noncentrosymmetric material platforms.",2403.05082v1
2024-03-25,Magnetic Order in Honeycomb Layered U$_2$Pt$_6$Ga$_{15}$ Studied by Resonant X-ray and Neutron Scatterings,"Antiferromagnetic (AF) order of U$_{2}$Pt$_{6}$Ga$_{15}$ with the ordering
temperature $T_{\rm N}$ = 26 K was investigated by resonant X-ray scattering
and neutron diffraction on single crystals. This compound possesses a unique
crystal structure in which uranium ions form honeycomb layers and then stacks
along the $c$-axis with slight offset, which gives rise to a stacking disorder.
The AF order can be described with the propagation vector of $q = (1/6, 1/6,
0)$ in the hexagonal notation. The ordered magnetic moments orient
perpendicular to the honeycomb layers, indicating a collinear spin structure
consistent with Ising-like anisotropy. The magnetic reflections are found to be
broadened along $c^*$ indicating that the stacking disorder results in
anisotropic correlation lengths. The semi-quantitative analysis of neutron
diffraction intensity, combined with group theory considerations based on the
crystallographic symmetry, suggests a zig-zag type magnetic structure for the
AF ground state, in which the AF coupling runs perpendicular to the stacking
offset, characterized as $q = (1, 0, 0)_{\rm orth}$. The realization of the
zig-zag magnetic structure implies the presence of frustrating intralayer
exchange interactions involving both ferromagnetic (FM) first-neighbor and AF
second and third-neighbor interactions in this compound.",2403.16672v1
2006-11-09,Conductance spectra of ferromagnetic superconductors: Quantum transport in a ferromagnetic metal/non-unitary ferromagnetic superconductor junction,"Recent findings of superconductors that simultaneously exhibit multiple
spontaneously broken symmetries, such as ferromagnetic order or lack of an
inversion center and even combinations of such broken symmetries, have led to
much theoretical and experimental research. We consider quantum transport in a
junction consisting of a ferromagnetic metal and a non-unitary ferromagnetic
superconductor. It is shown that the conductance spectra provides detailed
information about the superconducting gaps, and is thus helpful in determining
the pairing symmetry of the Cooper pairs in ferromagnetic superconductor.",0611242v1
2018-03-09,Non-local coupling between antiferromagnets and ferromagnets in cavities,"Microwaves couple to magnetic moments in both ferromagnets and
antiferromagnets. Although the magnons in ferromagnets and antiferromagnets
radically differ, they can become entangled via strong coupling to the same
microwave mode in a cavity. The equilibrium configuration of the magnetic
moments crucially governs the coupling between the different magnons because
the antiferromagnetic and ferromagnetic magnons have the opposite spins when
their dispersion relations cross. We derive analytical expressions for the
coupling strengths and find that the coupling between antiferromagnets and
ferromagnets is comparable to the coupling between two ferromagnets. Our
findings reveal a robust link between cavity spintronics with ferromagnets and
antiferromagnets.",1803.03486v1
2021-11-24,Platform for controllable Majorana zero modes using superconductor/ferromagnet heterostructures,"We propose a novel platform for the creation and manipulation of Majorana
zero modes consisting of a ferromagnetic metallic wire placed between
conventional superconductors which are in proximity to ferromagnetic
insulators. Our device relies on the interplay of applied supercurrents and
exchange fields emerging from the ferromagnetic insulators. We assert that the
proposed superconductor/ferromagnet heterostructures exhibit enhanced
controllability, since topological superconductivity can be tuned apart from
gate voltages applied on the ferromagnetic wire, also by manipulating the
applied supercurrents and/or the magnetisation of the ferromagnetic insulators.",2111.12344v2
1995-07-01,ORVB Mean-Field Calculation in the Tight-Binding Model with Anti-Ferromagnetic Exchange,"We give a mean-field calculation for the odd-resonating-valence-bond ORVB
pairing scheme. We obtain interesting quasi-particle excitation energy $E_{\bf
k}$ as a function of momentum ${\bf k}$. It is distinctively different from
those of the $d_{x^2-y^2}$-wave, the anisotropic-s-wave, and the p-wave. It is
a gapless theory for superconductivity with well defined Fermi surface. The
ground state of the ORVB scheme is not an eigenstate of the parity or the
time-reversal transformation, thus both symmetries are violated. Some of them
are already manifested in $E_{\bf k}\neq E_{-{\bf k}} $. It is interesting to
find out if such pairing order-parameter scheme exits in some materials in
nature.",9506143v1
1995-08-09,Numerical Study of the Spin-1 Antiferromagnetic Heisenberg Chain with a Spin-1/2 Impurity,"Low-lying excited states as well as the ground state of the spin-1
antiferromagnetic Heisenberg chain with a spin-1/2 impurity are studied by
means of a method of numerical diagonalization. The isotropic nearest-neighbor
exchange coupling plus the uniaxial single-ion-type anisotropy energy is
assumed for the host-system Hamiltonian. The energy differences between the
ground state and the low-lying excited states, which appear in the Haldane gap,
are estimated in the thermodynamic limit. The results are used to analyze the
electron-spin-resonance experimental data on
Ni(C$_2$H$_8$N$_2$)$_2$NO$_2$(ClO$_4$), abbreviated NENP, containing a small
amount of spin-1/2 Cu$^{2+}$ impurities. It is found that in this system, the
impurity-host $\bigl($Cu$^{2+}$-Ni$^{2+}$$\bigr)$ coupling is ferromagnetic and
its magnitude is about 5$\,$\% of the magnitude of the host-host
$\bigl($Ni$^{2+}$-Ni$^{2+}$$\bigr)$ coupling.",9508029v1
1996-12-11,Competition between Hund-Rule Coupling and Kondo Effect,"We investigate a problem about the competition between the hybridization and
the Hund-rule coupling by applying the Wilson numerical renormalization-group
method to the extended Kondo model where the impurity spin interacts via the
Hund-rule coupling, with an extra spin which is isolated from the conduction
electrons. It is shown that the Hund-rule coupling is an irrelevant
perturbation against the strong coupling fixed point. However, the Hund-rule
coupling decreases the characteristic energy $T_K$ drastically to the lower
side and the irrelevant operator, which describes the low energy physics, takes
a form of ferromagnetic exchange interaction between the extra spin and the
Kondo resonance states because of the existence of the Hund-rule coupling.",9612108v1
1997-12-08,High frequency magneto-electrodynamics of La_(1-x)Sr_xMnO3 single crystals,"The radio frequency (RF) response of La1-xSrxMnO3 single crystals reveal a
variety of features associated with the structural, electronic and magnetic
properties of the system. The resonance technique operating at ~ 4 MHz employed
in this study is sensitive to small changes in both the magnetic susceptibility
and resistivity of the samples. Very sharp changes in frequency are observed at
the ferromagnetic (FM) and structural phase transitions in both the metallic (x
= 0.175) and insulating (0.125) crystals studied. In addition to the known
transitions identified as FM and orthorhombic distortions, our experiments show
rich structures which are not observed in conventional DC magnetization and
transport experiments. Our results demonstrate that RF experiments are ideally
suited to investigate the complex phase diagram in the manganites. The colossal
frequency change that we observe at the FM transition in the La1-xSrxMnO3
crystals is indicative of the enormous potential for using these materials in
high frequency switching applications.",9712093v1
1998-05-10,Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides,"Different mechanisms of spin-dependent tunneling are analyzed with respect to
their role in tunnel magnetoresistance (TMR). Microscopic calculation within a
realistic model shows that direct tunneling in iron group systems leads to
about a 30% change in resistance, which is close but lower than experimentally
observed values. The larger observed values of the tunnel magnetoresistance
(TMR) might be a result of tunneling involving surface polarized states. It is
found that tunneling via resonant defect states in the barrier radically
decreases the TMR by order of magnitude. One-magnon emission is shown to reduce
the TMR, whereas phonons increase the effect. The inclusion of both magnons and
phonons reasonably explains an unusual bias dependence of the TMR. The model
presented here is applied qualitatively to half-metallics with 100% spin
polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO2/TiO2 and CrO2/RuO2.",9805114v1
1999-07-23,Structural phase transitions and sound velocity anomalies in La(1-x)Sr(x)MnO3,"The sound velocities dependencies on temperature V(T) were measured by means
of resonance method have on the thin plates of quasimonocrystalline manganites
La(1-x)Sr(x)MnO3. Results are presented for x=0.1, 0.125, 0.15, 0.175 and 0.2
in the temperature range from 70 to 350K. The V(T) behavior correlates with
those of susceptibilities and magnetic moment M(T). For x=0.175 and 0.2 the
transition to ferromagnetic state is accompanied by appearance of large but
smooth rise in V(T) whereas structural phase transition between the rhomboedral
(R) and orthorhombic (O) structures is accompanied by sharp increase up to
15-20% in V(T). For x=0.1, 0.125 and 0.15 the structural phase transition
between Jahn-Teller distorted orthorhombic structure (O') and pseudocubic one
(O'') is accompanied by deep minimum (~20-30%) in V(T).",9907361v1
2000-02-24,Evidence for a Goldstone Mode in a Double Layer Quantum Hall System,"The tunneling conductance between two parallel 2D electron systems has been
measured in a regime of strong interlayer Coulomb correlations. At total Landau
level filling $\nu_T=1$ the tunnel spectrum changes qualitatively when the
boundary separating the compressible phase from the ferromagnetic quantized
Hall state is crossed. A huge resonant enhancement replaces the strongly
suppressed equilibrium tunneling characteristic of weakly coupled layers. The
possible relationship of this enhancement to the Goldstone mode of the broken
symmetry ground state is discussed.",0002387v2
2000-09-28,Magnetic qubits as hardware for quantum computers,"We propose two potential realisations for quantum bits based on nanometre
scale magnetic particles of large spin S and high anisotropy molecular
clusters. In case (1) the bit-value basis states |0> and |1> are the ground and
first excited spin states Sz = S and S-1, separated by an energy gap given by
the ferromagnetic resonance (FMR) frequency. In case (2), when there is
significant tunnelling through the anisotropy barrier, the qubit states
correspond to the symmetric, |0>, and antisymmetric, |1>, combinations of the
two-fold degenerate ground state Sz = +- S. In each case the temperature of
operation must be low compared to the energy gap, \Delta, between the states
|0> and |1>. The gap \Delta in case (2) can be controlled with an external
magnetic field perpendicular to the easy axis of the molecular cluster. The
states of different molecular clusters and magnetic particles may be entangled
by connecting them by superconducting lines with Josephson switches, leading to
the potential for quantum computing hardware.",0009432v1
2000-11-21,Anomalous NMR Spin-Lattice Relaxation in SrB_{6} and Ca_{1-x}La_{x}B_{6},"We report the results of {11}B nuclear magnetic resonance (NMR) measurements
of SrB_{6} and Ca_{0.995}La_{0.05}B_{6} below room temperature. Although the
electrical resistivities of these two materials differ substantially, their
{11}B-NMR responses exhibit some strikingly common features. Both materials
exhibit ferromagnetic order, but their {11}B-NMR spectra reveal very small
hyperfine fields at the Boron sites. The spin lattice relaxation T_{1}^{-1}
varies considerably with external field but changes with temperature only below
a few K. We discuss these unusual results by considering various different
scenarios for the electronic structure of these materials.",0011352v2
2001-02-05,Electronic theory for superconductivity in Sr$_2$RuO$_4$: triplet pairing due to spin-fluctuation exchange,"Using a two-dimensional Hubbard Hamiltonian for the three electronic bands
crossing the Fermi level in Sr$_2$RuO$_4$ we calculate the band structure and
spin susceptibility $\chi({\bf q}, \omega)$ in quantitative agreement with
nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS)
experiments. The susceptibility has two peaks at {\bf Q}$_i = (2\pi/3, 2\pi/3)$
due to the nesting Fermi surface properties and at {\bf q}$_i = (0.6\pi, 0)$
due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange
theory as in layered cuprates we determine from $\chi({\bf q}, \omega)$,
electronic dispersions, and Fermi surface topology that superconductivity in
Sr$_2$RuO$_4$ consists of triplet pairing. Combining the Fermi surface topology
and the results for $\chi({\bf q}, \omega)$ we can exclude $s-$ and $d-$wave
symmetry for the superconducting order parameter. Furthermore, within our
analysis and approximations we find that $f$-wave symmetry is slightly favored
over p-wave symmetry due to the nesting properties of the Fermi surface.",0102074v3
2001-06-12,Single ion anisotropy of Mn doped GaAs measured by EPR,"Electron paramagnetic resonance (EPR) study of MBE grown Mn doped GaAs is
presented. The resolved fine structure allows us to evaluate the crystal field
parameters of the spin Hamiltonian. The obtained cubic constant is a= -14.1
10^-4/cm. The axial field parameter, D, increases with Mn concentration, x,
i.e., with the strain of (Ga,Mn)As layers. Extrapolation of D shows that the
single ion anisotropy is the important contribution to the magnetic anisotropy
which is observed in ferromagnetic layers with greater Mn concentrations. The
analysis of the EPR linewidth shows that native defects of the concentration of
5 10^19/cm^3, but not the Mn ions, are the main origin of crystal field
fluctuations.",0106227v1
2001-07-20,Bulk Band Gaps in Divalent Hexaborides,"Complementary angle-resolved photoemission and bulk-sensitive k-resolved
resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV
X-point gap between the valence and conduction bands, in contradiction to the
band overlap assumed in several models of their novel ferromagnetism. This
semiconducting gap implies that carriers detected in transport measurements
arise from defects, and the measured location of the bulk Fermi level at the
bottom of the conduction band implicates boron vacancies as the origin of the
excess electrons. The measured band structure and X-point gap in CaB_6
additionally provide a stringent test case for proper inclusion of many-body
effects in quasi-particle band calculations.",0107429v2
2002-06-25,"Zero Permeability Materials (ZmuM): A way out of the ""Left Handed Materials"" trap","Recently it has been shown that due to losses the claims on observation of
negative refraction using metamaterials are questionable. In this paper we
discus an interesting case that is based in almost zero permeability at a given
frequency: zero permeability materials. This represents a way out of the
problem of left handed materials, and constitutes a material that acts a band
pass filter with a very narrow band. The metamaterials claimed to present
negative refraction are just showing this effect. However, absorption can be
diminished in those metamaterials by using thicker wires. Materials based in
quasi metallic magnetic structures are proposed with ferromagnetic resonance at
microwave frequencies under applied magnetic fields. These materials, as well
as the zero permitivity in thin films, open a new ground for a new set of
optical devices.",0206476v1
2003-01-16,Insulator-metal transition shift related to magnetic polarons in La0.67-xYxCa0.33MnO3,"The magnetic transport properties have been measured for La0.67-xYxCa0.33MnO3
(0 <= x <= 0.14) system. It was found that the transition temperature Tp almost
linearly moves to higher temperature as H increases. Electron spin resonance
confirms that above Tp, there exist ferromagnetic clusters. From the magnetic
polaron point of view, the shift of Tp vs. H was understood, and it was
estimated that the size of the magnetic polaron is of 9.7~15.4 angstrom which
is consistent with the magnetic correlation length revealed by the small-angle
neutron-scattering technique. The transport properties at temperatures higher
than Tp conform to the variable-range hopping mechanism.",0301283v1
2003-02-06,"Nonequilibrium spintronic transport through an artificial Kondo impurity: Conductance, magnetoresistance and shot noise","We investigate the nonequilibrum transport properties of a quantum dot when
spin flip processes compete with the formation of a Kondo resonance in the
presence of ferromagnetic leads. Based upon the Anderson Hamiltonian in the
strongly interacting limit, we predict a splitting of the differential
conductance when the spin flip scattering amplitude is of the order of the
Kondo temperature. We discuss how the relative orientation of the lead
magnetizations strongly influences the electronic current and the shot noise in
a nontrivial way. Furthermore, we find that the zero-bias tunneling
magnetoresistance becomes negative with increasing spin flip scattering
amplitude.",0302125v1
2003-04-22,Charge and orbital excitations in Li2CuO2,"We report a resonant inelastic x-ray scattering study of electronic
excitations in Li_2CuO_2, an insulating compound comprised of ribbons of
edge-sharing copper-oxygen chains. Three excitations, which show little
dependence on momentum transfer, are observed in our measurements. The lowest
energy excitation at ~2.1 eV is dispersionless and is attributed to a localized
d-d orbital excitation. We also observe two excitations at ~5.4 eV and ~7.6 eV
which we assign to charge-transfer excitations. These high-energy excitations
are also dispersionless along the copper-oxygen chain direction. However, in
each case we observe a small energy dispersion along the direction
perpendicular to the copper-oxygen ribbons, suggesting a significant interchain
coupling in this system. We also discuss the possible implications of
ferromagnetic nearest-neighbor intrachain coupling on the charge excitation
spectra.",0304487v1
2003-08-08,Low frequency and Microwave Magnetoelectric Effects in Thick Film Heterostructures of Lithium Zinc Ferrite and Lead Zirconate Titanate,"Magnetoelectric (ME) coupling at low frequencies and at x-band have been
investigated in layered samples containing zinc substituted lithium ferrite and
lead zirconate titanate (PZT). Multilayers of Li0.5-x/2ZnxFe2.5-x/2O4 (LZFO)
(x=0-0.4) and PZT were prepared by lamination and sintering of thick films. At
low frequencies (10-1000 Hz), the ME voltage coefficient for transverse fields
is higher than for longitudinal fields. With Zn substitution in the ferrite,
transverse coupling increases to a maximum for x=0.3 and then decreases for
higher x. Analysis based on our model for a bilayer implies an efficient
magneto-mechanical coupling with Zn substitution, resulting in strong ME
interactions. Microwave ME coupling is studied through measurements of shift in
the ferromagnetic resonance field due to an applied electric field. Estimated
ME constants from such data are in agreement with our model for a ferrite-PZT
bilayer.",0308171v1
2004-05-24,"Study of Magnetic Properties of A_2B^'NbO_6 (A=Ba,Sr, (BaSr): and B^'=Fe and Mn) double perovskites","We have studied the magnetic properties of Ba_2FeNbO_6 and Ba_2MnNbO_6. it is
seen that Ba_2FeNbO_6 is an antiferromagnet with a weak ferromagnetic behaviour
at 5K while Ba_2MnNbO_6 shows two magnetic transitions one at 45 K and the
other at 12K. Electron spin resonance (ESR) measurements at room temperature
show that the Mn compound does not show any Jahn-Teller distortion. It is also
seen that the Neel temperature of the A_2FeNbO_6 (A=Ba,Sr, BaSr) compounds do
not vary significantly. However variations in the average A-site ionic radius
influence the formation of short range correlations that persist above T_N.",0405557v1
2004-06-05,Carrier-Induced Magnetic Circular Dichloism in the Magnetoresistive Pyrochlore Tl2Mn2O7,"Infrared magnetic circular dichloism (MCD), or equivalently magneto-optical
Kerr effect, has been measured on the Tl2Mn2O7 pyrochlore, which is well known
for exhibiting a large magnetoresistance around the Curie temperature T_C ~ 120
K. A circularly polarized, infrared synchrotron radiation is used as the light
source. A pronounced MCD signal is observed exactly at the plasma edge of the
reflectivity near and below T_c. However, contrary to the conventional behavior
of MCD for ferromagnets, the observed MCD of Tl2Mn2O7 grows with the applied
magnetic field, and not scaled with the internal magnetization. It is shown
that these results can be basically understood in terms of a classical
magnetoplasma resonance. The absence of a magnetization-scaled MCD indicates a
weak spin-orbit coupling of the carriers in Tl2Mn2O7. We discuss the present
results in terms of the microscopic electronic structures of Tl2Mn2O7.",0406133v2
2004-06-28,Shot noise in resonant tunneling through an interacting quantum dot with intradot spin-flip scattering,"In this paper, we present theoretical investigation of the zero-frequency
shot noise spectra in electron tunneling through an interacting quantum dot
connected to two ferromagnetic leads with possibility of spin-flip scattering
between the two spin states by means of the recently developed bias-voltage and
temperature dependent quantum rate equations. For this purpose, a
generalization of the traditional generation-recombination approach is made for
properly taking into account the coherent superposition of electronic states,
i.e., the nondiagonal density matrix elements. Our numerical calculations find
that the Fano factor increases with increasing the polarization of the two
leads, but decreases with increasing the intradot spin-flip scattering.",0406679v2
2004-08-11,"Conductivity, weak ferromagnetism and charge instability in $α-MnS$ single crystal","The temperature dependence of resistivity, magnetization and electron-spin
resonance of the $\alpha- MnS $ single crystal were measured in temperature
range of $5 K < T < 550 K$. Magnetization hysteresis in applied magnetic field
up to 0.7 T at $T=5 K, 77 K, 300 K$, irreversible temperature behavior of
magnetization and resistivity were found . The obtained data were explained in
terms of degenerate tight binding model using random phase approximation. The
contribution of holes in $t_{2g}$ and $e_g$ bands of manganese ions to the
conductivity, optical absorbtion spectra and charge instability in $\alpha -MnS
$ were studied. Charge susceptibility maxima resulted from the competition of
the on-site Coulomb interaction between the holes in different orbitals and
small hybridization of sub-bands were calculated at $T=160 K, 250 K, 475 K$.",0408232v1
2004-09-22,X-ray method to study temperature-dependent stripe domains in MnAs/GaAs(001),"MnAs films grown on GaAs (001) exhibit a progressive transition between
hexagonal (ferromagnetic) and orthorhombic (paramagnetic) phases at wide
temperature range instead of abrupt transition during the first-order phase
transition. The coexistence of two phases is favored by the anisotropic strain
arising from the constraint on the MnAs films imposed by the substrate. This
phase coexistence occurs in ordered arrangement alternating periodic terrace
steps. We present here a method to study the surface morphology throughout this
transition by means of specular and diffuse scattering of soft x-rays, tuning
the photon energy at the Mn 2p resonance. The results show the long-range
arrangement of the periodic stripe-like structure during the phase coexistence
and its period remains constant, in agreement with previous results using other
techniques.",0409582v1
2004-11-03,Theoretical investigations for shot noise in correlated resonant tunneling through a quantum coupled system,"In this paper, we carry out a theoretical analysis of the zero-frequency and
finite-frequency shot noise in electron tunneling through a two-level
interacting system connected to two leads, when a coherent coupling between the
two levels is present, by means of recently developed bias-voltage and
temperature dependent quantum rate equations. For this purpose, we generalize
the traditional generation-recombination approach for shot noise of
two-terminal tunneling devices properly to take into account the coherent
superposition of different electronic states (quantum effects). As
applications, analytical and numerical investigations have been given in detail
for two cases: (1) electron tunneling through a quantum dot connected to
ferromagnetic leads with intradot spin-flip scattering, and (2) spinless
fermions tunneling through seriesly coupled quantum dots, focusing on the shot
noise as functions of bias-voltage and frequency.",0411091v3
2005-01-06,Electron Spin Dynamics and Hyperfine Interactions in Fe/Al_0.1Ga_0.9As/GaAs Spin Injection Heterostructures,"We have studied hyperfine interactions between spin-polarized electrons and
lattice nuclei in Al_0.1Ga_0.9As/GaAs quantum well (QW) heterostructures. The
spin-polarized electrons are electrically injected into the semiconductor
heterostructure from a metallic ferromagnet across a Schottky tunnel barrier.
The spin-polarized electron current dynamically polarizes the nuclei in the QW,
and the polarized nuclei in turn alter the electron spin dynamics. The
steady-state electron spin is detected via the circular polarization of the
emitted electroluminescence. The nuclear polarization and electron spin
dynamics are accurately modeled using the formalism of optical orientation in
GaAs. The nuclear spin polarization in the QW is found to depend strongly on
the electron spin polarization in the QW, but only weakly on the electron
density in the QW. We are able to observe nuclear magnetic resonance (NMR) at
low applied magnetic fields on the order of a few hundred Oe by electrically
modulating the spin injected into the QW. The electrically driven NMR
demonstrates explicitly the existence of a Knight field felt by the nuclei due
to the electron spin.",0501096v1
2005-01-19,Observation of a Griffiths phase in paramagnetic La1-xSrxMnO3,"We report on the discovery of a novel triangular phase regime in the system
La1-xSrxMnO3 by means of electron spin resonance and magnetic susceptibility
measurements. This phase is characterized by the coexistence of ferromagnetic
entities within the globally paramagnetic phase far above the magnetic ordering
temperature. The nature of this phase can be understood in terms of Griffiths
singularities arising due to the presence of correlated quenched disorder in
the orthorhombic phase.",0501443v3
2005-03-14,Interference Effects on Kondo-Assisted Transport through Double Quantum Dots,"We systematically investigate electron transport through double quantum dots
with particular emphasis on interference induced via multiple paths of electron
propagation. By means of the slave-boson mean-field approximation, we calculate
the conductance, the local density of states, the transmission probability in
the Kondo regime at zero temperature. It is clarified how the Kondo-assisted
transport changes its properties when the system is continuously changed among
the serial, parallel and T-shaped double dots. The obtained results for the
conductance are explained in terms of the Kondo resonances influenced by
interference effects. We also discuss the impacts due to the spin-polarization
of ferromagnetic leads.",0503341v2
2005-12-29,Electron-magnon coupling and nonlinear tunneling transport in magnetic nanoparticles,"We present a theory of single-electron tunneling transport through a
ferromagnetic nanoparticle in which particle-hole excitations are coupled to
spin collective modes. The model employed to describe the interaction between
quasiparticles and collective excitations captures the salient features of a
recent microscopic study. Our analysis of nonlinear quantum transport in the
regime of weak coupling to the external electrodes is based on a rate-equation
formalism for the nonequilibrium occupation probability of the nanoparticle
many-body states. For strong electron-boson coupling, we find that the
tunneling conductance as a function of bias voltage is characterized by a large
and dense set of resonances. Their magnetic field dependence in the large-field
regime is linear, with slopes of the same sign. Both features are in agreement
with recent tunneling experiments.",0512697v2
2006-01-17,Frequency-Dependent Current Noise through Quantum-Dot Spin Valves,"We study frequency-dependent current noise through a single-level quantum dot
connected to ferromagnetic leads with non-collinear magnetization. We propose
to use the frequency-dependent Fano factor as a tool to detect single-spin
dynamics in the quantum dot. Spin precession due to an external magnetic and/or
a many-body exchange field affects the Fano factor of the system in two ways.
First, the tendency towards spin-selective bunching of the transmitted
electrons is suppressed, which gives rise to a reduction of the low-frequency
noise. Second, the noise spectrum displays a resonance at the Larmor frequency,
whose lineshape depends on the relative angle of the leads' magnetizations.",0601366v1
2006-03-31,Hybridization and multipole orders of 4f electrons in Pr skutterudites,"Characteristics of hybridization and multipole orders of $4f$-electrons in Pr
skutterudites are explained in terms of a pseudo-quartet composed of
crystalline electric field (CEF) singlet and the triplet. It is shown that the
contrasting behaviors observed in PrFe$_4$P$_{12}$ and PrOs$_4$Sb$_{12}$ are
ascribed to the difference in triplet wave functions and the CEF
splittings.Since a macroscopic degeneracy remains even in the ordered phase
with the $\Gamma_3$-type antiferro-quadrupole (AFQ) order,a model with strong
AFQ fluctuation and static monopole/hexadecapole order is proposed for
PrFe$_4$P$_{12}$.The remaining cubic symmetry explains qualitatively the
behavior of staggered magnetization observed by NMR and neutron scattering. For
identification of possible hexadecapole orders in PrFe$_4$P$_{12}$
andPrRu$_4$P$_{12}$, eightfold intensity pattern is predicted in the azimuthal
angle scan of resonant X-ray scattering. In PrOs$_4$Sb$_{12}$, the
ferromagnetic exchange coupling with the conduction band does not lead to
magnetic Kondo effect, but a momentum-dependent quadrupole coupling can give
rise to enhanced effective mass, which should be sensitive to disorder.",0603836v1
2006-05-22,Contact-less measurements of Shubnikov-de Haas oscillations in the magnetically ordered state of CeAgSb$_2$ and SmAgSb$_2$ single crystals,"Shubnikov - de Haas oscillations were measured in single crystals of highly
metallic antiferromagnetic SmAgSb$_{2}$ and ferromagnetic CeAgSb$_{2}$ using a
tunnel diode resonator. Resistivity oscillations as a function of applied
magnetic field were observed via measurements of skin depth variation. The
effective resolution of $\Delta\rho\simeq20$ p$\Omega$ allows a detailed study
of the SdH spectra as a function of temperature. The effects of the Sm long -
range magnetic ordering as well as its electronic structure ($4f$-electrons) on
the Fermi surface topology is discussed.",0605546v2
2006-07-30,Kondo effect with non collinear polarized leads: a numerical renormalization group analysis,"The Kondo effect in quantum dots attached to ferromagnetic leads with general
polarization directions is studied combining poor man scaling and Wilson's
numerical renormalization group methods. We show that polarized electrodes will
lead in general to a splitting of the Kondo resonance in the quantum dot
density of states except for a small range of angles close to the antiparallel
case. We also show that an external magnetic field is able to compensate this
splitting and restore the unitary limit. Finally, we study the electronic
transport through the device in various limiting cases.",0607794v2
2006-08-30,Current-Driven Domain-Wall Dynamics in Curved Ferromagnetic Nanowires,"The current-induced motion of a domain wall in a semicircle nanowire with
applied Zeeman field is investigated. Starting from a micromagnetic model we
derive an analytical solution which characterizes the domain-wall motion as a
harmonic oscillation. This solution relates the micromagnetic material
parameters with the dynamical characteristics of a harmonic oscillator, i.e.,
domain-wall mass, resonance frequency, damping constant, and force acting on
the wall. For wires with strong curvature the dipole moment of the wall as well
as its geometry influence the eigenmodes of the oscillator. Based on these
results we suggest experiments for the determination of material parameters
which otherwise are difficult to access. Numerical calculations confirm our
analytical solution and show its limitations.",0608680v1
2007-02-17,"Low Field, Current-Hysteretic Oscillations in Spin Transfer Nanocontacts","We have measured spin-transfer-driven, large amplitude, current hysteretic,
low frequency (< 500 MHz), narrowband oscillations in nanocontacts made to spin
valve structures. The oscillations occur in zero field, persist up to 5 mT for
in plane applied fields, and to beyond 400 mT for out of plane fields. Unlike
previous measurements, the oscillation frequency is well below that for
uniform-mode ferromagnetic resonance, is only a weak function of applied field,
and is highly anharmonic. The oscillations are hysteretic with applied dc
current, appearing at high currents but persisting to lower currents upon
decrease of the current. We suggest that these observations are consistent with
the dynamics of a nonuniform magnetic state in the vicinity of the contact
nucleated by both the spin transfer torque and dc current-generated Oersted
fields, with the dynamics driven by spin transfer. The electrical oscillation
amplitudes are large and narrowband, with the largest amplitudes on the order
of 1 mV and the narrowest linewidths below 1 MHz.",0702416v1
2007-02-23,"Evolution of the magnetic anisotropy with carrier density in hydrogenated (Ga,Mn)As","The magnetic properties of (Ga,Mn)As thin films depend on both the Mn doping
level and the carrier concentration. Using a post growth hydrogenation process
we show that it is possible to decrease the hole density from 1.1021 cm-3 to
<1017 cm-3 while maintaining the manganese concentration constant. For such a
series of films we have investigated the variation of the magnetization, the
easy and hard axes of magnetization, the critical temperatures, the coercive
fields and the magnetocrystalline anisotropy constants as a function of
temperature using magnetometry, ferromagnetic resonance and magneto-transport
measurements. In particular, we evidenced that magnetic easy axes flipped from
out-of-plane [001] to in-plane [100] axis, followed by the <110> axes, with
increasing hole density and temperature. Our study concluded on a general
agreement with mean-field theory predictions of the expected easy axis
reversals, and of the weight of uniaxial and cubic anisotropies in this
material.",0702548v1
2007-05-16,Spin Diode Based on Fe/MgO Double Tunnel Junction,"We demonstrate a spin diode consisting of a semiconductor free nano-scale
Fe/MgO-based double tunnel junction. The device exhibits a near perfect
spin-valve effect combined with a strong diode effect. The mechanism consistent
with our data is resonant tunneling through discrete states in the middle
ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent
transparency. The observed magneto-resistance is record high, ~4000%,
essentially making the structure an on/off spin-switch. This, combined with the
strong diode effect, ~100, offers a new device that should be promising for
such technologies as magnetic random access memory and re-programmable logic.",0705.2375v2
2007-05-31,Electronic reconstruction at SrMnO3-LaMnO3 superlattice interfaces,"We use resonant soft x-ray scattering to study electronic reconstruction at
the interface between the Mott insulator LaMnO3 and the ""band"" insulator
SrMnO3. Superlattices of these two insulators were shown previously to have
both ferromagnetism and metallic tendencies [Koida et al., Phys. Rev. B 66,
144418 (2002)]. By studying a judiciously chosen superlattice reflection we
show that the interface density of states exhibits a pronounced peak at the
Fermi level, similar to that predicted by Okamoto et al. [Phys. Rev. B 70,
241104(R) (2004)]. The intensity of this peak correlates with the conductivity
and magnetization, suggesting it is the driver of metallic behavior. Our study
demonstrates a general strategy for using RSXS to probe the electronic
properties of heterostructure interfaces.",0705.4501v2
2007-08-03,Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles,"The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.",0708.0463v1
2007-08-15,Insulator to semiconductor transition and magnetic properties of the one-dimensional S = 1/2 system In_2VO_5,"We report structural, magnetization, electrical resistivity and nuclear- and
electron spin resonance data of the complex transition metal oxide In_2VO_5 in
which structurally well-defined V-O chains are realized. An itinerant character
of the vanadium d-electrons and ferromagnetic correlations, revealed at high
temperatures, are contrasted with the insulating behavior and predominantly
antiferromagnetic exchange between the localized V^{4+} S = 1/2-magnetic
moments which develop below a certain characteristic temperature T* ~ 120 K.
Eventually the compound exhibits short-range magnetic order at $T_SRO ~ 20 K.
We attribute this crossover occurring around T* to the unusual anisotropic
thermal contraction of the lattice which changes significantly the overlap
integrals and the character of magnetic intra- and interchain interactions.",0708.2088v1
2007-09-11,Magnetic Behavior of Single La$_{0.67}$Ca$_{0.33}$MnO$_3$ Nanotubes: Surface and Shape Effects,"We report magnetization experiments in two magnetically isolated
ferromagnetic nanotubes of perovskite La$_{0.67}$Ca$_{0.33}$MnO$_3$. The
results show that the magnetic anisotropy is determined by the sample shape
although the coercive field is reduced by incoherent magnetization reversal
modes. The temperature dependence of the magnetization reveals that the
magnetic behavior is dominated by grain surface properties. These measurements
were acquired using a Silicon micro-mechanical oscillator working in its
resonant mode. The sensitivity was enough to measure the magnetic properties of
these two samples with a mass lower than 14 picograms and to obtain for the
first time the magnetization loop for one isolated nanotube.",0709.1707v2
2007-10-11,Electrically Tunable Spin Polarization in a Carbon-Nanotube Spin Diode,"We have studied the current through a carbon nanotube quantum dot with one
ferromagnetic and one normal-metal lead. For the values of gate voltage at
which the normal lead is resonant with the single available non-degenerate
energy level on the dot, we observe a pronounced decrease in the current for
one bias direction. We show that this rectification is spin-dependent, and that
it stems from the interplay between the spin accumulation and the Coulomb
blockade on the quantum dot. Our results imply that the current is
spin-polarized for one direction of the bias, and that the degree of spin
polarization is fully and precisely tunable using the gate and bias voltages.
As the operation of this spin diode does not require high magnetic fields or
optics, it could be used as a building block for electrically controlled
spintronic devices.",0710.2297v1
2008-03-14,Soft X-ray Absorption and Photoemission Studies of Ferromagnetic Mn-Implanted 3$C$-SiC,"We have performed x-ray photoemission spectroscopy (XPS), x-ray absorption
spectroscopy (XAS), and resonant photoemission spectroscopy (RPES) measurements
of Mn-implanted 3$C$-SiC (3$C$-SiC:Mn) and carbon-incorporated Mn$_{5}$Si$_{2}$
(Mn$_{5}$Si$_{2}$:C). The Mn 2$p$ core-level XPS and XAS spectra of 3$C$-SiC:Mn
and Mn$_{5}$Si$_{2}$:C were similar to each other and showed ""intermediate""
behaviors between the localized and itinerant Mn 3$d$ states.
  The intensity at the Fermi level was found to be suppressed in 3$C$-SiC:Mn
compared with Mn$_{5}$Si$_{2}$:C. These observations are consistent with the
formation of Mn$_{5}$Si$_{2}$:C clusters in the 3$C$-SiC host, as observed in a
recent transmission electron microscopy study.",0803.2185v3
2008-03-20,Colossal spin fluctuations in a molecular quantum dot magnet with ferromagnetic electrodes,"We study electronic transport through a magnetic molecule with an intrinsic
spin $S$ coupled to two magnetic electrodes, in the incoherent regime. The
molecule is modeled as a single resonant level with large Coulomb repulsion (no
double occupancy). The molecular spin is isotropic and it interacts with the
electronic spin through an exchange interaction. Using an alternative method to
the usual master equation approach, we are able to obtain analytical formulas
for various physical quantities of interest, such as the mean current and the
current fluctuations, but also the mean value of $J_z$ -the $z$ component of
the total spin on the molecule- and its fluctuations. This allows us to
understand how the electronic current between the magnetized electrodes can
control the polarization of the molecular spin. We observe in particular that
the fluctuations of $J_z$ reach unexpectedly high values.",0803.3058v1
2008-04-25,Magnetic Excitations in the High Tc Iron Pnictides,"We calculate the expected finite frequency neutron scattering intensity based
on the two-sublattice collinear antiferromagnet found by recent neutron
scattering experiments as well as by theoretical analysis on the iron
oxypnictide LaOFeAs. We consider two types of superexchange couplings between
Fe atoms: nearest-neighbor coupling J1 and next-nearest-neighbor coupling J2.
We show how to distinguish experimentally between ferromagnetic and
antiferromagnetic J1. Whereas magnetic excitations in the cuprates display a
so-called resonance peak at (pi,pi) (corresponding to a saddlepoint in the
magnetic spectrum) which is at a wavevector that is at least close to nesting
Fermi-surface-like structures, no such corresponding excitations exist in the
iron pnictides. Rather, we find saddlepoints near (pi,pi/2) and (0,pi/2)(and
symmetry related points). Unlike in the cuprates, none of these vectors are
close to nesting the Fermi surfaces.",0804.4115v4
2008-05-07,Frustration and entanglement in the $t_{2g}$ spin--orbital model on a triangular lattice: valence--bond and generalized liquid states,"We consider the spin--orbital model for a magnetic system with singly
occupied but triply degenerate $t_{2g}$ orbitals coupled into a planar,
triangular lattice, as would be exemplified by NaTiO$_2$. We investigate the
ground states of the model for interactions which interpolate between the
limits of pure superexchange and purely direct exchange interactions. By
considering ordered and dimerized states at the mean--field level, and by
interpreting the results from exact diagonalization calculations on selected
finite systems, we demonstrate that orbital interactions are always frustrated,
and that orbital correlations are dictated by the spin state, manifesting an
intrinsic entanglement of these degrees of freedom. In the absence of Hund
coupling, the ground state changes from a highly resonating, dimer--based,
symmetry--restored spin and orbital liquid phase, to one based on completely
static, spin--singlet valence bonds. The generic properties of frustration and
entanglement survive even when spins and orbitals are nominally decoupled in
the ferromagnetic phases stabilized by a strong Hund coupling. By considering
the same model on other lattices, we discuss the extent to which frustration is
attributable separately to geometry and to interaction effects.",0805.1028v1
2008-05-13,Modification of magnetic and transport properties of manganite layers in Au/La_0.67Sr_0.33MnO_3/SrTiO_3 interfaces,"The effect of gold capping on magnetic and transport properties of optimally
doped manganite thin films is studied. An extraordinary suppression of
conductivity and magnetic properties occurs in epitaxial (001)
La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of
Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity
increases by four orders of magnitude while the Curie temperature decreases by
180 K. Zero-field 55Mn nuclear magnetic resonance reveals a significant
reduction of ferromagnetic double-exchange mechanism in manganite films upon
the gold capping. We find evidence for the formation of a 1.9-nm thick magnetic
""dead-layer"" at the Au/LSMO interface, associated with the creation of
interfacial non double-exchange insulating phases.",0805.1813v1
2008-08-28,Bias and angular dependence of spin-transfer torque in magnetic tunnel junctions,"We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the
spin-transfer torque vector T in MgO-based magnetic tunnel junctions as a
function of the offset angle between the magnetic moments of the electrodes and
as a function of bias, V. We explain the conflicting conclusions of two
previous experiments by accounting for additional terms that contribute to the
ST-FMR signal at large |V|. Including the additional terms gives us improved
precision in the determination of T(V), allowing us to distinguish among
competing predictions. We determine that the in-plane component of has a weak
but non-zero dependence on bias, varying by 30-35% over the bias range where
the measurements are accurate, and that the perpendicular component can be
large enough to be technologically significant. We also make comparisons to
other experimental techniques that have been used to try to measure T(V).",0808.3810v2
2008-10-31,Magnetoresistance in Spin-Polarized Transport through a Carbon Nanotube,"We report on our theoretical study of the magnetoresistance in spin polarized
transport through a finite carbon nanotube (CNT). Varying the Fermi energy of a
CNT and the relative strength of couplings to two ferromagnetic (FM)
electrodes, we studied the conductance as well as the magnetoresistance (MR).
Due to resonant transport through discrete energy levels in a finite CNT, the
conductance and MR are oscillating as a function of the CNT Fermi energy. The
MR is peaked at the conductance valleys and dipped close to the conductance
peaks. When couplings to two FM electrodes are asymmetric, the MR dips become
negative under a rather strong asymmetry. When couplings are more or less
symmetric, the MR dips remain positive except for a very strong coupling case.
Under strong coupling case, the line broadening is significant and transport
channels through neighboring energy levels in a CNT interfere with each other,
leading to the negative MR.",0810.5719v1
2008-10-31,Quantum electric dipole glass and frustrated magnetism near a critical point in Li2ZrCuO4,"We report a new peculiar effect of the interaction between a sublattice of
frustrated quantum spin-1/2 chains and a sublattice of pseudospin-1/2 centers
(quantum electric dipoles) uniquely co-existing in the complex oxide Li2ZrCuO4.
7Li nuclear magnetic-, Cu2+ electron spin resonance and a complex dielectric
constant data reveal that the sublattice of Li+-derived electric dipoles orders
glass like at Tg ~ 70 K yielding a spin site nonequivalency in the CuO2 chains.
We suggest that such a remarkable interplay between electrical and spin degrees
of freedom might strongly influence the properties of the spiral spin state in
Li2ZrCuO4 that is close to a quantum ferromagnetic critical point. In
particular that strong quantum fluctuations and/or the glassy behavior of
electric dipoles might renormalize the exchange integrals affecting this way
the pitch angle of the spiral as well as be responsible for the missing
multiferroicity present in other helicoidal magnets.",0810.5754v3
2008-11-20,Magnetic structure of the field-induced multiferroic GdFe3(BO3)4,"We report a magnetic x-ray scattering study of the field-induced multiferroic
GdFe3(BO3)4. Resonant x-ray magnetic scattering at the Gd LII,III edges
indicates that the Gd moments order at TN ~ 37 K. The magnetic structure is
incommensurate below TN, with the incommensurability decreasing monotonically
with decreasing temperature until a transition to a commensurate magnetic phase
is observed at T ~ 10 K. Both the Gd and Fe moments undergo a spin
reorientation transition at TSR ~ 9 K such that the moments are oriented along
the crystallographic c axis at low temperatures. With magnetic field applied
along the a axis, our measurements suggest that the field-induced polarization
phase has a commensurate magnetic structure with Gd moments rotated ~45 degrees
toward the basal plane, which is similar to the magnetic structure of the Gd
subsystem observed in zero field between 9 and 10 K, and the Fe subsystem has a
ferromagnetic component in the basal plane.",0811.3369v1
2008-12-05,Tunnelling magnetoresistance anomalies of a Coulomb blockaded quantum dot,"We consider quantum transport and tunneling magnetoresistance (TMR) through
an interacting quantum dot in the Coulomb blockade regime, attached to
ferromagnetic leads. We show that there exist two kinds of anomalies of TMR,
which have different origin. One type, associated with TMR sign change and
appearing at conductance resonances, is of single particle origin. The second
type, inducing a pronounced increase of TMR value far beyond 100%, is caused by
electron correlations. It is manifested in-between Coulomb blockade conductance
peaks. Both types of anomalies are discussed for zero and finite bias and their
robustness to the temperature increase is also demonstrated. The results are
presented in the context of recent experiments on semiconductor quantum dots in
which similar features of TMR have been observed.",0812.1109v2
2009-02-06,Na ordering imprints a metallic kagome lattice onto the Co planes of Na2/3CoO2,"We report $^{23}$Na and $^{59}$Co nuclear magnetic (NMR) and quadrupolar
resonance (NQR) studies for the $x=2/3$ phase of the lamellar oxide
Na$_{x}$CoO$_{2}$, which allowed us to establish reliably the atomic order of
the Na layers and their stacking between the CoO$_{2}$ slabs. We evidence that
the Na$^{+}$ order stabilizes filled non magnetic Co$^{3+}$ ions on 25% of the
cobalt sites arranged in a triangular sublattice. The transferred holes are
delocalized on the 75% complementary cobalt sites which unexpectedly display a
planar cobalt kagom\'{e} structure. These experimental results resolve a
puzzling issue by precluding localized moments pictures for the magnetic
properties. They establish that the quasi ferromagnetic properties result from
a narrow band connecting a frustrated arrangement of atomic orbitals, and open
the route to unravel through similar studies the electronic properties of the
diverse ordered phases of sodium cobaltates.",0902.1108v1
2009-07-05,Determination of the mosaic angle distribution of Grafoil platelets using continuous-wave NMR spectra,"We described details of a method to estimate with good accuracy the mosaic
angle distributions of microcrystallites (platelets) in exfoliated graphite
like Grafoil which is commonly used as an adsorption substrate for helium thin
films. The method is based on analysis of resonance field shifts in
continuous-wave (CW) NMR spectra of $^{3}$He ferromagnetic monolayers making
use of the large nuclear polarization of the adsorbate itself. The mosaic angle
distribution of a Grafoil substrate analyzed in this way can be well fitted to
a gaussian form with a $27.5\pm2.5$ deg spread. This distribution is quite
different from the previous estimation based on neutron scattering data which
showed an unrealistically large isotropic powder-like component.",0907.0848v2
2009-07-22,Strong-field interactions between a nanomagnet and a photonic cavity,"We analyze the interaction of a nanomagnet with a single photonic mode of a
microcavity in a fully quantum-mechanical treatment and find that exceptionally
large quantum-coherent magnet-photon coupling can be achieved. Coupling terms
in excess of several THz are predicted to be achievable in a spherical cavity
of ~1 mm radius with a nanomagnet of ~100 nm radius and ferromagnetic resonance
frequency of ~200 GHz. Eigenstates of the magnet-photon system correspond to
entangled states of spin orientation and photon number, in which over 10^5
values of each quantum number are represented; conversely initial (coherent)
states of definite spin and photon number evolve dynamically to produce large
oscillations in the microwave power (and nanomagnet spin orientation), and are
characterized by exceptionally long dephasing times.",0907.3926v1
2009-08-25,Non-equilibrium dynamics of interacting Fermi systems in quench experiments,"We describe the dynamics of two component non-interacting ultracold Fermions
which are initially in thermal equilibrium and undergo a rapid quench to either
the repulsive or attractive side of a Feshbach resonance. The short time
dynamics is dominated by the exponentially growing collective modes. We study
the Stoner instability and formation of ferromagnetic textures on the repulsive
side, and the pairing instability towards BCS or FFLO-like states (determined
by the population imbalance) on the attractive side. In each case, we evaluate
the growth rate of unstable modes and predict the typical lengthscale of
textures to be formed.",0908.3483v2
2009-08-31,Hyperfine Interactions and Spin Transport in Ferromagnet-Semiconductor Heterostructures,"Measurements and modeling of electron spin transport and dynamics are used to
characterize hyperfine interactions in Fe/GaAs devices with $n$-GaAs channels.
Ga and As nuclei are polarized by electrically injected electron spins, and the
nuclear polarization is detected indirectly through the depolarization of
electron spins in the hyperfine field. The dependence of the electron spin
signal on injector bias and applied field direction is modeled by a coupled
drift-diffusion equation, including effective fields from both the electronic
and nuclear polarizations. This approach is used to determine the electron spin
polarization independently of the assumptions made in standard transport
measurements. The extreme sensitivity of the electron spin dynamics to the
nuclear spin polarization also facilitates the electrical detection of nuclear
magnetic resonance.",0909.0048v1
2009-11-20,Spin Transfer Dynamics in Spin Valves with Out-of-plane Magnetized CoNi Free Layers,"We have measured spin transfer-induced dynamics in magnetic nanocontact
devices having a perpendicularly magnetized Co/Ni free layer and an in-plane
magnetized CoFe fixed layer. The frequencies and powers of the excitations
agree well with the predictions of the single-domain model and indicate that
the excited dynamics correspond to precessional orbits with angles ranging from
zero to 90 degrees as the applied current is increased at a fixed field. From
measurements of the onset current as a function of applied field strength we
estimate the magnitude of the spin torque asymmetry parameter lambda ~ 1.5. By
combining these with spin torque ferromagnetic resonance measurements, we also
estimate the spin wave radiation loss in these devices.",0911.4077v1
2010-01-20,Precise probing spin wave mode frequencies in the vortex state of circular magnetic dots,"We report on detailed broadband ferromagnetic resonance measurements of
azimuthal and radial spin wave excitations in circular Permalloy dots in the
vortex ground state. Dots with aspect ratio (Beta =height over radius) varied
from 0.03 to 0.1 were explored. We found that for Beta exceeding approximately
0.05, variation of the spin wave eigenfrequencies with Beta deviates from the
predicted dependence. The frequency splitting of two lowest azimuthal modes was
observed. The experimentally observed dependence of the frequency splitting on
beta was reasonably well described by dynamic splitting model accounting the
spin-waves and, vortex gyrotropic mode interaction.",1001.3605v1
2010-04-30,Orbital glass and spin glass states of 3He-A in aerogel,"Glass states of superfluid A-like phase of 3He in aerogel induced by random
orientations of aerogel strands are investigated theoretically and
experimentally. In anisotropic aerogel with stretching deformation two glass
phases are observed. Both phases represent the anisotropic glass of the orbital
ferromagnetic vector l -- the orbital glass (OG). The phases differ by the spin
structure: the spin nematic vector d can be either in the ordered spin nematic
(SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN)
is formed under conventional cooling from normal 3He. The second phase (OG-SG)
is metastable, being obtained by cooling through the superfluid transition
temperature, when large enough resonant continuous radio-frequency excitation
are applied. NMR signature of different phases allows us to measure the
parameter of the global anisotropy of the orbital glass induced by deformation.",1004.5483v1
2010-07-14,Straining the Identity of Majorana Fermions,"We propose an experimental setup of an interferometer for the observation of
neutral Majorana fermions on topological insulator - superconductor -
ferromagnet junctions. We show that the extended lattice defects naturally
present in materials, dislocations, induce spin currents on the edges while
keeping the bulk time-reversal symmetry intact. We propose a simple two
terminal conductance measurement in an interferometer formed by two edge point
contacts, which reveals the nature of Majorana states through the effect of
dislocations. The zero temperature magneto-conductance changes from even
oscillations with period phi/2 (phi is the flux quantum hc/e) to odd
oscillations with period phi, when non-trivial dislocations are present and the
Majorana states are sufficiently strongly coupled. Additionally, the
conductance acquires a notable asymmetry as a function of the incident electron
energy, due to the topological influence of the dislocations, while resonances
appear at the coupling energy of Majorana states.",1007.2350v3
2010-09-16,Field and temperature dependence of the NMR relaxation rate in the magnetic quadrupolar liquid phase of spin-1/2 frustrated ferromagnetic chains,"It is generally difficult to experimentally distinguish magnetic multipolar
orders in spin systems. Recently, it was proposed that the temperature
dependence of the nuclear magnetic resonance relaxation rate 1/T_1 can involve
an indirect, but clear signature of the field-induced spin nematic or
multipolar Tomonaga-Luttinger (TL) liquid phase [Phys. Rev. B79, 060406(R)
(2009)]. In this paper, we evaluate accurately the field and temperature
dependence of 1/T_1 in spin-1/2 frustrated J1-J2 chains combining
field-theoretical techniques with numerical data. Our results demonstrate that
isotherms of 1/T_1 as a function of magnetic field also exhibit distinctive
non-monotonic behavior in spin nematic TL liquid, in contrast with the standard
TL liquid in the spin-1/2 Heisenberg chain. The relevance of our results to
quasi one-dimensional edge-sharing cuprate magnets, such as LiCuVO4, is
discussed.",1009.3206v2
2010-09-26,Detection and quantification of inverse spin Hall effect from spin pumping in permalloy/normal metal bilayers,"Spin pumping is a mechanism that generates spin currents from ferromagnetic
resonance (FMR) over macroscopic interfacial areas, thereby enabling sensitive
detection of the inverse spin Hall effect that transforms spin into charge
currents in non-magnetic conductors. Here we study the spin-pumping-induced
voltages due to the inverse spin Hall effect in permalloy/normal metal bilayers
integrated into coplanar waveguides for different normal metals and as a
function of angle of the applied magnetic field direction, as well as microwave
frequency and power. We find good agreement between experimental data and a
theoretical model that includes contributions from anisotropic
magnetoresistance (AMR) and inverse spin Hall effect (ISHE). The analysis
provides consistent results over a wide range of experimental conditions as
long as the precise magnetization trajectory is taken into account. The spin
Hall angles for Pt, Pd, Au and Mo were determined with high precision to be
$0.013\pm0.002$, $0.0064\pm0.001$, $0.0035\pm0.0003$ and $-0.0005\pm0.0001$,
respectively.",1009.5089v1
2010-12-10,Defect driven ferroelectricity and magnetism in nanocrystalline KTaO3,"Nominally pure nanocrystalline KTaO3 was thoroughly investigated by
micro-Raman and magnetic resonance spectroscopic techniques. In all samples the
defect driven ferroelectricity and magnetism are registered. Both ordering
states are suggested to appear due to the iron atoms and oxygen vacancies. The
concentration of defects was estimated to be 0.04 and 0.06-0.1 mole %,
respectively. Note that undoped single crystals of KTaO3 are nonmagnetic and
have never exhibited ferromagnetic properties. The results enable us to refer a
nanosized KTa(Fe)O3 to the class of multiferroics and assume that it could
perform the magnetoelectric effect at T<29 K. It was also established that the
critical concentration of impurity defects necessary to provoke the appearance
of the new phase states in the material strongly correlates with the size of
the particle; as the size of the particle decreases, the critical concentration
decreases as well.",1012.2295v1
2010-12-17,Observation of Andreev bound states at spin-active interfaces,"We report on high-resolution differential conductance experiments on
nanoscale superconductor/ferromagnet tunnel junctions with ultra-thin oxide
tunnel barriers. We observe subgap conductance features which are symmetric
with respect to bias, and shift according to the Zeeman energy with an applied
magnetic field. These features can be explained by resonant transport via
Andreev bound states induced by spin-active scattering at the interface. From
the energy and the Zeeman shift of the bound states, both the magnitude and
sign of the spin-dependent interfacial phase shifts between spin-up and
spin-down electrons can be determined. These results contribute to the
microscopic insight into the triplet proximity effect at spin-active
interfaces.",1012.3867v2
2011-03-01,Quantum Corrals and Quantum Mirages on the Surface of a Topological Insulator,"We study quantum corrals on the surface of a topological insulator (TI).
Different resonance states induced by nonmagnetic (NM), antiferromagnetic
(AFM), and ferromagnetic (FM) corrals are found. Intriguingly, the spin is
clearly energy-resolved in a FM corral, which can be effectively used to
operate surface carrier spins of TI. We also show that an observable quantum
mirage of a magnetic impurity can be projected from the occupied into the empty
focus of a FM elliptic corral, while in NM and AFM corrals the mirage signal
becomes negligibly weak. In addition, the modulation of the interaction between
two magnetic impurities in the quantum corrals is demonstrated. These prominent
effects may be measured by spin-polarized STM experiments.",1103.0130v2
2011-07-02,Spin-pumping-induced spin transport in p-type Si at room temperature,"A spin battery concept is applied for the dynamical generation of pure spin
current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance
and effective s-d coupling in Ni80Fe20 results in spin accumulation at the
Ni80Fe20/p-Si interface, inducing spin injection and the generation of spin
current in the p-Si. The pure spin current is converted to a charge current by
the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach
demonstrates the generation and transport of pure spin current in p-Si at room
temperature.",1107.0376v4
2011-07-04,Influence of randomness and retardation on the FMR-linewidth,"The theory predicts that the spin-wave lifetime $\tau_L$ and the linewidth of
ferromagnetic resonance $\Delta B$ can be governed by random fields and spatial
memory. To that aim the effective field around which the magnetic moments
perform a precession is superimposed by a stochastic time dependent magnetic
field with finite correlation time. The magnetization dynamics is altered by
inclusion of a spatial memory effect monitoring a non-local interaction of size
$\xi$. The underlying Landau-Lifshitz-Gilbert equation (LLG) is modified
accordingly. The stochastic LLG is equivalent to a Fokker-Planck equation which
enables to calculate the mean values of the magnetization vector. Within the
spin-wave approximation we present an analytical solution for the excitation
energy and its damping. The lifetime and the linewidth are analyzed depending
on the strength of the random field $D$ and its correlation time $\tau_c$ as
well as the retardation strength $\Gamma_0$ and the size $\xi$. Whereas
$\tau_L$ decreases with increasing $D$, retardation strength $\Gamma_0$ and
$\tau_c$, the lifetime is enhanced for growing width $\xi$ of the spatial
retardation kernel. In the same manner we calculate the experimentally
measurable linewidth $\Delta B$ is increased strongly when the correlation time
$\tau_c$ ranges in the nanosecond interval.",1107.0638v1
2011-07-06,Spin-Split Conduction band in \eb\ and Tuning of Half-Metallicity with External Stimuli,"We report Eu L3-edge resonant inelastic x-ray scattering (RIXS) investigation
of the electronic structure of EuB6. We observe that the RIXS spectral weight
around 1.1 eV increases dramatically when the system is cooled below the
ferromagnetic ordering temperature and follows the magnetic order parameter.
This spectral feature is attributed to the inter-site excitation from the local
4f orbital to the spin-split 5d orbital on the neighboring site, illustrating
the essential role of exchange splitting of the conducting electrons. Based on
our density functional theory calculations, the RIXS data suggest that EuB6 at
low temperature can be consistently described with a semi-metallic electronic
structure with incomplete spin-polarization. We propose routes to achieve
half-metallicity in EuB6, which utilize the strong tunability of the electronic
structure against gate voltage, strain, and magnetic field.",1107.1192v1
2011-07-14,LC-Circuit Calorimetry,"We present a new type of calorimeter in which we couple an unknown heat
capacity with the aid of Peltier elements to an electrical circuit. The use of
an electrical inductance and an amplifier in the circuit allows us to achieve
autonomous oscillations, and the measurement of the corresponding resonance
frequency makes it possible to accurately measure the heat capacity with an
intrinsic statistical error that decreases as ~t^{-3/2} with measuring time t,
as opposed to a corresponding error ~t^{-1/2} in the conventional alternating
current (a.c.) method to measure heat capacities. We have built a demonstration
experiment to show the feasibility of the new technique, and we have tested it
on a gadolinium sample at its transition to the ferromagnetic state.",1107.2801v1
2011-08-09,Correlations and Pair Formation in a Repulsively Interacting Fermi Gas,"A degenerate Fermi gas is rapidly quenched into the regime of strong
effective repulsion near a Feshbach resonance. The spin fluctuations are
monitored using speckle imaging and, contrary to several theoretical
predictions, the samples remain in the paramagnetic phase for arbitrarily large
scattering length. Over a wide range of interaction strengths a rapid decay
into bound pairs is observed over times on the order of 10\hbar/E_F, preventing
the study of equilibrium phases of strongly repulsive fermions. Our work
suggests that a Fermi gas with strong short-range repulsive interactions does
not undergo a ferromagnetic phase transition.",1108.2017v2
2011-08-31,Quantum impurity coupled to Majorana edge fermions,"We study a quantum impurity coupled to the edge states of a two-dimensional
helical topological superconductor, i.e., to a pair of counterpropagating
Majorana fermion edge channels with opposite spin polarizations. For an
impurity described by the Anderson impurity model, we show that the problem
maps onto a variant of the interacting resonant two-level model which, in turn,
maps onto the ferromagnetic Kondo model. Both magnetic and non-magnetic
impurities are considered. For magnetic impurities, the bosonization and
numerical renormalization group analyses show that the system flows to a fixed
point with residual ln 2 entropy and we find characteristically anisotropic
static and dynamic impurity magnetic susceptibilities. For non-magnetic
impurities, the system flows to a fixed point with no residual entropy and we
find diamagnetic response at low temperatures. We comment on the
Schrieffer-Wolff transformation for problems with non-standard conduction band
continua and on the issues related to the differences in describing the
impurities by either Anderson or Kondo impurity models.",1108.6142v2
2011-09-26,Anomalous Hall Effect in Ferromagnetic Metals: Role of Phonons at Finite Temperature,"The anomalous Hall effect in a multiband tight-binding model is numerically
studied taking into account both elastic scattering by disorder and inelastic
scattering by the electron-phonon interaction. The Hall conductivity is
obtained as a function of temperature $T$, inelastic scattering rate $\gamma$,
chemical potential $\mu$, and impurity concentration $x_{\rm imp}$. We find
that the new scaling law holds over a wide range of these parameters;
$-\sigma_{xy}= (\alpha \sigma_{xx0}^{-1} + \beta \sigma_{xx0}^{-2})
\sigma_{xx}^2 + b$, with $\sigma_{\mu \nu}$ ($\sigma_{\mu \nu 0}$) being the
conductivity tensor (with only elastic scattering), which corresponds to the
recent experimental observation [Phys. Rev. Lett. {\bf 103} (2009) 087206]. The
condition of this scaling is examined. Also, it is found that the intrinsic
mechanism depends on temperature under a resonance condition.",1109.5463v2
2012-02-19,Magnetoelastic Coupling and Possibility of Spintronic Electromagnetomechanical Effects,"Nanoelectromangetomechanical systems (NEMMS) open up a new path for the
development of high speed autonomous nanoresonators and signal generators that
could be used as actuators, for information processing, as elements of quantum
computers etc. Those NEMMS that include ferromagnetic layers could be
controlled by the electric current due to effects related with spin transfer.
In the present paper we discuss another situation when the current-controlled
behaviour of nanorod that includes an antiferro- (instead of one of ferro-)
magnetic layer. We argue that in this case ac spin-polarized current can also
induce resonant coupled magneto-mechanical oscillations and produce an
oscillating magnetization of antiferromagnetic (AFM) layer. These effects are
caused by \emph{i}) spin-transfer torque exerted to AFM at the interface with
nonmagnetic spacer and by \emph{ii}) the effective magnetic field produced by
the spin-polarized free electrons due to $sd$-exchange.The described nanorod
with an AFM layer can find an application in magnetometry and as a
current-controlled high-frequency mechanical oscillator.",1202.4181v1
2012-02-28,Spin-chain system as a tunable simulator of frustrated planar magnetism,"At low temperatures, weakly coupled spin chains develop a magnetic order that
reflects the character of gapless spin fluctuations along the chains. Using
nuclear magnetic resonance, we identify and characterize two ordered states in
the gapless region of the antiferromagnetic, Ising-like spin-chain system
BaCo2V2O8, both arising from the incommensurate fluctuations along the chains.
They correspond to the columnar and ferromagnetic ordered states of the
frustrated J1-J2 spin model on a square lattice, where the spins are encoded in
original spin chains. As a result of field-dependent incommensurate
fluctuations and frustrated interchain interaction, J1 can be tuned
continuously with the magnetic field, and its value with respect to a fixed J2
selects the ordered state. Spin-chain systems can thus be used as tunable
simulators of frustrated planar magnetism.",1202.6374v1
2012-03-14,Temperature dependence of in-plane correlation lengths in exchange biased Co/FeF2,"We have measured resonant soft x-ray diffuse magnetic scattering as a
function of temperature in a positively exchange biased Co/FeF2 bilayer and
analyzed the data in the distorted wave Born approximation to obtain in-plane
charge and magnetic correlation lengths associated with the Co and FeF2 layers
and estimate interfacial roughness. Tuning to the Fe and Co L3 edges reveals
significantly different temperature trends in these quantities in the
antiferromagnetic and ferromagnetic layers, respectively. While the magnetic
correlation length of the uncompensated interfacial spins in FeF2 layer
increase as temperature decreases, these quantities remain unchanged in the Co
layer. Our results indicate that uncompensated Fe spins order within a range of
few hundred nanometers in otherwise randomly distributed uncompensated magnetic
moments, giving rise to spin clusters in the antiferromagnet whose size
increase as the temperature decrease.",1203.3231v1
2012-07-12,Mean-Field Analysis of Spinor Bosons in Optical Superlattices,"We study the ground-state phase diagram of spinless and spin-1 bosons in
optical superlattices using a Bose-Hubbard Hamiltonian that includes
spin-dependent interactions. We decouple the unit cells of the superlattice via
a mean-field approach and take into account the dynamics within the unit cell
exactly. The system supports Mott-insulating as well as superfluid phases. The
transitions between these phases are second-order for spinless bosons and
second- or first-order for spin-1 bosons. Anti-ferromagnetic interactions
energetically penalize high-spin configurations and elongate all Mott lobes,
especially the ones corresponding to an even atom number on each lattice site.
We find that the quadratic Zeeman effect lifts the degeneracy between different
polar superfluid phases leading to additional metastable phases and first-order
phase transitions. Finally, we show that an energy offset between the two sites
of the unit cell induces a staircase of single-atom tunneling resonances which
surprisingly survives well into the superfluid regime.",1207.2911v1
2012-08-08,Spin transfer torque devices utilizing the giant spin Hall effect of tungsten,"We report a giant spin Hall effect (SHE) in {\beta}-W thin films. Using spin
torque induced ferromagnetic resonance with a {\beta}-W/CoFeB bilayer
microstrip we determine the spin Hall angle to be |\theta|=0.30\pm0.02, large
enough for an in-plane current to efficiently reverse the orientation of an
in-plane magnetized CoFeB free layer of a nanoscale magnetic tunnel junction
adjacent to a thin {\beta}-W layer. From switching data obtained with such
3-terminal devices we independently determine |\theta|=0.33\pm0.06. We also
report variation of the spin Hall switching efficiency with W layers of
different resistivities and hence of variable ({\alpha} and {\beta}) phase
composition.",1208.1711v1
2012-08-09,Attenuation characteristics of spin pumping signal due to travelling spin waves,"The authors have investigated the contribution of the surface spin waves to
spin pumping. A Pt/NiFe bilayer has been used for measuring spin waves and spin
pumping signals simultaneously. The theoretical framework of spin pumping
resulting from ferromagnetic resonance has been extended to incorporate spin
pumping due to spin waves. Equations for the effective area of spin pumping due
to spin waves have been derived. The amplitude of the spin pumping signal
resulting from travelling waves is shown to decrease more rapidly with
precession frequency than that resulting from standing waves and show good
agreement with the experimental data.",1208.1837v1
2012-08-13,Tunable photo-galvanic effect on topological insulator surfaces via proximity interactions,"An unusual photo-galvanic effect is predicted on the topological insulator
surface when its semi-metallic electronic spectrum is modified by an adjacent
ferromagnet. The effect is correlated with light absorption in a wide frequency
range (from a few to hundreds of meV) and produces a pronounced response that
is not only resonant to the photon energy but also tunable by an external
electrical bias. The exceptionally strong peak photocurrent of the order of
$\mu$A/cm may be achieved at elevated temperatures with the illumination power
of 1 W/cm$^2$ in the THz range on Bi$_2$Se$_3$. These advantages could enable
room-temperature detection of far-infrared radiation.",1208.2619v1
2012-10-25,Microwave properties of Nb/PdNi/Nb trilayers. Observation of flux flow in excess of Bardeen-Stephen theory,"We combine wideband (1-20 GHz) Corbino disk and dielectric resonator (8.2
GHz) techniques to study the microwave properties in Nb/PdNi/Nb trilayers,
grown by UHV dc magnetron sputtering, composed by Nb layers of nominal
thickness $d_S$=15 nm, and a ferromagnetic PdNi layer of thickness $d_F$= 1, 2,
8 and 9 nm. We focus on the vortex state. Magnetic fields up to $H_{c2}$ were
applied. The microwave resistivity at fixed $H/H_{c2}$ increases with $d_F$,
eventually exceeding the Bardeen Stephen flux flow value.",1210.6974v1
2012-11-02,Dynamic Spin Injection into Chemical Vapor Deposited Graphene,"We demonstrate dynamic spin injection into chemical vapor deposition (CVD)
grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic
resonance measurements at room temperature reveal a strong enhancement of the
Gilbert damping at the Py/graphene interface, exceeding that observed in even
Py/platinum interfaces. Similar results are also shown on Co/graphene layers.
This enhancement in the Gilbert damping is understood as the consequence of
spin pumping at the interface driven by magnetization dynamics. Our
observations suggest a strong enhancement of spin-orbit coupling in CVD
graphene, in agreement with earlier spin valve measurements.",1211.0492v1
2012-11-06,Experimental Verification of Comparability between Spin-Orbit and Spin-Diffusion Lengths,"We experimentally confirmed that the spin-orbit lengths of noble metals
obtained from weak anti-localization measurements are comparable to the spin
diffusion lengths determined from lateral spin valve ones. Even for metals with
strong spin-orbit interactions such as Pt, we verified that the two methods
gave comparable values which were much larger than those obtained from recent
spin torque ferromagnetic resonance measurements. To give a further evidence
for the comparability between the two length scales, we measured the disorder
dependence of the spin-orbit length of copper by changing the thickness of the
wire. The obtained spin-orbit length nicely follows a linear law as a function
of the diffusion coefficient, clearly indicating that the Elliott-Yafet
mechanism is dominant as in the case of the spin diffusion length.",1211.1222v2
2012-11-10,Quasibound States and Evidence for a Spin 1 Kondo Effect in Asymmetric Quantum Point Contacts,"Linear conductance below $2e^2/h$ shows resonance peaks in highly asymmetric
quantum point contacts (QPCs). As the channel length increases, the number of
peaks also increases. At the same time, differential conductance exhibits zero
bias anomalies (ZBAs) in correspondence with every other peak in the linear
conductance. This even odd effect, observable in the longer channels, is
consistent with the formation of quasi-localized states within the QPC. In rare
cases, triple peaks are observed, indicating the formation of a spin one Kondo
effect when the electron filling number is even. Changing the gate voltage
tunes this spin triplet to a singlet which exhibits no ZBA. The triple-peak
provides the first evidence suggestive of a spin singlet triplet transition in
a QPC, and the presence of a ferromagnetic spin interaction between electrons.",1211.2269v2
2013-01-13,Direct k-space mapping of the electronic structure in an oxide-oxide interface,"The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron
system of itinerant carriers, although both oxides are band insulators.
Interface ferromagnetism coexisting with superconductivity has been found and
attributed to local moments. Experimentally, it has been established that Ti 3d
electrons are confined to the interface. Using soft x-ray angle-resolved
resonant photoelectron spectroscopy we have directly mapped the interface
states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction
contributes to Fermi surface sheets, whereas a localized portion at higher
binding energies is tentatively attributed to electrons trapped by O-vacancies
in the SrTiO3. While photovoltage effects in the polar LaAlO3 layers cannot be
excluded, the apparent absence of surface-related Fermi surface sheets could
also be fully reconciled in a recently proposed electronic reconstruction
picture where the built-in potential in the LaAlO3 is compensated by surface
O-vacancies serving also as charge reservoir.",1301.2824v2
2013-02-10,Measurement of orbital asymmetry and strain in Co90Fe10/Ni multilayers and alloys: Origins of perpendicular anisotropy,"We use broadband ferromagnetic resonance spectroscopy and x-ray diffraction
to investigate the fundamental origin of perpendicular anisotropy in
Co90Fe10/Ni multilayers. By careful evaluation of the spectroscopic g-factor,
we determine the orbital moment along the out-of-plane and in-plane directions.
For the multilayers, we find a direct relationship between the orbital moment
asymmetry and the perpendicular anisotropy, consistent with the theory of Bruno
[P.Bruno, Phys. Rev. B, 39, 865 (1989)]. A systematic x-ray diffraction study
revealed the presence of a trigonal strain as high as 0.7 % in some samples.
However, we found no direct correlation between the strain and the anisotropy,
indicating that the anisotropy is not dominated by magnetoelastic effects. In
order to further study the interface structure on the anisotropy, we prepared a
set of equivalent alloy samples. The strain in the alloy samples was comparable
to that of the multilayer samples; however the orbital moment asymmetry in the
alloy samples showed a very different trend allowing us to isolate the effect
of the interfaces in the multilayers.",1302.2366v1
2013-02-27,Optimization of the yttrium iron garnet/platinum interface for spin pumping-based applications,"The dependence of the spin pumping efficiency and the spin mixing conductance
on the surface processing of yttrium iron garnet (YIG) before the platinum (Pt)
deposition has been investigated quantitatively. The ferromagnetic resonance
driven spin pumping injects a spin polarized current into the Pt layer, which
is transformed into an electromotive force by the inverse spin Hall effect. Our
experiments show that the spin pumping effect indeed strongly depends on the
YIG/Pt interface condition. We measure an enhancement of the inverse spin Hall
voltage and the spin mixing conductance of more than two orders of magnitude
with improved sample preparation.",1302.6697v1
2013-02-28,Spin-polarized Shapiro steps and spin-precession-assisted multiple Andreev reflection,"We investigate the charge and spin transport of a voltage-biased
superconducting point contact coupled to a nanomagnet. The magnetization of the
nanomagnet is assumed to precess with the Larmor frequency, $\omega_L$, due to
ferromagnetic resonance. The interplay between the ac Josephson current and the
magnetization dynamics leads to spin-polarized Shapiro steps at voltages
$|V|=\hbar \omega_L/2en$ for $n=1,2,...$ and the subharmonic steps with $n>1$
are a consequence of multiple Andreev reflection (MAR). Moreover, the
spin-precession-assisted MAR generates quasiparticle scattering amplitudes
that, due to interference, lead to current-voltage characteristics of the dc
charge and spin currents with subharmonic gap structures displaying an even-odd
effect.",1302.7107v1
2013-04-04,Dynamics of Antiferromagnets Driven by Spin Current,"When a spin-polarized current flows through a ferromagnetic (FM) metal,
angular momentum is transferred to the background magnetization via
spin-transfer torques. In antiferromagnetic (AFM) materials, however, the
corresponding problem is unsolved. We derive microscopically the dynamics of an
AFM system driven by spin current generated by an attached FM polarizer, and
find that the spin current exerts a driving force on the local staggered order
parameter. The mechanism does not rely on the conservation of spin angular
momentum, nor does it depend on the induced FM moments on top the AFM
background. Two examples are studied: (i) A domain wall is accelerated to a
terminal velocity by purely adiabatic effect where the Walker's break-down is
avoided; and (ii) Spin injection modifies the AFM resonance frequency, and spin
current injection triggers spin wave instability of local moments above a
threshold.",1304.1284v5
2013-05-28,Spin fluctuations with two-dimensional XY behavior in a frustrated S = 1/2 square-lattice ferromagnet,"The spin dynamics of the layered square-lattice vanadate Pb2VO(PO4)2 is
investigated by electron spin resonance at various magnetic fields and at
temperatures above magnetic ordering. The linewidth divergence towards low
temperatures seems to agree with isotropic Heisenberg-type spin exchange
suggesting that the spin relaxation in this quasi-two dimensional compound is
governed by low-dimensional quantum fluctuations. However, a weak easy- plane
anisotropy of the g factor points to the presence of a planar XY type of
exchange. Indeed, we found that the linewidth divergence is described best by
XY-like spin fluctuations which requires a single parameter only. Therefore,
ESR-probed spin dynamics could establish Pb2VO(PO4)2 as the first frustrated
square lattice system with XY-inherent spin topological fluctuations.",1305.6518v1
2013-07-01,Direct and converse magnetoelectric effects in Metglas/LiNbO3/Metglas trilayers,"Electromechanical and magnetoelectric properties of Metglas/LiNbO3/Metglas
trilayers have been studied in the frequency range from 20 Hz to 0.4 MHz. A
trilayer of Metglas/PMN-PT/Metglas prepared in the same way was used as a
reference. Though PMN-PT has much larger charge piezocoefficients than LiNbO3
(LNO), the direct magnetoelectric voltage coefficient is found to be comparable
in both trilayers due to the much lower dielectric permittivity of LNO. The
magnitude of the direct magnetoelectric effect in the LNO trilayers is about
0.4 V/cm*Oe in the quasistatic regime and about 90 V/cm*Oe at electromechanical
resonance. Calculations show that the magnetoelectric properties can be
significantly improved (up to 500 V/cm*Oe) via controlling the cut angle of
LNO, choosing the appropriate thickness ratio of the
ferroelectric/ferromagnetic layers, and a better bonding between Metglas and
LNO. Advantages of using LiNbO3-type ferroelectrics in magnetoelectric
composites are discussed.",1307.0425v2
2013-07-17,Low-amplitude magnetic vortex core reversal by non-linear interference between azimuthal spin waves and the vortex gyromode,"We demonstrate a non-linear interference due to an active 'dual frequency'
excitation of both, the sub-GHz vortex gyromode and multi-GHz magneto-static
spin waves in ferromagnetic micrometer sized platelets in the vortex state.
When the sub-GHz vortex gyromode is excited simultaneously a significant
broadband reduction of the switching threshold for spin wave mediated vortex
core reversal is observed in both, experiments and micromagnetic simulations.
Consequently, the magnetic field amplitudes required for vortex core reversal
can be lowered by nearly one order of magnitude. Moreover, additional spin wave
resonance frequencies are found which emerge only if the vortex gyromode is
actively excited simultaneously which can be explained by frequency doubling
and by the broken symmetry of the vortex state.",1307.4548v1
2013-10-24,Dynamics in spinor condensates controlled by a microwave dressing field,"We experimentally study spin dynamics in a sodium antiferromagnetic spinor
condensate with off-resonant microwave pulses. In contrast to a magnetic field,
a microwave dressing field enables us to explore rich spin dynamics under the
influence of a negative net quadratic Zeeman shift $q_{\rm net}$. We find an
experimental signature to determine the sign of $q_{\rm net}$, and observe
harmonic spin population oscillations at every $q_{\rm net}$ except near each
separatrix in phase space where spin oscillation period diverges. In the
negative and positive $q_{\rm net}$ regions, we also observe a remarkably
different relationship between each separatrix and the magnetization. Our data
confirms an important prediction derived from the mean-field theory:
spin-mixing dynamics in spin-1 condensates substantially depends on the sign of
the ratio of $q_{\rm net}$ and the spin-dependent interaction energy. This work
may thus be the first to use only one atomic species to reveal mean-field spin
dynamics, especially the separatrix, which are predicted to appear differently
in spin-1 antiferromagnetic and ferromagnetic spinor condensates.",1310.6785v1
2013-12-17,Low energy magnetic excitations in the spin-orbital Mott insulator Sr$_2$IrO$_4$,"We report a high-field electron spin resonance study in the sub-THz frequency
domain of a single crystal of Sr$_2$IrO$_4$ that has been recently proposed as
a prototypical spin-orbital Mott insulator. In the antiferromagnetically (AFM)
ordered state with noncollinear spin structure that occurs in this material at
$T_{\rm N} \approx 240$ K we observe both the ""low"" frequency mode due to the
precession of weak ferromagnetic moments arising from a spin canting, and the
""high"" frequency modes due to the precession of the AFM sublattices.
Surprisingly, the energy gap for the AFM excitations appears to be very small,
amounting to 0.83 meV only. This suggests a rather isotropic Heisenberg
dynamics of interacting Ir$^{4+}$ effective spins despite the spin-orbital
entanglement in the ground state.",1312.4847v2
2013-12-26,Where is magnetic anisotropy field pointing to?,"The desired result of magnetic anisotropy investigations is the determination
of value(s) of various anisotropy constant(s). This is sometimes difficult,
especially when the precise knowledge of saturation magnetization is required,
as it happens in ferromagnetic resonance (FMR) studies. In such cases we
usually resort to `trick' and fit our experimental data to the quantity called
\emph{anisotropy field}, which is strictly proportional to the ratio of the
searched anisotropy constant and saturation magnetization. Yet, this quantity
is scalar, simply a number, and is therefore of little value for modeling or
simulations of the magnetostatic or micromagnetic structures. Here we show how
to `translate' the values of magnetic anisotropy constants into the complete
vector of magnetic anisotropy field. Our derivation is rigorous and covers the
most often encountered cases, from uniaxial to cubic anisotropy.",1312.7130v1
2014-02-13,Resonance in Magnetostatically Coupled Transverse Domain Walls,"We have observed the eigenmodes of coupled transverse domain walls in a pair
of ferromagnetic nanowires. Although the pair is coupled magnetostatically, its
spectrum is determined by a combination of pinning by edge roughness and
dipolar coupling of the two walls. Because the corresponding energy scales are
comparable, the coupling can be observed only at the smallest wire separations.
A model of the coupled wall dynamics reproduces the experiment quantitatively,
allowing for comparisons with the estimated pinning and domain wall coupling
energies. The results have significant implications for the dynamics of devices
based on coupled domain walls.",1402.3202v2
2014-02-23,Light-induced spin polarizations in quantum rings,"Non-resonant circularly polarized electromagnetic radiation can exert torques
on magnetization by the Inverse Faraday Effect (IFE). Here we discuss the
enhancement of IFE by spin-orbit interactions (SOI). We illustrate the
principle by studying a simple generic model system, i.e. the quasi-1D ring in
the presence of linear/cubic Rashba and Dresselhaus interactions. We combine
the classical IFE in electron plasmas that is known to cause persistent
currents in the plane perpendicular to the direction of the propagation of
light with the concept of current and spin-orbit-induced spin transfer torques.
We calculate light-induced spin polarization that in ferromagnets might give
rise to magnetization switching.",1402.5590v1
2014-04-14,Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet|platinum bilayers,"We carried out a concerted effort to determine the absolute sign of the
inverse spin Hall effect voltage generated by spin currents injected into a
normal metal. We focus on yttrium iron garnet (YIG)|platinum bilayers at room
temperature, generating spin currents by microwaves and temperature gradients.
We find consistent results for different samples and measurement setups that
agree with theory. We suggest a right-hand-rule to define a positive spin Hall
angle corresponding to with the voltage expected for the simple case of
scattering of free electrons from repulsive Coulomb charges.",1404.3490v2
2014-07-25,Spin pumping using an Ni80Fe20 thin film annealed in a magnetic field,"Spin pumping controlled with the ferromagnetic resonance of an Ni80Fe20 thin
film annealed in a magnetic field was performed in order to investigate the
simple and efficient generation method of the pure spin current. At the
spin-pumping using the Ni80Fe20 on an annealed Pd/Ni80Fe20 stacked structure,
the electromotive force due to the inverse spin-Hall effect (ISHE) in the Pd
was found to be 30% stronger than that without annealing. When the angle
between the directions of localized magnetic moments in the Ni80Fe20 film and
the external magnetic field in the spin-pumping is zero, the spin injection
efficiency into the Pd layer, i.e., the spin current density generated in the
Pd layer can be the maximum. The annealing in a magnetic field is a convenient
technique for increasing the spin current density generated by the spin
pumping.",1407.7028v3
2014-08-01,Optimization of indirect magnetoelectric effect in thin-film/substrate/piezoelectric-actuator heterostructure using polymer substrate,"Indirect magnetoelectric effect has been studied in
magnetostrictive-film/substrate/piezoelectric-actuator heterostructures. Two
different substrates have been employed: a flexible substrate (Young's modulus
of 4 GPa) and a rigid one (Young's modulus of 180 GPa). A clear optimization of
the indirect magnetoelectric coupling, studied by micro-strip ferromagnetic
resonance, has been highlighted when using the polymer substrate. However, in
contrast to the rigid substrate, the flexible substrate also leads to an a
priori undesirable and huge uniaxial anisotropy which seems to be related to a
non equibiaxial residual stress inside the magnetostrictive film. The strong
amplitude of this non equibiaxiallity is due to the large Young's modulus
mismatch between the polymer and the magnetostrictive film which leads to a
slight curvature along a given direction during the elaboration process and
thus to a large magnetoelastic anisotropy.",1408.0123v1
2014-08-02,Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on Kapton,"Bending effect on the magnetic anisotropy in 20 nm Co$_{2}$FeAl Heusler thin
film grown on Kapton\textregistered{} has been studied by ferromagnetic
resonance and glued on curved sample carrier with various radii. The results
reported in this letter show that the magnetic anisotropy is drastically
changed in this system by bending the thin films. This effect is attributed to
the interfacial strain transmission from the substrate to the film and to the
magnetoelastic behavior of the Co$_{2}$FeAl film. Moreover two approaches to
determine the in-plane magnetostriction coefficient of the film, leading to a
value that is close to $\lambda^{CFA}=14\times10^{-6}$, have been proposed.",1408.0379v1
2014-08-08,Evidence for spin-triplet superconductivity in U$_2$PtC$_2$ from $^{195}$Pt NMR,"Nuclear magnetic resonance (NMR) measurements on the $^{195}$Pt nucleus in an
aligned powder of the moderately heavy-fermion material U2PtC2 are consistent
with spin-triplet pairing in its superconducting state. Across the
superconducting transition temperature and to much lower temperatures, the NMR
Knight shift is temperature independent for field both parallel and
perpendicular to the tetragonal c-axis, expected for triplet equal-spin pairing
superconductivity. The NMR spin-lattice relaxation rate 1/T$_1$, in the normal
state, exhibits characteristics of ferromagnetic fluctuations, compatible with
an enhanced Wilson ratio. In the superconducting state, 1/T$_1$ follows a power
law with temperature without a coherence peak giving additional support that
U$_2$PtC$_2$ is an unconventional superconductor. Bulk measurements of the
AC-susceptibility and resistivity indicate that the upper critical field
exceeds the Pauli limiting field for spin-singlet pairing and is near the
orbital limiting field, an additional indication for spin-triplet pairing.",1408.1969v1
2014-08-18,Element-resolved thermodynamics of magnetocaloric LaFe$_{13-x}$Si$_x$,"By combination of two independent approaches, nuclear resonant inelastic
X-ray scattering and first-principles calculations in the framework of density
functional theory, we determine the element-resolved vibrational density of
states in the ferromagnetic low temperature and paramagnetic high temperature
phase of LaFe$_{13-x}$Si$_x$. This allows us to derive the lattice and
electronic contribution to the entropy change at the first-order phase
transformation, which are both of considerable magnitude. The change in lattice
entropy is dominated by magneto-elastic softening, which originates from the
itinerant electron metamagnetism associated with Fe. This counteracts the large
volume change at the transition and leads to an unexpected, cooperative
behavior of magnetic, vibrational and electronic entropy change, which is
responsible for the large magneto- and barocaloric effect observed for this
material.",1408.4009v2
2014-08-27,Control of vibrational states by spin-polarized transport in a carbon nanotube resonator,"We study spin-dependent transport in a suspended carbon nanotube quantum dot
in contact with two ferromagnetic leads and with the dot's spin coupled to the
flexural mechanical modes. The spin-vibration interaction induces spin-flip
processes between the two energy levels of the dot. This interaction arises
from the spin-orbit coupling or a magnetic field gradient. The inelastic
vibration-assisted spin flips give rise to a mechanical damping and, for an
applied bias voltage, to a steady nonequilibrium occupation of the harmonic
oscillator. We analyze these effects as function of the energy-level separation
of the dot and the magnetic polarization of the leads. Depending on the
magnetic configuration and the bias-voltage polarity, we can strongly cool a
single mode or pump energy into it. In the latter case, we find that within our
approximation, the system approaches eventually a regime of mechanical
instability. Furthermore, owing to the sensitivity of the electron transport to
the spin orientation, we find signatures of the nanomechanical motion in the
current-voltage characteristic. Hence, the vibrational state can be read out in
transport measurements.",1408.6357v3
2014-09-11,Transient Exchange Interaction in a Helical Antiferromagnet,"We have performed time-resolved resonant x-ray scattering studies in the
Lanthanide metal Dy to reveal the dynamic response of the helical order
exchange coupling to injection of unpolarized spins. The observed spin dynamics
are significantly slower than that exhibited by the ferromagnetic phase in
Lanthanide metals and are strongly dependent on temperature and excitation
fluence. This unique behavior results from transient changes in the shape of
the conduction electron Fermi surface and subsequent scattering events that
transfer the excitation to the core spin.",1409.3614v1
2014-10-01,Transverse anisotropy effects on spin-resolved transport through large-spin molecules,"The transport properties of a large-spin molecule strongly coupled to
ferromagnetic leads in the presence of transverse magnetic anisotropy are
studied theoretically. The relevant spectral functions, linear-response
conductance and the tunnel magnetoresistance are calculated by means of the
numerical renormalization group method. We study the dependence of transport
characteristics on orbital level position, uniaxial and transverse
anisotropies, external magnetic field and temperature. It is shown that while
uniaxial magnetic anisotropy leads to the suppression of the Kondo effect,
finite transverse anisotropy can restore the Kondo resonance. The effect of
Kondo peak restoration strongly depends on the magnetic configuration of the
device and leads to nontrivial behavior of the tunnel magnetoresistance. We
show that the temperature dependence of the conductance at points where the
restoration of the Kondo effect occurs is universal and shows a scaling typical
for usual spin-one-half Kondo effect.",1410.0315v1
2014-10-22,Spin current generation from sputtered Y3Fe5O12 films,"Spin current injection from sputtered yttrium iron garnet (YIG) films into an
adjacent platinum layer has been investigated by means of the spin pumping and
the spin Seebeck effects. Films with a thickness of 83 and 96 nanometers were
fabricated by on-axis magnetron rf sputtering at room temperature and
subsequent post-annealing. From the frequency dependence of the ferromagnetic
resonance linewidth, the damping constant has been estimated to be
$(7.0\pm1.0)\times 10^{-4}$. Magnitudes of the spin current generated by the
spin pumping and the spin Seebeck effect are of the same order as values for
YIG films prepared by liquid phase epitaxy. The efficient spin current
injection can be ascribed to a good YIG|Pt interface, which is confirmed by the
large spin-mixing conductance $(2.0\pm0.2)\times 10^{18}$ m$^{-2}$.",1410.5987v1
2014-10-24,Non-linear spin-wave excitation at low bias fields,"Non-linear magnetization dynamics is essential for the operation of many
spintronics devices. For microwave assisted switching of magnetic elements the
low field regime is of particular interest. In addition a large number of
experiments uses high amplitude FMR in order to generate d.c. currents via spin
pumping mechanism. Here we use time resolved X-ray magnetic circular dichroism
experiments to determine the number density of excited magnons in magnetically
soft Ni_80Fe_20 thin films at small bias fields and large rf-excitation
amplitudes. Our data shows that the common model of non-linear ferromagnetic
resonance is not suitable to describe the low bias field limit. Here we derive
a new model of parametric spin-wave excitation which correctly predicts
threshold amplitudes and decay rates also at low bias fields. In fact a new
series of critical modes with amplitude phase oscillations is found,
generalizing the theory of parametric spin-wave excitation.",1410.6693v1
2014-11-10,Temperature evolution of the effective magnetic anisotropy in the MnCr$_2$O$_4$ spinel,"In this work we present a study of the low temperature magnetic phases of
polycrystalline MnCr$_2$O$_4$ spinel through dc magnetization and ferromagnetic
resonance spectroscopy (FMR). Through these experiments we determined the main
characteristic temperatures: T$_C$ $\sim$41 K and T$_H$ $\sim$18 K
corresponding, respectively, to the ferrimagnetic order and to the low
temperature helicoidal transitions. The temperature evolution of the system is
described by a phenomenological approach that considers the different terms
that contribute to the free energy density. Below the Curie temperature the FMR
spectra were modeled by a cubic magnetocrystalline anisotropy to the second
order, with $K_1$ and $K_2$ anisotropy constants that define the easy
magnetization axis along the <110> direction. At lower temperatures, the
formation of a helicoidal phase was considered by including uniaxial anisotropy
axis along the [1-10] propagation direction of the spiral arrange, with a $K_u$
anisotropy constant. The values obtained from the fittings at 5 K are
$K_1$=-2.3x10$^4$ erg/cm$^3$, $K^2$=6.4x10$^4$ erg/cm$^3$ and $K_u$=7.5x10$^4$
erg/cm$^3$.",1411.2461v1
2014-11-25,2D Superexchange mediated magnetization dynamics in an optical lattice,"The competition of magnetic exchange interactions and tunneling underlies
many complex quantum phenomena observed in real materials. We study
non-equilibrium magnetization dynamics in an extended 2D system by loading
effective spin-1/2 bosons into a spin-dependent optical lattice, and we use the
lattice to separately control the resonance conditions for tunneling and
superexchange. After preparing a non-equilibrium anti-ferromagnetically ordered
state, we observe relaxation dynamics governed by two well-separated rates,
which scale with the underlying Hamiltonian parameters associated with
superexchange and tunneling. Remarkably, with tunneling off-resonantly
suppressed, we are able to observe superexchange dominated dynamics over two
orders of magnitude in magnetic coupling strength, despite the presence of
vacancies. In this regime, the measured timescales are in agreement with simple
theoretical estimates, but the detailed dynamics of this 2D, strongly
correlated, and far-from-equilibrium quantum system remain out of reach of
current computational techniques.",1411.7036v1
2014-12-08,Anapoles and other magneto-electric multipoles in BaFe2Se3,"We submit that the magnetic space-group Cac (#9.41) is consistent with the
established magnetic structure of BaFe2Se3, with magnetic dipole moments in a
motif that uses two ladders [Caron J M et al 2011 Phys. Rev. B 84 180409(R)].
The corresponding crystal class m1' allows axial and polar dipoles and forbids
bulk ferromagnetism. The compound supports magneto-electric multipoles,
including a magnetic charge (monopole) and an anapole (magnetic toroidal
dipole) visible in the Bragg diffraction of x-rays and neutrons. Our
comprehensive simulation of neutron Bragg diffraction by BaFe2Se3 exploits
expressions of a general nature that can be of use with other magnetic
materials. Electric toroidal moments are also allowed in BaFe2Se3. A discussion
of our findings for resonant x-ray Bragg diffraction illustrates the benefit of
a common platform for neutron and x-ray diffraction.",1412.2536v1
2014-12-12,Spin waves in micro-structured yttrium iron garnet nanometer-thick films,"We investigated the spin-wave propagation in a micro-structured yttrium iron
garnet waveguide of $40$ nm thickness. Utilizing spatially-resolved Brillouin
light scattering microscopy, an exponential decay of the spin-wave amplitude of
$(10.06 \pm 0.83)$ $\mu$m was observed. This leads to an estimated Gilbert
damping constant of $\alpha=(8.79\pm 0.73)\times 10^{-4}$, which is larger than
damping values obtained through ferromagnetic resonance measurements in
unstructured films. The theoretically calculated spatial interference of
waveguide modes was compared to the spin-wave pattern observed experimentally
by means of Brillouin light scattering spectroscopy.",1412.4032v1
2014-12-23,Current-induced spin torque resonance of a magnetic insulator,"Pure spin currents transport angular momentum without an associated charge
flow. This unique property makes them attractive for spintronics applications,
such as torque induced magnetization control in nanodevices that can be used
for sensing, data storage, interconnects and logics. Up to now, however, most
spin transfer torque studies focused on metallic ferromagnets, while magnetic
insulators were largely ignored, in spite of superior magnetic quality factors.
Here, we report the observation of spin torque-induced magnetization dynamics
in a magnetic insulator. Our experiments show that in ultrathin magnetic
insulators the spin torque induced magnetization dynamics can be substantially
larger than those generated by the Oersted field. This opens new perspectives
for the efficient integration of ferro-, ferri-, and antiferromagnetic
insulators into electronic devices.",1412.7460v1
2015-01-22,Topologically Protected Dynamics of Spin Textures,"We study current-induced dynamics of spin textures in thin magnetic
nanowires. We derive effective equations of motion describing the dynamics of
the domain-wall soft modes associated with topological defects. Because the
magnetic domain walls are topological objects, these equations are universal
and depend only on a few parameters. We obtain spin spiral domain-wall
structure in ferromagnetic wires with Dzyaloshinskii-Moriya interaction and
critical current dependence on this interaction. We also find the most
efficient way to move the domain walls by resonant current pulses and propose a
procedure to determine their dynamics by measuring the voltage induced by a
moving domain wall. Based on translationally non-invariant nanowires, we show
how to make prospective magnetic memory nanodevices much more energy efficient.",1501.05366v1
2015-02-13,Spin-current injection and detection in strongly correlated organic conductor,"Spin-current injection into an organic semiconductor
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film induced by the spin
pumping from an yttrium iron garnet (YIG) film. When magnetization dynamics in
the YIG film is excited by ferromagnetic or spin-wave resonance, a voltage
signal was found to appear in the
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film.
Magnetic-field-angle dependence measurements indicate that the voltage signal
is governed by the inverse spin Hall effect in
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$. We found that the
voltage signal in the $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$/YIG
system is critically suppressed around 80 K, around which magnetic and/or glass
transitions occur, implying that the efficiency of the spin-current injection
is suppressed by fluctuations which critically enhanced near the transitions.",1502.05244v1
2015-02-24,High Quality Yttrium Iron Garnet Grown by Room Temperature Pulsed Laser Deposition and Subsequent Annealing,"We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG)
by annealing in oxygen atmosphere. Our findings show that well below the
melting temperature the material transforms into a fully epitaxial layer with
exceptional quality, both structural and magnetic.\\ In ferromagnetic resonance
(FMR) ultra low damping and extremely narrow linewidth can be observed. For a
56 nm thick layer a damping constant of
$\alpha$=(6.63$\pm$1.50)$\cdot$10$^{-5}$ is found and the linewidth at 9.6 GHz
is as small as 1.30$\pm$0.05 Oe which are the lowest values for PLD grown thin
films reported so far. Even for a 20 nm thick layer a damping constant of
$\alpha$=(7.51$\pm$1.40)$\cdot$10$^{-5}$ is found which is the lowest value for
ultrathin films published so far. The FMR linewidth in this case is
3.49$\pm$0.10 Oe at 9.6 GHz. Our results not only present a method of
depositing thin film YIG of unprecedented quality but also open up new options
for the fabrication of thin film complex oxides or even other crystalline
materials.",1502.06724v2
2015-03-04,Coherent spin mixing dynamics in thermal $^{87}$Rb spin-1 and spin-2 gases,"We study the non-equilibrium coherent spin mixing dynamics in ferromagnetic
spin-1 and antiferromagnetic spin-2 thermal gases of ultracold $^{87}$Rb atoms.
Long lasting spin population oscillations with magnetic field dependent
resonances are observed in both cases. Our observations are well reproduced by
Boltzmann equations of the Wigner distribution function. Compared to the
equation of motion of spinor Bose-Einstein condensates, the only difference
here is a factor of two increase in the spin-dependent interaction, which is
confirmed directly in the spin-2 case by measuring the relation between the
oscillation amplitude and the sample's density.",1503.01171v1
2015-03-04,Tunable negative thermal expansion related with the gradual evolution of antiferromagnetic ordering in antiperovskite manganese nitrides Ag1-xNMn3+x (0<x<0.6),"The thermal expansion and magnetic properties of antiperovskite manganese
nitrides Ag1-xNMn3+x were reported. The substitution of Mn for Ag effectively
broadens the temperature range of negative thermal expansion and drives it to
cryogenic temperatures. As x increases, the paramagnetic (PM) to
antiferromagnetic (AFM) phase transition temperature (TN) decreases. At x~0.2,
the PM-AFM transition overlaps with the AFM to glass-like state transition.
Above x=0.2, two new distinct magnetic transitions were observed: one occurs
above room temperature from PM to ferromagnetic (FM), and the other one evolves
at a lower temperature (T*) below which both AFM and FM orderings are involved.
Further electron spin resonance measurement suggests that the broadened volume
change near T* is closely related with the evolution of {\Gamma}5g AFM
ordering.",1503.01197v1
2015-03-06,Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature,"The thermal conductivity of YbRh2Si2 has been measured down to very low
temperatures under field in the basal plane. An additional channel for heat
transport appears below 30 mK, both in the antiferromagnetic and paramagnetic
states, respectively below and above the critical field suppressing the
magnetic order. This excludes antiferromagnetic magnons as the origin of this
additional contribution to thermal conductivity. Moreover, this low temperature
contribution prevails a definite conclusion on the validity or violation of the
Wiedemann-Franz law at the field-induced quantum critical point. At high
temperature in the paramagnetic state, the thermal conductivity is sensitive to
ferromagnetic fluctuations, previously observed by NMR or neutron scattering
and required for the occurrence of the sharp electronic spin resonance
fracture.",1503.01991v1
2015-03-13,Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces,"We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt
bilayers with direct and interrupted interfaces. The damping-like and
field-like torques are simultaneously measured with spin-torque ferromagnetic
resonance tuned by a dc bias current, whereas spin pumping is measured
electrically through the inverse spin Hall effect using a microwave cavity.
Insertion of an atomically thin Cu dusting layer at the interface reduces the
damping-like torque, field-like torque, and spin pumping by nearly the same
factor of ~1.4. This finding confirms that the observed spin-orbit torques
predominantly arise from diffusive transport of spin current generated by the
spin Hall effect. We also find that spin-current scattering at the NiFe/Pt
interface contributes to additional enhancement in magnetization damping that
is distinct from spin pumping.",1503.04104v3
2015-03-30,Suppression of Spin Pumping Between Ni$_{80}$Fe$_{20}$ and Cu by a Graphene Interlayer,"We compare ferromagnetic resonance measurements of Permalloy
Ni$_{80}$Fe$_{20}$ (Py) films sputtered onto Cu(111) films with and without a
graphene (Gr) interlayer grown by chemical vapor deposition before Py
deposition. A two-angle sputtering method ensured that neither Gr nor Py was
degraded by the sample preparation process. We find the expected damping
enhancement from spin pumping for the Py/Cu case and no detectable enhancement
for the Py/Gr/Cu case. Since damping is sensitive to effects other than spin
pumping, we used magnetometry to verify that differences in Py magnetostatic
properties are not responsible for the difference in damping. We attribute the
suppression of spin pumping in Py/Gr/Cu to the large contact resistance of the
Gr/Cu interface.",1503.08777v1
2015-04-08,Magnetic and nonmagnetic phases in doped AB2 t-J Hubbard chains,"We discuss the rich phase diagram of doped AB2 $t-J$ chains by using data
from density matrix renormalization group and exact diagonalization techniques.
The $J$ vs $\delta$ (hole doping) phase diagram exhibits regions of itinerant
ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states,
phase separation, and Luttinger liquid (LL) physics. Several features are
highlighted, such as the modulated ferrimagnetic structure, the occurrence of
Nagaoka spin polarons in the underdoped regime and small values of $J=4t^2/U$,
where $t$ is the first-neighbor hopping amplitude and $U$ is the on-site
repulsive Coulomb interaction, incommensurate structures with nonzero
magnetization, and strong-coupling LL physics in the high-doped regime. We also
verify that relevant findings are in agreement with the corresponding findings
in square and n-leg ladder lattices. In particular, we mention the instability
of Nagaoka ferromagnetism against $J$ and $\delta$.",1504.01951v1
2015-05-15,Direct detection of pure spin-current by x-ray pump-probe measurements,"By synchronizing a microwave waveform with the synchrotron x-ray pulses, we
use the ferromagnetic resonance (FMR) of the Py (Ni81Fe19) layer in a
Py/Cu/Cu75Mn25/Cu/Co multilayer to pump a pure spin current into the Cu75Mn25
spacer layer, and then directly probe the spin current in the Cu75Mn25 layer by
a time-resolved x-ray magnetic circular dichroism (XMCD). This element-specific
pump-probe measurement unambiguously identifies the AC spin current in the
Cu75Mn25 layer. In addition, phase resolved x-ray measurements reveal a
characteristic bipolar phase behavior of the Co spins that is a fingerprint of
spin-current driven spin precession.",1505.03959v2
2015-05-20,Structural and magnetic phase transitions in EuTi1-xNbxO3,"We investigate the structural and magnetic phase transitions in EuTi1-xNbxO3
with synchrotron powder X-ray diffraction (XRD), resonant ultrasound
spectroscopy (RUS), and magnetization measurements. Upon Nb-doping, the Pm-3m
to I4/mcm structural transition shifts to higher temperatures and the room
temperature lattice parameter increases while the magnitude of the octahedral
tilting decreases. In addition, Nb substitution for Ti destabilizes the
antiferromagnetic ground state of the parent compound and long range
ferromagnetic order is observed in the samples containing more than 10% Nb. The
structural transition in pure and doped compounds is marked by a step-like
softening of the elastic moduli in a narrow temperature interval near TS, which
resembles that of SrTiO3 and can be adequately modeled using the Landau free
energy model employing the same coupling between strain and octahedral tilting
order parameter as previously used to model SrTiO3.",1505.05528v1
2015-05-29,Topological Surface States Originated Spin-Orbit Torques in Bi2Se3,"Three dimensional topological insulator bismuth selenide (Bi2Se3) is expected
to possess strong spin-orbit coupling and spin-textured topological surface
states, and thus exhibit a high charge to spin current conversion efficiency.
We evaluate spin-orbit torques in Bi2Se3/Co40Fe40B20 devices at different
temperatures by spin torque ferromagnetic resonance measurements. As
temperature decreases, the spin-orbit torque ratio increases from ~ 0.047 at
300 K to ~ 0.42 below 50 K. Moreover, we observe a significant out-of-plane
torque at low temperatures. Detailed analysis indicates that the origin of the
observed spin-orbit torques is topological surface states in Bi2Se3. Our
results suggest that topological insulators with strong spin-orbit coupling
could be promising candidates as highly efficient spin current sources for
exploring next generation of spintronic applications.",1505.07937v1
2015-05-29,Detecting $π$-phase superfluids with $p$-wave symmetry in a quasi-1D optical lattice,"We propose an experimental protocol to study $p$-wave superfluidity in a
spin-polarized cold Fermi gas tuned by an $s$-wave Feshbach resonance. A
crucial ingredient is to add a quasi-1D optical lattice and tune the fillings
of two spins to the $s$ and $p$ band, respectively. The pairing order parameter
is confirmed to inherit $p$-wave symmetry in its center-of-mass motion. We find
that it can further develop into a state of unexpected $\pi$-phase modulation
in a broad parameter regime. Measurable quantities are calculated, including
time-of-flight distributions, radio-frequency spectra, and in situ
phase-contrast imaging in an external trap. The $\pi$-phase $p$-wave superfluid
is reminiscent of the $\pi$-state in superconductor-ferromagnet
heterostructures but differs in symmetry and origin. If observed, it would
represent another example of $p$-wave pairing, first discovered in He-3
liquids.",1505.08164v1
2015-06-09,Traveling surface spin-wave resonance spectroscopy using surface acoustic waves,"Coherent gigahertz-frequency surface acoustic waves (SAWs) traveling on the
surface of a piezoelectric crystal can, via the magnetoelastic interaction,
resonantly excite traveling spin waves in an adjacent thin-film ferromagnet.
These excited spin waves, traveling with a definite in-plane wave-vector q
enforced by the SAW, can be detected by measuring changes in the
electro-acoustical transmission of a SAW delay line. Here, we provide a first
demonstration that such measurements constitute a precise and quantitative
technique for spin-wave spectroscopy, providing a means to determine both
isotropic and anisotropic contributions to the spin-wave dispersion and
damping. We demonstrate the effectiveness of this spectroscopic technique by
measuring the spin-wave properties of a Ni thin film for a large range of wave
vectors,q = 2.5 x 10^4 - 8 x 10^4 cm^(-1), over which anisotropic dipolar
interactions vary from being negligible to quite significant.",1506.03056v3
2015-06-19,All electrical coherent control of the magnetization in thin Yittrium Iron Garnet film,"We demonstrate coherent control of time domain ferromagnetic resonance by all
electrical excitation and detection. Using two ultrashort magnetic field steps
with variable time delay we control the induction decay in yttrium iron garnet
(YIG). By setting suitable delay times between the two steps the precession of
the magnetization can either be enhanced or completely stopped. The method
allows for a determination of the precession frequency within a few precession
periods and with an accuracy much higher than can be achieved using fast
fourier transformation. Moreover it holds the promise to massively increase
precession amplitudes in pulsed inductive microwave magnetometry (PIMM) using
low amplitude finite pulse trains. Our experiments are supported by
micromagnetic simulations which nicely confirm the experimental results.",1506.05935v1
2015-07-13,Electronic and magnetic properties of orthorhombic iron selenide (FeSe),"Iron orbitals in orthorhombic iron selenide (FeSe) can produce charge-like
multipoles that are polar (parity-odd). Orbitals in question include Fe(3d),
Fe(4p) and p-type ligands that participate in transport properties and bonding.
The polar multipoles may contribute weak, space-group forbidden Bragg spots to
diffraction patterns collected with x-rays tuned in energy to a Fe atomic
resonance (Templeton & Templeton scattering). Ordering of conventional, axial
magnetic dipoles does not accompany the tetragonal-orthorhombic structural
phase transition in FeSe, unlike other known iron-based superconductors. We
initiate a new line of inquiry for this puzzling property of orthorhombic FeSe,
using a hidden magnetic-order that belongs to the m'm'm' magnetic
crystal-class. It is epitomized by the absence of ferromagnetism and axial
magnetic dipoles, and the appearance of magnetic monopoles and magneto-electric
quadrupoles. A similar magnetic order occurs in cuprate superconductors, YBCO &
Hg1201, where it was unveiled with the Kerr effect and in Bragg diffraction
patterns revealed by polarized neutrons. PACS number 75.25.-j",1507.03449v3
2015-08-06,Large spin-wave bullet in a ferrimagnetic insulator driven by spin Hall effect,"Due to its transverse nature, spin Hall effects (SHE) provide the possibility
to excite and detect spin currents and magnetization dynamics even in magnetic
insulators. Magnetic insulators are outstanding materials for the investigation
of nonlinear phenomena and for novel low power spintronics applications because
of their extremely low Gilbert damping. Here, we report on the direct imaging
of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the
ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ based on the excitation and
detection by SHEs. The driven spin dynamics in Y$_3$Fe$_5$O$_{12}$ is directly
imaged by spatially-resolved microfocused Brillouin light scattering (BLS)
spectroscopy. Previously, ST-FMR experiments assumed a uniform precession
across the sample, which is not valid in our measurements. A strong spin-wave
localization in the center of the sample is observed indicating the formation
of a nonlinear, self-localized spin-wave `bullet'.",1508.01427v1
2015-08-08,Statics and dynamics of magnetocapillary bonds,"When ferromagnetic particles are suspended at an interface under magnetic
fields, dipole-dipole interactions compete with capillary attraction. This
combination of forces has recently given promising results towards controllable
self-assemblies, as well as low Reynolds swimming systems. The elementary unit
of these assemblies is a pair of particles. Although equilibrium properties of
this interaction are well described, dynamics remain unclear. In this letter,
the properties of magnetocapillary bonds are determined by probing them with
magnetic perturbations. Two deformation modes are evidenced and discussed.
These modes exhibit resonances whose frequencies can be detuned to generate
non-reciprocal motion. A model is proposed which can become the basis for
elaborate collective behaviours.",1508.01885v2
2015-08-29,"Magnetic properties of Gd$T_2$Zn$_{20}$ (T = Fe, Co) investigated by X-ray diffraction and spectroscopy","We investigate the magnetic and electronic properties of the Gd$T_2$Zn$_{20}$
($T$ = Fe and Co) compounds using X-ray resonant magnetic scattering (XRMS),
X-ray absorption near-edge structure (XANES) and X-ray magnetic circular
dichroism (XMCD) techniques. The XRMS measurements reveal that the
GdCo$_2$Zn$_{20}$ compound has a commensurate antiferromagnetic spin structure
with a magnetic propagation vector $\vec{\tau}$ =
$(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ below the N\'eel temperature ($T_N
\sim$ 5.7 K). Only the Gd ions carry a magnetic moment forming an
antiferromagnetic structure with magnetic representation $\Gamma_6$. For the
ferromagnetic GdFe$_2$Zn$_{20}$ compound, an extensive investigation was
performed at low temperature and under magnetic field using XANES and XMCD
techniques. A strong XMCD signal of about 12.5 $\%$ and 9.7 $\%$ is observed
below the Curie temperature ($T_C \sim$ 85 K) at the Gd-$L_2$ and $L_3$ edges,
respectively. In addition, a small magnetic signal of about 0.06 $\%$ of the
jump is recorded at the Zn $K$-edge suggesting that the Zn 4$p$ states are spin
polarized by the Gd 5$d$ extended orbitals.",1508.07495v1
2015-09-09,Quantum spin transport and dynamics through a novel F/N junction,"We study the spin transport in the low temperature regime (often referred to
as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL)
and a normal metal metallic Fermi liquid (NFL), also known as the F/N junction,
which is considered as one of the most basic spintronic devices. In particular,
we explore the propagation of spin waves and transport of magnetization through
the interface of the F/N junction where nonequilibrium spin polarization is
created on the normal metal side of the junction by electrical spin injection.
We calculate the probable spin wave modes in the precession-dominated regime on
both sides of the junction especially on the NFL side where the system is out
of equilibrium. Proper boundary conditions at the interface are introduced to
establish the transport of the spin properties through the F/N junction. A
possible transmission conduction electron spin resonance (CESR) experiment is
suggested on the F/N junction to see if the predicted spin wave modes could
indeed propagate through the junction. Potential applications based on this
novel spin transport feature of the F/N junction are proposed in the end.",1509.02582v1
2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for
applications in spintronic devices due to its low magnetic damping and its rich
anisotropies. Here we use ferromagnetic resonance (FMR) measurements and
calculations from first principles to investigate how the composition of the
epitaxially grown NiMnSb influences the magnetodynamic properties of saturation
magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$.
$M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while
the Gilbert damping is minimum. We find excellent quantitative agreement
between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows
the same trend as the experimental data, but has a larger magnitude.
Additionally to the unique in-plane anisotropy of the material, these
tunabilities of the magnetodynamic properties can be taken advantage of when
employing NiMnSb films in magnonic devices.",1510.01894v1
2015-10-17,Direct evidence for minority spin gap in the Co2MnSi Heusler alloy,"Half Metal Magnets are of great interest in the field of spintronics because
of their potential full spin-polarization at the Fermi level and low
magnetization damping. The high Curie temperature and predicted 0.7eV minority
spin gap make the Heusler alloy Co2MnSi very promising for applications.We
investigated the half-metallic magnetic character of this alloy using
spin-resolved photoemission, ab initio calculation and ferromagnetic resonance.
At the surface of Co2MnSi, a gap in the minority spin channel is observed,
leading to 100% spin polarization. However, this gap is 0.3 eV below the Fermi
level and a minority spin state is observed at the Fermi level. We show that a
minority spin gap at the Fermi energy can nevertheless be recovered either by
changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi
or MgO. This results in extremely small damping coefficients reaching values as
low as 7x 10-4.",1510.05085v1
2015-10-23,Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet,"Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.",1510.06793v1
2015-11-01,Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review,"Spin Hall effect and its inverse provide essential means to convert charge to
spin currents and vice versa, which serve as a primary function for spintronic
phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck
effect. These effects can oscillate magnetization or detect a thermally
generated spin splitting in the chemical potential. Importantly this conversion
process occurs via the spin-orbit interaction, and requires neither magnetic
materials nor external magnetic fields. However, the spin Hall angle, i.e., the
conversion yield between the charge and spin currents, depends severely on the
experimental methods. Here we discuss the spin Hall angle and the spin
diffusion length for a variety of materials including pure metals such as Pt
and Ta, alloys and oxides determined by the spin absorption method in a lateral
spin valve structure.",1511.00332v1
2015-11-06,Spin- and valley-dependent transport through arrays of ferromagnetic silicene junctions,"We study ballistic transport of Dirac fermions in silicene through arrays of
barriers, of width $d$, in the presence of an exchange field $M$ and a tunable
potential of height $U$ or depth $-U$. The spin- and valley-resolved
conductances as functions of $U$ or $M$, exhibit resonances away from the Dirac
point (DP) and close to it a pronounced dip that becomes a gap when a critical
electric field $E_z$ is applied. This gap widens by increasing the number of
barriers and can be used to realize electric field-controlled switching of the
current. The spin $p_s$ and valley $p_v$ polarizations of the current near the
DP increase with $E_z$ or $M$ and can reach 100\% for certain of their values.
These field ranges widen significantly by increasing the number of barriers.
Also, $p_s$ and $p_v$ oscillate nearly periodically with the separation between
barriers or wells and can be inverted by reversing $M$.",1511.02035v1
2015-11-17,Itinerant and localized magnetization dynamics in antiferromagnetic Ho,"Using femtosecond time-resolved resonant magnetic x-ray diffraction at the Ho
L3 absorption edge, we investigate the demagnetization dynamics in
antiferromagnetically ordered metallic Ho after femtosecond optical excitation.
Tuning the x-ray energy to the electric dipole (E1, 2p -> 5d) or quadrupole
(E2, 2p -> 4f) transition allows us to selectively and independently study the
spin dynamics of the itinerant 5d and localized 4f electronic subsystems via
the suppression of the magnetic (2 1 3-tau ) satellite peak. We find
demagnetization timescales very similar to ferromagnetic 4f systems, suggesting
that the loss of magnetic order occurs via a similar spin-flip process in both
cases. The simultaneous demagnetization of both subsystems demonstrates strong
intra-atomic 4f-5d exchange coupling. In addition, an ultrafast lattice
contraction due to the release of magnetostriction leads to a transient shift
of the magnetic satellite peak.",1511.05315v1
2016-01-14,Vector spectroscopy for spin pumping,"We propose a method to separate the inverse spin Hall effect (ISHE) from
galvanomagnetic effects in spin pumping experiments on metallic bilayer systems
by measuring the dc electromotive force in two orthogonal directions.
Calculations of dc voltages in longitudinal and Hall directions induced in
Ni81Fe19 and Ni81Fe19/Pt films at ferromagnetic resonance in a microwave cavity
predict that contributions from ISHE and from the galvanomagnetic effects, i.e.
the anisotropic magnetoresistance and the anomalous Hall effect, exhibit
distinct signal symmetry as well as angular dependence when changing the
direction of the external field with respect to the film plane. According to
measurements on Ni81Fe19/Pt, only that dc voltage component which includes ISHE
is more than five times larger than purely galvanomagnetic components. This is
corroborated by results on La0.67Sr0.33MnO3/Pt samples, demonstrating
universality of this method.",1601.03588v1
2016-02-04,Investigation of the unidirectional spin heat conveyer effect in a 200nm thin Yttrium Iron Garnet film,"We have investigated the unidirectional spin wave heat conveyer effect in
sub-micron thick yttrium iron garnet (YIG) films using lock-in thermography
(LIT). Although the effect is small in thin layers this technique allows us to
observe asymmetric heat transport by magnons which leads to asymmetric
temperature profiles differing by several mK on both sides of the exciting
antenna, respectively. Comparison of Damon-Eshbach and backward volume modes
shows that the unidirectional heat flow is indeed due to non-reciprocal
spin-waves. Because of the finite linewidth, small asymmetries can still be
observed when only the uniform mode of ferromagnetic resonance is excited. The
latter is of extreme importance for example when measuring the inverse
spin-Hall effect because the temperature differences can result in
thermovoltages at the contacts. Because of the non-reciprocity these
thermovoltages reverse their sign with a reversal of the magnetic field which
is typically deemed the signature of the inverse spin-Hall voltage.",1602.01662v1
2016-02-17,Features of Low Temperature Tunnel Magnetoresistance in Pressed Powder of Chromium Dioxide,"Resistive and magnetoresistive properties of two samples of compacted powders
of ferromagnetic half-metal CrO_{2} with shape anisotropy of nanoparticles were
studied. The powders were prepared by the method of hydrothermal synthesis and
consisted of needle-like particles with average diameters 24-34 nm and mean
length of 300 nm. One of the samples has been made of compacted powder of pure
CrO_{2}, while another sample has been prepared from a substitution solid
solution Cr_{1-x}Fe_{x}O_{2}. The aim of this work was to study the effect of
Fe impurity on the value of tunnel resistance and tunnel magnetoresistance for
compacted CrO_{2} powders. It was found that the addition of Fe impurity leads
to an increase in the coercive force of the powder and reduce the tunnel
magnetoresistance. We assume resonant tunneling mechanism on the Fe impurities.
We found a strong dependence of the magnetoresistance on the spin relaxation
rate in the process of magnetization reversal. The possible reasons for such
dependence are discussed.",1602.05390v1
2016-02-25,All electrical propagating spin wave spectroscopy with broadband wavevector capability,"We develop an all electrical experiment to perform the broadband
phase-resolved spectroscopy of propagating spin waves in micrometer sized thin
magnetic stripes. The magnetostatic surface spin waves are excited and detected
by scaled down to 125 nm wide inductive antennas, which award ultra broadband
wavevector capability. The wavevector selection can be done by applying an
excitation frequency above the ferromagnetic resonance. Wavevector
demultiplexing is done at the spin wave detector thanks to the rotation of the
spin wave phase upon propagation. A simple model accounts for the main features
of the apparatus transfer functions. Our approach opens an avenue for the all
electrical study of wavevector-dependent spin wave properties including
dispersion spectra or non-reciprocal propagation.",1602.08091v2
2016-04-02,Relaxation-free and inertial switching in synthetic antiferromagnets subject to super-resonant excitation,"Applications of magnetic memory devices greatly benefit from ultra-fast,
low-power switching. Here we propose how this can be achieved efficiently in a
nano-sized synthetic antiferromagnet by using perpendicular-to-the-plane
picosecond-range magnetic field pulses. Our detailed micromagnetic simulations,
supported by analytical results, yield the parameter space where inertial
switching and relaxation-free switching can be achieved in the system. We
furthermore discuss the advantages of dynamic switching in synthetic
antiferromagnets and, specifically, their relatively low-power switching as
compared to that in single ferromagnetic particles. Finally, we show how
excitation of spin-waves in the system can be used to significantly reduce the
post-switching spin oscillations for practical device geometries.",1604.00559v2
2016-04-24,Optomagnonics in Magnetic Solids,"Coherent conversion of photons to magnons, and back, provides a natural
mechanism for rapid control of interactions between stationary spins with long
coherence times and high-speed photons. Despite the large frequency difference
between optical photons and magnons, coherent conversion can be achieved
through a three-particle interaction between one magnon and two photons whose
frequency difference is resonant with the magnon frequency, as in optomechanics
with two photons and a phonon. The large spin density of a transparent
ferromagnetic insulator (such as the ferrite yttrium iron garnet) in an optical
cavity provides an intrinsic photon-magnon coupling strength that we calculate
to exceed reported optomechanical couplings. A large cavity photon number and
properly selected cavity detuning produce a predicted effective coupling
strength sufficient for observing electromagnetically induced transparency and
the Purcell effect, and even to reach the ultra-strong coupling regime.",1604.07052v2
2016-04-28,Platinum/Yttrium Iron Garnet Inverted Structures for Spin Current Transport,"30-80 nm thick yttrium iron garnet (YIG) films are grown by pulsed laser
deposition on a 5 nm thick sputtered Pt atop gadolinium gallium garnet
substrate (GGG) (110). Upon post-growth rapid thermal annealing, single crystal
YIG(110) emerges as if it were epitaxially grown on GGG(110) despite the
presence of the intermediate Pt film. The YIG surface shows atomic steps with
the root-mean-square roughness of 0.12 nm on flat terraces. Both Pt/YIG and
GGG/Pt interfaces are atomically sharp. The resulting YIG(110) films show clear
in-plane uniaxial magnetic anisotropy with a well-defined easy axis along <001>
and a peak-to-peak ferromagnetic resonance linewidth of 7.5 Oe at 9.32 GHz,
similar to YIG epitaxilly grown on GGG. Both spin Hall magnetoresistance and
longitudinal spin Seebeck effects in the inverted bilayers indicate excellent
Pt/YIG interface quality.",1604.08465v1
2016-07-15,A versatile rotary-stage high frequency probe station for studying magnetic films and devices,"We present a rotary-stage microwave probe station suitable for magnetic films
and spintronic devices. Two stages, one for field rotation from parallel to
perpendicular to the sample plane (Out-of-Plane) and the other intended for
field rotation within the sample plane (In-Plane) have been designed. The
sample, probes and micro positioners are rotated simultaneously with the
stages, which allows the field orientation to cover $\theta$ from 0 to
$90^{\circ}$ and $\varphi$ from 0 to $360^{\circ}$. $\theta$ and $\varphi$
being the angle between the direction of current flow and field in a
Out-of-Plane and an In-Plane rotation, respectively. The operation frequency is
up to 40 GHz and the magnetic field up to 1 T. The sample holder, vision system
and probe assembly are compactly designed for the probes to land on a wafer
with diameter up to 3$\,$cm. Using homemade multi-pin probes and commercially
available high frequency probes, several applications including 4-probe DC
measurements, the determination of domain wall velocity and spin transfer
torque ferromagnetic resonance are demonstrated.",1607.04356v1
2016-09-15,Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy,"We analyze the structural and magnetic characteristics of (111)-oriented
lutetium iron garnet (Lu$_3$Fe$_5$O$_{12}$) films grown by molecular-beam
epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the
in- and out-of-plane ferromagnetic resonance allow us to quantify the effects
of two-magnon scattering, along with the surface anisotropy and the saturation
magnetization. We achieve effective damping coefficients of $11.1(9) \times
10^{-4}$ for 5.3 nm films and $32(3) \times 10^{-4}$ for 2.8 nm films, among
the lowest values reported to date for any insulating ferrimagnetic sample of
comparable thickness.",1609.04753v1
2016-09-20,Static and Dynamic Magnetic Response of Fragmented Haldane-like Spin Chains in Layered Li3Cu2SbO6,"The structure and the magnetic properties of layered Li3Cu2SbO6 are
investigated by powder X-ray diffraction, static susceptibility, and electron
spin resonance studies up to 330 GHz. The XRD data experimentally verify the
space group C2/m with halved unit cell volume in contrast to previously
reported C2/c. In addition, the data show significant Li/Cu-intersite exchange.
Static magnetic susceptibility and ESR measurements show two magnetic
contributions, i.e. quasi-free spins at low-temperature and a spin-gapped
magnetic subsystem, with about half of the spins being associated to each
subsystem. The data suggest ferromagnetic-antiferromagnetic alternating chains
with JFM = -285 K and JAFM = 160 K with a significant amount of Li-defects in
the chains. The results are discussed in the scenario of fragmented 1D S = 1
AFM chains with a rather high defect concentration of about 17% and associated
S = 1/2 edge states of the resulting finite Haldane chains.",1609.06091v1
2016-09-24,Field-like spin orbit torque in ultra-thin polycrystalline FeMn films,"Field-like spin orbit torque in FeMn/Pt bilayers with ultra-thin
polycrystalline FeMn has been characterized through planar Hall effect
measurements. A large effective field is obtained for FeMn in the thickness
range of 2 to 5 nm. The experimental observations can be reasonably accounted
for by using a macro-spin model under the assumption that the FeMn layer is
composed of two spin sublattices with unequal magnetizations. The large
effective field corroborates the spin Hall origin of the effective field
considering the much smaller uncompensated net moments in FeMn as compared to
NiFe. The effective absorption of spin current by FeMn is further confirmed by
the fact that spin current generated by Pt in NiFe/FeMn/Pt trilayers can only
travel through the FeMn layer with a thickness of 1 to 4 nm. By quantifying the
field-like effective field induced in NiFe, a spin diffusion length of 2 nm is
estimated in FeMn, in consistence with values reported in literature by
ferromagnetic resonance and spin-pumping experiments.",1609.07564v1
2016-10-10,Driving field amplitude gauged quantitative inverse spin Hall effect detection,"Spin transport in thin-film materials can be studied by ferromagnetic
resonantly (FMR) driven spin pumping of a charge-free spin current which
induces an electromotive force through the inverse spin Hall effect (ISHE). For
quantitative ISHE experiments, precise control of the FMR driving field
amplitude $B_1$ is crucial. This study exploits in situ monitoring of $B_1$ by
utilization of electron paramagnetic resonantly (EPR) induced transient
nutation of paramagnetic molecules (a 1:1 complex of
{\alpha},{\gamma}-bisdiphenylene-{\beta}-phenylallyl and benzene, BDPA) placed
as $B_1$ probe in proximity of a NiFe/Pt-based ISHE device. Concurrent to an
ISHE experiment, $B_1$ is obtained from the inductively measured BDPA
Rabi-nutation frequency. Higher reproducibility is achieved by renormalization
of the ISHE voltage to $B_1^2$ with an accuracy that is determined by the
homogeneity of the FMR driving field and thus by the applied microwave
resonator and ISHE device setup.",1610.02759v1
2016-10-18,Spin transport in antiferromagnetic NiO and magnetoresistance in Y$_3$Fe$_5$O$_{12}$/NiO/Pt structures,"We have studied spin transport and magnetoresistance in yttrium iron garnet
(YIG)/NiO/Pt trilayers with varied NiO thickness. To characterize the spin
transport through NiO we excite ferromagnetic resonance in YIG with a microwave
frequency magnetic field and detect the voltage associated with the inverse
spin-Hall effect (ISHE) in the Pt layer. The ISHE signal is found to decay
exponentially with the NiO thickness with a characteristic decay length of 3.9
nm. This is contrasted with the magnetoresistance in these same structures. The
symmetry of the magnetoresistive response is consistent with spin-Hall
magnetoresistance (SMR). However, in contrast to the ISHE response, as the NiO
thickness increases the SMR signal goes towards zero abruptly at a NiO
thickness of $\simeq$ 4 nm, highlighting the different length scales associated
with the spin-transport in NiO and SMR in such trilayers.",1610.05760v1
2017-02-17,Spin-pumping through a varying-thickness MgO interlayer in Fe/Pt system,"The spin-pumping mechanism is probed through a tunnelling MgO interlayer in
Fe/Pt bilayers. We show by ferromagnetic resonance technique and spin-pumping
experiments that spin currents can tunnel through the MgO interlayer for
thickness up to 2~{nm} and can produce significant voltages in the Pt layer.
The electrical detection of spin-pumping furthermore reveals the critical role
of rectification and shunting effects on the generated voltages. The non zero
spin current transport through a few monolayers of an insulating interlayer
might initiate further studies on the role of very thin oxides in spin-pumping
experiments.",1702.05298v1
2017-02-16,"Quantitative disentanglement of spin Seebeck, proximity-induced and intrinsic anomalous Nernst effect in NM/FM bilayers","We identify and investigate thermal spin transport phenomena in
sputter-deposited Pt/NiFe$_2$O$_{\textrm{4-x}}$ ($4\geq x \geq 0$) bilayers. We
separate the voltage generated by the spin Seebeck effect from the anomalous
Nernst effect contributions and even disentangle the intrinsic anomalous Nernst
effect (ANE) in the ferromagnet (FM) from the ANE produced by the Pt that is
spin polarized due to its proximity to the FM. Further, we probe the dependence
of these effects on the electrical conductivity and the band gap energy of the
FM film varying from nearly insulating NiFe$_2$O$_4$ to metallic
Ni$_{33}$Fe$_{67}$. A proximity-induced ANE could only be identified in the
metallic Pt/Ni$_{33}$Fe$_{67}$ bilayer in contrast to Pt/NiFe$_2$O$_{\rm x}$
($x>0$) samples. This is verified by the investigation of static magnetic
proximity effects via x-ray resonant magnetic reflectivity.",1702.05384v1
2017-02-22,High Curie temperature Mn 5 Ge 3 thin films produced by non-diffusive reaction,"Polycrystalline Mn 5 Ge 3 thin films were produced on SiO 2 using magnetron
sputtering and reactive diffusion (RD) or non-diffusive reaction (NDR). In situ
X-ray diffraction and atomic force microscopy were used to determine the layer
structures, and magnetic force microscopy, superconducting quantum interference
device and ferromagnetic resonance were used to determine their magnetic
properties. RD-mediated layers exhibit similar magnetic properties as MBE-grown
monocrystalline Mn 5 Ge 3 thin films, while NDR-mediated layers show magnetic
properties similar to monocrystalline C-doped Mn 5 Ge 3 C x thin films with
$0.1 \leq x \leq 0.2.$ NDR appears as a CMOS-compatible efficient method to
produce good magnetic quality high-curie temperature Mn 5 Ge 3 thin films.",1702.06864v1
2017-02-24,Phases of cold atoms interacting via photon-mediated long-range forces,"Atoms in high-finesse optical resonators interact via the photons they
multiply scatter into the cavity modes. The dynamics is characterized by
dispersive and dissipative optomechanical long-range forces, which are mediated
by the cavity photons, and exhibits a steady state for certain parameter
regimes. In standing-wave cavities the atoms can form stable spatial gratings.
Moreover, their asymptotic distribution is a Maxwell-Boltzmann whose effective
temperature is controlled by the laser parameters. In this work we show that in
a two-mode standing-wave cavity the stationary state possesses the same
properties and phases of the Generalized Hamiltonian Mean Field model in the
canonical ensemble. This model has three equilibrium phases: a paramagnetic, a
nematic, and a ferromagnetic one, which here correspond to different spatial
orders of the atomic gas and can be detected by means of the light emitted by
the cavities. We further discuss perspectives for investigating in this setup
the ensemble inequivalence predicted for the Generalized Hamiltonian Mean Field
model.",1702.07653v1
2017-03-13,Influence of the Dzyaloshinskii-Moriya interaction on the FMR spectrum of magnonic crystals and confined structures,"We study the effect of surface-induced Dzyaloshinskii-Moriya interaction
(DMI) on the ferromagnetic resonance (FMR) spectrum of thickness-modulated
one-dimensional magnonic crystals and isolated stripes. The DMI is found to
substantially increases the intensity of absorption peaks and shifts the
frequencies of the laterally quantized modes. The role of the DMI is determined
by analyzing the amplitude and phase distributions of dynamic magnetic
excitations calculated with frequency- and time-domain calculation methods. We
propose experimentally realizable magnonic crystals and confined structures
with multiple FMR absorption peaks. The frequency or magnetic field separation
between FMR lines is exploited to propose a method for estimation of the DMI
strength.",1703.04463v1
2017-03-13,Dynamical amplification of magnetoresistances and Hall currents up to the THz regime,"Spin-orbit-related effects offer a highly promising route for reading and
writing information in magnetic units of future devices. These phenomena rely
not only on the static magnetization orientation but also on its dynamics to
achieve fast switchings that can reach the THz range. In this work, we consider
Co/Pt and Fe/W bilayers to show that accounting for the phase difference
between different processes is crucial to the correct description of the
dynamical currents. By tuning each system towards its ferromagnetic resonance,
we reveal that dynamical spin Hall angles can non-trivially change sign and be
boosted by over 500%, reaching giant values. We demonstrate that charge and
spin pumping mechanisms can greatly magnify or dwindle the currents flowing
through the system, influencing all kinds of magnetoresistive and Hall effects,
thus impacting also dc and second harmonic experimental measurements.",1703.04493v2
2017-03-29,Thickness dependence and dimensionality effects of charge and magnetic orderings in La1/3Sr2/3FeO3 thin films,"We investigate the thickness effects on charge and magnetic orderings in Fe
perovskite oxide La1/3Sr2/3FeO3/SrTiO3 thin films by hard x-ray and resonant
soft x-ray scattering (RSXS) with changing thin film thickness systematically.
We found that the correlation lengths of the magnetic ordering along the
in-plane and out-of-plane directions are comparable and proportional to the
thickness, and shows stronger thickness dependence than those of charge orderg.
%the thickness dependence of correlation length of charge ordering is smaller
than that of magnetic orderings. The magnetic ordered states disappear when the
correlation length of magnetic ordering decreases to that of charge ordering
through the intrinsic thickness effects. Surface sensitive grazing-incident
RSXS revealed that the orderings exist even in the surface region, which
indicates that the observed orderings is not affected by surface effect like
oxygen vacancies. Critical thickness is in 5-15 nm, which corresponds to 4-11
antiferromagnetic ordering period. This critical value seems to be common to
other ferromagnetic oxide thin films.",1703.09995v1
2017-08-02,Strongly exchange-coupled and surface-state-modulated magnetization dynamics in Bi2Se3/YIG heterostructures,"We report strong interfacial exchange coupling in Bi2Se3/yttrium iron garnet
(YIG) bilayers manifested as large in-plane interfacial magnetic anisotropy
(IMA) and enhancement of damping probed by ferromagnetic resonance (FMR). The
IMA and spin mixing conductance reached a maximum when Bi2Se3 was around 6
quintuple-layer (QL) thick. The unconventional Bi2Se3 thickness dependence of
the IMA and spin mixing conductance are correlated with the evolution of
surface band structure of Bi2Se3, indicating that topological surface states
play an important role in the magnetization dynamics of YIG.
Temperature-dependent FMR of Bi2Se3/YIG revealed signatures of magnetic
proximity effect of $T_c$ as high as 180 K, and an effective field parallel to
the YIG magnetization direction at low temperature. Our study sheds light on
the effects of topological insulators on magnetization dynamics, essential for
development of TI-based spintronic devices.",1708.00593v1
2017-08-24,MgO thickness-induced spin reorientation transition in Co0.9Fe0.1/MgO/Co0.9Fe0.1 structure,"The magnetic anisotropy (MA) of Mo/Au/Co0.9Fe0.1/Au/MgO(0.7 - 3
nm)/Au/Co0.9Fe0.1/Au heterostructure has been investigated at room temperature
as a function of MgO layer thickness (tMgO). Our studies show that while the MA
of the top layer does not change its character upon variation of tMgO, the
uniaxial out-of-plane MA of the bottom one undergoes a spin reorientation
transition at tMgO of about 0.8 nm, switching to the regime where the
coexistence of in- and out-of-plane magnetization alignments is observed. The
magnitudes of the magnetic anisotropy constants have been determined from
ferromagnetic resonance and dc-magnetometry measurements. The origin of MA
evolution has been attributed to a presence of an interlayer exchange coupling
(IEC) between Co0.9Fe0.1 layers through the thin MgO film.",1708.07382v1
2017-08-30,Large enhancement of the spin Hall effect in Au by scattering with side-jump on Ta impurities,"We present measurements of the Spin Hall Effect (SHE) in AuW and AuTa alloys
for a large range of W or Ta concentrations by combining experiments on lateral
spin valves and Ferromagnetic-Resonance/spin pumping technique. The main result
is the identification of a large enhancement of the Spin Hall Angle (SHA) by
the side-jump mechanism on Ta impurities, with a SHA as high as + 0.5 (i.e
$50\%$) for about 10\% of Ta. In contrast the SHA in AuW does not exceed + 0.15
and can be explained by intrinsic SHE of the alloy without significant
extrinsic contribution from skew or side-jump scattering by W impurities. The
AuTa alloys, as they combine a very large SHA with a moderate resistivity
(smaller than $85\,\mu\Omega.cm$), are promising for spintronic devices
exploiting the SHE.",1708.09214v1
2018-02-07,Control of surface potential at polar domain walls in a nonpolar oxide,"Ferroic domain walls could play an important role in microelectronics, given
their nanometric size and often distinct functional properties. Until now,
devices and device concepts were mostly based on mobile domain walls in
ferromagnetic and ferroelectric materials. A less explored path is to make use
of polar domain walls in nonpolar ferroelastic materials. Indeed, while the
polar character of ferroelastic domain walls has been demonstrated,
polarization control has been elusive. Here, we report evidence for the
electrostatic signature of the domain-wall polarization in nonpolar calcium
titanate (CaTiO3). Macroscopic mechanical resonances excited by an ac electric
field are observed as a signature of a piezoelectric response caused by polar
walls. On the microscopic scale, the polarization in domain walls modifies the
local surface potential of the sample. Through imaging of surface potential
variations, we show that the potential at the domain wall can be controlled by
electron injection. This could enable devices based on nondestructive
information readout of surface potential.",1802.02510v1
2018-04-02,Anisotropic Gilbert damping in perovskite La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ thin film,"The viscous Gilbert damping parameter governing magnetization dynamics is of
primary importance for various spintronics applications. Although, the damping
constant is believed to be anisotropic by theories. It is commonly treated as a
scalar due to lack of experimental evidence. Here, we present an elaborate
angle dependent broadband ferromagnetic resonance study of high quality
epitaxial La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films. Extrinsic effects are suppressed
and we show convincing evidence of anisotropic damping with twofold symmetry at
room temperature. The observed anisotropic relaxation is attributed to the
magnetization orientation dependence of the band structure. In addition, we
demonstrated that such anisotropy can be tailored by manipulating the stain.
This work provides new insights to understand the mechanism of magnetization
relaxation.",1804.00554v1
2018-04-03,Selection rules for cavity-enhanced Brillouin light scattering from magnetostatic modes,"We experimentally identify the magnetostatic modes active for Brillouin light
scattering in the optical whispering gallery modes of a yttrium iron garnet
sphere. Each mode is identified by magnetic field dispersion of
ferromagnetic-resonance spectroscopy and coupling strength to the known field
distribution of the microwave drive antenna. Our optical measurements confirm
recent predictions that higher-order magnetostatic modes can also generate
optical scattering, according to the selection rules derived from the axial
symmetry. From this we summarize the selection rules for Brillouin light
scattering. We give experimental evidence that the optomagnonic coupling to
non-uniform magnons can be higher than that of the uniform Kittel mode.",1804.00965v2
2018-11-04,Role of gallium diffusion in the formation of a magnetically dead layer at Y3Fe5O12 / Gd3Ga5O12 epitaxial interface,"We have clarified the origin of magnetically dead interface layer formed in
yttrium iron garnet (YIG) films grown at above 700{\deg}C onto gadolinium
gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The
diffusion-assisted formation of a Ga-rich region at the YIG / GGG interface is
demonstrated by means of composition depth profiling performed by X-ray
photoelectron spectroscopy, secondary ion mass spectroscopy and X-ray and
neutron reflectometry. Our finding is in sharp contrast to the earlier
expressed assumption that Gd acts as a migrant element in the YIG/GGG system.
We further correlate the presence of Ga-rich transition layer with considerable
quenching of ferromagnetic resonance and spin wave propagation in thin YIG
films. Finally, we clarify the origin of the enigmatic low-density overlayer
that is often observed in neutron and X-ray reflectometry studies of the YIG /
GGG epitaxial system.",1811.01321v2
2019-05-27,Spin relaxation in Cs$_2$CuCl$_{4-x}$Br$_x$,"The quantum-spin S = 1=2 chain system Cs$_2$CuCl$_4$ is of high interest due
to competing anti-ferromagnetic intra-chain J and inter-chain exchange J'
interactions and represents a paramount example for Bose-Einstein condensation
of magnons [R. Coldea et al., Phys. Rev. Lett. 88, 137202 (2002)]. Substitution
of chlorine by bromine allows tuning the competing exchange interactions and
corresponding magnetic frustration. Here we report on electron spin resonance
(ESR) in single crystals of Cs$_2$CuCl$_{4-x}$Br$_x$ with the aim to analyze
the evolution of anisotropic exchange contributions. The main source of the ESR
linewidth is attributed to the uniform Dzyaloshinskii-Moriya interaction. The
vector components of the Dzyaloshinskii-Moriya interaction are determined from
the angular dependence of the ESR spectra using a high-temperature
approximation. The obtained results support the site selectivity of the Br
substitution suggested from the evolution of lattice parameters and magnetic
susceptibility dependent on the Br concentration.",1905.11186v1
2019-05-29,Extracting the Dynamic Magnetic Contrast in Time-Resolved X-ray Transmission Microscopy,"Using a time-resolved detection scheme in scanning transmission X-ray
microscopy (STXM) we measured element resolved ferromagnetic resonance (FMR) at
microwave frequencies up to 10\,GHz and a spatial resolution down to 20\,nm at
two different synchrotrons. We present different methods to separate the
contribution of the background from the dynamic magnetic contrast based on the
X-ray magnetic circular dichroism (XMCD) effect. The relative phase between the
GHz microwave excitation and the X-ray pulses generated by the synchrotron, as
well as the opening angle of the precession at FMR can be quantified. A
detailed analysis for homogeneous and inhomogeneous magnetic excitations
demonstrates that the dynamic contrast indeed behaves as the usual XMCD effect.
The dynamic magnetic contrast in time-resolved STXM has the potential be a
powerful tool to study the linear and non-linear magnetic excitations in
magnetic micro- and nano-structures with unique spatial-temporal resolution in
combination with element selectivity.",1905.12497v2
2020-07-14,Feedback Induced Magnetic Phases in Binary Bose-Einstein Condensates,"Weak measurement in tandem with real-time feedback control is a new route
toward engineering novel non-equilibrium quantum matter. Here we develop a
theoretical toolbox for quantum feedback control of multicomponent
Bose-Einstein condensates (BECs) using backaction-limited weak measurements in
conjunction with spatially resolved feedback. Feedback in the form of a
single-particle potential can introduce effective interactions that enter into
the stochastic equation governing system dynamics. The effective interactions
are tunable and can be made analogous to Feshbach resonances --
spin-independent and spin-dependent -- but without changing atomic scattering
parameters. Feedback cooling prevents runaway heating due to measurement
backaction and we present an analytical model to explain its effectiveness. We
showcase our toolbox by studying a two-component BEC using a stochastic
mean-field theory, where feedback induces a phase transition between easy-axis
ferromagnet and spin-disordered paramagnet phases. We present the steady-state
phase diagram as a function of intrinsic and effective spin-dependent
interaction strengths. Our result demonstrates that closed-loop quantum control
of Bose-Einstein condensates is a powerful new tool for quantum engineering in
cold-atom systems.",2007.07266v1
2020-07-20,Sizable spin-transfer torque in Bi/Ni80Fe20 bilayer film,"The search for efficient spin conversion in Bi has attracted great attention
in spin-orbitronics. In the present work, we employ spin-torque ferromagnetic
resonance to investigate spin conversion in Bi/Ni80Fe20(Py) bilayer films with
continuously varying Bi thickness. In contrast with previous studies, sizable
spin-transfer torque (i.e., a sizable spin-conversion effect) is observed in
Bi/Py bilayer film. Considering the absence of spin conversion in
Bi/yttrium-iron-garnet bilayers and the enhancement of spin conversion in
Bi-doped Cu, the present results indicate the importance of material
combinations to generate substantial spin-conversion effects in Bi.",2007.09830v1
2020-07-30,Dynamical torques from Shiba states in $s$-wave superconductors,"Magnetic impurities inserted in a $s$-wave superconductor give rise to
spin-polarized in-gap states called Shiba states. We study the back-action of
these induced states on the dynamics of the classical moments. We show that the
Shiba state pertains to both reactive and dissipative torques acting on the
precessing classical spin that can be detected through ferromagnetic resonance
measurements. Moreover, we highlight the influence of the bulk states as well
as the effect of the finite linewidth of the Shiba state on the magnetization
dynamics. Finally, we demonstrate that the torques are a direct measure of the
even and odd frequency triplet pairings generated by the dynamics of the
magnetic impurity. Our approach offers non-invasive alternative to the STM
techniques used to probe the Shiba states.",2007.15392v2
2010-05-11,NMR Measurements of Power-Law Behavior in the Spin-Wave and Critical Regions of Ferromagnetic EuO,"Precision continuous-wave NMR measurements have been carried out over the
entire magnetization curve of EuO and are presented in tabular form. Two very
closely spaced resonances are observed and are attributed to domain and
domain-wall signals. Both of the signals are useful for analysis in the
spin-wave region. Only the domain signal is measurable above ~50K. The latter
is used for fitting Tc and the critical exponent beta. The critical-region fits
agree with previous measurements, within experimental error. The
low-temperature data exhibit a clear-cut T^2 behavior, at variance with the
expectations of conventional spin-wave theory. This result is discussed in
relation to two semi-empirical spin-wave schemes, one formulated by N.
Bykovetz, and one by U. Koebler. The NMR signal at 4.2K gives no indication of
a quadrupole splitting, in contradiction to the interpretation of several
previous spin-echo NMR spectra observed in EuO. This issue remains unresolved.",1005.1692v1
2013-08-06,Loop Liquid in an Ising-Spin Kondo Lattice Model on a Kagome Lattice,"Phase diagram of an Ising-spin Kondo lattice model on a kagome lattice is
investigated by a Monte Carlo simulation. We find that the system exhibits a
peculiar ferrimagnetic state at a finite temperature, in which each triangle is
in a two-up one-down spin configuration but the spin correlation does not
develop any superstructure. We call this state the loop liquid, as it is
characterized by the emergent degree of freedom, self-avoiding up-spin loops.
We elucidate that the system shows phase transitions from the loop liquid to
ferrimagnetically ordered states and a crossover to a partially ferromagnetic
state by changing the electron density and temperature. These can be viewed as
crystallization and cohesion of the loops, respectively. We demonstrate that
the loop formation is observed in the optical conductivity as a characteristic
resonant peak.",1308.1441v1
2014-03-01,Spin filtering in a magnetic barrier structure: in-plane spin orientation,"We investigate ballistic spin transport in a two dimensional electron gas
system through magnetic barriers of various geometries using the transfer
matrix method. While most of the previous studies have focused on the effect of
magnetic barriers perpendicular to the two dimensional electron gas plane, we
concentrate on the case of magnetic barriers parallel to the plane. We show
that resonant oscillation occurs in the transmission probability without
electrostatic potential modulation which is an essential ingredient in the case
of ordinary out-of-plane magnetic barriers. Transmission probability of the
in-plane magnetic barrier structure changes drastically according to the number
of barriers and also according to the electrostatic potential modulation
applied in the magnetic barrier region. Using a hybrid model consisting of a
superconductor, ferromagnets, and a two dimensional electron gas plane, we show
that it can serve as a good in-plane oriented spin selector which can be
operated thoroughly by electrical modulation without any magnetic control.",1403.0067v1
2014-03-27,Finite temperature spin dynamics in a perturbed quantum critical Ising chain with an $E_8$ symmetry,"A spectrum exhibiting $E_8$ symmetry is expected to arise when a small
longitudinal field is introduced in the transverse-field Ising chain at its
quantum critical point. Evidence for this spectrum has recently come from
neutron scattering measurements in cobalt niobate, a quasi one-dimensional
Ising ferromagnet. Unlike its zero-temperature counterpart, the
finite-temperature dynamics of the model has not yet been determined. We study
the dynamical spin structure factor of the model at low frequencies and nonzero
temperatures, using the form factor method. Its frequency dependence is
singular, but differs from the diffusion form. The temperature dependence of
the nuclear magnetic resonance (NMR) relaxation rate has an activated form,
whose prefactor we also determine. We propose NMR experiments as a means to
further test the applicability of the $E_8$ description for CoNb$_2$O$_6$.",1403.7222v4
2014-03-28,Magnetic and structural properties of Co2FeAl thin films grown on Si substrate,"The correlation between magnetic and structural properties of Co_{2} FeAl
(CFA) thin films of different thickness (10 nm<d< 100 nm) grown at room
temperature on MgO-buffered Si/SiO2 substrates and annealed at
600\lyxmathsym{\textdegree}C has been studied. XRD measurements revealed an
(011) out-of-plane texture growth of the films. The deduced lattice parameter
increases with the film thickness. Moreover, pole figures showed no in-plane
preferential growth orientation. The magneto-optical Kerr effect hysteresis
loops showed the presence of a weak in-plane uniaxial anisotropy with a random
easy axis direction. The coercive field measured with an applied field along
the easy axis direction and the uniaxial anisotropy field increase linearly
with the inverse of the CFA thickness. The microstrip line ferromagnetic
resonance measurements for in-plane and perpendicular applied magnetic fields
revealed that the effective magnetization and the uniaxial in-palne anisotropy
field follow a linear variation versus the inverse CFA thickness. This allows
deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2",1403.7566v1
2014-03-29,Epitaxial stabilization of ultra thin films of electron doped manganites,"Ultra-thin films of the electron doped manganite La$_{0.8}$Ce$_{0.2}$MnO$_3$
were grown in a layer-by-layer growth mode on SrTiO$_3$ (001) substrates by
pulsed laser interval deposition. High structural quality and surface
morphology was confirmed by a combination of synchrotron based x-ray
diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy
measurements confirm the presence of Ce$^{+4}$ and Mn$^{+2}$ ions. In addition,
the electron doping signature was corroborated by Hall effect measurements. All
grown films show ferromagnetic ground state as revealed by both XMCD and
magnetoresistance measurements and remain insulating contrary to earlier
reports of metal-insulator transition. Our results hint at the possibility of
electron-hole asymmetry in the colossal magnetoresistive (CMR) manganite phase
diagram akin to high-$T_c$ cuprates.",1403.7674v1
2016-11-14,Local environment effects on a charge carrier injected into an Ising chain,"We present numerically exact results for the spectral function of a single
charge carrier that is injected into an Ising chain at finite temperature $T$.
Both ferromagnetic and antiferromagnetic coupling between the Ising spins are
considered. The interaction between the carrier and the Ising spins is assumed
to be on-site and of Ising type, as well. We find that the carrier's spectral
function exhibits a distinctive fine structure of resonances that are due to
the temporary entrapping of the carrier inside small magnetic domains. The
connection to models of disordered binary alloys where similar effects can
occur is explained. We use these results to construct an accurate
(quasi)analytic approximation for low and medium-$T$ spectral functions.",1611.04560v1
2016-11-22,Control and Local Measurement of the Spin Chemical Potential in a Magnetic Insulator,"The spin chemical potential characterizes the tendency of spins to diffuse.
Probing the spin chemical potential could provide insight into materials such
as magnetic insulators and spin liquids and aid optimization of spintronic
devices. Here, we introduce single-spin magnetometry as a generic platform for
non-perturbative, nanoscale characterization of spin chemical potentials. We
use this platform to investigate magnons in a magnetic insulator, surprisingly
finding that the magnon chemical potential can be efficiently controlled by
driving the system's ferromagnetic resonance. We introduce a symmetry-based
two-fluid theory describing the underlying magnon processes, realize the first
experimental determination of the local thermomagnonic torque, and illustrate
the detection sensitivity using electrically controlled spin injection. Our
results open the way for nanoscale control and imaging of spin transport in
mesoscopic spin systems.",1611.07408v1
2016-11-26,Specific Heat of Spin Excitations Measured by FerromagneticResonance,"Using ferromagnetic-resonance spectroscopy (FMR), we investigate the
anisotropic properties of epitaxial 3 nmPt/2 nmAg/10 nmFe/10 nmAg/GaAs(001)
films in fully saturated meta-stable states at temperatures ranging from 70 K
to 280 K. By comparison to spin-wave theory calculations, we identify the role
of thermal fluctuation of magnons in overcoming the energy barrier associated
with these meta-stable states. We show that the energy associated with the size
of the barrier that bounds the meta-stable regime is proportional to the heat
stored in the magnonic bath. Our findings offer the possibility to measure the
magnonic contribution to the heat capacity by FMR, independent of other
contributions at temperatures ranging from 0 K to ambient temperature and
above. The only requirement being that the selected sample exhibits magnetic
anisotropy, here, magnetocrystalline anisotropy.",1611.08713v2
2017-01-02,Important role of magnetization precession angle measurement in inverse spin Hall effect induced by spin pumping,"Here, we investigate spin Hall angle of Pt in Ni80Fe20/Pt bilayer system by
using a broadband spin pumping and inverse spin Hall effect measurement. An
out-of-plane excitation geometry with application of external magnetic field
perpendicular to the charge current direction is utilized in order to suppress
unwanted galvanomagnetic effects. Magnetization precession angle on
ferromagnetic resonance for wide excitation frequency range (4-14 GHz) is
estimated from the rectification voltage of anisotropic magnetoresistance (AMR)
and a conventional method of using microwave power in a coplanar waveguide. A
marked difference in the precession angle profiles for the different methods is
observed, resulting in the large variation in estimated values of spin current
density at Ni80Fe20/Pt interface. The frequency dependence of the spin current
density estimated using AMR effect is found to be similar to that of the
inverse spin Hall voltage. We obtain the frequency-invariant spin Hall angle of
0.067.",1701.00412v1
2017-01-09,"Magnetic properties of ultra-thin 3d transition-metal binary alloys I: spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior","The structure and static magnetic properties - saturation magnetization,
perpendicular anisotropy, spectroscopic g-factor, and orbital magnetization -
of thin-film 3d transition metal alloys are determined over the full range of
alloy compositions via X-ray diffraction, magnetometry, and ferromagnetic
resonance measurements. We determine the interfacial perpendicular magnetic
anisotropy by use of samples sets with varying thickness for specific alloy
concentrations. The results agree with prior published data and theoretical
predictions. They provide a comprehensive compilation of the magnetic
properties of thin-film Ni-Co, Ni-Fe and Co-Fe alloys that goes well beyond the
often-cited Slater-Pauling dependence of magnetic moment on alloy
concentration.",1701.02177v1
2017-01-10,Magnetic properties in ultra-thin 3d transition metal alloys II: Experimental verification of quantitative theories of damping and spin-pumping,"A systematic experimental study of Gilbert damping is performed via
ferromagnetic resonance for the disordered crystalline binary 3d transition
metal alloys Ni-Co, Ni-Fe and Co-Fe over the full range of alloy compositions.
After accounting for inhomogeneous linewidth broadening, the damping shows
clear evidence of both interfacial damping enhancement (by spin pumping) and
radiative damping. We quantify these two extrinsic contributions and thereby
determine the intrinsic damping. The comparison of the intrinsic damping to
multiple theoretical calculations yields good qualitative and quantitative
agreement in most cases. Furthermore, the values of the damping obtained in
this study are in good agreement with a wide range of published experimental
and theoretical values. Additionally, we find a compositional dependence of the
spin mixing conductance.",1701.02475v1
2017-01-23,Understanding stability diagram of perpendicular magnetic tunnel junctions,"Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference
layer and a composite free layer (FL) are investigated. Different thicknesses
of the FL were tested to obtain an optimal balance between tunneling
magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After
annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer
reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier
thickness corresponding to the resistance area product RA = 10
Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams
measured in pillar-shaped MTJs with 130 nm diameter indicate the competition
between spin transfer torque (STT), voltage controlled magnetic anisotropy
(VCMA) and temperature effects in the switching process. An extended stability
phase diagram model that takes into account all three parameters and the
effective damping measured independently using broadband ferromagnetic
resonance technique enabled the determination of both STT and VCMA coefficients
that are responsible for the FL magnetization switching.",1701.06411v1
2017-04-10,Lyapunov Exponent and Criticality in the Hamiltonian Mean Field Model,"We investigate the dependence of the largest Lyapunov exponent of a
$N$-particle self-gravitating ring model at equilibrium with respect to the
number of particles and its dependence on energy. This model has a continuous
phase-transition from a ferromagnetic to homogeneous phase, and we numerically
confirm with large scale simulations the existence of a critical exponent
associated to the largest Lyapunov exponent, although at variance with the
theoretical estimate. The existence of chaos in the magnetized state evidenced
by a positive Lyapunov exponent, even in the thermodynamic limit, is explained
by the resonant coupling of individual particle oscillations to the diffusive
motion of the center of mass of the system due to the thermal excitation of a
classical Goldstone mode. The transition from ""weak"" to ""strong"" chaos occurs
at the onset of the diffusive motion of the center of mass of the
non-homogeneous equilibrium state, as expected. We also discuss thoroughly for
the model the validity and limits of a geometrical approach for their
analytical estimate.",1704.02678v3
2017-04-10,Patterned growth of crystalline Y$_{3}$Fe$_{5}$O$_{12}$ nanostructures with engineered magnetic shape anisotropy,"We demonstrate patterned growth of epitaxial yttrium iron garnet (YIG) thin
films using lithographically defined templates on gadolinium gallium garnet
(GGG) substrates. The fabricated YIG nanostructures yield the desired
crystallographic orientation, excellent surface morphology, and narrow
ferromagnetic resonance (FMR) linewidth (~ 4 Oe). Shape-induced magnetic
anisotropy is clearly observed in a patterned array of nanobars engineered to
exhibit the larger coercivity (40 Oe) compared with that of continuous films.
Both hysteresis loop and angle-dependent FMR spectra measurements indicate that
the easy axis aligns along the longitudinal direction of the nanobars, with an
effective anisotropy field of 195 Oe. Our work overcomes difficulties in
patterning YIG thin films and provides an effective means to control their
magnetic properties and magnetic bias conditions.",1704.03056v2
2017-04-13,Spin pumping into superconductors: A new probe of spin dynamics in a superconducting thin film,"Spin pumping refers to the microwave-driven spin current injection from a
ferromagnet into the adjacent target material. We theoretically investigate the
spin pumping into superconductors by fully taking account of impurity
spin-orbit scattering that is indispensable to describe diffusive spin
transport with finite spin diffusion length. We calculate temperature
dependence of the spin pumping signal and show that a pronounced coherence peak
appears immediately below the superconducting transition temperature Tc, which
survives even in the presence of the spin-orbit scattering. The phenomenon
provides us with a new way of studying the dynamic spin susceptibility in a
superconducting thin film. This is contrasted with the nuclear magnetic
resonance technique used to study a bulk superconductor.",1704.04303v2
2017-04-17,Orbital order and fluctuations in the two-leg ladder materials BaFe$_2X_3$ ($X$ = S and Se) and CsFe$_2$Se$_3$,"The electronic structure of BaFe$_2X_3$ ($X$ = S and Se) and CsFe$_2$Se$_3$
in which two-leg ladders are formed by the Fe sites are studied by means of
x-ray absorption and resonant inelastic x-ray scattering spectroscopy. The
x-ray absorption spectra at the Fe L edges for BaFe$_2X_3$ exhibit two
components, indicating that itinerant and localized Fe 3$d$ sites coexist.
Substantial x-ray linear dichroism (XLD) is observed in polarization dependent
spectra, indicating the existence of orbital order or fluctuation in the
Fe-ladder even above the N\'{e}el temperature $T_N$. Direct exchange
interaction along the legs of the Fe-ladder stabilizes the orbital and
antiferromagnetic orders in BaFe$_2$S$_3$, while the ferromagnetic molecular
orbitals are realized between the rungs in CsFe$_2$Se$_3$.",1704.04864v2
2018-05-19,Optically driven spin pumping mediating collective magnetization dynamics in a spin valve structure,"We demonstrate spin pumping, i.e. the generation of a pure spin current by
precessing magnetization, without application of microwave radiation commonly
used in spin pumping experiments. We use femtosecond laser pulses to
simultaneously launch the magnetization precession in each of two ferromagnetic
layers of a Galfenol-based spin valve and monitor the temporal evolution of the
magnetizations. The spin currents generated by the precession cause a dynamic
coupling of the two layers. This coupling has dissipative character and is
especially efficient when the precession frequencies in the two layers are in
resonance, where coupled modes with strongly different decay rates are formed.",1805.07669v1
2018-05-27,Dynamical structure factors in the nematic phase of frustrated ferromagnetic spin chains,"Frustrated spin systems can show phases with spontaneous breaking of
spin-rotational symmetry without the formation of local magnetic order. We
study the dynamic response of the spin-nematic phase of one-dimensional
spin-1/2 systems, characterized by slow large-distance decay of quadrupolar
correlations, by numerically computing one-spin and two-spin dynamical
structure factors at zero temperature using time-dependent density matrix
renormalization group methods. We interpret the results in terms of an
effective theory of gapped magnon excitations interacting with a
quasi-condensate of bound magnon pairs. This employs an extension of the
well-known Tomonaga-Luttinger liquid theory which includes the magnon states as
a mobile impurity. A good qualitative understanding of the characteristic
thresholds and their intensity in the structure factors is obtained this way.
Our results are useful in the interpretation of inelastic neutron scattering
and resonant inelastic x-ray scattering experiments.",1805.10612v2
2008-07-29,Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole,"We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.",0807.4660v2
2009-12-01,Phase diagrams of XXZ model on depleted square lattice,"Using quantum Monte Carlo (QMC) simulations and a mean field (MF) theory, we
investigate the spin-1/2 XXZ model with nearest neighbor interactions on a
periodic depleted square lattice. In particular, we present results for 1/4
depleted lattice in an applied magnetic field and investigate the effect of
depletion on the ground state. The ground state phase diagram is found to
include an antiferromagnetic (AF) phase of magnetization $m_{z}=\pm 1/6$ and an
in-plane ferromagnetic (FM) phase with finite spin stiffness. The agreement
between the QMC simulations and the mean field theory based on resonating
trimers suggests the AF phase and in-plane FM phase can be interpreted as a
Mott insulator and superfluid of trimer states respectively. While the thermal
transitions of the in-plane FM phase are well described by the
Kosterlitz-Thouless transition, the quantum phase transition from the AF phase
to in-plane FM phase undergo a direct second order insulator-superfluid
transition upon increasing magnetic field.",0912.0069v2
2009-12-17,Textures and Vortices in d-Wave Fermi Condensates in Atomic Gases,"Fundamental properties of superfluids with d-wave pairing symmetry are
investigated theoretically. We consider neutral atomic Fermi gases in a
harmonic trap, the Cooper pairing being produced by a Feshbach resonance via a
d-wave interaction channel. A Ginzburg-Landau (GL) functional is constructed
which is symmetry constrained for five component order parameters (OPs). We
find stable OP textures and vortices for all the three phases which are known
to be the energy minimum of the GL functional; the ferromagnetic, polar and
cyclic phases both at rest and under rotation. In particular, we touch upon the
stability conditions for a non-Abelian fractional 1/3-vortex in the cyclic
phase under rotation. It is proposed how to create the intriguing 1/3-vortex
experimentally in atomic gases via optical means.",0912.3314v1
2011-11-05,119Sn NMR probe of magnetic fluctuations in SnO2 nanoparticles,"119Sn nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation
rate (1/T1) in SnO2 nanoparticles were measured as a function of temperature
and compared with those of SnO2 bulk sample. A 15% loss of 119Sn NMR signal
intensity for the nano sample compared to the bulk sample was observed. This is
indicative of ferromagnetism from a small fraction of the sample. Another major
finding is that the recovery of the 119Sn longitudinal nuclear magnetization in
the nano sample follows a stretched exponential behavior, as opposed to that in
bulk which is exponential. Further, the 119Sn 1/T1 at room temperature is found
to be much higher for the nano sample than for its bulk counterpart. These
results indicate the presence of magnetic fluctuations in SnO2 nanoparticles in
contrast to the bulk (non-nano) which is diamagnetic. These local moments could
arise from surface defects in the nanoparticles.",1111.1290v1
2012-01-02,Localized domain-wall excitations in patterned magnetic dots probed by broadband ferromagnetic resonance,"We investigate the magnetization dynamics in circular Permalloy dots with
spatially separated magnetic vortices interconnected by domain walls (double
vortex state). We identify a novel type of quasi one-dimensional (1D) localised
spin wave modes confined along domain walls, connecting each of two vortex
cores with two edge half-antivortices. Variation of the mode eigenfrequencies
with the dot size is in quantitative agreement with the developed model, which
considers a dipolar origin of the localized 1D spin waves or so-called
Winter\'s magnons [J.M. Winter, Phys.Rev. 124, 452 (1961)]. These spin waves
are analogous to the displacement waves of strings, and could be excited in a
wide class of patterned magnetic nanostructures possessing domain walls, namely
in triangular, square, circular or elliptic magnetic dots.",1201.0482v1
2012-01-10,Quantum spin pumping mediated by magnon,"We theoretically propose quantum spin pumping mediated by magnons, under a
time-dependent transverse magnetic field, at the interface between a
ferromagnetic insulator and a non-magnetic metal. The generation of a spin
current under a thermal equilibrium condition is discussed by calculating the
spin transfer torque, which breaks the spin conservation law for conduction
electrons and operates the coherent magnon state. Localized spins lose spin
angular momentum by emitting magnons and conduction electrons flip from down to
up by absorbing the momentum. The spin transfer torque has a resonance
structure as a function of the angular frequency of the applied transverse
field. This fact is useful to enhance the spin pumping effect induced by
quantum fluctuations. We also discuss the distinction between our quantum spin
pumping theory and the one proposed by Tserkovnyak et al.",1201.1947v3
2012-01-31,Entanglement probe of two-impurity Kondo physics in a spin chain,"We propose that real-space properties of the two-impurity Kondo model can be
obtained from an effective spin model where two single-impurity Kondo spin
chains are joined via an RKKY interaction between the two impurity spins. We
then use a DMRG approach, valid in all ranges of parameters, to study its
features using two complementary quantum-entanglement measures, the negativity
and the von Neumann entropy. This non-perturbative approach enables us to
uncover the precise dependence of the spatial extent $\xi_K$ of the Kondo
screening cloud with the Kondo and RKKY couplings. Our results reveal an
exponential suppression of the Kondo temperature $T_K \sim 1/\xi_K$ with the
size of the effective impurity spin in the limit of large ferromagnetic RKKY
coupling, a striking display of ""Kondo resonance narrowing"" in the two-impurity
Kondo model. We also show how the antiferromagnetic RKKY interaction produces
an effective decoupling of the impurities from the bulk already for
intermediate strengths of this interaction, and, furthermore, exhibit how the
non-Fermi liquid quantum critical point is signaled in the quantum entanglement
between various parts of the system.",1201.6668v2
2014-05-09,Current-induced magnetization dynamics in two magnetic insulators separated by a normal metal,"We study the dynamics of spin valves consisting of two layers of magnetic
insulators separated by a normal metal in the macrospin model. A current
through the spacer generates a spin Hall current that can actuate the
magnetization via the spin-transfer torque. We derive expressions for the
effective Gilbert damping and the critical currents for the onset of
magnetization dynamics including the effects of spin pumping that can be tested
by ferromagnetic resonance experiments. The current generates an amplitude
asymmetry between the in-phase and out-of-phase modes. We briefly discuss
superlattices of metals and magnetic insulators.",1405.2267v1
2014-06-15,Direct and inverse spin-orbit torques,"In collinear magnets lacking inversion symmetry application of electric
currents induces torques on the magnetization and conversely magnetization
dynamics induces electric currents. The two effects, which both rely on
spin-orbit interaction (SOI), are reciprocal to each other and denoted direct
spin-orbit torque (SOT) and inverse spin-orbit torque (ISOT), respectively. We
derive expressions for SOT and ISOT within the Kubo linear response formalism.
We show that expressions suitable for density-functional theory calculations
can be derived either starting from a Kohn-Sham Hamiltonian with time-dependent
exchange field or by expressing general susceptibilities in terms of the
Kohn-Sham susceptibilities. For the case of magnetic bilayer systems we derive
the general form of the ISOT current induced under ferromagnetic resonance.
Using \textit{ab initio} calculations within density-functional theory we
investigate SOT and ISOT in Co/Pt(111) magnetic bilayers. We determine the
spatial distribution of spin and charge currents as well as torques in order to
expose the mechanisms underlying SOT and ISOT and to highlight their
reciprocity on the microscopic level. We find that the spin Hall effect is
position-dependent close to interfaces.",1406.3866v2
2015-12-15,Moderate Positive Spin Hall Angle in Uranium,"We report measurements of spin pumping and the inverse spin Hall effect in
Ni80Fe20/Uranium bilayers designed to study the efficiency of spin-charge
interconversion in a super-heavy element. We employ broad-band ferromagnetic
resonance on extended films to inject a spin current from the Ni80Fe20
(permalloy) into the uranium layer, which is then converted into an electric
field by the inverse spin Hall effect. Surprisingly, our results suggest a spin
mixing conductance of order 2x10 e19 m-2 and a positive spin Hall angle of
0.004, which are both merely comparable to those of several transition metals.
These results thus support the idea that the electronic configuration may be at
least as important as the atomic number in governing spin pumping across
interfaces and subsequent spin Hall effects. In fact, given that both the
magnitude and the sign are unexpected based on trends in d-electron systems,
materials with unfilled f-electron orbitals may hold additional exploration
avenues for spin physics.",1512.04903v1
2016-05-06,Electrical measurement of magnetic-field-impeded polarity switching of a ferromagnetic vortex core,"Vortex core polarity switching in NiFe disks has been evidenced using an
all-electrical rectification scheme. Both simulation and experiments yield a
consistent loss of the rectified signal when driving the core at high powers
near its gyrotropic resonant frequency. The frequency range over which the loss
occurs grows and shifts with increasing signal power, consistent with
non-linear core dynamics and periodic switching of the core polarity induced by
the core attaining its critical velocity. We demonstrate that core polarity
switching can be impeded by displacing the core towards the disk's edge where
an increased core stiffness reduces the maximum attainable core velocity.",1605.01826v1
2016-05-06,"Exchange-mediated, non-linear, out-of-plane magnetic field dependence of the ferromagnetic vortex gyrotropic mode frequency driven by core deformation","We have performed micromagnetic simulations of the vortex gyrotropic mode
resonance in a range of disk geometries subject to spatially uniform
out-of-plane magnetic fields. For disks of small lateral dimensions, we observe
a drop-off in the mode's frequency for field amplitudes approaching the disk
saturation field. This non-linear frequency response is shown to be associated
with an increased vortex core deformation, which results from the demagnetizing
field created when the core is shifted laterally. Such deformation results in
an increase in the average out-of-plane magnetization of the displaced vortex
state, which through an exchange contribution, leads to a sharp decrease in the
vortex stiffness coefficient. It is this decrease in the vortex stiffness
coefficient which leads to the non-linear field dependence of the gyrotropic
mode frequency.",1605.01830v1
2016-05-19,Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures,"Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are
investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra
of microstrips with varying width are measured as a function of magnetic field
and frequency. The FMR frequency is shown to depend on the electric field
applied across the substrate, which induces strain in the NiFe layer. Electric
field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model
based on total energy minimization and the LLG equation, with magnetostriction
effect taken into account, is developed to explain the measured dynamics. Based
on this model, conditions for strong electric-field tunable spin diode FMR in
patterned NiFe/PMN-PT structures are derived.",1605.06019v1
2016-05-20,High-frequency behavior of FeN thin films fabricated by reactive sputtering,"We investigated high-frequency behavior of FeN thin films prepared by
reactive sputtering through ferromagnetic resonance (FMR) and its relationship
with the static magnetic properties. The FMR was observed in the frequency
range from 2 to 18 GHz in the FeN films fabricated at proper nitrogen flow rate
(NFR). In those FeN thin films, a decrease of the saturation magnetization and
the corresponding decrease of the FMR frequency were observed as NFR was
increased during the deposition. The external field dependences of the FMR
frequencies were well fit to the Kittel formula and the Land\'e g-factors
determined from the fit were found to be very close to the free electron value.
The high-field damping parameters were almost insensitive to the growth
condition of NFR. However, the low-field damping parameters exhibited high
sensitivity to NFR very similar to the dependence of the hard-axis coercivity
on NFR, suggesting that extrinsic material properties such as impurities and
defect structures could be important in deciding the low-field damping
behavior.",1605.06179v1
2016-05-26,Thickness and temperature dependence of the magnetodynamic damping of pulsed laser deposited $\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ on (111)-oriented SrTi$\text{O}_3$,"We have investigated the magnetodynamic properties of
$\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ (LSMO) films of thickness 10, 15
and 30 nm grown on (111)-oriented SrTi$\text{O}_3$ (STO) substrates by pulsed
laser deposition. Ferromagnetic resonance (FMR) experiments were performed in
the temperature range 100--300 K, and the magnetodynamic damping parameter
$\alpha$ was extracted as a function of both film thickness and temperature. We
found that the damping is lowest for the intermediate film thickness of 15 nm
with $\alpha \approx 2 \cdot 10^{-3}$, where $\alpha$ is relatively constant as
a function of temperature well below the Curie temperature of the respective
films.",1605.08195v2
2016-08-02,Spintronics of Organometal Trihalide Perovskites,"The family of organometal trihalide perovskite (OTP), CH3NH3PbX3 (where X is
halogen) has recently revolutionized the photovoltaics field and shows promise
in a variety of optoelectronic applications. The characteristic spin properties
of charge and neutral excitations in OTPs are influenced by the large
spin-orbit coupling of the Pb atoms, which may lead to spin-based device
applications. Here we report the first studies of pure spin-current and
spin-aligned carrier injection in OTP spintronics devices using spin-pumping
and spin-injection, respectively. We measure a relatively large
inverse-spin-Hall effect using pulsed microwave excitation in OTP devices at
resonance with a ferromagnetic substrate, from which we derive room temperature
spin diffusion length, lambda_sd~9nm; and low-temperature giant
magnetoresistance in OTP-based spin-valves from which we estimate
lambda_sd~85nm.",1608.00993v1
2016-12-06,Spin-Hall Torques Generated by Rare-Earth (Lanthanide) Thin Films,"We report an initial experimental survey of spin-Hall torques generated by
the rare-earth metals Gd, Dy, Ho, and Lu, along with comparisons to
first-principles calculations of their spin Hall conductivities. Using spin
torque ferromagnetic resonance (ST-FMR) measurements and DC-biased ST-FMR, we
estimate lower bounds for the spin-Hall torque ratio, $\xi_{SH}$, of $\approx$
0.04 for Gd, $\approx$ 0.05 for Dy, $\approx$ 0.14 for Ho, and $\approx$ 0.014
for Lu. The variations among these elements are qualitatively consistent with
results from first principles (density functional theory, DFT, in the local
density approximation with a Hubbard-U correction). The DFT calculations
indicate that the spin Hall conductivity is enhanced by the presence of the
partially-filled $f$ orbitals in Dy and Ho, which suggests a strategy to
further strengthen the contribution of the $f$ orbitals to the spin Hall effect
by shifting the electron chemical potential.",1612.01927v1
2016-12-06,Increased low-temperature damping in yttrium iron garnet thin films,"We report measurements of the frequency and temperature dependence of
ferromagnetic resonance (FMR) for a 15-nm-thick yttrium iron garnet (YIG) film
grown by off-axis sputtering. Although the FMR linewidth is narrow at room
temperature (corresponding to a damping coefficient $\alpha$ = (9.0 $\pm$ 0.2)
$\times 10^{-4}$), comparable to previous results for high-quality YIG films of
similar thickness, the linewidth increases strongly at low temperatures, by a
factor of almost 30. This increase cannot be explained as due to two-magnon
scattering from defects at the sample interfaces. We argue that the increased
low-temperature linewidth is due to impurity relaxation mechanisms that have
been investigated previously in bulk YIG samples. We suggest that the
low-temperature linewidth is a useful figure of merit to guide the optimization
of thin-film growth protocols because it is a particularly sensitive indicator
of impurities.",1612.01954v1
2016-12-07,Gilbert damping of magnetostatic modes in a yttrium iron garnet sphere,"The magnetostatic mode (MSM) spectrum of a 300$\mu$m diameter single
crystalline sphere of yttrium iron garnet is investigated using broadband
ferromagnetic resonance (FMR). The individual MSMs are identified via their
characteristic dispersion relations and the corresponding mode number tuples
$(nmr)$ are assigned. Taking FMR data over a broad frequency and magnetic field
range allows to analyze both the Gilbert damping parameter~$\alpha$ and the
inhomogeneous line broadening contribution to the total linewidth of the MSMs
separately. The linewidth analysis shows that all MSMs share the same Gilbert
damping parameter $\alpha=2.7(5) \times 10^{-5}$ irrespective of their mode
index. In contrast, the inhomogeneous line broadening shows a pronounced mode
dependence. This observation is modeled in terms of two-magnon scattering
processes of the MSMs into the spin-wave manifold, mediated by surface and
volume defects.",1612.02360v1
2017-06-10,Mapping the magnonic landscape in patterned magnetic structures,"We report the development of a hybrid numerical / analytical model capable of
mapping the spatially-varying distributions of the local ferromagnetic
resonance (FMR) frequency and dynamic magnetic susceptibility in a wide class
of patterned and compositionally modulated magnetic structures. Starting from
the numerically simulated static micromagnetic state, the magnetization is
deliberately deflected orthogonally to its equilibrium orientation, and the
magnetic fields generated in response to this deflection are evaluated using
micromagnetic software. This allows us to calculate the elements of the
effective demagnetizing tensor, which are then used within a linear analytical
formalism to map the local FMR frequency and dynamic magnetic susceptibility.
To illustrate the typical results that one can obtain using this model, we
analyze three micromagnetic systems boasting non-uniformity in either one or
two dimensions, and successfully explain the spin-wave emission observed in
each case, demonstrating the ubiquitous nature of the Schl\""omann excitation
mechanism underpinning the observations. Finally, the developed model of local
FMR frequency could be used to explain how spin waves could be confined and
steered using magnetic non-uniformities of various origins, rendering it a
powerful tool for the mapping of the graded magnonic index in magnonics.",1706.03212v1
2017-06-26,Perpendicular magnetic anisotropy in insulating ferrimagnetic gadolinium iron garnet thin films,"We present experimental control of the magnetic anisotropy in a gadolinium
iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by
simply changing the sample temperature. The magnetic hysteresis loops obtained
by SQUID magnetometry measurements unambiguously reveal a change of the
magnetically easy axis from out-of-plane to in-plane depending on the sample
temperature. Additionally, we confirm these findings by the use of temperature
dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to
determine the effective magnetization, we utilize the intrinsic advantage of
FMR spectroscopy which allows to determine the magnetic anisotropy independent
of the paramagnetic substrate, while magnetometry determines the combined
magnetic moment from film and substrate. This enables us to quantitatively
evaluate the anisotropy and the smooth transition from in-plane to
perpendicular magnetic anisotropy. Furthermore, we derive the temperature
dependent $g$-factor and the Gilbert damping of the GdIG thin film.",1706.08488v1
2017-07-12,Thickness dependence of spin-orbit torques generated by WTe2,"We study current-induced torques in WTe2/permalloy bilayers as a function of
WTe2 thickness. We measure the torques using both second-harmonic Hall and
spin-torque ferromagnetic resonance measurements for samples with WTe2
thicknesses that span from 16 nm down to a single monolayer. We confirm the
existence of an out-of-plane antidamping torque, and show directly that the
sign of this torque component is reversed across a monolayer step in the WTe2.
The magnitude of the out-of-plane antidamping torque depends only weakly on
WTe2 thickness, such that even a single-monolayer WTe2 device provides a strong
torque that is comparable to much thicker samples. In contrast, the
out-of-plane field-like torque has a significant dependence on the WTe2
thickness. We demonstrate that this field-like component originates
predominantly from the Oersted field, thereby correcting a previous inference
drawn by our group based on a more limited set of samples.",1707.03757v1
2017-07-29,Experimental study of extrinsic spin Hall effect in CuPt alloy,"We have experimentally studied the effects on the spin Hall angle due to
systematic addition of Pt into the light metal Cu. We perform spin torque
ferromagnetic resonance measurements on Py/CuPt bilayer and find that as the Pt
concentration increases, the spin Hall angle of CuPt alloy increases. Moreover,
only 28% Pt in CuPt alloy can give rise to a spin Hall angle close to that of
Pt. We further extract the spin Hall resistivity of CuPt alloy for different Pt
concentrations and find that the contribution of skew scattering is larger for
lower Pt concentrations, while the side-jump contribution is larger for higher
Pt concentrations. From technological perspective, since the CuPt alloy can
sustain high processing temperatures and Cu is the most common metallization
element in the Si platform, it would be easier to integrate the CuPt alloy
based spintronic devices into existing Si fabrication technology.",1707.09525v1
2017-07-30,Multi-second magnetic coherence in a single domain spinor Bose-Einstein condensate,"We describe a compact, robust and versatile system for studying magnetic
dynamics in a spinor Bose-Einstein condensate. Condensates of 87 Rb are
produced by all-optical evaporation in a 1560 nm optical dipole trap, using a
non-standard loading sequence that employs an auxiliary 1529 nm beam for
partial compensation of the strong differential light shift induced by the
dipole trap itself. We use near-resonance Faraday rotation probing to
non-destructively track the condensate magnetization, and demonstrate
few-Larmor-cycle tracking with no detectable degradation of the spin
polarization. In the ferromagnetic F = 1 ground state, we observe magnetic T1
and T2$^*$ coherence times limited only by the several-second residence time of
the atoms in the trap.",1707.09607v1
2017-10-17,"Phase Diagram of Ba$_{2}$NaOsO$_{6}$, a Mott insulator with strong spin orbit interactions","We report $^{23}$Na nuclear magnetic resonance (NMR) measurements of the Mott
insulator with strong spin-orbit interaction Ba$_{2}$NaOsO$_{6}$ as a function
of temperature in different magnetic fields ranging from 7 T to 29 T. The
measurements, intended to concurrently probe spin and orbital/lattice degrees
of freedom, are an extension of our work at lower fields reported in Nat.
Commun., v 8, 14407 (2017). We have identified clear quantitative NMR
signatures that display the appearance of a canted ferromagnetic phase, which
is preceded by local point symmetry breaking. We have compiled the field
temperature phase diagram extending up to 29 T. We find that the broken local
point symmetry phase extends over a wider temperature range as magnetic field
increases.",1710.06777v1
2018-01-03,Negative spin-Hall angle and anisotropic spin-orbit torques in epitaxial IrMn,"A spin-torque ferromagnetic resonance study is performed in epitaxial
$\mathrm{Fe / Ir_{15}Mn_{85}}$ bilayers with different Fe thicknesses. We
measure a negative spin-Hall angle of a few percent in the antiferromagnetic
IrMn in contrast to previously reported positive values. A large spin-orbit
field with Rashba symmetry opposing the Oersted field is also present.
Magnitudes of measured spin-orbit torques depend on the crystallographic
direction of current and are correlated with the exchange bias direction set
during growth. We suggest that the uncompensated moments at the Fe / IrMn
interface are responsible for the observed anisotropy. Our findings highlight
the importance of crystalline and magnetic structures for the spin-Hall effect
in antiferromagnets.",1801.01065v1
2018-01-18,Excellent microwave and magnetic properties of La-Cu substituted Ba-hexaferrites prepared by ceramic process,"We demonstrate exceptional microwave magnetic performance of
crystallographycally textured barium hexaferrites prepared by conventional
ceramic method. Vibrating sample magnetometer (VSM) and rectangular cavity
perturbation measurements indicate that bulk Ba0.8La0.2Fe11.2Cu0.2O19 samples
exhibit a strong magnetic anisotropy field Ha of 14.6kOe, the highest remanent
magnetization of 3.96kGs, and the lowest ferromagnetic resonance (FMR)
linewidth of 401Oe with zero applied bias field at Q-band. Broadband
millimeter-wave transmittance measurements determined the complex permeability
and permittivity. The remanent magnetization, anisotropy field Ha, and
effective linewidth were also estimated based on Schlomann's theory of the
complex permeability. These calculated values are in good agreement with the
VSM and FMR measurements.",1801.05945v1
2018-01-22,Spin-orbit torques in NbSe$_2$/Permalloy bilayers,"We present measurements of current-induced spin-orbit torques generated by
NbSe$_2$, a fully-metallic transition-metal dichalcogenide material, made using
the spin-torque ferromagnetic resonance (ST-FMR) technique with
NbSe$_{2}$/Permalloy bilayers. In addition to the out-of-plane Oersted torque
expected from current flow in the metallic NbSe$_{2}$ layer, we also observe an
in-plane antidamping torque with torque conductivity $\sigma_{S} \approx 10^{3}
(\hbar / 2e)$($\Omega$m)$^{-1}$ and indications of a weak field-like
contribution to the out-of-plane torque oriented opposite to the Oersted
torque. Furthermore, in some samples we also measure an in-plane field-like
torque with the form $\hat{m} \times \hat{z}$, where $\hat{m}$ is the Permalloy
magnetization direction and $\hat{z}$ is perpendicular to the sample plane. The
size of this component varies strongly between samples and is not correlated
with the NbSe$_{2}$ thickness. A torque of this form is not allowed by the bulk
symmetries of NbSe$_{2}$, but is consistent with symmetry breaking by a
uniaxial strain that might result during device fabrication.",1801.07281v1
2018-10-01,Determination of spin Hall angle in heavy metal/CoFeB-based heterostructures with interfacial spin-orbit fields,"Magnetization dynamics in W/CoFeB, CoFeB/Pt and W/CoFeB/Pt multilayers was
investigated using spin-orbit-torque ferromagnetic resonance (SOT-FMR)
technique. An analytical model based on magnetization dynamics due to SOT was
used to fit heavy metal (HM) thickness dependence of symmetric and
antisymmetric components of the SOT-FMR signal. The analysis resulted in a
determination of the properties of HM layers, such as spin Hall angle and spin
diffusion length. The spin Hall angle of -0.36 and 0.09 has been found in the
W/CoFeB and CoFeB/Pt bilayers, respectively, which add up in the case of
W/CoFeB/Pt trilayer. More importantly, we have determined effective interfacial
spin-orbit fields at both W/CoFeB and CoFeB/Pt interfaces, which are shown to
cancel Oersted field for particular thicknesses of the heavy metal layers,
leading to pure spin-current-induced dynamics and indicating the possibility
for a more efficient magnetization switching.",1810.00641v1
2018-10-17,Perpendicularly magnetized YIG films with small Gilbert damping constant and anomalous spin transport properties,"The Y3Fe5O12 (YIG) films with perpendicular magnetic anisotropy (PMA) have
recently attracted a great deal of attention for spintronics applications.
Here, we report the induced PMA in the ultrathin YIG films grown on
(Gd2.6Ca0.4)(Ga4.1Mg0.25Zr0.65)O12 (SGGG) substrates by epitaxial strain
without preprocessing. Reciprocal space mapping shows that the films are
lattice-matched to the substrates without strain relaxation. Through
ferromagnetic resonance and polarized neutron reflectometry measurements, we
find that these YIG films have ultra-low Gilbert damping constant with a
magnetic dead layer as thin as about 0.3 nm at the YIG/SGGG interfaces.
Moreover, the transport behavior of the Pt/YIG/SGGG films reveals an
enhancement of spin mixing conductance and a large non-monotonic magnetic field
dependence of anomalous Hall effect as compared with the Pt/YIG/Gd3Ga5O12 (GGG)
films. The non-monotonic anomalous Hall signal is extracted in the temperature
range from 150 to 350 K, which has been ascribed to the possible non-collinear
magnetic order at the Pt/YIG interface induced by uniaxial strain.",1810.07384v2
2018-10-19,Charge-spin current conversion in high quality epitaxial Fe/Pt systems: isotropic spin Hall angle along different in-plane crystalline directions,"We report the growth of MgO[001]//Fe(6 nm)/MgO(7 nm) and MgO[001]//Fe(6
nm)/Pt(6 nm) by molecular beam epitaxy and show that the full characterization
by spin-orbit ferromagnetic resonance (SO-FMR) allows the determination of
magnetic anisotropies as by classical FMR-only studies. The spin mixing
conductance of epitaxial Fe/Pt interface was measured to be (1.5 +- 0.5)x10^19
m^2, and the effective spin Hall angle (SHA), was estimated at different
in-plane crystalline directions. It was found that SHA is the same in all
directions. When taking into account high enough excitation frequencies to
achieve uniform precession of magnetization, the effective spin hall angle for
epitaxial Pt in Fe/Pt is 0.051 +- 0.005. We address about the proper conditions
to determine those relevant spintronics parameters.",1810.08716v2
2018-10-24,Nearly isotropic spin-pumping related Gilbert damping in Pt/Ni$_{81}$Fe$_{19}$/Pt,"A recent theory by Chen and Zhang [Phys. Rev. Lett. 114, 126602 (2015)]
predicts strongly anisotropic damping due to interfacial spin-orbit coupling in
ultrathin magnetic films. Interfacial Gilbert-type relaxation, due to the spin
pumping effect, is predicted to be significantly larger for magnetization
oriented parallel to compared with perpendicular to the film plane. Here, we
have measured the anisotropy in the Pt/Ni$_{81}$Fe$_{19}$/Pt system via
variable-frequency, swept-field ferromagnetic resonance (FMR). We find a very
small anisotropy of enhanced Gilbert damping with sign opposite to the
prediction from the Rashba effect at the FM/Pt interface. The results are
contrary to the predicted anisotropy and suggest that a mechanism separate from
Rashba spin-orbit coupling causes the rapid onset of spin-current absorption in
Pt.",1810.10595v4
2018-10-26,Superfluid Transport in Quantum Spin Chains,"Spin superfluids enable long-distance spin transport through classical
ferromagnets by developing topologically stable magnetic textures. For small
spins at low dimensions, however, the topological protection suffers from
strong quantum fluctuations. We study the remanence of spin superfluidity
inherited from the classical magnet by considering the two-terminal spin
transport through a finite spin-1/2 magnetic chain with planar exchange. By
fermionizing the system, we recast the spin-transport problem in terms of
quasiparticle transmission through a superconducting region. We show that the
topological underpinnings of a semiclassical spin superfluid relate to the
topological superconductivity in the fermionic representation. In particular,
we find an efficient spin transmission through the magnetic region of a
characteristic resonant length, which can be related to the properties of the
boundary Majorana zero modes.",1810.11470v1
2019-06-01,Coherent ac spin current transmission across an antiferromagnetic CoO insulator,"The recent discovery of spin-current transmission through antiferromagnetic
(AFM) insulating materials opens up unprecedented opportunities for fundamental
physics and spintronics applications. The great mystery currently surrounding
this topic is: how could THz AFM magnons mediate a GHz spin current? This
mis-match of frequencies becomes particularly critical for the case of coherent
ac spin-current, raising the fundamental question of whether a GHz ac
spin-current can ever keep its coherence inside an AFM insulator and so drive
the spin precession of another FM layer coherently? Utilizing element- and
time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001)
heterostructures, we demonstrate that a coherent GHz ac spin current pumped by
the permalloy (Py) ferromagnetic resonance (FMR) can transmit coherently across
an antiferromagnetic CoO insulating layer to drive a coherent spin precession
of the FM Fe75Co25 layer. Further measurement results favor thermal magnons
rather than evanescent spin waves as the mediator of the coherent ac spin
current in CoO.",1906.00155v1
2019-06-26,Spin-orbit torques and their associated effective fields from gigahertz to terahertz,"Terahertz spintronics offers the prospect of devices which are both faster
and more energy-efficient. A promising route to achieve this goal is to exploit
current-induced spin-orbit torques. However, the high-frequency properties of
these quantities remain unexplored both experimentally and theoretically,
within a realistic material-specific approach. Here we investigate the
dynamical transverse components of the torques and uncover contributions
longitudinal to the magnetic moment capable of changing its magnitude. We show
that, while the torques can be drastically altered in the dynamical regime, the
effective magnetic fields that accompany them present a frequency-independent
behaviour, ranging from the static limit up to the terahertz domain - including
the ferromagnetic resonance of the system. The outcomes of this work point to
new ways to control magnetic units in next-generation spintronic devices.",1906.11314v2
2019-07-01,"Structural, magnetostatic and magnetodynamic studies of Co/Mo-based uncompensated synthetic antiferromagnets","In this work, we comprehensively investigate and discuss the structural,
magnetostatic, dynamic, and magnetoresistive properties of epitaxial Co/Mo
superlattices. The magnetization of the Co sublayers is coupled
antiferromagnetically with a strength that depends on the thickness of the
nonmagnetic Mo spacer. The magnetization and magnetoresistance hysteresis loops
clearly reflect interlayer exchange coupling and the occurrence of uniaxial
magnetic anisotropy induced by the strained Co sublayers. Upon accounting for a
deviation of the sublayer thicknesses from the nominal value, theoretical
modeling, including both micromagnetic and macrospin approaches, precisely
reproduces experimental magnetic hysteresis loops, magnetoresistance curves,
and ferromagnetic resonance dispersion relations. The Mo spacer thickness as a
function of the interlayer magnetic coupling is determined as a fitting
parameter by modeling the experimental results.",1907.00592v2
2019-07-14,Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by $^{59}$Co NMR,"A $^{59}$Co nuclear magnetic resonance (NMR) measurement was performed on the
single-crystalline ferromagnetic (FM) superconductor UCoGe under a pressure of
1.09 GPa, where the FM state is suppressed and superconductivity occurs in the
paramagnetic (PM) state, to study the superconducting (SC) state in the
PMstate. $^{59}$Co-NMR spectra became broader but hardly shifted across the SC
transition temperature. The Knight-shift change determined from fitting the
spectral peak with a Gaussian was much smaller than the spin part of the Knight
shift; this is in good agreement with the spin-triplet pairing suggested from
the large upper critical field. The spectrum broadening in the SC state cannot
be attributed to the SC diamagnetic effect but is related to the properties of
spin-triplet superconductivity. The origins of the broadening are discussed
herein.",1907.06177v1
2019-07-16,Enhanced Magnetization from Proton Irradiated Bulk van der Waals Magnet CrSiTe3,"Van der Waals (vdWs) crystals have attracted a great deal of scientific
attention due to their interesting physical properties and widespread practical
applications. Among all, CrSiTe3 (CST) is a ferromagnetic semiconductor with
the Curie temperature (TC) of ~32 K. In this letter, we study the magnetic
properties of bulk CST single-crystal upon proton irradiation with the fluence
of 1x1018 protons/cm2. Most significantly, we observed an enhancement (23%) in
the saturation magnetization from 3.9 {\mu}B to 4.8 {\mu}B and is accompanied
by an increase in the coercive field (465-542 Oe) upon proton irradiation.
Temperature-dependent X-band electron paramagnetic resonance measurements show
no additional magnetically active defects/vacancies that are generated upon
proton irradiation. The findings from X-ray photoelectron spectroscopy and
Raman measurements lead us to believe that modification in the spin-lattice
coupling and introduction of disorder could cause enhancement in saturation
magnetization. This work demonstrates that proton irradiation is a feasible
method in modifying the magnetic properties of vdWs crystals, which represents
a significant step forward in designing future spintronic and
magneto-electronic applications.",1907.07222v2
2019-07-19,Optical injection of a spin current into a zigzag nanoribbon of monolayer MoS2 with antiferromagnetic Kekule distortion,"The Kekule pattern of the (anti)ferromagnetic exchange field on monolayer
MoS2 can be induced by proximity to the (111) surface of BiFeO3 on both sides.
The three-band tight binding model of the MoS2 layer with Kekule patterned
exchange field is applied to describe the heterostructures. The tight binding
model is justified by the first principle calculations. The magnetization
orientations of the substrates control the pattern of the exchange field, which
then switches the band structures of the lowest zigzag edge states between
being metallic and insulating. The lowest four zigzag edge bands provide
conducting channels with a spin-polarized current. Optical excitation of
carriers in these bands generates sizable spin and charge currents, which are
theoretically modeled by the perturbation solution of the semiconductor Bloch
equation. The injected spin currents have multiple resonant peaks at a few
frequencies, which can be switched off by rotating the magnetization
orientations of the substrates.",1907.08463v3
2019-09-10,Kondo effect in a Aharonov-Casher interferometer,"We consider a model describing a spin field-effect transistor based on a
quantum nanowire with a tunable spin-orbit interaction embedded between two
ferromagnetic leads with anticollinear magnetization. We investigate a regime
of a strong interplay between resonance Kondo scattering and interference
associated with the Aharonov-Casher effect. Using the Keldysh technique at weak
coupling regime we calculate perturbatively the charge current. It is predicted
that the effects of the spin-orbit interaction result in a non-vanishing
current for any spin polarization of the leads including the case of fully
polarized anti-collinear contacts. We analyze the influence of the
Aharonov-Casher phase and degree of spin polarization in the leads onto a Kondo
temperature.",1909.04524v2
2019-09-24,Manipulation of Inverse Spin Hall Effect in Palladium by Absorption of Hydrogen Gas,"The spintronic properties of a palladium thin film have been investigated in
the presence of hydrogen gas in cobalt/palladium bilayers. Measurements of the
inverse spin Hall Effect (ISHE) using cavity ferromagnetic resonance allow
estimations of the spin Hall conductivity and spin diffusion length in both
nitrogen and hydrogen gas atmospheres. Unwanted spin rectification effects are
removed using a simple method of inverting the spin current direction with
respect to the measurement setup. Absorption of hydrogen gas in the Pd layer at
just 3% concentration results in a reduced ISHE voltage amplitude and bilayer
resistance. Fitting the ISHE voltage against the Pd layer thickness
demonstrates that the spin diffusion length decreases by 23% in the presence of
a hydrogen gas. On the other hand, the results indicate that there is no
significant change in the spin Hall conductivity of Pd due to hydrogen
absorption.",1909.10661v1
2019-10-30,Transverse-Field Ising Dynamics in a Rydberg-Dressed Atomic Gas,"We report on the realization of long-range Ising interactions in a cold gas
of cesium atoms by Rydberg dressing. The interactions are enhanced by coupling
to Rydberg states in the vicinity of a F\""{o}rster resonance. We characterize
the interactions by measuring the mean-field shift of the clock transition via
Ramsey spectroscopy, observing one-axis twisting dynamics. We furthermore
emulate a transverse-field Ising model by periodic application of a microwave
field and detect dynamical signatures of the paramagnetic-ferromagnetic phase
transition. Our results highlight the power of optical addressing for achieving
local and dynamical control of interactions, enabling prospects ranging from
investigating Floquet quantum criticality to producing tunable-range spin
squeezing.",1910.13687v3
2019-10-31,Coherent spin pumping in a strongly coupled magnon-magnon hybrid system,"We experimentally identify coherent spin pumping in the magnon-magnon hybrid
modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband
ferromagnetic resonance, an ""avoided crossing"" is observed between the uniform
mode of Py and the spin wave mode of YIG due to the fieldlike interfacial
exchange coupling. We also identify additional linewidth suppression and
enhancement for the in-phase and out-of-phase hybrid modes, respectively,
\textcolor{black}{which can be interpreted as concerted dampinglike torque from
spin pumping}. Our analysis predicts inverse proportionality of both fieldlike
and dampinglike torques to the square root of the Py thickness, which
quantitatively agrees with experiments.",1910.14470v2
2020-04-10,Electron transport through antiferromagnetic spin textures and skyrmions in a magnetic tunnel junction,"An ideal layered $\hat{x}$-polarized antiferromagnet (AFM) between two
antialigned $\pm \hat{z}$ polarized ferromagnetic (FM) contacts transmits no
current due to a $\pi$ phase difference of the matrix elements coupling the
spin degenerate states to the two FM contacts. The ratio of the two matrix
elements coupling the two spin degenerate $\hat{x}$ AFM states to a $\hat{z}$
FM contact is determined by the exchange energy and the eigenstate energy.
Inserting a normal metal layer or tunnel barrier layer between one FM contact
and the AFM alters this phase difference, and, due to the unequal weighting of
the two spins at the interface, it also breaks the spin degeneracy of the two
AFM states. The broken symmetry of the matrix elements combined with the broken
degeneracy of the AFM states, result in a Fano resonance in the transmission
and a turn-on of the $T_{\uparrow,\downarrow}$ transmission channel. Such a
magnetic tunnel junction geometry with two antialigned $\pm \hat{z}$ FM
contacts can electrically detect an AFM skyrmion. The AFM skyrmion serves as an
analogue of the oblique polarizer in the triple polarizer experiment.
Resistances and resistance ratios are calculated and compared for FM and AFM
skyrmions in a magnetic tunnel junction.",2004.04969v1
2020-04-16,A Green's function approach to Topological Insulator junctions with magnetic and superconducting regions,"This work presents a Green's function approach, originally implemented in
graphene with well-defined edges, to the surface of a strong 3D Topological
Insulator (TI) with a sequence of proximitized superconducting (S) and
ferromagnetic (F) surfaces. This consists of the derivation of the Green's
functions for each region by the asymptotic solutions method, and their
coupling by a tight-binding Hamiltonian with the Dyson equation to obtain the
full Green's functions of the system. These functions allow the direct
calculation of the momentum-resolved spectral density of states, the
identification of subgap interface states, and the derivation of the
differential conductance for a wide variety of configurations of the junctions.
We illustrate the application of this method for some simple systems with two
and three regions, finding the characteristic chiral state of the Quantum
Anomalous Hall Effect (QAHE) at the NF interfaces, and chiral Majorana modes at
the NS interfaces. Finally, we discuss some geometrical effects present in
three-region junctions such as weak Fabry-P\'erot resonances and Andreev bound
states.",2004.07858v2
2020-04-17,Detection of the Chiral Spin Structure in Ferromagnetic SrRuO$_3$ Thin Film,"A SrRuO$_3$ (SRO) thin film and its heterostructure have brought much
attention because of the recently demonstrated fascinating properties, such as
topological Hall effect and skyrmions. Critical to the understanding of those
SRO properties is the study of the spin configuration. Here, we conduct
resonant soft x-ray scattering (RSXS) at oxygen K-edge to investigate the spin
configuration of a 4 unit-cell SRO film that was grown epitaxially on a single
crystal SrTiO$_3$. The RSXS signal under a magnetic field (~0.4 Tesla) clearly
shows a magnetic dichroism pattern around the specular reflection. Model
calculations on the RSXS signal demonstrate that the magnetic dichroism pattern
originates from a N\'eel-type chiral spin structure in this SRO thin film. We
believe that the observed spin structure of the SRO system is a critical piece
of information for understanding its intriguing magnetic and transport
properties.",2004.08092v1
2020-04-17,Spectroscopic signatures of next-nearest-neighbor hopping in the charge and spin dynamics of doped one-dimensional antiferromagnets,"We study the impact of next-nearest-neighbor (nnn) hopping on the low-energy
collective excitations of strongly correlated doped antiferromagnetic cuprate
spin chains. Specifically, we use exact diagonalization and the density matrix
renormalization group method to study the single-particle spectral function,
the dynamical spin and charge structure factors, and the Cu $L$-edge resonant
inelastic x-ray scattering (RIXS) intensity of the doped $t$-$t^\prime$-$J$
model for a set of $t^\prime$ values. We find evidence for the breakdown of
spin-charge separation as $|t^\prime|$ increases and identify its fingerprints
in the dynamical response functions. The inclusion of nnn hopping couples the
spinon and holon excitations, resulting in the formation of a spin-polaron,
where a ferromagnetic spin polarization cloud dresses the doped carrier. The
spin-polaron manifests itself as additional spectral weight in the dynamical
correlation functions, which appear simultaneously in the spin- and
charge-sensitive channels. We also demonstrate that RIXS can provide a unique
view of the spin-polaron, due to its sensitivity to both the spin and charge
degrees of freedom.",2004.08435v1
2020-12-10,Observation of Magnetic Droplets in Magnetic Tunnel Junctions,"Magnetic droplets, a class of highly non-linear magnetodynamical solitons,
can be nucleated and stabilized in nanocontact spin-torque nano-oscillators
where they greatly increase the microwave output power. Here, we experimentally
demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet
nucleation is accompanied by a power increase of over 300 times compared to its
ferromagnetic resonance modes. The nucleation and stabilization of droplets are
ascribed to the double-CoFeB free layer structure in the all-perpendicular MTJ
which provides a low Zhang-Li torque and a high pinning field. Our results
enable better electrical sensitivity in the fundamental studies of droplets and
show that the droplets can be utilized in MTJ-based applications.",2012.05596v1
2020-12-10,Magnetic properties of poly(trimethylene terephthalate-block-poly(tetramethylene oxide) copolymer nanocomposites reinforced by graphene oxide-Fe3O4 hybrid nanoparticles,"Thermoplastic elastomeric nanocomposites based on poly(trimethylene
terephthalate-block-poly(tetramethylene oxide) copolymer (PTT-PTMO) and
graphene oxide-Fe3O4 nanoparticle hybrid were prepared by in situ
polymerization. Superparamagnetic GO-Fe3O4 hybrid nanoparticles before
introducing to elastomeric matrix were characterized by X-ray photoelectron
spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA)
and scanning electron microscopy (SEM). The effect of loading (0.3 and 0.5 wt%)
of GO-Fe3O4 nanoparticle hybrid on the phase structure, tensile and magnetic
properties of synthesized nanocomposites was investigated. The phase structure
of nanocomposites was evaluated by differential scanning calorimetry (DSC) and
dynamic mechanical thermal analysis (DMTA). Dispersion of GO-Fe3O4
nanoparticles in elastomeric matrix was evaluated by transmission electron
microscopy (TEM). Magnetic properties of GO-Fe3O4 nanoparticle hybrid and
nanocomposites with their content were characterized by using two different
techniques: dc SQUID magnetization measurements as a function of temperature
(from 2 to 300 K) and external magnetic field and ferromagnetic resonance (FMR)
at microwave frequency.",2012.05819v1
2020-12-11,Compositional effect on auto-oscillation behavior of Ni100-xFex/Pt spin Hall nano-oscillators,"We demonstrate the compositional effect on the magnetodynamic and
auto-oscillations properties of Ni100-xFex/Pt (x= 10 to 40) nanoconstriction
based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance
(ST-FMR) performed on microstrips, we measure a significant reduction in both
damping and spin Hall efficiency with increasing Fe content, which lowers the
spin pumping contribution. The strong compositional effect on spin Hall
efficiency is primarily attributed to the increased saturation magnetization in
Fe-rich devices. As a direct consequence, higher current densities are required
to drive spin-wave auto-oscillations at higher microwave frequencies in Fe-rich
nano-constriction devices. Our results establish the critical role of the
compositional effect in engineering the magnetodynamic and auto-oscillation
properties of spin Hall devices for microwav eand magnonic applications.",2012.06121v2
2020-12-12,Magnetization Dynamics of Fibonacci-Distorted Kagome Artificial Spin Ice,"We present results of ferromagnetic resonance (FMR) experiments and
micromagnetic simulations for a distorted, 2D Kagome artificial spin ice. The
distorted structure is created by continuously modulating the 2D primitive
lattice translation vectors of a periodic honeycomb lattice, according to an
aperiodic Fibonacci sequence used to generate 1D quasicrystals. Experimental
data and micromagnetic simulations show the Fibonacci distortion causes
broadening and splitting of FMR modes into multiple branches, which accompany
the increasing number of segment lengths and orientations that develop with
increasing distortion. When the applied field is increased in the opposite
direction to the net magnetization of a segment, spin wave modes appear,
disappear or suddenly shift, to signal segment magnetization reversal events.
These results show the complex behavior of reversal events, as well as
well-defined frequencies and frequency-field slopes of FMR modes, can be
precisely tuned by varying the severity of the aperiodic lattice distortion.
This type of distorted structure could therefore provide a new tool for the
design of complicated magnonic systems.",2012.06837v1
2020-12-18,Spin and charge order in doped spin-orbit coupled Mott insulators,"We study a two-dimensional single band Hubbard Hamiltonian with antisymmetric
spin-orbit coupling. We argue that this is the minimal model to understand the
electronic properties of locally non-centrosymmetric transition-metal (TM)
oxides such as Sr$_2$IrO$_4$. Based on exact diagonalizations of small clusters
and the random phase approximation, we investigate the correlation effects on
charge and magnetic order as a function of doping and of the TM-oxygen-TM bond
angle $\theta$. For small doping and $\theta$ $\lesssim$ $15^\circ$ we find
dominant commensurate in-plane antiferromagnetic fluctuations while
ferromagnetic fluctuations dominate for $\theta$ $\gtrsim$ $25^\circ$.
Moderately strong nearest-neighbor Hubbard interactions can also stabilize a
charge density wave order. Furthermore, we compare the dispersion of magnetic
excitations for the hole-doped case to resonant inelastic X-ray scattering data
and find good qualitative agreement.",2012.10479v1
2020-12-29,Strongly modulated ultrafast demagnetization and magnetization precession dynamics in ferrimagnetic Gdx(CoFe)1-x alloys via 3d-4f intersublattice exchange coupling,"Manipulation of the intersublattice interaction strengh (JRE-TM) in rare
earth (RE)-transition metal (TM) alloys is a key issue to understand how
efficiently the laser-induced angular momentum transfers from 3d to 4f spins
and to have a better control of the ultrafast spin dynamics. In this work, the
relationships between laser-induced demagnetization process and the
intersublattice 3d-4f interaction for the GdCoFe alloys were systematically
studied. The ultrafast two-stage demagnetization process could change into a
one-stage mode as the angular momentum transferring channel between 3d and 4f
spins is switched off, which could be modulated by JRE-TM. Furthermore, both
the effective g-factor and damping constant deduced by the subsequently
laser-induced magnetization precession process diverge at the angular momentum
compensation point based on the ferromagnetic resonance method with the LLG
equations. The results provide an alternative way to efficiently manipulate the
ultrafast demagnetization time for practical applications.",2012.14620v1
2021-01-04,Absorption of Microwaves by Random-Anisotropy Magnets,"Microscopic model of the interaction of spins with a microwave field in a
random-anisotropy magnet has been developed. Numerical results show that
microwave absorption occurs in a broad range of frequencies due to the
distribution of Imry-Ma domains on sizes and effective anisotropy. That
distribution is also responsible for the weak dependence of the absorption on
the damping. At a fixed frequency of the ac-field the spatial pattern of the
amplitude of spin oscillations exhibits maxima corresponding to the
oscillations of resonant magnetic domains. The dependence of the peak
absorption frequency on the ratio of the magnitude of per-spin random
anisotropy to the strength of the ferromagnetic exchange agrees with the
scaling derived from the Imry-Ma argument. The effect noticeably increases in
low-dimensional systems, suggesting that materials comprised of microscopic
amorphous leaves and wires can be promising candidates for enhanced microwave
absorption.",2101.01230v1
2021-01-11,Tuning the morphology and magnetic properties of single-domain SrFe8Al4O19 particles prepared by citrate auto-combustion route,"Single-domain particles of SrFe8Al4O19 were prepared by thermal treatment at
1473 K of porous products of citrate-nitrate auto-combustion, and the influence
of synthesis time on the particle morphology and magnetic properties was
studied. The procedure allows to obtain SrFe8Al4O19 particles with mean
diameters 100 - 460 nm, and their coercivity ranges from 14.5 to 18.4 kOe,
while ferromagnetic resonance frequencies vary from 149 to 164 GHz.",2101.03993v1
2021-01-25,Raman Spectroscopy and Aging of the Low-Loss Ferrimagnet Vanadium Tetracyanoethylene,"Vanadium tetracyanoethylene (V[TCNE]$_{x}$, $x\approx 2$) is an organic-based
ferrimagnet with a high magnetic ordering temperature $\mathrm{T_C>600 ~K}$,
low magnetic damping, and growth compatibility with a wide variety of
substrates. However, similar to other organic-based materials, it is sensitive
to air. Although encapsulation of V[TCNE]$_{x}$ with glass and epoxy extends
the film lifetime from an hour to a few weeks, what is limiting its lifetime
remains poorly understood. Here we characterize encapsulated V[TCNE]$_{x}$
films using confocal microscopy, Raman spectroscopy, ferromagnetic resonance
and SQUID magnetometry. We identify the relevant features in the Raman spectra
in agreement with \textit{ab initio} theory, reproducing $\mathrm{C=C,C\equiv
N}$ vibrational modes. We correlate changes in the effective dynamic
magnetization with changes in Raman intensity and in photoluminescence. Based
on changes in Raman spectra, we hypothesize possible structural changes and
aging mechanisms in V[TCNE]$_x$. These findings enable a local optical probe of
V[TCNE]$_{x}$ film quality, which is invaluable in experiments where assessing
film quality with local magnetic characterization is not possible.",2101.10240v1
2012-05-21,Hubbard exciton revealed by time-domain optical spectroscopy,"We use broadband ultra-fast pump-probe spectroscopy in the visible range to
study the lowest excitations across the Mott-Hubbard gap in the orbitally
ordered insulator YVO3. Separating thermal and non-thermal contributions to the
optical transients, we show that the total spectral weight of the two lowest
peaks is conserved, demonstrating that both excitations correspond to the same
multiplet. The pump-induced transfer of spectral weight between the two peaks
reveals that the low-energy one is a Hubbard exciton, i.e. a resonance or bound
state between a doublon and a holon. Finally, we speculate that the pump-driven
spin-disorder can be used to quantify the kinetic energy gain of the excitons
in the ferromagnetic phase.",1205.4609v3
2012-05-22,"Thickness dependence of magnetic properties of (Ga,Mn)As","We report on a monotonic reduction of Curie temperature in dilute
ferromagnetic semiconductor (Ga,Mn)As upon a well controlled
chemical-etching/oxidizing thinning from 15 nm down to complete removal of the
ferro- magnetic response. The effect already starts at the very beginning of
the thinning process and is accompanied by the spin reorientation transition of
the in-plane uniaxial anisotropy. We postulate that a negative gradient along
the growth direction of self-compensating defects (Mn interstitial) and the
presence of surface donor traps gives quantitative account on these effects
within the p-d mean field Zener model with adequate mod- ifications to take a
nonuniform distribution of holes and Mn cations into account. The described
here effects are of practical importance for employing thin and ultrathin
layers of (Ga,Mn)As or relative compounds in concept spintronics devices, like
resonant tunneling devices in particular.",1205.4824v1
2017-05-11,Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6,"The compound SmB$_6$ is the best established realization of a topological
Kondo insulator, in which a topological insulator state is obtained through
Kondo coherence. Recent studies have found evidence that the surface of SmB$_6$
hosts ferromagnetic domains, creating an intrinsic platform for unidirectional
ballistic transport at the domain boundaries. Here, surface-sensitive X-ray
absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS)
spectra are measured at the Sm N$_{4,5}$-edge, and used to evaluate electronic
symmetries, excitations and temperature dependence near the surface of cleaved
samples. The XAS data show that the density of large-moment atomic multiplet
states on a cleaved surface grows irreversibly over time, to a degree that
likely exceeds a related change that has recently been observed in the surface
4f orbital occupation.",1705.04305v1
2017-05-19,Effect of proton irradiation on the normal state low-energy excitations of Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ superconductors,"We present a \asnmr Nuclear Magnetic Resonance (NMR) and resistivity study of
the effect of 5.5 MeV proton irradiation on the optimal electron doped ($x=$
0.068) and overdoped ($x=$ 0.107) Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron based
superconductors. While the proton induced defects only mildly suppress the
critical temperature and increase residual resistivity in both compositions,
sizable broadening of the NMR spectra was observed in all the irradiated
samples at low temperature. The effect is significantly stronger in the
optimally doped sample where the Curie Weiss temperature dependence of the line
width suggests the onset of ferromagnetic correlations coexisting with
superconductivity at the nanoscale. 1/T$_2$ measurements revealed that the
energy barrier characterizing the low energy spin fluctuations of these
compounds is enhanced upon proton irradiation, suggesting that the defects are
likely slowing down the fluctuations between ($0,\pi)$ and ($\pi$,0) nematic
ground states.",1705.06905v1
2017-09-12,How does a locally constrained quantum system localize?,"At low energy, the dynamics of excitations of many physical systems are
locally constrained. Examples include frustrated anti-ferromagnets, fractional
quantum Hall fluids and Rydberg atoms in the blockaded regime. Can such locally
constrained systems be fully many-body localized (MBL)? In this article, we
answer this question affirmatively and elucidate the structure of the
accompanying quasi-local integrals of motion. By studying disordered spin
chains subject to a projection constraint in the $z$-direction, we show that
full MBL is stable at strong $z$-field disorder and identify a new mechanism of
localization through resonance at strong transverse disorder. However MBL is
not guaranteed; the constraints can `frustrate' the tendency of the spins to
align with the transverse fields and lead to full thermalization or
criticality. We further provide evidence that the transition is discontinuous
in local observables with large sample-to-sample variations. Our study has
direct consequences for current quench experiments in Rydberg atomic chains.",1709.04067v2
2017-09-18,"Spin-selectable, region-tunable negative differential resistance in graphene double ferromagnetic barriers","We propose a graphene device that can generate spin-dependent negative
differential resistance (NDR). The device is composed of a sufficiently wide
and short graphene and two gated EuO strips deposited on top of it. This scheme
avoids graphene edge tailors required by previous proposals. More importantly,
we find clear significant of a spin selectivity and a region tunability in the
spin-dependent NDR: by changing the top gates of the device, NDR for spin up
only, spin down only, or both spins (occurring sequentially) can be
respectively realized; meanwhile, the central position of the NDR region in
each case can be monotonously tuned in a wide range of bias voltage. These
remarkable features are attributed to a gate controllability of the
spin-dependent resonant levels in the device hence their deviations from the
Fermi energy and Dirac point in the source electrode, respectively. They add a
spin and a bias degree of freedom to conventional NDR-based devices, which
paves a way for designing a whole new class of NDR circuits.",1709.06038v2
2017-09-18,Growth-Induced In-Plane Uniaxial Anisotropy in V$_{2}$O$_{3}$/Ni Films,"We report on a strain-induced and temperature dependent uniaxial anisotropy
in V$_{2}$O$_{3}$/Ni hybrid thin films, manifested through the interfacial
strain and sample microstructure, and its consequences on the angular dependent
magnetization reversal. X-ray diffraction and reciprocal space maps identify
the in-plane crystalline axes of the V$_{2}$O$_{3}$; atomic force and scanning
electron microscopy reveal oriented rips in the film microstructure.
Quasi-static magnetometry and dynamic ferromagnetic resonance measurements
identify a uniaxial magnetic easy axis along the rips. Comparison with films
grown on sapphire without rips shows a combined contribution from strain and
microstructure in the V$_{2}$O$_{3}$/Ni films. Magnetization reversal
characteristics captured by angular-dependent first order reversal curve
measurements indicate a strong domain wall pinning along the direction
orthogonal to the rips, inducing an angular-dependent change in the reversal
mechanism. The resultant anisotropy is tunable with temperature and is most
pronounced at room temperature, which is beneficial for potential device
applications.",1709.06100v1
2017-11-01,Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering,"We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature",1711.00406v1
2017-11-08,Magnetic skyrmion bubble motion driven by surface acoustic waves,"We study the dynamical control of a magnetic skyrmion bubble by using
counter-propagating surface acoustic waves (SAWs) in a ferromagnet. First, we
determine the bubble mass and derive the force due to SAWs acting on a magnetic
bubble using Thiele's method. The force that pushes the bubble is proportional
to the strain gradient for the major strain component. We then study the
dynamical pinning and motion of magnetic bubbles by SAWs in a nanowire. In a
disk geometry, we propose a SAWs-driven skyrmion bubble oscillator with two
resonant frequencies.",1711.03041v3
2017-11-09,Room Temperature Giant Charge-to-Spin Conversion at SrTiO3/LaAlO3 Oxide Interface,"Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3
(STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba
spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge
conversion) in the 2DEG layer is reported. However, the direct effect of
charge-to-spin conversion, an essential ingredient for spintronic devices in a
current induced spin-orbit torque scheme, has not been demonstrated yet. Here
we show, for the first time, a highly efficient spin generation with the
efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using
spin torque ferromagnetic resonance. In addition, we suggest that the spin
transmission through the LAO layer at high temperature range is attributed to
the inelastic tunneling via localized states in the LAO band gap. Our findings
may lead to potential applications in the oxide insulator based spintronic
devices.",1711.03268v1
2017-11-10,Impact of organic capping layer on the magnetic anisotropy of ultrathin Co films,"Using combined magnetometry and ferromagnetic resonance studies, it is shown
that introduction of a hydrocarbon cover layer leads to an increase of the
contribution of the surface anisotropy to the effective magnetic anisotropy
energy of hexagonal close-packed 0001 cobalt films, largely enhancing the
perpendicular anisotropy. Due to a weak electronic interaction of the organic
molecules with the Co atoms, an increase of surface anisotropy could be
explained by the presence of an electric field at the organic-material/Co
interface and by modification of surface atoms charge configuration.",1711.03858v1
2017-11-17,Measuring anisotropic spin relaxation in graphene,"We compare different methods to measure the anisotropy of the spin-lifetime
in graphene. In addition to out-of-plane rotation of the ferromagnetic
electrodes and oblique spin precession, we present a Hanle experiment where the
electron spins precess around either a magnetic field perpendicular to the
graphene plane or around an in-plane field. In the latter case, electrons are
subject to both in-plane and out-of-plane spin relaxation. To fit the data, we
use a numerical simulation that can calculate precession with anisotropies in
the spin-lifetimes under magnetic fields in any direction. Our data show a
small, but distinct anisotropy that can be explained by the combined action of
isotropic mechanisms, such as relaxation by the contacts and resonant
scattering by magnetic impurities, and an anisotropic Rashba spin-orbit based
mechanism. We also assess potential sources of error in all three types of
experiment and conclude that the in-plane/out-of-plane Hanle method is most
reliable.",1711.06472v2
2017-11-27,"Magnetic properties, spin waves and interaction between spin excitations and 2D electrons in interface layer in Y3Fe5O12 / AlOx / GaAs-heterostructures","We describe synthesis of submicron Y3Fe5O12 (YIG) films sputtered on
GaAs-based substrates and present results of the investigation of ferromagnetic
resonance (FMR), spin wave propagation and interaction between spin excitations
and 2D electrons in interface layer in YIG / AlOx / GaAs-heterostructures. It
is found that the contribution of the relaxation process to the FMR linewidth
is about 2 % of the linewidth \Delta H. At the same time, for all samples FMR
linewidths are high. Sputtered YIG films have magnetic inhomogeneity, which
gives the main contribution to the FMR linewidth. Transistor structures with
two-dimensional electron gas (2DEG) channels in AlOx / GaAs interface governed
by YIG-film spin excitations are designed. An effective influence of spin
excitations on the current flowing through the GaAs 2DEG channel is observed.
Light illumination results in essential changes in the FMR spectrum. It is
found that an increase of the 2DEG current leads to an inverse effect, which
represents essential changes in the FMR spectrum.",1711.09814v1
2018-03-04,Optimization of Time-Resolved Magneto-optical Kerr Effect Signals for Magnetization Dynamics Measurements,"Recently magnetic storage and magnetic memory have shifted towards the use of
magnetic thin films with perpendicular magnetic anisotropy (PMA). Understanding
the magnetic damping in these materials is crucial, but normal Ferromagnetic
Resonance (FMR) measurements face some limitations. The desire to quantify the
damping in materials with PMA has resulted in the adoption of Time-Resolved
Magneto-optical Kerr Effect (TR-MOKE) measurements. In this paper, we discuss
the angle and field dependent signals in TR-MOKE, and utilize a numerical
algorithm based on the Landau-Lifshitz-Gilbert (LLG) equation to provide
information on the optimal conditions to run TR-MOKE measurements.",1803.01280v2
2018-03-22,Voltage Control of Magnetic Monopoles in Artificial Spin Ice,"Current research on artificial spin ice (ASI) systems has revealed unique
hysteretic memory effects and mobile quasi-particle monopoles controlled by
externally applied magnetic fields. Here, we numerically demonstrate a
strain-mediated multiferroic approach to locally control the ASI monopoles. The
magnetization of individual lattice elements is controlled by applying voltage
pulses to the piezoelectric layer resulting in strain-induced magnetic
precession timed for 180 degree reorientation. The model demonstrates localized
voltage control to move the magnetic monopoles across lattice sites, in CoFeB,
Ni, and FeGa based ASI$'$s. The switching is achieved at frequencies near
ferromagnetic resonance and requires energies below 620 aJ. The results
demonstrate that ASI monopoles can be efficiently and locally controlled with a
strain-mediated multiferroic approach.",1803.08598v1
2018-06-02,Ultra-low damping insulating magnetic thin films get perpendicular,"A magnetic material combining low losses and large Perpendicular Magnetic
Anisotropy (PMA) is still a missing brick in the magnonic and spintronic
fields. We report here on the growth of ultrathin Bismuth doped
Y$_{3}$Fe$_{5}$O$_{12}$ (BiYIG) films on Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) and
substituted GGG (sGGG) (111) oriented substrates. A fine tuning of the PMA is
obtained using both epitaxial strain and growth induced anisotropies. Both
spontaneously in-plane and out-of-plane magnetized thin films can be
elaborated. Ferromagnetic Resonance (FMR) measurements demonstrate the high
dynamic quality of these BiYIG ultrathin films, PMA films with Gilbert damping
values as low as 3 10$^{-4}$ and FMR linewidth of 0.3 mT at 8 GHz are achieved
even for films that do not exceed 30 nm in thickness. Moreover, we measure
Inverse Spin Hall Effect (ISHE) on Pt/BiYIG stacks showing that the magnetic
insulator$'$s surface is transparent to spin current making it appealing for
spintronic applications.",1806.00658v1
2018-06-06,Control of magnetization dynamics by spin Nernst torque,"Control of magnetization dynamics is one of the primary goals in spintronics.
It has been demonstrated using spin Hall effect i.e charge current to spin
current conversion in non-magnetic metal which has large spin-orbit coupling
such as Pt, W etc. Recently different groups have shown generation of spin
current in Pt, W while thermal gradient is created by virtue of spin Nernst
effect. In this work we show the evidence of magnetization control by spin
Nernst torque in Pt/Py bi-layer. We compared relative strength of spin Nernst
Torque and spin Hall torque by measuring the systematic variation of magnetic
linewidth on application of constant heat or charge current. Spin-torque
ferromagnetic resonance (ST-FMR) technique is adopted to excite the magnet and
to measure line-width precisely from the symmetric and anti-symmetric voltage
component. Control of magnetization dynamics by spin Nernst torque will emerge
as an alternative way to manipulate nano-magnets.",1806.01978v1
2018-06-11,Strange superconductivity near an antiferromagnetic heavy fermion quantum critical point,"The heavy fermion CeMIn5 family with M = Co, Rh, Ir provide a prototypical
example of strange superconductors with unconventional d-wave pairing and
strange metal normal state, emerged near an antiferromagnetic quantum critical
point. The microscopic origin of strange superconductor and its link to
antiferromagnetic quantum criticality and strange metal state are still open
issues. We propose a microscopic mechanism for strange superconductor, based on
the coexistence and competition between the Kondo correlation and the quasi-2d
short-ranged antiferromagnetic resonating-valence-bond spin-liquid near the
antiferromagnetic quantum critical point via a large-N Kondo-Heisenberg model
and renormalization group analysis beyond the mean-field level. We find the
coexistence (competition) between the two types of correlations well explains
the overall features of superconducting and strange metal state. The interplay
of these two effects provides a qualitative understanding on how
superconductivity emerges from the SM state and the observed superconducting
phase diagrams for CeMIn5 near the anti-ferromagnetic quantum critical point.",1806.04060v1
2018-06-11,Oscillations of the Critical Temperature in a (Fe/Cr/Fe)/V/Fe Heterostructure,"The superconducting and magnetic properties of the (Fe/Cr/Fe)/V/Fe layered
system with variable thickness of the chromium layer have been experimentally
and theoretically studied. The magnetic properties of the system have been
studied by the ferromagnetic resonance method, and the superconducting
transition temperature has been measured from the jump in the magnetic
susceptibility. A wide variety of magnetic states are observed in the system;
in particular, the structure of small domains can arise in the iron layer
placed between vanadium and chromium. It has been shown experimentally that the
critical temperature $T_c$ of the superconducting transition undergoes
nonmonotonic oscillations with a noticeable amplitude in the given system with
the change in the thickness of the Cr layer. The proposed model based on the
proximity effect theory makes it possible to relate these $T_c$ oscillations to
the features of the magnetic structure of the samples.",1806.04180v1
2018-06-27,Josephson effect in silicene-based SNS Josephson junction: Andreev reflection and free energy,"We investigate the Josephson effcet in superconductor-normal-superconductor
junction (SNS) base on the doped unbiased silicene under the perpendicular
electric field and off-resonance circularly polarized light. The Andreev
reflection (including the retroreflection and specular one) during the subgap
transport, the free energy, and the reversal of the Josephson effect as well as
the emergence of $\phi_{0}$-junction are exploited. The Andreev reflection is
complete in the NS interface even for the clean interface and without the Fermi
wave vector mismatch, which is opposite to the case of
ferromagnet-superconductor interface. The important role played by the
dynamical polarization of the degrees of freedom to the $0-\pi$ transition and
the generation of $\phi_{0}$-junction are mentioned in this paper. The
scattering by the charged impurity in the substrate affects the transport
properties in the bulk as well as the valley relaxation, which can be taken
into consider by the macroscopic wave function. In short junction limit, the
approximated results about the Andreev level and free energy are also
discussed. Beside the low-energy limit of the tight-binding model, the
finite-size effect need to be taken into account as long as the spacing model
is much larger than the superconducting gap.",1806.10289v1
2018-07-02,Picosecond acoustic excitation driven ultrafast magnetization dynamics in dielectric Bi-substituted yttrium iron garnet,"Using femtosecond optical pulses, we have investigated the ultrafast
magnetization dynamics induced in a dielectric film of bismuth-substituted
yttrium iron garnet (Bi-YIG) buried below a thick Cu/Pt metallic bilayer. We
show that exciting the sample from Pt surface launches an acoustic strain pulse
propagating into the garnet film. We discovered that this strain pulse induces
a coherent magnetization precession in the Bi-YIG at the frequency of the
ferromagnetic resonance. The observed phenomena can be explain by
strain-induced changes of magnetocristalline anisotropy via the inverse
magnetostriction effect. These findings open new perspectives toward the
control of the magnetization in magnetic garnets embedded in complex
heterostructure devices.",1807.00610v1
2018-08-20,Gilbert damping of [Co/Pd]n/Py multilayer thin films,"Understanding the Gilbert damping in exchange-coupled multilayer materials is
particularly important to develop future fast switching spintronics devices.
Here, we report an experimental investigation of temperature-dependent Gilbert
damping in [Co/Pd]n/Py multilayer films of varying the number of Co/Pd
repetitions by ferromagnetic resonance. The results demonstrate that three
independent contributions to the Gilbert damping are identified, namely the
intrinsic Gilbert damping, the inhomogeneous linewidth broadening and the
two-magnon scattering contribution. Of particular interest, the two-magnon
scattering intensity increases as the enlargement of number repetitions of
Co/Pd due to the larger pinning effect at the interface between Py and the
Co/Pd layers. The Gilbert damping increases monotonically as the temperature
decreases from 300K to 50K. Our findings open the door to comprehend the
physical origin of the Gilbert damping in ultrathin exchange-coupled multilayer
films.",1808.06515v2
2018-12-05,Pure voltage controlled magnetic nano-oscillator,"Nanomagnetic oscillator is a key component for radio-frequency (RF) signal
generation in many nano-scale spintronic devices. However, the actuation
mechanisms of nanomagnetic oscillators are mostly current-based, which is
energy inefficient at nanoscale due to Joule heating. In this study, we present
a new actuation mechanism for nanomagnetic oscillator with pure voltage input
using a multiferroic structure. An AC voltage with a DC bias is applied to the
piezoelectric substrate, and steady perpendicular magnetic oscillation is
achieved in the attached Ni disk when the frequency of the voltage matches the
ferromagnetic resonance (FMR) of the Ni disk. The FMR can be tuned by simply
changing the voltage bias, therefore, the oscillation frequency has a wide
range. A systematic simulation study is conducted to investigate the impact of
the voltage amplitude, frequency, waveform, as well as the thickness of the
magnet on the magnetic oscillation. This opens new possibilities of designing
energy efficient nanomagnetic oscillators using multiferroics that have large
amplitude and wide frequency range.",1812.02264v1
2018-12-06,Damping and Anti-Damping Phenomena in Metallic Antiferromagnets: An ab-initio Study,"We report on a first principles study of anti-ferromagnetic resonance (AFMR)
phenomena in metallic systems [MnX (X=Ir,Pt,Pd,Rh) and FeRh] under an external
electric field. We demonstrate that the AFMR linewidth can be separated into a
relativistic component originating from the angular momentum transfer between
the collinear AFM subsystem and the crystal through the spin orbit coupling
(SOC), and an exchange component that originates from the spin exchange between
the two sublattices. The calculations reveal that the latter component becomes
significant in the low temperature regime. Furthermore, we present results for
the current-induced intersublattice torque which can be separated into the
Field-Like (FL) and Damping-Like (DL) components, affecting the intersublattice
exchange coupling and AFMR linewidth, respectively.",1812.02844v2
2019-01-17,Spin transport parameters of NbN thin films characterised by spin pumping experiments,"We present measurements of ferromagnetic-resonance - driven spin pumping and
inverse spin-Hall effect in NbN/Y3Fe5O12 (YIG) bilayers. A clear enhancement of
the (effective) Gilbert damping constant of the thin-film YIG was observed due
to the presence of the NbN spin sink. By varying the NbN thickness and
employing spin-diffusion theory, we have estimated the room temperature values
of the spin diffusion length and the spin Hall angle in NbN to be 14 nm and
-1.1 10-2, respectively. Furthermore, we have determined the spin-mixing
conductance of the NbN/YIG interface to be 10 nm-2. The experimental
quantification of these spin transport parameters is an important step towards
the development of superconducting spintronic devices involving NbN thin films.",1901.05753v1
2018-12-12,Substrate induced magnetic anisotropies and magneto-optical response in YIG nanosized epitaxial films on NdGG(111),"Nanosized Y3Fe5O12 epitaxial films have been grown on Nd3Ga5O12 substrates
using laser molecular beam epitaxy method. Magneto-optical polar Kerr effect,
ferromagnetic resonance and spin wave propagation measurements show that the
stress-related anisotropy field has an opposite sign, compared to that in the
YIG/GGG systems. This leads to a considerable decrease of the effective
magnetization that opens a perspective to get YIG films with perpendicular
magnetization for utilizing forward volume spin waves. Longitudinal
magnetooptical Kerr effect magnetometry reveals a large contribution of
quadratic in magnetization terms into dielectric permittivity tensor at optical
frequencies. This effect strongly increases with temperature decrease and is
explained by magnetization of the interface Nd3+ ions that are exchange coupled
to the Fe3+ ions.",1901.10800v1
2019-01-30,Surface dynamics of rough magnetic films,"The chirality of Damon-Eshbach (DE) magnons affects the transport of energy
and angular momentum at the surface of magnetic films and spheres. We calculate
the surface-disorder-limited dephasing and transport lifetimes of surface modes
of sufficiently thick high-quality magnetic films such as yttrium iron garnet.
In spite of their chirality surface magnons are not protected, but interact
strongly with smooth surface roughness. Nevertheless, for long-range disorder
the transport is much less affected by the suppressed back scattering (vertex
correction). Moreover, in the presence of roughness ferromagnetic resonance
under a \textit{uniform} microwave field can gennerate a considerable amount of
surface magnons.",1901.11046v2
2019-02-14,Vectorial observation of the spin Seebeck effect in epitaxial NiFe$_2$O$_4$ thin films with various magnetic anisotropy contributions,"We have developed a vectorial type of measurement for the spin Seebeck effect
(SSE) in epitaxial NiFe$_2$O$_4$ thin films which have been grown by pulsed
laser deposition on MgGa$_2$O$_4$ (MGO) with (001) and (011) orientation as
well as CoGa$_2$O$_4$ (011) (CGO), thus varying the lattice mismatch and
crystal orientation. We confirm that a large lattice mismatch leads to strain
anisotropy in addition to the magnetocrystalline anisotropy in the thin films
using vibrating sample magnetometry and ferromagnetic resonance measurements.
Moreover, we show that the existence of a magnetic strain anisotropy in
NiFe$_2$O$_4$ thin films significantly impacts the shape and magnitude of the
magnetic-field-dependent SSE voltage loops. We further demonstrate that
bidirectional field-dependent SSE voltage curves can be utilized to reveal the
complete magnetization reversal process, which establishes a vectorial
magnetometry technique based on a spin caloric effect.",1902.05384v2
2019-02-24,Evidence of a cluster spin-glass state in the B-site disordered perovskite SrTi0.5Mn0.5O3,"SrTi0.5Mn0.5O3 (STMO) is a chemically disordered perovskite having random
distribution of Ti and Mn over 1b site. Striking discrepancies about the
structural and magnetic properties of STMO demands detailed analysis which is
addressed. To explore the magnetic ground state of STMO, static and dynamic
magnetic properties were studied over a broad temperature range (2-300 K). The
dc, ac magnetization show a cusp like peak at Tf ~ 14 K, which exhibits field
and frequency dependence. The thermoremanent magnetization is characterized by
using stretched exponential function and characteristic time suggests the
existence of spin clusters. Also the other features observed in magnetic memory
effect, muon spin resonance/rotation and neutron powder diffraction confirm the
existence of cluster spin glass state in STMO, rather than the long range
ordered ground state. Intriguingly, the observed spin relaxation can be
attributed to the dilute magnetism due to non-magnetic doping at Mn-site and
competing antiferromagnetic and ferromagnetic interactions resulting from the
site disorder.",1902.08961v1
2019-02-28,A molecular diamond lattice antiferromagnet as a Dirac semimetal candidate,"The ground state of a molecular diamond-lattice compound (ET)Ag$_4$(CN)$_5$
is investigated by the magnetization and nuclear magnetic resonance
spectroscopy. We found that the system exhibits antiferromagnetic long-range
ordering with weak ferromagnetism at a high temperature of 102 K owing to the
strong electron correlation. The spin susceptibility is well fitted into the
diamond-lattice Heisenberg model with a nearest neighbor exchange coupling of
230 K, indicating the less frustrated interactions. The transition temperature
elevates up to $\sim$195 K by applying pressure of 2 GPa, which records the
highest temperature among organic molecular magnets. The first-principles band
calculation suggests that the system is accessible to a three-dimensional
topological semimetal with nodal Dirac lines, which has been extensively
searched for a half-filling diamond lattice.",1902.10856v1
2019-02-28,Magnetic structure and spin waves in the frustrated ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$,"Single crystal neutron diffraction, inelastic neutron scattering and electron
spin resonance experiments are used to study the magnetic structure and spin
waves in Pb$_2$VO(PO$_4$)$_2$, a prototypical layered $S=1/2$ ferromagnet with
frustrating next nearest neighbor antiferromagnetic interactions. The observed
excitation spectrum is found to be inconsistent with a simple square lattice
model previously proposed for this material. At least four distinct exchange
coupling constants are required to reproduce the measured spin wave dispersion.
The degree of magnetic frustration is correspondingly revised and found to be
substantially smaller than in all previous estimates.",1902.11172v3
2019-03-03,Near-Unity Spin Hall Ratio in Ni$_x$Cu$_{1-x}$ Alloys,"We report a large spin Hall effect in the 3$d$ transition metal alloy
Ni$_x$Cu$_{1-x}$ for $x\in\left\{ 0.3,0.75\right\} $, detected via the
ferromagnetic resonance of a Permalloy (Py = Ni$_{80}$Fe$_{20}$) film deposited
in a bilayer with the alloy. A thickness series at $x$ = 0.6, for which the
alloy is paramagnetic at room temperature, allows us to determine the spin Hall
ratio $\theta_{\rm{SH}}\approx1$, spin diffusion length $\lambda_{\rm{s}}$,
spin mixing conductance $G_{\uparrow\downarrow}$, and damping
$\alpha_{\rm{SML}}$ due to spin memory loss . We compare our results with
similar experiments on Py/Pt bilayers measured using the same method. Ab initio
band structure calculations with disorder and spin-orbit coupling suggest an
intrinsic spin Hall effect in Ni$_x$Cu$_{1-x}$ alloys, although the experiments
here cannot distinguish between extrinsic and intrinsic mechanisms.",1903.00910v2
2019-03-11,Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet,"The ultrastrong coupling of (quasi-)particles has gained considerable
attention due to its application potential and richness of the underlying
physics. Coupling phenomena arising due to electromagnetic interactions are
well explored. In magnetically ordered systems, the quantum-mechanical
exchange-interaction should furthermore enable a fundamentally different
coupling mechanism. Here, we report the observation of ultrastrong intralayer
exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We
experimentally study the spin dynamics in a gadolinium iron garnet single
crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic
compensation temperature, we observe ultrastrong coupling of clockwise and
anticlockwise magnon modes. The magnon-magnon coupling strength reaches more
than 30% of the mode frequency and can be tuned by varying the direction of the
external magnetic field. We theoretically explain the observed phenomenon in
terms of an exchange-enhanced mode-coupling mediated by a weak cubic
anisotropy.",1903.04330v2
2019-03-14,Electrical control of spin mixing conductance in a Y$_3$Fe$_5$O$_{12}$/Platinum bilayer,"We report a tunable spin mixing conductance, up to $\pm 22\%$, in a
Y${}_{3}$Fe${}_{5}$O${}_{12}$/Platinum (YIG/Pt) bilayer.This control is
achieved by applying a gate voltage with an ionic gate technique, which
exhibits a gate-dependent ferromagnetic resonance line width. Furthermore, we
observed a gate-dependent spin pumping and spin Hall angle in the Pt layer,
which is also tunable up to $\pm$ 13.6\%. This work experimentally demonstrates
spin current control through spin pumping and a gate voltage in a YIG/Pt
bilayer, demonstrating the crucial role of the interfacial charge density for
the spin transport properties in magnetic insulator/heavy metal bilayers.",1903.05865v1
2019-03-18,Thermal Hall Effect Induced by Magnon-Phonon Interactions,"We propose a new mechanism for the thermal Hall effect in exchange spin-wave
systems, which is induced by the magnon-phonon interaction. Using symmetry
arguments, we first show that this effect is quite general, and exists whenever
the mirror symmetry in the direction of the magnetization is broken. We then
demonstrate our result in a collinear ferromagnet on a square lattice, with
perpendicular easy-axis anisotropy and Dzyaloshinskii-Moriya interaction from
mirror symmetry breaking. We show that the thermal Hall conductivity is
controlled by the resonant contribution from the anti-crossing points between
the magnon and phonon branches, and estimate its size to be comparable to that
of the magnon mediated thermal Hall effect.",1903.07702v2
2019-04-01,Kitaev honeycomb models in magnetic fields: Dynamical response and hidden symmetries,"Motivated by recent reports of a field-induced intermediate phase (IP) in the
antiferromagnetic honeycomb Kitaev model that may be a spin liquid whose nature
is distinct from the Kitaev Z2 phase, we present a detailed numerical study on
the nature and dynamical response (such as dynamical spin-structure factors and
resonant inelastic x-ray scattering intensities) of this field-induced IP and
neighboring phases in a family of Kitaev-based models related by hidden
symmetries and duality transformations. We further show that the same
field-induced IP can appear in models relevant for $\alpha$-RuCl${_3}$, which
exhibit a ferromagnetic Kitaev coupling and additional interactions. In
$\alpha$-RuCl${_3}$, the IP represents a new phase, that is likely independent
from the putative field-induced (spin-liquid) phase recently reported from
thermal Hall conductivity measurements.",1904.01025v1
2019-04-11,Measurement of spin mixing conductance in Ni$_{81}$Fe$_{19}$/$α$-W and Ni$_{81}$Fe$_{19}$/$β$-W heterostrucutures via ferromagnetic resonance,"We present measurements of interfacial Gilbert damping due to the spin
pumping effect in Ni$_{81}$Fe$_{19}$/W heterostructures. Measurements were
compared for heterostructures in which the crystallographic phase of W, either
$\alpha$(bcc)-W or $\beta$(A15)-W, was enriched through deposition conditions
and characterized using X-ray diffraction (XRD) and high-resolution
cross-sectional transmission electron microscopy (HR-XTEM). Single phase
Ni$_{81}$Fe$_{19}$/$\alpha$-W heterostructures could be realized, but
heterostructures with $\beta$-W were realized as mixed $\alpha$-$\beta$ phase.
The spin mixing conductances (SMC) for W at interfaces with Ni$_{81}$Fe$_{19}$
were found to be significantly lower than those for similarly heavy metals such
as Pd and Pt, but comparable to those for Ta, and independent of enrichment in
the $\beta$ phase.",1904.05950v2
2019-04-23,Offset fields in perpendicularly magnetized tunnel junctions,"We study the offset fields affecting the free layer of perpendicularly
magnetized tunnel junctions. In extended films, the free layer offset field
results from interlayer exchange coupling with the reference layer through the
MgO tunnel oxide. The free layer offset field is thus accompanied with a shift
of the free layer and reference layer ferromagnetic resonance frequencies. The
shifts depend on the mutual orientation of the two magnetizations. The offset
field decreases with the resistance area product of the tunnel oxide.
Patterning the tunnel junction into an STT-MRAM disk-shaped cell changes
substantially the offset field, as the reduction of the lateral dimension comes
with the generation of stray fields by the reference and the hard layer. The
experimental offset field compares best with the spatial average of the sum of
these stray fields, thereby providing guidelines for the offset field
engineering.",1904.10170v1
2019-04-23,Quantum Adiabatic Doping with Incommensurate Optical Lattices,"Quantum simulations of Fermi-Hubbard models have been attracting considerable
efforts in the optical lattice research, with the ultracold anti-ferromagnetic
atomic phase reached at half filling in recent years. An unresolved issue is to
dope the system while maintaining the low thermal entropy. Here we propose to
achieve the low temperature phase of the doped Fermi-Hubbard model using
incommensurate optical lattices through adiabatic quantum evolution. In this
theoretical proposal, we find that one major problem about the adiabatic doping
that shows up is atomic localization in the incommensurate lattice, potentially
causing exponential slowing down of the adiabatic procedure. We study both one-
and two-dimensional incommensurate optical lattices, and find that the
localization prevents efficient adiabatic doping in the strong lattice regime
for both cases. With density matrix renormalization group calculation, we
further show that the slowing down problem in one dimension can be circumvented
by considering interaction induced many-body delocalization, which is
experimentally feasible using Feshbach resonance techniques. This protocol is
expected to be efficient as well in two dimensions where the localization
phenomenon is less stable.",1904.10553v2
2019-08-06,Electron Induced Massive Dynamics of Magnetic Domain Walls,"We study the dynamics of domain walls (DWs) in a metallic, ferromagnetic
nanowire. We develop a Keldysh collective coordinate technique to describe the
effect of conduction electrons on rigid magnetic structures. The effective
Lagrangian and Langevin equations of motion for a DW are derived. The DW
dynamics is described by two collective degrees of freedom: position and
tilt-angle. The coupled Langevin equations therefore involve two correlated
noise sources, leading to a generalized fluctuation-dissipation theorem (FDT).
The DW response kernel due to electrons contains two parts: one related to
dissipation via FDT, and another `inertial' part. We prove that the latter term
leads to a mass for both degrees of freedom, even though the intrinsic bare
mass is zero. The electron-induced mass is present even in a clean system
without pinning or specifically engineered potentials. The resulting equations
of motion contain rich dynamical solutions and point toward a new way to
control domain wall motion in metals via the electronic system properties. We
discuss two observable consequences of the mass, hysteresis in the DW dynamics
and resonant response to ac current.",1908.02299v1
2019-08-17,Band-pass Magnetic Tunnel Junction based Magnetoresistive Random Access Memory,"We propose spin transfer torque--magnetoresistive random access memory
(STT-MRAM) based on magneto-resistance and spin transfer torque physics of
band-pass spin filtering. Utilizing the electronic analogs of optical phenomena
such as anti-reflection coating and resonance for spintronic devices, we
present the design of an STT-MRAM device with improved features when compared
with a traditional trilayer device. The device consists of a superlattice
heterostructure terminated with the anti-reflective regions sandwiched between
the fixed and free ferromagnetic layers. Employing the Green's function spin
transport formalism coupled self-consistently with the stochastic
Landau-Lifshitz-Gilbert-Slonczewski equation, we present the design of an
STT-MRAM based on the band-pass filtering having an ultra-high TMR (3.5*10e4)
and large spin current. We demonstrate that the STT-MRAM design having
band-pass spin filtering are nearly 1100% more energy efficient than
traditional trilayer magnetic tunnel junction (MTJ) based STT-MRAM. We also
present detailed probabilistic switching and energy analysis for a trilayer MTJ
and band-pass filtering based STT-MRAM. Our predictions serve as a template to
consider the heterostructures for next-generation spintronic device
applications.",1908.06279v1
2019-08-30,"Magnetization reversal, damping properties and magnetic anisotropy of L10-ordered FeNi thin films","L10 ordered magnetic alloys such as FePt, FePd, CoPt and FeNi are well known
for their large magnetocrystalline anisotropy. Among these, L10-FeNi alloy is
economically viable material for magnetic recording media because it does not
contain rare earth and noble elements. In this work, L10-FeNi films with three
different strengths of anisotropy were fabricated by varying the deposition
process in molecular beam epitaxy system. We have investigated the
magnetization reversal along with domain imaging via magneto optic Kerr effect
based microscope. It is found that in all three samples, the magnetization
reversal is happening via domain wall motion. Further ferromagnetic resonance
(FMR) spectroscopy was performed to evaluate the damping constant and magnetic
anisotropy. It was observed that the FeNi sample with moderate strength of
anisotropy exhibits low value of damping constant ~ 4.9X10^-3. In addition to
this, it was found that the films possess a mixture of cubic and uniaxial
anisotropies.",1908.11761v1
2019-11-02,Tuning Non-Gilbert-type damping in FeGa films on MgO(001) via oblique deposition,"The ability to tailor the damping factor is essential for spintronic and
spin-torque applications. Here, we report an approach to manipulate the damping
factor of FeGa/MgO(001) films by oblique deposition. Owing to the defects at
the surface or interface in thin films, two-magnon scattering (TMS) acts as a
non-Gilbert damping mechanism in magnetization relaxation. In this work, the
contribution of TMS was characterized by in-plane angular dependent
ferromagnetic resonance (FMR). It is demonstrated that the intrinsic Gilbert
damping is isotropic and invariant, while the extrinsic mechanism related to
TMS is anisotropic and can be tuned by oblique deposition. Furthermore, the two
and fourfold TMS related to the uniaxial magnetic anisotropy (UMA) and
magnetocrystalline anisotropy were discussed. Our results open an avenue to
manipulate magnetization relaxation in spintronic devices.",1911.00728v1
2019-12-04,Light-driven ultrafast phonomagnetism,"Exciting atomic oscillations with light is a powerful technique to control
the electronic properties of materials, leading to remarkable phenomena such as
light-induced superconductivity and ultrafast insulator to metal transitions.
Here we show that light-driven lattice vibrations can be utilised to encode
efficiently spin information in a magnetic medium. Intense mid-infrared
electric field pulses, tuned to resonance with a vibrational normal mode of
antiferromagnetic DyFeO3, drive the emergence of long-living weak ferromagnetic
order. Light-driven phonon displacements promptly lower the energy barrier
separating competing magnetic states, allowing the alignment of spins to occur
within a few picoseconds, via non-equilibrium dynamics of the magnetic energy
landscape.",1912.01938v1
2019-12-29,Synchronized excitation of magnetization dynamics via spin waves in Bi-YIG thin film by slot line waveguide,"We have studied magnetization dynamics of a single Bi-YIG thin film by means
of the high frequency power response induced by a slot line waveguide. Multiple
absorption peaks that correspond to excitement states in magnetization dynamics
appeared without the ferromagnetic resonance (FMR) condition. The peaks were
strongly influenced by a waveguide line width and a distance between the lines.
Micromagnetics simulation reveals that each line induces a local magnetization
dynamics oscillation and generates spin waves. The spin wave that propagates
from one of the lines interferences with the other side of local magnetization
dynamics oscillation around the other line, resulting in an amplification of
the oscillation when they are in synchronization with each other. This
amplification occurs at both sides of the lines by the interference. Thus, the
possible mechanism of the excitation in the magnetization dynamics oscillation
is the synchronization of mutual magnetization dynamics oscillation via spin
waves. This technique resonantly excites the local magnetization dynamics
without the FMR condition, which is applicable as a highly coherent spin waves
source.",1912.12663v1
2019-12-31,Probing magnon-magnon coupling in exchange coupled Y$_3$Fe$_5$O$_{12}$/Permalloy bilayers with magneto-optical effects,"We demonstrate the magnetically-induced transparency (MIT) effect in
Y$_3$Fe$_5$O$_{12}$(YIG)/Permalloy(Py) coupled bilayers. The measurement is
achieved via a heterodyne detection of the coupled magnetization dynamics using
a single wavelength that probes the magneto-optical Kerr and Faraday effects of
Py and YIG, respectively. Clear features of the MIT effect are evident from the
deeply modulated ferromagnetic resonance of Py due to the
perpendicular-standing-spin-wave of YIG. We develop a phenomenological model
that nicely reproduces the experimental results including the induced amplitude
and phase evolution caused by the magnon-magnon coupling. Our work offers a new
route towards studying phase-resolved spin dynamics and hybrid magnonic
systems.",1912.13407v2
2020-05-06,Sub-Nanosecond Spin-Transfer Torque in an Ensemble of Superparamagnetic-Like Nanomagnets,"Spin currents can exert spin-transfer torques on magnetic systems even in the
limit of vanishingly small net magnetization, as is the case for
antiferromagnets. Here, we experimentally show that a spin-transfer torque is
operative in a material with weak, short-range magnetic order -- namely, a
macroscopic ensemble of superparamagnetic-like Co nanomagnets. We employ
element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to
directly detect sub-ns dynamics of the Co nanomagnets, excited into precession
with cone angle $\geq$0.003$^{\circ}$ by an oscillating spin current. XFMR
measurements reveal that as the net moment of the ensemble decreases, the
strength of the spin-transfer torque increases relative to those of magnetic
field torques. Our findings point to spin-transfer torque as an effective way
to manipulate the state of nanomagnet ensembles at sub-ns timescales.",2005.03081v1
2020-05-12,Magnetically induced topological transitions of hyperbolic dispersion in biaxial gyrotropic media,"Magnetically induced topological transitions of isofrequency surfaces of bulk
waves propagating through an unbounded biaxial gyrotropic medium are studied.
The medium is constructed from a two-component superlattice composed of
magnetized ferrite and semiconductor layers. To derive the constitutive
parameters of the gyrotropic medium, a homogenization procedure from the
effective medium theory is applied. The study is carried out in the frequency
range near the frequency of ferromagnetic resonance, where the magnetic
subsystem possesses the properties of natural hyperbolic dispersion. The
topological transitions from an open type-I hyperboloid to several intricate
hyperbolic-like forms are demonstrated for the extraordinary waves. We reveal
how realistic material losses change the form of isofrequency surface
characterizing hyperbolic dispersion. The obtained results broaden our
knowledge on the possible topologies of isofrequency surfaces that can appear
in gyrotropic media influenced by an external static magnetic field.",2005.05875v1
2020-05-16,Simultaneous observation of anti-damping and inverse spin Hall effect in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayer system,"Manganites have shown potential in spintronics because they exhibit high spin
polarization. Here, by ferromagnetic resonance we have studied the damping
properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayers which are prepared by
oxide molecular beam epitaxy. The damping coefficient ($\alpha$) of
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) single layer is found to be 0.0104.
However the LSMO/Pt bilayers exhibit decrease in $\alpha$ with increase in Pt
thickness. This decrease in the value of $\alpha$ is probably due to high
anti-damping like torque. Further, we have investigated the angle dependent
inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other
spin rectification effects such as anomalous Hall effect and anisotropic
magnetoresistance. We have observed high spin pumping voltage ($\sim$~20 $ \mu
V$). The results indicate that both anti-damping and spin pumping phenomena are
occuring simultaneously.",2005.07848v3
2020-06-01,Spin-wave spectroscopy of individual ferromagnetic nanodisks,"The increasing demand for ultrahigh data storage densities requires
development of 3D magnetic nanostructures. In this regard, focused electron
beam induced deposition (FEBID) is a technique of choice for direct-writing of
various complex nano-architectures. However, intrinsic properties of
nanomagnets are often poorly known and can hardly be assessed by local optical
probe techniques. Here, we demonstrate spatially resolved spin-wave
spectroscopy of individual circular magnetic elements with radii down to 100
nm. The key component of the setup is a microwave antenna whose microsized
central part is placed over a movable substrate with well-separated CoFe-FEBID
nanodisks. The circular symmetry of the disks gives rise to standing spin-wave
resonances and allows for the deduction of the saturation magnetization and the
exchange stiffness of the material using an analytical theory. The presented
approach is especially valuable for the characterization of direct-write
elements opening new horizons for 3D nanomagnetism and magnonics.",2006.00763v1
2020-06-02,Spin pumping and inverse spin Hall effect in iridium oxide,"Large charge-to-spin conversion (spin Hall angle) and spin Hall conductivity
are prerequisites for development of next generation power efficient spintronic
devices. In this context, heavy metals (e.g. Pt, W etc.), topological
insulators, antiferromagnets are usually considered because they exhibit high
spin-orbit coupling (SOC). In addition to the above materials, 5d transition
metal oxide e.g. Iridium Oxide (IrO 2 ) is a potential candidate which exhibits
high SOC strength. Here we report a study of spin pumping and inverse spin Hall
effect (ISHE), via ferromagnetic resonance (FMR), in IrO 2 /CoFeB system. We
identify the individual contribution of spin pumping and other spin
rectification effects in the magnetic layer, by investigating the in-plane
angular dependence of ISHE signal. Our analysis shows significant contribution
of spin pumping effect to the ISHE signal. We show that polycrystalline IrO 2
thin film exhibits high spin Hall conductivity and spin Hall angle which are
comparable to the values of Pt.",2006.01865v2
2020-06-04,Electron Tunneling Transport and Magnetic Field Modulation through a Superconductor-Kitaev layer-Superconductor Junction,"We present the electron tunneling transport and its magnetic field modulation
of a superconducting (SC) Josephson junction with a barrier of single
ferromagnetic (FM) Kitaev layer. We find that at H = 0, the Josephson current
IS displays two peaks at K/{\Delta} = 3.4 and 10, which stem from the resonant
tunnelings between the SC gap boundaries and the spinon flat bands and between
the SC gap edges and the spinon dispersive bands, respectively. With the
increasing magnetic field, IS gradually decreases and abruptly drops to a
platform at the critical magnetic field hc = g{\mu}BHc/{\Delta} =
0.03K/{\Delta}, since the applied field suppresses the spinon density of states
(DOS) once upon the Kitaev layer enters the polarized FM phase. These results
pave a new way to measure the spinon or Majorana fermion DOS of the Kitaev and
other spin liquid materials.",2006.02650v1
2020-06-07,Changes of Magnetism in a Magnetic Insulator due to Proximity to a Topological Insulator,"This letter reports the modification of magnetism in a magnetic insulator
Y3Fe5O12 thin film by topological surface states (TSS) in an adjacent
topological insulator Bi2Se3 thin film. Ferromagnetic resonance measurements
show that the TSS in Bi2Se3 produces a perpendicular magnetic anisotropy,
results in a decrease in the gyromagnetic ratio, and enhances the damping in
Y3Fe5O12. Such TSS-induced changes become more pronounced as the temperature
decreases from 300 K to 50 K. These results suggest a completely new approach
for control of magnetism in magnetic thin films.",2006.04035v1
2020-06-15,Femtosecond laser pulse driven caustic spin wave beams,"Controlling the directionality of spin waves is a key ingredient in
wave-based computing methods such as magnonics. In this paper, we demonstrate
this particular aspect by using an all-optical point-like source of continuous
spin waves based on frequency comb rapid demagnetization. The emitted spin
waves contain a range of k-vectors and by detuning the applied magnetic field
slightly off the ferromagnetic resonance (FMR), we observe X-shaped caustic
spin-wave patterns at $70^{\circ}$ propagation angles as predicted by theory.
When the harmonic of the light source approaches theFMR, the caustic pattern
gives way to uniaxial spin-wave propagation perpendicular to the in-plane
component of the applied field. This field-controlled propagation pattern and
directionality of optically emitted short-wavelength spin waves provide
additional degrees of freedom when designing magnonic devices.",2006.08219v1
2020-08-05,NMR study of the spin correlations in the $S=1$ armchair chain Ni$_2$NbBO$_6$,"We report our nuclear magnetic resonance (NMR) study on the structurally spin
chain compound Ni$_2$NbBO$_6$ with complex magnetic coupling. The
antiferromagnetic transition is monitored by the line splitting resulting from
the staggered internal hyperfine field. The magnetic coupling configuration
proposed by the first-principle density functional theory (DFT) is supported by
our NMR spectral analysis. For the spin dynamics, a prominent peak at $T\sim35$
K well above the N\'{e}el temperature ($T_N\sim20$ K at $\mu_0H=10$ T) is
observed from the spin-lattice relaxation data. As compared with the
dc-susceptibility, this behavior indicates a antiferromagnetic coupling with
the typical energy scale of $\sim3$ meV. Thus, the Ni$_2$NbBO$_6$ compound can
be viewed as strongly ferromagnetically coupled armchair spin chains along the
crystalline $b$-axis. These facts place strong constraints to the theoretical
model for this compound.",2008.01949v1
2020-08-13,Comparison of measured and simulated spin-wave mode spectra of magnetic nanostructures,"Motivated by the importance of magnetization dynamics in nanomagnets for the
development and optimization of magnetic devices and sensors, we measured and
modeled spin wave spectra in patterned elliptical nanomagnets. Ferromagnetic
resonance spectra for multiple nanomagnets of Ni80Fe20 , fabricated by
electron-beam lithography to have nominal short-axes of 200 nm or 100 nm, were
measured by use of heterodyne magneto-optical microwave microscopy. Scanning
electron microscope images taken of the same nanomagnets were used to define
element shapes for micromagnetic simulations. Measured spectra show significant
differences between nominally identical nanomagnets, which could be only
partially attributed to uncontrolled shape variations in the patterning
process, as evidence by the limited agreement between the measured and
simulated spectra. Agreement between measurements and simulations was improved
by including a zone of reduced magnetization and exchange at the edges of the
nanomagnets in the simulations. Our results show that the reduction of shape
variations between individual magnetic random-access memory elements can
potentially improve their performance. However, unambiguous determination of
materials parameters in nanomagnets based on analysis and modeling of spin wave
spectra remains problematic.",2008.05662v1
2020-09-09,Sub-pico-liter magneto-optical cavities,"Microwave-to-optical conversion via ferromagnetic magnons has so-far been
limited by the optical coupling rates achieved in mm-scale whispering gallery
mode resonators. Towards overcoming this limitation, we propose and demonstrate
an open magneto-optical cavity containing a thin-film of yttrium iron garnet
(YIG). We achieve a 0.1 pL (100 $\mu$m$^{3}$) optical mode volume, $\sim$50
times smaller than previous devices. From this, we estimate the magnon
single-photon coupling rate is $G\approx50$ Hz. This open cavity design offers
the prospect of wavelength scale mode volumes, small polarization splittings,
and good magneto-optical mode overlap. With achievable further improvements and
optimization, efficient microwave-optical conversion and magnon cooling devices
become a realistic possibility.",2009.04162v1
2020-09-15,Giant spin transfer torque in atomically thin magnetic bilayers,"In cavity quantum electrodynamics, the multiple reflections of a photon
between two mirrors defining a cavity is exploited to enhance the
light-coupling of an intra-cavity atom. We show that this paradigm for
enhancing the interaction of a flying particle with a localized object can be
generalized to spintronics based on van der Waals 2D magnets. Upon tunneling
through a magnetic bilayer, we find the spin transfer torques per electron
incidence can become orders of magnitude larger than $\hbar/2$, made possible
by electron's multi-reflection path through the ferromagnetic monolayers as an
intermediate of their angular momentum transfer. Over a broad energy range
around the tunneling resonances, the damping-like spin transfer torque per
electron tunneling features a universal value of $\frac{\hbar}{2}
\tan{\frac{\theta}{2}}$, depending only on the angle $\theta$ between the
magnetizations. These findings expand the scope of magnetization manipulations
for high-performance and high-density storage based on van der Waals magnets.",2009.06849v2
2020-09-16,Experimental realisation of Dual Periodicity Moiré Superlattice in a MoSe$_2$/WSe$_2$ Heterobilayer,"Moir\'e structures in van der Waals heterostructures lead to emergent
phenomena including superconductivity in twisted bilayer graphene and optically
accessible strongly-correlated electron states in transition metal
dichalcogenide heterobilayers. Dual periodicity moir\'e structures (DPMS)
formed in layered structures with more than two layers have been shown to lead
to ferromagnetism and multiple secondary Dirac points in TBG. Whilst in
principle it is possible to obtain DPMS in bilayers there has not been clear
experimental evidence of this yet. In this paper we present signatures of DPMS
in a twisted MoSe$_2$/WSe$_2$ bilayer revealed by resonance Raman spectroscopy.
We observed zone-folded acoustic and optical phonon modes with a wavevector
twice of the moir\'e wavevector, evidence of a dual periodicity moir\'e
heterostructure. These results simultaneously open up opportunities for new
emergent phenomena and an optical method for characterising DPMS in a wide
range of van der Waals heterostructures.",2009.07676v1
2020-09-28,Determination of spin-orbit torques by thickness-dependent spin-orbit torque FMR measurement,"Current induced spin-orbit torques (SOTs) in Fe/Pt bilayers have been
investigated utilizing the spin-orbit torque ferromagnetic resonance (SOT-FMR)
measurement. Characterization of thin films with different thicknesses
indicates existence of a sizable field-like spin-orbit torque competing with
the Oersted field induced torque (Oersted torque). The field-like torque is
neglected in the standard SOT-FMR method and the presence of a strong
field-like torque makes estimation of the spin Hall angle (SHA) problematic.
Also, it is challenging to differentiate the field-like torque from the Oersted
torque in a radiofrequency measurement. Based on the thickness dependence of
field-like torque, anti-damping torque, and Oersted torque, the
thickness-dependent SOT-FMR measurement is proposed as a more reliable,
self-calibrated approach for characterization of spin-orbit torques.",2009.13162v2
2020-10-12,Chiral high-harmonic generation and spectroscopy on solid surfaces using polarization-tailored strong fields,"Strong-field methods in solids enable new strategies for ultrafast nonlinear
spectroscopy and provide all-optical insights into the electronic properties of
condensed matter in reciprocal and real space. Additionally, solid-state media
offers unprecedented possibilities to control high-harmonic generation using
modified targets or tailored excitation fields. Here we merge these important
points and demonstrate circularly-polarized high-harmonic generation with
polarization-matched excitation fields for spectroscopy of chiral electronic
properties at surfaces. The sensitivity of our approach is demonstrated for
structural helicity and termination-mediated ferromagnetic order at the surface
of silicon-dioxide and magnesium oxide, respectively. Circularly polarized
radiation emanating from a solid sample now allows to add basic symmetry
properties as chirality to the arsenal of strong-field spectroscopy in solids.
Together with its inherent temporal (femtosecond) resolution and non-resonant
broadband spectrum, the polarization control of high harmonics from condensed
matter can illuminate ultrafast and strong field dynamics of surfaces, buried
layers or thin films.",2010.05558v2
2020-10-13,Large cross-polarized Raman signal in CrI$_3$: A first-principles study,"We find unusually large cross-polarized (and anti-symmetric) Raman signature
of A$_{\rm g}$ phonon mode in CrI$_3$, in agreement with experiments. The
signal is present only when the following three effects are considered in
concert: ferromagnetism on Cr atoms, spin-orbit interaction, and resonant
effects. Somewhat surprisingly, we find that the relevant spin-orbit
interaction potential originates from iodine atoms, despite magnetism being
mostly on chromium atoms. We analyze the Raman signature as a function of
magnetic order, the direction of the magnetic moment, energy and polarization
of light used for Raman scattering, as well as carrier lifetime. In addition to
a strong cross-polarized Raman signal, we also find unusually strong phonon
modulated magneto-optical Kerr effect (MOKE) in CrI$_3$.",2010.06633v2
2020-11-07,Photon Condensation and Enhanced Magnetism in Cavity QED,"A system of magnetic molecules coupled to microwave cavities ($LC$
resonators) undergoes the equilibrium superradiant phase transition. The
transition is experimentally observable. The effect of the coupling is first
illustrated by the vacuum-induced ferromagnetic order in a quantum Ising model
and then by the modification of the magnetic phase diagram of ${\rm Fe_8}$
dipolar crystals, exemplifying the cooperation between intrinsic and
photon-induced spin-spin interactions. Finally, a transmission experiment is
shown to resolve the transition, measuring the quantum electrodynamical control
of magnetism.",2011.03753v5
2020-11-19,Determining complex spin mixing conductance and spin diffusion length from spin pumping experiments in magnetic insulator/heavy metal bilayers,"Magnetic insulators are promising materials for the development of
energy-efficient spintronics. Unlike metallic counterparts, the magnetic
insulators are characterized by imaginary part of the interfacial spin mixing
conductance as well in a bilayer with heavy metals and it is responsible for
the field-like toque in spin-orbit torque devices. Here, we study the
underlying theoretical constructs and develop a general strategy to determine
the complex spin mixing conductance from the experimental results of
ferromagnetic resonance and spin pumping. The results show that the imaginary
part of the spin mixing conductance can be one order more than the real part
and it matches the critical trend of spin mixing conductance with thickness of
the heavy metal. The interpretation of experimental results also indicates that
at small thicknesses the interface contribution becomes significant and bulk
diffusion model cannot explain the results. A thickness-dependent spin
diffusion length is necessary too that is tantamount to Elliott-Yafet spin
relaxation mechanism in the heavy metals. Also, we effectively explain the
experimental results while inserting a copper layer with varying thicknesses in
between the magnetic insulator and the heavy metal using spin-circuit
formalism.",2011.11055v1
2021-02-10,Controlling the oxidation of magnetic and electrically conductive solid-solution iron-rhodium nanoparticles synthesized by Laser Ablation in Liquids,"This study focuses on the synthesis of FeRh nanoparticles via pulsed laser
ablation in liquid and on controlling the oxidation of the synthesized
nanoparticles. Formation of monomodal {\gamma}-FeRh nanoparticles was confirmed
by transmission electron microscopy (TEM) and their composition confirmed by
atom probe tomography (APT). On these particles, three major contributors to
oxidation were analysed: 1) dissolved oxygen in the organic solvents, 2) the
bound oxygen in the solvent and 3) oxygen in the atmosphere above the solvent.
The decrease of oxidation for optimized ablation conditions was confirmed
through energy-dispersive X-ray (EDX) and M\""ossbauer spectroscopy.
Furthermore, the time dependence of oxidation was monitored for dried FeRh
nanoparticles powders using ferromagnetic resonance spectroscopy (FMR). By
magnetophoretic separation, B2-FeRh nanoparticles could be extracted from the
solution and characteristic differences of nanostrand formation between
{\gamma}-FeRh and B2-FeRh nanoparticles were observed.",2102.05652v1
2021-02-12,Neutron scattering studies on spin fluctuations in Sr$_2$RuO$_4$,"The magnetic excitations in Sr$_2$RuO$_4$ are studied by polarized and
unpolarized neutron scattering experiments as a function of temperature. At the
scattering vector of the Fermi-surface nesting with a half-integer out-of-plane
component, there is no evidence for the appearance of a resonance excitation in
the superconducting phase. The body of existing data indicates weakening of the
scattered intensity in the nesting spectrum to occur at very low energies. The
nesting signal persists up to 290 K but is strongly reduced. In contrast, a
quasi-ferromagnetic contribution maintains its strength and still exhibits a
finite width in momentum space.",2102.06636v1
2021-02-15,"Angular-Dependent Dynamic Response and Magnetization Reversal in Fibonacci-Distorted, Kagome Artificial Spin Ice","We have measured the angular dependence of ferromagnetic resonance (FMR)
spectra for Fibonacci-distorted, Kagome artificial spin ice (ASI). The number
of strong modes in the FMR spectra depend on the orientation of the applied DC
magnetic field. In addition, discontinuities observed in the FMR
field-frequency dispersion curves also depend on DC field orientation, and
signal a multi-step DC magnetization reversal, which is caused by the reduced
energy degeneracy of Fibonacci-distorted vertices. The results suggest the
orientation of applied magnetic field and severity of Fibonacci distortion
constitute control variables for FMR modes and multi-step reversal in future
magnonic devices and magnetic switching systems.",2102.07532v1
2021-02-20,Observation of mode splitting in artificial spin ice,"We report the dependence of the magnetization dynamics in a square artificial
spin-ice lattice on the in-plane magnetic field angle. Using two complementary
measurement techniques - broadband ferromagnetic resonance and micro-focused
Brillouin light scattering spectroscopy - we systematically study the evolution
of the lattice dynamics, both for a coherent radiofrequency excitation and an
incoherent thermal excitation of spin dynamics. We observe a splitting of modes
facilitated by inter-element interactions that can be controlled by the
external field angle and magnitude. Detailed time-dependent micromagnetic
simulations reveal that the split modes are localized in different regions of
the square network. This observation suggests that it is possible to
disentangle modes with different spatial profiles by tuning the external field
configuration.",2102.10415v1
2021-03-11,Magnetoelastic Gilbert damping in magnetostrictive Fe$_{0.7}$Ga$_{0.3}$ thin films,"We report an enhanced magnetoelastic contribution to the Gilbert damping in
highly magnetostrictive Fe$_{0.7}$Ga$_{0.3}$ thin films. This effect is
mitigated for perpendicular-to-plane fields, leading to a large anisotropy of
the Gilbert damping in all of the films (up to a factor of 10 at room
temperature). These claims are supported by broadband measurements of the
ferromagnetic resonance linewidths over a range of temperatures (5 to 400 K),
which serve to elucidate the effect of both the magnetostriction and phonon
relaxation on the magnetoelastic Gilbert damping.",2103.07008v1
2021-03-16,Excited Rydberg States in TMD Heterostructures,"The functional form of Coulomb interactions in the transition metal
dichalcogenides and other van der Waals solids is critical to many of their
unique properties, e.g. strongly-correlated electron states, superconductivity
and emergent ferromagnetism. This paper presents measurements of key excitonic
energy levels in MoSe2/WSe2 heterostructures. These measurements are obtained
from resonance Raman experiments on specific Raman peaks only observed at
excited states of the excitons. This data is used to validate a model of the
Coulomb potential in these structures which predicts the exciton energies to
within ~5 meV / 2.5%. This model is used to determine the effect of
heterostructure formation on the single-particle band gaps of the layers and
will have a wide applicability in designing the next generation of more complex
transition metal dichalcogenide structures.",2103.09004v1
2021-03-26,Switching magnon chirality in artificial antiferromagnet,"Magnons in antiferromagnets can support both right-handed and left-handed
chiralities, which shed a light on the chirality-based spintronics. Here we
demonstrate the switching and reading of magnon chirality in an artificial
antiferromagnet. The coexisting antiferromagnetic and ferromagnetic
characteristic resonance modes are discovered, which permits a high tunability
in the modulation of magnon chirality. The reading of the chirality is
accomplished via the chirality-dependent spin pumping as well as spin
rectification effect. Our result illustrates an ideal antiferromagnetic
platform for handling magnon chirality and paves the way for chirality-based
spintronics.",2103.14483v2
2021-04-03,Growth and helicity of non-centrosymmetric Cu$_2$OSeO$_3$ crystals,"We have grown Cu$_2$OSeO$_3$ single crystals with an optimized chemical vapor
transport technique by using SeCl$_4$ as a transport agent. Our optimized
growth method allows to selectively produce large high quality single crystals.
The method is shown to consistently produce Cu$_2$OSeO$_3$ crystals of maximum
size 8 mm x 7 mm x 4 mm with a transport duration of around three weeks. We
found this method, with SeCl$_4$ as transport agent, more efficient and simple
compared to the commonly used growth techniques reported in literature with HCl
gas as transport agent. The Cu$_2$OSeO$_3$ crystals have very high quality and
the absolute structure are fully determined by simple single crystal x-ray
diffraction. We observed both type of crystals with left- and right-handed
chiralities. Our magnetization and ferromagnetic resonance data show the same
magnetic phase diagram as reported earlier.",2104.01465v1
2021-04-16,Large spin-to-charge conversion at room temperature in extended epitaxial Sb2Te3 topological insulator chemically grown on Silicon,"Spin-charge interconversion phenomena at the interface between magnetic
materials and topological insulators (TIs) are attracting enormous interest in
the research effort towards the development of fast and ultra-low power devices
for the future information and communication technology. We report a large
spin-to-charge conversion efficiency in Au/Co/Au/Sb2Te3/Si(111)
heterostructures based on Sb2Te3 TIs grown by metal organic chemical vapor
deposition on 4 inches Si(111) substrates. By conducting room temperature spin
pumping ferromagnetic resonance, we measure an inverse Edelstein Effect length
{\lambda}IEE up to 0.75 nm, a record value for 3-dimensional chalcogenide-based
TIs heterostructures. Our results open the path toward the use of chemical
methods to produce TIs on large area Si substrates and characterized by highly
performing spin-charge conversion, thus marking a milestone toward future
technology-transfer.",2104.08124v1
2021-04-22,Impact of Fe$_{80}$B$_{20}$ insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions,"We explore the impact of Fe80B20 inserted at both
Co$_{20}$Fe$_{80}$B$_{20}$/MgO interfaces of dual-MgO free layers (FLs) in
bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30
min at 350 $^\circ$C and 400 $^\circ$C in a vacuum after film deposition.
Current-in-plane tunneling measurements are carried out to characterize
magnetotransport properties of the MTJs. Conventional magnetometry measurements
and ferromagnetic resonance are conducted to estimate the saturation
magnetization, the effective perpendicular anisotropy field and the Gilbert
damping of dual-MgO FLs as a function of the Fe$_{80}$B$_{20}$ thickness and
annealing temperatures. With ultrathin Fe$_{80}$B$_{20}$ (0.2 - 0.4 nm)
inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar
tunnel magneto-resistance (TMR) and low damping values. As Fe$_{80}$B$_{20}$
layer thickness further increases (0.6 - 1.2 nm), both TMR and PMA degrade, and
damping increases dramatically. This study demonstrates a novel approach to
tune properties of MTJ stacks with dual-MgO FLs up to 400 $^\circ$C annealing,
which enables MTJ stacks for various applications.",2104.10918v1
2021-04-27,Mechanism of parametric pumping of magnetization precession in a nanomagnet. Parametric mechanism of current-induced magnetization reversal,"A mechanism of current-induced magnetization reversal based on the parametric
resonance is described. The source of the magnetization reversal is a
current-induced magnetic field, which is applied perpendicularly to the easy
axis of magnetic anisotropy of a ferromagnetic nanomagnet. The current-induced
magnetic field was measured in a FeCoB nanomagnet to be 60 Gauss at a current
density of 65 mA/um2. Two mechanisms of the magnetization reversal are
described and calculated. The first mechanism is the reversal by a RF
electrical current, which modulated at a frequency close to the precession
frequency of the nanomagnet. The second mechanism is the reversal by a DC
electrical current, in which the magneto-resistance and the current dependency
of the induced magnetic field create a positive feedback loop, which amplifies
a random tiny thermal fluctuation into a large magnetization precession leading
to the magnetization reversal. The combination of the proposed mechanism with
conventional magnetization-reversal mechanisms such as the Spin Torque and the
Spin-Orbit Torque can improve the performance of a Magnetic Random Access
Memory.",2104.13008v1
2021-05-09,Tailoring interfacial effect in multilayers with Dzyaloshinskii-Moriya interaction by helium ion irradiation,"We show a method to control magnetic interfacial effects in multilayers with
Dzyaloshinskii-Moriya interaction (DMI) using helium (He$^{+}$) ion
irradiation. We report results from SQUID magnetometry, ferromagnetic resonance
as well as Brillouin light scattering results on multilayers with DMI as a
function of irradiation fluence to study the effect of irradiation on the
magnetic properties of the multilayers. Our results show clear evidence of the
He$^{+}$ irradiation effects on the magnetic properties which is consistent
with interface modification due to the effects of the He$^{+}$ irradiation.
This external degree of freedom offers promising perspectives to further
improve the control of magnetic skyrmions in multilayers, that could push them
towards integration in future technologies.",2105.03976v2
2021-05-22,Ferromagnetic resonance modes in the exchange dominated limit in cylinders of finite length,"We analyze the magnetic mode structure of axially-magnetized, finite-length,
nanoscopic cylinders in a regime where the exchange interaction dominates,
along with simulations of the mode frequencies of the ferrimagnet yttrium iron
garnet. For the bulk modes we find that the frequencies can be represented by
an expression given by Herring and Kittel by using wavevector components
obtained by fitting the mode patterns emerging from these simulations. In
addition to the axial, radial, and azimuthal modes that are present in an
infinite cylinder, we find localized ""cap modes"" that are ""trapped"" at the top
and bottom cylinder faces by the inhomogeneous dipole field emerging from the
ends. Semi-quantitative explanations are given for some of the modes in terms
of a one-dimensional Schrodinger equation which is valid in the exchange
dominant case. The assignment of the azimuthal mode number is carefully
discussed and the frequency splitting of a few pairs of nearly degenerate modes
is determined through the beat pattern emerging from them.",2105.10795v1
2021-05-24,Cavity magnomechanics with surface acoustic waves,"Magnons, namely spin waves, are collective spin excitations in ferromagnets,
and their control through coupling with other excitations is a key technology
for future hybrid spintronic devices. Although strong coupling has been
demonstrated with microwave photonic structures, an alternative approach
permitting high density integration and minimized electromagnetic crosstalk is
required. Here we report a planar cavity magnomechanical system, where the
cavity of surface acoustic waves enhances the spatial and spectral power
density to thus implement magnon-phonon coupling at room temperature.
Excitation of spin-wave resonance involves significant acoustic power
absorption, whereas the collective spin motion reversely exerts a back-action
force on the cavity dynamics. The cavity frequency and quality-factor are
significantly modified by the back-action effect, and the resultant
cooperativity exceeds unity, suggesting coherent interaction between magnons
and phonons. The demonstration of a chip-scale magnomechanical system paves the
way to the development of novel spin-acoustic technologies for classical and
quantum applications.",2105.11127v1
2021-05-25,Realizing discontinuous quantum phase transitions in a strongly-correlated driven optical lattice,"Discontinuous quantum phase transitions and the associated metastability play
central roles in diverse areas of physics ranging from ferromagnetism to false
vacuum decay in the early universe. Using strongly-interacting ultracold atoms
in an optical lattice, we realize a driven many-body system whose quantum phase
transition can be tuned from continuous to discontinuous. Resonant shaking of a
one-dimensional optical lattice hybridizes the lowest two Bloch bands, driving
a novel transition from a Mott insulator to a $\pi$-superfluid, i.e., a
superfluid state with staggered phase order. For weak shaking amplitudes, this
transition is discontinuous (first-order) and the system can remain frozen in a
metastable state, whereas for strong shaking, it undergoes a continuous
transition toward a $\pi$-superfluid. Our observations of this metastability
and hysteresis are in good quantitative agreement with numerical simulations
and pave the way for exploring the crucial role of quantum fluctuations in
discontinuous transitions.",2105.12146v1
2021-05-31,Dilute magnetic moments in an exactly solvable interacting host,"Despite concerted efforts, the problem of dilute local moments embedded in a
correlated conduction electron host such as Nd$_{1-x}$Ce$_x$CuO$_2$ persists
due to lack of analytically controllable models. Here, we address the question:
how do local moments couple to correlated but integrable hosts? We describe the
conduction electrons by the model of Hatsugai-Kohmoto (HK) which has undergone
a recent resurgence arising from its exact solvability, existence of Luttinger
surfaces, and connections to Sachdev-Ye-Kitaev (SYK) thermodynamics. We derive
an exact low energy ""Kondo-HK"" Hamiltonian and show the existence of additional
spin-exchange coupling that is relevant in the renormalization group (RG)
sense. This term is ferromagnetic and does not vanish at low energies yielding
an algebraic enhancement of the Kondo temperature. ""Poor man's"" scaling of
couplings exhibits an exotic step-like RG flow between UV-IR fixed points
attributed to severely restricted scattering phase space. This phenomenon is
analogous to the flow of central charge in Zamolodchikov's diagonal resonance
scattering in integrable quantum field theories.",2105.15205v1
2021-06-04,Frustration enhanced by Kitaev exchange in a $\boldsymbol{\tilde{j}_{\text{eff}}=\frac12}$ triangular antiferromagnet,"Triangular Heisenberg antiferromagnets are prototypes of geometric
frustration, even if for nearest-neighbor interactions quantum fluctuations are
not usually strong enough to destroy magnetic ordering: stronger frustration is
required to stabilize a spin-liquid phase. On the basis of static magnetization
and electron spin resonance measurements, we demonstrate the emergence of
${\tilde{j}_{\text{eff}}=\frac12}$ moments in the triangular-lattice magnet
Na$_2$BaCo(PO$_4$)$_2$. These moments are subject to an extra source of
frustration that causes magnetic correlations to set in far above both the
magnetic ordering and Weiss temperatures. Corroborating the
$\tilde{j}_{\text{eff}}=\frac12$ ground state, theory identifies ferromagnetic
Kitaev exchange anisotropy as additional frustrating agent, altogether putting
forward Na$_2$BaCo(PO$_4$)$_2$ as a promising Kitaev spin-liquid material.",2106.02437v2
2021-06-08,Spectral-fingerprinting: Microstate readout via remanence ferromagnetic resonance in artificial spin systems,"Artificial spin ices are magnetic metamaterials comprising
geometrically-tiled interacting nanomagnets. There is significant interest in
these systems for reconfigurable magnonics due to their vast microstate
landscape. Studies to-date have focused on the in-field GHz spin-wave response,
convoluting effects from applied field, nanofabrication-imperfections
('quenched disorder') and microstate-dependent dipolar field landscapes. Here,
we study artificial spin ices in pure and disordered microstates and evaluate
their zero-field spectra. Removing the applied field allows us to deconvolute
contributions to reversal dynamics and spin-wave spectra, directly measuring
the dipolar field landscape and quenched disorder. Mode-amplitude provides
population readout of nanomagnet magnetisation direction, and hence net
magnetisation as well as local vertex populations. We demonstrate
microstate-fingerprinting via distinct spectral-readout of three microstates
with identical (zero) magnetisation, supported by simulation. These results
establish remanence 'spectral-fingerprinting' as a rapid, scalable on-chip
readout of both magnetic state and nanoscale dipolar field texture, a critical
step in realising next-generation functional magnonic devices.",2106.04406v2
2021-06-19,Approaching to the deep-strong photon-to-magnon coupling,"In this work, the ultra-strong photon-to-magnon coupling is demonstrated for
on-chip multilayered superconductor/ferromagnet/insulator hybrid thin film
structures reaching the coupling strength above 6 GHz, the coupling ratio about
0.6, the single-spin coupling strength about 350 Hz, and cooperativity about
10^4. High characteristics of coupling are achieved owing to a radical
suppression of the photon phase velocity in electromagnetic resonator. With
achieved coupling the spectrum reveals inapplicability of the Dicke model, and
evidences contribution of the diamagnetic A^2 interaction term in the
Hamiltonian of the system, which satisfies the Thomas-Reiche-Kuhn sum rule. The
contribution of the A^2 term denotes validity of the Hopfield quantum model and
manifests observation of a different hybrid polariton quasi-particle, namely,
the plasmon-magnon polariton.",2106.10450v1
2021-06-24,Low-dimensional antiferromagnetic fluctuations in the heavy-fermion paramagnetic ladder UTe$_2$,"Inelastic-neutron-scattering measurements were performed on a single crystal
of the heavy-fermion paramagnet UTe$_2$ above its superconducting temperature.
We confirm the presence of antiferromagnetic fluctuations with the
incommensurate wavevector $\mathbf{k}_1=(0,0.57,0)$. A quasielastic signal is
found, whose momentum-transfer dependence is compatible with fluctuations of
magnetic moments $\mu\parallel\mathbf{a}$, with a sine-wave modulation of
wavevector $\mathbf{k}_1$ and in-phase moments on the nearest U atoms. Low
dimensionality of the magnetic fluctuations, consequence of the ladder
structure, is indicated by weak correlations along the direction $\mathbf{c}$.
These fluctuations saturate below the temperature $T_1^*\simeq15$~K, in
possible relation with anomalies observed in thermodynamic,
electrical-transport and nuclear-magnetic-resonance measurements. The absence
or weakness of ferromagnetic fluctuations, in our data collected at
temperatures down to 2.1 K and energy transfers from 0.6 to 7.5 meV, is
emphasized. These results constitute constraints for models of
magnetically-mediated superconductivity in UTe$_2$.",2106.13087v1
2021-07-06,Co-existence of short- and long-range magnetic order in LaCo$_2$P$_2$,"The ferromagnetic (FM) nature of the metallic LaCo$_2$P$_2$ was investigated
with the positive muon spin rotation, relaxation and resonance ($\mu^+$SR)
technique. Transverse and zero field $\mu^+$SR measurements revealed that the
compound enters a long range FM ground state at $T_{\rm C}=130.91(65)$~K,
consistent with previous studies. Based on the reported FM structure, the
internal magnetic field was computed at the muon sites, which were predicted
with first principles calculations. The computed result agree well with the
experimental data. Moreover, although LaCo$_2$P$_2$ is a paramagnet at higher
temperatures $T>160$~K, it enters a short range ordered (SRO) magnetic phase
for $T_{\rm C}<T\leq160$~K. Measurements below the vicinity of $T_{\rm C}$
revealed that the SRO phase co-exists with the long range FM order at
temperatures $124\leq T\leq T_{\rm C}$. Such co-existence is an intrinsic
property and stems from competition between the 2D and 3D
interactions/fluctuations.",2107.02560v2
2021-07-12,Origin of Perpendicular Magnetic Anisotropy in Yttrium Iron Garnet Thin Films Grown on Si (100),"We report the magnetic properties of yttrium iron garnet (YIG) thin films
grown by pulsed laser deposition technique. The films were deposited on Si
(100) substrates in the range of 15-50 nm thickness. Magnetic characterizations
were investigated by ferromagnetic resonance spectra. Perpendicular magnetic
easy axis was achieved up to 50 nm thickness. We observed that the
perpendicular anisotropy values decreased by increasing the film thickness. The
origin of the perpendicular magnetic anisotropy (PMA) was attributed to the
texture and the lattice distortion in the YIG thin films. We anticipate that
perpendicularly magnetized YIG thin films on Si substrates pave the way for a
cheaper and compatible fabrication process.",2107.05591v1
2021-07-17,Magnetization switching in the inertial regime,"We have numerically solved the Landau-Lifshitz-Gilbert (LLG) equation in its
standard and inertial forms to study the magnetization switching dynamics in a
$3d$ thin film ferromagnet. The dynamics is triggered by ultrashort magnetic
field pulses of varying width and amplitude in the picosecond and Tesla range.
We have compared the solutions of the two equations in terms of switching
characteristic, speed and energy analysis. Both equations return qualitatively
similar switching dynamics, characterized by regions of slower precessional
behavior and faster ballistic motion. In case of inertial dynamics, ballistic
switching is found in a 25 % wider region in the parameter space given by the
magnetic field amplitude and width. The energy analysis of the dynamics is
qualitatively different for the standard and inertial LLG equations. In the
latter case, an extra energy channel, interpreted as the kinetic energy of the
system, is available. Such extra channel is responsible for a resonant energy
absorption at THz frequencies, consistent with the occurence of spin nutation.",2107.08234v1
2021-08-22,Nonlinear and Thermal Effects in the Absorption of Microwaves by Random Magnets,"Abstract We study the temperature dependence of the absorption of microwaves
by random-anisotropy magnets. It is governed by strong metastability due to the
broad distribution of energy barriers separating different spin configurations.
At a low microwave power, when the heating is negligible, the spin dynamics is
close to linear. It corresponds to the precession of ferromagnetically ordered
regions that are in resonance with the microwave field. Previously we have
shown (doi.org/10.1103/PhysRevB.103.214414) that in this regime a dielectric
substance packed with random magnets would be a strong microwave absorber in a
broad frequency range. Here we demonstrate that on increasing the power,
heating and over barrier spin transitions come into play, resulting in the
nonlinear behavior. At elevated temperatures the absorption of microwave power
decreases dramatically, making the dielectric substance with random magnets
transparent for the microwaves.",2108.09804v1
2021-08-23,Reconfigurable 3D magnonic crystal: tunable and localized spin-wave excitations in CoFeB meander-shaped film,"In this work, we study experimentally by broadband ferromagnetic resonance
measurements, the dependence of the spin-wave excitation spectra on the
magnetic applied field in CoFeB meander-shaped films. Two different
orientations of the external magnetic field were explored, namely parallel or
perpendicular to the lattice cores. The interpretation of the field dependence
of the frequency and spatial profiles of major spin-wave modes were obtained by
micromagnetic simulations. We show that the vertical segments lead to the
easy-axis type of magnetic anisotropy and support the in-phase and out-of-phase
spin-wave precession amplitude in the vertical segments. The latter could
potentially be used for the design of tunable metasurfaces or in magnetic
memories based on meandering 3D magnetic films.",2108.10232v1
2021-10-18,Depth Profile of the Phase Transition of the FeRh Alloy in FeRh/BaTiO3,"We report on the depth dependence and technological limits of the phase
transition of the iron rhodium alloy as function of temperature, external
magnetic and electric fields in the FeRh/BaTiO3 multiferroic, determined by
grazing-incidence nuclear resonant scattering measurements. The change of
temperature induces a continuous and homogenous antiferromagnetic /
ferromagnetic phase transition through the entire FeRh layer, except in the
near substrate region. External magnetic field does not affect this mechanism,
but the application of electric field changes it fundamentally (via
piezoelectric strain): the phase transition of the alloy suddenly propagates
from the substrate up to a height, defined by the combination of temperature
and external magnetic field, as soon as the applied electric field reaches ~ 20
kV/m.",2110.09219v2
2021-11-11,Spin dynamics in the Van der Waals magnet CrCl$_3$,"The magnetic nature of low dimensional compound, CrCl$_3$, was investigated
by muon spin rotation, relaxation and resonance ($\mu^+$SR). The $\mu^+$SR
measurements revealed three distinct phases as a function of temperature: an
antiferromagnetic state (AF) for $T\leq T_{\rm N}=14.32(6)$~K, a ferromagnetic
short range ordered state (FM-SRO) for $T_{\rm N}<T<\sim18$~K and a
paramagnetic phase (PM) above $\sim18$~K. Moreover, the AF state exhibits
appreciable spin dynamics, which increases with decreasing temperature below
$T_{\rm N}$. These dynamics originate from out of plane fluctuations, which
seem to settle for $9.5$~K$\leq T\leq T_{\rm N}$, evidenced from measurements
in ZF and complementary local field calculations. Moreover, the presented muon
Knight shift measurements just above $T_{\rm N}$ represent a clear microscopic
evidence for the absence of the previously speculated long range quasi-2D FM
order.",2111.06246v1
2021-11-16,Energy-efficient W$_{\text{100-x}}$Ta$_{\text{x}}$/CoFeB/MgO spin Hall nano-oscillators,"We investigate a W-Ta alloying route to reduce the auto-oscillation current
densities and the power consumption of nano-constriction based spin Hall nano
oscillators. Using spin-torque ferromagnetic resonance (ST-FMR) measurements on
microbars of W$_{\text{100-x}}$Ta$_{\text{x}}$(5 nm)/CoFeB(t)/MgO stacks with t
= 1.4, 1.8, and 2.0 nm, we measure a substantial improvement in both the
spin-orbit torque efficiency and the spin Hall conductivity. We demonstrate a
34\% reduction in threshold auto-oscillation current density, which translates
into a 64\% reduction in power consumption as compared to pure W-based SHNOs.
Our work demonstrates the promising aspects of W-Ta alloying for the
energy-efficient operation of emerging spintronic devices.",2111.08627v1
2021-12-14,Robust perpendicular magnetic anisotropy in Ce substituted yttrium iron garnet epitaxial thin films,"Cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films are
prepared on gadolinium gallium garnet (GGG) substrate with pulsed laser
deposition (PLD). It is observed that the films grown on GGG(111) substrate
exhibit perpendicular magnetic anisotropy (PMA) as compared to films grown on
GGG(100) substrate. The developed PMA is confirmed from magneto-optical Kerr
effect, bulk magnetization and ferromagnetic resonance measurements. Further,
the magnetic bubble domains are observed in the films exhibiting PMA. The
observations are explained in terms of the growth direction of Ce:YIG films and
the interplay of various magnetic anisotropy terms. The observed PMA is found
to be tunable with thickness of the film and a remarkable temperature stability
of the PMA is observed in all the studied films of Ce:YIG deposited on GGG(111)
substrate.",2112.07264v1
2022-01-11,Edge spin wave transmission through a vertex domain wall in triangular dots,"Spin waves (SWs), being usually reflected by domain walls, could also be
channeled along them. Edge domain walls yield the interesting, and potentially
applicable to real devices property of broadband spin waves confinement to the
edges of the structure. Here we investigate through numerical simulations the
propagation of quasi one-dimensional spin waves in triangle-shaped amorphous
YIG ($Y_3Fe_5O_{12}$) micron sized ferromagnets as a function of the angle
aperture. The edge spin waves (ESWs) have been propagated over the corner in
triangles of 2 microns side with a fixed thickness of 85 nm. Parameters such as
superior vertex angle (in the range of 40$^\circ$-75$^\circ$) and applied
magnetic field have been optimized in order to obtain a higher transmission
coefficient of the ESWs over the triangle vertex. We observed that for a
certain aperture angle for which dominated ESW frequency coincides with one of
the localised DW modes, the transmission is maximized near one and the phase
shift drops to $\pi/2$ indicating resonant transmission of ESWs through the
upper corner. We compare the obtained results with existing theoretical models.
These results could contribute to the development of novel basic elements for
spin wave computing.",2201.04054v2
2022-01-25,Complex vortex-antivortex dynamics in the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$,"We report on the investigation of the magnetic superconductor
EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ based on muon-spin spectroscopy and ac
magnetic susceptibility ($\chi$) measurements. The dependence of the internal
field at the muon site on temperature is indicative of a ferromagnetic ordering
of Eu$^{2+}$ magnetic moments and only the conventional magnon scattering
governs the longitudinal relaxation rate at low temperatures. At the same time,
we observe a rich phenomenology for the imaginary component of the
susceptibility $\chi^{\prime\prime}$ by means of both standard ac
susceptibility and a novel technique based on a microwave coplanar waveguide
resonator. In particular, we detect activated trends for several features in
$\chi^{\prime\prime}$ over frequencies spanning ten orders of magnitude. We
interpret our results in terms of the complex dynamics of vortices and
antivortices influenced by the underlying structure of magnetic domains.",2201.10216v1
2022-01-27,Effect of vertex corrections on the enhancement of Gilbert damping in spin pumping into a two-dimensional electron gas,"We theoretically consider the effect of vertex correction on spin pumping
from a ferromagnetic insulator (FI) into a two-dimensional electron gas (2DEG)
in which the Rashba and Dresselhaus spin-orbit interactions coexist. The
Gilbert damping in the FI is enhanced by elastic spin-flipping or magnon
absorption. We show that the Gilbert damping due to elastic spin-flipping is
strongly enhanced by the vertex correction when the ratio of the two spin-orbit
interactions is near a special value at which the spin relaxation time diverges
while that due to magnon absorption shows only small modification. We also show
that the shift in the resonant frequency due to elastic spin-flipping is
strongly enhanced in a similar way as the Gilbert damping.",2201.11498v3
2022-02-03,Element Doping Enhanced Charge-to-Spin Conversion Efficiency in Amorphous PtSn4 Dirac Semimetal,"Topological semimetals (TSs) are promising candidates for low-power
spin-orbit torque (SOT) devices due to their large charge-to-spin conversion
efficiency. Here, we investigated the charge-to-spin conversion efficiency of
amorphous PtSn4 (5 nm)/CoFeB (2.5-12.5 nm) layered structures prepared by a
magnetron sputtering method at room temperature. The charge-to-spin ratio of
PtSn4/CoFeB bilayers was 0.08, characterized by a spin torque ferromagnetic
resonance (ST-FMR) technique. This ratio can further increase to 0.14 by
inducing dopants, like Al and CoSi, into PtSn4. The dopants can also decrease
(Al doping) or increase (CoSi doping) the resistivity of PtSn4. The work
proposed a way to enhance the spin-orbit coupling (SOC) in amorphous TSs with
dopants.",2202.01384v1
2022-02-14,Tunable Excitons in Rhombohedral Trilayer Graphene,"Trilayer graphene is receiving an increasing level of attention due to its
stacking--dependent magnetoelectric and optoelectric properties, and its more
robust ferromagnetism relative to monolayer and bilayer variants.
  Additionally, rhombohedral stacked trilayer graphene presents the possibility
of easily opening a gap via either an external electric field perpendicular to
the layers, or via the application of external strain.
  In this paper, we consider an external electric field to open a bandgap in
rhombohedral trilayer graphene and study the excitonic optical response of the
system.
  This is done via the combination of a tight binding model with the
Bethe--Salpeter equation, solved semi--analytically and requiring only a simple
numerical quadrature.
  We then discuss the valley--dependent optical selection rules, followed by
the computation of the excitonic linear optical conductivity for the case of a
rhombohedral graphene trilayer encapsulated in hexagonal boron nitride.
  The tunability of the excitonic resonances via an external field is also
discussed, together with the increasing localization of the excitonic states as
the field increases.",2202.06695v1
2022-03-14,Noncollinear antiferromagnetic textures driven high harmonic generation from magnetic dynamics in the absence of spin-orbit coupling,"We demonstrate the generation of high order harmonics in carrier pumping from
precessing ferromagnetic or antiferromagnetic orders, excited via magnetic
resonance, in the presence of topological antiferromagnetic textures. This
results in an enhancement of the carrier dynamics by orders of magnitude.
Interestingly, the generation process occurs in an intrinsic manner, and is
solely governed by the interplay between the s-d exchange coupling underlying
the noncollinear antiferromagnetic order and the dynamical s-d exchange
parameter of the magnetic drive. Therefore, the relativistic spin-orbit
interaction is not required for the emergence of high harmonics in the pumped
currents. Accordingly, the noncollinear topological antiferromagnetic order is
presented as an alternative to spin-orbit interaction for the purpose of
harnessing high harmonic emission in carrier pumping. Our proposal initiates a
tantalizing perspective for the exploitation of topological magnetic textures
in the context of the highly active domain of ultrafast spintronics.",2203.07310v2
2022-04-04,Inverse Orbital Torque via Spin-Orbital Entangled States,"While current-induced torque by orbital current has been experimentally found
in various structures, evidence for its reciprocity has been missing so far.
Here, we report experimental evidence of strong inverse orbital torque in
YIG/Pt/CuOx (YIG = Y3Fe5O12) mediated by spin-orbital entangled electronic
states in Pt. By injecting spin current from YIG to Pt by the spin pumping via
ferromagnetic resonance and by the spin Seebeck effect, we find a pronounced
inverse spin Hall effect-like signal. While a part of the signal is explained
as due to the inverse spin-orbital Hall effect in Pt, we also find substantial
increase of the signal in YIG/Pt/CuOx structures compared to the signal in
YIG/Pt. We attribute this to the inverse orbital Rashba-Edelstein effect at
Pt/CuOx interface mediated by the spin-orbital entangled states in Pt. Our work
paves the way toward understanding of spin-orbital entangled physics in
nonequilibrium and provides a way for electrical detection of the orbital
current in orbitronic device applications.",2204.01825v2
2022-06-01,Spectral Recognition of Magnetic Nanoparticles with Artificial Neural Networks,"Ferromagnetic resonance (FMR) spectroscopy is a powerful method for
quantifying internal magnetic anisotropy fields in nanoparticles, which is
important in a wide range of biomedical and storage applications. The
interpretation of FMR spectra, however, can only be achieved with the use of an
appropriate model, and no inverse methods are available to extract internal
fields from FMR spectra. Here, we present the use of artificial neural networks
for spectral recognition, i.e., to identify the internal magnetic anisotropy
field from the FMR spectrum. We trained two different types of networks, a
convolutional neural network and a multi-layer perceptron, by feeding the
networks pre-computed FMR spectra labeled with the corresponding anisotropy
fields. Testing of the trained networks with unseen spectra showed that they
successfully predict the correct anisotropy fields and, surprisingly, the
networks performed well for data that was beyond their training range. These
results show the promise of using artificial neural networks for accelerated
high-throughput analysis of magnetic materials and nanostructures; for example
they could serve in automatizing and optimizing exploration missions where
nanomagnetic signals are often used as proxies.",2206.00166v1
2022-07-30,Spin transport properties in a naphthyl diamine derivative film investigated by the spin pumping,"We report the spin transport properties in a thin film of a naphthyl diamine
derivative: N,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine
(alpha-NPD). In a palladium(Pd)/alpha-NPD/Ni80Fe20 tri-layer structure sample,
a pure spin current is generated in the alpha-NPD layer with the spin pumping
driven by ferromagnetic resonance (FMR). The generated spin current is absorbed
into the Pd layer, and converted into a charge current with the inverse
spin-Hall effect (ISHE) in Pd. An electromotive force due to the ISHE in the Pd
layer is observed under the FMR of the Ni80Fe20 layer, which is clear evidence
for the spin transport in an alpha-NPD film. The spin diffusion length in an
alpha-NPD film is estimated to be about 62 nm at room temperature, which is
long enough as a spin transport material for spintronic devices.",2208.00170v3
2022-08-07,Transition state theory characterizes thin film macrospin dynamics driven by an oscillatory magnetic field: Inertial effects,"Understanding the magnetization switching process in ferromagnetic thin films
is essential for many technological applications. We investigate the effects of
periodic driving via magnetic fields on a macrospin system under explicit
consideration of inertial dynamics. This is usually achieved by extending the
Landau-Lifshitz-Gilbert equation with a term including the second time
derivative of the magnetization. The dynamics of the magnetization switching
can then be characterized by its switching rate. We apply methods from
transition state theory for driven systems to resolve the rate of magnetization
switching in this general case. In doing so, we find that magnetization
exhibits resonance-like behavior under certain driving conditions, and it can
be affected strongly by the system's relaxation rate.",2208.03613v1
2022-08-19,Phononic-crystal cavity magnomechanics,"Establishing a way to control magnetic dynamics and elementary excitations
(magnons) is crucial to fundamental physics and the search for novel phenomena
and functions in magnetic solid-state systems. Electromagnetic waves have been
developed as means of driving and sensing in magnonic and spintronics devices
used in magnetic spectroscopy, non-volatile memory, and information processors.
However, their millimeter-scale wavelengths and undesired cross-talk have
limited operation efficiency and made individual control of densely integrated
magnetic systems difficult. Here, we utilize acoustic waves (phonons) to
control magnetic dynamics in a miniaturized phononic crystal micro-cavity and
waveguide architecture. We demonstrate acoustic pumping of localized
ferromagnetic magnons, where their back-action allows dynamic and
mode-dependent modulation of phononic cavity resonances. The phononic crystal
platform enables spatial driving, control and read-out of tiny magnetic states
and provides a means of tuning acoustic vibrations with magnons. This
alternative technology enhances the usefulness of magnons and phonons for
advanced sensing, communications and computation architectures that perform
transduction, processing, and storage of classical and quantum information.",2208.09105v1
2022-08-29,Determining Kitaev interaction in spin-$S$ honeycomb Mott insulators,"The Kitaev interaction in a honeycomb lattice with higher-spin $S$ has been
one of the central attractions, as it may offer quantum spin liquids. A
microscopic theory showed that when the Hund's coupling at the transition metal
generates $S> \frac{1}{2}$, the spin-orbit coupling at the heavy ligands
provides a route to the Kitaev interaction. However, there have been debates
over its strength compared to other symmetry-allowed interactions.
Investigating the symmetry of the Hamiltonian for general $S$, we show the
magnon energies at two momentum points related by a broken mirror symmetry
reflect the Kitaev interaction when a magnetic field is in the mirror plane.
Applying the symmetry analysis to CrI$_3$ with $S=\frac{3}{2}$ together with
the available angle-dependent ferromagnetic resonance data, we estimate the
Kitaev interaction out of the full Hamiltonian and find that it is
sub-dominant. Our theory can be tested by inelastic neutron scattering on
candidate materials under the proposed magnetic field direction, which will
advance the search for general $S$ Kitaev materials.",2208.13807v2
2022-09-06,Current-driven magnetization dynamics and their correlation with magnetization configurations in perpendicularly magnetized tunnel junctions,"We study spin-transfer-torque driven magnetization dynamics of a
perpendicular magnetic tunnel junction (MTJ) nanopillar. Based on the
combination of spin-torque ferromagnetic resonance and microwave spectroscopy
techniques, we demonstrate that the free layer (FL) and the weak pinned
reference layer (RL) exhibit distinct dynamic behaviors with opposite frequency
vs. field dispersion relations. The FL can support a single coherent spin-wave
(SW) mode for both parallel and antiparallel configurations, while the RL
exhibits spin-wave excitation only for the antiparallel state. These two SW
modes corresponding to the FL and RL coexist at an antiparallel state and
exhibit a crossover phenomenon of oscillation frequency with increasing the
external magnetic field, which could be helpful in the mutual synchronization
of auto-oscillations for SW-based neuromorphic computing.",2209.02271v1
2022-09-22,Spin wave study of magnetic perpendicular surface anisotropy in single crystalline MgO$\text{/}$Fe$\text{/}$MgO films,"Broadband ferromagnetic resonance is measured in single crystalline Fe films
of varying thickness sandwiched between MgO layers. An exhaustive magnetic
characterization of the films (exchange constant, cubic, uniaxial and surface
anisotropies) is enabled by the study of the uniform and the first
perpendicular standing spin wave modes as a function of applied magnetic field
and film thickness. Additional measurements of non-reciprocal spin wave
propagation allow us to separate each of the two interface contributions to the
total surface anisotropy. The results are consistent with the model of a
quasi-bulk film interior and two magnetically different top and bottom
interfaces, a difference ascribed to different oxidation states.",2209.10906v2
2022-10-06,Current-induced perpendicular effective magnetic field in magnetic heterostructures,"Generation of perpendicular effective magnetic field or perpendicular spins
({\sigma}z) is central for the development of energy-efficient, scalable, and
external-magnetic-field-free spintronic memory and computing technologies.
Here, we report the first identification and the profound impacts of a
significant effective perpendicular magnetic field that can arise from
asymmetric current spreading within magnetic microstrips and Hall bars. This
effective perpendicular magnetic field can exhibit all the three
characteristics that have been widely assumed in the literature to ""signify""
the presence of a flow of {\sigma}z, i.e., external-magnetic-field-free current
switching of uniform perpendicular magnetization, a sin2{\phi}-dependent
contribution in spin-torque ferromagnetic resonance signal of in-plane
magnetization ({\phi} is the angle of the external magnetic field with respect
to the current, and a {\phi}-independent but field-dependent contribution in
the second harmonic Hall voltage of in-plane magnetization. This finding
suggests that it is critical to include current spreading effects in the
analyses of various spin polarizations and spin-orbit torques in magnetic
heterostructure. Technologically, our results provide perpendicular effective
magnetic field induced by asymmetric current spreading as a novel, universally
accessible mechanism for efficient, scalable, and external-magnetic-field-free
magnetization switching in memory and computing technologies.",2210.02916v1
2022-10-26,"Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers","Nb and its compounds are widely used in quantum computing due to their high
superconducting transition temperatures and high critical fields. Devices that
combine superconducting performance and spintronic non-volatility could deliver
unique functionality. Here we report the study of magnetic tunnel junctions
with Nb as the heavy metal layers. An interfacial perpendicular magnetic
anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO
heterostructures. The tunneling magnetoresistance was evaluated in junctions
with different thickness combinations and different annealing conditions. An
optimized magnetoresistance of 120% was obtained at room temperature, with a
damping parameter of 0.011 determined by ferromagnetic resonance. In addition,
spin-transfer torque switching has also been successfully observed in these
junctions with a quasistatic switching current density of 7.3*10^5 A/cm2.",2210.14969v1
2022-11-02,Disentangling Electron-Boson Interactions on the Surface of a Familiar Ferromagnet,"We report energy renormalizations from electron-phonon and electron-magnon
interactions in spin minority surface resonances on Ni(111). The different
interactions are identified, disentangled, and quantified from the
characteristic signatures they provide to the complex self-energy and the
largely different binding energies at which they occur. The observed
electron-magnon interactions exhibit a strong dependence on momentum and energy
band position in the bulk Brillouin zone. In contrast, electron-phonon
interactions from the same bands appear to be relatively momentum- and
symmetry-independent. Additionally, a moderately strong ($\lambda>0.5$)
electron-phonon interaction is distinguished from a near-parabolic spin
majority band not crossing the Fermi level.",2211.01431v2
2022-12-07,Acoustic Frequency Multiplication and Pure Second Harmonic Generation of Phonons by Magnetic Transducers,"We predict frequency multiplication of surface acoustic waves in dielectric
substrates via the ferromagnetic resonance of adjacent magnetic transducers
when driven by microwaves. We find pure second harmonic generation (SHG)
without any linear and third harmonic components by a magnetic nanowire. The
SHG and linear phonon pumping are switched by varying the saturated
magnetization direction of the wire, or resolved directionally when pumped by
magnetic nano-disc. We address the high efficiency of SHG with comparable
magnitude to that of linear response, as well as unique non-reciprocal phonon
transport that is remarkably distinct in different phonon harmonics. Such
acoustic frequency comb driven by microwaves should bring unprecedented
tunability for the miniaturized phononic and spintronic devices.",2212.03451v1
2023-01-20,Giant spin-vorticity coupling excited by shear-horizontal surface acoustic waves,"A non-magnetic layer can inject spin-polarized currents into an adjacent
ferromagnetic layer via spin vorticity coupling (SVC), inducing spin wave
resonance (SWR). In this work, we present the theoretical model of SWR
generated by shear-horizontal surface acoustic wave (SH-SAW) via SVC, which
contains distinct vorticities from well-studied Rayleigh SAW. Both Rayleigh-
and SH-SAW delay lines have been designed and fabricated with a Ni81Fe19/Cu
bilayer integrated on ST-cut quartz. Given the same wavelength, the measured
power absorption of SH-SAW is four orders of magnitudes higher than that of the
Rayleigh SAW. In addition, a high-order frequency dependence of the SWR is
observed in the SH-SAW, indicating SVC can be strong enough to compare with
magnetoelastic coupling.",2301.08586v1
2023-02-22,Advanced magnon-optic effects with spin-wave leaky modes,"We numerically demonstrate the excitation of leaky spin waves (SWs) guided
along a ferromagnetic stripe by an obliquely incident SW beam on the thin film
edge placed below the stripe. During propagation, leaky waves emit energy back
to the layer in the form of plane waves and several laterally shifted parallel
SW beams. This resonance excitation, combined with interference effects of the
reflected and re-emitted waves, results in the magnonic Woods anomaly and
significant increase of the Goos-Hanchen shift magnitude. Hence, we provide a
unique platform to control SW reflection and to transfer SWs from a 2D platform
into the 1D guiding mode that can be used to form a transdimensional magnonic
router.",2302.11507v3
2023-03-27,Temperature dependent study of the spin dynamics of coupled Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$/Pt trilayers,"In this study, we investigate the dynamic response of a Y$_3$Fe$_5$O$_{12}$
(YIG)/ Gd$_3$Fe$_5$O$_{12}$ (GdIG)/ Pt trilayer system by measurements of the
ferromagnetic resonance (FMR) and the pumped spin current detected by the
inverse spin Hall effect. This trilayer system offers the unique opportunity to
investigate the spin dynamics of the ferrimagnetic GdIG, close to its
compensation temperature. We show that our trilayer acts as a highly tunable
spin current source. Our experimental results are supported by micro-magnetic
simulations. As the detected spin current in the top Pt layer is distinctly
dominated by the GdIG layer, this gives the unique opportunity to investigate
the excitation and dynamic properties of GdIG while comparing it to the
broadband FMR absorption spectrum of the heterostructure.",2303.15085v1
2023-05-10,Investigation of Spin-Wave Dynamics in Gyroid Nanostructures,"A new concept in magnonics studies the dynamics of spin waves (SWs) in
three-dimensional nanosystems. It is a natural evolution from conventionally
used planar systems to explore magnetization configurations and dynamics in 3D
nanostructures with lengths near intrinsic magnetic scales. In this work, we
perform broadband ferromagnetic resonance (BBFMR) measurements and
micromagnetic simulations of nanoscale magnetic gyroids - a periodic chiral
structure consisting entirely of chiral triple junctions. Our results show
unique properties of the network, such as the localization of the SW modes,
evoking their topological properties, and the substantial sensitivity to the
direction of the static magnetic field. The presented results open a wide range
of applications in the emerging field of 3D magnonic crystals and spintronics.",2305.06319v2
2023-05-19,Phononic Switching of Magnetization by the Ultrafast Barnett Effect,"The Barnett effect, discovered more than a century ago, describes how an
inertial body with otherwise zero net magnetic moment acquires spontaneous
magnetization when mechanically spinning. Breakthrough experiments have
recently shown that an ultrashort laser pulse destroys the magnetization of an
ordered ferromagnet within hundreds of femtoseconds, with the spins losing
angular momentum to circularly-polarized optical phonons as part of the
ultrafast Einstein-de Haas effect. However, the prospect of using such
high-frequency vibrations of the lattice to reciprocally switch magnetization
in a nearby magnetic medium has not yet been experimentally explored. Here we
show that the spontaneous magnetization temporarily gained via the ultrafast
Barnett effect, through the resonant excitation of circularly-polarized optical
phonons in paramagnetic substrates, can be used to permanently reverse the
magnetic state of the substrate-mounted heterostructure. With the handedness of
the phonons steering the direction of magnetic switching, the ultrafast Barnett
effect offers a selective and potentially universal method for exercising
ultrafast non-local control over magnetic order.",2305.11551v1
2023-06-16,Magnetic structure and Kondo lattice behavior in CeVGe$_3$: an NMR and neutron scattering study,"We present nuclear magnetic resonance (NMR), neutron diffraction,
magnetization, and transport measurements on a single crystal and powder of
CeVGe$_3$. This material exhibits heavy fermion behavior at low temperature,
accompanied by antiferromagnetic (AFM) order below 5.8 K. We find that the
magnetic structure is incommensurate with AFM helical structure, characterized
by a magnetic modulated propagation vector of $(0, 0, 0.49)$ with in-plane
moments rotating around the $c$-axis. The NMR Knight shift and spin-lattice
relaxation rate reveal a coherence temperature $T^*\sim 15$ K, and the presence
of significant antiferromagnetic fluctuations reminiscent of the archetypical
heavy fermion compound CeRhIn$_5$. We further identify a metamagnetic
transition above $H_m\sim 2.5$ T for magnetic fields perpendicular to $c$. We
speculate that the magnetic structure in this field-induced phase consists of a
superposition with both ferromagnetic and antiferromagnetic components, which
is consistent with the NMR spectrum in this region of the phase diagram. Our
results thus indicate that CeVGe$_3$ is a hexagonal structure analog to
tetragonal CeRhIn$_5$.",2306.10166v1
2023-06-27,Incommensurate Magnetic Order in the $\mathbb{Z}_2$ Kagome Metal GdV$_6$Sn$_6$,"We characterize the magnetic ground state of the topological kagome metal
GdV$_6$Sn$_6$ via resonant X-ray diffraction. Previous magnetoentropic studies
of GdV$_6$Sn$_6$ suggested the presence of a modulated magnetic order distinct
from the ferromagnetism that is easily polarized by the application of a
magnetic field. Diffraction data near the Gd-$L_2$ edge directly resolve a
$c$-axis modulated spin structure order on the Gd sublattice with an
incommensurate wave vector that evolves upon cooling toward a partial lock-in
transition. While equal moment (spiral) and amplitude (sine) modulated spin
states can not be unambiguously discerned from the scattering data, the overall
phenomenology suggests an amplitude modulated state with moments predominantly
oriented in the $ab$-plane. Comparisons to the ``double-flat"" spiral state
observed in Mn-based $R$Mn$_6$Sn$_6$ kagome compounds of the same structure
type are discussed.",2306.15613v1
2023-07-06,Realization of the unidirectional amplification in a cavity magnonic system,"We experimentally demonstrate the nonreciprocal microwave amplification using
a cavity magnonic system, consisting of a passive cavity (i.e., the split-ring
resonator), an active feedback circuit integrated with an amplifier, and a
ferromagnetic spin ensemble (i.e., a yttrium-iron-garnet sphere). Combining the
amplification provided by the active circuit and the nonreciprocity supported
by the cavity magnonics, we implement a nonreciprocal amplifier with the
functions of both unidirectional amplification and reverse isolation. The
microwave signal is amplified by 11.5 dB in the forward propagating direction
and attenuated in the reverse direction by -34.7 dB, giving an isolation ratio
of 46.2 dB. Such a unidirectional amplifier can be readily employed in quantum
technologies, where the device can simultaneously amplify the weak signal
output by the quantum system and isolate the sensitive quantum system from the
backscattered external noise. Also, it is promising to explore more functions
and applications using a cavity magnonic system with real gain.",2307.02826v2
2023-07-13,Magnon-magnon coupling in synthetic ferrimagnets,"Magnetic multilayers with interlayer exchange coupling have been widely
studied for both static and dynamic regimes. Their dynamical responses depend
on the exchange coupling strength and magnetic properties of individual layers.
Magnetic resonance spectra in such systems are conveniently discussed in terms
of coupling of acoustic and optical modes. At a certain value of applied
magnetic field, the two modes come close to being degenerate and the spectral
gap indicates the strength of mode hybridisation. In this work, we
theoretically and experimentally study the mode hybridisation of
interlayer-exchange-coupled moments with dissimilar magnetisation and thickness
of two ferromagnetic layers. In agreement with symmetry analysis for
eigenmodes, our low-symmetry multilayers exhibit sizable spectral gaps for all
experimental conditions. The spectra agree well with the predictions from the
Landau-Lifshitz-Gilbert equation at the macrospin limit whose parameters are
independently fixed by static measurements.",2307.06888v2
2023-07-22,Dense plasma irradiated platinum with improved spin Hall effect,"The impurity incorporation in host high-spin orbit coupling materials like
platinum has shown improved charge-to-spin conversion by modifying the up-spin
and down-spin electron trajectories by bending or skewing them in opposite
directions. This enables efficient generation, manipulation, and transport of
spin currents. In this study, we irradiate the platinum with non-focus dense
plasma to incorporate the oxygen ion species. We systematically analyze the
spin Hall angle of the oxygen plasma irradiated Pt films using spin torque
ferromagnetic resonance. Our results demonstrate a 2.4 times enhancement in the
spin Hall effect after plasma treatment of Pt as compared to pristine Pt. This
improvement is attributed to the introduction of disorder and defects in the Pt
lattice, which enhances the spin-orbit coupling and leads to more efficient
charge-to-spin conversion without breaking the spin-orbit torque symmetries.
Our findings offer a new method of dense plasma-based modification of material
for the development of advanced spintronic devices based on Pt and other heavy
metals.",2307.12139v1
2023-07-29,Single-spin spectroscopy of spontaneous and phase-locked spin torque oscillator dynamics,"We employ N-$V$ magnetometry to measure the stray field dynamics of a
ferromagnetic permalloy nanowire driven by spin-orbit torques. Specifically, we
observe the optically detected magnetic resonance (ODMR) signatures of both
spontaneous DC-driven magnetic oscillations and phase-locking to a second
harmonic drive, developing a simple macrospin model that captures the salient
features. We also observe signatures of dynamics beyond the macrospin model,
including an additional ODMR feature (associated with a second SW mode) and one
mode sapping power from another. Our results provide additional insight into
N-$V$-spin wave coupling mechanisms, and represent a new modality for
sub-wavelength N-$V$ scanned probe microscopy of nanoscale magnetic
oscillators.",2307.16049v1
2023-08-15,Controlling Majorana hybridization in magnetic chain-superconductor systems,"We propose controlling the hybridization between Majorana zero modes at the
ends of magnetic adatom chains on superconductors by an additional magnetic
adatom deposited close by. By tuning the additional adatom's magnetization,
position, and coupling to the superconductor, we can couple and decouple the
Majorana modes as well as control the ground state parity. The scheme is
independent of microscopic details in ferromagnetic and helical magnetic chains
on superconductors with and without spin-orbit coupling, which we show by
studying their full microscopic models and their common low-energy description.
Our results show that scanning tunneling microscopy and electron spin resonance
techniques are promising tools for controlling the Majorana hybridization in
magnetic adatoms-superconductor setups, providing a basis for Majorana parity
measurements, fusion, and braiding techniques.",2308.07961v2
2023-08-20,Terahertz cavity magnon polaritons,"Hybrid light-matter coupled states, or polaritons, in magnetic materials have
attracted significant attention due to their potential for enabling novel
applications in spintronics and quantum information processing. However, most
studies to date have been carried out for ferromagnetic materials with magnon
excitations at gigahertz frequencies. Here, we have investigated strong
resonant photon-magnon coupling at frequencies above 1 terahertz for the first
time in a prototypical room-temperature antiferromagnetic insulator, NiO,
inside a Fabry-P\'erot cavity. The cavity was formed by the crystal itself when
it was thinned down to an optimized thickness. By using terahertz time-domain
spectroscopy in high magnetic fields up to 25 T, we swept the magnon frequency
through Fabry-P\'erot cavity modes and observed photon-magnon anticrossing
behavior, demonstrating clear vacuum Rabi splittings exceeding the polariton
linewidths. These results show that NiO is a promising platform for exploring
antiferromagnetic spintronics and cavity magnonics in the terahertz frequency
range.",2308.10159v1
2023-08-22,Observation of Current-induced Nonlinear Spin Polarization in Pt-Py Bilayers,"We experimentally observe nonlinear spin polarization in metallic bilayers of
platinum and permalloy by means of spin-torque ferromagnetic resonance (ST-FMR)
with the spin-Hall effects. The ST-FMR results under massive dc current
injection contain striking features, which are not caused by extrinsic Joule
heating, but by intrinsic nonlinear spin polarization. The emergence of
nonlinear spin polarization is consistent with observation of unidirectional
spin-Hall magnetoresistance due to magnon generation/annihilation. Moreover,
the magnon generation (annihilation) leads to effective magnetization shrinkage
(expansion) revealed by the ST-FMR measurements. The present study paves a way
to spin-Hall effect based nonlinear spintronic devices as well as
6th-generation mobile communication light sources.",2308.11156v2
2023-10-16,Generation and detection of spin current in iridate/manganite heterostructures,"The present study focuses on experimental investigations of spin current
across the interface of an iridate/manganite heterostructure
(SrIrO3/La0.7Sr0.3MnO3) consisting of oxide epitaxial films with nanometer
thickness. Pure spin current is induced by microwave irradiation in the GHz
frequency band, specifically under conditions of ferromagnetic resonance. The
detection of spin current is achieved through the inverse spin-Hall effect,
which measures the charge current arising on the electrically conductive SrIrO3
film with strong spin-orbit interaction. To quantify the efficiency of spin
current conversion to charge current, the angular dependences of spin
magnetoresistance of the iridate/manganite interface are measured, thereby
determining the spin- Hall angle.",2310.10297v1
2023-10-26,Spin wave behavior of a novel hopfion-like chiral state in Co/Pt nanodiscs,"This work discusses the rich phase diagram of non-trivial chiral spin
textures in confined ferromagnetic/heavy-metal (FM/HM) bilayer nanomagnets of
circular cross-section. These spin textures are realized as a minimum-energy
ground state during an external bias field sweep for a range of nanomagnet's
diameter (d). Our study, based on micromagnetic simulations, has revealed a
novel Hopfion-like state which can be stabilized for a wide range of diameters
and external magnetic fields. We explored the dynamical characteristics of this
novel Hopfion-like state under a transient magnetic field applied along the
plane's perpendicular direction. Simulation results have demonstrated the
excitation of nonreciprocal spin wave (SW) modes for this novel chiral state,
in contrast to other stabilized chiral states. These modes are characterized as
breathing and quantized radial modes, which also exhibit hybridization with
azimuthal modes. The resonant SW modes have been used to demonstrate the
switching from a Hopfion-like state to a skyrmion within a few nanoseconds of
SW excitation. Furthermore, we establish a correlation between the behavior of
excited SW modes as a function of external magnetic field strength and
underlying chiral spin texture states.",2310.17460v1
2023-11-01,A complementary experimental study of epitaxial La0.67Sr0.33MnO3 to identify morphological and chemical disorder,"Gaining insight into the characteristics of epitaxial complex oxide films is
essential to control the behavior of devices and catalytic processes. It is
known that substrate induced strain, doping, and layer growth can affect the
electronic and magnetic properties of the film's bulk. In this study, we
demonstrate a clear distinction between the bulk and surface of thin films of
La0.67Sr0.33MnO3 in terms of chemical composition, electronic disorder, and
surface morphology. We employed a combined experimental approach of X-ray based
characterization methods and scanning probe microscopy. X-ray diffraction and
resonant X-ray reflectivity revealed surface non-stochiometry in the strontium
and lanthanum, as well as an accumulation of oxygen vacancies. Scanning
tunneling microscopy showed a staggered growth surface morphology accompanied
by an electronic phase separation (EPS) related to this non-stochiometry. The
EPS is likely responsible for the temperature-dependent resistivity transition
and is a cause of a proposed mixed-phase ferromagnetic and paramagnetic state
near room temperature in these thin films.",2311.00504v1
2023-11-10,Exchange stiffness proportional to power of magnetization in permalloy co-doped with Mo and Cu,"The exchange stiffness of magnetic materials is one of the essential
parameters governing magnetic texture and its dynamics in magnetic devices. The
effect of single-element doping on exchange stiffness has been investigated for
several doping elements for permalloy (NiFe alloy), a soft magnetic material
whose soft magnetic properties can be controlled by doping. However, the impact
of more practical multi-element doping on the exchange stiffness of permalloy
is unknown. This study investigates the typical magnetic properties, including
exchange stiffness, of permalloy systematically co-doped with Mo and Cu using
broadband ferromagnetic resonance spectroscopy. We find that the exchange
stiffness, which decreases with increasing doping levels, is proportional to a
power of magnetization, which also decreases with increasing doping levels. The
magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$,
of all the investigated samples, irrespective of the doping levels of each
element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with
exponent $n$ close to 2. This empirical power-law relationship provides a
guideline for predicting unknown exchange stiffness in non-magnetic
element-doped permalloy systems.",2311.05852v2
2023-11-15,Broad-Wavevector Spin Pumping of Flat-Band Magnons,"We report the experimental observation of large spin pumping signals in
YIG/Pt system driven by broad-wavevector spin-wave spin current. 280 nm-wide
microwave inductive antennas offer broad-wavevector excitation which, in
combination with quasi-flatband of YIG, allows a large number of magnons to
participate in spin pumping at a given frequency. Through comparison with
ferromagnetic resonance spin pumping, we attribute the enhancement of the spin
current to the multichromatic magnons. The high efficiency of spin current
generation enables us to uncover nontrivial propagating properties in ultra-low
power regions. Additionally, our study achieves the spatially separated
detection of magnons, allowing the direct extraction of the decay length. The
synergistic combination of the capability of broad-wavevector excitation,
enhanced voltage signals, and nonlocal detection provides a new avenue for the
electrical exploration of spin waves dynamics.",2311.09098v1
2023-11-23,Effect of multi-layering and crystal orientation on spin-orbit torque efficiency in Ni/Pt layer stacking,"We study spin-orbit torques (SOTs) in Ni/Pt bi-layers and multi-layers by
ferromagnetic resonance (FMR) and harmonic-Hall measurements. The effect of
multi-layering and crystal orientation on field-like (FL) and damping-like (DL)
torque efficiencies is examined by exploiting the samples with different
crystal orientations: epitaxial and poly-crystalline structures on Sapphire and
SiO$_2$ substrates, respectively.
  We find that both DL and FL torque efficiencies are larger in multi-layer
samples and there is no complete cancellation of torque efficiencies that is
generally expected for ideal symmetric stacking structures. The results of
SOT-FMR indicate that the epitaxial samples show higher efficiency for SOT
generation compared to the poly-crystalline samples, suggesting that SOT
generation is modified depending on the interfacial contribution. In addition,
the spin Hall conductivity of the epitaxial multi-layer is the largest among
the samples. The present results signify the importance of crystal orientation,
multi-layering and interface-quality in improving the efficiency of SOTs
generation combined with larger spin hall angle for developing future
spintronic devices.",2311.13835v1
2023-11-23,Exciting high-frequency short-wavelength spin waves using high harmonics of a magnonic cavity mode,"Confined spin-wave modes are a promising object for studying nonlinear
effects and future quantum technologies. Here, using micromagnetic simulations,
we use a microwave magnetic field from a coplanar waveguide (CPW) to pump a
standing spin-wave confined in the cavity of magnonic crystal. We find that the
frequency of the fundamental cavity mode is equal to the ferromagnetic
resonance frequency of the plane film and overlaps with the magnonic bandgap,
allowing high magnetic field tunability. Multi-frequency harmonics of the
cavity mode are generated once the microwave amplitude surpasses a certain
threshold. Specifically, the second and third harmonics at 0.5 T equate to 48.6
and 72.9 GHz with wavelengths of 44 and 22 nm respectively, which propagate
into the crystal. This effect reaches saturation when the CPW covers the entire
cavity, making the system feasible for realization. These processes show
potential for the advancement of magnonics at high-frequencies and very
short-wavelengths.",2311.14143v1
2023-12-05,THz-Driven Coherent Magnetization Dynamics in a Labyrinth Domain State,"Terahertz (THz) light pulses can be used for an ultrafast coherent
manipulation of the magnetization. Driving the magnetization at THz frequencies
is currently the fastest way of writing magnetic information in ferromagnets.
Using time-resolved resonant magnetic scattering, we gain new insights to the
THz-driven coherent magnetization dynamics on nanometer length scales. We
observe ultrafast demagnetization and coherent magnetization oscillations that
are governed by a time-dependent damping. This damping is determined by the
interplay of lattice heating and magnetic anisotropy reduction revealing an
upper speed limit for THz-induced magnetization switching. We show that in the
presence of nanometer-sized magnetic domains, the ultrafast magnetization
oscillations are associated with a correlated beating of the domain walls. The
overall domain structure thereby remains largely unaffected which highlights
the applicability of THz-induced switching on the nanoscale.",2312.02654v1
2023-12-21,Generation of femtosecond spin-polarized current pulses at Fe/MgO interface by quasi-static voltage,"The generation of short spin-current pulses is essential for fast spintronic
devices. So far, spin current pulses are generated by femtosecond laser pulses
which drive spins from a ferromagnetic metal layer. However, the need for
miniaturization, simplicity and energy efficiency favour electric-field control
of spintronic devices over optic or thermal control. Here, we combine ab initio
calculations of electronic density of states at MgO/Fe interface with
continuous model for charge transport to investigate the dynamics of the
spin-dependent potential. We demonstrate that the voltage-driven instability of
the electronic band structure due to the electronic resonant states at the
Fe/MgO interface results in the generation of the femtosecond spin-polarized
current pulse with the spin polarization up to P=700% that propagates from the
interface to the bulk. The dynamics of the current pulses driven by the Stoner
instability depends neither on the dielectric relaxation time nor on the
details of how the instability is achieved by changing the voltage, i.e. as
long as the voltage changes are slow (quasi-static) with respect to the time
determined by the spin diffusion constant, being of the order of fs.The
presence of the instability may be detected by transport or magnetic
measurements.",2312.13698v1
2024-01-30,"Magneto-synthesis effect on magnetic order, phonons, and magnons in single-crystal Sr$_2$IrO$_4$","It was shown earlier that applying a magnetic field during the growth of
Sr$_2$IrO$_4$, also known as ""field-alteration"", induces significant changes to
its structural, magnetic, and transport properties. However, the microscopic
nature of these changes is enigmatic. In this study, we employed resonant
elastic and inelastic x-ray scattering, as well as Raman scattering, to
investigate samples from two batches of Sr$_2$IrO$_4$ grown in magnetic fields
of different strengths. Our findings reveal that samples grown in a weaker
magnetic field have similar magnetic order to non-altered samples, whereas
those grown in a stronger field show a different stacking of weak in-plane
ferromagnetic moments. Additionally, we observed significant softening and
broadening of select Raman-active phonons in the field altered samples, with a
stronger effect in the samples grown in the stronger field. We discuss insights
that our results provide into the microscopic nature of field-alteration in
Sr$_2$IrO$_4$.",2401.17407v1
2024-02-22,Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface,"We investigate the structural and electronic origin of antiferromagnetic
coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at
the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in
samples prepared with surface ion milling, indicative of antiferromagnetic
exchange coupling at the YIG/Py interface. Using scanning transmission electron
microscopy (STEM), we highlight significant interfacial differences introduced
by ion-milling. The observations suggests that the antiferromagnetic coupling
in YIG/Py bilayers is predominantly driven by an oxygen-mediated super-exchange
coupling mechanism on the tetrahedral Fe terminated YIG surface, which is
supported by density functional theory (DFT) calculations. This research
provides critical insight into the fundamental mechanisms governing the
efficiency of coupling in magnetic bilayers and underscores the pivotal role of
oxide surface termination in modulating magnetic interfacial dynamics.",2402.14553v2
2024-02-26,Giant resonant skew scattering of plasma waves in graphene off a micromagnet,"Electron skew scattering by impurities is one of the major mechanisms behind
the anomalous Hall effect in ferromagnetic nanostructures. It is particularly
strong at the surface of topological insulators where the Dirac equation
governs electron dynamics. Motivated by recently discovered mappings between
hydrodynamics and spin-1 Dirac equations, we consider the scattering of plasma
waves -- propagating charge density oscillations -- excited in graphene off a
non-uniform magnetic field created by an adjacent circular micromagnet. The
calculated scattering amplitude not only exhibits a giant asymmetry, or
skewness, but is resonantly enhanced if the frequency of the incoming wave
matches the frequency of the trapped mode circulating the micromagnet in only
one direction. Furthermore, if the frequency of incoming waves exceeds the
Larmor frequency, the angular distribution of scattered plasma waves is
indistinguishable from the one of Dirac electrons at the surface of a
topological insulator scattering off a magnetic impurity. The micrometer scale
of the proposed setup enables direct investigations of individual skew
scattering events previously inaccessible in electronic systems.",2402.16263v1
2001-07-02,Microscopic theory of non local pair correlations in metallic F/S/F trilayers,"We consider a microscopic theory of F/S/F trilayers with metallic or
insulating ferromagnets. The trilayer with metallic ferromagnets is controlled
by the formation of non local pair correlations among the two ferromagnets
which do not exist with insulating ferromagnets. The difference between the
insulating and ferromagnetic models can be understood from lowest order
diagrams. Metallic ferromagnets are controlled by non local pair correlations
and the superconducting gap is larger if the ferromagnetic electrodes have a
parallel spin orientation. Insulating ferromagnets are controlled by pair
breaking and the superconducting gap is smaller if the ferromagnetic electrodes
have a parallel spin orientation. The same behavior is found in the presence of
disorder in the microscopic phase variables and also in the presence of a
partial spin polarization of the ferromagnets. The different behaviors of the
metallic and insulating trilayers may be probed in experiments.",0107038v3
2008-01-22,Quantum Oscillations of Tunnel Magnetoresistance Induced by Spin-Wave Excitations in Ferromagnet-Ferromagnet-Ferromagnet Double Barrier Tunnel Junctions,"The possibility of quantum oscillations of the tunnel conductance and
magnetoresistance induced by spin-wave excitations in a
ferromagnet-ferromagnet-ferromagnet double barrier tunnel junction, when the
magnetizations of the two side ferromagnets are aligned antiparallel to that of
the middle ferromagnet, is investigated in a self-consistent manner by means of
Keldysh nonequilibrium Green function method. It has been found that owing to
the s-d exchange interactions between conduction electrons and the spin density
induced by spin accumulation in the middle ferromagnet, the differential
conductance and the TMR indeed oscillate with the increase of bias voltage,
being consistent with the phenomenon that is observed recently in experiments.
The effects of magnon modes, the energy levels of electrons as well as the
molecular field in the central ferromagnet on the oscillatory transport
property of the system are also discussed.",0801.3350v1
2009-10-20,Enhancement of ferromagnetism by p-wave Cooper pairing in superconducting ferromagnets,"In superconducting ferromagnets for which the Curie temperature $T_{m}$
exceeds the superconducting transition temperature $T_{c}$, it was suggested
that ferromagnetic spin fluctuations could lead to superconductivity with
p-wave spin triplet Cooper pairing. Using the Stoner model of itinerant
ferromagnetism, we study the feedback effect of the p-wave superconductivity on
the ferromagnetism. Below $T_{c}$, the ferromagnetism is enhanced by the p-wave
superconductivity. At zero temperature, the critical Stoner value for itinerant
ferromagnetism is reduced by the strength of the p-wave pairing potential, and
the magnetization increases correspondingly. More important, our results
suggest that once Stoner ferromagnetism is established, $T_m$ is unlikely to
ever be below $T_c$. For strong and weak ferromagnetism, three and two peaks in
the temperature dependence of the specific heat are respectively predicted, the
upper peak in the latter case corresponding to a first-order transition.",0910.3873v1
2012-05-24,Ferromagnetic features on zero-bias conductance peaks in ferromagnet/insulator/superconductor junction,"We present a formula for tunneling conductance in ballistic
ferromagnet/ferromagnetic insulator/superconductor junctions where the
superconducting state has opposite spin pairing symmetry. The formula can
involve correctly a ferromagnetism has been induced by effective mass
difference between up- and down-spin electrons. Then, this effective mass
mismatch ferromagnet and standard Stoner ferromagnet have been employed in this
paper. As an application of the formulation, we have studied the tunneling
effect for junctions including spin-triplet p-wave superconductor. The
conductace spectra show a clear difference between two ferromagnets depending
upon the way of normalization of the conductance. Especially, a essential
difference is seen in zero-bias conductance peaks reflecting characteristics of
each ferromagnets. From obtained results, it will be suggested that the
measurements of the tunneling conductance in the junction provide us a useful
information about the mechanism of itinerant ferromagnetism in metal.",1205.5394v2
2003-11-19,Two-dimensional array of magnetic particles: The role of an interaction cutoff,"Based on theoretical results and simulations, in two-dimensional arrangements
of a dense dipolar particle system, there are two relevant local dipole
arrangements: (1) a ferromagnetic state with dipoles organized in a triangular
lattice, and (2) an anti-ferromagnetic state with dipoles organized in a square
lattice. In order to accelerate simulation algorithms we search for the
possibility of cutting off the interaction potential. Simulations on a dipolar
two-line system lead to the observation that the ferromagnetic state is much
more sensitive to the interaction cutoff $R$ than the corresponding
anti-ferromagnetic state. For $R \gtrsim 8$ (measured in particle diameters)
there is no substantial change in the energetical balance of the ferromagnetic
and anti-ferromagnetic state and the ferromagnetic state slightly dominates
over the anti-ferromagnetic state, while the situation is changed rapidly for
lower interaction cutoff values, leading to the disappearance of the
ferromagnetic ground state. We studied the effect of bending ferromagnetic and
anti-ferromagnetic two-line systems and we observed that the cutoff has a major
impact on the energetical balance of the ferromagnetic and anti-ferromagnetic
state for $R \lesssim 4$. Based on our results we argue that $R \approx 5$ is a
reasonable choice for dipole-dipole interaction cutoff in two-dimensional
dipolar hard sphere systems, if one is interested in local ordering.",0311462v1
2017-03-21,Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks,"We study how the shape of the spinwave resonance lines in rf-voltage induced
FMR can be used to extract the spinwave density of states and the damping
within the precessing layer in nanoscale tunnel junctions that possess
perpendicular anisotropy. We work with a field applied along the easy axis to
preserve the uniaxial symmetry of the system. We describe the set-up to study
the susceptibility contributions of the spin waves in the field-frequency
space. We then identify the maximum device size above which the spinwaves can
no longer be studied in isolation as the linewidths of their responses make
them overlap. The rf-voltage induced signal is the sum of two voltages that
have comparable magnitudes: a first voltage that originates from the transverse
susceptibility and rectification by magnetoresistance and a second voltage that
arises from the non-linear longitudinal susceptibility and the resultant
time-averaged change of the micromagnetic configuration. The transverse and
longitudinal susceptibility signals have different dc bias dependences such
that they can be separated by measuring how the device rectifies the rf voltage
at different dc bias voltages. The transverse and longitudinal susceptibility
signals have different lineshapes; their joint studies can yield the Gilbert
damping of the free layer of the device with a degree of confidence that
compares well with standard FMR. Our method is illustrated on FeCoB-based free
layers in which the individual spin-waves can be sufficiently resolved only for
disk diameters below 200 nm. The resonance line shapes on devices with 90 nm
diameters are consistent with a Gilbert damping of 0.011. This damping of 0.011
exceeds the value of 0.008 measured on the unpatterned films, which indicates
that device-level measurements are needed for a correct evaluation of
dissipation.",1703.07310v2
2018-12-20,Nuclear magnetic resonance investigation of the heavy fermion system Ce$_2$CoAl$_7$Ge$_4$,"We present nuclear magnetic resonance (NMR) and nuclear quadrupole resonance
(NQR) measurements performed on single crystalline \ccag{}, a member of a
recently discovered family of heavy fermion materials Ce$_2M$Al$_7$Ge$_4$ ($M$
= Co, Ir, Ni, or Pd). Previous measurements indicated a strong Kondo
interaction as well as magnetic order below $T_M = 1.8$ K. Our NMR spectral
measurements show that the Knight shift $K$ is proportional to the bulk
magnetic susceptibility $\chi$ at high temperatures. A clear Knight shift
anomaly ($K \not\propto \chi$) is observed at coherence temperatures $T^* \sim
17.5$ K for $H_0 \parallel \hat{c}$ and 10 K for $H_0 \parallel \hat{a}$ at the
${}^{59}$Co site, and $T^* \sim 12.5$ K at the ${}^{27}$Al(3) site for $H_0
\parallel \hat{a}$ characteristic of the heavy fermion nature of this compound.
At high temperatures the ${}^{59}$Co NMR spin-lattice relaxation rate
$T_1^{-1}$ is dominated by spin fluctuations of the 4$f$ local moments with a
weak metallic background. The spin fluctuations probed by ${}^{59}$Co NMR are
anisotropic and larger in the basal plane than in the $c$ direction.
Furthermore, we find $(T_1TK)^{-1} \propto T^{-1/2}$ at the ${}^{59}$Co site as
expected for a Kondo system for $T > T^*$ and $T> T_K$. ${}^{59}$Co NQR \slrr{}
measurements at low temperatures indicate slowing down of spin fluctuations
above the magnetic ordering temperature $T_M \sim 1.8$ K. A weak ferromagnetic
character of fluctuations around $\mathbf{q}=0$ is evidenced by an increase of
$\chi T$ versus $T$ above the magnetic ordering temperature. We also find good
agreement between the observed and calculated electric field gradients at all
observed sites.",1812.08633v1
2022-06-25,Static and dynamic magnetization control of extrinsic multiferroics by the converse magneto-photostrictive effect,"In this work, photostrictive manipulations of static and dynamic magnetic
properties are demonstrated in an extrinsic multiferroic composite. The
photostriction is achieved with visible light in the blue region of the
spectrum. The composites consist of 5 nm or 10 nm magnetostrictive
Fe$_{81}$Ga$_{19}$ thin films coupled to a piezoelectric
(011)-Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$-Pb(Zr,Ti)O$_3$ substrate. Angular dependent
magnetization reversals properties are largely enhanced or reduced under a
converse magneto-photostrictive effect (CMPE). The CMPE strength is analysed
with a novel coefficient named the converse magneto-photostrictive coupling
coefficient. This coefficient is proposed as a general approach to analyse and
to compare different extrinsic multiferroics under the converse
magneto-photostrictive effect. Its thickness dependence reveals that the CMPE
strength decreases with an increase of the Fe$_{81}$Ga$_{19}$ thickness.
Experimental evidence for a control of dynamic magnetic properties under CMPE
is then revealed by ferromagnetic resonance measurements. Resonant fields are
shifted under CMPE, whereas their linewidths remain constant. Furthermore,
resonant field shifts can be either positive or negative depending on the
in-plane angle. The largest shift under CMPE of +5.7 % is obtained for the 5 nm
sample. Our study shows that the CMPE provides an efficient approach for a
control of not only the static but also the dynamic magnetic properties in
extrinsic multiferroics.",2206.12703v3
2023-03-05,"Low temperature Terahertz Spectroscopy of LaFeO$_3$, PrFeO$_3$, ErFeO$_3$, and LuFeO$_3$: Quasimagnon resonances and ground multiplet transitions","We report on zone center THz excitations of non-Jahn Teller LaFeO$_3$,
PrFeO$_3$, ErFeO$_3$, and LuFeO$_3$ distorted perovskites under external
magnetic fields up 7 T. Low temperature-low energy absorptions of LaFeO$_3$
show antiferromagnetic and ferromagnetic quasimagnons at $\omega$AFM ~31.4 and
$\omega$FM ~26.7 cm$^{-1}$ in the $\Gamma$4 (Gx, Ay, Fz) representation.
LuFeO$_3$ is characterized by zero field magnetic resonances at $\omega$AFM
~26.3 cm$^{-1}$ and $\omega$FM ~22.4 cm$^{-1}$ in addition to Fe$^{3+}$
Zeeman-split crystal field (CF) 6A$_1$ ground transitions at ~10.4 cm$^{-1}$
triggered by structural deviations induced by smaller Lu 4f$^{14}$. This local
non-centrosymmetric departure is also found in ErFeO$_3$ (Kramers 4f$^{11}$
Er$^{3+}$ (4I15/2); {\Gamma}2 (Fx, Cy, Gz) <TSR ~93 K), but with the ~4
cm$^{-1}$ Fe$^{3+}$ Zeeman branching strongly biased toward higher energies.
Quasimagnons at $\omega$AFM ~31.5 cm$^{-1}$ and $\omega$FM ~21.5 cm$^{-1}$ in
ErFeO$_3$ do not undergo field induced band splits but a 13-fold increase in
the antiferro ($\omega$AMF) /ferro($\omega$AFM) intensity ratio. There is a
remarkable field-dependent CF matching population balance between Fe$^{3+}$
higher and Er$^{3+}$ lower Zeeman branches. Antiferro- and ferro- resonances in
PrFeO$_3$ turn much broader as non-Kramers Pr$^3$ introduces ligand changes at
the A site leading into near degeneracy the antiferromagnetic mode and the
lowest Pr$^{3+}$ CF transition. We conclude that low energy excitations in
RFeO$_3$ (R=rare earth) strongly depend on the lanthanide ionic size. Minute
lattice displacements also underlie considering non-centrosymmetric the most
distorted RFeO$_3$ (R=rare earth). Changes triggered by the smaller rare earth
and the nonlinear intrinsic oxygen ion polarizability provide grounds for
interplay of ionic and electronic interactions yielding ferroelectric
spontaneous polarization.",2303.02786v2
2010-07-07,Magnetic Quantum Tunneling: Insights from Simple Molecule-Based Magnets,"This article takes a broad view of the understanding of magnetic bistability
and magnetic quantum tunneling in single-molecule magnets (SMMs), focusing on
three families of relatively simple, low-nuclearity transition metal clusters:
spin S = 4 Ni4, Mn(III)3 (S = 2 and 6) and Mn(III)6 (S = 4 and 12). The Mn(III)
complexes are related by the fact that they contain triangular Mn3 units in
which the exchange may be switched from antiferromagnetic to ferromagnetic
without significantly altering the coordination around the Mn(III) centers,
thereby leaving the single-ion physics more-or-less unaltered. This allows for
a detailed and systematic study of the way in which the individual-ion
anisotropies project onto the molecular spin ground state in otherwise
identical low- and high-spin molecules, thus providing unique insights into the
key factors that control the quantum dynamics of SMMs, namely: (i) the height
of the kinetic barrier to magnetization relaxation; and (ii) the transverse
interactions that cause tunneling through this barrier. Numerical calculations
are supported by an unprecedented experimental data set (17 different
compounds), including very detailed spectroscopic information obtained from
high-frequency electron paramagnetic resonance and low-temperature hysteresis
measurements. Diagonalization of the multi-spin Hamiltonian matrix is necessary
in order to fully capture the interplay between exchange and local anisotropy,
and the resultant spin-state mixing which ultimately gives rise to the
tunneling matrix elements in the high symmetry SMMs (ferromagnetic Mn3 and
Ni4). The simplicity (low-nuclearity, high-symmetry, weak disorder, etc..) of
the molecules highlighted in this study proves to be of crucial importance.",1007.1208v1
2015-07-14,Magnetization induced by odd-frequency spin-triplet Cooper pairs in a Josephson junction with metallic trilayers,"We theoretically study the magnetization inside a normal metal induced in an
s-wave superconductor/ferromagnetic metal/normal metal/ferromagnetic
metal/s-wave superconductor (S/F1/N/F2/S) Josephson junction. Using
quasiclassical Green's function method, we show that the magnetization becomes
finite inside N. The origin of this magnetization is due to odd-frequency
spin-triplet Cooper pairs formed by electrons of equal and opposite spins,
which are induced by proximity effect in the S/F1/N/F2/S junction. We find that
the magnetization M(d,q) in N can be decomposed into two parts,
M(d,q)=MI(d)+MII(d,q), where q is the superconducting phase difference between
two Ss and d is the thickness of N. MI(d) exists generally in S/F junctions,
while MII(d,q) carries all q dependence and represents the fingerprint of phase
coherence between two Ss in Josephson junctions. The q dependence thus allows
us to control the magnetization in N by tuning q for a fixed d. We show that
MI(d) weakly decreases with increasing d, while the q dependent magnetization
MII(d,q) rapidly decays with d. Moreover, we find that the time-averaged
magnetization <MII(d,q)> exhibits discontinuous peak at each resonance DC
voltage Vn=nhw_S/2e(n: integer) when DC voltage V as well as AC voltage v_ac(t)
with frequency w_S are both applied to the S/F1/N/F2/S junction. This is
because MII(d,q) oscillates generally in time t (AC magnetization) with
dq/dt=2e[V+v_ac(t)]/h and thus <MII(d,q)>=0, but can be converted into the
time-independent DC magnetization for DC voltage at Vn. We also discuss that
the magnetization induced in N can be measurably large in realistic systems.
Therefore, the measurement of the induced magnetization serves as an
alternative way to detect the phase coherence between two Ss in Josephson
junctions. Our results also provide a basic concept for tunable magnetization
in superconducting spintronics devices.",1507.03763v1
2016-02-04,Magnetic anisotropy in the frustrated spin chain compound $β$-TeVO$_4$,"Isotropic and anisotropic magnetic behavior of the frustrated spin chain
compound $\beta$-TeVO$_4$ is reported. Three magnetic transitions observed in
zero magnetic field are tracked in fields applied along different
crystallographic directions using magnetization, heat capacity, and
magnetostriction measurements. Qualitatively different temperature-field
diagrams are obtained below 10 T for the field applied along $a$ or $b$ and
along $c$, respectively. In contrast, a nearly isotropic high-field phase
emerges above 18 T and persists up to the saturation that occurs around 22.5 T.
Upon cooling in low fields, the transitions at $T_{\rm N1}$ and $T_{\rm N2}$
toward the spin-density-wave and stripe phases are of the second order, whereas
the transition at $T_{\rm N3}$ toward the helical state is of the first order
and entails a lattice component. Our microscopic analysis identifies frustrated
$J_1-J_2$ spin chains with a sizable antiferromagnetic interchain coupling in
the $bc$ plane and ferromagnetic couplings along the $a$ direction. The
competition between these ferromagnetic interchain couplings and the helical
order within the chain underlies the incommensurate order along the
$a$-direction, as observed experimentally. Although a helical state is
triggered by the competition between $J_1$ and $J_2$ within the chain, the
plane of the helix is not uniquely defined because of competing magnetic
anisotropies. Using high-resolution synchrotron diffraction and $^{125}$Te
nuclear magnetic resonance, we also demonstrate that the crystal structure of
$\beta$-TeVO$_4$ does not change down to 10 K, and the orbital state of
V$^{4+}$ is preserved.",1602.01632v2
2016-03-03,Thermodynamic conditions during growth determine the magnetic anisotropy in epitaxial thin-films of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$,"The suitability of a particular material for use in magnetic devices is
determined by the process of magnetization reversal/relaxation, which in turn
depends on the magnetic anisotropy. Therefore, designing new ways to control
magnetic anisotropy in technologically important materials is highly desirable.
Here we show that magnetic anisotropy of epitaxial thin-films of half-metallic
ferromagnet La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) is determined by the proximity
to thermodynamic equilibrium conditions during growth. We performed a series of
X-ray diffraction and ferromagnetic resonance (FMR) experiments in two
different sets of samples: the first corresponds to LSMO thin-films deposited
under tensile strain on (001) SrTiO$_{3}$ by Pulsed Laser Deposition (PLD; far
from thermodynamic equilibrium); the second were deposited by a slow Chemical
Solution Deposition (CSD) method, under quasi-equilibrium conditions. Thin
films prepared by PLD show a in-plane cubic anisotropy with an overimposed
uniaxial term. A large anisotropy constant perpendicular to the film plane was
also observed in these films. However, the uniaxial anisotropy is completely
suppressed in the CSD films. The out of plane anisotropy is also reduced,
resulting in a much stronger in plane cubic anisotropy in the chemically
synthesized films. This change is due to a different rotation pattern of
MnO$_{6}$ octahedra to accomodate epitaxial strain, which depends not only on
the amount of tensile stress imposed by the STO substrate, but also on the
growth conditions. Our results demonstrate that the nature and magnitude of the
magnetic anisotropy in LSMO can be tuned by the thermodynamic parameters during
thin-film deposition.",1603.01127v1
2017-08-22,Enhancement and sign change of magnetic correlations in a driven quantum many-body system,"Periodic driving can be used to coherently control the properties of a
many-body state and to realize new phases which are not accessible in static
systems. For example, exposing materials to intense laser pulses enables to
provoke metal-insulator transitions, control the magnetic order and induce
transient superconducting behaviour well above the static transition
temperature. However, pinning down the responsible mechanisms is often
difficult, since the response to irradiation is governed by complex many-body
dynamics. In contrast to static systems, where extensive calculations have been
performed to explain phenomena such as high-temperature superconductivity,
theoretical analyses of driven many-body Hamiltonians are more demanding and
new theoretical approaches have been inspired by the recent observations. Here,
we perform an experimental quantum simulation in a periodically modulated
hexagonal lattice and show that anti-ferromagnetic correlations in a fermionic
many-body system can be reduced or enhanced or even switched to ferromagnetic
correlations. We first demonstrate that in the high frequency regime, the
description of the many-body system by an effective Floquet-Hamiltonian with a
renormalized tunnelling energy remains valid, by comparing the results to
measurements in an equivalent static lattice. For near-resonant driving, the
enhancement and sign reversal of correlations is explained by a microscopic
model, in which the particle tunnelling and magnetic exchange energies can be
controlled independently. In combination with the observed sufficiently long
lifetime of correlations, Floquet engineering thus constitutes an alternative
route to experimentally investigate unconventional pairing in strongly
correlated systems.",1708.06751v3
2018-10-07,"Role of Spin, Phonon and Plasmon Dynamics on Ferromagnetism in Cr doped 3C-SiC","The defect induced magnetism has initiated a lot of interest in field of
spintronics. In this regard, SiC is a promising material because of its unique
properties under extreme conditions. Hence it will be very much interesting to
investigate the interaction between defects and itinerant carrier in doped SiC
for spintronics application. We report the structural stability and magnetic
interaction in Cr doped 3C-SiC synthesized by Thermal Plasma Technique. The EPR
spectrum of undoped 3C-SiC shows a sharp resonance line corresponding to
$g=2.00$ associated with the defects present in the system. Anomalous
temperature evolution tendency of the relative intensity of EPR spectra can be
attributed to magnetically correlated defects in the host matrix. For the first
time we report the detailed quantitative analysis of X-band and Q-band EPR
study in Cr doped 3C-SiC which reveals that Cr can be in multivalent state. The
non monotonous variation of Longitudinal Mode (LO) of the Raman spectra has
been explained based on the interaction between carriers and surface plasmon
using Longitudinal optical plasmon coupling model (LOPC). The carrier density
calculated by using LOPC fit with experimental data varies from
$1.8\times10^{15}$ to $4.2\times10^{17}$ cm$^{-3}$. Room temperature magnetic
measurements exhibit ferromagnetic behavior with non-zero coercivity for all
the samples up to 7 T field. We, for the first time, show the Curie temperature
to be above 760 K. Quantitative analysis of magnetic interaction validates the
applicability of Bound Magnetic Polaron Model (BMP) which probably arises from
the exchange interaction of Cr$^{3+}$ ions with related (Si, C) defects. The
polaron density estimated from the BMP fit agrees well with the carrier density
obtained from the line shape fitting of Raman spectra.",1810.03146v3
2017-11-14,"Growth, electrical, structural, and magnetic properties of half-Heusler CoTi$_{1-x}$Fe$_x$Sb","Epitaxial thin films of the substitutionally alloyed half-Heusler series
CoTi$_{1-x}$Fe$_x$Sb were grown by molecular beam epitaxy on InAlAs/InP(001)
substrates for concentrations 0.0$\leq$x$\leq$1.0. The influence of Fe on the
structural, electronic, and magnetic properties was studied and compared to
that expected from density functional theory. The films are epitaxial and
single crystalline, as measured by reflection high-energy electron diffraction
and X-ray diffraction. Using in-situ X-ray photoelectron spectroscopy, only
small changes in the valence band are detected for x$\leq$0.5. For films with
x$\geq$0.05, ferromagnetism is observed in SQUID magnetometry with a saturation
magnetization that scales linearly with Fe content. A dramatic decrease in the
magnetic moment per formula unit occurs when the Fe is substitutionally alloyed
on the Co site indicating a strong dependence on the magnetic moment with site
occupancy. A crossover from both in-plane and out-of-plane magnetic moments to
only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic
resonance indicates a transition from weak to strong interaction with a
reduction in inhomogeneous broadening as Fe content is increased.
Temperature-dependent transport reveals a semiconductor to metal transition
with thermally activated behavior for x$\leq$0.5. Anomalous Hall effect and
large negative magnetoresistance (up to -18.5% at 100 kOe for x=0.3) are
observed for higher Fe content films. Evidence of superparamagnetism for x=0.3
and x=0.2 suggests for moderate levels of Fe, demixing of the
CoTi$_{1-x}$Fe$_x$Sb films into Fe rich and Fe deficient regions may be
present. Atom probe tomography is used to examine the Fe distribution in a
x=0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe
atoms throughout the film, which is used to explain the observed magnetic and
electrical behavior.",1711.05320v1
2017-11-21,Determination of spin Hall effect and spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements,"Understanding the evolution of spin-orbit torque (SOT) with increasing
heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical
for the development of magnetic memory based on SOT. However, several
experiments have revealed an apparent discrepancy between damping enhancement
and damping-like SOT regarding their dependence on NM thickness. Here, using
linewidth and phase-resolved amplitude analysis of vector network analyzer
ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract
damping enhancement and both field-like and damping-like inverse SOT in
Ni$_{80}$Fe$_{20}$/Pt bilayers as a function of Pt thickness. By enforcing an
interpretation of the data which satisfies Onsager reciprocity, we find that
both the damping enhancement and damping-like inverse SOT can be described by a
single spin diffusion length ($\approx$ 4 nm), and that we can separate the
spin pumping and spin memory loss (SML) contributions to the total damping.
This analysis indicates that less than 40% of the angular momentum pumped by
FMR through the Ni$_{80}$Fe$_{20}$/Pt interface is transported as spin current
into the Pt. On account of the SML and corresponding reduction in total spin
current available for spin-charge transduction in the Pt, we determine the Pt
spin Hall conductivity ($\sigma_\mathrm{SH} = (2.36 \pm 0.04)\times10^6
\Omega^{-1} \mathrm{m}^{-1}$) and bulk spin Hall angle
($\theta_\mathrm{SH}=0.387 \pm0.008$) to be larger than commonly-cited values.
These results suggest that Pt can be an extremely useful source of SOT if the
FM/NM interface can be engineered to minimize SML. Lastly, we find that
self-consistent fitting of the damping and SOT data is best achieved by a model
with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such
that both the spin diffusion length and spin Hall conductivity are proportional
to the Pt charge conductivity.",1711.07654v2
2018-07-31,"Comparative study of methodologies to compute the intrinsic Gilbert damping: interrelations, validity and physical consequences","Relaxation effects are of primary importance in the description of magnetic
excitations, leading to a myriad of methods addressing the phenomenological
damping parameters. In this work, we consider several well-established forms of
calculating the intrinsic Gilbert damping within a unified theoretical
framework, mapping out their connections and the approximations required to
derive each formula. This scheme enables a direct comparison of the different
methods on the same footing and a consistent evaluation of their range of
validity. Most methods lead to very similar results for the bulk ferromagnets
Fe, Co and Ni, due to the low spin-orbit interaction strength and the absence
of the spin pumping mechanism. The effects of inhomogeneities, temperature and
other sources of finite electronic lifetime are often accounted for by an
empirical broadening of the electronic energy levels. We show that the
contribution to the damping introduced by this broadening is additive, and so
can be extracted by comparing the results of the calculations performed with
and without spin-orbit interaction. Starting from simulated ferromagnetic
resonance spectra based on the underlying electronic structure, we
unambiguously demonstrate that the damping parameter obtained within the
constant broadening approximation diverges for three-dimensional bulk magnets
in the clean limit, while it remains finite for monolayers. Our work puts into
perspective the several methods available to describe and compute the Gilbert
damping, building a solid foundation for future investigations of magnetic
relaxation effects in any kind of material.",1807.11808v3
2019-04-26,"Mixed magnetism, nanoscale electronic segregation and ubiquitous first order transitions in giant magnetocaloric MnFeSiP alloys detected by $^{55}$Mn NMR","We report on a study on a representative set of Fe$_{2}$P-based MnFePSi
samples by means of $^{55}$Mn NMR in both zero and applied magnetic field. The
first-order nature of the magnetic transition is demonstrated by truncated
order parameter curves with a large value of the local ordered moment at the
Curie point, even at compositions where the transition appears second order
from magnetic measurements. No weak ferromagnetic order could be detected at
Si-poor compositions showing the kinetic arrest phenomenon, but rather the
phase separation of fully ferromagnetic domains from volume fractions where Mn
spins are fluctuating. The more pronounced decrease of the ordered moment at
the $3f$ sites on approaching $T_C$, characteristic of the mixed magnetism of
these materials, is demonstrated to be driven by a vanishing spin density
rather than enhanced spin fluctuations at the $3f$ site. An upper limit of
0.03~$\mu_B$ is set for the fluctuating Mn moment at the $3f$ site by the
direct detection of a $^{55}$Mn NMR resonance peak in the Mn-rich samples above
$T_C$, showing nearly temperature-independent frequency shifts. A sharper
secondary peak observed at the same compositions reveals however the
disproportionation of a significant $3f$-Mn fraction with negligible hyperfine
couplings, which retains its diamagnetic character across the transition, down
to the lowest available temperatures. Such a diamagnetic fraction qualitatively
accounts for the reduced average $3f$ moment previously reported at large Mn
concentrations.",1904.11629v1
2019-12-16,Decay rates and decoherence of an interstitial two-level spin impurity in a ferromagnetic lattice,"The decay rate of an interstitial two-level spin impurity, located in the
center of a unit cell of an anisotropic ferromagnetic lattice subjected to an
external magnetic field is derived. The impurity is coupled to nearest-neighbor
spins through Heisenberg $XY$ interaction. By mapping the lattice spin
operators using the Holstein-Primakoff transformation, we establish the
similarity with the Fano-Anderson model at low temperatures, and we calculate
the retarded Green's function in one and two dimensions analytically for
arbitrary coupling strength. It is shown that the reduced density matrix of the
impurity satisfies an exact master equation in Lindblad form, from which the
decay rate and the Lamb shift are deduced. The evolution in time of the latter
together with the excited state occupation probability is investigated and its
dependence on the applied magnetic field is discussed. It is found that there
exists a critical resonance-like value of the magnetic field around which the
behavior of the decay rate and the density matrix changes drastically. The
Markovian decay law, as given by the Fermi golden rule, does not hold in the
weak-coupling regime unless the magnetic field is weak, typically less than the
critical value. The weak-coupling regime is further treated perturbatively up
to second order, and the obtained results are compared with the exact solution.
We also discuss the Zeno regime of the dynamics, where it is shown that at
short times, the effective decay rate is twice as small as the exact decay
rate, and that when the impurity energy lies outside the lattice continuum, the
measurement speeds up the decay of the survival probability.",1912.07556v3
2021-02-05,Inter-valence charge transfer and charge transport in the spinel ferrite ferromagnetic semiconductor Ru-doped CoFe$_2$O$_4$,"Inter-valence charge transfer (IVCT) is electron transfer between two metal
$M$ sites differing in oxidation states through a bridging ligand: $M^{n+1} +
M'^{m} \rightarrow M^{n} + M'^{m+1}$. It is considered that IVCT is related to
the hopping probability of electron (or the electron mobility) in solids. Since
controlling the conductivity of ferromagnetic semiconductors (FMSs) is a key
subject for the development of spintronic device applications, the manipulation
of the conductivity through IVCT may become a new approach of band engineering
in FMSs. In Ru-doped cobalt ferrite CoFe$_2$O$_4$ (CFO) that shows
ferrimagnetism and semiconducting transport properties, the reduction of the
electric resistivity is attributed to both the carrier doping caused by the Ru
substitution for Co and the increase of the carrier mobility due to
hybridization between the wide Ru $4d$ and the Fe $3d$ orbitals. The latter is
the so-called IVCT mechanism that is charge transfer between the mixed valence
Fe$^{2+}$/Fe$^{3+}$ states facilitated by bridging Ru $4d$ orbital: Fe$^{2+}$ +
Ru$^{4+}$ $\leftrightarrow$ Fe$^{3+}$ + Ru$^{3+}$. To elucidate the emergence
of the IVCT state, we have conducted x-ray absorption spectroscopy (XAS) and
resonant photoemission spectroscopy (RPES) measurements on non-doped CFO and
Co$_{0.5}$Ru$_{0.5}$Fe$_2$O$_4$ (CRFO) thin films. The observations of the XAS
and RPES spectra indicate that the presence of the mixed valence
Fe$^{2+}$/Fe$^{3+}$ state and the hybridization between the Fe $3d$ and Ru $4d$
states in the valence band. These results provide experimental evidence for the
IVCT state in CRFO, demonstrating a novel mechanism that controls the electron
mobility through hybridization between the $3d$ transition-metal cations with
intervening $4d$ states.",2102.03020v1
2021-02-17,Growth optimization of TaN for superconducting spintronics,"We have optimized the growth of superconducting TaN thin films on \ch{SiO2}
substrates via dc magnetron sputtering and extract a maximum superconducting
transition temperature of $T_{\mathrm{c}}=5$ K as well as a maximum critical
field $\mu_0H_{\mathrm{c2}}=(13.8\pm0.1)$ T. To investigate the impact of
spin-orbit interaction in superconductor/ferromagnet heterostructures, we then
analyze the magnetization dynamics of both normal state and superconducting
TaN/\ch{Ni80Fe20}(Permalloy, Py)-bilayers as a function of temperature using
broadband ferromagnetic resonance (bbFMR) spectroscopy. The phase sensitive
detection of the microwave transmission signal is used to quantitatively
extract the inverse current-induced torques of the bilayers. The results are
compared to our previous study on NbN/Py-bilayers. In the normal state of TaN,
we detect a positive damping-like current-induced torque $\sigma_{\mathrm{d}}$
from the inverse spin Hall effect (iSHE) and a small field-like torque
$\sigma_{\mathrm{f}}$ attributed to the inverse Rashba-Edelstein effect (iREE)
at the TaN/Py-interface. In the superconducting state of TaN, we detect a
negative $\sigma_{\mathrm{d}}$ attributed to the quasiparticle mediated inverse
spin Hall effect (QMiSHE) and the unexpected manifestation of a large positive
field-like $\sigma_{\mathrm{f}}$ of unknown origin matching our previous
results for NbN/Py-bilayers.",2102.09018v1
2021-03-24,Magnetism and Spin Dynamics in Room-Temperature van der Waals Magnet Fe$_5$GeTe$_2$,"Two-dimensional (2D) van der Waals (vdWs) materials have gathered a lot of
attention recently. However, the majority of these materials have Curie
temperatures that are well below room temperature, making it challenging to
incorporate them into device applications. In this work, we synthesized a
room-temperature vdW magnetic crystal Fe$_5$GeTe$_2$ with a Curie temperature
T$_c = 332$ K, and studied its magnetic properties by vibrating sample
magnetometry (VSM) and broadband ferromagnetic resonance (FMR) spectroscopy.
The experiments were performed with external magnetic fields applied along the
c-axis (H$\parallel$c) and the ab-plane (H$\parallel$ab), with temperatures
ranging from 300 K to 10 K. We have found a sizable Land\'e g-factor difference
between the H$\parallel$c and H$\parallel$ab cases. In both cases, the Land\'e
g-factor values deviated from g = 2. This indicates contribution of orbital
angular momentum to the magnetic moment. The FMR measurements reveal that
Fe$_5$GeTe$_2$ has a damping constant comparable to Permalloy. With reducing
temperature, the linewidth was broadened. Together with the VSM data, our
measurements indicate that Fe$_5$GeTe$_2$ transitions from ferromagnetic to
ferrimagnetic at lower temperatures. Our experiments highlight key information
regarding the magnetic state and spin scattering processes in Fe$_5$GeTe$_2$,
which promote the understanding of magnetism in Fe$_5$GeTe$_2$, leading to
implementations of Fe$_5$GeTe$_2$ based room-temperature spintronic devices.",2103.13433v2
2022-01-12,Intra-Atomic and Local Exchange Fields in the Van der Waals Magnet CrI3,"We report on a combined experimental and theoretical study on CrI3 single
crystals by employing the polarization dependence of resonant inelastic X-ray
scattering (RIXS). Our investigations reveal multiple Cr 3d orbital splitting
(dd excitations) as well as magnetic dichroism (MD) in the RIXS spectra which
is evidence of spin-flip in the dd excitation. Interestingly, the dd excitation
energies are similar on both sides of the ferromagnetic transition temperature,
TC of 61 K, although MD in RIXS is predominant at 0.4 tesla magnetic field
below TC. This demonstrates that the ferromagnetic superexchange interaction
that is responsible for the intra-atomic exchange field, is vanishingly small
compared to local exchange field that comes from exchange and correlation
interaction among the interacting Cr 3d orbitals. The investigation presented
here demonstrate that the electronic structure of bulk CrI3 is complex in the
sense that dynamical electron correlations are significant. The recorded RIXS
spectra reported here reveal clearly resolved Cr 3d intra-orbital dd
excitations that represent transitions between electronic levels that are
heavily influenced by multi-configuration effects. Our calculations employing
the crystal field TTmultiplet theory taking into account the Cr 3d
hybridization with the ligand valence states and the full multiplet structure
due to intra-atomic and crystal field interactions in Oh and D3d symmetry,
clearly reproduced the dichroic trend in experimental RIXS spectra.",2201.04400v1
2022-02-26,Investigation of metamagnetism and crystal-field splitting in pseudo-hexagonal CeRh$_3$Si$_2$,"CeRh$_3$Si$_2$ has been reported to exhibit metamagnetic transitions below
5~K, a giant crystal field splitting, and anisotropic magnetic properties from
single crystal magnetization and heat capacity measurements. Here we report
results of neutron and x-ray scattering studies of the magnetic structure and
crystal-field excitations to further understand the magnetism of this compound.
Inelastic neutron scattering (INS) and resonant inelastic x-ray scattering
(RIXS) reveal a $J_z$\,=\,1/2 groundstate for Ce when considering the
crystallographic $a$ direction as quantization axis, thus explaining the
anisotropy of the static susceptibility. Furthermore, we find a total splitting
of 78\,meV for the $J$\,=\,5/2 multiplet. The neutron diffraction study in zero
field reveals that on cooling from the paramagnetic state, the system first
orders at $T_{\text{N}_1}=4.7$\,K in a longitudinal spin density wave with
ordered Ce moments along the $b$-axis (i.e. the [0 1 0] crystal direction) and
an incommensurate propagation vector $\textbf{k}=(0,0.43,0$). Below the
lower-temperature transition $T_{\text{N}_2}=4.48$\,K, the propagation vector
locks to the commensurate value $\textbf{k}=(0,0.5,0)$, with a so-called
lock-in transition. Our neutron diffraction study in applied magnetic field
$H\parallel b$-axis shows a change in the commensurate propagation vector and
development of a ferromagnetic component at $H=3$\,kOe, followed by a series of
transitions before the fully field-induced ferromagnetic phase is reached at $H
= 7$\,kOe. This explains the nature of the steps previously reported in
field-dependent magnetization measurements. A very similar behaviour is also
observed for the $H\parallel$ [0 1 1] crystal direction.",2202.13195v1
2022-10-20,Ultrafast behavior of induced and intrinsic magnetic moments in CoFeB/Pt bilayers probed by element-specific measurements in the extreme ultraviolet spectral range,"The ultrafast and element-specific response of magnetic systems containing
ferromagnetic 3d transition metals and 4d/5d heavy metals is of interest both
from a fundamental as well as an applied research perspective. However, to date
no consensus about the main microscopic processes describing the interplay
between intrinsic 3d and induced 4d/5d magnetic moments upon femtosecond laser
excitation exist. In this work, we study the ultrafast response of CoFeB/Pt
bilayers by probing element-specific, core-to-valence band transitions in the
extreme ultraviolet spectral range using high harmonic radiation. We show that
the combination of magnetic scattering simulations and analysis of the energy-
and time-dependent magnetic asymmetries allows to accurately disentangle the
element-specific response in spite of overlapping Co and Fe M$_{2,3}$ as well
as Pt O$_{2,3}$ and N$_7$ resonances. We find a considerably smaller
demagnetization time constant as well as much larger demagnetization amplitudes
of the induced moment of Pt compared to the intrinsic moment of CoFeB. Our
results are in agreement with enhanced spin-flip probabilities due to the high
spin-orbit coupling localized at the heavy metal Pt, as well as with the
recently formulated hypothesis that a laser generated, incoherent magnon
population within the ferromagnetic film leads to an overproportional reduction
of the induced magnetic moment of Pt.",2210.11390v3
2023-02-02,Spin waves in a ferromagnetic topological metal,"In most metals, charges and spins can hop rapidly between atoms, yielding
strong dispersion of their energy versus momentum. There are, however, special
arrangements of atoms, such as twisted graphene bilayers or lattices which
resemble woven bamboo ""kagome"" mats, so that particle motion with strong
hopping between neighbours becomes nearly or even completely dispersionless.
Such flat bands are interesting because the interactions between the heavy
particles inhabiting them will become much more important than for strong
dispersion, resulting in novel quantum solid and liquid states, particularly
when topology enters on account of significant spin-orbit coupling for the
underlying electrons. Nonetheless, spectroscopic evidence for flat bands
engendered by lattice geometry rather than weak hopping is rare, particularly
for metallic single crystals. Here we report the discovery, using circularly
polarized X-Rays in resonant absorption and inelastic scattering (RIXS) for the
unambiguous isolation of magnetic signals, of a flat spin wave band and large
orbital moment for the metallic kagome ferromagnet Fe$_3$Sn$_2$, which has a
topologically non-trivial electronic band structure controllable by modest
external magnetic fields. The flat mode energy is consistent with the high
Curie temperature ($T_C$ ~ 640 K) as well as the strong acoustic mode
dispersion, implying, together with the substantial spin-orbit coupling
indicated by the large orbital moment, that the mode is topological. The
measured properties of the spin waves are highly unconventional, and include
very severe damping as well as the flat mode amplitude which is maximized in
the long wavelength limit where it is ordinarily expected to vanish. Our
results open the topic of interactions of topological bosons (spin waves) and
fermions (electrons) with the very specific target of explaining boson
lifetimes and amplitudes.",2302.01457v1
2023-05-05,Spin-phonon scattering-induced low thermal conductivity in a van der Waals layered ferromagnet Cr$_2$Si$_2$Te$_6$,"Layered van der Waals (vdW) magnets are prominent playgrounds for developing
magnetoelectric, magneto-optic and spintronic devices. In spintronics,
particularly in spincaloritronic applications, low thermal conductivity
($\kappa$) is highly desired. Here, by combining thermal transport measurements
with density functional theory calculations, we demonstrate low $\kappa$ down
to 1 W m$^{-1}$ K$^{-1}$ in a typical vdW ferromagnet Cr$_2$Si$_2$Te$_6$. In
the paramagnetic state, development of magnetic fluctuations way above
$T_\mathrm{c}=$ 33 K strongly reduces $\kappa$ via spin-phonon scattering,
leading to low $\kappa \sim$ 1 W m$^{-1}$ K$^{-1}$ over a wide temperature
range, in comparable to that of amorphous silica. In the magnetically ordered
state, emergence of resonant magnon-phonon scattering limits $\kappa$ below
$\sim$ 2 W m$^{-1}$ K$^{-1}$, which would be three times larger if magnetic
scatterings were absent. Application of magnetic fields strongly suppresses the
spin-phonon scattering, giving rise to large enhancements of $\kappa$. Our
calculations well capture these complex behaviours of $\kappa$ by taking the
temperature- and magnetic-field-dependent spin-phonon scattering into account.
Realization of low $\kappa$ which is easily tunable by magnetic fields in
Cr$_2$Si$_2$Te$_6$, may further promote spincaloritronic applications of vdW
magnets. Our theoretical approach may also provide a generic understanding of
spin-phonon scattering, which appears to play important roles in various
systems.",2305.13268v1
2023-08-05,Modulating Spin Current Induced Effective Damping in $β-W/Py$ Heterostructures by a Systematic Variation in Resistivity of the Sputtered Deposited $β-W$ films,"Utilizing the spin-induced pumping from a ferromagnet (FM) into a heavy metal
(HM) under the ferromagnetic resonance (FMR) condition, we report an
enhancement in effective damping in $\beta$- W/Py bilayers by systematically
varying resistivity ($\rho_{W}$) of $\beta$-W films. Different resistivity
ranging from 100 $\mu\Omega$-cm to 1400 $\mu\Omega$-cm with a thickness of 8 nm
can be achieved by varying the argon pressure ($P_{Ar}$) during the growth by
the method of sputtering. The coefficient of effective damping $\alpha_{eff}$
is observed to increase from 0.010 to 0.025 with $\rho_{W}$, which can be
modulated by $P_{Ar}$. We observe a modest dependence of $\alpha_{eff}$ on the
sputtering power ($p_{S}$) while keeping the $P_{Ar}$ constant. $\alpha_{eff}$
dependence on both $P_{Ar}$ and $p_{S}$ suggests that there exists a strong
correlation between $\alpha_{eff}$ and $\rho_{W}$. It is thus possible to
utilize $\rho_{W}$ as a tuning parameter to regulate the $\alpha_{eff}$, which
can be advantageous for faster magnetization dynamics switching. The thickness
dependence study of Py in the aforementioned bilayers manifests a higher spin
mixing conductance ($g^{\uparrow\downarrow}_{eff}$) which suggests a strong
spin pumping from Py into the $\beta$-W layer. The effective spin current
($J_{S(eff)}$) is also evaluated by considering the spin-back flow in this
process. Intrinsic spin mixing conductance ($g^{\uparrow\downarrow}_{W}$) and
spin diffusion length ($\lambda_{SD}$) of $\beta$-W are additionally
investigated using thickness variations in $\beta$-W. Furthermore, the
low-temperature study in $\beta$-W/Py reveals an intriguing temperature
dependence in $\alpha_{eff}$ which is quite different from $\alpha_{b}$ of
single Py layer and the enhancement in $\alpha_{eff}$ at low temperature can be
attributed to the spin-induced pumping from Py layer into $\beta$-W.",2308.02939v1
2023-08-18,Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films,"Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high
Curie temperature (TC) and sizeable spin polarization have emerged as potential
candidates for tunable spintronic applications. We report comprehensive
investigation of the temperature dependent ANE and intrinsic longitudinal spin
Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our
findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm)
film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders
of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (=
0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa
thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our
MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $\mu$V/K/$\Omega$ at
room temperature which is twice larger than that of the half-metallic
ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5
$\mu$V/K/$\Omega$). We show that both ANE and LSSE coefficients follow
identical temperature dependences and exhibit a maximum at $\cong$ 225 K which
is understood as the combined effects of inelastic magnon scatterings and
reduced magnon population at low temperatures. Our analyses not only indicate
that the extrinsic skew scattering is the dominating mechanism for ANE in these
films but also provide critical insights into the functional form of the
observed temperature dependent LSSE at low temperatures. Furthermore, by
employing radio frequency transverse susceptibility and broadband ferromagnetic
resonance in combination with the LSSE measurements, we establish a correlation
among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the
CoFeCrGa thin films, which will be beneficial for fabricating tunable and
highly efficient Heusler alloys based spincaloritronic nanodevices.",2308.09843v1
2024-03-28,"Kitaev Interactions Through an Extended Superexchange Pathway in the jeff = 1/2 Ru3+ Honeycomb Magnet, RuP3SiO11","Magnetic materials are composed of the simple building blocks of magnetic
moments on a crystal lattice that interact via short-range magnetic exchange
interactions. Yet from these simple building blocks emerges a remarkable
diversity of magnetic states. Some of these, such as ferromagnetism, are
familiar in our everyday lives, while others reveal the deep quantum mechanical
origins of magnetism. A prime example of the latter are quantum spin liquid
(QSL) states in which -- unlike in a ferromagnet where magnetic moments are
driven by their exchange interactions to adopt long-range order -- magnetic
moments remain disordered at low temperatures but are simultaneously correlated
over long length scales through quantum entanglement. A particularly promising
theoretical model of a QSL is the Kitaev model, composed of unusual
bond-dependent exchange interactions between magnetic moments on a honeycomb
lattice. However, the Kitaev QSL is extremely challenging to realise
experimentally as it is unstable to competing exchange interactions and crystal
lattice perturbations that inevitably arise in real materials. This makes it
essential to understand the relationship between the structure and interactions
that may give rise to Kitaev interactions in new candidate materials. Here we
show that the material requirements for the Kitaev QSL survive for an extended
pseudo-edge-sharing superexchange pathway of Ru3+ 4d5 octahedra within the
honeycomb layers of the inorganic framework solid, RuP3SiO11. Through materials
synthesis and structural characterisation, resonant inelastic X-ray and neutron
scattering experiments, we confirm the requisite jeff = 1/2 state of Ru3+ in
RuP3SiO11 and resolve the hierarchy of exchange interactions that provide
experimental access to an otherwise unexplored region of the extended Kitaev
phase diagram.",2403.19406v1
1997-06-06,Hole doping and weak quenched disorder effects on the 1D Kondo lattice for ferromagnetic Kondo couplings,"We investigate the one-dimensional Kondo lattice model (1D KLM) for
ferromagnetic Kondo couplings, by using the bosonization method. The
ferromagnet ic 2-leg spin ladder and the S=1 antiferromagnet occur as new
one-dimensional Kondo insulators, for a half-filled band. First,a very small
hole-doping makes the charge sector massless and it can produce, either an
incommensurate RKKY interaction or a S=1 ferromagnet according to the strength
of the ferromagnetic Kondo coupling. Second, we investigate, the effects of a
weak and quenched disorder on these two Kondo insulators, by applying
renormalization group methods: the Anderson localization is suppressed only in
the context of a strong ferromagnetic Kondo coupling.",9706068v1
1999-07-13,Interface resistance in ferromagnet/superconductor junctions,"Results of theoretical study of spin-polarized tunneling in
ferromagnet/superconductor junctions are presented. Spin and charge currents
are calculated as a function of applied voltage and spin polarization in a
ferromagnet. The model takes into account the splitting of different spin
subbands in a ferromagnet and impurity scattering in the contact. The excess
resistance of an FS contact due to the charge-imbalance in a superconductor is
calculated for the first time. The results have implications for spin-coupled
magnetoresistance in ferromagnet/superconductor contacts and for measuring spin
polarization in ferromagnets.",9907194v1
2000-07-27,Mesoscopic Ferromagnet/Superconductor Junctions and the Proximity Effect,"We have measured the electrical transport of submicron ferromagnets (Ni) in
contact with a mesoscopic superconductor (Al) for a range of interface
resistances. In the geometry measured, the interface and the ferromagnet are
measured separately. The ferromagnet itself shows no appreciable
superconducting proximity effect, but the ferromagnet/superconductor interface
exhibits strong temperature, field and current bias dependences. These effects
are dependent on the local magnetic field distribution near the interface
arising from the ferromagnet. We find that the temperature dependences may be
fit to a modified version of the Blonder-Tinkham-Klapwijk theory for
normal-superconductor transport.",0007433v1
2000-10-26,Magnon-assisted Andreev reflection in a ferromagnet-superconductor junction,"We study subgap transport in a ferromagnet-superconductor junction at low
temperature due to Andreev reflection. The mismatch of spin polarized current
in the ferromagnet and spinless current in the superconductor results in an
additional contact resistance which can be reduced by magnon emission in the
ferromagnet. Using the s-f model and focusing on half-metallic ferromagnets, we
calculate the corresponding nonlinear contribution to the current which is
asymmetric with respect to the sign of the bias voltage and is related to the
density of states of magnons in the ferromagnet.",0010421v1
2001-08-27,Gate-induced band ferromagnetism in an organic polymer,"We propose that a chain of five-membered rings (polyaminotriazole) should be
ferromagnetic with an appropriate doping that is envisaged to be feasible with
an FET structure. The ferromagnetism is confirmed by a spin density functional
calculation, which also shows that ferromagnetism survives the Peierls
instability. We explain the magnetism in terms of Mielke and Tasaki's flat-band
ferromagnetism with the Hubbard model. This opens a new possibility of band
ferromagnetism in purely organic polymers.",0108413v1
2002-01-18,Spin separation in digital ferromagnetic heterostructures,"In a study of the ferromagnetic phase of a multilayer digital ferromagnetic
semiconductor in the mean-field and effective-mass approximations, we find the
exchange interaction to have the dominant energy scale of the problem,
effectively controlling the spatial distribution of the carrier spins in the
digital ferromagnetic heterostructures. In the ferromagnetic phase, the
majority and minority carriers tend to be in different regions of the space
(spin separation). Hence, the charge distribution of carriers also changes
noticeably from the ferromagnetic to the paramagnetic phase. An example of a
design to exploit these phenomena is given.",0201326v1
2002-09-19,Thermodynamic properties of ferromagnetic/superconductor/ferromagnetic nanostructures,"The theoretical description of the thermodynamic properties of
ferromagnetic/superconductor/ferromagnetic (F/S/F) systems of nanoscopic scale
is proposed. Their superconducting characteristics strongly depend on the
mutual orientation of the ferromagnetic layers. In addition, depending on the
transparency of S/F interfaces, the superconducting critical temperature can
exhibit four different types of dependences on the thickness of the F-layer.
The obtained results permit to give some practical recommendations for the
spin-valve effect experimental observation. In this spin-valve sandwich, we
also expect a spontaneous transition from parallel to anti-parallel
ferromagnetic moment orientation, due to the gain in the superconducting
condensation energy.",0209466v1
2002-12-16,Odd triplet superconductivity in superconductor/ferromagnet multilayered structures,"We demonstrate that in multilayered superconductor-ferromagnet structures a
non-collinear alignment of the magnetizations of different ferromagnetic layers
generates a triplet superconducting condensate which is odd in frequency. This
triplet condensate coexists in the superconductors with the conventional
singlet one but decays very slowly in the ferromagnet, which should lead to a
large Josephson effect between the superconductors separated by the
ferromagnet. Depending on the mutual direction of the ferromagnetic moments the
Josephson coupling can be both of 0 and $\pi $ type.",0212348v3
2003-07-15,Electronic structures and ferromagnetism in transition metals codoped ZnO,"We have investigated electronic structures and magnetic properties of
potential ZnO based diluted magnetic semiconductors: (Fe, Co) and (Fe, Cu)
codoped ZnO. The origins of ferromagnetism are shown to be different between
two. (Fe, Co) codoped ZnO does not have a tendency of Fe-O-Co ferromagnetic
cluster formation, and so the double exchange mechanism will not be effective.
In contrast, (Fe, Cu) codoped ZnO has a tendency of the Fe-O-Cu ferromagnetic
cluster formation with the charge transfer between Fe and Cu, which would lead
to the ferromagnetism through the double-exchange mechanism. The ferromagnetic
and nearly half-metallic ground state is obtained for (Fe, Cu) codoped ZnO.",0307359v1
2003-11-14,Transport through ferromagnet/superconductor interfaces,"The differential resistance of submicron-size ferromagnet/superconductor
interface structures shows asymmetries as a function of the current through the
ferromagnet/superconductor interface. These asymmetries are a consequence of
spin-polarized electron transport from the ferromagnet to the superconductor,
coupled with the Zeeman-splitting of the superconducting quasiparticle density
of states. They are sensitive to the orientation of the magnetization of the
ferromagnet, as the magnetic field required to spin-split the quasiparticle
density of states can be provided by the ferromagnetic element itself.",0311334v2
2003-12-01,Microscopic theory of equilibrium properties of F/S/F trilayers with weak ferromagnets,"The aim of this paper is to explain the non monotonic temperature dependence
of the self-consistent superconducting gap of
ferromagnet/superconductor/ferromagnet (F/S/F) trilayers with weak ferromagnets
in the parallel alignment (equivalent to F/S bilayers). We show that this is
due to Andreev bound states that compete with the formation of a minigap. Using
a recursive algorithm we discuss in detail the roles of various parameters
(thicknesses of the superconductor and ferromagnets, relative spin orientation
of the ferromagnets, exchange field, temperature, disorder, interface
transparencies).",0312029v2
2004-08-19,Quantum Phase Transitions in the Itinerant Ferromagnet ZrZn$_2$,"We report a study of the ferromagnetism of ZrZn$_{2}$, the most promising
material to exhibit ferromagnetic quantum criticality, at low temperatures $T$
as function of pressure $p$. We find that the ordered ferromagnetic moment
disappears discontinuously at $p_c$=16.5 kbar. Thus a tricritical point
separates a line of first order ferromagnetic transitions from second order
(continuous) transitions at higher temperature. We also identify two lines of
transitions of the magnetisation isotherms up to 12 T in the $p-T$ plane where
the derivative of the magnetization changes rapidly. These quantum phase
transitions (QPT) establish a high sensitivity to local minima in the free
energy in ZrZn$_{2}$, thus strongly suggesting that QPT in itinerant
ferromagnets are always first order.",0408424v1
2005-04-21,Magnetic semiconductor artificial atom with many particles: Thomas-Fermi model and ferromagnetic phases,"Many-particle electron states in semiconductor quantum dots with
carrier-mediated ferromagnetism are studied theoretically within the
self-consistent Boltzmann equation formalism. Depending on the conditions, a
quantum dot may contain there phases: partially spin-polarized ferromagnetic,
fully spin-polarized ferromagnetic, and paramagnetic phases. The physical
properties of many-body ferromagnetic confined systems come from the competing
carrier-mediated ferromagnetic and Coulomb interactions. The magnetic phases in
gated quantum dots with holes can be controlled by the voltage or via optical
methods.",0504559v2
2008-01-10,Controllable spin transport in ferromagnetic graphene junctions,"We study spin transport in normal/ferromagnetic/normal graphene junctions
where a gate electrode is attached to the ferromagnetic graphene. We find that
due to the exchange field of the ferromagnetic graphene, spin current through
the junctions has an oscillatory behavior with respect to the chemical
potential in the ferromagnetic graphene, which can be tuned by the gate
voltage. Especially, we obtain a controllable spin current reversal by the gate
voltage. Our prediction of high controllability of spin transport in
ferromagnetic graphene junction may contribute to the development of the
spintronics.",0801.1552v2
2008-03-31,Optical Orientation in Ferromagnet/Semiconductor Hybrids,"The physics of optical pumping of semiconductor electrons in the
ferromagnet/semiconductor hybrids is discussed. Optically oriented
semiconductor electrons detect the magnetic state of the ferromagnetic film. In
turn, the ferromagnetism of the hybrid can be controlled optically with the
help of the semiconductor. Spin-spin interactions near the interface
ferromagnet/semiconductor play crucial role in the optical readout and the
manipulation of ferromagnetism.",0803.4401v1
2009-06-01,Current-voltage characteristics of tunable ferromagnet-silicon-ferromagnet channels in the spin blockade regime,"The steady current-voltage characteristics of ferromagnet-silicon-ferromagnet
channels with tunable emitter and collector polarizations are investigated in
the presence of spin blockade generalizing the model developed by Pershin Yu V
and Di Ventra M (2008 {\it Phys. Rev.} B {\bf 77} 073301). The dependence of
the critical current on both collector and emitter polarizations is obtained
analytically. It is found that the current amplitude in the channel can be
effectively tuned by varying the difference between the collector and emitter
ferromagnet polarizations which allows to perform the magnetic manipulation of
the electrical current in wide class of both n- and p-doped, low- and
high-Ohmic semiconductor channels coupled to ferromagnetic leads.",0906.0246v1
2009-09-27,Correlated versus Ferromagnetic State in Repulsively Interacting Two-Component Fermi Gases,"Whether a spin-1/2 Fermi gas will become ferromagnetic as the strength of
repulsive interaction increases is a long-standing controversial issue.
Recently this problem is studied experimentally by Jo et al, Science, 325, 1521
(2009) in which the authors claim a ferromagnetic transition is observed. This
work is to point out the results of this experiment can not distinguish whether
the system is in a ferromagnetic state or in a non-magnetic but strongly
short-range correlated state. A conclusive experimental demonstration of
ferromagnetism relies on the observation of ferromagnetic domains.",0909.4917v2
2013-02-13,Theory of ferromagnetism in vanadium-oxide based perovskites,"The conditions under which ferromagnetism may occur in transition metal
oxides with partially filled $t_{2g}$ shells such as vanadium-based perovskites
are studied using a combination of density functional and single-site dynamical
mean field methods. For reasonable values of the correlation strength,
rotations of the VO$_6$ octahedra play an important role in enabling
ferromagnetism, with ferromagnetism typically occurring for rotations larger
than a nonzero critical value. Ferromagnetism is suppressed near the Mott
insulating phase but the phase boundary is otherwise only weakly dependent on
carrier concentration. Design rules are suggested for new oxide systems
exhibiting ferromagnetism.",1302.3062v2
2014-07-18,Local characterization of ferromagnetic properties in ferromagnet/superconductor bilayer by Point Contact Andreev Reflection Spectroscopy,"We realized point contact spectroscopy experiment on
ferromagnet/superconductor bilayers. Differential conductance curves show
several features that we explained within Bogoliubov-de Gennes formalism
considering the presence of two interfaces in the
normal-metal-tip/ferromagnet/superconductor device. We demonstrate that such
configuration is suitable as local probe of the spin polarization and thickness
of ferromagnetic layer, directly on bilayer areas. This is due to the high
sensitivity of the Andreev surface states to the physical properties of the
ferromagnetic interlayer.",1407.4906v1
2011-11-08,Unusual ferromagnetism in nanoparticles of doped oxides and manganites,"The observation of unusually large ferromagnetism in the nanoparticles of
doped oxides and enhanced ferromagnetic tendencies in manganite nanoparticles
have been in focus recently. For the transition metal-doped oxide nanoparticles
a phenomenological `charge transfer ferromagnetism' model is recently proposed
by Coey et al. From a microscopic calculation with charge transfer between the
defect band and mixed valent dopants, acting as reservoir, we show how the
unusually high ferromagnetic response develops. The puzzle of nanosize-induced
ferromagnetic tendencies in manganites is also addressed within the same
framework where lattice imperfections and uncompensated charges at the surface
of the nanoparticle are shown to reorganize the surface electronic structures
with enhanced double exchange.",1111.1778v1
2019-12-20,Magnetic field-controlled 0-$π$ transitions and their experimental signatures in superconductor-ferromagnet-superconductor junctions,"Superconductor-ferromagnet-superconductor Josephson junctions are known to
exist in the $0$ and $\pi$ states with the transitions between them controlled
by the temperature and ferromagnetic interlayer thickness. We demonstrate that
these transitions can be controlled also by the external magnetic field
directed perpendicular to the layers. By varying the ratio of diffusion
coefficients in superconducting and ferromagnetic layers, these
field-controlled transitions can be made detectable for arbitrary large value
of the exchange energy in the ferromagnet. We also show that the $0$-$\pi$
transitions in the perpendicular field can be observed as the specific features
of the flux-flow conductivity dependencies on the ferromagnetic thickness in
accordance with recent experimental results.",1912.10144v1
2021-04-16,Ferromagnetism in 2D Vanadium Diselenide,"Two-dimensional (2D) Van der Waals ferromagnets carry the promise of
ultimately miniature spintronics and information storage devices. Among the
newly discovered 2D ferromagnets all inherit the magnetic ordering from their
bulk ancestors. Here we report a new 2D ferromagnetic semiconductor at room
temperature, 2H phase vanadium diselenide (VSe2) which show ferromagnetic at 2D
form only. This unique 2D ferromagnetic semiconductor manifests an enhanced
magnetic ordering owing to structural anisotropy at 2D limit.",2104.07937v1
2021-11-30,Majorana Zero Modes in Ferromagnetic Wires without Spin-Orbit Coupling,"We present a novel controllable platform for engineering Majorana zero modes.
The platform consists of a ferromagnetic metallic wire placed among
conventional superconductors, which are in proximity to ferromagnetic
insulators. We demonstrate that Majorana zero modes emerge localised at the
edges of the ferromagnetic wire, due to the interplay of the applied
supercurrents and the induced by proximity exchange fields with conventional
superconductivity. Our mechanism does not rely on the pairing of helical
fermions by combining conventional superconductivity with spin-orbit coupling,
but rather exploits the misalignment between the magnetization of the
ferromagnetic insulators and that of the ferromagnetic wire.",2111.15260v1
2011-11-14,Fermi liquid theory and ferromagnetism,"There is demonstrated that an isotropic ferromagnetic Fermi liquid reveals
instability of the ferromagnetic state in respect to the transversal
inhomogeneous deviations of magnetization from equilibrium. The result was
obtained by derivation of the spin waves spectrum by means of kinetic equation.",1111.3208v2
2019-03-15,Novel critical behavior of magnetization in URhSi:Similarities to uranium ferromagnetic superconductors UGe$_2$ and URhGe,"We study the critical behavior of dc magnetization in the uranium ferromagnet
URhSi around the paramagnetic to ferromagnetic phase transition at T_C~ 10 K
with a modified Arrott plot, a Kouvel-Fisher plot, the critical isotherm
analysis and the scaling analysis. URhSi is isostructural to uranium
ferromagnetic superconductors URhGe and UCoGe. The critical exponent beta for
the temperature dependence of the spontaneous magnetization below TC, gamma for
the magnetic susceptibility, and delta for the magnetic isotherm at T_C in
URhSi have been determined as beta = 0.300 +- 0.002, gamma = 1.00 +- 0.02, and
delta = 4.38 +- 0.04 by the scaling analysis and the critical isotherm
analysis. These critical exponents fulfill the Widom scaling law delta = 1+
gamma/beta. Magnetization has strong uniaxial magnetic anisotropy in the
ferromagnetic state of URhSi. However, the universality class of the
ferromagnetic transition does not belong to the 3D Ising system with
short-range exchange interactions between magnetic moments (beta = 0.325, gamma
= 1.241, and delta = 4.82). The obtained exponents in URhSi are similar to
those in the uranium ferromagnetic superconductors UGe_2 and URhGe, and uranium
ferromagnets UIr and U(Co_0.98Os_0.02)Al. We have previously reported the
unconventional critical behavior of magnetization in the uranium ferromagnetic
superconductors [N. Tateiwa et al. Phys. Rev. B 89, 064420 (2014)]. The
universality class of the ferromagnetic transition in URhSi may belong to the
same one in the uranium ferromagnetic superconductors and the uranium
ferromagnets. The unconventional critical behavior of the magnetization in the
uranium compounds cannot be understood with previous theoretical
interpretations of critical phenomena. The absence of the superconductivity in
URhSi is discussed from several viewpoints.",1903.06841v1
2024-01-08,Ferromagnetic Materials for Josephson π Junctions,"The past two decades have seen an explosion of work on Josephson junctions
containing ferromagnetic materials. Such junctions are under consideration for
applications in digital superconducting logic and memory. In the presence of
the exchange field, spin-singlet Cooper pairs from conventional superconductors
undergo rapid oscillations in phase as they propagate through a ferromagnetic
material. As a result, the ground-state phase difference across a ferromagnetic
Josephson junction oscillates between 0 and $\pi$ as a function of the
thickness of the ferromagnetic material. $\pi$-junctions have been proposed as
circuit elements in superconducting digital logic and in certain qubit designs
for quantum computing. If a junction contains two or more ferromagnetic layers
whose relative magnetization directions can be controlled by a small applied
magnetic field, then the junction can serve as the foundation for a memory
cell. Success in all of those applications requires careful choices of
ferromagnetic materials. Often, materials that optimize magnetic properties do
not optimize supercurrent propagation, and vice versa. In this review we
discuss the significant progress that has been made in identifying and testing
a wide range of ferromagnetic materials in Josephson junctions over the past
two decades. The review concentrates on ferromagnetic metals, partly because
eventual industrial applications of ferromagnetic Josephson junctions will most
likely start with metallic ferromagnets (either in all metal junctions or
junctions containing also an insulating layer). We will briefly mention work on
non-metallic barriers, including ferromagnetic insulators, and some of the
exciting work on spin-triplet supercurrent in junctions containing noncollinear
magnetic inhomogeneity.",2401.04219v2
1997-07-03,Hund's-Rule Coupling Effect in Itinerant Ferromagnetism,"We present a general model which includes the ferromagnetic Kondo lattice and
the Hubbard model as special cases. The stability of the ferromagnetic state is
investigated variationally. We discuss the mechanism of ferromagnetism in
metallic nickel, emphasizing the importance of orbital degeneracy and the
effect of the Hund's-rule coupling.",9707032v1
1999-09-06,Mesoscopic mechanism of exchange interaction in magnetic multilayers,"We discuss a mesoscopic mechanism of exchange interaction in
ferromagnet-normal metal-ferromagnet multilayers. We show that in the case when
the metal's thickness is larger than the electron mean free path, the relative
orientation of magnetizations in the ferromagnets is perpendicular. The
exchange energy between ferromagnets decays with the metal thickness as a power
law.",9909064v1
2000-11-21,Spin and Orbital Order in Itinerant Ferromagnets,"The long-standing problem of the effect of correlations on the ferromagnetism
of is apparently nearing solution. The ferromagnetism of transition metals
compounds, for instance doped manganites, poses a new question: is there some
kind of orbital order coexisting with itinerant ferromagnetism? The ideas and
techniques introduced by Gutzwiller should be of use again.",0011354v1
2002-09-04,Theory of exchange coupling in disordered magnetic multilayers,"We consider mechanism of exchange coupling based on interaction between
electrons in nonmagnetic layer. Depending on ratio of inverse time of diffusion
of electrons between ferromagnetic layers and ferromagnetic splitting of
conducting electrons this mechanism describes transition from ferromagnetic to
noncollinear ordering of magnetizations of ferromagnetic layers.",0209084v1
2003-05-26,Homogeneous Phase of Coexistence of Spin-Triplet Superconductivity and Ferromagnetism,"The coexistence of a homogeneous (Meissner-like) phase of spin-triplet
superconductivity and ferromagnetism is investigated within the framework of a
phenomenological model of spin-triplet ferromagnetic superconductors. The
results are discussed in view of application to metallic ferromagnets as
UGe$_2$, ZrZn$_2$, URhGe, and Fe.",0305602v1
2003-07-18,Induced Ferromagnetism due to Superconductivity in Superconductor-Ferromagnet structures,"We consider a superconductor-ferromagnet (S/F) structure and assume that
above the superconducting transition temperature $T_{c}$ the magnetic moment
exists only in F. {In a simple model of the ferromagnet (the exchange field is
of the ferromagnetic type for all energies)}we show by an explicit calculation
that below $T_{c}$ the magnetic moment may penetrate the superconductor. {In
this model} its direction in S is opposite {to the magnetization of free
electrons} in the ferromagnet. The magnetization spreads over a large distance
which is of the order of the superconducting coherence length $\xi_{S}$ and can
much exceed the ferromagnet film thickness. At the same time the magnetic
moment in the ferromagnet is reduced. This inverse proximity effect may explain
the reduction in magnetization observed in recent experiments and may lead to a
strong interaction between the ferromagnetic layers in F/S/F structures.",0307468v3
2004-11-18,Density of states in spin-valve structure with superconducting electrodes,"Energy variation of the density of states (DOS) has been calculated in the
superconductor/ferromagnet/ferromagnet/superconductor structure (SFFS) in the
frame of Gorkov equations taking into account the s-d electron scattering in
the ferromagnetic layers. DOS behavior is presented for the antiparallel and
parallel magnetic moments alignment of two adjacent F layers. The cases of
small and large values of exchange ferromagnetic field are discussed.",0411470v1
2005-01-10,Domain wall effects in ferromagnet-superconductor structures,"We investigate how domain structure of the ferromagnet in
superconductor-ferromagnet heterostructures may change their transport
properties. We calculate the distribution of current in the superconductor
induced by magnetic field of Bloch domain walls, find the ``lower critical''
magnetization of the ferromagnet that provides vortices in the superconductor.",0501210v1
2007-08-16,Spin-transfer torques in anti-ferromagnetic metals from first principles,"In spite of the absence of a macroscopic magnetic moment, an anti-ferromagnet
is spin-polarized on an atomic scale. The electric current passing through a
conducting anti-ferromagnet is polarized as well, leading to spin-transfer
torques when the order parameter is textured, such as in anti-ferromagnetic
non-collinear spin valves and domain walls. We report a first principles study
on the electronic transport properties of anti-ferromagnetic systems. The
current-induced spin torques acting on the magnetic moments are comparable with
those in conventional ferromagnetic materials, leading to measurable angular
resistances and current-induced magnetization dynamics. In contrast to
ferromagnets, spin torques in anti-ferromagnets are very nonlocal. The torques
acting far away from the center of an anti-ferromagnetic domain wall should
facilitate current-induced domain wall motion.",0708.2143v2
2009-03-12,Magnetic screening properties of superconductor-ferromagnet bilayers,"We study theoretically the magnetic screening properties of thin, diffusive
superconductor/ferromagnet bilayers subject to a perpendicular magnetic field.
We find that the effective penetration depth characterizing the magnetic
response oscillates with the thickness of the ferromagnetic layer on the scale
of the ferromagnetic coherence length.",0903.2245v2
2010-02-12,Quantum Spin Tomography in Ferromagnet-Normal Conductors,"We present a theory for a complete reconstruction of non-local spin
correlations in ferromagnet-normal conductors. This quantum spin tomography is
based on cross correlation measurements of electric currents into ferromagnetic
terminals with controllable magnetization directions. For normal injectors,
non-local spin correlations are universal and strong. The correlations are
suppressed by spin-flip scattering and, for ferromagnetic injectors, by
increasing injector polarization.",1002.2499v1
2010-06-29,Ferromagnetic phase diagram of neutron matter,"The magnetic properties of matter under extreme conditions are of particular
importance to understanding the neutron star interior. One contributing factor
to the magnetic field of a neutron star could be the ferromagnetic phase of
nuclear matter. In this letter we present a self-consistent, relativistic
description of ferromagnetism in dense matter, within which the ferromagnetic
phase diagram for neutron matter is calculated.",1006.5564v1
2011-12-28,Current conservation and ratio rules in magnetic metals with Coulomb repulsion,"From general considerations of spin-symmetry breaking associated with
(anti-)ferromagnetism in metallic systems with Coulomb repulsion, we obtain
interesting and simple all-order rules involving the ratios of the densities of
states. These are exact for ferromagnetism under reasonable conditions, and
nearly exact for anti-ferromagnetism. In the case of ferromagnetism, the
comparison with the available experimental and theoretical numbers yields
favourable results.",1112.6036v1
2019-06-26,"Room-temperature insulating ferromagnetic (Ni,Co)1+2xTi1-xO3 thin films","Insulating uniaxial room-temperature ferromagnets are a prerequisite for
commonplace spin wave-based devices, the obstacle in contemporary ferromagnets
being the coupling of ferromagnetism with large conductivity. We show that the
uniaxial $A^{1+2x}$Ti$^{4+}$$_{1-x}$O$_3$ (ATO), $A=$Ni$^{2+}$,Co$^{2+}$ and
$0.6<x \leq 1$, thin films are electrically insulating ferromagnets already at
room-temperature. The octahedra network of the ATO and ilmenite structures are
similar yet different octahedra-filling proved to be a route to switch from the
antiferromagnetic to ferromagnetic regime. Octahedra can continuously be filled
up to $x=1$, or vacated $(-0.24<x<0)$ in the ATO structure. TiO-layers, which
separate the ferromagnetic (Ni,Co)O-layers and intermediate the
antiferromagnetic coupling between the ferromagnetic layers in the NiTiO$_3$
and CoTiO$_3$ ilmenites, can continuously be replaced by (Ni,Co)O-layers to
convert the ATO-films to ferromagnetic insulator with abundant direct cation
interactions.",1906.10974v2
2023-06-08,Highly spin-polarized carriers and strong ferromagnetism in doped perovskite antiferromagnetic semiconductors,"In semiconductor spintronics, the generation of highly spin-polarized
carriers and the efficient probe of spin order (due to strong ferromagnetism)
-- at or above room temperature -- are crucial because it allows for the design
of spin-based semiconductor devices. Usually, such goals were fulfilled in
room-temperature ferromagnetic semiconductors, being rare materials in nature.
While room-temperature antiferromagnetic semiconductors are plentiful, the
possibility for creating highly spin-polarized carriers and strong
ferromagnetism in these materials remain to be unraveled. Here, we explore such
a possibility by first-principles simulations, working with CaTcO$_3$ and
NaOsO$_3$ perovskites -- being room-temperature antiferromagnetic
semiconductors. We find that doping them by electrons or holes results in these
materials to be highly spin-polarized, carrying enormous ferromagnetic moments.
Doping electrons with moderate carrier density can yield strong ferromagnetism
in them, with the ferromagnetic moments being comparable to that in typical
ferromagnetic semiconductors. Our work thus indicates the merit of perovskite
antiferromagnetic semiconductors in spintronics -- for a possible replacement
of ferromagnetic semiconductors.",2306.05040v1
2001-03-09,Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-Tc Cuprates,"The pseudogap phenomena in High-$T_{{\rm c}}$ cuprates are investigated on
the basis of the Hubbard model which includes only the on-site repulsive
interaction $U$. We consider the pairing scenario for the pseudogap. The
pseudogap arises from the resonance scattering due to the strong
superconducting fluctuations.
  First, the electronic state and the anti-ferromagnetic spin fluctuations are
calculated by using the FLEX approximation. The T-matrix (the propagator of the
superconducting fluctuations) is calculated by extending the $\acute{{\rm
E}}$liashberg equation. The self-energy due to the superconducting fluctuations
is calculated by the T-matrix approximation. The pseudogap is shown in the
single particle properties and the magnetic properties by the microscopic
calculation. A comprehensive explanation of the doping dependence of the
pseudogap is obtained. Furthermore, we apply the theory to the electron-doped
cuprates and obtain the consistent results with the recent experiments.
Finally, the self-consistent calculation for the spin fluctuations,
superconducting fluctuations and the single particle properties are carried out
within the FLEX and the self-consistent T-matrix approximations. The calculated
superconducting critical temperature $T_{{\rm c}}$ is remarkably reduced from
the results of the mean field (FLEX) calculation. It is shown that the critical
temperature decreases with decreasing doping in the under-doped region with
large $U$.",0103214v1
2002-04-22,Role of dipolar and exchange interactions in the positions and widths of EPR transitions for the single-molecule magnets Fe8 and Mn12,"We examine quantitatively the temperature dependence of the linewidths and
line shifts in electron paramagnetic resonance experiments on single crystals
of the single-molecule magnets Fe$_8$ and Mn$_{12}$, at fixed frequency, with
an applied magnetic field along the easy axis. We include inter-molecular
spin-spin interactions (dipolar and exchange) and distributions in both the
uniaxial anisotropy parameter $D$ and the Land\'{e} $g$-factor. The temperature
dependence of the linewidths and the line shifts are mainly caused by the
spin-spin interactions. For Fe$_8$ and Mn$_{12}$, the temperature dependence of
the calculated line shifts and linewidths agrees well with the trends of the
experimental data. The linewidths for Fe$_8$ reveal a stronger temperature
dependence than those for Mn$_{12}$, because for Mn$_{12}$ a much wider
distribution in $D$ overshadows the temperature dependence of the spin-spin
interactions. For Fe$_8$, the line-shift analysis suggests two competing
interactions: a weak ferromagnetic exchange coupling between neighboring
molecules and a longer-ranged dipolar interaction. This result could have
implications for ordering in Fe$_8$ at low temperatures.",0204481v2
2002-10-07,Anisotropic Colossal Magnetoresistance Effects in Fe_{1-x}Cu_xCr_2S_4,"A detailed study of the electronic transport and magnetic properties of
Fe$_{1-x}$Cu$_x$Cr$_2$S$_4$ ($x \leq 0.5$) on single crystals is presented. The
resistivity is investigated for $2 \leq T \leq 300$ K in magnetic fields up to
14 Tesla and under hydrostatic pressure up to 16 kbar. In addition
magnetization and ferromagnetic resonance (FMR) measurements were performed.
FMR and magnetization data reveal a pronounced magnetic anisotropy, which
develops below the Curie temperature, $T_{\mathrm{C}}$, and increases strongly
towards lower temperatures. Increasing the Cu concentration reduces this
effect. At temperatures below 35 K the magnetoresistance, $MR = \frac{\rho(0) -
\rho(H)}{\rho(0)}$, exhibits a strong dependence on the direction of the
magnetic field, probably due to an enhanced anisotropy. Applying the field
along the hard axis leads to a change of sign and a strong increase of the
absolute value of the magnetoresistance. On the other hand the
magnetoresistance remains positive down to lower temperatures, exhibiting a
smeared out maximum with the magnetic field applied along the easy axis. The
results are discussed in the ionic picture using a triple-exchange model for
electron hopping as well as a half-metal utilizing a band picture.",0210134v3
2003-04-22,Fabry-Perot interference and spin filtering in carbon nanotubes,"We study the two-terminal transport properties of a metallic single-walled
carbon nanotube with good contacts to electrodes, which have recently been
shown [W. Liang et al, Nature 441, 665-669 (2001)] to conduct ballistically
with weak backscattering occurring mainly at the two contacts. The measured
conductance, as a function of bias and gate voltages, shows an oscillating
pattern of quantum interference. We show how such patterns can be understood
and calculated, taking into account Luttinger liquid effects resulting from
strong Coulomb interactions in the nanotube. We treat back-scattering in the
contacts perturbatively and use the Keldysh formalism to treat non-equilibrium
effects due to the non-zero bias voltage. Going beyond current experiments, we
include the effects of possible ferromagnetic polarization of the leads to
describe spin transport in carbon nanotubes. We thereby describe both
incoherent spin injection and coherent resonant spin transport between the two
leads. Spin currents can be produced in both ways, but only the latter allow
this spin current to be controlled using an external gate. In all cases, the
spin currents, charge currents, and magnetization of the nanotube exhibit
components varying quasiperiodically with bias voltage, approximately as a
superposition of periodic interference oscillations of spin- and
charge-carrying ``quasiparticles'' in the nanotube, each with its own period.
The amplitude of the higher-period signal is largest in single-mode quantum
wires, and is somewhat suppressed in metallic nanotubes due to their sub-band
degeneracy.",0304496v1
2004-04-28,Effect of topology on the transport properties of two interacting dots,"The transport properties of a system of two interacting dots, one of them
directly connected to the leads constituting a side-coupled configuration
(SCD), are studied in the weak and strong tunnel-coupling limits. The
conductance behavior of the SCD structure has new and richer physics than the
better studied system of two dots aligned with the leads (ACD). In the weak
coupling regime and in the case of one electron per dot, the ACD configuration
gives rise to two mostly independent Kondo states. In the SCD topology, the
inserted dot is in a Kondo state while the side-connected one presents Coulomb
blockade properties. Moreover, the dot spins change their behavior, from an
antiferromagnetic coupling to a ferromagnetic correlation, as a consequence of
the interaction with the conduction electrons. The system is governed by the
Kondo effect related to the dot that is embedded into the leads. The role of
the side-connected dot is to introduce, when at resonance, a new path for the
electrons to go through giving rise to the interferences responsible for the
suppression of the conductance. These results depend on the values of the
intra-dot Coulomb interactions. In the case where the many-body interaction is
restricted to the side-connected dot, its Kondo correlation is responsible for
the scattering of the conduction electrons giving rise to the conductance
suppression.",0404691v1
2005-09-09,Theoretical Study of Spin-dependent Electron Transport in Atomic Fe Nanocontacts,"We present theoretical predictions of spintronic transport phenomena that
should be observable in ferromagnetic Fe nanocontacts bridged by chains of Fe
atoms. We develop appropriate model Hamiltonians based on semi-empirical
considerations and the known electronic structure of bulk Fe derived from ab
initio density functional calculations. Our model is shown to provide a
satisfactory description of the surface properties of Fe nano-clusters as well
as bulk properties. Lippmann-Schwinger and Green's function techniques are used
together with Landauer theory to predict the current, magneto-resistance, and
spin polarization of the current in Fe nanocontacts bridged by atomic chains
under applied bias. Unusual device characteristics are predicted including
negative magneto-resistance and spin polarization of the current, as well as
spin polarization of the current for anti-parallel magnetization of the Fe
nanocontacts under moderate applied bias. We explore the effects that
stretching the atomic chain has on the magneto-resistance and spin polarization
and predict a cross-over regime in which the spin polarization of the current
for parallel magnetization of the contacts switches from negative to positive.
We find resonant transmission due to dangling bond formation on tip atoms as
the chain is stretched through its breaking point to play an important role in
spin-dependent transport in this regime. The physical mechanisms underlying the
predicted phenomena are discussed.",0509253v1
2005-11-28,Interface effects in spin-dependent tunneling,"In the past few years the phenomenon of spin dependent tunneling (SDT) in
magnetic tunnel junctions (MTJs) has aroused enormous interest and has
developed into a vigorous field of research. The large tunneling
magnetoresistance (TMR) observed in MTJs garnered much attention due to
possible application in random access memories and magnetic field sensors. This
led to a number of fundamental questions regarding the phenomenon of SDT. One
such question is the role of interfaces in MTJs and their effect on the spin
polarization of the tunneling current and TMR. In this paper we consider
different models which suggest that the spin polarization is primarily
determined by the electronic and atomic structure of the ferromagnet/insulator
interfaces rather than by their bulk properties. First, we consider a simple
tight-binding model which demonstrates that the existence of interface states
and their contribution to the tunneling current depend on the degree of
hybridization between the orbitals on metal and insulator atoms. The decisive
role of the interfaces is further supported by studies of spin-dependent
tunneling within realistic first-principles models of Co/vacuum/Al,
Co/Al2O3/Co, Fe/MgO/Fe, and Co/SrTiO3/Co MTJs. We find that variations in the
atomic potentials and bonding strength near the interfaces have a profound
effect resulting in the formation of interface resonant states, which
dramatically affect the spin polarization and TMR. The strong sensitivity of
the tunneling spin polarization and TMR to the interface atomic and electronic
structure dramatically expands the possibilities for engineering optimal MTJ
properties for device applications.",0511663v1
2006-09-22,"Electronic structure, magnetism, and disorder in the Heusler compound Co$_2$TiSn","Polycrystalline samples of the half-metallic ferromagnet Heusler compound
Co$_2$TiSn have been prepared and studied using bulk techniques (X-ray
diffraction and magnetization) as well as local probes ($^{119}$Sn M\""ossbauer
spectroscopy and $^{59}$Co nuclear magnetic resonance spectroscopy) in order to
determine how disorder affects half-metallic behavior and also, to establish
the joint use of M\""ossbauer and NMR spectroscopies as a quantitative probe of
local ion ordering in these compounds. Additionally, density functional
electronic structure calculations on ordered and partially disordered
Co$_2$TiSn compounds have been carried out at a number of different levels of
theory in order to simultaneously understand how the particular choice of DFT
scheme as well as disorder affect the computed magnetization. Our studies
suggest that a sample which seems well-ordered by X-ray diffraction and
magnetization measurements can possess up to 10% of antisite (Co/Ti)
disordering. Computations similarly suggest that even 12.5% antisite Co/Ti
disorder does not destroy the half-metallic character of this material.
However, the use of an appropriate level of non-local DFT is crucial.",0609578v2
2006-10-03,Single-ion and exchange anisotropy in high-symmetry tetramer single molecule magnets,"For equal-spin $s_1$ tetramer single molecule magnets with ionic point groups
$g=T_d, D_{4h}, D_{2d}, C_{4h}, C_{4v}$, and $S_4$, we write the
group-invariant single-ion, Dzaloshinskii-Moriya, and symmetric anisotropic
near-neighbor and next-nearest-neighbor exchange Hamiltonians using the
respective local axial and azimuthal vector groups. The anisotropic exchange
renormalized near-neighbor and next-nearest-neighbor isotropic exchange
interactions are $\tilde{J}_g$ and $\tilde{J}_g'$. Using our exact, compact
forms for the single-ion matrix elements, we evaluate the eigenstates of the
full Hamiltonian to first order in the various interactions. There are two
types of ferromagnetic (FM) and antiferromagnetic (AFM) tetramers. In Type I,
$\tilde{J}_g'-\tilde{J}_g>0$, the tetramers act as two dimers with the maximal
pair quantum numbers $s_{13}=s_{24}=2s_1$ at low temperature. Type II tetramers
with $\tilde{J}_g'-\tilde{J}_g<0$ are frustrated, with minimal values of the
pair quantum numbers $s_{13}$ and $s_{24}$ at low temperature. For both Type I
and Type II AFM tetramers, we evaluate the first-order level-crossing
inductions analytically for arbitary $s_1$, and illustrate the results for
$s_1=1/2, 1, 3/2$. Accurate Hartree expressions for the thermodynamics,
electron paramagnetic resonance (EPR) absorption and inelastic neutron
scattering cross-section are given. A procedure to extract the effective
microscopic parameters for Types I and II tetramers using EPR is given.",0610084v1
2006-11-27,Spin-dependent electronic structure of transition-metal atomic chains adsorbed on single-wall carbon nanotubes,"We present a systematic study of the electronic and magnetic properties of
transition-metal (TM) atomic chains adsorbed on the zigzag single-wall carbon
nanotubes (SWNTs). We considered the adsorption on the external and internal
wall of SWNT and examined the effect of the TM coverage and geometry on the
binding energy and the spin polarization at the Fermi level. All those adsorbed
chains studied have ferromagnetic ground state, but only their specific types
and geometries demonstrated high spin polarization near the Fermi level. Their
magnetic moment and binding energy in the ground state display interesting
variation with the number of $d-$electrons of the TM atom. We also show that
specific chains of transition metal atoms adsorbed on a SWNT can lead to
semiconducting properties for the minority spin-bands, but semimetallic for the
majority spin-bands. Spin-polarization is maintained even when the underlying
SWNT is subjected to high radial strain. Spin-dependent electronic structure
becomes discretized when TM atoms are adsorbed on finite segments of SWNTs.
Once coupled with non-magnetic metal electrodes, these magnetic needles or
nanomagnets can perform as spin-dependent resonant tunnelling devices. The
electronic and magnetic properties of these nanomagnets can be engineered
depending on the type and decoration of adsorbed TM atom as well as the size
and symmetry of the tube. Our study is performed by using first-principles
pseudopotential plane wave method within spin-polarized Density Functional
Method.",0611670v1
2006-12-28,Demagnetization via Nucleation of the Nonequilibrium Metastable Phase in a Model of Disorder,"We study both analytically and numerically metastability and nucleation in a
two-dimensional nonequilibrium Ising ferromagnet. Canonical equilibrium is
dynamically impeded by a weak random perturbation which models homogeneous
disorder of undetermined source. We present a simple theoretical description,
in perfect agreement with Monte Carlo simulations, assuming that the decay of
the nonequilibrium metastable state is due, as in equilibrium, to the
competition between the surface and the bulk. This suggests one to accept a
nonequilibrium ""free-energy"" at a mesoscopic/cluster level, and it ensues a
nonequilibrium ""surface tension"" with some peculiar low-T behavior. We
illustrate the occurrence of intriguing nonequilibrium phenomena, including:
(i) Noise-enhanced stabilization of nonequilibrium metastable states; (ii)
reentrance of the limit of metastability under strong nonequilibrium
conditions; and (iii) resonant propagation of domain walls. The cooperative
behavior of our system may also be understood in terms of a Langevin equation
with additive and multiplicative noises. We also studied metastability in the
case of open boundaries as it may correspond to a magnetic nanoparticle. We
then observe burst-like relaxation at low T, triggered by the additional
surface randomness, with scale-free avalanches which closely resemble the type
of relaxation reported for many complex systems. We show that this results from
the superposition of many demagnetization events, each with a well- defined
scale which is determined by the curvature of the domain wall at which it
originates. This is an example of (apparent) scale invariance in a
nonequilibrium setting which is not to be associated with any familiar kind of
criticality.",0612675v1
2007-01-22,Generation of high-fidelity controlled-not logic gates by coupled superconducting qubits,"Building on the previous results of the Weyl chamber steering method, we
demonstrate how to generate high-fidelity controlled-not by direct application
of certain, physically relevant Hamiltonians with fixed coupling constants
containing Rabi terms. Such Hamiltonians are often used to describe two
superconducting qubits driven by local rf-pulses.
  It is found that in order to achieve 100% fidelity in a system with
capacitive coupling of strength g one Rabi term suffices. We give the exact
values of the physical parameters needed to implement such CNOT. The gate time
and all possible Rabi frequencies are found to be t=pi/(2g) and Omega_1/g =
sqrt(64n^2-1), n=1,2,3,... .
  Generation of a perfect CNOT in a system with inductive coupling,
characterized by additional constant k, requires the presence of both Rabi
terms. The gate time is again t = pi/(2g), but now there is an infinite number
of solutions, each of which is valid in a certain range of k and is
characterized by a pair of positive integers (n,m). We distinguish two cases,
depending on the sign of the coupling constant:
  (1) the antiferromagnetic case (k>=0);
  (2) the ferromagnetic case (k<=0).
  The paper concludes with consideration of fidelity degradation by switching
to resonance. Simulation of time-evolution based on the 4th order Magnus
expansion reveals characteristics of the gate similar to those found in the
exact case, with slightly shorter gate time and shifted values of Rabi
frequencies.",0701532v2
2007-01-25,Global phase diagram of the spin-1 antiferromagnet with uniaxial anisotropy on the kagome lattice,"The phase diagram of the XXZ spin-1 quantum magnet on the kagome lattice is
studied for all cases where the $J_z$ coupling is antiferromagnetic. In the
zero magnetic field case, the six previously introduced phases, found using
various methods, are: the nondegenerate gapped photon phase which breaks no
space symmetry or spin symmetry; the six-fold degenerate phase with plaquette
order, which breaks both time reversal symmetry and translational symmetry; the
""superfluid"" (ferromagnetic) phase with an in-plane global U(1) symmetry
broken, when $J_{xy} < 0$; the $\sqrt{3}\times\sqrt{3}$ order when $J_{xy} >
0$; the nematic phase when $D < 0$ and large; and a phase with resonating
dimers on each hexagon. We obtain all of these phases and partial information
about their quantum phase transitions in a single framework by studying
condensation of defects in the six-fold plaquette phases. The transition
between nematic phase and the six-fold degenerate plaquette phase is
potentially an unconventional second-order critical point. In the case of a
nonzero magnetic field along $\hat{z}$, another ordered phase with translation
symmetry broken is opened up in the nematic phase. Due to the breaking of
time-reversal symmetry by the field, a supersolid phase emerges between the
six-fold plaquette order and the superfluid phase. This phase diagram might be
accessible in nickel compounds, BF$_4$ salts, or optical lattices of atoms with
three degenerate states on every site.",0701635v1
2007-02-19,MnAs dots grown on GaN(0001)-(1x1) surface,"MnAs has been grown by means of MBE on the GaN(0001)-(1x1) surface. Two
options of initiating the crystal growth were applied: (a) a regular MBE
procedure (manganese and arsenic were delivered simultaneously) and (b)
subsequent deposition of manganese and arsenic layers. It was shown that
spontaneous formation of MnAs dots with the surface density of 1$\cdot 10^{11}$
cm$^{-2}$ and $2.5\cdot 10^{11}$ cm$^{-2}$, respectively (as observed by AFM),
occurred for the layer thickness higher than 5 ML. Electronic structure of the
MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led
to determination of the Mn 3d - related contribution to the total density of
states (DOS) distribution of MnAs. It has been proven that the electronic
structures of the MnAs dots grown by the two procedures differ markedly. One
corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to
that reported for half-metallic zinc-blende MnAs. Both system behave
superparamagnetically (as revealed by magnetization measurements), but with
both the blocking temperatures and the intra-dot Curie temperatures
substantially different. The intra-dot Curie temperature is about 260 K for the
former system while markedly higher than room temperature for the latter one.
Relations between growth process, electronic structure and other properties of
the studied systems are discussed. Possible mechanisms of half-metallic MnAs
formation on GaN are considered.",0702444v1
2003-01-08,"Russian Doll Renormalization Group, Kosterlitz-Thouless Flows, and the Cyclic sine-Gordon model","We investigate the previously proposed cyclic regime of the
Kosterlitz-Thouless renormalization group (RG) flows. The period of one cycle
is computed in terms of the RG invariant. Using bosonization, we show that the
theory has $U_q (\hat{sl(2)})$ quantum affine symmetry, with $q$ {\it real}.
Based on this symmetry, we study two possible S-matrices for the theory,
differing only by overall scalar factors. We argue that one S-matrix
corresponds to a continuum limit of the XXZ spin chain in the
anti-ferromagnetic domain $\Delta < -1$. The latter S-matrix has a periodicity
in energy consistent with the cyclicity of the RG. We conjecture that this
S-matrix describes the cyclic regime of the Kosterlitz-Thouless flows.
  The other S-matrix we investigate is an analytic continuation of the usual
sine-Gordon one. It has an infinite number of resonances with masses that have
a Russian doll scaling behavior that is also consistent with the period of the
RG cycles computed from the beta-function. Closure of the bootstrap for this
S-matrix leads to an infinite number of particles of higher spin with a mass
formula suggestive of a string theory.",0301042v3
2007-12-15,Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single molecule magnets,"We study single-ion and exchange anisotropy effects in equal-spin $s_1$
tetramer single molecule magnets exhibiting $T_d$, $D_{4h}$, $D_{2d}$,
$C_{4h}$, $C_{4v}$, or $S_4$ ionic point group symmetry. We first write the
group-invariant quadratic single-ion and symmetric anisotropic exchange
Hamiltonians in the appropriate local coordinates. We then rewrite these local
Hamiltonians in the molecular or laboratory representation, along with the
Dzyaloshinskii-Moriay (DM) and isotropic Heisenberg, biquadratic, and
three-center quartic Hamiltonians. Using our exact, compact forms for the
single-ion spin matrix elements, we evaluate the eigenstate energies
analytically to first order in the microscopic anisotropy interactions,
corresponding to the strong exchange limit, and provide tables of simple
formulas for the energies of the lowest four eigenstate manifolds of
ferromagnetic (FM) and anitiferromagnetic (AFM) tetramers with arbitrary $s_1$.
For AFM tetramers, we illustrate the first-order level-crossing inductions for
$s_1=1/2,1,3/2$, and obtain a preliminary estimate of the microscopic
parameters in a Ni$_4$ from a fit to magnetization data.
  Accurate analytic expressions for the thermodynamics, electron paramagnetic
resonance absorption and inelastic neutron scattering cross-section are given,
allowing for a determination of three of the microscopic anisotropy
interactions from the second excited state manifold of FM tetramers. We also
predict that tetramers with symmetries $S_4$ and $D_{2d}$ should exhibit both
DM interactions and multiferroic states, and illustrate our predictions for
$s_1=1/2, 1$.",0712.2518v2
2010-02-02,"Magnetic anisotropy of epitaxial (Ga,Mn)As on (113)A GaAs","The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers
grown by molecular beam epitaxy is studied by means of superconducting quantum
interference device (SQUID) magnetometry as well as by ferromagnetic resonance
(FMR) and magnetooptical effects. Experimental results are described
considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude
of cubic and uniaxial anisotropy constants is found to be proportional to the
fourth and second power of saturation magnetization, respectively. Similarly to
the case of (001) samples, the spin reorientation transition from uniaxial
anisotropy with the easy along the [-1, 1, 0] direction at high temperatures to
the biaxial <100> anisotropy at low temperatures is observed around 25 K. The
determined values of the anisotropy constants have been confirmed by FMR
studies. As evidenced by investigations of the polar magnetooptical Kerr
effect, the particular combination of magnetic anisotropies allows the
out-of-plane component of magnetization to be reversed by an in-plane magnetic
field. Theoretical calculations within the p-d Zener model explain the
magnitude of the out-of-plane uniaxial anisotropy constant caused by epitaxial
strain, but do not explain satisfactorily the cubic anisotropy constant. At the
same time the findings point to the presence of an additional uniaxial
anisotropy of unknown origin. Similarly to the case of (001) films, this
additional anisotropy can be explained by assuming the existence of a shear
strain. However, in contrast to the (001) samples, this additional strain has
an out-of-the-(001)-plane character.",1002.0563v2
2010-06-24,Direct ESR evidence for magnetic behaviour of graphene,"Recently, there have appeared theoretical works on the magnetic properties of
graphene and graphene nanoribbons envisaging possible spin-based applications
along with fundamental scientific insight. The theoretical efforts, however,
appear not paralleled by experimental investigation to test magnetic
properties. Yet, room temperature ferromagnetism (RTFM) has recently been
experimentally reported in graphene (G-600) [Nano. Letters 9, 220 (2009)], the
origin of which remains still unexplored. Inspired by this observation, and in
attempt to trace the origin of RTFM, we here report on low temperature K-band
electron spin resonance (ESR) observations on G-600. Two distinct C-related
paramagnetic signals are revealed, both of a Lorentzian shape: a) a broad at g
= 2.00278 which can be attributed to graphitic-like (GL) carbon; b) a narrower
signal at g = 2.00288 which is associated with free radical like (FL) carbon.
No other signals could be detected. We speculate that the GL ESR signal may
come from the conductive {\pi}-carriers propagating in the interior of graphene
sheets, while the FL ESR signal may stem from the edges of graphene sheets due
to non-bonding localized electronic states. It is suggested that the long range
direct/indirect exchange interaction between GL and FL C-related magnetic spin
centers may lead to the reported RTFM, this pointing to C origin of the later.",1006.4840v1
2010-06-28,Impurity-doped Kagome Antiferromagnet: A Quantum Dimer Model Approach,"The doping of quantum Heisenberg antiferromagnets on the kagome lattice by
non-magnetic impurities is investigated within the framework of a generalized
quantum dimer model (QDM) describing a) the valence bond crystal (VBC), b) the
dimer liquid and c) the critical region on equal footing. Following the
approach by Ralko et al. [Phys. Rev. Lett. 101, 117204 (2008)] for the square
and triangular lattices, we introduce the (minimal) extension of the QDM on the
Kagome lattice to account for spontaneous creation of mobile S=1/2 spinons at
finite magnetic field. Modulations of the dimer density (at zero or finite
magnetic field) and of the local field-induced magnetization in the vicinity of
impurities are computed using Lanczos Exact Diagonalization techniques on small
clusters (48 and 75 sites). The VBC is clearly revealed from its pinning by
impurities, while, in the dimer liquid, crystallization around impurities
involves only two neighboring dimers. We also find that a next-nearest-neighbor
ferromagnetic coupling favors VBC order. Unexpectedly, a small size
spinon-impurity bound state appears in some region of the the dimer liquid
phase. In contrast, in the VBC phase the spinon delocalizes within a large
region around the impurity, revealing the weakness of the VBC confining
potential. Lastly, we observe that an impurity concentration as small as 4%
enhances dimerization substantially. These results are confronted to the
Valence Bond Glass scenario [R.R.P. Singh, Phys. Rev. Lett. 104, 177203 (2010)]
and implications to the interpretation of the Nuclear Magnetic Resonance
spectra of the Herbertsmithite compound are outlined.",1006.5370v2
2010-07-24,"Antiferromagnetic, metal-insulator, and superconducting phase transitions in underdoped cuprates: Slave-fermion t-J model in the hopping expansion","In the present paper, we study a system of doped antiferromagnet in three
dimensions at finite temperatures by using the t-J model, a canonical model of
strongly-correlated electrons. We employ the slave-fermion representation of
electrons in which an electron is described as a composite of a charged
spinless holon and a chargeless spinon. We introduce two kinds of U(1) gauge
fields on links as auxiliary fields, one describing resonating valence bonds of
antiferromagnetic nearest-neighbor spin pairs and the other for
nearest-neighbor hopping amplitudes of holons and spinons in the ferromagnetic
channel. In order to perform numerical study of the system, we integrate out
the fermionic holon field by using the hopping expansion in powers of the
hopping amplitude, which is legitimate for the region in and near the
insulating phase. The resultant effective model is described in terms of
bosonic spinons and the two U(1) gauge fields, and a collective field for hole
pairs. We study this model by means of Monte-Carlo simulations, calculating the
specific heat, spin correlation functions, and instanton densities. We obtain a
phase diagram in the hole concentration-temperature plane, which is in good
agreement with that observed recently for clean and homogeneous underdoped
samples.",1007.4273v1
2010-10-22,Noisy Kondo impurities,"The anti-ferromagnetic coupling of a magnetic impurity carrying a spin with
the conduction electrons spins of a host metal is the basic mechanism
responsible for the increase of the resistance of an alloy such as
Cu${}_{0.998}$Fe${}_{0.002}$ at low temperature, as originally suggested by
Kondo . This coupling has emerged as a very generic property of localized
electronic states coupled to a continuum . The possibility to design artificial
controllable magnetic impurities in nanoscopic conductors has opened a path to
study this many body phenomenon in unusual situations as compared to the
initial one and, in particular, in out of equilibrium situations. So far,
measurements have focused on the average current. Here, we report on
\textit{current fluctuations} (noise) measurements in artificial Kondo
impurities made in carbon nanotube devices. We find a striking enhancement of
the current noise within the Kondo resonance, in contradiction with simple
non-interacting theories. Our findings provide a test bench for one of the most
important many-body theories of condensed matter in out of equilibrium
situations and shed light on the noise properties of highly conductive
molecular devices.",1010.4815v1
2010-11-04,"Magnetic order, metamagnetic transitions, and low-temperature spin freezing in Ca3Co2O6: an NMR study","We report on a 59Co NMR investigation of the trigonal cobaltate Ca3Co2O6
carried out on a single crystal, providing precise determinations of the
electric field gradient and chemical shift tensors, and of the internal
magnetic fields at the non-magnetic Co I sites, unavailable from former studies
on powders. The magnetic field-induced ferri- and ferromagnetic phases at
intermediate temperature (e.g. 10 K) are identified by distinct internal
fields, well accounted for by purely dipolar interactions. The vanishing
transferred hyperfine field at the Co I site indicates that the Co3+(I)
orbitals do not participate in the intra-chain superexchange, in disagreement
with a previous theoretical model. The strong Ising character of the system is
confirmed experimentally by the field dependence of the resonance lines,
indicating that local moments are saturated even at the phase boundaries. In
the vicinity of the critical fields, nuclear spin-spin relaxations detect the
spin reversal dynamics of large magnetic assemblies, either Ising chain
fragments or finite size domains, which drive the metamagnetic transitions.
Such collective excitations exhibit a glassy behavior, slowing down to
subacoustic frequencies and freezing at low temperature. The relevance of such
slow fluctuation modes for the low-temperature multi-step behavior reported in
the magnetization is discussed.",1011.1142v2
2011-02-28,Atom Loss Maximum in Ultra-cold Fermi Gases,"Recent experiments on atom loss in ultra-cold Fermi gases all show a maximum
at a magnetic field below Feshbach resonance, where the s-wave scattering
length is large (close to inter-particle distance) and positive. These
experiments have been performed over a wide range of conditions, with
temperatures and trap depths spanning over three decades. Different groups have
come up with different explanations, among them the emergence of Stoner
ferromagnetism. Here, we show that this maximum is a consequence of two major
steps. The first is the establishment of a population of shallow dimers, which
is the combined effect of dimer formation through three-body recombination, and
the dissociation of shallow dimers back to atoms through collisions. The
dissociation process will be temperature dependent, and is affected by Pauli
blocking at low temperatures. The second is the relaxation of shallow dimers
into tightly bound dimers through atom-dimer and dimer-dimer collisions.
  We have constructed a simple set of rate equations describing these
processes. Remarkably, even with only a few parameters, these equations
reproduce the loss rate observed in all recent experiments, despite their
widely different experimental conditions. Our studies show that the location of
the maximum loss rate depends crucially on experimental parameters such as trap
depth and temperature. These extrinsic characters show that this maximum is not
a reliable probe of the nature of the underlying quantum states. The physics of
our equations also explains some general trends found in current experiments.",1102.5687v1
2011-08-19,Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition,"Nanostructured Pd-Fe thin films with varied Fe content were prepared by
electrodeposition technique from organic electrolytes on Cu and brass
substrates. The structure and the magnetic properties of the films were
investigated prior to post-deposition annealing. The structure of the Pd1-xFex
thin films with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction
(XRD) and transmission electron microscopy (TEM) as a solid solution of iron in
palladium face-centered cubic lattice with the (111) orientation of nanograins
relatively to the substrate surface. The films with higher iron concentration,
x = 0.74, 0.91, have structure of a solid solution based on the body-centered
cubic lattice. The average grain size determined by the scanning electron
microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones
it is about 120 nm. The saturation magnetization of the films has linear
dependence on the iron content, but coercivity has non-monotonic dependence on
x, i.e. the films with x = 0.68 show highest coercivity. The magnetic
anisotropy of the samples is studied by ferromagnetic resonance (FMR)
spectroscopy.",1108.3888v1
2012-03-29,Crossover from spin accumulation into interface states to spin injection in the germanium conduction band,"Electrical spin injection into semiconductors paves the way for exploring new
phenomena in the area of spin physics and new generations of spintronic
devices. However the exact role of interface states in spin injection mechanism
from a magnetic tunnel junction into a semiconductor is still under debate. In
this letter, we demonstrate a clear transition from spin accumulation into
interface states to spin injection in the conduction band of $n$-Ge. We observe
spin signal amplification at low temperature due to spin accumulation into
interface states followed by a clear transition towards spin injection in the
conduction band from 200 K up to room temperature. In this regime, the spin
signal is reduced down to a value compatible with spin diffusion model. More
interestingly, we demonstrate in this regime a significant modulation of the
spin signal by spin pumping generated by ferromagnetic resonance and also by
applying a back-gate voltage which are clear manifestations of spin current and
accumulation in the germanium conduction band.",1203.6491v2
2012-11-06,Structure and magnetism of Cr2BP3O12: Towards the quantum-classical crossover in a spin-3/2 alternating chain,"Magnetic properties of the spin-3/2 Heisenberg system Cr2BP3O12 are
investigated by magnetic susceptibility chi(T) measurements, electron spin
resonance, neutron diffraction, and density functional theory (DFT)
calculations, as well as classical and quantum Monte Carlo (MC) simulations.
The broad maximum of chi(T) at 85K and the antiferromagnetic Weiss temperature
of 139 K indicate low-dimensional magnetic behavior. Below TN = 28 K, Cr2BP3O12
is antiferromagnetically ordered with the k = 0 propagation vector and an
ordered moment of 2.5 muB/Cr. DFT calculations, including DFT+U and hybrid
functionals, yield a microscopic model of spin chains with alternating
nearest-neighbor couplings J1 and J1' . The chains are coupled by two
inequivalent interchain exchanges of similar strength (~1-2 K), but different
sign (antiferromagnetic and ferromagnetic). The resulting spin lattice is
quasi-one-dimensional and not frustrated. Quantum MC simulations show excellent
agreement with the experimental data for the parameters J1 ~= 50 K and J1'/J1
~= 0.5. Therefore, Cr2BP3O12 is close to the gapless critical point (J1'/J1 =
0.41) of the spin-3/2 bond-alternating Heisenberg chain. The applicability
limits of the classical approximation are addressed by quantum and classical MC
simulations. Implications for a wide range of low-dimensional S = 3/2 materials
are discussed.",1211.1260v2
2013-01-28,Magnetization dynamics in Co2$MnGe/Al2$O3$/Co tunnel junctions grown on different substrates,"We study static and dynamic magnetic properties of Co2MnGe (13 nm)/Al2O3 (3
nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single
crystalline substrates (a-plane sapphire, MgO(100), Si(111)). The results are
compared to the magnetic properties of Co and of Co$_{2}$MnGe single films
lying on sapphire substrates. X-rays diffraction always shows a (110)
orientation of the Co$_{2}$MnGe films. Structural observations obtained by high
resolution transmission electron microscopy confirmed the high quality of the
TMJ grown on sapphire. Our vibrating sample magnetometry measurements reveal
in-plane anisotropy only in samples grown on a sapphire substrate. Depending on
the substrate, the ferromagnetic resonance spectra of the TMJs, studied by the
microstrip technique, show one or two pseudo-uniform modes. In the case of MgO
and of Si substrates only one mode is observed: it is described by magnetic
parameters (g-factor, effective magnetization, in-plane magnetic anisotropy)
derived in the frame of a simple expression of the magnetic energy density;
these parameters are practically identical to those obtained for the Co single
film. With a sapphire substrate two modes are present: one of them does not
appreciably differ from the observed mode in the Co single film while the other
one is similar to the mode appearing in the Co$_{2}$MnGe single film: their
magnetic parameters can thus be determined independently, using a classical
model for the energy density in the absence of interlayer exchange coupling.",1301.6563v1
2013-02-06,Configuration dependent demagnetizing field in assemblies of interacting magnetic particles,"A mean field model is presented for the configuration dependent effective
demagnetizing and anisotropy fields in assemblies of exchange decoupled
magnetic particles of arbitrary shape which are expressed in terms of the
demagnetizing factors of the particles and the volumetric shape containing the
assembly. Perpendicularly magnetized 2D assemblies have been considered, for
which it is shown that the demagnetizing field is lower than the continuous
thin film. As an example of these 2D systems, arrays of bistable cylindrical
nanowires have been characterized by remanence curves as well as ferromagnetic
resonance, which have served to show the correspondence of these measurements
with the model and also to validate the mean field approach. Linear chains of
cylinders and spheres have been analyzed leading to simple expressions to
describe the easy axis rotation induced by the interaction field in chains of
low aspect ratio cylindrical particles, and the dipolar magnetic anisotropy
observed in the linear chain of spheres. These examples serve to underline the
dependence on the dipolar interaction field and effective demagnetizing factor
on the contributions that arise from the shape of the outer volume.",1302.1607v1
2013-05-03,"Co2 FeAl thin films grown on MgO substrates: Correlation between static, dynamic and structural properties","Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have
been deposited on MgO(001) substrates by magnetron sputtering and then capped
by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA
axis is normal to the substrate and that all the CFA films exhibit full
epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$
phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and
vibrating sample magnetometer measurements show that, depending on the field
orientation, one or two-step switchings occur. Moreover, the films present a
quadratic MOKE signal increasing with the CFA thickness, due to the increasing
chemical order. Ferromagnetic resonance, MOKE transverse bias initial inverse
susceptibility and torque (TBIIST) measurements reveal that the in-plane
anisotropy results from the superposition of a uniaxial and of a fourfold
symmetry term. The fourfold anisotropy is in accord with the crystal structure
of the samples and is correlated to the biaxial strain and to the chemical
order present in the films. In addition, a large negative perpendicular
uniaxial anisotropy is observed. Frequency and angular dependences of the FMR
linewidth show two magnon scattering and mosaicity contributions, which depend
on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.",1305.0714v1
2013-12-11,Distinct magnetic phase transition at the surface of an antiferromagnet,"In the majority of magnetic systems the surface is required to order at the
same temperature as the bulk. In the present study, we report a distinct and
unexpected surface magnetic phase transition, uniquely at a lower temperature
than the N\'eel temperature. Employing grazing incidence X-ray resonant
magnetic scattering we have observed the near surface behavior of uranium
dioxide. UO$_2$ is a non-collinear, triple-q, antiferromagnet with the U ions
on an face-centered-cubic lattice. Theoretical investigations establish that at
the surface the energy increase, due to the lost bonds, reduces when the spins
near the surface rotate, gradually losing their normal to the surface
component. At the surface the lowest-energy spin configuration has a double-q
(planar) structure. With increasing temperature, thermal fluctuations saturate
the in-plane crystal field anisotropy at the surface, leading to soft
excitations that have ferromagnetic $XY$ character and are decoupled from the
bulk. The structure factor of a finite two-dimensional $XY$ model, fits the
experimental data well for several orders of magnitude of the scattered
intensity. Our results support a distinct magnetic transition at the surface in
the Kosterlitz-Thouless universality class.",1312.3136v2
2014-01-17,Co2FeAl Heusler thin films grown on Si and MgO substrates: annealing temperature effect,"10 nm and 50 nm Co$_{2}$FeAl (CFA) thin films have been deposited on MgO(001)
and Si(001) substrates by magnetron sputtering and annealed at different
temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth
(according to the relation CFA(001)[110]//MgO(001)[100] epitaxial relation),
respectively for CFA films grown on a Si and on a MgO substrate. For these
later, the chemical order varies from the A2 phase to the B2 phase when
increasing the annealing temperature (Ta) while only the A2 disorder type has
been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR)
measurements revealed that the in-plane anisotropy results from the
superposition of a uniaxial and of a fourfold symmetry term for CFA grown on
MgO substrates. This fourfold anisotropy, which disappears completely for
samples grown on Si, is in accord with the crystal structure of the samples.
The fourfold anisotropy field decreases when increasing Ta while the uniaxial
anisotropy field is nearly unaffected by Ta within the investigated range. The
MS-FMR data also allow for concluding that the gyromagnetic factor remains
constant and that the exchange stiffness constant increases with $T_{a}$.
Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement
of the chemical order. We derive a very low intrinsic damping parameter
(1.3*10^-3 and 1.1*10^-3 for films of 50 nm thickness annealed at 615 {\deg}C
grown on MgO and on Si, respectively).",1401.4397v1
2014-07-20,Functionalized Graphene in Quantizing Magnetic Field: The case of bunched impurities,"Resonant scattering at the atomic absorbates in graphene was investigated
recently in relation with the transport and gap opening problems. Attaching an
impurity atom to graphene is believed to lead to the creation of unusual zero
energy localized electron states. This paper aims to describe the behavior of
the localized impurity-induced levels in graphene in a quantizing magnetic
field. It is shown that in the magnetic field the impurity level effectively
hybridizes with one of the n=0 Landau level states and splits into two
opposite-energy states. The new hybridized state is doubly occupied, forming a
spin-singlet and reducing the polarization of a Quantum Hall ferromagnet in
undoped graphene. Taking into account the electron-electron interaction changes
radically the spectrum of the electrons surrounding the impurity, which should
be seen experimentally. While existing publications investigate graphene
uniformly covered by adatoms, here we address a possibly even more
experimentally relevant case of the clusterized impurity distribution. The
limit of a dense bunch of the impurity atoms is considered, and it is shown,
how such a bunch changes the spectrum and spin polarization of a large dense
electron droplet surrounding it. The droplet is encircled by an edge state
carrying a persistent current.",1407.5334v2
2014-07-24,The shape of the Hanle curve in spin-transport structures in the presence of the ac drive,"Resistance between two ferromagnetic electrodes coupled to a normal channel
depends on their relative magnetizations. The spin-dependent component, R, of
the resistance changes with magnetic field, B, normal to the directions of
magnetizations. In the field of spin transport, this change, R(B), originating
from the Larmour spin precession, is called the Hanle curve. We demonstrate
that the shape of the Hanle curve evolves upon application of an ac drive and
study this evolution theoretically as a function of the amplitude, B_1, and
frequency, w, of the drive. If the distance between the electrodes, L, is
smaller than the spin-diffusion length, l_s, the prime effect of a weak
circular-polarized drive is the shift of the center of the curve to the value
of B for which the Larmour frequency, w_L, is ~B_1^2 w. Magnetic resonance at
w_L~w manifests itself in the derivative, dR/dB. For large L >> l_s the ac
drive affects the Hanle curve if the drive amplitude exceeds the spin
relaxation rate, 1/t_s, i.e. at B_1 t_s > 1. The prime effect of the drive is
the elimination of a minimum in R(B). Linearly polarized drive has a
fundamentally different effect on the Hanle curve, affecting not its shape, but
rather its width.",1407.6440v1
2014-08-02,Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates,"We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based
magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate.
Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a
flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance
(TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on
a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching
was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a
switching layer. Using a thermal activation model, the intrinsic critical
current density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lower
than 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett.
100, 182403 (2012)]. We found that the Gilbert damping constant evaluated using
ferromagnetic resonance measurements for the polycrystalline CFA film was
~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0
for the polycrystalline MTJ was mainly attributed to the low damping of the CFA
layer compared with the value in the epitaxial one (~0.04).",1408.0341v1
2014-08-26,ESR evidence for partial melting of the orbital order in LaMnO$_3$ below the Jahn-Teller transition,"We report on high-temperature electron spin resonance studies of a detwinned
LaMnO$_3$ single crystal across the Jahn-Teller transition at $T_{\rm JT}$ =
750 K. The anisotropy of the linewidth and g-factor reflects the local
Jahn-Teller distortions in the orbitally ordered phase. A clear jump in the
linewidth accompanies the Jahn-Teller transition at $T_{\rm JT}$ = 750 K
confirming that the transition is of first order. Already at $T^*$ = 550 K a
significant decrease of the reduced linewidth is observed. This temperature
scale is discussed with respect to the interaction of the $e_g$-electrons of
the Mn$^{3+}$-ions and the elastic field of the cooperative distortions. Our
results support a partial melting of the orbital order along the
antiferromagnetically coupled $b$-axis at $T^*$. The remaining two-dimensional
orbital ordering within the ferromagnetically coupled $ac$-plane finally
disappears together with the cooperative distortion at $T_{\rm JT}$. Moreover
in our discussion we show that elastic strain field interactions can explain
the melting of the orbital order and, thus, has to be taken into account to
explain the orbital ordering in LaMnO$_3$.",1408.6160v1
2014-11-12,Large perpendicular magnetic anisotropy in magnetostrictive Fe$_{1-x}$Ga$_x$ thin films,"In this work we report the appearence of a large perpendicular magnetic
anisotropy (PMA) in Fe$_{1-x}$Ga$_x$ thin films grown onto ZnSe/GaAs(100). This
arising anisotropy is related to the tetragonal metastable phase in as-grown
samples recently reported [M. Eddrief {\it et al.}, Phys. Rev. B {\bf 84},
161410 (2011)]. By means of ferromagnetic resonance studies we measured PMA
values up to $\sim$ 5$\times$10$^5$ J/m$^3$. PMA vanishes when the cubic
structure is recovered upon annealing at 300$^{\circ}$C. Despite the important
values of the magnetoelastic constants measured via the cantilever method, the
consequent magnetoelastic contribution to PMA is not enough to explain the
observed anisotropy values in the distorted state. {\it Ab initio} calculations
show that the chemical ordering plays a crucial role in the appearance of PMA.
Through a phenomenological model we are able to explain that an excess of next
nearest neighbour Ga pairs (B$_2$-like ordering) along the perpendicular
direction arises as the source of PMA in Fe$_{1-x}$Ga$_x$ thin films.",1411.3055v2
2014-11-24,Manipulating Femtosecond Spin--Orbit Torques with Laser Pulse Sequences to Control Magnetic Memory States and Ringing,"Femtosecond (fs) coherent control of collective order parameters is important
for non--equilibrium phase dynamics in correlated materials. Here we propose a
possible scheme for fs control of a ferromagnetic order parameter based on
non--adiabatic optical manipulation of electron--hole ($e$--$h$)
photoexcitations between spin--orbit--coupled bands that are exchange--split by
magnetic interaction with local spins. We photoexcite fs carrier spin--pulses
with controllable direction and time profile without using
circularly--polarized light, via time--reversal symmetry--breaking by
non--perturbative interplay between spin--orbit and magnetic exchange coupling
of coherent photocarriers. We manipulate photoexcited {\em fs spin--orbit
torques} to control complex switching pathways of the magnetization between
multiple magnetic memory states. We calculate the photoinduced fs magnetic
anisotropy in the time domain by using density matrix equations of motion
rather than the quasi--equilibrium free energy. By comparing to pump--probe
experiments, we identify a ""sudden"" magnetization canting induced by laser
excitation, which displays magnetic hysteresis absent in static
magneto--optical measurements and agrees with switchings measured by Hall
magnetoresistivity. The fs magnetization canting switches direction with
magnetic state and laser frequency, which distinguishes it from nonlinear
optical and demagnetization longitudinal effects. By shaping two--color
laser--pulse sequences analogous to multi--dimensional Nuclear Magnetic
Resonance (NMR) spectroscopy, we show that sequences of clockwise or
counter--clockwise fs spin--orbit torques can enhance or suppress magnetic
ringing and switching rotation at any desired time. We propose protocols that
can provide controlled access to four magnetic states via consequative 90$^{o}$
switchings.",1411.6662v1
2014-12-05,Twisted toroidal vortex-solitons in inhomogeneous media with repulsive nonlinearity,"Toroidal modes in the form of so-called Hopfions, with two independent
winding numbers, a hidden one (twist, s), which characterizes a circular vortex
thread embedded into a three-dimensional soliton, and the vorticity around the
vertical axis m, appear in many fields, including the field theory,
ferromagnetics, and semi- and superconductors. Such topological states are
normally generated in multi-component systems, or as trapped quasi-linear modes
in toroidal potentials. We uncover that stable solitons with this structure can
be created, without any linear potential, in the single-component setting with
the strength of repulsive nonlinearity growing fast enough from the center to
the periphery, for both steep and smooth modulation profiles. Toroidal modes
with s=1 and vorticity m=0,1,2 are produced. They are stable for m<=1, and do
not exist for s>1. An approximate analytical solution is obtained for the
twisted ring with s=1, m=0. Under the application of an external torque, it
rotates like a solid ring. The setting can be implemented in BEC, by means of
the Feshbach resonance controlled by inhomogene-ous magnetic fields.",1412.2001v1
2015-01-16,Direct measurement of the magnetic anisotropy field in Mn--Ga and Mn--Co--Ga Heusler films,"The static and dynamic magnetic properties of tetragonally distorted Mn--Ga
based alloys were investigated. Static properties are determined in magnetic
fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film,
the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial
substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The
saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is
increased to 1~T.
  Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the
high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency
extrapolated to zero-field is found to be 125~GHz with a Gilbert damping,
$\alpha$, of 0.019. The anisotropy field is determined from both SQUID and
TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of
0.81~MJ/m$^3$.
  Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film,
pulsed magnetic fields up to 60~T are used to determine the field strength
required to saturate the film in the plane. For this, the extraordinary Hall
effect was employed as a probe of the local magnetisation. By integrating the
reconstructed in--plane magnetisation curve, the effective anisotropy energy
density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.",1501.03973v1
2015-08-10,Magneto-optical imaging of thin magnetic films using spins in diamond,"Imaging the fields of magnetic materials provides crucial insight into the
physical and chemical processes surrounding magnetism, and has been a key
ingredient in the spectacular development of magnetic data storage. Existing
approaches using the magneto-optic Kerr effect (MOKE), x-ray and electron
microscopy have limitations that constrain further development, and there is
increasing demand for imaging and characterisation of magnetic phenomena in
real time with high spatial resolution. In this work, we show how the
magneto-optical response of an array of negatively-charged nitrogen-vacancy
spins in diamond can be used to image and map the sub-micron stray magnetic
field patterns from thin ferromagnetic films. Using optically detected magnetic
resonance, we demonstrate wide-field magnetic imaging over 100x100 {\mu}m^2
with a diffraction-limited spatial resolution of 440 nm at video frame rates,
under ambient conditions. We demonstrate a novel all-optical spin relaxation
contrast imaging approach which can image magnetic structures in the absence of
an applied microwave field. Straightforward extensions promise imaging with
sub-{\mu}T sensitivity and sub-optical spatial and millisecond temporal
resolution. This work establishes practical diamond-based wide-field microscopy
for rapid high-sensitivity characterisation and imaging of magnetic samples,
with the capability for investigating magnetic phenomena such as domain wall
and skyrmion dynamics and the spin Hall effect in metals.",1508.02135v1
2015-08-28,Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching,"Electric-field modulation of magnetism in strain-mediated multiferroic
heterostructures is considered a promising scheme for enabling memory and
magnetic microwave devices with ultralow power consumption. However, it is not
well understood how electric-field-induced strain influences magnetic
relaxation, an important physical process for device applications. Here we
investigate resonant magnetization dynamics in ferromagnet/ferrolectric
multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct
strain states provided by electric-field-induced ferroelectric phase
transition. The strain not only modifies magnetic anisotropy but also magnetic
relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic
Gilbert damping by electric field, which is attributed to strain-induced tuning
of spin-orbit coupling. By contrast, a small but measurable change in extrinsic
linewidth broadening is attributed to inhomogeneous ferroelastic domain
switching during the phase transition of the PMN-PT substrate.",1508.07290v2
2015-10-13,Fermi level dependent charge-to-spin current conversion by Dirac surface state of topological insulators,"The spin-momentum locking at the Dirac surface state of a topological
insulator (TI) offers a distinct possibility of a highly efficient
charge-to-spin current (C-S) conversion compared with spin Hall effects in
conventional paramagnetic metals. For the development of TI-based spin current
devices, it is essential to evaluate its conversion efficiency quantitatively
as a function of the Fermi level EF position. Here we exemplify a coefficient
of qICS to characterize the interface C-S conversion effect by using spin
torque ferromagnetic resonance (ST-FMR) for (Bi1-xSbx)2Te3 thin films whose EF
is tuned across the band gap. In bulk insulating conditions, interface C-S
conversion effect via Dirac surface state is evaluated as nearly constant large
values of qICS, reflecting that the qICS is inversely proportional to the Fermi
velocity vF that is almost constant. However, when EF traverses through the
Dirac point, the qICS is remarkably suppressed possibly due to the degeneracy
of surface spins or instability of helical spin structure. These results
demonstrate that the fine tuning of the EF in TI based heterostructures is
critical to maximizing the efficiency using the spin-momentum locking
mechanism.",1510.03572v1
2016-01-28,Observation of a Three-Dimensional Quasi-Long-Range Electronic Supermodulation in YBa2Cu3O7-x/La0.7Ca0.3MnO3 Heterostructures,"Recent developments in high-temperature superconductivity highlight a generic
tendency of the cuprates to develop competing electronic (charge)
supermodulations. While coupled to the lattice and showing different
characteristics in different materials, these supermodulations themselves are
generally conceived to be quasi-two-dimensional, residing mainly in individual
CuO2 planes, and poorly correlated along the c-axis. Here we observed with
resonant elastic x-ray scattering a distinct type of electronic supermodulation
in YBa2Cu3O7-x (YBCO) thin films grown epitaxially on La0.7Ca0.3MnO3 (LCMO).
This supermodulation has a periodicity nearly commensurate with four lattice
constants in-plane, eight out-of-plane, with long correlation lengths in three
dimensions. It sets in far above the superconducting transition temperature and
competes with superconductivity below this temperature for electronic states
predominantly in the CuO2 plane. Our finding sheds new light on the nature of
charge ordering in cuprates as well as a reported long-range proximity effect
between superconductivity and ferromagnetism in YBCO/LCMO heterostructures.",1601.07682v1
2016-02-18,Second order anisotropy contribution in perpendicular magnetic tunnel junctions,"Magnetoresistance loops under in-plane applied field were measured on
perpendicularly magnetized magnetic tunnel junction (pMTJ) pillars with nominal
diameters ranging from 50 to 150 nm. By fitting the hard-axis magnetoresistance
loops to an analytical model, the effective anisotropy fields in both free and
reference layers were derived and their variations in temperature range between
340K and 5K were determined. It is found that an accurate fitting is possible
only if a second-order anisotropy term of the form $-K_{2}cos^4{\theta}$, is
added to the fitting model. This higher order contribution exists both in the
free and reference layers and its sign is opposite to that of the first order
anisotropy constant, $K_{1}$. At room temperatures the estimated $-K_{2}/K_{1}$
ratios are 0.1 and 0.24 for the free and reference layers, respectively. The
ratio is more than doubled at low temperatures altering the ground state of the
reference layer from 'easy-axis' to 'easy-cone' regime. Easy-cone state has
clear signatures in the shape of the hard-axis magnetoresistance loops. The
same behavior was observed in all measured devices regardless of their
diameter. The existence of this higher order anisotropy was confirmed
experimentally on FeCoB/MgO sheet films by ferromagnetic resonance technique.
It is of interfacial nature and is believed to be linked to spatial
fluctuations at the nanoscale of the anisotropy parameter at the FeCoB/MgO
interface, in agreement with Dieny-Vedyayev model.",1602.05815v1
2016-04-12,Influence of the FFLO-like State on the Upper Critical Field of a S/F Bilayer: Angular and Temperature Dependence,"We investigated the upper critical magnetic field, $H_{c}$, of a
superconductor-ferromagnet (S/F) bilayer of Nb/Cu$_{41}$Ni$_{59}$ and a Nb film
(as reference). We obtained the dependence of $H_{c\perp}$ and $H_{c\parallel}$
(perpendicular and parallel to the film plane, respectively) on the
temperature, $T$, by measurements of the resistive transitions and the
dependence on the inclination angle, $\theta$, of the applied field to the film
plane, by non-resonant microwave absorption. Over a wide range, $H_{c\perp}$
and $H_{c\parallel}$ show the temperature dependence predicted by the
Ginzburg-Landau theory. At low temperatures and close to the critical
temperature deviations are observed. While $H_{c}(\theta)$ of the Nb film
follows the Tinkham prediction for thin superconducting films, the
Nb/Cu$_{41}$Ni$_{59}$-bilayer data exhibit deviations when $\theta$ approaches
zero. We attribute this finding to the additional anisotropy induced by the
quasi-one-dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like state and
propose a new vortex structure in S/F bilayers, adopting the segmentation
approach from high-temperature superconductors.",1604.03361v1
2016-06-17,Long-range charge density wave proximity effect at cuprate-manganate interfaces,"The interplay between charge density waves (CDWs) and high-temperature
superconductivity is currently under intense investigation. Experimental
research on this issue is difficult because CDW formation in bulk copper-oxides
is strongly influenced by random disorder, and a long-range-ordered CDW state
in high magnetic fields is difficult to access with spectroscopic and
diffraction probes. Here we use resonant x-ray scattering in zero magnetic
field to show that interfaces with the metallic ferromagnet
La$_{2/3}$Ca$_{1/3}$MnO$_3$ greatly enhance CDW formation in the optimally
doped high-temperature superconductor YBa$_2$Cu$_3$O$_{6+\delta}$ ($\bf \delta
\sim 1$), and that this effect persists over several tens of nm. The wavevector
of the incommensurate CDW serves as an internal calibration standard of the
charge carrier concentration, which allows us to rule out any significant
influence of oxygen non-stoichiometry, and to attribute the observed phenomenon
to a genuine electronic proximity effect. Long-range proximity effects induced
by heterointerfaces thus offer a powerful method to stabilize the charge
density wave state in the cuprates, and more generally, to manipulate the
interplay between different collective phenomena in metal oxides.",1606.05531v2
2016-07-20,Electromagnon in the Z-type hexaferrite $({\rm Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$,"We studied experimentally the high-temperature magnetoelectric $({\rm
Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$ prepared as ceramics (x = 0,
0.2) and a single crystal (x = 0.5) using inelastic neutron scattering, THz
time-domain, Raman and far-infrared spectroscopies. The spectra, measured with
varying temperature and magnetic field, reveal rich information about the
collective spin and lattice excitations. In the ceramics, we observed an
infrared-active magnon which is absent in $E^{\omega}\perp z$ polarized THz
spectra of the crystal, and we assume that it is an electromagnon active in
$E^{\omega} \| z$ polarized spectra. On heating from 7 to 250 K, the frequency
of this electromagnon drops from 36 to 25 cm$^{-1}$ and its damping gradually
increases, so it becomes overdamped at room temperature. Applying external
magnetic field has a similar effect on the damping and frequency of the
electromagnon, and the mode is no more observable in the THz spectra above 2 T,
as the transverse-conical magnetic structure transforms into a collinear one.
Raman spectra reveal another spin excitation with a slightly different
frequency and much higher damping. Upon applying magnetic field higher than 3
T, in the low-frequency part of the THz spectra, a narrow excitation appears
whose frequency linearly increases with magnetic field. We interpret this
feature as the ferromagnetic resonance.",1607.05878v1
2016-09-19,Geometrical complexity of the antidots unit cell effect on the spin wave excitations spectra,"We have investigated theoretically (with micromagnetic simulations and plane
wave method) and experimentally (with ferromagnetic resonance and Brillouin
light scattering) three types of antidot lattices (ADLs) based on permalloy
thin films with increased complexity of the unit cell: simple square,
bi-component square and wave-like ADL. We have found that placing a small
additional antidot in the center of the unit cell of the square ADL modify
significantly the spin wave spectrum and its dependence on the orientation of
the in-plane magnetic field. We also check the further changes of spin wave
spectrum resulting from the introduction of air-gaps connecting small and large
antidots. In particular, the presence of small antidots change the dependence
of the frequency of the fundamental mode on the angle of the in-plane applied
magnetic field. The air-gaps strongly discriminates the propagation of spin
waves in two principal direction of ADL lattice, orthogonal to each other. In
spite of these spectral changes, the spatial distribution of the spin wave
amplitude generally preserves some similarities for all three structures. We
also highlighted out the role of defects in the ADL in the observed spectra.
The obtained results can be interesting for the magnonics applications of the
magnonic crystals.",1609.05663v1
2017-03-14,Two-dimensional ${J}_{\rm eff}$ = 1/2 antiferromagnetic insulator unraveled from interlayer exchange coupling in artificial perovskite iridate superlattices,"We report an experimental investigation of the two-dimensional ${J}_{\rm
eff}$ = 1/2 antiferromagnetic Mott insulator by varying the interlayer exchange
coupling in [(SrIrO$_3$)$_1$, (SrTiO$_3$)$_m$] ($m$ = 1, 2 and 3)
superlattices. Although all samples exhibited an insulating ground state with
long-range magnetic order, temperature-dependent resistivity measurements
showed a stronger insulating behavior in the $m$ = 2 and $m$ = 3 samples than
the $m$ = 1 sample which displayed a clear kink at the magnetic transition.
This difference indicates that the blocking effect of the excessive SrTiO$_3$
layer enhances the effective electron-electron correlation and strengthens the
Mott phase. The significant reduction of the Neel temperature from 150 K for
$m$ = 1 to 40 K for $m$ = 2 demonstrates that the long-range order stability in
the former is boosted by a substantial interlayer exchange coupling. Resonant
x-ray magnetic scattering revealed that the interlayer exchange coupling has a
switchable sign, depending on the SrTiO$_3$ layer number $m$, for maintaining
canting-induced weak ferromagnetism. The nearly unaltered transition
temperature between the $m$ = 2 and the $m$ = 3 demonstrated that we have
realized a two-dimensional antiferromagnet at finite temperatures with
diminishing interlayer exchange coupling.",1703.04645v2
2017-03-21,Annealing stability of magnetic tunnel junctions based on dual MgO free layers and [Co/Ni] based thin synthetic antiferromagnet fixed system,"We study the annealing stability of bottom-pinned perpendicularly magnetized
magnetic tunnel junctions based on dual MgO free layers and thin fixed systems
comprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Co
reference layer and a FeCoB polarizing layer. Using conventional magnetometry
and advanced broadband ferromagnetic resonance, we identify the properties of
each sub-unit of the magnetic tunnel junction and demonstrate that this
material option can ensure a satisfactory resilience to the 400$^\circ$C
thermal annealing needed in solid-state magnetic memory applications. The dual
MgO free layer possesses an anneal-robust 0.4 T effective anisotropy and
suffers only a minor increase of its Gilbert damping from 0.007 to 0.010 for
the toughest annealing conditions. Within the fixed system, the ferro-coupler
and texture-breaking TaFeCoB layer keeps an interlayer exchange above 0.8
mJ/m$^2$, while the Ru antiferrocoupler layer within the synthetic
antiferromagnet maintains a coupling above -0.5 mJ/m$^2$. These two strong
couplings maintain the overall functionality of the tunnel junction upon the
toughest annealing despite the gradual degradation of the thin Co layer
anisotropy that may reduce the operation margin in spin torque memory
applications. Based on these findings, we propose further optimization routes
for the next generation magnetic tunnel junctions.",1703.07154v1
2017-03-28,Local and collective magnetism of EuFe$_2$As$_2$,"We present an experimental study of the local and collective magnetism of
$\mathrm{EuFe_2As_2}$, that is isostructural with the high temperature
superconductor parent compound $\mathrm{BaFe_2As_2}$. In contrast to
$\mathrm{BaFe_2As_2}$, where only Fe spins order, $\mathrm{EuFe_2As_2}$ has an
additional magnetic transition below 20 K due to the ordering of the Eu$^{2+}$
spins ($J =7/2$, with $L=0$ and $S=7/2$) in an A-type antiferromagnetic texture
(ferromagnetic layers stacked antiferromagnetically). This may potentially
affect the FeAs layer and its local and correlated magnetism. Fe-K$_\beta$
x-ray emission experiments on $\mathrm{EuFe_2As_2}$ single crystals reveal a
local magnetic moment of 1.3$\pm0.15~\mu_B$ at 15 K that slightly increases to
1.45$\pm0.15~\mu_B$ at 300 K. Resonant inelastic x-ray scattering (RIXS)
experiments performed on the same crystals show dispersive broad (in energy)
magnetic excitations along $\mathrm{(0, 0)\rightarrow(1, 0)}$ and $\mathrm{(0,
0)\rightarrow(1, 1)}$ with a bandwidth on the order of 170-180 meV. These
results on local and collective magnetism are in line with other parent
compounds of the $\mathrm{AFe_2As_2}$ series ($A=$ Ba, Ca, and Sr), especially
the well characterized $\mathrm{BaFe_2As_2}$. Thus, our experiments lead us to
the conclusion that the effect of the high magnetic moment of Eu on the
magnitude of both Fe local magnetic moment and spin excitations is small and
confined to low energy excitations.",1703.09819v1
2018-04-13,Ni$_2$Mo$_3$O$_8$: zig-zag antiferromagnetic order an integer spin non-centrosymmetric honeycomb lattice,"Theoretical studies have predicted the existence of topological magnons in
honeycomb compounds with zig-zag antiferromagnetic (AFM) order. Here we report
the discovery of zig-zag AFM order in the layered and non-centrosymmetric
honeycomb nickelate Ni$_2$Mo$_3$O$_8$ through a combination of magnetization,
specific heat, x-ray and neutron diffraction and electron paramagnetic
resonance measurements. It is the first example of such order in an
integer-spin non-centrosymmetric structure ($P$$_6$3$mc$). Further, each of the
two distinct sites of the bipartite honeycomb lattice has a unique crystal
field environment, octahedral and tetrahedral Ni$^{2+}$ respectively, enabling
independent substitution on each sublattice. Replacement of Ni by Mg on the
octahedral site suppresses the long range magnetic order and results in a
weakly ferromagnetic state. Conversely, substitution of Fe for Ni enhances the
AFM ordering temperature. Thus Ni$_2$Mo$_3$O$_8$ provides a platform on which
to explore the rich physics of $S = 1$ on the honeycomb in the presence of
competing magnetic interactions with a non-centrosymmetric, formally
piezeo-polar, crystal structure.",1804.04776v1
2019-05-29,Coherent long-range transfer of angular momentum between magnon Kittel modes by phonons,"We report ferromagnetic resonance in the normal configuration of an
electrically insulating magnetic bilayer consisting of two yttrium iron garnet
(YIG) films epitaxially grown on both sides of a 0.5-mm-thick nonmagnetic
gadolinium gallium garnet (GGG) slab. An interference pattern is observed and
it is explained as the strong coupling of the magnetization dynamics of the two
YIG layers either in phase or out of phase by the standing transverse sound
waves, which are excited through a magnetoelastic interaction. This coherent
mediation of angular momentum by circularly polarized phonons through a
nonmagnetic material over macroscopic distances can be useful for future
information technologies.",1905.12523v3
2020-07-17,Coherent coupling between multiple ferrimagnetic spheres and a microwave cavity in the quantum-limit,"The spin resonance of electrons can be coupled to a microwave cavity mode to
obtain a photon-magnon hybrid system. These quantum systems are widely studied
for both fundamental physics and technological quantum applications. In this
article, the behavior of a large number of ferrimagnetic spheres coupled to a
single cavity is put under test. We use second-quantization modeling of
harmonic oscillators to theoretically describe our experimental setup and
understand the influence of several parameters. The magnon-polariton dispersion
relation is used to characterize the system, with a particular focus on the
vacuum Rabi mode splitting due to multiple spheres. We combine the results
obtained with simple hybrid systems to analyze the behavior of a more complex
one, and show that it can be devised in such a way to minimize the degrees of
freedom needed to completely describe it. By studying single-sphere coupling
two possible size-effects related to the sample diameter have been identified,
while multiple-spheres configurations reveal how to upscale the system. This
characterization is useful for the implementation of an
axion-to-electromagnetic field transducer in a ferromagnetic haloscope for dark
matter searches. Our dedicated setup, consisting in ten 2 mm-diameter YIG
spheres coupled to a copper microwave cavity, is used for this aim and studied
at mK temperatures. Moreover, we show that novel applications of
optimally-controlled hybrid systems can be foreseen for setups embedding a
large number of samples.",2007.08908v3
2020-07-24,"Determination of the spin Hall angle, spin mixing conductance and spin diffusion length in Ir/CoFeB for spin-orbitronic devices","Iridium is a very promising material for spintronic applications due to its
interesting magnetic properties such as large RKKY exchange coupling as well as
its large spin-orbit coupling value. Ir is for instance used as a spacer layer
for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However,
only a few studies of the spintronic parameters of this material have been
reported. In this paper, we present inverse spin Hall effect - spin pumping
ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the
values of the effective spin Hall angle, the spin diffusion length within
iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to
have reliable results, we performed the same experiments on CoFeB/Pt bilayers,
which behavior is well known due to numerous reported studies. Our experimental
results show that the spin diffusion length within iridium is 1.3 nm for
resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow
\downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle
of iridium has the same sign than the one of platinum and is evaluated at 26%
of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt
and 2% for Ir. These relevant parameters shall be useful to consider Ir in new
concepts and devices combining spin-orbit torque and spin-transfer torque.",2007.12413v1
2017-04-20,Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves,"We have investigated co-directional and contra-directional couplings between
spin wave and acoustic wave in one-dimensional periodic structure (magphonic
crystal). The system consists of two ferromagnetic layers alternating in space.
We have taken into consideration materials commonly used in magnonics: yttrium
iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT)
formalism have been successfully implemented to describe magnetoelastic
interaction as a periodic perturbation in the magphonic crystal. The results of
CMT calculations have been verified by more rigorous simulations by
frequency-domain plane wave method and time-domain finite element method. The
presented resonant coupling in the magphonic crystal is an active in-space
mechanism which spatially transfers energy between propagating spin and
acoustic modes, thus creating propagating magnetoelastic wave. We have shown,
that CMT analysis of the magnetoelastic coupling is an useful tool to optimize
and design a spin wave - acoustic wave transducer based on a magphonic
crystals. The effect of spin wave damping has been included to the model to
discuss the efficiency of such a device. Our model shows that it is possible to
obtain forward conversion of the acoustic wave to the spin wave in case of
co-directional coupling and backward conversion in case of contra-directional
coupling.",1704.06118v1
2018-05-02,Spin-pumping-induced inverse spin-Hall effect in Nb/Ni80Fe20 bilayers and its strong decay across the superconducting transition temperature,"We quantify the spin Hall angle {\theta}SH and spin diffusion length lsd of
Nb from inverse spin-Hall effect (iSHE) measurements in Nb/Ni80Fe20 bilayers
under ferromagnetic resonance. By varying the Nb thickness tNb and comparing to
a Ni80Fe20/Pt reference sample, room temperature values of {\theta}SH and lsd
for Nb are estimated to be approximately -0.001 and 30 nm, respectively. We
also investigate the iSHE as a function of temperature T for different tNb.
Above the superconducting transition temperature Tc of Nb, a clear
tNb-dependent T evolution of the iSHE is observed whereas below Tc, the iSHE
voltage drops rapidly and is below the sensitivity of our measurement setup at
a lower T. This suggests the strong decay of the quasiparticle (QP)
charge-imbalance relaxation length across Tc, as supported by an additional
investigation of the iSHE in a different sample geometry along with model
calculation. Our finding suggests careful consideration should be made when
developing superconductor spin-Hall devices that intend to utilize QP-mediated
spin-to-charge interconversion.",1805.00730v2
2016-05-22,Low Gilbert damping in Co2FeSi and Fe2CoSi films,"Thin highly textured Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si ($0 \leq$ x
$\leq 1$) films were prepared on MgO (001) substrates by magnetron
co-sputtering. The magneto-optic Kerr effect (MOKE) and ferromagnetic resonance
(FMR) measurements were used to investigate the composition dependence of the
magnetization, the magnetic anisotropy, the gyromagnetic ratio and the
relaxation of the films. The effective magnetization for the thin
Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films, determined by FMR measurements,
are consistent with the Slater Pauling prediction. Both MOKE and FMR
measurements reveal a pronounced fourfold anisotropy distribution for all
films. In addition we found a strong influence of the stoichiometry on the
anisotropy as the cubic anisotropy strongly increases with increasing Fe
concentration. The gyromagnetic ratio is only weakly dependent on the
composition. We find low Gilbert damping parameters for all films with values
down to $0.0012\pm0.00012$ for Fe$_{1.75}$Co$_{1.25}$Si. The effective damping
parameter for Co$_2$FeSi is found to be $0.0018\pm 0.0004$. We also find a
pronounced anisotropic relaxation, which indicates significant contributions of
two-magnon scattering processes that is strongest along the easy axes of the
films. This makes thin Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films ideal
materials for the application in STT-MRAM devices.",1605.06797v1
2016-05-30,Klein tunneling in Weyl semimetals under the influence of magnetic field,"Klein tunneling refers to the absence of normal backscattering of electrons
even under the case of high potential barriers. At the barrier interface, the
perfect matching of electron and hole wavefunctions enables a unit transmission
probability for normally incident electrons. It is theoretically and
experimentally well understood in two-dimensional relativistic materials such
as graphene. Here we investigate the Klein tunneling effect in Weyl semimetals
under the influence of magnetic field induced by anti-symmetric ferromagnetic
stripes placed at barrier boundaries. Our results show that the resonance of
Fermi wave vector at specific barrier lengths gives rise to perfect
transmission rings, i.e., three-dimensional analogue of the so-called magic
transmission angles in two-dimensional Dirac semimetals. Besides, the
transmission profile can be shifted by application of magnetic field, a
property which may be utilized in electro-optic applications. When the applied
potential is close to the Fermi level, a particular incident vector can be
selected for transmission by tuning the applied magnetic field, thus enabling
highly selective transmission of electrons in the bulk of Weyl semimetals. Our
analytical and numerical calculations obtained by considering Dirac electrons
in three regions and using experimentally feasible parameters can pave the way
for relativistic tunneling applications in Weyl semimetals.",1605.09108v1
2016-08-15,Superconductor to Mott insulator transition in YBa$_2$Cu$_3$O$_7$/LaCaMnO$_3$ heterostructures,"The superconductor-to-insulator transition (SIT) induced by means such as
external magnetic fields, disorder or spatial confinement is a vivid
illustration of a quantum phase transition dramatically affecting the
superconducting order parameter. In pursuit of a new realization of the SIT by
interfacial charge transfer, we developed extremely thin superlattices composed
of high $T_c$ superconductor YBa$_2$Cu$_3$O$_7$ (YBCO) and colossal
magnetoresistance ferromagnet La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO). By using
linearly polarized resonant X-ray absorption spectroscopy and magnetic circular
dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a
complete picture of the interfacial carrier doping in cuprate and manganite
atomic layers, leading to the transition from superconducting to an unusual
Mott insulating state emerging with the increase of LCMO layer thickness. In
addition, contrary to the common perception that only transition metal ions may
response to the charge transfer process, we found that charge is also actively
compensated by rare-earth and alkaline-earth metal ions of the interface. Such
deterministic control of $T_c$ by pure electronic doping without any hindering
effects of chemical substitution is another promising route to disentangle the
role of disorder on the pseudo-gap and charge density wave phases of underdoped
cuprates.",1608.04316v1
2016-12-22,Bismuth iron garnet Bi3Fe5O12: a room temperature magnetoelectric material,"The possibility to control the magnetic properties of a material with an
electric field at room temperature is highly desirable for modern applications.
Moreover, a coupling between magnetic and electric orders within a single
material presenting a wide range of exceptional physical properties, such as
bismuth iron garnet (BIG), may lead to great advances in the field of
spintronic applications. In particular, the combination of the magnetoelectric
(ME) coupling with the low damping of spin waves in BIG can allow the control
and manipulation of spin waves by an electric field in magnonic devices. Here
we report the unambiguous observation of linear magnetoelectric coupling above
300 K in BIG using ferromagnetic resonance technique with electric field
modulation. The measured coupling value is comparable with that observed for
prototypal magnetoelectric Cr2O3. On the basis of our experimental results, the
strength of this linear ME coupling is directly linked to the presence of
bismuth ions inducing strong spin orbit coupling and to the appearance of local
magnetic inhomogeneities related to the magnetic domain structure. The
unprecedented combination of magnetic, optical and magnetoelectrical properties
in BIG is expected to trigger significant interest for technological
applications as well as for theoretical studies.",1612.07531v3
2016-12-28,Photon-assisted transport in bilayer graphene flakes,"The electronic conductance of graphene-based bilayer flake systems reveal
different quantum interference effects, such as Fabry-P\'erot resonances and
sharp Fano antiresonances on account of competing electronic paths through the
device. These properties may be exploited to obtain spin-polarized currents
when the same nanostructure is deposited above a ferromagnetic insulator. Here
we study how the spin-dependent conductance is affected when a time-dependent
gate potential is applied to the bilayer flake. Following a Tien-Gordon
formalism we explore how to modulate the transport properties of such systems
via appropriate choices of the $ac$-field gate parameters. The presence of the
oscillating field opens the possibility of tuning the original antiresonances
for a large set of field parameters. We show that interference patterns can be
partially or fully removed by the time-dependent gate voltage. The results are
reflected in the corresponding weighted spin polarization which can reach
maximum values for a given spin component. We found that differential
conductance maps as functions of bias and gate potentials show interference
patterns for different $ac$-field parameter configurations. The proposed
bilayer graphene flake systems may be used as a frequency detector in the THz
range.",1612.08934v1
2017-06-22,Sign reversal of field like spin-orbit torque in ultrathin Chromium/Nickel bilayer,"In this work report unconventional sign change of field like spin orbit
torque in ultra-thin Chromium(1.5nm-5nm)/Nickel(8nm) bi-layer. We performed
standard spin-torque ferromagnetic resonance (ST-FMR) experiment in Cr/Ni
bi-layer by passing radio frequency current and measuring DC voltage. We
observe that when thickness of Cr layer is critically low (<6nm) spin orbit
torque by Cr on Ni significantly increases. Most importantly the sign of field
like torque is opposite to the Oersted field generated torque. To verify
interracial nature of this torque, 2 nm thin Cu is inserted between Cr and Ni
and field like torque behaves same as Oersted field induced torque. Hence
possible origin of such unconventional sign change of field like torque could
be inter-facial Rashba like spin orbit interaction which is present between Cr
and Ni but vanishes in Cr/Cu/Ni hetero-structure. From our experiment we can
estimate that approximately 35 Oe of effective Rashba like magnetic field is
created on 8 nm thicker Ni layer, when 1E12 A/m^2 current flows through Cr
layer. All experiments are done at room temperature. So Cr thin film is
expected to behave like paramagnet (Neel temperature of bulk Cr is 311K). Hence
Cr can be a good choice as a heavy metal to employ large spin orbit torque
combining bulk spin Hall effect and inter-facial Rashba interaction.",1706.07260v1
2017-07-19,Engineering elliptical spin-excitations by complex anisotropy fields in Fe adatoms and dimers on Cu(111),"We investigate the dynamics of Fe adatoms and dimers deposited on the Cu(111)
metallic surface in the presence of spin-orbit coupling, within time-dependent
density functional theory. The \textit{ab initio} results provide
material-dependent parameters that can be used in semiclassical approaches,
which are used for insightful interpretations of the excitation modes. By
manipulating the surroundings of the magnetic elements, we show that elliptical
precessional motion may be induced through the modification of the magnetic
anisotropy energy. We also demonstrate how different kinds of spin precession
are realized, considering the symmetry of the magnetic anisotropy energy, the
ferro- or antiferromagnetic nature of the exchange coupling between the
impurities, and the strength of the magnetic damping. In particular, the normal
modes of a dimer depend on the initial magnetic configuration, changing
drastically by going from a ferromagnetic metastable state to the
antiferromagnetic ground state. By taking into account the effect of the
damping into their resonant frequencies, we reveal that an important
contribution arises for strongly biaxial systems and specially for the
antiferromagnetic dimers with large exchange couplings. Counter intuitively,
our results indicate that the magnetic damping influences the quantum
fluctuations by decreasing the zero-point energy of the system.",1707.06087v2
2017-10-06,Investigation of the interfacial Dzyaloshinskii-Moriya interaction sign in Ir/Co2FeAl systems by Brillouin light scattering,"Co2FeAl (CFA) ultrathin films, of various thicknesses (0.9 nm<tCFA<1.8 nm),
have been grown by sputtering on Si substrates, using Ir as a buffer layer. The
magnetic properties of the structures have been studied by vibrating sample
magnetometry (VSM), miscrostrip ferromagnetic resonance (MS-FMR) and Brillouin
light scattering (BLS) in the Damon-Eshbach geometry. VSM characterizations
show that films are mostly in-plane magnetized and the perpendicular saturating
field increases with decreasing CFA thickness suggesting the existence of
interface anisotropy. The presence of magnetic dead layers of 0.44 nm has been
detected by VSM. The MS-FMR with perpendicular applied magnetic field has been
used to determine the gyromagnetic factor. The BLS measurements reveal a
pronounced nonreciprocal spin waves propagation, due to the interfacial
Dzyaloshinskii-Moriya interaction (DMI) induced by Ir interface with CFA, which
increases with decreasing CFA thickness. The DMI sign has been found to be the
same (negative) as that of Pt/Co, in contrast to the ab-initio calculation on
Ir/Co. The thickness dependence of the effective DMI constant shows the
existence of two regimes similarly to that of the perpendicular anisotropy
constant. The DMI constant Ds was estimated to be -0.37 pJ/m for the thickest
samples where a linear thickness dependence of the effective DMI constant has
been observed.",1710.02433v1
2017-10-17,Dirac-Surface-State-Dominated Spin to Charge Current Conversion in the Topological Insulator $(Bi_{0.22}Sb_{0.78})_2Te_3$ Films at Room Temperature,"We report the spin to charge current conversation in an intrinsic topological
insulator (TI) $(Bi_{0.22}Sb_{0.78})_2Te_3$ film at room temperature. The spin
currents are generated in a thin layer of permalloy (Py) by two different
processes, spin pumping (SPE) and spin Seebeck effects (SSE). In the first we
use microwave-driven ferromagnetic resonance of the Py film to generate a SPE
spin current that is injected into the TI $(Bi_{0.22}Sb_{0.78})_2Te_3$ layer in
direct contact with Py. In the second we use the SSE in the longitudinal
configuration in Py without contamination by the Nernst effect made possible
with a thin NiO layer between the Py and $(Bi_{0.22}Sb_{0.78})_2Te_3$ layers.
The spin-to-charge current conversion is attributed to the inverse Edelstein
effect (IEE) made possible by the spin-momentum locking in the electron Fermi
contours due to the Rashba field. The measurements by the two techniques yield
very similar values for the IEE parameter, which are larger than the reported
values in the previous studies on topological insulators.",1710.06224v1
2017-10-17,Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators,"We combine low energy muon spin rotation (LE-$\mu$SR) and soft-X-ray
angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and
electronic properties of magnetically doped topological insulators,
(Bi,Sb)$_2$Te$_3$. We find that one achieves a full magnetic volume fraction in
samples of (V/Cr)$_x$(Bi,Sb)$_{2-x}$Te$_3$ at doping levels x $\gtrsim$ 0.16.
The observed magnetic transition is not sharp in temperature indicating a
gradual magnetic ordering. We find that the evolution of magnetic ordering is
consistent with formation of ferromagnetic islands which increase in number
and/or volume with decreasing temperature. Resonant ARPES at the V $L_3$ edge
reveals a nondispersing impurity band close to the Fermi level as well as V
weight integrated into the host band structure. Calculations within the
coherent potential approximation of the V contribution to the spectral function
confirm that this impurity band is caused by V in substitutional sites. The
implications of our results on the observation of the quantum anomalous Hall
effect at mK temperatures are discussed.",1710.06238v2
2017-12-14,Determination of the spin Hall angle in single-crystalline Pt films from spin pumping experiments,"We report on the determination of the spin Hall angle and the identification
of the role of the interface roughness for the inverse spin Hall effect (ISHE)
in ultra-clean, defect-reduced epitaxial Pt films. By applying vector network
analyzer ferromagnetic resonance spectroscopy to a series of single crystalline
Fe (12 nm) /Pt (t$_\text{Pt}$) bilayers we determine the real part of the spin
mixing conductance $(4.4\:\pm\:0.2)\cdot 10^{19}\: $m$^{-2}$ and reveal a very
small spin diffusion length in the epitaxial Pt $(1.1\:\pm\:0.1)$ nm film. We
investigate the spin pumping and ISHE in a stripe microstucture excited by a
microwave coplanar waveguide (CPW) antenna. By using their different angular
dependencies, we distinguish between spin rectification effects and the inverse
spin Hall effect. The relatively large value of the spin Hall angle $(5.7 \pm
1.4)\: \% $ hints that interface engineering by epitaxially grown non-magnetic
materials can increase the spin-to-charge current conversion efficiency.",1712.05334v2
2017-12-16,Hybrid chiral domain walls and skyrmions in magnetic multilayers,"Noncollinear spin textures in ferromagnetic ultrathin films are currently the
subject of renewed interest since the discovery of the interfacial
Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange
interaction selects a given chirality for the spin textures and allows
stabilising configurations with nontrivial topology. Moreover, it has many
crucial consequences on the dynamical properties of these topological
structures, including chiral domain walls (DWs) and magnetic skyrmions. In the
recent years the study of noncollinear spin textures has been extended from
single ultrathin layers to magnetic multilayers with broken inversion symmetry.
This extension of the structures in the vertical dimension allows very
efficient current-induced motion and room-temperature stability for both N\'eel
DWs and skyrmions. Here we show how in such multilayered systems the interlayer
interactions can actually lead to more complex, hybrid chiral magnetisation
arrangements. The described thickness-dependent reorientation of DWs is
experimentally confirmed by studying demagnetised multilayers through circular
dichroism in x-ray resonant magnetic scattering. We also demonstrate a simple
yet reliable method for determining the magnitude of the DMI from static
domains measurements even in the presence of these hybrid chiral structures, by
taking into account the actual profile of the DWs. The advent of these novel
hybrid chiral textures has far-reaching implications on how to stabilise and
manipulate DWs as well as skymionic structures in magnetic multilayers.",1712.05978v2
2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1
2018-01-11,Efficient Charge-Spin Conversion and Magnetization Switching though Rashba Effect at Topological Insulator/Ag Interface,"We report the observation of efficient charge-to-spin conversion in the
three-dimensional topological insulator (TI) Bi2Se3 and Ag bilayer by the
spin-torque ferromagnetic resonance technique. The spin orbit torque ratio in
the Bi2Se3/Ag/CoFeB heterostructure shows a significant enhancement as the Ag
thickness increases to ~2 nm and reaches a value of 0.5 for 5 nm Ag, which is
~3 times higher than that of Bi2Se3/CoFeB at room temperature. The observation
reveals the interfacial effect of Bi2Se3/Ag exceeds that of the topological
surface states (TSS) in the Bi2Se3 layer and plays a dominant role in the
charge-to-spin conversion in the Bi2Se3/Ag/CoFeB system. Based on the
first-principles calculations, we attribute our observation to the large
Rashba-splitting bands which wrap the TSS band and has the same net spin
polarization direction as TSS of Bi2Se3. Subsequently, we demonstrate for the
first time the Rashba induced magnetization switching in Bi2Se3/Ag/Py with a
low current density of 5.8 X 10^5 A/cm2.",1801.03689v1
2018-01-29,Band-pass superlattice magnetic tunnel junctions,"Significant scientific and technological progress in the field of spintronics
is based on trilayer magnetic tunnel junction devices which principally rely on
the physics of single barrier tunneling. While technologically relevant devices
have been prototyped, the physics of single barrier tunneling poses ultimate
limitations on the performance of magnetic tunnel junction devices. Here, we
propose a fresh route toward high performance magnetic tunnel junctions by
making electronic analogs of optical phenomena such as anti-reflections and
Fabry-P\`erot resonances. The devices we propose feature anti-reflection
enabled superlattice heterostructures sandwiched between the fixed and the free
ferromagnets of the magnetic tunnel junction structure. Our predictions are
based on the non-equilibrium Green's function spin transport formalism coupled
self-consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation. Owing
to the physics of bandpass spin filtering in the bandpass superlattice magnetic
tunnel junction device, we demonstrate an ultra-high boost in the tunnel
magneto-resistance (TMR$\approx5\times10^4\%$) and nearly 92% suppression of
spin transfer torque switching bias in comparison to a traditional trilayer
magnetic tunnel junction device. We rationalize improvised spin transfer torque
switching via analysis of the Slonczewski spin current transmission spectra.
The proof of concepts presented here can lead to next-generation spintronics
device design harvesting the rich physics of superlattice heterostructures and
exploiting spintronic analogs of optical phenomena.",1801.09409v2
2018-09-12,Topological insulator Bi2Se3 films on rare earth iron garnets and their high-quality interfaces,"The integration of quantum materials like topological insulators (TIs) with
magnetic insulators (MIs) has important technological implications for
spintronics and quantum computing. Here we report excellent crystallinity of
c-axis oriented epitaxial TI films Bi2Se3 grown on MI films, a rare earth iron
garnet (ReIG), such as thulium iron garnet (Tm3Fe5O12, TmIG) by molecular beam
epitaxy (MBE) with a Se-buffered low-temperature (SBLT) growth technique. We
demonstrated a streaky reflection high-energy electron diffraction pattern
starting from the very first quintuple layer of Bi2Se3, indicating the
high-quality interface between TmIG and Bi2Se3, a prerequisite for studying
interfacial exchange coupling effects. The strong interfacial exchange
interaction was manifested by observations of anomalous Hall effect in the
Bi2Se3/TmIG bilayer and a shift of ferromagnetic resonance field of TmIG
induced by Bi2Se3. We have reproducibly grown high-quality Bi2Se3/ReIG and
interfaces using this new TI growth method, which may be applied to grow other
types of van der Waals (vdW) hetero-structures.",1809.04513v1
2018-10-03,Stable hump-like Hall effect and non-coplanar spin textures in SrRuO$_3$ ultrathin film,"We observed a hump-like feature in Hall effects of SrRuO$_3$ ultrathin films,
and systematically investigated it with controlling thicknesses, temperatures
and magnetic fields. The hump-like feature is extremely stable, even surviving
as a magnetic field is tilted by as much as 85$^\circ$. Based on the
atomic-level structural analysis of a SrRuO$_3$ ultrathin film with a
theoretical calculation, we reveal that atomic rumplings at the thin-film
surface enhance Dzyaloshinskii-Moriya interaction, which can generate stable
chiral spin textures and a hump-like Hall effect. Moreover, temperature
dependent resonant X-ray measurements at Ru L-edge under a magnetic field
showed that the intensity modulation of unexpected peaks was correlated with
the hump region in the Hall effect. We verify that the two-dimensional property
of ultrathin films generates stable non-coplanar spin textures having a
magnetic order in a ferromagnetic oxide material.",1810.01615v2
2019-06-21,"Anisotropic temperature-field phase diagram of single-crystalline $β$-Li$_2$IrO$_3$: magnetization, specific heat, and $^7$Li NMR study","Detailed magnetization, specific heat, and $^7$Li nuclear magnetic resonance
(NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet
$\beta$-Li$_2$IrO$_3$ are reported. At high temperatures, {\cred anisotropy of
the magnetization is reflected by the different Curie-Weiss temperatures for
different field directions}, in agreement with the combination of a
ferromagnetic Kitaev interaction ($K$) and a negative off-diagonal anisotropy
($\Gamma$) as two leading terms in the spin Hamiltonian. At low temperatures,
magnetic fields applied along $a$ or $c$ have only a weak effect on the system
and reduce the N\'eel temperature from 38 K at 0 T to about 35.5 K at 14 T,
with no field-induced transitions observed up to 58 T on a powder sample. In
contrast, the field applied along $b$ causes a drastic reduction in the $T_N$
that vanishes around $H_c=2.8$ T giving way to a crossover toward a quantum
paramagnetic state. $^7$Li NMR measurements in this field-induced state reveal
a gradual line broadening and a continuous evolution of the line shift with
temperature, suggesting the development of local magnetic fields. The
spin-lattice relaxation rate shows a peak around the crossover temperature 40 K
and follows power-law behavior below this temperature.",1906.09089v2
2019-07-05,Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy,"Materials suitable for magnonic crystals demand low magnetic damping and long
spin wave (SW) propagation distance. In this context Co based Heusler compounds
are ideal candidates for magnonic based applications. In this work, antidot
arrays (with different shapes) of epitaxial
$\mathrm{Co}_2\mathrm{Fe}_{0.4}\mathrm{Mn}_{0.6}\mathrm{Si}$ (CFMS) Heusler
alloy thin films have been prepared using e-beam lithography and sputtering
technique. Magneto-optic Kerr effect and ferromagnetic resonance analysis have
confirmed the presence of dominant cubic and moderate uniaxial magnetic
anisotropies in the thin films. Domain imaging via x-ray photoemission electron
microscopy on the antidot arrays reveals chain like switching or correlated
bigger domains for different shape of the antidots. Time-resolved MOKE
microscopy has been performed to study the precessional dynamics and magnonic
modes of the antidots with different shapes. We show that the optically induced
spin-wave spectra in such antidot arrays can be tuned by changing the shape of
the holes. The variation in internal field profiles, pinning energy barrier,
and anisotropy modifies the spin-wave spectra dramatically within the antidot
arrays with different shapes. We further show that by combining the
magnetocrystalline anisotropy with the shape anisotropy, an extra degree of
freedom can be achieved to control the magnonic modes in such antidot lattices.",1907.02746v1
2019-07-23,Magnetic structure and magnetoelastic coupling of GdNiSi3 and TbNiSi3,"The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows
interesting magnetic properties evolving with $R$ and metamagnetic transitions
under applied magnetic field for some of the compounds. The microscopic
magnetic structures must be determined to rationalize such rich behavior. Here,
resonant x-ray magnetic diffraction experiments are performed on single
crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic
unit cell matches the chemical cell below the N\'eel temperatures $T_{N}$ =
22.2 and 33.2 K, respectively. The magnetic structure is determined to be the
same for both compounds (magnetic space group $Cmmm'$). It features
ferromagnetic {\it ac} planes that are stacked in an antiferromagnetic $+-+-$
pattern, with the rare-earth magnetic moments pointing along the $\vec{a}$
direction, which contrasts with the $+--+$ stacking and moment direction along
the $\vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign
reversal of the coupling constant between second-neighbor $R$ planes as $R$ is
varied from Gd and Tb to Yb. The long {\it b} lattice parameter of GdNiSi$_{3}$
and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$,
pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice
expansion. A competition between distinct magnetic stacking patterns with
similar exchange energies tuned by the size of $R$ sets the stage for the
magnetic ground state instability observed along this series.",1907.09830v1
2019-09-30,Localized surface electromagnetic waves in CrI$_3$-based magnetophotonic structures,"Resulting from strong magnetic anisotropy two-dimensional ferromagnetism was
recently shown to be stabilized in chromium triiodide, CrI$_3$, in the
monolayer limit. While its properties remain largely unexplored, it provides a
unique material-specific platform to unveil its electromagnetic properties
associated with coupling of modes. Indeed, trigonal symmetry in the presence of
out-of-plane magnetization results in a non-trivial structure of the
conductivity tensor, including the off-diagonal terms. In this paper, we study
the surface electromagnetic waves localized in a CrI$_3$-based structure using
the results of {\it ab initio} calculations for the CrI$_3$ conductivity
tensor. In particular, we provide an estimate for the critical angle
corresponding to the surface plasmon polariton generation in the
Kretschmann-Raether configuration by a detailed investigation of reflectance
spectrum as well as the magnetic field distribution for different CrI$_3$ layer
thicknesses. We also study the bilayer structure formed by two CrI$_3$ layers
separated by a SiO$_2$ spacer and show that the surface plasmon resonance can
be achieved at the interface between CrI$_3$ and air depending on the spacer
thickness.",1909.13841v2
2019-10-02,A Low Temperature Functioning CoFeB/MgO Based Perpendicular Magnetic Tunnel Junction for Cryogenic Nonvolatile Random Access Memory,"We investigated the low temperature performance of CoFeB/MgO based
perpendicular magnetic tunnel junctions (pMTJs) by characterizing their
quasi-static switching voltage, high speed pulse write error rate and endurance
down to 9 K. pMTJ devices exhibited high magnetoresistance (>120%) and reliable
(error rate<10-4) bi-directional switching with 2 to 200 ns voltage pulses. The
endurance of the devices at 9 K surpassed that at 300 K by three orders of
magnitude under the same write conditions, functioning for more than 10^12
cycles with 10 ns write pulses. The critical switching voltage at 9 K was
observed to increase by 33% to 93%, depending on pulse duration, compared to
that at 350 K. Ferromagnetic resonance and magnetization measurements on
blanket pMTJ film stacks suggest that the increased switching voltage is
associated with an increase in effective magnetic anisotropy and magnetization
of free layer with decreasing temperature. Our work demonstrates that CoFeB/MgO
based pMTJs have great potential to enable cryogenic MRAM and that their low
temperature magnetization and effective magnetic anisotropy can be further
optimized to lower operating power and improve endurance.",1910.01149v1
2019-10-17,The valley Nernst effect in WSe$_2$,"The Hall effect can be extended by inducing a temperature gradient in lieu of
electric field that is known as the Nernst (-Ettingshausen) effect. The
recently discovered spin Nernst effect in heavy metals continues to enrich the
picture of Nernst effect-related phenomena. However, the collection would not
be complete without mentioning the valley degree of freedom benchmarked by the
observation of the valley Hall effect. Here we show the experimental evidence
of its missing counterpart, the valley Nernst effect. Using millimeter-sized
WSe$_{2}$ mono-multi-layers and the ferromagnetic resonance-spin pumping
technique, we are able to apply a temperature gradient by off-centering the
sample in the radio frequency cavity and address a single valley through
spin-valley coupling. The combination of a temperature gradient and the valley
polarization leads to the valley Nernst effect in WSe$_{2}$ that we detect
electrically at room temperature. The valley Nernst coefficient is in very good
agreement with the predicted value.",1910.08070v1
2019-10-25,Interplay of Bound Magnetic Polaron and p-d exchange interaction in Co-doped 3C-SiC,"Bound Magnetic Polarons (BMP) have been proposed to play an important role in
doped wide band gap semiconductors. We report the experimental evidence
supporting polaronic magnetism and the role of defects on it. Temperature
variation of electron paramagnetic resonance study reveals that the valence
state of cobalt is 2+ and its nearest environment in the system is distorted
tetrahedral in nature. Room temperature ferromagnetism have been found in all
the doped [Co (1, 3, 5) % doped 3C-SiC] samples. The Curie temperature, TC of
the samples have been found to be above 800 K. The isothermal magnetization
plots, to determine the strength of domain wall pinning were analyzed using the
Jiles-Atherton Model. The temperature variation of the anisotropic constant was
determined using Law of Approach to saturation (LAS), which decreases with
increase in temperature. Quantitative analysis of magnetic interaction has been
carried out and the result is explained by using BMP Model, which probably
arises out of the exchange interaction of Co2+ ions with related (Si, C)
defects.",1910.11899v3
2020-01-30,Electrical spectroscopy of forward volume spin waves in perpendicularly magnetized materials,"We study the potential of all-electrical inductive techniques for the
spectroscopy of propagating forward volume spin waves. We develop a
one-dimensional model to account for the electrical signature of spin-wave
reflection and transmission between inductive antennas and validate it with
experiments on a perpendicularly magnetized Co/Ni multilayer. We describe the
influence of the antenna geometry and antenna-to-antenna separation, as well as
that of the material parameters on the lineshape of the inductive signals. For
a finite damping, the broadband character of the antenna emission in the wave
vector space imposes to take into account the growing decoherence of the
magnetization waves upon their spatial propagation. The transmission signal can
be viewed as resulting from two contributions: a first one from propagating
spin-waves leading to an oscillatory phase of the broadband transmission
coefficient, and another one originating from the distant induction of
ferromagnetic resonance because of the long-range stray fields of realistic
antennas. Depending on the relative importance of these two contributions, the
decay of the transmitted signal with the propagation distance may not be
exponential and the oscillatory character of the spin-wave phase upon
propagation may be hidden. Our model and its experimental validation allow to
define geometrical and material specifications to be met to enable the use of
forward volume spin waves as efficient information carriers.",2001.11483v1
2020-02-20,Study of the spin-pump-induced inverse spin-Hall effect in Bi doped n-type Si,"An inverse spin Hall effect (ISHE) in n-type silicon was observed
experimentally when conduction electrons were scattered on the spin-orbit
potential of bismuth. The spin current in the silicon layer was generated by
excitation of the magnetization precession during ferromagnetic resonance in a
thin permalloy (Py) layer deposited on a Si layer doped by phosphor and
bismuth. From the angular dependences of the dc voltage for different
Py/n-Si:Bi structures aligned along the [011] or [100] crystal axes, we were
able to distinguish the planar Hall effect (PHE) and ISHE contributions. The
ISHE dc voltage signal was proportional to sin{\theta}*sin2{\theta} product for
the structure aligned to the [011] crystal axis and to sin{\theta}*cos2{\theta}
for the [100] direction. In addition, the PHE dc voltage was observed for the
angles corresponded to the sin2{\theta} dependence. It means that for silicon
as a many-valley semiconductor, the scattering of spins due to the spin-orbit
potential induced by shallow donor in n-type material is dependent on the
orientation of the valley axes relative to the direction of the magnetic field.",2002.08639v1
2020-12-02,Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements,"Media with engineered magnetization are essential building blocks in
superconductivity, magnetism and magnon spintronics. However, the established
thin-film and lithographic techniques insufficiently suit the realization of
planar components with on-demand-tailored magnetization in the lateral
dimension. Here, we demonstrate the engineering of the magnetic properties of
CoFe-based nanodisks fabricated by the mask-less technique of focused electron
beam induced deposition (FEBID). The material composition in the nanodisks is
tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their
post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange
stiffness $A$ of the disks are deduced from perpendicular ferromagnetic
resonance measurements. The achieved $M_s$ variation in the broad range from
$720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the
$M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The
presented approach paves a way towards nanoscale 2D and 3D systems with
controllable and space-varied magnetic properties.",2012.01481v1
2018-03-07,"Voltage driven, local, and efficient excitation of nitrogen-vacancy centers in diamond","Magnetic sensing technology has found widespread application in industries as
diverse as transportation, medicine, and resource exploration. Such use cases
often require highly sensitive instruments to measure the extremely small
magnetic fields involved, relying on difficult to integrate Superconducting
Quantum Interference Device (SQUID) and Spin-Exchange Relaxation Free (SERF)
magnetometers. A potential alternative, nitrogen vacancy (NV) centers in
diamond, has shown great potential as a high sensitivity and high resolution
magnetic sensor capable of operating in an unshielded, room-temperature
environment. Transitioning NV center based sensors into practical devices,
however, is impeded by the need for high power RF excitation to manipulate
them. Here we report an advance that combines two different physical phenomena
to enable a highly efficient excitation of the NV centers: magnetoelastic drive
of ferromagnetic resonance (FMR) and NV-magnon coupling. Our work demonstrates
a new pathway to combine acoustics and magnonics that enables highly energy
efficient and local excitation of NV centers without the need for any external
RF excitation, and thus could lead to completely integrated, on-chip, atomic
sensors.",1803.02863v2
2018-06-13,"Interplay of lattice, electronic and spin degrees of freedom in detwinned BaFe$_{2}$As$_{2}$: a Raman scattering study","We report results of Raman scattering experiments on twin-free
BaFe$_{2}$As$_{2}$ with the main focus placed on understanding the influence of
electronic and spin degrees of freedom on the lattice dynamics. In particular,
we scrutinize the $E_g$ modes and the As $A_{1g}$ mode. Each of the two $E_g$
phonons in the tetragonal phase is observed to split into a $B_{2g}$ and a
$B_{3g}$ mode upon entering the orthorhombic stripe-magnetic phase. The
splitting amounts to approximately 10\,cm$^{-1}$ and less than 5\,cm$^{-1}$ for
the low- and the high-energy $E_g$ mode, respectively. The detailed study of
the fully symmetric As mode using parallel incident and outgoing photon
polarizations along either the antiferromagnetic or the ferromagnetic Fe-Fe
direction reveals an anisotropic variation of the spectral weight with the
energy of the exciting laser indicating a polarization-dependent resonance
effect. Along with the experiments we present results from density functional
theory calculations of the phonon eigenvectors, the dielectric function, and
the Raman tensor elements. The comparison of theory and experiment indicates
that (i) orbital-selective electronic correlations are crucial to understand
the lattice dynamics and (ii) all phonon anomalies originate predominantly from
the magnetic ordering and the corresponding reconstruction of the electronic
bands at all energies.",1806.04989v1
2018-06-20,Quantum Speed-Up at Zero Temperature via Coherent Catalysis,"It is known that secondary non-stoquastic drivers may offer speed-ups or
catalysis in some models of adiabatic quantum computation accompanying the more
typical transverse field driver. Their combined intent is to raze potential
barriers to zero during adiabatic evolution from a false vacuum to a true
minimum; first order phase transitions are softened into second order
transitions. We move beyond mean-field analysis to a fully quantum model of a
spin ensemble undergoing adiabatic evolution in which the spins are mapped to a
variable mass particle in a continuous one-dimensional potential. We
demonstrate the necessary criteria for enhanced mobility or `speed-up' across
potential barriers is actually a quantum form of the Rayleigh criterion.
Quantum catalysis is exhibited in models where previously thought not possible,
when barriers cannot be eliminated. For the $3$-spin model with secondary
anti-ferromagnetic driver, catalysed time complexity scales between linear and
quadratically with the number of qubits. As a corollary, we identify a useful
resonance criterion for quantum phase transition that differs from the
classical one, but converges on it, in the thermodynamic limit.",1806.07602v3
2018-08-17,Temperature Dependence of Magnetic Properties of an 18-nm-thick YIG Film Grown by Liquid Phase Epitaxy: Effect of a Pt Overlayer,"Liquid phase epitaxy of an 18 nm thick Yttrium Iron garnet (YIG) film is
achieved. Its magnetic properties are investigated in the 100 -- 400 K
temperature range, as well as the influence of a 3 nm thick Pt overlayer on
them. The saturation magnetization and the magnetocrystalline cubic anisotropy
of the bare YIG film behave similarly to bulk YIG. A damping parameter of only
a few $10^{-4}$ is measured, together with a low inhomogeneous contribution to
the ferromagnetic resonance linewidth. The magnetic relaxation increases upon
decreasing temperature, which can be partly ascribed to impurity relaxation
mechanisms. While it does not change its cubic anisotropy, the Pt capping
strongly affects the uniaxial perpendicular anisotropy of the YIG film, in
particular at low temperatures. The interfacial coupling in the YIG/Pt
heterostructure is also revealed by an increase of the linewidth, which
substantially grows by lowering the temperature.",1808.05785v2
2018-08-19,Spin-dependent scattering and magnetic proximity effect in Ni-doped Co/Cu multilayers as a probe of atomic magnetism,"We investigate the spin transport and ferromagnetic resonance properties of
giant magnetoresistive (GMR) Co/Cu-Ni multilayers with variable levels of Ni
doping in the Cu spacer. We present an experimental evidence for a
magnetic-to-diamagnetic transition in the atomic magnetic moment of Ni in the
Cu matrix for concentrations below 15 at. % Ni. As its concentration is
increased, Ni atoms turn into spin scattering centers, which is manifested
experimentally as a step-like change in the GMR of the multilayers. This
behavior is observed in multilayers with gradient-doped Cu spacers, where only
the inner region was doped with Ni. In the uniformly doped spacers the GMR
decreases monotonously with increasing Ni content, indicating that Ni atoms are
magnetic and act as spin relaxation centers in the entire dopant-concentration
range studied. We explain the difference in the observed GMR behavior as due to
a strong magnetic proximity effect in the uniform spacers, which is efficiently
suppressed in the gradient spacers. The observed magnetic phase transition is
fully supported by our detailed ab-initio calculations, taking into
consideration structural relaxation in the system as well as potential Ni
clustering. Controlling the loss or gain of the atomic magnetism for a specific
dopant can be a tool in probing and controlling spin relaxation in materials
and devices for spin-valve and spin-torque based applications.",1808.06198v1
2018-12-24,Non-Reciprocal Spin Pumping in Asymmetric Magnetic Trilayers,"In magnetic trilayer systems, spin pumping is generally addressed as a
reciprocal mechanism characterized by one unique spin mixing conductance common
to both interfaces. However, this assumption is questionable in cases where
different types of interfaces are present in the material. Here, we present a
general theory for analyzing spin pumping in cases with more than one unique
interface. The theory is applied to analyze layer-resolved ferromagnetic
resonance experiments on the trilayer system
Ni$_{20}$Fe$_{80}$/Ru/Fe$_{49}$Co$_{49}$V$_2$ where the Ru spacer thickness is
varied to tune the indirect exchange coupling. The results show that the spin
pumping in trilayer systems with dissimilar magnetic layers is non-reciprocal,
with a surprisingly large difference between spin-pumping induced damping of
different interfaces. Our findings have importance on dynamics of spintronic
devices based on magnetic multilayer materials.",1812.09978v1
2019-01-21,Unoccupied surface and interface states in Pd thin films deposited on Fe/Ir(111) surface,"We present a systematic first-principles study of the electronic surface
states and resonances occuring in thin films of Pd of various thicknesses
deposited on a single ferromagnetic monolayer of Fe on top of Ir(111)
substrate. This system is of interest since one Pd layer deposited on
Fe/Ir(111) hosts small magnetic skyrmions. The latter are topological magnetic
objects with swirling spin-textures with possible implications in the context
of spintronic devices since they have the potential to be used as magnetic bits
for information technology. The stabilization, detection and manipulation of
such non-collinear magnetic entities require a quantitative investigation and a
fundamental understanding of their electronic structure. Here we investigate
the nature of the unoccupied electronic states in Pd/Fe/Ir(111), which are
essential in the large spin-mixing magnetoresistance (XMR) signature captured
using non spin-polarized scanning tunnelling microscopy [Crum et al., Nat.
Commun. {\bf 6} 8541 (2015); Hanneken et al., Nat. Nanotech. {\bf 10}, 1039
(2015)]. To provide a complete analysis, we investigate bare Fe/Ir(111) and
Pd$_{n=2,7}$/Fe/Ir(111) surfaces. Our results demonstrate the emergence of
surface and interface states after deposition of Pd monolayers, which are
strongly impacted by the large spin-orbit coupling of Ir surface.",1901.07029v2
2019-02-01,Photoinduced Rashba spin to charge conversion via interfacial unoccupied state,"At interfaces with inversion symmetry breaking, Rashba effect couples the
motion of electrons to their spin; as a result, spin-charge interconversion
mechanism can occur. These interconversion mechanisms commonly exploit Rashba
spin splitting at the Fermi level by spin pumping or spin torque ferromagnetic
resonance. Here, we report evidence of significant photoinduced spin to charge
conversion via Rashba spin splitting in an unoccupied state above the Fermi
level at the Cu(111)/$\alpha$-Bi$_{2}$O$_{3}$ interface. We predict an average
Rashba coefficient of $1.72\times 10^{-10}eV.m$ at 1.98 eV above the Fermi
level, by fully relativistic first-principles analysis of the interfacial
electronic structure with spin orbit interaction. We find agreement with our
observation of helicity dependent photoinduced spin to charge conversion
excited at 1.96 eV at room temperature, with spin current generation of
$J_{s}=10^{6}A/m^{2}$. The present letter shows evidence of efficient
spin-charge conversion exploiting Rashba spin splitting at excited states,
harvesting light energy without magnetic materials or external magnetic fields.",1902.00237v2
2019-02-26,Enhanced Gilbert Damping in Re doped FeCo Films: A Combined Experimental and Theoretical Study,"The effects of rhenium doping in the range 0 to 10 atomic percent on the
static and dynamic magnetic properties of Fe65Co35 thin films have been studied
experimentally as well as with first principles electronic structure
calculations focusing on the change of the saturation magnetization and the
Gilbert damping parameter. Both experimental and theoretical results show that
the saturation magnetization decreases with increasing Re doping level, while
at the same time Gilbert damping parameter increases. The experimental low
temperature saturation magnetic induction exhibits a 29 percent decrease, from
2.31 T to 1.64 T, in the investigated doping concentration range, which is more
than predicted by the theoretical calculations. The room temperature value of
the damping parameter obtained from ferromagnetic resonance measurements,
correcting for extrinsic contributions to the damping, is for the undoped
sample 0.0027, which is close to the theoretically calculated Gilbert damping
parameter. With 10 atomic percent Re doping, the damping parameter increases to
0.0090, which is in good agreement with the theoretical value of 0.0073. The
increase in damping parameter with Re doping is explained by the increase in
density of states at Fermi level, mostly contributed by the spin-up channel of
Re. Moreover, both experimental and theoretical values for the damping
parameter are observed to be weakly decreasing with decreasing temperature.",1902.09896v1
2019-03-05,All-optical cryogenic thermometry based on NV centers in nanodiamonds,"The nitrogen-vacancy (NV) center in diamond has been recognized as a
high-sensitivity nanometer-scale metrology platform. Thermometry has been a
recent focus, with attention largely confined to room temperature applications.
Thermometry has been a recent focus, with attention largely confined to room
temperature applications. Temperature sensing at low temperatures, however,
remains challenging as the sensitivity decreases for many commonly used
techniques which rely on a temperature dependent frequency shift of the NV
centers spin resonance and its control with microwaves. Here we use an
alternative approach that does not require microwaves, ratiometric all-optical
thermometry, and demonstrate that it may be utilized to liquid nitrogen
temperatures without deterioration of the sensitivity. The use of an array of
nanodiamonds embedded within a portably polydimethylsiloxane (PDMS) sheet
provides a versatile temperature sensing platform that can probe a wide variety
of systems without the configurational restrictions needed for applying
microwaves. With this device, we observe a temperature gradient over tens of
microns in a ferromagnetic-insulator substrate (YIG) under local heating by a
resistive heater. This thermometry technique provides a cryogenically
compatible, microwave-free, minimally invasive approach capable of probing
local temperatures with few restrictions on the substrate materials.",1903.01605v1
2019-03-31,"Element-specific soft X-ray spectroscopy, scattering and imaging studies of skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$","A room-temperature skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$ has been
examined by means of soft X-ray absorption spectroscopy, resonant small-angle
scattering and extended reference holography. An element-selective study was
performed by exciting the $2p$-to-$3d$ transitions near Co and Mn $L_{2,3}$
absorption edges. By utilizing the coherence of soft X-ray beams the
element-specific real-space distribution of local magnetization at different
temperatures has been reconstructed using iterative phase retrieval and
holography with extended reference. It was shown that the magnetic moments of
Co and Mn are ferromagnetically coupled and exhibit similar magnetic patterns.
Both imaging methods provide a real-space resolution of 30 nm and allowed to
record a magnetic texture in the temperature range between $T\,=\,20$ K and
$T\,=120\,$ K, demonstrating the elongation of the skyrmions along the
principal crystallographic axes at low temperatures. Micromagnetic simulations
have shown that such deformation is driven by decreasing ratio of symmetric
exchange interaction to antisymmetric Dzyaloshinskii-Moriya interaction in the
system and effect of the cubic anisotropy.",1904.00477v1
2019-04-21,Brillouin-Mandelstam Spectroscopy of Stress-Modulated Spatially Confined Spin Waves in Ni Thin Films on Piezoelectric Heterostructures,"We report results of micro-Brillouin-Mandelstam light scattering spectroscopy
of thermal magnons in the two-phase synthetic multiferroic structure consisting
of a piezoelectric (PMN-PT) substrate and a Ni thin film with the thickness of
64 nm. The experimental data reveal the first two modes of the perpendicular
standing spin waves (PSSW) spatially confined across the Ni thin film. A
theoretical analysis of the frequency dependence of the PSSW peaks on the
external magnetic field reveals the asymmetric boundary condition, i.e.
pinning, for variable magnetization at different surfaces of the Ni thin film.
The strain field induced by applying DC voltage to PMN-PT substrate leads to a
down shift of PSSW mode frequency owing to the magneto-elastic effect in Ni,
and corresponding changes in the spin wave resonance conditions. The observed
non-monotonic dependence of the PSSW frequency on DC voltage is related to an
abrupt change of the pinning parameter at certain values of the voltage. The
obtained results are important for understanding the thermal magnon spectrum in
ferromagnetic films and development of the low-power spin-wave devices.",1904.09553v1
2019-08-02,Tunable pure spin supercurrents and the demonstration of a superconducting spin-wave device,"Recent ferromagnetic resonance experiments and theory of Pt/Nb/Ni8Fe2
proximity-coupled structures strongly suggest that spin-orbit coupling (SOC) in
Pt in conjunction with a magnetic exchange field in Ni8Fe2 are the essential
ingredients to generate a pure spin supercurrent channel in Nb. Here, by
substituting Pt for a perpendicularly magnetized Pt/Co/Pt spin-sink, we are
able to demonstrate the role of SOC, and show that pure spin supercurrent
pumping efficiency across Nb is tunable by controlling the magnetization
direction of Co. By inserting a Cu spacer with weak SOC between Nb and
Pt/(Co/Pt) spin-sink, we also prove that Rashba type SOC is key for forming and
transmitting pure spin supercurrents across Nb. Finally, by engineering these
properties within a single multilayer structure, we demonstrate a prototype
superconducting spin-wave (SW) device in which lateral SW propagation is
gateable via the opening or closing of a vertical pure spin supercurrent
channel in Nb.",1908.00873v3
2019-08-17,Electronic phase separation at LaAlO3/SrTiO3 interfaces tunable by oxygen deficiency,"Electronic phase separation is crucial for the fascinating macroscopic
properties of the LaAlO3/SrTiO3 (LAO/STO) paradigm oxide interface, including
the coexistence of superconductivity and ferromagnetism. We investigate this
phenomenon using angle-resolved photoelectron spectroscopy (ARPES) in the
soft-X-ray energy range, where the enhanced probing depth combined with
resonant photoexcitation allow access to fundamental electronic structure
characteristics (momentum-resolved spectral function, dispersions and ordering
of energy bands, Fermi surface) of buried interfaces. Our experiment uses X-ray
irradiation of the LAO/STO interface to tune its oxygen deficiency, building up
a dichotomic system where mobile weakly correlated Ti t2g-electrons co-exist
with localized strongly correlated Ti eg-ones. The ARPES spectra dynamics under
X-ray irradiation shows a gradual intensity increase under constant Luttinger
count of the Fermi surface. This fact identifies electronic phase separation
(EPS) where the mobile electrons accumulate in conducting puddles with fixed
electronic structure embedded in an insulating host phase, and allows us to
estimate the lateral fraction of these puddles. We discuss the physics of EPS
invoking a theoretical picture of oxygen-vacancy clustering, promoted by the
magnetism of the localized Ti eg-electrons, and repelling of the mobile
t2g-electrons from these clusters. Our results on the irradiation-tuned EPS
elucidate the intrinsic one taking place at the stoichiometric LAO/STO
interfaces.",1908.06321v1
2019-11-21,Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy,"The field of magnon spintronics is experiencing an increasing interest in the
development of solutions for spin-wave-based data transport and processing
technologies that are complementary or alternative to modern CMOS
architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the
gold standard for insulator-based spintronics to date, but a potential process
technology that can deliver perfect, homogeneous large-diameter films is still
lacking. We report that liquid phase epitaxy (LPE) enables the deposition of
nanometer-thin YIG films with low ferromagnetic resonance losses and
consistently high magnetic quality down to a thickness of 20 nm. The obtained
epitaxial films are characterized by an ideal stoichiometry and perfect film
lattices, which show neither significant compositional strain nor geometric
mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is
similar to that of single crystalline bulk YIG. We found, that the Gilbert
damping coefficient alpha is independent of the film thickness and close to 1 x
10-4, and that together with an inhomogeneous peak-to-peak linewidth broadening
of delta H0|| = 0.4 G, these values are among the lowest ever reported for YIG
films with a thickness smaller than 40 nm. These results suggest, that
nanometer-thin LPE films can be used to fabricate nano- and micro-scaled
circuits with the required quality for magnonic devices. The LPE technique is
easily scalable to YIG sample diameters of several inches.",1911.09400v1
2019-12-06,Many-body wavefunctions for quantum impurities out of equilibrium,"We present a method for calculating the time-dependent many-body wavefunction
that follows a local quench. We apply the method to the voltage-driven
nonequilibrium Kondo model to find the exact time-evolving wavefunction
following a quench where the dot is suddenly attached to the leads at $t=0$.
The method, which does not use Bethe ansatz, also works in other quantum
impurity models (we include results for the interacting resonant level and the
Anderson impurity model) and may be of wider applicability. In the particular
case of the Kondo model, we show that the long-time limit (with the system size
taken to infinity first) of the time-evolving wavefunction is a
current-carrying nonequilibrium steady state that satisfies the
Lippmann-Schwinger equation. We show that the electric current in the
time-evolving wavefunction is given by a series expression that can be expanded
either in weak coupling or in strong coupling, converging to all orders in the
steady-state limit in either case. The series agrees to leading order with
known results in the well-studied regime of weak antiferromagnetic coupling and
also reveals another universal regime of strong ferromagnetic coupling, with
Kondo temperature $T_K^{(F)} = D e^{-\frac{3\pi^2}{8} \rho |J|}$ ($J<0$,
$\rho|J|\to\infty$). In this regime, the differential conductance $dI/dV$
reaches the unitarity limit $2e^2/h$ asymptotically at large voltage or
temperature.",1912.02956v3
2019-12-19,Unravelling competing microscopic interactions at a phase boundary: a single crystal study of the metastable antiferromagnetic pyrochlore Yb$_{2}$Ge$_{2}$O$_{7}$,"We report inelastic neutron scattering measurements from our newly
synthesized single crystals of the structurally metastable antiferromagnetic
pyrochlore Yb$_{2}$Ge$_{2}$O$_{7}$. We determine the four symmetry-allowed
nearest-neighbor anisotropic exchange parameters via fits to linear spin wave
theory supplemented by fits of the high-temperature specific heat. The exchange
parameters so-determined are strongly correlated to the values determined for
the $g$-tensor components, as previously observed for the related Yb pyrochlore
Yb$_{2}$Ti$_{2}$O$_{7}$. To address this issue, we directly determined the
$g$-tensor from electron paramagnetic resonance of 1% Yb-doped
Lu$_{2}$Ge$_{2}$O$_{7}$, thus enabling an unambiguous determination of the
exchange parameters. Our results show that Yb$_{2}$Ge$_{2}$O$_{7}$ resides
extremely close to the classical phase boundary between an antiferromagnetic
$\Gamma_5$ phase and a splayed ferromagnet phase. By juxtaposing our results
with recent ones on Yb$_{2}$Ti$_{2}$O$_{7}$, our work illustrates that the Yb
pyrochlore oxides represent ideal systems for studying quantum magnets in close
proximity to classical phase boundaries.",1912.09448v2
2019-12-27,Realizing spin-Hamiltonians in nanoscale active photonic lattices,"Spin models arise in the microscopic description of magnetic materials, where
the macroscopic characteristics are governed by exchange interactions among the
constituent magnetic moments. Recently, there has been a growing interest in
complex systems with spin Hamiltonians, largely due to the rich behaviors
exhibited by such interactions at the macroscale. Along these lines, it has
been shown that certain classes of optimization problems involving large
degrees of freedom can be effectively mapped into classical spin models. In
this vein, the respective extremum can be found by identifying the ground state
of the associated spin Hamiltonian. Here, we show both theoretically and
experimentally, that the cooperative interplay among vectorial electromagnetic
modes in coupled metallic nanolasers can be utilized as a means to emulate
certain types of spin-like systems. The ensuing spin exchange interactions are
in general anisotropic, in a way similar to that encountered in magnetic
materials involving spin-orbit coupling. For some topologies, we find that
these active nanophotonic structures are governed by a classical XY Hamiltonian
that exhibits two phases akin to those associated with ferromagnetic (FM) and
antiferromagnetic (AF) materials. In addition, we show that in certain
configurations, the electromagnetic field distribution can undergo geometrical
frustration, depending on the lattice shape and the transverse resonant modes
supported by the individual cavity elements. Our results could pave the way
towards a new scalable nanophotonic platform to study spin exchange
interactions, that can in turn be potentially exploited to investigate more
large-scale networks, emulate some magnetic materials, or to address a variety
of optimization problems.",1912.12075v1
2020-04-30,Local spin transfer torque and magnetoresistance in domain walls with variable width,"Use of a spin polarized current for the manipulation of magnetic domain walls
in ferromagnetic nanowires has been the subject of intensive research for many
years. Recently, due to technological advancements, creating nano-contacts with
special characteristics is becoming more and more prevalent. We now present a
full quantum investigation of the magnetoresistance and the spin transfer
torque in a domain wall, which is embedded in a nano-contact of Ni$_{80}$Fe$_
{20}$, where the size of the domain wall becomes a relevant tunable parameter.
The dependence on the domain wall width as well as the spatial dependence of
the torque along the domain wall can be analyzed in complete detail. The
magnetoresistance drops with increasing domain wall width as expected, but also
shows characteristic modulations and points of resonant spin-flip transmission.
The spin transfer torque has both significant in-plane and out-of-plane
contributions even without considering relaxation. A closer inspection
identifies contributions from the misalignment of the spin density for short
domain walls as well as an effective gauge field for longer domain walls, both
of which oscillate along the domain wall.",2005.00011v1
2020-05-07,Effect of interfacial oxidation layer in spin pumping experiments on Ni$_{80}$Fe$_{20}$/SrIrO$_3$ heterostructures,"SrIrO$_3$ with its large spin-orbit coupling and low charge conductivity has
emerged as a potential candidate for efficient spin-orbit torque magnetization
control in spintronic devices. We here report on the influence of an
interfacial oxide layer on spin pumping experiments in Ni$_{80}$Fe$_{20}$
(NiFe)/SrIrO$_3$ bilayer heterostructures. To investigate this scenario we have
carried out broadband ferromagnetic resonance (BBFMR) measurements, which
indicate the presence of an interfacial antiferromagnetic oxide layer. We
performed in-plane BBFMR experiments at cryogenic temperatures, which allowed
us to simultaneously study dynamic spin pumping properties (Gilbert damping)
and static magnetic properties (such as the effective magnetization and
magnetic anisotropy). The results for NiFe/SrIrO$_3$ bilayer thin films were
analyzed and compared to those from a NiFe/NbN/SrIrO$_3$ trilayer reference
sample, where a spin-transparent, ultra-thin NbN layer was inserted to prevent
oxidation of NiFe. At low temperatures, we observe substantial differences in
the magnetization dynamics parameters of these samples, which can be explained
by an antiferromagnetic interfacial layer in the NiFe/SrIrO$_3$ bilayers.",2005.03727v1
2020-05-20,Anomalous in-gap edge states in two-dimensional pseudospin-1 Dirac insulators,"Quantum materials that host a flat band, such as pseudospin-1 lattices and
magic-angle twisted bilayer graphene, can exhibit drastically new physical
phenomena including unconventional superconductivity, orbital ferromagnetism,
and Chern insulating behaviors. We report a surprising class of electronic
in-gap edge states in pseudospin-1 materials without the conventional need of
band-inversion topological phase transitions or introducing magnetism via an
external magnetic type of interactions. In particular, we find that, in
two-dimensional gapped (insulating) Dirac systems of massive spin-1
quasiparticles, in-gap edge modes can emerge through only an {\em electrostatic
potential} applied to a finite domain. Associated with these unconventional
edge modes are spontaneous formation of pronounced domain-wall spin textures,
which exhibit the feature of out-of-plane spin-angular momentum locking on both
sides of the domain boundary and are quite robust against boundary deformations
and impurities despite a lack of an explicit topological origin. The in-gap
modes are formally three-component evanescent wave solutions, akin to the
Jackiw-Rebbi type of bound states. Such modes belong to a distinct class due to
the following physical reasons: three-component spinor wave function, unusual
boundary conditions, and a shifted flat band induced by the external scalar
potential. Not only is the finding of fundamental importance, but it also paves
the way for generating highly controllable in-gap edge states with emergent
spin textures using the traditional semiconductor gate technology. Results are
validated using analytic calculations of a continuum Dirac-Weyl model and
tight-binding simulations of realistic materials through characterizations of
local density of state spectra and resonant tunneling conductance.",2005.10183v1
2020-06-01,Enhancement in Thermally Generated Spin Voltage at Pd/NiFe$_2$O$_4$ Interfaces by the Growth on Lattice-Matched Substrates,"Efficient spin injection from epitaxial ferrimagnetic NiFe$_2$O$_4$ thin
films into a Pd layer is demonstrated via spin Seebeck effect measurements in
the longitudinal geometry. The NiFe$_2$O$_4$ films (60 nm to 1 $\mu$m) are
grown by pulsed laser deposition on isostructural spinel MgAl$_2$O$_4$,
MgGa$_2$O$_4$, and CoGa$_2$O$_4$ substrates with lattice mismatch varying
between 3.2% and 0.2%. For the thinner films ($\leq$ 330 nm), an increase in
the spin Seebeck voltage is observed with decreasing lattice mismatch, which
correlates well with a decrease in the Gilbert damping parameter as determined
from ferromagnetic resonance measurements. High resolution transmission
electron microscopy studies indicate substantial decrease of antiphase boundary
and interface defects that cause strain-relaxation, i.e., misfit dislocations,
in the films with decreasing lattice mismatch. This highlights the importance
of reducing structural defects in spinel ferrites for efficient spin injection.
It is further shown that angle-dependent spin Seebeck effect measurements
provide a qualitative method to probe for in-plane magnetic anisotropies
present in the films.",2006.00777v1
2020-06-07,Magnetocrystalline anisotropy of the easy-plane metallic antiferromagnet Fe$_2$As,"Magnetocrystalline anisotropy is a fundamental property of magnetic materials
that determines the dynamics of magnetic precession, the frequency of spin
waves, the thermal stability of magnetic domains, and the efficiency of
spintronic devices. We combine torque magnetometry and density functional
theory calculations to determine the magnetocrystalline anisotropy of the
metallic antiferromagnet Fe$_2$As. Fe$_2$As has a tetragonal crystal structure
with the N\'eel vector lying in the (001) plane. We report that the four-fold
magnetocrystalline anisotropy in the (001)-plane of Fe$_2$As is extremely
small, ${K_{22}} = - 150~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$ at T = 4 K, much
smaller than perpendicular magnetic anisotropy of ferromagnetic structure
widely used in spintronics device. ${K_{22}}$ is strongly temperature dependent
and close to zero at T > 150 K. The anisotropy ${K_1}$ in the (010) plane is
too large to be measured by torque magnetometry and we determine ${K_1} =
-830~{\rm{ kJ/}}{{\rm{m}}^{\rm{3}}}$ using first-principles density functional
theory. Our simulations show that the contribution to the anisotropy from
classical magnetic dipole-dipole interactions is comparable to the contribution
from spin-orbit coupling. The calculated four-fold anisotropy in the (001)
plane ${K_{22}}$ ranges from $- 292~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$ to
$280~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$, the same order of magnitude as the
measured value. We use ${K_1}$ from theory to predict the frequency and
polarization of the lowest frequency antiferromagnetic resonance mode and find
that the mode is linearly polarized in the (001)-plane with $f = $ 670 GHz.",2006.04192v1
2020-06-30,Spin and density self-ordering in dynamic polarization gradients fields,"We study the zero-temperature quantum phase diagram for a two-component
Bose-Einstein condensate in an optical cavity. The two atomic spin states are
Raman coupled by two transverse orthogonally-polarized, blue detuned plane-wave
lasers inducing a repulsive cavity potential. For weak pump the lasers favor a
state with homogeneous density and predefined uniform spin direction. When one
pump laser is polarized parallel to the cavity mode polarization, the photons
coherently scattered into the resonator induce a polarization gradient along
the cavity axis, which mediates long-range density-density, spin-density, and
spin-spin interactions. We show that the coupled atom-cavity system implements
central aspects of the $t$-$J$-$V$-$W$ model with a rich phase diagram. At the
mean-field limit we identify at least four qualitatively distinct density- and
spin-ordered phases including ferro- and anti-ferromagnetic order along the
cavity axis, which can be controlled via the pump strength and detuning. A real
time observation of amplitude and phase of the emitted fields bears strong
signatures of the realized phase and allows for real-time determination of
phase transition lines. Together with measurements of the population imbalance
most properties of the phase diagram can be reconstructed.",2006.16582v2
2020-10-05,Quantitative comparison of the magnetic proximity effect in Pt detected by XRMR and XMCD,"X-ray resonant magnetic reflectivity (XRMR) allows for the simultaneous
measurement of structural, optical and magnetooptic properties and depth
profiles of a variety of thin film samples. However, a same-beamtime
same-sample systematic quantitative comparison of the magnetic properties
observed with XRMR and x-ray magnetic circular dichroism (XMCD) is still
pending. Here, the XRMR results (Pt L$_{3}$ absorption edge) for the magnetic
proximity effect in Pt deposited on the two different ferromagnetic materials
Fe and Co$_{33}$Fe$_{67}$ are compared with quantitatively analyzed XMCD
results. The obtained results are in very good quantitative agreement between
the absorption-based (XMCD) and reflectivity-based (XRMR) techniques taking
into account an ab initio calculated magnetooptic conversion factor for the
XRMR analysis. Thus, it is shown that XRMR provides quantitative reliable spin
depth profiles important for spintronic and spin caloritronic transport
phenomena at this type of magnetic interfaces.",2010.02195v2
2021-02-05,Metal/SrTiO$_3$ two-dimensional electron gases for spin-to-charge conversion,"SrTiO$_3$-based two-dimensional electron gases (2DEGs) can be formed through
the deposition of epitaxial oxides like LaAlO$_3$ or of reactive metals such as
Al. Such 2DEGs possess a finite Rashba spin-orbit coupling that has recently
been harnessed to interconvert charge and spin currents through the direct and
inverse Edelstein and spin Hall effects. Here we compare the formation and
properties of 2DEGs generated in SrTiO$_3$ by the growth of Al, Ta and Y
ultrathin films by magnetron sputtering. By combining in situ and ex situ X-ray
photoelectron spectroscopy (XPS) we gain insight into the reduction of the
SrTiO$_3$ and the appearance of Ti$^{3+}$ states associated with 2DEG
formation, its reoxidation by exposure to the air, and the transformation of
the metal into its binary oxides. We extract the carrier densities through
magnetotransport and compare them with the XPS data. Finally, working with
samples covered by an extra layer of NiFe, we perform spin-pumping
ferromagnetic resonance experiments and investigate spin-charge conversion as a
function of gate voltage. We identify trends in the data across the different
sample systems and discuss them as a function of the carrier density and the
transparency of the metal oxide tunnel barrier.",2102.03093v1
2021-03-16,Large Spin-to-Charge Conversion in Ultrathin Gold-Silicon Multilayers,"Investigation of the spin Hall effect in gold has triggered increasing
interest over the past decade, since gold combines the properties of a large
bulk spin diffusion length and strong interfacial spin-orbit coupling. However,
discrepancies between the values of the spin Hall angle of gold reported in the
literature have brought into question the microscopic origin of the spin Hall
effect in Au. Here, we investigate the thickness dependence of the spin-charge
conversion efficiency in single Au films and ultrathin Au/Si multilayers by
non-local transport and spin-torque ferromagnetic resonance measurements. We
show that the spin-charge conversion efficiency is strongly enhanced in
ultrathin Au/Si multilayers, reaching exceedingly large values of 0.99 +/- 0.34
when the thickness of the individual Au layers is scaled down to 2 nm. These
findings reveal the coexistence of a strong interfacial spin-orbit coupling
effect which becomes dominant in ultrathin Au, and bulk spin Hall effect with a
relatively low bulk spin Hall angle of 0.012 +/- 0.005. Our experimental
results suggest the key role of the Rashba-Edelstein effect in the
spin-to-charge conversion in ultrathin Au.",2103.08876v1
2021-04-08,Spin-orbit coupling induced ultra-high harmonic generation from magnetic dynamics,"The recent boost in data transfer rates puts a daring strain on information
technology. Sustaining such a growth rate requires the development of sources,
detectors and systems working in the so-called TeraHertz (THz) gap covering the
frequency window from 0.1 to 10 THz (1 THz = 10$^{12}$~Hz). This gap represents
a challenge for conventional electronic devices due to carrier transit delays
($\sim$1-10ps), as well as for photonic devices due to thermal fluctuations
(300K$\sim$6THz). Nonetheless, designing efficient, room-temperature THz
sources would constitute a key enabler to applications spanning from
high-resolution imaging to extreme wide band wireless communication. Whereas
high-harmonic generation in solid is usually limited to less than ten
harmonics, broadband THz emission has been demonstrated using laser-induced
superdiffusive spin currents in magnetic bilayers composed of a ferromagnet
deposited on top of a noble metal. While promising, this technique presents the
major disadvantage of necessitating optical pumping and hence lacks
scalability. Here, we demonstrate that extremely high harmonic emission can be
achieved by exploiting conventional spin pumping, without the need of optical
excitation. We show that when the spin-orbit coupling strength is close to the
s-d exchange energy, a strongly non linear regime resulting from resonant spin
flip scattering occurs leading to the generation of a thousand of harmonics at
realistic antiferromagnetic precession frequencies, thereby enhancing both spin
and charge dynamics by two orders of magnitude, and allowing for an emission at
frequencies above 300 THz.",2104.04001v1
2021-04-09,Spin diffusion length associated to out-of-plane resistivity of Pt thin films in spin pumping experiments,"We present a broadband ferromagnetic resonance study of the Gilbert damping
enhancement ($\Delta \alpha$) due to spin pumping in NiFe/Pt bilayers. The
bilayers, which have negligible interfacial spin memory loss, are studied as a
function of the Pt layer thickness ($t_{\text{Pt}}$) and temperature (100-293
K). Within the framework of diffusive spin pumping theory, we demonstrate that
Dyakonov-Perel (DP) or Elliot-Yaffet (EY) spin relaxation mechanisms acting
alone are incompatible with our observations. In contrast, if we consider that
the relation between spin relaxation characteristic time ($\tau_{\text{s}}$)
and momentum relaxation characteristic time ($\tau_{\text{p}}$) is determined
by a superposition of DP and EY mechanisms, the qualitative and quantitative
agreement with experimental results is excellent. Remarkably, we found that
$\tau_{\text{p}}$ must be determined by the out-of-plane electrical resistivity
($\rho$) of the Pt film and hence its spin diffusion length
($\lambda_{\text{Pt}}$) is independent of $t_{\text{Pt}}$. Our work settles the
controversy regarding the $t_{\text{Pt}}$ dependence of $\lambda_{\text{Pt}}$
by demonstrating its fundamental connection with $\rho$ considered along the
same direction of spin current flow. \end{abstract}",2104.04426v1
2021-06-08,Observation of the out-of-plane polarized spin current from CVD grown WTe2,"Weyl semimetal Td-phase WTe2 possesses the spin-resolved band structure with
strong spin-orbit coupling, holding promises as a useful spin source material.
The noncentrosymmetric crystalline structure of Td-WTe2 endows the generation
of the out-of-plane polarized spin, which is of great interest in magnetic
memory applications. Previously, WTe2 was explored in spin devices based on
mechanically exfoliated single crystal flakes with a size of micrometers. For
practical spintronics applications, it is highly desirable to implement
wafer-scale thin films. In this work, we utilize centimeter-scale chemical
vapor deposition (CVD)-grown Td-WTe2 thin films and study the spin current
generation by the spin torque ferromagnetic resonance technique. We find the
in-plane and out-of-plane spin conductivities of 7.36 x 10^3 (h/2e) (ohm-m)^-1
and 1.76 x 10^3 (h/2e) (ohm-m)^-1, respectively, in CVD-growth 5 nm-WTe2. We
further demonstrate the current-induced magnetization switching in WTe2/NiFe at
room temperature in the domain wall motion regime, which may invigorate
potential spintronic device innovations based on Weyl semimetals.",2106.04154v1
2021-07-02,Magnomechanics in suspended magnetic beams,"Cavity optomechanical systems have become a popular playground for studies of
controllable nonlinear interactions between light and motion. Owing to the
large speed of light, realizing cavity optomechanics in the microwave frequency
range requires cavities up to several mm in size, hence making it hard to embed
several of them on the same chip. An alternative scheme with much smaller
footprint is provided by magnomechanics, where the electromagnetic cavity is
replaced by a magnet undergoing ferromagnetic resonance, and the optomechanical
coupling originates from magnetic shape anisotropy. Here, we consider the
magnomechanical interaction occurring in a suspended magnetic beam -- a scheme
in which both magnetic and mechanical modes physically overlap and can also be
driven individually. We show that a sizable interaction can be produced if the
beam has some initial static deformation, as is often the case due to unequal
strains in the constituent materials. We also show how the magnetism affects
the magnetomotive detection of the vibrations, and how the magnomechanics
interaction can be used in microwave signal amplification. Finally, we discuss
experimental progress towards realizing the scheme.",2107.01051v3
2021-09-08,Room-Temperature Intrinsic and Extrinsic Damping in Polycrystalline Fe Thin Films,"We examine room-temperature magnetic relaxation in polycrystalline Fe films.
Out-of-plane ferromagnetic resonance (FMR) measurements reveal Gilbert damping
parameters of $\approx$ 0.0024 for Fe films with thicknesses of 4-25 nm,
regardless of their microstructural properties. The remarkable invariance with
film microstructure strongly suggests that intrinsic Gilbert damping in
polycrystalline metals at room temperature is a local property of nanoscale
crystal grains, with limited impact from grain boundaries and film roughness.
By contrast, the in-plane FMR linewidths of the Fe films exhibit distinct
nonlinear frequency dependences, indicating the presence of strong extrinsic
damping. To fit our in-plane FMR data, we have used a grain-to-grain two-magnon
scattering model with two types of correlation functions aimed at describing
the spatial distribution of inhomogeneities in the film. However, neither of
the two correlation functions is able to reproduce the experimental data
quantitatively with physically reasonable parameters. Our findings advance the
fundamental understanding of intrinsic Gilbert damping in structurally
disordered films, while demonstrating the need for a deeper examination of how
microstructural disorder governs extrinsic damping.",2109.03684v2
2021-09-10,Electrical spectroscopy of the spin-wave dispersion and bistability in gallium-doped yttrium iron garnet,"Yttrium iron garnet (YIG) is a magnetic insulator with record-low damping,
allowing spin-wave transport over macroscopic distances. Doping YIG with
gallium ions greatly reduces the demagnetizing field and introduces a
perpendicular magnetic anisotropy, which leads to an isotropic spin-wave
dispersion that facilitates spin-wave optics and spin-wave steering. Here, we
characterize the dispersion of a gallium-doped YIG (Ga:YIG) thin film using
electrical spectroscopy. We determine the magnetic anisotropy parameters from
the ferromagnetic resonance frequency and use propagating spin wave
spectroscopy in the Damon-Eshbach configuration to detect the small spin-wave
magnetic fields of this ultrathin weak magnet over a wide range of wavevectors,
enabling the extraction of the exchange constant $\alpha=1.3(2)\times10^{-12}$
J/m. The frequencies of the spin waves shift with increasing drive power, which
eventually leads to the foldover of the spin-wave modes. Our results shed light
on isotropic spin-wave transport in Ga:YIG and highlight the potential of
electrical spectroscopy to map out the dispersion and bistability of
propagating spin waves in magnets with a low saturation magnetization.",2109.05045v1
2021-09-23,Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium,"Spin torque is a promising tool for driving magnetization dynamics for novel
computing technologies. These torques can be easily produced by spin-orbit
effects, but for most conventional spin source materials, a high degree of
crystal symmetry limits the geometry of the spin torques produced. Magnetic
ordering is one way to reduce the symmetry of a material and allow exotic
torques, and antiferromagnets are particularly promising because they are
robust against external fields. We present spin torque ferromagnetic resonance
measurements and second harmonic Hall measurements characterizing the spin
torques in antiferromagnetic iron rhodium alloy. We report extremely large,
strongly temperature-dependent exotic spin torques with a geometry apparently
defined by the magnetic ordering direction. We find the spin torque efficiency
of iron rhodium to be (330$\pm$150) % at 170 K and (91$\pm$32) % at room
temperature. We support our conclusions with theoretical calculations showing
how the antiferromagnetic ordering in iron rhodium gives rise to such exotic
torques.",2109.11108v1
2021-09-29,Pairing interaction in superconducting UCoGe tunable by magnetic field,"The mechanism of unconventional superconductivity, such as
high-temperature-cuprate, Fe-based, and heavy-fermion superconductors, has been
studied as a central issue in condensed-matter physics. Spin fluctuations,
instead of phonons, are considered to be responsible for the formation of
Cooper pairs, and many efforts have been made to confirm this mechanism
experimentally. Although a qualitative consensus seems to have been obtained,
experimental confirmation has not yet been achieved. This is owing to a lack of
the quantitative comparison between theory and experiments. Here, we show a
semi-quantitative comparison between the superconducting-transition temperature
($T_{\rm SC}$) and spin fluctuations derived from the nuclear magnetic
resonance (NMR) experiment on the ferromagnetic (FM) superconductor UCoGe, in
which the FM fluctuations and superconductivity are tunable by external fields.
The enhancement and abrupt suppression of $T_{\rm SC}$ by applied fields, as
well as the pressure variation of $T_{\rm SC}$ around the FM criticality are
well understood by the change in the FM fluctuations on the basis of the
single-band spin-triplet theoretical formalism. The present comparisons
strongly support the theoretical formalism of spin-fluctuation-mediated
superconductivity, particularly in UCoGe.",2109.14426v1
2021-10-29,4D visualization of the photoexcited coherent magnon by an X-ray free electron laser,"X-ray free electron lasers (XFEL) create femtosecond X-ray pulses with high
brightness and high longitudinal coherence allowing to extend X-ray
spectroscopy and scattering techniques into the ultrafast time-domain. These
X-rays are a powerful probe for studying coherent quasiparticle excitations in
condensed matter triggered by an impulsive optical laser pump. However, unlike
coherent phonons, other quasiparticles have been rarely observed due to small
signal changes and lack of standards for the identification. Here, we exploit
resonant magnetic X-ray diffraction using an XFEL to visualize a photoexcited
coherent magnon in space and time. Large intensity oscillations in
antiferromagnetic and ferromagnetic Bragg reflections from precessing moment
are observed in a multiferroic Y-type hexaferrite. The precession trajectory
reveals that a large, long-lived, photoinduced magnetic-field changes the net
magnetization substantially through the large-amplitude of the magnon. This
work demonstrates an efficient XFEL probe for the coherent magnon in the
spotlight for opto-spintronics application.",2110.15626v1
2021-11-23,Pressure driven magnetic order in Sr$_{1-x}$Ca$_x$Co$_2$P$_2$,"The magnetic phase diagram of Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ as a function of
hydrostatic pressure and temperature is investigated by means of high pressure
muon spin rotation, relaxation and resonance ($\mu^+$SR). The weak pressure
dependence for the $x\neq1$ compounds suggests that the rich phase diagram of
Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ as a function of $x$ at ambient pressure may not
only be attributed to solely chemical pressure effects. The $x=1$ compound on
the other hand reveals a high pressure dependence, where the long range
magnetic order is fully suppressed at $p_{\rm c2}\approx9.8$~kbar, which seem
to be a first order transition. In addition, an intermediate phase consisting
of dilute ferromagnetic islands (FMI) is formed above $p_{\rm c1}\approx8$~kbar
where they co-exist with a magnetically disordered state. Moreover, such FMI
phase seems to consist of an high- (FMI-\textcircled{\small{1}}) and
low-temperature (FMI-\textcircled{\small{2}}) region, respectively, separated
by a phase boundary at $T_{\rm i}\approx20$~K.",2111.11962v1
2021-12-08,Dark discrete breather modes in monoaxial chiral helimagnet with easy-plane anisotropy,"Nonlinearity and discreteness are two pivotal factors for an emergence of
discrete breather excitations in various media. We argue that these
requirements are met in the forced ferromagnetic phase of the monoaxial chiral
helimagnet CrNb$_3$S$_6$ due to specific domain structure of the compound. The
stationary, time-periodic breather modes appear as the discrete breather
lattice solutions whose period mismatches with a system size. Thanks to
easy-plane single-ion anisotropy intrinsic to CrNb$_3$S$_6$, these modes are of
the dark type with frequencies lying within the linear spin-wave band, close to
its bottom edge. They represent cnoidal states of magnetization, similar to the
well-known soliton lattice ground state, with differing but limited number of
embedded $2\pi$-kinks. Linear stability of these dark breather modes is
verified by means of the Floquet analysis. Their energy controlled by two
parameters, namely the breather lattice period and amplitude, falls off
linearly with a growth of the kink number. These results may pave a new path to
design spintronic resonators on the base of chiral helimagnets.",2112.04341v1
2021-12-14,Enhanced valley polarization in WS$_2$/LaMnO$_3$ heterostructure,"Monolayer transition metal dichalcogenides have attracted great attentions
for potential applications in valleytronics. However, the valley polarization
degree is usually not high because of the intervalley scattering. Here, we
demonstrate a largely enhanced valley polarization up to 80\% in monolayer
WS$_2$ under non-resonant excitation at 4.2 K using WS$_2$/LaMnO$_3$ thin film
heterostructure, which is much higher than that for monolayer WS$_2$ on
SiO$_2$/Si substrate with a valley polarization of 15\%. Furthermore, the
greatly enhanced valley polarization can be maintained to a high temperature of
about 160 K with a valley polarization of 53\%. The temperature dependence of
valley polarization is strongly correlated with the thermomagnetic curve of
LaMnO$_3$, indicating an exciton-magnon coupling between WS$_2$ and LaMnO$_3$.
A simple model is introduced to illustrate the underlying mechanisms. The
coupling of WS$_2$ and LaMnO$_3$ is further confirmed with an observation of
two interlayer excitons with opposite valley polarizations in the
heterostructure, resulting from the spin-orbit coupling induced splitting of
the conduction bands in monolayer transition metal dichalcogenides. Our results
provide a pathway to control the valleytronic properties of transition metal
dichalcogenides by means of ferromagnetic van der Waals engineering, paving a
way to practical valleytronic applications.",2112.07321v1
2021-12-21,Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG,"Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing
attention from the perspective of novel magnon-based data processing
applications. For short wavelengths needed in small-scale devices, the group
velocity is directly proportional to the spin-wave exchange stiffness constant
$\lambda_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering
(BLS) spectroscopy, we directly measure $\lambda_\mathrm{ex}$ in Ga-substituted
YIG thin films and show that it is about three times larger than for pure YIG.
Consequently, the spin-wave group velocity overcomes the one in pure YIG for
wavenumbers $k > 4$ rad/$\mu$m, and the ratio between the velocities reaches a
constant value of around 3.4 for all $k > 20$ rad/$\mu$m. As revealed by
vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR)
spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert
damping ($\alpha < 10^{-3}$), a decreased saturation magnetization $\mu_0
M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy
of about $\mu_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane
easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport
for all wavelengths in nano-scale systems independently of dipolar effects.",2112.11348v1
2022-01-31,Tuning spin-orbit torques across the phase transition in VO$_2$/NiFe heterostructure,"The emergence of spin-orbit torques as a promising approach to
energy-efficient magnetic switching has generated large interest in material
systems with easily and fully tunable spin-orbit torques. Here, current-induced
spin-orbit torques in VO$_2$/NiFe heterostructures were investigated using
spin-torque ferromagnetic resonance, where the VO$_2$ layer undergoes a
prominent insulator-metal transition. A roughly two-fold increase in the
Gilbert damping parameter, $\alpha$, with temperature was attributed to the
change in the VO$_2$/NiFe interface spin absorption across the VO$_2$ phase
transition. More remarkably, a large modulation ($\pm$100%) and a sign change
of the current-induced spin-orbit torque across the VO$_2$ phase transition
suggest two competing spin-orbit torque generating mechanisms. The bulk spin
Hall effect in metallic VO$_2$, corroborated by our first-principles
calculation of spin Hall conductivity, $\sigma_{SH} \approx 10^4
\frac{\hbar}{e} \Omega^{-1} m^{-1}$, is verified as the main source of the
spin-orbit torque in the metallic phase. The self-induced/anomalous torque in
NiFe, of the opposite sign and a similar magnitude to the bulk spin Hall effect
in metallic VO$_2$, could be the other competing mechanism that dominates as
temperature decreases. For applications, the strong tunability of the torque
strength and direction opens a new route to tailor spin-orbit torques of
materials which undergo phase transitions for new device functionalities.",2201.12984v1
2022-03-23,Terphenylthiazole-based self-assembled monolayers on cobalt with high conductance photo-switching ratio for spintronics,"Two new photo-switchable terphenylthiazoles molecules are synthesized and
self-assembled as monolayers on Au and on ferromagnetic Co electrodes. The
electron transport properties probed by conductive atomic force microscopy in
ultra-high vacuum reveal a conductance of the light-induced closed (c) form
larger than for the open (o) form. We report an unprecedented conductance ratio
up to 380 between the closed and open forms on Co for the molecule with the
anchoring group (thiol) on the side of the two N atoms of the thiazole unit.
This result is rationalized by Density Functional Theory (DFT) calculations
coupled to the Non-Equilibrium Green's function (NEGF) formalism. These
calculations show that the high conductance in the closed form is due to a
strong electronic coupling between the terphenylthiazole molecules and the Co
electrode that manifests by a resonant transmission peak at the Fermi energy of
the Co electrode with a large broadening. This behavior is not observed for the
same molecules self-assembled on gold electrodes. These high conductance ratios
make these Co-based molecular junctions attractive candidates to develop and
study switchable molecular spintronic devices.",2203.12436v1
2022-04-20,Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques,"Spintronics is showing promising results in the search for new materials and
effects to reduce energy consumption in information technology. Among these
materials, ferrimagnets are of special interest, since they can produce large
spin currents that trigger the magnetization dynamics of adjacent layers or
even their own magnetization. Here, we present a study of the generation of
spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice
magnetization is dominant at room temperature. Magnetic properties such as the
saturation magnetization are deduced from magnetometry measurements while
damping constant is estimated from spin-torque ferromagnetic resonance
(ST-FMR). We show that the overall damping-like (DL) and field-like (FL)
effective fields as well as the associated spin Hall angles can be reliably
obtained by performing the dependence of ST-FMR by an added dc current. The sum
of the spin Hall angles for both the spin Hall effect (SHE) and the spin
anomalous Hall effect (SAHE) symmetries are: $\theta_{DL}^{SAHE} +
\theta_{DL}^{SHE}=-0.15 \pm 0.05$ and $\theta_{FL}^{SAHE} +
\theta_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find
that $\theta_{DL}^{SHE}$ is positive and dominated by the negative
$\theta_{DL}^{SAHE}$. The present study paves the way for tuning the different
symmetries in spin conversion in highly efficient ferrimagnetic systems.",2204.09776v1
2022-06-10,Correlated normal state fermiology and topological superconductivity in UTe2,"UTe2 is a promising candidate for spin-triplet superconductors, in which a
paramagnetic normal state becomes superconducting due to spin fluctuations. The
subsequent discovery of various unusual superconducting properties has promoted
the use of UTe2 as an exciting playground to study unconventional
superconductivity, but fathoming the normal state fermiology and its influence
on the superconductivity still requires further investigation. Here, we
theoretically show that electron correlation induces a dramatic change in the
normal state fermiology with an emergent correlated Fermi surface (FS) driven
by Kondo resonance at low temperatures. This emergent correlated FS can account
for various unconventional superconducting properties in a unified way. In
particular, the geometry of the correlated FS can naturally host topological
superconductivity in the presence of odd-parity pairings, which become the
leading instability due to strong ferromagnetic spin fluctuations. Moreover,
two pairs of odd-parity channels appear as accidentally degenerate solutions,
which can naturally explain the multicomponent superconductivity with broken
time-reversal symmetry. Interestingly, the resulting time-reversal breaking
superconducting state is a Weyl superconductor in which Weyl points migrate
along the correlated FS as the relative magnitude of nearly degenerate pairing
solutions varies. We believe that the correlated normal state fermiology we
discovered provides a unified platform to describe the unconventional
superconductivity in UTe2.",2206.04876v4
2022-06-20,Asymmetric magnetic proximity interactions in MoSe$_{2}$/CrBr$_{3}$ van der Waals heterostructures,"Magnetic proximity interactions (MPIs) between atomically-thin semiconductors
and two-dimensional magnets provide a means to manipulate spin and valley
degrees of freedom in nonmagnetic monolayers, without the use of applied
magnetic fields. In such van der Waals (vdW) heterostructures, MPIs originate
in the nanometer-scale coupling between the spin-dependent electronic
wavefunctions in the two materials, and typically their overall effect is
regarded as an effective magnetic field acting on the semiconductor monolayer.
Here we demonstrate that this picture, while appealing, is incomplete: The
effects of MPIs in vdW heterostructures can be markedly asymmetric, in contrast
to that from an applied magnetic field. Valley-resolved optical reflection
spectroscopy of MoSe$_{2}$/CrBr$_{3}$ vdW structures reveals strikingly
different energy shifts in the $K$ and $K'$ valleys of the MoSe$_2$, due to
ferromagnetism in the CrBr$_3$ layer. Strong asymmetry is observed at both the
A- and B-exciton resonances. Density-functional calculations indicate that
valley-asymmetric MPIs depend sensitively on the spin-dependent hybridization
of overlapping bands, and as such are likely a general feature of such hybrid
vdW structures. These studies suggest routes to selectively control
\textit{specific} spin and valley states in monolayer semiconductors.",2206.09958v1
2022-07-15,Origin of exchange bias in [Co/Pt]ML/Fe multilayer with orthogonal magnetic anisotropies,"Magnetization reversal of soft ferromagnetic Fe layer, coupled to [Co/Pt]ML
multilayer [ML] with perpendicular magnetic anisotropy (PMA), has been studied
in-situ with an aim to understand the origin of exchange bias (EB) in
orthogonal magnetic anisotropic systems. The interface remanant state of the ML
is modified by magnetic field annealing, and the effect of the same on the soft
Fe layer is monitored using the in-situ magneto-optical Kerr effect (MOKE). A
considerable shift in the Fe layer hysteresis loop from the centre and an
unusual increase in the coercivity, similar to exchange bias phenomena, is
attributed to the exchange coupling at the [Co/Pt]ML and Fe interface. The
effect of the coupling on spin orientation at the interface is further explored
precisely by performing an isotope selective grazing incident nuclear resonance
scattering (GINRS) technique. Here, the interface selectivity is achieved by
introducing a 2 nm thick Fe57 marker between [Co/Pt]ML and Fe layers. Interface
sensitivity is further enhanced by performing measurements under the x-ray
standing wave conditions. The combined MOKE and GINRS analysis revealed the
unidirectional pinning of the Fe layer due to the net in-plane magnetic spin at
the interface caused by magnetic field annealing. Unidirectional exchange
coupling or pinning at the interface, which may be due to the formation of
asymmetrical closure domains, is found responsible for the origin of EB with an
unusual increase in coercivity.",2207.07376v2
2022-08-01,Observation of gigantic spin conversion anisotropy in bismuth,"Whilst the g-factor can be anisotropic due to the spin-orbit interaction
(SOI), its existence in solids cannot be simply asserted from a band structure,
which hinders progress on studies from such the viewpoints. The g-factor in
bismuth (Bi) is largely anisotropic; especially for holes at T-point, the
g-factor perpendicular to the trigonal axis is negligibly small (< 0.112),
whereas the g-factor along the trigonal axis is very large (62.7). We clarified
in this work that the large g- factor anisotropy gives rise to the gigantic
spin conversion anisotropy in Bi from experimental and theoretical approaches.
Spin-torque ferromagnetic resonance was applied to estimate the spin conversion
efficiency in rhombohedral (110) Bi to be 17%, which is unlike the negligibly
small efficiency in Bi(111). Harmonic Hall measurements supports the large spin
conversion efficiency in Bi(110). This is the first observation of gigantic
spin conversion anisotropy as the clear manifestation of the g-factor
anisotropy. Beyond the emblematic case of Bi, our study unveiled the
significance of the g-factor anisotropy in condensed-matter physics and can
pave a pathway toward establishing novel spin physics under g-factor control.",2208.00589v3
2022-08-19,Engineering random spin models with atoms in a high-finesse cavity,"All-to-all interacting, disordered quantum many-body models have a wide range
of applications across disciplines, from spin glasses in condensed-matter
physics, over holographic duality in high-energy physics, to annealing
algorithms in quantum computing. Typically, these models are abstractions that
do not find unambiguous physical realisations in nature. Here, we realise an
all-to-all interacting, disordered spin system by subjecting an atomic cloud in
a cavity to a controllable light shift. Adjusting the detuning between atom
resonance and cavity mode, we can tune between disordered versions of a
central-mode model and a Lipkin-Meshkov-Glick model. By spectroscopically
probing the low-energy excitations of the system, we explore the competition of
interactions with disorder across a broad parameter range. We show how disorder
in the central-mode model breaks the strong collective coupling, making the
dark state manifold cross over to a random distribution of weakly-mixed
light-matter, ""grey"", states. In the Lipkin-Meshkov-Glick model the
ferromagnetic finite-size ground state evolves towards a paramagnet as disorder
is increased. In that regime, semi-localised eigenstates emerge, as we observe
by extracting bounds on the participation ratio. These results present
significant steps towards freely programmable cavity-mediated interactions for
the design of arbitrary spin Hamiltonians.",2208.09421v1
2022-09-01,Spin-dependent metastable He ($2^3S$) atom scattering from ferromagnetic surfaces: Potential application to polarized-gas production,"A spin-polarized triplet metastable helium (He*) beam has been used as a
probe for surface magnetism, but changes in the spin state during scattering
from a surface remain unclear. In the present study, we explored this issue by
constructing an apparatus that allows us to direct a spin-polarized He* beam to
a surface and measure the spin polarization of He* scattered from the surface.
Magnetic hexapoles were used for both the beam polarization and the spin
analysis. The results of the spin-dependent He* scattering experiments on clean
Fe$_3$O$_4$(100), H-terminated Fe$_3$O$_4$(100), benzene-adsorbed
Fe$_3$O$_4$(100), and non-magnetic Cu(100) surfaces indicated that although the
spin direction of He* was mostly preserved during scattering from these
surfaces, spin-flop scattering of surviving He* occurred with a probability up
to approximately 0.1. Our results showed that the survival probability was
higher when the spins of He* and the Fe$_3$O$_4$(100) film were parallel, which
can be understood based on the lower He* resonance ionization rate for this
spin orientation. Based on our findings, we estimate that a non-polarized He*
gas becomes 10% spin-polarized after a single collision with a clean
Fe$_3$O$_4$(100) surface.",2209.00254v2
2022-09-01,Growth parameters of Bi0.1Y2.9Fe5O12 thin films for high frequency applications,"The growth and characterization of Bismuth (Bi) substituted YIG (Bi-YIG,
Bi0.1Y2.9Fe5O12) thin films are reported. Pulsed laser deposited (PLD) films
with thicknesses ranging from 20 to 150 nm were grown on Gadolinium Gallium
Garnet substrates. Two substrate orientations of (100) and (111) were
considered. The enhanced distribution of Bi3+ ions at dodecahedral site along
(111) is observed to lead to an increment in lattice constant from 12.379
angstrom in (100) to 12.415 angstrom in (111) oriented films. Atomic force
microscopy images showed decreasing roughness with increasing film thickness.
Compared to (100) grown films, (111) oriented films showed an increase in
ferromagnetic resonance linewidth and consequent increase in Gilbert damping.
The lowest Gilbert damping values are found to be (1.06) * 10E-4 for (100) and
(2.30) * 10E-4 for (111) oriented films with thickness of 150 nm. The observed
values of extrinsic linewidth, effective magnetization, and anisotropic field
are related to thickness of the films and substrate orientation. In addition,
the in-plane angular variation established four-fold symmetry for the (100)
deposited films unlike the case of (111) deposited films. This study prescribes
growth conditions for PLD grown single-crystalline Bi-YIG films towards desired
high frequency and magneto-optical device applications.",2209.00558v1
2022-09-21,Performance enhancement of a spin-wave-based reservoir computing system utilizing different physical conditions,"The authors have numerically studied how to enhance reservoir computing
performance by thoroughly extracting their spin-wave device potential for
higher-dimensional information generation. The reservoir device has a 1-input
exciter and 120-output detectors on the top of a continuous magnetic garnet
film for spin-wave transmission. For various nonlinear and fading-memory
dynamic phenomena distributing in the film space, small in-plane magnetic
fields were used to prepare stripe domain structures and various damping
constants at the film sides and bottom were explored. The ferromagnetic
resonant frequency and relaxation time of spin precession clearly characterized
the change in spin dynamics with the magnetic field and damping constant. The
common input signal for reservoir computing was a 1 GHz cosine wave with random
6-valued amplitude modulation. A basic 120-dimensional reservoir output vector
was obtained from time-series signals at the 120 output detectors under each of
the three magnetic field conditions. Then, 240- and 360-dimensional reservoir
output vectors were also constructed by concatenating two and three basic ones,
respectively. In nonlinear autoregressive moving average (NARMA) prediction
tasks, the computational performance was enhanced as the dimension of the
reservoir output vector becomes higher and a significantly low prediction error
was achieved for the 10th-order NARMA using the 360-dimensional vector and
optimum damping constant. The results are clear evidence that the collection of
diverse output signals efficiently increases the dimensionality effective for
reservoir computing, i.e., reservoir-state richness. This paper demonstrates
that performance enhancement through various configuration settings is a
practical approach for on-chip reservoir computing devices with small numbers
of real output nodes.",2209.10123v1
2022-10-11,Topological superconductivity from doping a triplet quantum spin liquid in a flat band system,"We explore superconductivity in strongly interacting electrons on a decorated
honeycomb lattice (DHL). An easy-plane ferromagnetic interaction arises from
spin-orbit coupling in the Mott insulating phase, which favors a triplet
resonance valence bond spin liquid state. Hole doping leads to partial
occupation of a flat band and to triplet superconductivity. The order parameter
is highly sensitive to the doping level and the interaction parameters, with
$p+ip$, $f$ and $p+f$ superconductivity found, as the flat band leads to
instabilities in multiple channels. Typically, first order transitions separate
different superconducting phases, but a second order transition separates two
time reversal symmetry breaking $p+ip$ phases with different Chern numbers
($\nu=0$ and 1). The Majorana edge modes in the topological ($\nu=1$)
superconductor are almost localized due to the strong electronic correlations
in a system with a flat band at the Fermi level. This suggests that these modes
could be useful for topological quantum computing. The `hybrid' $p+f$ state
does not require two phase transitions as temperature is lowered. This is
because the symmetry of the model is lowered in the $p$-wave phase, allowing
arbitrary admixtures of $f$-wave basis functions as overtones. We show that the
multiple sites per unit cell of the DHL, and hence multiple bands near the
Fermi energy, lead to very different nodal structures in real and reciprocal
space. We emphasize that this should be a generic feature of
multi-site/multi-band superconductors.",2210.05275v1
2022-12-01,Proximity superconductivity in atom-by-atom crafted quantum dots,"Gapless materials in electronic contact with superconductors acquire
proximity-induced superconductivity in a region near the interface. Numerous
proposals build on this addition of electron pairing to originally
non-superconducting systems like ferromagnets and predict intriguing quantum
phases of matter, including topological-, odd-frequency-, or nodal-point
superconductivity. However, atomic-scale experimental investigations of the
microscopic mechanisms leading to proximity-induced Cooper pairing in surface
or interface states are missing. Here, we investigate the most miniature
example of the proximity effect on only a single quantum level of a surface
state confined in a quantum corral on a superconducting substrate, built
atom-by-atom by a scanning tunneling microscope. Whenever an eigenmode of the
corral is pitched close to the Fermi energy by adjusting the corral's size, a
pair of particle-hole symmetric states enters the superconductor's gap. We
identify the in-gap states as scattering resonances theoretically predicted 50
years ago by Machida and Shibata, which had so far eluded detection. We further
show that the observed anticrossings of the in-gap states indicate
proximity-induced pairing in the quantum corral's eigenmodes. Our results have
direct consequences on the interpretation of in-gap states in unconventional or
topological superconductors, corroborate concepts to induce superconductivity
into a single quantum level and further pave the way towards superconducting
artificial lattices.",2212.00657v1
2022-12-10,Topological Hall Effect Driven by Short-Range Magnetic Orders in EuZn$_2$As$_2$,"Short-range (SR) magnetic orders such as magnetic glass orders or
fluctuations in a quantum system usually host exotic states or critical
behaviors. As the long-range (LR) magnetic orders, SR magnetic orders can also
break time-reversal symmetry and drive the non-zero Berry curvature leading to
novel transport properties. In this work, we report that in EuZn$_2$As$_2$
compound, besides the LR A-type antiferromagnetic (AF) order, the SR magnetic
order is observed in a wide temperature region. The magnetization measurements
and electron spin resonance (ESR) measurements reveal the ferromagnetic (FM)
correlations for this SR magnetic order which results in an obvious anomalous
Hall effect above the AF transition. Moreover the ESR results reveal that this
FM SR order coexists with LR AF order exhibiting anisotropic magnetic
correlations below the AF transition. The interactions of LR and SR magnetism
evolving with temperature and field can host non-zero spin charility and berry
curvature leading the additional topological Hall contribution even in a
centrosymmetric simple AF system. Our results indicate that EuZn$_2$As$_2$ is a
fertile platform to investigate exotic magnetic and electronic states.",2212.05284v2
2022-12-24,Spin-to-charge conversion by spin pumping in sputtered polycrystalline Bi$_x$Se$_{1-x}$,"Topological materials are of high interest due to the promise to obtain low
power and fast memory devices based on efficient spin-orbit torque switching or
spin-orbit magnetic state read-out. In particular, sputtered polycrystalline
Bi$_x$Se$_{1-x}$ is one of the materials with more potential for this purpose
since it is relatively easy to fabricate and has been reported to have a very
high spin Hall angle. We study the spin-to-charge conversion in
Bi$_x$Se$_{1-x}$ using the spin pumping technique coming from the ferromagnetic
resonance in a contiguous permalloy thin film. We put a special emphasis on the
interfacial properties of the system. Our results show that the spin Hall angle
of Bi$_x$Se$_{1-x}$ has an opposite sign to the one of Pt. The charge current
arising from the spin-to-charge conversion is, in contrast, lower than Pt by
more than one order of magnitude. We ascribe this to the interdiffusion of
Bi$_x$Se$_{1-x}$ and permalloy and the changes in chemical composition produced
by this effect, which is an intrinsic characteristic of the system and is not
considered in many other studies.",2212.12697v2
2023-02-15,Momentum-independent magnetic excitation continuum in the honeycomb iridate H$_3$LiIr$_2$O$_6$,"In the search for realizations of Quantum Spin Liquids (QSL), it is essential
to understand the interplay between inherent disorder and the correlated
fluctuating spin ground state. H$_3$LiIr$_2$O$_6$ is regarded as a spin liquid
proximate to the Kitaev-limit (KQSL) in which H zero-point motion and stacking
faults are known to be present. Bond disorder has been invoked to account for
the existence of unexpected low-energy spin excitations. Controversy remains
about the nature of the underlying correlated state and if any KQSL physics
survives. Here, we use resonant X-ray spectroscopies to map the collective
excitations in H$_3$LiIr$_2$O$_6$ and characterize its magnetic state. We
uncover a broad bandwidth and momentum-independent continuum of magnetic
excitations at low temperatures that are distinct from the paramagnetic state.
The center energy and high-energy tail of the continuum are consistent with
expectations for dominant ferromagnetic Kitaev interactions between dynamically
fluctuating spins. The absence of a momentum dependence to these excitations
indicates a broken translational invariance. Our data support an interpretation
of H$_3$LiIr$_2$O$_6$ as a disordered topological spin liquid in close
proximity to bond-disordered versions of the KQSL. Our results shed light on
how random disorder affects topological magnetic states and have implications
for future experimental and theoretical works toward realizing the Kitaev model
in condensed matter systems",2302.07907v1
2023-02-16,Analytical theory of cat scars with discrete time crystalline dynamics in Floquet systems,"We reconstruct the spectral pairing (SP) theories to enable analytical
descriptions of eigenstate spatiotemporal orders in translation-invariant
systems without prethermal conditions. It is shown that the strong Ising
interactions and drivings alone stabilize a class of ``cat scar"" eigenstates
with tunable patterns, which lead to {\em local} discrete time crystal (DTC)
dynamics. They exhibit Fock space localization and long-range correlations
robust against generic perturbations in a disorder-free scenario. In
particular, we introduce a symmetry indicator method to enumerate cat scars,
with which a set of unexpected inhomogeneous scar patterns are identified in
addition to the ferromagnetic scars found before. These scars enforce DTC
dynamics with rigid inhomogeneous patterns, offering a viable way to verify
underlying eigenstate properties experimentally. Further, we prove rigorously
that the strong Ising interactions enforce a selection rule for perturbations
of different orders, which imposes an exponential suppression of spin
fluctuations for Floquet eigenstates. Based on this property, three analytical
scaling relations are proved to characterize the amplitudes, Fock space
localization, and lifetime for DTC dynamics associated with cat scars. We
further provide two practical methods to check whether certain DTC phenomena
are dominated by single-spin dynamics or due to genuine interaction effects.",2302.08056v3
2023-02-19,Hysteresis and training effect in the electric control of spin current in Pt/Y3Fe5O12 heterostructures,"We have reported on the hysteresis and training effect of spin current in
Pt/Y3Fe5O12 heterostructures during subsequent cycles of ionic liquid gate
voltage Vg. The inverse spin Hall effect voltage in spin pumping and spin Hall
magnetoresistance exhibit diode-like behaviors in the first half cycle of Vg
andalsoshowhysteresisinthe first cycle of Vg. Both the diode-like behavior and
the hysteresis become weak and even vanish in the second cycle of Vg due to the
training effect. The above experimental results can be well explained by the
screening charge doping model, in which the charge and the local magnetic
moment are asymmetrically distributed in the Pt layer. The applicability of
this model is further confirmed by measurements of anisotropic
magnetoresistance and ferromagnetic resonance. The diode-like behavior is
attributed to interplay between the asymmetrically distributed local magnetic
moment and the spin current relaxation in the Pt layer. The hysteresis and the
training effect arise from the incompletely reversible process between
oxidation and reduction of Pt atoms and the evolution of the surface morphology
at the ionic liquid/Pt interface under electric gating. This work provides new
insights to improve the functional performance of electrically controlled spin
current devices.",2302.09505v1
2023-03-18,Tunneling magnetoresistance in Mn$_2$Au-based pure antiferromagnetic tunnel junction,"Antiferromagnetic (AF) spintronics is merit on ultra-high operator speed and
stability in the presence of magnetic field. To fully use the merit, the device
should be pure rather than hybrid with ferromagnet or ferrimagnet. For the
magnetism in the antiferromagnet is canceled by that of different sublattices,
breaking the symmetry in the material can revive the native magnetism, which
can be detected by the magnetoresistance (MR) effect. Achieving noticeable MR
effect in the pure AF device is diffcult but essential for the AF spintronic
applications. Here, we study the tunnel magnetoresistance(TMR) effect in the
Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb pure AF magnetic tunnel junctions (AF-MTJs) based
on a first-principle scattering theory. Giant TMRs with order of 1000% are
predicted in some symmetric junctions, which is originated from the interfacial
resonance tunneling effect related with the k dependent complex band structures
of CdO and Mn$_2$Au in companion with the enhanced spin polarization of the
interfacial magnetic atoms. The effect of voltage bias and interfacial disorder
such as Oxygen vacancy, Manganese vacancy, and Manganese-Cadmium exchanges at
Mn2Au/CdO interfaces are studied also. Our studies suggest
Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb AFMTJs promising material for AF spintronic
application, and rocksalt CdO a potential symmetry filtering material for
spintronic applications.",2303.10448v1
2023-04-19,Thickness-dependent magnetic properties in Pt[CoNi]n multilayers with perpendicular magnetic anisotropy,"We systematically investigated the Ni and Co thickness-dependent
perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain
structures, and magnetization dynamics of Pt(5 nm)/[Co(t_Co nm)/Ni(t_Ni
nm)]5/Pt(1 nm) multilayers by combining the four standard magnetic
characterization techniques. The magnetic-related hysteresis loops obtained
from the field-dependent magnetization M and anomalous Hall resistivity (AHR)
\r{ho}_xy found that the two serial multilayers with t_Co = 0.2 and 0.3 nm have
the optimum PMA coefficient K_U well as the highest coercivity H_C at the Ni
thickness t_Ni = 0.6 nm. Additionally, the magnetic domain structures obtained
by Magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the
thickness and K_U of the films. Furthermore, the thickness-dependent linewidth
of ferromagnetic resonance is inversely proportional to K_U and H_C, indicating
that inhomogeneous magnetic properties dominate the linewidth. However, the
intrinsic Gilbert damping constant determined by a linear fitting of
frequency-dependent linewidth does not depend on Ni thickness and K_U. Our
results could help promote the PMA [Co/Ni] multilayer applications in various
spintronic and spin-orbitronic devices.",2304.09366v1
2023-04-21,Exploiting the close-to-Dirac point shift of Fermi level in Sb2Te3/Bi2Te3 topological insulator heterostructure for spin-charge conversion,"Properly tuning the Fermi level position in topological insulators is of
vital importance to tailor their spin-polarized electronic transport and to
improve the efficiency of any functional device based on them. Here we report
the full in situ Metal Organic Chemical Vapor Deposition (MOCVD) and study of a
highly crystalline Bi2Te3/Sb2Te3 topological insulator heterostructure on top
of large area (4'') Si(111) substrates. The bottom Sb2Te3 layer serves as an
ideal seed layer for the growth of highly crystalline Bi2Te3 on top, also
inducing a remarkable shift of the Fermi level to place it very close to the
Dirac point, as visualized by angle-resolved photoemission spectroscopy. In
order to exploit such ideal topologically-protected surface states, we
fabricate the simple spin-charge converter Si(111)/Sb2Te3/Bi2Te3/Au/Co/Au and
spin-charge conversion (SCC) is probed by spin pumping ferromagnetic resonance.
A large SCC is measured at room temperature, which is interpreted within the
inverse Edelstein effect (IEE), thus resulting in a conversion efficiency
lambda_IEE of 0.44 nm. Our results demonstrate the successful tuning of the
surface Fermi level of Bi2Te3 when grown on top of Sb2Te3 with a full in situ
MOCVD process, which is highly interesting in view of its future technology
transfer.",2304.10841v1
2023-04-23,Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator,"The scanning superconducting quantum interference device (SQUID) fabricated
on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile
tool for nanoscale imaging of magnetic, thermal, and transport properties of
microscopic devices of quantum materials. We present the design and performance
of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free
dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight
cell mounted at the bottom of the probe and is suspended by springs to suppress
vibrations caused by the pulse tube cryocooler. Two capillaries allow in-situ
control of helium exchange gas pressure in the cell that is required for
thermal imaging. A nanoscale heater is used to create local temperature
gradients in the sample, which enables quantitative characterization of the
relative vibrations between the tip and the sample. The spectrum of the
vibrations shows distinct resonant peaks with maximal power density of about 27
nm/Hz$^{1/2}$ in the in-plane direction. The performance of the SQUID-on-tip
microscope is demonstrated by magnetic imaging of the MnBi$_2$Te$_4$ magnetic
topological insulator, magnetization and current distribution imaging in a
SrRuO$_3$ ferromagnetic oxide thin film, and by thermal imaging of dissipation
in graphene.",2304.11667v1
2023-05-02,Synchronization of silicon thermal-free-carrier oscillators,"Recent exploration of collective phenomena in oscillator arrays has
highlighted its potential for accessing a range of physical phenomena, from
fundamental quantum many-body dynamics to the solution of practical
optimization problems using photonic Ising machines. Spontaneous oscillations
often arise in these oscillator arrays as an imbalance between gain and loss.
Due to coupling between array individuals, the spontaneous oscillation is
constrained and lead to interesting collective behavior, such as synchronized
oscillations in optomechanical oscillator arrays, ferromagnetic-like coupling
in delay-coupled optical parametric oscillators and binary phase states in
coupled laser arrays. A key aspect of arrays is not only the coupling between
its individuals but also their compliance towards neighbor stimuli. One
self-sustaining photonic oscillator that can be readily implemented in a
scalable foundry-based technology is based on the interaction of free-carriers,
temperature and optical field of a resonant silicon photonic microcavity. Here
we demonstrate that these silicon thermal-free-carrier oscillators are
extremely compliant to external excitation and can be synchronized up to their
16$^\text{th}$ harmonic using a weak seed. Exploring this unprecedented
compliance to external stimuli, we also demonstrate robust synchronization
between two thermal free carrier oscillators.",2305.01780v1
2023-05-08,Interfacial origin of unconventional spin-orbit torque in Py/$γ-$IrMn$_{3}$,"Angle-resolved spin-torque ferromagnetic resonance measurements are carried
out in heterostructures consisting of Py (Ni$_{81}$Fe$_{19}$) and a
noncollinear antiferromagnetic quantum material $\gamma-$IrMn$_{3}$. The
structural characterization reveals that $\gamma-$IrMn$_{3}$ is polycrystalline
in nature. A large exchange bias of 158~Oe is found in Py/$\gamma-$IrMn$_{3}$
at room temperature, while $\gamma-$IrMn$_{3}$/Py and Py/Cu/$\gamma-$IrMn$_{3}$
exhibited no exchange bias. Regardless of the exchange bias and stacking
sequence, we observe a substantial unconventional out-of-plane anti-damping
torque when $\gamma-$IrMn$_{3}$ is in direct contact with Py. The magnitude of
the out-of-plane spin-orbit torque efficiency is found to be twice as large as
the in-plane spin-orbit torque efficiency. The unconventional spin-orbit torque
vanishes when a Cu spacer is introduced between Py and $\gamma-$IrMn$_{3}$,
indicating that the unconventional spin-orbit torque in this system originates
at the interface. These findings are important for realizing efficient
antiferromagnet-based spintronic devices via interfacial engineering.",2305.04596v1
2023-06-01,Monte Carlo matrix-product-state approach to the false vacuum decay in the monitored quantum Ising chain,"In this work we characterize the false vacuum decay in the ferromagnetic
quantum Ising chain with a weak longitudinal field subject to continuous
monitoring of the local magnetization. Initializing the system in a metastable
state, the false vacuum, we study the competition between coherent dynamics,
which tends to create resonant bubbles of the true vacuum, and measurements
which induce heating and reduce the amount of quantum correlations. To this end
we exploit a numerical approach based on the combination of matrix product
states with stochastic quantum trajectories which allows for the simulation of
the trajectory-resolved non-equilibrium dynamics of interacting many-body
systems in the presence of continuous measurements. We show how the presence of
measurements affects the false vacuum decay: at short times the departure from
the local minimum is accelerated while at long times the system thermalizes to
an infinite-temperature incoherent mixture. For large measurement rates the
system enters a quantum Zeno regime. The false vacuum decay and the
thermalization physics are characterized in terms of the magnetization,
connected correlation function, and the trajectory-resolved entanglement
entropy.",2306.01067v3
2023-06-21,Emergent super-antiferromagnetic correlations in monolayers of Fe3O4 nanoparticles throughout the superparamagnetic blocking transition,"We report nanoscale inter-particle magnetic orderings in self-assemblies of
Fe3O4 nanoparticles (NPs), and the emergence of inter-particle
antiferromagnetic (AF) (super-antiferromagnetic) correlations near the coercive
field at low temperature. The magnetic ordering is probed via x-ray resonant
magnetic scattering (XRMS), with the x-ray energy tuned to the Fe-L3 edge and
using circular polarized light. By exploiting dichroic effects, a magnetic
scattering signal is isolated from the charge scattering signal. The magnetic
signal informs about nanoscale spatial orderings at various stages throughout
the magnetization process and at various temperatures throughout the
superparamagnetic blocking transition, for two different sizes of NPs, 5 and 11
nm, with blocking temperatures TB of 28 K and 170 K, respectively. At 300 K,
while the magnetometry data essentially shows superparamagnetism and absence of
hysteresis for both particle sizes, the XRMS data reveals the presence of
non-zero (up to 9/100) inter-particle AF couplings when the applied field is
released to zero for the 11 nm NPs. These AF couplings are drastically
amplified when the NPs are cooled down below TB and reach up to 12/100 for the
5 nm NPs and 48/100 for the 11 nm NPs, near the coercive point. The data
suggests that the particle size affects the prevalence of the AF couplings:
compared to ferromagnetic (F) couplings, the relative prevalence of AF
couplings at the coercive point increases from a factor ~ 1.6 to 3.8 when the
NP size increases from 5 to 11 nm.",2306.11994v1
2023-07-01,Ultrafast Ultraviolet C and Visible Laser Light with Broadly Tunable Spectrum,"We demonstrate a versatile technique for generating continuously
wavelength-tunable laser waveforms, with mJ pulse energies and ultrashort pulse
durations down to few-cycle in the ultraviolet C and visible spectral ranges.
Using the processes of self-phase modulation or Raman-induced spectral
broadening, we substantially expand the spectrum of a femtosecond 1030 nm
Yb:CaF$_{2}$ laser, allowing for an extensive wavelength-tunability of the
second and fourth harmonics of the laser within the visible and ultraviolet C
spectral regions at 460-580 nm and 230-290 nm. In addition, our approach
exploits nonlinearly assisted self-compression in the second harmonic
upconversion of the spectrally broadened infrared pulses with high-order
dispersion. This results in 8-30 femtosecond pulses in the visible with an
intensity enhancement of up to 30 times. Such an ultrashort visible and
ultraviolet C source is ideal for investigating ultrafast dynamics in
molecules, solids, and bio and nano systems. Furthermore, this tunable light
source enables the generation of bright, narrow-bandwidth, continuously
wavelength-tunable, coherent light in the extreme ultraviolet to soft X-ray
spectral region. Theoretically, the X-ray pulse structure can consist of
sub-200 as pulse trains, making such a source highly suitable for dynamic
multidimensional imaging. This includes coherent diffractive imaging of
ferromagnetic nanostructures where resonant X-ray scattering is essential, as
well as X-ray absorption spectroscopies of advanced quantum materials at
pico-nanometer spatial and atto-femtosecond temporal scales.",2307.00434v1
2023-07-14,Dark matter detection using nuclear magnetization in magnet with hyperfine interaction,"We consider the possibility to detect cosmic light dark matter (DM), i.e.,
axions and dark photons, of mass $\sim 10^{-6}$ eV and $\sim 10^{-4}$ eV, by
magnetic excitation in a magnet with strong hyperfine interaction. In
particular, we consider a canted anti-ferromagnet, MnCO$_3$, as a concrete
candidate material. With spin transfer between nuclear and electron spins
allowed by the hyperfine interaction, nuclear spins become naturally highly
polarized due to an effective (electron-spin-induced) magnetic field, and have
long-range interactions with each other. The collective precession of nuclear
spins, i.e., a nuclear magnon, can be generated by the DM field through the
nucleon-DM interaction, while they are also sensitive to the electron-DM
interaction through the electron-nuclear spin mixing. Compared with
conventional nuclear-spin precession experiments, this system as a DM sensor is
sensitive to higher frequency needing only a small static magnetic field
applied. The system also has collective precession of electron spins, mixed
with nuclear spins, as the additional channels that can be used for DM probes.
We estimate the sensitivity under appropriate readout setups such as an
inductive pick-up loop associated with an LC resonant circuit, or a photon
cavity with a photon counting device. We show that this method covers an
unexplored parameter region of light bosonic DM.",2307.08577v2
2023-08-11,Physics inspired quantum simulation of resonating valence bond states -- a prototypical template for a spin-liquid ground state,"Spin-liquids -- an emergent, exotic collective phase of matter -- have
garnered enormous attention in recent years. While experimentally, many
prospective candidates have been proposed and realized, theoretically modeling
real materials that display such behavior may pose serious challenges due to
the inherently high correlation content of emergent phases. Over the last few
decades, the second-quantum revolution has been the harbinger of a novel
computational paradigm capable of initiating a foundational evolution in
computational physics. In this report, we strive to use the power of the latter
to study a prototypical model -- a spin-$\frac{1}{2}$-unit cell of a Kagome
anti-ferromagnet. Extended lattices of such unit cells are known to possess a
magnetically disordered spin-liquid ground state. We employ robust classical
numerical techniques like Density-Matrix Renormalization Group (DMRG) to
identify the nature of the ground state through a matrix-product state (MPS)
formulation. We subsequently use the gained insight to construct an auxillary
hamiltonian with reduced measurables and also design an ansatz that is modular
and gate efficient. With robust error-mitigation strategies, we are able to
demonstrate that the said ansatz is capable of accurately representing the
target ground state even on a real IBMQ backend within $1\%$ accuracy in
energy. Since the protocol is linearly scaling $O(n)$ in the number of unit
cells, gate requirements, and the number of measurements, it is
straightforwardly extendable to larger Kagome lattices which can pave the way
for efficient construction of spin-liquid ground states on a quantum device.",2308.06360v1
2023-10-10,Large out-of-plane spin-orbit torque in topological Weyl semimetal candidate TaIrTe4,"Topological quantum materials, with novel spin textures and broken crystal
symmetries are suitable candidates for spintronic memory technologies. Their
unique electronic properties, such as protected surface states and exotic
quasiparticles, can provide an out-of-plane spin polarized current needed for
external field free magnetization switching of magnets with perpendicular
magnetic anisotropy. Conventional spin-orbit torque materials, such as heavy
metals and topological insulators, provide only an in-plane spin polarized
current, and recently explored materials with lower crystal symmetries provide
very low out-of-plane spin polarized current components, which is not suitable
for energy-efficient spin-orbit torque (SOT) applications. Here, we demonstrate
a large out-of-plane damping-like SOT at room temperature using a topological
Weyl semimetal candidate TaIrTe4 with a lower crystal symmetry. We performed
spin-orbit torque ferromagnetic resonance (STFMR) experiments in a
TaIrTe4/Ni80Fe20 heterostructure and observed a large out-of-plane damping-like
SOT efficiency. The out-of-plane spin Hall conductivity is estimated to be an
order of magnitude higher than the reported values in other materials. These
findings of high spin Hall conductivity and large out-of-plane SOT efficiency
are suitable for the development of energy efficient and external field-free
spintronic devices.",2310.06395v1
2023-12-26,All solution grown epitaxial magnonic crystal of thulium iron garnet thin film,"Magnonics has shown the immense potential of compatibility with CMOS devices
and the ability to be utilized in futuristic quantum computing. Therefore, the
magnonic crystals, both metallic and insulating, are under extensive
exploration. The presence of high spin-orbit interaction induced by the
presence of rare-earth elements in thulium iron garnet (TmIG) increases its
potential in magnonic applications. Previously, TmIG thin films were grown
using ultra-high vacuum-based techniques. Here, we present a cost-effective
solution-based approach that enables the excellent quality interface and
surface roughness of the epitaxial TmIG/GGG. The deposited TmIG (12.2 nm) thin
film's physical and spin dynamic properties are investigated in detail. The
confirmation of the epitaxy using X-ray diffraction in $\phi$-scan geometry
along with the X-ray reflectivity and atomic force for the thickness and
roughness analysis and topography, respectively. The epitaxial TmIG/GGG have
confirmed the perpendicular magnetic anisotropy utilizing the
polar-magneto-optic Kerr effect. Analyzing the ferromagnetic resonance study of
TmIG/GGG thin films provides the anisotropy constant K$_U$ = 20.6$\times$10$^3$
$\pm$ 0.2$\times$10$^3$ N/m$^2$ and the Gilbert damping parameter $\alpha$ =
0.0216 $\pm$ 0.0028. The experimental findings suggest that the
solution-processed TmIG/GGG thin films have the potential to be utilized in
device applications.",2312.15973v1
2024-01-09,Microwave magnetic excitations in U-type hexaferrite Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics,"Microwave (MW) spectra of ferrimagnetic U-hexaferrite
Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics were studied using several experimental
techniques from 100 MHz to 50 GHz at temperatures between 10 and 390 K. They
revealed 9 excitations, which exhibit remarkable temperature dependences near
the magnetic phase transitions at 145 K and 305 K. Some of them also change
under the application of a weak bias magnetic field at room temperature. Three
lowest-frequency modes seen between 200 MHz and 3 GHz were assigned to the
dynamics of the magnetic domains. The mode attributed to the natural
ferromagnetic resonance exhibits a dramatic critical slowing-down from 25 GHz
at 390 K to 5 GHz near the 305 K phase transition, and again a hardening to ~11
GHz on further cooling. The higher-frequency excitations are most likely spin
wave (magnon) modes arising from the complex ferrimagnetic structure of
Sr$_4$CoZnFe$_{36}$O$_{60}$. The high sensitivity of the MW spectra to the weak
magnetic bias field $H$ < 700 Oe at room temperature is shown to be caused by
the transformation of the polydomain magnetic structure in randomly oriented
ceramic grains to a monodomain one. The MW response measured above 2 GHz using
coplanar and microstrip lines with different electromagnetic field distribution
and sample coupling revealed the same excitations with similar temperature and
bias field dependences. It confirms the reliability of the results and proves
the effectiveness of the used MW techniques.",2401.04678v1
2024-01-12,Scanning spin probe based on magnonic vortex quantum cavities,"Performing nanoscale scanning electron paramagnetic resonance (EPR) requires
three essential ingredients. First, a static magnetic field together to field
gradients to Zeeman split the electronic energy levels with spatial resolution.
Second, a radiofrequency (rf) magnetic field capable of inducing spin
transitions. Finally, a sensitive detection method to quantify the energy
absorbed by spins. This is usually achieved by combining externally applied
magnetic fields with inductive coils or cavities, fluorescent defects or
scanning probes. Here, we theoretically propose the realization of a EPR
scanning sensor merging all three characteristics into a single device: the
vortex core stabilized in ferromagnetic thin-film discs. On one hand, the
vortex ground state generates a significant static magnetic field and field
gradients. On the other hand, the precessional motion of the vortex core around
its equilibrium position produces a circularly polarized oscillating magnetic
field, which is enough to produce spin transitions. Finally, the spin-magnon
coupling broadens the vortex gyrotropic frequency, suggesting a direct measure
of the presence of unpaired electrons. Moreover, the vortex core can be
displaced by simply using external magnetic fields of a few mT, enabling EPR
scanning microscopy with large spatial resolution. Our numerical simulations
show that, by using low damping magnets, it is theoretically possible to detect
single spins located on the disc's surface. Vortex nanocavities could also
attain strong coupling to individual spin molecular qubits, with potential
applications to mediate qubit-qubit interactions or to implement qubit readout
protocols.",2401.06549v1
2024-01-21,Kondo Screening of Local Moments in a Triangular Triple Quantum Dot Connected to Normal and Superconducting Leads,"We study the interplay between the Kondo and superconducting (SC) proximity
effects, taking place in a triangular triple quantum dot (TTQD) connected to
one normal and two SC leads. This system shows various quantum phases. Without
the SC leads, the lowest two states that belong to the different spin sectors,
$S=0$ and $S=1/2$, become energetically very close to each other near half
filling. The singlet one is a Kondo-screened state by conduction electrons from
the normal lead, and the doublet one is a resonating valence bond state with
unpaired free spin which remains unscreened. Furthermore, when one additional
electron enters the TTQD, the ground state becomes a doublet in which the $S=1$
local moment due to the Nagaoka ferromagnetism is partially screened by
conduction electrons.The Cooper pairs penetrating into the TTQD from the SC
leads reconstruct the wavefunctions and vary the phase boundaries between these
quantum states in the parameter space. We calculate ground-state phase diagrams
using the numerical renormalization group, and show that the SC proximity
effect induces a reentrant transition in-between the three- and four-electron
fillings.",2401.11444v1
2024-03-25,Skyrmionic device for three dimensional magnetic field sensing enabled by spin-orbit torques,"Magnetic skyrmions are topologically protected local magnetic solitons that
are promising for storage, logic or general computing applications. In this
work, we demonstrate that we can use a skyrmion device based on [W/CoFeB/MgO] 1
0 multilayers for three-dimensional magnetic field sensing enabled by
spin-orbit torques (SOT). We stabilize isolated chiral skyrmions and stripe
domains in the multilayers, as shown by magnetic force microscopy images and
micromagnetic simulations. We perform magnetic transport measurements to show
that we can sense both in-plane and out-of-plane magnetic fields by means of a
differential measurement scheme in which the symmetry of the SOT leads to
cancelation of the DC offset. With the magnetic parameters obtained by
vibrating sample magnetometry and ferromagnetic resonance measurements, we
perform finite-temperature micromagnetic simulations, where we investigate the
fundamental origin of the sensing signal. We identify the topological
transformation between skyrmions, stripes and type-II bubbles that leads to a
change in the resistance that is read-out by the anomalous Hall effect. Our
study presents a novel application for skyrmions, where a differential
measurement sensing concept is applied to quantify external magnetic fields
paving the way towards more energy efficient applications in skyrmionics based
spintronics.",2403.16725v1
2009-02-28,Nanostratification of optical excitation in self-interacting 1D arrays,"The major assumption of the Lorentz-Lorenz theory about uniformity of local
fields and atomic polarization in dense material does not hold in finite groups
of atoms, as we reported earlier [A. E. Kaplan and S. N. Volkov, Phys. Rev.
Lett., v. 101, 133902 (2008)]. The uniformity is broken at sub-wavelength
scale, where the system may exhibit strong stratification of local field and
dipole polarization, with the strata period being much shorter than the
incident wavelength. In this paper, we further develop and advance that theory
for the most fundamental case of one-dimensional arrays, and study nanoscale
excitation of so called ""locsitons"" and their standing waves (strata) that
result in size-related resonances and related large field enhancement in finite
arrays of atoms. The locsitons may have a whole spectrum of spatial
frequencies, ranging from long waves, to an extent reminiscent of ferromagnetic
domains, -- to super-short waves, with neighboring atoms alternating their
polarizations, which are reminiscent of antiferromagnetic spin patterns. Of
great interest is the new kind of ""hybrid"" modes of excitation, greatly
departing from any magnetic analogies. We also study differences between
Ising-like near-neighbor approximation and the case where each atom interacts
with all other atoms in the array. We find an infinite number of ""exponential
eigenmodes"" in the lossless system in the latter case. At certain ""magic""
numbers of atoms in the array, the system may exhibit self-induced (but linear
in the field) cancellation of resonant local-field suppression. We also studied
nonlinear modes of locsitons and found optical bistability and hysteresis in an
infinite array for the simplest modes.",0903.0045v2
2011-10-21,Magnetic properties and revisited exchange integrals of the frustrated chain cuprate PbCuSO$_4$(OH)$_2$ - linarite,"We present a detailed study in the paramagnetic regime of the frustrated $s$
= 1/2 spin-compound linarite, PbCuSO$_4$(OH)$_2$, with competing ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange
interactions. Our data reveal highly anisotropic values for the saturation
field along the crystallographic main directions, with $\sim$ 7.6, $\sim$ 10.5
and $\sim$ 8.5\,T for the $a$, $b$, and $c$ axes, respectively. In the
paramagnetic regime, this behavior is explained mainly by the anisotropy of the
\textit{g}-factor but leaving room for an easy-axis exchange anisotropy. Within
the isotropic $J_1$-$J_2$ spin model our experimental data are described by
various theoretical approaches yielding values for the exchange interactions
$J_1$ $\sim$ -100\,K and $J_2$ $\sim$ 36\,K. These main intrachain exchange
integrals are significantly larger as compared to the values derived in two
previous studies in the literature and shift the frustration ratio $\alpha =
J_2/|J_1|$ $\approx$ 0.36 of linarite closer to the 1D critical point at 0.25.
Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements
further prove that the static susceptibility is dominated by the intrinsic spin
susceptibility. The Knight shift as well as the broadening of the linewidth in
ESR and NMR at elevated temperatures indicate a highly frustrated system with
the onset of magnetic correlations far above the magnetic ordering temperature
$T_\mathrm{N}$ = 2.75(5)\,K, in agreement with the calculated exchange
constants.",1110.4729v1
2012-10-30,Electronic structure of TiO2 thin films and LaAlO3-SrTiO3 heterostructures: the role of titanium 3d1 states in magnetic and transport properties,"In this Thesis, a study of the electronic structure of two Ti-based oxide
systems, TiO2 thin films and the ultra-thin LaAlO3-SrTiO3 (LAO-STO)
heterojunctions, is given. A weak room-temperature ferromagnetism (FM) has been
detected in slightly reduced TiO2 thin film and in other oxides; as these
materials are insulating closed-shell systems, this phenomenon has been
classified as ""d0 magnetism"". Since this magnetism could be related to the
growth process and to the presence of defects (oxygen vacancies, VO), an
analysis of Ti electronic states (especially of Ti3+ energy levels) is
mandatory. The first part of this work is devoted to the magnetic
characterization of a set of TiO2 and N-doped TiO2 samples, together with the
analysis of Ti 3d-related states carried out with X-ray photoemission (XPS) and
resonant photoemission (ResPES). The hypothesis of clustered VO as the source
of FM is then discussed in the light of the experimental and theoretical
results. Another interesting oxide system in which the stoichiometry of Ti ions
play a fundamental role is the LAO-STO interface. In fact, while LAO and STO
separately are two band insulators, the interface created by growing LAO on the
top of STO (001) has found to become metallic, hosting a 2D electron gas. The
second part of this Thesis is devoted to the study of conductive and insulating
LAO-STO interfaces, carried out by XPS, X-ray absorption (XAS) and with ResPES.
The sample stoichiometry is evaluated through a comparison with LAO and STO
single crystals. A resonance enhancement of the conductive Ti states,
associated to Ti3+ ions, is reported and compared to theoretical calculations.
On the basis of these results, the origin of metallic states in ultra-thin
LAO-STO interfaces is properly addressed. In addition, a characterization of
the structural disorder at the interface is shown, carried out with
angle-resolved XPS.",1210.8000v1
2014-08-24,Thickness dependence of dynamic and static magnetic properties of pulsed laser deposited La$_{0.7}$Sr$_{0.3}$MnO$_3$ films on SrTiO$_3$(001),"We present a comprehensive study of the thickness dependence of static and
magneto-dynamic magnetic properties of La$_{0.7}$Sr$_{0.3}$MnO$_3$. Epitaxial
pulsed laser deposited La$_{0.7}$Sr$_{0.3}$MnO$_3$ / SrTiO$_3$(001) thin films
in the range from 3 unit cells (uc) to 40 uc (1.2 - 16 nm) have been
investigated through ferromagnetic resonance spectroscopy (FMR) and SQUID
magnetometry at variable temperature. Magnetodynamically, three different
thickness, $d$, regimes are identified: 20 uc $\lesssim d$ uc where the system
is bulk like, a transition region 8 uc $\le d \lesssim 20$ uc where the FMR
line width and position depend on thickness and $d=6$ uc which displays
significantly altered magnetodynamic properties, while still displaying bulk
magnetization. Magnetization and FMR measurements are consistent with a
nonmagnetic volume corresponding to $\sim$ 4 uc. We observe a reduction of
Curie temperature ($T_C$) with decreasing thickness, which is coherent with a
mean field model description. The reduced ordering temperature also accounts
for the thickness dependence of the magnetic anisotropy constants and resonance
fields. The damping of the system is strongly thickness dependent, and is for
thin films dominated by thickness dependent anisotropies, yielding both a
strong 2-magnon scattering close to $T_c$ and a low temperature broadening. For
the bulk like samples a large part of the broadening can be linked to spread in
magnetic anisotropies attributed to crystal imperfections/domain boundaries of
the bulk like film.",1408.5631v1
2015-02-03,Irreversible transformation of ferromagnetic ordered stripe domains in single-shot IR pump - resonant X-ray scattering probe experiments,"The evolution of a magnetic domain structure upon excitation by an intense,
femtosecond Infra-Red (IR) laser pulse has been investigated using single-shot
based time-resolved resonant X-ray scattering at the X-ray Free Electron laser
LCLS. A well-ordered stripe domain pattern as present in a thin CoPd alloy film
has been used as prototype magnetic domain structure for this study. The
fluence of the IR laser pump pulse was sufficient to lead to an almost complete
quenching of the magnetization within the ultrafast demagnetization process
taking place within the first few hundreds of femtoseconds following the IR
laser pump pulse excitation. On longer time scales this excitation gave rise to
subsequent irreversible transformations of the magnetic domain structure. Under
our specific experimental conditions, it took about 2 nanoseconds before the
magnetization started to recover. After about 5 nanoseconds the previously
ordered stripe domain structure had evolved into a disordered labyrinth domain
structure. Surprisingly, we observe after about 7 nanoseconds the occurrence of
a partially ordered stripe domain structure reoriented into a novel direction.
It is this domain structure in which the sample's magnetization stabilizes as
revealed by scattering patterns recorded long after the initial pump-probe
cycle. Using micro-magnetic simulations we can explain this observation based
on changes of the magnetic anisotropy going along with heat dissipation in the
film.",1502.00786v1
2015-06-23,Magnetism-induced massive Dirac spectra and topological defects in the surface state of Cr-doped Bi$_2$Se$_3$-bilayer topological insulators,"Proximity-induced magnetic effects on the surface Dirac spectra of
topological insulators are investigated by scanning tunneling spectroscopic
(STS) studies of bilayer structures consisting of undoped Bi2Se3 thin films on
top of Cr-doped Bi2Se3 layers. For thickness of the top Bi2Se3 layer equal to
or smaller than 3 quintuple layers (QL), a spatially inhomogeneous surface
spectral gap \Delta opens up below T_c^{2D}, which is much higher than the bulk
Curie temperature T_c^{3D}. The mean value and spatial homogeneity of the gap
\Delta generally increase with increasing c-axis magnetic field (H) and
increasing Cr doping level (x), suggesting that the physical origin of this
surface gap is associated with proximity-induced c-axis ferromagnetism. On the
other hand, the temperature (T) dependence of \Delta is non-monotonic, showing
an initial increase below T_c^{2D} followed by a dip and then reaching maximum
at T << T_c^{3D}. These phenomena may be attributed to proximity magnetism
induced by two types of contributions with different temperature dependence: a
3D contribution from the bulk magnetism that dominates at low T, and a 2D
contribution associated with the RKKY interactions mediated by surface Dirac
fermions, which dominates at T_c^{3D} << T < T_c^{2D}. Additionally, spatially
localized sharp resonant spectra are found along the boundaries of gapped and
gapless regions. These spectral resonances are long-lived at H = 0 and become
suppressed under strong c-axis magnetic fields, and are attributed to magnetic
impurity-induced topological defects in the spin texture of surface Dirac
fermions.",1506.06841v2
2015-09-15,Fermi Surfaces and $p$-$d$ Hybridization in the Diluted Magnetic Semiconductor Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ Studied by Soft X-ray Angle Resolved Photoemission Spectroscopy,"The electronic structure of the new diluted magnetic semiconductor
Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ ($x=0.30$, $y=0.15$) in
single crystal form has been investigated by angle-resolved photoemission
spectroscopy (ARPES). %High density of states of nondispersive bands composed
of the Zn $3d$ orbitals are observed with ultraviolet incident light.
Measurements with soft x-rays clarify the host valence-band electronic
structure primarily composed of the As $4p$ states. Two hole pockets around the
$\Gamma$ point, a hole corrugated cylinder surrounding the $\Gamma$ and Z
points, and an electron pocket around the Z point are observed, and explain the
metallic transport of Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$. This
is contrasted with Ga$_{1-x}$Mn$_{x}$As (GaMnAs), where it is located above the
As $4p$ valence-band maximum (VBM) and no Fermi surfaces have been clearly
identified. Resonance soft x-ray ARPES measurements reveal a nondispersive
(Kondo resonance-like) Mn $3d$ impurity band near the Fermi level, as in the
case of GaMnAs. However, the impurity band is located well below the VBM,
unlike the impurity band in GaMnAs, which is located around and above the VBM.
We conclude that, while the strong hybridization between the Mn $3d$ and the As
$4p$ orbitals plays an important role in creating the impurity band and
inducing high temperature ferromagnetism in both systems, the metallic
transport may predominantly occur in the host valence band in
Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ and in the impurity band in
GaMnAs.",1509.04520v2
2018-02-14,Systematics of electronic and magnetic properties in the transition metal doped Sb$_2$Te$_3$ quantum anomalous Hall platform,"The quantum anomalous Hall effect (QAHE) has recently been reported to emerge
in magnetically-doped topological insulators. Although its general
phenomenology is well established, the microscopic origin is far from being
properly understood and controlled. Here we report on a detailed and systematic
investigation of transition-metal (TM)-doped Sb$_2$Te$_3$. By combining density
functional theory (DFT) calculations with complementary experimental
techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission
(resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete
spectroscopic characterization of both electronic and magnetic properties. Our
results reveal that the TM dopants not only affect the magnetic state of the
host material, but also significantly alter the electronic structure by
generating impurity-derived energy bands. Our findings demonstrate the
existence of a delicate interplay between electronic and magnetic properties in
TM-doped TIs. In particular, we find that the fate of the topological surface
states critically depends on the specific character of the TM impurity: while
V- and Fe-doped Sb$_2$Te$_3$ display resonant impurity states in the vicinity
of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The
single-ion magnetic anisotropy energy and easy axis, which control the magnetic
gap opening and its stability, are also found to be strongly TM
impurity-dependent and can vary from in-plane to out-of-plane depending on the
impurity and its distance from the surface. Overall, our results provide
general guidelines for the realization of a robust QAHE in TM-doped
Sb$_2$Te$_3$ in the ferromagnetic state.",1802.05302v1
2020-07-16,Ultrafast time-evolution of chiral Néel magnetic domain walls probed by circular dichroism in x-ray resonant magnetic scattering,"Non-collinear spin textures in ferromagnetic ultrathin films are attracting a
renewed interest fueled by possible fine engineering of several magnetic
interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This
allows the stabilization of complex chiral spin textures such as chiral
magnetic domain walls (DWs), spin spirals, and magnetic skyrmions. We report
here on the ultrafast behavior of chiral DWs after optical pumping in
perpendicularly magnetized asymmetric multilayers, probed using time-resolved
circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe
a picosecond transient reduction of the CD-XRMS, which is attributed to the
spin current-induced coherent and incoherent torques within the continuously
dependent spin texture of the DWs. We argue that a specific demagnetization of
the inner structure of the DW induces a flow of hot spins from the interior of
the neighboring magnetic domains. We identify this time-varying change of the
DW textures shortly after the laser pulse as a distortion of the homochiral
N'eel shape toward a transient mixed Bloch-N\'eel-Bloch textures along a
direction transverse to the DW. Our study highlights how time-resolved CD-XRMS
can be a unique tool for studying the time evolution in other systems showing a
non-collinear electric/magnetic ordering such as skyrmion lattices,
conical/helical phases, as well as the recently observed antiskyrmion lattices,
in metallic or insulating materials.",2007.08583v2
2016-08-09,"Creation,transport and detection of imprinted magnetic solitons stabilized by spin-polarized current","With the recent proposition of skyrmion utilization in racetrack memories at
room temperature, skyrmionics has become a very attractive field. However, for
the stability of skyrmions, it is essential to incorporate the
Dzyaloshinskii-Moriya interaction (DMI) and the out-of-plane magnetic field
into the system. In this work, we explore a system without these interactions.
First, we propose a controlled way for the creation of magnetic skyrmions and
skyrmioniums imprinted on a ferromagnetic nanotrack via a nanopatterned
nanodisk with the magnetic vortex state. Then we investigate the detachment of
the imprinted spin textures from the underneath of the nanodisk, as well as its
transport by the spin-transfer torque imposed by spin-polarized current pulses
applied in the nanotrack. A prominent feature of the moving imprinted spin
texture is that its topological number Q is oscillating around the averaged
value of Q=0 as if it is a resonant state between the skyrmions with Q= +/- 1
and the bubble with Q=0. We may call it a resonant magnetic soliton (RMS). A
RMS moves along a straight line since it is free from the skyrmion Hall effect.
In our studied device, the same electrodes are employed to realize the
imprinted spin texture detachment and its transport. In addition, we have
investigated the interaction between the RMS and a magnetic tunnel junction
sensor, where the passing of the RMS in the nanotrack can be well detected. Our
results would be useful for the development of novel spintronic devices based
on moveable spin textures.",1608.02915v2
2019-03-07,"Uniaxial anisotropy, intrinsic and extrinsic damping in Co$_{2}$FeSi Heusler alloy thin films","Ferromagnetic resonance (FMR) technique has been used to study the
magnetization relaxation processes and magnetic anisotropy in two different
series of the Co2FeSi (CFS) Heusler alloy thin films, deposited on the Si(111)
substrate by UHV sputtering. While the CFS films of fixed (50 nm) thickness,
deposited at different substrate temperatures (TS) ranging from room
temperature (RT) to 600^C, constitute the series-I, the CFS films with
thickness t varying from 12 nm to 100 nm and deposited at 550^C make up the
series-II. In series-I, the CFS films deposited at TS = RT and 200^C are
completely amorphous, the one at TS = 300^C is partially crystalline, and those
at TS equal 450^C, 550^C and 600^C are completely crystalline with B2 order. By
contrast, all the CFS films in series-II are in the fully-developed B2
crystalline state. Irrespective of the strength of disorder and film thickness,
angular variation of the resonance field in the film plane unambiguously
establishes the presence of global in-plane uniaxial anisotropy. Angular
variation of the linewidth in the film plane reveals that, in the CFS thin
films of varying thickness, a crossover from the in-plane local four-fold
symmetry (cubic anisotropy) to local two-fold symmetry (uniaxial anisotropy)
occurs as t exceeds 50 nm. Gilbert damping parameter {\alpha} decreases
monotonously from 0.047 to 0.0078 with decreasing disorder strength (increasing
TS) and jumps from 0.008 for the CFS film with t = 50 nm to 0.024 for the film
with t equal 75 nm. Such variations of {\alpha} with TS and t are understood in
terms of the changes in the total (spin-up and spin-down) density of states at
the Fermi level caused by the disorder and film thickness.",1903.02976v1
2019-11-26,Free-standing and positionable microwave antenna device for magneto-optical spectroscopy experiments,"Modern spectroscopic techniques for the investigation of magnetization
dynamics in micro- and nano- structures or thin films use typically microwave
antennas which are directly fabricated on top of the sample by means of
electron-beam-lithography (EBL). Following this approach, every magnetic
structure on the sample needs its own antenna, resulting in additional EBL
steps and layer deposition processes. We demonstrate a new approach for
magnetization excitation that is suitable for optical and non-optical
spectroscopy techniques. By patterning the antenna on a separated flexible
glass cantilever and insulating it electrically, we solved the before mentioned
issues. Since we use flexible transparent glass as a substrate, optical
spectroscopy techniques like Brillouin-light-scattering microscopy ({\mu}BLS),
time resolved magneto-optical Kerr effect measurements (TRMOKE) or optical
detected magnetic resonance (ODMR) measurements can be carried out at visible
laser wavelengths. As the antenna is detached from the sample it can be freely
positioned in all three dimensions to adress only the desired magnetic sample
structures and to achieve effective excitation. We demonstrate the
functionality of these antennas using {\mu}BLS and compare coherently and
thermally excited magnon spectra to show the enhancement of the signal by a
factor of about 400 due to the excitation by the antenna. Moreover, we succeed
to characterize yttrium iron garnet thin films with spatial resolution using
optical ferromagnetic resonance (FMR) experiments. We analyse the spatial
excitation profile of the antenna by measuring the magnetization dynamics in
two dimensions. The technique is furthermore applied to investigate
injection-locking of spin Hall nano-oscillators.",1911.11517v1
2022-01-31,Magnetic Properties and Electronic Configurations of Mn Ions in the Diluted Magnetic Semiconductor Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ Studied by X-ray Magnetic Circular Dichroism and Resonant Inelastic X-ray Scattering,"The magnetic properties and the electronic excitations of the new diluted
magnetic semiconductor Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ have
been studied by x-ray magnetic circular dichroism (XMCD) and resonant inelastic
x-ray scattering (RIXS) at the Mn $L_{2,3}$ edge. The sum rule analysis of the
XMCD spectra yields the net spin moment of $0.45\mu_{\text{B}}$/Mn and the
small orbital moment of $0.05\mu_{\text{B}}$/Mn. This indicates that the Mn
atoms are in the high-spin configurations of $d^{5}$, whereas the presence of
competing ferromagnetic and antiferromagnetic interactions between the Mn ions
reduces the net spin moment. RIXS spectra show broad peaks from 1 to 6 eV
energy loss, which originate from the $d$-$d$ crystal field excitations of the
Mn ions. Based on a comparison of the RIXS line shapes with those of
Ga$_{1-x}$Mn$_{x}$As, we conclude that the ground state of Mn in
Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ consists not only of the
charge-transferred $3d^{5}\underline{L}$ electron configuration
($\underline{L}$: ligand hole) with weakly bound holes as in
Ga$_{1-x}$Mn$_{x}$As, but also of the pure $3d^{5}$ configuration with free
holes.",2201.13061v1
1998-05-06,On magnetoelastic solitons in ferromagnet,"We study the solitonic excitations in the compressible ferromagnetic
Heisenberg chain(in the continuum limit).",9805070v1
2000-11-24,Long-range effects in superconductor-ferromagnet structures,"We analyze the proximity effect in a superconductor/ferromagnet (S/F)
structure with a local inhomogeneity of the magnetization in the ferromagnet
near the S/F interface. We demonstrate that not only the singlet but also the
triplet component of the superconducting condensate is induced in the
ferromagnet due to the proximity effect. Although the singlet component of the
condensate penetrates into the ferromagnet over a short length $\xi
_{h}=\sqrt{D/h}$ ($h$ is the exchange field in the ferromagnet and $D$ the
diffusion coefficient), the triplet component, being of the order of the
singlet one at the S/F interface, penetrates over a long length
$\sqrt{D/\epsilon}$ ($\epsilon$ is the energy). This long-range penetration
into the ferromagnet leads to a significant increase of the ferromagnet
conductance below the superconducting critical temperature $T_{c}$.",0011425v2
2001-09-19,Spin filtering by ferromagnetic nanowires,"We show that electrical current flowing through nanowires made of
ferromagnetic disordered alloys can become highly spin polarized.",0109350v1
2003-03-17,Energy gap of ferromagnet-superconductor bilayers,"The excitation spectrum of clean ferromagnet-superconductor bilayers is
calculated within the framework of the self-consistent Bogoliubov-de Gennes
theory. Because of the proximity effect, the superconductor induces a gap in
the ferromagnet spectrum, for thin ferromagnetic layers. The effect depends
strongly on the exchange field in the ferromagnet. We find that as the
thickness of the ferromagnetic layer increases, the gap disappears, and that
its destruction arises from those quasiparticle excitations with wavevectors
mainly along the interface. We discuss the influence that the interface quality
and Fermi energy mismatch between the ferromagnet and superconductor have on
the calculated energy gap. We also evaluate the density of states in the
ferromagnet, and we find it in all cases consistent with the gap results.",0303326v1
2005-07-28,Transverse spin waves in isotropic ferromagnets,"The comparison of transverse spin wave spectra and its attenuation in
Heisenberg ferromagnet and in ferromagnetic Fermi liquid as well in polarized
Fermi liquid is undertaken. The transverse spin waves frequency in polarized
paramagnetic Fermi liquid as well in a Fermi liquid with spontaneous
magnetization is found to be proportional to the square of the wave vector with
complex diffusion coefficient such that the damping has a finite value
proportional to the scattering rate of quasiparticles at T=0.
  This behavior of polarized Fermi liquid contrasts with the behavior of
Heisenberg ferromagnet in hydrodynamic regime where the transverse spin wave
attenuation appears in terms proportional to the wave vector in fourth power.
  The reactive part of diffusion coefficient in paramagnetic state at T=0
proves to be inversely proportional to magnetization whereas in ferromagnetic
state it is directly proportional to magnetization. The dissipative part of
diffusion coefficient at T=0 in paramagnetic state is polarization independent,
whereas in ferromagnetic state it is proportional to square of magnetization.
Moreover, the spin wave spectrum in ferromagnetic Fermi liquid proves to be
unstable that demonstrates the difficulty of the Fermi liquid description of
itinerant ferromagnetism.",0507676v1
2005-08-03,Nonequilibrium Phase Transitions in Model Ferromagnets: A Review,"The nonequilibrium dynamic phase transitions in ferromagnetic models (Ising,
XY and Heisenberg) are reviewed on the basis of very recent work in this field.",0508105v1
2005-11-14,Magneto-optical properties of a new group-IV ferromagnetic semiconductor Ge1-xFex grown by low-temperature molecular beam epitaxy,"A new group-IV ferromagnetic semiconductor, Ge1-xFex, was successfully grown
by low-temperature molecular beam epitaxy (LT-MBE) without precipitation of
ferromagnetic Ge-Fe intermetallic compounds. The ferromagnetism of Ge1-xFex
films was investigated by magnetic circular dichroism (MCD). In particular, the
influence of the Fe content (FFe/FGe =1 - 10%) and growth temperature (100,
200OC) on the ferromagnetism was carefully studied. The MCD measurements
revealed that the band structure of the Ge1-xFex films was identical with that
of bulk Ge, and that the large spin splitting of the band structure was induced
by the incorporation of Fe atoms into the Ge matrix, indicating the existence
of s,p-d exchange interactions. The Ge1-xFex films showed ferromagnetic
behavior and the ferromagnetic transition temperature linearly increased with
increasing the Fe composition. These results indicate that the epitaxially
grown Ge1-xFex is an intrinsic ferromagnetic semiconductor.",0511328v1
2006-02-22,Odd triplet superconductivity in a superconductor/ferromagnet structure with a spiral magnetic structure,"We analyze a superconductor-ferromagnet (S/F) system with a spiral magnetic
structure in the ferromagnet F for a weak and strong exchange field. The
long-range triplet component (LRTC) penetrating into the ferromagnet over a
long distance is calculated for both cases. In the dirty limit (or weak
ferromagnetism) we study the LRTC for conical ferromagnets. Its spatial
dependence undergoes a qualitative change as a function of the cone angle
\theta. At small angles the LRTC decays in the ferromagnet exponentially in a
monotonic way. If the angle \theta exceeds a certain value, the exponential
decay of the LRTC is accompanied by oscillations with a period that depends on
\theta. This oscillatory behaviour leads to a similar dependence of the
Josephson critical current in SFS junctions on the thickness of the F layer. In
the case of a strong ferromagnet the LRTC decays over the length which is
determined by the wave vector of the magnetic spiral and by the exchange field.",0602522v3
2007-03-19,X-ray magnetic circular dichroism characterization of GaN/Ga1-xMnxN digital ferromagnetic heterostructure,"We have investigated the magnetic properties of a GaN/Ga1-xMnxN (x = 0.1)
digital ferromagnetic heterostructure (DFH) showing ferromagnetic behavior
using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD). The Mn L2,3-edge XAS spectra were similar to those of
Ga1-xMnxN random alloy thin films, indicating a substitutional doping of high
concentration Mn into GaN. From the XMCD measurements, it was revealed that
paramagnetic and ferromagnetic Mn atoms coexisted in the Ga1-xMnxN digital
layers. The ferromagnetic moment per Mn atom estimated from XMCD agreed well
with that estimated from SQUID measurements. From these results, we conclude
that the ferromagnetic behavior of the GaN/Ga1-xMnxN DFH sample arises only
from substitutional Mn2+ ions in the Ga1-xMnxN digital layers and not from
ferromagnetic precipitates. Subtle differences were also found from the XMCD
spectra between the electronic states of the ferromagnetic and paramagnetic
Mn2+ ions.",0703477v3
2012-08-08,Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling,"Magnetic properties of a charged spin-1 Bose gas with ferromagnetic
interactions is investigated within mean-field theory. It is shown that a
competition between paramagnetism, diamagnetism and ferromagnetism exists in
this system. It is shown that diamagnetism, being concerned with spontaneous
magnetization, cannot exceed ferromagnetism in very weak magnetic field. The
critical value of reduced ferromagnetic coupling of paramagnetic phase to
ferromagnetic phase transition $\bar I_{c}$ increases with increasing
temperature. The Lande-factor $g$ is introduced to describe the strength of
paramagnetic effect which comes from the spin degree of freedom. The
magnetization density $\bar M$ increases monotonically with $g$ for fixed
reduced ferromagnetic coupling $\bar I$ as $\bar I>\bar I_{c}$. In a weak
magnetic field, ferromagnetism makes immense contribution to the magnetization
density. While at a high magnetic field, the diamagnetism inclines to saturate.
Evidence for condensation can be seen in the magnetization density at weak
magnetic field.",1208.1580v1
2014-02-05,Re-entrant superspin glass phase in La$_{0.82}$Ca$_{0.18}$MnO$_3$ ferromagnetic insulator,"We report results of magnetization and ac susceptibility measurements down to
very low fields on a single crystal of the perovskite manganite,
La$_{0.82}$Ca$_{0.18}$MnO$_3$. This composition falls in the intriguing
ferromagnetic insulator region of the manganite phase diagram. In contrast to
earlier beliefs, our investigations reveal that the system is magnetically (and
in every other sense) single-phase with a ferromagnetic ordering temperature of
$\sim$ 170 K. However, this ferromagnetic state is magnetically frustrated, and
the system exhibits pronounced glassy dynamics below 90 K. Based on measured
dynamical properties, we propose that this quasi-long-ranged ferromagnetic
phase, and associated superspin glass behavior, is the true magnetic state of
the system, rather than being a macroscopic mixture of ferromagnetic and
antiferromagnetic phases as often suggested. Our results provide an
understanding of the quantum phase transition from an antiferromagnetic
insulator to a ferromagnetic metal via this ferromagnetic insulating state as a
function of $x$ in La$_{1-x}$Ca$_x$MnO$_3$, in terms of the possible formation
of magnetic polarons.",1402.1148v1
2016-02-01,Hubbard models with nearly flat bands: Ground-state ferromagnetism driven by kinetic energy,"We consider the standard repulsive Hubbard model with a flat lowest-energy
band for two one-dimensional lattices (diamond chain and ladder) as well as for
a two-dimensional lattice (bilayer) at half filling of the flat band. The
considered models do not fall in the class of Mielke-Tasaki flat-band
ferromagnets, since they do not obey the connectivity conditions. However, the
ground-state ferromagnetism can emerge, if the flat band becomes dispersive. To
study this kinetic-energy-driven ferromagnetism we use perturbation theory and
exact diagonalization of finite lattices. We find as a typical scenario that
small and moderate dispersion may lead to a ferromagnetic ground state for
sufficiently large on-site Hubbard repulsion $U>U_c$, where $U_c$ increases
monotonically with the acquired bandwidth. However, we also observe for some
specific parameter cases, that (i) ferromagnetism appears at already very small
$U_c$, (ii) ferromagnetism does not show up at all, (iii) the critical on-site
repulsion $U_c$ is a nonmonotonic function of the bandwidth, or that (iv) a
critical bandwidth is needed to open the window for ground-state
ferromagnetism.",1602.00439v1
2016-11-25,Phase diagram of UCoGe,"The temperature-pressure phase diagram of ferromagnetic superconductor UCoGe
includes four phase transitions. They are between the paramagnetic and the
ferromagnetic states with the subsequent transition in the superconducting
ferromagnetic state and between the normal and the superconducting states after
which has to occur the transition to the superconducting ferromagnetic state.
Here we have developed the Landau theory description of the phase diagram and
established the specific ordering arising at each type of transition.
  The phase transitions to the ferromagnetic superconducting state are
inevitably accompanied by the emergency of screening currents. The
corresponding magnetostatics considerations allow to establish the significant
difference between the transition from the ferromagnetic to the ferromagnetic
superconducting state and the transition from the superconducting to the
ferromagnetic superconducting state.",1611.08440v4
2019-06-17,Ferromagnetism and superconductivity in twisted double bilayer graphene,"We present a theory of competing ferromagnetic and superconducting orders in
twisted double bilayer graphene (TDBG). In our theory, ferromagnetism is
induced by Coulomb repulsion, while superconductivity with intervalley
equal-spin pairing can be mediated by electron-acoustic phonon interactions. We
calculate the transition temperatures for ferromagnetism and superconductivity
as a function of moir\'e band filling factor, and find that superconducting
domes can appear on both the electron and hole sides of the ferromagnetic
insulator at half filling. We show that the ferromagnetic insulating gap has a
dome shape dependence on the layer potential difference, which provides an
explanation to the experimental observation that the ferromagnetic insulator
only develops over a finite range of external displacement field. We also
verify the stability of the half-filled ferromagnetic insulator against two
types of collective excitations, i.e., spin magnons and valley magnons.",1906.07302v2
2019-10-04,Intrinsic 2D Ferromagnetism in V5Se8 Epitaxial Thin Films,"The discoveries of intrinsic ferromagnetism in atomically-thin van der Waals
crystals have opened up a new research field enabling fundamental studies on
magnetism at two-dimensional (2D) limit as well as development of magnetic van
der Waals heterostructures. To date, a variety of 2D ferromagnetism has been
explored mainly by mechanically exfoliating 'originally ferromagnetic (FM)' van
der Waals crystals, while bottom-up approach by thin film growth technique has
demonstrated emergent 2D ferromagnetism in a variety of 'originally non-FM' van
der Waals materials. Here we demonstrate that V5Se8 epitaxial thin films grown
by molecular-beam epitaxy (MBE) exhibit emergent 2D ferromagnetism with
intrinsic spin polarization of the V 3d electrons despite that the bulk
counterpart is 'originally antiferromagnetic (AFM)'. Moreover,
thickness-dependence measurements reveal that this newly-developed 2D
ferromagnet could be classified as an itinerant 2D Heisenberg ferromagnet with
weak magnetic anisotropy, broadening a lineup of 2D magnets to those
potentially beneficial for future spintronics applications.",1910.01959v1
2018-03-08,Hole-doping-induced half-metallic ferromagnetism in highly-air-stable PdSe2 monolayer under uniaxial stress,"Two-dimensional (2D) high-temperature ferromagnetic materials are important
for spintronic application. Fortunately, a highly-air-stable PdSe$_2$ monolayer
semiconductor has been made through exfoliation from the layered bulk material.
It is very highly desirable to realize robust ferromagnetism, even
half-metallic ferromagnetism (100\% spin polarization), in such excellent
nonmagnetic monolayer semiconductors. Here, the first-principles investigation
shows that the PdSe$_2$ monolayer can be made to attain Stoner ferromagnetism
with the maximal Curie temperature reaching to 800K, and the hole concentration
threshold for ferromagnetism decreases with applied uniaxial stress.
Furthermore, half-metallicity can be achieved in some hole concentration
regions. For the strain of 10\% (uniaxial tensile stress of 4.4 N/m), the
monolayer can attain half-metallic ferromagnetism up to 150 K. The magnetic
anisotropic energy is suitable to not only stabilizing the 2D ferromagnetism
but also realizing fast magnetization reversal. The magnetization can be also
controlled by applying a transverse uniaxial stress. The highly-air-stable
PdSe$_2$ monolayer, with these advantages, should be promising for spintronic
applications.",1803.03079v1
2021-12-23,Monte Carlo investigation of phase changes and the order of transition of Ising modeled single-walled Nanotube,"The Monte Carlo analysis for the magnetic response of a single-walled
nanotube using the Metropolis and Wang Landau algorithms is reported in the
present paper. The nanotube architecture used in the present study utilizes the
spin half Ising model with nearest neighbors interaction and obtained various
magnetic orderings namely, ferromagnetic, G-type anti-ferromagnetic, A-type
anti-ferromagnetic, and C-type anti-ferromagnetic. It is also found that the
phase changes from ferromagnetic/anti-ferromagnetic to paramagnetic with the
modification of system's control parameters. The transition temperatures is
determined for various interaction strength in the absence of magnetic field
and for fixed interaction strength with the inclusion of external magnetic
field. The present study confirms the transition from ferromagnetic
/anti-ferromagnetic to paramagnetic is a second order transition.",2112.12393v2
2022-12-23,Surface ferromagnetism in a chiral topological semimetal CoSi,"Despite the chiral topological semimetal CoSi is known as bulk diamagnetic,
it shows unusual surface ferromagnetism of debatable origin. The ferromagnetic
ordering has been attributed to the distorted bonds, the superlattice of
ordered vacancies, or even to topological surface textures due to the spin
polarization in the neighboring Fermi arcs. We experimentally compare
magnetization reversal curves for initially oxidized CoSi single crystals and
cleaved samples with a fresh, oxide-free surface. While the oxidized CoSi
samples do not show sizable ferromagnetism, the fresh CoSi surface gives a
strong ferromagnetic response, which is accompanied by the pronounced
modulation of the angle dependence of magnetization, as it can be expected for
easy and hard axes in a ferromagnet. In addition to the first order reversal
curves analysis, this observation allows us to distinguish between different
mechanisms of the ferromagnetic ordering in CoSi single crystals. We conclude
that the surface states-induced RKKY interaction between distorted bonds near
the sample surface is responsible for the strong ferromagnetic multi-domain
behavior for freshly cleaved samples.",2212.12383v2
2023-03-28,Flat-band ferromagnetism in the SU($N$) Hubbard and Kondo lattice models,"We develop a general theory of flat-band ferromagnetism in the SU($N$)
Fermi-Hubbard model, which describes the behavior of $N$-component fermions
with SU($N$) symmetric interactions. We focus on the case where the
single-particle spectrum has a flat band and establish a necessary and
sufficient condition for the SU($N$) Hubbard model to exhibit ferromagnetism
when the number of particles is the same as the degeneracy. We show that the
occurrence of ferromagnetism is equivalent to the irreducibility of the
projection matrix onto the space of single-particle ground states. We also
demonstrate that this result can be exploited to establish a rigorous result
for the ferromagnetic SU($N$) Kondo lattice model with a flat band.
Specifically, we prove that when the SU($N$) Hubbard model is ferromagnetic,
the ferromagnetic SU($N$) Kondo lattice model with the same hopping matrix also
exhibits SU($N$) ferromagnetism.",2303.15820v2
2023-05-08,Enhanced Itinerant Ferromagnetism in Hole-doped Transition Metal Oxides: Beyond the Canonical Double Exchange Mechanism,"Here we demonstrate the occurrence of robust itinerant ferromagnetism in
Mott-Hubbard systems at both low and high doping concentrations. Specifically,
we study the effect of hole doping on the experimentally synthesized LaCrAsO
via first-principles calculations and observe that the parent G-type
antiferromagnetism vanishes quickly at low doping concentration ($x$ $\sim$
0.20) and the system becomes ferromagnetic metal due to the canonical double
exchange (CDE) mechanism. As $x$ continues to increase, the onsite energy
difference between Cr 3$d$ and As 4$p$ orbitals decreases and the system
transitions to a ferromagnetic negative charge-transfer energy metal.
Therefore, the itinerant ferromagnetism doesn't terminate at intermediate $x$
as CDE mechanism usually predicts. Furthermore, our calculations reveal that
both nearest and next-nearest ferromagnetic exchange coupling strengths keep
growing with $x$, showing that ferromagnetism caused by negative
charge-transfer energy state is ""stronger"" than that of CDE picture. Our work
not only unveils an alternative mechanism of itinerant ferromagnetism, but also
has the potential to attract immediate interest among experimentalists.",2305.04459v1
2023-11-15,Polaronic mechanism of Nagaoka ferromagnetism in Hubbard models,"The search for elusive Nagaoka-type ferromagnetism in the Hubbard model has
recently enjoyed renewed attention with the advent of a variety of experimental
platforms enabling its realization, including moir\'e materials, quantum dots,
and ultracold atoms in optical lattices. Here, we demonstrate a universal
mechanism for Nagaoka ferromagnetism (that applies to both bipartite and
nonbipartite lattices) based on the formation of ferromagnetic polarons
consisting of a dopant dressed with polarized spins. Using large-scale
density-matrix renormalization group calculations, we present a comprehensive
study of the ferromagnetic polaron in an electron-doped Hubbard model,
establishing various polaronic properties such as its size and energetics.
Moreover, we systematically probe the internal structure of the magnetic
state$\unicode{x2014}$through the use of pinning fields and three-point
spin-charge-spin correlation functions$\unicode{x2014}$for both the
single-polaron limit and the high-density regime of interacting polarons. Our
results highlight the crucial role of mobile polarons in the birth of global
ferromagnetic order from local ferromagnetism and provide a unified framework
to understand the development and demise of the Nagaoka-type ferromagnetic
state across dopings.",2311.09279v1
1993-12-21,Magnetic Properties of the Spin-1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic Trimerized Heisenberg Chain:,"The magnetic properties of the ferromagnetic-ferromagnetic-antiferromagnetic
trimerized spin-1/2 Heisenberg chain are studied theoretically. The high
temperature susceptibilty and the ground state saturation magnetic field are
calculated and the exchange energies of the trimer compound 3CuCl${}_2\cdot$2dx
are determined. The magnetization curve is obtained by numerical
diagonalization of finite size systems. The result explains the low temperature
magnetization data for 3CuCl${}_2\cdot$2dx with the exchange energies obtained
as above. It is predicted that the magnetization curve has a plateau at 1/3 of
the saturation magnetization if the ferromagnetic exchange energy is comparable
to or smaller than the antiferromagnetic exchange energy.",9312084v1
1997-11-10,Magneto-Coulomb Oscillation in Ferromagnetic Single Electron Transistors,"The mechanism of the magneto-Coulomb oscillation in ferromagnetic single
electron transistors (SET's) is theoretically considered. Variations in the
chemical potentials of the conduction electrons in the ferromagnetic island
electrode and the ferromagnetic lead electrodes in magnetic fields cause
changes in the free energy of the island electrode of the SET. Experimental
results of the magneto-Coulomb oscillation in a Ni/Co/Ni ferromagnetic SET are
presented and discussed. Possible applications of this phenomenon are also
discussed.",9711075v2
1997-12-31,The influence of long-range hopping on ferromagnetism in the Hubbard model,"The phase diagram of the Hubbard model in an external magnetic field is
examined by extrapolation of small-cluster exact-diagonalization calculations.
Using a general expression for the hopping matrix elements ($t_{ij}\sim
q^{|i-j|}$) the influence of long-range hopping (band asymmetry) on
ferromagnetism in this model is studied. It is found that the long-range
hopping (nonzero $q$) stabilizes ferromagnetism in an external magnetic field
for $n > 1$. In the opposite limit $n \leq 1$ the fully polarized ferromagnetic
state is generally suppressed with increasing $q$. The critical value of
magnetic field $h$ below which the ferromagnetic state becomes unstable is
calculated numerically.",9712324v1
1998-09-03,Spin-Dependent Coulomb Blockade in Ferromagnet/Normal-Metal/Ferromagnet Double Tunnel Junctions,"We study theoretically the spin-dependent transport in
ferromagnet/normal-metal/ferromagnet double tunnel junctions by special
attention to cotunneling in the Coulomb blockade region. The spin accumulation
caused by cotunneling squeezes the Coulomb blockade region when the
magnetizations in the ferromagnetic electrodes are antiparallel. Outside the
squeezed Coulomb blockade region, we propose a new anomalous region, where the
sequential tunneling in one of the spin bands is suppressed by the Coulomb
blockade and that in the other is not. In this region, the tunnel
magnetoresistance oscillates as a function of bias voltage. The temperature
dependences of the tunnel magnetoresistance and the magnitude of the spin
accumulation are calculated.",9809058v1
1998-11-24,Local Density of States in Superconductor-Ferromagnetic Hybrid Systems,"In this Letter we discuss various properties of the local density of states
(DOS) for a superconductor-ferromagnet hybrid system. The DOS is modified at
small energies on both sides of the interface. Due to the interplay of
superconductivity and ferromagnetism, the local DOS depends on the spin
direction. The spin polarization effects extend over a long distance from the
interface both in the superconductor and in the ferromagnet. If the ferromagnet
is of finite lenght, the DOS shows a (spin dependent) gap.",9811334v1
1999-01-27,Spin-Imbalance and Magnetoresistance in Ferromagnet/Superconductor/Ferromagnet Double Tunnel Junctions,"We theoretically study the spin-dependent transport in a ferromagnet/super-
conductor/ferromagnet double tunnel junction. The tunneling current in the
antiferromagnetic alignment of the magnetizations gives rise to a spin
imbalance in the superconductor. The resulting nonequilibrium spin density
strongly suppresses the superconductivity with increase of bias voltage and
destroys it at a critical voltage Vc. The results provide a new method not only
for measuring the spin polarization of ferromagnets but also for controlling
superconductivity and tunnel magnetoresistance (TMR) by applying the bias
voltage.",9901300v2
1999-04-19,Ferromagnetism in single-band Hubbard models with a partially flat band,"A Hubbard model with a single, partially flat band has ferromagnetic ground
states. It is shown that local stability of ferromagnetism implies its global
stability in such a model: The model has only ferromagnetic ground states if
there are no single spin-flip ground states. Since a single-band Hubbard model
away from half filling describes a metal, this result may open a route to
metallic ferromagnetism in single band Hubbard models.",9904258v1
1999-10-25,Stability of Ferromagnetism in Hubbard models with degenerate single-particle ground states,"A Hubbard model with a N_d-fold degenerate single-particle ground state has
ferromagnetic ground states if the number of electrons is less or equal to N_d.
It is shown rigorously that the local stability of ferromagnetism in such a
model implies global stability: The model has only ferromagnetic ground states,
if there are no single spin-flip ground states. If the number of electrons is
equal to N_d, it is well known that the ferromagnetic ground state is unique if
and only if the single-particle density matrix is irreducible. We present a
simplified proof for this result.",9910385v1
1999-11-30,Coexistence of superconductivity and ferromagnetism in ferromagnetic metals,"In this paper we address the question of coexistence of superconductivity and
ferromagnetism in the high temperature superconductor
RuSr$_2$GdCu$_2$O$_{8-\delta}$. Using a field theoretical approach we study a
one-fermion effective model of a ferromagnetic superconductor in which the
quasiparticles responsible for the ferromagnetism form the Cooper pairs as
well. We discuss the physical features which are different in this model and
the standard BCS model and consider their experimental consequences.",9911489v1
2000-02-10,Cryptoferromagnetic state in superconductor-ferromagnet multilayers,"We study a possibility of a non-homogeneous magnetic order
(cryptoferromagnetic state) in heterostructures consisting of a bulk
superconductor and a ferromagnetic thin layer that can be due to the influence
of the superconductor. The exchange field in the ferromagnet may be strong and
exceed the inverse mean free time. A new approach based on solving the
Eilenberger equations in the ferromagnet and the Usadel equations in the
superconductor is developed. We derive a phase diagram between the
cryptoferromagnetic and ferromagnetic states and discuss the possibility of an
experimental observation of the CF state in different materials.",0002151v1
2001-03-14,Multispin Ising spin glasses with ferromagnetic interactions,"We consider the thermodynamics of an infinite-range Ising p-spin glass model
with an additional r-spin ferromagnetic interaction. For r=2 there is a
continuous transition to a ferromagnetic phase, while for r>2 the transition is
first order. We find both glassy and non-glassy ferromagnetic phases, with
replica symmetry breaking of both the one step and full varieties. We obtain
new results for the case where r=p>2, demonstrating the existence of a
non-glassy ferromagnetic phase, of significance to error-correcting codes.",0103292v2
2001-07-30,Andreev Reflection in Narrow Ferromagnet/Superconductor Point Contacts,"The Andreev reflection of narrow ferromagnet/superconductor point contacts is
theoretically studied. We show that the conductance quantization depends on
whether the contact region is superconducting or ferromagnetic as well as on
the strength of the exchange field in the ferromagnet. The Andreev reflection
of the ferromagnetic contact is more suppressed than that of the
superconducting contact. We also show that the conductance-voltage curve has a
bump at zero bias-voltage if there is no interfacial-scattering. On the
contrary, the conductance-voltage curve shows a dip if the system has an
interfacial-scattering.",0107588v1
2001-10-22,Anomalous Hall effect in ferromagnetic semiconductors,"We present a theory of the anomalous Hall effect in ferromagnetic (Mn,III)V
semiconductors. Our theory relates the anomalous Hall conductance of a
homogeneous ferromagnet to the Berry phase acquired by a quasiparticle
wavefunction upon traversing closed paths on the spin-split Fermi surface of a
ferromagnetic state. It can be applied equally well to any itinerant electron
ferromagnet. The quantitative agreement between our theory and experimental
data in both (In,Mn)As and (Ga,Mn)As systems suggests that this disorder
independent contribution to the anomalous Hall conductivity dominates in
diluted magnetic semiconductors.",0110484v1
2001-11-15,A Model for Superconductivity in Ferromagnetic ZrZn2,"This article proposes that superconductivity in the ferromagnetic state of
ZrZn$_2$ is stabilized by an exchange-type interaction between the magnetic
moments of triplet-state Cooper pairs and the ferromagnetic magnetization
density. This explains why superconductivity occurs in the ferromagnetic state
only, and why it persists deep into the ferromagnetic state. The model of this
article also yields a particular order parameter symmetry, which is a
prediction that can be checked experimentally.",0111292v2
2002-03-07,Ferromagnetism in Oriented Graphite Samples,"We have studied the magnetization of various, well characterized samples of
highly oriented pyrolitic graphite (HOPG), Kish graphite and natural graphite
to investigate the recently reported ferromagnetic-like signal and its possible
relation to ferromagnetic impurities. The magnetization results obtained for
HOPG samples for applied fields parallel to the graphene layers - to minimize
the diamagnetic background - show no correlation with the magnetic impurity
concentration. Our overall results suggest an intrinsic origin for the
ferromagnetism found in graphite. We discuss possible origins of the
ferromagnetic signal.",0203153v1
2002-04-12,Superconducting states in ferromagnetic metals,"The symmetry of the superconducting states arising directly from
ferromagnetic states in the crystals with cubic and orthorombic symmetries is
described. The symmetry nodes in the quasiparticle spectra of such the states
are pointed out if they exist. The superconducting phase transition in the
ferromagnet is accompanied by the formation of superconducting domain structure
consisting of complex conjugate states imposed on the ferromagnet domain
structure with the opposite direction of the magnetization in the adjacent
domains. The interplay between stimulation of a nonunitary superconducting
state by the ferromagnetic moment and supression of the superconductivity by
the diamagnetic orbital currents is established.",0204263v3
2002-08-15,High Ferromagnetic Transition Temperature (172K) in Mn delta-doped GaAs with p-type Selective Doping,"We have found high ferromagnetic transition temperature in Mn delta-doped
GaAs-based heterostructures grown on GaAs(001) substrates by molecular beam
epitaxy. A 0.3 ML Mn d-doped GaAs samples showed high resistivity at low
temperature and did not show a ferromagnetic behavior. However, in a
selectively doped heterostructure (Mn delta-doped GaAs / Be-doped AlGaAs),
where holes were supplied from the Be-doped AlGaAs layer, clear ferromagnetic
order was observed. The ferromagnetic transition temperature of the selectively
doped heterostructure was as high as 172K with suitable low-temperature (LT)
annealing treatment.",0208299v1
2002-08-28,Absence of an equilibrium ferromagnetic spin glass phase in three dimensions,"Using ground state computations, we study the transition from a spin glass to
a ferromagnet in 3-d spin glasses when changing the mean value of the spin-spin
interaction. We find good evidence for replica symmetry breaking up till the
critical value where ferromagnetic ordering sets in, and no ferromagnetic spin
glass phase. This phase diagram is in conflict with the droplet/scaling and
mean field theories of spin glasses. We also find that the exponents of the
second order ferromagnetic transition do not depend on the microscopic
Hamiltonian, suggesting universality of this transition.",0208566v2
2002-12-30,Quantum Critical Behavior in Disordered Itinerant Ferromagnets: Instability of the Ferromagnetic Phase,"An effective field theory is derived that describes the quantum critical
behavior of itinerant ferromagnets as the transition is approached from the
ferromagnetic phase. This complements a recent study of the critical behavior
on the paramagnetic side of the phase transition, and investigates the role of
the ferromagnetic Goldstone modes near criticality. We find that the Goldstone
modes have no direct impact on the critical behavior, and that the critical
exponents are the same as determined by combining results from the paramagnetic
phase with scaling arguments.",0212636v2
2003-06-12,Magnetoelectronic Spin Echo,"We predict a spin echo in electron transport through layered
ferromagnetic-normal-ferromagnetic metal structures: whereas a spin current
polarized perpendicular to the magnetization direction decays when traversing a
single homogeneous ferromagnet on the scale of the ferromagnetic spin-coherence
length, it reappears by adding a second identical but antiparallel ferromagnet.
This re-entrant transverse spin current resembles the spin-echo effect in the
magnetization of nuclei under pulsed excitations. We propose an experimental
setup to measure the magnetoelectronic spin echo.",0306344v2
2003-07-13,Crossed Andreev Reflection in Structures Consisting of a Superconductor with Ferromagnetic Leads,"A theory of crossed Andreev reflection in structures consisting of a
superconductor with two ferromagnetic leads is presented. The electric current
due to the crossed Andreev reflection strongly depends on the relative
orientation of the magnetization of two ferromagnetic leads. It is shown that
the dependence of the electric current and the magnetoresistance on the
distance between two ferromagnetic leads is understood by considering the
interference between the wave functions in ferromagnets. The current and the
magnetoresistance are calculated as functions of the exchange field and the
height of the interfacial barriers.",0307307v2
2003-07-31,Carrier induced ferromagnetism in room temperature ferromagnetic semiconductor rutile TiO2 doped with Co,"A ferromagnetic semiconductor, rutile (Ti,Co)O2, exhibits anomalous Hall
effect at room temperature. Strong dependence of the anomalous Hall effect, as
well as the magneto-optic response, on the carrier concentration suggests
carrier induced ferromagnetism in this compound. Both ferromagnetic responses
are caused by the charge carriers at the band edge of host semiconductor,
indicating possibilities of spintronics devices operable at room temperature.",0307760v1
2004-04-21,Reversible 300K Ferromagnetic Ordering in a Diluted Magnetic Semiconductor,"The discovery of reversible 300 K ferromagnetic ordering in a diluted
magnetic semiconductor is reported. Switching of room-temperature
ferromagnetism between ""on"" and ""off"" states is achieved in Co2+:ZnO by lattice
incorporation and removal of the native n-type defect, interstitial Zn.
Spectroscopic and magnetic data implicate a double-exchange mechanism for
ferromagnetism. These results demonstrate for the first time reversible
room-temperature ferromagnetic ordering in a diluted magnetic semiconductor,
and present new opportunities for integrating magnetism and conductivity in
semiconductor sensor or spin-based electronics devices.",0404518v1
2004-05-20,Ferromagnetic and random spin ordering in diluted magnetic semiconductors,"In a diluted magnetic semiconductor system, the exchange interaction between
magnetic impurities has two independent components: a direct antiferromagnetic
interaction and a ferromagnetic interaction mediated by charge carriers.
Depending on the system parameters, the ground state of the system may be
ordered either ferromagnetically or randomly. In this paper we use percolation
theory to find the ferromagnetic transition temperature and the location of the
quantum critical point separating the ferromagnetic phase and a valence bond
glass phase.",0405467v2
2004-08-12,Spin Screening and Antiscreening in a Ferromagnet/Superconductor Heterojunction,"We present a theoretical study of spin screening effects in a
ferromagnet/superconductor (F/S) heterojunction. It is shown that the magnetic
moment of the ferromagnet is screened or antiscreened, depending on the
polarization of the electrons at the Fermi level. If the polarization is
determined by the electrons of the majority (minority) spin band then the
magnetic moment of the ferromagnet is screened (antiscreened) by the electrons
in the superconductor. We propose experiments that may confirm our theory: for
ferromagnetic alloys with certain concentration of Fe or Ni ions there will be
screening or antiscreening respectively. Different configurations for the
density of states are also discussed.",0408273v1
2004-10-27,Suppression of the superconducting critical current of Nb in bilayers of Nb/SrRuO3,"In bilayers consisting of ferromagnetic and superconducting films, the
ferromagnetic film in its domain state induces inhomogeneous distribution of
magnetic fields in the superconducting film. When the ferromagnetic film has
bubble magnetic domains in a labyrinth structure, it has been found that the
pinning of the vortices increases; hence, the critical current of the
superconducting film becomes larger. Here we study the effect of parallel
ferromagnetic domain structure in Nb/SrRuO3 on the critical current of Nb with
current flowing perpendicularly to the domains and find that in this case the
ferromagnetic domain structure decreases the critical current.",0410715v2
2005-04-18,Itinerant Ferromagnetism in an Ultracold Atom Fermi Gas,"We address the possible occurrence of ultracold atom ferromagnetism by
evaluating the free energy of a spin polarized Fermi gas to second order in its
interaction parameter. We find that Hartree-Fock theory underestimates the
tendency toward ferromagnetism, predict that the ferromagnetic transition is
first order at low temperatures, and point out that the spin coherence time of
gases prepared in a ferromagnetic state is strongly enhanced as the transition
is approached. We relate our results to recent experiments.",0504459v1
2005-11-03,Superconducting phase coherent electron transport in proximity conical ferromagnets,"We report superconducting phase-periodic conductance oscillations in
ferromagnetic wires with interfaces to conventional superconductors. The
ferromagnetic wires were made of Ho, a conical ferromagnet. The distance
between the interfaces was much larger than the singlet superconducting
penetration depth. We explain the observed oscillations as due to the
long-range penetration of an unusual ""helical"" triplet component of the order
parameter that is generated at the superconductor/ferromagnet interfaces and
maintained by the intrinsic rotating magnetization of Ho.",0511077v1
2006-03-03,Theoretical Study on Coexistence of Ferromagnetism and Superconductivity,"On the basis of a two-dimensional t-t' Hubbard model in ferromagnetic and
paramagnetic states, the triplet superconducting mechanism is investigated by
the third-order perturbation theory with respect to the on-site Coulomb
interaction U. In general, the superconducting state is more stable in the
paramagnetic state than in the ferromagnetic state. As a special case, the
dominant ferromagnetic superconductivity is obtained by the electron-electron
correlation between the electronlike majority and holelike minority bands.
Furthermore, it is pointed out that in some cases the two bands play an
essential role for the coexistence of superconductivity and ferromagnetism.",0603066v1
2007-01-06,Spin Ladder with Anisotropic Ferromagnetic Legs in a Transverse Magnetic Field,"We study the ground state phase diagram of a two-leg spin ladder with
anisotropic ferromagnetic leg couplings under the influence of a symmetry
breaking transverse magnetic field by the exact diagonalization technique. In
the case of antiferromagnetic coupling between legs we identified two phase
transitions in the plane of magnetic field vs interchain coupling strength. The
first one corresponds to the transition from the gapped rung-singlet phase to
the gapped stripe-ferromagnetic phase. The second one represents the transition
from the gapped stripe-ferromagnetic phase into the fully polarized
ferromagnetic phase.",0701127v1
2007-06-28,Penetration of Andreev bound states into the ferromagnet in a SrRuO$_{3}$/(110)YBa$_2$Cu$_3$O$_{7-δ}$ bilayer: a scanning tunneling spectroscopy study,"Scanning tunneling spectroscopy of thin epitaxial
$SrRuO_{3}/(110)YBa_2Cu_3O_{7-\delta}$ ferromagnet/superconductor bilayers,
reveal a clear penetration of the Andreev bound states into the ferromagnetic
layer. The penetration is manifested in the density of states of the
ferromagnet as a split zero bias conductance peak with an imbalance between
peak heights. Our data indicate that the splitting occurs at the superconductor
side as a consequence of induced magnetization, confirming recent theoretical
predictions. The imbalance is attributed to the spin polarization in the
ferromagnet.",0706.4208v1
2007-10-30,Devitrification of a glass-like arrested ferromagnetic phase in La0.5Ca0.5MnO3,"Magnetization measurements in La0.5Ca0.5MnO3 manganite show that the
high-temperature long-range ferromagnetic-metallic phase transforms to
antiferromagnetic-insulating phase, although a fraction of
ferromagnetic-metallic phase undergoes glass-like kinetic arrest and coexists
at low temperature with the equilibrium antiferromagnetic-insulating phase. We
show here through resistivity measurements that the residual arrested
ferromagnetic-metallic fraction can be converted to the equilibrium
antiferromagnetic-insulating phase by successive annealing at higher
temperatures, possibly through heterogeneous nucleation of equilibrium phase.
Significantly, larger fractions of this glassy ferromagnetic-metallic phase can
be obtained by cooling in higher fields and larger conversion to equilibrium
antiferromagnetic-insulating phase results.",0710.5585v1
2008-03-03,Ferromagnetic Pairing States on Two-Coupled Chains,"We propose a concrete model which exhibits ferromagnetism and electron-pair
condensation simultaneously. The model is defined on two chains and consists of
the electron hopping term, the on-site Coulomb repulsion, and a ferromagnetic
interaction which describes ferromagnetic coupling between two electrons, one
on a bond in a chain and the other on a site in the other chain. It is
rigorously shown that the model has fullypolarized ferromagnetic pairing ground
states. The higher dimensional version of the model is also presented.",0803.0174v2
2009-02-02,Evolution of the local superconducting density of states in ErRh$_4$B$_{4}$ close to the ferromagnetic transition,"We present local tunneling spectroscopy experiments in the superconducting
and ferromagnetic phases of the reentrant superconductor ErRh$_4$B$_{4}$. The
tunneling conductance curves jump from showing normal to superconducting
features within a few mK close to the ferromagnetic transition temperature,
with a clear hysteretic behavior. Within the ferromagnetic phase, we do not
detect any superconducting correlations. Within the superconducting phase we
find a peculiar V-shaped density of states at low energies, which is produced
by the magnetically modulated phase that coexists with superconductivity just
before ferromagnetism sets in.",0902.0308v1
2009-04-02,Probing interaction-induced ferromagnetism in optical superlattices,"We propose a controllable method for observing interaction induced
ferromagnetism in ultracold fermionic atoms loaded in optical superlattices. We
first discuss how to probe and control Nagaoka ferromagnetism in an array of
isolated plaquettes (four lattice sites arranged in a square). Next, we show
that introducing a weak interplaquette coupling destroys the ferromagnetic
correlations. To overcome this instability we propose to mediate long-range
ferromagnetic correlations among the plaquettes via double-exchange processes.
Conditions for experimental realization and techniques to detect such states
are discussed.",0904.0412v2
2009-05-12,Trends in Ferromagnetism in Mn doped dilute III-V alloys from a density functional perspective,"Mn doping in dilute III-V alloys has been examined as a route to enhance
ferromagnetic stability. Strong valence band bowing is expected at the dilute
limit, implying a strong modification of the ferromagnetic stability upon
alloying, with even an increase in some cases. Using first principle electronic
structure calculations we show that while codoping with a group V anion
enhances the ferromagnetic stability in some cases when the effects of
relaxation of the lattice are not considered, strong impurity scattering in the
relaxed structure result in a reduction of the ferromagnetic stability.",0905.1762v1
2010-08-13,Neutral skyrmion configurations in the low-energy effective theory of spinor condensate ferromagnets,"We study the low-energy effective theory of spinor condensate ferromagnets
for the superfluid velocity and magnetization degrees of freedom. This
effective theory describes the competition between spin stiffness and a
long-ranged interaction between skyrmions, topological objects familiar from
the theory of ordinary ferromagnets. We find exact solutions to the non-linear
equations of motion describing neutral configurations of skyrmions and
anti-skyrmions. These analytical solutions provide a simple physical picture
for the origin of crystalline magnetic order in spinor condensate ferromagnets
with dipolar interactions. We also point out the connections to effective
theories for quantum Hall ferromagnets.",1008.2239v1
2010-09-03,Josephson current and $π-$state in ferromagnet with embedded superconducting nanoparticles,"On the basis of Usadel equations we investigate
superconductor/ferromagnet/superconductor (S/F/S) hybrid systems which consist
of superconducting nanostructures (spheres, rods) embedded in ferromagnetic
metal. The oscillations of the critical current of the S/F/S Josephson
junctions with the thickness of ferromagnetic spacer between superconducting
electrodes are studied. We demonstrate that the $\pi $ state can be realized in
such structures despite of a dispersion of the distances between different
parts of the electrodes. The transitions between 0 and $\pi $ states at some
thickness of ferromagnetic spacer can be triggered by temperature variation.",1009.0643v1
2010-09-19,Itinerant ferromagnetism in a two-dimensional atomic gas,"Motivated by the first experimental evidence of ferromagnetic behavior in a
three-dimensional ultracold atomic gas, we explore the possibility of itinerant
ferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a
formalism that demonstrates how quantum fluctuations drive the ferromagnetic
reconstruction first order, and consider the consequences of an imposed
population imbalance. Secondly, we adapt this formalism to elucidate the key
experimental signatures of ferromagnetism in a realistic trapped geometry.",1009.3614v1
2011-03-31,Pressure-induced s-band ferromagnetism in alkali metals,"First-principles density-functional-theory calculations show that compression
of alkali metals stabilizes open structures with localized interstitial
electrons which may exhibit a Stoner-type instability towards ferromagnetism.
We find ferromagnetic phases of the lithium-IV-type, simple cubic, and simple
hexagonal structures in the heavier alkali metals, which may be described as
s-band ferromagnets. We predict that the most stable phases of potassium at low
temperatures and pressures around 20 GPa are ferromagnets.",1103.6141v1
2011-06-20,Ferromagnetic state and phase transitions,"Evidence is summarized attesting that the standard exchange field theory of
ferromagnetism by Heisenberg has not been successful. It is replaced by the
crystal field and a simple assumption that spin orientation is inexorably
associated with the orientation of its carrier. It follows at once that both
ferromagnetic phase transitions and magnetization must involve a structural
rearrangement. The mechanism of structural rearrangements in solids is
nucleation and interface propagation. The new approach accounts coherently for
ferromagnetic state and its manifestations.",1106.3795v1
2011-08-24,Ferromagnetism and Superconductivity in Uranium Compounds,"Recent advances on ferromagnetic superconductors, UGe2, URhGe and UCoGe are
presented. The superconductivity (SC) peacefully coexists with the
ferromagnetism (FM), forming the spin-triplet state of Cooper pairs. The
striking new phenomena, such as SC reinforced by the magnetic field, are
associated with Ising-type ferromagnetic fluctuations. A variety of
ferromagnetic ordered moments between UGe2, URhGe and UCoGe affords to
understand the relation between FM, tricriticality and SC.",1108.4807v1
2012-07-06,Double Exchange Ferromagnetism in the Peierls Insulator State,"We study the effects of opening of the band gap on the double exchange
ferromagnetism. Applying the density-matrix renormalization group method and an
analytical expansion from the dimer limit to the one-dimensional double
exchange model, we demonstrate for a relevant region of the exchange coupling
that, in the weak dimerization regime, the Peierls gap opens in the fully
spin-polarized conduction band without affecting its ferromagnetism, whereas in
the strong dimerization regime, the ferromagnetism is destroyed and the Mott
gap opens instead, leading the system to the antiferromagnetic quasi-long-range
order. An insulator version of the double exchange ferromagnetism is thus
established.",1207.1525v1
2013-01-03,Integrable Heisenberg Ferromagnet Equations with self-consistent potentials,"In this paper, we consider some integrable Heisenberg Ferromagnet Equations
with self-consistent potentials. We study their Lax representations. In
particular we give their equivalent counterparts which are nonlinear
Schr\""odinger type equations. We present the integrable reductions of the
Heisenberg Ferromagnet Equations with self-consistent potentials. These
integrable Heisenberg Ferromagnet Equations with self-consistent potentials
describe nonlinear waves in ferromagnets with some additional physical fields.",1301.1649v2
2013-03-16,Designing ferromagnetism in vanadium-oxide based superlattices,"Motivated by recent reports (Phys. Rev. B\textbf{80}, 241102) of
room-temperature ferromagnetism in vanadium-oxide based superlattices, a
single-site dynamical mean field study of the dependence of the
paramagnetic-ferromagnetic phase boundary on superlattice geometry was
performed. An examination of variants of the experimentally determined crystal
structure indicate that ferromagnetism is found only in a small and probably
inaccessible region of the phase diagram. Design criteria for increasing the
range over which ferromagnetism might exist are proposed.",1303.4016v2
2015-11-09,Ferromagnetic instability of interlayer floating electrons in quasi-two-dimensional electride Y$_2$C,"Ab initio electronic structure calculations show that the recently identified
quasi-two-dimensional electride Y$_2$C is a weak itinerant ferromagnet or at
least close to a ferromagnetic instability. The ferromagnetism is induced by
the electride electrons, which are loosely bound around interstitial sites and
overlap with each other to form two-dimensional interlayer conduction bands.
The semimetallicity and two-dimensionality of the band structure are the key to
understanding this ferromagnetic instability.",1511.02561v1
2013-08-08,Ferromagnetism of the Repulsive Atomic Fermi Gas: three-body recombination and domain formation,"The simplest model for itinerant ferromagnetism, the Stoner model, has so far
eluded experimental observation in repulsive ultracold fermions due to rapid
three-body recombination at large scattering lengths. Here we show that a
ferromagnetic phase can be stabilised by imposing a moderate optical lattice.
The reduced kinetic energy drop upon formation of a polarized phase in an
optical lattice extends the ferromagnetic phase to smaller scattering lengths
where three-body recombination is small enough to permit experimental detection
of the phase. We also show, using time dependent density functional theory,
that in such a setup ferromagnetic domains emerge rapidly from a paramagnetic
initial state.",1308.1961v1
2018-01-05,Magnetoresistance originated from charge-spin conversion in ferromagnet,"Transverse magnetoresistance in a ferromagnetic/nonmagnetic/ferromagnetic
trilayer originated from charge-spin conversion by anomalous Hall effect is
investigated theoretically. Solving the spin diffusion equation in bulk and
using the spin-dependent Landauer formula at the ferromagnetic/nonmagnetic
interface, an analytical formula of the transverse resistivity is obtained. The
charge-spin conversion by the anomalous Hall effect contributes to the
magnetoresistance in a manner proportional to the square of the spin anomalous
Hall angle. The angular dependence of the magnetoresistance is basically
identical to that of planar Hall effect, but has an additional term which
depends on the relative angle of the magnetizations in two ferromagnets.",1801.01623v1
2018-07-26,Phase separation and proximity effects in itinerant ferromagnet-superconductor heterostructures,"Heterostructures made of itinerant ferromagnets and superconductors are
studied. In contrast to most previous models, ferromagnetism is not enforced as
an external Zeeman field but induced in a correlated single-band model (CSBM)
that displays itinerant ferromagnetism as a mean-field ground state. This
allows us to investigate the influence of an adjacent superconducting layer on
the properties of the ferromagnet in a self-consistent Bogoliubov-de Gennes
approach. The CSBM displays a variety features not present in the Zeeman
exchange model that influence the behavior of order parameters close to the
interface, as e.g. phase separation and the competition between magnetism and
superconducting orders.",1807.10387v1
2020-08-15,The inverse proximity effect in strong ferromagnet-superconductor structures,"The magnetization in a superconductor induced due to the inverse proximity
effect is investigated in hybrid bilayers containing a superconductor and a
ferromagnetic insulator or a strongly spin-polarized ferromagnetic metal. The
study is performed within a quasiclassical Green function framework, wherein
Usadel equations are solved with boundary conditions appropriate for strongly
spin-polarized ferromagnetic materials. A comparison with recent experimental
data is presented. The singlet to triplet conversion of the superconducting
correlations as a result of the proximity effect with a ferromagnet is studied.",2008.06757v1
2022-10-17,Flat band induced room temperature ferromagnetism in two dimensional systems,"The remarkable and fascinating properties of two-dimensional materials have
raised them to the rank of most promising candidates for technological
applications. In particular, the possibility of long-range ferromagnetic order
in 2D materials is generating a growing excitement. Here, we demonstrate that
flat bands (FBs) may pave the way to room temperature ferromagnetism in 2D
compounds. Indeed, the magnetic exchanges between localized spins are largely
dominated by the FB-FB contribution. This contribution is ferromagnetic and
scales linearly with the local coupling, thus leading to cross-over
temperatures (ferromagnetic phase/ paramagnetic phase) higher by an order of
magnitude than those currently reported in experiments. Cross-over temperatures
as high as $600~ K$ could be reached in micrometer-sized FB systems.",2210.08896v1
2023-03-21,Unique Itinerant Ferromagnetism in 4d-electron System Ca2RuO4,"We have studied the magnetic properties of pressure-induced ferromagnet
Ca2RuO4 to reveal the uniqueness of the 4d-electron ferromagnetism in the
quasi-two-dimensional conductor. The magnetic parameters have been estimated
from the paramagnetic susceptibility and the magnetisation process under
pressure up to 2 GPa. The parameters can well be interpreted on the basis of
the self-consistent renormalization theory of spin fluctuation for 3D-itinerant
ferromagnet. Nevertheless, the metallic Ca2RuO4 shows quite strong anisotropy
not only in the conductivity but also in the magnetisation process. Such the
strong anisotropy is rare for an itinerant ferromagnet and is a unique
characteristic of the 4d electron system Ca2RuO4.",2303.11604v1
2023-04-23,Spin-triplet superconductivity from quantum-geometry-induced ferromagnetic fluctuation,"We show that quantum geometry induces ferromagnetic fluctuation resulting in
spin-triplet superconductivity. The criterion for ferromagnetic fluctuation is
clarified by analyzing contributions from the effective mass and quantum
geometry. When the non-Kramers band degeneracy is present near the Fermi
surface, the Fubini-Study quantum metric strongly favors ferromagnetic
fluctuation. Solving the linearized gap equation with the effective interaction
obtained by the random phase approximation, we show that the spin-triplet
superconductivity is mediated by quantum-geometry-induced ferromagnetic
fluctuation.",2304.11536v2
2001-04-12,Ferromagnetism in the one-dimensional Hubbard model with orbital degeneracy: From low to high electron density,"We studied ferromagnetism in the one-dimensional Hubbard model with doubly
degenerate atomic orbitals by means of the density-matrix renormalization-group
method and obtained the ground-state phase diagrams. It was found that
ferromagnetism is stable from low to high (0< n < 1.75) electron density when
the interactions are sufficiently strong. Quasi-long-range order of triplet
superconductivity coexists with the ferromagnetic order for a strong Hund
coupling region, where the inter-orbital interaction U'-J is attractive. At
quarter-filling (n=1), the insulating ferromagnetic state appears accompanying
orbital quasi-long-range order. For low densities (n<1), ferromagnetism occurs
owing to the ferromagnetic exchange interaction caused by virtual hoppings of
electrons, the same as in the quarter-filled system. This comes from separation
of the charge and spin-orbital degrees of freedom in the strong coupling limit.
This ferromagnetism is fragile against variation of band structure. For high
densities (n>1), the phase diagram of the ferromagnetic phase is similar to
that obtained in infinite dimensions. In this case, the double exchange
mechanism is operative to stabilize the ferromagnetic order and this long-range
order is robust against variation of the band-dispersion. A partially polarized
state appears in the density region 1.68<n<1.75 and phase separation occurs for
n just below the half-filling (n=2).",0104223v2
2018-10-22,Long Range Intrinsic Ferromagnetism in Two Dimensional Materials and Dissipationless Future Technologies,"The inherent susceptibility of low-dimensional materials to thermal
fluctuations has long been expected to poses a major challenge to achieving
intrinsic long-range ferromagnetic order in two-dimensional materials. The
recent explosion of interest in atomically thin materials and their assembly
into van der Waals heterostructures has renewed interest in two-dimensional
ferromagnetism, which is interesting from a fundamental scientific point of
view and also offers a missing ingredient necessary for the realization of
spintronic functionality in van der Waals heterostructures. Recently several
atomically thin materials have been shown to be robust ferromagnets. Such
ferromagnetism is thought to be enabled by magneto crystalline anisotropy which
suppresses thermal fluctuations. In this article, we review recent progress in
two-dimensional ferromagnetism in detail and predict new possible
two-dimensional ferromagnetic materials. We also discuss the prospects for
applications of atomically thin ferromagnets in novel dissipationless
electronics, spintronics, and other conventional magnetic technologies.
Particularly atomically thin ferromagnets are promising to realize time
reversal symmetry breaking in two-dimensional topological systems, providing a
platform for electronic devices based on the quantum anomalous Hall Effect
showing dissipationless transport. Our proposed directions will assist the
scientific community to explore novel two-dimensional ferromagnetic families
which can spawn new technologies and further improve the fundamental
understanding of this fascinating area.",1810.09053v1
2019-08-08,Ferromagnetism in Quantum Dot Plaquettes,"Following the recent claimed obsevation of Nagaoka ferromagnetism in finite
size quantum dot plaquettes, a general theoretical analysis is warranted in
order to ascertain in rather generic terms which arrangements of a small number
of quantum dots can produce saturated ferromagnetic ground states and under
which constraints on interaction and inter-dot tunneling in the plaquette. This
is particularly necessary since Nagaoka ferromagnetism is fragile and arises
only under rather special conditions. We test the robustness of ground state
ferromagnetism in the presence of a long-range Coulomb interaction and
long-range as well as short-range interdot hopping by modeling a wide range of
different plaquette geometries accessible by arranging a few (~4) quantum dots
in a controlled manner. We find that ferromagnetism is robust to the presence
of long range Coulomb interactions, and we develop conditions constraining the
tunneling strength such that the ground state is ferromagnetic. Additionally,
we predict the presence of a partially spin-polarized ferromagnetic state for 4
electrons in a Y-shaped 4-quantum dot plaquette. Finally, we consider 4
electrons in a ring of 5 dots. This does not satisfy the Nagaoka condition,
however, we show that the ground state is spin one for strong, but not
infinite, onsite interaction. Thus, even though Nagaoka's theorem does not
apply, the ground state for the finite system with one hole in a ring of 5 dots
is partially ferromagnetic. We provide detailed fully analytical results for
the existence or not of ferromagnetic ground states in several quantum dot
geometries which can be studied in currently available coupled quantum dot
systems.",1908.03226v1
2019-08-21,Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance,"We report the novel critical behavior of magnetization in low carrier
concentration systems UTeS and USeS that exhibit the large negative
magnetoresistance around the ferromagnetic transition temperatures T_C ~ 85 and
23 K, respectively. UTeS and USeS crystallize in the same orthorhombic
TiNiSi-type crystal structure as those of uranium ferromagnetic superconductors
URhGe and UCoGe. We determine the critical exponents, beta for the spontaneous
magnetization M_s, gamma for the magnetic susceptibility chi, and delta for the
magnetization isotherm at T_C with several methods. The ferromagnetic states in
UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical
exponents in the two compounds are different from those in the
three-dimensional Ising model with short-range magnetic exchange interactions.
Similar sets of the critical exponents have been reported for the uranium
ferromagnetic superconductors UGe_2 and URhGe, and uranium intermetallic
ferromagnets URhSi, UIr and U(Co_0.98Os_0.02)Al. The universality class of the
ferromagnetic transitions in UTeS and USeS may belong to the same one for the
uranium compounds. The novel critical phenomenon associated with the
ferromagnetic transition is observed not only in the uranium intermetallic
ferromagnets with the itinerant 5f electrons but also in the low carrier
concentration systems UTeS and USeS with the localized 5f electrons. The large
negative magnetoresistance in UTeS and USeS, and the superconductivity in UGe_2
and URhGe share the similarity of their closeness to the ferromagnetism
characterized by the novel critical exponents.",1908.07652v1
2021-05-25,Spin State of Single Molecular Magnet (SMM) Creating Long Range Ordering on Ferromagnetic Layers of Magnetic Tunnel Junction -A Monte Carlo Study,"Single molecular magnet (SMM) like paramagnetic molecules interacting with
the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) produce a new
system that differs dramatically from the properties of isolated molecules and
ferromagnets. However, it is unknown how far deep in the ferromagnetic
electrode the impact of the paramagnetic molecule and ferromagnet interactions
can travel for various levels of molecular spin states. Our prior experimental
studies showed two types of paramagnetic SMMs, the hexanuclear Mn6 and
octanuclear Fe-Ni molecular complexes, covalently bonded to ferromagnets
produced unprecedented strong antiferromagnetic coupling between two
ferromagnets at room temperature leading to a number of intriguing
observations. In this paper, we report Monte Carlo Simulations (MCS) study
focusing on the impact of the molecular spin state on cross junction shaped MTJ
based molecular spintronics device (MTJMSD). Our MCS study focused on the
Heisenberg model of MTJMSD and investigated the impact of various molecular
coupling strengths, thermal energy, and molecular spin states. To gauge the
impact of the molecular spin state on the region of ferromagnetic electrodes,
we examined the spatial distribution of molecule-ferromagnet correlated phases.
Our MCS study shows that under a strong coupling regime molecular spin state
should be approximately 30 percent of the ferromagnetic electrode atomic spins
to create long-range correlated phases.",2105.11647v1
2023-02-01,Ferromagnetism of sputtered Fe3GeTe2 ultrathin films in the absence of two-dimensional crystalline order,"The discovery of ferromagnetism in two-dimensional (2D) monolayers has
stimulated growing research interest in both spintronics and material science.
However, these 2D ferromagnetic layers are mainly prepared through an
incompatible approach for large-scale fabrication and integration, and
moreover, a fundamental question whether the observed ferromagnetism actually
correlates with the 2D crystalline order has not been explored. Here, we choose
a typical 2D ferromagnetic material, Fe3GeTe2, to address these two issues by
investigating its ferromagnetism in an amorphous state. We have fabricated
nanometer-thick amorphous Fe3GeTe2 films approaching the monolayer thickness
limit of crystallized Fe3GeTe2 (0.8 nm) through magnetron sputtering. Compared
to crystallized Fe3GeTe2, we found that the basic ferromagnetic attributes,
such as the Curie temperature that directly reflects magnetic exchange
interactions and local anisotropic energy, do not change significantly in the
amorphous states. This is attributed to that the short-range atomic order, as
confirmed by valence state analysis, is almost the same for both phases. The
persistence of ferromagnetism in the ultrathin amorphous counterpart has also
been confirmed through magnetoresistance measurements, where two unconventional
switching dips arising from electrical transport within domain walls are
clearly observed in the amorphous Fe3GeTe2 single layer. These results indicate
that the long-range ferromagnetic order of crystallized Fe3GeTe2 may not
correlate to the 2D crystalline order and the corresponding ferromagnetic
attributes can be utilized in an amorphous state which suits large-scale
fabrication in a semiconductor technology-compatible manner for spintronics
applications.",2302.00553v1
1996-05-24,Ferromagnetism of dense matter and magnetic properties of neutron stars,"Possible consequences of ferromagnetic transition in dense matter suggested
recently by Kutschera and W{\'o}jcik, for the magnetic properties of neutron
stars, are studied. Specific model of dense matter, in which a small admixture
of protons is completely polarized due to their interaction with neutrons, is
considered. Magnetic field of neutron stars with a ferromagnetic core is
calculated within the framework of general relativity.
  Two types of boundary conditions at the ferromagnetic core edge are
considered, corresponding to normal and superconducting liquid envelope,
respectively. Numerical results for the neutron star magnetic dipole moment are
confronted with pulsar timing. To be consistent with observations,
ferromagnetic cores surrounded by a non-superconducting envelope, should
consist of weakly ordered ferromagnetic domains. If domains are highly ordered,
ferromagnetic core should be screened by a superconducting envelope.",9605149v1
2000-04-17,Ferromagnetism and phase separation in one-dimensional d-p and periodic Anderson models,"Using the Density Matrix Renormalization Group, we study metallic
ferromagnetism in a one-dimensional copper-oxide model which contains one
oxygen p-orbital and one copper d-orbital. The parameters for the d-p model can
be chosen so that it is similar to the one-dimensional periodic Anderson model.
For these parameters, we compare the ground-state phase diagram with that of
the Anderson model and find a ferromagnetic region analogous to one found in
the Anderson model, but which is pushed to somewhat higher densities and
interaction strengths. In both models, we find a region within the
ferromagnetic phase in which phase separation between a localized ferromagnetic
domain and a weakly antiferromagnetic regime occurs. We then choose a set of
parameter values appropriate for copper-oxide materials and explore the
ground-state phase diagram as a function of the oxygen-oxygen hopping strength
and the electron density. We find three disconnected regions of metallic
ferromagnetism and give physical pictures of the three different mechanisms for
ferromagnetism in these phases.",0004265v1
2001-05-02,Flat-band ferromagnetism in quantum dot superlattices,"Possibility of flat-band ferromagnetism in quantum dot arrays is
theoretically discussed. By using a quantum dot as a building block, quantum
dot superlattices are possible. We consider dot arrays on Lieb and kagome
lattices known to exhibit flat band ferromagnetism. By performing an exact
diagonalization of the Hubbard Hamiltonian, we calculate the energy difference
between the ferromagnetic ground state and the paramagnetic excited state, and
discuss the stability of the ferromagnetism against the second nearest neighbor
transfer. We calculate the dot-size dependence of the energy difference in a
dot model and estimate the transition temperature of the
ferromagnetic-paramagnetic transition which is found to be accessible within
the present fabrication technology. We point out advantages of semiconductor
ferromagnets and suggest other interesting possibilities of electronic
properties in quantum dot superlattices.",0105021v1
2001-08-17,Theory of itinerant-electron ferromagnetism,"A theory of Kondo lattices or a $1/d$ expansion theory, with $d$ spatial
dimensionality, is applied to studying itinerant-electron ferromagnetism. Two
relevant multi-band models are examined: a band-edge model where the chemical
potential is at one of band-edges, the top or bottom of bands, and a flat-band
model where one of bands is almost flat or dispersionless and the chemical
potential is at the flat band. In both the models, a novel ferromagnetic
exchange interaction arises from the virtual exchange of pair excitations of
quasiparticles; it has two novel properties such as its strength is in
proportion to the effective Fermi energy of quasiparticles and its temperature
dependence is responsible for the Curie-Weiss law. When the Hund coupling $J$
is strong enough, the superexchange interaction, which arises from the virtual
exchange of pair excitations of electrons across the Mott-Hubbard gap, is
ferromagnetic. In particular, it is definitely ferromagnetic for any nonzero
$J>0$ in the large limit of band multiplicity. Ferromagnetic instability
occurs, when the sum of the two exchange interactions is ferromagnetic and it
overcomes the quenching of magnetic moments by the Kondo effect or local
quantum spin fluctuations and the suppression of magnetic instability by the
mode-mode coupling among intersite spin fluctuations.",0108269v1
2002-09-05,Ground state properties of ferromagnetic metal/conjugated polymer interfaces,"We theoretically investigate the ground state properties of ferromagnetic
metal/conjugated polymer interfaces. The work is partially motivated by recent
experiments in which injection of spin polarized electrons from ferromagnetic
contacts into thin films of conjugated polymers was reported. We use a
one-dimensional nondegenerate Su-Schrieffer-Heeger (SSH) Hamiltonian to
describe the conjugated polymer and one-dimensional tight-binding models to
describe the ferromagnetic metal. We consider both a model for a conventional
ferromagnetic metal, in which there are no explicit structural degrees of
freedom, and a model for a half-metallic ferromagnetic colossal
magnetoresistance (CMR) oxide which has explicit structural degrees of freedom.
The Fermi energy of the magnetic metallic contact is adjusted to control the
degree of electron transfer into the polymer. We investigate electron charge
and spin transfer from the ferromagnetic metal to the organic polymer, and
structural relaxation near the interface. Bipolarons are the lowest energy
charge state in the bulk polymer for the nondegenerate SSH model Hamiltonian.
As a result electrons (or holes) transferred into the bulk of the polymer form
spinless bipolarons. However, there can be spin density in the polymer
localized near the interface.",0209145v1
2003-03-12,Spin-Flip Scattering Effect on the Current-Induced Spin Torque in Ferromagnet-Insulator-Ferromagnet Tunnel Junctions,"We have investigated the current-induced spin transfer torque of a
ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip
scatterings into account. It is found that the spin-flip scattering can induce
an additional spin torque, enhancing the maximum of the spin torque and giving
rise to an angular shift compared to the case when the spin-flip scatterings
are neglected. The effects of the molecular fields of the left and right
ferromagnets on the spin torque are also studied. It is found that $\tau
^{Rx}/I_{e}$ ($\tau ^{Rx}$ is the spin-transfer torque acting on the right
ferromagnet and $I_{e}$ is the tunneling elcetrical current) does vary with the
molecular fields. At two certain angles, $\tau ^{Rx}/I_{e}$ is independent of
the molecular field of the right ferromagnet, resulting in two crossing points
in the curve of $\tau ^{Rx}/I_{e}$ versus the relevant orientation for
different molecular fields.",0303215v1
2003-03-20,"Towards a Fully Ab-Initio Description of the Diluted Magnetic Semiconductor $Ga_{1-x}Mn_{x}As$. Ferromagnetism, Electronic Structure, and Optical Response","There are two competing views of itinerant ferromagnetism, the first viewing
ferromagnetism as resulting from the indirect coupling between local moments
via the itinerant carrier dynamics, the so-called RKKY mechanism, while in the
alternative picture, ferromagnetism results from the spin polarization of
itinerant carriers by the strong atomic Hund interaction - the so-called double
exchange (DE) scenario. Which view describes the ferromagnetism in diluted
magnetic semiconductors, materials with promise for spintronic applications, is
still unclear. Here, we describe the detailed physical response of the
prototype material $Ga_{1-x}Mn_{x}As$ using a combination of first-principles
bandstructure with methods based on dynamical mean field theory to incorporate
strong, dynamical correlations {\it and} intrinsic as well as extrinsic
disorder in one single theoretical picture. We show how ferromagnetism is
driven by DE, in agreement with very recent observations, along with a good
quantitative description of the details of the electronic structure, as probed
by scanning tunnelling microscopy (STM) and optical conductivity. Our results
show how ferromagnetism can be driven by DE even in diluted magnetic
semiconductors with small carrier concentration.",0303427v1
2004-06-21,"Different origin of the ferromagnetic order in (Ga,Mn)As and (Ga,Mn)N","The mechanism for the ferromagnetic order of (Ga,Mn)As and (Ga,Mn)N is
extensively studied over a vast range of Mn concentrations. We calculate the
electronic structures of these materials using density functional theory in
both the local spin density approximation and the LDA+U scheme, that we have
now implemented in the code SIESTA.
  For (Ga,Mn)As, the LDA+U approach leads to a hole mediated picture of the
ferromagnetism, with an exchange constant $N\beta$ =~ -2.8 eV. This is smaller
than that obtained with LSDA, which overestimates the exchange coupling between
Mn ions and the As $p$ holes.
  In contrast, the ferromagnetism in wurtzite (Ga,Mn)N is caused by the
double-exchange mechanism, since a hole of strong $d$ character is found at the
Fermi level in both the LSDA and the LDA+U approaches. In this case the
coupling between the Mn ions decays rapidly with the Mn-Mn separation. This
suggests a two phases picture of the ferromagnetic order in (Ga,Mn)N, with a
robust ferromagnetic phase at large Mn concentration coexisting with a diluted
weak ferromagnetic phase.",0406464v1
2005-04-08,Effect of an inhomogeneous exchange field on the proximity effect in disordered superconductor-ferromagnet hybrid structures,"We investigate the effect of an inhomogeneous exchange field on the proximity
effect in superconductor-ferromagnet hybrid structures within the
quasi-classical theory of superconductivity. As an example we study the
proximity effect in a superconductor-ferromagnet bilayer with an in-plane
spiral magnetic order in the ferromagnet. This model simulates a multiple
magnetic domain structure where the domain walls of the N\'{e}el type are of
equal size as the domains. Triplet correlations are induced in the bilayer by
the superconducting proximity effect, which are sensitive to the local
quantization axis of the exchange field in the ferromagnet. The coexistence of
singlet and triplet pair correlations in the bilayer results into a sensitivity
of the superconducting transition temperature on the spatial variation of the
exchange field in the ferromagnetic layer. We show that the inhomogeneity tends
to suppress the oscillating behavior of the pair amplitudes in the ferromagnet.
As a result, the superconducting critical temperature is found to be strongly
dependent on the spiral wavevector. We study the spin-dependent local density
of states and the effect of an induction of a spin magnetization in the
superconductor.",0504198v2
2005-12-29,Ferromagnetic phase transition in spinor Bose gases,"The achievement in cooling alkali atomic gases, such as $^{87}$Rb, $^{23}$Na
and $^{7}$Li, to quantum degeneracy opens up a way to study magnetism in spinor
bosons, because these constituent atoms usually have a hyperfine spin degree of
freedom. This article reviews several basic problems related to the
ferromagnetic phase transition in spinor atomic Bose gases from a theoretical
perspective. After a brief discussion on various possible origins of the
ferromagnetic interaction, the phase diagram of the ferromagnetically coupled
spinor bosons is investigated. It is found that the ferromagnetic transition
occurs always above Bose-Einstein condensation and the Bose condensate is fully
polarized. The low-lying collective excitations of the spinor condensate,
including spin and density modes, are discussed. The spectrum of the density
mode is of the Bogliubov form and the spin wave spectrum has a $k^2$-formed
dispersion relation at long wavelengths. The spin-wave stiffness coefficient
contains contribut",0512693v1
2006-07-11,Significant enhancement of ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te doped with iodine as an n-type dopant,"The effect of additional doping of charge impurities was investigated in a
ferromagnetic semiconductor Zn$_{1-x}$Cr$_{x}$Te. It was found that the doping
of iodine, which is expected to act as an n-type dopant in ZnTe, brought about
a drastic enhancement of the ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te while the
grown films remained electrically insulating. In particular, at a fixed Cr
composition of x = 0.05, the ferromagnetic transition temperature Tc increased
up to 300K at maximum due to the iodine doping from Tc = 30K of the undoped
counterpart, while the ferromagnetism disappeared due to the doping of nitrogen
as a p-type dopant. The observed systematic correlation of ferromagnetism with
the doping of charge impurities of both p- and n-type, suggesting a key role of
the position of Fermi level within the impurity d-state, is discussed on the
basis of the double exchange interaction as a mechanism of ferromagnetism in
this material.",0607273v1
2007-03-15,Signatures of retroreflection and induced triplet electron-hole correlations in ferromagnet/s-wave superconductor structures,"We present a theoretical study of a ferromagnet/s-wave superconductor
junction to investigate the signatures of induced triplet correlations in the
system. We apply the extended BTK-formalism and allow for an arbitrary
magnetization strength/direction of the ferromagnet, a spin-active barrier,
Fermi-vector mismatch, and different effective masses in the two systems. It is
found that the phase associated with the $xy$-components of the magnetization
in the ferromagnet couples with the superconducting phase and induces
spin-triplet pairing correlations in the superconductor, if the tunneling
barrier acts as a spin-filter. This feature leads to an induced spin-triplet
pairing correlation in the ferromagnet, along with a spin-triplet electron-hole
coherence due to an interplay between the ferromagnetic and superconducting
phase. As our main result, we investigate the experimental signatures of
retrorelection, manifested in the tunneling conductance of a ferromagnet/s-wave
superconductor junction with a spin-active interface.",0703398v1
2008-03-21,Induced Triplet Pairing in clean s-wave Superconductor/Ferromagnet layered structures,"We study induced triplet pairing correlations in clean
ferromagnet/superconductor/ferromagnet heterostructures. The pairing state in
the superconductor is the conventional singlet s-wave, and the angle $\alpha$
between the magnetizations of the two ferromagnetic layers is arbitrary. We use
a numerical fully self-consistent solution of the microscopic equations and
obtain the time-dependent triplet correlations via the Heisenberg equations of
motion. We find that in addition to the usual singlet correlations, triplet
correlations, odd in time as required by the Pauli principle, are induced in
both the ferromagnets and the superconductor. These time-dependent correlations
are largest at times of order of the inverse of the Debye cutoff frequency,
$\omega_D$, and we find that within that time scale they are often spatially
very long ranged. We discuss the behavior of the characteristic penetration
lengths that describe these triplet correlations. We also find that the
ferromagnets can locally magnetize the superconductor near the interface, and
that the local magnetization then undergoes strongly damped oscillations. The
local density of states exhibits a variety of energy signatures, which we
discuss, as a function of ferromagnetic strength and $\alpha$.",0803.3174v1
2008-12-11,Coexistence of triplet superconductivity and itinerant ferromagnetism,"The triplet superconductivity in $UGe_2$ and $URhGe$ coexists with itinerant
ferromagnetism such that in the pressure-temperature phase diagram the whole
region occupied by the superconducting state is situated inside a more vast
ferromagnetic region. In the same family metal UCoGe the pressure dependent
critical lines T_{Curie}(P) and T_{sc}(P) of the ferromagnet and the
superconducting phase transitions intersect each other. The two-band
multidomain superconducting ferromagnet state arises at temperatures below both
of these lines. Here I describe the symmetry and the order parameters of the
paramagnet as well of the multidomain ferromagnet superconducting states. The
Josephson coupling between two adjacent ferromagnet superconducting domains is
discussed.",0812.2171v2
2010-08-02,A Search for Defect Related Ferromagnetism in SrTiO$_3$,"Room temperature ferromagnetic hysteresis is observed in commercial SrTiO$_3$
substrates purchased from a variety of suppliers. It is shown that the
ferromagnetic signal comes from the unpolished surfaces. Surface impurity
phases cannot be detected using either x-ray diffraction or energy dispersive
x-ray spectra on the unpolished surfaces. However, a possible correlation
between surface disorder (xray diffraction peak linewidth) and ferromagnetism
is observed. Ar ion bombardment (10keV-90 keV) can be used to produce surface
layer disorder but is not found to induce ferromagnetism. Annealing of the
substrates at temperatures ranging from 600 to 1100 $^\circ$C is found to alter
the hysteresis curves differently depending on whether the annealing is
performed in air or in vacuum. Identical annealing behaviour is observed if the
substrates are artificially spiked with iron. This suggests that the
ferromagnetic hysteresis of as purchased SrTiO$_3$ could be due to Fe
contamination of the unpolished surfaces. In addition, it is shown that no
ferromagnetism is observed in samples that contain $10^{19}-10^{21}$ cm$^{-3}$
of oxygen vacancies if all the faces are polished.",1008.0299v1
2011-04-12,Properties of Ferromagnetic Superconductors,"Thanks to the discovery in the last decade of three uranium ferromagnetic
superconductors, UGe2, URhGe and UCoGe, the fascinating aspects of the
interplay between the triplet state of Cooper pairing and ferromagnetism have
emerged. Furthermore, as the ferromagnetic properties in the normal state are
quite different with respect to the proximity of the ferromagnetic-paramagnetic
instabilities, the feedback with the coexistence of superconductivity gives
rise to quite different boundaries in pressure and magnetic field. Special
attention is given on the location of the materials with respect to the
tricriticality and on the reinforcement of superconductivity in a transverse
field response with respect to the direction of the ferromagnetic sublattice
magnetization. The other facts of the interplay between ferromagnetism and
superconductivity is briefly mentioned.",1104.2279v1
2012-03-16,Universal low-temperature tricritical point in metallic ferromagnets and ferrimagnets,"An earlier theory of the quantum phase transition in metallic ferromagnets is
revisited and generalized in three ways. It is shown that the mechanism that
leads to a fluctuation-induced first-order transition in metallic ferromagnets
with a low Curie temperature is valid, (1) irrespective of whether the magnetic
moments are supplied by the conduction electrons or by electrons in another
band, (2) for ferromagnets in the XY and Ising universality classes as well as
for Heisenberg ferromagnets, and (3) for ferrimagnets as well as for
ferromagnets. This vastly expands the class of materials for which a
first-order transition at low temperatures is expected, and it explains why
strongly anisotropic ferromagnets, such as UGe2, display a first-order
transition as well as Heisenberg magnets.",1203.3826v1
2013-02-05,Reflection and refraction process of spinwave in a ferromagnet/frustrated ferromagnet junction system,"Frustration introduces a nontrivial dispersion relation of spinwave even in a
ferromagnetic phase in a spin system. We study the reflection and refraction
process of spinwaves in the ferromagnet/frustrated ferromagnet junction system
by using the Holstein-Primakoff spinwave expansion and taking the large-S
limit. We discuss the relation between the incident angle and refraction angle
of spinwave, namely, the Snell's low of spinwave. As concrete examples of
frustrated ferromagnets, we study the fully polarized ferromagnet phases in the
J1-J2 chains and the J1-J2 model on the square lattice. The interesting
refraction processes, such as the splitting of the incident spinwave and the
negative refraction, are discussed. We also study the transmittance and
reflectance in these concrete models.",1302.1003v2
2013-05-14,Interface induced room-temperature ferromagnetism in hydrogenated epitaxial graphene,"Due to the predominantly surface character of graphene, it is highly suitable
for functionalization with external atoms and/or molecules leading to a
plethora of new and interesting phenomena. Here we show ferromagnetic
properties of hydrogen-functionalized epitaxial graphene on SiC. Ferromagnetism
in such a material is not directly evident as it is inherently composed of only
non-magnetic constituents. Our results nevertheless show strong ferromagnetism,
which cannot be explained by simple magnetic impurities. The ferromagnetism is
unique to hydrogenated epitaxial graphene on SiC, where interactions with the
interfacial buffer layer play a crucial role. We argue that the origin of the
observed ferromagnetism is governed by electron correlation effects of the
narrow Si-dangling-bond (Si-DB) states in the buffer layer exchange-coupled to
localized states in the hydrogenated graphene layer. This forms a
quasi-three-dimensional ferromagnet with a Curie temperature higher than 300 K.",1305.3158v1
2014-04-22,Superconductivity-induced Magnetic Modulation in a Ferromagnet Through an Insulator in LaCaMnO3\SrTiO3\YBa2Cu3O7-δ Hybrid Heterostructures,"Coexistence of ferromagnetic and superconducting orders and their interplay
in ferromagnet-superconductor heterostructures is a topic of intense research.
While it is well known that proximity of a ferromagnet suppresses
superconducting order in the superconductor, there exist few studies indicating
the proximity of a superconductor suppressing ferromagnetic order in a
ferromagnet. Here we demonstrate a rare observation of the suppression of
ferromagnetic order in a LaCaMnO3 layer separated from a YBa2Cu3O7-{\delta}
layer by a thin insulator (SrTiO3). Polarized neutron reflectivity measurements
on LaCaMnO3\SrTiO3\YBa2Cu3O7-{\delta} trilayer deposited on [001] SrTiO3 single
crystal substrates shows the emergence of a thin magnetic dead layer in
LaCaMnO3 adjacent to the insulating layer below its superconducting transition
temperature of YBa2Cu3O7-{\delta}. Further, the magnetic dead layer grows in
thickness when the insulating layer is made thinner. This indicates a possible
tunneling of the superconducting order-parameter through the insulating SrTiO3
inducing modulation of magnetization in LaCaMnO3.",1404.5456v1
2014-10-17,Coexistence of ferromagnetism and superconductivity in iron based pnictides: a time resolved magnetooptical study,"Ferromagnetism and superconductivity are antagonistic phenomena. Their
coexistence implies either a modulated ferromagnetic order parameter on a
lengthscale shorter than the superconducting coherence length or a weak
exchange coupling between the itinerant superconducting electrons and the
localized ordered spins. In some iron based pnictide superconductors the
coexistence of ferromagnetism and superconductivity has been clearly
demonstrated. The nature of the coexistence, however, remains elusive since no
clear understanding of the spin structure in the superconducting state has been
reached and the reports on the coupling strength are controversial. We show, by
a direct optical pump-probe experiment, that the coupling is weak, since the
transfer of the excess energy from the itinerant electrons to ordered localized
spins is much slower than the electron-phonon relaxation, implying the
coexistence without the short-lengthscale ferromagnetic order parameter
modulation. Remarkably, the polarization analysis of the coherently excited
spin wave response points towards a simple ferromagnetic ordering of spins with
two distinct types of ferromagnetic domains.",1410.4651v1
2014-10-19,Coexistence and competition of ferromagnetism and p-wave superconductivity in holographic model,"By combining a holographic p-wave superconductor model and a holographic
ferromagnetism model, we study the coexistence and competition of
ferromagnetism and p-wave superconductivity. It is found that the results
depend on the self-interaction of magnetic moment of the complex vector field
and which phase appears first. In the case that the ferromagnetic phase appears
first, if the interaction is attractive, the system shows the ferromagnetism
and superconductivity can coexist in low temperatures. If the interaction is
repulsive, the system will only be in a pure ferromagnetic state. In the case
that the superconducting phase appears first, the attractive interaction will
leads to a magnetic p-wave superconducting phase in low temperatures. If the
interaction is repulsive, the system will be in a pure p-wave superconducting
phase or ferromagnetic phase when the temperature is lowered.",1410.5080v2
2014-12-14,Magnetic properties of spin-1/2 Fermi gases with ferromagnetic interaction,"We investigate the magnetic properties of spin-$1/2$ charged Fermi gases with
ferromagnetic coupling via mean-field theory, and find the interplay among the
paramagnetism, diamagnetism and ferromagnetism. Paramagnetism and diamagnetism
compete with each other. When increasing the ferromagnetic coupling the
spontaneous magnetization occurs in a weak magnetic field. The critical
ferromagnetic coupling constant of the paramagnetic phase to ferromagnetic
phase transition increases linearly with the temperature. Both the
paramagnetism and diamagnetism increase when the magnetic field increases. It
reveals the magnetization density $\bar M$ increases firstly as the temperature
increases, and then reaches a maximum. Finally the magnetization density $\bar
M$ decreases smoothly in the high temperature region. The domed shape of the
magnetization density $\bar M$ variation is different from the behavior of Bose
gas with ferromagnetic coupling. We also find the curve of susceptibility
follows the Curie-Weiss law, and for a given temperature the susceptibility is
directly proportional to the Land\'{e} factor.",1412.4297v2
2014-12-22,Possibility of ferromagnetic neutron matter,"We study ferromagnetism at high density of neutrons in the QCD hadron phase,
by using the simplest chiral effective model incorporating magnetic fields and
the chiral anomaly. Under the assumption of spatial homogeneity, we calculate
the energy density as a function of neutron density, with a magnetization and a
neutral pion condensation a la Dautry and Neyman. We find that at a high
density the energy of the ferromagnetic order is lower than that of the
ordinary neutron matter, and the reduction effect is enhanced by the anomaly.
Compared to the inhomogeneous phase with the alternating layer structure, our
ferromagnetic phase turns out to be unfavored. However, once an axial vector
meson condensation is taken into account in our simplest model, the
ferromagnetic energy density is lowered significantly, which still leaves some
room for a possible realization of a QCD ferromagnetic phase and ferromagnetic
magnetars.",1412.6960v2
2015-01-31,Room temperature local ferromagnetism and nanoscale domain growth in the ferromagnetic semiconductor GeFe,"We investigate the local electronic structure and magnetic properties of the
group IV based ferromagnetic semiconductor, GeFe, using soft X ray magnetic
circular dichroism. Our results show that the doped Fe 3d electrons are
strongly hybridized with the Ge 4p states, and have an unusually large orbital
magnetic moment relative to the spin magnetic moment; i.e., morb/mspin = 0.3.
We find that local ferromagnetic domains, which are formed through
ferromagnetic exchange interactions in the high Fe content regions of the GeFe
films, exist at room temperature, well above the Curie temperature. We
demonstrate the first observation of the intriguing nanoscale domain growth
process in which ferromagnetic domains expand as the temperature decreases,
followed by a transition of the entire film into a ferromagnetic state at the
Curie temperature.",1502.00118v1
2015-05-06,"Magnetization Process of the n-type Ferromagnetic Semiconductor (In,Fe)As:Be Studied by X-ray Magnetic Circular Dichroism","In order to investigate the mechanism of ferromagnetic ordering in the new
n-type magnetic semiconductor (In,Fe)As co-doped with Be, we have performed
X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD)
studies of ferromagnetic and paramagnetic samples. The spectral line shapes
suggest that the ferromagnetism is intrinsic originating from Fe atoms
incorporated into the Zinc-blende-type InAs lattice. The magnetization curves
of Fe measured by XMCD were well reproduced by the superposition of a Langevin
function representing superparamagnetic (SPM) behavior of nano-scale
ferromagnetic domains and a T-linear function representing Curie-Weiss
paramagnetism even much above the Curie temperatures. The data at 20 K showed a
deviation from the Langevin behavior, suggesting a gradual establishment of
macroscopic ferromagnetism on lowering temperature. The existence of nano-scale
ferromagnetic domains indicated by the SPM behavior suggests spatial
fluctuations of Fe concentration on the nano-scale.",1505.01402v1
2017-01-11,Emergent incommensurate correlations in the frustrated ferromagnetic spin-1 chains,"We study the frustrated ferromagnetic spin-1 chains, where the ferromagnetic
nearest-neighbor coupling competes with the antiferromagnetic
next-nearest-neighbor coupling. We use the density matrix renormalization group
to obtain the ground states. Through the analysis of spin-spin correlations we
identify the double Haldane phase as well as the ferromagnetic phase. It is
shown that the ferromagnetic coupling leads to incommensurate correlations in
the double Haldane phase. Such short-range correlations transform continuously
into the ferromagnetic instability at the transition to the ferromagnetic
phase. We also compare the results with the spin-1/2 and classical spin
systems, and discuss the string orders in the system.",1701.02832v1
2014-05-08,Peculiar long-range supercurrent in SFS junction containing a noncollinear magnetic domain in the ferromagnetic region,"We study the supercurrent in a superconductor-ferromagnet-superconductor
heterostructure containing a noncollinear magnetic domain in the ferromagnetic
region. It is demonstrated that the magnetic domain can lead to a spin-flip
process, which can reverse the spin orientations of the singlet Cooper pair
propagating through the magnetic domain region. If the ferromagnetic layers on
both sides of magnetic domain have the same features, the long-range proximity
effect will take place. That is because the singlet Cooper pair will create an
exact phase-cancellation effect and gets an additional $\pi$ phase shift as it
passes through the entire ferromagnetic region. Then the equal spin triplet
pair only exists in the magnetic domain region and can not diffuse into the
other two ferromagnetic layers. So the supercurrent mostly arises from the
singlet Cooper pairs and the equal spin triplet pairs are not involved. This
behavior is quite distinct from the common knowledge that long-range
supercurrent induced by inhomogeneous ferromagnetism stems from the equal spin
triplet pairs. The result we presented here provides a new way for generating
the long-range supercurrent.",1405.1951v2
2016-05-24,Superconductivity in Uranium Ferromagnets,"The theoretical description and the survey of physical properties of
superconducting states in the uranium ferromagnetic materials are presented. On
the basis of microscopic theory is shown that the coupling between the
electrons in these ferromagnetic metals by means of magnetization fluctuations
gives rise the triplet pairing superconducting state and the general form of
the order parameter dictated by the symmetry is established.
  The theory allows to explain some specific observations including peculiar
phenomenon of reentrant superconductivity in URhGe in magnetic field
perpendicular to the direction of spontaneous magnetization.
  In addition we describe several particular topics relating to uranium
superconducting ferromagnets: (i) critical magnetic relaxation in dual
localized-itinerant ferromagnets, (ii) phase transition to ferromagnetic state
in Fermi liquid and UGe$_2$, (iii) superconducting ordering in ferromagnetic
metals without inversion symmetry.",1605.07319v3
2016-08-11,Magnetoresistance generated from charge-spin conversion by anomalous Hall effect in metallic ferromagnetic/nonmagnetic bilayers,"A theoretical formulation of magnetoresistance effect in a metallic
ferromagnetic/nonmagnetic bilayer originated from the charge-spin conversion by
the anomalous Hall effect is presented. Analytical expressions of the
longitudinal and transverse resistivities in both nonmagnet and ferromagnet are
obtained by solving the spin diffusion equation. The magnetoresistance
generated from charge-spin conversion purely caused by the anomalous Hall
effect in the ferromagnet is found to be proportional to the square of the spin
polarizations in the ferromagnet and has fixed sign. We also find additional
magnetoresistances in both nonmagnet and ferromagnet arising from the mixing of
the spin Hall and anomalous Hall effects. The sign of this mixing resistance
depends on those of the spin Hall angle in the nonmagnet and the spin
polarizations of the ferromagnet.",1608.03359v2
2016-12-19,Spontaneous Distortion and Ferromagnetism Induced by Quantum-well States in Pd(100) Ultrathin Films,"We study the crystal structure of Pd(100) ultrathin films, which show
ferromagnetism induced by the quantum confinement effect, using in-situ X-ray
crystal truncation rod measurement and density functional calculation. The
energy gain due to the appearance of ferromagnetism in Pd results in flatter
and uniform film growth of ferromagnetic Pd films compared with paramagnetic
Pd. In addition, ferromagnetic Pd films expand the lattice constant in order to
suppress the increase in kinetic energy of electrons accompanied by the
occurrence of exchange splitting. Although the traditional theory of magnetism
in metals indicates that the increase in density of states that induces
ferromagnetism (Stoner criterion), our present finding reveals a mechanism of
modulation in the density of states via the appearance of ferromagnetism, i.e.,
the inverse mechanism of Stoner's theory.",1612.06216v1
2017-06-24,Random-field-induced disordering mechanism in a disordered ferromagnet: Between the Imry-Ma and the standard disordering mechanism,"Random fields disorder Ising ferromagnets by aligning single spins in the
direction of the random field in three space dimensions, or by flipping large
ferromagnetic domains at dimensions two and below. While the former requires
random fields of typical magnitude similar to the interaction strength, the
latter Imry-Ma mechanism only requires infinitesimal random fields. Recently,
it has been shown that for dilute anisotropic dipolar systems a third mechanism
exists, where the ferromagnetic phase is disordered by finite-size glassy
domains at a random field of finite magnitude that is considerably smaller than
the typical interaction strength. Using large-scale Monte Carlo simulations and
zero-temperature numerical approaches, we show that this mechanism applies to
disordered ferromagnets with competing short-range ferromagnetic and
antiferromagnetic interactions, suggesting its generality in ferromagnetic
systems with competing interactions and an underlying spin-glass phase. A
finite-size-scaling analysis of the magnetization distribution suggests that
the transition might be first order.",1706.07904v3
2017-10-30,RbEu(Fe$_{1-x}$Ni$_x$)$_4$As$_4$: From a ferromagnetic superconductor to a superconducting ferromagnet,"The intrinsically hole-doped RbEuFe$_4$As$_4$ exhibits bulk superconductivity
at $T_{\mathrm{sc}}=36.5$ K and ferromagnetic ordering in the Eu sublattice at
$T_\mathrm{m}=15$ K. Here we present a hole-compensation study by introducing
extra itinerant electrons via a Ni substitution in the ferromagnetic
superconductor RbEuFe$_4$As$_4$ with $T_{\mathrm{sc}}>T_{\mathrm{m}}$. With the
Ni doping, $T_{\mathrm{sc}}$ decreases rapidly, and the Eu-spin ferromagnetism
and its $T_{\mathrm{m}}$ remain unchanged. Consequently, the system
RbEu(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ transforms into a superconducting ferromagnet
with $T_{\mathrm{m}}>T_{\mathrm{sc}}$ for $0.07\leq x\leq0.08$. The occurrence
of superconducting ferromagnets is attributed to the decoupling between
Eu$^{2+}$ spins and superconducting Cooper pairs. The superconducting and
magnetic phase diagram is established, which additionally includes a recovered
yet suppressed spin-density-wave state.",1710.10895v2
2018-01-26,Enhancement of exchange bias in ferromagnetic/antiferromagnetic core-shell nanoparticles through ferromagnetic domain wall formation,"The spin configuration in the ferromagnetic part during the magnetization
reversal plays a crucial role in the exchange bias effect. Through Monte Carlo
simulation, the exchange bias effect in ferromagnetic-antiferromagnetic
core-shell nanoparticles is investigated. Magnetization reversals in the
ferromagnetic core were controlled between the coherent rotation and the domain
wall motion by modulating ferromagnetic domain wall width with parameters of
uniaxial anisotropy constant and exchange coupling strength. An anomalous
monotonic dependence of exchange bias on the uniaxial anisotropy constant is
found in systems with small exchange coupling, showing an obvious violation of
classic Meiklejohn-Bean model, while domain walls are found to form close to
the interface and propagate in the ferromagnetic core with larger uniaxial
anisotropy in both branches of the hysteresis. The asymmetric magnetization
reversal with the formation of a spherical domain wall dramatically reduces the
coercive field in the ascending branch, leading to the enhancement of the
exchange bias. The results provide another degree of freedom to optimize the
magnetic properties of magnetic nanoparticles for applications.",1801.08743v1
2017-09-27,Effects of geometrical frustration on ferromagnetism in the Hubbard model on the Shastry-Sutherland lattice,"The small-cluster exact-diagonalization calculations and the projector
quantum Monte Carlo method are used to examine the competing effects of
geometrical frustration and interaction on ferromagnetism in the Hubbard model
on the Shastry-Sutherland lattice. It is shown that the geometrical frustration
stabilizes the ferromagnetic state at high electron concentrations ($n \gtrsim
7/4$), where strong correlations between ferromagnetism and the shape of the
noninteracting density of states are observed. In particular, it is found that
ferromagnetism is stabilized only for these values of frustration parameters,
which lead to the single peaked noninterating density of states at the band
edge. Once, two or more peaks appear in the noninteracting density of states at
the band egde the ferromagnetic state is suppressed. This opens a new route
towards the understanding of ferromagnetism in strongly correlated systems.",1709.09461v1
2019-03-16,$S$ =1/2 ferromagnetic Heisenberg chain in a verdazyl-based complex,"We present a model compound for the $S$=1/2 ferromagnetic Heisenberg chain
composed of the verdazyl-based complex
$[$Zn(hfac)$_2]$$[$4-Cl-$o$-Py-V-(4-F)$_2]$. $Ab$ $initio$ MO calculations
indicate a predominant ferromagnetic interaction forming an $S$=1/2
ferromagnetic chain. The magnetic susceptibility and specific heat indicate a
phase transition to an AF order owing to the finite interchain couplings. We
explain the magnetic susceptibility and magnetization curve above the phase
transition temperature based on the $S$=1/2 ferromagnetic Heisenberg chain. The
magnetization curve in the ordered phase is described by a conventional AF
two-sublattice model. Furthermore, the obtained magnetic specific heat
reproduces the almost temperature-independent behavior of the $S$=1/2
ferromagnetic Heisenberg chain. In the low-temperature region, the magnetic
specific heat exhibits $\sqrt{T}$ dependence, which is attributed to the energy
dispersion in the ferromagnetic chain.",1903.06896v1
2019-04-02,Quantum storage in quantum ferromagnets,"We must protect inherently fragile quantum data to unlock the potential of
quantum technologies. A pertinent concern in schemes for quantum storage is
their potential for near-term implementation. Since Heisenberg ferromagnets are
readily available, we investigate their potential for robust quantum storage.
We propose to use permutation-invariant quantum codes to store quantum data in
Heisenberg ferromagnets, because the ground space of any Heisenberg ferromagnet
must be symmetric under any permutation of the underlying qubits. By exploiting
an area law on the expected energy of Pauli errors, we show that increasing the
effective dimension of Heisenberg ferromagnets can improve the storage
lifetime. When the effective dimension of Heisenberg ferromagnets is maximal,
we also obtain an upper bound for the storage error. This result relies on
perturbation theory, where we use Davis' divided difference representation for
Fr{\'e}chet derivatives along with the recursive structure of these divided
differences. Our numerical bounds allow us to better understand how quantum
memory lifetimes can be enhanced in Heisenberg ferromagnets.",1904.01458v3
2020-03-30,Impact of Next-Nearest-Neighbor hopping on Ferromagnetism in Diluted Magnetic Semiconductors,"Being a wide band gap system GaMnN attracted considerable interest after the
discovery of highest reported ferromagnetic transition temperature $T_C$ $\sim$
940 K among all diluted magnetic semiconductors. Later it become a debate due
to the observation of either a ferromagnetic state with very low $T_C$ $\sim$ 8
K or sometimes no ferromagnetic state at all. We address these issues by
calculating the ferromagnetic window, $T_C$ Vs $p$, within a $t-t'$ Kondo
lattice model using a spin-fermion Monte-Carlo method on a simple cubic
lattice. We exploit the next-nearest-neighbor hopping $t'$ to tune the degree
of delocalization of the free carriers and show that carrier localization
(delocalization) significantly widen (shrunken) the ferromagnetic window with a
reduction (enhancement) of the optimum $T_C$. We connect our results with the
experimental findings and try to understand the ambiguities in ferromagnetism
in GaMnN.",2003.13327v2
2020-11-27,d0 Ferromagnetism in Ag-doped Monoclinic ZrO2 Compounds,"Recently d0 or intrinsic ferromagnetism was believed to provide an
alternative pathway to transition metal induced ferromagnetism in oxide. In
pursuit of augmenting the area of d0 ferromagnetism; we have undertaken to
study the crystal structure and magnetic properties of Ag-doped ZrO2 compounds.
Polycrystalline samples of Zr1-xAgxO2 (with x=0, 0.02, 0.04, 0.06 and 0.08)
were prepared by solid-state reaction route. All the prepared compounds are
found to crystallize in monoclinic symmetry of ZrO2. In our study, pure ZrO2
compound exhibits paramagnetic behavior. However, the Ag-doped ZrO2 compounds
exhibit ferromagnetic to paramagnetic transition. The Curie temperature was
found to increase from 28.7 K for x=0.02 to 173.2 K for x= 0.08 doped ZrO2.
Thus, the introduction of Ag in ZrO2 induces ferromagnetism with a large
ThetaC. The measurements of hysteresis curves indicate that Ag doped ZrO2
compounds exhibit hysteresis loops with a coercivity of around 1350 Oe.
Moreover, increase in Ag concentration resulted increase in the value of
saturation magnetization (MS); the maximum value of MS was recorded as 0.01
{\mu}B/Ag ion for x= 0.06 sample. The sintering of sample at high temperature
(13500C) diminishes the ferromagnetism and it leads to paramagnetic behaviour.",2011.13727v1
2021-12-29,A unified theory of ferromagnetic quantum phase transitions in heavy fermion metals,"Motivated by the recent discovery of a continuous ferromagnetic quantum phase
transition in CeRh$_6$Ge$_4$ and its distinction from other U-based heavy
fermion metals such as UGe$_2$, we develop a unified explanation of their
different ground state properties based on an anisotropic ferromagnetic
Kondo-Heisenberg model. We employ an improved large-$N$ Schwinger boson
approach and predict a full phase diagram containing both a continuous
ferromagnetic quantum phase transition for large magnetic anisotropy and
first-order transitions for relatively small anisotropy. Our calculations
reveal three different ferromagnetic phases including a half-metallic spin
selective Kondo insulator with a constant magnetization. The Fermi surface
topologies are found to change abruptly between different phases, consistent
with that observed in UGe$_2$. At finite temperatures, we predict the
development of Kondo hybridization well above the ferromagnetic long-range
order and its relocalization near the phase transition, in good agreement with
band measurements in CeRh$_6$Ge$_4$. Our results highlight the importance of
magnetic anisotropy and provide a unified theory for understanding the
ferromagnetic quantum phase transitions in heavy fermion metals.",2112.14515v1
2022-02-03,On the Divergence of the Ferromagnetic Susceptibility in the SU(N) Nagaoka-Thouless Ferromagnet,"Using finite temperature strong coupling expansions for the SU(N) Hubbard
Model, we calculate the thermodynamic properties of the model in the
infinite-$U$ limit for arbitrary density $0\leq \rho \leq 1$ and all $N$. We
express the ferromagnetic susceptibility of the model as a Curie term plus a
$\Delta \chi$, an excess susceptibility above the Curie-behavior. We show that,
on a bipartite lattice, graph by graph the contributions to $\Delta \chi$ are
non-negative in the limit that the hole density $\delta=1-\rho$ goes to zero.
By summing the contributions from all graphs consisting of closed loops we find
that the low hole-density ferromagnetic susceptibility diverges exponentially
as $\exp{\Delta /T}$ as $T \to 0$ in two and higher dimensions. This
demonstrates that Nagaoka-Thouless ferromagnetic state exists as a
thermodynamic state of matter at low enough density of holes and sufficiently
low temperatures. The constant $\Delta$ scales with the SU(N) parameter $N$ as
$1/N$ implying that ferromagnetism is gradually weakened with increasing $N$ as
the characteristic temperature scale for ferromagnetic order goes down.",2202.01611v1
2022-04-04,Hole-doping induced ferromagnetism in 2D materials,"Two-dimensional (2D) ferromagnetic materials are considered as promising
candidates for the future generations of spintronic devices. Yet, 2D materials
with intrinsic ferromagnetism are scarce. High-throughput first-principles
simulations are performed in order to screen 2D materials that present a
non-magnetic to a ferromagnetic transition upon hole doping. A global
evolutionary search is subsequently performed, in order to identify alternative
possible atomic structures of the eligible candidates, and 122 materials
exhibiting a hole-doping induced ferromagnetism are identified. Their energetic
and dynamic stability, as well as their magnetic properties under hole doping
are investigated systematically. Half of these 2D materials are metal halides,
followed by chalcogenides, oxides and nitrides, some of them having predicted
Curie temperatures above 300 K. The exchange interactions responsible for the
ferromagnetic order in these 2D materials are also discussed. This work not
only provides theoretical insights into hole-doped 2D ferromagnetic materials,
but also enriches the family of 2D magnetic materials for possible spintronic
applications.",2204.01551v2
2023-08-04,Anisotropy of the spin Hall effect in a Dirac ferromagnet,"We study the intrinsic spin Hall effect of a Dirac Hamiltonian system with
ferromagnetic exchange coupling, a minimal model combining relativistic
spin-orbit interaction and ferromagnetism. The energy bands of the Dirac
Hamiltonian are split after introducing a Stoner-type ferromagnetic ordering
which breaks the spherical symmetry of pristine Dirac model. The totally
antisymmetric spin Hall conductivity (SHC) tensor becomes axially anisotropic
along the direction of external electric field. Interestingly, the anisotropy
does not vanish in the asymptotic limit of zero magnetization. We show that the
ferromagnetic ordering breaks the spin degeneracy of the eigenfunctions and
modifies the selection rules of the interband transitions for the intrinsic
spin Hall effect. The difference in the selection rule between the pristine and
the ferromagnetic Dirac phases causes the anisotropy of the SHC, resulting in a
discontinuity of the SHC as the magnetization, directed orthogonal to the
electric field, is reduced to zero in the ferromagnetic Dirac phase and enters
the pristine Dirac phase.",2308.02336v1
2023-08-29,Theory of Fractionally-magnetized Quantum Ferromagnet,"We present a theory to realize entangled quantum spin states with fractional
magnetization. The origin of magnetization reduction is partly emergent
antiferromagnetism, that is, spin-liquefaction of ferromagnetism. We study a
ferromagnetic bilinear coupling region of the spin-$S$ $({\geqq} 1)$
bilinear-biquadratic spin chain based on (i) a rigorous eigenstate
correspondence between the spin-$S$ model and spin-$\frac12$ model and (ii) a
numerical exact-diagonalization calculation up to $S=3$. As a result, we obtain
a fractional magnetized $M=1-1/(2S)$ phase, where ground states have quantum
entanglement-reflecting corresponding spin-$\frac12$ antiferromagnetic ground
states in a ferromagnetic background. This spin-liquefaction theory of
ferromagnets can be generalized to any-dimensional lattices even under a
magnetic field. This fractional ferromagnetism opens the new research field of
quantum ferromagnets.",2308.15372v1
2023-10-03,Stray magnetic fields from elliptical-shaped and stadium-shaped ferromagnets,"An artificial spin ice consisting of numerous ferromagnets has attracted
attention because of its applicability to practical devices. The ferromagnets
interact through their stray magnetic field and show various functionality. The
ferromagnetic element in the spin ice was recently made in elliptical-shape or
stadium-shape. The former has a narrow edge, expecting to generate a large
stray magnetic field. The latter has a large volume and is also expected to
generate a large stray magnetic field. Here, we estimate the stray magnetic
field by numerically integrating the solution of the Poisson equation. When
magnetization is parallel to an easy axis, the elliptical-shaped ferromagnet
generates a larger stray magnetic field than the stadium-shaped ferromagnet.
The stray magnetic fields from both ferromagnets for arbitrary magnetization
directions are also investigated.",2310.01721v2
2023-10-09,The influence of metallic overlayers on ferromagnetism in LaMnO$_3$,"LaMnO$_3$ (LMO) thin films epitaxially grown on SrTiO$_3$ (STO) usually
exhibit ferromagnetism above a critical layer thickness. We report the use of
scanning SQUID microscopy (SSM) to study the suppression of the ferromagnetism
in STO/LMO/metal structures. By partially covering the LMO surface with a
metallic layer, both covered and uncovered LMO regions can be studied
simultaneously. While Au does not significantly influence the ferromagnetic
order of the underlying LMO film, a thin Ti layer induces a strong suppression
of the ferromagnetism, over tens of nanometers, and a large change in the
out-of-plane lattice parameter. We relate the suppression of the ferromagnetism
to the scavenging of oxygen and diffusion of Ti approximately 5 nanometers deep
into the film, which takes place at timescales of days. Furthermore, we
demonstrate that by patterning Ti/Au overlayers, we can define ferromagnetic
structures down to sub-micrometer scales.",2310.05514v1
2023-12-23,Room temperature ferromagnetic semiconductors through metal-semiconductor transition in monolayer MnSe2,"To realize room temperature ferromagnetic semiconductors is still a challenge
in spintronics. Recent experiments have obtained two-dimensional (2D) room
temperature ferromagnetic metals, such as monolayer MnSe2. In this paper, we
proposed a way to obtain room temperature ferromagnetic semiconductors through
metal-semiconductor transition. By the density functional theory calculations,
a room temperature ferromagnetic semiconductor is obtained in monolayer MnSe2
with a few percent tensile strains, where a metal-semiconductor transition
occurs with 2.2% tensile stain. The tensile stains raise the energy of d
orbitals of Mn atoms and p orbitals of Se atoms near the Fermi level, making
the Fermi level sets in the energy gap of bonding and antibonding states of
these p and d orbitals, and opening a small band gap. The room temperature
ferromagnetic semiconductors are also obtained in the heterostructures MnSe2/X
(X = Al2Se3, GaSe, SiH, and GaP), where metal-semiconductor transition happens
due to the tensile strains by interface of heterostructures. In addition, a
large magneto-optical Kerr effect (MOKE) is obtained in monolayer MnSe2 with
tensile strain and MnSe2-based heterostructures. Our theoretical results pave a
way to obtain room temperature magnetic semiconductors from experimentally
obtained 2D room temperature ferromagnetic metals through metal-semiconductor
transitions.",2312.15259v1
2024-02-11,Quantum geometric bound for saturated ferromagnetism,"Despite its abundance in nature, predicting the occurrence of ferromagnetism
in the ground state is possible only under very limited conditions such as in a
flat band system with repulsive interaction or in a band with a single hole
under infinitely large Coulomb repulsion, etc. Here, we propose a general
condition to achieve saturated ferromagnetism based on the quantum geometry of
electronic wave functions in itinerant electron systems. By analyzing
multi-band repulsive Hubbard models with an integer band filling, relevant to
either ferromagnetic insulators or semimetals, we propose a rigorous quantum
geometric upper bound on the spin stiffness. By employing this geometric bound,
we establish that saturated ferromagnetism is prohibited in the absence of
interband coupling, even when the local Hubbard repulsion is infinitely large.
As a corollary, this shows that saturated ferromagnetism is forbidden in any
half-filled Hubbard model. We also derive the condition that the upper bound of
the spin stiffness can be completely characterized by the Abelian quantum
metric. We believe that our findings reveal a profound connection between
quantum geometry and ferromagnetism, which can be extended to various
symmetry-broken ground states in itinerant electronic systems.",2402.07171v1
2007-01-05,Colossal electroresistance in ferromagnetic insulating state of single crystal Nd$_0.7$Pb$_0.3$MnO$_3$,"Colossal electroresistance (CER) has been observed in the ferromagnetic
insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs
in the absence of magnetoresistance (MR). Measurements of electroresistance
(ER) and current induced resistivity switching have been performed in the
ferromagnetic insulating state of a single crystal manganite of composition
Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to
ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic
insulating state is realized for temperatures, T <~ 130 K. The colossal
electroresistance, arising from a strongly nonlinear dependence of resistivity
($\rho$) on current density (j), attains a large value ($\approx 100%$) in the
ferromagnetic insulating state. The severity of this nonlinear behavior of
resistivity at high current densities is progressively enhanced with decreasing
temperature, resulting ultimately, in a regime of negative differential
resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with
the build-up of the ER however, is a collapse of the MR to a small value (<
20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms
that give rise to ER and MR are effectively decoupled in the ferromagnetic
insulating phase of manganites. We establish that, the behavior of
ferromagnetic insulating phase is distinct from the ferromagnetic metallic
(FMM) phase as well as the charge ordered insulating (COI) phase, which are the
two commonly realized ground state phases of manganites.",0701090v1
2008-03-03,Phase separation and the effect of quenched disorder in $Pr_{0.5}Sr_{0.5}MnO_3$,"The nature of phase separation in $Pr_{0.5}Sr_{0.5}MnO_3$ has been probed by
linear as well as nonlinear magnetic susceptibilities and resistivity
measurements across the 2nd order paramagnetic to ferromagnetic transition
($T_C$) and 1st order ferromagnetic to antiferromagnetic transition ($T_N$). We
found that the ferromagnetic (metallic) clusters, which form with the onset of
long-range order in the system at $T_C$, continuously decrease their size with
the decrease in temperature and coexist with non-ferromagnetic (insulating)
clusters. These non-ferromagnetic clusters are identified to be
antiferromagnetic. Significantly, it is shown that they do not arise because of
the superheating effect of the lower temperature 1st order transition. Thus
reveals unique phase coexistence in a manganite around half-doping encompassing
two long-range order transitions. Both the ferromagnetic and antiferromagnetic
clusters form at $T_C$ and persist much below $T_N$. Substitution of quenched
disorder (Ga) at Mn-site promotes antiferromagnetism at the cost of
ferromagnetism without adding any magnetic interaction or introducing any
significant lattice distortion. Moreover, increase in disorder decreases the
ferromagnetic cluster size and with 7.5% Ga substitution clusters size reduces
to the single domain limit. Yet, all the samples show significant short-range
ferromagnetic interaction much above $T_C$. Resistivity measurements also
reveal the novel phase coexistence identified from the magnetic measurements.
It is significant that, increase in disorder up to 7.5% increases the
resistivity of the low temperature antiferromagnetic phase by about four
orders.",0803.0085v1
2011-01-25,Charge and spin transport through a ferromagnet/insulator/unconventional superconductor junction,"We analyze the charge and spin transport through a ballistic
ferromagnet/insulator/superconductor junction by means of the Bogoliubov-de
Gennes equations. For the ferromagnetic side we assume that ferromagnetism may
be driven by an unequal mass renormalization of oppositely polarized carriers,
i.e. a spin bandwidth asymmetry, and/or by a rigid splitting of up-and
down-spin electron bands, as in a standard Stoner ferromagnet, whereas the
superconducting side is assumed to exhibit a d-wave symmetry of the order
parameter, which can be pure or accompanied by a minority component breaking
time-reversal symmetry. Several remarkable features in the charge conductance
arise in this kind of junction, providing useful information about the
mechanism of ferromagnetism in the ferromagnetic electrode, as well as of the
order parameter symmetry in the superconducting one. In particular, we show
that when a time-reversal symmetry breaking superconductor is considered, the
use of the two kinds of ferromagnet mentioned above represents a valuable tool
to discriminate between the different superconducting mixed states. We also
explain how this junction may mimic a switch able to turn on and off a spin
current, leaving the charge conductance unchanged, and we show that for a wide
range of insulating barrier strengths, a spin bandwidth asymmetry ferromagnet
may support a spin current larger than a standard Stoner one.",1101.4782v1
2014-04-05,Theory of ferromagnetic superconductors with spin-triplet electron pairing,"A general quasi-phenomenological theory that describes phases and phase
transitions of ferromagnetic superconductors with spin-triplet electron Cooper
pairing is presented. The theory is based on extended Ginzburg-Landau expansion
in powers of superconducting and ferromagnetic order parameters. A simple form
for the dependence of theory parameters on the pressure ensures a correct
theoretical outline of the temperature-pressure phase diagram where a stable
phase of coexistence of p-wave superconductivity and itinerant ferromagnetism
appears. This new theory is in an excellent agreement with the experimental
data for intermetallic compounds, for example, UGe2, URhGe, UCoGe, and UIr that
are experimentally proven to be itinerant ferromagnets exhibiting spin-triplet
superconductivity. The mechanism of appearance of superconductivity due to
itinerant ferromagnetism ($M$-trigger effect) is established and demonstrated.
On the basis of the same theory, basic features of quantum phase transitions in
this type of ferromagnetic superconductors are explained in agreement with the
experimental data. The theory allows for a classification of the spin-triplet
ferromagnetic superconductors in two different types: type I and type II. The
classification is based on quantitative criteria, i.e., on simple relations
between theory parameters. Both theory and experiment indicate that the two
types of p-wave ferromagnetic superconductors are well distinguished by
essential differences in their physical properties.",1404.1497v1
2014-12-08,Voltage Controlled Magnetic Anisotropy Based Low Energy Switching of a Ferromagnet on a Topological Insulator,"We present a novel memory device that consists of a thin ferromagnetic layer
of Fe deposited on topological insulator thin film, Bi2Se3. The ferromagnetic
layer has perpendicular anisotropy, due to MgO deposited on the top surface of
Fe. When current is passed on the surface of Bi2Se3, the surface of the Bi2Se3
becomes spin polarized and strong exchange interaction occurs between the d
electrons in the ferromagnet and the electrons conducting the current on the
surface of the Bi2Se3. Part of the current is shunted through the ferromagnet
which generates spin transfer torque in the ferromagnet. The combination of the
spin transfer torque and exchange interaction torque along with
voltage-controlled magnetic anisotropy (VCMA) allows ultralow-energy switching
of the ferromagnet. We perform micromagnetic simulations and predict switching
time of the order of 2.5 ns and switching energy of the order of 0.45fJ for a
ferromagnetic bit with thermal stability of 43kBT. Such ultralow-energy and
high-speed VCMA-induced switching of a perpendicular anisotropy ferromagnet on
a topological insulator could be utilized for energy-efficient memory design.",1412.2434v3
2017-09-18,Magnetic field driven enhanced ferroelectric switching in self-grown ferroelectric-ferromagnetic composite in the BiFeO3-BaTiO3 multiferroic alloy system,"Over the years attempts have been made to compensate for the inherent
weaknesses in the bulk state of the multiferroic BiFeO3, such as high leakage
current and the absence of ferromagnetic correlation, and exploit its
magnetoelectric potential by forming solid solutions with other perovskites.
Studies in the recent few years have shown that alloying of BiFeO3 with BaTiO3,
both with and without additives, can induce both ferroelectric and
ferromagnetic switching. While the coexistence of both the ferroic orders is
encouraging from the view point of technological applications, the origin of
ferromagnetism in this system remains elusive. Here, we synthesized such
compositions and carried out a detailed structural analysis employing magnetic
separation of the powder particles. We found that the origin of ferromagnetism
lies in the spontaneous precipitation of a minor ( ~ 1 wt %) barium hexaferrite
(BaFe9O19) phase, often undetected in routine x-ray diffraction studies of
powders sampled from the entire specimen. We also demonstrate that inspite of
the insignificant fraction the ferrimagnetic phase, this self-grown composite
exhibit noticeably enhanced ferroelectric switching in the presence of external
magnetic field. We obtained a dc magnetoelectric coupling of ~ 9 x 10-8 s/m, a
value which is comparable to what has been reported for layered
ferroelectric/ferromagnetic laminates and bilayer thin film
ferroelectric-ferromagnetic hetrostructures. Our study suggests that reasonably
large magnetoelectric coupling is realizable in simple 0-3
ferroelectric-ferromagnetic bulk composites provided synthesis strategies are
developed which induces spontaneous precipitation of the ferromagnetic phase in
small volume fraction to ensure good insulating behaviour of the composite thus
developed.",1709.05898v1
2022-06-07,Spin and charge transport in ferromagnet-superconductor-ferromagnet heterostructures: Stoner versus spin mass mismatch mechanism,"We study transport phenomena through a ballistic
ferromagnet-superconductor-ferromagnet (F/S/F) junction, comparing the case in
which the ferromagnetic order in the two F layers is of the standard Stoner
type with the case where it is driven by a spin mass mismatch (SMM). It is
shown that the two mechanisms lead to a different behavior in the charge and
the spin conductances, especially when compared to the corresponding
non-superconducting ferromagnet-normal-ferromagnet (F/N/F) junctions. In
particular, when the injected current is perpendicular to the barrier, for high
barrier transparency and large magnetization of the F layers, the large mass
mismatch gives rise to an enhancement of both low-bias charge and spin
conductances of the F/S/F junction, which is not observed in the equal-mass
case. When all the allowed injection directions are considered, the low bias
enhancement of the charge conductance for SMM leads still holds for high
barrier transparency and large magnetization of the F layers. However, in the
case of non-transparent interfaces, spin transport with SMM ferromagnets
exhibits an opposite sign response with respect to the Stoner case at high
biases for all magnetization values, also manifesting a significant
amplification induced by superconductivity at the gap edge. The above mentioned
differences can be exploited to probe the nature of the electronic mechanism
underlying the establishment of the ferromagnetic order in a given material.",2206.03335v1
2023-06-11,Ferromagnetic Superconductivity in Two-dimensional Niobium Diselenide,"The co-existence of ferromagnetism and superconductivity becomes possible
through unconventional pairing in the superconducting state. Such materials are
exceedingly rare in solid-state systems but are promising platforms to explore
topological phases, such as Majorana bound states. Theoretical investigations
date back to the late 1950s, but only a few systems have so far been
experimentally identified as potential hosts. Here, we show that
atomically-thin niobium diselenide (NbSe$_2$) intercalated with dilute cobalt
atoms spontaneously displays ferromagnetism below the superconducting
transition temperature ($T_c$). We elucidate the origin of this phase by
constructing a magnetic tunnel junction that consists of cobalt and
cobalt-doped niobium diselenide (Co-NbSe$_2$) as the two ferromagnetic
electrodes, with an ultra-thin boron nitride as the tunnelling barrier. At a
temperature well below $T_c$, the tunnelling magnetoresistance shows a bistable
state, suggesting a ferromagnetic order in Co-NbSe$_2$. We propose a RKKY
exchange coupling mechanism based on the spin-triplet superconducting order
parameter to mediate such ferromagnetism. We further perform non-local lateral
spin valve measurements to confirm the origin of the ferromagnetism. The
observation of Hanle precession signals show spin diffusion length up to
micrometres below Tc, demonstrating an intrinsic spin-triplet nature in
superconducting NbSe$_2$. Our discovery of superconductivity-mediated
ferromagnetism opens the door to an alternative design of ferromagnetic
superconductors",2306.06659v1
2023-09-21,Ferromagnetic quantum critical point in a locally noncentrosymmetric and nonsymmorphic Kondo metal,"Quantum critical points (QCPs), zero-temperature phase transitions, are
windows to fundamental quantum-mechanical phenomena associated with universal
behaviour and can provide parallels to the physics of black holes. Magnetic
QCPs have been extensively investigated in the vicinity of antiferromagnetic
order. However, QCPs are rare in metallic ferromagnets due to the coupling of
the order parameter to electronic soft modes [1,2]. Recently, antisymmetric
spin-orbit coupling in noncentrosymmetric systems was suggested to protect
ferromagnetic QCPs [3]. Nonetheless, multiple centrosymmetric materials host FM
QCPs, suggesting a more general mechanism behind their protection. In this
context, CeSi$_{2-\delta}$, a dense Kondo lattice crystallising in a
centrosymmetric structure, exhibits ferromagnetic order when Si is replaced
with Ag. We report that the Ag-substitution controls the strength of the Kondo
coupling, leading to a transition between paramagnetic and ferromagnetic Kondo
phases. Remarkably, a ferromagnetic QCP accompanied by concurrent strange-metal
behaviour emerges. Herein, we suggest that, despite the centrosymmetric
structure, spin-orbit coupling arising from the local noncentrosymmetric
structure, in combination with nonsymmorphic symmetry, can protect
ferromagnetic QCPs. Our findings present a unique example of Kondo
coupling-driven ferromagnetic QCP through chemical doping and offer a general
guideline for discovering new ferromagnetic QCPs.",2309.12497v1
2012-11-12,Cyclotron resonant interactions in cosmic particle accelerators,"A review is given for cyclotron resonant interactions in space plasmas. After
giving a simple formulation for the test particle approach, illustrative
examples for resonant interactions are given. It is shown that for obliquely
propagating whistler waves, not only fundamental cyclotron resonance, but also
other resonances, such as transit-time resonance, anomalous cyclotron
resonance, higher-harmonic cyclotron resonance, and even subharmonic resonance
can come into play. A few recent topics of cyclotron resonant interactions,
such as electron injection in shocks, cyclotron resonant heating of solar wind
heavy ions, and relativistic modifications, are also reviewed.",1211.2852v1
1995-12-06,Ferromagnetism in the Hubbard Model on the Infinite Dimensional fcc Lattice,"The Hubbard model on the fcc lattice is studied in the limit of infinite
spatial dimensions. At sufficiently strong interaction finite temperature
Quantum Monte Carlo calculations yield a second order phase transition to a
highly polarized ferromagnetic state. Ferromagnetism is stable over a wide hole
doping regime but not for electron doping. A possible non-Fermi liquid behavior
is discussed.",9512044v1
1997-07-29,Spin Wave Instability of Itinerant Ferromagnet,"We show variationally that instability of the ferromagnetic state in the
Hubbard model is largely controlled by softening of a long-wavelength spin-wave
excitation, except in the over-doped strong-coupling region where the
individual-particle excitation becomes unstable first. A similar conclusion is
drawn also for the double exchange ferromagnet. Generally the spin-wave
instability may be regarded as a precursor of the metal-insulator transition.",9707300v1
1999-01-14,Spin dynamics in the generalized ferromagnetic Kondo model for manganites,"Dynamical spin susceptibility is calculated for the generalized ferromagnetic
Kondo model which describes itinerant $e_{g}$ electrons interacting with
localized $t_{2g}$ electrons with antiferromagnetic coupling. The calculations
done in the mean field approximation show that the spin-wave spectrum of the
system in ferromagnetic state has two branches, acoustic and optic ones.
Self-energy corrections to the spectrum are considered and the acoustic
spin-wave damping is evaluated.",9901141v1
2000-03-10,Quantum spin hydrodynamics and a new spin-current mode in ferromagnetic metals,"We derive the quantum spin hydrodynamic equations in a ferromagnetic metal.
  From these equations we show the existence of a new massive spin-current
mode. This mode can be observed in neutron scattering experiments and we
discuss the difficulties in seeing it. At the end we discuss the existence of
this mode in localized ferromagnets.",0003187v2
2000-07-31,Ferromagnetic ordering in a generalized Hubbard model: weak intra-atomic interaction limit,"In the present work ferromagnetic ordering in the Hubbard model generalized
by taking into account the inter-atomic exchange interaction and correlated
hopping in partially filled narrow band is considered. Expressions for the
magnetization and Curie temperature as functions of model parameters and band
filling are obtained in the case of weak intra-atomic Coulomb interaction.
Condition of ferromagnetic state realization is found. The obtained results
indicate the important role of correlated hopping.",0007501v1
2000-12-22,The re-examined phenomenological phase transitions theory for ferromagnets,"The existence of the linear on the order parameter term of the thermodynamic
functions expansion near the critical point is justified. The criticism of the
arguments, used for the rejection of the odd-power expansion terms of the
ferromagnets thermodynamic functions is presented. It is shown, that taking
into account the linear term in expansion one achieves the consentency with
experimental data on the magnetization behavior near the transition temperature
in ferromagnets.",0012431v1
2001-06-06,Ferromagnetism in a lattice of Bose condensates,"We show that an ensemble of spinor Bose-Einstein condensates confined in a
one dimensional optical lattice can undergo a ferromagnetic phase transition
and spontaneous magnetization arises due to the magnetic dipole-dipole
interaction. This phenomenon is analogous to ferromagnetism in solid state
physics, but occurs with bosons instead of fermions.",0106118v1
2001-07-13,Skyrmion Physics in Bose-Einstein Ferromagnets,"We show that a ferromagnetic Bose-Einstein condensate has not only line-like
vortex excitations, but in general also allows for point-like topological
excitations, i.e., skyrmions. We discuss the thermodynamic stability and the
dynamic properties of these skyrmions for both spin-1/2 and ferromagnetic
spin-1 Bose gases.",0107302v1
2001-11-29,Origin of room-temperature ferromagnetism in Mn doped semiconducting CdGeP2,"CdGeP2 chalcopyrites doped with Mn have been recently found to exhibit room
temperature ferromagnetism. Isovalent substitution of the Cd site is expected,
however, to create antiferromagnetism, in analogy with the well-known CdTe:Mn
(d^5) case. However, chalcopyrite semiconductors exhibit low-energy intrinsic
defects. We show theoretically how ferromagnetism results from the interaction
of Mn with hole-producing intrinsic defects.",0111570v1
2002-11-21,"Phase Separation, Magnetism and Superconductivity in Rutheno-Cuprates","The properties of the superconducting ferromagnets RuSr2(Gd/Eu)Cu2O8 and
RuSr2(Ln/Ce)2Cu2O10 are reviewed. The problem of coexistence and competition
between magnetic and superconducting states is discussed. A model of phase
separation into ferromagnetic and anti-ferromagnetic structures is proposed.",0211492v1
2003-10-29,"Comment on ``Coexistence of superconductivity and ferromagnetism in ferromagnetic metals""","We argue that a single-band itinerant electron model with short-range
interactions, proposed by Karchev et al. (cond-mat/9911489) and investigated
further by Jackiewicz et al. (cond-mat/0302449), cannot describe the
coexistence of superconducting and ferromagnetic order.",0310704v1
2003-12-22,Spin dynamics of the ferromagnetic superconductor UGe$_{2}$,"Inelastic neutron scattering was used to study the low energy magnetic
excitations of the ferromagnetic superconductor UGe$_{2}$. The ferromagnetic
fluctuations are of Ising nature with a non-conserved magnetization and have an
intermediate behavior between localized and itinerant magnetism.",0312584v1
2004-03-20,Nonequilibrium Dynamic Phase transitions in ferromagnetic systems: Some new phenomena,"The nonequilibrium dynamic phase transition in ferromagnetic systems is
reviewed. Very recent results of dynamic transition in kinetic Ising model and
that in Heisenberg ferromagnet is discussed.",0403530v2
2004-04-01,Mean Field in Long-Range Ferromagnets and Periodic Boundary Conditions,"Periodic boundary conditions are applied to a ferromagnetic spin lattice. A
symmetrical lattice and its contributions all over space are being used.
Results, for the Ising model with ferromagnetic interaction that decays as a
$1/r^{D+\nu}$ law, are discussed in the mean field approximation",0404032v1
2004-06-16,Superconductivity in ferromagnetic metals and in compounds without inversion centre,"The symmetry properties and the general overview of the superconductivity
theory in the itinerant ferromagnets and in materials without space parity are
presented. The basic notions of unconventional superconductivity are introduced
in broad context of multiband superconductivity which is inherent property of
ferromagnetic metals or metals without centre of inversion.",0406371v1
2005-02-03,Carrier-induced ferromagnetism in a diluted Hubbard model,"Carrier-induced ferromagnetism is investigated in a diluted Hubbard model for
ordered impurity arrangements. The delicate competition between particle-hole
processes contributing to the spin couplings results in a rich variety of
behaviour. The ferromagnetic transition temperature obtained within the
spin-fluctuation theory is in good agreement with reported values for $\rm
Ga_{1-x} Mn_x N$.",0502085v1
1999-09-06,Riemannian 2-D conical geometry of Heisenberg ferromagnets,"An exact 2-dimensional conical Riemannian defect solution of 3-dimensional
Euclidean Einstein equations of stresses and defects representing a shear-free
Heisenberg ferromagnet is given.The system is equivalent to the Einstein
equations in vacuum.Geodesics of magnetic monopoles around the ferromagnet are
also investigated.",9909019v2
2005-10-06,Ferromagnetism in quark matter and origin of the magnetic field in compact stars,"Two magnetic aspects of quark matter, ferromagnetism and spin density wave,
are discussed in the temperature-density plane. Some implications of
ferromagnetism are suggested on relativistic heavy-ion collisions and compact
stars.",0510068v1
2000-02-09,Existence of Algebraic Decay in Nonabelian Ferromagnets,"The low temperature regime of nonabelian two-dimensional ferromagnets is
investigated. The method involves mapping such models into certain site-bond
peroclation processes and using ergodicity in a novel fashion. It is concluded
that all ferromagnets possessing a continuous symmetry (abelian or not)
exihibit algebraic decay of correlations at sufficiently low temperatures.",0002028v1
2007-04-24,Theory of the tunneling spectroscopy of ferromagnetic superconductors,"We study tunneling conductance in normal metal / insulator / ferromagnetic
superconductor junctions. The tunneling spectra show a clear difference between
spin-singlet s-wave pairing, spin-triplet opposite spin pairing and
spin-triplet equal spin pairing: These pairings exhibit, respectively, gap
struture, double peak structure and zero bias peak in the spectra. The obtained
result may serve as a tool for determining the pairing symmetry of
ferromagnetic superconductors.",0704.3125v1
2007-12-19,Dynamic Phase Transitions for Ferromagnetic Systems,"This article presents a phenomenological dynamic phase transition theory for
ferromagnetism, leading to a precise description of the dynamic transitions,
and to a physical predication on the spontaneous magnetization. The analysis
also suggests asymmetry of fluctuations in both the ferromagnetism and the PVT
systems.",0712.3082v1
2008-04-22,Pressure-temperature phase diagram of ferromagnetic superconductors,"The symmetry approach to the description of the (P,T) phase diagram of
ferromagnet superconductors with triplet pairing is developed. Taking into
account the recent experimental observations made on UCoGe it is considered the
case of a crystal with orthorhombic structure and strong spin-orbital coupling.
It is shown that formation of ferromagnet superconducting state from a
superconducting state is inevitably accompanied by the first order type
transition.",0804.3546v1
2008-05-26,Magnetic anisotropy in ferromagnetic Josephson junctions,"Magnetotransport measurements were done on $\Nb/\Al_2\O_3/\Cu/\Ni/\Nb$
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Depending on ferromagnetic $\Ni$ interlayer thickness and geometry the standard
(1d) magnetic field dependence of critical current deviates from the text-book
model for Josephson junctions. The results are qualitatively explained by a
short Josephson junction model based on anisotropy and 2d remanent
magnetization.",0805.3925v2
2008-09-21,Quantized Conductance of a Single Magnetic Atom,"A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is
contacted with non-magnetic W or ferromagnetic Ni tips in a scanning tunneling
microscope. When the Co atom bridges two non-magnetic electrodes conductances
of 2e^2/h are found. With two ferromagnetic electrodes a conductance of e^2/h
is observed which may indicate fully spin-polarized transport.",0809.3567v1
2008-12-09,Spin-Wave Relaxation in a Quantum Hall Ferromagnet,"We study spin wave relaxation in quantum Hall ferromagnet regimes. Spin-orbit
coupling is considered as a factor determining spin nonconservation, and
external random potential as a cause of energy dissipation making spin-flip
processes irreversible. We compare this relaxation mechanism with other
relaxation channels existing in a quantum Hall ferromagnet.",0812.1703v1
2010-02-18,Paramagnetic limiting in ferromagnetic superconductors with triplet pairing,"The spin susceptibility in the uranium ferromagnet superconductors is
calculated.
  There is shown that the absence of superconductivity paramagnetic limitation
for the field directions perpendicular to the direction of the spontaneous
magnetization is explained by the itinerant ferromagnet band splitting rather
than by a rotation of magnetization toward the external field direction. The
qualitative description of the upper critical field temperature dependence is
given.",1002.3510v1
2010-07-26,Thermodynamics of classical frustrated spin chain at the ferromagnet-helimagnet transition point,"Low-temperature thermodynamics of the classical frustrated ferromagnetic spin
chain is studied. Using transfer-matrix method we found the behavior of the
correlation function and zero-field susceptibility at the ferromagnetic-helical
transition point. It is shown that the critical exponent for the susceptibility
is changed from 2 to 4/3 at the transition point.",1007.4536v1
2011-05-10,Triplet superconductivity in a ferromagnetic vortex,"We argue that odd-frequency triplet superconductivity can be conveniently
realized in hybrid superconductor-ferromagnet (SF) structures with a
ferromagnetic vortex. We demonstrate that due to proximity-induced long-range
triplet pairing such SFS junctions can sustain appreciable supercurrent which
can be directly measured in experiments.",1105.1916v1
2013-10-12,Spin diffusion and magnetoresistance in ferromagnet/topological-insulator junctions,"We study spin and charge diffusion in
metallic-ferromagnet/topological-insulator junctions. The coupled diffusion
equations are derived perturbatively with respect to the strength of the
interlayer tunneling. We calculate spin accumulation in the ferromagnet and
junction magnetoresistance associated with a current bias along the interface.",1310.3354v2
2020-03-27,Spin-polarized Current-driven Ferromagnetic Domain Wall Motion with a Skyrmion Building Block,"The purpose of the research is the construction of the analytical model for
description of spin-polarized current-driven ferromagnetic domain wall motion
with a skyrmion building block. The dependence of velocity of ferromagnetic
domain wall motion with a skyrmion building block is found as a function of
driving torques and an external magnetic field strength.",2003.12270v1
2022-08-26,Mechanics of a ferromagnetic domain wall,"This paper gives a pedagogical introduction to the mechanics of ferromagnetic
solitons. We start with the dynamics of a single spin and develop all the tools
required for the description of the dynamics of solitons in a ferromagnet.",2208.12799v3
2023-04-21,Soft Magnons in Anisotropic Ferromagnets,"We discuss spin-wave transport in anisotropic ferromagnets with an emphasis
on the zeroes of the band edges as a function of a magnetic field. An
associated divergence of the magnon spin should be observable by enhanced
magnon conductivities in non-local experiments, especially in two-dimensional
ferromagnets.",2304.10709v1
2008-04-21,Coupled-Resonator Optical Near-Field Lithography,"The problem of pattern formation in resonantly-enhanced near-field
lithography by the use of dielectric or plasmonic planar resonators is
investigated. Sub-diffraction-limited bright or dark spots can be produced by
taking advantage of the rotational invariance of planar resonators. To increase
the spatial bandwidth of the resonant enhancement, an array of coupled planar
resonators can open up a band of Bloch resonances, analogous to
coupled-resonator optical waveguides.",0804.3374v1
1999-07-28,Emergence of magnetic field due to spin-polarized baryon matter in neutron stars,"A model of the ferromagnetic origin of magnetic fields of neutron stars is
considered. In this model, the magnetic phase transition occurs inside the core
of neutron stars soon after formation. However, owing to the high electrical
conductivity the core magnetic field is initially fully screened. We study how
this magnetic field emerges for an outside observer. After some time, the
induced field that screens the ferromagnetic field decays enough to uncover a
detectable fraction of the ferromagnetic field. We conjecture that weak fields
of millisecond pulsars of 10^8-10^9 G could be identified with ferromagnetic
fields of unshielded fraction f=10^-4 resulting from the decay of screening
fields by a factor 1-f in 10^8 yr since their birth.",9907393v1
2004-10-09,Phase transitions to spin-triplet ferromagnetic superconductivity in neutron stars,"Effects of the anisotropy of Cooper pairs in spin-triplet ferromagnetic
superconductors are investigated on the basis of the Ginzburg-Landau theory. A
special attention is paid to the triggering of the superconducting state by the
ferromagnetic order. The ground states of these superconductors are outlined
and discussed. The idea about a possible coexistence of ferromagnetism and
spin-triplet superconductivity in neutron stars is introduced.",0410246v1
1993-07-08,Macroscopic Quantum Tunneling of a Domain Wall in a Ferromagnetic Metal,"The macroscopic quantum tunneling of a planar domain wall in a ferromagnetic
metal is studied based on the Hubbard model. It is found that the ohmic
dissipation is present even at zero temperature due to the gapless Stoner
excitation, which is the crucial difference from the case of the insulating
magnet. The dissipative effect is calculated as a function of width of the wall
and is shown to be effective in a thin wall and in a weak ferromagnet. The
results are discussed in the light of recent experiments on ferromagnets with
strong anisotropy. PACS numbers:75.60.Ch, 03.65.Sq, 75.10.Lp",9307012v1
1994-02-08,Method of effective potential for quantum Heisenberg ferromagnet theory,"Self - consistent temperature dependence of the average magnetization in
quantum Heisenberg ferromagnet is obtained as a first approximation of
perturbation theory on an inverse radius by application of the functional
method for quantum ferromagnet. The experimental data are compared with the
theoretical results for {\bf EuO} ferromagnet. A quantitative agreement is
observed between theoretical and experimental results outside interval near
Curie temperature. The theory is of critical behavior in the vicinity of Curie
temperature $T_c$. Theoretical $T_c$ value itself is agreed with the
experimental one with an accuracy of several percents.",9402037v1
1994-04-08,Excitation Spectrum of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain:,"The natural explanation of the excitation spectrum of the spin-1
antiferromagnetic Heisenberg chain is given from the viewpoint of the spin-1/2
ferromagnetic-antiferromagnetic alternating Heisenberg chain. The energy
spectrum of the latter is calculated with fixed momentum $k$ by numerical
diagonalization of finite size systems. It consists of a branch of propagating
triplet pair (triplet wave) and the continuum of multiple triplet waves for
weak ferromagnetic coupling. As the ferromagnetic coupling increases, the
triplet wave branch is absorbed in the continuum for small $k$, reproducing the
characteristics of the spin-1 antiferromagnetic Heisenberg chain.",9404017v1
1994-07-22,Numerical Study of a Two-Dimensional Quantum Antiferromagnet with Random Ferromagnetic Bonds,"A Monte Carlo method for finite-temperature studies of the two-dimensional
quantum Heisenberg antiferromagnet with random ferromagnetic bonds is
presented. The scheme is based on an approximation which allows for an analytic
summation over the realizations of the randomness, thereby significantly
alleviating the ``sign problem'' for this frustrated spin system. The
approximation is shown to be very accurate for ferromagnetic bond
concentrations of up to ten percent. The effects of a low concentration of
ferromagnetic bonds on the antiferromagnetism are discussed.",9407088v1
1995-10-04,Thermodynamics of Quantum Hall Ferromagnets,"The two-dimensional interacting electron gas at Landau level filling factor
$\nu =1$ and temperature $T=0$ is a strong ferromagnet; all spins are
completely aligned by arbitrarily weak Zeeman coupling. We report on a
theoretical study of its thermodynamic properties using a many-body
perturbation theory approach and concentrating on the recently measured
temperature dependence of the spin magnetization. We discuss the interplay of
collective and single-particle aspects of the physics and the opportunities for
progress in our understanding of itinerant electron ferromagnetism presented by
quantum Hall ferromagnets.",9510021v1
1996-02-11,Theory on the Itinerant Ferromagnetism in the $3d$-transition metal systems,"Keeping nickel, cobalt and iron in mind, we investigate the origin of the
itinerant ferromagnetism. In so doing, we generalize the Gutzwiller
approximation. In that,we take account of the effect of the band degeneracy and
the Hund's-rule coupling in addition to the on-site repulsion. After the
discussion on nickel, the condition for the incomplete ferromagnetism, observed
in cobalt and iron, is argued. Phase diagrams, which show the interplay between
the band shape peculiarity and the Hund's-rule coupling, are given. It is found
that for the $3d$-transition metal systems, both of the Hund's-rule coupling
and the special feature of the density of states are necessary to explain the
itinerant ferromagnetism.",9602058v1
1996-12-10,Band ferromagnetism versus collective Kondo state in lattice fermion models,"It is becoming widely recognized that, contrary to earlier expectations, the
usual one-band Hubbard model does not give an explanation for itinerant
ferromagnetism. After reviewing the status of magnetic ordering in the one-band
model, we discuss the possibility of ferromagnetism in some recently introduced
two-band Hubbard models, and in generalized Anderson lattices. It is argued
that these two classes of models are closely related and that it is their
common feature that the ferromagnetic phase has to compete with a collective
Kondo state.",9612090v1
1997-08-20,Ferromagnetism in the large-U Hubbard model,"We study the Hubbard model on a hypercubic lattice with regard to the
possibility of itinerant ferromagnetism. The Dynamical Mean Field theory is
used to map the lattice model on an effective local problem, which is treated
with help of the Non Crossing Approximation. By investigating spin dependent
one-particle Green's functions and the magnetic susceptibility, a region with
nonvanishing ferromagnetic polarization is found in the limit $U\to\infty$. The
$\delta$-T-phase diagram as well as thermodynamic quantities are discussed. The
dependence of the Curie temperature on the Coulomb interaction and the
competition between ferromagnetism and antiferromagnetism are studied in the
large $U$ limit of the Hubbard model.",9708156v1
1997-09-12,S-wave Superconductivity in Weak Ferromagnetic Metals,"We investigate the behavior of weak ferromagnetic metals close to the
ferromagnetic critical point. We show that in the limit of small magnetic
moment the low temperature metallic phase is rigorously described by a local
ferromagnetic Fermi liquid that has a momentum-independent self-energy.
Whereas, non-Fermi liquid features develop at higher temperatures. Furthermore,
we find that an instability towards s-wave superconductivity is possible when
the exchange splitting is comparable to the superconducting gap.",9709143v1
1997-09-26,Dynamics of a ferromagnetic domain wall and the Barkhausen effect,"We derive an equation of motion for the the dynamics of a ferromagnetic
domain wall driven by an external magnetic field through a disordered medium
and we study the associated depinning transition. The long-range dipolar
interactions set the upper critical dimension to be $d_c=3$, so we suggest that
mean-field exponents describe the Barkhausen effect for three-dimensional soft
ferromagnetic materials. We analyze the scaling of the Barkhausen jumps as a
function of the field driving rate and the intensity of the demagnetizing
field, and find results in quantitative agreement with experiments on
crystalline and amorphous soft ferromagnetic alloys.",9709300v1
1998-01-30,Disorder and the quantum Hall ferromagnet,"The distinguishing feature of the quantum Hall ferromagnet is the identity
between the electrical and topological charge densities of a spin distortion.
In addition to the wealth of physics associated with Skyrmionic excitations of
the quantum Hall ferromagnet, this identification permits a rather curious
coupling of spinwaves to the disorder potential. A wavepacket of spinwaves has
an associated, oscillating dipole charge distribution, due to the non-linear
form of the topological density. We investigate the way in which this coupling
modifies the conductivity and temperature dependence of magnetization of the
quantum Hall ferromagnet.",9801324v1
1998-03-18,Spinor Bose Condensates in Optical Traps,"In an optical trap, the ground state of spin-1 Bosons such as $^{23}$Na,
$^{39}$K, and $^{87}$Rb can be either a ferromagnetic or a ""polar"" state,
depending on the scattering lengths in different angular momentum channel. The
collective modes of these states have very different spin character and spatial
distributions. While ordinary vortices are stable in the polar state, only
those with unit circulation are stable in the ferromagnetic state. The
ferromagnetic state also has coreless (or Skyrmion) vortices like those of
superfluid $^{3}$He-A. Current estimates of scattering lengths suggest that the
ground states of $^{23}$Na and $^{87}$Rb condensate are a polar state and a
ferromagnetic state respectively.",9803231v1
1998-10-09,Low-Energy Structure of Heisenberg Ferrimagnetic Spin Chains,"Static and dynamic structure factors of Heisenberg ferrimagnetic spin chains
are numerically investigated. There exist two distinct branches of elementary
excitations, which exhibit ferromagnetic and antiferromagnetic aspects. The
ferromagnetic feature is smeared out with the increase of temperature, whereas
the antiferromagnetic one persists up to higher temperatures. The scattering
intensity is remarkably large at lower boundaries of the ferromagnetic and
antiferromagnetic spectra. All these observations are consistent with the
ferromagnetic-to-antiferromagnetic crossover in the thermal behavior which has
recently been reported.",9810113v1
1998-11-26,Competition between glassiness and order in a multi-spin glass,"A mean-field multi-spin interaction spin glass model is analyzed in the
presence of a ferromagnetic coupling. The static and dynamical phase diagrams
contain four phases (paramagnet, spin glass, ordinary ferromagnet and glassy
ferromagnet) and exhibit reentrant behavior. The glassy ferromagnet phase has
anomalous dynamical properties. The results are consistent with a
nonequilibrium thermodynamics that has been proposed for glasses.",9811373v2
1998-12-10,Effect of Ferromagnetic Spin Correlations on Superconductivity in Ferromagnetic Metals,"We study the renormalization of the quasiparticle properties in weak
ferromagnetic metals, due to spin fluctuations, away from the quantum critical
point for small magnetic moment. We explain the origin of the s-wave
superconducting instability in the ferromagnetic phase and find that the vertex
corrections are small and Migdal's theorem is satisfied away from the quantum
critical point.",9812171v1
1999-01-21,Interplay between Mesoscopic and Microscopic Fluctuations in Ferromagnets,"A model of a ferromagnet is considered, in which there arise mesoscopic
fluctuations of paramagnetic phase. The presence of these fluctuations
diminishes the magnetization of the ferromagnet, softens the spin-wave
spectrum, increases the spin-wave attenuation, shortens the magnon free path,
lowers the critical point, and can change the order of phase transition. A
special attention is paid to the interplay between these mesoscopic
paramagnetic fluctuations and microscopic fluctuations due to magnons. One of
the main results of this interplay is an essential extension of the region of
parameters where the ferromagnet-paramagnet phase transition is of first order.",9901213v1
1999-07-06,A generalization of the spherical model: Reentrant phase transition in the spin one ferromagnet,"By mapping the hamiltonian of the spin one ferromagnet onto that of the
classical spherical model we investigate the possible phase transitions and the
phase diagram of the spin one ferromagnet. Similarly to what happens in the
spherical model we find no phase transition in one and two dimensions.
Nonetheless, for three dimensions we obtain a phase diagram in which the most
important and unexpected feature is the existence of a
ferromagnetic-paramagnetic transition at low temperatures.",9907073v1
1999-10-25,Spin injection and magnetoresistance in ferromagnet/superconductor/ferromagnet tunnel junctions,"We theoretically study the spin-dependent transport in a
ferromagnet/superconductor/ferro-magnet double barrier tunnel junction. The
spin-polarized tunneling currents give rise to spin imbalance in the
superconductor. The resulting nonequilibrium spin density suppresses the
superconductivity with increase of the tunneling currents. We focus on the
effect of asymmetry in the double tunnel junction, where the barrier height of
the tunnel junction and the spin-polarization of the ferromagnets are
different, on spin injection, and discuss how the superconductivity is
suppressed in the asymmetric junction. Our results explain recent experimental
results on the critical current suppression in high-$T_c$ SCs by spin
injection.",9910388v1
1999-11-22,Quasiparticle energy spectrum in ferromagnetic Josephson weak links,"The quasiparticles energy spectrum in clean ferromagnetic weak links between
conventional superconductors is calculated. Large peaks in DOS, due to a
special case of Andreev reflection at the ferromagnetic barrier, correspond to
spin-splitt bound states. Their energies are obtained as a function of the
barrier thickness, exchange field strength, and of the macroscopic phase
difference $\phi$ at the link, related to the Josephson current. In the ground
state, $\phi$ can be 0 or $\pi$, depending on the ferromagnetic barrier
influence. Conditions for the appearence of the zero-energy bound states (ZES)
and for the spin polarized ground state (SPGS) are obtained analytically. It is
shown that ZES appear only outside the weak link ground state.",9911339v1
1999-11-23,New Spin-Wave Mode in Weak Ferromagnetic Fermi Liquids,"We study a phenomenological model for weak ferromagnetic Fermi liquids and
investigate the properties of the spin waves in the model. The Landau kinetic
equation is used to derive, in addition to the known Goldstone mode, a new
spin-wave mode -- the first Silin-like ferromagnetic mode. We discuss the role
of the interaction parameter F^a_1 on the behavior of the Goldstone mode and
the first Silin-like ferromagnetic mode.",9911363v1
1999-12-11,p>2 spin glasses with first order ferromagnetic transitions,"We consider an infinite-range spherical p-spin glass model with an additional
r-spin ferromagnetic interaction, both statically using a replica analysis and
dynamically via a generating functional method. For r>2 we find that there are
first order transitions to ferromagnetic phases. For r<p there are two
ferromagnetic phases, one non-glassy replica symmetric and one exhibiting
glassy one-step replica symmetry breaking and aging, whereas for r>=p only the
replica symmetric phase exists.",9912201v2
1999-12-13,Spin Anisotropy and Quantum Hall Effect in the Kagome Lattice - Chiral Spin State based on a Ferromagnet-,"A ferromagnet with spin anisotropies on the 2D Kagome lattice is
theoretically studied. This is a typical example of the flat-band ferromagnet.
The Berry phase induced by the tilting of the spins opens the band gap and
quantized Hall conductance \sigma_{xy}=\pm e^2/h is realized without external
magnetic field. This is the most realistic chiral spin state based on the
ferromagnetism. We also discuss the implication of our results to anomalous
Hall effect observed in the metallic pyrochlore ferromagnets R_2Mo_2O_7(R=Nd,
Sm, Gd).",9912206v1
1999-12-22,Probing the spin polarization in ferromagnets,"The emission of correlated electrons from an itinerant ferromagnet following
the impact of a polarized electron beam is analyzed in terms of irreducible
tensorial parameters that can be measured. Under favorable conditions,
specified in this work, these parameters are related to the spin polarization
in the ferromagnet. The formal results are illustrated by numerical studies of
the polarized electron pair emission from a Fe(110) surface and a novel
technique for the investigation of magnetic properties of ferromagnets is
suggested.",9912409v1
1999-12-29,Theory of Disordered Itinerant Ferromagnets II: Metal-Insulator Transition,"The theory for disordered itinerant ferromagnets developed in a previous
paper is used to construct a simple effective field theory that is capable of
describing the quantum phase transition from a ferromagnetic metal to a
ferromagnetic insulator. It is shown that this transition is in the same
universality class as the one from a paramagnetic metal to a paramagnetic
insulator in the presence of an external magnetic field, and that strong
corrections to scaling exist in this universality class. The experimental
consequences of these results are discussed.",9912478v2
2000-03-03,Ordered phase in the two-dimensional randomly coupled ferromagnet,"True ground states are evaluated for a 2d Ising model with random near
neighbor interactions and ferromagnetic second neighbor interactions (the
Randomly Coupled Ferromagnet). The spin glass stiffness exponent is positive
when the absolute value of the random interaction is weaker than the
ferromagnetic interaction. This result demonstrates that in this parameter
domain the spin glass like ordering temperature is non-zero for these systems,
in strong contrast to the 2d Edwards-Anderson spin glass.",0003042v2
2000-04-25,Weak ferromagnetism of quasi-one-dimensional S=1/2 antiferromagnet BaCu$_2$Ge$_2$O$_7$,"Weak ferromagnetism of quasi-one-dimensional S = 1/2 antiferromagnet
BaCu$_2$Ge$_2$O$_7$ is studied by the magnetization measurement. The
spontaneous magnetization appears along the b axis. The local symmetry between
the in-chain nearest neighbor spins allows the presence of
Dzyaloshinskii-Moriya interaction, and the only possible spatial configuration
of the weak ferromagnetic moment per spin determines the sign of the
inter-chain interaction. A weak $a$-axis magnetic field can change the
direction of the magnetization to the $a$-axis direction, which shows that the
spin chain forms a weakly coupled weak-ferromagnetic chain system.",0004403v2
2000-05-09,Spin-Waves in itinerant ferromagnets,"We introduce a novel approach for the investigation of spin-wave excitations
in itinerant ferromagnets. Our theory is based on a variational treatment of
general multi-band Hubbard models which describe elements and compounds of
transition metals. The magnon dispersion is derived approximately as the energy
of a variational spin-wave state in the limit of large spatial dimensions. A
numerical evaluation of our results is feasible for general multi-band models.
As a first application we consider a model with two degenerate orbitals per
lattice site. From our results we can conclude that spin-wave excitations in
strong itinerant ferromagnets are very similar to those in ferromagnetic spin
systems.",0005154v1
2000-07-05,"Competition of charge, orbital, and ferromagnetic correlations in layered manganites","The competition of charge, orbital, and ferromagnetic interactions in layered
manganites is investigated by magneto-Raman scattering spectroscopy. We find
that the colossal magnetoresistance effect in the layered compounds results
from the interplay of the orbital and ferromagnetic double-exchange
correlations. Inelastic scattering by charge-order fluctuations dominates the
quasiparticle dynamics in the ferromagnetic-metal state. The scattering is
suppressed at low frequencies, consistent with the opening of a charge-density
wave pseudogap.",0007082v1
2000-07-17,Long Range Proximity Effect in Hybrid Ferromagnetic/Superconducting Nanostructures,"We find that the dependence on temperature and magnetic field of the
electrical resistance of diffusive ferromagnetic nano-wires measured with
superconducting electrodes changes drastically with the distance, $L$, between
the ferromagnet/superconductor contacts, however is remarkably similar for the
wires with the same $L$ ranging from 300 nm to 1000 nm, prepared under
identical conditions. The result gives an evidence for the long-range
superconductor-induced changes in transport properties of ferromagnetic
nano-wires.",0007278v1
2000-08-09,Bulk experimental evidence of half-metallic ferromagnetism in doped manganites,"We report precise measurements and quantitative data analysis on the
low-temperature resistivity of several ferromagnetic manganite films. We
clearly show that there exists a T^{4.5} term in low-temperature resistivity,
and that this term is in quantitative agreement with the quantum theory of
two-magnon scattering for half metallic ferromagnets. Our present results
provide the first bulk experimental evidence of half-metallic ferromagnetism in
doped manganites.",0008151v1
2000-09-22,"spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models","The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site
complete graph extended with on-site repulsion is obtained from the underlying
spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic
ground state is realized for 1 and N+1 electrons only. We identify the large
density of states to be responsible for the suppression of the ferromagnetic
state and argue that a similar situation is encountered in the Kagome,
pyrochlore, and other lattices with flat bands in their one-particle density of
states.",0009358v1
2000-12-06,Magnons in the ferromagnetic Kondo-lattice model,"The magnetic properties of the ferromagnetic Kondo-lattice model (FKLM) are
investigated. Starting from an analysis of the magnon spectrum in the spin-wave
regime, we examine the ferromagnetic stability as a function of the occupation
of the conduction band $n$ and the strength $J$ of the coupling between the
localised moments and the conduction electrons. From the properties of the
spin-wave stiffness $D$ the ferromagnetic phase at zero temperature is derived.
Using an approximate formula the critical temperature $T_c$ is calculated as a
function of $J$ and $n$.",0012086v1
2000-12-22,Quantum Spin Fluctuations as a Source of Long-Range Proximity Effects in Diffusive Ferromagnet-Superconductor Structures,"We show that quantum spin fluctuations in inhomogeneous ferromagnets
drastically affect the Andreev reflection of electrons and holes at a
ferromagnet-superconductor interface. As a result a strong long-range proximity
effect appears, associated with electron-hole spin triplet correlations and
persisting on a lenght scale typical for non-magnetic materials, but
anomalously large for ferromagnets.",0012437v1
2001-01-17,Design of a semiconductor ferromagnet in a quantum dot artificial crystal,"We present the theoretical design of quantum dot (QD) artificial
ferromagnetic crystals. The electronic structure calculations based on local
spin density approximation (LSDA) show that our designed QD artificial crystal
from a structure comprising the crossing 0.104-micrometer-wide InAs quantum
wires (an effective Kagome lattice) has flat band characteristics. Our examined
QD artificial crystal has the ferromagnetic ground state when the flat band is
half-filled, even though it contains no magnetic elements. The ferromagnetic
and the paramagnetic state can be freely switched by changing the electron
filling via a gate voltage.",0101252v1
2001-01-25,Ferromagnetism in magnetically doped III-V semiconductors,"The origin of ferromagnetism in semimagnetic III-V materials is discussed.
The indirect exchange interaction caused by virtual electron excitations from
magnetic impurity level in the bandgap to the valence band can explain
ferromagnetism in GaAs(Mn) no matter samples are degenerated or not. Formation
of ferromagnetic clusters and percolation picture of phase transition describes
well all available experimental data and allows to predict the Mn-composition
dependence of transition temperature in wurtzite (Ga,In,Al)N epitaxial layers.",0101389v1
2001-02-21,Inverse proximity effect in superconductors near ferromagnetic material,"We study the electronic density of states in a mesoscopic superconductor near
a transparent interface with a ferromagnetic metal. In our tunnel spectroscopy
experiment, a substantial density of states is observed at sub-gap energies
close to a ferromagnet. We compare our data with detailed calculations based on
the Usadel equation, where the effect of the ferromagnet is treated as an
effective boundary condition. We achieve an excellent agreement with theory
when non-ideal quality of the interface is taken into account.",0102367v2
2001-03-01,A ferromagnet with a glass transition,"We introduce a finite-connectivity ferromagnetic model with a three-spin
interaction which has a crystalline (ferromagnetic) phase as well as a glass
phase. The model is not frustrated, it has a ferromagnetic equilibrium phase at
low temperature which is not reached dynamically in a quench from the
high-temperature phase. Instead it shows a glass transition which can be
studied in detail by a one step replica-symmetry broken calculation. This spin
model exhibits the main properties of the structural glass transition at a
solvable mean-field level.",0103026v2
2001-04-26,On metallic ferromagnetism of a generalized Hubbard model with correlated hopping,"In the paper a possibility of metallic ferromagnetic state realization in a
generalized Hubbard model with more complete accounting of electron-electron
interactions, in particular, the correlated hopping and exchange interaction
integrals is investigated. Recently obtained by means of mean-field
approximation single electron energy spectrum is used for the description of
finite temperature properties of the system. In the paper the expression for
the critical temperature of ferromagnet-paramagnet transition is found, the
behaviour of temperature dependencies of magnetization and paramagnetic
susceptibility is analyzed. Taking into account the correlated hopping allows
to explain some peculiarity of ferromagnetic behaviour of transition metals,
their alloys and compounds.",0104515v1
2001-05-08,Dissimilar Ferromagnetic Layer Dependence of Hot Electron Magnetotransport,"The material dependence of hot electron magnetotransport in a spin-valve
transistor has been theoretically explored. We calculate the parallel and
anti-parallel collector current changing the types and relative spin
orientation of the ferromagnetic layers. The magnetocurrent has been presented
as well. In this calculations, spin dependent self energy effect of hot
electron in ferromagnetic materials has been taken into account. The results
show that the magnetotransport property strongly depends on the combination of
different ferromagnetic metal layers since the hot electron has different
inelastic scattering strength in each material, and the hot electron spin
polarization enters importantly into the magnetocurrent at finite temperatures.
This calculations may suggest the guide for searching the best structural
combination of hot electron magnetoelectronic device such as a spin-valve
transistor.",0105168v1
2001-07-12,Magnetic exchange interaction induced by a Josephson current,"We show that a Josephson current flowing through a
ferromagnet-normal-metal-ferromagnet trilayer connected to two superconducting
electrodes induces an equilibrium exchange interaction between the magnetic
moments of the ferromagnetic layers. The sign and magnitude of the interaction
can be controlled by the phase difference between the order parameters of the
two superconductors. We present a general framework to calculate the Josephson
current induced magnetic exchange interaction in terms of the scattering
matrices of the different layers. The effect should be observable as the
periodic switching of the relative orientation of the magnetic moments of the
ferromagnetic layers in the ac Josephson effect.",0107258v1
2001-08-24,Influence of disorder on the ferromagnetism in diluted magnetic semiconductors,"Influence of disorder on the ferromagnetic phase transition in diluted
(III,Mn)V semiconductors is investigated analytically. The regime of small
disorder is addressed, and the enhancement of the critical temperature by
disorder is found both in the mean field approximation and from the analysis of
the zero temperature spin stiffness. Due to disorder, the spin wave
fluctuations around the ferromagnetically ordered state acquire a finite mass.
At large charge carrier band width, the spin wave mass squared becomes
negative, signaling the breakdown of the ferromagnetic ground state and the
onset of a noncollinear magnetic order.",0108396v2
2002-01-08,"Feromagnetic ""$π$""-junctions","We investigate Josephson coupling through a ferromagnetic thin film using
Superconductor-Insulator-Ferromagnet-Superconductor planar junctions. Damped
oscillations of the critical current are observed as a function of the
ferromagnetic layer thickness. We show that they result from the exchange
energy gained or lost by a quasiparticle Andreev-reflected at the
ferromagnet-superconductor interface. The critical current cancels out at the
transition from positive (""0"") to negative (""$\pi$"") coupling, in agreement
with theoretical calculations.",0201104v2
2002-03-15,Modified spin-wave study of random antiferromagnetic-ferromagnetic spin chains,"We study the thermodynamics of one-dimensional quantum spin-1/2 Heisenberg
ferromagnetic system with random antiferromagnetic impurity bonds. In the
dilute impurity limit, we generalize the modified spin-wave theory for random
spin chains, where local chemical potentials for spin-waves in ferromagnetic
spin segments are introduced to ensure zero magnetization at finite
temperature. This approach successfully describes the crossover from behavior
of pure one-dimensional ferromagnet at high temperatures to a distinct Curie
behavior due to randomness at low temperatures. We discuss the effects of
impurity bond strength and concentration on the crossover and low temperature
behavior.",0203326v1
2002-04-08,Pressure Effect on the Superconducting and Magnetic Transitions of the Superconducting Ferromagnet RuSr2GdCu2O8,"The superconducting ferromagnet RuSr2GdCu2O8 was investigated at high
pressure. The intra-grain superconducting transition temperature, Tc, is
resolved in ac-susceptibility as well as resistivity measurements. It is shown
that the pressure shift of Tc is much smaller than that of other high-Tc
compounds in a similar doping state. In contrast, the ferromagnetic transition
temperature, Tm, increases with pressure at a relative rate that is about twice
as large as that of Tc. The high-pressure data indicate a possible competition
of the ferromagnetic and superconducting states in RuSr2GdCu2O8.",0204185v1
2002-04-20,Coexistence of ferromagnetism and superconductivity,"A comprehensive theory is developed that describes the coexistence of p-wave,
spin-triplet superconductivity and itinerant ferromagnetism. It is shown how to
use field-theoretic techniques to derive both conventional strong-coupling
theory, and analogous gap equations for superconductivity induced by magnetic
fluctuations. It is then shown and discussed in detail that the magnetic
fluctuations are generically stronger on the ferromagnetic side of the magnetic
phase boundary, which substantially enhances the superconducting critical
temperature in the ferromagnetic phase over that in the paramagnetic one. The
resulting phase diagram is compared with the experimental observations in UGe_2
and ZrZn_2.",0204440v2
2002-05-23,Ferromagnetism in the Hubbard model with a generalized type of hopping,"The extrapolation of small-cluster exact-diagonalization calculations is used
to examine ferromagnetism in the one-dimensional Hubbard model with a
generalized type of hopping. It is found that the long-range hopping with power
decaying hopping amplitudes ($t_{ij}\sim q^{|i-j|}$) stabilizes the
ferromagnetic state for a wide range of electron interactions $U$ and electron
concentrations $n$. The critical value of the interaction strength $U_c(q)$
above which the ferromagnetic state becomes stable is calculated numerically
and the ground-state phase diagram of the model (in the $U$-$q$ plane) is
presented for physically the most interesting cases.",0205481v1
2002-05-27,Parity Effect and Tunnel Magnetoresistance of Ferromagnet / Superconductor / Ferromagnet Single-Electron Tunneling Transistors,"We theoretically study the tunnel magnetoresistance(TMR) of ferromagnet /
superconductor / ferromagnet single-electron tunneling transistors with a
special attention to the parity effect. It is shown that in the plateau region,
there is no spin accumulation in the island even at finite bias voltage.
However, the information of the injected spin is carried by the excess electron
and thus the TMR exists. The spin relaxation rate of the excess electron can be
estimated from the TMR. We also show that the TMR increases with decreasing the
size of the superconducting island.",0205541v1
2002-08-01,Magneto-optical study of ZnO based diluted magnetic semiconductors,"Magneto-optical properties of ZnO:Co and ZnO:Ni films were measured.
Magnetization measurements show that some of the films are paramagnetic and
others are ferromagnetic. Magnetic circular dichroism clarified that Zn1-xCoxO
and Zn1-xNixO included in samples are paramagnetic diluted magnetic
semiconductors. Ferromagnetic precipitations seem to be responsible for the
observed ferromagnetic behaviors. Criteria to judge the ferromagnetic DMS are
also discussed.",0208010v1
2002-09-30,Phase diagrams of spin ladders with ferromagnetic legs,"The low-temperature properties of the spin S=1/2 ladder with anisotropic
ferromagnetic legs are studied using the continuum limit bosonization approach.
The weak-coupling ground state phase diagram of the model is obtained for a
wide range of coupling constants and several unconventional gapless
''spin-liquid'' phases are shown to exist for ferromagnetic coupling. The
behavior of the ladder system in the vicinity of the ferromagnetic instability
point is discussed in detail.",0209677v1
2002-11-28,Proximity effect in ferromagnet-superconductor hybrid structures: role of the pairing symmetry,"The spatial variations of the pair amplitude, and the local density of states
in d-wave or s-wave superconductor-ferromagnet hybrid structures are calculated
self consistently using the Bogoliubov-deGennes formalism within the two
dimensional extended Hubbard model. We describe the proximity effect in
superconductor / ferromagnet (SF) bilayers, FSF trilayers, and interfaces
between a superconductor and a ferromagnetic domain wall. We investigate in
detail the role played by the pairing symmetry, the exchange field, interfacial
scattering and crossed Andreev reflection.",0211663v1
2002-12-05,Dynamic stiffness of spin valves,"The dynamics of the magnetic order parameters of
ferromagnet/normal-metal/ferromagnet spin valves and isolated ferromagnets may
be very different. We investigate the role of the nonequilibrium spin-current
exchange between the ferromagnets in the magnetization precession and
switching. We find a (low-temperature) critical current bias for a coherent
current-induced magnetization excitation in spin valves, which unifies and
generalizes previous ideas of Slonczewski and Berger. In the absence of an
applied bias, the effect of the spin transfer can be expressed as
magnetic--configuration-dependent Gilbert damping.",0212130v2
2003-02-17,Charge-ordered ferromagnetic phase in manganites,"A mechanism for charge-ordered ferromagnetic phase in manganites is proposed.
The mechanism is based on the double exchange in the presence of diagonal
disorder. It is modeled by a combination of the Ising double-exchange and the
Falicov-Kimball model. Within the dynamical mean-field theory the charge and
spin correlation function are explicitely calculated. It is shown that the
system exhibits two successive phase transitions. The first one is the
ferromagnetic phase transition, and the second one is a charge ordering. As a
result a charge-ordered ferromagnetic phase is stabilized at low temperature.",0302328v1
2003-04-15,Unconventional superconducting states induced in a ferromagnet by a d-wave superconductor,"We develop a quasi-classical theory for the superconducting proximity effect
in a ballistic ferromagnetic layer in contact with a d-wave superconductor. In
agreement with recent experiments we find that the density of states oscillate
around the normal state value with varying the thickness of the ferromagnetic
layer. We show that the phase, the amplitude, and the period of these
oscillations depend on the orientation of the superconductor. This effect
reveals spatial oscillations and anisotropy of the induced superconducting
correlations in the ferromagnet.",0304336v1
2003-04-28,Ferromagnetism and Superconductivity in the multi-orbital Hubbard Model: Hund's Rule Coupling versus Crystal-Field Splitting,"The multi-orbital Hubbard model in one dimension is studied using the
numerical diagonalization method. Due to the effect of the crystal-field
splitting $\Delta$, the fully polarized ferromagnetism which is observed in the
strong coupling regime becomes unstable against the partially polarized
ferromagnetism when the Hund's rule coupling $J$ is smaller than a certain
critical value of order of $\Delta$. In the vicinity of the partially polarized
ferromagnetism, the orbital fluctuation develops due to the competition between
the Hund's rule coupling and the crystal-field splitting. The superconducting
phase with the Luttinger liquid parameter $K_{\rho}>1$ is observed for the
singlet ground state in this region.",0304620v1
2003-05-14,Atomic thickness hybrid F/S/F structures,"We propose an exactly solvable model to describe the properties of atomic
thickness hybrid ferromagnet-superconductor-ferromagnet (F/S/F) structures. We
show that the superconducting critical temperature is always higher for
antiparallel orientation of the ferromagnetic moments. However at low
temperature the superconducting gap occurs to be larger for parallel
orientation of the ferromagnetic moments. This leads to a peculiar temperature
dependence of the proximity effect in (F/S/F) structures.",0305320v2
2003-05-26,Phase diagram of a class of spin-triplet ferromagnetic superconductors,"We investigate thermodynamic phases, including the phase of coexistence of
superconductivity and ferromagnetism, the possible phase transitions of first
and second order, and the shape of the phase diagram in mean-field
approximation for a phenomenological model of spin-triplet ferromagnetic
superconductors. The results are discussed in view of application to metallic
ferromagnets as UGe$_2$, ZrZn$_2$, URhGe, and Fe.",0305585v1
2003-05-27,Double Magnetic Transition in Pr0.5Sr0.5CoO3,"We report studies of polycrystalline samples of the metallic ferromagnet
Pr0.5Sr0.5CoO3 through measurements of the magnetization, a.c. magnetic
susceptibility, resistivity, and specific heat. We find an unusual anomaly
around TA = 120 K, much below the ferromagnetic transition (TC = 226 K). The
anomaly is manifested in field cooled magnetization as a downward step in low
fields (H less than or equal to 0.01 T) but is transformed into an upward step
for H greater than or equal to 0.05 T. The anomaly cannot be easily attributed
to antiferromagnetic ordering, but may correspond to a second ferromagnetic
transition or an alteration of the ferromagnetic state associated with orbital
ordering.",0305621v1
2003-07-11,Orange Peel coupling in granular ferromagnetic films,"We present magnetoresistance (MR) measurements performed on magnetic tunnel
junctions in which one of the electrodes is a granular ferromagnetic film.
These junctions exhibit a zero field resistance dip. The dip magnitude depends
on the size of the grains. We interpret these results as a consequence of the
orange peel effect between the continuous ferromagnetic film and the magnetic
grains. The coupling is found to be much stronger than that between continuous
ferromagnetic layers.",0307274v1
2003-08-26,Field dependence of the electronic phase separation in Pr0.67Ca0.33MnO3 by small angle magnetic neutron scattering,"We have studied by small angle neutron scattering the evolution induced by
the application of magnetic field of the coexistence of ferromagnetism (F) and
antiferromagnetism (AF) in a crystal of Pr$_{0.67}$Ca$_{0.33}$MnO$_3$. The
results are compared to magnetic measurements which provide the evolution of
the ferromagnetic fraction. These results show that the growth of the
ferromagnetic phase corresponds to an increase of the thickness of the
ferromagnetic ''cabbage'' sheets.",0308534v1
2003-10-01,Thermodynamic properties of the phase transitions in a class of spin-triplet ferromagnetic superconductors,"Magnetic susceptibility, entropy and specific heat are calculated at the
equilibrium points of phase transition to a phase of coexistence of
ferromagnetic order and superconductivity in a new class of spin-triplet
ferromagnetic superconductors. The results are discussed in view of application
to metallic ferromagnets as UGe$_2$, ZrZn$_2$, URhGe.",0310016v2
2003-10-06,"Ferromagnetism in (In,Mn)As alloy thin films grown by metalorganic vapor phase epitaxy","Ferromagnetic properties of In1-xMnxAs thin films were investigated. Room
temperature ferromagnetic order was observed in nominally single-phase films
with x = 0.01-0.10. Magnetization measurements indicated that these In1-xMnxAs
samples had a Curie temperature of 333 K. The Curie temperature was independent
of Mn concentration. The temperature dependent magnetization along with the
magnitude of the saturation magnetization and microstructural data indicate
that the source of the high-temperature ferromagnetism in single-phase films is
not attributable to MnAs nanoprecipitates. The high transition temperature is
attributed to the presence of near neighbor Mn pairs.",0310104v1
2003-12-12,Role of Inter-site Hybrid Interactions in Itinerant Ferromagnetism,"We study role of inter-site hybrid interactions in deciding ferromagnetic
state in the itinerant electron (narrow band) systems like some of the
transition metals. We have considered Hubbard like tight binding model
alongwith exchange and hybrid interactions. All interactions have been treated
within mean-field approximation. It is found here that hybrid interactions play
significant role at zero as well as infinite temperatures in deciding on-set of
ferromagnetic state. We have studied variation of effective mass of up and down
spin electrons in ferromagnetic state as a function of temperature. Also
studied are magnetic susceptibility, optical conductivity and magnetoresistance
as a function of temperature.",0312309v1
2003-12-18,Coherently photo-induced ferromagnetism in diluted magnetic semiconductors,"Ferromagnetism is predicted in undoped diluted magnetic semiconductors
illuminated by intense sub-bandgap laser radiation . The mechanism for
photo-induced ferromagnetism is coherence between conduction and valence bands
induced by the light which leads to an optical exchange interaction. The
ferromagnetic critical temperature T_C depends both on the properties of the
material and on the frequency and intensity of the laser and could be above 1
K.",0312445v1
2003-12-18,Controlled normal and inverse magnetoresistance and current-driven magnetization switching in magnetic nanopillars,"Combining pairs of ferromagnetic metals with different signs of scattering
anisotropies, let us independently invert the magnetoresistance and the
direction of current-driven switching in
ferromagnetic/non-magnetic/ferromagnetic metal nanopillars. We show all four
combinations of normal and inverse behaviors, at both room temperature and
4.2K. In all cases studied, the direction of switching is set by the net
scattering anisotropy of the fixed (polarizing) ferromagnet. We provide simple
arguments for what we see.",0312475v1
2003-12-18,Ferromagnetism in the Hubbard model with long-range and correlated hopping,"The extrapolation of small-cluster exact-diagonalization calculations is used
to examine ferromagnetism in the one-dimensional Hubbard model with long-range
and correlated hopping. It is found that the correlated hopping term stabilizes
the ferromagnetic state for a wide range of electron interactions $U$ and
electron concentrations $n$. The critical value of the interaction strength
$U_c$ above which the ferromagnetic state becomes stable is calculated
numerically and the ground-state phase diagram of the model is presented for
physically the most interesting cases.",0312486v1
2004-01-16,Ferromagnetism in Fe-doped SnO2 thin films,"Thin films grown by pulsed-laser deposition from targets of Sn0.95Fe0.05O2
are transparent ferromagnets with Curie temperature and spontaneous
magnetization of 610 K and 2.2 Am2kg-1, respectively. The 57Fe Mossbauer
spectra show the iron is all high-spin Fe3+ but the films are magnetically
inhomogeneous on an atomic scale, with only 23 % of the iron ordering
magnetically. The net ferromagnetic moment per ordered iron ion, 1.8 Bohr
magnetons, is greater than for any simple iron oxide. Ferromagnetic coupling of
ferric ions via an electron trapped in a bridging oxygen vacancy (F center) is
proposed to explain the high Curie temperature",0401293v1
2004-02-28,Superconductor-Ferromagnet Bi-Layers: a Comparison of s-Wave and d-Wave Order Parameters,"We study superconductor-ferromagnet bi-layers, not only for s-wave but also
for d-wave superconductors. We observe oscillations of the critical temperature
when varying the thickness of the ferromagnetic layer for both s-wave and
d-wave superconductors. However, for a rotated d-wave order parameter the
critical temperature differs considerably from that for the unrotated case. In
addition we calculate the density of states for different thicknesses of the
ferromagnetic layer; the results reflect the oscillatory behaviour of the
superconducting correlations.",0403009v1
2004-04-07,Interaction Between Superconducting and Ferromagnetic Order Parameters in Graphite-Sulfur Composites,"The superconductivity of graphite-sulfur composites is highly anisotropic and
associated with the graphite planes. The superconducting state coexists with
the ferromagnetism of pure graphite, and a continuous crossover from
superconducting to ferromagnetic-like behavior could be achieved by increasing
the magnetic field or the temperature. The angular dependence of the magnetic
moment m(alpha) provides evidence for an interaction between the ferromagnetic
and the superconducting order parameters.",0404169v1
2004-04-08,Incomplete Andreev reflection in a clean Superconductor/Ferromagnet/Superconductor junction,"We study the Josephson effect in a clean
Superconductor-Ferromagnet-Superconductor junction for arbitrarily large spin
polarizations. The Andreev reflection at a clean Ferromagnet-Superconductor
interface is incomplete, and Andreev channels with a large incidence angle are
progressively suppressed with increasing exchange energy. As a result, the
critical current exhibits oscillations as a function of the exchange energy and
of the length of the ferromagnet and has a temperature dependence which
deviates from the one predicted by the quasiclassical theory.",0404215v3
2004-04-12,Phases and phase transitions in spin-triplet ferromagnetic superconductors,"Recent results for the coexistence of ferromagnetism and unconventional
superconductivity with spin-triplet Cooper pairing are reviewed on the basis of
the quasi-phenomenological Ginzburg-Landau theory. New results are reported.
The results are discussed in view of applications to metallic compounds as
UGe2, URhGe, ZrZn2.",0404261v1
2004-06-25,Correlation Effects in Band Ferromagnetism,"We analyze the influence of different on-site and inter-site interactions on
the Curie temperature of transition metal magnetic elements. The numerical
calculations show the well known result that the on-site Coulomb repulsion
helps ferromagnetism mainly at half-filling of the band, where the 3d elements
are antiferromagnetic (Cr, Mn). The inter-site interactions, which in the new
approximation decrease the width of the band, favor ferromagnetism at both ends
of the band. At the same time they lower the ferromagnetic Curie temperature
towards experimental values, removing the paradox which persisted for a long
time.",0406634v1
2004-07-08,Singlet-Triplet Mixing in Superconductor-Ferromagnet Hybrid Devices,"We develop a theory which describes hybrid structures consisting out of
superconducting and ferromagnetic parts. We give two examples for applications.
First, we consider a hybrid structure containing a strong ferromagnet in the
ballistic limit. Second, we study for a weak ferromagnet the influence of a
domain wall on the superconducting proximity effect. In both cases we account
quantitatively for the mixing between singlet and triplet correlations.",0407194v1
2004-10-21,"Search For Hole Mediated Ferromagnetism In Cubic (Ga,Mn)N","Results of magnetisation measurements on p-type zincblende-(Ga,Mn)N are
reported. In addition to a small high temperature ferromagnetic signal, we
detect ferromagnetic correlation among the remaining Mn ions, which we assign
to the onset of hole-mediated ferromagnetism in (Ga,Mn)N.",0410551v1
2005-01-18,Ferromagnetism of Weakly-Interacting Electrons in Disordered Systems,"It was realized two decades ago that the two-dimensional diffusive Fermi
liquid phase is unstable against arbitrarily weak electron-electron
interactions. Recently, using the nonlinear sigma model developed by
Finkelstein, several authors have shown that the instability leads to a
ferromagnetic state. In this paper, we consider diffusing electrons interacting
through a ferromagnetic exchange interaction. Using the Hartree-Fock
approximation to directly calculate the electron self energy, we find that the
total energy is minimized by a finite ferromagnetic moment for arbitrarily weak
interactions in two dimensions and for interaction strengths exceeding a
critical proportional to the conductivity in three dimensions. We discuss the
relation between our results and previous ones.",0501431v1
2005-02-14,"Interlayer Exchange Coupling in (Ga,Mn)As-based Superlattices","The interlayer coupling between (Ga,Mn)As ferromagnetic layers in
all-semiconductor superlattices is studied theoretically within a tight-binding
model, which takes into account the crystal, band and magnetic structure of the
constituent superlattice components. It is shown that the mechanism originally
introduced to describe the spin correlations in antiferromagnetic EuTe/PbTe
superlattices, explains the experimental results observed in ferromagnetic
semiconductor structures, i.e., both the antiferromagnetic coupling between
ferromagnetic layers in IV-VI (EuS/PbS and EuS/YbSe) superlattices as well as
the ferromagnetic interlayer coupling in III-V ((Ga,Mn)As/GaAs) multilayer
structures. The model allows also to predict (Ga,Mn)As-based structures, in
which an antiferromagnetic interlayer coupling could be expected.",0502321v1
2005-02-16,Ferromagnetism in a hard-core boson model,"The problem of ferromagnetism -- associated with a ground state with maximal
total spin -- is discussed in the framework of a hard-core model, which forbids
the occupancy at each site with more than one particle. It is shown that the
emergence of ferromagnetism on finite square lattices crucially depends on the
statistics of the particles. Fermions (electrons) lead to the well-known
instabilities for finite hole densities, whereas for bosons (with spin)
ferromagnetism appears to be stable for all hole densities.",0502384v1
2005-03-11,Ferromagnetic fluctuation and superconductivity in Na_0.35CoO_2*1.3H_2O: FLEX study of multi-orbital Hubbard model,"Spin and charge fluctuations and superconductivity in Na_0.35CoO_2*1.3H_2O
are studied based on a multi-orbital Hubbard model. By applying the fluctuation
exchange (FLEX) approximation, we show that the Hund's-rule coupling between
the Co t2g orbitals causes ferromagnetic spin fluctuation. Triplet pairing is
favored by this ferromagnetic fluctuation on the hole-pocket band. We propose
that, in Na_0.35CoO_2*1.3H_2O, Co t2g orbitals and inter-orbital Hund's-rule
coupling play important roles on the triplet pairing, and this compound can be
a first example of the triplet superconductor mediated by
inter-orbital-interaction-induced ferromagnetic fluctuation.",0503262v1
2005-04-14,Ferromagnetism and Curie temperature of Vanadium-doped Nitrides,"Electronic structures, exchange interaction mechanism between magnetic ions
and Curie temperature of Vanadium - doped Nitrides (AlN, GaN, and InN) are
studied within KKR-LSDA-CPA. It is found that the ferromagnetic super-exchange
interaction mechanism is dominant at low concentrations of Vanadium, but the
anti-ferromagnetic super-exchange interaction appears and reduces the
stabilization of ferromagnetism at sufficiently high concentrations (x > 0.10),
especially for Vanadium-doped AlN and Vanadium- doped GaN. The estimation of
the Curie temperature within the mean field approximation shows the Curie
temperature of Vanadium-doped Nitrides exceeding the room temperature with a
few constituents of Vanadium.",0504355v1
2005-05-30,"Comment on ""Domain Structure in a Superconducting Ferromagnet""","According to Faure and Buzdin [Phys. Rev. Lett. 94, 187202 (2005)], in a
superconducting ferromagnet a domain structure with a period small compared
with the London penetration depth can arise. They claim that this contradicts
to the conclusion of Sonin [Phys. Rev. B, 66, 100504 (2002)] that ferromagnetic
domain structure in the Meissner state of a superconducting ferromagnet is
absent in equilibrium. This contradiction is imaginary, based on
misinterpretation of the results of these two papers.",0505712v2
2005-06-21,Enhancement of spin stiffness with dilution in a ferromagnetic Kondo lattice model,"Carrier-induced ferromagnetism is investigated in a diluted ferromagnetic
Kondo lattice model for several ordered impurity arrangements on square and
cubic lattices, allowing for quantitative comparison with different theoretical
pictures. The spin stiffness is found to be optimized with respect to hole
doping concentration, exchange interaction strength, as well as spin dilution
due to a competition involving magnitude of carrier spin polarization and its
oscillation length scale. The ferromagnetic transition temperature determined
within the spin-fluctuation theory is in good agreement with experimental
values for $\rm Ga_{1-x}Mn_xAs$.",0506523v2
2005-07-05,300 K Ferromagnetic Magnetic Circular Dichroism in Co2+-doped ZnO Activated by Shallow Donors,"Cobalt-doped ZnO (Co2+:ZnO) films were studied by magnetic circular dichroism
(MCD) spectroscopy. A broad 300 K ferromagnetic MCD signal was observed between
1.4 and 4.0 eV after introducing shallow donor states by exposure of
paramagnetic Co2+:ZnO films to zinc vapor. The new sub-bandgap ferromagnetic
MCD intensity is attributed to low-energy photoionization transitions
originating from a spin-split donor impurity band in ferromagnetic Co2+:ZnO.",0507121v1
2005-07-25,Surface magnetic anisotropy at a compensated interface of ferromagnetic antiferromagnetic bilayer,"The periodic deviations of ferromagnetic and antiferromagnetic spins from
corresponding uniform configurations are shown to be energetically favorable
close to a compensated interface of ferromagnetic antiferromagnetic bilayer.
The amplitude of the deviations decreases exponentially into the film volumes
as a function of a coordinate perpendicular to the interface. The interaction
energy is found to be proportional to a square of a scalar product of unit
ferromagnetic and antiferromagnetic vectors.",0507578v1
2005-09-05,CeMnNi4: A soft ferromagnet with a high degree of transport spin polarization,"In this letter we introduce a new soft ferromagnetic compound, i.e. CeMnNi4,
which exhibits a large moment (~4.95mu_B/Mn) and high degree of spin
polarization. The system has a ferromagnetic transition temperature of 148K.
Isothermal magnetization measurements at 5K reveal that the material is a soft
ferromagnet with a magnetization saturating at about 500Oe and a coercive field
of < 5 Oe. We determine the transport spin polarization of this material from
Point Contact Andreev Reflection measurements to be 66% thereby making this
material potentially important for spintronic applications.",0509101v2
2005-10-24,Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors,"A close link between the charge transfer electronic structures and polarity
dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is
demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs
predicted from their charge transfer energies reproduce experimental trends
well. These results provide a unified basis for understanding both n- and
p-type ferromagnetic oxide DMSs.",0510644v1
2005-12-13,Doping change and distortion effect on double-exchange ferromagnetism,"Doping change and distortion effect on the double-exchange ferromagnetism are
studied within a simplified double-exchange model. The presence of distortion
is modelled by introducing the Falicov-Kimball interaction between itinerant
electrons and classical variables. By employing the dynamical mean-field theory
the charge and spin susceptibility are exactly calculated. It is found that
there is a competition between the double-exchange induced ferromagnetism and
disorder-order transition. At low temperature various long-range order phases
such as charge ordered and segregated phases coexist with ferromagnetism
depending on doping and distortion. A rich phase diagram is obtained.",0512265v1
2005-12-24,Low-temperature thermodynamics of one-dimensional alternating-spin Heisenberg ferromagnets,"Motivated by a novel bimetallic chain compound in which alternating magnetic
centers are ferromagnetically coupled, we investigate thermodynamic properties
of one-dimensional spin-$(S,s)$ Heisenberg ferromagnets both numerically and
analytically. On the one hand, quantum Monte Carlo calculations illuminate the
overall thermal behavior. The specific heat may exhibit a double-peaked
structure at intermediate temperatures for $S\agt 3s$ in general. On the other
hand, a modified spin-wave theory precisely describes the low-temperature
properties. Expanding the specific heat and the magnetic susceptibility, we
reveal an analogy and a contrast between mixed-spin ferromagnets and
ferrimagnets.",0512630v1
2006-04-28,Evidence for Carrier-Induced High-Tc Ferromagnetism in Mn-doped GaN film,"A GaN film doped with 8.2 % Mn was grown by the molecular-beam-epitaxy
technique. Magnetization measurements show that this highly Mn-doped GaN film
exhibits ferromagnetism above room temperature. It is also revealed that the
high-temperature ferromagnetic state is significantly suppressed below 10 K,
accompanied by an increase of the electrical resistivity with decreasing
temperature. This observation clearly demonstrates a close relation between the
ferromagnetism with extremely high-Tc and the carrier transport in the Mn-doped
GaN film.",0604647v1
2006-05-23,Evidence for Crossed Andreev Reflections in bilayers of (100)YBCO and the itinerant ferromagnet SrRuO3,"Scanning tunneling spectroscopy measurements on thin epitaxial
SrRuO3/(100)YBCO ferromagnet/superconductor bilayers, reveal localized regions
in which the superconductor order parameter penetrates the ferromagnet to more
than 26 nm, an order of magnitude larger than the coherence length in the
ferromagnetic layer. These regions consist of narrow (< 10 nm) and long strips,
separated by at least 200 nm, consistent with the known magnetic domain wall
structure in SrRuO3. We attributed this behavior to Crossed Andreev
Reflections, taking place in the vicinity of the magnetic domain walls.",0605573v1
2006-09-06,Stability of Ferromagnetism in Hubbard models on two-dimensional line graphs,"It is well known that the Hubbard model on a line graph has a flat band and
ferromagnetic ground states in a certain density range. We show that for a
Hubbard model on a line graph of a planar bipartite graph the ferromagnetic
ground state is stable if one adds a special contribution to the kinetic energy
which lifts the degeneracy of the lowest single particle state. Stability holds
for sufficiently strong repulsion U. The model has extended single particle
eigenstates, no degeneracy, and no band gap. It is therefore a good candidate
for metallic ferromagnetism.",0609142v2
2006-09-17,Universal conductance fluctuations in epitaxial GaMnAs ferromagnets: structural and spin disorder,"Mesoscopic transport measurements reveal a large effective phase coherence
length in epitaxial GaMnAs ferromagnets, contrary to usual 3d-metal
ferromagnets. Universal conductance fluctuations of single nanowires are
compared for epilayers with a tailored anisotropy. At large magnetic fields,
quantum interferences are due to structural disorder only, and an unusual
behavior related to hole-induced ferromagnetism is evidenced, for both quantum
interferences and decoherence. At small fields, phase coherence is shown to
persist down to zero field, even in presence of magnons, and an additional spin
disorder contribution to quantum interferences is observed under domain walls
nucleation.",0609410v1
2006-10-25,Domain-Wall Waves (2D Magnons) in Superconducting Ferromagnets,"Propagation of the magnetization waves along domain walls (2D magnons) in a
superconducting ferromagnet has been studied theoretically. The magnetostatic
fields (long-range dipole-dipole interaction) have a crucial effect on the
spectrum of 2D magnons. But this effect is essentially affected by the
superconducting Meissner currents, which screen the magnetostatic fields and
modify the long-wavelength spectrum from square-root to linear. The excitation
of the domain wall waves by an electromagnetic wave incident on a
superconducting-ferromagnet sample has been considered. This suggests using
measurements of the surface impedance for studying the domain wall waves, and
eventually for effective probing of superconductivity-ferromagnetism
coexistence.",0610699v1
2006-12-10,Nonequilibrium Transport in Superconductor/Ferromagnet/Superconductor Diffusive Junctions: Interplay between Proximity Effect and Ferromagnetism,"The theory of the I-V characteristics in diffusive superconductor/weak
ferromagnet/superconductor (SFS) junction is developed. We show that the
exchange field $h$ of the ferromagnet manifests itself as an additional
conductance peak at $eV \sim \Delta+h$ in the phase-coherent regime, when the
Thouless energy is of the order of superconducting order parameter. The excess
current exhibits non-monotonous dependence on the exchange field and
non-trivial temperature behavior, which is strongly influenced by the
temperature dependence of the exchange field.",0612239v1
2007-01-27,Spin blockade at semiconductor/ferromagnet junctions,"We study theoretically extraction of spin-polarized electrons at nonmagnetic
semiconductor/ferromagnet junctions. The outflow of majority spin electrons
from the semiconductor into the ferromagnet leaves a cloud of minority spin
electrons in the semiconductor region near the junction, forming a local
spin-dipole configuration at the semiconductor/ferromagnet interface. This
minority spin cloud can limit the majority spin current through the junction
creating a pronounced spin-blockade at a critical current. We calculate the
critical spin-blockade current in both planar and cylindrical geometries and
discuss possible experimental tests of our predictions.",0701678v2
2007-02-12,Crystalline phases in chiral ferromagnets: Destabilization of helical order,"In chiral ferromagnets, weak spin-orbit interactions twist the ferromagnetic
order into spirals, leading to helical order. We investigate an extended
Ginzburg-Landau theory of such systems where the helical order is destabilized
in favor of crystalline phases. These crystalline phases are based on periodic
arrangements of double-twist cylinders and are strongly reminiscent of blue
phases in liquid crystals. We discuss the relevance of such blue phases for the
phase diagram of the chiral ferromagnet MnSi.",0702287v2
2007-02-17,Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co,"We report on the magnetic properties of thoroughly characterized Zn1-xCoxO
epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and
EPR measurements, combined with crystal field theory, reveal that isolated Co2+
ions in ZnO possess a strong single ion anisotropy which leads to an ""easy
plane"" ferromagnetic state when the ferromagnetic Co-Co interaction is
considered. We suggest that the peculiarities of the magnetization process of
this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co
materials.",0702410v1
2007-02-21,Enhancement of ferromagnetism upon thermal annealing in pure ZnO,"We report here enhancement of ferromagnetism in pure ZnO upon thermal
annealing with the ferromagnetic transition temperature Tc above room
temperature. We observe a finite coercive field upto 300K and a finite
thermoremanent magnetization upto 340K for the annealed sample. We propose that
magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur
due to either superexchange between vacancy clusters via isolated F+ centers,
or through a limited electron delocalization between vacancy clusters. Isolated
vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like
behaviour below 10K.",0702486v3
2003-09-08,Color Ferromagnetism of Quark Matter and Quantum Hall States of Gluons in SU(3) Gauge Theory,"We show a possibility that a color ferromagnetic state exists in SU(3) gauge
theory of quark matter with two flavors. Although the state involves three
types of unstable modes of gluons, all of these modes are stabilized by forming
a quantum Hall state of one of the modes. We also show that at large chemical
potential, a color superconducting state (2SC) appears even in the
ferromagnetic state. This is because Meissner effect by condensed anti-triplet
quark pairs does not work on the magnetic field in the ferromagnetic state.",0309066v1
2004-08-11,A Ferromagnetic Lieb-Mattis Theorem,"We prove ferromagnetic ordering of energy levels for XXX Heisenberg chains of
any spin and XXZ spin chains with all spins equal to 1/2. Ferromagnetic
ordering means that the minimum energies in the invariant subspaces of fixed
total spin are monotone decreasing as a function of the total spin. This result
provides a ferromagnetic analogue of the well-known theorem by Lieb and Mattis
about ordering of energy levels in antiferromagnetic and ferrimagnetic systems
on bipartite graphs.",0408020v3
2003-01-31,Competition of ferromagnetic and antiferromagnetic spin ordering in nuclear matter,"In the framework of a Fermi liquid theory it is considered the possibility of
ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear
matter with Skyrme effective interaction. The zero temperature dependence of
ferromagnetic and antiferromagnetic spin polarization parameters as functions
of density is found for SkM$^*$, SGII effective forces. It is shown that in the
density domain, where both type of solutions of self--consistent equations
exist, ferromagnetic spin state is more preferable than antiferromagnetic one.",0301101v1
2004-11-17,Universality in the entanglement structure of ferromagnets,"Systems of exchange-coupled spins are commonly used to model ferromagnets.
The quantum correlations in such magnets are studied using tools from quantum
information theory. Isotropic ferromagnets are shown to possess a universal
low-temperature density matrix which precludes entanglement between spins, and
the mechanism of entanglement cancellation is investigated, revealing a core of
states resistant to pairwise entanglement cancellation. Numerical studies of
one-, two-, and three-dimensional lattices as well as irregular geometries
showed no entanglement in ferromagnets at any temperature or magnetic field
strength.",0411125v2
1996-03-27,Ferromagnetic ground states of the Hubbard model on a complete graph,"We use group theory to derive the exact analytical expression of the
ferromagnetic ground states of the Hubbard model on a complete graph for
arbitrary lattice sites f and for arbitrary fillings $N$. We find that for
$t>0$ and for $N=f+1$ the ground state is maximally ferromagnetic with total
spin $S=(f-1)/2$. For $N > f+1$ the ground state is still ferromagnetic but
becomes degenerate with respect to $S$.",9603008v1
2007-04-30,Spectroscopy and critical temperature of diffusive superconducting/ferromagnetic hybrid structures with spin-active interfaces,"The description of the proximity effect in superconducting/ferromagnetic
heterostructures requires to use spin-dependent boundary conditions. Such
boundary conditions must take into account the spin dependence of the phase
shifts acquired by electrons upon scattering on the boundaries of ferromagnets.
The present article shows that this property can strongly affect the critical
temperature and the energy dependence of the density of states of diffusive
heterostructures. These effects should allow a better caracterisation of
diffusive superconductor/ferromagnet interfaces.",0704.3975v3
2007-05-23,Role of long range ferromagnetic order in the electronic structure of Sr$_{1-x}$Ca$_x$RuO$_3$,"We investigate the role of long range ferromagnetic order in the electronic
structure of Sr$_{1-x}$Ca$_x$RuO$_3$ using high resolution photoemission
spectroscopy. SrRuO$_3$ is a ferromagnetic metal but isostructural,
isoelectronic CaRuO$_3$ is an enhanced paramagnet. Surface spectra of CaRuO$_3$
exhibit temperature induced modifications. This is not significant in other
compositions. This may be attributed to the structural changes observed in
previous studies. Interestingly, the bulk spectra reveal unusual spectral
changes exhibiting large decrease in the coherent feature intensity
corresponding to only ferromagnetic samples, although the Ru moment is very
similar in all the compositions.",0705.3299v1
2007-06-05,Room-temperature ferromagnetism in nanoparticles of superconducting materials,"Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.",0706.0634v1
2007-06-30,Zooming into the coexisting regime of ferromagnetism and superconductivity in ErRh4B4 single crystals,"High resolution measurements of the dynamic magnetic susceptibility are
reported for ferromagnetic re-entrant superconductor, ErRh$_{4}$B$_{4}$.
Detailed investigation of the coexisting regime reveals unusual
temperature-asymmetric and magnetically anisotropic behavior. The
superconducting phase appears via a series of discontinuous steps upon warming
from the ferromagnetic normal phase, whereas the ferromagnetic phase develops
via a gradual transition. A model based on local field inhomogeneity is
proposed to explain the observations.",0707.0029v1
2007-07-22,Magnetic State Modification Induced by Superconducting Response in Ferromagnet/Superconductor Hybrids,"Magnetization measurements in superconductor/ferromagnet Nb/Co superlattices
show a complex behavior as a function of temperature, applied field and sample
history. In base to a simple model it is shown that this behavior is due to an
interplay between the superconductor magnetization temperature dependence, the
ferromagnet magnetization time dependence, and the stray fields of both
materials. It is also shown that the magnetic state of the Co layers is
modified by the Nb superconducting response, implying that the problem of a
superconductor/ferromagnetic heterogeneous sample has to be solved in a
self-consistent manner.",0707.3265v1
2007-08-13,Spin valve effect by ballistic transport in ferromagnetic metal (MnAs) / semiconductor (GaAs) hybrid heterostructures,"We demonstrate the spin valve effect by ballistic transport in fully
epitaxial MnAs ferromagnetic metal / GaAs semiconductor / GaAs:MnAs granular
hybrid heterostructures. The GaAs:MnAs material contains ferromagnetic MnAs
nanoparticles in a GaAs matrix, and acts as a spin injector and a spin
detector. Although the barrier height of the GaAs/MnAs interface was found to
be very small, relatively large magnetoresistance was observed. This result
shows that by using ballistic transport, we can realize a large spin valve
effect without inserting a high tunnel barrier at the ferromagnetic metal /
semiconductor interface.",0708.1681v1
2007-08-23,Current-induced torques due to compensated antiferromagnets,"We analyse the influence of current induced torques on the magnetization
configuration of a ferromagnet in a circuit containing a compensated
antiferromagnet. We argue that these torques are generically non-zero and
support this conclusion with a microscopic NEGF calculation for a circuit
containing antiferromagnetic NiMn and ferromagnetic Co layers. Because of
symmetry dictated differences in the form of the current-induced torque, the
phase diagram which expresses the dependence of ferromagnet configuration on
current and external magnetic field differs qualitatively from its
ferromagnet-only counterpart.",0708.3231v1
2007-08-24,Enhancement of the Gilbert damping constant due to spin pumping in noncollinear ferromagnet/nonmagnet/ferromagnet trilayer systems,"We analyzed the enhancement of the Gilbert damping constant due to spin
pumping in non-collinear ferromagnet / non-magnet / ferromagnet trilayer
systems. We show that the Gilbert damping constant depends both on the
precession angle of the magnetization of the free layer and on the direction of
the magntization of the fixed layer. We find the condition to be satisfied to
realize strong enhancement of the Gilbert damping constant.",0708.3323v1
2007-09-12,Two Ferromagnetic Phases in Spin-Fermion Systems,"We consider spin-fermion systems which get their magnetic properties from a
system of localized magnetic moments being coupled to conducting electrons. The
dynamical degrees of freedom are spin-$s$ operators of localized spins and
spin-1/2 fermi operators of itinerant electrons. We develop modified spin-wave
theory and obtain that system has two ferromagnetic phases. At the
characteristic temperature T* the magnetization of itinerant electrons becomes
zero, and high temperature ferromagnetic phase (T*<T<T_C) is a phase where only
localized electrons give contribution to the magnetization of the system. An
anomalous increasing of magnetization below T* is obtained in a good agrement
with experimental measurements of the ferromagnetic phase of UGe2.",0709.1759v2
2007-10-29,Thermoelectrical manipulation of nano-magnets,"We propose a device that can operate as a magneto-resistive switch or
oscillator. The device is based on a spin-thermo-electronic control of the
exchange coupling of two strong ferromagnets through a weakly ferromagnetic
spacer. We show that the local Joule heating due to a high concentration of
current in a magnetic point contact or a nanopillar can be used to reversibly
drive the weak ferromagnet through its Curie point and thereby
exchange-decouple the strongly ferromagnetic layers, which have an antiparallel
ground state. Such a spin-thermionic parallel-to-antiparallel switching causes
magnetoresistance oscillations where the frequency can be controlled by proper
biasing from essentially DC to GHz.",0710.5477v1
2007-11-05,Low density ferromagnetism in biased bilayer graphene,"We compute the phase diagram of a biased graphene bilayer. The existence of a
ferromagnetic phase is discussed with respect both to carrier density and
temperature. We find that the ferromagnetic transition is first order, lowering
the value of $U$ relatively to the usual Stoner criterion. We show that in the
ferromagnetic phase the two planes have unequal magnetization and that the
electronic density is hole like in one plane and electron like in the other.",0711.0758v2
2007-12-30,Lecture Notes on Semiconductor Spintronics,"These informal lecture notes describe the progress in semiconductor
spintronics in a historic perspective as well as in a comparison to
achievements of spintronics of ferromagnetic metals. After outlining
motivations behind spintronic research, selected results of investigations on
three groups of materials are presented. These include non-magnetic
semiconductors, hybrid structures involving semiconductors and ferromagnetic
metals, and diluted magnetic semiconductors either in paramagnetic or
ferromagnetic phase. Particular attention is paid to the hole-controlled
ferromagnetic systems whose thermodynamic, micromagnetic, transport, and
optical properties are described in detail together with relevant theoretical
models.",0801.0145v1
2008-02-27,"Ferromagnetic to spin glass cross over in (La,Tb)_{2/3}Ca_{1/3}MnO_{3}","In the series La_{2/3-x}Tb_{x}Ca_{1/3}MnO_{3}, it is known that the
compositions are ferromagnetic for smaller values of x and show spin glass
characteristics at larger values of x. Our studies on the magnetic properties
of various compositions in the La_{2/3-x}Tb_{x}Ca_{1/3}MnO_{3} series show that
the cross over from ferromagnetic to spin glass region takes place above x ~
1/8. Also, a low temperature anomaly at 30 K, observed in the ac susceptibility
curves, disappears for compositions above this critical value of x. A mixed
phase region coexists in the narrow compositional range 0.1 <= x <= 0.125,
indicating that the ferromagnetic to spin glass cross over is not abrupt.",0802.4009v1
2008-03-14,Spin-torque shot noise in magnetic tunnel junctions,"Spin polarized current may transfer angular momentum to a ferromagnet,
resulting in a spin-torque phenomenon. At the same time the shot noise,
associated with the current, leads to a non-equilibrium stochastic force acting
on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert
equation for a magnetization of a ''free'' ferromagnetic layer in contact with
a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and
show that the non-equilibrium noise yields to a non-monotonous dependence of
the precession spectrum linewidth on the current.",0803.2101v1
2008-03-14,Current-induced noise and damping in non-uniform ferromagnets,"In the presence of spatial variation of the magnetization direction, electric
current noise causes a fluctuating spin-transfer torque that increases the
fluctuations of the ferromagnetic order parameter. By the
fluctuation-dissipation theorem, the equilibrium fluctuations are related to
the magnetization damping, which in non-uniform ferromagnets acquires a
nonlocal tensor structure. In biased ferromagnets, shot noise can become the
dominant contribution to the magnetization noise at low temperatures.
Considering spin spirals as a simple example, we show that the current-induced
noise and damping is significant.",0803.2175v1
2008-03-18,Superconductivity in a model of two Hubbard chains coupled with ferromagnetic exchange interaction,"We study the ground-state properties of the double-chain Hubbard model
coupled with ferromagnetic exchange interaction by using the weak-coupling
theory, density-matrix renormalization group technique, and Lanczos
exact-diagonalization method. We determine the ground-state phase diagram in
the parameter space of the ferromagnetic exchange interaction and band filling.
We find that, in high electron density regime, the spin gap opens and the
spin-singlet $d_{xy}$-wave-like pairing correlation is most dominant, whereas
in low electron density regime, the fully-polarized ferromagnetic state is
stabilized where the spin-triplet $p_{y}$-wave-like pairing correlation is most
dominant.",0803.2590v1
2008-03-27,Current-induced persistent magnetization in a relaxorlike manganite,"A single crystal of 7% Fe-doped
(La$_{0.7}$Pr$_{0.3}$)$_{0.65}$Ca$_{0.35}$MnO$_3$ shows up as a typical relaxor
ferromagnet, where ferromagnetic metallic and charge-orbital-ordered insulating
clusters coexist with controllable volume fraction by external stimuli. There,
the persistent ferromagnetic metallic state can be produced by an
electric-current excitation as the filamentary region, the magnetization in
which is increased by ~0.4$\mu_{\rm B}$ per Mn. A clear distinction from the
current heating effect in a magnetic field, which conversely leads to a
decrease in ferromagnetic fraction, enables us to bi-directionally switch both
the magnetization and resistance by applying the voltages with different
magnitudes.",0803.3922v1
2008-05-24,Role of charge carriers for ferromagnetism in cobalt-doped rutile TiO2,"Electric and magnetic properties of a high temperature ferromagnetic oxide
semiconductor, cobalt-doped rutile TiO2, are summarized. The cobalt-doped
rutile TiO2 epitaxial thin films with different electron densities and cobalt
contents were grown on r-sapphire substrates with laser molecular beam epitaxy.
Results of magnetization, magnetic circular dichroism, and anomalous Hall
effect measurements were examined for samples with systematically varied
electron densities and cobalt contents. The samples with high electron
densities and cobalt contents show the high temperature ferromagnetism,
suggesting that charge carriers induce the ferromagnetism.",0805.3748v1
2008-08-18,Canted Magnetization Texture in Ferromagnetic Tunnel Junctions,"We study the formation of inhomogeneous magnetization texture in the vicinity
of a tunnel junction between two ferromagnetic wires nominally in the
antiparallel configuration and its influence on the magnetoresistance of such a
device. The texture, dependent on magnetization rigidity and crystalline
anisotropy energy in the ferromagnet, appears upon an increase of ferromagnetic
inter-wire coupling above a critical value and it varies with an external
magnetic field.",0808.2358v1
2008-10-07,Thermodynamic properties of the itinerant-boson ferromagnet,"Thermodynamics of a spin-1 Bose gas with ferromagnetic interactions are
investigated via the mean-field theory. It is apparently shown in the specific
heat curve that the system undergoes two phase transitions, the ferromagnetic
transition and the Bose-Einstein condensation, with the Curie point above the
condensation temperature. Above the Curie point, the susceptibility fits the
Curie-Weiss law perfectly. At a fixed temperature, the reciprocal
susceptibility is also in a good linear relationship with the ferromagnetic
interaction.",0810.1094v1
2008-10-17,Ferromagnetic Spin Coupling as the Origin of 0.7 Anomaly in Quantum Point Contacts,"We study one-dimensional itinerant electron models with ferromagnetic
coupling to investigate the origin of 0.7 anomaly in quantum point contacts.
Linear conductance calculations from the quantum Monte Carlo technique for spin
interactions of different spatial range suggest that $0.7(2e^{2}/h)$ anomaly
results from a strong interaction of low-density conduction electrons to
ferromagnetic fluctuations formed across the potential barrier. The conductance
plateau appears due to the strong incoherent scattering at high temperature
when the electron traversal time matches the time scale of dynamic
ferromagnetic excitations.",0810.3206v2
2008-10-22,Itinerant Ferromagnetism in the electronic localization limit,"We present Hall effect, $R_{xy}(H)$, and magnetoresistance, $R_{xx}(H)$,
measurements of ultrathin films of Ni, Co and Fe with thicknesses varying
between 0.2-8 nm and resistances between 1 M$\Omega$ - 100 $\Omega.$ Both
measurements show that films having resistance above a critical value, $R_{C}$,
(thickness below a critical value, $d_{C}$) show no signs for ferromagnetism.
Ferromagnetism appears only for films with $R<R_{C}$, where $R_{C}$ is material
dependent. We raise the possibility that the reason for the absence of
spontaneous magnetization is suppression of itinerant ferromagnetism by
electronic disorder in the strong localization regime.",0810.4081v2
2008-11-03,Critical thickness for itinerant ferromagnetism in ultrathin films of SrRuO$_3$,"Ultrathin films of the itinerant ferromagnet SrRuO$_3$ were studied using
transport and magnto-optic polar Kerr effect. We find that below 4 monolayers
the films become insulating and their magnetic character changes as they loose
their simple ferromagnetic behavior. We observe a strong reduction in the
magnetic moment which for 3 monolayers and below lies in the plane of the film.
Exchange-bias behavior is observed below the critical thickness, and may point
to induced antiferromagnetism in contact with ferromagnetic regions.",0811.0384v1
2008-11-26,Spin-Valve Effect of the Spin Accumulation Resistance in a Double Ferromagnet - Superconductor Junction,"We have measured the transport properties of Ferromagnet - Superconductor
nanostructures, where two superconducting aluminum (Al) electrodes are
connected through two ferromagnetic iron (Fe) ellipsoids in parallel. We find
that, below the superconducting critical temperature of Al, the resistance
depends on the relative alignment of the ferromagnets' magnetization. This
spin-valve effect is analyzed in terms of spin accumulation in the
superconducting electrode submitted to inverse proximity effect.",0811.4252v2
2008-11-26,Anomalous Ferromagnetism in TbMnO3 Thin Films,"Magnetometry, x-ray, and neutron scattering have been used to study the
structural and magnetic properties of a TbMnO3 thin film grown on a [001]
SrTiO3 substrate by pulsed laser deposition. Although bulk TbMnO3 is a low
temperature antiferromagnet, magnetometry measurements indicate the presence of
low temperature ferromagnetism. Depth profiling by x-ray and polarized neutron
reflectometry reveals a net sample magnetization that is commensurate with the
film thickness, indicating that the observed ferromagnetism is not due to an
altered surface phase (such as Mn3O4), or external impurities that might give
rise to an artificial magnetic signal. Instead, these results show that the
ferromagnetism is an intrinsic property of the TbMnO3 film.",0811.4430v1
2009-03-10,Amplification of the induced ferromagnetism in diluted magnetic semiconductor,"Magnetic properties of the planar structure consisting of a ferromagnetic
metal and the diluted magnetic semiconductor are considered (by the example of
the structure Fe/Ga(Mn)As, experimentally studied in [F. Maccherozzi, e.a.,
Phys. Rev. Lett., 101, 267201 (2008)]). In the framework of the mean field
theory, we demonstrate the presence of the significant amplification of the
ferromagnetism, induced by the ferromagnetic metal in the near-interface
semiconductor area, due to the indirect interaction of magnetic impurities.
This results in the substantial expansion of the temperature range where the
magnetization in the boundary semiconductor region exists, that might be
important for possible practical applications.",0903.1726v1
2009-03-28,Magnetic structure and charge ordering in Fe3BO5 ludwigite,"The crystal and magnetic structures of the three-leg ladder compound Fe3BO5
have been investigated by single crystal x-ray diffraction and neutron powder
diffraction. Fe3BO5 contains two types of three-leg spin ladders. It shows a
charge ordering transition at 283 K, an antiferromagnetic transition at 112 K,
ferromagnetism below 70 K and a weak ferromagnetic behavior below 40K. The
x-ray data reveal a smooth charge ordering and an incomplete charge
localization down to 110K. Below the first magnetic transition, the first type
of ladders orders as ferromagnetically coupled antiferromagnetic chains, while
below 70K the second type of ladders orders as antiferromagnetically coupled
ferromagnetic chains.",0903.4945v1
2009-08-12,Evolution of critical scaling behavior near a ferromagnetic quantum phase transition,"Magnetic critical scaling in URu2-xRexSi2 single crystals continuously
evolves as the ferromagnetic critical temperature is tuned towards zero via
chemical substitution. As the quantum phase transition is approached, the
critical exponents gamma and (delta-1) decrease to zero in tandem with the
critical temperature and ordered moment, while the exponent beta remains
constant. This novel trend distinguishes URu2-xRexSi2 from stoichiometric
quantum critical ferromagnets and appears to reflect an underlying competition
between Kondo and ferromagnetic interactions.",0908.1809v1
2009-08-21,Spin-transfer torque in disordered weak ferromagnets,"We study theoretically the spin transfer effect on a domain wall in
disordered weak ferromagnets. We have identified the adiabatic condition for
the disordered case as $\lambda \gg \lambda_{\rm D}\equiv \sqrt{{\hbar
D}/{\spol}}$, where $D$ and $\spol$ are the diffusion constant and the spin
splitting energy due to the $s$-$d$ type exchange interaction, respectively,
and found out that perfect spin-transfer effect occurs even in weak
ferromagnets as long as this condition is satisfied. The effective $\beta$ term
arising from the force turns out to govern the wall dynamics, and therefore,
the wall motion can be as efficient as in strong ferromagnets even if $\spol$
is small.",0908.3048v1
2010-01-30,Exchange coupling and magnetoresistance in CoFe/NiCu/CoFe spin-valves near the Curie point of the spacer,"Thermal control of exchange coupling between two strongly ferromagnetic
layers through a weakly ferromagnetic Ni-Cu spacer and the associated
magnetoresistance is investigated. The spacer, having a Curie point slightly
above room temperature, can be cycled between its paramagnetic and
ferromagnetic states by varying the temperature externally or using joule
heating. It is shown that the giant magnetoresistance vanishes due to a strong
reduction of the mean free path in the spacer at above ~30 % Ni concentration
-- before the onset of ferromagnetism. Finally, a device is proposed and
demonstrated which combines thermally controlled exchange coupling and large
magnetoresistance by separating the switching and the read out elements.",1002.0090v1
2010-04-26,High-temperature spin polarization of high-mobility charge carriers in hybrid metal-semiconductor structures,"We consider magnetic properties of the planar structure consisting of a
ferromagnetic metal, diluted magnetic semiconductor and the quantum well (by
the example of the hybrid heterostructure Fe--Ga(Mn)As--InGaAs). In the
framework of the mean-field theory, there is the significant amplification of
the ferromagnetism induced by the ferromagnetic metal (Fe) in the system of
magnetic impurities (Mn) due to their indirect interaction via the conductivity
channel in the quantum well. As a result, the high-temperature ferromagnetism
arises leading to the spin polarization of charge carriers (holes) localized in
the quantum well and preserving their high mobility.",1004.4425v1
2010-06-19,Intrinsic Ferromagnetism in Eu doped ZnO,"We report room temperature ferromagnetism in as-implanted Eu doped ZnO
(ZnO:Eu). To address the origin of ferromagnetism ab initio calculations of
ZnO:Eu system are performed. Results show that the ferromagnetism is induced by
ZnO point defects as Eu ions in perfect ZnO tend to align
antiferromagnetically.",1006.3856v1
2010-07-11,Robust half-metallic ferromagnet of cubic VGe3Si4,"To seek half-metallic ferromagnets compatible with the GeSi semiconductor, we
use state-of-the-art density-functional-theory methods to study cubic
$\mathrm{VGe_3Si_4}$. After optimizing its crystal structure with various
magnetic orders considered, we find the ferromagnetic structure is the ground
state phase and investigate its stability, and then study its spin-resolved
electronic structure with an improved method. Our calculated results show that
the cubic $\mathrm{VGe_3Si_4}$ is a half-metallic ferromagnet with
half-metallic gap 350 meV, and it is structurally stable against deformations
and magnetically robust against antiferromagnetic fluctuations. These results
make us believe that the cubic $\mathrm{VGe_3Si_4}$ could be synthesized as
good thin films soon and used in practical spintronic devices.",1007.1774v1
2010-07-30,Diamagnetic susceptibility of spin-triplet ferromagnetic superconductors,"We calculate the diamagnetic susceptibility in zero external magnetic field
above the phase transition from ferromagnetic phase to phase of coexistence of
ferromagnetic order and unconventional superconductivity. For this aim we use
generalized Ginzburg-Landau free energy of unconventional ferromagnetic
superconductor with spin-triplet electron pairing. A possible application of
the result to some intermetallic compounds is briefly discussed.",1007.5432v3
2010-11-16,Ferromagnetism in Dilute Magnetic Semiconductors,"We study the ferromagnetism of Ga1-xMnxAs by using a model Hamiltonian, based
on an impurity band and the anti-ferromagnetic exchange interaction between the
spins of Mn atoms and the charge carriers in the impurity band. Based on the
mean field approach we calculate the spontaneous magnetization as a function of
temperature and the ferromagnetic transition temperature as a function of the
Mn concentration. The random distribution of Mn impurities is taken into
account by Matsubara and Toyozawa theory of impurities in semiconductors. We
compare our results with experiments and other theoretical findings.",1011.3658v1
2011-07-29,Coexistence of Ferromagnetism and Superconductivity in Noncentrosymmetric Materials with Cubic Symmetry,"This is a model study for the emergence of superconductivity in
ferromagnetically ordered phases of cubic materials whose crystal structure
lacks inversion symmetry. A Ginzburg-Landau-type theory is used to find the
ferromagnetic state and to determine the coupling of magnetic order to
superconductivity. It is found that noncentrosymmetricity evokes a helical
magnetic phase. If the wavelength of the magnetic order is long enough, it
gives rise to modulations of the order parameter of superconductivity, both in
modulus and complex phase. At magnetic domain walls the nucleation of
superconductivity is found to be suppressed as compared to the interior of
ferromagnetic domains.",1107.5954v2
2011-08-05,Ferromagnetic spin coupling of 2p-impurities in band insulators stabilized by intersite Coulomb interaction: Nitrogen-doped MgO,"For a nitrogen dimer in insulating MgO, a ferromagnetic coupling between
spin-polarized $2p$-holes is revealed by calculations based on the density
functional theory amended by an on-site Coulomb interaction and corroborated by
the Hubbard model. It is shown that the ferromagnetic coupling is facilitated
by a T-shaped orbital arrangement of the $2p$-holes, which is in its turn
controlled by an intersite Coulomb interaction due to the directionality of the
$p$-orbitals. We thus conjecture that this interaction is an important
ingredient of ferromagnetism in band insulators with $2p$ dopants.",1108.1294v1
2011-08-12,Ferromagnetism in semiconductors and oxides: prospects from a ten years' perspective,"Over the last decade the search for compounds combining the resources of
semiconductors and ferromagnets has evolved into an important field of
materials science. This endeavour has been fuelled by continual demonstrations
of remarkable low-temperature functionalities found for ferromagnetic
structures of (Ga,Mn)As, p-(Cd,Mn)Te, and related compounds as well as by ample
observations of ferromagnetic signatures at high temperatures in a number of
non-metallic systems. In this paper, recent experimental and theoretical
developments are reviewed emphasising that, from the one hand, they disentangle
many controversies and puzzles accumulated over the last decade and, on the
other, offer new research prospects.",1108.2582v1
2011-09-13,Large Magnetoresistance Effects in $Ln$CoAsO with a Ferromagnetic-Antiferromagnetic Transition,"A large magnetoresistance (MR) effect was observed in the layered compounds
NdCoAsO and SmCoAsO, in which ferromagnetically ordered itinerant-electrons of
Co are sandwiched by localized 4$f$-electrons of $Ln^{3+}$, below
ferromagnetic-antiferromagnetic transition (FAFT) temperature $T_\mathrm{N}$ as
observed in other FAFT compounds. In SmCoAsO, the large MR effect is also
observed up to the Curie temperature $T_\mathrm{C}$, and it is found to be
originating in the presence of another antiferromagnetic phase in the
low-magnetic field region of the ferromagnetic phase.",1109.2730v2
2011-10-06,Ferromagnetism in YbCu2Si2 at high pressure,"We demonstrate from detailed ac-susceptibility and calorimetry studies under
hydrostatic pressure that YbCu2Si2 probably orders ferromagnetically at high
pressure. The (p,H,T) phase diagram, shows that the transition temperature
increases with pressure, but also with an applied magnetic field. We suggest
that many ytterbium systems may show a trend towards ferromagnetism and we
discuss the possible reasons for this. We also examine the implications,
including the potential of YbCu2Si2 and other Yb compounds for further studies
of the rich physical properties that may occur near a ferromagnetic critical
point.",1110.1278v1
2012-08-06,Interference phenomena and long - range proximity effect in clean superconductor -- ferromagnet systems,"We study peculiarities of proximity effect in clean superconductor --
ferromagnet structures caused by either spatial or momentum dependence of the
exchange field. Even a small modulation of the exchange field along the
quasiparticle trajectories is shown to provide a long range contribution to the
supercurrent due to the specific interference of particle- and hole- like wave
functions. The momentum dependence of the exchange field caused by the spin --
orbit interaction results in the long -- range superconducting correlations
even in the absence of ferromagnetic domain structure and can explain the
recent experiments on ferromagnetic nanowires.",1208.1089v1
2012-08-28,Triplet supercurrent in ferromagnetic Josephson junctions by spin injection,"We show that injecting nonequilibrium spins into the superconducting leads
strongly enhances the stationary Josephson current through a
superconductor-ferromagnet-superconductor junction. The resulting long-range
super-current through a ferromagnet is carried by triplet Cooper pairs that are
formed in s-wave superconductors by the combined effects of spin injection and
exchange interaction. We quantify the exchange interaction in terms of Landau
Fermi-liquid factors. The magnitude and direction of the long-range Josephson
current can be manipulated by varying the angles of the injected polarizations
with respect to the magnetization in the ferromagnet.",1208.5629v1
2012-11-13,About the two spin-channel model for ferromagnetic excitations and spin-dependent heat transfer equations,"The two spin-channel model is generalized to the case of transport of
ferromagnetic excitations in electric conductors and insulators. The two
channels are defined by reducing the ferromagnetic degrees of freedom to a
bivaluated variable, i.e. to an effective spin one-half. The reduction is
performed after defining the local magnetic configuration space by a sphere
$\Sigma_x$, and integrating the relevant physical quantities over the two
hemispheres $\Sigma_x^{\uparrow}$ and $\Sigma_x^{\downarrow}$. The
configuration space is then extended to the $x$ direction for non-uniform
magnetization excitations. The transport equations for both magnetic moments
and magnetic energy are deduced, including the relaxation from one channel to
the other. The heat transport equations for ferromagnets is deduced.",1211.3033v1
2013-01-04,Ferromagnetic bubble clusters in Y$_{0.67}$Ca$_{0.33}$MnO$_3$ thin films,"We studied the ferromagnetic topology in a Y$_{0.67}$Ca$_{0.33}$MnO$_3$ thin
film with a combination of magnetic force microscopy and magnetization
measurements. Our results show that the spin-glass like behavior, reported
previously for this system, could be attributed to frustrated interfaces of the
ferromagnetic clusters embedded in a non-ferromagnetic matrix. We found
temperature dependent changes of the magnetic topology at low temperatures,
which suggests a non-static Mn$^{3+}$/Mn$^{4+}$ ratio.",1301.0678v1
2013-01-18,Field-Free Synthetic-Ferromagnet Spin Torque Oscillator,"We study the magnetization dynamics of spin valve structures with a free
composite synthetic ferromagnet (SyF) that consists of two ferromagnetic layers
coupled through a normal metal spacer. A ferromagnetically coupled SyF can be
excited into dynamical precessional states by an applied current without
external magnetic fields. We analytically determine the stability of these
states in the space spanned by the current density and SyF interlayer exchange
coupling. Numerical simulations confirm our analytical results.",1301.4294v1
2013-02-18,Ferromagnetic planar Josephson junction with transparent interfaces: a φ junction proposal,"We calculate the current phase relation of a planar Josephson junction with a
ferromagnetic weak link located on top of a thin normal metal film. Following
experimental observations we assume transparent superconductor-ferromagnet
interfaces. This provides the best interlayer coupling and a low suppression of
the superconducting correlations penetrating from the superconducting
electrodes into the ferromagnetic layer. We show that this Josephson junction
is a promising candidate for an experimental {\phi} junction realization.",1302.4398v2
2013-04-18,Spontaneous ferromagnetism in the spinor Bose gas with Rashba spin-orbit coupling,"We show that in the two-component Bose gas with Rashba spin-orbit coupling an
arbitrarily small attractive interaction between bosons with opposite spin
induces spontaneous ferromagnetism below a finite critical temperature $T_c$.
In the ferromagnetic phase the single-particle spectrum exhibits a unique
minimum in momentum space in the direction of the magnetization. For
sufficiently small temperatures below $T_c$ the bosons eventually condense into
the unique state at the bottom of the spectrum, forming a ferromagnetic
Bose-Einstein condensate.",1304.5103v2
2013-06-05,Field-induced ferromagnetism in one-dimensional tight-binding lattices,"We theoretically show the possibility to induce magnetic ordering in
non-magnetic one-dimensional systems of strongly interacting electrons hopping
on a tight-binding lattice. Our analysis is provided within the framework of
the t1-t2 Hubbard Model, assuming non-zero second neighbor hopping rate. It is
shown that a high-frequency electric field can be exploited to induce
artificial ferromagnetism and eventually control
anti-ferromagnetic/ferromagnetic phase transition. Our analysis is validated by
numerical simulations in a low-density system of 2-particles on a lattice with
11 sites.",1306.1044v1
2013-06-05,Inertial longitudinal magnetization reversal for non-Heisenberg ferromagnets,"We analyze theoretically the novel pathway of ultrafast spin dynamics for
ferromagnets with high enough single-ion anisotropy (non-Heisenberg
ferromagnets). This longitudinal spin dynamics includes the coupled
oscillations of the modulus of the magnetization together with the quadrupolar
spin variables, which are expressed through quantum expectation values of
operators bilinear on the spin components. Even for a simple single-element
ferromagnet, such a dynamics can lead to an inertial magnetization reversal
under the action of an ultrashort laser pulse.",1306.1108v2
2013-07-24,Phase transitions in 2D $J_{1}-J_{2}$ model with arbitrary signs of exchange interactions,"The ground state of the $S=1/2$ $J_{1}-J_{1}$ Heisenberg model on the 2D
square lattice with arbitrary signs of exchange constants is considered. States
with different spin long-range order types (antiferromagnetic checkerboard,
stripe, collinear ferromagnetic) as well as disordered spin-liquid states are
described in the frames of one and the same analytical approach. It is shown
inter alia, that the phase transition between ferromagnetic spin liquid and
long-range order ferromagnet is a second-order one. On the ordered side of the
transition the ferromagnetic state with rapidly varying condensate function is
detected.",1307.6481v1
2013-10-14,Unveiling the Origin of the Insulating Ferromagnetism in LaMnO3 Thin Film,"By combining genetic algorithm optimizations, first-principles calculations
and the double-exchange model studies, we have unveiled that the exotic
insulating ferromagnetism in LaMnO3 thin film originates from the previously
unreported G-type d_{3z^2-r^2}/d_{x^2-y^2} orbital ordering. An insulating gap
opens as a result of both the orbital ordering and the strong electron-phonon
coupling. Therefore, there exist two strain induced phase transitions in the
LaMnO3 thin film, from the insulating A-type antiferromagnetic phase to the
insulating ferromagnetic phase and then to the metallic ferromagnetic phase.
These phase transitions may be exploited in tunneling magnetoresistance and
tunneling electroresistance related devices.",1310.3590v1
2013-11-24,Current induced torques between ferromagnets and compensated antiferromagnets: symmetry and phase coherence effects,"It is shown that the current-induced torques between a ferromagnetic layer
and an antiferromagnetic layer with a compensated interface vanish when the
ferromagnet is aligned with an axis of spin-rotation symmetry of the
antiferromagnet. For properly chosen geometries this implies that the current
induced torque can stabilize the out-of-plane (or hard axis) orientation of the
ferromagnetic layer. This current-induced torque relies on phase coherent
transport, and we calculate the robustness of this torque to phase breaking
scattering. From this it is shown that the torque is not linearly dependent on
applied current, but has an absolute maximum.",1311.6161v1
2013-12-19,Frustrated ferromagnetic spin chains: a variational approach to chirality transitions,"We study the energy per particle of a one-dimensional
ferromagnetic/anti-ferromagnetic frustrated spin chain with nearest and
next-to-nearest interactions close to the helimagnet/ferromagnet transition
point as the number of particles diverges. We rigorously prove the emergence of
chiral ground states and we compute, by performing the Gamma-limits of proper
renormalizations and scalings, the energy for a chirality transition.",1312.5573v3
2013-12-23,Ferromagnetism in Mn-doped Sb2Te,"We report that Sb2Te, a natural superlattice phase consisting of two
elemental Sb2 layers interleaved with single Sb2Te3 layers, becomes
ferromagnetic at low temperatures on doping with small percentages of Mn.
Ferromagnetism appears for Mn concentrations as low as Sb1.98Mn0.02Te, where a
ferromagnetic Tc of ~ 8.6 K is observed. Tc decreases with increasing Mn
content in the stoichiometric materials but increases with increasing Te excess
in materials of the type Sb1.93-yMn0.07Te1+y, starting at ~ 3 K at y = 0 and
reaching a Tc of ~ 8.9 K at y = 0.06.",1312.6628v1
2014-02-18,The Complexity of Ferromagnetic Two-spin Systems with External Fields,"We study the approximability of computing the partition function for
ferromagnetic two-state spin systems. The remarkable algorithm by Jerrum and
Sinclair showed that there is a fully polynomial-time randomized approximation
scheme (FPRAS) for the special ferromagnetic Ising model with any given uniform
external field. Later, Goldberg and Jerrum proved that it is #BIS-hard for
Ising model if we allow inconsistent external fields on different nodes. In
contrast to these two results, we prove that for any ferromagnetic two-state
spin systems except the Ising model, there exists a threshold for external
fields beyond which the problem is #BIS-hard, even if the external field is
uniform.",1402.4346v1
2014-08-15,Effects of impurity on tunnel magnetoresistance in a ferromagnetic electrode/carbon nanotube/ferromagnetic electrode junctio,"Effects of impurity on the spin-dependent transport in a single wall carbon
nanotube spin-valve, as ferromagnetic electrode/carbon nanotube/ferromagnetic
electrode model junction is numerically investigated. Using a generalized
Green's function method and the Landauer-Buttiker formalism, the impurity
conditions are determined by randomly substitution of carbon atoms in the
honeycomb carbon nanotube lattice by nitrogen and boron atoms. We have found
that transport characteristics, including the spin-dependent current and tunnel
magnetoresistance are strongly influenced by the impurity effects. We think
that the results of the present report could be useful for designing the future
spintronic devices.",1408.3675v1
2014-12-03,Paramagnetic spin pumping,"We have demonstrated spin pumping from a paramagnetic state of an insulator
La2NiMnO6 into a Pt film. Single-crystalline films of La2NiMnO6 which exhibit a
ferromagnetic order at TC ~ 270 K were grown by pulsed laser deposition. The
inverse spin Hall voltage induced by spin-current injection has been observed
in the Pt layer not only in the ferromagnetic phase of La2NiMnO6 but also in a
wide temperature range above TC. The efficient spin pumping in the paramagnetic
phase is ascribable to ferromagnetic correlation, not to ferromagnetic order.",1412.1281v1
2014-12-03,Proximity-induced ferromagnetism in graphene revealed by anomalous Hall effect,"We demonstrate the anomalous Hall effect (AHE) in single-layer graphene
exchange-coupled to an atomically flat yttrium iron garnet (YIG) ferromagnetic
thin film. The anomalous Hall conductance has magnitude of ~0.09(2e2/h) at low
temperatures and is measurable up to ~ 300 K. Our observations indicate not
only proximity-induced ferromagnetism in graphene/YIG with large exchange
interaction, but also enhanced spin-orbit coupling which is believed to be
inherently weak in ideal graphene. The proximity-induced ferromagnetic order in
graphene can lead to novel transport phenomena such as the quantized AHE which
are potentially useful for spintronics.",1412.1521v1
2016-02-05,Quantum transport in ferromagnetic graphene: Role of Berry curvature,"The magnetic effects in ferromagnetic graphene basically depend on the
principle of exchange interaction when ferromagntism is induced by depositing
an insulator layer on graphene. Here we deal with the consequences of
non-uniformity in the exchange coupling strength of the ferromagnetic graphene.
We discuss how the in- homogeneity in the coordinate and momentum of the
exchange vector field can provide interesting results in the conductivity
analysis of the ferromagnetic graphene. Our analysis is based on the Kubo
formalism of quantum transport.",1602.01976v1
2017-03-24,Probing the degree of spin polarization of a ferromagnet with ferromagnet/superconductor proximity effect,"Superconductor/ferromagnet proximity effect has been studied for
Pb/Co$_2$Cr$_{1-x}$Fe$_x$Al bilayers. Different substrate temperatures allowed
us to prepare the Heusler alloy Co$_2$Cr$_{1-x}$Fe$_x$Al films with different
degree of spin polarization of conduction band of the Heusler layer. We obtain
a strong correlation between the dependence of the superconducting transition
temperature on the Pb-layer thickness at fixed thickness of the Heusler layer
and the degree of spin polarization in the ferromagnetic layer.",1703.08422v1
2020-07-03,Unsaturated bipartite entanglement of a spin-1/2 Ising-Heisenberg model on a triangulated Husimi lattice,"A bipartite entanglement between two nearest-neighbor Heisenberg spins of a
spin-1/2 Ising-Heisenberg model on a triangulated Husimi lattice is quantified
using a concurrence. It is shown that the concurrence equals zero in a
classical ferromagnetic and a quantum disordered phase, while it becomes
sizable though unsaturated in a quantum ferromagnetic phase. A
thermally-assisted reentrance of the concurrence is found above a classical
ferromagnetic phase, whereas a quantum ferromagnetic phase displays a striking
cusp of the concurrence at a critical temperature.",2007.01700v1
2010-05-19,Non-local spin-sensitive electron transport in diffusive proximity heterostructures,"We formulate a quantitative theory of non-local electron transport in
three-terminal disordered ferromagnet-superconductor-ferromagnet structures. We
demonstrate that magnetic effects have different implications: While strong
exchange field suppresses disorder-induced electron interference in
ferromagnetic electrodes, spin-sensitive electron scattering at
superconductor-ferromagnet interfaces can drive the total non-local conductance
negative at sufficiently low energies. At higher energies magnetic effects
become less important and the non-local resistance behaves similarly to the
non-magnetic case. Our predictions can be directly tested in future experiments
on non-local electron transport in hybrid FSF structures.",1005.3426v1
2018-05-14,Study of the ferromagnetic-insulator phase in manganites,"Understanding the coexistence of ferromagnetism and insulating behavior in
manganites is an unsolved problem. We propose a localized-band model involving
effective intermediate-range electron-electron (electron-hole) repulsion
(attraction) generated by cooperative electron-phonon interaction. Double
exchange mechanism, involving holes virtually hopping to nearest neighbors and
back, produces magnetic polarons in an antiferromagnetic environment; when
these magnetic polarons coalesce and percolate the system, we get a
ferromagnetic insulator. Ferromagnetism gets more pronounced when the holes
(doping) increases or when the ratio hopping/polaronic-energy dominates over
superexchange-coupling/hopping.",1805.05172v1
2018-05-15,Ferromagnetic to paramagnetic transition in spherical spin glass,"We consider the spherical spin glass model defined by a combination of the
pure 2-spin spherical Sherrington-Kirkpatrick Hamiltonian and the ferromagnetic
Curie-Weiss Hamiltonian. In the large system limit, there is a two-dimensional
phase diagram with respect to the temperature and the coupling strength. The
phase diagram is divided into three regimes; ferromagnetic, paramagnetic, and
spin glass regimes. The fluctuations of the free energy are known in each
regime. In this paper, we study the transition between the ferromagnetic regime
and the paramagnetic regime in a critical scale.",1805.05630v1
2009-12-01,Controllability of ferromagnetism in graphene,"We systematically study magnetic correlations in graphene within Hubbard
model on a honeycomb lattice by using quantum Monte Carlo simulations. In the
filling region below the Van Hove singularity, the system shows a short-range
ferromagnetic correlation, which is slightly strengthened by the on-site
Coulomb interaction and markedly by the next-nearest-neighbor hopping integral.
The ferromagnetic properties depend on the electron filling strongly, which may
be manipulated by the electric gate. Due to its resultant controllability of
ferromagnetism, graphene-based samples may facilitate the development of many
applications.",0912.0094v2
2011-11-10,Static ferromagnetic materials: from the microscopic to the mesoscopic scale,"Thanks to averaging processes and Gamma-convergence techniques, we are able
to link a microscopic description of ferromagnetic materials based on spin
lattices and their mesoscopic description in the static framework for the three
fundamental contributions: exchange, magnetostatic and external field. The
results are in accordance with the classical continuous description of
ferromagnetic phenomena and justifies it. This work is a seed towards a dynamic
description of ferromagnetic materials.",1111.2421v3
2012-01-18,Spin-selective Kondo insulator: Cooperation of ferromagnetism and Kondo effect,"We propose the notion of spin-selective Kondo insulator, which provides a
fundamental mechanism to describe the ferromagnetic phase of the Kondo lattice
model with antiferromagnetic coupling. This unveils a remarkable feature of the
ferromagnetic metallic phase: the majority-spin conduction electrons show
metallic- while the minority-spin electrons show insulating-behavior. The
resulting Kondo gap in the minority spin sector, which is due to the
cooperation of ferromagnetism and partial Kondo screening, evidences a
dynamically-induced commensurability for a combination of minority-spin
electrons and parts of localized spins. Furthermore, this mechanism predicts a
nontrivial relation between the macroscopic quantities such as electron
magnetization, spin polarization and electron filling.",1201.3680v1
2013-09-17,Giant magnetoresistance in the junction of two ferromagnets on the surface of diffusive topological insulators,"We reveal the giant magnetoresistance induced by the spin-polarized current
in the ferromagnet (F_1)/topological insulator (TI)/ferromagnet (F_2) junction,
where two ferromagnets are deposited on the diffusive surface of the TI. We can
increase and reduce the value of the giant magnetoresistance by tuning the
spin-polarized current, which is controlled by the magnetization
configurations. The property is intuitively understood by the non-equilibrium
spin-polarized current, which plays the role of an effective electrochemical
potential on the surface of the TI.",1309.4195v1
2014-06-26,Exact ferromagnetic ground state of pentagon chains,"We model conducting pentagon chains with a multi orbital Hubbard model and
prove that well below half filling exact ferromagnetic ground states appear.
The rigorous method we use is based on the transformation of original
hamiltonian into positive semidefinite form. This technique is independent of
the spatial dimesion and does not require integrability of the model. The
obtained ferromagnetism is connected to dispersionless bands but in a much
broader sense than flat band ferromagnetism requires, where on every site a
Hubbard term is present. In our case only a small percentage of, even randomly
distributed, sites are only interacting.",1406.6796v1
2017-07-04,CrCTe$_3$: Computational design of a robust two-dimensional anti-ferromagnetic semiconductor,"Using density functional theory calculations we establish the hitherto
unknown compound CrCTe$_3$ to be a stable anti-ferromagnetic semiconductor in
the R$\bar{3}$ crystal structure with an indirect fundamental gap . Successive
layers in the bulk compound are weakly bound by van der Waals forces so that
individual layers can be easily exfoliated. A monolayer of CrCTe$_3$ is also an
anti-ferromagnetic semiconductor. The monolayer is structurally stable over a
large range of compressive and tensile strains, and the anti-ferromagnetic
state is robust over this strain range. Band gap of the monolayer can be tuned
by as much as 50% by applying strain in this range.",1707.00878v1
2018-10-17,Out-of-plane auto-oscillation in spin Hall oscillator with additional polarizer,"The theoretical investigation on magnetization dynamics excited by the spin
Hall effect in metallic multilayers having two ferromagnets is discussed. The
relaxation of the transverse spin in one ferromagnet enables us to manipulate
the direction of the spin-transfer torque excited in another ferromagnet,
although the spin-polarization originally generated by the spin Hall effect is
geometrically fixed. Solving the Landau-Lifshitz-Gilbert-Slonczewski equation,
the possibility to excite an out-of-plane auto-oscillation of an in-plane
magnetized ferromagnet is presented. An application to magnetic recording using
microwave-assisted magnetization reversal is also discussed.",1810.07831v1
2019-07-29,Magnetization Dynamics in Holographic Ferromagnets: Landau-Lifshitz Equation from Yang-Mills Fields,"We introduce a new approach to understand magnetization dynamics in
ferromagnets based on the holographic realization of ferromagnets. A
Landau-Lifshitz equation describing the magnetization dynamics is derived from
a Yang-Mills equation in the dual gravitational theory, and temperature
dependences of the spin-wave stiffness and spin transfer torque appearing in
the holographic Landau-Lifshitz equation are investigated by the holographic
approach. The results are consistent with the known properties of magnetization
dynamics in ferromagnets with conduction electrons.",1907.12306v1
2019-10-31,Terahertz emission from anomalous Hall effect in a single-layer ferromagnet,"We report on terahertz emission from a single layer ferromagnet which
involves the generation of backflow nonthermal charge current from the
ferromagnet/dielectric interface by femtosecond laser excitation and subsequent
conversion of the charge current to a transverse transient charge current via
the anomalous Hall effect, thereby generating the THz radiation. The THz
emission can be either enhanced or suppressed, or even the polarity can be
reversed, by introducing a magnetization gradient in the thickness direction of
the ferromagnet. Unlike spintronic THz emitters reported previously, it does
not require additional non-magnetic layer or Rashba interface.",1910.14338v1
2019-11-11,Domain wall motion in a diffusive weak ferromagnet,"We study the domain wall motion in a disordered weak ferromagnet, induced by
injecting a spin current from a strong ferromagnet. Starting from the spin
diffusion equation describing the spin accumulation in the weak ferromagnet, we
calculate the force and torque acting on the domain wall. We also study the
ensuing domain wall dynamics, and suggest a possible measurement method for
detecting the domain wall motion via measuring the additional resistance.",1911.04121v5
2020-08-16,Magnon dispersion in bilayers of two-dimensional ferromagnets,"We determine magnon spectra of an atomic bilayer magnet with ferromagnetic
intra- and both ferro- and anti- ferromagnetic interlayer coupling. Analytic
expressions for the full magnon band of the latter case reveal that both
exchange interactions govern the fundamental magnon gap. The inter and
intralayer magnetic ordering are not independent: the intralayer ferromagnetism
stabilizes antiferromagnetic inter-layer order. The topology of these
exchange-anisotropy spin models without spin-orbit interaction turns out to be
trivial.",2008.06875v2
2020-11-11,Reduction of back switching by large damping ferromagnetic material,"Recent studies on magnetization dynamics induced by spin-orbit torque have
revealed a weak dependence of the critical current for magnetization switching
on the damping constant of a ferromagnetic free layer. This study, however,
reveals that the damping constant nevertheless plays a key role in
magnetization switching induced by spin-orbit torque. An undesirable switching,
returning to an initial state, named as back switching, occurs in a ferromagnet
with an easy axis parallel to the current direction. Numerical and theoretical
analyses reveal that back switching is strongly suppressed when the damping
constant of the ferromagnet is large.",2011.05566v1
2021-09-21,Ferromagnetic Double Perovskite Semiconductors with Tunable Properties,"We successfully dope the magnetically silent double perovskite semiconductor
Sr2GaSbO6 to induce ferromagnetism and tune its band gap, with Ga3+ partially
substituted by the magnetic trivalent cation Mn3+, in a rigid cation ordering
with Sb5+. Our new ferromagnetic semiconducting Sr2Ga1-xMnxSbO6 double
perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and
has tunable ferromagnetic ordering temperature and band gap, suggests that
magnetic ion doping of double perovskites is a productive avenue towards
obtaining materials for application in next-generation oxide-based spintronic
devices.",2109.10405v1
2021-10-11,Magnetoelastic Coupling in Hole-doped Two-dimensional \b{eta}-PbO,"The realization of intertwined ferroelasticity and ferromagnetism in
two-dimensional (2D) lattices is of great interest for broad nanoscale
applications, but still remains a remarkable challenge. Here, we propose an
alternative approach to realize the strongly coupled ferromagnetism and
ferroelasticity by carrier doping. We demonstrate that prototypical 2D
\b{eta}-PbO is dynamically, thermally and mechanically stable. Under hole
doping, 2D \b{eta}-PbO possesses ferromagnetism and ferroelasticity
simultaneously. Moreover, the robustness of ferromagnetic and ferroelastic
orders are doping tunable. In particular, 2D \b{eta}-PbO features in-plane easy
magnetization axis that is coupled with lattice direction, enabling
ferroelastic manipulation of spin direction. Our work highlights a new
direction for 2D magnetoelastic research and enables the possibility for
multifunctional devices.",2110.05624v1
2021-10-13,Theoretical Study of Temperature Dependence of Spin Susceptibility in Anisotropic Itinerant Ferromagnets,"We developed a framework for directly calculating the spin susceptibility of
anisotropic itinerant ferromagnets in the full temperature range within the
coherent potential approximation in the disordered local moment picture. As a
test of our formulation, we demonstrate the computation for the temperature
($T$) dependence of the spin susceptibility for Rashba-type ferromagnets with
the Curie temperature $T_\mathrm{C}$. In a certain parameter, we found that the
inverse transverse susceptibility $1/\chi_\perp\simeq\mathrm{const.}$ for
$T<T_\mathrm{C}$ and $1/\chi_\perp\propto T-T_\mathrm{C}$ for $T>T_\mathrm{C}$,
which reflects characteristics of itinerant ferromagnets including a spin-orbit
interaction.",2110.06478v1
2022-02-03,Circular photogalvanic effects in topological insulator/ferromagnet hybrid structures,"We study laser driven spin-current effects at
ferromagnet/topological-insulator interfaces by two complementary experimental
approaches. The DC photocurrent is studied in ferromagnet/topological-insulator
bilayers with high spatial resolution. Dynamic interface currents are explored
via the emission of terahertz radiation emitted by these currents with high
temporal resolution. From our experiments, we reveal a lateral and dynamic
interaction of the ferromagnet and the topological insulator interface.",2202.01522v1
2022-12-22,Planar Magnetic Paul Traps for Ferromagnetic Particles,"We present a study on the trapping of hard ferromagnetic particles using
alternating magnetic fields, with a focus on planar trap geometries. First, we
realize and characterize a magnetic Paul trap design for millimeter-size
magnets based on a rotating magnetic potential. Employing a physically rotating
platform with two pairs of permanent magnets with opposite poles, we show
stable trapping of hard ferromagnets a centimeter above the trap and
demonstrate that the particle shape plays a critical role in the trapping.
Finally, we propose a chip trap design that will open a path to studies of
gyromagnetic effects with ferromagnetic micro-particles.",2212.11622v1
2023-12-28,Detecting bulk carbon ferromagnetism in graphene multi-edge structure,"The emergence of bulk carbon ferromagnetism is long-expected over years. At
nanoscale, carbon ferromagnetism was detected by analyzing the magnetic edge
states via scanning tunneling microscopy(STM), and its origin can be explained
by local redistribution of electron wave function. In larger scale, carbon
ferromagnetism can be created by deliberately producing defects in graphite,
and detected by macroscopic technical magnetization. Meanwhile, it becomes
crucial to determine that the detected magnetization is originated from carbon
rather than from magnetic impurities. One solution is X-ray magnetic circular
dichroism (XMCD). Nonetheless, a reproducible, full section of XMCD spectrum
across C-1s absorption energy has not appeared yet, which should be decisive
for assuring the indisputable existence of bulk carbon ferromagnetism. Besides,
the lack of direct observation on the atomic structure of the ferromagnetic
carbon leaves the structural origin of its ferromagnetism still in mist. In
this work, for detecting bulk carbon ferromagnetism, we managed to grow
all-carbon film consisting of vertically aligned graphene multi-edge (VGME),
which wove into a three-dimensional hyperfine-porous network. Magnetization
(M-H) curves and XMCD spectra co-confirmed bulk carbon ferromagnetism of VGME
at room temperature, with the average unit magnetic momentum of ~0.0006
miuB/atom. The influence of magnetic impurities on magnetization was excluded
by both absorption spectra and inductively coupled plasma mass spectrometry
measurements. The spin transfer behavior also verified the long-range and
robust feature of the bulk carbon ferromagnetism. Our work provides direct
evidence of elementary resolved bulk carbon ferromagnetism at room temperature
and clarifies its origin from pi-electrons at graphene edges.",2312.16925v1
2000-04-05,Ferromagnetism of quark liquid and magnetars,"Spontaneous magnetization of quark liquid is examined on the analogy with
that in electron gas. It is pointed out that quark liquid has potential to be
ferromagnetic at rather low densities, around nuclear saturation density. Somme
comments are given as for implications on magnetars.",0004062v1
1996-05-24,Ferromagnetism in the Hubbard model with an infinite-range hopping,"We prove, as recently conjectured, that the ground state of the Hubbard
Hamiltonian with an infinite-range hopping, when the number of electrons
$N_e=N+1$ ($N$ being the number of sites), is ferromagnetic fully polarized.",9605156v1
1996-06-06,Spherical P-spin glass at $P\to\infty$ and the information storing by continuous spins,"The $P\to\infty$ limit was considered in the spherical P-spin glass. It is
possible to store information in the vacuum configuration of ferromagnetic
phase. Maximal allowed level of noise was calculated in ferromagnetic phase.",9606034v1
1996-12-05,DMRG study of ferromagnetism in a one-dimensional Hubbard model,"The one dimensional Hubbard model with nearest and (negative) next-nearest
neighbour hopping has been studied with the density-matrix renormalization
group (DMRG) method. A large region of ferromagnetism has been found for finite
density and finite on-site interaction.",9612056v1
1997-03-28,Optical Spectra in the Ferromagnetic States near the Charge Ordering,"The optical conductivity is studied numerically for the ferromagnetic
metallic state close to the charge ordering observed in perovskite manganites.",9703245v1
1998-05-15,The gauge equivalence of the Zakharov equations and (2+1)-dimensional continuous Heisenberg ferromagnetic models,"The gauge equivalence between the (2+1)-dimensional Zakharov equations and
(2+1)-dimensional integrable continuous Heisenberg ferromagnetic model is
established. Also their integrable reductions are shown explicitly.",9805187v1
2004-07-28,"Comment on ""Exchange interaction parameters and adiabatic spin-wave spectra of ferromagnets: A 'renormalized magnetic force theorem'""","This is a comment on publication in Phys. Rev. Lett. 90, 087205 (2003):
``Exchange interaction parameters and adiabatic spin-wave spectra of
ferromagnets: A `renormalized magnetic force theorem'''",0407739v1
2005-11-21,"Reply to ""Comment on ""Domain Structure in a Superconducting Ferromagnet""""","This short article is a reply to the comment from E.B. Sonin on our paper on
the domain structure in a superconducting ferromagnet published in Phys. Rev.
Lett..",0511517v1
2003-10-09,A Criterion for Ferromagnetism in the Isotropic Quantum Heisenberg Model,"A criterion for ferromagnetism is presented suggesting a line of proof to
rigorously establish the phase transition. Spectral information will be
required in certain invariant subspaces of the Hamiltonian, hopefully the
relatively crude estimates needed will be not too difficult to establish.",0310013v1
2008-04-10,Nonergodic thermodynamics of disordered ferromagnets and ferroelectrics,"Phenomenological thermodynamic theory describing the properties of metastable
states in disordered ferromagnets and ferroelectrics with frustrative random
interactions is developed and its ability to describe various nonergodic
phenomena in real crystals is demonstrated.",0804.1713v1
2009-02-10,Nucleation of superconductivity and vortex matter in superconductor - ferromagnet hybrids,"The theoretical and experimental results concerning the thermodynamical and
low-frequency transport properties of hybrid structures, consisting of
spatially-separated conventional low-temperature superconductor (S) and
ferromagnet (F), is reviewed. Since the superconducting and ferromagnetic parts
are assumed to be electrically insulated, no proximity effect is present and
thus the interaction between both subsystems is through their respective
magnetic stray fields. Depending on the temperature range and the value of the
external field H_{ext}, different behavior of such S/F hybrids is anticipated.
Rather close to the superconducting phase transition line, when the
superconducting state is only weakly developed, the magnetization of the
ferromagnet is solely determined by the magnetic history of the system and it
is not influenced by the field generated by the supercurrents. In contrast to
that, the nonuniform magnetic field pattern, induced by the ferromagnet,
strongly affect the nucleation of superconductivity leading to an exotic
dependence of the critical temperature T_{c} on H_{ext}. Deeper in the
superconducting state the effect of the screening currents cannot be neglected
anymore. In this region of the phase diagram various aspects of the interaction
between vortices and magnetic inhomogeneities are discussed. In the last
section we briefly summarize the physics of S/F hybrids when the magnetization
of the ferromagnet is no longer fixed but can change under the influence of the
superconducting currents. As a consequence, the superconductor and ferromagnet
become truly coupled and the equilibrium configuration of this ""soft"" S/F
hybrids requires rearrangements of both, superconducting and ferromagnetic
characteristics, as compared with ""hard"" S/F structures.",0902.1630v1
2010-04-16,How to recognize a nearly-flat-band ferromagnet by means of thermodynamic measurements?,"We make an attempt at unveiling the thermodynamic ""signature"" of a specific
class of electronic systems, the so called nearly-flat-band paramagnets and
ferromagnets that can theoretically be described by appropriate versions of the
Hubbard model.",1004.2786v1
2010-07-15,Variational cluster approach to ferromagnetism in infinite dimensions and in one-dimensional chains,"The variational cluster approach (VCA) is applied to study spontaneous
ferromagnetism in the Hubbard model at zero temperature. We discuss several
technical improvements of the numerical implementation of the VCA which become
necessary for studies of a ferromagnetically ordered phase, e.g. more accurate
techniques to evaluate the variational ground-state energy, improved local as
well as global algorithms to find stationary points, and different methods to
locate the magnetic phase transition. Using the single-site VCA, i.e. the
dynamical impurity approximation (DIA), the ferromagnetic phase diagram of the
model in infinite dimensions is worked out. The results are compared with
previous dynamical mean-field studies for benchmarking purposes. The DIA
results provide a unified picture of ferromagnetism in the infinite-dimensional
model by interlinking different parameter regimes that are governed by
different mechanisms for ferromagnetic order. Using the DIA and the VCA, we
then study ferromagnetism in one-dimensional Hubbard chains with nearest and
next-nearest-neighbor hopping t2. In comparison with previous results from the
density-matrix renormalization group, the phase diagram is mapped out as a
function of the Hubbard-U, the electron filling and t2. The stability of the
ferromagnetic ground state against local and short-range non-local quantum
fluctuations is discussed.",1007.2517v1
2011-07-15,Ferromagnetic-glassy transitions in three-dimensional Ising spin glasses,"We investigate the ferromagnetic-glassy transitions which separate the
low-temperature ferromagnetic and spin-glass phases in the temperature-disorder
phase diagram of three-dimensional Ising spin-glass models. For this purpose,
we consider the cubic-lattice +-J (Edwards-Anderson) Ising model with bond
distribution $P(J) = p \delta(J - 1) + (1-p) \delta(J + 1)$, and present a
numerical Monte Carlo study of the critical behavior along the line that marks
the onset of ferromagnetism. The finite-size scaling analysis of the Monte
Carlo data shows that the ferromagnetic-glassy transition line is slightly
reentrant. As a consequence, for an interval of the disorder parameter p,
around p=0.77, the system presents a low-temperature glassy phase, an
intermediate ferromagnetic phase, and a high-temperature paramagnetic phase.
Along the ferromagnetic-glassy transition line magnetic correlations show a
universal critical behavior with critical exponents nu=0.96(2) and
eta=-0.39(2). The hyperscaling relation beta/nu = (1 + eta)/2 is satisfied at
the transitions, so that beta/nu = 0.305(10). This magnetic critical behavior
represents a new universality class for ferromagnetic transitions in Ising-like
disordered systems. Overlap correlations are apparently not critical and show a
smooth behavior across the transition.",1107.3005v1
2012-06-15,"Comment on ""Anisotropic Critical Magnetic Fluctuations in the Ferromagnetic Superconductor UCoGe""","We have presented the potential explanation of nonvanishing at q=0 Landau
damping measured experimentally in ferromagnetic compounds UGe2 and UCoGe based
on possible intersection of the Fermi sheets corresponding different bands.",1206.3468v1
2013-02-08,"Reply to the Comment on ""Unified Formulism of Andreev Reflection at a Ferromagnetic/Superconductor Interface"" by Eschrig et al","Reply to the Comment on ""Unified Formulism of Andreev Reflection at a
Ferromagnetic/Superconductor Interface"" by Eschrig et al",1302.2166v1
2018-11-29,Ferromagnetic Neutron Stars in Scalar-Tensor Theories of Gravity,"Ferromagnetic spin ordering can take place in neutron stars. This phase
transition alters the neutron star equation of state. Here, applying the
scalar-tensor theories of gravity, we investigate the structure of neutron
stars which are in the ferromagnetic phase. Considering the equation of state
of ferromagnetic neutron matter with Skyrme-type interactions at zero
temperature and using the scalar-tensor theories of gravity with sufficiently
negative coupling constant, we explore the spontaneous scalarization in
ferromagnetic neutron stars. In this regard, the mass versus the central
density, the profiles of scalar field and mass and density, the central scalar
field for different central densities, and the mass-radius relation of
ferromagnetic neutron stars are presented. Moreover, we investigate the
influences of the coupling constant on the scalarization of ferromagnetic
neutron stars. The effects of the coupling constant on the critical densities
of scalarization and the scalar charge of ferromagnetic neutron stars are also
calculated. In addition, we study the maximum value of the coupling constant at
which the spontaneous scalarization takes place presenting the influence of the
neutron matter equation of state on this critical value.",1811.12090v2
2014-03-25,Unconventional critical scaling of magnetization in uranium ferromagnetic superconductors UGe$_2$ and URhGe,"We report a dc magnetization study of the critical phenomenon around the
ferromagnetic transition temperature T_C in high-quality single crystals of
uranium ferromagnetic superconductors UGe2 and URhGe. The critical exponents,
beta for the temperature dependence of the magnetization below T_C, gamma for
the magnetic susceptibility, and delta for the magnetic isothermal at T_C have
been determined with a modified Arrott plot, a Kouvel-Fisher plot, and the
scaling analysis. Magnetization in the ferromagnetic state has strong uniaxial
magnetic anisotropy in the two compounds. However, the universality class of
the critical phenomena do not belong to the three dimensional (3D) Ising
system. Although the values of beta in UGe2 and URhGe are close to those in the
3D magnets, the values of gamma are close to unity, that expected from the mean
field theory. Similar critical exponents have been reported previously for the
3D Ising ferromagnet UIr where superconductivity appears under high pressure.
The critical behavior may be limited to a very narrow Ginzburg critical region
of 1 mK because of the strong itinerant character of the 5f electrons in the
ferromagnetic superconductor UCoGe where the mean field behavior of the
magnetization has been reported. The unconventional critical scaling of
magnetization in UGe2, URhGe and UIr cannot be explained via previous
approaches to critical phenomena. The ferromagnetic correlation between the 5f
electrons differs from that in the 3D Ising system and this difference may be a
key point for the understanding of the ferromagnetism where superconductivity
emerges.",1403.6197v1
2008-07-22,Anisotropic tunneling magnetoresistance and tunneling anisotropic magnetoresistance: spin-orbit coupling in magnetic tunnel junctions,"The effects of the spin-orbit interaction on the tunneling magnetoresistance
of ferromagnet/semiconductor/normal metal tunnel junctions are investigated.
Analytical expressions for the tunneling anisotropic magnetoresistance (TAMR)
are derived within an approximation in which the dependence of the
magnetoresistance on the magnetization orientation in the ferromagnet
originates from the interference between Bychkov-Rashba and Dresselhaus
spin-orbit couplings that appear at junction interfaces and in the tunneling
region. We also investigate the transport properties of
ferromagnet/semiconductor/ferromagnet tunnel junctions and show that in such
structures the spin-orbit interaction leads not only to the TAMR effect but
also to the anisotropy of the conventional tunneling magnetoresistance (TMR).
The resulting anisotropic tunneling magnetoresistance (ATMR) depends on the
absolute magnetization directions in the ferromagnets. Within the proposed
model, depending on the magnetization directions in the ferromagnets, the
interplay of Bychkov-Rashba and Dresselhaus spin-orbit couplings produces
differences between the rates of transmitted and reflected spins at the
ferromagnet/seminconductor interfaces, which results in an anisotropic local
density of states at the Fermi surface and in the TAMR and ATMR effects. Model
calculations for Fe/GaAs/Fe tunnel junctions are presented. Furthermore, based
on rather general symmetry considerations, we deduce the form of the
magnetoresistance dependence on the absolute orientations of the magnetizations
in the ferromagnets.",0807.3564v1
2017-12-19,"Ba(Zn,Co)2As2: a II-II-V Diluted Ferromagnetic Semiconductor with N-type Carriers","Diluted ferromagnetic semiconductors (DMSs) that combine the properties of
semiconductors with ferromagnetism have potential application in spin-sensitive
electronics (spintronics) devices. The search for DMS materials exploded after
the observation of ferromagnetic ordering in III-V (Ga,Mn)As films. Recently, a
series of DMS compounds isostructural to iron-based superconductors have been
reported. Among them, the highest Curie temperature $T_C$ of 230 K has been
achieved in (Ba,K)(Zn,Mn)$_2$As$_2$. However, most DMSs, including (Ga,Mn)As,
are p-type, i.e., the carriers that mediate ferromagnetism are holes. For
practical applications, DMS with n-type carriers are also advantageous. Here we
report the successful synthesis of a II-II-V diluted ferromagnetic
semiconductor with n-type carriers, Ba(Zn,Co)$_2$As$_2$. Magnetization
measurements show that the ferromagnetic transition occurs up to $T_{C} \sim$
45 K. Hall effect and Seebeck effect measurements jointly confirm that the
dominant carriers are electrons. Through muon spin relaxation ($\mu$SR), a
volume sensitive magnetic probe, we have also confirmed that the ferromagnetism
in Ba(Zn,Co)$_2$As$_2$ is intrinsic and the internal field is static.",1712.06764v1
2018-09-14,Non-collinearity and spin frustration in the itinerant kagome ferromagnet Fe3Sn2,"Frustrated itinerant ferromagnets, with non-collinear static spin structures,
are an exciting class of material as their spin chirality can introduce a Berry
phase in the electronic scattering and lead to exotic electronic phenomena such
as the anomalous Hall effect (AHE).
  This study presents a reexamination of the magnetic properties of
Fe$_3$Sn$_2$, a metallic ferromagnet, based on the 2-dimensional kagome bilayer
structure. Previously thought of as a conventional ferromagnet, we show using a
combination of SQUID measurements, symmetry analysis and powder neutron
diffraction, that Fe$_3$Sn$_2$ is a frustrated ferromagnet with a
temperature-dependent non-collinear spin structure. The complexity of the
magnetic interactions is further evidenced by a re-entrant spin glass
transition ($T_f\simeq80$\,K) at temperatures far below the main ferromagnetic
transition ($T\mathrm{_C}$ = 640\,K).
  Fe$_3$Sn$_2$ therefore provides a rare example of a frustrated itinerant
ferromagnet. Further, as well as being of great fundamental interest our
studies highlight the potential of Fe$_3$Sn$_2$ for practical application in
spintronics technology, as the AHE arising from the ferromagnetism in this
material is expected to be enhanced by the coupling between the conduction
electrons and the non-trivial magnetic structure over an exceptionally wide
temperature range.",1809.05466v1
2018-10-30,Effect of Coulomb interaction on the two-dimensional electronic structure of the van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$,"In order to investigate the electronic properties of the semiconducting van
der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$ (CGT), where ferromagnetic layers are
bonded through van der Waals forces, we have performed angle-resolved
photoemission spectroscopy (ARPES) measurements and density-functional-theory
(DFT+U) calculations. The valence-band maximum at the {\Gamma} point is located
$\sim$ 0.2 eV below the Fermi level, consistent with the semiconducting
property of CGT. Comparison of the experimental density of states with the DFT
calculation has suggested that Coulomb interaction between the Cr 3d electrons
U$_{\rm eff}$ $\sim$ 1.1 eV. The DFT+U calculation indicates that magnetic
coupling between Cr atoms within the layer is ferromagnetic if Coulomb U $_{\rm
eff}$ is smaller than 3.0 eV and that the inter-layer coupling is ferromagnetic
below U$_{\rm eff}$ $\sim$ 1.0 eV. We therefore conclude that, for U$_{\rm
eff}$ deduced by the experiment, the intra-layer Cr-Cr coupling is
ferromagnetic and the inter-layer coupling is near the boundary between
ferromagnetic and antiferromagnetic, which means experimentally deduced U$_{\rm
eff}$ is consistent with theoretical ferromagnetic condition.",1810.12564v4
2020-12-18,Tunable ferromagnetism at non-integer filling of a moiré superlattice,"The flat bands resulting from moir\'e superlattices in magic-angle twisted
bilayer graphene (MATBG) and ABC-trilayer graphene aligned with hexagonal boron
nitride (ABC-TLG/hBN) have been shown to give rise to fascinating correlated
electron phenomena such as correlated insulators and superconductivity. More
recently, orbital magnetism associated with correlated Chern insulators was
found in this class of layered structures centered at integer multiples of n0,
the density corresponding to one electron per moir\'e superlattice unit cell.
Here we report the experimental observation of ferromagnetism at fractional
filling of a flat Chern band in an ABC-TLG/hBN moir\'esuperlattice. The
ferromagnetic state exhibits prominent ferromagnetic hysteresis behavior with
large anomalous Hall resistivity in a broad region of densities, centered in
the valence miniband at n = -2.3 n0. This ferromagnetism depends very
sensitively on the control parameters in the moir\'e system: not only the
magnitude of the anomalous Hall signal, but also the sign of the hysteretic
ferromagnetic response can be modulated by tuning the carrier density and
displacement field. Our discovery of electrically tunable ferromagnetism in a
moir\'e Chern band at non-integer filling highlights the opportunities for
exploring new correlated ferromagnetic states in moir\'e heterostructures.",2012.10075v1
2019-03-28,High spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi$_{1-x}$Nb$_x$O$_3$,"The physical systems with ferromagnetism and ""bad"" metallicity hosting
unusual transport properties are playgrounds of novel quantum phenomena.
Recently EuTi$_{1-x}$Nb$_x$O$_3$ emerged as a ferromagnetic system where
non-trivial temperature dependent transport properties are observed due to
coexistence and competition of various magnetic and non-magnetic scattering
processes. In the ferromagnetic state, the resistivity shows a $T^2$
temperature dependence possibly due to electron-magnon scattering and above the
Curie temperature $T_c$, the dependence changes to $T^{3/2}$ behaviour
indicating a correlation between transport and magnetic properties. In this
paper, we show that the transport spin-polarization in EuTi$_{1-x}$Nb$_x$O$_3$,
a low Curie temperature ferromagnet, is as high ($\sim 40\%$) as that in some
of the metallic ferromagnets with high Curie temperatures. In addition, owing
to the low Curie temperature of EuTi$_{1-x}$Nb$_x$O$_3$, the temperature ($T$)
dependence of $P_t$ could be measured systematically up to $T_c$ which revealed
a proportionate relationship with magnetization $M_s$ vs. $T$. This indicates
that such proportionality is far more universally valid than the ferromagnets
with ideal parabolic bands. Furthermore, our band structure calculations not
only helped understand the origin of such high spin polarization in
EuTi$_{1-x}$Nb$_x$O$_3$ but also provided a route to estimate the Hubbard $U$
parameter in complex metallic ferromagnets in general using experimental
inputs.",1903.12022v1
2019-11-26,Modulating Super-Exchange Strength to Achieve Robust Ferromagnetic Couplings in Two-Dimensional Semiconductors,"Low-dimensional semiconducting ferromagnets have attracted considerable
attention due to their promising applications as nano-size spintronics.
However, realizing robust ferromagnetic couplings that can survive at high
temperature is restrained by two decisive factors: super-exchange couplings and
anisotropy. Despite widely explored low-dimensional anisotropy, strengthening
super-exchange couplings has rarely been investigated. Here, we found that
ligands with lower electronegativity can strengthen ferromagnetic
super-exchange couplings and further proposed the ligand modulation strategy to
enhance the Curie temperature of low-dimensional ferromagnets. Based on the
metallic CrX2 (X = S, Se, Te) family, substituting ligand atoms by halides can
form stable semiconducting phase as CrSeCl, CrSeBr and CrTeBr. It is
interesting to discover that, the nearest ferromagnetic super-exchange
couplings can be strengthened when substituting ligands from S to Se and Te.
Such evolution originates from the enhanced electron hopping integral and
reduced energy intervals between d and p orbits. While the second nearest
anti-ferromagnetic couplings are also benefitted due to delocalized p-p
interactions. Finally, ligand modulation strategy is applied in other
ferromagnetic monolayers, further verifying our theory and providing a
fundamental understanding on controlling super-exchange couplings in
low-dimension.",1911.11333v1
2020-11-24,Ground state properties and exact thermodynamics of a 2-leg anisotropic spin ladder system,"We study a frustrated two-leg spin ladder with alternate isotropic Heisenberg
and Ising rung exchange interactions, whereas, interactions along legs and
diagonals are Ising-type. All the interactions in the ladder are
anti-ferromagnetic in nature and induce frustration in the system. This model
shows four interesting quantum phases: (i) stripe rung ferromagnetic (SRFM),
(ii) stripe rung ferromagnetic with edge singlet (SRFM-E), (iii) anisotropic
antiferromagnetic (AAFM), and (iv) stripe leg ferromagnetic (SLFM) phase. We
construct a quantum phase diagram for this model and show that in stripe rung
ferromagnet (SRFM), the same type of sublattice spins (either $S$ or
$\sigma$-type spins) are aligned in the same direction. Whereas, in anisotropic
antiferromagnetic phase, both $S$ and $\sigma$-type of spins are
anti-ferromagnetically aligned with each other, two nearest $S$ spins along the
rung form an anisotropic singlet bond whereas two nearest $\sigma$ spins form
an Ising bond. In large Heisenberg rung exchange interaction limit, spins on
each leg are ferromagnetically aligned, but spins on different legs are
anti-ferromagnetically aligned. The thermodynamic quantities like $Cv(T)$,
$\chi(T)$ and $S(T)$ are also calculated using the transfer matrix method for
different phase. The magnetic gap in the SRFM and the SLFM can be notice from
$\chi(T)$ and $Cv(T)$ curves.",2011.11901v1
2021-03-17,Tunable electronic structure and magnetic anisotropy in bilayer ferromagnetic semiconductor Cr2Ge2Te6,"The emergence of ferromagnetism in two-dimensional van der Waals materials
has aroused broad interest. However, the ferromagnetic instability has been a
problem remained. In this work, by using the first-principles calculations, we
identified the critical ranges of strain and doping for the bilayer Cr2Ge2Te6
within which the ferromagnetic stability can be enhanced. Beyond the critical
range, the tensile strain can induce the phase transition from the
ferromagnetic to the antiferromagnetic, and the direction of magnetic easy axis
can be converted from out-of-plane to in-plane due to the increase of
compressive strain, or electrostatic doping. We also predicted an electron
doping range, within which the ferromagnetism can be enhanced, while the
ferromagnetic stability was maintained. Moreover, we found that the compressive
strain can reverse the spin polarization of electrons at the conduction band
minimum, so that two categories of half-metal can be induced by controlling
electrostatic doping in the bilayer Cr2Ge2Te6. These results should shed a
light on achieving ferromagnetic stability for low-dimensional materials.",2103.09456v1
2021-05-11,Pressure-enhanced ferromagnetism in layered CrSiTe3 flakes,"The research on van der Waals (vdW) layered ferromagnets have promoted the
development of nanoscale spintronics and applications. However, low-temperature
ferromagnetic properties of these materials greatly hinder their applications.
Here, we report pressure-enhanced ferromagnetic behaviours in layered CrSiTe3
flakes revealed by high-pressure magnetic circular dichroism (MCD) measurement.
At ambient pressure, CrSiTe3 undergoes a paramagnetic-to-ferromagnetic phase
transition at 32.8 K, with a negligible hysteresis loop, indicating a soft
ferromagnetic behaviour. Under 4.6 GPa pressure, the soft ferromagnet changes
into hard one, signalled by a rectangular hysteretic loop with remnant
magnetization at zero field. Interestingly, with further increasing pressure,
the coercive field (H_c) dramatically increases from 0.02 T at 4.6 GPa to 0.17
T at 7.8 GPa, and the Curie temperature (T_c^h: the temperature for closing the
hysteresis loop) also increases from ~36 K at 4.6 GPa to ~138 K at 7.8 GPa. The
influences of pressure on exchange interactions are further investigated by
density functional theory calculations, which reveal that the in-plane
nearest-neighbor exchange interaction and magneto-crystalline anisotropy
increase simultaneously as pressure increases, leading to increased H_c and
T_c^h in experiments. The effective interaction between magnetic couplings and
external pressure offers new opportunities for both searching room-temperature
layered ferromagnets and designing pressure-sensitive magnetic functional
devices.",2105.04740v1
2022-02-09,"Ferromagnetism induced by hybridization of Fe 3d orbitals with ligand InSb bands in n-type ferromagnetic semiconductor (In,Fe)Sb","Fe-doped III-V ferromagnetic semiconductor (FMS) (In,Fe)Sb is a promising
material for spintronic device applications because of the n-type carrier
conduction and the ferromagnetism with high Curie temperature (TC > 300 K). To
clarify the mechanism of the high-TC ferromagnetism, we have investigated the
electronic structure and magnetic properties of an (In,Fe)Sb thin film by
performing x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD) measurements at the Fe L2,3 edges. The magnetic-field
dependence of the XMCD spectra reveals that there are ferromagnetic-like Fe and
paramagnetic-like Fe components in the (In,Fe)Sb thin film. The XAS and XMCD
spectra of the ferromagnetic-like and paramagnetic-like Fe components resemble
those of other Fe-doped FMSs and extrinsic oxides, respectively. The finite
value of the ratio between the orbital and spin magnetic moments estimated by
applying the XMCD sum rules indicates that the valence state of the Fe ions
substituting for the In sites in (In,Fe)Sb is not purely ionic Fe3+, but
intermediate between Fe3+ and Fe2+. The qualitative correspondence between the
magnetic-field dependence of the visible-light magnetic circular dichroism
intensity and that of the XMCD intensity demonstrates that the Zeeman splitting
of the InSb band is proportional to the net magnetization of the doped Fe.
These results suggest that the ferromagnetism of (In,Fe)Sb originates from the
Fe 3d orbitals hybridized with the host InSb bands.",2202.04286v1
2022-04-26,Bulk domain Meissner state in the ferromagnetic superconductor EuFe$_{2}$(As$_{0.8}$P$_{0.2}$)$_{2}$: Consequence of compromise between ferromagnetism and superconductivity,"Small-angle neutron scattering (SANS) measurements are performed on the
ferromagnetic superconductor EuFe$_{2}$(As$_{0.8}$P$_{0.2}$)$_{2}$
($T\rm_{sc}=22.5\,$K) to probe the delicate interplay between ferromagnetism
and superconductivity. A clear signature of large ferromagnetic domains is
found below the ferromagnetic ordering temperature $T\rm_{C}$ = 18.5 K. In a
small temperature interval of $\sim$ 1.5 K below $T\rm_{C}$, additional SANS
signal is observed, of which the indirect Fourier transform reveals
characteristic length scales in between $\sim$ 80 nm to $\sim$ 160 nm. These
nanometer-scaled domain structures are identified to result from an
intermediate inhomogeneous Meissner effect denoted domain Meissner state, which
was recently observed on the surface of EuFe$_{2}$(As$_{0.79}$P$_{0.21}$)$_{2}$
crystals by means of magnetic force microscopy [V. S. Stolyarov $\mathit{et}$
$\mathit{al.}$, Sci. Adv. 4, 1061 (2018)], ascribing to the competition between
ferromagnetism and superconductivity. Our measurements clearly render the
domain Meissner state as a bulk phenomenon and provide a key solution to the
mystery regarding the intriguing coexistence of strong ferromagnetism and bulk
superconductivity in these compounds.",2204.12094v1
2022-06-16,Tunable Ferromagnetism in LaCoO3 Epitaxial Thin Films,"Ferromagnetic insulators play a crucial role in the development of
low-dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO3 thin
film is a prominent ferromagnetic insulator, in which the robust ferromagnetic
ordering emerges owing to epitaxial strain. Whereas it is evident that strong
spin-lattice coupling induces ferromagnetism, the reported ferromagnetic
properties of epitaxially strained LaCoO3 thin films were highly consistent.
For example, even under largely modulated degree of strain, the reported Curie
temperatures of epitaxially strained LaCoO3 thin films lie within 80-85 K,
without much deviation. In this study, substantial enhancement (~18%) in the
Curie temperature of epitaxial LaCoO3 thin films is demonstrated via
crystallographic orientation dependence. By changing the crystallographic
orientation of the films from (111) to (110), the crystal-field energy was
reduced and the charge transfer between the Co and O orbitals was enhanced.
These modifications led to a considerable enhancement of the ferromagnetic
properties (including the Curie temperature and magnetization), despite the
identical nominal degree of epitaxial strain. The findings of this study
provide insights into facile tunability of ferromagnetic properties via
structural symmetry control in LaCoO3.",2206.08196v1
2022-07-28,Evolution of short-range magnetic correlations in ferromagnetic Ni-V alloys,"We experimentally study how the magnetic correlations develop in a binary
alloy close to the ferromagnetic quantum critical point with small-angle
neutron scattering (SANS). Upon alloying the itinerant ferromagnet nickel with
vanadium, the ferromagnetic order is continuously suppressed. The critical
temperature Tc vanishes when vanadium concentrations reach the critical value
of xc=0.116 indicating a quantum critical point separating the ferromagnetic
and paramagnetic phases. Earlier magnetization and $\mu$SR data have indicated
the presence of magnetic inhomogeneities in Ni(1-x)V(x) and, in particular,
recognize the magnetic clusters close to xc, on the paramagnetic and on the
ferromagnetic sides with nontrivial dynamical properties [R. Wang et al., Phys.
Rev. Lett. 118, 267202 (2017)]. We present the results of SANS study with full
polarization analysis of polycrystalline Ni(1-x)V(x) samples with x=0.10 and
x=0.11 with low critical temperatures Tc below 50 K. For both Ni-V samples
close to xc we find isotropic magnetic short-range correlations in the
nanometer-scale persisting at low temperatures. They are suppressed gradually
in higher magnetic fields. In addition, signatures of long-range ordered
magnetic domains are present below Tc. The fraction of these magnetic clusters
embedded in the ferromagnetic ordered phase grows towards xc and agrees well
with the cluster fraction estimate from the magnetization and $\mu$SR data. Our
SANS studies provide new insights into the nature of the inhomogeneities in a
ferromagnetic alloy close to a quantum critical point.",2207.14196v2
2023-03-14,The unusual distribution of spin-triplet supercurrents in disk-shaped Josephson junctions,"The phenomenon of s-wave spin triplet Cooper pairs induced in ferromagnetic
metals has been researched now for more than a decade, and its main aspects are
well understood. Crucial in converting s-wave singlet pairs in the
superconductor to s-wave triplets in the ferromagnet is the engineering of
well-defined magnetic inhomogeneity (the 'generator') at the interface with the
superconductor. Vertical layer stacks are typically used as such, where two
separate thin ferromagnetic layers with homogeneous but non-collinear
magnetizations, provide the inhomogeneity. Alternatively, magnetic textures,
like ferromagnetic domain walls and vortices, are possible triplet generators,
although they are far less studied. In this paper we review our experiments on
lateral disk-shaped Josephson junctions where a ferromagnetic bottom layer
provides a weak link with a vortex magnetization imposed by the shape of the
disk. We present three different junction configurations, exhibiting their own
generator mechanism. In the first, we utilize the non-collinearity with a
second ferromagnetic layer to produce the triplet correlations. The second
configuration consists of only the bottom ferromagnet and the superconducting
contacts; it relies on the vortex magnetization itself to generate the
spin-polarized supercurrents. In the third case we exploit an intrinsic
generator by combining a conventional superconductor (NbTi) and a half-metallic
ferromagnetic oxide (La$_{0.7}$Sr$_{0.3}$MnO$_3$). We find strong supercurrents
in all cases. A particularly interesting finding is that the supercurrents are
strongly confined at the rims of the device, independent of the generating
mechanism, but directly related to their triplet nature. What causes these rim
currents remains an open question.",2303.07993v1
2024-01-31,Ferromagnetic Semiconductors and Spintronic Devices,"Ferromagnetic semiconductors play a crucial role in spintronic devices,
enabling effective control of electron spin over charge. This study explores
their unique properties, ongoing advancements in spin control, and potential
integration into next-generation semiconductor technologies.",2401.17554v1
1995-02-24,Ferromagnetism in Hubbard Models: Low Density Route,"Thirty years ago the Hubbard model was introduced by Gutzwiller, Hubbard and
Kanamori with the main purpose of mimicking the ferromagnetism of transition
metals. Soon after, Nagaoka and Thouless pointed out a basic mechanism for
ferromagnetism in strongly correlated electron systems by studying the motion
of a single hole in a half--filled Hubbard model. This important work was hoped
to shed light onto metallic ferromagnetism from the low doping regime.
Unfortunately, this low doping route towards ferromagnetism has not been
successful as far as rigorous results for finite doping concentrations are
concerned. In the work presented here, we start from the opposite limit of low
particle concentrations. In this limit we provide the first proof of a fully
polarized metallic ground state for a Hubbard model. The proof proceeds by
mapping Hubbard ``zigzag'' chains onto a continuum model with an additional
degree of freedom and local first Hund's rule coupling. For this model the
maximum total spin multiplet is shown to be the unique ground state for
infinite Hubbard coupling. Our proof may open a low density route towards the
understanding of the ferromagnetism of Hubbard models.",9502104v1
1999-08-02,Aging phenomena in spin glass and ferromagnetic phases: domain growth and wall dynamics,"We compare aging in a disordered ferromagnet and in a spin glass, by studying
the different phases of a reentrant system. We have measured the relaxation of
the low-frequency ac susceptibility, in both the ferromagnetic and spin-glass
phases of a CdCr_{1.9}In_{0.1}S_4 sample. A restart of aging processes when the
temperature is lowered (`chaos-like' effect) is observed in both phases. The
memory of previous aging at a higher temperature can be retrieved upon
re-heating, but in the ferromagnetic phase it can rapidly be erased by the
growth of ferromagnetic domains. We interpret the behaviour observed in the
ferromagnetic phase in terms of a combination of domain growth and pinned wall
reconformations, and suggest that aging in spin glasses is dominated by such
wall reconformation processes.",9908030v2
1999-11-11,"Field-induced segregation of ferromagnetic nano-domains in Pr$_{0.5}$Sr$_{0.5}$MnO$_3$, detected by $^{55}$Mn NMR","The antiferromagnetic manganite Pr$_{0.5}$Sr$_{0.5}$MnO$_3$ was investigated
at low temperature by means of magnetometry and $^{55}$Mn NMR. A field-induced
transition to a ferromagnetic state is detected by magnetization measurements
at a threshold field of a few tesla. NMR shows that the ferromagnetic phase
develops from zero field by the nucleation of microscopic ferromagnetic
domains, consisting of an inhomogeneous mixture of tilted and fully aligned
parts. At the threshold the NMR spectrum changes discontinuously into that of a
homogeneous, fully aligned, ferromagnetic state, suggesting a percolative
origin for the ferromagnetic transition.",9911164v1
2000-01-26,Double-exchange is not the cause of ferromagnetism in doped manganites,"The coexistence of ferromagnetism and metallic conduction in doped manganites
has long been explained by a double-exchange model in which the ferromagnetic
exchange arises from the carrier hopping. We evaluate the zero-temperature spin
stiffness D(0) and the Curie temperature T_{C} on the basis of the
double-exchange model using the measured values of the bare bandwidth W and the
Hund's rule coupling J_{H}. The calculated D(0) and T_{C} values are too small
compared with the observed ones even in the absence of interactions. A
realistic onsite interorbital Coulomb repulsion can reduce D(0) substantially
in the case of a 2-orbital model. Furthermore, experiment shows that D(0) is
simply proportional to x in La_{1-x}Sr_{x}MnO_{3} system, independent of
whether the ground state is a ferromagnetic insulator or metal. These results
strongly suggest that the ferromagnetism in manganites does not originate from
the double-exchange interaction. On the other hand, an alternative model based
on the d-p exchange can semi-quantitatively explain the ferromagnetism of doped
manganites at low temperatures.",0001390v4
2000-10-31,Superconducting crossed correlations in ferromagnets: implications for thermodynamics and quantum transport,"It is demonstrated that non local Cooper pairs can propagate in ferromagnetic
electrodes having an opposite spin orientation. In the presence of such crossed
correlations, the superconducting gap is found to depend explicitly on the
relative orientation of the ferromagnetic electrodes. Non local Cooper pairs
can in principle be probed with dc-transport. With two ferromagnetic
electrodes, we propose a ``quantum switch'' that can be used to detect
correlated pairs of electrons. With three or more ferromagnetic electrodes, the
Cooper pair-like state is a linear superposition of Cooper pairs which could be
detected in dc-transport. The effect also induces an enhancement of the
ferromagnetic proximity effect on the basis of crossed superconducting
correlations propagating along domain walls.",0010490v3
2000-11-22,"Do As antisites destroy the ferromagnetism of (Ga,Mn)As?","The effect of the inclusion of As antisites in the diluted magnetic
semiconductor (Ga,Mn)As is studied within density functional theory in the
local spin density approximation. In the case of homogeneous distribution of Mn
ions we find that the ferromagnetism is largely weakened by the presence of the
antisites. This is due to compensation of the free holes which mediate the long
range ferromagnetic order. In contrast, when two Mn ions are coupled through
only one As ion, ferromagnetic and antiferromagnetic order compete. In this
case the magnetic ground state depends on: i) the position of the As antisites
relative to the Mn, and ii) the As antisite concentration. We explain our
results using a model of competing antiferromagnetic super-exchange and
ferromagnetic double-exchange via localized Zener carriers. The strong
dependence of the ferromagnetic order on the microscopic configuration accounts
for the large variation in experimental data",0011372v1
2000-12-12,Metallic Ferromagnetism - an Electronic Correlation Phenomenon,"New insights into the microscopic origin of itinerant ferromagnetism were
recently gained from investigations of electronic lattice models within
dynamical mean-field theory (DMFT). In particular, it is now established that
even in the one-band Hubbard model metallic ferromagnetism is stable at
intermediate values of the interaction U and density n on regular, frustrated
lattices. Furthermore, band degeneracy along with Hund's rule couplings is very
effective in stabilizing metallic ferromagnetism in a broad range of electron
fillings. DMFT also permits one to investigate more complicated correlation
models, e.g., the ferromagnetic Kondo lattice model with Coulomb interaction,
describing electrons in manganites with perovskite structure. Here we review
recent results obtained with DMFT which help to clarify the origin of
band-ferromagnetism as a correlation phenomenon.",0012203v1
2001-02-22,Low-Temperature Properties of Quasi-One-Dimensional Molecule-Based Ferromagnets,"Quantum and thermal behaviors of low-dimensional mixed-spin systems are
investigated with particular emphasis on the design of molecule-based
ferromagnets. One can obtain a molecular ferromagnet by assembling molecular
bricks so as to construct a low-dimensional system with a magnetic ground state
and then coupling the chains or the layers again in a ferromagnetic fashion.
Two of thus-constructed quasi-one-dimensional bimetallic compounds are
qualitatively viewed within the spin-wave treatment, one of which successfully
grows into a bulk magnet, while the other of which ends in a singlet ground
state. Then, concentrating on the ferrimagnetic arrangement on a two-leg ladder
which is well indicative of general coupled-chain ferrimagnets, we develop the
spin-wave theory and fully reveal its low-energy structure. We inquire further
into the ferromagnetic aspect of the ferrimagnetic ladder numerically
calculating the sublattice magnetization and the magnetic susceptibility. There
exists a moderate coupling strength between the chains in order to obtain the
most ferromagnetic ferrimagnet.",0102417v2
2001-05-15,Shot noise in ferromagnet--normal metal systems,"A semiclassical theory of the low frequency shot noise in ferromagnet -
normal metal systems is formulated. Non-collinear magnetization directions of
the ferromagnetic leads, arbitrary junctions and the elastic and inelastic
scattering regimes are considered. The shot noise is governed by a set of
mesoscopic parameters that are expressed in terms of the microscopic details of
the junctions in the circuit. Explicit results in the case of ballistic,
tunnel, and diffusive junctions are evaluated. The shot noise, the current and
the Fano factor are calculated for a double barrier ferromagnet - normal metal
- ferromagnet system. It is demonstrated that the shot noise can have a
non-monotonic behavior as a function of the relative angle between the
magnetizations of the ferromagnetic reservoirs.",0105305v2
2001-06-08,Subgap transport in ferromagnet-superconductor junctions due to magnon-assisted Andreev reflection,"We propose a new process of magnon-assisted Andreev reflection at a
ferromagnetic metal - superconductor interface, which consists of the
simultaneous injection of a Cooper pair from the superconductor and the
emission of a magnon inside the ferromagnet. At low temperature this process
represents an additional channel for sub-gap transport across an FS interface,
which lifts restrictions on the current resulting from the necessity to match
spin-polarized current in the ferromagnet with spin-less current in the
superconductor. For a junction between a superconductor and a ferromagnet with
an arbitrary degree of polarization, the inelastic magnon-assisted Andreev
reflection process would manifest itself as a nonlinear addition to the $I(V)$
characteristics which is asymmetric with respect to the sign of the bias
voltage and is related to the density of states of magnons in the ferromagnet.
Expressions for the subgap $I(V)$ characteristics are given for arbitrary
interfacial quality whilst the limiting cases of uniformly transparent and
disordered interfaces are discussed in detail.",0106161v1
2001-09-26,Ferromagnetic Domain Walls in finite systems: mean-field critical exponents and applications,"The distribution of magnetic moments in finite ferromagnetic bodies was first
investigated by Landau and Lifshitz in a famous paper [\textit{Phys. Z. Soviet
Union}, \textbf{8}, 153 (1935)], where they obtained the domain structure of a
ferromagnetic crystal at low temperatures, in the regime of saturated
magnetization. In this article, we investigate the general properties of
ferromagnetic domain walls of uniaxial crystals from the view point of the
Landau free energy. We present the basic ideas at an introductory level, for
non-experts. Extending the formalism to the vicinity of the Curie temperature,
where a general qualitative description by the Landau theory of phase
transitions can be applied, we find that domain walls tend to suppress the
layers, leading to a continuous vanishing of the domain structure with
anomalous critical exponents. In the saturated regime, we discuss the role of
domain walls in mesoscopic systems and ferromagnetic nanojunctions, relating
the observed magnetoresistance with promising applications in the recent area
of spintronics.",0109499v2
2002-05-30,Collective ferromagnetism in two-component Fermi-degenerate gas trapped in finite potential,"Spin asymmetry of the ground states is studied for the trapped
spin-degenerate (two-component) gases of the fermionic atoms with the repulsive
interaction between different components, and, for large particle number, the
asymmetric (collective ferromagnetic) states are shown to be stable because it
can be energetically favorable to increase the fermi energy of one component
rather than the increase of the interaction energy between up-down components.
We formulate the Thomas-Fermi equations and show the algebraic methods to solve
them. From the Thomas-Fermi solutions, we find three kinds of ground states in
finite system: 1) paramagnetic (spin-symmetric), 2) ferromagnetic (equilibrium)
and 3) ferromagnetic (nonequilibrium) states. We show the density profiles and
the critical atom numbers for these states obtained analytically, and, in
ferromagnetic states, the spin-asymmetries are shown to occur in the central
regions of the trapped gas, and grows up with increasing particle number. Based
on the obtained results, we discuss the experimental conditions and current
difficulties to realize the ferromagnetic states of the trapped atom gas, which
should be overcome.",0205638v2
2002-10-06,Andreev Reflection in Ferromagnet/Superconductor/Ferromagnet Double Junction Systems,"We present a theory of Andreev reflection in a
ferromagnet/superconductor/ferromagnet double junction system. The spin
polarized quasiparticles penetrate to the superconductor in the range of
penetration depth from the interface by the Andreev reflection. When the
thickness of the superconductor is comparable to or smaller than the
penetration depth, the spin polarized quasiparticles pass through the
superconductor and therefore the electric current depends on the relative
orientation of magnetizations of the ferromagnets. The dependences of the
magnetoresistance on the thickness of the superconductor, temperature, the
exchange field of the ferromagnets and the height of the interfacial barriers
are analyzed. Our theory explains recent experimental results well.",0210127v1
2003-01-20,Magnetic Polarons in the 1D FM Kondo Model,"The ferromagnetic Kondo model with classical corespins is studied via
unbiased Monte-Carlo simulations. We show that with realistic parameters for
the manganites and at low temperatures, the double-exchange mechanism does not
lead to phase separation in one-dimensional chains but rather stabilizes
individual ferromagnetic polarons. Within the ferromagnetic polaron picture,
the pseudogap in the one-particle spectral function A_k(\omega) can easily be
explained. Ferromagnetic polarons also clear up a seeming failure of the
double-exchange mechanism in explaining the comparable bandwidths in the
ferromagnetic and paramagnetic phase. For our analysis, we extend a simplified
model, the finite temperature uniform hopping approach (UHA), to include
polarons. It can easily be evaluated numerically and provides a simple
quantitative understanding of the physical features of the ferromagnetic Kondo
model.",0301350v2
2003-03-01,Relaxor ferromagnetic behavior below the antiferromagnetic transition in La0.5Ca0.5MnO3,"A detailed reinvestigation of magnetization in La0.5Ca0.5MnO3 reveals that
although a field of H = 7 T applied at T = 5 K after zero field cooling is
insufficient to convert the low temperature charge ordered antiferromagnetic
phase into ferromagnetic, annealing in a magnetic field as small as H = 1 T
induces ferromagnetic clusters in the charge ordered matrix. The volume phase
fraction of the ferromagnetic clusters increases nearly linearly with the
annealing field until Han = 4 T and then changes dramatically from about 11 %
at 5 T to 60 % at Han = 7 T. This is analogous to the field-induced micro to
macro polar domains in relaxor ferroelectrics. It is suggested that charge
ordered clusters coexist with ferromagnetic phase above the Neel temperature
(TN) and these clusters which transform into ferromagnetic by external magnetic
fields are supercooled below TN. Our results will be relevant to the
observation of many orders of decrease in the resistivity found for H << HC,
where HC is the critical field for metamagnetic transition.",0303007v1
2003-04-24,Ferromagnetism in a dilute magnetic semiconductor -- Generalized RKKY interaction and spin-wave excitations,"Carrier-mediated ferromagnetism in a dilute magnetic semiconductor has been
studied using i) a single-impurity based generalized RKKY approach which goes
beyond linear response theory, and ii) a mean-field-plus-spin-fluctuation
(MF+SF) approach within a (purely fermionic) Hubbard-model representation of
the magnetic impurities, which incorporates dynamical effects associated with
finite frequency spin correlations in the ordered state. Due to a competition
between the magnitude of the carrier spin polarization and its oscillation
length scale, the ferromagnetic spin coupling is found to be optimized with
respect to both hole doping concentration and impurity-carrier spin coupling
energy $J$ (or equivalently $U$). The ferromagnetic transition temperature
$T_c$, deteremined within the spin-fluctuation theory, corresponds closely with
the observed $T_c$ values. Positional disorder of magnetic impurities causes
significant stiffening of the high-energy magnon modes. We also explicitly
study the stability/instability of the mean-field ferromagnetic state, which
highlights the role of competing AF interactions causing spin twisting and
noncollinear ferromagnetic ordering.",0304557v2
2003-06-05,Andreev drag effect in ferromagnetic-normal-superconducting systems,"We investigate conductances and current correlations in a system consisting
of a normal multichannel conductor connected to one superconducting and two
ferromagnetic electrodes. For antiparallel orientation of the ferromagnet
polarizations, current injection from one ferromagnet can, due to Andreev
reflection, lead to a net drag of current from the second ferromagnet toward
the superconductor. We present the conditions for the Andreev drag in terms of
the degree of lead polarizations, contact conductances and spin-flip
scattering. Remarkably, both equilibrium and nonequilibrium zero-frequency
current correlations between the ferromagnets become positive even in the
presence of spin relaxation.",0306132v2
2003-06-25,Static magnetic response of clusters in Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel oxide,"Earlier investigation of Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel has
shown the existence of ""super-ferromagnetic "" clusters containing Fe^{3+} and
Ho^{3+} ions along with small size clusters of Fe^{3+} ions (Bhowmik et al, J.
Magn. Magn. Mater. {247}, 83 (2002)). Here, We report the static magnetic
response of these clusters. The experimental data suggests some interesting
magnetic features, such as, enhancement of magnetization; re-entrant magnetic
transitions with paramagnetic to ferromagnetic state below 225 K and
ferromagnetic to spin glass state below 120 K; appearance of field induced
ferromagnetism. We also observe an unusual maximum in the thermoremanent
magnetization (TRM) vs temperature data. Our measurements suggest that this
unusuality in TRM is related to the blocking of ""super-ferromagnetic"" clusters
,out of the ferromagnetic state, along their local anisotropy axis.",0306653v1
2004-01-15,Driven Random Field Ising Model: some exactly solved examples in threshold activated kinetics,"The random field Ising model driven by a slowly varying uniform external
field at zero temperature provides a caricature of several threshold activated
systems. In this model, the non-equilibrium response of the system can be
obtained analytically on a Bethe lattice if the initial state of the system has
all spins aligned parallel to each other. We consider ferromagnetic as well as
anti-ferromagnetic interactions. The ferromagnetic model exhibits avalanches
and non-equilibrium critical behavior. The anti-ferromagnetic model is marked
by the absence of these features. The ferromagnetic model is Abelian, and the
anti-ferromagnetic model is non-Abelian. Theoretical approaches based on the
probabilistic method are discussed in the two cases, and illustrated by
deriving some basic results.",0401252v1
2004-04-06,"Topological Defects in Ferromagnetic, Antiferromagnetic and Cyclic Spinor Condensates -- A Homotopy Theory","We apply the homotopy group theory in classifying the topological defects in
atomic spin-1 and spin-2 Bose-Einstein condensates. The nature of the defects
depends crucially on the spin-spin interaction between the atoms. We find the
topologically stable defects both for spin-1 ferromagnetic and
anti-ferromagnetic states, and for spin-2 ferromagnetic and cyclic states. With
this rigorous approach we clarify the previously controversial identification
of symmetry groups and order parameter spaces for the spin-1 anti-ferromagnetic
state, and show that the spin-2 cyclic case provides a rare example of a
physical system with non-Abelian line defects, like those observed in biaxial
nematics. We also show the possibility to produce vortices with fractional
winding numbers of 1/2, 1/3 and their multiples in spinor condensates.",0404138v1
2004-05-17,Itinerant Ferromagnetism and Superconductivity,"Superconductivity has again become a challenge following the discovery of
unconventional superconductivity. Resistance-free currents have been observed
in heavy-fermion materials, organic conductors and copper oxides. The discovery
of superconductivity in a single crystal of $UGe_2$, $ZrZn_2$ and $URhGe$
revived the interest in the coexistence of superconductivity and
ferromagnetism. The experiments indicate that: i)The superconductivity is
confined to the ferromagnetic phase. ii)The ferromagnetic order is stable
within the superconducting phase (neutron scattering experiments). iii) The
specific heat anomaly associated with the superconductivity in these materials
appears to be absent. The specific heat depends on the temperature linearly at
low temperature.
  I present a review of the recent experimental results and the basic
theoretical ideas concerning ferromagnetic superconductivity
(FM-superconductivity) induced by the ferromagnetic spin fluctuations. A
particular attention is paid to the magnon exchange mechanism of
FM-superconductivity.",0405371v2
2004-06-18,Spin pumping and magnetization dynamics in ferromagnet-Luttinger liquid junctions,"We study spin transport between a ferromagnet with time-dependent
magnetization and a conducting carbon nanotube or quantum wire, modeled as a
Luttinger liquid. The precession of the magnetization vector of the ferromagnet
due for instance to an outside applied magnetic field causes spin pumping into
an adjacent conductor. Conversely, the spin injection causes increased
magnetization damping in the ferromagnet. We find that, if the conductor
adjacent to the ferromagnet is a Luttinger liquid, spin pumping/damping is
suppressed by interactions, and the suppression has clear Luttinger liquid
power law temperature dependence. We apply our result to a few particular
setups. First we study the effective Landau-Lifshitz-Gilbert (LLG) coupled
equations for the magnetization vectors of the two ferromagnets in a FM-LL-FM
junction. Also, we compute the Gilbert damping for a FM-LL and a FM-LL-metal
junction.",0406437v1
2004-09-21,Ferromagnet-superconductor proximity effect: The clean limit,"We study theoretically the influence of ferromagnetic metals on a
superconducting film in the clean limit. Using a self-consistent solution of
the Bogoliubov--de Gennes equation for a ferromagnet-superconductor-ferromagnet
double junction we calculate the pair potential and conductance spectra as a
function of the superconducting layer thickness $d$ for different strengths of
ferromagnets and interface transparencies. We find that the pair potential and
the critical temperature are weakly perturbed by the exchange interaction and
do not drop to zero for any finite $d$. On the other hand, for thin
superconducting films charge transport is spin polarized and exhibits a
significant dependence on the ferromagnetic strength and magnetization
alignment.",0409544v3
2004-10-12,"Ferromagnetic Polarons, Phase Separation, Stripes and Polaron Lattice: The two- and three-dimensional ferromagnetic Kondo Model","We investigate the two- and three-dimensional ferromagnetic Kondo lattice
model by unbiased Monte Carlo simulations. A phase diagram for the
two-dimensional model is presented, in which the stability of magnetic order
and ferromagnetic polarons is examined with respect to the antiferromagnetic
superexchange J' and temperature. The Monte Carlo simulations reveal that J' >
0.02 strengthens individual polarons while small J' < 0.02 favors larger
clusters and phase separation except for small doping. Lowering the temperature
stabilizes ferromagnetic polarons for realistic J' > 0.01, while phase
separation is only favored for very small J' < 0.01. Our Monte Carlo
simulations show that low temperatures can lead to diagonal or vertical stripes
depending on J'.
  Simulations for three-dimensional systems yield ferromagnetic polarons, which
form a `polaron lattice' at higher doping levels 0.2 < x < 0.23, when
independent polarons do no longer fit into the system. No tendency to phase
separation is observed in three dimensions.",0410274v1
2004-12-13,Evidence for Uniform Coexistence of Ferromagnetism and Unconventional Superconductivity in UGe_2: A ^73Ge-NQR Study under Pressure,"We report on the itinerant ferromagnetic superconductor UGe_2 through
^73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum
signals a first-order transition from the low-temperature (T) and low-P
ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical
pressure of P_x ~ 1.2 GPa. The superconductivity exhibiting a maximum value of
T_sc=0.7 K at P_x ~ 1.2 GPa, was found to take place in connection with the
P-induced first-order transition. The nuclear spin-lattice relaxation rate
1/T_1 has probed the ferromagnetic transition, exhibiting a peak at the Curie
temperature as well as a decrease without the coherence peak below T_sc. These
results reveal the uniformly coexistent phase of ferromagnetism and
unconventional superconductivity with a line-node gap. We remark on an intimate
interplay between the onset of superconductivity and the underlying electronic
state for the ferromagnetic phases.",0412311v1
2005-02-09,HfO$_2$: a new direction for intrinsic defect driven ferromagnetism,"In view of the recent experimental reports of unexpected ferromagnetism in
HfO$_{2}$ thin films, we carried out first principles investigations looking
for magnetic order possibly brought about by the presence of small
concentrations of intrinsic point defects. {\it Ab initio} electronic structure
calculations using density functional theory (DFT) show that isolated cation
vacancy sites in HfO$_{2}$ lead to the formation of high spin defect states.
Furthermore these appear to be ferromagnetically coupled with a rather short
range magnetic interaction, resulting in a ferromagnetic ground state for the
whole system. More interestingly, the occurrence of these high spin states and
ferromagnetism is in the low symmetry monoclinic phase of HfO$_{2}$. This is
radically different from other systems previously known to exhibit point defect
ferromagnetism, warranting a closer look at the phenomenon.",0502246v1
2005-05-24,Proximity effects in superconductor-ferromagnet heterostructures,"The very special characteristic of the proximity effect in
superconductor-ferromagnet systems is the damped oscillatory behavior of the
Cooper pair wave function in a ferromagnet. In some sense, this is analogous to
the inhomogeneous superconductivity, predicted long time ago by Larkin and
Ovchinnikov (1964), and Fulde and Ferrell (1964), and constantly searched since
that. After the qualitative analysis of the peculiarities of the proximity
effect in the presence of the exchange field, the author provides a unified
description of the properties of the superconductor-ferromagnet
heterostructures. Special attention is paid to the striking non-monotonous
dependance of the critical temperature of the multilayers and bilayers on the
ferromagnetic layer thickness and conditions of the realization of the ""Pi""-
Josephson junctions. The recent progress in the preparation of the high quality
hybrid systems permitted to observe on experiments many interesting effects,
which are also discussed in the article. Finally, the author analyzes the
phenomenon of the domain-wall superconductivity and the influence of
superconductivity on the magnetic structure in superconductor-ferromagnet
bilayers.",0505583v1
2005-10-14,Phase diagram of a dilute ferromagnet model with antiferromagnetic next-nearest-neighbor interactions,"We have studied the spin ordering of a dilute classical Heisenberg model with
spin concentration $x$, and with ferromagnetic nearest-neighbor interaction
$J_1$ and antiferromagnetic next-nearest-neighbor interaction $J_2$. Magnetic
phases at absolute zero temperature $T = 0$ are determined examining the
stiffness of the ground state, and those at finite temperatures $T \neq 0$ are
determined calculating the Binder parameter $g_L$ and the spin correlation
length $\xi_L$. Three ordered phases appear in the $x-T$ phase diagram: (i) the
ferromagnetic (FM) phase; (ii) the spin glass (SG) phase; and (iii) the mixed
(M) phase of the FM and the SG. Near below the ferromagnetic threshold $x_{\rm
F}$, a reentrant SG transition occurs. That is, as the temperature is decreased
from a high temperature, the FM phase, the M phase and the SG phase appear
successively. The magnetization which grows in the FM phase disappears in the
SG phase. The SG phase is suggested to be characterized by ferromagnetic
clusters. We conclude, hence, that this model could reproduce experimental
phase diagrams of dilute ferromagnets Fe$_x$Au$_{1-x}$ and Eu$_x$Sr$_{1-x}$S.",0510372v1
2005-11-15,Precipitation of amorphous ferromagnetic semiconductor phase in epitaxially grown Mn-doped Ge thin films,"We investigated the origin of ferromagnetism in epitaxially grown Mn-doped Ge
thin films. Using low-temperature molecular beam epitaxy, Mn-doped Ge films
were successfully grown without precipitation of ferromagnetic Ge-Mn
intermetallic compounds, such as Mn5Ge3. Magnetic circular dichroism
measurements revealed that the epitaxially grown Mn-doped Ge films exhibited
clear ferromagnetic behavior, but the Zeeman splitting observed at the critical
points was not induced by the s,p-d exchange interactions. High-resolution
transmission electron microscopy and energy dispersive X-ray spectroscopy
analyses show phase separation of amorphous Ge1-xMnx clusters with high Mn
content from a Mn-free monocrystalline Ge matrix. Since amorphous Ge1-xMnx was
characterized as a homogeneous ferromagnetic semiconductor, the precipitation
of the amorphous Ge1-xMnx clusters is the origin of the ferromagnetic
semiconductor behavior of the epitaxially grown Mn-doped Ge films.",0511361v1
2005-11-17,Intrinsic mechanism for high temperature ferromagnetism in GaMnN,"Considerable efforts have been devoted recently to synthesize diluted
magnetic semiconductors having ferromagnetic properties at room temperature
because of their technological impacts for spintronic devices. In 2001
successful growth of GaMnN films showing room temperature ferromagnetism and
p-type conductivity has been reported. The estimated Curie temperature was 940K
at 5.7% of Mn, which is highest among diluted magnetic semiconductors ever been
reported. However, the electronic mechanism behind the ferromagnetic behaviour
has still been controversial. Here we show experimental evidence using the
ferromagnetic samples that Mn atoms are substitutionally dissolved into the GaN
lattice and they exhibit mixed valences of +2 (majority) and +3 (minority). The
p-type carrier density decreases significantly at very low temperatures. At the
same time, magnetization dramatically decreases. The results imply that the
ferromagnetic coupling between Mn atoms is mediated by holes in the mid-gap Mn
band.",0511435v1
2006-01-02,Three--body Correlation Effects on the Spin Dynamics of Double--Exchange Ferromagnets,"We present a variational calculation of the spin wave excitation spectrum of
double--exchange ferromagnets in different dimensions. Our theory recovers the
Random Phase approximation and 1/S expansion results as limiting cases and can
be used to study the intermediate exchange coupling and electron concentration
regime relevant to the manganites. In particular, we treat exactly the long
range three--body correlations between a Fermi sea electron--hole pair and a
magnon excitation and show that they strongly affect the spin dynamics in the
parameter range relevant to experiments in the manganites. The manifestations
of these correlations are many-fold. We demonstrate that they significantly
change the ferromagnetic phase boundary. In addition to a decrease in the
magnon stiffness, we obtain an instability of the ferromagnetic state against
spin wave excitations close to the Brillouin zone boundary.Within a range of
intermediate concentrations, we find a strong softening of the spin wave
dispersion as compared to the Heisenberg ferromagnet with the same stiffness,
which changes into hardening for other concentrations. We discuss the relevance
of these results to experiments in colossal magnetoresistance ferromagnets.",0601025v2
2006-08-09,Temperature dependence of transport spin polarization in NdNi5 measured using Point Contact Andreev reflection,"We report a study in which Point contact Andreev reflection (PCAR)
spectroscopy using superconducting Nb tip has been carried out on NdNi5, a
ferromagnet with a Curie temperature of TC~7.7K. The measurements were carried
out over a temperature range of 2-9K which spans across the ferromagnetic
transition temperature. From an analysis of the spectra, we show that (i) the
temperature dependence of the extracted value of transport spin polarization
closely follows the temperature dependence of the spontaneous magnetization;
(ii) the superconducting quasiparticle lifetime shows a large decrease close to
the Curie temperature of the ferromagnet. We attribute the latter to the
presence of strong ferromagnetic spin fluctuations in the ferromagnet close to
the ferromagnetic transition temperature.",0608214v3
2006-11-14,Re-entrant ferromagnetism in a generic class of diluted magnetic semiconductors,"Considering a general situation where a semiconductor is doped by magnetic
impurities leading to a carrier-induced ferromagnetic exchange coupling between
the impurity moments, we show theoretically the possible generic existence of
three ferromagnetic transition temperatures, T_1 > T_2 > T_3, with two distinct
ferromagnetic regimes existing for T_1 > T > T_2 and T < T_3. Such an
intriguing re-entrant ferromagnetism, with a paramagnetic phase (T_2 > T > T_3)
between two ferromagnetic phases, arises from a subtle competition between
indirect exchange induced by thermally activated carriers in an otherwise empty
conduction band versus the exchange coupling existing in the impurity band due
to the bound carriers themselves. We comment on the possibility of observing
such a re-entrance phenomenon in diluted magnetic semiconductors and magnetic
oxides.",0611384v1
2007-02-22,Ferromagnetism in Fe-doped ZnO Nanocrystals: Experimental and Theoretical investigations,"Fe-doped ZnO nanocrystals are successfully synthesized and structurally
characterized by using x-ray diffraction and transmission electron microscopy.
Magnetization measurements on the same system reveal a ferromagnetic to
paramagnetic transition temperature > 450 K with a low-temperature transition
from ferromagnetic to spin-glass state due to canting of the disordered surface
spins in the nanoparticle system. Local magnetic probes like EPR and Mossbauer
indicate the presence of Fe in both valence states Fe2+ and Fe3+. We argue that
the presence of Fe3+ is due to the possible hole doping in the system by cation
(Zn) vacancies. In a successive ab-initio electronic structure calculation, the
effects of defects (e.g. O- and Zn-vacancy) on the nature and origin of
ferromagnetism are investigated for Fe-doped ZnO system. Electronic structure
calculations suggest hole doping (Zn-vacancy) to be more effective to stabilize
ferromagnetism in Fe doped ZnO and our results are consistent with the
experimental signature of hole doping in the ferromagnetic Fe doped ZnO
samples.",0702525v1
2007-07-10,Superexchange induced canted ferromagnetism in dilute magnets,"We argue, in contrast to recent studies, that the antiferromagnetic
superexchange coupling between nearest neighbour spins does not fully destroy
the ferromagnetism in dilute magnets with long-ranged ferromagnetic couplings.
Above a critical coupling, we find a \textit{canted} ferromagnetic phase with
unsaturated moment. We have calculated the transition temperature using a
simplified local Random Phase Approximation procedure which accounts for the
canting. For the dilute magnetic semiconductors, such as GaMnAs, using
\textit{ab-initio} couplings allows us to predict the existence of a canted
phase and provide an explanation to the apparent contradictions observed in
experimental measurements. Finally, we have compared with previous studies that
used RKKY couplings and reported non-ferromagnetic state when the superexchange
is too strong. Even in this case the ferromagnetism should remain essentially
stable in the form of a canted phase.",0707.1522v1
2007-08-30,A dynamical mean-field theory study of Nagaoka ferromagnetism,"We revisit Nagaoka ferromagnetism in the U=oo Hubbard model within the
dynamical mean-field theory (DMFT) using the recently developed continuous time
quantum Monte Carlo method as the impurity solver. The stability of Nagaoka
ferromagnetism is studied as a function of the temperature, the doping level,
and the next-nearest-neighbor lattice hopping t'. We found that the nature of
the phase transition as well as the stability of the ferromagnetic state is
very sensitive to the t' hopping. Negative t'=-0.1t stabilizes ferromagnetism
up to higher doping levels. The paramagnetic state is reached through a first
order phase transition. Alternatively, a second order phase transition is
observed at t'=0. Very near half-filling, the coherence temperature T_{coh} of
the paramagnetic metal becomes very low and ferromagnetism evolves out of an
incoherent metal rather than conventional Fermi liquid. We use the DMFT results
to benchmark slave-boson method which might be useful in more complicated
geometries.",0708.4240v2
2007-10-11,Analytical investigation of magnetic field distributions around superconducting strips on ferromagnetic substrates,"The complex-field approach is developed to derive analytical expressions of
the magnetic field distributions around superconducting strips on ferromagnetic
substrates (SC/FM strips). We consider the ferromagnetic substrates as ideal
soft magnets with an infinite magnetic permeability, neglecting the
ferromagnetic hysteresis. On the basis of the critical state model for a
superconducting strip, the ac susceptibility $\chi_1'+i\chi_1''$ of a SC/FM
strip exposed to a perpendicular ac magnetic field is theoretically
investigated, and the results are compared with those for superconducting
strips on nonmagnetic substrates (SC/NM strips). The real part $\chi_1'$ for
$H_0/j_cd_s\to 0$ (where $H_0$ is the amplitude of the ac magnetic field, $j_c$
is the critical current density, and $d_s$ is the thickness of the
superconducting strip) of a SC/FM strip is 3/4 of that of a SC/NM strip. The
imaginary part $\chi_1''$ (or ac loss $Q$) for $H_0/j_cd_s<0.14$ of a SC/FM
strip is larger than that of a SC/NM strip, even when the ferromagnetic
hysteresis is neglected, and this enhancement of $\chi_1''$ (or $Q$) is due to
the edge effect of the ferromagnetic substrate.",0710.2151v1
2008-04-03,Pressure-temperature Phase Diagram of Polycrystalline UCoGe Studied by Resistivity Measurement,"Recently, coexistence of ferromagnetism (T_Curie = 2.8K) and
superconductivity (T_sc = 0.8K) has been reported in UCoGe, a compound close to
a ferromagnetic instability at ambient pressure P. Here we present resistivity
measurements under pressure on a UCoGe polycrystal. The phase diagram obtained
from resistivity measurements on a polycrystalline sample is found to be
qualitatively different to those of all other ferromagnetic superconductors. By
applying high pressure, ferromagnetism is suppressed at a rate of 1.4 K/GPa. No
indication of ferromagnetic order has been observed above P ~ 1GPa. The
resistive superconducting transition is, however, quite stable in temperature
and persists up to the highest measured pressure of about 2.4GPa.
Superconductivity would therefore appear also in the paramagnetic phase.
However, the appearance of superconductivity seems to change at a
characteristic pressure P* ~ 0.8GPa. Close to a ferromagnetic instability, the
homogeneity of the sample can influence strongly the electronic and magnetic
properties and therefore bulk phase transitions may differ from the
determination by resistivity measurements.",0804.0500v1
2008-06-01,Spin-glass instability of short-range spherical ferromagnet,"In structurally disordered ferromagnets the weak random dipole-dipole
exchange may transform the polydomain state into a spin-glass one. To some
extent the properties of such phase in disordered isotropic ferromagnet can be
qualitatively described by the spherical model with the short-range
ferromagnetic interaction and weak frustrated infinite-range random-bond
exchange. This model is shown to predict that spin-glass phase substitute the
ferromagnetic one at the arbitrary small disorder strength and that its
thermodynamics has some similarity to that of polydomain state along with some
significant distinctions. In particular, the longitudinal susceptibility at
small fields becomes frozen below transition point at a constant value
depending on the disorder strength, while the third order nonlinear magnetic
susceptibilitiy exhibits the temperature oscillations in small field near the
transition point. The relation of these predictions to the experimental data
for some disordered isotropic ferromagnets is discussed.",0806.0125v1
2008-09-12,Proximity effect and its enhancement by ferromagnetism in high-temperature superconductor-ferromagnet structures,"We consider a bi-layer consisting of a $d-$wave layerd superconductor and
diffusive ferromagnet with a domain wall (DW). The $c-$axis in the
superconductor and DW in the ferromagnet are assumed to be perpendicular to the
interface. We demonstrate that in such a heterostructure the inhomogeneous
exchange field enhances the proximity effect. It is shown that, whereas in the
absence of the exchange field the $d-$wave condensate decays in the normal
metal on the mean free path $l$, the superconductivity penetrates the
ferromagnet along the DW over much larger distances. This happens because the
presence of DW results in a generation of an odd frequency triplet s-wave
component of the condensate. The phenomenon discovered here may help to explain
a recent experiment on high temperature superconductor-ferromagnet bi-lyers.",0809.2199v2
2008-10-01,Lattice disorder and Ferromagnetism in La0.67Ca0.33MnO3 nanoparticle,"We study the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline,
nanocrystalline and amorphous phase. The structural change from crystalline
phase to amorphous phase exhibited a systematic decrease of TC(paramagnetic to
ferromagnetic transition temperature) and spontaneous magnetization (MS). The
experimental results suggested few more features, e.g., appearance of large
magnetic irreversibility in the temperature dependence of magnetization, lack
of magnetic saturation at high magnetic field, blocking of magnetization below
TB, and enhancement of coercivity. In addition, the magnetic phase transition
near to TC has changed from first order character in bulk sample to second
order character in nanocrystalline and amorphous samples. We understand the
observed magnetic features as the effects of decreasing particle size and
increasing magnetic (spin- lattice) disorder. We noted that magnetic dynamics
of amorphous samples is distinctly different from the nanocrystalline samples.
The ferromagnetism of amorphous samples are comparable with the properties of
reported amorphous ferromagnetic nanoparticles. We also demonstrate the effect
of disorder shell in controlling the dynamics of ferromagnetic cores.",0810.0090v1
2008-10-12,The Quantum Noise of Ferromagnetic $π$-Bloch Domain Walls,"We quantify the probability per unit Euclidean-time of reversing the
magnetization of a $\pi$-Bloch vector, which describes the Ferromagnetic Domain
Walls of a Ferromagnetic Nanowire at finite-temperatures, by evaluating the
saddlepoint solution of the grand canonical partition function for the
Ferromagnetic Nanowire consisting of $N$ such soliton and anti-soliton states.
Our approach, based on Langer's Theory, treats the double Sine-Gordon model
that defines the $\pi$-Bloch vectors via a procedure of nonperturbative
renormalization, and uses importance sampling methods to minimise the free
energy of the system, and identify the saddlepoint solution corresponding to
the reversal probability. We identify that whilst the general solution for the
free energy minima cannot be expressed in closed form, we can obtain a closed
expression for the saddlepoint by maximizing the entanglement entropy of the
system. We use this approach to quantify the geometric and non-geometric
contributions to the entanglement entropy of the Ferromagnetic Nanowire,
defined between entangled Ferromagnetic Domain Walls, and evaluate the
Euclidean-time dependence of the domain wall width and angular momentum
transfer at the domain walls, which has been recently proposed as a mechanism
for Quantum Memory Storage.",0810.2087v2
2008-11-09,Thermodynamics of ferromagnetic superconductors with spin-triplet electron pairing,"We present a general thermodynamic theory that describes phases and phase
transitions of ferromagnetic superconductors with spin-triplet electron Cooper
pairing. The theory is based on extended Ginzburg-Landau expansion in powers of
superconducting and ferromagnetic order parameters. We propose a simple form
for the dependence of theory parameters on the pressure that allows correct
theoretical outline of the temperature-pressure phase diagram for which at low
temperatures a stable phase of coexistence of p-wave superconductivity and
itinerant ferromagnetism appears. We demonstrate that the theory is in an
agreement with the experimental data for some intermetallic compounds that are
experimentally proven to be itinerant ferromagnetic exhibiting spin-triplet
superconductivity. Some basic features of quantum phase transitions in such
systems are explained and clarified. We propose to group the spin-triplet
ferromagnetic superconductors in two different types of thermodynamic behavior,
on the basis of quantitative criterion deduced from the present theory and the
analysis of experimental data.",0811.1344v3
2008-12-04,Metallic Ferromagnetism in the Kondo Lattice,"Metallic magnetism is both ancient and modern, occurring in such familiar
settings as the lodestone in compass needles and the hard drive in computers.
Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still
largely missing. The Stoner approach perturbatively treates Coulomb
interactions when the latter need to be large, while the Nagaoka approach
incorporates thermodynamically negligible electrons into a half-filled band.
Here, we show that the ferromagnetic order of the Kondo lattice is amenable to
an asymptotically exact analysis over a range of interaction parameters. In
this ferromagnetic phase, the conduction electrons and local moments are
strongly coupled but the Fermi surface does not enclose the latter (i.e. it is
small). Moreover, non-Fermi liquid behavior appears over a range of frequencies
and temperatures. Our results provide the basis to understand some
long-standing puzzles in the ferromagnetic heavy fermion metals, and raises the
prospect for a new class of ferromagnetic quantum phase transitions.",0812.0819v3
2009-02-24,Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study,"We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on
top of which ferromagnetic SRO islands were grown epitaxially in-situ. When
measured on the ferromagnetic islands, the density of states exhibits small
gap-like features consistent with the expected short range penetration of the
order parameter into the ferromagnet. However, anomalous split-gap structures
are measured on the superconductor in the vicinity of ferromagnetic islands.
This observation may provide evidence for the recently predicted induced
magnetization in the superconductor side of a superconductor/ ferromagnet
junction. The length scale of the effect inside the superconductor was found to
be an order of magnitude larger than the superconducting coherence length. This
is inconsistent with the theoretical prediction of a penetration depth of only
a few superconducting coherence lengths. We discuss a possible origin for this
discrepancy.",0902.4140v1
2009-03-10,Reproducibility of room temperature ferromagnetism in Zn0.95Mn0.05O and its understanding,"The present work reproduces the room temperature ferromagnetism by doping
magnetic Mn atoms in diamagnetic ZnO. The ferromagnetic ordering is extended up
to 640 K in mechanical milled Zn0.95Mn0.05O samples. The bulk and
nanocrystalline samples are stabilized in hexagonal crystal structure with
space group p63mc. The grain size and lattice strain of the samples, estimated
from XRD spectrum using Williamson-Hall plot, showed a significant variation
with milling time. Surface structure (morphology, distribution of grains and
elements) is observed to be reasonably good from SEM picture and EDX spectrum
at room temperature. The ferromagnetic ordering in bulk, milled and alloyed
samples is primarily due to the diffusion of Mn(2+) ions into the lattice sites
of ZnO. The enhancement of magnetic moment and ferromagnetic ordering
temperature with reducing the grain size is discussed in terms of the existing
theoretical predictions and experimental works. The role of mechanical milling
induced disorder for the enhancement of room temperature ferromagnetism in
Zn0.95Mn0.05O (dilute magnetic semiconductor) is also highlighted.",0903.1691v1
2009-10-18,"Response to comment by Tin-Lun Ho on ""Itinerant Ferromagnetism in a Strongly Interacting Fermi Gas of Ultracold Atoms"", Science 325, 1521 (2009)","Ho claims in his comment that our experiment is direct evidence that
itinerant ferromagnetism does not exist in ultracold Fermi gases. This claim is
incorrect and based on an invalid estimate of relaxation times and an erroneous
interpretation of the detectability of ferromagnetic domains. We point out that
the experimental evidence is consistent with the existence of ferromagnetism,
but further experiments are needed to distinguish a ferromagnetic ground state
from a non-magnetic ground state with ferromagnetic correlations.",0910.3419v2
2009-11-10,Co-doped Ceria: Tendency towards ferromagnetism driven by oxygen vacancies,"We perform an electronic structure study for cerium oxide homogeneously-doped
with cobalt impurities, focusing on the role played by oxygen vacancies and
structural relaxation. By means of full-potential ab-initio methods, we explore
the possibility of ferromagnetism as observed in recent experiments. Our
results indicate that oxygen vacancies seem to be crucial for the appearance of
a ferromagnetic alignment among Co impurities, obtaining an increasing tendency
towards ferromagnetism with growing vacancy concentration. The estimated
couplings cannot explain though, the experimentally observed room-temperature
ferromagnetism. In this systematic study, we draw relevant conclusions
regarding the location of the oxygen vacancies and the magnetic couplings
involved. In particular, we find that oxygen vacancies tend to nucleate in the
neighborhood of Co impurities and we get a remarkably strong ferromagnetic
coupling between Co atoms and the Ce^{3+} neighboring ions. The calculated
magnetic moments per cell depend on the degree of reduction which could explain
the wide spread in the magnetization values observed in the experiments.",0911.1959v1
2010-06-15,Field-induced multiple metamagnetization in phase transition from paramagnetic austenite to ferromagnetic martensite in MnNi1-xFexGe,"Tailoring the phase stability and magnetic structure by combining the
antiferromagnetic MnNiGe martensite with ferromagnetic MnFeGe austenite, a
magnetic-field-induced martensitic transformation has been achieved in
MnNi1-xFexGe system. The doped Fe enables the isolated structural and magnetic
transitions of MnNiGe to coincide at room temperature and also establishes
ferromagnetic couplings in six-Mn-centering-one-Fe-atom clusters. The
ferromagnetic clusters transit the antiferromagnetic state in martensite to a
ferromagnetic state and the alloys are further induced to a stronger
ferromagnetic state by external field, resulting in a large magnetization
difference up to 50 emu/g across the transformation. The field-induced
martensitic transformation thus experiences a multiple metamagnetization
process.",1006.2907v1
2010-07-08,Absence of Meissner State and Robust Ferromagnetism in the Superconducting State of UCoGe: Possible Evidence of Spontaneous Vortex State,"We report ac magnetic susceptibility and dc magnetization measurements on the
superconducting ferromagnet UCoGe (with superconducting and Curie temperatures
of $T_{{\rm SC}} \sim 0.5$~K and $T_{{\rm Curie}} \sim 2.5$~K, respectively).
In the normal, ferromagnetic state ($T_{{\rm SC}} < T < T_{{\rm Curie}}$), the
magnetization curve exhibits a hysteresis loop similar to that of a regular
itinerant ferromagnet. Upon lowering the temperature below $T_{{\rm SC}}$, the
spontaneous magnetization is unchanged, but the hysteresis is markedly
enhanced. Even deeply inside the superconducting state, ferromagnetism is not
completely shielded, and there is no Meissner region, a magnetic field region
of $H < H_{\rm c1}$ (a lower critical field). From these results, we suggest
that UCoGe is the first material in which ferromagnetism robustly survives in
the superconducting state and a spontaneous vortex state without the Meissner
state is realized.",1007.1344v1
2011-01-25,Does a ferromagnet with spin-dependent masses produce a spin-filtering effect in a ferromagnetic/insulator/superconductor junction?,"We analyze charge transport through a ballistic
ferromagnet/insulator/superconductor junction by means of the Bogoliubov-de
Gennes equations. We take into account the possibility that ferromagnetism in
the first electrode may be driven by a mass renormalization of oppositely
polarized carriers, i.e. by a spin bandwidth asymmetry, rather than by a rigid
splitting of up-and down-spin electron bands as in a standard Stoner
ferromagnet. By evaluating the averaged charge conductance for both an s- and a
$d_{x^2-y^2}$-wave order parameter for the S side, we show that the mass
mismatch in the ferromagnetic electrode may mimic a spin active barrier.
Indeed, in the $s$-wave case we show that under suitable conditions the spin
dependent conductance of minority carriers below the energy gap $\Delta_0$ can
be larger than for majority carriers, and lower above $\Delta_0$. On the other
hand, for a d_{x^2-y^2}-wave superconductor similar spin-dependent effects give
rise to an asymmetric peak splitting in the conductance. These results suggest
that the junction may work as a spin-filtering device.",1101.4780v1
2011-04-07,Itinerant ferromagnetism in an interacting Fermi gas with mass imbalance,"We study the emergence of itinerant ferromagnetism in an ultra-cold atomic
gas with a variable mass ratio between the up and down spin species. Mass
imbalance breaks the SU(2) spin symmetry leading to a modified Stoner
criterion. We first elucidate the phase behavior in both the grand canonical
and canonical ensembles. Secondly, we apply the formalism to a harmonic trap to
demonstrate how a mass imbalance delivers unique experimental signatures of
ferromagnetism. These could help future experiments to better identify the
putative ferromagnetic state. Furthermore, we highlight how a mass imbalance
suppresses the three-body loss processes that handicap the formation of a
ferromagnetic state. Finally, we study the time dependent formation of the
ferromagnetic phase following a quench in the interaction strength.",1104.1439v2
2013-01-09,Weak ferromagnetism with the Kondo screening effect in the Kondo lattice systems,"We carefully consider the interplay between ferromagnetism and the Kondo
screening effect in the conventional Kondo lattice systems at finite
temperatures. Within an effective mean-field theory for small conduction
electron densities, a complete phase diagram has been determined. In the
ferromagnetic ordered phase, there is a characteristic temperature scale to
indicate the presence of the Kondo screening effect. We further find two
distinct ferromagnetic long-range ordered phases coexisting with the Kondo
screening effect: spin fully polarized and partially polarized states. A
continuous phase transition exists to separate the partially polarized
ferromagnetic ordered phase from the paramagnetic heavy Fermi liquid phase.
These results may be used to explain the weak ferromagnetism observed recently
in the Kondo lattice materials.",1301.1771v3
2013-05-13,Ferromagnetism and Fermi-surface transition in the periodic Anderson model: Second-order phase transition without symmetry breaking,"We study ferromagnetism in the periodic Anderson model with and without a
magnetic field by the Gutzwiller theory. We find three ferromagnetic phases: a
weak ferromagnetic phase (FM0), a half-metallic phase without Fermi surface for
the majority spin (FM1), and a ferromagnetic phase with almost completely
polarized f-electrons (FM2). The Fermi surface changes from the large
Fermi-surface in the paramagnetic state to the small Fermi-surface in FM2. We
also find that the transitions between the ferromagnetic phases can be
second-order phase transitions in spite of the absence of symmetry breaking.
While we cannot define an order parameter for such transitions in an ordinary
way, the topology of the Fermi surface characterizes the transitions, i.e.,
they are Lifshitz transitions.",1305.2653v1
2013-05-20,The 'Higgs' amplitude mode in weak ferromagnetic metals,"Using Ferromagnetic Fermi liquid theory, Bedell and Blagoev derived the
collective low-energy excitations of a weak ferromagnet. They obtained the
well-known magnon (Nambu-Goldstone) mode and found a new gapped mode that was
never studied in weak ferromagnetic metals. In this article we have identified
this mode as the Higgs boson (amplitude mode) of a ferromagnetic metal. This is
identified as the Higgs since it can be show that it corresponds to a
fluctuation of the amplitude of the order parameter. We use this model to
describe the itinerant-electron ferromagnetic material MnSi. By fitting the
model with the existing experimental results, we calculate the dynamical
structure function and see well-defined peaks contributed from the magnon and
the Higgs. Our estimates of the relative intensity of the Higgs amplitude mode
suggest that it can be seen in neutron scattering experiments on MnSi.",1305.4674v2
2013-07-30,Interfacial Ferromagnetism in LaNiO3/CaMnO3 Superlattices,"We observe interfacial ferromagnetism in superlattices of the paramagnetic
metal LaNiO3 and the antiferromagnetic insulator CaMnO3. LaNiO3 exhibits a
thickness dependent metal-insulator transition and we find the emergence of
ferromagnetism to be coincident with the conducting state of LaNiO3. That is,
only superlattices in which the LaNiO3 layers are metallic exhibit
ferromagnetism. Using several magnetic probes, we have determined that the
ferromagnetism arises in a single unit cell of CaMnO3 at the interface.
Together these results suggest that ferromagnetism can be attributed to a
double exchange interaction among Mn ions mediated by the adjacent itinerant
metal.",1307.8050v1
2014-02-23,Superconductivity and Ferromagnetic Quantum Criticality in Uranium Compounds,"We review our recent studies on ferromagnetic superconductors, UGe2, URhGe
and UCoGe, together with the ferromagnetic quantum criticality and paramagnetic
singularity on the Ising 5f-itinerant system UCoAl. Thanks to the variety of
ordered moment in ferromagnetic superconductors from 1.5 muB to 0.05 muB,
interesting systematic changes or similarities are clarified. All ferromagnetic
superconductors show large upper critical field Hc2, and the field-reentrant
(-reinforced) phenomena are observed in the field-temperature phase diagram,
when the pressure or field direction is tuned for particular conditions. These
phenomena are well explained by the ferromagnetic longitudinal fluctuations,
which are induced by the magnetic field in transverse configurations. The large
Hc2 might be also associated with possible additional effects of Fermi surface
instabilities, such as Lifshitz-type singularities.",1402.5628v1
2014-04-08,Ferromagnetism and impurity band in a new magnetic semiconductor: InMnP,"We have synthesized ferromagnetic InMnP, a member of III-Mn-V ferromagnetic
semiconductor family, by Mn ion implantation and pulsed laser annealing. Clear
ferromagnetic hysteresis loops and a perpendicular magnetic anisotropy are
observed up to a Curie temperature of 42 K. Large values of negative
magnetoresistance and magnetic circular dichroism as well as anomalous Hall
effect are further evidences of a ferromagnetic order in InMnP. An effort is
made to understand the transport mechanism in InMnP using the theoretical
models. We find that the valence band of InP does not merge with the impurity
band of the heavily doped ferromagnetic InMnP. Our results suggest that
impurity band conduction is a characteristic of Mn-doped III-V semiconductors
which have deep Mn-acceptor levels.",1404.2023v1
2014-08-05,Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films,"We investigate the magnetization dynamics through the magnetoimpedance effect
in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance
response is dependent on the thickness of the non-magnetic Cu spacer material,
a fact associated to the kind of the magnetic interaction between the
ferromagnetic layers. Thus, we present an experimental study on asymmetric
magnetoimpedance in ferromagnetic films with biphase magnetic behavior and
explore the possibility of tuning the linear region of the magnetoimpedance
curves around zero magnetic field by varying the thickness of the non-magnetic
spacer material, and probe current frequency. We discuss the experimental
magnetoimpedance results in terms of the different mechanisms governing the
magnetization dynamics at distinct frequency ranges, quasi-static magnetic
properties, thickness of the non-magnetic spacer material, and the kind of the
magnetic interaction between the ferromagnetic layers. The results place
ferromagnetic films with biphase magnetic behavior exhibiting asymmetric
magnetoimpedance effect as a very attractive candidate for application as probe
element in the development of auto-biased linear magnetic field sensors.",1408.0992v1
2014-11-05,Homogenization of Composite Ferromagnetic Materials,"Nowadays, nonhomogeneous and periodic ferromagnetic materials are the subject
of a growing interest. Actually such periodic configurations often combine the
attributes of the constituent materials, while sometimes, their properties can
be strikingly different from the properties of the different constituents.
These periodic configurations can be therefore used to achieve physical and
chemical properties difficult to achieve with homogeneous materials. To predict
the magnetic behavior of such composite materials is of prime importance for
applications. The main objective of this paper is to perform, by means of
Gamma-convergence and two-scale convergence, a rigorous derivation of the
homogenized Gibbs-Landau free energy functional associated to a composite
periodic ferromagnetic material, i.e. a ferromagnetic material in which the
heterogeneities are periodically distributed inside the ferromagnetic media. We
thus describe the Gamma-limit of the Gibbs-Landau free energy functional, as
the period over which the heterogeneities are distributed inside the
ferromagnetic body shrinks to zero.",1411.1231v1
2014-11-14,Pairing gaps near ferromagnetic quantum critical points,"We address the quantum-critical behavior of a two-dimensional itinerant
ferromagnetic systems described by a spin-fermion model in which fermions
interact with close to critical bosonic modes. We consider Heisenberg
ferromagnets, Ising ferromagnets, and the Ising nematic transition. Mean-field
theory close to the quantum critical point predicts a superconducting gap with
spin-triplet symmetry for the ferromagnetic systems and a singlet gap for the
nematic scenario. Studying fluctuations in this ordered phase using a nonlinear
sigma model, we find that these fluctuations are not suppressed by any small
parameter. As a result, we find that a superconducting quasi-long-range order
is still possible in the Ising-like models but long-range order is destroyed in
Heisenberg ferromagnets.",1411.4055v2
2014-12-03,Heat-driven spin transport in a ferromagnetic metal,"As a non-magnetic heavy metal is attached to a ferromagnet, a vertically
flowing heat-driven spin current is converted to a transverse electric voltage,
which is known as the longitudinal spin Seebeck effect (SSE). If the
ferromagnet is a metal, this voltage is also accompanied by voltages from two
other sources, i.e. the anomalous Nernst effect in both the ferromagnet and the
proximity-induced ferromagnetic boundary layer. By properly identifying and
carefully separating those different effects, we find that in this pure spin
current circuit the additional spin current drawn by the heavy metal generates
another significant voltage by the ferromagnetic metal itself which should be
present in all relevant experiments.",1412.1139v1
2014-12-04,Thermal and electrical quantum Hall effects in ferromagnet-topological insulator-ferromagnet junction,"We present the theoretical description for a class of experimental setups
that measure quantum Hall coefficients in ferromagnet-topological
insulator-ferromagnet (FM-TI-FM) junctions. We predict that varying the
magnetization direction in ferromagnets, one can change the induced Hall
voltage and transverse temperature gradient from the maximal values,
corresponding to the quantized Hall coefficients, down to their complete
suppression to zero. We provide detailed analysis of thermal and electrical
Hall resistances as functions of the magnetization directions in ferromagnets,
the spin-scattering time in TI, and geometrical positions of FM leads and
measurement contacts.",1412.1697v3
2014-12-22,Control of Edge Currents at a Ferromagnet - Triplet Superconductor Interface by Multiple Helical Majorana Modes,"We study the spin and charge currents flowing at the interface of an
itinerant ferromagnet with a topological spin-triplet superconductor having
different number of time-reversal-invariant Majorana helical modes. Depending
on the number of helical modes, the capacity of carrying spin and charge
currents is shown to be directly related to the amplitude and orientation of
the ferromagnetic magnetization with respect to the superconducting
$\vec{d}$-vector. Differently from the one-helical mode spin-triplet
superconductor, we find that the presence of a finite amount of electronic
hybridization with the two pairs of Majorana helical modes leads to
nonvanishing charge current independently of the ferromagnetic exchange. The
competition between the two pairs of Majorana helical modes remarkably yields a
spin-current response that is almost constant in the range of weak to
intermediate ferromagnetism. The behavior of the spin current is tightly linked
to the direction of the spin-polarization in the ferromagnet and tends to be
flatten for a magnetization that is coplanar to the spin-triplet
$\vec{d}$-vector independently of the number of helical modes.",1412.7053v1
2015-01-13,Doping control of realization of an extended Nagaoka ferromagnetic state from the Mott state,"Inspired by the Nagaoka ferromagnetism, we propose an itinerant model to
study the transition between the Mott singlet state and a ferromagnetic state
by emulating a doping process in finite lattices. In the Nagaoka
ferromagnetism, the total spin of the system takes the maximum value when an
electron is removed from the half-filled system. To incorporate a procedure of
the electron removal, our model contains extra sites as a reservoir of
electrons, and the chemical potential of the reservoir controls the
distribution of electrons. As a function of the chemical potential, the system
exhibits ground-state phase transitions among various values of the total spin,
including a saturated ferromagnetic state due to the Nagaoka mechanism at
finite hole density. We discuss the nature of the ferromagnetism by measuring
various physical quantities, such as the distribution of electrons, the spin
correlation functions, the magnetization process in the magnetic field, and
also the entanglement entropy.",1501.02899v1
2015-02-10,The effect of the heating rate on the order to order phase transition,"The simple cubic spin-1 Ising (BEG) model exhibits the ferromagnetic (F) -
ferromagnetic (F) phase transition at low temperature region for the interval
1.40<d=D/J<1.48 at k=K/J=-0.5. The degree of the F-F phase transtion determines
the special point on the (kT/J, d) phase diagram In this paper, the critical
behavior of the ferromagnetic (F) - ferromagnetic (F) phase transition has been
investigated for different heating rates using the cellular automaton (CA)
heating algorithm. The variations with heating rate for the F-F phase
transition order are quite important at the creation of phase diagrams.
Therefore, the universality class and the type of ferromagnetic (F) -
ferromagnetic (F) phase transition have been researched using the finite - size
scaling theory, the power law relations and the probability distributions. The
results show that the F-F phase transition can be the second order, the first
order or the weak first order depending on the heating rate in the interval
1.40<d<1.48 for k=-0.5.",1502.02924v2
2015-03-02,Carbon p Electron Ferromagnetism in Silicon Carbide,"Ferromagnetism can occur in wide-band gap semiconductors as well as in
carbon-based materials when specific defects are introduced. It is thus
desirable to establish a direct relation between the defects and the resulting
ferromagnetism. Here, we contribute to revealing the origin of defect-induced
ferromagnetism using SiC as a prototypical example. We show that the long-range
ferromagnetic coupling can be attributed to the p electrons of the
nearest-neighbor carbon atoms around the VSiVC divacancies. Thus, the
ferromagnetism is traced down to its microscopic, electronic origin.",1503.00487v1
2015-03-27,Haydeeite: a spin-1/2 kagome ferromagnet,"The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet
that displays long-range magnetic order below TC=4.2 K with a strongly reduced
moment. Our inelastic neutron scattering data show clear spin-wave excitations
that are well described by a Heisenberg Hamiltonian with ferromagnetic
nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K
across the hexagons of the kagome lattice. These values place haydeeite very
close to the quantum phase transition between ferromagnetic order and
non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic
short-range ferromagnetic correlations observed above TC persist well into the
ferromagnetically ordered phase with a behavior distinct from critical
scattering.",1503.08023v2
2015-06-19,Spin superfluidity and long-range transport in thin-film ferromagnets,"In ferromagnets, magnons may condense into a single quantum state. Analogous
to superconductors, this quantum state may support transport without
dissipation. Recent works suggest that longitudinal spin transport through a
thin-film ferromagnet is an example of spin superfluidity. Although intriguing,
this tantalizing picture ignores long-range dipole interactions; we demonstrate
that such interactions dramatically affect spin transport. In single-film
ferromagnets, ""spin superfluidity"" only exists at length scales (a few hundred
nanometers in yttrium iron garnet) somewhat larger than the exchange length.
Over longer distances, dipolar interactions destroy spin superfluidity.
Nevertheless, we predict re-emergence of spin superfluidity in tri-layer
ferromagnet--normal metal--ferromagnet films of $\sim 1\, \mu$m in size. Such
systems also exhibit other types of long-range spin transport in samples
several micrometers in size.",1506.06029v1
2015-07-15,Neutron investigation of the magnetic scattering in an iron-based ferromagnetic superconductor,"Neutron diffraction and small angle scattering experiments have been carried
out on the double-isotopic polycrystalline sample (7Li0.82Fe0.18OD)FeSe.
Profile refinements of the diffraction data establish the composition and
reveal an essentially single phase material with lattice parameters of a=
3.7827 {\AA} and c= 9.1277 {\AA} at 4 K, in the ferromagnetic-superconductor
regime, with a bulk superconducting transition of TC = 18 K. Small angle
neutron scattering (SANS) measurements in zero applied field reveal the onset
of ferromagnetic order below TF ~ 12.5 K, with a wave vector and temperature
dependence consistent with an inhomogeneous ferromagnet of spontaneous vortices
or domains in a mixed state. No oscillatory long range ordered magnetic state
is observed. Field dependent measurements establish a separate component of
magnetic scattering from the vortex lattice, which occurs at the expected wave
vector. The temperature dependence of the vortex scattering does not indicate
any contribution from the ferromagnetism, consistent with diffraction data that
indicate that the ordered ferromagnetic moment is quite small.",1507.04311v1
2015-09-10,Role of hexagonal boron nitride in protecting ferromagnetic nanostructures from oxidation,"Ferromagnetic contacts are widely used to inject spin polarized currents into
non-magnetic materials such as semiconductors or 2-dimensional materials like
graphene. In these systems, oxidation of the ferromagnetic materials poses an
intrinsic limitation on device performance. Here we investigate the role of
ex-situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as
an oxidation barrier for nanostructured cobalt and permalloy electrodes. The
chemical state of the ferromagnets was investigated using X-ray photoemission
electron microscopy owing to its high sensitivity and lateral resolution. We
have compared the oxide thickness formed on ferromagnetic nanostructures
covered by hBN to uncovered reference structures. Our results show that hBN
reduces the oxidation rate of ferromagnetic nanostructures suggesting that it
could be used as an ultra-thin protection layer in future spintronic devices.",1509.03087v2
2015-10-23,Ferromagnetic clouds caused by hole motion in a one-dimensional $t$-$J$ mode,"The one-dimensional $t_1$-$t_2$-$J_1$-$J_2$ model is examined in the one-hole
case, in which the total number of electrons is one less than the number of the
lattice sites. The ground-state phase diagram includes a series of partial
ferromagnetic phases, which are stacked in a regime of positive and small
$J_1$. We find that the ground state in each of these partial ferromagnetic
phases includes a ferromagnetic cloud, which is a multiple-spin bound state
together with the hole. The ferromagnetic cloud is a large magnetic polaron
with a heavy mass in a single-band electronic system and is supposedly formed
as a result of Nagaoka ferromagnetism which locally works around the hole.",1510.06881v1
2015-11-04,Lattice-pseudospin and spin-valley polarizations in dual ferromagnetic-gated silicene junction,"We study spin-valley and lattice-pseudo spin currents in a dual
ferromagnetic-gated silicene-based junction. Silicene has buckled atomic
structure which allows us to take sublattice-dependent ferromagnetism into
account in the investigation. One of the study results show that transmission
at the junctions exhibits anisotropic property only in anti-parallel cases.
Interestingly, the studied junctions can be switched from a pure spin-polarizer
to a pure valley-polarizer by reversing directions of exchange fields in the
parallel junctions. The perfect control of spin-valley currents can be done
only in the parallel cases and its resolution can be enhanced by increasing
gate potential between the ferromagnetic barriers. The asymmetric barriers of
anti-parallel junction is found to destroy both spin and valley filtering
effects and yield a novel result, pure sub-lattice pseudo-spin polarization.
The current in the anti-parallel junctions can be controlled to flow solely in
either A or B sub-lattice, saying that the controllable lattice current in
silicene is created in double ferromagnetic-gated junction. Our work reveals
the potential of dual ferromagnetic-gated silicene junction which may be
possible for applications in spin-valleytronics and lattice-pseudospintronics.",1511.01204v1
2016-01-05,Proximity induced room-temperature ferromagnetism in graphene probed with spin currents,"The introduction and control of ferromagnetism in graphene opens up a range
of new directions for fundamental and applied studies. Several approaches have
been pursued so far, such as introduction of defects, functionalization with
adatoms, and shaping of graphene into nanoribbons with well-defined zigzag
edges. A more robust and less invasive method utilizes the introduction of an
exchange interaction by a ferromagnetic insulator in proximity with graphene.
  Here we present a direct measurement of the exchange interaction in room
temperature ferromagnetic graphene. We study the spin transport in exfoliated
graphene on a yttrium-iron-garnet substrate where the observed spin precession
clearly indicates the presence and strength of an exchange field that is an
unambiguous evidence of induced ferromagnetism. We describe the results with a
modified Bloch diffusion equation and extract an average exchange field of the
order of 0.2 T. Further, we demonstrate that a proximity induced 2D ferromagnet
can efficiently modulate a spin current by controlling the direction of the
exchange field. These results can create a building block for magnetic-gate
tuneable spin transport in one-atom-thick spintronic devices.",1601.00995v1
2016-03-25,The quantum ferromagnetic transition in a clean Kondo lattice is discontinuous,"The Kondo-lattice model, which couples a lattice of localized magnetic
moments to conduction electrons, is often used to describe heavy-fermion
systems. Because of the interplay between Kondo physics and magnetic order it
displays very complex behavior and is notoriously hard to solve. The
ferromagnetic Kondo-lattice model, with a ferromagnetic coupling between the
local moments, describes a phase transition from a paramagnetic phase to a
ferromagnetic one as a function of either temperature or the ferromagnetic
local-moment coupling. At zero temperature, this is a quantum phase transition
that has received considerable attention. It has been theoretically described
to be continuous, or second order. Here we show that this belief is mistaken;
in the absence of quenched disorder the quantum phase transition is first
order, in agreement with experiments, as is the corresponding transition in
other metallic ferromagnets.",1603.07973v2
2017-08-24,Double-slit Fraunhofer pattern as the signature of the Josephson effect between Berezinskii superconductors through the ferromagnetic vortex,"I apply the recently developed formalism of generalized quasiclassical theory
to show that using hybrid superconducting systems with non-collinear strong
ferromagnets one can realize the Josephson junction between Berezinskii-type
superconductors. The reported calculation reproduces main features observed in
the recent experiment, namely the the slightly asymmetric double-slit
Fraunhofer interference pattern of the Josephson current through the
ferromagnetic vortex. The double-slit structure results from the spatially
inhomogeneous Berezinskii state with the amplitude controlled by the local
angle between magnetic moments in two ferromagnetic layers. The critical
current asymmetry by the sign of magnetic field can signal the presence of
spontaneous supercurrents generated by the non-coplanar magnetic texture near
the core of the ferromagnetic vortex core. I demonstrate that ferromagnetic
vortex can induce spontaneous vorticity in the odd-frequency order parameter
manifesting the possibility of the emergent magnetic field to create
topological defects.",1708.07467v2
2020-07-26,Fractionalized Spin Excitations in the Edge Ferromagnetic State of Graphene: Signature of the Ferromagnetic Luttinger Liquid,"The elementary excitations from the conventional magnetic ordered states,
such as ferromagnets and antiferromagnets, are magnons. Here, we elaborate a
case where the well-defined magnons are absent completely and the spin
excitation spectra exhibit an entire continuum in the itinerant edge
ferromagnetic state of graphene arising from the flatband edge electronic
states. Based on the further studies of the entanglement entropy and
finite-size analysis, we show that the continuum other than the Stoner part
results from the spin-1/2 spinons deconfined from magnons. The spinon continuum
in a magnetically ordered state is ascribed to a ferromagnetic Luttinger liquid
in this edge ferromagnet. The investigation is carried out by using the
numerical exact diagonalization method with a projection of the interacting
Hamiltonian onto the flat band.",2007.13142v1
2010-05-07,"Magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO: first-principles calculations","The electronic structure and magnetic coupling properties of rare-earth
metals (Gd, Nd) doped ZnO have been investigated using first-principles
methods. We show that the magnetic coupling between Gd or Nd ions in the
nearest neighbor sites is ferromagnetic. The stability of the ferromagnetic
coupling between Gd ions can be enhanced by appropriate electron doping into
ZnO:Gd system and the room-temperature ferromagnetism can be achieved. However,
for ZnO:Nd system, the ferromagnetism between Nd ions can be enhanced by
appropriate holes doping into the sample. The room-temperature ferromagnetism
can also be achieved in the \emph{n}-conducting ZnO:Nd sample. Our calculated
results are in good agreement with the conclusions of the recent experiments.
The effect of native defects (V$_{\rm{Zn}}$, V$_{\rm{O}}$) on the
ferromagnetism is also discussed.",1005.1115v1
2010-05-12,Ferromagnetism of $UGe_2$,"Magnetism of $UGe_2$ is due to the magnetic ordered moments of $5f$ uranium
electrons. The strong spin-orbit coupling splits them into two groups. The
magnetization is investigated in terms of two vector fields ${\bf M}_{1i}$ and
${\bf M}_{2i}$ which identify the local orientation of the magnetization of the
two groups of $f$ electrons. Renormalized spin-wave theory, which accounts for
the magnon-magnon interaction, and its extension are developed to describe two
ferromagnetic phases in the system: low temperature large moment phase
$0<T<T^{*}$ (FM2), where all $5f$ electrons contribute the ordered
ferromagnetic moment, and high temperature low-moment phase $T^{*}<T<T_C$
(FM1), where $f$ electrons are partially ordered. Both phases are strictly
ferromagnetic in accordance with experiment. The magnetization as a function of
temperature is calculated. The anomalous temperature dependence of the ordered
moment, known from the experiments with $UGe_2$, is very well reproduced
theoretically. Below $T_x$ ($T^*$ in the present paper) the ferromagnetic
moment increases in an anomalous way. The new understanding of the anomalous
$FM2\to FM1$ transition, as a result of the magnetic order of two well
separated groups of $f$ electrons, yields the key to an understanding of the
ferromagnetism and transport properties in these compounds.",1005.2032v1
2017-04-04,Model Hamiltonian and Time Reversal Breaking Topological Phases of Anti-ferromagnetic Half-Heusler Materials,"In this work, we construct a generalized Kane model with a new coupling term
between itinerant electron spins and local magnetic moments of
anti-ferromagnetic ordering in order to describe the low energy effective
physics in a large family of anti-ferromagnetic half-Heusler materials.
Topological properties of this generalized Kane model is studied and a large
variety of topological phases, including Dirac semimetal phase, Weyl semimetal
phase, nodal line semimetal phase, type-B triple point semimetal phase,
topological mirror (or glide) insulating phase and anti-ferromagnetic
topological insulating phase, are identified in different parameter regions of
our effective models. In particular, we find that the system is always driven
into the anti-ferromagnetic topological insulator phase once a bulk band gap is
open, irrespective of the magnetic moment direction, thus providing a robust
realization of anti-ferromagentic topological insulators. Furthermore, we
discuss the possible realization of these topological phases in realistic
anti-ferromagnetic half-Heusler materials. Our effective model provides a basis
for the future study of physical phenomena in this class of materials.",1704.01138v1
2012-01-31,Field Tuning of Ferromagnetic Domain Walls on Elastically Coupled Ferroelectric Domain Boundaries,"We report on the evolution of ferromagnetic domain walls during magnetization
reversal in elastically coupled ferromagnetic-ferroelectric heterostructures.
Using optical polarization microscopy and micromagnetic simulations, we
demonstrate that the spin rotation and width of ferromagnetic domain walls can
be accurately controlled by the strength of the applied magnetic field if the
ferromagnetic walls are pinned onto 90 degrees ferroelectric domain boundaries.
Moreover, reversible switching between magnetically charged and uncharged
domain walls is initiated by magnetic field rotation. Switching between both
wall types reverses the wall chirality and abruptly changes the width of the
ferromagnetic domain walls by up to 1000%.",1201.6521v1
2014-06-11,Relationship between Ferromagnetic Criticality and the Enhancement of Superconductivity Induced by Transverse Magnetic Fields in UCoGe,"We have performed 59Co NMR experiments on the ferromagnetic superconductor
UCoGe under magnetic fields (H) along the a- and b- axes to investigate the
relationship between ferromagnetic properties and superconductivity. The
ferromagnetic ordering temperature TCurie is suppressed and the nuclear
spin-lattice relaxation rate 1/T1 at 2 K is enhanced in H || b, although TCurie
and 1/T1 are unchanged in H || a, indicating that the ferromagnetic criticality
is induced only when H is applied along the b axis. We show the close
relationship between the magnetic anisotropies and the superconducting ones
reported by Aoki et al.: the superconductivity is gradually suppressed in H ||
a, but enhanced in H || b above 5 T. We strongly suggest that the enhancement
of the superconductivity observed in H || b originates from the field induced
ferromagnetic criticality, as pointed out by Aoki et al and Mineev.",1406.2836v1
2017-06-11,Transitions from a Kondo-like diamagnetic insulator into a modulated ferromagnetic metal in $\bm{\mathrm{FeGa}_{3-y}\mathrm{Ge}_y}$,"One initial and essential question of magnetism is whether the magnetic
properties of a material are governed by localized moments or itinerant
electrons. Here we expose the case for the weakly ferromagnetic system
FeGa$_{3-y}$Ge$_y$ wherein these two opposite models are reconciled, such that
the magnetic susceptibility is quantitatively explained by taking into account
the effects of spin-spin correlation. With the electron doping introduced by Ge
substitution, the diamagnetic insulating parent compound FeGa$_3$ becomes a
paramagnetic metal as early as at $ y=0.01 $, and turns into a weakly
ferromagnetic metal around the quantum critical point $ y=0.15 $. Within the
ferromagnetic regime of FeGa$_{3-y}$Ge$_y$, the magnetic properties are of a
weakly itinerant ferromagnetic nature, located in the intermediate regime
between the localized and the itinerant dominance. Our analysis implies a
potential universality for all itinerant-electron ferromagnets.",1706.03326v1
2017-06-19,Competing Ferromagnetic and Anti-Ferromagnetic interactions in Iron Nitride $ζ$-Fe$_2$N,"The paper discusses the magnetic state of zeta phase of iron nitride viz.
$\zeta$-Fe$_2$N on the basis of spin polarized first principles electronic
structure calculations together with a review of already published data.
Results of our first principles study suggest that the ground state of
$\zeta$-Fe$_2$N is ferromagnetic (FM) with a magnetic moment of 1.528
$\mu_\text{B}$ on the Fe site. The FM ground state is lower than the
anti-ferromagnetic (AFM) state by 8.44 meV and non-magnetic(NM) state by 191
meV per formula unit. These results are important in view of reports which
claim that $\zeta$-Fe$_2$N undergoes an AFM transition below 10K and others
which do not observe any magnetic transition up to 4.2K. We argue that the
experimental results of AFM transition below 10K are inconclusive and we
propose the presence of competing FM and AFM superexchange interactions between
Fe sites mediated by nitrogen atoms, which are consistent with
Goodenough-Kanamori-Anderson rules. We find that the anti-ferromagnetically
coupled Fe sites are outnumbered by ferromagnetically coupled Fe sites leading
to a stable FM ground state. A Stoner analysis of the results also supports our
claim of a FM ground state.",1706.05879v1
2018-10-01,Stabilizing Mechanism for Bose-Einstein Condensation of Interacting Magnons in Ferrimagnets and Ferromagnets,"We propose a stabilizing mechanism for the Bose-Einstein condensation (BEC)
of interacting magnons in ferrimagnets and ferromagnets. By studying the
effects of the magnon-magnon interaction on the stability of the magnon BEC in
a ferrimagnet and two ferromagnets, we show that the magnon BEC remains stable
even in the presence of the magnon-magnon interaction in the ferrimagnet and
ferromagnet with a sublattice structure, whereas it becomes unstable in the
ferromagnet without a sublattice structure. This indicates that the existence
of a sublattice structure is the key to stabilizing the BEC of interacting
magnons, and the difference between the spin alignments of a ferrimagnet and a
ferromagnet is irrelevant. Our result can resolve a contradiction between
experiment and theory in the magnon BEC of yttrium iron garnet. Our theoretical
framework may provide a starting point for understanding the physics of the
magnon BEC including the interaction effects.",1810.00584v2
2019-10-31,Ferromagnetic fluctuations in the Rashba-Hubbard model,"We study the occurrence and the origin of ferromagnetic fluctuations in the
longitudinal spin susceptibility of the $t$-$t'$-Rashba-Hubbard model on the
square lattice. The combined effect of the second-neighbor hopping $t'$ and the
spin-orbit coupling leads to ferromagnetic fluctuations in a broad filling
region. The spin-orbit coupling splits the energy bands, leading to two van
Hove fillings, where the sheets of the Fermi surface change their topology.
Between these two van Hove fillings the model shows ferromagnetic fluctuations.
We find that these ferromagnetic fluctuations originate from interband
contributions to the spin susceptibility. These interband contributions only
arise if there is one holelike and one electronlike Fermi surface, which is the
case for fillings in between the two van Hove fillings. We discuss implications
for experimental systems and propose a test on how to identify these types of
ferromagnetic fluctuations in experiments.",1910.14621v2
2020-02-13,Stabilized Interfacial Ferromagnetism and Enhanced Magnetoelectric Properties of Ultrathin FeRh Films Capped with Heavy Transition Metal Ta,"Thin FeRh film was extensively studied recently, and an emergent substrate-
and capping-dependent interfacial ferromagnetism (FM) was widely observed in
experiments. However, the voltage modulation of this interfacial ferromagnetism
is barely studied, which would have profound applications in antiferromagnetic
(AFM) FeRh-based magnetoelectric-random access memory (MeRAM). Using ab initio
techniques, we comparatively study the interfacial ferromagnetic properties and
magnetoelectric responses of ultrathin FeRh films capped by heavy transition
metal Ta. We find that Ta capping reverses the phase stability of ultrathin
FeRh film below 1.5 nm and gigantically stabilizes the ferromagnetic phase and
interfacial ferromagnetism. Besides, small magnetic moment of 2.2 $\mu_B$ for
neighboring Fe atoms, regardless of magnetic configurations and film thickness,
is induced by Ta capping. Compared with FeRh/MgO bilayers, magnetic
anisotropies (in-plane for AFM, perpendicular for FM and interfacial-FM
reconstructed trilayers) and magnetoelectric responses of these trilayers are
enhanced. Furthermore, the VCMA behavior in FM phase is changed from
$\vee$-shaped to linear. These findings demonstrate the manipulation of
magnetic ordering of FeRh films with heavy metal capping and electric field and
can promote the application of FeRh alloy in magnetic memory and
antiferromagnetic spintronics.",2002.05621v1
2020-04-29,High throughput computational screening for two-dimensional magnetic materials based on experimental databases of three-dimensional compounds,"We perform a computational screening for two-dimensional magnetic materials
based on experimental bulk compounds present in the Inorganic Crystal Structure
Database and Crystallography Open Database. A recently proposed geometric
descriptor is used to extract materials that are exfoliable into
two-dimensional derivatives and we find 85 ferromagnetic and 61
anti-ferromagnetic materials for which we obtain magnetic exchange and
anisotropy parameters using density functional theory. For the easy-axis
ferromagnetic insulators we calculate the Curie temperature based on classical
Monte Carlo simulations of anisotropic Heisenberg models. We find good
agreement with the experimentally reported Curie temperatures of known 2D
ferromagnets and identify 10 potentially exfoliable two-dimensional
ferromagnets that have not been reported previously. In addition, we find 18
easy-axis anti-ferromagnetic insulators with several compounds exhibiting very
strong exchange coupling and magnetic anisotropy.",2004.14460v1
2021-01-22,Localized 4f-electrons in the quantum critical heavy fermion ferromagnet CeRh$_6$Ge$_4$,"Ferromagnetic quantum critical points were predicted to be prohibited in
clean itinerant ferromagnetic systems, yet such a phenomenon was recently
revealed in CeRh$_6$Ge$_4$, where the Curie temperature can be continuously
suppressed to zero under a moderate hydrostatic pressure. Here we report the
observation of quantum oscillations in CeRh$_6$Ge$_4$ from measurements using
the cantilever and tunnel-diode oscillator methods in fields up to 45 T,
clearly demonstrating that the ferromagnetic quantum criticality occurs in a
clean system. In order to map the Fermi surface of CeRh$_6$Ge$_4$, we performed
angle-dependent measurements of quantum oscillations at ambient pressure, and
compared the results to density functional theory calculations. The results are
consistent with the Ce 4f electrons remaining localized, and not contributing
to the Fermi surface, suggesting that localized ferromagnetism is a key factor
for the occurrence of a ferromagnetic quantum critical point in CeRh$_6$Ge$_4$.",2101.08972v1
2017-04-29,Theory of magnetism in La$_2$NiMnO$_6$,"The magnetism of ordered and disordered La$_2$NiMnO$_6$ is explained using a
model involving double exchange and superexchange. The concept of majority spin
hybridization in the large coupling limit is used to explain the ferromagnetism
of La$_2$NiMnO$_6$ as compared to the ferrimagnetism of Sr$_{2}$FeMoO$_{6}$.
The ferromagnetic insulating ground state in the ordered phase is explained.
The essential role played by the Ni-Mn superexchange between the Ni $e_{g}$
electron spins and the Mn $t_{2g}$ core electron spins in realizing this ground
state, is outlined. In presence of antisite disorder, the model system is found
to exhibit a tendency of becoming a spin-glass at low temperatures, while it
continues to retain a ferromagnetic transition at higher temperatures, similar
to recent experimental observations [D. Choudhury .et.al., Phys. Rev. Lett.
108, 127201 (2012)]. This reentrant spin-glass or reentrant ferromagnetic
behaviour is explained in terms of the competition of the ferromagnetic double
exchange between the Ni $e_{g}$ and the Mn $e_{g}$ electrons, and the
ferromagnetic Ni-Mn superexchange, with the antiferromagnetic antisite Mn-Mn
superexchange.",1705.00177v2
2018-07-03,Antiferromagnetism emerging in a ferromagnet with gain,"We present a theoretical mapping to show that a ferromagnet with gain (loss)
is equivalent to an antiferromagnet with an equal amount of loss (gain). Our
finding indicates a novel first-order ferromagnet-antiferromagnet phase
transition by tuning the gain-loss parameter. As an appealing application, we
demonstrate the realization as well as the manipulation of the
antiferromagnetic skyrmion, a stable topological quasiparticle not yet observed
experimentally, in a chiral ferromagnetic thin film with gain. We also consider
ferromagnetic bilayers with balanced gain and loss, and show that the
antiferromagnetic skyrmion can be found only in the cases with broken
parity-time symmetry phase. Our results pave a way for investigating the
emerging antiferromagnetic spintronics and parity-time symmetric magnonics in
ferromagnets.",1807.01048v2
2019-01-07,"Heavily Fe-doped n-type ferromagnetic semiconductor (In,Fe)Sb with high Curie temperature and large magnetic anisotropy","We present high-temperature ferromagnetism and large magnetic anisotropy in
heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 -
35%) thin films grown by low-temperature molecular beam epitaxy. The
(In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and
band structure with single-phase ferromagnetism. The Curie temperature (TC) of
(In1-x,Fex)Sb reaches 390 K at x = 35%, which is significantly higher than room
temperature and the highest value so far reported in III-V based ferromagnetic
semiconductors. Moreover, large coercive force (HC = 160 Oe) and large remanent
magnetization (Mr/MS = 71%) have been observed for a (In1-x,Fex)Sb thin film
with x = 35%. Our results indicate that the n-type ferromagnetic semiconductor
(In1-x,Fex)Sb is very promising for spintronics devices operating at room
temperature.",1901.01996v1
2019-04-09,On the origin and the manipulation of ferromagnetism in Fe$_3$GeTe$_2$: defects and dopings,"To understand the magnetic properties of Fe$_3$GeTe$_2$, we performed the
detailed first-principles study. Contrary to the conventional wisdom, it is
unambiguously shown that Fe$_3$GeTe$_2$ is not ferromagnetic but
antiferromagnetic carrying zero net moment in its stoichiometric phase. Fe
defect and hole doping are the keys to make this material ferromagnetic, which
are shown by the magnetic force response as well as the total energy
calculation with the explicit Fe defects and the varied system charges.
Further, we found that the electron doping also induces the antiferro- to
ferromagnetic transition. It is a crucial factor to understand the notable
recent experiment of gate-controlled ferromagnetism. Our results not only
unveil the origin of ferromagnetism of this material but also show how it can
be manipulated with defect and doping.",1904.04510v1
2019-12-05,Magnetic-field effect in the heterostructure Ba$_{0.8}$Sr$_{0.2}$TiO$_3$/LaMnO$_3$,"We have studied transport and magnetotransport properties of the
heterostructure consisting of the ferroelectric Ba$_{0.8}$Sr$_{0.2}$TiO$_3$
film deposited on the single crystalline manganite LaMnO$_3$. Two-dimensional
electron gas arising at the interface transforms the interface region of the
antiferromagnetic manganite to the ferromagnetic state with the reoriented
magnetic moments. We obtained that the contribution of these ferromagnetic
regions to the resistance of the heterostructure appears to be dependent on the
external magnetic field applied perpendicularly to the interface (and parallel
to {\it c}-axis of the ferromagnetic state of LaMnO$_3$). We believe that the
decrease of the resistance of the studied heterostructure under the influence
of the external magnetic field is caused by an appearance of the ferromagnetic
order in the interface area. This leads to a relatively small resistance. In
turn, the cycling of the applied magnetic field leads to the increase of the
regions of the ferromagnetic order and, as a result, to decreasing scattering
of the current carriers at the ferromagnetic disordering.",1912.02507v1
2020-03-20,Emergence of a ferromagnetic insulating state in LaMnO$_3$/SrTiO$_3$ heterostructures: The role of strong electronic correlations and strain,"Inspired by the experimental findings of an exotic ferromagnetic insulating
state in LaMnO$_3$/SrTiO$_3$ heterostructures, we calculate the electronic and
magnetic state of LaMnO$_3$/SrTiO$_3$ superlattices with comparable thicknesses
employing ab-initio dynamical mean-field theory. Projecting on the low-energy
subspace of Mn $3d$ and Ti $3d$ states, and solving a multi-impurity problem,
our approach emphasizes on local correlations at Mn and Ti sites. We find that
a ferromagnetic insulating state emerges due to intrinsic effects of strong
correlations in the system, in agreement with experimental studies. We also
predict that, due to electronic correlations, the emerging 2D electron gas is
located at the LMO side of the interface. This is in contrast to DFT results
that locate the electron gas on the STO side. We estimate the transition
temperature for the paramagnetic to ferromagnetic phase transition, which may
be verified experimentally. Importantly, we also clarify that the epitaxial
strain is a key ingredient for the emergence of the exotic ferromagnetic
insulating state. This becomes clear from calculations on a strained LaMnO$_3$
system, also showing ferromagnetism which is not seen in the unstrained bulk
material.",2003.09189v1
2020-06-16,Gravity Probe Spin: Prospects for measuring general-relativistic precession of intrinsic spin using a ferromagnetic gyroscope,"An experimental test at the intersection of quantum physics and general
relativity is proposed: measurement of relativistic frame dragging and geodetic
precession using intrinsic spin of electrons. The behavior of intrinsic spin in
spacetime dragged and warped by a massive rotating body is an experimentally
open question, hence the results of such a measurement could have important
theoretical consequences. Such a measurement is possible by using mm-scale
ferromagnetic gyroscopes in orbit around the Earth. Under conditions where the
rotational angular momentum of a ferromagnet is sufficiently small, a
ferromagnet's angular momentum is dominated by atomic electron spins and is
predicted to exhibit macroscopic gyroscopic behavior. If such a ferromagnetic
gyroscope is sufficiently isolated from the environment, rapid averaging of
quantum uncertainty via the spin-lattice interaction enables readout of the
ferromagnetic gyroscope dynamics with sufficient sensitivity to measure both
the Lense-Thirring (frame dragging) and de Sitter (geodetic precession) effects
due to the Earth.",2006.09334v1
2020-09-28,Coexistence of intrinsic piezoelectricity and ferromagnetism induced by small biaxial strain in septuple-atomic-layer $\mathrm{VSi_2P_4}$,"The septuple-atomic-layer $\mathrm{VSi_2P_4}$ with the same structure of
experimentally synthesized $\mathrm{MoSi_2N_4}$ is predicted to be a
spin-gapless semiconductor (SGS). In this work, the biaxial strain is applied
to tune electronic properties of $\mathrm{VSi_2P_4}$, and it spans a wide range
of properties upon the increasing strain from ferromagnetic metal (FMM) to SGS
to ferromagnetic semiconductor (FMS) to SGS to ferromagnetic half-metal (FMHM).
Due to broken inversion symmetry, the coexistence of ferromagnetism and
piezoelectricity can be achieved in FMS $\mathrm{VSi_2P_4}$ with strain range
of 0\% to 4\%. The calculated piezoelectric strain coefficients $d_{11}$ for
1\%, 2\% and 3\% strains are 4.61 pm/V, 4.94 pm/V and 5.27 pm/V, respectively,
which are greater than or close to a typical value of 5 pm/V for bulk
piezoelectric materials. Finally, similar to $\mathrm{VSi_2P_4}$, the
coexistence of piezoelectricity and ferromagnetism can be realized by strain in
the $\mathrm{VSi_2N_4}$ monolayer. Our works show that $\mathrm{VSi_2P_4}$ in
FMS phase with intrinsic piezoelectric properties can have potential
applications in spin electronic devices.",2009.13022v1
2020-10-09,Interface-induced field-like optical spin torque in a ferromagnet/heavy metal heterostructure,"The manipulation of magnetization in a metallic ferromagnet by using optical
helicity has been much attracted attention for future opto-spintronic devices.
The optical helicity induced torques on the magnetization, {\it optical spin
torque}, have been observed in ferromagnetic thin films recently. However, the
interfacial effect of the optical spin torque in ferromagnet/nonmagnetic heavy
metal heterostructures have not been addressed so far, which are widely
utilized to efficiently control magnetization via electrical means. Here, we
studied optical spin torque vectors in the ferromagnet/nonmagnetic heavy metal
heterostructures and observed that in-plane field-like optical spin torque was
significantly increased with decreasing ferromagnetic layer thicknesses. The
interfacial field-like optical spin torque was explained by the optical
Rashba-Edelstein effect caused by the structural inversion symmetry breaking.
This work will aid in the efficient optical manipulation of thin film
nanomagnets using optical helicity.",2010.04341v2
2020-10-10,Ferroelectricity and ferromagnetism in VOI$_2$ monolayer: the role of Dzyaloshinskii-Moriya interaction,"Multiferroics with intrinsic ferromagnetism and ferroelectricity are highly
desired but rather rare, while most ferroelectric magnets are
antiferromagnetic. A recent theoretical work [Phys. Rev. B {\bf 99}, 195434
(2019)] predicted that oxyhalides VO$X_2$ ($X$: halogen) monolayers are
two-dimensional multiferroics by violating the empirical $d^0$ rule. Most
interestingly, the member VOI$_2$ are predicted to exhibit spontaneous
ferromagnetism and ferroelectricity. In this work, we extend the previous study
on the structure and magnetism of VOI$_2$ monolayer by using density functional
theory and Monte Carlo simulation. The presence of the heavy element iodine
with a strong spin-orbit coupling leads an effective Dzyaloshinskii-Moriya
interaction in the polar structure, which favors a short-period spiral a
magnetic structure.. Another interesting result is that the on-site Coulomb
interaction can strongly suppress the polar distortion thus leading to a
ferromagnetic metallic state. Therefore, the VOI2 monolayer is either a
ferroelectric insulator with spiral magnetism or a ferromagnetic metal, instead
of a ferromagnetic ferroelectric system. Our study highlights the key physical
role of the Dzyaloshinskii-Moriya interaction.",2010.04986v2
2021-12-23,Curvature control of the superconducting proximity effect in diffusive ferromagnetic nanowires,"Coupling a conventional s-wave superconductor to a ferromagnet allows, via
the proximity effect, to generate superconducting triplet correlations. This
feature can be employed to achieve a superconducting triplet spin-valve effect
in superconductor-ferromagnet (SF) hybrid structures, for example by switching
the magnetizations of the ferromagnets between parallel and antiparallel
configurations in F1SF2 and SF1F2 trilayers, or in SF bilayers with both Rashba
and Dresselhaus SOC. It was recently reported that geometric curvature can
control the generation of long ranged triplets. We use this property to show
that the superconducting critical temperature of an SF hybrid nanowire can be
tuned by varying the curvature of the ferromagnetic side alone, with no need of
another ferromagnet or SOC. We show that the variation of the critical
temperature as a function of the curvature can be exploited to obtain a robust,
curvature-controlled, superconducting triplet spin-valve effect. Furthermore,
we perform an analysis with the inclusion of spin-orbit coupling and explain
how it modifies the spin-valve effect both quantitatively and qualitatively.",2112.12797v1
2022-03-03,Achieving high-temperature ferromagnetism by means of magnetic ions dimerization,"Magnetic two-dimensional materials have potential application in
next-generation electronic devices and have stimulated extensive interest in
condensed matter physics and material fields. However, how to realize
high-temperature ferromagnetism in two-dimensional materials remains a great
challenge in physics.
  Herein, we propose an effective approach that the dimerization of magnetic
ions in two-dimensional materials can enhance the exchange coupling and
stabilize the ferromagnetism.
  Manganese carbonitride Mn$_2$N$_6$C$_6$ with a planar monolayer structure is
taken as an example to clarify the method, in which two Mn atoms are gathered
together to form a ferromagnetic dimer of Mn atoms and further these dimers are
coupled together to form the overall ferromagnetism of the two-dimensional
material.
  In Mn$_2$N$_6$C$_6$ monolayer, the near-room-temperature ferromagnetism with
the Curie temperature of 272.3 K is determined by solving Heisenberg model
using Monte Carlo simulations method.",2203.01775v3
2022-03-15,Optimal mixing for two-state anti-ferromagnetic spin systems,"We prove an optimal $\Omega(n^{-1})$ lower bound for modified log-Sobolev
(MLS) constant of the Glauber dynamics for anti-ferromagnetic two-spin systems
with $n$ vertices in the tree uniqueness regime. Specifically, this optimal MLS
bound holds for the following classes of two-spin systems in the tree
uniqueness regime:
  $\bullet$ all strictly anti-ferromagnetic two-spin systems (where both edge
parameters $\beta,\gamma<1$), which cover the hardcore models and the
anti-ferromagnetic Ising models;
  $\bullet$ general anti-ferromagnetic two-spin systems on regular graphs.
  Consequently, an optimal $O(n\log n)$ mixing time holds for these
anti-ferromagnetic two-spin systems when the uniqueness condition is satisfied.
These MLS and mixing time bounds hold for any bounded or unbounded maximum
degree, and the constant factors in the bounds depend only on the gap to the
uniqueness threshold. We prove this by showing a boosting theorem for MLS
constant for distributions satisfying certain spectral independence and
marginal stability properties.",2203.07771v1
2022-03-29,Continuous ferromagnetic quantum phase transition on an anisotropic Kondo lattice,"Motivated by the recent discovery of ferromagnetic quantum criticality in the
heavy fermion compound CeRh$_6$Ge$_4$, we develop a numerical algorithm of
infinite projected entangled pair states for the anisotropic ferromagnetic
Kondo-Heisenberg model in two dimensions and study the ferromagnetic quantum
phase transitions with varying magnetic and hopping anisotropy. Our
calculations reveal a continuous ferromagnetic quantum phase transition in the
large anisotropic region and first-order quantum phase transitions for smaller
anisotropy. Our results highlight the importance of magnetic anisotropy on
ferromagnetic quantum criticality in Kondo lattice systems and provide a
possible explanation for the experimental observation in CeRh$_6$Ge$_4$ with a
quasi-one-dimensional magnetic structure. Our work opens the avenue for future
studies of the rich Kondo lattice physics using state-of-the-art tensor network
approaches.",2203.15475v2
2022-10-10,Subgap modes in two-dimensional magnetic Josephson junctions,"We consider two-dimensional superconductor/ferromagnet/superconductor
junctions and investigate the subgap modes along the junction interface. The
subgap modes exhibit characteristics similar to the Yu-Shiba-Rusinov states
that originate form the interplay between superconductivity and ferromagnetism
in the magnetic junction. The dispersion relation of the subgap modes shows
qualitatively different profiles depending on the transport state (metallic,
half-metallic, or insulating) of the ferromagnet. As the spin splitting in the
ferromagnet is increased, the subgap modes bring about a $0$-$\pi$ transition
in the Josephson current across the junction, with the Josephson current
density depending strongly on the momentum along the junction interface (i.e.,
the direction of the incident current). For clean superconductor-ferromagnet
interfaces (i.e., strong coupling between superconductors and ferromagnet), the
subgap modes develop flat quasi-particle bands that allow to engineer the wave
functions of the subgap modes along an inhomogeneous magnetic junction.",2210.04558v1
2023-04-21,Room-temperature van der Waals 2D ferromagnet switching by spin-orbit torques,"Emerging wide varieties of the two-dimensional (2D) van der Waals (vdW)
magnets with atomically thin and smooth interfaces holds great promise for
next-generation spintronic devices. However, due to the lower Curie temperature
of the vdW 2D ferromagnets than room temperature, electrically manipulating its
magnetization at room temperature has not been realized. In this work, we
demonstrate the perpendicular magnetization of 2D vdW ferromagnet Fe3GaTe2 can
be effectively switched at room temperature in Fe3GaTe2/Pt bilayer by
spin-orbit torques (SOTs) with a relatively low current density of 1.3
10^7A/cm2. Moreover, the high SOT efficiency of \xi_{DL}~0.22 is quantitatively
determined by harmonic measurements, which is higher than those in Pt-based
heavy metal/conventional ferromagnet devices. Our findings of room-temperature
vdW 2D ferromagnet switching by SOTs provide a significant basis for the
development of vdW-ferromagnet-based spintronic applications.",2304.10718v1
2023-06-01,High transport spin polarization in the van der Waals ferromagnet Fe$_4$GeTe$_2$,"The challenging task of scaling-down the size of the power saving electronic
devices can be accomplished by exploiting the spin degree of freedom of the
conduction electrons in van der Waals (vdW) spintronic architectures built with
2D materials. One of the key components of such a device is a near-room
temperature 2D ferromagnet with good metallicity that can generate a highly
spin-polarized electronic transport current. However, most of the known 2D
ferromagnets have either a very low temperature ordering, poor conductivity, or
low spin polarization. In this context, the Fe$_n$GeTe$_2$ (with $n\geq3$)
family of ferromagnets stand out due to their near-room temperature
ferromagnetism and good metallicity. We have performed spin-resolved Andreev
reflection spectroscopy on Fe$_4$GeTe$_2$ ($T_{Curie} \sim$ 273 K) and
demonstrated that the ferromagnet is capable of generating a very high
transport spin polarization, exceeding 50$\%$. This makes Fe$_4$GeTe$_2$ a
strong candidate for application in all-vdW power-saving spintronic devices.",2306.00556v1
2023-09-15,Ferromagnetic response of thin NiI$_2$ flakes up to room temperatures,"We investigate the magnetic response of thin NiI$_2$ flakes for temperatures
above 80~K. Since no magnetic ordering is expected for bulk NiI$_2$, we observe
clear paramagnetic response for massive NiI$_2$ single crystals. In contrast,
thin NiI$_2$ flakes show well-defined ferromagnetic hysteresis loop within
$\pm2$~kOe field range. The value of the response does not scale with the
sample mass, ferromagnetic hysteresis can be seen for any flake orientation in
the external field, so it originates from the sample surface, possibly, due to
the anisotropic exchange (Kitaev interaction). The observed ferromagnetism is
weakly sensitive to temperature up to 300~K. If a flake is multiply exposed to
air, ferromagnetic hysteresis is accompanied by the periodic modulation of the
magnetization curves, which is usually a fingerprint of the multiferroic state.
While NiI$_2$ flakes can not be considered as multiferroics above 80~K, surface
degradation due to the crystallohydrate formation decreases the symmetry of
NiI$_2$ surface, which produces the surface ferroelectric polarization in
addition to the described above ferromagnetic one.",2309.08392v1
2023-10-16,Ferromagnetic Haldane State and Dimer Multiplet State of Quantum Ferromagnets,"We present a theory of the realization of a ferromagnetic Haldane state in a
spin-2 bilinear-biquadratic spin system on an orthogonal-dimer chain. The
coexistence of a ferromagnetic state and a Haldane state is due to the rigorous
correspondence between the eigenstates of a spin-2 model and a spin-1/2
Heisenberg model; i.e., ""eigensystem embedding."" Numerical
exact-diagonalization calculations indicate that the ground state in the model
is a fractionally magnetized M = 3/4 Haldane state. Moreover, a
ferromagnetic-dimer multiplet state is an exact ground state on a lattice,
where the direct product of dimer singlet states is the ground state in a
spin-1/2 Heisenberg model that includes one-, two-, and three-dimensional
orthogonal-dimer lattices. Eigensystem embedding demonstrates that a quantum
ferromagnet can be obtained for an arbitrary spin S >= 2 in any dimension and
for any lattice in which anomalous ground states are realized in a spin-1/2
Heisenberg model.",2310.10287v1
2023-10-16,Trompe L'oeil Ferromagnetism: magnetic point group analysis,"Ferromagnetism can be characterized by various unique phenomena such as
non-zero magnetization (inducing magnetic attraction/repulsion), diagonal
piezomagnetism, nonreciprocal circular dichroism (such as Faraday effect),
odd-order (including linear) anomalous Hall effect, and magneto-optical Kerr
effect. We identify all broken symmetries requiring each of the above
phenomena, and also the relevant magnetic point groups (MPGs) with those broken
symmetries. All of ferromagnetic point groups, relevant for ferromagnets,
ferri-magnets and weak ferromagnets, can certainly exhibit all of these
phenomena, including non-zero magnetization. Some of true antiferromagnets,
which are defined as magnets with MPGs that do not belong to ferromagnetic
point groups, can display these phenomena through magnetization induced by
external perturbations such as applied current, electric fields, light
illumination, and strain. Such MPGs are identified for each external
perturbation. Since high-density and ultrafast spintronic technologies can be
enabled by antiferromagnets, our findings will be an essential guidance for the
future magnetism-related science as well as technology.",2310.10562v1
2024-01-23,Altermagnetism with Non-collinear Spins,"Altermagnetism is introduced as a category of magnetic states with vanishing
net magnetic moment, and consists of collinear alternating (i.e.,
antiferromagnetic-like) spins and alternating variations of local structures
around spins in such a way that the symmetry allows ferromagnetic behaviors
such as anomalous Hall effect and magneto-optical Kerr effects. Altermagnets
exhibiting ferromagnetic behaviors without any external perturbations (called
type-I) turn out to belong to the ferromagnetic point group, and represent a
form of weak ferromagnetic states. Other altermagnets (called type-II and
type-III) can have ferromagnetic behaviors only with external perturbations,
which conserve parity-time reversal (PT) symmetry. All types of altermagnets
themselves have broken PT symmetry. The concept of altermagnetism can be
extended to accommodate multiple spin and local-structure variations (thus,
include non-collinear spins), and this extended form of altermagnetism offers
an intriguing opportunity to leverage complementary advantages of both
ferromagnetism and antiferromagnetism, and thus holds great promise for, for
example, various spintronic applications.",2401.13069v1
2024-03-12,Probing quantum criticality in ferromagnetic CeRh6Ge4,"CeRh$_6$Ge$_4$ is unusual in that its ferromagnetic transition can be
suppressed continuously to zero temperature, i.e., to a ferromagnetic
quantum-critical point (QCP), through the application of modest hydrostatic
pressure. This discovery has raised the possibility that the ferromagnetic QCP
may be of the Kondo-breakdown type characterized by a jump in Fermi volume, to
which thermopower S measurements should be sensitive. Though $S/T$ changes both
sign and magnitude around the critical pressure P$_{c}\approx{}0.8$ GPa, these
changes are not abrupt but extend over a pressure interval from within the
ferromagnetic state up to P$_c$. Together with temperature and pressure
variations in electrical resistivity and previously reported heat capacity,
thermopower results point to the near coincidence of two sequential effects
near P$_c$, delocalization of 4f degrees-of-freedom through orbital-selective
hybridization followed by quantum criticality of itinerant ferromagnetism.",2403.07812v1
2024-03-14,Electronic structure of above-room-temperature van der Waals ferromagnet Fe$_3$GaTe$_2$,"Fe$_3$GaTe$_2$, a recently discovered van der Waals ferromagnet, demonstrates
intrinsic ferromagnetism above room temperature, necessitating a comprehensive
investigation of the microscopic origins of its high Curie temperature
($\textit{T}$$_C$). In this study, we reveal the electronic structure of
Fe$_3$GaTe$_2$ in its ferromagnetic ground state using angle-resolved
photoemission spectroscopy and density functional theory calculations. Our
results establish a consistent correspondence between the measured band
structure and theoretical calculations, underscoring the significant
contributions of the Heisenberg exchange interaction ($\textit{J}$$_{ex}$) and
magnetic anisotropy energy to the development of the high-$\textit{T}$$_C$
ferromagnetic ordering in Fe$_3$GaTe$_2$. Intriguingly, we observe substantial
modifications to these crucial driving factors through doping, which we
attribute to alterations in multiple spin-splitting bands near the Fermi level.
These findings provide valuable insights into the underlying electronic
structure and its correlation with the emergence of high-$\textit{T}$$_C$
ferromagnetic ordering in Fe$_3$GaTe$_2$.",2403.09846v1
2024-03-29,Piezomagnetism in the Ising ferromagnet URhGe,"Piezomagnetism, linear response between strain and magnetic field, is
relatively unexplored cross-correlation but has promising potential as a novel
probe of time-reversal-symmetry breaking in various classes of materials.
Interestingly, there has been no report of piezomagnetism in ferromagnets, most
archetypal time-reversal-symmetry-broken materials. This half-century absence
of piezomagnetic ferromagnets is attributable to complications originating from
multiple-domain states, as well as from changes in the magnetic point group by
rotation of magnetic moment. Here, we report characteristic V-shaped
magnetostriction in the Ising itinerant ferromagnet URhGe, observed by
simultaneous multi-axis strain measurement technique utilizing optical fiber
Bragg grating sensors. This novel magnetostriction occurs only under fields
along the c axis and does not scale with the square of magnetization. Such
unconventional feature indicates piezomagnetism as its origin. Our observation,
marking the first report of piezomagnetism in ferromagnets, is owing to the
mono-domain switching and the Ising magnetization. The obtained piezomagnetic
coefficients are fairly large, implying that Ising ferromagnets are promising
frontiers when seeking for materials with large piezomagnetic responses.",2403.19998v1
2006-07-26,59Co-NMR Probe for Stepwise Magnetization and Magnetotransport in SrCo6O11 with Metallic Kagome Layer and Triangular Lattice with Local Moments,"We report on novel magnetic and electronic properties of SrCo6O11 that
exhibits a unique stepwise magnetization and its relevant magnetotransport
phenomena investigated by the site-selective 59Co nuclear magnetic resonance
(NMR) at zero and applied magnetic fields. This compound is composed of three
Co sites in the unit cell, i.e., Co(1) in the metallic Kagome layer, a Co(2)
dimerized pillar between the layers and Co(3) in the triangular lattice.
Zero-field NMR spectra have revealed that large local moments at the Co(3)
sites are magnetically ordered without any trace of bulk magnetization M at
zero field. The field-swept NMR spectra show that the internal hyperfine field
at the Co(1) site is derived from fully polarized moments Ms at the Co(3) sites
in the ""1""-plateau state at fields higher than 2.5 T, whereas it is partially
cancelled out in the ""1/3""-plateau state in which one-third of Ms is induced at
intermediate fields once a small field is applied. It has been clarified from a
microscopic point of view that the local moments at Co(3) site undergo a
field-induced ferrimagnetic (up-up-down)-to-ferromagnetic (up-up-up)
transition, which is consistent with the evidence obtained from the recent
neutron diffraction experiment. The Co(1) Kagome layer and the dimerized pillar
Co(2) site between the layers are of nonmagnetic origin, suggesting that the
nearly quasi-2D metallic conductivity is dominated by nonmagnetic Co(1) and
Co(2) sites. Consequently, unique magneto-transport phenomena observed in
SrCo6O11 are demonstrated owing to the interaction between the conduction
electrons at the Co(1) and Co(2) sites and the local moments at Co(3) sites.",0607677v1
2006-10-05,Fundamental Magnetic Properties and Structural Implications for Nanocrystalline Fe-Ti-N Thin Films,"The magnetization (M) as a function of temperature (T) from 2 to 300 K and
in-plane field (H) up to 1 kOe, room temperature easy and hard direction
in-plane field hysteresis loops for fields between -100 and +100 Oe, and 10 GHz
ferromagnetic resonance (FMR) profiles have been measured for a series of
soft-magnetic nano-crystalline 50 nm thick Fe-Ti-N films made by magnetron
sputtering in an in-plane field. The nominal titanium concentration was 3 at. %
and the nitrogen concentrations (xN) ranged from zero to 12.7 at. %. The
saturation magnetization (Ms) vs. T data and the extracted exchange parameters
as a function of xN are consistent with a lattice expansion due to the addition
of interstitial nitrogen in the body-centered-cubic (bcc) lattice and a
structural transition to body-centered-tetragonal (bct) in the 6-8 at. %
nitrogen range. The hysteresis loop and FMR data show a consistent picture of
the changes in both the uniaxial and cubic anisotropy as a function of xN.
Films with xN > 1.9 at. % show an overall uniaxial anisotropy, with an
anisotropy field parameter Hu that increases with xN. The corresponding
dispersion averaged uniaxial anisotropy energy density parameter <Ku> = HuMs/2
is a linear function of xN, with a rate of increase of 950 erg/cm3 per at. %
nitrogen. The estimated uniaxial anisotropy energy per nitrogen atom is 30
J/mol, a value consistent with other systems. For xN below 6 at. %, the scaling
of coercive force Hc data with the sixth power of the grain size D indicate a
grain averaged effective cubic anisotropy energy density parameter <K1> that is
about an order of magnitude smaller that the nominal K1 values for iron, and
give a quantitative <K1> vs. D response that matches predictions for exchange
coupled random grains with cubic anisotropy.",0610160v1
2008-12-21,"Comment on ""Influence of Dzyaloshinskii-Moriya Exchange Interaction on Quantum Phase Interference of Spins""","In a recent Letter [1], Wernsdorfer et al. report an experimental study of a
Mn12 molecular wheel which shows essentially identical behavior to the Mn12
wheel studied by Ramsey et al. [2]. In their Letter, Wernsdorfer et al. use the
same model of a dimer of two exchange-coupled spins used in [2] as a basis to
extend the study of the influence of the Dzyaloshinskii-Moriya (DM) interaction
on the quantum tunneling of the magnetization of this system; in particular,
they show that a tilt of the DM vector away from the uniaxial anisotropy axis
can account for the asymmetric nature of the quantum interference minima
associated with resonances between states of opposite parity, e.g., k = 1(A).
We want to stress that the inclusion of DM interactions in a system with
inversion symmetry cannot mix states of opposite parity; i.e., the parity
operator commutes with the Hamiltonian. Consequently, the use by Wernsdorfer et
al. of a single DM vector in a centrosymmetric dimer is strictly forbidden
since it implicitly violates parity conservation. The authors correctly point
out that the lack of an inversion center between each pair of manganese ions on
the wheel justifies the possibility of local DM interactions, even though the
complete molecule has an inversion center. However, these local DM interactions
must also satisfy the molecular inversion symmetry; i.e., they cannot mix
states of opposite parity.We agree that such DM interactions are not always
completely innocuous; e.g., they can mix spin states having the same parity.
Indeed, in kagome systems [3] (cited in [1]), this can lead to weak
ferromagnetism. Nevertheless, the inversion symmetry of the lattice is
preserved and parity is still conserved.",0812.4070v2
2009-09-18,Single Crystal 31P NMR Studies of the Frustrated Square Lattice Compound Pb2(VO)(PO4)2,"The static and dynamic properties of V^{4+} spins (S = 1/2) in the frustrated
square lattice compound Pb2(VO)(PO4)2 were investigated by means of magnetic
susceptibility chi and 31P nuclear magnetic resonance (NMR) shift (K) and 31P
nuclear spin-lattice relaxation rate 1/T1 measurements on a single crystal.
This compound exhibits long-range antiferromagnetic order below TN \simeq 3.65
K. NMR spectra above TN show two distinct lines corresponding to two
inequivalent P sites present in the crystal structure. The observed asymmetry
in hyperfine coupling constant for the in-plane (P1) P site directly points
towards a distortion in the square lattice at the microscopic level, consistent
with the monoclinic crystal structure. The nearest- and next-nearest-neighbor
exchange couplings were estimated to be J1/kB = (-5.4 \pm 0.5) K
(ferromagnetic) and J2/kB = (9.3 \pm 0.6) K (antiferromagnetic), respectively.
1/(T1 T chi) is almost T-independent at high temperatures due to random
fluctuation of spin moments. Below 20 K, the compound shows an enhancement of
1/(T1 T chi) which arises from a growth of antiferromagnetic spin correlations
above TN. Below TN and for the field applied along the c-axis, the NMR spectrum
for the P1 site splits into two satellites and the spacing between them
increases monotonically with decreasing T which is a direct evidence of a
columnar antiferromagnetic ordering with spins lying in the ab-plane. This type
of magnetic ordering is consistent with expectation from the J2/J1 \simeq -1.72
ratio. The critical exponent beta = 0.25 \pm 0.02 estimated from the
temperature dependence of sublattice magnetization as measured by 31P NMR at
11.13 MHz is close to the value (0.231) predicted for the two-dimensional XY
model.",0909.3536v2
2010-11-05,Tin telluride: a weakly co-elastic metal,"We report resonant ultrasound spectroscopy (RUS),
dilatometry/magnetostriction, magnetotransport, magnetization, specific heat,
and $^{119}$Sn M\""ossbauer spectroscopy measurements on SnTe and
Sn$_{0.995}$Cr$_{0.005}$Te. Hall measurements at $T=77$ K indicate that our
Bridgman-grown single crystals have a $p$-type carrier concentration of $3.4
\times 10^{19}$ cm$^{-3}$ and that our Cr-doped crystals have an $n$-type
concentration of $5.8 \times 10^{22}$ cm$^{-3}$. Although our SnTe crystals are
diamagnetic over the temperature range $2\, \text{K} \leq T \leq 1100\,
\text{K}$, the Cr-doped crystals are room temperature ferromagnets with a Curie
temperature of 294 K. For each sample type, three-terminal capacitive
dilatometry measurements detect a subtle 0.5 micron distortion at $T_c \approx
85$ K. Whereas our RUS measurements on SnTe show elastic hardening near the
structural transition, pointing to co-elastic behavior, similar measurements on
Sn$_{0.995}$Cr$_{0.005}$Te show a pronounced softening, pointing to
ferroelastic behavior. Effective Debye temperature, $\theta_D$, values of SnTe
obtained from $^{119}$Sn M\""ossbauer studies show a hardening of phonons in the
range 60--115K ($\theta_D$ = 162K) as compared with the 100--300K range
($\theta_D$ = 150K). In addition, a precursor softening extending over
approximately 100 K anticipates this collapse at the critical temperature, and
quantitative analysis over three decades of its reduced modulus finds $\Delta
C_{44}/C_{44}=A|(T-T_0)/T_0|^{-\kappa}$ with $\kappa = 0.50 \pm 0.02 $, a value
indicating a three-dimensional softening of phonon branches at a temperature
$T_0 \sim 75$ K, considerably below $T_c$. We suggest that the differences in
these two types of elastic behaviors lie in the absence of elastic domain wall
motion in the one case and their nucleation in the other.",1011.1445v1
2011-05-05,Electronic structure of the substitutional vacancy in graphene: Density-functional and Green's function studies,"We study the electronic structure of graphene with a single substitutional
vacancy using a combination of the density-functional, tight-binding, and
impurity Green's function approaches. Density functional studies are performed
with the all-electron spin-polarized linear augmented plane wave (LAPW) method.
The three $sp^2 \sigma$ dangling bonds adjacent to the vacancy introduce
localized states (V$\sigma$) in the mid-gap region, which split due to the
crystal field and a Jahn-Teller distortion, while the $p_z \pi$ states
introduce a sharp resonance state (V$\pi$) in the band structure. For a planar
structure, symmetry strictly forbids hybridization between the $\sigma$ and the
$\pi$ states, so that these bands are clearly identifiable in the calculated
band structure. As for the magnetic moment of the vacancy, the Hund's-rule
coupling aligns the spins of the four localized V$\sigma_1 \uparrow
\downarrow$, V$\sigma_2 \uparrow $, and the V$\pi \uparrow$ electrons resulting
in a S=1 state, with a magnetic moment of $2 \mu_B$, which is reduced by about
$0.3 \mu_B$ due to the anti-ferromagnetic spin-polarization of the $\pi$ band
itinerant states in the vicinity of the vacancy. This results in the net
magnetic moment of $1.7 \mu_B$. Using the Lippmann-Schwinger equation, we
reproduce the well-known $\sim 1/r$ decay of the localized V$\pi$ wave function
with distance and in addition find an interference term coming from the two
Dirac points, previously unnoticed in the literature. The long-range nature of
the V$\pi$ wave function is a unique feature of the graphene vacancy and we
suggest that this may be one of the reasons for the widely varying relaxed
structures and magnetic moments reported from the supercell band calculations
in the literature.",1105.1129v4
2011-12-12,Spectral properties of the two-impurity Anderson model with varying distance and various interactions,"We present a novel approximation for two interacting magnetic impurities
immersed into a noninteracting metallic host. The scheme is based on direct
perturbation theory in the hybridization between the impurity and band
electrons. This two-impurity enhanced noncrossing approximation (TIE) fully
incorporates the indirect interaction between the impurities which are mediated
by the conduction electrons as well as additional arbitrary direct interaction
matrix elements. We qualify the approximation by investigating the uncoupled
case and conclude the TIE to be equally accurate as its single impurity
counterpart. The physical properties of the two-impurity Anderson model are
first investigated in some limiting cases. In a regime, where each of the
uncoupled two impurities would exhibit a pronounced Kondo effect, we ignore the
indirect coupling via the conduction band and only incorporate direct
interactions. For a ferromagnetic direct exchange coupling, the system displays
a behavior similar to a spin-one Kondo effect, while an antiferromagnetic
coupling competes with the Kondo effect and produces a pseudogap in the
many-body Kondo resonance of the single-particle spectral function.
Interestingly, a direct one-particle hopping also produces a pseudogap but
additionally pronounced side-peaks emerge. This gap is characteristically
different from the case with antiferromagnetic coupling, since it emerges as a
consequence of distinct Kondo effects for the bonding and anti-bonding orbital,
i.e.\ it reflects a splitting of even and odd parity states.For the general
case of only indirect coupling the results show signatures of all the
previously discussed limiting cases as function of the impurity-impurity
distance. We are led to the conclusion that the well known Doniach-scenario
captures essential aspects this model, but the details especially at small
distances are more complicated.",1112.2724v2
2012-07-04,"Infrared conductivity of hole accumulation and depletion layers in (Ga,Mn)As- and (Ga,Be)As-based electric field-effect devices","We have fabricated electric double-layer field-effect devices to
electrostatically dope our active materials, either $x$=0.015
Ga$_{1-x}$Mn$_x$As or $x$=3.2$\times10^{-4}$ Ga$_{1-x}$Be$_x$As. The devices
are tailored for interrogation of electric field induced changes to the
frequency dependent conductivity in the accumulation or depletions layers of
the active material via infrared (IR) spectroscopy. The spectra of the
(Ga,Be)As-based device reveal electric field induced changes to the IR
conductivity consistent with an enhancement or reduction of the Drude response
in the accumulation and depletion polarities, respectively. The spectroscopic
features of this device are all indicative of metallic conduction within the
GaAs host valence band (VB). For the (Ga,Mn)As-based device, the spectra show
enhancement of the far-IR itinerant carrier response and broad mid-IR resonance
upon hole accumulation, with a decrease of these features in the depletion
polarity. These later spectral features demonstrate that conduction in
ferromagnetic (FM) Ga$_{1-x}$Mn$_x$As is distinct from genuine metallic
behavior due to extended states in the host VB. Furthermore, these data support
the notion that a Mn-induced impurity band plays a vital role in the electron
dynamics of FM Ga$_{1-x}$Mn$_x$As. We add, a sum-rule analysis of the spectra
of our devices suggests that the Mn or Be doping does not lead to a substantial
renormalization of the GaAs host VB.",1207.0895v2
2012-10-10,Universal Disorder in Bi2Sr2CaCu2O8+x,"The cuprates contain a range of nanoscale phenomena that consist of both
LDOS(E) features and spatial excitations. Many of these phenomena can only be
observed through the use of a SI-STM and their disorder can be mapped out
through the fitting of a phenomenological model to the LDOS(E). We present a
study of the nanometer scale disorder of single crystal cryogenically cleaved
samples of Bi2Sr2CaCu2O8+x whose dopings range from p = 0.19 to 0.06. The
phenomenological model used is the Tripartite model that has been successfully
applied to the average LDOS(E) previously. The resulting energy scale maps show
a structured patchwork disorder of three energy scales, which can be described
by a single underlying disordered parameter. This spatial disorder structure is
universal for all dopings and energy scales. It is independent of the oxygen
dopant negative energy resonances and the interface between the different
patches takes the form of a shortened lifetime pseudogap/superconducting gap
state. The relationship between the energy scales and the spatial modulations
of the dispersive QPI, static q1* modulation and the pseudogap shows that the
energy scales signatures in the LDOS(E) are tied to the onset and termination
of the spatial excitations. The static q1* modulations local energy range is
measured and its signature in the LDOS(E) is the kink, whose number of states
are modulated with a wave vector of q1*. This analysis of both the LDOS(r,E)
and the spatial modulations in q-space show a picture of a single underlying
disordered parameter that determines both the LDOS(E) structure as well as the
energy ranges of the QPI, q1* modulation and the pseudogap states. This
parameter for a single patch can be defined by the Fermi surface crossing of
the parent compound anti-ferromagnetic zone boundary for a model homogeneous
superconductor with the same electronic properties as the patch.",1210.3002v1
2013-12-04,Structure and Properties of α-NaFeO2-type Ternary Sodium Iridates,"The synthesis, structure, and elementary magnetic and electronic properties
are reported for layered compounds of the type Na3-xMIr2O6 and Na3-xM2IrO6,
where M is a transition metal from the 3d series (M=Zn, Cu, Ni, Co, Fe and Mn).
The rhombohedral structures, in space group R-3m, were determined by refinement
of neutron and synchrotron powder diffraction data. No clear evidence for long
range 2:1 or 1:2 honeycomb-like M/Ir ordering was found in the neutron powder
diffraction patterns except in the case of M = Zn, thus in general the
compounds are best designated as sodium deficient {\alpha}-NaFeO2-type phases
with formulas Na1-xM1/3Ir2/3O2 or Na1-xM2/3Ir1/3O2. Synchrotron powder
diffraction patterns indicate that several of the compounds likely have
honeycomb in-plane metal-iridium ordering with disordered stacking of the
layers. All the compounds are sodium deficient under our synthetic conditions
and are black and insulating. Weiss constants derived from magnetic
susceptibility measurements indicate that Na0.62Mn0.61Ir0.39O2,
Na0.80Fe2/3Ir1/3O2, Na0.92Ni1/3Ir2/3O2, Na0.86Cu1/3Ir2/3O2, and
Na0.89Zn1/3Ir2/3O2 display dominant antiferromagnetic interactions. For
Na0.90Co1/3Ir2/3O2 the dominant magnetic interactions at low temperature are
ferromagnetic while at high temperatures they are antiferromagnetic; there is
also a change in the effective moment. Low temperature specific heat
measurements (to 2 K) on Na0.92Ni1/3Ir2/3O2 indicate the presence of a broad
magnetic ordering transition. X-ray absorption spectroscopy shows that iridium
is at or close to the 4+ oxidation state in all compounds. 23Na nuclear
magnetic resonance measurements comparing Na2IrO3 to Na0.92Ni1/3Ir2/3O2 and
Na0.89Zn1/3Ir2/3O2 provide strong indications that the electron spins are
short-range ordered in the latter two materials. All of the compounds are spin
glasses.",1312.0995v1
2015-09-02,Scanning nano-spin ensemble microscope for nanoscale magnetic and thermal imaging,"Quantum sensors based on solid-state spins provide tremendous opportunities
in a wide range of fields from basic physics and chemistry to biomedical
imaging. However, integrating them into a scanning probe microscope to enable
practical, nanoscale quantum imaging is a highly challenging task. Recently,
the use of single spins in diamond in conjunction with atomic force microscopy
techniques has allowed significant progress towards this goal, but
generalisation of this approach has so far been impeded by long acquisition
times or by the absence of simultaneous topographic information. Here we report
on a scanning quantum probe microscope which solves both issues, by employing a
nano-spin ensemble hosted in a nanodiamond. This approach provides up to an
order of magnitude gain in acquisition time, whilst preserving sub-100 nm
spatial resolution both for the quantum sensor and topographic images. We
demonstrate two applications of this microscope. We first image nanoscale
clusters of maghemite particles through both spin resonance spectroscopy and
spin relaxometry, under ambient conditions. Our images reveal fast magnetic
field fluctuations in addition to a static component, indicating the presence
of both superparamagnetic and ferromagnetic particles. We next demonstrate a
new imaging modality where the nano-spin ensemble is used as a thermometer. We
use this technique to map the photo-induced heating generated by laser
irradiation of a single gold nanoparticle in a fluid environment. This work
paves the way towards new applications of quantum probe microscopy such as
thermal/magnetic imaging of operating microelectronic devices and magnetic
detection of ion channels in cell membranes.",1509.00586v2
2018-05-15,Persistence of antiferromagnetic order upon La substitution in the $4d^4$ Mott insulator Ca$_2$RuO$_4$,"The chemical and magnetic structures of the series of compounds
Ca$_{2-x}$La$_x$RuO$_4$ [$x = 0$, $0.05(1)$, $0.07(1)$, $0.12(1)$] have been
investigated using neutron diffraction and resonant elastic x-ray scattering.
Upon La doping, the low temperature S-Pbca space group of the parent compound
is retained in all insulating samples [$x\leq0.07(1)$], but with significant
changes to the atomic positions within the unit cell. These changes can be
characterised in terms of the local RuO$_6$ octahedral coordination: with
increasing doping the structure, crudely speaking, evolves from an orthorhombic
unit cell with compressed octahedra to a quasi-tetragonal unit cell with
elongated ones. The magnetic structure on the other hand, is found to be
robust, with the basic $k=(0,0,0)$, $b$-axis antiferromagnetic order of the
parent compound preserved below the critical La doping concentration of
$x\approx0.11$. The only effects of La doping on the magnetic structure are to
suppress the A-centred mode, favouring the B mode instead, and to reduce the
N\'{e}el temperature somewhat. Our results are discussed with reference to
previous experimental reports on the effects of cation substitution on the
$d^4$ Mott insulator Ca$_2$RuO$_4$, as well as with regard to theoretical
studies on the evolution of its electronic and magnetic structure. In
particular, our results rule out the presence of a proposed ferromagnetic
phase, and suggest that the structural effects associated with La substitution
play an important role in the physics of the system.",1805.05796v2
2018-05-23,Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator,"Injection of a radio frequency (RF) current was used to phase lock the SHNO
to the TRSKM. The out of plane magnetization was detected by means of the polar
magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were
dominated by an artifact arising from the edges of the Au NCs. Time resolved
imaging revealed the simultaneous excitation of a non-linear `bullet' mode at
the centre of the device, once the DC current exceeded a threshold value, and
ferromagnetic resonance (FMR) induced by the RF current. However, the FMR
response observed for sub-critical DC current values exhibits an amplitude
minimum at the centre, which is attributed to spreading of the RF spin current
due to the reactance of the device structure. This FMR response can be
subtracted to yield images of the bullet mode. As the DC current is increased
above threshold, the bullet mode appears to increase in size, suggesting
increased translational motion. The reduced spatial overlap of the bullet and
FMR modes, and this putative translational motion, may impede the injection
locking and contribute to the reduced locking range observed within NC-SHNO
devices. This illustrates a more general need to control the geometry of an
injection-locked oscillator so that the autonomous dynamics of the oscillator
exhibit strong spatial overlap with those resulting from the injected signal.",1805.09212v5
2011-11-29,Magnetic properties and spin dynamics of 3d-4f molecular complexes,"We present the magnetic properties of three recently synthesized binuclear
molecular complexes [NiNd], [NiGd] and [ZnGd] investigated by dc magnetization
and proton nuclear magnetic resonance (NMR) measurements. The high-temperature
magnetic properties are related to the independent paramagnetic behavior of the
two magnetic metal ions within the binuclear entities both in [NiNd] and
[NiGd]. On lowering the temperature, the formation of a magnetic dimer, with a
low-spin ground state due to antiferromagnetic interaction (J/kB = -25 K)
between Ni2+ and Nd3+, is found in the case of [NiNd], while in [NiGd] a
ferromagnetic interaction (J/kB = 3.31 K) between the magnetic ions leads to a
high-spin (S = 9/2) ground state. The temperature dependence of the proton
nuclear spin lattice relaxation rate 1/T1 in [NiNd] is driven by the
fluctuation of the hyperfine field at the nuclear site due to relaxation of the
magnetization. At high temperature the independent Ni2+ and Nd3+ spins
fluctuate fast while at low temperature we observe a slowing down of the
fluctuation of the total magnetization of the dimer because of the insurgence
of antiferromagnetic spin correlations. The relaxation mechanism in [NiNd] at
low temperature is interpreted by a single, temperature dependent, correlation
frequency wc\simT^3.5, which reflects the life time broadening of the exchange
coupled spins via spin-phonon interaction. The proton NMR signal in [NiGd]
could be detected just at room temperature, due to the shortening of relaxation
times when T is decreased. The magnetic properties of [ZnGd] are the ones
expected from a weakly interacting assembly of isolated moments except for
anomalies in the susceptibility and NMR results below 15 K which currently
cannot be explained.",1111.7008v1
2014-06-10,Unusual scenario of the temperature evolution of magnetic state in novel carbon-based nanomaterials,"Two porous carbon-based samples doped with Au and Co are investigated. The
neutron diffraction study reveals an amorphous structure of both samples. The
Co-doped sample exhibits a long-range ferromagnetic (FM) ordering at 2.6 K. The
NMR investigations demonstrate, that the samples are obtained with a partial
carbonization of initial aromatic compounds and do not reach a state of glassy
carbon. The magnetization, longitudinal nonlinear response to a weak ac field
and electron magnetic resonance data give evidences for presence of FM clusters
in the samples well above 300 K. A short-range character of the FM ordering in
the Au-doped sample transforms below T$_C \approx$ 210 K into another
inhomogeneous FM state. Besides the FM clusters, this state contains a
subsystem with a long-range FM ordering (matrix) formed by paramagnetic
centers, existing outside the clusters. The nonlinear response data suggest a
percolative character of the long-range FM matrix, which is connected probably
with a porous sample structure. The magnetization data give evidence for the
formation of an inhomogeneous state in the Co-doped sample, similar to that in
the Au-doped one. However, this state is formed at higher temperatures, lying
well above 350 K, and exhibits a more homogeneous arrangement of the FM
nanoparticles and the FM matrix. Temperature dependence of the magnetization in
the Au-doped sample is attributable to changes of the domain formation regime
in the FM matrix on cooling, connected with the inhomogeneous character of its
FM state. Such peculiarity is absent in the Co-doped sample below 350 K, which
is in agreement with formation of the FM state in this sample at much higher
temperatures. Further cooling below T ~ 3(10) K leads to a steep increase of
the magnetization in both samples. This is attributable to the domain
rearrangement in the inhomogeneous FM state at low temperatures.",1406.2556v2
2016-08-15,Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films,"We present phonon dispersions, element-resolved vibrational density of states
(VDOS) and corresponding thermodynamic properties obtained by a combination of
density functional theory (DFT) and nuclear resonant inelastic X-ray scattering
(NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and
thin epitaxial films. We see distinct differences in the VDOS of the
antiferromagnetic (AF) and ferromagnetic (FM) phase which provide a microscopic
proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a particular
sensitivity to the slight tetragonal distortions present in epitaxial films,
which is not encountered in the AF phase. This results in a notable change in
lattice entropy, which is important for the comparison between thin film and
bulk results. Our calculations confirm the recently reported lattice
instability in the AF phase. The imaginary frequencies at the $X$-point depend
critically on the Fe magnetic moment and atomic volume. Analyzing these non
vibrational modes leads to the discovery of a stable monoclinic ground state
structure which is robustly predicted from DFT but not verified in our thin
film experiments. Specific heat, entropy and free energy calculated within the
quasiharmonic approximation suggest that the new phase is possibly suppressed
because of its relatively smaller lattice entropy. In the bulk phase, lattice
degrees of freedom contribute with the same sign and in similar magnitude to
the isostructural AF-FM phase transition as the electronic and magnetic
subsystems and therefore needs to be included in thermodynamic modeling.",1608.04268v1
2016-12-17,Electrons and polarons at oxide interfaces explored by soft-X-ray ARPES,"Soft-X-ray ARPES (SX-ARPES) with its enhanced probing depth and chemical
specificity allows access to fundamental electronic structure characteristics -
momentum-resolved spectral function, band structure, Fermi surface - of systems
difficult and even impossible for the conventional ARPES such as
three-dimensional materials, buried interfaces and impurities. After a recap of
the spectroscopic abilities of SX-ARPES, we review its applications to oxide
interfaces, focusing on the paradigm LaAlO3-SrTiO3 interface. Resonant SX-ARPES
at the Ti L-edge accentuates photoemission response of the mobile interface
electrons and exposes their dxy-, dyz- and dxz-derived subbands forming the
Fermi surface in the interface quantum well. After a recap of the
electron-phonon interaction physics, we demonstrate that peak-dip-hump
structure of the experimental spectral function manifests the Holstein-type
large polaron nature of the interface charge carriers, explaining their
fundamentally reduced mobility. Coupling of the charge carriers to polar soft
phonon modes defines dramatic drop of mobility with temperature. Oxygen
deficiency adds another dimension to the rich physics of LaAlO3-SrTiO3
resulting from co-existence of mobile and localized electrons introduced by
oxygen vacancies. Oxygen deficiency allows tuning of the polaronic coupling and
thus mobility of the charge carriers, as well as of interfacial ferromagnetism
connected with various atomic configurations of the vacancies. Finally, we
discuss spectroscopic evidence of phase separation at the LaAlO3-SrTiO3
interface. Concluding, we put prospects of SX-ARPES for complex
heterostructures, spin-resolving experiments opening the totally unexplored
field of interfacial spin structure, and in-operando field-effect experiments
paving the way towards device applications of the reach physics of oxide
interfaces.",1612.05791v2
2018-09-07,EPR measurements of Eu{+2} spins in metallic EuCo{2-y}As2 single crystals,"The Eu{+2} spins S = 7/2 in the metallic compound EuCo{2-y}As2 order into an
antiferromagnetic helical structure below a Neel temperature TN = 40 to 45 K.
The effective magnetic moment mu_eff of the Eu spins in the paramagnetic state
from 100 to 300 K is found from static magnetic susceptibility measurements to
be enhanced by about 7% compared to the value expected for spectroscopic
splitting factor g = 2, and the saturation moment at high applied fields H and
low temperatures T is also sometimes enhanced. Here
electron-paramagnetic-resonance (CW EPR) measurements versus applied magnetic
field H at fixed X-band rf (microwave) angular frequency omega were carried out
using a linearly-polarized rf magnetic field oriented perpendicular to H to
study the microscopic magnetic properties of the Eu spins. In order to analyze
the data, the complex magnetic susceptibility chi(omega) at fixed H was used
that was derived for linearly-polarized rf fields from the modified Bloch
equations [M. A. Garstens and J. I. Kaplan, Phys. Rev. 99, 459 (1955)] (GK). It
is shown that their formulation when applied to calculate the Dysonian
absorptive susceptibility chi_D''(H) of local magnetic moments in metals yields
a prediction that can be very different from the traditionally-used form of
chi_D''(H). By fitting the derivative of the field-swept CW EPR data for
EuCo{2-y}As2 by chi_D''(H) at fixed omega derived from the GK chi_D''(omega) at
fixed H, the Eu spin spectroscopic splitting factor (g-factor) is found to be
approximately 2.00 from 300 to ~125 K, and then to continuously increase to
approximately 2.16 on further cooling to 50 K. We speculate that the
enhancement of the Eu g-factor on cooling from 125 to 50 K arises from
continuously-increasing local short-range ferromagnetic correlations between
the Co 3d-band electrons and the Eu spins.",1809.02653v4
2019-10-11,"Low-Damping Ferromagnetic Resonance in Electron-Beam Patterned, High-$Q$ Vanadium Tetracyanoethylene Magnon Cavities","Integrating patterned, low-loss magnetic materials into microwave devices and
circuits presents many challenges due to the specific conditions that are
required to grow ferrite materials, driving the need for flip-chip and other
indirect fabrication techniques. The low-loss ($\alpha = 3.98 \pm 0.22 \times
10^{-5}$), room-temperature ferrimagnetic coordination compound vanadium
tetracyanoethylene ($\mathrm{V[TCNE]}_x$) is a promising new material for these
applications that is potentially compatible with semiconductor processing. Here
we present the deposition, patterning, and characterization of
$\mathrm{V[TCNE]}_x$ thin films with lateral dimensions ranging from 1 micron
to several millimeters. We employ electron-beam lithography and liftoff using
an aluminum encapsulated poly(methyl methacrylate), poly(methyl
methacrylate-methacrylic acid) copolymer bilayer (PMMA/P(MMA-MAA)) on sapphire
and silicon. This process can be trivially extended to other common
semiconductor substrates. Films patterned via this method maintain low-loss
characteristics down to 25 microns with only a factor of 2 increase down to 5
microns. A rich structure of thickness and radially confined spin-wave modes
reveals the quality of the patterned films. Further fitting, simulation, and
analytic analysis provides an exchange stiffness, $A_{ex} = 2.2 \pm 0.5 \times
10^{-10}$ erg/cm, as well as insights into the mode character and surface spin
pinning. Below a micron, the deposition is non-conformal, which leads to
interesting and potentially useful changes in morphology. This work establishes
the versatility of $\mathrm{V[TCNE]}_x$ for applications requiring highly
coherent magnetic excitations ranging from microwave communication to quantum
information.",1910.05325v1
2020-01-15,Ubiquitous impact of localised impurity states on the exchange coupling mechanism in magnetic topological insulators,"Since the discovery of the quantum anomalous Hall effect in the magnetically
doped topological insulators (MTI) Cr:(Bi,Sb)$_2$Te$_3$ and
V:(Bi,Sb)$_2$Te$_3$, the search for the exchange coupling mechanisms underlying
the onset of ferromagnetism has been a central issue, and a variety of
different scenarios have been put forward. By combining resonant photoemission,
X-ray magnetic dichroism and multiplet ligand field theory, we determine the
local electronic and magnetic configurations of V and Cr impurities in
(Bi,Sb)$_2$Te$_3$. While strong pd hybridisation is found for both dopant
types, their 3d densities of states show pronounced differences.
State-of-the-art first-principles calculations show how these impurity states
mediate characteristic short-range pd exchange interactions, whose strength
sensitively varies with the position of the 3d states relative to the Fermi
level. Measurements on films with varying host stoichiometry support this
trend. Our results establish the essential role of impurity-state mediated
exchange interactions in the magnetism of MTI.",2001.05541v1
2020-04-10,Ion beam modification of magnetic tunnel junctions,"The impact of 400 keV $Ar^+$ ion irradiation on the magnetic and electrical
properties of in-plane magnetized magnetic tunnel junction (MTJ) stacks was
investigated by ferromagnetic resonance, vibrating sample magnetometry and
current-in-plane tunneling techniques. The irradiation-induced changes of the
magnetic anisotropy, coupling energies and tunnel magnetoresistance (TMR)
exhibited a correlated dependence on the ion fluence, which allowed us to
distinguish between two irradiation regimes. In the low-fluence regime, ${\Phi}
< 10^{14} cm^{-2}$, the parameters required for having a functioning MTJ were
preserved: the anisotropy of the FeCoB free layer (FL) was weakly modulated
following a small decrease in the saturation magnetization $M_S$; the TMR
decreased continuously; the interlayer exchange coupling (IEC) and the exchange
bias (EB) decreased slightly. In the high-fluence regime, ${\Phi} > 10^{14}
cm^{-2}$, the MTJ was rendered inoperative: the modulation of the FL anisotropy
was strong, caused by a strong decrease in $M_S$, ascribed to a high degree of
interface intermixing between the FL and the Ta capping; the EB and IEC were
also lost, likely due to intermixing of the layers composing the synthetic
antiferromagnet; and the TMR vanished due to the irradiation-induced
deterioration of the MgO barrier and MgO/FeCoB interfaces. We demonstrate that
the layers surrounding the FL play a decisive role in determining the trend of
the magnetic anisotropy evolution resulting from the irradiation, and that an
ion-fluence window exists where such a modulation of magnetic anisotropy can
occur, while not losing the TMR or the magnetic configuration of the MTJ.",2004.05025v1
2018-03-02,Long lifetime of thermally-excited magnons in bulk yttrium iron garnet,"Spin currents are generated within the bulk of magnetic materials due to heat
flow, an effect called intrinsic spin-Seebeck. This bulk bosonic spin current
consists of a diffusing thermal magnon cloud, parametrized by the magnon
chemical potential ($\mu_{m}$), with a diffusion length of several microns in
yttrium iron garnet (YIG). Transient opto-thermal measurements of the
spin-Seebeck effect (SSE) as a function of temperature reveal the time
evolution of $\mu_{m}$ due to intrinsic SSE in YIG. The interface SSE develops
at times < 2 ns while the intrinsic SSE signal continues to evolve at times >
500 $\mu$s, dominating the temperature dependence of SSE in bulk YIG.
Time-dependent SSE data are fit to a multi-temperature model of coupled
spin/heat transport using finite element method (FEM), where the magnon spin
lifetime ($\tau$) and magnon-phonon thermalization time ($\tau_{mp}$) are used
as fit parameters. From 300 K to 4 K, $\tau_{mp}$ varies from 1 to 10 ns,
whereas $\tau$ varies from 2 to 60 $\mu$s with the spin lifetime peaking at 90
K. At low temperature, a reduction in $\tau$ is observed consistent with
impurity relaxation reported in ferromagnetic resonance measurements. These
results demonstrate that the thermal magnon cloud in YIG contains extremely low
frequency magnons (~10 GHz) providing spectral insight to the microscopic
scattering processes involved in magnon spin/heat diffusion.",1803.01054v3
2019-11-25,Influence of hydrogenation on the vibrational density of states of magnetocaloric $\mathrm{LaFe}_\mathrm{11.4}\mathrm{Si}_\mathrm{1.6}\mathrm{H}_{1.6}$,"We report on the impact of magnetoelastic coupling on the magnetocaloric
properties of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ in terms of the vibrational
density of states, which we determined with $^{57}$Fe nuclear resonant
inelastic X-ray scattering measurements and with density-functional-theory
based first-principles calculations in the ferromagnetic low-temperature and
paramagnetic high-temperature phase. In experiments and calculations, we
observe pronounced differences in the shape of the Fe-partial VDOS between
non-hydrogenated and hydrogenated samples. This shows that hydrogen does not
only shift the temperature of the first-order phase transition, but also
affects the elastic response of the Fe-subsystem significantly. In turn, the
anomalous redshift of the Fe VDOS, observed by going to the low-volume PM
phase, survives hydrogenation. As a consequence, the change in the Fe specific
vibrational entropy $\Delta S_\mathrm{lat}$ across the phase transition has the
same sign as the magnetic and electronic contribution. DFT calculations show
that the same mechanism, which is a consequence of the itinerant electron
metamagnetism associated with the Fe subsystem, is effective in both the
hydrogenated and he hydrogen-free compounds. Although reduced by 50 % as
compared to the hydrogen-free system, the measured change $\Delta
S_\mathrm{lat}$ of 3.2\pm1.9 J/kgK across the FM to PM transition contributes
with 35 % significantly and cooperatively to the total isothermal entropy
change $\Delta S_\mathrm{iso}$. Hydrogenation is observed to induce an overall
blueshift of the Fe-VDOS with respect to the H-free compound; this effect,
together with the enhanced Debye temperature observed, is a fingerprint of the
hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean
Debye velocity of sound of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ was determined from
the NRIXS and the DFT data.",1911.11087v1
2020-10-15,Unconventional superparamagnetic behavior in the modified cubic spinel compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$,"Structural, electronic, and magnetic properties of modified cubic spinel
compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ are studied via x-ray diffraction,
resistivity, DC and AC magnetization, heat capacity, neutron diffraction,
$^7$Li nuclear magnetic resonance, magnetocaloric effect, magnetic relaxation,
and magnetic memory effect experiments. We stabilized this compound in a cubic
structure with space group $P4_{3}32$. It exhibits semiconducting character
with an electronic band gap of $\Delta/k_{\rm B} \simeq 0.4$ eV. The
interaction within each Mn$^{4+}$ and Ni$^{2+}$ sub-lattice and between
Mn$^{4+}$ and Ni$^{2+}$ sublattices is found to be ferromagnetic (FM) and
antiferromagnetic (AFM), respectively which leads to the onset of a
ferrimagnetic transition at $T_{\rm C} \simeq 125$~K. The reduced values of
frustration parameter ($f$) and ordered moments reflect magnetic frustration
due to competing FM and AFM interactions. From the $^7$Li NMR shift vs
susceptibility plot, the average hyperfine coupling between $^7$Li nuclei and
Ni$^{2+}$ and Mn$^{4+}$ spins is calculated to be $\sim 672.4$~Oe/$\mu_{\rm
B}$. A detailed critical behaviour study is done in the vicinity of $T_{\rm C}$
using modified-Arrott plot, Kouvel-Fisher plot, and universal scaling of
magnetization isotherms. The estimated critical exponents correspond to the 3D
XY universality class. A large magneto-caloric effect is observed with a
maximum isothermal change in entropy $\Delta S_m \simeq - 11.3$~J/Kg-K and a
maximum relative cooling power $RCP \simeq 604$~J/Kg for 9~T magnetic field
change. The imaginary part of the AC susceptibility depicts a strong frequency
dependent hump at $T=T_{\rm f2}$ well below the blocking temperature $T_{\rm
b}\simeq120$~K. The Arrhenius behaviour of frequency dependent $T_{\rm f2}$ and
the absence of ZFC memory confirm the existence of superparamagnetism in the
ferrimagnetically ordered state.",2010.07709v1
2021-04-07,Imaging the Néel vector switching in the monolayer antiferromagnet MnPSe$_3$ with strain-controlled Ising order,"The family of monolayer two-dimensional (2D) materials hosts a wide range of
interesting phenomena, including superconductivity, charge density waves,
topological states and ferromagnetism, but direct evidence for
antiferromagnetism in the monolayer has been lacking. Nevertheless,
antiferromagnets have attracted enormous interest recently in spintronics due
to the absence of stray fields and their terahertz resonant frequency. Despite
the great advantages of antiferromagnetic spintronics, controlling and
detecting N\'eel vectors have been limited in bulk materials. In this work, we
developed a sensitive second harmonic generation (SHG) microscope and detected
long-range N\'eel antiferromagnetic (AFM) order and N\'eel vector switching
down to the monolayer in MnPSe$_3$. Temperature-dependent SHG measurement in
repetitive thermal cooling surprisingly collapses into two curves, which
correspond to the switching of an Ising type N\'eel vector reversed by the
time-reversal operation, instead of a six-state clock ground state expected
from the threefold rotation symmetry in the structure. We imaged the spatial
distribution of the N\'eel vectors across samples and rotated them by an
arbitrary angle irrespective of the lattice in the sample plane by applying
strain. By studying both a Landau theory and a microscopic model that couples
strain to nearest-neighbor exchange, we conclude that the phase transition of
the XY model in the presence of strain falls into the Ising universality class
instead of the XY one, which could explain the extreme strain tunability.
Finally, we found that the 180{\deg} AFM domain walls are highly mobile down to
the monolayer after thermal cycles, paving the way for future control of the
antiferromagnetic domains by strain or external fields on demand for
ultra-compact 2D AFM terahertz spintronics.",2104.03069v1
2021-05-18,Computational Micromagnetics based on Normal Modes: bridging the gap between macrospin and full spatial discretization,"The Landau-Lifshitz equation governing magnetization dynamics is written in
terms of the amplitudes of normal modes associated with the micromagnetic
system's appropriate ground state. This results in a system of nonlinear
ordinary differential equations (ODEs), the right-hand side of which can be
expressed as the sum of a linear term and nonlinear terms with increasing order
of nonlinearity (quadratic, cubic, etc.). The application of the method to
nanostructured magnetic systems demonstrates that the accurate description of
magnetization dynamics requires a limited number of normal modes, which results
in a considerable improvement in computational speed. The proposed method can
be used to obtain a reduced-order dynamical description of magnetic
nanostructures which allows to adjust the accuracy between low-dimensional
models, such as macrospin, and micromagnetic models with full spatial
discretization. This new paradigm for micromagnetic simulations is tested for
three problems relevant to the areas of spintronics and magnonics: directional
spin-wave coupling in magnonic waveguides, high power ferromagnetic resonance
in a magnetic nanodot, and injection-locking in spin-torque nano-oscillators.
The case studies considered demonstrate the validity of the proposed approach
to systematically obtain an intermediate order dynamical model based on normal
modes for the analysis of magnetic nanosystems. The time-consuming calculation
of the normal modes has to be done only one time for the system. These modes
can be used to optimize and predict the system response for all possible
time-varying external excitations (magnetic fields, spin currents). This is of
utmost importance for applications where fast and accurate system simulations
are required, such as in electronic circuits including magnetic devices.",2105.08829v2
2021-05-18,Nonperturbative Waveguide Quantum Electrodynamics,"Understanding physical properties of quantum emitters strongly interacting
with quantized electromagnetic modes is one of the primary goals in the
emergent field of waveguide quantum electrodynamics (QED). When the
light-matter coupling strength is comparable to or even exceeds energies of
elementary excitations, conventional approaches based on perturbative treatment
of light-matter interactions, two-level description of matter excitations, and
photon-number truncation are no longer sufficient. Here we study in and out of
equilibrium properties of waveguide QED in such nonperturbative regimes on the
basis of a comprehensive and rigorous theoretical approach using an asymptotic
decoupling unitary transformation. We uncover several surprising features
ranging from symmetry-protected many-body bound states in the continuum to
strong renormalization of the effective mass and potential; the latter may
explain recent experiments demonstrating cavity-induced changes in chemical
reactivity as well as enhancements of ferromagnetism or superconductivity. To
illustrate our general results with concrete examples, we use our formalism to
study a model of coupled cavity arrays, which is relevant to experiments in
superconducting qubits interacting with microwave resonators or atoms coupled
to photonic crystals. We examine the relation between our results and
delocalization-localization transition in the spin-boson model; notably, we
point out that a reentrant transition can occur in the regimes where the
coupling strength becomes the dominant energy scale. We also discuss
applications of our results to other problems in different fields, including
quantum optics, condensed matter physics, and quantum chemistry.",2105.08833v5
2021-10-01,"High-resolution real-space evaluation of the self-energy operator of disordered lattices: Gade singularity, spin-orbit effects and p-wave superconductivity","Disorder is a key factor influencing the behavior of condensed states of
matter, however the true extent of its impact is generally difficult to
determine due to the prominent roles played by quantum interference,
entanglement between spin and orbital degrees of freedom and proximity to
quantum critical points. Here we show that the one-particle disorder
self-energy -- a direct probe of the renormalization of low-energy excitations
due to defects and impurities distributed randomly in a crystal -- can be
obtained by means of unbiased spectral expansions of lattice Green's functions
in a computationally expedient manner. Our scheme provides a powerful framework
to map out the frequency and wavevector dependence of electronic excitations in
unprecedented large tight-binding systems, up to $10^9$ orbitals, with energy
resolution only limited by the mean level spacing. We demonstrate the
versatility of our approach in 3 distinct problems: (i) the Gade singularity in
honeycomb layers with dilute topological defects; (ii) the rich landscape of
impurity resonances in a spin-orbit-coupled ferromagnet; and (iii) the
tailoring of emergent s-wave and p-wave superconducting phases in graphene via
atomic defects. These examples reveal rich features in the disorder self-energy
$\Sigma_{\textrm{dis}}(\mathbf{k},\omega)$ that are absent from the
self-consistent T-matrix approach and other common approximation schemes, which
include regimes of nontrivial wavevector dependence and anomalous dependence
upon the impurity concentration. Our study unravels puzzling, and so far
largely inaccessible, manifestations of strong nonperturbative quantum
interference effects in quantum materials and disordered phases of matter.",2110.00574v2
2022-02-17,"Doping control of magnetic anisotropy for stable antiskyrmion formation in schreibersite (Fe,Ni)$_3$P with $S_4$ symmetry","Magnetic skyrmions, vortex-like topological spin textures, have attracted
much interest in a wide range of research fields from fundamental physics to
spintronics applications. Recently, growing attention has also been paid to
antiskyrmions emerging in opposite topological charge in non-centrosymmetric
magnets with $D_{2\mathrm{d}}$ or $S_4$ symmetry. In these magnets, complex
interplay among anisotropic Dzyaloshinskii-Moriya interaction, uniaxial
magnetic anisotropy, and magnetic dipolar interactions generates a variety of
magnetic structures. However, the relation between the stability of
antiskyrmions and these magnetic interactions remains to be elucidated. In this
work, we control the uniaxial magnetic anisotropy of schreibersite (Fe,Ni)$_3$P
with $S_4$ symmetry by doping and investigate its impact on the stability of
antiskyrmions. Our magnetometry study, supported by ferromagnetic resonance
spectroscopy, shows that the variation of the Ni content and slight doping with
4$d$ transition metals considerably change the magnetic anisotropy. In
particular, doping with Pd induces easy-axis anisotropy, giving rise to
formation of antiskyrmions, while a temperature-induced spin reorientation is
observed in a Rh-doped compound. In combination with Lorentz transmission
electron microscopy and micromagnetic simulations, we quantitatively analyze
the stability of antiskyrmion as functions of uniaxial anisotropy and
demagnetization energy, and demonstrate that subtle balance between them is
necessary to stabilize the antiskyrmions.",2202.08483v1
2022-07-18,Room temperature spin-orbit torque efficiency in sputtered low-temperature superconductor delta-TaN,"In the course of searching for promising topological materials for
applications in future topological electronics, we evaluated spin-orbit torques
(SOTs) in high-quality sputtered ${\delta}-$TaN/Co20Fe60B20 devices through
spin-torque ferromagnetic resonance ST-FMR and spin pumping measurements. From
the ST-FMR characterization we observed a significant linewidth modulation in
the magnetic Co20Fe60B20 layer attributed to the charge-to-spin conversion
generated from the ${\delta}-$TaN layer. Remarkably, the spin-torque efficiency
determined from ST-FMR and spin pumping measurements is as large as ${\Theta}
=$ 0.034 and 0.031, respectively. These values are over two times larger than
for ${\alpha}-$Ta, but almost five times lower than for ${\beta}-$Ta, which can
be attributed to the low room temperature electrical resistivity $\sim
74{\mu}{\Omega}$ cm in ${\delta}-$TaN. A large spin diffusion length of at
least $\sim8$ nm is estimated, which is comparable to the spin diffusion length
in pure Ta. Comprehensive experimental analysis, together with density
functional theory calculations, indicates that the origin of the pronounced SOT
effect in ${\delta}-$TaN can be mostly related to a significant contribution
from the Berry curvature associated with the presence of a topically nontrivial
electronic band structure in the vicinity of the Fermi level (EF). Through
additional detailed theoretical analysis, we also found that an isostructural
allotrope of the superconducting ${\delta}-$TaN phase, the simple hexagonal
structure, ${\theta}-$TaN, has larger Berry curvature, and that, together with
expected reasonable charge conductivity, it can also be a promising candidate
for exploring a generation of spin-orbit torque magnetic random access memory
as cheap, temperature stable, and highly efficient spin current sources.",2207.08872v2
2022-09-06,Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers,"We study inserting Co layer thickness-dependent spin transport and spin-orbit
torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic
resonance. The interfacial perpendicular magnetic anisotropy energy density
($K_s = 2.7~erg/cm^2$), which is dominated by interfacial spin-orbit coupling
(ISOC) in the Pt/Co interface, total effective spin-mixing conductance
($G_{eff,tot} = 0.42 {\times} 10^{15}~{\Omega}^{-1} m^{-2}$) and two-magnon
scattering (${\beta}_{TMS} = 0.46~nm^2$) are first characterized, and the
damping-like torque (${\xi}_{DL}$ = 0.103) and field-like torque (${\xi}_{FL}$
= -0.017) efficiencies are also calculated quantitatively by varying the
thickness of the inserting Co layer. The significant enhancement of
${\xi}_{DL}$ and ${\xi}_{FL}$ in Pt/Co/Py than Pt/Py bilayer system originates
from the interfacial Rashba-Edelstein effect due to the strong ISOC between
Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a
considerable out-of-plane spin polarization SOT, which is ascribed to the spin
anomalous Hall effect and possible spin precession effect due to IPMA-induced
perpendicular magnetization at the Pt/Co interface. Our results demonstrate
that the ISOC of the Pt/Co interface plays a vital role in spin transport and
SOTs-generation. Our finds offer an alternative approach to improve the
conventional SOTs efficiencies and generate unconventional SOTs with
out-of-plane spin polarization to develop low power Pt-based spintronic via
tailoring the Pt/FM interface.",2209.02282v1
2023-01-24,Spin Dynamics in van der Waals Magnetic Systems,"The discovery of atomic monolayer magnetic materials has stimulated intense
research activities in the two-dimensional (2D) van der Waals (vdW) materials
community. The field is growing rapidly and there has been a large class of 2D
vdW magnetic compounds with unique properties, which provides an ideal platform
to study magnetism in the atomically thin limit. In parallel, based on
tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and
their heterostructures, emerging concepts of spintronic and optoelectronic
applications such as spin tunnel field-effect transistors and spin-filtering
devices are explored. While the magnetic ground state has been extensively
investigated, reliable characterization and control of spin dynamics play a
crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance
(FMR) allows direct measurements of magnetic excitations, which provides
insight into the key parameters of magnetic properties such as exchange
interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling,
damping rate, and domain structure. In this review article, we present an
overview of the essential progress in probing spin dynamics of 2D vdW magnets
using FMR techniques. Given the dynamic nature of this field, we focus mainly
on broadband FMR, optical FMR, and spin-torque FMR, and their applications in
studying prototypical 2D vdW magnets. We conclude with the recent advances in
laboratory- and synchrotron-based FMR techniques and their opportunities to
broaden the horizon of research pathways into atomically thin magnets.",2301.09822v2
2023-02-01,Evolution of interface magnetism in Fe/Alq3 bilayer,"Interface magnetism and topological structure of Fe on organic semiconductor
film (Alq3) have been studied and compared with Fe film deposited directly on
Si (100) substrate. To get information on the diffused Fe layer at the Fe/Alq3
interface, grazing incident nuclear resonance scattering (GINRS) measurements
are made depth selective by introducing a 95% enriched thin 57Fe layer at the
Interface and producing x-ray standing wave within the layered structure.
Compared with Fe growth on Si substrate, where film exhibits a hyperfine field
value of 32 T (Bulk Fe), a thick Fe- Alq3 interface has been found with reduced
electron density and hyperfine fields providing evidence of deep penetration of
Fe atoms into Alq3 film. Due to the soft nature of Alq3, Fe moments relax in
the film plane. At the same time, Fe on Si has a resultant ~43 deg out-of-plane
orientation of Fe moments at the Interface due to the stressed and rough Fe
layer near Si. The evolution of magnetism at the Fe-Alq3 Interface is monitored
using in-situ magneto-optical Kerr effect (MOKE) during the growth of Fe on the
Alq3 surface and small-angle x-ray scattering (SAXS) measurements. It is found
that the Fe atom tries to organize into clusters to minimize their
surface/interface energy. The origin of the 2.4 nm thick magnetic dead layer at
the Interface is attributed to the small Fe clusters of paramagnetic or
superparamagnetic nature. The present work provides an understanding of
interfacial magnetism at metal-organic interfaces and the topological study
using the GI-NRS technique, which is made depth selective to probe magnetism of
the diffused ferromagnetic layer, which is otherwise difficult for lab-based
techniques.",2302.00283v1
2023-08-14,Temperature Evolution of Magnon Propagation Length in Tm$_3$Fe$_5$O$_{12}$ Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping,"The magnon propagation length ($\langle\xi\rangle$) of a ferro/ferrimagnet
(FM) is one of the key factors that controls the generation and propagation of
thermally-driven spin current in FM/heavy metal (HM) bilayer based
spincaloritronic devices. Theory predicts that for the FM layer,
$\langle\xi\rangle$ is inversely proportional to the Gilbert damping ($\alpha$)
and the square root of the effective magnetic anisotropy constant ($K_{\rm
eff}$). However, direct experimental evidence of this relationship is lacking.
To experimentally confirm this prediction, we employ a combination of
longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and
ferromagnetic resonance experiments to investigate the temperature evolution of
$\langle\xi\rangle$ and establish its correlation with the effective magnetic
anisotropy field, $H_K^{\rm eff}$ ($\propto K_{\rm eff}$) and $\alpha$ in
Tm$_3$Fe$_5$O$_{12}$ (TmIG)/Pt bilayers. We observe concurrent drops in the
LSSE voltage and $\langle\xi\rangle$ below 200$^\circ$K in TmIG/Pt bilayers
regardless of TmIG film thickness and substrate choice and attribute it to the
noticeable increases in $H_K^{\rm eff}$ and $\alpha$ that occur within the same
temperature range. From the TmIG thickness dependence of the LSSE voltage, we
determined the temperature dependence of $\langle\xi\rangle$ and highlighted
its correlation with the temperature-dependent $H_K^{\rm eff}$ and $\alpha$ in
TmIG/Pt bilayers, which will be beneficial for the development of rare-earth
iron garnet-based efficient spincaloritronic nanodevices.",2308.07236v3
2024-01-16,Structure and lattice excitations of the copper substituted lead oxyapatite Pb$_{9.06(7)}$Cu$_{0.94(6)}$(PO$_{3.92(4)}$)$_{6}$O$_{0.96(3)}$,"The copper substituted lead oxyapatite,
Pb$_{10-x}$Cu$_{x}$(PO$_{3.92(4)}$)$_{6}$O$_{0.96(3)}$ (x=0.94(6)) was studied
using neutron and x-ray diffraction and neutron spectroscopy techniques. The
crystal structure of the main phase of our sample, which has come to be
colloquially known as LK-99, is verified to possess a hexagonal structure with
space group $P 6_{3}/m$, alongside the presence of impurity phases Cu and
Cu$_2$S. We determine the primary substitution location of the Cu as the Pb1
($6h$) site, with a small substitution at the Pb2 ($4f$) site. Consequently, no
clear Cu-doping-induced structural distortion was observed in the investigated
temperature region between 10~K and 300~K. Specially, we did not observe a
reduction of coordinate number at the Pb2 site or a clear tilting of PO$_4$
tetrahedron. Magnetic characterization reveals a diamagnetic signal in the
specimen, accompanied by a very weak ferromagnetic component at 2 K. No
long-range magnetic order down to 10 K was detected by the neutron diffraction.
Inelastic neutron scattering measurements did not show magnetic excitations for
energies up to 350 meV. There is no sign of a superconducting resonance in the
excitation spectrum of this material. The measured phonon density of states
compares well with density functional theory calculations performed for the
main LK-99 phase and its impurity phases. Our study may shed some insight into
the role of the favored substitution site of copper in the absence of
structural distortion and superconductivity in LK-99.",2401.08834v1
2024-02-01,Exploring inverse orbital Hall and orbital Rashba effects: unveiling the oxidation states of the Cu surface,"In this work, employing spin-pumping techniques driven by both ferromagnetic
resonance (SP-FMR) and longitudinal spin Seebeck effect (LSSE) to manipulate
and direct observe orbital currents, we investigated the volume conversion of
spin-orbital currents into charge-current in YIG(100nm)/Pt(2nm)/NM2 structures,
where NM2 represents Ti or Ru. While the YIG/Ti bilayer displayed a negligible
SP-FMR signal, the YIG/Pt/Ti structure exhibited a significantly stronger
signal attributed to the orbital Hall effect of Ti. Substituting the Ti layer
with Ru revealed a similar phenomenon, wherein the effect is ascribed to the
combined action of both spin and orbital Hall effects. Furthermore, we measured
the SP-FMR signal in the YIG/Pt(2)/Ru(6)/Ti(6) and YIG/Pt(2)/Ti(6)/Ru(6)
heterostructures by just altering the stack order of Ti and Ru layers, where
the peak value of the spin pumping signal is larger for the first sample. To
verify the influence on the oxidation of Ti and Ru films, we studied a series
of thin films subjected to controlled and natural oxidation. As Cu and CuOx is
a system that is already known to be highly influenced by oxidation, this metal
was chosen to carry out this study. We investigated these samples using SP-FMR
in YIG/Pt(2)/CuOx(tCu) and X-ray absorption spectroscopy and concluded that
samples with natural oxidation of Cu exhibit more significant results than
those when the CuOx is obtained by reactive sputtering. In particular, samples
where the Cu layer is naturally oxidized exhibit a Cu2O-rich phase. Our
findings help to elucidate the mechanisms underlying the inverse orbital Hall
and inverse orbital Rashba-Edelstein-like effects. These insights indeed
contribute to the advancement of devices that rely on orbital-charge
conversion.",2402.00297v1
2024-02-09,Ubiquitous order-disorder transition in the Mn antisite sublattice of the (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ magnetic topological insulators,"Magnetic topological insulators (TIs) herald a wealth of applications in
spin-based technologies, relying on the novel quantum phenomena provided by
their topological properties. Particularly promising is the
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ layered family of established intrinsic
magnetic TIs that can flexibly realize various magnetic orders and topological
states. High tunability of this material platform is enabled by
manganese-pnictogen intermixing, whose amounts and distribution patterns are
controlled by synthetic conditions. Positive implication of the strong
intermixing in MnSb$_2$Te$_4$ is the interlayer exchange coupling switching
from antiferromagnetic to ferromagnetic, and the increasing magnetic critical
temperature. On the other side, intermixing also implies atomic disorder which
may be detrimental for applications. Here, we employ nuclear magnetic resonance
and muon spin spectroscopy, sensitive local probe techniques, to scrutinize the
impact of the intermixing on the magnetic properties of
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ and MnSb$_2$Te$_4$. Our measurements not
only confirm the opposite alignment between the Mn magnetic moments on native
sites and antisites in the ground state of MnSb$_2$Te$_4$, but for the first
time directly show the same alignment in (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$
with n = 0, 1 and 2. Moreover, for all compounds, we find the static magnetic
moment of the Mn antisite sublattice to disappear well below the intrinsic
magnetic transition temperature, leaving a homogeneous magnetic structure
undisturbed by the intermixing. Our findings provide a microscopic
understanding of the crucial role played by Mn-Bi intermixing in
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ and offer pathways to optimizing the
magnetic gap in its surface states.",2402.06340v1
2024-02-19,Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures,"Quantum magnonics investigates the quantum-mechanical properties of magnons
such as quantum coherence or entanglement for solid-state quantum information
technologies at the nanoscale. The most promising material for quantum
magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons
with the longest lifetimes. YIG films of the highest quality are grown on a
paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has
reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at
temperatures below 50 K despite the increase in YIG magnetization. We
investigated a 97 nm-thick YIG film grown on 500 $\mathrm{\mu}$m-thick GGG
substrate through a series of experiments conducted at temperatures as low as
30 mK, and using both analytical and numerical methods. Our findings suggest
that the primary factor contributing to the FMR frequency shift is the stray
magnetic field created by the partially magnetized GGG substrate. This stray
field is antiparallel to the applied external field and is highly
inhomogeneous, reaching up to 40 mT in the center of the sample. At
temperatures below 500 mK, the GGG field exhibits a saturation that cannot be
described by the standard Brillouin function for a paramagnet. Including the
calculated GGG field in the analysis of the FMR frequency versus temperature
dependence allowed the determination of the cubic and uniaxial anisotropies. We
find that the total anisotropy increases more than three times with the
decrease in temperature down to 2 K. Our findings enable accurate predictions
of the YIG/GGG magnetic systems behavior at low and ultra-low millikelvin
temperatures, crucial for developing quantum magnonic devices.",2402.12112v1
2010-03-29,Ferromagnetism in defect-ridden oxides and related materials,"The existence of high-temperature ferromagnetism in thin films and
nanoparticles of oxides containing small quantities of magnetic dopants remains
controversial. Some regard these materials as dilute magnetic semiconductors,
while others think they are ferromagnetic only because the magnetic dopants
form secondary ferromagnetic impurity phases such as cobalt metal or magnetite.
There are also reports in d0 systems and other defective oxides that contain no
magnetic ions. Here, we investigate TiO2 (rutile) containing 1 - 5% of iron
cations and find that the room-temperature ferromagnetism of films prepared by
pulsed-laser deposition is not due to magnetic ordering of the iron. The films
are neither dilute magnetic semiconductors nor hosts to an iron-based
ferromagnetic impurity phase. A new model is developed for defect-related
ferromagnetism which involves a spin-split defect band populated by charge
transfer from a proximate charge reservoir in the present case a mixture Fe2+
and Fe3+ ions in the oxide lattice. The phase diagram for the model shows how
inhomogeneous Stoner ferromagnetism depends on the total number of electrons
Ntot, the Stoner exchange integral I and the defect bandwidth W; the band
occupancy is governed by the d-d Coulomb interaction U. There are regions of
ferromagnetic metal, half-metal and insulator as well as nonmagnetic metal and
insulator. A characteristic feature of the high-temperature Stoner magnetism is
an an anhysteretic magnetization curve which is practically temperature
independent below room temperature. This is related to a wandering
ferromagnetic axis which is determined by local dipole fields. The
magnetization is limited by the defect concentration, not by the 3d doping.
Only 1-2 % of the volume of the films is magnetically ordered.",1003.5558v1
2016-01-08,Coexistence of interacting-ferromagnetic and small-antiferromagnetic clusters in La$_{0.5}$Ba$_{0.5}$CoO$_3$,"We report detailed dc magnetization, linear and non-linear ac susceptibility
measurements on the hole doped disordered cobaltite
La$_{0.5}$Ba$_{0.5}$CoO$_3$. Our results show that the magnetically ordered
state of the system consists of coexisting non-ferromagnetic phases along with
percolating ferromagnetic-clusters. The percolating ferromagnetic-clusters
possibly start a magnetic ordering at the Curie temperature of 201.5(5)~K. The
non-ferromagnetic phases mainly consist of antiferromagnetic-clusters with size
smaller than the ferromagnetic-clusters. Below Curie temperature the system
exhibits an irreversibility in the field cooled and zero field cooled
magnetization and frequency dependence in the peak of ac susceptibility. These
dynamical features indicate towards the possible coexistence of spin-glass
phase along with ferromagnetic-clusters similar to La$_{1-x}$Sr$_{x}$CoO$_3$
(x$\geq$0.18), but the absence of field divergence in third harmonic of ac
susceptibility and zero field cooled memory clearly rule out any such
possibility. We argue that the spin-glass phase in La$_{1-x}$Sr$_{x}$CoO$_3$
(x$\geq$0.18) is associated with the presence of incommensurate
antiferromagnetic ordering in non-ferromagnetic phases which is absent in
La$_{0.5}$Ba$_{0.5}$CoO$_3$. Our analysis show that the observed dynamical
features in La$_{0.5}$Ba$_{0.5}$CoO$_3$ are possibly due to progressive thermal
blocking of ferromagnetic-clusters which is further confirmed by the
Wohlfarth's model of superparamagnetism. The frequency dependence of the peak
of ac susceptibility obeys the Vogel-Fulcher law with $\tau_0\approx10^{-9}$s.
This together with the existence of an AT line in H-T space indicates the
presence of significant inter-cluster interaction among these
ferromagnetic-clusters.",1601.01995v1
2004-07-20,Mapping of Euclidean resonance on static resonant tunneling,"Quantum tunneling through an almost classical potential barrier can be
strongly enhanced by a nonstationary field so that the penetration through the
barrier becomes not exponentially small. This constitutes an extremely unusual
phenomenon of quantum physics called Euclidean resonance. A certain
nonstationary barrier is proposed with a very low WKB tunneling rate. The
quantum dynamics of this barrier is mapped on resonant tunneling across a
static double barrier with a resonant level inside. The real penetration
through the dynamical barrier is not exponentially small providing an example
of Euclidean resonance. Therefore, the Schoedinger equation allows solutions of
the type of Euclidean resonance. The counterintuitive phenomenon of Euclidean
resonance is a dynamical analogue of static resonant tunneling.",0407163v1
2011-07-30,Enhancement of second harmonic generation in a doubly resonant metamaterial,"We investigate second harmonic (SH) generation in a doubly resonant
metamaterial. We show that SH generation can be enhanced when the resonant
condition is satisfied for the SH frequency as well as for the fundamental
frequency. A unit cell of the doubly resonant metamaterial consists of two
coupled resonators, one of which resonates at the fundamental frequency,
whereas the other resonates around the SH frequency. We observe that the SH
generation in the doubly resonant metamaterial is 4.6 times as large as that in
a singly resonant metamaterial.",1108.0044v1
2013-03-03,Optomechanical Transductions in Single and Coupled Wheel Resonators,"In this report, the optomechanical transductions in both single and two
side-coupled wheel resonators are investigated. In the single resonator, the
optomechanical transduction sensitivity is determined by the optical and
mechanical quality factors of the resonator. In the coupled resonators, the
optomechanical transduction is related to the energy distribution in the two
resonators, which is strongly dependent on the input detuning. Compared to a
single resonator, the coupled resonators can still provide very sensitive
optomechanical transduction even if the optical and mechanical quality factors
of one resonator are degraded.",1303.0440v1
2015-03-20,Frequency stabilization of the non resonant wave of a continuous-wave singly resonant optical parametric oscillator,"We present an experimental technique allowing to stabilize the frequency of
the non resonant wave in a singly resonant optical parametric oscillator (SRO)
down to the kHz level, much below the pump frequency noise level. By comparing
the frequency of the non resonant wave with a reference cavity, the pump
frequency noise is imposed to the frequency of the resonant wave, and is thus
subtracted from the frequency of the non resonant wave. This permits the non
resonant wave obtained from such a SRO to be simultaneously powerful and
frequency stable, which is usually impossible to obtain when the resonant wave
frequency is stabilized.",1503.06138v1
2009-12-05,Delta-Interference of Two Friedel Resonances,"When a single resonator is coupled to a continuous spectrum one obtains a
resonance of finite half-width. Such a resonance is known in many fields of
physics. The Friedel resonance is an example where a d-impurity is dissolved in
a simple metal. If two resonators are coupled to the continuous spectrum the
resonances interfere. For identical coupling and frequencies one obtains two
effective resonances. The effective coupling of one of them to the continuum
can be tuned to zero yielding a delta-like resonance.",0912.1049v1
2012-01-25,Efficient second harmonic generation in a metamaterial with two resonant modes coupled through two varactor diodes,"We present an effective method to generate second harmonic (SH) waves using
nonlinear metamaterial composed of coupled split ring resonators (CSRRs) with
varactor (variable capacitance) diodes. The CSRR structure has two resonant
modes: a symmetric mode that resonates at the fundamental frequency and an
anti-symmetric mode that resonates at the SH frequency. Resonant fundamental
waves in the symmetric mode generate resonant SH waves in the anti-symmetric
mode. The double resonance contributes to effective SH radiation. In the
experiment, we observe 19.6 dB enhancement in the SH radiation in comparison
with the nonlinear metamaterial that resonates only for the fundamental waves.",1201.5196v1
2023-09-25,New narrow resonance in the $e^+ e^- \to φη$ data by Belle collaboration,"Fitting the recent $e^+e^-\ra\phi\,\eta$ data by the Belle collaboration with
a theoretical formula reveals, besides the dominant $\phi(1680)$ resonance, two
narrow resonances: expected $\phi(2170)$ resonance and an unexpected resonance
with the mass of about 1851 MeV. Close proximity to the $X(1835)$ resonance
suggests that the new resonance may be interpreted as the $p \bar p$ baryonium
in an excited state. Follow-up analysis found the same resonance also in
$e^+e^-\ra\omega\,\eta$ data by CMD-3 experiment.",2309.14520v2
2023-10-10,Mean-Motion Resonances in the Quadrantid Meteoroid Stream and Dynamic Evolution of Dust Trail of (196256) 2003 EH1,"The paper presents numerical models of mean-motion resonances detected in the
Quadrantid meteoroid stream consisting of particles of mass 0.003 to 0.03 g,
which helps to prove the presence of the following mean-motion resonances: the
1:9 resonance with Venus, 1:5 resonance with Earth, 1:3 and 3:8 resonances with
Mars, and 2:1,7:3, 9:4 resonances with Jupiter. Resonance particles create dust
trails far from the Earth orbit. Indeed, there is no observational support for
resonant effects in the observed Quadrantid meteoroid stream.",2310.07037v1
2015-08-07,"Energetic, spatial and momentum character of a buried interface: the two-dimensional electron gas between two metal oxides","The interfaces between two condensed phases often exhibit emergent physical
properties that can lead to new physics and novel device applications, and are
the subject of intense study in many disciplines. We here apply novel
experimental and theoretical techniques to the characterization of one such
interesting interface system: the two-dimensional electron gas (2DEG) formed in
multilayers consisting of SrTiO$_3$ (STO) and GdTiO$_3$ (GTO). This system has
been the subject of multiple studies recently and shown to exhibit very high
carrier charge densities and ferromagnetic effects, among other intriguing
properties. We have studied a 2DEG-forming multilayer of the form [6 unit cells
STO/3 unit cells of GTO]$_{20}$ using a unique array of photoemission
techniques including soft and hard x-ray excitation, soft x-ray angle-resolved
photoemission, core-level spectroscopy, resonant excitation, and standing-wave
effects, as well as theoretical calculations of the electronic structure at
several levels and of the actual photoemission process. Standing-wave
measurements below and above a strong resonance have been introduced as a
powerful method for studying the 2DEG depth distribution. We have thus
characterized the spatial and momentum properties of this 2DEG with
unprecedented detail, determining via depth-distribution measurements that it
is spread throughout the 6 u.c. layer of STO, and measuring the momentum
dispersion of its states. The experimental results are supported in several
ways by theory, leading to a much more complete picture of the nature of this
2DEG, and suggesting that oxygen vacancies are not the origin of it. Similar
multi-technique photoemission studies of such states at buried interfaces,
combined with comparable theory, will be a very fruitful future approach for
exploring and modifying the fascinating world of buried-interface physics and
chemistry.",1508.01832v3
2023-07-12,exoMMR: a New Python Package to Confirm and Characterize Mean Motion Resonances,"The study of orbital resonances allows for the constraint of planetary
properties of compact systems. We can predict a system's resonances by
observing the orbital periods of the planets, as planets in or near mean motion
resonance have period ratios that reduce to a ratio of small numbers. However,
a period ratio near commensurability does not guarantee a resonance; we must
study the system's dynamics and resonant angles to confirm resonance. Because
resonances require in-depth study to confirm, and because two-body resonances
require a measurement of the eccentricity vector which is quite challenging,
very few resonant pairs or chains have been confirmed. We thus remain in the
era of small number statistics, not yet able to perform large population
synthesis or informatics studies. To address this problem, we build a python
package to find, confirm, and analyze mean motion resonances, primarily through
N-body simulations. We then analyze all near-resonant planets in the Kepler/K2
and TESS catalogues, confirming over 60 new resonant pairs and various new
resonant chains. We additionally demonstrate the package's functionality and
potential by characterizing the mass-eccentricity degeneracy of Kepler-80g,
exploring the likelihood of an exterior giant planet in Kepler-80, and
constraining the masses of planets in Kepler-305. We find that our methods
overestimate the libration amplitudes of the resonant angles and struggle to
confirm resonances in systems with more than three planets. We identify various
systems that are likely resonant chains but that we are unable to confirm, and
highlight next steps for exoplanetary resonances.",2307.06171v1
2005-06-09,Transversal plasma resonance in a nonmagnetized plasma and possibilities of practical employment of it,"It is shown that in a nonmagnetized plasma, beside the longitudinal Langmuir
resonance, there may also exist the transversal resonance. Both these resonance
kinds are degenerated. Employment of the transversal resonance makes it
possible to design resonators and filters, as well as powerful single-frequency
lasers operating on the basis of collective oscillations of plasma.",0506081v1
2007-10-30,On the ambiguity of the interfering resonances parameters determination,"In this paper the interfering resonances parameters determination ambiguity
is considered. It is shown that there are two solutions for two fixed width
resonances. Analytical relation between different solutions is derived. Numeric
experiments for fixed width three and four resonances, and for model
energy-dependent width two resonances confirm ambiguity of the resonances
parameters determination.",0710.5627v1
2011-06-06,Optimal lower bound of the resonance widths for a Helmhotz tube-shaped resonator,"The study of the resonances of the Helmholtz resonator has been broadly
described in previous works. Here, for a simple tube-shaped two dimensional
resonator, we can perform a careful analysis of the transition zone where
oscillations start to appear. In that way, we obtain an optimal lower bound of
the width of the resonances.",1106.0990v1
2012-08-17,All-Resonant Control of Superconducting Resonators,"An all-resonant method is proposed to control the quantum state of
superconducting resonators. This approach uses a tunable artificial atom
linearly coupled to resonators, and allows for efficient routes to Fock state
synthesis, qudit logic operations, and synthesis of NOON states. This resonant
approach is theoretically analyzed, and found to perform signficantly better
than existing proposals using the same technology.",1208.3657v1
2018-02-15,Effects of Symmetry Breaking in Resonance Phenomena,"We show that resonance phenomena can be treated as nonequilibrium phase
transitions. Resonance phenomena, similar to equilibrium phase transitions, are
accompanied by some kind of symmetry breaking and can be characterized by order
parameters. This is demonstrated for spin-wave resonance, helicon resonance,
and spin-reversal resonance.",1802.05589v1
2017-09-04,Excited resonance widths for Helmholtz resonators with straight neck,"We consider resonances associated with excited eigenvalues of the cavity of a
general Helmholtz resonator with straight neck. Under the assumption that the
neck stays away from the nodal set of the corresponding eigenstate, we
generalise the optimal exponential lower bound on the width of the resonance,
that we have obtained in a previous paper for the ground resonance only.",1709.00894v1
1999-08-10,Existence of Saturated Ferromagnetic and Spiral States in 1D Lieb-Ferrimagnetic Models away from Half-Filling,"In order to study conditions for the appearance of ferromagnetism in a wide
filling region, we investigate numerically three types of one-dimensional
Lieb-ferrimagnetic Hubbard models: a periodic diamond (PD) chain, a periodic
alternately-attached leg (PAAL) chain and an open diamond (OD) chain. All of
these models have a flat band (or equivalently, degenerate single-electron
eigenvalues). The PD and OD chains commonly have a local-loop structure.
Nagaoka's theorem holds only in the PD chain. At half-filling, it have been
rigorously proven that all of these models are ferrimagnet. Away from
half-filling, however, quite different magnetic properties are found. In the
fillings 1/3< rho_e <1/2, the ground state of the PD chain for a
infinitely-large U is the extended ferromagnetic state, that is, the saturated
ferromagnetic state or the spiral state for odd or even number of electrons,
respectively. In the PAAL chain, on the other hand, there is no magnetic order.
Thus, the flat band is found to be not a sufficient condition of the extended
ferromagnetic state. We find, moreover, that the saturated ferromagnetism
appears in the OD chain, although the Nagaoka theorem does not hold on this
chain. This indicates that the local-loop structure plays an important role on
the appearance of the extended ferromagnetic state.",9908144v1
1999-12-29,Theory of Disordered Itinerant Ferromagnets I: Metallic Phase,"A comprehensive theory for electronic transport in itinerant ferromagnets is
developed. We first show that the Q-field theory used previously to describe a
disordered Fermi liquid also has a saddle-point solution that describes a
ferromagnet in a disordered Stoner approximation. We calculate transport
coefficients and thermodynamic susceptibilities by expanding about the saddle
point to Gaussian order. At this level, the theory generalizes previous
RPA-type theories by including quenched disorder. We then study soft-mode
effects in the ferromagnetic state in a one-loop approximation. In
three-dimensions, we find that the spin waves induce a square-root frequency
dependence of the conductivity, but not of the density of states, that is
qualitatively the same as the usual weak-localization effect induced by the
diffusive soft modes. In contrast to the weak-localization anomaly, this effect
persists also at nonzero temperatures. In two-dimensions, however, the spin
waves do not lead to a logarithmic frequency dependence. This explains
experimental observations in thin ferromagnetic films, and it provides a basis
for the construction of a simple effective field theory for the transition from
a ferromagnetic metal to a ferromagnetic insulator.",9912477v2
2000-03-23,Conductance modulation by spin precession in non-collinear ferromagnet-normal metal-ferromagnet systems,"We study diffusive transport through ferromagnet - normal metal - ferromagnet
(F-N-F) systems, with arbitrary but fixed magnetization directions of the
ferromagnetic reservoirs and orientations of a magnetic field applied to the
normal metal. For non-collinear configurations, the complex mixing conductance
describes the transport of spins non-collinear to the magnetizations of the
ferromagnetic reservoirs. When the imaginary part of the mixing conductance is
different from zero, the total conductance of the system in the presence of a
magnetic field can be asymmetric with respect to time reversal. The total
conductance changes non-monotonically with the magnetic field strength for
different magnetic configurations. This modulation of the conductance is due to
the precession of the spin accumulation in the normal metal. The difference
between the conductance of the parallel and antiparallel configurations can be
either positive or negative as a function of the applied magnetic field. This
effect should be best observable on Al single crystals attached to
ferromagnetic electrodes by means of tunnel junctions or metallic contacts.",0003382v4
2002-11-14,Ferromagnetism of a graphite nodule from the Canyon Diablo meteorite,"There have recently been various reports of weak ferromagnetism in graphite
(1,2) and synthetic carbon materials (3) such as rhombohedral C60 (4), as well
as a theoretical prediction of a ferromagnetic instability in graphene sheets
(5). With very small ferromagnetic signals, it is difficult to be certain that
the origin is intrinsic, rather than due to minute concentrations of iron-rich
impurities. Here we take a different experimental approach to study
ferromagnetism in graphitic materials, by making use of meteoritic graphite,
which is strongly ferromagnetic at room temperature. We examined ten samples of
extraterrestrial graphite from a nodule in the Canyon Diablo meteorite.
Graphite is the major phase in every sample but there are minor amounts of
magnetite, kamacite, akaganeite, and other phases. By analysing the phase
composition of a series of samples, we find that these iron-rich minerals can
only account for about two-thirds of the observed magnetization. The remainder
is somehow associated with graphite, corresponding to an average magnetization
of 23 Am2kg-1, or 0.05 Bohr magnetons per carbon atom. The magnetic ordering
temperature is near 570 K. We suggest that the ferromagnetism is a magnetic
proximity effect induced at the interface with magnetite or kamacite
inclusions.",0211275v1
2002-12-20,Magnon Exchange Mechanism of Ferromagnetic Superconductivity,"The magnon exchange mechanism of ferromagnetic superconductivity
(FM-superconductivity) was developed to explain in a natural way the fact that
the superconductivity in $UGe_2$, $ZrZn_2$ and $URhGe$ is confined to the
ferromagnetic phase.The order parameter is a spin anti-parallel component of a
spin-1 triplet with zero spin projection. The transverse spin fluctuations are
pair forming and the longitudinal ones are pair breaking. In the present paper,
a superconducting solution, based on the magnon exchange mechanism, is obtained
which closely matches the experiments with $ZrZn_2$ and $URhGe$. The onset of
superconductivity leads to the appearance of complicated Fermi surfaces in the
spin up and spin down momentum distribution functions. Each of them consist of
two pieces, but they are simple-connected and can be made very small by varying
the microscopic parameters. As a result, it is obtained that the specific heat
depends on the temperature linearly, at low temperature, and the coefficient
$\gamma=\frac {C}{T}$ is smaller in the superconducting phase than in the
ferromagnetic one. The absence of a quantum transition from ferromagnetism to
ferromagnetic superconductivity in a weak ferromagnets $ZrZn_2$ and $URhGe$ is
explained accounting for the contribution of magnon self-interaction to the
spin fluctuations' parameters. It is shown that in the presence of an external
magnetic field the system undergoes a first order quantum phase transition.",0212520v1
2005-09-04,Itinerant Ferromagnetism and Metamagnetism in Cr Doped Perovskite Ruthenates,"We report results of structural, magnetic and transport properties of single
crystal CaRu1-xCrxO3 (0&#8804;x&#8804;0.36) and SrRu1-xCrxO3
(0&#8804;x&#8804;0.30). Cr substitution as low as x=0.08 drives CaRu1-xCrxO3
from the paramagnetic state to an itinerant ferromagnetic state with
field-driven first-order metamagnetic transitions leading to a sizeable
saturation moment (~0.4&#61549;B/f.u.within the ab plane). The ferromagnetism
occurs abruptly and reaches as high as TC=123 K for x=0.22. The Cr-driven
ferromagnetism is highly anisotropic, suggesting an important role for
spin-orbit coupling. Lattice constant and magnetic measurements strongly
support the valence of the Cr as tetravalent (Cr4+, 3d2 configuration). Cr
substitution for Ru in SrRuO3 (TC=165 K) enhances the itinerant ferromagnetism,
with TC reaching 290 K for x=0.30, consistent with Cr-induced ferromagnetism in
paramagnetic CaRuO3. Preliminary pressure-dependent magnetization of
CaRu0.85Cr0.15O3 shows strong enhancement of the saturation magnetization (25%
for P~0.7 GPa). All results indicate a coupling of Ru 4d and Cr 3d electrons
that is unexpectedly favorable for itinerant ferromagnetism which often exists
delicately in the ruthenates.",0509084v1
2007-11-07,Spin-flip scattering and non-ideal interfaces in dirty ferromagnet/superconductor junctions,"We study the proximity-induced superconducting correlations as well as the
local density of states of a ferromagnet, in a ferromagnet/s-wave
superconductor heterostructure. We include the effects of spin-flip scattering,
non-ideal interfaces, and the presence of impurities in the sample. We employ
the quasiclassical theory of superconductivity, solving the Usadel equation
with emphasis on obtaining transparent analytical results. As our main result,
we report that in a certain parameter regime the spatial oscillations of the
anomalous (superconducting) part of the Green's function induced in the
ferromagnet by the proximity effect from the s-wave superconductor, are damped
out due to the presence of spin-flip processes. As a consequence, spin-flip
scattering may under certain conditions actually enhance the local density of
states due to the oscillatory behaviour of the latter in
ferromagnet/superconductor structures. We also conjecture that the damping
could be manifested in the behaviour of the critical temperature ($T_c$) of the
s-wave superconductor in contact with the ferromagnet. More specifically, we
argue that the non-monotonic decrease of $T_c$ in ferromagnet/s-wave
superconductor junctions without magnetic impurities is altered to a monotonic,
non-oscillatory decrease when the condition $1>16\tau_\text{sf}^2h^2$ is
fulfilled, where $\tau_\text{sf}$ is the spin-flip relaxation time and $h$ is
the exchange field.",0711.1062v1
2009-07-21,Search for Ferromagnetism in doped semiconductors in the absence of transition metal ions,"In contrast to semiconductors doped with transition metal magnetic elements,
which become ferromagnetic at temperatures below ~ 100K, semiconductors doped
with non-magnetic ions (e.g. silicon doped with phosphorous) have not shown
evidence of ferromagnetism down to millikelvin temperatures. This is despite
the fact that for low densities the system is expected to be well modeled by
the Hubbard model, which is predicted to have a ferromagnetic ground state at
T=0 on 2- or 3-dimensional bipartite lattices in the limit of strong
correlation near half-filling. We examine the impurity band formed by
hydrogenic centers in semiconductors at low densities, and show that it is
described by a generalized Hubbard model which has, in addition to strong
electron-electron interaction and disorder, an intrinsic electron-hole
asymmetry. With the help of mean field methods as well as exact diagonalization
of clusters around half filling, we can establish the existence of a
ferromagnetic ground state, at least on the nanoscale, which is more robust
than that found in the standard Hubbard model. This ferromagnetism is most
clearly seen in a regime inaccessible to bulk systems, but attainable in
quantum dots and 2D heterostructures. We present extensive numerical results
for small systems that demonstrate the occurrence of high-spin ground states in
both periodic and positionally disordered 2D systems. We consider how
properties of real doped semiconductors, such as positional disorder and
electron-hole asymmetry, affect the ground state spin of small 2D systems. We
also discuss the relationship between this work and diluted magnetic
semiconductors, such as Ga_(1-x)Mn_(x)As, which though disordered, show
ferromagnetism at relatively high temperatures.",0907.3671v1
2010-02-11,The frustrated spin-1/2 J1-J2 Heisenberg ferromagnet on the square lattice: Exact diagonalization and Coupled-Cluster study,"We investigate the ground-state magnetic order of the spin-1/2 J1-J2
Heisenberg model on the square lattice with ferromagnetic nearest-neighbor
exchange J1<0 and frustrating antiferromagnetic next-nearest neighbor exchange
J2>0. We use the coupled-cluster method to high orders of approximation and
Lanczos exact diagonalization of finite lattices of up to N=40 sites in order
to calculate the ground-state energy, the spin-spin correlation functions, and
the magnetic order parameter. We find that the transition point at which the
ferromagnetic ground state disappears is given by J2^{c1}=0.393|J1| (exact
diagonalization) and J2^{c1}=0.394|J1| (coupled-cluster method). We compare our
results for ferromagnetic J1 with established results for the spin-1/2 J1-J2
Heisenberg model with antiferromagnetic J1. We find that both models (i.e.,
ferro- and antiferromagnetic J1) behave similarly for large J2, although
significant differences between them are observed for J2/|J1| \lesssim 0.6.
Although the semiclassical collinear magnetic long-range order breaks down at
J2^{c2} \approx 0.6J1 for antiferromagnetic J1, we do not find a similar
breakdown of this kind of long-range order until J2 \sim 0.4|J1| for the model
with ferromagnetic J1. Unlike the case for antiferromagnetic J1, if an
intermediate disordered phase does occur between the phases exhibiting
semiclassical collinear stripe order and ferromagnetic order for ferromagnetic
J1 then it is likely to be over a very small range below J2 \sim 0.4|J1|.",1002.2299v1
2010-02-12,Magnetic materials and the problem of thermal Casimir force,"We investigate the thermal Casimir interaction between two magnetodielectric
plates made of real materials. On the basis of the Lifshitz theory, it is shown
that for diamagnets and for paramagnets in the broad sense (with exception of
ferromagnets) the magnetic properties do not influence the magnitude of the
Casimir force. For ferromagnets, taking into account the realistic dependence
of magnetic permeability on frequency, we conclude that the impact of magnetic
properties on the Casimir interaction arises entirely from the contribution of
the zero-frequency term in the Lifshitz formula. The computations of the
Casimir free energy and pressure are performed for the configurations of two
plates made of ferromagnetic metals (Co and Fe), for one plate made of
ferromagnetic metal and the other of nonmagnetic metal (Au), for two
ferromagnetic dielectric plates (on the basis of polystyrene), and for a
ferromagnetic dielectric plate near a nonmagnetic metal plate. The dielectric
permittivity of metals is described using both the Drude and the plasma model
approaches. It is shown that the Casimir repulsion through the vacuum gap can
be realized in the configuration of a ferromagnetic dielectric plate near a
nonmagnetic metal plate described by the plasma model. In all cases considered,
the respective analytical results in the asymptotic limit of large separations
between the plates are obtained. The impact of the magnetic phase transition
through the Curie temperature on the Casimir interaction is considered. In
conclusion, we propose several experiments allowing to determine whether the
magnetic properties really influence the Casimir interaction and to
independently verify the Drude and plasma model approaches to the thermal
Casimir force.",1002.2484v1
2010-09-14,Spin-triplet Supercurrent through Inhomogeneous Ferromagnetic Trilayers,"Motivated by a recent experiment [J. W. A. Robinson, J. D. S. Witt and M. G.
Blamire, Science, \textbf{329}, 5987 (2010)], we here study the possibility of
establishing a long-range spin-triplet supercurrent through an inhomogeneous
ferromagnetic region consisting of a Ho$\mid$Co$\mid$Ho trilayer sandwiched
between two conventional s-wave superconductors. We utilize a full numerical
solution in the diffusive regime of transport and study the behavior of the
supercurrent for various experimentally relevant configurations of the
ferromagnetic trilayer. We obtain qualitatively very good agreement with
experimental data regarding the behavior of the supercurrent as a function of
the width of the Co-layer, $L_\text{Co}$. Moreover, we find a synthesis of
0-$\pi$ oscillations with superimposed rapid oscillations when varying the
width of the Ho-layer which pertain specifically to the spiral magnetization
texture in Ho. We are not able to reproduce the anomalous peaks in the
supercurrent observed experimentally in this regime, but note that the results
obtained are quite sensitive to the exact magnetization profile in the
Ho-layers, which could be the reason for the discrepancy between our model and
the experimental reported data for this particular aspect. We also investigate
the supercurrent in a system where the intrinsically inhomogeneous Ho
ferromagnets are replaced with domain-wall ferromagnets, and find similar
behavior as in the Ho$\mid$Co$\mid$Ho case. Furthermore, we propose a novel
type of magnetic Josephson junction including only a domain-wall ferromagnet
and a homogeneous ferromagnetic layer, which in addition to simplicity
regarding the magnetization profile also offers a tunable long-range
spin-triplet supercurrent. Finally, we discuss some experimental aspects of our
findings.",1009.2754v1
2012-10-19,"Ferromagnetic structures in Mn2CoGa and Mn2CoAl doped by Co, Cu, V, and Ti","The structure and magnetic properties in doped Heusler alloys of Mn2CoGa and
Mn2CoAl have been investigated by experiments and calculations. The main group
elements of Ga and Al are substituted by the magnetic or non-magnetic
transition metals, Co, Cu, V, and Ti in the alloy systems. Three kinds of local
ferromagnetic structures, Co-Mn-Co, Mn-Co-Mn and Mn-Co-V, have been found. They
embed in the native ferrimagnetic matrix and increase the magnetization with
different increments. The Co-Mn-Co ferromagnetic structure shows the largest
increment of 6.18{\mu}B /atom. In addition, interesting results for
non-magnetic Cu increasing the magnetization and the V atom having a large
ferromagnetic moment of about 1.0{\mu}B have been obtained. The exchange
interaction energy can be increased by the newly added Co and depleted by
supporting a ferromagnetic coupling in other substitution cases, and showing
the variation of the TC. Our calculation of electronic structure verifies the
strong d-d hybridization when the three ferromagnetic structures are achieved.
It has also been found that the covalent effect from the Ga and Al determines
the generation of the local ferromagnetic structure and the tolerance for
dopant content.",1210.5357v1
2013-07-22,Self-consistent Gutzwiller study of bcc Fe: interplay of ferromagnetic order and kinetic energy,"The Gutzwiller technique has long been known as a method to include
correlations in electronic structure calculations. Here we implement an
ab-initio Gutzwiller+LDA calculation, and apply it to a classic problem, the
ferromagnetism of bulk bcc Fe, whose nature has attracted recent interest. In
the conventional Stoner-Wohlfarth model, the ferromagnetic ordering of iron
sets in so that the electrons can reduce their mutual Coulomb repulsion at the
extra cost of some increase of electron kinetic energy. Density functional
theory within the spin polarized local density approximation (LDA) has long
supported that picture, showing that ferromagnetic alignment causes band
narrowing and a corresponding wavefunction localization, whence a kinetic
energy increase. However, because of its inadequate treatment of strong
intra-site correlations for localized d orbitals, LDA cannot be relied upon,
particularly when it comes to separately describing fine potential and kinetic
energy imbalances. With ab-initio Gutzwiller+LDA, we indeed find that the
effect of correlations is to dramatically reverse the balance, the
ferromagnetic ordering of Fe in fact causing a decrease of kinetic energy, at
the cost of some increase of potential energy. The underlying physical
mechanism, foreshadowed long ago by Goodenough and others, and more recently
supported by LDA+DMFT calculations, is that correlations cause eg and t2g 3d
orbitals to behave very differently. Weakly dispersive eg states are
spin-polarized and almost localized, while, more than half filled, the t2g are
broad band, fully delocalized states. Owing to intra-atomic Hund's rule
exchange which aligns eg and t2g spins, the propagation of itinerant t2g holes
is only allowed when different atomic spins are ferromagnetically aligned. We
thus conclude that double exchange is at work already in the most popular
ferromagnetic metal.",1307.5738v1
2014-07-22,Fermi Surface Instabilities in Ferromagnetic Superconductor URhGe,"The field-reentrant (field-reinforced) superconductivity on ferromagnetic
superconductors is one of the most interesting topics in unconventional
superconductivity. The enhancement of effective mass and the induced
ferromagnetic fluctuations play key roles for reentrant superconductivity.
However, the associated change of the Fermi surface, which is often observed at
(pseudo-) metamagnetic transition, can also be a key ingredient. In order to
study the Fermi surface instability, we performed Hall effect measurements in
the ferromagnetic superconductor URhGe. The Hall effect of URhGe is well
explained by two contributions, namely by the normal Hall effect and by the
large anomalous Hall effect due to skew scattering. The large change in the
Hall coefficient is observed at low fields between the paramagnetic and
ferromagnetic states for H // c-axis (easy-magnetization axis) in the
orthorhombic structure, indicating that the Fermi surface is reconstructed in
the ferromagnetic state below the Curie temperature (T_Curie=9.5K). At low
temperatures (T << T_Curie), when the field is applied along the b-axis, the
reentrant superconductivity was observed in both the Hall resistivity and the
magnetoresistance below 0.4K. Above 0.4K, a large jump with the first-order
nature was detected in the Hall resistivity at a spin-reorientation field H_R ~
12.5T, demonstrating that the marked change of the Fermi surface occurs between
the ferromagnetic state and the polarized state above H_R. The results can be
understood by the Lifshitz-type transition, induced by the magnetic field or by
the change of the effective magnetic field.",1407.5799v1
2014-10-18,Colossal proximity effect in a superconducting triplet spin valve based on halfmetallic ferromagnetic CrO2,"Ferromagnets can sustain supercurrents through the formation of equal spin
triplet Cooper pairs and the mechanism of odd-frequency pairing. Since such
pairs are not broken by the exchange energy of the ferromagnet, superconducting
triplet correlations are long-ranged and spin-polarized, with promises for
superconducting spintronics devices. The main challenge is to understand how
triplets are generated at the superconductor (S)/ ferromagnet (F) interface.
Here we use the concept of a so-called triplet spin valve (TSV) to investigate
the conversion of singlets in a conventional superconductor to triplets in the
halfmetallic ferromagnet CrO_2. TSV's are composed of two ferromagnetic layers
(separated by a thin normal metal (N) layer) and a superconductor
(F_1/N/F_2/S). The package F_1/N/F_2 generates triplets in F_1 when the
magnetization directions of the F_{1,2}-layers are not collinear. This drains
singlet pairs from the S-layer, and triplet generation is therefore signalled
by a decrease of the critical temperature $T_c$. Recently, experiments with
TSV's were reported with Co draining layers, using in-plane fields, and finding
T_c-shifts up to 100~mK. Using CrO_2 instead of Co and rotating a magnetic
field from in-plane to out-of-plane, we find strong T_c variations of almost a
Kelvin up to fields of the order of a Tesla. Such strong drainage is consistent
with the large lengths over which supercurrents can flow in CrO_2, which are
significantly larger than in conventional ferromagnets. Our results point to
the special interest of halfmetals for superconducting spintronics.",1410.4973v1
2015-05-14,Superconductivity in the ferromagnetic semiconductor SmN,"The discovery of materials that simultaneously host different phases of
matter has often initially confounded, but ultimately enhanced, our basic
understanding of the coexisting types of order. The associated intellectual
challenges, together with the promise of greater versatility for potential
applications, have made such systems a focus of modern materials science. In
particular, great efforts have recently been devoted to making semiconductors
ferromagnetic and metallic ferromagnets superconducting. Here we report the
unprecedented observation of a heavily donor-doped ferromagnetic semiconductor,
SmN, becoming superconducting with ferromagnetism remaining intact. The
extremely large exchange splitting of the conduction and valence bands in this
material necessitates that the superconducting order hosted by SmN is of an
unconventional triplet type, most likely exhibiting p-wave symmetry. Short
range spin fluctuations, which are thought to be the cause of pairing
interactions in currently known triplet superconductors, are quenched in SmN,
suggesting its superconductivity to be the result of phonon- or
Coulomb-mediated pairing mechanisms. This scenario is further supported by the
inferred heavy mass of superconducting charge carriers. The unique near-zero
magnetisation associated with the ferromagnetic state in SmN further aids its
coexistence with superconductivity. Presenting this novel material system where
semiconducting, ferromagnetic and superconducting properties are combined
provides a versatile new laboratory for studying quantum phases of matter.
Moreover it is a major step towards identifying materials that merge
superconductivity and spintronics, urgently needed to enable the design of
electronic devices with superior functionality.",1505.03621v2
2015-07-15,"Conductance, Valley and Spin polarization and Tunnelling magneto-resistance in ferromagnetic-normal-ferromagnetic junctions of silicene","We investigate charge conductance and spin and valley polarization along with
the tunnelling magneto-resistance (TMR) in silicene junctions composed of
normal silicene and ferromagnetic silicene. We show distinct features of the
conductances for parallel and anti-parallel spin configurations and the TMR, as
the ferromagnetic-normal-ferromagnetic (FNF) junction is tuned by an external
electric field. We analyse the behavior of the charge conductance and valley
and spin polarizations in terms of the independent conductances of the
different spins at the two valleys and the band structure of ferromagnetic
silicene and show how the conductances are affected by the vanishing of the
propagating states at one or the other valley. In particular, unlike in
graphene, the band structure at the two valleys are independently affected by
the spin in the ferromagnetic regions and lead to non-zero, and in certain
parameter regimes, pure valley and spin polarizations, which can be tuned by
the external electric field. We also investigate the oscillatory behavior of
the TMR with respect to the strength of the barrier potential (both
spin-independent and spin-dependent barriers) in the normal silicene region and
note that in some parameter regimes, the TMR can even go from positive to
negative values, as a function of the external electric field.",1507.04225v2
2015-11-24,"Coexistence of superconductivity and itinerant ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), the first non-U material with Tc < TFM","We have carried out detailed magnetic and transport studies of the new
Sr0.5Ce0.5FBiS2-xSex (x = 0.5, 1) superconductors derived by doping Se in
Sr0.5Ce0.5FBiS2. Se-doping produces several effects: it suppresses
semiconducting like behavior observed in the undoped Sr0.5Ce0.5FBiS2,
ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in
Sr0.5Ce0.5FBiS2) to 3.5 K and superconducting transition temperature, Tc, gets
enhanced slightly to 2.9 - 3.3 K. Thus in these Se-doped materials, TFM is just
marginally higher than Tc. Magnetization studies provide an evidence of bulk
superconductivity in Sr0.5Ce0.5FBiS2-xSex. Quite remarkably, as compared with
the effective paramagnetic Ce-moment (~ 2.2 muB), the ferromagnetically ordered
Ce-moment in the superconducting state is rather small (~ 0.1 muB). To the best
of our knowledge, the title compounds are the first Ce-based superconducting
itinerant ferromagnetic materials (Tc < TFM). We stress that Ce-4f electrons
are responsible for both superconductivity and ferromagnetism just as U-5f
electrons are in UCoGe. Furthermore, a novel feature of these materials is a
dual hysteresis loop corresponding to both the ferromagnetism and the
coexisting superconductivity. Such features of Sr0.5Ce0.5FBiS2-xSex put these
materials apart from the well known U-containing superconducting ferromagnets
reported so far.",1511.07692v2
2016-06-15,Topological Magnon Bands in Ferromagnetic Star Lattice,"The experimental observation of topological magnon bands and thermal Hall
effect in a kagom\'e lattice ferromagnet Cu(1-3, bdc) has inspired the search
for topological magnon effects in various insulating ferromagnets that lack an
inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction.
The star lattice (also known as the decorated honeycomb lattice) ferromagnets
is an ideal candidate for this purpose because it is a variant of the kagom\'e
lattice with additional links that connect the up-pointing and down-pointing
triangles. This gives rise to twice the unit cell of the kagom\'e lattice,
hence a more interesting topological magnon effects. In particular, the
triangular bridges on the star lattice can be coupled either ferromagnetically
or antiferromagnetically which is not possible on the kagome lattice
ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge
modes, and thermal magnon Hall effect on the star lattice ferromagnet in
different parameter regimes. The star lattice can also be visualized as the
parent material from which topological magnon bands can be realized for the
kagom\'e and honeycomb lattices in some limiting cases.",1606.04904v8
2018-04-12,Spin Transport in Half-Metallic Ferromagnet-Superconductor Junctions,"We investigate the charge and spin transport in half-metallic ferromagnet
($F$) and superconductor ($S$) nanojunctions. We utilize a self-consistent
microscopic method that can accommodate the broad range of energy scales
present, and ensures proximity effects that account for the interactions at the
interfaces are accurately determined. Two experimentally relevant half-metallic
junction types are considered: The first is a $F_1 F_2 S$ structure, where a
half-metallic ferromagnet $F_1$ adjoins a weaker conventional ferromagnet
$F_2$. The current is injected through the $F_1$ layer by means of an applied
bias voltage. The second configuration involves a $S F_1 F_2 F_3 S$ Josephson
junction whereby a phase difference $\Delta\varphi$ between the two
superconducting electrodes generates the supercurrent flow. In this case, the
central half-metallic $F_2$ layer is surrounded by two weak ferromagnets $F_1$
and $F_3$. By placing a ferromagnet with a weak exchange field adjacent to an
$S$ layer, we are able to optimize the conversion process in which
opposite-spin triplet pairs are converted into equal-spin triplet pairs that
propagate deep into the half-metallic regions in both junction types. For the
tunnel junctions, we study the bias-induced local magnetization, spin currents,
and spin transfer torques for various orientations of the relative
magnetization angle $\theta$ in the $F$ layers. We find that the bias-induced
equal-spin triplet pairs are maximized in the half-metal for
$\theta\approx90^\circ$ and as part of the conversion process, are
anticorrelated with the opposite-spin pairs. We show that the charge current
density is maximized, corresponding to the occurrence of a large amplitude of
equal-spin triplet pairs, when the exchange interaction of the weak ferromagnet
is about $0.1E_F.$",1804.04275v1
2020-07-28,"Critical behavior of ferromagnets CrI3, CrBr3, CrGeTe3, and anti-ferromagnet FeCl2: a detailed first-principles study","We calculate the Curie temperature of layered ferromagnets, chromium
tri-iodide (CrI3), chromium tri-bromide (CrBr3), chromium germanium
tri-telluride (CrGeTe3), and the Neel temperature of a layered anti-ferromagnet
iron di-chloride (FeCl2), using first-principles density functional theory
calculations and Monte-Carlo simulations. We develop a computational method to
model the magnetic interactions in layered magnetic materials and calculate
their critical temperature. We provide a unified method to obtain the magnetic
exchange parameters (J) for an effective Heisenberg Hamiltonian from
first-principles, taking into account both the magnetic ansiotropy as well as
the out-of-plane interactions. We obtain the magnetic phase change behavior, in
particular the critical temperature, from the susceptibility and the
specific-heat, calculated using the three-dimensional Monte-Carlo (Metropolis)
algorithm. The calculated Curie temperatures for ferromagnetic materials (CrI3,
CrBr3 and CrGeTe3), match very well with experimental values. We show that the
interlayer interaction in bulk CrI3 with R3 stacking is significantly stronger
than the C2/m stacking, in line with experimental observations. We show that
the strong interlayer interaction in R3 CrI results in a competition between
the in-plane and the out-of-plane magnetic easy axis. Finally, we calculate the
Neel temperature of FeCl2 to be 47 +- 8 K, and show that the magnetic phase
transition in FeCl2 occurs in two steps with a high-temperature intralayer
ferromagnetic phase transition, and a low-temperature interlayer
anti-ferromagnetic phase transition.",2007.14379v3
2017-01-28,Dominant Majorana bound energy and critical current enhancement in ferromagnetic-superconducting topological insulator,"Among the potential applications of topological insulators, we theoretically
study the coexistence of proximity-induced ferromagnetic and superconducting
orders in the surface states of a 3-dimensional topological insulator. The
superconducting electron-hole excitations can be significantly affected by the
magnetic order induced by a ferromagnet. In one hand, the surface state of the
topological insulator, protected by the time-reversal symmetry, creates a
spin-triplet and, on the other hand, magnetic order causes to renormalize the
effective superconducting gap. We find Majorana mode energy along the
ferromagnet/superconductor interface to sensitively depend on the magnitude of
magnetization $m_{zfs}$ from superconductor region, and its slope around
perpendicular incidence is steep with very low dependency on $m_{zfs}$. The
superconducting effective gap is renormalized by a factor $\eta(m_{zfs})$, and
Andreev bound state in
ferromagnet-superconductor/ferromagnet/ferromagnet-superconductor (FS/F/FS)
Josephson junction is more sensitive to the magnitude of magnetizations of FS
and F regions. In particular, we show that the presence of $m_{zfs}$ has a
noticeable impact on the gap opening in Andreev bound state, which occurs in
finite angle of incidence. This directly results in zero-energy Andreev state
being dominant. By introducing the proper form of corresponding Dirac spinors
for FS electron-hole states, we find that via the inclusion of $m_{zfs}$, the
Josephson supercurrent is enhanced and exhibits almost abrupt crossover curve,
featuring the dominant zero-energy Majorana bound states.",1701.08277v1
2017-07-15,Itinerant ferromagnetism in actinide 5f electrons system: Phenomenological analysis with spin fluctuation theory,"We have carried out an analysis of magnetic data in 69 uranium, 7 neptunium
and 4 plutonium ferromagnets with the spin fluctuation theory developed by
Takahashi (Y. Takahashi, J. Phys. Soc. Jpn. 55, 3553 (1986)). The basic and
spin fluctuation parameters of the actinide ferromagnets are determined and the
applicability of the spin fluctuation theory to actinide 5f system has been
discussed. Itinerant ferromagnets of the 3d transition metals and their
intermetallics follow a generalized Rhodes-Wohlfarth relation between p_eff/p_s
and T_C/T_0, viz., p_eff/p_s ~ (T_C/T_0)^(-3/2). Here, p_s, p_eff, T_C, and T_0
are the spontaneous and effective magnetic moments, the Curie temperature and
the width of spin fluctuation spectrum in energy space, respectively. The same
relation is satisfied for T_C/T_0 < 1.0 in the actinide ferromagnets. However,
the relation is not satisfied in a few ferromagnets with T_C/T_0 ~1.0 that
corresponds to local moment system in the spin fluctuation theory. The
deviation from the theoretical relation may be due to several other effects not
included in the spin fluctuation theory such as the crystalline electric field
effect on the 5f electrons from ligand atoms. The value of the spontaneous
magnetic moment p_s increases linearly as a function of T_C/T_0 in the uranium
and neptunium ferromagnets below (T_C/T_0)_kink = 0.32 +- 0.02 where a kink
structure appears in relation between the two quantities. p_s increases more
weakly above (T_C/T_0)_kink. A possible interpretation with the
T_C/T_0-dependence of p_s is given.",1707.04772v1
2018-09-13,Spin-current driven spontaneous coupling of ferromagnets,"A theoretical framework is proposed for the spin-current driven synchronized
self-oscillations in ferromagnets in the spin Hall geometry. The spin current
generated by the spin Hall effect in a bottom nonmagnetic heavy metal excites a
self-oscillation of the magnetization in an attached ferromagnet through
spin-transfer effect. The spin current simultaneously creates spin accumulation
inside the ferromagnet. Therefore, when the top surfaces of two ferromagnets
are connected by a nonmagnetic material having a long spin diffusion length,
another spin current flows according to the gradient of the spin accumulations
between the ferromagnets. This additional spin current excites an additional
spin torque leading to a coupled motion of the magnetizations. This coupling
mechanism comes purely from spin degree of freedom in the system without using
electric and/or magnetic interactions. The additional spin torque acts as a
repulsive force between the magnetizations, and prefers an antiphase
synchronization between the oscillators. The phase difference in a synchronized
state is determined by the competition between this additional spin torque and
spin pumping. Eventually, either an in-phase or antiphase synchronization is
spontaneously excited in the individual ferromagnets, depending on the current
magnitude. These conclusions are obtained by deriving the theoretical formula
of the additional spin torque from the diffusive spin transport theory and
solving the equation of motion of the magnetizations both numerically and
analytically.",1809.05195v1
2019-06-10,Direct Imaging Revealing Halved Ferromagnetism in Tensile-Strained LaCoO3 Thin Films,"The enigma of the emergent ferromagnetic state in tensile-strained LaCoO3
thin films remains to be explored because of the lack of a well agreed
explanation. The direct magnetic imaging technique using a low-temperature
magnetic force microscope (MFM) is critical to reveal new aspects of the
ferromagnetism by investigating the lateral magnetic phase distribution. Here
we show the experimental demonstration of the rare halved occupation of the
ferromagnetic state in tensile-strained LaCoO3 thin films on SrTiO3 substrates
using the MFM. The films have uniformly strained lattice structure and minimal
oxygen vacancies (less than 2%) beyond the measurement limit. It is found that
percolated ferromagnetic regions with typical sizes between 100 nm and 200 nm
occupy about 50% of the entire film, even down to the lowest achievable
temperature of 4.5 K and up to the largest magnetic field of 13.4 T. Preformed
ferromagnetic droplets were still observed when the temperature is 20 K above
the Curie temperature indicating the existence of possible Griffiths phase. Our
study demonstrated a sub-micron level phase separation in high quality LaCoO3
thin films, which has substantial implications in revealing the intrinsic
nature of the emergent ferromagnetism.",1906.03825v1
2019-06-24,"Weak ferromagnetism in hexagonal Mn3Z (Z=Sn, Ge, Ga) alloys","We present combined spin model and first principles electronic structure
calculations to study the weak ferromagnetism in bulk Mn$_3$Z (Z=Sn, Ge, Ga)
compounds. The spin model parameters were determined from a spin-cluster
expansion technique based on the relativistic disordered local moment formalism
implemented in the screened Korringa--Kohn--Rostoker method. We describe the
magnetic ground state of the system within a three-sublattice model and
investigate the formation of the weak ferromagnetic states in terms of the
relevant model parameters. First, we give a group-theoretical argument how the
point-group symmetry of the lattice leads to the formation of weak
ferromagnetic states. Then we study the ground states of the classical spin
model and derive analytical expressions for the weak ferromagnetic distortions
by recovering the main results of the group-theoretical analysis. As a third
approach we obtain the weak ferromagnetic ground states from self-consistent
density functional calculations and compare our results with previous first
principles calculations and with available experimental data. In particular, we
demonstrate that the orbital moments follow a decomposition predicted by group
theory. For a deeper understanding of the formation of weak ferromagnetism we
selectively trace the effect of the spin-orbit coupling at the Mn and Z sites.
In addition, for the case of Mn$_3$Ga, we gain information on the role of the
induced moment of Ga from constrained local density functional calculations.",1906.10062v1
2019-09-24,Controlling the strength of ferromagnetic order in YBa$_2$Cu$_3$O$_7$/La$_{2/3}$Ca$_{1/3}$MnO$_3$ multilayers,"With dc magnetisation and polarized neutron reflectometry we studied the
ferromagnetic response of YBa$_2$Cu$_3$O$_7$/La$_{2/3}$Ca$_{1/3}$MnO$_3$
(YBCO/LCMO) multilayers that are grown with pulsed laser deposition. We found
that whereas for certain growth conditions (denoted as A-type) the
ferromagnetic moment of the LCMO layer is strongly dependent on the structural
details of the YBCO layer on which it is deposited, for others (B-type) the
ferromagnetism of LCMO is much more robust. Both kinds of multilayers are of
similar structural quality, but electron energy-loss spectroscopy (EELS)
studies with a scanning transmission electron microscope reveal an enhanced
average Mn oxidation state of +3.5 for the A-type as opposed to the B-type
samples for which it is close to the nominal value of +3.33. The related,
additional hole doping of the A-type LCMO layers, which likely originates from
La and/or Mn vacancies, can explain their fragile ferromagnetic order since it
places them close to the boundary of the ferromagnetic order at which even weak
perturbations can induce an antiferromagnetic or glassy state. On the other
hand, we show that the B-type samples allow one to obtain YBCO/LCMO
heterostructures with very thick YBCO layers and, yet, strongly ferromagnetic
LCMO layers.",1909.10997v1
2020-12-03,Ferromagnetic and spin-glass like transition in the $q$-neighbor Ising model on random graphs,"The $q$-neighbor Ising model is investigated on homogeneous random graphs
with a fraction of edges associated randomly with antiferromagnetic exchange
integrals and the remaining edges with ferromagnetic ones. It is a
nonequilibrium model for the opinion formation in which the agents, represented
by two-state spins, change their opinions according to a Metropolis-like
algorithm taking into account interactions with only a randomly chosen subset
of their $q$ neighbors. Depending on the model parameters in Monte Carlo
simulations phase diagrams are observed with first-order ferromagmetic
transition, both first- and second-order ferromagnetic transitions and
second-order ferromagnetic and spin-glass-like transitions as the temperature
and fraction of antiferromagnetic exchange integrals are varied; in the latter
case the obtained phase diagrams qualitatively resemble those for the dilute
spin-glass model. Homogeneous mean-field and pair approximations are extented
to take into account the effect of the antiferromagnetic exchange interactions
on the ferromagnetic phase transition in the model. For a broad range of
parameters critical temperatures for the first- or second-order ferromagnetic
transition predicted by the homogeneous pair approximation show quantitative
agreement with those obtained from Monte Carlo simulations; significant
differences occur mainly in the vicinity of the tricritical point in which the
critical lines for the second-order ferromagnetic and spin-glass-like
transitions meet.",2012.01948v1
2017-09-12,Macroscopic phase separation of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex revealed by muSR,"The compound Sr$_{0.5}$Ce$_{0.5}$FBiS$_{2}$ belongs to the intensively
studied family of layered BiS$_2$ superconductors. It attracts special
attention because superconductivity at $T_{sc} = 2.8$ K was found to coexist
with local-moment ferromagnetic order with a Curie temperature $T_C = 7.5$ K.
Recently it was reported that upon replacing S by Se $T_C$ drops and
ferromagnetism becomes of an itinerant nature (Thakur et al., Sci. Reports 6,
37527 (2016)). At the same time $T_{sc}$ increases and it was argued
superconductivity coexists with itinerant ferromagnetism. Here we report a muon
spin rotation and relaxation study ($\mu$SR) conducted to investigate the
coexistence of superconductivity and ferromagnetic order in
Sr$_{0.5}$Ce$_{0.5}$FBiS$_{2-x}$Se$_x$ with $x=0.5$ and $1.0$. By inspecting
the muon asymmetry function we find that both phases do not coexist on the
microscopic scale, but occupy different sample volumes. For $x=0.5$ and $x=1.0$
we find a ferromagnetic volume fraction of $\sim \, 8 \%$ and $\sim \, 30 \%$
at $T=0.25$ K, well below $T_{C} = 3.4$ K and $T_C = 3.3$ K, respectively. For
$x=1.0$ ($T_{sc} = 2.9$ K) the superconducting phase occupies the remaining
sample volume ($\sim \, 70 \%$), as shown by transverse field experiments that
probe the Gaussian damping due to the vortex lattice. We conclude
ferromagnetism and superconductivity are macroscopically phase separated.",1709.03632v1
2018-03-07,Two-Dimensional Itinerant Ising Ferromagnetism in Atomically thin Fe3GeTe2,"Recent discoveries of intrinsic two-dimensional (2D) ferromagnetism in
insulating/semiconducting van der Waals (vdW) crystals open up new
possibilities for studying fundamental 2D magnetism and devices employing
localized spins. However, a vdW material that exhibits 2D itinerant magnetism
remains elusive. In fact, the synthesis of such single-crystal ferromagnetic
metals with strong perpendicular anisotropy at the atomically thin limit has
been a long-standing challenge. Here, we demonstrate that monolayer Fe3GeTe2 is
a robust 2D itinerant ferromagnet with strong out-of-plane anisotropy.
Layer-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism
for thicknesses less than 4 nm (five layers), accompanying a fast drop of the
Curie temperature from 207 K down to 130 K in the monolayer. For Fe3GeTe2
flakes thicker than ~15 nm, a peculiar magnetic behavior emerges within an
intermediate temperature range, which we show is due to the formation of
labyrinthine domain patterns. Our work introduces a novel atomically thin
ferromagnetic metal that could be useful for the study of controllable 2D
itinerant Ising ferromagnetism and for engineering spintronic vdW
heterostructures.",1803.02559v1
2019-02-11,"Magnetization process of the insulating ferromagnetic semiconductor (Al,Fe)Sb","We have studied the magnetization process of the new insulating ferromagnetic
semiconductor (Al,Fe)Sb by means of x-ray magnetic circular dichroism. For an
optimally doped sample with 10% Fe, a magnetization was found to rapidly
increase at low magnetic fields and to saturate at high magnetic fields at room
temperature, well above the Curie temperature of 40 K. We attribute this
behavior to the existence of nanoscale Fe-rich ferromagnetic domains acting as
superparamagnets. By fitting the magnetization curves using the Langevin
function representing superparamagnetism plus the paramagnetic linear function,
we estimated the average magnetic moment of the nanoscale ferromagnetic domain
to be 300-400 $\mu_{B}$, and the fraction of Fe atoms participating in the
nano-scale ferromagnetism to be $\sim$50%. Such behavior was also reported for
(In,Fe)As:Be and Ge:Fe, and seems to be a universal characteristic of the
Fe-doped ferromagnetic semiconductors. Further Fe doping up to 14% led to the
weakening of the ferromagnetism probably because antiferromagnetic
superexchange interaction between nearest-neighbor Fe-Fe pairs becomes
dominant.",1902.03742v1
2019-02-19,Micromagnetometry of two-dimensional ferromagnets,"The study of atomically thin ferromagnetic crystals has led to the discovery
of unusual magnetic behaviour and provided insight into the magnetic properties
of bulk materials. However, the experimental techniques that have been used to
explore ferromagnetism in such materials cannot probe the magnetic field
directly. Here, we show that ballistic Hall micromagnetometry can be used to
measure the magnetization of individual two-dimensional ferromagnets. Our
devices are made by van der Waals assembly in such a way that the investigated
ferromagnetic crystal is placed on top of a multi-terminal Hall bar made from
encapsulated graphene. We use the micromagnetometry technique to study
atomically thin chromium tribromide (CrBr3). We find that the material remains
ferromagnetic down to monolayer thickness and exhibits strong out-of-plane
anisotropy. We also find that the magnetic response of CrBr3 varies little with
the number of layers and its temperature dependence cannot be described by the
simple Ising model of two-dimensional ferromagnetism.",1902.06988v2
2019-11-17,A Monte Carlo Study on the Variation of Residual Magnetisation with the Ratio of Coupling Strengths and Non-magnetic Impurities in an Ising Trilayer,"We have studied a spin-1/2, ABA, Ising trilayer system with two different
types of interactions, in-plane ferromagnetic and out-of-plane
anti-ferromagnetic, among the lattice sites, on different layers. In the pure
case, devoid of any impurity, we employed Monte-Carlo method with single
spin-flip Metropolis algorithm to find out the anti-ferromagnetic critical
temperature (N\'eel temperature) and another lower temperature, called the
compensation temperature, both with total magnetisation zero, in accordance
with already established results for square lattice. Then non-magnetic
impurities, (spin value= 0) were implanted on each layer at randomly picked
sites and their concentration was increased in steps from 5% to 20%. The ratio
of inter-planar anti-ferromagnetic to mid-layer ferromagnetic coupling strength
as well as the ratio of top and bottom layer ferromagnetic to mid layer
ferromagnetic coupling strength were also varied and N\'eel and compensation
temperatures, both were observed shifting towards lower temperature values with
increase in concentration of impurities in the lattice for any fixed ratio of
different coupling strengths, in absence of any external magnetic field. In
addition, the magnitude of the residual magnetisation i.e. the ratio of the
peak value of the magnetisation in between N\'eel and compensation points and
the saturated value of magnetisation, was also observed to vary with different
values of controlling parameters.",1911.07261v2
2020-03-09,Spin-Triplet Superconductivity in UTe2 and Ferromagnetic Superconductors,"The spin-triplet state is most likely realized in uranium ferromagnetic
superconductors, UGe2, URhGe, UCoGe. The microscopic coexistence of
ferromagnetism and superconductivity means that the Cooper pair should be
realized under the strong internal field due the ferromagnetism, leading to the
spin-triplet state with equal spin pairing. The field-reinforced
superconductivity, which is observed in all three materials when the
ferromagnetic fluctuations are enhanced, is one of the strong evidences for the
spin-triplet superconductivity. We present here the results of a newly
discovered spin-triplet superconductor, UTe2, and compare those with the
results of ferromagnetic superconductors. Although no magnetic order is found
in UTe2, there are similarities between UTe2 and ferromagnetic superconductors.
For example, the huge upper critical field exceeding the Pauli limit and the
field-reentrant superconductivity for H || b-axis are observed in UTe2, URhGe
and UCoGe. We also show the specific heat results on UTe2 in different quality
samples, focusing on the residual density of states in the superconducting
phase.",2003.04055v1
2020-03-31,"Observation of a possible diluted ferromagnetism above room temperature in cobalt-substituted LaTa(O,N)3-d","Since 2000, the intensive effort in materials research to develop a diluted
magnetic semiconductor exhibiting high-temperature (HT) ferromagnetism above
room temperature was not successful. Here, the possible first bulk diluted
HT-ferromagnetic non-metallic materials, based on the perovskite-type
oxynitrides LaTa1-xCox(O,N)3-d (x = 0.01, 0.03, 0.05) are realized. The Curie
temperature of the synthesized powders exceeds 600 K and the sample
magnetizations are large enough to be directly attracted by permanent magnets.
Cobalt clusters as a possible source for the observed HT-ferromagnetism can be
excluded, since all applied characterization methods verify phase purity.
Applied conventional and element-specific magnetometry imply ferromagnetic
intermediate spin (IS) Co3+ which is included in a ferromagnetic host matrix.
This indicates a complex magnetic interplay between the existing crystal
structure, the observed anionic vacancies, and the introduced cobalt ions.
These results lay the foundation for the experimental investigation and design
of further diluted HT-ferromagnetic semiconductors.",2003.14259v4
2021-11-10,Layer-controlled Ferromagnetism in Atomically Thin CrSiTe$_3$ Flakes,"The research on two-dimensional (2D) van der Waals (vdW) ferromagnets has
promoted the development of ultrahigh-density and nanoscale data storage.
However, intrinsic ferromagnetism in layered magnets is always subject to many
factors, such as stacking orders, interlayer couplings, and the number of
layers. Here, we report a magnetic transition from soft to hard ferromagnetic
behaviors as the thickness of CrSiTe$_3$ flakes decreases down to several
nanometers. Phenomenally, in contrast to the negligible hysteresis loop in the
bulk counterparts, atomically thin CrSiTe$_3$ shows a rectangular loop with
finite magnetization and coercivity as thickness decreases down to ~8 nm,
indicative of a single-domain and out-of-plane ferromagnetic order. We find
that the stray field is weakened with decreasing thickness, which suppresses
the formation of the domain wall. In addition, thickness-dependent
ferromagnetic properties also reveal a crossover from 3 dimensional to 2
dimensional Ising ferromagnets at a ~7 nm thickness of CrSiTe$_3$, accompanied
by a drop of the Curie temperature from 33 K for bulk to ~17 K for 4 nm sample.",2111.05495v1
2022-04-05,Cr doping-induced ferromagnetism in the spin-glass Cd1-xMnxTe studied by x-ray magnetic circular dichroism,"The prototypical diluted magnetic semiconductor Cd1-xMnxTe is a spin glass
(x<0.6) or an antiferromagnet (x>0.6), but becomes ferromagnetic upon doping
with a small amount of Cr atoms substituting for Mn. In order to investigate
the origin of the ferromagnetism in Cd1-x-yMnxCryTe, we have studied its
element specific magnetic properties by x-ray absorption spectroscopy (XAS) and
x-ray magnetic circular dichroism (XMCD) at the Cr and Mn L2,3 edges. Thin
films were grown by molecular beam epitaxy with a fixed Mn content of x = 0.2
and varying Cr content in the range of y = 0 - 0.04. Measured XAS and XMCD
spectra indicate that both Cr and Mn atoms are divalent and that the
ferromagnetic or superparamagnetic components of Cr and Mn are aligned in the
same directions. The magnetization of Mn increases with increasing Cr content.
These results can be explained if ferromagnetic interaction exists between
neighboring Mn and Cr ions although interaction between Mn atoms is largely
antiferromagnetic. We conclude that each ferromagnetic or superparamagnetic
cluster consists of ferromagnetically coupled several Cr and a much larger
number of Mn ions.",2204.02042v1
2022-08-11,Ferromagnetism and Skyrmions in the Hofstadter-Fermi-Hubbard Model,"Strongly interacting fermionic systems host a variety of interesting quantum
many-body states with exotic excitations. For instance, the interplay of strong
interactions and the Pauli exclusion principle can lead to Stoner
ferromagnetism, but the fate of this state remains unclear when kinetic terms
are added. While in many lattice models the fermions' dispersion results in
delocalization and destabilization of the ferromagnet, flat bands can restore
strong interaction effects and ferromagnetic correlations. To reveal this
interplay, here we propose to study the Hofstadter-Fermi-Hubbard model using
ultracold atoms. We demonstrate, by performing large-scale DMRG simulations,
that this model exhibits a lattice analog of the quantum Hall ferromagnet at
magnetic filling factor $\nu=1$. We reveal the nature of the low energy
spin-singlet states around $\nu\approx1$ and find that they host
quasi-particles and quasi-holes exhibiting spin-spin correlations reminiscent
of skyrmions. Finally, we predict the breakdown of flat-band ferromagnetism at
large fields. Our work paves the way towards experimental studies of lattice
quantum Hall ferromagnetism, including prospects to study many-body states of
interacting skyrmions and explore the relation to high-$T_{\rm c}$
superconductivity.",2208.05960v2
2023-08-06,Anatomy of spin Hall effect in ferromagnetic metals,"The spin Hall effect in nonmagnetic materials has been intensively studied
and became one of the most crucial spin-charge conversion mechanism in
spintronics. However, the spin Hall effect in ferromagnetic metals has been
less investigated and remains unclear. In this work, we investigate the spin
Hall effect in representative ferromagnetic alloy by using first-principles
calculations. We first clarify the spin Hall effect into three different types
including conventional (CSHE), spin anomalous (SAHE) and magnetic spin Hall
effect (MSHE) and then calculate the corresponding spin Hall conductivity and
spin Hall angle for (Fe, Co, Ni)Pt, NiFe and CoFe alloy. We find the above
three spin Hall mechanisms do coexist in ferromagnetic metals. Particularly,
for Pt-based ferromagnetic alloy, a sizable conventional and magnetic spin Hall
angles comparable to that of Pt have been predicted. The remarkable
unconventional spin Hall effect in ferromagnetic metal may enrich the
spin-charge conversion phenomena. For instance, the spin current generated by
remarkable MSHE with out-of-plane spin-polarization should be helpful for
field-free switching of perpendicular magnetization through spin-orbit torque
effect. This work may stimulate future studies on the spin Hall effect in
ferromagnetic metals and pave their promising applications for spin-charge
conversion devices in spintronics.",2308.03111v1
2023-08-08,Activity-induced ferromagnetism in one-dimensional quantum many-body systems,"We study a non-Hermitian quantum many-body model in one dimension analogous
to the Vicsek model or active spin models, and investigate its quantum phase
transitions. The model consists of two-component hard-core bosons with
ferromagnetic interactions and activity, i.e., spin-dependent asymmetric
hopping. Numerical results show the emergence of a ferromagnetic order induced
by the activity, a quantum counterpart of flocking, that even survives in the
absence of ferromagnetic interaction. We confirm this phenomenon by proving
that activity generally increases the ground state energies of the paramagnetic
states, whereas the ground state energy of the ferromagnetic state does not
change. By solving the two-particle case, we find that the effective alignment
is caused by avoiding the bound state formation due to the non-Hermitian skin
effect in the paramagnetic state. We employ a two-site mean-field theory based
on the two-particle result and qualitatively reproduce the phase diagram. We
further numerically study a variant of our model with the hard-core condition
relaxed, and confirm the robustness of ferromagnetic order emerging due to
activity.",2308.04382v4
2023-08-24,Nearly-room-temperature ferromagnetism and tunable anomalous Hall effect in atomically thin Fe4CoGeTe2,"Itinerant ferromagnetism at room temperature is a key ingredient for spin
transport and manipulation. Here, we report the realization of
nearly-room-temperature itinerant ferromagnetism in Co doped Fe5GeTe2 thin
flakes. The ferromagnetic transition temperature TC (323 K - 337 K) is almost
unchanged when thickness is down to 12 nm and is still about 284 K at 2 nm
(bilayer thickness). Theoretical calculations further indicate that the
ferromagnetism persists in monolayer Fe4CoGeTe2. In addition to the robust
ferromagnetism down to the ultrathin limit, Fe4CoGeTe2 exhibits an unusual
temperature- and thickness-dependent intrinsic anomalous Hall effect. We
propose that it could be ascribed to the dependence of band structure on
thickness that changes the Berry curvature near the Fermi energy level subtly.
The nearly-room-temperature ferromagnetism and tunable anomalous Hall effect in
atomically thin Fe4CoGeTe2 provide opportunities to understand the exotic
transport properties of two-dimensional van der Waals magnetic materials and
explore their potential applications in spintronics.",2308.12765v1
2023-08-28,Anisotropic magnetism and band evolution induced by ferromagnetic phase transition in titanium-based kagome ferromagnet SmTi3Bi4,"Kagome magnets with diverse topological quantum responses are crucial for
next-generation topological engineering. The anisotropic magnetism and band
evolution induced by ferromagnetic phase transition (FMPT) is reported in a
newly discovered titanium-based kagome ferromagnet S mTi3 Bi4, which features a
distorted Ti kagome lattice and S m atomic zig-zag chains.
Temperature-dependent resistivity, heat capacity, and magnetic susceptibility
reveal a ferromagnetic ordering temperature Tc of 23.2 K. A large magnetic
anisotropy, observed by applying the magnetic field along three
crystallographic axes, identifies the b axis as the easy axis. Angle-resolved
photoemission spectroscopy with first-principles calculations unveils the
characteristic kagome motif, including the Dirac point at the Fermi level and
multiple van Hove singularities. Notably, a band splitting and gap closing
attributed to FMPT is observed, originating from the exchange coupling between
S m 4 f local moments and itinerant electrons of the kagome Ti atoms, as well
as the time-reversal symmetry breaking induced by the long-range ferromagnetic
order. Considering the large in-plane magnetization and the evolution of
electronic structure under the influence of ferromagnetic ordering, such
materials promise to be a new platform for exploring the intricate electronic
properties and magnetic phases based on the kagome lattice.",2308.14349v2
2023-09-12,Proximity-induced interfacial room-temperature ferromagnetism in semiconducting Fe3GeTe2,"The discoveries of two-dimensional ferromagnetism and magnetic semiconductors
highly enrich the magnetic material family for constructing spin-based
electronic devices but with an acknowledged challenge that the Curie
temperature (Tc) is usually far below room temperature. Many efforts such as
voltage control and magnetic ion doping are currently underway to enhance the
functional temperature, in which the involvement of additional electrodes or
extra magnetic ions limits their plenty of applications in practical devices.
Here we demonstrate that the magnetic proximity, a robust effect but with
elusive mechanisms, can induce room-temperature ferromagnetism at the interface
between sputtered Pt and semiconducting Fe3GeTe2, both of which do not show
ferromagnetism at 300 K. The independent electrical and magnetization
measurements, structure analysis, and control samples with Ta highlighting the
role of Pt confirm that the ferromagnetism with the Tc of above 400 K arises
from the Fe3GeTe2/Pt interfaces, rather than Fe aggregation or other artificial
effects. Moreover, contrary to conventional ferromagnet/Pt structures, the spin
current generated by the Pt layer is enhanced more than two times at the
Fe3GeTe2/Pt interfaces, indicating the potential applications of the unique
proximity effect in building high-efficient spintronic devices. These results
may pave a new avenue to create room-temperature functional spin devices based
on low-Tc materials and provide clear evidences of magnetic proximity effects
by using non-ferromagnetic materials.",2309.06204v1
2023-11-13,Robust magnetic proximity induced anomalous Hall effect in a room temperature van der Waals ferromagnetic semiconductor based 2D heterostructure,"Developing novel high-temperature van der Waals ferromagnetic semiconductor
materials and investigating their interface coupling effects with
two-dimensional topological semimetals are pivotal for advancing
next-generation spintronic and quantum devices. However, most van der Waals
ferromagnetic semiconductors exhibit ferromagnetism only at low temperatures,
limiting the proximity research on their interfaces with topological
semimetals. Here, we report an intrinsic, van der Waals layered
room-temperature ferromagnetic semiconductor crystal, FeCr0.5Ga1.5Se4 (FCGS),
with a Curie temperature as high as 370 K, setting a new record for van der
Waals ferromagnetic semiconductors. The saturation magnetization at low
temperature (2 K) and room temperature (300 K) reaches 8.2 emu/g and 2.7 emu/g,
respectively. Furthermore, FCGS possesses a bandgap of approximately 1.2 eV,
which is comparable to the widely used commercial silicon. The FCGS/graphene
heterostructure exhibits an impeccably smooth and gapless interface, thereby
inducing a robust magnetic proximity coupling effect between FCGS and graphene.
After the proximity coupling, graphene undergoes a charge carrier transition
from electrons to holes, accompanied by a transition from non-magnetic to
ferromagnetic transport behavior with robust anomalous Hall effect. Notably,
the anomalous Hall effect remains robust even temperatures up to 400 K.",2311.07183v1
2023-12-07,Direct and indirect spin current generation and spin-orbit torques in ferromagnet/nonmagnet/ferromagnet trilayers,"Spin-orbit torques in ferromagnet/nonmagnet/ferromagnet trilayers are studied
using a combination of symmetry analysis, circuit theory, semiclassical
simulations, and first-principles calculations using the non-equilibrium
Green's function method with supercell disorder averaging. We focus on
unconventional processes involving the interplay between the two ferromagnetic
layers, which are classified into direct and indirect mechanisms. The direct
mechanism involves spin current generation by one ferromagnetic layer and its
subsequent absorption by the other. In the indirect mechanism, the in-plane
spin-polarized current from one ferromagnetic layer ``leaks'' into the other
layer, where it is converted into an out-of-plane spin current and reabsorbed
by the original layer. The direct mechanism results in a predominantly
dampinglike torque, which damps the magnetization towards a certain direction
$\mathbf{s}_d$. The indirect mechanism results in a predominantly fieldlike
torque with respect to a generally different direction $\mathbf{s}_f$. Similar
to the current-in-plane giant magnetoresistance, the indirect mechanism is only
active if the thickness of the nonmagnetic spacer is smaller than or comparable
to the mean-free path. Numerical calculations for a semiclassical model based
on the Boltzmann equation confirm the presence of both direct and indirect
mechanisms of spin current generation. First-principles calculations reveal
sizeable unconventional spin-orbit torques in Co/Cu/Co, Py/Cu/Py, and Co/Pt/Co
trilayers and provide strong evidence of indirect spin current generation.",2312.04538v1
2023-12-12,Dzyaloshinskii-Moriya interaction inducing weak ferromagnetism in centrosymmetric altermagnets and weak ferrimagnetism in noncentrosymmetric altermagnets,"The Dzyaloshinskii-Moriya interaction (DMI) has explained successfully the
weak ferromagnetism in some centrosymmetric antiferromagnets. However, in the
last years, it was generally claimed that the DMI is not effective in
centrosymmetric systems. We reconciled these views by separating the
conventional antiferromagnets and altermagnets. Altermagnets represent
collinear antiferromagnetic compounds with spin-up and spin-down sublattices
connected only by mirror and roto-translational symmetries. Consequently, the
system shows even-parity wave spin order in the k-space lifting the Kramer's
degeneracy in the non-relativistic band structure. We emphasize that the DMI
can create weak ferromagnetism in centrosymmetric altermagnets while it is not
effective in centrosymmetric conventional antiferromagnets. Additionally, DMI
can create weak ferromagnetism or weak ferrimagnetism in noncentrosymmetric
altermagnets. Once the spin-orbit coupling is included in an altermagnetic
system without time-reversal symmetry, the components of spin moments of the
two sublattices along the Neel vector are antiparallel but the other two spin
components orthogonal to the N\'eel vector can be either parallel or
antiparallel for centrosymetric systems. For noncentrosymmetric systems, we can
have different bands showing parallel or antiparallel spin components resulting
in weak ferrimagnetism. We can divide the altermagnetic compounds into classes
based on the weak ferromagnetism or weak ferrimagnetism properties. The weak
ferromagnetism and weak ferrimagnetism induced by DMI is a property exclusively
of the altermagnets, not present in either ferromagnets or conventional
antiferromagnets so we propose that altermagnets should be classified based on
this property.",2312.07678v2
2011-12-06,The periodic and chaotic regimes of motion in the exoplanet 2/1 mean-motion resonance,"We present the dynamical structure of the phase space of the planar planetary
2/1 mean-motion resonance (MMR). Inside the resonant domain, there exist two
families of periodic orbits, one associated to the librational motion of the
critical angle ($\sigma$-family) and the other related to the circulatory
motion of the angle between the pericentres ($\Delta\varpi$-family). The
well-known apsidal corotation resonances (ACR) appear at the intersections of
these families. A complex web of secondary resonances exists also for low
eccentricities, whose strengths and positions are dependent on the individual
masses and spatial scale of the system.
  Depending on initial conditions, a resonant system is found in one of the two
topologically different states, referred to as \textit{internal} and
\textit{external} resonances. The internal resonance is characterized by
symmetric ACR and its resonant angle is $2\,\lambda_2-\lambda_1-\varpi_1$,
where $\lambda_i$ and $\varpi_i$ stand for the planetary mean longitudes and
longitudes of pericentre, respectively. In contrast, the external resonance is
characterized by asymmetric ACR and the resonant angle is
$2\,\lambda_2-\lambda_1-\varpi_2$. We show that systems with more massive outer
planets always envolve inside internal resonances. The limit case is the
well-known asteroidal resonances with Jupiter. At variance, systems with more
massive inner planets may evolve in either internal or external resonances; the
internal resonances are typical for low-to-moderate eccentricity
configurations, whereas the external ones for high eccentricity configurations
of the systems. In the limit case, analogous to Kuiper belt objects in
resonances with Neptune, the systems are always in the external resonances
characterized by asymmetric equilibria.",1112.1208v1
2019-09-11,An Integrable Model for the Dynamics of Planetary Mean Motion Resonances,"I consider the dynamics of mean motion resonances between pairs of co-planar
planets and derive a new integrable Hamiltonian model for planets' resonant
motion. The new model generalizes previously-derived integrable Hamiltonians
for first-order resonances to treat higher-order resonances by exploiting a
surprising near-symmetry of the full, non-integrable Hamiltonians of
higher-order resonances. Whereas past works have frequently relied on truncated
disturbing function expansions to derive integrable approximations to resonant
motion, I show that no such expansion is necessary, thus enabling the new model
to accurately capture the dynamics of both first- and higher-order resonances
for eccentricities up to orbit-crossing. I demonstrate that predictions of the
new integrable model agree well with numerical integrations of resonant planet
pairs. Finally, I explore the secular evolution of resonant planets'
eccentricities. I show that the secular dynamics are governed by conservation
of an AMD-like quantity.
  I also demonstrate that secular frequencies depend on planets' resonant
libration amplitude and this generally gives rise to a secular resonance inside
the mean motion resonance at large libration amplitudes. Outside of the secular
resonance the long-term dynamics are characterized small adiabatic modulations
of the resonant motion while inside the secular resonance planets can
experience large variations of the resonant trajectory over secular timescales.
The integrable model derived in this work can serve as a framework for
analyzing the dynamics of planetary MMRs in a wide variety of contexts.",1909.05264v1
2022-02-23,Resonators with tailored optical path by cascaded-mode conversions,"Optical resonators enable the generation, manipulation, and storage of
electromagnetic waves. They are widely used in technology and fundamental
research, in telecommunications, lasers and nonlinear optics, ultra-sensitive
measurements in cavity optomechanics, and the study of light-matter
interactions in the context of cavity QED. The physics underlying their
operation is determined by the constructive interference of electromagnetic
waves at specific frequencies, giving rise to the resonance spectrum. This
mechanism causes the limitations and trade-offs of resonator design, such as
the difficulty of confining waves larger than the resonator and the fixed
relationship between free spectral range, modal linewidth, and the resonator's
refractive index and size. Here, we introduce a new class of optical
resonators, generating resonances by designing the optical path through
transverse mode coupling in a cascaded process created by mode-converting
mirrors. The generalized round-trip phase condition leads to resonator
characteristics that are markedly different from Fabry-Perot resonators and can
be tailored over a wide range, such as the largest resonant wavelength, the
free spectral range, the linewidth, and the quality factor. We confirm the
existence of these modes experimentally in an integrated waveguide cavity with
mode converters coupling two transverse modes into one supermode. The resonance
signature of the cascaded-mode resonator is a spectrum resulting from the
coherent superposition of the coupled transverse modes. We also demonstrate a
transverse mode-independent transmission through the resonator and show that
its engineered spectral properties agree with theoretical predictions.
Cascaded-mode resonators introduce properties not found in traditional
resonators and provide a mechanism to overcome the existing trade-offs in the
design of resonators in various application areas.",2202.11775v1
2023-11-27,Selective active resonance tuning for multi-mode nonlinear photonic cavities,"Resonant enhancement of nonlinear photonic processes is critical for the
scalability of applications such as long-distance entanglement generation. To
implement nonlinear resonant enhancement, multiple resonator modes must be
individually tuned onto a precise set of process wavelengths, which requires
multiple linearly-independent tuning methods. Using coupled auxiliary
resonators to indirectly tune modes in a multi-resonant nonlinear cavity is
particularly attractive because it allows the extension of a single physical
tuning mechanism, such as thermal tuning, to provide the required independent
controls. Here we model and simulate the performance and tradeoffs of a
coupled-resonator tuning scheme which uses auxiliary resonators to tune
specific modes of a multi-resonant nonlinear process. Our analysis determines
the tuning bandwidth for steady-state mode field intensity can significantly
exceed the inter-cavity coupling rate if the total quality factor of the
auxiliary resonator is higher than the multi-mode main resonator. Consequently,
over-coupling a nonlinear resonator mode to improve the maximum efficiency of a
frequency conversion process will simultaneously expand the auxiliary resonator
tuning bandwidth for that mode, indicating a natural compatibility with this
tuning scheme. We apply the model to an existing small-diameter triply-resonant
ring resonator design and find that a tuning bandwidth of 136 GHz ~ 1.1 nm can
be attained for a mode in the telecom band while limiting excess scattering
losses to a quality factor of 10^6. Such range would span the distribution of
inhomogeneously broadened quantum emitter ensembles as well as resonator
fabrication variations, indicating the potential for the auxiliary resonators
to enable not only low-loss telecom conversion but also the generation of
indistinguishable photons in a quantum network.",2311.15606v1
2023-11-25,Ultrasensitive vibrational resonance induced by small disturbances,"We have found two kinds of ultra-sensitive vibrational resonance in coupled
nonlinear systems. It is particularly worth pointing out that this
ultra-sensitive vibrational resonance is a transient behavior caused by
transient chaos. Considering long-term response, the system will transform from
transient chaos to periodic response. The pattern of vibrational resonance will
also transform from ultra-sensitive vibrational resonance to conventional
vibrational resonance. This article focuses on the transient ultra-sensitive
vibrational resonance phenomenon. It is induced by a small disturbance of the
high-frequency excitation and the initial simulation conditions, respectively.
The damping coefficient and the coupling strength are the key factors to induce
the ultra-sensitive vibrational resonance. By increasing these two parameters,
the vibrational resonance pattern can be transformed from an ultra-sensitive
vibrational resonance to a conventional vibrational resonance. The reason for
different vibrational resonance patterns to occur lies in the state of the
system response. The response usually presents transient chaotic behavior when
the ultra-sensitive vibrational resonance appears and the plot of the response
amplitude versus the controlled parameters shows a highly fractalized pattern.
When the response is periodic or doubly-periodic, it usually corresponds to the
conventional vibrational resonance. The ultra-sensitive vibrational resonance
not only occurs at the excitation frequency, but it also occurs at some more
nonlinear frequency components. The ultra-sensitive vibrational resonance as a
transient behavior and the transformation of vibrational resonance patterns are
new phenomena in coupled nonlinear systems.",2312.11474v1
2018-04-18,"Electromagnetic-Power-based Modal Classification, Modal Expansion, and Modal Decomposition for Perfect Electric Conductors","Traditionally, all working modes of a perfect electric conductor are
classified into capacitive modes, resonant modes, and inductive modes, and the
resonant modes are further classified into internal resonant modes and external
resonant modes. In this paper, the capacitive modes are further classified into
intrinsically capacitive modes and non-intrinsically capacitive modes; the
resonant modes are alternatively classified into intrinsically resonant modes
and non-intrinsically resonant modes, and the intrinsically resonant modes are
further classified into non-radiative intrinsically resonant modes and
radiative intrinsically resonant modes; the inductive modes are further
classified into intrinsically inductive modes and non-intrinsically inductive
modes. Based on the modal expansion corresponding to these new modal
classifications, an alternative modal decomposition method is proposed. In
addition, it is also proved that: all intrinsically resonant modes and all
non-radiative intrinsically resonant modes constitute linear spaces
respectively, but other kinds of resonant modes cannot constitute linear
spaces; by including the mode 0 into the intrinsically capacitive mode set and
the intrinsically inductive mode set, these two modal sets become linear spaces
respectively, but other kinds of capacitive modes and inductive modes cannot
constitute linear spaces.",1804.09246v1
2019-10-01,Weak signal enhancement by non-linear resonance control in a forced nano-electromechanical resonator,"Driven non-linear resonators can display sharp resonances or even multistable
behaviours amenable to induce strong enhancements of weak signals. Such
enhancements can make use of the phenomenon of vibrational resonance whereby a
weak low-frequency signal applied to a bistable resonator can be amplified by
driving the non-linear oscillator with another appropriately-adjusted
non-resonant high-frequency field. Here we demonstrate the resonant enhancement
of a weak signal by use of a vibrational force yet in a monostable system
consisting of a driven nano-electromechanical nonlinear resonator. The
oscillator is subjected to a strong quasi-resonant drive and to two additional
tones: a weak signal at lower frequency and a non-resonant driving at an
intermediate frequency. We show experimentally and theoretically a significant
enhancement of the weak signal thanks to the occurence of vibrational resonance
enabled by the presence of the intermediate frequency driving. We analyse this
phenomenon in terms of coherent nonlinear resonance manipulation. Our results
illustrate a general mechanism which may have applications in the fields of
radio-frequency signal processing or sensing for instance.",1910.04686v1
2019-10-13,Tunable High-Quality Fano Resonance in Coupled Terahertz Whispering-Gallery-Mode Resonators,"Fano resonance is widely discussed in designing novel terahertz components,
such as sensors, filters, modulators, and group delay modules. Usually, high
quality (Q) factor and flexible tunability of Fano resonance are key
requirements for these applications. Here, we present tunable terahertz Fano
resonance with a Q factor of 2095 at 0.439 THz in coupled terahertz
whispering-gallery-mode resonators (WGMRs). Coupling between a relatively low Q
(578) quartz ring and a high Q (2095) silicon ring is employed to generate the
Fano resonance. The resonant frequency of the Fano resonance can be actively
manipulated by tuning the resonant frequency of the high Q WGMR, which is
achieved through utilizing an electrical thermo-optic tuning method, meanwhile,
the resonance intensity of the Fano resonance can be engineered by adjusting
the coupling strength between two WGMRs. This coupled-WGMR scheme delivers high
Q tunable Fano resonance and may contribute to the design of high-performance
configurable terahertz devices.",1910.05716v1
2023-02-15,Non-perturbative investigation of low eccentricity exterior mean motion resonances,"Mean motion resonances are important in the analysis and understanding of the
dynamics of planetary systems. While perturbative approaches have been dominant
in many previous studies, recent non-perturbative approaches have revealed
novel properties in the low eccentricity regime for interior mean motion
resonances of Jupiter in the fundamental model of the circular planar
restricted three body model. Here we extend the non-perturbative investigation
to exterior mean motion resonances in the low eccentricity regime (up to about
0.1) and for perturber mass in the range 5e-5 to 1e-3 (in units of the central
mass). Our results demonstrate that first order exterior resonances have two
branches at low eccentricity as well as low-eccentricity bridges connecting
neighboring first order resonances. With increasing perturber mass, higher
order resonances dissolve into chaos whereas low order resonances persist with
larger widths in their radial extent but smaller azimuthal widths. For low
order resonances, we also detect secondary resonances arising from small
integer commensurabilities between resonant librations and the synodic
frequency. These secondary resonances contribute significantly to generating
the chaotic sea that typically occurs near mean motion resonances of
higher-mass perturbers.",2302.07900v1
2012-05-21,Random Transverse Field Ising model on the Cayley Tree : analysis via Boundary Strong Disorder Renormalization,"Strong Disorder Renormalization for the Random Transverse Field Ising model
leads to a complicated topology of surviving clusters as soon as $d>1$. Even if
one starts from a Cayley tree, the network of surviving renormalized clusters
will contain loops, so that no analytical solution can been obtained. Here we
introduce a modified procedure called 'Boundary Strong Disorder
Renormalization' that preserves the tree structure, so that one can write
simple recursions with respect to the number of generations. We first show that
this modified procedure allows to recover exactly most of the critical
exponents for the one-dimensional chain. After this important check, we study
the RG equations for the quantum Ising model on a Cayley tree with a uniform
ferromagnetic coupling $J$ and random transverse fields with support
$[h_{min},h_{max}]$. We find the following picture (i) for $J>h_{max}$, only
bonds are decimated, so that the whole tree is a quantum ferromagnetic cluster
(ii) for $J<h_{min}$, only sites are decimated, so that no quantum
ferromagnetic cluster is formed, and the ferromagnetic coupling to the boundary
coincides with the partition function of a Directed Polymer model in a random
medium (iii) for $h_{min}<J<h_{max}$, both sites and bonds can be decimated :
the quantum ferromagnetic clusters can either remain finite (the physics is
then similar to (ii), with a quantitative mapping to a modified Directed
Polymer model) or an infinite quantum ferromagnetic cluster appears. We find
that the quantum transition can be of two types : (a) either the quantum
transition takes place in the region where quantum ferromagnetic clusters
remain finite, and the singularity of the ferromagnetic coupling to the
boundary involves the typical correlation length exponent $\nu_{typ}=1$ (b) or
the quantum transition takes place at the point where an extensive quantum
ferromagnetic cluster appears.",1205.4512v2
1995-01-24,"Ferromagnetism in the Hubbard model: instability of the Nagaoka state on the triangular, honeycomb and kagome lattices","In order to analyse the lattice dependence of ferromagnetism in the
two-dimensional Hubbard model we investigate the instability of the fully
polarized ferromagnetic ground state (Nagaoka state) on the triangular,
honeycomb and kagome lattices. We mainly focus on the local instability,
applying single spin flip variational wave functions which include majority
spin correlation effects. The question of global instability and phase
separation is addressed in the framework of Hartree-Fock theory. We find a
strong tendency towards Nagaoka ferromagnetism on the non-bipartite lattices
(triangular, kagome) for more than half filling. For the triangular lattice we
find the Nagaoka state to be unstable above a critical density of $n=1.887$ at
$U=\infty$, thereby significantly improving former variational results. For the
kagome lattice the region where ferromagnetism prevails in the phase diagram
widely exceeds the flat band regime. Our results even allow the stability of
the Nagaoka state in a small region below half filling. In the case of the
bipartite honeycomb lattice several disconnected regions are left for a
possible Nagaoka ground state.",9501116v1
1995-11-13,Ferromagnetism in Correlated Electron Systems: Generalization of Nagaoka's Theorem,"Nagaoka's theorem on ferromagnetism in the Hubbard model with one electron
less than half filling is generalized to the case where all possible
nearest-neighbor Coulomb interactions (the density-density interaction $V$,
bond-charge interaction $X$, exchange interaction $F$, and hopping of double
occupancies $F'$) are included. It is shown that for ferromagnetic exchange
coupling ($F>0$) ground states with maximum spin are stable already at finite
Hubbard interaction $U>U_c$. For non-bipartite lattices this requires a hopping
amplitude $t\leq0$. For vanishing $F$ one obtains $U_c\to\infty$ as in
Nagaoka's theorem. This shows that the exchange interaction $F$ is important
for stabilizing ferromagnetism at finite $U$. Only in the special case $X=t$
the ferromagnetic state is stable even for $F=0$, provided the lattice allows
the hole to move around loops.",9511060v1
1998-04-08,Ferromagnetism in the Hubbard model with orbital degeneracy in infinite dimensions,"We study the ferromagnetism due to orbital degeneracy in the Hubbard model in
infinite dimensions. The model contains the intraorbital repulsion $U$, the
interorbital repulsion $U^\prime$, the exchange $J$ (Hund coupling) and the
pair hopping $J^\prime$, where all of them originate from the on-site Coulomb
interaction. The ground state of the effective one-site problem was obtained by
exact diagonalizations. At the 1/4-filling, we found two insulating phases; one
is a ferromagnetic phase with alternating orbital order and the other is
antiferromagnetic one with uniform orbital order. If electrons are doped into
the 1/4-filling, the ferromagnetic phase still survives and becomes metallic,
while the antiferromagnetic phase disappears. This result indicates that the
double-exchange mechanism is relevant to stabilize metallic ferromagnetism in
infinite dimensions.",9804096v2
1998-04-09,Metallic ferromagnetism: Progress in our understanding of an old strong-coupling problem,"Metallic ferromagnetism is in general an intermediate to strong coupling
phenomenon. Since there do not exist systematic analytic methods to investigate
such types of problems, the microscopic origin of metallic ferromagnetism is
still not sufficiently understood. However, during the last two or three years
remarkable progress was made in this field: It is now certain that even in the
one-band Hubbard model metallic ferromagnetism is stable in dimensions $d=1,$
2, and $\infty$ on regular lattices and at intermediate values of the
interaction $U$ and density $n$. In this paper the basic questions and recent
insights regarding the microscopic conditions favoring metallic ferromagnetism
in this model are reviewed. These findings are contrasted with the results for
the orbitally degenerate case.",9804112v2
1998-10-21,Ferromagnetic ground state of an orbital degenerate electronic model for transition-metal oxides: exact solution and physical mechanism,"We present an exact ground state solution of a one-dimensional electronic
model for transition-metal oxides in the strong coupling limit. The model
contains doubly degenerated orbit for itinerant electrons and the Hund coupling
between the itinerant electrons and localized spins. The ground state is proven
to be a full ferromagnet for any density of electrons. Our model provides a
rigorous example for metallic ferromagnetism in narrow band systems. The
physical mechanism for ferromagnetism and its relevance to high-dimensional
systems, like R$_{1-x}$X$_x$MnO$_3$, are discussed. Due to the orbital
degeneracy of itinerant electrons, the superexchange coupling can be
ferromagnetic rather than antiferromagnetic in the one-band case.",9810268v1
1999-08-02,Breakdown of the magnetization plateau of the S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic trimerized spin chain with anisotropy,"We study the breakdown of the magnetization plateau at the magnetization
M=M_{S}/3 (M_{S} is the saturation magnetization) of the S=1/2 anisotropic spin
chain with ferromagnetic-ferromagnetic-antiferromagnetic interactions. We
consider the model with the isotropic ferromagnetic (trimer) coupling J_{F},
and anisotropic antiferromagnetic coupling (J_{x}=J_{y}=J_{AF} and J_{z}=\Delta
J_{AF}). For the limit of large \gamma\equiv J_{F}/J_{AF}, the model is
equivalent to the S=3/2 XXZ chain with the exchange anisotropy \Delta. There is
a phase transition between the plateau (small-\gamma) and the no-plateau
(large-\gamma) regions. This phase transition is of the
Berezinskii-Kosterlitz-Thouless type, and we determine the phase boundary from
the numerical diagonalization data. For \Delta=1, in particular, the phase
transition between the plateau and the no-plateau regions occurs at the point
\gamma_{c}=15.4.",9908027v2
2000-02-10,The ground state of Sr3Ru2O7 revisited; Fermi liquid close to a ferromagnetic instability,"We show that single-crystalline Sr3Ru2O7 grown by a floating-zone technique
is an isotropic paramagnet and a quasi-two dimensional metal as spin-triplet
superconducting Sr2RuO4 is. The ground state is Fermi liquid with very low
residual resistivity (3 micro ohm cm for in-plane currents) and a nearly
ferromagnetic metal with the largest Wilson ratio Rw>10 among paramagnets so
far. This contrasts with the ferromagnetic order at Tc=104 K reported on single
crystals grown by a flux method [Cao et al., Phys. Rev. B 55, R672 (1997)]. We
have also found a dramatic changeover from paramagnetism to ferromagnetism
under applied pressure. This suggests the existence of a substantial
ferromagnetic instability on the verge of a quantum phase transition in the
Fermi liquid state.",0002147v2
2000-03-27,Pseudospin Anisotropy Classification of Quantum Hall Ferromagnets,"Broken symmetry ground states with uniform electron density are common in
quantum Hall systems when two Landau levels simultaneously approach the
chemical potential at integer filling factor $\nu$. The close analogy between
these two-dimensional electron system states and conventional itinerant
electron ferromagnets can be emphasized by using a pseudospin label to
distinguish the two Landau levels. As in conventional ferromagnets, the
evolution of the system's state as external field parameters are varied is
expected to be sensitive to the dependence of ground state energy on pseudospin
orientation. We discuss the predictions of Hartree-Fock theory for the
dependence of the sign and magnitude of the pseudospin anisotropy energy on the
nature of the crossing Landau levels. We build up a classification scheme for
quantum Hall ferromagnets that applies for single layer and bilayer systems
with two aligned Landau levels distinguished by any combination of real-spin,
orbit-radius, or growth direction degree-of-freedom quantum numbers. The
possibility of in-situ tuning between easy-axis and easy-plane quantum Hall
ferromagnets is discussed for biased bilayer systems with total filling factors
$\nu=3$ or $\nu=4$. Detailed predictions are made for the bias dependence of
pseudospin reversal properties in $\nu=3$ bilayer systems.",0003430v1
2000-05-11,Spin-accumulation and Andreev-reflection in a mesoscopic ferromagnetic wire,"The electron transport though ferromagnetic metal-superconducting hybrid
devices is considered in the non-equilibrium Green's function formalism in the
quasiclassical approximation. Attention if focused on the limit in which the
exchange splitting in the ferromagnet is much larger than the superconducting
energy gap. Transport properties are then governed by an interplay between
spin-accumulation close to the interface and Andreev reflection at the
interface. We find that the resistance can either be enhanced or lowered in
comparison to the normal case and can have a non-monotonic temperature and
voltage dependence. In the non-linear voltage regime electron heating effects
may govern the transport properties, leading to qualitative different behaviour
than in the absence of heating effects. Recent experimental results on the
effect of the superconductor on the conductance of the ferromagnet can be
understood by our results for the energy-dependent interface resistance
together with effects of spin- accumulation without invoking long range pairing
correlations in the ferromagnet.",0005188v1
2000-07-27,Superconductivity and Ferromagnetism from Effective Mass Reduction,"Within a simple model Hamiltonian, both superconductivity and metallic
ferromagnetism can be understood as arising from lowering of kinetic energy as
the ordered state develops, due to a reduction in the carriers effective mass,
or equivalently, a bandwidth expansion. Experimental manifestation of this
physics has been detected in both high Tc superconductors and large
magnetoresistance ferromagnets, as an anomalous transfer of spectral weight in
optical absorption from high to low frequencies as the ordered state develops.
It is proposed that this general principle is common to the essential physics
of superconductivity and ferromagnetism in nature, and hence that these effects
in optical properties, although often smaller in magnitude, should exist in all
superconductors and metallic ferromagnets.",0007453v1
2000-08-30,"Ferromagnetism in the Periodic Anderson Model: A Comparison of Spectral Density Approximation (SDA), Modified Alloy Analogy (MAA) and Modified Perturbation Theory (MPT)","We compare different approximation schemes for investigating ferromagnetism
in the periodic Anderson model. The use of several approximations allows for a
detailed analysis of the implications of the respective methods, and also of
the mechanisms driving the ferromagnetic transition. For the Kondo limit, our
results confirm a previously proposed mechanism leading to ferromagnetic order,
namely an RKKY exchange mediated via the formation of Kondo screening clouds in
the conduction band. The contrary case is found in the intermediate-valence
regime. Here, the bandshift correction ensuring a correct high-energy expansion
of the self-energy is essential. Inclusion of damping effects reduces stability
of the ferromagnetic phase.",0008445v1
2000-09-08,Ferromagnetism in the Two-Dimensional Periodic Anderson Model,"Using the constrained-path Monte Carlo method, we studied the magnetic
properties of the two-dimensional periodic Anderson model for electron fillings
between 1/4 and 1/2. We also derived two effective low energy theories to
assist in interpreting the numerical results. For 1/4 filling we found that the
system can be a Mott or a charge transfer insulator, depending on the relative
values of the Coulomb interaction and the charge transfer gap between the two
non-interacting bands. The insulator may be a paramagnet or antiferromagnet. We
concentrated on the effect of electron doping on these insulating phases. Upon
doping we obtained a partially saturated ferromagnetic phase for low
concentrations of conduction electrons. If the system were a charge transfer
insulator, we would find that the ferromagnetism is induced by the well-known
RKKY interaction. However, we found a novel correlated hopping mechanism
inducing the ferromagnetism in the region where the non-doped system is a Mott
insulator. Our regions of ferromagnetism spanned a much smaller doping range
than suggested by recent slave boson and dynamical mean field theory
calculations, but they were consistent with that obtained by density matrix
renormalization group calculations of the one-dimensional periodic Anderson
model.",0009128v1
2001-01-17,Weak localization in ferromagnets with spin-orbit interaction,"Weak localization corrections to conductivity of ferromagnetic systems are
studied theoretically in the case when spin-orbit interaction plays a
significant role. Two cases are analyzed in detail: (i) the case when the
spin-orbit interaction is due to scattering from impurities, and (ii) the case
when the spin-orbit interaction results from reduced dimensionality of the
system and is of the Bychkov-Rashba type. Results of the analysis show that the
localization corrections to conductivity of ferromagnetic metals lead to a
negative magnetoresistance -- also in the presence of the spin-orbit
scattering. Positive magnetoresistance due to weak antilocalization, typical of
nonmagnetic systems, does not occur in ferromagnetic systems. In the case of
two-dimensional ferromagnets, the quantum corrections depend on the
magnetization orientation with respect to the plane of the system.",0101260v2
2001-06-29,Stabilization of d-Band Ferromagnetism by Hybridization with Uncorrelated Bands,"We investigate the influence of s-d or p-d hybridization to d-band
ferromagnetism to estimate the importance of hybridization for the magnetic
properties of transition metals. To focus our attention to the interplay
between hybridization and correlation we investigate a simple model system
consisting of two non-degenerated hybridized bands, one strongly correlated,
the other one quasi-free. To solve this extended Hubbard model, we apply simple
approximations, namely SDA and MAA, that, concerning ferromagnetism in the
single-band model, are known to give qualitatively satisfactory results. This
approach allows us to discuss the underlying mechanism, by which d-band
ferromagnetism is influenced by the hybridization on the basis of analytical
expressions. The latter clearly display the order and the functional
dependencies of the important effects. It is found, that spin-dependent
inter-band particle fluctuations cause a spin-dependent band shift and a
spin-dependent band broadening of the Hubbard bands. The shift stabilizes, the
broadening tends to destabilize ferromagnetism. Stabilization requires
relatively high band distances and small hybridization matrix elements.
Super-exchange and RKKY coupling are of minor importance.",0106638v1
2001-07-12,P-wave pairing and ferromagnetism in the metal-insulator transition in two dimensions,"Based on recent experimental evidence for a spin polarized ground state in
the insulating phase of the two-dimensional electron system, we propose that
ferromagnetic spin fluctuations lead to an attractive interaction in the
triplet channel and cause p-wave pairing in the conducting phase. We use the
Landau Fermi liquid phenomenology to explain how the enhanced spin
susceptibility near the critical density yields an attractive potential, in a
similar mechanism to superfluidity in $^3$He. As the density is decreased, the
p-wave order parameter undergoes a transition from a unitary to a nonunitary
state, in which it coexists with ferromagnetism for a range of densities. As
the density is further reduced, the pairing amplitude vanishes and the system
is described by a ferromagnetic insulator. Thus, we find two quantum critical
points as a function of density associated with the polarization of the paired
state and ferromagnetism. We explain the magnetotransport measurements in
parallel and perpendicular magnetic fields and propose a shot noise experiment
to measure the pair charge.",0107271v1
2001-08-29,Current and Spin-Torque in Double Tunnel Barrier Ferromagnet - Superconductor - Ferromagnet Systems,"We calculate the current and the spin-torque in small symmetric double tunnel
barrier ferromagnet - superconductor - ferromagnet (F-S-F) systems.
Spin-accumulation on the superconductor governs the transport properties when
the spin-flip relaxation time is longer than the transport dwell time. In the
elastic transport regime, it is demonstrated that the relative change in the
current (spin-torque) for F-S-F systems equals the relative change in the
current (spin-torque) for F-N-F systems upon changing the relative
magnetization direction of the two ferromagnets. This differs from the results
in the inelastic transport regime where spin-accumulation suppresses the
superconducting gap and dramatically changes the magnetoresistance [S.
Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999)]. The
experimental relevance of the elastic and inelastic transport regimes,
respectively, as well as the reasons for the change in the transport properties
are discussed.",0108490v2
2001-11-14,Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides,"This review is focused on extrinsic magnetotransport effects in ferromagnetic
oxides. It consists of two parts; the second part is devoted to an overview of
experimental data and theoretical models for extrinsic magnetotransport
phenomena. Here a critical discussion of domain-wall scattering is given.
Results on surfacial and interfacial magnetism in oxides are presented.
Spin-polarized tunnelling in ferromagnetic junctions is reviewed and
grain-boundary magnetoresistance is interpreted within a model of
spin-polarized tunnelling through natural oxide barriers. The situation in
ferromagnetic oxides is compared with data and models for conventional
ferromagnets. The first part of the review summarizes basic material
properties, especially data on the spin-polarization and evidence for
half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed.
An outlook on the further development of oxide spin-electronics concludes this
review.",0111263v1
2002-01-02,Kinetic exchange vs. room temperature ferromagnetism in diluted magnetic semiconductors,"Guided by the internal-reference rule and the known band offsets in III-V and
II-VI diluted magnetic semiconductors, we discuss the feasibility of obtaining
p-type conductivity, required for the carrier-induced ferromagnetism, as well
as the cases for which the doping by shallow impurities may lead to the
ferromagnetism driven by the double exchange. We consider the dependence of
kinetic exchange on the p-d hybridization, on the electronic configurations of
the magnetic ions, and on the energies of the charge transfer between the
valence band of host materials and the magnetic ions. In the case of Mn-based
II-VI compounds, the doping by acceptors is necessary for the hole-induced
ferromagnetism. The latter is, however, possible without any doping for some of
Mn-, Fe- or Co-based III-V magnetic semiconductors. In nitrides with Fe or Co
carrier-induced ferromagnetism with T_C>300K is expected in the presence of
acceptor doping.",0201012v1
2002-01-10,"Curie Temperature Trends in (III,Mn)V Ferromagnetic Semiconductors","We present a theoretical survey of ferromagnetic transition temperatures in
cubic (III,Mn)V semiconductors based on a model with $S=5/2$ local moments
exchange-coupled to itinerant holes in the host semiconductor valence band.
Starting from the simplest mean-field theory of this model, we estimate the
$T_c$ enhancement due to exchange and correlation in the itinerant-hole system,
and the $T_c$ suppression due to collective fluctuations of the ordered
moments. We show that high critical temperatures in these ferromagnetic
semiconductors require both the large magnetic susceptibility contribution from
the valence band's heavy holes and the large spin stiffness that results from
strong spin-orbit coupling in the valence band. Our calculations demonstrate
that this model for the ferromagnetism of these systems is fully consistent
with the room-temperature ferromagnetism reported for Mn doped nitrides.",0201157v2
2002-01-29,Inhomogeneous magnetism induced in a superconductor at superconductor-ferromagnet interface,"We study a magnetic proximity effect at superconductor (S) - ferromagnet (F)
interface. It is shown that due to an exchange of electrons between the F and S
metals ferromagnetic correlations extend into the superconductor, being
dependent on interface parameters. We show that ferromagnetic exchange field
pair breaking effect leads to a formation of subgap bands in the S layer local
density of states, that accommodate only one spin-polarized quasiparticles.
Equilibrium magnetization leakage into the S layer as function of SF interface
quality and a value of ferromagnetic interaction have also been calculated. We
show that a damped-oscillatory behavior versus distance from SF interface is a
distinguished feature of the exchange-induced magnetization of the S layer.",0201534v2
2002-03-08,Spontaneous Spin Polarized Currents in Superconductor-Ferromagnetic Metal Heterostructures,"We study a simple microscopic model for thin, ferromagnetic, metallic layers
on semi-infinite bulk superconductor. We find that for certain values of the
exchange spliting, on the ferromagnetic side, the ground states of such
structures feature spontaneously induced spin polarized currents. Using a
mean-field theory, which is selfconsistent with respect to the pairing
amplitude $\chi$, spin polarization $\vec{m}$ and the spontaneous current
$\vec{j}_s$, we show that not only there are Andreev bound states in the
ferromagnet but when their energies $E_n$ are near zero they support
spontaneous currents parallel to the ferromagnetic-superconducting interface.
Moreover, we demonstrate that the spin-polarization of these currents depends
sensitively on the band filling.",0203184v1
2002-03-19,Magnetic contributions to the low-temperature specific heat of the ferromagnetic insulator: Pr0.8Ca0.2MnO3,"The Pr(1-x}CaxMnO3 system exhibits a ferromagnetic insulating state for the
composition range x<0.25. A metallic ferromagnetic state is never realized
because of the low hole concentration and the very small averaged A-site cation
radius. In the present study, the nature of the magnetic excitations at low
temperature has been investigated by specific heat measurements on a
Pr0.8Ca0.2MnO3 single crystal. The decrease of the specific heat under magnetic
field is qualitatively consistent with a suppression of ferromagnetic spin
waves in a magnetic field. However, at low temperature, the qualitative
agreement with the ferromagnetic spin waves picture is poor. It appears that
the large reduction of the specific heat due to the spin waves is compensated
by a Schottky-like contribution possibly arising from a Zeeman splitting of the
ground state multiplet of the Pr{3+} ions.",0203365v1
2002-04-12,Disorder and interactions in quantum Hall ferromagnets: effects of disorder in Skyrmion physics,"We present a Hartree-Fock study of the competition between disorder and
interactions in quantum Hall ferromagnets near $\nu=1$. We find that the ground
state at $\nu=1$ evolves with increasing interaction strength from a
quasi-metallic paramagnet, to a partially spin-polarized ferromagnetic Anderson
insulator, and to a fully spin-polarized ferromagnet with a charge gap. Away
from $\nu=1$, the ground state evolves from a conventional Anderson insulator,
to a conventional quasiparticle glass, and finally to a ferromagnetic Skyrmion
quasiparticle glass. These different regimes can be measured in low-temperature
transport and NMR experiments. We present calculations for the NMR spectra in
different disorder regimes.",0204288v1
2002-06-02,Ground state of a double-exchange system containing impurities: bounds of ferromagnetism,"We study the boundary between ferromagnetic and non-ferromagnetic ground
state of a double-exchange system with quenched disorder for arbitrary relation
between Hund exchange coupling and electron band width. The boundary is found
both from the solution of the Dynamical Mean Field Approximation equations and
from the comparison of the energies of the saturated ferromagnetic and
paramagnetic states. Both methods give very similar results. To explain the
disappearance of ferromagnetism in part of the parameter space we derive from
the double-exchange Hamiltonian with classical localized spins in the limit of
large but finite Hund exchange coupling the $t-J$ model (with classical
localized spins).",0206018v2
2002-06-27,Magnon-Mediated Superconductivity in Itinerant Ferromagnets,"The present paper discusses magnon-mediated superconductivity in
ferromagnetic metals. The mechanism explains in a natural way the fact that the
superconductivity in UGe_2, ZrZn_2 and URhGe is apparently confined to the
ferromagnetic phase.The order parameter is a spin anti-parallel component ofa
spin-1 triplet with zero spin projection. The transverse spinfluctuations are
pair forming and the longitudinal ones are pair breaking.The competition
between magnons and paramagnons explains the existence of two successive
quantum phase transitions in UGe_2, from ferromagnetism to ferromagnetic
superconductivity, and at higher pressure to paramagnetism. The maximum T_{SC}
results from the suppression of the paramagnon contribution. To form a Cooper
pair an electron transfers from one Fermi surface to the other. As a result,
the onset of superconductivity leads to the appearance of two Fermi surfaces in
each of the spin up and spin down momentum distribution functions. This fact
explains the linear temperaturedependence at low temperature of the specific
heat, and the experimental results for UGe_2.",0206534v2
2002-07-02,"Magnon Exchange Mechanism of Superconductivity: ZrZn_2, URhGe","The magnon exchange mechanism of superconductivity was developed to explain
in a natural way the fact that the superconductivity in $UGe_2$, $ZrZn_2$ and
$URhGe$ is confined to the ferromagnetic phase.The order parameter is a spin
anti-parallel component of a spin-1 triplet with zero spin projection. The
transverse spin fluctuations are pair forming and the longitudinal ones are
pair breaking. In the present paper, a superconducting solution, based on the
magnon exchange mechanism, is obtained which closely matches the experiments
with $ZrZn_2$ and $URhGe$. The onset of superconductivity leads to the
appearance of complicated Fermi surfaces in the spin up and spin down momentum
distribution functions. Each of them consist of two pieces, but they are
simple-connected and can be made very small by varying the microscopic
parameters. As a result, it is obtained that the specific heat depends on the
temperature linearly, at low temperature, and the coefficient $\gamma=\frac
{C}{T}$ is smaller in the superconducting phase than in the ferromagnetic one.
The absence of a quantum transition from ferromagnetism to ferromagnetic
superconductivity in a weak ferromagnets $ZrZn_2$ and $URhGe$ is explained
accounting for the contribution of magnon self-interaction to the spin
fluctuations' parameters. It is shown that in the presence of an external
magnetic field the system undergoes a first order quantum phase transition.",0207078v1
2002-09-18,Charge ordered ferromagnetic phase in La0.5Ca0.5MnO3,"Mixed valent manganites are noted for their unusual magnetic,electronic and
structural phase transitions. The La1-xCaxMnO3 phase diagram shows that below
transition temperatures in the range 100-260 K, compounds with 0.2 < x < 0.5
are ferromagnetic and metallic whereas those with 0.5 < x < 0.9 are
antiferromagnetic and charge ordered. In a narrow region around x = 0.5, these
totally dissimilar states are thought to coexist. Uehara et al. have shown that
charge order and charge disorder can coexist in the related compound
La0.25Pr0.375Ca0.375MnO3. Here, we present electron microscopy data for
La0.5Ca0.5MnO3 that sheds light on the distribution of coexisting phases and
uncovers a novel and unexpected phase. Using electron holography and Fresnel
imaging, we find micron sized ferromagnetic regions spanning several grains
coexisting with similar sized regions with no local magnetisation. Holography
shows that the ferromagnetic regions have a local magnetisation of 3.4 +- 0.2
mB/Mn (the spin aligned value is 3.5 mB/Mn). We use electron diffraction and
dark field imaging to show that charge order exists in regions with no net
magnetisation and, surprisingly, can also occur in ferromagnetic regions.",0209436v1
2002-12-02,Dilatometry study of the ferromagnetic order in single-crystalline URhGe,"Thermal expansion measurements have been carried out on single-crystalline
URhGe in the temperature range from 2 to 200 K. At the ferromagnetic transition
(Curie temperature T_C = 9.7 K), the coefficients of linear thermal expansion
along the three principal orthorhombic axes all exhibit pronounced positive
peaks. This implies that the uniaxial pressure dependencies of the Curie
temperature, determined by the Ehrenfest relation, are all positive.
Consequently, the calculated hydrostatic pressure dependence dT_C/dp is
positive and amounts to 0.12 K/kbar. In addition, the effective Gruneisen
parameter was determined. The low-temperature electronic Gruneisen parameter
\Gamma_{sf} = 14 indicates an enhanced volume dependence of the ferromagnetic
spin fluctuations at low temperatures. Moreover, the volume dependencies of the
energy scales for ferromagnetic order and ferromagnetic spin fluctuations were
found to be identical.",0212038v1
2003-01-07,Ferromagnetism in the Hubbard model: A constructive approach,"It is believed that strong ferromagnetic orders in some solids are generated
by subtle interplay between quantum many-body effects and spin-independent
Coulomb interactions between electrons. Here we describe our rigorous and
constructive approach to ferromagnetism in the Hubbard model, which is a
standard idealized model for strongly interacting electrons in a solid. We
introduce a class of Hubbard models in any dimensions which are nonsingular in
the sense that both the Coulomb interaction and the density of states (at the
Fermi level) are finite. We then prove that the ground states of the models
exhibit saturated ferromagnetism, i.e., have maximum total spins. Combined with
our earlier results, the present work provides nonsingular models of itinerant
electrons with only spin-independent interactions where low energy behaviors
are proved to be that of a ``healthy'' ferromagnetic insulator.",0301071v4
2003-03-15,Tuning of the superconducting and ferromagnetic transitions by Cu doping for Ru in GdSr2RuCu2O8,"In order to explore the possibility of tuning superconducting and
ferromagnetic transitions by Cu doping (for Ru) in GdSr2RuCu2O8, we have
carried out synthesis and characterization of GdSr2Ru{1-x}Cu{2+x)O8 (x = 0,
0.05, 0.1, 0.2) and studied their physical properties. Coexistence of
superconductivity and ferromagnetism is observed in all the Cu doped samples
studied here. The zero field susceptibility data suggests formation of a
spontaneous vortex phase. Cu doping decreases the ferromagnetic Curie
temperature, whereas the superconducting transition temperature increases until
an optimal concentration x~0.1. This reflects an increase in hole transfer to
the CuO2 planes and reduction of ferromagnetic order within the ruthenate
layers.",0303287v1
2003-05-15,Ferromagnetism and Metamagnetism in Copper-doped Germanium Clathrate,"Cu-doped type-I germanium clathrate can exhibit dilute magnetism, including
ferromagnetism, antiferromagnetism, and metamagnetic transitions up to 90 K.
63Cu NMR measurements confirm that these transitions are due to a dilute
composition of magnetic defects coupled by conduction electrons, behavior
similar to that of magnetic semiconductors. Magnetic measurements indicate
localized magnetic moments, attributed to clusters of magnetic ions, with
competition between ferromagnetic and antiferromagnetic exchange, and also
indications of glassy behavior in the ferromagnetic phase. NMR Knight shifts
and relaxation times show that the conduction band is metallic with a large
Korringa ratio. Comparison to a mean-field theory for the ordering behavior
gives a good accounting for the ferromagnetic transition.",0305369v1
2003-05-27,"Ferromagnetism and metallic state in digital (Ga,Mn)As heterostructures","We present an extensive density functional theory study of the electronic,
magnetic and transport properties of GaAs and AlAs digital ferromagnetic
heterostructures. These can be obtained by $\delta$-doping with Mn the GaAs
layers of a GaAs/AlAs superlattice. Our analysis spans a range of Mn
concentrations and considers the presence of compensating defects such as As
antisites.
  In the defect-free case all the heterostructures studied present an
half-metallic electronic structure. In contrast when As antisites are present
the half-metallic state is destroyed and the heterostructures behave as dirty
planar metals. In this case they show a large $p$-type metallic conductance in
the Mn plane mainly due to majority spin electrons, and an $n$-type
hopping-like conductance in the GaAs planes mainly due to minority spin
electrons. This suggests that if the As antisites can be kept far from the Mn
planes, spatial separation of the different spin currents can be achieved.
Finally we show that in the case of AlAs/(Ga,Mn)As digital ferromagnetic
heterostructures the AlAs/GaAs valence band offset produces an additional
confining potential for the holes responsible for the ferromagnetism. Therefore
the ferromagnetic coupling between the Mn ions becomes larger and more robust
to the presence of As antisites.",0305615v1
2003-06-11,Diameter dependence of ferromagnetic spin moment in Au nanocrystals,"Au nanoparticles exhibit ferromagnetic spin polarization and show diameter
dependence in magnetization. The magnetic moment per Au atom in the particle
attains its maximum value at a diameter of about 3 nanometer (nm) in the
Magnetization-Diameter curve. Because Au metal is a typical diamagnetic
material, its ferromagnetic polarization mechanism is thought to be quite
different from the ferromagnetism observed in transition metals. The size
effect strongly suggests the existence of some spin correlation effect at the
nanoscale. The so-called ``Fermi hole effect'' is the most probable one given
in the free electron gas system. Ferromagnetism in Au nanoparticles is
discussed using this model.",0306261v2
2003-06-25,Ferromagnetic insulating phase in Pr{1-x}Ca{x}MnO3,"A ferromagnetic insulating (FM-I) state in Pr0.75Ca0.25MnO3 has been studied
by neutron scattering experiment and theoretical calculation. The insulating
behavior is robust against an external magnetic field, and is ascribed to
neither the phase separation between a ferromagnetic metallic (FM-M) phase and
a non-ferromagnetic insulating one, nor the charge ordering. We found that the
Jahn-Teller type lattice distortion is much weaker than PrMnO3 and the magnetic
interaction is almost isotropic. These features resembles the ferromagnetic
metallic state of manganites, but the spin exchange interaction J is much
reduced compared to the FM-M state. The theoretical calculation based on the
staggered type orbital order well reproduces several features of the spin and
orbital state in the FM-I phase.",0306631v1
2003-08-25,Non-Fermi liquid behavior near the ferromagnetic quantum critical point in the series Ca(x)Sr(1-x)RuO(3),"A series of epitaxial films were grown across the solid solution
Ca(x)Sr(1-x)RuO(3) in order to pinpoint the ferromagnetic to paramagnetic
quantum phase transition in this system and to study the evolution of transport
and magnetic properties in its vicinity. The ferromagnetic Tc of SrRuO(3) was
found to decrease linearly with Ca doping levels up to 70%. Further doping
resulted in the abrupt elimination of ferromagnetic order, and the onset of low
temperature (< 10K) non-Fermi liquid (NFL) resistivity of the form rho ~ rho(0
+ AT^(1.5) for samples with x <= 0.75 <= 1.0. The resistivity exponent of 1.5
matches that previously observed for MnSi, indicating possible universality of
the NFL behavior of itinerant ferromagnets. Field-dependent specific heat
measurements on bulk samples at compositions near the quantum phase transition
provide additional evidence for NFL behavior (C/T ~ log T) and show the
conditions nder which spin fluctuations contribute to the specific heat.",0308514v2
2003-09-11,Resistance control of a magnetoresistive manganite by spin-injection,"We report a new spin-injection effect found for a manganite using a specially
fabricated sample. A wire of La0.7Sr0.3MnO3 was patterned by means of focused
ion beam etching, and the central part was subsequently irradiated with Ga+
ions lightly. The ferromagnetic Curie temperature was reduced locally by the
irradiation from Tc to Tc', and thus a sequential
ferromagnetic/paramagnetic/ferromagnetic structure was realized along the wire
between Tc and Tc'. The injection of spin-polarized current from the
ferromagnetic manganite into the paramagnetic part rendered the latter
ferromagnetic and more conductive. This can be explained by assuming the
suppression of spin fluctuation in the paramagnet by the injected spins.",0309274v1
2003-10-07,Weak ferromagnetism in magnetoelectrics LiCoPO4 and LiNiPO4,"The magnetic properties of the antiferromagnetic magnetoelectric
single-crystals LiCoPO4 and LiNiPO4 were investigated using the
SQUID-magnetometer. The magnetization was measured in a longitudinal
experimental geometry (M // H) along the crystallographic axes a, b and c. The
carried out investigations have shown that these compounds exhibit weak
ferromagnetism. The weak ferromagnetic (WFM) moment is directed along the
antiferromagnetic axis in both crystals. But the temperature behaviours of the
weak ferromagnetic moments in LiCoPO4 and LiNiPO4 are different. The weak
ferromagnetic moment in LiCoPO4 changes non-monotonically. The essential
horizontal negative bias of the magnetic hysteresis loop is observed in LiCoPO4",0310156v1
2003-10-10,The Silicon Inversion Layer With A Ferromagnetic Gate: A Novel Spin Source,"Novel spin transport behavior is theoretically shown to result from replacing
the usual metal (or poly-silicon) gate in a silicon field-effect transistor
with a ferromagnet, separated from the semiconductor by an ultra-thin oxide.
The spin-dependent interplay between the drift current (due to a source-drain
bias) and the diffusion current (due to carrier leakage into the ferromagnetic
gate) results in a rich variety of spin dependence in the current that flows
through such a device. We examine two cases of particular interest: (1)
creating a 100% spin-polarized electrical current and (2) creating a pure spin
current without a net electrical current. A spin-valve consisting of two
sequential ferromagnetic gates is shown to exhibit magnetoresistance dependent
upon the relative orientations of the magnetization of the two ferromagnets.
The magnetoresistance ratio grows to arbitrarily large values in the regime of
low source-drain bias, and is limited only by the spin-flip time in the
channel.",0310259v1
2003-11-19,Shape memory ferromagnets,"In ferromagnetic alloys with shape memory large reversible strains can be
obtained by rearranging the martensitic domain structure by a magnetic field.
Magnetization through displacement of domain walls is possible in the presence
of high magnetocrystalline anisotropy, when martensitic structure rearrangement
is energetically favorable compared to the reorientation of magnetic moments.
In ferromagnetic Heusler alloys Ni$_{2+x}$Mn$_{1-x}$Ga the Curie temperature
exceeds the martensitic transformation temperature. The fact that these two
temperatures are close to room temperature offers the possibility of
magnetically controlling the shape and size of ferromagnets in the martensitic
state. In Ni$_{2+x}$Mn$_{1-x}$Ga single crystals, a reversible strain of $\sim
6$% is obtained in fields of $\sim 1$ T.",0311433v1
2004-01-27,Non-linear sigma-model for odd triplet superconductivity in superconductor/ferromagnet structures,"We consider some properties of odd frequency triplet superconducting
condensates. In order to describe fluctuations we construct a supermatrix
sigma-model for the superconductor/ferromagnet or superconductor/normal-metal
structures. We show that an odd frequency triplet superconductor, when in
isolation or coupled to a normal metal, generally displays behaviour comparable
to a superconductor with the usual singlet pairings. However, for spin
dependent systems such as the superconductor/ferromagnet the two types of
superconductor have quite different behaviour. We discuss this difference by
considering transformations under which the sigma-model is invariant. Finally,
we calculate the low energy density of states in a ferromagnet coupled to a
singlet superconductor. If odd frequency triplet components are induced in the
ferromagnet the density of states will have a micro-gap similar to the
micro-gap found in normal metals coupled to a superconductor.",0401530v1
2004-03-08,Mean-field magnetization relaxation in conducting ferromagnets,"Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
""spin-pumping"" and the ""breathing Fermi-surface"" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.",0403224v2
2004-05-05,Spin waves in a Bose Ferromagnet,"It is shown that the ferromagnetic transition takes place always above
Bose-Einstein condensation in ferromagnetically coupled spinor Bose gases. We
describe the Bose ferromagnet within Ginzburg-Landau theory by a ""two-fluid""
model below Bose-Einstein condensation. Both the Bose condensate and the normal
phase are spontaneously magnetized. As a main result we show that spin waves in
the two fluids are coupled together so as to produce only one mixed spin-wave
mode in the coexisting state. The long wavelength spectrum is quadratic in the
wave vector ${\bf k}$, consistent with usual ferromagnetism theory, and the
spin-wave stiffness coefficient $c_s$ includes contributions from both the two
phases, implying the ""two-fluid"" feature of the system. $c_s$ can show a sharp
bend at the Bose-Einstein condensation temperature.",0405094v1
2004-06-11,F/S interfaces: point contact versus atomic thickness geometries,"We contrast perturbative expansions of ferromagnet / superconductor
interfaces in two geometries: (i) a point contact geometry where a single weak
link connects a 3D ferromagnet to a 3D superconductor and (ii) an atomic
thickness geometry with an infinite planar interface connecting a quasi-2D
ferromagnet to a quasi-2D superconductor. Perturbation theories are rather
different in the two approaches but they both break down at order $t^4$ ($t$ is
the tunnel amplitude). The regimes of strong ferromagnets are in a qualitative
agreement in both geometries. The regime of weak ferromagnets exists only for
the atomic thickness geometry and is related to Andreev bound states due to
lateral confinement in the superconductor.",0406280v1
2004-06-29,Ferromagnetism in substituted zinc oxide,"Room-temperature ferromagnetism is observed in (110) oriented ZnO films
containing 5 at % of Sc, Ti, V, Fe, Co or Ni, but not Cr, Mn or Cu ions. There
are large moments, 1.9 and 0.5 muB/atom for Co- and Ti-substituted oxides,
respectively. Sc-substituted ZnO shows also a moment of 0.3 muB/Sc.
Magnetization is very anisotropic, with variations of up to a factor three
depending on the orientation of the applied field relative to the R-cut
sapphire substrates. Results are interpreted in terms of a spin-split donor
impurity band model, which can account for ferromagnetism in insulating or
conducting high-k oxides with concentrations of magnetic ions that lie far
below the percolation threshold. The variation of the ferromagnetism with
oxygen pressure used during film growth is evidence of a link between
ferromagnetism and defect concentration.",0406719v1
2004-07-05,Absence of ferromagnetism in Mn- and Co-doped ZnO,"Following the theoretical predictions of ferromagnetism in Mn- and Co-doped
ZnO, several workers reported ferromagnetism in thin films as well as in bulk
samples of these materials. While some observe room-temperature ferromagnetism,
others find magnetization at low temperatures. Some of the reports, however,
cast considerable doubt on the magnetism of Mn- and Co-doped ZnO. In order to
conclusively establish the properties of Mn- and Co-doped ZnO, samples with 6
percent and 2 percent dopant concentrations, have been prepared by the
low-temperature decomposition of acetate solid solutions. The samples have been
characterized by x-ray diffraction, EDAX and spectroscopic methods to ensure
that the dopants are substitutional. All the Mn- and Co-doped ZnO samples
(prepared at 400 deg C and 500 deg C) fail to show ferromagnetism. Instead,
their magnetic properties are best described by a Curie-Weiss type behavior. It
appears unlikely that these materials would be useful for spintronics, unless
additional carriers are introduced by some means.",0407108v2
2004-07-16,Strong Room-Temperature Ferromagnetism in Co2+-Doped TiO2 made from Colloidal Nanocrystals,"Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and
studied by electronic absorption, magnetic circular dichroism, transmission
electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption
spectroscopy, and extended X-ray absorption fine structure measurements. The
nanocrystals were paramagnetic when isolated by surface-passivating ligands,
weakly ferromagnetic (Ms = 1.5 x 10-3 mB/Co2+ at 300 K) when aggregated, and
strongly ferromagnetic (up to Ms = 1.9 mB/Co2+ at 300 K) when spin-coated into
nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co2+
oxidation state in all samples. In addition to providing strong experimental
support for the existence of intrinsic ferromagnetism in cobalt-doped TiO2,
these results demonstrate the possibility of using colloidal TiO2 diluted
magnetic semiconductor nanocrystals as building blocks for assembly of
ferromagnetic semiconductor nanostructures with potential spintronics
applications.",0407451v1
2004-09-06,Ferromagnet-Superconductor Hybrids,"A new class of phenomena discussed in this review is based on interaction
between spatially separated, but closely located ferromagnets and
superconductors. They are called Ferromagnet-Superconductor Hybrids (FSH).
These systems include coupled smooth and textured Ferromagnetic and
Superconducting films, magnetic dots, wires etc.The interaction may be provided
by the magnetic flux from magnetic textures and supercurrents. The magnetic
flux from magnetic textures or topological defects can pin vortices or create
them, changing drastically the properties of the superconductor. On the other
hand, the magnetic field from supercurrents (vortices) strongly interacts with
the magnetic subsystem leading to formation of coupled magnetic-superconducting
topological defects. We discuss possible experimental realization of the FSH.
The presence of ferromagnetic layer can change dramatically the properties of
the superconducting film due to proximity effect. We discuss experimental and
theoretical studies of the proximity effect in the FSH including transition
temperature and order parameter oscillations and triplet superconductivity.",0409137v1
2004-09-08,Tailoring of ferromagnetic Pr0.85Ca0.15MnO3/ferroelectric Ba0.6Sr0.4TiO3 superlattices for multiferroic properties,"Superlattices composed of ferromagnetic Pr0.85Ca0.15MnO3 and ferroelectric
Ba0.6Sr0.4TiO3 layers were fabricated on (100) SrTiO3 substrates by a
pulsed-laser deposition method. The capacitance and resistive parts of the
samples were analyzed from the complex impedance measurements, performed on the
samples using a special experimental set-up. The superlattice with larger
ferroelectric thickness shows unique characteristics which are not present in
the parent ferromagnetic thin film. The superlattice show both ferromagnetic
and ferroelectric transitions which is an evidence for the coexistence of both
the properties. The high magnetoresistance (40 % at 80K) shown by the
superlattice can be attributed to the coupling between ferromagnetic and
ferroelectric layers, i.e, to the magnetoelectric effect.",0409182v1
2004-12-01,Magnetoresistive Effects in Ferromagnet-Superconductor Multilayers,"We consider a nanoscale system consisting of Manganite-ferromagnet and
Cuprate-superconductor multilayers in a spin valve configuration. The
magnetization of the bottom Manganite-ferromagnet is pinned by a
Manganite-antiferromagnet. The magnetization of the top Manganite-ferromagnet
is coupled to the bottom one via indirect exchange through the superconducting
layers. We study the behavior of the critical temperature and the
magnetoresistance as a function of an externally applied parallel magnetic
field, when the number of Cuprate-superconductor layers are changed. There are
two typical behaviors in the case of a few monolayers of the Cuprates: a) For
small magnetic fields, the critical temperature and the magnetoresistance
change abruptly when the flipping field of the top Manganite-ferromagnet is
reached. b) For large magnetic fields, the multilayered system re-enters the
zero-resistance (superconducting) state after having become resistive (normal).",0412005v1
2005-01-25,Spin-polarized transport through a single-level quantum dot in the Kondo regime,"Nonequilibrium electronic transport through a quantum dot coupled to
ferromagnetic leads (electrodes) is studied theoretically by the nonequilibrium
Green function technique. The system is described by the Anderson model with
arbitrary correlation parameter $U$. Exchange interaction between the dot and
ferromagnetic electrodes is taken into account {\it via} an effective molecular
field. The following situations are analyzed numerically: (i) the dot is
symmetrically coupled to two ferromagnetic leads, (ii) one of the two
ferromagnetic leads is half-metallic with almost total spin polarization of
electron states at the Fermi level, and (iii) one of the two electrodes is
nonmagnetic whereas the other one is ferromagnetic. Generally, the Kondo peak
in the density of states (DOS) becomes spin-split when the total exchange field
acting on the dot is nonzero. The spin-splitting of the Kondo peak in DOS leads
to splitting and suppression of the corresponding zero bias anomaly in the
differential conductance.",0501605v1
2005-01-28,One-dimensional itinerant ferromagnets with Heisenberg symmetry and the ferromagnetic quantum critical point,"We study one-dimensional itinerant ferromagnets with Heisenberg symmetry near
a ferromagnetic quantum critical point. It is shown that the Berry phase term
arises in the effective action of itinerant ferromagnets when the full SU(2)
symmetry is present. We explicitly demonstrate that dynamical critical exponent
of the theory with the Berry term is $z=2 +{\rm O}(\epsilon^2)$ in the sense of
$\epsilon$ expansion, as previously discovered in the Ising limit. It appears,
however, that the universality class at the interacting fixed point is not the
same. We point out that even though the critical theory in the Ising limit can
be obtained by the standard Hertz-Millis approach, the Heisenberg limit is
expected to be different. We also calculate the exact electron Green functions
$G(x,t=0)$ and $G(x=0,t)$ near the transition in a range of temperature, which
can be used for experimental signatures of the associated critical points.",0501689v3
2005-03-04,Can the interface between a non-ideal ferromagnet and a semiconductor quantum wire acts as an ideal spin filter?,"The problem of spin injection across the interface between a non-ideal
ferromagnet (less than 100% spin polarization) and a semiconductor
(paramagnetic) quantum wire is examined in the presence of Rashba spin orbit
coupling and an axial magnetic field along the wire axis. The field is caused
by the ferromagnet magnetized along the wire axis. At low temperatures and for
certain injection energies, the interface can act as an ideal spin filter
allowing injection only from the majority spin band of the ferromagnet. Thus,
100% spin filtering can take place even if the ferromagnet itself is less than
100% spin polarized. Below a critical value of the magnetic field, there are
two injection energies for which ideal (100%) spin filtering is possible; above
this critical field, there is only one such injection energy.",0503112v1
2005-03-08,"Ferromagnetic Semiconductors: Moving Beyond (Ga,Mn)As","The recent development of MBE techniques for growth of III-V ferromagnetic
semiconductors has created materials with exceptional promise in spintronics,
i.e. electronics that exploit carrier spin polarization. Among the most
carefully studied of these materials is (Ga,Mn)As, in which meticulous
optimization of growth techniques has led to reproducible materials properties
and ferromagnetic transition temperatures well above 150 K. We review progress
in the understanding of this particular material and efforts to address
ferromagnetic semiconductors as a class. We then discuss proposals for how
these materials might find applications in spintronics. Finally, we propose
criteria that can be used to judge the potential utility of newly discovered
ferromagnetic semiconductors, and we suggest guidelines that may be helpful in
shaping the search for the ideal material.",0503185v1
2005-03-28,Giant oscillations of the density of states and the conductance in a ferromagnetic conductor coupled to two superconductors,"Giant oscillations of the density of electronic states and the differential
conductance of a superconductor-ferromagnet-superconductor structure are
predicted for the case when the exchange energy, $I_0$, due to the interaction
between the electron spin and the spontaneous moment of the ferromagnet is
smaller than the superconductor energy gap, $\Delta$. The effect is due to the
extremely large degeneration of the energy level $\epsilon = I_0$ when the
superconductor phase difference $\phi$ is close to odd multiple of $\pi$
($\epsilon$ is the electron energy measured from the Fermi-energy). This
quantum interference effect persists even in long ferromagnetic bridges whose
length much exceeds the ''magnetic length'' ($\hbar v_{F}/I_{0}$ in the
ballistic regime and $\sqrt{\hbar D/I_0}$ in the diffusive regime; $D$ is the
electron diffusion constant). The predicted effect allows a direct spectroscopy
of Andreev levels in the ferromagnet as well as a direct measurement of the
exchange energy,$I_0$.",0503643v1
2005-05-04,Meissner phases in spin-triplet ferromagnetic superconductors,"We present new results for the properties of phases and phase transitions in
spin-triplet ferromagnetic superconductors. The superconductivity of the mixed
phase of coexistence of ferromagnetism and unconventional superconductivity is
triggered by the presence of spontaneous magnetization. The mixed phase is
stable but the other superconducting phases that usually exist in
unconventional superconductors are either unstable or for particular values of
the parameters of the theory some of them are metastable at relatively low
temperatures in a quite narrow domain of the phase diagram. Phase transitions
from the normal phase to the phase of coexistence is of first order while the
phase transition from the ferromagnetic phase to the coexistence phase can be
either of first or second order depending on the concrete substance. Cooper
pair and crystal anisotropies determine a more precise outline of the phase
diagram shape and reduce the degeneration of ground states of the system but
they do not change drastically phase stability domains and thermodynamic
properties of the respective phases. The results are discussed in view of
application to metallic ferromagnets as UGe2, ZrZn2, URhGe.",0505087v1
2005-05-11,Stoner gap in the superconducting ferromagnet UGe2,"We report the temperature ($T$) dependence of ferromagnetic Bragg peak
intensities and dc magnetization of the superconducting ferromagnet UGe2 under
pressure ($P$). We have found that the low-$T$ behavior of the uniform
magnetization can be explained by a conventional Stoner model. A functional
analysis of the data produces the following results: The ferromagnetic state
below a critical pressure can be understood as the perfectly polarized state,
in which heavy quasiparticles occupy only majority spin bands. A Stoner gap
$\Delta(P)$ decreases monotonically with increasing pressure and increases
linearly with magnetic field. We show that the present analysis based on the
Stoner model is justified by a consistency check, i.e., comparison of density
of states at the Fermi energy deduced from the analysis with observed
electronic specific heat coeffieients. We also argue the influence of the
ferromagnetism on the superconductivity.",0505266v2
2005-06-16,Meissner superconductivity in itinerant ferromagnets,"Recent results about the coexistence of ferromagnetism and unconventional
superconductivity with spin-triplet Cooper pairing are reviewed on the basis of
the quasi-phenomenological Ginzburg-Landau theory. The superconductivity in the
mixed phase of coexistence of ferromagnetism and unconventional
superconductivity is triggered by the spontaneous magnetization. The mixed
phase is stable whereas the other superconducting phases that usually exist in
unconventional superconductors are either unstable or metastable at relatively
low temperatures in a quite narrow domain of the phase diagram and the
stability properties are determined by the particular values of Landau
parameters. The phase transitions from the normal phase to the phase of
coexistence is of first order while the phase transition from the ferromagnetic
phase to the coexistence phase can be either of first or second order depending
on the concrete substance. The Cooper pair and crystal anisotropy are relevant
to a more precise outline of the phase diagram shape and reduce the
degeneration of the ground states of the system. The results are discussed in
view of application to itinerant ferromagnetic compounds as UGe2, ZrZn2, URhGe.",0506396v1
2005-07-01,Critical fields and spontaneous vortex state in the weak-ferromagnetic superconductor RuSr2GdCu2O8,"A spontaneous vortex state (SVS) between 30 K and 56 K was observed for the
weak-ferromagnetic superconductor RuSr2GdCu2O8 with ferromagnetic Curie
temperature TC = 131 K and superconducting transition temperature Tc = 56 K.
The low field (20 G) Superconducting hysteresis loop indicates a narrow
Meissner state region within average lower critical field Bc1(T)= Bc1(0)[1 -
(T/T0)2], with average Bave c1 (0) = 12 G and T0 = 30 K. Full Meissner
shielding signal in very low applied field indicates an ab-plane Bab c1(0) ~ 4
G with an estimated anisotropic parameter g ~ 7 for this layered system. The
existence of a spontaneous vortex state between 30 K and 56 K is the result of
weak-ferromagnetic order with a net spontaneous magnetic moment of ~ 0.1
muB/Ru, which generates a weak magnetic dipole field around 10 G in the CuO2
bi-layers. The upper critical field Bc2 varies linearly as (1 - T/Tc) up to 7-T
field. The vortex melting line Bm varies as (1 - T/Tm)3.5 with melting
transition temperature Tm = 39 K and a very broad vortex liquid region due to
the coexistence and the interplay between superconductivity and
weak-ferromagnetic order.",0507014v1
2005-07-03,Coulomb Interactions and Ferromagnetism in Pure and Doped Graphene,"We study the presence of ferromagnetism in the phase diagram of the
two-dimensional honeycomb lattice close to half-filling (graphene) as a
function of the strength of the Coulomb interaction and doping. We show that
exchange interactions between Dirac fermions can stabilize a ferromagnetic
phase at low doping when the coupling is sufficiently large. In clean systems,
the zero temperature phase diagram shows both first order and second order
transition lines and two distinct ferromagnetic phases: one phase with only one
type of carriers (either electrons or holes) and another with two types of
carriers (electrons and holes). Using the coherent phase approximation (CPA) we
argue that disorder further stabilizes the ferromagnetic phase.",0507061v2
2005-10-13,Direct Measurements of Spin-Dependent and Coherent Effects in Conductance of a Ferromagnet/Superconductor System,"In the systems ferromagnet/superconductor ([Fe, Ni]/In), the temperature
dependent transport has been investigated within the temperature range
including superconducting transition temperature for Indium. It has been found
that when Indium becomes superconducting, the system resistance acquires two
positive additions. The first, numerically equal to the resistance of a
ferromagnet part, of order of a spin--polarized region in length, corresponds
to the manifestation of ""spin accumulation"" effect. The second agrees in
magnitude with an interference reduction in the ferromagnet conductance over
the coherence length for singlet ""Andreev pairs"" which is established by the
exchange field in the ferromagnet. From the experimental data, the degree of
current spin polarization, the coherence length in the exchange field, and the
lower limit of spin--relaxation length in Fe and Ni have been estimated.",0510352v1
2005-12-15,Nematic order in square lattice frustrated ferromagnets,"We present a new scenario for the breakdown of ferromagnetic order in a
two-dimensional quantum magnet with competing ferromagnetic and
antiferromagnetic interactions. In this, dynamical effects lead to the
formation of two-magnon bound states, which undergo Bose-Einstein condensation,
giving rise to bond-centered nematic order. This scenario is explored in some
detail for an extended Heisenberg model on a square lattice. In particular, we
present numerical evidence confirming the existence of a state with d-wave
nematic correlations but no long range magnetic order, lying between the
saturated ferromagnetic and collinear antiferromagnetic phases of the
ferromagnetic J1-J2 model. We argue by continuity of spectra that this phase is
also present in a model with 4-spin cyclic exchange.",0512349v1
2006-02-15,A spin triplet supercurrent through the half-metallic ferromagnet CrO2,"In general, conventional superconductivity should not occur in a ferromagnet,
though it has been seen in iron under pressure. Moreover, theory predicts that
the current is always carried by pairs of electrons in a spin singlet state, so
conventional superconductivity decays very rapidly when in contact with a
ferromagnet, which normally prohibits the existence of singlet pairs. It has
been predicted that this rapid spatial decay would not occur when spin triplet
superconductivity could be induced in the ferromagnet. Here we report a
Josephson supercurrent through the strong ferromagnet CrO2, from which we infer
that it is a spin triplet supercurrent. Our experimental setup is different
from those envisaged in the earlier predictions, but we conclude that the
underlying physical explanation for our result is a conversion from spin
singlet to spin triplets at the interface. The supercurrent can be switched
with the direction of the magnetization, analogous to spin valve transistors,
and therefore could enable magnetization-controlled Josephson junctions.",0602359v1
2006-02-28,Magnetic field dependence of the magnetic phase separation in Pr1-xCaxMnO3 manganites studied by small-angle neutron scattering,"Transport properties of manganese oxides suggest that their colossal
magnetoresistance (CMR) is due to percolation between ferromagnetic metallic
(FM) clusters in an antiferromagnetic insulating (AFI) matrix. We have studied
small-angle neutron scattering under applied magnetic field in CMR Pr1-xCaxMnO3
crystals for x around 0.33. Quantitative analysis of the small-angle magnetic
neutron scattering shows that the magnetic heterogeneities take place at
different scales. At the mesoscopic scale (200nm), the inhomogeneities
correspond to the percolation of the conducting ferromagnetic phase into the
insulating phases. It is at the origin of the colossal magnetoresistance of the
compound. The other inhomogeneities are nanoscopic: inside the
antiferromagnetic phase (AFI), there exist small ferromagnetic clusters. Inside
the ferromagnetic phase which exists in absence of magnetic field in some
compounds and is in fact insulating (FI), there also exist small non
ferromagnetic objects. No evolution of this nanostructure is observed when the
magnetic field is applied. The existence of such nanoscale objects is discussed
in relation to the cationic disorder of these compounds.",0602668v1
2006-04-20,Influence of the microstructure on the magnetism of Co-doped ZnO thin films,"The prediction of ferromagnetism at room temperature in Co-ZnO thin films has
generated a large interest in the community due to the possible applications.
However, the results are controversial, going from ferromagnetism to
non-ferromagnetism, leading to a large debate about its origin (secondary
phase, Co clusters or not). By carefully studying the micro-structure of
various Co-ZnO films, we show that the Co2+ partly substitutes the ZnO wurtzite
matrix without forming Co clusters. Surprisingly, the ferromagnetism nature of
the films disappears as the Co content increases. In addition, our results
suggest that the observed ferromagnetism is likely associated to a large amount
of defects- close to the interface and strongly depending on the growth
temperature- which may explained the spreading of the results.",0604468v1
2006-05-09,"Superexchange in Dilute Magnetic Dielectrics: Application to (Ti,Co)O_2","We extend the model of ferromagnetic superexchange in dilute magnetic
semiconductors to the ferromagnetically ordered highly insulating compounds
(dilute magnetic dielectrics). The intrinsic ferromagnetism without free
carriers is observed in oxygen-deficient films of anatase TiO_2 doped with
transition metal impurities in cation sublattice. We suppose that ferromagnetic
order arises due to superexchange between complexes [oxygen vacancies +
magnetic impurities], which are stabilized by charge transfer from vacancies to
impurities. The Hund rule controls the superexchange via empty vacancy related
levels so that it becomes possible only for the parallel orientation of
impurity magnetic moments. The percolation threshold for magnetic ordering is
determined by the radius of vacancy levels, but the exchange mechanism does not
require free carriers. The crucial role of the non-stoichiometry in formation
of the ferromagnetism makes the Curie temperatures extremely sensitive to the
methods of sample preparation.",0605242v1
2006-05-14,Ballistic transport in ferromagnet-superconductor-ferromagnet trilayers with arbitrary orientation of magnetizations,"Transport phenomena in clean ferromagnet-superconductor-ferromagnet (FSF)
trilayers are studied theoretically for a general case of arbitrary orientation
of in-plane magnetizations and interface transparencies. Generalized
expressions for scattering probabilities are derived and the differential
conductance is computed using solutions of the Bogoliubov-de Gennes equation.
We focus on size and coherence effects that characterize ballistic transport,
in particular on the subgap transmission and geometrical oscillations of the
conductance. We find a monotonic dependence of conductance spectra and
magnetoresistance on the angle of misorientation of magnetizations as their
alignment is changed from parallel to antiparallel. Spin-triplet pair
correlations in FSF heterostructures induced by non-collinearity of
magnetizations are investigated by solving the Gor'kov equations in the clean
limit. Unlike diffusive FSF junctions, where the triplet correlations have a
long-range monotonic decay, we show that in clean ferromagnet-superconductor
hybrids both singlet and triplet pair correlations induced in the F layers are
oscillating and power-law decaying with the distance from the S-F interfaces.",0605355v1
2006-05-23,Josephson coupling through ferromagnetic heterojunctions with noncollinear magnetizations,"We study the Josephson effect in clean heterojunctions that consist of
superconductors connected through two metallic ferromagnets with insulating
interfaces. We solve the scattering problem based on the Bogoliubov--de Gennes
equation for any relative orientation of in-plane magnetizations, arbitrary
transparency of interfaces, and mismatch of Fermi wave vectors. Both spin
singlet and triplet superconducting correlations are taken into account, and
the Josephson current is calculated as a function of the ferromagnetic layers
thicknesses and of the angle $\alpha$ between their magnetizations. We find
that the critical Josephson current $I_c$ is a monotonic function of $\alpha$
when the junction is far enough from $0-\pi$ transitions. This holds when
ferromagnets are relatively weak. For stronger ferromagnets, variation of
$\alpha$ induces switching between 0 and $\pi$ states and $I_c(\alpha)$ is
non-monotonic function, displaying characteristic dips at the transitions.
However, the non-monotonicity is the effect of a weaker influence of the
exchange potential in the case of non-parallel magnetizations. No substantial
impact of spin-triplet superconducting correlations on the Josephson current
has been found in the clean limit. Experimental control of the critical current
and $0-\pi$ transitions by varying the angle between magnetizations is
suggested.",0605562v2
2006-06-06,Variational Mote Carlo Study of Flat Band Ferromagnetism -- Application to CeRh_3 B_2,"A new mechanism for ferromagnetism in CeRh_3B_2 is proposed on the basis of
variational Monte Carlo results. In a one-dimensional Anderson lattice where
each 4f electron hybridizes with a ligand orbital between neighboring Ce sites,
ferromagnetism is stabilized due to a nearly flat band which is a mixture of
conduction and 4f electron states. Because of the strong spin-orbit interaction
in 4f electron states, and of considerable amount of hybridization in the
nearly flat band, the magnetic moments from 4f and conduction electrons tend to
cancel each other. The resultant ferromagnetic moment becomes smaller as
compared with the local 4f moment, and the Fermi surface in the ferromagnetic
ground state is hardly affected by the presence of 4f electrons. These
theoretical results are consistent with experimental observations in CeRh_3B_2
by neutron scattering and dHvA effects.",0606143v1
2006-06-13,Magneto-optical investigation of the field-induced spin-glass insulator to ferromagnetic metallic transition of the bilayer manganite (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$,"We measured the magneto-optical response of
(La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ in order to investigate the
microscopic aspects of the magnetic field driven spin-glass insulator to
ferromagnetic metal transition. Application of a magnetic field recovers the
ferromagnetic state with an overall redshift of the electronic structure,
growth of the bound carrier localization associated with ferromagnetic domains,
development of a pseudogap, and softening of the Mn-O stretching and bending
modes that indicate a structural change. We discuss field- and
temperature-induced trends within the framework of the Tomioka-Tokura global
electronic phase diagram picture and suggest that controlled disorder near a
phase boundary can be used to tune the magnetodielectric response. Remnants of
the spin-glass insulator to ferromagnetic metallic transition can also drive
300 K color changes in (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$.",0606339v1
2006-06-19,Magnetic phase diagram of the Kondo lattice model with quantum localized spins,"The magnetic phase diagram of the ferromagnetic Kondo lattice model is
determined at T=0 in 1D, 2D, and 3D for various magnitudes of the quantum
mechanical localized spins ranging from S=1/2 to classical spins. We consider
the ferromagnetic phase, the paramagnetic phase, and the
ferromagnetic/antiferromagnetic phase separated regime. There is no significant
influence of the spin quantum number on the phase boundaries except for the
case S=1/2, where the model exhibits an instability of the ferromagnetic phase
with respect to spin disorder. Our results give support, at least as far as the
low temperature magnetic properties are concerned, to the classical treatment
of the S=3/2-spins in the intensively investigated manganites, for which the
ferromagnetic Kondo-lattice model is generally employed to account for
magnetism.",0606485v1
2006-08-04,Compositional tuning of ferromagnetism in Ga1-xMnxP,"We report the magnetic and transport properties of Ga1-xMnxP synthesized via
ion implantation followed by pulsed laser melting over a range of x, namely
0.018 to 0.042. Like Ga1-xMnxAs, Ga1-xMnxP displays a monotonic increase of the
ferromagnetic Curie temperature with x associated with the hole-mediated
ferromagnetic phase while thermal annealing above 300 C leads to a quenching of
ferromagnetism that is accompanied by a reduction of the substitutional
fraction of Mn. However, contrary to observations in Ga1-xMnxAs, Ga1-xMnxP is
non-metallic over the entire composition range. At the lower temperatures over
which the films are ferromagnetic, hole transport occurs via hopping conduction
in a Mn-derived band; at higher temperatures it arises from holes in the
valence band which are thermally excited across an energy gap that shrinks with
x.",0608133v1
2006-09-07,"Mn-doped Ga(As,P) and (Al,Ga)As ferromagnetic semiconductors","A remarkable progress towards functional ferromagnetic semiconductor
materials for spintronics has been achieved in p-type (Ga,Mn)As. Robust
hole-mediated ferromagnetism has, however, been observed also in other III-V
hosts such as antimonides, GaP or (Al,Ga)As which opens a wide area of
possibilities for optimizing the host composition towards higher ferromagnetic
Curie temperatures. Here we explore theoretically ferromagnetism and Mn
incorporation in Ga(As,P) and (Al,Ga)As ternary hosts. While alloying (Ga,Mn)As
with Al has only a small effect on the Curie temperature we predict a sizable
enhancement of Curie temperatures in the smaller lattice constant Ga(As,P)
hosts. Mn-doped Ga(As,P) is also favorable, as compared to (Al,Ga)As, with
respect to the formation of carrier and moment compensating interstitial Mn
impurities. In (Ga,Mn)(As,P) we find a marked decrease of the partial
concentration of these detrimental impurities with increasing P content.",0609158v1
2006-12-23,Magnetic phase diagram of Ce2Fe17,"Rare-earth-based permanent-magnet materials rich in iron have relatively low
ferromagnetic ordering temperatures. This is believed to be due to the presence
of antiferromagnetic exchange interactions, besides the ferromagnetic
interactions responsible for the magnetic order. The magnetic properties of
Ce2Fe17 are anomalous. Instead of ferromagnetic, it is antiferromagnetic, and
instead of one ordering temperature, it shows two, at the Neel temperature TN ~
208 K and at TT ~ 124 K. Ce2Fe17, doped by 0.5% Ta, also shows two ordering
temperatures, one to an antiferromagnetic phase, at TN ~ 214 K, and one to a
ferromagnetic phase, at T0 ~ 75 K. In order to clarify this behavior,
single-crystalline samples were prepared by solution growth, and characterized
by electron microscopy, single crystal x-ray diffraction, temperature-dependent
specific heat, and magnetic field and temperature-dependent electrical
resistivity and magnetization. From these measurements, magnetic H-T phase
diagrams were determined for both Ta-doped Ce2Fe17 and undoped Ce2Fe17. These
phase diagrams can be very well described in terms of a theory that gives
magnetic phase diagrams of systems with competing antiferro- and
ferromagnetism.",0612603v1
2007-01-19,"Reversible Ferromagnetic Switching in Zno:(Co,Mn) Powders","We report here on the magnetic properties of ZnO:Mn and ZnO:Co doped
nanoparticles. We have found that the ferromagnetism of ZnO:Mn can be switched
on and off by consecutive low-temperature annealings in O2 and N2 respectively,
while the opposite phenomenology was observed for ZnO:Co. These results suggest
that different defects (presumably n-type for ZnO:Co and p-type for ZnO:Mn) are
required to induce a ferromagnetic coupling in each case. We will argue that
ferromagnetism is likely to be restricted to a very thin, nanometric layer, at
the grain surface. These findings reveal and give insight into the dramatic
relevance of surface effects for the occurrence of ferromagnetism in ZnO doped
oxides.",0701473v1
2007-01-25,Role of magnetic scattering in 0-pi transitions in a superconductor/ferromagnetic metal/superconductor junction,"We study the influence of magnetic scattering on the Josephson critical
current, Ic, in a superconductor/ferromagnetic metal/superconductor (SFS)
junction by a tunneling Hamiltonian approach. An analytical formula of Ic is
given in the fourth order perturbation theory as regards the tunneling matrix
element. The Ic exhibits the damped oscillatory dependence on the thickness of
the ferromagnetic metal, d, and shows the transition between 0- and pi-states
with d. When the superconducting transition temperature is comparable to the
ferromagnetic Curie temperature, the period of oscillation is obviously changed
by increasing temperature, T, due to the magnetic scattering, which induces the
0-pi transition with T. The magnetic scattering provides rich variety of
Josephson effect in the SFS junction. Our results present an appropriate
condition of a superconductor and a ferromagnetic metal to control the 0- and
the pi-states.",0701610v2
2007-04-03,Fabrication of half metallicity in a ferromagnetic metal,"We investigate the growth of half metallic phase in a ferromagnetic material
using state-of-the-art full potential linearized augmented plane wave method.
To address the issue, we have substituted Ti at the Ru-sites in SrRuO3, where
SrRuO3 is a ferromagnetic material. Calculated results establish Ti4+ valence
states (similar to SrTiO3), which was predicted experimentally. Thus, Ti
substitution dilutes the Ru-O-Ru connectivity, which is manifested in the
calculated results in the form of significant band narrowing leading to finite
gap between t2g and eg bands. At 75% substitution, a large gap (> 2 eV) appears
at the Fermi level, e_F in the up spin density of states, while the down spin
states contributes at e_F characterizing the system a half-metallic
ferromagnet. The t2g - eg gap can be tailored judiciously by tuning Ti
concentrations to minimize thermal effects, which is often the major bottleneck
to achieve high spin polarization at elevated temperatures in other materials.
This study, thus, provides a novel but simple way to fabricate half-metallicity
in ferromagnetic materials, which are potential candidates for spin-based
technology.",0704.0321v1
2007-08-10,Superconductivity on the border of weak itinerant ferromagnetism in UCoGe,"We report the coexistence of ferromagnetic order and superconductivity in
UCoGe at ambient pressure. Magnetization measurements show that UCoGe is a weak
ferromagnet with a Curie temperature T_{C}= 3 K and a small ordered moment
$m_{0}$= 0.03 $\mu_B$. Superconductivity is observed with a resistive
transition temperature T_{s} = 0.8 K for the best sample. Thermal-expansion and
specific-heat measurements provide solid evidence for bulk magnetism and
superconductivity. The proximity to a ferromagnetic instability, the defect
sensitivity of T_{s}, and the absence of Pauli limiting, suggest triplet
superconductivity mediated by critical ferromagnetic fluctuations.",0708.1388v1
2007-08-21,Magnetic and transport properties of the one-dimensional ferromagnetic Kondo lattice model with an impurity,"We have studied the ferromagnetic Kondo lattice model (FKLM) with an Anderson
impurity on finite chains with numerical techniques. We are particularly
interested in the metallic ferromagnetic phase of the FKLM. This model could
describe either a quantum dot coupled to one-dimensional ferromagnetic leads
made with manganites or a substitutional transition metal impurity in a MnO
chain. We determined the region in parameter space where the impurity is empty,
half-filled or doubly-occupied and hence where it is magnetic or nonmagnetic.
The most important result is that we found, for a wide range of impurity
parameters and electron densities where the impurity is magnetic, a singlet
phase located between two saturated ferromagnetic phases which correspond
approximately to the empty and double-occupied impurity states. Transport
properties behave in general as expected as a function of the impurity
occupancy and they provide a test for a recently developed numerical approach
to compute the conductance. The results obtained could be in principle
reproduced experimentally in already existent related nanoscopic devices or in
impurity doped MnO nanotubes.",0708.2826v2
2007-09-10,Exotic Ground State Phases of $S=1/2$ Heisenberg $Δ$-Chain with Ferromagnetic Main Chain,"The ground state phase diagram of the spin-1/2 Heisenberg frustrated
$\Delta$-chain with a ferromagnetic main chain is investigated. In addition to
the ferromagnetic phase, various nonmagnetic ground states are found. If the
ferromagnetic coupling between apical spins and the main chain is strong, this
model is approximated by a spin-1 bilinear-biquadratic chain and the spin
quadrupolar phase with spin-2 gapless excitation is realized in addition to the
Haldane and ferromagnetic phases. In the regime where the coupling between the
apical spins and the main chain is weak, the numerical results which suggest
the possibility of a series of phase transitions among different nonmagnetic
phases are obtained. Physical pictures of these phases are discussed based on
the numerical results.",0709.1423v3
2007-10-31,Charge Density Wave Driven Ferromagnetism in the Periodic Anderson Model,"We demonstrate the existence of ferromagnetism in the Periodic Anderson Model
(PAM) at conduction-band filling near a quarter. We show that this
ferromagnetism is not supported by Ruderman-Kittel-Kasuya-Yosida (RKKY)
interactions but is instead driven by the precursors of charge density wave
(CDW) formation in the conduction electron band. To study the effect of spatial
correlations, we compare Dynamical Mean field Approximation (DMFA) and
Dynamical Cluster Approximation (DCA) results. We find that both RKKY and CDW
driven ferromagnetism persist as short-range correlations are incorporated into
the theory. Both DMFA and DCA show the precursors of CDW formation through the
strong enhancement of the d-electron CDW susceptibility as the temperature
decreases, up to the ferromagnetic transition temperature. In addition, the DCA
captures the signal of a band gap opening due to Peierls instability.",0710.5937v1
2007-11-02,Origin of ferromagnetic response in diluted magnetic semiconductors and oxides,"This paper reviews the present understanding of the origin of ferromagnetic
response of diluted magnetic semiconductors and diluted magnetic oxides as well
as in some nominally magnetically undoped materials. It is argued that these
systems can be grouped into four classes. To the first belong composite
materials in which precipitations of a known ferromagnetic, ferrimagnetic or
antiferromagnetic compound account for magnetic characteristics at high
temperatures. The second class forms alloys showing chemical nano-scale phase
separation into the regions with small and large concentrations of the magnetic
constituent. To the third class belong (Ga,Mn)As, heavily doped p-(Zn,Mn)Te,
and related semiconductors. In these solid solutions the theory built on p-d
Zener's model of hole-mediated ferromagnetism and on either the Kohn-Luttinger
kp theory or the multi-orbital tight-binding approach describes qualitatively,
and often quantitatively many relevant properties. Finally, in a number of
carrier-doped DMS and DMO a competition between long-range ferromagnetic and
short-range antiferromagnetic interactions and/or the proximity of the
localisation boundary lead to an electronic nano-scale phase separation.",0711.0340v1
2007-11-29,The underscreened Kondo lattice model applied to heavy fermion uranium compounds,"We present theoretical results for the underscreened Kondo lattice model with
localized S=1 spins coupled to a conduction band through a Kondo coupling,
$J_K$, and interacting among them ferromagnetically. We use a fermionic
representation for the spin operators and expand the Hamiltonian in terms of
bosonic fields. For large values of $J_K$, we obtain a ferromagnetically
ordered solution and a Kondo regime with a Kondo temperature, $T_K$, larger
than the Curie temperature, $T_C$. This finding suggests a scenario for a
coexistence of Kondo effect and ferromagnetic order. In some uranium compounds,
like $UTe$ or $UCu_{0.9}Sb_{2}$, this kind of coexistence has been
experimentally observed: they order ferromagnetically with a Curie temperature
of order $T_C \sim 100K$ and exhibit a Kondo behavior for $T > T_C$. The
proposed underscreened Kondo lattice model accounts well for the coexistence
between magnetic order and Kondo behavior and yields to a new ``ferromagnetic
Doniach diagram''.",0711.4765v1
2007-12-18,Defect-induced ferromagnetism in fullerenes,"Based on the ab initio electronic structure calculations the picture of
ferromagnetism in polimerized C60 is proposed which seems to explain the whole
set of controversial experimental data. We have demonstrated that, in contrast
with cubic fullerene, in rhombohedral C60 the segregation of iron atoms is
energetically unprofitable which is a strong argument in favor of intrinsic
character of carbon ferromagnetism which can be caused by vacancies with
unpaired magnetic electrons. It is shown that: (i) energy formation of the
vacancies in the rhombohedral phase of C60 is essentially smaller than in the
cubic phase, (ii) there is a strong ferromagnetic exchange interactions between
carbon cages containing the vacancies, and (iii) the fusion of the magnetic
vacancies into nonmagnetic bivacancy is energetically profitable. The latter
can explain a fragility of the ferromagnetism.",0712.2928v2
2008-01-03,Fabrication and Characterization of Short Josephson Junctions with Stepped Ferromagnetic Barrier,"We present novel low-T_c superconductor-insulator-ferromagnet-superconductor
(SIFS) Josephson junctions with planar and stepped ferromagnetic interlayer. We
optimized the fabrication process to set a step in the ferromagnetic layer
thickness. Depending on the thickness of the ferromagnetic layer the ground
state of the SIFS junction has a phase drop of either 0 or pi. So-called 0-pi
Josephson junctions, in which 0 and pi ground states compete with each other,
were obtained. These stepped junctions may have a double degenerate ground
state, corresponding to a vortex of supercurrent circulating clock- or
counterclockwise and creating a magnetic flux which carries a fraction of the
magnetic flux quantum \Phi_0. Here, we limit the presentation to static
properties of short junctions.",0801.0515v2
2008-01-11,Quasiparticle Trapping In Three Terminal Ferromagnetic Tunneling Devices,"Hybrid Superconductor/Ferromagnet structures have been investigated recently
to address the interplay between ferromagnetism and superconductivity. They
also open up new routes for the investigation of out of equilibrium
superconductivity. Here, we show how it is possible for out of equilibrium
excitations produced in a superconducting thin film (S) to be localized in a
ferromagnetic trap (F). Specifically, a ferromagnetic nano-volume in good
contact with S represents a potential well for the quasiparticles (QPs) at the
gap edge. As the superconducting proximity effect is highly suppressed in F,
QPs get efficiently trapped and they share their energy with the free electrons
in the trap. The electronic temperature Te in the trap can be increased by up
to 60% from the bath temperature at 320 mK as measured by tunneling
spectroscopy using a second junction.",0801.1799v3
2008-01-31,Enhancement of ferromagnetism by Co and Ni substitution in the perovskite LaBiMn2O6+d,"The substitution of cobalt and nickel for manganese in the perovskite
manganate LaBiMn2O6+d; has been realized, leading to the perovskites
LaBiMn2-x(M)xO6+d, with M = Co, Ni and x =0-2/3. In contrast to the literature
those phases are found to be orthorhombic with Pnma symmetry. More importantly,
it is shown that ferromagnetism is enhanced, TC being increased from 80 K for
the parent compound (x = 0) to 97 K for Ni-phase, and to 130 K for the
Co-phase. Moreover, a strong competition between ferromagnetism and a
glassy-ferromagnetic state in the case of nickel or a spin-glass behaviour in
the case of cobalt is observed. These phenomena are interpreted in the frame of
a phase separation scenario, where the ferromagnetic Mn4+/Ni2+ and Mn4+/Co2+
interactions reinforce the Mn3+/Mn4+ interactions. These compounds are found to
be insulating with a relatively large positive value of thermoelectric power.",0801.4916v1
2008-02-25,Current-induced spin torques in III-V ferromagnetic semiconductors,"We formulate a theory of current-induced spin torques in inhomogeneous III-V
ferromagnetic semiconductors. The carrier spin-3/2 and large spin-orbit
interaction, leading to spin non-conservation, introduce significant conceptual
differences from spin torques in ferromagnetic metals. We determine the spin
density in an electric field in the weak momentum scattering regime,
demonstrating that the torque on the magnetization is intimately related to
spin precession under the action of both the spin-orbit interaction and the
exchange field characteristic of ferromagnetism. The spin polarization excited
by the electric field is smaller than in ferromagnetic metals and, due to lack
of angular momentum conservation, cannot be expressed in a simple closed
vectorial form. Remarkably, scalar and spin-dependent scattering do not affect
the result. We use our results to estimate the velocity of current-driven
domain walls.",0802.3717v2
2008-04-11,Simultaneous suppression of ferromagnetism and superconductivity in UCoGe by Si substitution,"We investigate the effect of substituting Si for Ge in the ferromagnetic
superconductor UCoGe. Dc-magnetization, ac-susceptibility and electrical
resistivity measurements on polycrystalline UCoGe$_{1-x}$Si$_x$ samples show
that ferromagnetic order and superconductivity are progressively depressed with
increasing Si content and simultaneously vanish at a critical concentration
$x_{cr} \simeq 0.12$. The non-Fermi liquid temperature variation in the
electrical resistivity near $x_{cr}$ and the smooth depression of the ordered
moment point to a continuous ferromagnetic quantum phase transition.
Superconductivity is confined to the ferromagnetic phase, which provides
further evidence for magnetically mediated superconductivity.",0804.1891v1
2008-05-17,Ferromagnetic tendency at the surface of CE charge-ordered manganites,"Most previous investigations have shown that the surface of a ferromagnetic
material may have antiferromagnetic tendencies. However, experimentally the
opposite effect has been recently observed: ferromagnetism appears in some
nano-sized manganites with a composition such that the antiferromagnetic
charge-ordered CE state is observed in the bulk. A possible origin is the
development of ferromagnetic correlations at the surface of these small
systems. To clarify these puzzling experimental observations, we have studied
the two-orbital double-exchange model near half-doping n=0.5, using open
boundary conditions to simulate the surface of either bulk or nano-sized
manganites. Considering the enhancement of surface charge density due to a
possible AO termination (A = trivalent/divalent ion composite, O = oxygen), an
unexpected surface phase-separated state emerges when the model is studied
using Monte Carlo techniques on small clusters. This tendency suppresses the CE
charge ordering and produces a weak ferromagnetic signal that could explain the
experimental observations.",0805.2702v2
2008-08-17,Inhomogeneous Phases in a Double-Exchange Magnet with Long Range Coulomb Interactions,"We consider a model with competing double-exchange (ferromagnetic) and
super-exchange (anti-ferromagnetic) interactions in the regime where phase
separation takes place. The presence of a long range Coulomb interaction
frustrates a macroscopic phase separation, and favors microscopically
inhomogeneous configurations. We use the variational Hartree-Fock approach, in
conjunction with Monte-Carlo simulations to study the geometry of such
configurations in a two-dimensional system. We find that an array of diamond
shaped ferromagnetic droplets is the preferred configuration at low electronic
densities, while alternating ferromagnetic and anti-ferromagnetic diagonal
stripes emerge at higher densities. These findings are expected to be relevant
for thin films of colossal magneto-resistive manganates.",0808.2290v2
2008-09-17,The effect of Coulomb interaction at ferromagnetic-paramagnetic metallic perovskite junctions,"We study the effect of Coulomb interactions in transition metal oxides
junctions. In this paper we analyze charge transfer at the interface of a three
layer ferromagnetic-paramagnetic-ferromagnetic metallic oxide system. We choose
a charge model considering a few atomic planes within each layer and obtain
results for the magnetic coupling between the ferromagnetic layers. For large
number of planes in the paramagnetic spacer we find that the coupling
oscillates with the same period as in RKKY but the amplitude is sensitive to
the Coulomb energy. At small spacer thickness however, large differences may
appear as function of : the number of electrons per atom in the ferromagnetics
and paramagnetics materials, the dielectric constant at each component, and the
charge defects at the interface plane emphasizing the effects of charge
transfer.",0809.2984v1
2008-09-25,Magnetic Behavior of Single Crystalline Pr_{5}Ge_{3} and Tb_{5}Ge_{3}Compounds,"The results of the magnetization studies on Pr_{5}Ge_{3}and Tb_{5}Ge_{3}
single crystals are reported. Single Crystals of Pr_{5}Ge_{3} and Tb_{5}Ge_{3}
compounds were successfully grown by Czochralski method. These compounds
crystallize in a Mn_{5}Si_{3} type hexagonal structure with space group
P6_{3}/mcm. Ferromagnetic correlations set in at around 36 K in Pr_{5}Ge_{3} in
the ab plane followed by an antiferromagnetic transition at 13 K. Along the
c-axis the magnetization shows a ferromagnetic transition around 13 K with an
overall ferrimagnetic behavior. At 2K, the magnetic isotherm of the compound
along [0001] direction is typical for a ferromagnet, while a field induced
ferromagnetic type response is observed along the [10\overline{\mathit{1}}0]
direction. Hexagonal ab plane or [10\overline{\mathit{1}}0] direction was found
to be the easy axis of magnetization. Tb_{5}Ge_{3} orders antiferromagneticaly
at 85 K with the hexagonal ab plane as easy axis of magnetization. The compound
shows a field induced ferromagnetic behavior in its magnetic isotherm at 2 K.",0809.4467v2
2008-10-07,Nontrivial interplay between superconductivity and spin-orbit coupling in non-centrosymmetric ferromagnets,"Motivated by the recent discoveries of ferromagnetic and non-centrosymmetric
superconductors, we present a mean-field theory for a superconductor that
\textit{both} lacks inversion symmetry and displays ferromagnetism, a scenario
which is believed to be realized in UIr. We study the interplay between the
order parameters to clarify how superconductivity is affected by the presence
of ferromagnetism and spin-orbit coupling. One of our key findings is that the
spin-orbit coupling seems to enhance both ferromagnetism and superconductivity
in all spin channels. We discuss our results in the context of the heavy
fermion superconductor UIr and analyze possible symmetries of the order
parameter by the group theory method.",0810.1281v1
2008-10-08,Transverse spin diffusion in ferromagnets,"We discuss the dissipative diffusion-type term of the form
$\mathbf{m}\times\nabla^2\partial_t\mathbf{m}$ in the phenomenological
Landau-Lifshitz equation of ferromagnetic precession, which describes enhanced
Gilbert damping of finite-momentum spin waves. This term arises physically from
itinerant-electron spin flows through a perturbed ferromagnetic configuration
and can be understood to originate in the ferromagnetic spin pumping in the
continuum limit. We develop a general phenomenology as well as provide
microscopic theory for the Stoner and s-d models of ferromagnetism, taking into
account disorder and electron-electron scattering. The latter is manifested in
our problem through the Coulomb drag between the spin bands. The spin diffusion
is identified in terms of the transverse spin conductivity, in analogy with the
Einstein relation in the kinetic theory.",0810.1340v2
2008-10-09,Polaron formation in the optimally doped ferromagnetic manganites La0.7Ba0.3MnO3 and La0.7Ba0.3MnO3,"The nature of the polarons in the optimally doped colossal magnetoresistive
(CMR) materials La0.7Ba0.3MnO3 (LBMO) and La0.7Sr0.3MnO3 (LSMO) is studied by
elastic and inelastic neutron scattering. In both materials, dynamic nanoscale
polaron correlations develop abruptly in the ferromagnetic state. However, the
polarons are not able to lock-in to the lattice and order, in contrast to the
behavior of La0.7Ca0.3MnO3. Therefore ferromagnetic order in LBMO and LSMO
survives their formation, explaining the conventional second order nature of
the ferromagnetic--paramagnetic transition. Nevertheless, the results
demonstrate that the fundamental mechanism of polaron formation is a universal
feature of these ferromagnetic perovskite manganites.",0810.1772v2
2008-11-03,Coexistence of Ferromagnetism with Spin Triplet Superconductivity,"The experimental results for ZrZn$_{2}$, URhGe, and in some pressure ranges
also for UGe$_{2}$, have shown that the ferromagnetic superconductors are weak
itinerant ferromagnets. Guided by these results we describe the phenomenon of
coexistence between equal spin triplet pairing superconductivity (SC) and
ferromagnetism (F) using the extended Stoner model, which includes in
Hamiltonian the on-site Coulomb interaction, $U$, and occupation dependent
hopping integral. We use Hartree-Fock (H-F) approximation and the Green
functions technique. In the H-F approximation the on-site Coulomb interaction
plays the role of the on-site exchange (Hund's) field. All inter-site
interactions will have included the inter-site kinetic correlation,
$<c_{i\sigma}^{+}c_{j\sigma}>$, within the H-F approximation. We introduce the
pressure-dependence to the hopping integral. Numerical results are compared
with experimental data for ZrZn$_{2}$. The kinetic correlation creates the
superconductivity without help of negative values of Coulomb interactions. The
model can explain stimulation of triplet SC by the weak itinerant
ferromagnetism. This effect was observed experimentally in ZrZn$_{2}$.
Numerical analysis also confirms the experimental effect of decrease in
critical temperatures (Curie and superconducting) with increasing external
pressure.",0811.0278v1
2008-11-21,Room temperature ferromagnetism in carbon-implanted ZnO,"Unexpected ferromagnetism has been observed in carbon doped ZnO films grown
by pulsed laser deposition [Phys. Rev. Lett. 99, 127201 (2007)]. In this
letter, we introduce carbon into ZnO films by ion implantation. Room
temperature ferromagnetism has been observed. Our analysis demonstrates that
(1) C-doped ferromagnetic ZnO can be achieved by an alternative method, i.e.
ion implantation, and (2) the chemical involvement of carbon in the
ferromagnetism is indirectly proven.",0811.3487v1
2008-12-02,Hybridization of Spin and Plasma Waves in Josephson Tunnel Junctions Containing a Ferromagnetic Layer,"We study dynamics of tunnel Josephson junctions with a thin ferromagnetic
layer F [superconductor-insulator-ferromagnet-superconductor (SIFS) junctions].
On the basis of derived equations relating the superconducting phase and
magnetic moment to each other we analyze collective excitations in the system
and find a new mode which is a hybrid of plasmalike and spin waves. The latter
are coupled together in a broad range of parameters characterizing the system.
Using the solution describing the collective modes we demonstrate that besides
the Fiske steps new peaks appear on the I-V characteristics due to oscillations
of the magnetic moment M in the ferromagnetic layer. Thus, by measuring the I-V
curve of the SIFS junctions, one can extract information about the spectrum of
spin excitations in the ferromagnet F.",0812.0512v3
2008-12-10,Possible d0 ferromagnetism in MgO doped with nitrogen,"We study the possibility of d0 ferromagnetism in the compound
  MgO doped with nitrogen (N). The Haldane-Anderson impurity model is
formulated within the tight-binding approximation for determining the host
band-structure and the impurity-host hybridization. Using the quantum Monte
Carlo technique, we observe a finite local moment for an N impurity, and
long-range ferromagnetic correlations between two N impurities. The
ferromagnetic correlations are strongly influenced by the impurity bound state.
When the ferromagnetic correlation between a pair of impurities is mapped onto
the isotropic Heisenberg model for two spin-1/2 particles, the effective
exchange constant J12 is found to increase with increasing temperature. Similar
temperature dependence of J12 is also obtained in other diluted magnetic
semiconductors, such as zincblende ZnO doped with Mn. The temperature
dependence of J12 suggests that the mapping of the full Hamiltonian onto the
spin Hamiltonian cannot fully describe the magnetic correlations for the
diluted magnetic semiconductors at least in the limit of low impurity spin.",0812.1836v1
2008-12-15,Polaron Exchange Model for Ferromagnetic Ordering in Manganite Films,"In doped manganites, the strong electron-phonon coupling due to the
Jahn-Teller effect localizes the conduction-band electrons as polarons. This
results in polarons are carriers responsible for transport and ferromagnetic
ordering rather than the bare eg electrons, and sequentially polaron exchange
model is emerged for describing ferromagnetic ordering. In
Pr0.7(Sr1-xCax)0.3MnO3(x=0.3-0.6) epitaxial thin films, for higher-temperature
paramagnetic state and lower-temperature ferromagnetic state, both the
temperature dependent transports present behaviors of small polaron; for
paramagnetic-ferromagnetic transition, the experimental data of Curie
temperature are well described by an energy balance expression induced by
polaron exchange model. These results demonstrate that the polaron models are
proper ways to describe the strongly correlated electrons in the doped
manganites.",0812.2722v1
2009-01-28,Variational Monte Carlo study of ferromagnetism in the two-orbital Hubbard model on a square lattice,"To understand effects of orbital degeneracy on magnetism, in particular
effects of Hund's rule coupling, we study the two-orbital Hubbard model on a
square lattice by a variational Monte Carlo method. As a variational wave
function, we consider a Gutzwiller projected wave function for a staggered spin
and/or orbital ordered state. We find a ferromagnetic phase with staggered
orbital order around quarter-filling, i.e., electron number n=1 per site, and
an antiferromagnetic phase without orbital order around half-filling n=2. In
addition, we find that another ferromagnetic phase without orbital order
realizes in a wide filling region for large Hund's rule coupling. These two
ferromagnetic states are metallic except for quarter filling. We show that
orbital degeneracy and strong correlation effects stabilize the ferromagnetic
states.",0901.4415v1
2009-04-03,Muon spin rotation and relaxation in the superconducting ferromagnet UCoGe,"We report zero-field muon spin rotation and relaxation measurements on the
superconducting ferromagnet UCoGe. Weak itinerant ferromagnetic order is
detected by a spontaneous muon spin precession frequency below the Curie
temperature $T_C = 3$ K. The $\mu^+$ precession frequency persists below the
bulk superconducting transition temperature $T_{sc} = 0.5$ K, where it measures
a local magnetic field $B_{loc} = 0.015$ T. The amplitude of the $\mu$SR signal
provides unambiguous proof for ferromagnetism present in the whole sample
volume. We conclude ferromagnetism coexists with superconductivity on the
microscopic scale.",0904.0532v1
2009-05-29,Ultracold Gases of Ytterbium: Ferromagnetism and Mott States in an SU(6) Fermi System,"It is argued that ultracold quantum degenerate gas of ytterbium $^{173}$Yb
atoms having nuclear spin $I = 5/2$ exhibits an enlarged SU$(6)$ symmetry.
Within the Landau Fermi liquid theory, stability criteria against Fermi liquid
(Pomeranchuk) instabilities in the spin channel are considered. Focusing on the
SU$(n > 2)$ generalizations of ferromagnetism, it is shown within mean-field
theory that the transition from the paramagnet to the itinerant ferromagnet is
generically first order. On symmetry grounds, general SU$(n)$ itinerant
ferromagnetic ground states and their topological excitations are also
discussed. These SU$(n > 2)$ ferromagnets can become stable by increasing the
scattering length using optical methods or in an optical lattice. However, in
an optical lattice at current experimental temperatures, Mott states with
different filling are expected to coexist in the same trap, as obtained from a
calculation based on the SU$(6)$ Hubbard model.",0905.4948v3
2009-06-09,Stable half-metallic ferromagnetism in nonstoichiometric cubic binary chromium chalcogenides,"We find that three nonstoichiometric cubic binary chromium chalcogenides,
namely Cr3S4, Cr3Se4, and Cr3Te4, are stable half-metallic ferromagnets with
wide half-metallic gaps on the basis of systematic state-of-the-arts
first-principles calculations. We optimize their structures, and then calculate
their magnetic moments, electronic structures, formation heats, and elastic
moduli and investigate their structural stability and robustness of
ferromagnetism against antiferromagnetic fluctuations. Our calculated results
show that the three sulvanite phases are structurally stable and
ferromagnetically robust, and hence could be realized as epitaxial thin films.
We attribute the structural and ferromagnetic stability and the better
half-metallicity to their special effective Cr valence 2.667+. These findings
will open doors for much more high-performance spintronic materials compatible
with current semiconductor technology.",0906.1794v2
2009-07-16,Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms,"Can a gas of spin-up and spin-down fermions become ferromagnetic due to
repulsive interactions? This question which has not yet found a definitive
theoretical answer was addressed in an experiment with an ultracold
two-component Fermi gas. The observation of non-monotonic behavior of lifetime,
kinetic energy, and size for increasing repulsive interactions provides strong
evidence for a phase transition to a ferromagnetic state. It implies that
itinerant ferromagnetism of delocalized fermions is possible without lattice
and band structure and validates the most basic model for ferromagnetism
introduced by Stoner.",0907.2888v1
2009-08-17,Enhancement of superconductivity near the ferromagnetic quantum critical point in UCoGe,"We report a high-pressure single crystal study of the superconducting
ferromagnet UCoGe. Ac-susceptibility and resistivity measurements under
pressures up to 2.2 GPa show ferromagnetism is smoothly depressed and vanishes
at a critical pressure $p_c = 1.4$ GPa. Near the ferromagnetic critical point
superconductivity is enhanced. Upper-critical field measurements under pressure
show $B_{c2}(0)$ attains remarkably large values, which provides solid evidence
for spin-triplet superconductivity over the whole pressure range. The obtained
$p-T$ phase diagram reveals superconductivity is closely connected to a
ferromagnetic quantum critical point hidden under the superconducting `dome'.",0908.2325v1
2009-08-20,Pressure-phase diagram of UCoGe by ac-susceptibility and resistivity measurements,"UCoGe is one of the few compounds showing the coexistence of ferromagnetism
and superconductivity at ambient pressure. With T_Curie = 3 K and T_SC = 0.6 K
it is near a quantum phase transition; the pressure needed to suppress the
magnetism is slightly higher than 1 GPa. We report simultaneous resistivity and
ac-susceptibility measurements under pressure on a polycrystal with very large
single-crystalline domains and a resistivity ratio of about 6. Both methods
confirm the phase diagram established before by resistivity measurements on a
polycrystal. The ferromagnetic phase is suppressed for P approximately 1.2 GPa.
Astonishingly, the superconductivity persists at pressures up to at least 2.4
GPa. In other superconducting and ferromagnetic heavy fermion compounds like
UGe2 and URhGe, the superconducting state is situated only inside the larger
ferromagnetic region. Therefore, UCoGe seems to be the first example where
superconductivity extends from the ferromagnetic to the paramagnetic region.",0908.2945v1
2009-09-30,Two-Dimensional Spin Dynamics in the Itinerant Ferromagnet LaCoPO Revealed by Magnetization and $^{31}$P-NMR Measurements,"We have performed magnetization and $^{31}$P-NMR measurements on the
itinerant ferromagnet LaCoPO (Curie temperature $T_{\rm Curie}\sim 44$ K) with
a layered structure in order to investigate spin dynamics in the paramagnetic
state. The linear scaling between the Knight shift $K$ at the P site and the
bulk susceptibility $\chi$ above $T_{\rm Curie}$ indicates that the P nucleus
is suitable for investigating magnetic properties. The temperature and magnetic
field dependences of the nuclear spin-lattice relaxation rate divided by the
temperature $1/T_1T$ at the P site show characteristic features of itinerant
ferromagnets, such as ZrZn$_2$ and Y(Co$_{1-x}$Al$_x$)$_2$. In addition, the
relationship between $1/T_1T$ and $\chi$ above $T_{\rm Curie}$ suggests that
ferromagnetic fluctuations possess a two-dimensional (2D) characteristic. The
present data show that LaCoPO is a unique ferromagnet, where the 2D
fluctuations anticipated from the crystal structure are predominant down to
almost $T_{\rm Curie}$.",0909.5641v1
2009-10-12,Room-temperature ferromagnetism in graphite driven by 2D networks of point defects,"Ferromagnetism in carbon-based materials is appealing for both applications
and fundamental science purposes because carbon is a light and bio-compatible
material that contains only s and p electrons in contrast to traditional
ferromagnets based on 3d or 4f electrons. Here we demonstrate direct evidence
for ferromagnetic order locally at defect structures in highly oriented
pyrolytic graphite (HOPG) with magnetic force microscopy and in bulk
magnetization measurements at room temperature. Magnetic impurities have been
excluded as the origin of the magnetic signal after careful analysis supporting
an intrinsic magnetic behavior of carbon. The observed ferromagnetism has been
attributed to originate from unpaired electron spins localized at grain
boundaries of HOPG. Grain boundaries form two-dimensional arrays of point
defects, where their spacing depends on the mutual orientation of two grains.
Depending on the distance between these point defects, scanning tunneling
spectroscopy of grain boundaries showed two intense split localized states for
small distances between defects (< 4 nm) and one localized state at the Fermi
level for large distances between defects (> 4 nm).",0910.2130v1
2009-11-02,Inverse Spin-Galvanic Effect in a Topological-Insulator/Ferromagnet Interface,"When a ferromagnet is deposited on the surface of a topological insulator the
topologically protected surface state develops a gap and becomes a
2-dimensional quantum Hall liquid. We demonstrate that the Hall current in such
a liquid, induced by an external electric field, can have a large effect on the
magnetization dynamics of the ferromagnet by changing the effective anisotropy
field. This change is dissipationless and may be substantial even in weakly
spin-orbit coupled ferromagnets. We study the possibility of dissipationless
current-induced magnetization reversal in monolayer-thin, insulating
ferromagnets with a soft perpendicular anisotropy and discuss possible
applications of this effect.",0911.0106v1
2009-11-09,High frequency susceptibility of a weak ferromagnet with magnetostrictive magnetoelectric coupling: using heterostructures to tailor electromagnon frequencies,"In the first part of this work we calculate the high frequency
magnetoelectric susceptibility of a simultaneously ferroelectric and canted
antiferromagnetic (also know as weak ferromagnetic) thin film with
magnetostrictive magnetoelectric coupling. We show that a dynamic coupling
exists between the ferroelectric and optic antiferromagnetic excitations. In
the second part of the paper, we calculate using an effective medium method the
susceptibility of a heterostructure comprising alternating thin films of such a
material together with a ferromagnet. Dipolar magnetic fields serve to couple
the ferromagnetic and optic antiferromagnetic modes, which in turn couples the
ferromagnetic and ferroelectric excitations. This provides a mechanism for
creating ""electromagnon"" modes in the microwave regime which may be useful for
applications.",0911.1577v1
2009-11-15,Effect of three-body loss on itinerant ferromagnetism in an atomic Fermi gas,"A recent experiment has provided the first evidence for itinerant
ferromagnetism in an ultracold atomic gas of fermions with repulsive
interactions. However, the gas in this regime is also subject to significant
three-body loss. We adopt an extended Hertz-Millis theory to account for the
effect of loss on the transition and on the ferromagnetic state. We find that
the losses damp quantum fluctuations and thereby significantly increase the
critical interaction strength needed to induce ferromagnetism. This effect may
resolve a discrepancy between the experiment and previous theoretical
predictions of the critical interaction strength. We further illuminate the
impact of loss by studying the collective spin excitations in the ferromagnet.
Even in the fully polarized state, where loss is completely suppressed, spin
waves acquire a decay rate proportional to the three-body loss coefficient.",0911.2839v1
2010-01-27,The development of ferromagnetism in the doped topological insulator Bi2-xMnxTe3,"The development of ferromagnetism in Mn-doped Bi2Te3 is characterized through
measurements on a series of single crystals with different Mn content. Scanning
tunneling microscopy analysis shows that the Mn substitutes on the Bi sites,
forming compounds of the type Bi2-xMnxTe3, and that the Mn substitutions are
randomly distributed, not clustered. Mn doping first gives rise to local
magnetic moments with Curie-like behavior, but by the compositions
Bi1.96Mn0.04Te3 and Bi1.91Mn0.09Te3 a second order ferromagnetic transition is
observed, with Tc ~ 9-12 K. The easy axis of magnetization in the ferromagnetic
phase is perpendicular to the Bi2Te3 basal plane. Thermoelectric power and Hall
effect measurements show that the Mn-doped Bi2Te3 crystals are p-type. Angle
resolved photoemission spectroscopy measurements show that the topological
surface states that are present in pristine Bi2Te3 are also present in
ferromagnetic Mn-doped Bi2-xMnxTe3, and that the dispersion relations of the
surface states are changed in a subtle fashion.",1001.4834v1
2010-02-07,\textit{Additional} carrier-mediated ferromagnetism in GdN,"The mechanism behind ferromagnetic exchange interaction in GdN is not well
understood. It has been argued that it can be due to fourth order cross process
of \textit{d-f} mixing and \textit{d-f} exchange. An alternative explanation
suggests an anti- ferromagnetic interaction between Gd \textit{d} and N
\textit{p} induced moments on the rock salt structure which aligns the nearest
neighbor Gd \textit{f} moments ferromagnetically through the \textit{d-f}
exchange. In this paper we present results of Curie temperature in GdN as a
function of carrier density calculated within our multiband modified RKKY- like
exchange interaction. It includes realistic bandstructure of the 5\textit{d}
conduction band as an input for single particle energies. We analyze the
possibility of carrier- mediated ferromagnetism in GdN and also demonstrate a
simple phenomenological model which justifies the role of charge carriers.",1002.1426v1
2010-02-11,Spin drag in an ultracold Fermi gas on the verge of a ferromagnetic instability,"Recent experiments [Jo et al., Science 325, 1521 (2009)] have presented
evidence of ferromagnetic correlations in a two-component ultracold Fermi gas
with strong repulsive interactions. Motivated by these experiments we consider
spin drag, i.e., frictional drag due to scattering of particles with opposite
spin, in such systems. We show that when the ferromagnetic state is approached
from the normal side, the spin drag relaxation rate is strongly enhanced near
the critical point. We also determine the temperature dependence of the spin
diffusion constant. In a trapped gas the spin drag relaxation rate determines
the damping of the spin dipole mode, which therefore provides a precursor
signal of the ferromagnetic phase transition that may be used to experimentally
determine the proximity to the ferromagnetic phase.",1002.2371v2
2010-02-18,Ferromagnetic transition in the double-exchange model on the pyrochlore lattice,"The double-exchange model, which has been extensively studied in the context
of colossal magneto-resistance in perovskite manganese oxides, is known to
exhibit a ferromagnetic metallic state at low temperatures because of the
interplay between localized moments and itinerant electrons through the
Hund's-rule coupling. Here we investigate numerically the ferromagnetic
transition in the double-exchange model defined on the frustrated pyrochlore
lattice as a simple model for ferromagnetic pyrochlore oxides. We demonstrate
that the finite-size corrections are largely reduced by implementing averages
over the twisted boundary conditions in the Monte Carlo simulation, which
enables to estimate the ferromagnetic transition temperature in relatively
small size clusters. The estimate is compared with that for the non-frustrated
cubic lattice system.",1002.3642v1
2010-02-25,In-Plane Magnetoresistance on the Surface of Topological Insulator,"We study the tunneling magneto-transport properties of the Ferromagnetic
Insulator-Normal Insulator-Ferromagnetic Insulator(F$\mid$N$\mid$F) and
Ferromagnetic Insulator-Barrier Insulator-Ferromagnetic Insulator
(F$\mid$B$\mid$F) junctions on the surface of topological insulator in which
in-plane magnetization directions of both ferromagnetic sides can be parallel
and antiparallel. We derive analytical expressions for electronic conductances
of the two mentioned junctions with both parallel and antiparallel directions
of magnetization and using them calculate magnetoresistance of the two
junctions. We use thin barrier approximation for investigating the
F$\mid$B$\mid$F junction. We find that although magnetoresistance of the
F$\mid$N$\mid$F and F$\mid$B$\mid$F junctions are tunable by changing the
strength of magnetization texture, they show different behaviors with variation
of magnetization. In contrast to the magnetoresistance of F$\mid$N$\mid$F,
magnetoresistance of F$\mid$B$\mid$F junctions shows very smooth enhance by
increasing the strength of magnetization. We suggest an experimental set up to
detect our predicted effects.",1002.4882v2
2010-03-18,Magnetoresistance and transistor-like behavior of double quantum dots connected to ferromagnetic and superconductor leads,"The electric current and the magnetoresistance effect are studied in a double
quantum-dot system, where one of the dots QDa is coupled to two ferromagnetic
electrodes (F1,F2), while the second QDb is connected to a superconductor S.
For energy scales within the superconductor gap, electric conduction is allowed
by Andreev reflection processes. Due to the presence of two ferromagnetic
leads, non-local crossed Andreev reflections are possible. We found that the
magnetoresistance sign can be changed by tuning the external potential applied
to the ferromagnets. In addition, it is possible to control the current of the
first ferromagnet (F1) through the potential applied to the second one (F2). We
have also included intradot interaction and gate voltages at each quantum dot
and analyzed their influence through a mean field approximation. The
interaction reduces the current amplitudes with respect to the non-interacting
case, but the switching effect still remains as a manifestation of quantum
coherence, in scales of the order of the superconductor coherence length.",1003.3688v2
2010-03-24,Strain-induced half-metallic ferromagnetism in zinc blende CrP/MnP superlattice: First-principles study,"Using first-principles calculations within generalized gradient
approximation, the electronic and magnetic properties of zinc blende (zb)
CrP/MnP superlattice are investigated. The equilibrium lattice constant is
calculated to be $5.33\,$\AA. The stability of ferromagnetic zb CrP/MnP
superlattice against antiferromagnetism is considered and it is found that the
ferromagnetic CrP/MnP superlattice is more stable than the antiferromagnetic
one. It is shown that at the equilibrium lattice constant the CrP/MnP
superlattice does not show any half metallicity mainly due to the minority
$t_{2g}$ states of Cr and Mn. However, if strain is imposed on the CrP/MnP
superlattice then the minority $t_{2g}$ electrons shift to higher energies and
the proposed superlattice becomes a half-metal ferromagnet. The effect of
tetragonal and orthorhombic distortions on the half metallicity of zb CrP/MnP
superlattice is also discussed. It is also shown that InP-CrP/MnP/InP is a true
half-metal ferromagnet. The half metallicity and magnetization of these
superlattices are robust against tetragonal/ orthorhombic deformation.",1003.5142v2
2010-08-18,Phase-separated Ferromagnetism in Spin-imbalanced Fermi Atoms Loaded on an Optical Ladder: a DMRG study,"We consider repulsively-interacting cold fermionic atoms loaded on an optical
ladder lattice in a trapping potential. The density-matrix
renormalization-group method is used to numerically calculate the ground state
for systematically varied values of interaction U and spin imbalance p in the
Hubbard model on the ladder. The system exhibits rich structures, where a fully
spin polarized phase, spatially separated from other domains in the trapping
potential, appears for large enough U and p. The phase-separated ferromagnetism
can be captured as a real-space image of the energy gap between the
ferromagnetic and other states arising from a combined effect of Nagaoka's
ferromagnetism extended to the ladder and the density dependence of the energy
separation between competing states. We also predict how to maximize the
ferromagnetic region.",1008.3055v2
2010-09-07,Three dimensional instability of flexible ferromagnetic filament loop,"Dynamics of flexible ferromagnetic filaments in an external magnetic field is
considered. We report the existence of a buckling instability of the
ferromagnetic filament at the magnetic field reversion, which leads to the
formation of a metastable loop. Its relaxation through three dimensional
transformation of the configurations is observed experimentally and confirmed
by numerical simulations. Bending modulus of the flexible ferromagnetic
filaments synthesized by linking micron size core-shell ferromagnetic particles
with DNA fragments is estimated by comparison of the parameters of the loops
observed in the experiment with theoretical calculations. Formation of the loop
and its relaxation are characterized by the numerically calculated writhe
number. The relaxation time of the loop allows us to estimate the hydrodynamic
drag of the filament.",1009.1276v1
2010-09-09,Antiferromagnetic Order and Phase Coexistence in Antisite Disordered Double Perovskites,"In addition to the well known ferromagnetism, double perovskites are also
expected to exhibit antiferromagnetic (AF) order driven by electron
delocalisation. This has been seen in model Hamiltonian studies and confirmed
via ab initio calculations. The AF phases should occur, for example, on
sufficient electron doping of materials like Sr_2FeMoO_6 (SFMO) via La
substitution for Sr. Clear experimental indication of such AF order is limited,
possibly because of increase in antisite disorder with La doping on SFMO,
although intriguing signatures of non ferromagnetic behaviour are seen. We
study the survival of electronically driven antiferromagnetism in the presence
of spatially correlated antisite disorder and extract the signals in magnetism
and transport. We discover that A and G type AF order, that is predicted in the
clean limit, is actually suppressed less strongly than ferromagnetism by
antisite disorder. The AF phases are metallic, and, remarkably, more conducting
that the ferromagnet for similar antisite disorder. We also highlight the phase
coexistence window that connects the ferromagnetic regime to the A type
antiferromagnetic phase.",1009.1709v1
2010-10-08,Angular Dependence of the Superconducting Transition Temperature in Ferromagnet-Superconductor-Ferromagnet Trilayers,"The superconducting transition temperature, $T_c$, of a ferromagnet (F) -
superconductor (S) - ferromagnet trilayer depends on the mutual orientation of
the magnetic moments of the F layers. This effect has been previously observed
in F/S/F systems as a $T_c$ difference between parallel and antiparallel
configurations of the F layers. Here we report measurements of $T_c$ in
CuNi/Nb/CuNi trilayers as a function of the angle between the magnetic moments
of the CuNi ferromagnets. The observed angular dependence of $T_c$ is in
qualitative agreement with a F/S proximity theory that accounts for the odd
triplet component of the condensate predicted to arise for non-collinear
orientation of the magnetic moments of the F layers.",1010.1752v1
2010-11-02,Tricritical point and wing structure in the itinerant ferromagnet UGe2,"Precise resistivity measurements on the ferromagnetic superconductor UGe2
under pressure p and magnetic field H reveal a previously unobserved change of
the anomaly at the Curie temperature. Therefore, the tricritical point (TCP)
where the paramagnetic-to-ferromagnetic transition changes from a second order
to a first order transition is located in the p-T phase diagram. Moreover, the
evolution of the TCP can be followed under the magnetic field in the same way.
It is the first report of the boundary of the first order plane which appears
in the p-T-H phase diagram of weak itinerant ferromagnets. This line of
critical points starts from the TCP and will terminate at a quantum critical
point. These measurements provide the first estimation of the location of the
quantum critical point in the p-H plane and will inspire similar studies of the
other weak itinerant ferromagnets.",1011.0754v2
2010-12-06,Diamagnetic critical singularity in unconventional ferromagnetic superconductors,"The scaling properties of the free energy, the diamagnetic moment, and the
diamagnetic susceptibility above the phase transition from the ferromagnetic
phase to the phase of coexistence of ferromagnetic order and superconductivity
in unconventional ferromagnetic superconductors with spin-triplet (p-wave)
electron paring are considered. The crossover from weak to strong magnetic
induction is described for both quasi-2D (thin films) and 3D (bulk)
superconductors. The singularities of diamagnetic moment and diamagnetic
susceptibility are dumped for large variations of the pressure and, hence, such
singularities could hardly be observed in experiments. The results are obtained
within Gaussian approximation on the basis of general theory of ferromagnetic
superconductors with p-wave electron pairing.",1012.1205v3
2011-01-03,Effect of size reduction on the ferromagnetism of the manganite La1-xCaxMnO3 (x = 0.33),"In this paper we report an investigation on the ferromagnetic state and the
nature of ferromagnetic transition of nanoparticles of
$\mathrm{La_{0.67}Ca_{0.33}MnO_3}$ using magnetic measurements and neutron
diffraction. The investigation was made on nanoparticles with crystal size down
to $15$ nm. The neutron data show that even down to a size of $15$ nm the
nanoparticles show finite spontaneous magnetization ($M_S$) although the value
is much reduced compared to the bulk sample. We observed a non-monotonic
variation of the ferromagnetic to paramagnetic transition temperature $T_C$
with size $d$ and found that $T_C$ initially enhances on size reduction, but
for $d < 50$ nm it decreases again. The initial enhancement in $T_C$ was
related to an increase in the bandwidth that occured due to a compaction of the
Mn-O bond length and a straightening of the Mn-O-Mn bond angle, as determined
form the neutron data. The size reduction also changes the nature of the
ferromagnetic to paramagnetic transition from first order to second order with
critical exponents approaching mean field values. This was explained as arising
from a truncation of the coherence length by the finite sample size.",1101.0494v1
2011-01-21,Asymmetric nano graphene model applied to graphite-like room-temperature ferromagnetism,"Room temperature ferromagnetic materials composed only by light elements like
carbon, hydrogen and/or nitrogen, so called carbon magnet, are very attractive
for creating new material categories both in science and industry. Recently
several experiments suggest ferromagnetic features at a room temperature,
especially in graphite base materials. This paper reveals a mechanism of such
ferromagnetic features by modeling nanometer size asymmetric graphene molecule
by using both a semi-empirical molecular orbital method and a first principle
density function theory. Asymmetrically dihydrogenated zigzag edge graphene
molecule shows that high spin state is more stable in total molecular energy
than low spin state. Proton ion irradiation play an important role to create
such asymmetric features. Also, nitrogen contained graphite ferromagnetism is
explained by a similar asymmetric molecule model.",1101.4079v1
2011-01-31,"Electronic structure, magnetism and spin fluctuations in the superconducting weak ferromagnet Y4Co3","Results of the first principles study on the electronic structure and
magnetism of the superconducting weak ferromagnet Y$_4$Co$_3$, are presented.
Using the full potential Korringa-Kohn-Rostoker (FP-KKR) method, densities of
states, dispersion curves and magnetic moments were calculated for
quasi-ordered structural model of the compound in the framework of the local
density approximation. Spin-polarized KKR calculations confirm that weak
ferromagnetic properties of Y$_4$Co$_3$ can be attributed to only one cobalt
atom located on (2b) site in the unit cell, while other twenty Co and Y atoms
acts as a diamagnetic environment. Moreover, the magnetic Co atoms form a
quasi-one-dimensional chains along $z$ direction. The magnitude of Co(2b)
magnetic moment ($0.55~\mu_B$) markedly overestimates the experimental value
(0.23~$\mu_B$), which suggests the importance of spin fluctuations in this
system. Calculated distribution of spin magnetization in the unit cell provides
a background for discussion of the coexistence of ferromagnetism and
superconductivity in Y$_4$Co$_3$. Finally, the effect of pressure on magnetism
is discussed and compared with experimental data, also supporting weak
ferromagnetic behaviors in the system.",1101.5932v1
2011-02-17,Ferromagnetic instability and finite-temperature properties of two-dimensional electron systems with van Hove singularities,"We study a ferromagnetic tendency in the two-dimensional Hubbard model near
van Hove filling by using a functional renormalization-group method. We compute
temperature dependences of magnetic susceptibilities including incommensurate
magnetism. The ferromagnetic tendency is found to occur in a dome-shaped region
around van Hove filling with an asymmetric property: incommensurate magnetism
is favored near the edge of the dome above van Hove filling whereas a
first-order-like transition to the ferromagnetic ground state is expected below
van Hove filling. The dome-shaped phase diagram is well captured in the Stoner
theory by invoking a smaller Coulomb interaction. Triplet p-wave
superconductivity tends to develop at low temperatures inside the dome and
extends more than the ferromagnetic region above van Hove filling.",1102.3606v1
2011-04-18,The Kondo effect in magnetic impurities and ferromagnetic contacts,"Planar macroscopic magnetic tunnel junctions exhibit well defined zero bias
anomalies when a thin layer of ferromagnetic CoFe(B) nanodots is inserted
within a MgO based tunnel barrier. The conductance curves exhibit a single and
a double peak, respectively, for anti-parallel and parallel alignment of the
magnetizations of the electrodes which sandwich the tunnel barrier. This leads
to a suppression of the tunneling magnetoresistance near zero bias. We show
that the double peak structure indicates that the zero-bias anomaly is
spin-split due to a magnetic exchange interaction between the magnetic nanodots
and the ferromagnetic electrodes. Using a model based on an Anderson quantum
dot coupled to ferromagnetic leads, we show that these results imply the
coexistence of a Kondo effect and ferromagnetism.",1104.3403v1
2011-06-15,Dissipative hydrodynamic equation of a ferromagnetic Bose-Einstein condensate: Analogy to magnetization dynamics in conducting ferromagnets,"The hydrodynamic equation of a spinor Bose-Einstein condensate (BEC) gives a
simple description of spin dynamics in the condensate. We introduce the
hydrodynamic equation of a ferromagnetic BEC with dissipation originating from
the energy dissipation of the condensate. The dissipative hydrodynamic equation
has the same form as an extended Landau-Lifshitz-Gilbert (LLG) equation, which
describes the magnetization dynamics of ferromagnets interacting with
spin-polarized currents. Employing the dissipative hydrodynamic equation, we
demonstrate the magnetic domain pattern dynamics of a ferromagnetic BEC in the
presence and absence of a current of particles, and discuss the effects of the
current on domain pattern formation. We also discuss the characteristic lengths
of domain patterns that have domain walls with and without finite
magnetization.",1106.2876v4
2011-06-29,"Ferromagnetism, spiral magnetic structures and phase separation in the two-dimensional Hubbard model","The quasistatic approximation and equation-of-motion decoupling for the
electron Green's functions are applied to trace the effect of electronic
dispersion and electron correlations on the ferromagnetism of two-dimensional
itinerant-electron systems. It is found that next-nearest-neighbor hopping t'
is of crucial importance for ferromagnetism formation yielding the magnetic
phase diagram which is strongly asymmetric with respect to half-filling. At
small t' in the vicinity of half-filling the ferromagnetic phase region is
restricted by the spin-density wave instability, and far from half-filling by
one-particle (spin-polaron) instability. At t' close to t/2 ferromagnetism is
stabilized at moderate Hubbard U due to substantial curvature of the Fermi
surface which passes in the vicinity of the van Hove singularity points. The
results obtained are of possible importance for high-T_c compounds and layered
ruthenates.",1106.5842v2
2011-09-29,Orbital Ferromagnetism and Quantum Collapse in Stellar Plasmas,"The possibility of quantum collapse and characteristics of nonlinear
localized excitations is examined in dense stars with Landau orbital
ferromagnetism in the framework of conventional quantum magnetohydrodynamics
(QMHD) model including Bohm force and spin-orbit polarization effects.
Employing the concepts of effective potential and Sagdeev pseudopotential, it
is confirmed that the quantum collapse and Landau orbital ferromagnetism
concepts are consistent with the magnetic field and mass-density range present
in some white dwarf stars. Furthermore, the value of ferromagnetic-field found
in this work is about the same order of magnitude as the values calculated
earlier. It is revealed that the magnetosonic nonlinear propagations can behave
much differently in the two distinct non-relativistic and relativistic
degeneracy regimes in a ferromagnetic dense astrophysical object. Current
findings should help to understand the origin of the most important mechanisms
such as gravitational collapse and the high magnetic field present in many
compact stars.",1109.6674v1
2012-02-23,Spin current and polarization reversal through a single-molecule magnet with ferromagnetic electrodes,"We theoretically study the spin-polarized transport through a single-molecule
magnet, which is weakly coupled to ferromagnetic leads, by means of the
rate-equation approach. We consider both the ferromagnetic and
antiferromagnetic exchange-couplings between the molecular magnet and
transported electron-spin in the nonlinear tunneling regime. For the
ferromagnetic exchangecoupling, spin current exhibits step- and basin-like
behaviors in the parallel and antiparallel configurations respectively. An
interesting observation is that the polarization reversal of spin-current can
be realized and manipulated by the variation of bias voltage in the case of
antiferromagnetic exchange-coupling with antiparallel lead-configuration, which
may be useful in the development of spintronic devices, while the bias voltage
can only affect the magnitude of spin-polarization in the ferromagnetic
coupling.",1202.5173v1
2012-02-24,Quantum Griffiths singularities in ferromagnetic metals,"We present a theory of the quantum Griffiths phases associated with the
ferromagnetic quantum phase transition in disordered metals. For Ising spin
symmetry, we study the dynamics of a single rare region within the variational
instanton approach. For Heisenberg symmetry, the dynamics of the rare region is
studied using a renormalization group approach. In both cases, the rare region
dynamics is even slower than in the usual quantum Griffiths case because the
order parameter conservation of an itinerant ferromagnet hampers the relaxation
of large magnetic clusters. The resulting quantum Griffiths singularities in
ferromagnetic metals are stronger than power laws. For example, the low-energy
density of states $\rho(\epsilon)$ takes the asymptotic form
$\exp[\{-\tilde{\lambda}\log (\epsilon_0/\epsilon)\}^{3/5}]/\epsilon$ with
$\tilde{\lambda}$ being non-universal. We contrast these results with the
antiferromagnetic case in which the systems show power-law quantum Griffiths
singularities in the vicinity of the quantum critical point. We also compare
our result with existing experimental data of ferromagnetic alloy
${\rm{Ni}}_{x}{\rm{V}}_{1-x}$.",1202.5562v3
2012-06-01,d0 Ferromagnetic Interface Between Non-magnetic Perovskites,"We use computational and experimental methods to study d0 ferromagnetism at a
charge- imbalanced interface between two perovskites. In SrTiO3/KTaO3
superlattice calculations, the charge imbalance introduces holes in the SrTiO3
layer, inducing a d0 ferromagnetic half-metallic 2D electron gas at the
interface oxygen 2p orbitals. The charge imbalance overrides doping by
vacancies at realistic concentrations. Varying the constituent materials shows
ferromagnetism to be a gen- eral property of hole-type d0 perovskite
interfaces. Atomically sharp epitaxial d0 SrTiO3/KTaO3, SrTiO3 /KNbO3 and
SrTiO3 /NaNbO3 interfaces are found to exhibit ferromagnetic hysteresis at room
temperature. We suggest the behavior is due to high density of states and
exchange coupling at the oxygen t1g band in comparison with the more studied d
band t2g symmetry electron gas.",1206.0140v2
2012-06-10,High bias anomaly in YBa2Cu3O7/LaMnO_{3+delta}/YBa2Cu3O7 Superconductor/Ferromagnetic Insulator/Superconductor junctions: Evidence for a long-range superconducting proximity effect through the conduction band of a ferromagnetic insulator,"We study the perpendicular transport characteristics of small
superconductor/ferromagnetic insulator/superconductor
(YBa$_2$Cu$_3$O$_{7-x}$/LaMnO$_{3+\delta}$/YBa$_2$Cu$_3$O$_{7-x}$) tunnel
junctions. At a large bias voltage $V\sim 1$ V we observe a step-like onset of
excess current that occurs below the superconducting transition temperature
$T<T_c$ and is easily suppressed by a magnetic field. The phenomenon is
attributed to a novel type of the superconducting proximity effect of
non-equilibrium electrons injected into the conduction band of the
ferromagnetic insulator via a Fowler-Nordheim tunneling process. The occurrence
of a strongly non-equilibrium population is confirmed by the detection of
photon emission at large bias voltage. Since the conduction band in our
ferromagnetic insulator is strongly spin polarized, the long-range (20 nm) of
the observed proximity effect provides evidence for an unconventional
spin-triplet superconducting state.",1206.2053v2
2012-08-04,Critical Behavior of the Three-Dimensional Ising model with Anisotropic Bond Randomness at the Ferromagnetic-Paramagnetic Transition Line,"We study the $\pm J$ three-dimensional Ising model with a spatially
uniaxially anisotropic bond randomness on the simple cubic lattice. The $\pm J$
random exchange is applied in the $xy$ planes, whereas in the z direction only
a ferromagnetic exchange is used. After sketching the phase diagram and
comparing it with the corresponding isotropic case, the system is studied, at
the ferromagnetic-paramagnetic transition line, using parallel tempering and a
convenient concentration of antiferromagnetic bonds ($p_z=0 ; p_{xy}=0.176$).
The numerical data point out clearly to a second-order
ferromagnetic-paramagnetic phase transition belonging in the same universality
class with the 3d random Ising model. The smooth finite-size behavior of the
effective exponents describing the peaks of the logarithmic derivatives of the
order parameter provides an accurate estimate of the critical exponent
$1/\nu=1.463(3)$ and a collapse analysis of magnetization data gives an
estimate $\beta/ \nu=0.516(7)$. These results, are in agreement with previous
studies and in particular with those of the isotropic $\pm J$ three-dimensional
Ising at the ferromagnetic-paramagnetic transition line, indicating the
irrelevance of the introduced anisotropy.",1208.0883v1
2012-11-08,The Ising ferromagnet in dimension five: link and spin overlaps,"In the simple [hyper]cubic five dimension near neighbor interaction Ising
ferromagnet, extensive simulation measurements are made of the link overlap and
the spin overlap distributions. These ""two replica"" measurements are standard
in the Spin Glass context but are not usually recorded in ferromagnet
simulations. The moments and moment ratios of these distributions (the
variance, the kurtosis and the skewness) show clear critical behaviors at the
known ordering temperature of the ferromagnet. Analogous overlap effects can be
expected quite generally in Ising ferromagnets in any dimension. The link
overlap results in particular, with peaks at criticality in the kurtosis and
the skewness, also have implications for Spin Glasses.",1211.2006v2
2012-11-12,Quasiparticle Mass Enhancement and Temperature Dependence of the Electronic Structure of Ferromagnetic SrRuO3 Thin Films,"We report high-resolution angle-resolved photoemission studies of epitaxial
thin films of the correlated 4d transition metal oxide ferromagnet SrRuO3. The
Fermi surface in the ferromagnetic state consists of well-defined Landau
quasiparticles, exhibiting strong coupling to low-energy bosonic modes which
contributes to the large effective masses observed by transport and
thermodynamic measurements. Upon warming the material through its Curie
temperature, we observe a substantial decrease in quasiparticle coherence, but
negligible changes in the ferromagnetic exchange splitting, suggesting that
local moments play an important role in the ferromagnetism in SrRuO3.",1211.2828v2
2012-12-19,Ferromagnetism in ABC-trilayer graphene,"In this article we study the ferromagnetic behavior of ABC-stacked trilayer
graphene. This is done using a nearest-neighbor tight-binding model, in the
presence of long-range Coulomb interactions. For a given electron-electron
interaction g and doping level n, we determine whether the total energy is
minimized for a paramagnetic or ferromagnetic configuration of our variational
parameters. The g versus n phase diagram is first calculated for the unscreened
case. We then include the effects of screening using a simplified expression
for the fermion bubble diagram. We show that ferromagnetism in ABC-trilayer
graphene is more robust than in monolayer, in bilayer, and in ABA-trilayer
graphene. Although the screening reduces the ferromagnetic regime in
ABC-trilayer graphene, the critical doping level remains one order of magnitude
larger than in unscreened bilayer graphene.",1212.4716v1
2012-12-25,Topological Phases of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain with Frustrated Next-Nearest-Neighbour Interaction,"The spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain
with ferromagnetic next-nearest-neighbour (NNN) interaction is investigated.
The ground state is the Haldane phase for weak NNN interaction, and is the
ferromagnetic phase for weak antiferromagnetic interaction. We find a series of
topologically distinct spin-gap phases with various magnitudes of edge spins
for strong NNN interaction. The phase boundaries between these phases are
determined on the basis of the DMRG calculation with additional spins that
compensate the edge spins. It is found that each of the exact solutions with
short-range antiferromagnetic correlation on the ferromagnetic-nonmagnetic
phase boundary is representative of each spin gap phase.",1212.6012v2
2013-01-10,Lifshitz phase transitions in the ferromagnetic regime of the Kondo lattice model,"We establish the low-temperature phase diagrams of the spin-1/2 and spin-1
Kondo lattice models as a function of the conduction-band filling n and the
exchange coupling strength J in the regime of ferromagnetic effective exchange
interactions (n ~< 0.5). We show that both models have several distinct
ferromagnetic phases separated by continuous Lifshitz transitions of the
Fermi-pocket vanishing or emergence type: one of the phases has a true gap in
the minority band (half metal), the others only a pseudogap. They can be
experimentally distinguished by their magnetization curves; only the gapped
phase exhibits magnetization rigidity. We find that, quite generically,
ferromagnetism and Kondo screening coexist rather than compete, both in
spin-1/2 and spin-1 models. We compute the Curie temperatures and establish a
""ferromagnetic Doniach diagram"" for both models.",1301.2117v2
2013-01-24,Ferromagnetism in itinerant two-dimensional t2g systems,"Motivated by the recent indications of ferromagnetism in transition metal
oxide heterostructures, we propose a possible mechanism to generate
ferromagnetism for itinerant t2g systems in two spatial dimensions that does
not rely on the coupling between local moments and conduction electrons. We
particularly emphasize the orbital nature of different bands and show that,
when the Fermi level lies near the bottom of the upper bands, a
non-perturbative interaction effect due to the quasi-one-dimensional nature of
the upper bands may drive a transition to a state in which the upper bands are
ferromagnetically polarized. In the quasi-one-dimensional limit, the full
thermodynamics may be obtained exactly. We discuss the connection between our
mechanism with several itinerant t2g systems that may have ferromagnetic
instabilities.",1301.5681v3
2013-01-25,Itinerant ferromagnetism with finite ranged interactions,"Quantum fluctuations are of central importance in itinerant ferromagnets; in
the case of the Stoner Hamiltonian, with contact interactions, they deliver a
rich phase diagram featuring a first order ferromagnetic transition preempted
by a spin spiral and a paired density wave. However, to date all analyses of
fluctuation corrections neglect the finite ranged nature of the Coulomb
interaction. We develop the formalism to consider the effects of fluctuations
with a realistic screened Coulomb potential. The finite ranged interaction
suppresses the tricritical point temperature of the first order ferromagnetic
transition, bringing theory into line with experiment, whilst retaining the
exotic spin spiral and paired density wave. In an ultracold atomic gas a finite
ranged interaction damps the competing molecular instability, permitting the
observation of ferromagnetic correlations.",1301.6036v1
2013-02-01,"Unveiling the impurity band inducing ferromagnetism in magnetic semiconductor (Ga,Mn)As","(Ga,Mn)As is a paradigm diluted magnetic semiconductor which shows
ferromagnetism induced by doped hole carriers. With a few controversial models
emerged from numerous experimental and theoretical studies, the mechanism of
the ferromagnetism in (Ga,Mn)As still remains a puzzling enigma. In this
Letter, we use soft x-ray angle-resolved photoemission spectroscopy to
positively identify the ferromagnetic Mn 3d-derived impurity band in (Ga,Mn)As.
The band appears hybridized with the light-hole band of the host GaAs. These
findings conclude the picture of the valence band structure of (Ga,Mn)As
disputed for more than a decade. The non-dispersive character of the IB and its
location in vicinity of the valence-band maximum indicate that the Mn
3d-derived impurity band is formed as a split-off Mn-impurity state predicted
by the Anderson impurity model. Responsible for the ferromagnetism in (Ga,Mn)As
is the transport of hole carriers in the impurity band.",1302.0063v1
2013-02-12,"The Kitaev-Ising model, Transition between topological and ferromagnetic order","We study the Kitaev-Ising model, where ferromagnetic Ising interactions are
added to the Kitaev model on a lattice. This model has two phases which are
characterized by topological and ferromagnetic order. Transitions between these
two kinds of order are then studied on a quasi-one dimensional system, a
ladder, and on a two dimensional periodic lattice, a torus. By exactly mapping
the quasi-one dimensional case to an anisotropic XY chain we show that the
transition occurs at zero $\lambda$ where $\lambda$ is the strength of the
ferromagnetic coupling. In the two dimensional case the model is mapped to a 2D
Ising model in transverse field, where it shows a transition at finite value of
$\lambda$. A mean field treatment reveals the qualitative character of the
transition and an approximate value for the transition point. Furthermore with
perturbative calculation, we show that expectation value of Wilson loops behave
as expected in the topological and ferromagnetic phases.",1302.2868v2
2013-04-24,"Low temperature ferromagnetism, surface paramagnetism and exchange bias effect in nano-grained alpha-Fe1.4Ga0.6O3 oxide","The compound alpha-Fe1.4Ga0.6O3 has been prepared by mechanical alloying of
alpha-Fe2O3 and Ga2O3 and subsequent heating of the mechanical alloyed samples
in vacuum condition. Magnetic ordering of alpha-Fe2O3 has been modified by
substitution of non-magnetic Ga atoms. The ferromagnetism in alpha-Fe1.4Ga0.6O3
is more soft and enhanced in comparison to alpha-Fe2O3. M\""ossbauer
spectroscopy also confirmed enhanced ferromagnetic order in alpha-Fe1.4Ga0.6O3.
The room temperature soft ferromagnetism by Ga substitution is interesting for
designing alpha-Fe2O3 based unconventional ferromagnet, which is a great
challenge to the materials scientists. The alpha-Fe1.4Ga0.6O3 samples also
exhibited features of exchange bias, low temperature surface paramagnetism, and
suppression of Morin transition. These features have been affected up to
certain extent by the nano-sized grains of the samples.",1304.6512v1
2013-05-06,Superconductor/ferromagnet heterostructures exhibit potential for significant reduction of hysteretic losses,"First experimental observations of the ferromagnetic shielding effect in
high-Tc superconducting coated conductors were carried out. Experimental
results were compared to simulations calling upon finite-element calculations
based on the H-formulation of Maxwell equations to model superconducting strips
with ferromagnetic shields. Samples of copper-stabilized coated conductors were
electroplated with nickel shields and afterwards characterized. Both externally
applied oscillating transverse magnetic fields as well as transport currents
were studied. Having observed promising gains with respect to the reduction of
ac losses in both cases, we further investigated the potential of ferromagnetic
shielding. The numerical model was able to reproduce and also predict
experimental results very well and will serve as an indispensable tool to
determine the potential of soft ferromagnetic materials to significantly reduce
hysteretic losses.",1305.1296v1
2013-07-03,Universal properties of magnetization dynamics in polycrystalline ferromagnetic films,"We investigate the scaling behavior in the statistical properties of
Barkhausen noise in ferromagnetic films. We apply the statistical treatment
usually employed for bulk materials in experimental Barkhausen noise time
series measured with the traditional inductive technique in polycrystalline
ferromagnetic films having different thickness from 100 up to 1000 nm, and
investigate the scaling exponents. Based on this procedure, we can group the
samples in a single universality class, characterized by exponents \tau \sim
1.5, \alpha \sim 2.0, and 1/\sigma \nu z \sim \vartheta \sim 2.0. We interpret
these results in terms of theoretical models and provide experimental evidence
that a well-known mean-field model for the dynamics of a ferromagnetic domain
wall in three-dimensional ferromagnets can be extended for films. We identify
that the films present an universal three-dimensional magnetization dynamics,
governed by long-range dipolar interactions, even at the smallest thicknesses,
indicating that the two-dimensional magnetic behavior commonly verified for
films cannot be generalized for all thickness ranges.",1307.1154v1
2013-07-18,Reduction of conductivity and ferromagnetism induced by Ag doping in ZnO:Co,"Cobalt and silver co-doping has been undertaken in ZnO thin films grown by
pulsed laser deposition in order to investigate the ferromagnetic properties in
ZnO-based diluted magnetic materials and to understand the eventual relation
between ferromagnetism and charge carriers. Hall transport measurements reveal
that Ag doping up to 5% leads to a progressive compensation of the native
n-type carriers. The magnetization curves show ferromagnetic contributions for
all samples at both 5 K and room temperature, decreasing with increasing the Ag
concentration. First principles modeling of the possible configurations of
Co-Ag defects suggest the formation of nano-clusters around interstitial Co
impurity as the origin of the ferromagnetism. The Ag co-doping results in a
decrease of the total spin of these clusters and of the Curie temperature.",1307.4820v1
2013-11-13,Proximity effect in superconductor/conical magnet/ferromagnet heterostructures,"At the interface between a superconductor and a ferromagnetic metal
spin-singlet Cooper pairs can penetrate into the ferromagnetic part of the
heterostructure with an oscillating and decaying spin-singlet Cooper pair
density. However, if the interface allows for a spin-mixing effect, equal-spin
spin-triplet Cooper pairs can be generated that can penetrate much further into
the ferromagnetic part of the heterostructure, known as the long-range
proximity effect. Here, we present results of spin-mixing based on
self-consistent solutions of the microscopic Bogoliubov-de Gennes equations
incorporating a tight-binding model. In particular, we include a conical magnet
into our model heterostructure to generate the spin-triplet Cooper pairs and
analyse the influence of conical and ferromagnetic layer thickness on the
unequal-spin and equal-spin spin-triplet pairing correlations. It will be show
that, in agreement with experimental observations, a minimum thickness of the
conical magnet is necessary to generate a sufficient amount of equal-spin
spin-triplet Cooper pairs allowing for the long-range proximity effect.",1311.3278v1
2013-11-18,Coexistence of bulk superconductivity and ferromagnetism in CeO1-xFxBiS2,"We show the observation of the coexistence of bulk superconductivity and
ferromagnetism in CeO1-xFxBiS2(x = 0 - 1.0) prepared by annealing under
high-pressure. In CeO1-xFxBiS2 system, both superconductivity and two types of
ferromagnetism with respective magnetic transition temperatures of 4.5 K and
7.5 K are induced upon systematic F substitution. This fact suggests that
carriers generated by the substitution of O by F are supplied to not only the
BiS2 superconducting layers but also the CeO blocking layers. Furthermore, the
highest superconducting transition temperature is observed when the
ferromagnetism is also enhanced, which implies that superconductivity and
ferromagnetism are linked to each other in the CeO1-xFxBiS2 system.",1311.4267v1
2014-02-28,Annealing-induced enhancement of ferromagnetism and nano-particle formation in ferromagnetic-semiconductor GeFe,"We report the annealing-induced enhancement of ferromagnetism and
nano-particle formation in group-IV-based ferromagnetic-semiconductor GeFe. We
successfully increase the Curie temperature of the Ge0.895Fe0.105 film up to
~220 K while keeping a single ferromagnetic phase when the annealing
temperature is lower than 500{\deg}C. In contrast, when annealed at 600{\deg}C,
single-crystal GeFe nano-particles with stacking faults and twins, which have a
high Curie temperature nearly up to room temperature, are formed in the film.
Our results show that annealing is quite effective to improve the magnetic
properties of GeFe for high-temperature-operating spin-injection devices based
on Si or Ge.",1402.7209v1
2014-04-07,Co-existence of ferromagnetic and antiferromagnetic interactions in Mn$_3$Ga$ _{(1-x)} $Sn$_x$C,"The magnetic properties of the Mn$_3$Ga$_{(1-x)}$Sn$_x$C, 0 $\le$ x $\le$ 1
antiperovskite compounds have been investigated in detail. Though all compounds
of this series crystallize in a cubic structure, the Ga rich (x $\le$ 0.2)
compounds transform, via a first order transformation, to an antiferromagnetic
ground state and the Sn rich (x $\ge$ 0.8) compounds exhibit dominant
ferromagnetic interactions at low temperature. In the intermediate range (0.4
$\le$ x $\le$ 0.7) co-existence of ferromagnetic and antiferromagnetic
interactions can be seen. The results have been explained to be due to growth
of ferromagnetic sub-lattice at the expense of antiferromagnetic sub-lattice
with increasing Sn concentration in Mn$_3$Ga$_{(1-x)}$Sn$_x$C. This growth
occurs to a point where the first-order transition is altered from a
ferromagnetic - antiferromagnetic type in Ga rich compounds to a paramagnetic -
ferrimagnetic type in Mn$_3$SnC.",1404.1753v1
2014-07-24,Unambiguous separation of the inverse spin Hall and anomalous Nernst Effects within a ferromagnetic metal using the spin Seebeck effect,"The longitudinal spin Seebeck effect is measured on the ferromagnetic
insulator Fe$_3$O$_4$ with the ferromagnetic metal
Co$_{0.2}$Fe$_{0.6}$B$_{0.2}$ (CoFeB) as the spin detector. By using a
non-magnetic spacer material between the two materials (Ti), it is possible to
decouple the two ferromagnetic materials and directly observe pure spin flow
from Fe$_3$O$_4$ into CoFeB. It is shown, that in a single ferromagnetic metal
the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur
simultaneously with opposite polarity. Using this and the large difference in
the coercive fields between the two magnets, it is possible to unambiguously
separate the contributions of the spin Seebeck effect from the ANE and observe
the degree to which each effect contributes to the total response. These
experiments show conclusively that the ISHE and ANE in CoFeB are separate
phenomena with different origins and can coexist in the same material with
opposite response to a thermal gradient.",1407.6758v1
2014-08-28,Stable non-Fermi liquid phase of itinerant spin-orbit coupled ferromagnets,"Direct coupling between gapless bosons and a Fermi surface results in the
destruction of Landau quasiparticles and a breakdown of Fermi liquid theory.
Such a non-Fermi liquid phase arises in spin-orbit coupled ferromagnets with
spontaneously broken continuous symmetries due to strong coupling between
rotational Goldstone modes and itinerant electrons. These systems provide an
experimentally accessible context for studying non-Fermi liquid physics.
Possible examples include low-density Rashba coupled electron gases, which have
a natural tendency towards spontaneous ferromagnetism, or topological insulator
surface states with proximity-induced ferromagnetism. Crucially, unlike the
related case of a spontaneous nematic distortion of the Fermi surface, for
which the non-Fermi liquid regime is expected to be masked by a superconducting
dome, we show that the non-Fermi liquid phase in spin-orbit coupled
ferromagnets is stable.",1408.6826v2
2014-09-13,Coexistence of 3d-ferromagnetism and superconductivity in [(Li(1-x)Fex)OH](Fe(1-y)Liy)Se,"Superconducting [(Li(1-x)Fex)OH](Fe(1-y)Liy)Se (x ~ 0.2, y ~ 0.08) was
synthesized by hydrothermal methods and structurally characterized by single
crystal X-ray diffraction. The crystal structure contains anti-PbO type
(Fe(1-y)Liy)Se layers separated by layers of (Li(1-x)Fex)OH. Electrical
resistivity and magnetic susceptibility measurements reveal superconductivity
at 43 K. An anomaly in the diamagnetic shielding indicates ferromagnetic
ordering near 10 K while superconductivity is retained. The ferromagnetism
emerges from the iron atoms in the (Li(1-x)Fex)OH layer. Isothermal
magnetization measurements confirm the superposition of ferromagnetic with
superconducting hysteresis. The internal ferromagnetic field is larger than the
lower, but smaller than the upper critical field of the superconductor, which
gives evidence for a spontaneous vortex phase where both orders coexist.
57Fe-M\""ossbauer spectra, 7Li-NMR spectra, and muSR experiments consistently
support this rare situation, especially in a bulk material where magnetism
emerges from a 3d-element.",1409.3982v1
2014-11-06,Molecule-assisted ferromagnetic atomic chain formation,"One dimensional systems strongly enhance the quantum character of electron
transport. Such systems can be realized in 5d transition metals Au, Pt and Ir,
in the form of suspended monatomic chains between bulk leads. Atomic chains
between ferromagnetic leads would open up many perspectives in the context of
spin-dependent transport and spintronics, but the evidence suggests that for
pure metals only the mentioned three 5d metals are susceptible to chain
formation. It has been argued that the stability of atomic chains made up from
ferromagnetic metals is compromised by the same exchange interaction that
produces the local moments. Here we demonstrate that magnetic atomic chains can
be induced to form in break junctions under the influence of light molecules.
Explicitly, we find deuterium assisted chain formation in the 3d ferromagnetic
transition metals Fe and Ni. Chain lengths up to eight atoms are formed upon
stretching the ferromagnetic atomic contact in deuterium atmosphere at
cryogenic temperatures. From differential conductance spectra vibronic states
of D$_2$ can be identified, confirming the presence of deuterium in the atomic
chains.",1411.1692v1
2014-11-17,"(Sr,Na)(Zn,Mn)2As2: A new diluted ferromagnetic semiconductor with the hexagonal CaAl2Si2 type structure","A new diluted ferromagnetic semiconductor (Sr,Na)(Zn,Mn)2As2 is reported, in
which charge and spin doping are decoupled via Sr/Na and Zn/Mn substitutions,
respectively, being distinguished from classic (Ga,Mn)As where charge & spin
doping are simultaneously integrated. Different from the recently reported
ferromagnetic (Ba,K)(Zn,Mn)2As2, this material crystallizes into the hexagonal
CaAl2Si2-type structure. Ferromagnetism with a Curie temperature up to 20 K has
been observed from magnetization. The muon spin relaxation measurements suggest
that the exchange interaction between Mn moments of this new system could be
different to the earlier DMS systems. This system provides an important means
for studying ferromagnetism in diluted magnetic semiconductors.",1411.4536v1
2014-11-25,Ultrafast Probes of Nonequilibrium Hole Spin Relaxation in Ferromagnetic Semiconductor GaMnAs,"We directly measure the hole spin lifetime in ferromagnetic GaMnAs via time-
and polarization-resolved spectroscopy. Below the Curie temperature Tc, an
ultrafast photoexcitation with linearly-polarized light is shown to create a
non-equilibrium hole spin population via the dynamical polarization of holes
through p-d exchange scattering with ferromagnetically-ordered Mn spins, and we
characterize their relaxation dynamics. The observed relaxation consists of a
distinct three-step recovery : (i) femtosecond (fs) hole spin relaxation ~
$160-200 fs, (ii) picosecond (ps) hole energy relaxation ~ 1-2 ps, and (iii) a
coherent, damped Mn spin precession with a period of ~ 250 ps. The transient
amplitude of the hole spin component diminishes with increasing temperature,
directly following the ferromagnetic order, while the hole energy amplitude
shows negligible temperature change, consistent with our interpretation. Our
results thus establish the hole spin lifetimes in ferromagnetic semiconductors
and demonstrate a novel spectroscopy method for studying non-equilibrium hole
spins in the presence of correlation and magnetic order.",1411.6979v1
2014-12-11,Magnon Hall effect and anisotropic thermal transport in NiFe and YIG ferromagnets,"The Righi-Leduc effect refers to the thermal analogue of the Hall effect, for
which the electric current is replaced by the heat current and the electric
field by the temperature gradient. In both cases, the magnetic field generates
a transverse force that deviates the carriers (electron, phonon, magnon) in the
direction perpendicular to the current. In a ferromagnet, the magnetization
plays the role of the magnetic field, and the corresponding effect is called
anomalous Hall effect. Furthermore, a second transverse contribution due to the
anisotropy, the planar Hall effect, is superimposed to the anomalous Hall
effect. We report experimental evidence of the thermal counterpart of the Hall
effects in ferromagnets, namely the magnon Hall effect (or equivalently the
anomalous Righi-Leduc effect) and the planar Righi-Leduc effect, measured on
ferromagnets that are either electrical conductor (NiFe) or insulator (YIG).
The study shows the universal character of these new thermokinetic effects,
related to the intrinsic chirality of the anisotropic ferromagnetic degrees of
freedom.",1412.3723v1
2015-03-02,A route to room temperature ferromagnetic ultrathin SrRuO$_3$ films,"Experimental efforts to stabilize ferromagnetism in ultrathin films of
transition metal oxides have so far failed, despite expectations based on
density functional theory (DFT) and DFT+U. Here, we investigate one of the most
promising materials, SrRuO$_3$, and include correlation effects beyond DFT by
means of dynamical mean field theory. In agreement with experiment we find an
intrinsic thickness limitation for metallic ferromagnetism in SrRuO$_3$ thin
films. Indeed, we demonstrate that the realization of ultrathin ferromagnetic
films is out of reach of standard thin-film techniques. Proposing charge
carrier doping as a new route to manipulate thin films, we predict room
temperature ferromagnetism in electron-doped SrRuO$_3$ ultra thin films.",1503.00640v1
2015-03-06,Spin-Motive Forces and Current-Induced Torques in Ferromagnets,"In metallic ferromagnets, the spin-transfer torque and spin-motive force are
known to exhibit a reciprocal relationship. Recent experiments on ferromagnets
with strong spin-orbit coupling have revealed a rich complexity in the
interaction between itinerant charge carriers and magnetization, but a full
understanding of this coupled dynamics is lacking. Here, we develop a general
phenomenology of the two reciprocal processes of charge pumping by spin-motive
forces and current-driven magnetization dynamics. The formalism is valid for
spin-orbit coupling of any strength and presents a systematic scheme for
deriving all possible torque and charge-pumping terms that obey the symmetry
requirements imposed by the point group of the system. We demonstrate how the
different charge pumping and torque contributions are connected via the Onsager
reciprocal relations. The formalism is applied to two important classes of
systems: isotropic ferromagnets with non-uniform magnetization and homogeneous
ferromagnets described by the point group $C_{2v}$.",1503.01899v2
2015-03-08,Conserved momenta of a ferromagnetic soliton,"Linear and angular momenta of a soliton in a ferromagnet are commonly derived
through the application of Noether's theorem. We show that these quantities
exhibit unphysical behavior: they depend on the choice of a gauge potential in
the spin Lagrangian and can be made arbitrary. To resolve this problem, we
exploit a similarity between the dynamics of a ferromagnetic soliton and that
of a charged particle in a magnetic field. For the latter, canonical momentum
is also gauge-dependent and thus unphysical; the physical momentum is the
generator of magnetic translations, a symmetry combining physical translations
with gauge transformations. We use this analogy to unambiguously define
conserved momenta for ferromagnetic solitons. General considerations are
illustrated on simple models of a domain wall in a ferromagnetic chain and of a
vortex in a thin film.",1503.02329v3
2015-03-30,Divacancy-induced Ferromagnetism in Graphene Nanoribbons,"Zigzag graphene nanoribb ons have spin-polarized edges,
anti-ferromagnetically coupled in the ground state with total spin zero.
Customarily, these ribbons are made ferromagnetic by producing an imbalance
between the two sublattices. Here we show that zigzag ribbons can be
ferromagnetic due to the presence of reconstructed divacancies near one edge.
This effect takes place despite the divacancies are produced by removing two
atoms from opposite sublattices, being balanced before reconstruction to 5-8-5
defects. We demonstrate that there is a strong interaction between the
defect-localized and edge bands which mix and split away from the Fermi level.
This splitting is asymmetric, yielding a net edge spin-polarization. Therefore,
the formation of reconstructed divacancies close to the edges of the
nanoribbons can be a practical way to make them partially ferromagnetic.",1503.08750v1
2015-07-18,Addressing the Challenges of Using Ferromagnetic Electrodes in the Molecular Spintronics Devices,"Ferromagnetic electrodes chemically bonded with thiol functionalized
molecules can produce novel molecular spintronics devices. However, major
challenges lie in developing Ferromagnetic electrodes based commercially viable
device fabrication scheme that consider the susceptibility of ferromagnetic
electrodes to oxidation, chemical etching, and stress induced deformations
during fabrication and usage. This paper studies NiFe, an alloy used in the
present day memory devices and high-temperature engineering applications, as a
candidate FM electrode for the fabrication of MSDs. Our spectroscopic
reflectance studies show that NiFe start oxidizing aggressively beyond 90 C.
The NiFe surfaces, aged for several months or heated for several minutes below
90 C, exhibited remarkable electrochemical activity and were suitable for
chemical bonding with the thiol functionalized molecular device elements. NiFe
also demonstrated excellent etching resistance and minimized the mechanical
stress induced deformities. This paper demonstrates the successful utilization
of NiFe electrodes in the tunnel junction based molecular device fabrication
approach. This paper is expected to fill the knowledge gap impeding the
experimental development of ferromagnetic electrode based molecular spintronics
devices for realizing novel logic and memory devices and observing a numerous
theoretically predicted phenomenon.",1507.05146v1
2015-07-24,Analytic models for density of a ground-state spinor condensate,"We demonstrate that the ground state of a trapped spin-1 and spin-2 spinor
ferromagnetic Bose-Einstein condensate (BEC) can be well approximated by a
single decoupled Gross-Pitaevskii (GP) equation. Useful analytic models for the
ground-state densities of ferromagnetic BECs are obtained from the Thomas-Fermi
approximation (TFA) to this decoupled equation. Similarly, for the ground
states of spin-1 anti-ferromagnetic and spin-2 anti-ferromagnetic and cyclic
BECs, some of the spin component densities are zero which reduces the coupled
GP equation to a simple reduced form. Analytic models for ground state
densities are also obtained for anti-ferromagnetic and cyclic BECs from the TFA
to the respective reduced GP equations. The analytic densities are illustrated
and compared with the full numerical solution of the GP equation with realistic
experimental parameters.",1507.06883v1
2015-09-10,Electronic and magnetic transitions in perovskite SrRu1-xIrxO3 thin films,"We have investigated the electronic and magnetic properties of perovskite
SrRu1-xIrxO3 thin films grown by pulsed laser deposition on atomically-flat
(001) SrTiO3 substrates. SrRuO3 has the properties of a ferromagnetic metal
with Curie temperature 150 K. Substituting Ir for Ru in SrRuO3, films showed
fully-metallic behavior and ferromagnetic ordering, although resistivity
increased and the ferromagnetic TC decreased. Films with x = 0.25 underwent the
metal-to-insulator transition at 75 K, and spin-glass-like ordering at 45 K
with the elimination of ferromagnetic long-range ordering caused by the
electron localization at the substitution sites. In ferromagnetic films,
resistivity increased near-linearly with T, but in paramagnetic film (x = 0.25)
resistivity increased as T3/2. Moreover, observed spin-glass-like (TSG)
ordering with the negative magnetoresistance in film with x = 0.25; validates
the hypothesis that (Anderson) localization favors glassy ordering at amply
disorder limit. These observations provide a promising approach for future
applications and of fundamental interest in 4d and 5d mixed perovskites.",1509.02987v1
2015-09-14,Itinerant chiral ferromagnetism in a trapped Rashba spin-orbit coupled Fermi gas,"How ferromagnetic phases emerge in itinerant systems is an outstanding
problem in quantum magnetism. Here we consider a repulsive two-component Fermi
gas confined in a two dimensional isotropic harmonic potential and subject to a
large Rashba spin-orbit (SO) coupling, whose single-particle dispersion can be
tailored by adjusting the SO coupling strength. We show that the interplay
among SO coupling, correlation effects and mean-field repulsion leads to a
competition between ferromagnetic and non-magnetic phases. At intermediate
interaction strengths, ferromagnetic phase emerges which can be well described
by the mean-field Hartree-Fock theory; whereas at strong interaction strengths,
a strongly correlated non-magnetic phase is favored due to the
beyond-mean-field quantum correlation effects. Furthermore, the ferromagnetic
phase of this system possesses a chiral current density induced by the Rashba
spin-orbit coupling, whose experimental signature is investigated.",1509.04095v1
2015-11-06,Defect-impurity complex induced long-range ferromagnetism in GaN nanowires,"Present work investigates the structural, electronic and magnetic properties
of wurtzite (0001) GaN nanowires (NWs) doped with Gd and point defects by
employing the GGA+U approximation. We find that Ga vacancies (VGa) exhibit
lower formation energy compared to N vacancies (VN). Further stabilization of
point defects occurs due to the presence of Gd and ambient ferromagnetism (FM)
can be stabilized in the NW by the additional positive charge induced by the
VGa. Electronic structure analysis shows that VGa introduces additional levels
in the band gap leading to ferromagnetic coupling due to the hybridization of
the p states of the Ga and N atoms with the Gd d and f states. Ferromagnetic
exchange coupling energy of 76.4meV is obtained in presence of Gd-VGa complex,
and hence the FM is largely determined by the cation vacancy-rare earth complex
defects in GaN NWs. On the other hand, the VN, which introduce additional
electron carriers, does not assist in increasing the ferromagnetic exchange
energy.",1511.01991v1
2015-11-14,Exchange interactions in the Hubbard-Stratonovich transformation for the stability analysis of itinerant ferromagnetism,"Itinerant ferromagnetism, i.e. spontaneous polarization of non-localized
particles, is expected to occur for strong repulsive interactions in a spin-1/2
Fermi system. However, this state has proven notoriously hard to find
experimentally, both in ultracold gases and in solids. This raises questions
about the stability of the itinerant ferromagnetic state itself. Here we
develop a new approach to describe both the direct and exchange interactions
for a general interaction potential in the path-integral formalism and we apply
this method to itinerant ferromagnetism in three-dimensional ultracold Fermi
gases. We show that the exchange interactions are lost in the
Hubbard-Stratonovich transformation and we propose to explicitly include the
exchange effects in a new modified interaction potential. In the saddle-point
approximation, the effect of interactions can be taken into account using only
three parameters. If the interactions become too strong, all saddle points
become unstable to density fluctuations. This greatly restricts the area in the
phase diagram where uniform itinerant ferromagnetism is expected to occur.",1511.04502v1
2015-11-27,Realization of Stable Ferromagnetic Order in Topological Insulator: Codoping Enhanced Magnetism in 4f Transition Metal Doped Bi2Se3,"The realization of long range and insulating ferromagnetic states in
topological insulator (TI) has been a pressing issue since its discovery. Only
recently, such state was achieved in Cr-doped Bi2-xSbxTe3, leading to the
discovery of quantum anomalous Hall effect (QAHE). However, the effect is only
observed at extremely low temperatures mainly due to the limited magnetism. To
fully understand the mechanism of the ferromagnetic ordering whereby improving
the ferromagnetism, we investigated 4f transition metal-doped Bi2Se3, using
density-functional-theory approaches. We found that Eu and Sm prefer the Bi
substitutional sites with large magnetic moments to ensure stable long-range
ferromagnetic states. Additionally, codoping can be a novel strategy to
preserve the insulating property of the host material as well as improving the
incorporation of magnetic dopants. Our findings thus offer the critical step in
facilitating the realization of QAHE in TI systems.",1511.08646v1
2016-01-17,Metallic ferromagnetism supported by a single band in a multi-band Hubbard model,"We construct a multi-band Hubbard model on the lattice obtained by
""decorating"" a closely packed $d$-dimensional lattice $\mathcal{M}$ (such as
the triangular lattice) where $d\ge2$. We take the limits in which the Coulomb
interaction and the band gap become infinitely large. Then there remains only a
single band with finite energy, on which electrons are supported. Let the
electron number be $N_\mathrm{e}=|\mathcal{M}|-N_\mathrm{h}$, where
$|\mathcal{M}|$ corresponds to the electron number which makes the lowest
(finite energy) band half-filled, and $N_\mathrm{h}$ is the number of ""holes"".
It is expected that the model exhibits metallic ferromagnetism if
$N_\mathrm{h}/|\mathcal{M}|$ is nonvanishing but sufficiently small. We prove
that the ground states exhibit saturated ferromagnetism if
$N_\mathrm{h}\le(\text{const.})|\mathcal{M}|^{2/(d+2)}$, and exhibit (not
necessarily saturated) ferromagnetism if
$N_\mathrm{h}\le(\mathrm{const.})|\mathcal{M}|^{(d+1)/(d+2)}$. This may be
regarded as a rigorous example of metallic ferromagnetism provided that the
system size $|\mathcal{M}|$ is not too large.",1601.04265v2
2016-02-02,Effect of the change in the interface structure of Pd(100)/SrTiO3 for quantum-well induced ferromagnetism,"Pd(100) ultrathin films show ferromagnetism induced by the confinement of
electrons in the film, i.e., the quantum-well mechanism. In this study, we
investigate the effect of the change in the interface structure between a Pd
film and SrTiO3 substrate on quantum-well induced ferromagnetism using the
structural phase transition of SrTiO3. During repeated measurement of
temperature- dependent magnetization of the Pd/SrTiO3 system, cracks were
induced in the Pd overlayer near the interface region by the structural phase
transition of SrTiO3, thereby changing the film-thickness dependence of the
magnetic moment. This is explained by the concept that as the magnetic moment
in Pd(100) changed, so too did the thickness of the quantum-well. In addition,
we observed that the ferromagnetism in the Pd(100) disappeared with the
accumulation of cracks due to the repetition of the temperature cycle through
the phase-transition temperature. This suggests that lowering the crystallinity
of the interface structure by producing a large number of cracks has a negative
effect on quantum-well induced ferromagnetism.",1602.00799v1
2016-09-19,Switching ferromagnetic spins by an ultrafast laser pulse: Emergence of giant optical spin-orbit torque,"Faster magnetic recording technology is indispensable to massive data storage
and big data sciences. {All-optical spin switching offers a possible solution},
but at present it is limited to a handful of expensive and complex rare-earth
ferrimagnets. The spin switching in more abundant ferromagnets may
significantly expand the scope of all-optical spin switching. Here by studying
40,000 ferromagnetic spins, we show that it is the optical spin-orbit torque
that determines the course of spin switching in both ferromagnets and
ferrimagnets. Spin switching occurs only if the effective spin angular momentum
of each constituent in an alloy exceeds a critical value. Because of the strong
exchange coupling, the spin switches much faster in ferromagnets than
weakly-coupled ferrimagnets. This establishes a paradigm for all-optical spin
switching. The resultant magnetic field (65 T) is so big that it will
significantly reduce high current in spintronics, thus representing the
beginning of photospintronics.",1609.05855v1
2017-02-14,Dilution of Ferromagnets via a Random Graph-based Strategy,"The dynamics and behavior of ferromagnets have a great relevance even beyond
the domain of statistical physics. In this work, we propose a Monte Carlo
method, based on random graphs, for modeling their dilution. In particular, we
focus on ferromagnets with dimension $D \ge 4$, which can be approximated by
the Curie-Weiss model. Since the latter has as graphic counterpart a complete
graph, a dilution can be in this case viewed as a pruning process. Hence, in
order to exploit this mapping, the proposed strategy uses a modified version of
the Erd\H{o}s-Renyi graph model. In doing so, we are able both to simulate a
continuous dilution, and to realize diluted ferromagnets in one step. The
proposed strategy is studied by means of numerical simulations, aimed to
analyze main properties and equilibria of the resulting diluted ferromagnets.
To conclude, we also provide a brief description of further applications of our
strategy in the field of complex networks.",1702.04324v2
2017-08-14,The Current-Phase Relation of Ferromagnetic Josephson Junction Between Triplet Superconductors,"We study the Josephson effect of a $\rm{T_1 F T_2}$ junction, consisting of
spin-triplet superconductors (T), a weak ferromagnetic metal (F), and
ferromagnetic insulating interfaces. Two types of the triplet order parameters
are considered; $(k_x +ik_y)\hat{z}$ and $k_x \hat{x}+k_y\hat{y}$. We compute
the current density in the ballistic limit by using the generalized
quasiclassical formalism developed to take into account the interference effect
of the multilayered ferromagnetic junction. We discuss in detail how the
current-phase relation is affected by orientations of the d-vectors of
superconductor and the magnetizations of the ferromagnetic tunneling barrier.
General condition for the anomalous Josephson effect is also derived.",1708.04351v2
2018-02-25,Discovery of Intrinsic Ferromagnetic Ferroelectricity in Transition Metal Halides Monolayer,"The realization of multiferroics in nanostructures, combined with a large
electric dipole and ferromagnetic ordering, could lead to new applications,
such as high-density multi-state data storage. Although multiferroics have been
broadly studied for decades, ferromagnetic ferroelectricity is rarely explored,
especially in two-dimensional (2D) systems. Here we report the discovery of 2D
ferromagnetic ferroelectricity in layered transition metal halide systems. On
the basis of first-principles calculations, we reveal that charged CrBr3
monolayer exhibits in-plane multiferroicity, which is ensured by the
combination of orbital and charge ordering as realized by the asymmetric
Jahn-Teller distortions of octahedral Cr-Br6 units. As an example, we further
show that (CrBr3)2Li is a ferromagnetic ferroelectric multiferroic. The
explored phenomena and mechanism of multiferroics in this 2D system are not
only useful for fundamental research in multiferroics but also enable a wide
range of applications in nano-devices.",1802.09033v1
2018-02-27,Phenomenological approach to study the degree of the itinerancy of the $5f$ electrons in actinide ferromagnets with spin fluctuation theory,"Actinide compounds with 5f electrons have been attracting much attention
because of their interesting magnetic and electronic properties such as heavy
fermion state, unconventional superconductivity, co-existence of the
superconductivity and magnetism. Recently, we have reported a phenomenological
analysis on 80 actinide ferromagnets with the spin fluctuation theory
originally developed to explain the ferromagnetic properties of itinerant
ferromagnets in the 3d transition metals and their intermetallics (N. Tateiwa
et al., Phys. Rev. B 96, 035125 (2017)). Our study suggests the itinerancy of
the $5f$ electrons in most of the actinide ferromagnets and the applicability
of the spin fluctuation theory to actinide 5f system. In this paper, we present
a new analysis for the spin fluctuation parameter obtained with a different
theoretical formula not used in the reference. We also discuss the results of
the analysis from different points of views.",1802.09672v1
2019-05-09,Mn2C monolayer: hydrogenation/oxygenation induced strong room-temperature ferromagnetism and potential applications,"Two-dimensional ferromagnetic materials with strong ferromagnetism and high
Curie temperature are significantly desired for the applications of nanoscale
devices. Here, based on first-principles computations, we report
hydrogenated/oxygenated Mn2C monolayer is a such material with strong
room-temperature ferromagnetism. The bare Mn2C monolayer is an
antiferromagnetic metal with the local magnetic moment of Mn ~ 3{\mu}B.
However, the antiferromagnetic coupling of Mn atoms can transform into the
ferromagnetic order under hydrogenation/oxygenation. Especially, the magnetic
moments in hydrogenated/oxygenated Mn2C monolayer can be as large as 6 {\mu}B
per unit cell, and the Curie temperatures are above 290K. Beside the potential
applications in spintronic devices, our work suggests that Mn2C monolayer is
also promising to be used in hydrogen/oxygen detection and removal devices.",1905.03435v1
2019-05-23,Interface ferromagnetism and anomalous Hall effect of CdO/ferromagnetic insulator heterostructures,"The experimental observation of quantum anomalous Hall effect (QAHE) in
magnetic topological insulators has stimulated enormous interest in
condensed-matter physics and materials science. For the purpose of realizing
high-temperature QAHE, several material candidates have been proposed, among
which the interface states in the CdO/ferromagnetic insulator heterostructures
are particularly interesting and favorable for technological applications.
Here, we report the experimental observation of the interfacial ferromagnetism
and anomalous Hall effect in the Fe3O4/CdO/Fe3O4 heterostructures grown via
oxide molecular-beam epitaxy. Systematical variation of the CdO thickness
reveals the interface ferromagnetism as the major cause for the observed planar
magnetoresistance and anomalous Hall effect. Our results might pave the way to
engineer oxide interface states for the exploration of QAHE towards exotic
quantum-physical phenomena and potential applications.",1905.09425v1
2020-07-01,Microscopic origin of magnetization reversal in exchange-coupled ferro-/ferrimagnetic bilayers,"In this study, the magnetic reversal process of exchange-coupled bilayer
systems, consisting of a ferrimagnetic TbFeCo alloy layer and a ferromagnetic
[Co/Ni/Pt]N multilayer, was investigated. In particular, minor loop studies,
probing solely the reversal characteristics of the softer ferromagnetic layer,
reveal two distinct reversal mechanisms, which depend strongly on the thickness
of the ferromagnetic layer. For thick layers, irreversible switching of the
macroscopic minor loop is observed. The underlying microscopic origin of this
reversal process was studied in detail by high-resolution magnetic force
microscopy, showing that the reversal is triggered by in-plane domain walls
propagating through the ferromagnetic layer. In contrast, thin ferromagnetic
layers show a hysteresis-free reversal, which is nucleation-dominated due to
grain-to-grain variations in magnetic anisotropy of the Co/Ni/Pt multilayer and
an inhomogeneous exchange coupling with the magnetically hard TbFeCo layer, as
confirmed by micromagnetic simulations.",2007.00333v1
2020-07-08,Flat-band ferromagnetism in twisted bilayer graphene,"We discuss twisted bilayer graphene (TBG) based on a theorem of flat band
ferromagnetism put forward by Mielke and Tasaki. According to this theorem,
ferromagnetism occurs if the single particle density matrix of the flat band
states is irreducible and we argue that this result can be applied to the
quasi-flat bands of TBG that emerge around the charge-neutrality point for
twist angles around the magic angle $\theta\sim1.05^\circ$. We show that the
density matrix is irreducible in this case, thus predicting a ferromagnetic
ground state for neutral TBG ($n=0$). We then show that the theorem can also be
applied only to the flat conduction or valence bands, if the substrate induces
a single-particle gap at charge neutrality. Also in this case, the
corresponding density matrix turns out to be irreducible, leading to
ferromagnetism at half filling ($n=\pm2$).",2007.04076v2
2020-07-16,Thermal noise effects on the magnetization switching of a ferromagnetic anomalous Josephson junction,"We discuss the effects of thermal noise on the magnetic response of a lateral
ferromagnetic Josephson junction with spin-orbit coupling and out-of-plane
magnetization. The direction of the magnetic moment in the ferromagnetic layer
can be inverted by using controlled current pulses. This phenomenon is due to
the magnetoelectric effect that couples the flowing charge current and the
magnetization of the ferromagnet. We investigate the magnetization reversal
effect versus intrinsic parameters of the ferromagnet, such as the Gilbert
damping and strength of the spin-orbit coupling. We estimate the magnetization
reversing time and find the optimal values of the parameters for fast
switching. With the aim of increasing the operation temperature we study the
effects induced by thermal fluctuations on the averaged stationary
magnetization, and find the conditions that make the system more robust against
noise.",2007.08414v3
2010-05-11,Long-range spin-triplet proximity effect in Josephson junctions with multilayered ferromagnets,"We study the proximity effect in SF'(AF)F'S and SF'(F)F'S planar junctions,
where S is a clean conventional (s-wave) superconductor, while F' and middle
layers are clean or moderately diffusive ferromagnets. Middle layers consist of
two equal ferromagnets with antiparallel (AF) or parallel (F) magnetizations
that are not collinear with magnetizations in the neighboring F' layers. We use
fully self-consistent numerical solutions of the Eilenberger equations to
calculate the superconducting pair amplitudes and the Josephson current for
arbitrary thickness of ferromagnetic layers and the angle between in-plane
magnetisations. For moderate disorder in ferromagnets the triplet proximity
effect is practically the same for AF and F structures, like in the dirty
limit. Triplet Josephson current is dominant for $d'\approx\hbar v_F/2h'$,
where $d'$ is the F' layer thickness and $h'$ is the exchange energy. Our
results are in a qualitative agreement with the recent experimental
observations [T. S. Khaire, M. A. Khasawneh, W. P. Pratt, and N. O. Birge,
Phys. Rev. Lett. \textbf{104}, 137002 (2010)].",1005.1867v2
2013-08-07,Ferromagnetism of a Repulsive Atomic Fermi Gas in an Optical Lattice: a Quantum Monte Carlo Study,"Using continuous-space quantum Monte Carlo methods we investigate the
zero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas
under the influence of periodic potentials that describe the effect of a
simple-cubic optical lattice. Simulations are performed with balanced and with
imbalanced components, including the case of a single impurity immersed in a
polarized Fermi sea (repulsive polaron). For an intermediate density below half
filling, we locate the transitions between the paramagnetic, and the partially
and the fully ferromagnetic phases. As the intensity of the optical lattice
increases, the ferromagnetic instability takes place at weaker interactions,
indicating a possible route to observe ferromagnetism in experiments performed
with ultracold atoms. We compare our findings with previous predictions based
on the standard computational method used in material science, namely density
functional theory, and with results based on tight-binding models.",1308.1672v2
2014-03-08,Spin and valley transports in junctions of Dirac fermions,"We study spin and valley transports in junctions composed of silicene and
topological crystalline insulators. We consider normal/magnetic/normal Dirac
metal junctions where a gate electrode is attached to the magnetic region. In
normal/antiferromagnetic/normal silicene junction, we show that the current
through this junction is valley and spin polarized due to the coupling between
valley and spin degrees of freedom, and the valley and spin polarizations can
be tuned by local application of a gate voltage. In particular, we find a fully
valley and spin polarized current by applying the electric field. In
normal/ferromagnetic/normal topological crystalline insulator junction with a
strain induced in the ferromagnetic segment, we investigate valley resolved
conductances and clarify how the valley polarization stemming from the strain
and exchange field appears in this junction. It is found that changing the
direction of the magnetization and the potential in the ferromagnetic region,
one can control the dominant valley contribution out of four valley degrees of
freedom. We also review spin transport in normal/ferromagnetic/normal graphene
junctions, and spin and valley transports in normal/ferromagnetic/normal
silicene junctions for comparison.",1403.1962v2
2016-11-10,Energy efficient and fast reversal of a fixed skyrmions with spin current assisted by voltage controlled magnetic anisotropy,"Recent work [1,2] suggests that ferromagnetic reversal with spin transfer
torque (STT) requires more current in a system in the presence of DMI than
switching a typical ferromagnet of the same dimensions and perpendicular
magnetic anisotropy (PMA). However, DMI promotes stabilization of skyrmions and
we report that when the perpendicular anisotropy is modulated (reduced) for
both the skyrmion and ferromagnet, it takes much smaller current to reverse the
fixed skyrmion than to reverse the ferromagnet in the same time, or the
skyrmion reverses much faster than the ferromagnet at similar levels of
current. We show with rigorous micromagnetic simulations and energy portraits
that the skyrmion switching proceeds along a different path at very low PMA
which results in a significant reduction in the spin current required or time
required for reversal. This can have potential for memory application where a
relatively simple modification of the standard STT-RAM to include a heavy metal
adjacent to the soft magnetic layer and with appropriate design of the tunnel
barrier can lead to energy efficient and fast magnetic memory device based on
the reversal of fixed skyrmions.",1611.03138v2
2017-01-19,Separation of inverse spin Hall effect and anomalous Nernst effect in ferromagnetic metals,"Inverse spin Hall effect (ISHE) in ferromagnetic metals (FM) can also be used
to detect the spin current generated by longitudinal spin Seebeck effect in a
ferromagnetic insulator YIG. However, anomalous Nernst effect(ANE) in FM itself
always mixes in the thermal voltage. In this work, the exchange bias structure
(NiFe/IrMn)is employed to separate these two effects. The exchange bias
structure provides a shift field to NiFe, which can separate the magnetization
of NiFe from that of YIG in M-H loops. As a result, the ISHE related to
magnetization of YIG and the ANE related to the magnetization of NiFe can be
separated as well. By comparison with Pt, a relative spin Hall angle of NiFe
(0.87) is obtained, which results from the partially filled 3d orbits and the
ferromagnetic order. This work puts forward a practical method to use the ISHE
in ferromagnetic metals towards future spintronic applications.",1701.05320v1
2017-04-20,Realization of room-temperature ferromagnetic semiconducting state in graphene monolayer,"Room-temperature ferromagnetic semiconductor is vital in nonvolatile digital
circuits and it can provide an idea system where we can make use of both charge
and spin of electrons. However, seeking room-temperature ferromagnetic
semiconductors is still just an appealing idea that has never been realized in
practice up to now. Here we demonstrate that graphene monolayer, hybridized
with underlying Ni(111) substrate, is the room-temperature ferromagnetic
semiconductor that has been continuously searched for decades. Our
spin-polarized scanning tunnelling microscopy (STM) experiments, complemented
by first-principles calculations, demonstrate explicitly that the interaction
between graphene and the Ni substrate generates a large gap in graphene and
simultaneously leads to a relatively shift between majority- and minority-spin
bands. Consequently, the graphene sheet on the Ni substrate exhibits a
spin-polarized gap with energy of several tens meV even at room-temperature.
This result makes the science and applications of room-temperature
ferromagnetic semiconductors achievable and raises hopes of graphene-based
novel information technologies.",1704.05965v3
2008-07-06,Enhanced Ferromagnetic Stability in Cu Doped Passivated GaN Nanowires,"Density functional calculations are performed to investigate the room
temperature ferromagnetism in GaN:Cu nanowires (NWs). Our results indicate that
two Cu dopants are most stable when they are near each other. Compared to bulk
GaN:Cu, we find that magnetization and ferromagnetism in Cu doped NWs is
strongly enhanced because the band width of the Cu td band is reduced due to
the 1D nature of the NW. The surface passivation is shown to be crucial to
sustain the ferromagnetism in GaN:Cu NWs. These findings are in good agreement
with experimental observations and indicate that ferromagnetism in this type of
systems can be tuned by controlling the size or shape of the host materials.",0807.0918v1
2008-07-29,Hubbard Model with Inter-Site Kinetic Correlations,"We introduced the inter-site electron-electron correlation to the Hubbard III
approximation. This correlation was excluded in the Hubbard III approximation
and also in the equivalent coherent potential approximation. Including it
brings two spin dependent effects: the bandwidth correction and the bandshift
correction, which both stimulate the ferromagnetic ground state. The bandshift
correction factor causes an exchange splitting between the spin-up and
spin-down spectrum, and its role is similar to the exchange interaction in the
classic Stoner model. The spin dependent bandwidth correction lowers the
kinetic energy of electrons by decreasing the majority spin bandwidth for some
electron occupations with respect to the minority spin bandwidth. In certain
conditions it can lead to ferromagnetic alignment. A gain in the kinetic energy
achieved in this way is the opposite extreme to the effect of a gain in
potential energy due to exchange splitting. The bandshift factor is a dominant
force behind the ferromagnetism. The influence of the bandwidth factor is too
weak to create ferromagnetism and the only result is the correction to the
classic coherent potential approximation in favor of ferromagnetism.",0807.4633v1
2012-01-03,Nematic ferromagnetism on the Lieb lattice,"We discuss the properties of possible ferromagnetic orders on the Lieb
lattice. We show that the presence of a quadratic-flat band crossing point
(QFBCP) at half filling will dramatically affect the magnetic ordering. In the
presence of a weak on-site repulsive interaction, we find the ground state is a
nematic ferromagnetic order with simultaneously broken of time-reversal and
rotational symmetries. When the interaction strength increases, the rotational
symmetry will restore at some critical value, and the system enters a
conventional ferromagnetic regime. We also point out that the spin gap in both
the nematic and conventional ferromagnetic phases is of the order of
interaction. This observation suggests that these magnetic orders can be
realized and detected in cold atomic systems with present technology.",1201.0722v2
2012-01-05,"First-principles study on the magnetic properties of six potential half-metallic ferromagnets: alkaline-earth (Ca, Sr) doped XC (X=Si, Ge, Sn)","Six half-metallic ferromagnets X0.75Y0.25C (X=Si, Ge, Sn and Y =Ca and Sr)
with zinc-blende structure, resulting from alkaline-earth (Ca, Sr) substitution
for X, are predicted based on the density functional theory. The calculated
total magnetic moments of these ferromagnets are all integer 2.00{\mu}B per
supercell, which are one of important characters of half-metallic ferromagnets.
Our calculations indicate that X0.75Y0.25C have wide spin gap and potentially
have high Curie temperature. Alkaline-earth doping results in the
spin-polarization and half-metallicity of these compounds. It is confirmed that
the p-d exchange coupling is responsible for the ferromagnetism of X0.75Y0.25C
except Sn0.75Ca0.25C.",1201.1053v1
2012-01-05,Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures,"In heterostructures of LaAlO3 (LAO) and SrTiO3 (STO), two nonmagnetic
insulators, various forms of magnetism have been observed [1-7], which may [8,
9] or may not [10] arise from interface charge carriers that migrate from the
LAO to the interface in an electronic reconstruction [11]. We image the
magnetic landscape [5] in a series of n-type samples of varying LAO thickness.
We find ferromagnetic patches that appear only above a critical thickness,
similar to that for conductivity [12]. Consequently we conclude that an
interface reconstruction is necessary for the formation of magnetism. We
observe no change in ferromagnetism with gate voltage, and detect
ferromagnetism in a non-conducting p-type sample, indicating that the carriers
at the interface do not need to be itinerant to generate magnetism. The fact
that the ferromagnetism appears in isolated patches whose density varies
greatly between samples strongly suggests that disorder or local strain induce
magnetism in a population of the interface carriers.",1201.1063v1
2012-01-06,Surface Roughness Dominated Pinning Mechanism of Magnetic Vortices in Soft Ferromagnetic Films,"Although pinning of domain walls in ferromagnets is ubiquitous, the absence
of an appropriate characterization tool has limited the ability to correlate
the physical and magnetic microstructures of ferromagnetic films with specific
pinning mechanisms. Here, we show that the pinning of a magnetic vortex, the
simplest possible domain structure in soft ferromagnets, is strongly correlated
with surface roughness, and we make a quantitative comparison of the pinning
energy and spatial range in films of various thickness. The results demonstrate
that thickness fluctuations on the lateral length scale of the vortex core
diameter, i.e. an effective roughness at a specific length scale, provides the
dominant pinning mechanism. We argue that this mechanism will be important in
virtually any soft ferromagnetic film.",1201.1334v1
2012-01-19,Electronic configuration of Mn ions in the $π$-d molecular ferromagnet $β$-Mn phthalocyanine studied by soft x-ray magnetic circular dichroism,"We have studied the electronic structure of the molecular ferromagnet
$\beta$-Mn phthalocyanine ($\beta$-MnPc) in a polycrystalline form, which has
been reported to show ferromagnetism at T$<$8.6 K, by x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the
experimental results and subsequent cluster-model calculation, we find that the
ferromagnetic Mn ion in $\beta$-MnPc is largely in the $^4$$E$$_g$ ground state
arising from the ($e$$_{g}$)$^3$($b$$_{2g}$)$^1$($a$$_{1g}$)$^1$
[($d_{xz,yz}$)$^3$($d_{xy}$)$^1$($d_{z^{2}}$)$^1$] configuration of the
Mn$^{2+}$ state. Considering that the highest occupied molecular orbital (HOMO)
of MnPc with the $^4$$E$$_g$ ground state originates from the $a$$_{1g}$
orbital of the Mn$^{2+}$ ion, it is proposed that $a$$_{1g}$-$a$$_{1g}$
exchange coupling via the $\pi$ orbitals of the phthalocyanine ring plays a
crucial role in the ferromagnetism of $\beta$-MnPc.",1201.4076v2
2012-01-30,Revealing common artifacts due to ferromagnetic inclusions in highly-oriented pyrolytic graphite,"We report on an extensive investigation to figure out the origin of
room-temperature ferromagnetism that is commonly observed by SQUID magnetometry
in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray
microanalysis revealed the presence of micron-size magnetic clusters
(predominantly Fe) that are rare and would be difficult to detect without
careful search in a scanning electron microscope in the backscattering mode.
The clusters pin to crystal boundaries and their quantities match the amplitude
of typical ferromagnetic signals. No ferromagnetic response is detected in
samples where we could not find such magnetic inclusions. Our experiments show
that the frequently reported ferromagnetism in pristine HOPG is most likely to
originate from contamination with Fe-rich inclusions introduced presumably
during crystal growth.",1201.6374v1
2013-08-31,"Electron carrier-mediated room temperature ferromagnetism in anatase (Ti,Co)O2","Since the discovery of room temperature ferromagnetism in (Ti,Co)O2, the
mechanism has been under discussion for a decade. Particularly, the central
concern has been whether or not the ferromagnetic exchange interaction is
mediated by charge carriers like (Ga,Mn)As. Recent two studies on the control
of ferromagnetism in anatase (Ti,Co)O2 at room temperature via electric field
effect [Y. Yamada et al., Science 332, 1065 (2011)] and chemical doping [Y.
Yamada et al., Appl. Phys. Lett. 99, 242502 (2011)] indicate a principal role
of electrons in the carrier-mediated exchange interaction. In this article, the
authors review fundamental properties of anatase (Ti,Co)O2 and discuss the
carrier mediated ferromagnetism.",1309.0078v1
2013-09-07,Phase segregation of superconductivity and ferromagnetism at LaAlO$_3$/SrTiO$_3$ interface,"The highly conductive two-dimensional electron gas formed at the interface
between insulating SrTiO$_3$ and LaAlO$_3$ shows low-temperature
superconductivity coexisting with inhomogeneous ferromagnetism. The Rashba
spin-orbit interaction with in-plane Zeeman field of the system favors $p_x \pm
i p_y$-wave superconductivity at finite momentum. Owing to the intrinsic
disorder at the interface, the role of spatial inhomogeneity on the
superconducting and ferromagnetic states becomes important. We find that for
strong disorder, the system breaks up into mutually excluded regions of
superconductivity and ferromagnetism. This inhomogeneity-driven electronic
phase separation accounts for the unusual coexistence of superconductivity and
ferromagnetism observed at the interface.",1309.1861v2
2013-09-13,Lattice effects on ferromagnetism in perovskite ruthenates,"Ferromagnetism and its evolution in the orthorhombic perovskite system
Sr1-xCaxRuO3 have been widely believed to correlate with the structural
distortion. The recent development of high-pressure synthesis of the Ba
substituted Sr1-yBayRuO3 makes it possible to study ferromagnetism over a
broader phase diagram, which includes new orthorhombic Imma and the cubic
phases. However, the chemical substitutions introduce the A-site disorder
effect on Tc, which complicates determination of the relationship between
ferromagnetism and the structural distortion. By clarifying the site disorder
effect on Tc in several new series of ruthenates in which the average bond
length <A-O> keeps the same, but the bond-length variance varies, we are able
to demonstrate a parabolic curve of Tc versus mean bond length <A-O>. A much
higher Tc ~ 177 K than that found in orthorhombic SrRuO3 can be obtained from
the curve at a bond length <A-O> which makes the geometric factor t =
<A-O>/(sqrt(2)<Ru-O>) = 1. This new result reveals not only that the
ferromagnetism in the ruthenates is extremely sensitive to the lattice strain,
but also that it has an important implication for exploring the
structure-property relationship in a broad range of oxides with perovskite or
perovskite-related structure.",1309.3359v1
2013-09-20,"Control of ferromagnetism by manipulating the carrier wavefunction in ferromagnetic semiconductor (In,Fe)As quantum wells","We demonstrated the control of ferromagnetism in a surface quantum well
containing a 5-nm-thick n-type ferromagnetic semiconductor (In,Fe)As layer
sandwiched between two InAs layers, by manipulating the carrier wavefunction.
The Curie temperature (Tc) of the (In,Fe)As layer was effectively changed by up
to 12 K ({\Delta}Tc/Tc = 55%). Our calculation using the mean-field Zener
theory reveals an unexpectedly large s-d exchange interaction in (In,Fe)As. Our
results establish an effective way to control the ferromagnetism in quantum
heterostructures of n-type FMSs, as well as require reconsideration on the
current understanding of the s-d exchange interaction in narrow gap FMSs.",1309.5283v1
2013-09-26,Proximity effect of spin orbit coupling in Pt/Co2FeAl and Pt/Permalloy bilayers_810571,"Proximity effect of spin orbit coupling is investigated through anomalous
Hall effect in Pt/Co2FeAl and Pt/Permalloy bilayers. A series of nontrivial
magnetotransport behaviors, resulting from a strong impact of phonons on skew
scattering, is observed in these films with ultrathin ferromagnetic layers. The
parameters representing skew scattering, side jump and intrinsic contributions
are dramatically enhanced when the ferromagnetic layer is very thin, and they
have clear linear dependences on the reciprocal of ferromagnetic layer
thickness, indicating a powerful influence of Pt/Ferromagnet interface. Further
study on Cu/Co2FeAl and Ta/Co2FeAl bilayers reveals that a simple interface
scattering without intense spin orbit coupling is not sufficient to trigger
such a phenomenon. The proximity effect of spin orbit coupling is thus
suggested to occur at the Pt/Ferromagnet interface, and as a result quite large
anomalous Hall angle (0.036) and Nernst angle (0.23) are confirmed in the
Pt/CFA films at room temperature.",1309.7023v1
2014-04-30,Spin Controlled Coexistence of 0 and π States in SFSFS Josephson Junctions,"Using the Keldysh-Usadel formalism, we theoretically study the $0$-$\pi$
transition profiles and current-phase relations of magnetic $SFSFS$ and
$SFSFFS$ Josephson nanojunctions in the diffusive regime. By allowing the
magnetizations of the ferromagnetic layers to take arbitrary orientations, the
strength and direction of the charge supercurrent flowing through the
ferromagnetic regions can be controlled via the magnetization rotation in one
of the ferromagnetic layers. Depending on the junction parameters, we find
opposite current flow in the ferromagnetic layers, revealing that remarkably
such configurations possess well-controlled $0$- and $\pi$-states
simultaneously, creating a three-terminal $0$-$\pi$ spin switch. We demonstrate
that the spin-controlled $0$-$\pi$ profiles trace back to the proximity induced
odd-frequency superconducting correlations generated by the ferromagnetic
layers. It is also shown that the spin-switching effect can be more pronounced
in $SFSFFS$ structures. The current-phase relations reveal the important role
of the middle $S$ electrode, where the spin controlled supercurrent depends
crucially on its thickness and phase differences with the outer $S$ terminals.",1405.0012v1
2015-12-27,Topological properties of ferromagnetic superconductors,"A variety of heavy fermion superconductors, such as UCoGe, UGe$_2$, and URhGe
exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In
these systems, the magnetic moment decreases with pressure, and vanishes at a
ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity
in UCoGe varies smoothly with pressure across the qcp and exists in both the
ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit
interactions stabilize a time-reversal invariant odd-parity superconductor in
the high pressure paramagnetic regime. Based on a simple phenomenological
model, we predict that the transition from the paramagnetic normal state to the
phase where superconductivity and ferromagnetism coexist, is a first-order
transition.",1512.08286v2
2015-12-30,Topological insulator associated with quantum anomalous Hall phase in ferromagnetic perovskite superlattices,"We do a search for topological insulators which are associated with
ferromagnetic ordering and show anomalous quantum Hall effect, among transition
metal oxide superlattices taking the parent compounds as LaAlO3 and SrTiO3.
Among the various superlattices which are studied here, (LaAlO3)10/(LaOsO3)2
exhibits a ferromagnetic ground state with a topologically non-trivial energy
gap when a spin-orbit interaction is turned on. The study of transverse
conductivity shows that the system has quantized Hall conductivity inside the
topological energy gap without applying any external magnetic field. The
ferromagnetic order parameters and the ordering temperature (Tc) have been
estimated by taking a simple Heisenberg model of ferromagnetism.",1512.08843v1
2016-08-06,Spin Transfer Torque in the Semiconductor/Ferromagnetic Structure in the Presence of Rashba Effect,"Spin transfer torque in magnetic structures occurs when the transverse
component of the spin current that flows from the nonmagnetic medium to
ferromagnetic medium are absorbed by the interface. In this paper, considering
the Rashba effect on semiconductor region, we have discussed the spin transfer
torque in semiconductor/ferromagnetic structure and obtained the components of
spin-current density for two models: (I)-single electron and (II)- the
distribution of electrons. We have shown that whatever the difference between
Fermi surfaces in semiconductor and Fermi spheres for the up and down spins in
ferromagnetic increase, the transmission probability decreases. The obtained
results for the values used in this article illustrate that Rashba effect
increases the difference between a Fermi sphere in semiconductors and Fermi
sphere for the up and down spins in ferromagnetic. The results also show that
the Rashba effect, brings an additional contribution to the components of spin
transfer torque, which is not exist in the absence of the Rashba interaction.
Moreover, the Rashba term has also different effects on the transverse
components of the spin torque transfer.",1608.02129v1
2016-08-09,"Local atomic and magnetic structure of dilute magnetic semiconductor (Ba,K)(Zn,Mn)$_2$As$_2$","We have studied the atomic and magnetic structure of the dilute ferromagnetic
semiconductor system (Ba,K)(Zn,Mn)$_2$As$_2$ through atomic and magnetic pair
distribution function analysis of temperature-dependent x-ray and neutron total
scattering data. We detected a change in curvature of the temperature-dependent
unit cell volume of the average tetragonal crystallographic structure at a
temperature coinciding with the onset of ferromagnetic order. We also observed
the existence of a well-defined local orthorhombic structure on a short length
scale of $\lesssim 5$ \AA, resulting in a rather asymmetrical local environment
of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic
alignment of Mn spins along the crystallographic $c$-axis, with robust
nearest-neighbor ferromagnetic correlations that exist even above the
ferromagnetic ordering temperature. We discuss these results in the context of
other experiments and theoretical studies on this system.",1608.02684v1
2016-12-27,Isotope shift of the ferromagnetic transition temperature in itinerant ferromagnets,"We present a theory of the isotope effect of the Curie temperature $T_{\rm
c}$ in itinerant ferromagnets. The isotope effect in ferromagnets occurs via
the electron-phonon vertex correction and the effective attractive interaction
mediated by the electron-phonon interaction. The decrease of the Debye
frequency increases the relative strength of the Coulomb interaction, which
results in a positive isotope shift of $T_{\rm c}$ when the mass $M$ of an atom
increases. Following this picture, we evaluate the isotope effect of $T_{\rm
c}$ by using the Stoner theory and a spin-fluctuation theory. When $T_{\rm c}$
is large enough as large as or more than 100K, the isotope effect on $T_{\rm
c}$ can be measurable. Recently, precise measurements on the oxygen isotope
effect on $T_{\rm c}$ have been performed for itinerant ferromagnet SrRuO$_3$
with $T_{\rm c}\sim 160$K. A clear isotope effect has been observed with the
positive shift of $T_{\rm c}\sim 1$K by isotope substitution
($^{16}O\rightarrow ^{18}O$). This experimental result is consistent with our
theory.",1612.08511v1
2018-01-08,Stability of the Nagaoka-type Ferromagnetic State in a $t_{2g}$ Orbital System on a Cubic Lattice,"We generalize the previous exact results of the Nagaoka-type itinerant
ferromagnetic states in a three dimensional $t_{2g}$-orbital system to allow
for multiple holes. The system is a simple cubic lattice with each site
possessing $d_{xy}$, $d_{yz}$, and $d_{xz}$ orbitals, which allow
two-dimensional hopping within each orbital plane. In the strong coupling limit
of $U\to \infty$, the orbital-generalized Nagaoka ferromagnetic states are
proved degenerate with the ground state in the thermodynamic limit when the
hole number per orbital layer scales slower than $L^{\frac{1}{2}}$. This result
is valid for arbitrary values of the ferromagnetic Hund's coupling $J>0$ and
inter-orbital repulsion $V\ge 0$. The stability of the Nagaoka-type state at
finite electron densities with respect to a single spin-flip is investigated.
These results provide helpful guidance for studying the mechanism of itinerant
ferromagnetism for the $t_{2g}$-orbital materials.",1801.02583v2
2018-10-20,Dynamics of a Ferromagnetic Particle Levitated Over a Superconductor,"Under conditions where the angular momentum of a ferromagnetic particle is
dominated by intrinsic spin, applied torque is predicted to cause gyroscopic
precession of the particle. If the particle is sufficiently isolated from the
environment, a measurement of spin precession can potentially yield sensitivity
to torque beyond the standard quantum limit. Levitation of a micron-scale
ferromagnetic particle above a superconductor is a possible method of near
frictionless suspension enabling observation of ferromagnetic particle
precession and ultrasensitive torque measurements. We experimentally
investigate the dynamics of a micron-scale ferromagnetic particle levitated
above a superconducting niobium surface. We find that the levitating particles
are trapped in potential minima associated with residual magnetic flux pinned
by the superconductor and, using an optical technique, characterize the
quasiperiodic motion of the particles in these traps.",1810.08748v5
2019-06-18,Discovery of room temperature ferromagnetism in metal-free organic semiconductors,"Creating magnetic semiconductors that work at warm circumstance is still a
great challenge in the physical sciences. Here, we report the discovery of
ferromagnetism in the metal-free perylene diimide semiconductor, whose Curie
temperature is higher than 400 Kelvin. A solvothermal approach is used to
reduce and dissolve the rigid-backbone perylene diimide crystallites, and
radical anion aggregates were fabricated by the subsequent self-assembly and
oxidation process. Magnetic measurements exhibit the ferromagnetic ordering
with the saturated magnetization of 0.48 $\mu_{\rm B}$ per molecule and the
appreciable magnetic anisotropy. X-ray magnetic circular dichroism spectra
suggest the ferromagnetism stems from $\pi$ orbitals of radicals. Our findings
unambitiously demonstrate the long-range ferromagnetic ordering can survive at
room temperature in organic semiconductors, although which are intuitively
regarded to be nonmagnetic.",1906.07531v2
2019-07-10,Dynamical mean-field study of Vanadium diselenide monolayer ferromagnetism,"To understand the magnetism of VSe$_2$, whose monolayer form has recently
been reported to be a room temperature ferromagnet, Here, the combined method
of conventional density functional theory with dynamical mean-field theory has
been adopted. This higher-level computation method enables us to resolve many
of existing controversies and contradictions in between theory and experiment.
First of all, this new approach is shown to give the correct magnetic
properties of both bulk and two-dimensional limit of VSe$_2$ which demonstrates
its superiority to the conventional methods. The results demonstrate that
monolayer VSe$_2$ without charge density waves is a ferromagnet with ordering
temperature of 250K. From the direct simulation of temperature-dependent
magnetic susceptibility and ordered moment, it is shown that its ferromagnetism
is clearly two-dimensional in nature. Further, it is shown that this
ferromagnetic order is vulnerable to extra charge dopings which provides the
important insight to elucidate recent experimental controversies.",1907.04790v3
2019-10-09,Nature vs. Nurture: Dynamical Evolution in Disordered Ising Ferromagnets,"We study the predictability of zero-temperature Glauber dynamics in various
models of disordered ferromagnets. This is analyzed using two independent
dynamical realizations with the same random initialization (called twins). We
derive, theoretically and numerically, trajectories for the evolution of the
normalized magnetization and twin overlap as the system size tends to infinity.
The systems we treat include mean-field ferromagnets with light-tailed and
heavy-tailed coupling distributions, as well as highly-disordered models with a
variety of other geometries. In the mean-field setting with light-tailed
couplings, the disorder averages out and the limiting trajectories of the
magnetization and twin overlap match those of the homogenous Curie--Weiss
model. On the other hand, when the coupling distribution has heavy tails, or
the geometry changes, the effect of the disorder persists in the thermodynamic
limit. Nonetheless, qualitatively all such random ferromagnets share a similar
time evolution for their twin overlap, wherein the two twins initially
decorrelate, before either partially or fully converging back together due to
the ferromagnetic drift.",1910.04144v1
2019-10-15,CrAs monolayer: Low buckled two-dimensional half-metal ferromagnet,"\textit{Ab-initio} calculations based on density functional theory (DFT) are
performed to study the structural, electronic, and magnetic properties of
two-dimensional (2D) free-standing honeycomb CrAs. We show that CrAs has low
buckled stable structure. Magnetic CrAs has larger buckling than non-magnetic
CrAs. 2D-CrAs is a ferromagnetic semiconductor for lattice constant $a \leq
3.71$\AA, and above this lattice constant CrAs is a half-metal ferromagnet.
2D-CrAs is shown to be half-metal ferromagnetic with magnetic moment of
3.0$\mu_{\rm{B}}$ per unit cell, at equilibrium structure. The $d_{z}^{2}$
orbital of $e_{g}$ band is completely empty in the spin-down state whereas it
is almost occupied in the spin-up state, and the magnetic moment in the $e_{g}$
band is mainly dominated by the $d_{z}^{2}$ orbital of Cr. The $d_{zx}/d_{zy}$
and $d_{xy}$ orbitals of $t_{2g}$ band are partially occupied in the spin-up
state and behaves as metal whereas they are insulator in the spin-down state.
Phonon calculations confirm the thermodynamic stability of 2D-CrAs. The
ferromagnetic (FM) and antiferromagnetic (AFM) interaction between the Cr atoms
reveal that the FM state is more stable than the AFM state of 2D-CrAs.",1910.06935v1
2019-10-24,Stabilization of coupled Dzyaloshinskii domain walls in fully compensated synthetic anti-ferromagnets,"We examine the combined effects of interlayer exchange coupling (IEC) and the
interfacial Dzyaloshinskii-Moriya Interaction (DMI) on the structure of
magnetic domain walls in fully compensated synthetic anti-ferromagnets (SAFs).
Ir-based SAFs with ferromagnetic (FM) layers based on [Pt/(Co/Ni)M]N were
characterized by Lorentz transmission electron microscopy (LTEM). The
multi-layer design of the individual ferromagnetic layers enables control of
the interfacial Dzyaloshinskii-Moriya interaction (via 'M') and, in turn, the
structure and chirality of domain walls (DWs). We compare the Fresnel-mode LTEM
images in SAF designs with only a change in the purported strength of the DMI.
The existence of anti-ferromagnetically coupled Dzyaloshinskii domain walls
(DWs) in a high DMI SAF is confirmed through application of in-situ
perpendicular magnetic field and sample tilt. This conclusion is based on a
unique set of conditions required to observe contrast in Fresnel-mode LTEM,
which we outline in this document.",1910.11421v1
2020-02-07,Anomalous current-voltage characteristics of SFIFS Josephson junctions with weak ferromagnetic interlayers,"We present a quantitative study of the current-voltage characteristics (CVC)
of SFIFS Josephson junctions (S denotes bulk superconductor, F - metallic
ferromagnet, I - insulating barrier) with weak ferromagnetic interlayers in the
diffusive limit. The problem is solved in the framework of the nonlinear Usadel
equations. We consider the case of a strong tunnel barrier such that the left
SF and the right FS bilayers are decoupled. We calculate the density of states
(DOS) in SF bilayers using a self-consistent numerical method. Then we obtain
the CVC of corresponding SFIFS junctions, and discuss their properties for
different set of parameters including the thicknesses of ferromagnetic layers,
the exchange field, and the magnetic scattering time. We observe the anomalous
nonmonotonic CVC behavior in case of weak ferromagnetic interlayers, which we
ascribe by DOS energy dependencies in case of small exchange fields in F
layers.",2002.02725v1
2020-11-30,Topological superconductivity in tripartite superconductor-ferromagnet-semiconductor nanowires,"Motivated by recent experiments searching for Majorana zero modes in
tripartite semiconductor nanowires with epitaxial superconductor and
ferromagnetic-insulator layers, we explore the emergence of topological
superconductivity in such devices for paradigmatic arrangements of the three
constituents. Accounting for the competition between magnetism and
superconductivity, we treat superconductivity self consistently and describe
the electronic properties, including the superconducting and ferromagnetic
proximity effects, within a direct wave-function approach. We conclude that the
most viable mechanism for topological superconductivity relies on a
superconductor-semiconductor-ferromagnet arrangement of the constituents, in
which spin splitting and superconductivity are independently induced in the
semiconductor by proximity and superconductivity is only weakly affected by the
ferromagnetic insulator.",2012.00055v1
2021-01-08,Appearance of ferromagnetism in Pt(100) ultrathin films originated from quantum-well states,"Ferromagnetism was observed in a Pt(100) ultrathin film deposited on a
SrTiO3(100) substrate. The ferromagnetism, which appears in films with
thicknesses of 2.2-4.4 nm, periodically changes with a period of approximately
1 nm (5-6 monolayers) depending on the film thickness. This is consistent with
the period derived from the quantum-well states formed in the thin film. X-ray
magnetic circular dichroism measurements show the evidence of appearance of
intrinsic ferromagnetism in Pt(100) ultra-thin film. In addition, present
results suggest a possibility that the orbital magnetic moment of pure Pt is
much smaller than that of the Pt/ferromagnetic multilayer system. These results
will provide a potential new mechanism for origin of the large magnetic
anisotropy in Pt components.",2101.02818v4
2017-09-25,Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2,"Ferromagnetic van der Waals (vdW) materials are in demand for spintronic
devices with all-two-dimensional-materials heterostructures. Here, we
demonstrate mechanical exfoliation of magnetic-atom-intercalated transition
metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such
intercalated materials were thought difficult to exfoliate. Magnetotransport in
exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering
below its Curie temperature TC ~ 110 K as well as strong in-plane magnetic
anisotropy; these are identical to its bulk properties. Further, van der Waals
heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet
Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated
heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide
tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing
possible spin injection and detection with these exfoliatable ferromagnetic
materials through the vdW junction.",1709.08313v1
2017-11-07,Quantum tricritical point in the temperature-pressure-magnetic field phase diagram of CeTiGe$_3$,"We report the temperature-pressure-magnetic field phase diagram of the
ferromagnetic Kondo-lattice CeTiGe$_3$ determined by means of electrical
resistivity measurements. Measurements up to $\sim$ 5.8 GPa reveal a rich phase
diagram with multiple phase transitions. At ambient pressure, CeTiGe$_3$ orders
ferromagnetically at $T_\text{C}$ = 14 K. Application of pressure suppresses
$T_\text{C}$, but a pressure induced ferromagnetic quantum criticality is
avoided by the appearance of two new successive transitions for $p$ $>$ 4.1 GPa
that are probably antiferromagnetic in nature. These two transitions are
suppressed under pressure, with the lower temperature phase being fully
suppressed above 5.3 GPa. The critical pressures for the presumed quantum phase
transitions are $p_1$ $\cong$ 4.1 GPa and $p_2$ $\cong$ 5.3 GPa. Above 4.1 GPa,
application of magnetic field shows a tricritical point evolving into a wing
structure phase with a quantum tricritical point at 2.8 T at 5.4 GPa, where the
first order antiferromagnetic-ferromagnetic transition changes into the second
order antiferromagnetic-ferromagnetic transition.",1711.02605v2
2018-03-11,Electromagnetic proximity effect in planar superconductor-ferromagnet structures,"The spread of the Cooper pairs into the ferromagnet in proximity coupled
superconductor - ferromagnet (SF) structures is shown to cause a strong inverse
electromagnetic phenomenon, namely, the long-range transfer of the magnetic
field from the ferromagnet to the superconductor. Contrary to the previously
investigated inverse proximity effect resulting from the spin polarization of
superconducting surface layer, the characteristic length of the above inverse
electrodynamic effect is of the order of the London penetration depth, which
usually much larger than the superconducting coherence length. The
corresponding spontaneous currents appear even in the absence of the stray
field of the ferromagnet and are generated by the vector-potential of
magnetization near the S/F interface and they should be taken into account at
the design of the nanoscale S/F devices. Similarly to the well-known
Aharonov-Bohm effect, the discussed phenomenon can be viewed as a manifestation
of the role of vector potential in quantum physics.",1803.03926v2
2018-03-27,Spin flip scattering engendered quantum spin torque in a Josephson junction,"We examine a Josephson junction with two Ferromagnets and a spin flipper
sandwiched between two superconductors. In such Ferromagnetic Josephson
junctions, equilibrium spin torque exists only when Ferromagnets are
misaligned. This is explained via the ""conventional"" mechanism of spin transfer
torque, which owes its origin to the misalignment of two Ferromagnets. However,
we see surprisingly when the magnetic moments of the Ferromagnets are aligned
parallel or antiparallel, there is a finite equilibrium spin torque due to the
quantum mechanism of spin-flip scattering. We explore the properties of this
unique spin-flip scattering induced equilibrium quantum spin torque, especially
its tunability via exchange coupling and phase difference across the
superconductors.",1803.10105v2
2018-06-07,Ferromagnet/Semiconductor/Ferromagnet Hybrid Trilayers grown using solid phase epitaxy,"The direct growth of semiconductors over metals by molecular beam epitaxy is
a difficult task due to the large differences in crystallization energy between
these types of materials. This aspect is problematic in the context of
spintronics, where coherent spin-injection must proceed via ballistic transport
through sharp interfacial Schottky barriers. We report the realization of
single-crystalline ferromagnet/semiconductor/ferromagnet hybrid trilayers using
solid-phase epitaxy, with combinations of Fe3Si, Co2FeSi, and Ge. The slow
annealing of amorphous Ge over Fe3Si results in a crystalline filmlm identified
as FeGe2. When the annealing is performed over Co2FeSi, reflected high-energy
electron diffraction and X-ray diffraction indicate the creation of a different
crystalline Ge(Co,Fe,Si) compound, which also preserves growth orientation. It
was possible to observe independent magnetization switching of the
ferromagnetic layers in a Fe3Si/FeGe2/Co2FeSi sample, thanks to the different
coercive fields of the two metals and to the quality of the interfaces. This
result is a step towards the implementation of vertical spin-selective
transistor-like devices.",1806.02733v1
2018-07-31,New room-temperature ferromagnet: B-added Pd0.75Mn0.25 alloy,"Mn-based room-temperature ferromagnets attract considerable attention due to
their high ordered Mn moment. We have found that a Pd0.75Mn0.25 alloy with
added B (Pd0.75Mn0.25Bx) shows room-temperature soft ferromagnetism, whereas
the parent Pd0.75Mn0.25 alloy is a spin-glass system. The saturated Mn moment
at room temperature systematically increases to 2.68\muB/Mn as x increases to
0.125. The maximum Curie temperature of 390 K is also realized at an x of
0.125. The experimental results suggest a tunable soft ferromagnetism, which is
governed only by the boron concentration. Our results will pave the way in
chemical control of room-temperature bulk ferromagnetism in Mn compounds based
on the addition of an atom with a small atomic radius.",1807.11640v1
2018-12-03,The Magnetic Properties of 1111-type Diluted Magnetic Semiconductor (La$_{1-x}$Ba$_{x}$)(Zn$_{1-x}$Mn$_{x}$)AsO in the Low Doping Regime,"We investigated the magnetic properties of
(La$_{1-x}$Ba$_{x}$)(Zn$_{1-x}$Mn$_{x}$)AsO with $x$ varying from 0.005 to 0.05
at an external magnetic field of 1000 Oe. For doping levels of $x$ $\leq$ 0.01,
the system remains paramagnetic down to the lowest measurable temperature of 2
K. Only when the doping level increases to $x$ = 0.02 does the ferromagnetic
ordering appear. Our analysis indicates that antiferromagnetic exchange
interactions dominate for $x$ $\leq$ 0.01, as shown by the negative Weiss
temperature fitted from the magnetization data. The Weiss temperature becomes
positive, i.e., ferromagnetic coupling starts to dominate, for $x$ $\geq$ 0.02.
The Mn-Mn spin interaction parameter $\mid$$2J/k_B$$\mid$ is estimated to be in
the order of 10 K for both $x$ $\leq$ 0.01 (antiferromagnetic ordered state)
and $x$ $\geq$ 0.02 (ferromagnetic ordered state). Our results unequivocally
demonstrate the competition between ferromagnetic and antiferromagnetic
exchange interactions in carrier-mediated ferromagnetic systems.",1812.00824v1
2018-12-05,Strong correlation between ferromagnetic superconductivity and pressure-enhanced ferromagnetic fluctuations in UGe$_2$,"We have measured magnetization at high pressure in the uranium ferromagnetic
superconductor UGe$_2$ and analyzed the magnetic data using Takahashi's spin
fluctuation theory. There is a peak in the pressure dependence of the width of
the spin fluctuation spectrum in the energy space $T_0$ at $P_x$, the phase
boundary of FM1 and FM2 where the superconducting transition temperature
$T_{sc}$ is highest. This suggests a clear correlation between the
superconductivity and pressure-enhanced magnetic fluctuations developed at
$P_x$. The pressure effect on $T_{Curie}/T_0$, where $T_{Curie}$ is the Curie
temperature, suggests that the less itinerant ferromagnetic state FM2 is
changed to a more itinerant one FM1 across $P_x$. Peculiar features in
relations between $T_0$ and $T_{sc}$ in uranium ferromagnetic superconductors
UGe$_2$, URhGe and UCoGe are discussed in comparison with those in high-$T_c$
cuprate and heavy fermion superconductors.",1812.01771v2
2018-12-14,VI3 - a new layered ferromagnetic semiconductor,"Two-dimensional (2D) materials are promising candidates for next-generation
electronic devices. In this regime, insulating 2D ferromagnets, which remain
rare, are of special importance due to their potential for enabling new device
architectures. Here we report the discovery of ferromagnetism in a layered van
der Waals semiconductor, VI3, which is based on honeycomb vanadium layers
separated by an iodine-iodine van der Waals gap. It has a BiI3-type structure
(R-3, No.148) at room temperature, and our experimental evidence suggests that
it may undergo a subtle structural phase transition at 78 K. VI3 becomes
ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly
shows ferromagnetic domains, which can be manipulated by the applied external
magnetic field. The optical band gap determined by reflectance measurements is
0.6 eV, and the material is highly resistive.",1812.05982v1
2019-01-21,Non-collinear coupling across RuCo and RuFe alloys,"Spintronic applications, which rely on spin torques for operation, would
greatly benefit from a non-collinear alignment between magnetizations of
adjacent ferromagnetic layers for maximum performance and reliability. We
demonstrate that such an alignment can be created and controlled by coupling
two ferromagnetic layers across magnetic coupling layers. These coupling layers
consist of a non-magnetic material, Ru, alloyed with ferromagnetic elements of
Co or Fe. Changing the composition and thickness of the coupling layer enables
control of the relative angle between the magnetizations of ferromagnetic
layers between 0 and 180 degrees. The onset of the non-collinear alignment
between ferromagnetic layers coincide with the advent of magnetic order in the
coupling layer. This study will map the range of concentrations and thicknesses
of RuCo and RuFe coupling layers that give rise to non-collinearity between Co
layers.",1901.07055v1
2019-02-01,Tuning of Magnetic Activity in Spin-Filter Josephson Junctions Towards Spin-Triplet Transport,"The study of superconductor-ferromagnet interfaces has generated great
interest in the last decades, leading to the observation of spin-aligned
triplet supercurrents and 0-pi transitions in Josephson junctions where two
superconductors are separated by an itinerant ferromagnet. Recently,
spin-filter Josephson junctions with ferromagnetic barriers have shown unique
transport properties, when compared to standard metallic ferromagnetic
junctions, due to the intrinsically nondissipative nature of the tunneling
process. Here we present the first extensive characterization of spin polarized
Josephson junctions down to 0.3 K, and the first evidence of an incomplete 0-pi
transition in highly spin polarized tunnel ferromagnetic junctions.
Experimental data are consistent with a progressive enhancement of the magnetic
activity with the increase of the barrier thickness, as neatly captured by the
simplest theoretical approach including a nonuniform exchange field. For very
long junctions, unconventional magnetic activity of the barrier points to the
presence of spin-triplet correlations.",1902.00406v1
2019-02-22,Strongly Enhanced Gilbert Damping in 3d Transition Metal Ferromagnet Monolayers in Contact with Topological Insulator Bi2Se3,"Engineering Gilbert damping of ferromagnetic metal films is of great
importance to exploit and design spintronic devices that are operated with an
ultrahigh speed. Based on scattering theory of Gilbert damping, we extend the
torque method originally used in studies of magnetocrystalline anisotropy to
theoretically determine Gilbert dampings of ferromagnetic metals. This method
is utilized to investigate Gilbert dampings of 3d transition metal ferromagnet
iron, cobalt and nickel monolayers that are contacted by the prototypical
topological insulator Bi2Se3. Amazingly, we find that their Gilbert dampings
are strongly enhanced by about one order in magnitude, compared with dampings
of their bulks and free-standing monolayers, owing to the strong spin-orbit
coupling of Bi2Se3. Our work provides an attractive route to tailoring Gilbert
damping of ferromagnetic metallic films by putting them in contact with
topological insulators.",1902.08700v1
2019-04-03,Ferromagnetic Instability for single-band Hubbard model in the strong-coupling regime,"We study a ferromagnetic instability in a doped single-band Hubbard model by
means of dynamical mean-field theory with the continuous-time quantum Monte
Carlo simulations. Examining the effect of the strong correlations in the
system on the hypercubic and Bethe lattice, we find that the ferromagnetically
ordered state appears in the former, while it does not in the latter. We also
reveal that the ferromagnetic order is more stable in the case that the
noninteracting DOS exhibits a slower decay in the high-energy region. The
present results suggest that, in the strong-coupling regime, the high-energy
part of DOS plays an essential role for the emergence of the ferromagnetically
ordered state, in contrast to the Stoner criterion justified in the weak
interaction limit.",1904.01724v1
2019-04-10,Intrinsic Ferromagnetism in Electrenes,"We report intrinsic ferromagnetism in monolayer electrides or electrenes, in
which excess electrons act as anions. Our first-principles calculations
demonstrate that magnetism in such electron-rich two-dimensional (2D) materials
originates from the anionic electrons rather than partially filled d orbitals,
which is fundamentally different from ferromagnetism found in other 2D
intrinsic magnetic materials. Taking the honeycomb LaBr$_2$
(La$^{3+}$Br$^{-}_{2}\cdot e^{-}$) as an example, our calculations reveal that
the excess electron is localized at the center of the hexagon, which leads to
strong Stoner-instability of the associated states at the Fermi energy,
resulting in spontaneous magnetization and formation of a local moment. The
overlap of extended tails of the wave functions of these electrons mediates a
long-range ferromagnetic interaction, contributing to a Curie temperature
($T_\textrm{c}$) of 235 K and a coercive field ($H_\textrm{c}$) of 0.53 T,
which can be further enhanced by hole doping. The dual nature, localization and
extension, of the electronic states suggests a unique mechanism in such
magnetic-element-free electrenes as intrinsic 2D ferromagnets.",1904.04952v1
2019-04-24,Ultra-low-power orbital-controlled magnetization switching using a ferromagnetic oxide interface,"A major challenge in spin-based electronics is reducing power consumption for
magnetization switching of ferromagnets, which is being implemented by
injecting a large spin-polarized current. The alternative approach is to
control the magnetic anisotropy (MA) of the ferromagnet by an electric field.
However, the voltage-induced MA is too weak to deterministically switch the
magnetization without an assisting magnetic field, and the strategy towards
this goal remains elusive. Here, we demonstrate a new scheme of
orbital-controlled magnetization switching (OCMS): A sharp change in the MA is
induced when the Fermi level is moved between energy bands with different
orbital symmetries. Using a ferromagnetic oxide interface, we show that OCMS
can be used to achieve a deterministic and magnetic-field-free 90
degree-magnetization switching solely by applying an extremely small electric
field of 0.05 V/nm with a negligibly small current density of 10^-2 A/cm^2. Our
results highlight the huge potential of band engineering in ferromagnetic
materials for efficient magnetization control.",1904.10599v1
2019-08-07,"Structural, Electronic and Magnetic Properties of Bulk and Epitaxial LaCoO$_3$ through Diffusion Monte Carlo","Magnetism in lanthanum cobaltite (LCO, LaCoO$_3$) appears to be strongly
dependent on strain, defects, and nanostructuring. LCO on strontium titanate
(STO, SrTiO$_3$) is a ferromagnet with an interesting strain relaxation
mechanism that yields a lattice modulation. However, the driving force of the
ferromagnetism is still controversial. Experiments debate between a
vacancy-driven or strain-driven mechanism for the ferromagnetism of epitaxial
LCO. We found that a weak lateral modulation of the superstructure is
sufficient to promote ferromagnetism. We find that ferromagnetism appears under
uniaxial compression and expansion. Although earlier experiments suggest that
bulk LCO is nonmagnetic, we find an antiferromagnetic ground state for bulk
LCO. We discuss the recent experiments which indicate a more complicated
picture for bulk magnetism and a closer agreement with our calculations. Role
of defects are also discussed through excited state calculations.",1908.02811v3
2019-08-16,Spin Seebeck effect in the layered ferromagnetic insulators CrSiTe$_3$ and CrGeTe$_3$,"We have studied the longitudinal spin Seebeck effect (LSSE) in the layered
ferromagnetic insulators CrSiTe$_3$ and CrGeTe$_3$ covered by Pt films in the
measurement configuration where spin current traverses the ferromagnetic Cr
layers. The LSSE response is clearly observed in the ferromagnetic phase and,
in contrast to a standard LSSE magnet Y$_3$Fe$_5$O$_{12}$, persists above the
critical temperatures in both CrSiTe$_3$/Pt and CrGeTe$_3$/Pt samples. With the
help of a numerical calculation, we attribute the LSSE signals observed in the
paramagnetic regime to exchange-dominated interlayer transport of in-plane
paramagnetic moments reinforced by short-range ferromagnetic correlations and
strong Zeeman effects.",1908.05807v1
2019-08-25,Anomalous Hall effect mechanisms in quasi-2D van der Waals ferromagnet Fe0.29TaS2,"The recent emergence of two-dimensional (2D) van der Waals ferromagnets has
provided a new platform for exploring magnetism in the flatland and for
designing 2D ferromagnet-based spintronics devices. Despite intensive studies,
the anomalous Hall effect (AHE) mechanisms in 2D van der Waals ferromagnets
have not been investigated yet. In this paper, we report the AHE mechanisms in
quasi-2D van der Waals ferromagnet Fe0.29TaS2 via systematically measuring
Fe0.29TaS2 devices with thickness from 14 nm to bulk single crystal. The AHE
mechanisms are investigated via the scaling relationship between the anomalous
Hall and channel conductivities. As the Fe0.29TaS2 thickness decreases, the
major AHE mechanism changes from extrinsic scattering to intrinsic
contribution. The crossover of the AHE mechanisms is found to be highly
associated with the channel conductivities as the Fe0.29TaS2 thickness varies.",1908.09280v1
2019-08-26,Phase-controlled spin and charge currents in superconductor-ferromagnet hybrids,"We investigate spin-dependent quasiparticle and Cooper-pair transport through
a central node interfaced with two superconductors and two ferromagnets. We
demonstrate that voltage biasing of the ferromagnetic contacts induces
superconducting triplet correlations on the node and reverses the supercurrent
flowing between the two superconducting contacts. We further find that such
triplet correlations can mediate a tunable spin current flow into the
ferromagnetic contacts. Our key finding is that unequal spin-mixing
conductances for the two interfaces with the ferromagnets result in equal-spin
triplet correlations on the node, detectable via a net charge current between
the two magnets. Our proposed device thus enables the generation, control, and
detection of the typically elusive equal-spin triplet Cooper pairs.",1908.09610v1
2020-04-30,Controlled Two-Dimensional Ferromagnetism in 1T-CrTe$_2$. The role of charge density wave and strain,"Transition metal dichalcogenides are promising candidates to show long-range
ferromagnetic order in the single-layer limit. Based on ab initio calculations,
we report the emergence of a charge density wave (CDW) phase in monolayer
1T-CrTe$_2$. We demonstrate that this phase is the ground state in the
single-layer limit at any strain value. We obtain an optical phonon mode of
$1.96$ THz that connects CDW phase with the undistorted 1T phase. Localization
of the $a_{1g}$ orbital of CrTe$_2$ produces an out-of-plane orientation of the
magnetic moments, circumventing the restrictions of the Mermin-Wagner theorem
and producing ferromagnetic long-range order in the two-dimensional limit. This
orbital-localization is enhanced by the CDW phase. Tensile strain also
increases the localization of this orbital driving the system to become
ordered. CrTe$_2$ becomes an example of a material where the CDW phase produces
the stabilization of the long-range ferromagnetic order. Our results show that
both strain and phase switching are mechanisms to control the 2D ferromagnetic
order of CrTe$_2$.",2005.00097v2
2020-05-12,Thermoelectricity carried by proximity-induced odd-frequency pairing in ferromagnet/superconductor junctions,"We explore the role of proximity-induced odd-frequency pairing in the
thermoelectricity of a ferromagnet when coupled to a conventional $s$-wave
spin-singlet superconductor through a spin-active interface. By varying both
the polarization and its direction in the ferromagnet and the interfacial
spin-orbit interaction strength, we analyze the behavior of all
proximity-induced pair amplitudes in the ferromagnet and their contributions to
the thermoelectric coefficients. Based on our results for the Seebeck
coefficient, we predict that odd-frequency spin-triplet Cooper pairs are much
efficient than the conventional spin-singlet even-frequency pairs in enhancing
thermoelectricity of the junction, especially mixed-spin triplet pairing is
favorable. Our results on the thermoelectric figure of merit show that
ferromagnet/superconductor junctions are very good thermoelectric systems when
superconductivity is dominated by odd-frequency pairing.",2005.05950v2
2020-06-03,Superconductivity-induced change in magnetic anisotropy in epitaxial ferromagnet-superconductor hybrids with spin-orbit interaction,"The interaction between superconductivity and ferromagnetism in thin film
superconductor/ferromagnet heterostructures is usually reflected by a change in
superconductivity of the S layer set by the magnetic state of the F layers.
Here we report the converse effect: transformation of the magnetocrystalline
anisotropy of a single Fe(001) layer, and thus its preferred magnetization
orientation, driven by the superconductivity of an underlying V layer through a
spin-orbit coupled MgO interface. We attribute this to an additional
contribution to the free energy of the ferromagnet arising from the controlled
generation of triplet Cooper pairs, which depends on the relative angle between
the exchange field of the ferromagnet and the spin-orbit field. This is
fundamentally different from the commonly observed magnetic domain modification
by Meissner screening or domain wall-vortex interaction and offers the ability
to fundamentally tune magnetic anisotropies using superconductivity - a key
step in designing future cryogenic magnetic memories.",2006.02118v2
2020-06-09,The spin-polarized ferromagnetic state of a cold Fermi gas,"The spin-polarized ferromagnetic state of a cold Fermi gas is investigated
for interacting and non-interacting charge-neutral and $\beta$-equilibrated
gases. The standard minimal couplings between the magnetic field and the
fermions' charges and magnetic dipole moments define the fermions' interaction
with the magnetic field. Assuming a variable coupling strength between the
magnetic field and the fermion (baryon) dipole moments, it is shown that a
ferromagnetized state can be achieved that corresponds to a lower energy
spin-polarized state with a magnetic field entirely due to the gas's magnetic
response. We find that, depending on the density, a very large increase in the
baryon dipole moments is needed to achieve this ferromagnetized state. While
the required increase seems unlikely, the induced magnetic field is of the
order $\sim10^{17}$ gauss. Furthermore, while externally magnetized Fermi gases
have an anisotropic pressure, the pressure of the ferromagnetized gas is
completely isotropic and the thermodynamically preferred magnetized state.",2006.05247v2
2020-06-17,LiHoF$_4$: Cuboidal Demagnetizing Factor in an Ising Ferromagnet,"The demagnetizing factor has an important effect on the physics of
ferromagnets. For cuboidal samples it depends on susceptibility and the
historic problem of determining this function continues to generate theoretical
and experimental challenges. To test a recent theory, we measure the magnetic
susceptibility of the Ising dipolar ferromagnet LiHoF$_4$, using samples of
varying aspect ratio, and we reconsider the demagnetizing transformation
necessary to obtain the intrinsic material susceptibility. Our experimental
results confirm that the microscopic details of the material significantly
affect the transformation, as predicted. In particular, we find that the
uniaxial Ising spins require a demagnetizing transformation that differs from
the one needed for Heisenberg spins and that use of the wrong demagnetizing
transformation would result in unacceptably large errors in the measured
physical properties of the system. Our results further shed light on the origin
of the mysterious `flat' susceptibility of ordered ferromagnets by
demonstrating that the intrinsic susceptibility of the ordered ferromagnetic
phase is infinite, regardless of sample shape.",2006.10090v1
2020-09-01,Pseudo spin-valve switch based on ferromagnet/superconductor/ferromagnet trilayer microbridge,"A noticeable magnetoresistive effect has been observed on
ferromagnet/superconductor/ferromagnet (FSF) microbridges based on diluted
ferromagnetic PdFe alloy containing as small as 1% magnetic atoms.
Microstructuring of the FSF trilayers does not destroy the effect: the most
pronounced curves were obtained on the smallest bridges of 6-8 um wide and
10-15 um long. Below the superconducting transition we are able to control the
critical current of microbridges by switching between P and AP orientations of
magnetizations of PdFe layers. The operation of FSF-bridge as a magnetic switch
is demonstrated in several regimes providing significant voltage discrimination
between digital states or remarkably low bit error rate.",2009.00498v1
2020-09-19,Enhanced Ferromagnetism of CrI3 Bilayer by Self-Intercalation,"Two-dimensional (2D) ferromagnets with high Curie temperature have long been
the pursuit for electronic and spintronic applications. CrI3 is a rising star
of intrinsic 2D ferromagnets, however, it suffers from weak exchange coupling.
Here we propose a general strategy of self-intercalation to achieve enhanced
ferromagnetism in bilayer CrI3. We showed that filling either Cr or I atoms
into the van der Waals gap of stacked and twisted CrI3 bilayers can induce the
double exchange effect and significantly strengthen the interlayer
ferromagnetic coupling. According to our first-principles calculations, the
intercalated native atoms act as covalent bridge between two CrI3 layers and
lead to discrepant oxidation states for the Cr atoms. These theoretical results
offer a facile route to achieve high-Curie-temperature 2D magnets for device
implementation.",2009.09212v1
2020-09-24,Phase diagram of multi-layer ferromagnet system with dipole-dipole interaction,"We investigate various magnetic configurations caused by the dipole-dipole
interaction (DDI) in the thin-film magnet with the perpendicular anisotropy
under the open boundary conditions. Two different approaches are simulated: one
starts from a random magnetic configuration and decreases temperatures
step-wisely; the other starts from the saturated out-of-plane ferromagnetic
state to evaluate its metastability. As typical patterns of magnetic
configuration, five typical configurations are found: an out-of-plane
ferromagnetic, in-plane ferromagnetic, vortex, multi-domain, and canted
multi-domain states. Notably, the canted multi-domain forms a concentric
magnetic-domain-pattern with an in-plane vortex structure, resulting from the
open boundary conditions. Concerning to the coercivity, a comparison of the
magnetic configurations in both processes reveals that the out-of-plane
ferromagnetic state exhibits metastability in the multi-domain state, while not
in the vortex state. We also confirm that the so-called Neel-cap
magnetic-domain-wall structure, which is originally discussed in the in-plane
anisotropy system, appears at the multi-domain state.",2009.11574v1
2020-09-28,Ferromagnetic-electrodes-induced Hall effect in topological Dirac semimetals,"We propose an unconventional type of Hall effect in a topological Dirac
semimetal with ferromagnetic electrodes. The topological Dirac semimetal itself
has time-reversal symmetry, whereas attached ferromagnetic electrodes break it,
causing the large Hall response. This induced Hall effect is a characteristic
of the helical surface/edge states that arise in topological materials, such as
topological Dirac semimetals or quantum spin Hall insulators. We compute the
Hall conductance/resistance and the Hall angle by using a lattice model with
four-terminal geometry. For topological Dirac semimetals with four electrodes,
the induced Hall effect occurs whether the current electrodes or the voltage
electrodes are ferromagnetic. When the spins in electrodes are almost fully
polarized, the Hall angle becomes as large as that of quantum Hall states or
ideal magnetic Weyl semimetals. We show the robustness of the induced Hall
effect against impurities and also discuss the spin injection and spin decay
problems. This Hall response can be used to detect whether the magnetizations
of the two ferromagnetic electrodes are parallel or antiparallel.",2009.13195v2
2020-09-30,Switching induced by spin Hall effect in an in-plane magnetized ferromagnet with the easy axis parallel to the current,"Magnetization switching in a fine-structured ferromagnet of nanoscale by the
spin-transfer torque excited via the spin Hall effect has attracted much
attention because it enables us to manipulate the magnetization without
directly applying current to the ferromagnet. However, the switching mechanism
is still unclear in regard to the ferromagnet having an in-plane easy axis
parallel to the current. Here, we develop an analytical theory of the
magnetization switching in this type of ferromagnet, and reveal the threshold
current formulas for a deterministic switching. It is clarified that the
current should be in between a certain range determined by two threshold
currents because the spin-transfer torque due to a large current outside the
range brings the magnetization in an energetically unstable state, and causes
magnetization precession around the hard axis.",2010.00136v1
2020-10-06,Chirality memory stored in magnetic domain walls in the ferromagnetic state of MnP,"Chirality in a helimagnetic structure is determined by the sense of magnetic
moment rotation. We found that the chiral information did not disappear even
after the phase transition to the high-temperature ferromagnetic phase in a
helimagnet MnP. The 2nd harmonic resistivity $\rho^{\rm 2f}$, which reflects
the breaking down of mirror symmetry, was found to be almost unchanged after
heating the sample above the ferromagnetic transition temperature and cooling
it back to the helimagnetic state. The application of a magnetic field along
the easy axis in the ferromagnetic state quenched the chirality-induced
$\rho^{\rm 2f}$. This indicates that the chirality memory effect originated
from the ferromagnetic domain walls.",2010.02491v1
2020-11-05,Engineering the ligand states by surface functionalization: A new way to enhance the ferromagnetism of CrI3,"The newly discovered 2D magnetic materials provide new opportunities for
basic physics and device applications. However, their low Curie temperature
(TC) is a common weakness. In this paper, by combining magnetic Hamiltonian,
Wannier functions and first-principle calculations, we systematically study the
magnetic properties of monolayer CrI3 functionalized by halogen. The magnetic
exchange coupling (EX) and magnetic anisotropy (MA) are found to increase
significantly by X (X=F, Cl and Br) atom adsorption, and increase along with
the coverage of X atom. In the frame work of superexchange theory, the enhanced
EX can be ascribed to the reduced energy difference and increased hopping
strength between Cr d and I p orbitals, due to the states of I ligand are
engineered by X adatom. Besides, the X adatom may provide additional
ferromagnetic superexchange channel. Finally, the CrI3 that one side is fully
adsorbed by F atoms is found to be a room temperature ferromagnetic
semiconductor with TC=650 K. Our results not only give an insightful
understanding for the enhancement of ferromagnetism of CrI3 by atom adsorption,
but also propose a promising way to improve the ferromagnetism of 2D magnetic
materials.",2011.02775v1
2021-02-08,Evidence of orbital ferromagnetism in twisted bilayer graphene aligned to hexagonal boron nitride,"We have previously reported ferromagnetism evinced by a large hysteretic
anomalous Hall effect in twisted bilayer graphene (tBLG). Subsequent
measurements of a quantized Hall resistance and small longitudinal resistance
confirmed that this magnetic state is a Chern insulator. Here we report that,
when tilting the sample in an external magnetic field, the ferromagnetism is
highly anisotropic. Because spin-orbit coupling is negligible in graphene such
anisotropy is unlikely to come from spin, but rather favors theories in which
the ferromagnetism is orbital. We know of no other case in which ferromagnetism
has a purely orbital origin. For an applied in-plane field larger than $5\
\mathrm{T}$, the out-of-plane magnetization is destroyed, suggesting a
transition to a new phase.",2102.04039v2
2021-04-27,Magnon modes as a joint effect of surface ferromagnetism and spin-orbite coupling in CoSi chiral topological semimetal,"CoSi single crystal is a known realization of a chiral topological semimetal
with simultaneously broken mirror and inversion symmetries. In addition to the
symmetry-induced spin-orbit coupling, surface ferromagnetism is known in
nominally diamagnetic CoSi structures, which appears due to the distorted bonds
and ordered vacancies near the surface. We experimentally investigate electron
transport through a thin CoSi flake at high current density. Surprisingly, we
demonstrate $dV/dI(I)$ curves which are qualitatively similar to ones for
ferromagnetic multilayers with characteristic $dV/dI$ magnon peaks and
unconventional magnetic field evolution of the peaks' positions. We understand
these observations as a result of current-induced spin polarization due to the
significant spin-orbit coupling in CoSi. Scattering of non-equilibrium
spin-polarized carriers within the surface ferromagnetic layer is responsible
for the precessing spin-wave excitations, so the observed magnon modes are the
joint effect of surface ferromagnetism and spin-orbit coupling in a CoSi chiral
topological semimetal. Thus, thin CoSi flakes behave as magnetic conductors
with broken inversion symmetry, which is important for different spintronic
phenomena.",2104.13252v1
2021-04-28,Emission of electromagnetic radiation due to spin-flip transitions in a ferromagnet,"We theoretically analyze a possibility of electromagnetic wave emission due
to electron transitions between spin subbands in a ferromagnet. Different
mechanisms of such spin-flip transitions are cousidered. One mechanism is the
electron transitions caused by magnetic field of the wave. Another mechanism is
due to Rashba spin-orbit interaction. While two mentioned mechanisms exist in a
homogeneously magnetized ferromagnet, there are two other mechanisms that exist
in non-collinearly magnetized medium. First mechanism is known and is due to
the dependence of exchange interaction constant on the quasimomentum of
conduction electrons. Second one exists in any non-collinearly magnetized
medium. We study these mechanisms in a non-collinear ferromagnet with
helicoidal magnetization distribution. The estimations of probabilities of
electron transitions due to different mechanisms are made for realistic
parameters, and we compare the mechanisms. We also estimate the radiation power
and threshold current in a simple model in which spin is injected into the
ferromagnet by a spin-polarized electric current through a tunnel barrier.",2104.13943v1
2021-05-05,Strain-induced atomic-scale building blocks for ferromagnetism in epitaxial LaCoO3,"The origin of strain-induced ferromagnetism, which is robust regardless of
the type and degree of strain in LaCoO3 (LCO) thin films, is enigmatic despite
intensive research efforts over the past decade. Here, by combining scanning
transmission electron microscopy with ab initio density functional theory plus
U calculations, we report that the ferromagnetism does not emerge directly from
the strain itself, but rather from the creation of compressed structural units
within ferroelastically formed twin-wall domains. The compressed structural
units are magnetically active with the rocksalt-type high-spin/low-spin order.
Our study highlights that the ferroelastic nature of ferromagnetic structural
units is important for understanding the intriguing ferromagnetic properties in
LCO thin films.",2105.01837v1
2021-05-20,Coexistence of ferromagnetism and spin-orbit coupling by incorporation of platinum in two-dimensional VSe$_2$,"We report on a novel material, namely two-dimensional (2D)
V$_{1-x}$Pt$_x$Se$_2$ alloy, exhibiting simultaneously ferromagnetic order and
Rashba spin-orbit coupling. While ferromagnetism is absent in 1T-VSe$_2$ due to
the competition with the charge density wave phase, we demonstrate
theoretically and experimentally that the substitution of vanadium by platinum
in VSe$_2$ (10-50 %) to form an homogeneous 2D alloy restores ferromagnetic
order with Curie temperatures of 6 K for 5 monolayers and 25 K for one
monolayer of V$_{0.65}$Pt$_{0.35}$Se$_2$. Moreover, the presence of platinum
atoms gives rise to Rashba spin-orbit coupling in (V,Pt)Se$_2$ providing an
original platform to study the interplay between ferromagnetism and spin-orbit
coupling in the 2D limit.",2105.10022v1
2021-05-29,"Magnetic Impurity Effects on Ferromagnetic Fluctuations in Heavily Overdoped (Bi,Pb)$_2$Sr$_2$Cu$_{1-y}$Fe$_y$O$_{6+δ}$ Cuprates","We investigated Fe-substitution effects on ferromagnetic fluctuations in the
superconducting overdoped and non-superconducting heavily overdoped regimes of
the Bi-2201 cuprates by the magnetization and electrical-resistivity
measurements. It was found that the spin-glass state was induced at low
temperatures by the Fe substitution. The Curie constant and the effective Bohr
magneton, estimated from the magnetic susceptibility, as well as the
dimensionality of the ferromagnetic fluctuations from the resistivity, suggest
the enhancement of the ferromagnetic fluctuations owing to the Fe substitution.
A ferromagnetic spin-cluster model is proposed in the heavily overdoped regime
of Bi-2201, while an antiferromagnetic spin-cluster model has been proposed in
the overdoped regime of Bi-2201 [Hiraka et al., Phys. Rev. B 81, 144501
(2010)].",2105.14288v2
2021-06-16,"Unusual dynamic susceptibility arising from soft ferromagnetic domains in MnBi8Te13 and Sb-doped MnBi2nTe3n+1 (n=2, 3)","MnBi2nTe3n+1(MBT) is the first intrinsic magnetic topological insulator and
is promising to hostemergent phenomena such as quantum anomalous Hall effect.
They can be made ferromagnetic by having n >= 4 or with Sb doping. We studied
the magnetic dynamics in a few selected ferromag-netic (FM) MBT compounds,
including MnBi8Te13and Sb doped MnBi2nTe3n+1(n= 2,3) usingAC susceptibility and
magneto-optical imaging. Slow relaxation behavior is observed in all
threecompounds, suggesting its universality among FM MBT. We attribute the
origin of the relaxationbehavior to the irreversible domain movements since
they only appear below the saturation fieldswhen ferromagnetic domains form.
The very soft ferromagnetic domain nature is revealed by thelow-field
fine-structured domains and high-field sea-urchin-shaped remanent-state domains
imagedvia our magneto-optical measurements. Finally, we ascribe the rare
""double-peak"" behavior ob-served in the AC susceptibility under small DC bias
fields to the very soft ferromagnetic domainformations.",2106.08969v1
2021-07-16,Prediction of 2D ferromagnetism and monovalent europium ions in the EuBr/graphene heterojunctions,"Europium, one of the rare earth elements, exhibits +2 and +3 valence states
and has been widely used for magnetic modification of materials. Based on
density functional theory calculations, we predict the 2D EuBr/graphene
heterojunctions to exhibit metallicity, huge intrinsic-ferromagnetism nearly
7.0 {\mu}B per Eu and the special monovalent Eu ions. Electron localization
function (ELF), difference charge densities and Bader charge analyses
demonstrate that there are cation-{\pi} interactions between the EuBr films and
graphene, which explains the stability of these unusual heterojunctions.
Graphene works as substrate to enable the stability of EuBr monolayer crystals
where EuBr plays an important role to yield ferromagnetism and enhance
metallicity in the heterojunctions. Monte Carlo simulations are used to
estimate a Curie temperature of about 7 K, which, together with magnetic
configurations, can be further modulated by external strains and charge-carrier
doping. In general, our theoretical work predicts the properties of the novel
2D ferromagnetic EuBr/graphene heterojunctions, suggests the possibility of
combining the 2D intrinsic-ferromagnetic metal halide crystals and graphene,
and opens up a new perspective in next-generation electronic, spintronic
devices and high-performance sensors.",2107.08833v2
2021-08-02,Electrically tunable room-temperature ferromagnetism in CrBr$_3$,"The recent discovery of magnetic ordering in two-dimension has lead to
colossal efforts to find atomically thin materials that order at high
temperatures. However, due to fundamental spin fluctuation in reduced
dimension, the room-temperature ferromagnetism remains elusive. Here, we report
a dramatic manipulation of magnetic ordering up to room temperature in the
monolayer CrBr$_3$, within the first-principles Heisenberg XXZ model. The
exchange and anisotropic magnetic interactions are externally modulated by a
gate-induced charge carrier doping that triggers a nontrivial phase diagram.
High-temperature ferromagnetism is associated with a substantial increase in
both effective ferromagnetic exchange and overall magnetic anisotropy under
experimentally attainable hole doping. In contrast, electron doping quickly
switches the magnetic easy axis. The gate-tuneable room temperature
ferromagnetism in CrBr$_3$ presents new possibilities in electrically
controlled spintronic and magnetoelectric devices based on atomically thin
crystals.",2108.00684v1
2021-10-08,Fermi surface expansion above critical temperature in a Hund ferromagnet,"Using a cluster extension of the dynamical mean-field theory, we show that
strongly correlated metals subject to Hund's physics exhibit significant
electronic structure modulations above magnetic transition temperatures. In
particular, in a ferromagnet having a large local moment due to Hund's coupling
(Hund's ferromagnet), the Fermi surface expands even above the Curie
temperature ($T_{\rm C}$) as if a spin polarization occurred. Behind this
phenomenon, effective ``Hund's physics'' works in momentum space, originating
from ferromagnetic fluctuations in the strong coupling regime. The resulting
significantly momentum-dependent (spatially nonlocal) electron correlations
induce an electronic structure reconstruction involving a Fermi-surface volume
change and a redistribution of the momentum-space occupation. Our finding will
give a deeper insight into the physics of Hund's ferromagnets above $T_{\rm
C}$.",2110.04288v2
2021-11-05,Giant oscillatory Gilbert damping in superconductor/ferromagnet/superconductor junctions,"Interfaces between materials with differently ordered phases present unique
opportunities for exotic physical properties, especially the interplay between
ferromagnetism and superconductivity in the ferromagnet/superconductor
heterostructures. The investigation of zero- and pi-junctions has been of
particular interest for both fundamental physical science and emerging
technologies. Here, we report the experimental observation of giant oscillatory
Gilbert damping in the superconducting Nb/NiFe/Nb junctions with respect to the
NiFe thickness. This observation suggests an unconventional spin pumping and
relaxation via zero-energy Andreev bound states that exist only in the
Nb/NiFe/Nb pi-junctions, but not in the Nb/NiFe/Nb zero-junctions. Our findings
could be important for further exploring the exotic physical properties of
ferromagnet/superconductor heterostructures, and potential applications of
ferromagnet pi-junctions in quantum computing, such as half-quantum flux
qubits.",2111.03233v1
2021-11-19,Ferromagnetic and metamagnetic transitions in itinerant electron systems: a microscopic study,"We perform a microscopic study of itinerant ferromagnetic systems. We reveal
a very rich phase diagram in the three-dimensional space spanned by the
chemical potential, a magnetic field, and temperature beyond the Landau theory
analyzed so far. Besides a generic wing structure near a tricritical point upon
introducing the magnetic field, we find that an additional wing can be
generated close to a quantum critical end point (QCEP) and also even from
deeply inside the ferromagnetic phase. A tilting of the wing controls the
entropy jump associated with the metamagnetic transition. Ferromagnetic and
metamagnetic transitions are usually accompanied by a Lifshitz transition at
low temperatures, i.e., a change of Fermi surface topology including the
disappearance of the Fermi surface. In particular, the Fermi surface of either
spin band vanishes at the QCEP. These rich phase diagrams are understood in
terms of the density of states and the breaking of particle-hole symmetry in
the presence of a next nearest-neighbor-hopping integral t', which is expected
in actual materials. The obtained phase diagrams are discussed in a possible
connection to itinerant ferromagnetic systems such as UGe2, UCoAl, ZrZn2, and
others including materials exhibiting the magnetocaloric effect.",2111.10068v2
2021-11-30,Nonreciprocity of spin waves in a double layer ferromagnet with Dzyaloshinskii-Moriya interactions,"In this paper, boundary conditions for Landau-Lifshitz equations at the
interface between two ferromagnets with different Dzyaloshinskii-Moriya
interactions are derived. We calculated and verified the analytical expression
for the energy flux density continuity for the spin-wave propagation through
the interface between two ferromagnets with/without Dzyaloshinskii-Moriya
interactions considering the boundary conditions mentioned. Analytical
expressions for reflection, transmission coefficients and the nonreciprocity
factor are calculated in the case of spin-wave propagation through a double
layer ferromagnet with/without Dzyaloshinskii-Moriya interactions in the
first/second layer. Two principally different types of nonreciprocity effects
for spin waves are revealed in such a double layer system. The material
parameters of a double layer ferromagnet with/without Dzyaloshinskii-Moriya
interactions in the first/second layer are found for which the extremely high
nonreciprocity factor (>10) is expected according to the results of
calculations. The results of the paper deepen the knowledge about the spin-wave
propagation control in magnonic devices.",2111.15244v1
2021-12-06,Quantum phases of ferromagnetically coupled dimers on Shastry-Sutherland lattice,"The ground state (gs) of antiferromagnetically coupled dimers on the
Shastry-Sutherland lattice (SSL) stabilizes many exotic phases and has been
extensively studied. The gs properties of ferromagnetically coupled dimers on
SSL are equally important but unexplored. In this model the exchange coupling
along the $x$-axis ($J_x$) and $y$-axis ($J_y$) are ferromagnetic and the
diagonal exchange coupling ($J$) is antiferromagnetic. In this work we explore
the quantum phase diagram of ferromagnetically coupled dimer model numerically
using density matrix renormalization group (DMRG) method. We note that in
$J_x$-$J_y$ parameter space this model exhibits six interesting phases:(I)
stripe $(0,\pi)$, (II) stripe $(\pi,0)$, (III) perfect dimer, (IV) $X$-spiral,
(V) $Y$-spiral and (VI) ferromagnetic phase. Phase boundaries of these quantum
phases are determined using the correlation functions and gs energies. We also
notice the correlation length in this system is less than four lattice units in
most of the parameter regimes. The non-collinear behaviour in $X$-spiral and
$Y$-spiral phase and the dependence of pitch angles on model parameters are
also studied.",2112.02975v1
2022-01-31,Anomalous Nernst effect in La0.5Ca0.5Coo3,"We report the occurrence of the anomalous Nernst effect (ANE) in
polycrystalline perovskite La0.5Ca0.5CoO3. The sample is ferromagnetic below TC
= 147 K and resistivity shows non-metallic behavior above and below the TC with
only a small negative magnetoresistance (~2%) around TC. Field dependence of
magnetization at 10 K shows large hysteresis with a coercive field of 6 kOe but
a small magnetization ~ 0.64 Bohr magneton/Co even in a field of 50 kOe, which
indicates the presence of magnetically heterogeneous ground state consisting of
ferromagnetic and non-ferromagnetic phases. The field dependence of the Nernst
thermopower (Sxy) at low temperatures shows complete saturation but the
magnetization does not. This indicates that the ANE in La0.5Ca0.5CoO3 depends
only on the transport properties of the ferromagnetic phase, while it is not
affected by the non-ferromagnetic phase. Due to the higher value of remnant
Sxy, the magnetized polycrystalline sample exhibits ANE in absence of an
external magnetic field.",2201.12982v1
2022-03-18,Prediction of novel two-dimensional rare-earth material with room-temperature ferromagnetism and large perpendicular magnetic anisotropy,"Novel 2D ferromagnets with high Curie temperature and large perpendicular
magnetic anisotropy are especially attractive owing to the future promising
application in modern spintronics, but meanwhile the 2D ferromagnetic materials
with high Curie temperature and large perpendicular magnetic anisotropy are
rarely reported. Based on density functional theory (DFT) calculations, we
predict a new kind of 2D ferromagnetic materials - GdB2N2, which possesses
large magnetic moment, high Curie temperature (335 K) and large perpendicular
magnetic anisotropy (10.38 meV/f.u.). Biaxial strain ranging from -0.5% to 5%
and different concentrations of charge-carrier doping are applied to reveal the
influence on the Curie temperature and magnetic anisotropy energy (MAE).
Besides, magnetic coupling process within GdB2N2 is found to be via a
Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. In summary, our work here
predicts a novel 2D rare-earth material GdB2N2, which not only enriches the
category of 2D room-temperature ferromagnets, but also proposes a new
possibility of combining traditional 2D materials and rare-earth materials to
achieve more intriguing magnetic properties, finally it carves out the path for
the next-generation spintronic devices and sensors.",2203.10969v1
2022-03-23,Effective decoupling of ferromagnetic sublattices by frustration in Heusler alloys,"Magnetic frustration in ferromagnetic metallic systems is unusual due to the
long-range and symmetric nature of the exchange interactions. In this work we
prove that it is possible to obtain a highly frustrated ferromagnetic phase in
a multi-sublattices cubic structure through a fine tuning of the magnetic
interactions. This peculiar state is achieved in Ni-Mn-(In, Sn) Heusler alloys
and results in the effective decoupling of their two intertwined ferromagnetic
sublattices. One sublattice is ferromagnetic long range ordered below the
macroscopic Curie temperature (TC ) whereas the second one remains disordered
until a crossover to a polarized state occurs at T << TC . This result points
out that a fine engineering of the magnetic interactions in metallic systems
can lead to interesting novel and emergent phenomena.",2203.12498v2
2022-04-04,Two-Dimensional Ferromagnetic Half-Metallic Janus V2AsP Monolayer,"Two-dimensional (2D) ferromagnetic materials present promising candidates for
spintronic devices, and the half-metallic materials with 100% spin polarization
at Fermi energy level are highly desired for many spin-based devices. 2D Janus
materials have attracted great attention in recent years due to their excellent
properties induced by breaking the symmetry. Here, using the density functional
theory, we report that the Janus V2AsP monolayer demonstrates a charming
ferromagnetic half-metallic feature. It is dynamically stable in view of the
absence of imaginary frequency phonon. The half-metallic gap is about 0.38 eV
and the spin splitting of about 1.34eV for the V2AsP monolayer. Interestingly,
a tensile strain of 4.9% can induce it to undergo a phase transition from
ferromagnetic to anti-ferromagnetic state. Moreover, the Curie temperature (Tc)
enhances with the increase of compressive strain. All there appealing
properties make the half-metallic Janus V2AsP monolayer a promising material
for 2D spintronic applications.",2204.01274v3
2022-04-24,Generating Two-dimensional Ferromagnetic Charge Density Waves via External Fields,"Two-dimensional (2D) ferromagnetic charge density wave (CDW), an exotic
quantum state for exploring the intertwining effect between correlated charge
and spin orders in 2D limit, has not been discovered in the experiments yet.
Here, we propose a feasible strategy to realize 2D ferromagnetic CDWs under
external fields, which is demonstrated in monolayer VSe$_2$ using
first-principles calculations. Under external tensile strain, two novel
ferromagnetic CDWs ($\sqrt{3}$$\times$$\sqrt{3}$ and 2$\times2\sqrt{3}$ CDWs)
can be generated, accompanied by distinguishable lattice reconstructions of
magnetic V atoms. Remarkably, because the driving forces for generating these
two ferromagnetic CDWs are strongly spin-dependent, fundamentally different
from that in conventional CDWs, the $\sqrt{3}$$\times$$\sqrt{3}$ and
2$\times2\sqrt{3}$ CDWs can exhibit two dramatically different half-metallic
phases under a large strain range, along with either a flat band or a Dirac
cone around Fermi level. Our proposed strategy and material demonstration may
open a door to generate and manipulate correlation effect between collective
charge and spin orders via external fields.",2204.11179v1
2022-05-03,"Carrier Doping Modulates 2D Intrinsic Ferromagnetic Mn2Ge2Te6 Monolayer High Curie Temperature, Large Magnetic Crystal Anisotropy","The Mn2Ge2Te6 shows intrinsic ferromagnetic (FM) order, with Curie
temperature (Tc) of 316 K. The FM order origins from superexchange interaction
between Mn and Te atoms. Mn2Ge2Te6 is half-metal (HM), and spin-\b{eta}
electron is a semiconductor with gap of 1.462 eV. Mn2Ge2Te6 tends in-plane
anisotropy (IPA), with magnetic anisotropy energy (MAE) of -13.2 meV/f.u.. The
Mn2Ge2Te6 shows good dynamical and thermal stability. Moreover, Mn2Ge2Te6
presents good ferromagnetic and half-metallic stability under charge doping.
The carriers doping could effectively tune magnetic and electronic properties.
Specifically, the magnetic moment, exchange parameter, and MAE could be
efficiently tuned. The total magnetic moment changes linearly with charges
doping. The exchange parameters could be controlled by the doping carriers. The
carriers doping could modulate MAE to -18.4 (+0.4 e), -0.85 (-1.6 e), 1.31
(-2.4 e) meV/f.u., by changing hybridization between Te atoms' py and pz
orbitals. Mn2Ge2Te6 with intrinsic ferromagnetism, high tunable MAE, good
stability of ferromagnetism and half-metallicity could help researchers to
investigate its wide application in the electronics and spintronics.",2205.01498v1
2022-06-14,Interstitial-induced ferromagnetism in a two-dimensional Wigner crystal,"The two-dimensional Wigner crystal (WC) occurs in the strongly interacting
regime ($r_s \gg 1$) of the two-dimensional electron gas (2DEG). The magnetism
of a pure WC is determined by tunneling processes that induce multi-spin
ring-exchange interactions, resulting in fully polarized ferromagnetism for
large enough $r_s$. Recently, Hossain et al. [PNAS 117 (51) 32244-32250]
reported the occurrence of a fully polarized ferromagnetic insulator at $r_s
\gtrsim 35$ in an AlAs quantum well, but at temperatures orders of magnitude
larger than the predicted exchange energies for the pure WC. Here, we analyze
the large $r_s$ dynamics of an interstitial defect in the WC, and show that it
produces local ferromagnetism with much higher energy scales. Three hopping
processes are dominant, which favor a large, fully polarized ferromagnetic
polaron. Based on the above results, we speculate concerning the phenomenology
of the magnetism near the metal-insulator transition of the 2DEG.",2206.07191v2
2022-07-14,Finite-temperature properties of extended Nagaoka ferromagnetism,"We study finite-temperature properties of a Hubbard model including sites of
a particle bath which was proposed as a microscopic model to show itinerant
ferromagnetism at finite electron density. We use direct numerical methods,
such as exact diagonalization and random vector methods. The temperature
dependence of quantities is surveyed in the full range of the temperature. We
find that the specific heat has several peaks, which correspond to ordering
processes in different energy scales. In particular, magnetic order appears at
very low temperature. Depending on the chemical potential of the particle bath
and the Coulomb interaction, the system exhibits an itinerant ferromagnetic
state or an antiferromagnetic state of the Mott insulator. Microscopically the
competition between these two types of orderings causes a peculiar ordering
process of local spin correlations. Some local ferromagnetic correlations are
found to be robust, which indicates that the ferromagnetic correlation
originates from the motion of itinerant electrons in a short-range cluster.",2207.06588v1
2022-08-15,Absorption of Transverse Spin Current in Ferromagnetic NiCu: Dominance of Bulk Dephasing over Spin-Flip Scattering,"In ferromagnetic metals, transverse spin currents are thought to be absorbed
via dephasing -- i.e., destructive interference of spins precessing about the
strong exchange field. Yet, due to the ultrashort coherence length of
$\approx$1 nm in typical ferromagnetic thin films, it is difficult to
distinguish dephasing in the bulk from spin-flip scattering at the interface.
Here, to assess which mechanism dominates, we examine transverse spin-current
absorption in ferromagnetic NiCu alloy films with reduced exchange fields. We
observe that the coherence length increases with decreasing Curie temperature,
as weaker dephasing in the film bulk slows down spin absorption. Moreover,
nonmagnetic Cu impurities do not diminish the efficiency of spin-transfer
torque from the absorbed spin current. Our findings affirm that transverse spin
current is predominantly absorbed by dephasing inside the nanometer-thick
ferromagnetic metals, even with high impurity contents.",2208.07294v1
2022-08-23,Nematic Tomonaga-Luttinger Liquid Phase in an $S=1/2$ Ferromagnetic-Antiferromagnetic Bond-Alternating Chain,"We numerically investigate the ground-state phase diagram of the $S=1/2$
ferromagnetic-antiferromagnetic bond-alternating chain, in which the
ferromagnetic interactions are stronger than the antiferromagnetic ones, and
the anisotropies of the former and latter interactions are of the Ising-type
and the $XY$-type, respectively. We use various numerical methods, such as the
level spectroscopy and phenomenological renormalization-group analyses of the
numerical data obtained by the exact diagonalization method, and so on. The
resultant phase diagrams contain the ferromagnetic, $XY$1, singlet-dimer, and
up-up-down-down phases as well as the nematic Tomonaga-Luttinger liquid (nTLL)
phase which appears in a wide region of the interaction parameters.
Perturbation calculations from the strong limit of the ferromagnetic
interactions reproduce fairly well the numerical results of the phase boundary
lines associated with the nTLL phase in the phase diagrams.",2208.10988v2
2022-09-06,High-spin orbital interactions across van der Waals gaps controlling the interlayer ferromagnetism in van der Waals ferromagnets,"We examined what interactions control the sign and strength of the interlayer
coupling in van der Waals ferromagnets such as Fe3-xGeTe2, Cr2Ge2Te6, CrI3 and
VI3, to find that high-spin orbital interaction across the van der Waals gaps
are a key to understanding their ferromagnetism. Interlayer ferromagnetic
coupling in Fe3-xGeTe2 Cr2Ge2Te6, and CrI3 is governed by the high-spin
two-orbital two-electron destabilization, but that in VI3 by the high-spin
four-orbital two-electron stabilization. These interactions explain a number of
seemingly puzzling observations in van der Waals fer-romagnets.",2209.02233v1
2022-09-22,Neutron Depolarization due to Ferromagnetism and Spin Freezing in CePd$_{1-x}$Rh$_x$,"We report neutron depolarization measurements of the suppression of
long-range ferromagnetism and the emergence of magnetic irreversibilities and
spin freezing in CePd$_{1-x}$Rh$_x$ around $x^*\approx0.6$. Tracking the
temperature versus field history of the neutron depolarization, we find clear
signatures of long-range Ising ferromagnetism below a Curie temperature $T_{\rm
C}$ for $x=0.4$ and a spin freezing of tiny ferromagnetic clusters below a
freezing temperature $T_{\rm F1}$ for $x>x^*$. Under
zero-field-cooling/field-heating and for $x>x^*$ a reentrant temperature
dependence of the neutron depolarization between $T_{\rm F2}<T_{\rm F1}$ and
$T_{\rm F1}$ is microscopically consistent with a thermally activated growth of
the cluster size. The evolution of the depolarization as well as the reentrant
temperature dependence as a function of Rh content are consistent with the
formation of a Kondo-cluster glass below $T_{\rm F1}$ adjacent to a
ferromagnetic quantum phase transition at $x^*$.",2209.11246v1
2022-10-21,Ferromagnetic domains in the large-$U$ Hubbard model with a few holes: an FCIQMC study,"Two-dimensional Hubbard lattices with two or three holes are investigated as
a function of $U$ in the large-$U$ limit. In the so-called Nagaoka limit
(one-hole system at infinite $U$), it is known that the Hubbard model exhibits
a ferromagnetic ground-state. Here, by means of exact FCIQMC simulations
applied to periodic lattices up to 24 sites, we compute spin-spin correlation
functions as a function of increasing $U$. The correlation functions clearly
demonstrate the onset of ferromagnetic domains, centred on individual holes.
The overall total spin of the wavefunctions remain the lowest possible (0, or
$\frac{1}{2}$, depending on the number of holes). The ferromagnetic domains
appear at interaction strengths comparable to the critical interaction
strengths of the Nagaoka transition in finite systems with strictly one hole.
The existence of such ferromagnetic domains is the signature of Nagaoka physics
in Hubbard systems with a small (but greater than one) number of holes.",2210.12049v1
2022-11-29,Interlayer ferromagnetism and insulator-metal transition in element-doped CrI3 thin films,"The exploration of magnetism in two-dimensional layered materials has
attracted extensive research interest. For the monoclinic phase CrI3 with
interlayer antiferromagnetism, finding a static and robust way of realizing the
intrinsic interlayer ferromagnetic coupling is desirable. In this Letter, we
study the electronic structure and magnetic properties of the nonmagnetic
element (e.g., O, S, Se, N, P, As and C) doped bi- and triple-layer CrI3
systems via first-principles calculations. Our results demonstrate that O, P,
S, As, and Se doped CrI3 bilayer can realize interlayer ferromagnetism. Further
analysis shows that the interlayer ferromagnetic coupling in the doped
few-layer CrI3 is closely related to the formation of localized spin-polarized
state. This finding indicates that insulated interlayer ferromagnetism can be
realized at high doping concentration (larger than 8.33%). When the doping
concentration is less than 8.33%, but larger than 2.08%, an insulator-metal
phase transition can occur since the localized spin-polarized states percolate
to form contiguous grids in few-layer CrI3.",2211.15972v1
2022-11-29,3D time-resolved analysis of the evolution metamagnetic phase transition in FeRh system,"The FeRh alloy is an attractive material for studies of magnetic first-order
phase transitions. The phase transition in FeRh from an antiferromagnetic to
the ferromagnetic state is accompanied by the nucleation, growth, and merging
of ferromagnetic clusters. The ferromagnetic phase evolution is studied in
detail, and its various stages are distinguished. Both static properties and
phase transition kinetics (time dependences of magnetization) are investigated.
A comprehensive analysis allows us to determine the ferromagnetic phase
nucleation regions and the main features of phase growth. In addition, the
mechanisms that lead to a change in the ferromagnetic phase growth rate (the
limitation effect and the magnetocaloric effect) were determined. The variation
of phase transition evolution dominant mechanisms depending on the sample
microstructure was shown.",2211.15984v1
2023-02-07,Control of vortex chirality in a symmetric ferromagnetic ring using ferromagnetic nanoelement,"Controlling the vortex chirality in ferromagnetic nanodots and nanorings has
been a topic of investigation for the last few years. Many control methods have
been proposed and it has been found that the control is related to the breaking
of the circular symmetry. In this paper, we present a theoretical study
demonstrating the control of chirality in ferromagnetic nanoring without
directly breaking its symmetry, but instead by placing elongated ferromagnetic
nanoelement inside the ring, Here, the stray magnetostatic field exerted by the
asymmetrically placed nanoelement determines the movement of the domain walls
upon remagnetization of the nanoring and the resulting chirality in the
remanence. This approach allows the chirality of the vortex state to be
controlled and also promises its control in a dense array of nanorings, thus
suitable for spintronic and magnonic applications.",2302.03626v1
2023-03-28,Analysis of ultrafast magnetization switching dynamics in exchange-coupled ferromagnet-ferrimagnet heterostructures,"Magnetization switching in ferromagnets has so far been limited to the
current-induced spin-orbit-torque effects. Recent observation of
helicity-independent all-optical magnetization switching in exchange-coupled
ferromagnet ferrimagnet heterostructures expanded the range and applicability
of such ultrafast heat-driven magnetization switching. Here we report the
element-resolved switching dynamics of such an exchange-coupled system, using a
modified microscopic three-temperature model. We have studied the effect of i)
the Curie temperature of the ferromagnet, ii) ferrimagnet composition, iii) the
long-range RKKY exchange-coupling strength, and iv) the absorbed optical energy
on the element-specific time-resolved magnetization dynamics. The phase-space
of magnetization illustrates how the RKKY coupling strength and the absorbed
optical energy influence the switching time. Our analysis demonstrates that the
threshold switching energy depends on the composition of the ferrimagnet and
the switching time depends on the Curie temperature of the ferromagnet as well
as RKKY coupling strength. This simulation anticipates new insights into
developing faster and more energy-efficient spintronics devices.",2303.16294v1
2023-04-01,Itinerant ferromagnetism entrenched by the anisotropy of spin-orbit coupling in a dipolar Fermi gas,"We investigate the the itinerant ferromagnetism in a dipolar Fermi atomic
system with the anisotropic spin-orbit coupling (SOC),which is traditionally
explored with isotropic contact interaction.We first study the ferromagnetism
transition boundaries and the properties of the ground states through the
density and spin-flip distribution in momentum space, and we find that both the
anisotropy and the magnitude of the SOC play an important role in this process.
We propose a helpful scheme and a quantum control method which can be applied
to conquering the difficulties of previous experimental observation of
itinerant ferromagnetism. Our further study reveals that exotic Fermi surfaces
and an abnormal phase region can exist in this system by controlling the
anisotropy of SOC, which can provide constructive suggestions for the research
and the application of a dipolar Fermi gas. Furthermore, we also calculate the
ferromagnetism transition temperature and novel distributions in momentum space
at finite temperature beyond the ground states from the perspective of
experiment.",2304.00286v1
2023-06-03,Critical behaviours of anisotropic XY ferromagnet in the presence of random field,"The anisotropic XY ferromagnet has been studied by Monte Carlo simulation in
a three dimensional simple cubic lattice. The increase in critical temperature
(ferro-para transition) has been noticed with increasing the strength of
anisotropy. The effects of random fields (both with full circular symmetry and
in angular window) on the critical temperature are investigated systematically
in the anisotropic XY ferromagnet in three dimensions. Reduction in the
critical temperature of anisotropic XY ferromagnet has been observed in the
presence of random field. The compensating field (the required amount of field
which preserves the critical temperature for isotropic XY ferromagnet) has been
studied as a function of the strength of anisotropy. The compensating field was
found to depend linearly on the strength of anisotropy. We have also studied
the effects of random field confined in the angular window and observed the
reduction of the critical temperature with increase of the angular extension.
The critical behaviours are formalized by the usual finite size analysis and
the estimation of critical exponents for the susceptibility and the specific
heat. .",2306.02162v2
2023-06-22,Ultrafast Dynamics of Orbital Angular Momentum of Electrons Induced by Femtosecond Laser Pulses: Generation and Transfer Across Interfaces,"The orbital angular momenta (OAM) of electrons play an increasingly important
role in ultrafast electron and magnetization dynamics. In this theoretical
study, we investigate the electron dynamics induced by femtosecond laser pulses
in a normal metal, a ferromagnet, and a ferromagnet/normal metal
heterostructure. We analyze the spatio-temporal distributions of the
laser-induced OAM and their respective currents. Our findings demonstrate that
a circularly polarized laser pulse can induce a sizable and long-lasting OAM
component in a normal metal. Furthermore, an interface between a ferromagnet
and a normal metal facilitates the demagnetization of the magnet by the OAM
contribution to the total magnetization. Finally, to transfer OAM from a
ferromagnet into a normal metal, it is advantageous to use a laser setup that
induces the desired OAM component in the ferromagnet, but not in the normal
metal.",2306.12810v1
2023-06-27,Magnetic proximity in a coupled Ferromagnet-Spin glass system,"We study the competition between ferromagnetic and spin glass phases using a
system of coupled infinite-range Ising and Sherrington-Kirkpatrick models. We
obtain the replica-symmetric solution for the free energy of this system in
terms of magnetization and Edwards-Anderson order parameters in both
subsystems. Using these order parameters we are able to identify different
phases in the system and determine which phase is dominant for different
strengths of the coupling between two subsystems. We observe that both
subsystems are in the same phase although with different order parameters. The
phase boundary between paramagnetic-ferromagnetic and paramagnetic-spin glass
phases is more or less similar to that in the Sherrington-Kirkpatrick phase
diagram. But the boundary between ferromagnetic-spin glass phases becomes
qualitatively different as the coupling between the two subsystems changes.
Remarkably, for intermediate values of the coupling, this phase boundary is
such that there could be a reentrant transition between spin glass and
ferromagnetic phases by increasing the temperature. We found that for some
range of the coupling, the second order transition between these phases turns
into first order at a tricritical point. Further, we carry out the stability
analysis by considering deviations from the replica symmetric solution.",2306.15426v1
2023-07-07,Interacting topological magnons in a checkerboard ferromagnet,"This work is devoted to studying the magnon-magnon interaction effect in a
two-dimensional checkerboard ferromagnet with the Dzyaloshinskii-Moriya
interaction. By means of the first-order Green function formalism, the
influence of magnon-magnon interaction on the magnon band topology is analyzed.
In order to verify that the gap-closing phenomenon is a signature for the
topological phase transitions of the checkerboard ferromagnet, we display that
the Chern numbers of renormalized magnon bands are distinct above and below the
critical temperature. Our results show that the checkerboard ferromagnet
possesses two topological phases and its topological phase can be controlled
either by the temperature or applied magnetic field due to magnon-magnon
interactions. Interestingly, we find that the topological phase transition
occurs twice with the increase of the temperature, which is different from the
result of the honeycomb ferromagnet.",2307.03361v1
2023-07-10,Angular dependence of spin-orbit torque in monolayer $Fe_3GeTe_2$,"In ferromagnetic systems lacking inversion symmetry, an applied electric
field can control the ferromagnetic order parameters through the spin-orbit
torque. The prototypical example is a bilayer heterostructure composed of a
ferromagnet and a heavy metal that acts as a spin current source. In addition
to such bilayers, spin-orbit coupling can mediate spin-orbit torques in
ferromagnets that lack bulk inversion symmetry. A recently discovered example
is the two-dimensional monolayer ferromagnet $Fe_3GeTe_2$. In this work, we use
first-principles calculations to study the spin-orbit torque and ensuing
magnetic dynamics in this material. By expanding the torque versus
magnetization direction as a series of vector spherical harmonics, we find that
higher order terms (up to $\ell=4$) are significant and play important roles in
the magnetic dynamics. They give rise to deterministic, magnetic field-free
electrical switching of perpendicular magnetization.",2307.04900v2
2023-07-13,Tailoring the ferromagnetic surface potential landscape by a templating two-dimensional metal-organic porous network,"Two-dimensional metal-organic porous networks (2D-MOPNs) have been identified
as versatile nanoarchitectures to tailor surface electronic and magnetic
properties on noble metals. In this context, we propose a protocol to
redecorate a ferromagnetic surface potential landscape using a 2D-MOPN.
Ultrathin cobalt (Co) films grown on Au(111) exhibit a well-ordered surface
triangular reconstruction. On the ferromagnetic surface, the adsorbed
2,4,6-tris(4-pyridyl)-1,3,5triazine (T4PT) molecules can coordinate with the
native Co atoms to form a large-scale Co-T4PT porous network. The Co-T4PT
network with periodic nanocavities serves as a templating layer to reshape the
ferromagnetic surface potential. The subsequently deposited C60 molecules are
steered by the network porous potential and the neighboring C60 interactions.
The prototype of the ferromagnetic-supported 2D-MOPN is a promising template
for the tailoring of molecular electronic and spin properties.",2307.06818v1
2023-09-01,Ordering kinetics and steady states of XY-model with ferromagnetic and nematic interaction,"The two-dimensions XY model, undergoes the Berezinskii Kosterlitz Thouless
(BKT) transition through unbinding of defect pairs of opposite signs. When the
interaction between spins is purely ferromagnetic, these defects have +-1
charge, whereas for pure nematic interaction between spins, they have charge
+-1/2. Two-dimensional XY-model in the presence of both ferromagnetic and
nematic interactions has been studied both theoretically and experimentally. In
this paper, we have studied dynamics of defects in the presence of both
ferromagnetic and nematic interactions on a square lattice. Varying the
strength of ferromagnetic and nematic interactions, we have observed behavior
of both integer and half integer defects and based on that we propose a phase
diagram which exhibit three distinct regions in the phase diagram below the
critical TBKT : polar phase, nematic phase and coexistence phase and a
disordered regions above it. Also, for pure polar and pure nematic case, our
results show that the exponent, for algebraic decay of number of defects with
time, decays linearly with temperature.",2309.00455v1
2023-10-12,Optimising motion-induced spin transfer,"In this paper, the spin transfer between two ferromagnetic insulators is
studied. There is a narrow gap between the ferromagnetic insulators so that
they are weakly interacting with each other. One of the ferromagnetic
insulators is moving at a constant speed while the other is at rest; hence, the
system is out of equilibrium. In the presence of the shearing motion, the
interaction amplitude is periodically modulated at the Doppler frequency. A
unitary transformation allows us to regard the periodic modulation of the
interaction amplitude as an effective potential, which drives the spin
transfer. The amount of the spin current is controlled by the spectral overlap
and the carrier population difference between the two ferromagnetic media. If
the spectra of the two ferromagnets are moderately broadened, the overlap in
the spectral domain increases, enlarging the spin current. However, too much
broadening spoils the spectral overlap and, hence, the spin current. This
implies that there is an optimal condition for maximising the spin transfer.",2310.08200v2
2023-10-20,Magnetization of Flat Superconducting Films on Ferromagnetic Substrates,"Ferromagnetic substrate influences the electromagnetic response of a type-II
superconducting film to the applied magnetic field. We present a
two-dimensional integrodifferential model for the magnetization of a flat
superconductor/ferromagnet bilayer of an arbitrary shape using a thin shell
quasistatic model for the ferromagnetic substrate and an infinitely thin
approximation for the superconducting layer. An efficient numerical method is
developed and used to investigate the effect of a ferromagnetic substrate. In
particular, we simulate the thin bilayer magnetization in a parallel field and,
for a high field, the critical-state distributions of the superconducting
current density. These critical-state distributions are different from those
known for a normal external field.",2310.13475v2
2023-10-20,Discontinuous phase transition from ferromagnetic to oscillating states in a nonequilibrium mean-field spin model,"We study a nonequilibrium ferromagnetic mean-field spin model exhibiting a
phase with spontaneous temporal oscillations of the magnetization, on top of
the usual paramagnetic and ferromagnetic phases. This behavior is obtained by
introducing dynamic field variables coupled to the spins through non-reciprocal
couplings. We determine a nonequilibrium generalization of the Landau free
energy in terms of the large deviation function of the magnetization and of an
appropriately defined smoothed stochastic time derivative of the magnetization.
While the transition between paramagnetic and oscillating phase is continuous,
the transition between ferromagnetic and oscillating phases is found to be
discontinuous, with a coexistence of both phases, one being stable and the
other one metastable. Depending on parameter values, the ferromagnetic points
may either be inside or outside the limit cycle, leading to different
transition scenarios. The stability of these steady states is determined from
the large deviation function. We also show that in the coexistence region, the
entropy production has a pronounced maximum as a function of system size.",2310.13488v1
2023-10-20,Exchange-driven spin Hall effect in anisotropic ferromagnets,"Crystallographic anisotropy of the spin-dependent conductivity tensor can be
exploited to generate transverse spin-polarized current in a ferromagnetic
film. This ferromagnetic spin Hall effect is analogous to the spin-splitting
effect in altermagnets and does not require spin-orbit coupling.
First-principles screening of 41 non-cubic ferromagnets revealed that many of
them, when grown as a single crystal with tilted crystallographic axes, can
exhibit large spin Hall angles comparable with the best available
spin-orbit-driven spin Hall sources. Macroscopic spin Hall effect is possible
for uniformly magnetized ferromagnetic films grown on some low-symmetry
substrates with epitaxial relations that prevent cancellation of contributions
from different orientation domains. Macroscopic response is also possible for
any substrate if magnetocrystalline anisotropy is strong enough to lock the
magnetization to the crystallographic axes in different orientation domains.",2310.13688v2
2023-11-10,Room-temperature ferromagnetism in epitaxial bilayer FeSb/SrTiO3(001) terminated with a Kagome lattice,"Two-dimensional (2D) magnets exhibit unique physical properties for potential
applications in spintronics. To date, most 2D ferromagnets are obtained by
mechanical exfoliation of bulk materials with van der Waals interlayer
interactions, and the synthesis of single or few-layer 2D ferromagnets with
strong interlayer coupling remains experimentally challenging. Here, we report
the epitaxial growth of 2D non-van der Waals ferromagnetic bilayer FeSb on
SrTiO3(001) substrates stabilized by strong coupling to the substrate, which
exhibits in-plane magnetic anisotropy and a Curie temperature above 300 K.
In-situ low-temperature scanning tunneling microscopy/spectroscopy and
density-functional theory calculations further reveal that a Fe Kagome layer
terminates the bilayer FeSb. Our results open a new avenue for further
exploring emergent quantum phenomena from the interplay of ferromagnetism and
topology for application in spintronics.",2311.05833v1
2023-12-18,The Type-II/Type-I Crossover in Dirty Ferromagnetic Superconductors,"In this work we investigate the intertype (IT) domain in strongly disordered
ferromagnetic superconductors with a Curie temperature lower than the
superconducting critical temperature. In such unique materials, the coexistence
of superconductivity and ferromagnetism allows for the exploration of both
unconventional superconductivity and interplay between magnetism and
superconductivity. The study utilizes an extended Ginzburg-Landau model for the
dirty limit to calculate the boundaries of the IT domain which is characterized
by a complex vortex-vortex interaction and exotic vortex configurations. The
analysis reveals that the IT domain in dirty ferromagnetic superconductors is
not qualitatively different from the clean case and remains similarly large,
suggesting that disorder does not hinder the exploration of the rich variety of
IT superconductivity in ferromagnetic superconductors. This work expands
understanding of the interplay between superconductivity and magnetism in
complex materials and could guide future experimental studies.",2312.10955v1
2024-01-26,Superconducting flux qubit with ferromagnetic Josephson pi junction operating at zero magnetic field,"The operation of a conventional superconducting flux qubit requires the
application of a precisely tuned magnetic field to set the operation point at
half a flux quantum through the qubit loop, which makes the scaling of quantum
circuits based on this type of qubits difficult. It has been proposed that, by
inducing a pi phase shift in the superconducting order parameter using a
precisely controlled nanoscale-thickness
superconductor/ferromagnet/superconductor Josephson junction, commonly referred
to as pi-junction, it is possible to realize a flux qubit operating at zero
magnetic flux. We report the realization of a zero-flux-biased flux qubit based
on three NbN/AlN/NbN Josephson junctions and a NbN/PdNi/NbN ferromagnetic
pi-junction. The qubit lifetime is in the microsecond range, which we argue is
limited by quasiparticle excitations in the metallic ferromagnet layer. With
further improvements in the materials of the ferromagnetic junction, the
zero-flux-biased flux qubits can become a promising platform for quantum
computing.",2401.14597v2
2024-02-15,Critical temperature of triplet superconductor-ferromagnet bilayers as a probe for pairing symmetry,"Identifying superconducting materials with spin-polarized Cooper pairs is an
important objective both for exploration of new fundamental physics and for
cryogenic applications in spintronics and quantum sensing. We here compute the
critical temperature $T_c$ of the superconducting transition in a bilayer
comprised of a superconductor with an intrinsic spin-triplet order parameter
and a ferromagnet. We determine how $T_c$ varies both with the thickness of the
ferromagnet and its magnetization direction. We show that both the orbital and
spin part of the triplet superconducting order parameter leave clear signatures
in $T_c$ which do not appear in a bilayer of a conventional s-wave
superconductor and a ferromagnet. In particular, the dependence of $T_c$ on
these variables changes depending on whether or not the superconducting order
parameter features Andreev bound-states and also changes qualitatively when the
magnetization is rotated in the plane of the ferromagnetic film. Measurements
of $T_c$ in such bilayers are therefore useful to identify the pairing symmetry
of intrinsic triplet superconductors.",2402.10266v1
2024-02-21,Interplay between 2D ferromagnetism and transport at the surface of FeSi,"FeSi is a curious example of a $d$-electron system that manifests many of the
same phenomena associated with $f$-electron Kondo insulators, including
conducting surface states with potentially non-trivial topology. Here we
investigate the magnetization and magnetotransport of these surface states and
how a 2D ferromagnetic state at the surface of FeSi influences the surface
conductivity. We confirm the 2D ferromagnetism via a systematic study of
magnetization on groups of filtered fragments with increasing surface
area-to-volume ratios, identifying characteristic temperatures and magnetic
fields associated with the ordered state. The paramagnetic to ferromagnetic
transition appears broadened, suggesting disorder, which allows spin
fluctuations to manifest up to at least 9 T at 2 K. This highlights the need to
understand the relation between the disorder of the 2D ferromagnetism and the
surface conductivity in FeSi.",2402.14006v1
2024-02-29,Exchange bias induced by spin-glass-like state in Te-rich FeGeTe van der Waals ferromagnet,"We have experimentally investigated the mechanism of the exchange bias in the
2D van der Waals (vdW) ferromagnets by means of the anomalous Hall effect (AHE)
together with the dynamical magnetization property. The temperature dependence
of the AC susceptibility with its frequency response indicates a glassy
transition of the magnetic property for the Te-rich FeGeTe vdW ferromagnet. We
also found that the irreversible temperature dependence in the anomalous Hall
voltage follows the Almeida-Thouless line. Moreover, the freezing temperature
of the spin-glass-like phase is found to correlate with the disappearance
temperature of the exchange bias. These important signatures suggest that the
emergence of magnetic exchange bias in the 2D van der Waals ferromagnets is
induced by the presence of the spin-glass-like state in FeGeTe. The
unprecedented insights gained from these findings shed light on the underlying
principles governing exchange bias in vdW ferromagnets, contributing to the
advancement of our understanding in this field.",2402.18887v1
2024-03-21,Epitaxial growth and magnetic properties of Mn5(SixGe1-x)3 thin films,"Structural and magnetic properties of Mn5(SixGe1-x)3 thin films were
investigated. Ferromagnetic Mn5Ge3 and anti-ferromagnetic Mn5Si3 thin films
have been synthesized and characterized as these compounds exhibit interesting
features for the development of spintronics. Here, Mn5(SixGe1-x)3 thin films
were grown on Ge(111) substrates by co-deposition using molecular beam epitaxy.
Crystalline thin films can be produced with controlled Si concentrations
ranging from 0 to 1. The thin films were relaxed by dislocations at the
interface with the substrate. A lattice parameter variation was observed as the
Si content increased, which is comparable to previous works done in bulk.
Reflection highenergy electron diffraction diagrams and X-ray diffraction
profiles showed that lattice parameters a and c are shrinking and that the
surface roughness and crystallinity degrade as the Si amount increases.
Magnetometric measurements revealed a ferromagnetic behavior for all Si
concentrations. The measured average ferromagnetic moment per manganese atom
decreased from 2.33 to 0.05 {\mu}B/Mn atom. No ferro to anti-ferromagnetic
transition was observed contrary to the bulk Mn5(SixGe1-x)3 compound.",2403.14215v1
2024-04-04,Competitive coexistence of ferromagnetism and metal--insulator transition of VO$_2$ nanoparticles,"We investigated the magnetic and electric properties of nanometer-sized
vanadium dioxide (VO$_2$) particles. VO$_2$ nanoparticles were formed by
milling VO$_2$ powder. We measured the magnetic field dependence of the
magnetization of the VO$_2$ powder and nanoparticles. The VO$_2$ powder did not
exhibit ferromagnetism, whereas the VO$_2$ nanoparticles exhibited
ferromagnetism. In addition, we fabricated samples by bridging between
electrodes with the VO$_2$ nanoparticles, and the temperature dependence of
their resistance was measured. Metal-insulator transitions (MITs) were
observed, and the temperature range where the MIT occurred was wider than that
in a typical bulk VO$_2$. The VO$_2$ nanoparticles exhibited these properties
of ferromagnetism and MIT possibly because of the surface and size effects of
the VO$_2$ nanoparticles. These results indicate the first observation of the
competitive coexistence of ferromagnetism and MIT of VO$_2$ nanoparticles.",2404.03207v1
2005-06-20,New broad 8Be nuclear resonances,"Energies, total and partial widths, and reduced width amplitudes of 8Be
resonances up to an excitation energy of 26 MeV are extracted from a coupled
channel analysis of experimental data. The presence of an extremely broad J^pi
= 2^+ ``intruder'' resonance is confirmed, while a new 1^+ and very broad 4^+
resonance are discovered. A previously known 22 MeV 2^+ resonance is likely
resolved into two resonances. The experimental J^pi T = 3^(+)? resonance at 22
MeV is determined to be 3^-0, and the experimental 1^-? (at 19 MeV) and 4^-?
resonances to be isospin 0.",0506063v2
2012-02-14,Simultaneous radiation pressure induced heating and cooling of an opto-mechanical resonator,"Cavity opto-mechanics enabled radiation-pressure coupling between optical and
mechanical modes of a micro-mechanical resonator gives rise to dynamical
backaction, enabling amplification and cooling of mechanical motion. Due to a
combination of large mechanical oscillations and necessary saturation of
amplification, the noise floor of the opto-mechanical resonator increases,
rendering it ineffective at transducing small signals, and thereby cooling
another mechanical resonance of the system. Here we show amplification of one
mechanical resonance in a micro-mechanical ring resonator while simultaneously
cooling another mechanical resonance by exploiting two closely spaced optical
whispering gallery mode cavity resonances.",1202.3154v1
2012-02-25,Anisotropy-induced Fano resonance,"An optical Fano resonance, which is caused by birefringence control rather
than frequency selection, is discovered. Such birefringence-induced Fano
resonance comes with fast-switching radiation. The resonance condition
$\varepsilon_t< 1/\varepsilon_r$ is revealed and a tiny perturbation in
birefringence is found to result in a giant switch in the principal light pole
induced near surface plasmon resonance. The loss and size effects upon the Fano
resonance have been studied Fano resonance is still pronounced, even if the
loss and size of the object increase. The evolutions of the radiation patterns
and energy singularities illustrate clearly the sensitive dependence of Fano
resonance upon the birefringence.",1202.5613v1
2013-10-14,Localized and complete resonance in plasmonic structures,"This paper studies a possible connection between the way the time averaged
electromagnetic power dissipated into heat blows up and the anomalous localized
resonance in plasmonic structures. We show that there is a setting in which the
localized resonance takes place whenever the resonance does and moreover, the
power is always bounded and might go to $0$. We also provide another setting in
which the resonance is complete and the power goes to infinity whenever
resonance occurs; as a consequence of this fact there is no localized
resonance. This work is motivated from recent works on cloaking via anomalous
localized resonance.",1310.3633v2
2016-10-06,Analytic Solution of the Electromagnetic Eigenvalues Problem in a Cylindrical Resonator,"Resonant accelerating cavities are key components in modern particles
accelerating facilities. These take advantage of electromagnetic fields
resonating at microwave frequencies to accelerate charged particles. Particles
gain finite energy at each passage through a cavity if in phase with the
resonating field, reaching energies even of the order of $TeV$ when a cascade
of accelerating resonators are present. In order to understand how a resonant
accelerating cavity transfers energy to charged particles, it is important to
determine how the electromagnetic modes are exited into such resonators. In
this paper we present a complete analytical calculation of the resonating
fields for a simple cylindrical-shaped cavity.",1610.02083v1
2020-01-14,Close-to-touching acoustic subwavelength resonators: eigenfrequency separation and gradient blow-up,"In this paper, we study the behaviour of the coupled subwavelength resonant
modes when two high-contrast acoustic resonators are brought close together. We
consider the case of spherical resonators and use bispherical coordinates to
derive explicit representations for the capacitance coefficients which, we
show, capture the system's resonant behaviour at leading order. We prove that
the pair of resonators has two subwavelength resonant modes whose frequencies
have different leading-order asymptotic behaviour. We, also, derive estimates
for the rate at which the gradient of the scattered pressure wave blows up as
the resonators are brought together.",2001.04888v2
2021-08-03,"Resonances in finitely perturbed quantum walks, resonance expansion and generic simplicity","We define resonances for finitely perturbed quantum walks as poles of the
scattering matrix in the lower half plane. We show a resonance expansion which
describes the time evolution in terms of resonances and corresponding Jordan
chains. In particular, the decay rate of the survival probability is given by
the imaginary part of resonances and the multiplicity. We prove generic
simplicity of the resonances, although there are quantum walks with multiple
resonances.",2108.01345v1
2007-07-29,Resonance sticking in the scattered disk,"We investigate the dynamical evolution of trans-Neptunian objects (TNOs) in
typical scattered disk orbits (scattered TNOs) by performing simulations using
several thousand particles lying initially on Neptune-encountering orbits. We
explore the role of resonance sticking in the scattered disk, a phenomenon
characterized by multiple temporary resonance captures ('resonances' refers to
external mean motion resonances with Neptune, which can be described in the
form r:s, where the arguments r and s are integers). First, all scattered TNOs
evolve through intermittent temporary resonance capture events and
gravitational scattering by Neptune. Each scattered TNO experiences tens to
hundreds of resonance captures over a period of 4 Gyr, which represents about
38% of the object's lifetime (mean value). Second, resonance sticking plays an
important role at semimajor axes a < 250 AU, where the great majority of such
captures occurred. It is noteworthy that the stickiest (i.e., dominant)
resonances in the scattered disk are located within this distance range and are
those possessing the lowest argument s. This was evinced by r:1, r:2 and r:3
resonances, which played the greatest role during resonance sticking evolution,
often leading to captures in several of their neighboring resonances. Finally,
the timescales and likelihood of temporary resonance captures are roughly
proportional to resonance strength. The dominance of low s resonances is also
related to the latter. In sum, resonance sticking has an important impact on
the evolution of scattered TNOs, contributing significantly to the longevity of
these objects.",0707.4301v2
2020-07-03,Method to Determine the Closed-Loop Precision of Resonant Sensors from Open-Loop Measurements,"Resonant sensors determine a sensed parameter by measuring the resonance
frequency of a resonator. For fast continuous sensing, it is desirable to
operate resonant sensors in a closed-loop configuration, where a feedback loop
ensures that the resonator is always actuated near its resonance frequency, so
that the precision is maximized even in the presence of drifts or fluctuations
of the resonance frequency. However, in a closed-loop configuration, the
precision is not only determined by the resonator itself, but also by the
feedback loop, even if the feedback circuit is noiseless. Therefore, to
characterize the intrinsic precision of resonant sensors, the open-loop
configuration is often employed. To link these measurements to the actual
closed-loop performance of the resonator, it is desirable to have a relation
that determines the closed-loop precision of the resonator from open-loop
characterisation data. In this work, we present a methodology to estimate the
closed-loop resonant sensor precision by relying only on an open-loop
characterization of the resonator. The procedure is beneficial for fast
performance estimation and benchmarking of resonant sensors, because it does
not require actual closed-loop sensor operation, thus being independent on the
particular implementation of the feedback loop. We validate the methodology
experimentally by determining the closed-loop precision of a mechanical
resonator from an open-loop measurement and comparing this to an actual
closed-loop measurement.",2007.01706v3
2020-04-01,Development of planar microstrip resonators for electron spin resonance spectroscopy,"This work focuses on the development of planar microwave resonators which are
to be used in electron spin resonance spectroscopic studies. Two half
wavelength microstrip resonators of different geometrical shapes, namely
straight ribbon and omega, are fabricated on commercially available copper clad
microwave laminates. Both resonators have a characteristic impedance of 50
{\Omega}. We have performed electromagnetic field simulations for the two
microstrip resonators and have extracted practical design parameters which were
used for fabrication. The effect of the geometry of the resonators on the
quasi-transverse electromagnetic (quasi-TEM) modes of the resonators is noted
from simulation results. The fabrication is done using optical lithography
technique in which laser printed photomasks are used. This rapid prototyping
technique allows us to fabricate resonators in a few hours with accuracy up to
6 mils. The resonators are characterized using a Vector Network Analyzer. The
fabricated resonators are used to standardize a home built low-temperature
continuous wave electron spin resonance (CW-ESR) spectrometer which operates in
S-band, by capturing the absorption spectrum of the free radical DPPH, at both
room temperature and 77 K. The measured value of g-factor using our resonators
is consistent with the values reported in literature. The designed half
wavelength planar resonators will be eventually used in setting up a pulsed
electron spin resonance spectrometer by suitably modifying the CW-ESR
spectrometer.",2004.00457v1
2017-05-23,Asymptotics of resonances for 1d Stark operators,"We consider the Stark operator perturbed by a compactly supported potentials
on the real line. We determine forbidden domain for resonances, asymptotics of
resonances at high energy and asymptotics of the resonance counting function
for large radius.",1705.08072v1
2018-12-21,Structure of resonances in a simple quantum-mechanical model,"We study the structure of resonances derived from the solution of an exactly
solvable Lippmann-Schwinger equation. Within this framework, we discuss the
concept of ""resonance form factors"", and the description of the resonant
amplitudes in terms of effective energy-dependent potentials.",1812.09003v1
2021-11-17,New results on orbital resonances,"Perturbative analyses of planetary resonances commonly predict singularities
and/or divergences of resonance widths at very low and very high
eccentricities. We have recently re-examined the nature of these divergences
using non-perturbative numerical analyses, making use of Poincar\'e sections
but from a different perspective relative to previous implementations of this
method. This perspective reveals fine structure of resonances which otherwise
remains hidden in conventional approaches, including analytical,
semi-analytical and numerical-averaging approaches based on the critical
resonant angle. At low eccentricity, first order resonances do not have
diverging widths but have two asymmetric branches leading away from the nominal
resonance location. A sequence of structures called ``low-eccentricity resonant
bridges"" connecting neighboring resonances is revealed. At planet-grazing
eccentricity, the true resonance width is non-divergent. At higher
eccentricities, the new results reveal hitherto unknown resonant structures and
show that these parameter regions have a loss of some -- though not necessarily
entire -- resonance libration zones to chaos. The chaos at high eccentricities
was previously attributed to the overlap of neighboring resonances. The new
results reveal the additional role of bifurcations and co-existence of
phase-shifted resonance zones at higher eccentricities. By employing a
geometric point of view, we relate the high eccentricity phase space structures
and their transitions to the shapes of resonant orbits in the rotating frame.
We outline some directions for future research to advance understanding of the
dynamics of mean motion resonances.",2111.09289v1
2013-12-17,Virial expansion of a harmonically trapped Fermi gas across a narrow Feshbach resonance,"We theoretically investigate the high-temperature thermodynamics of a
harmonically trapped Fermi gas across a narrow Feshbach resonance, by using the
second-order quantum virial expansion, and point out some new features compared
to the broad resonance. The interatomic interaction is modeled by the
pseudopotential with an additional parameter, i.e., the effective range, to
characterize the narrow resonance width. Deeply inside the width of a narrow
Feshbach resonance, we find the second virial coefficient evolves with the
effective range from the well-known universal value 1/4 in the broad-resonance
limit to one another value 1/2 in the narrow-resonance limit. This means the
Fermi gas is more strongly interacted at the narrow resonance. In addition, far
beyond the resonance width, we find the harmonically trapped Fermi gas still
manifests appreciable interaction effect across a narrow Feshbach resonance,
which is contrary to our knowledge of the broad Feshbach resonance. All our
results can be directly tested in current narrow Feshbach resonance
experiments, which are generally carried out in a harmonic trap.",1312.4662v1
2015-11-18,Fano resonance scattering in waveguide with an impedance boundary condition,"Sound propagation in a waveguide lined with one section of locally reactive
material is studied by resonance scattering approach. The objective is to
understand the effects of mode coupling in the lined section on the
transmission. It is shown that a transmission zero is present in the vicinity
of a resonance peak when a numerically real resonance frequency of the open
lined section (opened to infinities through the rigid parts of the waveguide)
is crossed. The transmission zero and immediate resonance peak form a Fano
resonance, it has been explained as an interaction between a resonance and the
non-resonant background. The real resonance frequency and its corresponding
trapped mode are formed by the interferences (couplings) between two neighbor
modes with complex resonance frequencies. It is also linked to the avoided
crossing of eigenvalues and the exceptional point. The scattering matrix is
expressed in terms of a matrix $\mathsf{H_{eff}}$ which describes approximately
the complex resonances in the open lined section. With the aid of the
eigenvalues and eigenfunctions of matrix $\mathsf{H_{eff}}$, the traditional
acoustic resonance scattering formula can be extended to describe the coupling
effects between the open lined section and the rigid parts of the waveguide.",1511.05588v1
2018-11-07,Quantitative modeling of superconducting planar resonators with improved field homogeneity for electron spin resonance,"We present three designs for planar superconducting microwave resonators for
electron spin resonance (ESR) experiments. We implement finite element
simulations to calculate the resonance frequency and quality factors as well as
the three-dimensional microwave magnetic field distribution of the resonators.
One particular resonator design offers an increased homogeneity of the
microwave magnetic field while the other two show a better confinement of the
mode volume. We extend our model simulations to calculate the collective
coupling rate between a spin ensemble and a microwave resonator in the presence
of an inhomogeneous magnetic resonator field. Continuous-wave ESR experiments
of phosphorus donors in $^\mathrm{nat}$Si demonstrate the feasibility of our
resonators for magnetic resonance experiments. We extract the collective
coupling rate and find a good agreement with our simulation results,
corroborating our model approach. Finally, we discuss specific application
cases for the different resonator designs.",1811.02971v2
2019-09-11,Tunable group delay in a doubly resonant metasurface composed of two dissimilar split-ring resonators,"We develop a method to control the group delay of electromagnetic waves
continuously using a doubly resonant metasurface. The method is based on the
dependences of i) the group velocity in a medium featuring two resonance lines
on the resonance linewidths and ii) the resonance linewidth of a metasurface
composed of split-ring resonators on an incidence angle of electromagnetic
wave. To verify this method for group-delay control, we design a terahertz
metasurface composed of two split-ring resonators with different resonance
frequencies and numerically analyze the transmission characteristic of the
metasurface. Double resonance lines are observed for oblique incidence and the
resonance transmission dips become deeper and broader with increasing the
incidence angle. The group delay at around the center frequency of the double
resonance lines is found to vary in the range about from 0s to 20 times the
period of the incident wave with the incidence angle. In contrast with a
previously reported method for variable control of group delay using
electromagnetically-induced-transparency-like metamaterials, a high
transmittance is achieved for a small group delay condition.",1909.04833v1
2019-12-10,Three dimensional structure of mean motion resonances beyond Neptune,"We propose a semianalytical method for the calculation of widths, libration
centers and small amplitude libration periods of the mean motion resonances
k_p:k in the framework of the circular restricted three body problem valid for
arbitrary eccentricities and inclinations. Applying the model to the trans
Neptunian region (TNR) we obtain several atlas of resonances between 30 and 100
au showing their domain in the plane (a,e) for different orbital inclinations.
The resonance width may change substantially when varying the argument of the
perihelion of the resonant object and in order to take into account these
variations we introduce the concept of resonance fragility. Resonances 1:k and
2:k are the widest, strongest, most isolated ones and with lower fragility for
all interval of inclinations and eccentricities. We discuss about the existence
of high k_p:k resonances. We analyze the distribution of the resonant
populations inside resonances 1:1, 2:3, 3:5, 4:7, 1:2 and 2:5. We found that
the populations are in general located near the regions of the space (e,i)
where the resonances are wider and less fragile with the notable exception of
the population inside the resonance 4:7 and in a lesser extent the population
inside 3:5 which are shifted to lower eccentricities.",1912.04676v1
2021-10-25,Resonance order-dependent plasmon-induced transparency in orthogonally-arranged nanoscale cavities,"In this study, we investigate plasmon-induced transparency (PIT) in a
resonator structure consisting of two orthogonally-arranged
metal-insulator-metal (MIM) nanocavities with the aim of spectral modulation of
a specific resonant order of the resonator. Our FDTD simulations demonstrate
that when both cavities in this structure resonate at the same frequency, the
PIT effect can be used to induce spectral modulation. This spectral modulation
depends on the resonance order of the cavity coupled directly to the external
field, occurring when first-order resonance is exhibited, but not with
second-order resonance. We confirmed that this behavior is caused by the
discrepancies between odd-order and even-order resonances using classical
mechanical models analogous to the nanocavities. By tuning the resonance
frequency and resonance order of the cavities, one can modulate the spectrum of
the resonator structure in an order-selective manner.",2110.12619v1
1994-03-16,Quantum Hall Ferromagnets,"It is pointed out recently that the $\nu=1/m$ quantum Hall states in bilayer
systems behave like easy plane quantum ferromagnets. We study the
magnetotransport of these systems using their ``ferromagnetic"" properties and a
novel spin-charge relation of their excitations. The general transport is a
combination of the ususal Hall transport and a time dependent transport with
$quantized$ time average. The latter is due to a phase slippage process in
$spacetime$ and is characterized by two topological constants. (Figures will be
provided upon requests).",9403063v1
1994-04-04,Ferromagnetism in the Infinite-U Hubbard Model,"We have studied the stability of the ferromagnetic state in the infinite-U
Hubbard model on a square lattice by approximate diagonalization of finite
lattices using the density matrix renormalization group technique. By studying
lattices with up to 5X20 sites, we have found the ferromagnetic state to be
stable below the hole density of 22 percent. Beyond 22 percent of hole doping,
the total spin of the ground state decreased gradually to zero with increasing
hole density.",9404003v2
1994-04-27,Three-State Anti-ferromagnetic Potts Model in Three Dimensions: Universality and Critical Amplitudes,"We present the results of a Monte Carlo study of the three-dimensional
anti-ferromagnetic 3-state Potts model. We compute various cumulants in the
neighbourhood of the critical coupling. The comparison of the results with a
recent high statistics study of the 3D XY model strongly supports the
hypothesis that both models belong to the same universality class. From our
numerical data for the anti-ferromagnetic 3-state Potts model we obtain for the
critical coupling $\coup_c=0.81563(3)$, and for the static critical exponents
$\gamma /\nu=1.973(9)$ and $\nu=0.664(4)$.",9404087v1
1994-07-02,Incommensurate and Collinear Phases in a Doped Quantum Anti-ferromagnet,"The Schwinger Boson mean field theories of the `t-J' model are extended by
the consideration of anisotropic order parameters. This has two effects. First,
a collinear phase, in which the spins are anti-ferromagnetically aligned in one
direction and ferromagnetically aligned in the other, is found to be stable
over a significant range of the phase diagram. Second, the (1,1) and (1,0)
spiral phases become very close in energy. The inclusion of weak
intra-sublattice coupling may therefore stabilise the (1,0) spiral with respect
to the (1,1) spiral, thus harmonising theory and experiment.",9407007v1
1995-04-05,Quantum ferromagnetic transition in disordered itinerant electron systems,"An effective field theory is derived for the ferromagnetic transition of
diffusive electrons at T=0. The static disorder which leads to diffusive
electron dynamics induces an effective long-range interaction between the spins
of the form 1/r^(2d-2). This leads to unusual scaling behavior at the quantum
critical point, which is determined exactly. The crossover from this quantum
fixed point to the classical Heisenberg fixed point should be observable in
ferromagnetic materials with low Curie temperatures.",9504021v2
1995-06-07,TDAE-\c60: Can a Mott insulator be a ferromagnet?,"Motivated by the structure of TDAE-\c60, we derive a multicomponent
superexchange Hamiltonian for the spins and orbital (``isospin'') degrees of
freedom in the Mott-insulating phase. We explore its phase diagram and identify
points of special interest: an SU(4) antiferromagnet (solved by Sutherland) and
two ferromagnet$\otimes$antiferromagnet points where the ground state is known.
For the ferromagnetic regime, we apply interchain mean field theory and derive
an expression for the Curie temperature where spin ordering occurs and a lower
Ne{\'e}l temperature for a conjectured isospin ordering.",9506031v1
1995-07-24,Continuum quantum ferromagnets at finite temperature and the Quantum Hall effect,"We study finite temperature ($T$) properties of the continuum quantum field
theory of systems with a ferromagnetic ground state. A scaling theory of the
$T=0$ system is discussed carefully, and its consequences for crossovers
between different finite $T$ regimes in dimensions 1, 2, and 3 are described.
The results are compared with recent NMR measurements of the magnetization of a
quantum Hall system with filling factor $\nu=1$; we predict that the relaxation
rate $1/T_1$ of this system may have a finite $T$ ``ferromagnetic coherence
peak''.",9507103v1
1995-09-12,Ferromagnetism in Hubbard Models,"We present the first rigorous examples of non-singular Hubbard models which
exhibit ferromagnetism at zero temperature. The models are defined in arbitrary
dimensions, and are characterized by finite-ranged hoppings, dispersive bands,
and finite on-site Coulomb interaction U. The picture, which goes back to
Heisenberg, that sufficiently large Coulomb interaction can revert Pauli
paramagnetism into ferromagnetism has finally been confirmed in concrete
examples.",9509063v2
1996-04-29,Unconventional Ferromagnetic Transition in La1-xCaxMnO3,"Neutron scattering has been used to study the magnetic correlations and long
wavelength spin dynamics of La1-xCaxMnO3 in the ferromagnetic regime
(0<=x<1/2). For x=1/3 (Tc=250K) where the magnetoresistance effects are largest
the system behaves as an ideal isotropic ferromagnet at low T, with a gapless
(<0.04meV) dispersion relation E=Dq^2 and D(T=0)~170 meV-A-1. However, an
anomalous strongly-field-dependent diffusive component develops above ~200K and
dominates the fluctuation spectrum as T approaches Tc. This component is not
present at lower x.",9604170v1
1996-11-13,"Impact of Charge Ordering on Magnetic Correlations in Perovskite (Bi,Ca)MnO_3","Single crystalline (Bi,Ca)MnO3 (74< %Ca <82) were studied with neutron
scattering, electron diffraction and bulk magnetic measurement. We discovered
dynamic ferromagnetic spin correlations at high temperatures, which are
replaced by antiferromagnetic spin fluctuations at a concomitant charge
ordering and structural transition. Our results indicate that thermal-activated
hopping of the Jahn-Teller active e_g electrons in these insulating materials,
nevertheless, induce ferromagnetic interaction through double-exchange
mechanism. It is the ordering of these charges competing with the
double-exchange ferromagnetic metallic state.",9611110v1
1996-11-20,Skyrmion Liquid Phase of the Quantum Ferromagnet in Two Dimensions,"The two-dimensional quantum ferromagnet filled with a liquid of skyrmions is
studied theoretically in the context of the quantum Hall effect near electronic
filling factor $\nu = 1$. A cross-over between the classical ferromagnetic
phase at $\nu =1$ and a classical paramagnetic phase at $\nu \neq 1$ is
obtained, which is consistent with recent Knight-shift measurements. A new
collective mode associated with the skyrmion liquid that is of the cyclotron
type is also identified.",9611152v2
1997-04-28,Ferromagnetism in the Hubbard Model on fcc-type lattices,"The Hubbard model on fcc-type lattices is studied in the dynamical mean-field
theory of infinite spatial dimensions. At intermediate interaction strength
finite temperature Quantum Monte Carlo calculations yield a second order phase
transition to a highly polarized, metallic ferromagnetic state. The Curie
temperatures are calculated as a function of electronic density and interaction
strength. A necessary condition for ferromagnetism is a density of state with
large spectral weight near one of the band edges.",9704229v2
1997-05-09,CrO2: a self-doped double exchange ferromagnet,"Band structure calculations of CrO2 carried out in the LSDA+U approach reveal
a clear picture of the physics behind the metallic ferromagnetic properties.
Arguments are presented that the metallic ferromagnetic oxide CrO2 belongs to a
class of materials in which magnetic ordering exists due to double exchange (in
this respect CrO2 turns out to be similar to the CMR manganates). It is
concluded that CrO2 has small or even negative charge transfer gap which can
result in self-doping. Certain experiments to check the proposed picture are
suggested.",9705091v1
1997-08-08,Magnetoresistance in Mn pyrochlore: electrical transport in a low carrier density ferromagnet,"We discuss magnetotransport in a low density electron gas coupled to spin
fluctuations near and above a ferromagnetic transition. Provided the density is
low enough ($n \lesssim 1/\xi^{3}(T)$, with $\xi(T)$ the ferromagnetic
correlation length), spin polarons form in an intermediate temperature regime
above $T_c$. Both in the spin polaron regime, and in the itinerant regime
nearer $T_c$, the magnetoresistance is large. We propose that this provides a
good model for ``colossal'' magnetoresistance in the pyrochlore
Tl$_{2-x}$Sc$_x$Mn$_2$O$_7$, fundamentally different from the mechanism in the
perovskite manganites such as La$_{1-x}$Sr$_x$MnO$_3$.",9708068v1
1997-10-15,Evolution of the low-frequency spin dynamics in ferromagnetic manganites,"Elastic and inelastic neutron scattering was used to study two ferromagnetic
manganites A$_{1-x}$B$_{x}$MnO$_3$ (x $\approx$ 0.3) with $T_c$=197.9 K and
300.9 K. The spin dynamical behavior of these is similar at low temperatures,
but drastically different at temperatures around $T_c$. While the formation of
spin clusters of size ($\sim20$ \AA) dominates the spin dynamics of the 197.9 K
sample close to $T_c$, the paramagnetic to ferromagnetic transition for the
300.9 K sample is more conventional. These results, combined with seemingly
inconsistent earlier reports, reveal clear systematics in the spin dynamics of
the manganites.",9710160v1
1997-12-23,The edge theory of ferromagnetic quantum Hall states,"We propose an effective low-energy theory for ferromagnetic Hall states. It
describes the charge degrees of freedom, on the edge, by a (1 + 1) dimensional
chiral boson theory, and the spin degrees of freedom by the (2 + 1)dimensional
quantum ferromagnet theory in the spin-wave approximation. The usual chiral
boson theory for spinless electrons is modified to include the charge degrees
of freedom with spin. Our total, bulk plus edge, effective action is gauge
invariant and we find a generalized ""chiral anomaly"" in this case. We describe
two, charged and neutral, sets of edge spin-wave solutions. The spreading of
these waves is much larger than the one for the charge (edge) waves and they
have linear dispersion relations.",9712279v1
1998-01-15,Solitary Waves of Planar Ferromagnets and the Breakdown of the Spin-Polarized Quantum Hall Effect,"A branch of uniformly-propagating solitary waves of planar ferromagnets is
identified. The energy dispersion and structures of the solitary waves are
determined for an isotropic ferromagnet as functions of a conserved momentum.
With increasing momentum, their structure undergoes a transition from a form
ressembling a droplet of spin-waves to a Skyrmion/anti-Skyrmion pair. An
instability to the formation of these solitary waves is shown to provide a
mechanism for the electric field-induced breakdown of the spin-polarized
quantum Hall effect.",9801160v1
1998-01-21,Crossovers in the Two Dimensional Ising Spin Glass with ferromagnetic next-nearest-neighbor interactions,"By means of extensive computer simulations we analyze in detail the two
dimensional $\pm J$ Ising spin glass with ferromagnetic next-nearest-neighbor
interactions. We found a crossover from ferromagnetic to ``spin glass'' like
order both from numerical simulations and analytical arguments. We also present
evidences of a second crossover from the ``spin glass'' behavior to a
paramagnetic phase for the largest volume studied.",9801215v2
1998-01-23,Flat-band ferromagnetism induced by off-site repulsions,"Density matrix renormalization group method is used to analyze how the
nearest-neighbor repulsion V added to the Hubbard model on 1D triangular
lattice and a railway trestle (t-t') model will affect the electron-correlation
dominated ferromagnetism arising from the interference (frustration). Obtained
phase diagram shows that there is a region in smaller-t' side where the
critical on-site repulsion above which the system becomes ferromagnetic is
reduced when the off-site repulsion is introduced.",9801242v1
1998-03-14,Microscopic conditions favoring itinerant ferromagnetism: Hund's rule coupling and orbital degeneracy,"The importance of Hund's rule coupling for the stabilization of itinerant
ferromagnetism is investigated within a two-band Hubbard model. The magnetic
phase diagram is calculated by finite-temperature quantum Monte Carlo
simulations within the dynamical mean-field theory. Ferromagnetism is found in
a broad range of electron fillings whereas antiferromagnetism exists only near
half filling. The possibility of orbital ordering at quarter filling is also
analyzed.",9803182v2
1998-05-19,Magnetic Anisotropy in Quantum Hall Ferromagnets,"We show that the sign of magnetic anisotropy energy in quantum Hall
ferromagnets is determined by a competition between electrostatic and exchange
energies. Easy-axis ferromagnets tend to occur when Landau levels whose states
have similar spatial profiles cross. We report measurements of integer QHE
evolution with magnetic-field tilt. Reentrant behavior observed for the $\nu =
4$ QHE at high tilt angles is attributed to easy-axis anisotropy. This
interpretation is supported by a detailed calculation of the magnetic
anisotropy energy.",9805240v1
1998-06-02,The stabilizing role of itinerant ferromagnetism in inter-granular cohesion in iron,"We present a simple, general energy functional for ferromagnetic materials
based upon a local spin density extension to the Stoner theory of itinerant
ferromagnetism. The functional reproduces well available ab initio results and
experimental interfacial energies for grain boundaries in iron. The model shows
that inter-granular cohesion along symmetric tilt boundaries in iron is
dependent upon strong magnetic structure at the interface, illuminates the
mechanisms underlying this structure, and provides a simple explanation for
relaxation of the atomic structure at these boundaries.",9806034v1
1998-06-12,Superconducting proximity effect in a mesoscopic ferromagnetic wire,"We present an experimental study of the transport properties of a
ferromagnetic metallic wire (Co) in metallic contact with a superconductor
(Al). As the temperature is decreased below the Al superconducting transition,
the Co resistance exhibits a significant dependence on both temperature and
voltage. The differential resistance data show that the decay length for the
proximity effect is much larger than we would simply expect from the exchange
field of the ferromagnet.",9806161v2
1998-09-18,Microphase Separation and modulated phases in a Coulomb frustrated Ising ferromagnet,"We study a 3-dimensional Ising model in which the tendency to order due to
short-range ferromagnetic interactions is frustrated by competing long-range
(Coulombic) interactions. Complete ferromagnetic ordering is impossible for any
nonzero value of the frustration parameter, but the system displays a variety
of phases characterized by periodically modulated structures. We have performed
extensive Monte-Carlo simulations which provide strong evidence that the
microphase separation transition between paramagnetic and modulated phases is a
fluctuation-induced first-order transition. Additional transitions to various
commensurate phases may also occur when further lowering the temperature.",9809250v1
1998-10-08,Interlayer coupling in ferromagnetic semiconductor superlattices,"We develop a mean-field theory of carrier-induced ferromagnetism in diluted
magnetic semiconductors. Our approach represents an improvement over standard
RKKY model allowing spatial inhomogeneity of the system, free-carrier spin
polarization, finite temperature, and free-carrier exchange and correlation to
be accounted for self-consistently. As an example, we calculate the electronic
structure of a Mn$_x$Ga$_{1-x}$As/GaAs superlattice with alternating
ferromagnetic and paramagnetic layers and demonstrate the possibility of
semiconductor magnetoresistance systems with designed properties.",9810100v2
1998-10-20,Unconventional ferromagnetic and spin-glass states of the reentrant spin glass Fe0.7Al0.3,"Spin excitations of single crystal Fe0.7Al0.3 were investigated over a wide
range in energy and reciprocal space with inelastic neutron scattering. In the
ferromagnetic phase, propagating spin wave modes become paramagnon-like
diffusive modes beyond a critical wave vector q0, indicating substantial
disorder in the long-range ordered state. In the spin glass phase, spin
dynamics is strongly q-dependent, suggesting remnant short-range spin
correlations. Quantitative model for S(energy,q) in the ``ferromagnetic'' phase
is determined.",9810265v2
1998-10-31,An SO(5) model of p-wave superconductivity and ferromagnetism,"We study an SO(5) model unifying p-wave superconductivity and ferromagnetism.
If only a single p-wave pairing wavefunction is involved, the p-wave
superconducting (pSC) and ferromagnetic (F) states can be unified to form
10-dimensional multiplet of SO(5). The collective modes in pSC and F states are
studied from this viewpoint in terms of a non-linear sigma model.",9811001v3
1998-11-09,Sub-gap conductance in ferromagnetic-superconducting mesoscopic structures,"We study the sub-gap conductance of a ferromagnetic mesoscopic region
attached to a ferromagnetic and a superconducting electrode by means of tunnel
junctions. In the absence of the exchange field, the ratio $r= \gamma /
\epsilon_T$ of the two tunnel junction resistances determines the behaviour of
the sub-gap conductance which possesses a zero-bias peak for $r\gg 1$ and for
$r\ll 1$ a peak at finite voltage. We show that the inclusion of the exchange
field leads to a peak splitting for $r\ll 1$, while it shifts the zero-bias
anomaly to finite voltages for $r\gg 1$.",9811117v1
1998-12-19,How to calculate the degree of spin polarization in ferromagnets?,"Different ways to define and to calculate the degree of spin polarization in
a ferromagnet are discussed, particularly with respect to spin-polarized
tunneling and Andreev reflection at the boundary between a superconductor and
ferromagnet. As an example, the degrees of spin polarization for different
experiments in Fe and Ni are calculated in the framework of the local spin
density approximation (LSDA) and used to illustrate the differences between
various definitions of spin polarization.",9812327v2
1999-01-28,Spin accumulation induced resistance in mesoscopic ferromagnet/ superconductor junctions,"We present a description of spin-polarized transport in mesoscopic
ferromagnet-superconductor (F/S) systems, where the transport is diffusive, and
the interfaces are transparent. It is shown that the spin reversal associated
with Andreev reflection generates an excess spin density close to the F/S
interface, which leads to a spin contact resistance. Expressions for the
contact resistance are given for two terminal and four terminal geometries. In
the latter the sign depends on the relative magnetization of the ferromagnetic
electrodes.",9901323v1
1999-04-22,Excitonic ferromagnetism in the hexaborides,"A ferromagnet with a small spontaneous moment but with a high Curie
temperature can be obtained by doping an excitonic insulator made from a spin
triplet exciton condensate. Such a condensate can occur in a semimetal with a
small overlap or a semiconductor with a small bandgap. We propose that it is
responsible for the unexpected ferromagnetism in the doped hexaboride material
Ca_{1-x}La_xB_6.",9904330v1
1999-06-04,Finite-element theory of transport in ferromagnet-normal metal systems,"We formulate a theory of spin dependent transport of an electronic circuit
involving ferromagnetic elements with non-collinear magnetizations which is
based on the conservation of spin and charge current. The theory considerably
simplifies the calculation of the transport properties of complicated
ferromagnet-normal metal systems. We illustrate the theory by considering a
novel three terminal device.",9906065v2
1999-08-27,Phase Diagram of the 1D Kondo Lattice Model,"We determine the boundary of the fully polarized ferromagnetic ground state
in the one dimensional Kondo lattice model at partial conduction electron band
filling by using a newly developed infinite size DMRG method which conserves
the total spin quantum number. The obtained paramagnetic to ferromagnetic phase
boundary is below $J \approx 3.5$ for the whole range of band filling. By this
we solve the controversy in the phase diagram over the extent of the
ferromagnetic region close to half filling.",9908414v1
1999-09-20,Phase diagram of S=1/2 XXZ chain with NNN interaction,"We study the ground state properties of one-dimensional XXZ model with
next-nearest neighbor coupling alpha and anisotropy Delta. We find the direct
transition between the ferromagnetic phase and the spontaneously dimerized
phase. This is surprising, because the ferromagnetic phase is classical,
whereas the dimer phase is a purely quantum and nonmagnetic phase. We also
discuss the effect of bond alternation which arises in realistic systems due to
lattice distortion. Our results mean that the direct transition between the
ferromagnetic and spin-Peierls phase occur.",9909290v1
1999-10-07,Negative Domain Wall Resistance in Ferromagnets,"The electrical resistance of a diffusive ferromagnet with magnetic domain
walls is studied theoretically, taking into account the spatial dependence of
the magnetization. The semiclassical domain wall resistance is found to be
either negative or positive depending on the difference between the
spin-dependent scattering life-times. The predictions can be tested
experimentally by transport studies in doped ferromagnets.",9910100v1
1999-10-26,Overlooked Contribution to the Hall Effect in Ferromagnetic Metals,"It is pointed out that in ferromagnetic metals a contribution to the Hall
voltage arises when a non-zero spin current exists, which is generally the case
in the presence of a charge current. This contribution is independent of any
scattering effects and exists down to zero temperature. The sign of the
resulting Hall coefficient may be either equal or opposite to the one of the
ordinary Hall coefficient depending on the band filling. This effect seems to
have been left out in previous analyses of the Hall effect in ferromagnetic
metals.",9910408v1
1999-11-01,A non-perturbative real-space renormalization group scheme for the spin-1/2 XXX Heisenberg model,"In this article we apply a recently invented analytical real-space
renormalization group formulation which is based on numerical concepts of the
density matrix renormalization group. Within a rigorous mathematical framework
we construct non-perturbative renormalization group transformations for the
spin-1/2 XXX Heisenberg model in the finite temperature regime. The developed
renormalization group scheme allows for calculating the renormalization group
flow behaviour in the temperature dependent coupling constant. The constructed
renormalization group transformations are applied within the ferromagnetic and
the anti-ferromagnetic regime of the Heisenberg chain. The ferromagnetic fixed
point is computed and compared to results derived by other techniques.",9910512v2
1999-11-09,Heat capacity and transport studies of the ferromagnetic superconductor RuSr2GdCu2O8,"Resistivity, thermoelectric power and heat capacity are investigated in the
ferromagnetic superconductor RuSr2GdCu2O8 with and without Zn substitution. The
thermodynamic signatures of the ordering of the Ru moments and the paramagnetic
Gd moments as well as the onset of superconductivity are all clearly seen and
quantified. The materials are shown to exhibit bulk superconductivity which
coexists with spatially-uniform ferromagnetism. They appear to be typical
underdoped superconducting cuprates in which the pseudogap dominates
normal-state transport, thermodynamic and substitutional properties. However, a
field-induced increase in Tc could suggest some degree of triplet pairing.",9911135v1
1999-11-20,Exact ground state for 1D electronic models,"We have found the exact ground state for two electronic models on a linear
chain. The first model describes half-filling electron system in the
ferromagnet--antiferromagnet transition point. In the singlet ground state the
spin correlators show giant spiral magnetic ordering with the period of a
spiral equals to the system size. The second electronic model describes the
point where the ground state has giant spiral off-diagonal long-range order
and, therefore, superconducting. We suggest the formation of the ground state
with giant spiral order (ferromagnetic or off-diagonal) as a probable scenario
of the subsequent destruction of the ferromagnetism and the superconductivity.",9911327v1
1999-12-21,Magnetotransport in the low carrier density ferromagnet EuB_6,"We present a magnetotransport study of the low--carrier density ferromagnet
EuB_6. This semimetallic compound, which undergoes two ferromagnetic
transitions at T_l = 15.3 K and T_c = 12.5 K, exhibits close to T_l a colossal
magnetoresistivity (CMR). We quantitatively compare our data to recent
theoretical work, which however fails to explain our observations. We attribute
this disagreement with theory to the unique type of magnetic polaron formation
in EuB_6.",9912390v1
2000-01-03,Superconductivity in Ferromagnetic RuSr_2GdCu_2O_8,"The phase diagram of temperature versus exchange field is obtained within a
BCS model for d-wave superconductivity in CuO_2 layers which is coupled to
ferromagnetic RuO_2 layers in RuSr_2GdCu_2O_8. It is found that the
Fulde-Ferrell-Larkin-Ovchinnikov state is very sensitive to the band filling
factor. For strong exchange field, we point out that superconductivity could
only exist in the interfaces between ferromagnetic domains. The magnetization
curve is calculated and its comparison with experiment is discussed. We also
propose the measuring of tunneling conductance near a single unitary impurity
to detect the strength of the exchange interaction.",0001024v2
2000-01-21,Theory of Diluted Magnetic Semiconductor Ferromagnetism,"We present a theory of carrier-induced ferromagnetism in diluted magnetic
semiconductors (III_{1-x} Mn_x V) which allows for arbitrary itinerant-carrier
spin polarization and dynamic correlations. Both ingredients are essential in
identifying the system's elementary excitations and describing their
properties. We find a branch of collective modes, in addition to the spin waves
and Stoner continuum which occur in metallic ferromagnets, and predict that the
low-temperature spin stiffness is independent of the strength of the exchange
coupling between magnetic ions and itinerant carriers. We discuss the
temperature dependence of the magnetization and the heat capacity.",0001320v2
2000-03-07,Ferromagnetism and Colossal Magnetoresistance from the Coexistence of Comparable Charge and Spin Density Orders,"We report a complete multicomponent mean-field-theory for the coexistence and
competition of charge ordering (CO), antiferromagnetic (AFM) and ferromagnetic
(FM) spin ordering in the presence of a uniform magnetic field. Doping the AFM
or CO state always generates a ferromagnetic component. Itinerant FM, AFM and
CO, necessarily coexist and compete in a particle-hole asymmetric system.
Melting of large AFM-CO orders by small magnetic fields and the related
phenomenon of Colossal Magnetoresistance (CMR) may arise whenever the CO and
AFM order parameters have similar magnitude and momentum structure. Hole doping
favors FM metallic states and CMR while electron doping favors AFM-CO states in
agreement with the phase diagram of perovskite manganites.",0003107v1
2000-03-08,"Comment on ""Phase Diagram of the Random Energy Model with Higher-Order Ferromagnetic Term and Error Correcting Codes due to Sourlas""","In a recent Physics Review Letter, Dorlas and Wedagedera have studied the
random energy model with an additional p-spin ferromagnetic interaction. Here
we note that (i) we have solved the corresponding problem of a spherical spin
system with p-spin glass interactions and r-spin ferromagnetic interactions,
and (ii) a simple mapping yields the results of DW and generalizations.
  Reference: http://arXiv.org/abs/cond-mat/9912201",0003137v1
2000-05-25,Electron Transport in Hybrid Ferromagnetic/Superconducting Nanostructures,"We observe large amplitude changes in the resistance of ferromagnetic (F)
wires at the onset of superconductivity of adjacent superconductors (S). New
sharp peaks of large amplitude are found in the magnetoresistance of the
F-wires. We discuss a new mechanism for the long-range superconducting
proximity effect in F/S nanostructures based on the analysis of the topologies
of actual Fermi-surfaces in ferromagnetic metals.",0005437v1
2000-05-29,Orbital-ordering-induced anomalous softening of the ferromagnetic spin waves in perovskite manganites,"Spin wave excitations were measured in the ferromagnetic phase of
Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$ by neutron scattering. This compound is located
in proximity to the A-type antiferromagnetic state, and it shows a clear
anisotropy and anomalous softening of the spin wave excitations. The softening
in the ferromagnetic phase is induced by the orbital ordering.",0005497v2
2000-09-13,Oscillations of the superconducting order parameter in a ferromagnet,"Planar tunneling spectroscopy reveals damped oscillations of the
superconducting order parameter induced into a ferromagnetic thin film by the
proximity effect. The oscillations are due to the finite momentum transfer
provided to Cooper pairs by the splitting of the spin up and down bands in the
ferromagnet. As a consequence, for negative values of the superconducting order
parameter the tunneling spectra are capsized (""$\pi$-state""). The oscillations'
damping and period are set by the same length scale, which depends on the spin
polarization.",0009192v1
2000-09-20,Impurity-induced Ferromagnetism in Doped Triplet Excitonic Insulator,"The theory of impurities in excitonic insulator is investigated in the light
of the recent experiments on hexaborides. First, we study the bound state
around the impurity and find that the bound state emerges when ${Re}\Delta$ is
positive. Second, we study the continuum state using Abrikosov-Gor'kov's
approach. We find that the energy gap is reduced strongly when ${Im}\Delta=0$.
Finally, we solve Bogoliubov-de Gennes equations for excitonic insulator
numerically. We get the results consistent with the analytic ones.
  We also find that incomplete ferromagnetism appears in doped triplet
excitonic insulator with impurity. We make a short qualitative discussion on
the ferromagnetism of doped hexaborides using our result.",0009290v1
2000-09-28,The quantum phase transition of itinerant helimagnets,"We investigate the quantum phase transition of itinerant electrons from a
paramagnet to a state which displays long-period helical structures due to a
Dzyaloshinskii instability of the ferromagnetic state. In particular, we study
how the self-generated effective long-range interaction recently identified in
itinerant quantum ferromagnets is cut-off by the helical ordering. We find that
for a sufficiently strong Dzyaloshinskii instability the helimagnetic quantum
phase transition is of second order with mean-field exponents. In contrast, for
a weak Dzyaloshinskii instability the transition is analogous to that in
itinerant quantum ferromagnets, i.e. it is of first order, as has been observed
in MnSi.",0009441v2
2000-11-04,Orbital polarons and ferromagnetic insulators in manganites,"We argue that in lightly hole doped perovskite-type Mn oxides the holes
(Mn$^{4+}$ sites) are surrounded by nearest neighbor Mn$^{3+}$ sites in which
the occupied $3d$ orbitals have their lobes directed towards the central hole
(Mn$^{4+}$) site and with spins coupled ferromagnetically to the central spin.
This composite object, which can be viewed as a combined orbital-spin-lattice
polaron, is accompanied by the breathing type (Mn$^{4+}$) and Jahn-Teller type
(Mn$^{3+}$) local lattice distortions. We present calculations which indicate
that for certain doping levels these orbital polarons may crystallize into a
charge and orbitally ordered ferromagnetic insulating state.",0011070v1
2000-11-20,Effects of Disorder on Ferromagnetism in Diluted Magnetic Semiconductors,"We present results of a numerical mean field treatment of interacting spins
and carriers in doped diluted magnetic semiconductors, which takes into account
the positional disorder present in these alloy systems. Disorder is found to
enhance the ferromagnetic transition temperature significantly for metallic
densities not too far from the metal-insulator transition. Concurrently, the
ferromagnetic phase is found to have very unusual temperature dependence of the
magnetization as well as specific heat as a result of disorder. Unusual spin
and charge transport is implied.",0011319v2
2000-11-21,Fast Incomplete Decoherence of Nuclear Spins in Quantum Hall Ferromagnet,"A scenario of quantum computing process based on the manipulation of a large
number of nuclear spins in Quantum Hall (QH) ferromagnet is presented. It is
found that vacuum quantum fluctuations in the QH ferromagnetic ground state at
filling factor $\nu =1$, associated with the virtual excitations of spin waves,
lead to fast incomplete decoherence of the nuclear spins. A fundamental upper
bound on the length of the computer memory is set by this fluctuation effect.",0011361v2
2000-11-30,Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites,"The effect of an exchange field on electrical transport in thin films of
metallic ferromagnetic manganites has been investigated. The exchange field was
induced both by direct exchange coupling in a ferromagnet/antiferromagnet
multilayer and by indirect exchange interaction in a ferromagnet/paramagnet
superlattice. The electrical resistance of the manganite layers was found to be
determined by the absolute value of the vector sum of the effective exchange
field and the external magnetic field.",0011528v1
2000-12-08,Phase Separation and the Low-Field Bulk Magnetic Properties of Pr0.7Ca0.3MnO3,"We present a detailed magnetic study of the perovskite manganite
Pr0.7Ca0.3MnO3 at low temperatures including magnetization and a.c.
susceptibility measurements. The data appear to exclude a conventional spin
glass phase at low fields, suggesting instead the presence of correlated
ferromagnetic clusters embedded in a charge-ordered matrix. We examine the
growth of the ferromagnetic clusters with increasing magnetic field as they
expand to occupy almost the entire sample at H ~ 0.5 T. Since this is well
below the field required to induce a metallic state, our results point to the
existence of a field-induced ferromagnetic insulating state in this material.",0012143v1
2000-12-08,Two-dimensional topological solitons in small exchange-dominated cylindrical ferromagnetic particles,"A general approach allowing to construct the magnetization distributions of
arbitrary topological charge in small exchange-dominated cylindrical
ferromagnetic particles is presented. The exchange energy functional is
minimized by these distributions exactly. The magnetostatic energy is accounted
partially, so that it facilitates a choice between the topologically equivalent
exchange-only solutions. The resulting magnetization distributions can be
easily generalized to a variety of non-circular cylindrical shapes by means of
a conformal transformation. As an example a magnetic structures of a thin
circular ferromagnetic cylinder both with centered and displaced magnetic
vortex and of a finite Bloch domain wall in an elongated particle is given.",0012146v1
2000-12-21,Ground state energy of metallic ferromagnet in a generalized Hubbard model,"In the present work ferromagnetic ordering in the Hubbard model generalized
by taking into account the inter-atomic exchange interaction and correlated
hopping in partially filled narrow band is considered. In the case of weak
electron-electron interaction the ground state energy and condition of
ferromagnetic state realization are found using the Green function technique.
The obtained results indicate the important role of correlated hopping.",0012402v1
2000-12-27,First order transition from antiferromagnetism to ferromagnetism in Ce(Fe$_{0.96}$Al$_{0.04})_2$,"Results of dc magnetization study are presented showing interesting
thermomagnetic history effects across the antiferromagnetic to ferromagnetic
transition in Ce(Fe$_{0.96}$Al$_{0.04})_2$. Specifically, we observe (i)ZFC/FC
irreversibility rising with increasing field; (ii) virgin curve lying outside
the envelope M-H curve. We argue that these effects are quite different from
the characteristics seen in spin-glasses or in hard ferromagnets; they can be
understood as metastabilities associated with a first order magnetic phase
transition.",0012472v1
2001-02-21,Disorder Induced Ferromagnetism in CaRuO3,"The magnetic ground state of perovskite structure CaRuO3 has been enigmatic
for decades. Here we show that paramagnetic CaRuO3 can be made ferromagnetic by
very small amounts of partial substitution of Ru by Ti. Magnetic hysteresis
loops are observed at 5 K for as little as 2% Ti substitution. Ti is
non-magnetic and isovalent with Ru, indicating that the primary effect of the
substitution is the disruption of the magnetic ground state of CaRuO3 through
disorder. The data suggest that CaRuO3 is poised at a critical point between
ferromagnetic and paramagnetic ground states.",0102364v1
2001-02-26,Ferromagnetic transition in a double-exchange system,"We study ferromagnetic transition in three-dimensional double-exchange model.
The influence of strong spin fluctuations on conduction electrons is described
in coherent potential approximation. In the framework of thermodynamic approach
we construct for the system ""electrons (in a disordered spin configuration) +
spins"" the Landau functional, from the analysis of which critical temperature
of ferromagnetic transition is calculated.",0102469v2
2001-02-27,Ground state ferromagnetism in a doubly orbitally degenerate model,"In the present paper the ground state of a double orbitally degenerate model
at weak intra-atomic interaction is studied using the Green functions method.
Beside the diagonal matrix elements of electron-electron interactions the model
includes correlated hopping integrals and inter-atomic exchange interaction.
The influence of orbital degeneracy with Hund's rule coupling, correlated
hopping and inter-atomic direct exchange on the ferromagnetic ordering is
investigated. The expressions for ground state energy and magnetization, the
criterion of transition from paramagnetic to ferromagnetic ground state as
functions of the model parameters are obtained. The obtained results are
compared with some experimental data for magnetic materials.",0102495v1
2001-03-14,First order phase transition from ferromagnetism to antiferromagnetism in Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$,"Taking the pseudobinary C15 Laves phase compound
Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$ as a paradigm for studying a ferromagnetic to
antiferromagnetic phase transition, we present interesting thermomagnetic
history effects in magnetotransport as well as magnetisation measurements
across this phase transition. A comparison is made with history effects
observed across the ferromagnetic to antiferromagnetic transition in
R$_{0.5}$Sr$_{0.5}$MnO$_3$ crystals.",0103291v1
2001-04-19,Itinerant Ferromagnetism for Mixed Valence Systems,"We introduce a novel mechanism for the unusual itinerant ferromagnetism found
in mixed valence systems like Ce(Rh$_{1-x}$Ru$_x$)$_3$B$_2$,
La$_x$Ce$_{1-x}$Rh$_3$B$_2$, US, USe, and UTe. With it we can provide an
explanation for the long-unexplained large value of $T_c$ ($\sim$ 100$^\circ$K)
value and the maximum in the magnetization below $T_c$ found experimentally. We
also show that this novel itinerent ferromagnetism can be continuously
connected with the localized case for which the energy scale is much smaller
($J_{RKKY} \sim$ 1$^\circ$K).",0104351v1
2001-05-09,La-site shift as probe for Jahn-Teller effect,"We observe two consecutive transitions in La1-xCaxMnO3, x=0.19: ferromagnetic
ordering at Tc = 177 K and Jahn-Teller orbital ordering at T_JT = 150 K. The
presence of a ferromagnetic insulating state below T_JT shows that the metallic
phase is bound by ferromagnetic and Jahn- Teller ordering, and not induced by a
critical doping concentration. The A-site shift is found to be a good indicator
of Jahn-Teller ordering. Furthermore, the A-site shift does not disapppear
above T_JT, indicating a dynamical behaviour of the distorted MnO6 octahedra.",0105197v1
2001-05-24,Parity-sensitive measurements based on ferromagnet/superconductor tunneling junctions,"A method to identify the parity of unconventional superconductors is proposed
based on tunneling spectroscopy. For a model of calculation, we adopt a
ferromagnet/superconductor (F/S) junction of which tunneling current is spin
polarized. The tunneling conductance spectra are shown to be quite sensitive to
the direction of the magnetization axis in the ferromagnet only when the
superconductor has odd parity. Therefore, it is possible to distinguish the
parity of the superconductor by measuring the tunneling spectroscopy in F/S
junctions.",0105468v2
2001-05-28,Effects of annealing time on defect-controlled ferromagnetism in Ga1-xMnxAs,"We have studied the evolution of the magnetic, electronic, and structural
properties of annealed epilayers of Ga1-xMnxAs grown by low temperature
molecular beam epitaxy. Annealing at the optimal temperature of 250 C for less
than 2 hours significantly enhances the conductivity and ferromagnetism, but
continuing the annealing for longer times suppresses both. These data indicate
that such annealing induces the defects in Ga1-xMnxAs to evolve through at
least two different processes, and they point to a complex interplay between
the different defects and ferromagnetism in this material.",0105541v1
2001-05-31,Strong Enhancement of Superconducting T_c in Ferromagnetic Phases,"It is shown that the critical temperature for spin-triplet, p-wave
superconductivity mediated by spin fluctuations is generically much higher in a
Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling
of the magnons to the longitudinal magnetic susceptibility. Together with the
tendency of the low-temperature ferromagnetic transition in very clean
Heisenberg magnets to be of first order, this qualitatively explains the phase
diagram recently observed in UGe_2.",0105627v2
2001-06-10,Critical temperature of superconductor/ferromagnet bilayers,"Superconductor/ferromagnet bilayers are known to exhibit nontrivial
dependence of the critical temperature T_c on the thickness d_f of the
ferromagnetic layer. We develop a general method for investigation of T_c as a
function of the bilayer's parameters. It is shown that interference of
quasiparticles makes T_c(d_f) a nonmonotonic function. The results are in good
agreement with experiment. Our method also applies to multilayered structures.",0106185v2
2001-06-14,Spontaneous vortex phase in ErNi2B2C,"Below T_{WFM} ~ 2.75K, a weak ferromagnetism and superconductivity coexist in
ErNi2B2C. In the present paper, a possibility of a spontaneous vortex phase was
examined directly by small angle neutron scattering technique. An external
magnetic field was applied to align ferromagnetic domains so that the internal
magnetic field induced by the weak ferromagnetism becomes uniform and uniaxial
over the bulk sample. When the field is removed, the flux line lattice
subsisted below T_{WFM} but disappeared above it. A pinning effect is also
discussed. We conclude that the spontaneous vortex state is realized in
ErNi2B2C.",0106273v1
2001-06-26,Field Effect Magnetization Reversal in Ferromagnetic Semiconductor Quantum Wells,"We predict that a novel bias-voltage assisted magnetization reversal process
will occur in Mn doped II-VI semiconductor quantum wells or heterojunctions
with carrier induced ferromagnetism. The effect is due to strong
exchange-coupling induced subband mixing that leads to electrically tunable
hysteresis loops. Our model calculations are based on the mean-field theory of
carrier induced ferromagnetism in Mn-doped quantum wells and on a
semi-phenomenological description of the host II-VI semiconductor valence
bands.",0106536v1
2001-07-09,Critical Exponents for the Ferromagnetism in Colossal Magnetoresistance Manganites,"Critical phenomena of ferromagnetic transition in colossal magnetoresistance
manganites are theoretically studied. Concerning the critical exponents for
this transition, there still remains controversy among experimental results. In
order to clarify intrinsic physics of the manganites through a comparison with
theoretical prediction, we investigate the critical phenomena of
double-exchange models by using finite-size scaling analysis on unbiased
numerical results. As a result, we show that the critical exponents of the
ferromagnetic transition of the three-dimensional double-exchange model is
consistent with those of the Heisenberg model, but are distinct from the
mean-field one.",0107172v1
2001-07-11,Theory of Ferromagnetism in Ca1-xLaxB6,"Novel ferromagnetism in Ca$_{1-x}$La$_{x}$B$_6$ is studied in terms of the
Ginzburg-Landau theory for excitonic order parameters, taking into account
symmetry of the wavefunctions. We found that the minima of the free energy
break both inversion and time-reversal symmetries, while the product of these
two remains preserved. This explains various novelties of the ferromagnetism
and predicts a number of magnetic properties, including the magnetoelectric
effect, which can be tested experimentally.",0107215v3
2001-07-13,Longitudinal spin-fluctuations and superconductivity in ferromagnetic ZrZn$_{2}$ from ab initio calculations,"The recent discovery of superconductivity coexisting with weak itinerant
ferromagnetism in the $d$-electron intermetallic compound ZrZn$_{2}$ strongly
suggests spin-fluctuation mediated superconductivity. {\it Ab initio}
electronic structure calculations of the Fermi surface and generalized
susceptibilities are performed to investigate the viability of longitudinal
spin-fluctuation-induced spin-triplet superconductivity in the ferromagnetic
state. The critical temperature is estimated to be of the order of 1 K.
Additionally, it is shown that in spite of a strong electron-phonon coupling
($\lambda_{ph}=0.7$), conventional s-wave superconductivity is inhibited by the
presence of strong spin-fluctuations.",0107304v1
2001-07-26,Layer-dependent magnetization at the surface of a band-ferromagnet,"The temperature-dependence of the magnetization near the surface of a
band-ferromagnet is measured with monolayer resolution. The simultaneous
application of novel highly surface-sensitive techniques enables one to deduce
the layer-dependent magnetization curves at a Fe(100) surface. Analysis of data
is based on a simple mean-field approach. Implications for modern theories of
itinerant-electron ferromagnetism are discussed.",0107545v1
2001-10-08,Phase Diagram of Multilayer Magnetic Structures,"Multilayer ""ferromagnet-layered antiferromagnet"" (Fe/Cr) structures
frustrated due to the roughness of layer interfaces are studied by numerical
modeling methods. The ""thickness-roughness"" phase diagrams for the case of thin
ferromagnetic film on the surface of bulk antiferromagnet and for two
ferromagnetic layers separated by an antiferromagnetic interlayer are obtained
and the order parameter distributions for all phases are found. The phase
transitions nature in such systems is considered. The range of applicability
for the ""magnetic proximity model"" proposed by Slonczewski is evaluated.",0110157v1
2001-10-10,Ferromagnetism and disorder: A dynamical mean-field study,"We investigate ferromagnetism in the periodic Anderson model with diagonal
disorder. Using dynamical mean-field theory in combination with the modified
perturbation theory, the disorder can be included in the calculation
consistently, which turns out to be equivalent to the CPA method. Disorder
generally reduces the Curie temperature and can for certain configurations
completely suppress ferromagnetic order. This can be ascribed to the enhanced
quasiparticle damping and the special structure of the density of states.",0110209v1
2001-10-11,Enhanced Gilbert Damping in Thin Ferromagnetic Films,"Using a scattering matrix approach, the precession of the magnetization of a
ferromagnet is shown to transfer spins into adjacent normal metal layers. This
``pumping'' of spins slows down the precession corresponding to an enhanced
Gilbert damping factor in the Landau-Lifshitz equation. The damping is
expressed in terms of the scattering matrix of the ferromagnet-normal metal
interface, which is accessible to model and first-principles calculations. Our
estimates for permalloy thin films explain the trends observed in recent
experiments.",0110247v2
2001-11-12,Itinerant-electron Ferromagnetism in W(Nb)O3-d,"The crystal structure and the magnetic properties of the W1-xNbxO3-d,
(x<0.03) system have been investigated. In contrast to the orthorhombic
diamagnetic WO3, the material with x=0.01 is paramagnetic down to 5 K.
Introducing of 2.5 at. % of Nb into WO3 leads to a tetragonal structure and to
a weak itinerant ferromagnetic ordering below TC= 225 K. The saturation
magnetic moment at 5 K is 1.07*10-3 mB, whereas the paramagnetic effective
moment is 0.06 mB per mole. This high ratio indicates itinerant ferromagnetism
in W0.975Nb0.025O3-d.",0111210v1
2001-11-19,Phase transitions in the steady state behavior of mechanically perturbed spin glasses and ferromagnets,"We analyze the steady state regime of systems interpolating between spin
glasses and ferromagnets under a tapping dynamics recently introduced by
analogy with the dynamics of mechanically perturbed granular media. A crossover
from a second order to first order ferromagnetic transition as a function of
the spin coupling distribution is found. The flat measure over blocked states
introduced by Edwards for granular media is used to explain this scenario.
Annealed calculations of the Edwards entropy are shown to qualitatively explain
the nature of the phase transitions. A Monte-Carlo construction of the Edwards
measure confirms that this explanation is also quantitatively accurate.",0111331v1
2001-11-27,"Comment on ""Effects of Disorder on Ferromagnetism in Diluted Magnetic Semiconductors""","In a recent Letter, Berciu and Bhatt have presented a mean-field theory of
ferromagnetism in III-V semiconductors doped with manganese, starting from an
impurity band model. We show that this approach gives an unphysically broad
impurity band and is thus not appropriate for (Ga,Mn)As containing 1-5% Mn. We
also point out a microscopically unmotivated sign change in the overlap
integrals in the Letter. Without this sign change, stable ferromagnetism is not
obtained.",0111504v1
2001-12-05,Exchange Bias in Ferromagnetic/Compensated Antiferromagnetic Bilayers,"By means of micromagnetic spin dynamics calculations, a quantitative
calculation is carried out to explore the mechanism of exchange bias (EB) in
ferromagnetic (FM)/compensated antiferromagnetic (AFM) bilayers. The
antiferromagnets with low and high Neel temperatures have been both considered,
and the crossover from negative to positive EB is found only in the case with
low Neel temperature. We propose that the mechanism of EB in FM/compensated AFM
bilayers is due to the symmetry broken of AFM that yields some net
ferromagnetic components.",0112064v1
2002-01-21,"Ferromagnetic semiconductor (In,Ga,Mn)As with Curie temperature above 100 K","We have grown (InyGa1-y)1-xMnxAs ferromagnetic semiconductor layers with Mn
composition x up to 0.13 on InP substrates by molecular beam epitaxy. Near the
lattice-matched composition, i.e., y ~ 0.53, the Curie temperature increases
linearly with the ferromagnetically effective Mn composition x_eff, following
the empirical equation T_C=1300x_eff. We obtained Curie temperatures above 100
K when x is relatively high (x>0.1; x_eff>0.08) and the hole concentration is
in the order of 10^19 cm^-3.",0201363v1
2002-02-12,Domain structure of superconducting ferromagnets,"In superconducting ferromagnets the equilibrium domain structure is absent in
the Meissner state, but appears in the spontaneous vortex phase (the mixed
state in zero external magnetic field), though with a period, which can
essentially exceed that in normal ferromagnets. Metastable domain walls are
possible even in the Meissner state. The domain walls create magnetostatic
fields near the sample surface, which can be used for experimental detection of
domain walls.",0202193v1
2002-02-22,Spin-polarized light emitting diode using metal/insulator/semiconductor structures,"We have succeeded in growing ferromagnetic metals (Co, Fe, and NiFe)/ Al2O3/
AlGaAs heterostructures with homogeneous and flat interfaces. The
electro-luminescence (EL) from the light emitting diode (LED) consisting of the
metal/insulator/semiconductor (MIS) structure depends on the magnetization
direction of the ferromagnetic electrode at room temperature. This fact shows
that a spin-injection from the ferromagnetic metal to the semiconductor is
achieved. The spin-injection efficiency is estimated to be the order of 1 % at
room temperature.",0202389v1
2002-02-26,Magnetothermopower and magnon-assisted transport in ferromagnetic tunnel junctions,"We present a model of the thermopower in a mesoscopic tunnel junction between
two ferromagnetic metals based upon magnon-assisted tunneling processes. In our
model, the thermopower is generated in the course of thermal equilibration
between two baths of magnons, mediated by electrons. We predict a particularly
large thermopower effect in the case of a junction between two half-metallic
ferromagnets with antiparallel polarizations, $S_{AP} \sim - (k_B/e)$, in
contrast to $S_{P} \approx 0$ for a parallel configuration.",0202475v1
2002-02-27,Spin-dependent Transparency of Ferromagnet/Superconductor Interfaces,"Because the physical interpretation of the spin-polarization of a ferromagnet
determined by point-contact Andreev reflection (PCAR) is non-trivial, we have
carried out parameter-free calculations of PCAR spectra based upon a
scattering-theory formulation of Andreev reflection generalized to
spin-polarized systems and a tight-binding linear muffin tin orbital method for
calculating the corresponding scattering matrices. PCAR is found to measure the
spin-dependent interface transparency rather than the bulk polarization of the
ferromagnet which is strongly overestimated by free electron model fitting.",0202515v1
2002-03-05,Ferromagnetism in Diluted Magnetic Semiconductor Heterojunction Systems,"Diluted magnetic semiconductors (DMSs), in which magnetic elements are
substituted for a small fraction of host elements in a semiconductor lattice,
can become ferromagnetic when doped. In this article we discuss the physics of
DMS ferromagnetism in systems with semiconductor heterojunctions. We focus on
the mechanism that cause magnetic and magnetoresistive properties to depend on
doping profiles, defect distributions, gate voltage, and other system
parameters that can in principle be engineered to yield desired results.",0203080v1
2002-03-06,A new mechanism of exchange interaction in ferromagnetic semiconductors,"We propose a new mechanism of indirect exchange interaction, which can be
responsible for the ferromagnetic ordering in Mn-doped semiconductors (like
GaMnAs) at low carrier concentration. The mechanism is based on the interplay
of the hybridization of band states (conduction or valence) with localized
impurity (donor or acceptor) states and the direct exchange interaction between
localized spins and the band states. The indirect exchange coupling between two
impurities occurs when the wavefunctions of the corresponding localized donor
(acceptor) states overlap. This coupling is independent of the free carrier
concentration and therefore may be responsible for ferromagnetic transition at
low or vanishing carrier concentration.",0203119v1
2002-04-04,Generalized boundary conditions for the circuit theory of mesoscopic transport,"The circuit theory of mesoscopic transport provides a unified framework to
describe spin-dependent or superconductivity-related phenomena. We extend this
theory to hybrid systems of normal metals, ferromagnets and superconductors.
Our main result is an expression for the current through an arbitrary contact
between two general isotropic ""nodes"", which is suitable to describe the
presence of superconducting and ferromagnetic elements in the system, as well
as magnetically active interfaces/contacts. In certain cases (weak ferromagnet
and magnetic tunnel junction) we derive transparent and simple results for the
matrix current.",0204116v1
2002-05-08,Epitaxial Growth of an n-type Ferromagnetic Semiconductor CdCr2Se4 on GaAs(001) and GaP(001),"We report the epitaxial growth of CdCr2Se4, an n-type ferromagnetic
semiconductor, on both GaAs and GaP(001) substrates, and describe the
structural, magnetic and electronic properties. Magnetometry data confirm
ferromagnetic order with a Curie temperature of 130 K, as in the bulk material.
The magnetization exhibits hysteretic behavior with significant remanence, and
an in-plane easy axis with a coercive field of ~125 Oe. Temperature dependent
transport data show that the films are semiconducting in character and n-type
as grown, with room temperature carrier concentrations of n ~ 1 x 10^18 cm-3.",0205162v1
2002-05-15,Magnetism in a lattice of spinor Bose condensates,"We study the ground state magnetic properties of ferromagnetic spinor
Bose-Einstein condensates confined in a deep optical lattices. In the Mott
insulator regime, the ``mini-condensates'' at each lattice site behave as
mesoscopic spin magnets that can interact with neighboring sites through both
the static magnetic dipolar interaction and the light-induced dipolar
interaction. We show that such an array of spin magnets can undergo a
ferromagnetic or anti-ferromagnetic phase transition under the magnetic dipolar
interaction depending on the dimension of the confining optical lattice. The
ground-state spin configurations and related magnetic properties are
investigated in detail.",0205319v1
2002-05-30,Spin-dependent properties of a two-dimensional electron gas with ferromagnetic gates,"A theoretical prediction of the spin-dependent electron self-energy and
in-plane transport of a two-dimensional electron gas in proximity with a
ferromagnetic gate is presented. The application of the predicted
spin-dependent properties is illustrated by the proposal of a device
configuration with two neighboring ferromagnetic gates which produces a
magnetoresistance effect on the channel current generated by nonmagnetic source
and drain contacts. Specific results are shown for a silicon inversion layer
with iron gates. The gate leakage current is found to be beneficial to the spin
effects.",0205651v2
2002-06-22,Breakdown of the coexistence of spin-singlet superconductivity and itinerant ferromagnetism,"We discuss the possibility of coexistence of spin-singlet superconductivity
and ferromagnetism in a model where the same electrons are assumed responsible
for both of them. Our calculations include both zero and finite momentum
pairing states with both s-wave and d-wave pairing symmetry. Under the
mean-field approximation, the thermodynamic potential of the non-magnetic
superconducting (SC) state is shown to be always lower than that of the
superconducting ferromagnetic (SF) state. It follows that the spin-singlet SF
state is energetically unfavorable, and a spin-triplet SF state is more likely
to survive in metals such as UGe$_{2}$ and ZrZn$_{2}$.",0206418v1
2002-07-18,Spin-transfer in diffusive ferromagnet-normal metal systems with spin-flip scattering,"The spin-transfer in biased disordered ferromagnet (F) - normal metal (N)
systems is calculated by the diffusion equation. For F1-N2-F2 and
N1-F1-N2-F2-N3 spin valves, the effect of spin-flip processes in the normal
metal and ferromagnet parts are obtained analytically. Spin-flip in the center
metal N2 reduces the spin-transfer, whereas spin-flip in the outer normal
metals N1 and N3 can increase it by effectively enhancing the spin polarization
of the device.",0207458v1
2002-08-21,A key to room-temperature ferromagnetism in Fe-doped ZnO: Cu,"Successful synthesis of room-temperature ferromagnetic semiconductors,
Zn$_{1-x}$Fe$_{x}$O, is reported. The essential ingredient in achieving
room-temperature ferromagnetism in bulk Zn$_{1-x}$Fe$_{x}$O was found to be
additional Cu doping. A transition temperature as high as 550 K was obtained in
Zn$_{0.94}$Fe$_{0.05}$Cu$_{0.01}$O; the saturation magnetization at room
temperature reached a value of $0.75 \mu_{\rm B}$ per Fe. Large
magnetoresistance was also observed below $100 $K.",0208399v1
2002-08-23,Even-odd effects in magnetoresistance of ferromagnetic domain walls,"Difference in density of states for the spin's majority and minority bands in
a ferromagnet changes the electrostatic potential along the domains,
introducing the discontinuities of the potential at domain boundaries. The
value of discontinuity oscillates with number of domains. Discontinuity depends
on the positions of domain walls, their motion or collapse of domain walls in
applied magnetic field. Large values of magnetoresistance are explained in
terms of spin-accumulation. We suggest a new type of domain walls in nanowires
of itinerant ferromagnets, in which the magnetization vector changes without
rotation. Absence of transverse magnetization components allows considerable
spin accumulation assuming the spin relaxation length, L_S, is large enough.",0208463v1
2002-09-10,Canted ferromagnetism in RuSr$_2$GdCu$_2$O$_8$,"First principles calculations using the full-potential linearized augmented
plane wave (FLAPW) method including intra-atomic noncollinear magnetism have
been performed to determine the magnetic structures of
RuSr$_{2}$GdCu$_{2}$O$_{8}$. The magnetism clearly arises from the RuO$_{6}$
octahedra where the moments on neighboring Ru sites order antiferromagnetically
but cant perpendicular to the AFM axis - and so induce a weak ferromagnetism.
The projected Ru moments along the AFM and FM axes result in magnetic moments
of 1.16 and 0.99 $\mu_{B}$ respectively. The results are consistent with the
possible coexistence of canted ferromagnetism and superconductivity in the
RuSr$_{2}$GdCu$_{2}$O$_{8}$ - inferred from experiments.",0209224v1
2002-09-10,Transport properties of ferromagnet/d-wave superconductor/ferromagnet double junctions,"We investigate transport properties of a trilayer made of a d-wave
superconductor connected to two ferromagnetic electrodes. Using Keldysh
formalism we show that crossed Andreev reflection and elastic cotunneling exist
also with d-wave superconductors. Their properties are controlled by the
existence of zero energy states due to the anisotropy of the d-wave pair
potential.",0209238v3
2002-09-13,Self-compensation in manganese-doped ferromagnetic semiconductors,"We present a theory of interstitial Mn in Mn-doped ferromagnetic
semiconductors. Using density-functional theory, we show that under the
non-equilibrium conditions of growth, interstitial Mn is easily formed near the
surface by a simple low-energy adsorption pathway. In GaAs, isolated
interstitial Mn is an electron donor, each compensating two substitutional Mn
acceptors. Within an impurity-band model, partial compensation promotes
ferromagnetic order below the metal-insulator transition, with the highest
Curie temperature occurring for 0.5 holes per substitutional Mn.",0209329v1
2002-09-18,Stability of ferromagnetism in the Hubbard model on the kagomé lattice,"The Hubbard model on the kagom\'e lattice has highly degenerate ground states
(the flat lowest band) in the corresponding single-electron problem and
exhibits the so-called flat-band ferromagnetism in the many-electron ground
states as was found by Mielke. Here we study the model obtained by adding extra
hopping terms to the above model. The lowest single-electron band becomes
dispersive, and there is no band gap between the lowest band and the other
band. We prove that, at half-filling of the lowest band, the ground states of
this perturbed model remain saturated ferromagnetic if the lowest band is
nearly flat.",0209423v1
2002-10-04,Current-induced spin-wave excitations in a single ferromagnetic layer,"A new current induced spin-torque transfer effect has been observed in a
single ferromagnetic layer without resorting to multilayers. At a specific
current density of one polarity injected from a point contact, abrupt
resistance changes due to current-induced spin wave excitations have been
observed. The critical current at the onset of spin-wave excitations depends
linearly on the external field applied perpendicular to the layer. The observed
effect is due to current-driven heterogeneity in an otherwise uniform
ferromagnetic layer.",0210116v1
2002-12-03,Thermal stability of coupled ferromagnetic and superparamagnetic particles,"We consider a single-domain ferromagnetic particle with uniaxial anisotropy
coupled to a single-domain soft ferromagnetic particle (superparamagnetic
particle). The problem of thermally agitated magnetization reversal in this
case can be reduced to the random magnetization dynamics of the first particle
with an effectively larger anisotropy field. The magnetic external field is
also altered in a manner that depends on the sign of the coupling and can be
either enhanced or suppressed.",0212041v1
2002-12-06,Electron space charge effect on spin injection into semiconductors,"We consider spin polarized transport in a
ferromagnet-insulator/semiconductor/insulator-ferromagnet (F1-I-S-I-F2)
junction. We find that the spin current is strongly dependent on the spin
configurations, the doping and space charge distribution in the semiconductor.
When the ferromagnet-semiconductor interface resistance is comparable to the
semiconductor resistance, the magnetoresistance ratio of this junction can be
greatly enhanced under appropriate doping when the space charge effect in the
nonequilibrium transport processes is taken into consideration.",0212133v2
2003-01-24,Classical Infinite-Range-Interaction Heisenberg Ferromagnetic Model: Metastability and Sensitivity to Initial Conditions,"A N-sized inertial classical Heisenberg ferromagnet, which consists in a
modification of the well-known standard model, where the spins are replaced by
classical rotators, is studied in the limit of infinite-range interactions. The
usual canonical-ensemble mean-field solution of the inertial classical
$n$-vector ferromagnet (for which $n=3$ recovers the particular Heisenberg
model considered herein) is briefly reviewed, showing the well-known
second-order phase transition. This Heisenberg model is studied numerically
within the microcanonical ensemble, through molecular dynamics.",0301492v1
2003-02-03,Proximity Effect and Spontaneous Vortex Phase in Planar SF-Structures,"The proximity effect in SF structures was examined. It is shown that, due to
the oscillations of the induced superconducting order parameter in a
ferromagnet, the critical temperature of an SF-bilayer becomes minimal when the
thickness of the ferromagnetic layer is close to a quarter of the period of
spatial oscillations. It is found that the spontaneous vortex state arisen in
the superconductor due to the proximity of the magnetic domain structure of a
ferromagnet brings about noticeable magnetoresistive effects.",0302028v1
2003-02-21,A model for coexistent superconductivity and ferromagnetism,"We explore various temperature dependencies and thermodynamic quantities of a
mean field model of a ferromagnetic-superconducting system. The starting point
for this model is based on an s-wave pairing scheme in the singlet channel of
the superconducting state and a spontaneously broken symmetry phase in the
ferromagnetic state. We show numerically and analytically that a state of
coexistence reveals itself and is favored energetically over other possible
states, and a simple phase diagram is developed. Finally, a comparison of the
specific heat with experiment is shown.",0302449v2
2003-02-25,On the Ordering Instability of Weakly-Interacting Electrons in a Dirty Metal,"In a dirty metal, electron-electron interactions in the spin-triplet channel
lead to singular corrections to a variety of physical quantities. We show that
these singularities herald the emergence of ferromagnetism. We calculate the
effective action for the magnetic moment of weakly-interacting electrons in a
dirty metal and show that a state with finite ferromagnetic moment minimizes
this effective action. The saddle-point approximation is exact in an
appropriate large-N limit. We discuss the physics of the ferromagnetic state
with particular regard to thermal fluctuations and localization effects.",0302503v1
2003-03-19,Many-body Green's function theory for thin ferromagnetic anisotropic Heisenberg films: treatment of the exchange anisotropy,"The many-body Green's function theory developed in our previous work for
treating the reorientation of the magnetization of thin ferromagnetic films is
extended to include the exchange anisotropy. This leads to additional momentum
dependencies which require some non-trivial changes in the formalism. The
theory is developed for arbitrary spin values S and for multilayers. The
effects of the exchange anisotropy and the single-ion anisotropy, which was
treated in our earlier work, on the magnetic properties of thin ferromagnetic
films are compared.",0303389v1
2003-04-01,The enhancement of ferromagnetism in uniaxially stressed diluted magnetic semiconductors,"We predict a new mechanism of enhancement of ferromagnetic phase transition
temperature $T_c$ in uniaxially stressed diluted magnetic semiconductors (DMS)
of p-type. Our prediction is based on comparative studies of both Heisenberg
(inherent to undistorted DMS with cubic lattice) and Ising (which can be
applied to strongly enough stressed DMS) models in a random field approximation
permitting to take into account the spatial inhomogeneity of spin-spin
interaction. Our calculations of phase diagrams show that area of parameters
for existence of DMS-ferromagnetism in Ising model is much larger than that in
Heisenberg model.",0304012v1
2003-05-01,Ultrafast Photoinduced Softening in a III-V Ferromagnetic Semiconductor for Non-thermal Magneto-Optical Recording,"Through time-resolved two-color magneto-optical Kerr spectroscopy we have
demonstrated that photogenerated transient carriers decrease the coercivity of
ferromagnetic InMnAs at low temperatures. This transient ``softening'' persists
only during the carrier lifetime ($\sim$ 2 ps) and returns to its original
value as soon as the carriers recombine to disappear. We discuss the origin of
this unusual phenomenon in terms of carrier-enhanced ferromagnetic exchange
interactions between Mn ions and propose an entirely nonthermal scheme for
magnetization reversal.",0305017v2
2003-05-08,Superconducting Transition Temperature in Heterogeneous Ferromagnet-Superconductor Systems,"We study the shift of the the superconducting transition temperature $T_c$ in
ferromagnetic-superconducting bi-layers and in a superconducting film supplied
a square array of ferromagnetic dots. We find that the transition temperature
in these two cases change presumably in opposite direction and that its change
is not too small. We extend these results to multilayer structures. We predict
that rather small external magnetic field $\sim 10$ Oe can change the
transition temperature of the bilayer by 10% .",0305153v1
2003-05-14,Magnetodielectric Effects from Spin Fluctuations in Isostructural Ferromagnetic and Antiferromagnetic Systems,"We report on the effects of spin fluctuations, magnetic ordering, and
external magnetic field on the dielectric constant of the ferromagnet SeCuO3,
and the antiferromagnet TeCuO3. A model based on the coupling between uniform
polarization and the q-dependent spin-spin correlation function is presented to
explain the different behaviors for these isostructural compounds. The large
magnetocapacitance near the transition temperature in the ferromagnet SeCuO3
suggests routes to enhancing the magnetodielectric response for practical
applications.",0305333v1
2003-05-19,Exploration of oxide-based diluted magnetic semiconductors toward transparent spintronics,"A review is given for the recent progress of research in the field of
oxide-based diluted magnetic semiconductor (DMS), which was triggered by
combinatorial discovery of transparent ferromagnet. The possible advantages of
oxide semiconductor as a host of DMS are described in comparison with
conventional compound semiconductors. Limits and problems for identifying novel
ferromagnetic DMS are described in view of recent reports in this field.
Several characterization techniques are proposed in order to eliminate
unidentified ferromagnetism of oxide-based DMS (UFO). Perspectives and possible
devices are also given.",0305435v1
2003-06-18,A search for ferromagnetism in transition-metal-doped piezoelectric ZnO,"We present the results of a computational study of ZnO in the presence of Co
and Mn substitutional impurities. The goal of our work is to identify potential
ferromagnetic ground states within the (Zn,Co)O or (Zn,Mn)O material systems
that are also good candidates for piezoelectricity. We find that, in contrast
to previous results, robust ferromagnetism is not obtained by substitution of
Co or Mn on the Zn site, unless additional carriers (holes) are also
incorporated. We propose a practical scheme for achieving such $p$-type doping
in ZnO.",0306477v1
2003-07-02,Ferromagnetic phase transition and Bose-Einstein condensation in spinor Bose gases,"Phase transitions in spinor Bose gases with ferromagnetic (FM) couplings are
studied via mean-field theory. We show that an infinitesimal value of the
coupling can induce a FM phase transition at a finite temperature always above
the critical temperature of Bose-Einstein condensation. This contrasts sharply
with the case of Fermi gases, in which the Stoner coupling $I_s$ can not lead
to a FM phase transition unless it is larger than a threshold value $I_0$. The
FM coupling also increases the critical temperatures of both the ferromagnetic
transition and the Bose-Einstein condensation.",0307063v1
2003-07-10,Capping-induced suppression of annealing in Ga(1-x)Mn(x)As epilayers,"We have studied the effects of capping ferromagnetic Ga(1-x)Mn(x)As epilayers
with a thin layer of undoped GaAs, and we find that even a few monolayers of
GaAs have a significant effect on the ferromagnetic properties. In particular,
the presence of a capping layer only 10 monolayers thick completely suppresses
the enhancement of the ferromagnetism associated with low temperature
annealing. This result, which demonstrates that the surface of a Ga(1-x)Mn(x)As
epilayer strongly affects the defect structure, has important implications for
the incorporation of Ga(1-x)Mn(x)As into device heterostructures.",0307255v1
2003-07-15,Signatures of pairing mechanisms and order parameters in ferromagnetic superconductors,"Two predictions are made for properties of the ferromagnetic superconductors
discovered recently. The first one is that spin-triplet, p-wave pairing in such
materials will give the magnons a mass inversely proportional to the square of
the magnetization. The second one is based on a specific mechanism for p-wave
pairing, and predicts that the observed broad anomaly in the specific heat of
URhGe will be resolved into a split transition with increasing sample quality.
These predictions will help discriminate between different possible mechanisms
for ferromagnetic superconductivity.",0307348v1
2003-08-23,Half-metallic ferromagnetism and structural stability of zincblende phases of the transition-metal chalcogenides,"An accurate density-functional method is used to study systematically
half-metallic ferromagnetism and stability of zincblende phases of
3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases
are found to be excellent half-metallic ferromagnets with large half-metallic
gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53
eV per formula unit higher in total energy than the corresponding
nickel-arsenide ground-state phases, and therefore would be grown epitaxially
in the form of films and layers thick enough for spintronic applications.",0308463v1
2003-09-02,Giant fluctuations of superconducting order parameter in Ferromagnet/superconductor single electron transistors,"Spin dependent transport in a ferromagnet/superconductor/ferromagnet single
electron transistor is studied theoretically with spin accumulation, spin
relaxation, gap suppression, and charging effects taken into account. A strong
dependence of the gap on the magnetic state of the outer electrodes is found,
which gives rise to a negative magneto-resistance of up to 100 %. We predict
that fluctuations of the spin accumulation due to tunneling of quasi-particles
can play such an important role as to cause the island to fluctuate between the
superconducting",0309055v3
2003-09-23,External Control of Magnetism in Semiconductors at High Temperature (~100K),"We demonstrate the electrical and optical control of ferromagnetism in
semiconductor heterostructures at high temperatures of 100-117 K. The
heterostructures consist of Mn delta-doped GaAs and p-type AlGaAs, where the
overlap of the hole wavefunction with the Mn delta-doping profile leads to high
ferromagnetic transition temperature TC of over 100 K (max. 172 K). We are able
to isothermally change the paramagnetic state to the ferromagnetic state and
vice versa, by applying a gate electric-field or by light irradiation. The
large modulation of TC (DTC ~15 K) at high temperatures (> ~100 K) demonstrated
here may pave the way to functional device applications compatible with the
present semiconductor technology.",0309532v1
2003-10-02,Dynamic ferromagnetic proximity effect in photoexcited semiconductors,"The spin dynamics of photoexcited carriers in semiconductors in contact with
a ferromagnet is treated theoretically and compared with time-dependent Faraday
rotation experiments. The long time response of the system is found to be
governed by the first tens of picoseconds in which the excited plasma interacts
strongly with the intrinsic interface between semiconductor and ferromagnet in
spite of the existence of a Schottky barrier in equilibrium.",0310031v1
2003-11-11,The internal magnetic field in superconducting ferromagnets,"We have measured the nonlinear response to the ac magnetic field in the
superconducting weak ferromagnet Ru-1222, at different regimes of sample
cooling which provides unambiguous evidence of the interplay of the domain
structure and the vorticity in the superconducting state. This is {\em direct}
proof of coexistence of ferromagnetic and superconductive order parameters in
high-$T_c$ ruthenocuprates.",0311245v1
2003-11-20,Single-ion versus exchange anisotropy in calculating anisotropic susceptibilities of thin ferromagnetic Heisenberg films within many-body Green's function theory,"We compare transverse and parallel static susceptibilities of in-plane
uniaxial anisotropic ferromagnetic Heisenberg films calculated in the framework
of many-body Green's function theory using single-ion anisotropies with the
previously investigated case of exchange anisotropies. On the basis of the
calculated observables (easy and hard axes magnetizations and susceptibilities)
no significant differences are found, i. e. it is not possible to propose an
experiment that might decide which kind of anisotropy is acting in an actual
ferromagnetic film.",0311482v1
2003-12-15,Split transition in ferromagnetic superconductors,"The split superconducting transition of up-spin and down-spin electrons on
the background of ferromagnetism is studied within the framework of a recent
model that describes the coexistence of ferromagnetism and superconductivity
induced by magnetic fluctuations. It is shown that one generically expects the
two transitions to be close to one another. This conclusion is discussed in
relation to experimental results on URhGe. It is also shown that the magnetic
Goldstone modes acquire an interesting structure in the superconducting phase,
which can be used as an experimental tool to probe the origin of the
superconductivity.",0312378v1
2004-01-05,Enhancement of flux-line pinning in all-oxide superconductor/ferromagnet heterostructures,"We have studied the local critical current density, jc, in the superconductor
thin film of bilayer structures consisting of YBa2Cu3O7 and the ferromagnets
La2/3Ca1/3MnO3 and SrRuO3, respectively, by means of quantitative
magneto-optics. A pronounced hysteresis of jc was observed which is ascribed to
the magnetization state of the ferromagnetic layer. The results are discussed
within the frame of magnetic vortex - wall interactions.",0401033v1
2004-01-09,Ferromagnetic Transition in One-Dimensional Itinerant Electron Systems,"We use bosonization to derive the effective field theory that properly
describes ferromagnetic transition in one-dimensional itinerant electron
systems. The resultant theory is shown to have dynamical exponent z=2 at tree
leve and upper critical dimension d_c=2. Thus one dimension is below the upper
critical dimension of the theory, and the critical behavior of the transition
is controlled by an interacting fixed point, which we study via epsilon
expansion. Comparisons will be made with the Hertz-Millis theory, which
describes the ferromagnetic transition in higher dimensions.",0401149v3
2004-01-24,Normal metal to ferromagnetic superconductor tunneling,"We study the point-contact tunneling between normal metal and ferromagnetic
superconductor. In the case of magnon-induced pairing the tunneling conductance
is continuous and smooth function of the applied voltage. For small values of
the applied voltage the Ohm law holds. We show that one can obtain the
magnetization and the superconducting order parameter from the tunneling
conduc- tance. In the case of paramagnon-induced superconductivity the
tunneling does not depend on the magnetization. We argue that tunneling
experiment can unambiguously determine the correct pairing mechanism in the
ferromagnetic superconductors.",0401480v2
2004-02-16,Uniform Magnetic Order in a Ferromagnetic-Antiferromagnetic Random Alternating Quantum Spin Chain,"An $S=1/2$ ferromagnetic (F) - antiferromagnetic (AF) random alternating
Heisenberg quantum spin chain model is investigated in connection to its
realization compound: (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$. The
exchange interaction bonds have alternating strong F-AF random bonds and weak
uniform AF bonds. Using the quantum Monte Carlo method we have found that the
excitation energy gap closes and the uniform AF order becomes critical in the
intermediate concentration region. This finding explains the experimental
observation of the magnetic transition by considering weak interchain
interactions. Present results suggest that the uniform AF order survives even
in the presence of randomly located ferromagnetic bonds. This may be a new
quantum effect.",0402402v1
2004-03-30,Superfluid vs Ferromagnetic Behaviour in a Bose Gas of Spin-1/2 Atoms,"We study the thermodynamic phases of a gas of spin-1/2 atoms in the
Hartree-Fock approximation. Our main result is that, for repulsive or
weakly-attractive inter-component interaction strength, the superfluid and
ferromagnetic phase transitions occur at the same temperature. For
strongly-attractive inter-component interaction strength, however, the
ferromagnetic phase transition occurs at a higher temperature than the
superfluid phase transition. We also find that the presence of a condensate
acts as an effective magnetic field that polarizes the normal cloud. We finally
comment on the validity of the Hartree-Fock approximation in describing
different phenomena in this system.",0403720v2
2004-04-16,Changes in magnetic scattering anisotropy at a ferromagnetic/superconducting interface,"We show that some metals and alloys (X = Cu, Ag, FeMn, or Cu and Ag combined
with each other), sputtered between ferromagnetic Co and superconducting Nb,
produce no change in current-perpendicular-to-plane magnetoresistance (CPP-MR)
in a carefully designed CPP-spin-valve. In contrast, other metals (Ru or Au) or
combinations (Cu or Ag combined with Au, Ru, or FeMn) change the CPP-MR, in
some cases even reversing its sign. We ascribe these changes to activation of
magnetic scattering anisotropies at a ferromagnetic/superconducting interface,
apparently by strong spin-flipping between the Co and Nb layers.",0404396v1
2004-05-19,"Softer than normal, but not as soft as one might think: Spontaneous flux lattices in ferromagnetic spin-triplet superconductors","A theory is developed for the spontaneous vortex lattice that is expected to
occur in the ferromagnetic superconductors ZrZn_2, UGe_2, and URhGe, where the
superconductivity is likely of spin-triplet nature. The long-wavelength
fluctuations of this spontaneous flux lattice are predicted to be huge compared
to those of a conventional flux lattice, and to be the same as those for
spin-singlet ferromagnetic superconductors. It is shown that these fluctuations
lead to unambiguous experimental signatures which may provide the easiest way
to observe the spontaneous flux lattice.",0405461v1
2004-07-02,Spin accumulation in ferromagnets,"Using a density matrix formulation for the effective action, we obtain a set
of macroscopic equations that describe spin accumulation in a non-homogeneous
ferromagnet. We give a new expression for the spin current which extends
previous work by taking into account the symmetry of the ferromagnetic state
through a careful treatment of the exchange term between the conduction
electrons and the magnetization, i.e, d-electrons. We consider a simple
application which has been discussed previously and show that in this case spin
accumulation is an interface effect confirming earlier results arrived at by
different methods.",0407051v1
2004-08-10,Quantum coherence in a ferromagnetic metal: time-dependent conductance fluctuations,"Quantum coherence of electrons in ferromagnetic metals is difficult to assess
experimentally. We report the first measurements of time-dependent universal
conductance fluctuations in ferromagnetic metal (Ni$_{0.8}$Fe$_{0.2}$)
nanostructures as a function of temperature and magnetic field strength and
orientation. We find that the cooperon contribution to this quantum correction
is suppressed, and that domain wall motion can be a source of
coherence-enhanced conductance fluctuations. The fluctuations are more strongly
temperature dependent than those in normal metals, hinting that an unusual
dephasing mechanism may be at work.",0408221v2
2004-08-27,Disorder-Induced Resistive Anomaly Near Ferromagnetic Phase Transitions,"We show that the resistivity rho(T) of disordered ferromagnets near, and
above, the Curie temperature T_c generically exhibits a stronger anomaly than
the scaling-based Fisher-Langer prediction. Treating transport beyond the
Boltzmann description, we find that within mean-field theory, d\rho/dT exhibits
a |T-T_c|^{-1/2} singularity near T_c. Our results, being solely due to
impurities, are relevant to ferromagnets with low T_c, such as SrRuO3 or
diluted magnetic semiconductors, whose mobility near T_c is limited by
disorder.",0408602v2
2004-09-12,"Trends in ferromagnetism, hole localization, and acceptor level depth for Mn substitution in","We examine the intrinsic mechanism of ferromagnetism in dilute magnetic
semiconductors by analyzing the trends in the electronic structure as the host
is changed from GaN to GaP, GaAs and GaSb, keeping the transition metal
impurity fixed. In contrast with earlier interpretations which depended on the
host semiconductor, we found that a single mechanism is sufficient to explain
the ferromagnetic stabilization energy for the entire series.",0409296v1
2004-09-13,Spin order in the one-dimensional Kondo and Hund lattices,"We study numerically the one-dimensional Kondo and Hund lattices consisting
of localized spins interacting antiferro or ferromagnetically with the
itinerant electrons, respectively. Using the Density Matrix Renormalization
Group we find, for both models and in the small coupling regime, the existence
of new magnetic phases where the local spins order forming ferromagnetic
islands coupled antiferromagnetically. Furthermore, by increasing the
interaction parameter $|J|$ we find that this order evolves toward the
ferromagnetic regime through a spiral-like phase with longer characteristic
wave lengths. These results shed new light on the zero temperature magnetic
phase diagram for these models.",0409332v1
2004-09-16,Weak ferromagnetism of La_{1.99}Sr_{0.01}CuO_4 thin films: evidence for removal of corrugation in CuO_2 plane by epitaxial strain,"The weak ferromagnetism of La_{1.99}Sr_{0.01}CuO_4 epitaxial thin films is
investigated using magnetoresistance measurement. While a steplike negative
magnetoresistance associated with the weak ferromagnetic transition is clearly
observed in the films grown on YAlO_3(001), it is notably suppressed in the
films grown on SrTiO_3(100) and
(LaAlO_3)_{0.3}(SrAl_{0.5}Ta_{0.5}O_3)_{0.7}(100), and almost disappears in
films grown on LaSrAlO_4(001). The strong suppression of the steplike
magnetoresistance provides evidence that the CuO_2 planes are much less
corrugated in thin films grown on tetragonal substrates, particularly on
LaSrAlO_4(001), than in bulk crystals.",0409436v1
2004-10-19,The Meservey-Tedrov effect in FSF double tunneling junctions,"Double tunneling junctions of ferromagnet-superconductor-ferromagnet
electrodes (FSF) show a jump in the conductance when a parallel magnetic field
reverses the magnetization of one of the ferromagnetic electrodes. This change
is generally attributed to the spin-valve effect or to pair breaking in the
superconductor because of spin accumulation. In this paper it is shown that the
Meservey-Tedrov effect causes a similar change in the conductance since the
magnetic field changes the energy spectrum of the quasi-particles in the
superconductor. A reversal of the bias reverses the sign in the conductance
jump.",0410486v1
2004-10-22,Phenomenological theory of superconductivity near domain walls in ferromagnets,"We develop a phenomenological model of superconductivity near a domain wall
in a ferromagnet. In addition to the electromagnetic interaction of the order
parameter with the ferromagnetic magnetization, we take into account the
possibility of a local enhancement or suppression of superconducting pairing in
the vicinity of the wall, and also a non-perfect transparency of the wall to
electrons. It is found that the critical temperature of superconductivity near
the domain wall might be substantially higher than in the bulk.",0410587v1
2004-11-17,Optical response of a ferromagnetic/DMS hybrid structure,"We investigate the possibility of using local magnetic fields to produce
one-dimensional traps in hybrid structures for any quasiparticle possessing
spin degree of freedom. We consider a system composed of a diluted magnetic
semiconductor quantum well buried below a micron-sized ferromagnetic island.
Localized magnetic field is produced by a rectangular ferromagnet in close
proximity of a single domain phase. We make quantitative predictions for the
optical response of the system as a function of distance between the
micromagnet and the quantum well, electronic g-factor, and thickness of the
micromagnet.",0411456v1
2004-12-04,"Ferromagnetic Instability in AFe4Sb12 (A = Ca, Sr, and Ba)","Magnetic, transport and thermal properties of AFe4Sb12 (A = Ca, Sr, Ba) are
reported. All three compounds show a maximum in both the magnetic
susceptibility and thermopower at 50 K, and a large electronic specific heat
coefficient of 100 mJ/mol K2. These properties are the characteristics of a
nearly ferromagnetic metal. Furthermore, a remanent moment of the order of
10-3muB/Fe was observed below 54, 48, and 40 K for A = Ca, Sr, and Ba,
respectively. The volume fraction of the ferromagnetic component was estimated
to be 10-20% by zero-field muSR measurements.",0412094v1
2004-12-08,Interplay between ferromagnetism and superconductivity in tunneling currents,"We study tunneling currents in a model consisting of two non-unitary
ferromagnetic spin-triplet superconductors separated by a thin insulating
layer. We find a novel interplay between ferromagnetism and superconductivity,
manifested in the Josephson effect. This offers the possibility of tuning
dissipationless currents of charge and spin in a well-defined manner by
adjusting the magnetization direction on either side of the junction.",0412193v3
2004-12-15,Effects of edges in spin-1/2 bond-alternating Heisenberg chains: Matrix-product variational approach,"We make a matrix-product variational approach to spin-1/2
ferromagnetic-antiferromagnetic bond-alternating chains with anisotropy on
their ferromagnetic bonds, especially under the open boundary condition. The
rich phase diagram containing the Haldane, large-D, and two types of Neel
phases is well reproduced with only two variational parameters. The on-bond
anisotropy has a significant effect on the ferromagnetic coupling between
neighboring spins and induces novel edge states peculiar to spin-1/2 chains.",0412390v1
2004-12-17,Mesoscopic bound on anisotropy in itinerant ferromagnets,"We calculate the anisotropy energy of a single-domain ferromagnetic particle
in which the only source of anisotropy is the presence of non-magnetic
impurities. We find that such anisotropy takes the form of combined easy-axis
and easy-plane anisotropies, with random orientations of the axes. Typically
the anisotropy energy is of order $N^{1/2} \hbar/tau_{so}$, where $N$ is the
number of electrons in the ferromagnetic particle and $\tau_{so}$ is the
spin-orbit time.",0412488v1
2005-01-10,Exchange instabilities in electron systems: Bloch versus Stoner Ferromagnetism,"We show that 2D and 3D electron systems with the long-range Coulomb
electron-electron interaction could develop ferromagnetic instabilities due to
strong exchange effects at low densities. The critical densities in both 2D and
3D systems at which the magnetic instability, which could either be of Stoner
type (second-order) or of Bloch type (first-order), are higher than the
dispersion instability critical density where effective mass at the Fermi
surface diverges. We discuss the theoretical as well as experimental
implications of the ferromagnetic instability at low electron densities,
particularly in low-disorder semiconductor-based two-dimensional systems.",0501213v2
2005-01-12,Onset of metallic ferromagnetism in a doped spin-orbital chain,"Starting from a spin-orbital model for doped manganites, we investigate a
competition between ferromagnetic and antiferromagnetic order in a
one-dimensional model at finite temperature. The magnetic and orbital order at
half filling support each other and depend on a small antiferromagnetic
superexchange between t_{2g} spins and on an alternating Jahn-Teller potential.
The crossover to a metallic ferromagnetic phase found at finite doping is
partly suppressed by the Jahn-Teller potential which may localize e_g
electrons.",0501290v1
2005-01-12,Nanoengineered Curie Temperature in Laterally-Patterned Ferromagnetic Semiconductor Heterostructures,"We demonstrate the manipulation of the Curie temperature of buried layers of
the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the
effect of annealing. Patterning the GaAs-capped ferromagnetic layers into
nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As
layers and thus allows the removal of Mn interstitials using annealing. This
leads to an enhanced Curie temperature and reduced resistivity compared to
unpatterned samples. For a fixed annealing time, the enhancement of the Curie
temperature is larger for narrower nanowires.",0501298v2
2005-01-25,Novel Josephson Effect in Triplet Superconductor - Ferromagnet - Triplet Superconductor Junctions,"We predict a novel type of Josephson effect to occur in triplet
superconductor - ferromagnet - triplet superconductor Josephson junctions. We
show that the Josephson current, I_J, exhibits a rich dependence on the
relative orientation between the ferromagnetic moment and the d-vectors of the
superconductors. This dependence can be used to build several types of
Josephson current switches. Moreover, we predict an unconventional temperature
dependence of I_J in which I_J changes sign with increasing temperature",0501614v1
2005-01-28,Pseudospin ferromagnetism in double-quantum-wire systems,"We propose that a pseudospin ferromagnetic (i.e inter-wire coherent) state
can exist in a system of two parallel wires of finite width in the presence of
a perpendicular magnetic field. This novel quantum many-body state appears when
the inter wire distance decreases below a certain critical value which depends
on the magnetic field. We determine the phase boundary of the ferromagnetic
phase by analyzing the softening of the spin-mode velocity using the
bosonization approach. We also discuss signatures of this state in tunneling
and Coulomb drag experiments.",0501694v2
2005-02-11,Self-generated locality near a ferromagnetic quantum-critical point,"We analyze the behavior of interacting fermions near a ferromagnetic
  Stoner instability.
  We show that the Landau damping of the spin susceptibility is a relevant
perturbation near a ferromagnetic quantum-critical point (FQCP). We argue that,
as the system approaches a FQCP, the fermionic self-energy crosses over from
predominantly momentum dependent away from the transition to predominantly
frequency dependent in the immediate vicinity of the transition. We argue that
due to this self-generated locality, the quasiparticle effective mass does not
diverge before a FQCP is reached.",0502302v1
2005-03-14,Exchange coupling induced antiferromagnetic-ferromagnetic transition in $Pr_{0.5}Ca_{0.5}MnO_3/La_{0.5}Ca_{0.5}MnO_3$ superlattices,"Superlattices built from two antiferromagnetic (AFM) charge/orbital order
compounds, $Pr_{0.5}Ca_{0.5}MnO_3$ and $La_{0.5}Ca_{0.5}MnO_3$, have been
studied as the thickness of $La_{0.5}Ca_{0.5}MnO_3$ ($LCMO$) varied. High
structural quality thin films were obtained on $LaAlO_3$ substrates using the
pulsed laser deposition technique. An antiferromagnetic-to-ferromagnetic
transition, in addition to an enhancement of the coercivity, are observed as
the $LCMO$ layer thickness increases. The small shift in the origin of the
field-cooled hysteresis loop along the field axis indicates the presence of
ferromagnetic and antiferromagnetic phases in the superlattices. We attribute
these features to the AFM spin fluctuations at the
$Pr_{0.5}Ca_{0.5}MnO_3/La_{0.5}Ca_{0.5}MnO_3$ interfaces resulting from the
strain effects.",0503327v1
2005-04-07,Evolution of ferromagnetic circular dichroism coincident with magnetization and anomalous Hall effect in Co-doped rutile TiO2,"Magnetic circular dichroism (MCD) of rutile Ti1-xCoxO2-d is systematically
examined with various x and d to reveal a phase diagram for the appearance of
ferromagnetism at higher carrier concentration and Co content. The phase
diagram exactly matches with that determined from anomalous Hall effect (AHE).
The magnetic field dependence of MCD also shows good coincidence with those of
the magnetization and AHE. The coincidence of these independent measurements
strongly suggests single and intrinsic ferromagnetic origin.",0504167v1
2005-04-07,Magnetic oxide semiconductors,"Magnetic oxide semiconductors, oxide semiconductors doped with transition
metal elements, are one of the candidates for a high Curie temperature
ferromagnetic semiconductor that is important to realize semiconductor
spintronics at room temperature. We review in this paper recent progress of
researches on various magnetic oxide semiconductors. The magnetization,
magneto-optical effect, and magneto-transport such as anomalous Hall effect are
examined from viewpoint of feasibility to evaluate the ferromagnetism. The
ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.",0504168v1
2005-04-16,Spontaneous magnetization and structure formation in a spin-1 ferromagnetic Bose-Einstein condensate,"Motivated by recent experiments involving the non-destructive imaging of
magnetization of a spin-1 87Rb Bose gas (Higbie et al., cond-mat/0502517), we
address the question of how the spontaneous magnetization of a ferromagnetic
BEC occurs in a spin-conserving system. Due to competition between the
ferromagnetic interaction and the total spin conservation, various spin
structures such as staggered magnetic domains, and helical and concentric ring
structures are formed, depending on the geometry of the trapping potential.",0504398v1
2005-04-18,Determination of the magnetic domain size in the ferromagnetic superconductor UGe2 by three dimensional neutron depolarization,"Three dimensional neutron depolarization measurements have been carried out
on single-crystalline UGe2 between 4 K and 80 K in order to determine the
average ferromagnetic domain size d. It is found that below T_C = 52K uniaxial
ferromagnetic domains are formed with an estimated magnetic domain size of d =
4 - 5 micrometer.",0504430v1
2005-04-26,Spin filtering through ferromagnetic BiMnO3 tunnel barriers,"We report on experiments of spin filtering through ultra-thin single-crystal
layers of the insulating and ferromagnetic oxide BiMnO3 (BMO). The spin
polarization of the electrons tunneling from a gold electrode through BMO is
analyzed with a counter-electrode of the half-metallic oxide La2/3Sr1/3MnO3
(LSMO). At 3 K we find a 50% change of the tunnel resistances according to
whether the magnetizations of BMO and LSMO are parallel or opposite. This
effect corresponds to a spin filtering effciency of up to 22%. Our results thus
show the potential of complex ferromagnetic insulating oxides for spin
filtering and injection.",0504667v1
2005-05-10,Propagating Coherent Acoustic Phonon Wavepackets in InMnAs/GaSb,"We observe pronounced oscillations in the differential reflectivity of a
ferromagnetic InMnAs/GaSb heterostructure using two-color pump-probe
spectroscopy. Although originally thought to be associated with the
ferromagnetism, our studies show that the oscillations instead result from
changes in the position and frequency-dependent dielectric function due to the
generation of coherent acoustic phonons in the ferromagnetic InMnAs layer and
their subsequent propagation into the GaSb. Our theory accurately predicts the
experimentally measured oscillation period and decay time as a function of
probe wavelength.",0505261v1
2005-06-13,Magnetism via superconductivity in SF proximity structures,"We consider the proximity effects in hybrid superconductor (S) - ferromagnet
(F) structures drawing attention to the induced ferromagnetism of the S metal.
The analysis is based on a quasiclassical theory of proximity effect for metals
in the dirty limit conditions. It is shown that, below the superconducting
critical temperature, ferromagnetic correlations extend a distance of order of
the superconducting coherence length \xi_{S} into the superconductor, being
dependent on the S/F interface parameters. We argue that the properties of
mesoscopic SF hybrids may drastically depend upon the magnetic proximity
effect, and recent experiments lend support to the model of SF structures where
the superconducting and magnetic parameters are tightly coupled.",0506277v1
2005-06-14,Spin-wave softening and Hund's coupling in ferromagnetic manganites,"Using one-orbital model of hole-doped manganites, we show with the help of
Holstein-Primakov transformation that finite Hund's coupling is responsible for
the spin-wave softening in the ferromagnetic $B$-phase manganites. We obtain an
analytical result for the spin-wave spectrum for $\JH\gg t$. In the limit of
infinte Hund's coupling, the spectrum is the conventional nearest-neighbor
Heisenberg ferromagnetic spin-wave. The $o(t/\JH)$-order correction is negative
and thus accounts for the softening near the zone boundary.",0506321v1
2005-06-15,Saturated Ferromagnetism from Statistical Transmutation in Two Dimensions,"The total spin of the ground state is calculated in the U -> infinity Hubbard
model with uniform magnetic flux perpendicular to a square lattice, in the
absence of Zeeman coupling. It is found that the saturated ferromagnetism
emerges in a rather wide region in the space of the flux density \phi and the
electron density n_e. In particular, the saturated ferromagnetism at \phi = n_e
is induced by the formation of a spin-1/2 boson, which is a composite of an
electron and the unit flux quantum.",0506352v3
2005-07-06,A ferromagnetic oxide semiconductor as spin injection electrode in magnetic tunnel junction,"A magnetic tunnel junctions composed of room temperature ferromagnetic
semiconductor rutile Ti1-xCoxO2-d and ferromagnetic metal Fe0.1Co0.9 separated
by AlOx barrier showed positive tunneling magnetoresistance (TMR) with a ratio
of ~11 % at 15 K, indicating that Ti1-xCoxO2-d can be used as a spin injection
electrode. The TMR decreased with increasing temperature and vanished above 180
K. TMR action at high temperature is likely prohibited by the inelastic
tunneling conduction due to the low quality of the amorphous barrier layer
and/or the junction interface.",0507137v1
2005-07-16,Interplay of Magnetic and Superconducting Proximity Effects in FSF Trilayers,"We present theoretical results on the interplay of magnetic and
superconducting orders in diffusive ferromagnet-superconductor-ferromagnet
trilayers. The induced triplet superconducting correlations throughout the
trilayer lead to an induced spin magnetization. We include self-consistency of
the order parameter in the superconducting layer at arbitrary temperatures,
arbitrary interface transparency, and any relative orientation of the exchange
fields in the two ferromagnets. We propose to use the torque on the trilayer in
an external magnetic field as a probe of the presence of triplet correlations
in the superconducting phase.",0507398v1
2005-07-20,Spin-lattice relaxation phenomena in manganite La0.7Sr0.3MnO3 thin films,"Time-resolved magneto-optics was used to study spin-lattice relaxation
dynamics in thin epitaxial La0.7Sr0.3MnO3 films. Two distinct recovery regimes
of the ferromagnetic order can be resolved upon photoexcitation, which manifest
themselves by two different relaxation times. A pump pulse energy independent
spin-lattice relaxation time can be deduced. Due to a weak spin-orbit coupling
in manganites this spin-lattice relaxation time is much longer than in
ferromagnetic metals. Heat flow into the substrate sets the ultimate recovery
speed of the ferromagnetic order and allows for a determination of heat
diffusion properties of manganite films.",0507481v1
2005-08-17,Magnetic Composites: Magnonic Excitations vs. Three-Dimensional Structural Periodicity,"This study deals with the spin wave spectrum in magnetic macrostructure
(composed of two ferromagnetic materials) showing a 3D periodicity: spherical
ferromagnetic grains disposed in the nodes of a simple cubic crystal lattice
are embedded in a matrix with different ferromagnetic properties. It is shown
that the \textit{magnonic spectrum} of this composite structure exhibits
frequency regions \textit{forbidden} for magnon propagation, and the energy
gaps are found to be sensitive to the exchange contrast between the constituent
materials as well as to the magnetization contrast. The widths of the
respective magnonic gaps are studied as functions of parameters characterizing
the magnetic structure.",0508390v1
2005-08-24,Double-reversal thickness dependence of critical current in superconductor-ferromagnet-superconductor Josephson junctions,"We report the first experimental observation of the two-node thickness
dependence of the critical current in Josephson junctions with a ferromagnetic
interlayer. Vanishings of the critical current correspond to transitions into
pi-state and back into conventional 0-state. The experimental data allow to
extract the superconducting order parameter oscillation period and the pair
decay length in the ferromagnet. We develope a theoretical approach based on
Usadel equations, which takes into account the spin-flip scattering. Results of
numerical calculations are in good agreement with the experimental data.",0508573v1
2005-08-26,Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field,"We use neutron diffraction to probe the magnetization components of a crystal
of Mn12 single-molecule magnets. Each of these molecules behaves, at low
temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the
crystallographic c axis. Application of a magnetic field perpendicular to c
induces quantum tunneling between opposite spin orientations, enabling the
spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular
interactions turn this equilibrium state into a ferromagnetically ordered
phase. However, long range ferromagnetic correlations nearly disappear for
fields larger 5.5 T, possibly suggesting the existence of a quantum critical
point.",0508627v1
2005-08-30,Effects of spin current on ferromagnets,"When a spin-polarized current flows through a ferromagnet, the local
magnetization receives a spin torque. Two consequences of this spin torque are
studied. First, the uniformly magnetized ferromagnet becomes unstable if a
sufficiently large current is applied. The characteristics of the instability
include spin wave generation and magnetization chaos. Second, the spin torque
has profound effects on the structure and dynamics of the magnetic domain wall.
A detail analysis on the domain wall mass, kinetic energy and wall depinning
threshold is given.",0508735v1
2005-09-15,Ferromagnetic Domain Structure of La0.78Ca0.22MnO3 Single Crystals,"The magneto-optical technique has been employed to observe spontaneous
ferromagnetic domain structures in La0.78Ca0.22MnO3 single crystals. The
magnetic domain topology was found to be correlated with the intrinsic twin
structure of the investigated crystals. With decreasing temperature the regular
network of ferromagnetic domains undergoes significant changes resulting in
apparent rotation of the domain walls in the temperature range of 70-150 K. The
apparent rotation of the domain walls can be understood in terms of the
Jahn-Teller deformation of the orthorhombic unit cell, accompanied by
additional twinning.",0509423v1
2005-09-16,First principles investigation of the electronic structure of La2MnNiO6: A room-temperature insulating ferromagnet,"Using first principles calculations within DFT based on the full potential
APW+lo method, we calculated the electronic and magnetic structures for the
ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site
projected density of states and electronic band structures. Our calculations
show that the ground state of La2MnNiO6 is ferromagnetic insulating with the
magnetization in agreement with Hund's first rule and experimental findings.",0509431v1
2005-09-21,Zero-temperature magnetic-field-induced phase transition between two ordered gapped phases in spin-ladders with ferromagnetic legs,"We suggest that under an increase of a magnetic field a spin-ladder with
ferromagnetic legs does not pass without fail through an incommensurate phase
but possibly in a straight way turns into a fully polarized ferromagnetic
phase. The spin gap remains finite at the transition point. This scenario is
demonstrated for the special spin-ladder model with exact singlet-rung ground
state. We suppose that this kind of behavior realizes for the spin-ladder
material (5IAP)_2CuBr_4*H_2O",0509556v2
2005-09-26,Crossed Andreev reflection as a probe for the pairing symmetry of Ferromagnetic Superconductors,"The coexistence of superconductivity and ferromagnetism has brought about the
phenomena of ferromagnetic superconductors. The theory needed to understand the
compatibility of such antagonistic phenomena cannot be built until the pairing
symmetry of such superconductors is correctly identified. The proper and
unambiguous identification of the pairing symmetry of such superconductors is
the subject of this paper. This work shows that crossed Andreev reflection can
be a very effective tool in order to identify the pairing symmetry of these
superconductors.",0509669v2
2005-10-21,Origin of Spontaneous Currents in a Superconductor-Ferromagnet Proximity System,"We have previously shown that a ferromagnet-superconductor heterostructure
may possess a spontaneous current circulation parallel to the interface. This
current is caused by Andreev bound states in the thin ferromagnetic layer, and
can be fully spin-polarized. Here we investigate the total energy of the system
in cases where the current either does or does not flow. We show that the
current is a true quantum ground state effect, and examine the effect of the
current on the different contributions to the total energy.",0510591v1
2005-11-03,Non-equilibrium Magnetic Properties of Single Crystalline La0.7Ca0.3CoO3,"Magnetic and electric properties of a single crystal of La0.7Ca0.3CoO3 have
been experimentally studied. The system attains a ferromagnetic spontaneous
moment below 170 K and exhibits a re-entrant spin-glass phase below 100 K. In
the ordered and the re-entrant phases, the low field magnetic properties are
strongly direction dependent, showing considerably higher magnetization values
perpendicular than parallel to the c-axis. Magnetic relaxation experiments show
that both the ferromagnetic and the re-entrant spin-glass phases are
non-equilibrium states, where the system exhibits magnetic aging characteristic
of spin-glasses and disordered and frustrated ferromagnets.",0511066v1
2005-11-03,Probable absence of a quadrupolar spin-nematic phase in the bilinear-biquadratic spin-1 chain,"We study numerically the ground-state phase diagram of the
bilinear-biquadratic spin-1 chain near the ferromagnetic instability point,
where the existence of a gapped or gapless nondimerized quantum nematic phase
has been suggested. Our results, obtained by a highly accurate density-matrix
renormalization-group (DMRG) calculation are consistent with the view that the
order parameter characterizing the dimer phase vanishes only at the point where
the system becomes ferromagnetic, although the existence of a gapped or gapless
nondimerized phase in a very narrow parameter range between the ferromagnetic
and the dimerized regimes cannot be ruled out.",0511079v1
2005-11-17,Collective states of interacting ferromagnetic nanoparticles,"Discontinuous magnetic multilayers [CoFe/Al2O3] are studied by use of
magnetometry, susceptometry and numeric simulations. Soft ferromagnetic
Co80Fe20 nanoparticles are embedded in a diamagnetic insulating a-Al2O3 matrix
and can be considered as homogeneously magnetized superspins exhibiting
randomness of size (viz. moment), position and anisotropy. Lacking
intra-particle core-surface ordering, generic freezing processes into
collective states rather than individual particle blocking are encountered.
With increasing particle density one observes first superspin glass and then
superferromagnetic domain state behavior. The phase diagram resembles that of a
dilute disordered ferromagnet. Criteria for the identification of the
individual phases are given.",0511428v1
2005-11-22,Electronic properties of EuB6 in the ferromagnetic regime: Half-metal versus semiconductor,"To understand the halfmetallic ferromagnet EuB6 we use the Kondo lattice
model for valence and conduction band. By means of a recently developed
many-body theory we calculate the electronic properties in the ferromagnetic
regime up to the Curie temperature. The decreasing magnetic order induces a
transition from halfmetallic to semiconducting behavior along with a band
broadening. We show the temperature dependence of the quasiparticle density of
states and the quasiparticle dispersion as well as the effective mass, the
number of carriers and the plasma frequency which are in good agreement with
the experimental data.",0511536v1
2005-11-22,Fabrication of high quality ferromagnetic Josephson junctions,"We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with
an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized
regarding junction insulation and homogeneity of current transport. Using
ion-beam-etching and anodic oxidation we defined and insulated the junction
mesas. The additional 2 nm thin Cu layer below the ferromagnetic NiCu (SINFS)
lowered interface roughness and ensured very homogeneous current transport. A
high yield of junctional devices with jc spreads less than 2% was obtained.",0511546v1
2005-12-05,Crossed Andreev reflection-induced magnetoresistance,"We show that very large negative magnetoresistance can be obtained in
magnetic trilayers in a current-in-plane geometry owing to the existence of
crossed Andreev reflection. This spin-valve consists of a thin superconducting
film sandwiched between two ferromagnetic layers whose magnetization is allowed
to be either parallelly or antiparallelly aligned. For a suitable choice of
structure parameters and nearly fully spin-polarized ferromagnets the
magnetoresistance can exceed -80%. Our results are relevant for the design and
implementation of spintronic devices exploiting ferromagnet-superconductor
structures.",0512090v2
2005-12-13,Mesoscopic anisotropic magnetoconductance fluctuations in ferromagnets,"The conductance of a ferromagnetic particle depends on the relative
orientation of the magnetization with respect to the direction of current flow.
This phenomenon is known as ""anisotropic magnetoresistance"". Quantum
interference leads to an additional, random dependence of the conductance on
the magnetization direction. These ""anisotropic magnetoresistance fluctuations""
are caused by spin-orbit scattering, which couples the electron motion to the
exchange field in the ferromagnet. We report a calculation of the dependence of
the conductance autocorrelation function on the rotation angle of the
magnetization direction.",0512287v1
2005-12-20,In-plane ferromagnetism in charge-ordering $Na_{0.55}CoO_2$,"The magnetic and transport properties are systematically studied on the
single crystal $Na_{0.55}CoO_2$ with charge ordering and divergency in
resistivity below 50 K. A long-range ferromagnetic ordering is observed in
susceptibility below 20 K with the magnetic field parallel to Co-O plane, while
a negligible behavior is observed with the field perpendicular to the Co-O
plane. It definitely gives a direct evidence for the existence of in-plane
ferromagnetism below 20 K. The observed magnetoresistance (MR) of 30 % at the
field of 6 T at low temperatures indicates an unexpectedly strong spin-charge
coupling in triangle lattice systems.",0512507v1
2006-02-05,Half-metallic ferromagnetism induced by dynamic electron correlations in VAs,"The electronic structure of the VAs compound in the zinc-blende structure is
investigated using a combined density-functional and dynamical mean-field
theory approach. Contrary to predictions of a ferromagnetic semiconducting
ground state obtained by density-functional calculations, dynamical
correlations induce a closing of the gap and produce a half-metallic
ferromagnetic state. These results emphasize the importance of dynamic
correlations in materials suitable for spintronics.",0602112v2
2006-03-07,Theory of carrier mediated ferromagnetism in dilute magnetic oxides,"We analyze the origin of ferromagnetism as a result of carrier mediation in
diluted magnetic oxide semiconductors in the light of the experimental evidence
reported in the literature. We propose that a combination of percolation of
magnetic polarons at lower temperature and Ruderman-Kittel-Kasuya-Yosida
ferromagnetism at higher temperature may be the reason for the very high
critical temperatures measured (up to ~700 K).",0603182v2
2006-03-10,Model Hamiltonian parameters for half-metallic ferromagnets NiMnSb and CrO2,"Using the recently developed Nth-order muffin-tin-orbital (NMTO) based
downfolding technique we revisit the electronic properties of half-metallic
ferromagnets, the semi-Heusler NiMnSb and rutile CrO2. The NMTO Wannier
orbitals for the Mn-d and Cr-t2g manifolds are constructed and the mechanism of
chemical bonding is discussed. The effective hopping Hamiltonian parameters are
calculated using a NMTO downfolded basis set. We propose model Hamiltonian
parameters with possibly minimal basis sets for both half-metallic
ferromagnetic alloys.",0603305v2
2006-03-20,Critical behavior of Griffiths ferromagnets,"From a heuristic calculation of the leading order essential singularity in
the distribution of Yang-Lee zeroes, we obtain new scaling relations near the
ferromagnetic-Griffiths transition, including the prediction of a discontinuity
on the analogue of the critical isotherm. We show that experimental data for
the magnetization and heat capacity of $\mathrm{La_{0.7}Ca_{0.3}MnO_3}$ are
consistent with these predictions, thus supporting its identification as a
Griffiths ferromagnet.",0603533v2
2006-03-29,Exchange Bias with Interacting Random Anti-ferromagnetic Grains,"A model consisting of random interacting anti-ferromagnetic (AF) grains
coupled to a ferromagnetic (FM) layer is developed to study the exchange bias
phenomenon. This simple model is able to describe several exchange bias
behavior observed in real materials. Shifts in hysteresis loops are observed as
a function of cooling field and average grain size. We establish a direct
relationship between cooling field dependence of exchange bias, coercivity and
magnetization state on the AF-FM interface. We also verify that the exchange
bias field is inversely proportional to the grain size, and this behavior is
independent of the inter-grain interactions, AF/FM coupling and cooling field.",0603780v1
2006-04-06,Origin of ferromagnetism in Cs$_2$AgF$_4$: importance of Ag - F covalency,"The magnetic nature of Cs$_{2}$AgF$_{4}$, an isoelectronic and isostructural
analogue of La$_2$CuO$_4$, is analyzed using density functional calculations.
The ground state is found to be ferromagnetic and nearly half metallic. We find
strong hybridization of Ag-$d$ and F-$p$ states. Substantial moments reside on
the F atoms, which is unusual for the halides and reflects the chemistry of the
Ag(II) ions in this compound. This provides the mechanism for ferromagnetism,
which we find to be itinerant in character, a result of a Stoner instability
enhanced by Hund's coupling on the F.",0604167v1
2006-04-21,Dissipationless spin-current between Heisenberg ferromagnets with spin-orbit coupling,"A system exhibiting multiple simultaneously broken symmetries offers the
opportunity to influence physical phenomena such as tunneling currents by means
of external control parameters. Time-reversal symmetry and inversion symmetry
are both absent in ferromagnetic metals with substantial spin-orbit coupling.
We here study transport of spin in a system consisting of two ferromagnets with
spin-orbit coupling separated by an insulating tunneling junction. A persistent
spin-current across the junction is found, which can be controlled in a
well-defined manner by external magnetic and electric fields. The behavior of
the spin-current for important geometries and limits is studied.",0604510v1
2006-05-08,High resolution determination of ferromagnetic metallic limit in epitaxial La1-xCaxMnO3 films on NdGaO3,"The physical properties of manganites depend strongly on sample morphology,
probably due to strain. We investigate the influence of NdGaO3 substrates on
the limit of the ferromagnetic-metallic phase field in La1-xCaxMnO3, doping
with x=1% resolution. Films with x=0.40 show a metal-insulator transition, but
the ferromagnetic volume fraction is half the spin aligned value. Films with
x=0.41 are similar but the metal-insulator transition is not always seen. Films
with x=0.42, 0.43, 0.44, 0.45 are insulating, and the magnetization is
dramatically reduced. The observed phase boundary indicates where to search for
enhanced phase separation effects that may be exploited in thin films and
devices.",0605187v1
2006-05-12,Domain wall superconductivity in superconductor/ferromagnet bilayers,"We analyze the enhancement of the superconducting critical temperature of
superconducting/ferromagnetic bilayers due to the appearance of localized
superconducting states in the vicinity of magnetic domain walls in the
ferromagnet. We consider the case when the main mechanism of the
superconductivity destruction via the proximity effect is the exchange field.
We demonstrate that the influence of the domain walls on the superconducting
properties of the bilayer may be quite strong if the domain wall thickness is
of the order of superconducting coherence length.",0605326v1
2006-05-29,Nuclear spin effect in metallic spin valve,"We study electronic transport through a ferromagnet normal-metal ferromagnet
system and we investigate the effect of hyperfine interaction between electrons
and nuclei in the normal-metal part. A switching of the magnetization
directions of the ferromagnets causes nuclear spins to precess. We show that
the effect of this precession on the current through the system is large enough
to be observed in experiment.",0605703v2
2006-06-14,Ferromagnetic ground state of the robust charge-ordered manganite Pr(0.5)Ca(0.5MnO(3)obtained by minimal Al-substitution,"We show that minimal disturbance to the robust charge ordered
Pr(0.5)Ca(0.5)MnO(3) by 2.5% Al substitution on Mn-site drives the system
towards ferromagnetic ground state. The history-dependent coexisting phases
observed are explained as an outcome of a hindered first order transition with
glass like arrest of kinetics resulting in irreversibility. Consistent with a
simple phase diagram having ferromagnetic ground state, it is experimentally
shown that these coexisting phases are far from the equilibrium.",0606371v2
2006-06-20,Comment on ''Superconducting decay length in a ferromagnetic metal'',"In the paper "" Superconducting decay length in a ferromagnetic metal"" by
Gusakova, Kupriyanov and Golubov [Pis'ma v ZhETF 83, 487 (2006);
cond-mat/0605137], the authors claim that they solved the linearized
Eilenberger equation in the ferromagnetic region of an S/F heterostructure at
arbitrary mean free path. In this comment we show that the solution suggested
by the authors is not correct and explain details of the exact solution found
by us in an earlier work several years ago (Phys. Rev. B 64, 134506, (2001).",0606528v1
2006-07-07,Broken axisymmetry phase of a spin-1 ferromagnetic Bose-Einstein condensate,"A spin-1 ferromagnetic Bose-Einstein condensate subject to a certain magnetic
field exhibits a broken-axisymmetry phase in which the magnetization tilts
against the applied magnetic field due to the competition between
ferromagnetism and linear and quadratic Zeeman effects. The Bogoliubov analysis
shows that in this phase two Goldstone modes associated with U(1) and SO(2)
symmetry breakings exist, in which phonons and magnons are coupled to restore
the two broken symmetries.",0607184v1
2006-07-25,Quantum Hall Ferrimagnetism in lateral quantum dot molecules,"We demonstrate the existance of ferrimagnetic and ferromagnetic phases in a
spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall
regime. The spin phase diagram is determined from Hartree-Fock Configuration
Interaction method as a function of electron numbers N, magnetic field B,
Zeeman energy, and tunneling barrier height. The quantum Hall ferrimagnetic
phase corresponds to spatially imbalanced spin droplets resulting from strong
inter-dot coupling of identical dots. The quantum Hall ferromagnetic phases
correspond to ferromagnetic coupling of spin polarization at filling factors
between $\nu=2$ and $\nu=1$.",0607638v1
2006-09-02,A new diluted magnetic semiconductor: The half-metallic ferromagnet CoTi(1-x)FexSb,"Half-Heusler compounds with 18 valence electrons are semi-conducting. It will
be shown that doping with electrons results in half-metallic ferromagnets,
similar to the case of diluted semi-conductors. CoTiSb is known to be a
semi-conducting Half-Heusler compound. Doping by Fe is expected to result in
ferromagnetic order. It was found that Ti can be replaced by up to about 10% Fe
while its crystal structure still remains C1b, which was proved by X-ray powder
diffraction. SQUID magnetometry revealed a magnetic moment of 0.32 mB per unit
cell at 5K.",0609042v1
2006-09-14,Derivation of the Ginzburg-Landau equations of a ferromagnetic p-wave superconductor,"We derive a Ginzburg-Landau free energy for a p-wave ferromagnetic
superconductor. The starting point is a microscopic Hamiltonian including a
spin generalised BCS term and a Heisenberg exchange term. We find that
coexistence of magnetisation and superconductivity depends on the sign of the
energy-gradient of the DOS at Fermi level. We also compute the tunneling
contribution to the Ginzburg-Landau free energy, and find expressions for the
spin-currents and Josephson currents across a tunneling junction separating two
ferromagnetic p-wave superconductors.",0609334v1
2006-09-20,Interplay between ferromagnetism and superconductivity in tunneling currents,"We study tunneling currents in a model consisting of two non-unitary
ferromagnetic spin-triplet superconductors separated by a thin insulating
layer. We find a novel interplay between ferromagnetism and superconductivity,
manifested in the Josephson effect. This offers the possibility of tuning
dissipationless currents of charge and spin in a well-defined manner by
adjusting the magnetization direction on either side of the junction.",0609500v2
2006-09-22,Complete spin polarization of degenerate electrons in semiconductors near ferromagnetic contacts,"We show that spin polarization of electron density in nonmagnetic degenerate
semiconductors can achieve 100%. This effect is realized in
ferromagnet-semiconductor $FM-n^{+}$-$n$ junctions even at moderate spin
selectivity of the $FM-n^{+}$ contact when the electrons are extracted from the
heavily doped $n^{+}-$semiconductor into the ferromagnet. We derived a general
equation relating spin polarization of the current to that of the electron
density in nonmagnetic semiconductors. We found that the effect of the complete
spin polarization is achieved near $n^{+}$-$n$ interface when an effective
diffusion coefficient goes to zero in this region while the diffusion current
remains finite.",0609599v1
2006-10-04,A new kind of vortex pinning in superconductor / ferromagnet nanocomposites,"This paper reports the observation of hysteresis in the vortex pinning in a
superconductor / ferromagnetic epitaxial nanocomposite consisting of fcc Gd
particles incorporated in a Nb matrix. We show that this hysteretic pinning is
associated with magnetic reversal losses in the Gd particles and is
fundamentally different in origin to pinning interactions previously observed
for ferromagnetic particles or other microstructural features.",0610105v1
2006-10-05,Magnetic properties of Hydrogenated Li and Co doped ZnO nanoparticles,"The effect of hydrogenation on magnetic properties of Zn0.85Co0.05Li0.10O
nanoparticles is presented. It was found that the sample hydrided at room
temperature (RT) showed weak ferromagnetism (FM) while that hydrided at 400oC
showed robust ferromagnetism at room temperature. In both cases reheating the
sample at 400oC in air converts it back into paramagnetic state (P) completely.
The characterization of samples by X-ray and electron diffraction (ED) showed
that room temperature ferromagnetism observed in the samples hydrogenated at RT
is intrinsic in nature whereas that observed in the samples hydrogenated at
400oC is partly due to the cobalt metal clusters.",0610145v1
2006-10-13,Ferromagnetism in the Mott insulator Ba2NaOsO6,"Results are presented of single crystal structural, thermodynamic, and
reflectivity measurements of the double-perovskite Ba2NaOsO6. These
characterize the material as a 5d^1 ferromagnetic Mott insulator with an
ordered moment of ~0.2 Bohr magnetons per formula unit and TC = 6.8(3) K. The
magnetic entropy associated with this phase transition is close to Rln2,
indicating that the quartet groundstate anticipated from consideration of the
crystal structure is split, consistent with a scenario in which the
ferromagnetism is associated with orbital ordering.",0610385v2
2006-11-03,Scanning probe imaging of coexistent ferromagnetism and ferroelectricity at room temperature,"Room temperature coexistence of ferromagnetism and ferroelectricity in a thin
film of a novel material of nominal composition PbTi0.5Fe0.5O3-d is probed by
standard ferroelectric and ferromagnetic hysteresis loop measurements and by
scanning probe microscopy of various kinds. Both magnetic domains and
ferroelectric domains are observed in the same spatial region of the material,
implying phase coexistence in this system. For both order parameters, sample
morphology strongly affects roughness of the domain walls.",0611084v1
2006-11-13,Metallic ferromagnetism in the Hubbard model: A rigorous example,"We present the first rigorous example of the Hubbard model in any dimensions
which exhibits metallic ferromagnetism. The model is a genuine Hubbard model
with short-range hopping and on-site Coulomb repulsion, and has multi
single-electron bands. In the limit where the band gap and the Coulomb
repulsion become infinite, we prove that the ground states are completely
ferromagnetic and at the same time conducting.",0611318v2
2006-11-16,New critical behavior in unconventional ferromagnetic superconductors,"New critical behavior in unconventional superconductors and superfluids is
established and described by the Wilson-Fisher renormalization-group method.
For certain ordering symmetries a new type of fluctuation-driven first order
phase transitions at finite and zero temperature are predicted. The results can
be applied to a wide class of ferromagnetic superconducting and superfluid
systems, in particular, to itinerant ferromagnets as UGe2 and URhGe.",0611431v1
2006-11-22,Electronic Phase Separation in Manganite/Insulator Interfaces,"By using a realist microscopic model, we study the electric and magnetic
properties of the interface between a half metallic manganite and an insulator.
We find that the lack of carriers at the interface debilitates the double
exchange mechanism, weakening the ferromagnetic coupling between the Mn ions.
In this situation the ferromagnetic order of the Mn spins near the interface is
unstable against antiferromagnetic CE correlations, and a separation between
ferromagnetic/metallic and antiferromagnetic/insulator phases at the interfaces
can occur. We obtain that the insertion of extra layers of undoped manganite at
the interface introduces extra carriers which reinforce the double exchange
mechanism and suppress antiferromagnetic instabilities.",0611594v1
2006-12-15,Surface phase separation in nanosized charge-ordered manganites,"Recent experiments showed that the robust charge-ordering in manganites can
be weakened by reducing the grain size down to nanoscale. Weak ferromagnetism
was evidenced in both nanoparticles and nanowires of charge-ordered manganites.
To explain these observations, a phenomenological model based on surface phase
separation is proposed. The relaxation of superexchange interaction on the
surface layer allows formation of a ferromagnetic shell, whose thickness
increases with decreasing grain size. Possible exchange bias and softening of
the ferromagnetic transition in nanosized charge-ordered manganites are
predicted.",0612391v2
2006-12-27,Interface dominated biferroic La0.6Sr0.4MnO3/0.7Pb(Mg0.33Nb0.66)O3 0.3PbTiO3 epitaxial superlattices,"Superlattices composed of ferromagnetic La0.6Sr0.4MnO3 and ferroelectric
0.7Pb(Mg0,33Nb0.66)O3 0.3(PbTiO3) layers were fabricated on (100) LaAlO3
substrates by pulsed laser deposition technique. Ferromagnetic and frequency
independent ferroelectric hysteresis characteristics established the biferroic
nature of the superlattices. Influence of magnetic field was observed in tuning
the P-E characteristics of the superlattices. Similar effect was observed on
application of a high DC electric field to the samples. The nature of the
observed ferroelectric properties and their modulation by applied magnetic and
electric fields were thus discussed in connection to existence of dielectric
passive layers at the ferroelectric/ferromagnetic interface.",0612647v1
2007-02-16,Left-handed Ferromagnet,"The dynamics of the total magnetization in metallic ferromagnet is studied
theoretically taking into account the relativistic spin-orbit interaction. It
is found that its quantum dynamics is seriously influenced by the band
crossings near the Fermi energy, and sometimes the direction of the precession
can be reversed from what expected from the commutation relation
$[S^{x},S^{y}]= i\hbar S^{z}$ ($h = 2\pi \hbar$: Planck constant), i.e., the
left-handed ferromagnet can be realized.",0702379v1
1994-02-16,Ferromagnetic Vacuum and Galactic Magnetic Fields,"Non-abelian gauge theories may have a ferromagnet-like vacuum with a non-zero
magnetic field, which also exists at finite temperature. We argue that the
formation of the ferromagnet-like vacuum at GUT scales gives rise to a Maxwell
magnetic field imprinted on the comoving plasma, and that it is energetically
favourable to align the field in different correlation volumes. This results in
a coherent magnetic field pertaining the whole universe, with a magnitude
$B_{now}\simeq 10^{-14}\G$, which is of the correct size to serve as the seed
field for the galactic dynamo.",9402295v1
2003-11-11,Color Ferromagnetism and Quantum Hall states in Quark Matter,"We discuss a possibility of the presence of a stable color ferromagnetic
state in SU(2) gauge theory of quark matter; a color magnetic field is
spontaneously generated due tothe gluon's dynamics. The state arises between
the hadronic state and the color superconducting state when the density of
quarks is varied. Although the state has been known to have unstable modes, we
show that unstable modes form quantum Hall states, in which the instability
disappears. Namely, the quark matter possesses a stable phase with the
ferromagnetic state and the quantum Hall state of gluons.",0311136v1
2005-07-11,Competition of Color Ferromagnetic and Superconductive States in a Quark-Gluon System,"The possibility of color ferromagnetism in an SU(2) gauge field model is
investigated. The conditions allowing a stable color ferromagnetic state of the
quark system in the chromomagnetic field occupying small domains are
considered. A phase transition between this state and the color superconducting
state is considered. The effect of finite temperature is analyzed.",0507125v1
2005-07-13,Color Ferromagnetic Quark Matter in Neutron Stars,"We show that color ferromagnetic phase of quark matter is energetically more
favored than color superconducting phases in neutron stars. Namely, increasing
baryon density in neutron stars transforms nuclear matter into the quark matter
of the color ferromagnetic phase. Further increase of the density makes the
quark matter take the color superconducting phases. We find that a critical
mass of the neutron star with such an internal structure is about
$1.6M_{\odot}$. We stress that analysis of gluon dynamics is crucial for
exploring dense quark matter.",0507151v2
1996-04-08,More on Generalized Heisenberg Ferromagnet Models,"We generalize the integrable Heisenberg ferromagnet model according to each
Hermitian symmetric spaces and address various new aspects of the generalized
model. Using the first order formalism of generalized spins which are defined
on the coadjoint orbits of arbitrary groups, we construct a Lagrangian of the
generalized model from which we obtain the Hamiltonian structure explicitly in
the case of $CP(N-1)$ orbit. The gauge equivalence between the generalized
Heisenberg ferromagnet and the nonlinear Schr\""{o}dinger models is given. Using
the equivalence, we find infinitely many conserved integrals of both models.",9604031v1
1997-03-27,Self-dual Chern-Simons Solitons in the Planar Ferromagnet,"We consider a uniaxial planar ferromagnet coupled minimally to an Abelian
Chern-Simons gauge field and study self-dual solitons which saturate the
Bogomol'nyi bound. We find a rich structure of rotationally symmetric static
soliton solutions for various uniform background charge densities. For a given
ferromagnet material, the properties of these solitons are controlled only by
the external magnetic field and the background charge.",9703193v1
2001-04-02,Quantum Spin Chains and Riemann Zeta Function with Odd Arguments,"Riemann zeta function is an important object of number theory. It was also
used for description of disordered systems in statistical mechanics. We show
that Riemann zeta function is also useful for the description of integrable
model. We study XXX Heisenberg spin 1/2 anti-ferromagnet. We evaluate a
probability of formation of a ferromagnetic string in the anti-ferromagnetic
ground state in thermodynamics limit. We prove that for short strings the
probability can be expressed in terms of Riemann zeta function with odd
arguments.",0104008v2
2001-05-15,Evaluation of Integrals Representing Correlations in XXX Heisenberg Spin Chain,"We study XXX Heisenberg spin 1/2 anti-ferromagnet. We evaluate a probability
of formation of a ferromagnetic string in the anti-ferromagnetic ground state
in thermodynamics limit. We prove that for short strings the probability can be
expressed in terms of Riemann zeta function with odd arguments.",0105144v3
1998-06-16,The continuous spin random field model: Ferromagnetic ordering in d>=3,"We investigate the Gibbs-measures of ferromagnetically coupled continuous
spins in double-well potentials subjected to a random field (our specific
example being the $\phi^4$ theory), showing ferromagnetic ordering in $d\geq 3$
dimensions for weak disorder and large energy barriers. We map the random
continuous spin distributions to distributions for an Ising-spin system by
means of a single-site coarse-graining method described by local transition
kernels. We derive a contour- representation for them with notably positive
contour activities and prove their Gibbsianness. This representation is shown
to allow for application of the discrete-spin renormalization group developed
by Bricmont/Kupiainen implying the result in $d\geq 3$.",9806010v1
2002-09-02,Nonlinear Behavior in Ferromagnetism: Simple Example and Possible Implications,"Two cases of a phenomenological model for ferromagnetism are considered,
discrete and continuous. And the relationship, in general, between discrete and
continuous models explored. In a similar way to the logistic map behavior, the
continuous case is exactly solvable while the discrete one contains the
bifurcation route to chaos. Through the ferromagnetic interpretation I comment
on the relevance of this to understanding evolution of systems in time, the
role of the configuration space in chaotic behavior, and how this understanding
may lead to new exotic magnetic phenomena.",0209006v1
2003-04-02,Color Ferromagnetism in Quark Matter,"We show a possibility that there exists a color ferromagnetic state in quark
matter, in which a color magnetic field is spontaneously generated. The state
arises between the hadronic state and the color superconducting state when the
density of quarks is varied.Although the state (Savvidy state) has been known
to involve unstablemodes of gluons, we show that the modes compose a quantum
Hall state to stabilize the ferromagnetic state. Such a quantum Hall statecan
arise only when quarks matter is present. We also show that the order of the
phase transition between the state andthe quark gluon plasma is of the first
order.",0304005v2
2003-11-16,Nonlinear Phenomena In Ferromagnetic Double Layers,"The non-stationary nonlinear models of magnetostatic waves propagation in
layered ferromagnetic structures are developed. This models are based on use of
the coupled nonlinear Schrodinger equations for amplitude of a bending around
taking into account an electrodynamic coupling between layers. The basic
nonlinear processes in such structures, in particular, the effects of
self-modulation and solitons formation are studied numerically, in comparison
with the similar effects in single ferromagnetic films.",0311078v1
2006-03-29,Ferromagnetic fluid as a model of social impact,"The paper proposes a new model of spin dynamics which can be treated as a
model of sociological coupling between individuals. Our approach takes into
account two different human features: gregariousness and individuality. We will
show how they affect a psychological distance between individuals and how the
distance changes the opinion formation in a social group. Apart from its
sociological aplications the model displays the variety of other interesting
phenomena like self-organizing ferromagnetic state or a second order phase
transition and can be studied from different points of view, e.g. as a model of
ferromagnetic fluid, complex evolving network or multiplicative random process.",0603248v1
2006-04-05,Thermal entanglement of spins in mean-field clusters,"We determine thermal entanglement in mean field clusters of $N$ spin one-half
particles interacting via the anisotropic Heisenberg interaction, with and
without external magnetic field. For the $xxx$ cluster in the absence of
magnetic field we prove that only the N=2 ferromagnetic cluster shows
entanglement. An external magnetic field $B$ can only entangle $xxx$
anti-ferromagnetic clusters in certain regions of the $B-T$ plane. On the other
hand, the $xxz$ clusters of size $N>2$ are entangled only when the interaction
is ferromagnetic. Detailed dependence of the entanglement on various parameters
is investigated in each case.",0604031v2
2007-04-16,Coherent dynamics of domain formation in the Bose Ferromagnet,"We present a theory to describe domain formation observed very recently in a
quenched Rb-87 gas, a typical ferromagnetic spinor Bose system. An overlap
factor is introduced to characterize the symmetry breaking of M_F=\pm 1
components for the F=1 ferromagnetic condensate. We demonstrate that the domain
formation is a co-effect of the quantum coherence and the thermal relaxation. A
thermally enhanced quantum-oscillation is observed during the dynamical process
of the domain formation. And the spatial separation of domains leads to
significant decay of the M_F=0 component fraction in an initial M_F=0
condensate.",0704.1995v2
2007-04-16,"Bound hole states in a ferromagnetic (Ga,Mn)As environment","A numerical technique is developed to solve the Luttinger-Kohn equation for
impurity states directly in k-space and is applied to calculate bound hole wave
functions in a ferromagnetic (Ga,Mn)As host. The rich properties of the band
structure of an arbitrarily strained, ferromagnetic zinc-blende semiconductor
yields various features which have direct impact on the detailed shape of a
valence band hole bound to an active impurity. The role of strain is discussed
on the basis of explicit calculations of bound hole states.",0704.2028v1
2007-04-18,New fluctuation-driven phase transitions and critical phenomena in unconventional superconductors,"Using the renormalization group method, new type of fluctuation-driven first
order phase transitions and critical phenomena are predicted for certain
classes of ferromagnetic superconductors and superfluids with unconventional
(spin-triplet) Cooper pairing. The problem for the quantum phase transitions at
extremely low and zero temperatures is also discussed. The results can be
applied to a wide class of ferromagnetic superconductive and superfluid
systems, in particular, to itinerant ferromagnets as UGe2 and URhGe.",0704.2287v1
2007-04-25,Quantized spin excitations in a ferromagnetic microstrip from microwave photovoltage measurements,"Quantized spin excitations in a single ferromagnetic microstrip have been
measured using the microwave photovoltage technique. Several kinds of spin wave
modes due to different contributions of the dipole-dipole and the exchange
interactions are observed. Among them are a series of distinct dipole-exchange
spin wave modes, which allow us to determine precisely the subtle spin boundary
condition. A comprehensive picture for quantized spin excitations in a
ferromagnet with finite size is thereby established. The dispersions of the
quantized spin wave modes have two different branches separated by the
saturation magnetization.",0704.3397v1
2007-05-07,Two Dimensional Quantum Well of Gluons in Color Ferromagnetic Quark Matter,"We have recently pointed out that color magnetic field is generated in dense
quark matter, i.e. color ferromagnetic phase of quark matter. Using light cone
quantization, we show that gluons occupying the lowest Landau level under the
color magnetic field effectively form a two dimensional quantum well (layer),
in which infinitely many zero modes of the gluons are present. We discuss that
the zero modes of the gluons form a quantum Hall state by interacting
repulsively with each other, just as electrons do in semiconductors. Such a
ferromagnetic quark matter with the layer structure of the gluons is a possible
origin of extremely strong magnetic field observed in magnetars.",0705.0852v1
2007-05-21,Long range triplet Josephson effect through a ferromagnetic trilayer,"We study the Josephson current through a ferromagnetic trilayer, both in the
diffusive and clean limits. For colinear (parallel or antiparallel)
magnetizations in the layers, the Josephson current is small due to short range
proximity effect in superconductor/ferromagnet structures. For non colinear
magnetizations, we determine the conditions for the Josephson current to be
dominated by another contribution originating from long range triplet proximity
effect.",0705.2929v1
2007-05-27,Kinetic ferromagnetism on a kagome lattice,"We study strongly correlated electrons on a kagome lattice at 1/6 and 1/3
filling. They are described by an extended Hubbard Hamiltonian. We are
concerned with the limit |t|<<V<<U with hopping amplitude t, nearest-neighbor
repulsion V and on-site repulsion U. We derive an effective Hamiltonian and
show, with the help of the Perron-Frobenius theorem, that the system is
ferromagnetic at low temperatures. The robustness of ferromagnetism is
discussed and extensions to other lattices are indicated.",0705.3941v2
2007-05-27,The transition temperature of Ising ferromagnetic thin film with aniaxial anisotropy,"The magnetic properties in the Ising ferromagnetic thin films are studied. By
transfer matrix method, the transition temperatures are calculated as a
function of the intra- and interlayer exchange interactions. The transition
temperatures in the Ising ferromagnetic thin films with uniaxial anisotropy are
also studied. The results show that the transition temperature changes with the
film thickness.",0705.3955v3
2007-05-30,Thermodynamics of carrier-mediated magnetism in semiconductors,"We propose a model of carrier-mediated ferromagnetism in semiconductors that
accounts for the temperature dependence of the carriers. The model permits
analysis of the thermodynamic stability of competing magnetic states, opening
the door to the construction of magnetic phase diagrams. As an example we
analyze the stability of a possible reentrant ferromagnetic semiconductor, in
which increasing temperature leads to an increased carrier density, such that
the enhanced exchange coupling between magnetic impurities results in the onset
of ferromagnetism as temperature is raised.",0705.4464v1
2007-06-08,Evidence for a ferromagnetic quantum critical point in URhGe doped with Ru,"We have investigated the evolution of ferromagnetic order in the correlated
metal series URh_{1-x}Ru_{x}Ge. Magnetization, transport and specific heat
measurements provide convincing evidence for a ferromagnetic quantum critical
point at the critical concentration x_{c} = 0.38. Here we report
ac-susceptibility and magnetization measurements on selected samples with Ru
doping concentrations near the critical point.",0706.1245v1
2007-06-18,Vortex States Induced by Proximity Effect in Hybrid Ferromagnet-Superconductor Systems,"We consider superconductivity nucleation in multiply connected mesoscopic
samples such as thin-walled cylinders or rings placed in electrical contact
with a ferromagnet. The superconducting critical temperature and order
parameter structure are studied on the basis of linearized Usadel equations. We
suggest a mechanism of switching between the superconducting states with
different vorticities caused by the exchange field and associated with the
oscillatory behavior of the Cooper pair wave function in a ferromagnet.",0706.2584v1
2007-06-25,0-pi Transitions in a Superconductor/Chiral Ferromagnet/Superconductor Junction induced by a Homogeneous Cycloidal Spiral,"We study the pi phase in a superconductor-ferromagnet-superconductor
Josephson junction, with a ferromagnet showing a cycloidal spiral spin
modulation with in-plane propagation vector. Our results reveal a high
sensitivity of the junction to the spiral order and indicate the presence of
0-pi quantum phase transitions as function of the spiral wave vector. We find
that the chiral magnetic order introduces chiral superconducting triplet pairs
that strongly influence the physics in such Josephson junctions, with potential
applications in nanoelectronics and spintronics.",0706.3594v2
2007-07-30,Current-voltage characteristics of semiconductor/ferromagnet junctions in the spin blockade regime,"It was recently predicted [Phys. Rev. B 75, 193301 (2007)] that spin blockade
may develop at nonmagnetic semiconductor/perfect ferromagnet junctions when the
electron flow is directed from the semiconductor into the ferromagnet. Here we
consider current-voltage characteristics of such junctions. By taking into
account the contact resistance, we demonstrate a current stabilization effect:
by increasing the applied voltage the current density through the junction
saturates at a specific value. The transient behavior of the current density is
also investigated.",0707.4475v1
2007-08-16,Ferromagnetism in cobalt doped n-GaN,"Ferromagnetic ordering is reported in the post-annealed samples of Co doped
n-GaN formed by Co+ implantation. A maximum Curie temperature ~ 250K is
recorded for the sample with 8 atomic percent Co. Particle induced x-ray
emission-channeling study confirmed the substitutional Co in Ga lattice site.
Local atomic arrangement around magnetic impurities is also analyzed using
Raman study. A disordered model with carrier mediated coupling of localized
magnetic moments is made responsible for the observed ferromagnetic ordering.",0708.2217v1
2007-09-16,Reentrant temperature dependence of critical current in superconductor - ferromagnet - superconductor junctions based on PdFe alloys,"The magnetic and transport properties of $Pd_{0.99}Fe_{0.01}$ thin films have
been studied. We have found that the Curie temperature of the films is about 20
K and the magnetic properties strongly depend on temperature below $T_{Curie}$.
We have also fabricated the set of superconductor-ferromagnet-superconductor
josephson junctions $Nb-PdFe-Nb$. The temperature dependence of the junctions
with the ferromagnet layer thickness of about 36 nm shows the reentrant
behaviour that is the evidence of the transition of the junction into the
$\pi$-state.",0709.2495v1
2007-10-11,Theory of shot noise in single-walled metallic carbon nanotubes weakly coupled to nonmagnetic and ferromagnetic leads,"We present theoretical study of shot noise in single wall metallic carbon
nanotubes weakly coupled to either nonmagnetic or ferromagnetic leads. Using
the real-time diagrammatic technique, we calculate the current, Fano factor and
tunnel magnetoresistance in the sequential tunneling regime. It is shown that
the differential conductance displays characteristic four-fold periodicity,
indicating single-electron charging. Such a periodicity is also visible in
tunnel magnetoresistance of the system as well as in the Fano factor. The
present studies elucidate the impact of ferromagnetic (vs. nonmagnetic)
contacts on the transport characteristics under consideration.",0710.2327v1
2007-10-17,Phase Diagram of the One Dimensional $S=1/2$ $XXZ$ model with Ferromagnetic nearest-neighbor and Antiferromagnetic next-nearest neighbor interactions,"We have studied the phase diagram of the one dimensional $S=1/2$ $XXZ$ model
with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest neighbor
interactions. We have applied the quantum renormalization group (QRG) approach
to get the stable fixed points and the running of coupling constants. The
second order QRG has been implemented to get the self similar Hamiltonian. This
model shows a rich phase diagram which consists of different phases which
possess the quantum spin-fluid and dimer phases in addition to the classical
N\'{e}el and ferromagnetic ones. The border between different phases has been
shown as a projection onto two different planes in the phase space.",0710.3239v1
2007-11-02,Origin and control of ferromagnetism in dilute magnetic semiconductors and oxides,"The author reviews the present understanding of the hole-mediated
ferromagnetism in magnetically doped semiconductors and oxides as well as the
origin of high temperature ferromagnetism in materials containing no valence
band holes. It is argued that in these systems spinodal decomposition into
regions with a large and a small concentration of magnetic component takes
place. This self-organized assembling of magnetic nanocrystals can be
controlled by co-doping and growth conditions. Functionalities of these
multicomponent systems are described together with prospects for their
applications in spintronics, nanoelectronics, photonics, plasmonics, and
thermoelectrics.",0711.0343v1
2007-11-02,Properties of tunnel Josephson junctions with a ferromagnetic interlayer,"We investigate superconductor/insulator/ferromagnet/superconductor (SIFS)
tunnel Josephson junctions in the dirty limit, using the quasiclassical theory.
We formulate a quantitative model describing the oscillations of critical
current as a function of thickness of the ferromagnetic layer and use this
model to fit recent experimental data. We also calculate quantitatively the
density of states (DOS) in this type of junctions and compare DOS oscillations
with those of the critical current.",0711.0365v2
2007-12-20,"Griffiths-McCoy singularities, Lee-Yang zeros and the cavity method in a solvable diluted ferromagnet","We study the diluted Ising ferromagnet on the Bethe lattice as a case study
for the application of the cavity method to problems with Griffiths-McCoy
singularities. Specifically, we are able to make much progress at infinite
coupling where we compute, from the cavity method, the density of Lee-Yang
zeroes in the paramagnetic Griffiths region as well as the properties of the
phase transition to the ferromagnet. This phase transition is itself of a
Griffiths-McCoy character albeit with a power law distribution of cluster
sizes.",0712.3540v1
2008-01-11,Weak Ferromagnetism in Fe1-xCoxSb2,"Weak ferromagnetism in Fe1-xCoxSb2 is studied by magnetization and Mossbauer
measurements. A small spontaneous magnetic moment of the order of 10^-3 uB
appears along the b-axis for 0.2<= x <= 0.4. Based on the structural analysis,
we argue against extrinsic sources of weak ferromagnetism. We discuss our
results in the framework of the nearly magnetic electronic structure of the
parent compound FeSb2.",0801.1688v1
2008-01-11,Giant dynamical Zeeman split in inverse spin valves,"The inversion of a spin valve device is proposed. Opposite to a conventional
spin valve of a non-magnetic spacer sandwiched between two ferromagnetic
metals, an inverse spin valve is a ferromagnet sandwiched between two
non-magnetic metals. It is predicted that, under a bias, the chemical
potentials of spin-up and spin-down electrons in the metals split at
metal-ferromagnet interfaces, a dynamical Zeeman effect. This split is of the
order of an applied bias. Thus, there should be no problem of generating an
$eV$ split that is not possible to be realized on the earth by the usual Zeeman
effect.",0801.1775v1
2008-01-20,Cryptoferromagnetism in Superconductors with Broken Time-Reversal Symmetry,"The cryptoferromagnetic state (the state with intrinsic domain structure) in
superconducting ferromagnets subjected to external magnetic field is studied
theoretically. Ferromagnetism originates either from electron spin or the
intrinsic angular momentum of Cooper pairs (chiral p-wave superconductors like
$\mathrm{Sr_2 Ru O_4}$). The phase transitions towards the Meissner and the
mixed states are investigated, and the magnetic phase diagrams are obtained.
Cryptoferromagnetism, as a form coexistence of superconductivity and
ferromagnetism, can be detected by observation of magnetization curves
predicted in the present analysis.",0801.3091v1
2008-02-07,Mesoscopic competition of superconductivity and ferromagnetism: conductance peak statistics in metallic grains,"We investigate the competition between superconductivity and ferromagnetism
in chaotic ultra-small metallic grains in a regime where both phases can
coexist. We use an effective Hamiltonian that combines a BCS-like pairing term
and a ferromagnetic Stoner-like spin exchange term. We study the transport
properties of the grain in the Coulomb blockade regime and identify signatures
of the coexistence between pairing and exchange correlations in the mesoscopic
fluctuations of the conductance peak spacings and peak heights.",0802.0901v1
2008-02-22,Weak Ferromagnetism Accompanying Loop current order in Underdoped Cuprates,"We discuss the necessary symmetry conditions and the different ways in which
they can be physically realized for the occurrence of ferromagnetism
accompanying the loop current orbital magnetic order observed by polarized
neutron-diffraction experiments or indeed any other conceivable principal order
in the under-doped phase of cuprates. We contrast the Kerr effect experiments
in single crystals observing ferromagnetism with the direct magnetization
measurements in large powder samples, which do not observe it. We also suggest
experiments to resolve the differences among the experiments, all of which we
believe to be correct.",0802.3258v2
2008-02-25,Electronic structure and ferromagnetic behavior in the $Mn_{1-x}A_xAs_{1-y}B_y$ alloys,"In this work, a systematic ab initio study of the influence of doping on
electronic structure and local magnetic moments of ferromagnetic MnAs has been
carried out. The majority of the considered substitution elements, potentially
suitable for modification of MnAs as working material of magnetic refrigerators
is shown to result in reduction of the ferromagnetic moment. But there are
variants of anionic substitution (for example, substitution of As for S and Se)
when the magnetic moment grows.",0802.3686v1
2008-03-17,Coupled charge and valley excitations in graphene quantum Hall ferromagnets,"Graphene is a two-dimensional carbon material with a honeycomb lattice and
Dirac-type low-energy spectrum. In a strong magnetic field, where Coulomb
interactions dominate against disorder broadening, quantum Hall ferromagnetic
states realize at integer fillings. Extending the quantum Hall ferromagnetism
to the fractional filling case of massless Dirac fermions, we study the
elementally charge excitations which couple with the valley degrees of freedom
(so-called valley skyrmions). With the use of the density matrix renomalization
group (DMRG) method, the excitation gaps are calculated and extrapolated to the
thermodynamic limit. These results exhibit numerical evidences and criterions
of the skyrmion excitations in graphene.",0803.2418v2
2008-04-02,Superconductor-ferromagnet junction phase qubit,"We propose a scheme for a phase qubit in an SIFIS junction, consisting of
bulk superconductors (S), a proximity-induced ferromagnet (F), and insulating
barriers (I). The qubit state is constituted by 0 and $\pi$ phase states of the
junction, in which the charging energy of the junction leads to the
superposition of the two states. The qubit is operated by the gate voltage
applied to the ferromagnet, and insensitive to the decoherence sources existing
in other superconducting qubits. We discuss a scalable scheme for qubit
measurement and tunable two-qubit coupling.",0804.0349v2
2008-04-24,GdI_2: A New Ferromagnetic Excitonic Solid?,"The two-dimensional, colossal magnetoresistive system GdI_2 develops an
unusual metallic state below its ferromagnetic transition and becomes
insulating at low temperatures. It is argued that this geometrically
frustrated, correlated poor metal is a possible candidate for a ferromagnetic
excitonic liquid. The renormalized Fermi surface supports a further breaking of
symmetry to a charge ordered, excitonic solid ground state at lower
temperatures via order by disorder mechanism. Several experimental predictions
are made to investigate this unique orbitally correlated ground state.",0804.3940v2
2008-04-29,Giant Magnetoelectric Effect via Strain-Induced Spin-Reorientation Transitions in Ferromagnetic Films,"It is shown theoretically that a giant magnetoelectric susceptibility
exceeding 10^-6 s/m may be achieved in the ferromagnetic/ferroelectric
epitaxial systems via the magnetization rotation induced by an electric field
applied to the substrate. The predicted magnetoelectric anomaly results from
the strain-driven spin-reorientation transitions in ferromagnetic films, which
take place at experimentally accessible misfit strains in CoFe2O4 and Ni films.",0804.4569v1
2008-04-30,Ferromagnetic Ising spin systems on the growing random tree,"We analyze the ferromagnetic Ising model on a scale-free tree; the growing
random network model with the linear attachment kernel $A_k=k+\alpha$
introduced by [Krapivsky et al.: Phys. Rev. Lett. {\bf 85} (2000) 4629-4632].
We derive an estimate of the divergent temperature $T_s$ below which the
zero-field susceptibility of the system diverges. Our result shows that $T_s$
is related to $\alpha$ as $\tanh(J/T_s)=\alpha/[2(\alpha+1)]$, where $J$ is the
ferromagnetic interaction. An analysis of exactly solvable limit for the model
and numerical calculation support the validity of this estimate.",0804.4731v1
2008-05-25,Itinerant Ferromagnetism in an Atom Trap,"We propose an experiment to explore the magnetic phase transitions in
interacting fermionic Hubbard systems, and describe how to obtain the
ferromagnetic phase diagram of itinerant electron systems from these
observations. In addition signatures of ferromagnetic correlations in the
observed ground states are found: for large trap radii (trap radius $R_T > 4$,
in units of coherence length $\xi$), ground states are topological in nature --
a ""skyrmion"" in 2D, and a ""hedgehog"" in 3D.",0805.3693v2
2008-06-25,Hidden Orbital Liquid State Within Ferromagnetically Ordered Metallic SrRuO3,"We have experimentally found related anomalies in electrical resistivity, dc
and ac magnetic susceptibility, appearing deeply within ferromagnetically
ordered state in SrRuO3. Lack of Jahn-Teller distortion in this regime rules
out conventional orbital order, forcing one to describe these in terms of an
orbital liquid ground state coexisting with ferromagnetic spin order. We
suggest that weak spin-orbit coupling in such an unusual state underpins the
observed anomalies.",0806.4198v1
2008-08-07,Density of states near a vortex core in ferromagnetic superconductors: Application to STM measurements,"We investigate numerically the local density of states (LDOS) in the vicinity
of a vortex core in a ferromagnetic superconductor. Specifically, we
investigate how the LDOS is affected by the relative weight of the spin bands
in terms of the superconducting pairing, and we also examine the effect of
different pairing symmetries for the superconducting order parameter. Our
findings are directly related to scanning tunneling microscopy measurements and
may thus be highly useful to clarify details of the superconducting pairing in
recently discovered ferromagnetic superconductors.",0808.0983v1
2008-08-07,Ferromagnetism and spin polarized charge carriers in In$_{2}$O$_{3}$ thin films,"We present evidence for spin polarized charge carriers in In$_2$O$_3$ films.
Both In$_2$O$_3$ and Cr doped In$_2$O$_3$ films exhibit room temperature
ferromagnetism after vacuum annealing, with a saturation moment of
approximately 0.5 emu/cm$^3$. We used Point Contact Andreev Reflection
measurements to directly determine the spin polarization, which was found to be
approximately 50$\pm$5% for both compositions. These results are consistent
with suggestions that the ferromagnetism observed in certain oxide
semiconductors may be carrier mediated.",0808.1123v1
2008-08-27,Quantum Hall to Insulator Transition in the Bilayer Quantum Hall Ferromagnet,"We describe a new phase transition of the bilayer quantum Hall ferromagnet at
filling fraction $\nu = 1$. In the presence of static disorder (modeled by a
periodic potential), bosonic $S=1/2$ spinons can undergo a superfluid-insulator
transition while preserving the ferromagnetic order. The Mott insulating phase
has an emergent U(1) photon, and the transition is between Higgs and Coulomb
phases of this photon. Physical consequences for charge and counterflow
conductivity, and for interlayer tunneling conductance in the presence of
quenched disorder are discussed.",0808.3702v1
2008-08-28,Gilbert Damping in Conducting Ferromagnets II: Model Tests of the Torque-Correlation Formula,"We report on a study of Gilbert damping due to particle-hole pair excitations
in conducting ferromagnets. We focus on a toy two-band model and on a four-band
spherical model which provides an approximate description of ferromagnetic
(Ga,Mn)As. These models are sufficiently simple that disorder-ladder-sum vertex
corrections to the long-wavelength spin-spin response function can be summed to
all orders. An important objective of this study is to assess the reliability
of practical approximate expressions which can be combined with electronic
structure calculations to estimate Gilbert damping in more complex systems.",0808.3923v1
2008-09-05,Ferromagnetism in Mn Substituted Zirconia: A Density-functional Theory Study,"We study the electronic structure and magnetism of 25% Mn substituted cubic
Zirconia (ZrO2) with several homogeneous and heterogeneous doping profiles
using density-functional theory calculations. We find that all doping profiles
show half-metallic ferromagnetism (HMF), and delta-doping is most energy
favorable while homogeneous doping has largest ferromagnetic stabilization
energy. Using crystal field theory, we discuss the formation scheme of HMF.
Finally, we speculate the potential spintronics applications for Mn doped ZrO2,
especially as spin direction controllment.",0809.0971v1
2008-10-02,"Novel critical exponent of magnetization curves near the ferromagnetic quantum phase transitions of Sr1-xAxRuO3 (A = Ca, La0.5Na0.5, and La)","We report a novel critical exponent delta=3/2 of magnetization curves
M=H^{1/delta} near the ferromagnetic quantum phase transitions of Sr1-xAxRuO3
(A = Ca, La0.5Na0.5, and La), which the mean field theory of the
Ginzburg-Landau-Wilson type fails to reproduce. The effect of dirty
ferromagnetic spin fluctuations might be a key.",0810.0343v1
2008-10-15,Inverse proximity effect in superconductor-ferromagnet bilayer structures,"Measurements of the polar Kerr effect using a zero-area-loop Sagnac
magnetometer on Pb/Ni and Al/(Co-Pd) proximity-effect bilayers show unambiguous
evidence for the ""inverse proximity effect,"" in which the ferromagnet (F)
induces a finite magnetization in the superconducting (S) layer. To avoid
probing the magnetic effects in the ferromagnet, the superconducting layer was
prepared much thicker than the light's optical penetration depth. The sign and
size of the effect, as well as its temperature dependence agree with recent
predictions by Bergeret et al..",0810.2605v1
2008-10-16,Epitaxial ferromagnetic Fe$_{3}$Si/Si(111) structures with high-quality hetero-interfaces,"To develop silicon-based spintronic devices, we have explored high-quality
ferromagnetic Fe$_{3}$Si/silicon (Si) structures. Using low-temperature
molecular beam epitaxy at 130 $^circ$C, we realize epitaxial growth of
ferromagnetic Fe$_{3}$Si layers on Si (111) with keeping an abrupt interface,
and the grown Fe$_{3}$Si layer has the ordered $DO_{3}$ phase. Measurements of
magnetic and electrical properties for the Fe$_{3}$Si/Si(111) yield a magnetic
moment of ~ 3.16 $mu_{B}$/f.u. at room temperature and a rectifying
Schottky-diode behavior with the ideality factor of ~ 1.08, respectively.",0810.2835v1
2008-10-31,Defect-induced ferromagnetism in graphite,"We demonstrate direct evidence for ferromagnetic order at defect structures
in highly oriented pyrolytic graphite with magnetic force microscopy at room
temperature. Magnetic impurities have been excluded as the origin of the
magnetic signal after careful analysis supporting an intrinsic magnetic
behavior of carbon-based materials. The observed ferromagnetism has been
attributed to originate from unpaired electron spins localized at grain
boundaries. Scanning tunneling spectroscopy of grain boundaries showed intense
localized states and enhanced charge density compared to bare graphite.",0810.5657v1
2008-11-01,Room Temperature Ferromagnetic Semiconductor Rutile Ti1-xCoxO2-δ Epitaxial Thin Films Grown by Sputtering Method,"Room temperature ferromagnetic semiconductor rutile Ti1-xCoxO2-\delta (101)
epitaxial thin films were grown on r-sapphire substrates by a dc sputtering
method. Ferromagnetic magnetization, magnetic circular dichroism, and anomalous
Hall effect were clearly observed at room temperature in sputter-grown films
for the first time. The magnetization value is nearly as large as 3\mu B/Co
that is consistent with the high spin state Co2+ in this compound recently
established by spectroscopic methods. Consequently, its originally large
magneto-optical response is further enhanced.",0811.0073v1
2008-11-13,Peierls Instability Induced Ferromagnetic Insulator at Orbital Order Transition,"The origin of ferromagnetic insulating state of La$_{7/8}$Sr$_{1/8}$MnO$_3$
is investigated. Based on the tight-binding model, it is shown that this state
can be attributed to the Peierls instability arisen from the interplay of spin
and orbital ordering. The importance of the hole-orbiton-phonon intercoupling
in doped manganites is revealed. This picture explains well the recent
experimental finding of the reentrance of ferromagnetic metal state at low
temperature [Phys. Rev. Lett. 96, 097201 (2006)].",0811.2019v2
2008-11-19,Nonlocal Spin Transport in Lateral Spin Valves with Multiple Ferromagnetic Electrodes,"We study the nonlocal spin transport in a lateral spin valve with multiple
ferromagnetic (FM) electrodes. When two current-injecting and two spin
current-detecting electrodes are all ferromagnetic, the number of possible
nonlocal spin signal states is four at maximum. In reality, this number is
reduced, depending on the inter-probe distance and the relative magnitudes of
the spin resistances. Our theoretical results are in agreement with recent
experiments of spin injection into an Al island, a carbon nanotube, and
graphene.",0811.3138v1
2008-11-27,Anisotropic magnetoresistance in ferromagnetic atomic-sized metal contacts,"Recent experiments in ferromagnetic atomic-sized contacts have shown that the
anisotropic magnetoresistance (AMR) is greatly enhanced and has an asymmetric
angular dependence as compared with that of bulk samples. The origin of these
effects is still under debate. In this work we present a theoretical analysis
of the AMR in atomic contacts of the 3d ferromagnetic materials. Our results
strongly suggest that the anomalous AMR stems from the reduced symmetry of the
atomic contact geometries. We also present calculations supporting the idea
that the pronounced voltage- and temperature dependence in some experiments can
be attributed to impurities near the constrictions.",0811.4491v1
2008-12-02,Ferromagnetism in the Extended Periodic Anderson Model Near Selective Mott Localization,"Motivated by the experimental finding of Ferromagnetism (FM) near non-FL
quantum phase transitions (QPT), I investigate FM in an Extended Periodic
Anderson Model (EPAM). Using the Frobenius-Perron theorem, a FM {\it metallic}
phase near the selective Mott localization is rigorously found. Interesting
connections with Tasaki's flat-band ferromagnetism, as well as with the
well-known double exchange (DE) mechanism are elucidated. This finding is a
higher dimensional generalization of numerical work on the D=1 PAM, and
constitutes a robust way to FM metallic behavior in $D>1$. Finally, we discuss
a concrete manifestation of our results to $UGe_{2}$.",0812.0472v1
2008-12-04,Phase transitions and ordering of confined dipolar fluids,"We apply a modified mean-field density functional theory to determine the
phase behavior of Stockmayer fluids in slitlike pores formed by two walls with
identical substrate potentials. Based on the Carnahan-Starling equation of
state, a fundamental-measure theory is employed to incorporate the effects of
short-ranged hard sphere - like correlations while the long-ranged
contributions to the fluid interaction potential are treated perturbatively.
The liquid-vapor, ferromagnetic liquid - vapor, and ferromagnetic liquid -
isotropic liquid first-order phase separations are investigated. The local
orientational structure of the anisotropic and inhomogeneous ferromagnetic
liquid phase is also studied. We discuss how the phase diagrams are shifted and
distorted upon varying the pore width.",0812.0969v1
2008-12-08,Multi-magnon bound states in easy-axis ferromagnetic zigzag spin chain,"The frustrated spin-1/2 chain with weakly anisotropic ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest-neighbor exchanges is
studied. We focus on the excitation spectrum and the low-temperature
thermodynamics in the ferromagnetic region of the ground state phase diagram.
It is shown that the excitation spectrum of the model is characterized by the
existence of the multi-magnon bound states. These excitations determine the
low-temperature magnetic susceptibility. The energy of the bound magnon
complexes is found using the scaling estimates of the perturbation theory and
numerical calculations. The relation of the considered model to the
edge-sharing cuprate $Li_2CuO_4$ is discussed.",0812.1425v1
2009-01-07,Electrically Controlled Magnetic Memory and Programmable Logic based on Graphene/Ferromagnet Hybrid Structures,"It has been shown that the combining of the electrical effect on the exchange
bias field with giant magneto-resistance effect of the graphene/ferromagnet
hybrid structures reveals a new non-volatile magnetic random access memory
device conception. In such device an electric bias realizes the writing bits
instead a magnetic field of remote word line with high energy consumption.
Interplay of two graphene mediated exchange bias fields applied to different
sides of free ferromagnet results in programable logic operations that depends
on specific realization of the structure.",0901.0926v1
2009-01-12,The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact,"The influence of phase shifts of electron waves passing through and reflected
by the potential barrier on the Andreev reflection in a
ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is
found that in a superconductor the surface spin-dependent Andreev bound states
inside the superconducting gap are formed as a result of the interference of
electron-like and hole-like quasiparticles due to repeated Andreev reflections.
The peak in the conductance of the FIS contact at the zero potential for the
(110)-oriented superconductor disappears rapidly as the polarization of a
ferromagnet increases, whereas for the (100)-oriented superconductor it
appears. The physical reason for this behavior of conductance is discussed.",0901.1558v1
2009-01-26,Room temperature ferromagnetism in Cr-doped hydrogenated amorphous Si films,"Ferromagnetism above room temperature was observed in Cr-doped hydrogenated
amorphous silicon films deposited by rf magnetron-sputtering. Structure
analysis reveals that films are amorphous without any detectable precipitates
up to the solubility limit 16 atomic percentages of Cr. Experimental results
suggest that hydrogenation has a dramatic influence on magnetic properties,
electrical conductivity and carrier concentration in the thin films. Pronounced
anomalous Hall effect and magnetization curve both suggest the origin of the
ferromagnetism may arises from percolation of magnetic polarons.",0901.4123v1
2009-01-28,Relativistic ferromagnetic magnon at the zigzag edge of graphene,"We study the spin-wave excitations near the zigzag edge of graphene. It is
rather interesting that we obtain a single branch of relativistic ferromagnetic
magnon due to the presence of the open boundary. Note that magnons in
antiferomagnets appear in pairs, while the single brach magnon in ferromagnets
does not have relativistic dispersion. Thus, the magnon near the zigzag edge of
graphene is a hybrid of both, signaling its intrinsic property as a boundary
excitation that must be embedded in a higher dimensional bulk system.",0901.4567v1
2009-03-15,On the possibility of a long range proximity effect in a ferromagnetic nanoparticle,"We study the proximity effect in a ferromagnetic nanoparticle having a vortex
magnetization pattern. We show that for axisymmetric system consisting of a
circular particle and a magnetic vortex situated at the center of it no long
range superconducting correlations are induced. It means that induced
superconductivity is localized in the small area near the superconducting
electrode. However, in the real systems axial symmetry can be broken by either
a shift of the magnetic vortex from the origin or geometrical anisotropy of the
ferromagnetic particle. In this case a long range proximity effect is possible.",0903.2613v1
2009-04-01,Spin-dependent Cooper Pair Phase and Pure Spin Supercurrents in Strongly Polarized Ferromagnets,"We study heterostructures of singlet superconductors (SC) and strongly
spin-polarized ferromagnets (sFM) and show that a relative phase arises between
the superconducting proximity amplitudes in the two ferromagnetic spin bands.
We find a tunable pure spin supercurrent in a sFM contacted with only one SC
electrode. We show that Josephson junctions are most effective for a spin
polarization $P\sim 0.3$, and that critical currents for positive and negative
bias differ for a high transmission Josephson junction, due to a relative phase
between single and double pair transmission.",0904.0149v2
2009-04-06,Characterisation of Ferromagnetic Contacts to Carbon Nanotubes,"We present an investigation of different thin-film evaporated ferromagnetic
materials for their suitability as electrodes in individual single-wall and
multi-wall carbon nanotube-based spin devices. Various electrode shapes made
from permalloy (Ni_{81}Fe_{19}), the diluted ferromagnet PdFe, and PdFe/Fe
bilayers are studied for both their micromagnetic properties and their contact
formation to carbon nanotubes. Suitable devices are tested in low-temperature
electron transport measurements, displaying the typical tunneling
magnetoresistance of carbon nanotube pseudo spin valves.",0904.0907v2
2009-04-15,Ferromagnetic spin-polaron on complex lattices,"We present a simpler derivation of the exact solution of a spin-polaron in a
ferromagnet and generalize it to complex lattices and/or longer range exchange
interactions. As a specific example, we analyze a two-dimensional MnO$_2$-like
lattice (as in the ferromagnetic layers in LaMnO$_3$) and discuss the
properties of the resulting spin-polaron in various regimes. At strong
couplings the solution is reminiscent of the Zhang-Rice singlet, however the
electronic wavefunction involved in the singlet is dependent on the momentum of
the singlet, and multiple bands may appear.",0904.2367v1
2009-05-02,Implications and consequences of ferromagnetism universally exhibited by inorganic nanoparticles,"Occurrence of surface ferromagnetism in inorganic nanoprticles as a universal
property not only explains many of the unusual magnetic features of oxidic thin
films, but also suggests its possible use in creating new materials, as
exemplified by multiferroic BaTiO3 nanoparticles. While the use of Mn-doped ZnO
and such materials in spintronics appears doubtful, it is possible to have
materials exhibiting coexistence of (bulk) superconductivity with (surface)
ferromagnetism.",0905.0183v1
2009-05-04,Room-temperature ferromagnetism in dielectric GaN(Gd),"We present an explanation of recently observed giant magnetic moment and
room-temperature ferromagnetism in the dielectric GaN doped with Gd. Our
approach uses the polarization mechanism of exchange interaction, which occurs
if the d-level of Gd appears in the bandgap close to the valence band edge.
Calculated ferromagnetic critical temperature and the value of the magnetic
moment well correspond to experimental findings.",0905.0500v1
2009-05-08,The making of ferromagnetic Fe doped ZnO nano-clusters,"In this letter, the authors present a study of the energetics and magnetic
interactions in Fe doped ZnO clusters by ab-initio density functional
calculations. The results indicate that defects under suitable conditions can
induce ferromagnetic interactions between the dopant Fe atoms whereas
antiferromagnetic coupling dominates in a neutral defect-free cluster. The
calculations also reveal an unusual ionic state of the dopant Fe atom residing
at the surface of the cluster, a feature that is important to render the
cluster ferromagnetic.",0905.1176v1
2009-05-15,Planar superconductor/ferromagnet hybrids: Anisotropy of resistivity induced by magnetic templates,"We investigated experimentally the transport properties of a superconducting
cross-shaped aluminium microbridge fabricated on top of ferromagnetic BaFe12O19
single crystal. It was demonstrated that a one-dimensional domain structure in
the ferromagnetic substrate can induce the formation of superconducting
channels above magnetic domains. This leads to a giant anisotropy of
resistivity of the superconducting bridge, caused by the appearance of
continuous paths of supercurrents flowing along domain walls.",0905.2590v1
2009-05-22,Interlayer and interfacial exchange coupling in ferromagnetic metal/semiconductor heterostructures,"We describe a systematic study of the exchange coupling between a
magnetically hard metallic ferromagnet (MnAs) and a magnetically soft
ferromagnetic semiconductor (GaMnAs) in bilayer and trilayer heterostructures.
An exchange spring model of MnAs/GaMnAs bilayers accounts for the variation of
the exchange bias field with layer thickness and composition. We also present
evidence for hole-mediated interlayer exchange coupling in MnAs/p-GaAs/\GaMnAs
trilayers and study the dependence of the exchange bias field on the thickness
of the spacer layer.",0905.3691v2
2009-05-28,Spin Hall Current and Spin-transfer Torque in Ferromagnetic Metal,"We theoretically examine the spin-transfer torque in the presence of
spin-orbit interaction (SOI) at impurities in a ferromagnetic metal on the
basis of linear response theory. We obtained, in addition to the usual
spin-transfer torque, a new contributioin $\sim {\bm j}_{\rm
SH}^{\phantom{\dagger}} \cdot \nabla {\bm n}$ in the first order in SOI, where
${\bm j}_{\rm SH}^{\phantom{\dagger}}$ is the spin Hall current driven by an
external electric field. This is a reaction to inverse spin Hall effect driven
by spin motive force in a ferromagnet.",0905.4561v1
2009-06-06,Stable two-dimensional ferromagnets made of regular single-layered lattices of single-molecule nanomagnets on substrates,"We propose that stable two-dimensional (2D) ferromagnets can be made of
regular single-layered lattices of single-molecule nanomagnets with enough
uniaxial magnetic anisotropy on appropriate substrates by controlling the
inter-nanomagnet magnetic interaction. Our Monte Carlo simulated results show
that such ideal 2D ferromagnets are thermodynamically stable when the
anisotropy is strong enough. If the anisotropy energy equals 80 K,
approximately that of the Mn12, the T_c varies from zero to 15 K depending on
different inter-nanomagnet coupling constants. Such stable spin systems,
experimentally accessible, should be promising for information applications.",0906.1298v1
2009-06-09,Spin-wave theory for dimerized ferromagnetic chains,"We describe a Peierls dimerization which occurs in ferromagnetic spin chains
at finite temperature, within the modified spin-wave theory. Usual spin-wave
theory is modified by introducing a Lagrange multiplier which enforces a
nonmagnetic state at finite temperature. It is shown that this method gives
results in excellent agreement with the density--matrix renormalization group
applied to transfer matrices for dimerized ferromagnetic chains. We study bond
correlation functions and explore the characteristic features of dimerization
in the specific heat.",0906.1758v1
2009-06-23,Mass Enhancement and Reentrant Ground State in Magnetic Field,"Three different cases of magnetic field reentrant ground states in heavy
fermion systems, URhGe, UGe$_2$ and CeRhIn$_5$ recently studied in Grenoble,
are discussed. URhGe is a ferromagnetic superconductor with reentrace of
superconductivity under magnetic field ($H$) which is associated to the spin
reorientation field. UGe$_2$ is a ferromagnetic superconductor with an
enhancement of the upper critical field $H_{c2}$ of superconductivity at its
metamagnetic transition between 2 ferromagnetic phases. CeRhIn$_5$ is a
superconductor with $H$ reentrant antiferromagnetism. We analyze the links
between the $H$ enhancement of the different contributions to the effective
mass and the field reentrant phase.",0906.4204v1
2009-06-23,Theory of charge transport in ferromagnetic semiconductor/s-wave superconductor junction,"We study tunneling conductance in ferromagnetic
semiconductor/insulator/s-wave superconductor junction where Rashba spin-orbit
interaction (RSOI) and exchange field are taken into account in the
ferromagnetic semiconductor. We show that normalized conductance at zero
voltage has a maximum as a function of RSOI for high transparent interface and
finite exchange field. This is because Andreev reflection probability shows a
nonmonotonic dependence on RSOI in the presence of the exchange field. On the
other hand, for intermediate transparent interface, normalized conductance at
zero voltage has a reentrant shape at zero or small exchange field with
increasing RSOI but is monotonically increasing by RSOI at large exchange
field.",0906.4244v1
2009-06-29,Influence of Demagnetization Effect on Giant Magneto Impedance of soft Ferromagnetic Metal,"The large change in electromagnetic impedance in ferromagnetic state of soft
magnetic metals in presence of biasing magnetic field is associated with change
in screening of electromagnetic field. The screening depends on the
permeability of the metal. Apart from dependence on intrinsic properties of
metal the permeability depends on size of the sample. It is observed that the
decrease in MI in amorphous ferromagnetic ribbon of Fe40Ni40B20 alloy is large
for long sample whereas corresponding change is small for short one with same
biasing field. As intrinsic magnetic properties and bias field are same and the
demagnetization factor increases with reduction of length of the sample the
reduction of MI effect is associated with demagnetization field.",0906.5203v1
2009-06-30,Photoinduced magnetism in the ferromagnetic semiconductors,"We study the enhancement of the magnetic transition temperature $T_c$ due to
incident light in ferromagnetic semiconductors such as EuS. The photoexcited
carriers mediate an extra ferromagnetic interaction due to the coupling with
the localized magnetic moments. The Hamiltonian consists of a Heisenberg model
for the localized moments and an interaction term between the photoexcited
carriers and the localized moments. The model predicts a small enhancement of
the transition temperature in semi-quantitative agreement with the experiments.",0906.5514v1
2009-10-22,Quantum critical behavior of a magnetic quantum paraelectric,"We discuss the interplay between anti-ferromagnetic order and polarization
fluctuations in a magnetic quantum paraelectric. Using an action where
anti-ferromagnetic order parameter couples to the polarization fluctuations and
as well as magnetic field, we derive a set of self consistent equations to
study both the temperature and the magnetic field dependence of the static
dielectric susceptibility. The temperature dependence of dielectric
susceptibility near both the anti-ferromagnetic quantum critical point and
ferroelectric quantum critical point are described using scaling arguments.
Discussions on achieving various quantum critical points in experiments are
also made.",0910.4374v2
2009-10-28,Interacting spin waves in the ferromagnetic Kondo lattice model,"We present an new approach for the ferromagnetic, three-dimensional,
translational-symmetric Kondo lattice model which allows us to derive both
magnon energies and linewidths (lifetimes) and to study the properties of the
ferromagnetic phase at finite temperatures. Both ""anomalous softening"" and
""anomalous damping"" are obtained and discussed. Our method consists of mapping
the Kondo lattice model onto an effective Heisenberg model by means of the
""modified RKKY interaction"" and the ""interpolating self-energy approach"". The
Heisenberg model is approximatively solved by applying the Dyson-Maleev
transformation and using the ""spectral density approach"" with a broadened
magnon spectral density.",0910.5478v2
2009-10-30,Interplay of Quantum Criticality and Geometric Frustration in Columbite,"Motivated by CoNb2O6 (belonging to the columbite family of minerals), we
theoretically study the physics of quantum ferromagnetic Ising chains coupled
anti-ferromagnetically on a triangular lattice in the plane perpendicular to
the chain direction. We combine exact solutions of the chain physics with
perturbative approximations for the transverse couplings. When the triangular
lattice has an isosceles distortion (which occurs in the real material), the
T=0 phase diagram is rich with five different states of matter: ferrimagnetic,
N\'eel, anti-ferromagnetic, paramagnetic and incommensurate phases, separated
by quantum phase transitions. Implications of our results to experiments on
CoNb2O6 are discussed.",0911.0038v1
2009-11-09,Triplet contribution to the Josephson current in the nonequilibrium superconductor/ferromagnet/superconductor junction,"The Josephson current through a long s-wave superconductor/weak
ferromagnet/s-wave superconductor weak link is studied theoretically in the
regime of nonequilibrium spin-dependent occupation of electron states in the
ferromagnetic intelayer. While under the considered nonequilibrium condition
the standard supercurrent, carried by the singlet part of current-carrying
density of states, is not modified, the additional supercurrent flowing via the
triplet part of the current-carrying density of states appears. Depending on
voltage, controlling the particular form of spin-dependent nonequilibrium in
the interlayer, this additional current can enhance or reduce the usual current
of the singlet component and also switch the junction between 0- and
$\pi$-states.",0911.1646v1
2010-01-14,The phase transition in the localized ferromagnet EuO probed by muSR,"We report results of muon spin rotation measurements performed on the
ferromagnetic semiconductor EuO, which is one of the best approximations to a
localized ferromagnet. We argue that implanted muons are sensitive to the
internal field primarily through a combination of hyperfine and Lorentz fields.
The temperature dependences of the internal field and the relaxation rate have
been measured and are compared with previous theoretical predictions.",1001.2556v2
2010-01-26,Effect of spin-conserving scattering on Gilbert damping in ferromagnetic semiconductors,"The Gilbert damping in ferromagnetic semiconductors is theoretically
investigated based on the $s$-$d$ model. In contrast to the situation in
metals, all the spin-conserving scattering in ferromagnetic semiconductors
supplies an additional spin relaxation channel due to the momentum dependent
effective magnetic field of the spin-orbit coupling, thereby modifies the
Gilbert damping. In the presence of a pure spin current, we predict a new
contribution due to the interplay of the anisotropic spin-orbit coupling and a
pure spin current.",1001.4576v1
2010-02-15,Domain wall motion in ferromagnetic nanowires driven by arbitrary time-dependent fields: An exact result,"We address the dynamics of magnetic domain walls in ferromagnetic nanowires
under the influence of external time-dependent magnetic fields. We report a new
exact spatiotemporal solution of the Landau-Lifshitz-Gilbert equation for the
case of soft ferromagnetic wires and nanostructures with uniaxial anisotropy.
The solution holds for applied fields with arbitrary strength and time
dependence. We further extend this solution to applied fields slowly varying in
space and to multiple domain walls.",1002.2913v1
2010-02-24,Evidence of Ferrimagnetism in Ferromagnetic La0_{67}Ca0_{33}MnO_3 nanoparticle,"The present report is dedicated to show that ferromagnetic La0.67Ca0.33MnO3
(LCMN) particles can be better described in the framework of ferrimagnetic
model. To confirm the ferrimagnetic signature in ferromagnetic LCMN particles,
the temperature dependence of the inverse of magnetic susceptibility in the
paramagnetic state of the samples was taken as a tool of data analysis. The
observed ferrimagnetism is understood as an effect of of the core-shell spin
structure in LCMN particles.",1002.4574v2
2010-03-23,Supercurrents through half-metallic ferromagnetic CrO$_2$ revisited,"We report on the observation of a supercurrent through the half metallic
ferromagnet CrO$_2$ grown on hexagonal Al$_2$O$_3$ (sapphire). The current was
observed to flow over a distance of 700 nm between two superconducting
amorphous Mo$_{70}$Ge$_{30}$ electrodes which were deposited on the CrO$_2$
film. The critical current $I_c$ increases as function of decreasing
temperature. Upon applying an in-plane magnetic field, $I_c$ goes through a
maximum at the rather high field of 80 mT. We believe this to be a long range
proximity effect in the ferromagnet, carried by odd-frequency pairing
correlations.",1003.4446v1
2010-03-31,Half-metallic ferromagnetism in transition-metal doped germanium nitride: A first-principles study,"The electronic and magnetic properties of transition-metal doped
$\beta$-Ge3N4 have been studied using first-principles calculations. The
results show that the substitutional transition-metal impurities tend to
cluster. The V and Cr doped Ge3N4 compounds are ferromagnetic semiconductors,
while the compounds with Mn and Fe doping show a half-metallic ferromagnetic
character.",1003.5982v2
2010-04-14,Theory of the ferromagnetism in TiCrN solid solutions,"First-principles calculations are used to investigate the magnetic properties
of Ti$_{1-x}$Cr$_{x}$N solid solutions. We show that the magnetic interactions
between Cr spins that favour antiferromagnetism in CrN is changed upon alloying
with TiN leading to the appearance of ferromagnetism in the system at
approximately $x \leq 0.50$ in agreement with experimental reports. Furthermore
we suggest that this effect originates in an electron density redistribution
from Ti to Cr that decreases the polarization of Cr d-states with t$_{2g}$
symmetry while it increases the polarization of Cr d-states with e$_g$
symmetry, both changes working in favour of ferromagnetism.",1004.2337v1
2010-04-15,Ground-state configurations in ferromagnetic nanotori,"Magnetization ground states are studied in toroidal nanomagnets. The
energetics associated to the ferromagnetic, vortex and onion-like
configurations are explicitly computed. The analysis reveals that the vortex
appears to be the most prominent of such states, minimizing total energy in
every torus with internal radius $r\gtrsim10\,{\rm nm}$ (for Permalloy). For
$r\lesssim10\,{\rm nm}$ the vortex remains the most favorable pattern whenever
$R/\ell_{ex}\gtrsim1.5$ ($R$ is the torus external radius and $\ell_{ex}$ is
the exchange length), being substituted by the ferromagnetic state whenever
$R/\ell_{ex}\lesssim1.5$.",1004.2689v1
2010-06-28,Emergence Of Ferromagnetism In Nanoparticles Of Antiferromagnetic Nd0.4Sr0.6MnO3,"We have investigated the magnetic state of Nd0.4Sr0.6MnO3 with the variation
of its grain size down to average nanometric diameter (40 nm). The bulk sample
is antiferromagnetic (AFM) in nature. However, on reduction of the grain size,
emergence of ferromagnetic behavior is experimentally observed. Linear and
nonlinear ac magnetic susceptibility measurements reveal that ferromagnetic
nature is enhanced as the grain size is reduced. Large coercivity and
bifurcation between zero field cooled and field cooled magnetization curves
indicate an intrinsic disorder and large anisotropy in the system. Observed
behaviors are attributed to surface disorder as well as to possible pressure
effect on nano grains.",1006.5351v1
2010-08-17,Anisotropic magnetic fluctuations in the ferromagnetic superconductor UCoGe studied by angle-resolved ^{59}Co NMR,"We have carried out direction-dependent ^{59}Co NMR experiments on a single
crystal sample of the ferromagnetic superconductor UCoGe in order to study the
magnetic properties in the normal state. The Knight shift and nuclear
spin-lattice relaxation rate measurements provide microscopic evidence that
both static and dynamic susceptibilities are ferromagnetic with strong Ising
anisotropy. We discuss that superconductivity induced by these magnetic
fluctuations prefers spin-triplet pairing state.",1008.2837v1
2010-08-25,Upper critical field in superconductors near ferromagnetic quantum critical points; UCoGe,"We study the strong-coupling superconductivity near ferromagnetic quantum
critical points, mainly focusing on the upper critical fields $H_{c2}$. Based
on our simple model calculations, we discuss experimentally observed unusual
behaviors of $H_{c2}$ in a recently discovered ferromagnetic superconductor
UCoGe. Especially, the large anisotropy between $H_{c2}\parallel a$-axis and
$H_{c2}\parallel c$-axis, and the strong-coupling behaviors in
$H_{c2}^{\parallel a}$ are investigated. We also examine effects of
non-analytic corrections in the spin susceptibility on the superconductivity,
which can arise from effective long range interactions due to particle-hole
excitations.",1008.4204v1
2010-09-28,Ferromagnetic Behavior of High Purity ZnO nanoparticles,"ZnO nanoparticles with Wurtzite structure were prepared by chemical methods
at low temperature in aqueous solution. Nanoparticles are in the range from
about 10 to 30 nm. Ferromagnetic properties were observed from 2 K to room
temperature and above. Magnetization vs temperature, M(T) and isothermal
measurements M(H) were determined. The coercive field clearly shows
ferromagnetism above room temperature. The chemical synthesis, structural
defects in the bulk related to oxygen vacancies are the main factors for the
observed magnetic behavior.
  PACS numbers: 61.46.Hk Nanocrystals, 75.50.Pp Magnetic semiconductors,
81.05.Dz II-VI semiconductors",1009.5641v1
2010-10-01,Thermally induced 0-pi phase transition in Josephson junctions through a ferromagnetic oxide film,"We investigate the Josephson transport through a ferromagnetic oxide film,
e.g., La$_2$BaCuO$_5$, theoretically. Using the recursive Green's function
technique, we found the formation of a pi-junction in such systems. Moreover
the 0-pi phase transition is induced by increasing the temperature. Such
ferromagnetic-oxide based Josephson junctions may become an element in the
architecture of future quantum computers.",1010.0042v1
2010-10-20,Spin Josephson effect with a single superconductor,"A thin ferromagnetic layer on a bulk equal-spin-pairing triplet
superconductor is shown to mediate a Josephson coupling between the spin
$\uparrow$ and $\downarrow$ condensates of the superconductor. By deriving
analytic expressions for the bound states at the triplet
superconductor-ferromagnet interface, we show that this spin Josephson effect
establishes an effective anisotropy axis in the ferromagnetic layer. The
associated Josephson spin current is predicted to cause a measurable precession
of the magnetization about the vector order parameter of the triplet
superconductor.",1010.4238v2
2010-11-16,Magnetic field dependence of pairing interaction in ferromagnetic superconductors with triplet pairing,"It is developed a microscopic description of superconductivity in
ferromagnetic materials with triplet pairing triggered by the exchange of
magnetic fluctuations. Instead widely used paramagnon model we work with
phenomenological spectrum of fluctuations in the orthorhombic ferromagnet with
strong magnetic anisotropy. Depending of the field orientation parallel or
perpendicular to the direction of spontaneous magnetization the effective
amplitude of pairing interaction proves to be decreasing or increasing function
of magnetic field that allows to explain the drastic difference in magnitudes
of upper critical field in these directions.",1011.3753v1
2010-12-21,Itinerant Ferromagnetism in ultracold Fermi gases,"Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is
studied applying the Jastrow-Slater approximation generalized to finite
polarization and temperature. For two components at zero temperature a second
order transition is found at $ak_F\simeq0.90$ compatible with QMC.
Thermodynamic functions and observables such as the compressibility and spin
susceptibility and the resulting fluctuations in number and spin are
calculated. For trapped gases the resulting cloud radii and kinetic energies
are calculated and compared to recent experiments. Spin polarized systems are
recommended for effective separation of large ferromagnetic domains. Collective
modes are predicted and tri-critical points are calculated for multi-component
systems.",1012.4569v1
2011-02-13,Dark Energy from ferromagnetic condensation of cosmic magninos,"It is proposed that an ultra-light fermionic species, dubbed cosmic magnino
has condensed into a ferromagnetic state in the Universe. The extended
structure of domain walls associated with this ferromagnetism accounts for the
observed Dark Energy. In modification of the situation with an electron gas, it
is proposed that the Stoner criterion is satisfied due to magnetic dipolar
repulsion. The cosmological requirements then yeild a lower bound on the
magnetic moment of the cosmic magnino. The proposed magnetism is supposed to be
associated with a new non-standard electromagnetism. If the magnino is also
electrically charged under this electromagnetism, the corresponding oppositely
charged heavier species would account partially or entirely for the Dark Matter
in the Universe.",1102.2562v1
2011-04-05,Enhancement of the ferromagnetic order of graphite after sulphuric acid treatment,"We have studied the changes in the ferromagnetic behavior of graphite powder
and graphite flakes after treatment with diluted sulphuric acid. We show that
this kind of acid treatment enhances substantially the ferromagnetic
magnetization of virgin graphite micrometer size powder as well as in graphite
flakes. The anisotropic magnetoresistance (AMR) amplitude at 300 K measured in
a micrometer size thin graphite flake after acid treatment reaches values
comparable to polycrystalline cobalt.",1104.0812v1
2011-04-11,Hydrogen mediated ferromagnetism in ZnO single crystals,"We investigated the magnetic properties of hydrogen plasma treated ZnO single
crystals by SQUID magnetometry. In agreement with the expected hydrogen
penetration depth we found ferromagnetic behavior located at the first 20 nm of
the H-treated surface of ZnO with magnetization at saturation up to 6 emu/g at
300 K and Curie temperature T$_c$ $\gtrsim $ 400 K. In the ferromagnetic
samples a hydrogen concentration of a few atomic percent in the first 20 nm
surface layer was determined by nuclear reaction analysis. The saturation
magnetization of H-treated ZnO increases with the concentration of hydrogen.",1104.1899v1
2011-04-15,The ground state energy of the frustrated ferromagnetic spin chain near the transition point,"The one-dimensional quantum spin-1/2 model with nearest-neighbor
ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is
considered. The Hamiltonian is first bosonized by using the linear spin wave
approximation, and then is treated by using the Green's function approach. An
integral expression of the quantum correction to the classical ground state
energy is derived. The critical behavior of the ground state energy in the
vicinity of the transition point from the ferromagnetic to the singlet ground
state is analyzed by numerical calculation, and the result is $-8\gamma^2$.",1104.2946v1
2011-05-30,A ferromagnetic-like phase transition in new oxychalcogenide HgOCuSe,"We report the synthesis of a new oxychalcogenide HgOCuSe sample. The
resistivity decreases as a function of $T^{1.75}$ with decreasing temperature
from room temperature down to around 80 K. There exists a very sharp
ferromagnetic-like phase transition at around 60 K under a field of $H$ = 100
Oe. Contrary to the usual ferromagnetic materials, the descending and ascending
branches of the magnetic hysteresis curve, at 30 K, are reversed in the whole
irreversible field range and the reverse irreversibility decreases at 5 K.",1105.5868v1
2011-06-20,Anisotropic supercurrent due to inhomogeneous magnetization in ferromagnet/superconductor junctions,"We investigate transverse charge and spin dc supercurrents in a ferromagnet
coupled to a superconductor where the ferromagnet has inhomogeneous magnetic
structure. These transverse supercurrents arise from non-trivial structure of
the magnetization. The magnetic structure manifested in the transverse charge
supercurrent is essentially different from that discussed in the context of
anomalous Hall effect, reflecting the disspationless nature of supercurrent.
Possible candidates of magnetic structure to verify our prediction are also
discussed.",1106.3801v4
2011-06-28,Oxygen adsorption effect on magnetic properties of graphite,"Both experimental and theoretical studies of the magnetic properties of
micrographite and nanographite indicate a crucial role of the partial oxidation
of graphitic zigzag edges in ferromagnetism. In contrast to total and partial
hydrogenation, the oxidation of half of the carbon atoms on the graphite edges
transforms the antiferromagnetic exchange interaction between graphite planes
and over graphite ribbons to the ferromagnetic interaction. The stability of
the ferromagnetism is discussed.",1106.5565v1
2011-07-01,Charge pumping due to triplet vector chirality in ferromagnet/triplet superconductor junctions,"We investigate charge pumping in ferromagnet/triplet superconductor junctions
where the magnetization of the ferromagnet is inhomogeneous and dynamical. It
is shown that charge current is pumped due to the coupling of the localized
spin with triplet vector spin chirality, vector spin chirality formed by the
triplet vector of Cooper pairing. Physical mechanism of the charge pumping is
also discussed.",1107.0119v2
2011-07-30,Polaronic transport in the ferromagnetic phase of Gd1-xCaxBaCo2O5.53,"Temperature dependent electrical resistivity and thermopower measurements
were carried out on Gd1-xCaxBaCo2O5.53 with x varying between 0 and 0.25. Ca
subsitution leads to the incorporation of holes (Co4+) into the system that
leads to a reduction in resistivity and a stabilisation of the ferromagnetic
phase at low temperatures. The temperature dependence of resistivity and
thermopower are markedly different in the Ca doped sample, with a dramatic
reduction in the resistivity, as compared to that in the pristine sample. The
variation in both the resistivity and thermopower with temperature is explained
in terms of the transport of polarons in the ferromagnetic phase of Ca doped
system.",1108.0059v1
2011-08-01,A non isothermal phase-field model for the ferromagnetic transition,"We propose a model for non isothermal ferromagnetic phase transition based on
a phase field approach, in which the phase parameter is related but not
identified with the magnetization. The magnetization is split in a paramagnetic
and in a ferromagnetic contribution, dependent on a scalar phase parameter and
identically null above the Curie temperature. The dynamics of the magnetization
below the Curie temperature is governed by the order parameter evolution
equation and by a Landau-Lifshitz type equation for the magnetization vector.
In the simple situation of a uniaxial magnet it is shown how the order
parameter dynamics reproduces the hysteresis effect of the magnetization.",1108.0378v1
2011-08-29,Proximity-induced density-of-states oscillations in a superconductor/strong-ferromagnet system,"We have measured the evolution of the tunneling density of states (DOS) in
superconductor/ferromagnet (S/F) bilayers with increasing F-layer thickness,
where F in our experiment is the strong ferromagnet Ni. As a function of
increasing Ni thickness, we detect multiple oscillations in the DOS at the
Fermi energy from differential conductance measurements. The features in the
DOS associated with the proximity effect change from normal to inverted twice
as the Ni thickness increases from 1 to 5 nm.",1108.5613v1
2011-09-17,Break-junction experiments on the zero-bias anomaly of non-magnetic and ferromagnetically ordered metals,"We have investigated break junctions of normal non-magnetic metals as well as
ferromagnets at low temperatures. The point contacts with radii 0.15 - 15 nm
showed zero-bias anomalies which can be attributed to Kondo scattering at a
single Kondo impurity at the contact or to the switching of a single conducting
channel. The Kondo temperatures derived from the width of the anomalies varied
between 10 and 1000 K. These results agree well with literature data on
atomic-size contacts of the ferromagnets as well as with spear-anvil type
contacts on a wide variety of metals.",1109.3774v1
2011-09-20,Hysteresis for ferromagnetism: asymptotics of some 2-scale Landau-Lifshitz model,"We study a 2-scale version of the Landau-Lifshitz system of ferromagnetism,
introduced by Starynkevitch to modelize hysteresis: the response of the
magnetization is fast compared to a slowly varying applied magnetic fi eld.
Taking the exchange term into account, in space dimension 3, we prove that,
under some natural stability assumption on the equilibria of the system, the
strong solutions follow the dynamics of these equilibria. We also give explicit
examples of relevant equilibria and exterior magnetic fields, when the
ferromagnetic medium occupies some ellipsoidal domain.",1109.4352v1
2012-02-22,Transverse Field Ising Ferromagnetism in Mn$_{12}$-acetate-MeOH,"We report measurements of the magnetic susceptibility of single crystals of
Mn$_{12}$-acetate-MeOH, a new high-symmetry variant of the original single
molecule magnet Mn$_{12}$-acetate. A comparison of these data to theory and to
data for the Mn$_{12}$ acetate material shows that Mn$_{12}$-acetate-MeOH is a
realization of a transverse-field Ising ferromagnet in contrast to the original
Mn$_{12}$ acetate material, in which solvent disorder leads to effects
attributed to random field Ising ferromagnetism.",1202.4963v1
2012-02-29,Inverse Spin Hall Effect in Ferromagnetic Metal with Rashba Spin Orbit Coupling,"We report an intrinsic form of the inverse spin Hall effect (ISHE) in
ferromagnetic (FM) metal with Rashba spin orbit coupling (RSOC), which is
driven by a normal charge current. Unlike the conventional form, the ISHE can
be induced without the need for spin current injection from an external source.
Our theoretical results show that Hall voltage is generated when the FM moment
is perpendicular to the ferromagnetic layer. The polarity of the Hall voltage
is reversed upon switching the FM moment to the opposite direction, thus
promising a useful readback mechanism for memory or logic applications.",1202.6428v1
2012-03-13,Monopoles in ferromagnetic metals,"The aim of this short review is to give an introduction to monopoles and to
present theoretical derivation of two particular monopoles in ferromagnetic
metals, a hedgehog monopole and a spin damping monopole. Spin damping monopoles
can be generated in simple systems such as a junction of a ferromagnet and a
heavy element with strong spin-orbit interaction such as Pt. This monopole is
essential in coupling electronics with magnetism, and is thus expected to play
an essential role in spintronics.",1203.2709v1
2012-06-13,Ferromagnetism and orbital order in a topological ferroelectric,"We explore via density functional calculations the magnetic doping of a
topological ferroelectric as an unconventional route to multiferroicity.
Vanadium doping of the layered perovskite La$_{2}$Ti$_{2}$O$_{7}$ largely
preserves electric polarization and produces robust ferromagnetic order, hence
proper multiferroicity. The marked tendency of dopants to cluster into chains
results in an insulating character at generic doping. Ferromagnetism stems from
the symmetry breaking of the multi-orbital V system via an unusual
""antiferro""-orbital order, and from the host's low-symmetry layered structure.",1206.2879v2
2012-06-23,"Novel Aharonov-Bohm-like effect: Detectability of the vector potential in a solenoidal configuration with a ferromagnetic core covered by superconducting lead, and surrounded by a thin cylindrical shell of aluminum","The flux as measured by the Josephson effect in a SQUID-like configuration
with a ferromagnetic core inserted into its center, is shown to be sensitive to
the vector potential arising from the central ferromagnetic core, even when the
core is covered with a superconducting material that prevents any magnetic
field lines from ever reaching the perimeter of the SQUID-like configuration.
This leads to a macroscopic, Aharonov-Bohm-like effect that is observable in an
asymmetric hysteresis loop in the response of the SQUID-like configuration to
an externally applied magnetic field.",1206.5362v1
2012-09-03,Pressure induced ferromagnetism in antiferromagnetic Fe_1.03Te,"The magnetic properties of Fe1.03Te under hydrostatic pressure up to p ~ 5.7
GPa were investigated by means of muon spin rotation, dc magnetization, and
neutron depolarization measurements. With increasing pressure the
antiferromagnetic ordering temperature TN decreases continuously from 70 K at
ambient pressure towards higher pressures. Surprisingly, the commensurate
antiferromagnetic order of FeTe enters a region of incommensurate and dynamical
magnetic order before at p ~ 1.7 GPa the system turns ferromagnetic. The
ferromagnetic ordering temperature TC increases with increasing pressure.",1209.0383v1
2012-09-09,Temperature-dependent proximity magnetism in Pt,"We experimentally demonstrate the existence of magnetic coupling between two
ferromagnets separated by a thin Pt layer. The coupling remains ferromagnetic
regardless of the Pt thickness, and exhibits a significant dependence on
temperature. Therefore, it cannot be explained by the established mechanisms of
magnetic coupling across nonmagnetic spacers. We show that the experimental
results are consistent with the presence of magnetism induced in Pt in
proximity to ferromagnets, in direct analogy to the well-known proximity
effects in superconductivity.",1209.1802v1
2012-09-19,Asymmetry of modal profiles of dipole-exchange spin waves in thin high-magnetic moment metallic ferromagnetic films,"The asymmetry of the modal profiles for dipole-exchange spin waves
propagating in in-plane magnetized ferromagnetic films at a right angle to the
applied magnetic field has been investigated theoretically. It was found that
in the large-magnetic moment ferromagnetic metallic films with typical
thicknesses 10-60 nm the fundamental mode of the spectrum is localized at the
surface opposite to the surface of localization of the exchange-free
Damon-Eshbach surface wave. This anomalous localization of the wave does not
affect the non-reciprocity of spin wave excitation by microstrip and coplanar
transducers but may be detected in other types of experiments.",1209.4153v1
2012-09-19,Spin-Transfer and Exchange Torques in Ferromagnetic Superconductors,"We consider how superconducting correlations influence spin-transfer torques
in ferromagnetic superconductors. It is demonstrated that there is a novel
torque arising from particle-hole interference that depends on the U(1) phase
associated with the superconducting order parameter. We also show that there is
an equilibrium exchange torque between two ferromagnetic superconductors in
contact via a normal metal mediated by Andreev states. The latter equilibrium
magnetic torque is also sensitive to spin-resolved phase differences in the
superconducting order parameters as well as to an externally applied phase
difference.",1209.4356v2
2012-09-26,Ferromagnetic InMnAs on InAs Prepared by Ion Implantation and Pulsed Laser Annealing,"Ferromagnetic InMnAs has been prepared by Mn ion implantation and pulsed
laser annealing. The InMnAs layer reveals a saturated magnetization of 2.6
mu_B/Mn at 5 K and a perpendicular magnetic anisotropy. The Curie temperature
is determined to be 46 K, which is higher than those in previous reports with
similar Mn concentrations. Ferromagnetism is further evidenced by the large
magnetic circular dichroism.",1209.5865v1
2012-10-12,The role of magnetic polarons in ferromagnetic GdN,"We report an interplay between magnetism and charge transport in the
ferromagnetic semiconductor GdN, pointing to the formation of magnetic polarons
centred on nitrogen vacancies. The scenario goes some way to resolving a
long-standing disagreement between the measured and predicted Curie temperature
in GdN. It further constitutes an extension of concepts that relate closely to
the behaviour of ferromagnetic semiconductors generally, and EuO in particular.",1210.3441v1
2012-11-06,Spin Wave Scattering in Ferromagnetic Cross,"Spin wave scattering in the right angle ferromagnetic cross was measured.
Shape anisotropy defined magnetization ground states at zero biasing magnetic
fields. Scattering of the spin waves in the center of ferromagnetic cross is
strongly dependent on the amplitude and angle of the biasing magnetic field.
Micromagnetic simulations indicate that low in-plane biasing magnetic fields
rotate the magnetization of the cross center while the arms stay axially
magnetized due to the shape anisotropy. We discuss effect of biasing magnetic
fields on the spin wave scattering and approaches to an effective spin wave
switch based on the fabricated structure.",1211.1259v1
2013-01-08,Exactly solvable spin-glass models with ferromagnetic couplings: the spherical multi-$p$-spin model in a self-induced field,"We report some results on the quenched disordered Spherical multi-$p$-Spin
Model in presence of ferromagnetic couplings. In particular, we present the
phase diagrams of some representative cases that schematically describe, in the
mean-field approximation, the behavior of most known transitions in glassy
materials, including dynamic arrest in super-cooled liquids,
amorphous-amorphous transitions and spin-glass transitions. A simplified
notation is introduced in order to compute systems properties in terms of an
effective, self-induced, field encoding the whole ferromagnetic information.",1301.1475v1
2013-03-07,Spin and Orbital Splitting in Ferromagnetic Contacted Single Wall Carbon Nanotube Devices,"We observed the coulomb blockade phenomena in ferromagnetic contacting single
wall semiconducting carbon nanotube devices. No obvious Coulomb peaks shift was
observed with existing only the Zeeman splitting at 4K. Combining with other
effects, the ferromagnetic leads prevent the orbital spin states splitting with
magnetic field up to 2 Tesla at 4K. With increasing magnetic field further,
both positive or negative coulomb peaks shift slopes are observed associating
with clockwise and anticlockwise orbital state splitting. The strongly
suppressed/enhanced of the conductance has been observed associating with the
magnetic field induced orbital states splitting/converging.",1303.1580v1
2013-04-19,Spin nematic states in antiferromagnets containing ferromagnetic bonds,"The majority of recent works devoted to spin nematic phases deal with either
frustrated magnets or with those described by Hamiltonians with large
non-Heisenberg terms. We show in the present study that nonfrustrated
antiferromagnets (AFs) containing ferromagnetic (FM) bonds can show nematic
phases in a strong magnetic field. Among the particular spin systems discussed
are a ladder with FM rungs, two AF layers coupled ferromagnetically, a chain
containing alternating AF and FM bonds, and an AF anisotropic spin-1 chain.",1304.5463v1
2013-04-22,Coexistence of p-wave Cooper pairing and ferromagnetism,"A two-band model for coexistence of p-wave superconductivity with localized
ferromagnetism is studied using the equation of motion approach. It shows that
ferromagnetic and superconducting states enhance each other but in a different
way from that of the one-band model. The Curie temperature is not only
determined by the exchange interactions between localized spins, but also can
be increased with the coupling between electrons and spins, and with the p-wave
Cooper-pairing interaction. These results are complementary to those of the
one-band model, which suggest that the Curie temperature is unlikely to ever be
below the superconducting transition temperature.",1304.5854v1
2013-05-06,Quantum Monte Carlo study of the two-dimensional ferromagnet,"We present Quantum Monte Carlo calculations that probe the
paramagnet-ferromagnet phase transition in a two-dimensional Stoner
Hamiltonian. With a screened Coulomb interaction we observe a first order
ferromagnetic transition for short screening lengths, and a second order
transition with a longer screening length, accompanied by a rising critical
interaction strength. Finally, we discuss the consequences of our results for
an ultracold atomic gas with finite ranged interactions.",1305.1198v1
2013-06-12,Controllable valley and spin transports in ferromagnetic silicene junctions,"We investigate charge, valley, and spin transports in
normal/ferromagnetic/normal silicene junc- tion. We show that the charge,
valley, and spin conductances in this junction oscillate with the length of the
ferromagnetic silicene. It is also found that the current through this junction
is valley and spin polarized due to the coupling between valley and spin
degrees of freedom, and the valley and spin polarizations can be tuned by local
application of a gate voltage. In particular, we find fully valley and spin
polarized current by applying the electric field. We also obtain the condition
for observing the fully valley and spin polarized current.",1306.2824v1
2013-06-18,Magnetic domain growth in a ferromagnetic Bose-Einstein condensate: Effects of current,"Magnetic domain patterns in a ferromagnetic Bose-Einstein condensate (BEC)
show different properties depending on the quadratic Zeeman effect and
dissipation. Another important factor that affects domain patterns and domain
growth is superfluid flow of atoms. Domain growth in a ferromagnetic BEC with
negative quadratic Zeeman energy is characterized by the same growth law as
(classical) binary fluid in the inertial hydrodynamic regime. In the absence of
the superfluid flow, the domain growth law for negative quadratic Zeeman energy
is the same as that of scalar conserved fields such as binary alloys.",1306.4129v2
2013-12-09,Pseudofermion ferromagnetism in the Kondo lattices: a mean-field approach,"Ground state ferromagnetism of the Kondo lattices is investigated within
slave fermion approach by Coleman and Andrei within a mean-field approximation
in the effective hybridization model. Conditions for formation of both
saturated (half-metallic) and non-saturated magnetic state are obtained for
various lattices. A description in terms of universal functions which depend
only on bare electron density of states (DOS) is presented. A crucial role of
the energy dependence of the bare DOS (especially, of DOS peaks) for the
small-moment ferromagnetism formation is demonstrated.",1312.2438v2
2013-12-13,Impurity-vacancy complexes and ferromagnetism in doped sesquioxides,"Based on hybrid density-functional calculations, we propose that
ferromagnetism in the prototypical bixbyite sesquioxide In$_2$O$_3$ doped with
Cr is due to Cr-oxygen vacancy complexes, while isolated Cr cannot support
carrier-mediated magnetic coupling. Our proposal is consistent with
experimental facts such as the onset of ferromagnetism in O-lean conditions
only, the low or vanishing net moment in unintentionally doped material, and
its increase upon intentional doping.",1312.3793v2
2013-12-30,Some remarks on the magnetic phase diagram of ferromagnetic superconductor UGe2,"The phase transition to ferromagnetic order in itinerant ferromagnetic
superconductor UGe$_2$ as function of pressure shows change of phase transition
order. At low temperature and high pressure the transition is of first order
and at pressure of about 1.42 GPa the order changes to second. On the basis of
Landau expansion of free energy up to the sixth order in magnetization we
calculate the phase diagram taking into account the magneto-elastic interaction
as the mechanism responsible for this change. We propose a simple Stoner-like
dependence of the Curie temperature on the pressure and present the results for
measurable thermodynamic quantities as the entropy jump at the first order
phase transition.",1312.7773v1
2014-01-14,Defects induced ferromagnetism in plasma-enabled graphene nanopetals,"Ferromagnetism in graphene is fascinating, but it is still a big challenge
for practical applications due to the weak magnetization. In order to enhance
the magnetization, here, we design plasma-enabled graphene nanopetals with
ultra-long defective edges of up to 105 m/g, ultra-dense lattice vacancies and
hydrogen chemisorptions. The designed graphene nanopetals display robust
ferromagnetism with large saturation magnetization of up to 2 emu/g at 5 K and
1.2 emu/g at room temperatures. This work identifies the plasma-enabled
graphene nanopetals as a promising candidate for graphene-based magnetic
devices.",1401.3060v1
2014-01-22,Disentangling defect-induced ferromagnetism in SiC,"We present a detailed investigation of the magnetic properties in SiC single
crystals bombarded with neon ions. Through careful measuring of the
magnetization of virgin and irradiated SiC, we decompose the magnetization of
SiC into paramagnetic, superparamagnetic, and ferromagnetic contributions. The
ferromagnetic contribution persists well above room temperature and exhibits a
pronounced magnetic anisotropy. We qualitatively explain the magnetic
properties as a result of the intrinsic clustering tendency of defects.",1401.5576v1
2014-04-08,Darboux Transformation and Exact Solutions of the integrable Heisenberg ferromagnetic equation with self-consistent potentials,"Integrable Heisenberg ferromagnetic equations are an important subclass of
integrable systems. The M-XCIX equation is one of a generalizations of the
Heisenberg ferromagnetic equation and are integrable. In this paper, the
Darboux transformation of the M-XCIX equation is constructed. Using the DT, a
1-soliton solution of the M-XCIX equation is presented.",1404.2270v2
2014-07-03,Imprinting skyrmions in thin films by ferromagnetic and superconducting templates,"Magnetic skyrmions are promising candidates as information carriers in a new
generation of memories. How to generate and stabilize skyrmions is essential
for their successful application to technology. Here we theoretically
demonstrate that arrays of skyrmions can be imprinted in ultrathin
ferromagnetic films in large numbers by bringing a magnetic nanostructured
template close to the film. Two kind of templates, allowed by present-day
nanotechnologies, are studied: arrays of ferromagnetic nanorods and
superconducting vortices. Skyrmions are generated when exposing magnetic films
to the template fields for short times and remain stable after removing the
template.",1407.0928v1
2014-08-05,Self-consistent model of spin accumulation magnetoresistance in ferromagnet-insulator-semiconductor tunnel junctions,"Spin accumulation in a paramagnetic semiconductor due to voltage-biased
current tunneling from a polarized ferromagnet is experimentally manifest as a
small additional spin-dependent resistance. We describe a rigorous model
incorporating the necessary self-consistency between electrochemical potential
splitting, spin-dependent injection current, and applied voltage that can be
used to simulate this so-called ""3T"" signal as a function of temperature,
doping, ferromagnet bulk spin polarization, tunnel barrier features and
conduction nonlinearity, and junction voltage bias.",1408.1003v2
2014-09-16,Tuning ferromagnetism at interfaces between insulating perovskite oxides,"We use density functional theory calculations to show that the LaAlO3|SrTiO3
interface between insulating perovskite oxides is borderline in satisfying the
Stoner criterion for itinerant ferromagnetism and explore other oxide
combinations with a view to satisfying it more amply. The larger lattice
parameter of an LaScO3|BaTiO3 interface is found to be less favorable than the
greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the
latter is predicted to exhibit robust magnetism with a larger saturation moment
and a higher Curie temperature. Our results provide support for a ""two phase""
picture of coexistent superconductivity and ferromagnetism.",1409.4554v1
2014-11-10,Magnon spectrum in ferromagnets with a skyrmion,"The analysis of the spin wave excitations in two-dimensional isotropic
Heisenberg ferromagnet is performed with a single skyrmion in the ground state.
We employ the ideas of semiclassical quantization method, duly modified for the
use of the lattice model and Maleyev-Dyson boson representation of spin
operators. The resulting Schr\""odinger equation for magnons describes the
dispersion and wave functions of spin-wave excitations with strictly
non-negative spectrum. In contrast to usual ferromagnet, we demonstrate the
existence of three zero modes, corresponding to conformal symmetries
spontaneously violated by the skyrmion configuration.",1411.2452v2
2014-12-19,"Erratum: Glassy Chimeras Could Be Blind to Quantum Speedup. . . [Phys. Rev. X 4, 021008 (2014)]","Erratum to Phys. Rev. X 4, 021008 (2014): The critical exponent associated
with the ferromagnetic susceptibility was computed incorrectly. Furthermore,
Ising ferromagnets on the Chimera topology have the same universality class as
two-dimensional Ising ferromagnets.",1412.6320v2
2014-12-21,Recovering of superconductivity in S/F bilayers under spin-dependent nonequilibrium quasiparticle distribution,"We study theoretically the influence of spin accumulation on
superconductivity in a superconductor/ferromagnet bilayer. It is well-known
that the superconductivity in S/F bilayers is suppressed by the proximity to a
ferromagnet. The spin accumulation by itself is also a depairing factor. But
here we show that creation of the spin accumulation on top of effective
exchange depairing, caused by the proximity to a ferromagnet, can lead to an
opposite result. The superconductivity can be partially recovered by
spin-dependent quasiparticle distribution. The systems with realistic
parameters are considered and the possible experimental setup is proposed.",1412.6846v1
2014-12-22,"Thickness dependent Curie temperature and power-law behavior of layering transitions in ferromagnetic classical and quantum thin films described by Ising, XY and Heisenberg models","Ferromagnetic-paramagnetic phase transitions in classical and quantum thin
films have been studied up to 50 mono-layers using effective field theory with
two-site cluster approximation. Variation of the Curie temperature as a
function of film thickness has been examined. The relative shift of the Curie
temperature from the corresponding bulk value has been investigated in terms of
the shift exponent $\lambda$. We have found that shift exponent $\lambda$
clearly depends on the strength of the ferromagnetic exchange coupling of the
surface. Moreover, we have not observed any significant difference between
classical and quantum exponents for a particular model.",1412.7189v1
2015-01-02,Non-quasiparticle states in a half-metallic ferromagnet with antiferromagnetic $s-d(f)$ interaction,"Non-quasiparticle (incoherent) states which play an important role in the
electronic structure of half-metallic ferromagnets (HMF) are investigated
consistently in the case of antiferromagnetic $s-d(f)$ exchange interaction.
Their appropriate description in the limit of strong correlations requires a
rearrangement of perturbation series in comparison with the usual Dyson
equation. This consideration provides a solution of the Kondo problem in the
HMF case and can be important for first-principle HMF calculations performed
earlier for ferromagnetic $s-d(f)$ interaction.",1501.00345v3
2015-01-24,Magnetic Coupling in Ferromagnetic Semiconductor GaMnAs/AlGaMnAs Bilayer Devices,"We carefully investigated the ferromagnetic coupling in the as-grown and
annealed ferromagnetic semiconductor GaMnAs/AlGaMnAs bilayer devices. We
observed that the magnetic interaction between the two layers strongly affects
the magnetoresistance of the GaMnAs layer with applying out of plane magnetic
field. After low temperature annealing, the magnetic easy axis of the AlGaMnAs
layer switches from out of plane into in-plane and the interlayer coupling
efficiency is reduced from up to 0.6 to less than 0.4. However, the magnetic
coupling penetration depth for the annealed device is twice that of the
as-grown bilayer device.",1501.05993v1
2015-02-12,Spin-current diode with a ferromagnetic semiconductor,"Diode is a key device in electronics: the charge current can flow through the
device under a forward bias, while almost no current flows under a reverse
bias. Here we propose a corresponding device in spintronics: the spin-current
diode, in which the forward spin current is large but the reversed one is
negligible. We show that the lead/ferromagnetic quantum dot/lead system and the
lead/ferromagnetic semiconductor/lead junction can work as spin-current diodes.
The spin-current diode, a low dissipation device, may have important
applications in spintronics, as the conventional charge-current diode does in
electronics.",1502.03599v1
2015-03-17,Disorder effect on magneto-transport on the surface of a topological insulator,"We study the magneto-transport properties on the disordered surface of a
topological insulator attached with a ferromagnet/ferromagnet junction. Since,
in the surface Dirac Hamiltonian, out-of-plane magnetization induces a mass
gap, while in-plane magnetization has a role of the effective vector potential,
the mechanism of magneto-transport is different between these two cases. The
former is similar to the conventional one in ferromagnetic metals, while the
latter is due to the shift of Fermi circles in momentum space. Our numerical
calculations show that the magnetoconductance in in-plane configuration is
robust against disorder compared to that in out-of-plane configuration.",1503.04953v2
2015-03-23,Spin-Orbit Torques in Two-Dimensional Rashba Ferromagnets,"Magnetization dynamics in single-domain ferromagnets can be triggered by
charge current if spin-orbit coupling is sufficiently strong. We apply
functional Keldysh theory to investigate Rashba spin-orbit torques in metallic
two-dimensional ferromagnets. A reactive, anti-damping-like spin-orbit torque
as well as a dissipative, field-like torque are calculated microscopically, to
the leading order in the spin-orbit interaction strength. By calculating the
first vertex correction we show that the intrinsic anti-damping-like torque
vanishes unless the scattering rates are spin-dependent.",1503.06872v2
2015-04-22,Fork stamping of pristine carbon nanotubes onto ferromagnetic contacts for spin-valve devices,"We present a fabrication scheme called 'fork stamping' optimized for the dry
transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic
contact electrodes fabricated by standard lithography. We demonstrate the
detailed recipes for a residue-free device fabrication and in-situ current
annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py)
contacts and report preliminary transport characterization and
magnetoresistance experiments at cryogenic temperatures. This scheme can
directly be used to implement more complex device structures, including
multiple gates or superconducting contacts.",1504.05693v1
2015-04-22,Controlled domain wall pinning in ferromagnetic nanowire by nanoparticles stray fields,"We report the results of experimental investigations of controlled domain
wall (DW) pinning in a ferromagnetic nanowire (NW) by stray fields of two
uniformly magnetized bistable ferromagnetic nanoparticles (NPs) placed on
either side of the NW and elongated parallel to the NW axis. We show by
magnetic force microscopy measurements that DW pinning strength essentially
depends on the orientation of the NP magnetic moments relative to the NW
magnetization and can reach 20 mT. We also performed micromagnetic simulations
confirming the influence of the magnetostatic interaction of the DW with the NP
stray fields on the pinning strength. The possible realization of logic cell
with switchable logic function is discussed.",1504.05784v1
2015-04-24,Universal coarsening dynamics of a quenched ferromagnetic spin-1 condensate,"We demonstrate that a quasi-two-dimensional spin-1 condensate quenched to a
ferromagnetic phase undergoes universal coarsening in its late time dynamics.
The quench can be implemented by a sudden change in the applied magnetic field
and, depending on the final value, the ferromagnetic phase has easy-axis
(Ising) or easy-plane (XY) symmetry, with different dynamical critical
exponents. Our results for the easy-plane phase reveal a fractal domain
structure and the crucial role of polar-core spin vortices in the coarsening
dynamics.",1504.06404v2
2015-09-08,Anomalous Hall effect driven by dipolar spin waves in uniform ferromagnets,"A new type of anomalous Hall effect is shown to arise from the interaction of
conduction electrons with dipolar spin waves in ferromagnets. This effect
exists even in homogeneous ferromagnets without relativistic spin-orbit
coupling. The leading contribution to the Hall conductivity is proportional to
the chiral spin correlation of dynamical spin textures and is physically
understood in terms of the skew scattering by dipolar magnons.",1509.02284v1
2015-09-11,Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide,"We investigate the micromechanical exfoliation and van der Waals (vdW)
assembly of ferromagnetic layered dichalcogenide Fe0.25TaS2. The vdW interlayer
coupling at the Fe-intercalated plane of Fe0.25TaS2 allows exfoliation of
flakes. A vdW junction between the cleaved crystal surfaces is constructed by
dry transfer method. We observe tunnel magnetoresistance in the resulting
junction under an external magnetic field applied perpendicular to the plane,
demonstrating spin-polarized tunneling between the ferromagnetic layered
material through the vdW junction.",1509.03525v1
2015-09-19,Spin torque and Nernst effects in Dzyaloshinskii-Moriya ferromagnets,"We predict that a temperature gradient can induce a magnon-mediated intrinsic
torque and a transverse spin current in systems with non-trivial magnon Berry
curvature. With the help of a microscopic linear response theory of
nonequilibrium magnon-mediated torques and spin currents we identify the
interband and intraband components that manifest in ferromagnets with
Dzyaloshinskii-Moriya interactions and magnetic textures. To illustrate and
assess the importance of such effects, we apply our theory to the
magnon-mediated spin Nernst and torque responses in a kagome lattice
ferromagnet.",1509.05847v3
2015-11-06,Dynamic Response in a Finite Size Composite Multiferroic Thin Film,"Composite multiferroics, heterostructures of ferromagnetic (FM) and
ferroelectric (FE) materials, are characterized by a remarkable magnetoelectric
effect at the interface. Previous work has supported the ferromagnetic
structure with magnetic spins and the ferroelectric with pseudospins which act
as electric dipoles in a microscopic model, coupled with a magnetoelectric
interaction [J. Appl. Phys. 118, 124109 (2015)]. In this work, by solving the
stochastic Landau-Lifshitz-Gilbert equation, the electric-field-induced
magnetization switching in a twisted boundary condition has been studied, and a
behavior of domain wall in the ferromagnetic structure is discussed.",1511.01982v2
2015-11-26,Spin textures and spin-wave excitations in doped Dirac-Weyl semimetals,"We study correlations and magnetic textures of localized spins, doped in
three-dimensional Dirac semimetals. An effective field theory for magnetic
moments is constructed by integrating out the fermionic degrees of freedom. The
spin correlation shows a strong anisotropy, originating from spin-momentum
locking of Dirac electrons, in addition to the conventional Heisenberg-like
ferromagnetic correlation. The anisotropic spin correlation allows
topologically nontrivial magnetic excitation textures such as a transient
hedgehog state, as well as the ferromagnetic ground state. The spin-wave
dispersion in ferromagnetic Weyl semimetal also becomes anisotropic, being less
dispersed perpendicular to the magnetization.",1511.08381v1
2016-02-24,Application of the Maximum relative Entropy method to the physics of ferromagnetic materials,"It is known that the Maximum relative Entropy (MrE) method can be used to
both update and approximate probability distributions functions in statistical
inference problems. In this manuscript, we apply the MrE method to infer
magnetic properties of ferromagnetic materials. In addition to comparing our
approach to more traditional methodologies based upon the Ising model and Mean
Field Theory, we also test the effectiveness of the MrE method on
conventionally unexplored ferromagnetic materials with defects.",1603.00068v2
2016-04-02,A Theoretical Prediction on the Intrinsic Half-Metallicity in the Surface-Oxygen-Passivated Cr2N MXene,"Two-dimensional Cr2N MXene as well as the surface-passivated Cr2NF2,
Cr2N(OH)2 and Cr2NO2 are investigated by using density functional theory. The
Cr2N is an anti-ferromagnetic metal. The F atom or OH group-passivation does
not change the anti-ferromagnetic characteristics. However, Cr2NO2 has a
ferromagnetic ground state, which is a half-metal. The half-metallicity of
Cr2NO2 is still robust when bias is applied to the nanometer sized device. The
half-metallicity is intrinsic and does not require atomically clean surfaces.
Therefore the stable surface-oxygen-passivated MXene is a good candidate for
spintronics.",1604.00510v2
2016-04-05,Strongly Spinor Ferromagnetic Bose Gases,"By studying the zero-temperature and nonzero-temperature phase diagrams of
the ferromagnetic spin-1 Bose-Hubbard model under an external magnetic field,
we find that the competition between ferromagnetism and the quadratic Zeeman
energy yields two superfluid phases, which feature discontinuous first-order
phase transitions between them for a strongly spinor Bose gas such as ${}^7$Li,
contrary to the corresponding continuum system.",1604.01163v4
2016-04-21,Model for multi-shot all-thermal all-optical switching in ferromagnets,"All optical magnetic switching (AOS) is a recently observed rich and puzzling
phenomenon that offers promis- ing technological applications. However,
fundamental understanding of the underlying mechanisms remains elusive. Here we
present a new model for multi-shot helicity-dependent AOS in ferromagnetic
materials based on a purely heat-driven mechanism in the presence of Magnetic
Circular Dichroism (MCD). We predict that AOS should be possible with as little
as 0.5% of MCD, after a minimum number of laser shots. Finally, we re- produce
previous AOS results by simulating the sweeping of a laser beam on an FePtC
granular ferromagnetic film.",1604.06441v1
2016-06-24,Current-Induced Instability of a Perpendicular Ferromagnet in Spin Hall Geometry,"We develop a theoretical formula of spin Hall torque in the presence of two
ferromagnets. While the direction of the conventional spin Hall torque always
points to the in-plane direction, the present system enables to manipulate the
torque direction acting on one magnetization by changing the direction of
another magnetization. Based on the diffusion equation of the spin accumulation
and the Landauer formula, we derive analytical formula of the spin Hall torque.
The present model provides a solution to switch a perpendicular ferromagnet
deterministically at zero field using the spin Hall effect.",1606.07540v1
2016-06-24,Stochastic modelling of thermal effects on a ferromagnetic nano particle,"In this work, we are interested in the behaviour of a single ferromagnetic
mono--domain particle submitted to an external field with a stochastic
perturbation. This model is a step toward the mathematical understanding of
thermal effects on ferromagnets. In a first part, we discuss modelling issues
and propose several ways to integrate a random noise in the deterministic
model. Then, among all these approaches, we focus on the more natural one and
study its long time behaviour. We prove that the system converges to the unique
stable equilibrium of the deterministic model and make precise the L^p rate of
the convergence. Finally, we illustrate the theoretical results by numerical
simulations.",1606.07708v1
2016-06-29,Damped Topological Magnons in the Kagomé-Lattice Ferromagnets,"We demonstrate that interactions can substantially undermine the
free-particle description of magnons in ferromagnets on geometrically
frustrated lattices. The anharmonic coupling, facilitated by the
Dzyaloshinskii-Moriya interaction, and a highly-degenerate two-magnon continuum
yield a strong, non-perturbative damping of the high-energy magnon modes. We
provide a detailed account of the effect for the $S=1/2$ ferromagnet on the
kagom\'e lattice and propose further experiments.",1606.09249v3
2016-07-13,Easy Axis orientation of Ferromagnetic Films as Described by Third Order Perturbed Heisenberg Hamiltonian,"The magnetic easy axis orientation was studied by the third order perturbed
Heisenberg Hamiltonian. Ferromagnetic CoPt/AlN multilayer thin films with
number of layers N=11, 16 and 21 synthesized on fused quartz substrates using
dc magnetron sputtering technique have been employed as experimental data.
According to experimental research performed by some other researchers, easy
axis of these fcc structured ferromagnetic films is oriented in the plane of
the film at one particular temperature. Average value of out of plane spin
component was plotted against temperature in order to determine the spin
reorientation temperature. The spin reorientation temperature was highly
sensitive to 2nd order magnetic anisotropy constant.",1607.03588v1
2016-09-13,Spin-dependent transport and current modulation in a current-in-plane field-effect transistor,"We propose a current-in-plane spin-valve field-effect transistor
(CIP-SV-FET), which is composed of a ferromagnet / nonferromagnet / ferromagnet
trilayer structure and a gate electrode. This is a promising device alternative
to spin metal-oxide-semiconductor field-effect transistors. Here, we fabricate
a ferromagnetic-semiconductor GaMnAs-based CIP-SV-FET and demonstrate its basic
operation of the resistance modulation both by the magnetization configuration
and by the gate electric field. Furthermore, we present the
electric-field-assisted magnetization reversal in this device.",1609.05859v1
2016-10-02,Study of the effect of nearest neighbors on ferromagnetic to paramagnetic phase transition in 2D lattices by Monte Carlo algorithm,"In this work we try to use the Monte Carlo algorithm, metropolis, to study
the behavior of 2D magnetic systems; honeycomb, hexagonal and square lattices.
In this study we use Ising Model of magnetism, with considering only nearest
neighbors in the Hamiltonian and with the Ferromagnetic correlation constant.
The code was written in Payton. In this calculation, by comparing the results
obtained for all lattices, we will show that the paramagnetic to ferromagnetic
phase transition depends on the number of neighbor and it is a direct
dependence.",1610.00359v2
2016-10-12,New p- and n-type ferromagnetic semiconductors: Cr-doped BaZn2As2,"We find new ferromagnetic semiconductors, Cr-doped BaZn2As2, by employing a
combined method of the density functional theory and the quantum Monte Carlo
simulation. Due to a narrow band gap of 0.2 eV in host BaZn2As2 and the
different hybridization of 3d orbitals of Cr impurity, the impurity bound
states have been induced both below the top of valence band and above the
bottom of conduction band. The long-range ferromagnetic coupling between Cr
impurities is obtained with both p- and n-type carriers.",1610.03578v1
2016-10-14,DC Magnetization study of Ni$_{1-x}$Rh$_x$ nanoalloy,"Ni$_{1-x}$Rh$_x$ bulk alloys exhibit a ferromagnetic to paramagnetic quantum
phase transition (QPT) at the critical concentration $x_c \sim$ 0.37. A spin
glass phase arises below the Ferromagnetism by controlling the short range
interaction between Ni and Rh atoms. we have synthesized nanoalloys of two
different concentrations with two different reaction times by chemical reflux
method. From the dc magnetization measurements, existence of ferromagnetism and
spin glass phase in these nanoalloys is confirmed. A step like feature in both
ZFC and FC curve at certain temperature indicates the existence of the spin
glass phase.",1610.04487v1
2017-03-04,Dynamics of domain walls in weak ferromagnets,"It is shown that the total set of equations, which determines the dynamics of
the domain bounds (DB) in a weak ferromagnet, has the same type of specific
solution as the well-known Walker's solution for ferromagnets. We calculated
the functional dependence of the velocity of the DB on the magnetic field,
which is described by the obtained solution. This function has a maximum at a
finite field and a section of the negative differential mobility of the DB.
According to the calculation, the maximum velocity $ c \approx 2 \times 10^6$
cm/sec in YFeO$_3$ is reached at $H_m \approx 4 \times 10^3$ Oe.",1703.01502v1
2017-03-10,A microscopic formulation of dynamical spin injection in ferromagnetic-nonmagnetic heterostructures,"We develop a microscopic formulation of dynamical spin injection in
heterostructure comprising nonmagnetic metals in contact with ferromagnets. The
spin pumping current is expressed in terms of Green's function of the
nonmagnetic metal attached to the ferromagnet where a precessing magnetization
is induced. The formulation allows for the inclusion of spin-orbit coupling and
disorder. The Green's functions involved in the expression for the current are
expressed in real-space lattice coordinates and can thus be efficiently
computed using recursive methods.",1703.03775v2
2018-04-04,Theoretical prediction of two-dimensional CrOF sheet as a ferromagnetic semiconductor or a half-metal,"Two-dimensional chromium oxide fluoride CrOF sheet was studied based on
density functional theory. The investigation indicates that the CrOF sheet is
an intrinsic ferromagnetic semiconductor. The calculated low cleavage energy
implies that the ferromagnetic semiconductor can be exfoliated from its bulk
form. The corresponding Curie temperature is 150 K. In particular, the Curie
temperature increases up to 410 K under hole doping and the CrOF sheet becomes
a half-metal. The versatile electronic and magnetic properties indicate that
the two-dimensional CrOF sheet can be a promising candidate for next-generation
spintronic devices.",1804.01621v1
2010-05-11,Dilatometric Study of LiHoF4 In a Transverse Magnetic Field,"Theoretical and experimental work have not provided a consistent picture of
the phase diagram of the nearly ideal Ising ferromagnet LiHoF4 in a transverse
magnetic field. Using a newly fabricated capacitive dilatometer, we have
investigated the thermal expansion and magnetostriction of LiHoF4 in magnetic
fields applied perpendicular to the Ising direction. Critical points for the
ferromagnetic phase transition have been determined from both methods in the
classical paramagnetic to ferromagnetic regime. Excellent agreement has been
found with existing experimental data suggesting that, in this regime, the
current theoretical calculations have not entirely captured the physics of this
interesting model system.",1005.1935v1
2013-08-16,Influence of ferromagnetic ordering on Raman scattering in CoS$_2$,"The effects of phonon anharmonicity, phonon-magnon and electron-phonon
interactions on the temperature dependence of Raman optical phonon modes are
theoretically investigated. Besides of the Klemens result for the phonon width
due to anharmonicity, the corresponding lineshift is derived. We argue that the
phonon decay into two magnons has very low intensity in ferromagnets with low
Curie temperatures. Therefore, the electron interband transitions accompanied
with the ferromagnetic ordering are included in considerations to get a good
quantitative agreement with experiments.",1308.3571v1
2014-03-19,Spin-orbit coupling effects on spin-dependent inelastic electronic lifetimes in ferromagnets,"For the 3d ferromagnets iron, cobalt and nickel we compute the spin-dependent
inelastic electronic lifetimes due to carrier-carrier Coulomb interaction
including spin-orbit coupling. We find that the spin-dependent
density-of-states at the Fermi energy does not, in general, determine the spin
dependence of the lifetimes because of the effective spin-flip transitions
allowed by the spin mixing. The majority and minority electron lifetimes
computed including spin-orbit coupling for these three 3-d ferromagnets do not
differ by more than a factor of 2, and agree with experimental results.",1403.4728v1
2014-03-25,Strong ferromagnetic-dielectric coupling in multiferroic Lu2CoMnO6 single crystals,"We have grown single crystals of multiferroic double-perovskite Lu2CoMnO6 and
studied the directional dependence of their magnetic and dielectric properties.
The ferromagnetic order emerges below TC ~ 48K along the crystallographic c
axis. Dielectric anomaly arises along the b axis at TC, contrary to the
polycrystalline work suggesting ferroelectricity along the c axis. Through the
strongly coupled ferromagnetic and dielectric states, the highly non-linear
variation of both dielectric constant and magnetization was achieved in
application of magnetic fields. This concurrent tunability provides an
efficient route to manipulation of multiple order parameters in multiferroics.",1403.6236v1
2016-11-03,New applications of the Lambert and generalized Lambert functions to ferromagnetism and quantum mechanics,"The applications of the recent results obtained in the theory of generalized
Lambert functions, to the mean field theory of ferromagnetism are presented. As
a consequence, all the predictions of the Weiss theory of ferromagnetism can be
explicitly and exactly formulated. In several quantum mechanical problems
involving delta function potentials, the solutions of the transcendental
eigenvalue equations are expressed in terms of two parameters generalized
Lambert functions. Some others, till unnoticed examples of eigenvalue equations
whose solutions can be written using the Lambert W function, are also
presented.",1611.01014v3
2016-11-15,Dipolar ordering and domains in crystals of Mn$_{12}$ Ac molecular magnets,"Dipolar coupling in crystals of the Mn$_{12}$Ac molecular magnet elongated
along the anisotropy axis favors ferromagnetic ordering below the mean-field
Curie temperature 0.71 K. With the help of Monte Carlo on crystals of up to one
million Mn$_{12}$ molecules, it is shown that ordering occurs at 0.36 K. The
resulting state is split into ferromagnetic domains with domain walls
preferring the diagonal orientation. Domain walls are pinned by the lattice at
low temperatures. Making the crystal shorter makes domains finer and smoothens
out the singularity at the transition, decreasing susceptibility in the domain
state. Hysteresis loops look ferromagnetic for prolate crystals and
antiferromagnetic for oblate crystals.",1611.04697v1
2016-11-26,Nagaoka's theorem in the Holstein-Hubbard model,"Nagaoka's theorem on ferromagnetism in the Hubbard model is extended to the
Holstein-Hubbard model. This shows that Nagaoka's ferromagnetism is stable even
if the electron-phonon interaction is taken into account. We also prove that
Nagaoka's ferromagnetism is stable under the influence of the quantized
radiation field.",1611.08659v4
2016-11-28,A new class of half-metallic ferromagnets from first principles,"Half-metallic ferromagnetism (HMFM) occurs rarely in materials and yet offers
great potential for spintronic devices. Recent experiments suggest a class of
compounds with the `ThCr$_{2}$Si$_{2}$' (122) structure -- isostructural and
containing elements common with Fe pnictide-based superconductors -- can
exhibit HMFM. Here we use $ab$ $initio$ density-functional theory calculations
to understand the onset of half-metallicity in this family of materials and
explain the appearance of ferromagnetism at a quantum critical point. We also
predict new candidate materials with HMFM and high Curie temperatures through
A-site alloying.",1611.09422v2
2017-04-11,Ferromagnetic and insulating behavior of LaCoO3 films grown on a (001) SrTiO3 substrate. A simple ionic picture explained ab initio,"This paper shows that the oxygen vacancies observed experimentally in thin
films of LaCoO3 subject to tensile strain are thermodynamically stable
according to ab initio calculations. By using DFT calculations, we show that
oxygen vacancies on the order of 6 % forming chains perpendicular to the (001)
direction are more stable than the stoichiometric solution. These lead to
magnetic Co2+ ions surrounding the vacancies that couple ferromagnetically. The
remaining Co3+ cations in an octahedral environment are non magnetic. The gap
leading to a ferromagnetic insulating phase occurs naturally and we provide a
simple ionic picture to explain the resulting electronic structure.",1704.03240v1
2017-04-24,Thermoelectric effects in superconductor-ferromagnet tunnel junctions on europium sulfide,"We report on large thermoelectric effects in superconductor-ferromagnet
tunnel junctions in proximity contact with the ferromagnetic insulator europium
sulfide. The combination of a spin-splitting field and spin-polarized tunnel
conductance in these systems breaks the electron-hole symmetry and leads to
spin-dependent thermoelectric currents. We show that the exchange splitting
induced by the europium sulfide boosts the thermoelectric effect in small
applied fields and can therefore eliminate the need to apply large magnetic
fields, which might otherwise impede applications in thermometry or cooling.",1704.07241v1
2018-05-09,Crossover of skyrmion and helical modulations in noncentrosymmetric ferromagnets,"The coupling between angular (twisting) and longitudinal modulations arising
near the ordering temperature of noncentrosymmetric ferromagnets strongly
influences the structure of skyrmion states and their evolution in an applied
magnetic field. In the precursor states of cubic helimagnets, a continuous
transformation of skyrmion lattices into the saturated state is replaced by the
first-order processes accompanied by the formation of multidomain states.
Recently the effects imposed by dominant longitudinal modulations have been
reported in bulk MnSi and FeGe. Similar phenomena can be observed in the
precursor regions of cubic helimagnet epilayers and in easy-plane chiral
ferromagnets (e.g. in the hexagonal helimagnet CrNb3S6).",1805.03360v1
2008-07-14,Numerical study of the frustrated ferromagnetic spin-1/2 chain,"The ground state phase diagram of the frustrated ferromagnetic spin-1/2 chain
is investigated using the exact diagonalization technique. It is shown that
there is a jump in the spontaneous magnetization and the ground state of the
system undergos to a phase transition from a ferromagnetic phase to a phase
with dimer ordering between next-nearest-neighbor spins. Near the quantum
transition point, the critical behavior of the ground state energy is analyzed
numerically. Using a practical finite-size scaling approach, the critical
exponent of the ground state energy is computed. Our numerical results are in
good agreement with the results obtained by other theoretical approaches.",0807.2094v2
2008-07-15,Magnetic properties of the insulating ferromagnetic phase in strained Pr_0.6Ca_0.4MnO_3 thin films,"Bulk magnetization in Pr_{0.6}Ca_{0.4}MnO_3 thin films with tensile (SrTiO_3)
and compressive (LaAlO_3) substrate-induced strain is compared to the
magnetooptical Kerr effect (MOKE) measurements. In the absence of an external
magnetic field, in both films, a stable ferromagnetic insulating majority phase
coexists with an antiferromagnetic insulating phase below ~120K. MOKE
measurements indicate that at 5K a metastable ferromagnetic metallic (FM) phase
is formed at the surface of the stretched film in a magnetic field below 1.1T
already, while in the bulk the FM phase starts to form in the field above ~4T
in both films.",0807.2312v1
2008-07-16,Nonsinusoidal current-phase relation in strongly ferromagnetic and moderately disordered SFS junctions,"We study the Josephson current in a junction comprising two superconductors
linked by a strong ferromagnet in presence of impurities. We focus on a regime
where the electron (and hole) motion is ballistic over the exchange length and
diffusive on the scale of the weak link length. The current-phase relation is
obtained for both two- and three dimensional ferromagnetic weak links. In the
clean limit, the possibility of temperature-induced 0- transitions is
demonstrated while the corresponding critical current versus temperature
dependences are also studied.",0807.2560v1
2008-07-17,Quasi-reversible Magnetoresistance in Exchange Spring Tunnel Junctions,"We report a large, quasi-reversible tunnel magnetoresistance in
exchange-biased ferromagnetic semiconductor tunnel junctions wherein a soft
ferromagnetic semiconductor (\gma) is exchange coupled to a hard ferromagnetic
metal (MnAs). Our observations are consistent with the formation of a region of
inhomogeneous magnetization (an ""exchange spring"") within the biased \gma
layer. The distinctive tunneling anisotropic magnetoresistance of \gma produces
a pronounced sensitivity of the magnetoresistance to the state of the exchange
spring.",0807.2885v1
2008-07-30,Mott Relation for Anomalous Hall and Nernst effects in Ga1-xMnxAs Ferromagnetic Semiconductors,"The Mott relation between the electrical and thermoelectric transport
coefficients normally holds for phenomena involving scattering. However, the
anomalous Hall effect (AHE) in ferromagnets may arise from intrinsic spin-orbit
interaction. In this work, we have simultaneously measured AHE and the
anomalous Nernst effect (ANE) in Ga1-xMnxAs ferromagnetic semiconductor films,
and observed an exceptionally large ANE at zero magnetic field. We further show
that AHE and ANE share a common origin and demonstrate the validity of the Mott
relation for the anomalous transport phenomena.",0807.4942v2
2009-12-29,Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite,"We report on unusual magnetic properties observed in the nanofluid
room-temperature ferromagnetic graphite (with an average particle size of
l=10nm). More precisely, the measured magnetization exhibits a low-temperature
anomaly (attributed to manifestation of finite size effects below the quantum
temperature) as well as pronounced temperature oscillations above T=50K
(attributed to manifestation of the hard-sphere type pair correlations between
ferromagnetic particles in the nanofluid).",0912.5350v1
2011-11-23,Rashba spin torque in an ultrathin ferromagnetic metal layer,"In a two-dimensional ferromagnetic metal layer lacking inversion symmetry,
the itinerant electrons mediate the interaction between the Rashba spin-orbit
interaction and the ferromagnetic order parameter, leading to a Rashba spin
torque exerted on the magnetization. Using Keldysh technique, in the presence
of both magnetism and a spin-orbit coupling, we derive a spin diffusion
equation that provides a coherent description to the diffusive spin dynamics.
The characteristics of the spin torque and its implication on magnetization
dynamics are discussed in the limits of large and weak spin-orbit coupling.",1111.5466v1
2012-01-04,Quantum Kinetic Theory of Current-Induced Torques in Rashba Ferromagnets,"Motivated by recent experimental studies of thin-film devices containing a
single ferromagnetic layer, we develop a quantum kinetic theory of
current-induced magnetic torques in Rashba-model ferromagnets. We find that
current-induced spin-densities that are responsible for the switching behavior
are due most essentially to spin-dependent quasiparticle lifetimes and derive
analytic expressions for relevant limits of a simple model. Quantitative model
parameter estimates suggest that spin-orbit coupling in the adjacent metal
normal magnetic layer plays an essential role in the strength of the switching
effect.",1201.0990v1
2012-04-09,Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles,"We investigated the reversible ferromagnetic (FM) behavior of pure and Co
doped CeO2 nanopowders. The as-sintered samples displayed an increasing
paramagnetic contribution upon Co doping. Room temperature FM is obtained
simply by performing thermal treatments in vacuum at temperatures as low as
500^{\circ}C and it can be switched off by performing thermal treatments in
oxidizing conditions. The FM contribution is enhanced as we increase the time
of the thermal treatment in vacuum. Those systematic experiments establish a
direct relation between ferromagnetism and oxygen vacancies and open a path for
developing materials with tailored properties.",1204.1959v1
2012-04-28,Nearly itinerant ferromagnetism in CaNi2 and CaNi3,"Single crystals of CaNi2 and CaNi3 were successfully grown out of excess Ca.
Both compounds manifest a metallic ground state with enhanced, temperature
dependent magnetic susceptibility. The relatively high Stoner factors of Z =
0.79 and Z = 0.87 found for CaNi2 and CaNi3, respectively, reveal their close
vicinity to ferromagnetic instabilities. The pronounced field dependence of the
magnetic susceptibility of CaNi3 at low temperatures (T < 25 K) suggests strong
ferromagnetic fluctuations. A corresponding contribution to the specific heat
with a temperature dependence of T^3lnT was also observed.",1204.6355v2
2014-05-30,Diffraction induced Spin Pumping in Normal-Metal/Multiferroic-Helimagnet/Ferromagnet Heterostructures,"Generally the adiabatic quantum pumping phenomenon can be interpreted by the
surface integral of the Berry curvature inside the cyclic loop. Spin angular
momentum flow without charge current can be pumped out by magnetization
precession in ferromagnet-based structures. When an electron is scattered by a
helimagnet, spin-dependent diffraction occurs due to the spatial modulation of
the spiral. In this work, we consider the charge and spin flow driven by
magnetization precession in normal-metal/multiferroic-helimagnet/ferromagnet
heterostructures. The pumping behavior is governed by the diffracted states.
Gauge dependence in the pumped current was encountered, which does not occur in
the static transport properties or pumping behaviors in other systems.",1405.7750v1
2014-06-22,Disorder dependence of the ferromagnetic quantum phase transition,"We quantitatively discuss the influence of quenched disorder on the
ferromagnetic quantum phase transition in metals, using a theory that describes
the coupling of the magnetization to gapless fermionic excitations. In clean
systems, the transition is first order below a tricritical temperature T_tc.
Quenched disorder is predicted to suppress T_tc until it vanishes for residual
resistivities rho_0 on the order of several microOhmcm for typical quantum
ferromagnets. We discuss experiments that allow to distinguish the mechanism
considered from other possible realizations of a first-order transition.",1406.5745v2
2015-12-02,Current driven domain wall creation in ferromagnetic nano-wires,"We predict the electrical generation and injection of domain walls into a
ferromagnetic nano-wire without the need of an assisting magnetic field. Our
theory shows that above a critical current $j_{c}$ domain walls are injected
into the nano-wire with a period $T\sim (j-j_{c})^{-1/2}$. In a uniaxial
anisotropy geometry this process does not require Dzyaloshinskii-Moria or
dipole-dipole interaction and can be done in a simple exchange ferromagnet. We
also show that this process and the period exponents are universal and do not
depend on the peculiarities of the microscopic Hamiltonian.",1512.00784v2
2015-12-16,Magnetism in Co$_{1-{\rm x}}$Fe$_{\rm x}$Sb$_{3}$ skutterudites from density functional theory,"We have investigated the electronic and magnetic properties of Co$_{1-{\rm
x}}$Fe$_{\rm x}$Sb$_{3}$ skutterudites from density functional theory and Monte
Carlo simulations. We find that above a certain threshold in the Fe
concentration, somewhere between x=0.125 and x=0.25, Co$_{1-{\rm x}}$Fe$_{\rm
x}$Sb$_{3}$ is ferromagnetic with an atomic moment which increases
asymptotically towards about 1 $\mu_{B}$/Fe and a non-zero Curie temperature
which reaches 70 K for FeSb$_{3}$. Ferromagnetism is favored due to a Stoner
instability in the electronic structure, where a large density of states at the
Fermi-level makes it favorable to form the ferromagnetic ground state.",1512.05124v1
2016-08-12,Magnetotransport signatures of the proximity exchange and spin-orbit couplings in graphene,"Graphene on an insulating ferromagnetic substrate---ferromagnetic insulator
or ferromagnetic metal with a tunnel barrier---is expected to exhibit giant
proximity exchange and spin-orbit couplings. We use a realistic transport model
of charge-disorder scattering and solve the linearized Boltzmann equation
numerically exactly for the anisotropic Fermi contours of modified Dirac
electrons to find magnetotransport signatures of these proximity effects:
proximity anisotropic magnetoresistance, inverse spin-galvanic effect, and the
planar Hall resistivity. We establish the corresponding anisotropies due to the
exchange and spin-orbit couplings, with respect to the magnetization
orientation. We also present parameter maps guiding towards optimal regimes for
observing transport magnetoanisotropies in proximity graphene.",1608.03879v1
2017-07-16,Indirect excitation of self-oscillation in perpendicular ferromagnet by spin Hall effect,"A possibility to excite a stable self-oscillation in a perpendicularly
magnetized ferromagnet by the spin Hall effect is investigated theoretically.
It had been shown that such self-oscillation cannot be stabilized solely by the
direct spin torque by the spin Hall effect. Here, we consider adding another
ferromagnet, referred to as pinned layer, on the free layer. The pinned layer
provides another spin torque through the reflection of the spin current. The
study shows that the stable self-oscillation is excited by the additional spin
torque when the magnetization in the pinned layer is tilted from the film
plane.",1707.04825v1
2017-10-02,Electrical resistivity across the tricriticality in itinerant ferromagnet,"We investigate the discontinuous ferromagnetic phase diagram near tricritical
point in UCo 1-x Ru x Al compounds by electrical resistivity measurements.
Separation of phases in UCo 0.995 Ru 0.005 Al at ambient pressure and in UCo
0.990 Ru 0.010 Al at pressure of 0.2 GPa and disappearance of ferromagnetism at
0.4 GPa is confirmed. The exponent of temperature dependence of electrical
resistivity implies change from Fermi liquid behavior to non-Fermi liquid at
0.2 GPa and reaches minimum at 0.4 GPa. Our results are compared to results
obtained on the pure UCoAl and explanation for different exponents is given.",1710.00860v1
2018-01-22,Ferromagnetic domain wall as a nonreciprocal string,"We present a simple model of a domain wall in a thin-film ferromagnet. A
domain wall is represented as a nonreciprocal string, on which transverse waves
propagate with different speeds in opposite directions. The model has three
parameters: mass density, tension, and a gyroscopic constant quantifying the
nonreciprocity. We discuss the unusual dynamics of a nonreciprocal string in
finite geometry. It agrees well with numerically simulated motion of a
ferromagnetic domain wall in a strip of constant width.",1801.07166v4
2018-10-25,Hyperfine interaction in cobalt by high-resolution neutron spectroscopy,"We have investigated the ferromagnetic phase transition of elemental Co by
high-resolution neutron backscattering spectroscopy. We monitored the splitting
of the nuclear levels by the hyperfine field at the Co nucleus. The energy of
this hyperfine splitting is identified as the order parameter of the
ferromagnetic phase transition. By measuring the temperature dependence of the
energy we determined the critical exponent $\beta = 0.350 \pm 0.002$ and the
ferromagnetic Curie temperature of $T_{\text{C}} = 1400$~K. The present result
of the critical exponent agrees better with the predicted value (0.367) of the
3-dimensional Heisenberg model than that determined previously by NMR.",1810.10906v1
2019-06-23,Quantum Ferromagnetic Transition in Clean Dirac Metals,"The ferromagnetic quantum phase transition in clean metals with a negligible
spin-orbit interaction is known to be first order due to a coupling of the
magnetization to soft fermionic particle-hole excitations. A spin-orbit
interaction gives these excitations a mass, suggesting the existence of a
ferromagnetic quantum critical point in metals with a strong spin-orbit
interaction. We show that this expectation is not borne out in a large class of
materials with a Dirac spectrum, since the chirality degree of freedom leads to
new soft modes that again render the transition first order.",1906.09605v1
2019-07-19,Nonlocal thermoelectric effects in high-field superconductor-ferromagnet hybrid structures,"We report on the experimental observation of nonlocal spin-dependent
thermoelectric effects in superconductor-ferromagnet multiterminal structures.
Our samples consist of a thin superconducting aluminum wire with several
ferromagnetic tunnel junctions attached to it. When a thermal excitation is
applied to one of the junctions in the presence of a Zeeman splitting of the
density of states of the superconductor, a thermoelectric current is observed
in remote junctions at distances exceeding $10~\mathrm{\mu m}$. The results can
be explained by recent theories of coupled spin and heat transport in
high-field superconductors.",1907.08441v1
2019-09-06,Families of magnetic semiconductors -- an overview,"The interplay of magnetic and semiconducting properties has been in the focus
since more than a half of the century. In this introductory article we briefly
review the key properties and functionalities of various magnetic semiconductor
families, including europium chalcogenides, chromium spinels, dilute magnetic
semiconductors, dilute ferromagnetic semiconductors and insulators, mentioning
also sources of non-uniformities in the magnetization distribution, accounting
for an apparent high Curie temperature ferromagnetism in many systems. Our
survey is carried out from today's perspective of ferromagnetic and
antiferromagnetic spintronics as well as of the emerging fields of magnetic
topological materials and atomically thin 2D layers.",1909.02999v1
2019-09-11,Quantum statistics of vortices from a dual theory of the XY ferromagnet,"We extend the well-known mapping between the easy-plane ferromagnet and
electrostatics in $d=2$ spatial dimensions to dynamical and quantum phenomena
in a $d=2+1$ spacetime. Ferromagnetic vortices behave like quantum particles
with an electric charge equal to the vortex number and a magnetic flux equal to
the transverse spin of the vortex core. Vortices with half-integer core spin
exhibit fermionic statistics.",1909.05248v3
2019-10-17,Spin-dependent electronic lenses based on hybrid graphene nanostructures,"We study electronic transport in graphene/ferromagnetic insulator hybrid
devices. The system comprises an armchair graphene nanoribbon with a
lens-shaped EuO ferromagnetic insulator layer deposited on top of it. When the
device supports a large number of propagating modes, the proximity exchange
interaction of electrons with the magnetic ions of the ferromagnetic insulator
results in electrons being spatially localised at different spots depending on
their spin. We found the spin-dependent electron focusing is robust under
moderate edge disorder. A spin-polarised electric current can be generated by
placing a third contact in the proper place. This opens the possibility to use
these effects for fabricating tunable sources of polarized electrons.",1910.07828v1
2019-10-23,Mechanism of ferromagnetic ordering of the Mn chains in CaMnGe$_2$O$_6$ clinopyroxene,"The electronic and magnetic properties of clinopyroxene CaMnGe$_2$O$_6$ were
studied using density function calculations within the GGA+U approximation. It
is shown that anomalous ferromagnetic ordering of neighboring chains is due to
a ""common-enemy"" mechanism. Two antiferromagnetic exchange couplings between
nearest neighbours within the Mn-Mn chain and interchain coupling via two
GeO$_4$ tetrahedra suppress antiferromagnetic exchange via single GeO$_4$
tetrahedron and stabilize ferromagnetic ordering of Mn chains.",1910.10530v1
2019-10-23,Effect of Demagnetization Method on Remnance Magnetization States in Metallic Ferromagnets,"Parametric plots of the remagnetization versus demagnetization remnances were
found for four metallic ferromagnets -- nickel wire, two types of AlNiCo, and
samarium cobalt 2:17. These plots, known as Henkel plots, were compared to
Wohlfarth's model for noninteracting magnetic particles and several Preisach
models. The remagnetization data were taken with a variety of paths to the net
zero magnetization state. The resulting Henkel plots exhibit similarities to
independent Monte Carlo simulations. The differences can be mostly explained by
considering that the magnetization in the metallic ferromagnets occur by domain
wall motion.",1910.10648v1
2020-01-10,Long-Range Phonon Spin Transport in Ferromagnet-Nonmagnetic Insulator Heterostructures,"We investigate phonon spin transport in an insulating
ferromagnet-nonmagnet-ferromagnet heterostructure. We show that the
magnetoelastic interaction between the spins and the phonons leads to nonlocal
spin transfer between the magnets. This transfer is mediated by a local phonon
spin current and accompanied by a phonon spin accumulation. The spin
conductance depends nontrivially on the system size, and decays over millimeter
length scales for realistic material parameters, far exceeding the decay
lengths of magnonic spin currents.",2001.03462v2
2020-04-16,An extension of the cell-construction method for the flat-band ferromagnetism,"We present an extension of the cell-construction method for the flat-band
ferromagnetism. In a rather general setting, we construct Hubbard models with
highly degenerate single-electron ground states and obtain a formal
representation of these single-electron ground states. By our version of the
cell-construction method, various types of flat-band Hubbard models, including
the one on line graphs, can be designed and shown to have the unique
ferromagnetic ground states when the electron number is equal to the degeneracy
of the single-electron ground states.",2004.07516v2
2020-12-02,Piezomagnetism in ferromagnetic superconductors,"The appearance of magnetization during the application of mechanical stress
and the creation of elastic deformation during the application of a magnetic
field are two fundamental properties of piezomagnetic materials. The symmetry
of superconducting ferromagnets UGe_2, URhGe, UCoGe allows piezomagnetism. In
addition to conventional piezomagnetic properties occurring in both normal and
superconducting states, superconducting state of these piezomagnets has its own
specificity. Unlike conventional superconductors, in uranium ferromagnets, the
critical transition temperature to the superconducting state changes its value
when the direction of the field changes to the opposite.",2012.01207v2
2000-06-09,Strongly reduced gap in the zigzag spin chain with a ferromagnetic interchain coupling,"We study a spin 1/2 Heisenberg zigzag spin chain model near decoupled two
chains. Taking into account a symmetry breaking perturbation, we discuss the
existence of an energy gap in the ferromagnetic interchain coupling as well as
the antiferromagnetic one. In the ferromagnetic model, a marginally relevant
fixed line reduces the gap strongly, so that the correlation length becomes an
astronomical length scale even in order 1 coupling. This result agrees with
density matrix renormalization group results.",0006155v3
2000-06-10,Spin-transport in multi-terminal normal metal - ferromagnet systems with non-collinear magnetizations,"A theory of spin-transport in hybrid normal metal - ferromagnetic electronic
circuits is developed, taking into account non-collinear spin-accumulation.
Spin-transport through resistive elements is described by 4 conductance
parameters. Microscopic expression for these conductances are derived in terms
of scattering matrices and explicitly calculated for simple models. The circuit
theory is applied to 2-terminal and 3-terminal devices attached to
ferromagnetic reservoirs.",0006174v2
2017-05-04,Reduced models for ferromagnetic thin films with periodic surface roughness,"We investigate the influence of periodic surface roughness in thin
ferromagnetic films on shape anisotropy and magnetization behavior inside the
ferromagnet. Starting from the full micromagnetic energy and using methods of
homogenization and $\Gamma$-convergence we derive a two dimensional local
reduced model. Investigation of this model provides an insight on the formation
mechanism of {\it perpendicular magnetic anisotropy} and uniaxial anisotropy
with an {\it arbitrary} preferred direction of magnetization.",1705.01742v1
2017-09-08,Room temperature ferromagnetism in transparent and conducting Mn-doped $SnO_{2}$ thin films,"The magnetization as a function of magnetic field showed hysteretic behavior
at room temperature. According to the temperature dependence of the
magnetization, the Curie temperature $(T_{C})$ is higher than 350 K.
Ferromagnetic Mn-doped tin oxide thin films exhibited low electrical
resistivity and high optical transmittance in the visible region (400-800 nm).
The coexistence of ferromagnetism, high visible transparency and high
electrical conductivity in the Mn-doped $SnO_{2}$ films is expected to be a
desirable trait for spintronics devices.",1709.05930v1
2018-03-28,Quasi-one-dimensional Bose-Einstein Condensation in the Spin-1/2 Ferromagnetic-leg Ladder 3-I-V,"Quantum criticality of the spin-1/2 ferromagnetic-leg ladder 3-I-V
[=3-(3-iodophenyl)-1,5-diphenylverdazyl] has been examined with respect to the
antiferromagnetic to paramagnetic phase transition near the saturation field
$H_{c}$. The phase boundary $T_{c}(H)$ follows the power-law $T_{c}(H)\propto
H_{c}-H$ for a wide temperature range. This characteristic behavior is
discussed as a quasi-one-dimensional (quasi-1D) Bose-Einstein condensation,
which is predicted theoretically for weakly coupled quasi-1D ferromagnets.
Thus, 3-I-V provides the first promising candidate for this attractive
prediction.",1803.10388v1
2018-08-13,Mechanism for transitions between ferromagnetic and antiferromagnetic orders in $d$-electron metallic magnets,"We propose mechanism for pressure-induced transitions between ferromagnetic
and antiferromagnetic phases that relies on a competition between
characteristic energy scales ubiquitous among $d$-electron metallic magnetic
compounds. Principles behind the mechanism are demonstrated on the example of
the minimal two-orbital $p$-$d$ lattice model. We suggest that LaCrGe$_3$,
where pressure-induced ferromagnetic-to-antiferromagnetic phase transition has
been recently observed, is a promising candidate to realize discussed
mechanism.",1808.04109v3
2019-08-07,Robust magnetotransport in disordered ferromagnetic kagome layers with quantum anomalous Hall effect,"The magnetotransport properties of disordered ferromagnetic kagome layers are
investigated numerically. We show that a large domain-wall magnetoresistance or
negative magnetoresistance can be realized in kagome layered materials (e.g.
Fe$_3$Sn$_2$, Co$_3$Sn$_2$S$_2$, and Mn$_3$Sn), which show the quantum
anomalous Hall effect. The kagome layers show a strong magnetic anisotropy and
a large magnetoresistance depending on their magnetic texture. These
domain-wall magnetoresistances are expected to be robust against disorder and
observed irrespective of the domain-wall thickness, in contrast to conventional
domain-wall magnetoresistance in ferromagnetic metals.",1908.02727v2
2019-11-06,Ferromagnetic Quantum Critical Point in Non-Centrosymmetric Systems,"Ferromagnetic quantum criticality in clean metals has proven elusive due to
fermionic soft modes that drive the transition first order. We show that
non-centrosymmetric metals with a strong spin-orbit interaction provide a
promising class of materials for realizing a ferromagnetic quantum critical
point in clean systems. The spin-orbit interaction renders massive the soft
modes that interfere with quantum criticality in most materials, while the
absence of spatial inversion symmetry precludes the existence of new classes of
soft modes that could have the same effect.",1911.02649v2
2019-12-03,Ferromagnetic phase in graphene-based planar heterostructures induced by charged impurity,"The spontaneous self-consistent generation of axial current and corresponding
dipole-like magnetic field in a planar electron-positron system similar to
graphene and related hetero-structures doped by charged impurity with charge
$Z$ is explored. It is shown that this effect takes place for $Z \geq Z^{\ast}$
with $Z^{\ast}$ being a peculiar analogue of the Curie point in ferromagnetics.
The properties of induced ferromagnetic state are studied in detail. It is
shown also that the arising this way magnetic dipole leads to a significant
decrease of the total Casimir (vacuum) energy of the system, which in turn
provides its spontaneous generation above the ""Curie point"" $Z \geq Z^{\ast}$.",1912.01696v1
2019-12-10,Ferromagnetically ordered metal in the single-band Hubbard model,"We study a ferromagnetic instability in a single-band Hubbard model on the
hypercubic lattice away from half filling. Using dynamical mean-field theory
with the continuous-time quantum Monte Carlo simulations based on the segment
algorithm, we calculate the magnetic susceptibility in the weak and strong
coupling regions systematically. We then find how ferromagnetic fluctuations
are enhanced when the interaction strength and density of holes are varied. The
efficiency of the double flip updates in the Monte Carlo simulations is also
addressed.",1912.05053v1
2019-12-11,Magnetic polaron and antiferro-ferromagnetic transition in doped bilayer CrI$_3$,"Gate-induced magnetic switching in bilayer CrI$_3$ has opened new ways for
the design of novel low-power magnetic memories based on van der Waals
heterostructures. The proposed switching mechanism seems to be fully dominated
by electrostatic doping. Here we explain, by first-principle calculations, the
ferromagnetic transition in doped bilayer CrI$_3$. For the case of a very small
electron doping, our calculations predict the formation of magnetic polarons
(""ferrons"", ""fluctuons"") where the electron is self-locked in a ferromagnetic
droplet in an antiferromagnetic insulating matrix. The self-trapping of holes
is impossible, at least, within our approximation.",1912.05280v1
2020-03-19,Symplectic ferromagnetism and phase transitions in multi-component fermionic systems,"In this paper, we study the itinerant ferromagnetic phase in multi-component
fermionic systems with symplectic (Sp(4), or isomorphically SO(5)) symmetry.
Two different microscopic models have been considered and an effective field
theory has been proposed to study the critical behavior of the
nonmagnetism-magnetism phase transition. It has been shown that such systems
exhibit intriguing ferromagnetism and critical behavior that different from
those in spin-$\frac 12$ fermionic systems, or in high-spin systems with SU(N)
symmetry. An extension of our results to higher spin systems with Sp(2N)
symmetry has also been discussed.",2003.08566v1
2020-09-02,Skyrmion-antiskyrmion droplets in a chiral ferromagnet,"We find numerically skyrmionic textures with skyrmion number Q=0 in
ferromagnets with the Dzyaloshinskii-Moriya interaction and perpendicular
anisotropy. These have the form of a skyrmion-antiskyrmion pair and may be
called chiral droplets. They are stable in an infinite film as well as in
disc-shaped magnetic elements. Droplets are found for values of the parameters
close to the transition from the ferromagnetic to the spiral phase. We study
their motion under spin-transfer torque. They move in the direction of the spin
flow and, thus, their dynamics are drastically different than the Hall dynamics
of the standard Q=0 skyrmion.",2009.00890v1
2020-10-05,Localized excitations and scattering of spin waves in ferromagnetic chains containing magnetic nanoclusters,"The spectrum of localized excitations in an anisotropic one-dimensional
ferromagnet containing a spin cluster of arbitrary size is found exactly within
the framework of the discrete Takeno-Homma model. The boundaries of stability
of spin nanoclusters are determined, depending on their size, and the exchange
and the anisotropy parameter of the ferromagnet. The problem of the spin waves
scattering against nanoclusters is solved and explicit analytical expressions
for their reflection and transmission coefficients are obtained. A model of a
metamaterial consisting of weakly interacting magnetic molecular nanoclusters
and possessing revealed dynamic properties is proposed.",2010.01861v1
2020-11-26,Multicomponent Nonlinear Evolution Equations of the Heisenberg Ferromagnet Type. Local versus Nonlocal Reductions,"The paper is dedicated to a system of matrix nonlinear evolution equations
related to a Hermitian symmetric space of the type $\mathbf{A.III}$. The system
under consideration extends the $1+1$ dimensional Heisenberg ferromagnet
equation in the sense that its Lax pair has a form rather similar to the pair
of the original Heisenberg ferromagnet model. We shall present here certain
local and nonlocal reductions. A local integrable deformation and some of its
reductions will be discussed too.",2011.13437v1
2021-03-29,Hydrodynamic model of skyrmions and vorticities in the spin-1 Bose-Einstein condensate in ferromagnetic phase at finite temperatures,"Quantum hydrodynamic of skyrmions in spinor ultracold bosons at the finite
temperature is described. The limit regime of BEC appearing at the zero
temperature is discussed either. The skyrmions are found as the solution of the
spin evolution equation for the ferromagnetic phase of spin-1 ultracold bosons.
It is demonstrated that the quantum part of the spin current gives major
contribution in the formation of the skyrmions. The interplay between the
quantum (spin) vorticity and the classic vorticity is considered for the finite
temperatures. Bosons are presented as two fluids associated with the
Bose-Einstein condensate and the normal fluid. All effects are considered for
the ferromagnetic phase.",2103.15930v1
2021-03-31,Spin charge conversion in Rashba split ferromagnetic interfaces,"We show here theoretically and experimentally that a Rashba-split electron
state inside a ferromagnet can efficiently convert a dynamical spin
accumulation into an electrical voltage. The effect is understood to stem from
the Rashba splitting but with a symmetry linked to the magnetization direction.
It is experimentally measured by spin pumping in a CoFeB/MgO structure where it
is found to be as efficient as the inverse spin Hall effect at play when Pt
replaces MgO, with the extra advantage of not affecting the damping in the
ferromagnet.",2103.16867v1
2021-04-08,Ferromagnetism in a Semiconductor with Mobile Carriers via Low-Level Nonmagnetic Doping,"We show that doped cubic iron pyrite, which is a diamagnetic semiconductor,
becomes ferromagnetic when $p$-type doped. We furthermore find that this
material can exhibit high spin polarization both for tunneling and transport
devices. These results are based on first principles electronic structure and
transport calculations. This illustrates the use of $p$-type doping without
magnetic impurities as a strategy for obtaining ferromagnetic semiconducting
behavior, with implications for spintronic applications that require both
magnetic ordering and good mobility. This is a combination that has been
difficult to achieve by doping semiconductors with magnetic impurities. We show
that phosphorus and arsenic may be effective dopants for achieving this
behavior.",2104.03877v1
2021-07-07,Fluctuation theorem for spin transport at insulating ferromagnetic junctions,"General relations for nonequilibrium spin transport at a magnetic junction
between a normal metal and a ferromagnetic insulator are derived from the
quantum fluctuation theorem. They include the extended Onsager relations
between the spin conductance and the spin-current noise that hold for
nonequilibrium states driven by an external current. These relations, that are
valid for a general setup of spin Hall magnetoresistance, provide a
comprehensive viewpoint for understanding of unidirectional spin Hall
magnetoresistance in insulating ferromagnetic junctions.",2107.03001v3
2021-09-15,Nanograin ferromagnets from non-magnetic bulk materials: the case of gold nanoclusters,"The ferromagnetism of Au nanograins is analysed based on a two-dimensional
itinerant lattice model with on-site Coulomb repulsion, many-body spin-orbit
interactions, and holding two hybridized bands, one correlated and one
uncorrelated. Using periodic boundary conditions in both directions, an exact
ferromagnetic ground state is deduced for this non-integrable system by
applying special techniques based on positive semidefinite operators.",2109.07297v1
2021-10-15,A micromagnetic theory of skyrmion lifetime in ultrathin ferromagnetic films,"We use the continuum micromagnetic framework to derive the formulas for
compact skyrmion lifetime due to thermal noise in ultrathin ferromagnetic films
with relatively weak interfacial Dzyaloshinskii-Moriya interaction. In the
absence of a saddle point connecting the skyrmion solution to the ferromagnetic
state, we interpret the skyrmion collapse event as ``capture by an absorber''
at microscale. This yields an explicit Arrhenius collapse rate with both the
barrier height and the prefactor as functions of all the material parameters,
as well as the dynamical paths to collapse.",2110.08107v1
2021-12-29,Spin Wave Propagation through Antiferromagnet/Ferromagnet Interface,"We study the problem of controlling spin waves propagation through an
antiferromagnet/ferromagnet interface via tuning material parameters. It is
done by introducing the degree of sublattice noncompensation of antiferromagnet
(DSNA), which is a physical characteristic of finite-thickness interfaces. The
DSNA value can be varied by designing interfaces with a particular disorder or
curvilinear geometry. We describe a spin-wave propagation through any designed
antiferromagnet/ferromagnet interface considering a variable DSNA and
appropriate boundary conditions. As a result, we calculate the physical
transmittance and reflectance of the spin waves as a function of frequency and
show how to control them via the exchange parameters tuning.",2112.14583v1
2021-12-31,Searching for new ferromagnetism precursors in two-dimensional model materials in frame of local force theorem,"In this work we conduct a numerical search of non-trivial mechanisms, leading
to new tendencies towards long-range ferromagnetic ordering in two-dimensional
materials. For this purpose we employ an original variant of pairwise
infinitesimal spin rotations technique to establish the magnetic transition
temperature as the rigid function of basic crystal's parameters. It favored the
numerical optimization of this function using modified genetic algorithm,
designed to harvest local extrema. It resulted in revealing the moderate
metallicity, accompanied by essential orbital anisotropy, as the prime
configuration, which provides the most favoring conditions to ferromagnetic
ordering, related to double-exchange and superexchange mechanisms.",2112.15374v1
2022-01-17,Perpendicularly Polarized Spin Hall Effects Induced by Spin-Dependent Scattering in Ferromagnetic Metals,"Spin currents in ferromagnets afford diverse functionalities. We evaluate the
extrinsic spin Hall effects of magnetic impurity scattering in ferromagnetic
metals. We show that spin-dependent scattering can provide a high spin current
polarized perpendicularly to the magnetization direction and is a dominant
mechanism in the moderate-conductivity regime. We find that the superposition
of the spin-conserve and spin-flip channels causes the spin currents. These
findings suggest that optimizing alloy composition is an effective strategy to
control the spin Hall effect.",2201.06222v2
2022-01-27,Temperature Dependence of Magnetocrystalline Anisotropy in Itinerant Ferromagnets,"We theoretically investigated magnetocrystalline anisotropy (MA) at a finite
temperature $T$ in ferromagnetic metals. Assuming a Rashba-type ferromagnet
with uniaxial MA, we defined the MA constants $K_\mathrm{u}(T)$ derived from
several different concepts. Our purpose was to examine the equality between
them and to confirm a power law between $K_\mathrm{u}(T)$ and magnetization
$M(T)$ in the form of $K_\mathrm{u}(T)/K_\mathrm{u}(0)=[M(T)/M(0)]^\alpha$. We
demonstrate that $\alpha$ equals 2 in the itinerant-electron limit and
increases with the localized feature of electrons passing through $\alpha=3$,
predicted for the single-ion MA in spin models.",2201.11269v1
2022-04-19,On multi-soliton solutions to the Heisenberg ferromagnetic spin chain equation in (2+1)-dimensions,"This paper concentrates on the Heisenberg ferromagnetic spin chain (HFSC)
equation in (2+1)-dimensions modelling nonlinear wave propagation in
ferromagnetic spin chain. A variable transformation is first employed to reduce
the studied equation. And then an associated matrix Riemann-Hilbert problem is
built on the real line through analyzing spectral problem of the reduced
equation. As a consequence, solving the obtained matrix Riemann-Hilbert problem
with the identity jump matrix, corresponding to the reflectionless, the general
multi-soliton solutions to the HFSC equation in (2+1)-dimensions are acquired.
Specially, the one- and two-soliton solutions are worked out and analyzed
graphically.",2204.08679v1
2022-05-14,Magnetization Plateau of the Distorted Diamond Spin Chain with Anisotropic Ferromagnetic Interaction,"The $S=1/2$ distorted diamond spin chain with the anisotropic ferromagnetic
interaction is investigated using the numerical diagonalization and the level
spectroscopy analysis. It is known that the system exhibits a plateau of the
magnetization curve at the 1/3 of the saturation. The present study indicates
that as the anisotropy is varied the quantum phase transition occurs between
two different mechanisms of the 1/3 magnetization plateau. The phase diagram
with respect to the anisotropy and the ferromagnetic coupling is also
presented.",2205.07027v1
2022-08-16,Magnetocaloric effect in multilayers studied by membrane-based calorimetry,"We study magnetic multilayers, incorporating dilute ferromagnetic spacers
between strongly-ferromagnetic layers exhibiting a proximity-enhanced
magnetocaloric effect. Using magnetometry and direct measurements of the
adiabatic temperature change based on a nanomembrane-calorimetry, we find that
the magnetocaloric effect in the studied multilayer is indeed enhanced compared
to that in the bulk spacer material. We develop a phenomenological numerical
model of the studied trilayer and find that a long-range exchange interaction
through the weakly-ferromagnetic spacer is required to adequately describe the
magnetic and magnetocaloric properties of the system.",2208.07761v1
2022-10-11,Intrinsic localized modes in a two-dimensional checkerboard ferromagnetic lattice,"An analytical work on intrinsic localized modes in a two-dimensional
Heisenberg ferromagnet on the checkerboard lattice is presented. Taking
advantage of an asymptotic method, the governing lattice dynamical equations
are reduced to one (2+1) -dimensional nonlinear Schr\""odinger. In our work, we
obtain two types of nonlinear localized mode solutions, namely, Brillouin zone
center modes and Brillouin zone corner modes. The occurrence conditions for
these intrinsic localized modes are given in detail. Especially, we find that
the competition between the Dzialozinskii-Moriy interaction and the
next-nearest neighbor interaction of the checkerboard ferromagnet has an effect
on the local structure of the Brillouin zone corner acoustic mode.",2210.05585v1
2023-01-03,Amplitude representation of Landau-Lifshitz equation and its application to ferromagnetic films,"The purpose of this article is to develop a systematic approach to the
solution of the Landau-Lifshitz equation in terms of the magnon wave function
{\psi} (r) and apply it to physical phenomena in a thin ferromagnetic film.
This article has also a purpose to represent the modern state of art for the
properties of ferromagnetic films and the pumping-induced Bose-Einstein
condensation of magnons in them at room temperature. Thus, it can be considered
as a review on basic principles and the recent advances in the field.",2301.01391v1
2023-01-19,Interfacial Magnon-Mediated Superconductivity in Twisted Bilayer Graphene,"The interfacial coupling between electrons and magnons in adjacent layers can
mediate an attractive electron-electron interaction and induce
superconductivity. We consider magic-angle twisted bilayer graphene sandwiched
between two ferromagnetic insulators to optimize this effect. As a result,
magnons induce an interlayer superconducting state characterized by $p$-wave
symmetry. We investigate two candidate ferromagnets. The van der Waals
ferromagnet CrI$_3$ stands out because it allows compression to tune the
superconducting state with an exponential sensitivity. This control adds a new
dimension to the tunability of twisted bilayer graphene. Our results open a new
path for exploring magnon-induced superconductivity.",2301.07909v1
2023-03-11,The electronic structure of intrinsic magnetic topological insulator MnBi2Te4 quantum wires,"The ferromagnetic and antiferromagnetic nanostructure are crucial for
fundamental spintronics devices, motivated by its potential application in
spintronics, we theoretically investigate the electronic structure of the
ferromagnetic and antiferromagnetic phases of the cylindrical intrinsically
magnetic topological insulator $\mathrm{MnBi_{2}Te_{4}}$ quantum wires for both
cases. We demonstrate that a few surface states exist between the bulk band gap
in the ferromagnetic phase, with only one spin branch. In the antiferromagnetic
phase, we show that three coexistent states exist between the energy gaps of
the quantum wires.",2303.06303v1
2023-03-31,Stable magnetic levitation of soft ferromagnets for macroscopic quantum mechanics,"We propose a system for passive magnetic levitation and three-dimensional
harmonic trapping of soft ferromagnets. Our protocol utilizes the magnetic
field gradient for vertical trapping, and the finite size effect of the
Meissner effect for horizontal trapping. We provide numerical and analytical
estimations of possible mechanical dissipations to show that our system allows
high mechanical Q-factors above $ Q > 10^8 $, and quantum control of the
levitated object is within reach of current technologies. The utilization of
soft ferromagnet's internal collective spin excitation may allow quantum
mechanical phenomena with particles as large as the sub-millimeter-scale.",2303.17847v2
2023-04-08,Integral Absorption of Microwave Power by Random-Anisotropy Magnets,"We study analytically and numerically on lattices containing $10^5$ spins,
the integral absorption of microwaves by a random-anisotropy magnet, $\int
d\omega P(\omega)$. It scales as $D^2_R/J$ on the random-anisotropy strength
$D_R$ and the strength of the ferromagnetic exchange $J$ in low-anisotropy
amorphous magnetic materials. At high anisotropy and in low-anisotropy
materials sintered of sufficiently large ferromagnetic grains, the integral
power scales linearly on $D_R$. The maximum bandwidth, combined with the
maximum absorption power, is achieved when the amorphous structure factor, or
grain size, is of an order of the domain wall thickness in a conventional
ferromagnet that is of the order of $(J/D_R)^{1/2}$ lattice spacings.",2304.04121v1
2023-05-22,Stoner ferromagnetism in a momentum-confined interacting 2D electron gas,"In this work we investigate the ground state of a momentum-confined
interacting 2D electron gas, a momentum-space analog of an infinite quantum
well. The study is performed by combining analytical results with a numerical
exact diagonalization procedure. We find a ferromagnetic ground state near a
particular electron density and for a range of effective electron (or hole)
masses. We argue that this observation may be relevant to the generalized
Stoner ferromagnetism recently observed in multilayer graphene systems. The
collective magnon excitations exhibit a linear dispersion, which originates
from a diverging spin stiffness.",2305.13373v1
2023-05-21,An Alternative Derivation of the Landau-Lifshitz-Gilbert Equation for Saturated Ferromagnets,"The Landau-Lifshitz-Gilbert equation for rigid and saturated ferromagnets is
derived using a two-continuum model constructed by H.F. Tiersten for elastic
and saturated ferromagnets. The relevant basic laws of physics are applied
systematically to the two continua or their combination. The exchange
interaction is introduced into the model through surface distributed magnetic
couples. This leads to a continuum theory with magnetization gradients in the
stored energy density. The saturation condition of the magnetization functions
as constraints on the energy density and has implications in the constitutive
relations.",2305.18232v1
2023-07-31,Phase diagram of a ferromagnetic semiconductor. The origin of superparamagnetism,"We study the theoretical model of a ferromagnetic semiconductor as a system
of randomly distributed Ising spins with a long-range exchange interaction.
Using the density-of-states approach, we analytically obtain the magnetic
susceptibility and heat capacity over a wide range of temperatures and magnetic
fields. It is shown that the finite system of spins in magnetic field less than
a certain critical field is in a superparamagnetic state due to thermodynamic
fluctuations. The complex phase structure of a ferromagnetic semiconductor is
discussed.",2307.16538v2
2023-09-29,Micromagnetics of ferromagnetic/antiferromagnetic nanocomposite materials. Part I: Towards the mesoscopic approach,"In the first of two articles, we present here a novel mesoscopic
micromagnetic approach for simulating materials composed of ferromagnetic and
antiferromagnetic phases. Starting with the atomistic modeling of quasi
one-dimensional systems, we explicitly show how the material parameters for the
mesoscopic model of an antiferromagnet can be derived. The comparison between
magnetization profiles obtained in atomistic and mesoscopic calculations (using
a Heusler alloy as an example) proves the validity of our method. This approach
opens up the possibility to recover the details of the magnetization
distribution in ferromagnetic/antiferromagnetic materials with the resolution
of a few nanometers covering length scales up to several hundreds of
nanometers.",2309.17131v1
2023-10-20,HTS Dynamo Flux Pump: The Impact of a Ferromagnetic Stator Substrate,"HTS dynamo magnetic flux pumps are perspective devices for contactless
charging the superconductor magnets and coils. In this work, we investigate the
influence of a ferromagnetic substrate of a coated conductor used as the pump
stator. We use the thin shell model of a coated conductor with a ferromagnetic
substrate and show that such a conductor increases the pump-generated voltage
if the superconducting layer is between the rotor and the substrate. Chebyshev
spectral method is employed for numerical solution. Using simulation results
for problems with a given transport current we also derive a simple analytical
description for feeding a current to a coil.",2310.13491v1
2024-03-12,Nodal d-wave pairing from spin fluctuations in a thermally disordered anti-ferromagnet,"We consider electron pairing in a two-dimensional thermally disordered
itinerant anti-ferromagnet. It is shown that transverse spin fluctuations in
such a state can give rise to superconductivity with a sizeable critical
temperature $T_c$. Below $T_c$ there is quasi-long-range spin-singlet and
$d_{x^2-y^2}$ superconducting order, together with fluctuating triplet order at
momentum $(\pi,\pi)$. The singlet pairs we find are tightly bound together, and
the pair wavefunction has a purely inter-sublattice structure due to the U(1)
spin rotation symmetry of the anti-ferromagnet.",2403.07999v1
2024-03-27,A Generic Nonlinear Evolution Equation of Magnetic Type II. Particular Solutions,"We consider a matrix nonlinear partial differential equation that generalizes
Heisenberg ferromagnet equation. This generalized Heisenberg ferromagnet
equation is completely integrable with a linear bundle Lax pair related to the
pseudo-unitary algebra. This allows us to explicitly derive particular
solutions by using dressing technique. We shall discuss two classes of
solutions over constant background: soliton-like solutions and quasi-rational
solutions. Both classes have their analogues in the case of the Heisenberg
ferromagnet equation related to the same Lie algebra.",2403.18165v1
1997-09-03,The Ferromagnetic Kondo Model for Manganites: Phase Diagram and Charge Segregation Effects,"The phase diagram of the ferromagnetic Kondo model for manganites is
investigated using computational techniques. In clusters of dimensions 1 and 2,
Monte Carlo simulations in the limit where the localized spins are classical
show a rich low temperature phase diagram with three dominant regions: (i) a
ferromagnetic phase, (ii) phase separation between hole-poor antiferromagnetic
and hole-rich ferromagnetic domains, and (iii) a phase with incommensurate spin
correlations. Possible experimental consequences of the regime of phase
separation are discussed. Studies using the Lanczos algorithm and the Density
Matrix Renormalization Group method applied to chains with localized spin 1/2
(with and without Coulombic repulsion for the mobile electrons) and spin 3/2
degrees of freedom give results in excellent agreement with those in the spin
localized classical limit. The Dynamical Mean Field ($D=\infty$) approximation
was also applied to the same model. At large Hund coupling phase separation and
ferromagnetism were identified, again in good agreement with results in low
dimensions. In addition, a Monte Carlo study of spin correlations allowed us to
estimate the critical temperature for ferromagnetism $T_c^{FM}$ in 3
dimensional clusters. It is concluded that $T_c^{FM}$ is compatible with
current experimental results.",9709029v1
1998-09-21,Influence of Nearest-Neighbor Coulomb Interactions on the Phase Diagram of the Ferromagnetic Kondo Model,"The influence of a nearest-neighbor Coulomb repulsion of strength V on the
properties of the Ferromagnetic Kondo model is analyzed using computational
techniques. The Hamiltonian studied here is defined on a chain using localized
S=1/2 spins, and one orbital per site. Special emphasis is given to the
influence of the Coulomb repulsion on the regions of phase separation recently
discovered in this family of models, as well as on the double-exchange-induced
ferromagnetic ground state. When phase separation dominates at V=0, the Coulomb
interaction breaks the large domains of the two competing phases into small
``islands'' of one phase embedded into the other. This is in agreement with
several experimental results, as discussed in the text. Vestiges of the
original phase separation regime are found in the spin structure-factor as
incommensurate peaks, even at large values of V. In the ferromagnetic regime
close to density $n=0.5$, the Coulomb interaction induces tendencies to charge
ordering without altering the fully polarized character of the state. This
regime of ``charge- ordered ferromagnetism'' may be related with experimental
observations of a similar phase by C. H. Chen and S-W. Cheong (Phys. Rev. Lett.
76, 4042 (1996)). Our results reinforce the recently introduction notion (see
e.g., S. Yunoki et al., Phys. Rev. Lett. 80, 845 (1998)) that in realistic
models for manganites analyzed with unbiased many-body techniques, the ground
state properties arise from a competition between ferromagnetism and
phase-separation/charge-ordering tendencies.",9809281v1
2001-08-09,Extraordinary Hall effect in hybrid ferromagnetic/superconductor (F/S) bilayer,"Extraordinary Hall effect (EHE) in bilayer F/S(N) was investigated
theoretically. The conductivity tensor $\sigma_{\alpha\beta}$ is calculated in
the Kubo formalism with Green functions found as the solutions of the Gorkov
equations. We considered diffuse transport in the ferromagnetic layer, taking
into account as a main mechanism of electron resistivity s-d scattering. In
this model Gorkov equations for s-electrons in the ferromagnetic layer remain
linear and are solved easily. It is shown that Hall field $E^H$ for both F/S
and F/N contacts are step-functions of the coordinate perpendicular to the
planes of the layers and have zero value in S(N) layer. The Andreev reflection
increases the value of Hall constant $R_s$ for F/S case. The value of the Hall
constant is $R_H^{F/S} = R_H^{bulk} (\sigma^{\uparrow} + \sigma^{\downarrow})^2
/ 4 \sigma^{\uparrow}\sigma^{\downarrow}$, where $\sigma^{\uparrow}$ and
$\sigma^{\downarrow}$ are conductivities of electrons with up and down spins,
and $R_H^{bulk}$ is the Hall constant in the bulk ferromagnetic metal. In fact,
$R_H^{F/S}$ coincides with EHE constant of the bilayer of two ferromagnetic
metals with equal thickness and opposite directions of their magnetizations. So
we can make a conclusion, that the ideal interface between ferromagnetic metal
and superconductor may be considered like a mirror with inversion in spin
space.",0108161v2
2003-06-24,First-order transition in the itinerant ferromagnet CoS$_{1.9}$Se$_{0.1}$,"Undoped CoS$_2$ is an isotropic itinerant ferromagnet with a continuous or
nearly continuous phase transition at $T_{\rm C} = 122$ K. In the doped
CoS$_{1.9}$Se$_{0.1}$ system, the Curie temperature is lowered to $T_{\rm C} =
90$ K, and the transition becomes clearly first order in nature. In particular
we find a discontinuous evolution of the spin dynamics as well as strong time
relaxation in the ferromagnetic Bragg intensity and small angle neutron
scattering in vicinity of the ferromagnetic transition. In the ordered state
the long-wavelength spin excitations were found to be conventional
ferromagnetic spin-waves with negligible spin-wave gap ($ < 0.04$ meV),
indicating that this system is also an excellent isotropic (soft) ferromagnet.
In a wide temperature range up to $0.9T_{\rm C}$, the spin-wave stiffness
$D(T)$ follows the prediction of the two-magnon interaction theory, $D(T) =
D(0)(1 - AT^{5/2})$, with $D(0) = 131.7 \pm 2.8$ meV-\AA$^{2}$. The stiffness,
however, does not collapse as $T \to T_{\rm C}$ from below. Instead a
quasielastic central peak abruptly develops in the excitation spectrum, quite
similar to results found in the colossal magnetoresistance oxides such as
(La-Ca)MnO$_3$.",0306618v1
2005-09-21,Effect of iron-doping on spin-state transition and ferromagnetism in Pr$_{0.5}$Ca$_{0.5}$CoO$_{3-δ}$ cobalt oxides,"Resistivity and dc magnetization measurements were performed for the
polycrystalline Pr$_{0.5}$Ca$_{0.5}$Co$_{1-x}$Fe$_{x}$O$_{3-\delta}$ ($x$ = 0,
0.05, 0.10 and 0.15) samples. The as-fabricated samples exhibit ferromagnetic
(FM) transition and the transition temperature increases with increasing the
iron doping level. Annealing under high oxygen pressure induces a spin-state
transition of Co ions in the \emph{iron-free} sample and such transition is
reinforced with increasing the annealing oxygen pressure, while the annealing
under high oxygen pressure suppresses the ferromagnetic ordering. Contrary to
the case of the \emph{iron-free} sample, no spin-state transition is induced by
the annealing under high oxygen pressure for the \emph{iron-doped} samples, and
the ferromagnetic transition temperature is nearly independent of the annealing
procedures. The enhancement of the spin-state transition in the
\emph{iron-free} sample after annealing under high oxygen pressure should be
attributed to the reduction of the cell volume. The suppression of the
spin-state transition by the Fe doping is related to the enlargement of the
cell volume and the stronger Fe-O bonds than Co-O bonds. The enhancement of the
ferromagnetism by the iron-doping might arise from the ferromagnetic exchange
interaction between Fe$^{3+}$ and Co$^{4+}$ through oxygen
(Fe$^{3+}$-O-Co$^{4+}$).",0509533v1
2006-06-15,Ferromagnetic -spin glass transition induced by pressure in Gd$_2$Mo$_2$O$_7$,"R$_2$Mo$_2$O$_7$ compounds show a ferromagnetic metal-insulator spin glass
transition tuned by the radius of the rare earth ion R$^{3+}$. We have studied
Gd$_2$Mo$_2$O$_7$ located on the verge of the transition, by neutron
diffraction on a $^{160}$Gd isotopic sample, $\mu$SR and X ray diffraction
using the synchrotron radiation. All measurements were done both at ambient and
under applied pressure. At ambient pressure, a ferromagnetic state is observed
below the Curie temperature (T$_{\rm C}$ = 70 K). The ordered magnetic moments
at 1.7 K are parallel and equal to 5.7(5) $\mu_{\rm B}$ and 0.8(2) $\mu_{\rm
B}$ for Gd and Mo, respectively. The relaxation rate measured by $\mu$SR
evidences strong spin fluctuations below T$_{\rm C}$ and down to the lowest
temperature (6.6 K). A spin reorientation occurs in the range 20
K$<$T$<$T$_{\rm C}$. The ferromagnetic state is strongly unstable under
pressure. T$_{\rm C}$ sharply decreases (down to 38 K at 1.3 GPa) and Bragg
peaks start to coexist with mesoscopic ferromagnetic correlations. The ordered
moments decrease under pressure. At 2.7 GPa long range magnetic order
completely breaks down. In this spin glass state, Gd-Gd spin correlations
remain ferromagnetic with a correlation length limited to the fourth neighbor,
and Gd-Mo spin correlations turn to antiferromagnetic. The unique combination
of three microscopic probes under pressure provides a detailed description of
the magnetic transition, crucial for further theories.",0606420v1
2006-07-28,Atom-by-Atom Substitution of Mn in GaAs and Visualization of their Hole-Mediated Interactions,"The discovery of ferromagnetism in Mn doped GaAs [1] has ignited interest in
the development of semiconductor technologies based on electron spin and has
led to several proof-of-concept spintronic devices [2-4]. A major hurdle for
realistic applications of (Ga,Mn)As, or other dilute magnetic semiconductors,
remains their below room-temperature ferromagnetic transition temperature.
Enhancing ferromagnetism in semiconductors requires understanding the
mechanisms for interaction between magnetic dopants, such as Mn, and
identifying the circumstances in which ferromagnetic interactions are maximized
[5]. Here we report the use of a novel atom-by-atom substitution technique with
the scanning tunnelling microscope (STM) to perform the first controlled atomic
scale study of the interactions between isolated Mn acceptors mediated by the
electronic states of GaAs. High-resolution STM measurements are used to
visualize the GaAs electronic states that participate in the Mn-Mn interaction
and to quantify the interaction strengths as a function of relative position
and orientation. Our experimental findings, which can be explained using
tight-binding model calculations, reveal a strong dependence of ferromagnetic
interaction on crystallographic orientation. This anisotropic interaction can
potentially be exploited by growing oriented Ga1-xMnxAs structures to enhance
the ferromagnetic transition temperature beyond that achieved in randomly doped
samples. Our experimental methods also provide a realistic approach to create
precise arrangements of single spins as coupled quantum bits for memory or
information processing purposes.",0607765v1
2006-11-04,Suppressed Magnetization at the Surfaces and Interfaces of Ferromagnetic Metallic Manganites,"What happens to ferromagnetism at the surfaces and interfaces of manganites?
With the competition between charge, spin, and orbital degrees of freedom, it
is not surprising that the surface behavior may be profoundly different than
that of the bulk. Using a powerful combination of two surface probes, tunneling
and polarized x-ray interactions, this paper reviews our work on the nature of
the electronic and magnetic states at manganite surfaces and interfaces. The
general observation is that ferromagnetism is not the lowest energy state at
the surface or interface, which results in a suppression or even loss of
ferromagnetic order at the surface. Two cases will be discussed ranging from
the surface of the quasi-2D bilayer manganite
(La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$) to the 3D Perovskite
(La$_{2/3}$Sr$_{1/3}$MnO$_3$)/SrTiO$_3$ interface. For the bilayer manganite,
that is, ferromagnetic and conducting in the bulk, these probes present clear
evidence for an intrinsic insulating non-ferromagnetic surface layer atop
adjacent subsurface layers that display the full bulk magnetization. This
abrupt intrinsic magnetic interface is attributed to the weak inter-bilayer
coupling native to these quasi-two-dimensional materials. This is in marked
contrast to the non-layered manganite system
(La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrTiO$_3$), whose magnetization near the interface
is less than half the bulk value at low temperatures and decreases with
increasing temperature at a faster rate than the bulk.",0611112v1
2007-02-15,Theory of Nonequilibrium Spin Transport and Spin Transfer Torque in Superconducting-Ferromagnetic Nanostructures,"Spin transport currents and the spin-transfer torques in voltage-biased
superconducting-ferromagnetic nanopillars (SFNFS point contacts) are computed.
We develop and implement an algorithm based on the Ricatti formulation of the
quasiclassical theory of superconductivity to solve the time-dependent boundary
conditions for the nonequilibrium Green's functions for spin transport through
the ferromagnetic interfaces. A signature of the nonequilibrium torque is a
component perpendicular to the plane spanned by the two ferromagnetic moments.
The perpendicular component is absent in normal-metal-ferromagnetic nanopillars
(NFNFN) contacts, but is shown to have the same order of magnitude as the
in-plane torque for non-equilibrium SFNFS contacts. The out-of-plane torque is
due to the rotation of quasiparticle spin by the exchange fields of the
ferromagnetic layers. In the ballistic limit the equilibrium torque is related
to the spectrum of spin-polarized Andreev bound states, while the {\sl ac}
component, for small bias voltages, is determined by the nearly adiabatic
dynamics of the Andreev bound states. The nonlinear voltage dependence of the
non-equilibrium torque, including the subharmonic gap structure and the
high-voltage asymptotics, is attributed to the interplay between multiple
Andreev reflections, spin filtering and spin mixing. These properties of spin
angular momentum transport may be exploited to control the state of
nanomagnets.",0702371v3
2007-05-15,Nonhomogeneous magnetization and superconductivity in superconductor-ferromagnet structures,"We study two different superconductor-ferromagnet (S/F) structures. We
consider first a Josephson junction which consists of two S/F bilayers
separated by an insulating layer. We show that for an antiparallel alignment of
the magnetization in the two F layers the Josephson critical current $I_c$
increases with increasing exchange field $h$. The second system we consider is
a S/F structure with a local inhomogeneity of the magnetization in the
ferromagnet near the S/F interface. Due to the proximity effect not only a
singlet but also a triplet component of the superconducting condensate is
induced in the ferromagnet. The latter penetrates over the length
$\sqrt{D/\epsilon}$ ($D$ is the diffusion coefficient and $\epsilon$ the
energy). In the case of temperatures of the order of the Thouless energy this
length is comparable to the length of the ferromagnet. This long-range
penetration leads to a significant increase of the ferromagnet conductance
below the superconducting critical temperature $T_c$. Contrary to the case of
the singlet component, the contribution to the conductance due to the odd
triplet component is not zero at $T = 0$ and $V = 0$ ($V$ is the voltage) and
decays with increasing temperature T in a monotonic way",0705.2174v1
2007-07-19,Quantum transport in noncentrosymmetric superconductors and thermodynamics of ferromagnetic superconductors,"We consider a general Hamiltonian describing coexistence of itinerant
ferromagnetism, spin-orbit coupling and mixed spin-singlet/triplet
superconducting pairing in the context of mean-field theory. The Hamiltonian is
diagonalized and exact eigenvalues are obtained, thus allowing us to write down
the coupled gap equations for the different order parameters. Our results may
then be applied to any model describing coexistence of any combination of these
three phenomena. As a specific application of our results, we consider
tunneling between a normal metal and a noncentrosymmetric superconductor with
mixed singlet and triplet gaps. The conductance spectrum reveals information
about these gaps in addition to how the influence of spin-orbit coupling is
manifested. We also consider the coexistence of itinerant ferromagnetism and
triplet superconductivity as a model for recently discovered ferromagnetic
superconductors. The coupled gap equations are solved self-consistently, and we
study the conditions necessary to obtain the coexistent regime of
ferromagnetism and superconductivity. Analytical expressions are presented for
the order parameters, and we provide an analysis of the free energy to identify
the preferred system state. Moreover, we make specific predictions concerning
the heat capacity for a ferromagnetic superconductor. In particular, we report
a nonuniversal relative jump in the specific heat, depending on the
magnetization of the system, at the uppermost superconducting phase transition.
[Shortened abstract due to arXiv submission.]",0707.2875v2
2008-01-15,Exchange Interaction and $T_c$ in Alkaline-earth-metal-oxide-based DMS without Magnetic Impurities: First Principle Pseudo-SIC and Monte Carlo Calculation,"The prospects of half-metallic ferromagnetism being induced by the
incorporation of C atoms into alkaline-earth-metal-oxides are investigated by
the first principle calculation. The origin of the ferromagnetism is discussed
through the calculation of the electronic structure and exchange coupling
constant by using the pseudo-potential-like self-interaction-corrected local
spin density method. The Curie temperature ($T_c$) is also predicted by
employing the Monte Carlo simulation. It is shown that by taking the electron
self-interaction into account, the half-metallic ferromagnetism induced by C in
the host materials is more stabilized in comparison with the standard LDA case,
and the C's $2p$ electron states in the bandgap become more localized resulting
in the predominance of the short-ranged exchange interaction. While the
ferromagnetism in MgO$_{1-x}$C$_x$ is stabilized due to the exchange
interaction of the $1st$-nearest neighbor pairs and might be suppressed by the
anti-ferromagnetic super-exchange interaction at higher $x$, the ferromagnetism
in CaO$_{1-x}$C$_x$, SrO$_{1-x}$C$_x$, and BaO$_{1-x}$C$_x$ is stabilized by
both the $1st$- and $2nd$-nearest neighbor pairs, and $T_c$ monotonously
increases with the C concentration.",0801.2249v1
2008-12-08,Ferromagnetism and Lattice Distortions in the Perovskite YTiO$_3$,"The thermodynamic properties of the ferromagnetic perovskite YTiO$_3$ are
investigated by thermal expansion, magnetostriction, specific heat, and
magnetization measurements. The low-temperature spin-wave contribution to the
specific heat, as well as an Arrott plot of the magnetization in the vicinity
of the Curie temperature $T_C\simeq27$ K, are consistent with a
three-dimensional Heisenberg model of ferromagnetism. However, a magnetic
contribution to the thermal expansion persists well above $T_C$, which
contrasts with typical three-dimensional Heisenberg ferromagnets, as shown by a
comparison with the corresponding model system EuS. The pressure dependences of
$T_C$ and of the spontaneous moment $M_s$ are extracted using thermodynamic
relationships. They indicate that ferromagnetism is strengthened by uniaxial
pressures $\mathbf{p}\parallel \mathbf{a}$ and is weakened by uniaxial
pressures $\mathbf{p}\parallel \mathbf{b},\mathbf{c}$ and hydrostatic pressure.
Our results show that the distortion along the $a$- and $b$-axes is further
increased by the magnetic transition, confirming that ferromagnetism is favored
by a large GdFeO$_3$-type distortion. The c-axis results however do not fit
into this simple picture, which may be explained by an additional
magnetoelastic effect, possibly related to a Jahn-Teller distortion.",0812.1533v1
2009-02-15,Sudden Critical Current Drops Induced in S/F Structures,"In the search for new physical properties of S/F structures, we have found
that the superconductor critical current can be controlled by the domain state
of the neighboring ferromagnet. The superconductor is a thin wire of thickness
d_{s} ~ 2 xi_{S}. Nb/Co and Nb/Py (Permalloy Ni_{80}Fe_{20}) bilayer structures
were grown with a significant magnetic anisotropy. Critical current
measurements of Nb/Co structures with ferromagnet thickness d_{F} > 30nm show
sudden drops in two very defined steps when the measurements are made along the
hard axes direction (i.e. current track parallel to hard anisotropy axes
direction). These drops disappear when they are made along the easy axis
direction or when the ferromagnet thickness is below 30nm. The drops are
accompanied by vortex flux flow. In addition magnetorestistance measurements
close to Tc show a sharp increase near saturation fields of the ferromagnet.
Similar results are reproduced in Nb/Py bilayer structure with the ferromagnet
thickness d_{F} ~ 50nm along the easy anisotropy axes. These results are
explained as being due to spontaneous vortex formation and flow induced by
Bloch domain walls of the ferromagnet underneath. We argue these Bloch domain
walls produce a 2D vortex-antivortex lattice structure.",0902.2572v2
2009-04-30,"Structural, optical, magnetic and electrical properties of Zn1-x Co (x) O thin films","Despite a considerable effort aiming at elucidating the nature of
ferromagnetism in ZnO-based magnetic semiconductor, its origin still remains
debatable. Although the observation of above room temperature ferromagnetism
has been reported frequently in the literature by magnetometry measurement, so
far there has been no report on correlated ferromagnetism in magnetic, optical
and electrical measurements. In this paper, we investigate systematically the
structural, optical, magnetic and electrical properties of Zn1-x Co (x) O:Al
thin films prepared by sputtering with x ranging from 0 to 0.33. We show that
correlated ferromagnetism is present only in samples with x > 0.25. In
contrast, samples with x < 0.2 exhibit weak ferromagnetism only in magnetometry
measurement which is absent in optical and electrical measurements. We
demonstrate, by systematic electrical transport studies that carrier
localization indeed occurs below 20-50 K for samples with x < 0.2; however,
this does not lead to the formation of ferromagnetic phase in these samples
with an electron concentration in the range of 6 x 10(19) cm(-3) 1 x 10(20)
cm(-3). Detailed structural and optical transmission spectroscopy analyses
revealed that the anomalous Hall effect observed in samples with x > 0.25 is
due to the formation of secondary phases and Co clusters.",0904.4807v1
2009-08-04,Fe-implanted ZnO: Magnetic precipitates versus dilution,"Nowadays ferromagnetism is often found in potential diluted magnetic
semiconductor systems. However, many authors argue that the observed
ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition
rather than from carrier mediated magnetic impurities, as required for a
diluted magnetic semiconductor. In the present paper we answer this question
for Fe-implanted ZnO single crystals comprehensively. Different implantation
fluences and temperatures and post-implantation annealing temperatures have
been chosen in order to evaluate the structural and magnetic properties over a
wide range of parameters. Three different regimes with respect to the Fe
concentration and the process temperature are found: 1) Disperse Fe$^{2+}$ and
Fe$^{3+}$ at low Fe concentrations and low processing temperatures, 2)
FeZn$_2$O$_4$ at very high processing temperatures and 3) an intermediate
regime with a co-existence of metallic Fe (Fe$^0$) and ionic Fe (Fe$^{2+}$ and
Fe$^{3+}$). Ferromagnetism is only observed in the latter two cases, where
inverted ZnFe$_2$O$_4$ and $\alpha$-Fe nanocrystals are the origin of the
observed ferromagnetic behavior, respectively. The ionic Fe in the last case
could contribute to a carrier mediated coupling. However, their separation is
too large to couple ferromagnetically due to the lack of p-type carrier. For
comparison investigations of Fe-implanted epitaxial ZnO thin films are
presented.",0908.0405v1
2010-01-20,Theory of Room Temperature Ferromagnet V(TCNE)_x (1.5 < x < 2): Role of Hidden Flat Bands,"Theoretical studies on the possible origin of room temperature ferromagnetism
(ferromagnetic once crystallized) in the molecular transition metal complex,
V(TCNE)_x (1.5<x<2) have been carried out. For this family, there have been no
definite understanding of crystal structure so far because of sample quality,
though the effective valence of V is known to be close to +2. Proposing a new
crystal structure for the stoichiometric case of x=2, where the valence of each
TCNE molecule is -1 and resistivity shows insulating behavior, exchange
interaction among d-electrons on adjacent V atoms has been estimated based on
the cluster with 3 vanadium atoms and one TCNE molecule. It turns out that
Hund's coupling among d orbitals within the same V atoms and antiferromagnetic
coupling between d oribitals and LUMO of TCNE (bridging V atoms) due to
hybridization result in overall ferromagnetism (to be precise, ferrimagnetism).
This view based on localized electrons is supplemented by the band picture,
which indicates the existence of a flat band expected to lead to ferromagnetism
as well consistent with the localized view. The off-stoichiometric cases (x<2),
which still show ferromagnetism but semiconducting transport properties, have
been analyzed as due to Anderson localization.",1001.3512v2
2011-06-22,Novel Magnetic Chiral Structures and Unusual Temperature Hysteresis in the Metallic Helimagnet MnP,"We have reinvestigated the magnetic properties of the classical metallic
helimagnet MnP by magnetization and neutron scattering experiments. Our neutron
scattering results indicate that the previously reported magnetic structure in
the low-temperature (LT) helimagnetic phase (T < 47K) should be modified to an
alternately tilted helimagnetic structure pro- duced by the
Dzyaloshinsky-Moriya interaction. In the intermediate temperature (IT) range
between the LT helimagnetic phase and the high-temperature (HT) ferromagnetic
phase along the c-axis, 47K < T < 282K, we have found a weak ferromagnetic
behavior along the b-axis. Surprisingly, the IT weak ferromagnetic phase has
two different states, namely, the large magnetization (LM) and small
magnetization (SM) states. The SM state emerges with cooling from the
paramagnetic phase above 292 K via the HT ferromagnetic phase and LM state
emerges with warming from the LT helimagnetic phase. The weak ferromagnetism
along the b-axis and the unusual temperature hysteresis in the IT phase can be
understood by assuming a spontaneous formation of the stripe structure
consisting of alternately arranged HT ferromagnetic and LT helimagnetic
domains.",1106.4599v3
2011-09-13,Interference Effects of the Superconducting Pairing Wave Function due to the Fulde-Ferrell-Larkin-Ovchinnikov like State in Ferromagnet/Superconductor Bilayers,"The theoretical description of the Fulde-Ferrell-Larkin-Ovchinnikov like
state establishing in nanostructered bilayers of ferromagnetic (F) and
superconducting (S) material leads to critical temperature oscillations and
reentrant superconductivity as the F-layer thickness gradually increases. The
experimental realization of these phenomena is an important prerequisite for
the fabrication of the Ferromagnet/Superconductor/Ferromagnet core structure of
the superconducting spin-valve. A switching of the spin-valve is only expected
if such non-monotonic critical temperature behavior is observed in F/S bilayers
as well as in the S/F bilayers, a combination of which the spin-valve core
structure can be regarded to consist of. In our former investigations we could
demonstrate the required non-monotonic behavior of the critical temperature in
S/F bilayers. In this study we succeeded in the preparation of F/S bilayers,
where the superconducting material is now grown on top of the ferromagnetic
metal, which show deep critical temperature oscillations as a function of the
ferromagnetic layer thickness as well as an extinction and recovery, i.e. a
reentrant behavior, of superconductivity. Especially, the latter is necessary
to obtain a spin-valve with a large critical temperature shift between the
parallel and antiparallel configurations of magnetizations in the F layers.",1109.2759v1
2012-11-21,A critical examination of magnetic states of La$_{0.5}$Ba$_{0.5}$CoO$_3$: non-Griffiths phase and interacting ferromagnetic-clusters,"We report detailed dc magnetization, linear and non-linear ac susceptibility
measurements on the hole doped disordered cobaltite
La$_{0.5}$Ba$_{0.5}$CoO$_3$. Our results show that the magnetically ordered
state of the system consists of coexisting non-ferromagnetic phases along with
percolating ferromagnetic-clusters. The percolating ferromagnetic-clusters
possibly undergo a 3D Hisenberg like magnetic ordering at the Curie temperature
of 202(3) K. In between 202 and 220 K, the linear and non-linear ac
susceptibility measurements show the presence of magnetic correlations even
when the spontaneous magnetization is zero which indicates the presence of
preformed short range magnetic-clusters. The characteristics of these short
range magnetic-clusters that exist above Curie temperature are quite distinct
than that of Griffiths phase e.g the inverse dc susceptibility exhibits an
field independent upward deviation, and the second harmonic of ac
susceptibility is non-negative. Below Curie temperature the system exhibit
spin-glass like features such as irreversibility in the field cooled and zero
field cooled magnetization and frequency dependence in the peak of ac
susceptibility. The presence of a spin or cluster -glass like state is ruled
out by the absence of field divergence in third harmonic of ac susceptibility
and zero field cooled memory. This indicates that the observed spin-glass like
features are possibility due to progressive thermal blocking of
ferromagnetic-clusters which is further confirmed by the Wohlfarth's model of
superparamagnetism. The frequency dependence of the peak of ac susceptibility
obeys the Vogel-Fulcher law with $\tau_0\approx 10^{-9}$ s. This together with
the existence of an AT line in H-T space indicates the existence of significant
inter-cluster interaction among these ferromagnetic-clusters.",1211.4936v1
2013-01-15,Interplay of 4f-3d Magnetism and Ferroelectricity in DyFeO3,"DyFeO3 exhibits a weak ferromagnetism (TNFe ~ 645 K) that disappears below a
spin-reorientation (Morin) transition at TSRFe ~ 50 K. It is also known that
applied magnetic field induces ferroelectricity at the magnetic ordering
temperature of Dy-ions (TNDy ~ 4.5 K). Here, we show that the ferroelectricity
exists in the weak ferromagnetic state (TSRFe < T < TN,C) without applying
magnetic field, indicating the crucial role of weak ferromagnetism in inducing
ferroelectricity. 57Fe M\""ossbauer studies show that hyperfine field (Bhf)
deviates from mean field-like behaviour that is observed in the weak
ferromagnetic state and decreases below the onset of spin-reorientation
transition (80 K), implying that the Bhf above TSR had additional contribution
from Dy-ions due to induced magnetization by the weak ferromagnetic moment of
Fe-sublattice and below TSR, this contribution decreases due to collinear
ordering of Fe-sublattice. These results clearly demonstrate the presence of
magnetic interactions between Dy(4f) and Fe(3d) and their correlation with
ferroelectricity in the weak ferromagnetic state of DyFeO3.",1301.3263v1
2013-04-23,Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids,"We experimentally investigate and quantitatively analyze the spin Hall
magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic
insulator/nonferromagnetic metal/platinum hybrid structures. For the
ferromagnetic insulator we use either yttrium iron garnet, nickel ferrite or
magnetite and for the nonferromagnet copper or gold. The spin Hall
magnetoresistance effect is theoretically ascribed to the combined action of
spin Hall and inverse spin Hall effect in the platinum metal top layer. It
therefore should characteristically depend upon the orientation of the
magnetization in the adjacent ferromagnet, and prevail even if an additional,
nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our
experimental data corroborate these theoretical conjectures. Using the spin
Hall magnetoresistance theory to analyze our data, we extract the spin Hall
angle and the spin diffusion length in platinum. For a spin mixing conductance
of $4\times10^{14}\;\mathrm{\Omega^{-1}m^{-2}}$ we obtain a spin Hall angle of
$0.11\pm0.08$ and a spin diffusion length of $(1.5\pm0.5)\;\mathrm{nm}$ for Pt
in our thin film samples.",1304.6151v1
2013-05-24,"On Ultrafast Spin Dynamics: Spin Dependent Fast Response of Hot Electrons, of Band--Structure","Different energy shifts for majority and minority electrons occur. Thus, for
example in case of (laser) excited ferromagnetic metals majority and minority
electrons may respond differently in time during closing the exchange
splitting. Spin flip transitions of the hot electrons due to electron
interactions cause quasi hybridization of the spin split states. This is also
the case in itinerant ferromagnetic metals due to hopping between sites having
magnetic moments pointing in direction of the magnetization (+) and opposite
direction (-) and with energy levels $\varepsilon^+_{i\sigma}$ and
$\varepsilon^-_{i\sigma}$. For energetic reasons the molecular field acts
asymmetrically on the spins of the electrons and on spin flip transitions and
thus causes different lifetimes of minority and majority electrons and spin
dependent electron energy shifts. Quite general minority hot electrons in spin
split states may respond faster than majority electrons at non--equilibrium.
The molecular field acting on the spins delays spin flip transitions $\uparrow
\rightarrow \downarrow$ and thus a response of the hot majority electrons and
their energy levels. The closing of the exchange splitting in the electron
spectrum of ferromagnetic transition and rare--earth metals, ferromagnetic
semiconductors, spin split quantum well states in thin ferromagnetic films,
etc. will reflect this. The time and spin dependent energy shifts of electrons
at non--equilibrium may cause interesting behavior, in particular of magnetic
tunnel junctions, spin currents etc.. In ferromagnets the moment reversal
lifetime of (local) magnetic moments parallel to the global magnetization is
larger than of moments pointing in opposite direction.",1305.5698v1
2013-05-31,Ferromagnetic Phase Transitions in Neutron Stars,"The ferromagnetic phase in pure neutron matter as well as charge neutral,
beta-equilibrated nuclear matter is considered. We employ Quantum
Hadrodynamics, a relativistic field theory description of nuclear matter with
meson degrees of freedom, and include couplings between the baryon (proton and
neutron) magnetic dipole moment as well as between their charge and the
magnetic field in the Lagrangian density describing such a system. We vary the
strength of the baryon magnetic dipole moment till a non-zero value of the
magnetic field, for which the total energy density of the magnetised system is
at a minimum, is found. The system is then assumed to be in the ferromagnetic
state.
  The ferromagnetic equation of state is employed to study matter in the
neutron star interior. We find that as the density increases the ferromagnetic
field does not increase continuously, but exhibit sudden rapid increases. These
sudden increases in the magnetic field correspond to shifts between different
configurations of the charged particle's Landau levels and can have significant
observational consequences for neutron stars. We also found that although the
ferromagnetic phase softens the neutron star equation of state it does not
significantly alter the star's mass-radius relationship.
  The properties of magnetised symmetric nuclear matter were also studied. We
confirm that magnetised matter tends to be more proton-rich but become more
weakly bound for stronger magnetic fields. We show that the behaviour of the
compressibility of nuclear matter is influenced by the Landau quantisation and
tends to have an oscillatory character as it increases with the magnetic field.
The symmetry energy also exhibits similar behaviour.",1305.7346v1
2014-02-04,"Partition Function in One, Two and Three Spatial Dimensions from Effective Lagrangian Field Theory","The systematic effective Lagrangian method was first formulated in the
context of the strong interaction: chiral perturbation theory (CHPT) is the
effective theory of Quantum Chromodynamics (QCD). It was then pointed out that
the method can be transferred to the nonrelativistic domain -- in particular,
to describe the low-energy properties of ferromagnets. Interestingly, whereas
for Lorentz-invariant systems the effective Lagrangian method fails in one
spatial dimension ($d_s$=1), it perfectly works for nonrelativistic systems in
$d_s$=1. In the present brief review, we give an outline of the method and then
focus on the partition function for ferromagnetic spin chains, ferromagnetic
films and ferromagnetic crystals up to three loops in the perturbative
expansion -- an accuracy never achieved by conventional condensed matter
methods. We then compare ferromagnets in $d_s$=1,2,3 with the behavior of QCD
at low temperatures by considering the pressure and the order parameter. The
two apparently very different systems (ferromagnets and QCD) are related from a
universal point of view based on the spontaneously broken symmetry. In either
case, the low-energy dynamics is described by an effective theory containing
Goldstone bosons as basic degrees of freedom.",1402.0806v2
2014-11-03,Sign problem free quantum Monte-Carlo study on thermodynamic properties and magnetic phase transitions in orbital-active itinerant ferromagnets,"The microscopic mechanism of itinerant ferromagnetism is a long-standing
problem due to the lack of non-perturbative methods to handle strong magnetic
fluctuations of itinerant electrons. We have non-pertubatively studied
thermodynamic properties and magnetic phase transitions of a two-dimensional
multi-orbital Hubbard model exhibiting ferromagnetic ground states. Quantum
Monte-Carlo simulations are employed, which are proved in a wide density region
free of the sign problem usually suffered by simulations for fermions. Both
Hund's coupling and electron itinerancy are essential for establishing the
ferromagnetic coherence. No local magnetic moments exist in the system as a
priori, nevertheless, the spin channel remains incoherent showing the
Curie-Weiss type spin magnetic susceptibility down to very low temperatures at
which the charge channel is already coherent exhibiting a weakly
temperature-dependent compressibility. For the SU(2) invariant systems, the
spin susceptibility further grows exponentially as approaching zero temperature
in two dimensions. In the paramagnetic phase close to the Curie temperature,
the momentum space Fermi distributions exhibit strong resemblance to those in
the fully polarized state. The long-range ferromagnetic ordering appears when
the symmetry is reduced to the Ising class, and the Curie temperature is
accurately determined. These simulations provide helpful guidance to searching
for novel ferromagnetic materials in both strongly correlated $d$-orbital
transition metal oxide layers and the $p$-orbital ultra-cold atom optical
lattice systems.",1411.0340v2
2014-12-29,Evolution of ferromagnetic and non-Fermi liquid state with doping:the case of Ru doped UCoGe,"We have investigated the impact of Ru substitution for Co on the behavior of
the ferromagnetic superconductor UCoGe by performing x-ray diffraction,
magnetization, specific heat and electrical resistivity measurements on
polycrystalline samples of the $\mathrm{UCo}_{1-x}\mathrm{Ru}_{x}\mathrm{Ge}$
series ($0\geq x\leq0.9$). The initial Ru substitution up to $x\approx0.1$
leads to a simultaneous sharp increase of the Curie temperature and spontaneous
magnetization up to maximum values of $T_{\mathrm{C}}=8.6 K$ and
$M_{\mathrm{S}}=0.1 \mu_{\mathrm{B}}$ per formula unit, respectively, whereas
superconductivity vanishes already for $x\approx0.03$. Further increase of the
Ru content beyond $x\approx0.1$ leads to a precipitous decrease of both,
$T_{\mathrm{C}}$ and $M_{\mathrm{S}}$ towards a ferromagnetic quantum critical
point (QCP) at $x_{\mathrm{cr}}=0.31$. Consequently the $T-x$ magnetic phase
diagram consists of a well-developed ferromagnetic dome. We discuss the
evolution of ferromagnetism with $x$ on the basis of band structure changes due
to varying 5$f$-ligand hybridization. This scenario is supported by the results
of electronic structure calculations and consideration of the simplified
periodic Anderson model. The analysis of the temperature dependencies of the
electrical resistivity and heat capacity at low temperatures of the samples in
the vicinity of the QCP reveals a non-Fermi liquid behavior and assigns the
ferromagnetic quantum phase transition to be most likely of a continuous
Hertz-Millis type.",1412.8355v3
2015-01-06,Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism,"Defect-induced ferromagnetism has triggered a lot of investigations and
controversies. The major issue is that the induced ferromagnetic signal is so
weak that it can sufficiently be accounted for by trace contamination. To
resolve this issue, we studied the variation of the magnetic properties of SiC
after neutron irradiation with fluence covering four orders of magnitude. A
large paramagnetic component has been induced and scales up with defect
concentration, which can be well accounted for by uncoupled divacancies.
However, the ferromagnetic contribution is still weak and only appears in the
low fluence range of neutrons or after annealing treatments. First-principles
calculations hint towards a mutually exclusive role of the concentration of
defects: Defects favor spin polarization at the expense of magnetic
interaction. Combining both experimental and first-principles calculation
results, the defect-induced ferromagnetism can be understood as a local effect
which cannot be scaled up with the volume. Therefore, our investigation answers
the long-standing question why the defect-induced ferromagnetic signal is weak.",1501.01096v2
2015-06-12,Mechanisms and origins of half-metallic ferromagnetism in CrO2,"Chromium dioxide (CrO2) offers a rare example of metallic ferromagnetism
among stoichiometric transition-metal oxides. What makes it even more
remarkable is the half-metallic electronic structure. Today, CrO2 is widely
used in magnetorecording and regarded as a promising spintronic material.
Nevertheless, the key question ""Why is it ferromagnetic?"" remains largely
unanswered, despite general interest to the problem and practical importance of
CrO2. In the present work we challenge this question by combining
first-principles electronic structure calculations with the model Hamiltonian
approach and modern many-body methods for treating electron correlations. Our
analysis demonstrates that the problem is indeed highly nontrivial: at the
first glance, the ferromagnetism in CrO2 can be easily explained by Hund's rule
related exchange processes in the narrow t2g band. However, the electron
correlations, rigorously treated in the frameworks of dynamical mean-field
theory, tend to destabilize this state. The ferromagnetism reemerges if,
besides conventional kinetic energy changes in the t2g band, to consider other
mechanism, involving direct exchange and magnetic polarization of the oxygen
band. We show how all these contributions can be evaluated using
first-principles electronic structure calculations. Our results explain the
overall stability of the ferromagnetic state and provide the firm microscopic
basis for understanding the magnetism of CrO2.",1506.03886v1
2016-03-09,Extended Magnetic Exchange Interactions in the High-Temperature Ferromagnet MnBi,"The high-temperature ferromagnet MnBi continues to receive attention as a
candidate to replace rare-earth-containing permanent magnets in applications
above room temperature. This is due to a high Curie temperature, large magnetic
moments, and a coercivity that increases with temperature. The synthesis of
MnBi also allows for crystals that are free of interstitial Mn, enabling more
direct access to the key interactions underlying the physical properties of
binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering
to measure the spin waves of MnBi in order to characterize the magnetic
exchange at low temperature. Consistent with the spin reorientation that occurs
below 140 K, we do not observe a spin gap in this system above our experimental
resolution. A Heisenberg model was fit to the spin wave data in order to
characterize the long-range nature of the exchange. It was found that
interactions up to sixth nearest neighbor are required to fully parameterize
the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic,
and the realization of a ferromagnetic ground state relies on the more numerous
ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic
ground state arises as a consequence of the long-ranged interactions in the
system.",1603.02750v2
2016-07-04,Ferromagnetic Quantum Critical Point Avoided by the Appearance of Another Magnetic Phase in LaCrGe$_3$ under Pressure,"The temperature-pressure phase diagram of the ferromagnet LaCrGe$_3$ is
determined for the first time from a combination of magnetization,
muon-spin-rotation and electrical resistivity measurements. The ferromagnetic
phase is suppressed near $2.1$~GPa, but quantum criticality is avoided by the
appearance of a magnetic phase, likely modulated, AFM$_Q$. Our density
functional theory total energy calculations suggest a near degeneracy of
antiferromagnetic states with small magnetic wave vectors $Q$ allowing for the
potential of an ordering wave vector evolving from $Q=0$ to finite $Q$, as
expected from the most recent theories on ferromagnetic quantum criticality.
Our findings show that LaCrGe$_3$ is a very simple example to study this
scenario of avoided ferromagnetic quantum criticality and will inspire further
study on this material and other itinerant ferromagnets.",1607.01061v1
2016-07-28,Ferromagnetic ground state of SU(3) Hubbard model on the Lieb lattice,"We investigate the magnetic properties of a repulsive fermionic SU($3$)
Hubbard model on the Lieb lattice from weak to strong interaction by means of
the mean-field approximation. To validate the method we employed, we first
discuss the SU($2$) Hubbard model at the mean-field level, and find that our
results are consistent with known rigorous theorems. We then extend the
calculation to the case of SU($3$) symmetry. We find that, at $4/9$ filling,
the SU$(3)$ symmetry spontaneously breaks into the SU$(2)\times$U$(1)$ symmetry
in the ground state, leading to a staggered ferromagnetic state for any
repulsive $U$ at zero temperature. We then investigate the stability of the
ferromagnetic state by relaxing the filling away from $4/9$, and conclude that
the ferromagnetic state is sensitive but robust to fillings, as it can persist
within a certain filling regime. We also apply the mean-field approximation to
finite temperature to calculate the critical temperature and the critical
entropy of the ferromagnetic state. As the resulting critical entropy per
particle is significantly greater than that can be realized in experiments, we
expect some quasi-long-range-ordered features of such a ferromagnetic state can
be realized and observed with fermionic alkaline-earth-metal(-like) atoms
loaded into optical lattices.",1607.08618v3
2018-04-13,Direct evidence of ferromagnetism in a quantum anomalous Hall system,"Quantum anomalous Hall (QAH) systems are of great fundamental interest and
potential application because of their dissipationless conduction without the
need for external magnetic field. The QAH effect has been realized in
magnetically doped topological insulator thin films. However, full quantization
requires extremely low temperature ($T< 50\,$mK) in the initial works, though
it has been significantly improved with modulation doping or co-doping of
magnetic elements. Improved ferromagnetism has been shown in these thin films,
yet direct evidence of long-range ferromagnetic order is lacking. Herein, we
present direct visualization of long-range ferromagnetic order in thin films of
Cr and V co-doped (Bi,Sb)$_2$Te$_3$ using low-temperature magnetic force
microscopy with $\textit{in-situ}$ transport. The magnetization reversal
process reveals typical ferromagnetic domain behavior, i.e., domain nucleation
and possibly domain wall propagation, in contrast to much weaker magnetic
signals observed in the end members, possibly due to superparamagnetic
behavior. The observed long-range ferromagnetic order resolves one of the major
challenges in QAH systems, and paves the way to high-temperature
dissipationless conduction by exploring magnetic topological insulators.",1804.04991v2
2020-07-28,Defect Induced Room Temperature Ferromagnetism in High Quality Co-doped ZnO Bulk Samples,"The nature of the often reported room temperature ferromagnetism in
transition metal doped oxides is still a matter of huge debate. Herein we
report on room temperature ferromagnetism in high quality Co-doped ZnO
(Zn1-xCoxO) bulk samples synthesized via standard solid-state reaction route.
Reference paramagnetic Co-doped ZnO samples with low level of structural
defects are subjected to heat treatments in a reductive atmosphere in order to
introduce defects in the samples in a controlled way. A detailed structural
analysis is carried out in order to characterize the induced defects and their
concentration. The magnetometry revealed the coexistence of a paramagnetic and
a ferromagnetic phase at room temperature in straight correlation with the
structural properties. The saturation magnetization is found to increase with
the intensification of the heat treatment, and, therefore, with the increase of
the density of induced defects. The magnetic behavior is fully explained in
terms of the bound magnetic polaron model. Based on the experimental findings,
supported by theoretical calculations, we attribute the origin of the observed
defect-induced-ferromagnetism to the ferromagnetic coupling between the Co ions
mediated by magnetic polarons due to zinc interstitial defects.",2007.14140v1
2017-01-12,Dynamic coupling of ferromagnets via spin Hall magnetoresistance,"The synchronized magnetization dynamics in ferromagnets on a nonmagnetic
heavy metal caused by the spin Hall effect is investigated theoretically. The
direct and inverse spin Hall effects near the ferromagnetic/nonmagnetic
interface generate longitudinal and transverse electric currents. The
phenomenon is known as the spin Hall magnetoresistance effect, whose magnitude
depends on the magnetization direction in the ferromagnet due to the spin
transfer effect. When another ferromagnet is placed onto the same nonmagnet,
these currents are again converted to the spin current by the spin Hall effect
and excite the spin torque to this additional ferromagnet, resulting in the
excitation of the coupled motions of the magnetizations. The in-phase or
antiphase synchronization of the magnetization oscillations, depending on the
value of the Gilbert damping constant and the field-like torque strength, is
found in the transverse geometry by solving the Landau-Lifshitz-Gilbert
equation numerically. On the other hand, in addition to these synchronizations,
the synchronization having a phase difference of a quarter of a period is also
found in the longitudinal geometry. The analytical theory clarifying the
relation among the current, frequency, and phase difference is also developed,
where it is shown that the phase differences observed in the numerical
simulations correspond to that giving the fixed points of the energy supplied
by the coupling torque.",1701.03201v2
2012-01-03,Reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals,"The search for oxide-based room-temperature ferromagnetism has been one of
the holy grails in condensed matter physics. Room-temperature ferromagnetism
observed in Nb-doped SrTiO3 single crystals is reported in this Rapid
Communication. The ferromagnetism can be eliminated by air annealing (making
the samples predominantly diamagnetic) and can be recovered by subsequent
vacuum annealing. The temperature dependence of magnetic moment resembles the
temperature dependence of carrier density, indicating that the magnetism is
closely related to the free carriers. Our results suggest that the
ferromagnetism is induced by oxygen vacancies. In addition, hysteretic
magnetoresistance was observed for magnetic field parallel to current,
indicating that the magnetic moments are in the plane of the samples. The x-ray
photoemission spectroscopy, the static time-of-flight and the dynamic secondary
ion mass spectroscopy and proton induced x-ray emission measurements were
performed to examine magnetic impurities, showing that the observed
ferromagnetism is unlikely due to any magnetic contaminant.",1201.0579v4
2012-01-10,"Microscopic theory for a ferromagnetic-nanowire/superconductor heterostructure: Transport, fluctuations and topological superconductivity","Motivated by the recent experiment of Wang et al. [Nature Physics 6, 389
(2010)], who observed a highly unusual transport behavior of ferromagnetic
Cobalt nanowires proximity-coupled to superconducting electrodes, we study
proximity effect and temperature-dependent transport in such a mesoscopic
hybrid structure. It is assumed that the asymmetry in the tunneling barrier
gives rise to the Rashba spin-orbit-coupling in the barrier that enables
induced p-wave superconductivity in the ferromagnet to exist. We first develop
a microscopic theory of Andreev scattering at the spin-orbit-coupled interface,
derive a set of self-consistent boundary conditions, and find an expression for
the p-wave minigap in terms of the microscopic parameters of the contact.
Second, we study temperature-dependence of the resistance near the
superconducting transition and find that it should generally feature a
fluctuation-induced peak. The upturn in resistance is related to the
suppression of the single-particle density of states due to the formation of
fluctuating pairs, whose tunneling is suppressed. In conclusion, we discuss
this and related setups involving ferromagnetic nanowires in the context of
one-dimensional topological superconductors. It is argued that to realize
unpaired end Majorana modes, one does not necessarily need a half-metallic
state, but a partial spin polarization may suffice. Finally, we propose yet
another related class of material systems -- ferromagnetic semiconductor wires
coupled to ferromagnetic superconductors -- where direct realization of
Kitaev-Majorana model should be especially straightforward.",1201.2180v2
2014-06-14,MuSR Investigation and Suppression of TC by overdoped Li in Diluted Ferromagnetic Semiconductor Li1+y(Zn1-xMnx)P,"We use muon spin relaxation (muSR) to investigate the magnetic properties of
a bulk form diluted ferromagnetic semiconductor (DFS) Li1.15(Zn0.9Mn0.1)P with
T_C ~ 22 K. MuSR results confirm the gradual development of ferromagnetic
ordering below T_C with a nearly 100% magnetic ordered volume. Despite its low
carrier density, the relation between static internal field and Curie
temperature observed for Li(Zn,Mn)P is consistent with the trend found in
(Ga,Mn)As and other bulk DFSs, indicating these systems share a common
mechanism for the ferromagnetic exchange interaction. Li1+y(Zn1-xMnx)P has the
advantage of decoupled carrier and spin doping, where Mn2+ substitution for
Zn2+ introduces spins and Li+ off-stoichiometry provides carriers. This
advantage enables us to investigate the influence of overdoped Li on the
ferromagnetic ordered state. Overdoping Li suppresses both T_C and saturation
moments for a certain amount of spins, which indicates that more carriers are
detrimental to the ferromagnetic exchange interaction, and that a delicate
balance between charge and spin densities is required to achieve highest T_C.",1406.3744v1
2016-08-05,Quantum Criticality in the Ferromagnetic Superconductor UCoGe under Pressure and Magnetic Field,"The pressure-temperature phase diagram of the orthorhombic ferromagnetic
superconductor UCoGe was determined by resistivity measurements up to
$10.5~$GPa. The Curie temperature $T_C$ is suppressed with pressure and
vanishes at the critical pressure $p_c\approx1~$GPa. Superconductivity is
observed in both the ferromagnetic state at low pressure, and in the
paramagnetic state above $p_c$ up to about 4$~$GPa. Non-Fermi liquid behavior
appears in a large pressure range. The resistivity varies linearly with
temperature around $p_c$ and evolves continuously with pressure to a $T^2$
Fermi-liquid behavior for $p \gtrapprox 5$~GPa. The residual resistivity as a
function of pressure shows a maximum far above $p_c$ at $p^\star=7.2~$GPa and
the amplitude of the inelastic scattering term of the resistivity decreases by
more than one order in magnitude at $p^\star$, which appears to mark the
entrance into a weakly correlated regime. The pressure dependence of the upper
critical field for magnetic field applied along the $b$ and $c$ axis
illustrates the drastic difference in the field dependence of the ferromagnetic
superconducting pairing. While for $H\parallel b$ axis $H_{c2}(T)$ is driven by
the suppression of the ferromagnetic order, it is dominated by the strong
initial suppression of the ferromagnetic fluctuations for a field applied in
the easy magnetization axis $c$.",1608.01949v1
2016-08-08,Ferromagnetism and glassiness on the surface of topological insulators,"We investigate the nature of the ordering among magnetic adatoms, randomly
deposited on the surface of topological insulators. Restricting ourselves to
dilute impurity and weak coupling (between itinerant fermion and magnetic
impurities) limit, we show that for arbitrary amount of chemical doping away
from the apex of the surface Dirac cone the magnetic impurities tend to arrange
themselves in a spin-density-wave pattern, with the periodicity approximately
$\pi/k_F$, where $k_F$ is the Fermi wave vector, when magnetic moment for
impurity adatoms is isotropic. However, when magnetic moment possesses strong
Ising or easy-axis anisotropy, pursuing both analytical and numerical
approaches we show that the ground state is ferromagnetic for low to moderate
chemical doping, despite the fragmentation of the system into multiple
ferromagnetic islands. For high doping away from the Dirac point as well, the
system appears to fragment into many ferromagnetic islands, but the
magnetization in these islands is randomly distributed. Such magnetic ordering
with net zero magnetization, is referred here as ferromagnetic spin glass,
which is separated from the pure ferromagnet state by a first order phase
transition. We generalize our analysis for cubic topological insulators
(supporting three Dirac cones on a surface) and demonstrate that the nature of
magnetic orderings and the transition between them remains qualitatively the
same. We also discuss the possible relevance of our analysis to recent
experiments.",1608.02576v1
2016-08-31,Critical Current Oscillations of Elliptical Josephson Junctions with Single-Domain Ferromagnetic Layers,"Josephson junctions containing ferromagnetic layers are of considerable
interest for the development of practical cryogenic memory and superconducting
qubits. Such junctions exhibit a phase shift of $\pi$ for certain ranges of
ferromagnetic layer thickness. We present studies of Nb based micron-scale
elliptically-shaped Josephson junctions containing ferromagnetic barriers of
Ni$_{81}$Fe$_{19}$ or Ni$_{65}$Co$_{20}$Fe$_{15}$. By applying an external
magnetic field, the critical current of the junctions are found to follow
characteristic Fraunhofer patterns, and display sharp switching behavior
suggestive of single-domain magnets. The high quality of the Fraunhofer
patterns enables us to extract the maximum value of the critical current even
when the peak is shifted significantly outside the range of the data due to the
magnetic moment of the ferromagnetic layer. The maximum value of the critical
current oscillates as a function of the ferromagnetic barrier thickness,
indicating transitions in the phase difference across the junction between
values of zero and $\pi$. We compare the data to previous work and to models of
the 0-$\pi$ transitions based on existing theories.",1608.08998v2
2016-12-15,Ba2NiOsO6: A Dirac-Mott insulator with ferromagnetism near 100 K,"The ferromagnetic semiconductor Ba2NiOsO6 (Tmag ~100 K) was synthesized at 6
GPa and 1500 {\deg}C. It crystallizes into a double perovskite structure
[Fm-3m; a = 8.0428(1) {\AA}], where the Ni2+ and Os6+ ions are perfectly
ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+
plays an essential role in opening the charge gap. The magnetic state was
investigated by density functional theory calculations and powder neutron
diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe
magnetic field at 5 K. The ferromagnetic gapped state is fundamentally
different from that of known dilute magnetic semiconductors such as (Ga,Mn)As
and (Cd,Mn)Te (Tmag < 180 K), the spin-gapless semiconductor Mn2CoAl (Tmag ~720
K), and the ferromagnetic insulators EuO (Tmag ~70 K) and Bi3Cr3O11 (Tmag ~220
K). It is also qualitatively different from known ferrimagnetic
insulator/semiconductors, which are characterized by an antiparallel spin
arrangement. Our finding of the ferromagnetic semiconductivity of Ba2NiOsO6
should increase interest in the platinum group oxides, because this new class
of materials should be useful in the development of spintronic, quantum
magnetic, and related devices.",1612.05041v1
2019-07-12,Ferromagnetic phase transition in topological crystalline insulator thin films: interplay of anomalous Hall angle and magnetic anisotropy,"In magnetic topological phases of matter, the quantum anomalous Hall (QAH)
effect is an emergent phenomenon driven by ferromagnetic doping, magnetic
proximity effects and strain engineering. The realization of QAH states with
multiple dissipationless edge and surface conduction channels defined by a
Chern number $\mathcal{C}\geq1$ was foreseen for the ferromagnetically ordered
SnTe class of topological crystalline insulators (TCIs). From magnetotransport
measurements on Sn$_{1-x}$Mn$_{x}$Te ($0.00\leq{x}\leq{0.08}$)(111) epitaxial
thin films grown by molecular beam epitaxy on BaF$_{2}$ substrates, hole
mediated ferromagnetism is observed in samples with $x\geq0.06$ and the highest
$T_\mathrm{c}\sim7.5\,\mathrm{K}$ is inferred from an anomalous Hall behavior
in Sn$_{0.92}$Mn$_{0.08}$Te. The sizable anomalous Hall angle $\sim$0.3
obtained for Sn$_{0.92}$Mn$_{0.08}$Te is one of the greatest reported for
magnetic topological materials. The ferromagnetic ordering with perpendicular
magnetic anisotropy, complemented by the inception of anomalous Hall effect in
the Sn$_{1-x}$Mn$_{x}$Te layers for a thickness commensurate with the decay
length of the top and bottom surface states, points at Sn$_{1-x}$Mn$_{x}$Te as
a preferential platform for the realization of QAH states in ferromagnetic
TCIs.",1907.05716v1
2019-07-31,Ferromagnetism and its stability from the one-magnon spectrum in twisted bilayer graphene,"We study ferromagnetism and its stability in twisted bilayer graphene. We
work with a Hubbard-like interaction that corresponds to the screened Coulomb
interaction in a well-defined limit where the Thomas-Fermi screening length
$l_\text{TF}$ is much larger than monolayer graphene's lattice spacing $l_g \ll
l_\text{TF}$ and much smaller than the Moir\'e super lattice's spacing $
l_\text{TF} \ll l_{\text{Moir\'e}}$. We show that in the perfectly flat band
""chiral"" limit and at filling fractions $\pm 3/4$, the saturated ferromagnetic
(spin and valley polarized) states are ideal ground states candidates in the
large band-gap limit. By assuming a large enough substrate (hBN) induced
sub-lattice potential, the same argument can be applied to filling fractions
$\pm 1/4$. We estimate the regime of stability of the ferromagnetic phase
around the chiral limit by studying the exactly calculated spectrum of
one-magnon excitations. The instability of the ferromagnetic state is signaled
by a negative magnon excitation energy. This approach allows us to deform the
results of the idealized chiral model (by increasing the bandwidth and/or
modified interactions) towards more realistic systems. Furthermore, we use the
low energy part of the exact one-magnon spectrum to calculate the
spin-stiffness of the Goldstone modes throughout the ferromagnetic phase. The
calculated value of spin-stiffness can determine the excitation energy of
charged skyrmions.",1907.13633v1
2019-10-16,Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires built from Iron Phthalocyanine Chains,"Iron phthalocyanine (FePc) is a molecular semiconductor whose building blocks
are one-dimensional ferromagnetic chains. We show that its optical and magnetic
properties are controlled by the growth strategy, obtaining extremely high
coercivities of over 1 T and modulating the exchange constant between 15 and 29
K through tuning the crystal phase by switching from organic molecular beam
deposition, producing continuous thin films of nanocrystals with controlled
orientations, to organic vapour phase deposition, producing ultralong
nanowires. Magnetisation measurements are analysed using a suite of concepts
and simply stated formulas with broad applicability to all one-dimensional
ferromagnetic chains. They show that FePc is best described by a Heisenberg
model with a preference for the moments to lie in the molecular planes, where
the chain Hamiltonian is very similar to that for the classic inorganic magnet
CsNiF3, but with ferromagnetic rather than antiferromagnetic interchain
interactions. The data at large magnetic fields are well-described by the
soliton picture, where the dominant (and topologically non-trivial) degrees of
freedom are moving one-dimensional magnetic domain walls, which was successful
for CsNiF3, and at low temperatures and fields by the super-Curie-Weiss law of
1/(T^2+theta^2) characteristic of nearly one-dimensional xy and Heisenberg
ferromagnets. The ability to control the molecular orientation and
ferromagnetism of FePc systems, and produce them on flexible substrates as thin
films or nanowires, taken together with excellent transistor characteristics
reported previously for nanowires of copper and cobalt analogues, makes them
potentially useful for magneto-optical and spintronic devices.",1910.07229v1
2020-01-14,2D van der Waals Nanoplatelets with Robust Ferromagnetism,"We have synthesized unique colloidal nanoplatelets of the ferromagnetic
two-dimensional (2D) van der Waals material CrI3 and have characterized these
nanoplatelets structurally, magnetically, and by magnetic circular dichroism
spectroscopy. The isolated CrI3 nanoplatelets have lateral dimensions of ~25 nm
and ensemble thicknesses of only ~4 nm, corresponding to just a few CrI3
monolayers. Magnetic and magneto-optical measurements demonstrate robust 2D
ferromagnetic ordering in these nanoplatelets with Curie temperatures similar
to those observed in bulk CrI3, despite the strong spatial confinement. These
data also show magnetization steps akin to those observed in micron-sized
few-layer 2D sheets and associated with concerted spin-reversal of individual
CrI3 layers within few-layer van der Waals stacks. Similar data have also been
obtained for CrBr3 and anion-alloyed Cr(I1-xBrx)3 nanoplatelets. These results
represent the first example of laterally confined 2D van der Waals ferromagnets
of any composition. The demonstration of robust ferromagnetism at nanometer
lateral dimensions opens new doors for miniaturization in spintronics devices
based on van der Waals ferromagnets.",2001.04594v1
2020-02-28,Metallic ferroelectric-ferromagnetic multiferroics in strained EuTiO$_{3-x}$H$_x$,"Polar metals are defined by the coexistence of metallicity and polar crystal
structure. They have potential applications in non-linear optics, ferroelectric
devices, and quantum devices. Meanwhile, ferroelectric-ferromagnetic (FE-FM)
multiferroics display simultaneous ferroelectricity and ferromagnetism, leading
to new technologies in information storage. It remains an open question whether
metallicity, ferroelectricity, and ferromagnetism can coexist in a single
domain of a material. EuTiO$_3$ is actively studied for potential applications
in magnetic sensors, memories, magneto-optical devices, and energy conversion
devices. It stabilizes at a multi-critical equilibrium and exhibits a rich
range of intriguing properties. Here, using the results from hybrid density
functional theory calculations, we report metallic FE-FM multiferroics in
strain-engineered epitaxial EuTiO$_3$ with H doping. The emergence of the
magnetism in polar metals provides a new degree of freedom to control these
materials in applications. The underlying mechanism for the coexistence of
metallicity, ferroelectricity, and ferromagnetism is discussed. The
ferromagnetism in metallic EuTiO$_{3-x}$H$_x$ is explained by the
Ruderman-Kittel-Kasuya- Yosida (RKKY) interaction, which agrees with
experiments. The coexistence of metallicity and ferroelectricity is allowed
because the electrons at the Fermi level are weakly coupled to the
ferroelectric distortion. Our results suggest that the combined effect of
strain and doping is responsible for achieving EuTiO$_3$-based metallic FE-FM
multiferroics and may provide a new way for obtaining metallic FE-FM
multiferroics in other materials.",2002.12783v1
2012-05-23,Low-Temperature Properties of Two-Dimensional Ideal Ferromagnets,"The manifestation of the spin-wave interaction in the low-temperature series
of the partition function has been investigated extensively over more than
seven decades in the case of the three-dimensional ferromagnet. Surprisingly,
the same problem regarding ferromagnets in two spatial dimensions, to the best
of our knowledge, has never been addressed in a systematic way so far. In the
present paper the low-temperature properties of two-dimensional ideal
ferromagnets are analyzed within the model-independent method of effective
Lagrangians. The low-temperature expansion of the partition function is
evaluated up to two-loop order and the general structure of this series is
discussed, including the effect of a weak external magnetic field. Our results
apply to two-dimensional ideal ferromagnets which exhibit a spontaneously
broken spin rotation symmetry O(3) $\to $ O(2) and are defined on a square,
honeycomb, triangular or Kagom\'e lattice. Remarkably, the spin-wave
interaction only sets in at three-loop order. In particular, there is no
interaction term of order $T^3$ in the low-temperature series for the free
energy density. This is the analog of the statement that, in the case of
three-dimensional ferromagnets, there is no interaction term of order $T^4$ in
the free energy density. We also provide a careful discussion of the
implications of the Mermin-Wagner theorem in the present context and thereby
put our low-temperature expansions on safe grounds.",1205.5293v1
2017-11-30,Room-Temperature Ferromagnetic Topological Phase in CrO$_{2}$: From Tripe Fermions to Weyl Fermions,"Ferromagnetic topological semimetals due to their band topology co-existing
with intrinsic magnetization exerted important influences on early study of
topological fermions. However, they have not been observed in experiments up to
now. In this work, we propose that rutile CrO$_{2}$, a widely used
half-metallic ferromagnetic material in magnetic recording taps, exhibits
unexpected ferromagnetic topological features. Using first-principles
calculations and symmetry analysis, we reveal that rutile CrO$_2$ hosts the
triple nodal points in the absence of spin orbital coupling (SOC). By taking
into account of SOC, each triple nodal point splits into two Weyl points, which
are located on the magnetic axis with four-fold rotational symmetry. Notably,
the Fermi arcs and accompanying quasiparticle interference patterns are clearly
visible, which facilitate experimental observations. In addition, we find that
another experimentally synthesized CrO$_{2}$ in CaCl$_2$ structure, also hosts
the topologically nontrivial ferromagnetic phase. Our findings substantially
advance the experimental realization of ferromagnetic topological semimetals.
More importantly, room-temperature time-reversal-breaking Weyl fermions in
CrO$_{2}$ may result in promising applications related to the topological
phenomena in industry.",1711.11203v1
2017-11-30,Appearance and disappearance of ferromagnetism in ultra-thin LaMnO$_3$ on SrTiO$_3$ substrate: a viewpoint from first-principles,"The intrinsic magnetic state (ferromagnetic or antiferromagnetic) of
ultra-thin LaMnO$_3$ films on the mostly used SrTiO$_3$ substrate is a
long-existing question under debate. Either strain effect or non-stoichiometry
was argued to be responsible for the experimental ferromagnetism. In a recent
experiment [Science \textbf{349}, 716 (2015)], one more mechanism, namely the
self-doping due to polar discontinuity, was argued to be the driving force of
ferromagnetism beyond the critical thickness. Here systematic first-principles
calculations have been performed to check these mechanisms in ultra-thin
LaMnO$_3$ films as well as superlattices. Starting from the very precise
descriptions of both LaMnO$_3$ and SrTiO$_3$, it is found that the compressive
strain is the dominant force for the appearance of ferromagnetism, while the
open surface with oxygen vacancies leads to the suppression of ferromagnetism.
Within LaMnO$_3$ layers, the charge reconstructions involve many competitive
factors and certainly go beyond the intuitive polar catastrophe model
established for LaAlO$_3$/SrTiO$_3$ heterostructures. Our study not only
explains the long-term puzzle regarding the magnetism of ultra-thin LaMnO$_3$
films, but also shed light on how to overcome the notorious magnetic dead layer
in ultra-thin manganites.",1711.11329v1
2018-03-05,Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds,"Newly emerged materials from the family of Heuslers and complex oxides
exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much
higher than even room temperature. In this work, using the semiclassical
top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that
utilizes such ferromagnetic semiconductors as channel materials, in addition to
ferromagnetic source/drain contacts. Such a device could retain the spin
polarization of injected electrons in the channel, the loss of which limits the
operation of traditional spin transistors with non-ferromagnetic channels. We
examine the operation of four material systems that are currently considered
some of the most prominent known ferromagnetic semiconductors, three
Heusler-type alloys (Mn2CoAl, CrVZrAl, CoVZrAl) and one from the oxide family
(NiFe2O4). We describe their bandstructures by using data from DFT
calculations. We investigate under which conditions high spin polarization and
significant ION/IOFF ratio, two essential requirements for the spin-MOSFET
operation, are both achieved. We show that these particular Heusler channels,
in their bulk form, do not have adequate bandgap to provide high ION/IOFF
ratios, and have small magnetoconductance compared to state-of-the-art devices.
However, with confinement into ultra-narrow sizes down to a few nanometers, and
by engineering their spin dependent contact resistances, they could prove
promising channel materials for the realization of spin-MOSFET transistor
devices that offer combined logic and memory functionalities. Although the main
compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4
alone, we expect that the insight we provide is relevant to other classes of
such materials as well.",1803.01789v1
2018-06-18,Room-temperature ferromagnetism in monolayer WSe2 semiconductor via vanadium dopant,"Diluted magnetic semiconductors including Mn-doped GaAs are attractive for
gate-controlled spintronics but Curie transition at room temperature with
long-range ferromagnetic order is still debatable to date. Here, we report the
room-temperature ferromagnetic domains with long-range order in semiconducting
V-doped WSe2 monolayer synthesized by chemical vapor deposition. Ferromagnetic
order is manifested using magnetic force microscopy up to 360K, while retaining
high on/off current ratio of ~105 at 0.1% V-doping concentration. The
V-substitution to W sites keep a V-V separation distance of 5 nm without V-V
aggregation, scrutinized by high-resolution scanning transmission-electron
microscopy, which implies the possibility of the Ruderman-Kittel-Kasuya-Yoshida
interaction (or Zener model) by establishing the long-range ferromagnetic order
in V-doped WSe2 monolayer through free hole carriers. More importantly, the
ferromagnetic order is clearly modulated by applying a back gate. Our findings
open new opportunities for using two-dimensional transition metal
dichalcogenides for future spintronics.",1806.06479v2
2019-04-18,Supercurrent in ferromagnetic Josephson junctions with heavy metal interlayers. II. Canted magnetization,"It has been suggested by theoretical works that equal spin-triplet Cooper
pairs can be generated in Josephson junctions containing both a ferromagnet and
a source of spin-orbit coupling. Our recent experimental work suggested that
spin-triplet Cooper pairs were not generated by a Pt spin-orbit coupling layer
when the ferromagnetic weak link had entirely in-plane anisotropy (N. Satchell
and N.O. Birge, Phys. Rev. B 97, 214509 (2018)). Here, we revisit the
experiment using Pt again as a source for spin-orbit coupling and a [Co(0.4
nm)/Ni(0.4 nm)]$_{\times8}$/Co(0.4 nm) ferromagnetic weak link with both
in-plane and out-of-plane magnetization components (canted magnetization). The
canted magnetization more closely matches theoretical predictions than our
previous experimental work. Our results suggest that there is no supercurrent
contribution in our junctions from equal spin-triplets. In addition, this work
includes the first systematic study of supercurrent dependence on Cu interlayer
thickness, a common additional layer used to buffer the growth of the
ferromagnet and which for Co may significantly improve the growth morphology.
We report that the supercurrent in the [Co(0.4 nm)/Ni(0.4
nm)]$_{\times8}$/Co(0.4 nm) ferromagnetic weak links can be enhanced by over
two orders of magnitude by tuning the Cu interlayer thickness. This result has
important application in superconducting spintronics, where large critical
currents are desirable for devices.",1904.08798v2
2019-11-18,"Vector-boson condensates, spin-triplet superfluidity of paired neutral and charged fermions, and $3P_2$ pairing of nucleons","After reminding of properties of the condensate of the complex scalar field
in the external uniform magnetic field $H$ focus is made on the study of phases
of the complex neutral vector boson fields coupled with magnetic field by the
Zeeman coupling and phases of the charged vector boson fields. These systems
may behave as nonmagnetic and ferromagnetic superfluids and ordinary and
ferromagnetic superconductors. Response of the ferromagnetic superfluid and
superconducting systems occupying half of space on the external uniform static
magnetic field $H$ is thoroughly studied. Then the spin-triplet pairing of
neutral fermions at conserved spin is considered. Novel phases are found. In
external magnetic field the phase with zero mean spin proves to be unstable to
the formation of a phase with a non-zero spin. For $H>H_{\rm cr 2}$ the
spin-triplet pairing and ferromagnetic superfluidity continue to exist above
the ""old"" phase transition critical temperature $T_{\rm cr}$. For a certain
parameter choice ferromagnetic superfluid phases are formed already for $H=0$,
characterized by an own magnetic field $h$. Formation of domains is discussed.
Next, spin-triplet pairing of charged fermions is studied. Novel phases are
found with a ferromagnetic superconductivity. Then, the 3P$_2$ $nn$ pairing in
neutron star matter is studied. Also a 3P$_2$ $pp$ pairing is considered.
Numerical estimates are performed in the BCS weak coupling limit and beyond it
for the $3P_2$ $nn$ and $pp$ pairings, as well as for the 3S$_1$ $np$ pairing.",1911.07502v2
2019-12-19,Metallic states beyond Tomonaga-Luttinger liquids in one dimension,"In this paper, we propose some new strongly correlated gapless states (or
critical states) of spin-1/2 electrons in 1+1-dimensions, such as doped
anti-ferromagnetic spin-1/2 Ising chain. We find doped anti-ferromagnetic Ising
chain to be a different metallic phase from the doped ferromagnetic Ising
chain, despite the two have identical symmetry. The doped anti-ferromagnetic
Ising chain has a finite energy gap for all charge-1 fermionic excitations even
without pairing caused by attractive interactions, resembling the pseudo-gap
phase of underdoped high Tc superconductors. Applying a transverse field to the
ferromagnetic and anti-ferromagnetic metallic phases can restore the $Z_2$
symmetry, which gives rise to two distinct critical points despite that the two
transitions have exactly the same symmetry breaking pattern. We also propose
new chiral metallic states. All those new gapless states are strongly
correlated in the sense that they do not belong to the usual Tomonaga-Luttinger
phase of fermions, i.e., they cannot be smoothly deformed into the
non-interacting fermion systems of the same symmetry. Our non-perturbative
results are obtained by noticing that gapless quantum systems have emergent
categorical symmetries, i.e., non-invertible gravitational anomalies), which
are described by multi-component partition functions that are modular
covariant. This allows us to calculate the scaling dimensions and quantum
numbers of all the low energy operators for those strongly correlated gapless
states. This demonstrates an application of emergent categorical symmetries in
determining low energy properties of strongly correlated gapless states, which
are hard to obtain otherwise.",1912.09391v3
2020-06-03,First-principles calculation of gate-tunable ferromagnetism in magic-angle twisted bilayer graphene under pressure,"Magic-angle twisted bilayer graphene (MATBG) is notable as a highly tunable
platform for investigating strongly correlated phenomena such as high-$T_c$
superconductivity and quantum spin liquids, due to easy control of doping level
through gating and sensitive dependence of the magic angle on hydrostatic
pressure. Experimental observations of correlated insulating states,
unconventional superconductivity and ferromagnetism in MATBG indicate that this
system exhibits rich exotic phases. In this work, using density functional
theory calculations in conjunction with the effective screening medium method,
we find the MATBG under pressure at a twisting angle of $2.88\unicode{xb0}$ and
simulate how its electronic states evolve when doping level and out-of-plane
electric field are gate-tuned. Our calculations show that, at doping levels
between two electrons and four holes per moir\'{e} unit cell, a ferromagnetic
solution with spin density localized at AA stacking sites is lower in energy
than the nonmagnetic solution. The magnetic moment of this ferromagnetic state
decreases with both electron and hole doping and vanishes at four
electrons/holes doped per moir\'{e} unit cell. Hybridization between the flat
bands at the Fermi level and the surrounding dispersive bands can take place at
finite doping. Moreover, upon increasing the out-of-plane electric field at
zero doping, a transition from the ferromagnetic state to the nonmagnetic one
is seen. We also analyze the interlayer bonding character due to the flat bands
via Wannier functions. Finally, we report trivial band topology of the flat
bands in the ferromagnetic state at a certain doping level.",2006.02362v1
2021-03-14,Toward a systematic discovery of artificial functional magnetic materials,"Although ferromagnets are found in all kinds of technological applications,
only few substances are known to be intrinsically ferromagnetic at room
temperature. In the past twenty years, a plethora of new artificial
ferromagnetic materials have been found by introducing defects into
non-magnetic host materials. In contrast to the intrinsic ferromagnetic
materials, they offer an outstanding degree of material engineering freedom,
provided one finds a type of defect to functionalize every possible host
material to add magnetism to its intrinsic properties. Still, one controversial
question remains: Are these materials really technologically relevant
ferromagnets? To answer this question, in this work the emergence of a
ferromagnetic phase upon ion irradiation is systematically investigated both
theoretically and experimentally. Quantitative predictions are validated
against experimental data from the literature of SiC hosts irradiated with high
energy Ne ions and own experiments on low energy Ar ion irradiation of TiO$_2$
hosts. In the high energy regime, a bulk magnetic phase emerges, which is
limited by host lattice amorphization, whereas at low ion energies an ultrathin
magnetic layer forms at the surface and evolves into full magnetic percolation.
Lowering the ion energy, the magnetic layer thickness reduces down to a
bilayer, where a perpendicular magnetic anisotropy appears due to magnetic
surface states.",2103.08045v3
2021-07-29,Superconducting triplet pairings and anisotropic magnetoresistance effects in ferromagnet/superconductor/ferromagnet double-barrier junctions,"Ferromagnetic spin valves offer the key building blocks to integrate giant-
and tunneling-magnetoresistance effects into spintronics devices. Starting from
a generalized Blonder-Tinkham-Klapwijk approach, we theoretically investigate
the impact of interfacial Rashba and Dresselhaus spin-orbit couplings on the
tunneling conductance, and thereby the magnetoresistance characteristics, of
ferromagnet/superconductor/ferromagnet spin-valve junctions embedding thin
superconducting spacers between the either parallel or antiparallel magnetized
ferromagnets. We focus on the unique interplay between usual electron
tunnelings-that fully determine the magnetoresistance in the normal-conducting
state-and the peculiar Andreev reflections in the superconducting state. In the
presence of interfacial spin-orbit couplings, special attention needs to be
paid to the spin-flip (""unconventional"") Andreev-reflection process that is
expected to induce superconducting triplet correlations in proximitized
regions. As a transport signature of these triplet pairings, we detect
conductance double peaks around the singlet-gap energy, reflecting the
competition between the singlet and an additionally emerging triplet gap; the
latter is an effective superconducting gap that can be ascribed to the
formation of triplet Cooper pairs through interfacial spin-flip scatterings
(i.e., to the generation of an effective triplet-pairing term in the order
parameter). We thoroughly analyze the Andreev reflections' role in connection
with superconducting magnetoresistance phenomena, and eventually unravel huge
conductance and magnetoresistance magnetoanisotropies-easily exceeding their
normal-state counterparts by several orders of magnitude-as another
experimentally accessible fingerprint of unconventional Andreev reflections.",2107.13818v2
2021-12-18,Itinerant ferromagnetism in narrow-band metals,"Since its introduction in 1963, the Hubbard model has becomes one of the most
popular models used in the literature to study cooperative phenomena in
narrow-band metals (ferromagnetism, metal-insulator transitions, charge-density
waves, high-T$_c$ superconductivity). Amongst all these cooperative phenomena,
the problem of itinerant ferromagnetism in the Hubbard model has the longest
history. However, in spite of an impressive research activity in the past, the
underlying physics (microscopic mechanisms) that leads to the stabilization of
itinerant ferromagnetism in Hubbard model (narrow-band metals) is still far
from being understood. In this review we present our numerical results
concerning this subject, which have been reached by small cluster exact
diagonalization, density matrix renormalization group and quantum Monte Carlo
calculations within various extensions of the Hubbard model. Particular
attention is paid to a description of crucial mechanisms (interactions) that
support the stabilization of the ferromagnetic state, and namely: (i) the
long-range hopping, (ii) the correlated hopping, (iii) the long-range Coulomb
interaction, (iv) the flat bands and (v) the lattice structure. Most of the
presented results have been obtained for the one-dimensional case, but the
influence of the increasing dimension of the system on the ferromagnetic state
is also intensively discussed.",2112.09913v1
2022-01-16,Evolution from helical to collinear ferromagnetic order of the Eu$^{2+}$ spins in RbEu(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$,"The ground-state magnetic structures of the Eu$^{2+}$ spins in recently
discovered RbEu(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ superconductors have been
investigated by neutron powder diffraction measurements. It is found that as
the superconductivity gets suppressed with the increase of Ni doping, the
magnetic propagation vector of the Eu sublattice diminishes, corresponding to
the decrease of the rotation angle between the moments in neighboring Eu
layers. The ferromagnetic Eu layers are helically modulated along the
$\mathit{c}$ axis with an incommensurate magnetic propagation vector in both
the ferromagnetic superconductor RbEu(Fe$_{0.95}$Ni$_{0.05}$)$_{4}$As$_{4}$ and
the superconducting ferromagnet RbEu(Fe$_{0.93}$Ni$_{0.07}$)$_{4}$As$_{4}$.
Such a helical structure transforms into a purely collinear ferromagnetic
structure for non-superconducting RbEu(Fe$_{0.91}$Ni$_{0.09}$)$_{4}$As$_{4}$,
with all the Eu$^{2+}$ spins lying along the tetragonal (1 1 0) direction. The
evolution from helical to collinear ferromagnetic order of the Eu$^{2+}$ spins
with increasing Ni doping is supported by first-principles calculations. The
variation of the rotation angle between adjacent Eu$^{2+}$ layers can be well
explained by considering the change of magnetic exchange couplings mediated by
the indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction.",2201.05988v1
2022-03-01,Cu-doping effects on the ferromagnetic semimetal CeAuGe,"We present a study of Cu-substitution effects in 4f-Ce intermetallic compound
CeAu1-xCuxGe, with potentially unusual electronic states, in the whole
concentration range (x = 0.0 - 1.0). The parent CeAuGe compound, crystallizing
in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with
Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu1-xCuxGe, changes
the crystal structure from the non-centrosymmetric (P63mc) to centrosymmetric
(P63/mmc) space group at the concentration x ~ 0.5, where the c-lattice
constant has a maximum value. Magnetic susceptibility and electrical
resistivity measurements reveal that all Cu-doped compounds undergo magnetic
phase transition near 10 K, with the maximum transition temperature of 12 K for
x = 0.5. The neutron powder diffraction experiments show the ferromagnetic
ordering of Ce3+ magnetic moments with a value of ~ 1.2 Bohr magneton at 1.8 K,
oriented perpendicular to the hexagonal c-axis. By using symmetry analysis, we
have found the solutions for the magnetic structure in the ferromagnetic
Shubnikov space groups Cmc'21' and P21'/m' for x < 0.5 and x >= 0.5,
respectively. Electrical resistivity exhibits a metallic temperature behaviour
in all compounds. The resistivity has a local minimum in the paramagnetic state
due to Kondo effects at high doping x = 0.8 and 1.0. At the small Cu-doping
level, x = 0.2, the resistivity shows a broad feature at the ferromagnetic
transition temperature and an additional transition-like peculiarity at 2.5 K
in the ferromagnetic state.",2203.00335v1
2022-03-22,Unconventional spin frustration due to two competing ferromagnetic interactions of a spin-1/2 Ising-Heisenberg model on martini and martini-diced lattice,"The spin-1/2 Ising-Heisenberg model on martini and martini-diced lattice is
exactly solved using a star-triangle transformation, which affords an exact
mapping correspondence to an effective spin-1/2 Ising model on a triangular
lattice. The ground-state phase diagram of both investigated quantum spin
models display two spontaneously ordered ferromagnetic phases and one
macroscopically degenerate disordered phase. In contrast to a classical
ferromagnetic phase where the spontaneous magnetization of the Ising as well as
Heisenberg spins acquire fully saturated values the spontaneous magnetization
of the Heisenberg spins is subject to a quantum reduction to one-third of its
saturated value within a quantum ferromagnetic phase. The spontaneous
magnetization and logarithmic divergence of the specific heat as the most
essential features of both ferromagnetic phases disappear whenever the
investigated quantum spin model is driven to the highly degenerate disordered
phase. The disordered phase with nonzero residual entropy originates either
from a geometric spin frustration caused by antiferromagnetic interactions or
more strikingly it may also alternatively arise from a competition of the
ferromagnetic Ising and Heisenberg interactions of easy-axis and easy-plane
type, respectively. All three available ground states coexist together at a
single triple point, around which anomalous magnetic and thermodynamic behavior
can be detected.",2203.11582v1
2022-07-05,"Prediction of High Curie Temperature, Large Magnetic Crystal Anisotropy in 2D Ferromagnetic Co$_2$Ge$_2$Te$_6$ Monolayer and Multilayer","The Co$_2$Ge$_2$Te$_6$ shows intrinsic ferromagnetic (FM) order, which
origins from superexchange interaction between Co and Te atoms, with higher
Curie temperature ($T_c$) of 161 K. Co$_2$Ge$_2$Te$_6$ monolayer (ML) is
half-metal (HM), and spin-$\beta$ electron is a semiconductor with gap of 1.311
eV. Co$_2$Ge$_2$Te$_6$ ML tends in-plane anisotropy (IPA), with magnetic
anisotropy energy (MAE) of -10.2 meV/f.u.. Co$_2$Ge$_2$Te$_6$ ML shows good
dynamical and thermal stability. Most interestingly, bilayers present
ferromagnetic half-metallicity independent of the stacking orders. Notley, the
multilayers ($N\ge 6$) present ferromagnetic HM, while the magnetoelectronic
properties are related with the stacking patterns in thinner multilayers.
Moreover, the magnetoelectronic properties are dependent on the stacking orders
of bulk. The magnetic order with multilayers is determined by the super-super
exchange and weak van der Waals (vdW) interaction. Co$_2$Ge$_2$Te$_6$ with
intrinsic ferromagnetism, good stability of ferromagnetism and half-metallicity
could help researchers to investigate its wide application in the spintronics.",2207.02024v1
2022-08-31,Surface state mediated ferromagnetism in Mn$_{0.14}$Bi$_{1.86}$Te$_3$ thin films,"A spontaneous ferromagnetic moment can be induced in Bi$_{2}$Te$_{3}$ thin
films below a temperature T $\approx$ 16 K by the introduction of Mn dopants.
We demonstrate that films grown via molecular beam epitaxy with the
stoichiometry Mn$_{0.14}$Bi$_{1.86}$Te$_3$ maintain the crystal structure of
pure Bi$_{2}$Te$_{3}$. The van der Waals nature of inter-layer forces in the
Mn$_{0.14}$Bi$_{1.86}$Te$_3$ crystal causes lattice mismatch with the
underlayer to have a limited effect on the resulting crystal structure, as we
demonstrate by thin film growth on tetragonal MgF$_{2}$ (110) and NiF$_{2}$
(110). Electronic transport and magnetic moment measurements show that the
ferromagnetic moment of the Mn$_{0.14}$Bi$_{1.86}$Te$_3$ thin films is enhanced
as the Fermi level moves from the bulk conduction band and towards the bulk
band gap, suggesting that electronic surface states play an important role in
mediating the ferromagnetic order. Ferromagnetic
Mn$_{0.14}$Bi$_{1.86}$Te$_3$/antiferromagnetic NiF$_{2}$ bilayers show evidence
that the ferromagnetic moment of the Mn$_{0.14}$Bi$_{1.86}$Te$_3$ film is
suppressed, suggesting the existence of an interface effect between the two
magnetic layers.",2209.00155v2
2023-02-10,Discovery of Superconductivity in Van der Waals Ferromagnetic Sn$_{0.06}$Cr$_3$Te$_4$,"Coexistence of superconductivity and ferromagnetism, though a very few
systems show this, is one of the exciting properties of a solid from the
fundamental science point of view. Here, we report on the discovery of
superconductivity in the van der Waals ferromagnetic Cr$_3$Te$_4$ that is
coexisted with ferromagnetism, induced by the Sn intercalation
(Sn$_{0.06}$Cr$_{3}$Te$_4$), below a transition temperature of $T_c$=3.5 K. In
addition, despite the magnetism and Meissner effects are anisotropic, the
superconductivity observed from the in-plane electrical resistivity
($\rho_{\it{bc}}$) is nearly isotropic between $H\parallel \it{bc}$ and
$H\parallel \it{a}$, suggesting separate channels of conduction electrons
responsible for the superconductivity and ferromagnetism of this system which
is supported by our spin-resolved DFT calculations. We identify two orders
increase in the carrier density of Cr$_{3}$Te$_4$ by Sn intercalation compared
to the parent Cr$_3$Te$_4$. We think, the enhanced carrier density could be
playing a key role for the discovered superconductivity in ferromagnetic
Sn$_{0.06}$Cr$_{3}$Te$_4$. We also explored other mechanisms such as the Fermi
surface nesting to understand microscopically the superconductivity of this
system.",2302.05145v1
2023-03-17,Large-area synthesis of ferromagnetic Fe$_{5-x}$GeTe$_{2}$/graphene van der Waals heterostructures with Curie temperature above room temperature,"Van der Waals (vdW) heterostructures combining layered ferromagnets and other
two-dimensional (2D) crystals are promising building blocks for the realization
of ultra-compact devices with integrated magnetic, electronic and optical
functionalities. Their implementation in various technologies depends strongly
on the development of a bottom-up scalable synthesis approach allowing to
realize highly uniform heterostructures with well-defined interfaces between
different 2D layered materials. It also requires that each material component
of the heterostructure remains functional, which ideally includes ferromagnetic
order above room temperature for 2D ferromagnets. Here, we demonstrate
large-area growth of Fe$_{5-x}$GeTe$_{2}$/graphene heterostructures achieved by
vdW epitaxy of Fe$_{5-x}$GeTe$_{2}$ on epitaxial graphene. Structural
characterization confirmed the realization of a continuous vdW heterostructure
film with a sharp interface between Fe$_{5-x}$GeTe$_{2}$ and graphene. Magnetic
and transport studies revealed that the ferromagnetic order persists well above
300 K with a perpendicular magnetic anisotropy. In addition, epitaxial graphene
on SiC(0001) continues to exhibit a high electronic quality. These results
represent an important advance beyond non-scalable flake exfoliation and
stacking methods, thus marking a crucial step toward the implementation of
ferromagnetic 2D materials in practical applications.",2303.10252v1
2023-05-02,Frustration induced Itinerant Ferromagnetism of Fermions in Optical Lattice,"When the Fermi Hubbard model was first introduced sixty years ago, one of the
original motivations was to understand correlation effects in itinerant
ferromagnetism. In the past two decades, ultracold Fermi gas in an optical
lattice has been used to study the Fermi Hubbard model. However, the metallic
ferromagnetic correlation was observed only in a recent experiment using
frustrated lattices, and its underlying mechanism is not clear yet. In this
letter, we point out that, under the particle--hole transformation, the
single-particle ground state can exhibit double degeneracy in such a frustrated
lattice. Therefore, the low-energy state exhibits valley degeneracy,
reminiscent of multi-orbit physics in ferromagnetic transition metals. The
local repulsive interaction leads to the valley Hund's rule, responsible for
the observed ferromagnetism. We generalize this mechanism to distorted
honeycomb lattices and square lattices with flux. This mechanism was first
discussed by M\""uller-Hartmann in a simpler one-dimension model. However, this
mechanism has not been widely discussed and has not been related to
experimental observations before. Hence, our study not only explains the
experimental findings but also enriches our understanding of itinerant
ferromagnetism.",2305.01682v1
2023-05-02,Exciton and light induced ferromagnetism from doping a moiré Mott insulator,"Significant efforts have been dedicated to achieving excitonic insulators. In
this paper, we explore a new problem of doping excitons into a Mott insulator
instead of a band insulator. Specifically, we start with a Mott insulator on a
triangular moir\'e superlattice in a transition metal dichalcogenides (TMD)
layer and inject excitons by either transferring particles to a different layer
or optically pumping electrons from the valence to the conduction band. In both
cases, the excitons move in the presence of local spin moments inherited from
the Mott insulator. When the Heisenberg spin coupling $J$ is small, the kinetic
energy of the excitons decides the magnetism, akin to Nagaoka ferromagnetism in
hole-doped Mott insulators. Through density matrix renormalization group (DMRG)
calculations, we demonstrate that the spin moments originating from the Mott
insulator form $120^\circ$ antiferromagnetic or ferromagnetic order for the two
signs of the exciton hoppings over a broad range of exciton densities. Notably,
the optical pump case may result in an antiferromagnetic to ferromagnetic
transition with increasing exciton density, indicating a potential mechanism
for light-induced ferromagnetism. A similar exciton-induced ferromagnetism
could be achieved in a moir\'e-monolayer system where the monolayer is
electron-doped while the moir\'e Mott insulator is hole-doped. Our works
demonstrates a new possibility to engineering magnetism through doping neutral
excitons.",2305.01702v2
2023-07-18,Coexistence of Logarithmic and SdH Quantum Oscillations in Ferromagnetic Cr-doped Tellurium Single Crystals,"We report the synthesis of transition-metal-doped ferromagnetic elemental
single-crystal semiconductors with quantum oscillations using the physical
vapor transport method. The 7.7 atom% Cr-doped Te crystals (Cr_Te) show
ferromagnetism, butterfly-like negative magnetoresistance in the low
temperature (< 3.8 K) and low field (< 0.15 T) region, and high Hall mobility,
e.g., 1320 cm2 V-1 s-1 at 30 K and 350 cm2 V-1 s-1 at 300 K, implying that
Cr_Te crystals are ferromagnetic elemental semiconductors. When B // c // I,
the maximum negative MR is -27% at T = 20 K and B = 8 T. In the low temperature
semiconducting region, Cr_Te crystals show strong discrete scale invariance
dominated logarithmic quantum oscillations when the direction of the magnetic
field B is parallel to the [100] crystallographic direction and show Landau
quantization dominated Shubnikov-de Haas (SdH) oscillations for B // [210]
direction, which suggests the broken rotation symmetry of the Fermi pockets in
the Cr_Te crystals. The findings of coexistence of multiple quantum
oscillations and ferromagnetism in such an elemental quantum material may
inspire more study of narrow bandgap semiconductors with ferromagnetism and
quantum phenomena.",2307.09139v1
2023-07-25,Unusual band evolution and persistence of topological surface states in high-T_C magnetic topological insulator,"Understanding the mechanism of ferromagnetism in ferromagnetic topological
insulators (TIs) is a key to realize exotic time-reversal-symmetry-broken
quantum phases. However, electronic states relevant to the ferromagnetism are
highly controversial. Here we report angle-resolved photoemission spectroscopy
on (CrxSb1-x)2Te3 thin films, high-Curie-temperature (T_C) ferromagnetic TIs,
spanning the non-doped (T_C=0 K) to highly-doped (T_C=192 K) region. We found
that, upon Cr doping to Sb2Te3, the bulk valence-band valley exhibits
filling-in behavior while retaining band inversion, leading to the formation of
a nearly-flat band in high-T_C regime and evolution from a six-petal flower to
a Star-of-David Fermi surface. Despite the weakening of spin-orbit coupling
with Cr doping, the Dirac-cone state persists up to the highest-T_C sample, and
shows a clear magnetic-gap opening below TC accompanied with an unexpected band
shift, signifying its strong coupling with spontaneous ferromagnetism. The
present result lays the foundation for understanding the interplay between band
topology and ferromagnetism in TIs.",2307.13388v1
2023-08-23,Room-Temperature Highly-Tunable Coercivity and Highly-Efficient Nonvolatile Multi-States Magnetization Switching by Small Current in Single 2D Ferromagnet Fe$_3$GaTe$_2$,"Room-temperature electrically-tuned coercivity and nonvolatile multi-states
magnetization switching is crucial for next-generation low-power 2D
spintronics. However, most methods have limited ability to adjust the
coercivity of ferromagnetic systems, and room-temperature electrically-driven
magnetization switching shows high critical current density and high power
dissipation. Here, highly-tunable coercivity and highly-efficient nonvolatile
multi-states magnetization switching are achieved at room temperature in
single-material based devices by 2D van der Waals itinerant ferromagnet
Fe$_3$GaTe$_2$. The coercivity can be readily tuned up to ~98.06% at 300 K by a
tiny in-plane electric field that is 2-5 orders of magnitude smaller than that
of other ferromagnetic systems. Moreover, the critical current density and
power dissipation for room-temperature magnetization switching in 2D
Fe$_3$GaTe$_2$ are down to ~1.7E5 A cm$^{-2}$ and ~4E12 W m$^{-3}$,
respectively. Such switching power dissipation is 2-6 orders of magnitude lower
than that of other 2D ferromagnetic systems. Meanwhile, multi-states
magnetization switching are presented by continuously controlling the current,
which can dramatically enhance the information storage capacity and develop new
computing methodology. This work opens the avenue for room-temperature
electrical control of ferromagnetism and potential applications for
vdW-integrated 2D spintronics.",2308.12007v1
2023-09-27,From Stoner to Local Moment Magnetism in Atomically Thin Cr2Te3,"The field of two-dimensional (2D) ferromagnetism has been proliferating over
the past few years, with ongoing interests in basic science and potential
applications in spintronic technology. However, a high-resolution spectroscopic
study of the 2D ferromagnet is still lacking due to the small size and air
sensitivity of the exfoliated nanoflakes. Here, we report a thickness-dependent
ferromagnetism in epitaxially grown Cr2Te3 thin films and investigate the
evolution of the underlying electronic structure by synergistic angle-resolved
photoemission spectroscopy, scanning tunneling microscopy, x-ray absorption
spectroscopy, and first-principle calculations. A conspicuous ferromagnetic
transition from Stoner to Heisenberg-type is directly observed in the
atomically thin limit, indicating that dimensionality is a powerful tuning knob
to manipulate the novel properties of 2D magnetism. Monolayer Cr2Te3 retains
robust ferromagnetism, but with a suppressed Curie temperature, due to the
drastic drop in the density of states near the Fermi level. Our results
establish atomically thin Cr2Te3 as an excellent platform to explore the dual
nature of localized and itinerant ferromagnetism in 2D magnets.",2309.15371v1
2024-03-04,Order-by-disorder without quantum zero-point fluctuations in the pyrochlore Heisenberg ferromagnet with Dzyaloshinskii-Moriya interactions,"Order-by-disorder, whereby fluctuations lift an accidental classical ground
state degeneracy to stabilize a subset of ordered states, is a recurrent and
prominent theme in the field of frustrated magnetism where magnetic moments, or
spins, are subject to competing interactions. Thus far, such a phenomenon has
been discussed in systems where the quantum ground state is not a product
state. In this circumstance, both thermal and quantum fluctuations act to lift
the accidental classical degeneracy, begging the question whether one mechanism
of order-by-disorder is possible without the other. In this paper, we present
results exposing a novel route to order-by-disorder, without quantum zero-point
fluctuations, in a family of ferromagnetic Heisenberg materials with the
Dzyaloshinskii-Moriya (DM) interaction as the leading perturbation. We prove
that any colinear ferromagnetic state is an exact eigenstate, even in the
presence of the anisotropic DM interaction, while thermal fluctuations give
rise to a preference in the magnetization direction. Here, we present in detail
an example of the pyrochlore Heisenberg ferromagnet with DM interactions. Using
both linear spin-wave theory and classical Monte Carlo simulations, we find
that the magnetization can spontaneously rotate at intermediate temperature(s)
within the colinear ferromagnetic phase when the DM interaction is large.
Additionally, we find that in the large DM regime, the ferromagnetic ground
state becomes unstable within the framework of non-linear spin-wave theory. Our
results show that thermal order-by-disorder is possible even in the absence of
quantum zero-point fluctuations.",2403.02391v1
2002-02-25,Eccentricity Evolution for Planets in Gaseous Disks,"We investigate the hypothesis that interactions between a giant planet and
the disk from which it forms promote eccentricity growth. These interactions
are concentrated at discrete Lindblad and corotation resonances. Interactions
at principal Lindblad resonances cause the planet's orbit to migrate and open a
gap in the disk if the planet is sufficiently massive. Those at first order
Lindblad and corotation resonances change the planet's orbital eccentricity.
Eccentricity is excited by interactions at external Lindblad resonances which
are located on the opposite side of corotation from the planet, and damped by
co-orbital Lindblad resonances which overlap the planet's orbit. If the planet
clears a gap in the disk, the rate of eccentricity damping by co-orbital
Lindblad resonances is reduced. Density gradients associated with the gap
activate eccentricity damping by corotation resonances at a rate which
initially marginally exceeds that of eccentricity excitation by external
Lindblad resonances. But the corotation torque drives a mass flux which reduces
the density gradient near the resonance. Sufficient partial saturation of
corotation resonances can tip the balance in favor of eccentricity excitation.
A minimal initial eccentricity of a few percent is required to overcome viscous
diffusion which acts to unsaturate corotation resonances by reestablishing the
large scale density gradient. Thus eccentricity growth is a finite amplitude
instability. Formally, interactions at the apsidal resonance, which is a
special kind of co-orbital Lindblad resonance, appears to damp eccentricity
faster than external Lindblad resonances can excite it. However, apsidal waves
have such long wavelengths that they do not propagate in protoplanetary disks.
This reduces eccentricity damping by the apsidal resonance to a modest level.",0202462v1
2020-12-16,Non-Invasive Near-field Spectroscopy of Single Sub-Wavelength Complementary Resonators,"Subwavelength metallic resonators provide a route to achieving strong
light-matter coupling by means of tight confinement of resonant electromagnetic
fields. Investigation of such resonators however often presents experimental
difficulties, particularly at terahertz (THz) frequencies. A single
subwavelength resonator weakly interacts with THz beams, making it difficult to
probe it using far-field methods; whereas arrays of resonators exhibit
inter-resonator coupling, which affects the resonator spectral signature and
field confinement. Here, traditional far-field THz spectroscopy is
systematically compared with aperture-type THz near-field microscopy for
investigating complementary THz resonators. Whilst the far-field method proves
impractical for measuring single resonators, the near-field technique gives
high signal-to-noise spectral information, only achievable in the far-field
with resonator arrays. At the same time, the near-field technique allows us to
analyze single resonators - free from inter-resonator coupling present in
arrays - without significant interaction with the near-filed probe.
Furthermore, the near-field technique allows highly confined fields and surface
waves to be mapped in space and time. This information gives invaluable insight
into resonator spectral response in arrays. This near-field microscopy and
spectroscopy method enables investigations of strong light-matter coupling at
THz frequencies in the single-resonator regime.",2012.09137v1
2012-05-04,Study of Resonances for the Restricted 3-Body Problem,"Our aim is to identify and classify mean-motion resonances (MMRs) for the
coplanar circular restricted three-body problem (CR3BP) for mass ratios between
0.10 and 0.50. Our methods include the maximum Lyapunov exponent, which is used
as an indicator for the location of the resonances, the Fast Fourier Transform
(FFT) used for determining what kind of resonances are present, and the
inspection of the orbital elements to classify the periodicity. We show that
the 2:1 resonance occurs the most frequently. Among other resonances, the 3:1
resonance is the second most common, and furthermore both 3:2 and 5:3
resonances occur more often than the 4:1 resonance. Moreover, the resonances in
the coplanar CR3BP are classified based on the behaviour of the orbits. We show
that orbital stability is ensured for high values of resonance (i.e., high
ratios) where only a single resonance is present. The resonances attained are
consistent with the previously established resonances for the Solar System,
i.e., specifically, in regards to the asteroid belt. Previous work employed
digital filtering and Lyapunov characteristic exponents to determine
stochasticity of the eccentricity, which is found to be consistent with our
usage of Lyapunov exponents as an alternate approach based on varying the mass
ratio instead of the eccentricity. Our results are expected to be of principal
interest to future studies, including augmentations to observed or proposed
resonances, of extra-solar planets in binary stellar systems.",1205.0950v1
2024-02-12,Uranus's influence on Neptune's exterior mean motion resonances,"Neptune's external mean motion resonances play an important role in sculpting
the observed population of transneptunian objects (TNOs). The population of
scattering TNOs are known to 'stick' to Neptune's resonances while evolving in
semimajor axis ($a$), though simulations show that resonance sticking is less
prevalent at $a\gtrsim200-250$ au. Here we present an extensive numerical
exploration of the strengths of Neptune's resonances for scattering TNOs with
perihelion distances $q=33$ au. We show that the drop-off in resonance sticking
for the large $a$ scattering TNOs is not a generic feature of scattering
dynamics, but can instead be attributed to the specific configuration of
Neptune and Uranus in our solar system. In simulations with just Uranus removed
from the giant planet system, Neptune's resonances are strong in the scattering
population out to at least $\sim300$ au. Uranus and Neptune are near a 2:1
period ratio, and the variations in Neptune's orbit resulting from this near
resonance are responsible for destabilizing Neptune's resonances for high-$e$
TNO orbits beyond the $\sim20$:1 resonance at $a\approx220$ au. Direct
interactions between Uranus and the scattering population are responsible for
slightly weakening Neptune's closer-in resonances. In simulations where Neptune
and Uranus are placed in their mutual 2:1 resonance, we see almost no stable
libration of scattering particles in Neptune's external resonances. Our results
have important implications for how the strengths of Neptune's distant
resonances varied during the epoch of planet migration when the Neptune-Uranus
period ratio was evolving. These strength variations likely affected the
distant resonant and detached TNO populations.",2402.07824v1
1992-07-15,Ferromagnetism of the 1-D Kondo Lattice Model: A Quantum Monte Carlo Study,"The one dimensional Kondo lattice model is investigated using Quantum Monte
Carlo and transfer matrix techniques. In the strong coupling region
ferromagnetic ordering is found even at large band fillings. In the weak
coupling region the system shows an RKKY like behavior.",9207016v1
1994-01-25,Curie Temperatures for Binary Ising Ferromagnets on the Square Lattice,"High-accuracy Swendsen and Wang Monte Carlo simulations were performed to
study the Curie temperature of ferromagnetic, binary Ising systems on the
square lattice. Our results are compared with mean-field like approaches. Based
on these former theories, we give a new formula to estimate the Curie
temperature of the system.",9401052v1
1994-02-03,Curie Temperatures for Three-Dimensional Binary Ising Ferromagnets,"Using the Swendsen and Wang algorithm, high accuracy Monte Carlo simulations
were performed to study the concentration dependence of the Curie temperature
in binary, ferromagnetic Ising systems on the simple-cubic lattice. Our results
are in good agreement with known mean-field like approaches. Based on former
theoretical formulas we propose a new way of estimating the Curie temperature
of these systems.",9402013v1
1995-06-26,Weak universality in the two dimensional randomly disordered three-state Potts ferromagnet,"For the two dimensional randomly disordered three-state Potts ferromagnet, we
find numerically that the critical exponent $\eta$ unchanges with the degree of
disorder while those of the correlation length ($\nu$) and magnetic
susceptibility ($\gamma$) increase with it continuously. We discuss some
consequences of the finding.",9506117v1
1996-03-18,Renormalization-Group Approach to Spin-Wave Theory of Quantum Heisenberg Ferromagnet,"The renormalization-group method is used to analyze the low-temperature
behaviour of a two-dimentional, spin-$s$ quantum Heisenberg ferromagnet. A set
of recursion equations is derived in an one-loop approximation. The
low-temperature asymptotics of the correlation length and the uniform
susceptibility are obtained. For small spins ($s= 1/2,1$) the results are
essentially different from those in the spin-wave theory.",9603123v1
1996-04-18,Ferromagnetism in an itinerant electron system: Hubbard model on complete graph,"In this work, the ground states of the Hubbard model on complete graph are
studied, for a finite lattice size $L$ and arbitrary on-site energy $U$. We
construct explicitly the ground states of the system when the number of the
electrons $N_e \ge L+1$. In particular, for $N_e=L+1$, the ground state is
ferromagnetic with total spin $s_g=(N_e-2)/2$.",9604121v1
1996-05-01,Circular phase of a two dimensional ferromagnet with dipolar interactions,"We make for the first time a large-scale Monte-Carlo simulation of a
ferromagnetic Heisenberg model with dipolar interactions on a two dimensional
square lattice with open boundaries using an efficient new technique. We find
that a phase transition occurs in the model and the ordered phase is
characterized by a circular arrangement of the spins.",9604190v1
1996-07-30,Magnetization and overlap distributions of the ferromagnetic Ising model on the Cayley tree,"We analyze the magnetization and the overlap distributions on the
ferromagnetic Cayley tree. Two quantities are investigated: the asymptotic
scaling of all the moments of the magnetization and overlap distributions, as
well as the computation of the fractal dimension of the magnetization and
overlap probability measures.",9607215v1
1996-09-20,Variationnal study of ferromagnetism in the t1-t2 Hubbard chain,"A one-dimensional Hubbard model with nearest and (negative) next-nearest
neighbour hopping is studied variationally. This allows to exclude saturated
ferromagnetism for $U < U_c$. The variational boundary $U_c (n)$ has a minimum
at a ``critical density'' $n_c$ and diverges for $n \rightarrow 1$.",9609198v1
1996-11-05,The Generalized Gutzwiller Method for n=>2 Correlated Orbitals: Itinerant Ferromagnetism in eg-bands,"Using the generalized Gutzwiller method we present results on the
ferromagnetic behavior of extended Hubbard models with two degenerate eg
orbitals. We find significant differences to results obtained from Hartree-Fock
theory.",9611031v1
1997-03-04,Dissipative Dynamics of Solitons in Planar Ferromagnets,"Dynamics of magnetic bubbles in planar ferromagnets described by the
Landau-Lifshitz equation with dissipation is analyzed. The pure O(3) sigma
model has static multisoliton solutions, characterized by a number of
parameters. The parameters describe a finite dimensional manifold. A small
perturbation of energy functional with respect to the sigma model forces
solitons to move. Multisoliton dynamics is effectively reduced to a flow in the
parameter space.",9703045v1
1997-10-06,Multi-Magnon Scattering in the Ferromagnetic XXX-Model with Inhomogeneities,"We determine the transition amplitude for multi-magnon scattering induced
through an inhomogeneous distribution of the coupling constant in the
ferromagnetic XXX-model. The two and three particle amplitudes are explicitely
calculated at small momenta. This suggests a rather plausible conjecture also
for a formula of the general n-particle amplitude.",9710055v1
1997-10-15,Theoretical study of the Josephson current through a junction including ferromagnetic insulator,"The properties of Josephson junction including a ferromagnetic insulating
layer are studied theoretically. The calculated current shows the anomalous
dependence on the magnitude of the exchange interaction at the interface. The
Josephson junction changes from 0-junction to $\pi$-junction with the increase
of the magnitude of the exchange interaction.",9710149v1
1997-10-28,Field-induced quasi-particle coherence effects in certain small magnets,"Small ferromagnets and anti-ferromagnets with an easy-plane anisotropy have a
ground to first excited state (tunnel) splitting which is quasi-periodic in the
magnitude of a field applied perpendicular to a principal anisotropy axis. The
associated oscillations in thermodynamic quantities might be used to prove the
existence of a coherent ground state even when the tunnel splitting itself
cannot be directly detected.",9710302v1
1998-05-15,Gauge Equivalence between Two-Dimensional Heisenberg Ferromagnets with Single-Site Anisotropy and Zakharov Equations,"Gauge equivalence between the two-dimensional continuous classical Heisenberg
ferromagnets(CCHF) of spin 1/2 - the M-I equation with single site anisotropy
and the Zakharov equation(ZE) is established for the easy axis case. The
anisotropic CCHF is shown to be gauge equivalent to the isotropic CCHF.",9805188v1
1998-10-09,Magnetic Properties of Quantum Ferrimagnetic Spin Chains,"Magnetic susceptibilities of spin-$(S,s)$ ferrimagnetic Heisenberg chains are
numerically investigated. It is argued how the ferromagnetic and
antiferromagnetic features of quantum ferrimagnets are exhibited as functions
of $(S,s)$. Spin-$(S,s)$ ferrimagnetic chains behave like combinations of
spin-$(S-s)$ ferromagnetic and spin-$(2s)$ antiferromagnetic chains provided
$S=2s$.",9810112v1
1998-10-21,Competition of Ferromagnetic and Antiferromagnetic Order in the Spin-1/2 XXZ Chain at Finite Temperature,"An analytical study is presented of the crossover in the gapless attractive
XXZ chain from antiferromagnetic to ferromagnetic behaviour at low to high
temperature, respectively. In particular, an analytic formula for the crossover
in the long distance asymptotics and explicit results for the nearest-neighbour
longitudinal correlation are obtained. We also provide results for the specific
heat and magnetic susceptibility for various anisotropies.",9810278v1
1998-11-10,Coupling between electron-spin and ferromagnetic clusters,"We analyze the adiabatic magnetization of ferromagnetic clusters in an
intermediate coupling regime, where the anisotropic potential is comparable to
other energy scales. We find a non-monotonic behavior of the magnetic
susceptibility as a function of coupling with a peak. Coriolis coupling effects
are calculated for the first time; they reduce the susceptibility somewhat.",9811126v1
1999-03-09,Skyrmion dynamics in quantum Hall ferromagnets,"Exploring a classical solution of the non-linear sigma model for a quantum
Hall ferromagnet, a skyrmion-magnon effective hamiltonian is obtained via the
collective coordinates method. Using the Feynman-Vernon functional integral
formalism for this model we find the temperature dependent transport
coefficients which characterize a single skyrmion dynamics.",9903143v1
1999-04-22,Orbital Dynamics: The Origin of Anomalous Magnon Softening in Ferromagnetic Manganites,"We study the renormalization of magnons by charge and coupled orbital-lattice
fluctuations in colossal magnetoresistance compounds. The model considered is
an orbitally degenerate double-exchange system coupled to Jahn-Teller active
phonons. The modulation of ferromagnetic bonds by low-energy orbital
fluctuations is identified as the main origin of the unusual softening of the
zone-boundary magnons observed experimentally in manganites.",9904316v2
1999-04-27,Finite temperature phase transition in the two-dimension Randomly Coupled Ferromagnet,"We show using extensive simulation results and physical arguments that an
Ising system on a two dimensional square lattice, having interactions of random
sign between first neighbors and ferromagnetic interactions between second
neighbors, presents a phase transition at a non-zero temperature.",9904397v1
1999-10-03,Hysteretic Response of an Anti-Ferromagnetic Random-Field Ising Model in One Dimension at Zero Temperature,"We consider the hysteretic response of a one-dimensional anti-ferromagnetic
random-field Ising model at zero temperature for a uniform bounded distribution
of quenched random fields, and present analytic results in a limited range of
the applied field.",9910021v1
1999-11-11,Ferromagnetic correlations in quasi-one-dimensional conducting channels,"We propose a model which explains the experimental observation of spontaneous
spin polarization of conducting electrons in quasi- one-dimensional GaAs/AlGaAs
channels. We show that a ferromagnetic order is a generic property of a
quasi-one-dimensional conducting channel embedded in a Wigner crystal. We also
discuss gate voltage, magnetic field and temperature dependences of the
channel's conductance.",9911175v1
2000-04-25,Multiscaling at ferromagnetic-spin glass transition point of Random Energy Model and complexity,"We calculate moments of free energy's finite size correction for the
transition point between ferromagnetic and spin glass phases. We find, that
those moments scale with the number of spins with different critical indices,
characteristic for the multiscaling. This critical point corresponds to
threshold of errorless coding for a gaussian noisy channel. We are give the
definition of statistical complexity using this free energy approach.",0004406v1
2000-05-24,Bloch Walls and Macroscopic String States in Bethe's solution of the Heisenberg Ferromagnetic Linear Chain,"We present a calculation of the lowest excited states of the Heisenberg
ferromagnet in 1-d for any wave vector. These turn out to be string solutions
of Bethe's equations with a macroscopic number of particles in them. These are
identified as generalized quantum Bloch wall states, and a simple physical
picture provided for the same.",0005397v1
2000-05-25,Quantum critical effects on transition temperature of magnetically mediated p-wave superconductivity,"We determine the behavior of the critical temperature of magnetically
mediated p-wave superconductivity near a ferromagnetic quantum critical point
in three dimensions, distinguishing universal and non-universal aspects of the
result. We find that the transition temperature is non-zero at the critical
point, raising the possibility of superconductivity in the ferromagnetic phase.",0005449v2
2000-08-17,Theory of Ferromagnetic Superconductivity,"It is argued that the pairing symmetry realized in a ferromagnetic
superconductor UGe$_2$ must be a non-unitary triplet pairing. This particular
state is free from the Pauli limitation and can survive under a huge internal
molecular filed. To check our identification we examine its basic properties
and several experiments are proposed. In particular, the external field is used
to raise $T_c$ by controlling the internal spontaneous dipole field.",0008245v1
2000-09-28,"Reply to Comment of Yang, Sun, and Chang on ""Theory of Diluted Magnetic Semiconductor Ferromagnetism""","We reply to the comment cond-mat/0008098 by Yang, Sun, and Chang on our paper
""Theory of Diluted Magnetic Semiconductor Ferromagnetism"", Phys. Rev. Lett. 84,
5628 (2000).",0009453v1
2000-11-29,Dissipationless Spin Transport in Thin Film Ferromagnets,"Metallic thin film ferromagnets generically possess spiral states that carry
dissipationless spin currents. We relate the critical values of these
supercurrents to micromagnetic material parameters, identify the circumstances
under which the supercurrents will be most robust, and propose experiments
which could reveal this new collective transport behavior.",0011504v2
2001-01-25,Specific heat of a Fermi system near ferromagnetic quantum phase transition,"We calculate the specific heat for an interacting Fermi system near the
ferromagnetic phase transition using the Renormalization Group method. The
temperature dependence of the specific heat present for dimension D=3 a
logarithmic dependence which shows that the fermionic excitations reaches a non
- Fermi behavior. The result is in good agreement with the experimental data
obtained recently for $Ni_x Pd_{1-x}$ alloys.",0101392v1
2001-02-06,"Comment on ""Ferromagnetic film on a superconducting substrate""","A superconducting substrate is not able to shrink drastically domains in a
ferromagnetic film, contrary to the prediction of Bulaevskii and Chudnovsky
[Phys. Rev. B, 63, issue1 (2001)]. This is shown on the basis of the exact
solution for the stripe domain structure.",0102102v2
2001-03-22,Thermally activated interface motion in a disordered ferromagnet,"We investigate interface motion in disordered ferromagnets by means of Monte
Carlo simulations. For small temperatures and driving fields a so-called creep
regime is found and the interface velocity obeys an Arrhenius law. We analyze
the corresponding energy barrier as well as the field and temperature
dependence of the prefactor.",0103464v1
2001-04-13,Dipolar induced anisotropy in the random-field Ising model,"The crystalline ferromagnet with dipole-dipole interactions is studied within
the framework of the three-dimensional random-field Ising model. The field
distribution function and the analytic expression for temperature dependent
free energy are found. The dipolar induced magnetic anisotropy energy of bulk
cubic ferromagnetic materials is calculated.",0104246v1
2001-07-12,Theory of electron spectroscopies,"The basic theory of photoemission, inverse photoemission, Auger-electron and
appearance-potential spectroscopy is developed within a unified framework
starting from Fermi's golden rule. The spin-resolved and temperature-dependent
appearance-potential spectroscopy of band-ferromagnetic transition metals is
studied in detail. It is shown that the consideration of electron correlations
and orbitally resolved transition-matrix elements is essential for a
quantitative agreement with experiments for Ni.",0107257v1
2001-08-21,Orbital ferromagnetism and anomalous Hall effect in antiferromagnets on distorted fcc lattice,"The Berry phase due to the spin wavefunction gives rise to the orbital
ferromagnetism and anomalous Hall effect in the non-coplanar antiferromagnetic
ordered state on face centered cubic (fcc) lattice once the crystal is
distorted perpendicular to (1,1,1) or (1,1,0)- plane. The relevance to the real
systems $\gamma$-FeMn and NiS$_2$ is also discussed.",0108322v1
2002-02-05,Optical Conductivity of Ferromagnetic Semiconductors,"The dynamical mean field method is used to calculate the frequency and
temperature dependent conductivity of dilute magnetic semiconductors.
Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism.",0202071v1
2002-03-07,A new spinwave expansion for the ordered Kondo lattice,"We present a concise introduction to a new spinwave expansion scheme for
magnetically ordered Kondo lattice models. This is motivated by consideration
of the ferromagnetically ordered phase of the ""double exchange"" system
La(1-x)Ca(x)MnO3. A brief overview is given of the consequences of quantum and
thermal fluctuation effects for the magnetic properties of the double exchange
ferromagnet.",0203156v1
2002-03-07,Segmented Band Mechanism for Itinerant Ferromagnetism,"We introduce a novel mechanism for itinerant ferromagnetism, which is based
on a simple two-band model, and using numerical and analytical methods, we show
that the Periodic Anderson Model (PAM) contains this mechanism. We propose that
the mechanism, which does not assume an intra-atomic Hund's coupling, is
present in both the iron group and some $f$ electron compounds.",0203172v1
2002-03-12,Mermin-Ho vortex in ferromagnetic spinor Bose-Einstein condensates,"The Mermin-Ho and Anderson-Toulouse coreless non-singular vortices are
demonstrated to be thermodynamically stable in ferromagnetic spinor
Bose-Einstein condensates with the hyperfine state F=1. The phase diagram is
established in a plane of the rotation drive vs the total magnetization by
comparing the energies for other competing non-axis-symmetric or singular
vortices. Their stability is also checked by evaluating collective modes.",0203242v1
2002-03-20,Oscillations of the superconducting critical current in Nb-Cu-Ni-Cu-Nb junctions,"We report on experimental studies of superconductor-ferromagnet layered
structures. Strong oscillations of the critical supercurrent were observed with
the thickness variation of the ferromagnet. Using known microscopic parameters
of Ni, we found reasonable agreement between the period of oscillations and the
decay of the measured critical current, and theoretical calculations.",0203408v1
2002-07-05,Gap nodes in the superconducting phase of the itinerant ferromagnet $UGe_2$,"For the UGe$_2$ ferromagnetic superconductor the forms of the order parameter
admitted by the crystal symmetry within the strong spin-orbit coupling scheme
are written down. For each of the two possible phases existence of gap nodes
required by symmetry is discussed and the nodes are found. Some consequences of
presence of the nodes, which may be useful for experimental identification of
the phases are discussed as well.",0207152v1
2002-08-20,Monte Carlo Study of an Extended 3-State Potts Model on the Triangular Lattice,"By introducing a chiral term into the Hamiltonian of the 3-state Potts model
on a triangular lattice additional symmetries are achieved between the
clockwise and anticlockwise states and the ferromagnetic state. This model is
investigated using Monte Carlo methods. We investigate the full phase diagram
and find evidence for a line tricritical points separating the ferromagnetic
and antiferromagnetic phases.",0208387v1
2002-08-21,Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide,"We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C} $\leq$
270K and ferromagnetic to canted spin glass state at T_f$ $\leq$ 125K is
observed.",0208416v1
2002-11-17,Ferromagnetic transition in a double-exchange model,"We calculate the temperature of a ferromagnetic transition in a
double-exchange model with classical core spins for arbitrary relation between
Hund exchange coupling and electron band width by solving the Dynamical Mean
Field Approximation equations.",0211354v3
2002-12-20,Lockin to Weak Ferromagnetism in TbNi2B2C and ErNi2B2C,"This article describes a model in which ferromagnetism necessarily
accompanies a spin-density-wave lockin transition in the borocarbide structure
provided the commensurate phase wave vector satisfies Q = (m/n)a* with m even
and n odd. The results account for the magnetic properties of TbNi2B2C, and are
also possibly relevant also for those of ErNi2B2C.",0212535v1
2002-12-27,On the Competition between Ferromagnetic and Antiferromagnetic States in Sr$_2$MnMoO$_6,"It is argued that the magnetic behavior of Sr$_2$MnMoO$_6$ is determined by
the existence of two total energy minima corresponding to the metallic
ferromagnetic and insulating antiferromagnetic states, which may be nearly
degenerate depending on the magnitude of the breathing distortion.",0212607v1
2003-04-14,On the Ising-Heisenberg model with the doubly decorated network structure I,"Using an exact mapping transformation method, magnetic properties of a
spin-1/2 and spin-1 doubly decorated Ising-Heisenberg model are investigated in
detail. By assuming that both interaction parameters are ferromagnetic, we
found in addition to an usual ferromagnetic phase another two phases with a
nontrivial long-range order.",0304310v1
2003-07-06,Equilibrium current temperature quasi-oscillations in a ferromagnetic loop,"Equilibrium persistent current carried by a small ferromagnet-metal loop is
considered. This current is shown to be quasi periodic in temperature at low
temperatures. The quasi period is determined mainly by the temperature
dependence of the magnetization.",0307128v1
2003-07-18,The Heisenberg antiferromagnet: an explicitly rotational invariant formulation,"A simple derivation of an explicitly rotational invariant Lagrangian
describing the dynamics of an antiferromagnetic spin system is presented. The
scope of the derived Lagrangian is analysed in the context of schematic models.
It is shown that the Lagrangian describes the behaviour of spin systems from
the anti-ferromagnetic to the ferromagnetic regimes.",0307461v1
2003-07-22,Ferromagnetism and triplet superconductivity in the two-dimensional Hubbard model,"We review magnetic and superconducting instabilities in the t-t' Hubbard
model on the two-dimensional square lattice as obtained with functional
one-loop renormalization group techniques. Special emphasis is put on
ferromagnetic and triplet superconducting tendencies that could be relevant to
the triplet superconductor Sr2RuO4.",0307541v1
2003-07-23,Spin order manipulations in nanostructures of II-VI ferromagnetic semiconductors,"An overview of recent studies on ferromagnetism in Cr- and Mn-based II-VI
diluted magnetic semiconductors is presented emphasizing differences in
underlying exchange mechanisms. Examples of manipulations with spin ordering by
carrier density, dimensionality, light, and electric field are given.",0307573v1
2003-08-31,Theory of Striped Hall Ferromagnets,"We study spin and charge striped states at the half-filled high Landau level
in the zero Zeeman energy limit using a Hartree-Fock approximation. It is shown
that a ferromagnetic striped Hall state is more stable than the
antiferromagnetic striped state or charge striped state. We calculate the
collective excitations using the single mode approximation.",0309013v1
2003-10-06,Breakup of a Stoner model for the 2D ferromagnetic quantum critical point,"Re-interpretation of the results by [A. V. Chubukov et. al., Phys. Rev. Lett.
90, 077002 (2003)] leads to the conclusion that ferromagnetic quantum critical
point (FQCP) cannot be described by a Stoner model because of a strong
interplay between the paramagnetic fluctuations and the Cooper channel, at
least in two dimensions.",0310124v1
2003-12-10,Spin Gain Transistor in Ferromagnetic Semiconductors: the Semiconductor Bloch Equations Approach,"Scheme and principle of operation of a spin gain transistor are proposed: a
large unmagnetized current creates density sufficient for the ferromagnetic
transition; a small magnetized current initiates spontaneous magnetization;
large magnetized current is extracted. Therefore spin gain of more than 1000 is
predicted. Collective dynamics of spins under Coulomb exchange interaction is
described via Semiconductor Bloch Equations.",0312243v1
2004-04-07,Absence of room temperature ferromagnetism in bulk Mn-doped ZnO,"Structural and magnetic properties have been studied for polycrystalline
Zn_1-xMn_xO (x=0.02, 0.03, 0.05). Low-temperature (~500 oC) synthesis leaves
unreacted starting ZnO and manganese oxides. Contrary to a recent report, no
bulk ferromagnetism was observed for single-phase materials synthesized in air
at temperatures above 900 oC. Single-phase samples show paramagnetic
Curie-Weiss behavior.",0404186v1
2004-06-30,Hysteresis in Ferromagnetic Random Field Ising Model with an Arbitrary Initial State,"We present exact expressions for hysteresis loops in the ferromagnetic random
field Ising model in the limit of zero temperature and zero driving frequency
for an arbitrary initial state of the model on a Bethe lattice. This work
extends earlier results that were restricted to an initial state with all spins
pointing parallel to each other.",0406749v1
2004-07-05,Boosting the Curie temperature with correlations in diluted magnetic semiconductors,"We present a quantitative theory for the effects of correlated doping on the
ferromagnetism of diluted magnetic semiconductors. It predicts that room
temperature ferromagnetism should be possible in homogeneous, but correlated,
samples of Mn$_x$Ga$_{1-x}$As. The theory predicts lower critical temperatures
for Mn$_x$Ga$_{1-x}$N.",0407101v1
2005-08-09,Geometry and the anomalous Hall effet in ferromagnets,"The geometric ideas underlying the Berry phase and the modern viewpoint of
Karplus and Luttinger's theory of the anomalous Hall effect are discussed in an
elementary way. We briefly review recent Hall and Nernst experiments which
support the dominant role of the KL velocity term in ferromagnets.",0508236v1
2005-12-10,Breaking of Chiral Symmetry and Spontaneous Rotation in a Spinor Bose-Einstein Condensate,"We show that a spin-1 Bose-Einstein condensate with ferromagnetic
interactions spontaneously generates a topological spin texture, in which the m
= \pm 1 components of the magnetic sublevels form vortices with opposite
circulations. This phenomenon originates from an interplay between
ferromagnetic interactions and spin conservation.",0512216v1
2006-03-08,Electronic Structure of Nearly Ferromagnetic compound HfZn$_{2}$,"The electronic structure of HfZn$_{2}$ has been studied based on the density
functional theory within the local-density approximation. The calculation
indicates that HfZn$_{2}$ shows ferromagnetic instability. Large enhancement of
the static susceptibility over its non-interacting value is found due to a peak
in the density of states at the Fermi level.",0603203v1
2006-03-11,Electronic Structure and Magnetic Properties of $β$-Ti$_{6}$Sn$_{5}$,"The electronic structure of $\beta$-Ti$_{6}$Sn$_{5}$ has been studied based
on the density functional theory within the local-density approximation. The
calculation indicates that $\beta$-Ti$_{6}$Sn$_{5}$ is very close to
ferromagnetic instability and shows ferromagnetic ordering after rare earth
element doping. Large enhancement of the static susceptibility over its
non-interacting value is found due to a peak in the density of states at the
Fermi level.",0603313v1
2006-07-28,Anisotropic thermal expansion and uniaxial pressure dependence of superconducting and magnetic transitions in ErNi2B2C,"We present anisotropic thermal expansion measurements on single crystalline
ErNi2B2C. All three, superconducting, antiferromagnetic and weak ferromagnetic
phase transitions are unambiguously distinguished in the data. Anisotropic
uniaxial pressure dependencies of the transitions are estimated based on the
Ehrenfest relation, leading to a conclusion, in particular, that weak
ferromagnetic state will be suppressed by small, order of several kbar,
hydrostatic pressure.",0607762v1
2006-09-20,Ferromagnetism and Superconductivity in Carbon-Based Systems,"In this article we shortly review previous and recently published
experimental results that provide evidence for intrinsic,
magnetic-impurity-free ferromagnetism and for high-temperature
superconductivity in carbon-based materials. The available data suggest that
the origin of those phenomena is related to structural disorder and the
presence of light elements like hydrogen, oxygen and/or sulfur.",0609497v1
2006-09-29,Negative four-terminal resistance as a probe of crossed Andreev reflection,"We report on the experimental investigation of electronic transport in
superconductor-ferromagnet spin-valve structures. Our samples consist of two
ferromagnetic iron leads forming planar tunnel contacts to a superconducting
aluminum wire. At energies below the superconducting gap, we observe a negative
four-probe resistance that can be explained by crossed Andreev reflection.",0609766v1
2006-11-27,Formation of ferromagnetic bulk amorphous Fe40Ni40P14B6 alloys,"Ferromagnetic bulk amorphous Fe40Ni40P14B6 alloy rods with a diameter of 1.2
mm can be prepared by means of a rapid quenching technique. If a fluxing
technique is also used, amorphous rods with a diameter as large as 2.5 mm can
be synthesized. The critical cooling rate Rc for the glass formation
Fe40Ni40P14B6 is estimated to be on the order of 100 K.s-1",0611661v1
2007-01-18,The Berry phase in ferromagnetic spin systems and anomalous Hall Effect,"We have shown that the study of topological aspects of the underlying
geometry in a ferromagnetic spin system gives rise to an intrinsic Berry phase.
This real space Berry phase arises due to the spin rotations of conducting
electrons which can be manifested as a further contribution in anomalous Hall
effect.",0701440v1
2007-03-11,Dynamic magnetic response of infinite arrays of ferromagnetic particles,"Recently developed techniques to find the eigenmodes of a ferromagnetic
particle of arbitrary shape, as well as the absorption in the presence of an
inhomogeneous radio-frequency field, are extended to treat infinite lattices of
such particles. The method is applied to analyze the results of recent FMR
experiments, and yields substantially good agreement between theory and
experiment.",0703273v1
2003-12-26,Possibility of color magnetic superconductivity,"Two aspects of quark matter at high density are addressed: one is color
superconductivity and the other is ferromagnetism. We are mainly concerned with
the latter and its relation to color superconductivity, which we call ""color
magnetic superconductivity"". The relation of ferromagnetism and chiral symmetry
restoration is also discussed.",0312351v1
1992-10-28,Thermodynamics of the 3-State Potts Spin Chain,"We demonstrate the relation of the infrared anomaly of conformal field theory
with entropy considerations of finite temperature thermodynamics for the
3-state Potts chain. We compute the free energy and compute the low temperature
specific heat for both the ferromagnetic and anti-ferromagnetic spin chains,
and find the central charges for both.",9210146v2
1996-12-13,The Field Theory of Generalized Ferromagnet on the Hermitian Symmetric Spaces,"We discuss the recent developments in the generalized continuous Heisenberg
ferromagnet model formulated as a nonrelativistic field theory defined on the
target space of the coadjoint orbits. Hermitian symmetric spaces are special
because they provide completely integrable field theories in 1+1 dimension and
self-dual Chern-Simons solitons and vortices in 2+1 dimension.",9612132v1
2000-11-23,"Hopf instantons, Chern-Simons vortices, and Heisenberg ferromagnets","The dimensional reduction of the three-dimensional fermion-Chern-Simons model
(related to Hopf maps) of Adam et el. is shown to be equivalent to (i) either
the static, fixed--chirality sector of our non-relativistic spinor-Chern-Simons
model in 2+1 dimensions, (ii) or a particular Heisenberg ferromagnet in the
plane.",0011210v1
2003-03-05,Differential geometry of surfaces and Heisenberg ferromagnets,"The relation between differential geometry of surfaces and some Heisenberg
ferromagnet models is considered.",0303056v2
2003-04-23,Rigorous Non-Perturbative Ornstein-Zernike Theory for Ising Ferromagnets,"We rigorously derive the Ornstein-Zernike asymptotics of the pair-correlation
functions for finite-range Ising ferromagnets in any dimensions and at any
temperature above critical.",0304349v1
2006-07-20,Stability for Walls in Ferromagnetic Nanowire,"We study the stability of travelling wall profiles for a one dimensional
model of ferromagnetic nanowire submitted to an exterior magnetic field. We
prove that these profiles are asymptotically stable modulo a
translation-rotation for small applied magnetic fields.",0607499v1
1999-03-01,Mathematical Structure of Magnons in Quantum Ferromagnets,"We provide the mathematical structure and a simple, transparent and rigorous
derivation of the magnons as elementary quasi-particle excitations at low
temperatures and in the infinite spin limit for a large class of Heisenberg
ferromagnets. The magnon canonical variables are obtained as fluctuation
operators in the infinite spin limit. Their quantum character is governed by
the size of the magnetization.",9903004v1
2000-12-28,On the Ground State of Ferromagnetic Hamiltonians,"It is generally believed that the ground state of the ferromagnetic
Heisenberg-Dirac-Van Vleck Hamiltonians acting on s=1/2 spins of a lattice with
N sites has the maximal possible value of the total spin S=N/2 and is N+1 times
degenerate. We present a rigorous proof of this statement, independent of the
lattice dimension and topology.",0012048v1
2002-10-08,Ferromagnetic Antenna and its Application to Generation and Detection of Gravitational Radiation,"A new type of antenna, which we have called Ferromagnetic Antenna, has been
considered for Generation and Detection of Gravitational Radiation. A simple
experiment, in which gravitational radiation at 10 GHz can be emitted and
received in laboratory, is presented.",0210034v4
1997-10-07,Shock waves in one-dimensional Heisenberg ferromagnets,"We use SU(2) coherent state path integral formulation with the stationary
phase approximation to investigate, both analytically and numerically, the
existence of shock waves in the one- dimensional Heisenberg ferromagnets with
anisotropic exchange interaction. As a result we show the existence of shock
waves of two types,""bright"" and ""dark"", which can be interpreted as moving
magnetic domains.",9710003v1
2007-08-10,Prediction for new magnetoelectric fluorides,"We use symmetry considerations in order to predict new magnetoelectric
fluorides. In addition to these magnetoelectric properties, we discuss among
these fluorides the ones susceptible to present multiferroic properties. We
emphasize that several materials present ferromagnetic properties. This
ferromagnetism should enhance the interplay between magnetic and dielectric
properties in these materials.",0708.1475v1
2007-10-12,Dynamical instability of the XY spiral state of ferromagnetic condensates,"We calculate the spectrum of collective excitations of the XY spiral state
prepared adiabatically or suddenly from a uniform ferromagnetic F=1 condensate.
For spiral wavevectors past a critical value, spin wave excitation energies
become imaginary indicating a dynamical instability. We construct phase
diagrams as functions of spiral wavevector and quadratic Zeeman energy.",0710.2499v1
2008-08-31,Magnetic Monopoles in Ferromagnetic Spin-Triplet Superconductors,"Using the $\phi$-mapping method, we argue that ferromagnetic spin-triplet
superconductors allow formation of unstable magnetic monopoles. In particular,
we show that the limit points and the bifurcation points of the $\phi$-mapping
will serve as the interaction points of these magnetic monopoles.",0809.0120v1
2008-10-21,"Coherent manipulation of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As with successive optical pumping","We report dynamic control of magnetization precession by light alone. A
ferromagnetic (Ga,Mn)As epilayer was used for experiments. Amplitude of
precession was modulated to a large extent by tuning the time interval between
two successive optical pump pulses which induced torques on magnetization
through a non-thermal process. Nonlinear effect in precession motion was also
discussed.",0810.3728v1
2009-05-23,Influence of a Transport Current on Magnetic Anisotropy in Gyrotropic Ferromagnets,"Current-induced torques are commonly used to manipulate non-collinear
magnetization configurations. In this article we discuss current-induced
torques present in a certain class of collinear magnetic systems, relating them
to current-induced changes in magnetic anisotropy energy. We present a
quantitative estimate of their characteristics in uniform strained
ferromagnetic (Ga,Mn)As.",0905.3856v1
2009-11-02,Dynamical Toroidal Hopfions in a Ferromagnet with Easy-Axis Anisotropy,"Three-dimensional toroidal precession solitons with a nonzero Hopf index,
which uniformly move along the anisotropy axis in a uniaxial ferromagnet, have
been found. The structure and existence region of the solitons have been
numerically determined by solving the Landau-Lifshitz equation.",0911.0451v1
2010-01-19,The Pairing Symmetry in the Ferromagnetic Superconductor $UGe_{2}$,"We give an extensive treatment of the pairing symmetry in the ferromagnetic
superconductor $UGe_{2}$. We show that one can draw important conclusions
concerning the superconducting state, considering only the transformation
properties of the pairing function, without assumptions about the form of the
pairing amplitudes.",1001.3309v1
2010-07-28,Route to ferromagnetism in organic polymers,"Employing a rigorous theoretical method for the construction of exact
many-electron ground states we prove that interactions can be employed to tune
a bare dispersive band structure such that it develops a flat band. Thereby we
show that pentagon chain polymers with electron densities above half filling
may be designed to become ferromagnetic or half metallic.",1007.4994v1
2010-08-16,Possible kinetic arrest of the ferromagnetic to anti-ferromagnetic transition in SmCoAsO: The interplay of Sm4f and Co3d spins,The article is withdrawn and its revised version will be submitted later.,1008.2593v3
2010-08-24,Electronic and magnetic properties of the graphene-ferromagnet interface,"The article presents the work on the investigation of the surface structure
as well as electronic and magnetic properties of graphene layer on a lattice
matched surface of a ferromagnetic material, Ni(111).",1008.3975v1
2011-03-11,Scattering of quasiparticle of spin-triplet pairs in diffusive superconductor-ferromagnetic nanowire-superconductor junction,"We analyze the proximity effect of superconductor/ferromagnet nanostructures
and point out that the scattering of quasiparticle of spin-triplet pairs by
local magnetic moments leads to large resistance peak slightly below the
superconducting transition temperature of the superconductor. Both the
temperature and the magnitude of the resistance peak decrease with increasing
magnetic field, which agree quite well with the experimental results reported
in [Nature Phys. 6, 389 (2010)].",1103.2176v1
2011-05-16,Anisotropic thermoelectric effect in helimagnetic tunnel junctions,"Thermoelectric transport across
normal-metal/helical-multiferroic/ferromagnetic heterojunctions is
theoretically investigated. We find a anisotropic charge and spin thermopower
with a $C_{2v}$ symmetry. The angular dependence on the magnetization
orientation of the ferromagnetic layer is substantiated by a phenomenological
theory based on the symmetry of the effective spin-orbit interaction induced by
the topology of the spiral magnetic order in the multiferroic barrier.",1105.3075v1
2012-11-07,The ferromagnetic order in graphene,"The conditions for spontaneous magnetization in a single graphene sheet are
discussed in the context of Mermin-Wagner theorem. It is rigorously proved that
at any nonzero temperature the graphene monolayer is nonmagnetic as long as its
intrinsic symmetry is preserved. Any electronic fluctuations breaking the
pseudospin conservation law can be responsible for the existence of
ferromagnetic order inside the graphene structure.",1211.1508v1
2013-02-04,Andreev experiments on superconductor/ferromagnet point contacts,"Andreev reflection is a smart tool to investigate the spin polarisation P of
the current through point contacts between a superconductor and a ferromagnet.
We compare different models to extract P from experimental data and investigate
the dependence of P on different contact parameters.",1302.0660v1
2013-04-15,Enhancement of the superconducting transition temperature of MgB2 by proximity effect of d0 ferromagnet,"Heterostructures of superconducting and ferromagnetic materials are of
fundamental interest because of the mutual interaction of antagonistic kinds of
ordering at the S-F interface. Normally, the superconducting transition
temperature Tc should be strongly suppressed at the S-F interface owing to the
penetration of Cooper pairs into the ferromagnetic side. Nevertheless,
constructive interactions between S and F orders have been suggested to occur
via the modification of ferromagnetic order by the superconducting state. This
may induce an inhomogeneous magnetic state, often called a cryptoferromagnetic
state, and the relevant domain wall effect, which will lead to a local decrease
of the pair-breaking parameter. However, the domain wall effect, even if it
exists, is quite subtle from the experimental view point and is normally
difficult to observe. Here we show that the defect-related d0 ferromagnetism in
MgO and the superconductivity in MgB2 do not antagonize, but rather enhance the
superconducting transition temperature Tc to any significant degree. We found
in superconducting MgB2-d0 ferromagnetic MgO composites that the
superconducting transition proceeds in two steps. The first at the S-F
interface, between 110-120 K, then in the rest of the bulk at 39 K, which is
the Tc of single phase MgB2 superconductor. Moreover, the additional transition
emerges at 60 K at the S-F interface especially in the ferromagnetic side,
showing a spin-glass-like magnetic state. Our findings reveal that the
proximity effect in the superconductor-d0 ferromagnet heterostructures will
provide the knowledge and basis to enhance the Tc value of the existing
superconductors.",1304.4105v3
2013-05-09,"Itinerant origin of the ferromagnetic quantum critical point in Fe(Ga,Ge)3","The electronic structure and magnetic properties of FeGa3 and doped FeGa3 are
studied using density functional calculations. An itinerant mechanism for
ferromagnetism is found both for n-type doping with Ge and also for p-type
doping. Boltzmann transport calculations of the thermopower are also reported.",1305.2063v1
2013-10-27,Fundamental limitations of half-metallicicity in spintronic materials,"Zero-point spin fluctuations are shown to strongly influence the ground state
of ferromagnetic metals and to impose limitations for the fully spin polarized
state assumed in half-metallic ferromagnets, which may influence their
applications in spintronics. This phenomenon leads to the low-frequency Stoner
excitations and cause strong damping and softening of magnons in
magnetoresistive manganites observed experimentally.",1310.7174v1
2015-03-02,Andreev Reflection Spectroscopy in Transition Metal Oxides,"Here we review the literature concerning measurement of the Andreev
reflection between a superconductor (S) and ferromagnet (F), with particular
attention to the case where the ferromagnet is a transition metal oxide. We
discuss the practicality of utilisation of the current models for determination
of the transport current spin polarisation and examine the evidence for Andreev
bound states.",1503.00533v1
2015-04-27,Spontaneous Appearance of Low-dimensional Magnetic Electron System on Semiconductor Nanostructures,"We find that spin-polarized ground states emerge in nanofacets which are
self-organized on SiC (0001) surfaces. Our large-scale density-functional
calculations reveal that the nanofacet formed by bunching of single bilayer
steps generates peculiar carbon dangling bond states localized at but extended
along step edges. The flat-band characteristics of those C states cause either
ferromagnetic or anti-ferromagnetic chains on covalent semiconductors.",1504.06934v1
2015-06-04,Three magnons in an isotropic $S=1$ ferromagnetic chain as an exactly solvable non-integrable system,"It is shown that a generalization of Bethe Ansatz based on an utilization of
{\it degenerative discrete-diffractive} wave functions solves the three-magnon
problem for the $S=1$ isotropic ferromagnetic infinite chain. The four-magnon
problem is briefly discussed.",1506.01554v2
2015-10-23,Self-consistent approach to magnetic ordering and excited site occupation processes in a two-level system,"Ferromagnetic ordering in a two-level partially excited system is studied in
detail. Magnitudes of magnetization (magnetic order parameter) and lattice
ordering (excited level occupation number) are calculated self-consistently.
The influence of an external magnetic field and excited level gap on the
ferromagnetic phase transition is discussed.",1510.06907v1
2016-02-24,The Landau-Lifshitz equation of the ferromagnetic spin chain and Oseen-Frank flow,"In this paper, we consider the Landau-Lifshitz equation of the ferromagnetic
spin chain from $\R^2$ to the unit sphere $S^2$ under the general Oseen-Frank
energy. We obtain global existence and uniqueness of weak solutions for large
energy data; moreover, the number of singular points is finite.",1602.07549v1
2016-07-20,MegaOhm Extraordinary Hall effect in oxidized CoFeB,"We report on development of controllably oxidized CoFeB ferromagnetic films
demonstrating the extraordinary Hall effect (EHE) resistivity exceeding 1 Ohmcm
and magnetic field sensitivity up to 10^6 Ohm/T. Such EHE resistivity is four
orders of magnitude higher than previously observed in ferromagnetic materials,
while sensitivity is two orders larger than the best of semiconductors",1607.05923v1
2016-09-26,Bethe Ansatz approach to the three-magnon problem in an infinite $XX$ spin chain with Izing next neighboring ferromagnetic interaction,"Using the traditional and degenerative discrete-diffractive versions of Bethe
Ansatz we construct a rude set of three-magnon states in the infinite $XX$ spin
chain with Izing next neighboring ferromagnetic term.",1609.07941v1
2016-10-20,Optimal design of mixtures of ferromagnetic interactions,"We provide a general framework for the optimal design of surface energies on
networks. We prove sharp bounds for the homogenization of discrete systems
describing mixtures of ferromagnetic interactions by constructing optimal
microgeometries, and we prove a localization principle which allows to reduce
to the periodic setting in the general nonperiodic case.",1610.06455v1
2018-02-10,New Reductions of a Matrix Generalized Heisenberg Ferromagnet Equation,"We present in this report 1+1 dimensional nonlinear partial differential
equation integrable through inverse scattering transform. The integrable system
under consideration is a pseudo-Hermitian reduction of a matrix generalization
of classical 1+1 dimensional Heisenberg ferromagnet equation. We derive
recursion operators and describe the integrable hierarchy related to that
matrix equation.",1802.03591v1
2018-04-06,Magnon excitations and quantum critical behavior of the ferromagnet U$_4$Ru$_7$Ge$_6$,"We present an extensive study of the ferromagnetic heavy fermion compound
U$_4$Ru$_7$Ge$_6$. Measurements of electrical resistivity, specific heat and
magnetic properties show that U$_4$Ru$_7$Ge$_6$ orders ferromagnetically at
ambient pressure with a Curie temperature $T_{C} = 6.8 \pm 0.3$ K. The low
temperature magnetic behavior of this soft ferromagnet is dominated by the
excitation of gapless spin-wave modes. Our results on the transport properties
of U$_4$Ru$_7$Ge$_6$ under pressures up to $2.49$ GPa suggest that
U$_4$Ru$_7$Ge$_6$ has a putative ferromagnetic quantum critical point (QCP) at
$P_c \approx 1.7 \pm 0.02$ GPa. In the ordered phase, ferromagnetic magnons
scatter the conduction electrons and give rise to a well defined power law
temperature dependence in the resistivity. The coefficient of this term is
related to the spin-wave stiffness and measurements of the very low temperature
resistivity allow to accompany the behavior of this quantity as the the
ferromagnetic QCP is approached. We find that the spin-wave stiffness decreases
with increasing pressure implying that the transition to the non-magnetic Fermi
liquid state is driven by the softening of the magnons. The observed quantum
critical behavior of the magnetic stiffness is consistent with the influence of
disorder in our system. At quantum criticality ($P = P_c \approx 1.7 \pm 0.02$
GPa), the resistivity shows the behavior expected for an itinerant metallic
system near a ferromagnetic QCP.",1804.02420v1
2018-11-26,The mean-field quantum Heisenberg ferromagnet via representation theory,"We use representation theory to write a formula for the magnetisation of the
quantum Heisenberg ferromagnet. The core new result is a spectral decomposition
of the function $\alpha_k 2^{\alpha_1+\dotsb+\alpha_n}$ where $\alpha_k$ is the
number of cycles of length k of a permutation. In the mean-field case, we
simplify the formula further, arriving at a closed-form expression for the
magnetisation, which allows to analyse the phase transition.",1811.10530v1
2018-11-28,Notes on Integrable Motion of Two Interacting Curves and Two-layer Generalized Heisenberg Ferromagnet Equations,"In the present paper, we study the integrable 2-layer generalized Heisenberg
ferromagnet equation (HFE). The relation between this generalized HFE and
differential geometry of curves is established. Using this relation we found
the geometrical equivalent counterpart of the 2-layer spin system which is the
2-component KdV equation. Finally, the gauge equivalence between these
equations is established.",1811.12216v1
2014-03-23,Effect of electron-phonon interactions on Raman line at ferromagnetic ordering,"The theory of Raman scattering in half-metals by optical phonons interacting
with conduction electrons is developed. We evaluate the effect of
electron-phonon interactions at ferromagnetic ordering in terms of the
Boltzmann equation for carriers. The chemical potential is found to decrease
with temperature decreasing. Both the linewidth and frequency shift exhibit a
dependence on temperature.",1403.5736v1
2016-11-17,Spin breather and rogue formations in a Heisenberg ferromagnetic system,"We construct explicit spin configurations for the breather solution of a
one-dimensional Heisenberg ferromagnetic spin system. This corresponds to the
breather soliton solution of the gauge equivalent nonlinear Schr\""{o}dinger
equation. There are three broad cases, wherein the solution shows distinct
behavior. Of particular interest to our study is the rogue behavior in spin
field terms.",1611.05615v1
2012-04-04,A compilation of metallic systems that show a quantum ferromagnetic transition,"We provide a compilation of metallic systems in which a low-temperature
ferromagnetic or similar transition is observed. Our objective is to
demonstrate the universal first-order nature of such transitions in clean
systems in two or three spatial dimensions. Please contact the authors with
information about omissions, corrections, or any other information.",1204.0873v1
2013-09-22,Ferromagnetism in the one-dimensional Kondo lattice: mean-field approach via Majorana fermion canonical transformation,"Using a canonical transformation it is possible to faithfully represent the
Kondo lattice model in terms of Majorana fermions. Studying this representation
we discovered an exact mapping between the Kondo lattice Hamiltonian and a
Hamiltonian describing three spinless fermions interacting on a lattice. We
investigate the effectiveness of this three fermion representation by
performing a zero temperature mean-field study of the phase diagram at
different couplings and fillings for the one-dimensional case, focusing on the
appearance of ferromagnetism. The solutions agree in many respects with the
known numerical and analytical results. In particular, in the ferromagnetic
region connected to the solution at zero electron density, we have a
quantitative agreement on the value of the commensurability parameter
discovered in recent DMRG (in one dimension) and DMFT (in infinite dimensions)
simulations; furthermore we provide a theoretical justification for it,
identifying a symmetry of the Hamiltonian. This ferromagnetic phase is
stabilized by the emergence of a spin-selective Kondo insulator that is
described quite conveniently by the three spinless fermions. We discovered also
a different ferromagnetic phase at high filling and low couplings. This phase
resembles the RKKY ferromagnetic phase existing at vanishing filling, but it
incorporates much more of the Kondo effect, making it energetically more
favorable than the typical spiral (spin ordered) mean field ground states. We
believe that this second phase represents a prototype for the strange
ferromagnetic tongue identified by numerical simulations inside the
paramagnetic dome. At the end of the work we also provide a discussion of
possible orders different from the ferromagnetic one. In particular at
half-filling, where we obtain as ground state at high coupling the correct
Kondo insulating state.",1309.5573v2
2019-03-21,Dispersionless Limits of Integrable Generalized Heisenberg Ferromagnet Equations,"This paper is a continuation of our previous work in which we studied a
dispersionless limits of some integrable spin systems (magnetic equations).
Now, we shall present dispersionless limits of some integrable generalized
Heisenberg ferromagnet equations.",1903.09195v1
2022-03-16,Flux Qubit Based on Hybrid Ferromagnetic-Superconducting Device,"We propose a realization of flux qubit based on the hybrid
ferromagnetic-superconducting device where the flux bias is induced purely by
vector potential of the vanishing magnetic field. We support our conclusions
with theoretical analysis and self-consistent three-dimensional simulations for
material specific parameters.",2203.08752v1
2022-06-12,Exchange-enhancement of the ultrafast magnetic order dynamics in antiferromagnets,"We theoretically demonstrate that the ultrafast magnetic order dynamics in
antiferromagnets is exchange-enhanced in comparison to their ferromagnetic
counterparts. We provide an equation of motion for the magnetic order dynamics
validated by computer simulations using atomistic spin dynamics methods. The
exchange of angular momentum between sublattices speeds up the dynamics in
antiferromagnets, a process absent in ferromagnets.",2206.05783v1
2022-09-09,Spin parity effects in monoaxial chiral ferromagnetic chain,"We present a fully quantum mechanical account of a novel {\it spin parity
effect} -- physics which depend sharply on whether the spin quantum number $S$
is half-odd integral or integral, which we find to be present in models of
monoaxial chiral ferromagnetic spin chains.",2209.04227v2
2022-12-15,Triplet odd-frequency superconductivity in hybrid superconductor-ferromagnet structures,"We present an overview of the contributions made by Konstantin B. Efetov and
the authors to the field of triplet odd-frequency superconductivity in hybrid
ferromagnet-superconductor structures and the repercussions they had on
experimental and theoretical research. Konstantin B. Efetov passed away in
August 2021. We hope the present short review gives a faithful testimony of an
important part of his scientific legacy.",2212.08107v1
2024-01-15,Room-temperature intrinsic ferromagnetism of two-dimensional Na2Cl crystals originated by s- and p-orbitals,"Ferromagnetism, as one of the most valuable properties of materials, has
attracted sustained and widespread interest in basic and applied research from
ancient compasses to modern electronic devices. Traditionally, intrinsic
ferromagnetism has been attributed to the permanent magnetic moment induced by
partially filled d- or f-orbitals. However, the development of ferromagnetic
materials has been limited by this electronic structure convention. Thus, the
identification of additional materials that are not constrained by this
conventional rule but also exhibit intrinsic ferromagnetism is highly expected
and may impact all the fields based on ferromagnetism. Here, we report the
direct observation of room-temperature intrinsic ferromagnetism in
two-dimensional (2D) Na2Cl crystals, in which there are only partially filled
s- and p-orbitals rather than d- or f-orbitals, using the superconducting
quantum interference device (SQUID) and magnetic force microscope (MFM). These
Na2Cl crystals formed in reduced graphene oxide (rGO) membranes have an
unconventional stoichiometric structure leading to unique electron and spin
distributions. And the structure of these 2D Na2Cl crystals, including the Na
and Cl sites, is characterized in situ for the first time and directly observed
by cryo-electron microscopy (cryo-EM) based on the observed difference in
contrast between Na stacked with Cl and single Na. These findings break the
conventional rule of intrinsic ferromagnetism and provide new insights into the
design of novel magnetic and electronic devices and transistors with a size
down to the atomic scale.",2401.07524v1
2006-01-10,Fast Resonance Frequency Modulation in Superconducting Stripline Resonator,"Fast resonance frequency modulation of a superconducting stripline resonator
is investigated. The experiments are performed using a novel device which
integrates a hot electron detector (HED) into a superconducting stripline ring
resonator. Frequency modulation is demonstrated by both applying dc current or
voltage to the HED, and by applying optical illumination, with modulation
frequencies of up to 4.2GHz. Potential applications for such a device are in
telecommunication, quantum cryptography and biofluorescence.",0601190v1
2003-02-11,A classical scaling theory of quantum resonances,"The quantum resonances occurring with delta-kicked particles are studied with
the help of a fictitious classical limit, establishing a direct correspondence
between the nearly resonant quantum motion and the classical resonances of a
related system. A scaling law which characterizes the structure of the resonant
peaks is derived and numerically demonstrated.",0302018v2
2001-08-29,Resonant mesomolecule formation,"The dtm and ddm resonant fusion rates are calculated taking into account
finite resonance width and subthreshold resonances. Calculations do not use
multipole expansion of the potential. The obtained ddm resonant fusion rates
are compared with recent data at 30-360 K.",0108068v1
2005-05-10,Resonance Absorption and Regeneration in Relativistic Heavy Ion Collisions,"The regeneration of hadronic resonances is discussed for heavy ion collisions
at SPS and SIS-300 energies. The time evolutions of Delta, rho and phi
resonances are investigated. Special emphasize is put on resonance regeneration
after chemical freeze-out. The emission time spectra of experimentally
detectable resonances are explored.",0505027v1
2000-08-07,Resonance Offset Tailored Pulses for NMR Quantum Computation,"We describe novel composite pulse sequences which act as general rotors and
thus are suitable for nuclear magnetic resonance (NMR) quantum computation. The
Resonance Offset Tailoring To Enhance Nutations (ROTTEN) approach permits
perfect compensation of off-resonance errors at two selected frequencies placed
symmetrically around the frequency of the RF source.",0008034v1
2013-01-22,Stability for the inverse resonance problem for the CMV operator,"For the class of unitary CMV operators with super-exponentially decaying
Verblunsky coefficients we give a new proof of the inverse resonance problem of
reconstructing the operator from its resonances - the zeros of the Jost
function. We establish a stability result for the inverse resonance problem
that shows continuous dependence of the operator coefficients on the location
of the resonances.",1301.5078v1
2013-02-19,Resonances for 1D massless Dirac operators,"We consider the 1D massless Dirac operator on the real line with compactly
supported potentials. We study resonances as the poles of scattering matrix or
equivalently as the zeros of modified Fredholm determinant. We obtain the
following properties of the resonances: 1) asymptotics of counting function, 2)
estimates on the resonances and the forbidden domain, 3) the trace formula in
terms of resonances.",1302.4632v1
2013-06-11,An optical equilibrium in lateral waveguide-resonator optical force,"We consider the lateral optical force between resonator and waveguide, and
study the possibility of an equilibrium that occurs solely from the optical
force. We prove analytically that a single- resonance system cannot give such
an equilibrium in resonator-waveguide force. We then show that two-resonance
systems can provide such an equilibrium. We provide an intuitive way to predict
the existence of an equilibrium, and give numerical examples.",1306.2417v1
2016-04-12,PT-symmetry breaking in resonant tunneling heterostructures,"We present fermionic model based on symmetric resonant tunneling
heterostructure, which demonstrates spontaneous symmetry breaking in respect to
combined operations of space inversion (P) and time reversal (T). PT-symmetry
breaking manifests itself in resonance coalescence (collapse of resonances). We
show that resonant energies are determined by eigenvalues of auxiliary
pseudo-Hermitian PT-invariant Hamiltonian.",1604.03385v1
2016-05-06,Resonances of third order differential operators,"We consider resonances for third order ordinary differential operator with
compactly supported coefficients on the real line. Resonance are defined as
zeros of a Fredholm determinant on a non-physical sheet of three sheeted
Riemann surface. We determine upper bounds of the number of resonances in
complex discs at large radius. We express the trace formula in terms of
resonances only.",1605.01842v1
2005-07-27,Dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor,"We present an analysis of the dynamics of a nanomechanical resonator coupled
to a superconducting single electron transistor (SSET) in the vicinity of the
Josephson quasiparticle (JQP) and double Josephson quasiparticle (DJQP)
resonances. For weak coupling and wide separation of dynamical timescales, we
find that for either superconducting resonance the dynamics of the resonator is
given by a Fokker-Planck equation, i.e., the SSET behaves effectively as an
equilibrium heat bath, characterised by an effective temperature, which also
damps the resonator and renormalizes its frequency. Depending on the gate and
drain-source voltage bias points with respect to the superconducting resonance,
the SSET can also give rise to an instability in the mechanical resonator
marked by negative damping and temperature within the appropriate Fokker-Planck
equation. Furthermore, sufficiently close to a resonance, we find that the
Fokker-Planck description breaks down. We also point out that there is a close
analogy between coupling a nanomechanical resonator to a SSET in the vicinity
of the JQP resonance and Doppler cooling of atoms by means of lasers.",0507645v1
2013-04-02,Coupled Magnetic Resonator Optical Waveguides - mimicking spin waves in coupled metamaterials,"Optical resonators are important devices that control the properties of light
and manipulate light-matter interaction. Various optical resonators are
designed and fabricated using different techniques. For example, in coupled
resonator optical waveguides, light energy is transported to other resonators
through near-field coupling. In recent years, magnetic optical resonators based
on LC resonance have been realized in several metallic microstructures. Such
devices possess stronger local resonance and lower radiation loss compared with
electric optical resonators. This study provides an overall introduction on the
latest progress in coupled magnetic resonator optical waveguide (CMROW).
Various waveguides composed of different magnetic resonators are presented and
Lagrangian formalism is used to describe the CMROW. Moreover, several
interesting properties of CMROW, such as abnormal dispersions and slow light
effects, are discussed and CMROW applications in nonlinear and quantum optics
are shown. Future novel nanophotonic devices can be developed using CMROW.",1304.0573v1
2015-09-03,Quasi-Normal Mode Theory for Thermal Radiation from Lossy and Dispersive Optical Resonators,"Although optical resonators are widely used for controlling and engineering
thermal radiation, what has been lacking is a general theoretical framework to
elucidate the thermal emission of optical resonators, and guide the design and
application of thermally driven optical resonators. We developed a general and
self-consistent formalism to describe the thermal radiation from arbitrary
optical resonators made by lossy and dispersive materials like metals, with the
only assumption that the resonators have a single predominant resonance mode.
Our formalism demonstrates that the thermal emission of an optical resonator is
maximized when the mode losses to the emitter and the absorber (or far-field
background) are matched, and meanwhile the predominant resonant modes are
electrically quasi-static. By efficiently calculating the resonant modes using
the finite element methods, our formalism serves as a general principle of
designing the arbitrary optical resonator thermal emitters with perfect or
maximized emission.",1509.00939v2
2015-10-06,Multiple resonance and anti-resonance in coupled Duffing oscillators,"We investigate the resonance behaviour in a system composed by n-coupled
Duffing oscillators where only the first oscillator is driven by a periodic
force, assuming a nearest neighbour coupling. We have derived the
frequency-response equations for a system composed of two-coupled oscillators
by using a theoretical approach. Interestingly, the frequency-response curve
displays two resonance peaks and one anti-resonance. A theoretical prediction
of the response amplitudes of two oscillators closely match with the
numerically computed amplitudes. We analyse the effect of the coupling strength
on the resonance and anti-resonance frequencies and the response amplitudes at
these frequencies. For the n-coupled oscillators system, in general, there are
n-resonant peaks and (n-1) anti-resonant peaks. For large values of n, except
for the first resonance, other resonant peaks are weak due to linear damping.
The resonance behaviours observed in the n-coupled Duffing oscillators are also
realized in an electronic analog circuit simulation of the equations.
Understanding the role of coupling and system size has the potential
applications in music, structural engineering, power systems, biological
networks, electrical and electronic systems.",1510.01564v1
2018-02-25,Resonant and off-resonant microwave signal manipulation in coupled superconducting resonators,"We present an experimental demonstration as well as a theoretical model of an
integrated circuit designed for the manipulation of a microwave field down to
the single-photon level. The device is made of a superconducting resonator
coupled to a transmission line via a second frequency-tunable resonator. The
tunable resonator can be used as a tunable coupler between the fixed resonator
and the transmission line. Moreover, the manipulation of the microwave field
between the two resonators is possible. In particular, we demonstrate the
swapping of the field from one resonator to the other by pulsing the frequency
detuning between the two resonators. The behavior of the system, which
determines how the device can be operated, is analyzed as a function of one key
parameter of the system, the damping ratio of the coupled resonators. We show a
good agreement between experiments and simulations, realized by solving a set
of coupled differential equations.",1802.09034v2
2013-08-01,Asteroids in retrograde resonance with Jupiter and Saturn,"We identify a set of asteroids among Centaurs and Damocloids, that orbit
contrary to the common direction of motion in the Solar System and that enter
into resonance with Jupiter and Saturn. Their orbits have inclinations I >= 140
deg and semi-major axes a < 15 AU. Two objects are currently in retrograde
resonance with Jupiter: 2006 BZ8 in the 2/-5 resonance and 2008 SO218 in the
1/-2 resonance. One object, 2009 QY6, is currently in the 2/-3 retrograde
resonance with Saturn. These are the first examples of Solar System objects in
retrograde resonance. The present resonant configurations last for several
thousand years. Brief captures in retrograde resonance with Saturn are also
possible during the 20,000 years integration timespan, particularly in the 1/-1
resonance (2006 BZ8) and the 9/-7 resonance (1999 LE31).",1308.0216v1
2009-12-26,Theory of Combined Photoassociation and Feshbach Resonances in a Bose-Einstein Condensate,"We model combined photoassociation and Feshbach resonances in a Bose-Einstein
condensate, where the shared dissociation continuum allows for quantum
interference in losses from the condensate, as well as a dispersive-like shift
of resonance. A simple analytical model, based on the limit of weakly bound
molecules, agrees well with numerical experiments that explicitly include
dissociation to noncondensate modes. For a resonant laser and an off-resonant
magnetic field, constructive interference enables saturation of the
photoassociation rate at user-friendly intensities, at a value set by the
interparticle distance. This rate limit is larger for smaller condensate
densities and, near the Feshbach resonance, approaches the rate limit for
magnetoassociation alone. Also, we find agreement with the unitary limit--set
by the condensate size--only for a limited range of near-resonant magnetic
fields. Finally, for a resonant magnetic field and an off-resonant laser,
magnetoassociation displays similar quantum interference and a dispersive-like
shift. Unlike photoassociation, interference and the fieldshift in resonant
magnetoassociation is tunable with both laser intensity and detuning. Also, the
dispersive-like shift of the Feshbach resonance depends on the size of the
Feshbach molecule, and is a signature of non-universal physics in a strongly
interacting system.",0912.5035v1
2013-09-20,Constraining the mass and width of the $N^*(1685)$ resonance,"We have examined the existence of the $N^*(1685)$ resonance, which is
recently listed by the Particle Data Group as a one-star nucleon resonance, by
using a covariant isobar model for kaon photoproduction and assuming that the
resonance has $J^p=1/2^+$, in accordance with our previous finding. After the
inclusion of this resonance the changes in the total $\chi^2$ show two clear
minima at $M_{N^*}=1650$ and 1696 MeV, which correspond to two different
resonance states. The former corresponds to the narrow nucleon resonance found
in our previous investigation, whereas the latter corresponds to a new
resonance found as we increase the resonance width. From the latter we derive
the mass and width relation of the $N^*(1685)$ resonance. We observe that the
properties of both the $N^*(1685)$ and $N^*(1710)P_{11}$ resonances are
strongly correlated. Although the best fit of the present work yields
$M_{N^*}=1696$ MeV and $\Gamma_{N^*}=76$ MeV, the apparently small
$N^*(1710)P_{11}$ coupling constant to the $K^+\Lambda$ channel found in
previous investigations suggests that $\Gamma_{N^*}\lesssim 35$ MeV, which,
according to the mass and width relation, corresponds to $M_{N^*}\lesssim 1680$
MeV.",1309.5191v1
2014-06-26,Vibrational and Ghost-Vibrational Resonances in A Modified Chua's Circuit Model Equation,"The role of the number of breakpoints $N$ in the sawtooth form of the
characteristic function in the modified Chua's circuit model equation on
vibrational and ghost-vibrational resonances is investigated in this paper. To
observe vibrational resonance the system should be driven by two periodic
forces of frequencies $\omega$ and $\Omega$, with $\Omega\gg\omega$. Resonance
occurs at the frequency $\omega$ when the amplitude of the high-frequency force
is varied. When the system is subjected to an input signal containing
multi-frequencies which are higher-order of a certain (missing) fundamental
frequency, then a resonance at the missing fundamental frequency is induced by
the high-frequency input signal and is called ghost-vibrational resonance. In
both types of resonances, the number of resonances is $N$ and hysteresis occurs
in each resonance region. There are some similarities and differences in these
two resonance phenomena. We report in detail the influence of the role of
number of breakpoints $N$ on the features of vibrational and ghost-vibrational
resonances.",1406.6836v1
2019-09-19,Resonant Laplace-Lagrange theory for extrasolar systems in mean-motion resonance,"Extrasolar systems with planets on eccentric orbits close to or in
mean-motion resonances are common. The classical low-order resonant Hamiltonian
expansion is unfit to describe the long-term evolution of these systems. We
extend the Laplace-Lagrange secular approximation for coplanar systems with two
planets by including (near-)resonant harmonics, and realize an expansion at
high order in the eccentricities of the resonant Hamiltonian both at orders one
and two in the masses. We show that the expansion at first order in the masses
gives a qualitative good approximation of the dynamics of resonant extrasolar
systems with moderate eccentricities, while the second order is needed to
reproduce more accurately their orbital evolutions. The resonant approach is
also required to correct the secular frequencies of the motion given by the
Laplace-Lagrange secular theory in the vicinity of a mean-motion resonance. The
dynamical evolutions of four (near-)resonant extrasolar systems are discussed,
namely GJ 876 (2:1 resonance), HD 60532 (3:1), HD 108874 and GJ 3293 (close to
4:1).",1909.09462v1
2020-02-05,Resonance libration and width at arbitrary inclination,"We apply the analytical disturbing function for arbitrary inclination derived
in our previous work to characterize resonant width and libration of mean
motion resonances at arbitrary inclination obtained from direct numerical
simulations of the three-body problem. We examine the 2:1 and 3:1 inner Jupiter
and 1:2 and 1:3 outer Neptune resonances and their possible asymmetric
librations using a new analytical pendulum model of resonance that includes the
simultaneous libration of multiple arguments and their second harmonics. The
numerically-derived resonance separatrices are obtained using the Mean
Exponential Growth factor of Nearby Orbits (MEGNO chaos indicator). We find
that the analytical and numerical estimates are in agreement and that resonance
width is determined by the first few fundamental resonance modes that librate
simultaneously on the resonant timescale. Our results demonstrate that the new
pendulum model may be used to ascertain resonance width analytically, and more
generally, that the disturbing function for arbitrary inclination is a powerful
analytical tool that describes resonance dynamics of low as well as high
inclination asteroids in the solar system.",2002.01832v2
2018-03-16,Resonances in the asteroid and trans-Neptunian belts: a brief review,"Mean motion resonances play a fundamental role in the dynamics of the small
bodies of the Solar System. The last decades of the 20th century gave us a
detailed description of the dynamics as well as the process of capture of small
bodies in coplanar or small inclination resonant orbits. More recently,
semianalytical or numerical methods allowed us to explore the behavior of
resonant motions for arbitrary inclination orbits. The emerging dynamics is
very rich, including large orbital changes due to secular effects inside mean
motion resonances. The process of capture in highly inclined or retrograde
resonant orbits was addressed showing that the capture in retrograde resonances
is more efficient than in direct ones. A new terminology appeared in order to
characterize the properties of the resonances. Numerical explorations in the
transneptunian region showed the relevance and the particular dynamics of the
exterior resonances with Neptune which can account for some of the known high
perihelion orbits in the scattered disk. Moreover, several asteroids evolving
in resonance with planets other than Jupiter or Neptune were found and a large
number of asteroids in three-body resonances were identified.",1803.06245v1
2019-11-04,Fano resonance in metallic grating via strongly coupled subwavelength resonators,"We investigate the Fano resonance in grating structures by using coupled
resonators. The grating consists of a perfectly conducting slab with
periodically arranged subwavelength slit holes, where inside each period, a
pair of slits sit very close to each other. The slit holes act as resonators
and are strongly coupled. It is shown rigorously that there exist two groups of
resonances corresponding to poles of the scattering problem. One sequence of
resonances have imaginary part on the order of $\varepsilon$, where
$\varepsilon$ is the size of the slit aperture, while the other sequence have
imaginary part on the order of $\varepsilon^2$. When coupled with the incident
wave at resonant frequencies, the narrow-band resonant scattering induced by
the latter will interfere with the broader background resonant radiation
induced by the former. The interference of these two resonances generates the
Fano type transmission anomaly, which persists in the whole radiation continuum
of the grating structure as long as the slit aperture size is small compared to
the incident wavelength.",1911.01025v2
2020-06-16,On the Divergence of First Order Resonance Widths at Low Eccentricities,"Orbital resonances play an important role in the dynamics of planetary
systems. Classical theoretical analyses found in textbooks report that
libration widths of first order mean motion resonances diverge for nearly
circular orbits. Here we examine the nature of this divergence with a
non-perturbative analysis of a few first order resonances interior to a
Jupiter-mass planet. We show that a first order resonance has two branches, the
pericentric and the apocentric resonance zone. As the eccentricity approaches
zero, the centers of these zones diverge away from the nominal resonance
location but their widths shrink. We also report a novel finding of ""bridges""
between adjacent first order resonances: at low eccentricities, the apocentric
libration zone of a first order resonance smoothly connects with the
pericentric libration zone of the neighboring first order resonance. These
bridges may facilitate resonant migration across large radial distances in
planetary systems, entirely in the low eccentricity regime.",2006.09452v1
2023-03-28,Characterization of harmonic modes and parasitic resonances in multi-mode superconducting coplanar resonators,"Planar superconducting microwave transmission line resonators can be operated
at multiple harmonic resonance frequencies. This allows covering wide spectral
regimes with high sensitivity, as it is desired e.g. for cryogenic microwave
spectroscopy. A common complication of such experiments is the presence of
undesired 'spurious' additional resonances, which are due to standing waves
within the resonator substrate or housing box. Identifying the nature of
individual resonances ('designed' vs. 'spurious') can become challenging for
higher frequencies or if elements with unknown material properties are
included, as is common for microwave spectroscopy. Here we discuss various
experimental strategies to distinguish designed and spurious modes in coplanar
superconducting resonators that are operated in a broad frequency range up to
20 GHz. These strategies include tracking resonance evolution as a function of
temperature, magnetic field, and microwave power. We also demonstrate that
local modification of the resonator, by applying minute amounts of dielectric
or ESR-active materials, lead to characteristic signatures in the various
resonance modes, depending on the local strength of the electric or magnetic
microwave fields.",2303.15914v1
2023-04-06,Laboratory electron screening in nuclear resonant reactions,"Both nonresonant and resonance reaction data are subject to laboratory
electron screening effects. For nonresonant reactions, such effects are well
documented and the measured cross sections can be corrected to find the
unscreened ones. Frequently, the procedure and expression to calculate
laboratory electron screening factors for nonresonant reactions are also
applied to isolated narrow resonances, without much theoretical support or
experimental evidence. A simple model is applied to estimate electron screening
factors, lengths, and potentials for narrow resonances. The corrections to the
measured data result in an enhancement of the unscreened resonance strengths by
less than 0.2%, contrary to published narrow-resonance screening correction
factors, which predict a reduction of the unscreened strengths by up to 25%.
Unless it can be proven otherwise, it is recommended that measured strengths of
isolated narrow resonances not be corrected for laboratory electron screening.
The prospects of investigating laboratory electron screening effects by
measuring almost negligible differences in resonance strengths are not
promising. Instead, the difference of the resonance energy for the unscreened
and screened situation may be measurable. As an example, the case of the E_cm =
956-keV resonance in the 27Al(p,gamma)28Si reaction is discussed. It is also
demonstrated that the claim of a previously reported detection of a resonance
near 800 keV in the 176Lu(p,n)176}Hf reaction is incorrect.",2304.03383v1
2000-02-15,Features of first passage time density function for coherent stochastic resonance in the case of two absorbing boundaries,"Coherent stochastic resonance is explained in terms of first passage time
density functions. Scaling relation between first passage time density
functions at resonance for different lengths of the medium is obtained. A
formula for first passage time density function at resonance is derived in
terms of two universal functions, which demonstrates the universal feature of
coherent stochastic resonance. A simple approximate expression for first
passage time density function at resonance is proposed which is shown to
explain the behavior at resonance fairly accurately.",0002223v1
2004-11-10,First evidence of a strong Magneto-capacitance coupling at room temperature in integrated piezoelectric resonators,"In the vicinity of their resonance frequency, piezoelectric resonators are
highly sensitive to small perturbations. The present report is focussed on the
magnetic field as a perturbation source. First, magneto-dielectric modulation
of more than 10% is achieved at room temperature on both ferroelectric single
crystals and quartz discs. Since such piezoelectric resonators are now
available as membranes directly integrated on Silicon wafer, we have checked
the magneto-dielectric modulation in such resonators. We show here for the
first time that a moderate magnetic field of 2.104 Oersteds is able to
efficiently tune the impedance of these resonators in their resonance window.",0411265v1
2005-01-06,Observation of Bifurcations and Hysteresis in Nonlinear NbN Superconducting Microwave Resonators,"In this paper we report some extraordinary nonlinear dynamics measured in the
resonance curve of NbN superconducting stripline microwave resonators. Among
the nonlinearities observed: aburpt bifurcations in the resonance response at
relatively low input powers, asymmetric resonances, multiple jumps within the
resonance band, resonance frequency drift, frequency hysteresis, hysteresis
loops changing direction and critical coupling phenomenon. Weak links in the
NbN grain structure are hypothesized as the source of the nonlinearities.",0501114v2
2005-08-31,Dispersion management using betatron resonances in an ultracold-atom storage ring,"Specific velocities of particles circulating in a storage ring can lead to
betatron resonances at which static perturbations of the particles' orbit yield
large transverse (betatron) oscillations. We have observed betatron resonances
in an ultracold-atom storage ring by direct observation of betatron motion.
These resonances caused a near-elimination of the longitudinal dispersion of
atomic beams propagating at resonant velocities, an effect which can improve
the performance of atom interferometric devices. Both the resonant velocities
and the strength of the resonances were varied by deliberate modifications to
the storage ring.",0508765v1
2006-12-11,On geometrical scaling of split-ring and double-bar resonators at optical frequencies,"In this paper we consider the resonant frequency of split-ring resonators and
double-bar resonators used to create artificial magnetic response at terahertz
and optical frequencies. It is known that geometrical scaling of the resonant
frequency of split rings breaks down at high frequencies (in the visible) due
to electromagnetic properties of metals at those frequencies. Here we will
discuss this phenomenon in terms of equivalent inductance and capacitance of
the ring, derive an approximate formula for the resonant frequency of split
rings in the visible and show how the limiting value of the resonant frequency
of extremely small split rings and double bars depends on particle shape.",0612247v1
1997-12-11,Double giant resonances in deformed nuclei,"We report on the first microscopic study of the properties of two-phonon
giant resonances in deformed nuclei. The cross sections of the excitation of
the giant dipole and the double giant dipole resonances in relativistic heavy
ion collisions are calculated. We predict that the double giant dipole
resonance has a one-bump structure with a centroid 0.8 MeV higher than twice
energy for the single giant dipole resonance in the reaction under
consideration. The width of the double resonance equals to 1.33 of that for the
single resonance.",9712041v1
2000-08-30,Direct-decay properties of charge-exchange spin giant resonances,"An extended continuum-RPA approach is applied to describe direct-decay
properties of spin giant resonances in $^{208}$Bi and $^{90}$Nb. Partial
branching ratios for direct proton decay from these resonances are evaluated.
The branching ratio for $\gamma$-decay from the spin-dipole resonance to the
Gamow-Teller resonance (main peak) is estimated. The saturation-like behaviour
of the mean doorway-state spreading width in $^{208}$Pb is discussed in
connection with the branching ratio for direct proton decay from the
spin-monopole resonance and the Gamow-Teller strength distribution.",0008062v1
2007-04-17,Theoretical study of the accuracy limits for the optical resonance frequency measurements,"The principal limits for the accuracy of the resonance frequency measurements
set by the asymmetry of the natural resonance line shape are studied and
applied to the recent accurate frequency measurements in the two-photon 1s-2s
resonance and in the one-photon 1s-2p resonance in hydrogen atom. This limit
for 1s-2s resonance is found to be $\sim 10^{-5}$ Hz compared to the accuracy
achieved in experiment $\pm 46$ Hz. In case of deuterium atom the limit is
essentially larger: $10^{-2}$ Hz. For 1s-2p resonance the accuracy limit is
0.17 MHz while the uncertainty of the recent frequency measurement is about 6
MHz.",0704.2190v1
2008-10-14,Numerical and experimental studies of resonators with reduced resonant frequencies and small electrical sizes,"Methods on reducing resonant frequencies and electrical sizes of resonators
are reported in this paper. Theoreti-cal and numerical analysis has been used
and the results for the broadside-coupled resonators from both studies exhibit
good agreement. Initial fabrication techniques are proposed and measurement
results are compared with simulations. Further high resolution techniques have
been envisaged to enhance the performance of the resona-tors. This class of
small resonators with low resonant frequencies indicates a variety of
applications in the design of microwave devices.",0810.2490v1
2011-03-29,Ultra-Efficient Cooling of Resonators: Beating Sideband Cooling with Quantum Control,"The present state-of-the-art in cooling mechanical resonators is a version of
""sideband"" cooling. Here we present a method that uses the same configuration
as sideband cooling --- coupling the resonator to be cooled to a second
microwave (or optical) auxiliary resonator --- but will cool significantly
colder. This is achieved by varying the strength of the coupling between the
two resonators over a time on the order of the period of the mechanical
resonator. As part of our analysis, we also obtain a method for fast,
high-fidelity quantum information-transfer between resonators.",1103.5750v1
2012-07-05,Investigation of Surface Plasmon Resonance in Super-Period Gold Nanoslit Arrays,"Surface plasmon resonance in super-period metal nanoslits can be observed in
the first order diffraction as well in the zeroth order transmission. In this
paper, surface plasmon resonance modes in various super-period gold nanoslit
arrays are investigated. It is found that the surface plasmon resonance
frequencies are determined by the small period of the nanoslits in super-period
nanoslits. The number of nanoslits in the unit cell super-period and the
nanoslit width do not control the surface plasmon resonance frequencies. It is
also found that the resonance wavelength observed in the first order
diffraction reveals more accurate the real surface plasmon resonance wavelength
in the metal super-period nanoslit array device.",1207.1143v1
2012-09-25,Discontinuous design of negative index metamaterials based on mode hybridization,"An electric inductor-capacitor (ELC) resonator provides a series of
electrical resonances and a pair of ELC resonators leads to the split of each
resonance into two modes, i.e., magnetic and electric modes, corresponding to
antisymmetric and symmetric current distributions. With the meticulous design
of the ELC resonator, we can achieve a negative index metamaterial through mode
hybridization by overlapping the first electric resonance mode and the second
magnetic resonance mode. Such non-connected designs may offer opportunities to
achieve three-dimensional negative index metamaterials.",1209.5761v1
2013-04-07,Nucleon resonance production in $K^+N$ interactions,"In this work, we discuss the possibility of studying nucleon resonances in
the $K^+N$ interactions. Based on our model calculations, it is found that the
hyperon exchange plays an important role for the excitation of nucleon
resonances in the $K^+N$ interactions. Therefore, the studies on nucleon
resonance production in the $K^+N$ interactions can offer us valuable
information about the couplings of nucleon resonances with strange particles.
By selecting suitable decay channels of nucleon resonances, some reactions are
also suitable to look for missing resonances.",1304.1958v1
2015-03-31,Local resonance and Bragg bandgaps in sandwich beams containing periodically inserted resonators,"We study the low frequency wave propagation behavior of sandwich beams
containing periodically embedded internal resonators. A closed form expression
for the propagation constant is obtained using a phased array approach and
verified using finite element simulations. We show that local resonance and
Bragg bandgaps coexist in such a system and that the width of both bandgaps is
a function of resonator parameters as well as their periodicity. The
interaction between the two bandgaps is studied by varying the local resonance
frequency. We find that a single combined bandgap does not exist for this
system and that the Bragg bandgaps transition into sub-wavelength bandgaps when
the local resonance frequency is above their associated classical Bragg
frequency.",1503.09048v1
2015-08-10,Resonant transmission of light in arrays of high-index dielectric nanoparticles,"We study numerically, analytically and experimentally the resonant
transmission of light in a waveguide formed by a periodic array of high-index
dielectric nanoparticles with a side-coupled resonator. We demonstrate that a
resonator with high enough Q-factor provides the conditions for the Fano-type
interference allowing to control the resonant transmission of light. We suggest
a practical realization of this resonant effect based on the quadrupole
resonance of a dielectric particle and demonstrate it experimentally for
ceramic spheres at microwaves.",1508.02208v1
2015-11-10,Waveguide-loaded silica fibers for coupling to high-index micro-resonators,"Tapered silica fibers are often used to rapidly probe the optical properties
of micro-resonators. However, their low refractive index precludes
phase-matching when coupling to high-index micro-resonators, reducing
efficiency. Here we demonstrate efficient optical coupling from tapered fibers
to high-index micro-resonators by loading the fibers with an ancillary
adiabatic waveguide-coupler fabricated via angled-etching. We demonstrate
greatly enhanced coupling to a silicon multimode micro-resonator when compared
to coupling via the bare fiber only. Signatures of resonator optical
bistability are observed at high powers. This scheme can be applied to
resonators of any size and material, increasing the functional scope of fiber
coupling.",1511.03332v1
2010-05-04,A double scale fast algorithm for the transient evolution of a resonant tunneling diode,"The simulation of the time-dependent evolution of the resonant tunneling
diode is done by a multiscale algorithm exploiting the existence of resonant
states. After revisiting and improving the algorithm developed in [N. Ben
Abdallah, O. Pinaud, J. Comp. Phys. 213 (2006) 288-310] for the stationary
case, the time-dependent problem is dealt with. The wave function is decomposed
into a non resonant part and a resonant one. The projection method to compute
the resonant part leads to an accurate algorithm thanks to a suitable
interpolation of the non resonant one. The simulation times are largely
reduced.",1005.0444v2
2014-03-20,Equivalent Circuit Model for Thick Split Ring Resonators and Thick Spiral Resonators,"A simple theoretical model which provides circuit parameters and resonance
frequency of metallic thick resonators is presented. Two different topologies
were studied: the original Pendry's SRR and spiral resonators of two and three
turns. Theoretical computations of resonant frequencies are in good agreement
with values obtained with a commercial electromagnetic solver. The model could
be helpful for designing thick frequency selective surfaces (FSS) based on this
types of resonators, so called metasurfaces.",1403.5144v1
2017-01-30,Extracting losses from asymmetric resonances in micro-ring resonators,"Propagation losses in micro-ring resonator waveguides can be determined from
the shape of individual resonances in their transmission spectrum. The losses
are typically extracted by fitting these resonances to an idealized model that
is derived using scattering theory. Reflections caused by waveguide boundaries
or stitching errors, however, cause the resonances to become asymmetric,
resulting in poor fits and unreliable propagation loss coefficients. We derive
a model that takes reflections into account and, by performing full-wave
simulations, we show that this model accurately describes the asymmetric
resonances that result from purely linear effects, yielding accurate
propagation loss coefficients.",1701.08464v2
2017-04-10,Generation of the superposition of mesoscopic states of nano-mechanical resonator by a single two-level system,"We propose measurement based conditional generation of superposition of
motional states of nanomechanical resonator. We consider a two level quantum
mechanical system coupled with nanomechanical resonator through phonon
exchange. An interaction, which produces shifts in the state of nanomechanical
resonator depending on the state of the qubit, is realized by driving qubit
through two resonant lasers. The measurement of the state of quantum mechanical
system produces superposition states of nanomechanical resonator. We show that
the quantum interference between states in superposition may lead to arbitrary
large displacement in resonator. We also discuss decoherence of generated
states using Wigner function.",1704.02735v1
2017-04-10,Fano Resonance in a Subwavelength Mie-based Metamolecule with Split Ring Resonator,"In this letter, we report a method of symmetry-breaking in an artificial
Mie-based metamolecule. A Fano resonance with a Q factor of 96 is observed at
microwave frequencies in a structure combining a split ring resonator (SRR) and
a high-permittivity dielectric cube. Calculations indicate resonant frequency
tunability will result from altering the cube's permittivity. The asymmetric
spectrum is attributed to both constructive and destructive near-field
interactions between the two distinct resonators. Experimental data and
simulation results are in good agreement. The underlying physics is seen in
field distribution and dipole analysis. This work substantiates an approach for
the manipulation of Mie resonances which can potentially be utilized in light
modulating and sensing.",1704.02758v1
2012-01-22,Mid-range adiabatic wireless energy transfer via a mediator coil,"A technique for efficient mid-range wireless energy transfer between two
coils via a mediator coil is proposed. By varying the coil frequencies three
resonances are created: emitter-mediator (EM), mediator-receiver (MR) and
emitter-receiver (ER). If the frequency sweeps are adiabatic and such that the
ER resonance precedes the MR resonance, the energy flows sequentially along the
chain emitter-mediator-receiver. If the MR resonance precedes the ER resonance,
then the energy flows directly from the emitter to the receiver via the ER
resonance; then the losses from the mediator are suppressed. This technique is
robust to noise, resonant constraints and external interferences.",1201.4592v1
2014-06-30,Resonant activation in 2D and 3D systems driven by multi-variate Lévy noises,"Resonant activation is one of classical effects demonstrating constructive
role of noise. In resonant activation cooperative action of barrier modulation
process and noise lead to the optimal escape kinetics as measured by the mean
first passage time. Resonant activation has been observed in versatilities of
systems for various types of barrier modulation processes and noise types.
Here, we show that resonant activation is also observed in 2D and 3D systems
driven by bi-variate and tri-variate $\alpha$-stable noises. Strength of
resonant activation is sensitive to the exact value of the noise parameters. In
particular, the decrease in the stability index $\alpha$ results in the
disappearance of the resonant activation.",1406.7810v1
2015-12-08,Effects of pairing correlation on low-lying quasi-particle resonance in neutron drip-line nuclei,"We discuss effects of pairing correlation on quasi-particle resonance. We
analyze in detail how the width of low-lying quasi-particle resonance is
governed by the pairing correlation in the neutron drip-line nuclei. We
consider the 46Si + n system to discuss low-lying p wave quasi-particle
resonance. Solving the Hartree-Fock-Bogoliubov equation in the coordinate space
with scattering boundary condition, we calculate the phase shift, the elastic
cross section, the resonance width and the resonance energy. We found that the
pairing correlation has an effect to reduce the width of quasi-particle
resonance which originates from a particle-like orbit in weakly bound nuclei.",1512.02675v1
2017-06-12,Tunable coupling-induced resonance splitting in self-coupled Silicon ring cavity with robust spectral characteristics,"We propose and demonstrate a self-coupled microring resonator for resonance
splitting by mutual mode coupling of cavity mode and counter-propagating mode
in Silicon-on-Insulator platform The resonator is constructed with a
self-coupling region that can excite counter-propagating mode. We
experimentally study the effect of self-coupling on the resonance splitting,
resonance extinction, and quality-factor evolution and stability. Based on the
coupling, we achieve 72% of FSR splitting for a cavity with FSR 2.1 nm with <
5% variation in the cavity quality factor. The self-coupled resonance splitting
shows highly robust spectral characteristic that can be exploited for sensing
and optical signal processing.",1706.03810v1
2017-07-29,EIT-Enhanced Coupled-Resonance Spectroscopy,"Coupled-resonance spectroscopy has been recently reported and applied for
spectroscopic measurements and laser stabilizations. With coupled-resonance
spectroscopy, one may indirectly measure some transitions between the excited
states that are hard to be measured directly because of the lack of populations
in the excited states. An improvement of the coupled-resonance spectroscopy by
combining the technology of electromagnetically induced transparency (EIT) is
proposed. The coupled-resonance spectroscopy signal can be significantly
enhanced by EIT. Several experimental schemes have been discussed. The line
shape of the EIT-enhanced coupled-resonance spectroscopy has been
calculated.The EIT-enhanced coupled-resonance spectroscopy can be used for
simultaneously stabilizing two lasers to the same atomic source.",1707.09559v1
2019-11-29,Omni-resonant space-time wave packets,"We describe theoretically and verify experimentally a novel class of
diffraction-free pulsed optical beams that are `Omni-resonant': they have the
remarkable property of transmission through planar Fabry-Perot resonators
without spectral filtering even if their bandwidth far exceeds the cavity
resonant linewidth. Ultrashort wave packets endowed with a specific
Spatio-temporal structure couple to a \textit{single} resonant mode
independently of its linewidth. We confirm that such `space-time' Omni-resonant
wave packets retain their bandwidth (1.6~nm), Spatio-temporal profile (1.3-ps
pulse width, 4-$\mu$m beam width), and diffraction-free behavior upon
transmission through cavities with resonant linewidths of 0.3-nm and 0.15-nm.",1912.00092v1
2019-12-16,Continuously Tunable Acoustic Metasurface with Rotatable Anisotropic Three-component Resonators,"We propose a tunable acoustic metasurface consisting of identical units. And
units are rotatable anisotropic three-component resonators, which can induce
the non-degenerate dipolar resonance, causing an evident phase change in low
frequencies. Compared with the monopole resonance widely used in Helmholtz
resonators, the polarization direction of the dipole resonance is a new degree
of freedom for phase manipulation. The proposed metasurface is constructed by
identical units that made with real (not rigid) materials. And the phase
profile can continuously change by rotating the anisotropic resonators. We
present a wide-angle and broad-band acoustic focusing by the metasurface under
a water background.",1912.07149v1
2020-03-27,Inverse resonance scattering for Dirac operators on the half-line,"We consider massless Dirac operators on the half-line with compactly
supported potentials. We solve the inverse problems in terms of Jost function
and scattering matrix (including characterization). We study resonances as
zeros of Jost function and prove that a potential is uniquely determined by its
resonances. Moreover, we prove the following:
  1) resonances are free parameters and a potential continuously depends on a
resonance,
  2) the forbidden domain for resonances is estimated,
  3) asymptotics of resonance counting function is determined,
  4) these results are applied to canonical systems.",2003.12502v2
2020-10-24,A Short Review of Plasmonic Graphene-Based Resonators: Recent Advances and Prospects,"This article aims to study graphene-based resonators published in the
literature. Graphene resonators are designed based on graphene conductivity, a
variable parameter that can be changed by either electrostatic or magnetostatic
gating. A historical review of plasmonic graphene resonators is presented in
this paper, which can give physical insight to the researchers to be
familiarized with four types of graphene-based resonators: 1-Ring resonators,
2- planar, 3- Fabry-Perot, and 4-other resonators which are not categorized in
any of the other three groups.",2011.14767v1
2021-10-23,Optical interface for a hybrid magnon-photon resonator,"We study optical detection of magnetic resonance of a ferrimagnetic sphere
resonator, which is strongly coupled to a microwave loop gap resonator. Optical
fibers are employed for coupling the sphere resonator with light in the telecom
band. We find that magnetic resonance can be optically detected in the region
of anti-crossing between the loop gap and the ferrimagnetic resonances. By
measuring the response time of the optical detection we rule out the
possibility that microwave induced heating is responsible for the optical
detectability.",2110.13644v1
2022-02-15,Resonant phase lags of a Duffing oscillator,"This paper revisits the resonant behavior of a harmonically-forced Duffing
oscillator with a specific attention to phase resonance and to its relation
with amplitude resonance. To this end, the different families of resonances,
namely primary (1:1), superharmonic (k:1), subharmonic (1:{\nu}) and
ultra-subharmonic (k:{\nu}) resonances are carefully studied using first and
higher-order averaging. When the phase lag is calculated between the k-th
harmonic of the displacement and the harmonic forcing, this study evidences
that phase resonance occurs when the phase lag is equal to either {\pi}/2
(phase quadrature) or 3{\pi}/4{\nu}.",2202.07556v2
2022-03-31,Effect of Diffraction on Wigner Distributions of Optical Fields and how to Use It in Optical Resonator Theory. III -- Ray Tracing in Resonators,"The third part of the paper is devoted to ray tracing in optical resonators.
The employed method for dealing with the issue uses the elliptical or
hyperbolic rotations that Wigner distributions associated with optical fields
undergo during propagation from one spherical mirror of a resonator to the
other. It is illustrated by various examples concerning meridional or skew
rays, reentrant in stable resonators or propagating in unstable resonators.
  A classification of optical resonators is eventually deduced.",2203.16905v1
2024-03-06,High-Impedance Microwave Resonators with Two-Photon Nonlinear Effects,"In this article, we present an experimental study of a Josephson junction
-based high-impedance resonator. By taking the resonator to the limit of
consisting effectively only of one junction, results in strong non-linear
effects already for the second photon while maintaining a high impedance of the
resonance mode. Our experiment yields thus resonators with the strong
interactions both between individual resonator photons and from the resonator
photons to other electric quantum systems. We also present an energy diagram
technique which enables to measure, identify and analyse different multi-photon
optics processes along their energy conservation lines.",2403.03779v1
2004-07-19,On the saturation of corotation resonances: a numerical study,"[Abridged] The torque exerted by an external potential on a two-dimensional
gaseous disk at non-co-orbital corotation resonances is studied by means of
numerical simulations. The degree of saturation of these resonances is
important in determining whether an eccentric giant planet embedded in a
protoplanetary disk experiences an eccentricity excitation or damping. We
perform calculations restricted to one or two resonances to investigate the
properties of two neighboring corotation resonances, as well as the properties
of a corotation resonance that overlaps a Lindblad resonance. We find that
these properties hardly differ from the case of an isolated corotation
resonance. In particular, although the torque of two neighboring corotation
resonances may differ from the sum of the torques of the corresponding
resonances considered as isolated, it never exceeds the sum of the fully
unsaturated isolated corotation resonances, and it saturates in a fashion
similar to an isolated resonance. Similarly, the presence of an underlying
Lindblad resonance hardly affects the corotation torque, even if that resonance
implies a torque strong enough to significantly redistribute the azimuthally
averaged surface density profile, in which case the corotation torque scales
with the resulting vortensity gradient. This set of numerical experiments thus
essentially validates previous analytic studies. As a side result, we show that
corotation libration islands misrepresented by a mesh of too low resolution can
lead to a strongly overestimated corotation torque. This may be an explanation
why the eccentricity of embedded Jupiter-sized planets was never observed to
undergo an excitation in the numerical simulations performed so far.",0407403v1
2013-12-20,Atlas of three body mean motion resonances in the Solar System,"We present a numerical method to estimate the strengths of arbitrary three
body mean motion resonances between two planets in circular coplanar orbits and
a massless particle in an arbitrary orbit. This method allows us to obtain an
atlas of the three body resonances in the Solar System showing where are
located and how strong are thousands of resonances involving all the planets
from 0 to 1000 au. This atlas confirms the dynamical relevance of the three
body resonances involving Jupiter and Saturn in the asteroid belt but also
shows the existence of a family of relatively strong three body resonances
involving Uranus and Neptune in the far Trans-Neptunian region and relatively
strong resonances involving terrestrial and jovian planets in the inner
planetary system. We calculate the density of relevant resonances along the
Solar System resulting that the main asteroid belt is located in a region of
the planetary system with the lowest density of three body resonances. The
method also allows the location of the equilibrium points showing the existence
of asymmetric librations (sigma different from 0 or 180 degrees). We obtain the
functional dependence of the resonance's strength with the order of the
resonance and the eccentricity and inclination of the particle's orbit. We
identify some objects evolving in or very close to three body resonances with
Earth-Jupiter, Saturn-Neptune and Uranus-Neptune apart from Jupiter-Saturn, in
particular the NEA 2009 SJ18 is evolving in the resonance 1-1E-1J and the
centaur 10199 Chariklo is evolving under the influence of the resonance
5-2S-2N.",1312.6068v1
2018-05-10,Apparent spectral shift of thermally generated surface phonon-polariton resonance mediated by a non-resonant film,"The physical origin of spectral shift of thermally generated surface
phonon-polariton (SPhP) resonance of a silicon carbide (SiC) bulk mediated by a
non-resonant film is elucidated. The local density of electromagnetic states
(LDOS) in a non-resonant intrinsic silicon (Si) film due to thermal emission by
SiC, derived using fluctuational electrodynamics, exhibits a local maximum near
SPhP resonant frequency in addition to a lower frequency resonance generated by
gap modes emerging in the vacuum gap separating the SiC and Si layers. Multiple
reflections within the vacuum gap also induce a LDOS drop around SPhP resonant
frequency. As a result, depending on the film thickness to vacuum gap ratio and
the location where the LDOS is calculated in the film, the low-frequency
resonance can dominate the LDOS, such that SPhP resonance appears to be
redshifted. A similar spectral behavior is observed on the monochromatic
radiative heat flux absorbed by the Si film. It is shown that apparent spectral
(red and blue) shift of SPhP resonance mediated by a non-resonant film is
bounded by the transverse and longitudinal optical phonon frequencies of SiC.
This work is of importance in applications involving dissimilar materials, such
as thermophotovoltaics and thermal rectification, where gap modes may
significantly disrupt flux resonance. Gap modes may also be at the origin of
the resonance redshift systematically observed in near-field thermal
spectroscopy.",1805.03768v2
2016-05-20,Three-body resonance in meteoroid streams,"Mean-motion resonances play an important role in the evolution of various
meteoroid streams. Previous works have studied the effects of two-body
resonances in different comets and streams. These already established two-body
resonances were mainly induced either by Jovian or Saturnian effects but not
both at the same time. Some of these resonances have led to spectacular meteor
outbursts and storms in the past. In this work, we find a new resonance
mechanism involving three bodies -- i.e. meteoroid particle, Jupiter and
Saturn, in the Perseid meteoroid stream. Long-term three-body resonances are
not very common in real small bodies in our solar system although they can
mathematically exist at many resonant sweet spots in an abstract sense in any
dynamical system. This particular resonance combination in the Perseid stream
is such that it is close to the ratio of 1:4:10 if the orbital periods of
Perseid particle, Saturn and Jupiter are considered respectively. These
resonant Perseid meteoroids stay resonant for typically about 2 kyr. Highly
compact dust trails due to this unique resonance phenomenon are present in our
simulations. Some past and future years are presented where three-body resonant
meteoroids of different sizes (or subject to different radiation pressures) are
computed to come near the Earth. This is the first theoretical example of an
active and stable three-body resonance mechanism in the realm of meteoroid
streams.",1605.06340v1
2018-07-03,Structure resonance crossing in space charge dominated beams,"As an extension of previous theoretical study on the coherent structure
resonance due to space charge effects [Chao Li and R. A. Jameson, Phys. Rev.
Accel. Beams 21, 024204, 2018], this paper aims to demonstrate how the beam, as
a whole, is spontaneously affected when the predicted mixed coherent 2nd/4th
order structure resonance stop band around $90^{\circ}$ phase advance is
crossed. The beam characteristics during the structure resonance crossing, such
as the rms emittance growth and the appearance of 2-fold/4-fold structure in
phase space, are well explained by the mixture characteristic of different
orders of structure resonance. The related `attracting' and `repulsive' effects
in the structure resonance stop band from below and above crossing are
considered as a natural beam reaction to the coherent structure resonance that
the beam spontaneously moves to a structure resonance free region then the
space charge takes a weaker importance. In the PIC simulation, it is found that
the emittance growth is positively related to the time that the beam spends
inside the structure resonance stop band. As a potential candidate mechanism,
the incoherent particle-core resonance also has been checked. It is found that
this incoherent resonance has basic difficulties in explaining the results
obtained from the self-consistent PIC simulation. The incoherent particle-core
resonance might lead to phase space distortion, emittance growth, or beam halo
formation only on a long-time scale. This clarity of the discrepancies between
coherent and incoherent resonance mechanisms will lead to a better
understanding of the numerical study and experimental researches obtained
recently. In addition, similar understanding can be extended to the study of
higher order structure resonance.",1807.01204v1
2020-06-19,Robust interface-state laser in non-Hermitian micro-resonator arrays,"We propose a scheme to achieve the analogous interface-state laser by dint of
the interface between the two intermediate-resonator-coupled non-Hermitian
resonator chains. We find that, after introducing the couplings between the two
resonator chains and the intermediate resonator at the interface, the photons
of the system mainly gather into the three resonators near the intermediate
resonator. The phenomenon of the photon gathering towards the certain
resonators is expected to construct the photon storage and even the laser
generator. We reveal that the phenomenon is induced via the joint effect
between the isolated intermediate resonator and two kinds of non-Hermitian skin
effects. Specially, we investigate the interface-state laser in topologically
trivial non-Hermitian resonator array in detail. We find that the pulsed
interface-state laser can be achieved accompanying with the intermittent
proliferation of the photons at the intermediate resonator when an arbitrary
resonator is excited. Also, we reveal that the pulsed interface-state laser in
the topologically trivial non-Hermitian resonator array is immune to the
on-site defects in some cases, whose mechanism is mainly induced by the
nonreciprocal couplings instead of the protection of topology. Our scheme
provides a promising and excellent platform to investigate interface-state
laser in the micro-resonator array.",2006.10943v1
2023-06-30,Confirming Resonance in Three Transiting Systems,"Although resonant planets have orbital periods near commensurability,
resonance is also dictated by other factors, such as the planets'
eccentricities and masses, and therefore must be confirmed through a study of
the system's dynamics. Here, we perform such a study for five multi-planet
systems: Kepler-226, Kepler-254, Kepler-363, Kepler-1542, and K2-32. For each
system, we run a suite of N-body simulations that span the full parameter-space
that is consistent with the constrained orbital and planetary properties. We
study the stability of each system and look for resonances based on the
libration of the critical resonant angles. We find strong evidence for a
two-body resonance in each system; we confirm a 3:2 resonance between
Kepler-226c and Kepler-226d, confirm a 3:2 resonance between Kepler-254c and
Kepler-254d, and confirm a three-body 1:2:3 resonant chain between the three
planets of Kepler-363. We explore the dynamical history of two of these systems
and find that these resonances most likely formed without migration. Migration
leads to the libration of the three-body resonant angle, but these angles
circulate in both Kepler-254 and Kepler-363. Applying our methods to additional
near-resonant systems could help us identify which systems are truly resonant
or non-resonant and which systems require additional follow-up analysis.",2306.17751v1
2007-03-21,Resonances in Barred Galaxies,"The inner parts of many spiral galaxies are dominated by bars. These are
strong non-axisymmetric features which significantly affect orbits of stars and
dark matter particles. One of the main effects is the dynamical resonances
between galactic material and the bar. We detect and characterize these
resonances in N-body models of barred galaxies by measuring angular and radial
frequencies of individual orbits. We found narrow peaks in the distribution of
orbital frequencies with each peak corresponding to a specific resonance. We
found five different resonances in the stellar disk and two in the dark matter.
The corotation resonance and the inner and outer Lindblad resonances are the
most populated. The spatial distributions of particles near resonances are
wide. For example, the inner Lindblad resonance is not localized at a given
radius. Particles near this resonance are mainly distributed along the bar and
span a wide range of radii. On the other hand, particles near the corotation
resonance are distributed in two broad areas around the two stable Lagrange
points. The distribution resembles a wide ring at the corotation radius.
Resonances capture disk and halo material in near-resonant orbits. Our analysis
of orbits in both N-body simulations and in simple analytical models indicates
that resonances tend to prevent the dynamical evolution of this trapped
material. Only if the bar evolves as a whole, resonances drift through the
phase space. In this case particles anchored near resonant orbits track the
resonance shift and evolve. The criteria to ensure a correct resonant behavior
discussed in Weinberg & Katz (2007a) can be achieved with few millions
particles because the regions of trapped orbits near resonances are large and
evolving.",0703544v2
2018-08-06,Microscopic effects of Dy-doping in the topological insulator Bi2Te3,"Magnetic doping with transition metal ions is the most widely used approach
to break timereversal symmetry in a topological insulator, a prerequisite for
unlocking the TIs exotic potential. Recently, we reported the doping of Bi2Te3
thin films with rare earth ions, which, owing to their large magnetic moments,
promise commensurately large magnetic gap openings in the topological surface
states. However, only when doping with Dy has a sizable gap been observed in
angle-resolved photoemission spectroscopy, which persists up to
room-temperature. Although disorder alone could be ruled out as a cause of the
topological phase transition, a fundamental understanding of the magnetic and
electronic properties of Dy:Bi2Te3 remained elusive. Here, we present an X-ray
magnetic circular dichroism, polarized neutron reflectometry, muon spin
rotation, and resonant photoemission study of the microscopic magnetic and
electronic properties. We find that the films are not simply paramagnetic but
that instead the observed behavior can be well explained by the assumption of
slowly fluctuating, inhomogeneous magnetic patches with increasing volume
fraction as the temperature decreases. At liquid helium temperatures, a large
effective magnetization can be easily introduced by the application of moderate
magnetic fields, implying that this material is very suitable for proximity
coupling to an underlying ferromagnetic insulator or in a heterostructure with
transition metal-doped layers. However, the introduction of some charge
carriers by the dopants cannot be excluded at least in these highly doped
samples. Nevertheless, we find that the magnetic order is not mediated via the
conduction channel in these rare earth doped samples and therefore magnetic
order and carrier concentration are expected to be independently controllable.
This is not generally the case for transition metal doped topological
insulators.",1808.01938v1
2012-06-07,Massive identification of asteroids in three-body resonances,"An essential role in the asteroidal dynamics is played by the mean motion
resonances. Two-body planet-asteroid resonances are widely known, due to the
Kirkwood gaps. Besides, so-called three-body mean motion resonances exist, in
which an asteroid and two planets participate. Identification of asteroids in
three-body (namely, Jupiter-Saturn-asteroid) resonances was initially
accomplished by D.Nesvorny and A.Morbidelli (1998), who, by means of visual
analysis of the time behaviour of resonant arguments, found 255 asteroids to
reside in such resonances. We develop specialized algorithms and software for
massive automatic identification of asteroids in the three-body, as well as
two-body, resonances of arbitrary order, by means of automatic analysis of the
time behaviour of resonant arguments. In the computation of orbits, all
essential perturbations are taken into account. We integrate the asteroidal
orbits on the time interval of 100000 yr and identify main-belt asteroids in
the three-body Jupiter-Saturn-asteroid resonances up to the 6th order
inclusive, and in the two-body Jupiter-asteroid resonances up to the 9th order
inclusive, in the set of ~250000 objects from the ""Asteroids - Dynamic Site""
(AstDyS) database. The percentages of resonant objects, including
extrapolations for higher-order resonances, are determined. In particular, the
observed fraction of pure-resonant asteroids (those exhibiting resonant
libration on the whole interval of integration) in the three-body resonances up
to the 6th order inclusive is approximately 0.9% of the whole set; and, using a
higher-order extrapolation, the actual total fraction of pure-resonant
asteroids in the three-body resonances of all orders is estimated as
approximately 1.1% of the whole set.",1206.1451v2
2014-10-08,Statistical distributions of mean motion resonances and near-resonances in multiplanetary systems,"The orbits of the confirmed exoplanets from all multiple systems known to
date are investigated. Observational data from 1890 objects, of which 1176 are
found in multiplanetary systems, are compiled and analyzed. Mean motion
resonances and near-resonances up to the outer/inner orbital period ratio's
value of 5 and the denominator 4 are tested for all adjacent exoplanet orbits.
Each host star's snow line is calculated using a simple algorithm. The planets
are reclassified into categories as a function of the semimajor axis size
relative to the snow line location and the semimajor axis vs mass distribution.
The fraction of planets in/near resonance is then plotted as a function of both
resonance number and resonance order for all the exoplanet population and,
separately, for each planet type. In the resonance number plot it appears that
the 2/1 and 3/2 resonances and near-resonances are dominant overall and for the
giant planets, but the observed distribution profile changes significantly with
each planet category, with terrestrial planets, neptunes and mini-neptunes
showing the largest variation. Resonances/near resonances around the value 5/3
were dominant for mini neptunes and terrestrial planets. In the order-based
resonance/near-resonance plot, the observed distribution appears to follow an
exponential decay for the general population and its profile appears to be
influenced by the planet type. Approximate methods to estimate resonance/near
resonance distributions are also attempted for the systems with unknown planet
mass or with unknown star and/or planet mass and compared with the distribution
of the planets with all the parameters known. A separate study of the
resonance/near resonance fraction distribution as a function of mass is also
attempted, but the low statistical data at very high planetary masses prevent
the finding of an accurate equation to describe such a dependency.",1410.2478v3
2015-04-29,The 5:1 Neptune Resonance as Probed by CFEPS: Dynamics and Population,"The Canada-France Ecliptic Plane Survey discovered four trans-Neptunian
objects with semi-major axes near the 5:1 resonance, revealing a large and
previously undetected intrinsic population. Three of these objects are
currently resonant with Neptune, and the fourth is consistent with being an
object that escaped the resonance at some point in the past. The non-resonant
object may be representative of a detached population that is stable at
slightly lower semi-major axes than the 5:1 resonance. We generated clones of
these objects by resampling the astrometric uncertainty and examined their
behavior over a 4.5 Gyr numerical simulation. The majority of the clones of the
three resonant objects (>90%) spend a total of 10^7 years in resonance during
their 4.5 Gyr integrations; most clones experience multiple periods of
resonance capture. Our dynamical integrations reveal an exchange between the
5:1 resonance, the scattering objects, and other large semi-major axis
resonances, especially the 4:1, 6:1, and 7:1. The multiple capture events and
relatively short resonance lifetimes after capture suggest that these objects
are captured scattering objects that stick in the 5:1 resonance. These 5:1
resonators may be representative of a temporary population, requiring regular
contributions from a source population. We examined the dynamical
characteristics (inclination, eccentricity, resonant island, libration
amplitude) of the detected objects and their clones in order to provide an
empirical model of the orbit structure of the 5:1 resonance. This resonance is
dynamically hot and includes primarily symmetric librators. Given our orbit
model, the intrinsic population necessary for the detection of these three
objects in the 5:1 resonance is 1900(+3300 -1400, 95% confidence) with H_g< 8
and e > 0.5.",1504.08041v1
1993-05-24,Ferromagnetism in the Hubbard Model-- Examples from Models with Degenerate Single-Electron Ground States,"Whether spin-independent Coulomb interaction can be the origin of a realistic
ferromagnetism in an itinerant electron system has been an open problem for a
long time. Here we study a class of Hubbard models on decorated lattices, which
have a special property that the corresponding single-electron Schr\""{o}dinger
equation has $N_{\rm d}$-fold degenerate ground states. The degeneracy $N_{\rm
d}$ is proportional to the total number of sites $\abs{\Lambda}$. We prove that
the ground states of the models exhibit ferromagnetism when the electron
filling factor is not more than and sufficiently close to $\rho_0=N_{\rm
d}/(2\abs{\Lambda})$, and paramagnetism when the filling factor is sufficiently
small. An important feature of the present work is that it provides examples of
three dimensional itinerant electron systems which are proved to exhibit
ferromagnetism in a finite range of the electron filling factor.",9305026v2
1994-02-11,Macroscopic Quantum Tunneling of a Domain Wall in a Ferromagnetic Metal,"The macroscopic quantum tunneling of a planar domain wall in a ferromagnetic
metal is studied by use of an instanton method. Based on the Hubbard model, the
effective action of the magnetization is derived within the assumption of slow
dependences on space and time. The resulting action is formally similar to that
of a ferromagnetic Heisenberg model but with a term non-local in time that
describes the dissipation due to the itinerant electron. The crucial difference
from the case of the insulator is the presence of the ohmic dissipation even at
zero temperature due to the gapless Stoner excitation. The reduction of the
tunneling rate due to the dissipation is calculated. The dissipative effect is
found to be very large for a thin domain wall with thickness of a few times the
lattice spacing, but is negligible for a thick domain wall. The results are
discussed in the light of recent experiments on ferromagnets with strong
anisotropy. (Submitted to J. Phys. Soc. Jpn)",9402050v1
1994-12-02,Fluctuations and Instabilities of Ferromagnetic Domain Wall pairs in an External Magnetic Field,"Soliton excitations and their stability in anisotropic quasi-1D ferromagnets
are analyzed analytically. In the presence of an external magnetic field, the
lowest lying topological excitations are shown to be either soliton-soliton or
soliton-antisoliton pairs. In ferromagnetic samples of macro- or mesoscopic
size, these configurations correspond to twisted or untwisted pairs of Bloch
walls. It is shown that the fluctuations around these configurations are
governed by the same set of operators. The soliton-antisoliton pair has exactly
one unstable mode and thus represents a critical nucleus for thermally
activated magnetization reversal in effectively one-dimensional systems. The
soliton-soliton pair is stable for small external fields but becomes unstable
for large magnetic fields. From the detailed expression of this instability
threshold and an analysis of nonlocal demagnetizing effects it is shown that
the relative chirality of domain walls can be detected experimentally in thin
ferromagnetic films. The static properties of the present model are equivalent
to those of a nonlinear sigma-model with anisotropies. In the limit of large
hard-axis anisotropy the model reduces to a double sine-Gordon model.",9412009v2
1996-12-27,Low Energy Properties of the Random Spin-1/2 Ferromagnetic-Antiferromagnetic Heisenberg Chain,"The low energy properties of the spin-1/2 random Heisenberg chain with
ferromagnetic and antiferromagnetic interactions are studied by means of the
density matrix renormalization group (DMRG) and real space renormalization
group (RSRG) method for finite chains. The results of the two methods are
consistent with each other. The deviation of the gap distribution from that of
the random singlet phase and the formation of the large-spin state is observed
even for relatively small systems. For a small fraction of the ferromagnetic
bond, the effect of the crossover to the random singlet phase on the low
temperature susceptibility and specific heat is discussed. The crossover
concentration of the ferromagnetic bond is estimated from the numerical data.",9612232v1
1997-01-21,Non-perturbative approaches to magnetism in strongly correlated electron systems,"The microscopic basis for the stability of itinerant ferromagnetism in
correlated electron systems is examined. To this end several routes to
ferromagnetism are explored, using both rigorous methods valid in arbitrary
spatial dimensions, as well as Quantum Monte Carlo investigations in the limit
of infinite dimensions (dynamical mean-field theory). In particular we discuss
the qualitative and quantitative importance of (i) the direct Heisenberg
exchange coupling, (ii) band degeneracy plus Hund's rule coupling, and (iii) a
high spectral density near the band edges caused by an appropriate lattice
structure and/or kinetic energy of the electrons. We furnish evidence of the
stability of itinerant ferromagnetism in the pure Hubbard model for appropriate
lattices at electronic densities not too close to half-filling and large enough
$U$. Already a weak direct exchange interaction, as well as band degeneracy, is
found to reduce the critical value of $U$ above which ferromagnetism becomes
stable considerably. Using similar numerical techniques the Hubbard model with
an easy axis is studied to explain metamagnetism in strongly anisotropic
antiferromagnets from a unifying microscopic point of view.",9701150v1
1997-03-03,Low density ferromagnetism in Extended Hubbard ( t-t'-U ) Model,"We study the existence of ferromagnetism in one dimensional Hubbard Model
with on site interaction and nearest and next nearest neighbor hopping. Using
the Hubbard I approximation, a self consistent equation for $<n_\sigma>$, the
particle density with spin $\sigma$ is obtained. We find that ferromagnetism
exists over a wide range of values of the next nearest neighbor hopping element
t' when on-site interaction U is large. The phase diagram as a function of t'/t
and the electron density $<n>$ has been obtained by numerically solving the
self consistent equation. It is found that the maximum density at which
ferromagnetism can occur, peaks around $t'/t \approx -0.53$. We show that this
phenomenon is a result of the peculiar way in which the t' term modifies the
density of states.",9703022v1
1997-06-17,Generalized calculation of magnetic coupling constants for Mott-Hubbard insulators: Application to ferromagnetic Cr compounds,"Using a Rayleigh-Schr\""odinger perturbation expansion of multi-band Hubbard
models, we present analytic expressions for the super-exchange coupling
constants between magnetic transition metal ions of arbitrary separation in
Mott-Hubbard insulators. The only restrictions are i) all ligand ions are
closed shell anions and ii) all contributing interaction paths are of equal
length. For short paths, our results essentially confirm the
Goodenough-Kanamori-Anderson rules, yet in general there does not exist any
simple rule to predict the sign of the magnetic coupling constants. The most
favorable situation for ferromagnetic coupling is found for ions with less than
half filled d shells, the (relative) tendency to ferromagnetic coupling
increases with increasing path length. As an application, the magnetic
interactions of the Cr compounds Rb$_2$CrCl$_4$, CrCl$_3$, CrBr$_3$ and CrI$_3$
are investigated, all of which except CrCl$_3$ are ferromagnets.",9706175v1
1997-12-14,Static and Dynamical Properties of the Ferromagnetic Kondo Model with Direct Antiferromagnetic Coupling Between the localized $t_{2g}$ Electrons,"The phase diagram of the Kondo lattice Hamiltonian with ferromagnetic Hund's
coupling in the limit where the spin of the localized $t_{2g}$ electrons is
classical is analyzed in one dimension as a function of temperature, electronic
density, and a direct antiferromagnetic coupling $J'$ between the localized
spins. Studying static and dynamical properties, a behavior that qualitatively
resembles experimental results for manganites occurs for $J'$ smaller than 0.11
in units of the $e_g$ hopping amplitude. In particular a coexistence of
ferromagnetic and antiferromagnetic excitations is observed at low-hole density
in agreement with neutron scattering experiments on
$\rm{La_{2-2x}Sr_{1+2x}Mn_2O_7}$ with$x=0.4$. This effect is caused by the
recently reported tendency to phase separation between hole-rich ferromagnetic
and hole-undoped antiferromagnetic domains in electronic models for manganites.
As $J'$ increases metal-insulator transitions are detected by monitoring the
optical conductivity and the density of states. The magnetic correlations
reveal the existence of spiral phases without long-range order but with fairly
large correlation lengths. Indications of charge ordering effects appear in the
analysis of charge correlations.",9712152v1
1998-01-31,Evidence for a Genuine Ferromagnetic to Paramagnetic Reentrant Phase Transition in a Potts Spin Glass Model,"uch experimental and theoretical efforts have been devoted in the past twenty
years to search for a genuine thermodynamic reentrant phase transition from a
ferromagnetic to either a paramagnetic or spin glass phase in disordered
ferromagnets. So far, no real system or theoretical model of a short-range spin
glass system has been shown to convincingly display such a reentrant
transition. We present here results from Migdal-Kadanoff real-space
renormalization-group calculations that provide for the first time strong
evidence for ferromagnetic to paramagnetic reentrance in Potts spin glasses on
hierarchical lattices. Our results imply that there is no fundamental reason
ruling out thermodynamic reentrant phase transitions in all non mean-field
randomly frustrated systems, and may open the possibility that true reentrance
might occur in some yet to be discovered real randomly frustrated materials.",9802003v1
1998-03-06,Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices,"The magneto-Coulomb oscillation, the single electron repopulation induced by
external magnetic field, observed in a ferromagnetic single electron transistor
is further examined in various ferromagnetic single electron devices. In case
of double- and triple-junction devices made of Ni and Co electrodes, the single
electron repopulation always occurs from Ni to Co electrodes with increasing a
magnetic field, irrespective of the configurations of the electrodes. The
period of the magneto-Coulomb oscillation is proportional to the single
electron charging energy. All these features are consistently explained by the
mechanism that the Zeeman effect induces changes of the Fermi energy of the
ferromagnetic metal having a non-zero spin polarizations. Experimentally
determined spin polarizations are negative for both Ni and Co and the magnitude
is larger for Ni than Co as expected from band calculations.",9803070v1
1998-05-04,Phase diagram of the anti-ferromagnetic xxz model in the presence of an external magnetic field,"The anisotropic s=1/2 anti-ferromagnetic Heisenberg chain in the presence of
an external magnetic field is studied by using the standard quantum
renormalization group. We obtain the critical line of the transition from
partially magnetized (PM) phase to the saturated ferromagnetic (SFM) phase. The
crossover exponent between the PM phase and anti-ferromagnetic Ising (AFI)
phase is evaluated. Our results show that the anisotropy($\d$) term is relevant
and causes crossover. These results indicate that the standard RG approach
yields fairly good values for the critical points and their exponents. The
magnetization curve, correlation functions and the ground state energy per site
are obtained and compared with the known exact results.",9805024v2
1998-05-21,"Metal-Insulator Transition and Ferromagnetism in the Electron Doped Layered Manganites La2.3-xYxCa0.7Mn2O7 (x=0,0.3,0.5)","Bulk samples of La2.3-xYxCa0.7Mn2O7, x=0,0.3,0.5, with layered perovskite
structure have been synthesized and investigated with respect to their
electrical, electronic and magnetic properties. It is found that
La1.8Y0.5Ca0.7Mn2O7 has tetragonal structure and is a metallic ferromagnet with
a magnetic transition temperature of 170 K. The compound shows metallic
behavior below 140 K and has a large magnetoresistance (MR)
Delta-rho/rho(0)~94% at 100 K at 34 kOe. For x=0 and 0.3 the structure is
monoclinic with a suppression of metallicity. For x=0 the material is an
ferromagnetic insulator. We observed a large increase in the coefficient of the
linear term in specific heat with decreasing x. As far as we are aware, this is
the first report of an electron doped manganite showing metal-insulator
transition and ferromagnetism.",9805274v1
1998-07-06,Spin polarized tunneling in the half-metallic ferromagnet La0.7Sr0.3MnO3: experiment and theory,"The magnetoresistance (MR) in polycrystalline colossal magnetoresistive
compounds follows a behavior different from single crystals below the
ferromagnetic transition temperature. This difference is usually attributed to
spin polarized tunneling at the grain boundaries of the polycrystalline sample.
Here we derive a theoretical expression for the contribution of spin polarized
tunneling to the magnetoresistance in granular ferromagnetic systems under the
mean field approximation. We apply this model to our experimental data on the
half metallic ferromagnet La0.7Sr0.3MnO3, and find that the theoretical
predictions agree quite well with the observed dependence of the spin polarized
MR on the spontaneous magnetization.",9807084v1
1998-08-18,Itinerant Electron Ferromagnetism in the Quantum Hall Regime,"We report on a study of the temperature and Zeeman-coupling-strength
dependence of the one-particle Green's function of a two-dimensional (2D)
electron gas at Landau level filling factor $\nu =1$ where the ground state is
a strong ferromagnet. Our work places emphasis on the role played by the
itinerancy of the electrons, which carry the spin magnetization and on
analogies between this system and conventional itinerant electron ferromagnets.
We discuss the application to this system of the self-consistent Hartree-Fock
approximation, which is analogous to the band theory description of metallic
ferromagnetism and fails badly at finite temperatures because it does not
account for spin-wave excitations. We go beyond this level by evaluating the
one-particle Green's function using a self-energy, which accounts for
quasiparticle spin-wave interactions. We report results for the temperature
dependence of the spin magnetization, the nuclear spin relaxation rate, and
2D-2D tunneling conductances. Our calculations predict a sharp peak in the
tunneling conductance at large bias voltages with strength proportional to
temperature. We compare with experiment, where available, and with predictions
based on numerical exact diagonalization and other theoretical approaches.",9808186v1
1998-09-03,Sensitivity to temperature perturbations of the ageing states in a re-entrant ferromagnet,"Dynamic magnetic properties and ageing phenomena of the re-entrant
ferromagnet (Fe0.20Ni0.80)75P16B6Al3 are investigated by time dependent zero
field cooled magnetic relaxation, m (t), measurements. The influence of a
temperature cycling (perturbation), +/- *T, (prior the field application) on
the relaxation rate is investigated both in the low temperature re-entrant spin
glass 'phase' and in the ferromagnetic phase. In the ferromagnetic phase the
influence of a positive and a negative temperature cycle (of equal magnitude)
on the response is almost the same (symmetric response). The result at lower
temperatures, in the RSG 'phase' is asymmetric, with a strongly affected
response for positive, and hardly no influence on the response for negative
temperature cycles. The behaviour at low temperatures is similar to what is
observed in ordinary spin glasses.",9809059v1
1998-09-23,Transport Properties of the One Dimensional Ferromagnetic Kondo Lattice Model : A Qualitative Approach to Oxide Manganites,"The transport properties of the ferromagnetic Kondo lattice model in one
dimension are studied via bosonization methods. The antiferromagnetic
fluctuations, which normally appear because of the RKKY interactions, are
explicitly taken into account as a direct exchange between the ``core'' spins.
It is shown that in the paramagnetic regime with the local antiferromagnetic
fluctuations, the resistivity decays exponentially as the temperature increases
while in the ferromagnetic regime the system is an almost perfect conductor. %A
non-perturbative description of localized spin polarons %in the paramagnetic
region is obtained.
  The effect of a weak applied field is discussed to be reduced to the case of
the ferromagnetic state leading to band splitting. The qualitative relevance of
the results for the problem of the Oxide Manganites is emphasized.",9809309v1
1998-11-25,Metallic ferromagnetism without exchange splitting,"In the band theory of ferromagnetism there is a relative shift in the
position of majority and minority spin bands due to the self-consistent field
due to opposite spin electrons. In the simplest realization, the Stoner model,
the majority and minority spin bands are rigidly shifted with respect to each
other. Here we consider models at the opposite extreme, where there is no
overall shift of the energy bands. Instead, upon spin polarization one of the
bands broadens relative to the other. Ferromagnetism is driven by the resulting
gain in kinetic energy. A signature of this class of mechanisms is that a
transfer of spectral weight in optical absorption from high to low frequencies
occurs upon spin polarization. We show that such models arise from generalized
tight binding models that include off-diagonal matrix elements of the Coulomb
interaction. For certain parameter ranges it is also found that reentrant
ferromagnetism occurs. We examine properties of these models at zero and finite
temperatures, and discuss their possible relevance to real materials.",9811346v1
1998-12-09,Spin current in ferromagnet/insulator/superconductor junctions,"A theory of spin polarized tunneling spectroscopy based on a scattering
theory is given for tunneling junctions between ferromagnets and d-wave
superconductors. The spin filtering effect of an exchange field in the
insulator is also treated. We clarify that the properties of the Andreev
reflection are largely modified due to a presence of an exchange field in the
ferromagnets, and consequently the Andreev reflected quasiparticle shows an
evanescent-wave behavior depending on the injection angle of the quasiparticle.
Conductance formulas for the spin current as well as the charge current are
given as a function of the applied voltage and the spin-polarization in the
ferromagnet for arbitrary barrier heights. It is shown that the surface bound
states do not contribute to the spin current and that the zero-bias conductance
peak expected for a d-wave superconductor splits into two peaks under the
influence of the exchange interaction in the insulator.",9812160v3
1999-06-05,Two ferromagnetic phases in La1-xSrxMnO3(x ~1/8),"It was discovered in La1-xSrxMnO3(x~1/8) that a field induced phase
transition occurs from a ferromagnetic metal(FM) phase to a ferromagnetic
insulator (FI) phase. The magnetization shows a sharp jump at the transition
field accompanying with a remarkable increase of magnetoresistance. Striction
measurements clarified that this transition is associated with the structural
change from a Jahn-Teller(JT) distorted orthorhombic phase to a pseudo cubic
phase. These results evidently show that the FI phase with a pseudo cubic
symmetry is more stable in high fields than the FM phase due to the double
exchange interaction. The driving force of this transition is explained by the
enhancement of the ferromagnetic superexchange interaction induced by an
antiferromagnetic type orbital ordering in the pseudo cubic phase, which was
recently found in the anomalous X-ray scattering experiments.",9906075v1
1999-07-02,The temperature dependent bandstructure of a ferromagnetic semiconductor film,"The electronic quasiparticle spectrum of a ferromagnetic film is investigated
within the framework of the s-f model. Starting from the exact solvable case of
a single electron in an otherwise empty conduction band being exchange coupled
to a ferromagnetically saturated localized spin system we extend the theory to
finite temperatures. Our approach is a moment-conserving decoupling procedure
for suitable defined Green functions. The theory for finite temperatures
evolves continuously from the exact limiting case. The restriction to zero
conduction band occupation may be regarded as a proper model description for
ferromagnetic semiconductors like EuO and EuS. Evaluating the theory for a
simple cubic film cut parallel to the (100) crystal plane, we find some marked
correlation effects which depend on the spin of the test electron, on the
exchange coupling, and on the temperature of the local-moment system.",9907049v1
1999-07-26,Quantum critical behavior of itinerant ferromagnets,"We investigate the quantum phase transition of itinerant ferromagnets. It is
shown that correlation effects in the underlying itinerant electron system lead
to singularities in the order parameter field theory that result in an
effective long-range interaction between the spin fluctuations. This
interaction turns out to be generically {\em antiferromagnetic} for clean
systems. In disordered systems analogous correlation effects lead to even
stronger singularities. The resulting long-range interaction is, however,
generically ferromagnetic.
  We discuss two possibilities for the ferromagnetic quantum phase transition.
In clean systems, the transition is generically of first order, as is
experimentally observed in MnSi. However, under certain conditions the
transition may be continuous with non-mean field critical behavior. In
disordered systems, one finds a very rich phase diagram showing first order and
continuous phase transitions and several multicritical points.",9907404v2
1999-08-02,Magnon-Paramagnon Effective Theory of Itinerant Ferromagnets,"The present work is devoted to the derivation of an effective
magnon-paramagnon theory starting from a microscopic lattice model of
ferromagnetic metals. For some values of the microscopic parameters it
reproduces the Heisenberg theory of localized spins. For small magnetization
the effective model describes the physics of weak ferromagnets in accordance
with the experimental results. It is written in a way which keeps O(3) symmetry
manifest,and describes both the order and disordered phases of the system.
  Analytical expression for the Curie temperature,which takes the magnon
fluctuations into account exactly, is obtained. For weak ferromagnets $T_c$ is
well below the Stoner's critical temperature and the critical temperature
obtained within Moriya's theory.",9908024v3
1999-10-11,Suppression of ferromagnetic ordering in doped manganites: Effects of the superexchange interaction,"From a Monte Carlo study of the ferromagnetic Kondo lattice model for doped
manganites, including the antiferromagnetic superexchange interaction
($J_{AF}$), we found that the ferromagnetic ordering was suppressed as $J_{AF}$
increased. The ferromagnetic transition temperature $T_c$, as obtained from a
mean field fit to the calculated susceptibilities, was found to decrease
monotonically with increasing $J_{AF}$. Further, the suppression in $T_c$
scales with the bandwidth narrowing induced by the antiferromagnetic
frustration originating from $J_{AF}$. From these results, we propose that the
change in the superexchange interaction strength between the $t_{2g}$ electrons
of the Mn ions is one of the mechanisms responsible for the suppression in
$T_c$ observed in manganites of the type
(La$_{0.7-y}$Pr$_{y}$)Ca$_{0.3}$MnO$_3$.",9910152v1
2000-04-18,Disorder and interactions in quantum Hall ferromagnets near $ν=1$,"We report on a finite-size Hartree-Fock study of the competition between
disorder and interactions in a two-dimensional electron gas near Landau level
filling factor $\nu=1$. The ground state at $\nu=1$ evolves with increasing
disorder from a fully spin-polarized ferromagnet with a charge gap, to a
partially spin-polarized ferromagnetic Anderson insulator, to a quasi-metallic
paramagnet at the critical point between $i=0$ and $i=2$ quantum Hall plateaus.
Away from $\nu=1$, the ground state evolves from a ferromagnetic Skyrmion
quasiparticle glass, to a conventional quasiparticle glass, and finally to a
conventional Anderson insulator. We comment on signatures of these different
regimes in low-temperature transport and NMR lineshape and peak position data.",0004319v2
2000-05-03,Current driven switching of magnetic layers,"The switching of magnetic layers is studied under the action of a spin
current in a ferromagnetic metal/non-magnetic metal/ferromagnetic metal spin
valve. We find that the main contribution to the switching comes from the
non-equilibrium exchange interaction between the ferromagnetic layers. This
interaction defines the magnetic configuration of the layers with minimum
energy and establishes the threshold for a critical switching current.
Depending on the direction of the critical current, the interaction changes
sign and a given magnetic configuration becomes unstable. To model the time
dependence of the switching process, we derive a set of coupled Landau-Lifshitz
equations for the ferromagnetic layers. Higher order terms in the
non-equilibrium exchange coupling allow the system to evolve to its
steady-state configuration.",0005064v2
2000-07-19,Electrical spin injection and detection in a semiconductor. Is it feasible?,"The electrical injection of spin polarized electrons in a semiconductor can
be achieved in principle by driving a current from a ferromagnetic metal, where
current is known to be significantly spin polarized, into the semiconductor via
ohmic conduction. For detection a second ferromagnet can be used as drain. We
studied submicron lateral spin valve junctions, based on high mobility
InAs/AlSb two-dimensional electron gas (2DEG), with Ni, Co and Permalloy as
ferromagnetic electrodes. In the standard geometry it is very difficult to
separate true spin injection from other effects, including local Hall effect,
anomalous magnetoresistance (AMR) contribution from the ferromagnetic
electrodes and weak localization/anti-localization corrections, which can
closely mimic the signal expected from spin valve effect. The reduction in
size, and the use of a multiterminal non-local geometry allowed us to reduce
the unwanted effects to a minimum. Despite all our efforts, we have not been
able to observe spin injection. However, we find that this 'negative' result in
these systems is actually consistent with theoretical predictions for spin
transport in diffusive systems.",0007307v1
2000-07-28,Ferromagnetism from Undressing,"We have recently proposed that superconductivity may be understood as driven
by the undressing of quasiparticles as the superconducting state develops.
Similarly we propose here that ferromagnetism in metals may be understood as
driven by the undressing of quasiparticles as the ferromagnetic state develops.
In ferromagnets, the undressing is proposed to occur due to the reduction in
$bond$ $charge$ caused by spin polarization, in contrast to superconductors
where the undressing is proposed to occur due to the reduction in $site$
$charge$ caused by (hole) pairing. The undressing process manifests itself in
the one and two-particle Green's functions as a transfer of spectral weight
from high to low frequencies. Hence it should have universal observable
consequences in one- and two-particle spectroscopies such as photoemission and
optical absorption.",0007454v1
2000-10-24,Quantum critical behavior in disordered itinerant ferromagnets: Logarithmic corrections to scaling,"The quantum critical behavior of disordered itinerant ferromagnets is
determined exactly by solving a recently developed effective field theory. It
is shown that there are logarithmic corrections to a previous calculation of
the critical behavior, and that the exact critical behavior coincides with that
found earlier for a phase transition of undetermined nature in disordered
interacting electron systems. This confirms a previous suggestion that the
unspecified transition should be identified with the ferromagnetic transition.
The behavior of the conductivity, the tunneling density of states, and the
phase and quasiparticle relaxation rates across the ferromagnetic transition is
also calculated.",0010377v2
2000-12-21,Ferromagnetism and large negative magnetoresistance in Pb doped Bi-Sr-Co-O misfit-layer compound,"Ferromagnetism and accompanying large negative magnetoresistance in
Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail.
Recent structural analysis of (Bi,Pb)${}_2$Sr${}_{3}$Co${}_2$O${}_9$, which has
been believed to be a Co analogue of
Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta}$, revealed that it has a more complex
structure including a CoO${}_2$ hexagonal layer [T. Yamamoto {\it et al.}, Jpn.
J. Appl. Phys. {\bf 39} (2000) L747]. Pb substitution for Bi not only
introduces holes into the conducting CoO${}_2$ layers but also creates a
certain amount of localized spins. Ferromagnetic transition appears at $T$ =
3.2 K with small spontaneous magnetization along the $c$ axis, and around the
transition temperature large and anisotropic negative magnetoresistance was
observed. This compound is the first example which shows ferromagnetic
long-range order in a two-dimensional metallic hexagnonal CoO${}_2$ layer.",0012395v1
2001-01-11,Tapping Spin Glasses,"We consider a tapping dynamics, analogous to that in experiments on granular
media, on spin glasses and ferromagnets on random thin graphs. Between taps,
zero temperature single spin flip dynamics takes the system to a metastable
state. Tapping, corresponds to flipping simultaneously any spin with
probability $p$. This dynamics leads to a stationary regime with a steady state
energy $E(p)$. We analytically solve this dynamics for the one dimensional
ferromagnet and $\pm J$ spin glass. Numerical simulations for spin glasses and
ferromagnets of higher connectivity are carried out, in particular we find a
novel first order transition for the ferromagnetic systems.",0101166v1
2001-01-16,Low Temperature Magnetothermodynamics of Pr{0.7}Ca{0.3}MnO{3},"We present a detailed magnetothermal study of Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$,
a perovskite manganite in which an insulator-metal transition can be driven by
magnetic field, but also by pressure, visible light, x-rays, or high currents.
We find that the field-induced transition is associated with a large release of
energy which accounts for its strong irreversibility.
  In the ferromagnetic metallic state, specific heat and magnetization
measurements indicate a much smaller spin wave stiffness than that seen in any
other ferromagnetic manganite, which we explain in terms of ferromagnetism
among the Pr moments. The Pr ferromagnetism also appears to influence the low
temperature thermodynamic phase diagram of this material and the uniquely
sensitive metastability of the insulating state.",0101223v1
2001-02-20,"On the Belitz-Kirkpatrick comment on ""Specific heat of a Fermi system near ferromagnetic quantum phase transition"", by I.Grosu, D.Bodea and M.Crisan (cond-mat/0101392)","We reply to Belitz and Kirkpatrick comment cond-mat/0102064, on
cond-mat/0101392.",0102354v1
2001-02-20,"Theory of ferromagnetism in (A,Mn)B semiconductors","A brief review of theory of ferromagnetism of dilute magnetic semiconductors
of the form (A,Mn)B based on the double exchange model is first given. A
systematic investigation of the phenomena extending the current theory is
outlined. We begin with an investigation of the regions of instability of the
nonmagnetic towards the ferromagnetic state of a system of Mn-atoms doped in
AB-type semiconductor. A self-consistent many-body theory of the ferromagnetic
state is then developed, going beyond the mean field approaches by including
fluctuations of the Mn-spins and the itinerant hole-gas. A functional theory
suitable for computation of system properties such as Curie temperature as a
function of hole and the Mn-concentration, spin-current, etc. is formulated.",0102361v1
2001-05-10,The temperature-flow renormalization group and the competition between superconductivity and ferromagnetism,"We derive a differential equation for the one-particle-irreducible vertex
functions of interacting fermions as a function of the temperature. Formally,
these equations correspond to a Wilsonian renormalization group scheme which
uses the temperature as an explicit scale parameter. Our novel method allows us
to analyze the competition between superconducting and various magnetic Fermi
surface instabilities in the one-loop approximation. In particular this
includes ferromagnetic fluctuations, which are difficult to treat on an equal
footing in conventional Wilsonian momentum space techniques. Applying the
scheme to the two-dimensional t-t' Hubbard model we investigate the RG flow of
the interactions at the van Hove filling with varying next-nearest neighbor
hopping t'. Starting at t'=0 we describe the evolution of the flow to strong
coupling from an antiferromagnetic nesting regime over a d-wave regime at
moderate t' to a ferromagnetic region at larger absolute values of t'. Upon
increasing the particle density in the latter regime the ferromagnetic
tendencies are cut off and the leading instability occurs in the triplet
superconducting pairing channel.",0105218v1
2001-05-26,Direct Observation of Coexistence of Ferromagnetism and Superconductivity in RuSr2(Gd0.7Ce0.3)2Cu2O10,"Recent reports of the detecting of ferromagnetism and superconductivity in
ruthenium-cuprates have aroused great interest. Unfortunately, whether the two
antagonistic phenomena coexist in the same space in the compounds remains
unresolved. By employing the magneto-optical-imaging technique, ferromagnetism
and superconductivity were indeed directly observed to coexist in the same
space in RuSr2(Gd0.7Ce0.3)2Cu2O10 within the experimental resolution of ~ 10
(mu)m. The observation sets a length scale limit for models proposed to account
for the competition between ferromagnetism and superconductivity, especially
d-wave superconductivity, in this interesting class of compounds.",0105510v1
2001-06-05,Phase diagram of the random field Ising model on the Bethe lattice,"The phase diagram of the random field Ising model on the Bethe lattice with a
symmetric dichotomous random field is closely investigated with respect to the
transition between the ferromagnetic and paramagnetic regime. Refining
arguments of Bleher, Ruiz and Zagrebnov [J. Stat. Phys. 93, 33 (1998)] an exact
upper bound for the existence of a unique paramagnetic phase is found which
considerably improves the earlier results. Several numerical estimates of
transition lines between a ferromagnetic and a paramagnetic regime are
presented. The obtained results do not coincide with a lower bound for the
onset of ferromagnetism proposed by Bruinsma [Phys. Rev. B 30, 289 (1984)]. If
the latter one proves correct this would hint to a region of coexistence of
stable ferromagnetic phases and a stable paramagnetic phase.",0106074v3
2001-06-12,Steady State Behavior of Mechanically Perturbed Spin Glasses and Ferromagnets,"A zero temperature dynamics of Ising spin glasses and ferromagnets on random
graphs of finite connectivity is considered, like granular media these systems
have an extensive entropy of metastable states. We consider the problem of what
energy a randomly prepared spin system falls to before becoming stuck in a
metastable state. We then introduce a tapping mechanism, analogous to that of
real experiments on granular media, this tapping, corresponding to flipping
simultaneously any spin with probability $p$, leads to stationary regime with a
steady state energy $E(p)$. We explicitly solve this problem for the one
dimensional ferromagnet and $\pm J$ spin glass and carry out extensive
numerical simulations for spin systems of higher connectivity. The link with
the density of metastable states at fixed energy and the idea of Edwards that
one may construct a thermodynamics with a flat measure over metastable states
is discussed. In addition our simulations on the ferromagnetic systems reveal a
novel first order transition, whereas the usual thermodynamic transition on
these graphs is second order.",0106220v1
2001-06-24,Spontaneous Magnetization of the O(3) Ferromagnet at Low Temperatures,"We investigate the low-temperature behavior of ferromagnets with a
spontaneously broken symmetry O(3) $\to$ O(2). The analysis is performed within
the perspective of nonrelativistic effective Lagrangians, where the dynamics of
the system is formulated in terms of Goldstone bosons. Unlike in a
Lorentz-invariant framework (chiral perturbation theory), where loop graphs are
suppressed by two powers of momentum, loops involving ferromagnetic spin waves
are suppressed by three momentum powers. The leading coefficients of the
low-temperature expansion for the partition function are calculated up to order
$p^{10}$. In agreement with Dyson's pioneering microscopic analysis of the
cubic ferromagnet, we find that, in the spontaneous magnetization, the
magnon-magnon interaction starts manifesting itself only at order $T^4$. The
striking difference with respect to the low-temperature properties of the O(3)
antiferromagnet is discussed from a unified point of view, relying on the
effective Lagrangian technique.",0106492v1
2001-07-03,"Sr$_3$CuIrO$_6$, a spin-chain compound with random ferromagnetic-antiferromagnetic interactions","Ac and dc magnetization and heat-capacity (C) measurements performed on the
pseudo-one-dimensional compound Sr$_3$CuIrO$_6$ reveal a competition between
antiferromagnetic (AF) and ferromagnetic (F) exchange couplings, as evidenced
by frequency dependence of ac susceptibility and by the absence of a C anomaly
at the magnetic transition. The value of the saturation moment (about 0.35
$\mu_B$/formula unit) is much smaller than expected for ferromagnetism from the
two S=1/2 ions (Cu and Ir). Thus, this compound is not a ferromagnet in zero
magnetic field, in contrast to earlier beliefs. Of particular importance is the
finding that the value of the magnetic ordering temperature is sample
dependent, sensitive to synthetic conditions resulting from deviations in
oxygen/Cu content. We propose that this compound serves as a unique model
system to test theories on random AF-F interaction in a chain system,
considering that this competition can be tuned without any chemical
substitution.",0107069v1
2001-07-11,Proximity effects at ferromagnet-superconductor interfaces,"We study proximity effects at ferromagnet superconductor interfaces by
self-consistent numerical solution of the Bogoliubov-de Gennes equations for
the continuum, without any approximations. Our procedures allow us to study
systems with long superconducting coherence lengths. We obtain results for the
pair potential, the pair amplitude, and the local density of states. We use
these results to extract the relevant proximity lengths. We find that the
superconducting correlations in the ferromagnet exhibit a damped oscillatory
behavior that is reflected in both the pair amplitude and the local density of
states. The characteristic length scale of these oscillations is approximately
inversely proportional to the exchange field, and is independent of the
superconducting coherence length in the range studied. We find the
superconducting coherence length to be nearly independent of the ferromagnetic
polarization.",0107232v1
2001-08-08,Spin-Glass Phase in the Random Temperature Ising Ferromagnet,"In this paper we study the phase diagram of the disordered Ising ferromagnet.
Within the framework of the Gaussian variational approximation it is shown that
in systems with a finite value of the disorder in dimensions D=4 and D < 4 the
paramagnetic and ferromagnetic phases are separated by a spin-glass phase. The
transition from paramagnetic to spin-glass state is continuous (second-order),
while the transition between spin-glass and ferromagnetic states is
discontinuous (first-order). It is also shown that within the considered
approximation there is no replica symmetry breaking in the spin-glass phase.
The validity of the Gaussian variational approximation for the present problem
is discussed, and we provide a tentative physical interpretation of the
results.",0108136v2
2001-08-09,Critical exponents at the ferromagnetic transition in tetrakis(diethylamino)ethylene-C$_{60}$ (TDAE-C$_{60}$),"Critical exponents at the ferromagnetic transition were measured for the
first time in an organic ferromagnetic material tetrakis(dimethylamino)ethylene
fullerene[60] (TDAE-C$_{60}$). From a complete magnetization-temperature-field
data set near $T_{c}=16.1\pm 0.05,$ we determine the susceptibility and
magnetization critical exponents $\gamma =1.22\pm 0.02$ and $\beta =0.75 \pm
0.03$ respectively, and the field vs. magnetization exponent at $T_{c}$ of
$\delta =2.28\pm 0.14$. Hyperscaling is found to be violated by $\Omega \equiv
d^{\prime}-d \approx -1/4$, suggesting that the onset of ferromagnetism can be
related to percolation of a particular contact configuration of C$_{60}$
molecular orientations.",0108156v1
2001-09-21,Gate-controlled spin polarized current in ferromagnetic single electron transistors,"We theoretically investigate spin dependent transport in ferromagnetic/normal
metal/ferromagnetic single electron transistors by applying master equation
calculations using a two dimensional space of states involving spin and charge
degrees of freedom. When the magnetizations of ferromagnetic leads are in
anti-parallel alignment, the spins accumulate in the island and a difference of
chemical potentials of the two spins is built up. This shift in chemical
potential acts as charge offset in the island and alternates the gate
dependence of spin current. Taking advantage of this effect, one can control
the polarization of current up to the polarization of lead by tuning gate
voltages.",0109401v1
2001-12-03,Local density of states in superconductor-strong ferromagnet structures,"We study the dependence of the local density of states (LDOS) on coordinates
for a superconductor-ferromagnet (S/F) bilayer and a S/F/S structure assuming
that the exchange energy h in the ferromagnet is sufficiently large: $% h\tau
>>1,$ where $\tau $ is the elastic relaxation time. This limit cannot be
described by the Usadel equation and we solve the more general Eilenberger
equation. We demonstrate that, in the main approximation in the parameter $%
(h\tau)^{-1}$, the proximity effect does not lead to a modification of the LDOS
in the S/F system and a non-trivial dependence on coordinates shows up in next
orders in $(h\tau) ^{-1}.$ In the S/F/S sandwich the correction to the LDOS is
nonzero in the main approximation and depends on the phase difference between
the superconductors. We also calculate the superconducting critical temperature
$T_{c}$ for the bilayered system and show that it does not depend on the
exchange energy of the ferromagnet in the limit of large h and a thick F layer.",0112024v1
2002-02-01,Metal-Insulator Transition and Ferromagnetism in Diluted Magnetic Semiconductors,"We have investigated the interplay between the metal-insulator transition and
ferromagnetism in $({\rm III}_{1-x},{\rm Mn}_x){\rm V}$ ferromagnetic
semiconductors. Our study is based on a model in which $S=5/2$ Mn local moments
are exchange-coupled to band electrons that interact via Coulomb interactions
which each other, with ionized Mn acceptors, and with the antisite defects
present in these materials. We find quasiparticle participation ratios that are
consistent with a metal-insulator transition that occurs in the ferromagnetic
state near $x \sim 0.01$. By evaluating the distribution of mean-field exchange
coupling strengths at Mn moment sites, we provide evidence in favor of the
applicability of small polaron and hole gas models on insulating and metallic
sides of the phase transition respectively.",0202021v1
2002-02-07,Ferromagnetism in the Kondo-lattice model,"We propose a modified RKKY-technique to evaluate the magnetic properties of
the ferromagnetic Kondo-lattice model. Together with a previously developed
selfenergy approach to the conduction electron part of the model we get a
closed system of equations which can be solved self-consistently.
Ferromagnetism appears for relatively low electron (hole) densities, while it
is excluded around half-filling ($n=1$). For small $J$ conventional RKKY ($\sim
J^2$) is reproduced; however, with strong deviations already for very moderate
exchange couplings. For not too small $n$ a critical $J_c$ is needed to produce
ferromagnetism with a finite Curie temperature $T_{\textrm{C}}$, which
increases with $J$, then running into a kind of saturation, in order to fall
off again and disappearing above an upper critical exchange $J$.",0202114v3
2002-02-20,Transport and triplet superconducting condensate in mesoscopic ferromagnet-superconductor structures,"We calculate the conductance of a superconductor/ferromagnet (S/F) mesoscopic
structure in the dirty limit. First we assume that the ferromagnet exhibits a
homogeneous magnetization and consider the case that the penetration of the
condensate into the F wire is negligible and the case in which the proximity
effect is taken into account. It is shown that if the exchange field is large
enough, the conductance below the critical temperature $T_C$, is always smaller
than the conductance in the normal state. At last, we calculate the conductance
for a F/S structure with a local inhomogeneity of the magnetization in the
ferromagnet. We demonstrate that a triplet component of the condensate is
induced in the F wire.This leads to a increase of the conductance below $T_C$.",0202348v2
2002-03-05,Magnetic relaxation in La0.250Pr0.375Ca0.375MnO3 with varying phase separation,"We have studied the magnetic relaxation properties of the phase-separated
manganite compound La0.250Pr0.375Ca0.375MnO3 . A series of polycrystalline
samples was prepared with different sintering temperatures, resulting in a
continuous variation of phase fraction between metallic (ferromagnetic) and
charge-ordered phases at low temperatures. Measurements of the magnetic
viscosity show a temperature and field dependence which can be correlated to
the static properties. Common to all the samples, there appears to be two types
of relaxation processes - at low fields associated with the reorientation of
ferromagnetic domains and at higher fields associated with the transformation
between ferromagnetic and non-ferromagnetic phases.",0203102v1
2002-03-11,High TC ferromagnetism in diluted magnetic semiconducting GaN:Mn films,"Wurtzite GaN:Mn films on sapphire substrates were successfully grown by use
of the molecular beam epitaxy (MBE) system. The film has an extremely high
Curie temperature of around 940 K, although the Mn concentration is only about
3 ~ 5 %. Magnetization measurements were carried out in magnetic fields
parallel to the film surface up to 7 T. The magnetization process shows the
coexistence of ferromagnetic and paramagnetic contributions at low
temperatures, while the typical ferromagnetic magnetization process is mainly
observed at high temperatures because of the decrease of the paramagnetic
contributions. The observed transport characteristics show a close relation
between the magnetism and the impurity conduction. The double exchange
mechanism of the Mn-impurity band is one of the possible models for the high-TC
ferromagnetism in GaN:Mn.",0203223v1
2002-03-26,Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys,"We study the origin of the gap and the role of chemical composition in the
half-ferromagnetic Heusler alloys using the full-potential screened KKR method.
In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap.
Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are
semiconductors, but when Z_t > 18 antibonding states are also populated, thus
the paramagnetic phase becomes unstable and the half-ferromagnetic one is
stabilized. The minority occupied bands accommodate a total of nine electrons
and the total magnetic moment per unit cell in mu_B is just the difference
between Z_t and $2 \times 9$. While the substitution of the transition metal
atoms may preserve the half-ferromagnetic character, substituting the $sp$ atom
results in a practically rigid shift of the bands and the loss of
half-metallicity. Finally we show that expanding or contracting the lattice
parameter by 2% preserves the minority-spin gap.",0203534v3
2002-04-05,Electron transport in a mesoscopic superconducting / ferromagnetic hybrid conductor,"We present electrical transport experiments performed on submicron hybrid
devices made of a ferromagnetic conductor (Co) and a superconducting (Al)
electrode. The sample was patterned in order to separate the contributions of
the Co conductor and of the Co-Al interface. We observed a strong influence of
the Al electrode superconductivity on the resistance of the Co conductor. This
effect is large only when the interface is highly transparent. We characterized
the dependence of the observed resistance decrease on temperature, bias current
and magnetic field. As the differential resistance of the ferromagnet exhibits
a non-trivial asymmetry, we claim that the magnetic domain structure plays an
important role in the electron transport properties of superconducting /
ferromagnetic conductors.",0204140v2
2002-05-25,A possible path to a new class of ferromagnetic and half metallic ferromagnetic materials,"We introduce a path to a possibly new class of magnetic materials whose
properties are determined entirely by the presence of a low concentration of
specific point defects in their crystal structure. Using model Hamiltonian and
ab-initio band structure methods we demonstrate that even large band gap
nonmagnetic materials as simple as CaO can exhibit extraordinary properties
like half metallic ferromagnetism upon introducing a small concentration of Ca
vacancies. We show that such defects will initially bind the introduced charge
carriers at neighboring sites and depending on the internal symmetry of the
clusters formed by neighboring sites form ""local"" magnetic moments which for
concentrations as low as 3% transform this non-magnetic insulator into a half
metallic ferromagnet.",0205530v1
2002-05-27,Properties of Ferromagnetic Ga1-xMnxN Films Grown by Ammonia-MBE,"Using ammonia as nitrogen source for molecular beam epitaxy, the GaN-based
diluted magnetic semiconductor Ga1-xMnxN is successfully grown with Mn
concentration up to x~6.8% and with p-type conductivity. The films have
wurtzite structure with substitutional Mn on Ga site in GaN. Magnetization
measurements revealed that Ga1-xMnxN is ferromagnetic at temperatures higher
than room temperature. The ferromagnetic-paramagnetic transition temperature,
Tc, depends on the Mn concentration of the film. At low temperatures, the
magnetization increases with increasing of magnetic field, implying that a
paramagnetic-like phase coexists with ferromagnetic one. Possible explanations
will be proposed for the coexistence of two magnetic phases in the grown films.",0205560v1
2002-06-07,"Charge dynamics and ""ferromagnetism"" of A1-xLaxB6 (A=Ca and Sr)","Ferromagnetism has been reported recently in La-doped alkaline-earth
hexaborides, A1-xLaxB6 (A=Ca, Sr, and Ba). We have performed the reflectivity,
Hall resistivity, and magnetization measurements of A1-xLaxB6. The results
indicate that A1-xLaxB6 can be regarded as a simple doped semimetal, with no
signature of an excitonic state as suggested by several theories. It is also
found that the surface of as-grown samples (10 micrometer in thickness) has a
different electronic structure from a bulk one, and a fairly large number of
paramagnetic moments are confined in this region. After eliminating these
paramagnetic moments at the surface, we could not find any evidence of an
intrinsic ferromagnetic moment in our samples, implying the possibility that
the ferromagnetism of A1-xLaxB6 reported so far is neither intrinsic.",0206101v1
2002-06-18,On the probability of ferromagnetic strings in antiferromagnetic spin chains,"We study the probability of formation of ferromagnetic string in the
antiferromagnetic spin-1/2 XXZ chain. We show that in the limit of long strings
with weak magnetization per site the bosonization technique can be used to
address the problem. At zero temperature the obtained probability is Gaussian
as a function of the length of the string. At finite but low temperature there
is a crossover from the Gaussian behavior at intermediate lengths of strings to
the exponential decay for very long strings. Although the weak magnetization
per site is a necessary small parameter justifying our results, the
extrapolation of obtained results to the case of maximally ferromagnetic
strings is in qualitative agreement with known numerics and exact results. The
effect of an external magnetic field on the probability of formation of
ferromagnetic strings is also studied.",0206353v1
2002-07-06,Spin-polarized Tunneling in Hybrid Metal-Semiconductor Magnetic Tunnel Junctions,"We demonstrate efficient spin-polarized tunneling between a ferromagnetic
metal and a ferromagnetic semiconductor with highly mismatched conductivities.
This is indicated by a large tunneling magnetoresistance (up to 30%) at low
temperatures in epitaxial magnetic tunnel junctions composed of a ferromagnetic
metal (MnAs) and a ferromagnetic semiconductor (GaMnAs) separated by a
nonmagnetic semiconductor (AlAs). Analysis of the current-voltage
characteristics yields detailed information about the asymmetric tunnel
barrier. The low temperature conductance-voltage characteristics show a zero
bias anomaly and a V^1/2 dependence of the conductance, indicating a
correlation gap in the density of states of GaMnAs. These experiments suggest
that MnAs/AlAs heterostructures offer well characterized tunnel junctions for
high efficiency spin injection into GaAs.",0207178v1
2002-08-02,Ferromagnetic insulating state in manganites:55Mn study,"55Mn NMR was used to study the ferromagnetic insulating state in four
different manganites. In all cases the coexistence of two types of regions
possessing different NMR spectra and nuclear spin dynamics was found. In the
ferromagnetic insulating clusters the hopping frequency fhop of the electron
holes is slower comparing to the NMR frequency fres and two lines ascribed to
3+ and 4+ valence states of Mn are observed. The relaxation rate increases
rapidly with the increasing temperature, so that these spectra can no longer be
observed for temperatures higher than approx 60 K. In ferromagnetic metallic
clusters fres < fhop and the motionally narrowed spectrum is observed in a
broad temperature interval, as the relaxation remains only moderately fast.",0208033v1
2002-08-06,Spin pumping and magnetization dynamics in metallic multilayers,"We study the magnetization dynamics in thin ferromagnetic films and small
ferromagnetic particles in contact with paramagnetic conductors. A moving
magnetization vector causes \textquotedblleft pumping\textquotedblright of
spins into adjacent nonmagnetic layers. This spin transfer affects the
magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology.
The additional Gilbert damping is significant for small ferromagnets, when the
nonmagnetic layers efficiently relax the injected spins, but the effect is
reduced when a spin accumulation build-up in the normal metal opposes the spin
pumping. The damping enhancement is governed by (and, in turn, can be used to
measure) the mixing conductance or spin-torque parameter of the
ferromagnet--normal-metal interface. Our theoretical findings are confirmed by
agreement with recent experiments in a variety of multilayer systems.",0208091v2
2002-10-18,Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions,"Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagnetic
junctions is studied theoretically within the Landauer framework of ballistic
transport. We show that quantum coherence can have unexpected implications for
spin injection and that some intuitive spintronic concepts which are founded in
semi-classical physics no longer apply: A quantum spin-valve (QSV) effect
occurs even in the absence of a net spin polarized current flowing through the
device, unlike in the classical regime. The converse effect also arises, i.e. a
zero spin-valve signal for a non-vanishing spin-current. We introduce new
criteria useful for analyzing quantum and classical spin transport phenomena
and the relationships between them. The effects on QSV behavior of
spin-dependent electron transmission at the interfaces, interface Schottky
barriers, Rashba spin-orbit coupling and temperature, are systematically
investigated. While the signature of the QSV is found to be sensitive to
temperature, interestingly, that of its converse is not. We argue that the QSV
phenomenon can have important implications for the interpretation of
spin-injection in quantum spintronic experiments with spin-valve geometries.",0210391v1
2002-10-31,Temperature-dependence of spin-polarized transport in ferromagnet / unconventional superconductor junctions,"Tunneling conductance in ferromagnet / unconventional superconductor
junctions is studied theoretically as a function of temperatures and
spin-polarization in feromagnets. In d-wave superconductor junctions, the
existence of a zero-energy Andreev bound state drastically affects the
temperature-dependence of the zero-bias conductance (ZBC). In p-wave triplet
superconductor junctions, numerical results show a wide variety in
temperature-dependence of the ZBC depending on the direction of the magnetic
moment in ferromagnets and the pairing symmetry in superconductors such as
$p_{x}$, $p_{y}$ and $p_{x}+ip_{y}$-wave pair potential. The last one is a
promising symmetry of Sr$_2$RuO$_4$. From these characteristic features in the
conductance, we may obtain the information about the degree of
spin-polarization in ferromagnets and the direction of the $d$-vector in
triplet superconductors.",0210693v2
2002-12-12,Observation of the spin-charge thermal isolation of ferromagnetic Ga_{0.94}Mn_{0.06}As by time-resolved magneto-optical measurement,"The dynamics of magnetization under femtosecond optical excitation is studied
in a ferromagnetic semiconductor Ga_{0.94}Mn_{0.06}As with a time-resolved
magneto-optical Kerr effect measurement with two color probe beams. The
transient reflectivity change indicates the rapid rise of the carrier
temperature and relaxation to a quasi-thermal equilibrium within 1 ps, while a
very slow rise of the spin temperature of the order of 500ps is observed. This
anomalous behavior originates from the thermal isolation between the charge and
spin systems due to the spin polarization of carriers (holes) contributing to
ferromagnetism. This constitutes experimental proof of the half-metallic nature
of ferromagnetic Ga_{0.94}Mn_{0.06}As arising from double exchange type
mechanism originates from the d-band character of holes.",0212276v2
2002-12-17,Magneto-Optical Spectroscopy of Anatase TiO2 Doped with Co,"Magneto-optical spectroscopy of a transparent ferromagnetic semiconductor,
anatase TiO2 doped with Co, is carried out at room temperature. A large
magneto-optical response with ferromagnetic field dependence is observed
throughout from ultraviolet to visible range and increases with increasing Co
content or carrier concentration. The magnitude of magnetic circular dichroism
(MCD) per unit thickness has a peak around the absorption edge such a huge
value of ~10400 degree/cm at 3.57 eV for a 10 mol% Co-doped specimen. Although
the results are not sufficient to prove that the ferromagnetism is in the
ordinary framework of diluted magnetic semiconductors, the coexistence of Co
impurity and mobile carrier is shown to transform the band structure of host
TiO2 to generate ferromagnetism.",0212389v1
2003-01-19,Fermi surface topology and ferromagnetic superconductivity in UGe$_2$,"We consider a Stoner ferromagnet in presence of a quasi-one dimensional Fermi
surface in its spin majority band. Assuming a twin $\delta$-function peaked
density of state due to the low dimensionality, we computed the single particle
self-energy. There appears an additional divergence in the self-energy and
hence in the effective mass inside the ferromagnetic phase (besides the
standard logarithmic divergence at the Stoner critical point). Since such an
effect is purely due to density of states, it might correspond to a first order
phase transition making the ferromagnetic phase into two distinct phases. This
result is in qualitative agreement with the recent specific heat capacity
measurement. We also discuss its relevance to the superconducting state in
UGe$_2$.",0301333v1
2003-02-03,Andreev bound states in ferromagnet-superconductor nanostructures,"We discuss the properties of a ferromagnet - superconductor heterostructure
on the basis of a Hubbard model featuring exchange splitting in the ferromagnet
and electron - electron attraction in the superconductor. We have solved the
spin - polarized Hartree - Fock - Gorkov equations together with the Maxwell's
equation (Ampere's law) fully self-consistently. We have found that a Proximity
Effect - Fulde - Ferrell - Larkin - Ovchinnikov state is realized in such a
heterostructure. It manifests itself in an oscillatory behavior of the pairing
amplitude in the ferromagnet and spontaneously generated spin polarized current
in the ground state. We argue that it is built up from the Andreev bound
states, whose energy can be tuned by the exchange splitting and hence can
coincide with the Fermi energy giving rise to a current carrying $\pi$-state.
We also suggest experiments to verify these predictions.",0302025v1
2003-02-08,Current carrying Andreev bound states in a Superconductor-Ferromagnet proximity system,"We study the ground state properties of a ferromagnet-superconductor
heterostructure on the basis of a quasiclassical theory. We have solved the
Eilenberger equations together with Maxwell's equation fully self-consistently
and found that due to the proximity effect a Fulde-Ferrel-Larkin-Ovchinnikov
(FFLO) like state is realized in such system. Moreover this state has
oscillations of the pairing amplitude in either one or two directions,
depending on the exchange splitting and thickness of the ferromagnet. In
particular, using semiclassical arguments (Bohr-Sommerfeld quantization rule)
we show that owing to the presence of the Andreev bound states in the
ferromagnet, a spontaneous current in the ground state is generated as a
hallmark of the FFLO state in the direction parallel to the interface. We also
discuss the effects of the the elastic disorder and finite transparency of the
interface on the properties of the $FFLO$ state in the system.",0302162v1
2003-02-24,Magnon-assisted transport and thermopower in ferromagnet-normal metal tunnel junctions,"We develop a theoretical model of magnon-assisted transport in a mesoscopic
tunnel junction between a ferromagnetic metal and a normal (non-magnetic)
metal. The current response to a bias voltage is dominated by the contribution
of elastic processes rather than magnon-assisted processes and the degree of
spin polarization of the current, parameterized by a function $P (\Pi_{\uparrow
(\downarrow)},\Pi_{N})$, $0 \leq P \leq 1$, depends on the relative sizes of
the majority $\Pi_{\uparrow}$ and minority $\Pi_{\downarrow}$ band Fermi
surface in the ferromagnet and of the Fermi surface of the normal metal
$\Pi_{N}$. On the other hand, magnon-assisted tunneling gives the dominant
contribution to the current response to a temperature difference across the
junction. The resulting thermopower is large, $S \sim - (k_B/e)
(k_BT/\omega_{D})^{3/2} P (\Pi_{\uparrow (\downarrow)},\Pi_{N})$, where the
temperature dependent factor $(k_{B}T/\omega_{D})^{3/2}$ reflects the
fractional change in the net magnetization of the ferromagnet due to thermal
magnons at temperature $T$ (Bloch's $T^{3/2}$ law) and $\omega_{D}$ is the
magnon Debye energy.",0302485v1
2003-03-11,In(1-x)Mn(x)Sb - a new narrow gap ferromagnetic semiconductor,"A narrow-gap ferromagnetic In(1-x)Mn(x)Sb semiconductor alloy was
successfully grown by low-temperature molecular beam epitaxy on CdTe/GaAs
hybrid substrates. Ferromagnetic order in In(1-x)Mn(x)Sb was unambiguously
established by the observation of clear hysteresis loops both in direct
magnetization measurements and in the anomalous Hall effect, with Curie
temperatures T_C ranging up to 8.5 K. The observed values of T_C agree well
with the existing models of carrier-induced ferromagnetism.",0303212v1
2003-04-09,How to make semiconductors ferromagnetic: A first course on spintronics,"The rapidly developing field of ferromagnetism in diluted magnetic
semiconductors, where a semiconductor host is magnetically doped by transition
metal impurities to produce a ferromagnetic semiconductor (e.g. Ga_{1-x}Mn_xAs
with x ~ 1-10 %), is discussed with the emphasis on elucidating the physical
mechanisms underlying the magnetic properties. Recent key developments are
summarized with critical discussions of the roles of disorder, localization,
band structure, defects, and the choice of materials in producing good magnetic
quality and high Curie temperature. The correlation between magnetic and
transport properties is argued to be a crucial ingredient in developing a full
understanding of the properties of ferromagnetic semiconductors.",0304219v1
2003-04-24,Competing Orders and Disorder-induced Insulator to Metal Transition in Manganites,"Effects of disorder on the two competing phases, i.e., the ferromagnetic
metal and the commensurate charge/lattice ordered insulator, are studied by
Monte Carlo simulation. The disorder suppresses the charge/lattice ordering
more strongly than the ferromagnetic order, driving the commensurate insulator
to the ferromagnetic metal near the phase boundary in the pure case. Above the
ferromagnetic transition temperature, on the contrary, the disorder makes the
system more insulating, which might cause an enhanced colossal
magnetoresistance as observed in the half-doped or Cr-substituted manganites.
No indication of the percolation or the cluster formation is found, and there
remain the charge/lattice fluctuations instead which are enhanced toward the
transition temperature.",0304543v2
2003-05-27,Probing a ferromagnetic critical regime using nonlinear susceptibility,"The second order para-ferromagnetic phase transition in a series of amorphous
alloys (Fe{_5}Co{_{50}}Ni{_{17-x}}Cr{_x}B{_{16}}Si{_{12}}) is investigated
using nonlinear susceptibility. A simple molecular field treatment for the
critical region shows that the third order suceptibility (chi{_3}) diverges on
both sides of the transition temperature, and changes sign at T{_C}. This
critical behaviour is observed experimentally in this series of amorphous
ferromagnets, and the related assymptotic critical exponents are calculated. It
is shown that using the proper scaling equations, all the exponents necessary
for a complete characterization of the phase transition can be determined using
linear and nonlinear susceptiblity measurements alone. Using meticulous
nonlinear susceptibility measurements, it is shown that at times chi{_3} can be
more sensitive than the linear susceptibility (chi{_1}) in unravelling the
magnetism of ferromagnetic spin systems. A new technique for accurately
determining T{_C} is discussed, which makes use of the functional form of
chi{_3} in the critical region.",0305617v1
2003-06-15,Room-Temperature Ferromagnetism in Co-Doped TiO$_2$ Anatase: Role of Interstitial Co,"TiO$_2$ anatase doped with Co has been recently reported to exhibit
room-temperature ferromagnetism. $Ab$ $initio$ study on substitutional Co
doping, however, yielded much larger magnetic moment for Co than experiment.
Our calculations based on density-functional theory show that the
substitutional Co ions incorporated into TiO$_2$ anatase tend to cluster and
then the neighboring interstitial tetrahedral sites become energetically
favorable for Co to reside, yielding a local environment more like Co$_3$O$_4$
than CoTiO$_3$. The interstitial Co destroys the spin-polarization of the
surrounding substitutional Co but enhances the stability of the ferromagnetism
significantly. In the absence of carriers, this room-temperature ferromagnetism
can only be accounted for by superexchange interaction.",0306389v1
2003-06-18,Hall effect and magnetoresistance in p-type ferromagnetic semiconductors,"Recent works aiming at understanding magnetotransport phenomena in
ferromagnetic III-V and II-VI semiconductors are described. Theory of the
anomalous Hall effect in p-type magnetic semiconductors is discussed, and the
relative role of side-jump and skew-scattering mechanisms assessed for
(Ga,Mn)As and (Zn,Mn)Te. It is emphasized that magnetotransport studies of
ferromagnetic semiconductors in high magnetic fields make it possible to
separate the contributions of the ordinary and anomalous Hall effects, to
evaluate the role of the spins in carrier scattering and localization as well
as to determine the participation ratio of the ferromagnetic phase near the
metal-insulator transition. A sizable negative magnetoresistance in the regime
of strong magnetic fields is assigned to the weak localization effect.",0306484v2
2003-06-29,The Origin of Weak Ferromagnetism in CaB6,"We have combined the results of magnetization and Hall effect measurements to
conclude that the ferromagnetic moments of lightly doped CaB6 samples display
no systematic variation with electron doping level. Removal of the surface with
acid etching substantially reduces the measured moment, although the Hall
constant and resistivity are unaffected, indicating that the ferromagnetism
largely resides on and near the sample surface. Electron microprobe experiments
reveal that Fe and Ni are found at the edges of facets and growth steps, and on
other surface features introduced during growth. Our results indicate that the
weak ferromagnetism previously reported in undoped CaB6 is at least partly
extrinsic.",0306709v1
2003-07-10,Axial and off-axial dynamic transitions in uniaxially anisotropic Heisenberg ferromagnet: A comparison,"Uniaxially anisotropic Heisenberg ferromagnet, in the presence of a magnetic
fieldvarying sinusoidally in time, is studied by Monte Carlo Simulation. The
axial (field applied only along the direction of anisotropy) and off-axial
(field applied only along the direction which is prependicular to the direction
of anisotropy) dynamic transitions are studied. By studying the distribution of
the dynamic order parameter component, it is observed that the axial transition
is discontinuous for low anisotropy and becomes continuous in high anisotropy.
The off-axial transition is found to be continuous for all values of
anisotropy. In the infinite anisotropy limit, both types of transitions are
compared with athat observed in an Ising ferromagnet for the same value of the
field and frequency. The infinitely anisotropic axial transition and dynamic
transition in the Ising ferromagnet occur at different temperatures, whereas
the infinitely anisotropic off-axial transition and the equilibrium ferro-para
transition in the Ising model occur at the same temperature.",0307225v1
2003-08-07,Spin-Fermion model of $UGe_2$,"It is assumed that U atoms in $UGe_2$ have a number of $f$ electrons
appropriate to give them each a spin $s=1$ as well as one extra itinerant
electron which may equally well be on one or other U atom. The dynamical
degrees of freedom are spin-s operators of localized spins and spin-1/2 fermi
operators of itinerant electrons. Applying hydrostatic pressure changes the
bandwidths of spin-up and spin-down itinerant electrons in different way, which
leads to decreasing of the contribution of the fermions to the magnetization
keeping the spin-fermion interaction unchanged. In turn the local spin-fermion
interaction leads to ferromagnetic superconductivity. The model accounts, in a
quantitative and natural way, for the characteristics of the coexistence of
superconductivity and ferromagnetism in $UGe_2$, including many of the key
experimental results: metamagnetic transitions, quantum transition from
ferromagnetism to ferromagnetic superconductivity, the position of the highest
superconducting critical temperature etc.",0308134v1
2003-08-08,Flat-Band Ferromagnetism in Organic Polymers Designed by a Computer Simulation,"By coupling a first-principles, spin-density functional calculation with an
exact diagonalization study of the Hubbard model, we have searched over various
functional groups for the best case for the flat-band ferromagnetism proposed
by R. Arita et al. [Phys. Rev. Lett. {\bf 88}, 127202 (2002)] in organic
polymers of five-membered rings. The original proposal (poly-aminotriazole) has
turned out to be the best case among the materials examined, where the reason
why this is so is identified here. We have also found that the ferromagnetism,
originally proposed for the half-filled flat band, is stable even when the band
filling is varied away from the half-filling. All these make the ferromagnetism
proposed here more experimentally inviting.",0308154v1
2003-08-08,Flat-band ferromagnetism proposed for an organic polymer crystal,"Motivated from the flat-band ferromagnetism conceived theoretically for a
single chain of five membered rings (polyaminotriazole) by Arita {\it et al.},
[Phys. Rev. Lett. {\bf 88}, 127202 (2002)], we have studied whether the
magnetism can indeed occur as a bulk, i.e., in a three-dimensional crystal of
the polymer, by means of the spin density functional calculation. We find that
the intra-chain ferromagnetism is robust against crystallization as far as the
flat band is made half-filled. We have further investigated the actual crystal
doped with various compounds, where HF$_2$ is shown to put the system close to
the bulk ferromagnetism while stronger anions such as BF$_4$ or PF$_6$ should
be promising.",0308156v1
2003-09-15,Theory of Spin Transport Induced by Ferromagnetic Proximity On a Two-Dimensional Electron Gas,"A theory of the proximity effects of the exchange splitting in a
ferromagnetic metal on a two dimensional electron gas (2DEG) in a semiconductor
is presented. The resulting spin-dependent energy and lifetime in the 2DEG
create a marked spin-splitting in the driven in-plane current. The theory of
the planar transport allows for current leakage into the ferromagnetic layer
through the interface, which leads to a competition between drift and
diffusion. The spin-dependent in-plane conductivity of the 2DEG may be
exploited to provide a new paradigm for spintronics devices based on planar
devices in a field-effect transistor configuration. An illustrative example is
provided through the transport theory of a proposed spin-valve which consists
of a field-effect transistor configuration with two ferromagnetic gates.
Results are provided for two experimentally accessible systems: the silicon
inversion layer and the naturally-formed InAs accumulation layer.",0309353v1
2003-10-03,Formation of mid-gap states and ferromagnetism in semiconducting CaB$_6$,"We present a consistent overall picture of the electronic structure and
ferromagnetic interaction in CaB$_6$, based on our joint transport, optical,
and tunneling measurements on high-quality {\em defect-controlled} single
crystals. Pure CaB$_6$ single crystals, synthesized with 99.9999 %-pure boron,
exhibited fully {\em semiconducting} characteristics, such as monotonic
resistance for 2--300 K, a tunneling conductance gap, and an optical absorption
threshold at 1.0 eV. {\em Boron-related defects} formed in CaB$_6$ single
crystals synthesized with 99.9 %-pure boron induced {\em mid-gap states} 0.18
eV below the conduction band and extra free charge carriers, with the
transport, optical, and tunneling properties substantially modified.
Remarkably, no ferromagnetic signals were detected from single crystals made
with 99.9999 %-pure boron, regardless of stoichiometry, whereas those made with
99.9 %-boron exhibited ferromagnetism within a finite range of carrier density.
The possible surmise between the electronic state and magnetization will be
discussed.",0310068v1
2003-10-06,"Origin of room temperature ferromagnetism in homogeneous (In,Mn)As thin films","The microstructure of (In,Mn)As thin films grown using metalorganic vapor
phase epitaxy (MOVPE) was investigated to determine the origin of room
temperature ferromagnetism in these films. Transmission electron microscopy
(TEM) based techniques were used to investigate phase purity and compositional
homogeneity. Microanalysis of an In1-xMnxAs film with x = 0.01 and a Curie
temperature of 330 K exhibited a homogeneous distribution of Mn. High Mn
concentration films with x = 0.20 exhibited MnAs precipitates within the
(In,Mn)As matrix. The analysis indicates that room temperature ferromagnetic,
single-phase (In,Mn)As can be formed by MOVPE. The origin of ferromagnetism is
attributed to (In,Mn)As solid solution rather than distinct secondary Mn-rich
magnetic phase(s).",0310106v1
2003-10-17,Effects of Density of States Asymmetry on Boundary Resistance of Ferromagnetic-Nonferromagnetic Metal Interface,"Asymmetry of conduction of electrons in the spin majority and minority bands
of a ferromagnetic metal is well known to produce spin accumulation at the
boundary with a normal metal when a current is injected through the interface.
However, little emphasis has been put on the density of states (DOS) asymmetry
in diffusive ferromagnetic-nonferromagnetic multilayers. We found that if DOS
and conduction asymmetry differ, the electric potential in a ferromagnet falls
off to its bulk value exponentially on a scale of the spin diffusion length.
Therefore the boundary contribution to resistance dramatically depends on
whether the potential difference is measured close to the interface or farther
than the spin diffusion length from it. This result is not altered by taking
surface resistance or spin-flips on the intermetallic boundary into account.
Explicit answers for common multilayered spin-valve structures are given.",0310431v1
2003-10-21,Return to return point memory,"We describe a new class of systems exhibiting return point memory (RPM) that
are different from those discussed before in the context of ferromagnets. We
show numerically that one dimensional random Ising antiferromagnets have RPM,
when configurations evolve from a large field. However, RPM is violated when
started from some stable configurations at finite field unlike in the
ferromagnetic case. This implies that the standard approach to understanding
ferromagnetic RPM systems will fail for this case. We also demonstrate RPM with
a set of variables that keep track of spin flips at each site. Conventional RPM
for the spin configuration is a projection of this result, suggesting that spin
flip variables might be a more fundamental representation of the dynamics. We
also present a mapping that embeds the antiferromagnetic chain in a two
dimensional ferromagnetic model, and prove RPM for spin exchange dynamics in
the interior of the chain with this mapping.",0310484v1
2003-11-05,Ferromagnetism from localized deep impurities in magnetic semiconductors,"We propose that localized defects in magnetic semiconductors act as deep
impurities and can be described by the Anderson model. Within this model,
hybridization of d-orbitals and p-orbitals gives rise to a non-RKKY indirect
exchange mechanism, when the localized d-electrons are exchanged through both
conduction and valence bands. For semiconductors with indirect band gap the
non-RKKY part of exchange integral is antiferromagnetic, which suppresses
ferromagnetism. In case of direct band gap, this exchange mechanism can, under
certain conditions, lead to enhancement of ferromagnetism. The indirect
exchange intergral is much stronger than RKKY, and can be sufficiently long
range. Thus, a potentially new class of high-temperature magnetic
semiconductors emerges, where doped carriers are not necessary to mediate
ferromagnetism. Curie temperatures in such magnetic semiconductors are
determined mostly by the interaction between localized impurities, not Zener
mechanism. This effect could also be responsible for unusually high Curie
temperatures in some magnetic semiconductors with direct band gap, such as
GaMnAs.",0311114v1
2003-12-01,A theoretical investigation of ferromagnetic tunnel junctions with 4-valued conductances,"In considering a novel function in ferromagnetic tunnel junctions consisting
of ferromagnet(FM)/barrier/FM junctions, we theoretically investigate multiple
valued (or multi-level) cell property, which is in principle realized by
sensing conductances of four states recorded with magnetization configurations
of two FMs; that is, (up,up), (up,down), (down,up), (down,down). To obtain such
4-valued conductances, we propose FM1/spin-polarized barrier/FM2 junctions,
where the FM1 and FM2 are different ferromagnets, and the barrier has spin
dependence. The proposed idea is applied to the case of the barrier having
localized spins. Assuming that all the localized spins are pinned parallel to
magnetization axes of the FM1 and FM2, 4-valued conductances are explicitly
obtained for the case of many localized spins. Furthermore, objectives for an
ideal spin-polarized barrier are discussed.",0312019v1
2003-12-11,Design of electron correlation effects in interfaces and nanostructures,"We propose that one of the best grounds for the materials design from the
viewpoint of {\it electron correlation} such as ferromagnetism,
superconductivity is the atomically controlled nanostructures and
heterointerfaces, as theoretically demonstrated here from three examples with
first-principles calculations: (i) Band ferromagnetism in a purely organic
polymer of five-membered rings, where the flat-band ferromagnetism due to the
electron-electron repulsion is proposed. (ii) Metal-induced gap states (MIGS)
of about one atomic monolayer thick at insulator/metal heterointerfaces,
recently detected experimentally, for which an exciton-mechanism
superconductivity is considered. (iii) Alkali-metal doped zeolite, a class of
nanostructured host-guest systems, where ferromagnetism has been experimentally
discovered, for which a picture of the ""supercrystal"" composed of ""superatoms""
is proposed and Mott-insulator properties are considered. These indicate that
design of electron correlation is indeed a promising avenue for nanostructures
and heterointerfaces.",0312275v2
2003-12-16,Polaronic Aspects of the two-dimensional Ferromagnetic Kondo Model,"The 2D ferromagnetic Kondo model with classical corespins is studied for a
hole doping up to x = 0.125 via unbiased Monte Carlo (MC) simulations. A
canonical algorithm for finite temperatures is developed.
  We show that with realistic parameters for the manganites and at low
temperatures, the double-exchange mechanism does not lead to phase separation
on a two-dimensional lattice but rather stabilizes individual ferromagnetic
polarons. A detailed analysis of unbiased MC results reveals that the polarons
can be treated as independent particles.
  It is found that a simple polaron model perfectly describes the physics of
the FM Kondo model. The ferromagnetic polaron picture provides an obvious
explanation for the pseudogap in the one-particle spectral function
$A_k(\omega)$ observed in the FM Kondo model.",0312394v2
2004-01-05,Influence of s-d scattering on the electron density of states in ferromagnet/superconductor bilayer,"We study the dependence of the electronic density of states (DOS) on the
distance from the boundary for a ferromagnet/superconductor bilayer. We
calculate the electron density of states in such structure taking into account
the two-band model of the ferromagnet (FM) with conducting s and localized d
electrons and a simple s-wave superconductor (SC). It is demonstrated that due
to the electron s-d scattering in the ferromagnetic layer in the third order of
s-d scattering parameter the oscillation of the density of states has larger
period and more drastic decrease in comparison with the oscillation period for
the electron density of states in the zero order.",0401037v2
2004-01-09,Tailoring ferromagnetic chalcopyrites,"If magnetic semiconductors are ever to find wide application in real
spintronic devices, their magnetic and electronic properties will require
tailoring in much the same way that band gaps are engineered in conventional
semiconductors. Unfortunately, no systematic understanding yet exists of how,
or even whether, properties such as Curie temperatures and band gaps are
related in magnetic semiconductors. Here we explore theoretically these and
other relationships within 64 members of a single materials class, the Mn-doped
II-IV-V2 chalcopyrites, three of which are already known experimentally to be
ferromagnetic semiconductors. Our first-principles results reveal a variation
of magnetic properties across different materials that cannot be explained by
either of the two dominant models of ferromagnetism in semiconductors. Based on
our results for structural, electronic, and magnetic properties, we identify a
small number of new stable chalcopyrites with excellent prospects for
ferromagnetism.",0401157v2
2004-02-19,Quantum fluctuation driven first order phase transition in weak ferromagnetic metals,"In a local Fermi liquid (LFL), we show that there is a line of weak first
order phase transitions between the ferromagnetic and paramagnetic phases due
to purely quantum fluctuations. We predict that an instability towards
superconductivity is only possible in the ferromagnetic state. At T=0 we find a
point on the phase diagram where all three phases meet and we call this a
quantum triple point (QTP). A simple application of the Gibbs phase rule shows
that only these three phases can meet at the QTP. This provides a natural
explanation of the absence of superconductivity at this point coming from the
paramagnetic side of the phase diagram, as observed in the recently discovered
ferromagnetic superconductor, $UGe_{2}$.",0402507v1
2004-03-26,Spin screening of magnetic moments in superconductors,"We consider ferromagnetic particles embedded into a superconductor and study
the screening of their magnetic moments by the spins of the Cooper pairs in the
superconductor. It is shown that a magnetic moment opposite to the one of the
ferromagnetic particle is induced in the superconductor. In the case of a small
itinerant ferromagnet grain and low temperatures the full screening of the
magnetic moment takes place, \textit{% i.e} the absolute value of the total
magnetic moment induced in the superconductor is equal to the one of the
ferromagnetic particle. In type II superconductors the proposed screening by
spins of the conduction electrons can be much stronger than the conventional
screening by Meissner currents.",0403658v1
2004-05-02,Spin Dynamics and Multiple Reflections in Ferromagnetic Film in Contact with Normal Metal Layers,"Spin dynamics of a metallic ferromagnetic film imbedded between normal metal
layers is studied using the spin-pumping theory of Tserkovnyak et al. [Phys.
Rev. Lett. 88, 117601 (2002)]. The scattering matrix for this structure is
obtained using a spin-dependent potential with quantum well in the
ferromagnetic region. Owing to multiple reflections in the well, the excess
Gilbert damping and the gyromagnetic ratio exhibit quantum oscillations as a
function of the thickness of the ferromagnetic film. The wavelength of the
oscillations is given by the depth of the quantum well. For iron film imbedded
between gold layers, the amplitude of the oscillations of the Gilbert damping
is in an order of magnitude agreement with the damping observed by Urban et al.
[Phys. Rev. Lett. 87, 217204 (2001)]. The results are compared with the linear
response theory of Mills [Phys. Rev. B 68, 0144419 (2003)].",0405020v1
2004-05-10,Quantum and thermal effects in the double exchange ferromagnet,"The physics of the ferromagnetic phase of the ``double exchange'' model has
been widely discussed in the context of the CMR manganites. Usually, the double
exchange ferromagnet is treated is classically, by mapping it onto an effective
Heisenberg model. However this mapping does not permit a correct treatment of
quantum or thermal fluctuation effects, and the results obtained lack many of
the interesting features seen in experiments on the manganites. Here we outline
a new analytic approach to systematically evaluating quantum and thermal
corrections to the magnetic and electronic properties of the double exchange
ferromagnet.",0405189v1
2004-05-15,Positive exchange bias in ferromagnetic La0.67Sr0.33MnO3 / SrRuO3 bilayers,"Epitaxial La0.67Sr0.33MnO3 (LSMO)/ SrRuO3 (SRO) ferromagnetic bilayers have
been grown on (001) SrTiO3 (STO) substrates by pulsed laser deposition with
atomic layer control. We observe a shift in the magnetic hysteresis loop of the
LSMO layer in the same direction as the applied biasing field (positive
exchange bias). The effect is not present above the Curie temperature of the
SRO layer (), and its magnitude increases rapidly as the temperature is lowered
below . The direction of the shift is consistent with an antiferromagnetic
exchange coupling between the ferromagnetic LSMO layer and the ferromagnetic
SRO layer. We propose that atomic layer charge transfer modifies the electronic
state at the interface, resulting in the observed antiferromagnetic interfacial
exchange coupling.",0405338v1
2004-06-01,Diagnosis of transport properties in Ferromagnets,"The resistivity model as a function of temperature and ionization energy
(doping) is derived with further confinements from spin-disorder scattering in
ferromagnetic phase. Magnetization and polaronic effects capture the mechanism
of both spin independent and spin-assisted charge transport of ferromagnets,
including the newly reported Mn$_x$Ge$_{1-x}$ ferromagnetic semiconductor. The
computed $T_{crossover}$ below $T_C$ and carrier density in Ga$_{1-x}$Mn$_x$As
system are 8-12 K and 10$^{19}$ cm$^{-3}$, remarkably identical with the
experimental values of 10-12 K and 10$^{18}-10^{20}$ cm$^{-3}$ respectively.
The calculated charge carriers density for Mn$_x$Ge$_{1-x}$ is 10$^{19}$
cm$^{-3}$, which is also in the same order with the experimental values.",0406030v8
2004-06-23,Carrier induced ferromagnetism in concentrated and diluted local-moment systems,"For modeling the magnetic properties of concentrated and diluted magnetic
semiconductors, we use the Kondo-lattice model. The magnetic phase diagram is
derived by inspecting the static susceptibility of itinerant band electrons,
which are exchange coupled to localized magnetic moments. It turns out that
rather low band occupations favour a ferromagnetic ordering of the local moment
systems due to an indirect coupling mediated by a spin polarization of the
itinerant charge carriers. The disorder in diluted systems is treated by adding
a CPA-type concept to the theory. For almost all moment concentrations x,
ferromagnetism is possible, however, only for carrier concentrations n
distinctly smaller than x. The charge carrier compensation in real magnetic
semiconductors (in Ga_{1-x}Mn_{x}As by e.g. antisites) seems to be a necessary
condition for getting carrier induced ferromagnetism.",0406569v1
2004-08-10,The role of intra-atomic non-collinear magnetization density in weak ferromagnetism,"We investigate the mechanism behind the breakdown of the compensation of
large magnetic moments leading to weak ferromagnetism. For this we use
first-principles calculations within density functional theory and we focus on
the weak ferromagnetic compound Mn3Sn. Our new implementation allows for an
exact treatment of the spin-density matrix and non-collinearity. In order to
gain some insight, our results are compared to the ones obtained by using the
atomic moment approximation (AMA) and its role is discussed. We find that the
appearance of the weak ferromagnetic moment in this compound originates not so
much as an effect of spin-orbit coupling as suggested previously from AMA
calculations, as from the non-collinearity of the Sn atom magnetization
density. This is confirmed by non-collinear calculations in which the SOC
effects are neglected.",0408200v1
2004-09-15,Low temperature ferromagnetic properties of the diluted magnetic semiconductor Sb2-xCrxTe3,"We report on magnetic and electrical transport properties of Sb2-xCrxTe3
single crystals with 0 <= x <= 0.095 over temperatures from 2 K to 300 K. A
ferromagnetic state develops in these crystals at low temperatures with Curie
temperatures that are proportional to x (for x > 0.014), attaining a maximum
value of 20 K for x = 0.095. Hysteresis below TC for applied field parallel to
the c-axis is observed in both magnetization and Hall effect measurements.
Magnetic as well as transport data indicate that Cr takes the 3+ (3d3) valence
state, substituting for antimony in the host lattice structure, and does not
significantly affect the background hole concentration. Analysis of the
anomalous Hall effect reveals that skew scattering is responsible for its
presence. These results broaden the scope of ferromagnetism in the V2-VI3
diluted magnetic semiconductors (DMS) and in ferromagnetic DMS structures
generally",0409403v1
2004-10-26,Spintronics at Nanoscale: Flat-Band Ferromagnetism in Armchair Nanoribbons and Nanotubes,"We study the electronic correlation effects in armchair nanoribbon and
nanotube using weak-coupling approach and non-Abelian density-matrix
renormalization-group method. We show that upon appropriate doping, the system
exhibits a new type of flat-band ferromagnetism, different from the well-known
Milke-Tasaki one. The strongly correlated ground state consists of intrinsic
magnetic moments of flat-band states and itinerant carriers of dispersive
bands, and the exchange coupling between them yields a ferromagnetism. The
resultant ferromagnetic state with metallic conductivity has a potential in
spintronics applications at nanoscale.",0410654v2
2004-11-13,Theory of polarized Fermi liquid,"The dispersion law of transverse spin waves known in the Stoner-Hubbard model
of itinerant ferromagnetism corresponds to that is well known in more broder
and well controlled approach of Fermi-liquid theory. Making use the
quantum-field theoretical approach we derive the dispersion law for the
transverse spin waves in a weakly polarized Fermi liquid at T=0. Along with the
dissipationless part inversely proportional to the polarization it contains
also the finite zero-temperature damping. It is shown that similar derivation
for ""ferromagnetic Fermi liquid"" taking into consideration the divergency of
static transverse susceptibility also leads to the same attenuating spin wave
spectrum. Hence, in both cases we deal in fact with spin polarized Fermi liquid
but not with isotropic itinerant ferromagnet where the zero temperature
atenuation is prohibited by Goldstone theorem. It demonstrates, the troubles of
the Fermi liquid formulation of a theory of itinerant ferromagnetic systems.",0411361v1
2004-11-26,Room-temperature ferromagnetism in Sr_(1-x)Y_xCoO_(3-delta) (0.2 < x < 0.25),"We have measured magnetic susceptibility and resistivity of
Sr$_{1-x}$Y$_x$CoO$_{3-\delta}$ ($x=$ 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that Sr$_{1-x}$Y$_x$CoO$_{3-\delta}$ is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 $\leq x\leq$ 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for $x=$
0.225 is 0.25 $\mu_B$/Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.",0411671v3
2004-12-03,High frequency magnetic permeability of nanocomposite film,"The high frequency magnetic permeability of nanocomposite film consisting of
the single-domain spherical ferromagnetic particles in the dielectric matrix is
studied. The permeability is assumed to be determined by rotation of the
ferromagnetic inclusion magnetic moments around equilibrium direction in AC
magnetic field. The composite is modeled by a cubic array of ferromagnetic
particles. The magnetic permeability tensor is calculated by solving the
Landau-Lifshits-Gilbert equation accounting for the dipole interaction of
magnetic particles. The permeability tensor components are found as functions
of the frequency, temperature, ferromagnetic inclusions density and magnetic
anisotropy. The obtained results show that nanocomposite films could have
rather high value of magnetic permeability in the microwave range.",0412073v1
2004-12-03,New Challenges in Cellular Automata Due to Network Geometry - Ferromagnetic Transition Study,"Self-organization to ferromagnetic phase transition in cellular automata of
spins governed by stochastic majority rule and when topology between spins is
changed, is investigated numerically. Three types of edge rewiring are
considered. The algorithm of Watts and Strogatz is applied at each time step to
establish a network evolving stochastically (the first network). The preference
functions are defined to amplify the role of strongly connected vertices (the
second network). Demand to preserve graph connectivity provides the third way
of edge rewiring. Each of these processes yields the different network:
small-world, scattered nodes with one strongly connected component, and
scale-free network when rewiring is properly adjusted. The stochastic majority
rule applied to these networks can lead or not to ferromagnetic transition.
Classical mean-field transition in case of the first and third network is
observed. Scale-free ferromagnetic transition can be observed when rewiring is
properly adjusted.",0412082v1
2004-12-09,Coexistence of ferromagnetism and superconductivity near quantum phase transition: The Heisenberg- to Ising-type crossover,"A microscopic mean-field theory of the phase coexistence between
ferromagnetism and superconductivity in the weakly ferromagnetic itinerant
electron system is constructed, while incorporating a realistic mechanism for
superconducting pairing due to the exchange of critical spin fluctuations. The
self-consistent solution of the resulting equations determines the
superconducting transition temperature which is shown to depend strongly on the
exchange splitting. The effect of phase crossover from isotropic
(Heisenberg-like) to uniaxial (Ising-like) spin fluctuations near the quantum
phase transition is analysed and the generic phase diagram is obtained. This
scenario is then applied to the case of itinerant ferromagnet ZrZn2, which
sheds light on the proposed phase diagram of this compound. Possible
explanation of superconductivity in UGe2 is also discussed.",0412247v1
2004-12-15,Local Environment of Ferromagnetically Ordered Mn in Epitaxial InMnAs,"The magnetic properties of the ferromagnetic semiconductor In0.98Mn0.02As
were characterized by x-ray absorption spectroscopy and x-ray magnetic circular
dichroism. The Mn exhibits an atomic-like L2,3 absorption spectrum that
indicates that the 3d states are highly localized. In addition, a large
dichroism at the Mn L2,3 edge was observed from 5-300 K at an applied field of
2T. A calculated spectrum assuming atomic Mn2+ yields the best agreement with
the experimental InMnAs spectrum. A comparison of the dichroism spectra of MnAs
and InMnAs show clear differences suggesting that the ferromagnetism observed
in InMnAs is not due to hexagonal MnAs clusters. The temperature dependence of
the dichroism indicates the presence of two ferromagnetic species, one with a
transition temperature of 30 K and another with a transition temperature in
excess of 300 K. The dichroism spectra are consistent with the assignment of
the low temperature species to random substitutional Mn and the high
temperature species to Mn near-neighbor pairs.",0412384v1
2004-12-22,"Crystal structures and magnetic order of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba): Possible orbital glass ferromagnetic state","The crystallographic and magnetic properties of
La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba)
were investigated by means of neutron powder diffraction. All studied samples
show the orthorhombic perovskite crystal structure, space group Pnma, with
regular (Mn,Ru)O{6} octahedra and no chemical ordering of the Mn3+ and Ru4+
ions. Ferromagnetic spin structures were observed below Tc ~ 200-250 K, with an
average ordered moment of ~ 1.8-2.0 Bohr magnetons per (Mn,Ru). The observation
of long-range ferromagnetism and the absence of orbital ordering are
rationalized in terms a strong Mn-Ru hybridization, which may freeze the
orbital degree of freedom and broaden the eg valence band, leading to an
orbital-glass state with carrier-mediated ferromagnetism.",0412621v1
2005-02-02,Scanning Tunneling Spectroscopy of the superconducting proximity effect in a diluted ferromagnetic alloy,"We studied the proximity effect between a superconductor (Nb) and a diluted
ferromagnetic alloy (CuNi) in a bilayer geometry. We measured the local density
of states on top of the ferromagnetic layer, which thickness varies on each
sample, with a very low temperature Scanning Tunneling Microscope. The measured
spectra display a very high homogeneity. The analysis of the experimental data
shows the need to take into account an additional scattering mechanism. By
including in the Usadel equations the effect of the spin relaxation in the
ferromagnetic alloy, we obtain a good description of the experimental data.",0502050v2
2005-02-16,Global phase diagrams of binary dipolar fluid mixtures,"We apply a modified mean-field density functional theory to determine the
phase behavior of binary mixtures of Stockmayer fluids whose spherical
constituents interact according to Lennard-Jones (LJ) pair potentials with
embedded pointlike dipole moments. On the basis of systematic numerical
calculations we construct the global phase diagrams of these systems in the
three-dimensional thermodynamic space of temperature, pressure, and chemical
potential difference of the two components. The vapor-liquid, isotropic liquid
- isotropic liquid, isotropic liquid - ferromagnetic liquid, and ferromagnetic
liquid - ferromagnetic liquid first-order phase separations are investigated.
The loci of the second-order isotropic fluid - ferromagnetic fluid transition
are calculated from Landau theory. Liquid-vapor and liquid-liquid critical
lines, tricritical lines, triple lines, and lines of critical end points of the
binary Stockmayer mixtures are also determined. We discuss how the topology of
the phase diagrams change upon varying the strengths of the two dipole moments
of the two species as well as their sizes.",0502405v3
2005-02-24,Nonlocal pure spin current injection via quantum pumping and crossed Andreev reflection,"A pure spin current injector is proposed based on adiabatic pumping and
crossed normal/Andreev reflection. The device consists of a three-terminal
ferromagnet-superconductor-semiconductor system in which the injection of a
pure spin current is into the semiconductor which is coupled to the
superconductor within a coherence length away from the ferromagnet enabling the
phenomena of crossed normal /Andreev reflection to operate. Quantum pumping is
induced by adiabatically modulating two independent parameters of the
ferromagnetic lead, namely the magnetization strength and the strength of
coupling between the ferromagnet and the superconductor. The competition
between the normal/Andreev reflection and the crossed normal/Andreev
reflection, both induced by pumping, leads to non-local injection of a pure
spin current into the semiconductor. The experimental realization of the
proposed device is also discussed.",0502589v2
2005-03-01,Berry phase of magnons in textured ferromagnets,"We study the energy spectrum of magnons in a ferromagnet with topologically
nontrivial magnetization profile. In the case of inhomogeneous magnetization
corresponding to a metastable state of ferromagnet, the spin-wave equation of
motion acquires a gauge potential leading to a Berry phase for the magnons
propagating along a closed contour. The effect of magnetic anisotropy is
crucial for the Berry phase: we show that the anisotropy suppresses its
magnitude, which makes the Berry phase observable in some cases, similar to the
Aharonov-Bohm effect for electrons. For example, it can be observed in the
interference of spin waves propagating in mesoscopic rings. We discuss the
effect of domain walls on the interference in ferromagnetic rings, and propose
some experiments with a certain geometry of magnetization. We also show that
the nonvanishing average topological field acts on the magnons like a uniform
magnetic field on electrons. It leads to the quantization of the magnon
spectrum in the topological field.",0503013v1
2005-03-17,Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4,"Multiferroic materials, which reveal magnetic and electric order, are in the
focus of recent solid state research. Especially the simultaneous occurrence of
ferroelectricity and ferromagnetism, combined with an intimate coupling of
magnetization and polarization via magneto-capacitive effects, could pave the
way for a new generation of electronic devices. Here we present measurements on
a simple cubic spinel with unusual properties: It shows ferromagnetic order and
simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state,
reached by a smeared-out phase transition, both with sizable ordering
temperatures and moments. Close to the ferromagnetic ordering temperature the
magneto-capacitive coupling, characterized by a variation of the dielectric
constant in an external magnetic field, reaches colossal values of nearly 500%.
We attribute the relaxor properties to geometric frustration, which is well
known for magnetic moments, but here is found to impede long-range order of the
structural degrees of freedom.",0503434v1
2005-04-07,Observation of spin-wave characteristics in the two-dimensional ferromagnetic ordering of in-plane spins,"The role of dipolar interactions and anisotropy are important to obtain,
otherwise forbidden, ferromagnetic ordering at finite temperature for ions
arranged in two-dimensional (2D) arrays (monolayers). Here we demonstrate that
conventional low temperature magnetometry and polarized neutron scattering
measurements can be performed to study ferromagnetic ordering of in-plane spins
in 2D systems using a multilayer stack of non-interacting monolayers of
gadolinium ions. The spontaneous magnetization is absent in the heterogenous
magnetic phase observed here and the saturation value of the net magnetization
was found to depend on the applied magnetic field. The net magnetization rises
exponentially with lowering temperature and then reaches saturation following a
$T\ln(\beta T)$ dependence. These findings verify predictions of the spin-wave
theory of 2D in-plane spin system with ferromagnetic interaction and will
initiate further theoretical development.",0504155v1
2005-04-15,"Competition between ferromagnetism and spin glass: the key for large magnetoresistance in oxygen deficient perovskites SrCo1-xMxO3-d (M = Nb, Ru)","The magnetic and magnetotransport properties of the oxygen deficient
perovskites, SrCo1-xMxO3-d with M = Nb and Ru, were investigated. Both Nb- and
Ru-substituted cobaltites are weak ferromagnets, with transition temperatures
Tm of 130-150 K and 130-180 K, respectively, and both exhibit a spin glass
behavior at temperatures below Tf = 80-90 K. It is demonstrated that there
exists a strong competition between ferromagnetism and spin glass state, where
Co4+ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites
induces magnetic disorder, and this particular magnetic behavior is the origin
of large negative magnetoresistance of these oxides, reaching up to 30% at 5 K
in 7 T. The differences between Nb- and Ru-substituted cobaltites are discussed
on the basis of the different electronic configuration of niobium and ruthenium
cations.",0504379v1
2005-05-15,"Ion Irradiation Control of Ferromagnetism in (Ga,Mn)As","We report on a promising approach to the artificial modification of
ferromagnetic properties in (Ga,Mn)As using a Ga$^+$ focused ion beam (FIB)
technique. The ferromagnetic properties of (Ga,Mn)As such as magnetic
anisotropy and Curie temperature can be controlled using Ga$^+$ ion
irradiation, originating from a change in hole concentration and the
corresponding systematic variation in exchange interaction between Mn spins.
This change in hole concentration is also verified using micro-Raman
spectroscopy. We envisage that this approach offers a means of modifying the
ferromagnetic properties of magnetic semiconductors on the micro- or nano-meter
scale.",0505365v1
2005-05-24,Appearance of room temperature ferromagnetism in Cu-doped TiO$_{2-δ}$ films,"In recent years there has been an intense search for room temperature
ferromagnetism in doped dilute semiconductors, which have many potentially
applications in spintronics and optoelectronics. We report here the unexpected
observation of significant room temperature ferromagnetism in a semiconductor
doped with nonmagnetic impurities, Cu-doped TiO$_2$ thin films grown by Pulsed
Laser Deposition. The magnetic moment, calculated from the magnetization
curves, resulted surprisingly large, about 1.5 $\mu_B$ per Cu atom. A large
magnetic moment was also obtained from ab initio calculations using the
supercell method for TiO$_2$ with Cu impurities, but only if an oxygen vacancy
in the nearest-neighbour shell of Cu was present. This result suggests that the
role of oxygen vacancies is crucial for the appearance of ferromagnetism. The
calculations also predict that Cu doping favours the formation of oxygen
vacancies.",0505602v2
2005-06-01,Stability of thermodynamic and dynamical order in a system of globally coupled rotors,"A system of globally coupled rotors is studied in a unified framework of
microcanonical and canonical ensembles. We consider the Fokker-Planck equation
governing the time evolution of the system, and examine various stationary as
well as non-stationary solutions. The canonical distribution, describing
equilibrium, provides a stationary solution also in the microcanonical
ensemble, which leads to order in a system with ferromagnetic coupling at low
temperatures. On the other hand, the microcanonical ensemble admits additional
stationary and non-stationary solutions; the latter allows dynamical order,
characterized by multiple degrees of clustering, for both ferromagnetic and
antiferromagnetic interactions. We present a detailed stability analysis of
these solutions: In a ferromagnetic system, the canonical distribution is
observed stable down to a certain temperature, which tends to get lower as the
number of Fourier components of the perturbed distribution is increased in the
analysis. The non-stationary solution remains neutrally stable below the
critical temperature, indicating inequivalence between the two ensembles. For
antiferromagnetic systems, all solutions are found to be neutrally stable at
all temperatures, suggesting that dynamical ordering is relatively easy to
observe at low temperatures compared with ferromagnetic systems.",0506014v1
2005-06-02,Odd Triplet Superconductivity and Related Phenomena in Superconductor-Ferromagnet Structures,"We consider novel unusual effects in superconductor-ferromagnet (S/F)
structures. In particular we analyze the triplet component (TC) of the
condensate generated in those systems.This component is odd in frequency and
even in the momentum, which makes it insensitive to non-magnetic impurities. If
the exchange field is not homogeneous in the system the triplet component is
not destroyed even by a strong exchange field and can penetrate the ferromagnet
over long distances. Some other effects considered here and caused by the
proximity effect are: enhancement of the Josephson current due to the presence
of the ferromagnet, induction of a magnetic moment in superconductors resulting
in a screening of the magnetic moment, formation of periodic magnetic
structures due to the influence of the superconductor, etc. We compare the
theoretical predictions with existing experiments.",0506047v2
2005-06-06,Unusual transport properties of ferromagnetic Heusler alloy Co$_2$TiSn,"We report results of magnetization, zero field resistivity and
magnetoresistance measurements in ferromagnetic Heusler alloy Co$_2$TiSn. There
is a striking change in the character of electron transport as the system
undergoes the paramagnetic to ferromagnetic transition. In the paramagnetic
state the nature of the electron transport is like that of a semiconductor and
this changes abruptly to metallic behaviour at the onset of ferromagnetic
ordering. Application of external magnetic field tends to suppress this
semiconducting like transport leading to a negative magnetoresistance which
reaches a peak in the vicinity of Curie temperature. Comparison is made with
the similar unusual behaviour observed in other systems including UNiSn and
manganites.",0506126v1
2005-06-06,Nanoscale ferromagnet-superconductor-ferromagnet switches controlled by magnetization orientation,"We study clean ferromagnet-superconductor-ferromagnet (FSF) nanostructures in
which the magnetization of the F layers can be parallel (P) or antiparallel
(AP). We consider the case where the thickness of the S layer is of order of
the coherence length, with thinner F layers. We find that reversing the
direction of the magnetization in one of the F layers leads in general to
drastic changes in the superconductor's state. Under a wide variety of
conditions, the AP geometry favors superconductivity. Magnetization reversal in
one of the F layers can lead to the superconductivity turning on and off, or to
switching between different states. Our results are obtained via self
consistent solution of the Bogoliubov-de Gennes equations and evaluation of the
condensation energies of the system.",0506147v1
2005-06-15,IPA-CuCl$_3$: a S=1/2 Ladder with Ferromagnetic Rungs,"The spin gap material IPA-CuCl3 has been extensively studied as a
ferromagnetic-antiferromagnetic bondalternating S = 1/2 chain. This description
of the system was derived from structural considerations and bulk measurements.
New inelastic neutron scattering experiments reveal a totally different
picture: IPA-CuCl3 consists of weakly coupled spin ladders with
antiferromagnetic legs and ferromagnetic rungs. The ladders run perpendicular
to the originally supposed bondalternating chain direction. The ferromagnetic
rungs make this system equivalent to a Haldane S = 1 antiferromagnet. With a
gap energy of 1.17(1) meV, a zone-boundary energy of 4.1(1) meV, and almost no
magnetic anisotropy, IPA-CuCl3 may the best Haldane-gap material yet, in terms
of suitability for neutron scattering studies in high magnetic fields.",0506382v1
2005-08-05,Triplet Pairing Superconductivity Induced by Short-Range Ferromagnetic Correlations in Sr$_2$RuO$_4$,"The microscopic origin of triplet superconductivity in Sr$_2$RuO$_4$ is
discussed, paying attention to the role of Coulomb interaction, $U_{pp}$, at
the O site. It is shown on the $d$-$p$ model that $U_{pp}$ induces a
ferromagnetic exchange interaction between ""d-electrons"" (molecular orbital
with $d_{xy}$-symmetry) at adjacent Ru sites, leading to short-range
ferromagnetic correlations and promoting Cooper pairing with ($\sin
p_x\pm\ii\sin p_y$)-symmetry on the $\gamma$-band. The reason why such
ferromagnetic correlations work effectively may be traced back to the fact that
the level of 4d-electrons at Ru sites is relatively low and located near that
of $2p$-electrons at O sites.",0508147v1
2005-09-06,Inverse spin switch effects in Ferromagnet / Superconductor hybrids with strong ferromagnets,"In F/S/F trilayers where the magnetization directions of the F layers can be
controlled separately, it has theoretically been predicted that the
antiparallel (AP) configuration can have a higher superconducting transition
temperature T_c than the parallel configuration. This is the so-called spin
switch, which also experimentally has been found for the case of weak
ferromagnets. Here we show that strong ferromagnets yield the opposite effect.
We study the transport properties of F/S/F trilayers with F = Ni_0.80Fe_0.20
(Permalloy, Py) and S = Nb, structured in strips of different sizes. Using two
different thicknesses for the Py layers, we can switch in a well-defined way
between the AP- and P-configurations. In the superconducting transition we find
a clear increase of the resistance in the AP-state. We ascribe this to enhanced
reflection of spin-polarized quasiparticles at the S/F interfaces which leads
to a stronger suppression of superconductivity on the S-side.",0509156v1
2005-09-23,Clustering in disordered ferromagnets: The Curie temperature in diluted magnetic semiconductors,"We theoretically investigate impurity correlation and magnetic clustering
effects on the long-range ferromagnetic ordering in diluted magnetic
semiconductors, such as $\textrm{Ga}_{1-x}\textrm{Mn}_{x}\textrm{As}$, using
analytical arguments and direct Monte Carlo simulations. We obtain an analytic
formula for the ferromagnetic transition temperature $T_{c}$ which becomes
asymptotically exact in the strongly disordered, highly dilute (i.e. small $x$)
regime. We establish that impurity correlations have only small effects on
$T_{c}$ with the neutrally correlated random disorder producing the nominally
highest $T_{c}$. We find that the ferromagnetic order is approached from the
high temperature paramagnetic side through a random magnetic clustering
phenomenon consistent with the percolation transition scenario.",0509614v2
2005-09-28,Effect of weak disorder on the ground state of uniaxial dipolar spin systems in the upper critical dimension,"Extensive Monte Carlo simulations are used to investigate the stability of
the ferromagnetic ground state in three-dimensional systems of Ising dipoles
with added quenched disorder. These systems model the collective ferromagnetic
order observed in various systems with dipolar long-range interactions. The
uniaxial dipolar spins are arranged on a face-centred cubic lattice with
periodic boundary conditions. Finite-size scaling relations for the pure
dipolar ferromagnetic system are derived by a renormalisation group
calculation. These functions include logarithmic corrections to the expected
mean field behaviour since the system is in its upper critical dimension.
Scaled data confirm the validity of the finite-size scaling description and
results are compared with subsequent analysis of weakly disordered systems. A
disorder-temperature phase diagram displays the preservation of the
ferromagnetic ground state with the addition of small amounts of disorder,
suggesting the irrelevance of weak disorder in these systems.",0509751v1
2005-10-14,Ferromagnetism Induced by Uniaxial Pressure in the Itinerant Metamagnet Sr3Ru2O7,"We report a uniaxial-pressure study on the magnetisation of single crystals
of the bilayer perovskite Sr3Ru2O7, a metamagnet close to a ferromagnetic
instability. We observed that the application of a uniaxial pressure parallel
to the c-axis induces ferromagnetic ordering with a Curie temperature of about
80 K and critical pressures of about 4 kbar or higher. This value for the
critical pressure is even higher than the value previously reported (~ 1 kbar),
which might be attributed to the difference of the impurity level. Below the
critical pressure parallel to the c-axis, the metamagnetic field appears to
hardly change. We have also found that uniaxial pressures perpendicular to the
c-axis, in contrast, do not induce ferromagnetism, but shift the metamagnetic
field to higher fields.",0510383v1
2005-11-17,One-Dimensional Transition Metal-Benzene Sandwich Polymers: Possible Ideal Conductors for Spin Transport,"We investigate the electronic and magnetic properties of the proposed
one-dimensional transition metal (TM=Sc, Ti, V, Cr, and Mn)-benzene (Bz)
sandwich polymers by means of density functional calculations.
[V(Bz)]$_{\infty}$ is found to be a quasi-half-metallic ferromagnet and
half-metallic ferromagnetism is predicted for [Mn(Bz)]$_{\infty}$. Moreover, we
show that stretching the [TM(Bz)]$_{\infty}$ polymers could have dramatic
effects on their electronic and magnetic properties. The elongated
[V(Bz)]$_{\infty}$ displays half-metallic behavior, and [Mn(Bz)]$_{\infty}$
stretched to a certain degree becomes an antiferromagnetic insulator. The
possibilities to stabilize the ferromagnetic order in [V(Bz)]$_{\infty}$ and
[Mn(Bz)]$_{\infty}$ polymers at finite temperature are discussed. We suggest
that the hexagonal bundles composed by these polymers might display intrachain
ferromagnetic order at finite temperature by introducing interchain exchange
coupling.",0511417v1
2005-12-08,Modulation of the Curie Temperature in Ferromagnetic/Ferroelectric Hybrid Double Quantum Wells,"We propose a ferromagnetic/ferroelectric hybrid double quantum well
structure, and present an investigation of the Curie temperature (Tc)
modulation in this quantum structure. The combined effects of applied electric
fields and spontaneous electric polarization are considered for a system that
consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well.
We calculate the change in the envelope functions of carriers at the lowest
energy sub-band, resulting from applied electric fields and switching the
dipole polarization. By reversing the depolarizing field, we can achieve two
different ferromagnetic transition temperatures of the ferromagnetic quantum
well in a fixed applied electric field. The Curie temperature strongly depends
on the position of the Mn \delta-doped layer and the polarization strength of
the ferroelectric well.",0512166v2
2005-12-14,Spin-wave dispersion in orbitally ordered La(0.5)Sr(1.5)MnO(4),"The magnon dispersion in the charge, orbital and spin ordered phase in
La(0.5)Sr(1.5)MnO(4) has been studied by means of inelastic neutron scattering.
We find an excellent agreement with a magnetic interaction model basing on the
CE-type superstructure. The magnetic excitations are dominated by ferromagnetic
exchange parameters revealing a nearly-one dimensional character at high
energies. The nearest neighbor ferromagnetic interaction in
La(0.5)Sr(1.5)MnO(4) is significantly larger than the one in the metallic
ferromagnetically ordered manganites. The large ferromagnetic interaction in
the charge/orbital ordered phase appears to be essential for the capability of
manganites to switch between metallic and insulating phases.",0512305v1
2005-12-29,Current-induced magnetization dynamics in disordered itinerant ferromagnets,"Current-driven magnetization dynamics in ferromagnetic metals are studied in
a self-consistent adiabatic local-density approximation in the presence of
spin-conserving and spin-dephasing impurity scattering. Based on a quantum
kinetic equation, we derive Gilbert damping and spin-transfer torques entering
the Landau-Lifshitz equation to linear order in frequency and wave vector.
Gilbert damping and a current-driven dissipative torque scale identically and
compete, with the result that a steady current-driven domain-wall motion is
insensitive to spin dephasing in the limit of weak ferromagnetism. A uniform
magnetization is found to be much more stable against spin torques in the
itinerant than in the \textit{s}-\textit{d} model for ferromagnetism. A dynamic
spin-transfer torque reminiscent of the spin pumping in multilayers is
identified and shown to govern the current-induced domain-wall distortion.",0512715v4
2006-01-04,Prospect for room temperature tunneling anisotropic magnetoresistance effect: density of states anisotropies in CoPt systems,"Tunneling anisotropic magnetoresistance (TAMR) effect, discovered recently in
(Ga,Mn)As ferromagnetic semiconductors, arises from spin-orbit coupling and
reflects the dependence of the tunneling density of states in a ferromagnetic
layer on orientation of the magnetic moment. Based on ab initio relativistic
calculations of the anisotropy in the density of states we predict sizable TAMR
effects in room-temperature metallic ferromagnets. This opens prospect for new
spintronic devices with a simpler geometry as these do not require
antiferromagnetically coupled contacts on either side of the tunnel junction.
We focus on several model systems ranging from simple hcp-Co to more complex
ferromagnetic structures with enhanced spin-orbit coupling, namely bulk and
thin film L1$_0$-CoPt ordered alloys and a monatomic-Co chain at a Pt surface
step edge. Reliability of the predicted density of states anisotropies is
confirmed by comparing quantitatively our ab initio results for the
magnetocrystalline anisotropies in these systems with experimental data.",0601071v1
2006-01-07,Temperature dependent bilayer ferromagnetism in Sr3Ru2O7,"The Ruthenium based perovskites exhibit a wide variety of interesting
collective phenomena related to magnetism originating from the Ru 4d electrons.
Much remains unknown concerning the nature of magnetic fluctuations and
excitations in these systems. We present results of detailed inelastic neutron
scattering measurements of Sr3Ru2O7 as a function of temperature, probing the
ferromagnetic fluctuations of the bilayer structure. A magnetic response is
clearly visible for a range of temperatures, T = 3.8 K up to T = 100 K, and for
energy transfers between 2 and 14 meV. These measurements indicate that the
ferromagnetic fluctuations manifest in the bilayer structure factor persist to
surprisingly large temperatures. This behavior may be related to the proximity
of the system in zero magnetic field to the metamagnetic/ferromagnetic
transition.",0601134v1
2006-01-22,Borderline magnetism in Sr4Ru3O10: Impact of dilute La and Ca doping on itinerant ferromagnetism and metamagnetism,"An investigation of La and Ca doped Sr4Ru3O10, featuring a coexistence of
interlayer ferromagnetism and intralayer metamagnetism, is presented. La doping
readily changes magnetism between ferromagnetism and metamagnetism by tuning
the density of states. It also results in different Curie temperatures for the
c-axis and the basal plane, highlighting a rare spin-orbit coupling with the
crystal field states. In contrast, Ca doping enhances the c-axis ferromagnetism
and the magnetic anisotropy. La doping also induces a dimensional crossover in
the interlayer transport whereas Ca doping exhibits a tunneling
magnetoresistance and an extraordinary T3/2-dependence of the resisitivity. The
drastic changes caused by the dilute doping demonstrate a rare borderline
magnetism that is delicately linked to the interplay of the density of states
and spin-orbit coupling.",0601498v1
2006-01-25,Aging dynamics of ferromagnetic and reentrant spin glass phases in stage-2 Cu$_{0.80}$C$_{0.20}$Cl$_{2}$ graphite intercalation compound,"Aging dynamics of a reentrant ferromagnet stage-2
Cu$_{0.8}$Co$_{0.2}$Cl$_{2}$ graphite intercalation compound has been studied
using DC magnetic susceptibility. This compound undergoes successive
transitions at the transition temperatures $T_{c}$ ($\approx 8.7$ K) and
$T_{RSG}$ ($\approx 3.3$ K). The relaxation rate $S_{ZFC}(t)$ exhibits a
characteristic peak at $t_{cr}$ below $T_{c}$. The peak time $t_{cr}$ as a
function of temperature $T$ shows a local maximum around 5.5 K, reflecting a
frustrated nature of the ferromagnetic phase. It drastically increases with
decreasing temperature below $T_{RSG}$. The spin configuration imprinted at the
stop and wait process at a stop temperature $T_{s}$ ($<T_{c}$) during the
field-cooled aging protocol, becomes frozen on further cooling. On reheating,
the memory of the aging at $T_{s}$ is retrieved as an anomaly of the
thermoremnant magnetization at $T_{s}$. These results indicate the occurrence
of the aging phenomena in the ferromagnetic phase ($T_{RSG}<T<T_{c}$) as well
as in the reentrant spin glass phase ($T<T_{RSG}$).",0601561v1
2006-01-31,Phase coexistence and resistivity near the ferromagnetic transition of manganites,"Pairing of oxygen holes into heavy bipolarons in the paramagnetic phase and
their magnetic pair-breaking in the ferromagnetic phase [the so-called
current-carrier density collapse (CCDC)] has accounted for the first-order
ferromagnetic phase transition, colossal magnetoresistance (CMR), isotope
effect, and pseudogap in doped manganites. Here we propose an explanation of
the phase coexistence and describe the magnetization and resistivity of
manganites near the ferromagnetic transition in the framework of CCDC. The
present quantitative description of resistivity is obtained without any fitting
parameters by using the experimental resistivities far away from the transition
and the experimental magnetization, and essentially model independent.",0601712v2
2006-02-19,Re-entrant superconductivity in Nb/Cu(1-x)Ni(x) bilayers,"We report on the first observation of a pronounced re-entrant
superconductivity phenomenon in superconductor/ferromagnetic layered systems.
The results were obtained using a superconductor/ferromagnetic-alloy bilayer of
Nb/Cu(1-x)Ni(x). The superconducting transition temperature T_{c} drops sharply
with increasing thickness d_{CuNi} of the ferromagnetic layer, until complete
suppression of superconductivity is observed at d_{CuNi}= 4 nm. Increasing the
Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at
d_{CuNi}=13 nm. Our experiments give evidence for the pairing function
oscillations associated with a realization of the quasi-one dimensional
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.",0602448v1
2006-03-22,Electronic structure and exchange constants in magnetic semiconductors digital alloys: chemical and band-gap effects,"First-principles simulations have been performed for [001]-ordered Mn/Ge and
Mn/GaAs ""digital alloys"", focusing on the effects of i) a larger band-gap and
ii) a different semiconducting host on the electronic structure of the magnetic
semiconductors of interest. Our results for the exchange constants in Mn/Ge,
evaluated using a frozen-magnon scheme, show that a larger band-gap tends to
give a stronger nearest-neighbor ferromagnetic coupling and an overall enhanced
in-plane ferromagnetic coupling even for longer-ranged coupling constants. As
for the chemical effects on the exchange constants, we show that Mn/GaAs shows
a smaller nearest-neighbor ferromagnetic coupling than Mn/Ge, but exchange
constants for higher Mn-Mn distance show an overall increased ferromagnetic
behavior in Mn/GaAs. As a result, from the magnetic-coupling point of view, the
two systems behave on average rather similarly.",0603589v1
2006-04-06,Shot Noise of Spin-Decohering Transport in Spin-Orbit Coupled Nanostructures,"We generalize the scattering theory of quantum shot noise to include the full
spin-density matrix of electrons injected from a spin-filtering or
ferromagnetic electrode into a quantum-coherent nanostructure governed by
various spin-dependent interactions. This formalism yields the spin-resolved
shot noise power for different experimental measurement setups--with
ferromagnetic source and ferromagnetic or normal drain electrodes--whose
evaluation for the diffusive multichannel quantum wires with the Rashba (SO)
spin-orbit coupling shows how spin decoherence and dephasing lead to
substantial enhancement of charge current fluctuations (characterized by Fano
factors $> 1/3$). However, these processes and the corresponding shot noise
increase are suppressed in narrow wires, so that charge transport experiments
measuring the Fano factor $F_{\uparrow \to \uparrow \downarrow}$ in a
ferromagnet/SO-coupled-wire/paramagnet setup also quantify the degree of
phase-coherence of transported spin--we predict a one-to-one correspondence
between the magnitude of the spin polarization vector and $F_{\uparrow \to
\uparrow \downarrow}$.",0604187v2
2006-04-20,Suppression of ferromagnetism in CeSi_1.81 under temperature and pressure,"We have studied the pressure dependence of the magnetization of single
crystalline CeSi_1.81. At ambient pressure ferromagnetism develops below T_C =
9.5 Below ~ 5 K an additional shoulder in low-field hysteresis loops and a
metamagnetic crossover around 4 T suggest the appearance of an additional
magnetic modulation to the ferromagnetic state. The suppression of the magnetic
order in CeSi_1.81 as function of temperature at ambient pressure and as
function of pressure at low temperature are in remarkable qualitative
agreement. The continuous suppression of the ordered moment at p ~ 13.1 kbar
suggests the existence of a ferromagnetic quantum critical point in this
material.",0604470v1
2006-04-27,Ferromagnetic - spin glass transition induced by pressure in the geometrically frustrated pyrochlore (Tb$_{1-x}$La$_x$)$_2$Mo$_2$O$_7$,"We have studied (Tb$_{1-x}$La$_x$)$_2$Mo$_2$O$_7$ pyrochlores by neutron
diffraction and $\mu$SR at ambient and under applied pressure. Substitution of
Tb for La expands the lattice and induces a change from a spin-glass like state
({\itshape x}=0) to a non collinear ferromagnet ({\itshape x}=0.2). In the
ferromagnetic structure, the Tb moments orient close to their local anisotropy
axis as for an ordered spin ice, while the Mo moments orient close to the net
moment. The $\mu$SR dynamical relaxation rate shows a cusp-like peak at the
Curie temperature T$_C$ and a broad anomaly at T$^\star$$<$T$_C$, suggesting a
second transition of local or dynamical nature. Under pressure, the long range
order breaks down and a spin glass-like state is recovered. The whole set of
data provide a microscopic picture of the spin correlations and fluctuations in
the region of the ferromagnetic-spin glass threshold.",0604627v1
2006-05-07,Phase Diagrams of Ferromagnet-Superconductor Multilayers with Misaligned Exchange Fields,"We study the influence of misalignment of the ferromagnetic exchange field on
the equilibrium properties of hybrid structures, composed of superconducting
(S) and ferromagnetic (F) parts. In particular, we study numerically the
superconducting critical temperature Tc in F-S-F trilayers and in F-S-F-S-F
Josephson junctions as a function of the misalignment angle theta of the
ferromagnetic magnetization. We discuss the corresponding phase diagrams for
these hybrid structures. For the Josephson junctions, a transition between the
zero-phase and the pi-phase ground state as a function of theta takes place
under certain conditions. Within the quasiclassical Green's function technique
in the diffusive limit, we introduce a fast and effective method for
calculating Tc in such multilayer structures.",0605172v1
2006-05-21,High-temperature ferromagnetism of $sp$ electrons in narrow impurity bands: Application to CaB$_6$,"Ferromagnetism with high Curie temperature $T_c$, well above room
temperature, and very small saturation moment has been reported in various
carbon and boron systems. It is argued that the magnetization must be very
inhomogeneous with only a small fraction of the sample ferromagnetically
ordered. It is shown that a possible source of high $T_c$ within the
ferromagnetic regions is itinerant electrons occupying a narrow impurity band.
Correlation effects do not reduce the effective interaction which enters the
Stoner criterion in the same way as in a bulk band. It is also shown how, in
the impurity band case, spin wave excitations may not be effective in lowering
$T_c$ below its value given by Stoner theory. These ideas are applied to
CaB$_6$ and a thorough review of the experimental situation in this material is
given. It is suggested that the intrinsic magnetism of the B$_2$ and O$_2$
dimers might be exploited in suitable structures containing these elements.",0605495v1
2006-05-26,Carrier-induced ferromagnetism in n-type ZnMnAlO and ZnCoAlO thin films at room temperature,"The realization of semiconductors that are ferromagnetic above room
temperature will potentially lead to a new generation of spintronic devices
with revolutionary electrical and optical properties. Transition temperatures
in doped ZnO are high but, particularly for Mn doping, the reported moments
have been small. We show that by careful control of both oxygen deficiency and
aluminium doping the ferromagnetic moments measured at room temperature in
n-type ZnMnO and ZnCoO are close to the ideal values of 5mB and 3mB
respectively. Furthermore a clear correlation between the magnetisation per
transition metal ion and the ratio of the number of carriers to the number of
transition metal donors was established as is expected for carrier induced
ferromagnetism for both the Mn and Co doped films. The dependence of the
magnetisation on carrier density is similar to that predicted for the
transition temperature for a dilute magnetic semiconductor in which the
exchange between the transition metal ions is through the free carriers.",0605654v1
2006-05-26,Collective Modes and Skyrmion Excitations in Graphene SU(4) Quantum Hall Ferromagnets,"Graphene exhibits quantum Hall ferromagnetism in which an approximate SU(4)
symmetry involving spin and valley degrees of freedom is spontaneously broken.
We construct a set of integer and fractional quantum Hall states that break the
SU(4) spin/valley symmetry, and study their neutral and charged excitations.
Several properties of these ferromagnets can be evaluated analytically in the
SU(4) symmetric limit, including the full collective mode spectrum at integer
fillings. By constructing explicit wave functions we show that the lowest
energy skyrmion states carry charge $\pm 1$ for {\em any} integer filling, and
that skyrmions are the lowest energy charged excitations for graphene Landau
level index $|n| \le 3$. We also show that the skyrmion lattice states which
occur near integer filling factors support four gapless collective mode
branches in the presence of full SU(4) symmetry. Comparisons are made with the
more familiar SU(2) quantum Hall ferromagnets studied previously.",0605666v3
2006-05-29,Disturbance of spin equilibrium by current through the interface of noncollinear ferromagnets,"Boundary conditions are derived that determine the penetration of spin
current through an interface of two non-collinear ferromagnets with an
arbitrary angle between their magnetization vectors. We start from the
well-known transformation properties of an electron spin wave functions under
the rotation of a quantization axis. It allows directly find the connection
between partial electric current densities for different spin subbands of the
ferromagnets. No spin scattering is assumed in the near interface region, so
that spin conservation takes place when electron intersects the boundary. The
continuity conditions are found for partial chemical potential differences in
the situation. Spatial distribution of nonequilibrium electron magnetizations
is calculated under the spin current flowing through a contact of two
semi-infinite ferromagnets. The distribution describes the spin accumulation
effect by current and corresponding shift of the potential drop at the
interface. These effects appear strongly dependent on the relation between spin
contact resistances at the interface.",0605694v2
2006-06-20,Comparison between ab-initio and phenomenological modeling of the exchange couplings in diluted magnetic semiconductors: the case of $Zn_{1-x}Cr_{x}Te$,"Using a recently developed semi-analytical method (Self-Consistent Local RPA
or SC-LRPA) we study the stability of the ferromagnetic phase in diluted
magnetic systems where the exchange coupling between magnetic impurities are of
RKKY form. A short discussion of the relevance of these calculations with
respect to the ferromagnetism observed in diluted ferromagnetic materials is
provided. Then, within a two step approach, we study ferromagnetism in
$Zn_{1-x}Cr_{x}Te$. In the first step of our study, we calculate the magnetic
couplings between Mn impurities within the LDA. In the second step, we
diagonalize the resulting effective Heisenberg Hamiltonian using the SC-LRPA.
We also compare, when available, our calculations with Monte Carlo simulations
and experimental measurements.",0606523v1
2006-06-20,Magnetic Percolation and the Phase Diagram of the Disordered RKKY model,"We consider ferromagnetism in spatially randomly located magnetic moments, as
in a diluted magnetic semiconductor, coupled via the carrier-mediated indirect
exchange RKKY interaction. We obtain via Monte Carlo the magnetic phase diagram
as a function of the impurity moment density $n_{i}$ and the relative carrier
concentration $n_{c}/n_{i}$. As evidenced by the diverging correlation length
and magnetic susceptibility, the boundary between ferromagnetic (FM) and
non-ferromagnetic (NF) phases constitutes a line of zero temperature critical
points which can be viewed as a magnetic percolation transition. In the dilute
limit, we find that bulk ferromagnetism vanishes for $n_{c}/n_{i}>.1$. We also
incorporate the local antiferromagnetic direct superexchange interaction
between nearest neighbor impurities, and examine the impact of a damping factor
in the RKKY range function.",0606532v2
2006-07-11,Density of Yang-Lee zeros for the Ising ferromagnet,"The densities of Yang-Lee zeros for the Ising ferromagnet on the $L\times L$
square lattice are evaluated from the exact grand partition functions
($L=3\sim16$). The properties of the density of Yang-Lee zeros are discussed as
a function of temperature $T$ and system size $L$. The three different classes
of phase transitions for the Ising ferromagnet, first-order phase transition,
second-order phase transition, and Yang-Lee edge singularity, are clearly
distinguished by estimating the magnetic scaling exponent $y_h$ from the
densities of zeros for finite-size systems. The divergence of the density of
zeros at Yang-Lee edge in high temperatures (Yang-Lee edge singularity), which
has been detected only by the series expansion until now for the square-lattice
Ising ferromagnet, is obtained from the finite-size data. The identification of
the orders of phase transitions in small systems is also discussed using the
density of Yang-Lee zeros.",0607257v1
2006-08-01,Josephson current in a superconductor-ferromagnet junction with two non-collinear magnetic domains,"We study the Josephson effect in a
superconductor--ferromagnet--superconductor (SFS) junction with ferromagnetic
domains of non-collinear magnetization. As a model for our study we consider a
diffusive junction with two ferromagnetic domains along the junction. The
superconductor is assumed to be close to the critical temperature $T_c$, and
the linearized Usadel equations predict a sinusoidal current-phase relation. We
find analytically the critical current as a function of domain lengths and of
the angle between the orientations of their magnetizations. As a function of
those parameters, the junction may undergo transitions between 0 and $\pi$
phases. We find that the presence of domains reduces the range of junction
lengths at which the $\pi$ phase is observed. For the junction with two domains
of the same length, the $\pi$ phase totally disappears as soon as the
misorientation angle exceeds $\pi/2$. We further comment on possible
implication of our results for experimentally observable 0--$\pi$ transitions
in SFS junctions.",0608009v3
2006-08-24,Observation of standard spin-switch effects in F/S/F trilayers with a strong ferromagnet,"We have measured the superconducting transition temperature T_c of F/S/F
trilayers using Permalloy (Py=Ni_84 Fe_16) as a strongly polarized
ferromagnetic material. For a parallel (P) or anti-parallel (AP) alignment of
the magnetization directions of the outer ferromagnets, we observe a T_c
difference as large as 20 mK, with a stronger suppression of superconductivity
in the P state than in the AP state. This behavior is opposite to the recent
observations of Rusanov et al., Phys. Rev. B 73, 060505 (2006) in Py/Nb/Py
trilayers, but is consistent with earlier results on trilayers with Ni or CuNi
alloy as the ferromagnetic material.",0608545v1
2006-09-13,Tunneling currents in ferromagnetic systems with multiple broken symmetries,"SHORTENED ABSTRACT: A system exhibiting multiple simultaneously broken
symmetries offers the opportunity to influence physical phenomena such as
tunneling currents by means of external control parameters. In this paper, we
consider the broken SU(2) (internal spin) symmetry of ferromagnetic systems
coexisting with \textit{i)} the broken U(1) symmetry of superconductors and
\textit{ii)} the broken spatial inversion symmetry induced by a Rashba term in
a spin-orbit coupling Hamiltonian. In order to study the effect of these broken
symmetries, we consider tunneling currents that arise in two different systems;
tunneling junctions consisting of non-unitary spin-triplet ferromagnetic
superconductors and junctions consisting of ferromagnets with spin-orbit
coupling.",0609314v2
2006-09-14,Role of coexisting ferromagnetic and antiferromagnetic phases on the magnetocaloric effect in metamagnetic Tb2Ni2Sn,"We report the anomalous magnetocaloric behavior in the polycrystalline
compound Tb2Ni2Sn. The magnetization measurements show that this compound shows
multiple magnetic transitions, which are attributed to the coexistence of
ferromagnetic and antiferromagnetic phases at low temperatures. With increase
in field and temperature, the compound undergoes a metamagnetic transition to a
ferromagnetic state. In the temperature range where the antiferromagnetic phase
is dominant, it exhibits inverse (negative) magnetocaloric effect. At
temperatures close to the Neel temperature, the compound shows positive
magnetocaloric effect. Below the critical field needed for the metamagnetic
transition, the temperature variation of the magnetocaloric effect is seen to
be correlated with the ferromagnetic fraction.",0609335v2
2006-09-20,Ferromagnetism below 10 K in Mn doped BiTe,"Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.",0609519v1
2006-10-03,Enhancement of ferromagnetism by nickel doping in the 112 cobaltite EuBaCo2O5.50,"The study of the ordered oxygen deficient perovskite EuBaCo2-xNixO5.50 shows
that the doping of cobalt sites by nickel induces a strong ferromagnetic
component at low temperature in the antiferromagnetic matrix of EuBaCo2O5.50.
This system exhibits indeed phase separation, i.e. consists of ferromagnetic
domains embedded in the antiferromagnetic matrix of EuBaCo2O5.50. Besides, a
magnetic transition is observed for the first time at 40K in the undoped and
nickel doped phases, which can be attributed to the ferromagnetic ordering of
the Eu3+ moments below this temperature. Moreover sharp ultra magnetization
multisteps are observed below 5K, characteristic of motion of domain walls in a
strong pinning system and very different from any metamagnetic transition.",0610064v1
2006-10-10,Spin-transfer in an open ferromagnetic layer: from negative damping to effective temperature,"Spin-transfer is a typical spintronics effect that allows a ferromagnetic
layer to be switched by spin-injection. Most of the experimental results about
spin transfer are described on the basis of the Landau-Lifshitz-Gilbert
equation of the magnetization, in which additional current-dependent damping
factors are added, and can be positive or negative. The origin of the damping
can be investigated further by performing stochastic experiments, like one shot
relaxation experiments under spin-injection in the activation regime of the
magnetization. In this regime, the N\'eel-Brown activation law is observed
which leads to the introduction of a current-dependent effective temperature.
In order to justify the introduction of these counterintuitive parameters
(effective temperature and negative damping), a detailed thermokinetic analysis
of the different sub-systems involved is performed. We propose a thermokinetic
description of the different forms of energy exchanged between the electric and
the ferromagnetic sub-systems at a Normal/Ferromagnetic junction. The
corresponding Fokker Planck equations, including relaxations, are derived. The
damping coefficients are studied in terms of Onsager-Casimir transport
coefficients, with the help of the reciprocity relations. The effective
temperature is deduced in the activation regime.",0610264v1
2006-10-12,Universal Scaling Behavior of Anomalous Hall Effect and Anomalous Nernst Effect in Itinerant Ferromagnets,"Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in a variety of
ferromagnetic metals including pure metals, oxides, and chalcogenides, are
studied to obtain unified understandings of their origins. We show a universal
scaling behavior of anomalous Hall conductivity $\sigma_{xy}$ as a function of
longitudinal conductivity $\sigma_{xx}$ over five orders of magnitude, which is
well explained by a recent theory of the AHE taking into account both the
intrinsic and extrinsic contributions. ANE is closely related with AHE and
provides us with further information about the low-temperature electronic state
of itinerant ferromagnets. Temperature dependence of transverse Peltier
coefficient $\alpha_{xy}$ shows an almost similar behavior among various
ferromagnets, and this behavior is in good agreement quantitatively with that
expected from the Mott rule.",0610324v1
2006-10-16,Inelastic scattering in ferromagnetic and antiferromagnetic metal spintronics,"We use a ferromagnetic voltage probe model to study the influence of
inelastic scattering on giant magnetoresistance and current-induced torques in
ferromagnetic and antiferromagnetic metal spin valves. The model is based on
the Green's function formulation of transport theory and represents
spin-dependent and spin-independent inelastic scatterers by interior voltage
probes that are constrained to carry respectively no charge current and no spin
or charge current. We find that giant magnetoresistance and spin transfer
torques in ferromagnetic metal spin valve structures survive arbitrarily strong
spin-independent inelastic scattering, while the recently predicted analogous
phenomena in antiferromagnetic metal spin valves are partially suppressed. We
use toy-model numerical calculations to estimate spacer layer thickness
requirements for room temperature operation of antiferromagnetic metal spin
valves.",0610417v1
2006-10-31,Spin-transfer torque in magnetic multilayer nanopillars,"We consider a quasi one-dimensional configuration consisting of two small
pieces of ferromagnetic material separated by a metallic one and contacted by
two metallic leads. A spin-polarized current is injected from one lead. Our
goal is to investigate the correlation induced between the magnetizations of
the two ferromagnets by spin-transfer torque. This torque results from the
interaction between the magnetizations and the spin polarization of the
current. We discuss the dynamics of a single ferromagnet, the extension to the
case of two ferromagnets, and give some estimates for the parameters based on
experiments.",0610878v1
2006-11-01,A review of the electronic and magnetic properties of tetrahedrally bonded half-metallic ferromagnets,"The emergence of the field of spintronics brought half-metallic ferromagnets
to the center of scientific research. A lot of interest was focused on newly
created transition-metal pnictides (such as CrAs) and chalcogenides (such as
CrTe) in the metastable zinc-blende lattice structure. These compounds were
found to present the advantage of high Curie temperature values in addition to
their structural similarity to semiconductors. Significant theoretical activity
has been devoted to the study of the electronic and magnetic properties of
these compounds in an effort to achieve a better control of their experimental
behaviour in realistic applications. This review is devoted to an overview of
the studies of these compounds, with emphasis on theoretical results, covering
their bulk properties (electronic structure, magnetism, stability of the
zinc-blende phase, stability of ferromagnetism) as well as low-dimensional
structures (surfaces, interfaces, nanodots and transition-metal delta-doped
semiconductors) and phenomena that can possibly destroy the half-metallic
property, like structural distortions or defects.",0611006v1
2006-11-02,Order from Disorder in Graphene Quantum Hall Ferromagnet,"Valley-polarized quantum Hall states in graphene are described by a
Heisenberg O(3) ferromagnet model, with the ordering type controlled by the
strength and sign of valley anisotropy. A mechanism resulting from electron
coupling to strain-induced gauge field, giving leading contribution to the
anisotropy, is described in terms of an effective random magnetic field aligned
with the ferromagnet z axis. We argue that such random field stabilizes the XY
ferromagnet state, which is a coherent equal-weight mixture of the $K$ and $K'$
valley states. Other implications such as the Berezinskii-Kosterlitz-Thouless
ordering transition and topological defects with half-integer charge are
discussed.",0611062v1
2006-11-07,Phase diagram of the $p$-spin-interacting spin glass with ferromagnetic bias and a transverse field in the infinite-$p$ limit,"The phase diagram of the $p$-spin-interacting spin glass model in a
transverse field is investigated in the limit $p \to \infty$ under the presence
of ferromagnetic bias. Using the replica method and the static approximation,
we show that the phase diagram consists of four phases: Quantum paramagnetic,
classical paramagnetic, ferromagnetic, and spin-glass phases. We also show that
the static approximation is valid in the ferromagnetic phase in the limit $p
\to \infty$ by using the large-$p$ expansion. Since the same approximation is
already known to be valid in other phases, we conclude that the obtained phase
diagram is exact.",0611168v2
2006-11-09,Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets,"We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05
films to their magnetic properties. The formation of ferromagnetic nanometer
sized inclusions in a defect free Ge matrix fabricated by low temperature
molecular beam epitaxy is observed down to substrate temperatures T_S as low as
70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron
energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions
as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount
of these precipitates decreases with decreasing T_S. Magnetometry of the films
containing precipitates reveals distinct temperature ranges: Between the
characteristic ferromagnetic transition temperature of Mn_5Ge_3 at
approximately room temperature and a lower, T_S dependent blocking temperature
T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3
precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates
with blocked magnetic moments is observed. At the lowest temperatures, the
films show features characteristic for a metastable state.",0611241v1
2006-11-24,Magnetic and transport properties of a one dimensional frustrated t-J model for vanadate nanotubes,"We propose a one-dimensional model consisting of a chain with a t-J
Hamiltonian coupled to a Heisenberg chain in a frustrated geometry to describe
the appearance of the ferromagnetic phase which has been experimentally
observed in vanadate nanotubes. This model contains a mechanism of frustration
suppressed by doping suggested by L. Krusin-Elbaum, et al. [Nature 431, 672
(2004)]. We study, using numerical techniques in small clusters, the relation
between magnetic order and transport properties in the proposed model, and we
perform a detailed comparison of the physical properties of this model with
those of the ferromagnetic Kondo lattice model. For this comparison, a number
of results for the latter model, obtained using the same numerical techniques,
will be provided to complement those results already available in the
literature. We conclude that it does not appear to be a true ferromagnetic
order in the proposed model, but rather an incommensurate ferrimagnetic one,
and contrary to what happens in the ferromagnetic Kondo lattice model,
electronic transport is somewhat suppressed by this ferrimagnetic order.",0611603v2
2007-01-06,Sequential tunneling and shot noise in ferromagnet/normal-metal/ferromagnet double tunnel junctions,"The tunneling through a ferromagnet/normal metal/ferromagnet double junction
in the Coulomb blockade regime is studied, assuming that the spin relaxation
time of electron in the central metallic island is sufficiently large. Using
the master equation, the current, the tunnel magnetoresistance (TMR), and the
current noise spectrum have been calculated for devices of different
parameters. It was shown that the interplay between spin and charge
correlations strongly depends on the asymmetry of measured device. The charge
correlation makes both the chemical potential shift, which describes the spin
accumulation in the central island, and the TMR oscillated with the same period
as the Coulomb staircase in current-voltage characteristics. This effect is
smeared by the temperature. The spin correlation may cause an enhancement of
noise at finite frequencies, while the zero frequency noise is still always
sub-poissonian. The gate voltage causes an oscillation of not only conductance,
but also TMR and noise.",0701123v1
2007-01-11,Bulk ferromagnetism and large changes in photoluminescence intensity by magnetic field in $β$-Ga$_2$O$_3$,"In this letter we report observation of room temperature ferromagnetism in
bulk Ga$_2$O$_3$ . We also observe large (10-60%) increase/decrease in
photoluminescence. In the red(700 nm wavelength)/blue(500 nm), with the
application of small magnetic field(0.4 Tesla). We argue, that ferromagnetism
occurs entirely due to chains of oxygen(O(3) sites, Fig. 5) vacancies. We
propose a simple model to explain, origin and location of moment, formation of
ferromagnetic dislocation needles, and strong increase/decrease ofred/blue
photoluminescence intensity with magnetic field.",0701232v1
2007-01-29,Ferromagnetic 0-pi Josephson junctions,"We present a study on low-$T_c$
superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions.
SIFS junctions have gained considerable interest in recent years because they
show a number of interesting properties for future classical and quantum
computing devices. We optimized the fabrication process of these junctions to
achieve a homogeneous current transport, ending up with high-quality samples.
Depending on the thickness of the ferromagnetic layer and on temperature, the
SIFS junctions are in the ground state with a phase drop either 0 or $\pi$. By
using a ferromagnetic layer with variable step-like thickness along the
junction, we obtained a so-called 0-$\pi$ Josephson junction, in which 0 and
$\pi$ ground states compete with each other. At a certain temperature the 0 and
$\pi$ parts of the junction are perfectly symmetric, i.e. the absolute critical
current densities are equal. In this case the degenerate ground state
corresponds to a vortex of supercurrent circulating clock- or counterclockwise
and creating a magnetic flux which carries a fraction of the magnetic flux
quantum $\Phi_0$.",0701693v2
2007-01-29,Intrinsic anomalous Hall effect in ferromagnetic metals studied by the multi d-orbital tight-binding model,"To elucidate the origin of anomalous Hall effect (AHE) in ferromagnetic
transition metals, we study the intrinsic AHE based on a multi-orbital
(xz,yz)-tight-binding model. We find that a large anomalous velocity comes from
the off-diagonal (inter-orbital) hopping. By this reason, the present model
shows a large intrinsic anomalous Hall conductivity (AHC) which is compatible
with typical experimental values in ferromagnets [100-1000 [1/\Omega cm]],
without necessity to assume a special band structure at the Fermi level. In
good metals where resistivity \rho is small, the intrinsic AHC is constant
(dissipation-less) as found by Karplus and Luttinger. In bad metals, however,
we find that the AHC is proportional to \rho^{-2} when \hbar/2\tau is larger
than the minimum band-splitting measured from the Fermi level. This crossover
behavior of the intrinsic AHE, which was first derived in J. Phys. Soc. Jpn. 63
(1994) 2627, is recently observed in various ferromagnetic metals universally
by A. Asamitsu et al. We also stress that the present (xz,yz)-tight binding
model shows a huge spin Hall effect in a paramagnetic state.",0701696v2
1998-11-25,Dynamical Generation of the Primordial Magnetic Field by Ferromagnetic Domain Walls,"The spontaneous generation of uniform magnetic condensate in $QED_3$ gives
rise to ferromagnetic domain walls at the electroweak phase transition. These
ferromagnetic domain walls are caracterized by vanishing effective surface
energy density avoiding, thus, the domain wall problem. Moreover we find that
the domain walls generate a magnetic field $B \simeq 10^{24} Gauss$ at the
electroweak scale which account for the seed field in the so called dynamo
mechanism for the cosmological primordial magnetic field. We find that the
annihilation processes of walls with size $R \simeq 10^5 Km$ could release an
energy of order $10^{52} erg$ indicating the invisible ferromagnetic walls as
possible compact sources of Gamma Ray Bursts.",9811221v1
2000-02-04,Magnetic instability of quark matter,"Spontaneous magnetization of quark liquid is examined. It is pointed out that
quark liquid has potential to be ferromagnetic at rather low densities.",0002014v1
2005-03-01,Large Magnetic Moments of Arsenic-Doped Mn Clusters and their Relevance to Mn-Doped III-V Semiconductor Ferromagnetism,"We report electronic and magnetic structure of arsenic-doped manganese
clusters from density-functional theory using generalized gradient
approximation for the exchange-correlation energy. We find that arsenic
stabilizes manganese clusters, though the ferromagnetic coupling between Mn
atoms are found only in Mn$_2$As and Mn$_4$As clusters with magnetic moments 9
$\mu_B$ and 17 $\mu_B$, respectively. For all other sizes, $x=$ 3, 5-10,
Mn$_x$As clusters show ferrimagnetic coupling. It is suggested that, if grown
during the low temperature MBE, the giant magnetic moments due to ferromagnetic
coupling in Mn$_2$As and Mn$_4$As clusters could play a role on the
ferromagnetism and on the variation observed in the Curie temperature of
Mn-doped III-V semiconductors.",0503009v1
2007-02-23,Quantum annealing of the random-field Ising model by transverse ferromagnetic interactions,"We introduce transverse ferromagnetic interactions, in addition to a simple
transverse field, to quantum annealing of the random-field Ising model to
accelerate convergence toward the target ground state. The conventional
approach using only the transverse-field term is known to be plagued by slow
convergence when the true ground state has strong ferromagnetic characteristics
for the random-field Ising model. The transverse ferromagnetic interactions are
shown to improve the performance significantly in such cases. This conclusion
is drawn from the analyses of the energy eigenvalues of instantaneous
stationary states as well as by the very fast algorithm of Bethe-type
mean-field annealing adopted to quantum systems. The present study highlights
the importance of a flexible choice of the type of quantum fluctuations to
achieve the best possible performance in quantum annealing. The existence of
such flexibility is an outstanding advantage of quantum annealing over
simulated annealing.",0702214v1
2007-05-01,Criticality in inhomogeneous magnetic systems: Application to quantum ferromagnets,"We consider a $\phi^4$-theory with a position-dependent distance from the
critical point. One realization of this model is a classical ferromagnet
subject to non-uniform mechanical stress. We find a sharp phase transition
where the envelope of the local magnetization vanishes uniformly. The
first-order transition in a quantum ferromagnet also remains sharp. The
universal mechanism leading to a tricritical point in an itinerant quantum
ferromagnet is suppressed, and in principle one can recover a quantum critical
point with mean-field exponents. Observable consequences of these results are
discussed.",0705.0152v2
2007-05-14,Nanoscale ferromagnetism in non-magnetic doped semiconductors,"While ferromagnetism at relatively high temperatures is seen in diluted
magnetic semiconductors such as Ga_(1-x)Mn_(x)As, doped semiconductors without
magnetic ions have not shown evidence for ferromagnetism. Using a generalized
disordered Hubbard model designed to characterize hydrogenic centers in
semiconductors, we find that such systems may also exhibit a ferromagnetic
ground state, at least on the nanoscale. This is found most clearly in a regime
inaccessible to bulk systems, but attainable in quantum dots as well as
heterostructures. We present numerical results demonstrating the occurrence of
high spin ground states in both lattice and positionally disordered systems. We
examine how the magnetic phases are affected by characteristics of real doped
semiconductors, such as positional disorder and electron-hole asymmetry.",0705.2038v3
2007-05-17,Ferromagnetism in nanoscale BiFeO3,"A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room
temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40
nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization
(~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops,
however, exhibit exchange bias as well as vertical asymmetry which could be
because of spin pinning at the boundaries between ferromagnetic and
antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the
calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit
characteristic features at the magnetic transition point. These features
establish formation of a true ferromagnetic-ferroelectric system with a
coupling between the respective order parameters in nanoscale BiFeO_3.",0705.2498v1
2007-06-12,Josephson current in a superconductor -- ferromagnet -- superconductor junction with in-plane ferromagnetic domains,"We study a diffusive superconductor--ferromagnet--superconductor (SFS)
junction with in-plane ferromagnetic domains. Close to the superconducting
transition temperature, we describe the proximity effect in the junction with
the linearized Usadel equations. We find that properties of such a junction
depend on the size of the domains relative to the magnetic coherence length. In
the case of large domains, the junction exhibits transitions to the $\pi$
state, similarly to a single-domain SFS junction. In the case of small domains,
the magnetization effectively averages out, and the junction is always in the
zero state, similarly to a superconductor--normal metal--superconductor (SNS)
junction. In both those regimes, the influence of domain walls may be
approximately described as an effective spin-flip scattering. We also study the
inhomogeneous distribution of the local current density in the junction. Close
to the 0--$\pi$ transitions, the directions of the critical current may be
opposite in the vicinity of the domain wall and in the middle of the domains.",0706.1638v1
2007-06-21,Quantum and thermal fluctuations in a two-dimensional correlated band ferromagnet -- Goldstone-mode preserving investigation with self-energy and vertex corrections,"Ferromagnetism in the t-t' Hubbard model is investigated on a square lattice.
Correlation effects in the form of self-energy and vertex corrections are
systematically incorporated within a spin-rotationally-symmetric scheme which
explicitly preserves the Goldstone mode and is therefore in accord with the
Mermin-Wagner theorem. Interplay of band dispersion and correlation effects on
ferromagnetic-state stability are highlighted with respect to both long- and
short-wavelength fluctuations, which are shown to have substantially different
behaviour. Our approach provides a novel understanding of the enhancement of
ferromagnetism near van Hove filling for t'~0.5 in terms of strongly suppressed
saddle-point contribution to the destabilizing exchange part of spin stiffness.
Finite-temperature electron spin dynamics is investigated directly in terms of
spectral-weight transfer across the Fermi energy due to electron-magnon
coupling. Relevant in the context of recent magnetization measurements on
ultrathin films, the role of strong thermal spin fluctuations in low dimensions
is highlighted, in the anisotropy-stabilized ordered state, by determining the
thermal decay of magnetization and T_c within a renormalized spin-fluctuation
theory.",0706.3088v1
2007-06-21,Itinerant ferromagnetism in the multiorbital Hubbard model: a dynamical mean-field study,"In order to resolve the long-standing issue of how the itinerant
ferromagnetism is affected by the lattice structure and Hund's coupling, we
have compared various three-dimensional lattice structures in the single- and
multiorbital Hubbard models with the dynamical mean-field theory with an
improved quantum Monte Carlo algorithm that preserves the spin-SU(2) symmetry.
The result indicates that {\it both} the lattice structure and the d-orbital
degeneracy are essential for the ferromagnetism in the parameter region
representing a transition metal. Specifically, (a) Hund's coupling, despite the
common belief, is important, which is here identified to come from
particle-hole scatterings, and (b) the ferromagnetism is a correlation effect
(outside the Stoner picture) as indicated from the band-filling dependence.",0706.3109v1
2007-06-22,Visualization of ferromagnetic domains in TbNi$_2$B$_2$C and ErNi$_2$B$_2$C single crystals: Weak ferromagnetism and its coexistence with superconductivity,"The magnetic flux structure in the basal plane, (001), of single crystals of
superconducting (R = Er) and non-superconducting (R = Tb) RNi$_2$B$_2$C was
studied by high resolution Bitter decoration at temperatures below $T_c$
(superconducting transition) and/or $T_N$ (antiferromagnetic transition). For
both materials two sets of domain boundaries, in \{110\} and \{100\} planes,
were observed. The temperature ranges in which the \{100\} domain boundaries
were observed in TbNi$_2$B$_2$C and ErNi$_2$B$_2$C coincide with the weak
ferromagnetic (WFM) ordering in these materials. On the other hand, the \{110\}
twin boundaries - the antiferromagnetic domain boundaries - were observed in
both compounds below $T_N$. The possibility of interpretation of \{100\}
boundaries as Bloch domain walls in the weakly ferromagnetic phase, for $T <
T_{WFM} < T_N$ (TbNi$_2$B$_2$C) or $T < T_{WFM} < T_N < T_c$ (ErNi$_2$B$_2$C)
is discussed.",0706.3340v1
2007-06-25,Odd-frequency Pairs and Josephson Current through a Strong Ferromagnet,"We study Josephson current in superconductor / diffusive ferromagnet
/superconductor junctions by using the recursive Green function method. When
the exchange potential in a ferromagnet is sufficiently large as compared to
the pair potential in a superconductor, an ensemble average of Josephson
current is much smaller than its mesoscopic fluctuations. The Josephson current
vanishes when the exchange potential is extremely large so that a ferromagnet
is half-metallic. Spin-flip scattering at junction interfaces drastically
changes the characteristic behavior of Josephson current. In addition to
spin-singlet Cooper pairs, equal-spin triplet pairs penetrate into a half
metal. Such equal-spin pairs have an unusual symmetry property called
odd-frequency symmetry and carry the Josephson current through a half metal.
The penetration of odd-frequency pairs into a half metal enhances the low
energy quasiparticle density of states, which could be detected experimentally
by scanning tunneling spectroscopy. We will also show that odd-frequency pairs
in a half metal cause a nonmonotonic temperature dependence of the critical
Josephson current.",0706.3542v2
2007-06-26,Magnetic confinement of the superconducting condensate in superconductor/ferromagnet hybrid composites,"The influence of an inhomogeneous magnetic field on the magnetoresistance of
thin Al films, used in different superconductor/ferromagnet hybrids, has been
investigated. Two contrasting magnetic textures with out-of-plane magnetization
are explored, namely (i) a plain film in a multidomain state and (ii) an array
of micro-sized dots. The stray fields of the ferromagnetic structures confine
the superconducting condensate and, accordingly, modify the condition for the
nucleation of superconductivity. By switching between different magnetic states
of the ferromagnet, this confinement can be tuned at will, hereby reversibly
changing the dependence of the critical temperature Tc on an external magnetic
field H. In particular, the continuous evolution from a conventional linear
Tc(H) dependence with a single maximum to a reentrant superconducting phase
boundary with multiple Tc peaks has been demonstrated.",0706.3803v1
2007-07-04,Ferromagnetic behaviour in the strongly interacting two-component Bose gas,"We investigate the low temperature behaviour of the integrable 1D
two-component spinor Bose gas using the thermodynamic Bethe ansatz. We find
that for strong coupling the characteristics of the thermodynamics at low
temperatures are quantitatively affected by the spin ferromagnetic states,
which are described by an effective ferromagnetic Heisenberg chain. The free
energy, specific heat, susceptibility and local pair correlation function are
calculated for various physical regimes in terms of temperature and interaction
strength. These thermodynamic properties reveal spin effects which are
significantly different than those of the spinless Bose gas. The zero-field
susceptibility for finite strong repulsion exceeds that of a free spin
paramagnet. The critical exponents of the specific heat $c_v \sim T^{1/2}$ and
the susceptibility $\chi \sim T^{-2}$ are indicative of the ferromagnetic
signature of the two-component spinor Bose gas. Our analytic results are
consistent with general arguments by Eisenberg and Lieb for polarized spinor
bosons.",0707.0613v2
2007-07-10,Vortex rings in ferromagnets,"Vortex ring solutions are presented for the Landau-Lifshitz equation, which
models the dynamics of a three-dimensional ferromagnet. The vortex rings
propagate at constant speed along their symmetry axis and are characterized by
the integer-valued Hopf charge. They are stable to axial perturbations, but it
is demonstrated that an easy axis anisotropy results in an instability to
perturbations which break the axial symmetry. The unstable mode corresponds to
a migration of spin flips around the vortex ring that leads to a pinching
instability and ultimately the collapse of the vortex ring. It is found that
this instability does not exist for an isotropic ferromagnet. Similarities
between vortex rings in ferromagnets and vortons in cosmology are noted.",0707.1383v1
2007-07-11,Spin-Dependent Ringing and Beats in a Quantum Dot System,"We report spin-dependent quantum coherent oscillations (ringing) and beats of
the total and spin currents flowing through a quantum dot with Zeeman split
levels. The spin dependent transport is calculated via nonequilibrium Green
function in the transient after a bias voltage is turned on at t=0. The dot is
coupled to two electrodes that can be ferromagnetic or nonmagnetic. In the
ferromagnetic case both parallel and antiparallel alignments are considered.
The coherent oscillation and beat frequencies are controlled via the Zeeman
energy E_Z. In particular, for E_Z=0 no beats are observed and the spin current
is zero for nonmagnetic leads. In the ferromagnetic case a finite spin current
is found for E_Z=0. The effects of temperature are also analyzed. We observe
that with increasing temperature the ringing response and the beats tend to
disappear. Additionally, the spin current goes to zero for nonmagnetic leads,
remaining finite in the ferromagnetic case. The tunnel magnetoresistance (TMR)
also reveals quantum coherent oscillations and beats, and it attains negative
values for small enough temperatures and short times.",0707.1631v2
2007-07-21,Ferromagnetism as a universal feature of nanoparticles of the otherwise nonmagnetic oxides,"Room-temperature ferromagnetism has been observed in the nanoparticles (7 -
30 nm dia) of nonmagnetic oxides such as CeO2, Al2O3, ZnO, In2O3 and SnO2. The
saturated magnetic moments in CeO_2 and Al_2O_3 nanoparticles are comparable to
those observed in transition metal doped wide band semiconducting oxides. The
other oxide nanoparticles show somewhat lower values of magnetization but with
a clear hysteretic behavior. Conversely, the bulk samples obtained by sintering
the nanoparticles at high temperatures in air or oxygen became diamagnetic. As
there were no magnetic impurities present, we assume that the origin of
ferromagnetism may be due to the exchange interactions between localized
electron spin moments resulting from oxygen vacancies at the surfaces of
nanoparticles. We suggest that ferromagnetism may be a universal characteristic
of nanopartilces of metal oxides",0707.3183v1
2007-08-02,Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature,"The alpha-beta magneto-structural phase transition in MnAs/GaAs(111)
epilayers is investigated by elastic neutron scattering. The in-plane parameter
of MnAs remains almost constant with temperature from 100 K to 420 K, following
the thermal evolution of the GaAs substrate. This induces a temperature
dependent biaxial strain that is responsible for an alpha-beta phase
coexistence and, more important, for the stabilization of the ferromagnetic
alpha-phase at higher temperature than in bulk. We explain the premature
appearance of the beta-phase at 275 K and the persistence of the ferromagnetic
alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase
diagram. It results that the biaxial strain in the hexagonal plane is the key
parameter to extend the ferromagnetic phase well over room temperature.",0708.0350v1
2007-08-08,"Magnetic properties of Gd_xY_{1-x}Fe_2Zn_{20}: dilute, large, $\textbf {S}$ moments in a nearly ferromagnetic Fermi liquid","Single crystals of the dilute, rare earth bearing, pseudo-ternary series,
Gd_xY_{1-x}Fe_2Zn_{20} were grown out of Zn-rich solution. Measurements of
magnetization, resistivity and heat capacity on Gd_xY_{1-x}Fe_2Zn_{20} samples
reveal ferromagnetic order of Gd^{3+} local moments across virtually the whole
series ($x \geq 0.02$). The magnetic properties of this series, including the
ferromagnetic ordering, the reduced saturated moments at base temperature, the
deviation of the susceptibilities from Curie-Weiss law and the anomalies in the
resistivity, are understood within the frame work of dilute, $\textbf {S}$
moments (Gd^{3+}) embedded in a nearly ferromagnetic Fermi liquid
(YFe_2Zn_{20}). The s-d model is employed to further explain the variation of
$T_{\mathrm{C}}$ with x as well as the temperature dependences of of the
susceptibilities.",0708.1170v1
2007-08-26,Weak ferromagnetism and spin glass state with nano-sized nickel carbide,"Ni3C nanoparticles of about 40 nm have been studied experimentally to exhibit
weak ferromagnetic (FM), spin-glass (SG) and paramagnetic (PM) properties. The
freezing temperature of the SG phase at zero applied field is determined as,
TF0 ~ 11.0 K. At T > TF0, a very weak ferromagnetism has been observed over a
PM background. The Curie temperature, TC, is shown to exceed 300 K and the
ferromagnetism at 300 K is determined as about 0.02 emu/g (~6.7*10^{-4}mu_B per
Ni3C formula unit) by subtracting the background paramagnetism. An anomalous
dip appears in the temperature dependent coercivity, HC(T), near the freezing
temperature, TF0. It reflects a distortedly reduced coercivity in the M(H)
hysteresis loop measured at T = TF0 with the applied sweeping field around H =
0. This is attributable to the exchange coupling effect between the SG and the
weak FM phases. The possible origin of the magnetic moments that account for
the observed FM, SG and PM properties is discussed.",0708.3468v2
2007-09-13,Ferromagnetism in 2p Light Element-Doped II-oxide and III-nitride Semiconductors,"II-oxide and III-nitride semiconductors doped by nonmagnetic 2p light
elements are investigated as potential dilute magnetic semiconductors (DMS).
Based on our first-principle calculations, nitrogen doped ZnO, carbon doped
ZnO, and carbon doped AlN are predicted to be ferromagnetic. The ferromagnetism
of such DMS materials can be attributed to a p-d exchange-like p-p coupling
interaction which is derived from the similar symmetry and wave function
between the impurity (p-like t_2) and valence (p) states. We also propose a
co-doping mechanism, using beryllium and nitrogen as dopants in ZnO, to enhance
the ferromagnetic coupling and to increase the solubility and activity.",0709.2059v1
2007-09-22,Quantum-Mechanically Induced Asymmetry in the Phase Diagrams of Spin-Glass Systems,"The spin-1/2 quantum Heisenberg model is studied in all spatial dimensions d
by renormalization-group theory. Strongly asymmetric phase diagrams in
temperature and antiferromagnetic bond probability p are obtained in dimensions
d \geq 3. The asymmetry at high temperatures approaching the pure ferromagnetic
and antiferromagnetic systems disappears as d is increased. However, the
asymmetry at low but finite temperatures remains in all dimensions, with the
antiferromagnetic phase receding to the ferromagnetic phase. A
finite-temperature second-order phase boundary directly between the
ferromagnetic and antiferromagnetic phases occurs in d \geq 6, resulting in a
new multicritical point at its meeting with the boundaries to the paramagnetic
phase. In d=3,4,5, a paramagnetic phase reaching zero temperature intervenes
asymmetrically between the ferromagnetic and reentrant antiferromagnetic
phases. There is no spin-glass phase in any dimension.",0709.3589v2
2007-10-22,Fe-doping-induced evolution of charge-orbital ordering in a bicritical-state manganite,"Impurity effects on the stability of a ferromagnetic metallic state in a
bicritical-state manganite, (La0.7Pr0.3)0.65Ca0.35MnO3, on the verge of
metal-insulator transition have been investigated by substituting a variety of
transition-metal atoms for Mn ones. Among them, Fe doping exhibits the
exceptional ability to dramatically decrease the ferromagnetic transition
temperature. Systematic studies on the magnetotransport properties and x-ray
diffraction for the Fe-doped crystals have revealed that charge-orbital
ordering evolves down to low temperatures, which strongly suppresses the
ferromagnetic metallic state. The observed glassy magnetic and transport
properties as well as diffuse phase transition can be attributed to the
phase-separated state where short-range charge-orbital-ordered clusters are
embedded in the ferromagnetic metallic matrix. Such a behavior in the Fe-doped
manganites form a marked contrast to the Cr-doping effects on
charge-orbital-ordered manganites known as impurity-induced collapse of
charge-orbital ordering.",0710.4069v1
2007-11-07,Soft x-ray magnetic circular dichroism study of Ca_1-xSr_xRuO_3 across the ferromagnetic quantum phase transition,"Ca_1-xSr_xRuO_3, which is ferromagnetic for Sr concentration x > 0.3, has
been studied by x-ray magnetic circular dichroism (XMCD) in Ru 3p and O 1s
core-level x-ray absorption. XMCD signals appear at x ~ 0.3 and monotonically
increases with x in the ferromagnetic phase. While the monotonic increase of
the XMCD signals with x is of a typical Stoner-type, the absence of appreciable
change in the spectral line shapes of both the Ru 3p and O 1s XMCD spectra
indicate that the itinerant-electron ferromagnetism in Ca_1-xSr_xRuO_3 is
influenced by strong electron correlation.",0711.1000v2
2007-12-10,Chirality tunneling and quantum dynamics for domain walls in mesoscopic ferromagnets,"We studied the quantum dynamics of ferromagnetic domain walls (topological
kink-type solitons) in one dimensional ferromagnetic spin chains. We show that
the tunneling probability does not depend on the number of spins in a domain
wall; thus, this probability can be large even for a domain wall containing a
large number of spins. We also predict that there is a strong interplay between
the tunneling of a wall from one lattice site to another (tunneling of the kink
coordinate) and the tunneling of the kink topological charge (so-called
chirality). Both of these elementary processes are suppressed for kinks in
one-dimensional ferromagnets with half-integer spin. The dispersion law (i.e.,
the domain wall energy versus momentum) is essentially different for chains
with either integer or half-integer spins. The predicted quantum effects could
be observed for mesoscopic magnetic structures, e.g., chains of magnetic
clusters, large-spin molecules, or nanosize magnetic dots.",0712.1392v1
2008-01-11,Melting of magnetic correlations in charge-orbital ordered La(0.5)Sr(1.5)MnO(4) : competition of ferro and antiferromagnetic states,"The magnetic correlations in the charge- and orbital-ordered manganite
La(0.5)Sr(1.5)MnO(4) have been studied by elastic and inelastic neutron
scattering techniques. Out of the well-defined CE-type magnetic structure with
the corresponding magnons a competition between CE-type and ferromagnetic
fluctuations develops. Whereas ferromagnetic correlations are fully suppressed
by the static CE-type order at low temperature, elastic and inelastic CE-type
correlations disappear with the melting of the charge-orbital order at high
temperature. In its charge-orbital disordered phase, La(0.5)Sr(1.5)MnO(4)
exhibits a dispersion of ferromagnetic correlations which remarkably resembles
the magnon dispersion in ferromagnetically ordered metallic perovskite
manganites.",0801.1787v1
2008-01-17,Unusual upper critical field of the ferromagnetic superconductor UCoGe,"We report upper critical field $B_{c2}(T)$ measurements on a
single-crystalline sample of the ferromagnetic superconductor UCoGe.
$B_{c2}(0)$ obtained for fields applied along the orthorhombic axes exceeds the
Pauli limit for $B \parallel a,b$ and shows a strong anisotropy $B_{c2}^{a}
\simeq B_{c2}^{b} \gg B_{c2} ^{c}$. This provide evidence for an equal spin
pairing state and a superconducting gap function of axial symmetry with point
nodes along the c axis, which is also the direction of the uniaxial
ferromagnetic moment $m_0 = 0.07 \mu_{B}$. An unusual curvature or kink is
observed in the temperature variation of $B_{c2}$, which possibly indicates
UCoGe is a two-band ferromagnetic superconductor.",0801.2628v1
2008-01-17,Exotic (anti)ferromagnetism in single crystals of Pr6Ni2Si3,"The ternary intermetallic compound Pr6Ni2Si3, is a member of a structure
series of compounds based on a triangular structure where the number of Pr
atoms in the prism cross section can be systematically varied. Pr6Ni2Si3
contains two distinct Pr lattice sites which result in complex interactions
between the magnetic ions. Extensive measurements of specific heat and
magnetization on single crystal samples indicate that Pr6Ni2Si3 orders with
both a ferromagnet and an antiferromagnet component, with ordering temperatures
of 39.6 K and ~ 32 K, respectively. The ferromagnetic component // c-axis is
accompanied by a large hysteresis, and the antiferromagnetic component,_|_
c-axis is accompanied by a spin-flop-type transition. More detailed
measurements, of the vector magnetization, indicate that the ferromagnetic and
the antiferromagnetic order appear independent of each other. These results not
only clarify the behavior of Pr6Ni2Si3 itself, but also of the other members of
the structure series, Pr5Ni2Si3 and Pr15Ni7Si10.",0801.2704v1
2008-01-24,Ferromagnet proximity effects and magnetoresistance of bilayer graphene,"A drastic modification of electronic band structure is predicted in bilayer
graphene when it is placed between two ferromagnetic insulators. Due to the
exchange interaction with the proximate ferromagnet, the electronic energy
dispersion in the graphene channel strongly depends on the magnetization
orientation of two ferromagnetic layers, $\mathbf{M_{1}}$ and $\mathbf{M_{2}}
$. While the parallel configuration $\mathbf{M_{1}}= \mathbf{M_{2}}$ leads to
simple spin splitting of both conduction and valence bands, an energy gap is
induced as soon as the angle $\theta$ between $\mathbf{M_{1}}$ and $%
\mathbf{M_{2}}$ becomes non-zero with the maximum achieved at $\theta=\pi$
(i.e., antiparallel alignment). Consequently, bilayer graphene may exhibit a
sizable magnetoresistive effect in the current-in-plane configuration. A rough
estimate suggests the resistance changes on the order of tens of percent at
room temperature. This effect is expected to become more pronounced as the
temperatures decreases.",0801.3829v2
2008-02-21,Extended Scaling for the high dimension and square lattice Ising Ferromagnets,"In the high dimension (mean field) limit the susceptibility and the second
moment correlation length of the Ising ferromagnet depend on temperature as
chi(T)=tau^{-1} and xi(T)=T^{-1/2}tau^{-1/2} exactly over the entire
temperature range above the critical temperature T_c, with the scaling variable
tau=(T-T_c)/T. For finite dimension ferromagnets temperature dependent
effective exponents can be defined over all T using the same expressions. For
the canonical two dimensional square lattice Ising ferromagnet it is shown that
compact ""extended scaling"" expressions analogous to the high dimensional limit
forms give accurate approximations to the true temperature dependencies, again
over the entire temperature range from T_c to infinity. Within this approach
there is no cross-over temperature in finite dimensions above which
mean-field-like behavior sets in.",0802.3011v1
2008-03-09,Doping-dependent Phase Diagram of LaO{\it M}As ({\it M}=V--Cu) and Electron-type Superconductivity near Ferromagnetic Instability,"By first-principles calculations, we present a doping-dependent phase diagram
of LaO{\it M}As ({\it M}=V--Cu) family. It is characterized as
antiferromagnetic semiconductor around LaOMnAs side and ferromagnetic metal
around LaOCoAs. Both LaOFeAs and LaONiAs, where superconductivity were
discovered, are located at the borderline of magnetic phases. Extensive Fermi
surface analysis suggests that the observed superconductivity is of
electron-type in its origin. We discuss possible pairing mechanisms in the
context of competing ferromagnetic phases found in this work and the
ferromagnetic spin fluctuations.",0803.1282v3
2008-03-29,Tunnel-barrier-enhanced dc voltage signals induced by magnetization dynamics in magnetic tunnel junctions,"We theoretically study the recently observed tunnel-barrier-enhanced dc
voltage signals generated by magnetization precession in magnetic tunnel
junctions. While the spin pumping is suppressed by the high tunneling
impedance, two complimentary processes are predicted to result in a sizable
voltage generation in ferromagnet (F)|insulator (I)|normal-metal (N) and F|I|F
junctions, with one ferromagnet being resonantly excited. Magnetic dynamics in
F|I|F systems induces a robust charge pumping, translating into voltage in open
circuits. In addition, dynamics in a single ferromagnetic layer develops
longitudinal spin accumulation inside the ferromagnet. A tunnel barrier then
acts as a nonintrusive probe that converts the spin accumulation into a
measurable voltage. Neither of the proposed mechanisms suffers from spin
relaxation, which is typically fast on the scale of the exponentially slow
tunneling rates. The longitudinal spin-accumulation buildup, however, is very
sensitive to the phenomenological ingredients of the spin-relaxation picture.",0803.4228v2
2008-04-02,Origin and control of high-temperature ferromagnetism in semiconductors,"The extensive experimental and computational search for multifunctional
materials has resulted in the development of semiconductor and oxide systems,
such as (Ga,Mn)N, (Zn,Cr)Te, and HfO2, which exhibit surprisingly stable
ferromagnetic signatures despite having a small or nominally zero concentration
of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and
the associated magnetooptical and magnetotransport functionalities, are
dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded
in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these
nanocrystals can be controlled by manipulating the charge state of Cr ions
during the epitaxy. The findings provide insight into the origin of
ferromagnetism in a broad range of semiconductors and oxides, and indicate
possible functionalities of these composite systems. Furthermore, they
demonstrate a bottom-up method for self-organized nanostructure fabrication
that is applicable to any system in which the charge state of a constituent
depends on the Fermi-level position in the host semiconductor.",0804.0322v1
2008-04-11,Room temperature soft ferromagnetism in the nanocrystalline form of YCo2 - a well-known bulk Pauli paramagnet,"The Laves phase compound, YCo2, is a well-known exchange-enahnced Pauli
paramagnet. We report here that, in the nanocrystalline form, this compound
interestingly is an itinerant ferromagnet at room temperature with a low
coercive-field. The magnitude of the saturation moment (about 1 Bohr-magneton
per formula unit) is large enough to infer that the ferromagnetism is not a
surface phenomenon in these nanocrystallites. Since these ferromagnetic
nanocrystallines are easy to synthesize with a stable form in air, one can
explore applications, particularly where hysteresis is a disadvantage.",0804.1926v2
2008-05-05,"Orbital degeneracy, Hund's coupling, and band ferromagnetism: effective quantum parameter, suppression of quantum corrections, and enhanced stability","An effective quantum parameter is obtained for the band ferromagnet in terms
of orbital degeneracy and Hund's coupling. This quantum parameter determines,
in analogy with 1/N for the generalized Hubbard model and 1/S for quantum spin
systems, the strength of quantum corrections to spin stiffness and spin-wave
energies. Quantum corrections are obtained by incorporating correlation effects
in the form of self-energy and vertex corrections within a
spin-rotationally-symmetric approach in which the Goldstone mode is explicitly
preserved order by order. It is shown that even a relatively small Hund's
coupling is rather efficient in strongly suppressing quantum corrections,
especially for large N, resulting in strongly enhanced stability of the
ferromagnetic state. This mechanism for the enhancement of ferromagnetism by
Hund's coupling implicitly involves a subtle interplay of lattice,
dimensionality, band dispersion, spectral distribution, and band filling
effects.",0805.0470v1
2008-05-20,A theory of ferromagnetism by Ettore Majorana,"We present and analyze in detail an unknown theory of ferromagnetism
developed by Ettore Majorana as early as the beginnings of 1930s, substantially
different in the methods employed from the well-known Heisenberg theory of 1928
(and from later formulations by Bloch and others). Similarly to this, however,
it describes successfully the main features of ferromagnetism, although the key
equation for the spontaneous mean magnetization and the expression for the
Curie temperature are different from those deduced in the Heisenberg theory
(and in the original phenomenological Weiss theory). The theory presented here
contains also a peculiar prediction for the number of nearest neighbors
required to realize ferromagnetism, which avoids the corresponding arbitrary
assumption made by Heisenberg on the basis of known (at that time) experimental
observations. Some applications of the theory (linear chain, triangular chain,
etc.) are, as well, considered.",0805.3057v1
2008-06-17,"Coexistence of ferromagnetism and superconductivity: the role of kinetic interactions, kinetic correlations, and external pressure","We use the Hubbard type model to describe the coexistence between
superconductivity (SC) and ferromagnetism (F). Our Hamiltonian contains
single-site and two-site interactions. All inter-site interactions will have
included the inter-site kinetic correlation: $<c_{i\sigma}^{+}c_{j\sigma}>$,
within the Hartree-Fock approximation. To obtain the SC transition temperature
$T_{SC}$ and Curie temperature $T_{C}$ we use the Green's functions method. The
numerical results show that the singlet SC is eliminated by F, but the triplet
SC is either enhanced or depleted by F, depending on the carrier concentration
and direction of a superconducting spin pair with respect to magnetization. The
kinetic correlation is capable of creating superconductivity. We find that the
ferromagnetism created by change of the bandwidth can coexist with singlet
superconductivity. In the case of triplet superconductivity the ferromagnetism
creates different critical SC temperatures for the $A_{1}$ and $A_{2}$ phase
(the pair's spin parallel and antiparallel to magnetization, respectively).",0806.2774v1
2008-08-04,Measuring entropy generated by spin-transfer,"An experimental protocol is presented that allows the entropy generated by
spin-transfer to be measured. The effect of a strong spin-polarized current
injected on a ferromagnetic nanostructure is investigated with focusing on the
quasi-static equilibrium states of a ferromagnetic single domain. The samples
are single contacted Ni nanowires obtained by electrodeposition in a nanoporous
template. The thermal susceptibility of the magnetoresistance is measured as a
function of the magnetic field for different values of the current injected
through the wire. This quantity is related to the thermal magnetic
susceptibility of the ferromagnetic wire through the anisotropic
magnetoresistance. The ferromagnetic entropy generated by the current injection
is deduced thanks to a thermodynamic Maxwell relation. This study shows that
the effect of the spin-transfer in our samples results in the generation of
incoherent excitations instead of rotation of the magnetization.",0808.0463v1
2008-08-14,Half-metallic ferromagnetism in binary compounds of alkali metals with nitrogen: Ab initio calculations,"The first-principles full-potential linearized augmented plane-wave method
based on density functional theory is used to investigate electronic structure
and magnetic properties of hypothetical binary compounds of I$^{A}$ subgroup
elements with nitrogen (LiN, NaN, KN and RbN) in assumed three types of
cristalline structure (rock salt, wurtzite and zinc-blende). We find that, due
to the spin polarized \textit{p} orbitas of N, all four compounds are
half-metallic ferromagnets with wide energy bandgaps (up to 2.0 eV). The
calculated total magnetic moment in all investigated compounds for all three
types of crystal structure is exactly 2.00 $\mu_{\text{B}}$ per formula unit.
The predicted half-metallicity is robust with respect to lattice-constant
contraction. In all the cases ferromagnetic phase is energetically favored with
respect to the paramagnetic one. The mechanism leading to half-metallic
ferromagnetism and synthesis possibilities are discussed.",0808.1951v2
2008-08-22,Ferromagnetism in transparent Mn(II)-doped indium tin oxide films prepared by sol-gel process,"We observe remarkably strong room temperature ferromagnetism (~1.5 Bohr
Magneton/Mn) in optically transparent Mn(II)-doped indium tin oxide (ITO)
films. The nanocrystalline films with average grain size 10-22 nm and thickness
150-350 nm are prepared by sol-gel coating technique on sodalime silica glass
substrate. The ferromagnetic property is, of course, weak for films deposited
on pure silica glass substrate. The structural parameters of the films appear
to be governing the magnetic property strongly which vary appreciably depending
on the substrate. The observation of room temperature ferromagnetism in
transparent conducting ITO films may find a plethora of applications in the
area of magneto-optics.",0808.3063v1
2008-08-27,Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbour interactions,"By using the method of density-matrix renormalization-group to solve the
different spin-spin correlation functions, the nearest-neighbouring
entanglement(NNE) and next-nearest-neighbouring entanglement(NNNE) of
one-dimensional alternating Heisenberg XY spin chain is investigated in the
presence of alternating nearest neighbour interactions of exchange couplings,
external magnetic fields and next-nearest neighbouring interactions. For
dimerized ferromagnetic spin chain, NNNE appears only above the critical
dimerized interaction, meanwhile, the dimerized interaction effects quantum
phase transition point and improves NNNE to a large value. We also study the
effect of ferromagnetic or antiferromagnetic next-nearest neighboring (NNN)
interactions on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction
increases and shrinks NNE below and above critical frustrated interaction
respectively, while the antiferromagnetic NNN interaction always decreases NNE.
The antiferromagnetic NNN interaction results to a larger value of NNNE in
comparison to the case when the NNN interaction is ferromagnetic.",0808.3686v1
2008-09-09,Sign reversal of ac Josephson current in a ferromagnetic Josephson junction,"The ac Josephson effect in a ferromagnetic Josephson junction, which is
composed of two superconductors separated by a ferromagnetic metal (FM), is
studied by a tunneling Hamiltonian and Green's function method. We obtain two
types of superconducting phase dependent current, i.e., Josephson current and
quasiparticle-pair-interference current (QPIC). These currents change their
signs with thickness of the FM layer due to the 0-$\pi$ transition
characteristic to the ferromagnetic Josephson junction. As a function of
applied voltage, the Josephson critical current shows a logarithmic divergence
called the Riedel peak at the gap voltage, while the QPIC shows a discontinuous
jump. The Riedel peak reverses due to the 0-$\pi$ transition and disappears
near the 0-$\pi$ transition point. The discontinuous jump in the QPIC also
represents similar behaviors to the Riedel peak. These results are in contrast
to the conventional ones.",0809.1470v2
2008-10-07,Interface Ferromagnetism in (110)-Oriented La0.7Sr0.3MnO3/SrTiO3 Ultrathin Superlattices,"We explore manganite interface magnetism in epitaxially grown
La0.7Sr0.3MnO3(LSMO)/SrTiO3 ultrathin superlattices (SL) along (110)
orientation. we show that robust ferromagnetism persists down to four
monolayers LSMO(MLs) (~1.1 nm in thickness), of which 50% Mn is at the
interface state. Above eight MLs, the magnetic moment is nearly saturated to
the theoretical value of 3.7u_B, with an estimated interface moment of 3.2u_B.
In comparison to (100)-oriented SLs which were previously shown to have a spin
canted ground state, (110)-oriented SLs exhibit stronger low-dimensional
ferromagnetism and better metallicity, suggesting a ferromagnetic interface
spin state well suited for all-oxide spintronic devices. The underlining
mechanism is qualitatively discussed.",0810.1309v2
2008-10-28,Nitrogen defects and ferromagnetism of Cr-doped AlN diluted magnetic semiconductor from first principles,"High Curie temperature of 900 K has been reported in Cr-doped AlN diluted
magnetic semiconductors prepared by various methods, which is exciting for
spintronic applications. It is believed that N defects play important roles in
achieving the high temperature ferromagnetism in good samples. Motivated by
these experimental advances, we use a full-potential density-functional-theory
method and supercell approach to investigate N defects and their effects on
ferromagnetism of (Al,Cr)N with N vacancies (V_N). Calculated results are in
agreement with experimental observations and facts of real Cr-doped AlN samples
and their synthesis. Our first-principles results are useful to elucidating the
mechanism for the ferromagnetism and exploring high-performance Cr-doped AlN
diluted magnetic semiconductors.",0810.5048v1
2008-11-13,Strong-disorder paramagnetic-ferromagnetic fixed point in the square-lattice +- J Ising model,"We consider the random-bond +- J Ising model on a square lattice as a
function of the temperature T and of the disorder parameter p (p=1 corresponds
to the pure Ising model). We investigate the critical behavior along the
paramagnetic-ferromagnetic transition line at low temperatures, below the
temperature of the multicritical Nishimori point at T*= 0.9527(1),
p*=0.89083(3). We present finite-size scaling analyses of Monte Carlo results
at two temperature values, T=0.645 and T=0.5. The results show that the
paramagnetic-ferromagnetic transition line is reentrant for T<T*, that the
transitions are continuous and controlled by a strong-disorder fixed point with
critical exponents nu=1.50(4) and eta=0.128(8), and beta = 0.095(5). This fixed
point is definitely different from the Ising fixed point controlling the
paramagnetic-ferromagnetic transitions for T>T*. Our results for the critical
exponents are consistent with the hyperscaling relation 2 beta/nu - eta = d - 2
= 0.",0811.2101v3
2008-11-28,Proximity-driven source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor voltage-biased Josephson junction,"We theoretically investigate an opportunity to implement a source of highly
spin-polarized ac current on the basis of superconductor/weak
ferromagnet/superconductor (SFS) voltage-biased junction in the regime of
essential proximity effect and calculate the current flowing through the probe
electrode tunnel coupled to the ferromagnetic interlayer region. It is shown
that while the polarization of the dc current component is generally small in
case of weak exchange field of the ferromagnet, there is an ac component of the
current in the system. This ac current is highly spin-polarized and entirely
originated from the non-equilibrium proximity effect in the interlayer. The
frequency of the current is controlled by the voltage applied to SFS junction.
We discuss a possibility to obtain a source of coherent ac currents with a
certain phase shift between them by tunnel coupling two probe electrodes at
different locations of the interlayer region.",0811.4659v1
2009-01-09,Critical Current Behavior in Josephson Junctions with the Weak Ferromagnet PdNi,"We have studied the variation of critical current in
Superconductor/Ferromagnet/Superconductor (S/F/S) Josephson Junctions as a
function of ferromagnet thickness using a weakly-ferromagnetic alloy Pd82Ni12.
Measurements were performed for the thickness range 32 to 100 nm, over which
the critical current density decreases by five orders of magnitude. The
critical current density oscillates with a period of 12.9 +/- 0.3 nm, and
decays over a characteristic length of 8.0 +/- 0.5 nm. There is no evidence of
a crossover to a slower decay, which might indicate the presence of long-range
spin-triplet pair correlations. We discuss possible reasons for their absence,
including the possibility of strong spin flip scattering in PdNi.",0901.1321v1
2009-01-10,Enhanced Ferromagnetic Ordering in GdBaCo$_{2}$O$_{5.5+δ}$ Films on SrTiO3 (001) Substrate,"The authors investigated the structure and properties of
GdBaCo$_{2}$O$_{5.5+\delta}$ thin films epitaxially grown on SrTiO$_{3}$ (001)
single crystal substrates. The thin films were found to have a notable remnant
magnetization above room temperature, which is much higher than that observed
in bulk material. Transmission electron microscopy and x-ray diffraction
patterns reveal that phase separation occurs in these films, and the phase
responsible for the enhanced ferromagnetic order is $a$-oriented. The enhanced
ferromagnetic order is attributed to the enhanced orbital order of Co$^{3+}$ in
CoO$_{5}$ pyramids, and the disappearance of ferromagnetic to antiferromagnetic
transition is explained the stabilization of higher spin state of Co$^{3+}$ in
CoO$_{6}$ octahedra.",0901.1388v1
2009-01-14,What is the Mechanism Underlying 3-D Heisenberg-like Ferromagnetism Across the Compositional Metal-Insulator Transition in La1-xCaxMnO3 (0.18 < xc < 0.22)?,"Detailed measurements of the magnetic and transport properties of the two
La1-xCaxMnO3 (x = 0.18, x = 0.20) single crystals straddling the compositional
metal-insulator transition boundary (0.18 < xc < 0.22) are summarized. The
analysis of magnetization/susceptibility data reveals the occurrence of a
second order/continuous ferromagnetic-paramagnetic phase transition described
not only by nearest neighbour, 3-D Heisenberg model exponents (gamma = 1.387,
beta = 0.365, delta = 4.783), but also with comparable values of the critical
amplitudes in both the insulating and the metallic samples. These results
support the assertion that double exchange cannot be the underlying mechanism
supporting ferromagnetism in this composition range, and arguments are
presented that the relevant interaction is ferromagnetic super exchange
modulated by proximity to the orbitally ordered to disordered transition.",0901.1926v1
2009-01-27,Ferromagnetism in armchair graphene nanoribbon,"Due to the weak spin-orbit interaction and the peculiar relativistic
dispersion in graphene, there are exciting proposals to build spin qubits in
graphene nanoribbons with armchair boundaries. However, the mutual interactions
between electrons are neglected in most studies so far and thus motivate us to
investigate the role of electronic correlations in armchair graphene nanoribbon
by both analytical and numerical methods. Here we show that the inclusion of
mutual repulsions leads to drastic changes and the ground state turns
ferromagnetic in a range of carrier concentrations. Our findings highlight the
crucial importance of the electron-electron interaction and its subtle
interplay with boundary topology in graphene nanoribbons. Furthermore, since
the ferromagnetic properties sensitively depends on the carrier concentration,
it can be manipulated at ease by electric gates. The resultant ferromagnetic
state with metallic conductivity is not only surprising from an academic
viewpoint, but also has potential applications in spintronics at nanoscale.",0901.4177v1
2009-02-02,Ferromagnetic Kondo Effect at Nanocontacts,"Magnetic impurities bridging nanocontacts and break junctions of nearly
magnetic metals may lead to permanent moments, analogous to the giant moments
well known in the bulk case. A numerical renormalization group (NRG) study
shows that, contrary to mean field based expectations, a permanent moment never
arises within an Anderson model, which invariably leads to strong Kondo
screening. By including in the model an additional ferromagnetic exchange
coupling between leads and impurity, the NRG may instead stabilize a permanent
moment through a ferromagnetic Kondo effect. The resulting state is a
rotationally invariant spin, which differs profoundly from mean field. A sign
inversion of the zero-bias anomaly and other spectroscopic signatures of the
switch from regular to ferromagnetic Kondo are outlined.",0902.0254v1
2009-04-17,Ferromagnetism and Electronic Structures of Nonstoichiometric Heusler-Alloy Fe_3-xMn_xSi Epilayers Grown on Ge(111),"For the study of ferromagnetic materials which are compatible with group-IV
semiconductor spintronics, we demonstrate control of the ferromagnetic
properties of Heusler-alloys Fe_3-xMn_xSi epitaxially grown on Ge(111) by
tuning the Mn composition x. Interestingly, we obtain L2_1-ordered structures
even for nonstoichiometric atomic compositions. The Curie temperature of the
epilayers with x ~ 0.6 exceeds 300 K. Theoretical calculations indicate that
the electronic structures of the nonstoichiometric Fe_3-xMn_xSi alloys become
half-metallic for 0.75 < x < 1.5. We discuss the possibility of
room-temperature ferromagnetic Fe_3-xMn_xSi/Ge epilayers with high spin
polarization.",0904.2610v1
2009-04-29,Magnetism in tunable quantum rings,"We have studied the spin structure of circular four-electron quantum rings
using tunable confinement potentials. The calculations were done using the
exact diagonalization method. Our results indicate that ringlike systems can
have oscillatory flips between ferromagnetic and antiferromagnetic behaviour as
a function of the magnetic field. Furthermore, at constant external magnetic
fields there were seen similar oscillatory changes between ferromagnetism and
antiferromagnetism when the system parameters were changed. Ackording to our
results, the magnetism of quantum rings could be tuned by system parameters.We
have studied the spin structure of circular four-electron quantum rings using
tunable confinement potentials. The calculations were done using the exact
diagonalization method. Our results indicate that ringlike systems can have
oscillatory flips between ferromagnetic and antiferromagnetic behaviour as a
function of the magnetic field. Furthermore, at constant external magnetic
fields there were seen similar oscillatory changes between ferromagnetism and
antiferromagnetism when the system parameters were changed. According to our
results, the magnetism of quantum rings could be tuned by system parameters.",0904.4580v3
2009-04-30,A microscopic model for current-induced switching of magnetization for half-metallic leads,"We study the behaviour of the magnetization in a half-metallic
ferromagnet/nonmagnetic insulator/ferromagnetic metal/paramagnetic metal
(FM1/NI/FM2/PM) tunnel junction. It is calculated self-consistently within the
nonequilibrium Keldysh formalism. The magnetic regions are treated as band
ferromagnets and are described by the single-band Hubbard model. We developed a
nonequilibrium spectral density approach to solve the Hubbard model
approximately in the switching magnet. By applying a voltage to the junction it
is possible to switch between antiparallel (AP) and parallel (P) alignment of
the magnetizations of the two ferromagnets. The transition from AP to P occurs
for positive voltages while the inverse transition from P to AP can be induced
by negative voltages only. This behaviour is in agreement with the Slonczewski
model of current-induced switching and appears self-consistently within the
model, i.e. without using half-classical methods like the
Landau-Lifshitz-Gilbert equation.",0904.4821v1
2009-05-04,Ferromagnetism in Carbon doped Zinc Oxide Systems,"We report spin polarized density functional calculations of ferromagnetic
properties of a series of ZnO clusters and solid containing one or two
substitutional carbon impurities. We analyze the eigen value spectra, spin
densities and molecular orbitals, and induced magnetic moments for ZnC,
Zn$_{2}$C, Zn$_{2}$OC, carbon substituted clusters Zn$_{n}$O$_{n}$ (n=3--10,
12) and ZnO solid. The results show that the doping induces magnetic moment of
the $\sim$2 $\mu_{B}$ in all the cases. All the systems with two carbon
impurities show ferromagnetic interaction except when the carbon atoms share
the same Zn atom as the nearest neighbor. This ferromagnetic interaction is
predominantly mediated via $\pi$ bonds in ring structures and through $\pi$ and
$\sigma$ bonds in three dimensional structure. The calculations also show that
the interaction is significantly enhanced in solid, bringing out the role of
dimensionality of Zn-O network connecting two carbon atoms.",0905.0366v1
2009-05-20,Coexistence of Weak Ferromagnetism and Ferroelectricity in the High Pressure LiNbO3-type Phase of FeTiO3,"We report the magnetic and electrical characteristics of a polycrystalline
specimen of FeTiO3 synthesized at high pressure that is isostructural with
acentric LiNbO3 (LBO). Piezoresponse force microscopy, optical second harmonic
generation, and magnetometry demonstrate that FeTiO3-II is ferroelectric at and
below room temperature and weakly ferromagnetic below ~120 K. These results
validate symmetry-based materials design criteria and first principles
calculations of coexistence between ferroelectricity and weak ferromagnetism in
a series of transition metal titanates crystallizing in the LBO structure. The
high-pressure form of FeTiO3 stands out as a rare example of a ferroelectric
exhibiting weak ferromagnetism generated by a Dzyaloshinskii-Moriya
interaction.",0905.3332v1
2009-08-05,Non-DMS related ferromagnetism in transition metal doped zinc oxide,"We review pitfalls in recent efforts to make a conventional semiconductor,
namely ZnO, ferromagnetic by means of doping with transition metal ions. Since
the solubility of those elements is rather low, formation of secondary phases
and the creation of defects upon low temperature processing can lead to
unwanted magnetic effects. Among others, ion implantation is a method of
doping, which is highly suited for the investigation of those effects. By
focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that
there are manifold sources for ferromagnetism in this material which can easily
be confused with the formation of a ferromagnetic diluted magnetic
semiconductor (DMS). We will focus on metallic as well as oxide precipitates
and the difficulties of their identification.",0908.0645v1
2009-08-09,Microscopic Model versus Systematic Low-Energy Effective Field Theory for a Doped Quantum Ferromagnet,"We consider a microscopic model for a doped quantum ferromagnet as a test
case for the systematic low-energy effective field theory for magnons and
holes, which is constructed in complete analogy to the case of quantum
antiferromagnets. In contrast to antiferromagnets, for which the effective
field theory approach can be tested only numerically, in the ferromagnetic case
both the microscopic and the effective theory can be solved analytically. In
this way the low-energy parameters of the effective theory are determined
exactly by matching to the underlying microscopic model. The low-energy
behavior at half-filling as well as in the single- and two-hole sectors is
described exactly by the systematic low-energy effective field theory. In
particular, for weakly bound two-hole states the effective field theory even
works beyond perturbation theory. This lends strong support to the quantitative
success of the systematic low-energy effective field theory method not only in
the ferromagnetic but also in the physically most interesting antiferromagnetic
case.",0908.1225v1
2009-08-27,Magnetic groundstates in a correlated two orbital Hubbard model,"We examine the orbital and magnetic order of the two orbital Hubbard model
within dynamical mean field theory. The model describes the low energy physics
of a partially filled $e_g$-band as can be found in some transition metal
compounds. The model shows antiferromagnetic as well as ferromagnetic phases.
For stabilizing ferromagnetism we find that Hund's coupling is particularly
important. Quarter filling represents a very special situation in the phase
diagram, where the coupling of spin, charge, and orbital degrees of freedom are
involved. Exactly at quarter filling we find a metal insulator transition (MIT)
between two almost fully polarized ferromagnetic states. This MIT can be tuned
by changing the local interaction strength and seems to be a first order
transition at zero temperature. Apart from these ferromagnetic states we were
also able to stabilize antiferromagnetic and charge ordered phases at quarter
filling, depending on the interaction parameters.",0908.3990v2
2009-08-27,Spontaneous spin current due to triplet superconductor--ferromagnet interfaces,"We examine the appearance of a spontaneous bulk spin current in a triplet
superconductor in contact with a metallic ferromagnet. The spin current results
from the spin-flip of Cooper pairs upon reflection from the interface with the
ferromagnet, and is shown to display strong similarities to the spontaneous
charge current in a Josephson junction. We express the spin current in terms of
the Andreev reflection coefficients, which are derived by the construction of
the quasiclassical scattering wavefunctions. The dependence of the spin current
upon a number of parameters is investigated, in particular the orientation of
the magnetic moment of the ferromagnet, the exchange splitting, the
temperature, and the orbital pairing state of the triplet superconductor.",0908.4065v2
2009-09-09,Magnetic phase diagram of a spin-1 condensate in two dimensions with dipole interaction,"Several new features arise in the ground-state phase diagram of a spin-1
condensate trapped in an optical trap when the magnetic dipole interaction
between the atoms is taken into account along with confinement and spin
precession. The boundaries between the regions of ferromagnetic and polar
phases move as the dipole strength is varied and the ferromagnetic phases can
be modulated. The magnetization of the ferromagnetic phase perpendicular to the
field becomes modulated as a helix winding around the magnetic field direction,
with a wavelength inversely proportional to the dipole strength. This
modulation should be observable for current experimental parameters in
$^{87}$Rb. Hence the much-sought supersolid state, with broken continuous
translation invariance in one direction and broken global U(1) invariance,
occurs generically as a metastable state in this system as a result of dipole
interaction. The ferromagnetic state parallel to the applied magnetic field
becomes striped in a finite system at strong dipolar coupling.",0909.1751v2
2009-10-07,Extremely Large and Anisotropic Upper Critical Field and the Ferromagnetic Instability in UCoGe,"Magnetoresistivity measurements with fine tuning of the field direction on
high quality single crystals of the ferromagnetic superconductor UCoGe show
anomalous anisotropy of the upper critical field H_c2. H_c2 for H // b-axis
(H_c2^b) in the orthorhombic crystal structure is strongly enhanced with
decreasing temperature with an S-shape and reaches nearly 20 T at 0 K. The
temperature dependence of H_c2^a shows upward curvature with a low temperature
value exceeding 30 T, while H_c2^c at 0 K is very small (~ 0.6 T). Contrary to
conventional ferromagnets, the decrease of the Curie temperature with
increasing field for H // b-axis marked by an enhancement of the effective mass
of the conduction electrons appears to be the origin of the S-shaped H_c2^b
curve. These results indicate that the field-induced ferromagnetic instability
or magnetic quantum criticality reinforces superconductivity.",0910.1157v1
2009-11-02,Double-Exchange Ferromagnetism and Orbital-Fluctuation-Induced Superconductivity in Cubic Uranium Compounds,"A double-exchange mechanism for the emergence of ferromagnetism in cubic
uranium compounds is proposed on the basis of a $j$-$j$ coupling scheme. The
idea is {\it orbital-dependent duality} of $5f$ electrons concerning itinerant
$\Gamma_8^-$ and localized $\Gamma_7^-$ states in the cubic structure. Since
orbital degree of freedom is still active in the ferromagnetic phase,
orbital-related quantum critical phenomenon is expected to appear. In fact,
odd-parity p-wave pairing compatible with ferromagnetism is found in the
vicinity of an orbital ordered phase. Furthermore, even-parity d-wave pairing
with significant odd-frequency components is obtained. A possibility to observe
such exotic superconductivity in manganites is also discussed briefly.",0911.0250v1
2009-11-02,Giant anomalous Hall resistivity of the room temperature ferromagnet Fe3Sn2 - a frustrated metal with the kagome-bilayer structure,"We have investigated magnetic and transport properties of the {\it
kagom\'{e}-bilayer} ferromagnet Fe$_{3}$Sn$_{2}$. A soft ferromagnetism and a
large anomalous Hall effect are observed. The saturated Hall resistivity of
Fe$_{3}$Sn$_{2}$ is 3.2 $\mu\Omega$cm at 300 K, which is almost 20 times higher
than that of typical itinerant-ferromagnets such as Fe and Ni. The anomalous
Hall coefficient $R_{{\rm s}}$ is 6.7$\times10^{-9}$ $\Omega$cm/G at 300 K,
which is three orders of magnitude larger than that of pure Fe. $R_{{\rm s}}$
obeys an unconventional scaling to the longitudinal resistivity, $\rho_{xx}$,
of $R_{{\rm s}} \propto \rho_{xx}^{3.3}$. Such a relationship cannot be
explained by the skew and/or side-jump mechanisms and indicates that the origin
of the anomalous Hall effect in the frustrated magnet Fe$_{3}$Sn$_{2}$ is
indeed extraordinary.",0911.0289v1
2009-11-13,Electrically driven magnetism on a Pd thin film,"Using first-principles density functional calculations we demonstrate that
ferromagnetism can be induced and modulated on an otherwise paramagnetic Pd
metal thin-film surface through application of an external electric field. As
free charges are either accumulated or depleted at the Pd surface to screen the
applied electric field there is a corresponding change in the surface density
of states. This change can be made sufficient for the Fermi-level density of
states to satisfy the Stoner criterion, driving a transition locally at the
surface from a paramagnetic state to an itinerant ferromagnetic state above a
critical applied electric field, Ec. Furthermore, due to the second-order
nature of this transition, the surface magnetization of the ferromagnetic state
just above the transition exhibits a substantial dependence on electric field,
as the result of an enhanced magnetoelectric susceptibility. Using a linearized
Stoner model we explain the occurrence of the itinerant ferromagnetism and
demonstrate that the magnetic moment on the Pd surface follows a square-root
variation with electric field consistent with our first-principles
calculations.",0911.2678v1
2009-11-22,Phase transition in a one-dimensional Ising ferromagnet at zero-temperature under Glauber dynamics with a synchronous updating mode,"In the past decade low-temperature Glauber dynamics for the one-dimensional
Ising system has been several times observed experimentally and occurred to be
one of the most important theoretical approaches in a field of molecular
nanomagnets. On the other hand, it has been shown recently that Glauber
dynamics with the Metropolis flipping probability for the zero-temperature
Ising ferromagnet under synchronous updating can lead surprisingly to the
antiferromagnetic steady state. In this paper the generalized class of Glauber
dynamics at zero-temperature will be considered and the relaxation into the
ground state, after a quench from high temperature, will be investigated. Using
Monte Carlo simulations and a mean field approach, discontinuous phase
transition between ferromagnetic and antiferromagnetic phases for a
one-dimensional ferromagnet will be shown.",0911.4242v3
2010-01-09,Correlation induced half-metallicity in a ferromagnetic single-layered compound: Sr$_2$CoO$_4$,"The electronic and magnetic properties of Sr$_2$CoO$_4$ compound have been
studied using $\emph{ab initio}$ electronic structure calculations. As opposed
to GGA calculation, which gives ferromagnetic metallic solution, GGA+$U$
calculations provide two kind of ferromagnetic solutions: (i) half-metallic and
(ii) metallic. The half-metallic solution is a ground state of the system and
the metallic one is a metastable state. The strong hybridization between Co
3$d$ and O 2$p$ orbitals decides the electronic and magnetic properties of the
compound. The total magnetic moment per formula unit is found to be $\sim$ 3
$\mu_B$ ($S$ = 3/2). Our calculations give the magnetocrystalline anisotropy
energy of $\sim$ 2.7 meV, which provides a good description of experimentally
observed large magnetocrystalline anisotropy. The Heisenberg exchange
parameters up to fourth nearest neighbours are also calculated. The mean-field
theory gives the $T_C$ = 887 K. The possible physical implications of the
ferromagnetic half-metallic ground state are also discussed.",1001.1405v1
2010-01-18,Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders,"Using the Density Matrix Renormalization Group and two-leg ladders, we
investigate an electronic two-orbital Hubbard model including plaquette
diagonal hopping amplitudes. Our goal is to search for regimes where charges
added to the undoped state form pairs, presumably a precursor of a
superconducting state.For the electronic density $\rho=2$, i.e. the undoped
limit, our investigations show a robust $(\pi,0)$ antiferromagnetic ground
state, as in previous investigations. Doping away from $\rho=2$ and for large
values of the Hund coupling $J$, a ferromagnetic region is found to be stable.
Moreover, when the interorbital on-site Hubbard repulsion is smaller than the
Hund coupling, i.e. for $U'<J$ in the standard notation of multiorbital Hubbard
models, our results indicate the coexistence of pairing tendencies and
ferromagnetism close to $\rho=2$. These results are compatible with previous
investigations using one dimensional systems. Although further research is
needed to clarify if the range of couplings used here is of relevance for real
materials, such as superconducting heavy fermions or pnictides, our theoretical
results address a possible mechanism for pairing that may be active in the
presence of short-range ferromagnetic fluctuations.",1001.3097v1
2010-01-19,Ground-state phase diagram of the two-dimensional t-J model,"The ground-state phase diagram of the two-dimensional t-J model is
investigated in the context of the tensor network algorithm in terms of the
graded Projected Entangled-Pair State representation of the ground-state wave
functions. There is a line of phase separation between the Heisenberg
anti-ferromagnetic state without hole and a hole-rich state. For both J=0.4t
and J=0.8t, a systematic computation is performed to identify all the competing
ground states for various dopings. It is found that, besides a possible
Nagaoka's ferromagnetic state, the homogeneous regime consists of four
different phases: one phase with charge and spin density wave order coexisting
with a p_x (p_y)-wave superconducting state, one phase with the symmetry mixing
of d+s-wave superconductivity in the spin-singlet channel and p_x (p_y)-wave
superconductivity in the spin-triplet channel in the presence of an
anti-ferromagnetic background, one superconducting phase with extended s-wave
symmetry, and one superconducting phase with p_x (p_y)-wave symmetry in a
ferromagnetic background.",1001.3343v1
2010-01-28,Possible Room Temperature Ferromagnetism in Hydrogenated Carbon Nanotubes,"We find that ferromagnetism can be induced in carbon nanotubes (CNTs) by
introducing hydrogen. Multiwalled CNTs grown inside porous alumina templates
contain a large density of defects resulting in significant hydrogen uptake
when annealed at high temperatures. This hydrogen incorporation produces
H-complex and adatom magnetism which generates a sizeable ferromagnetic moment
and a Curie temperature near Tc=1000 K. We studied the conditions for the
incorporation of hydrogen, the temperature-dependent magnetic behavior, and the
dependence of the ferromagnetism on the size of the nanotubes.",1001.5204v2
2010-03-01,Switchable Hardening of a Ferromagnet at Fixed Temperature,"The intended use of a magnetic material, from information storage to power
conversion, depends crucially on its domain structure, traditionally crafted
during materials synthesis. By contrast, we show that an external magnetic
field applied transverse to the preferred magnetization of a model disordered
uniaxial ferromagnet is an isothermal regulator of domain pinning. At elevated
temperatures, near the transition into the paramagnet, modest transverse fields
increase the pinning, stabilize the domain structure, and harden the magnet,
until a point where the field induces quantum tunneling of the domain walls and
softens the magnet. At low temperatures, tunneling completely dominates the
domain dynamics and provides an interpretation of the quantum phase transition
in highly disordered magnets as a localization/delocalization transition for
domain walls. While the energy scales of the rare earth ferromagnet studied
here restrict the effects to cryogenic temperatures, the principles discovered
are general and should be applicable to existing classes of highly anisotropic
ferromagnets with ordering at room temperature or above.",1003.0369v1
2010-03-05,Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Co(0001) trilayers,"Epitaxially grown multilayer systems offer the possibility to study the
influence of ferromagnetism on superconductivity in a new and controlled way.
In this paper, we explore how the superconducting properties of high quality,
epitaxially-grown superconductor/normal-metal/ferromagnet trilayers evolve as a
function of the exchange splitting in the ferromagnet, and the thickness of the
normal metal layer. We report results for Nb(110)/Au(111)/Co(0001), and make a
detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use
quantitative FFT analysis to confirm the existence of a long-period (2.1 nm)
oscillation in the superconducting transition temperature Tc as a function of
the Au-layer thickness tAu, for tAu>2 nm, and highlight an additional
short-period (0.76 nm) oscillation for tAu<3 nm in Nb/Au/Co. This short-period
oscillation can be explained in terms of a damped RKKY-like oscillation of the
spin-polarization in Au. The robustness of the long-period oscillation against
the substitution of Co for Fe suggests that it is intrinsic to the Au(111)
layer on Nb, and may represent a new form of quantum interference in very clean
trilayer systems.",1003.1181v1
2010-03-23,Intrinsic Room Temperature Ferromagnetism in Boron-doped ZnO,"We report room temperature ferromagnetism in boron-doped ZnO both
experimentally and theoretically. The single phase Zn1-xBxO films deposited
under high oxygen pressure by pulsed-laser deposition show ferromagnetic
behavior at room temperature. The saturation magnetization increases
monotonously from 0 to 1.5 emu/cm3 with the increasing of B component x from 0
to 6.8%. The first-principles calculations based on density functional theory
demonstrate that the ferromagnetism in B-doped ZnO originates from the induced
magnetic moments of oxygen atoms in the nearest neighbor sites to the B-Zn
vacancy pair. The calculated total magnetic moment increasing tendency with B
component is well consistent with experiments.",1003.4423v1
2010-04-05,The suppression of hidden order and onset of ferromagnetism in URu2Si2 via Re substitution,"Substitution of Re for Ru in the heavy fermion compound URu2Si2 suppresses
the hidden order transition and gives rise to ferromagnetism at higher
concentrations. The hidden order transition of URu(2-x)Re(x)Si2, tracked via
specific heat and electrical resistivity measurements, decreases in temperature
and broadens, and is no longer observed for x>0.1. A critical scaling analysis
of the bulk magnetization indicates that the ferromagnetic ordering temperature
and ordered moment are suppressed continuously towards zero at a critical
concentration of x = 0.15, accompanied by the additional suppression of the
critical exponents gamma and (delta-1) towards zero. This unusual trend appears
to reflect the underlying interplay between Kondo and ferromagnetic
interactions, and perhaps the proximity of the hidden order phase.",1004.0704v1
2010-04-30,Epitaxial integration of the intrinsic ferromagnetic semiconductor GdN with silicon technology,"A major challenge for the next generation of spintronics devices is the
implementation of ferromagnetic-semiconductor thin films as spin injectors and
detectors. Spin-polarised carrier injection cannot be accomplished efficiently
from metals, and coupled with the rarity of intrinsic ferromagnetic
semiconductors this has driven intensive study of diluted magnetic
semiconductors. Chief among these is the doped III-V compound (Ga,Mn)As. These
materials suffer from a number of drawbacks; they (i) require magnetic-ion
doping well above the solubility limit, and (ii) must be hole doped to above
the degenerate limit, preventing independent control of the carrier
concentration and charge sign. Here we demonstrate the first epitaxial growth
of a recently-characterised intrinsic ferromagnetic semiconductor, GdN, on
silicon substrates, providing an essential step on the way to integrate new
spintronics functionalities into Si-based technology. The films have been
characterised as regards their growth toward fully relaxed GdN, the density and
mobility of their carriers, and their magnetic behaviour.",1004.5428v1
2010-06-01,The superconducting ferromagnet UCoGe,"The correlated metal UCoGe is a weak itinerant ferromagnet with a Curie
temperature T_C = 3 K and a superconductor with a transition temperature T_s =
0.6 K. We review its basic thermal, magnetic - on the macro and microscopic
scale - and transport properties, as well as the response to high pressure. The
data unambiguously show that superconductivity and ferromagnetism coexist below
T_s = 0.6 K and are carried by the same 5f electrons. We present evidence that
UCoGe is a p-wave superconductor and argue that superconductivity is mediated
by critical ferromagnetic spin fluctuations.",1006.0065v1
2010-07-04,Transport Properties in Ferromagnetic Josephson Junction between Triplet Superconductors,"Charge and spin Josephson currents in a ballistic
superconductor-ferromagnet-superconductor junction with spin-triplet pairing
symmetry are studied using the quasiclassical Eilenberger equation. The gap
vector of superconductors has an arbitrary relative angle with respect to
magnetization of the ferromagnetic layer. We clarify the effects of the
thickness of ferromagnetic layer and magnitude of the magnetization on the
Josephson charge and spin currents. We find that 0-\pi transition can occur
except for the case that the exchange field and d-vector are in nearly
perpendicular configuration. We also show how spin current flows due to
misorientation between the exchange field and d-vector.",1007.0529v2
2010-07-05,Laser-induced Spin Dynamics in Metallic Multilayers,"Electronic excitations in a ferromagnet can trigger ultrafast spin dynamics
with potential applications in a speed increase in magnetic recording. The
project investigates ultrafast magnetization dynamics, which is driven in
metallic layers by ballistic hot electrons. In a ferromagnet these electrons
induce a change in the absolute value of the magnetization M through
spin-dependent scattering. If the electrons are spin-polarized, scattering at
the interface of a noble metal and a ferromagnet results in spin-transfer
torque and hence modifies the direction of M. To reveal the underlying
mechanisms, we study model systems, which are realized by layers of Au with its
large ballistic mean free path and Fe as an itinerant ferromagnet. We aim at
understanding ultrafast demagnetization and femtosecond all-optical generation
of spin transfer torque effects (excitation of hot electrons with a femtosecond
laser). The launched dynamics are probed by magneto-optics in a time-resolved
experiment.",1007.0726v1
2010-07-15,Full spin switch effect for the superconducting current in a superconductor/ferromagnet thin film heterostructure,"Superconductor/ferromagnet (S/F) proximity effect theory predicts that the
superconducting critical temperature of the F1/F2/S or F1/S/F2 trilayers for
the parallel orientation of the F1 and F2 magnetizations is smaller than for
the antiparallel one. This suggests a possibility of a controlled switching
between the superconducting and normal states in the S layer. Here, using the
spin switch design F1/F2/S theoretically proposed by Oh et al. [Appl. Phys.
Lett. 71, 2376 (1997)], that comprises a ferromagnetic bilayer separated by a
non-magnetic metallic spacer layer as a ferromagnetic component, and an
ordinary superconductor as the second interface component, we have successfully
realized a full spin switch effect for the superconducting current.",1007.2511v1
2010-08-03,Absence of weak antilocalization in ferromagnetic films,"We present magnetoresistance measurements performed on ultrathin films of
amorphous Ni and Fe. In these films the Curie temperature drops to zero at
small thickness, making it possible to study the effect of ferromagnetism on
localization. We find that non-ferromagnetic films are characterized by
positive magnetoresistance. This is interpreted as resulting from weak
antilocalization due to strong Bychkov-Rashba spin orbit scattering. As the
films become ferromagnetic the magnetoresistance changes sign and becomes
negative. We analyze our data to identify the individual contributions of weak
localization, weak antilocalization and anisotropic magnetoresistance and
conclude that the magnetic order suppresses the influence of spin-orbit effects
on localization phenomena in agreement with theoretical predictions.",1008.0456v1
2010-08-10,Transition from a ferromagnetic insulating to a ferromagnetic metallic state in nanoparticles of Nd0.8Sr0.2MnO3 : Study of the electronic - and magneto - transport properties,"A detailed investigation of the electronic - and magneto - transport
properties of Nd0.8Sr0.2MnO3 with the variation of grain size (down to 42 nm)
is presented here. Interestingly, we observe that the ferromagnetic insulating
state is suppressed and a metallic state is stabilized as the grain size of the
sample is reduced. As a result, metal insulator transition is observed in this
low doped manganite which is insulating in nature in its bulk form.
Destabilization of polaronic order in the ferromagnetic insulating state due to
enhanced surface disorder on grain size reduction has been attributed to this
effect. A phenomenological model has been proposed to represent the concept of
destabilization of polaron formation in the surface region of the nano grains.
Resistivity and magnetoresistance data have been carefully analyzed employing
different suitable models. Electrical third harmonic resistance has been
measured to directly probe the electrical nonlinearity in the samples.",1008.1693v1
2010-08-13,Unusual signatures of the ferromagnetic transition in the heavy Fermion compound UMn$_2$Al$_{20}$,"Magnetic susceptibility results for single crystals of the new cubic
compounds UT$_2$Al$_{20}$ (T=Mn, V, and Mo) are reported. Magnetization,
specific heat, resistivity, and neutron diffraction results for a single
crystal and neutron diffraction and inelastic spectra for a powder sample are
reported for UMn$_2$Al$_{20}$. For T = V and Mo, temperature independent Pauli
paramagnetism is observed. For UMn$_2$Al$_{20}$, a ferromagnetic transition is
observed in the magnetic susceptibility at $T_c$ = 20 K. The specific heat
anomaly at $T_c$ is very weak while no anomaly in the resistivity is seen at
$T_c$. We discuss two possible origins for this behavior of UMn$_2$Al$_{20}$:
moderately small moment itinerant ferromagnetism, or induced local moment
ferromagnetism.",1008.2235v1
2010-08-19,Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions,"We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb
superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson
junctions with high critical current densities, large normal resistance times
area products, high quality factors, and very good spatial uniformity. For
these junctions a transition from 0- to \pi-coupling is observed for a
thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The
magnetic field dependence of the \pi-coupled junctions demonstrates good
spatial homogeneity of the tunneling barrier and ferromagnetic interlayer.
Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane
anisotropy and large saturation magnetization, indicating negligible dead
layers at the interfaces. A careful analysis of Fiske modes provides
information on the junction quality factor and the relevant damping mechanisms
up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at
low frequencies, the damping is dominated by the finite surface resistance of
the junction electrodes at high frequencies. High quality factors of up to 30
around 200 GHz have been achieved. Our analysis shows that the fabricated
junctions are promising for applications in superconducting quantum circuits or
quantum tunneling experiments.",1008.3341v1
2010-08-23,Self-magnetic compensation and Exchange Bias in ferromagnetic Samarium systems,"For Sm(3+) ions in a vast majority of metallic systems, the following
interesting scenario has been conjured up for long, namely, a magnetic lattice
of tiny self (spin-orbital) compensated 4f-moments exchange coupled (and phase
reversed) to the polarization in the conduction band. We report here the
identification of a self-compensation behavior in a variety of ferromagnetic Sm
intermetallics via the fingerprint of a shift in the magnetic hysteresis (M-H)
loop from the origin. Such an attribute, designated as exchange bias in the
context of ferromagnetic/antiferromagnetic multilayers, accords these compounds
a potential for niche applications in spintronics. We also present results on
magnetic compensation behavior on small Gd doping (2.5 atomic percent) in one
of the Sm ferromagnets (viz. SmCu(4)Pd). The doped system responds like a
pseudo-ferrimagnet and it displays a characteristic left-shifted linear M-H
plot for an antiferromagnet.",1008.3779v1
2010-08-26,Modulation of the ferromagnetic insulating phase in Pr0.8Ca0.2MnO3 by Co substitution,"Ferromagnetic insulator Pr0.8Ca0.2Mn1-yCoyO3 (0 <= y <= 0.7) thin films were
epitaxially grown on (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (100) substrates by pulsed
laser deposition. To probe the ferromagnetic insulator state of hole-doped
manganites, the Co content dependences of the structural, magnetic, and
transport properties were studied. Variation of lattice constant by the
substitution of Co ions is well reproduced considering that divalent and
trivalent Co ions substitute for Mn ions at the perovskite B-sites. For 0 <= y
<= 0.3, the Curie temperature, saturation magnetization, and magnetoresistance
increase with increasing Co content, retaining the insulating properties.
Detailed analyses of transport and magnetic properties indicate the
contribution of both double exchange and superexchange interactions to the
appearance of the ferromagnetic insulating phase.",1009.1524v2
2010-09-14,Uncompensated magnetization and exchange-bias field in La$_{0.7}$Sr$_{0.3}$MnO$_3$/YMnO$_3$ bilayers: The influence of the ferromagnetic layer,"We studied the magnetic behavior of bilayers of multiferroic and nominally
antiferromagnetic o-YMnO$_3$ (375~nm thick) and ferromagnetic
La$_{0.7}$Sr$_{0.3}$MnO$_3$ and La$_{0.67}$Ca$_{0.33}$MnO$_3$ ($8 \ldots
225~$nm), in particular the vertical magnetization shift $M_E$ and exchange
bias field $H_E$ for different thickness and magnetic dilution of the
ferromagnetic layer at different temperatures and cooling fields. We have found
very large $M_E$ shifts equivalent to up to 100\% of the saturation value of
the o-YMO layer alone. The overall behavior indicates that the properties of
the ferromagnetic layer contribute substantially to the $M_E$ shift and that
this does not correlate straightforwardly with the measured exchange bias field
$H_E$.",1009.2619v1
2010-09-23,Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders,"Oxide based diluted magnetic semiconductor (DMS) materials have been a
subject of increasing interest due to reports of room temperature
ferromagnetism in several systems and their potential use in the development of
spintronic devices. However, concerns on the stability of the magnetic
properties of different DMS systems have been raised. Their magnetic moment is
often unstable, vanishing with a characteristic decay time of weeks or months,
which precludes the development of real applications. This paper reports on the
ferromagnetic properties of two-year-aged Ti1-xCoxO2-{\delta} reduced anatase
nanopowders with different Co contents (0.03<x<0.10). Aged samples retain
rather high values of magnetization, remanence and coercivity which provide
strong evidence for a quite preserved long-range ferromagnetic order. In what
concern Co segregation, some degree of metastability of the diluted Co doped
anatase structure could be inferred in the case of the sample with the higher
Co content.",1009.4671v1
2010-09-28,Role of non-collinear magnetization: from ferromagnetic nano wires to quantum rings,"We consider interaction effects related to a nonuniform magnetization in
ferromagnetic nanowires and their possible generalization to nanorings. First
we show that the electric current in a ferromagnetic nanowire with more than
one domain wall induces an exchange coupling between the walls mediated by the
spin-dependent interference of scattered carriers. This interaction reveals a
complex behavior as a function of mutual orientations and separation of the
domain walls, thus affecting the domain wall dynamics. Then we consider how the
theory should be modified in the case of a magnetized quantum ring. In this
case the situation is more complicated because the vortex and onion
magnetization states in the ring are not truly ferromagnetic.",1009.5688v1
2010-10-03,Long range proximity effect in La2/3Ca1/3MnO3 (LCMO)/(100)YBa2Cu3O7-delta (YBCO) ferromagnet/superconductor bilayers: Evidence for induced triplet superconductivity in the ferromagnet,"Scanning tunneling spectroscopy measurements conducted on epitaxially grown
bilayers of half-metallic ferromagnetic La2/3Ca1/3MnO3 (LCMO) on
superconducting (SC) (100)YBa2Cu3O7-delta (YBCO) reveal long-range penetration
of superconducting order into the LCMO. This anomalous proximity effect
manifests itself in the tunneling spectra measured on the LCMO layer as gaps
and zero bias conductance peaks. Remarkably, these proximity-induced spectral
features were observed for bilayers with LCMO thickness of up to 30 nm, an
order of magnitude larger than the expected ferromagnetic coherence length in
LCMO. We argue that this long-range proximity effect can be accounted for by
the formation of spin triplet pairing at the LCMO side of the bilayer due to
magnetic inhomogeneity at the interface or at domain walls. Possible symmetries
of the induced order parameter are discussed.",1010.0390v1
2010-11-19,"Interplay of antiferromagnetism, ferromagnetism and superconductivity in EuFe_2(As_1-xP_x)_2 single crystals","We report a systematic study on the influence of antiferromagnetic and
ferromagnetic phases of Eu^2+ moments on the superconducting phase upon doping
the As site by isovalent P, which acts as chemical pressure on EuFe_2As_2. Bulk
superconductivity with transition temperatures of 22 K and 28 K are observed
for x=0.16 and 0.20 samples respectively. The Eu ions order
antiferromagnetically for x<=0.13, while a crossover is observed for x>=0.22
whereupon the Eu ions order ferromagnetically. Density functional theory based
calculations reproduce the observed experimental findings consistently. We
discuss in detail the coexistence of superconductivity and magnetism in a tiny
region of the phase space and comment on the competition of ferromagnetism and
superconductivity in the title compound.",1011.4481v2
2010-12-02,Estimating the Hubbard repulsion sufficient for the onset of nearly-flat-band ferromagnetism,"We consider nearly-flat-band Hubbard models of a ferromagnet, that is the
models that are weak perturbations of those flat-band Hubbard models whose
ground state is ferromagnetic for any nonzero strength $U$ of the Hubbard
repulsion. In contrast to the flat-band case, in the nearly-flat-band case the
ground state, being paramagnetic for $U$ in a vicinity of zero, turns into a
ferromagnetic one only if $U$ exceeds some nonzero threshold value $U_{th}$. We
address the question whether $U_{th}$ of the considered models is in a physical
range, therefore we attempt at obtaining possibly good estimates of the
threshold value $U_{th}$. A rigorous method proposed by Tasaki is extended and
the resulting estimates are compared with small-system, finite-size scaling
results obtained for open- and periodic-boundary conditions. Contrary to
suggestions in literature, we find the latter conditions particularly useful
for our task.",1012.0443v1
2010-12-06,Room temperature ferromagnetism and anomalous Hall effect in Si$_{1-x}$Mn$_x$ ($x\approx 0.35$) alloys,"A detailed study of the magnetic and transport properties of Si$_{1-x}$Mn$_x$
($x\approx 0.35$) films is presented. We observe the anomalous Hall effect
(AHE) in these films up to room temperature. The results of the magnetic
measurements and the AHE data are consistent and demonstrate the existence of
long-range ferromagnetic (FM) order in the systems under study. A correlation
of the AHE and the magnetic properties of Si$_{1-x}$Mn$_x$ ($x\approx 0.35$)
films with their conductivity and substrate type is shown. A theoretical model
based on the idea of a two-phase magnetic material, in which molecular clusters
with localized magnetic moments are embedded in the matrix of a weak itinerant
ferromagnet, is discussed. The long-range ferromagnetic order at high
temperatures is mainly due to the Stoner enhancement of the exchange coupling
between clusters through thermal spin fluctuations (paramagnons) in the matrix.
Theoretical predictions and experimental data are in good qualitative
agreement.",1012.1172v1
2010-12-07,Magnetoelectric coupling at the interface of BiFeO3/La0.7Sr0.3MnO3 multilayers,"Electric-field controlled exchange bias in a heterostructure composed of the
ferromagnetic manganite La0.7Sr0.3MO3 and the ferroelectric antiferromagnetic
BiFeO3 has recently been demonstrated experimentally. By means of a microscopic
model Hamiltonian we provide a possible explanation of the origin of this
magnetoelectric coupling. We find, in agreement with experimental results, a
net ferromagnetic moment at the BiFeO3 interface. The induced ferromagnetic
moment is the result of the competition between the e_g-electrons double
exchange and the t_2g-spins antiferromagnetic superexchange that dominate in
bulk BiFeO3. The balance of these simultaneous ferromagnetic and
antiferromagnetic tendencies is strongly affected by the interfacial electronic
charge density which, in turn, can be controlled by the BiFeO3 ferroelectric
polarization.",1012.1448v1
2010-12-09,Spin-Currents and Spin-Pumping Forces for Spintronics,"A general definition of the Spintronics concept of spin-pumping is proposed
as generalized forces conjugated to the spin degrees of freedom in the
framework of the theory of mesoscopic non-equilibrium thermodynamics. It is
shown that at least three different kinds of spin-pumping forces and associated
spin-currents can be defined in the most simple spintronics system (the
Ferromagnetic/Non-Ferromagnetic metal interface). Furthermore, the generalized
force associated to the ferromagnetic collective variable is also introduced in
an equal footing, in order to describe the coexistence of the spin of the
conduction electrons (paramagnetic spins attached to $s$-band electrons) and
the ferromagnetic-order parameter. The dynamical coupling between these two
kinds of magnetic degrees of freedom is presented, and interpreted in terms of
spin-transfer effects.",1012.2083v1
2010-12-20,Conduction Electron Scattering and Spin-Flipping at Sputtered Co/Ni Interfaces,"Current-perpendicular-to-plane magnetoresistance (CPP-MR) measurements let us
quantify conduction electron scattering and spin-flipping at a sputtered
ferromagnetic/ferromagnetic (F1/F2 = Co/Ni) interface, with important
consequences for CPP-MR and spin-torque experiments with perpendicular
anisotropy. We use ferromagnetically coupled ([Ni/Co]xn)Ni multilayers, and
Py-based, symmetric double exchange-biased spin-valves (DEBSVs) containing
inserts of ferromagnetically coupled ([Co/Ni]xn)Co or ([Ni/Co]xn)Ni
multilayers, to derive Co/Ni interface specific resistances AR(Co/Ni)(Up) =
0.03 (+0.02)(-0.03) f-ohm-m^2 and AR(Co/Ni)(down) = 1.00 +/- 0.07 f-ohm-m^2,
and interface spin-flipping parameter delta(Co/Ni) = 0.35 +/- 0.05. The
specific resistances are consistent with our no-free-parameter calculations for
an interface thickness between 2 and 4 monolayers (ML) that is compatible with
expectations.",1012.4388v1
2011-01-05,"Non-thermal laser induced precession of magnetization in ferromagnetic semiconductor (Ga,Mn)As","Non-thermal laser induced spin excitations, recently discovered in
conventional oxide and metal ferromagnets, open unprecedented opportunities for
research and applications of ultrafast optical manipulation of magnetic
systems. Ferromagnetic semiconductors, and (Ga,Mn)As in particular, should
represent ideal systems for exploring this new field. Remarkably, the presence
of non-thermal effects has remained one of the outstanding unresolved problems
in the research of ferromagnetic semiconductors to date. Here we demonstrate
that coherent magnetization dynamics can be excited in (Ga,Mn)As non-thermally
by a transfer of angular momentum from circularly polarized femtosecond laser
pulses and by a combination of non-thermal and thermal effects due to a
transfer of energy from laser pulses. The thermal effects can be completely
suppressed in piezo-electrically controlled samples. Our work is based on
pump-and-probe measurements in a large set of (Ga,Mn)As epilayers and on
systematic analysis of circular and linear magneto-optical coefficients. We
provide microscopic theoretical interpretation of the experimental results.",1101.1049v1
2011-01-10,A story of high-temperature ferromagnetism in semiconductors,"The comprehensive search for multifunctional materials has resulted in the
discovery of semiconductors and oxides showing ferromagnetic features
persisting to room temperature. In this tutorial review the methods of
synthesis of these materials, as well as the application of element-specific
nano-analytic tools, particularly involving synchrotron radiation and electron
microscopy, are described and shown to reveal the presence of nano-scale phase
separations. Various means to control the aggregation of magnetic cations are
discussed together with the mechanisms accounting for ferromagnetism of either
condensed or diluted magnetic semiconductors. Finally, the question of whether
high temperature ferromagnetism is possible in semiconductors not containing
magnetic ions is touched upon.",1101.1981v1
2011-01-28,"Pairing, Ferromagnetism, and Condensation of a normal spin-1 Bose gas","We theoretically study the stability of a normal, spin disordered, homogenous
spin-1 Bose gas against ferromagnetism, pairing, and condensation through a
Random Phase Approximation which includes exchange (RPA-X). Repulsive
spin-independent interactions stabilize the normal state against both
ferromagnetism and pairing, and for typical interaction strengths leads to a
direct transition from an unordered normal state to a fully ordered single
particle condensate. Atoms with much larger spin-dependent interaction may
experience a transition to a ferromagnetic normal state or a paired superfluid,
but, within the RPA-X, there is no instability towards a normal state with
spontaneous nematic order. We analyze the role of the quadratic Zeeman effect
and finite system size.",1101.5639v1
2011-02-01,Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases,"We analyze the properties of a single impurity immersed in a Fermi sea. At
positive energy and scattering lengths, we show that the system possesses a
well-defined but metastable excitation, the repulsive polaron, and we calculate
its energy, quasiparticle residue and effective mass. From a thermodynamic
argument we obtain the number of particles in the dressing cloud, illustrating
the repulsive character of the polaron. Identifying the important 2- and 3-body
decay channels, we furthermore calculate the lifetime of the repulsive polaron.
The stability conditions for the formation of fully spin polarized
(ferromagnetic) domains are then examined for a binary mixture of atoms with a
general mass ratio. Our results indicate that mass imbalance lowers the
critical interaction strength for phase-separation, but that very short
quasiparticle decay times will complicate the experimental observation of
itinerant ferromagnetism. Finally, we present the spectral function of the
impurity for various coupling strengths and momenta.",1102.0121v2
2011-02-27,Phase Transition of Generalized Ferromagnetic Potts Model - Effect of Invisible States -,"We investigate the nature of the phase transition of the ferromagnetic Potts
model with invisible states. The ferromagnetic Potts model with invisible
states can be regarded as straightforward extension of the standard
ferromagnetic Potts model. The invisible states contribute the entropy, however
they do not affect the internal energy. They also do not change the symmetry
which breaks at the transition temperature. The invisible states stimulate a
first-order phase transition. We confirm that the first-order phase transition
with spontaneous $q$-fold symmetry breaking for $q=2,3$, and 4 takes place even
on two-dimensional lattice by Monte Carlo simulation. We also find that the
transition temperature decreases and the latent heat increases as the number of
invisible states increases.",1102.5475v1
2011-03-01,Josephson effect and spin-triplet pairing correlations in SF1F2S junctions,"We study theoretically the Josephson effect and pairing correlations in
planar SF1F2S junctions that consist of conventional superconductors (S)
connected by two metallic monodomain ferromagnets (F1 and F2) with transparent
interfaces. We obtain both spin-singlet and -triplet pair amplitudes and the
Josephson current-phase relations for arbitrary orientation of the
magnetizations using the self-consistent solutions of Eilenberger equations in
the clean limit and for a moderate disorder in ferromagnets. We find that the
long-range spin-triplet correlations cannot prevail in symmetric junctions with
equal ferromagnetic layers. Surprisingly, the long-range spin-triplet
correlations give the dominant second harmonic in the Josephson current-phase
relation of highly asymmetric SF1F2S junctions. The effect is robust against
moderate disorder and variations in the layers thickness and exchange energy of
ferromagnets.",1103.0293v2
2011-03-05,Three-dimensional quantum phase diagram of the exact ground states of a mixture of two species of spin-1 Bose gases with interspecies spin exchange,"We find nearly all the exact ground states of a mixture of two species of
spin-1 atoms with both interspecies and intraspecies spin exchanges in absence
of a magnetic field. The quantum phase diagram in the three-dimensional
parameter space and its two-dimensional cross sections are described. The
boundaries where the ground states are either continuous or discontinuous are
determined, with the latter identified as where quantum phase transitions take
place. The two species are always disentangled if the interspecies spin
coupling is ferromagnetic or zero. Quantum phase transitions occur when the
interspecies spin coupling varies between antiferromagtic and zero or
ferromagnetic while the two intraspecies spin couplings both remain
ferromagnetic. On the other hand, by tuning the interspecies spin coupling from
zero to antiferromagnetic and then back to zero, one can circumvent the quantum
phase transition due to sign change of the intraspecies spin coupling of a
single species, which is spin-decoupled with the other species with
ferromagnetic intraspecies spin coupling. Overall speaking, interplay among
interspecies and two intraspecies spin exchanges significantly enriches quantum
phases of spinor atomic gases.",1103.1023v1
2011-03-08,Exact diagonalization study of the tunable edge magnetism in graphene,"The tunable magnetism at graphene edges with lengths of up to 48 unit cells
is analyzed by an exact diagonalization technique. For this we use a
generalized interacting one-dimensional model which can be tuned continuously
from a limit describing graphene zigzag edge states with a ferromagnetic phase,
to a limit equivalent to a Hubbard chain, which does not allow ferromagnetism.
This analysis sheds light onto the question why the edge states have a
ferromagnetic ground state, while a usual one-dimensional metal does not.
Essentially we find that there are two important features of edge states: (a)
umklapp processes are completely forbidden for edge states; this allows a
spin-polarized ground state. (b) the strong momentum dependence of the
effective interaction vertex for edge states gives rise to a regime of partial
spin-polarization and a second order phase transition between a standard
paramagnetic Luttinger liquid and ferromagnetic Luttinger liquid.",1103.1645v1
2011-03-11,Hysteresis and nucleation in condensed matter,"The physical origin of hysteresis in condensed matter had not been previously
identified. The current ""science of hysteresis"" is useful, but limited by
phenomenological modeling. This article fills the void by revealing the
exclusive cause of the hysteresis in structural, ferromagnetic and
ferroelectric phase transitions, as well as upon magnetization in magnetic
fields and polarization in electric fields. This exclusive cause is nucleation
lags. The lags are inevitable due to the nucleation specifics, far from the
classical ""random fluctuation"" model. A major assumption that spin orientation
is determined by the orientation of its carrier explains why ferromagnetic
transitions and magnetization in magnetic fields materialize by structural
rearrangements at interfaces, as well as why magnetization by ""rotation"" is
impossible. Formation of the structural and ferromagnetic hysteresis loops is
considered in detail.",1103.2194v1
2011-03-22,Tracking defect-induced ferromagnetism in GaN:Gd,"We report on the magnetic properties of GaN:Gd layers grown by molecular beam
epitaxy (MBE). A poor reproducibility with respect to the magnetic properties
is found in these samples. Our results show strong indications that defects
with a concentration of the order of 10^19 cm^-3 might play an important role
for the magnetic properties. Positron annihilation spectroscopy does not
support the suggested connection between the ferromagnetism and the Ga vacancy
in GaN:Gd. Oxygen co-doping of GaN:Gd promotes ferromagnetism at room
temperature and points to a role of oxygen for mediating ferromagnetic
interactions in Gd doped GaN.",1103.4256v2
2011-04-04,FMR and voltage induced transport in normal metal-ferromagnet-superconductor trilayers,"We study the subgap spin and charge transport in normal
metal-ferromagnet-superconductor trilayers induced by bias voltage and/or
magnetization precession. Transport properties are discussed in terms of
time-dependent scattering theory. We assume the superconducting gap is small on
the energy scales set by the Fermi energy and the ferromagnetic exchange
splitting, and compute the non-equilibrium charge and spin current response to
first order in precession frequency, in the presence of a finite applied
voltage. We find that the voltage-induced instantaneous charge current and
longitudinal spin current are unaffected by the precessing magnetization, while
the pumped transverse spin current is determined by spin-dependent conductances
and details of the electron-hole scattering matrix. A simplified expression for
the transverse spin current is derived for structures where the ferromagnet is
longer than the transverse spin coherence length.",1104.0552v1
2011-04-13,Unusual ferromagnetic superexchange in CdVO3: The role of Cd,"A microscopic magnetic model of the low-pressure modification of CdVO3 is
established, based on density functional theory (DFT) band-structure
calculations, magnetization measurements, and quantum Monte-Carlo simulations.
This compound is a rare example of a quasi-one-dimensional spin-1/2 system
showing exclusively ferromagnetic exchange. The spin lattice of CdVO3 entails
zigzag chains with an effective intrachain coupling J ~ -90 K and interchain
couplings of Jc ~ -18 K and Ja ~ -3 K. Quantum fluctuations are partially
suppressed by the sizable interchain coupling Jc that leads to an intermediate
regime between one-dimensional and two-dimensional ferromagnetic systems. Apart
from the peculiar spin model, CdVO3 features an unusual mechanism of
ferromagnetic superexchange. The couplings largely originate from Cd 5s states
mediating hoppings between half-filled and empty 3d states of V+4.",1104.2495v2
2011-04-14,Aggregation of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite,"In this work, we report that when ferromagnetic metals (Fe, Co and Ni) are
thermally evaporated onto n-layer graphenes and graphite, a metal nanowire and
adjacent nanogaps can be found along the edges regardless of its zigzag or
armchair structure. Similar features can also be observed for paramagnetic
metals, such as Mn, Al and Pd. Meanwhile, metal nanowires and adjacent nanogaps
can not be found for diamagnetic metals (Au and Ag). An external magnetic field
during the evaporation of metals can make these unique features disappear for
ferromagnetic and paramagnetic metal; and the morphologies of diamagnetic metal
do not change after the application of an external magnetic field. We discuss
the possible reasons for these novel and interesting results, which include
possible one dimensional ferromagnets along the edge and edge-related binding
energy.",1104.2666v1
2011-05-10,Spontaneous magnon decays in planar ferromagnet,"We predict that spin-waves in an easy-plane ferromagnet have a finite
lifetime at zero temperature due to spontaneous decays. In zero field the
damping is determined by three-magnon decay processes, whereas decays in the
two-particle channel dominate in a transverse magnetic field. Explicit
calculations of the magnon damping are performed in the framework of the
spin-wave theory for the $XXZ$ square-lattice ferromagnet with an anisotropy
parameter $\lambda<1$. In zero magnetic field the decays occur for
$\lambda^*<\lambda<1$ with $\lambda^*\approx 1/7$. We also discuss possibility
of experimental observation of the predicted effect in a number of
ferromagnetic insulators.",1105.1893v1
2011-05-17,Superconductivity and ferromagnetism in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$,"Superconductivity and ferromagnetism are two antagonistic cooperative
phenomena, which makes it difficult for them to coexist. Here we demonstrate
experimentally that they do coexist in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ with
$0.2\leq x\leq0.4$, in which superconductivity is associated with Fe-3$d$
electrons and ferromagnetism comes from the long-range ordering of Eu-4$f$
moments via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The coexistence
is featured by large saturated ferromagnetic moments, high and comparable
superconducting and magnetic transition temperatures, and broad coexistence
ranges in temperature and field. We ascribe this unusual phenomenon to the
robustness of superconductivity as well as the multi-orbital characters of iron
pnictides.",1105.3255v1
2011-06-01,The ground state phase diagram of the diluted ferromagnetic Kondo-lattice model,"We investigate the existence of several (anti-)ferromagnetic phases in the
diluted ferromagnetic Kondo-lattice model, i.e. ferromagnetic coupling of local
moment and electron spin. To do this we use a coherent potential approximation
(CPA) with a dynamical alloy analogy. For the CPA we need effective potentials,
which we get first from a mean-field approximation. To improve this treatment
we use in the next step a more appropriate moment conserving decoupling
approach and compare both methods. The different magnetic phases are modelled
by defining two magnetic sublattices. As a result we present zero-temperature
phase diagrams according to the important model parameters and different
dilutions.",1106.0181v1
2011-07-05,Critical current measurements in superconductor - ferromagnet - superconductor junctions of $YBa_2Cu_3O_y$-$SrRuO_3$-$YBa_2Cu_3O_y$: No evidence for a dominant proximity induced triplet superconductivity in the ferromagnetic barrier,"Transport measurements in ramp-type junctions of
$YBa_2Cu_3O_y-SrRuO_3-YBa_2Cu_3O_y$ with $T_c$ values of either 80-90 K or
60-70 K are reported. In both type of junctions but without a barrier
(""shorts""), the supercurrent densities at 4.2 K reached 7.5 and 3.5 MA/cm$^2$,
respectively, indicating the high quality of the fabrication process. Plots of
the critical current versus thickness of the ferromagnetic barrier at 4.2 K
show exponential decays with decay lengths of 1.1 nm for the 90 K phase and 1.4
nm for the 60 K phase, which are much shorter than the relevant coherence
lengths $\xi_F\sim 5-6$ nm or $\xi_N\sim$16 nm of $SrRuO_3$. We thus conclude
that there is no dominant proximity induced triplet superconductivity in the
ferromagnet in our junctions.",1107.0808v1
2011-07-13,Size of stripe domains in a superconducting ferromagnet,"In a superconducting ferromagnet, the superconducting state appears in the
ferromagnetic phase where usually a domain structure has already developed. We
study the influence of the superconducting screening currents on a stripe
structure with out-of-plane magnetization, in a film of arbitrary thickness. We
find that superconductivity always induces a shrinkage of the domains, and
there is a critical value of penetration depth below which a mono-domain
structure is more stable than the periodic one. Furthermore we investigate the
possible different effects of singlet and triplet superconductivity on the
domain width, as well as the conditions for the existence of vortices in the
domains. The obtained results are then discussed in light of the experimental
data of superconducting ferromagnets URhGe, UGe2, and UCoGe.",1107.2608v1
2011-07-21,Superconductivity and Ferromagnetism in Oxide Interface Structures: Possibility of Finite Momentum Pairing,"We introduce a model to explain the observed ferromagnetism and
superconductivity in LAO/STO oxide interface structures. Due to the polar
catastrophe mechanism, 1/2 charge per unit cell is transferred to the interface
layer. We argue that this charge localizes and orders ferromagnetically via
exchange with the conduction electrons. Ordinarily this ferromagnetism would
destroy superconductivity, but due to strong spin-orbit coupling near the
interface, the magnetism and superconductivity can coexist by forming an
FFLO-type condensate of Cooper pairs at finite momentum, which is surprisingly
robust in the presence of strong disorder.",1107.4352v3
2011-08-11,Spin- and band-ferromagnetism in trilayer graphene,"We study the ground state properties of an ABA-stacked trilayer graphene. The
low energy band structure can be described by a combination of both a linear
and a quadratic particle-hole symmetric dispersions, reminiscent of monolayer-
and bilayer-graphene, respectively. The multi-band structure offers more
channels for instability towards ferromagnetism when the Coulomb interaction is
taken into account. Indeed, if one associates a pseudo-spin 1/2 degree of
freedom to the bands (parabolic/linear), it is possible to realize also a
band-ferromagnetic state, where there is a shift in the energy bands, since
they fill up differently. By using a variational procedure, we compute the
exchange energies for all possible variational ground states and identify the
parameter space for the occurrence of spin- and band-ferromagnetic
instabilities as a function of doping and interaction strength.",1108.2445v2
2011-08-22,Ferromagnetic Quantum Criticality in the Quasi-One-Dimensional Heavy Fermion Metal YbNi4P2,"We present a new Kondo-lattice system, YbNi4P2, which is a clean
heavy-fermion metal with a severely reduced ferromagnetic ordering temperature
at T_C=0.17K, evidenced by distinct anomalies in susceptibility, specific-heat,
and resistivity measurements. The ferromagnetic nature of the transition, with
only a small ordered moment of ~0.05mu_B, is established by a diverging
susceptibility at T_C with huge absolute values in the ferromagnetically
ordered state, severely reduced by small magnetic fields. Furthermore, YbNi4P2
is a stoichiometric system with a quasi-one-dimensional crystal and electronic
structure and strong correlation effects which dominate the low temperature
properties. This is reflected by a stronger-than-logarithmically diverging
Sommerfeld coefficient and a linear-in-T resistivity above T_C which cannot be
explained by any current theoretical predictions. These exciting
characteristics are unique among all correlated electron systems and make this
an interesting material for further in-depth investigations.",1108.4274v1
2011-09-06,Low Field Magnetic Susceptibility and the Hidden Order Transition in URu2Si2,"Despite several decades of both experimental and theoretical work the nature
of the hidden order transition at THO = 17.5 K in URu2Si2 remains enigmatic. We
report here low field DC magnetization as well as AC susceptibility
measurements performed on single crystals with field along the c-axis. A peak
in the first order AC susceptibility is observed at T=16 K in close proximity
to the well known change in slope at THO=17.5 K. Third order susceptibility
measurements on the other hand reveal a signature only at 16 K with no
discernible change at THO. However, both transitions are visible in the fifth
order susceptibility. A signature at this lower transition, as a spontaneous
ferromagnetic signal, also appears in low field DC magnetization measurements.
A similar but larger ferromagnetic response appears at T~35 K. Both these
ferromagnetic signatures are suppressed in a small field (B ~ 40 Gauss
||c-axis). The close proximity of the lower signature to the hidden order
transition and the simultaneous presence and suppression of a ferromagnetic
signature at 35 K could be due to the removal of degeneracy in the complex
order-parameter of the hidden order transition due a ""symmetry breaking field"",
at least locally within the crystals of URu2Si2.",1109.1038v1
2011-09-16,Superconductor-insulator-ferromagnet-superconductor Josephson junction: From the dirty to the clean limit,"The proximity effect and the Josephson current in a
superconductor-insulator-ferromagnet-superconductor (SIFS) junction are
investigated within the framework of the quasiclassical Eilenberger equations.
This investigation allows us to compare the dirty and the clean limits, to
investigate an arbitrary impurity scattering, and to determine the
applicability limits of the Usadel equations for such structures. The role of
different types of the FS interface is analyzed. It is shown that the decay
length and the spatial oscillation period of the Eilenberger function may
exhibit a nonmonotonic dependence on the properties of the ferromagnetic layer
such as exchange field or electron mean free path. The results of our
calculations are applied to the interpretation of experimentally observed
dependencies of the critical current density on the ferromagnet thickness in
Josephson junctions containing a Ni layer with an arbitrary scattering.",1109.3658v1
2011-10-04,Low-temperature thermodynamics of the classical frustrated ferromagnetic chain in magnetic field,"Low-temperature magnetization curves of the classical frustrated
ferromagnetic chain in the external magnetic field near the transition point
between the ferromagnetic and the helical phases is studied. It is shown that
the calculation of the partition function in the scaling limit reduces to the
solution of the Schr\""{o}dinger equation of the special form for the quantum
particle. It is proposed that the magnetization of the classical model in the
ferromagnetic part of the phase diagram including the transition point defines
the universal scaling function which is valid for quantum model as well.
Explicit analytical formulae for the magnetization are given in the limiting
cases of low and high magnetic fields. The influence of the easy-axis
anisotropy on the magnetic properties of the model is studied. It is shown that
even small anisotropy essentially changes the behavior of the susceptibility in
the vicinity of the transition point.",1110.0771v2
2011-10-10,First-principles characterization of ferromagnetism in N-doped SrTiO3 and BaTiO3,"The spin-polarization and magnetic coupling character of N-doped SrTiO3 and
BaTiO3 are studied through first-principles calculations. The substitutional N
doping at O sites leads to a half-metallic property and produces a magnetic
moment of 1.0 {\mu}B. The magnetic interaction between the nearest and
next-nearest N dopants results in a strong ferromagnetic coupling. When the
distance between the N dopants is larger than 7 {\AA}, the ground state of the
system tends to be paramagnetic. A nitrogen-concentration threshold to produce
the ferromagnetism is estimated. The calculated results give a good explanation
for the experimentally observed ferromagnetism in N-doped SrTiO3 and BaTiO3.",1110.2138v2
2011-10-17,Crossed Andreev reflection and spin-resolved non-local electron transport,"The phenomenon of crossed Andreev reflection (CAR) is known to play a key
role in non-local electron transport across three-terminal
normal-superconducting-normal (NSN) devices. Here we review our general theory
of non-local charge transport in three-terminal disordered
ferromagnet-superconductor-ferromagnet (FSF) structures. We demonstrate that
CAR is highly sensitive to electron spins and yields a rich variety of
properties of non-local conductance which we describe non-perturbatively at
arbitrary voltages, temperature, degree of disorder, spin-dependent interface
transmissions and their polarizations. We demonstrate that magnetic effects
have different implications: While strong exchange field suppresses
disorder-induced electron interference in ferromagnetic electrodes,
spin-sensitive electron scattering at SF interfaces can drive the total
non-local conductance negative at sufficiently low energies. At higher energies
magnetic effects become less important and the non-local resistance behaves
similarly to the non-magnetic case. Our results can be applied to
multi-terminal hybrid structures with normal, ferromagnetic and half-metallic
electrodes and can be directly tested in future experiments.",1110.3654v1
2011-12-05,Magnetotransport in the Kondo model with ferromagnetic exchange interaction,"We consider the transport properties in an applied magnetic field of the spin
S=1/2 Kondo model with ferromagnetic exchange coupling to electronic
reservoirs, a description relevant for the strong coupling limit of
underscreened spin S=1 Kondo impurities. Because the ferromagnetic Kondo
interaction is marginally irrelevant, perturbative methods should prove
accurate down to low energies. For the purpose of this study, we use a
combination of Majorana diagrammatic theory with Density Matrix Numerical
Renormalization Group simulations. In the standard case of antiferromagnetic
Kondo exchange, we first show that our technique recovers previously obtained
results for the T-matrix and spin relaxation at weak coupling (above the Kondo
temperature). Considering then the ferromagnetic case, we demonstrate how the
low-energy Kondo anomaly splits for arbitrary small values of the Zeeman
energy, in contrast to fully screened Kondo impurities near the strong coupling
Fermi liquid fixed point, and in agreement with recent experimental findings
for spin S=1 molecular quantum dots.",1112.0925v2
2011-12-07,Exchange bias of mu-metal thin films,"The exchange bias of the soft ferromagnet mu-metal, Ni77Fe14Cu5Mo4, with the
metallic antiferromagnet Fe50Mn50 has been studied as a function of ferromagnet
thickness and buffer layer material. Mu-metal exhibits classic exchange bias
behavior: the exchange bias (HEB) and coercive fields scale inversely with the
ferromagnet's thickness, with HEB varying as the cosine of the in-plane applied
field angle. While the exchange bias, coercivity, and exchange energy are
greatest when the buffer layer material is (111) oriented Cu, amorphous Ta
buffers allow the mu-metal to retain more of its soft magnetic character. The
ability to preserve soft ferromagnetic behavior in an exchange biased
heterostructure may be useful for low field sensing and other device
applications.",1112.1604v1
2011-12-08,Photovoltaic Effect on Molecule Coupled Ferromagnetic Films of a Magnetic Tunnel Junction,"Economical solar energy conversion to electricity can be boosted by the
discovery of fundamentally new photovoltaic mechanism, and a suitable system to
realize it with commonly available materials like iron (Fe) and nickel (Ni).
This paper reports the observation of photovoltaic effect on a molecular
spintronics device, composed of magnetic tunnel junction (MTJ) and
organometallic molecular clusters (OMCs). A prefabricated MTJ with exposed side
edges, after enabling the bridging of OMC channels between its two
ferromagnetic films, exhibited following phenomenon (i) dramatic increase in
exchange coupling, (ii) 3-6 orders current suppression and (iii) photovoltaic
effect. This paper focuses on the photovoltaic effect. Control experiments on
isolated ferromagnetic films suggested that OMCs neither affected the magnetic
properties nor produced any photovoltaic effect; photovoltaic effect was only
observed on the ferromagnetic films serving as magnetic electrodes in a MTJ.
Present paper invites further investigation of the similar photovoltaic effect
on other combinations of MTJs and promising magnetic molecules, like single
molecular magnets, organometallic clusters and porphyrins. This research can
lead to mass producible and economical spin photovoltaic devices.",1112.1879v2
2011-12-19,Signature of the long range triplet proximity effect in the density of states,"We study the impact of the long-range spin-triplet proximity effect on the
density of states (DOS) in planar SF1F2S Josephson junctions that consist of
conventional superconductors (S) connected by two metallic monodomain
ferromagnets (F1 and F2) with transparent interfaces. We determine the
electronic DOS in F layers and the Josephson current for arbitrary orientation
of the magnetizations using the solutions of Eilenberger equations in the clean
limit and for a moderate disorder in ferromagnets. We find that fully developed
long-range proximity effect can occur in highly asymmetric ferromagnetic
bilayer Josephson junctions with orthogonal magnetizations. The effect
manifests itself as an enhancement in DOS, and as a dominant second harmonic in
the Josephson current-phase relation. Distinctive variation of DOS in
ferromagnets with the angle between magnetizations is experimentally observable
by tunneling spectroscopy. This can provide an unambiguous signature of the
long-range spin-triplet proximity effect.",1112.4450v1
2012-02-02,Towards precise measurement of oscillatory domain wall by ferromagnetic Josephson junction,"We theoretically propose a principle for precise measurement of oscillatory
domain wall (DW) by a ferromagnetic Josephson junction, which is composed of a
ferromagnetic wire with DW and two superconducting electrodes. The
current-voltage curve exhibits stepwise structures, only when DW oscillates in
the ferromagnetic wire. The voltage step appears at V = n(\hbar/2e)\omega_DW
with the fundamental constant \hbar/e, integer number n, and the DW frequency
\omega_DW. Since V can be determined in the order of 10^9 accuracy, the
oscillatory DW will be measured more precisely than present status by
conventional method.",1202.0382v2
2012-02-16,Disorder promotes ferromagnetism: Rounding of the quantum phase transition in Sr_{1-x}Ca_xRuO_3,"The subtle interplay of randomness and quantum fluctuations at low
temperatures gives rise to a plethora of unconventional phenomena in systems
ranging from quantum magnets and correlated electron materials to ultracold
atomic gases. Particularly strong disorder effects have been predicted to occur
at zero-temperature quantum phase transitions. Here, we demonstrate that the
composition-driven ferromagnetic-to-paramagnetic quantum phase transition in
Sr1-xCaxRuO3 is completely destroyed by the disorder introduced via the
different ionic radii of the randomly distributed Sr and Ca ions. Using a
magneto-optical technique, we map the magnetic phase diagram in the
composition-temperature space. We find that the ferromagnetic phase is
significantly extended by the disorder and develops a pronounced tail over a
broad range of the composition x. These findings are explained by a microscopic
model of smeared quantum phase transitions in itinerant magnets. Moreover, our
theoretical study implies that correlated disorder is even more powerful in
promoting ferromagnetism than random disorder.",1202.3810v1
2012-02-26,Understanding ferromagnetism in Cr-based 3d-5d double perovskites,"Ferromagnetism in Cr-based double perovskites is analyzed using effective
model as well as simulation approach.
  Starting from a microscopic model proposed recently for this class of double
perovskites, an effective spin-only model is derived in the limit of large
exchange coupling at the B-site. Analytic expressions for the resultant
exchange coupling is derived in certain limiting cases.
  The behaviour of this exchange is used to provide a plausible explanation for
the enhanced ferromagnetic tendency as also the enigmatic increase in Curie
temperature observed in Cr-based DP-s, in the series
Sr$_{2}$CrWO$_{6}$,Sr$_{2}$CrReO$_{6}$ to Sr$_{2}$CrOsO$_{6}$. The
superexchange between neighbouring B and B' sites is found to play a crucial
role both in stabilizing ferromagnetism, especially in the latter two
compounds, as well as increasing the T$_{c}$.",1202.5735v3
2012-03-14,Oxygen vacancy enhanced room temperature ferromagnetism in Al-doped MgO nanoparticles,"We have investigated the room temperature ferromagnetic order that develops
in Al-substituted magnesium oxide, Mg(Al)O, nanoparticles with Al fractions of
up to 5 at.%. All samples, including undoped MgO nanoparticles, exhibit room
temperature ferromagnetism, with the saturation magnetization reaching a
maximum of 0.023 emu/g at 2 at.% of Al. X-ray photoelectron spectroscopy
identifies the presence of oxygen vacancies in both doped and undoped MgO
nanoparticles, with the vacancy concentration increasing upon vacuum annealing
of Mg(Al)O, resulting in two-fold enhancement of the saturation magnetization
for 2 at.% Al-doped MgO. Our results suggest that the oxygen vacancies are
largely responsible for room temperature ferromagnetism in MgO.",1203.2991v3
2012-03-28,Ferromagnetic condensation in high density hadronic matter,"We investigate the occurrence of a ferromagnetic phase transition in high
density hadronic matter (e.g., in the interior of a neutron star). This could
be induced by a four fermion interaction analogous to the one which is
responsible for chiral symmetry breaking in the Nambu-Jona-Lasinio model, to
which it is related through a Fierz transformation. Flavor SU(2) and flavor
SU(3) quark matter are considered. A second order phase transition is predicted
at densities about 5 times the normal nuclear matter density, a magnetization
of the order of $10^{16}$ gauss being expected. It is also found that in flavor
SU(3) quark matter, a first order transition from the so-called 2 flavor
super-conducting (2SC) phase to the ferromagnetic phase arises. The
color-flavor-locked (CFL) phase may be completely hidden by the ferromagnetic
phase.",1203.6272v2
2012-06-15,Single-parameter quantum charge and spin pumping in armchair graphene nanoribbons,"We investigate quantum charge and spin pumping in armchair graphene
nanoribbons under a single ac gate voltage connected with
nonmagnetic/ferromagnetic leads via the nonequilibrium Green's function method.
In the case of nonmagnetic leads, where only part of the nanoribbon is subject
to an ac gate voltage to break the left-right spatial symmetry, we discover
that peaks of the charge pumping current appear at the Fermi energies around
the subband edges in the ac-field-free region of the nanoribbon. In the case of
ferromagnetic leads with the lead magnetizations being antiparallel to break
the left-right symmetry, similar peaks appear in the spin pumping current when
the Fermi energies are around the edges of the the majority-spin subbands in
the ferromagnetic leads. All these peaks originate from the pronounced symmetry
breaking in the transmissions with energies being around the corresponding
subband edges. Moreover, we predict a {\em pure} spin current in the case of
ferromagnetic leads with the whole graphene nanoribbon under an ac gate
voltage. The ac-field-strength and -frequency dependences of the pumping
current are also investigated with the underlying physics revealed.",1206.3435v1
2012-06-26,The coexistence of superconductivity and ferromagnetism in nano-scale metallic grains,"A nano-scale metallic grain in which the single-particle dynamics are chaotic
is described by the so-called universal Hamiltonian. This Hamiltonian includes
a superconducting pairing term and a ferromagnetic exchange term that compete
with each other: pairing correlations favor minimal ground-state spin, while
the exchange interaction favors maximal spin polarization. Of particular
interest is the fluctuation-dominated regime where the bulk pairing gap is
comparable to or smaller than the single-particle mean level spacing and the
Bardeen-Cooper-Schrieffer theory of superconductivity breaks down.
Superconductivity and ferromagnetism can coexist in this regime. We identify
signatures of the competition between superconductivity and ferromagnetism in a
number of quantities: ground-state spin, conductance fluctuations when the
grain is weakly coupled to external leads and the thermodynamic properties of
the grain, such as heat capacity and spin susceptibility.",1206.6059v2
2012-06-28,Spin-orbit coupled transport and spin torque in a ferromagnetic heterostructure,"Ferromagnetic heterostructures provide an ideal platform to explore the
nature of spin-orbit torques arising from the interplay mediated by itinerant
electrons between a Rashba-type spin-orbit coupling and a ferromagnetic
exchange interaction. For such a prototypic system, we develop a set of coupled
diffusion equations to describe the diffusive spin dynamics and spin-orbit
torques. We characterize the spin torque and its two prominent--out-of-plane
and in-plane--components for a wide range of relative strength between the
Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence
of the spin torque emerging from our simple Rashba model is in an agreement
with experiments. The spin diffusion equation can be generalized to incorporate
dynamic effect such as spin pumping and magnetic damping.",1206.6726v2
2012-07-25,Thermodynamics of Two-Dimensional Ideal Ferromagnets - Three-Loop Analysis,"Within the effective Lagrangian framework, we explicitly evaluate the
partition function of two-dimensional ideal ferromagnets up to three loops at
low temperatures and in the presence of a weak external magnetic field. The
low-temperature series for the free energy density, energy density, heat
capacity, entropy density, as well as the magnetization are given and their
range of validity is critically examined in view of the Mermin-Wagner theorem.
The calculation involves the renormalization and numerical evaluation of a
particular three-loop graph which is discussed in detail. Interestingly, in the
low-temperature series for the two-dimensional ideal ferromagnet, the spin-wave
interaction manifests itself in the form of logarithmic terms. In the free
energy density the leading such term is of order $T^4 \ln T$ -- remarkably, in
the case of the three-dimensional ideal ferromagnet no logarithmic terms arise
in the low-temperature series. While the present study demonstrates that it is
straightforward to consider effects up to three-loop order in the effective
field theory framework, this precision seems to be far beyond the reach of
microscopic methods such as modified spin-wave theory.",1207.5937v1
2012-07-30,Ferromagnetic state in the one-dimensional Kondo lattice model,"In our recent study, Phys. Rev. Lett. 108 086402 (2012), we have revealed the
intriguing properties of the ferromagnetic state in the Kondo lattice model
with antiferromagnetic coupling in infinite dimensions: within the
ferromagnetic metallic phase, the minority conduction electrons form a gap at
the Fermi energy and do not participate in transport irrespective of
interaction strength and filling. This half-metallic state is referred to as a
spin-selective Kondo insulator. We here show that the spin-selective Kondo
insulator can also be realized in the one-dimensional Kondo lattice model by
studying static and dynamical quantities with the density matrix
renormalization group. The emergence of the spin selective Kondo insulator both
in one and infinite dimensions certainly demonstrates that this mechanism is
quite general and ubiquitous for the ferromagnetic state in the Kondo lattice
model irrespective of the dimensionality of the system.",1207.6835v2
2012-07-31,Effects of Magnetovolume and Spin-orbit Coupling in the Ferromagnetic Cubic Perovskite BaRuO3,"BaRuO3 having five different crystal structures has been synthesized by
varying the pressure while sintering. Contrary to the other phases being
nonmagnetic, the cubic perovskite phase synthesized recently shows an itinerant
ferromagnetic character. We investigated this ferromagnetic BaRuO3 using first
principles calculations. A few van Hove singularities appear around the Fermi
energy, causing unusually high magnetovolume effects of $\Delta M/\Delta a$ ~
4.3 $\mu_B$/\AA as well as a Stoner instability [IN(0) ~ 1.2]. At the optimized
lattice parameter a, the magnetic moment M is 1.01 $\mu_B$ in the local spin
density approximation. When spin-orbit coupling is included, the topologies of
some Fermi surfaces are altered, and the net moment is reduced by 10% to a
value very close to the experimentally observed value of ~ 0.8 $\mu_B$. Our
results indicate that this ferromagnetism is induced by the Stoner instability,
but the combined effects of the p-d hybridization, the magnetovolume, and the
spin-orbit coupling determine the net moment. In addition, we briefly discuss
the results of the tight-binding Wannier function technique.",1207.7145v2
2012-08-07,Temperature-controlled interlayer exchange coupling in strong/weak ferromagnetic multilayers: a thermo-magnetic Curie-switch,"We investigate a novel type of interlayer exchange coupling based on driving
a strong/weak/strong ferromagnetic tri-layer through the Curie point of the
weakly ferromagnetic spacer, with the exchange coupling between the strongly
ferromagnetic outer layers that can be switched, on and off, or varied
continuously in magnitude by controlling the temperature of the material. We
use Ni-Cu alloy of varied composition as the spacer material and model the
effects of proximity-induced magnetism and the interlayer exchange coupling
through the spacer from first principles, taking into account not only thermal
spin-disorder but also the dependence of the atomic moment of Ni on the
nearest-neighbor concentration of the non-magnetic Cu. We propose and
demonstrate a gradient-composition spacer, with a lower Ni-concentration at the
interfaces, for greatly improved effective-exchange uniformity and
significantly improved thermo-magnetic switching in the structure. The reported
magnetic multilayer materials can form the base for a variety of novel magnetic
devices, such as sensors, oscillators, and memory elements based on
thermo-magnetic Curie-switching in the device.",1208.1493v1
2012-09-03,"Growth and characterization of n-type electron-induced ferromagnetic semiconductor (In,Fe)As","We show that by introducing isoelectronic iron (Fe) magnetic impurities and
Beryllium (Be) double-donor atoms into InAs, it is possible to grow a n-type
ferromagnetic semiconductor (FMS) with the ability to control ferromagnetism by
both Fe and independent carrier doping by low-temperature molecular-beam
epitaxy. We demonstrate that (In,Fe)As doped with electrons behaves as an
n-type electron-induced FMS. This achievement opens the way to realize novel
spin-devices such as spin light-emitting diodes or spin field-effect
transistors, as well as helps understand the mechanism of carrier-mediated
ferromagnetism in FMSs.",1209.0250v1
2012-09-13,Artificial ferroelectricity due to anomalous Hall effect in magnetic tunnel junctions,"We theoretically investigated Anomalous Hall Effect (AHE) and Spin Hall
Effect (SHE) transversally to the insulating spacer O, in magnetic tunnel
junctions of the form F/O/F where F are ferromagnetic layers and O represents a
tunnel barrier. We considered the case of purely ballistic (quantum mechanical)
transport, taking into account the assymetric scattering due to spin-orbit
interaction in the tunnel barrier. AHE and SHE in the considered case have a
surface nature due to proximity effect. Their amplitude is in first order of
the scattering potential. This contrasts with ferromagnetic metals wherein
these effect are in second (side-jump scattering) and third (skew scattering)
order on these potentials. The value of AHE voltage in insulating spacer may be
much larger than in metallic ferromagnetic electrodes. For the antiparallel
orientation of the magnetizations in the two F-electrodes, a spontaneous Hall
voltage exists even at zero applied voltage. Therefore an insulating spacer
sandwiched between two ferromagnetic layers can be considered as exhibiting a
spontaneous ferroelectricity.",1209.2872v1
2012-09-24,Magnetic-coupling-dependent spin-triplet supercurrents in helimagnet/ferromagnet Josephson junctions,"The experimental achievements during the past year in demonstrating the
existence of long-ranged spin-triplet supercurrents in ferromagnets proximity
coupled to singlet superconductors open up the possibility for new interesting
physics and applications [for a review, see M. Eschrig, Phys. Today 64(1), 43
(2011)]. Our group reported the injection of triplet supercurrents into a
magnetically uniform ferromagnet (Co) by sandwiching it between two
helimagnet/superconductor (Ho/Nb) bilayers to form a Nb/Ho/Co/Ho/Nb-type
Josephson device. In the function of the Ho layer thicknesses, the supercurrent
was found to modulate in a complex way that seemed to depend on the magnetic
structure of Ho. To understand this unusual behavior, we have theoretically
studied the properties of an ideal Josephson device with a
helimagnet/ferromagnet/helimagnet (HM/F/HM) barrier in the clean limit using
the Eilenberger equation; we show, in particular, that the maximum triplet
supercurrent that can pass across the barrier will depend non-monotonically on
the thicknesses of the HM layers if the HM and F layers are magnetically
exchange coupled at their interface.",1209.5355v1
2012-10-03,Easy-axis ferromagnetic chain on a metallic surface,"The phases and excitation spectrum of an easy-axis ferromagnetic chain of
S=1/2 magnetic impurities built on the top of a clean metallic surface are
studied. As a function of the (Kondo) coupling to the metallic surface and at
low temperatures, the spin chain exhibits a quantum phase transition from an
Ising ferromagnetic phase with long-range order to a paramagnetic phase where
quantum fluctuations destroy the magnetic order. In the paramagnetic phase, the
system consists of a chain of Kondo-singlets where the impurities are
completely screened by the metallic host. In the ferromagnetic phase, the
excitations above the Ising gap are damped magnons, with a finite lifetime
arising due to the coupling to the substrate. We discuss the experimental
consequences of our results to spin-polarized electron energy loss spectroscopy
(SPEELS), and we finally analyze possible extensions to spin chains with S>1/2.",1210.1195v1
2012-10-17,Ferromagnetic Quantum Critical Point in Heavy-Fermion Iron Oxypnictide Ce(Ru$_{1-x}$Fe$_x$)PO,"We have performed ^{31}P-NMR measurements on Ce(Ru_{1-x}Fe_{x})PO in order to
investigate ferromagnetic (FM) quantum criticality, since heavy-fermion (HF)
ferromagnet CeRuPO with a two-dimensional structure turns to a HF paramagnet by
an isovalent Fe-substitution for Ru. We found that Ce(Ru_{0.15}Fe_{0.85})PO
shows critical fluctuations down to \sim 0.3 K, as well as the continuous
suppression of Curie temperature and the ordered moments by the
Fe-substitution. These experimental results suggest the presence of a FM
quantum critical point (QCP) at x \sim 0.86, which is a rare example among
itinerant ferromagnets. In addition, we point out that the critical behaviors
in Ce(Ru_{0.15}Fe_{0.85})PO share the similarity with those in YbRh_{2}Si_{2},
where the local criticality of $f$ electrons has been discussed. We reveal that
Ce(Ru_{1-x}Fe_{x})PO is a new system to study FM quantum criticality in HF
compounds.",1210.4604v1
2012-11-28,Gate voltage controlled electronic transport through a ferromagnet/normal/ferromagnet junction on the surface of a topological insulator,"We investigate the electronic transport properties of a
ferromagnet/normal/ferromagnet junction on the surface of a topological
insulator with a gate voltage exerted on the normal segment. It is found that
the conductance oscillates with the width of normal segment and gate voltage,
and the maximum of conductance gradually decreases while the minimum of
conductance approaches zero as the width increases. The conductance can be
controlled by tuning the gate voltage like a spin field-effect transistor. It
is found that the magnetoresistance ratio can be very large, and can also be
negative owing to the anomalous transport. In addition, when there exists a
magnetization component in the surface plane, it is shown that only the
component parallel to the junction interface has an influence on the
conductance.",1211.6511v1
2012-12-27,Interacting spin-droplets and magnetic properties of a low-density two-dimensional electron gas,"We argue that the magnetic susceptibility data, Refs. 1-3, for the
low-density two-dimensional (2D) silicon-based electron gas indicate that
magnetically active electrons are localised in spin-droplets. The droplets
exist in both the insulating and metallic phases, and interact
ferromagnetically, forming an effective 2D Heisenberg ferromagnet. Comparing
the data with known analytical and numerical results for a 2D Heisenberg
ferromagnet, we determine that JS^2 \approx 0.6K, where S is the spin of the
droplet and J is the ferromagnetic exchange constant between droplets. We
further argue that most likely S=1 with four electrons occupying each droplet
on average. We discuss the dependence of the magnetic susceptibility and the
specific heat on the external magnetic field, which follows from the model, and
hence we suggest further experimental tests of the model.",1212.6438v1
2012-12-31,Electrical and magnetic transport study on strain driven ferromagnetic insulating thin film of low doped manganite,"In this paper we have created a strain driven single crystal like
ferromagnetic insulating (FMI) state in a PLD grown thin film of low doped
LCMO(X = 0.15)on NGO(100) substrate and make a thorough study of strain effects
on the electric and magnetic transport of this film. We have studied and
compared the FMI state, ferromagnetic transition temperature (TC),
ferromagnetic insulating temperature (TFMI) and the resistivity of the film in
details with bulk single crystals of X=0.18 to 0.22 doping region. We have
found that TFMI and the localisation length of the carriers are increased and
there is also a decrease in the Coulomb gap. The magneto transport behavior of
the film also differs from the bulk single crystals and the magnetoresistance
of the sample is nearly 20 to 75% with the application of the applied field(0
to 10 T) and it falls up to 5 to 40% below a certain temperature and the TC of
the film increases to higher temperature with the increasing field. The film
also shows anisotropic magnetoresistance as large as 20% depending on applied
magnetic field direction.",1212.6858v1
2013-01-31,Current-field diagram of magnetic states of a surface spin valve in a point contact with a single ferromagnetic film,"We present a study of the influence of an external magnetic field H and an
electric current I on the spin-valve (SV) effect between a ferromagnetic thin
film (F) and a sharp tip of a nonmagnetic metal (N). To explain our
observations, we propose a model of a local surface SV which is formed in such
a N/F contact. In this model, a ferromagnetic cluster at the N/F interface
plays the role of the free layer in this SV. This cluster exhibits a larger
coercive field than the bulk of the ferromagnetic film, presumably due to its
nanoscale nature. Finally, we construct a magnetic state diagram of the surface
SV as a function of I and H.",1301.7635v1
2013-02-27,Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet,"The specific heat and thermal conductivity of the insulating ferrimagnet
Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured
down to 50 mK. The ferromagnetic magnon specific heat $C$$_m$ shows a
characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward
deviation is observed, which is attributed to the magnetic dipole-dipole
interaction with typical magnitude of 10$^{-4}$ eV. The ferromagnetic magnon
thermal conductivity $\kappa_m$ does not show the characteristic $T^2$
dependence below 0.8 K. To fit the $\kappa_m$ data, both magnetic defect
scattering effect and dipole-dipole interaction are taken into account. These
results complete our understanding of the thermodynamic and thermal transport
properties of the low-lying ferromagnetic magnons.",1302.6739v1
2013-03-18,Theory of spin pumping through an interacting quantum dot tunnel coupled to a ferromagnet with time-dependent magnetization,"We investigate two schemes for pumping spin adiabatically from a ferromagnet
through an interacting quantum dot into a normal lead, which exploit the
possibility to vary in time the ferromagnet's magnetization, either its
amplitude or its direction. For this purpose, we extend a diagrammatic
real-time technique for pumping to situations in which the leads' properties
are time dependent. In the first scheme, the time-dependent magnetization
amplitude is combined with a time-dependent level position of the quantum dot
to establish both a charge and a spin current. The second scheme uses a uniform
rotation of the ferromagnet's magnetization direction to generate a pure spin
current without a charge current. We discuss the influence of an
interaction-induced exchange field on the pumping characteristics.",1303.4184v2
2013-04-08,Temperature dependence of spin polarization in ferromagnetic metals using lateral spin valves,"A high reproducibility in the performance of cobalt/copper and
permalloy/copper lateral spin valves with transparent contacts is obtained by
optimizing the interface quality and the purity of copper. This allows us to
study comprehensively the spin injection properties of both ferromagnetic
materials, as well as the spin transport properties of copper, which are not
affected by the used ferromagnetic material, leading to long spin diffusion
lengths. Spin polarizations of permalloy and cobalt are obtained as a function
of temperature. Analysis of the temperature dependence of both the spin
polarization and conductivity of permalloy using the standard two-channel model
for ferromagnetic metals suggests that a correction factor of ~2 is needed for
the spin polarization values obtained by lateral spin valve experiments.",1304.2123v3
2013-04-24,Long-range spin current driven by superconducting phase difference in a Josephson junction with double layer ferromagnets,"We theoretically study spin current through ferromagnet (F) in a Josephson
junction composed of s-wave superconductors and two layers of ferromagnets.
Using quasiclassical theory, we show that the long-range spin current can be
driven by the superconducting phase difference without voltage drop. The origin
of this spin current is due to spin-triplet Cooper pairs (STCs) formed by
electrons of equal-spin, which are induced by proximity effect inside the F. We
find that the spin current carried by the STCs exhibits long-range propagation
in the F even where the Josephson charge current is practically zero. We also
show that this spin current persists over a remarkably longer distance than the
ordinary spin current carried by spin polarized conduction electrons in the F.
Our results thus indicate the promising potential of Josephson junctions based
on multilayer ferromagnets for spintronics applications with long-range
propagating spin current.",1304.6452v1
2013-04-26,Strain-induced ferromagnetism in antiferromagnetic LuMnO3 thin films,"Single phase and strained LuMnO3 thin films are discovered to display
co-existing ferromagnetic and antiferromagnetic orders. A large moment
ferromagnetism (approx. 1 muB), which is absent in bulk samples, is shown to
display a magnetic moment distribution that is peaked at the highly-strained
substrate-film interface. We further show that the strain-induced
ferromagnetism and the antiferromagnetic order are coupled via an exchange
field, therefore demonstrating strained rare-earth managanite thin films as
promising candidate systems for new multifunctional devices.",1304.7200v1
2013-05-23,Realization of stripes and slabs in two and three dimensions,"We consider Ising models in two and three dimensions with nearest neighbor
ferromagnetic interactions and long range, power law decaying,
antiferromagnetic interactions. If the strength of the ferromagnetic coupling J
is larger than a critical value J_c, then the ground state is homogeneous and
ferromagnetic. As the critical value is approached from smaller values of J, it
is believed that the ground state consists of a periodic array of stripes (d=2)
or slabs (d=3), all of the same size and alternating magnetization. Here we
prove rigorously that the ground state energy per site converges to that of the
optimal periodic striped/slabbed state, in the limit that J tends to the
ferromagnetic transition point. While this theorem does not prove rigorously
that the ground state is precisely striped/slabbed, it does prove that in any
suitably large box the ground state is striped/slabbed with high probability.",1305.5323v1
2013-05-23,In situ observation of strongly interacting ferromagnetic domains in a shaken optical lattice,"Solid state systems derive their richness from the interplay between
interparticle interactions and novel band structures that deviate from those of
free particles. Strongly interacting systems, where both of these phenomena are
of equal importance, exhibit a variety of theoretically interesting and
practically useful phases. Systems of ultracold atoms are rapidly emerging as
precise and controllable simulators, and it is precisely in this strongly
interacting regime where simulation is the most useful. Here we demonstrate how
to hybridize Bloch bands in optical lattices to introduce long-range
ferromagnetic order in an itinerant atomic system. We find spontaneously broken
symmetry for bosons with a double-well dispersion condensing into one of two
distinct minima, which we identify with spin-up and spin-down. The density
dynamics following a rapid quench to the ferromagnetic state confirm quantum
interference between the two states as the mechanism for symmetry breaking.
Unlike spinor condensates, where interaction is driven by small spin-dependent
differences in scattering length, our interactions scale with the scattering
length itself, leading to domains which equilibrate rapidly and develop sharp
boundaries characteristic of a strongly interacting ferromagnet.",1305.5487v1
2013-05-27,Thermal entanglement in the mixed three spin XXZ Heisenberg Model on a triangular cell,"We numerically investigate thermal entanglement of the spins (1/2,1) and
(1/2,1/2) in the three-mixed (1/2,1,1/2) anisotropic Heisenberg XXZ spin system
on a simple triangular cell under an inhomogeneous magnetic field. We show that
the external magnetic field induces strong plateau formation in pairwise
thermal entanglement for fixed parameters of Hamiltonian in the case of the
ferromagnetic and anti-ferromagnetic interactions. We also observe an
unexpected critical point at finite temperature in the thermal entanglement of
the spins (1/2,1) for antiferromagnetic case while the entanglement of the
spins (1/2,1) for ferromagnetic case and the entanglement of the spins
(1/2,1/2) for both ferromagnetic and antiferromagnetic cases almost decays
exponentially to zero with increasing temperature. The critical point in
entanglement of the spins (1/2,1) for antiferromagnetic case may be signature
of the quantum phase transition at finite temperature.",1305.6230v2
2013-05-27,Understanding the metamagnetic transition and magnetic behavior of Ni48Co6Mn26Al20 polycrystalline ribbons,"In this work we demonstrate that the polycrystalline ribbons of
(Ni48Co6)Mn26Al20 with B2 structure at room temperature show a magnetic
behavior with competing magnetic exchange interactions leading to frozen
disorders at low temperatures. It is established that by considering the
presence of both antiferromagnetic and ferromagnetic sublattices, we can
explain the observed magnetic behavior including the metamagnetic transition
observed in these samples. From the Arrott plots, the N\'eel temperature of
(Ni48Co6)Mn26Al20 is deduced to be ~170 K and the broad ferro to para like
magnetic phase transition is observed at ~ 200 K. Based on N\'eel theory, a
cluster model is used to explain the presence of ferromagnetic and
anti-ferromagnetic clusters in the studied ribbons. Formation of ferromagnetic
clusters can be understood in terms of positive exchange interactions among the
Mn atoms that are neighboring to Co atoms which are located on the Ni sites.",1305.6255v3
2013-05-28,Emergence of ferromagnetism and Jahn-Teller distortion in low Cr-substituted LaMnO3,"The emergence of a ferromagnetic component in $LaMnO_{3}$ with low Cr-for-Mn
substitution has been studied by x-ray absorption spectroscopy and x-ray
magnetic circular dichroism at the Mn and Cr K edges. The local magnetic moment
strength for the Mn and Cr are proportional to each other and follows the
macroscopic magnetization. The net ferromagnetic components of $Cr^{3+}$ and
$Mn^{3+}$ are found antiferromagnetically coupled. Unlike hole doping by La
site substitution, the inclusion of $Cr^{3+}$ ions up to x = 0.15 does not
decrease the Jahn-Teller (JT) distortion and consequently does not
significantly affect the orbital ordering. This demonstrates that the emergence
of the ferromagnetism is not related to JT weakening and likely arises from a
complex orbital mixing.",1305.6486v1
2013-05-29,Theory of Self-Induced Vortex State in Ferromagnetic Superconductors,"We have developed the quasi-classical formalism for a self-induced vortex
state in ferromagnetic superconductors. By combining the spatially averaged
approximation of the superconductivity with the phenomenological form of the
ferromagnetism, we demonstrate the thermodynamic properties of the p-wave
triplet equal-spin-pairing state with the spontaneous vortex lattice. The
occurrence condition for the self-induced vortex state is discussed within this
formalism. The comparison of the calculated quantities with the observed ones
indicates that the self-induced vortex state indeed occurs in UCoGe, and its
pairing symmetry seems to be the A2-type with a small spin difference in the
gap magnitudes. In the vicinity of the ferromagnetic quantum critical point
with a large uniform susceptibility, it is possible to exhibit the type-II to
the type-I transition in the magnetization process.",1305.6835v1
2013-05-30,Suppression of ferromagnetism in the LaVxCr1-xGe3 system,"We report synthesis of hexagonal LaVxCr1-xGe3 (x = 0-0.21, 1.00) single
crystals, and present a systematic study of this series by measurements of
temperature and field dependent magnetic susceptibility, magnetization,
resistivity, and specific heat. Ferromagnetism has been observed for x =
0-0.21, and the system manifests a strong axial anisotropy in its ordered
state. The decrease of the saturated moment and the effective moment per Cr
with the increase of V-concentration suggests this is an itinerant
ferromagnetic system. The Curie temperature declines monotonically as the
V-concentration increases. Single crystalline samples could only be grown for
x-values up to 0.21 for which the transition temperature was suppressed down to
36 K. Although we could not fully suppress TC via V-substitution, for x = 0.16,
we performed magnetization measurements under pressure. The ferromagnetic state
is suppressed under pressure at an initial rate of dTC/dp = -11.7 K/GPa and
vanishes by 3.3 GPa.",1305.7258v1
2013-06-01,Inverse proximity effect and influence of disorder on triplet supercurrents in strongly spin-polarized ferromagnets,"We discuss the Josephson effect in strongly spin-polarized ferromagnets where
triplet correlations are induced by means of spin-active interface scattering,
extending our earlier work [Phys. Rev. Lett. 102, 227005 (2009)] by including
impurity scattering in the ferromagnetic bulk and the inverse proximity effect
in a fully self-consistent way. Our quasiclassical approach accounts for the
differences of Fermi momenta and Fermi velocities between the two spin bands of
the ferromagnet, and thereby overcomes an important short-coming of previous
work within the framework of Usadel theory. We show that non-magnetic disorder
in conjunction with spin-dependent Fermi velocities may induce a reversal of
the spin-current as a function of temperature.",1306.0141v1
2013-07-04,Electronic transport in ferromagnetic barriers on the surface of a topological insulator with $δ$ doping,"We investigate electron transporting through a two-dimensional
ferromagnetic/normal/ferromagnetic tunnel junction on the surface of a
three-dimensional topological insulator with taking into $\delta$ doping
account. It is found that the conductance oscillates with the Fermi energy, the
position and the aptitude of the $\delta$ doping. Also the conductance depends
sensitively on the direction of the magnetization of the two ferromagnets,
which originate from the control of the spin flow due to spin-momentum locked.
It is found that the conductance is the maximum at the parallel configuration
while it is minimum at the antiparallel configuration and vice versa, which may
stem from the half wave loss due to the electron wave entering through the
antiparallel configuration. These characters are very helpful for making new
types of magnetoresistance devices due to the practical applications.",1307.1283v1
2013-07-12,Angular and Linear Momentum of Excited Ferromagnets,"The angular momentum vector of a Heisenberg ferromagnet with isotropic
exchange interaction is conserved, while under uniaxial crystalline anisotropy
the projection of the total spin along the easy axis is a constant of motion.
Using Noether's theorem, we prove that these conservation laws persist in the
presence of dipole-dipole interactions. However, spin and orbital angular
momentum are not conserved separately. We also define the linear momentum of
ferromagnetic textures. We illustrate the general principles with special
reference to the spin transfer torques and identify the emergence of a
non-adiabatic effective field acting on domain walls in ferromagnetic
insulators.",1307.3432v1
2013-07-16,Anomalous Hall effect in two-phase semiconductor structures: the crucial role of ferromagnetic inclusions,"The Hall effect in InMnAs layers with MnAs inclusions of 20-50 nm in size is
studied both theoretically and experimentally. We find that the anomalous Hall
effect can be explained by the Lorentz force caused by the magnetic field of
ferromagnetic inclusions and by an inhomogeneous distribution of the current
density in the layer. The hysteretic dependence of the average magnetization of
ferromagnetic inclusions on an external magnetic field results in a hysteretic
dependence of RH(Hext). Thus we show the possibility of a hysteretic RH(Hext)
dependence (i.e. observation of the anomalous Hall effect) in thin conductive
layers with ferromagnetic inclusions in the absence of carriers spin
polarization.",1307.4225v1
2013-07-16,Phase diagram with enhanced spin-glass region of mixed Ising / XY magnets LiHo$_{x}$Er$_{1-x}$F$_{4}$,"We present the experimental phase diagram of LiHo$_x$Er$_{1-x}$F$_4$, a
dilution series of dipolar-coupled model magnets.The phase diagram was
determined using a combination of AC susceptibility and neutron scattering.
Three unique phases in addition to the Ising ferromagnet LiHoF$_4$ and the XY
anti-ferromagnet LiErF$_4$ have been identified. Below $x=0.86$ an embedded
spin-glass phase is observed, where a spin-glass exists within the
ferromagnetic structure. Below $x=0.57$ an Ising spin-glass is observed
consisting of frozen needle-like clusters. For $x \sim 0.3 - 0.1$ an
antiferromagnetically coupled spin-glass occurs. A reduction of $T_C(x)$ for
the ferromagnet is observed which disobeys the mean-field predictions that
worked for LiHo$_x$Y$_{1-x}$F$_4$.",1307.4271v1
2013-07-25,Reentrant Superconductivity and Superconducting Critical Temperature Oscillations in F/S/F trilayers of Cu41Ni59/Nb/Cu41Ni59 Grown on Cobalt Oxide,"Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core
of a superconducting spin valve. The switching effect of the spin valve is
based on interference phenomena occurring due to the proximity effect at the
S/F interfaces. A remarkable effect is only expected if the core structure
exhibits strong critical temperature oscillations, or most favorable, reentrant
superconductivity, when the thickness of the ferromagnetic layer is increased.
The core structure has to be grown on an antiferromagnetic oxide layer (or such
layer to be placed on top) to pin by exchange bias the
magnetization-orientation of one of the ferromagnetic layers. In the present
paper we demonstrate that this is possible, keeping the superconducting
behavior of the core structure undisturbed.",1307.6737v1
2013-10-13,Spin-wave-induced corrections to the electronic density of states in metallic ferromagnets,"We calculate the correction to the electronic density of states in a
disordered ferromagnetic metal induced by spin-wave mediated interaction
between the electrons. Our calculation is valid for the case that the exchange
splitting in the ferromagnet is much smaller than the Fermi energy, but we make
no assumption on the relative magnitude of the exchange splitting and the
elastic electronic scattering time. In the ""clean limit"", where the exchange
splitting is much larger than the electronic scattering rate, we find a
correction with a T^{d/2} temperature dependence, where d is the effective
dimensionality of the ferromagnet. In the opposite ""dirty limit"" the
density-of-states correction is a non-monotonous function of energy and
temperature.",1310.3511v1
2013-10-29,Ferromagnetic Order Analysis of Fe- and FeO-modified Graphene-nano-ribbon,"Graphene-nano-ribbon (GNR) is very attractive for ultra-high density
spintronics devices. For checking a capability of self-induced ferromagnetic
order, Fe- and FeO-modified GNR were analyzed based on the density functional
theory. Model unit cells were [C32H2Fe2] and [C32H2Fe2O2]. Calculated results
show the most stable spin state to be Sz=8/2 in [C32H2Fe2], whereas Sz=6/2 in
[C32H2Fe2O2]. Magnetic moment M of Fe in [C32H2Fe2] was 3.65{\mu}B, which could
be explained based on the Hund-rule considering donated charge to carbon to be
M*=3.67{\mu}B . There is a capability of ferromagnetic Fe spin array through an
interaction with carbon {\pi}-conjugated spin system. There shows a long-range
super-exchange order in [C32H2Fe2O2]. Optimized atomic configuration gave the
typical 90 degree super-exchange coupling between Fe-3d and O-2p orbit.
Magnetic moment of Fe by DFT was 2.58{\mu}B, whereas super-exchange model
considering donated charge to oxygen gave an estimated magnetic moment to be
2.60{\mu}B. Sign of magnetic moment of Fe and O are all up-spin each other. We
could expect ferromagnetic long-range-order. Band structure was analyzed in
FeO-modified case, which suggested half-metal like behavior. We can expect
several spintronics applications as like a spin filter.",1310.7740v1
2013-11-01,Magnetism in nanoparticle LaCoO3,"LaCoO3 (LCO) nanoparticles were synthesized and their magnetic and structural
properties were examined using SQUID magnetometery and neutron diffraction. The
nanoparticles exhibit ferromagnetic long-range order beginning at T_C
approximately 87K that persists to low temperatures. This behavior is
contrasted with the ferromagnetism of bulk LCO, which also starts at T_C
approximately 87K but is suppressed below a second transition at T_o
approximately 37K, due to a structural phase transition. The ferromagnetism in
both systems is attributed to the tensile stress from particle surfaces and
impurity phase interfaces. This stress locally increases the Co-O-Co bond angle
gamma, and competes with the thermal contraction of the lattice. It has
recently been shown that LCO loses long-range ferromagnetic order when gamma
decreases below the critical value gamma_c = 162.8 degrees. Consistent with
this model, we show that gamma in nanoparticles remains larger than gamma_c at
low temperatures, likely a consequence of all spins being in close proximity to
surfaces or interfaces.",1311.0240v1
2013-11-02,Stimulation of a Singlet Superconductivity in SFS Weak Links by Spin-Exchange Scattering of Cooper Pairs,"Josephson junctions with a ferromagnetic metal weak link reveal a very strong
decrease of the critical current compared to a normal metal weak link. We
demonstrate that in the ballistic regime the presence of a small region with a
non-collinear magnetization near the center of a ferromagnetic weak link
restores the critical current inherent to the normal metal. The above effect
can be stimulated by additional electrical bias of the magnetic gate which
induces a local electron depletion of ferromagnetic barrier. The underlying
physics of the effect is the interference phenomena due to the magnetic
scattering of the Cooper pair, which reverses its total momentum in the
ferromagnet and thus compensates the phase gain before and after the
spin-reversed scattering. In contrast with the widely discussed triplet long
ranged proximity effect we elucidate a new singlet long ranged proximity
effect. This phenomenon opens a way to easily control the properties of SFS
junctions and inversely to manipulate the magnetic moment via the Josephson
current.",1311.0369v2
2013-12-03,Stoner instability revisited: Emergence of local quantum criticality?,"We revisit Stoner instability, an old problem but in a modern point of view.
An idea is to extract out dynamics of directional fluctuations of spins
explicitly, resorting to the CP$^{1}$ representation and integrating over their
amplitude fluctuations. As a result, we derive an effective field theory for
ferromagnetic quantum phase transitions in terms of bosonic spinons and
fermionic holons. We show that this effective field theory reproduces
overdamped spin dynamics in a paramagnetic Fermi liquid and magnon spectrum in
a ferromagnetic Fermi liquid. An interesting observation is that the velocity
of spinons becomes zero, approaching the ferromagnetic quantum critical point,
which implies emergence of local quantum criticality. Based on this scenario,
we predict the $\omega/T$ scaling behavior near ferromagnetic quantum
criticality beyond the conventional scenario of the weak-coupling approach.",1312.0807v2
2013-12-03,Reconsidering the possibility of room temperature ferromagnetism in Mn doped Zirconium oxide,"The possibility to induce long range ferromagnetic order by doping oxides
with transition metal ions has become a very exciting challenge in the last
decade. Theoretically, it has been claimed that Mn doped ZrO$_2$ could be a
very promising spintronic candidate and that high critical temperatures could
be already achieved even for a low Mn concentration. Some experiments have
reported room temperature ferromagnetism (RT-FM) whilst some others only
paramagnetism. When observed, the nature of RT-FM appears to be controversial
and not clearly understood. In this study, we propose to clarify and shed light
on some of theses existing issues. A detailed study of the critical
temperatures and low energy magnetic excitations in Mn doped ZrO$_2$ is
performed. We show that the Curie temperatures were largely overestimated
previously, due to the inadequate treatment of both thermal and transverse
fluctuations, and disorder. It appears that the Mn-Mn couplings can not explain
the observed RT-FM. We argue, that this can be attributed to the interaction
between large moments induced in the vicinity of the manganese. This is similar
to the non-magnetic defect induced ferromagnetism reported in oxides,
semiconductors and graphene/graphite.",1312.0808v1
2013-12-11,New Green function approach describing the ferromagnetic state in the simple Hubbard model,"We consider a Hubbard model with occupation dependent hopping integrals.
Using the Hartree-Fock (H-F) approximation and the new Green function approach
with inter-site kinetic averages included, we analyze the influence of the
correlated hopping on ferromagnetic ordering. The influence of correlated
hopping on the nonlocal quasiparticle energies and corresponding k-dependent
spectral weights is included. In addition we obtain the shift of the spin bands
which is a major factor in creating spontaneous ferromagnetism. At some
parameters of the model the correlated hopping effect is strong enough to
achieve saturated ferromagnetism. This state may be obtained at the asymmetric
density of states (DOS) and the Fermi energy located in the region of large
spectral weight near the band edge. The results are compared with DMFT-Quantum
Monte Carlo calculations and with the Hubbard III approximation which includes
the correlated hopping effect.",1312.3150v1
2013-12-13,Full Counting Statistics of Generic Spin Entangler with Quantum Dot-Ferromagnet detectors,"Entanglement between spatially separated electrons in nanoscale transport is
a fundamental property, yet to be demonstrated experimentally. Here we propose
and analyse theoretically the transport statistics of a generic spin entangler
coupled to a hybrid quantum dot-ferromagnet detector system. We show that the
full distribution of charges arriving at the ferromagnetic terminals provide
complete information on the spin state of the particles emitted by the
entangler. This provides means for spin entanglement detection via electrical
current correlations, with optimal measurement strategies depending on the a
priori knowledge of ferromagnet polarization and spin-flip rates in the
detector dots. The scheme is exemplified by applying it to Andreev and triple
dot entanglers.",1312.3982v1
2014-01-02,Evidence for Majorana bound states in transport properties of hybrid structures based on helical liquids,"Majorana bound states can emerge as zero-energy modes at the edge of a
two-dimensional topological insulator in proximity to an ordinary s-wave
superconductor. The presence of an additional ferromagnetic domain close to the
superconductor can lead to their localization. We consider both N-S and S-N-S
junctions based on helical liquids and study their spectral properties for
arbitrary ferromagnetic scatterers in the normal region. Thereby, we explicitly
compute Andreev wave-functions at zero energy. We show under which conditions
these states form localized Majorana bound states in N-S and S-N-S junctions.
Interestingly, we can identify Majorana-specific signatures in the transport
properties of N-S junctions and the Andreev bound levels of S-N-S junctions
that are robust against external perturbations. We illustrate these findings
with the example of a ferromagnetic double barrier (i.e. a quantum dot) close
to the N-S boundaries.",1401.0507v2
2014-01-20,Topological insulator in junction with ferromagnets: quantum Hall effects,"The ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction
exhibits thermal and electrical quantum Hall effects. The generated Hall
voltage and transverse temperature gradient can be controlled by the directions
of magnetizations in the FM leads, which inspires the use of FM-TI-FM junctions
as electrical and as heat switches in spintronic devices. Thermal and
electrical Hall coefficients are calculated as functions of the magnetization
directions in ferromagnets and the spin-relaxation time in TI. Both the Hall
voltage and the transverse temperature gradient decrease but are not completely
suppressed even at very short spin-relaxation times. The Hall coefficients turn
out to be independent of the spin-relaxation time for symmetric configuration
of FM leads.",1401.4986v3
2014-01-29,Nonreciprocal Dispersion of Spin Waves in Ferromagnetic Thin Films Covered with a Finite-Conductivity Metal,"We study the effect of one-side metallization of a uniform ferromagnetic thin
film on its spin-wave dispersion relation in the Damon-Eshbach geometry. Due to
the finite conductivity of the metallic cover layer on the ferromagnetic film
the spin-wave dispersion relation may be nonreciprocal only in a limited
wave-vector range. We provide an approximate analytical solution for the
spin-wave frequency, discuss its validity and compare it with numerical
results. The dispersion is analyzed systematically by varying the parameters of
the ferromagnetic film, the metal cover layer and the value of the external
magnetic field. The conclusions drawn from this analysis allow us to define a
structure based on a 30 nm thick CoFeB film with an experimentally accessible
nonreciprocal dispersion relation in a relatively wide wave-vector range.",1401.7454v1
2014-01-29,A first order phase transition and self-organizing states in unidomain ferromagnet,"Unidomain ferromagnet during the first order phase transition induced by a
magnetic field directed along the axis of anisotropy, has been analyzed. It is
shown that there is continuous spectrum of stationary states, which depends of
relation between acting field value and the demagnetisation field. At addition
action of the periodic field perpendicular to the main magnetic field with a
certain frequency, there are dynamic equilibrium state, ie ""self-organizing
states"" of ferromagnet, when the entropy increase connected with dissipation is
compensated by the negative entropy flow due to the periodic field. It is shown
that under these conditions, by varying the frequency of the periodic field, we
can control the self-organising system, ie decrease or increase the system
energy and, correspondingly, change the direction of magnetisation in
ferromagnet.",1401.7521v1
2014-04-03,Enhanced DC Spin Pumping into a Fluctuating Ferromagnet near Tc,"A linear-response formulation of the dc spin pumping, i.e., a spin injection
from a precessing ferromagnet into an adjacent spin sink, is developed in view
of describing many-body effects caused by spin fluctuations in the spin sink.
It is shown that, when an itinerant ferromagnet near Tc is used as the spin
sink, the spin pumping is largely increased owing to the fluctuation
enhancement of the spin conductance across the precessing ferromagnet/spin sink
interface. As an example, the enhanced spin pumping from permalloy into nickel
palladium alloy (Tc ~ 20K) is analyzed by means of a self-consistent
renormalization scheme, and it is predicted that the enhancement can be as
large as tenfold.",1404.0768v2
2014-04-12,New room temperature multiferroics on the base of single-phase nanostructured perovskites,"The theoretical description of the nanostructured
Pb(Fe1/2Ta1/2)x(Zr1/2Ti1/2)1-xO3 (PFTx-PZT(1-x)) and
Pb(Fe1/2Nb1/2)x(Zr1/2Ti1/2)1-xO3 (PFNx-PZT(1-x)) intriguing ferromagnetic,
ferroelectric and magnetoelectric properties at temperatures higher than 100 K
are absent to date. The goal of this work is to propose the theoretical
description of the physical nature and the mechanisms of the aforementioned
properties, including room temperature ferromagnetism, phase diagram dependence
on the composition x with a special attention to the multiferroic properties at
room temperature, including anomalous large value of magnetoelectric
coefficient. The comparison of the developed theory with experiments
establishing the boundaries between paraelectric, ferroelectric, paramagnetic,
antiferromagnetic, ferromagnetic and magnetoelectric phases, as well as the
characteristic features of ferroelectric domain switching by magnetic field are
performed and discussed. The experimentally established absence of
ferromagnetic phase in PFN, PFT and in the solid solution of PFN with PbTiO3
(PFNx-PT(1-x)) was explained in the framework of the proposed theory.",1404.3267v1
2014-04-29,Nanowire Spin Torque Oscillator Driven by Spin Orbit Torques,"Spin torque from spin current applied to a nanoscale region of a ferromagnet
can act as negative magnetic damping and thereby excite self-oscillations of
its magnetization. In contrast, spin torque uniformly applied to the
magnetization of an extended ferromagnetic film does not generate
self-oscillatory magnetic dynamics but leads to reduction of the saturation
magnetization. Here we report studies of the effect of spin torque on a system
of intermediate dimensionality - a ferromagnetic nanowire. We observe coherent
self-oscillations of magnetization in a ferromagnetic nanowire serving as the
active region of a spin torque oscillator driven by spin orbit torques. Our
work demonstrates that magnetization self-oscillations can be excited in a
one-dimensional magnetic system and that dimensions of the active region of
spin torque oscillators can be extended beyond the nanometer length scale.",1404.7262v2
2014-07-02,Induced Ferromagnetism at BiFeO3/YBa2Cu3O7 Interfaces,"Transition metal oxides (TMOs) exhibit many emergent phenomena ranging from
high-temperature superconductivity and giant magnetoresistance to magnetism and
ferroelectricity. In addition, when TMOs are interfaced with each other, new
functionalities can arise, which are absent in individual components. Here, we
report results from first-principles calculations on the magnetism at the
BiFeO3/YBa2Cu3O7 interfaces. By comparing the total energy for various magnetic
spin configurations inside BiFeO3, we are able to show that a metallic
ferromagnetism is induced near the interface. We further develop an interface
exchange-coupling model and place the extracted exchange coupling interaction
strengths, from the first-principles calculations, into a resultant generic
phase diagram. Our conclusion of interfacial ferromagnetism is confirmed by the
presence of a hysteresis loop in field-dependent magnetization data. The
emergence of interfacial ferromagnetism should have implications to electronic
and transport properties.",1407.0722v1
2014-07-12,Role of dimensionality in spontaneous magnon decay: easy-plane ferromagnet,"We calculate magnon lifetime in an easy-plane ferromagnet on a tetragonal
lattice in transverse magnetic field. At zero temperature magnons are unstable
with respect to spontaneous decay into two other magnons. Varying ratio of
intrachain to interchain exchanges in this model we consider the effect of
dimensionality on spontaneous magnon decay. The strongest magnon damping is
found in the quasi-one-dimensional case for momenta near the Brillouin zone
boundary. The sign of a weak interchain coupling has a little effect on the
magnon decay rate. The obtained theoretical results suggest possibility of
experimental observation of spontaneous magnon decay in a quasi-one-dimensional
ferromagnet CsNiF$_3$. We also find an interesting enhancement of the magnon
decay rate for a three-dimensional ferromagnet. The effect is present only for
the nearest-neighbor model and is related to effective dimensionality reduction
in the two-magnon continuum.",1407.3402v1
2014-07-20,Half-metallic magnetism and the search for better spin valves,"We use a previously proposed theory for the temperature dependence of
tunneling magnetoresistance to shed light on ongoing efforts to optimize spin
valves. First we show that a mechanism in which spin valve performance at
finite temperatures is limited by uncorrelated thermal fluctuations of
magnetization orientations on opposite sides of a tunnel junction is in good
agreement with recent studies of the temperature-dependent magnetoresistance of
high quality tunnel junctions with MgO barriers. Using this insight, we propose
a simple formula which captures the advantages for spin-valve optimization of
using materials with a high spin polarization of Fermi-level tunneling
electrons, and of using materials with high ferromagnetic transition
temperatures. We conclude that half-metallic ferromagnets can yield better
spin-value performance than current elemental transition metal ferromagnet/MgO
systems only if their ferromagnetic transition temperatures exceed $\sim
950~\mathrm{K}$.",1407.5240v1
2014-08-26,Ferromagnetic and Nematic Non-Fermi Liquids in Spin-Orbit Coupled Two-Dimensional Fermi Gases,"We study the fate of a two-dimensional system of interacting fermions with
Rashba spin-orbit coupling in the dilute limit. The interactions are strongly
renormalized at low densities, and give rise to various fermionic liquid
crystalline phases, including a spin-density wave, an in-plane ferromagnet, and
a non-magnetic nematic phase, even in the weak coupling limit. The nature of
the ground state in the low-density limit depends on the range of the
interactions: for short range interactions it is the ferromagnet, while for
dipolar interactions the nematic phase is favored. Interestingly, the
ferromagnetic and nematic phases exhibit strong deviations from Fermi liquid
theory, due to the scattering of the Fermionic quasi-particles off
long-wavelength collective modes. Thus, we argue that a system of interacting
fermions with Rashba dispersion is generically a non-Fermi liquid at low
densities.",1408.6250v3
2014-10-02,Strong coupling between a permalloy ferromagnetic contact and a helical edge channel in a narrow HgTe quantum well,"We experimentally investigate spin-polarized electron transport between a
permalloy ferromagnet and the edge of a two-dimensional electron system with
band inversion, realized in a narrow, 8~nm wide HgTe quantum well. In zero
magnetic field, we observe strong asymmetry of the edge potential distribution
with respect to the ferromagnetic ground lead. This result indicates, that the
helical edge channel, specific for the structures with band inversion even at
the conductive bulk, is strongly coupled to the ferromagnetic side contact,
possibly due to the effects of proximity magnetization. It allows selective and
spin-sensitive contacting of helical edge states.",1410.0585v5
2014-10-12,Differences and analogies between quantum chromodynamics and ferromagnets,"The low-energy physics of quantum chromodynamics (QCD) and ferromagnets is
dominated by Goldstone bosons. While the effective theory of QCD - chiral
perturbation theory - is well established in the particle physics community,
the systematic studies of ferromagnetic systems within the effective Lagrangian
framework are not well-known. We analyze the low-temperature properties of
ferromagnets in one, two and three space dimensions up to three-loop order in
the effective expansion, i.e., beyond the accuracy of any previous results
obtained with conventional condensed matter methods. In particular, in the
nonrelativistic domain, the effective method perfectly works in one space
dimension.",1410.3107v1
2014-10-30,Critical aspects of three-dimensional anisotropic spin-glass models,"We study the $\pm J$ three-dimensional Ising model with a longitudinal
anisotropic bond randomness on the simple cubic lattice. The random exchange
interaction is applied only in the $z$ direction, whereas in the other two
directions, $xy$ - planes, we consider ferromagnetic exchange. By implementing
an effective parallel tempering scheme, we outline the phase diagram of the
model and compare it to the corresponding isotropic one, as well as to a
previously studied anisotropic (transverse) case. We present a detailed
finite-size scaling analysis of the ferromagnetic - paramagnetic and spin glass
- paramagnetic transition lines, and we also discuss the ferromagnetic - spin
glass transition regime. We conclude that the present model shares the same
universality classes with the isotropic model, but at the symmetric point has a
considerably higher transition temperature from the spin-glass state to the
paramagnetic phase. Our data for the ferromagnetic - spin glass transition line
are supporting a forward behavior in contrast to the reentrant behavior of the
isotropic model.",1410.8397v2
2014-11-12,Coexistence of ferromagnetism and superconductivity in CeO$_{0.3}$F$_{0.7}$BiS$_{2}$,"Bulk magnetization, transport and neutron scattering measurements were
performed to investigate the electronic and magnetic properties of a
polycrystalline sample of the newly discovered ferromagnetic superconductor,
CeO$_{0.3}$F$_{0.7}$BiS$_{2}$. Ferromagnetism develops below T$_{FM}$ = 6.54(8)
K and superconductivity is found to coexist with the ferromagnetic state below
T$_{SC}$ ~ 4.5 K. Inelastic neutron scattering measurements reveal a very
weakly dispersive magnetic excitation at 1.8 meV that can be explained by an
Ising-like spin Hamiltonian. Under application of an external magnetic field,
the direction of the magnetic moment changes from the c-axis to the ab-plane
and the 1.8 meV excitation splits into two modes. A possible mechanism for the
unusual magnetism and its relation to superconductivity is discussed.",1411.3394v1
2014-11-23,Gate controllable spin pumping in graphene via rotating magnetization,"We investigate pure spin pumping in graphene by imposing a ferromagnet (F)
with rotating magnetization on top of it. Using the generalized scattering
approach for adiabatic spin pumping, we obtain the spin current pumped through
magnetic graphene to a neighboring normal (N) region. The spin current can be
easily controlled by gate voltages and under certain conditions, becomes
sufficiently large to be measurable in current experimental setups. In fact it
reaches a maximum value when one of the spins are completely filtered due to
the vanishing density of states of the corresponding spin species in the
ferromagnetic part. Considering an N|F|N structure with a finite ferromagnetic
region, it is found that in contrast to the metallic ferromagnetic materials
the transverse spin coherence length can be comparable to the length of F
denoted by $L$. Subsequently, due to the quantum interferences, the spin
current becomes oscillatory function of $JL/\hbar v_F$ in which $J$ is the spin
splitting inside F. Finally we show, originated from the controllability of
pumped spin into two different normal sides, a profound spin battery effect can
be seen in the hybrid N|F|N device.",1411.6261v1
2014-12-01,Experimental Verification of Van Vleck Nature of Long-Range Ferromagnetic Order in Vanadium-Doped Three-Dimensional Topological Insulator Sb$_{2}$Te$_{3}$,"We demonstrate by high resolution low temperature electron energy loss
spectroscopy (EELS) measurements that the long range ferromagnetic (FM) order
in vanadium (V)-doped topological insulator Sb$_2$Te$_3$ has the nature of van
Vleck-type ferromagnetism. The positions and the relative amplitudes of two
core-level peaks (L$_3$ and L$_2$) of the V EELS spectrum show unambiguous
change when the sample is cooled from room temperature to T=10K.
Magnetotransport and comparison of the measured and simulated EELS spectra
confirm that these changes originate from onset of FM order. Crystal field
analysis indicates that in V-doped Sb$_2$Te$_3$, partially filled core states
contribute to the FM order. Since van Vleck magnetism is a result of summing
over all states, this magnetization of core level verifies the van Vleck-type
ferromagnetism in a direct manner.",1412.0636v1
2014-12-01,Dissipation due to pure spin-current generated by spin pumping,"Based on spin-dependent transport theory and thermodynamics, we develop a
generalized theory of the Joule heating in the presence of a spin current.
Along with the conventional Joule heating consisting of an electric current and
electrochemical potential, it is found that the spin current and spin
accumulation give an additional dissipation because the spin-dependent
scatterings inside bulk and ferromagnetic/nonmagnetic interface lead to a
change of entropy. The theory is applied to investigate the dissipation due to
pure spin-current generated by spin pumping across a
ferromagnetic/nonmagnetic/ferromagnetic multilayer. The dissipation arises from
an interface because the spin pumping is a transfer of both the spin angular
momentum and the energy from the ferromagnet to conduction electrons near the
interface. It is found that the dissipation is proportional to the enhancement
of the Gilbert damping constant by spin pumping.",1412.0688v1
2014-12-15,A Minimal tight-binding model for ferromagnetic canted bilayer manganites,"Half-metallicity in materials has been a subject of extensive research due to
its potential for applications in spintronics. Ferromagnetic manganites have
been seen as a good candidate, and aside from a small minority-spin pocket
observed in La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ $(x=0.38)$, transport
measurements show that ferromagnetic manganites essentially behave like half
metals. Here we develop robust tight-binding models to describe the electronic
band structure of the majority as well as minority spin states of
ferromagnetic, spin-canted antiferromagnetic, and fully antiferromagnetic
bilayer manganites. Both the bilayer coupling between the MnO$_2$ planes and
the mixing of the $|x^2 - y^2>$ and $|3z^2 - r^2>$ Mn 3d orbitals play an
important role in the subtle behavior of the bilayer splitting. Effects of
$k_z$ dispersion are included.",1412.4728v1
2014-12-16,Non-uniform magnetic system driven by non-magnetic ion substitution in CaRu1-xScxO3:Two-component analysis,"We have studied magnetic and transport properties in polycrystalline
CaRu1-xScxO3 for 0 =< x =< 0.20 in order to clarify the substitution effects of
a non-magnetic trivalent ion. We find that a ferromagnetic transition with Tc =
30 K is observed in Sc-substituted samples. The composition dependence of the
Curie-Weiss temperature implies that the magnetic susceptibility has a
paramagnetic contribution with negative theta and a ferromagnetic contribution
with positive theta. The field dependence of magnetization at 2 K is also
understood as a summation of the ferromagnetic and paramagnetic components.
These results suggest that CaRu1-xScxO3 is a non-uniform magnetic system. The
relationship between the ferromagnetic ordering and the transport properties is
also discussed.",1412.4947v1
2014-12-19,Reentrant superconductivity in URhGe,"There is presented a phenomenological description of phase diagram of
ferromagnet superconductor URhGe. In frame of the Landau phenomenological
theory it was found that phase transition between anisotropic ferromagnetic and
paramagnetic states under strong enough magnetic field perpendicular to
direction of easy magnetization changes from the second to the first order
type. It is shown that magnetic susceptibility corresponding to longitudinal
magnetic fluctuations strongly increases in vicinity of the first order
transition stimulating reentrance of superconducting state.
  The reentrant superconductivity observed near the first order transition line
at temperatures about twice lower than the tricritical point temperature exists
both in ferromagnet and paramagnet state. The critical temperature of
transition to superconducting state falls down at intersection with line of
ferromagnet-paramagnet phase transition.",1412.6289v2
2015-01-03,Exact results for itinerant ferromagnetism in a $t_{2g}$ orbital system on cubic and square lattices,"We study itinerant ferromagnetism in a $t_{2g}$ multi-orbital Hubbard system
in the cubic lattice, which consists of three planar oriented orbital bands of
$d_{xy}$, $d_{yz}$, and $d_{zx}$. Electrons in each orbital band can only move
within a two-dimensional plane in the three-dimensional lattice parallel to the
corresponding orbital orientation. Electrons of different orbitals interact
through the on-site multi-orbital interactions including Hund's coupling. The
strong coupling limit is considered in which there are no doubly occupied
orbitals but multiple on-site occupations are allowed. We show that, in the
case in which there is one and only one hole for each orbital band in each
layer parallel to the orbital orientation, the ground state is a fully
spin-polarized itinerant ferromagnetic state, which is unique apart from the
trivial spin degeneracy. When the lattice is reduced into a single
two-dimensional layer, the $d_{zx}$ and $d_{yz}$ bands become
quasi-one-dimensional while the $d_{xy}$ band remains two-dimensional. The
ground state ferromagnetism also appears in the strong-coupling limit as a
generalization of the double exchange mechanism. Possible applications to the
systems of SrRuO$_3$ and LaAlO$_3$/SrTiO$_3$ interface are discussed.",1501.00536v2
2015-01-08,Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6,"Exchange bias effect in the ferromagnetic double perovskite compound
Y$_2$CoMnO$_6$, which is also a multiferroic, is reported. The exchange bias,
observed below 8~K, is explained as arising due to the interface effect between
the ferromagnetic and antiferromagnetic clusters created by {\it antisite}
disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with
metamagnetic ""steps"" and significant coercive field, $H_c \approx$ 10~kOe are
observed in this compound which has a $T_c \approx$ 75~K. A model based on
growth of ferromagnetic domains overcoming the elastic energy of structurally
pinned magnetic interfaces, which closely resembles martensitic-like
transitions, is adapted to explain the observed effects. The role of {\it
antisite} disorder in creating the domain structure leading to exchange bias
effect is highlighted in the present work.",1501.01766v1
2015-01-16,La displacement driven Double-exchange like mediation in Titanium $d_{xy}$ ferromagnetism at the LaAlO$_3$/SrTiO$_3$,"The epitaxial atomistic interfaces of two insulating oxides, LaAlO$_3$
(LAO)/SrTiO$_3$ (STO), have attracted great interest owing to rich emergent
phenomena \cite{hwang12:nmat,coey13:mrs,ohtomo04:} such as interface
metallicity \cite{ohtomo04:,nakagawa06:}, thickness dependent insulator-metal
transition \cite{huijben06:nmat}, superconductivity \cite{N.Reyren08312007},
ferromagnetism \cite{brinkman.07:natmat}, and even their coexistence
\cite{bert11:nphys,li11:nphys,dikin11:prl}. However, the physics origin of
ferromagnetic ordering in the $n$-type LAO/STO interface is in debate. Here we
propose that the polar distortion of La atom can ignite the ferromagnetism at
the interface even without oxygen vacancy. The induced hybridization between La
$d_{z^2}$ and O $p_{x,y}$ states can mediate double-exchange like interaction
between Ti $d_{xy}$ electrons. We further suggest that the structural and
electrical modification of the outermost surface of LAO or switching the
polarization direction of ferroelectric overlayers on LAO/STO can promote such
La displacement.",1501.03877v1
2015-02-10,Metallic Quantum Ferromagnets,"This review gives an overview of the quantum phase transition (QPT) problem
in metallic ferromagnets, discussing both experimental and theoretical aspects.
These QPTs can be classified with respect to the presence and strength of
quenched disorder: Clean systems generically show a discontinuous, or
first-order, QPT from the ferromagnetic state to a paramagnetic one as a
function of some control parameter, as predicted by theory. Disordered systems
are much more complicated, depending on the disorder strength and the distance
from the QPT. In many disordered materials the QPT is continuous, or second
order, and Griffiths-phase effects coexist with QPT singularities near the
transition. In other systems the transition from the ferromagnetic state at low
temperatures is to a different type of long-range order, such as an
antiferromagnetic or a spin-density-wave state. In still other materials a
transition to a state with glass-like spin dynamics is suspected. The review
provides a comprehensive discussion of the current understanding of these
various transitions, and of the relation between experimental and theoretical
developments.",1502.02898v2
2015-02-23,The nature of Itinerant Ferromagnetism of SrRuO3 : A DFT+DMFT Study,"We have investigated the temperature (T)-dependent evolution of electronic
structures and magnetic properties of an itinerant ferromagnet SrRuO3,
employing the combined scheme of the density functional theory and the
dynamical mean-field theory (DFT+DMFT). The inclusion of finite dynamical
correlation effects beyond the DFT well describes not only the incoherent hump
structure observed in the photoemission experiment but also the T-dependent
magnetic properties in accordance with experiments. We have shown that the
magnetization of SrRuO3 evolves with the Stoner behavior below the Curie
temperature (Tc), reflecting the weak itinerant ferromagnetic behavior, but the
local residual magnetic moment persists even above Tc, indicating the local
magnetic moment behavior. We suggest that the ferromagnetism of SrRuO3 has dual
nature of both weak and local moment limits, even though the magnetism of
SrRuO3 is more itinerant than that of Fe.",1502.06322v1
2015-02-24,Coarsening dynamics driven by vortex-antivortex annihilation in ferromagnetic Bose-Einstein condensates,"In ferromagnetic Bose-Einstein condensates (BECs), the quadratic Zeeman
effect controls magnetic anisotropy, which affects on magnetic domain pattern
formation. While the longitudinal magnetization is dominant (similar to the
Ising model) for a negative quadratic Zeeman energy, the transverse
magnetization is dominant (similar to the XY model) for a positive one. When
the quadratic Zeeman energy is positive, the coarsening dynamics is driven by
vortex-antivortex annihilation in the same way as the XY model. However, due to
superfluid flow of atoms, there exist several combinations of vortex-antivortex
pairs in ferromagnetic BECs, which makes the coarsening dynamics more
complicated than that of the XY model. We propose a revised domain growth law,
which is based on the growth law of the two-dimensional XY model, for a
two-dimensional ferromagnetic BEC with a positive quadratic Zeeman energy.",1502.06673v3
2015-03-11,Analytic results for the Casimir free energy between ferromagnetic metals,"We derive perturbation analytic expressions for the Casimir free energy and
entropy between two dissimilar ferromagnetic plates which are applicale at
arbitrarily low temperature. The dielectric properties of metals are described
using either the nondissipative plasma model or the Drude model taking into
account the dissipation of free charge carriers. Both cases of constant and
frequency-dependent magnetic permeability are considered. It is shown that for
ferromagnetic metals described by the plasma model the Casimir entropy goes to
zero when the temperature vanishes, i.e., the Nernst heat theorem is satisfied.
For ferromagnetic metals with perfect crystal lattices described by the Drude
model the Casimir entropy goes to a nonzero constant depending on the
parameters of a system with vanishing temperature, i.e., the Nernst heat
theorem is violated. This constant can be positive which is quite different
from the earlier investigated case of two nonmagnetic metals.",1503.03470v2
2015-03-22,Nitrogen-induced Ferromagnetism in BaO,"Density functional theory with local spin density approximation has been used
to propose possible room temperature ferromagnetism in N-doped NaCl-type BaO.
Pristine BaO is a wide bandgap semiconductor, however, N induces a large
density of states at the Fermi level in the nonmagnetic state, which suggests
magnetic instability within the Stoner mean field model. The spin-polarized
calculations show that N-doped BaO is a true half- metal, where N has a large
magnetic moment, which is mainly localized around the N atoms and a small
polarization at the O sites is also observed. The origin of magnetism is linked
to the electronic structure. The ferromagnetic(FM) and antiferromagnetic (AFM)
coupling between the N atoms in BaO reveal that doping N atoms have a FM ground
state, and the calculated transition temperature ($T_{C}$), within the
Heisenberg mean field theory, theorizes possible room temperature FM in N-doped
BaO. Nitrogen also induces ferromagnetism when doping occurs at surface O site
and has a smaller defect formation energy than the bulk N-doped BaO. The
magnetism of N-doped BaO is also compared with Co-doped BaO, and we believe
that N has a greater potential for tuning magnetism in BaO than Co.",1503.06455v2
2015-03-31,Spin Hall magnetoresistance in metallic bilayers,"Spin Hall magnetoresistance (SMR) is studied in metallic bilayers that
consist of heavy metal (HM) layer and a ferromagnetic metal (FM) layer. We find
nearly a ten-fold increase of SMR in W/CoFeB compared to previously studied
HM/ferromagnetic insulator (FI) systems. The SMR increases with decreasing
temperature despite the negligible change in the W layer resistivity with
temperature. A model is developed to account for the absorption of the
longitudinal spin current to the FM layer, one of the key characteristics of a
metallic ferromagnet. We find that the model not only quantitatively describes
the HM layer thickness dependence of SMR, allowing accurate estimation of the
spin Hall angle and the spin diffusion length of the HM layer, but also can
account for the temperature dependence of SMR by assuming a temperature
dependent spin polarization of the FM layer. These results illustrate the
unique role a metallic ferromagnetic layer plays in defining spin transmission
across the HM/FM interface.",1503.08903v2
2015-04-01,Surface Transport in the ν=0 Quantum Hall Ferromagnetic State in the Organic Dirac Fermion System,"We discuss the surface magnetotransport in the quantum Hall (QH)
ferromagnetic state expected in the organic Dirac fermion system
\alpha-(BEDT-TTF)_2I_3. The QH ferromagnetic state is one of the possible \nu=0
QH states in the two-dimensional Dirac fermion system resulting from the
degeneracy breaking of the n=0 Landau level. It is characterized by the helical
edge state. We have studied the interlayer surface transport via helical edge
state in the multilayer QH ferromagnet, in which the bulk region is insulating.
We have clarified that the surface conductivity is much less than e^2/h and
decreases as the magnetic field is tilted to the normal direction of the side
surface. These features explain the observed interlayer magnetoresistance in
\alpha-(BEDT-TTF)_2I_3.",1504.00270v1
2015-04-03,Spin-flipping with Holmium: Case study of proximity effect in superconductor/ferromagnet/superconductor heterostructures,"Superconductor/ferromagnet/superconductor heterostructures exhibit a
so-called long-range proximity effect provided some layers of conical magnet
Holmium are included in the respective interface regions. The Ho layers lead to
a spin-flip process at the interface generating equal-spin spin-triplet pairing
correlations in the ferromagnet. These equal-spin spin-triplet pairing
correlations penetrate much further into the heterostructure compared to the
spin-singlet and unequal-spin spin-triplet correlations which occur in the
absence of Ho. Here we present calculations of this effect based on the
spin-dependent microscopic Bogoliubov-de Gennes equations solved within a
tight-binding model in the clean limit. The influence of the ferromagnet and
conical magnet layer thickness on the induced equal-spin spin-triplet pairing
correlations is obtained and compared to available experimental data. It is
shown that, in agreement with experiment, a critical minimum thickness of
conical magnet layers has to be present in order to observe a sizeable amount
of equal-spin spin-triplet pairing correlations.",1504.00816v1
2015-04-10,Enhancement of the Anti-Damping Spin Torque Efficacy of Platinum by Interface Modification,"We report a strong enhancement of the efficacy of the spin Hall effect (SHE)
of Pt for exerting anti-damping spin torque on an adjacent ferromagnetic layer
by the insertion of $\approx$ 0.5 nm layer of Hf between a Pt film and a thin,
< 2 nm, Fe$_{60}$Co$_{20}$B$_{20}$ ferromagnetic layer. This enhancement is
quantified by measurement of the switching current density when the
ferromagnetic layer is the free electrode in a magnetic tunnel junction. The
results are explained as the suppression of spin pumping through a substantial
decrease in the effective spin-mixing conductance of the interface, but without
a concomitant reduction of the ferromagnet\' s absorption of the SHE generated
spin current.",1504.02806v1
2015-05-01,Exposure of the Hidden Anti-Ferromagnetism in Paramagnetic CdSe:Mn Nanocrystals,"We present theoretical and experimental investigations of the magnetism of
paramagnetic semiconductor CdSe:Mn nanocrystals and propose an efficient
approach to the exposure and analysis of the underlying anti-ferromagnetic
interactions between magnetic ions therein. A key advance made here is the
build-up of an analysis method with the exploitation of group theory technique
that allows us to distinguish the anti-ferromagnetic interactions between
aggregative Mn2+ ions from the overall pronounced paramagnetism of magnetic ion
doped semiconductor nanocrystals. By using the method, we clearly reveal and
identify the signatures of anti-ferromagnetism from the measured temperature
dependent magnetisms, and furthermore determine the average number of Mn2+ ions
and the fraction of aggregative ones in the measured CdSe:Mn nanocrystals.",1505.00126v1
2015-05-06,Magnetoresistance control in granular Zn/1-x-y/Cd/x/Mn/y/GeAs/2/ nanocomposite ferromagnetic semiconductors,"We present studies of structural, magnetic and electrical properties of
Zn/1-x-y/Cd/x/Mn/y/GeAs/2/ nanocomposite ferromagnetic semiconductor samples
with changeable chemical composition. The presence of MnAs clusters induces in
the studied alloy room temperature ferromagnetism with the Curie temperature,
TC, around 305 K. The chemical composition of the chalcopyrite matrix controls
the geometrical parameters of the clusters inducing different magnetoresistance
effects in the crystals. The presence of ferromagnetic clusters in the alloy
induces either negative or positive magnetoresistance with different values.
The Cd-content allows a change of magnetoresistance sign in our samples from
negative (for x = 0.85) to positive (for x = 0.12). The negative
magnetoresistance present in the samples with x = 0.85 is observed at
temperatures T < 25 K with maximum values of about -32% at T = 1.4 K and B = 13
T, strongly depending on the Mn content, y. The positive magnetoresistance
present in the samples with x = 0.12 is observed with maximum values not
exceeding 50% at B =13 T and T = 4.3 K, changing with the Mn content, y.",1505.01357v1
2015-05-08,Itinerant Ferromagnetism and $p+ip'$ Superconductivity in Doped Bilayer Silicene,"We study the electronic instabilities of doped bilayer silicene using the
random phase approximation. In contrast to the singlet $d+id'$
superconductivity at the low doping region, we find that the system is an
itinerant ferromagnet in the narrow doping regions around the Van Hove
singularities, and a triplet $p+ip'$ superconductor in the vicinity of these
regions. Adding a weak Kane-Mele spin-orbit coupling to the system further
singles out the time-reversal invariant equal-spin helical $p+ip'$ pairing as
the leading instability. The triplet pairing identified here is driven by the
ferromagnetic fluctuations, which become strong and enhance the superconducting
critical temperature remarkably near the phase boundaries between
ferromagnetism and superconductivity.",1505.01971v1
2015-05-18,Evidence on the macroscopic length scale spin coherence for the edge currents in a narrow HgTe quantum well,"We experimentally investigate spin-polarized electron transport between two
ferromagnetic contacts, placed at the edge of a two-dimensional electron system
with band inversion. The system is realized in a narrow (8~nm) HgTe quantum
well, the ferromagnetic side contacts are formed from a pre-magnetized
permalloy film. In zero magnetic field, we find a significant edge current
contribution to the transport between two ferromagnetic contacts. We
experimentally demonstrate that this transport is sensitive to the mutual
orientation of the magnetization directions of two 200~$\mu$m-spaced
ferromagnetic leads. This is a direct experimental evidence on the
spin-coherent edge transport over the macroscopic distances. Thus, the spin is
extremely robust at the edge of a two-dimensional electron system with band
inversion, confirming the helical spin-resolved nature of edge currents.",1505.04535v1
2015-05-21,Ferromagnetism in Cr-doped topological insulator TlSbTe2,"We have synthesized a new ferromagnetic topological insulator by doping Cr to
the ternary topological-insulator material TlSbTe2. Single crystals of
Tl_{1-x}Cr_{x}SbTe2 were grown by a melting method and it was found that Cr can
be incorporated into the TlSbTe2 matrix only within the solubility limit of
about 1%. The Curie temperature \theta_c was found to increase with the Cr
content but remained relatively low, with the maximum value of about 4 K. The
easy axis was identified to be the c-axis and the saturation moment was 2.8
\mu_B (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples
studied showed metallic behavior with p-type carriers. Shubnikov-de Hass (SdH)
oscillations were observed in samples with the Cr-doping level of up to 0.76%.
We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no
ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility
limit of Cr which turned out to be also about 1%.",1505.05631v1
2015-05-26,High-$T_c$ $d^{0}$ ferromagnetism in a doped Mott insulator: the case of hydrogenated epitaxial graphene on SiC(0001),"We show that the $d^{0}$ ferromagnetism with high Curie temperature ($T_c$)
can be achieved in the electron doped hydrogenated epitaxial graphene on some
certain SiC substrates through first-principles calculations. The pristine
systems are found to be a Mott insulator independent of SiC polytypes (2$H$,
4$H$ or 6$H$) which, however, play a significant role in the modulation of
magnetic interaction. Carrier doping enhances the ferromagnetic coupling due to
the double exchange mechanism and thus realizes the phase transition from
antiferromagnetism to ferromagnetism. A $T_c$ of around 400 K is predicted on
the 2$H$-SiC. We employ a non-degenerate Hubbard model to demonstrate how the
SiC affects the interfacial magnetism in intra-atomic Coulomb repulsion and
intersite hopping interactions.",1505.06823v1
2015-05-28,Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal,"We explore the ferromagnetic quantum critical point in a three-dimensional
semimetallic system with upward- and downward-dispersing bands touching at the
Fermi level. Evaluating the static spin susceptibility to leading order in the
coupling between the fermions and the fluctuating ferromagnetic order
parameter, we find that the ferromagnetic quantum critical point is masked by
an incommensurate, longitudinal spin density wave phase. We first analyze an
idealized model which, despite having strong spin-orbit coupling, still
possesses O(3) rotational symmetry generated by the total angular momentum
operator. In this case, the direction of the incommensurate spin density wave
propagation can point anywhere, while the magnetic moment is aligned along the
direction of propagation. Including symmetry-allowed anisotropies in the
fermion dispersion and the coupling to the order parameter field, however, the
ordering wavevector instead breaks a discrete symmetry and aligns along either
the [111] or [100] direction, depending on the signs and magnitudes of these
two types of anisotropy.",1505.07685v1
2015-06-01,Magnetism in Na-filled Fe-based skutterudites,"The interplay of superconductivity and magnetism is a subject of ongoing
interest, stimulated most recently by the discovery of Fe-based
superconductivity and the recognition that spin-fluctuations near a magnetic
quantum critical point may provide an explanation for the superconductivity and
the order parameter. Here we investigate magnetism in the Na filled Fe-based
skutterudites using first principles calculations. NaFe4Sb12 is a known
ferromagnet near a quantum critical point. We find a ferromagnetic metallic
state for this compound driven by a Stoner type instability, consistent with
prior work. In accord with prior work, the magnetization is overestimated, as
expected for a material near an itinerant ferromagnetic quantum critical point.
NaFe4P12 also shows a ferromagnetic instability at the density functional
level, but this instability is much weaker than that of NaFe4Sb12, possibly
placing it on the paramagnetic side of the quantum critical point. NaFe4As12
shows intermediate behavior. We also present results for skutterudite FeSb3,
which is a metastable phase that has been reported in thin film form.",1506.00514v1
2015-06-02,Screened moments and absence of ferromagnetism in FeAl,"While the stoichiometric intermetallic compound FeAl is found to be
paramagnetic in experiment, standard band-theory approaches predict the
material to be ferromagnetic. We show that this discrepancy can be overcome by
a better treatment of electronic correlations with density functional plus
dynamical mean field theory. Our results show no ferromagnetism down to 100 K
and since the susceptibility is decreasing at the lowest temperatures studied
we also do not expect ferromagnetism at even lower temperatures. This behavior
is found to originate from temporal quantum fluctuations that screen
short-lived local magnetic moments of 1.6 $\mu_B$ on Fe.",1506.00908v2
2015-06-23,Monte Carlo Methods for the Ferromagnetic Potts Model Using Factor Graph Duality,"Normal factor graph duality offers new possibilities for Monte Carlo
algorithms in graphical models. Specifically, we consider the problem of
estimating the partition function of the ferromagnetic Ising and Potts models
by Monte Carlo methods, which are known to work well at high temperatures, but
to fail at low temperatures. We propose Monte Carlo methods (uniform sampling
and importance sampling) in the dual normal factor graph, and demonstrate that
they behave differently: they work particularly well at low temperatures. By
comparing the relative error in estimating the partition function, we show that
the proposed importance sampling algorithm significantly outperforms the
state-of-the-art deterministic and Monte Carlo methods. For the ferromagnetic
Ising model in an external field, we show the equivalence between the valid
configurations in the dual normal factor graph and the terms that appear in the
high-temperature series expansion of the partition function. Following this
result, we discuss connections with Jerrum-Sinclair's polynomial randomized
approximation scheme (the subgraphs-world process) for evaluating the partition
function of ferromagnetic",1506.07044v4
2015-06-25,Quantum Hall ferromagnets and transport properties of buckled Dirac materials,"We study the ground states and low-energy excitations of a generic Dirac
material with spin-orbit coupling and a buckling structure in the presence of a
perpendicular magnetic field. The ground states can be classified into three
types under different conditions: SU(2), easy-plane, and Ising quantum Hall
ferromagnets. For the SU(2) and the easy-plane quantum Hall ferromagnets there
are goldstone modes in the collective excitations, while all the modes are
gapped in an Ising-type ground state. We compare the Ising quantum Hall
ferromagnet with that of bilayer graphene and present the domain wall solution
at finite temperatures. We then specify the phase transitions and transport
gaps in silicene in Landau levels 0 and 1. The phase diagram strongly depends
on the magnetic field and the dielectric constant. We note that there exists
triple points in the phase diagrams in Landau level N = 1 that could be
observed in experiments.",1506.07896v1
2015-07-03,Magnetization switching by spin-orbit torque in an antiferromagnet/ferromagnet bilayer system,"Spin-orbit torque (SOT)-induced magnetization switching shows promise for
realizing ultrafast and reliable spintronics devices. Bipolar switching of
perpendicular magnetization via SOT is achieved under an in-plane magnetic
field collinear with an applied current. Typical structures studied so far
comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in
the NM is responsible for the switching. Here we show that an
antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large
enough to switch the magnetization of FM. In this material system, thanks to
the exchange-bias effect of the AFM, we observe the switching under no applied
field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer
with a perpendicular easy axis. Furthermore, tailoring the stack achieves a
memristor-like behaviour where a portion of the reversed magnetization can by
controlled in an analogue manner. The AFM/FM system is thus a promising
building block for SOT devices as well as providing an attractive pathway
towards neuromorphic computing.",1507.00888v1
2015-07-21,Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases,"Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of
transition-group d-metals and main-group p-elements. Here, we report the
realization of FSMAs in Heusler phases that completely consist of d metals. By
introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is
obtained and the martensitic transformation temperature is decreased
efficiently. Strong ferromagnetism is established by further doping Co atoms
into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the
magnetic-field-induced martensitic transformations, collective multifunctional
properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only
facilitate the formation of B2-type Heusler phases, but also establish strong
ferromagnetic coupling and offer the possibility to tune the martensitic
transformation.",1507.05907v1
2015-07-23,Ba{0.4}Rb{0.6}Mn2As2: A Prototype Half-Metallic Ferromagnet,"Half-metallic ferromagnetism (FM) in single-crystal
Ba{0.39(1)}Rb{0.61(1)}Mn2As2 below its Curie temperature TC = 103(2) K is
reported. The magnetization M versus applied magnetic field H isotherm data at
1.8 K show complete polarization of the itinerant doped-hole magnetic moments
that are introduced by substituting Rb for Ba. The material exhibits extremely
soft FM, with unobservably small remanent magnetization and coercive field.
Surprisingly, and contrary to typical itinerant FMs, the M(H) data follow the
Arrott-plot paradigm that is based on a mean-field theory of local-moment FMs.
The in-plane electrical resistivity data are fitted well by an activated-T^2
expression for T < TC, whereas the data sharply deviate from this model for T >
TC. Hence the activated-T^2 resistivity model is an excellent diagnostic for
determining the onset of half-metallic FM in this compound, which in turn
demonstrates the presence of a strong correlation between the electronic
transport and magnetic properties of the material. Together with previous data
on 40% hole-doped Ba{0.6}K{0.4}Mn2As2, these measurements establish 61%-doped
Ba{0.39}Rb{0.61}Mn2As2 as a prototype for a new class of half-metallic
ferromagnets in which all the itinerant carriers in the material are
ferromagnetic.",1507.06679v1
2015-08-05,Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor,"Considerable evidence for proximity-induced triplet superconductivity on the
ferromagnetic side of a superconductor-ferromagnet (S-F) interface now exists;
however, the corresponding effect on the superconductor side has hardly been
addressed. We have performed scanning tunneling spectroscopy measurements on
NbN superconducting thin films proximity coupled to the half-metallic
ferromagnet La2/3Ca1/3MnO3 (LCMO) as a function of magnetic field. We have
found that at zero and low applied magnetic fields the tunneling spectra on NbN
typically show an anomalous gap structure with suppressed coherence peaks and,
in some cases, a zero-bias conductance peak. As the field increases to the
magnetic saturation of LCMO where the magnetization is homogeneous, the spectra
become more BCS-like and the critical temperature of the NbN increases,
implying a reduced proximity effect. Our results therefore suggest that
triplet-pairing correlations are also induced in the S side of an S-F bilayer.",1508.01070v1
2015-08-05,Comparison of the ferromagnetic Blume-Emery-Griffiths model and the AF spin-1 longitudinal Ising model at low temperature,"We derive the exact Helmholtz free energy (HFE) of the standard and staggered
one-dimensional Blume-Emery-Griffiths (BEG) model in the presence of an
external longitudinal magnetic field. We discuss in detail the thermodynamic
behavior of the ferromagnetic version of the model, which exhibits magnetic
field-dependent plateaux in the $z$-component of its magnetization at low
temperatures. We also study the behavior of its specific heat and entropy, both
per site, at finite temperature. The degeneracy of the ground state, at $T=0$,
along the lines that separate distinct phases in the phase diagram of the
ferromagnetic BEG model is calculated, extending the study of the phase diagram
of the spin-1 antiferromagnetic (AF) Ising model in[S.M. de Souza and M.T.
Thomaz, J. of Mag. and Mag. Mat. {354} (2014) 205]. We explore the implications
of the equality of phase diagrams, at $T=0$, of the ferromagnetic BEG model
with $\frac{K}{|J|} = -2$ and of the spin-1 AF Ising model for $\frac{D}{|J|} >
\frac{1}{2}$.",1508.01245v1
2015-08-14,Spatially resolved penetration depth measurements and vortex manipulation in the ferromagnetic superconductor ErNi2B2C,"We present a local probe study of the magnetic superconductor,
ErNi$_2$B$_2$C, using magnetic force microscopy at sub-Kelvin temperatures.
ErNi$_2$B$_2$C is an ideal system to explore the effects of concomitant
superconductivity and ferromagnetism. At 500 mK, far below the transition to a
weakly ferromagnetic state, we directly observe a structured magnetic
background on the micrometer scale. We determine spatially resolved absolute
values of the magnetic penetration depth $\lambda$ and study its temperature
dependence as the system undergoes magnetic phase transitions from paramagnetic
to antiferromagnetic, and to weak ferromagnetic, all within the superconducting
regime. In addition, we estimate the absolute pinning force of Abrikosov
vortices, which shows a position- and temperature dependence as well, and
discuss the possibility of the purported spontaneous vortex formation.",1508.03462v1
2015-09-03,Investigation of ferromagnetic domain behavior and phase transition at nanoscale in bilayer manganites,"Understanding the underlying mechanism and phenomenology of colossal
magnetoresistance in manganites has largely focused on atomic and nanoscale
physics such as double exchange, phase separation, and charge order. Here we
consider a more macroscopic view of manganite materials physics, reporting on
the ferromagnetic domain behavior in a bilayer manganite sample with a nominal
composition of La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ with $x=0.38$, studied using
in-situ Lorentz transmission electron microscopy. The role of
magnetocrystalline anisotropy on the structure of domain walls was elucidated.
On cooling, magnetic domain contrast was seen to appear first at the Curie
temperature within the $a-b$ plane. With further reduction in temperature, the
change in area fraction of magnetic domains was used to estimate the critical
exponent describing the ferromagntic phase transition. The ferromagnetic phase
transition was accompanied by a distinctive nanoscale granular contrast close
to the Curie temperature, which we infer to be related to the presence of
ferromagnetic nanoclusters in a paramagnetic matrix, which has not yet been
reported in bilayer manganites.",1509.01106v1
2015-09-11,"Growth and characterization of insulating ferromagnetic semiconductor (Al,Fe)Sb","We investigate the crystal structure, transport and magnetic properties of
Fe-doped ferromagnetic semiconductor (Al1-x,Fex)Sb thin films up to x = 14%
grown by molecular beam epitaxy. All the samples show p-type conduction at room
temperature and insulating behavior at low temperature. The (Al1-x,Fex)Sb thin
films with x lower or equal to 10% maintain the zinc blende crystal structure
of the host material AlSb. The (Al1-x,Fex)Sb thin film with x = 10% shows
intrinsic ferromagnetism with a Curie temperature (TC) of 40 K. In the
(Al1-x,Fex)Sb thin film with x = 14%, a sudden drop of mobility and TC was
observed, which may be due to microscopic phase separation. The observation of
ferromagnetism in (Al,Fe)Sb paves the way to realize a spin-filtering tunnel
barrier that is compatible with well-established III-V semiconductor devices.",1509.03430v1
2015-09-22,Field-effect Modulation of Anomalous Hall Effect in Diluted Ferromagnetic Topological Insulator Epitaxial Films,"High quality chromium (Cr) doped three-dimensional topological insulator (TI)
Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating
SrTiO3(111) substrates. We report that the Dirac surface states are insensitive
to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled
in epitaxial Sb2-xCrxTe3 films. The anomalous Hall effect is modulated by
applying a bottom gate, contrary to the ferromagnetism in conventional diluted
magnetic semiconductors (DMSs), here the coercivity field is not significantly
changed with decreasing carrier density. Carrier-independent ferromagnetism
heralds Sb2-xCrxTe3 films as the base candidate TI material to realize the
quantum anomalous Hall (QAH) effect. These results also indicate the potential
of controlling anomalous Hall voltage in future TI-based magneto-electronics
and spintronics.",1509.06608v1
2015-10-04,Tunneling Magnetoresistance in Junctions Composed of Ferromagnets and Time-Reversal Invariant Topological Superconductors,"Tunneling Magnetoresistance between two ferrromagnets is an issue of
fundamental importance in spintronics. In this work, we show that tunneling
magnetoresistance can also emerge in junctions composed of ferromagnets and
time-reversal invariant topological superconductors without spin-rotation
symmetry. Here the physical origin is that when the spin-polarization direction
of injected electron from the ferromagnet lying in the same plane of the
spin-polarization direction of Majorana zero modes, the electron will undergo a
perfect spin-equal Andreev reflection, while injected electrons with other
spin-polarization direction will be partially Andreev reflected and partially
normal reflected, which consequently have a lower conductance, and therefore,
the magnetoresistance effect emerges. Compared to conventional magnetic tunnel
junctions, an unprecedented advantage of the junctions studied here is that
arbitrary high tunneling magnetoresistance can be obtained even the
magnetization of the ferromagnets are weak and the insulating tunneling
barriers are featureless. Our findings provide a new fascinating mechanism to
obtain high tunneling magnetoresistance.",1510.00901v2
2015-10-07,Towards ferromagnetic quantum criticality in FeGa3-xGex: 71Ga NQR as a zero field microscopic probe,"71Ga NQR, magnetization and specific heat measurements have been performed on
polycrystalline Ge doped FeGa3 samples. A crossover from an insulator to a
correlated local moment metal in the low doping regime and the evolution of
itinerant ferromagnet upon further doping is found. For the nearly critical
concentration at the threshold of ferromagnetic order, xC=0.15, (1/T1T)
exhibits a pronounced T4/3 power law over two orders of magnitude in
temperature which indicates 3D quantum critical ferromagnetic fluctuations.
Furthermore, for the ordered x = 0.2 sample (TC = 6 K) 1/T1T could be fitted
well in the frame of Moriya's SCR theory for weakly FM systems with 1/T1T
proportional to chi. In contrast to this, the low doping regime nicely displays
local moment behavior where 1/T1T proportional to chi2 is valid. For
temperature tending to zero the Sommerfeld ratio = (C/T) is enhanced (70
mJ/mole-K2 for x = 0.1) which indicates the formation of heavy 3d-electrons.",1510.01974v1
2015-10-07,Spontaneous Liquid Crystal and Ferromagnetic Ordering of Colloidal Magnetic Nanoplates,"Ferrofluids are familiar as colloidal suspensions of ferromagnetic
nanoparticles in aqueous or organic solvents. The dispersed particles are
randomly oriented but their moments become aligned if a magnetic field is
applied, producing a variety of exotic and useful magneto-mechanical effects. A
longstanding interest and challenge has been to make such suspensions
macroscopically ferromagnetic, that is having uniform magnetic alignment in
absence of a field. Here we report a fluid suspension of magnetic nanoplates
which spontaneously aligns into an equilibrium nematic liquid crystal phase
that is also macroscopically ferromagnetic. Its zero-field magnetization
produces distinctive magnetic self-interaction effects, including liquid
crystal textures of fluid block domains arranged in closed flux loops, and
makes this phase highly sensitive, with it dramatically changing shape even in
the Earth's magnetic field.",1510.02161v2
2015-10-26,Doping-Induced Ferromagnetism and Possible Triplet Pairing in d4 Mott Insulators,"We study the effects of electron doping in Mott insulators containing d^4
ions such as Ru4+, Os4+, Rh5+, and Ir5+ with J=0 singlet ground state.
Depending on the strength of the spin-orbit coupling, the undoped systems are
either nonmagnetic or host an unusual, excitonic magnetism arising from a
condensation of the excited J=1 triplet states of t_2g^4. We find that the
interaction between J-excitons and doped carriers strongly supports
ferromagnetism, converting both the nonmagnetic and antiferromagnetic phases of
the parent insulator into a ferromagnetic metal, and further to a nonmagnetic
metal. Close to the ferromagnetic phase, the low-energy spin response is
dominated by intense paramagnon excitations that may act as mediators of a
triplet pairing.",1510.07508v2
2015-10-28,Magnetic Impurity in a Tonks Gas of Fermions,"In this letter we consider a magnetic impurity in a one-dimensional
spin-$1/2$ Fermi gas with infinitely strong repulsive interaction between
fermions. We rigorously prove that, independent of whether the magnetic
coupling between impurity and fermions is ferromagnetic or anti-ferromagnetic,
the ground state is always a fully polarized ferromagnetic state for the
itinerant fermions. This ferromagnetism can be understood as a cooperative
effect of avoiding frustration of magnetic coupling during fermion hopping and
the large spin degeneracy of a fermion Tonks gas. By numerically diagonalizing
a finite size system, we show that the spin gap first increases linearly with
magnetic coupling strength in the weak coupling regime, while decreases in the
strong coupling regime. Our results show that a magnetic impurity in a strongly
correlated gas can exhibit effect different from the Kondo effect as in a
weakly correlated Fermi liquid.",1510.08303v2
2015-11-07,Quantum triangular ice in the easy-axis ferromagnetic phase,"We use spin wave theory to investigate the ground state properties of the
$Z_2$-invariant quantum XXZ model on the triangular lattice in the
ferromagnetic phase. The Hamiltonian comprises nearest and
next-nearest-neighbour Ising couplings, external magnetic fields, and a
$Z_2$-invariant ferromagnetic coupling. We show that quantum fluctuations are
suppressed in this system, hence linear spin wave theory gives reasonable
estimates of the ground state thermodynamic properties. Our results show that,
at half-filling (zero magnetic fields), the spontaneous breaking of $Z_2$
symmetry leads to a ferromagnetic phase whose energy spectrum is gapped at all
excitations with a maxon dispersion at $\mathbf{k}=0$. This is in sharp
contrast to rotational invariant systems with a vanishing phonon dispersion. We
show that the $\mathbf{k}=0$ mode enhances the estimated values of the
thermodynamic quantities. We obtain the trends of the particle density and the
condensate fraction. The density of states and the dynamical structure factors
exhibit fascinating peaks at unusual wave vectors, which should be of interest.",1511.02311v3
2016-01-14,Topological textures and their bifurcation processes in 2D ferromagnetic thin films,"In this paper, by the use of the topological current theory, the topological
structures and the dynamic processes in thin-film ferromagnetic systems are
investigated directly from viewpoint of topology. It is found that the
topological charge of a thin-film ferromagnetic system can be changed by
annihilation or creation processes of opposite polarized vortex-antivortex
pairs taking place at space-time singularities of the normalized magnetization
vector field of the system, the variation of the topological charge is integer
and can further be expressed in terms of the Hopf indices and Brouwer degrees
of the magnetization vector field around the singularities. Moreover, the
change of the topological charge of the system is crucial to vortex core
reversal processes in ferromagnetic thin films. With the help of the
topological current theory and implicit function theorem, the processes of
vortex merging, splitting as well as vortex core",1601.03487v1
2016-01-18,Incommensurate spin-density-wave antiferromagnetism in CeRu$_2$Al$_2$B,"The newly discovered Ising-type ferromagnet CeRu$_2$Al$_2$B exhibits an
additional phase transition at $T_\textrm{N}$ = 14.2 K before entering the
ferromagnetic ground state at $T_\textrm{C}$ = 12.8 K. We clarify the nature of
this transition through high resolution neutron diffraction measurements. The
data reveal the presence of a longitudinal incommensurate spin-density wave
(SDW) in the temperature range of $T_\textrm{C}<T<T_\textrm{N}$. The
propagation vector ${\bf q} \sim (0,0,0.148)$ is nearly temperature independent
in this region and discontinuously locks into ${\bf q} = 0$ at $T_\textrm{C}$.
Mean-field calculations of an effective Ising model indicate that the modulated
SDW phase is stabilized by a strong competition between ferromagnetic and
antiferromagnetic exchange interactions. This makes CeRu$_2$Al$_2$B a
particularly attractive model system to study the global phase diagram of
ferromagnetic heavy-fermion metals under influence of magnetic frustration.",1601.04430v1
2016-02-25,Ferromagnetic ordering of minority Ce$^{3+}$ spins in a quasi-skutterudite Ce${_3}$Os${_4}$Ge$_{13}$ single crystal,"We report site disorder driven ferromagnetic ordering of nearly 8$\%$ Ce
atoms in single crystalline Ce${_3}$Os${_4}$Ge$_{13}$ below 0.5~K.
Ce${_3}$Os${_4}$Ge$_{13}$ crystallizes in a cubic structure with space group
$\it{Pm\bar{3}n}$. The structural analysis shows the presence of site-disorder
in the system, where 2(a) Ge site is partially occupied by the Ce atoms. Due to
the small Ce $4f$-ligand hybridization, these Ce atoms are in the Ce$^{3+}$
(magnetic) state while rest of the Ce atoms in the unit cell are in
Ce$^{4-\delta}$ (non-magnetic) state. The heat capacity shows a peak below
0.5~K corresponding to the ferromagnetic ordering of the Ce$^{3+}$ moments. The
ferromagnetic ordering below 0.5~K is also seen in the ac-susceptibility data.
At low temperatures (1.8~K$\leq T\leq 6$~K), the magnetization shows $log(T)$
dependence, whereas the resistivity shows power law ($T^n$) temperature
dependence indicating the non-Fermi liquid behavior of the quasiparticles.",1602.07899v1
2016-02-26,Theory of light-induced effective magnetic field in Rashba ferromagnets,"Motivated by recent experiments on all-optical magnetization reversal in
conductive ferromagnetic thin films we use nonequilibrium formalism to
calculate the effective magnetic field induced in a Rashba ferromagnet by a
short laser pulse. The main contribution to the effect originates in the direct
optical transitions between spin-split subbands. The resulting effective
magnetic field is inversely proportional to the impurity scattering rate and
can reach the amplitude of a few Tesla in the systems like Co/Pt bilayers. We
showthat the total light-induced effective magnetic field in ferromagnetic
systems is the sum of two contributions: a helicity dependent term, which is an
even function of magnetization, and a helicity independent term, which is an
odd function of magnetization. The primary role of the spin-orbit interaction
is to widen the frequency range for direct optical transitions.",1602.08305v2
2016-03-14,Spin Hall Effect Induced Spin Transfer Through an Insulator,"When charge current passes through a normal metal that exhibits spin Hall
effect, spin accumulates at the edge of the sample in the transverse direction.
We predict that this spin accumulation, or spin voltage, enables quantum
tunneling of spin through an insulator or vacuum to reach a ferromagnet without
transferring charge. In a normal metal/insulator/ferromagnetic insulator
trilayer (such as Pt/oxide/YIG), the quantum tunneling explains the
spin-transfer torque and spin pumping that exponentially decay with the
thickness of the insulator. In a normal metal/insulator/ferromagnetic metal
trilayer (such as Pt/oxide/Co), the spin transfer in general does not decay
monotonically with the thickness of the insulator. Combining with the spin Hall
magnetoresistance, this tunneling mechanism points to the possibility of a new
type of tunneling spectroscopy that can probe the magnon density of states of a
ferromagnetic insulator in an all-electrical and noninvasive manner.",1603.04240v2
2016-03-30,Magnetic Interactions and Electronic Structure of Pt$_{2}$Mn$_{1-x}$Y$_{x}$Ga (Y = Cr and Fe) system : An ab-initio calculation,"First principles density functional theory based calculations have been
carried out to predict the effects of Mn replacement by Fe and Cr on electronic
as well as magnetic properties of Pt$_{2}$MnGa as well as Ni$_{2}$MnGa. All the
materials studied here are predicted to have conventional Heusler alloy
structure in their ground state and they are found to be electronically stable
on the basis of their respective formation energy. The replacement of Mn by Fe
leads to a ferromagnetic ground state whereas in case of Mn replacement by Cr
an {\it intra-sublattice} anti-ferromagnetic configuration has been observed to
have lower energy. We study the magnetic exchange interaction between the atoms
for the materials with ferromagnetic and anti-ferromagnetic configurations to
show the effects of Fe and Cr substitution at Mn site on the magnetic
interactions of these systems. Detailed analysis of electronic structure in
terms of density of states has been carried out to study the effect of
substitution.",1603.09139v1
2016-04-04,Ferromagnetism in a Repulsive Atomic Fermi Gas with Correlated Disorder,"We investigate the zero-temperature ferromagnetic behavior of a two-component
repulsive Fermi gas in the presence of a correlated random field that
represents an optical speckle pattern. The density is tuned so that the
(noninteracting) Fermi energy is close to the mobility edge of the Anderson
localization transition. We employ quantum Monte Carlo simulations to determine
various ground-state properties, including the equation of state, the magnetic
susceptibility, and the energy of an impurity immersed in a polarized Fermi gas
(repulsive polaron). In the weakly interacting limit, the magnetic
susceptibility is found to be suppressed by disorder. However, it rapidly
increases with the interaction strength, and it diverges at a much weaker
interaction strength compared to the clean gas. Both the transition from the
paramagnetic phase to the partially ferromagnetic phase, and the one from the
partially to the fully ferromagnetic phase are strongly favored by disorder,
indicating a case of order induced by disorder.",1604.01052v1
2016-04-06,Metallic ferromagnetism-insulating charge order transition in doped manganites,"We show that an interplay of double exchange and impurity randomness can
explain the competition between metal-ferromagnetic and insulating charge
ordered states in doped manganites. The double exchange is simplified in the
Ising type, whereas the randomness is modeled by the Falicov-Kimball binary
distribution. The combined model is considered in a framework of dynamical
mean-field theory. Using the Kubo-Greenwood formalism, the transport
coefficients are explicitly expressed in terms of single particle spectral
functions. Dividing the system into two sublattices we have pointed out a
direct calculation to the checkerboard charge order parameter and the
magnetizations. Numerical results show us that the checkerboard charge order
can settle inside the ferromagnetic state at low temperature. An
insulator-metal transition is also found at the point of the checkerboard
charge order-ferromagnetic transition.",1604.01511v2
2016-04-19,Electric field control of deterministic current-induced magnetization switching in a hybrid ferromagnetic/ferroelectric structure,"All-electrical and programmable manipulations of ferromagnetic bits are
highly pursued for the aim of high integration and low energy consumption in
modern information technology. Methods based on the spin-orbit torque switching
in heavy metal/ferromagnet structures have been proposed with magnetic field,
and recently are heading toward deterministic switching without external
magnetic field. Here we demonstrate that an in-plane effective magnetic field
can be induced by an electric field without breaking the symmetry of the
structure of the thin film, and realize the deterministic magnetization
switching in a hybrid ferromagnetic/ferroelectric structure with Pt/Co/Ni/Co/Pt
layers on PMN-PT substrate. The effective magnetic field can be reversed by
changing the direction of the applied electric field on the PMN-PT substrate,
which fully replaces the controllability function of the external magnetic
field. The electric field is found to generate an additional spin-orbit torque
on the CoNiCo magnets, which is confirmed by macrospin calculations.",1604.05561v1
2016-04-29,Magneto-Elastic Coupling in a potential ferromagnetic 2D Atomic Crystal,"Cr2Ge2Te6 has been of interest for decades, as it is one of only a few
naturally forming ferromagnetic semiconductors. Recently, this material has
been revisited due to its potential as a 2 dimensional semiconducting
ferromagnet and a substrate to induce anomalous quantum Hall states in
topological insulators. However, many relevant properties of Cr2Ge2Te6 still
remain poorly understood, especially the spin-phonon coupling crucial to
spintronic, multiferrioc, thermal conductivity, magnetic proximity and the
establishment of long range order on the nanoscale. We explore the interplay
between the lattice and magnetism through high resolution micro-Raman
scattering measurements over the temperature range from 10 K to 325 K. Strong
spin-phonon coupling effects are confirmed from multiple aspects: two low
energy modes splits in the ferromagnetic phase, magnetic quasielastic
scattering in paramagnetic phase, the phonon energies of three modes show clear
upturn below Tc, and the phonon linewidths change dramatically below Tc as
well. Our results provide the first demonstration of spin-phonon coupling in a
potential 2 dimensional atomic crystal.",1604.08745v1
2016-06-02,Band structure and spin texture of Bi$_2$Se$_3$/3d ferromagnetic metal interface,"The spin-helical surface states in three-dimensional topological insulator
(TI), such as Bi2Se3, are predicted to have superior efficiency in converting
charge current into spin polarization. This property is said to be responsible
for the giant spin-orbit torques observed in ferromagnetic metal/TI structures.
In this work, using first-principles and model tight-binding calculations, we
investigate the interface between the topological insulator Bi2Se3 and
3d-transition ferromagnetic metals Ni and Co. We find that the difference in
the work functions of the topological insulator and the ferromagnetic metals
shift the topological surface states down about 0.5 eV below the Fermi energy
where the hybridization of these surface states with the metal bands destroys
their helical spin structure. The band alignment of Bi2Se3 and Ni (Co) places
the Fermi energy far in the conduction band of bulk Bi2Se3, where the spin of
the carriers is aligned with the magnetization in the metal. Our results
indicate that the topological surface states are unlikely to be responsible for
the huge spin-orbit torque effect observed experimentally in these systems.",1606.00763v1
2016-06-24,Tunable magnon Weyl points in ferromagnetic pyrochlores,"The dispersion relations of magnons in ferromagnetic pyrochlores with
Dzyaloshinskii-Moriya interaction is shown to possess Weyl points, i.\,e.,
pairs of topological nontrivial crossings of two magnon branches with opposite
topological charge. As a consequence of their topological nature, their
projections onto a surface are connected by magnon arcs, thereby resembling
closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions
of the Weyl points in reciprocal space can be tuned widely by an external
magnetic field: rotated within the surface plane, the Weyl points and magnon
arcs are rotated as well; tilting the magnetic field out-of-plane shifts the
Weyl points toward the center $\bar{\Gamma}$ of the surface Brillouin zone. The
theory is valid for the class of ferromagnetic pyrochlores, i.\,e.,
three-dimensional extensions of topological magnon insulators on kagome
lattices. In this Letter, we focus on the $(111)$ surface, identify candidates
of established ferromagnetic pyrochlores which apply to the considered spin
model, and suggest experiments for the detection of the topological features.",1606.07612v1
2016-07-15,Chiral Phonons and Electrical Resistivity of Ferromagnetic Metals at Low Temperatures,"Ferromagnetism is an exciting phase of matter exhibiting strongly correlated
electron behavior and a standard example of spontaneously broken rotational
symmetry: below the Curie temperature, atomic magnets in an isotropic
single-domain ferromagnetic metal align along a spontaneously chosen direction.
The scattering of conduction electrons from thermal perturbations to this spin
order, together with electron-electron collisions, mark the material electrical
behavior at low temperatures, where the resistivity varies mostly quadratically
with the temperature. Around liquid-helium temperatures however, an interesting
phenomenon occurs, giving rise to an extra \emph{linear} contribution to the
variation of the electrical resistivity with temperature, whose theoretical
explanation has encountered problems for a long time. Here I introduce a
spin-flip scattering mechanism of conduction electrons in ferromagnetic metals
arising from their interaction with the internal magnetic induction and
mediated by chiral modes of the crystal lattice vibrations carrying spin 1.
This mechanism is able to explain the above anomaly and give a good account of
the spin-lattice relaxation times of iron, cobalt and nickel at room
temperatures.",1607.04585v2
2016-07-21,Collapse of ferromagnetism and Fermi surface instability near reentrant superconductivity of URhGe,"We present thermoelectric power and resistivity measurements in the
ferromagnetic superconductor URhGe for magnetic field applied along the hard
magnetization b axis of the orthorhombic crystal. Reentrant superconductivity
is observed near the the spin reorientation transition at $H_{R}$=12.75 T,
where a first order transition from the ferromagnetic to the polarized
paramagnetic state occurs. Special focus is given to the longitudinal
configuration, where both electric and heat current are parallel to the applied
field. The validity of the Fermi-liquid $T^2$ dependence of the resistivity
through $H_R$ demonstrates clearly that no quantum critical point occurs at
$H_R$. Thus the ferromagnetic transition line at $H_R$ becomes first order
implying the existence of a tricritical point at finite temperature. The
enhancement of magnetic fluctuations in the vicinity of the tricritical point
stimulates the reentrance of superconductivity. The abrupt sign change observed
in the thermoelectric power with the thermal gradient applied along the b axis
together with the strong anomalies in the other directions is a definitive
macroscopic evidence that in addition a significant change of the Fermi surface
appears through $H_R$.",1607.06399v1
2016-07-29,Weak de-localization in graphene on a ferromagnetic insulating film,"Graphene has been predicted to develop a magnetic moment by proximity effect
when placed on a ferromagnetic film, a promise that could open exciting
possibilities in the fields of spintronics and magnetic data recording. In this
work, we study in detail the interplay between the magnetoresistance of
graphene and the magnetization of an underlying ferromagnetic insulating film.
A clear correlation between both magnitudes is observed but we find, through a
careful modelling of the magnetization and the weak localization measurements,
that such correspondence can be explained by the effects of the magnetic stray
fields arising from the ferromagnetic insulator. Our results emphasize the
complexity arising at the interface between magnetic and two-dimensional
materials.",1607.08772v1
2016-10-12,Microscopic derivation of magnon spin current in a topological insulator/ferromagnet heterostructure,"We investigate a spin-electricity conversion effect in a topological
insulator/ferromagnet heterostructure. In the spin-momentum-locked surface
state, an electric current generates nonequilibrium spin accumulation, which
causes a spin-orbit torque that acts on the ferromagnet. When spins in the
ferromagnet are completely parallel to the accumulated spin, this spin-orbit
torque is zero. In the presence of spin excitations, however, a coupling
between magnons and electrons enables us to obtain a nonvanishing torque. In
this paper, we consider a model of the heterostructure in which a
three-dimensional magnon gas is coupled with a two-dimensional massless Dirac
electron system at the interface. We calculate the torque induced by an
electric field, which can be interpreted as a magnon spin current, up to the
lowest order of the electron-magnon interaction. We derive the expressions for
high and low temperatures and estimate the order of magnitude of the induced
spin current for realistic materials at room temperature.",1610.03636v3
2017-02-10,Orbital and spin order in spin-orbit coupled $d^1$ and $d^2$ double perovskites,"We consider strongly spin-orbit coupled double perovskites A$_2$BB'O$_6$ with
B' magnetic ions in either $d^1$ or $d^2$ electronic configuration and
non-magnetic B ions. We provide insights into several experimental puzzles,
such as the predominance of ferromagnetism in $d^1$ versus antiferromagnetism
in $d^2$ systems, the appearance of negative Curie-Weiss temperatures for
ferromagnetic materials, and the size of effective magnetic moments. We develop
and solve a microscopic model with both spin and orbital degrees of freedom
within the Mott insulating regime at finite temperature using mean field
theory. The interplay between anisotropic orbital degrees of freedom and
spin-orbit coupling results in complex ground states in both $d^1$ and $d^2$
systems. We show that the ordering of orbital degrees of freedom in $d^1$
systems results in coplanar canted ferromagnetic and 4-sublattice
antiferromagnetic structures. In $d^2$ systems we find additional colinear
antiferromagnetic and ferromagnetic phases not appearing in $d^1$ systems. At
finite temperatures, we find that orbital ordering driven by both superexchange
and Coulomb interactions may occur at much higher temperatures compared to
magnetic order and leads to distinct deviations from Curie-Weiss law.",1702.03199v1
2017-02-12,"Micromagnetic study of a feasibility of the magnetic anisotropy engineering in nano-structured epitaxial films of (III,Mn)V ferromagnetic semiconductors","The attainability of modification of the apparent magnetic anisotropy in
(III,Mn)V ferromagnetic semiconductors is probed by means of the
finite-elements-based modelling. The most representative case of (Ga,Mn)As and
its in-plane uniaxial anisotropy is investigated. The hysteresis loops of the
continuous films of a ferromagnetic semiconductor as well as films structured
with the elliptic antidots are modelled for various eccentricity, orientation,
and separation of the anti dots. The effect of anti-dots on the magnetic
anisotropy is confirmed but overall is found to be very weak. The subsequent
modelling for (Ga,Mn)As film with the elliptic dots comprising of metallic NiFe
shows much stronger effect, revealing switching of the magnetic moment in the
ferromagnetic semiconductor governed by the switching behavior of the metallic
inclusions.",1702.03509v1
2017-03-25,$d^0$ half-metallic ferromagnetism in CaN and CaAs pnictides: An ab initio study,"Conventional magnetism occurs in systems which contain transition metals or
rare earth ions with partially filled $d$ or $f$ shells. It is theoretically
predicted that compounds of groups IA and IIA with IV and V, in some structural
phases, are ferromagnetic half-metals which made them new candidates for
spintronics applications. Employing density functional theory (DFT) we
investigate magnetism in binary compounds CaN and CaAs. Regarding the structure
of analogous magnetic materials and experimental results of CaAs synthesis, we
have considered two cubic structures: rocksalt (RS) and zincblende (ZB), and
four hexagonal structures: NiAs, wurtzite (WZ), anti-NiAs, and NaO. The
calculated results show that CaN in cubic, NiAs, and wurtzite structures, and
CaAs only in zincblende phase have ferromagnetic ground states with a magnetic
moment of $1\mu _B$. Electronic structure analysis of these materials indicates
that magnetism originates from anion $p$ states. Existence of flat $p$ bands
and consequently high density of states at the Fermi level of magnetic
structures gives rise to Stoner spin splitting and spontaneous ferromagnetism.",1703.08691v1
2017-03-28,Coarsening dynamics of an isotropic ferromagnetic superfluid,"In zero magnetic field the ground state manifold of a ferromagnetic spin-1
condensate is SO(3) and exhibits $\mathbb{Z}_2$ vortices as topological
defects. We investigate the phase ordering dynamics of this system after being
quenched into this ferromagnetic phase from a zero temperature unmagnetized
phase. Following the quench, we observe the ordering of both magnetic and gauge
domains. We find that these domains grow diffusively, i.e. with domain size
$L(t)\sim t^{1/2}$, and exhibit dynamic scale invariance. The coarsening
dynamics progresses as $\mathbb{Z}_2$ vortices annihilate, however we find that
at finite energy a number of these vortices persist in small clumps without
influencing magnetic or gauge order. We consider the influence of a small
non-zero magnetic field, which reduces the ground state symmetry, and show that
this sets a critical length scale such that when the domains reach this size
the system dynamically transitions in order parameter and scaling behaviour
from an isotropic to an anisotropic ferromagnetic superfluid.",1703.09360v2
2017-03-29,A new route to enhance the ferromagnetic transition temperature in diluted magnetic semiconductors,"We investigate the magnetic and the transport properties of diluted magnetic
semiconductors using a spin-fermion Monte-Carlo method on a 3D lattice in the
intermediate coupling regime. The ferromagnetic transition temperature $T_c$
shows an optimization behavior, first increases and then decreases, with
respect to the absolute carrier density $p_{abs}$ for a given magnetic impurity
concentration $x$, as seen in the experiment. Our calculations also show an
insulator-metal-insulator transition across the optimum $p_{abs}$ where the
$T_c$ is maximum. Remarkably, the optimum $p_{abs}$ values lie in a narrow
range around 0.11 for all $x$ values and the ferromagnetic $T_c$ increases with
$x$. We explain our results using the polaron percolation mechanism and outline
a new route to enhance the ferromagnetic transition temperature in experiments.",1703.10129v1
2018-02-01,An analytical computation of magnetic field generated from a cylinder ferromagnet,"An analytical formulation to compute a magnetic field generated from an
uniformly magnetized cylinder ferromagnet is developed. Exact solutions of the
magnetic field generated from the magnetization pointing in an arbitrary
direction are derived, which are applicable both inside and outside the
ferromagnet. The validities of the present formulas are confirmed by comparing
them with demagnetization coefficients estimated in earlier works. The results
will be useful for designing practical applications, such as high-density
magnetic recording and microwave generators, where nanostructured ferromagnets
are coupled to each other through the dipole interactions and show cooperative
phenomena such as synchronization. As an example, the magnetic field generated
from a spin torque oscillator for magnetic recording based on microwave
assisted magnetization reversal is studied.",1802.00384v1
2018-02-19,Borderline Magnetism: How Does Adding Magnesium to Paramagnetic CeCo$_3$ Make a 450 K Ferromagnet with Large Magnetic Anisotropy?,"A recent experimental study (Phys. Rev. Appl. 9, 024023, 2018) on
paramagnetic CeCo$_3$ finds that Magnesium alloying induces a ferromagnetic
transition with intrinsic properties large enough for permanent magnet
applications. Here we explain these surprising results \textit{via} a first
principles study of the electronic structure and magnetism of Magnesium-alloyed
CeCo$_3$. We find the origin of this Magnesium-induced ferromagnetic transition
to be Stoner physics - the substantial increase in the Fermi-level
density-of-states $N(E_F)$ with Mg alloying. Our calculations suggest that both
Ce and Co atoms are important for generating large magnetic anisotropy
suggesting the viability of Co-3$d$, and Ce-4$f$ interaction for the generation
of magnetic anisotropy in magnetic materials. These results offer a new route
to the discovery of ferromagnetic materials and provide fundamental insight
into the magnetic properties of these alloys",1802.06747v2
2018-02-21,Spin inversion in graphene spin valves by gate-tunable magnetic proximity effect at one-dimensional contacts,"Graphene has remarkable opportunities for spintronics due to its high
mobility and long spin diffusion length, especially when encapsulated in
hexagonal boron nitride (h-BN). Here, for the first time, we demonstrate
gate-tunable spin transport in such encapsulated graphene-based spin valves
with one-dimensional (1D) ferromagnetic edge contacts. An electrostatic
backgate tunes the Fermi level of graphene to probe different energy levels of
the spin-polarized density of states (DOS) of the 1D ferromagnetic contact,
which interact through a magnetic proximity effect (MPE) that induces
ferromagnetism in graphene. In contrast to conventional spin valves, where
switching between high- and low-resistance configuration requires magnetization
reversal by an applied magnetic field or a high-density spin-polarized current,
we provide an alternative path with the gate-controlled spin inversion in
graphene. The resulting tunable MPE employing a simple ferromagnetic metal
holds promise for spintronic devices and to realize exotic topological states,
from quantum spin Hall and quantum anomalous Hall effects, to Majorana fermions
and skyrmions.",1802.07790v1
2018-02-28,The effects of thermal and correlated noise on magnons in a quantum ferromagnet,"The dynamics and thermal equilibrium of spin waves (magnons) in a quantum
ferromagnet as well as the macroscopic magnetisation are investigated. Thermal
noise due to an interaction with lattice phonons and the effects of spatial
correlations in the noise are considered. We first present a Markovian master
equation approach with analytical solutions for any homogeneous spatial
correlation function of the noise. We find that spatially correlated noise
increases the decay rate of magnons with low wave vectors to their thermal
equilibrium, which also leads to a faster decay of the ferromagnet's
magnetisation to its steady-state value. For long correlation lengths and
higher temperature we find that additionally there is a component of the
magnetisation which decays very slowly, due to a reduced decay rate of fast
magnons. This effect could be useful for fast and noise-protected quantum or
classical information transfer and magnonics. We further compare ferromagnetic
and antiferromagnetic behaviour in noisy environments and find qualitatively
similar behaviour in Ohmic but fundamentally different behaviour in super-Ohmic
environments.",1802.10258v2
2018-04-02,Spin torques and magnetic texture dynamics driven by the supercurrent in superconductor/ferromagnet structures,"We introduce the general formalism to describe spin torques induced by the
supercurrents injected from the adjacent superconducting electrodes into the
spin-textured ferromagnets. By considering the adiabatic limit for the
equal-spin superconducting correlations in the ferromagnet we show that the
supercurrent can generate both the field-like spin transfer torque and the
spin-orbital torque. These dissipationless spin torques are expressed through
the current-induced corrections to the effective field derived from the system
energy. The general formalism is applied to show that the supercurrent can
either shift or move the magnetic domain walls depending on their structure and
the type of spin-orbital interaction in the system. These results can be used
for the prediction and interpretation of the experiments studying magnetic
texture dynamics in superconductor/ferromagnet/superconductor Josephson
junctions and other hybrid structures.",1804.00718v2
2018-04-04,Direct observation of the magnetic proximity effect in amorphous exchange-spring magnets by neutron reflectometry,"In this letter we report a direct observation of a magnetic proximity effect
in an amorphous thin film exchange-spring magnet by the use of neutron
reflectometry. The exchange-spring magnet is a trilayer consisting of two
ferromagnetic layers with high $T_c$'s separated by a ferromagnetic layer,
which is engineered to have a significantly lower $T_c$ than the embedding
layers. This enables us to measure magnetization depth profiles at which the
low $T_c$ material is in a ferromagnetic or paramagnetic state, while the
embedding layers are ferromagnetic. A clear proximity effect is observed 7 K
above the $T_c$ of the embedded layer, with a range extending 50
$\unicode{xC5}$.",1804.01479v2
2018-04-19,Absence of ferromagnetism in VSe2 caused by its charge density wave phase,"In this study we present a detailed ab initio analysis of the magnetic
properties of VSe2 . Ab initio calculations in the so-called 1T structure yield
a ferromagnetic phase as most stable, with a magnetic moment of about 0.6 {\mu}
B /V. According to our calculations this ferromagnetic state is on the verge of
instability. We have modeled ab initio the charge density wave state reported
in the literature. This introduces a periodic lattice distortion leading to a
supercell with periodicity 4a x 4a x 3c (4a x 4a for the monolayer) in which we
have fully relaxed the atomic positions. We demonstrate that this structural
rearrangement causes a strong reduction in the density of states at the Fermi
level and the ground state of the system becomes non-magnetic for the bulk. In
the monolayer limit the rearrangement induces a Peierls distortion causing an
energy gap opening at the Fermi level and the quenching of ferromagnetism.",1804.07102v2
2018-04-19,Ferromagnetic phases due to competing short- and long-range interactions in the spin-S Blume-Capel model,"We broaden the study of the statistical physics of the spin-$S$ Blume-Capel
model with ferromagnetic mean-field interactions $J$ in competition with
short-range antiferromagnetic interactions $K$ in a linear chain in the
thermodynamic limit. This work describes the critical behavior of the model
when the $S$ takes a half integer and an integer value. In both cases the phase
diagrams exhibit new ferromagnetic phases (for certain values of $K$) enclosed
by branches emerging from the first-order frontiers of the pure ferromagnetic
model. For finite temperatures the complex topologies were obtained by
numerical minimization of the free energy.",1804.07228v1
2018-04-20,Theory of tunneling spectroscopy of normal metal/ferromagnet/spin-triplet superconductor junctions,"We study the tunneling conductance of a ballistic normal metal / ferromagnet
/ spin-triplet superconductor junction using the extended
Blonder-Tinkham-Klapwijk formalism as a model for a $c$-axis oriented Au /
SrRuO$_{3}$ / Sr$_{2}$RuO$_{4}$ junction. We compare chiral $p$-wave (CPW) and
helical $p$-wave (HPW) pair potentials, combined with ferromagnet magnetization
directions parallel and perpendicular to the interface. For fixed $\theta_{M}$,
where $\theta_{M}$ is a direction of magnetization in the ferromagnet measured
from the $c$-axis, the tunneling conductance of CPW and HPW clearly show
different voltage dependencies. It is found that the cases where the $d$-vector
is perpendicular to the magnetization direction (CPW with $\theta_{M} = \pi/2$
and HPW with $\theta_{M} = 0$) are identical. The obtained results serve as a
guide to determine the pairing symmetry of the spin-triplet superconductor
Sr$_{2}$RuO$_{4}$.",1804.07678v2
2018-11-06,Electrically-Tunable High Curie Temperature Two-Dimensional Ferromagnetism in Van der Waals Layered Crystals,"Identifying intrinsic low-dimensional ferromagnets with high transition
temperature and electrically tunable magnetism is crucial for the development
of miniaturized spintronics and magnetoelectrics. Recently long-range 2D
ferromagnetism was observed in van der Waals crystals CrI$_3$ and
Cr$_2$Ge$_2$Te$_6$, however their Curie temperature is significantly lowered
when reducing down to monolayer/few layers. Herein, using renormalized
spin-wave theory and first-principles electronic structure theory, we present a
theoretical study of electrically tunable 2D ferromagnetism in van der Waals
layered CrSBr and CrSeBr semiconductors with high Curie temperature of ~150K
and sizable band gap. High transition temperature is attributed to strong
anion-mediated superexchange interaction and a sizable spin-wave excitation gap
due to large exchange and single-ion anisotropy. Remarkably, hole and electron
doping can switch magnetization easy axis from in-plane to out-of-plane
direction. These unique characteristics establish monolayer CrSBr and CrSeBr as
promising platform for realizing 2D spintronics and magnetoelectrics such as 2D
spin field effect transistor.",1811.02674v2
2018-11-28,Interfacial spin glass mediated unusual spontaneous exchange bias effect in epitaxial self-assembled La0.7Sr0.3MnO3:NiO nanocomposite thin films,"Zero field cooled spontaneous exchange bias (SEB) is observed in epitaxial
La0.7Sr0.3MnO3 (LSMO):NiO self-assembled nanocomposite thin films grown on
(001) SrTiO3 single crystal substrate by pulsed laser deposition. SEB is
displayed by the novel asymmetry in the hysteresis loop of the composite film
along with the field cooled conventional exchange bias (CEB) effect. The
training effect shows that exchange bias relaxation is disorder mediated. It is
revealed from DC magnetization results that such nanocomposite film divulges
spin glass like behaviour, which is arising due to competing ferromagnetic and
antiferromagnetic inteactions at the assorted interfaces of ferromagnetic LSMO
and antiferromagnetic NiO. Also corroborated by x-ray magnetic circular
dichroism (XMCD) measurements, we conclude that SEB is mainly originating due
to ferromagnetic coupling of unstable interfacial antiferromagnetic spin due to
NiO with the ferromagnetic LSMO at the disordered interface. These results of
self-assembled thin films provide a useful input to realize and understand
microscopic origin of SEB for device application.",1811.11461v1
2018-11-29,Control of magnetism in bilayer CrI$_{3}$ by an external electric field,"Recently intrinsic ferromagnetism in two-dimensional(2D) van der Waals
materials was discovered [1, 2, 3]. A monolayer of Chromiun triiodide(CrI3) is
ferromagnetic while a bilayer structure was reported to be anti-ferro magnetic,
moreover an external electric field changes its magnetic phase [4]. We have
studied the two found in nature stackings of CrI3 bilayers and found that
indeed the magnetic phase of one of them can be tuned by an external electric
field while the other remains ferromagnetic. We simulate those results with ab
initio calculations and explain them with a simple model based on a rigid shift
of the bands associated with different spins. The model can be applied to
similar van der Waal stacked insulating bilayer anti-ferromagnets.",1811.11910v1
2019-05-02,Anomalous spin Hall angle of a metallic ferromagnet determined by a multiterminal spin injection/detection device,"We report on the determination of the anomalous spin Hall angle in the
ferromagnetic metal alloy cobalt-iron (Co$_{25}$Fe$_{75}$, CoFe). This is
accomplished by measuring the spin injection/detection efficiency in a
multiterminal device with nanowires of platinum (Pt) and CoFe deposited onto
the magnetic insulator yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). Applying
a spin-resistor model to our multiterminal spin transport data, we determine
the magnon conductivity in YIG, the spin conductance at the YIG/CoFe interface
and finally the anomalous spin Hall angle of CoFe as a function of its spin
diffusion length in a single device. Our experiments clearly reveal a negative
anomalous spin Hall angle of the ferromagnetic metal CoFe, but a vanishing
ordinary spin Hall angle. This is in contrast to the results reported for the
ferromagnetic metals Co and permalloy.",1905.00663v1
2019-05-09,Evolution of nematic and ferromagnetic ordering in suspensions of magnetic nanoplatelets,"Suspensions of magnetic nanoplatelets in isotropic solvents are very
interesting examples of ferrofluids. It has been shown that above a certain
concentration {\Phi}NI such suspensions form a ferromagnetic nematic phase,
which makes this system a unique example of a dipolar fluid. The formation of a
nematic phase is driven by anisotropic electrostatic and long-range dipolar
magnetic interactions. Here, we present studies of the evolution of short range
positional and orientational magnetic order in the suspensions with volume
fractions below and above {\Phi}NI, using small angle neutron scattering
(SANS). The results show that in the absence of an external magnetic field,
short range positional and orientational order already exist at relatively low
volume fractions. Polarized SANS revealed that the contribution of
ferromagnetic ordering to the formation of the nematic phase is significant.
The ferromagnetic correlations can be qualitatively explained by a simple
model, which takes into account anisotropic screened electrostatic and dipolar
magnetic interactions.",1905.03572v1
2019-05-28,Spin-Orbit Torque in a Single Ferromagnetic Layer with Large Spin-Orbit Coupling,"Spin-orbit torque in heavy metal/ferromagnet heterostructures with broken
spatial inversion symmetry provides an efficient mechanism for manipulating
magnetization using a charge current. Here, we report the presence of a spin
torque in a single ferromagnetic layer in both asymmetric MgO/Fe0.8Mn0.2 and
symmetric MgO/Fe0.8Mn0.2/MgO structures, which manifests itself in the form of
an effective field transverse to the charge current. The current to effective
field conversion efficiency, which is characterized using both the nonlinear
magnetoresistance and second-order planar Hall effect methods, is comparable to
the efficiency in typical heavy metal/ferromagnet bilayers. We argue that the
torque is caused by spin rotation in the vicinity of the surface via impurity
scattering in the presence of a strong spin-orbit coupling. Instead of
cancelling off with each other, the torques from the top and bottom surfaces
simply add up, leading to a fairly large net torque, which is readily observed
experimentally.",1905.11565v1
2020-07-02,An Origin of Dzyaloshinskii-Moriya Interaction at Graphene-Ferromagnet Interfaces Due to the Intralayer RKKY/BR Interaction,"We present a theory of both the itinerant carrier-mediated RKKY interaction
and the virtual excitations-mediated Bloembergen-Rowland (BR) interaction
between magnetic moments in graphene induced by proximity effect with a
ferromagnetic film. We show that the RKKY/BR interaction consists of the
Heisenberg, Ising, and Dzyaloshinskii-Moriya (DM) terms. In the case of the
nearest distance, we estimate the DM term from the RKKY/BR interaction is about
0.13 meV for the graphene/Co interface, which is consistent with the
experimental result of DM interaction $0.16 \pm 0.05$ meV. Our calculations
indicate that the intralayer RKKY/BR interaction may be a possible physical
origin of the DM interaction in the graphene-ferromagnet interface. This work
provides a new perspective to comprehend the DM interaction in
graphene/ferromagnet systems.",2007.02690v1
2020-07-08,Pressure-induced suppression of ferromagnetism in CePd$_2$P$_2$,"The correlated electron material CePd$_2$P$_2$ crystallizes in the
ThCr$_2$Si$_2$ structure and orders ferromagnetically at 29 K. Lai et al.
[Phys. Rev. B 97, 224406 (2018)] found evidence for a ferromagnetic quantum
critical point induced by chemical compression via substitution of Ni for Pd.
However, disorder effects due to the chemical substitution interfere with a
simple analysis of the possible critical behavior. In the present work, we
examine the temperature - pressure - magnetic field phase diagram of single
crystalline CePd$_2$P$_2$ to 25 GPa using a combination of resistivity,
magnetic susceptibility, and x-ray diffraction measurements. We find that the
ferromagnetism appears to be destroyed near 12 GPa, without any change in the
crystal structure.",2007.04165v1
2020-07-17,Entangling the vibrational modes of two massive ferromagnetic spheres using cavity magnomechanics,"We present a scheme to entangle the vibrational phonon modes of two massive
ferromagnetic spheres in a dual-cavity magnomechanical system. In each cavity,
a microwave cavity mode couples to a magnon mode (spin wave) via the magnetic
dipole interaction, and the latter further couples to a deformation phonon mode
of the ferromagnetic sphere via a nonlinear magnetostrictive interaction. We
show that by directly driving the magnon mode with a red-detuned microwave
field to activate the magnomechanical anti-Stokes process a
cavity-magnon-phonon state-swap interaction can be realized. Therefore, if the
two cavities are further driven by a two-mode squeezed vacuum field, the
quantum correlation of the driving fields is successively transferred to the
two magnon modes and subsequently to the two phonon modes, i.e., the two
ferromagnetic spheres become remotely entangled. Our work demonstrates that
cavity magnomechanical systems allow to prepare quantum entangled states at a
more massive scale than currently possible with other schemes.",2007.09083v3
2010-05-28,Controlling the Local Spin-Polarization at the Organic-Ferromagnetic Interface,"By means of ab initio calculations and spin-polarized scanning tunneling
microscopy experiments we show how to manipulate the local spin-polarization of
a ferromagnetic surface by creating a complex energy dependent magnetic
structure. We demonstrate this novel effect by adsorbing organic molecules
containing pi(pz)-electrons onto a ferromagnetic surface, in which the
hybridization of the out-of-plane pz atomic type orbitals with the d-states of
the metal leads to the inversion of the spin-polarization at the organic site
due to a pz - d Zener exchange type mechanism. As a key result, we demonstrate
that it is possible to selectively inject spin-up and spin-down electrons from
the same ferromagnetic surface, an effect which can be exploited in future
spintronic devices.",1005.5411v1
2013-08-18,Pulsed Laser Deposition of High-Quality Thin Films of the Insulating Ferromagnet EuS,"High-quality thin films of the ferromagnetic-insulator europium(II) sulfide
(EuS) were fabricated by pulsed laser deposition on Al2O3 (0001) and Si (100)
substrates. A single orientation was obtained with the [100] planes parallel to
the substrates, with atomic-scale smoothness indicates a near-ideal surface
topography. The films exhibit uniform ferromagnetism below 15.9 K, with a
substantial component of the magnetization perpendicular to the plane of the
films. Optimization of the growth condition also yielded truly insulating films
with immeasurably large resistance. This combination of magnetic and electric
properties open the gate for novel devices that require a true ferromagnetic
insulator.",1308.3820v2
2013-08-20,Dynamic-Symmetry-Breaking Breathing and Spreading Transitions in Ferromagnetic Film Irradiated by Spherical Electromagnetic Wave,"The dynamical responses of a ferromagnetic film to a propagating spherical
electromagnetic wave passing through it are studied by Monte Carlo simulation
of two dimensional Ising ferromagnet. For a fixed set of values of the
frequency and wavelength of the spherical EM wave, and depending on the values
of amplitude of the EM wave and temperature of the system, three different
modes are identified. The static pinned mode, the localised dynamical breathing
mode and extended dynamical spreading mode are observed. The nonequilibrium
dynamical-symmetry-breaking breathing and spreading phase transitions are also
observed and the transition temperatures are obtained as functions of the
amplitude of the magnetic field of EM wave. A comprehensive phase diagram is
drawn. The boundaries of breathing and spreading transitions merge eventually
at the equilibrium transition temperature for two dimensional Ising ferromagnet
as the value of the amplitude of the magnetic field becomes vanishingly small.",1308.4277v1
2014-03-03,Ferromagnetic SrRuO3 thin-film deposition on a spin-triplet superconductor Sr2RuO4 with highly conducting interface,"Ferromagnetic SrRuO3 thin films are deposited on the ab-surface of single
crystals of the spin-triplet superconductor Sr2RuO4 as substrates using pulsed
laser deposition. The films are under a severe in-plane compressive strain.
Nevertheless, the films exhibit ferromagnetic order with the easy axis along
the c-direction below the Curie temperature of 158 K. The electrical transport
reveals that the SrRuO3/Sr2RuO4 interface is highly conducting, in contrast
with the interface between other normal-metals and the ab-surface of Sr2RuO4.
Our results will stimulate the investigations on proximity effects between a
ferromagnet and a spin-triplet superconductor.",1403.0345v2
2017-01-17,Optical patterning of magnetic domains and defects in ferromagnetic liquid crystal colloids,"A promising approach in designing composite materials with unusual physical
behavior combines solid nanostructures and orientationally ordered soft matter
at the mesoscale. Such composites not only inherit properties of their
constituents but also can exhibit emergent behavior, such as ferromagnetic
ordering of colloidal metal nanoparticles forming mesoscopic magnetization
domains when dispersed in a nematic liquid crystal. Here we demonstrate the
optical patterning of domain structures and topological defects in such
ferromagnetic liquid crystal colloids, which allows for altering their response
to magnetic fields. Our findings reveal the nature of the defects in this soft
matter system which is different as compared to non-polar nematics and
ferromagnets alike.",1701.04840v1
2017-01-27,Control of superconductivity with a single ferromagnetic layer in niobium/erbium bilayers,"Superconducting spintronics in hybrid superconductor/ferromagnet (S-F)
heterostructures provides an exciting potential new class of device. The
prototypical super-spintronic device is the superconducting spin-valve, where
the critical temperature, $T_c$, of the S-layer can be controlled by the
relative orientation of two (or more) F-layers. Here, we show that such control
is also possible in a simple S/F bilayer. Using field history to set the
remanent magnetic state of a thin Er layer, we demonstrate for a Nb/Er bilayer
a high level of control of both $T_c$ and the shape of the resistive
transition, R(T), to zero resistance. We are able to model the origin of the
remanent magnetization, treating it as an increase in the effective exchange
field of the ferromagnet and link this, using conventional S-F theory, to the
suppression of $T_c$. We observe stepped features in the R(T) which we argue is
due to a fundamental interaction of superconductivity with inhomogeneous
ferromagnetism, a phenomena currently lacking theoretical description.",1701.08065v2
2017-04-01,Asymmetric isolated skyrmions in polar magnets with easy-plane anisotropy,"We introduce a new class of isolated magnetic skyrmions emerging within
tilted ferromagnetic phases of polar magnets with easy-plane anisotropy. The
asymmetric magnetic structure of these skyrmions is associated with an
intricate pattern of the energy density, which exhibits positive and negative
asymptotics with respect to the surrounding state with a ferromagnetic moment
tilted away from the polar axis. Correspondingly, the skyrmion-skyrmion
interaction has an anisotropic character and can be either attractive or
repulsive depending on the relative orientation of the skyrmion pair. We
investigate the stability of these novel asymmetric skyrmions against the
elliptical cone state and follow their transformation into axisymmetric
skyrmions, when the tilted ferromagnetic moment of the host phase is reduced.
Our theory gives clear directions for experimental studies of isolated
asymmetric skyrmions and their clusters embedded in tilted ferromagnetic
phases.",1704.00100v1
2017-04-11,Tuning Interfacial Ferromagnetism in LaNiO$_3$/CaMnO$_3$ Superlattices by Stabilizing Non-Equilibrium Crystal Symmetry,"Perovskite oxide heterostructures offer an important path forward for
stabilizing and controlling low-dimensional magnetism. One of the guiding
design principles for these materials systems is octahedral connectivity. In
superlattices composed of perovskites with different crystal symmetries,
variation of the relative ratio of the constituent layers as well as the
individual layer thicknesses gives rise to non-equilibrium crystal symmetries
that, in turn, lead to unprecedented control of interfacial ferromagnetism. We
have found that in superlattices of CaMnO$_3$ (CMO) and LaNiO$_3$ (LNO),
interfacial ferromagnetism can be modulated by a factor of three depending on
LNO and CMO layer thicknesses as well as their relative ratio. Such an effect
is only possible due to the non-equilibrium crystal symmetries at the
interfaces and can be understood in terms of the anisotropy of the exchange
interactions and modifications in the interfacial Ni-O-Mn and Mn-O-Mn bond
angles and lengths with increasing LNO layer thickness. These results
demonstrate the potential of engineering non-equilibrium crystal symmetries in
designing ferromagnetism.",1704.03154v2
2017-04-28,Single-domain ferromagnet of noncentrosymmetric uniaxial magnetic ions and magnetoelectric interaction,"The feasibility of a single-domain ferromagnet based on uniaxial magnetic
ions was examined. For a noncentrosymmetric uniaxial magnetic ion of magnetic
moment at a site of local electric dipole moment p, it is unknown to date
whether the magnetic moment prefers to be parallel or antiparallel to the
electric dipole moment. The nature of this magnetoelectric interaction was
probed in terms of analogical reasoning based on the Rashba effect and density
functional calculations. We show that the magnetic and electric dipole moments
prefer an antiparallel arrangement, predict that Fe-doped CaZnOS is a
single-domain ferromagnet like a bar magnet, and find the probable cause for
the ferromagnetism and weak magnetization hysteresis in Fe-doped hexagonal ZnO
and ZnS at very low dopant concentrations.",1704.08940v1
2018-05-15,Gate-tunable magnetism of C adatoms on graphene,"We have performed density functional theory calculations of graphene
decorated with carbon adatoms, which bind at the bridge site of a C--C bond.
Earlier studies have shown that the C adatoms have magnetic moments and have
suggested the possibility of ferromagnetism with high Curie temperature. Here
we propose to use a gate voltage to fine tune the magnetic moments from zero to
1$\mu_B$ while changing the magnetic coupling from antiferromagnetism to
ferromagnetism and again to antiferromagnetism. These results are rationalized
within the Stoner and RKKY models. When the SCAN meta-GGA correction is used,
the magnetic moments for zero gate voltage are reduced and the Stoner band
ferromagnetism is slightly weakened in the ferromagnetic region.",1805.06044v2
2018-05-22,Loss of Hall Conductivity Quantization in a Non-Hermitian Quantum Anomalous Hall Insulator,"Recent work has extended topological band theory to open, non-Hermitian
Hamiltonians, yet little is understood about how non-Hermiticity alters the
topological quantization of associated observables. We address this problem by
studying the quantum anomalous Hall effect (QAHE) generated in the Dirac
surface states of a 3D time-reversal-invariant topological insulator (TI) that
is proximity-coupled to a metallic ferromagnet. By constructing a contact
self-energy for the ferromagnet, we show that in addition to generating a mass
gap in the surface spectrum, the ferromagnet can introduce a non-Hermitian
broadening term, which can obscure the mass gap in the spectral function. We
calculate the Hall conductivity for the effective non-Hermitian Hamiltonian
describing the heterostructure and show that it is no longer quantized despite
being classified as a Chern insulator based on non-Hermitian topological band
theory. Our results indicate that the QAHE will be challenging to
experimentally observe in ferromagnet-TI heterostructures due to the finite
lifetime of quasi-particles at the interface.",1805.08892v2
2018-05-25,"Suppression of ferromagnetic order by Ag-doping: A neutron scattering investigation on Ce2(Pd1-xAgx)2In (x = 0.20, 0.50)","The ground state magnetic behaviour of Ce2(Pd0.8Ag0.2)2In and
Ce2(Pd0.5Ag0.5)2In, found in the ferromagnetic branch of Ce2Pd2In, has been
investigated by neutron powder diffraction at low temperature.
Ce2(Pd0.8Ag0.2)2In is characterized by a ferromagnetic structure with the Ce
moments aligned along the c-axis and values of 0.96(2) mB. The compound retains
the P4/mbm throughout the magnetic transition, although the magnetic ordering
is accompanied by a significant decrease of the lattice strain along [00l],
suggesting a magnetostructural contribution. The magnetic behaviour of
Ce2(Pd0.5Ag0.5)2In is very different; this compound exhibits an extremely
reduced magnetic scattering contribution in the diffraction pattern, that can
be ascribed to a different kind of ferromagnetic ordering, with extremely
reduced magnetic moments (~ 0.1 mB) aligned along [0l0]. These results point to
a competition between different types of magnetic correlations induced by
Ag-substitution, giving rise to a magnetically frustrated scenario in
Ce2(Pd0.5Ag0.5)2In.",1805.10023v1
2008-07-02,Numerical Studies of Quantum Hall Ferromagnetism in Two-Subband Systems,"We carry out a numerical study of the quantum Hall ferromagnetism in a
two-subband system using a set of experimental parameters in a recently
experiment [X. C. Zhang, I. Martin, and H. W. Jiang, Phys. Rev. B \textbf{74},
073301 (2006)]. Employing the self-consistence local density approximation for
growth direction wave function and the Hartree-Fock theory for the pseudospin
anisotropy energy, we are able to account for the easy-axis and easy-plane
quantum Hall ferromagnetism observed at total filling factor $\nu = 3$ and
$\nu= 4$, respectively. Our study provides some insight of how the anisotropy
energy, which highly depends upon the distribution of growth direction wave
functions, determines the symmetry of the quantum Hall ferromagnets.",0807.0297v1
2008-07-23,First order ferromagnetic phase transition in the low electronic density regime of a biased graphene bilayer,"The phase diagram of a biased graphene bilayer is computed and the existence
of a ferromagnetic phase is discussed both in the critical on-site interaction
$U_{c}$ versus doping density and versus temperature. We show that in the
ferromagnetic phase the two planes have unequal magnetization and that the
electronic density is hole like in one plane and electron like in the other. We
give evidence for a \emph{first-order} phase transition between paramagnetic
and ferromagnetic phases induced by doping at zero temperature.",0807.3623v1
2011-11-04,Phase diagram of UGe2. Whether there are quantum phase transitions ?,"The phase diagram of several itinerant ferromagnets reveals the common
feature. The phase transition temperature decreases with pressure increase and
reaches zero value at some critical pressure $P_c$ such that at low enough
temperatures one can expect critical behavior specific for quantum phase
transition. It is not the case, however. Being the second order at ambient
pressure the transition from paramagnetic to ferromagnetic state at high
pressures - low temperatures is transformed to the discontinuous jump. We
discuss the magneto-elastic mechanism of development of the first order type
instability at the phase transition to the ferromagnet state in strongly
anisotropic ferromagnet UGe2. Using the parameters characterizing the
properties of UGe$_2$ we argue the effectiveness of this mechanism transforming
the very weak first order type transition to the really observable one.",1111.1089v1
2011-11-04,Diffusive spin dynamics in ferromagnetic thin films with a Rashba interaction,"In a ferromagnetic metal layer, the coupled charge and spin diffusion
equations are obtained in the presence of both Rashba spin-orbit interaction
and magnetism. The mis-alignment between the magnetization and the
non-equilibrium spin density induced by the Rashba field gives rise to Rashba
spin torque acting on the ferromagnetic order parameter. In a general form, we
find that the Rashba torque consists of both in-plane and out-of-plane
components, ie $\bm{T}=T_{\bot}\hat{\bm{y}}\times{\hat{\bm
m}}+T_{\parallel}{\hat{\bm m}}\times({\hat{\bm y}}\times{\hat{\bm m}})$.
Numerical simulations on a two dimensional nano-wire discuss the impact of
diffusion on the Rashba torque, which reveals a large enhancement to the ratio
$T_{\parallel}/T_{\bot}$ for thin wires. Our theory provides an explanation to
the mechanism that drives the magnetization switching in a single ferromagnet
as observed in the recent experiments.",1111.1216v2
2011-11-14,Nematic phase and phase separation near saturation field in frustrated ferromagnets,"We study the effects of quantum fluctuations in magnetic properties of
quantum frustrated ferromagnets in a magnetic field. It is shown that a
non-classical phase or a phase separation appears due to quantum fluctuations
below the saturation field in a parameter range close to the classical
zero-field phase boundary between ferromagnetic and antiferromagnetic phases,
for the case that the classical antiferromagnetic state is not an eigenstate of
the quantum model. As an example to which this argument is applicable, we study
the S=1/2 J1-J2 Heisenberg model with ferromagnetic J1 (J1<0) on the bcc
lattice using a dilute Bose gas approach. For -1.50097 < J1/J2 < -1.389,
magnons form f-wave two-magnon bound states, leading to a spin nematic phase,
and for -1.389 < J1/J2 < -0.48 a canted coplanar antiferromagnetic phase
appears accompanied with a phase separation below the saturation field.",1111.3184v3
2011-11-17,"Theory of magnetization precession induced by a picosecond strain pulse in ferromagnetic semiconductor (Ga,Mn)As","A theoretical model of the coherent precession of magnetization excited by a
picosecond acoustic pulse in a ferromagnetic semiconductor layer of (Ga,Mn)As
is developed. The short strain pulse injected into the ferromagnetic layer
modifies the magnetocrystalline anisotropy resulting in a tilt of the
equilibrium orientation of magnetization and subsequent magnetization
precession. We derive a quantitative model of this effect using the
Landau-Lifshitz equation for the magnetization that is precessing in the
time-dependent effective magnetic field. After developing the general
formalism, we then provide a numerical analysis for a certain structure and two
typical experimental geometries in which an external magnetic field is applied
either along the hard or the easy magnetization axis. As a result we identify
three main factors, which determine the precession amplitude: the
magnetocrystalline anisotropy of the ferromagnetic layer, its thickness, and
the strain pulse parameters.",1111.4043v1
2012-01-05,Thermoelectricity of the Ferromagnetic Superconductor UCoGe,"UCoGe exhibits superconductivity in the presence of ferromagnetism. When a
field is applied along the b axis (perpendicular to the easy axis),
ferromagnetism is weakened and superconductivity is enhanced. This enhancement
has been attributed to an increase in coupling as observed in the enhanced
effective mass produced by the critical fluctuations as the ferromagnetic
transition is strongly suppressed. However it is also important to know if and
how the Fermi surface changes near the critical point. Here we report
measurements of the thermoelectricity of UCoGe which reveal a low carrier
density metal. Under magnetic field applied along the b axis, a sharp peak is
observed in the thermopower of UCoGe at H*=11.1T and low temperature which
becomes broader at higher temperatures. At higher field, the thermopower
changes sign which suggests a modification of the Fermi Surface. We analyze
these results using a topological change in Fermi surface and show that this
can explain both the thermopower and the enhanced superconductivity.",1201.1147v1
2012-01-14,Non-local spin valve in Van der Pauw cross geometry with four ferromagnetic electrodes,"We consider a non-local spin valve in a Van der Pauw cross geometry with four
ferromagnetic electrodes. Two antiparallel ferromagnets are used as (charge)
source and drain while the detector circuit involves measuring the voltage
between two collinear ferromagnets with parallel or antiparallel
magnetizations. We find a potentially large increase of the non-local spin
voltage. The setup displays several additional interesting properties: (i)
infinite GMR for the non-local resistance (if a symmetry requirement for the
device is met); (ii) ON-OFF switch effect, when the injector electrodes are
parallel instead of antiparallel; (iii) insensitivity to offset voltages. The
device can additionally be used as a Direct Spin Hall Effect probe and as a
reprogrammable magneto-logic gate implementing basic operations (NOR, NAND,
inverter, AND, OR,...).",1201.2982v1
2012-01-20,Modified Spin Wave Analysis of Low Temperature Properties of Spin-1/2 Frustrated Ferromagnetic Ladder,"Low temperature properties of the spin-1/2 frustrated ladder with
ferromagnetic rungs and legs, and two different antiferromagnetic next nearest
neighbor interaction are investigated using the modified spin wave
approximation in the region with ferromagnetic ground state. The temperature
dependence of the magnetic susceptibility and magnetic structure factors is
calculated. The results are consistent with the numerical exact diagonalization
results in the intermediate temperature range. Below this temperature range,
the finite size effect is significant in the numerical diagonalization results,
while the modified spin wave approximation gives more reliable results. The low
temperature properties near the limit of the stability of the ferromagnetic
ground state are also discussed.",1201.4242v1
2012-04-04,Electron transport in a ferromagnetic/normal/ferromagnetic tunnel junction based on the surface of a topological insulator,"We theoretically study the electron transport properties in a
ferromagnetic/normal/ferromagnetic tunnel junction, which is deposited on the
top of a topological surface. The conductance at the parallel (\textbf{P})
configuration can be much bigger than that at the antiparallel (\textbf{AP})
configuration. Compared \textbf{P} with \textbf{AP} configuration, there exists
a shift of phase which can be tuned by gate voltage. We find that the exchange
field weakly affects the conductance of carriers for \textbf{P} configuration
but can dramatically suppress the conductance of carriers for \textbf{AP}
configuration. This controllable electron transport implies anomalous
magnetoresistance in this topological spin valve, which may contribute to the
development of spintronics . In addition, we find that there is a
Fabry-Perot-like electron interference.",1204.0956v2
2012-04-05,The Magnon Spectrum in the Domain Ferromagnetic State of Antisite Disordered Double Perovskites,"In their ideal structure, double perovskites like Sr_2FeMoO_6 have
alternating Fe and Mo along each cubic axes, and a homogeneous ferromagnetic
metallic ground state. Imperfect annealing leads to the formation of structural
domains. The moments on mislocated Fe atoms that adjoin each other across the
domain boundary have an antiferromagnetic coupling between them. This leads to
a peculiar magnetic state, with ferromagnetic domains coupled
antiferromagnetically. At short distance the system exhibits ferromagnetic
correlation while at large lengthscales the net moment is strongly suppressed
due to inter-domain cancellation. We provide a detailed description of the spin
wave excitations of this complex magnetic state, obtained within a 1/S
expansion, for progressively higher degree of mislocation, i.e., antisite
disorder. At a given wavevector the magnons propagate at multiple energies,
related, crudely, to `domain confined' modes with which they have large
overlap. We provide a qualitative understanding of the trend observed with
growing antisite disorder, and contrast these results to the much broader
spectrum that one obtains for uncorrelated antisites.",1204.1194v1
2012-04-09,Free Energy Distribution Function of a Random Ising ferromagnet,"We study the free energy distribution function of weakly disordered Ising
ferromagnet in terms of the D-dimensional random temperature Ginzburg-Landau
Hamiltonian. It is shown that besides the usual Gaussian ""body"" this
distribution function exhibits non-Gaussian tails both in the paramagnetic and
in the ferromagnetic phases. Explicit asymptotic expressions for these tails
are derived. It is demonstrated that the tails are strongly asymmetric: the
left tail (for large negative values of the free energy) is much more slow than
the right one (for large positive values of the free energy). It is argued that
in the critical point the free energy of the random Ising ferromagnet in
dimensions D<4 is described by a non-trivial universal distribution function
being non self-averaging",1204.1831v1
2012-04-13,Quantum corrections of the biquadratic interaction in the 1D spin-1/2 frustrated ferromagnetic systems,"Quantum corrections of the biquadratic interaction in the 1D spin-1/2
frustrated ferromagnetic Heisenberg model are studied. The biquadratic
interaction for spin-1/2 chains is eliminated and transformed to the quadratic
interaction. Doing a numerical experiment, new insight as to how the classical
phases get modified on the inclusion of quantum fluctuations is provided.
Observed results suggest the existence of an intermediate region in the ground
state phase diagram of the frustrated ferromagnetic spin-1/2 chains with
combination of dimer and chiral orders. In addition, from the quantum
entanglement view point, differences between quantum phases are also obtained.
The nearest neighbor spins never be entangled in the frustrated ferromagnetic
chains but are entangled up to the Majumdar-Ghosh point in the frustrated
antiferromagnetic chains. On the other hand, the next nearest neighbor spins in
the mentioned intermediate region are entangled.",1204.2905v1
2012-04-18,Universal low-temperature magnetic properties of the classical and quantum dimerized ferromagnetic spin chain,"Low-temperature magnetic properties of both classical and quantum dimerized
ferromagnetic spin chains are studied. It is shown that at low temperatures the
classical dimerized model reduces to the classical uniform model with the
effective exchange integral $J_{0}=J(1-\delta^{2})$, where $\delta$ is the
dimerization parameter. The partition function and spin correlation function
are calculated by means of mapping to the continuum limit, which is justified
at low temperatures. In the continuum limit the calculation of the partition
function and spin correlation function is reduced to the eigenvalue problem of
quantum rotator in gravitational field. Quantum model is studied using
Dyson-Maleev representation of the spin operators. It is shown that in the
long-wavelength limit the Hamiltonian of the quantum dimerized chain reduces to
that of the uniform ferromagnetic chain with the effective exchange integral
$J_{0}=J(1-\delta^{2})$. This fact implies that the known equivalence of the
low-temperature magnetic properties of classical and quantum ferromagnetic
chains remains for the dimerized chains. The considered model can be
generalized to include the next-neighbor antiferromagnetic interaction.",1204.4076v2
2012-04-26,Ballistic spin filtering across the ferromagnetic-semiconductor interface,"The ballistic spin-filter effect from a ferromagnetic metal into a
semiconductor has theoretically been studied with an intention of detecting the
spin polarizability of density of states in FM layer at a higher energy level.
The physical model for the ballistic spin filtering across the interface
between ferromagnetic metals and semiconductor superlattice is developed by
exciting the spin polarized electrons into n-type AlAs/GaAs superlattice layer
at a much higher energy level and then ballistically tunneling through the
barrier into the ferromagnetic film. Since both the helicity-modulated and
static photocurrent responses are experimentally measurable quantities, the
physical quantity of interest, the relative asymmetry of spin-polarized
tunneling conductance, could be extracted experimentally in a more
straightforward way, as compared with previous models. The present physical
model serves guidance for studying spin detection with advanced performance in
the future.",1204.5826v1
2014-05-01,Spin injection from a ferromagnet into a semiconductor in the case of a rough interface,"The effect of the interface roughness on the spin injection from a
ferromagnet into a semiconductor is studied theoretically. Even a small
interface irregularity can lead to a significant enhancement of the injection
efficiency. When a typical size of the irregularity, a, is within a domain
lambda_F << a << lambda_N, where lambda_F and lambda_N are the spin-diffusion
lengths in the ferromagnet and semiconductor, respectively, the geometrical
enhancement factor is ~lambda_N. The origin of the enhancement is the
modification of the local electric field on small scales ~a near the interface.
We demonstrate the effect of enhancement by considering a number of
analytically solvable examples of injection through curved
ferromagnet-semiconductor interfaces. For a generic curved interface the
enhancement factor is ~lambda_N / R, where R is the local radius of curvature.",1405.0059v1
2014-05-12,Carrier transport properties of the Group-IV ferromagnetic semiconductor Ge1-xFex with and without boron doping,"We have investigated the transport and magnetic properties of group-IV
ferromagnetic semiconductor Ge1-xFex films (x = 1.0 and 2.3 %) with and without
boron doping grown by molecular beam epitaxy (MBE). In order to accurately
measure the transport properties of 100-nm-thick Ge1-xFex films, (001)-oriented
silicon-on-insulator (SOI) wafers with an ultra-thin Si body layer (~5 nm) were
used as substrates. Owing to the low Fe content, the hole concentration and
mobility in the Ge1-xFex films were exactly estimated by Hall measurements
because the anomalous Hall effect in these films was found to be negligibly
small. By boron doping, we increased the hole concentration in Ge1-xFex from
~1018 cm-3 to ~1020 cm-3 (x = 1.0%) and to ~1019 cm-3 (x = 2.3%), but no
correlation was observed between the hole concentration and magnetic
properties. This result presents a contrast to the hole-induced ferromagnetism
in III-V ferromagnetic semiconductors.",1405.2764v1
2014-05-19,Controllable generation of a spin-triplet supercurrent in a Josephson spin-valve,"It has been predicted theoretically that an unconventional odd-frequency
spin-triplet component of superconducting order parameter can be induced in
multilayered ferromagnetic structures with non-collinear magnetization. In this
work we study experimentally nano-scale devices, in which a ferromagnetic spin
valve is embedded into a Josephson junction. We demonstrate two ways of in-situ
analysis of such Josephson spin valves: via magnetoresistance measurements and
via in-situ magnetometry based on flux quantization in the junction. We observe
that supercurrent through the device depends on the relative orientation of
magnetization of the two ferromagnetic layers and is enhanced in the
non-collinear state of the spin valve. This provides a direct prove of
controllable generation of the spin-triplet superconducting component in a
ferromagnet.",1405.4754v1
2014-05-19,Ferromagnetic phase in the polarized two-species bosonic Hubbard Model,"We recently studied a doped two-dimensional bosonic Hubbard model with two
hard-core species, with different masses, using quantum Monte Carlo simulations
[Phys. Rev. B 88, 161101(R) (2013)]. Upon doping away from half-filling, we
find several distinct phases, including a phase-separated ferromagnet with Mott
behavior for the heavy species and both Mott insulating and superfluid
behaviors for the light species. Introducing polarization, an imbalance in the
population between species, we find a fully phase-separated ferromagnet. This
phase exists for a broad range of temperatures and polarizations. By using
finite size scaling of the susceptibility, we find a critical exponent which is
consistent with the two-dimensional Ising universality class. Significantly,
since the global entropy of this phase is higher than that of the ferromagnetic
phase with single species, its experimental observation in cold atoms may be
feasible.",1405.4849v2
2014-05-22,Role of the Ce valence in the coexistence of superconductivity and ferromagnetism of CeO$_{1-x}$F$_{x}$BiS$_{2}$ revealed by Ce $L_3$-edge x-ray absorption spectroscopy,"We have performed Ce $L_3$-edge x-ray absorption spectroscopy (XAS)
measurements on CeO$_{1-x}$F$_x$BiS$_2$, in which the superconductivity of the
BiS$_2$ layer and the ferromagnetism of the CeO$_{1-x}$F$_x$ layer are induced
by the F-doping, in order to investigate the impact of the F-doping on the
local electronic and lattice structures. The Ce $L_3$-edge XAS spectrum of
CeOBiS$_2$ exhibits coexistence of $4f^1$ (Ce$^{3+}$) and $4f^0$ (Ce$^{4+}$)
state transitions revealing Ce mixed valency in this system. The spectral
weight of the $4f^0$ state decreases with the F-doping and completely
disappears for $x>0.4$ where the system shows the superconductivity and the
ferromagnetism. The results suggest that suppression of Ce-S-Bi coupling
channel by the F-doping appears to drive the system from the valence
fluctuation regime to the Kondo-like regime, leading to the coexistence of the
superconducting BiS$_2$ layer and the ferromagnetic CeO$_{1-x}$F$_x$ layer.",1405.5639v1
2014-05-22,Giant magnetoelectric effect in magnetic tunnel junctions coupled to an electromagnetic environment,"We study the magnetization dynamics in
ferromagnet$\mid$insulator$\mid$ferromagnet and
ferromagnet$\mid$insulator$\mid$normal metal ultra-small tunnel junctions, and
the associated voltage drop in the presence of an electromagnetic environment
assisting the tunneling processes. We show that the environment strongly
affects the resulting voltage, which becomes a highly non-linear function of
the precession cone angle $\theta$. We find that voltages comparable to the
driving frequency $\omega$ can be reached even for small precession cone angles
$\theta$, in stark contrast to the case where the environment is absent. Such
an effect could be useful for the detection local magnetization precessions in
textured ferromagnets or, conversely, for probing the environment via the
magnetization dynamics.",1405.5744v2
2014-06-05,"Magnetotransport in ferromagnetic Mn5Ge3, Mn5Ge3C0.8, and Mn5Si3C0.8 thin films","The electrical resistivity, anisotropic magnetoresistance (AMR), and
anomalous Hall effect of ferromagnetic Mn5Ge3, Mn5Ge3C0.8, and Mn5Si3C0.8 thin
films has been investigated. The data show a behavior characteristic for a
ferromagnetic metal, with a linear increase of the anomalous Hall coefficient
with Curie temperature. While for ferromagnetic Mn5Si3C0.8 the normal Hall
coefficient R0 and the AMR ratio are independent of temperature, these
parameters strongly increase with temperature for the germanide films. This
difference is attributed to the different hybridization of electronic states in
the materials due different lattice parameters and different atomic
configurations (Ge vs. Si metalloid). The concomitant sign change of R0 and the
AMR ratio with temperature observed for the germanide films is discussed in a
two-current model indicating an electron-like minority-spin transport at low
temperatures.",1406.1442v1
2014-06-10,Multiferroic interfaces composed of d0 perovskites oxides,"We investigate the electronic, ferroelectric and magnetic properties of
KTaO3/PbTiO3 interfaces by using conventional density functional theory (DFT)
and advanced DFT such as hybrid functional HSE06. We show that doped holes in
valence bands or electrons in conduction bands give rise to ferromagnetism at
the interfaces. The ferromagnetic states are ground states for both hole-doped
(p-type) and electron-doped (n-type) interfaces by comparison with their
corresponding nonmagnetic and antiferromagnetic states. Carriers (holes or
electrons) concentrate near the interface to screen the polarization charge and
thus the concentration of carrier varies with the ferroelectric polarization.
Furthermore, the interface magnetization, which is nearly proportional to the
concentration of carrier, can be tuned by ferroelectric polarization reversal,
leading to strong intrinsic magnetoelectric effects at the interface of
originally nonmagnetic KTaO3 and PbTiO3. Interestingly, a
ferromagnetic-nonmagnetic transition tuned by an applied electric field can be
realized at the p-type interface. This suggests an illuminating approach to
multiferroic materials beyond conventional single-phase multiferroics and
multi-phase multiferroics such as ferroelectric/ferromagnet heterostructures.
The KTaO3/PbTiO3 interfaces may be promising in future multiferroic devices
applications.",1406.2595v2
2014-06-16,The suppression of Curie temperature by Sr doping in diluted ferromagnetic semiconductor (La1-xSrx)(Zn1-yMny)AsO,"(La1-xSrx)(Zn1-yMny)AsO is a two dimensional diluted ferromagnetic
semiconductor that has the advantage of decoupled charge and spin doping. The
substitution of Sr2+ for La3+ and Mn2+ for Zn2+ into the parent semiconductor
LaZnAsO introduces hole carriers and spins, respectively. This advantage
enables us to investigate the influence of carrier doping on the ferromagnetic
ordered state through the control of Sr concentrations in
(La1-xSrx)(Zn0.9Mn0.1)AsO. 10 % Sr doping results in a ferromagnetic ordering
below TC ~ 30 K. Increasing Sr concentration up to 30 % heavily suppresses the
Curie temperature and saturation moments. Neutron scattering measurements
indicate that no structural transition occurs for (La0.9Sr0.1)(Zn0.9Mn0.1)AsO
below 300 K.",1406.4439v1
2015-12-20,Piezo Voltage Controlled Planar Hall Effect Devices,"The electrical control of the magnetization switching in ferromagnets is
highly desired for future spintronic applications. Here we report on hybrid
piezoelectric (PZT) /ferromagnetic (Co2FeAl) devices in which the planar Hall
voltage in the ferromagnetic layer is tuned solely by piezo voltages. The
change of planar Hall voltage is associated with magnetization switching
through 90 in the plane under piezo voltages. Room temperature magnetic NOT and
NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar
Hall effect devices without the external magnetic field. Our demonstration may
lead to the realization of both information storage and processing using
ferromagnetic materials.",1512.06374v2
2015-12-29,Effect of External Magnetic Field on the Co-existence of Superconductivity and Antiferromagnetism in rare Earth Nickle Borocarbides (RNi2B2C),"In this paper we have studied the effect of external magnetic field in the
co-existing phase of superconducting and anti-ferromagnetism of rare earth
nickel borocarbides. The anti-ferromagnetism in these systems might have
originated due to both localized 'f' electrons as well as itinerant electrons
which are responsible for conduction. On the other hand, superconductivity is
due to spin density wave, arising out of Fermi surface instability. The
anti-ferromagnetism order is mostly influenced by hybridization of the 'f'
electron with the conduction electron. Here we have obtained the dependence of
superconducting energy gap as well as staggered magnetic field on temperature T
and energy $\epsilon_k$ in a framework based on mean field Hamiltonian using
double time electron Green's function. We have shown in our calculation the
effect of external magnetic field on superconducting and anti-ferromagnetic
order parameter for $YNi_2B_2C$ in the presence of hybridization. The ratio of
the calculated effective gap and $T_C$ is close to BCS value which agrees quite
well with experimental results.",1512.08702v1
2016-05-17,Self-current induced spin-orbit torque in FeMn/Pt multilayers,"Extensive efforts have been devoted to the study of spin-orbit torque in
ferromagnetic metal/heavy metal bilayers and exploitation of it for
magnetization switching using an in-plane current. As the spin-orbit torque is
inversely proportional to the thickness of the ferromagnetic layer, sizable
effect has only been realized in bilayers with an ultrathin ferromagnetic
layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately,
both ferromagnetic properties and current induced spin-orbit torque can be
achieved in FeMn/Pt multilayers without any constraint on its total thickness.
The critical behavior of these multilayers follows closely three-dimensional
Heisenberg model with a finite Curie temperature distribution. The spin torque
effective field is about 4 times larger than that of NiFe/Pt bilayer with a
same equivalent NiFe thickness. The self-current generated spin torque is able
to switch the magnetization reversibly without the need for an external field
or a thick heavy metal layer. The removal of both thickness constraint and
necessity of using an adjacent heavy metal layer opens new possibilities for
exploiting spin-orbit torque for practical applications.",1605.05135v1
2016-05-18,Neutron depolarization imaging of the hydrostatic pressure dependence of inhomogeneous ferromagnets,"The investigation of fragile and potentially inhomogeneous forms of
ferromagnetic order under extreme conditions, such as low temperatures and high
pressures, is of central interest for areas such as geophysics, correlated
electron systems, as well as the optimization of materials synthesis for
applications where particular material properties are required. We report
neutron depolarization imaging measurements on the weak ferromagnet Ni$_3$Al
under pressures up to 10kbar using a Cu:Be clamp cell. Using a polychromatic
neutron beam with wavelengths $\lambda\geq$ 4\AA in combination with $^3$He
neutron spin filter cells as polarizer and analyzer we were able to track
differences of the pressure response in inhomogeneous samples by virtue of high
resolution neutron depolarization imaging. This provides spatially resolved and
non-destructive access to the pressure dependence of the magnetic properties of
inhomogeneous ferromagnetic materials.",1605.05459v1
2016-05-21,Magnetism and Superconductivity in Ferromagnetic Heavy Fermion System UCoGe under In-plane Magnetic Fields,"We study the ferromagnetic superconductor UCoGe at ambient pressure under
$ab$-plane magnetic fields $\vec{H}$ which are perpendicular to the
ferromagnetic easy axis. It is shown that, by taking into account the
Dyaloshinskii-Moriya interaction arising from the zigzag chain crystal
structure of UCoGe, we can qualitatively explain the experimentally observed
in-plane anisotropy for critical magnetic fields of the paramagnetic
transition. Because of this strong dependence on the magnetic field direction,
upper critical fields of superconductivity, which is mediated by ferromagnetic
spin fluctuations, also become strongly anisotropic. The experimental
observation of ""S-shaped"" $H_{c2}\parallel b$-axis is qualitatively explained
as a result of enhancement of the spin fluctuations due to decreased Curie
temperature by the $b$-axis magnetic field. We also show that the S-shaped
$H_{c2}$ is accompanied by a rotation of the $d$-vector, which would be a key
to understand the experiments not only at ambient pressure but also under
pressure.",1605.06625v1
2016-05-23,An effective mean field theory for the coexistence of anti-ferromagnetism and superconductivity: Applications to iron-based superconductors and cold Bose-Fermi atomic mixtures,"We study an effective fermion model on a square lattice to investigate the
cooperation and competition of superconductivity and anti-ferromagnetism. In
addition to particle tunneling and on-site interaction, a bosonic excitation
mediated attractive interaction is also included in the model. We assume that
the attractive interaction is mediated by spin fluctuations and excitations of
Bose-Einstein condensation (BEC) in electronic systems and Bose-Fermi mixtures
on optical lattices, respectively. Using an effective mean-field theory to
treat both superconductivity and anti-ferromagnetism at equal footing, we study
the model within the Landau energy functional approach and a linearized theory.
Within our approaches, we find possible co-existence of superconductivity and
anti-ferromagnetism for both electronic and cold-atomic models. Our linearized
theory shows while spin fluctuations favor d-wave superconductivity and BEC
excitations favor s-wave superconductivity.",1605.07073v3
2016-05-29,A New Ferromagnetic Superconductor: CsEuFe$_4$As$_4$,"Superconductivity (SC) and ferromagnetism (FM) are in general antagonistic,
which makes their coexistence very rare. Following our recent discovery of
robust coexistence of SC and FM in RbEuFe$_4$As$_4$ [Y. Liu et al., arXiv:
1605.04396 (2016)], here we report another example of such a coexistence in its
sister compound CsEuFe$_4$As$_4$, synthesized for the first time. The new
material exhibits bulk SC at 35.2 K and Eu$^{2+}$-spin ferromagnetic ordering
at 15.5 K, demonstrating that it is a new robust ferromagnetic superconductor.",1605.09007v1
2016-05-31,Pure spin current devices based on ferromagnetic topological insulators,"Two-dimensional topological insulators possess two counter propagating edge
channels with op- posite spin direction. Recent experimental progress allowed
to create ferromagnetic topological insulators realizing a quantum anomalous
Hall (QAH) state. In the QAH state one of the two edge channels disappears due
to the strong ferromagnetic exchange field. We investigate heterostuctures of
topological insulators and ferromagnetic topological insulators by means of
numerical transport calculations. We show that spin current flow in such
heterostructures can be controlled with high fidelity. Specifically, we propose
spintronic devices that are capable of creating, switching and de- tecting pure
spin currents using the same technology. In these devices electrical currents
are directly converted into spin currents, allowing a high conversion
efficiency. Energy independent transport properties in combination with large
bulk gaps in some topological insulator materials may allow operation even at
room temperature.",1605.09590v1
2016-08-03,Magnetoanisotropic Josephson effect due to interfacial spin-orbit fields in superconductor/ferromagnet/superconductor junctions,"We study theoretically the effects of interfacial Rashba and Dresselhaus
spin-orbit coupling in superconductor/ferromagnet/superconductor (S/F/S)
Josephson junctions---with allowing for tunneling barriers between the
layers---by solving the Bogoljubov-de Gennes equation for a realistic
heterostructure and applying the Furusaki-Tsukada technique to calculate the
electric current at a finite temperature. The presence of spin-orbit couplings
leads to out- and in-plane magnetoanisotropies of the Josephson current, which
are giant in comparison to current magnetoanisotropies in similar normal-state
ferromagnet/normal metal (F/N) junctions. Especially huge anisotropies appear
in the vicinity of $ 0 $-$ \pi $ transitions, caused by the exchange-split
bands in the ferromagnetic metal layer. We also show that the direction of the
Josephson critical current can be controlled (inducing $ 0 $-$ \pi $
transitions) by the strength of the spin-orbit coupling and, more crucial, by
the orientation of the magnetization. Such a control can bring new
functionalities into Josephson junction devices.",1608.01218v2
2016-08-08,Biaxial-stress-driven full spin polarization in ferromagnetic hexagonal chromium telluride,"It is important to spintronics to achieve fully-spin-polarized magnetic
materials that are stable and can be easily fabricated. Here, through
systematical density-functional-theory investigations, we achieve high and even
full spin polarization for carriers in the ground-state phase of CrTe by
applying tensile biaxial stress. The resulting strain is tensile in the xy
plane and compressive in the z axis. With the in-plane tensile strain
increasing, the ferromagnetic order is stable against antiferromagnetic
fluctuations, and a half-metallic ferromagnetism is achieved at an in-plane
strain of 4.8%. With the spin-orbit coupling taken into account, the spin
polarization is equivalent to 97% at the electronic phase transition point, and
then becomes 100.0% at the in-plane strain of 6.0%. These make us believe that
the full-spin-polarized ferromagnetism in this stable and easily-realizable
hexagonal phase could be realized soon, and applied in spintronics.",1608.02405v3
2016-12-10,Devil's Staircase Continuum in the Chiral Clock Spin Glass with Competing Ferromagnetic-Antiferromagnetic and Left-Right Chiral Interactions,"The chiral clock spin-glass model with q=5 states, with both competing
ferromagnetic-antiferromagnetic and left-right chiral frustrations, is studied
in d=3 spatial dimensions by renormalization-group theory. The global phase
diagram is calculated in temperature, antiferromagnetic bond concentration p,
random chirality strength, and right-chirality concentration c. The system has
a ferromagnetic phase, a multitude of different chiral phases, a chiral
spin-glass phase, and a critical (algebraically) ordered phase. The
ferromagnetic and chiral phases accumulate at the disordered phase boundary and
form a spectrum of devil's staircases, where different ordered phases
characteristically intercede at all scales of phase-diagram space. Shallow and
deep reentrances of the disordered phase, bordered by fragments of regular and
temperature-inverted devil's staircases, are seen. The extremely rich phase
diagrams are presented as continuously and qualitatively changing videos.",1612.03330v2
2016-12-21,Quantum Griffiths phase inside the ferromagnetic phase of Ni$_{1-x}$V$_x$,"We study by means of bulk and local probes the d-metal alloy Ni$_{1-x}$V$_x$
close to the quantum critical concentration, $x_c \approx 11.6\%$, where the
ferromagnetic transition temperature vanishes. The magnetization-field curve in
the ferromagnetic phase takes an anomalous power-law form with a nonuniversal
exponent that is strongly $x$-dependent and mirrors the behavior in the
paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous
magnetic order and indicate the presence of dynamic fluctuating magnetic
clusters. These results provide strong evidence for a quantum Griffiths phase
on the ferromagnetic side of the quantum phase transition.",1612.07207v2
2016-12-21,Chirality transitions in frustrated ferromagnetic spin chains: a link with the gradient theory of phase transitions,"We study chirality transitions in frustrated ferromagnetic spin chains, in
view of a possible connection with the theory of Liquid Crystals. A variational
approach to the study of these systems has been recently proposed by Cicalese
and Solombrino, focusing close to the helimagnet-ferromagnet transition point
corresponding to the critical value of the frustration parameter $\alpha=4$. We
reformulate this problem for any $\alpha\geq0$ in the framework of surface
energies in nonconvex discrete systems with nearest neighbors ferromagnetic and
next-to-nearest neighbors antiferromagnetic interactions and we link it to the
gradient theory of phase transitions, by showing a uniform equivalence by
$\Gamma$-convergence on $[0,4]$ with Modica-Mortola type functionals.",1612.07262v4
2017-06-07,Density-controlled quantum Hall ferromagnetic transition in a two-dimensional hole system,"Quantum Hall ferromagnetic transitions are typically achieved by increasing
the Zeeman energy through in-situ sample rotation, while transitions in systems
with pseudo-spin indices can be induced by gate control. We report here a
gate-controlled quantum Hall ferromagnetic transition between two real spin
states in a conventional two-dimensional system without any in-plane magnetic
field. We show that the ratio of the Zeeman splitting to the cyclotron gap in a
Ge two-dimensional hole system increases with decreasing density owing to
inter-carrier interactions. Below a critical density of $\sim2.4\times 10^{10}$
cm$^{-2}$, this ratio grows greater than $1$, resulting in a ferromagnetic
ground state at filling factor $\nu=2$. At the critical density, a resistance
peak due to the formation of microscopic domains of opposite spin orientations
is observed. Such gate-controlled spin-polarizations in the quantum Hall regime
opens the door to realizing Majorana modes using two-dimensional systems in
conventional, low-spin-orbit-coupling semiconductors.",1706.02044v1
2017-06-13,Generalized quasiclassical theory of the long-range proximity effect and spontaneous currents in superconducting heterostructures with strong ferromagnets,"We present the generalized quasiclassical theory of the long-range
superconducting proximity effect in heterostructures with strong ferromagnets,
where the exchange splitting is of the order of Fermi energy. In the
ferromagnet the propagation of spin-triplet Cooper pairs residing on the
spin-split Fermi surfaces is shown to be governed by the spin-dependent Abelian
gauge field which results either from the spin-orbital coupling or from the
magnetic texture. The additional gauge field enters into the quasiclassical
equations in superposition with the usual electromagnetic vector potential and
results in the generation of spontaneous superconducting currents and phase
shifts in various geometries which provide the sources of long-range
spin-triplet correlations. We derive the Usadel equations and boundary
conditions for the strong ferromagnet and consider several generic examples of
the Josephson systems supporting spontaneous currents.",1706.04239v2
2017-06-15,First order magneto-structural transition and magnetocaloric effect in MnNiGe$_{0.9}$Ga$_{0.1}$,"The first order magneto-structural transition ($T_t\simeq95$ K) and
magnetocaloric effect in MnNiGe$_{0.9}$Ga$_{0.1}$ are studied via powder x-ray
diffraction and magnetization measurements. Temperature dependent x-ray
diffraction measurements reveal that the magneto-structural transition remains
incomplete down to 23 K, resulting in a coexistence of antiferromagnetic and
ferromagnetic phases at low temperatures. The fraction of the high temperature
Ni$_2$In-type hexagonal ferromagnetic and low temperature TiNiSi-type
orthorhombic antiferromagnetic phases is estimated to be $\sim 40\%$ and $\sim
60\%$, respectively at 23 K. The ferromagnetic phase fraction increases with
increasing field which is found to be in non-equilibrium state and gives rise
to a weak re-entrant transition while warming under field-cooled condition. It
shows a large inverse magnetocaloric effect across the magneto-structural
transition and a conventional magnetocaloric effect across the second order
paramagnetic to ferromagnetic transition. The relative cooling power which
characterizes the performance of a magnetic refrigerant material is found to be
reasonably high compared to the other reported magnetocaloric alloys.",1706.04740v1
2017-06-26,Magnetic Proximity Effect in Pt/CoFe2O4 Bilayers,"We observe the magnetic proximity effect (MPE) in Pt/CoFe2O4 bilayers grown
by molecular beam epitaxy. This is revealed through angle-dependent
magnetoresistance measurements at 5 K, which isolate the contributions of
induced ferromagnetism (i.e. anisotropic magnetoresistance) and spin Hall
effect (i.e. spin Hall magnetoresistance) in the Pt layer. The observation of
induced ferromagnetism in Pt via AMR is further supported by density functional
theory calculations and various control measurements including insertion of a
Cu spacer layer to suppress the induced ferromagnetism. In addition, anomalous
Hall effect measurements show an out-of-plane magnetic hysteresis loop of the
induced ferromagnetic phase with larger coercivity and larger remanence than
the bulk CoFe2O4. By demonstrating MPE in Pt/CoFe2O4, these results establish
the spinel ferrite family as a promising material for MPE and spin manipulation
via proximity exchange fields.",1706.08473v1
2017-07-10,Theory of in-plane current induced spin torque in metal/ferromagnet bilayers,"Using a semiclassical approach that simultaneously incorporates the spin Hall
effect (SHE), spin diffusion, quantum well states, and interface spin-orbit
coupling (SOC), we address the interplay of these mechanisms as the origin of
the in-plane current induced spin torque observed in the normal
metal/ferromagnetic metal bilayer thin films. Focusing on the bilayers with a
ferromagnet much thinner than its spin diffusion length, such as Pt/Co with
$\sim 10$nm thickness, our approach addresses simultaneously the two
contributions to the spin torque, namely the spin-transfer torque (SHE-STT) due
to SHE induced spin injection, and the spin-orbit torque (SOT) due to SOC
induced spin accumulation. The SOC produces an effective magnetic field at the
interface, hence it modifies the angular momentum conservation expected for the
SHE-STT. The SHE induced spin voltage and the interface spin current are
mutually dependent, hence are solved in a self-consistent manner. In addition,
the spin transport mediated by the quantum well states may be responsible for
the experimentally observed rapid variation of the spin torque with respect to
the thickness of the ferromagnet.",1707.02771v1
2017-07-13,Ferromagnetism in the Hubbard model with a gapless nearly-flat band,"We present a version of the Hubbard model with a gapless nearly-flat lowest
band which exhibits ferromagnetism in two or more dimensions. The model is
defined on a lattice obtained by placing a site on each edge of the hypercubic
lattice, and electron hopping is assumed to be only between nearest and next
nearest neighbor sites. The lattice, where all the sites are identical, is
simple, and the corresponding single-electron band structure, where two
cosine-type bands touch without an energy gap, is also simple. We prove that
the ground state of the model is unique and ferromagnetic at half-filling of
the lower band, if the lower band is nearly flat and the strength of on-site
repulsion is larger than a certain value which is independent of the lattice
size. This is the first example of ferromagnetism in three dimensional
non-singular models with a gapless band structure.",1707.03944v2
2017-10-11,Weak ferromagnetism and glassy state in kappa-(BEDT-TTF)2Hg(SCN)2Br,"Since the first observation of weak ferromagnetism in the charge-transfer
salt kappa-(BEDT-TTF)2-Cu[N(CN)2]Cl [U. Welp et al., Phys. Rev. Lett. 69, 840
(1992)], no further evidence of ferromagnetism in this class of organic
materials has been reported. Here we present static and dynamic spin
susceptibility measurements on kappa-(BEDT-TTF)2Hg(SCN)2Br revealing weak
ferromagnetism below about TWF = 20 K. We suggest that frustrated spins in the
molecular dimers suppress long-range order, forming a spin-glass ground state
in the insulating phase.",1710.04028v3
2017-10-25,Dimensionality driven enhancement of ferromagnetic superconductivity in URhGe,"In most unconventional superconductors, like the high-Tc cuprates, iron
pnictides, or heavy fermion systems, superconductivity emerges in the proximity
of an electronic instability. Identifying unambiguously the pairing mechanism
remains nevertheless an enormous challenge. Among these systems, the
orthorhombic uranium ferromagnetic superconductors have a unique position,
notably because magnetic fields couple directly to ferromagnetic order, leading
to the fascinating discovery of the re-emergence of superconductivity in URhGe
at high field. Here we show that uniaxial stress is a remarkable tool allowing
fine-tuning of the pairing strength. With a relatively small stress, the
superconducting phase diagram is spectacularly modified, with a merging of the
low and high field superconducting states and a significant enhancement of
superconductivity. The superconducting critical temperature increases both at
zero field and under field, reaching 1K, more than twice higher than at ambient
pressure. The enhancement of superconductivity is directly related to a change
of the magnetic dimensionality with an increase of the transverse magnetic
susceptibility, demonstrating that in addition to the Ising-type longitudinal
ferromagnetic fluctuations, transverse magnetic fluctuations also play an
important role in the superconducting pairing.",1710.09097v1
2017-12-13,Comparison of dynamic behavior of ferroelectric and ferromagnetic nematic suspensions,"The pioneering realization of suspensions of ferroelectric nanoparticles in a
nematic host was one of excellent contributions of Yuri Reznikov to the science
of liquid crystals [Y. Reznikov et al., Appl. Phys. Lett. 82 (2003) 191]. This
achievement created great excitement as entailed the enhancement of materials
dielectric properties and increase of the phase transition temperature between
nematic and isotropic phase. In this contribution, we examine the spectrum of
fundamental fluctuations in one of his ferroelectric suspensions by dynamic
light scattering measurements, which gives insight into the coupling between
the particles and the orientation of the liquid crystalline matrix. We set side
by side these results with the equivalent ones obtained for the case of stable
suspensions of ferromagnetic nanoplatelets in a nematic matrix showing
macroscopic ferromagnetic ordering. The underlying origin of the difference
between the particle-matrix coupling observed in both cases is discussed and
its effect on the orientational fluctuations spectrum is compared.",1712.04668v1
2017-12-14,Theoretical prediction of a two-dimensional intrinsic double-metal ferromagnetic semiconductor MnCoO4,"A two-dimensional double-metal oxide MnCoO4 was predicted to be an intrinsic
ferromagnetic semiconductor by using density functional theory. The low
cleavage energy 0.36 Jm-2, which is similar to that of graphene, indicates that
it can be easily exfoliated. The bulk structure has an antiferromagnetic ground
state while the ferromagnetic configuration is the ground state against two
antiferromagnetic and three ferrimagnetic configurations in the two-dimensional
structure. The spin flip gaps for valence and conduction bands are 0.41 and
0.10 eV calculated with the HSE06 density functional, which are much larger
than the thermal energy at room temperature. The Curie temperature obtained
from the Monte Carlo simulation is 40 K. Under 9% tensile strain, the spin flip
gaps increase largely so that the spin flip can be suppressed. The direct
antiferromagnetic coupling between the Mn and Co atoms reduces largely while
the indirect ferromagnetic couplings between two Mn or two Co atoms mediated by
the O atoms do not decrease much in the stretched structure. The Curie
temperature increases to 230 K, higher than the dry ice temperature. Moreover,
phonon dispersion indicates that the MnCoO4 is also stable under the tensile
stain. Therefore, two-dimensional MnCoO4 could be a good candidate for
low-dimensional spintronics.",1712.05071v1
2018-01-08,Direct observation of double exchange in ferromagnetic La$_{0.7}$Sr$_{0.3}$CoO$_3$ by broadband ellipsometry,"We present results of our broadband ellipsometry measurements of the optical
response of ferromagnetic La$_{0.7}$Sr$_{0.3}$CoO$_3$. Our data show that the
ferromagnetic transition is accompanied by a transfer of optical spectral
weight from an absorption band centered at 1.5 eV to a narrow component of the
Drude-like peak. The associated reduction of the intraband kinetic energy is
significantly larger than $k_{\rm B}T_c$, confirming that the double exchange
plays a major role in the ferromagnetism of doped cobaltites. In conjunction
with results of recent theoretical studies, the temperature dependence of the
Drude-like peak suggests that the double exchange is mediated by $t_{2g}$
orbitals.",1801.02424v2
2018-01-10,The hidden magnetization in ferromagnetic material: Miamagnetism,"This paper presents the hidden magnetization features of ferromagnetic
materials: called miamagnetism. As we know, we have several forms of
magnetization: the diamagnetism, the paramagnetism, the ferromagnetism etc. The
main character of the diamagnetism is that its magnetic susceptibility is
negative (from -1e-9 for gas and -1e-6 for liquid and solid to -1 for
superconducting materials of type I) and it is not less than -1 unless for
special materials like metamaterials at high frequencies. The miamagnetism has
the character that the magnetic susceptibility can reach at low frequencies a
negative value of -155 of magnitude leading to a negative permeability. We can
not see it because it is hidden by the ferromagnetic character which has a high
positive magnetic susceptibility. We use the discrete Fourier transform to
illustrate this hidden character and the hysteresis model can be represented
only by harmonics of (2n+1)f0 of magnitude. This magnetization follows a
Boltzmann distribution for the modulus of theses harmonics.",1801.03479v1
2018-01-30,Critical behavior of two-dimensional intrinsically ferromagnetic semiconductor CrI3,"CrI3, which belongs to a rare category of two-dimensional (2D) ferromagnetic
semiconductors, is of great interest for spintronic device applications. Unlike
CrCl3 whose magnetism presents a 2D-Heisenberg behavior, CrI3 exhibits a larger
van der Waals gap, smaller cleavage energy, and stronger magnetic anisotropy
which could lead to a 3D magnetic characteristic. Hence, we investigate the
critical behavior of CrI3 in the vicinity of magnetic transition. We use the
modified Arrott plot and Kouvel-Fisher method, and conduct critical isotherm
analysis to estimate the critical exponents near the ferromagnetic phase
transition. This shows that the magnetism of CrI3 follows the crossover
behavior of a 3D-Ising model with mean field type interactions where the
critical exponents \b{eta}, {\gamma}, and {\delta} are 0.323, 0.835, and 3.585,
respectively, at the Curie temperature of 64 K. We propose the crossover
behavior can be attributed to the strong uniaxial anisotropy and inevitable
interlayer coupling. Our experiment demonstrates the applicability of crossover
behavior to a 2D ferromagnetic semiconductor.",1801.09878v1
2018-09-10,Electrodynamics of Josephson junctions containing strong ferromagnets,"Triplet supercurrents in multilayer ferromagnetic Josephson junctions with
misaligned magnetization can penetrate thicker ferromagnetic barriers compared
to the singlet component. Although the static properties of these junctions
have been extensively studied, the dynamic characteristics remain largely
unexplored. Here we report a comprehensive electrodynamic characterization of
multilayer ferromagnetic Josephson junctions composed of Co and Ho. By
measuring the temperature-dependent current-voltage characteristics and the
switching current distributions down to 0.3 K, we show that phase dynamics of
junctions with triplet supercurrents exhibits long (in terms of proximity)
junction behavior and moderately damped dynamics with renormalized capacitance
and resistance. This unconventional behavior possibly provides a different way
to dynamically detect triplets. Our results show new theoretical models are
required to fully understand the phase dynamics of triplet Josephson junctions
for applications in superconducting spintronics.",1809.03301v1
2018-09-13,Enhanced magnetoelectric effect of exactly solved spin-electron model on a doubly decorated square lattice in vicinity of a continuous phase transition,"Magnetoelectric properties of a coupled spin-electron model on a doubly
decorated square lattice in an external electric field applied along the
crystallographic axis [11] are rigorously examined with the help of generalized
decoration-iteration transformation. The phase diagram, spontaneous
magnetization and electric polarization are exactly calculated and their
dependencies are comprehensively investigated under a concurrent influence of
temperature and electric field. It is found that the electric field mostly
stabilizes at zero temperature the spontaneous antiferromagnetic order with
respect to the ferromagnetic one. At finite temperatures the external electric
field gradually suppresses a spontaneous ferromagnetic (antiferromagnetic)
order emergent close to a quarter (half) filling. An enhanced magnetoelectric
response is detectable in vicinity of a continuous phase transition at which
the spontaneous magnetization vanishes and the electric polarization displays a
weak-type singularity. It is demonstrated that reentrant phase transitions of
the ferromagnetic or antiferromagnetic phase may be induced at moderate values
of the electric field, which simultaneously produces a sharp kink in a critical
line of the ferromagnetic phase nearby a quarter filling.",1809.04889v1
2018-09-21,Defect Induced Room Temperature Ferromagnetism in Methylammonium Lead Iodide Perovskite,"The defect tolerance nature of organic-inorganic hybrid perovskite is
reflected from its stupendous growth in photovoltaic performances. The presence
of lattice defect can manipulate or even gives rise to some exceptional
properties which otherwise would have remained unseen. One of such properties
reported in this article is the experimental observation of defect mediated
room temperature ferromagnetism in methylammonium lead halide perovskite for
the very first time, ably supported by ab-initio calculations. Theoretical
analysis predicts the ferromagnetism principally arises from the iodide
vacancies in the orthorhombic and cubic crystal phases but not in the
tetragonal phase. The low temperature (100 K) ferromagnetic hysteresis loop was
stable even at a high temperature of 380 K substantiating the fact that the
origin of magnetism embedded in its defective nature.",1809.07957v1
2018-10-02,Spin-dependent (inverse) spin Hall effect in Co$_{60}$Fe$_{20}$B$_{20}$,"In ferromagnetic metals, the interconversion of spin and charge currents via
the spin Hall effect and its inverse can depend on the angle between the
ferromagnets magnetization and the spin current polarization direction. Here,
such a spin-dependent (inverse) spin Hall effect is found in the ferromagnetic
alloy Co$_{60}$Fe$_{20}$B$_{20}$. In a nonlocal magnon transport experiment,
Co$_{60}$Fe$_{20}$B$_{20}$ is used to both excite and detect magnonic spin
currents flowing in the ferrimagnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$. We
find that the signal amplitude is significantly modulated by tuning the
direction of the Co$_{60}$Fe$_{20}$B$_{20}$ magnetization. We design a sample
structure that completely prevents direct magnonic coupling between the
ferromagnets. Thus, we can identify unambiguously an intrinsic electronic
origin of the observed effect.",1810.01227v3
2018-10-03,Induced Energy Gap in Finite-Sized Superconductor/Ferromagnet Hybrids,"We theoretically study self-consistent proximity effects in finite-sized
systems consisting of ferromagnet ($\rm F$) layers coupled to an $s$-wave
superconductor ($\rm S$). We consider both $\rm SF_1F_2$ and $\rm SH$
nanostructures, where the $\rm F_1 F_2$ bilayers are uniformly magnetized, and
the ferromagnetic $\rm H$ layer possesses a helical magnetization profile. We
find that when the $\rm F_1 F_2$ layers are weakly ferromagnetic, a hard gap
can emerge when the relative magnetization directions are rotated from parallel
to antiparallel. Moreover, the gap is most prominent when the thicknesses of
$\rm F_1$ and $\rm F_2$ satisfy $\rm d_{F1}\leq d_{F2}$, respectively. For the
$\rm SH$ configuration, increasing the spatial rotation period of the exchange
field can enhance the induced hard gap. Our investigations reveal that the
origin of these findings can be correlated with the propagation of
quasiparticles with wavevectors directed along the interface. To further
clarify the source of the induced energy gap, we also examine the spatial and
energy resolved density of states, as well as the spin-singlet, and
spin-triplet superconducting correlations, using experimentally accessible
parameter values. Our findings can be beneficial for designing magnetic hybrid
structures where a tunable superconducting hard gap is needed.",1810.01886v1
2018-10-19,Ferromagnetic nodal-line metal in monolayer {\em h}-InC,"Based on first-principles calculations, we predict a new two-dimensional
ferromagnetic material that exhibits exotic Fermi surface topology. We show
that monolayer hexagonal indium carbide ({\em h}-InC) is thermodynamically and
dynamically stable, and it energetically favors the ferromagnetic ordering of
spins. The perfectly planar geometry in two dimensions, together with
ferromagnetism, gives rise to a unique opportunity to encounter intriguing
electronic properties, captured in the Fermi surface and band topology. We show
that multiple nodal lines coexist in momentum space, accompanied by the
electron and hole pockets that touch each other linearly at the nodal lines.
Inclusion of spin-orbit coupling enriches the magnetic and electronic
properties of {\em h}-InC. Spin-orbit coupling leads to an easy-plane type
magnetocrystalline anisotropy, and the nodal lines can be tuned into
topological nodal points, contingent upon the magnetization direction. Symmetry
analysis and a tight-binding model are provided to explain the nodal structure
of the bands. Our findings suggest {\em h}-InC as a new venue for supporting
carbon-based magnetism and exotic band topology in two dimensions.",1810.08563v2
2019-06-18,Two Dimensional Ferromagnetic Semiconductor: Monolayer CrGeS$_3$,"Recently, two-dimensional ferromagnetic semiconductors have been an important
class of materials for many potential applications in spintronic devices. Based
on density functional theory, we systematically explore the magnetic and
electronic properties of CrGeS$_3$ with the monolayer structures. The
comparison of total energy between different magnetic states ensures the
ferromagnetic ground state of monolayer CrGeS$_3$. It is also shown that
ferromagnetic and semiconducting properties are exhibited in monolayer
CrGeS$_3$ with the magnetic moment of 3 $\mu_{B}$ for each Cr atom, donated
mainly by the intense $dp$$\sigma$-hybridization of Cr $e_g$-S $p$. There are
the bandgap of 0.70 eV of spin-up state in the monolayer structure when 0.77 eV
in spin-down state. The global gap is 0.34 eV (2.21 eV by using HSE06
functional), which originates from bonding $dp\sigma$ hybridized states of Cr
$e_g$-S $p$ and unoccupied Cr $t_{2g}$-Ge $p$ hybridization. Besides, we
estimate that the monolayer CrGeS$_3$ possesses the Curie temperature of 161 K
by mean-field theory.",1906.07396v1
2019-06-27,Perspectives of Electrically generated spin currents in ferromagnetic materials,"Spin-orbit coupling enables charge currents to give rise to spin currents and
vice versa, which has applications in non-volatile magnetic memories, miniature
microwave oscillators, thermoelectric converters and Terahertz devices. In the
past two decades, a considerable amount of research has focused on electrical
spin current generation in different types of nonmagnetic materials. However,
electrical spin current generation in ferromagnetic materials has only recently
been actively investigated. Due to the additional symmetry breaking by the
magnetization, ferromagnetic materials generate spin currents with different
orientations of spin direction from those observed in nonmagnetic materials.
Studies centered on ferromagnets where spin-orbit coupling plays an important
role in transport open new possibilities to generate and detect spin currents.
We summarize recent developments on this subject and discuss unanswered
questions in this emerging field.",1906.11772v1
2019-07-21,Layer Dependence of Stacking Order in Nonencapsulated Few-layer CrI3,"Long-range magnetic orders in atomically thin ferromagnetic CrI3 give rise to
new fascinating physics and application perspectives. The physical properties
of two-dimensional (2D) ferromagnetism CrI3 are significantly influenced by
interlayer spacing and stacking order, which are sensitive to the hydrostatic
pressure and external environments. However, there remains debate on the
stacking order at low temperature. Here, we study the interlayer coupling and
stacking order of non-encapsulated 2-5 layer and bulk CrI3 at 10 K by Raman
spectroscopy; demonstrate a rhombohedral stacking in both antiferromagnetic and
ferromagnetic CrI3. The opposite helicity dependence of Ag and Eg modes arising
from phonon symmetry further validate the rhombohedral stacking. An anomalous
temperature-dependent behavior is observed due to spin-phonon coupling below 60
K. Our work provides insights into the interlayer coupling and stacking orders
of 2D ferromagnetic materials.",1907.08886v2
2019-07-23,Indication of Ferromagnetic Quantum Critical Point in Kondo Lattice CeRh$_6$Ge$_4$,"We report resistivity measurements under pressure for Kondo-lattice
ferromagnet CeRh$_6$Ge$_4$, and present that a quantum ferromagnetic (FM) phase
transition is easily achieved. In most clean metallic ferromagnets, a quantum
critical point (QCP) at zero field is avoided by changing the FM transition to
a discontinuous transition or to an antiferromagnetic transition. In
CeRh$_6$Ge$_4$, to the contrary, the Curie temperature of 2.5 K decreases
continuously as increasing pressure without any clear signature that the
transition changes to first order. The obvious non Fermi liquid behavior is
observed in the vicinity of the quantum FM phase transition. The experimental
data do not contradict a picture in which CeRh$_6$Ge$_4$ shows the FM QCP at
zero field. Band structure calculation suggests the unusual electronic state of
CeRh$_6$Ge$_4$ among Ce-based Kondo lattices. CeRh$_6$Ge$_4$ deserves further
investigations and will be a key material to understand the matter of the FM
QCP.",1907.09802v2
2019-07-30,Understanding the ferromagnetic insulating state in Cr doped VO$_2$,"Experimentally Cr doping in the rutile phase of VO$_2$ is found to stabilize
a charge ordered ferromagnetic insulating state in the doping range of 10\% to
20\%. In this work, we investigated its origin at 12.5\% Cr doping using a
combination of ab-initio electronic structure calculations as well as
microscopic modeling. Our calculations are found to reproduce the ferromagnetic
insulating state as well as a charge ordering at the V and Cr sites. The
mapping of the ab-initio band structure onto a tight-binding Hamiltonian allows
one to calculate the energy gain from different exchange pathways. This gain is
quantified in this work for the first time and the role of charge ordering in
stabilizing a ferromagnetic insulating state is understood.",1907.12803v2
2019-07-31,Carrier free long-range magnetism in Mo doped one quintuple layer Bi2Te3 and Sb2Te3,"One of the keys to the realization of Quantum Anomalous Hall effect (QAHE) is
long range ferromagnetism, which is only experimentally realized in Cr or V
doped (Bi,Sb)2Te3 system. Both elements are 3d transition metals and 4d
transition metals are found to be ineffective to produce long range
ferromagnetism in Bi2Se3. Still, whether long range ferromagnetism can be
realized by magnetic doping of 4d elements is an open question. Based on
density functional theory calculations, we predict that long range
ferromagnetism can be realized in Mo doped Bi2Te3 and Sb2Te3, which are
semiconducting. The coupling strength is comparable with that of Cr doped
Bi2Te3 and Sb2Te3. Therefore, Mo doped Bi2Te3 and Sb2Te3 or their alloys can be
new systems to realize diluted magnetic semiconductors and QAHE.",1907.13282v1
2019-09-04,Proximity-induced ferromagnetism and chemical reactivity in few layers VSe2 heterostructures,"Among Transition-Metal Dichalcogenides, mono and few-layers thick VSe2 has
gained much recent attention following claims of intrinsic room-temperature
ferromagnetism in this system, which have nonetheless proved controversial.
Here, we address the magnetic and chemical properties of Fe/VSe2
heterostructure by combining element sensitive absorption spectroscopy and
photoemission spectroscopy. Our x-ray magnetic circular dichroism results
confirm recent findings that both native mono/few-layer and bulk VSe2 do not
show any signature of an intrinsic ferromagnetic ordering. Nonetheless, we find
that ferromagnetism can be induced, even at room temperature, after coupling
with a Fe thin film layer, with antiparallel alignment of the moment on the V
with respect to Fe. We further consider the chemical reactivity at the Fe/VSe2
interface and its relation with interfacial magnetic coupling.",1909.01713v1
2019-09-11,Spin dynamics of the planar kagome lattice ferromagnet with four-site ring exchange processes,"By means of quantum Monte Carlo simulations, combined with a stochastic
analytic continuation, we examine the spin dynamics of the spin-1/2 planar (XY)
ferromagnet on the kagome lattice with additional four-site ring exchange
terms. Such exchange processes were previously considered to lead into an
extended $Z_2$ quantum spin liquid phase beyond a quantum critical point from
the XY-ferromagnet. We examine the dynamical spin structure factor in the
non-magnetic regime and probe for signatures of spin fractionalization.
Furthermore, we contrast our findings and the corresponding energy scales of
the excitation gaps in the ring exchange model to those emerging in a related
Balents-Fisher-Girvin model with a $Z_2$ quantum spin liquid phase, and monitor
the softening of the magnon mode upon approaching the quantum critical point
from the XY-ferromagnetic regime.",1909.04877v1
2019-09-16,Onset of ferromagnetism for strongly correlated electrons in one-dimensional chains,"The existence of the Nagaoka ferromagnetism is examined in the context of the
one-dimensional $U=\infty$ Hubbard model. We construct the exact quantum
partition function to describe the physics of such a regime. Our calculation
reveals that, while the ground state in an open chain is always
spin-degenerate, in a finite size closed chain with at least one vacancy, the
ground state can only be ferromagnetic when the number of electrons is less or
equal to three. Our results shed more light on a very recent experimental
verification of Nagaoka ferromagnetism in a quantum dot set up.",1909.07349v3
2019-09-30,Phase diagram for ensembles of random close packed Ising-like dipoles as a function of texturation,"We study random close packed systems of magnetic spheres by Monte Carlo
simulations in order to estimate their phase diagram. The uniaxial anisotropy
of the spheres makes each of them behave as a single Ising dipole along a fixed
easy axis. We explore the phase diagram in terms of the temperature and the
degree of alignment (or texturation) among the easy axes of all spheres. This
degree of alignment ranges from the textured case (all easy axes pointing along
a common direction) to the non-textured case (randomly distributed easy axes).
In the former case we find long-range ferromagnetic order at low temperature
but, as the degree of alignment is diminished below a certain threshold, the
ferromagnetic phase gives way to a spin-glass phase. This spin-glass phase is
similar to the one previously found in other dipolar systems with strong frozen
disorder. The transition between ferromagnetism and spin-glass passes through a
narrow intermediate phase with quasi-long-range ferromagnetic order.",1909.13573v1
2019-10-21,Dynamics of an elliptical ferromagnetic skyrmion driven by the spin-orbit torque,"Magnetic skyrmion is a promising building block for developing information
storage and computing devices. It can be stabilized in a ferromagnetic thin
film with the Dzyaloshinskii-Moriya interaction (DMI). The moving ferromagnetic
skyrmion may show the skyrmion Hall effect, that is, the skyrmion shows a
transverse shift when it is driven by a spin current. Here, we numerically and
theoretically study the current-driven dynamics of a ferromagnetic nanoscale
skyrmion in the presence of the anisotropic DMI, where the skyrmion has an
elliptical shape. The skyrmion Hall effect of the elliptical skyrmion is
investigated. It is found that the skyrmion Hall angle can be controlled by
tuning the profile of elliptical skyrmion. Our results reveal the relation
between the skyrmion shape and the skyrmion Hall effect, which could be useful
for building skyrmion-based spintronic devices with preferred skyrmion Hall
angle. Also, our results provide a method for the minimization of skyrmion Hall
angle for applications based on in-line motion of skyrmions.",1910.09341v2
2019-10-25,Local minima in disordered mean-field ferromagnets,"We consider the complexity of random ferromagnetic landscapes on the
hypercube $\{\pm 1\}^N$ given by Ising models on the complete graph with i.i.d.
non-negative edge-weights. This includes, in particular, the case of Bernoulli
disorder corresponding to the Ising model on a dense random graph $\mathcal
G(N,p)$. Previous results had shown that, with high probability as
$N\to\infty$, the gradient search (energy-lowering) algorithm, initialized
uniformly at random, converges to one of the homogeneous global minima
(all-plus or all-minus). Here, we devise two modified algorithms tailored to
explore the landscape at near-zero magnetizations (where the effect of the
ferromagnetic drift is minimized). With these, we numerically verify the
landscape complexity of random ferromagnets, finding a diverging number of
(1-spin-flip-stable) local minima as $N\to\infty$. We then investigate some of
the properties of these local minima (e.g., typical energy and magnetization)
and compare to the situation where the edge-weights are drawn from a
heavy-tailed distribution.",1910.11862v1
2019-10-29,Steady one-dimensional domain wall motion in biaxial ferromagnets: mapping of the Landau-Lifshitz equation to the sine-Gordon equation,"Motivated by the difference between the dynamics of magnetization textures in
ferromagnets and antiferromagnets, the Landau-Lifshitz equation of motion is
explored. A typical one-dimensional domain wall in a bulk ferromagnet with
biaxial magnetic anisotropy is considered. In the framework of Walker-type of
solutions of steady-state ferromagnetic domain wall motion, the reduction of
the non-linear Landau-Lifshitz equation to a Lorentz-invariant sine-Gordon
equation typical for antiferromagnets is formally possible for velocities lower
than a critical velocity of the topological soliton. The velocity dependence of
the domain wall energy and the domain wall width are expressed in the
relativistic-like form in the limit of large ratio of the easy-plane/easy-axis
anisotropy constants. It is shown that the mapping of the Landau-Lifshitz
equation of motion to the sine-Gordon equation can be performed only by going
beyond the steady-motion Walker-type of solutions.",1910.13266v2
2020-01-04,Persistent currents and spin torque caused by percolated quantum spin Hall state,"Motivated by recent experiments, we investigate the quantum spin Hall state
in 2D topological insulator/ferromagnetic metal planar junctions by means of a
tight-binding model and linear response theory. We demonstrate that whether the
edge state Dirac cone is submerged into the ferromagnetic subbands and the
direction of the magnetization dramatically affect (i) how the edge state
percolates into the ferromagnet, and (ii) the spin-momentum locking of the edge
state. Laminar flows of room temperature persistent charge and spin currents
near the interface are uncovered. In addition, the current-induced spin
polarization at the edge of the 2D topological insulator is found to be
dramatically enhanced near the impurities. The current-induced spin
polarization in the ferromagnet is mainly polarized in the out-of-plane
direction ${\hat{\bf z}}$, rendering a current-induced spin torque that is
predominantly field-like $\propto {\bf S}\times{\hat{\bf z}}$.",2001.01081v3
2020-01-09,High-Temperature Ferromagnetic Semiconductors: Janus Monolayer Vanadium Trihalides,"Two-dimensional (2D) intrinsic ferromagnetic semiconductors are expected to
stand out in the spintronic field. Recently, the monolayer VI$_{3}$ has been
experimentally synthesized but the weak ferromagnetism and low Curie
temperature ($T_C$) limit its potential application. Here we report that the
Janus structure can elevate the $T_C$ to 240 K. And it is discussed that the
reason for high $T_C$ in Janus structure originates from the lower virtual
exchange gap between $t_{2g}$ and $e_{g}$ states of nearest-neighbor V atoms.
Besides, $T_C$ can be further substantially enhanced by tensile strain due to
the increasing ferromagnetism driven by rapidly quenched direct exchange
interaction. Our work supports a feasible approach to enhance Curie temperature
of monolayer VI$_{3}$ and unveils novel stable intrinsic FM semiconductors for
realistic applications in spintronics.",2001.02846v2
2020-01-15,Quantum critical point in the itinerant ferromagnet Ni$_{1-x}$Rh$_x$,"We report a chemical substitution-induced ferromagnetic quantum critical
point in polycrystalline Ni$_{1-x}$Rh$_x$ alloys. Through magnetization and
muon spin relaxation measurements, we show that the ferromagnetic ordering
temperature is suppressed continuously to zero at $x_{crit} = 0.375$ while the
magnetic volume fraction remains 100% up to $x_{crit}$, pointing to a second
order transition. Non-Fermi liquid behavior is observed close to $x_{crit}$,
where the electronic specific heat $C_{el}/T$ diverges logarithmically, while
immediately above $x_{crit}$ the volume thermal expansion coefficient
$\alpha_{V}/T$ and the Gr\""uneisen ratio $\Gamma = \alpha_{V}/C_{el}$ both
diverge logarithmically in the low temperature limit, further indication of a
ferromagnetic quantum critical point in Ni$_{1-x}$Rh$_x$.",2001.05533v1
2020-02-06,Spin-orbit torque switching of perpendicular magnetization in ferromagnetic trilayers,"In ferromagnetic trilayers, a spin-orbit-induced spin current can have a spin
polarization of which direction is deviated from that for the spin Hall effect.
Recently, magnetization switching in ferromagnetic trilayers has been proposed
and confirmed by the experiments. In this work, we theoretically and
numerically investigate the switching current required for perpendicular
magnetization switching in ferromagnetic trilayers. We confirm that the tilted
spin polarization enables field-free deterministic switching at a lower current
than conventional spin-orbit torque or spin-transfer torque switching, offering
a possibility for high-density and low-power spin-orbit torque devices.
Moreover, we provide analytical expressions of the switching current for an
arbitrary spin polarization direction, which will be useful to design
spin-orbit torque devices and to interpret spin-orbit torque switching
experiments.",2002.02132v1
2020-02-17,Study of polycrystalline bulk Sr$_3$OsO$_6$ double-perovskite insulator: comparison with 1000 K ferromagnetic epitaxial films,"Polycrystalline Sr$_3$OsO$_6$, which is an ordered double-perovskite
insulator, is synthesized via solid-state reaction under high-temperature and
high-pressure conditions of 1200 $^\circ$C and 6 GPa. The synthesis enables us
to conduct a comparative study of the bulk form of Sr$_3$OsO$_6$ toward
revealing the driving mechanism of 1000 K ferromagnetism, which has recently
been discovered for epitaxially grown Sr$_3$OsO$_6$ films. Unlike the film, the
bulk is dominated by antiferromagnetism rather than ferromagnetism. Therefore,
robust ferromagnetic order appears only when Sr$_3$OsO$_6$ is under the
influence of interfaces. A specific heat capacity of 39.6(9) 10$^{-3}$ J
mol$^{-1}$ K$^{-2}$ is found at low temperatures ($<$17 K). This value is
remarkably high, suggesting the presence of possible fermionic-like excitations
at the magnetic ground state. Although the bulk and film forms of Sr$_3$OsO$_6$
share the same lattice basis and electrically insulating state, the magnetism
is entirely different between them.",2002.06743v1
2020-02-26,Extreme narrow magnetic domain walls in U ferromagnets: The UCoGa case,"Surface magnetic domains of a UCoGa single crystal during
magnetization/demagnetization processes in increasing/decreasing magnetic
fields were investigated by means of magnetic-force-microscopy (MFM) images at
low temperatures. The observed domain structure is typical for a ferromagnet
with strong uniaxial anisotropy. The evolution of magnetic domains during
cooling of the crystal below TC has also been manifested by MFM images.
Analysis of the available data reveals that the high uniaxial
magnetocrystalline energy in combination with the relatively small
ferromagnetic exchange interaction in UCoGa gives rise to the formation of very
narrow domain walls formed by the pairs of the nearest U neighbor ions with
antiparallel magnetic moments within the basal plane. Since the very high
anisotropy energy is a common feature of the majority of the uniaxial U
ferromagnets, analogous domain-wall properties are expected for all these
materials.",2002.11517v1
2020-04-06,High Curie Temperature Ferromagnetism and High Hole Mobility in Tensile Strained Mn-doped SiGe Thin Films,"Diluted magnetic semiconductors (DMSs) based on group-IV materials are
desirable for spintronic devices compatible with current silicon technology. In
this work, amorphous Mn-doped SiGe thin films were first fabricated on Ge
substrates by radio frequency magnetron sputtering and then crystallized by
rapid thermal annealing (RTA). After the RTA, the samples became ferromagnetic
(FM) semiconductors, in which the Curie temperature increased with increasing
Mn doping concentration and reached 280 K with 5% Mn concentration. The data
suggest that the ferromagnetism came from the hole-mediated process and was
enhanced by the tensile strain in the SiGe crystals. Meanwhile, the Hall effect
measurement up to 33 T to eliminate the influence of anomalous Hall effect
(AHE) reveals that the hole mobility of the annealed samples was greatly
enhanced and the maximal value was ~1000 cm2/Vs, owing to the tensile
strain-induced band structure modulation. The Mn-doped SiGe thin films with
high Curie temperature ferromagnetism and high hole mobility may provide a
promising platform for semiconductor spintronics.",2004.02676v1
2020-04-09,Hysteresis-free magnetization reversal of exchange-coupled bilayers with finite magnetic anisotropy,"Exchange-coupled structures consisting of ferromagnetic and ferrimagnetic
layers become technologically more and more important. We show experimentally
the occurrence of completely reversible, hysteresis-free minor loops of [Co(0.2
nm)/Ni(0.4 nm)/Pt(0.6 nm)]$_N$ multilayers exchange-coupled to a 20 nm thick
ferrimagnetic Tb$_{28}$Co$_{14}$Fe$_{58}$ layer, acting as hard magnetic
pinning layer. Furthermore, we present detailed theoretical investigations by
means of micromagnetic simulations and most important a purely analytical
derivation for the condition of the occurrence of full reversibility in
magnetization reversal. Hysteresis-free loops always occur if a domain wall is
formed during the reversal of the ferromagnetic layer and generates an
intrinsic hard-axis bias field that overcomes the magnetic anisotropy field of
the ferromagnetic layer. The derived condition further reveals that the
magnetic anisotropy and the bulk exchange of both layers, as well as the
exchange coupling strength and the thickness of the ferromagnetic layer play an
important role for its reversibility.",2004.04419v1
2020-04-11,Strain engineering of ferromagnetic-graphene-ferroelectric nanostructures,"We calculated a spin-polarized conductance in the almost unexplored
nanostructure ""high temperature ferromagnetic insulator/ graphene/
ferroelectric film"" with a special attention to the impact of electric
polarization rotation in a strained multiaxial ferroelectric film. The rotation
and value of polarization vector are controlled by a misfit strain. We proposed
a phenomenological model, which takes into account the shift of the Dirac point
due to the proximity of ferromagnetic insulator and uses the Landauer formula
for the conductivity of the graphene channel. We derived analytical
expressions, which show that the strain-dependent ferroelectric polarization
governs the concentration of two-dimensional charge carriers and Fermi level in
graphene in a self-consistent way. We demonstrate the realistic opportunity to
control the spin-polarized conductance of graphene by a misfit strain (""strain
engineering"") at room and higher temperatures in the nanostructures
CoFeO4/graphene/PZT and Y3Fe5O12/graphene/PZT. Obtained results open the
possibilities for the applications of ferromagnetic/graphene/ferroelectric
nanostructures as non-volatile spin filters and spin valves.",2004.05338v1
2020-04-21,Pairing symmetry in monolayer of orthorhombic CoSb,"Ferromagnetism and superconductivity are generally considered to be
antagonistic phenomena in condensed matter physics. Here, we theoretically
study the interplay between the ferromagnetic and superconducting orders in a
recent discovered monolayered CoSb superconductor with an orthorhombic symmetry
and net magnetization, and demonstrate the pairing symmetry of CoSb as a
candidate of non-unitary superconductor with time-reversal symmetry breaking.
By performing the group theory analysis and the first-principles calculations,
the superconducting order parameter is suggested to be a triplet pairing with
the irreducible representation of $^3B_{2u}$, which displays intriguing nodal
points and non-zero periodic modulation of Cooper pair spin polarization on the
Fermi surface topologies. These findings not only provide a significant
theoretical insight into the coexistence of superconductivity and
ferromagnetism, but also reveal the exotic spin polarized Cooper pairing driven
by ferromagnetic spin fluctuations in a triplet superconductor.",2004.10200v2
2021-01-29,Magnetization Reversal Mechanism in Exchange-Biased Spring-like Thin-Film Composite,"Development of modern spintronic devices requires materials exhibiting
specific magnetic effects. In this paper, we investigate a magnetization
reversal mechanism in a [Co/Pdx]7/CoO/[Co/Pdy]7 thin-film composite where an
antiferromagnet is sandwiched between a hard and a soft ferromagnets with
different coercivities. The antiferromagnet/ferromagnet interfaces give rise to
the exchange bias effect. The application of soft and hard ferromagnetic films
causes exchange-spring-like behavior while the choice of the Co/Pd multilayers
provides large out-of-plane magnetic anisotropy. We observed that the magnitude
and the sign of the exchange bias anisotropy field are related to the
arrangement of the magnetic moments in the antiferromagnetic layer. This
ordering is induced by the spin orientation present in neighboring
ferromagnetic films which is, in turn, dependent on the orientation and
strength of the external magnetic field.",2101.12495v1
2017-05-22,Interaction between magnetic moments and itinerant carriers in d0 ferromagnetic SiC,"Elucidating the interaction between magnetic moments and itinerant carriers
is an important step to spintronic applications. Here, we investigate magnetic
and transport properties in d0 ferromagnetic SiC single crystals prepared by
postimplantation pulsed laser annealing. Magnetic moments are contributed by
the p states of carbon atoms, but their magnetic circular dichroism is
different from that in semi-insulating SiC samples. The anomalous Hall effect
and negative magnetoresistance indicate the influence of d0 spin order on free
carriers. The ferromagnetism is relatively weak in N-implanted SiC compared
with that in Al-implanted SiC after annealing. The results suggest that d0
magnetic moments and itinerant carriers can interact with each other, which
will facilitate the development of SiC spintronic devices with d0
ferromagnetism.",1705.07793v1
2017-09-15,"Interplay between localization and magnetism in (Ga,Mn)As and (In,Mn)As","Ion implantation of Mn combined with pulsed laser melting is employed to
obtain two representative compounds of dilute ferromagnetic semiconductors
(DFSs): Ga1-xMnxAs and In1-xMnxAs. In contrast to films deposited by the widely
used molecular beam epitaxy, neither Mn interstitials nor As antisites are
present in samples prepared by the method employed here. Under these conditions
the influence of localization on the hole-mediated ferromagnetism is examined
in two DFSs with a differing strength of p-d coupling. On the insulating side
of the transition, ferromagnetic signatures persist to higher temperatures in
In1-xMnxAs compared to Ga1-xMnxAs with the same Mn concentration x. This
substantiates theoretical suggestions that stronger p-d coupling results in an
enhanced contribution to localization, which reduces hole-mediated
ferromagnetism. Furthermore, the findings support strongly the heterogeneous
model of electronic states at the localization boundary and point to the
crucial role of weakly localized holes in mediating efficient spin-spin
interactions even on the insulator side of the metal-insulator transition.",1709.05043v1
2017-09-24,Why rare-earth ferromagnets are so rare: insights from the p-wave Kondo model,"Magnetic exchange in Kondo lattice systems is of the
Ruderman-Kittel-Kasuya-Yosida type, whose sign depends on the Fermi wave
vector, $k_F$ . In the simplest setting, for small $k_F$ , the interaction is
predominately ferromagnetic, whereas it turns more antiferromagnetic with
growing $k_F$. It is remarkable that even though $k_F$ varies vastly among the
rare-earth systems, an overwhelming majority of lanthanide magnets are in fact
antiferromagnets. To address this puzzle, we investigate the effects of a
p-wave form factor for the Kondo coupling pertinent to nearly all rare-earth
intermetallics. We show that this leads to interference effects which for small
kF are destructive, greatly reducing the size of the RKKY interaction in the
cases where ferromagnetism would otherwise be strongest. By contrast, for large
$k_F$, constructive interference can enhance antiferromagnetic exchange. Based
on this, we propose a new route for designing ferromagnetic rare-earth magnets.",1709.08241v1
2017-11-07,Critical scaling of the mutual information in two-dimensional disordered Ising models,"Renyi Mutual information (RMI), computed from second Renyi entropies, can
identify classical phase transitions from their finite-size scaling at the
critical points. We apply this technique to examine the presence or absence of
finite temperature phase transitions in various two-dimensional models on a
square lattice, which are extensions of the conventional Ising model by adding
a quenched disorder. When the quenched disorder causes the nearest neighbor
bonds to be both ferromagnetic and antiferromagnetic, (a) a spin glass phase
exists only at zero temperature, and (b) a ferromagnetic phase exists at a
finite temperature when the antiferromagnetic bond distributions are
sufficiently dilute. Furthermore, finite temperature paramagnetic-ferromagnetic
transitions can also occur when the disordered bonds involve only ferromagnetic
couplings of random strengths. In our numerical simulations, the ""zero
temperature only"" phase transitions are identified when there is no consistent
finite-size scaling of the RMI curves, while for finite temperature critical
points, the curves can identify the critical temperature $T_c$ by their
crossings at $T_c$ and $2\, T_c $.",1711.02352v2
2017-11-10,Quantum Spin Liquid with Even Ising Gauge Field Structure on Kagome Lattice,"Employing large-scale quantum Monte Carlo simulations, we study the extended
$XXZ$ model on the kagome lattice. A $\mathbb Z_2$ quantum spin liquid phase
with effective even Ising gauge field structure emerges from the delicate
balance among three symmetry-breaking phases including stripe solid, staggered
solid and ferromagnet. This $\mathbb{Z}_2$ spin liquid is stabilized by an
extended interaction related to the Rokhsar-Kivelson potential in the quantum
dimer model limit. The phase transitions from the staggered solid to a spin
liquid or ferromagnet are found to be first order and so is the transition
between the stripe solid and ferromagnet. However, the transition between a
spin liquid and ferromagnet is found to be continuous and belongs to the 3D
$XY^*$ universality class associated with the condensation of spinons. The
transition between a spin liquid and stripe solid appears to be continuous and
associated with the condensation of visons.",1711.03679v2
2017-11-29,Pressure-induced ferromagnetism due to an anisotropic electronic topological transition in Fe1.08Te,"A rapid and anisotropic modification of the Fermi-surface shape can be
associated with abrupt changes in crystalline lattice geometry or in the
magnetic state of a material. In this study we show that such an electronic
topological transition is at the basis of the formation of an unusual
pressure-induced tetragonal ferromagnetic phase in Fe$_{1.08}$Te. Around 2 GPa,
the orthorhombic and incommensurate antiferromagnetic ground-state of
Fe$_{1.08}$Te is transformed upon increasing pressure into a tetragonal
ferromagnetic state via a conventional first-order transition. On the other
hand, an isostructural transition takes place from the paramagnetic
high-temperature state into the ferromagnetic phase as a rare case of a `type
0' transformation with anisotropic properties. Electronic-structure
calculations in combination with electrical resistivity, magnetization, and
x-ray diffraction experiments show that the electronic system of Fe$_{1.08}$Te
is instable with respect to profound topological transitions that can drive
fundamental changes of the lattice anisotropy and the associated magnetic
order.",1711.10745v1
2018-03-14,Electronically Mediated Magnetic Anisotropy in Vibrating Magnetic Molecules,"We address the electronically induced anisotropy field acting on a spin
moment comprised in a vibrating magnetic molecule located in the junction
between ferromagnetic metals. Under weak coupling between the electrons and
molecular vibrations, the nature of the anisotropy can be changed from favoring
a high spin (easy axis) magnetic moment to a low spin (easy plane) by applying
a temperature difference or a voltage bias across the junction. For unequal
spin-polarizations in the ferromagnetic metals it is shown that the character
of the anisotropy is essentially determined by the properties of the weaker
ferromagnet. By increasing the temperature in this metal, or introducing a
voltage bias, its influence can be suppressed such that the dominant
contribution to the anisotropy is interchanged to the stronger ferromagnet.
With increasing coupling strength between the molecular vibrations and the
electrons, the nature of the anisotropy is locked into favoring easy plane
magnetism.",1803.05480v1
2018-06-08,Anomalous Hall magnetoresistance in a ferromagnet,"The anomalous Hall effect, observed in conducting ferromagnets with broken
time-reversal symmetry, offers the possibility to couple spin and orbital
degrees of freedom of electrons in ferromagnets. In addition to charge, the
anomalous Hall effect also leads to spin accumulation at the surfaces
perpendicular to both the current and magnetization direction. Here we
experimentally demonstrate that the spin accumulation, subsequent spin
backflow, and spin-charge conversion can give rise to a different type of spin
current related magnetoresistance, dubbed here as the anomalous Hall
magnetoresistance, which has the same angular dependence as the recently
discovered spin Hall magnetoresistance. The anomalous Hall magnetoresistance is
observed in four types of samples: co-sputtered (Fe1-xMnx)0.6Pt0.4, Fe1-xMnx
and Pt multilayer, Fe1-xMnx with x = 0.17 to 0.65 and Fe, and analyzed using
the drift-diffusion model. Our results provide an alternative route to study
charge-spin conversion in ferromagnets and to exploit it for potential
spintronic applications.",1806.03083v1
2018-06-14,Tailoring ferromagnetism through electrically controlled morphology,"Converse magnetoelectric coupling in artificial multiferroics is generally
modelled through three possible mechanisms: charge transfer, strain mediated or
ion migration. Here we demonstrate a novel and highly reliable approach, where
electrically controlled morphological modifications control the ferromagnetic
response of a magnetoelectric heterostructure, specifically FexMn1-x
ferromagnetic films on ferroelectric PMN-PT (001) substrates. The ferroelectric
PMN-PT substrates present, in correspondence to electrical switching, fully
reversible morphological changes at the surface, to which correspond
reproducible modifications of the ferromagnetic response of the FexMn1-x films.
Topographic analysis by atomic force microscopy shows the formation of surface
cracks after application of a positive electric field up to 6 kV/cm, which
disappear after application of negative voltage of the same amplitude.
In-operando x-ray magnetic circular dichroic spectroscopy at Fe edge in
FexMn1-x layers shows local variations of dichroic signal up to a factor 2.5 as
a function of the electrically-driven morphological state. These findings
highlight the role of morphology and surface topography as a key aspect in
magnetoelectric coupling, whose proof of electrically reversible modification
of the magnetic response adds a new possibility in the design of multiferroic
heterostructures with electrically controlled functionalities.",1806.05414v1
2018-06-21,Spin triplet superconducting proximity effect in a ferromagnetic semiconductor,"Conventional spin-singlet superconductivity that deeply penetrates into
ferromagnets is typically killed by the exchange interaction, which destroys
the spin-singlet pairs. Under certain circumstances, however, superconductivity
survives this interaction by adopting the pairing behavior of spin triplets.
The necessary conditions for the emergence of triplet pairs are
well-understood, owing to significant developments in theoretical frameworks
and experiments. The long-term challenges to inducing superconductivity in
magnetic semiconductors, however, involve difficulties in observing the finite
supercurrent, even though the generation of superconductivity in host materials
has been well-established and extensively examined. Here, we show the first
evidence of proximity-induced superconductivity in a ferromagnetic
semiconductor (In, Fe)As. The supercurrent reached a distance scale of $\sim
1~\mu$m, which is comparable to the proximity range in two-dimensional
electrons at surfaces of pure InAs. Given the long range of its proximity
effects and its response to magnetic fields, we conclude that spin-triplet
pairing is dominant in proximity superconductivity. Therefore, this progress in
ferromagnetic semiconductors is a breakthrough in semiconductor physics
involving unconventional superconducting pairing.",1806.08035v1
2018-06-22,Observation of a pressure-induced transition from interlayer ferromagnetism to intralayer antiferromagnetism in Sr4Ru3O10,"Sr4Ru3O10 is a Ruddlesden-Popper compound with triple Ru-O perovskite layers
separated by Sr-O alkali layers. This compound presents a rare coexistence of
interlayer (c-axis) ferromagnetism and intralayer (basal-plane) metamagnetism
at ambient pressure. Here we report the observation of pressure-induced,
intralayer itinerant antiferromagnetism arising from the interlayer
ferromagnetism. The application of modest hydrostatic pressure generates an
anisotropy that causes a flattening and a tilting of RuO6 octahedra. All
magnetic and transport results from this study indicate these lattice
distortions diminish the c-axis ferromagnetism and basal-plane metamagnetism,
and induce a basal-plane antiferromagnetic state. The unusually large
magnetoelastic coupling and pressure tunability of Sr4Ru3O10 makes it a unique
model system for studies of itinerant magnetism.",1806.08466v1
2018-06-23,Magnetic and magnetoresistive behavior of the ferromagnetic heavy fermion YbNi$_2$,"We present a study on the magnetic susceptibility $\chi(T)$ and electrical
resistance, as a function of temperature and magnetic field $R(T,H)$, of the
ferromagnetic heavy fermion YbNi$_2$. The X-ray diffraction analysis shows that
the synthesized polycrystalline samples crystallizes in the cubic Laves phase
structure C15, with a spatial group $Fd\overline{3}m$. The magnetic
measurements indicate a ferromagnetic behavior with transition temperature at 9
K. The electrical resistance is metallic-like at high temperatures and no
signature of Kondo effect was observed. In the ferromagnetic state, the
electrical resistance can be justified by electron-magnon scattering
considering the existence of an energy gap in the magnonic spectrum. The energy
gap was determined for various applied magnetic fields. Magnetoresistance as a
function of applied magnetic field, subtracted from the $R(T,H)$ curves at
several temperatures, is negative from 2 K until about 40 K for all applied
magnetic fields. The negative magnetoresistance originates from the suppression
of magnetic disorder by the magnetic field.",1806.08881v1
2018-07-07,Two-Dimensional Multiferroic Semiconductors with Coexisting Ferroelectricity and Ferromagnetism,"Low-dimensional multiferroicity, though highly scarce in nature, has
attracted great attention due to both fundamental and technological interests.
Using first-principles density functional theory, we show that ferromagnetism
and ferroelectricity can coexist in monolayer transition metal phosphorus
chalcogenides (TMPCs) - CuMP$_2$X$_6$ (M=Cr, V; X=S, Se). These van der Waals
layered materials represent a class of 2D multiferroic semiconductors that
simultaneously possess ferroelectric and ferromagnetic orders. In these
monolayer materials, Cu atoms spontaneously move away from the center atomic
plane, giving rise to nontrivial electric dipole moment along the plane normal.
In addition, their ferromagnetism originates from indirect exchange interaction
between Cr/V atoms, while their out-of-plane ferroelectricity suggests the
possibility of controlling electric polarization by external vertical electric
field. Monolayer semiconducting TMPCs thus provide a solid-state 2D materials
platform for realizing 2D nanoscale switches and memory devices patterned with
top and bottom electrodes.",1807.02717v1
2018-07-19,Three-Dimensional Quantum Anomalous Hall Effect in Ferromagnetic Insulators,"The quantum anomalous Hall effect (QAHE) hosts the dissipationless chiral
edge states associated with the nonzero Chern number, providing potentially
significant applications in future spintronics. The QAHE usually occurs in a
two-dimensional (2D) system with time-reversal symmetry breaking. In this work,
we propose that the QAHE can exist in three-dimensional (3D) ferromagnetic
insulators. By imposing inversion symmetry, we develop the topological
constraints dictating the appearance of 3D QAHE based on the parity analysis at
the time-reversal invariant points in reciprocal space. Moreover, using
first-principles calculations, we identify that 3D QAHE can be realized in a
family of intrinsic ferromagnetic insulating oxides, including layered and
non-layered compounds that share a centrosymmetric structure with space group
$R\bar{3}m$ (No. 166). The Hall conductivity is quantized to be
$-\frac{3e^2}{hc}$ with the lattice constant $c$ along $c$-axis. The chiral
surface sheet states are clearly visible and uniquely distributed on the
surfaces that are parallel to the magnetic moment. Our findings open a
promising pathway to realize the QAHE in 3D ferromagnetic insulators.",1807.07262v1
2018-07-30,Topological spin excitations in honeycomb ferromagnet CrI$_3$,"In two dimensional honeycomb ferromagnets, bosonic magnon quasiparticles
(spin waves) may either behave as massless Dirac fermions or form topologically
protected edge states. The key ingredient defining their nature is the
next-nearest neighbor Dzyaloshinskii-Moriya (DM) interaction that breaks the
inversion symmetry of the lattice and discriminates chirality of the associated
spin-wave excitations. Using inelastic neutron scattering, we find that spin
waves of the insulating honeycomb ferromagnet CrI$_3$ ($T_C=61$ K) have two
distinctive bands of ferromagnetic excitations separated by a $\sim$4 meV gap
at the Dirac points. These results can only be understood by considering a
Heisenberg Hamiltonian with DM interaction, thus providing experimental
evidence that spin waves in CrI$_3$ can have robust topological properties
useful for dissipationless spintronic applications.",1807.11452v3
2018-08-18,Electric-field controlled superconductor-ferromagnetic insulator transition,"How to control collectively ordered electronic states is a core interest of
condensed matter physics. We report an electric field controlled reversible
transition from superconductor to ferromagnetic insulator in (Li,Fe)OHFeSe thin
flake using solid ion conductor as the gate dielectric. By driving Li ions into
and out of the (Li,Fe)OHFeSe thin flake with electric field, we obtained a
dome-shaped superconducting region with optimal Tc ~ 43 K, which is separated
by a quantum critical point from ferromagnetically insulating phase. The
ferromagnetism arises from the long range order of the interstitial Fe ions
expelled from the (Li,Fe)OH layers by Li injection. The device can reversibly
manipulate collectively ordered electronic states and stabilize new metastable
structures by electric field.",1808.06051v1
2018-08-24,Tunable room-temperature ferromagnetism in the SiC monolayer,"It is essential to explore two-dimensional (2D) material with magnetic
ordering in new generation spintronic devices. Particularly, the seeking of
room-temperature 2D ferromagnetic (FM) materials is a hot topic of current
research. Here, we study magnetism of the Mn-doped and electron-doped SiC
monolayer using first-principle calculations. For the Mn-doped SiC monolayer,
we find that either electron or hole could mediate the ferromagnetism in the
system and the Curie temperature ($T_C$) can be improved by appropriate carrier
doping. The codoping strategy is also discussed on improving $T_C$. The
transition between antiferromagnetic and FM phase can be found by strain
engineering. The $T_C$ is improved above room temperature (RT) under the strain
larger than $0.06$. Moreover, the Mn-doped SiC monolayer develops half-metal at
the strain range of $0.05-0.1$. On the other hand, the direct electron doping
can induce ferromagnetism due to the van Hove singularity in density of states
of the conduction band edge of the SiC monolayer. The $T_C$ is found to be
around RT. These fascinating controllable electronic and magnetic properties
are desired for spintronic applications.",1808.07995v2
2018-12-12,Room-temperature ferromagnetic insulating state in highly cation-ordered epitaxial oxide double perovskite,"Ferromagnetic insulators (FMIs) are one of the most important components in
developing dissipationless electronic and spintronic devices. However, since
ferromagnetism generally accompanies metallicity, FMIs are innately rare to
find in nature. Here, novel room-temperature FMI films are epitaxially
synthesized by deliberate control of the ratio of two B-site cations in the
double perovskite Sr2FeReO6. In contrast to the known ferromagnetic metallic
phase in stoichiometric Sr2FeReO6, a FMI state with a high Curie temperature
(Tc~400 K) and a large saturation magnetization (MS~1.8 {\mu}B/f.u.) is found
in highly cation-ordered Fe-rich phases. The stabilization of the FMI state is
attributed to the formation of extra Fe3+-Fe3+ and Fe3+-Re6+ bonding states,
which originate from the excess Fe. The emerging FMI state by controlling
cations in the epitaxial oxide perovskites opens the door to developing novel
oxide quantum materials & heterostructures.",1812.04953v1
2018-12-14,Current Control of Magnetism in Two-Dimensional Fe3GeTe2,"The recent discovery of magnetism in two-dimensional van der Waals systems
opens the door to discovering exciting physics. We investigate how a current
can control the ferromagnetic properties of such materials. Using symmetry
arguments, we identify a recently realized system in which the current-induced
spin torque is particularly simple and powerful. In Fe3GeTe2, a single
parameter determines the strength of the spin-orbit torque for a uniform
magnetization. The spin-orbit torque acts as an effective out-of-equilibrium
free energy. The contribution of the spin-orbit torque to the effective free
energy introduces new in-plane magnetic anisotropies to the system. Therefore,
we can tune the system from an easy-axis ferromagnet via an easy-plane
ferromagnet to another easy-axis ferromagnet with increasing current density.
This finding enables unprecedented control and provides the possibility to
study the Berezinskii-Kosterlitz-Thouless phase transition in the 2D XY model
and its associated critical exponents.",1812.06096v2
2018-12-17,Spin chirality fluctuation in two-dimensional ferromagnets with perpendicular anisotropy,"Non-coplanar spin textures with scalar spin chirality can generate effective
magnetic field that deflects the motion of charge carriers, resulting in
topological Hall effect (THE), a powerful probe of the ground state and
low-energy excitations of correlated systems. However, spin chirality
fluctuation in two-dimensional ferromagnets with perpendicular anisotropy has
not been considered in prior studies. Herein, we report direct evidence of
universal spin chirality fluctuation by probing the THE above the transition
temperatures in two different ferromagnetic ultra-thin films, SrRuO$_3$ and V
doped Sb$_2$Te$_3$. The temperature, magnetic field, thickness, and carrier
type dependences of the THE signal, along with our Monte-Carlo simulations,
unambiguously demonstrate that the spin chirality fluctuation is a universal
phenomenon in two-dimensional Ising ferromagnets. Our discovery opens a new
paradigm of exploring the spin chirality with topological Hall transport in
two-dimensional magnets and beyond",1812.07005v2
2019-01-04,Weak ferromagnetic insulator with huge coercivity in monoclinic double perovskite La2CuIrO6,"Insulating ferromagnets with high TC are required for many new magnetic
devices. More complexity arises when strongly correlated 3d ions coexist with
strongly spin-orbit coupled 5d ones in a double perovskite. Here, we perform
the structural, magnetic, and density functional theory study of such double
perovskite La2CuIrO6. A new P21/n polymorph is found according to the
comprehensive analysis of x-ray, Raman scattering and phonon spectrum. The
magnetization reveals a weak ferromagnetic (FM) transition at TC = 62 K and
short range FM order in higher temperature range. A huge coercivity is found as
high as HC~11.96 kOe at 10K, which in combination with the negative trapped
field results in the magnetization reversal in the zero field cooling
measurement. The first principle calculations confirm the observed FM state and
suggest La2CuIrO6 of this polymorph is a Mott insulating ferromagnet assisted
by the spin-orbit coupling.",1901.01106v4
2019-01-09,Anisotropic magnetic entropy change in Cr$_2$X$_2$Te$_6$ (X = Si and Ge),"Intrinsic, two-dimensional (2D) ferromagnetic semiconductors are an important
class of materials for spintronics applications. Cr$_2$X$_2$Te$_6$ (X = Si and
Ge) semiconductors show 2D Ising-like ferromagnetism, which is preserved in
few-layer devices. The maximum magnetic entropy change associated with the
critical properties around the ferromagnetic transition for Cr$_2$Si$_2$Te$_6$
$-\Delta S_M^{max} \sim$ 5.05 J kg$^{-1}$ K$^{-1}$ is much larger than $-\Delta
S_M^{max} \sim$ 2.64 J kg$^{-1}$ K$^{-1}$ for Cr$_2$Ge$_2$Te$_6$ with an
out-of-plane field change of 5 T. The rescaled $-\Delta S_M(T,H)$ curves
collapse onto a universal curve independent of temperature and field for both
materials. This indicates similar critical behavior and 2D Ising magnetism,
confirming the magnetocrystalline anisotropy that could preserve the long-range
ferromagnetism in few-layers of Cr$_2$X$_2$Te$_6$.",1901.02876v1
2019-01-13,Intrinsic spin currents in ferromagnets,"First principles calculations show that electric fields applied to
ferromagnets generate spin currents flowing perpendicularly to the electric
field. Reduced symmetry in these ferromagnets enables a wide variety of such
spin currents. However, the total spin current is approximately the sum of a
magnetization-independent spin Hall current and an anisotropic spin anomalous
Hall current. Intrinsic spin currents are not subject to dephasing, enabling
their spin polarizations to be misaligned with the magnetization, which enables
the magnetization-independent spin Hall effect. The spin Hall conductivity and
spin anomalous Hall conductivities of transition metal ferromagnets are
comparable to those found in heavy metals, opening new avenues for efficient
spin current generation in spintronic devices.",1901.04022v2
2019-01-14,Spin polarization and orbital effects in superconductor-ferromagnet structures,"We study theoretically spontaneous currents and magnetic field induced in a
superconductor-ferromagnet (S-F) bilayer due to direct and inverse proximity
effects. The induced currents {are Meissner currents that appear even in the
absence of an external magnetic field due to the magnetic moment in the
ferromagnet }and {to the magnetization } in the superconductor . The latter is
induced by the inverse proximity effect over a distance of the order of the
superconducting correlation length $\xi _{S}$. On the other hand the magnetic
induction $B$, caused by Meissner currents, penetrates the S film over the
London length $\lambda _{S}$. Even though $\lambda _{S}$ usually exceeds
considerably the correlation length, the amplitude and sign of $B$ at distances
much larger than $\xi _{S}$ depends crucially on the strength of the exchange
energy in the ferromagnet and on the magnetic moment induced in the in the S
layer.",1901.04446v2
2019-01-19,Concentration of multi-overlaps for random ferromagnetic spin models,"We consider ferromagnetic spin models on dilute random graphs and prove that,
with suitable one-body infinitesimal perturbations added to the Hamiltonian,
the multi-overlaps concentrate for all temperatures, both with respect to the
thermal Gibbs average and the quenched randomness. Results of this nature have
been known only for the lowest order overlaps, at high temperature or on the
Nishimori line. Here we treat all multi-overlaps by a non-trivial application
of Griffiths-Kelly-Sherman correlation inequalities. Our results apply in
particular to the pure and mixed p-spin ferromagnets on random dilute
Erdoes-R\'enyi hypergraphs. On physical grounds one expects that multi-overlap
concentration directly implies the correctness of the cavity (or replica
symmetric) formula for the pressure. The proof of this formula for the general
p-spin ferromagnet on a random dilute hypergraph remains an open problem.",1901.06521v1
2019-01-27,Strain-Induced Room-Temperature Ferromagnetic Semiconductors with Large Anomalous Hall Conductivity in Two-Dimensional Cr2Ge2Se6,"By density functional theory calculations, we predict a stable
two-dimensional (2D) ferromagnetic semiconductor Cr$_2$Ge$_2$Se$_6$, where the
Curie temperature $T$$_c$ can be dramatically enhanced beyond room temperature
by applying a few percent strain. In addition, the anomalous Hall conductivity
in 2D Cr$_2$Ge$_2$Se$_6$ and Cr$_2$Ge$_2$Te$_6$ is predicted to be comparable
to that in ferromagnetic metals of Fe and Ni, and is an order of magnitude
larger than that in diluted magnetic semiconductor Ga(Mn,As). Based on
superexchange interactions, the enhanced $T$$_c$ in 2D Cr$_2$Ge$_2$Se$_6$ by
strain can be understood by the decreased energy difference between 3$d$
orbitals of Cr and 4$p$ orbitals of Se. Our finding highlights the microscopic
mechanism to obtain the room temperature ferromagnetic semiconductors by
strain.",1901.09306v2
2019-01-30,Magnetization direction dependent spin Hall effect in 3d ferromagnets,"We have studied the intrinsic spin Hall conductivity of 3d transition metal
ferromagnets using first-principles calculations. We find the spin Hall
conductivity of bcc Fe and fcc Ni, prototypes of ferromagnetic systems, depends
on the direction of magnetization. The spin Hall conductivity of electrons with
their spin orientation orthogonal to the magnetization are found to be larger
than that when the two are parallel. For example, the former can be more than
four times larger than the latter in bcc Fe. Such a difference arises due to
the anisotropy of the spin current operator in the spinor space: Its
expectation value with the Bloch states depends on the relative angle between
the conduction electron spin and the magnetization. A simple analytical form is
developed to describe the relation between the spinor states, with respect to
the magnetization direction, and the Berry and spin Berry curvatures. The model
can account for the characteristics found in the calculations. These results
show that ferromagnets can be used to generate spin current and its magnitude
can be controlled by the magnetization direction.",1901.10740v2
2019-02-11,Interplay of electronic and spin degrees in ferromagnetic SrRuO$_3$: anomalous softening of magnon gap and stiffness,"The magnon dispersion of ferromagnetic SrRuO$_3$ was studied by inelastic
neutron scattering experiments on single crystals as function of temperature.
Even at low temperature the magnon modes exhibit substantial broadening
pointing to strong interaction with charge carriers. We find an anomalous
temperature dependence of both the magnon gap and the magnon stiffness, which
soften upon cooling in the ferromagnetic phase. Both effects trace the
temperature dependence of the anomalous Hall effect. We argue that these
results show that Weyl points and the anomalous Hall effect can directly
influence the spin dynamics in metallic ferromagnets.",1902.04036v1
2019-02-20,Direct photoluminescence probing of ferromagnetism in monolayer two-dimensional CrBr3,"Atomically thin magnets are the key element to build up spintronics based on
two-dimensional materials. The surface nature of two-dimensional ferromagnet
opens up opportunities to improve the device performance efficiently. Here, we
report the intrinsic ferromagnetism in atomically thin monolayer CrBr3,
directly probed by polarization resolved magneto-photoluminescence. The
spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature
of 34 K. The development of magnons by the thermal excitation is in line with
the spin-wave theory. We attribute the layer-number dependent hysteresis loops
in thick layers to the magnetic domain structures. As a stable monolayer
material in air, CrBr3 provides a convenient platform for fundamental physics
and pushes the potential applications of the two-dimensional ferromagnetism.",1902.07446v1
2019-03-03,Goos-Hanchen Shift of a Spin-Wave Beam at the Interface Between Two Ferromagnets,"Spin waves are promising information carriers which can be used in modern
magnonic devices, characterized by higher performance and lower energy
consumption than presently used electronic circuits. However, before practical
application of spin waves, the efficient control over spin wave amplitude and
phase needs to be developed. We analyze analytically reflection and refraction
of the spin waves at the interface between two ferromagnetic materials. In the
model we consider the system consisting of two semi-infinite ferromagnetic
media, separated by the ultra-narrow interface region with the magnetic
anisotropy. We have found the Goos-Hanchen shift for spin waves in transmission
and reflection, and performed detailed investigations of its dependence on the
anisotropy at the interface and materials surrounding the interface. We have
demonstrated possibility of obtaining Goos-Hanchen shift of several wavelengths
in reflection for realistic material parameters. That proves the possibility
for change of the spin waves phase in ferromagnetic materials at subwavelength
distances, which can be regarded as a metasurface for magnonics.",1903.00861v1
2019-03-22,Spin-mechanics with levitating ferromagnetic particles,"We propose and demonstrate first steps towards schemes where the librational
mode of levitating ferromagnets is strongly coupled to the electronic spin of
Nitrogen-Vacancy (NV) centers in diamond. Experimentally, we levitate
ferromagnets in a Paul trap and employ magnetic fields to attain oscillation
frequencies in the hundreds of kHz range with Q factors close to $10^4$. These
librational frequencies largely exceed the decoherence rate of NV centers in
typical CVD grown diamonds offering prospects for sideband resolved operation.
We also prepare and levitate composite diamond-ferromagnet particles and
demonstrate both coherent spin control of the NV centers and read-out of the
particle libration using the NV spin. Our results will find applications in
ultra-sensitive gyroscopy and bring levitating objects a step closer to
spin-mechanical experiments at the quantum level.",1903.09699v3
2019-03-24,Theory of the magnetic domains phases in ferromagnetic superconductors,"Recently discovered superconducting P-doped EuFe$_2$As$_2$ compounds reveal
the situation when the superconducting critical temperature substantially
exceeds the ferromagnetic transition temperature. The main mechanism of the
interplay between magnetism and superconductivity occurs to be an
electromagnetic one and a short period magnetic domain structure was observed
just below Curie temperature [Stolyarov et al., Sci. Adv. \textbf{4}, eaat1061
(2018)]. We elaborate a theory of such transition and demonstrate how the
initial sinusoidal magnetic structure gradually transforms into a soliton-like
domain one. Further cooling may trigger a first-order transition from the
short-period domain Meissner phase to the self-induced ferromagnetic vortex
state and we calculate the parameters of this transition. The size of the
domains in the vortex state is basically the same as in the normal ferromagnet,
but with the domain walls which should generate the set of vortices
perpendicular to the vortices in the domains.",1903.09953v1
2019-03-28,Non-Hermitian Weyl Physics in Topological Insulator Ferromagnet Junctions,"We introduce and investigate material junctions as a generic and tuneable
electronic platform for the realization of exotic non-Hermitian (NH)
topological states of matter, where the NH character is induced by the surface
self-energy of a thermal reservoir. As a conceptually rich and immediately
experimentally realizable example, we consider a three-dimensional topological
insulator (TI) coupled to a ferromagnetic lead. Remarkably, the symmetry
protected TI is promoted in a dissipative fashion to a non-symmetry protected
NH Weyl phase with no direct Hermitian counterpart and which exhibits
robustness against any perturbation. The transition between a gapped phase and
the NH Weyl phase may be readily tuned experimentally with the magnetization
direction of the ferromagnetic lead. Given the robustness of this exotic nodal
phase, our general analysis also applies to, e.g., a two-dimensional electron
gas close to criticality in proximity to a ferromagnetic lead. There, the
predicted bulk Fermi arcs are directly amenable to surface spectroscopy methods
such as angle-resolved photoemission spectroscopy.",1903.12187v2
2019-04-08,"YBa2Cu3O7/LaXMnO3 (X: Ca, Sr) based Superconductor/Ferromagnet/Superconductor junctions with memory functionality","Complex oxides exhibit a variety of unusual physical properties, which can be
used for designing novel electronic devices. Here we fabricate and study
experimentally nano-scale Superconductor/ Ferromagnet/Superconductor junctions
with the high-Tc cuprate superconductor YBa2Cu3O7 and the colossal
magnetoresistive (CMR) manganite ferromagnets LaXMnO3 (X: Ca or Sr). We
demonstrate that in a broad temperature range the magnetization of a manganite
nanoparticle, forming the junction interface, switches abruptly in a
mono-domain manner. The CMR phenomenon translates the magnetization loop into a
hysteretic magnetoresistance loop. The latter facilitates a memory
functionality of such a junction with just a single CMR ferromagnetic layer.
The orientation of the magnetization (stored information) can be read out by
simply measuring the junction resistance in an applied magnetic field. The CMR
facilitates a large read-out signal in a small applied field. We argue that
such a simple single layer CMR junction can operate as a memory cell both in
the superconducting state at cryogenic temperatures and in the normal state up
to room temperature.",1904.03951v1
2019-04-09,Manipulation of Magnetic Skyrmions by Superconducting Vortices in Ferromagnet-Superconductor Heterostructures,"Dynamics of magnetic skyrmions in hybrid ferromagnetic films harbors novel
physical phenomena and holds promise for technological applications. In this
work, we discuss the behavior of magnetic skyrmions when coupled to
superconducting vortices in a ferromagnet-superconductor heterostructure. We
use numerical simulations and analytic arguments to reveal broader
possibilities for manipulating the skyrmion-vortex dynamic correlations in the
hybrid system, that are not possible in its separated constituents. We explore
the thresholds of particular dynamic phases, and quantify the phase diagram as
a function of the relevant material parameters, applied current and induced
magnetic torques. Finally, we demonstrate the broad and precise tunability of
the skyrmion Hall-angle in presence of vortices, with respect to currents
applied to either or both the superconductor and the ferromagnet within the
heterostructure.",1904.04537v3
2019-04-18,Electrical control of magnetization in S/F/S junctions on a 3D topological insulator,"Strong dependence of the Josephson energy on the magnetization orientation in
Josephson junctions with ferromagnetic interlayers and spin-orbit coupling
opens a way to control magnetization by Josephson current or Josephson phase.
Here we investigate the perspectives of magnetization control in
superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions on the
surface of a 3D topological insulator hosting Dirac quasiparticles. Due to the
spin-momentum locking of these Dirac quasiparticles a strong dependence of the
Josephson current-phase relation on the magnetization orientation is realized.
It is demonstrated that this can lead to splitting of the ferromagnet's
easy-axis in the voltage driven regime. We show that such a splitting can lead
to stabilization of an unconventional four-fold degenerate ferromagnetic state.",1904.09009v2
2019-04-24,Two-Dimensional Room Temperature Ferromagnetic Semiconductors with Quantum Anomalous Hall Effect,"To obtain room temperature ferromagnetic semiconductors is one of big
challenges in science, and also premises essentially to realize room
temperature quantum anomalous Hall effect (QAHE), both of which are quite
expected for a long time. Here we report that, based on first-principles
calculations, PdBr3, PtBr3, PdI3 and PtI3 monolayers are ferromagnetic
semiconductors with possible high temperature QAHE. Monte Carlo simulations
give Curie temperatures 350 K and 375 K for PdBr3 and PtBr3 monolayers,
respectively. These two-dimensional (2D) materials are Chern insulators. The
band gaps of PdBr3 and PtBr3 are 58.7 meV and 28.1 meV with GGA and 100.8 meV
and 45 meV with HSE06, respectively, quite well in favor of observing room
temperature QAHE. The large band gaps were unveiled from multi-orbital electron
correlations. By carefully checking the stability, PdBr3, PtBr3, and PtI3
monolayers are all predicted to be feasible in experiment. The present work
sheds new light on developing promising spintronic devices by using the room
temperature ferromagnetic semiconductors, and dissipationless devices by
applying room temperature QAHE.",1904.11357v4
2019-04-29,Dependence of the magnetic interactions in MoS$_2$ monolayer on Mn-doping configurations,"Understanding the magnetic properties of the various Mn doping configurations
that can be encountered in $2H$-MoS$_2$ monolayer could be beneficial for its
use in spintronics. Using density functional theory plus Hubbard U (DFT$+$U)
approach, we study how a single isolated, double- and triple-substitution
configurations of Mn atoms within a MoS$_2$ monolayer could contribute to its
total magnetization. We find that the doping-configuration plays a critical
role in stabilizing a ferromagnetic state in a Mn-doped MoS$_2$ monolayer.
Indeed, the Mn-Mn magnetic interaction is found to be ferromagntic and strong
for Mn in equidistant substitution positions where the separation average range
of 6-11 {\AA}. The strongest ferromagnetic interaction is found when
substitutions are in second nearest neighbors Mo-sites of the armchair chain.
Clustering is energetically favorable but it strongly reduces the ferromagnetic
exchange energies. Our results suggest that ordering the Mn dopants on MoS$_2$
monolayer is needed to increase its potential ferromagnetism.",1904.12905v2
2019-08-17,Ferromagnetism in the SU($n$) Hubbard model with a nearly flat band,"We present rigorous results for the SU($n$) Fermi-Hubbard model on the
railroad-trestle lattice. We first study the model with a flat band at the
bottom of the single-particle spectrum and prove that the ground states exhibit
SU($n$) ferromagnetism when the total fermion number is the same as the number
of unit cells. We then perturb the model by adding extra hopping terms and make
the flat band dispersive. Under the same filling condition, it is proved that
the ground states of the perturbed model remain SU($n$) ferromagnetic when the
bottom band is nearly flat. This is the first rigorous example of the
ferromagnetism in nonsingular SU($n$) Hubbard models in which both the
single-particle density of states and the on-site repulsive interaction are
finite.",1908.06286v5
2019-11-01,Giant unidirectional magnetoresistance in topological insulator -- ferromagnetic semiconductor heterostructures,"The unidirectional magnetoresistance (UMR) is one of the most complex
spin-dependent transport phenomena in ferromagnet/non-magnet bilayers, which
involves spin injection and accumulation due to the spin Hall effect (SHE) or
Rashba-Edelstein effect (REE), spin-dependent scattering, and magnon scattering
at the interface or in the bulk of the ferromagnet. While UMR in metallic
bilayers has been studied extensively in very recent years, its magnitude is as
small as 10$^-$$^5$, which is too small for practical applications. Here, we
demonstrate a giant UMR effect in a heterostructure of BiSb topological
insulator -- GaMnAs ferromagnetic semiconductor. We obtained a large UMR ratio
of 1.1%, and found that this giant UMR is governed not by the giant
magnetoresistance (GMR)-like spin-dependent scattering, but by magnon
emission/absorption and strong spin-disorder scattering in the GaMnAs layer.
Our results provide new insight into the complex physics of UMR, as well as a
strategy for enhancing its magnitude for device applications.",1911.00247v1
2019-11-25,Fe$_{5-x}$Ge$_2$Te$_2$ -- A new exfoliable itinerant ferromagnet with high Curie temperature and large perpendicular magnetic anisotropy,"Layered van der Waals (vdW) crystals with intrinsic magnetic properties such
as high Curie temperature (TC) and large perpendicular magnetic anisotropy
(PMA) are key to the development and application of spintronic devices. The
ferromagnetic vdW metal Fe3-xGeTe2 (FGT) has gained prominence recently due to
its high TC (220 K) and strong PMA. Here, we introduce a new metallic vdW
ferromagnets, Fe5-xGe2Te2 or FG2T, which was successfully synthesized and fully
characterized. FG2T is a metal that orders ferromagnetically with a very sharp
transition at 250 K (bulk and single crystal thin flakes) and shows large PMA,
as found by both experimental and computational studies. This work enables
novel heterostructure devices with near room temperature capabilities by using
FG2T as spin injector.",1911.11259v1
2019-12-03,Stable and Metastable Kinetic Ferromagnetism on a Ring,"Performing an exact diagonalization of the effective spin problem, a
ferromagnetic ground state of kinetic origin is shown to emerge in a system of
$N$ strongly correlated electrons on a $L$-site ring ($L > N$). This phenomenon
is brought about by the quantum necklace statistics originated from the no
double occupancy constraint leading to a fractional shifted electron momentum
quantization. As a consequence of such special energy level distribution, the
kinetic ferromagnetism is stable only for $N=3$. For odd $N>3$ the fully
polarized FM state energy is only a local minimum but it is protected by a
finite energy barrier that inhibits one spin-flip processes. The metastable
ferromagnetic state survives perturbations of small magnitude opening up a
possibility of being experimentally observed by an appropriate tuning of the
interdot tunneling amplitudes in currently available quantum dot arrays.",1912.01535v1
2019-12-16,Magnon-mediated superconductivity on the surface of a topological insulator,"We study superconductivity on the surface of a topological insulator,
mediated by magnetic fluctuations in an adjacent ferromagnetic or
antiferromagnetic insulator. Superconductivity can arise from effective
interactions between helical fermions induced by interfacial fermion-magnon
interactions. For both ferromagnetic and antiferromagnetic insulators, these
fermion-fermion interactions have the correct structure to facilitate pairing
between particles located on the same side of the Fermi surface, also known as
Amperean pairing. In antiferromagnets, the strength of the induced interactions
can be enhanced by coupling the topological insulator asymmetrically to the two
sublattices of the antiferromagnet. This effect is further amplified by next
nearest neighbor frustration in the antiferromagnetic insulator. The
enhancement makes the induced interactions significantly stronger in the
antiferromagnetic case, as compared to the ferromagnetic case. These results
indicate that an uncompensated antiferromagnetic interface might be a better
candidate than a ferromagnetic interface for proximity-induced magnon-mediated
superconductivity on the surface of a topological insulator.",1912.07607v2
2019-12-23,Peculiarities of electronic transport and magnetic state in half-metallic ferromagnetic and spin gapless semiconducting Heusler alloys,"A brief survey of experimental and theoretical studies of half-metallic
ferromagnets (HMFs) and spin gapless semiconductors is given, the possible
candidates being the X$_2$YZ (X = Mn, Fe, Co; Y = Ti, V, Cr, Mn, Fe, Co, Ni; Z
= Al, Si, Ga, Ge, In, Sn, Sb) Heusler alloys. The data on the electrical
resistivity, normal and anomalous Hall Effect, and magnetic properties are
presented. It is shown that the Co$_2$FeZ alloys demonstrate properties of
conventional ferromagnets, the HMF properties being also manifested at the
variation of the Z-component. The Fe$_2$YAl and Mn$_2$YAl alloys show at the
variation of the Y-component both metallic and semiconducting electronic
characteristics, the magnetic properties, changing from the ferromagnetic to
compensated ferrimagnetic state. The HMF and spin gapless semiconductor states
are supposed to exist in these Heusler alloys systems.",1912.10771v1
2019-12-27,Ferromagnetic state above room temperature in a proximitized topological Dirac semimetal,"We report an above-room-temperature ferromagnetic state realized in a
proximitized Dirac semimetal, which is fabricated by growing typical Dirac
semimetal Cd$_3$As$_2$ films on a ferromagnetic garnet with strong
perpendicular magnetization. Observed anomalous Hall conductivity with
substantially large Hall angles is found to be almost proportional to
magnetization and opposite in sign to it. Theoretical calculations based on
first-principles electronic structure also demonstrate that the Fermi-level
dependent anomalous Hall conductivity reflects the Berry curvature originating
in the split Weyl nodes. The present Dirac-semimetal/ferromagnetic-insulator
heterostructure will provide a novel platform for exploring Weyl-node transport
phenomena and spintronic functions lately proposed for topological semimetals.",1912.11964v1
2020-03-15,Magnetic critical behavior of the van der Waals Fe5GeTe2 crystal with near room temperature ferromagnetism,"The van der Waals ferromagnet Fe5GeTe2 has a Curie temperature TC of about
270 K, which can be raised above room temperature by tuning the Fe deficiency
content. To achieve insights into its ferromagnetic exchange, we have studied
the critical behavior by measuring the magnetization in bulk Fe5GeTe2 crystal
around the ferromagnetic to paramagnetic phase transition. The analysis of the
magnetization by employing various techniques including the modified Arrott
plot, Kouvel-Fisher plot and critical isotherm analysis achieved a set of
reliable critical exponents with TC = 273.7 K, beta = 0.3457, gamma = 1.40617,
and delta = 5.021, suggesting a three-dimensional magnetic exchange with the
distance decaying as J(r) ~ (r)$^-4.916, which is close to that of a
three-dimensional Heisenberg model with long-range magnetic coupling.",2003.06825v1
2020-03-18,Directed transport of suspended ferromagnetic nanoparticles under both gradient and uniform magnetic fields,"The suspended ferromagnetic particles subjected to the gradient and uniform
magnetic fields experience both the translational force generated by the field
gradient and the rotational torque generated by the fields strengths. Although
the uniform field does not contribute to the force, it nevertheless influences
the translational motion of these particles. This occurs because the
translational force depends on the direction of the particle magnetization,
which in turn depends on the fields strengths. To study this influence, a
minimal set of equations describing the coupled translational and rotational
motions of nanosized ferromagnetic particles is introduced and solved in the
low Reynolds number approximation. Trajectory analysis reveals that, depending
on the initial positions of nanoparticles, there exist four regimes of their
directed transport. The intervals of initial positions that correspond to
different dynamical regimes are determined, their dependence on the uniform
magnetic field is established, and strong impact of this field on the directed
transport is demonstrated. The ability and efficiency of the uniform magnetic
field to control the separation of suspended ferromagnetic nanoparticles is
also discussed.",2003.08498v2
2020-03-20,Phase Diagram of the Dynamics of a Precessing Qubit under Quantum Measurement,"We study the phase transitions induced by sequentially measuring a single
qubit precessing under an external transverse magnetic field. Under projective
quantum measurement, the probability distribution of the measurement outcomes
can be mapped exactly to the thermodynamic probability distribution of a
one-dimensional Ising model, whose coupling can be varied by the magnetic field
from ferromagnetic to anti-ferromagnetic. For the general case of sequential
quantum measurement,we develop a fast and exact algorithm to calculate the
probability distribution function of the ferromagnetic order and
anti-ferromagnetic order, and a phase diagram is obtained in the parameter
space spanned by the measurement strength and magnetic field strength. The
mapping to a long-range interacting Ising model is obtained in the limit of
small measurement strength. Full counting statistical approach is applied to
understand the phase diagram, and to make connections with the topological
phase transition that is characterized by the braid group. This work deepens
the understanding of phase transitions induced by quantum measurement, and may
provide a new method to characterize and steer the quantum evolution.",2003.09056v1
2020-05-20,Ferromagnetism and giant magnetoresistance in zinc-blende FeAs monolayers embedded in semiconductor structures,"Material structures containing tetrahedral FeAs bonds, depending on their
density and geometrical distribution, can host several competing quantum ground
states ranging from superconductivity to ferromagnetism. Here we examine
structures of quasi two-dimensional (2D) layers of tetrahedral Fe-As bonds
embedded with a regular interval in a semiconductor InAs matrix, which
resembles the crystal structure of Fe-based superconductors. Contrary to the
case of Fe-based pnictides, these FeAs/InAs superlattices (SLs) exhibit
ferromagnetism, whose Curie temperature (Tc) increases rapidly with decreasing
the InAs interval thickness t_InAs (Tc ~ t_InAs^-3), and an extremely large
magnetoresistance up to 500% that is tunable by a gate voltage. Our first
principles calculations reveal the important role of disordered positions of Fe
atoms in the establishment of ferromagnetism in these quasi-2D FeAs-based SLs.
These unique features mark the FeAs/InAs SLs as promising structures for
spintronic applications.",2005.10181v2
2020-05-20,Correlating magnetic structure and magnetotransport in semimetal thin films of Eu$_{1-x}$Sm$_x$TiO$_3$,"We report on the evolution of the average and depth-dependent magnetic order
in thin film samples of biaxially stressed and electron-doped EuTiO$_3$ for
samples across a doping range $<$0.1 to 7.8 $\times 10^{20}$ cm$^{-3}$. Under
an applied in-plane magnetic field, the G-type antiferromagnetic ground state
undergoes a continuous spin-flop phase transition into in-plane,
field-polarized ferromagnetism. The critical field for ferromagnetism slightly
decreases with an increasing number of free carriers, yet the field evolution
of the spin-flop transition is qualitatively similar across the doping range.
Unexpectedly, we observe interfacial ferromagnetism with saturated Eu$^{2+}$
moments at the substrate interface at low fields preceding ferromagnetic
saturation throughout the bulk of the degenerate semiconductor film. We discuss
the implications of these findings for the unusual magnetotransport properties
of this compound.",2005.10339v1
2020-05-22,Pressure-induced suppression of ferromagnetism in the itinerant ferromagnet LaCrSb$_3$,"We have performed an extensive pressure-dependent structural, spectroscopic,
and electrical transport study of LaCrSb$_3$. The ferromagnetic phase (T$_C$ =
120 K at p = 0 GPa) is fully suppressed by p = 26.5 GPa and the Cr-moment
decreases steadily with increasing pressure. The unit cell volume decreases
smoothly up to p = 55 GPa. We find that the bulk modulus and suppression of the
magnetism are in good agreement with theoretical predictions, but the Cr-moment
decreases smoothly with pressure, in contrast to steplike drops predicted by
theory. The ferromagnetic ordering temperature appears to be driven by the
Cr-moment.",2005.11356v1
2020-05-30,Ferromagnetic MnSn monolayer epitaxially grown on silicon substrate,"Two-dimensional (2D) ferromagnetic materials have been exhibiting promising
potential in applications, such as spintronics devices. To grow epitaxial
magnetic films on silicon substrate, in the single-layer limit, is practically
important but challenging. In this study, we realized the epitaxial growth of
MnSn monolayer on Si(111) substrate, with an atomically thin
Sn/Si(111)-$2\sqrt{3}\times2\sqrt{3}$- buffer layer, and controlled the MnSn
thickness with atomic-layer precision. We discovered the ferromagnetism in MnSn
monolayer with the Curie temperature (Tc) of ~54 K. As the MnSn film is grown
to 4 monolayers, Tc increases accordingly to ~235 K. The lattice of the
epitaxial MnSn monolayer as well as the Sn/Si(111)-$2\sqrt{3}\times2\sqrt{3}$
is perfectly compatible with silicon, and thus an sharp interface is formed
between MnSn, Sn and Si. This system provides a new platform for exploring the
2D ferromagnetism, integrating magnetic monolayers into silicon-based
technology, and engineering the spintronics heterostructures.",2006.00333v1
2020-06-01,Dynamical quantum phase transitions in a spin chain with deconfined quantum critical points,"We analytically and numerically study the Loschmidt echo and the dynamical
order parameters in a spin chain with a deconfined phase transition between a
dimerized state and a ferromagnetic phase. For quenches from a dimerized state
to a ferromagnetic phase, we find that the model can exhibit a dynamical
quantum phase transition characterized by an associating dimerized order
parameters. In particular, when quenching the system from the Majumdar-Ghosh
state to the ferromagnetic Ising state, we find an exact mapping into the
classical Ising chain for a quench from the paramagnetic phase to the classical
Ising phase by analytically calculating the Loschmidt echo and the dynamical
order parameters. By contrast, for quenches from a ferromagnetic state to a
dimerized state, the system relaxes very fast so that the dynamical quantum
transition may only exist in a short time scale. We reveal that the dynamical
quantum phase transition can occur in systems with two broken symmetry phases
and the quench dynamics may be independent on equilibrium phase transitions.",2006.00726v2
2020-08-21,Confinement effect enhanced Stoner ferromagnetic instability in monolayer 1T-VSe2,"Monolayer 1T-VSe2 has been reported as a room-temperature ferromagnet. In
this work, by using first-principles calculations, we unveil that the
ferromagnetism in monolayer 1T-VSe2 is originated from its intrinsic huge
Stoner instability enhanced by the confinement effect, which can eliminate the
interlayer coupling, and lead to a drastic increase of the density of states at
the Fermi level due to the presence of Van Hove singularity. Our calculations
also demonstrate that the Stoner instability is very sensitive to the
interlayer distance. These results provide a useful route to modulate the
nonmagnetic to ferromagnetic transition in few-layers or bulk 1T-VSe2, which
also shed light on the enhancement of its Curie temperature by enlarging the
interlayer distance.",2008.09562v1
2020-08-25,Kondo holes in the 2D itinerant Ising ferromagnet Fe3GeTe2,"Heavy fermion (HF) states emerge in correlated quantum materials due to the
interplay between localized magnetic moments and itinerant electrons, but
rarely appear in 3d-electron systems due to high itinerancy of d-electrons.
Here, an anomalous enhancement of Kondo screening is observed at the Kondo hole
of local Fe vacancies in Fe3GeTe2 which is a recently discovered 3d-HF system
featuring of Kondo lattice and two-dimensional itinerant ferromagnetism. An
itinerant Kondo-Ising model is established to reproduce the experimental
results which provides insight of the competition between Ising ferromagnetism
and Kondo screening. This work explains the microscopic origin of the
d-electron HF states and inspires study of the enriched quantum many-body
phenomena with Kondo holes in Ising ferromagnets.",2008.10842v2
2020-08-25,A topological current divider,"We study the transport properties of a hybrid junction made of a
ferromagnetic lead in electrical connection with the helical edge modes of a
two-dimensional topological insulator. In this system, the time reversal
symmetry, which characterizes the ballistic edge modes of the topological
insulator, is explicitly broken inside the ferromagnetic region. This conflict
situation generates unusual transport phenomena at the interface which are the
manifestation of the interplay between the spin polarization of the injected
current and the spin-momentum locking mechanism operating inside the
topological insulator. We show that the spin polarized current originated in
the ferromagnetic region is asymmetrically divided in spatially separated
branch currents sustained by edge channels with different helicity inside the
topological insulator. The above findings provide the working principle of a
topological current divider in which the relative intensity of the branch
currents is determined by the polarization of the incoming current. We discuss
the relevance of this effect in spintronics where, for instance, it offers an
alternative way to measure the current polarization generated by a
ferromagnetic electrode.",2008.10905v1
2020-09-07,Tuneable Magneto-Resistance by Severe Plastic Deformation,"Bulk metallic samples were synthesized from different binary powder mixtures
consisting of elemental Cu, Co, and Fe using severe plastic deformation. Small
particles of the ferromagnetic phase originate in the conductive Cu phase,
either by incomplete dissolution or by segregation phenomena during the
deformation process. These small particles are known to give rise to granular
giant magnetoresistance. Taking advantage of the simple production process, it
is possible to perform a systematic study on the influence of processing
parameters and material compositions on the magneto-resistance. Furthermore, it
is feasible to tune the magnetoresistive behavior as a function of the
specimens chemical composition. It was found that specimens of low
ferromagnetic content show an almost isotropic drop in resistance in a magnetic
field. With increasing ferromagnetic content, percolating ferromagnetic phases
cause an anisotropy of the magnetoresistance. By changing the parameters of the
high pressure torsion process, i.e., sample size, deformation temperature, and
strain rate, it is possible to tailor the magnitude of giant
magneto-resistance. A decrease in room temperature resistivity of approx. 3.5%
was found for a bulk specimen containing an approximately equiatomic fraction
of Co and Cu.",2009.02952v1
2020-09-08,Electrical detection of magnetic circular dichroism: application to magnetic microscopy in ultra-thin ferromagnetic films,"Imaging the magnetic configuration of thin-films has been a long-standing
area of research. Since a few years, the emergence of two-dimensional
ferromagnetic materials calls for innovation in the field of magnetic imaging.
As the magnetic moments are extremely small, standard techniques like SQUID,
torque magnetometry, magnetic force microscopy and Kerr effect microscopy are
challenging and often lead to the detection of parasitic magnetic contributions
or spurious effects. In this work, we report a new magnetic microscopy
technique based on the combination of magnetic circular dichroism and Seebeck
effect in semiconductor/ferromagnet bilayers. We implement this method with
perpendicularly magnetized (Co/Pt) multilayers sputtered on Ge (111). We
further show that the electrical detection of MCD is more sensitive than the
Kerr magnetometry, especially in the ultra-thin film regime, which makes it
particularly promising for the study of emergent two-dimensional ferromagnetic
materials.",2009.03982v1
2020-09-30,Imprint from ferromagnetic skyrmions in an antiferromagnet via exchange bias,"Magnetic skyrmions are topological spin textures holding great potential as
nanoscale information carriers. Recently, skyrmions have been predicted in
antiferromagnets, with key advantages in terms of stability, size, and
dynamical properties over their ferromagnetic analogs. However, their
experimental demonstration is still lacking. Here, we show the imprint from
ferromagnetic skyrmions into a thin film of an IrMn antiferromagnet, at room
temperature and zero external magnetic field, using exchange-bias. Using
high-spatial-resolution x-ray magnetic circular dichroism photoemission
electron microscopy (XMCD-PEEM), we observed the imprinted spin textures within
the IrMn from the XMCD signal of the uncompensated Mn spins at the interface
with the ferromagnet. This result opens up a path for logic and memory devices
based on skyrmion manipulation in antiferromagnets.",2009.14796v2
2020-10-08,Chiral Hinge Magnons in Second-Order Topological Magnon Insulators,"When interacting spins in condensed matter order ferromagnetically, their
ground state wave function is topologically trivial. Nonetheless, in two
dimensions, the ferromagnetic state can support spin excitations with
nontrivial topology, an exotic state known as topological magnon insulator
(TMI). Here, we theoretically unveil and numerically confirm a novel
ferromagnetic state in three dimensions dubbed second-order TMI, whose
hallmarks are excitations at its hinges, where facets intersect. Since
ferromagnetism naturally comes with broken time-reversal symmetry, the hinge
magnons are chiral, rendering backscattering impossible. Hence, they trace out
a three-dimensional path about the sample unimpeded by defects and are
topologically protected by the spectral gap. They are remarkably robust against
disorder and simultaneously highly tunable by atomic-level engineering of the
sample termination. Our findings empower magnonics with the tools of
higher-order topology, a promising route to combine low-energy information
transfer free of Joule heating with three-dimensional vertical integration.",2010.04142v1
2020-10-09,Electronic and magnetic properties of $α$-FeGe$_2$ films embedded in vertical spin valve devices,"We studied metastable $\alpha$-FeGe$_2$, a novel layered tetragonal material,
embedded as a spacer layer in spin valve structures with ferromagnetic Fe$_3$Si
and Co$_2$FeSi electrodes. For both types of electrodes, spin valve operation
is demonstrated with a metallic transport behavior of the $\alpha$-FeGe$_2$
spacer layer. The spin valve signals are found to increase both with
temperature and spacer thickness, which is discussed in terms of a decreasing
magnetic coupling strength between the ferromagnetic bottom and top electrodes.
The temperature-dependent resistances of the spin valve structures exhibit
characteristic features, which are explained by ferromagnetic phase transitions
between 55 and 110~K. The metallic transport characteristics as well as the
low-temperature ferromagnetism are found to be consistent with the results of
first-principles calculations.",2010.04453v2
2020-10-15,"Microscopic mechanism of high-temperature ferromagnetism in Fe, Mn, and Cr-doped InSb, InAs, and GaSb magnetic semiconductors","In recent experiments, high Curie temperatures Tc above room temperature were
reported in ferromagnetic semiconductors Fe-doped GaSb and InSb, while low Tc
between 20 K to 90 K were observed in some other semiconductors with the same
crystal structure, including Fe-doped InAs and Mn-doped GaSb, InSb, and InAs.
Here we study systematically the origin of high temperature ferromagnetism in
Fe, Mn, Cr-doped GaSb, InSb, and InAs magnetic semiconductors by combining the
methods of density functional theory and quantum Monte Carlo. In the diluted
impurity limit, the calculations show that the impurities Fe, Mn, and Cr have
similar magnetic correlations in the same semiconductors. Our results suggest
that high (low) Tc obtained in these experiments mainly comes from high (low)
impurity concentrations. In addition, our calculations predict the
ferromagnetic semiconductors of Cr-doped InSb, InAs, and GaSb that may have
possibly high Tc. Our results show that the origin of high Tc in (Ga,Fe)Sb and
(In,Fe)Sb is not due to the carrier induced mechanism because Fe3+ does not
introduce carriers.",2010.07454v1
2020-11-20,Crystal growth and metallic ferromagnetism induced by electron doping in FeSb$_2$,"In order to study the metallic ferromagnetism induced by electron doping in
the narrow-gab semiconductor FeSb$_2$, single crystals of FeSb$_2$,
Fe$_{1-x}$Co$_x$Sb$_2$ ($0 \le x \le 0.5$) and FeSb$_{2-y}$Te$_y$ ($0 \le y \le
0.4$), were grown by a simplified self-flux method. From powder x-ray
diffraction (XRD) patterns, wavelength-dispersive x-ray spectroscopy (WDX) and
x-ray Laue diffraction, pure and doped high-quality single crystals, within the
selected solubility range, show only the orthorhombic $Pnnm$ structure of
FeSb$_2$ with a monotonic change in lattice parameters with increasing the
doping level. In consistence with the model of nearly ferromagnetic small-gap
semiconductor, the energy gap of FeSb$_2$ Pauli paramagnet gradually collapses
by electron doping before it closes at about $x$ or $y$ = 0.15 and subsequent
itinerant electron anisotropic ferromagnetic states are observed with higher
doping levels. A magnetic phase diagram is established and discussed in view of
proposed theoretical scenarios.",2011.10343v2
2020-11-23,Quantum Oscillations in the Field-induced Ferromagnetic State of MnBi$_{2-x}$Sb$_{x}$Te$_{4}$,"The intrinsic antiferromagnetic topological insulator MnBi$_{2}$Te$_{4}$
undergoes a metamagnetic transition in a c-axis magnetic field. It has been
predicted that ferromagnetic MnBi$_{2}$Te$_{4}$ is an ideal Weyl semimetal with
a single pair of Weyl nodes. Here we report measurements of quantum
oscillations detected in the field-induced ferromagnetic phase of
MnBi$_{2-x}$Sb$_{x}$Te$_{4}$, where Sb substitution tunes the majority carriers
from electrons to holes. Single frequency Shubnikov-de Haas oscillations were
observed in a wide range of Sb concentrations (0.54 $\leq$ x $\leq$ 1.21). The
evolution of the oscillation frequency and the effective mass shows reasonable
agreement with the Weyl semimetal band-structure of ferromagnetic
MnBi$_{2}$Te$_{4}$ predicted by density functional calculations. Intriguingly,
the quantum oscillation frequency shows a strong temperature dependence,
indicating that the electronic structure sensitively depends on magnetism.",2011.11798v1
2021-02-22,Crossover between short and long range proximity effects in SFS junctions with Ni-based ferromagnets,"We study Superconductor/Ferromagnet/Superconductor junctions with CuNi, PtNi,
or Ni interlayers. Remarkably, we observe that supercurrents through Ni can be
significantly larger than through diluted alloys. The phenomenon is attributed
to the dirtiness of disordered alloys leading to a short coherence length
despite a small exchange energy. To the contrary, pure Ni is clean resulting in
a coherence length as long as in a normal metal. Analysis of temperature
dependencies of critical currents reveals a crossover from short (dirty) to
long (clean) range proximity effects in Pt1-xNix with increasing Ni
concentration. Our results point out that structural properties of a
ferromagnet play a crucial role for the proximity effect and indicate that
conventional strong-but-clean ferromagnets can be advantageously used in
superconducting spintronic devices.",2102.10927v1
2021-03-11,Flatband-Induced Itinerant Ferromagnetism in RbCo$_2$Se$_2$,"$A$Co$_2$Se$_2$ ($A$=K,Rb,Cs) is a homologue of the iron-based
superconductor, $A$Fe$_2$Se$_2$. From a comprehensive study of RbCo$_2$Se$_2$
via measurements of magnetization, transport, neutron diffraction,
angle-resolved photoemission spectroscopy, and first-principle calculations, we
identify a ferromagnetic order accompanied by an orbital-dependent
spin-splitting of the electronic dispersions. Furthermore, we identify the
ordered moment to be dominated by a $d_{x^2-y^2}$ flatband near the Fermi
level, which exhibits the largest spin splitting across the ferromagnetic
transition, suggesting an itinerant origin of the ferromagnetism. In the
broader context of the iron-based superconductors, we find this $d_{x^2-y^2}$
flatband to be a common feature in the band structures of both
iron-chalcogenides and iron-pnictides, accessible via heavy electron doping.",2103.06528v1
2021-03-30,Large voltage-tunable spin valve based on a double quantum dot,"We study the spin-dependent transport properties of a spin valve based on a
double quantum dot. Each quantum dot is assumed to be strongly coupled to its
own ferromagnetic lead, while the coupling between the dots is relatively weak.
The current flowing through the system is determined within the perturbation
theory in the hopping between the dots, whereas the spectrum of a quantum
dot-ferromagnetic lead subsystem is determined by means of the numerical
renormalization group method. The spin-dependent charge fluctuations between
ferromagnets and quantum dots generate an effective exchange field, which
splits the double dot levels. Such field can be controlled, separately for each
quantum dot, by the gate voltages or by changing the magnetic configuration of
external leads. We demonstrate that the considered double quantum dot spin
valve setup exhibits enhanced magnetoresistive properties, including both
normal and inverse tunnel magnetoresistance. We also show that this system
allows for the generation of highly spin-polarized currents, which can be
controlled by purely electrical means. The considered double quantum dot with
ferromagnetic contacts can thus serve as an efficient voltage-tunable spin
valve characterized by high output parameters.",2103.16059v1
2021-04-08,Anisotropic c-f hybridization in the ferromagnetic quantum critical metal CeRh$_6$Ge$_4$,"Heavy fermion compounds exhibiting a ferromagnetic quantum critical point
have attracted considerable interest. Common to two known cases, i.e.,
CeRh$_6$Ge$_4$ and YbNi$_4$P$_2$, is that the 4f moments reside along chains
with a large inter-chain distance, exhibiting strong magnetic anisotropy that
was proposed to be vital for the ferromagnetic quantum criticality. Here we
report an angle-resolved photoemission study on CeRh6Ge4, where we observe
sharp momentum-dependent 4f bands and clear bending of the conduction bands
near the Fermi level, indicating considerable hybridization between conduction
and 4f electrons. The extracted hybridization strength is anisotropic in
momentum space and is obviously stronger along the Ce chain direction. The
hybridized 4f bands persist up to high temperatures, and the evolution of their
intensity shows clear band dependence. Our results provide spectroscopic
evidence for anisotropic hybridization between conduction and 4f electrons in
CeRh$_6$Ge$_4$, which could be important for understanding the electronic
origin of the ferromagnetic quantum criticality.",2104.03600v1
2021-05-03,Giant anomalous Hall conductivity in the itinerant ferromagnet LaCrSb3 and the effect of f-electrons,"Itinerant ferromagnets constitute an important class of materials wherein
spin-polarization can affect the electric transport properties in nontrivial
ways. One such phenomenon is anomalous Hall effect which depends on the details
of the band structure such as the amount of band crossings in the valence band
of the ferromagnet. Here, we have found extraordinary anomalous Hall effect in
an itinerant ferromagnetic metal LaCrSb3. The rather two-dimensional nature of
the magnetic subunit imparts large anisotropic anomalous Hall conductivity of
1250 S/cm at 2K. Our investigations suggest that a strong Berry curvature by
abundant momentum-space crossings and narrow energy-gap openings are the
primary sources of the anomalous Hall conductivity. An important observation is
the existence of quasi-dispersionless bands in LaCrSb3 which is now known to
increase the anomalous Hall conductivity. After introducing f-electrons,
anomalous Hall conductivity experiences more than two-fold increase and reaches
2900 S/cm in NdCrSb3.",2105.00906v1
2021-06-10,Room-temperature spin injection and spin-to-charge conversion in a ferromagnetic semiconductor / topological insulator heterostructure,"Spin injection using ferromagnetic semiconductors at room temperature is a
building block for the realization of spin-functional semiconductor devices.
Nevertheless, this has been very challenging due to the lack of reliable
room-temperature ferromagnetism in well-known group IV and III-V based
semiconductors. Here, we demonstrate room-temperature spin injection by using
spin pumping in a (Ga,Fe)Sb / BiSb heterostructure, where (Ga,Fe)Sb is a
ferromagnetic semiconductor (FMS) with high Curie temperature (TC) and BiSb is
a topological insulator (TI). Despite the very small magnetization of (Ga,Fe)Sb
at room temperature (45 emu/cc), we are able to detect spin injection from
(Ga,Fe)Sb by utilizing the inverse spin Hall effect (ISHE) in the topological
surface states of BiSb with a large inverse spin Hall angle of 2.5. Our study
provides the first demonstration of spin injection as well as spin-to-charge
conversion at room temperature in a FMS/TI heterostructure.",2106.05902v1
2021-06-23,"Magnetic anisotropy in uranium monosulfide, probed by the magnetic torque measurements","We have studied the magnetic torque in uranium monosulfide (US) single
crystals to explore the magnetic anisotropy in this material. Uranium
monosulfide crystallizes in cubic, NaCl-type of crystal structure and exhibits
the largest magneto-crystalline anisotropy observed in cubic systems. By
performing detailed torque measurements we observe a strongly anisotropic
behavior in the paramagnetic phase due to crystal defects and quadrupolar pair
interactions. Our studies also confirm the presence of a large anisotropy in
the ferromagnetic state of the US system with the <100>, <111>, and <110>
directions being hard, easy, and intermediate axis, respectively. Furthermore,
the anisotropy in the paramagnetic phase shows similar characteristics to the
anisotropy observed in the ferromagnetic phase, as characterized by second and
fourth rank susceptibility terms. The similarity of the anisotropic behaviors
in paramagnetic and ferromagnetic phases is the consequence of strong
magneto-elastic properties in this system, which possibly lead to the
rhombohedral structural distortion, not only in the ferromagnetic phase but
also in the paramagnetic phase (induced by applied magnetic fiield).",2106.12464v1
2021-07-09,Two-dimensional ferromagnetic spin-orbital excitations in the honeycomb VI$_{3}$,"VI$_{3}$ is a ferromagnet with planar honeycomb sheets of bonded V$^{3+}$
ions held together by van der Waals forces. We apply neutron spectroscopy to
measure the two dimensional ($J/J_{c} \approx 17$) magnetic excitations in the
ferromagnetic phase, finding two energetically gapped ($\Delta \approx k_{B}
T_{c} \approx$ 55 K) and dispersive excitations. We apply a multi-level spin
wave formalism to describe the spectra in terms of two coexisting domains
hosting differing V$^{3+}$ orbital ground states built from contrasting
distorted octahedral environments. This analysis fits a common nearest neighbor
in-plane exchange coupling ($J$=-8.6 $\pm$ 0.3 meV) between V$^{3+}$ sites. The
distorted local crystalline electric field combined with spin-orbit coupling
provides the needed magnetic anisotropy for spatially long-ranged
two-dimensional ferromagnetism in VI$_{3}$.",2107.04311v1
2021-07-14,"Phase-manipulation-induced Majorana Mode and Braiding Realization in Iron-based Superconductor Fe(Te,Se)","Recent experiment reported the evidence of dispersing one-dimensional
Majorana mode trapped by the crystalline domain walls in
FeSe$_{0.45}$Te$_{0.55}$. Here, we perform the first-principles calculations to
show that iron atoms in the domain wall spontaneously form the ferromagnetic
order in line with orientation of the wall. The ferromagnetism can impose a
$\pi$ phase difference between the domain-wall-separated surface
superconducting regimes under the appropriate width and magnetization of the
wall. Accordingly, the topological surface superconducting state of
FeSe$_{0.45}$Te$_{0.55}$ can give rise to one-dimensional Majorana modes
trapped by the wall. More interestingly, we further propose a surface junction
in the form of FeSe$_{0.45}$Te$_{0.55}$/ferromagnet/FeSe$_{0.45}$Te$_{0.55}$,
which can be adopted to create and fuse the Majorana zero modes through
controlling the width or magnetization of the interior ferromagnetic barrier.
The braiding and readout of Majorana zero modes can be realized by the designed
device. Such surface junction has the potential application in the
superconducting topological quantum computation.",2107.06558v3
2021-07-23,Green's function formalism for nonlocal elliptical magnon transport,"We develop a non-equilibrium Green's function formalism to study magnonic
spin transport through a strongly anisotropic ferromagnetic insulator contacted
by metallic leads. We model the ferromagnetic insulator as a finite-sized
one-dimensional spin chain, with metallic contacts at the first and last sites
that inject and detect spin in the form of magnons. In the presence of
anisotropy, these ferromagnetic magnons become elliptically polarized, and spin
conservation is broken. We show that this gives rise to a novel parasitic spin
conductance, which becomes dominant at high anisotropy. Moreover, the spin
state of the ferromagnet becomes squeezed in the high-anisotropy regime. We
show that the squeezing may be globally reduced by the application of a local
spin bias.",2107.11072v2
2021-07-28,"Controlling phase transition in monolayer metal diiodides XI$_{2}$ (X: Fe, Co, and Ni) by carrier doping","We applied the generalized Bloch theorem to verify the ground state (most
stable state) in monolayer metal diiodides 1T-XI$_{2}$ (X: Fe, Co, and Ni), a
family of metal dihalides, using the first-principles calculations. The ground
state, which can be ferromagnetic, antiferromagnetic, or spiral state, was
specified by a wavevector in the primitive unit cell. While the ground state of
FeI$_{2}$ is ferromagnetic, the spiral state becomes the ground state for
CoI$_{2}$ and NiI$_{2}$. Since the multiferroic behavior in the metal dihalide
can be preserved by the spiral structure, we believe that CoI$_{2}$ and
NiI$_{2}$ are promising multiferroic materials in the most stable state. When
the lattice parameter increases, we also show that the ground state of
NiI$_{2}$ changes to a ferromagnetic state while others still keep their
initial ground states. For the last discussion, we revealed the phase
transition manipulated by hole-electron doping due to the spin-spin competition
between the ferromagnetic superexchange and the antiferromagnetic direct
exchange. These results convince us that metal diiodides have many benefits for
future spintronic devices.",2107.13287v1
2021-07-30,Emergence of Ferromagnetism Through the Metal-Insulator Transition in Undoped Indium Tin Oxide Films,"We present a detailed study of the emergence of bulk ferromagnetism in low
carrier density samples of undoped indium tin oxide (ITO). We used annealing to
increase the density of oxygen vacancies and change sample morphology without
introducing impurities through the metal insulator transition (MIT). We
utilized a novel and highly sensitive ""Corbino-disk torque magnetometry""
technique to simultaneously measure the thermodynamic and transport effects of
magnetism on the same sample after successive annealing. With increased sample
granularity, carrier density increased, the sample became more metallic, and
ferromagnetism appeared as resistance approached the MIT. Ferromagnetism was
observed through the detection of magnetization hysteresis, anomalous Hall
effect (AHE), and hysteretic magnetoresistance. A sign change of the AHE as the
MIT is approached may elucidate the interplay between the impurity band and the
conduction band in the weakly insulating side of the MIT.",2107.14463v1
2021-08-02,Antiferromagnetic order of ferromagnetically coupled dimers in the double pyrovanadate CaCoV$_2$O$_7$,"Magnetic properties of the pyrovanadate CaCoV$_2$O$_7$ have been studied by
means of the bulk magnetization and neutron powder diffraction measurements.
Magnetic susceptibility in the paramagnetic phase shows Curie-Weiss behavior
with negative Weiss temperature $\Theta \simeq -22.5$ K, indicating dominant
antiferromagnetic interactions. At $T_{\rm N} = 3.44$ K, CaCoV$_2$O$_7$ shows
antiferromagnetic order, accompanied by a weak net ferromagnetic moment of
$\sim 0.05$~$\mu_{\rm B}/{\rm Co}^{2+}$. Neutron powder diffraction confirms
the formation of antiferromagnetic order below $T_{\rm N}$. It was further
confirmed from the magnetic structure determination that the two Co$^{2+}$ ions
in the adjacent edge-sharing octahedra have almost parallel (ferromagnetic)
spin arrangement, indicative of a formation of a ferromagnetic spin dimer. The
antiferromagnetic order is, in turn, stabilized by sizable inter-dimer
antiferromagnetic interactions.",2108.00715v1
2021-08-26,Pressure-induced collapse of ferromagnetism in Nickel,"Transition metals, Fe, Co and Ni, are the canonical systems for studying the
effect of external perturbations on ferromagnetism. Among these, Ni stands out
as it undergoes no structural phase transition under pressure. Here we have
investigated the long-debated issue of pressure-induced magnetisation drop in
Ni from first-principles. Our calculations confirm an abrupt quenching of
magnetisation at high pressures, not associated with any structural phase
transition. We find that the pressure substantially enhances the crystal field
splitting of Ni-$3d$ orbitals, driving the system towards a new metallic phase
violating the Stoner Criterion for ferromagnetic ordering. Analysing the charge
populations in each spin channel, we show that the next nearest neighbour
interactions play a crucial role in quenching ferromagnetic ordering in Ni and
materials alike.",2108.11977v1
2021-09-30,Theoretical prediction of Curie temperature in two-dimensional ferromagnetic monolayer,"Theoretical prediction of Curie temperature (TC) is of vital importance for
designing the spintronic devices in two-dimensional (2D) ferromagnetic
materials. Herein, based on the extensive investigation of Monte Carlo
simulations, we summary and propose an improved method to estimate TC more
precisely, which includes the different contributions of multiple near-neighbor
interactions. Taking monolayer CrI3 as an example, the trends of TC with
biaxial strain are investigated via Monte Carlo simulations, mean-field
formulas and our method. Besides, our method is not only accurate and
convenient to predicting the TC in 2D ferromagnetic honeycomb lattice CrI3 but
it can be extended for predicting the TC of other 2D lattices. Our work paves
the way to accelerate the prediction and discovery of novel 2D ferromagnets for
spintronic applications.",2109.14802v2
2021-10-14,Ferromagnetic Negative Charge-Transfer Insulator: from Theoretical Proposal to Material Realization,"Here we propose another type of ferromagnetic semiconductors: ferromagnetic
negative charge-transfer insulator (FNCTI). In FNCTI, the negative
charge-transfer states strongly enhance the ferromagnetic (FM) exchange
interactions and the orbital hybridization gap permits the magnetic molecular
orbitals as the underlying magnetic units rather than local atomic orbitals.
Thus the FM exchange interactions are rather strong and decay slowly due to the
large spearding of magnetic molecular orbitals. This is distinct from the
superexchange mechanism where FM exchange interactions are quite weak as
summarized in the well-known Goodenough-Kanamori-Anderson semi-empirical
rules.Through first-principle calculations with the hybrid functional, PbO-type
CrAs monolayer is mapped out to be a FNCTI, which possesses a band gap $\sim$
0.35 eV, FM nearest-/next-nearest-neighbor exchange coupling strength $\sim$
57/40 meV, and a high $T_c$ $\sim$ 1500 K respectively. It is believed that the
existence of FNCTI validates the long-pending hypothesis by D. I. Khomskii and
G. A. Sawatzky in 1997 [Solid State Commun. 102, 87 (1997)].",2110.07372v2
2021-10-20,Nonlinear response induced by Ferromagnetism in a Noncentrosymmetric Kondo Lattice system,"Recently, nonlinear responses have been actively studied in both experiments
and theory. Particularly interesting are inversion-symmetry broken systems,
where an even-order nonlinear electrical conductivity can be nonzero, resulting
in nonreciprocity. Second-order nonlinear conductivities attract much attention
because of their sensitivity to detect inversion-symmetry breaking in materials
and their functionalities. However, while the nonlinear response has been
actively studied in noninteracting systems for a long time, the nonlinear
response in strongly correlated materials is still poorly understood. This
paper analyzes the nonlinear conductivity in a correlated noncentrosymmetric
system, namely a Kondo lattice system with Rashba type spin-orbit coupling. We
mainly focus on the ferromagnetic phase, in which the second-order nonlinear
conductivity becomes finite. Remarkably, we find that the second-order
conductivity becomes only finite perpendicular to the ferromagnetic
magnetization and has a strong spin dependence; due to a gap at the Fermi
energy for one spin direction, the linear and nonlinear conductivity is only
finite for the ungapped spin direction. Finally, we analyze sign changes in the
nonlinear conductivity, which can be explained by a combination of correlation
effects and the energetic shift due to the occurring ferromagnetism.",2110.10496v1
2021-10-20,Spin Fluctuations Yield zT Enhancement in Ferromagnets,"Thermal fluctuation of local magnetization in magnetic metals intercoupled
with charge carriers and phonons offers a path to enhance thermoelectric
performance. The thermopower enhancement by spin fluctuations (SF) has been
observed before. However, the crucial evidence for enhancing
thermoelectric-figure-of-merit (zT) by SF has not been reported until now. Here
we report evidence for such enhancement in the ferromagnetic CrTe. The SF leads
to nearly 80% zT enhancement in ferromagnetic CrTe near and below TC~335 K. The
ferromagnetism in CrTe is originated from the collective electronic and
localized magnetic moments. The field-dependent transport properties
demonstrate the profound impact of SF on the electrons and phonons. The SF
simultaneously enhances the thermopower and reduces the thermal conductivity.
Under an external magnetic field, the enhancement in thermopower is suppressed,
and the thermal conductivity is enhanced, evidencing the existence of a strong
SF near and below TC. The anomalous thermoelectric transport properties are
analyzed based on theoretical models, and a good agreement with experimental
data is found. Furthermore, the detailed analysis proves an insignificant
impact from spin-wave contribution to the transport properties. This study
contributes to the fundamental understanding of spin fluctuation for designing
high-performance spin-driven thermoelectric materials.",2110.10798v1
2021-10-25,Superconducting triplet rim currents in a spin-textured ferromagnetic disk,"Since the discovery of the long-range superconducting proximity effect, the
interaction between spin-triplet Cooper pairs and magnetic structures such as
domain walls and vortices has been the subject of intense theoretical
discussions, while the relevant experiments remain scarce. We have developed
nanostructured Josephson junctions with highly controllable spin texture, based
on a disk-shaped Nb/Co bilayer. Here, the vortex magnetization of Co and the
Cooper pairs of Nb conspire to induce long-range triplet (LRT)
superconductivity in the ferromagnet. Surprisingly, the LRT correlations emerge
in highly localized (sub-80 nm) channels at the rim of the ferromagnet, despite
its trivial band structure. We show that these robust rim currents arise from
the magnetization texture acting as an effective spin-orbit coupling, which
results in spin accumulation at the bilayer-vacuum boundary. Lastly, we
demonstrate that by altering the spin texture of a single ferromagnet, both $0$
and $\pi$-channels can be realized in the same device.",2110.13035v2
2021-11-06,Tuning the electronic band structure in a kagome ferromagnetic metal via magnetization,"Materials with zero energy band gap display intriguing properties including
high sensitivity of the electronic band structure to external stimulus such as
pressure or magnetic field. An interesting candidate for zero energy band gap
are Weyl nodes at the Fermi level EF. A prerequisite for the existence of Weyl
nodes is to either have inversion or time reversal symmetry broken. Weyl nodes
in systems with broken time reversal symmetry are ideal to realize the
tunability of the electronic band structure by magnetic field. Theoretically,
it has been shown that in ferromagnetic Weyl materials, the band structure is
dependent upon the magnetization direction and thus the electronic bands can be
tuned by controlling the magnetization direction. Here, we demonstrate tuning
of the band structure in a kagome Weyl ferromagnetic metal Fe3Sn2 with
magnetization and magnetic field. Owing to spin-orbit coupling, we observe
changes in the band structure depending on the magnetization direction that
amount to a decrease in the carrier density by a factor of four when the
magnetization lies in the kagome plane as compared to when the magnetization is
along the c axis. Our discovery opens a way for tuning the carrier density in
ferromagnetic materials.",2111.03826v1
2021-11-22,Excitation and reception of magnetostatic surface spin waves in thin conducting ferromagnetic films by coplanar microwave antennas. Part I: Theory,"A fully self-consistent model for the excitation and reception of
magnetostatic surface waves in thin ferromagnetic films by a set of coplanar
antennas was developed and implemented numerically. The model assumes that the
ferromagnetic film is highly conducting and is interfaced with non-magnetic
metallic films, but is also suitable for modeling magneto-insulating films.
Perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction can be
included at both interfaces of the ferromagnetic layer. The model calculates
the coupling impedances between the different strips constituting the coplanar
antennas. In some situations, this leads to a frequency non-reciprocity between
counter-propagating waves even in the case of no asymmetry in the spin-wave
dispersion relation. Several intermediate results of the model were checked
numerically and the final output of the model, given as the scattering
parameters, $S_{11}$, $S_{12}$, and $S_{21}$ of the antenna system, were in
good agreement with previous experimental studies.",2111.11106v3
2021-12-01,Electric Field Control of Magnetism of Mn dimer supported on Carbon-doped-h-BN surface,"Using density functional theory we show that the interaction between two Mn
atoms can be tuned from anti-ferromagnetic (AFM) to ferromagnetic (FM) state by
creating charge disproportion between the two on a 2D surface. The non-metallic
planar heterostructures, the 2D surface, in our work is designed by doping
carbon hexagon rings in a hexagonal boron nitride (h-BN) sheet. In addition, we
show that an external electric field can be used to control the charge
disproportion and hence the magnetism. In fact, our calculations demonstrate
that the magnetic states of the dimer can be switched from AFM to FM or vice
versa in an external electric field. The origin of this magnetic switching is
explained using the charge transfer from (or to) the Mn dimer to (or from) the
2D material. The switching between anti-ferromagnetic to ferromagnetic states
can be useful for future spintronic applications.",2112.00638v1
2021-12-07,Nanometers-thick Ferromagnetic Surface Produced by Laser Cutting of Diamond,"In this work, we demonstrate that cutting diamond crystals with a laser
(532~nm wavelength, 0.5~mJ energy, 200~ns pulse duration at 15~kHz) produces a
$\lesssim 20~$nm thick surface layer with magnetic order at room temperature.
We have measured the magnetic moment of five natural and six CVD diamond
crystals of different size, nitrogen content and surface orientations with a
SQUID magnetometer. A robust ferromagnetic response at 300~K is observed only
for crystals that were cut with the laser along the (100) surface orientation.
The magnetic signals are much weaker for the (110) and negligible for the (111)
orientations. We attribute the magnetic order to the disordered graphite layer
produced by the laser at the diamond surface. The ferromagnetic signal vanished
after chemical etching or after moderate temperature annealing. The obtained
results indicate that laser treatment of diamond may pave the way to create
ferromagnetic spots at its surface.",2112.03671v2
2021-12-11,Itinerant ferromagnetism of a dipolar Fermi gas with Raman-induced spin-orbit coupling,"We elucidate the itinerant ferromagnetism of a dipolar Fermi gas with a
Raman-induced spin-orbit coupling by investigating the exotic phase diagrams at
zero and finite temperature. It is revealed that the dipolar interaction along
with spin-orbit coupling can corroborate the formation of ferromagnetism and
the Raman coupling adversely eliminates the tendency to this ferromagnetism
transition, which greatly transcends the general understanding of this subject
with contact interaction only. We explore the ground states through the density
and spin-flip distribution in momentum space, which exhibits novel degeneracy
at strong Raman coupling indicated by a non-zero entropy at zero temperature.
We calculate the transition temperatures well within the reach of an
experimental system when altering the dipolar and spin-orbit coupling strength,
which paves a way to the further experimental realization.",2112.05898v2
2021-12-18,Zeroth-Order Nucleation Transition under Nanoscale Phase Separation,"Materials with nanoscale phase separation are considered. A system
representing a heterophase mixture of ferromagnetic and paramagnetic phases is
studied. After averaging over phase configurations, a renormalized Hamiltonian
is derived describing the coexisting phases. The system is characterized by
direct and exchange interactions and an external magnetic field. The properties
of the system are studied numerically. The stability conditions define the
stable state of the system. At a temperature of zero, the system is in a pure
ferromagnetic state. However, at finite temperature, for some interaction
parameters, the system can exhibit a zeroth-order nucleation transition between
the pure ferromagnetic phase and the mixed state with coexisting ferromagnetic
and paramagnetic phases. At the nucleation transition, the finite concentration
of the paramagnetic phase appears via a jump.",2112.09953v1
2021-12-21,Nonreciprocal spin-wave dynamics in Pt/Co/W/Co/Pt multilayers,"We present a detailed study of the spin-wave dynamics in single Pt/Co/W and
double Pt/Co/W/Co/Pt ferromagnetic layer systems. The dispersion of spin waves
was measured by wavevector-resolved Brillouin light scattering spectroscopy
while the in-plane and out-of-plane magnetization curves were measured by
alternating gradient field magnetometry. The interfacial Dzyaloshinskii-Moriya
interaction induced nonreciprocal dispersion relation was demonstrated for both
single and double ferromagnetic layers and explicated by numerical simulations
and theoretical formulas. The results indicate the crucial role of the order of
layers deposition on the magnetic parameters. A significant difference between
the perpendicular magnetic anisotropy constant in double ferromagnetic layer
systems conduces to the decline of the interlayer interactions and different
dispersion relations for the spin-wave modes. Our study provides a significant
contribution to the realization of the multifunctional nonreciprocal magnonic
devices based on ultrathin ferromagnetic/heavy-metal layer systems.",2112.11206v1
2022-01-05,Absence of a critical nematic phase in the vicinity of the $\rm {SU}(3)$ ferromagnetic point for the one-dimensional spin-1 bilinear-biquadratic model,"The absence of a critical nematic phase in the vicinity of the $\rm {SU}(3)$
ferromagnetic point for the one-dimensional spin-1 bilinear-biquadratic model
is demonstrated by means of the tensor network algorithms. As it turns out, the
phase transition from the ferromagnetic phase to the dimerized phase at the
$\rm {SU}(3)$ ferromagnetic point is direct, but not of the first-order. The
transition point features highly degenerate ground states, which are scale but
not conformally invariant, with the fractal dimension being equal to 2. The
conceptual developments in effective field theories - the fractal dimension and
the counting rule of the Goldstone modes - play a pivotal role in clarifying
the numerical artifacts arising from the finiteness of the bond dimension in
the tensor network simulations, which are attributed to a proximity effect to a
highly entangled scale or conformally invariant ground state.",2201.01434v2
2022-01-28,Itinerant ferromagnetism in a spin-fermion model for diluted spin systems,"We investigate the itinerant ferromagnetism using a diluted spin-fermion
model, derived from a repulsive Hubbard model, where itinerant fermions are
coupled antiferromagnetically to auxiliary fields in a three-dimensional simple
cubic lattice. We focus, in particular, on understanding the spin-dependent
transport properties of the itinerant fermions in the impurity band by taking
positional disorder of the auxiliary fields into account. For on-site repulsion
$U$ $\sim$ bandwidth the density of the itinerant carriers confined to the
impurity band, play a key role in determining the kinetic energy of the system
and consequently the carrier spin polarization. Our semi-classical Monte Carlo
calculations show that the ferromagnetic transition temperature of the carrier
spins indeed shows an optimization behavior with the carrier density. We
calculate the transport properties in details to establish a one-to-one
correspondence between the magnetic and transport properties of the carriers.
Our results obtained beyond the perturbative regime are significant for
understanding the ferromagnetism in diluted magnetic semiconductors.",2201.12182v1
2022-02-15,"Theoretical Investigation of Structural, Electronic Properties and Half-Metallic Ferromagnetism in Ti doped CaS","In this research paper, we investigated the structural, electronic, and
magnetic features of titanium atom substituting calciumatom in rock salt
structure of CaS to explore the new dilute magnetic semiconductor compounds.
The calculations are carried out using the full potential linearized augmented
plane wave (FP-LAPW) method based on spin-polarized density functional theory,
implemented in WIEN2k code. The generalized gradient approximation and
Tran-Balaha modified Becke-Johnson exchange potential. The stability of Ti
doped CaS in ferromagnetic state is provided by the total energy released from
the optimized structures and defect formation energies. The classical model of
Heisenberg is employed to estimate Curie temperature of these compounds. It is
found that the room temperature ferromagnetism is achieved at low
concentrations. The studied materials exhibit half metallic ferromagnetic
demeanor. The half metallic gaps (GHM) are the extremely significant factors to
consider for spintronic applications. The insertion of impurity significantly
decreased the value of GHM due the broadening of 3d Ti states in the gap of the
minority spin. Furthermore, to evaluate the effects of the exchange splitting
process, the pd exchange splitting and the exchange constants are predicted.",2202.06947v1
2022-02-28,Suppression of ferromagnetism and influence of disorder in silicon-substituted CeRh6Ge4,"We report a study of isoelectronic chemical substitution in the recently
discovered quantum critical ferromagnet CeRh$_6$Ge$_4$. Upon silicon-doping,
the ferromagnetic ordering temperature of CeRh$_6$(Ge$_{1-x}$Si$_x$)$_4$ is
continuously suppressed, and no transition is observed beyond
$x_c$$\approx$0.125. Non-Fermi liquid behavior with $C/T \propto$log($T^*/T$)
is observed close to $x_c$, indicating the existence of strong quantum
fluctuations, while the $T$-linear behavior observed upon pressurizing the
parent compound is absent in the resistivity, which appears to be a consequence
of the disorder induced by silicon doping. Our findings provide evidence for
the role played by disorder on the unusual ferromagnetic quantum criticality in
CeRh$_6$Ge$_4$, and provides further evidence for understanding the origin of
this behavior.",2202.13582v1
2022-03-09,Ferromagnetism in layered metallic Fe1/4TaS2 in the presence of conventional and Dirac carriers,"In this paper we present the microscopic origin of the ferromagnetism of
Fe0.25TaS2 and its finite-temperature magnetic properties. We first obtain the
band structures of Fe0.25TaS2 by the first-principles calculations and find
that both conventional and Dirac carriers coexist in metallic Fe0.25TaS2.
Accordingly, considering the spin-orbit coupling of Fe 3d ion, we derive an
effective RKKY-type Hamiltonian between Fe spins in the presence of both the
conventional parabolic-dispersion and the Dirac linear-dispersion carriers,
which contains a Heisenberg-like, an Ising-like and an XY-like term. In
addition, we obtain the ferromagnetic Curie temperature Tc by using the cluster
self-consistent field method. Our results could address not only the high
ferromagnetic Curie temperature, but also the large magnetic anisotropy in
FexTaS2.",2203.04505v1
2022-03-24,Giant electromagnetic proximity effect in superconductor/ferromagnet superlattices,"We show that in superlattices with alternating superconducting (S) and
ferromagnetic (F) layers the spontaneous magnetic field induced in the
superconducting layers due to the electromagnetic proximity effect becomes
dramatically enhanced compared to the previously studied S/F bilayers. The
effect reveals itself for the in-plane orientation of the magnetic moments both
for ferromagnetic and anti-ferromagnetic ordering of the moments in the F
layers. In the finite size samples the magnetic field decays from the sample
surface towards the bulk of the structure, and the decay length strongly
depends on the relative orientation of the sample surface, the layers planes
and magnetic moments in the F layers. The obtained results provide additional
insights into experimental data on the neutron scattering in Nb/Gd
superlattices.",2203.13003v1
2022-03-31,High-temperature ferromagnetism in two-dimensional material MnSn originated from interlayer coupling,"MnSn monolayer synthesized recently is a novel two-dimensional ferromagnetic
material with a hexagonal lattice, in which three Mn atom come together to form
a trimer, making it remarkably different from other magnetic two-dimensional
materials. Most impressively, there happens a sharp increase of Curie
temperature from 54 K to 225 K when the number of layers increase from 1 to 3.
However, no quantitative explanation is reported in previous studies. Herein,
by means of first-principle calculations method and Monte carlo method, we
demonstrate that strong interlayer ferromagnetic coupling is the essential role
in enhancing its critical temperature, which act as a magnetic field to
stabilize the ferromagnetism in the MnSn multilayers.",2203.17126v1
2022-04-04,Phase-field modeling of paramagnetic austenite-ferromagnetic martensite transformation coupled with mechanics and micromagnetics,"A three-dimensional phase-field model is proposed for simulating the magnetic
martensitic phase transformation. The model considers a paramagnetic cubic
austenite to ferromagnetic tetragonal martensite transition, as it occurs in
magnetic Heusler alloys like Ni2 MnGa, and is based on a Landau 2-3-4
polynomial with temperature dependent coefficients. The
paramagnetic-ferromagnetic transition is recaptured by interpolating the
micromagnetic energy as a function of the order parameter for the ferroelastic
domains. The model is numerically implemented in real space by finite element
(FE) method. FE simulations in the martensitic state show that the model is
capable to correctly recapture the ferroelastic and -magnetic microstructures,
as well as the influence of external stimuli. Simulation results indicate that
the paramagnetic austenite to ferromagnetic martensite transition shifts
towards higher temperatures when a magnetic field or compressive stress is
applied. The dependence of the phase transition temperature shift on the
strength of the external stimulus is uncovered as well. Simulation of the phase
transition in magnetocaloric materials is of high interest for the development
of energy-efficient magnetocaloric cooling devices.",2204.01308v1
2022-04-06,Unconventional ferromagnetism and spin-triplet superconductivity in the imbalanced Kagome-lattice Hubbard model,"Unconventional ferromagnetism and superconductivity in the imbalanced
kagome-lattice Hubbard model are investigated by the mean-field theory and
determinant quantum Monte Carlo method. Due to the asymmetric band structure of
kagome lattice, the spin-$z$ ferromagnetic order intrinsically exists in the
system, which is first enhanced by the interaction, and then continuously
destructed after reaching a maximum at a moderate interaction strength. In
contrast, the $xy$-plane ferromagnetism develops only above a critical
interaction, which is estimated to be $U_c/t=3.65 \pm 0.05$ by finite-size
scaling. We further verify the nature of the above transverse magnetic
transition, and demonstrate it belongs to the three-dimensional $XY$
universality class. Finally, we study the superconducting property, and reveal
the possible superconducting state has a triplet $f$-wave pairing symmetry. Our
results uncover the exotic quantum states induced by the interactions on kagome
lattice, and provide important insights regarding the interplay between
electronic correlations and geometry frustrations.",2204.02554v1
2022-04-22,Emerging research landscape of altermagnetism,"Magnetism is one of the largest, most fundamental, and technologically most
relevant fields of condensed-matter physics. Traditionally, two basic magnetic
phases have been considered -- ferromagnetism and antiferromagnetism. The
breaking of the time-reversal symmetry and spin splitting of the electronic
states by the magnetization in ferromagnets underpins a range of macroscopic
responses in this extensively explored and exploited type of magnets. By
comparison, antiferromagnets have vanishing net magnetization. This Perspective
reflects on recent observations of materials hosting an intriguing
ferromagnetic-antiferromagnetic dichotomy, in which spin-split spectra and
macroscopic observables, akin to ferromagnets, are accompanied by antiparallel
magnetic order with vanishing magnetization, typical of antiferromagnets. An
unconventional non-relativistic symmetry-group formalism offers a resolution of
this apparent contradiction by delimiting a third basic magnetic phase, dubbed
altermagnetism. Our Perspective starts with an overview of the still emerging
unique phenomenology of the phase, and of the wide array of altermagnetic
material candidates. In the main part of the article, we illustrate how
altermagnetism can enrich our understanding of overarching condensed-matter
physics concepts, and have impact on prominent condensed-matter research areas.",2204.10844v1
2022-05-31,Electrical measurement of the Spin Hall Effect isotropy in a ferromagnet,"The spin-dependent transport properties of paramagnetic metals are roughly
invariant under rotation. By contrast, in ferromagnetic materials the
magnetization breaks the rotational symmetry, and thus the spin Hall effect is
expected to become anisotropic. Here, using a specific design of lateral spin
valves, we measure electrically the spin Hall Effect anisotropy in NiCu and
NiPd, both in their ferromagnetic and paramagnetic phases. We show that the
appearance of the ferromagnetic order does not lead to a sizeable anisotropy of
the spin charge interconversion in these materials.",2205.15651v2
2022-06-14,Sign-reversed anomalous Nernst effect in the ferromagnetic Weyl-semimetal Fe$_{3-x}$GeTe$_2$: the role of Fe vacancies,"Anomalous Nernst effect, as a thermal partner of anomalous Hall effect, is
particularly sensitive to the Berry curvature anomaly near the Fermi level, and
has been used to probe the topological nature of quantum materials. In this
work, we report the observation of both effects in the ferromagnetic
Weyl-semimetal Fe$_{3-x}$GeTe$_2$ with tunable Fe vacancies. With decreasing Fe
vacancies, the anomalous Hall conductivity evolves as a function of the
longitudinal conductivity from the hopping region to the region where the
intrinsic Berry curvature contribution dominates. Concomitant evolutions in the
anomalous Nernst signal and the anomalous off-diagonal thermoelectric
coefficient are observed below the Curie temperature, displaying a unique sign
change caused by the Fe vacancies. Combining these results with
first-principles calculations, we argue that the Fe-vacancy concentration plays
a unique role in simultaneously tuning the chemical potential and
ferromagnetism, which in turn controls the Berry curvature contribution in this
family of ferromagnetic topological semimetals.",2206.06545v1
2022-06-29,Ferromagnetism in Magic-angle Twisted Bilayer Graphene: A Monte Carlo Study,"Ferromagnetism emerges when the Moire superlattice formed by stacking two
graphene monolayers in a magic twist angle are filled with integer number
electrons. This work investigates the ferromagnetism based on the Ising models
for a triangular lattice at one-quarter filling, a square lattice at half
filling and a Kagome lattice at three-quarters filling of electrons. The
temperature dependent heat capacity, magnetic susceptibility, energy and
magnetization curves are calculated at zero magnetic field with a Monte Carlo
method, leading to derive the phase transition temperatures, T_c=0.76, 1.33 and
4.75 K, respectively. Magnetization curves at finite magnetic field show strong
hysteresis at temperature below 0.5 K for all the fillings considered,
indicating the ferromagnetism of the system; the results are in agreement with
experimental observations.",2206.14432v1
2022-07-15,Anisotropic field response of specific heat for a ferromagnetic superconductor UCoGe in magnetic fields,"Magnetic-field-angle-resolved specific heat and magnetization measurements
were conducted on a ferromagnetic superconductor UCoGe with remarkable
anisotropic upper critical field $H_{\rm c2}$. Although $H_{\rm c2}$ reaches a
high magnetic field ($\sim 20$~T) along the $b$ axis, it is small
($\sim~0.6$~T) when a magnetic field is applied along the magnetic easy
$c$-axis. This study indicates that the specific heat is abruptly suppressed
when the magnetic field is applied toward the $c$ axis from the $a$ and $b$
axes in the ferromagnetic state. The field response of density of states (DOS)
is anisotropic, relative to the $c$ axis, and its angle dependence is slightly
singular. The Ising-type magnetic anisotropy of the ferromagnetic state is
dominant even in the anisotropic reinforced superconducting state. These facts
indicate that the suppression of DOS may closely relate to the superconducting
state. We theoretically analyze these findings together with URhGe and UTe$_2$
by highlighting the common and distinctive features among three compounds.",2207.07266v2
2022-07-15,Engineering a skyrmion crystal in ferromagnetic/antiferromagnetic bilayers free from the DM interaction,"We theoretically propose a new stabilization mechanism of a skyrmion crystal
(SkX) in a bilayer triangular lattice system consisting of the ferromagnetic
and the antiferromagnetic layers. By performing variational calculations and
Monte Carlo simulations in a complementary way, we find that a magnetic
frustration between the ferromagnetic and antiferromagnetic layers is a source
of a finite-Q spiral state and the SkX in the strong interlayer coupling
regime. We also show that the degree of frustration is related to the
interlayer exchange interaction. The stronger interlayer coupling tends to make
the effect of frustration larger, which results in the stabilization of the
SkX. The present results not only provide a way of engineering the SkX in the
ferromagnetic/antiferromagnetic domain and heterostructure but also imply the
possibility of the SkX based on interorbital frustration scenario.",2207.07375v1
2022-07-19,Nature of visons in the perturbed ferromagnetic and antiferromagnetic Kitaev honeycomb models,"The Kitaev honeycomb model hosts a fascinating fractionalized state of matter
featuring emergent Majorana fermions and a vison particle that carries the flux
of an emergent gauge field. In the exactly solvable model these visons are
static but certain perturbations can induce their motion. We show that the
nature of the vison motion induced by a Zeeman field is sharply distinct in the
ferromagnetic vs the antiferromagnetic Kitaev models. Namely, in the
ferromagnetic model the vison has a trivial non-projective translational
symmetry, whereas in the antiferromagnetic Kitaev model it has a projective
translational symmetry with $\pi$-flux per unit cell. The vison band of the
ferromagnetic case has zero Berry curvature, and no associated intrinsic
contribution to the thermal Hall effect. In contrast, in the antiferromagnetic
case there are two gapped vison bands with opposite Chern numbers and an
associated intrinsic vison contribution to the thermal Hall effect. We discuss
these findings in the light of the physics of the spin liquid candidate
$\alpha$-RuCl$_3$.",2207.09492v2
2022-08-19,Strongly correlated itinerant magnetism on the boundary of superconductivity in a magnetic transition metal dichalcogenide,"Metallic ferromagnets with strongly interacting electrons often exhibit
remarkable electronic phases such as ferromagnetic superconductivity, complex
spin textures, and nontrivial topology. In this report, we discuss the
synthesis of a layered magnetic metal NiTa$_4$Se$_8$ (or Ni$_{1/4}$TaSe$_{2}$)
with a Curie temperature of 58 Kelvin. Magnetization data and \textit{ab
initio} calculations indicate that the nickel atoms host uniaxial ferromagnetic
order of about 0.7$\mu_{B}$ per atom, while an even smaller moment is generated
in the itinerant tantalum conduction electrons. Strong correlations are evident
in flat bands near the Fermi level, a high heat capacity coefficient, and a
high Kadowaki-Woods ratio. When the system is diluted of magnetic ions, the
samples become superconducting below about 2 Kelvin. Remarkably, electron and
hole Fermi surfaces are associated with opposite spin polarization. We discuss
the implications of this feature on the superconductivity that emerges near
itinerant ferromagnetism in this material, including the possibility of
spin-polarized superconductivity.",2208.09475v1
2022-09-04,Spin-Polarisation measurement using NbN-Insulator-Ferromagnet Tunnel Junction with oxidized barrier,"We report a two-step process for the fabrication of
superconductor-insulator-normal metal tunnel junctions using NbN as the
superconducting electrode and its surface oxide as the insulating tunnel
barrier, and investigate its efficacy in measuring spin-polarisation of
ferromagnets using the Meservey-Tedrow technique. We observe that for NbN film
thickness below 10 nm, under the application of parallel magnetic field, the
superconducting density of states show clear ""Zeeman"" splitting into spin-up
and spin-down sub-bands. Tunnelling measurements on devices where ferromagnetic
Co is used as the normal electrode shows that these devices can be used to
reliably measure spin polarisation of a ferromagnet at temperatures up to 1.6
K. The simplicity of our fabrication process, and the ability to perform
spin-polarisation measurements at 4He temperatures makes NbN a very attractive
candidate for spin polarisation measurements.",2209.01626v1
2022-09-08,Terahertz Magnetic and Lattice Excitations in van der Waals Ferromagnet VI3,"We use the synergy of infrared, terahertz, and Raman spectroscopies with DFT
calculations to shed light on the magnetic and lattice properties of VI3. The
structural transition at TS1 = 79 K is accompanied by a large splitting of
polar phonon modes. Below TS1, strong ferromagnetic fluctuations are observed.
The variations of phonon frequencies at 55 K induced by magnetoelastic coupling
enhanced by spin-orbit interaction indicate the proximity of long-range
ferromagnetic order. Below TC = 50 K, two Raman modes simultaneously appear and
show dramatic softening in the narrow interval around the temperature TS2 of
the second structural transition associated with the order-order magnetic phase
transition. Below TS2, a magnon in the THz range appears in Raman spectra. The
THz magnon observed in VI3 indicates the application potential of 2D van der
Waals ferromagnets in ultrafast THz spintronics, which has previously been
considered an exclusive domain of antiferromagnets.",2209.03725v2
2022-09-13,Spin-flip induced superfluidity in a ring of spinful hard-core bosons,"The t - J Hamiltonian of the spinful hard-core bosonic ring in the Nagaoka
limit is solved. The energy spectrum becomes quantized due to presence of spin,
where each energy level corresponds to a cyclic permutation state of the spin
chains. The ground state is true ferromagnetic when the ring contains N = 2, 3
spinful hard-core bosons; for all other N it is a mixture of the ferromagnetic
and non-ferromagnetic states. This behaviour is different from the fermionic
ring, where ground state is true ferromagnetic only for N = 3. It is shown that
the intrinsic spin generated gauge fields are analogous to the synthetic gauge
fields generated by rotation of either the condensate or the confining
potential. It is argued that the low lying excited levels of the spin flipped
states intrinsically support the superfluidity. Possible ways to experimentally
verify these results are also discussed.",2209.06149v1
2022-09-16,Observation of thermodynamics originating from a mixed-spin ferromagnetic chain,"We present a model compound that forms a mixed-spin ferromagnetic chain. Our
material design, based on the organic radicals, affords a verdazyl-based
complex (p-Py-V)2[Mn(hfac)2]. The molecular orbital calculations of the
compound indicate the formation of a mixed spin-(1/2, 1/2, 5/2) ferromagnetic
chain. The temperature dependence of magnetic susceptibility reveals its
ferromagnetic behavior. The magnetic specific heat exhibits a double-peak
structure and indicates a phase transition at the low-temperature peak. The
observed characteristics are explained using the quantum Monte Carlo
calculations. Furthermore, the modified spin-wave theory verifies that the
double-peak structure of the specific heat significantly reflects the relative
ration of the acoustic excitation band and the optical excitation gap.",2209.07681v1
2022-10-21,Spin-Dependent High-Order Topological Insulator and Two Types of Distinct Corner Modes in Monolayer FeSe/GdClO Heterostructure,"We propose that a spin-dependent second-order topological insulator can be
realized in monolayer FeSe/GdClO heterostructure, in which substrate GdClO
helps to stabilize and enhance the antiferromagnetic order in FeSe. The
second-order topological insulator is free from spin-orbit coupling and
in-plane magnetic field. We also find that there exist two types of distinct
corner modes residing in intersections of two ferromagnetic edges and two
antiferromagnetic edges, respectively. The underlying physics for ferromagnetic
corner mode follows a sublattice-chirality-kink picture. More interestingly,
ferromagnetic corner mode shows spin-dependent property, which is also robust
against spin-orbit coupling. Unexpectedly, antiferromagnetic corner mode can be
taken as a typical emergent and hierarchical phenomenon from an array of
ferromagnetic corner modes. Remarkably, antiferromagnetic corner modes violate
general kink picture and can be understood as bound states of a one-dimensional
Schrodinger equation under a connected potential well. Our findings not only
provide a promising second-order topological insulator in electronic materials,
but uncover some new properties of corner modes in high-order topological
insulator.",2210.11813v1
2022-10-27,Electron-phonon mediated spin-flip as driving mechanism for ultrafast magnetization dynamics in 3$d$ ferromagnets,"Despite intense experimental effort, theoretical proposals and modeling
approaches, a lack of consensus exists about the intrinsic mechanisms driving
ultrafast magnetization dynamics in 3$d$ ferromagnets. In this work, we find
evidence of electron-phonon mediated spin-flip as the driving mechanism for the
ultrafast magnetization dynamics in all three 3$d$ ferromagnets; nickel, iron
and cobalt. We use a microscopic three temperature model with parameters
calculated from first-principles, which has been validated by direct comparison
to the electron and lattice dynamics extracted from previous experiments. By
direct comparison to the experimentally measured magnetization dynamics for
different laser fluence, we determine the spin-flip probability of each
material. In contrast to previous findings but in agreement to ab-initio
predictions, we find that relatively small values of the spin-flip probability
enable ultrafast demagnetization in all three 3$d$ ferromagnets.",2210.15269v1
2022-11-29,Semiconducting Electronic Structure of the Ferromagnetic Spinel $\mathbf{Hg}\mathbf{Cr}_2\mathbf{Se}_4$ Revealed by Soft-X-Ray Angle-Resolved Photoemission Spectroscopy,"We study the electronic structure of the ferromagnetic spinel
$\mathrm{Hg}\mathrm{Cr}_2\mathrm{Se}_4$ by soft-x-ray angle-resolved
photoemission spectroscopy (SX-ARPES) and first-principles calculations. While
a theoretical study has predicted that this material is a magnetic Weyl
semimetal, SX-ARPES measurements give direct evidence for a semiconducting
state in the ferromagnetic phase. Band calculations based on the density
functional theory with hybrid functionals reproduce the experimentally
determined band gap value, and the calculated band dispersion matches well with
ARPES experiments. We conclude that the theoretical prediction of a Weyl
semimetal state in $\mathrm{Hg}\mathrm{Cr}_2\mathrm{Se}_4$ underestimates the
band gap, and this material is a ferromagnetic semiconductor.",2211.15884v2
2022-12-08,Impact of a ferromagnetic insulating barrier in magnetic tunnel junctions,"We investigate spin-dependent conductance across a magnetic tunnel junction
(MTJ) including a ferromagnetic insulating barrier. The MTJ consists of two
half-metallic ferromagnetic La2/3Sr1/3MnO3 (LSMO) manganites as electrodes and
La2NiMnO6 (LNMO) double perovskite as a ferromagnetic insulating barrier. The
resistance of the junction is strongly dependent not only on the orientation of
the magnetic moments in LSMO electrodes, but also on the direction of the
magnetization of the LNMO barrier with respect to that of LSMO. The ratio of
tunnel magnetoresistance reaches a maximum value of 24% at 10 K, and it
decreases with temperature until it completely disappears above the critical
temperature of LNMO at 280 K. The tunneling process is described using a
mechanism which involves both empty and filled eg states of the LNMO barrier
acting as a spin-filter. A magnetic insulating barrier is an interesting path
for achieving room temperature magnetoresistance in oxide-based
heterostructures.",2212.04416v1
2022-12-13,Non-local correlation effects due to virtual spin-flip processes in itinerant electron ferromagnets,"We present an ab initio method for eletcronic structure calculations, which
accounts for the interaction of electrons and magnons in ferromagnets. While it
is based on a many body perturbation theory we approximate numerically complex
quantities with quantities from time dependent density functional theory. This
results in a simple and affordable algorithm which allows us to consider more
complex materials than those usually studied in this context ($3d$
ferromagnets) while still being able to account for the non-locality of the
self energy. Furthermore, our approach allows for a relatively simple way to
incorporate self-consistency. Our results are in a good agreement with
experimental and theoretical findings for iron and nickel. Especially the
experimental exchange splitting of nickel is predicted accurately within our
theory. Additionally, we study the halfmetallic ferromagnet NiMnSb concerning
its non-qusiparticle states appearing in the bandgap due to spin-flip
excitations.",2212.06420v3
2023-02-11,Room Temperature d$^0$ Ferromagnetism in Carbon Doped LaH$_3$: Insights From Density Functional Theory Simulations,"Employing the state-of-the-art Density Functional Theory with both GGA and
hybrid HSE06 functional along with the incorporation of spin-orbit coupling, we
have engineered stable room temperature ferromagnetism in non-magnetic LaH$_3$
through C substitution at octahedral and tetrahedral H sites where the induced
magnetic moment is mostly contributed by 2p orbital of C atom. It is
interesting that the magnetic signature is switched on with an impurity
concentration as low as 1.04 at% with a magnetic moment of $\approx$ 1.0
$\mu_B$ per impurity, where the localized behavior of the 2p states of C along
with significant exchange splitting energy can be attributed as the origin of
the induced magnetic moment. The verification of the Stoner criterion in the
material further confirmed the onset of ferromagnetism in the system, and the
computed Curie temperature is found to be well above room temperature. Reduced
formation energy and requirement of lower impurity concentration ensure
practical feasibility towards a spintronic device where room temperature
ferromagnetism is established from the non-magnetic host and the dopant.",2302.05625v1
2023-03-02,"Synthesis and physical properties of a new layered ferromagnet, Cr1.21Te2","Single crystals of a new layered compound, Cr1.21Te2, was synthesized via a
vapor transport method. The crystal structure and physical properties were
characterized by single crystal and powder x-ray diffraction, temperature- and
field-dependent magnetization, zero-field heat capacity and angle-resolved
photoemission spectroscopy. Cr1.21Te2, containing two Cr sites, crystalizes in
a trigonal structure with a space group P-3 (No. 147). The Cr site in the
interstitial layer is partially occupied. Physical property characterizations
indicate that Cr1.21Te2 is metallic with hole pockets at the Fermi energy and
undergoes a ferromagnetic phase transition at ~173 K. The magnetic moments
align along the c-axis in the ferromagnetic state. Based on low temperature
magnetization, the spin stiffness constant D and spin excitation gap $\Delta$
were estimated according to Bloch's law to be D = 99 $\pm$ 24 meV $\r{A}^2$ and
$\Delta$ = 0.46 $\pm$ 0.33 meV, suggesting its possible application as a low
dimensional ferromagnet.",2303.00956v1
2023-04-19,Jahn-Teller distortion driven ferromagnetism in a perovskite fluoride monolayer,"The Jahn-Teller distortion and the resulting orbital order usually cause some
fascinating correlated electronic behaviors, and generally lead to
antiferromagnetism in perovskite bulks. Here we demonstrate that the
Jahn-Teller distortion present in the perovskite fluoride KCrF$_3$ bulk can be
retained to the two-dimensional limit, resulting in a staggered orbital order
and ferromagnetism in the perovskite monolayer. Octahedral tilt and rotation
distortion also appear in the ground-state structure of the perovskite
monolayer, which have minor effects on the electronic and magnetic properties
with respect to the Jahn-Teller distortion. In addition, in the prototype phase
without structural distortion, the partial occupation of the $e_g$ orbitals
leads to a ferromagnetic metallic state. This work facilitates the design of
two-dimensional ferromagnets and functional properties based on Jahn-Teller
distortion and orbital order",2304.09359v1
2023-04-19,Cavity magnomechanical coupling with coupled magnon modes in a synthetic antiferromagnet,"On-chip cavity magnomechanics is an emerging field exploring acoustic and
magnonic functionalities of various ferromagnetic materials and structures
using strongly confined phonons. It is expected that such cavity magnomechanics
can be extended to multilayer ferromagnets, especially synthetic
antiferromagnets (SAFs) that exhibit zero net magnetization through interlayer
exchange coupling. However, the conventional theoretical framework for a single
ferromagnet cannot be used directly because of the antiferromagnetic
magnetization dynamics associated with the interlayer exchange coupling. In
this paper, we theoretically investigate phonon-magnon coupling with a
three-layer SAF. Our formulation of the phonon-magnon coupling constants
reveals that the acoustic (optical) magnon mode dominantly couples to the
cavity phonon when the magnetization angles in the two ferromagnetic layers are
antiparallel (orthogonal). Moreover, numerical calculations including the
effects of dipole-dipole interactions and in-plane uniaxial magnetic anisotropy
allow us to predict phonon frequency shifts and linewidth broadening that can
be detected in experiments. These theoretical insights would greatly help us to
make a strategy for bringing the system into the strong coupling regime and to
devise novel control protocols in analogy to cavity quantum electrodynamics and
cavity optomechanics.",2304.09458v2
2023-04-22,Entanglement entropy for scale-invariant states: universal finite-size scaling,"A universal finite system-size scaling analysis of the entanglement entropy
is presented for highly degenerate ground states arising from spontaneous
symmetry breaking with type-B Goldstone modes in exactly solvable
one-dimensional quantum many-body systems. These states appear to be
scale-invariant, but not conformally invariant. Our findings are based on a
physical argument, imposing three constraints on the entanglement entropy, in
addition to further confirmation from an asymptotic analysis of the
entanglement entropy for the ${\rm SU}(2)$ spin-$1/2$ ferromagnetic states. The
resulting universal scaling form is demonstrated for three fundamental models
-- the ${\rm SU}(2)$ spin-$s$ Heisenberg ferromagnetic model, the ${\rm
SU}(N+1)$ ferromagnetic model, and the staggered ${\rm SU}(3)$ spin-1
ferromagnetic biquadratic model. The results point towards a classification for
distinct types of scale-invariant states, relevant to a complete classification
of quantum states of matter.",2304.11339v1
2023-05-09,Nagaoka ferromagnetism in doped Hubbard models in optical lattices,"The search for ferromagnetism in the Hubbard model has been a problem of
outstanding interest since Nagaoka's original proposal in 1966. Recent advances
in quantum simulation have today enabled the study of tunable doped Hubbard
models in ultracold atomic systems. Here, we examine a realistic variant of
such a model wherein any second electron on a single lattice site is weakly
bound compared to the first one. Employing large-scale density-matrix
renormalization group calculations, we establish the existence of high-spin
ground states on square and triangular lattices, analyze the microscopic
mechanisms behind their origin, and investigate the interplay between
ferromagnetism and other competing orders, such as stripes. Our results also
explain$\unicode{x2014}$and shed new light on$\unicode{x2014}$the intriguing
observations of ferromagnetic correlations in recent optical-lattice
experiments.",2305.05683v1
2023-05-10,Electron doping induced stable ferromagnetism in two-dimensional GdI_3 monolayer,"As a two-dimensional material with a hollow hexatomic ring structure,
N\'eel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to
study the effect of electron doping. Based on first-principles calculations, we
find that the Fermi surface nesting occurs when more than 1/3 electron per Gd
is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state.
More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns
to be half-metallic FM state. This AFM-FM transition results from the transfer
of doped electrons to the spatially expanded Gd-5d orbital, which leads to the
FM coupling of local half-full Gd-4f electrons through 5d-4f hybridization.
Moreover, the shortened Gd-Gd length is the key to the formation of the stable
ferromagnetic coupling. Our method provides new insights into obtaining stable
FM materials from AFM materials.",2305.05872v1
2023-05-31,Pressure evolution of electronic structure and magnetism in the layered van der Waals ferromagnet CrGeTe$_3$,"Layered van der Waals ferromagnets, which preserve their magnetic properties
down to exfoliated monolayers, are fueling an abundance of fundamental research
and nanoscale device demonstration. CrGeTe$_3$ is a prime example for this
class of materials. Its temperature-pressure phase diagram features an
insulator-to-metal transition and a significant increase of ferromagnetic
Curie-Weiss temperatures upon entering the metallic state. We use density
functional theory to understand the magnetic exchange interactions in
CrGeTe$_3$ at ambient and elevated pressure. We calculate Heisenberg exchange
couplings, which provide the correct ferromagnetic ground state and explain the
experimentally observed pressure dependence of magnetism in CrGeTe$_3$.
Furthermore, we combine density functional theory with dynamical mean field
theory to investigate the effects of electronic correlations and the nature of
the high pressure metallic state in CrGeTe$_3$.",2306.00081v2
2023-06-01,Ferromagnetic phase transitions in $SU(N)$,"We study the thermodynamics of a non-abelian ferromagnet consisting of
""atoms"" each carrying a fundamental representation of $SU(N)$, coupled with
long-range two-body quadratic interactions. We uncover a rich structure of
phase transitions from non-magnetized, global $SU(N)$-invariant states to
magnetized ones breaking global invariance to $SU(N-1) \times U(1)$. Phases can
coexist, one being stable and the other metastable, and the transition between
states involves latent heat exchange, unlike in usual $SU(2)$ ferromagnets.
Coupling the system to an external non-abelian magnetic field further enriches
the phase structure, leading to additional phases. The system manifests
hysteresis phenomena both in the magnetic field, as in usual ferromagnets, and
in the temperature, in analogy to supercooled water. Potential applications are
in fundamental situations or as a phenomenological model.",2306.01051v3
2023-06-23,Spin transport between polarized Fermi gases near the ferromagnetic phase transition,"We theoretically study the spin current between two polarized Fermi gases
with repulsive interactions near the itinerant ferromagnetic phase transition.
We consider a two-terminal model where the left reservoir is fixed to be fully
polarized while the polarization of the right reservoir is tuned through a
fictitious magnetic field defined by the chemical-potential difference between
different atomic hyperfine states. We calculate the spectra of the spin-flip
susceptibility function, which displays a magnon dispersion emerging from the
Stoner continuum at low momentum in the ferromagnetic phase. Based on the
spin-flip susceptibility and using Keldysh Green's function formalism, we
investigate the spin current induced by quasiparticle and spin-flip tunneling
processes, respectively, and show their dependence on the polarization bias
between two reservoirs. The one-body (quasiparticle) tunneling demonstrates a
linear dependence with respect to the polarization bias. In contrast, the
spin-flip process manifests a predominantly cubic dependence on the bias. While
indicating an enhanced magnon tunneling in the strong-coupling regime, our
results also demonstrate a characteristic behavior around the critical
repulsive strength for ferromagnetic phase transition at low temperatures.",2306.13536v2
2023-07-08,Magnon influence on the superconducting density of states in superconductor$-$ferromagnetic-insulator bilayers,"Superconductor$-$ferromagnetic-insulator heterostructures are paradigmatic
systems for studying the mutual influence of superconductivity and magnetism
via proximity effects. In particular, spin-split superconductivity is realized
in such structures. Recent experiments and theories demonstrate a rich variety
of transport phenomena occurring in devices based on such heterostructures that
suggest direct applications in thermoelectricity, low-dissipative spintronics,
radiation detection, and sensing. In this work we investigate the influence of
the electron-magnon interaction at the superconductor$-$ferromagnetic-insulator
interface on the spin-split superconductivity. It is predicted that due to the
magnon-mediated electron spin-flip processes the spin-split quasiparticle
branches are partially mixed and reconstructed, and the BCS-like spin-split
shape of the superconducting density of states, which is typical for
superconductors in the effective exchange field, is strongly modified. An
odd-frequency superconducting order parameter admixture to the leading singlet
order parameter is also found. These findings expand the physical picture of
spin-split superconductivity beyond the mean-field description of the
ferromagnet exchange field.",2307.03954v2
2023-07-10,Porous CrO$_2$: a ferromagnetic half-metallic member in sparse hollandite oxide family,"A stable polymorph of CrO$_2$ is predicted using PBE+U method. The porous
material is isostructural with $\alpha$-MnO$_2$ making it the second transition
metal oxide in sparse hollandite group of materials. However, unlike the
anti-ferromagnetic semiconducting character of the $\alpha$-MnO$_2$, it is
found to be a ferromagnetic half-metal. At Fermi level, the hole pocket has
ample contribution from O-2$p$ orbital, though, the electron pocket is mostly
contributed by Cr-3$d_{xy}$ and Cr-3d$_{x^2-y^2}$. A combination of negative
charge transfer through orbital mixing and extended anti-bonding state near
Fermi level is responsible for the half-metallic ferromagnetic character of the
structure. A comparative study of rutile and hollandite CrO$_2$ and hollandite
MnO$_2$ structures delineate the interplay between structural, electronic and
magnetic properties. The material shows a robust magnetic character under
hydrothermal pressure, as well as, the band topology is conserved under
uniaxial strain. Moderate magneto-crystalline anisotropy is observed and it
shows a correspondence with the anisotropy of elastic constants.",2307.04584v1
2023-07-20,Superconductivity Induced Ferromagnetism In The Presence of Spin-Orbit Coupling,"We investigate the behavior of magnetic impurities placed on the surface of
superconductor thin films with spin-orbit coupling. Our study reveals
long-range interactions between the impurities, which decay according to a
power law, mediated by the supercurrents. Importantly, these interactions
possess a ferromagnetic component when considering the influence of the
electromagnetic field, leading to the parallel alignment of the magnetic
moments in the case of two impurities. In a Bravais lattice of magnetic
impurities, superconductivity facilitates the establishment of ferromagnetic
order within specific parameter ranges. These findings challenge the
conventional understanding that ferromagnetism and superconductivity are
mutually exclusive phenomena. Our theoretical framework provides a plausible
explanation for the recently observed remanent flux in iron-based
superconductors, particularly Fe(Se,Te).",2307.10723v3
2023-07-29,Unveiling Exotic Magnetic Phases in Fibonacci Quasicrystalline Stacking of Ferromagnetic Layers through Machine Learning,"In this study, we conduct a comprehensive theoretical analysis of a Fibonacci
quasicrystalline stacking of ferromagnetic layers, potentially realizable using
van der Waals magnetic materials. We construct a model of this magnetic
heterostructure, which includes up to second neighbor interlayer magnetic
interactions, that displays a complex relationship between geometric
frustration and magnetic order in this quasicrystalline system. To navigate the
parameter space and identify distinct magnetic phases, we employ a machine
learning approach, which proves to be a powerful tool in revealing the complex
magnetic behavior of this system. We offer a thorough description of the
magnetic phase diagram as a function of the model parameters. Notably, we
discover among other collinear and non-collinear phases, a unique ferromagnetic
alternating helical phase. In this non-collinear quasiperiodic ferromagnetic
configuration the magnetization decreases logarithmically with the stack
height.",2307.16052v1
2023-08-06,Ferromagnetic half levitation of LK-99-like synthetic samples,"We successfully synthesized polycrystalline LK-99-like ceramic samples with a
solid-state-sintering method. Powder X-ray diffraction shows that the main
contents are $\mathrm{Pb_{10-x}Cu_x(PO_4)_6O}$ and $\mathrm{Cu_2S}$, consistent
with recent reports [arXiv:2307.12037; arXiv:2308.01192]. In some small flaky
fragments, we successfully observed ``half levitation'' atop a
$\mathrm{Nd_2Fe_{14}B}$ magnet. Using magnetization measurements on such small
pieces, as well as on a large piece which does not exhibit the half levitation,
we show that the samples ubiquitously contain weak yet definitive soft
ferromagnetic components. We argue that, together with the pronounced shape
anisotropy of the small fragments, the soft ferromagnetism is sufficient to
explain the observed half levitation in strong vertical magnetic fields. Our
measurements do not indicate the presence of the Meissner effect, nor zero
resistance, in our samples, leading us to believe that our samples do not
exhibit superconductivity. The precise chemical composition and the physics
behind the ferromagnetic component remain outstanding questions to be addressed
in future research.",2308.03110v2
2023-08-21,Two-orbital spin-fermion model study of ferromagnetism in honeycomb lattice,"The spin-fermion model was previously successful to describe the complex
phase diagrams of colossal magnetoresistive manganites and iron-based
superconductors. In recent years, two-dimensional magnets have rapidly raised
up as a new attractive branch of quantum materials, which are theoretically
described based on classical spin models in most studies. Alternatively, here
the two-orbital spin-fermion model is established as a uniform scenario to
describe the ferromagnetism in a two-dimensional honeycomb lattice. This model
connects the magnetic interactions with the electronic structures. Then the
continuous tuning of magnetism in these honeycomb lattices can be predicted,
based on a general phase diagram. The electron/hole doping, from the empty
$e_{g}$ to half-filled $e_{g}$ limit, is studied as a benchmark. Our Monte
Carlo result finds that the ferromagnetic $T_{C}$ reaches the maximum at the
quarter-filled case. In other regions, the linear relationship between $T_{C}$
and doping concentration provides a theoretical guideline for the experimental
modulations of two-dimensional ferromagnetism tuned by ionic liquid or
electrical gating.",2308.10535v1
2023-08-21,Photoinduced topological phase transitions in Kitaev-Heisenberg honeycomb ferromagnets with the Dzyaloshinskii-Moriya interaction,"We theoretically study topological properties of Floquet magnon in a
laser-irradiated Kitaev-Heisenberg honeycomb ferromagnet with the
Dzyaloshinskii-Moriya interaction by means of the Floquet-Bloch theory. It is
found that the Kitaev-Heisenberg ferromagnet can reveal two topological phases
with different Chern numbers when it is irradiated by a circular-polarized
light laser. Our results show that the topological phase of the system can be
switched from one topological phase to another one via varying the light
intensity. The intrinsic DMI plays a crucial role in the occurrence of
photoinduced topological phase transition. It is shown that the sign reversal
of the thermal hall conductivity is an important indicator on photoinduced
topological phase transitions in the Kitaev-Heisenberg honeycomb ferromagnet.",2308.11077v1
2023-08-30,Impact of epitaxial strain relaxation on ferromagnetism in a freestanding La2/3Sr1/3MnO3 membrane,"Manganite perovskites host emerging physical properties of
strongly-correlated electrons with charge, spin, and lattice degrees of
freedom. Using epitaxial lift-off technique, we report enhancement of
saturation magnetization and ferromagnetic transition temperature of the
freestanding La2/3Sr1/3MnO3 membrane compared with the as-grown film on SrTiO3
substrate involving lateral tensile strain. Structural analysis reveals
shrinkage of unit-cell volume by tensile strain relaxation in the freestanding
membrane, which causes enhancement of the ferromagnetic interaction. The impact
of the microscopic lattice deformation on the ferromagnetism of La2/3Sr1/3MnO3
indicates a high potential of this material for flexible electronics
application with intriguing functionalities in strongly-correlated electron
systems.",2308.16045v1
2023-09-12,Non-constant ground configurations in the disordered ferromagnet,"The disordered ferromagnet is a disordered version of the ferromagnetic Ising
model in which the coupling constants are non-negative quenched random. A
ground configuration is an infinite-volume configuration whose energy cannot be
reduced by finite modifications. It is a long-standing challenge to ascertain
whether the disordered ferromagnet on the $\mathbb{Z}^D$ lattice admits
non-constant ground configurations. We answer this affirmatively in dimensions
$D\ge 4$, when the coupling constants are sampled independently from a
sufficiently concentrated distribution. The obtained ground configurations are
further shown to be translation-covariant with respect to $\mathbb{Z}^{D-1}$
translations of the disorder.
  Our result is proved by showing that the finite-volume interface formed by
Dobrushin boundary conditions is localized, and converges to an infinite-volume
interface. This may be expressed in purely combinatorial terms, as a result on
the fluctuations of certain minimal cutsets in the lattice $\mathbb{Z}^D$
endowed with independent edge capacities.",2309.06437v2
2023-09-16,Investigation of the Anomalous and Topological Hall Effects in Layered Monoclinic Ferromagnet Cr$_{2.76}$Te$_4$,"We studied the electrical transport, Hall effect, and magnetic properties of
monoclinic layered ferromagnet Cr$_{2.76}$Te$_4$. Our studies demonstrate
Cr$_{2.76}$Te$_4$ to be a soft ferromagnet with strong magnetocrystalline
anisotropy. Below 50 K, the system shows an antiferromagnetic-like transition.
Interestingly, between 50 and 150 K, we observe fluctuating magnetic moments
between in-plane and out-of-plane orientations, leading to non-coplanar spin
structure. On the other hand, the electrical resistivity data suggest it to be
metallic throughout the measured temperature range, except a $kink$ at around
50 K due to AFM ordering. The Rhodes-Wohlfarth ratio
$\frac{\mu_{eff}}{\mu_{s}}=1.89 (>1)$ calculated from our magnetic studies
confirms that Cr$_{2.76}$Te$_4$ is an itinerant ferromagnet. Large anomalous
Hall effect has been observed due to the skew-scattering of impurities and the
topological Hall effect has been observed due to non-coplanar spin-structure in
the presence of strong magnetocrystalline anisotropy. We examined the mechanism
of anomalous Hall effect by employing the first principles calculations.",2309.08898v1
2023-09-16,Electronic and Topological Properties of a Topological Insulator Thin Film Sandwiched between Ferromagnetic Insulators,"We consider a thin film of a topological insulator (TI) sandwiched between
two ferromagnetic (FM) layers. The system is additionally under an external
gate voltage. The surface electron states of TI are magnetized due to the
magnetic proximity effect to the ferromagnetic layers. The magnetization of
ferromagnetic layers can be changed by applying an external magnetic field or
by varying thickness of the topological insulator (owing to the interlayer
exchange coupling). The change in the magnetic configuration of the system
affects the transport properties of the surface electronic states. Using the
Green function formalism, we calculate spin polarization, anomalous Hall
effect, and magnetoresistance of the system. We show, among others, that by
tuning the gate voltage and magnetizations of the top and bottom FM layers, one
can observe the topological transition to the anomalous quantum Hall state.",2309.09014v1
2023-09-26,Orbital Pumping by Magnetization Dynamics in Ferromagnets,"We show that dynamics of the magnetization in ferromagnets can pump the
orbital angular momentum, which we denote by orbital pumping. This is the
reciprocal phenomenon to the orbital torque that induces magnetization dynamics
by the orbital angular momentum in non-equilibrium. The orbital pumping is
analogous to the spin pumping established in spintronics but requires the
spin-orbit coupling for the orbital angular momentum to interact with the
magnetization. We develop a formalism that describes the generation of the
orbital angular momentum by magnetization dynamics within the adiabatic
perturbation theory. Based on this, we perform first-principles calculation of
the orbital pumping in prototypical $3d$ ferromagnets, Fe, Co, and Ni. The
results show that the ratio between the orbital pumping and the spin pumping
ranges from 5 to 15 percents, being smallest in Fe and largest in Ni. This
implies that ferromagnetic Ni is a good candidate for measuring the orbital
pumping. Implications of our results on experiments are also discussed.",2309.14817v2
2023-09-27,Goodenough-Kanamori-Anderson high-temperature ferromagnetism in tetragonal transition-metal xenes,"Seminal Goodenough-Kanamori-Anderson (GKA) rules provide the inceptive
understanding of the superexchange interaction of two magnetic metal ions
bridged with an anion, and suggest fostered ferromagnetic interaction for
orthogonal bridging bonds. However, there are no examples of two-dimensional
(2D) materials with structure that optimizes the GKA arguments towards enhanced
ferromagnetism and its critical temperature. Here we reveal that an ideally
planar GKA ferromagnetism is indeed stable in selected tetragonal
transition-metal xenes (tTMXs), with Curie temperature above 300~K found in CrC
and MnC. We provide the general orbitally-resolved analysis of magnetic
interactions that supports the claims and sheds light at the mechanisms
dominating the magnetic exchange process in these structures. With recent
advent of epitaxially-grown tetragonal 2D materials, our findings earmark tTMXs
for facilitated spintronic and magnonic applications, or as a desirable
magnetic constituent of functional 2D heterostructures.",2309.15445v1
2023-10-13,Magnon spin capacitor,"In this work we show that a magnon spin capacitor can be realized at a
junction between two exchange coupled ferromagnets. In this junction, the
buildup of magnon spin over the junction is coupled to the difference in magnon
chemical potential, realizing the magnon spin analogue of an electrical
capacitor. The relation between magnon spin and magnon chemical potential
difference directly follows from considering the magnon density-density
interaction between the two ferromagnets. We analyse the junction in detail by
considering spin injection and detection from normal metal leads, the tunneling
current across the junction and magnon decay within the ferromagnet, showing
that such a structure realizes a magnon spin capacitor in series with a spin
resistor. Choosing yttrium iron garnet as the ferromagnet, we numerically
calculate the capacitance, which ranges from picofarad to microfarad, depending
on the area of the junction. We therefore conclude that the magnon spin
capacitor could directly be of use in applications.",2310.09064v3
2023-11-18,Design of spin-orbital-textures in ferromagnetic/topological insulator interfaces,"Spin-orbital textures in topological insulators due to the spin locking with
the electron momentum, play an important role in spintronic phenomena that
arise from the interplay between charge and spin degrees of freedom. We have
explored interfaces between a ferromagnetic system (CrI$_3$) and a topological
insulator (Bi$_2$Se$_3$) that allow the manipulation of spin-orbital textures.
Within an {\it ab initio} approach we have extracted the spin-orbital-textures
dependence of experimentally achievable interface designs. The presence of the
ferromagnetic system introduces anisotropic transport of the electronic spin
and charge. From a parameterized Hamiltonian model we capture the anisotropic
backscattering behavior, showing its extension to other
ferromagnetic/topological insulator interfaces. We verified that the van der
Waals TI/MI interface is an excellent platform for controlling the spin degree
of freedom arising from topological states, providing a rich family of
unconventional spin texture configurations.",2311.11084v1
2023-11-21,Influence of interlayer exchange coupling on ultrafast laser-induced magnetization reversal in ferromagnetic spin valves,"In this study, we explore the influence of interlayer exchange coupling on
magnetization reversal triggered by femtosecond laser pulses in ferromagnetic
spin valves. Our experiments, focused on femtosecond laser-induced
magnetization reversal, methodically vary the thickness of the copper (Cu)
spacer layer. We identify a critical Cu thickness threshold at 2.32 nm. Above
this threshold, a stable reversed magnetic domain is consistently generated
upon exposure to a single laser pulse. Conversely, with a Cu spacer thinner
than 2.32 nm, the observed magnetization reversal from parallel (P) to
anti-parallel (AP) states occurs only under continuous laser irradiation. Once
the laser is stopped, the magnetic configuration relaxes back to its initial P
state, influenced by ferromagnetic exchange coupling. This research enhances
our understanding of the mechanisms that drive optically induced ultrafast
magnetization reversal in ferromagnetic spin valves.",2311.12753v2
2023-11-27,Gilbert damping in two-dimensional metallic anti-ferromagnets,"A finite spin life-time of conduction electrons may dominate Gilbert damping
of two-dimensional metallic anti-ferromagnets or anti-ferromagnet/metal
heterostructures. We investigate the Gilbert damping tensor for a typical
low-energy model of a metallic anti-ferromagnet system with honeycomb magnetic
lattice and Rashba spin-orbit coupling for conduction electrons. We distinguish
three regimes of spin relaxation: exchange-dominated relaxation for weak
spin-orbit coupling strength, Elliot-Yafet relaxation for moderate spin-orbit
coupling, and Dyakonov-Perel relaxation for strong spin-orbit coupling. We
show, however, that the latter regime takes place only for the in-plane Gilbert
damping component. We also show that anisotropy of Gilbert damping persists for
any finite spin-orbit interaction strength provided we consider no spatial
variation of the N\'eel vector. Isotropic Gilbert damping is restored only if
the electron spin-orbit length is larger than the magnon wavelength. Our theory
applies to MnPS3 monolayer on Pt or to similar systems.",2311.16268v2
2023-12-28,Anomalous exchange bias effect in ferromagnetic VI3 flakes,"The exchange bias (EB) effect, pivotal in magnetic data storage and sensing
devices, has been observed not only in interfacial regions but also in
intrinsic ferromagnetic materials. Here, we've uncovered a robust and stable
exchange bias effect within the layered van der Waals (vdW) ferromagnet VI3
employing magnetic circular dichroism microscopy. At 10 K, we observed a
significant exchange field of approximately 0.1 T, accompanied by random shifts
(positive or negative relative to zero magnetic field) after zero-field
cooling. Notably, this effect is effectively controllable after field cooling,
with shift direction opposing the applied magnetic field. The presence of
strong magnetic anisotropic energy within VI3 results in larger
coercivity-bound magnetic domains. These domains dictate the neighboring
ferromagnetic alignment and induce shifts in the hysteresis loop. Our study not
only contributes to comprehending fundamental nanoscale magnetic interactions
but also sheds light on emergent phenomena within layered van der Waals
magnets.",2312.16899v1
2023-12-29,Prediction of Magnetic State of UO2 within Hubbard-corrected Density-Functional Theory: A self-consistent approach,"The magnetic state of UO$_2$ was determined experimentally to be
anti-ferromagnetic. Starting from this experimental fact, researchers have
calculated other properties within the Hubbard-corrected density-functional
theory, DFT+U. Up to now, the Hubbard parameters for UO$_2$ were usually so
chosen that the calculations give good results for some experimental data.
Also, to our knowledge there exists no valid theoretical research report on the
energetically stable magnetic state of this system. In present work, employing
the new method which is based on density-functional perturbation theory, we
have determined self-consistently the Hubbard parameters and ground-state
energies for UO$_2$ crystal in both ferromagnetic and anti-ferromagnetic
configurations, and the calculated results show that UO$_2$ crystal
energetically favors an anti-ferromagnetic state with a small energy
difference. In all the calculations the PBE-sol approximation was used for the
exchange-correlation energy functional.",2401.00864v1
2024-01-07,Deformation of a planar ferromagnetic elastic ribbon,"While extensive studies have been conducted on purely elastic ribbons, in
this paper we explore the influence of magnetisation on the deformation of
planar ferromagnetic elastic ribbons. We begin the investigation by deriving
the leading-order magnetic energy associated with a curved planar ferromagnetic
elastic ribbon. The sum of the magnetic and the elastic energy is the total
energy of the ribbon. We derive the equilibrium equations by taking the first
variation of the total energy. We then systematically determine and analyse
solutions to these equilibrium equations under various canonical boundary
conditions. We also analyse the stability of the equilibrium solutions.
Comparing our findings with the well-studied Euler's Elastica provides insights
into the magnetic effects on the deformation behaviour of elastic ribbons. Our
analysis contributes to a deeper understanding of the interplay between
magnetisation and the mechanical response of planar ferromagnetic structures,
and offers valuable insights for both theoretical and practical applications.",2401.03447v1
2024-01-13,Field theory of collinear and noncollinear magnetic order,"These lecture notes from the 2023 Summer ""School Principles and Applications
of Symmetry in Magnetism"" introduce the reader to the classical field theory of
ferromagnets and antiferromagnets.",2401.07171v1
2024-01-23,Superfluid transition of a ferromagnetic Bose gas,"The strongly ferromagnetic spin-1 Bose-Einstein condensate (BEC) has recently
been realized with atomic $^{7}$Li. It was predicted that a strong
ferromagnetic interaction can drive the normal gas into a magnetized phase at a
temperature above the superfluid transition, and $^{7}$Li likely satisfies the
criterion. We re-examine this theoretical proposal employing the
two-particle-irreducible (2PI) effective potential, and conclude that there
exists no stable normal magnetized phase for a dilute ferromagnetic Bose gas.
For $^{7}$Li, we predict that the normal gas undergoes a joint first order
transition and jump directly into a state with finite condensate density and
magnetization. We estimate the size of the first order jump, and examine how a
partial spin polarization in the initial sample affects the first order
transition. We propose a qualitative phase diagram at fixed temperature for the
trapped gas.",2401.12541v1
2024-01-31,Giant Anomalous Hall and Nernst Effects in a Heavy Fermion Ferromagnet,"The anomalous Hall and Nernst effects describe the voltage drop perpendicular
to an applied current and temperature gradient due to the magnetization of a
magnetic material. These effects can be utilized to measure the Berry curvature
at the Fermi energy, and have potential applications in future electronic
devices and thermoelectric energy conversion. In this paper, we report giant
anomalous Hall conductivity and anomalous Nernst coefficient, as high as about
1000 $\Omega^{-1}$ cm$^{-1}$ and 10 $\mu$V K$^{-1}$, respectively, in a heavy
fermion ferromagnet, CeCrGe$_3$. This compound uniquely manifests strong
hybridization between the 4$f$ and conduction electrons, leading to a Kondo
lattice state in the presence of ferromagnetic order. Unlike conventional
topological semimetals in which the electron correlation is weak, CeCrGe$_3$
manifests a strong Berry curvature field of the heavy fermion with an extremely
low Fermi energy. Our findings pave the way for exploring correlation-driven
topological responses in a ferromagnetic Kondo lattice environment.",2401.17624v1
2024-02-02,Coexistence of Ferromagnetism and Antiferromagnetic Dimers in Topological Insulators,"The addition of magnetic impurities in topological insulators can drive
ferromagnetic order that leads to novel quantum anomalous Hall transport well
below the Curie temperature. The fragility of the quantized regime has been
ascribed to the random nature of the magnetic moment distribution. Here, we
refine this hypothesis by using inelastic neutron scattering and
density-functional theory calculations to show that two antagonistic components
define the magnetism in Mn-substituted SnTe, thereby limiting the effectiveness
of dilute magnetic TIs. One component is strongly bound antiferromagnetic
dimers that compete with ferromagnetic order. The other component consists of
undimerized moments where ferromagnetic order develops via long-range
interactions.",2402.01531v1
2024-03-04,Half-Metallic Ferromagnetic Weyl Fermions Related to Dynamic Correlations in the Zinc-blende Compound VAs,"The realization of 100\% polarized topological Weyl fermions in half-metallic
ferromagnets is of particular importance for fundamental research and
spintronic applications. Here, we theoretically investigate the electronic and
topological properties of the zinc-blende compound VAs, which was deemed as a
half-metallic ferromagnet related to dynamic correlations. Based on the
combination of density functional theory and dynamical mean field theory, we
uncover that the half-metallic ferromagnet VAs exhibit attractive Weyl
semimetallic behaviors with twelve pairs of Weyl points, which are very close
to the Fermi level. Meanwhile, we also investigate the magnetization-dependent
topological properties; the results show that the change of magnetization
directions only slightly affects the positions of Weyl points, which is
attributed to the weak spin-orbital coupling effects. The topological surface
states of VAs projected on semi-infinite (001) and (111) surfaces are
investigated. The Fermi arcs of all Weyl points are clearly visible on the
projected Fermi surfaces. Our findings suggest that VAs is a fully
spin-polarized Weyl semimetal with many-body correlated effects for spintronic
applications.",2403.02157v2
2024-03-18,Numerical observation of $\mathrm{SU}(N)$ Nagaoka ferromagnetism,"We provide numerical evidence of the Nagaoka's theorem in the
$\mathrm{SU}(N)$ Fermi-Hubbard model on various cluster geometries, such as the
square, the honeycomb and the triangular lattices. In particular, by
diagonalizing several finite-size clusters, we show that for one hole away from
filling $1/N$, the itinerant ferromagnetism arises for $U$ (the positive
on-site interaction) larger than $U_c$ (the value at the transition), which
strongly depends on the coordination number $z$ and on $N$, the number of
degenerate orbitals, that we vary from $N=2$ to $N=6$ in our simulations. We
prove that $U_c$ is a non decreasing function of $N$. In addition, we find that
the lattice dependency is rooted in the kinetic energy of the hole. We find
that large coordination numbers $z$ lower the value of $U_c$. Complementary, we
explore the effect of long-range hopping on the appearance of itinerant
ferromagnetism and demonstrate that it acts as an increased coordination
number, protecting the ferromagnetic phase at small $U$. Finally, both the
effects of the presence of some additional holes and of the finite size of the
clusters are briefly discussed.",2403.11588v1
2024-03-20,Dipole-dipole-interaction-induced entanglement between two-dimensional ferromagnets,"We investigate the viability of dipole-dipole interaction as a means of
entangling two distant ferromagnets. To this end we make use of the Bogoliubov
transformation as a symplectic transformation. We show that the coupling of the
uniform magnon modes can be expressed using four squeezing parameters which we
interpret in terms of hybridization, one-mode and two-mode squeezing. We
utilize the expansion in terms of the squeezing parameters to obtain an
analytic formula for the entanglement in the magnon ground state using the
logarithmic negativity as entanglement measure. Our investigation predicts that
for infinitely large two-dimensional ferromagnets, the dipole-dipole
interaction does not lead to significant long-range entanglement. However, in
the case of finite ferromagnets, finite entanglement can be expected",2403.13354v1
1998-02-25,Extensive spiral structure and corotation resonance,"Spiral density wave theories demand that grand design spiral structure be
bounded, at most, between the inner and outer Lindblad resonances of the spiral
pattern. The corotation resonance lies between the outer and inner Lindblad
resonances. The locations of the resonances are at radii whose ratios to each
other are rather independent of the shape of the rotation curve. The measured
ratio of outer to inner extent of spiral structure for a given spiral galaxy
can be compared to the standard ratio of corotation to inner Lindblad resonance
radius. In the case that the measured ratio far exceeds the standard ratio, it
is likely that the corotation resonance is within the bright optical disk.
Studying such galaxies can teach us how the action of resonances sculpts the
appearance of spiral disks. This paper reports observations of 140 disk
galaxies, leading to resonance ratio tests for 109 qualified spirals. It lists
candidates that have a good chance of having the corotation resonance radius
within the bright optical disk.",9802325v1
2006-06-29,Parametric coupling between macroscopic quantum resonators,"Time-dependent linear coupling between macroscopic quantum resonator modes
generates both a parametric amplification also known as a {}""squeezing
operation"" and a beam splitter operation, analogous to quantum optical systems.
These operations, when applied properly, can robustly generate entanglement and
squeezing for the quantum resonator modes. Here, we present such coupling
schemes between a nanomechanical resonator and a superconducting electrical
resonator using applied microwave voltages as well as between two
superconducting lumped-element electrical resonators using a r.f.
SQUID-mediated tunable coupler. By calculating the logarithmic negativity of
the partially transposed density matrix, we quantitatively study the
entanglement generated at finite temperatures. We also show that
characterization of the nanomechanical resonator state after the quantum
operations can be achieved by detecting the electrical resonator only. Thus,
one of the electrical resonator modes can act as a probe to measure the
entanglement of the coupled systems and the degree of squeezing for the other
resonator mode.",0606787v2
2007-03-06,Dynamical instabilities of a resonator driven by a superconducting single-electron transistor,"We investigate the dynamical instabilities of a resonator coupled to a
superconducting single-electron transistor (SSET) tuned to the Josephson
quasiparticle (JQP) resonance. Starting from the quantum master equation of the
system, we use a standard semiclassical approximation to derive a closed set of
mean field equations which describe the average dynamics of the resonator and
SSET charge. Using amplitude and phase coordinates for the resonator and
assuming that the amplitude changes much more slowly than the phase, we explore
the instabilities which arise in the resonator dynamics as a function of
coupling to the SSET, detuning from the JQP resonance and the resonator
frequency. We find that the locations (in parameter space) and sizes of the
limit cycle states predicted by the mean field equations agree well with
numerical solutions of the full master equation for sufficiently weak
SSET-resonator coupling. The mean field equations also give a good qualitative
description of the set of dynamical transitions in the resonator state that
occur as the coupling is progressively increased.",0703150v1
1999-04-08,Analysis of Narrow s-channel Resonances at Lepton Colliders,"The procedures for studying a single narrow s-channel resonance or nearly
degenerate resonances at a lepton collider, especially a muon collider, are
discussed. In particular, we examine four methods for determining the
parameters of a narrow s-channel resonance: scanning the resonance, measuring
the convoluted cross section, measuring the Breit-Wigner area, and sitting on
the resonance while varying the beam energy resolution. This latter procedure
is new and appears to be potentially very powerful. Our focus is on computing
the errors in resonance parameters resulting from uncertainty in the beam
energy spread. Means for minimizing these errors are discussed. The discussion
is applied to the examples of a light SM-Higgs, of the lightest pseudogoldstone
boson of strong electroweak breaking, and of the two spin-1 resonances of the
Degenerate BESS model (assuming that the beam energy spread is less than their
mass splitting). We also examine the most effective procedures for nearly
degenerate resonances, and apply these to the case of Degenerate BESS
resonances with mass splitting of order the beam energy spread.",9904268v1
2004-10-05,"Above-well, Stark, and potential-barrier resonances of an open square well in a static external electric field","Besides the well known Stark resonances, which are localized in the potential
well and tunnel through the potential barrier created by the dc-field,
""strange"" long and short-lived resonances are analytically obtained. These
resonances are not localized inside the potential well. We show that the narrow
ones are localized above the potential well. These narrow resonances give rise
to a {\it peak structure} in a 1D scattering experiment. We also show that the
broad overlapping resonances are associated with the static electric field
potential barrier. These ""strange"" overlapping resonances do not give rise to a
{\it peak structure} in a 1D scattering experiment. We propose a 2D
experimental set-up where in principle these short-lived states should be
observed as {\it peaks}. Broad overlapping resonances, associated only with the
static electric field potential barrier, could also have observable effects in
a $N>1$ array of quantum wells in the presence of a truncated static electric
field. This last problem is associated with the resonance tunnelling phenomena
which are used in the construction of resonance-tunnelling diodes and
transistors.",0410026v1
2007-06-26,Dynamical Response of Nanomechanical Resonators to Biomolecular Interactions,"We studied the dynamical response of a nanomechanical resonator to
biomolecular (e.g. DNA) adsorptions on a resonator's surface by using a
theoretical model, which considers the Hamiltonian H such that the potential
energy consists of elastic bending energy of a resonator and the potential
energy for biomolecular interactions. It was shown that the resonant frequency
shift of a resonator due to biomolecular adsorption depends on not only the
mass of adsorbed biomolecules but also the biomolecular interactions.
Specifically, for dsDNA adsorption on a resonator's surface, the resonant
frequency shift is also dependent on the ionic strength of a solvent, implying
the role of molecular interactions on the dynamic behavior of a resonator. This
indicates that nanomechanical resonators may enable one to quantify the
biomolecular mass, implying the enumeration of biomolecules, as well as gain
insight into intermolecular interactions between adsorbed biomolecules on the
surface.",0706.3743v3
2007-08-06,Noise Suppression for Micromechanical Resonator via Intrinsic Dynamic Feedback,"We study a dynamic mechanism to passively suppress the thermal noise of a
micromechanical resonator through an intrinsic self-feedback that is genuinely
non-Markovian. We use two coupled resonators, one as the target resonator and
the other as an ancillary resonator, to illustrate the mechanism and its noise
reduction effect. The intrinsic feedback is realized through the dynamics of
coupling between the two resonators: the motions of the target resonator and
the ancillary resonator mutually influence each other in a cyclic fashion.
Specifically, the states that the target resonator has attained earlier will
affect the state it attains later due to the presence of the ancillary
resonator. We show that the feedback mechanism will bring forth the effect of
noise suppression in the spectrum of displacement, but not in the spectrum of
momentum.",0708.0706v2
2007-12-19,Formation and transformation of the 3:1 mean-motion resonance in 55 Cancri System,"We report in this paper the numerical simulations of the capture into the 3:1
mean-motion resonance between the planet b and c in the 55 Cancri system. The
results show that this resonance can be obtained by a differential planetary
migration. The moderate initial eccentricities, relatively slower migration and
suitable eccentricity damping rate increase significantly the probability of
being trapped in this resonance. Otherwise, the system crosses the 3:1
commensurability avoiding resonance capture, to be eventually captured into a
2:1 resonance or some other higher-order resonances. After the resonance
capture, the system could jump from one orbital configuration to another one if
the migration continues, making a large region of the configuration space
accessible for a resonance system. These investigations help us understand the
diversity of resonance configurations and put some constrains on the early
dynamical evolution of orbits in the extra-solar planetary systems.",0712.3138v1
2008-08-08,Fano-like Anti-resonances in Nanomechanical and Optomechanical Systems,"We study a resonator coupled to a generic detector and calculate the noise
spectra of the two sub-systems. We describe the coupled system by a closed,
linear, set of Langevin equations and derive a general form for the finite
frequency noise of both the resonator and the detector. The resonator spectrum
is the well-known thermal form with an effective damping, frequency shift and
diffusion term. In contrast, the detector noise shows a rather striking
Fano-like resonance, i.e. there is a resonance at the renormalized frequency,
and an anti-resonance at the bare resonator frequency. As examples of this
effect, we calculate the spectrum of a normal state single electron transistor
coupled capacitively to a resonator and of a cavity coupled parametrically to a
resonator.",0808.1169v2
2011-07-14,Decoherence Suppression by Cavity Optomechanical Cooling,"We consider a cavity optomechanical cooling configuration consisting of a
mechanical resonator (denoted as resonator b) and an electromagnetic resonator
(denoted as resonator a), which are coupled in such a way that the effective
resonance frequency of resonator a depends linearly on the displacement of
resonator b. We study whether back-reaction effects in such a configuration can
be efficiently employed for suppression of decoherence. To that end, we
consider the case where the mechanical resonator is prepared in a superposition
of two coherent states and evaluate the rate of decoherence. We find that no
significant suppression of decoherence is achievable when resonator a is
assumed to have a linear response. On the other hand, when resonator a exhibits
Kerr nonlinearity and/or nonlinear damping the decoherence rate can be made
much smaller than the equilibrium value provided that the parameters that
characterize these nonlinearities can be tuned close to some specified optimum
values.",1107.2746v1
2011-09-05,Nucleon resonances in the fourth resonance region,"Nucleon and $\Delta$ resonances in the fourth resonance region are studied in
a multichannel partial-wave analysis which includes nearly all available data
on pion- and photo-induced reactions off protons. In the high-mass range, above
1850\,MeV, several alternative solutions yield a good description of the data.
For these solutions, masses, widths, pole residues and photo-couplings are
given. In particular, we find evidence for nucleon resonances with
spin-parities $J^P=1/2^+...7/2^+$. For one set of solutions, there are four
resonances forming naturally a spin-quartet of resonances with orbital angular
momentum L=2 and spin S=3/2 coupling to $J=1/2,...,7/2$. Just below 1.9\,GeV we
find a spin doublet of resonances with $J^P=1/2^-$ and $3/2^-$. Since a spin
partner with $J^P=5/2^-$ is missing at this mass, the two resonances form a
spin doublet which must have a symmetric orbital-angular-momentum wave function
with L=1. For another set of solutions, the four positive-parity resonances are
accompanied by mass-degenerate negative-parity partners -- as suggested by the
conjecture of chiral symmetry restoration. The possibility of a $J^P=1/2^+,
3/2^+$ spin doublet at 1900\,MeV belonging to a 20-plet is discussed.",1109.0970v1
2014-02-06,Higher order transmission resonances in above-barrier reflection of ultra-cold atoms,"The reflectionless transmission resonances in above-barrier reflection of
Bose-Einstein condensates by the Rosen-Morse potential are considered using the
mean field Gross-Pitaevskii approach. Applying an exact third order nonlinear
differential equation obeyed by the condensate's density, the exact solution of
the problem for the first resonance is derived. It is shown that in the
nonlinear case the total transmission is possible for positive potential
heights, i.e., for potential barriers. Further, it is shown that an appropriate
approximation for higher-order resonances can be constructed using a limit
solution of the equation for the density written as a root of a polynomial
equation of the third degree. Using this limit function and the solution for
the first resonance, a simple approximation for the shift of the nonlinear
resonance potential's depth from the corresponding linear resonance's position
is constructed for higher order resonances. The result is written as a linear
function of the resonance order. This behavior notably differs from the case of
the rectangular barrier for which the nonlinear shift is approximately constant
for all the resonance orders.",1402.1311v1
2014-11-24,A Broadband Dipolar Resonance in THz Metamaterials,"We demonstrate a THz metamaterial with broadband dipole resonance originating
due to the hybridization of LC resonances. The structure optimized by finite
element method simulations is fabricated by electron beam lithography and
characterized by terahertz time-domain spectroscopy. Numerically, we found that
when two LC metamaterial resonators are brought together, an electric dipole
resonance arises in addition to the LC resonances. We observed a strong
dependence of the width of these resonances on the separation between the
resonators. This dependence can be explained based on series and parallel RLC
circuit analogies. The broadband dipole resonance appears when both the
resonators are fused together. The metamaterial has a stopband with FWHM of
0.47 THz centered at 1.12 THz. The experimentally measured band features are in
reasonable agreement with the simulated ones. The experimental power extinction
ratio of THz in the stopbands is found to be 15 dB.",1411.6464v1
2015-04-14,Theory of the nanoparticle-induced frequency shifts of whispering-gallery-mode resonances in spheroidal optical resonators,"Nanoparticle-induced modifications of the spectrum of
whispering-gallery-modes (WGM) of optical spheroidal resonators are studied
theoretically. Combining an ab initio solution of a single resonator problem
with a dipole approximation for the particle, we derive simple analytical
expressions for frequencies and widths of the particle-modified resonances,
which are valid for resonators with moderate deviations from the spherical
shape. The derived expressions are used to analyze spectral properties of the
resonator-particle system as functions of the particle's position, the size of
the resonators and the characteristics of WGMs. The obtained results are shown
to agree well with available experimental data. It is also demonstrated that
the particle-induced spectral effects can be significantly enhanced by careful
selection of resonator's size, refractive index and other experimental
parameters. The results presented in the paper can be useful for applications
of WGM resonators in biosensing, cavity QED, optomechanics and others.",1504.03399v2
2016-01-05,Collective resonances of atomic xenon from the linear to the nonlinear regime,"XUV nonlinear spectroscopy has recently discovered that there is more than
one collective dipole resonance state in the energy range of the giant dipole
resonance (GDR) of atomic Xe. This resonance-state substructure, hidden in the
linear regime, raises imminent questions regarding our understanding of the
collective electronic behavior of Xe, which has been largely founded on linear
spectroscopic studies. Here, we approach the collective response of Xe from a
new perspective: we study directly the resonance eigenstates, and then analyze
their spectroscopic manifestations. We find that linear spectroscopy captures
only partial information on the resonance substructure as a result of quantum
interferences. Moreover, we show that the resonance state dominating the GDR in
linear spectroscopy has no adiabatic connection to the resonance state
governing the corresponding cross section when multielectron interactions are
neglected. Going beyond the dipole-allowed correlated electronic structure, we
predict the existence of collective multipole resonances of Xe. Unlike any
known collective feature in atoms, these resonances live exceptionally long
(more than 100 attoseconds), thus providing a new playground for studying the
collective nonlinear response of Xe using advanced light sources.",1601.00869v2
2016-03-31,Resonant terms on gyrocenter coordinates introduced by resonant electromagnetic perturbations,"It's pointed out that the treatment of the resonant electromagnetic
perturbation with the Lie transform method adopted in the gyrokinetic theory
generates some nonphysical terms in the trajectory equations. By utilizing a
modified application of this transform method, the resonant terms in the
trajectory equations satisfying each resonant condition are found out up to the
second harmonic resonance. Through separating the fast-dynamic terms from the
slow-dynamic ones, the slow-dynamic trajectory equations including the resonant
terms are derived for various resonant conditions. The slow-dynamic evolution
equation of gyroangle reveals that the real gyrating frequency of the charged
particle around the magnetic field line under driving by the resonant wave has
a shift from the cyclotron frequency without the wave driving. To study the
effect caused by the frequency shift, a simple example for the
fundamental-frequency cyclotron resonance is presented.",1603.09632v5
2017-06-28,Towards N-mode parametric electromechanical resonances,"The ubiquity of parametric resonance is continually evident in the repeated
experimental observations of this phenomenon in multiple physical systems. The
elementary case of 2 mode parametric resonance of order 1 involves the
excitation of a spectral tone of a parametrically driven mode at a sub-harmonic
frequency of the higher directly driven mode. Historically, such examples of
parametric resonance have been predominantly researched in a system of micro-
and nanoelectromechanical resonators. Here, in this paper, we break this
convention by showcasing a collection of experimental signatures in support of
the concept of ""N-mode parametric resonance"" using a number of elementary
microelectromechanical devices. Specifically, we present observations of 2, 3,
(2+3) and (3+3) mode parametric resonances demonstrating co-existence of
different regimes within the same device. In addition, we also present
observations of intrinsic ""Four-Wave Mixing"" of parametric excitations. This
paper presents contributions towards the existence proof for such multimode
parametric resonances which can also be exploited for engineering benefit
within the field of ""micro and nanoelectromechanical resonators"". The
experimental results further point towards the possibility of the ultimate
observation of N-mode parametric resonance in such physical system.",1708.01660v1
2016-07-30,Spoof surface plasmon Fabry-Perot open resonators in a surface-wave photonic crystal,"We report on the proposal and experimental realization of a spoof surface
plasmon Fabry-Perot (FP) open resonator in a surface-wave photonic crystal.
This surface-wave FP open resonator is formed by introducing a finite line
defect in a surface-wave photonic crystal. The resonance frequencies of the
surface-wave FP open resonator lie exactly within the forbidden band gap of the
surface-wave photonic crystal and the FP open resonator uses this complete
forbidden band gap to concentrate surface waves within a subwavelength cavity.
Due to the complete forbidden band gap of the surface-wave photonic crystal, a
new FP plasmonic resonance mode that exhibits monopolar features which is
missing in traditional FP resonators and plasmonic resonators is demonstrated.
Near-field response spectra and mode profiles are presented in the microwave
regime to characterize properties of the proposed FP open resonator for spoof
surface plasmons.",1608.00080v1
2017-06-22,Multipole resonances and directional scattering by hyperbolic-media antennas,"We propose to use optical antennas made out of natural hyperbolic material
hexagonal boron nitride (hBN), and we demonstrate that this medium is a
promising alternative to plasmonic and all-dielectric materials for realizing
efficient subwavelength scatterers and metasurfaces based on them. We
theoretically show that particles out of hyperbolic medium possess different
resonances enabled by the support of high-k waves and their reflection from the
particle boundaries. Among those resonances, there are electric quadrupole
excitations, which cause magnetic resonance of the particle similar to what
occurs in high-refractive-index particles. Excitations of the particle
resonances are accompanied by the drop in the reflection from nanoparticle
array to near-zero value, which can be ascribed to resonant Kerker effect. If
particles are arranged in the spacer array with period d, narrow lattice
resonances are possible at wavelength d, d/2, d/3 etc. This provides an
additional degree of control and possibility to excite resonances at the
wavelength defined by the array spacing. For the hBN particle with hyperbolic
dispersion, we show that the full range of the resonances, including magnetic
resonance and a decrease of reflection, is possible.",1706.07259v1
2019-06-06,Evolution of the resonances of two parallel dielectric cylinders with distance between them,"We study behavior of resonant modes under change of the distance between two
parallel dielectric cylinders. The processes of mutual scattering of Mie
resonant modes by cylinders result in an interaction between the cylinders
which lifts a degeneracy of resonances of the isolated cylinders. There are two
basic scenarios of evolution of resonances with the distance. For strong
interaction of cylinders resonances are unbound with avoided crossings from the
of the Mie resonances with increasing of the distance. That scenario is typical
for low exciting resonances (monopole and dipole). For weak interaction of
cylinders the resonances are bound around highly excited Mie resonances. Both
scenarios demonstrate a significant enhancement of the $Q$ factor compared to
the case of isolated cylinder.",1906.02409v1
2020-04-17,S-band electron spin resonance spectroscopy using a short-circuited coplanar waveguide resonator,"In this work, we study the development of a coplanar waveguide (CPW)
resonator and its use in an electron spin resonance (ESR) spectrometer. The CPW
resonator is designed to operate in S-band. It has a short circuit
configuration which leads to miniaturization. It is so constructed such that it
has a characteristic impedance of 50 ohms. Detailed electromagnetic simulation
with a particular emphasis on the excitation of the structure has been
performed for this resonator owing to its uniplanar nature. The design
parameters and the electromagnetic field distribution are obtained from the
simulation. The resonator is fabricated using optical lithography with a rapid
prototyping technique. The characteristic response of the resonator is measured
by coupling it to a Vector Network Analyzer (VNA). The ESR absorption spectrum
of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) is captured by using this
resonator in reflection geometry. The microwave magnetic field distribution at
the sample position is investigated.The measured g-factor value is found to be
consistent with that reported in the literature. The quality factor of this
resonator is found to be low and this makes it suitable for use in a Pulsed ESR
spectrometer.",2004.08061v1
2019-01-10,From Fano resonances to bound states in the continuum in dipole arrays at THz frequencies,"Fano resonances and bound states in the continuum (BICs) exhibit a rich
phenomenology stemming from, respectively, their asymmetric line shapes and
infinite quality factors. Here, we show experimentally and theoretically that
rod dimer metasurfaces exhibit narrow (high-Q) Fano resonances at THz
frequencies. These resonances evolve continuously into a BIC as the rods in
each dimer become identical. We demonstrate analytically that this is a
universal behavior occurring in arrays of dimers consisting of detuned resonant
dipoles. Fano resonances arise as a result of the interference between broad
and narrow lattice dipole resonances, with high-Q factors tending to infinity
in the detuning parameter space as the narrow lattice resonance becomes a BIC
for identical resonant dipoles. Similar configurations can be straightforwardly
envisioned throughout the electromagnetic spectrum leading to ultrahigh-Q Fano
resonances and BICs of interest in photonics applications such as sensing and
lasing.",1901.03122v1
2019-03-22,On the geometry optimization of X-band resonator for electron paramagnetic resonance application,"The microwave resonator is one of the key components in the modern Electron
Paramagnetic Resonance (EPR) spectroscopy setup, as it largely determines the
performance characteristics and limitations of the entire spectrometer. In this
research note the possible way of resonator optimization is described. A
detailed computer model describing the distribution of the electromagnetic
field for Bruker 4118X-MD-5W1 design resonator has been developed. All details
including a dielectric insert, conductive screen, coupling antenna and PTFE
supports were included in the model. All dissipation processes were considered
in the calculation. The influence of the resonator geometry on the Q-factor,
filling factor and operating frequency of the resonant mode has been
investigated. The resonator geometric parameters are optimized to achieve
maximum sensitivity. According to the calculations, the optimized resonator
structure has in 10 times greater sensitivity than the original MD-5 design.",1904.01657v1
2020-10-28,Phase resonance nonlinear modes of mechanical systems,"The resonances of forced dynamical systems occur when either the amplitude of
the frequency response undergoes a local maximum (amplitude resonance) or phase
lag quadrature takes places (phase resonance). This study focuses on the phase
resonance of nonlinear mechanical systems subjected to single-point,
single-harmonic excitation. In this context, the main contribution of this
paper is to develop a computational framework which can predict the mode shapes
and oscillation frequencies at phase resonance. The resulting nonlinear modes
are termed phase resonance nonlinear modes (PRNMs). A key property of PRNMs is
that, besides primary resonances, they can accurately characterize
superharmonic, subharmonic and ultra-subharmonic resonances for which, as shall
be shown in this paper, phase lags at resonance may be different from pi/2. The
proposed developments are demonstrated using one- and two-degree-of-freedom
systems featuring a cubic nonlinearity.",2010.14892v4
2022-01-28,Three-Body Resonances in the Saturnian System,"Saturn has a dynamically rich satellite system, which includes at least three
orbital resonances between three pairs of moons: Mimas-Tethys 4:2,
Enceladus-Dione 2:1, and Titan-Hyperion 4:3 mean-motion resonances. Studies of
the orbital history of Saturn's moons usually assume that their past dynamics
was also dominated solely by two-body resonances. Using direct numerical
integrations, we find that three-body resonances among Saturnian satellites
were quite common in the past, and could result in a relatively long-term, but
finite capture time (10 Myr or longer). We find that these three-body
resonances are invariably of the eccentricity type, and do not appear to affect
the moons' inclinations. While some three-body resonances are located close to
two-body resonances (but involve the orbital precession of the third body),
others are isolated, with no two-body arguments being near resonance. We
conclude that future studies of the system's past must take full account of
three-body resonances, which have been overlooked in the past work.",2201.12313v1
2022-02-21,Efimov resonance position near a narrow Feshbach resonance in $^6$Li-$^{133}$Cs mixture,"In the vicinity of a narrow Feshbach resonances Efimov features are expected
to be characterized by the resonance's properties rather than the van der Waals
length of the interatomic potential. Although this theoretical prediction is
well-established by now, it still lacks experimental confirmation. Here, we
apply our recently developed three-channel model [Yudkin and Khaykovich, Phys.
Rev. A 103, 063303 (2021)] to the experimental result obtained in a
mass-imbalanced $^6$Li-$^{133}$Cs mixture in the vicinity of the narrowest
resonance explored to date [Johansen at. al. Nat. Phys. 13, 731 (2017)]. We
confirm that the observed position of the Efimov resonance is dictated mainly
by the resonance physics while the influence of the van der Waals tail of the
interatomic potential is minor. We show that the resonance position is strongly
influenced by the presence of another Feshbach resonance which significantly
alters the effective background scattering length at the narrow resonance
position.",2202.10358v1
2023-05-23,The interaction between two close-to-touching convex acoustic subwavelength resonators,"The Minneart resonance is a low frequency resonance in which the wavelength
is much larger than the size of the resonators. It is interesting to study the
interaction between two adjacent bubbles when they are brought close together.
Because the bubbles are usually compressible, in this paper we mainly
investigate resonant modes of two general convex resonators with arbitrary
shapes to extend the results of Ammari, Davies, Yu in [4], where a pair of
spherical resonators are considered by using bispherical coordinates. We
combine the layer potential method for Helmholtz equation in [4,5] and the
elliptic theory for gradient estimates in [26,30] to calculate the capacitance
coefficients for the coupled $C^{2,\alpha}$ resonators, then show the
leading-order asymptotic behaviors of two different resonant modes and reveal
the dependance of the resonant frequencies on their geometric properties, such
as convexity, volumes and curvatures. By the way, the blow-up rates of gradient
of the scattered pressure are also presented.",2305.13789v1
2000-12-21,The Capture of Particles by Chaotic Resonances During Orbital Migration,"Because a chaotic zone can reduce the long timescale capture probabilities
and cause catastrophic events such as close encounters with a planet or star
during temporary capture, the dynamics of migrating planets is likely to be
strongly dependent on the widths of the resonance chaotic zones. Previous
theoretical work on the resonant capture of particles into mean-motion
resonances by orbital migration has been restricted to the study of integrable
models. By exploring toy drifting Hamiltonian models we illustrate how the
structure in phase space of a resonance can be used to generalize this
integrable capture theory to include the richer phenomenology of chaotic
resonances. We show that particles are temporarily captured into the chaotic
zone of a resonance with fixed shape for a time that is given by the width of
the chaotic zone divided by the resonance drift rate. Particles can be
permanently captured into a drifting chaotic resonance only if they are
captured into a growing integrable region. Therefore resonances containing wide
chaotic zones have lower permanent capture probabilities than those lacking
chaotic zones. We expect large deviations from the predictions of integrable
capture theories when the chaotic zone is large and the migration rate is
sufficiently long that many Lyapunov times pass while particles are temporarily
captured in the resonance. The 2:1 mean-motion resonance with Neptune in the
Kuiper Belt contains a chaotic zone, even when integrated on short timescales
such as a million years. Capture probabilities are lower than estimated
previously from drifting integrable models. This may offer an explanation for
low eccentricity Kuiper Belt objects between 45-47 AU which should have been
previously captured in the 2:1 resonance by Neptune's migration.",0012466v2
2005-07-20,Reducing the Probability of Capture into Resonance,"A migrating planet can capture planetesimals into mean motion resonances.
However, resonant trapping can be prevented when the drift or migration rate is
sufficiently high. Using a simple Hamiltonian system for first and second order
resonances, we explore how the capture probability depends on the order of the
resonance, drift rate and initial particle eccentricity. We present scaling
factors as a function of the planet mass and resonance strength to estimate the
planetary migration rate above which the capture probability drops to less than
1/2. Applying our framework to multiple extra solar planetary systems that have
two planets locked in resonance, we estimate lower limits for the outer
planet's migration rate allowing resonance capture of the inner planet. Mean
motion resonances are comprised of multiple resonant subterms. We find that the
corotation subterm can reduce the probability of capture when the planet
eccentricity is above a critical value. We present factors that can be used to
estimate this critical planet eccentricity. Applying our framework to the
migration of Neptune, we find that Neptune's eccentricity is near the critical
value that would make its 2:1 resonance fail to capture twotinos. The capture
probability is affected by the separation between resonant subterms and so is
also a function of the precession rates of the longitudes of periapse of both
planet and particle near resonance.",0507477v2
2008-06-09,Current noise of a superconducting single electron transistor coupled to a resonator,"We analyze the current and zero-frequency current noise properties of a
superconducting single electron resonator (SSET) coupled to a resonator,
focusing on the regime where the SSET is operated in the vicinity of the
Josephson quasiparticle resonance. We consider a range of coupling strengths
and resonator frequencies to reflect the fact that in practice the system can
be tuned to quite a high degree with the resonator formed either by a
nanomechanical oscillator or a superconducting stripline fabricated in close
proximity to the SSET. For very weak couplings the SSET acts on the resonator
like an effective thermal bath. In this regime the current characteristics of
the SSET are only weakly modified by the resonator. Using a mean field
approach, we show that the current noise is nevertheless very sensitive to the
correlations between the resonator and the SSET charge. For stronger couplings,
the SSET can drive the resonator into limit cycle states where self-sustained
oscillation occurs and we find that regions of well-defined bistability exist.
Dynamical transitions into and out of the limit cycle state are marked by
strong fluctuations in the resonator energy, but these fluctuations are
suppressed within the limit cycle state. We find that the current noise of the
SSET is strongly influenced by the fluctuations in the resonator energy and
hence should provide a useful indicator of the resonator's dynamics.",0806.1441v2
2012-11-11,Resonances for activity waves in spherical mean field dynamos,"We study activity waves of the kind that determine cyclic magnetic activity
of various stars, including the Sun, as a more general physical rather than a
purely astronomical problem. We try to identify resonances which are expected
to occur when a mean-field dynamo excites waves of quasi-stationary magnetic
field in two distinct spherical layers. We isolate some features that can be
associated with resonances in the profiles of energy or frequency plotted
versus a dynamo governing parameter. Rather unexpectedly however the resonances
in spherical dynamos take a much less spectacular form than resonances in many
more familiar branches of physics. In particular, we find that the magnitudes
of resonant phenomena are much smaller than seem detectable by astronomical
observations, and plausibly any related effects in laboratory dynamo
experiments (which of course are not in gravitating spheres!) are also small.
We discuss specific features relevant to resonant phenomena in spherical
dynamos, and find parametric resonance to be the most pronounced type of
resonance phenomena. Resonance conditions for these dynamo wave resonances are
rather different from those for more conventional branches of physics. We
suggest that the relative insignificance of the phenomenon in this case is
because the phenomena of excitation and propagation of the activity waves are
not well-separated from each other and this, together with the nonlinear nature
of more-or-less realistic dynamos, suppress the resonances and makes them much
less pronounced than resonant effects, for example in optics.",1211.2414v1
2013-07-31,Discrete exact and quasi-resonances of Rossby/drift waves on $\b$-plane with periodic boundary conditions,"Analysis of resonance clustering in weakly nonlinear dispersive wave systems,
also called discrete wave turbulent systems, is a new methodology successfully
used in the last years for characterizing energy transport due to exact and
quasi-resonances. Quite recently this methodology has been used in the paper by
M. D. Bustamante, U. Hayat ""Complete classification of discrete resonant
Rossby/drift wave triads on periodic domains"", \cite{BH13}, in order to show
that resonance clustering is very sparse and quasi-resonances (that is,
resonances with small enough detuning) play major role in the energy transport
in this specific wave system. On the other hand, in the paper by M. Yamada, T.
Yoneda ""Resonant interaction of Rossby waves in two-dimensional flow on
$\beta$-plane"", \cite{YaYo13}, the same physical system is studied and a
mathematically rigorous theorem is proven: at high $\b$, the flow dynamics is
governed exclusively by resonant interactions. In our present paper we
demonstrate that this seeming contradiction between numerical results
\cite{BH13} and analytical results \cite{YaYo13} are due to some pitfalls in
numerical studies of exact and quasi-resonances presented in \cite{BH13}. We
also demonstrate that resonance clustering of drift waves on periodic
$\b$-plane differs substantially from characteristic resonance clustering in
other 3-wave systems: instead of a usual set of isolated triads and a few
bigger clusters, there exists \emph{no isolated triads} in this case. Resonant
triads are interconnected in a complicated way and the smallest cluster
consists of 6 connected triads.",1307.8272v1
2014-10-20,Resonance capture at arbitrary inclination,"Resonance capture is studied numerically in the three-body problem for
arbitrary inclinations. Massless particles are set to drift from outside the
1:5 resonance with a Jupiter-mass planet thereby encountering the web of the
planet's diverse mean motion resonances. Randomly constructed samples explore
parameter space for inclinations from 0 to 180 deg with 5deg increments
totalling nearly 6x10^5 numerical simulations. Thirty resonances internal and
external to the planet's location are monitored. We find that retrograde
resonances are unexpectedly more efficient at capture than prograde resonances
and that resonance order is not necessarily a good indicator of capture
efficiency at arbitrary inclination. Capture probability drops significantly at
moderate sample eccentricity for initial inclinations in the range
[10deg,110deg]. Orbit inversion is possible for initially circular orbits with
inclinations in the range [60deg,130deg]. Capture in the 1:1 coorbital
resonance occurs with great likelihood at large retrograde inclinations. The
planet's orbital eccentricity, if larger than 0.1, reduces the capture
probabilities through the action of the eccentric Kozai-Lidov mechanism. A
capture asymmetry appears between inner and outer resonances as prograde orbits
are preferentially trapped in inner resonances. The relative capture efficiency
of retrograde resonance suggests that the dynamical lifetimes of Damocloids and
Centaurs on retrograde orbits must be significantly larger than those on
prograde orbits implying that the recently identified asteroids in retrograde
resonance, 2006 BZ8, 2008 SO218, 2009 QY6 and 1999 LE31(Morais and Namouni,
2013, MNRAS 436, L30) may be among the oldest small bodies that wander between
the outer giant planets.",1410.5383v1
2015-07-07,Thermal Resonance Fusion,"We first show a possible mechanism to create a new type of nuclear fusion,
thermal resonance fusion, i.e. low energy nuclear fusion with thermal resonance
of light nuclei or atoms, such as deuterium or tritium. The fusion of two light
nuclei has to overcome the Coulomb barrier between these two nuclei to reach up
to the interacting region of nuclear force. We found nuclear fusion could be
realized with thermal vibrations of crystal lattice atoms coupling with light
atoms at low energy by resonance to overcome this Coulomb barrier. Thermal
resonances combining with tunnel effects can greatly enhance the probability of
the deuterium fusion to the detectable level. Our low energy nuclear fusion
mechanism research - thermal resonance fusion mechanism results demonstrate how
these light nuclei or atoms, such as deuterium, can be fused in the crystal of
metal, such as Ni or alloy, with synthetic thermal vibrations and resonances at
different modes and energies experimentally. The probability of tunnel effect
at different resonance energy given by the WKB method is shown that indicates
the thermal resonance fusion mode, especially combined with the tunnel effect,
is possible and feasible. But the penetrating probability decreases very
sharply when the input resonance energy decreases less than 3 keV, so for
thermal resonance fusion, the key point is to increase the resonance peak or
make the resonance sharp enough to the acceptable energy level by the suitable
compound catalysts, and it is better to reach up more than 3 keV to make the
penetrating probability larger than 10^{-10}.",1507.01650v1
2012-04-26,Higher Order Spin Resonances in a 2.1 GeV/c Polarized Proton Beam,"Spin resonances can depolarize or spin-flip a polarized beam. We studied 1st
and higher order spin resonances with stored 2.1 GeV/c vertically polarized
protons. The 1st order vertical ({\nu}y) resonance caused almost full
spin-flip, while some higher order {\nu}y resonances caused partial
depolarization. The 1st order horizontal ({\nu}x) resonance caused almost full
depolarization, while some higher order {\nu}x resonances again caused partial
depolarization. Moreover, a 2nd order {\nu}x resonance is about as strong as
some 3rd order {\nu}x resonances, while some 3rd order {\nu}y resonances are
much stronger than a 2nd order {\nu}y resonance. One thought that {\nu}y spin
resonances are far stronger than {\nu}x, and that lower order resonances are
stronger than higher order; the data do not support this.",1204.6002v1
2020-04-16,The onset of instability in resonant chains,"There is evidence that most chains of mean motion resonances of type
$k$:$k-1$ among exoplanets become unstable once the dissipative action from the
gas is removed from the system, particularly for large $N$ (the number of
planets) and $k$ (indicating how compact the chain is). We present a novel
dynamical mechanism that can explain the origin of these instabilities and thus
the dearth of resonant systems in the exoplanet sample. It relies on the
emergence of secondary resonances between a fraction of the synodic frequency
$2 \pi (1/P_1-1/P_2)$ and the libration frequencies in the mean motion
resonance. These secondary resonances excite the amplitudes of libration of the
mean motion resonances thus leading to an instability. We detail the emergence
of these secondary resonances by carrying out an explicit perturbative scheme
to second order in the planetary masses and isolating the harmonic terms that
are associated with them. Focusing on the case of three planets in the 3:2 --
3:2 mean motion resonance as an example, a simple but general analytical model
of one of these resonances is obtained which describes the initial phase of the
activation of one such secondary resonance. The dynamics of the excited system
is also briefly described. This scheme shows how one can obtain analytical
insight into the emergence of these resonances, and into the dynamics that they
trigger. Finally, a generalisation of this dynamical mechanism is obtained for
arbitrary $N$ and $k$. This leads to an explanation of previous numerical
experiments on the stability of resonant chains, showing why the critical
planetary mass allowed for stability decreases with increasing $N$ and $k$.",2004.07789v1
2018-03-14,Resonance Capture and Dynamics of 3-Planet Systems,"We present a series of dynamical maps for fictitious 3-planets systems in
initially circular coplanar orbits. These maps have unveiled a rich resonant
structure involving two or three planets, as well as indicating possible
migration routes from secular to double resonances or pure 3-planet
commensurabilities. These structures are then compared to the present-day
orbital architecture of observed resonant chains. In a second part of the paper
we describe N-body simulations of type-I migration. Depending on the orbital
decay timescale, we show that 3-planet systems may be trapped in different
combinations of independent commensurabilities: (i) double resonances, (ii)
intersection between a 2-planet and a first-order 3-planet resonance, and (iii)
simultaneous libration in two first-order 3-planet resonances. These latter
outcomes are found for slow migrations, while double resonances are almost
always the final outcome in high-density disks. Finally, we discuss an
application to the TRAPPIST-1 system. We find that, for low migration rates and
planetary masses of the order of the estimated values, most 3-planet
sub-systems are able to reach the observed double resonances after following
evolutionary routes defined by pure 3-planet resonances. The final orbital
configuration shows resonance offsets comparable with present-day values
without the need of tidal dissipation. For the 8/5 resonance proposed to
dominate the dynamics of the two inner planets, we find little evidence of its
dynamical significance; instead, we propose that this relation between mean
motions could be a consequence of the interaction between a pure 3-planet
resonance and a 2-planet commensurability between planets c and d.",1803.05305v1
2019-03-08,Perfect Absorption Metasurfaces with Multiple Meta-Resonances,"We show that the hybrid resonances of a DMR backed by a cavity are
meta-resonances, in that they can be made as perfect as possible by fine tuning
the structural parameters but without the requirements of extreme materials
properties, such as zero dissipation. Instead, dissipation in the DMR is
essential for the realization of perfect meta-resonances. We experimentally
demonstrate such perfection by tuning the structure of a HMR till its
reflection is as low as 0.426 % . Besides the primary meta-resonances that are
originated from the strong resonances of the DMR, weak hitchhiker resonances
can also produce meta-resonances as perfect as the primary ones. The depth of
the reflection dips is insensitive to the strength of the resonances involved,
but critically depends on the degree of impedance match to air brought mostly
by fine tuning the structure parameters, such as the cavity volume, the mass of
the platelet, or the pre-tension in the membrane. Using the eccentricity of the
platelet position in the DMR, a number of resonances and anti-resonances are
generated, resulting in up to five meta-resonances within the range of 200 Hz
to 1000 Hz, with the highest reflection being 7 % and the lowest being 1.2 % .
Other means of introducing hitchhiker meta-resonances are also reported.",1903.03493v2
2019-08-15,Connections between resonance and nonlinearity in swimming performance of a flexible heaving plate,"We investigate the role of resonance in finite-amplitude swimming of a
flexible flat plate in a viscous fluid. The role of resonance in performance
remains unclear for two reasons: i) a lack of definition of resonance for the
fully-coupled fluid-structure interaction system in a viscous flow, and ii) the
presence of nonlinear effects, which makes it difficult to disentangle resonant
and non-resonant mechanisms in finite-amplitude swimming. We address point i)
and provide an unambiguous definition for system resonance by computing global
linear stability modes of the fully-coupled fluid-structure interaction system
that account for the viscous fluid, the plate, and the coupling between them.
We then resolve point ii) by considering high-fidelity nonlinear simulations of
systematically increased amplitude. By comparing the results for different
amplitudes with one another and with the linear stability modes, we separate
linear and/or resonant effects from nonlinear and/or non-resonant effects.
Resonant behavior is observed over a wide range of plate stiffnesses, with
peaks in trailing-edge motion and thrust occurring near the resonant frequency
defined by the global linear analysis. The peaks broaden and weaken with
increasing heave amplitude, consistent with an increased damping effect from
the fluid. At the same time, non-resonant mechanisms are present at large heave
amplitudes. The input power exhibits qualitatively different dynamics at large
heave amplitudes compared to smaller heave amplitudes, where resonance
dominates. Moreover, leading-edge separation is present for stiff plates at
large heave amplitudes, which can drastically alter the performance
characteristics from what one would expect through linear predictions.",1908.05704v1
2020-10-06,Multi-harmonic Hamiltonian models with applications to first-order resonances,"In this work, two multi-harmonic Hamiltonian models for mean motion
resonances are formulated and their applications to first-order resonances are
discussed. For the $k_p$:$k$ resonance, the usual critical argument $\varphi =
k \lambda - k_p \lambda_p + (k_p - k) \varpi$ is taken as the resonant angle in
the first model, while the second model is characterized by a new critical
argument $\sigma = \varphi / k_p$. Based on canonical transformations, the
resonant Hamiltonians associated with these two models are formulated. It is
found that the second Hamiltonian model holds two advantages in comparison to
the first model: (a) providing a direct correspondence between phase portraits
and Poincar\'e sections, and (b) presenting new phase-phase structures where
the zero-eccentricity point is a visible saddle point. Then, the second
Hamiltonian model is applied to the first-order inner and outer resonances,
including the 2:1, 3:2, 4:3, 2:3 and 3:4 resonances. The phase-space structures
of these first-order resonances are discussed in detail and then the libration
centers and associated resonant widths are identified analytically. Simulation
results show that there are pericentric and apocentric libration zones where
the libration centers diverge away from the nominal resonance location as the
eccentricity approaches zero and, in particular, the resonance separatrices do
not vanish at arbitrary eccentricities for both the inner and outer
(first-order) resonances.",2010.02431v1
2022-04-12,Band-type resonance: non-discrete energetically-optimal resonant states,"Structural resonance involves the absorption of inertial loads by a tuned
structural elasticity: a process playing a key role in a wide range of
biological and technological systems, including many biological and
bio-inspired locomotion systems. Conventional linear and nonlinear resonant
states typically exist at specific discrete frequencies, and specific symmetric
waveforms. This discreteness can be an obstacle to resonant control modulation:
deviating from these states, by breaking waveform symmetry or modulating drive
frequency, generally leads to losses in system efficiency. Here, we demonstrate
a new strategy for achieving these modulations at no loss of energetic
efficiency. Leveraging fundamental advances in nonlinear dynamics, we
characterise a new form of structural resonance: band-type resonance,
describing a continuous band of energetically-optimal resonant states existing
around conventional discrete resonant states. These states are a counterexample
to the common supposition that deviation from a linear (or nonlinear) resonant
frequency necessarily involves a loss of efficiency. We demonstrate how
band-type resonant states can be generated via a spectral shaping approach:
with small modifications to the system kinematic and load waveforms, we
construct sets of frequency-modulated and symmetry-broken resonant states that
show equal energetic optimality to their conventional discrete analogues. The
existence of these non-discrete resonant states in a huge range of oscillators
- linear and nonlinear, in many different physical contexts - is a new
dynamical-systems phenomenon. It has implications not only for biological and
bio-inspired locomotion systems but for a constellation of forced oscillator
systems across physics, engineering, and biology.",2204.10409v1
2022-07-28,Chaotic diffusion of asteroids in the exterior 1:2 mean motion resonance with Mars,"The inner asteroid belt between 2.1 and 2.5 au is of particular dynamical
significance because it is the dominant source of both chondritic meteorites
and near-Earth asteroids. This inner belt is bounded by an eccentricity-type
secular resonance and by the 1:3 mean motion resonance with Jupiter. Unless
asteroid perihelia are low enough to allow scattering by Mars, escape requires
transport to one of the bounding resonances. In addition Yarkovsky forces are
generally ineffective in changing either the eccentricity and/or inclination
for asteroids with diameter $\gtrsim$30 km. Thus, large asteroids with
pericentres far from Mars may only escape from the inner belt through large
changes in their eccentricities. In this paper we study chaotic diffusion of
orbits near the 1:2 mean motion resonance with Mars in a systematic way. We
show that, while chaotic orbital evolution in both resonant and non-resonant
orbits increase the dispersion of the inclinations and eccentricities, it does
not significantly change their mean values. We show further that, while the
dispersive growth is greatest for resonant orbits, at high $e$ the resonance
acts to mitigate asteroid scattering by Mars - making the asteroid lifetime in
the belt longer than it would have been for a non-resonant orbit. For asteroids
of all sizes in both resonant and non-resonant orbits, the changes in
eccentricity needed to account for the observations cannot be achieved by
gravitational forces alone. The role of resonant trapping in protecting
asteroids from encounters with Mars is also analysed.",2207.14047v2
2024-03-03,Vibrational resonance: A review,"Over the past two decades, vibrational resonance has garnered significant
interest and evolved into a prominent research field. Classical vibrational
resonance examines the response of a nonlinear system excited by two signals: a
weak, slowly varying characteristic signal, and a fast-varying auxiliary
signal. The characteristic signal operates on a much longer time scale than the
auxiliary signal. Through the cooperation of the nonlinear system and these two
excitations, the faint input can be substantially amplified, showcasing the
constructive role of the fast-varying signal. Since its inception, vibrational
resonance has been extensively studied across various disciplines, including
physics, mathematics, biology, neuroscience, laser science, chemistry, and
engineering. Here, we delve into a detailed discussion of vibrational resonance
and the most recent advances, beginning with an introduction to characteristic
signals commonly used in its study. Furthermore, we compile numerous nonlinear
models where vibrational resonance has been observed to enhance readers'
understanding and provide a basis for comparison. Subsequently, we present the
metrics used to quantify vibrational resonance, as well as offer a theoretical
formulation. This encompasses the method of direct separation of motions,
linear and nonlinear vibrational resonance, re-scaled vibrational resonance,
ultrasensitive vibrational resonance, and the role of noise in vibrational
resonance. Later, we showcase two practical applications of vibrational
resonance: one in image processing and the other in fault diagnosis. This
presentation offers a comprehensive and versatile overview of vibrational
resonance, exploring various facets and highlighting promising avenues for
future research in both theory and engineering applications.",2403.06997v1
2001-12-03,Theory of proximity effect in superconductor/ferromagnet heterostructures,"We present a microscopic theory of proximity effect in the
ferromagnet/superconductor/ferromagnet (F/S/F) nanostructures where S is s-wave
low-T_c superconductor and F's are layers of 3d transition ferromagnetic metal.
Our approach is based on the solution of Gor'kov equations for the normal and
anomalous Green's functions together with a self-consistent evaluation of the
superconducting order parameter. We take into account the elastic
spin-conserving scattering of the electrons assuming s-wave scattering in the S
layer and s-d scattering in the F layers. In accordance with the previous
quasiclassical theories, we found that due to exchange field in the ferromagnet
the anomalous Green's function F(z) exhibits the damping oscillations in the
F-layer as a function of distance z from the S/F interface. In the given model
a half of period of oscillations is determined by the length \xi_m^0 = \pi
v_F/E_ex, where v_F is the Fermi velocity and E_ex is the exchange field, while
damping is governed by the length l_0 = (1/l_{\uparrow} +
1/l_{\downarrow})^{-1} with l_{\uparrow} and l_{\downarrow} being
spin-dependent mean free paths in the ferromagnet. The superconducting
transition temperature T_c(d_F) of the F/S/F trilayer shows the damping
oscillations as a function of the F-layer thickness d_F with period \xi_F =
\pi/\sqrt{m E_ex}, where m is the effective electron mass. We show that strong
spin-conserving scattering either in the superconductor or in the ferromagnet
significantly suppresses these oscillations. The calculated T_c(d_F)
dependences are compared with existing experimental data for Fe/Nb/Fe trilayers
and Nb/Co multilayers.",0112034v3
2009-01-14,Theory of superconducting and magnetic proximity effect in S$\mid$F structures with inhomogeneous magnetization textures and spin-active interfaces,"We present a study of the proximity effect and the inverse proximity effect
in a superconductor$\mid$ferromagnet bilayer, taking into account several
important factors which mostly have been ignored in the literature so far.
These include spin-dependent interfacial phase shifts (spin-DIPS) and
inhomogeneous textures of the magnetization in the ferromagnetic layer, both of
which are expected to be present in real experimental samples. Our approach is
numerical, allowing us to access the full proximity effect regime. In Part I of
this work, we study the superconducting proximity effect and the resulting
local density of states in an inhomogeneous ferromagnet with a non-trivial
magnetic texture.
  Our two main results in Part I are a study of how Bloch and N\'eel domain
walls affect the proximity-induced superconducting correlations and a study of
the superconducting proximity effect in a conical ferromagnet. The latter topic
should be relevant for the ferromagnet Ho, which was recently used in an
experiment to demonstrate the possibility to generate and sustain long-range
triplet superconducting correlations. In Part II of this work, we investigate
the inverse proximity effect with emphasis on the induced magnetization in the
superconducting region as a result of the ""leakage"" from the ferromagnetic
region. It is shown that the presence of spin-DIPS modify conclusions obtained
previously in the literature with regard to the induced magnetization in the
superconducting region. In particular, we find that the spin-DIPS can trigger
an anti-screening effect of the magnetization, leading to an induced
magnetization in the superconducting region with \textit{the same sign} as in
the proximity ferromagnet.",0901.1961v1
2012-07-13,Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films,"We report room-temperature ferromagnetism in highly conducting transparent
anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on
LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray
diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption
spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry
(TOF-SIMS) indicated negligible magnetic contaminants in the films. The
presence of ferromagnetism with concomitant large carrier densities was
determined by a combination of superconducting quantum interference device
(SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic
circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD)
and was supported by first-principle calculations. SXMCD and XAS measurements
revealed a 90% contribution to ferromagnetism from the Ti ions and a 10%
contribution from the O ions. RBS/channelling measurements show complete Ta
substitution in the Ti sites though carrier activation was only 50% at 5% Ta
concentration implying compensation by cationic defects. The role of Ti vacancy
and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS)
respectively. It was found that in films with strong ferromagnetism, the Ti
vacancy signal was strong while Ti3+ signal was absent. We propose (in the
absence of any obvious exchange mechanisms) that the localised magnetic
moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers.
Cationic-defect-induced magnetism is an alternative route to ferromagnetism in
wide-band-gap semiconducting oxides without any magnetic elements.",1207.3156v1
2013-11-19,Ferromagnetic Potts Model: Refined #BIS-hardness and Related Results,"Recent results establish for 2-spin antiferromagnetic systems that the
computational complexity of approximating the partition function on graphs of
maximum degree D undergoes a phase transition that coincides with the
uniqueness phase transition on the infinite D-regular tree. For the
ferromagnetic Potts model we investigate whether analogous hardness results
hold. Goldberg and Jerrum showed that approximating the partition function of
the ferromagnetic Potts model is at least as hard as approximating the number
of independent sets in bipartite graphs (#BIS-hardness). We improve this
hardness result by establishing it for bipartite graphs of maximum degree D. We
first present a detailed picture for the phase diagram for the infinite
D-regular tree, giving a refined picture of its first-order phase transition
and establishing the critical temperature for the coexistence of the disordered
and ordered phases. We then prove for all temperatures below this critical
temperature that it is #BIS-hard to approximate the partition function on
bipartite graphs of maximum degree D. As a corollary, it is #BIS-hard to
approximate the number of k-colorings on bipartite graphs of maximum degree D
when k <= D/(2 ln D).
  The #BIS-hardness result for the ferromagnetic Potts model uses random
bipartite regular graphs as a gadget in the reduction. The analysis of these
random graphs relies on recent connections between the maxima of the
expectation of their partition function, attractive fixpoints of the associated
tree recursions, and induced matrix norms. We extend these connections to
random regular graphs for all ferromagnetic models and establish the Bethe
prediction for every ferromagnetic spin system on random regular graphs. We
also prove for the ferromagnetic Potts model that the Swendsen-Wang algorithm
is torpidly mixing on random D-regular graphs at the critical temperature for
large q.",1311.4839v3
2016-07-22,Magnon-induced long-range correlations and their neutron-scattering signature in quantum magnets,"We consider the coupling of the magnons in both quantum ferromagnets and
antiferromagnets to the longitudinal order-parameter fluctuations, and the
resulting nonanalytic behavior of the longitudinal susceptibility. In classical
magnets it is well known that long-range correlations induced by the magnons
lead to a singular wave-number dependence of the form $1/k^{4-d}$ in all
dimensions 2<d<4, for both ferromagnets and antiferromagnets. At zero
temperature we find a profound difference between the two cases. Consistent
with naive power counting, the longitudinal susceptibility in a quantum
antiferromagnet scales as $k^{d-3}$ for 1<d<3, whereas in a quantum ferromagnet
the analogous result, $k^{d-2}$, is absent due to a zero scaling function. This
absence of a nonanalyticity in the longitudinal susceptibility is due to the
lack of magnon number fluctuations in the ground state of a quantum
ferromagnet; correlation functions that are sensitive to other fluctuations do
exhibit the behavior predicted by simple power counting. Also of interest is
the dynamical behavior as expressed in the longitudinal part of the dynamical
structure factor, which is directly measurable via neutron scattering. For both
ferromagnets and antiferromagnets there is a logarithmic singularity at the
magnon frequency with a prefactor that vanishes as $T\to 0$. In the
antiferromagnetic case there also is a nonzero contribution at T=0 that is
missing for ferromagnets. Magnon damping due to quenched disorder restores the
expected scaling behavior of the longitudinal susceptibility in the
ferromagnetic case; it scales as $k^{d-2}$ if the order parameter is not
conserved, or as $k^d$ if it is. Detailed predictions are made for both two-
and three-dimensional systems at both T=0 and in the limit of low temperatures,
and the physics behind the various nonanalytic behaviors is discussed.",1607.06790v1
2017-03-16,Discovery of intrinsic ferromagnetism in 2D van der Waals crystals,"It has been long hoped that the realization of long-range ferromagnetic order
in two-dimensional (2D) van der Waals (vdW) crystals, combined with their rich
electronic and optical properties, would open up new possibilities for
magnetic, magnetoelectric and magneto-optic applications. However, in 2D
systems, the long-range magnetic order is strongly hampered by thermal
fluctuations which may be counteracted by magnetic anisotropy, according to the
Mermin-Wagner theorem. Prior efforts via defect and composition engineering,
and proximity effect only locally or extrinsically introduce magnetic
responses. Here we report the first experimental discovery of intrinsic
long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers by scanning
magneto-optic Kerr microscopy. In such a 2D vdW soft ferromagnet, for the first
time, an unprecedented control of transition temperature of ~ 35% - 57%
enhancement is realized via surprisingly small fields (<= 0.3 Tesla in this
work), in stark contrast to the stiffness of the transition temperature to
magnetic fields in the three-dimensional regime. We found that the small
applied field enables an effective anisotropy far surpassing the tiny
magnetocrystalline anisotropy, opening up a sizable spin wave excitation gap.
Confirmed by renormalized spin wave theory, we explain the phenomenon and
conclude that the unusual field dependence of transition temperature
constitutes a hallmark of 2D soft ferromagnetic vdW crystals. Our discovery of
2D soft ferromagnetic Cr2Ge2Te6 presents a close-to-ideal 2D Heisenberg
ferromagnet for studying fundamental spin behaviors, and opens the door for
exploring new applications such as ultra-compact spintronics.",1703.05753v1
2008-07-05,Electrical and magnetic properties of nano-scale Pi-junctions,"The physics of the ""Pi"" phase shift in ferromagnetic Josephson junctions
enables a range of applications for spin-electronic devices and quantum
computing. In this respect our research is devoted to the evaluation of the
best materials for the development and the realization of the quantum devices
based on superconductors and at the same point towards the reduction of the
size of the employed heterostructures towards and below nano-scale. In this
chapter we report our investigation of transitions from ""0"" to ""Pi"" states in
Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni,
Ni$_{80}$Fe$_{20}$ (Py) and Fe. We show that it is possible to fabricate
nanostructured Nb/ Ni(Co, Py, Fe)/Nb $\pi$-junctions with a nano-scale magnetic
dead layer and with a high level of control over the ferromagnetic barrier
thickness variation. In agreement with the theoretical model we estimate, from
the oscillations of the critical current as function of the ferromagnetic
barrier thickness, the exchange energy of the ferromagnetic material and we
obtain that it is close to bulk ferromagnetic materials implying that the
ferromagnet is clean and S/F roughness is minimal. We conclude that S/F/S
Josephson junctions are viable structures in the development of
superconductor-based quantum electronic devices; in particular Nb/Co/Nb and
Nb/Fe/Nb multilayers with their low value of the magnetic dead layer and high
value of the exchange energy can readily be used in controllable two-level
quantum information systems. In this respect, we discuss applications of our
nano-junctions to engineering magnetoresistive devices such as programmable
pseudo-spin-valve Josephson structures.",0807.0849v1
2013-08-31,Kondo lattice model: from local to non-local descriptions,"In this paper, we study the influence of spatial fluctuations in a
two-dimentional Kondo-Lattice model (KLM) with anti-ferromagnetic couplings. To
accomplish this, we first present an implementation of the dual-fermion (DF)
approach based on the hybridization expansion continuous-time quantum Monte
Carlo impurity solver (CT-HYB), which allows us to consistently compare the
local and non-local descriptions of this model. We find that, the inclusion of
non-locality restores the self-energy dispersion of the conduction electrons,
{\it i.e.} the $\vec{k}$ dependence of $\Sigma(\vec{k}, i\omega_{n})$. The
anti-ferromagnetic correlations result in an additional symmetry in
$\Sigma(\vec{k}, i\omega_{n})$, which is well described by the N\'eel
antiferromagnetic wave-vector. A ""metal""-""anti-ferromagnetic insulator""-""Kondo
insulator"" transition is observed at finite temperatures, which is driven by
the competition of the effective RKKY interaction (at the weak coupling regime)
and the Kondo singlet formation mechanism (at the strong coupling regime). Away
from half-filling, the anti-ferromagnetic phase becomes unstable against hole
doping. The system tends to develop a ferromagnetic phase with the spin
susceptibility $\chi_{s}(Q)$ peaking at $Q=\Gamma$. However, for small $J/t$,
no divergence of $\chi_{s}(\Gamma)$ is really observed, thus, we find no sign
of long-range ferromagnetism in the hole-doped two-dimension KLM. The
ferromagnetism is found to be stable at larger $J/t$ regime. Interestingly, we
find the local approximation employed in this work, {\it i.e.} the dynamical
mean-field theory (DMFT), is still a very good description of the KLM,
especially in the hole-doped case. However, at half-filling, the non-local
fluctuation effect is indeed pronounced. We observe a strong reduction of the
critical coupling strength for the onset of the Kondo insulating phase.",1309.0156v1
2015-12-08,The nature of the electrical conduction in ferromagnetic atomic-size contacts: insights from shot noise measurements and theoretical simulations,"With the goal to elucidate the nature of spin-dependent electronic transport
in ferromagnetic atomic contacts, we present here a combined experimental and
theoretical study of the conductance and shot noise of metallic atomic contacts
made of the 3d ferromagnetic materials Fe, Co, and Ni. For comparison, we also
present the corresponding results for the noble metal Cu. Conductance and shot
noise measurements, performed using a low-temperature break junction setup,
show that in these ferromagnetic nanowires: (i) there is no conductance
quantization of any kind, (ii) transport is dominated by several partially-open
conduction channels, even in the case of single-atom contacts, and (iii) the
Fano factor of large contacts saturates to values that clearly differs from
those of monovalent (nonmagnetic) metals. We rationalize these observations
with the help of a theoretical approach that combines molecular dynamics
simulations to describe the junction formation with nonequilibrium Green's
function techniques to compute the transport properties within the
Landauer-Buettiker framework. Our theoretical approach successfully reproduces
all the basic experimental results and it shows that all the observations can
be traced back to the fact that the d bands of the minority-spin electrons play
a fundamental role in the transport through ferromagnetic atomic-size contacts.
These d bands give rise to partially open conduction channels for any contact
size, which in turn lead naturally to the different observations described
above. Thus, the transport picture for these nanoscale ferromagnetic wires that
emerges from the ensemble of our results is clearly at variance with the well
established conduction mechanism that governs the transport in macroscopic
ferromagnetic wires, where the d bands are responsible for the magnetism but do
not take part in the charge flow.",1512.02601v1
2019-01-09,Stability of Ferromagnetism in Hubbard Models with Nearly-Flat Bands,"Whether spin-independent Coulomb interaction in an electron system can be the
origin of ferromagnetism has been an open problem for a long time. Recently, a
""constructive"" approach to this problem has been developed, and the existence
of ferromagnetism in the ground states of certain Hubbard models was
established rigorously. A special feature of these Hubbard models is that their
lowest bands (in the corresponding single-electron problems) are completely
flat. Here we study models obtained by adding small but arbitrary
translation-invariant perturbation to the hopping Hamiltonian of these
flat-band models. The resulting models have nearly-flat lowest bands. We prove
that the ferromagnetic state is stable against a single-spin flip provided that
Coulomb interaction U is sufficiently large. (It is easily found that the same
state is unstable against a single-spin flip if U is small enough.) We also
prove upper and lower bounds for the dispersion relation of the lowest energy
eigenstate with a single flipped spin, which bounds establish that the model
has ""healthy"" spin-wave excitation. It is notable that the (local) stability of
ferromagnetism is proved in non-singular Hubbard models, in which we must
overcome competition between the kinetic energy and the Coulomb interaction. We
also note that this is one of the very few rigorous and robust results which
deal with truly nonperturbative phenomena in many electron systems. The local
stability strongly suggests that the Hubbard models with nearly flat bands have
ferromagnetic ground states. We believe that the present models can be studied
as paradigm models for (insulating) ferromagnetism in itinerant electron
systems.",1901.02617v2
2020-09-07,Analysis of landscape hierarchy during coarsening and aging in Ising spin glasses,"We use record dynamics (RD), a coarse-grained description of the ubiquitous
relaxation phenomenology known as ""aging"", as a diagnostic tool to find
universal features that distinguish between the energy landscapes of Ising spin
models and the ferromagnet. According to RD, a non-equilibrium system after a
quench relies on fluctuations that randomly generate a sequence of irreversible
record-sized events (quakes or avalanches) that allow the system to escape
ever-higher barriers of meta-stable states within a complex, hierarchical
energy landscape. Once these record events allow the system to overcome such
barriers, the system relaxes by tumbling into the following meta-stable state
that is marginally more stable. Within this framework, a clear distinction can
be drawn between the coarsening dynamics of an Ising ferromagnet and the aging
of the spin glass, which are often put in the same category. To that end, we
interpolate between the spin glass and ferromagnet by varying the admixture $p$
of ferromagnetic over anti-ferromagnetic bonds from the glassy state (at 50%
each) to wherever clear ferromagnetic behavior emerges. The accumulation of
record events grows logarithmic with time in the glassy regime, with a sharp
transition at a specific admixture into the ferromagnetic regime where such
activations saturate quickly. We show this effect both for the Edwards-Anderson
model on a cubic lattice as well as the Sherrington-Kirkpatrick (mean-field)
spin glass. While this transition coincides with a previously observed
zero-temperature equilibrium transition in the former, that transition has not
yet been described for the latter.",2009.03412v2
2022-10-23,Anomalous supercurrent modulated by interfacial magnetizations in Josephson junctions with ferromagnetic bilayers,"Based on the Bogoliubov-de Gennes equations, we investigate the transport of
the Josephson current in a S/$f_L$-F$_1$-$f_C$-F$_2$-$f_R$/S junction, where S
and F$_{1,2}$ are superconductors and ferromagnets, and $f_{L, C, R}$ are the
left, central, and right spin-active interfaces. These interfaces have
noncollinear magnetizations, and the azimuthal angles of the magnetizations at
the $f_{L, C, R}$ interfaces are $\chi_{L, C, R}$. We demonstrate that, if both
the ferromagnets have antiparallel magnetizations, the critical current
oscillates as a function of the exchange field and the thickness of the
ferromagnets for particular $\chi_L$ or $\chi_R$. By contrast, when the
magnetization at the $f_C$ interface is perpendicular to that at the $f_L$ and
$f_R$ interfaces, the critical current reaches a larger value and is hardly
affected by the exchange field and the thickness. Interestingly, if both the
ferromagnets are converted to antiparallel half-metals, the critical current
maintains a constant value and rarely changes with the ferromagnetic
thicknesses and the azimuthal angles. At this time, an anomalous supercurrent
can appear in the system, in which case the Josephson current still exists even
if the superconducting phase difference $\phi$ is zero. This supercurrent
satisfies the current-phase relation $I=I_c\sin(\phi+\phi_0)$ with $I_c$ being
the critical current and $\phi_0=2\chi_C-\chi_L-\chi_R$. We deduce that the
additional phase $\phi_0$ arises from phase superposition, where the phase is
captured by the spin-triplet pairs when they pass through each spin-active
interface. In addition, when both the ferromagnets are transformed into
parallel half-metals, the $f_C$ interface never contributes any phase to the
supercurrent and $\phi_0=\chi_R-\chi_L+\pi$. In such a case, the current-phase
relation is similar to that in a S/$f_L$-F-$f_R$/S junction.",2210.12718v1
2024-04-05,Nagaoka Ferromagnetism in $3 \times 3$ Arrays and Beyond,"Nagaoka ferromagnetism (NF) is a long-predicted example of itinerant
ferromagnetism (IF) in the Hubbard model that has been studied theoretically
for many years. The condition for NF, an infinite onsite Coulomb repulsion and
a single hole in a half-filled band, does not arise naturally in materials, and
was only realized recently for the first time in experiments on a 2 \times 2
array of gated quantum dots. Atomically precise fabrication of dopant arrays in
Si allows for engineering highly controllable systems with complex geometries.
This makes dopant arrays a good candidate to study NF in different array
geometries through analog quantum simulation. Here we present theoretical
simulations done for $3 \times 3$ arrays and larger $N \times N $ arrays of
quantum dots, and predict the emergence of different forms of ferromagnetism in
different geometries. We find NF in perfect $3 \times 3$ arrays, as well as in
$N \times N $ arrays for one hole less than half-filling. The ratio of the
Hubbard on-site repulsion U to hopping t that defines the onset of NF increases
as N increases, approaching the bulk limit of infinite U for large N.
Additional simulations are done for geometries made by removing sites from $N
\times N $ arrays. Different forms of ferromagnetism are found for different
geometries. Loops show ferromagnetism, but only for three electrons. For loops,
the critical U/t for the onset of ferromagnetism decreases as the loop length
increases. We show that this different dependence on size for loops and $N
\times N $ arrays can be understood by a scaling argument. Our results show how
analog quantum simulation with small arrays can elucidate the role of effects
including wavefunction connectivity; system geometry, size and symmetry; bulk
and edge sites; and kinetic energy in determining the quantum magnetism of
small systems.",2404.03889v1
1999-10-22,Evidence of anisotropic magnetic polarons in la$_{0.94}$Sr$_{0.06}$MnO$_3$ by neutron scattering and comparison with Ca-doped manganites,"Elastic and inelastic neutron scattering experiments have been performed in a
La$_{0.94}$Sr$_{0.06}$MnO$_3$ untwinned crystal, which exhibits an
antiferromagnetic canted magnetic structure with ferromagnetic layers.
  The elastic small q scattering exhibits a modulation with an anisotropic
q-dependence. It can be pictured by ferromagnetic inhomogeneities or polarons
with a platelike shape, the largest size ($\approx17\AA$) and largest
inter-polaron distance ($\approx$ 38$\AA$) being within the ferromagnetic
layers. Comparison with observations performed on Ca-doped samples, which show
the growth of the magnetic polarons with doping, suggests that this growth is
faster for the Sr than for the Ca substitution. Below the gap of the spin wave
branch typical of the AF layered magnetic structure, an additional spin wave
branch reveals a ferromagnetic and isotropic coupling, already found in
Ca-doped samples. Its q-dependent intensity, very anisotropic, closely reflects
the ferromagnetic correlations found for the static clusters. All these results
agree with a two-phase electronic segregation occurring on a very small scale,
although some characteristics of a canted state are also observed suggesting a
weakly inhomogeneous state.",9910361v2
2000-09-19,"Ferromagnetism in a (001), (110), and (111)-oriented Ru mololayer on Ag, Au, and Cu-substrates","We have studied the magnetic behavior of a 4d transition metal Ru monolayer
(ML) on different substrates and orientations. In the ground state, a Ru-ML is
expected to be ferromagnetic on Ag(001) and Au(001) with a magnetic moment
$(\mu) $ of 1.73 Bohr magnetons $(\mu_{B}) $ in both cases. On Cu(001), a Ru-ML
is not magnetic. In this paper, we study the magnetic behavior of a Ru-ML at
other orientations, i.e., (110) and (111). We found magnetism on Au (111), and
Ag (111) ($\mu\thicksim 1.3\mu_{B}$ for both) but no magnetic activity on a Cu
substrate in any orientation. Further, we found that on Ag(110), a Ru-ML is
ferromagnetic with $\mu =1.3\mu_{B}$. On Au(110), a Ru-ML is not magnetic.
Since on the (001) and (111) orientations a Ru-ML has about the same magnetic
activity on Ag as on Au, we found surprising the behavior in the (110)
orientation. We analyze it in detail in the final part of the paper. We found
that there exists a metastable ferromagnetic state, in this case, and that a
Ru-ML becomes ferromagnetic under a small expansion of the Au-lattice. This is
not the case for Cu.",0009280v1
2001-08-04,Giant anisotropic magnetostriction in Pr$_{0.5}$Sr$_{0.5}$MnO$_3$,"Magnetic, linear thermal expansion (LTE), anisotropic ($\lambda_t$) and
volume ($\omega $) magnetostriction properties of Pr$_{0.5}$Sr$_{0.5}$MnO$_3$
were investigated. The LTE decreases smoothly from 300 K without a clear
anomaly either around the Curie (T$_C$ = 270 K) or the Neel temperature (T$_N$
= 100 K) and it exhibits hysteresis over a wide temperature range (60 K-270 K)
upon warming. Isothermal magnetization study suggests that 13 % of the
ferromagnetic phase coexists with 87 % of the antiferromagnetic phase at 25 K.
The parallel and perpendicular magnetostrictions undergo rapid changes during
the metamagnetic transition. Contrary to the isotropic giant volume
magnetostriction reported in manganites so far, this compound exhibits a giant
anisotropic magnetostriction ($\lambda_t \approx 10^{-3}$) and smaller volume
($\omega \approx 10^{-4}$) magnetostrictions below T$_N$. We suggest that the
field induced antiferromagnetic to ferromagnetic transition is accompanied by a
structural transition from the d$_{x^2-y^2}$ orbital ordered antiferromagnetic
(orthorhombic) to the orbital disordered ferromagnetic (tetragonal) phase. The
metamagnetic transition proceeds through nucleation and growth of the
ferromagnetic domains at the expense of the antiferromagnetic phase. The
preferential orientation of the ferromagnetic (tetragonal) domains along the
field direction increases the linear dimension of the sample in the field
direction and decreases in the orthogonal direction leading to the observed
giant anisotropic magnetostriction effect. Our study also suggests that
nanodomains of the low temperature antiferromagnetic phase possibly exist in
the temperature region T$_N$ < T < T$_C$.",0108078v2
2002-03-20,Temperature-dependent electronic structure and magnetic stability of thin ferromagnetic films,"We study correlation effects and temperature dependencies in the electronic
structure of thin ferromagnetic local-moment films. In a first step the
Kondo-lattice model is investigated as a candidate for a proper representation
of local-moment ferromagnets. Magnetic and electronic key-quantities as the
Curie-temperature and the quasiparticle density of states are derived with
previously tested many-body procedures. It is shown that the magnetic
properties can be interpreted exclusively in terms of the temperature-dependent
electronic quasiparticle structure. An extended RKKY theory leads to effective
Heisenberg exchange integrals, which turn out to be functionals of the
conduction electron selfenergy, getting therewith a remarkable temperature and
band occupation dependence.
  In a second step the model studies are combined with tight binding-LMTO
bandstructure calculations in order to get for real ferromagnetic films
quasiparticle densities of states and quasiparticle bandstructures. The
proposed method avoids the double-counting of relevant interactions and takes
into account the correct symmetry of the atomic orbitals. Special results are
given for thin ferromagnetic EuO (100) films. The Curie temperature
$T_{\textrm{C}}$ of the EuO film turns out to be strongly thickness-dependent,
starting from a very low value ($\simeq 15K$) for the monolayer and reaching
the bulk value at about 30 layers. For a 20-layer film we predict the existence
of a surface state, the temperature-behaviour of which can lead to a surface
halfmetal-insulator transition.",0203417v1
2002-04-29,Proximity effect in multiterminal hybrid structures,"We consider the proximity effect in multiterminal ferromagnet superconductor
(FSF) hybrid structures in which two or three electrodes are connected to a
superconductor. We show that two competing effects take place in these systems:
(i) pair breaking effects due to the response to the exchange field induced in
the superconductor; (ii) a reduction of the \SOP at the interface that takes
place already in NS junctions. We focus on this second effect that dominates if
the thickness of the S layer is small enough. We consider several
single-channel electrodes connected to the same site. We calculate the
superconducting order parameter and the local density of state (LDOS). With two
ferromagnetic electrodes connected to a superconductor we find that the
superconducting order parameter in the ferromagnetic alignment is larger than
the superconducting order parameter in the antiferromagnetic alignment
($\Delta_{\rm F} >\Delta_{\rm AF}$), in agreement with [Eur. Phys. J. B {\bf
25}, 373 (2002)]. If a third spin polarized electrode is connected to a
superconductor we find that $\Delta_{\rm F}-\Delta_{\rm AF}$ can change sign as
the transparency of the third electrode increases. This can be understood from
the fact that the superconducting order parameter is reduced if pair
correlations among the ferromagnetic electrodes increase. If the two
ferromagnetic electrodes are within a finite distance we find Friedel
oscillations in the Gorkov function but we still obtain $\Delta_{\rm F} >
\Delta_{\rm AF}$.",0204610v2
2002-07-16,Magnetic and Transport Properties of La$_{0.7}$Sr$_{0.3}$Co$_{1-y}$Mn$_y$O$_3$,"While both La$_{0.7}$Sr$_{0.3}$MnO$_3$ and La$_{0.7}$Sr$_{0.3}$CoO$_3$ are
ferromagnets with metallic conductivity below $T_\mathrm{c}$ (360K and 220K,
respectively), partial substitutions of Co by Mn in
La$_{0.7}$Sr$_{0.3}$Co$_{1-y}$Mn$_y$O$_3$ ($y < 0.1$) drastically suppress the
ferromagnetic long-range order pre-established by Co-O-Co double exchange and
tune the conductivity towards insulating behavior. Since Mn-O-Mn
double-exchange interactions are avoidable at low Mn-substitution levels, the
deterioration of ferromagnetism and conductivity thus provides evidence for no
Mn-O-Co double exchange (but antiferromagnetic superexchange) in the present
system. At $y = 0.1$, the ferromagnetism is no longer observed; the system
becomes an insulating spin-glass with $T_\mathrm{g}\approx 62$K as estimated
from the ac-susceptibility data using the conventional critical slowing-down
scaling law. With further substitution ($y\geq 0.3$), the ferromagnetism is
recovered ($T_\mathrm{c} = 165$K for $y = 0.3$ and 200K for $y = 0.5$) while
the resistivity continues increasing and exhibits insulating behavior. These
results indicate that the substitution is not simply a mixture of
La$_{0.7}$Sr$_{0.3}$MnO$_3$ and La$_{0.7}$Sr$_{0.3}$CoO$_3$, but produces a
more complicated scenario of spin states, interactions and disorder.",0207380v1
2002-09-23,Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions,"We present a theoretical description of the thermopower due to
magnon-assisted tunneling in a mesoscopic tunnel junction between two
ferromagnetic metals. The thermopower is generated in the course of thermal
equilibration between two baths of magnons, mediated by electrons. For a
junction between two ferromagnets with antiparallel polarizations, the ability
of magnon-assisted tunneling to create thermopower $S_{AP}$ depends on the
difference between the size $\Pi_{\uparrow, \downarrow}$ of the majority and
minority band Fermi surfaces and it is proportional to a temperature dependent
factor $(k_{B}T/\omega_{D})^{3/2}$ where $\omega_{D}$ is the magnon Debye
energy. The latter factor reflects the fractional change in the net
magnetization of the reservoirs due to thermal magnons at temperature $T$
(Bloch's $T^{3/2}$ law). In contrast, the contribution of magnon-assisted
tunneling to the thermopower $S_P$ of a junction with parallel polarizations is
negligible. As the relative polarizations of ferromagnetic layers can be
manipulated by an external magnetic field, a large difference $\Delta S =
S_{AP} - S_P \approx S_{AP} \sim - (k_B/e) f (\Pi_{\uparrow},\Pi_{\downarrow})
(k_BT/\omega_{D})^{3/2}$ results in a magnetothermopower effect. This
magnetothermopower effect becomes giant in the extreme case of a junction
between two half-metallic ferromagnets, $\Delta S \sim - k_B/e$.",0209520v1
2002-12-16,Significant suppression of weak ferromagnetism in (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$,"The magnetic structure of (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$ has been
studied by magnetization measurements of single crystals, which show
antiferromagnetic long-range order below $T_N$ = 265 K and a structural phase
transition at $T_s$ = 130 K. At $T_s < T < T_N$, the Cu spin susceptibility
exhibits almost the same behavior as that of La${}_2$CuO${}_4$ in the
low-temperature orthorhombic phase, which indicates the existence of finite
spin canting out of the CuO${}_2$ plane. At $T < T_s$, the magnitude of the
weak-ferromagnetic moment induced by the spin canting is suppressed
approximately by 70{%}. This significant suppression of the weak-ferromagnetic
moment is carefully compared with the theoretical analysis of weak
ferromagnetism by Stein {\it et al.} (Phys. Rev. B {\bf 53}, 775 (1996)), in
which the magnitude of weak-ferromagnetic moments strongly depend on the
crystallographic symmetry. Based on such comparison, below $T_s$
(La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$ is in the low-temperature less-orthorhombic
phase with a space group of $Pccn$. We also discuss the possible magnetic
structure of the pure low-temperature tetragonal phase with space group
$P4_2/{ncm}$, which is relevant for rare-earth and alkaline-earth ions co-doped
La${}_2$CuO${}_4$.",0212360v2
2003-03-10,"Electronic structure, exchange interactions and Curie temperature in diluted III-V magnetic semiconductors: (GaCr)As, (GaMn)As, (GaFe)As","We complete our earlier (Phys. Rev. B, {\bf 66}, 134435 (2002)) study of the
electronic structure, exchange interactions and Curie temperature in (GaMn)As
and extend the study to two other diluted magnetic semiconductors (GaCr)As and
(GaFe)As. Four concentrations of the 3d impurities are studied: 25%, 12.5%,
6.25%, 3.125%. (GaCr)As and (GaMn)As are found to possess a number of similar
features. Both are semi-metallic and ferromagnetic, with similar properties of
the interatomic exchange interactions and the same scale of the Curie
temperature. In both systems the presence of the charge carriers is crucial for
establishing the ferromagnetic order. An important difference between two
systems is in the character of the dependence on the variation of the number of
carriers. The ferromagnetism in (GaMn)As is found to be very sensitive to the
presence of the donor defects, like As$_{\rm Ga}$ antisites. On the other hand,
the Curie temperature of (GaCr)As depends rather weakly on the presence of this
type of defects but decreases strongly with decreasing number of electrons. We
find the exchange interactions between 3d atoms that make a major contribution
into the ferromagnetism of (GaCr)As and (GaMn)As and propose an exchange path
responsible for these interactions. The properties of (GaFe)As are found to
differ crucially from the properties of (GaCr)As and (GaMn)As. (GaFe)As does
not show a trend to ferromagnetism and is not half-metallic that makes this
system unsuitable for the use in spintronic semiconductor devices.",0303172v3
2003-08-26,Ferromagnetic materials in the zinc-blende structure,"New materials are currently sought for use in spintronics applications.
Ferromagnetic materials with half metallic properties are valuable in this
respect. Here we present the electronic structure and magnetic properties of
binary compounds consisting of 3d transition metals and group V elements viz.
P, Sb and As in the zinc-blende structure. We demonstrate that compounds of V,
Cr and Mn show half metallic behavior for appropriate lattice constants.
  By comparing the total energies in the ferromagnetic and antiferromagnetic
structures, we have ascertained that the ferromagnetic phase is stable over the
antiferromagnetic one. Of the different compounds studied, the Cr based systems
exhibit the strongest interatomic exchange interactions, and are hence
predicted to have the highest critical temperatures. Also, we predict that VAs
under certain growth conditions should be a semiconducting ferromagnet.
Moreover, critical temperatures of selected half metallic compounds have been
estimated from mean field theory and Monte Carlo simulations using parameters
obtained from a {\it ab-initio} non-collinear, tight binding linearized
muffin-tin orbital method. From a simple model, we calculate the reflectance
from an ideal MnAs/InAs interface considering the band structures of MnAs and
InAs. Finally we present results on the relative stabilities of MnAs and CrSb
compounds in the NiAs and zinc-blende structures, and suggest a parameter space
in substrate lattice spacings for when the zinc-blende structure is expected to
be stable.",0308524v1
2003-09-22,Ferromagnetism in Mn doped GaAs due to substitutional-interstitial complexes,"While most calculations on the properties of the ferromagnetic semiconductor
GaAs:Mn have focussed on isolated Mn substituting the Ga site (Mn$_{Ga}$), we
investigate here whether alternate lattice sites are favored and what the
magnetic consequences of this might be. Under As-rich (Ga-poor) conditions
prevalent at growth, we find that the formation energies are lower for
Mn$_{Ga}$ over interstitial Mn (Mn$_i$).As the Fermi energy is shifted towards
the valence band maximum via external $p$-doping, the formation energy of
Mn$_i$ is reduced relative to Mn$_{Ga}$. Furthermore, under epitaxial growth
conditions, the solubility of both substitutional and interstitial Mn are
strongly enhanced over what is possible under bulk growth conditions. The high
concentration of Mn attained under epitaxial growth of p-type material opens
the possibility of Mn atoms forming small clusters. We consider various types
of clusters, including the Coulomb-stabilized clusters involving two Mn$_{Ga}$
and one Mn$_i$. While isolated Mn$_i$ are hole killers (donors), and therefore
destroy ferromagnetism,complexes such as Mn$_{Ga}$-Mn$_i$-Mn$_{Ga}$) are found
to be more stable than complexes involving Mn$_{Ga}$-Mn$_{Ga}$-Mn$_{Ga}$. The
former complexes exhibit partial or total quenching of holes, yet Mn$_i$ in
these complexes provide a channel for a ferromagnetic arrangement of the spins
on the two Mn$_{Ga}$ within the complex. This suggests that ferromagnetism in
Mn doped GaAs arises both from holes due to isolated Mn$_{Ga}$ as well as from
strongly Coulomb stabilized Mn$_{Ga}$-Mn$_i$-Mn$_{Ga}$ clusters.",0309502v1
2004-09-09,Nonlocal magnetization dynamics in ferromagnetic heterostructures,"Two complementary effects modify the GHz magnetization dynamics of nanoscale
heterostructures of ferromagnetic and normal materials relative to those of the
isolated magnetic constituents: On the one hand, a time-dependent ferromagnetic
magnetization pumps a spin angular-momentum flow into adjacent materials and,
on the other hand, spin angular momentum is transferred between ferromagnets by
an applied bias, causing mutual torques on the magnetizations. These phenomena
are manifestly nonlocal: they are governed by the entire spin-coherent region
that is limited in size by spin-flip relaxation processes. We review recent
progress in understanding the magnetization dynamics in ferromagnetic
heterostructures from first principles, focusing on the role of spin pumping in
layered structures. The main body of the theory is semiclassical and based on a
mean-field Stoner or spin-density--functional picture, but quantum-size effects
and the role of electron-electron correlations are also discussed. A growing
number of experiments support the theoretical predictions. The formalism should
be useful to understand the physics and to engineer the characteristics of
small devices such as magnetic random-access memory elements.",0409242v3
2004-12-20,Ferromagnetism in Fe-substituted spinel semiconductor ZnGa$_2$O$_4$,"Motivated by the recent experimental observation of long range ferromagnetic
order at a relatively high temperature of 200K in the Fe-doped ZnGa$_2$O$_4$
semiconducting spinel, we propose a possible mechanism for the observed
ferromagnetism in this system. We show, supported by band structure
calculations, how a model similar to the double exchange model can be written
down for this system and calculate the ground state phase diagram for the two
cases where Fe is doped either at the tetrahedral position or at the octahedral
position. We find that in both cases such a model can account for a stable
ferromagnetic phase in a wide range of parameter space. We also argue that in
the limit of high Fe$^{2+}$ concentration at the tetrahedral positions a
description in terms of a two band model is essential. The two $e_g$ orbitals
and the hopping between them play a crucial role in stabilizing the
ferromagnetic phase in this limit. The case when Fe is doped simultaneously at
both the tetrahedral and the octahedral position is also discussed.",0412530v3
2005-08-29,"Magnetic Properties of J-J-J' Quantum Heisenberg Chains with Spin S=1/2, 1, 3/2 and 2 in a Magnetic Field","By means of the density matrix renormalization group (DMRG) method, the
magnetic properties of the J-J-J$^{\prime}$ quantum Heisenberg chains with spin
$S=1/2$, 1, 3/2 and 2 in the ground states are investigated in the presence of
a magnetic field. Two different cases are considered: (a) when $J$ is
antiferromagnetic and $J^{\prime}$ is ferromagnetic (i.e. the AF-AF-F chain),
the system is a ferrimagnet. The plateaus of the magnetization are observed. It
is found that the width of the plateaus decreases with increasing the
ferromagnetic coupling, and disappears when $% J^{\prime}/J$ passes over a
critical value. The saturated field is observed to be independent of the
ferromagnetic coupling; (b) when $J$ is ferromagnetic and $J^{\prime}$ is
antiferromagnetic (i.e. the F-F-AF chain), the system becomes an
antiferromagnet. The plateaus of the magnetization are also seen. The width of
the plateaus decreases with decreasing the antiferromagnetic coupling, and
disappears when $J^{\prime}/J $ passes over a critical value. Though the ground
state properties are quite different, the magnetization plateaus in both cases
tend to disappear when the ferromagnetic coupling becomes more dominant.
Besides, no fundamental difference between the systems with spin half-integer
and integer has been found.",0508685v1
2006-02-14,Can a non-ideal metal ferromagnet inject spin into a semiconductor with 100% efficiency without a tunnel barrier?,"Current understanding of spin injection tells us that a metal ferromagnet can
inject spin into a semiconductor with 100% efficiency if either the ferromagnet
is an ideal half metal with 100% spin polarization, or there exists a suitable
tunnel barrier at the interface. In this paper, we show that, at absolute zero
temperature, 100% spin injection efficiency from a non-ideal metal ferromagnet
into a semiconductor quantum wire can be reached at certain injection energies,
without a tunnel barrier, provided there is an axial magnetic field along the
direction of current flow as well as a spin orbit interaction in the
semiconductor. At these injection energies, spin is injected only from the
majority spin band of the ferromagnetic contact, resulting in 100% spin
injection efficiency. This happens because of the presence of antiresonances in
the transmission coefficient of the minority spins when their incident energies
coincide with Zeeman energy states in the quantum wire.
  At absolute zero and below a critical value of the axial magnetic field,
there are two distinct Zeeman energy states and therefore two injection
energies at which ideal spin filtering is possible; above the critical magnetic
field there is only one such injection energy. The spin injection efficiency
rapidly decreases as the temperature increases. The rate of decrease is slower
when the magnetic field is above the critical value. The appropriate choice of
semiconductor materials and structures necessary to maintain a large spin
injection efficiency at elevated temperatures is discussed.",0602335v1
2006-06-16,Spin transfer in an antiferromagnet,"An electrical current can transfer spin angular momentum to a ferromagnet.
This novel physical phenomenon, called spin transfer, offers unprecedented
spatial and temporal control over the magnetic state of a ferromagnet and has
tremendous potential in a broad range of technologies, including magnetic
memory and recording. Recently, it has been predicted that spin transfer is not
limited to ferromagnets, but can also occur in antiferromagnetic materials and
even be stronger under some conditions. In this paper we demonstrate transfer
of spin angular momentum across an interface between ferromagnetic and
antiferromagnetic metals. The spin transfer is mediated by an electrical
current of high density (~10^12 A/m^2) and revealed by variation in the
exchange bias at the ferromagnet/antiferromagnet interface. We find that,
depending on the polarity of the electrical current flowing across the
interface, the strength of the exchange bias can either increase or decrease.
This finding is explained by the theoretical prediction that a spin polarized
current generates a torque on magnetic moments in the antiferromagnet.
Current-mediated variation of exchange bias can be used to control the magnetic
state of spin-valve devices, e.g., in magnetic memory applications.",0606462v1
2003-08-05,Ferromagnetic Ordering of Energy Levels,"We study a natural conjecture regarding ferromagnetic ordering of energy
levels in the Heisenberg model which complements the Lieb-Mattis Theorem of
1962 for antiferromagnets: for ferromagnetic Heisenberg models the lowest
energies in each subspace of fixed total spin are strictly ordered according to
the total spin, with the lowest, i.e., the ground state, belonging to the
maximal total spin subspace. Our main result is a proof of this conjecture for
the spin-1/2 Heisenberg XXX and XXZ ferromagnets in one dimension. Our proof
has two main ingredients. The first is an extension of a result of Koma and
Nachtergaele which shows that monotonicity as a function of the total spin
follows from the monotonicity of the ground state energy in each total spin
subspace as a function of the length of the chain. For the second part of the
proof we use the Temperley-Lieb algebra to calculate, in a suitable basis, the
matrix elements of the Hamiltonian restricted to each subspace of the highest
weight vectors with a given total spin. We then show that the positivity
properties of these matrix elements imply the necessary monotonicity in the
volume. Our method also shows that the first excited state of the XXX
ferromagnet on any finite tree has one less than maximal total spin.",0308006v2
2003-10-30,Competition of Two Terms in Exchange Hamiltonian for magnetic substances,"The unjustifiable or wrong in the previous magnetism theories has been
indicated in this paper. For a N electrons system with Heisenberg exchange
integral, the correct exchange Hamilton should be of two terms, not only one as
in the previous magnetism theories. The role of the minor term in the exchange
Hamilton was considered. Based on the principle of superposition of state, the
eigenstate of the system with Heisenberg exchange integral, the sum of a
positive term and a negative term, and the energy (relative to exchange
interaction) eigenvalue were attained. When the positive term is equal to the
absolute value of the negative term, the system is in the spin glass state, the
probabilities of parallel and antiparallel arrange for every pair of spins of
electron of nearest neighbours in the system are equal. When the positive term
is not equal to the absolute value of the negative term,the probabilities are
not equal, and there coexist the ferromagnetic states and spin glass or
antiferromagnetic state and spin glass,when ferromagnetic states and spin glass
or antiferromagnetic state and spin glass coexist, the energy of the system is
lower than that when only ferromagnetic states or antiferromagnetic state
exists as in previous theory. Weiss ferromagnetic state or Neel anti
ferromagnetic state is just a special state as the positive term is equal to
zero or negative term is equal to zero.",0310178v1
2007-07-11,Changeover from Glassy ferromagnetism of the orbital domain state to long range ferromagnetic ordering in La{_{0.9}}Sr_{0.1}MnO{_3},"An attempt is made to resolve the controversy related to the low temperature
phase (ground state) of the low-doped ferromagnetic (FM)- insulator(I)
manganite through bulk magnetic measurements on La${_{0.9}}$Sr$_{0.1}$MnO${_3}$
sample. It is shown that the FM phase, formed out of well defined transition in
the low-doped system, becomes inhomogeneous with decrease in temperature. This
inhomogeniety is considered to be an outcome of the formation of orbital domain
state of e$_g$-electrons having hole rich (metallic) walls separating the hole
deficient (insulating) regions. The resulting complexity brings in
metastability and glassy behaviour within the FM phase at low temperature,
however, with no resemblance to spin glass, cluster glass or reentrant phases.
It shows ageing effect without memory but magnetic relaxation shows signatures
of inter-cluster interaction. The energy landscape picture of this glassy phase
is described in terms of hierarchical model. Further, it is shown that this
inhomogeneity disappear in La${_{0.9}}$Sr$_{0.1}$MnO$_{3.08}$ where, the
orbital domain state is destroyed by self doping resulting in reduction of
Mn$^{3+}$ and hence e$_g$-electrons. The ferromagnetic phase of the
non-stoichiometric sample, does not show glassy behaviour. It neither follows
'hierarchical model' nor 'droplet model' generally used to explain glassy or
inhomogeneous systems. Its magnetic response can be explained simply from the
domain wall dynamics of otherwise homogeneous ferromagnet.",0707.1555v1
2008-04-10,Electrical transport and ferromagnetism in Ga1-xMnxAs synthesized by ion implantation and pulsed-laser melting,"We present a detailed investigation of the magnetic and magnetotransport
properties of thin films of ferromagnetic Ga1-xMnxAs synthesized using ion
implantation and pulsed-laser melting (II-PLM). The field and
temperature-dependent magnetization, magnetic anisotropy, temperature-dependent
resistivity, magnetoresistance, and Hall effect of II-PLM Ga1-xMnxAs films have
all of the characteristic signatures of the strong p-d interaction of holes and
Mn ions observed in the dilute hole-mediated ferromagnetic phase. The
ferromagnetic and electrical transport properties of II-PLM films correspond to
the peak substitutional Mn concentration meaning that the non-uniform Mn depth
distribution is unimportant in determining the film properties. Good
quantitative agreement is found with films grown by low temperature molecular
beam epitaxy (LT-MBE) and having the similar substitutional Mn_Ga composition.
Additionally, we demonstrate that II-PLM Ga1-xMnxAs films are free from
interstitial Mn_I because of the high temperature processing. At high Mn
implantation doses the kinetics of solute redistribution during solidification
alone determine the maximum resulting Mn_Ga concentration. Uniaxial anisotropy
between in-plane [-110]and [110] directions is present in II-PLM Ga1-xMnxAs
giving evidence for this being an intrinsic property of the carrier-mediated
ferromagnetic phase.",0804.1612v1
2008-05-05,The role of interface transparency and spin-dependent scattering in diffusive ferromagnet/superconductor heterostructures,"We present a numerical study of the density of states in a
ferromagnet/superconductor junction and the Josephson current in a
superconductor/ferromagnet/superconductor junction in the diffusive limit by
solving the Usadel equation with Nazarov's boundary conditions. Our
calculations are valid for an arbitrary interface transparency and arbitrary
spin-dependent scattering rate, which allows us to explore the entire
proximity-effect regime. We first investigate how the proximity-induced
anomalous Green's function affects the density of states in the ferromagnet for
several values of the exchange field. In each case, we consider the effect of
the barrier transparency and allow for various concentrations of magnetic
impurities. In particular, we address how the zero-energy peak and minigap
observed in experiments may be understood in terms of the interplay between the
singlet and triplet anomalous Green's function and their dependence on the
concentration of magnetic impurities. We also investigate the role of the
barrier transparency and spin-flip scattering in a
superconductor/ferromagnet/superconductor junction. We suggest that such
diffusive Josephson junctions with large residual values of the supercurrent at
the 0-$\pi$ transition, where the first harmonic term in the current vanishes,
may be used as efficient supercurrent-switching devices. It is also found that
uniaxial spin-flip scattering has very different effect on the 0-$\pi$
transition points depending on whether one regards the width- or
temperature-dependence of the current.",0805.0533v1
2009-04-07,Thermoelectrical manipulation of nanomagnets,"We investigate the interplay between the thermodynamic properties and
spin-dependent transport in a mesoscopic device based on a magnetic multilayer
(F/f/F), in which two strongly ferromagnetic layers (F) are exchange-coupled
through a weakly ferromagnetic spacer (f) with the Curie temperature in the
vicinity of room temperature. We show theoretically that the Joule heating
produced by the spin-dependent current allows a spin-thermo-electronic control
of the ferromagnetic-to-paramagnetic (f/N) transition in the spacer and,
thereby, of the relative orientation of the outer F-layers in the device
(spin-thermo-electric manipulation of nanomagnets). Supporting experimental
evidence of such thermally controlled switching from parallel to antiparallel
magnetization orientations in F/f(N)/F sandwiches is presented. Furthermore, we
show theoretically that local Joule heating due to a high concentration of
current in a magnetic point contact or a nanopillar can be used to reversibly
drive the weakly ferromagnetic spacer through its Curie point and thereby
exchange couple and decouple the two strongly ferromagnetic F-layers. For the
devices designed to have an antiparallel ground state above the Curie point of
the spacer, the associated spin-thermionic parallel-to-antiparallel switching
causes magneto-resistance oscillations whose frequency can be controlled by
proper biasing from essentially DC to GHz. We discuss in detail an experimental
realization of a device that can operate as a thermo-magneto-resistive switch
or oscillator.",0904.1156v2
2009-07-31,Effects of Disorder and Interactions in the Quantum Hall Ferromagnet,"This work treats the effects of disorder and interactions in a quantum Hall
ferromagnet, which is realized in a two-dimensional electron gas (2DEG) in a
perpendicular magnetic field at Landau level filling factor equal one. We study
the problem by projecting the original fermionic Hamiltonian into magnon
states, which behave as bosons in the vicinity of the ferromagnetic ground
state. The approach permits the reformulation of a strongly interacting model
into a non-interacting one. The latter is a non-perturbative scheme that
consists in treating the two-particle neutral excitations of the electron
system as a bosonic single-particle. Indeed, the employment of bosonization
facilitates the inclusion of disorder in the study of the system. It has been
shown previously that disorder may drive a quantum phase transition in the Hall
ferromagnet. However, such studies have been either carried out in the
framework of nonlinear sigma model, as an effective low-energy theory, or
included the long-range Coulomb interaction in a quantum description only up to
the Hartree-Fock level. Here, we establish the occurrence of a disorder-driven
quantum phase transition from a ferromagnetic 2DEG to a spin glass phase by
taking into account interactions between electrons up to the random phase
approximation level in a fully quantum description.",0907.5513v1
2009-08-30,Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys,"Weakly ferromagnetic alloys are being used by several groups in the study of
superconducting/ferromagnetic hybrid systems. Because spin-flip and spin-orbit
scattering in such alloys disrupt the penetration of pair correlations into the
ferromagnetic material, it is desirable to have a direct measurement of the
spin memory length in such alloys. We have measured the spin memory length at
4.2 K in sputtered Pd0.88Ni0.12 and Pd0.987Fe0.013 alloys using methods based
on current-perpendicular-to-plane giant magnetoresistance. The alloys are
incorporated into hybrid spin valves of various types, and the spin memory
length is determined by fits of the Valet-Fert spin-transport equations to data
of magnetoresistance vs. alloy thickness. For the case of PdNi alloy, the
resulting values of the spin memory length are lsf(PdNi) = 2.8 +/- 0.5 nm and
5.4 +/- 0.6 nm, depending on whether or not the PdNi is exchange biased by an
adjacent Permalloy layer. For PdFe, the spin memory length is somewhat longer,
lsf(PdFe) = 9.6 +/- 2 nm, consistent with earlier measurements indicating lower
spin-orbit scattering in that material. Unfortunately, even the longer spin
memory length in PdFe may not be long enough to facilitate observation of
spin-triplet superconducting correlations predicted to occur in
superconducting/ferromagnetic hybrid systems in the presence of magnetic
inhomogeneity.",0908.4375v1
2009-09-29,Spin-polarized Josephson current in SFS junctions with inhomogeneous magnetization,"SHORTENED ABSTRACT: We study numerically the properties of spin- and
charge-transport in a nanoscale diffusive
superconductor$\mid$ferromagnet$\mid$superconductor junction when the
magnetization texture is non-uniform. Specifically, we incorporate the presence
of a Bloch/Neel domain walls and conical ferromagnetism, including spin-active
interfaces. The superconducting leads are assumed to be of s-wave type. We
investigate how the 0-$\pi$ transition is influenced by the inhomogeneous
magnetization texture and focus on the particular case where the charge-current
vanishes while the spin-current is non-zero. In the case of a Bloch/Neel
domain-wall, the spin-current can be seen only for one component of the spin
polarization, whereas in the case of conical ferromagnetism the spin-current
has the three components. We explain all of these results in terms of the
interplay between the triplet anomalous Green's function induced in the
ferromagnetic region and the local direction of the magnetization vector in the
ferromagnet. Interestingly, we find that the spin-current exhibits
discontinuous jumps at the 0--$\pi$ transition points of the critical
charge-current. We explain this result in terms of the different symmetry
obeyed by the current-phase relation when comparing the charge- and
spin-current. Specifically, we find that whereas the charge-current obeys the
well-known relation $I_c(\phi) = -I_c(2\pi-\phi)$, the spin-current satisfies
$I_s(\phi) = I_s(2\pi-\phi)$, where $\phi$ is the superconducting phase
difference.",0909.5427v1
2009-11-02,Direct Search for a Ferromagnetic Phase in a Heavily Overdoped Nonsuperconducting Copper Oxide,"The doping of charge carriers into the CuO2 planes of copper oxide Mott
insulators causes a gradual destruction of antiferromagnetism and the emergence
of high-temperature superconductivity. Optimal superconductivity is achieved at
a doping concentration p beyond which further increases in doping cause a
weakening and eventual disappearance of superconductivity. A potential
explanation for this demise is that ferromagnetic fluctuations compete with
superconductivity in the overdoped regime. In this case a ferromagnetic phase
at very low temperatures is predicted to exist beyond the doping concentration
at which superconductivity disappears. Here we report on a direct examination
of this scenario in overdoped La2-xSrxCuO4 using the technique of muon spin
relaxation. We detect the onset of static magnetic moments of electronic origin
at low temperature in the heavily overdoped nonsuperconducting region. However,
the magnetism does not exist in a commensurate long-range ordered state.
Instead it appears as a dilute concentration of static magnetic moments. This
finding places severe restrictions on the form of ferromagnetism that may exist
in the overdoped regime. Although an extrinsic impurity cannot be absolutely
ruled out as the source of the magnetism that does occur, the results presented
here lend support to electronic band calculations that predict the occurrence
of weak localized ferromagnetism at high doping.",0911.0407v3
2011-01-01,Current-voltage characteristics of tunnel Josephson junctions with a ferromagnetic interlayer,"We present a quantitative study of the current-voltage characteristics (CVC)
of diffusive superconductor/ insulator/ ferromagnet/ superconductor (SIFS)
tunnel Josephson junctions. In order to obtain the CVC we calculate the density
of states (DOS) in the F/S bilayer for arbitrary length of the ferromagnetic
layer, using quasiclassical theory. For a ferromagnetic layer thickness larger
than the characteristic penetration depth of the superconducting condensate
into the F layer, we find an analytical expression which agrees with the DOS
obtained from a self-consistent numerical method. We discuss general properties
of the DOS and its dependence on the parameters of the ferromagnetic layer. In
particular we focus our analysis on the DOS oscillations at the Fermi energy.
Using the numerically obtained DOS we calculate the corresponding CVC and
discuss their properties. Finally, we use CVC to calculate the macroscopic
quantum tunneling (MQT) escape rate for the current biased SIFS junctions by
taking into account the dissipative correction due to the quasiparticle
tunneling. We show that the influence of the quasiparticle dissipation on the
macroscopic quantum dynamics of SIFS junctions is small, which is an advantage
of SIFS junctions for superconducting qubits applications.",1101.0361v2
2011-02-10,An effective quantum parameter for strongly correlated metallic ferromagnets,"The correlated motion of electrons in multi-orbital metallic ferromagnets is
investigated in terms of a realistic Hubbard model with {\cal N}-fold orbital
degeneracy and arbitrary intra- and inter-orbital Coulomb interactions U and J
using a Goldstone-mode-preserving non-perturbative scheme. An effective quantum
parameter '\hbar'=\frac{U^2+({\cal N}-1)J^2}{(U+({\cal N}-1)J)^2} is obtained
which determines, in analogy with 1/S for quantum spin systems and 1/N for the
N-orbital Hubbard model, the strength of correlation-induced quantum
corrections to magnetic excitations. The rapid suppression of this quantum
parameter with Hund's coupling J, especially for large {\cal N}, provides
fundamental insight into the phenomenon of strong stabilization of metallic
ferromagnetism by orbital degeneracy and Hund's coupling. This approach is
illustrated for the case of ferromagnetic iron and the half metallic Heusler
alloy Co_2 Mn Si. For realistic values for iron, the calculated spin stiffness
and Curie temperature values obtained are in quantitative agreement with
measurements. Significantly, the contribution of long wavelength modes is shown
to yield a nearly ~25% reduction in the calculated Curie temperature. Finally,
an outline is presented for extending the approach to generic multi-band
metallic ferromagnets including realistic band-structure features of
non-degenerate orbitals and inter-orbital hopping as obtained from LDA
calculations.",1102.2115v1
2011-02-22,Incoherent Effect of Fe and Ni Substitutions in the Ferromagnetic-Insulator La0.6Bi0.4MnO3+d,"A comparative study of the effect of Fe and Ni doping on the bismuth based
perovskite La0.6Bi0.4MnO3.1, a projected spintronics magnetic semiconductor has
been carried out. The doped systems show an expressive change in magnetic
ordering temperature. However, the shifts in ferromagnetic transition (TC) of
these doped phases are in opposite direction with respect to the parent phase
TC of 115 K. The Ni-doped phase shows an increase in TC ~200 K, whereas the
Fe-doped phase exhibits a downward shift to TC~95 K. Moreover, the Fe-doped is
hard-type whereas the Ni-doped compound is soft-type ferromagnet. It is
observed that the materials are semiconducting in the ferromagnetic phase with
activation energies of 77 & 82 meV for Fe & Ni-doped phases respectively. In
the presence of external magnetic field of 7 Tesla, they exhibit minor changes
in the resistivity behaviours and the maximum isothermal magnetoresistance is
around -20 % at 125 K for the Ni-phase. The results are explained on the basis
of electronic phase separation and competing ferromagnetic and
antiferromagnetic interactions between the various mixed valence cations.",1102.4471v2
2011-03-21,Spontaneous Magnetization of an Ideal Ferromagnet: Beyond Dyson's Analysis,"Using the low-energy effective field theory for magnons, we systematically
evaluate the partition function of the O(3) ferromagnet up to three loops.
Dyson, in his pioneering microscopic analysis of the Heisenberg model, showed
that the spin-wave interaction starts manifesting itself in the low-temperature
expansion of the spontaneous magnetization of an ideal ferromagnet only at
order $T^4$. Although several authors tried to go beyond Dyson's result, to the
best of our knowledge, a fully systematic and rigorous investigation of higher
order terms induced by the spin-wave interaction, has never been achieved. As
we demonstrate in the present paper, it is straightforward to evaluate the
partition function of an ideal ferromagnet beyond Dyson's analysis, using
effective Lagrangian techniques. In particular, we show that the
next-to-leading contribution to the spontaneous magnetization resulting from
the spin-wave interaction already sets in at order $T^{9/2}$ -- in contrast to
all claims that have appeared before in the literature. Remarkably, the
corresponding coefficient is completely determined by the leading-order
effective Lagrangian and is thus independent of the anisotropies of the cubic
lattice. We also consider even higher-order corrections and thereby solve --
once and for all -- the question of how the spin-wave interaction in an ideal
ferromagnet manifests itself in the spontaneous magnetization beyond the Dyson
term.",1103.4110v1
2011-05-31,Weak ferromagnetism and magnetic phase transitions in Gd$_2$CuO$_4$,"We report a polarised neutron study of the magnetic structures and phase
trasitions in \gdc\ in low magnetic fields. These experiments have been
complemented by integrated intensity measurements with unpolarised neutrons in
zero field. Polarised neutron flipping ratio measurements have been made with
magnetic fields $H = 0.05$, 0.10 and 0.5 T in the temperature range 4-20 K.
These have enabled us to deduce that the anomalous temperature behaviour of the
coherent magnetic scattering from the Cu sublattice, which shows sharp
intensity minima at \Tcn1 $\approx 18$K and \Tcn2 $\approx 8$ K, is due to
cross-overs in the sign of the interaction between strongly coupled, weakly
ferromagnetic, CuO$_2$ layers. At \Tcn1\ the coupling changes from
ferromagnetic to anti-ferromagnetic and long-range order between layers is
temporarily lost. \Tcn2\ is the temperature at which the Gd moments order and a
further reorganisation of the interlayer order takes place. The weak
ferromagnetism of the CuO layers is found to be due to a small rotation of the
Cu moments in the same direction as that in which their coordinating oxygen
squares rotate in the tetragonal to orthorhombic distortion of the crystal
structure. Further analysis of the flipping ratio measurements has enabled us
to model the magnetic structures of the zero-field and the field-induced phases
of Gd$_2$CuO$_4$.",1105.6196v1
2011-06-03,Iron-based n-type electron-induced ferromagnetic semiconductor,"Carrier-induced ferromagnetic semiconductors (FMSs) have been intensively
studied for decades as they have novel functionalities that cannot be achieved
with conventional metallic materials. These include the ability to control
magnetism by electrical gating or light irradiation, while fully inheriting the
advantages of semiconductor materials such as band engineering. Prototype FMSs
such as (In,Mn)As or (Ga,Mn)As, however, are always p-type, making it difficult
to be used in real spin devices. This is because manganese (Mn) atoms in those
materials work as local magnetic moments and acceptors that provide holes for
carrier-mediated ferromagnetism. Here we show that by introducing iron (Fe)
into InAs, it is possible to fabricate a new FMS with the ability to control
ferromagnetism by both Fe and independent carrier doping. Despite the general
belief that the tetrahedral Fe-As bonding is antiferromagnetic, we demonstrate
that (In,Fe)As doped with electrons behaves as an n-type electron-induced FMS,
a missing piece of semiconductor spintronics for decades. This achievement
opens the way to realise novel spin-devices such as spin light-emitting diodes
or spin field-effect transistors, as well as helps understand the mechanism of
carrier-mediated ferromagnetism in FMSs.",1106.0561v3
2011-07-09,Ferroelectricity and ferromagnetism in EuTiO3 nanowires,"We predicted the ferroelectric-ferromagnetic multiferroic properties of
EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature
and wire radii. The calculations were performed within the
Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted
from tabulated experimental data and first principles calculations. Since bulk
EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric
at all temperatures, our goal was to investigate the possibility of inducing
the ferroelectric and ferromagnetic properties of EuTiO3 by reducing the bulk
to nanosystems. Our results indicate that ferroelectric spontaneous
polarization of ~0.1-0.5C/m2 is induced in EuTiO3 nanowires due to the
intrinsic surface stress, which is inversely proportional to the nanowire
radius. The spontaneous polarization exists at temperatures lower than 300 K,
for the wire radius less than 1 nm and typical surface stress coefficients ~ 15
N/m. Due to the strong biquadratic magnetoelectric coupling, the spontaneous
polarization in turn induces the ferromagnetic phase at temperatures lower than
30 K for 2 nm nanowire, and at temperatures lower than 10 K for 4 nm nanowire
in EuTiO3. Thus we predicted that the EuTiO3 nanowires can be the new
ferroelectric-ferromagnetic multiferroic.",1107.1785v1
2011-07-12,Approximation algorithms for two-state anti-ferromagnetic spin systems on bounded degree graphs,"In a seminal paper (Weitz, 2006), Weitz gave a deterministic fully polynomial
approximation scheme for count- ing exponentially weighted independent sets
(equivalently, approximating the partition function of the hard-core model from
statistical physics) on graphs of degree at most d, up to the critical activity
for the uniqueness of the Gibbs measure on the infinite d-regular tree. More
recently Sly (Sly, 2010) showed that this is optimal in the sense that if there
is an FPRAS for the hard-core partition function on graphs of maximum degree d
for activities larger than the critical activity on the infinite d-regular tree
then NP = RP. In this paper, we extend Weitz's approach to derive a
deterministic fully polynomial approx- imation scheme for the partition
function of the anti-ferromagnetic Ising model with arbitrary field on graphs
of maximum degree d, up to the corresponding critical point on the d-regular
tree. The main ingredient of our result is a proof that for two-state
anti-ferromagnetic spin systems on the d-regular tree, weak spatial mixing
implies strong spatial mixing. This in turn uses a message-decay argument which
extends a similar approach proposed recently for the hard-core model by
Restrepo et al (Restrepo et al, 2011) to the case of the anti-ferromagnetic
Ising model with arbitrary field. By a standard correspondence, these results
translate to arbitrary two-state anti-ferromagnetic spin systems with soft
constraints.",1107.2368v3
2012-07-10,"Successive spin glass, cluster ferromagnetic, and superparamagnetic transitions in RuSr2Y1.5Ce0.5Cu2O10 complex magneto-superconductor","We report structural, DC magnetization, detailed linear/non-linear AC
susceptibility, (with applied frequency and amplitude) isothermal and
thermoremanent magnetization (TRM) behavior for RuSr2Y1.5Ce0.5Cu2O10 (YRu-1222)
magneto-superconductor to understand its complex magnetism. Studied sample is
synthesized through the novel solid state High Pressure (6 GPa) High
Temperature (1450oC) (HPHT) technique. The compound is crystallized in
tetragonal structure with space group I4/mmm (No. 139). DC magnetic
susceptibility shows that studied YRu-1222 is magneto-superconducting with Ru
spins magnetic ordering at around 110 K and superconductivity (SC) in the Cu-O2
planes below ~ 30 K. Frequency and field dependent detailed AC magnetic
susceptibility measurements confirms the spin-glass (SG) behavior with
homogeneous/non-homogeneous ferromagnetic (FM) clusters in this system.
Variation of cusp position with applied AC frequency follows the famous
Vogel-Fulcher law, which is commonly accepted feature for spin-glass (SG)
system with homogeneous/non-homogeneous ferromagnetic clusters embedded in
spin-glass (SG) matrix. Above the freezing temperature (Tf), first and third
harmonics AC susceptibility analysis indicated possibility of the co-existence
of spin cluster ferromagnetism with superparamagnetism (SPM). The M-H loops at
low temperature exhibit the ferromagnetic behavior with rather small coercive
field (Hc) and remnant magnetization (Mr). Summarily, the magnetic (DC and AC)
susceptibility measurements and their analysis have enabled us to unearth the
complex magnetism in terms of successive SG-FM-SPM transitions with
temperature.",1207.2219v1
2013-01-29,Spin/orbit moment imbalance in the near-zero moment ferromagnetic semiconductor SmN,"SmN is ferromagnetic below 27 K, and its net magnetic moment of 0.03 Bohr
magnetons per formula unit is one of the smallest magnetisations found in any
ferromagnetic material. The near-zero moment is a result of the nearly equal
and opposing spin and orbital moments in the 6H5/2 ground state of the Sm3+
ion, which leads finally to a nearly complete cancellation for an ion in the
SmN ferromagnetic state. Here we explore the spin alignment in this compound
with X-ray magnetic circular dichroism at the Sm L2,3 edges. The spectral
shapes are in qualitative agreement with computed spectra based on an LSDA+U
(local spin density approximation with Hubbard-U corrections) band structure,
though there remain differences in detail which we associate with the anomalous
branching ratio in rare-earth L edges. The sign of the spectra determine that
in a magnetic field the Sm 4f spin moment aligns antiparallel to the field; the
very small residual moment in ferromagnetic SmN aligns with the 4f orbital
moment and antiparallel to the spin moment. Further measurements on very thin
(1.5 nm) SmN layers embedded in GdN show the opposite alignment due to a strong
Gd-Sm exchange, suggesting that the SmN moment might be further reduced by
about 0.5 % Gd substitution.",1301.6829v1
2014-01-03,Detection of small exchange fields in S/F structures,"Ferromagnetic materials with exchange fields E_ex smaller or of the order of
the superconducting gap Delta are important for applications of corresponding
(s-wave) superconductor/ ferromagnet/ superconductor (SFS) junctions. Presently
such materials are not known but there are several proposals how to create
them. Small exchange fields are in principle difficult to detect. Based on our
results we propose reliable detection methods of such small E_ex. For exchange
fields smaller than the superconducting gap the subgap differential conductance
of the normal metal - ferromagnet - insulator - superconductor (NFIS) junction
shows a peak at the voltage bias equal to the exchange field of the
ferromagnetic layer, eV=E_ex. Thus measuring the subgap conductance one can
reliably determine small E_ex < Delta. In the opposite case E_ex > Delta one
can determine the exchange field in scanning tunneling microscopy (STM)
experiment. The density of states of the FS bilayer measured at the outer
border of the ferromagnet shows a peak at the energy equal to the exchange
field, E=E_ex. This peak can be only visible for small enough exchange fields
of the order of few Delta.",1401.0646v2
2014-02-22,Ferromagnetism and Spin-dependent Transport in n-type Mn-Bi2Te3 Thin Films,"We describe a detailed study of the structural, magnetic, and
magneto-transport properties of single-crystal, n-type, Mn-doped Bi2Te3 thin
films grown by molecular beam epitaxy. With increasing Mn concentration, the
crystal structure changes from the tetradymite structure of the Bi2Te3 parent
crystal at low Mn concentrations towards a BiTe phase in the (Bi2Te3)m(Bi2)n
homologous series. Magnetization measurements reveal the onset of
ferromagnetism with a Curie temperature in the range 13.8 K - 17 K in films
with 2 % - 10 % Mn concentration. Magnetization hysteresis loops reveal that
the magnetic easy axis is along the c-axis of the crystal (perpendicular to the
plane). Polarized neutron reflectivity measurements of a 68 nm-thick sample
show that the magnetization is uniform through the film. The presence of
ferromagnetism is also manifest in a strong anomalous Hall effect and a
hysteretic magnetoresistance arising from domain wall scattering. Ordinary Hall
effect measurements show that the carrier density is n-type, increases with Mn
doping, and is high enough (> 2.8 x 10^{13} cm^{-2}) to place the chemical
potential in the conduction band. Thus, the observed ferromagnetism is likely
associated with both bulk and surface states. Surprisingly, the Curie
temperature does not show any clear dependence on the carrier density but does
increase with Mn concentration. Our results suggest that the ferromagnetism
probed in these Mn-doped Bi2Te3 films is not mediated by carriers in the
conduction band or in an impurity band.",1402.5546v1
2014-02-24,Raman studies of nearly half-metallic ferromagnet CoS2,"We measured the Raman spectra of ferromagnetic nearly half metal CoS2 in a
broad temperature range. All five Raman active modes Ag, Eg, Tg(1), Tg(2) and
Tg(3) were observed. The magnetic ordering is indicated by a change of the
temperature dependences of the frequency and the line width of Ag and T g(2)
modes at the Curie point. The temperature dependence of the frequencies and
linewidths of the Ag, Eg, Tg(1), T g(2) modes in the paramagnetic phase can be
described in the framework of the Klemens approach. Hardening of the Tg(2),
Tg(1) and A g modes on cooling can be unambiguously seen in the ferromagnetic
phase. The linewidths of Tg(2) and Ag modes behave a natural way at low
exciting laser power (decrease with decreasing temperature) in the
ferromagnetic phase. At high exciting laser power the corresponding linewidths
increase at temperature decreasing below the Curie temperature. Then as can be
seen the line width of Ag mode reaches a maxima at about 80K. This intriging
feature probably signifies a specific channel of the optical phonon decay in
the ferromagnetic phase of CoS2. Tentative explanations of some of the observed
effects are given, taking into account the nearly half metallic nature of CoS2.",1402.5785v1
2014-09-03,Stoner ferromagnetism in a thermal pseudospin-1/2 Bose gas,"We compute the finite-temperature phase diagram of a pseudospin-$1/2$ Bose
gas with contact interactions, using two complementary methods: the random
phase approximation (RPA) and self-consistent Hartree-Fock theory. We show that
the inter-spin interactions, which break the (pseudo) spin-rotational symmetry
of the Hamiltonian, generally lead to the appearance of a magnetically ordered
phase at temperatures above the superfluid transition. In three dimensions, we
predict a normal easy-axis/easy-plane ferromagnet for sufficiently strong
repulsive/attractive inter-species interactions respectively. The normal
easy-axis ferromagnet is the bosonic analog of Stoner ferromagnetism known in
electronic systems. For the case of inter-spin attraction, we also discuss the
possibility of a \textit{bosonic} analog of the Cooper paired phase. This state
is shown to significantly lose in energy to the transverse ferromagnet in three
dimensions, but is more energetically competitive in lower dimensions.
Extending our calculations to a spin-orbit-coupled Bose gas with equal Rashba
and Dresselhaus-type couplings (as recently realized in experiment), we
investigate the possibility of stripe ordering in the normal phase. Within our
approximations however, we do not find an instability towards stripe formation,
suggesting that the stripe order melts below the condensation temperature,
which is consistent with the experimental observations of Ji \textit{et al.}
[Ji \textit{et al.}, Nature Physics \textbf{10}, 314 (2014)].",1409.1242v2
2014-09-16,Distribution of critical temperature at Anderson localization,"Based on a local mean-field theory approach at Anderson localization, we find
a distribution function of critical temperature from that of disorder. An
essential point of this local mean-field theory approach is that the
information of the wave-function multifractality is introduced. The
distribution function of the Kondo temperature ($T_{K}$) shows a power-law tail
in the limit of $T_{K} \rightarrow 0$ regardless of the Kondo coupling
constant. We also find that the distribution function of the ferromagnetic
transition temperature ($T_{c}$) gives a power-law behavior in the limit of
$T_{c} \rightarrow 0$ when an interaction parameter for ferromagnetic
instability lies below a critical value. However, the $T_{c}$ distribution
function stops the power-law increasing behavior in the $T_{c} \rightarrow 0$
limit and vanishes beyond the critical interaction parameter inside the
ferromagnetic phase. These results imply that the typical Kondo temperature
given by a geometric average always vanishes due to finite density of the
distribution function in the $T_{K} \rightarrow 0$ limit while the typical
ferromagnetic transition temperature shows a phase transition at the critical
interaction parameter. We propose that the typical transition temperature
serves a criterion for quantum Griffiths phenomena vs. smeared transitions:
Quantum Griffiths phenomena occur above the typical value of the critical
temperature while smeared phase transitions result at low temperatures below
the typical transition temperature. We speculate that the ferromagnetic
transition at Anderson localization shows the evolution from quantum Griffiths
phenomena to smeared transitions around the critical interaction parameter at
low temperatures.",1409.4531v3
2014-10-30,The effects of Co3O4 on the Structure and Unusual Magnetism of LaCoO3,"Bulk La_wCoO3 particles with w=1.1, 1.0, 0.9, 0.8, and 0.7 were synthesized
using starting materials with varying molar ratios of La2O3 and Co3O4. The
resulting particles are characterized as LaCoO3 crystals interfaced with a
crystalline Co3O4 phase. X-ray and neutron scattering data show little effect
on the average structure and lattice parameters of the LaCoO3 phase resulting
from the Co3O4 content, but magnetization data indicate that the amount of
Co3O4 strongly affects the ferromagnetic ordering at the interfaces below T_C
~89K. In addition to ferromagnetic long-range order, LaCoO3 exhibits
antiferromagnetic behavior with an unusual temperature dependence. The
magnetization for fields 20 Oe < H < 5 kOe is fit to a combination of a power
law ((T-T_C)/T_C)^beta behavior representing the ferromagnetic long-range order
and sigmoid-convoluted Curie-Weiss-like behavior representing the
antiferromagnetic behavior. The critical exponent beta=0.63 +- 0.02 is
consistent with 2D (surface) ordering. Increased Co3O4 correlates well to
increased ferromagnetism. The weakening of the antiferromagnetism below T ~ 40K
is a consequence of the lattice reaching a critical rhombahedral distortion as
T is decreased for core regions far from the Co3O4 interfaces. We introduce a
model that describes the ferromagnetic behavior of the interface regions and
the unusual antiferromagnetism of the core regions.",1410.8284v1
2014-12-22,Polarized neutron diffraction and X-ray magnetic circular dichroism study of Ru doped UCoGe,"We report on microscopic study of the ferromagnetism enhancement in the Ru
doped ferromagnetic superconductor (FM SC) UCoGe. For that purpose, two single
crystals with composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge were prepared.
Both single crystals were investigated by polarized neutron diffraction (PND)
at low temperatures in magnetic fields and the latter one also by the soft
X-ray magnetic circular dichroism (XMCD) method. UCo0.96Ru0.03Ge and
UCo0.88Ru0.12Ge have been found ordering ferromagnetically below the Curie
temperature TC = 6 K and 8.5 K, respectively, which are considerable higher
than TC = 3 K of UCoGe. The increase of TC is accompanied by enhancement of the
spontaneous moment to ms = 0.11 mB/f.u. and ms = 0.21 mB/f.u., respectively.
The analysis of the PND results assigns the ferromagnetism enhancement mainly
to the growth of the orbital part of uranium 5 f moment. In contrast to the
published results of PND study of the parent UCoGe, we have found parallel
orientation of the U and Co moments in both doped compounds. Evolution of
magnetic characteristics with Ru concentration is discussed within a scenario
considering the varying 5 f-ligand hybridization as the key mechanism.",1412.7087v2
2015-02-11,Anisotropic defect-induced ferromagnetism and transport in Gd-doped GaN two-dimensional electron gasses,"Here we report on the effect of rare earth Gd-doping on the magnetic
properties and magnetotransport of GaN two-dimensional electron gasses (2DEGs).
Samples are grown by plasma-assisted molecular beam epitaxy and consist of
AlN/GaN heterostructures where Gd is delta-doped within a polarization-induced
2DEG. Ferromagnetism is observed in these Gd-doped 2DEGs with a Curie
temperature above room temperature and an anisotropic spontaneous magnetization
preferring an out-of-plane (c-axis) orientation. At magnetic fields up to 50
kOe, the magnetization remains smaller for in-plane configuration than for
out-of-plane, which is indicative of exchange coupled spins locked along the
polar c-axis. The sample with the lowest Gd concentration (2.3 $\times$
$10^{14}$ cm$^{-2}$) exhibits a saturation magnetization of 41.1
$\mu_B/Gd^{3+}$ at 5 K revealing that the Gd ion spins (7 ${\mu}_B$) alone do
not account for the magnetization. Surprisingly, control samples grown without
any Gd display inconsistent magnetic properties; in some control samples weak
ferromagnetism is observed and in others paramagnetism. The ferromagnetic 2DEGs
do not exhibit the anomalous Hall effect; the Hall resistance varies
non-linearly with the magnetic field, but does not track the magnetization
indicating the lack of coupling between the ferromagnetic phase and the
conduction band electrons within the 2DEG.",1502.03478v2
2015-02-23,Swendsen-Wang Algorithm on the Mean-Field Potts Model,"We study the $q$-state ferromagnetic Potts model on the $n$-vertex complete
graph known as the mean-field (Curie-Weiss) model. We analyze the Swendsen-Wang
algorithm which is a Markov chain that utilizes the random cluster
representation for the ferromagnetic Potts model to recolor large sets of
vertices in one step and potentially overcomes obstacles that inhibit
single-site Glauber dynamics. Long et al. studied the case $q=2$, the
Swendsen-Wang algorithm for the mean-field ferromagnetic Ising model, and
showed that the mixing time satisfies: (i) $\Theta(1)$ for $\beta<\beta_c$,
(ii) $\Theta(n^{1/4})$ for $\beta=\beta_c$, (iii) $\Theta(\log n)$ for
$\beta>\beta_c$, where $\beta_c$ is the critical temperature for the
ordered/disordered phase transition. In contrast, for $q\geq 3$ there are two
critical temperatures $0<\beta_u<\beta_{rc}$ that are relevant. We prove that
the mixing time of the Swendsen-Wang algorithm for the ferromagnetic Potts
model on the $n$-vertex complete graph satisfies: (i) $\Theta(1)$ for
$\beta<\beta_u$, (ii) $\Theta(n^{1/3})$ for $\beta=\beta_u$, (iii)
$\exp(n^{\Omega(1)})$ for $\beta_u<\beta<\beta_{rc}$, and (iv)
$\Theta(\log{n})$ for $\beta\geq\beta_{rc}$. These results complement refined
results of Cuff et al. on the mixing time of the Glauber dynamics for the
ferromagnetic Potts model.",1502.06593v4
2015-05-29,Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties of BaFeO$_{3-δ},"We studied structural, electronic and magnetic properties of a cubic
perovskite BaFeO$_{3-\delta}$ ($0 \le \delta \le 0.5$) within the density
functional theory using a generalized gradient approximation and a GGA+U
method. According to our calculations, BaFeO$_3$ in its stoichiometric cubic
structure should be half-metallic and strongly ferromagnetic, with extremely
high Curie temperature ($T_C$) of 700 - 900 K. However, a such estimate of
$T_C$ disagrees with all available experiments, which report that $T_C$ of the
BaFeO$_3$ and undoped BaFeO$_{3-\delta}$ films varies between 111 K and 235 K
or, alternatively, that no ferromagnetic order was detected there. Fitting the
calculated x-ray magnetic circular dichroism spectra to the experimental
features seen for BaFeO$_3$, we concluded that the presence of oxygen vacancies
in our model enables a good agreement. Thus, the relatively low $T_C$ measured
in BaFeO$_3$ can be explained by oxygen vacancies intrinsically presented in
the material. Since iron species near the O vacancy change their oxidation
state from $4+$ to $3+$, the interaction between Fe$^{4+}$ and Fe$^{3+}$, which
is antiferromagnetic, weakens the effective magnetic interaction in the system,
which is predominantly ferromagnetic. With increasing $\delta$ in
BaFeO$_{3-\delta}$, its $T_C$ decreases down to the critical value when the
magnetic order becomes antiferromagnetic. Our calculations of the electronic
structure of BaFeO$_{3-\delta}$ illustrate how the ferromagnetism originates
and also how one can keep this cubic perovskite robustly ferromagnetic far
above the room temperature.",1505.07942v1
2015-09-17,Controllable 0-pi Josephson junctions containing a ferromagnetic spin valve,"Superconductivity and ferromagnetism are antagonistic forms of order, and
rarely coexist. Many interesting new phenomena occur, however, in hybrid
superconducting/ferromagnetic systems. For example, a Josephson junction
containing a ferromagnetic material can exhibit an intrinsic phase shift of pi
in its ground state for certain thicknesses of the material. Such
""pi-junctions"" were first realized experimentally in 2001, and have been
proposed as circuit elements for both high-speed classical superconducting
computing and for quantum computing. Here we demonstrate experimentally that
the phase state of a Josephson junction containing two ferromagnetic layers can
be toggled between 0 and pi by changing the relative orientation of the two
magnetizations. These controllable 0-pi junctions have immediate applications
in cryogenic memory where they serve as a necessary component to an ultra-low
power superconducting computer. Such a fully superconducting computer is
estimated to be orders of magnitude more energy-efficient than current
semiconductor-based supercomputers. Phase controllable junctions also open up
new possibilities for superconducting circuit elements such as superconducting
""programmable logic,"" where they could function in superconducting analogs to
field-programmable gate arrays.",1509.05368v1
2016-01-08,Spin-glass like dynamics of ferromagnetic clusters in La$_{0.75}$Ba$_{0.25}$CoO$_3$,"We report the magnetization study of the compound
La$_{0.75}$Ba$_{0.25}$CoO$_3$ where Ba$^{2+}$ doping is just above the critical
limit for percolation of ferromagnetic clusters. The field cooled (FC) and zero
field cooled (ZFC) magnetization exhibit a thermomagnetic irreversibility and
the ac susceptibility show a frequency dependent peak at the ferromagnetic
ordering temperature (T$_C$$\approx$203~K) of the clusters. These features
indicate about the presence of a non-equilibrium state below T$_C$. In the
non-equilibrium state, the dynamic scaling of the imaginary part of ac
susceptibility and the static scaling of the nonlinear susceptibility clearly
establish a spin-glass like cooperative freezing of ferromagnetic clusters at
200.9(2)~K. The existence of spin-glass like freezing of ferromagnetic clusters
is further substantiated by the ZFC aging and memory experiments. We also
observe certain dynamical features which are not present in a typical
spin-glass, such as, initial magnetization after ZFC aging first increases and
then decreases with the wait time and an imperfect recovery of relaxation in
negative temperature cycling experiments. This imperfect recovery transforms to
perfect recovery on concurrent field cycling. Our analysis suggests that these
additional dynamical features have their origin in inter-cluster exchange
interaction and cluster size distribution. The inter-cluster exchange
interaction above the magnetic percolation gives a superferromagnetic state in
some granular thin films but our results show the absence of typical
superferromagnetic like state in La$_{0.75}$Ba$_{0.25}$CoO$_3$.",1601.02009v1
2016-01-15,X-ray absorption study of the ferromagnetic Cu moment at the $\mathbf{{YBa_2Cu_3O_7}/{La_{2/3}Ca_{1/3}MnO_3}}$ interface and the variation of its exchange interaction with the Mn moment,"With x-ray absorption spectroscopy and polarized neutron reflectometry we
studied how the magnetic proximity effect at the interface between the cuprate
high-$T_C$ superconductor $\mathrm{YBa_2Cu_3O_7}$ (YBCO) and the ferromagnet
$\mathrm{La_{2/3}Ca_{1/3}MnO_3}$ (LCMO) is related to the electronic and
magnetic properties of the LCMO layers. In particular, we explored how the
magnitude of the ferromagnetic Cu moment on the YBCO side depends on the
strength of the antiferromagnetic (AF) exchange coupling with the Mn moment on
the LCMO side. We found that the Cu moment remains sizeable if the AF coupling
with the Mn moments is strongly reduced or even entirely suppressed. The
ferromagnetic order of the Cu moments thus seems to be intrinsic to the
interfacial CuO$_2$ planes and related to a weakly ferromagnetic intra-planar
exchange interaction. The latter is discussed in terms of the partial
occupation of the Cu $3d_{3z^2-r^2}$ orbitals, which occurs in the context of
the so-called orbital reconstruction of the interfacial Cu ions.",1601.03844v2
2016-07-01,The Chiral Potts Spin Glass in d=2 and 3 Dimensions,"The chiral spin-glass Potts system with q=3 states is studied in d=2 and 3
spatial dimensions by renormalization-group theory and the global phase
diagrams are calculated in temperature, chirality concentration p, and
chirality-breaking concentration c, with determination of phase chaos and
phase-boundary chaos. In d=3, the system has ferromagnetic, left-chiral,
right-chiral, chiral spin-glass, and disordered phases. The phase boundaries to
the ferromagnetic, left- and right-chiral phases show, differently, an unusual,
fibrous patchwork (microreentrances) of all four (ferromagnetic, left-chiral,
right-chiral, chiral spin-glass) ordered ordered phases, especially in the
multicritical region. The chaotic behavior of the interactions, under scale
change, are determined in the chiral spin-glass phase and on the boundary
between the chiral spin-glass and disordered phases, showing Lyapunov exponents
in magnitudes reversed from the usual ferromagnetic-antiferromagnetic
spin-glass systems. At low temperatures, the boundaries of the left- and
right-chiral phases become thresholded in p and c. In the d=2, the chiral
spin-glass system does not have a spin-glass phase, consistently with the
lower-critical dimension of ferromagnetic-antiferromagnetic spin glasses. The
left- and right-chirally ordered phases show reentrance in chirality
concentration p.",1607.00112v2
2017-02-27,Single shot ultrafast all optical magnetization switching of ferromagnetic Co/Pt multilayers,"In a number of recent experiments, it has been shown that femtosecond laser
pulses can control magnetization on picosecond timescales, which is at least an
order of magnitude faster compared to conventional magnetization dynamics.
Among these demonstrations, one material system (GdFeCo ferromagnetic films) is
particularly interesting, as deterministic toggle-switching of the magnetic
order has been achieved without the need of any symmetry breaking magnetic
field. This phenomenon is often referred to as all optical switching (AOS).
However, so far, GdFeCo remains the only material system where such
deterministic switching has been observed. When extended to ferromagnetic
systems, which are of greater interest in many technological applications, only
a partial effect can be achieved, which in turn requires repeated laser pulses
for full switching. However, such repeated pulsing is not only energy hungry,
it also negates the speed advantage of AOS. Motivated by this problem, we have
developed a general method for single-shot, picosecond timescale, complete all
optical switching of ferromagnetic materials. We demonstrate that in
exchange-coupled layers of Co/Pt and GdFeCo, single shot, switching of the
ferromagnetic Co/Pt layer is achieved within 7 picoseconds after irradiation by
a femtosecond laser pulse. We believe that this approach will greatly expand
the range of materials and applications for ultrafast magnetic switching.",1702.08491v3
2018-04-12,"The melilite-type compound (Sr$_{1-x}$,$A_x$)$_2$MnGe$_2$S$_6$O ($A$=K, La) being a room temperature ferromagnetic semiconductor","The seeking of room temperature ferromagnetic semiconductors, which take
advantages of both the charge and spin degrees of freedom of electrons to
realize a variety of functionalities in devices integrated with electronic,
optical, and magnetic storage properties, has been a long-term goal of
scientists and engineers. Here, by using the spin-polarized density functional
theory calculations, we predict a new series of high temperature ferromagnetic
semiconductors based on the melilite-type oxysulfide Sr$_2$MnGe$_2$S$_6$O
through hole (K) and electron (La) doping. Due to the lack of strong
antiferromagnetic superexchange between Mn ions, the weak antiferromagnetic
order in the parent compound Sr$_2$MnGe$_2$S$_6$O can be suppressed easily by
charge doping with either $p$-type or $n$-type carriers, giving rise to the
expected ferromagnetic order. At a doping concentration of 25%, both the
hole-doped and electron-doped compounds can achieve a Curie temperature
($T_\text{c}$) above 300 K. The underlying mechanism is analyzed. Our study
provides an effective approach for exploring new types of high temperature
ferromagnetic semiconductors.",1804.04519v1
2018-11-02,Spinning superconductors and ferromagnets,"When a magnetic field is applied to a ferromagnetic body it starts to spin
(Einstein-de Haas effect). This demonstrates the intimate connection between
the electron's magnetic moment $\mu_B=e\hbar/2m_ec$, associated with its spin
angular momentum $S=\hbar/2$, and ferromagnetism. When a magnetic field is
applied to a superconducting body it also starts to spin (gyromagnetic effect),
and when a normal metal in a magnetic field becomes superconducting and expels
the magnetic field (Meissner effect) the body also starts to spin. Yet
according to the conventional theory of superconductivity the electron's spin
only role is to label states, and the electron's magnetic moment plays no role
in superconductivity. Instead, within the unconventional theory of hole
superconductivity, the electron's spin and associated magnetic moment play a
fundamental role in superconductivity. Just like in ferromagnets the
magnetization of superconductors is predicted to result from an aggregation of
magnetic moments with angular momenta $\hbar/2$. This gives rise to a ""Spin
Meissner effect"", the existence of a spin current in the ground state of
superconductors. The theory explains how a superconducting body starts spinning
when it expels magnetic fields, it provides a dynamical explanation for the
Meissner effect, and it explains how supercurrents stop without dissipation,
all of which we argue the conventional theory fails to explain. Essential
elements of the theory of hole superconductivity are that superconductivity is
driven by lowering of kinetic energy, which we have also proposed is true for
ferromagnets], that the normal state charge carriers in superconducting
materials are holes, and that the spin-orbit interaction plays a key role in
superconductivity. The theory is proposed to apply to all superconductors.",1811.03938v1
2013-08-25,Enhanced ferromagnetic moment in Co-doped BiFeO3 thin films studied by soft X-ray circular dichroism,"BiFeO$_3$ (BFO) shows both ferroelectricity and magnetic ordering at room
temperature but its ferromagnetic component, which is due to spin canting, is
negligible. Substitution of transition-metal atoms such as Co for Fe is known
to enhance the ferromagnetic component in BFO. In order to reveal the origin of
such magnetization enhancement, we performed soft x-ray absorption spectroscopy
(XAS) and soft x-ray magnetic circular dichroism (XMCD) studies of
BiFe$_{1-x}$Co$_x$O$_3$ ({\it x} = 0 to 0.30) (BFCO) thin films grown on
LaAlO$_3$(001) substrates. The XAS results indicated that the Fe and Co ions
are in the Fe$^{3+}$ and Co$^{3+}$ states. The XMCD results showed that the Fe
ions show ferromagnetism while the Co ions are antiferromagnetic at room
temperature. The XAS and XMCD measurements also revealed that part of the
Fe$^{3+}$ ions are tetrahedrally co-ordinated by oxygen ions but that the XMCD
signals of the octahedrally coordinated Fe$^{3+}$ ions increase with Co
content. The results suggest that an impurity phase such as the ferrimagnetic
$\gamma$-Fe$_2$O$_3$ which exists at low Co concentration decreases with
increasing Co concentration and that the ferromagnetic component of the
Fe$^{3+}$ ion in the octrahedral crystal fields increases with Co
concentration, probably reflecting the increased canting of the Fe$^{3+}$ ions.",1308.5672v1
2014-03-03,Pressure-induced ferromagnetism with strong Ising-type anisotropy in YbCu$_2$Si$_2$,"We report dc magnetic measurements on YbCu$_2$Si$_2$ at pressures above 10
GPa using a miniature ceramic anvil cell. YbCu$_2$Si$_2$ shows a
pressure-induced transition from the non-magnetic to a magnetic phase at 8 GPa.
We find a spontaneous dc magnetization in the pressure-induced phase above 9.4
GPa. The pressure dependence of the ferromagnetic transition temperature T_C
and the spontaneous magnetic moment m_0 at 2.0 K have been determined. The
value of m_0 in the present macroscopic measurement is less than half of that
determined via Mossbauer experiment. The difference may be attributed to
spatial phase separation between the ferromagnetic and paramagnetic phases.
This separation suggests that the pressure-induced phase boundary between the
paramagnetic and ferromagnetic states is of first order. Further, we have
studied the magnetic anisotropy in the pressure-induced ferromagnetic state.
The effect of pressure on the magnetization with magnetic field along the
magnetic easy $c$-axis is much larger than for field along the hard $a$-axis in
the tetragonal structure. The pressure-induced phase has strong Ising-type
uniaxial anisotropy, consistent with the two crystal electric field (CEF)
models proposed for YbCu$_2$Si$_2$.",1403.0290v2
2016-11-01,Thermoelectric properties of a ferromagnet-superconductor hybrid junction: Role of interfacial Rashba spin-orbit interaction,"We investigate thermoelectric properties of a ferromagnet-superconductor
hybrid structure with Rashba spin-orbit interaction and delta function
potential barrier at the interfacial layer. The exponential rise of thermal
conductance with temperature manifests a cross-over temperature scale
separating two opposite behaviors of it with the change of polarization in the
ferromagnet whereas the inclusion of interfacial Rashba spin-orbit field
results in a non-monotonic behavior of it with the strength of Rashba field. We
employ scattering matrix approach to determine the amplitudes of all the
scattering processes possible at the interface to explain the thermoelectric
properties of the device. We examine Seebeck effect and show that higher
thermopower can be achieved when the polarization of the ferromagnet tends
towards the half-metallic limit. It can be enhanced even for lower polarization
in presence of the finite potential barrier. In presence of interfacial Rashba
spin-orbit interaction, Seebeck coefficient rises with the increase of barrier
strength and polarization at weak or moderate interfacial Rashba field. From
the application perspective, we compute the figure of merit and show that
$zT\sim 4-5$ with higher polarization of the ferromagnet both in absence and
presence of weak or moderate Rashba spin-orbit interaction along with the
scalar potential barrier.",1611.00353v3
2016-11-03,Tricritical wings and modulated magnetic phases in LaCrGe$ _{3}$ under pressure,"We determined on the temperature-pressure-magnetic field ($T$-$p$-$H$) phase
diagram of the ferromagnet LaCrGe$_3$ from electrical resistivity measurements
on single crystals. In ferromagnetic systems, quantum criticality is avoided
either by a change of the transition order, becoming of the first order at a
tricritical point, or by the appearance of modulated magnetic phases. In the
first case, the application of a magnetic field reveals a wing-structure phase
diagram as seen in itinerant ferromagnets such as ZrZn$_2$ and UGe$_2$. In the
second case, no tricritical wings have been observed so far. Our investigation
of LaCrGe$_3$ reveals a double-wing structure indicating strong similarities
with ZrZn$_2$ and UGe$_2$. But, unlike these, simpler systems, LaCrGe$_3$ is
thought to exhibit a modulated magnetic phase under pressure which already
precludes it from a pressure-driven paramagnetic-ferromagnetic quantum phase
transition in zero field. As a result, the $T$-$p$-$H$ phase diagram of
LaCrGe$_3$ shows both the wing structure as well as the appearance of new
magnetic phases, providing the first example of this new possibility for the
phase diagram of metallic quantum ferromagnets.",1611.01212v1
2017-04-26,Ultra-small moment incommensurate spin density wave order masking a ferromagnetic quantum critical point in NbFe$_2$,"In the metallic magnet Nb$_{1-y}$Fe$_{2+y}$, the low temperature threshold of
ferromagnetism can be investigated by varying the Fe excess $y$ within a narrow
homogeneity range. We use elastic neutron scattering to track the evolution of
magnetic order from Fe-rich, ferromagnetic Nb$_{0.981}$Fe$_{2.019}$ to
approximately stoichiometric NbFe$_2$, in which we can, for the first time,
characterise a long-wavelength spin density wave state burying a ferromagnetic
quantum critical point. The associated ordering wavevector $\mathbf{q}_{\rm
SDW}=$(0,0,$l_{\rm SDW}$) is found to depend significantly on $y$ and $T$,
staying finite but decreasing as the ferromagnetic state is approached. The
phase diagram follows a two order-parameter Landau theory, for which all the
coefficients can now be determined. Our findings suggest that the emergence of
SDW order cannot be attributed to band structure effects alone. They indicate a
common microscopic origin of both types of magnetic order and provide strong
constraints on related theoretical scenarios based on, e.g., quantum order by
disorder.",1704.08379v2
2011-11-13,Thermal spin pumping and magnon-phonon-mediated spin-Seebeck effect,"The spin-Seebeck effect (SSE) in ferromagnetic metals and insulators has been
investigated systematically by means of the inverse spin-Hall effect (ISHE) in
paramagnetic metals. The SSE generates a spin voltage as a result of a
temperature gradient in a ferromagnet, which injects a spin current into an
attached paramagnetic metal. In the paramagnet, this spin current is converted
into an electric field due to the ISHE, enabling the electric detection of the
SSE. The observation of the SSE is performed in longitudinal and transverse
configurations consisting of a ferromagnet/paramagnet hybrid structure, where
thermally generated spin currents flowing parallel and perpendicular to the
temperature gradient are detected, respectively. Our results explain the SSE in
terms of a two-step process: (1) the temperature gradient creates a
non-equilibrium state in the ferromagnet governed by both magnon and phonon
propagations and (2) the non-equilibrium between magnons in the ferromagnet and
electrons in the paramagnet at the contact interface leads to ""thermal spin
pumping"" and the ISHE signal. The non-equilibrium state of metallic magnets
(e.g. Ni81Fe19) under a temperature gradient is governed mainly by the phonons
in the sample and the substrate, while in insulating magnets (e.g. Y3Fe5O12)
both magnon and phonon propagations appear to be important. The phonon-mediated
non-equilibrium that drives the thermal spin pumping is confirmed also by
temperature-dependent measurements, giving rise to a giant enhancement of the
SSE signals at low temperatures.",1111.3036v2
2011-11-30,Correlation Decay up to Uniqueness in Spin Systems,"We give a complete characterization of the two-state anti-ferromagnetic spin
systems which are of strong spatial mixing on general graphs. We show that a
two-state anti-ferromagnetic spin system is of strong spatial mixing on all
graphs of maximum degree at most $\Delta$ if and only if the system has a
unique Gibbs measure on infinite regular trees of degree up to $\Delta$, where
$\Delta$ can be either bounded or unbounded. As a consequence, there exists an
FPTAS for the partition function of a two-state anti-ferromagnetic spin system
on graphs of maximum degree at most $\Delta$ when the uniqueness condition is
satisfied on infinite regular trees of degree up to $\Delta$. In particular, an
FPTAS exists for arbitrary graphs if the uniqueness is satisfied on all
infinite regular trees. This covers as special cases all previous algorithmic
results for two-state anti-ferromagnetic systems on general-structure graphs.
  Combining with the FPRAS for two-state ferromagnetic spin systems of
Jerrum-Sinclair and Goldberg-Jerrum-Paterson, and the hardness results of
Sly-Sun and independently of Galanis-Stefankovic-Vigoda, this gives a complete
classification, except at the phase transition boundary, of the approximability
of all two-state spin systems, on either degree-bounded families of graphs or
family of all graphs.",1111.7064v3
2016-05-14,Superconductivity and Ferromagnetism in Hole-Doped RbEuFe$_4$As$_4$,"We discover a robust coexistence of superconductivity and ferromagnetism in
an iron arsenide RbEuFe$_4$As$_4$. The new material crystallizes in an
intergrowth structure of RbFe$_2$As$_2$ and EuFe$_2$As$_2$, such that the Eu
sublattice turns out to be primitive instead of being body-centered in
EuFe$_2$As$_2$. The FeAs layers, featured by asymmetric As coordinations, are
hole doped due to charge homogenization. Our combined measurements of
electrical transport, magnetization and heat capacity unambiguously and
consistently indicate bulk superconductivity at 36.5 K in the FeAs layers and
ferromagnetism at 15 K in the Eu sublattice. Interestingly, the Eu-spin
ferromagnetic ordering belongs to a rare third-order transition, according to
the Ehrenfest classification of phase transition. We also identify an
additional anomaly at $\sim$ 5 K, which is possibly associated with the
interplay between superconductivity and ferromagnetism.",1605.04396v3
2017-07-20,Optical manifestation of the Stoner ferromagnetic transition in 2D electron systems,"We perform a magneto-optical study of a two-dimensional electron systems
(2DES) in the regime of the Stoner ferromagnetic instability for even quantum
Hall filling factors on Mg$_x$Zn$_{1-x}$O/ZnO heterostructures. Under
conditions of Landau-level crossing, caused by enhanced spin susceptibility in
combination with the tilting of the magnetic field, the transition between two
rivaling phases- paramagnetic and ferromagnetic- is traced in terms of optical
spectra reconstruction. Synchronous sharp transformations are observed both in
the photoluminescence structure and parameters of collective excitations upon
transition from paramagnetic to ferromagnetic ordering. Based on these
measurements, a phase diagram is constructed in terms of the 2D electron
density and tilt angle of the magnetic field. Apart from stable paramagnetic
and ferromagnetic phases, an instability region is found at intermediate
parameters with the Stoner transition occurring at $\nu\approx 2$. The spin
configuration in all cases is unambiguously determined by means of inelastic
light scattering by spin-sensitive collective excitations. One indicator of the
spin ordering is the intra-Landau-level spin exciton, which acquires a large
spectral weight in the ferromagnetic phases. The other - is an abrupt energy
shift of the intersubband charge density excitation due to change in the
many-particle energy contribution upon spin rearrangement. From our analysis of
photoluminescence and light scattering data, we estimate the ratio of surface
areas occupied by the domains of the two phases in the vicinity of a transition
point. In addition, the thermal smearing of a phase transition is
characterized.",1707.06421v1
2018-09-21,Hybrid superlattices of graphene and hexagonal boron nitride: A ferromagnetic semiconductor at room temperature,"Carbon (C) doped hexagonal boron nitride (hBN) has been experimentally
reported to be ferromagnetic at room temperature. Substitution by C in hBN has
been also reported to form islands of graphene. In this work we derive a
mechanistic understanding of ferromagnetism with graphene islands in hBN from
first principles and mean-field Hubbard model. We find a general property, that
in bipartite lattices where the sublattices differ in on-site energies, as in
hBN, the ordering between local magnetic moments can be substantial and
predominantly anti-ferromagnetic (AFM) if they are embedded in the same
sublattice, unless dominated by Mott like inter-sublattice spin separation due
to strong localization. The dominant AFM order is rooted at spin resolved
spatial separation of lone pairs of nitrogen (N) and back transferred electrons
on boron (B) due to Coulomb repulsion thus essentially implying a
super-exchange pathway. Subsequently we propose a class of ferri-magnetically
ordered inter-penetrating super-lattices of magnetic graphene islands in hBN,
which can be chosen to be a ferromagnetic semiconductor or a half-metal, and
retain a net non-zero magnetic moment at room temperature.",1809.08270v3
2018-10-29,Ferromagnetism and spin excitations in topological Hubbard models with a flatband,"We study the spin-1 excitation spectra of the flatband ferromagnetic phases
in interacting topological insulators. As a paradigm, we consider a quarter
filled square lattice Hubbard model whose free part is the $\pi$ flux state
with topologically nontrivial and nearly-flat electron bands, which can realize
either the Chern or $Z_2$ Hubbard model. By using the numerical exact
diagonalization method with a projection onto the nearly-flat band, we obtain
the ferromagnetic spin-1 excitation spectra for both the Chern and $Z_2$
Hubbard models, consisting of spin waves and Stoner continuum. The spectra
exhibit quite distinct dispersions for both cases, in particular the spin wave
is gapless for the Chern Hubbard model, while gapped for the $Z_2$ Hubbard
model. Remarkably, in both cases, the nonflatness of the free electron bands
introduces dips in the lower boundary of the Stoner continuum. It significantly
renormalizes the energies of the spin waves around these dips downward and
leads to roton-like spin excitations. We elaborate that it is the softening of
the roton-like modes that destabilizes the ferromagnetic phase, and determine
the parameter region where the ferromagnetic phase is stable.",1810.11986v2
2019-06-17,Imaging uncompensated moments and exchange-biased emergent ferromagnetism in FeRh thin films,"Uncompensated moments in antiferromagnets are responsible for exchange bias
in antiferromagnet/ferromagnet heterostructures; however, they are difficult to
directly detect because any signal they contribute is typically overwhelmed by
the ferromagnetic layer. We use magneto-thermal microscopy to image
uncompensated moments in thin films of FeRh, a room-temperature antiferromagnet
that exhibits a 1st-order phase transition to a ferromagnetic state near
100~$^\circ$C. FeRh provides the unique opportunity to study both uncompensated
moments in the antiferromagnetic phase and the interaction of uncompensated
moments with emergent ferromagnetism within a relatively broad
(10-15~$^\circ$C) temperature range near $T_C$. In the AF phase below $T_C$, we
image both pinned UMs, which cause local vertical exchange bias, and unpinned
UMs, which exhibit an enhanced coercive field that reflects exchange-coupling
to the AF bulk. Near $T_C$, where AF and FM order coexist, we find that the
emergent FM order is exchange-coupled to the bulk N\'eel order. This exchange
coupling leads to the nucleation of unusual configurations in which different
FM domains are pinned parallel, antiparallel, and perpendicular to the applied
magnetic field before suddenly collapsing into a state uniformly parallel to
the field.",1906.07243v1
2019-06-26,In Quest of a Ferromagnetic Insulator -- Structure Controlled Magnetism in Mg-Ti-O Thin Films,"Ferromagnetic insulator thin films can convey information by spin waves,
avoiding charge displacement and Eddy current losses. The sparsity of
high-temperature insulating ferromagnetic materials hinders the development of
spin wave based devices. Stoichiometric magnesium titanate, MgTiO$_3$, has an
electronic-energy-band structure in which all bands are either full or empty,
being a paramagnetic insulator. The MgTiO$_3$ ilmenite consists of ordered
octahedra and cation network in which one third of the octahedra are vacant,
one third host magnesium and one third titanium. By giving up these
characteristics, a rich variety of different magnetic structures can be formed.
Our experiments and electronic-energy-band-structure computations show that the
magnetic and electric properties of Mg-Ti-O films can drastically be changed
and controlled by Mg- and Ti-cation arrangement and abundancy in the octahedra.
Insulating titanium- and semiconducting magnesium-rich films were ferromagnetic
up to elevated temperatures. The presence and origin of ferromagnetic
insulating phase in the films is not apparent - the expectation, based on the
well-established rules set by Goodenough and Kanamori, is paramagnetic or
antiferromagnetic ordering. We show that ferro- and paramagnetic phases,
possessing the same stoichiometry, can be obtained by merely rearranging the
cations, thus allowing defect-free interfaces in multilayer structures.",1906.10975v1
2019-10-28,"Realization of an intrinsic, ferromagnetic topological state in MnBi8Te13","The interplay between topology and magnetism is essential for realizing novel
topological states including the axion insulator, the magnetic Weyl semimetal,
etc. An intrinsically ferromagnetic topological material with only the
topological bands at the charge neutrality energy has so far remained elusive.
By rationally designing the natural heterostructure consisting of [MnBi2Te4]
septuple layers and [Bi2Te3] quintuple layers, we report MnBi8Te13 as the first
intrinsic ferromagnetic topological material with clean low-energy band
structure. Based on the thermodynamic, transport and neutron diffraction
measurements, our data show that despite the adjacent [MnBi2Te4] being 44.1
{\AA} apart, MnBi8Te13 manifests long-range ferromagnetism below 10.5 K with
strong coupling between magnetism and charge carriers. Our first-principles
calculations and angle-resolved photoemission spectroscopy measurements further
demonstrate that MnBi8Te13 is an intrinsic ferromagnetic axion state.
Therefore, MnBi8Te13 serves as an ideal system to investigate rich emergent
phenomena, including the quantized anomalous Hall effect and quantized
topological magnetoelectric effect.",1910.12847v2
2020-02-12,Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures,"Multiferroic materials with coupled ferroelectric and ferromagnetic
properties are important for multifunctional devices due to their potential
ability of controlling magnetism via electric field, and vice versa. The recent
discoveries of two-dimensional ferromagnetic and ferroelectric materials have
ignited tremendous research interest and aroused hope to search for
two-dimensional multiferroics. However, intrinsic two-dimensional multiferroic
materials and, particularly, those with strong magnetoelectric couplings are
still rare to date. In this paper, using first-principles simulations, we
propose artificial two-dimensional multiferroics via a van der Waals
heterostructure formed by ferromagnetic bilayer chromium triiodide (CrI3) and
ferroelectric monolayer Sc2CO2. In addition to the coexistence of
ferromagnetism and ferroelectricity, our calculations show that, by switching
the electric polarization of Sc2CO2, we can tune the interlayer magnetic
couplings of bilayer CrI3 between ferromagnetic and antiferromagnetic states.
We further reveal that such a strong magnetoelectric effect is from a dramatic
change of the band alignment induced by the strong build-in electric
polarization in Sc2CO2 and the subsequent change of the interlayer magnetic
coupling of bilayer CrI3. These artificial multiferroics and enhanced
magnetoelectric effect give rise to realizing multifunctional nanoelectronics
by van der Waals heterostructures.",2002.05213v1
2021-01-12,Van der Waals Ferromagnetic Josephson Junctions,"Superconductor-ferromagnet (S-F) interfaces in two-dimensional (2D)
heterostructures present a unique opportunity to study the interplay between
superconductivity and ferromagnetism. The realization of such nanoscale
heterostructures in van der Waals (vdW) crystals remains largely unexplored due
to the challenge of making an atomically-sharp interface from their layered
structures. Here, we build a vdW ferromagnetic Josephson junction (JJ) by
inserting a few-layer ferromagnetic insulator Cr2Ge2Te6 into two layers of
superconductor NbSe2. Owing to the remanent magnetic moment of the barrier, the
critical current and the corresponding junction resistance exhibit a hysteretic
and oscillatory behavior against in-plane magnetic fields, manifesting itself
as a strong Josephson coupling state. Through the control of this hysteresis,
we can effectively trace the magnetic properties of atomic Cr2Ge2Te6 in
response to the external magnetic field. Also, we observe a central minimum of
critical current in some thick JJ devices, evidencing the coexistence of 0 and
{\pi} phase coupling in the junction region. Our study paves the way to
exploring the sensitive probes of weak magnetism and multifunctional building
blocks for phase-related superconducting circuits with the use of vdW
heterostructures.",2101.04323v1
2017-09-07,Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures,"Emergent phenomena at polar-nonpolar oxide interfaces have been studied
intensely in pursuit of next-generation oxide electronics and spintronics. Here
we report the disentanglement of critical thicknesses for electron
reconstruction and the emergence of ferromagnetism in polar-mismatched
LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific
X-ray absorption spectroscopy and dichroism, and first-principles calculations,
interfacial electron accumulation and ferromagnetism have been observed within
the polar, antiferromagnetic insulator LaMnO3. Our results show that the
critical thickness for the onset of electron accumulation is as thin as 2 unit
cells (UC), significantly thinner than the observed critical thickness for
ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely
induced by electron over-accumulation. In turn, by controlling the doping of
the LaMnO3, we are able to neutralize the excessive electrons from the polar
mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as
thin as 3 UC, extending the limits of our ability to synthesize and tailor
emergent phenomena at interfaces and demonstrating manipulation of the
electronic and magnetic structures of materials at the shortest length scales.",1709.02035v1
2017-11-15,Phase diagrams and multistep condensations of spin-1 bosonic gases in optical lattices,"Motivated by recent experimental processes, we systemically investigate
strongly correlated spin-1 ultracold bosons trapped in a three-dimensional
optical lattice in the presence of an external magnetic field. Based on a
recently developed bosonic dynamical mean-field theory (BDMFT), we map out
complete phase diagrams of the system for both antiferromagnetic and
ferromagnetic interactions, where various phases are found as a result of the
interplay of spin-dependent interaction and quadratic Zeeman energy. For
antiferromagnetic interactions, the system demonstrates competing magnetic
orders, including nematic, spin-singlet and ferromagnetic insulating phase,
depending on longitudinal magnetization, whereas, for ferromagnetic case, a
ferromagnetic-to-nematic-insulating phase transition is observed for small
quadratic Zeeman energy, and the insulating phase demonstrates the nematic
order for large Zeeman energy. Interestingly, at low magnetic field and finite
temperature, we find an abnormal multi-step condensation of the strongly
correlated superfluid, i.e. the critical condensing temperature of the $m_F=-1$
component with antiferromagnetic interactions demonstrates an increase with
longitudinal magnetization, while, for ferromagnetic case, the Zeeman component
$m_F = 0$ demonstrates a local minimum for the critical condensing temperature,
in contrast to weakly interacting cases.",1711.05470v2
2017-11-28,Nanoclustering phase competition induces the resistivity hump in colossal magnetoresistive manganites,"Using a two-band double-exchange model with Jahn-Teller lattice distortions
and super-exchange interactions, supplemented by quenched disorder, at electron
density $n=0.65$, we explicitly demonstrate the coexistence of the $n$ =
1/2-type ($\pi, \pi$) charge-ordered and the ferromagnetic nanoclusters above
the ferromagnetic transition temperature $T_{\rm c}$ in colossal
magnetoresistive (CMR) manganites. The resistivity increases due to the
enhancement of the volume fraction of the charge-ordered and the ferromagnetic
nanoclusters with decreasing the temperature down to $T_{\rm c}$. The
ferromagnetic nanoclusters start to grow and merge, and the volume fraction of
the charge-ordered nanoclusters decreases below $T_{\rm c}$, leading to the
sharp drop in the resistivity. By applying a small external magnetic field $h$,
we show that the resistivity above $T_{\rm c}$ increases, as compared with the
case when $h=0$, a fact which further confirms the coexistence of the
charge-ordered and the ferromagnetic nanoclusters. In addition, we show that
the volume fraction of the charge-ordered nanoclusters decreases with
increasing the bandwidth and consequently the resistivity hump diminishes for
large bandwidth manganites, in good qualitative agreement with experiments. The
obtained insights from our calculations provide a complete pathway to
understand the phase competition in CMR manganites.",1711.10211v1
2018-03-06,Gate-tunable Room-temperature Ferromagnetism in Two-dimensional Fe$_3$GeTe$_2$,"Material research has been a major driving force in the development of modern
nano-electronic devices. In particular, research in magnetic thin films has
revolutionized the development of spintronic devices; identifying new magnetic
materials is key to better device performance and new device paradigm. The
advent of two-dimensional van der Waals crystals creates new possibilities.
This family of materials retain their chemical stability and structural
integrity down to monolayers and, being atomically thin, are readily tuned by
various kinds of gate modulation. Recent experiments have demonstrated that it
is possible to obtain two-dimensional ferromagnetic order in insulating
Cr$_2$Ge$_2$Te$_6$ and CrI$_3$ at low temperatures. Here, we developed a new
device fabrication technique, and successfully isolated monolayers from layered
metallic magnet Fe$_3$GeTe$_2$ for magnetotransport study. We found that the
itinerant ferromagnetism persists in Fe$_3$GeTe$_2$ down to monolayer with an
out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition
temperature, $T_c$, is suppressed in pristine Fe$_3$GeTe$_2$ thin flakes. An
ionic gate, however, dramatically raises the $T_c$ up to room temperature,
significantly higher than the bulk $T_c$ of 205 Kelvin. The gate-tunable
room-temperature ferromagnetism in two-dimensional Fe$_3$GeTe$_2$ opens up
opportunities for potential voltage-controlled magnetoelectronics based on
atomically thin van der Waals crystals.",1803.02038v1
2018-06-18,Anomalous Nernst effect beyond the magnetization scaling relation in the ferromagnetic Heusler compound Co$_2$MnGa,"Applying a temperature gradient in a magnetic material generates a voltage
that is perpendicular to both the heat flow and the magnetization. This is the
anomalous Nernst effect (ANE) which was thought to be proportional to the value
of the magnetization for a long time. However, more generally, the ANE has been
predicted to originate from a net Berry curvature of all bands near the Fermi
level. Subsequently, a large anomalous Nernst thermopower has recently been
observed in topological materials with no net magnetization but large net Berry
curvature around E$_F$. These experiments clearly fall outside the scope of the
conventional magnetization-model of the ANE, but a significant question
remains: Can the value of the ANE in topological ferromagnets exceed the
highest values observed in conventional ferromagnets? Here, we report a
remarkably high anomalous Nernst thermopower value of ~6.0 \mu V/K at 1 T in
the ferromagnetic topological Heusler compound Co$_2$MnGa at room temperature,
which is around 7-times larger than any anomalous Nernst thermopower value ever
reported for a conventional ferromagnet. Combined electrical, thermoelectric
and first-principles calculations reveal that this high value of the ANE arises
from a large net Berry curvature near the Fermi level associated with nodal
lines and Weyl points.",1806.06753v1
2018-08-22,Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe$_2$Ge$_2$,"We report neutron scattering measurements of single-crystalline YFe$_2$Ge$_2$
in the normal state, which has the same crystal structure to the 122 family of
iron pnictide superconductors. YFe$_2$Ge$_2$ does not exhibit long range
magnetic order, but exhibits strong spin fluctuations. Like the iron pnictides,
YFe$_2$Ge$_2$ displays anisotropic stripe-type antiferromagnetic spin
fluctuations at ($\pi$, $0$, $\pi$). More interesting, however, is the
observation of strong spin fluctuations at the in-plane ferromagnetic
wavevector ($0$, $0$, $\pi$). These ferromagnetic spin fluctuations are
isotropic in the ($H$, $K$) plane, whose intensity exceeds that of stripe spin
fluctuations. Both the ferromagnetic and stripe spin fluctuations remain
gapless down to the lowest measured energies. Our results naturally explain the
absence of magnetic order in YFe$_2$Ge$_2$ and also imply that the
ferromagnetic correlations may be a key ingredient for iron-based materials.",1808.07262v1
2018-12-04,Anomalous orbital moment in the ferromagnetic phase of the Sr4Ru3O10,"The coupling of spin and orbital degrees of freedom in the trilayer Sr4Ru3O10
sets a long-standing puzzle, due to the peculiar anisotropic coexistence of
out-of-plane ferromagnetism and in-plane metamagnetism. Recently, the induced
magnetic structure by in-plane applied fields has been investigated by means of
spin-polarized neutron diffraction, which allowed to extract a substantial
orbital component of the magnetic densities at Ru sites. It has been argued
that the latter is at the origin of the evident layer dependent magnetic
anisotropy, where the inner layers carry larger magnetic moments than the outer
ones. We present a spin-polarized neutron diffraction study in order to
characterize the nature of the ferromagnetic state of Sr4Ru3O10, in the
presence of a magnetic field applied along the c-axis. The components of the
magnetic densities at the Ru sites reveal a vanishing contribution of the
orbital magnetic moment which is unexpected for a material system where orbital
and spin degeneracy are lifted by spin-orbit coupling and ferromagnetism. We
employ a model that includes the Coulomb interaction and spin-orbit coupling at
the Ru site to address the origin of the suppression of the orbital magnetic
moment. The emerging scenario is that of non-local orbital degrees of freedom
playing a significant role in the ferromagnetic phase, with the Coulomb
interaction that is crucial to make anti-aligned orbital moments at short
distance resulting in a ground state with vanishing local orbital moments.",1812.01359v2
2019-01-08,Ferromagnetic ordering along the hard axis in the Kondo lattice YbIr3Ge7,"Ferromagnetic Kondo lattice compounds are far less common than their
antiferromagnetic analogs. In this work, we report the discovery of a new
ferromagnetic Kondo lattice compound, YbIr3Ge7. Like almost all ferromagnetic
Kondo lattice systems, YbIr3Ge7 shows magnetic order with moments aligned
orthogonal to the crystal electric field (CEF) easy axis. YbIr3Ge7 is unique in
that it is the only member of this class of compounds that crystallizes in a
rhombohedral structure with a trigonal point symmetry of the magnetic site, and
it lacks broken inversion symmetry at the local moment site. AC magnetic
susceptibility, magnetization, and specific heat measurements show that
YbIr3Ge7 has a Kondo temperature TK = 14 K and a Curie temperature TC = 2.4 K.
Ferromagnetic order occurs along the crystallographic [100] hard CEF axis
despite the large CEF anisotropy of the ground state Kramers doublet with a
saturation moment along [001] almost four times larger than the one along
[100]. This implies that a mechanism which considers the anisotropy in the
exchange interaction to explain the hard axis ordering is unlikely. On the
other hand, the broad second-order phase transition at TC favors a
fluctuation-induced mechanism.",1901.02489v1
2019-02-21,Asymmetric Ferromagnetic Criticality in Pyrochlore Ferromagnet Lu$_2$V$_2$O$_7$,"Critical phenomenon at the phase transition reveals the universal and
long-distance properties of the criticality. We study the ferromagnetic
criticality of the pyrochlore magnet Lu$_2$V$_2$O$_7$ at the ferromagnetic
transition ${T_\text{c}\approx 70\, \text{K}}$ from the isotherms of
magnetization $M(H)$ via an iteration process and the Kouvel-Fisher method. The
critical exponents associated with the transition are determined as ${\beta =
0.32(1)}$, ${\gamma = 1.41(1)}$, and ${\delta = 5.38}$. The validity of these
critical exponents is further verified by scaling all the $M(H)$ data in the
vicinity of $T_\text{c}$ onto two universal curves in the plot of
$M/|\varepsilon|^\beta$ versus $H/|\varepsilon|^{\beta+\gamma}$, where
${\varepsilon = T/T_\text{c} -1}$. The obtained $\beta$ and $\gamma$ values
show asymmetric behaviors on the ${T < T_\text{c}}$ and the ${T > T_\text{c}}$
sides, and are consistent with the predicted values of 3D Ising and cubic
universality classes, respectively. This makes Lu$_2$V$_2$O$_7$ a rare example
in which the critical behaviors associated with a ferromagnetic transition
belong to different universality classes. We describe the observed criticality
from the Ginzburg-Landau theory with the quartic cubic anisotropy that
microscopically originates from the anti-symmetric Dzyaloshinskii-Moriya
interaction as revealed by recent magnon thermal Hall effect and theoretical
investigations.",1902.07924v1
2019-03-19,Spin-polarized Correlated Insulator and Superconductor in Twisted Double Bilayer Graphene,"Ferromagnetism and superconductivity typically compete with each other since
the internal magnetic field generated in a magnet suppresses the formation of
spin-singlet Cooper pairs in conventional superconductors. Only a handful of
ferromagnetic superconductors are known in heavy fermion systems, where
many-body electron interactions promoted by the narrow energy bands play a key
role in stabilizing these emergent states. Recently, interaction-driven
superconductivity and ferromagnetism have been demonstrated as separate
phenomena in different density regimes of flat bands enabled by graphene moire
superlattices. Combining superconductivity and magnetism in a single ground
state may lead to more exotic quantum phases. Here, employing van der Waals
heterostructures of twisted double bilayer graphene (TDBG), we realize a flat
electron band that is tunable by perpendicular electric fields. Similar to the
magic angle twisted bilayer graphene, TDBG exhibits energy gaps at the half and
quarter filled flat bands, indicating the emergence of correlated insulating
states. We find that the gaps of these insulating states increase with in-plane
magnetic field, suggesting a ferromagnetic order. Upon doping the ferromagnetic
half-filled insulator, superconductivity emerges with a critical temperature
controlled by both density and electric fields. We observe that the in-plane
magnetic field enhances the superconductivity in the low field regime,
suggesting spin-polarized electron pairing. Spin-polarized superconducting
states discovered in TDBG provide a new route to engineering interaction-driven
topological superconductivity.",1903.08130v2
2019-03-26,Magnetic competition induced colossal magnetoresistance in n-type HgCr2Se4 under high pressures,"The n-type HgCr2Se4 exhibits a sharp semiconductor-to-metal transition (SMT)
in resistivity accompanying the ferromagnetic order at TC = 106 K. Here, we
investigate the effects of pressure and magnetic field on the concomitant SMT
and ferromagnetic order by measuring resistivity, dc and ac magnetic
susceptibility, as well as single-crystal neutron diffraction under various
pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate
that the ferromagnetic metallic ground state of n-type HgCr2Se4 is destabilized
and gradually replaced by an antiferromagnetic, most likely a spiral magnetic,
and insulating ground state upon the application of high pressure. On the other
hand, the application of external magnetic fields can restore the ferromagnetic
metallic state again at high pressures, resulting in a colossal
magnetoresistance (CMR) as high as ~ 3 * 10^11 % under 5 T and 2 K at 4 GPa.
The present study demonstrates that n-type HgCr2Se4 is located at a peculiar
critical point where the balance of competion between ferromagnetic and
antiferromagnetic interactions can be easily tipped by the external stimuli,
providing a new platform for achieving CMR in a single-valent system.",1903.10689v1
2019-04-11,Nagaoka ferromagnetism observed in a quantum dot plaquette,"Engineered, highly-controllable quantum systems hold promise as simulators of
emergent physics beyond the capabilities of classical computers. An important
problem in many-body physics is itinerant magnetism, which originates purely
from long-range interactions of free electrons and whose existence in real
systems has been subject to debate for decades. Here we use a quantum simulator
consisting of a four-site square plaquette of quantum dots to demonstrate
Nagaoka ferromagnetism. This form of itinerant magnetism has been rigorously
studied theoretically but has remained unattainable in experiment. We load the
plaquette with three electrons and demonstrate the predicted emergence of
spontaneous ferromagnetic correlations through pairwise measurements of spin.
We find the ferromagnetic ground state is remarkably robust to engineered
disorder in the on-site potentials and can induce a transition to the low-spin
state by changing the plaquette topology to an open chain. This demonstration
of Nagaoka ferromagnetism highlights that quantum simulators can be used to
study physical phenomena that have not yet been observed in any system before.
The work also constitutes an important step towards large-scale quantum dot
simulators of correlated electron systems.",1904.05680v3
2019-08-19,Coherent Epitaxial Semiconductor-Ferromagnetic Insulator InAs/EuS Interfaces: Band Alignment and Magnetic Structure,"Hybrid semiconductor-ferromagnetic insulator heterostructures are interesting
due to their tunable electronic transport, self-sustained stray field and local
proximitized magnetic exchange. In this work, we present lattice matched hybrid
epitaxy of semiconductor - ferromagnetic insulator InAs/EuS heterostructures
and analyze the atomic-scale structure as well as their electronic and magnetic
characteristics. The Fermi level at the InAs/EuS interface is found to be close
to the InAs conduction band and in the bandgap of EuS, thus preserving the
semiconducting properties. Both neutron and X-ray reflectivity measurements
show that the ferromagnetic component is mainly localized in the EuS thin film
with a suppression of the Eu moment in the EuS layer nearest the InAs. Induced
moments in the adjacent InAs layers were not detected although our ab initio
calculations indicate a small exchange field in the InAs layer. This work
presents a step towards realizing high quality semiconductor - ferromagnetic
insulator hybrids, which is a critical requirement for development of various
quantum and spintronic applications without external magnetic fields.",1908.07096v1
2019-11-03,Optically Driven Magnetic Phase Transition of Monolayer RuCl3,"Strong light-matter interactions within nanoscale structures offer the
possibility of optically controlling material properties. Motivated by the
recent discovery of intrinsic long-range magnetic order in two-dimensional
materials, which allows for the creation of novel magnetic devices of
unprecedented small size, we predict that light can couple with magnetism and
efficiently tune magnetic orders of monolayer ruthenium trichloride (RuCl3).
First-principles calculations show that both free carriers and optically
excited electron-hole pairs can switch monolayer RuCl3 from the proximate
spin-liquid phase to a stable ferromagnetic phase. Specifically, a moderate
electron-hole pair density (on the order of 10^13 cm-2) can significantly
stabilize the ferromagnetic phase by 10 meV/f.u. in comparison to the zigzag
phase, so that the predicted ferromagnetism can be driven by optical pumping
experiments. Analysis shows that this magnetic phase transition is driven by a
combined effect of doping-induced lattice strain and itinerant ferromagnetism.
According to the Ising-model calculation, we find that the Curie temperature of
the ferromagnetic phase can be increased significantly by raising carrier or
electron-hole pair density. This enhanced opto-magnetic effect opens new
opportunities to manipulate two-dimensional magnetism through non-contact,
optical approaches.",1911.00979v1
2019-11-08,Effect of strain on magnetic and orbital ordering of LaSrCrO$_3$/LaSrMnO$_3$ heterostructures,"We investigate the effect of strain and film thickness on the orbital and
magnetic properties of LaSrCrO$_3$ (LSCO)/LaSrMnO$_3$ (LSMO) heterostructures
using bulk magnetometry, soft X-ray magnetic spectroscopy, first-principles
density functional theory, high-resolution electron microscopy and X-ray
diffraction. We observe an anti-parallel ordering of the magnetic moments
between the ferromagnetic LSMO layers and the LSCO spacers leading to a
strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures
for LSMO layers as thin as 2 unit cells. As the LSMO thickness is increased, a
net ferromagnetic state is maintained, however, the average magnetic moment per
Mn is found to be dependent on the magnitude of the substrate-induced strain.
The differences in the magnetic responses are related to preferential
occupation of the Mn $x^2-y^2$ (in-plane) d-orbitals for tensile strain and
$3z^2-r^2$ (out-of-plane) orbitals under compressive strain leading to
competing ferromagnetic and anti-ferromagnetic exchange interactions within the
LSMO layers. These results underscore the relative contributions of orbital,
structural and spin degree of freedom and their tunability in atomically-thin
crystalline complex oxide layers.",1911.03007v2
2020-06-23,Avoided quantum criticality and cluster-glass formation in itinerant ferromagnet Sr$_{1-x}$(La$_{0.5}$K$_{0.5}$)$_x$RuO$_3$,"We demonstrate that the cluster-glass state emerges as ferromagnetic quantum
criticality is avoided in itinerant ferromagnet Sr1-x(La0.5K0.5)xRuO3. In this
compound, the ferromagnetic order is suppressed by increasing x, and then
disappears at the critical concentration: x=0.5. In this x range, the present
study reveals that no prominent feature is ascribed to the quantum critical
fluctuations in specific heat. Instead, ac magnetic susceptibility exhibits a
broad peak due to spontaneous spin freezing, and the peak temperature depends
significantly on the frequency of the applied ac magnetic field. Furthermore,
specific heat is enhanced within a wide temperature range, whereas specific
heat shows no salient anomaly associated with spin freezing. These features are
characteristics of the formation of cluster-glass; in particular, the observed
frequency variations in ac magnetic susceptibility are well described by the
Vogel-Fulcher law. We compare the features concerning the suppression of the
ferromagnetic order in this doped compound with those in isostructural Ca- and
La-doped SrRuO3, and suggest that a local correlated disorder effect and the
very small coherence of itinerant Ru 4d electrons are responsible for the
cluster-glass formation instead of the quantum phase transition in
Sr1-x(La0.5K0.5)xRuO3.",2006.12981v1
2020-06-28,Tuning the magneto-electrical properties of multiferroic multilayers through interface strain and disorder,"Artificially engineered superlattices were designed and fabricated to induce
different growth mechanisms and structural characteristics. DC sputtering was
used to grow ferromagnetic (La$_{0.8}$Ba$_{0.2}$MnO$_3$) / ferroelectric
(Ba$_{0.25}$Sr$_{0.75}$TiO$_3$ or BaTiO$_3$) superlattices. We systematically
modified the thickness of the ferromagnetic layer to analyze dimensional and
structural effects on the superlattices with different structural
characteristics. The crystalline structure was characterized by X-Ray
diffraction and transmission electron microscopy. The magnetic and electronic
properties were investigated by SQUID magnetometry and resistance measurements.
The results show that both strain and structural disorder can significantly
affect the physical properties of the systems. Compressive strain tends to
increase the competition between the magnetic interactions decreasing the
ferromagnetism of the samples and the localization of the charge carrier
through the electron-phonon interaction. Tensile strain reduces the charge
carrier localization, increasing the ferromagnetic transition temperature.
Structural defects have a stronger influence on the magnetic properties than on
the transport properties, reducing the ferromagnetic transition temperature
while increasing the magnetic hardness of the superlattices. These results help
to further understand the role of strain and interface effects in the magnetic
and transport properties of manganite based multiferroic systems.",2006.15748v1
2020-08-08,Tuning interchain ferromagnetic instability in A2Cr3As3 ternary arsenides by chemical pressure and uniaxial strain,"We analyze the effects of chemical pressure induced by alkali metal
substitution and uniaxial strain on magnetism in the A2Cr3As3 (A = Na, K, Rb,
Cs) family of ternary arsenides with quasi-one dimensional structure. Within
the framework of the density functional theory, we predict that the
non-magnetic phase is very close to a 3D collinear ferrimagnetic state, which
realizes in the regime of moderate correlations, such tendency being common to
all the members of the family with very small variations due to the different
interchain ferromagnetic coupling. We uncover that the stability of such
interchain ferromagnetic coupling has a non-monotonic behavior with increasing
the cation size, being critically related to the degree of structural
distortions which is parametrized by the Cr-As-Cr bonding angles along the
chain direction. In particular, we demonstrate that it is boosted in the case
of the Rb, in agreement with recent experiments. We also show that uniaxial
strain is a viable tool to tune the non-magnetic phase towards an interchain
ferromagnetic instability. The modifcation of the shape of the Cr triangles
within the unit cell favors the formation of a net magnetization within the
chain and of a ferromagnetic coupling among the chains. This study can provide
relevant insights about the interplay between superconductivity and magnetism
in this class of materials.",2008.03552v4
2020-08-31,Electronic properties in itinerant ferromagnet SrRu$_{1-x}$Ti$_x$O$_3$,"Here, we study the electrical transport and specific heat in 4$d$ based
ferromagnetic material SrRuO$_3$ and its Ti substituted SrRu$_{1-x}$Ti$_x$O$_3$
series ($x$ $\le$ 0.7). The SrRuO$_3$ is a metal and shows itinerant
ferromagnetism with transition temperature $T_c$ $\sim$ 160 K. The nonmagnetic
Ti$^{4+}$ (3$d^0$) substitution would not only weaken the active Ru-O-Ru
channel but is also expected to tune the electronic density and electron
correlation effect. A metal to insulator transition has been observed around
$x$ $\sim$ 0.4. The nature of charge transport in paramagnetic-metallic state
($x$ $\leq$ 0.4) and in insulating state ($x$ $>$ 0.4) follows modified Mott's
variable range hopping model. In ferromagnetic-metallic state, resistivity
shows a $T^2$ dependence below $T_c$ which though modifies to $T^{3/2}$
dependence at low temperature. In Ti substituted samples, temperature range for
$T^{3/2}$ dependence extends to higher temperature. Interestingly, this
$T^{3/2}$ dependence dominates in whole ferromagnetic regime in presence of
magnetic field. This evolution of electronic transport behavior can be
explained within the framework of Fermi liquid theory and electron-magnon
scattering mechanism. The negative magnetoresistance exhibits a hysteresis and
a crossover between negative and positive value with magnetic field which is
connected with magnetic behavior in series. The decreasing electronic
coefficient of specific heat with $x$ supports the increasing insulating
behavior in present series. We calculate a high Kadowaki-Woods ratio ($x$
$\leq$ 0.3) for SrRuO$_3$ which increases with substitution concentration. This
signifies an increasing electronic correlation effect with substitution
concentration.",2009.00076v1
2020-09-14,"Minority-Spin Impurity Band in n-Type (In,Fe)As: A Materials Perspective for Ferromagnetic Semiconductors","Fully understanding the properties of n-type ferromagnetic semiconductors
(FMSs), complementary to the mainstream p-type ones, is a challenging goal in
semiconductor spintronics because ferromagnetism in n-type FMSs is
theoretically non-trivial. Soft-x-ray angle-resolved photoemission spectroscopy
(SX-ARPES) is a powerful approach to examine the mechanism of carrier-induced
ferromagnetism in FMSs. Here our SX-ARPES study on the prototypical n-type FMS
(In,Fe)As reveals the entire band structure including the Fe-3d impurity bands
(IBs) and the host InAs ones, and provides direct evidence for electron
occupation of the InAs-derived conduction band (CB). A minority-spin Fe-3d IB
is found to be located just below the conduction-band minimum (CBM). The IB is
formed by the hybridization of the unoccupied Fe-3d states with the occupied
CBM of InAs in a spin-dependent way, resulting in the large spin polarization
of CB. The band structure with the IB is varied with band filling, which cannot
be explained by the rigid-band picture, suggesting a unified picture for
realization of carrier-induced ferromagnetism in FMS materials.",2009.06285v1
2020-10-02,Spontaneous vortex state in a superconductor/ferromagnet nanocomposite,"The mechanism of the interplay between superconductivity and magnetism is one
of the intriguing and challenging problems in physics. Theory has predicted
that the ferromagnetic order can coexist with the superconducting order in the
form of a spontaneous vortex phase in which magnetic vortices nucleate in the
absence of an external field. However, there has been no rigorous demonstration
of spontaneous vortices by bulk magnetic measurements. Here we show the results
of experimental observations of spontaneous vortices using a
superconductor/ferromagnet fractal nanocomposite, in which superconducting MgB2
and ferromagnetic nanograins are dispersedly embedded in the normal matrix to
realize the remote electromagnetic interaction and also to induce a long-range
Josephson coupling. We found from bulk magnetization measurements that the
sample with nonzero remanent magnetization exhibits the magnetic behaviors
which are fully consistent with a spontaneous vortex scenario predicted
theoretically for magnetic inclusions in a superconducting material. The
resulting spontaneous vortex state is in equilibrium and coexists surprisingly
with a Meissner state (complete shielding of an external magnetic field). The
present observation not only reveals the evolution process of the spontaneous
vortices in superconductor/ferromagnet hybrids, but it also sheds light on the
role of the fractal disorder and structural heterogeneity on the vortex
nucleation under the influence of Josephson superconducting currents.",2010.00842v1
2020-10-07,Apparent Ferromagnetism in Exfoliated Ultra-thin Pyrite Sheets,"Experimental evidence for ferromagnetic ordering in isotropic atomically thin
two-dimensional crystals has been missing until a bilayer Cr2Ge2Te6, and a
three-atom thick monolayer CrI3 are shown to retain ferromagnetic ordering at
finite temperatures. Here, we demonstrate successful isolation of a non-van der
Waals type ultra-thin nanosheet of FeS2 derived from naturally occurring pyrite
mineral (FeS2) by means of liquid-phase exfoliation. Structural
characterizations imply that (111) oriented sheets are predominant and is
supported theoretically by means of density functional theory surface energy
calculations. Spin-polarized density theory calculations further predicted that
(111) oriented three-atom thick pyrite sheet has a stable ferromagnetic ground
state different from its diamagnetic bulk counterpart. This theoretical finding
is evaluated experimentally employing low temperature superconducting quantum
interference device measurements and observed an anomalous ferromagnetic kind
of behavior.",2010.03113v2
2020-10-22,Skyrmion zoo in graphene at charge neutrality in a strong magnetic field,"As a consequence of the approximate spin-valley symmetry in graphene, the
ground state of electrons in graphene at charge neutrality is a particular
SU(4) quantum-Hall ferromagnet to minimize their exchange energy. If only the
Coulomb interaction is taken into account, this ferromagnet can appeal either
to the spin degree of freedom or equivalently to the valley pseudo-spin degree
of freedom. This freedom in choice is then limited by subleading energy scales
that explicitly break the SU(4) symmetry, the simplest of which is given by the
Zeeman effect that orients the spin in the direction of the magnetic field. In
addition, there are also valley symmetry breaking terms that can arise from
short-range interactions or electron-phonon couplings. Here, we build upon the
phase diagram, which has been obtained by Kharitonov [Phys. Rev. B \textbf{85},
155439 (2012)], in order to identify the different skyrmions that are
compatible with these types of quantum-Hall ferromagnets. Similarly to the
ferromagnets, the skyrmions at charge neutrality are described by the
$\text{Gr}(2,4)$ Grassmannian at the center, which allows us to construct the
skyrmion spinors. The different skyrmion types are then obtained by minimizing
their energy within a variational approach, with respect to the remaining free
parameters that are not fixed by the requirement that the skyrmion at large
distances from their center must be compatible with the ferromagnetic
background. We show that the different skyrmion types have a clear signature in
the local, sublattice-resolved, spin magnetization, which is in principle
accessible in scanning-tunneling microscopy and spectroscopy.",2010.11830v2
2020-11-27,d0 Ferromagnetism in Li-doped ZnO Compounds,"Recently, d0 ferromagnetic materials have been projected as one of the
promising novel materials for spintronics applications. In this work, we have
studied Li-doped ZnO compounds, i.e. Zn1-xLixO (x=0, 0.02, 0.04, and 0.06)
samples, prepared by the solid-state reaction route method. From the study of
crystal structure using X-ray diffraction (XRD) patterns, it is evident that
the prepared materials have been formed in a single-phase of the hexagonal
wurtzite structure. The refinement of the XRD patterns suggests that there are
very small changes in the lattice parameters upon Li-incorporation in ZnO. The
average crystallite size (SC), estimated from XRD patterns was found to be in
the range of 35-50 nm. The microstructural study by scanning electron
microscope reveals the uniform morphology of the grains of the order of 50-70
nm. The energy dispersive spectrum indicates that no unwanted ferromagnetic
impurities have crept into the final prepared samples. The measurement of the
temperature (T) variation of magnetization (M) with SQUID magnetometer
indicates that undoped ZnO exhibits diamagnetic property but all Li-doped
compounds exhibit room-temperature ferromagnetism and with a magnetic
irreversibility behavior between zero-field cooled and field cooled M-T data.
From the magnetization versus field measurements at 3 and 300 K, it is observed
that Li-doped samples exhibit ferromagnetic loops with ultra-soft coercivity
(~50 Oe) and with a maximum saturation magnetization of 0.10 emu/gm for x= 0.02
sample, which decreases with the increase in Li concentration.",2011.13713v1
2021-03-18,Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co$_2$MnGa,"Weyl semimetals are playing a major role in condensed matter physics due to
exotic topological properties, and their coexistence with ferromagnetism may
lead to enhanced spin-related phenomena. Here, the inverse spin Hall effect
(ISHE) in the ferromagnetic Weyl-semimetal Heusler alloy Co$_2$MnGa was
investigated at room temperature by means of electrical spin injection in
lateral spin valve structures. Spin transport properties such as spin
polarization and spin diffusion length in this material were precisely
extracted in order to estimate the spin Hall angle $\theta_{\textrm{SH}}$,
which was found to be $-0.19\pm0.04$ and is among the highest reported for a
ferromagnet. Although this value is on the same order of magnitude of known
heavy metals, the significantly higher resistivity of Co$_2$MnGa implies an
improvement on the magnitude of detection voltages, while its ferromagnetic
nature allows controlling the intensity of SHE through the magnetization
direction. It was also shown that Onsager's reciprocity does not hold for this
system, which is in part attributable to a different spin-dependent Hall
conductivity for spin-up and spin-down carriers.",2103.10188v1
2021-04-02,The atlas of ferroicity in two dimensional MGeX3 family: room-temperature ferromagnetic half metals and unexpected ferroelectricity and ferroelasticity,"Two-dimensional (2D) ferromagnetic and ferroelectric materials attract
unprecedented attention due to the spontaneous-symmetry-breaking induced novel
properties and multifarious potential applications. Here we systematically
investigate a large family (148) of 2D MGeX3 (M = metal elements, X =
O/S/Se/Te) by means of the high-throughput first-principles calculations, and
focus on their possible ferroic properties including ferromagnetism,
ferroelectricity, and ferroelasticity. We discover eight stable 2D ferromagnets
including five semiconductors and three half-metals, 21 2D antiferromagnets,
and 11 stable 2D ferroelectric semiconductors including two multiferroic
materials. Particularly, MnGeSe3 and MnGeTe3 are predicted to be
room-temperature 2D ferromagnetic half metals with Tc of 490 and 308 K,
respectively. It is probably for the first time that ferroelectricity is
uncovered in 2D MGeX3 family, which derives from the spontaneous symmetry
breaking induced by unexpected displacements of Ge-Ge atomic pairs, and we also
reveal that the electric polarizations are in proportion to the ratio of
electronegativity of X and M atoms, and IVB group metal elements are highly
favored for 2D ferroelectricity. Magnetic tunnel junction and water-splitting
photocatalyst based on 2D ferroic MGeX3 are proposed as examples of wide
potential applications. The atlas of ferroicity in 2D MGeX3 materials will spur
great interest in experimental studies and would lead to diverse applications.",2104.00865v1
2021-04-09,"Spatially modulated, orbital selective ferromagnetism in La$_5$Co$_2$Ge$_3$","We present density functional theory calculations for low-$T_c$ metallic
ferromagnet La$_5$Co$_2$Ge$_3$ at ambient and applied pressures. Our
investigations reveal that the system is a quasi-one-dimensional ferromagnet
with a peculiar coexistence of two different orbital-selective magnetic moments
at two crystallographically inequivalent cobalt atoms, Co1 and Co2. Namely, due
to different crystal-field splitting, the magnetic moment of Co1 atoms
predominantly derives from $d_{xz}$ orbital whereas of Co2 atoms from $d_{xy}$
orbital. Consequently, Co1 and Co2 atoms develop unequal net magnetic moments,
a feature that gives rise to a periodic, spatial modulation of magnetization
along crystallographic $c$-direction. The amplitude of the spatial modulation,
small at ambient pressure, drastically increases with applied pressure, until
Co2 atoms become nonmagnetic. With the help of a toy model mimicking found
orbital-selective ferromagnetic order, we demonstrate that the increasing
amplitude of spatial modulation provides a consistent interpretation to the
recently observed resistivity anomaly emerging at applied pressure identified
as the appearance of the {\it new state}. Although, proposed here structural
origin of the spatial modulation of magnetic moments in La$_5$Co$_2$Ge$_3$ is
an alternative one to the advocated for this material ferromagnetic quantum
criticality avoidance, the effects of quantum fluctuations can still play an
important role at pressure larger than up-to-date measured 5GPa.",2104.04245v2
2021-06-14,Quantum Kibble-Zurek mechanism: Kink correlations after a quench in the quantum Ising chain,"The transverse field in the quantum Ising chain is linearly ramped from the
para- to the ferromagnetic phase across the quantum critical point at a rate
characterized by a quench time $\tau_Q$. We calculate a connected kink-kink
correlator in the final state at zero transverse field. The correlator is a sum
of two terms: a negative (anti-bunching) Gaussian that depends on the
Kibble-Zurek (KZ) correlation length only and a positive term that depends on a
second longer scale of length. The second length is made longer by dephasing of
the state excited near the critical point during the following ramp across the
ferromagnetic phase. This interpretation is corroborated by considering a
linear ramp that is halted in the ferromagnetic phase for a finite waiting time
and then continued at the same rate as before the halt. The extra time
available for dephasing increases the second scale of length that
asymptotically grows linearly with the waiting time. The dephasing also
suppresses magnitude of the second term making it negligible for waiting times
much longer than $\tau_Q$. The same dephasing can be obtained with a smooth
ramp that slows down in the ferromagnetic phase. Assuming sufficient dephasing
we obtain also higher order kink correlators and the ferromagnetic correlation
function.",2106.07335v3
2021-06-15,Long-Range Orbital Magnetoelectric Torque in Ferromagnets,"While it is often assumed that the orbital response is suppressed and
short-ranged due to strong crystal field potential and orbital quenching, we
show that the orbital magnetoelectric response can be remarkably long-ranged in
ferromagnets. In a bilayer consisting of a nonmagnet and a ferromagnet, spin
injection from the interface results in spin accumulation and torque in the
ferromagnet, which rapidly oscillate and decay by spin dephasing. In contrast,
we find that even when an external electric field is applied only on the
nonmagnet, we find substantially long-ranged orbital magnetoelectric response
in the FM, which can go far beyond the spin dephasing length. This unusual
feature is attributed to nearly degenerate orbital characters imposed by the
crystal symmetry, which form hotspots for the intrinsic orbital response.
Because only the states near the hotspots contribute dominantly, the induced
orbital angular momentum does not exhibit destructive interference among states
with different momentum as in the case of the spin dephasing. This gives rise
to a distinct type of orbital torque on the magnetization, increasing with the
thickness of the ferromagnet. Such behavior may serve as critical long-sought
evidence of orbital transport to be directly tested in experiments. Our
findings open the possibility of using long-range orbital magnetoelectric
effect in orbitronic device applications.",2106.07928v2
2021-07-16,Long-Range Superconducting Proximity Effect in Nickel Nanowires,"When a ferromagnet is placed in contact with a superconductor, owing to
incompatible spin order, the Cooper pairs from the superconductor cannot
survive more than one or two nanometers inside the ferromagnet. This is
confirmed in the measurements of ferromagnetic nickel (Ni) nanowires contacted
by superconducting niobium (Nb) leads. However, when a 3 nm thick copper oxide
(CuO) buffer layer made by exposing an evaporated or a sputtered 3 nm Cu film
to air, is inserted between the Nb electrodes and the Ni wire, the spatial
extent of the superconducting proximity range is dramatically increased from 2
to a few tens of nanometers. Scanning transmission electron microscope study
confirms the formation of a 3 nm thick CuO layer when an evaporated Cu film is
exposed to air. Magnetization measurements of such a 3 nm CuO film on a SiO2/Si
substrate and on Nb/SiO2/Si show clear evidence of ferromagnetism. One way to
understand the long-range proximity effect in the Ni nanowire is that the CuO
buffer layer with ferromagnetism facilitates the conversion of singlet
superconductivity in Nb into triplet supercurrent along the Ni nanowires.",2107.08018v3
2021-10-18,Air Stable and Layer Dependent Ferromagnetism in Atomically Thin van der Waals CrPS$_{4}$,"Ferromagnetism in two-dimensional materials presents a promising platform for
the development of ultrathin spintronic devices with advanced functionalities.
Recently discovered ferromagnetic van der Waals crystals such as CrI$_{3}$,
readily isolated two-dimensional crystals, are highly tunable through external
fields or structural modifications. However, there remains a challenge because
of material instability under air exposure. Here, we report the observation of
an air stable and layer dependent ferromagnetic (FM) van der Waals crystal,
CrPS$_{4}$, using magneto-optic Kerr effect microscopy. In contrast to the
antiferromagnetic (AFM) bulk, the FM out-of-plane spin orientation is found in
the monolayer crystal. Furthermore, alternating AFM and FM properties observed
in even and odd layers suggest robust antiferromagnetic exchange interactions
between layers. The observed ferromagnetism in these crystals remains resilient
even after the air exposure of about a day, providing possibilities for the
practical applications of van der Waals spintronics.",2110.09061v1
2021-11-02,Evidence for anisotropic spin-triplet Andreev reflection at the 2D van der Waals ferromagnet/superconductor interface,"Fundamental symmetry breaking and relativistic spin-orbit coupling give rise
to fascinating phenomena in quantum materials. Of particular interest are the
interfaces between ferromagnets and common s-wave superconductors, where the
emergent spin-orbit fields support elusive spin-triplet superconductivity,
crucial for superconducting spintronics and topologically-protected Majorana
bound states. Here, we report the observation of large magnetoresistances at
the interface between a quasi-two-dimensional van der Waals ferromagnet
Fe0.29TaS2 and a conventional s-wave superconductor NbN, which provides the
possible experimental evidence for the spin triplet Andreev reflection and
induced spin-triplet superconductivity at ferromagnet/superconductor interface
arising from Rashba spin-orbit coupling. The temperature, voltage, and
interfacial barrier dependences of the magnetoresistance further support the
induced spin-triplet superconductivity and spin-triplet Andreev reflection.
This discovery, together with the impressive advances in two-dimensional van
der Waals ferromagnets, opens an important opportunity to design and probe
superconducting interfaces with exotic properties.",2111.01360v2
2021-11-09,Tunable intrinsic ferromagnetic topological phases in bulk van der Waals crystal MnSb6Te10,"Intrinsic ferromagnetism is a crucial ingredient to realize quantum anomalous
Hall effect in quasi two dimensional materials, thus the search of intrinsic
ferromagnetic topological materials is one of the most concerned issues in the
field of topological phases of matter. In this work, combining magnetotransport
measurements, first principles calculations, and angle-resolved photoemission
spectroscopy studies, we find that in MnSb6Te10, the n = 2 member of the
MnSb2Te4/(Sb2Te3)n family, the strong magnetic competition realizes a fragile
ferromagnetic ground state, which whereas easily enters into ferrimagnetic and
the Z_2 antiferromagnetic topological insulator phase with warming to higher
temperature. Interestingly, the system stays in an inversion-symmetry-protected
axion insulator phase in the ferromagnetic ground state as well as in the
external magnetic field driven spin-polarized FM phase and can be converted
into a Weyl semimetal with multiple Weyl nodes in the valence bands with hole
doping, which are manifested by the measured notable intrinsic anomalous Hall
effect. Our work thus provides an intrinsic magnetic topological material which
is highly tunable into versatile topological phases by temperature, magnetic
field, as well as carrier doping.",2111.04973v1
2021-11-11,High temperature ideal Weyl semimetal phase and Chern insulator phase in ferromagnetic BaEuNiOsO6 and its (111) (BaEuNiOsO6)/(BaTiO3)10 superlattice,"Weyl semimetals (WSMs) have recently stimulated intensive interest because
they exhibit fascinating physical properties and also promise exciting
technological applications. So far, however, the few conrmed magnetic WSMs
generally have a large number of Weyl points either located away from the Fermi
level (EF ) or shrouded by nontopological Fermi surface pockets. Based on first
principles density functional theory calculations, we establish cubic double
perovskite BaEuNiOsO6 to be a high Curie temperature (Tc) ferromagnetic WSM
with magnetization along the [111] direction, just two pairs of Weyl points at
the EF and Tc = 325 K. The strong ferromagnetism is attributed to the strong
ferromagnetic Ni 3d-Eu 4f-Os 5d coupling induced by the substitution of half of
Ba atoms with Eu atoms in double perovskite Ba2NiOsO6. Moreover, the momentum
separation of one Weyl point pair is large, thus giving rise to not only a long
(001) surface Fermi arc but also large anomalous Hall conductivity.
Intriguingly, as a unique physical result of a ferromagnetic WSM, the (111)
BaEuNiOsO6 monolayer superlattice (BaEuNiOsO6)/(BaTiO3)10, being its (111)
quantum-well structure, is found to be a high temperature (Tc = 210 K) Chern
insulator with a large band gap of 190 meV. Therefore, cubic double perovskite
BaEuNiOsO6 will provide a superior high temperature material plotform for
exploring fundamental physics of Weyl fermions and its (111) monolayer
superlattices will offer a high temperature magnetic topological insulator for
studying exotic quantum phenomena such as quantum anomalous Hall effect.",2111.06035v1
2021-11-29,Superconductivity coexisting with ferromagnetism in a quasi-one dimensional non-centrosymmetric (TaSe$_4$)$_3$I,"Low-dimensional materials with broken inversion symmetry and strong
spin-orbit coupling can give rise to fascinating quantum phases and phase
transitions. Here we report coexistence of superconductivity and ferromagnetism
below 2.5\,K in the quasi-one dimensional crystals of non-centrosymmetric
(TaSe$_4$)$_3$I (space group: $P\bar{4}2_1c$). The unique phase is a direct
consequence of inversion symmetry breaking as the same material also stabilizes
in a centro-symmetric structure (space group: $P4/mnc$) where it behaves like a
non-magnetic insulator. The coexistence here upfront contradicts the popular
belief that superconductivity and ferromagnetism are two apparently
antagonistic phenomena. Notably, here, for the first time, we have clearly
detected Meissner effect in the superconducting state despite the coexisting
ferromagnetic order. The coexistence of superconductivity and ferromagnetism
projects non-centrosymmetric (TaSe$_4$)$_3$I as a host for complex ground
states of quantum matter including possible unconventional superconductivity
with elusive spin-triplet pairing.",2111.14525v2
2021-12-08,Tailoring Magnetic Exchange Interactions in Ferromagnet-Intercalated MnBi2Te4 Superlattices,"The intrinsic magnetic topological insulator MnBi2Te4 (MBT) has provided a
platform for the successful realization of exotic quantum phenomena. To broaden
the horizons of MBT-based material systems, we intercalate ferromagnetic MnTe
layers to construct the [(MBT)(MnTe)m]N superlattices by molecular beam
epitaxy. The effective incorporation of ferromagnetic spacers mediates the
anti-ferromagnetic interlayer coupling among the MBT layers through the
exchange spring effect at the MBT/MnTe hetero-interfaces. Moreover, the precise
control of the MnTe thickness enables the modulation of relative strengths
among the constituent magnetic orders, leading to tunable magnetoelectric
responses, while the superlattice periodicity serves as an additional tuning
parameter to tailor the spin configurations of the synthesized multi-layers.
Our results demonstrate the advantages of superlattice engineering for
optimizing the magnetic interactions in MBT-family systems, and the
ferromagnet-intercalated strategy opens up new avenues in magnetic topological
insulator structural design and spintronic applications.",2112.04303v1
2021-12-17,"Gate-controlled proximity magnetoresistance in In1-xGaxAs/(Ga,Fe)Sb bilayer heterostructures","The magnetic proximity effect (MPE), ferromagnetic coupling at the interface
of magnetically dissimilar layers, attracts much attention as a promising
pathway for introducing ferromagnetism into a high-mobility non-magnetic
conducting channel. Recently, our group found giant proximity magnetoresistance
(PMR), which is caused by MPE at an interface between a non-magnetic
semiconductor InAs quantum well (QW) layer and a ferromagnetic semiconductor
(Ga,Fe)Sb layer. The MPE in the non-magnetic semiconductor can be modulated by
applying a gate voltage and controlling the penetration of the electron
wavefunction in the InAs QW into the neighboring insulating ferromagnetic
(Ga,Fe)Sb layer. However, optimal conditions to obtain strong MPE at the
InAs/(Ga,Fe)Sb interface have not been clarified. In this paper, we
systematically investigate the PMR properties of In1-xGaxAs (x = 0%, 5%, 7.5%,
and 10%) / (Ga,Fe)Sb bilayer semiconductor heterostructures under a wide range
of gate voltage. The inclusion of Ga alters the electronic structures of the
InAs thin film, in particular changing the effective mass and the QW potential
of electron carriers. Our experimental results and theoretical analysis of the
PMR in these In1-xGaxAs/(Ga,Fe)Sb heterostructures show that the MPE depends
not only on the degree of penetration of the electron wavefunction into
(Ga,Fe)Sb but also on the electron density. These findings help us to unveil
the microscopic mechanism of MPE in semiconductor-based
non-magnetic/ferromagnetic heterojunctions.",2112.09286v1
2021-12-19,The origin of insulating and non-ferromagnetic SrRuO3 monolayers,"The electro-magnetic properties of ultrathin epitaxial ruthenate films have
long been the subject of debate. Here we combine experimental with theoretical
investigations of (SrTiO3)5-(SrRuO3)n-(SrTiO3)5 (STO5-SROn-STO5)
heterostructures with n = 1 and 2 unit cells, including extensive
atomic-resolution scanning-transmission-electron-microscopy imaging,
electron-energy-loss-spectroscopy chemical mapping, as well as transport and
magneto-transport measurements. The experimental data demonstrate that the
STO5-SRO2-STO5 heterostructure is stoichiometric, metallic, and ferromagnetic
with TC ~ 128 K, even though it lacks the characteristic bulk-SRO octahedral
tilts and matches the cubic STO structure. In contrast, the STO5-SRO1-STO5
heterostructure features Ru-Ti intermixing in the RuO2 layer, also without
octahedral tilts, but is accompanied by a loss of metallicity and
ferromagnetism. Density-functional-theory calculations show that stoichiometric
n = 1 and n = 2 heterostructures are metallic and ferromagnetic with no
octahedral tilts, while non-stoichiometry in the Ru sublattice in the n = 1
case opens an energy gap and induces antiferromagnetic ordering. Thus, the
results indicate that the observed non-stoichiometry is the cause of the
observed loss of metallicity and ferromagnetism in the n = 1 case.",2112.10076v1
2021-12-30,Non-uniform magnetization profile in ferromagnetic heterostructures leading to topological Hall effect like signatures,"Anomalous Hall effect (AHE), which arises when a current is passed through a
ferromagnetic material subjected to a perpendicular magnetic field, is
proportional to the magnetization of the sample.Additional hump-like features
in AHE are often attributed to the presence of non trivial spin textures
leading to topological Hall effect (THE). However, several recent reports have
emphasized in context of ferromagnetic SrRuO$_3$ based heterostructures that
the sample inhomogeneity can also result in THE-like features. In order to
investigate this issue in general for any ferromagnetic heterostructure, we
have considered a phenomenological model to calculate the changes in the shape
of hysteresis loop due to various interfacial effects. These changes in the
magnetization have been accounted for by considering that the interdomain
magnetic coupling parameter ($\alpha$) varies exponentially with the distance
from the interface along the growth direction of the heterostructure. In case
of symmetric interfaces on both sides of a ferromagnet, we have considered the
variation of $\alpha$ as a Gaussian function. We have found that the additional
AHE contribution due to the net change in magnetization in such cases are akin
to experimentally observed THE, even though we have not considered any
topological quantity explicitly in our model. Thus, we propose another
situation with nonuniform magnetization profile that may be used to explain
additional features in AHE, which might not necessarily be intrinsic THE.",2112.15020v1
2022-01-31,Magnetostriction in microwave synthesized La0.5Ba0.5CoO3,"A single-phase polycrystalline La0.5Ba0.5CoO3-d sample was synthesized by
microwave irradiation within 20 minutes of processing time and its structural,
magnetic, electrical, and magnetostrictive properties were investigated. While
the temperature dependence of field-cooled magnetization (M) in a field of H =
0.5 kOe indicates the onset of ferromagnetic transition at TC = 177 K,
irreversibility between the zero field-cooled and field cooled M(T) persists
even at H = 3 kOe. M(H) at 10 K does not saturate at the maximum available
field and has a much smaller value (0.87 {\mu}B/Co in a field of 50 kOe) than
1.9 {\mu}B/Co expected for spin-only contribution from intermediate Co3+ and
Co4+ spins. The resistivity shows insulating behavior down to 10 K and only a
small magnetoresistance (~ 2% for H = 70 kOe) occurs around TC. All these
results suggest a magnetically heterogeneous ground state with weakly
interacting ferromagnetic clusters coexisting with a non-ferromagnetic phase.
The length of the sample expands in the direction of the applied magnetic field
(positive magnetostriction) and does not show saturation even at 50 kOe. The
magnetostriction has a maximum value (= 252 ppm) at 10 K and it decreases with
increasing temperature. The smaller value of magnetostriction compared to the
available data on La0.5Sr0.5CoO3 suggests that non-ferromagnetic matrix is most
likely antiferromagnetic and it restrains the field-induced expansion of
ferromagnetic clusters in the microwave synthesized La0.5Ba0.5CoO3-d sample.",2201.12979v1
2022-02-01,1T-FeS$_2$$:$ a new type of two-dimensional metallic ferromagnet,"Discovery of intrinsic two-dimensional (2D) magnetic materials is crucial for
understanding the fundamentals of 2D magnetism and realizing next-generation
magnetoelectronic and magneto-optical devices. Although significant efforts
have been devoted to identifying 2D magnetism by exfoliating bulk magnetic
layered materials, seldom studies are performed to synthesize ultra-thin
magnetic materials directly for non-layered magnetic materials. Here, we report
the successful synthesis of a new type of theoretically proposed 2D metallic
ferromagnet 1T FeS2, through the molten-salt-assisted chemical vapor deposition
(CVD) method. The long-range 2D ferromagnetic order is confirmed by the
observation of a large anomalous Hall effect (AHE) and a hysteretic
magnetoresistance. The experimentally detected out-of-plane ferromagnetic
ordering is theoretically suported with Stoner criterion. Our findings open up
new possibilities to search novel 2D ferromagnets in non-layered compounds and
render opportunities for realizing realistic ultra-thin spintronic devices.",2202.00252v1
2022-03-01,Ultrafast enhancement of interfacial exchange coupling in ferromagnetic bilayer,"Fast spin manipulation in magnetic heterostructures, where magnetic
interactions between different materials often define the functionality of
devices, is a key issue in the development of ultrafast spintronics. Although
recently developed optical approaches such as ultrafast spin-transfer and
spin-orbit torques open new pathways to fast spin manipulation, these processes
do not fully utilize the unique possibilities offered by interfacial magnetic
coupling effects in ferromagnetic multilayer systems. Here, we experimentally
demonstrate ultrafast photo-enhanced interfacial exchange interactions in the
ferromagnetic Co$_2$FeAl/(Ga,Mn)As system at low laser fluence levels. The
excitation efficiency of Co$_2$FeAl with the (Ga,Mn)As layer is 30-40 times
higher than the case with the GaAs layer at 5 K due to a photo-enhanced
exchange coupling interaction via photoexcited charge transfer between the two
ferromagnetic layers. In addition, the coherent spin precessions persist to
room temperature, excluding the drive of photo-enhanced magnetization in the
(Ga,Mn)As layer and indicating a proximity-effect-related optical excitation
mechanism. The results highlight the importance of considering the range of
interfacial exchange interactions in ferromagnetic heterostructures and how
these magnetic coupling effects can be utilized for ultrafast, low-power spin
manipulation.",2203.00293v3
2022-04-14,Piezoelectric ferromagnetism in Janus monolayer YBrI: a first-principle prediction,"Coexistence of intrinsic ferromagnetism and piezoelectricity, namely
piezoelectric ferromagnetism (PFM), is crucial to advance multifunctional
spintronic technologies. In this work, we demonstrate that Janus monolayer YBrI
is a PFM, which is dynamically, mechanically and thermally stable. Electronic
correlation effects on physical properties of YBrI are investigated by using
generalized gradient approximation plus $U$ (GGA+$U$) approach. For
out-of-plane magnetic anisotropy, YBrI is a ferrovalley (FV) material, and the
valley splitting is larger than 82 meV in considered $U$ range. The anomalous
valley Hall effect (AVHE) can be achieved under an in-plane electric field.
However, for in-plane magnetic anisotropy, YBrI is a common ferromagnetic (FM)
semiconductor. When considering intrinsic magnetic anisotropy, the easy axis of
YBrI is always in-plane with magnetic anisotropy energy (MAE) from 0.309 meV to
0.237 meV ($U$=0.0 eV to 3.0 eV). However, the magnetization can be adjusted
from the in-plane to off-plane direction by external magnetic field, and then
lead to the occurrence of valley polarization. Moreover, missing centrosymmetry
along with mirror symmetry breaking results in both in-plane and out-of-plane
piezoelectricity in YBrI monolayer. At a typical $U$=2.0 eV, the $d_{11}$ is
predicted to be -5.61 pm/V, which is higher than or compared with ones of other
two-dimensional (2D) known materials. The electronic and piezoelectric
properties of YBrI can be effectively tuned by applying a biaxial strain. For
example, tensile strain can enhance valley splitting and $d_{11}$ (absolute
value). The predicted Curie temperature of YBrI is higher than those of
experimentally synthesized 2D ferromagnetic materials $\mathrm{CrI_3}$ and
$\mathrm{Cr_2Ge_2Te_6}$.",2204.06713v1
2022-09-13,Emergence of mesoscale quantum phase transitions in a ferromagnet,"Mesoscale patterns as observed, e.g., in ferromagnets, ferroelectrics,
superconductors, mono-molecular films, or block-copolymers, reflect spatial
variations of a pertinent order parameter at length- and time-scales that may
be described classically. This raises the question for the relevance of
mesoscale patterns near zero temperature phase transitions, also known as
quantum phase transitions (QPTs). Here we report the magnetic susceptibility of
LiHoF$_4$ -- a dipolar Ising ferromagnet -- near a well-understood
transverse-field quantum critical point (TF-QCP). When tilting the magnetic
field away from the hard axis such that the Ising symmetry is always broken, a
line of well-defined phase transitions emerges from the TF-QCP characteristic
of an additional symmetry breaking, in stark contrast to a crossover expected
microscopically. We show that a continuous suppression of ferromagnetic
domains, representing a breaking of translation symmetry on mesoscopic scales
in an environment of broken magnetic Ising symmetry on microscopic scales, is
in excellent qualitative and quantitative agreement with the field- and
temperature dependence of the susceptibility and the magnetic phase diagram of
LiHoF$_4$ under tilted field. This identifies a new type of phase transition
that may be referred to as mesocale quantum criticality, which emanates from
the text-book example of a microscopic ferromagnetic TF-QCP. Our results
establish the surroundings of QPTs as a regime of mesoscale pattern formation,
where non-analytical quantum dynamics and materials properties without
classical analogue may be expected.",2209.06224v1
2022-09-20,Modeling of 3D Printable Electrical Machineries Ferromagnetic Parts,"The electrical machinery core is formed with a ferromagnetic material that
offers high magnetic properties. As ferromagnetic materials have high relative
magnetic permeability, they are important in the formation of electromagnetic
device cores. Conventional subtractive and powder metallurgy methods for
fabrication electrical machineries offer significant core losses and reduce
magnetic flux density and magnetic permeability. With the advancement of
technology, the limitation of the traditional process can be overcome by using
the additive manufacturing process. Hence, this paper proposes a 3D printable
model of two types of single-phase transformers, referred to as E-I shape and
U-I shape transformers respectively. Possibilities of designing the electrical
machinery part which has a ferromagnetic core are investigated. The efficiency
of the transformers is evaluated in terms of magnetic flux density distribution
and volumetric loss density based on the results of a large number of Finite
element simulation methods under various operating situations on COMSOL. The
performance of various ferromagnetic materials such as Soft Iron (Fe) and
Ferrite (Fe2O3) on the transformer core is evaluated. This analysis reveals
that if U-I shaped transformer can be made from 3D printing, it will be the
best feasible structure for higher operating frequency.",2209.09894v1
2022-10-20,Increased localization of Majorana modes in antiferromagnetic chains on superconductors,"Magnet-superconductor hybrid (MSH) systems are a key platform for
custom-designed topological superconductors. Ideally, the ends of a
one-dimensional MSH structure will host Majorana zero-modes (MZMs), the
fundamental unit of topological quantum computing. However, some of the
experiments with ferromagnetic chains show a more complicated picture. Due to
tiny gap sizes and hence long coherence lengths MZMs might hybridize and lose
their topological protection. Recent experiments on a niobium surface have
shown that both ferromagnetic and antiferromagnetic chains may be engineered,
with the magnetic order depending on the crystallographic direction of the
chain. While ferromagnetic chains are well understood, antiferromagnetic chains
are less so. Here we study two models inspired by the niobium surface: a
minimal model to elucidate the general topological properties of
antiferromagnetic chains, and an extended model to more closely simulate a real
system by mimicking the proximity effect. We find that in general for
antiferromagnetic chains the topological gap is larger than for ferromagnetic
ones and thus coherence lengths are shorter for antiferromagnetic chains,
yielding more pronounced localization of MZMs in these chains. While
topological phases for both ferromagnetic and antiferromagnetic chains both
depend on the magnetic moment of the adatoms and the chemical potential, we
find that antiferromagnetic chains also have a strong dependence on the
magnitude of Rashba spin-orbit coupling at the surface.",2210.11587v2
2022-12-08,Ferromagnetic instability in itinerant fcc lattice electron systems with higher order van Hove singularities: Functional renormalization group study,"We investigate the possibility of ferromagnetic ordering in the
non-degenerate Hubbard model on the face-centered cubic lattice within the
functional renormalization group technique using temperature as a scale
parameter. We assume the relations between nearest, next-nearest, and
next-next-nearest hopping parameters providing higher order (giant) van Hove
singularity of the density of states. The ferromagnetic instability formation
with lowering temperature is described consistently in the one-loop
approximation for a one-particle irreducible vertex of two-particle electron
interaction. The chemical potential versus temperature phase diagrams are
calculated. We find ferromagnetic order only for sufficiently strong divergence
of the density of states and fillings in the vicinity of van Hove singularity.
The obtained Curie temperature is more than an order of magnitude smaller than
the results of the random-phase approximation. The main origin of the
suppression of ferromagnetism is the screening of interaction in the
particle-particle channel. We also do not find the pronounced tendency towards
incommensurate order when the Fermi level is moved away from a van Hove
singularity, such that the first order quantum phase transitions from the
ferro- to paramagnetic phase are obtained.",2212.04135v2
2023-02-13,Spin State Disproportionation in Insulating Ferromagnetic LaCoO3 Epitaxial Thin Films,"The origin of insulating ferromagnetism in epitaxial LaCoO3 films under
tensile strain remains elusive despite extensive research efforts have been
devoted. Surprisingly, the spin state of its Co ions, the main parameter of its
ferromagnetism, is still to be determined. Here, we have systematically
investigated the spin state in epitaxial LaCoO3 thin films to clarify the
mechanism of strain induced ferromagnetism using element-specific x-ray
absorption spectroscopy and dichroism. Combining with the configuration
interaction cluster calculations, we unambiguously demonstrate that Co3+ in
LaCoO3 films under compressive strain (on LaAlO3 substrate) are practically a
low spin state, whereas Co3+ in LaCoO3 films under tensile strain (on SrTiO3
substrate) have mixed high spin and low spin states with a ratio close to 1:3.
From the identification of this spin state ratio, we infer that the dark strips
observed by high-resolution scanning transmission electron microscopy indicate
the position of Co3+ high spin state, i.e., an observation of a spin state
disproportionation in tensile-strained LaCoO3 films. This consequently explains
the nature of ferromagnetism in LaCoO3 films.",2302.06063v1
2023-02-23,GaTe-Assisted CVD Growth of Ultrathin Large-Scale 2D Ferromagnetic Cr5Te8,"Recently, 2D Cr5Te8 has been successfully synthesized experimentally and has
attracted widespread research interest due to its intriguing magnetic
properties, such as hard magnetism with strong perpendicular anisotropy.
However, exploring new methods for growing ultrathin 2D Cr5Te8 with a larger
scale and their controllable synthesis remain challenging. Herein, the
synthesis of ultrathin 2D ferromagnetic Cr5Te8 nanosheets by chemical vapor
deposition (CVD) using GaTe as growth source is reported, whose size is up to
~160 {\mu}m and the thickness is lower to only 5 nm. The GaTe promotes the
concentration of effective Te atoms to facilitate the direction of the
synthesis reaction, enabling the rapid lateral growth rate. As a result, the
synthesis of ultrathin, large-scale 2D ferromagnetic Cr5Te8 was achieved. By
precisely adjusting the growth temperature and the source-substrate distance
(Dss), the lateral size of the Cr5Te8 nanosheets can be tuned from a few to
~164 {\mu}m. Furthermore, magnetic property measurement system (MPMS) suggested
that Cr5Te8 nanosheets possess intense out-of-plane ferromagnetism and the
Curie temperature exhibits a monotonic increase from 163 to 175 K as the Cr5Te8
thickness. This work not only paves a way for the controllable growth of
ultrathin, large-scale 2D ferromagnetic crystalline, but also provides a new
platform for the spintronics and the practical application of magnetic memory
devices.",2302.12169v2
2023-04-12,Co-existence of charge density wave and anti-ferromagnetic coupling in the spin-chain compound Ba$_6$Cr$_2$S$_{10}$,"Here we have performed detailed first principles calculations for the
electronic structure and magnetic properties of Ba$_6$Cr$_2$S$_{10}$ to study
the origin of the anti-ferromagnetic exchange interaction between spins on Cr
ions for the spin-chain compound Ba$_6$Cr$_2$S$_{10}$ synthesised recently.
Most importantly, we have found the co-existence of a charge density wave phase
along one line and an anti-ferromagnetic spin chain along another. The
dimerization of sulfur atoms loosely bonded with Ba atoms drives the system
into an insulating state owing to the formation of charge density wave.
Meanwhile, the small size of the effective Hubbard $U$ parameter ($\sim 0.5$
eV) due to electrostatic screening mainly accounts for the anti-ferromagnetic
ground state. This co-existence equips us with a platform to tune the charge
and spin degrees of freedom independently. Moreover, there exists a
next-nearest-neighbouring anti-ferromagnetic interaction along the chain, which
could bring forward spin frustration and hence quantum spin liquid.",2304.06156v3
2023-07-24,Temperature and thickness dependence of the thermal conductivity in 2D ferromagnet Fe$_3$GeTe$_2$,"The emergence of symmetry-breaking orders such as ferromagnetism and the weak
interlayer bonding in van der Waals materials, offers a unique platform to
engineer novel heterostructures and tune transport properties like thermal
conductivity. Here, we report the experimental and theoretical study of the
cross-plane thermal conductivity, $\kappa_\perp$, of the van der Waals 2D
ferromagnet Fe$_3$GeTe$_2$. We observe a non-monotonic increase of
$\kappa_\perp$ with the thickness and a large suppression in
artificially-stacked layers, indicating a diffusive transport regime with
ballistic contributions. These results are supported by the theoretical
analyses of the accumulated thermal conductivity, which show an important
contribution of phonons with mean free paths between 10 and 200 nm. Moreover,
our experiments show a reduction of the $\kappa_\perp$ in the low-temperature
ferromagnetic phase occurring at the magnetic transition. The calculations show
that this reduction in $\kappa_\perp$ is associated with a decrease in the
group velocities of the acoustic phonons and an increase in the phonon-phonon
scattering of the Raman modes that couple to the magnetic phase. These results
demonstrate the potential of van der Waals ferromagnets for thermal transport
engineering.",2307.12863v1
2023-11-09,Electrically induced angular momentum flow between separated ferromagnets,"Converting angular momentum between different degrees of freedom within a
magnetic material results from a dynamic interplay between electrons, magnons
and phonons. This interplay is pivotal to implementing spintronic device
concepts that rely on spin angular momentum transport. We establish a new
concept for long-range angular momentum transport that further allows to
address and isolate the magnonic contribution to angular momentum transport in
a nanostructured metallic ferromagnet. To this end, we electrically excite and
detect spin transport between two parallel and electrically insulated
ferromagnetic metal strips on top of a diamagnetic substrate. Charge-to-spin
current conversion within the ferromagnetic strip generates electronic spin
angular momentum that is transferred to magnons via electron-magnon coupling.
We observe a finite angular momentum flow to the second ferromagnetic strip
across a diamagnetic substrate over micron distances, which is electrically
detected in the second strip by the inverse charge-to-spin current conversion
process. We discuss phononic and dipolar interactions as the likely cause to
transfer angular momentum between the two strips. Moreover, our work provides
the experimental basis to separate the electronic and magnonic spin transport
and thereby paves the way towards magnonic device concepts that do not rely on
magnetic insulators.",2311.05290v1
2023-12-20,Singular Hall response from a correlated ferromagnetic flat nodal-line semimetal,"Topological quantum phases have been largely understood in weakly correlated
systems, which have identified various quantum phenomena such as spin Hall
effect, protected transport of helical fermions, and topological
superconductivity. Robust ferromagnetic order in correlated topological
materials particularly attracts attention, as it can provide a versatile
platform for novel quantum devices. Here, we report singular Hall response
arising from a unique band structure of flat topological nodal lines in
combination with electron correlation in an itinerant, van der Waals
ferromagnetic semimetal, Fe3GaTe2, with a high Curie temperature of Tc=360 K.
High anomalous Hall conductivity violating the conventional scaling,
resistivity upturn at low temperature, and a large Sommerfeld coefficient are
observed in Fe3GaTe2, which implies heavy fermion features in this
ferromagnetic topological material. Our circular dichroism in angle-resolved
photoemission spectroscopy and theoretical calculations support the original
electronic features in the material. Thus, low-dimensional Fe3GaTe2 with
electronic correlation, topology, and room-temperature ferromagnetic order
appears to be a promising candidate for robust quantum devices.",2312.12889v1
2024-01-25,Thermal and Magnetoelastic Properties of the van der Waals Ferromagnet Fe$_{3-δ}$GeTe$_2$: Anisotropic Spontaneous Magnetostriction and Ferromagnetic Magnon Excitations,"By determining the lattice parameters as a function of temperature of the
hexagonal van der Waals ferromagnet Fe$_{2.92(1)}$Ge$_{1.02(3)}$Te$_2$ we
obtain the temperature dependence of the spontaneous in-plane magnetostriction
in the ferromagnetic and the linear thermal expansion coefficients in the
paramagnetic state. The spontaneous magnetostriction is clearly seen in the
temperature dependence of the in-plane lattice parameter $a(T)$, but less well
pronounced perpendicular to the planes along $c$. Below $T_{\rm C}$ the
spontaneous magnetostriction follows the square of the magnetization and leads
to an expansion of the hexagonal layers. Extrapolating to $T\rightarrow$ 0~K we
obtain a spontaneous in-plane saturation magnetostriction of $\lambda_{{\rm
sp},a}(T \rightarrow 0) \approx-220 ~\times~10^{-6}$. In the paramagnetic state
the linear thermal expansion coefficients amount to
13.9(1)$\times$10$^{-6}$~K$^{-1}$ and to 23.2(2)$\times$10$^{-6}$~K$^{-1}$ for
the in-plane and out-of-plane direction, respectively, indicating a linear
volume thermal expansion coefficient of 50.8(4)$\times$10$^{-6}$K$^{-1}$ which
we use to estimate the volume thermal expansion contribution to the heat
capacity determined at constant pressure. A Sommerfeld-type linear term in the
low-temperature heat capacities can be quantitatively ascribed to 2dim
ferromagnetic magnon excitations.",2401.14050v1
2024-02-24,Observation of the In-plane Anomalous Hall Effect induced by Octupole in Magnetization Space,"The Anomalous Hall Effect (AHE) manifests as a transverse voltage
proportional to magnetization in ferromagnetic materials under the application
of a charge current, being an indispensable tool for probing magnetism,
especially in nanoscale devices. However, the AHE primarily sensitizes to
out-of-plane magnetization, thereby hindering its capacity to discern the
in-plane magnetization, a characteristic prevalent in ferromagnetic films. Here
we challenge this conventional understanding by demonstrating the in-plane
magnetization-induced AHE in iron and nickel, two ubiquitous ferromagnets. This
observation of the in-plane AHE is remarkable as it contradicts existing
theories that forbid such phenomena in cubic crystal systems. We trace the
origin of this unanticipated phenomenon to a hitherto unconsidered octupole of
the anomalous Hall conductivity in the magnetization space, a mechanism we
propose could enable the detection of in-plane AHE in a wide range of
ferromagnetic materials. This work realizes the in-plane AHE in common
ferromagnets by exploiting the anomalous Hall conductivity octupole, revealing
a new physical origin of the AHE and promising to revolutionize the design of
magnetic devices and sensors.",2402.15741v1
2024-03-13,Chiral spin state and nematic ferromagnet in the spin-1 Kitaev-$Γ$ model,"The higher-spin Kitaev magnets, in which the Kitaev interaction and
off-diagonal exchange couplings are overwhelmingly large, have emerged as a
fertile avenue to explore exotic phases and unusual excitations. In this work,
we study the quantum phase diagram of the spin-1 Kitaev-$\Gamma$ model on the
honeycomb lattice using density-matrix renormalization group. It harbours six
distinct phases and the intriguing findings are three magnetically ordered
phases in which both time-reversal symmetry and lattice symmetry albeit of
different sort are broken spontaneously. The chiral spin state originates from
the order-by-disorder effect and exhibits an almost saturated scalar spin
chirality at the quantum level. Depending on the relative strength of the two
interactions, it also features columnar or plaquette valence-bond-solid-like
pattern as a consequence of the translational symmetry breaking. In parallel,
the nematic ferromagnets are situated at ferromagnetic Kitaev side and possess
small but finite ferromagnetic ordering. The lattice-rotational symmetry
breaking enforces nonequivalent bond energy along one of the three bonds.
Although the intrinsic difference between the two nematic ferromagnets remains
elusive, the discontinuities in the von Neumann entropy, hexagonal plaquette
operator, and Wilson loop operator convincingly suggest that they are separated
via a first-order phase transition.",2403.08382v1
2013-07-31,A Vertical Resonance Heating Model for X- or Peanut-Shaped Galactic Bulges,"We explore a second order Hamiltonian vertical resonance model for X-shaped
or peanut-shaped galactic bulges. The X-shape is caused by the 2:1 vertical
Lindblad resonance with the bar, with two vertical oscillation periods per
orbital period in the bar frame. We examine N-body simulations and find that
due to the bar slowing down and disk thickening during bar buckling, the
resonance and associated peanut-shape moves outward. The peanut-shape is
consistent with the location of the vertical resonance, independent of whether
the bar buckled or not. We estimate the resonance width from the potential m=4
Fourier component and find that the resonance is narrow, affecting orbits over
a narrow range in the angular momentum distribution, dL/L ~ 0.05. As the
resonance moves outward, stars originally in the mid plane are forced out of
the mid plane into orbits just within the resonance separatrix. The height of
the separatrix orbits, estimated from the Hamiltonian model, is approximately
consistent with the peanut-shape height. The X-shape is comprised of stars in
the vicinity of the resonance separatrix. The velocity distributions from the
simulations illustrate that low inclination orbits are depleted within
resonance. Within resonance, the vertical velocity distribution is broad,
consistent with resonant heating caused by the passage of the resonance through
the disk. In the Milky Way bulge we relate the azimuthally averaged mid-plane
mass density near the vertical resonance to the rotation curve and bar pattern
speed. At an estimated vertical resonance galactocentric radius of ~1.3 kpc, we
confirm a mid-plane density of ~5x10^8 Msol/kpc^3, consistent with recently
estimated mass distributions. We find that the rotation curve, bar pattern
speed, 2:1 vertical resonance location, X-shape tips, and mid-plane mass
density, are all self-consistent in the Milky Way galaxy bulge.",1307.8441v2
2020-01-04,Long-term evolution of the Galilean satellites: the capture of Callisto into resonance,"Context. The strong tidal dissipation in the couple Jupiter-Io is spread to
all the moons involved in the Laplace resonance (Io, Europa, and Ganymede),
leading to a migration of their orbits.
  Aims. We aim to characterize the future behavior of the Galilean satellites
over the Solar System lifetime and to quantify the stability of the Laplace
resonance. Since tidal dissipation makes possible the exit from the current
resonances or capture into new ones, we investigate the capture of Callisto
into resonance.
  Methods. We perform hundreds of propagations using an improved version of a
recent semi-analytical model. As Ganymede moves outwards, it approaches the 2:1
resonance with Callisto, inducing a temporary chaotic motion in the system. For
this reason, we draw a statistical picture of the outcome of the resonant
encounter.
  Results. The system can settle into two distinct outcomes: A) a chain of
three 2:1 two-body resonances (Io-Europa, Europa-Ganymede and
Ganymede-Callisto), or B) a resonant chain involving the 2:1 two-body resonance
Io-Europa plus at least one pure 4:2:1 three-body resonance, most frequently
between Europa, Ganymede and Callisto. In case A (56\% of the simulations), the
Laplace resonance is always preserved and the eccentricities remain confined to
small values below 0.01. In case B (44\% of the simulations), the Laplace
resonance is generally disrupted and the eccentricities of Ganymede and
Callisto can increase up to about 0.1, making this configuration unstable and
driving the system into new resonances.
  Conclusion. From our results, the capture of Callisto into resonance appears
to be extremely likely (100\% of our simulations). Assuming the most recent
estimate of the dissipation between Io and Jupiter, the resonant encounter
happens at about 1.5 Gyrs from now. Therefore, the stability of the Laplace
resonance is guaranteed at least up to about 1.5 Gyrs.",2001.01106v2
2005-10-20,The autoparametric 3:2 resonance in conservative systems,"In the resonance model, high-frequency quasi-periodic oscillations (QPOs) are
supposed to be a consequence of nonlinear resonance between modes of
oscillations occurring within the innermost parts of an accretion disk. Several
models with a prescribed mode--mode interaction were proposed in order to
explain the characteristic properties of the resonance in QPO sources. In this
paper, we examine nonlinear oscillations of a system having two degrees of
freedom and we show that this case could be particularly relevant for QPOs. We
present a very convenient way how to study autoparametric resonances of a fully
general system using the method of multiple scales. We concentrate to
conservative systems and discuss their behavior near the 3:2 parametric
resonance.",0510605v1
1993-12-07,Resonance Lineshapes in Quasi-One-Dimensional Scattering,"An S matrix approach is developed to describe elastic scattering resonances
of systems where the scattered particle is asymptotically confined and the
scattering potential lacks continuous symmetry. Examples are conductance
resonances in microstructures or transmission resonances in waveguide
junctions. The generic resonance is shown to have the asymmetric Fano
lineshape. The asymmetry parameter q is independent of coupling to the
quasi-bound level implying a scaling property of the resonances which can be
tested in transport experiments.",9312033v1
2000-03-23,Resonant tunneling in GaAs/AlGaAs triple-barrier structures under uniform transverse magnetic field,"The effect of an in-plane magnetic field on resonant tunneling in a symmetric
GaAs/AlYGa1-YAs triple-barrier resonant tunneling TBRT structure is presented.
The splitting of the resonant lines (and hence the coupling energy vs. magnetic
induction) for the ground and the first excited resonant doublet shifts up in
energy by increasing the magnetic induction. Each of branches in the resonant
dispersion relations shows a parabolic behavior with the location of the
cyclotron orbit center. It is expected that, at very high fields, the
interaction with confined phonons be enhanced, due to phonon coupling between
electron states in the ground quasibound doublet.",0003373v1
2002-10-01,Tunable Molecular Resonances of Double Quantum Dots Embedded in an Aharonov-Bohm Interferometer,"We investigate resonant tunneling through molecular states of coupled double
quantum dots embedded in an Aharonov-Bohm (AB) interferometer. The conductance
through the system consists of two resonances associated with the bonding and
the antibonding quantum states. We predict that the two resonances are composed
of a Breit-Wigner resonance and a Fano resonance, those widths and Fano factor
depending on the AB phase very sensitively.
  Further, we point out that the bonding properties, such as the covalent and
the ionic bonding, can be identified by the AB oscillations.",0210009v1
2003-01-15,Quantum Measurement of a Coupled Nanomechanical Resonator -- Cooper-Pair Box System,"We show two effects as a result of considering the second-order correction to
the spectrum of a nanomechanical resonator electrostatically coupled to a
Cooper-pair box. The spectrum of the Cooper-pair box is modified in a way which
depends on the Fock state of the resonator. Similarly, the frequency of the
resonator becomes dependent on the state of the Cooper-pair box. We consider
whether these frequency shifts could be utilized to prepare the nanomechanical
resonator in a Fock state, to perform a quantum non-demolition measurement of
the resonator Fock state, and to distinguish the phase states of the
Cooper-pair box.",0301252v2
2003-08-29,Lifetime of molecule-atom mixtures near a Feshbach resonance in 40K,"We report a dramatic magnetic field dependence in the lifetime of trapped,
ultracold diatomic molecules created through an s-wave Feshbach resonance in
40K. The molecule lifetime increases from less than 1 ms away from the Feshbach
resonance to greater than 100 ms near resonance. We also have measured the
trapped atom lifetime as a function of magnetic field near the Feshbach
resonance; we find that the atom loss is more pronounced on the side of the
resonance containing the molecular bound state.",0308606v1
2004-04-02,Three-boson problem near a narrow Feshbach resonance,"We consider a three-boson system with resonant binary interactions and show
that three-body observables depend only on the resonance width and the
scattering length. The effect of narrow resonances is qualitatively different
from that of wide resonances revealing novel physics of three-body collisions.
We calculate the rate of three-body recombination to a weakly bound level and
the atom-dimer scattering length and discuss implications for experiments on
Bose-Einstein condensates and atom-molecule mixtures near Feshbach resonances.",0404036v2
2004-06-04,Observation of Feshbach resonances between two different atomic species,"We have observed three Feshbach resonances in collisions between lithium-6
and sodium-23 atoms. The resonances were identified as narrow loss features
when the magnetic field was varied. The molecular states causing these
resonances have been identified, and additional lithium-sodium resonances are
predicted. These resonances will allow the study of degenerate Bose-Fermi
mixtures with adjustable interactions, and could be used to generate ultracold
heteronuclear molecules.",0406129v1
2004-07-14,Feshbach Resonances in Fermionic Lithium-6,"Feshbach resonances in lithium-6 were experimentally studied and
theoretically analyzed. In addition to two previously known s-wave resonances,
we found three p-wave resonances. Four of these resonances are narrow and yield
a precise value of the singlet scattering length, but do not allow us to
accurately predict the location of the broad resonance near 83 mT. Its position
was previously measured in a molecule-dissociation experiment for which we,
here, discuss systematic shifts.",0407373v1
2004-12-28,Resonant plasmon scattering by discrete breathers in Josephson junction ladders,"We study the resonant scattering of plasmons (linear waves) by discrete
breather excitations in Josephson junction ladders. We predict the existence of
Fano resonances, and find them by computing the resonant vanishing of the
transmission coefficient. We propose an experimental setup of detecting these
resonances, and conduct numerical simulations which demonstrate the possibility
to observe Fano resonances in the plasmon scattering by discrete breathers in
Josephson junction ladders.",0412727v1
2006-08-03,High frequency study of the orbital ordering resonance in the strongly correlated heavy fermion metal CeB6,"We report results of the study of the recently discovered magnetic resonance
in the orbitally ordered phase of CeB6 (the orbital ordering resonance) in a
wide frequency range 44-360 GHz. It is found that the g-factor for this
resonance increases with frequency from g(44 GHz)~1.55 to g(>250 GHz)~1.7. In
addition to the orbital ordering resonance for the frequencies exceeding 200
GHz a new magnetic resonance with the g-factor 1.2-1.3 is detected.",0608079v1
1998-03-14,The Balmer-Like Formula for Mass Distribution of Elementary Particle Resonances,"Elementary particle resonances have been systematically analysed using all
available experimental data. We have come to the conclusion that the resonance
decay prodact momenta and masses of resonances are to be quantized. The Balmer-
like formula for masses of elementary particle resonances was obtained. These
observations allow us to formulate a strategy of experimental searches for new
resonances and systematize the known one.",9803352v2
2001-04-25,How parametric resonance mechanism follows quench mechanism in disoriented chiral condensate,"We show how parametric resonance mechanism follows quench mechanism in the
classical linear sigma model. The parametric resonance amplifies long
wavelength modes of the pion for more than $10 fm/c$. The shifting from the
quench mechanism to the parametric resonance mechanism is described by a time
dependent quantity. After the quench mechanism is over, that quantity has an
oscillating part, which causes the parametric resonance. Since its frequency is
$2 m_\pi ~(m_\pi$ : pion mass), very long wavelength modes such as k = 40 MeV
of the pion are amplified by the parametric resonance.",0104255v1
2001-10-05,Two-photon mediated resonance production in e+e- collisions: cross sections and density matrices,"Earlier described model amplitudes are used in this paper to evaluate both
cross sections and density matrices for two-photon mediated resonance
production in e^+e^- collisions. All 25 q\bar{q} low-lying ^1S_0, ^3P_J and
^1D_2 resonances can thus be treated. Two independent methods are described to
obtain the resonance production density matrices and cross sections. These
density matrices combined with a resonance decay density matrix give the
detailed angular distributions of the resonance decay products. For two
particular decays, \chi_{c2},\chi_{c1}\to\gamma J/\psi the details are given.
Several numerical results are presented as well.",0110086v1
2006-07-21,Resonance Production in Heavy Ion Collisions - what can we learn from RHIC?,"In these proceedings we concentrate on the refeeding and rescattering
probability of hadronic resonances. We discuss the probability to form
resonances in binary baryon-meson or meson-meson collisions as a function of
time for various resonances using a transport model approach (UrQMD). We give
an estimate of the re-feeding probability using a simplified thermal approach
and discuss the relevance for the resonance/non-resonance ratio measured by
STAR.",0607242v3
2007-02-05,Stochastic Resonance: from climate to biology,"In this paper I will review some basic aspects of the mechanism of stochastic
resonance. Stochastic resonance was first introduced as a possible mechanism to
explain long term climatic variation. Since then, there have been many
applications of stochastic resonance in physical and biological systems. I will
show that in complex system, stochastic resonance can substantially change as a
function of the ``system complexity''. Also, I will briefly mention how to
apply stochastic resonance for the case of Brownian motors.",0702008v1
1995-11-30,Do we have three $S_{11}$ resonances in the second resonance region?,"We review the status of the $S_{11}$ N$^*$ resonances in light of some recent
theoretical and phenomenological results. Whereas the quark model predicts two
such resonances around 1.6 GeV, there is considerable evidence for a third
$S_{11}$ resonance in this energy range. This suggests that a $K\Sigma$ or
$K\Lambda$ quasi-bound state may indeed exist below the kaon production
threshold. We show that kaon production experiments, in particular $K^0$
photoproduction off nucleons, would be very sensitive to the existence of the
third $S_{11}$ resonance.",9511041v1
2000-10-31,Few-body resonances in light nuclei,"We have localized several few-body resonances in light nuclei, using methods
which can properly handle two- or three-body resonant states. Among other
results, we predict the existence of a three-neutron resonance, small
spin-orbit splittings between the low-lying states in He-5 and Li-5, the
nonexistence of the soft dipole resonance in He-6, new 1+ states in Li-8 and
B-8, and the presence of a nonlinear amplification phenomenon in the 0+_2 state
of C-12.",0010105v1
2004-11-18,Nuclear giant resonances,"This talk presents the recent status of theoretical and experimental studies
of giant resonances in nuclei with the emphasis on: (1) charge-exchange
Gamow-Teller resonance, (2) multiple-phonon resoanances, (3) giant dipole
resonances in highly excited nuclei, and (4) pygmy dipole resonances in neutron
rich nuclei. In particular, the description of these resonances within the
framework of the phonon damping model is discussed in detail.",0411073v1
2006-10-24,Negative Energy Resonances of Bosons in a Magnetic Quadrupole Trap,"We investigate resonances of spin 1 bosons in a three-dimensional magnetic
quadrupole field. Complementary to the well-known positive energy resonances it
is shown that there exist short-lived, i.e. broad, negative energy resonances.
The latter are characterized by an atomic spin that is aligned antiparallel to
the local magnetic field direction. In contrast to the positive energy
resonances the lifetimes of the negative energy resonances decreases with
increasing total magnetic quantum number. We derive a mapping of the two
branches of the spectrum.",0610207v1
2007-06-05,Resonance Production in RHIC Collisions,"Results of resonance particle production measured at RHIC in $\sqrt{s_{\rm
NN}} = $ 200 GeV Au+Au collisions are compared to measurements in p+p and d+Au
collisions in order to verify the existence of an extended hardronically
interacting medium. Yield and momentum distributions of resonances maybe
modified during the fireball lifetime due to resonance decay and the subsequent
rescattering of their decay daughters as well as the regeneration of resonances
from their decay products. Modified momentum spectra in heavy ion collisions
may change the nuclear modification factor R$_{\rm AA}$. The influence on the
elliptic flow v$_{2}$ due to late regeneration of resonances is discussed.",0706.0729v1
2007-09-05,Electron spin manipulation and resonator readout in a double quantum dot nano-electromechanical system,"Magnetically coupling a nano-mechanical resonator to a double quantum dot
confining two electrons can enable the manipulation of a single electron spin
and the readout of the resonator's natural frequency. When the Larmor frequency
matches the resonator frequency, the electron spin in one of the dots can be
selectively flipped by the magnetised resonator. By simultaneously measuring
the charge state of the two-electron double quantum dots, this transition can
be detected thus enabling the natural frequency of the mechanical resonator to
be determined.",0709.0593v2
2007-09-09,Strongly Resonant Transmission of Electromagnetic Radiation in Periodic Anisotropic Layered Media,"The electromagnetic dispersion in periodic layered media can be tailored and
their resonant properties can be considerably improved by utilizing anisotropic
materials. Periodic structures with a photonic band edge split into two parts,
or so-called split band edge, exhibit superior resonant properties including
exceptionally high Q-values of transmission resonances and nearly perfect
impedance matching at the boundaries, even when the number of unit cells N is
not large. A microwave transmission resonance with Q~220 is demonstrated in a
periodic stack of form-birefringent layers with N=12 realized in a waveguide
geometry.",0709.1250v2
2008-02-07,How Resonances can synchronise with Thresholds,"The mechanism by which a threshold may capture a resonance is examined. It
involves a threshold cusp interfering constructively with either or both (i) a
resonance produced via confinement, (ii) attractive t- and u-channel exchanges.
The fo(980), X(3872) and Z(4430) are studied in detail. The fo(980) provides a
valuable model of the locking mechanism. The X(3872) is too narrow to be fitted
by a cusp, and requires either a resonance or virtual state. The Z(4430) can be
fitted as a resonance but also can be fitted successfully by a cusp with no
nearby resonant pole.",0802.0934v2
2008-04-07,Nuclear-resonant electron scattering,"We investigate nuclear-resonant electron scattering as occurring in the
two-step process of nuclear excitation by electron capture (NEEC) followed by
internal conversion. The nuclear excitation and decay are treated by a
phenomenological collective model in which nuclear states and transition
probabilities are described by experimental parameters. We present capture
rates and resonant strengths for a number of heavy ion collision systems
considering various scenarios for the resonant electron scattering process. The
results show that for certain cases resonant electron scattering can have
significantly larger resonance strengths than NEEC followed by the radiative
decay of the nucleus. We discuss the impact of our findings on the possible
experimental observation of NEEC.",0804.0950v1
2008-04-22,Contribution of dielectrics to frequency and noise of NbTiN superconducting resonators,"We study NbTiN resonators by measurements of the temperature dependent
resonance frequency and frequency noise. Additionally, resonators are studied
covered with SiOx dielectric layers of various thicknesses. The resonance
frequency develops a non-monotonic temperature dependence with increasing SiOx
layer thickness. The increase in the noise is independent of the SiOx
thickness, demonstrating that the noise is not dominantly related to the low
temperature resonance frequency deviations.",0804.3499v2
2009-03-23,Three Resonant Ultra-Cold Bosons: Off-Resonance Effects,"We solve a finite range two-channel model for three resonant identical
bosons. The model provides a minimal description of the various magnetic
Feshbach resonances in single species ultra-cold bosonic systems, including
off-resonant scattering. We obtain important insights into the interpretation
of seminal experiments: the three-body recombination rate measured in Sodium
and the Efimov resonances observed in Caesium. This approach quantifies non
universal effects appearing for a finite magnetic field detuning.",0903.3808v3
2009-06-06,Efficient readout of micromechanical resonator arrays in ambient conditions,"We present a method for efficient spectral readout of mechanical resonator
arrays in dissipative environments. Magnetomotive drive and detection is used
to drive double clamped resonators in the nonlinear regime. Resonators with
almost identical resonance frequencies can be tracked individually by sweeping
the drive power. Measurements are performed at room temperature and atmospheric
pressure. These conditions enable application in high throughput resonant
sensor arrays.",0906.1304v1
2009-07-16,Anharmonicity Induced Resonances for Ultracold Atoms and their Detection,"When two atoms interact in the presence of an anharmonic potential, such as
an optical lattice, the center of mass motion cannot be separated from the
relative motion. In addition to generating a confinement-induced resonance (or
shifting the position of an existing Feshbach resonance), the external
potential changes the resonance picture qualitatively by introducing new
resonances where molecular excited center of mass states cross the scattering
threshold. We demonstrate the existence of these resonances, give their
quantitative characterization in an optical superlattice, and propose an
experimental scheme to detect them through controlled sweeping of the magnetic
field.",0907.2906v2
2009-07-17,Resonance production from jet fragmentation,"Short lived resonances are sensitive to the medium properties in heavy-ion
collisions. Heavy hadrons have larger probability to be produced within the
quark gluon plasma phase due to their short formation times. Therefore heavy
mass resonances are more likely to be affected by the medium, and the
identification of early produced resonances from jet fragmentation might be a
viable option to study chirality. The high momentum resonances on the away-side
of a triggered di-jet are likely to be the most modified by the partonic or
early hadronic medium. We will discuss first results of triggered
hadron-resonance correlations in Cu+Cu heavy ion collisions.",0907.3161v1
2009-09-14,Distribution of Resonant Eigenvalues of Quantum Potential Scattering,"We formulate the Born approximation for finding resonance poles in the
complex plane for potential scattering problems. Using the method, we study the
distribution of resonance poles for several scattering potentials. In
particular, we find for an exponential potential with a cutoff that the cutoff
generates an infinite series of extra resonance poles below and along the real
axis, which would not exist without the cutoff. We also find for a Gaussian
potential that the series of resonance poles approach the imaginary axis of the
complex energy plane from left. In other words, the real parts of the resonant
eigenenergis are all negative.",0909.2463v1
2009-09-18,Random terahertz metamaterials,"Using terahertz time domain spectroscopy we investigate the normal incidence
transmission through periodically and randomly arranged planar split ring
resonators (SRRs). Introduction of positional disorder in metamaterials has no
effect on the quality factor of the fundamental Inductive-Capacitive (LC)
resonance. The dipole resonances undergo broadening and shift in their
resonance frequencies. The experiment reveals that the randomly distributed SRR
structures interact incoherently at LC resonance but couple coherently at the
higher frequency dipole resonance.",0909.3539v1
2009-11-16,Reducing microwave loss in superconducting resonators due to trapped vortices,"Microwave resonators with high quality factors have enabled many recent
breakthroughs with superconducting qubits and photon detectors, typically
operated in shielded environments to reduce the ambient magnetic field.
Insufficient shielding or pulsed control fields can introduce vortices, leading
to reduced quality factors, although increased pinning can mitigate this
effect. A narrow slot etched into the resonator surface provides a
straightforward method for pinning enhancement without otherwise affecting the
resonator. Resonators patterned with such a slot exhibited over an order of
magnitude reduction in the excess loss due to vortices compared with identical
resonators from the same film with no slot.",0911.3131v1
2010-01-22,Ultracompact plasmonic racetrack resonators in metal-insulator-metal waveguides,"Among various plasmonic waveguides, the metal-insulator-metal (MIM) type is
the most promising for true subwavelength photonic integration. To date, many
photonic devices based on MIM waveguides have been investigated, including
resonators. However, most of the reported MIM ring resonators suffer from low
extinction ratios. In this paper, we present a comprehensive analysis of the
intrinsic reasons for the low performance of MIM ring resonators, and give the
analytical transmission relation for a universal all-pass ring resonator which
has coupling loss. Based on the analysis we propose the plasmonic racetrack
resonators in MIM waveguides and show that the performance can be greatly
improved.",1001.4052v2
2010-01-28,Study of nucleon resonances at EBAC@JLab,"We present the dynamical origin of the P11 nucleon resonances resulting from
a dynamical coupled-channels (DCC) analysis of meson production reactions off a
nucleon target, which is conducted at Excited Baryon Analysis Center (EBAC) of
Jefferson Lab. Two resonance poles are found in the energy region where the
Roper resonance P11(1440) was identified. Furthermore, the two resonance poles
and the next higher resonance pole corresponding to P11(1710) are found to
originate from a single bare state.",1001.5080v1
2010-07-06,Detecting molecules with plasmonic resonators - Analytic expressions and bounds for the sensitivity and figure of merit,"We derive analytic expressions for the sensitivity and figure of merit for
refractive index sensing with plasmonic resonators in the quasistatic limit.
Based on these expressions the limits of detection and their origins are
investigated. The critical role of limited energy concentration within the
resonators surrounding is shown. The classical figure of merit is found to be
solely dependent on the ratio of real to imaginary part of the resonators
permittivity . Based on these findings we discuss the optimum resonance
wavelength and resonator size and shape for single molecule detection.",1007.0837v1
2010-07-21,Dynamics of Morphology-Dependent Resonances by Openness in Dielectric Disk for TE polarization,"We have studied the dynamics of morphology-dependent resonances by openness
in a dielectric microdisk for TE polarization. For the first time, we report
that the dynamics exhibits avoided resonance crossings between inner and outer
resonances even though the corresponding billiard is integrable. Due to the
avoidance, inner and outer resonances can be exchanged and $Q$-factor of inner
resonances is strongly affected. We analyze the diverse phenomena aroused from
the dynamics including the avoided crossings.",1007.3590v2
2010-07-22,Chiral dynamics and baryon resonances,"The structure of baryon resonance in coupled-channel meson-baryon scattering
is studied from the viewpoint of chiral dynamics. The meson-baryon scattering
amplitude can be successfully described together with the properties of the
resonance in the scattering, by implementing the unitarity condition for the
amplitude whose low energy structure is constrained by chiral theorem.
Recently, there have been a major progress in the study of the structure of the
resonance in chiral dynamics. We review the methods to clarify the structure of
the resonance by focusing on the Lambda(1405) resonance.",1007.3912v1
2010-10-28,Capacitive Spring Softening in Single-Walled Carbon Nanotube Nanoelectromechanical Resonators,"We report the capacitive spring softening effect observed in single-walled
carbon nanotube (SWNT) nanoelectromechanical (NEM) resonators. The nanotube
resonators adopt dual-gate configuration with both bottom-gate and side-gate
capable of tuning the resonance frequency through capacitive coupling.
Interestingly, downward resonance frequency shifting is observed with
increasing side-gate voltage, which can be attributed to the capacitive
softening of spring constant. Furthermore, in-plane vibrational modes exhibit
much stronger spring softening effect than out-of-plan modes. Our dual-gate
design should enable the differentiation between these two types of vibrational
modes, and open up new possibility for nonlinear operation of nanotube
resonators.",1010.6099v1
2011-01-10,Resonances On-Demand for Plasmonic Nano-Particles,"A method for designing plasmonic particles with desired resonance spectra is
presented. The method is based on repetitive perturbations of an initial
particle shape while calculating the eigenvalues of the various quasistatic
resonances. The method is rigorously proved, assuring a solution exists for any
required spectral resonance location. Resonances spanning the visible and the
near-infrared regimes, as designed by our method, are verified using
finite-difference time-domain simulations. A novel family of particles with
collocated dipole-quadrupole resonances is designed, demonstrating the unique
power of the method. Such on-demand engineering enables strict realization of
nano-antennas and metamaterials for various applications requiring specific
spectral functions.",1101.1769v1
2011-02-28,Resonant d-wave scattering in harmonic waveguides,"We observe and analyze d-wave resonant scattering of bosons in tightly
confining harmonic waveguides. It is shown that the d-wave resonance emerges in
the quasi-1D regime as an imprint of a 3D d-wave shape resonance. A scaling
relation for the position of the d-wave resonance is provided. By changing the
trap frequency, ultracold scattering can be continuously tuned from s-wave to
d-wave resonant behavior. The effect can be utilized for the realization of
ultracold atomic gases interacting via higher partial waves and opens a novel
possibility for studying strongly correlated atomic systems beyond s-wave
physics.",1102.5686v2
2011-04-22,Semiclassical Szego limit of resonance clusters for the hydrogen atom Stark Hamiltonian,"We study the weighted averages of resonance clusters for the hydrogen atom
with a Stark electric field in the weak field limit. We prove a semiclassical
Szego-type theorem for resonance clusters showing that the limiting
distribution of the resonance shifts concentrates on the classical energy
surface corresponding to a rescaled eigenvalue of the hydrogen atom
Hamiltonian. This result extends Szego-type results on eigenvalue clusters to
resonance clusters. There are two new features in this work: first, the study
of resonance clusters requires the use of non self-adjoint operators, and
second, the Stark perturbation is unbounded so control of the perturbation is
achieved using localization properties of coherent states corresponding to
hydrogen atom eigenvalues.",1104.4466v1
2011-05-12,Ab initio theory of Fano resonances in plasmonic nanostructures and metamaterials,"An ab initio theory for Fano resonances in plasmonic nanostructures and
metamaterials is developed using Feshbach formalism. It reveals the role played
by the electromagnetic modes and material losses in the system, and enables the
engineering of Fano resonances in arbitrary geometries. A general formula for
the asymmetric resonance in a non-conservative system is derived. The influence
of the electromagnetic interactions on the resonance line shape is discussed
and it is shown that intrinsic losses drive the resonance contrast, while its
width is mostly determined by the coupling strength between the non-radiative
mode and the continuum. The analytical model is in perfect agreement with
numerical simulations.",1105.2503v1
2011-05-30,Analytic description of atomic interaction at ultracold temperatures II: Scattering around a magnetic Feshbach resonance,"Starting from a multichannel quantum-defect theory, we derive analytic
descriptions of a magnetic Feshbach resonance in an arbitrary partial wave $l$,
and the atomic interactions around it. An analytic formula, applicable to both
broad and narrow resonances of arbitrary $l$, is presented for ultracold atomic
scattering around a Feshbach resonance. Other related issues addressed include
(a) the parametrization of a magnetic Feshbach resonance of arbitrary $l$, (b)
rigorous definitions of ""broad"" and ""narrow"" resonances of arbitrary $l$ and
their different scattering characteristics, and (c) the tuning of the effective
range and the generalized effective range by a magnetic field.",1105.5846v1
2011-07-01,Quasi-particle continuum and resonances in the Hartree-Fock-Bogoliubov theory,"The quasi-particle energy spectrum of the Hartree-Fock-Bogoliubov (HFB)
equations contains discrete bound states, resonances, and non-resonant
continuum states. We study the structure of the unbound quasi-particle spectrum
of weakly bound nuclei within several methods that do not rely on imposing
scattering or outgoing boundary conditions. Various approximations are examined
to estimate resonance widths. It is shown that the stabilization method works
well for all HFB resonances except for very narrow ones.
  The Thomas-Fermi approximation to the non-resonant continuum has been shown
to be very effective, especially for coordinate-space HFB calculations in large
boxes that involve huge amounts of discretized quasi-particle continuum states.",1107.0274v1
2011-09-01,Effects of mutual coupling in dual-resonance metamaterials,"This Letter presents an investigation on the effects of mutual coupling in a
metamaterial comprising two sets of electric-LC (ELC) resonators with different
resonance frequencies. Through simulation and experiment, it is found that the
two resonances experience significant shifting and weakening as they become
spectrally close. An equivalent circuit model suggests that inductive coupling
among the two resonator sets is a primary cause of the change in the resonance
properties. This study is fundamental to designing metamaterials with an
extended bandwidth or spatially variable response.",1109.0055v1
2011-09-20,Optically-gated resonant emission in single quantum dots,"We report on the resonant emission in coherently-driven single semiconductor
quantum dots. We demonstrate that an ultra-weak non-resonant laser acts as an
optical gate for the quantum dot resonant response. We show that the gate laser
suppresses Coulomb blockade at the origin of a resonant emission quenching, and
that the optically-gated quantum dots systematically behave as ideal two-level
systems in both regimes of coherent and incoherent resonant emission.",1109.4304v1
2012-09-12,Simulating many-body lattice systems on a single nano-mechanical resonator,"We show that lattice systems, such as the Bose-Hubbard model, can be
simulated on a single nano- or micro-mechanical resonator, by exploiting its
many modes. The on-site Hamiltonians are engineered by coupling the mechanical
modes to the modes of a pair of optical or stripline resonators, and the
connections between the lattice sites are engineered in a similar way. The
lattice network structure is encoded in the frequency components of the fields
driving the resonators. This three-resonator configuration also allows
universal quantum computing on the nano-resonator.",1209.2499v1
2012-09-25,Analysis of light scattering off photonic crystal slabs in terms of Feshbach resonances,"Techniques to deal with Feshbach resonances are applied to describe resonant
light scattering off one dimensional photonic crystal slabs. Accurate
expressions for scattering amplitudes, free of any fitting parameter, are
obtained for isolated as well as overlapping resonances. They relate the
resonance properties to the properties of the optical structure and of the
incident light. For the most common case of a piecewise constant dielectric
function, the calculations can be carried out essentially analytically. After
establishing the accuracy of this approach we demonstrate its potential in the
analysis of the reflection coefficients for the diverse shapes of overlapping,
interacting resonances.",1209.5648v1
2013-01-27,"Cavity piezooptomechanics: piezoelectrically excited, optically transduced optomechanical resonators","We present a monolithic integrated aluminum nitride (AlN) optomechanical
resonator in which the mechanical motion is actuated by piezoelectric force and
the displacement is transduced by a high-Q optical cavity. The AlN
optomechanical resonator is excited from a radio-frequency electrode via a
small air gap to eliminate resonator-to-electrode loss. We observe the
electrically excited mechanical motion at 47.3 MHz, 1.04 GHz, and 3.12 GHz,
corresponding to the 1st, 2nd, and 4th radial-contour mode of the wheel
resonator respectively. An equivalent circuit model is developed to describe
the observed Fano-like resonance spectrum.",1301.6333v1
2013-03-26,Resonance asymptotics for Schrodinger operators on hyperbolic space,"We study the asymptotic distribution of resonances for scattering by
compactly supported potentials in hyperbolic space. We first establish an upper
bound for the resonance counting function that depends only on the dimension
and the support of the potential. We then establish the sharpness of this
estimate by proving the a Weyl law for the resonance counting function holds in
the case of radial potentials vanishing to some finite order at the edge of the
support. As an application of the existence of potentials that saturate the
upper bound, we derive additional resonance asymptotics that hold in a suitable
generic sense. These generic results include asymptotics for the resonance
count in sectors.",1303.6660v1
2013-07-29,Counter operation in nonlinear micro-electro-mechanical resonators,"This paper discusses a logical operation of multi-memories that consist of
coupled nonlinear micro-electro-mechanical systems (MEMS) resonators. A MEMS
resonator shows two coexisting stable states when nonlinear responses appear.
Previous studies addressed that a micro- or nano-electrical-mechanical
resonator can be utilized as a mechanical 1-bit memory or mechanical logic
gates. The next phase is the development of logic system with coupled
multi-resonators. From the viewpoint of application of nonlinear dynamics in
coupled MEMS resonators, we show the first experimental success of the
controlling nonlinear behavior as a 2-bit binary counter.",1307.7575v1
2013-12-14,Plasmon resonance and heat generation model in nanostructures,"In this paper, we investigate the photothermal effects of the plasmon
resonance. Metal nanoparticles efficiently generate heat in the presence of
electromagnetic radiation. The process is strongly enhanced when a fixed
frequency of the incident wave illuminate on nanoprticles such that plasmon
resonance happen. We shall introduce the electromagnetic radiation model and
show exactly how and when the plasmon resonance happen. We then construct the
heat generation and transfer model and derive the heat effect induced by
plasmon resonance. Finally, we consider the heat generation under plasmon
resonance in a concentric nanoshell structure.",1312.3994v1
2014-04-02,Crystalline Whispering Gallery Mode Resonators: In Search of The Optimal Material,"Different applications of crystalline whispering gallery mode resonators call
for different properties of the resonator host material. We report on our
recent study of resonators made out of sapphire, diamond, and quartz crystals
and discuss possible applications of these resonators. In particular, we
demonstrate Kerr frequency comb generation in sapphire microresonators.",1404.0426v1
2015-03-28,Hyperbolic Resonances of Metasurface Cavities,"We propose a new class of optical resonator structures featuring one or two
metasurface reflectors or metacavities and predict that such resonators support
novel hyperbolic resonances. As an example of such resonances we introduce
hyperbolic Tamm plasmons (HTPs) and hyperbolic Fabry-Perot resonances (HFPs).
The hyperbolic optical modes feature low-loss incident power re-distribution
over TM and TE polarization output channels, clover-leaf anisotropic
dispersion, and other unique properties which are tunable and are useful for
multiple applications.",1503.08260v1
2015-04-27,Overcoming limitations of nanomechanical resonators with simultaneous resonances,"Dynamic stabilization by simultaneous primary and superharmonic resonances
for high order nonlinearity cancellation is demonstrated with an
electrostatically-actuated, piezoresistively-transduced nanomechanical
resonator. We prove experimentally how the combination of both the third-order
nonlinearity cancellation and simultaneous resonances can be used to linearly
drive a nanocantilever up to very large amplitudes compared to fundamental
limits like pull-in occurrence, opening the way towards resonators with high
frequency stability for high-performance sensing or time reference.",1504.07533v1
2015-05-18,Improving LHC searches for strong EW symmetry breaking resonances,"Composite Higgs models generically predict the existence of heavy spin-1
resonances with the same quantum numbers as electroweak gauge bosons. The
effective lagrangian description of these resonances is presented, pointing out
the origin of their interactions with SM matter fields and the resulting LHC
phenomenology. Search strategies for spin-1 resonances are discussed,
mentioning possible advantages offered by boosted decay products. The impact of
interactions between spin-1 resonances and fermion resonances, crucial for the
proper interpretation of LHC searches, is pointed out.",1505.04645v2
2015-07-03,Symmetric and Standard Matter-Neutrino Resonances Above Merging Compact Objects,"Matter-neutrino resonances (MNR) can occur in environments where the flux of
electron antineutrinos is greater than the flux of electron neutrinos. These
resonances may result in dramatic neutrino flavor transformation. Compact
object merger disks are an example of an environment where electron
antineutrinos outnumber neutrinos. We study MNR resonances in several such disk
configurations and find two qualitatively different types of matter-neutrino
resonances: a standard MNR and a symmetric MNR. We examine the transformation
that occurs in each type of resonance and explore the consequences for
nucleosynthesis.",1507.00946v1
2015-07-14,Graphene fish-scale array as controllable reflecting photonic structure,"We report resonant features of novel controllable reflectarray which consists
of meander-like graphene strips placed on a metal-backed dielectric substrate.
The structure manifests two kinds of resonances appeared as sharp deeps of
reflectivity. The first one exists because the strips of periodic cells of the
structure have resonant sizes for induced surface plasmon-polaritons. The
second kind of resonances is defined by excitation of TM eigenwaves of the
whole structure as a plane photonic crystal. The latter resonances do not
depend on whether the strips of the unit cells have resonant sizes or not.",1507.03950v1
2015-11-02,Engineering Photonic Floquet Hamiltonians through Fabry Pérot Resonators,"In this letter we analyze an optical Fabry-P\'erot resonator as a
time-periodic driving of the (2D) optical field repeatedly traversing the
resonator, uncovering that resonator twist produces a synthetic magnetic field
applied to the light within the resonator, while mirror aberrations produce
relativistic dynamics, anharmonic trapping, and spacetime curvature. We develop
a Floquet formalism to compute the effective Hamiltonian for the 2D field,
generalizing the idea that the intra-cavity optical field corresponds to an
ensemble of non-interacting, massive, harmonically trapped particles. This work
illuminates the extraordinary potential of optical resonators for exploring the
physics of quantum fluids in gauge fields and exotic space-times.",1511.00595v1
2015-11-11,Can we trust the relationship between resonance poles and lifetimes?,"We show that the shape resonances induced by a one dimensional well of delta
functions disappear as soon as a small constant electric field is applied. In
particular, in any compact subset below the positive real axis there are no
resonances if the non-zero field is small enough. In contrast to the lack of
convergence of the lifetimes computed from the widths of the resonances we show
that the ""experimental lifetimes"" are continuous at zero field. The shape
resonances are replaced by an infinite set of other resonances whose location
and number we analyze.",1511.03724v1
2016-01-25,Cryogenic resonator design for trapped ion experiments in Paul traps,"Trapping ions in Paul traps requires high radio-frequency voltages, which are
generated using resonators. When operating traps in a cryogenic environment, an
in-vacuum resonator showing low loss is crucial to limit the thermal load to
the cryostat. In this study, we present a guide for the design and production
of compact, shielded cryogenic resonators. We produced and characterized three
different types of resonators and furthermore demonstrate efficient impedance
matching of these resonators at cryogenic temperatures.",1601.06699v1
2016-07-08,Resonant electron-phonon-electron interaction,"The effect of the resonance of electron scattering energy difference and
phonon energy on the electron-phonon-electron interaction (EPEI) is studied.
Results show that the resonance of electron transition energy and phonon energy
can enhance EPEI by a magnitude of 1 to 2. Moreover, the anisotropic S-wave
electron or dx2-y2 electron can enhance resonance EPEI, and the self-energy
correction of the electron will weaken resonance EPEI. Particularly, the
asymmetrical spin-flip scattering process in k space can reduce the effect of
electronic self-energy to enhance resonance EPEI",1607.02338v1
2016-09-19,Linear spreading speeds from nonlinear resonant interaction,"We identify a new mechanism for propagation into unstable states in spatially
extended systems, that is based on resonant interaction in the leading edge of
invasion fronts. Such resonant invasion speeds can be determined solely based
on the complex linear dispersion relation at the unstable equilibrium, but rely
on the presence of a nonlinear term that facilitates the resonant coupling. We
prove that these resonant speeds give the correct invasion speed in a simple
example, we show that fronts with speeds slower than the resonant speed are
unstable, and corroborate our speed criterion numerically in a variety of model
equations, including a nonlocal scalar neural field model.",1609.05757v1
2017-02-02,Physical properties of resonances as the building blocks of multichannel scattering amplitudes,"We propose a simple formula for multichannel resonant scattering with
parameters related to physical resonant properties. It can be used to predict
residue phase from other resonant parameters and describe the shape of
scattering amplitudes close to the resonance without any background
contributions or fitting. It works well even for overlapping resonances.
Imposing unitarity to the proposed formula enabled us to explain some puzzling
features of much more advanced models.",1702.00659v1
2018-02-02,Nonlinear resonances in the $ABC$-flow,"In this paper we study resonances of the $ABC$-flow in the near integrable
case ($C\ll 1$). This is an interesting example of a Hamiltonian system with
3/2 degrees of freedom in which simultaneous existence of two resonances of the
same order is possible. Analytical conditions of the resonance existence are
received. It is shown numerically that the largest $n:1$ ($n=1,2,3$) resonances
exist, and their energies are equal to theoretical energies in the near
integrable case. We provide analytical and numerical evidences for existence of
two branches of the two largest $n:1$ ($n=1,2$) resonances in the region of
finite motion.",1802.00557v1
2017-04-03,Resonances for Euler-Bernoulli operator on the half-line,"We consider resonances for fourth order differential operators on the
half-line with compactly supported coefficients. We determine asymptotics of a
counting function of resonances in complex discs at large radius, describe the
forbidden domain for resonances and obtain trace formulas in terms of
resonances. We apply these results to the Euler-Bernoulli operator on the
half-line. The coefficients of this operator are positive and constants outside
a finite interval. We show that this operator does not have any eigenvalues and
resonances iff its coefficients are constants on the whole half-line.",1704.00499v1
2017-10-02,Qubit-assisted transduction for a detection of surface acoustic waves near the quantum limit,"We demonstrate ultra-sensitive measurement of fluctuations in a
surface-acoustic-wave~(SAW) resonator using a hybrid quantum system consisting
of the SAW resonator, a microwave (MW) resonator and a superconducting qubit.
The nonlinearity of the driven qubit induces parametric coupling, which
up-converts the excitation in the SAW resonator to that in the MW resonator.
Thermal fluctuations of the SAW resonator near the quantum limit are observed
in the noise spectroscopy in the MW domain.",1710.00467v1
2019-09-11,Precise Feshbach resonance spectroscopy using tight anharmonic traps,"Feshbach resonances are among the essential control tools used in ultracold
atom experiments. However, for complex atomic species the theoretical
characterization of resonances becomes challenging. For closely spaced
resonances, the measurement of three-body losses does not provide sufficient
resolution to discriminate them. For this reason, resonance spectroscopy of
trapped isolated atoms is becoming the state of the art. Here we show that
trapping the atoms in a double well potential such as an optical lattice or a
pair of optical tweezers enables precise characterization of not only the
resonance position and width, but also its pole strength, giving valuable
information about the atomic structure relevant for subsequent many-body
studies.",1909.04932v1
2021-01-27,Detection of electron spin resonance down to 10 K using localized spoof surface plasmon,"In this study, novel use of the electromagnetic field profile of a localized
spoof surface plasmonic mode to detect electron spin resonance is being
reported. The mode is supported on a resonator with a complementary metallic
spiral structure, etched on the ground plane of a microstrip line having a
characteristic impedance of 50 $\Omega$. The change in characteristics of the
mode of interest with lowering of temperature has been observed and analyzed.
Electron spin resonance spectra of a standard paramagnetic sample,
2,2-diphenyl-1-picrylhydrazyl, are recorded using this resonator down to 10 K.
Potential application of the mode in the detection of microwave Rashba
field-driven electron spin resonance has been discussed.",2101.11528v1
2018-03-18,High frequency limits for invariant Ruelle densities,"We establish an equidistribution result for Ruelle resonant states on compact
locally symmetric spaces of rank one. More precisely, we prove that among the
first band Ruelle resonances there is a density one subsequence such that the
respective products of resonant and co-resonant states converge weakly to the
Liouville measure. We prove this result by establishing an explicit
quantum-classical correspondence between eigenspaces of the scalar Laplacian
and the resonant states of the first band of Ruelle resonances which also leads
to a new description of Patterson-Sullivan distributions.",1803.06717v2
2018-03-20,A fast method to identify mean motion resonances,"The identification of mean motion resonances in exoplanetary systems or in
the Solar System might be cumbersome when several planets and large number of
smaller bodies are to be considered. Based on the geometrical meaning of the
resonance variable, an efficient method is introduced and described here, by
which mean motion resonances can be easily find without any a priori knowledge
on them. The efficiency of this method is clearly demonstrated by using known
exoplanets engaged in mean motion resonances, and also some members of
different families of asteroids and Kuiper-belt objects being in mean motion
resonances with Jupiter and Neptune respectively.",1803.07458v1
2018-03-30,Resonance in the $Y_{c}N$ potential model,"We calculate two-body $J^{\pi}=0^{+}, 1^{+}$, and $J^{\pi}=2^{+}$ resonance
states of $Y_{c}$ ($= \Lambda_{c}$, $\Sigma_{c}$, or $\Sigma_{c}^{*}$) and $N$
using the complex scaling method. We employ the $Y_{c}N$-CTNN potentials, which
were proposed in our previous study, and obtain four resonances near
$\Sigma_{c}N$ and $\Sigma_{c}^{*}N$ thresholds. From the analysis by the
binding energies of partial channel systems, we conclude that these resonance
states are Feshbach resonances. We compare the results with the $Y_{c}N$
resonance states in the heavy quark limit, where the $\Sigma_{c}N$ and
$\Sigma_{c}^{*}N$ thresholds are degenerate, and find that they form two pairs
of the heavy-quark doublets in agreement with the heavy quark spin symmetry.",1803.11349v1
2019-01-24,Semiclassical study of shape resonances in the Stark effect,"Semiclassical behavior of Stark resonances is studied. The complex distortion
outside a cone is introduced to study resonances in any energy region for the
Stark Hamiltonians with non-globally analytic potentials. The non-trapping
resolvent estimate is proved by the escape function method. The Weyl law and
the resonance expansion of the propagator are proved in the shape resonance
model. To prove the resonance expansion theorem, the functional
pseudodifferential calculus in the Stark effect is established, which is also
useful in the study of the spectral shift function.",1901.08315v2
2019-04-25,Double Quantum Dot scenario for spin resonance in current noise,"We show that interference between parallel currents through two quantum dots,
in presence of spin orbit interactions and strong on-site Coulomb repulsion,
leads to resonances in current noise at the corresponding Larmor frequencies.
An additional resonance at the difference of Larmor frequencies is present even
without spin-orbit interaction. The resonance lines have strength comparable to
the background shot noise and therefore can account for the numerous
observations of spin resonance in STM noise with non-polarized leads. We solve
also several other models that show similar resonances.",1904.11221v2
2021-03-30,Ultrahigh Q SOI Ring Resonator With Strip Waveguide,"The design and experimental demonstration of a large-area,
ultra-high-Q-factor and single-mode operation silicon ring resonator based on a
strip silicon photonic waveguide are presented, which is suitable for photon
gyroscopic application. Based on these designs, simulation results show that
the resonance depth is 0.9979 while the resonator is in an undercoupled state
with the coupling length L=2um and coupling gap d=0.2um. For the fabricated
resonator, the ultrahigh Q factor of 1.54*106 is experimentally demonstrated,
with the free spectrum range (FSR) of 0.036nm and the resonance depth is
0.9810.",2103.16016v1
2021-04-06,Bound States in the Continuum in Compact Acoustic Resonators,"We reveal that finite-size solid acoustic resonators can support genuine
bound states in the continuum (BICs) completely localized inside the resonator.
The developed theory provides the multipole classification of such BICs in the
resonators of various shapes. It is shown how breaking of the resonator's
symmetry turns BICs into quasi-BICs manifesting themselves in the scattering
spectra as high-Q Fano resonances. We believe that the revealed novel states
will push the performance limits of acoustic devices and will serve as high-Q
building blocks for acoustic sensors, antennas, and topological acoustic
structures.",2104.05539v1
2021-05-08,Strain effects on optical properties of linearly polarized resonant modes in the presence of monolayer graphene,"Recently, huge attention has been drawn to improve optical sensing devices
based on photonic resonators in the presence of graphene. In this paper, based
on the transfer matrix approach and TE polarization for the incident
electromagnetic waves, we numerically evaluate the transmission and reflection
spectra for one-dimensional photonic resonators and surface plasmon resonances
with strained graphene, respectively. We proved that a relatively small strain
field in graphene can modulate linearly polarized resonant modes within the
photonic bandgap of the defective crystal. Moreover, we study the strain
effects on the surface plasmon resonances created by the evanescent wave
technique at the interference between a monolayer graphene and prism.",2105.03633v1
2021-11-05,Enhanced Purcell factor for nanoantennas supporting interfering resonances,"We study the effect of coupled resonances and quasi-bound states in the
continuum (quasi-BICs) on the Purcell factor in dielectric resonant
nanoantennas. We analyze numerically interfering resonances in a nanodisk with
and without a substrate when the modes are coupled to an emitter localized
inside the nanodisk, and we quantify the modal contributions to the Purcell
factor also reconstructing the radiation patterns of the resonant system. It is
revealed that the Purcell effect can be boosted substantially for a strong
coupling of resonances in the quasi-BIC regime.",2111.03339v3
2022-05-06,Resonance nucleon scattering amplitude in the photonuclear reaction,"The cross section of the photonuclear reaction in the nucleon-resonance
region is calculated to search the resonance-nucleon scattering amplitude in
the nucleus. It is assumed that the resonance $R$ is produced and decayed in
the elementary photon-nucleon $(\gamma N)$ reaction in the nucleus as $\gamma N
\to R \to \gamma N$. The resonance interacts with the nucleons while
propagating through the nucleus. Therefore, the calculated photonuclear
reaction cross section is compared with the data to extract the
resonance-nucleon scattering parameters in the nucleus.",2205.03025v3
2022-07-27,Degenerate bound states in the continuum in square and triangular open acoustic resonators,"We consider square and equilateral triangular open acoustic resonators with
the $C_{4v}$ and $C_{3v}$ symmetries, respectively. There is an unique property
of square and triangular resonators of accidental number four-fold degeneracy
of eigenstates that gives rise to two-fold degenerate Friedrich-Wintgen (FW)
BICs. Compared to usual FW BICs the degenerate FW BICs maintain high $Q$-factor
in wide range of the size of resonators. That removes the fabrication
difficulties of proper choice of resonator. The presence of degenerate BICs in
triangular resonators is extremely sensitive to switch output flows by small
perturbations with $100\%$ efficiency.",2207.14162v1
2022-11-10,Resonances for rational Anosov maps on the torus,"A complete description of resonances for rational toral Anosov
diffeomorphisms preserving certain Reinhardt domains is presented. As a
consequence it is shown that every homotopy class of two-dimensional Anosov
diffeomorphisms contains maps with the sequence of resonances decaying
stretched-exponentially. This is achieved by introducing a certain group of
rational toral diffeomorphisms and computing the resonances of the respective
composition operator considered on suitable anisotropic spaces of
hyperfunctions. The class of examples is sufficiently rich to also include
non-linear Anosov maps with trivial resonances, or resonances decaying
exponentially, as well as with or without area-preservation or reversing
symmetries.",2211.05925v1
2023-05-30,Photonic Flatband Resonances in Multiple Light Scattering,"We introduce the concept of photonic flatband resonances for the example of
an array of high index dielectric particles. We employ the multiple Mie
scattering theory and reveal that both short range and long range interactions
between the resonators are crucial for the emerging collective resonances and
their associated photonic flatbands. By examining both nearfield and far field
characteristics, we uncover how the flatbands emerge due to fine tuning of
resonators radiation fields, and predict that hybridization of a flatband
resonance with an electric hotspot can lead to giant values of the Purcell
factor for the electric dipolar emitters.",2305.19456v1
2023-07-03,Generation of narrow beams of ultrarelativistic positrons (electrons) in the resonant strong electromagnetic field-assisted Breit-Wheeler process,"The resonant external field-assisted Breit-Wheeler process (Oleinik
resonances) for strong electromagnetic fields with intensities less than the
critical Schwinger field has been theoretically studied. The resonant
kinematics has been studied in detail. The case of high-energy initial gamma
quanta and emerging ultrarelativistic electron-positron pairs is studied. The
resonant differential cross section is obtained. The generation of narrow beams
of ultrarelativistic positrons (for Channel A) and electrons (for Channel B) is
predicted with a probability significantly exceeding corresponding to the
non-resonant process.",2307.00913v1
2023-09-01,Optical LC-like resonances in high-index particles,"Electric LC resonances, occurring in metallic circuits, govern the motion of
free electrons or electric signals. In this paper, optical LC-like resonances
in high-index particles (HIPs) or dielectric LC resonances have been studied,
which involve bounded electrons and optical fields instead. The resonance
effect is dominated by optical analogues of inductance and capacitance, which
can be determined according to the electromagnetic energy bounded near the
particle. The viewpoint of dielectric optical circuit with equivalent
parameters facilitates the understanding of dielectric resonance effect. The
result also provides a method for studying the optical properties of the HIPs.",2309.00179v2
2023-11-01,Singularities and asymptotic distribution of resonances for Schrödinger operators in one dimension,"We obtain new results about the high-energy distribution of resonances for
the one-dimensional Schr\""odinger operator. Our primary result is an upper
bound on the density of resonances above any logarithmic curve in terms of the
singular support of the potential. We also prove results about the distribution
of resonances in sectors away from the real axis, and construct a class of
potentials producing multiple sequences of resonances along distinct
logarithmic curves, explicitly calculating the asymptotic location of these
resonances. The results are unified by the use of an integral representation of
the reflection coefficients.",2311.00804v1
2023-11-22,The Potsdam astroComb (POCO) Part I: Mode crossing effect in feedback resonators,"We investigate theoretically and experimentally the mode interaction in an
integrated Silicon Nitride (Si3N4) microring resonator with interferometric
coupling realized by a feedback loop as an adjustable optical path path length
connecting the ring to the bus waveguide at two coupling sections. From the
transmission spectra recorded at different optical path lengths, two
resonances, 1596.5~nm and 1570.5~nm, were selected for detailed investigation.
Both resonances show the possibility of adjusting the resonance width and
depth. However, the transmission spectra around the first resonance also show
the effect of mode interaction. This is also well captured in the theoretical
model, from which we can derive a coupling rate for the mode interaction of
$3.4~\textrm{rad}~\textrm{ns}^{-1}$.",2311.13505v1
2024-03-19,Compositeness of near-threshold $s$-wave resonances,"The near-threshold clustering phenomenon is well understood by the low-energy
universality, for shallow bound states below the threshold. Nevertheless, the
characteristics of resonances slightly above the threshold still lack thorough
elucidation. We introduce a novel probabilistic interpretation scheme for
complex compositeness of resonances, in which the resonances with unphysically
large decay widths are inherently excluded. Employing this scheme to analyze
resonances via the effective range expansion, we demonstrate that
near-threshold resonances have small composite fraction, in sharp contrast to
shallow bound states below the threshold.",2403.12635v1
1999-02-03,Partial Averaging Near a Resonance in Planetary Dynamics,"Following the general numerical analysis of Melita and Woolfson (1996), I
showed in a recent paper that a restricted, planar, circular planetary system
consisting of Sun, Jupiter and Saturn would be captured in a near (2:1)
resonance when one would allow for frictional dissipation due to interplanetary
medium (Haghighipour, 1998). In order to analytically explain this resonance
phenomenon, the method of partial averaging near a resonance was utilized and
the dynamics of the first-order partially averaged system at resonance was
studied. Although in this manner, the finding that resonance lock occurs for
all initial relative positions of Jupiter and Saturn was confirmed, the
first-order partially averaged system at resonance did not provide a complete
picture of the evolutionary dynamics of the system and the similarity between
the dynamical behavior of the averaged system and the main planetary system
held only for short time intervals. To overcome these limitations, the method
of partial averaging near a resonance is extended to the second order of
perturbation in this paper and a complete picture of dynamical behavior of the
system at resonance is presented. I show in this study that the dynamics of the
second-order partially averaged system at resonance resembles the dynamical
evolution of the main system during the resonance lock in general, and I
present analytical explanations for the evolution of the orbital elements of
the main system while captured in resonance.",9902049v1
1999-04-02,Geometric Solutions for the Neutrino Oscillation Length Resonance,"We give a geometric interpretation of the neutrino 'oscillation length
resonance' recently discovered by Petcov. We use this picture to identify two
new solutions for oscillation length resonances in a 3-layer earth model.",9904023v1
2000-01-21,Q-Factor Measurement of Nonlinear Superconducting Resonators,"A novel method, which combined a multi-bandwidth measurement and an
extrapolation procedure, is proposed for extracting the loaded Q-factor (Q_{L})
with improved accuracy from non-Lorentzian resonances of nonlinear
superconducting resonators.",0001310v1
2004-02-10,Feshbach resonances with large background scattering length: interplay with open-channel resonances,"Feshbach resonances are commonly described by a single-resonance Feshbach
model, and open-channel resonances are not taken into account explicitly.
However, an open-channel resonance near threshold limits the range of validity
of this model. Such a situation exists when the background scattering length is
much larger than the range of the interatomic potential. The open-channel
resonance introduces strong threshold effects not included in the
single-resonance description. We derive an easy-to-use analytical model that
takes into account both the Feshbach resonance and the open-channel resonance.
We apply our model to $^{85}$Rb, which has a large background scattering
length, and show that the agreement with coupled-channels calculations is
excellent. The model can be readily applied to other atomic systems with a
large background scattering length, such as $^6$Li and $^{133}$Cs. Our approach
provides full insight into the underlying physics of the interplay between
open-channel (or potential) resonances and Feshbach resonances.",0402278v2
2004-11-12,Resonance spin filter,"A design of the resonance spin finter is suggested in form of a quantum well
with three quantum wires attached. Explicit formula is suggested for
transmission coefficients accross the well in terms of the resonance
eigenfunction of the Schredinger operator on the well with Rashba spin-orbital
interaction.",0411354v1
2003-09-11,BABAR Resonance and Four-quark Mesons,"The new narrow resonance which has been observed at the B factories is
assigned to the I_z=0 component of iso-triplet charmed four-quark mesons, and
as its consequence, existence of additional narrow resonances in different
channels is predicted.",0309119v1
2003-11-06,On the charmed scalar resonances,"It is discussed that a newly observed broad bump around 2.3 GeV in the D\pi
mass distribution can include two scalar resonances, and is predicted that a
broad scalar resonance can be observed around 2.45 GeV in the DK channels.",0311069v1
2005-11-09,Enhancing switching in bistable nanomechanical oscillators by geometrical resonance,"It is shown how the cooperative effect of the geometrical resonance and
stochastic resonance mechanisms explains recent results on bistable
nanomechanical silicon oscillators (R. L. Badzey and P. Mohanty, Nature, vol.
437, 995-998 (2005)).",0511077v1
2001-03-27,Resonance absolute quantum reflection at selected energies,"The possibility of the resonance reflection (100 % at maximum) is revealed.
The corresponding exactly solvable models with the controllable numbers of
resonances, their positions and widths are presented.",0103148v1
2007-03-01,Entangling a nanomechanical resonator with a microwave field,"We show how the coherent oscillations of a nanomechanical resonator can be
entangled with a microwave cavity in the form of a superconducting coplanar
resonator. Dissipation is included and realistic values for experimental
parameters are estimated.",0703003v1
2012-11-04,Global estimates of resonances for 1D Dirac operators,"We discuss resonances for 1D massless Dirac operators with compactly
supported potentials on the line. We estimate the sum of the negative power of
all resonances in terms of the norm of the potential and the diameter of its
support.",1211.0714v1
2013-07-30,Electrodynamics of a ring-shaped spiral resonator,"We present analytical, numerical and experimental investigations of
electromagnetic resonant modes of a compact monofilar Archimedean spiral
resonator shaped in a ring, with no central part. Planar spiral resonators are
interesting as components of metamaterials for their compact deep-subwavelength
size. Such resonators couple primarily to the magnetic field component of the
incident electromagnetic wave, offering properties suitable for magnetic
meta-atoms. Surprisingly, the relative frequencies of the resonant modes follow
the sequence of the odd numbers, despite the nearly identical boundary
conditions for electromagnetic fields at the extremities of the resonator. In
order to explain the observed spectrum of resonant modes, we show that the
current distribution inside the spiral satisfies a particular Carleman type
singular integral equation. By solving this equation, we obtain a set of
resonant frequencies. The analytically calculated resonance frequencies and the
current distributions are in good agreement with experimental data and the
results of numerical simulations. By using low-temperature laser scanning
microscopy of a superconducting spiral resonator, we compare the experimentally
visualized ac current distributions over the spiral with the calculated ones.
Theory and experiment agree well with each other. Our analytical model allows
for calculation of a detailed three-dimensional magnetic field structure of the
resonators.",1307.7959v1
2014-10-08,Tailoring dielectric resonator geometries for directional scattering and Huygens' metasurfaces,"In this paper we describe a methodology for tailoring the design of
metamaterial dielectric resonators, which represent a promising path toward
low-loss metamaterials at optical frequencies. We first describe a procedure to
decompose the far field scattered by subwavelength resonators in terms of
multipolar field components, providing explicit expressions for the multipolar
far fields. We apply this formulation to confirm that an isolated
high-permittivity cube resonator possesses frequency separated electric and
magnetic dipole resonances, as well as a magnetic quadrupole resonance in close
proximity to the electric dipole resonance. We then introduce multiple
dielectric gaps to the resonator geometry in a manner suggested by perturbation
theory, and demonstrate the ability to overlap the electric and magnetic dipole
resonances, thereby enabling directional scattering by satisfying the first
Kerker condition. We further demonstrate the ability to push the quadrupole
resonance away from the degenerate dipole resonances to achieve local behavior.
These properties are confirmed through the multipolar expansion and show that
the use of geometries suggested by perturbation theory is a viable route to
achieve purely dipole resonances for metamaterial applications such as
wave-front manipulation with Huygens' metasurfaces. Our results are fully
scalable across any frequency bands where high-permittivity dielectric
materials are available, including microwave, THz, and infrared frequencies.",1410.2315v2
2015-01-28,Resonant normal form and asymptotic normal form behavior in magnetic bottle Hamiltonians,"We consider normal forms in `magnetic bottle' type Hamiltonians of the form
$H=\frac{1}{2}(\rho^2_\rho+\omega^2_1\rho^2) +\frac{1}{2}p^2_z+hot$ (second
frequency $\omega_2$ equal to zero in the lowest order). Our main results are:
i) a novel method to construct the normal form in cases of resonance, and ii) a
study of the asymptotic behavior of both the non-resonant and the resonant
series. We find that, if we truncate the normal form series at order $r$, the
series remainder in both constructions decreases with increasing $r$ down to a
minimum, and then it increases with $r$. The computed minimum remainder turns
to be exponentially small in $\frac{1}{\Delta E}$, where $\Delta E$ is the
mirror oscillation energy, while the optimal order scales as an inverse power
of $\Delta E$. We estimate numerically the exponents associated with the
optimal order and the remainder's exponential asymptotic behavior. In the
resonant case, our novel method allows to compute a `quasi-integral' (i.e.
truncated formal integral) valid both for each particular resonance as well as
away from all resonances. We applied these results to a specific magnetic
bottle Hamiltonian. The non resonant normal form yields theorerical invariant
curves on a surface of section which fit well the empirical curves away from
resonances. On the other hand the resonant normal form fits very well both the
invariant curves inside the islands of a particular resonance as well as the
non-resonant invariant curves. Finally, we discuss how normal forms allow to
compute a critical threshold for the onset of global chaos in the magnetic
bottle.",1501.07018v1
2016-03-19,Crosstalk-insensitive method for simultaneously coupling multiple pairs of resonators,"In a circuit consisting of two or more resonators, the inter-cavity crosstalk
is inevitable, which could create some problems, such as degrading the
performance of quantum operations and the fidelity of various quantum states.
The focus of this work is to propose a crosstalk-insensitive method for
simultaneously coupling multiple pairs of resonators, which is important in
large-scale quantum information processing and communication in a network
consisting of resonators or cavities. In this work, we consider 2N resonators
of different frequencies, which are coupled to a three-level quantum system
(qutrit). By applying a strong pulse to the coupler qutrit, we show that an
effective Hamiltonian can be constructed for simultaneously coupling multiple
pairs of resonators.~The main advantage of this proposal is that the effect of
inter-resonator crosstalks is greatly suppressed by using resonators of
different frequencies. In addition, by employing the qutrit-resonator
dispersive interaction, the intermediate higher-energy level of the qutrit is
virtually excited and thus decoherence from this level is suppressed. This
effective Hamiltonian can be applied to implement quantum operations with
photonic qubits distributed in different resonators. As one application of this
Hamiltonian, we show how to simultaneously generate multiple EPR pairs of
photonic qubits distributed in 2N resonators. Numerical simulations show that
it is feasible to prepare two high-fidelity EPR photonic pairs using a setup of
four one-dimensional transmission line resonators coupled to a superconducting
flux qutrit with current circuit QED technology.",1603.06108v1
2016-10-05,The arrow of time in open quantum systems and dynamical breaking of the resonance-antiresonance symmetry,"Open quantum systems are often represented by non-Hermitian effective
Hamiltonians that have complex eigenvalues associated with resonances. In
previous work we showed that the evolution of tight-binding open systems can be
represented by an explicitly time-reversal symmetric expansion involving all
the discrete eigenstates of the effective Hamiltonian. These eigenstates
include complex-conjugate pairs of resonant and anti-resonant states. An
initially time-reversal-symmetric state contains equal contributions from the
resonant and anti-resonant states. Here we show that as the state evolves in
time, the symmetry between the resonant and anti-resonant states is
automatically broken, with resonant states becoming dominant for $t>0$ and
anti-resonant states becoming dominant for $t<0$. Further, we show that there
is a time-scale for this symmetry-breaking, which we associate with the ""Zeno
time."" We also compare the time-reversal symmetric expansion with an asymmetric
expansion used previously by several researchers. We show how the present
time-reversal symmetric expansion bypasses the non-Hilbert nature of the
resonant and anti-resonant states, which previously introduced exponential
divergences into the asymmetric expansion.",1610.01548v3
2010-05-19,Evidence for the psi(5S) and psi(4D) c-cbar vector resonances,"We present evidence for the psi(5S) and psi(4D) c-cbar vector resonances in
experimental data published by the Belle and BaBar Collaborations. Central
masses and resonance widths are estimated.",1005.3490v1
2017-01-06,Frequency-Temperature sensitivity reduction with optimized microwave Bragg resonators,"Dielectric resonators are employed to build state-of-the-art low-noise and
high- stability oscillators operating at room and cryogenic temperatures. A
resonator temperature coefficient of frequency is one criterion of performance.
This paper reports on predictions and measurements of this temperature
coefficient of frequency for three types of cylindrically-symmetric Bragg
resonators operated at microwave frequencies. At room temperature, microwave
Bragg resonators have the best potential to reach extremely high Q-factors.
Research has been conducted over the last decade on modeling, optimizing and
realizing such high Q-factor devices for applications such as filtering,
sensing, and frequency metrology. We present an optimized design, which has a
temperature sensitivity 2 to 4 times less than current whispering gallery mode
resonators without using temperature compensating techniques and about 30% less
than other existing Bragg resonators. Also, the performance of a new generation
single-layered Bragg resonators, based on a hybrid-Bragg-mode, is reported with
a sensitivity of about -12ppm/K at 295K. For a single reflector resonator, it
achieves a similar level of performance as a double-Bragg-reflector resonator
but with a more compact structure and performs six times better than
whispering-gallery-mode resonators. The hybrid resonator promises to deliver a
new generation of high-sensitivity sensors and high-stability room-temperature
oscillators.",1701.01600v1
2018-05-29,A highly accurate measurement of resonator $Q$-factor and resonance frequency,"The microwave cavity perturbation method is often used to determine material
parameters (electric permittivity and magnetic permeability) at high
frequencies and it relies on measurement of the resonator parameters. We
present a method to determine the $Q$-factor and resonance frequency of
microwave resonators which is conceptually simple but provides a sensitivity
for these parameters which overcomes those of existing methods by an order of
magnitude. The microwave resonator is placed in a feedback resonator setup,
where the output of an amplifier is connected to its own input with the
resonator as a band pass filter. After reaching steady-state oscillation, the
feedback circuit is disrupted by a fast microwave switch and the transient
signal, which emanates from the resonator, is detected using down-conversion.
The Fourier transform of the resulting time-dependent signal yields directly
the resonance profile of the resonator. Albeit the method is highly accurate,
this comes with a conceptual simplicity, ease of implementation and lower
circuit cost. We compare existing methods for this type of measurement to
explain the sensitivity of the present technique and we also make a prediction
for the ultimate sensitivity for the resonator $Q$ and $f_0$ determination.",1805.11347v3
2017-12-11,Two-photon driven Kerr resonator for quantum annealing with three-dimensional circuit QED,"We propose a realizable circuit QED architecture for engineering states of a
superconducting resonator off-resonantly coupled to an ancillary
superconducting qubit. The qubit-resonator dispersive interaction together with
a microwave drive applied to the qubit gives rise to a Kerr resonator with
two-photon driving that enables us to efficiently engineer the quantum state of
the resonator such as generation of the Schrodinger cat states for
resonator-based universal quantum computation. Moreover, the presented
architecture is easily scalable for solving optimization problem mapped into
the Ising spin glass model, and thus served as a platform for quantum
annealing. Although various scalable architecture with superconducting qubits
have been proposed for realizing quantum annealer, the existing annealers are
currently limited to the coherent time of the qubits. Here, based on the
protocol for realizing two-photon driven Kerr resonator in three-dimensional
circuit QED (3D cQED), we propose a flexible and scalable hardware for
implementing quantum annealer that combines the advantage of the long coherence
times attainable in 3D cQED and the recently proposed resonator based
Lechner-Hauke-Zoller (LHZ) scheme. In the proposed resonator based LHZ
annealer, each spin is encoded in the subspace formed by two coherent state of
3D microwave superconducting resonator with opposite phase, and thus the
fully-connected Ising model is mapped onto the network of the resonator with
local tunable three-resonator interaction. This hardware architecture provides
a promising physical platform for realizing quantum annealer with improved
coherence.",1712.03613v2
2020-01-17,Resonances in non-axisymmetric gravitational potentials,"We study sectoral resonances of the form $j\kappa= m(n-\Omega)$ around a
non-axisymmetric body with spin rate $\Omega$, where $\kappa$ and $n$ are the
epicyclic frequency and mean motion of a particle, respectively, where $j>0$
and $m$ ($<0$ or $>0$) are integers, $j$ being the resonance order. This
describes $n/\Omega \sim m/(m-j)$ resonances inside and outside the corotation
radius,as well as prograde and retrograde resonances. Results are: (1) the
kinematics of a periodic orbit depends only on $(m',j')$, the irreducible
(relatively prime) version of $(m,j)$. In a rotating frame, the periodic orbit
has $j'$ braids, $|m'|$ identical sectors and $|m'|(j'-1)$ self-crossing
points; (2) thus, Lindblad resonances (with $j=1$) are free of self-crossing
points; (3) resonances with same $j'$ and opposite $m'$ have the same
kinematics, and are called $twins$; (4) the order of a resonance at a given
$n/\Omega$ depends on the symmetry of the potential. A potential that is
invariant under a $2\pi/k$-rotation creates only resonances with $m$ multiple
of $k$; (5) resonances with same $j$ and opposite $m$ have the same kinematics
and same dynamics, and are called $true~twins$; (6) A retrograde resonance
($n/\Omega < 0$) is always of higher order than its prograde counterpart
($n/\Omega > 0$); (7) the resonance strengths can be calculated in a compact
form with the classical operators used in the case of a perturbing satellite.
Applications to Chariklo and Haumea are made.",2001.06382v1
2020-02-22,Is the K-matrix approach adequate for describing overlapping resonances?,"The K-matrix method is widely used unitary parametrization for several
resonances with the same quantum numbers. But in fact resonances in this
approach are separated and do not overlap.",2002.10949v1
2017-05-22,Horocyclic invariance of Ruelle resonant states for contact Anosov flows in dimension 3,"We show that for smooth contact Anosov flows in dimension 3, the resonant
states associated to the first band of Ruelle resonances are distributions that
are killed by the unstable derivative.",1705.07965v1
2017-09-25,HTS YBCO Resonator Configuration with Coplanar Optimized Flux Concentrator Strongly Coupled to rf SQUID,"We developed a novel magnetic coupling module formed of a monolayer
superconducting flux concentrator, which is integrated with a coplanar
resonator strongly coupled to HTS rf-SQUID. Three types of resonators,
including a long stripline resonator between input loop and pick-up loop of the
flux concentrator, a complementary split ring resonator (CSRR), and also a
spiral shape inside the input loop are explored. The resonance quality factors
as well as the coupling to the SQUID of different patterns of these three types
of the resonators is evaluated using Finite Element Method (FEM) simulations.
Several readout methods to couple the electronic system to the resonators are
tested, including inductive (coil) and capacitive (transmission line)
couplings, and the optimum readout is reported for each of the resonators.
Among the evaluated resonator types, a spiral shape resonator with optimal
design showing the highest quality factor (5900) together with the strongest
coupling to the SQUID (-0.5 dB) at resonance frequency of 836 MHz, is
fabricated using 200 nm thick superconducting YBCO on a 1 mm thick crystalline
LaAlO3 substrate. The flux concentrator of the module is optimized by the
variation of its linewidths and also its input loop radius to obtain maximum
flux transformation efficiency.",1709.09960v1
2020-10-28,Chains of Planets in Mean Motion Resonances Arising from Oligarchic Growth,"Exoplanet systems with multiple planets in mean motion resonances have often
been hailed as a signpost of disk driven migration. Resonant chains like
Kepler-223 and Kepler-80 consist of a trio of planets with the three-body
resonant angle librating and/or with a two-body resonant angle librating for
each pair. Here we investigate whether close-in super-Earths and mini-Neptunes
forming in situ can lock into resonant chains due to dissipation from a
depleted gas disk. We simulate the giant impact phase of planet formation,
including eccentricity damping from a gaseous disk, followed by subsequent
dynamical evolution over tens of millions of years. In a fraction of simulated
systems, we find that planets naturally lock into resonant chains. These
planets achieve a chain of near-integer period ratios during the gas disk
stage, experience eccentricity damping that captures them into resonance, stay
in resonance as the gas disk dissipates, and avoid subsequent giant impacts,
eccentricity excitation, and chaotic diffusion that would dislodge the planets
from resonance. Disk conditions that enable planets to complete their formation
during the gas disk stage enable those planets to achieve tight period ratios
<= 2 and, if they happen to be near integer period ratios, lock into resonance.
Using the weighting of different disk conditions deduced by MacDonald et al.
(2020) and forward modeling Kepler selection effects, we find that our
simulations of in situ formation via oligarchic growth lead to a rate of
observable trios with integer period ratios and librating resonant angles
comparable to observed Kepler systems.",2010.14743v1
2021-03-18,Resonant and non-resonant relaxation of globular clusters,"Globular clusters contain a finite number of stars. As a result, they
inevitably undergo secular evolution (`relaxation') causing their mean
distribution function (DF) to evolve on long timescales. On one hand, this
long-term evolution may be interpreted as driven by the accumulation of local
deflections along each star's mean field trajectory -- so-called `non-resonant
relaxation'. On the other hand, it can be thought of as driven by non-local,
collectively dressed and resonant couplings between stellar orbits, a process
termed `resonant relaxation'. In this paper we consider a model globular
cluster represented by a spherical, isotropic isochrone DF, and compare in
detail the predictions of both resonant and non-resonant relaxation theories
against tailored direct $N$-body simulations. In the space of orbital actions
(namely the radial action and total angular momentum), we find that both
resonant and non-resonant theories predict the correct morphology for the
secular evolution of the cluster's DF, although non-resonant theory
over-estimates the amplitude of the relaxation rate by a factor ${\sim 2}$. We
conclude that the secular relaxation of hot isotropic spherical clusters is not
dominated by collectively amplified large-scale potential fluctuations, despite
the existence of a strong ${\ell = 1}$ damped mode. Instead, collective
amplification affects relaxation only marginally even on the largest scales.
The predicted contributions to relaxation from smaller scale fluctuations are
essentially the same from resonant and non-resonant theories.",2103.10165v1
2021-09-21,Surviving Lower Dimensional Invariant Tori of a Resonant Torus with any Number of Resonances,"We provide sufficient conditions on integrable analytic Hamiltonians that
guarantee the existence, under arbitrary sufficiently small analytic
perturbations, of invariant lower dimensional tori associated to an invariant
resonant torus of the unperturbed Hamiltonian.",2109.10064v1
2021-10-07,TRAPPIST-1: Dynamical analysis of the transit-timing variations and origin of the resonant chain,"We analyze solutions drawn from the recently published posterior distribution
of the TRAPPIST-1 system, which consists of seven Earth-size planets appearing
to be in a resonant chain around a red dwarf. We show that all the planets are
simultaneously in two-planet and three-planet resonances, apart from the
innermost pair for which the two-planet resonant angles circulate. By means of
a frequency analysis, we highlight that the transit-timing variation (TTV)
signals possess a series of common periods varying from days to decades, which
are also present in the variations of the dynamical variables of the system.
Shorter periods (e.g., the TTVs characteristic timescale of 1.3 yr) are
associated with two-planet mean-motion resonances, while longer periods arise
from three-planet resonances. By use of $N$-body simulations with migration
forces, we explore the origin of the resonant chain of TRAPPIST-1 and find that
for particular disc conditions, a chain of resonances - similar to the observed
one - can be formed which accurately reproduces the observed TTVs. Our analysis
suggests that while the 4-yr collected data of observations hold key
information on the two-planet resonant dynamics, further monitoring of
TRAPPIST-1 will soon provide signatures of three-body resonances, in particular
the 3.3 and 5.1 yr periodicities expected for the current best-fit solution.
dditional observations would help to assess whether the innermost pair of
planets is indeed resonant (its proximity to the 8:5 resonance being
challenging to explain), and therefore give additional constraints on formation
scenarios.",2110.03340v2
2023-08-14,Dynamical characterization of the 6/1 mean motion resonance between Quaoar's ring and Weywot,"Recently, it has been reported the discovery of a dense ring around the
trans-Neptunian object 50000 Quaoar. The ring particles seem to be very close
to the 6/1 mean motion resonance with Weywot, the only known satellite in the
system. In this work we investigate the dynamical environment in the close
vicinity of the 6/1 orbital resonance in the context of the restricted three
body problem. We aim to analyze whether, in view of observational constraints,
the ring could be effectively evolving in resonant motion with the satellite.
Through the technique of dynamical maps we identify and characterize the 6/1
mean motion resonance, finding that the main location of the resonance deviates
by only $29$ km from the central part of the ring. This difference lies within
the 3$\sigma$ confidence level, considering the uncertainties in the
observational parameters. We also show that the Weywot's eccentricity plays a
significant role in the dynamical structure of the 6/1 resonance. The results
show that the resonance width is smaller than the estimated ring's width. Under
assumption of a ring with eccentricity smaller than 0.05, clumping of test
particles appears at the position of the different resonant multiplets,
considering the nominal value of Weywot's eccentricity. This is in agreement
with observations, which indicate that the estimated resonance width ($\leq$ 10
km) is comparable with the narrow and dense arc of material within Quaoar's
ring. Our results may be an indicative that the 6/1 resonance resonance plays a
key role in confining the arc ring.",2308.07189v1
2023-12-08,Boosting Resonant Sensing in Fluids: A Surprising Discovery,"Micro-mechanical resonators are widely used in modern sensing technology due
to their high quality-factor (Q), enabling sensitive detection of various
stimuli. However, the performance of these resonators in fluid environments is
limited by significant viscous and acoustic radiation losses that reduce their
Q. Here, we present a paradigm-shifting discovery that challenges the
conventional wisdom of resonant sensing in fluids. We report an optimal volume
of fluid over a 2D micro-resonator that increases the Q by up to 1000% compared
to that in air. We have conducted precise experiments on piezoelectric,
circular, membrane-type micro-resonators of 4 mm diameter fabricated using MEMS
technology on silicon-on-insulator (SOI) wafers. The top side of the resonator
was filled with different volumes of fluid and its Q was measured through
resonance tracking by actuating the resonator with an appropriate voltage. We
found the existence of an optimal volume of fluid that maximized the Q. We
argue that this phenomenon is a result of a balance between the enhancement of
kinetic energy of the resonator due to mass loading of the fluid and the energy
dissipation through viscous and acoustic radiation losses in the fluid medium.
This remarkable enhancement in Q substantially improves the sensitivity of the
resonator, with important implications for diverse applications such as
biosensing, chemical detection, and environmental monitoring. Our findings
challenge the prevailing understanding of resonant sensing in fluids and open
up new avenues for the development of highly sensitive and accurate sensors.",2312.05214v1
2005-05-18,The Effect of Gravity Between Particles on the Shape and Resonant Structure of Planetary Rings,"The resonance perturbation of planetary ring by distant satellite is
considered. The gravity interaction between rings particles is taken into
account. The gravitation interaction between particles in rings can change
shape of non-circular rings, so it is differ from keplerian ellipse. The shift
between simple mean motion resonances and parametric resonance zones is
detected. This shift depends on ring properties.",0505364v1
1999-06-15,Dynamics near Resonance Junctions in Hamiltonian Systems,"An approximate Poincare map near equally strong multiple resonances is
reduced by means the method of averaging. Near the resonance junction of three
degrees of freedom, we find that some homoclinic orbits ``whiskers'' in single
resonance lines survive and form nearly periodic orbits, each of which looks
like a pair of homoclinic orbits.",9906025v1
1997-04-03,Search for the πResonance in Two Particle Tunneling Experiments of YBCO Superconductors,"A recent theory of the resonant neutron scattering peaks in YBCO
superconductors predicts the existence of a sharp spin triplet two particle
collective mode (the ``\pi resonance"") in the normal state. In this paper, we
propose an experiment in which the \pi resonance could be probed directly in a
two particle tunneling measurement.",9704022v1
1998-07-16,Resonant multiple Andreev reflections in mesoscopic superconducting junctions,"We investigate the properties of subharmonic gap structure (SGS) in
superconducting quantum contacts with normal-electron resonances. We find two
distinct new features of the SGS in resonant junctions which distinguish them
from non-resonant point contacts: (i) The odd-order structures on the
current-voltage characteristics of resonant junctions are strongly enhanced and
have pronounced peaks, while the even-order structures are suppressed, in the
case of a normal electron resonance being close to the Fermi level. (ii)
Tremendous current peaks develop at $eV=\pm 2E_0$ where $E_0$ indicates a
distance of the resonance to the Fermi level. These properties are determined
by the effect of narrowing of the resonance during multiple Andreev reflections
and by overlap of electron and hole resonances.",9807240v2
1999-03-24,Coherent stochastic resonance in the case of two absorbing boundaries,"The coherent stochastic resonance is observed and studied with multi-step
periodic signal in continuous medium having two absorbing boundaries. The
general features of this process are exihibited. The universal features at the
resonance point are demonstrated. The kinetic behaviors around the resonance
point are also presented.",9903358v2
2001-02-21,Theory of magnetophonon resonance in 2D electron gas in tilted magnetic field,"A theory of magnetophonon resonance in quantum wells in a magnetic field
tilted to the perpendicular to 2DEG is developed. The resonance is due to the
resonant interaction of 2D conduction electrons with the longitudinal optic
phonons. The electrons are assumed to be nondegenerate. The angular dependence
of the resonant maxima is investigated. The sharpness of the angular
dependence, as well as the existence of double resonances, i.e. two resonant
peaks for each resonance number is explained. A relation between the electron
concentration dependence of the resonance amplitude in the perpendicular
magnetic field and the angular dependence in the tilted field is analyzed.
Investigation of the angular dependence can give information concerning the
electron spectra, optic phonon and electron damping and the electron-phonon
interaction in quantum wells.",0102380v2
2003-07-22,Classical dynamics of a nano-mechanical resonator coupled to a single-electron transistor,"We analyze the dynamics of a nano-mechanical resonator coupled to a
single-electron transistor (SET) in the regime where the resonator behaves
classically. A master equation is derived describing the dynamics of the
coupled system which is then used to obtain equations of motion for the average
charge state of the SET and the average position of the resonator. We show that
the action of the SET on the resonator is very similar to that of a thermal
bath, as it leads to a steady-state probability-distribution for the resonator
which can be described by mean values of the resonator position, a renormalized
frequency, an effective temperature and an intrinsic damping constant.
Including the effects of extrinsic damping and finite temperature, we find that
there remain experimentally accessible regimes where the intrinsic damping of
the resonator still dominates its behavior. We also obtain the average current
through the SET as a function of the coupling to the resonator.",0307528v1
2003-08-19,Resonance approximation and charge loading/unloading in adiabatic quantum pumping,"Quantum pumping through mesoscopic quantum dots is known to be enhanced by
resonant transmission. The pumped charge is close to an integer number of
electrons when the pumping contour surrounds a resonance, but the transmission
remains small on the contour. For non-interacting electrons, we give a
quantitative account of the detailed exchange of electrons between the dot and
the leads (to the electron reservoirs) during a pumping cycle. Near isolated
distinct resonances, we use approximate Breit-Wigner expressions for the dot's
Green function to discuss the loading/unloading picture of the pumping: the
fractional charge exchanged between the dot and each lead through a single
resonance point is related to the relative couplings of the dot and the leads
at this resonance. If each resonance point along the pumping contour is
dominated by the coupling to a single lead (which also implies a very small
transmission), then the crossing of each such resonance results in a single
electron exchange between the dot and that lead, ending up with a net quantized
charge. When the resonance approximation is valid, the fractional charges can
also be extracted from the peaks of the transmissions between the various
leads.",0308382v1
2005-09-06,Strong Resonance of Light in a Cantor Set,"The propagation of an electromagnetic wave in a one-dimensional fractal
object, the Cantor set, is studied. The transfer matrix of the wave amplitude
is formulated and its renormalization transformation is analyzed. The focus is
on resonant states in the Cantor set. In Cantor sets of higher generations,
some of the resonant states closely approach the real axis of the wave number,
leaving between them a wide region free of resonant states. As a result, wide
regions of nearly total reflection appear with sharp peaks of the transmission
coefficient beside them. It is also revealed that the electromagnetic wave is
strongly enhanced and localized in the cavity of the Cantor set near the
resonant frequency. The enhancement factor of the wave amplitude at the
resonant frequency is approximately $6/|\eta_\mathrm{r}|$, where
$\eta_\mathrm{r}$ is the imaginary part of the corresponding resonant
eigenvalue. For example, a resonant state of the lifetime
$\tau_\mathrm{r}=4.3$ms and of the enhancement factor $M=7.8\times10^7$ is
found at the resonant frequency $\omega_\mathrm{r}=367$GHz for the Cantor set
of the fourth generation of length L=10cm made of a medium of the dielectric
constant $\epsilon=10$.",0509145v1
2006-03-14,Quantum resonance and anti-resonance for a periodically kicked Bose-Einstein Condensate in a one dimensional Box,"We investigate the quantum dynamics of a periodically kicked Bose-Einstein
Condensate confined in a one dimensional (1D) Box both numerically and
theoretically, emphasizing on the phenomena of quantum resonance and
anti-resonance. The quantum resonant behavior of BEC is different from the
single particle case but the anti-resonance condition ($T = 2\pi$ and $\alpha =
0$) is not affected by the atomic interaction. For the anti-resonance case, the
nonlinearity (atom interaction) causes the transition between oscillation and
quantum beating. For the quantum resonance case, because of the coherence of
BEC, the energy increase is oscillating and the rate is dramatically affected
by the many-body interaction. We also discuss the relation between the quantum
resonant behavior and the KAM or non-KAM property of the corresponding
classical system.",0603362v1
2007-02-26,Graphene-based resonant-tunneling strucures,"Resonant electronic transmission through graphene-based double barriers
(wells) is studied as a function of the incident wave vector, the widths and
heights (depths) of the barriers (wells), and the separation between them.
Resonant features in the transmission result from resonant electron states in
the wells or hole states in the barriers and strongly influence the ballistic
conductance of the structures.",0702596v1
1999-03-09,Remarks on parametric resonance of neutrino oscillations in the earth,"Neutrino oscillations in matter can exhibit a specific resonance enhancement
-- parametric resonance, which is different from the MSW resonance. Recently it
has been shown that the oscillations of atmospheric and solar neutrinos inside
the earth can undergo parametric enhancement when neutrino trajectories cross
the core of the earth. In this paper we continue the study of the parametric
resonance of neutrino oscillations in the earth. The following issues are
discussed: stability of the resonance with respect to the variations of the
zenith angle of the neutrino source; higher-order resonances; prospects of the
experimental observation of the parametric resonance of neutrino oscillations.
We also comment on a recent controversy regarding the physical nature of the
resonance enhancement of the oscillations of the core crossing neutrinos in the
earth.",9903302v1
2002-05-17,Time advancement in resonance regions of pi-N scattering,"We evaluate the time delay in some of the established resonance regions of
$\pi N$ elastic scattering. In addition to the positive peaks corresponding to
resonances, we identify broad regions of negative time delay or time
advancement which restrict the energy ranges within which the resonances can be
located.",0205188v1
2003-05-23,Resonances for steplike potentials: forward and inverse results,"We consider resonances associated to the operator $-\frac{d^2}{dx^2}+V(x)$,
where $V(x)=V_+$ if $x>x_M$ and $V(x)=V_-$ if $x<-x_M$, with $V_+\not = V_-$.
We obtain asymptotics of the resonance-counting function in several regions.
Moreover, we show that in several situations, the resonances, $V_+$, and $V_-$
determine $V$ uniquely up to translation.",0305335v1
2004-12-30,"Noncommutative Algebras, Nano-Structures, and Quantum Dynamics Generated by Resonances","We observe ``quantum'' properties of resonance equilibrium points and
resonance univariant submanifolds in the phase space. Resonances between
Birkhoff or Floquet--Lyapunov frequencies generate quantum algebras with
polynomial commutation relations. Irreducible representations and coherent
states of these algebras correspond to certain quantum nano-structure near the
classical resonance motion. Based on this representation theory and
nano-geometry, for equations of Schr\""odinger or wave type in various regimes
and zones (up to quantum chaos borders) we describe the resonance spectral and
long-time asymptotics, resonance localization and focusing, resonance adiabatic
and spin-like effects. We discuss how the mathematical phase space
nano-structures relate to physical nanoscale objects like dots, quantum wires,
etc. We also demonstrate that even in physically macroscale Helmholtz channels
the resonance implies a specific quantum character of classical wave
propagation.",0412542v2
1998-10-26,Resonances In a Box,"We investigate a numerical method for studying resonances in quantum
mechanics. We prove rigorously that this method yields accurate approximations
to resonance energies and widths for shape resonances in the semiclassical
limit.",9810018v1
2004-03-19,Scattering of solitons on resonance,"We investigate a propagation of solitons for nonlinear Schrodinger equation
under small driving force. The driving force passes the resonance. The process
of scattering on the resonance leads to changing of number of solitons. After
the resonance the number of solitons depends on the amplitude of the driving
force.",0403038v1
2000-05-02,A Relationship Between Parametric Resonance and Chaos,"In this paper we study two types of exponential instability -- parametric
resonance and chaos. We show that a given equation may produce chaos or
parametric resonance, depending how the problem is defined. In so doing we
establish a relationship between the Floquet indices (associated with
parametric resonance) and Lyapunov exponents (associated with chaos).",0005005v1
2003-09-27,Renormalization Analysis of Resonance Structure in 2-D Symplectic Map,"A symplecticity-preserving RG analysis is carried out to study a resonance
structure near an elliptic fixed point of a proto-type symplectic map in two
dimensions. Through analyzing fixed points of a reduced RG map, a topology of
the resonance structure such as a chain of resonant islands can be determined
analytically. An application of this analysis to the Henon map is also
presented.",0309072v1
2005-05-08,Resonance-assisted tunneling in three degrees of freedom without discrete symmetry,"We study dynamical tunneling in a near-integrable Hamiltonian with three
degrees of freedom. The model Hamiltonian does not have any discrete symmetry.
Despite this lack of symmetry we show that the mixing of near-degenerate
quantum states is due to dynamical tunneling mediated by the nonlinear
resonances in the classical phase space. Identifying the key resonances allows
us to suppress the dynamical tunneling via the addition of weak
counter-resonant terms.",0505020v1
2005-01-11,The search for missing baryon resonances,"Experiments with electromagnetic probes are promising to search for baryon
resonances that have been predicted by quark models but have not yet been
observed. Data sets from different experiments show interesting resonance
structures possibly due to so far unknow states. This might indicate that at
least some of the missing baryon resonances start to show up.",0501007v1
2000-05-13,Probing the Structure of Nucleons in the Resonance Region,"Status, open questions, and future prospects of the physics of excited
nucleons are discussed. Emphasis is on the study of the structure of nucleons
via measurements of their electromagnetic transition form factors, the search
for ""missing"" resonances, the spin structure of the nucleon in the resonance
region, and connections between the resonance and the deep-inelastic regimes.",0005033v1
2002-01-23,Relativistic Heavy Ion Excitation of Giant Resonances,"Giant resonances and giant resonances built on other giant resonances in
nuclei are observed with very large cross sections in relativistic heavy ion
collisions. A theoretical effort is underway to understand the reaction
mechanism which leads to this process, as well as a better understanding of the
microscopic properties of multiphonon states, e.g., their strength, energy
centroids, widths and anharmonicities.",0201060v1
2002-02-03,Search for new baryon resonances,"Within a chiral constituent quark formalism, allowing the inclusion of all
known resonances, a comprehensive study of the recent eta photoproduction data
on the proton up to 2 GeV is performed. This study shows evidence for a new S11
resonances and indicates the presence of an additional missing P13 resonance.",0202007v1
2004-06-17,Nucleon resonances and processes involving strange particles,"An existing single resonance model with S11, P11 and P13 Breit-Wiegner
resonances in the s-channel has been re-applied to the old pi N --> K Lambda
data. It has been shown that the standard set of resonant parameters fails to
reproduce the shape of the differential cross section. The resonance parameter
determination has been repeated retaining the most recent knowledge about the
nucleon resonances. The extracted set of parameters has confirmed the need for
the strong contribution of a P11(1710) resonance. The need for any significant
contribution of the P13 resonance has been eliminated. Assuming that the Baker.
et al data set\cite{Bak78} is a most reliable one, the P11 resonance can not
but be quite narrow. It emerges as a good candidate for the non-strange counter
partner of the established pentaquark anti-decuplet.",0406057v1
2002-10-23,170 Nanometer Nuclear Magnetic Resonance Imaging using Magnetic Resonance Force Microscopy,"We demonstrate one-dimensional nuclear magnetic resonance imaging of the
semiconductor GaAs with 170 nanometer slice separation and resolve two regions
of reduced nuclear spin polarization density separated by only 500 nanometers.
This is achieved by force detection of the magnetic resonance, Magnetic
Resonance Force Microscopy (MRFM), in combination with optical pumping to
increase the nuclear spin polarization. Optical pumping of the GaAs creates
spin polarization up to 12 times larger than the thermal nuclear spin
polarization at 5 K and 4 T. The experiment is sensitive to sample volumes
containing $\sim 4 \times 10^{11}$ $^{71}$Ga$/\sqrt{Hz}$. These results
demonstrate the ability of force-detected magnetic resonance to apply magnetic
resonance imaging to semiconductor devices and other nanostructures.",0210099v1
2004-09-21,"Electrodynamical properties of a ""grid"" volume resonator for travelling wave tube and backward wave oscillator","The electrodynamical properties of a volume resonator formed by a perodic
structure built from the metallic threads inside a rectangular waveguide
(""grid"" volume resonator) is considered for travelling wave tube and backward
wave oscillator operation. Peculiarities of passing of electromagnetic waves
with different polarizations through such volume resonator are discussed.",0409107v2
2007-05-30,"Resonant spin polarization in a two-dimensional hole gas: Effect of the Luttinger term, structural inversion asymmetry and Zeeman splitting","The electric-field-induced resonant spin polarization of a two-dimensional
hole gas described by Luttinger Hamiltonian with structural inversion asymmetry
and Zeeman splitting in a perpendicular magnetic field was studied. The spin
polarization arising from splitting between the light and the heavy hole bands
shows a resonant peak at a certain magnetic field. Especially, the competition
between the Luttinger term and the structural inversion asymmetry leads to a
rich resonant peaks structure, and the required magnetic field for the
resonance may be effectively reduced by enlarging the effective width of the
quantum well. Furthermore, the Zeeman splitting tends to move the resonant spin
polarization to a relative high magnetic field and destroy these rich resonant
spin phenomena. Finally, both the height and the weight of the resonant peak
increase as the temperature decreases. It is believed that such resonant spin
phenomena can be verified in the sample of a two-dimensional hole gas, and it
may provide an efficient way to control spin polarization by an external
electric field.",0705.4355v2
2007-10-03,Magnetic and Electric Excitations in Split Ring Resonators,"We studied the electric and magnetic resonance of U-shaped SRRs. We showed
that higher order excitation modes exist in both of the electric and magnetic
resonances. The nodes in the current distribution were found for all the
resonance modes. It turns out that the magnetic resonances are the modes with
odd-number of half-wavelength of the current wave, i.e. 1/2, 3/2 and 5/2
wavelengths modes, and the electric resonances are modes with integer number of
whole-wavelength of current wave, i.e. 1, 2 and 3 wavelengths modes. We
discussed the electric moment and magnetic moment of the electric and magnetic
resonances, and their dependence to the length of two parallel side arms. We
show that the magnetic moment of magnetic resonance vanishes as the length side
arms of the SRR reduces to zero, i.e. a rod does not give any magnetic moment
or magnetic resonance.",0710.0812v2
2007-10-19,Unified description of resonance and decay phenomena,"In the Feshbach projection operator formalism, resonance as well as decay
phenomena are described by means of the complex eigenvalues and eigenfunctions
of the non-Hermitian Hamilton operator $H_{\rm eff}$ that appears in an
intermediate stage of the formalism. The formalism can be applied for the
description of isolated resonances as well as for resonances in the overlapping
regime. Time asymmetry is related to the time operator which is a part of
$H_{\rm eff}$. An expression for the decay rates of resonance states is
derived. For isolated resonance states $\lambda$, this expression gives the
fundamental relation $\tau_\lambda = \hbar / \Gamma_\lambda$ between life time
and width of a resonance state. A similar relation holds for the average values
obtained for narrow resonances superposed by a smooth background term. In the
cross over between these two cases (regime of overlapping resonances), the
decay rate decreases monotonously as a function of increasing time.",0710.3661v1
2008-01-09,Derivation of the spatio-temporal model equations for the thermoacoustic resonator,"We derive the model equations describing the thermoacoustic resonator, that
is, an acoustical resonator containing a viscous medium inside. Previous
studies on this system have addressed this sytem in the frame of the plane-wave
approximation, we extend the previous model to by considering spatial effects
in a large aperture resonator. This model exhibits pattern formation and
localized structures scenario.",0801.1454v1
2008-05-07,Brillouin Lasing with a CaF_2 Whispering Gallery Mode Resonator,"Stimulated Brillouin scattering with both pump and Stokes beams in resonance
with whispering gallery modes of an ultra high Q CaF_2 resonator is
demonstrated for the first time. The resonator is pumped with 1064 nm light and
has a Brillouin lasing threshold of 3.5 microwatt. Potential applications
include optical generation of microwaves and sensitive gyros.",0805.0803v1
2008-05-22,Lineshape Asymmetry for joint CPT and three photon N resonances,"We show that a characteristic two photon lineshape asymmetry arises in
coherent population trapping (CPT) and three photon (N) resonances because both
resonances are simultaneously induced by modulation sidebands in the
interrogating laser light. The N resonance is a three-photon resonance in which
a two-photon Raman excitation is combined with a resonant optical pumping
field. This joint CPT and N resonance can be the dominant source of lineshape
distortion, with direct relevance for the operation of miniaturized atomic
frequency standards. We present the results of both an experimental study and
theoretical treatment of the asymmetry of the joint CPT and N resonance under
conditions typical to the operation of an N resonance clock.",0805.3384v1
2008-08-20,Inverse resonance scattering for Jacobi operators,"We consider the Jacobi operator $(Jf)_n= a_{n-1}f_{n-1}+a_nf_{n+1}+b_nf_n$ on
$\Z$ with a real compactly supported sequences $(a_n-1)_{n\in\Z}$ and
$(b_n)_{n\in\Z}$. We give the solution of two inverse problems (including
characterization): $ (a,b)\to \{$zeros of the reflection coefficient$\}$ and
$(a,b)\to \{$bound states and resonances$\}$. We describe the set of
""iso-resonance operators $J$"", i.e., all operators $J$ with the same resonances
and bound states.",0808.2805v1
2008-12-01,On the validity of nonlinear Alfven resonance in space plasmas,"In the approximation of linear dissipative magnetohydrodynamics (MHD) it can
be shown that driven MHD waves in magnetic plasmas with high Reynolds number
exhibit a near resonant behaviour if the frequency of the wave becomes equal to
the local Alfven (or slow) frequency of a magnetic surface. This near resonant
behaviour is confined to a thin region, known as the dissipative layer, which
embraces the resonant magnetic surface. Although driven MHD waves have small
dimensionless amplitude far away from the resonant surface, this near-resonant
behaviour in the dissipative layer may cause a breakdown of linear theory. Our
aim is to study the nonlinear effects in the Alfven dissipative layer. In the
present paper, the method of simplified matched asymptotic expansions developed
for nonlinear slow resonant waves is used to describe nonlinear effects inside
the Alfven dissipative layer. The nonlinear corrections to resonant waves in
the Alfven dissipative layer are derived and it is proved that at the Alfven
resonance (with isotropic/anisotropic dissipation) wave dynamics can be
described by the linear theory with great accuracy.",0812.0291v1
2009-02-17,Fano resonances in nanoscale structures,"Nowadays nanotechnology allows to scale-down various important devices
(sensors, chips, fibres, etc), and, thus, opens up new horizon for their
applications. Nevertheless, the efficiency most of them is still based on the
fundamental physical phenomena, such as resonances. Thus, the understanding of
the resonance phenomena will be beneficial. One of the well-known examples is
the resonant enhancement of the transmission known as Breit-Wigner resonances,
which can be described by a Lorentzian function. But, in many physical systems
the scattering of waves involves propagation along different paths, and, as a
consequence, results in interference phenomena, where constructive interference
corresponds to resonant enhancement and destructive interference to resonant
suppression of the transmission. Recently, a variety of experimental and
theoretical work has revealed such patterns in different branches of physics.
The purpose of this Review is to demonstrate that this kind of resonant
scattering is related to the Fano resonances, known from atomic physics. One of
the main features of the Fano resonances is the asymmetric profile. The
asymmetry comes from the close coexistence of resonant transmission and
resonant reflection. Fano successfully explained such a phenomenon in his
seminal paper in 1961 in terms of interaction of a discrete (localized) state
with a continuum of propagation modes. It allows to describe both resonant
enhancement and resonant suppression in a unified manner. All of these
properties can be demonstrated in the frame of a very simple model, which will
be used throughout the Review to show that resonant reflections observed in
different complex systems are indeed closely related to the Fano resonances.",0902.3014v4
2009-03-10,Spectrum of a fluid-loaded vibrating plate: the multiple resonance phenomenon,"It was recently observed in a numerical study on a high order perturbation
method under heavy fluid loading that a loaded vibrating plate results, not
only in the classical frequency shift of the in vacuo single resonance (in both
the real part because of the fluid added mass and the imaginary part because of
energy lost by radiation), but also in an increase in the number of the
resonance. As a result of the loading, a single in vacuo resonance of the
structure is transformed into a multiple resonance. Here we show that this
phenomenon is a refinement of the Sanchez's classical result where it was
established, using asymptotic analysis, that in the case of a light loading
conditions "" the scattering frequencies of a fluid loaded elastic structure (ie
the resonance frequencies) are nearly the real eigenfrequencies of the elastic
body alone and the complex scattering frequencies of the fluid with a rigid
solid "". A theoretical explanation of the multiple resonances is given using
classical results on theory of entire functions. It is established that every
single in vacuo resonance of a simply supported rectangular plate is
transformed into an infinite number of resonances under fluid-loading
condition.",0903.1704v1
2009-03-24,Outer Resonances and Effective Potential Analogy in Two-Dimensional Dielectric Cavities,"Outer resonances are studied as one type of quasinormal modes in
two-dimensional dielectric cavities with refractive index $n>1$. The outer
resonances can be verified as the resonances which survive only outside the
cavity in the small opening limit of the dielectric disk. We have confirmed
that the outer resonances universally exist in deformed cavities irrespective
of the geometry of cavity and they split into nearly degenerate states in
slightly deformed cavity. Also we pointed out that the effective potential
analogy is inapplicable to the description of outer resonances. Since most
outer resonances in the dielectric cavities have quite high leakages, they
would affect to the broad background in the density of states. Especially, for
TE polarization case, relatively low-leaky outer resonances exist and it
presents the possibility that they can interact with the inner resonances and
affect lasing modes.",0903.4034v3
2009-05-01,Nonlinear resonances of water waves,"In the last fifteen years, a great progress has been made in the
understanding of the nonlinear resonance dynamics of water waves. Notions of
scale- and angle-resonances have been introduced, new type of energy cascade
due to nonlinear resonances in the gravity water waves have been discovered,
conception of a resonance cluster has been much and successful employed, a
novel model of laminated wave turbulence has been developed, etc. etc. Two
milestones in this area of research have to be mentioned: a) development of the
$q$-class method which is effective for computing integer points on the
resonance manifolds, and b) construction of the marked planar graphs, instead
of classical resonance curves, representing simultaneously all resonance
clusters in a finite spectral domain, together with their dynamical systems.
Among them, new integrable dynamical systems have been found that can be used
for explaining numerical and laboratory results. The aim of this paper is to
give a brief overview of our current knowledge about nonlinear resonances among
water waves, and formulate three most important open problems at the end.",0905.0050v2
2009-07-04,On resonance parameter measurement and luminosity determination at e+e- collider,"Expounded are the parameter measurement for narrow resonance and
determination of corresponding luminosity at e+e- collider. The detailed
theoretical formulas are compiled and the crucial experimental effects on
observed cross section are taken into account. For luminosity determination,
the iteration method is put forth which is mainly used to separate the
interference effect between resonance and non-resonance decays.",0907.0734v1
2009-09-08,Giant Slow Wave Resonance for Light Amplification and Lasing,"We apply the idea of giant slow wave resonance associated with a degenerate
photonic band edge to gain enhancement of active media. This approach allows to
dramatically reduce the size of slow wave resonator while improving its
performance as gain enhancer for light amplification and lasing. It also allows
to reduce the lasing threshold of the slow wave optical resonator by at least
an order of magnitude.",0909.1393v1
2009-11-12,Spin Resonance and dc Current Generation in a Quantum Wire,"We show that in a quantum wire the spin-orbit interaction leads to a narrow
spin resonance at low temperatures, even in the absence of an external magnetic
field. Resonance absorption by linearly polarized radiation gives a dc spin
current; resonance absorption by circularly polarized radiation gives a dc
electric current or magnetization.",0911.2433v1
2009-11-22,Power-dependent internal loss in Josephson bifurcation amplifiers,"We have studied nonlinear superconducting resonators: lambda/2
coplanar-waveguide (CPW) resonators with Josephson junctions (JJs) placed in
the middle and lambda/4 CPW resonators terminated by JJs, which can be used for
the qubit readout as ""bifurcation amplifiers."" The nonlinearity of the
resonators arises from the Josephson junctions, and because of the
nonlinearity, the resonators with appropriate parameters are expected to show a
hysteretic response to the frequency sweep, or ""bifurcation,"" when they are
driven with a sufficiently large power. We designed and fabricated resonators
whose resonant frequencies were around 10 GHz. We characterized the resonators
at low temperatures, T<0.05 K, and confirmed that they indeed exhibited
hysteresis. The sizes of the hysteresis, however, are sometimes considerably
smaller than the predictions based on the loaded quality factor in the weak
drive regime. When the discrepancy appears, it is mostly explained by taking
into account the internal loss, which often increases in our resonators with
increasing drive power in the relevant power range. As a possible origin of the
power-dependent loss, the quasiparticle channel of conductance of the JJs is
discussed.",0911.4221v1
2010-08-17,Loss Dependence on Geometry and Applied Power in Superconducting Coplanar Resonators,"The loss in superconducting microwave resonators at low-photon number and low
temperatures is not well understood but has implications for achievable
coherence times in superconducting qubits. We have fabricated single-layer
resonators with a high quality factor by patterning a superconducting aluminum
film on a sapphire substrate. Four resonator geometries were studied with
resonant frequencies ranging from 5 to 7 GHz: a quasi-lumped element resonator,
a coplanar strip waveguide resonator, and two hybrid designs that contain both
a coplanar strip and a quasi-lumped element. Transmitted power measurements
were taken at 30 mK as a function of frequency and probe power. We find that
the resonator loss, expressed as the inverse of the internal quality factor,
decreases slowly over four decades of photon number in a manner not merely
explained by loss from a conventional uniform spatial distribution of two-level
systems in an oxide layer on the superconducting surfaces of the resonator.",1008.2929v2
2011-10-25,Transitional dynamics of a phase qubit-resonator system: requirements for fast readout of a phase qubit,"We examine the non-stationary evolution of a coupled qubit-transmission
line-resonator system coupled to an external drive and the resonator
environment. By solving the equation for a non-stationary resonator field, we
determined the requirements for a single-shot non-destructive dispersive
measurement of the phase qubit state. Reliable isolation of the qubit from the
""electromagnetic environment"" is necessary for a dispersive readout and can be
achieved if the whole system interacts with the external fields only through
the resonator that is weakly coupled to the qubit. A set of inequalities
involving resonator-qubit detuning and coupling parameter, the resonator
leakage and the measurement time, together with the requirement of multi-photon
outgoing flux is derived. It is shown, in particular, that a decrease of the
measurement time requires an increase of the resonator leakage. This increase
results in reducing the quality factor and decreasing the resolution of the
resonator eigenfrequencies corresponding to different qubit states. The
consistent character of the derived inequalities for two sets of experimental
parameters is discussed. The obtained results will be useful for optimal design
of experimental setups, parameters, and measurement protocols.",1110.5566v1
2012-09-01,Complex Permittivity Measurements at Variable Temperatures of Low Loss Dielectric Substrates Employing Split Post and Single Post Dielectric Resonators,"A split post dielectric resonator in a copper enclosure and a single post
dielectric resonator in a cavity with superconducting end-plates have been
constructed and used for the complex permittivity measurements of single
crystal substrates. (La,Sr)(Al,Ta)O3, LaAlO3, MgO and quartz substrates have
been measured at temperatures from 20 K to 300 K in the split post resonator
and from 15 K to 80 K in the single post resonator. The TE01delta mode resonant
frequencies and unloaded Qo-factors of the empty resonators at temperature of
20 K were: 9.952 GHz and 25,000 for the split post resonator and 10.808 GHz and
240,000 for the single post resonator respectively.",1209.0111v1
2012-10-30,Shifts and widths of Feshbach resonances in atomic waveguides,"We develop and analyze a theoretical model which yields the shifts and widths
of Feshbach resonances in an atomic waveguide. It is based on a multichannel
approach for confinement-induced resonances (CIRs) and atomic transitions in
the waveguides in the multimode regime. We replace in this scheme the
single-channel scalar interatomic interaction by the four-channel tensorial
potential modeling resonances of broad, narrow and overlapping character
according to the two-channel parametrization of A.D.Lange et al. As an input
the experimentally known parameters of Feshbach resonances in the absence of
the waveguide are used. We calculate the shifts and widths of s-, d- and g-wave
magnetic Feshbach resonances of Cs atoms emerging in harmonic waveguides as
CIRs and resonant enhancement of the transmission at zeros of the free space
scattering length. We have found the linear dependence of the width of the
resonance on the longitudinal atomic momentum and quadratic dependence on the
waiveguide width. Our model opens novel possibilities for quantitative studies
of the scattering processes in ultracold atomic gases in waveguides beyond the
framework of s-wave resonant scattering.",1210.7984v2
2012-11-29,Pumping K-Alpha Resonance Fluorescence by Monochromatic X-Ray Sources,"We demonstrate the correspondence between theoretically calculated K-shell
resonances lying below the K-edge in multiple ionization states of an element
(Pradhan et al. 2009), and recently observed K-alpha resonances in
high-intensity X-ray free-electron laser (XFEL) plasmas (Vinko et al. 2012).
Resonant absorptions in aluminum ions are computed and found to reproduce
experimentally observed features. Results are also presented for titanium for
possible observation of K-alpha resonances in the 4.5-5.0 keV energy range. A
possibly sustainable excitation mechanism for K-alpha resonance fluorescence
might be implemented using two monochromatic X-ray beams tuned to the K-edge
and the K-alpha resonant energies simultaneously. This targeted
ionization/excitation would create inner-shell vacancies via Auger decay, as
well as pump K-alpha resonances. The required X-ray fluence to achieve
resonance fluorescence would evidently be much less than in the XFEL
experiments, and might enable novel biomedical applications.",1211.7041v1
2012-12-19,Topological Resonances in Scattering on Networks (Graphs),"We report on a hitherto unnoticed type of resonances occurring in scattering
from networks (quantum graphs) which are due to the complex connectivity of the
graph - its topology. We consider generic open graphs and show that any cycle
leads to narrow resonances which do not fit in any of the prominent paradigms
for narrow resonances (classical barriers, localization due to disorder,
chaotic scattering). We call these resonances `topological' to emphasize their
origin in the non-trivial connectivity. Topological resonances have a clear and
unique signature which is apparent in the statistics of the resonance
parameters (such as e.g., the width, the delay time or the wave-function
intensity in the graph). We discuss this phenomenon by providing analytical
arguments supported by numerical simulation, and identify the features of the
above distributions which depend on genuine topological quantities such as the
length of the shortest cycle (girth). These signatures cannot be explained
using any of the other paradigms for narrow resonances. Finally, we propose an
experimental setting where the topological resonances could be demonstrated,
and study the stability of the relevant distribution functions to moderate
dissipation.",1212.4682v1
2013-03-16,Method of images applied to an opto-mechanical Fabry-Perot resonator,"The method of images, when applied to an opto-mechanical Fabry-Perot
resonator with a heavy, charged mirror, and a light, charged mirror that can be
driven into motion, reveals that the highest order images can move
relativistically when the Q of the superconducting resonator is on the order of
10^10. The implications of such relativistic motions of the charge and mass of
these images to the emission of electromagnetic and gravitational radiation
within the resonator is explored.",1303.4020v1
2013-04-08,Energy and lifetime of resonant states with real basis sets,"Using a probabilistic interpretation of resonant states, we propose a formula
useful to calculate the lifetime of a resonance using square-integrable real
basis-set expansion techniques. Our approach does not require an estimation of
the density of states. The method is illustrated with calculations of $s$ and
$p$ resonant-state energies and lifetimes.",1304.2136v2
2013-04-15,Vibrational Resonance in the Morse Oscillator,"We investigate the occurrence of vibrational resonance in both classical and
quantum mechanical Morse oscillators driven by a biharmonic force. The
biharmonic force consists of two forces of widely different frequencies \omega
and \Omega with \Omega>>\omega. In the damped and biharmonically driven
classical Morse oscillator applying a theoretical approach we obtain an
analytical expression for the response amplitude at the low-frequency \omega.
We identify the conditions on the parameters for the occurrence of the
resonance. The system shows only one resonance and moreover at resonance the
response amplitude is 1/(d\omega) where d is the coefficient of linear damping.
When the amplitude of the high-frequency force is varied after resonance the
response amplitude does not decay to zero but approaches a nonzero limiting
value. We have observed that vibrational resonance occurs when the sinusoidal
force is replaced by a square-wave force. We also report the occurrence of
resonance and anti-resonance of transition probability of quantum mechanical
Morse oscillator in the presence of the biharmonic external field.",1304.3988v1
2013-05-28,Analytical Treatment of Planetary Resonances,"An ever-growing observational aggregate of extrasolar planets has revealed
that systems of planets that reside in or near mean-motion resonances are
relatively common. While the origin of such systems is attributed to
protoplanetary disk-driven migration, a qualitative description of the
dynamical evolution of resonant planets remains largely elusive. Aided by the
pioneering works of the last century, we formulate an approximate, integrable
theory for first-order resonant motion. We utilize the developed theory to
construct an intuitive, geometrical representation of resonances within the
context of the unrestricted three-body problem. Moreover, we derive a simple
analytical criterion for the appearance of secondary resonances between
resonant and secular motion. Subsequently, we demonstrate the onset of rapid
chaotic motion as a result of overlap among neighboring first-order mean-motion
resonances, as well as the appearance of slow chaos as a result of secular
modulation of the planetary orbits. Finally, we take advantage of the
integrable theory to analytically show that, in the adiabatic regime, divergent
encounters with first-order mean-motion resonances always lead to persistent
apsidal anti-alignment.",1305.6513v1
2013-07-09,Resonances for Dirac operators on the half-line,"We consider the 1D Dirac operator on the half-line with compactly supported
potentials. We study resonances as the poles of scattering matrix or
equivalently as the zeros of modified Fredholm determinant. We obtain the
following properties of the resonances: 1) asymptotics of counting function, 2)
estimates on the resonances and the forbidden domain.",1307.2478v1
2013-11-15,Singular evanescent wave resonances,"Resonators fold the path of light by reflections leading to a phase balance
and thus constructive addition of propagating waves. However, amplitude
decrease of these waves due to incomplete reflection or material absorption
leads to a finite quality factor of all resonances. Here we report on our
discovery that evanescent waves can lead to a perfect phase and amplitude
balance causing an ideal Fabry-Perot resonance condition in spite of material
absorption and non-ideal reflectivities. This counterintuitive resonance occurs
if and only if the metallic Fabry-Perot plates are in relative motion to each
other separated by a critical distance. We show that the energy needed to
approach the resonance arises from the conversion of the mechanical energy of
motion to electromagnetic energy. The phenomenon is similar to lasing where the
losses in the cavity resonance are exactly compensated by optical gain media
instead of mechanical motion. Nonlinearities and non-localities in material
response will inevitably curtail any singularities however we show the giant
enhancement in non-equilibrium phenomena due to such resonances in moving
media.",1311.3718v3
2013-12-01,Differential Entropy Dynamics: A Possible Cause of Coherence Resonance,"Coherence resonance can be explained using differential entropy and mutual
information. This theory explores the role of external noise in stabilising
chaotic circuits such as the uni-junction transistor relaxation oscillator.The
phenomenon of coherence resonance maximizes differential entropy and mutual
information.Thus most natural chaotic oscillators show coherence resonance in
the presence of an external driving noise.",1312.0203v1
2014-02-26,Optimal lower bound of the resonance widths for the Helmholtz Resonator,"Under a geometric assumption on the region near the end of its neck, we prove
an optimal exponential lower bound on the widths of resonances for a general
two-dimensional Helmholtz resonator. An extension of the result to the
n-dimensional case, n smaller than 12, is also obtained.",1402.6493v2
2014-04-24,Resonances for the radial Dirac operators,"We consider the radial Dirac operator with compactly supported potentials. We
study resonances as the poles of scattering matrix or equivalently as the zeros
of modified Fredholm determinant. We obtain the following properties of the
resonances: 1) asymptotics of counting function, 2) in the massless case we get
the trace formula in terms of resonances.",1404.6078v2
2014-04-25,Waveguide couplers for ferroelectric optical resonators,"We report a study of using the same material to fabricate a whispering
gallery mode resonator and a coupler. Coupling to high Q whispering gallery
modes of the lithium niobate resonator is demonstrated by means of the
titanium-doped waveguide. The waveguide coupling approach opens possibilities
for simpler and wider practical usage of whispering gallery mode resonators and
their integration into optical devices.",1404.6582v1
2014-04-29,Temporal behavior of laser induced elastic plate resonances,"This paper investigates the dependence on Poisson's ratio of local plate
resonances in low attenuating materials. In our experiments, these resonances
are generated by a pulse laser source and detected with a heterodyne
interferometer measuring surface displacement normal to the plate. The laser
impact induces a set of resonances that are dominated by Zero Group Velocity
(ZGV) Lamb modes. For some Poisson's ratio, thickness-shear resonances are also
detected. These experiments confirm that the temporal decay of ZGV modes
follows a $t^{-0.5}$ law and show that the temporal decay of the thickness
resonances is much faster. Similar decays are obtained by numerical simulations
achieved with a finite difference code. A simple model is proposed to describe
the thickness resonances. It predicts that a thickness mode decays as
$t^{-1.5}$ for large times and that the resonance amplitude is proportional to
$D^{-1.5}$ where $D$ is the curvature of the dispersion curve $\omega(k)$ at
$k=0$. This curvature depends on the order of the mode and on the Poisson's
ratio, and it explains why some thickness resonances are well detected while
others are not.",1404.7464v2
2014-09-03,A number theoretical observation of a resonant interaction of Rossby waves,"Rossby waves are generally expected to dominate the $\beta$ plane dynamics in
geophysics, and here in this paper we give a number theoretical observation of
the resonant interaction with a Diophantine equation. The set of resonant
frequencies does not have any frequency on the horizontal axis. We also give
several clusters of resonant frequencies.",1409.1031v1
2015-02-23,Demonstration of whispering-gallery-mode resonant enhancement of optical forces,"We experimentally studied whispering-gallery modes(WGMs) and demonstrated
resonance enhancement of optical forces evanescently exerted on dielectric
microspheres. We showed that the resonant light pressure can be used for
optical sorting of microparticles with extraordinary uniform resonant
properties that is unachievable by conventional sorting techniques.",1502.06298v1
2015-02-26,Active and reactive power in stochastic resonance for energy harvesting,"A power allocation to active and reactive power in stochastic resonance is
discussed for energy harvesting from mechanical noise. It is confirmed that
active power can be increased at stochastic resonance, in the same way of the
relationship between energy and phase at an appropriate setting in resonance.",1503.04084v1
2015-04-21,Resonance widths for general Helmholtz Resonators with straight neck,"We prove an optimal exponential lower bound on the width of the resonance
associated to the first eigenvalue of the cavity for a general Helmholtz
resonator with straight neck, in any dimension.",1504.05425v1
2015-04-17,On the ambiguity of determination of interfering resonances parameters,"The general form of solutions for parameters of interfering Breit-Wigner
resonances is found. The number of solutions is determined by the properties of
roots of corresponding characteristic equation and does not exceed $2^{N-1}$,
where $N$ is the number of resonances. For resonances of more complicated form,
provided that their amplitudes satisfy certain conditions, for any $N\ge2$
multiple solutions also exist.",1505.01509v1
2015-05-26,A time domain based method for the accurate measurement of Q-factor and resonance frequency of microwave resonators,"We present a novel method to determine the resonant frequency and quality
factor of microwave resonators which is faster, more stable, and conceptually
simpler than the yet existing techniques. The microwave resonator is irradiated
at a frequency away from its resonance. It then emits an exponentially decaying
radiation at its eigen-frequency when the excitation is rapidly switched off.
The emission is down-converted with a microwave mixer, digitized and its
Fourier transformation (FT) directly yields the resonance curve in a single
shot. Being an FT based method, this technique possesses the Fellgett
(multiplex) and Connes (accuracy) advantages and it conceptually mimics that of
pulsed nuclear magnetic resonance. We also establish a novel benchmark to
compare accuracy of the different approaches of microwave resonator
measurements. This shows that the present method have similar accuracy to the
existing ones.",1505.06863v1
2015-05-26,Spectral Engineering with Coupled Microcavities: Active Control of Resonant Mode-Splitting,"Optical mode-splitting is an efficient tool to shape and fine-tune the
spectral response of resonant nanophotonic devices. The active control of
mode-splitting, however, is either small or accompanied by undesired resonance
shifts, often much larger than the resonance-splitting. We report a control
mechanism that enables reconfigurable and widely tunable mode-splitting while
efficiently mitigating undesired resonance shifts. This is achieved by actively
controlling the excitation of counter-traveling modes in coupled resonators.
The transition from a large splitting (80 GHz) to a single-notch resonance is
demonstrated using low power microheaters (35 mW). We show that the spurious
resonance-shift in our device is only limited by thermal crosstalk and
resonance-shift-free splitting control may be achieved.",1505.07097v1
2015-06-04,Resonant infiltration of an opal: reflection lineshape and contribution from in-depth regions,"We analyze the resonant variation of the optical reflection on an infiltrated
artificial opal made of transparent nanospheres. The resonant infiltration is
considered as a perturbation in the frame of a previously described
one-dimensional model based upon a stratified effective index. We show that for
a thin slice of resonant medium, the resonant response oscillates with the
position of this slice. We derive that for adequate conditions of incidence
angle, this spatially oscillating behavior matches the geometrical periodicity
of the opal, and hence the related density of resonant infiltration. Close to
these matching conditions, the resonant response of the global infiltration
varies sharply in amplitude and shape with the incidence angle and
polarization. The corresponding resonant reflection originates from a rather
deep infiltration, up to several wavelengths or layers of spheres. Finally, we
discuss the relationship between the present predictions and our previous
observations on an opal infiltrated with a resonant vapor.",1506.01521v1
2015-08-31,Dissipation and resonance frequency shift of a resonator magnetically coupled to a semiclassical spin,"We calculate the change of the properties of a resonator, when coupled to a
semiclassical spin by means of the magnetic field. Starting with the Lagrangian
of the complete system, we provide an analytical expression for the linear
response function for the motion of the resonator, thereby considering the
influence of the resonator on the spin and vice versa. This analysis shows that
the resonance frequency and effective dissipation factor can change
significantly due to the relaxation times of the spin. We first derive this for
a system consisting of a spin and mechanical resonator and thereafter apply the
same calculations to an electromagnetic resonator. Moreover, the applicability
of the method is generalized to a resonator coupled to general two and more
level systems, providing a key to understand some of the problems of two level
systems in quantum devices.",1508.07972v2
2015-09-06,Creating a zero-order resonator using an optical surface transformation,"A novel zero-order resonator has been designed by an optical surface
transformation (OST) method. The resonator proposed here has many novel
features. Firstly, the mode volume can be very small (e.g. in the subwavelength
scale). Secondly, the resonator is open (no reflecting walls are utilized) and
resonant effects can be found in a continuous spectrum (i.e. a continuum of
eigenmodes). Thirdly, we only need one homogenous medium to realize the
proposed resonator. The shape of the resonator can be a ring structure of
arbitrary shape. In addition to the natural applications (e.g. optical storage)
of an optical resonator, we also suggest some other applications of our novel
optical open resonator (e.g. power combination, squeezing electromagnetic
energy in the free space).",1509.02552v1
2016-02-21,"Orbital Feshbach Resonance: A ""Wide"" Narrow Resonance for Higher Transition Temperature Fermi Superfluid","In this letter we show that the recently theoretically predicted and
experimentally observed ""orbital Feshbach resonance"" in alkali-earth-like
Yb-173 atom is a narrow resonance in energy, while it is hundreds Gauss wide in
term of magnetic field strength, taking the advantage that the magnetic moment
difference between the open and closed channels is quite small. Therefore this
is an ideal platform for the experimental realization of a strongly interacting
Fermi superfluid with narrow resonance. We show that the transition temperature
for the Fermi superfluid in this system, especially at the BCS side of the
resonance, is even higher than that in a wide resonance, which is also due to
the narrow character of this resonance. Our results will encourage experimental
efforts to realize Fermi superfluid in the alkali-earth-like Yb-173 system, the
properties of which will be complementary to extensively studied Fermi
superfluids nearby a wide resonance in alkali K-40 and Li-6 systems.",1602.06513v1
2016-03-08,Resonant enhancement of Raman scattering in metamaterials with hybrid electromagnetic and plasmonic resonances,"A tri-layer metamaterial perfect absorber of light, consisting of (Al/ZnS/Al)
films with the top aluminium layer patterned as an array of circular disk
nanoantennas, is investigated for resonantly enhancing Raman scattering from
C-60 fullerene molecules deposited on the metamaterial. The metamaterial is
designed to have resonant bands due to plasmonic and electromagnetic resonances
at the Raman pump frequency (725 nm) as well as Stokes emission bands. The
Raman scattering from C60 on the metamaterial with resonantly matched bands is
measured to be enhanced by an order of magnitude more than from C60 on
metamaterials with off-resonant absorption bands peaked at 1090 nm. The Raman
pump is significantly enhanced due to the resonance with a propagating surface
plasmon band, while the highly impedance matched electromagnetic resonance is
expected to couple out the Raman emission efficiently. The nature and
hybridization of the plasmonic and electromagnetic resonances to form compound
resonances are investigated by numerical simulations.",1603.02561v1
2016-04-12,Resonant capture of multiple planet systems under dissipation and stable orbital configurations,"Migration of planetary systems caused by the action of dissipative forces may
lead the planets to be trapped in a resonance. In this work we study the
conditions and the dynamics of such resonant trapping. Particularly, we are
interested in finding out whether resonant capture ends up in a long-term
stable planetary configuration. For two planet systems we associate the
evolution of migration with the existence of families of periodic orbits in the
phase space of the three-body problem. The family of circular periodic orbits
exhibits a gap at the 2:1 resonance and an instability and bifurcation at the
3:1 resonance. These properties explain the high probability of 2:1 and 3:1
resonant capture at low eccentricities. Furthermore, we study the resonant
capture of three-planet systems. We show that such a resonant capture is
possible and can occur under particular conditions. Then, from the migration
path of the system, stable three-planet configurations, either symmetric or
asymmetric, can be determined.",1604.03341v1
2016-06-21,On three-dimensional plasmon resonance in elastostatics,"We consider the plasmon resonance for the elastostatic system in
$\mathbb{R}^3$ associated with a very broad class of sources. The plasmonic
device takes a general core-shell-matrix form with the metamaterial located in
the shell. It is shown that the plasmonic device in the literature which
induces resonance in $\mathbb{R}^2$ does not induce resonance in
$\mathbb{R}^3$. We then construct two novel plasmonic devices with suitable
plasmon constants, varying according to the source term or the loss parameter,
which can induce resonances. If there is no core, we show that resonance always
occurs. If there is a core of an arbitrary shape, we show that the resonance
strongly depends on the location of the source. In fact, there exists a
critical radius such that resonance occurs for sources lying within the
critical radius, whereas resonance does not occur for source lying outside the
critical radius. Our argument is based on the variational technique by making
use of the primal and dual variational principles for the elastostatic system,
along with the highly technical construction of the associated perfect plasmon
elastic waves.",1606.06440v1
2016-07-19,Theoretical Investigation of Phonon Polaritons in SiC Micropillar Resonators,"Of late there has been a surge of interest in localised phonon polariton
resonators which allow for sub-diffraction confinement of light in the
mid-infrared spectral region by coupling to optical phonons at the surface of
polar dielectrics. Resonators are generally etched on deep substrates which
support propagative surface phonon polariton resonances. Recent experimental
work has shown that understanding the coupling between localised and
propagative surface phonon polaritons in these systems is vital to correctly
describe the system resonances. In this paper we comprehensively investigate
resonators composed of arrays of cylindrical SiC resonators on SiC substrates.
Our bottom-up approach, starting from the resonances of single, free standing
cylinders and isolated substrates, and exploiting both numerical and analytical
techniques, allows us to develop a consistent understanding of the parameter
space of those resonators, putting on firmer ground this blossoming technology.",1607.05741v1
2016-10-13,Quasi-perfect absorption by sub-wavelength acoustic panels in transmission using accumulation of resonances due to slow sound,"We theoretically and experimentally report sub-wavelength resonant panels for
low-frequency quasi-perfect sound absorption including transmission by using
the accumulation of cavity resonances due to the slow sound phenomenon. The
sub-wavelength panel is composed of periodic horizontal slits loaded by
identical Helmholtz resonators (HRs). Due to the presence of the HRs, the
propagation inside each slit is strongly dispersive, with near-zero phase
velocity close to the resonance of the HRs. In this slow sound regime, the
frequencies of the cavity modes inside the slit are down-shifted and the slit
behaves as a subwavelength resonator. Moreover, due to strong dispersion, the
cavity resonances accumulate at the limit of the bandgap below the resonance
frequency of the HRs. Near this accumulation frequency, simultaneously
symmetric and antisymmetric quasi-critical coupling can be achieved. In this
way, using only monopolar resonators quasi-perfect absorption can be obtained
in a material including transmission.",1610.04645v1
2017-03-31,Resonances for 1d Stark operators,"We consider the Stark operator perturbed by a compactly supported potential
(of a certain class) on the real line. We prove the following results: (a)
upper and lower bounds on the number of resonances in complex discs with large
radii,
  (b) the trace formula in terms of resonances only, (c) all resonances
determine the potential uniquely.",1703.10820v1
2017-08-01,First transneptunian object in polar resonance with Neptune,"Capture in mean motion resonance has been observed in the Solar System for
small objects with prograde as well as retrograde orbits of moderate
inclinations. However, no example of an object with a nearly polar orbit was
known to be in resonance with a planet. In this Letter, we report that the
nearly-polar transneptunian object (471325), nicknamed Niku, is in a 7:9
resonance with Neptune, with a mean lifetime in resonance of 16 +- 11 million
years. While entrance and exit in the 7:9 resonance is caused by close
encounters with Neptune the resonant configuration provides a temporary
protection mechanism against disruptive close encounters with this planet. The
other nearly polar transneptunian objects do not seem to be in resonance with
the planets with the possible exception of 2008 KV42, also known as Drac, that
has a small chance of being in the 8:13 resonance with Neptune.",1708.00346v1
2018-04-09,"Periodic oscillators, isochronous centers and resonance","An oscillator is called isochronous if all motions have a common period. When
the system is forced by a time-dependent perturbation with the same period the
dynamics may change and the phenomenon of resonance can appear. In this
context, resonance means that all solutions are unbounded. The theory of
resonance is well known for the harmonic oscillator and we extend it to
nonlinear isochronous oscillators.",1804.03127v2
2018-04-29,Dynamic portrait of the retrograde 1:1 mean motion resonance,"Asteroids in mean motion resonances with giant planets are common in the
solar system, but it was not until recently that several asteroids in
retrograde mean motion resonances with Jupiter and Saturn were discovered. A
retrograde co-orbital asteroid of Jupiter, 2015 BZ509 is confirmed to be in a
long-term stable retrograde 1:1 mean motion resonance with Jupiter, which gives
rise to our interests in its unique resonant dynamics. In this paper, we
investigate the phase-space structure of the retrograde 1:1 resonance in detail
within the framework of the circular restricted three-body problem. We
construct a simple integrable approximation for the planar retrograde resonance
using canonical contact transformation and numerically employ the averaging
procedure in closed form. The phase portrait of the retrograde 1:1 resonance is
depicted with the level curves of the averaged Hamiltonian. We thoroughly
analyze all possible librations in the co-orbital region and uncover a new
apocentric libration for the retrograde 1:1 resonance inside the planet's
orbit. We also observe the significant jumps in orbital elements for outer and
inner apocentric librations, which are caused by close encounters with the
perturber.",1804.10893v1
2018-11-01,Enhancement of Fluctuation-Induced Electromagnetic Phenomena in dynamically nonequilibrium systems at Resonant Photon Emission,"We study the resonances in Casimir friction, radiative heat transfer and heat
generation for two plates sliding relative to each other. Resonances have a
different origin in the frequency range of the \textit{normal} (NDE) and
\textit{anomalous} (ADE) Doppler effect. In the frequency range of NDE,
resonances are associated with resonant photon tunnelling between surface
phonon/plasmon polaritons of plates. For two identical plates, such resonances
exist only at a relative sliding velocity $v=0$. However, for different plates
such resonance can exist at $v\neq 0$. In the frequency range of ADE,
resonances are associated with the creation of excitations in both plates.
While in the frequency range of NDE the photon emission rate has an upper
limit, in the frequency range of ADE, the photon emission rate can diverge even
in the presence of dissipation in the system. We consider resonances for the
identical and different sliding plates. We discuss the possibility to detect
Casimir friction with its limiting case of quantum friction using an atomic
force microscope in graphene structures.",1811.00888v1
2019-05-20,Coupling Matrix Representation of Nonreciprocal Filters Based on Time Modulated Resonators,"This paper addresses the analysis and design of non-reciprocal filters based
on time modulated resonators. We analytically show that time modulating a
resonator leads to a set of harmonic resonators composed of the unmodulated
lumped elements plus a frequency invariant element that accounts for
differences in the resonant frequencies. We then demonstrate that harmonic
resonators of different order are coupled through non-reciprocal admittance
inverters whereas harmonic resonators of the same order couple with the
admittance inverter coming from the unmodulated filter network. This coupling
topology provides useful insights to understand and quickly design
non-reciprocal filters and permits their characterization using an
asynchronously tuned coupled resonators network together with the coupling
matrix formalism. Two designed filters, of orders three and four, are
experimentally demonstrated using quarter wavelength resonators implemented in
microstrip technology and terminated by a varactor on one side. The varactors
are biased using coplanar waveguides integrated in the ground plane of the
device. Measured results are found to be in good agreement with numerical
results, validating the proposed theory.",1905.08340v1
2020-07-22,Mathematical analysis of plasmon resonances for curved nanorods,"We investigate plasmon resonances for curved nanorods which present
anisotropic geometries. We analyze quantitative properties of the plasmon
resonance and its relationship to the metamaterial configurations and the
anisotropic geometries of the nanorods. Based on delicate and subtle asymptotic
and spectral analysis of the layer potential operators, particularly the
Neumann-Poincar\'e operators, associated with anisotropic geometries, we derive
sharp asymptotic formulae of the corresponding scattering field in the
quasi-static regime. By carefully analyzing the asymptotic formulae, we
establish sharp conditions that can ensure the occurrence of the plasmonic
resonance. The resonance conditions couple the metamaterial parameters, the
wave frequency and the nanorod geometry in an intricate but elegant manner. We
provide thorough resonance analysis by studying the wave fields both inside and
outside the nanorod. Furthermore, our quantitative analysis indicates that
different parts of the nanorod induce varying degrees of resonance.
Specifically, the resonant strength at the two end-parts of the curved nanorod
is more outstanding than that of the facade-part of the nanorod. This paper
presents the first theoretical study on plasmon resonances for nanostructures
within anisotropic geometries.",2007.11181v1
2014-03-30,"Resonance chains in open systems, generalized zeta functions and clustering of the length spectrum","In many non-integrable open systems in physics and mathematics resonances
have been found to be surprisingly ordered along curved lines in the complex
plane. In this article we provide a unifying approach to these resonance chains
by generalizing dynamical zeta functions. By means of a detailed numerical
study we show that these generalized zeta functions explain the mechanism that
creates the chains of quantum resonance and classical Ruelle resonances for
3-disk systems as well as geometric resonances on Schottky surfaces. We also
present a direct system-intrinsic definition of the continuous lines on which
the resonances are strung together as a projection of an analytic variety.
Additionally, this approach shows that the existence of resonance chains is
directly related to a clustering of the classical length spectrum on multiples
of a base length. Finally, this link is used to construct new examples where
several different structures of resonance chains coexist.",1403.7771v2
2017-01-17,Longitudinal near-field coupling between acoustic resonators grafted onto a waveguide,"We investigate longitudinal near-field coupling between acoustic resonators
grafted onto a waveguide. Experiments are performed in the audible range with a
simple acoustic system composed of a finite aperiodic sequence of air
resonators. Transmission typically shows a zero around a resonance frequency of
a single resonator, as is well known. When two identical resonators are brought
in close proximity, however, we observe that longitudinal near-field coupling
strongly influences the acoustic transmission. When the separation between
resonators is increased so that they can be considered in the far field of one
another, we further observe the appearance of Fano-like transmission profiles.
We explain this observation by the formation of locally resonant Fabry-Perot
interferometers from every pair of resonators. All experimental results are
compared to three-dimensional finite element analysis of the acoustic system.",1701.04654v1
2011-11-01,Feshbach resonances and their interaction in light scattering off photonic crystal slabs,"The concept of Feshbach resonances developed for quantum mechanical
scattering is applied in the analysis of classical light scattering off
photonic crystal slabs. It is shown that this concept can be realized almost
perfectly in these systems. As an application guided-mode resonances in the
grating waveguide structure (GWS) are studied in detail. Using simple resonance
dominance approximation the characteristic properties of isolated Feshbach
resonances in light scattering are exhibited. Formation and interaction of
overlapping resonances are investigated. The relevant parameters of the GWS are
identified which control the shape of the reflectivity of interacting
resonances as well as the enhancement of the electromagnetic field. The
differences in the properties of TE and TM resonances is emphasized for both
isolated and interacting resonances.",1111.0208v1
2011-11-01,Identifying Non-Resonant Kepler Planetary Systems,"The Kepler mission has discovered a plethora of multiple transiting planet
candidate exosystems, many of which feature putative pairs of planets near mean
motion resonance commensurabilities. Identifying potentially resonant systems
could help guide future observations and enhance our understanding of planetary
formation scenarios. We develop and apply an algebraic method to determine
which Kepler 2-planet systems cannot be in a 1st-4th order resonance, given the
current, publicly available data. This method identifies when any potentially
resonant angle of a system must circulate. We identify and list 70
near-resonant systems which cannot actually reside in resonance, assuming a
widely-used formulation for deriving planetary masses from their observed radii
and that these systems do not contain unseen bodies that affect the
interactions of the observed planets. This work strengthens the argument that a
high fraction of exoplanetary systems may be near resonance but not actually in
resonance.",1111.0299v1
2011-11-15,Resonances in Extreme Mass-Ratio Inspirals: Asymptotic and Hyperasymptotic Analysis,"An expected source of gravitational waves for future detectors in space are
the inspirals of small compact objects into much more massive black holes.
These sources have the potential to provide a wealth of information about
astronomy and fundamental physics. On short timescales the orbit of the small
object is approximately geodesic. Generic geodesics for a Kerr black hole
spacetime have a complete set of integrals and can be characterized by three
frequencies of the motion. Over the course of an inspiral, a typical system
will pass through resonances where two of these frequencies become
commensurate. The effect of the resonance will be to alter significantly the
rate of inspiral for the duration of the resonance. Understanding the impact of
these resonances on gravitational wave phasing is important to detect and
exploit these signals for astrophysics and fundamental physics. Two
differential equations that might describe the passage of an inspiral through
such a resonance are investigated. These differ depending on whether it is the
phase or the frequency components of a Fourier expansion of the motion that are
taken to be continuous through the resonance. Asymptotic and hyperasymptotic
analysis are used to find the late-time analytic behavior of the solution for a
system that has passed through a resonance. Linearly growing (weak resonances)
or linearly decaying (strong resonances) solutions are found depending on the
strength of the resonance. In the weak-resonance case, frequency resonances
leave an imprint (a resonant memory) on the gravitational frequency evolution.
The transition between weak and strong resonances is characterized by a
square-root singularity, and as one approaches this transition from above, the
solutions to the frequency resonance equation bunch up into families
exponentially fast.",1111.3605v1
2014-06-08,Storage and on-demand release of microwaves using superconducting resonators with tunable coupling,"We present a system which allows to tune the coupling between a
superconducting resonator and a transmission line. This storage resonator is
addressed through a second, coupling resonator, which is frequency-tunable and
controlled by a magnetic flux applied to a superconducting quantum interference
device (SQUID). We experimentally demonstrate that the lifetime of the storage
resonator can be tuned by more than three orders of magnitude. A field can be
stored for 18 {\mu}s when the coupling resonator is tuned off resonance and it
can be released in 14 ns when the coupling resonator is tuned on resonance. The
device allows capture, storage, and on-demand release of microwaves at a
tunable rate.",1406.2005v1
2016-05-02,Super-Resonant Intracavity Coherent Absorption,"The capability of optical resonators to extend the effective radiation-matter
interaction length originates from a multipass effect, hence is intrinsically
limited by the resonator quality factor. Here, we show that this constraint can
be overcome by combining the concepts of resonant interaction and coherent
perfect absorption. We demonstrate and investigate super-resonant coherent
absorption in a coupled Fabry-Perot-ring cavity structure. At the FP resonant
wavelengths, the described phenomenon gives rise to split modes with a
nearly-transparent peak and a peak whose transmission is exceptionally
sensitive to the intracavity loss. For small losses, the effective interaction
pathlength of these modes is proportional respectively to the ratio and the
product of the individual finesse coefficients of the two resonators. The
results presented extend the conventional definition of resonant absorption and
point to a way of circumventing the technological limitations of
ultrahigh-quality resonators in spectroscopy and optical sensing schemes",1605.00389v2
2016-05-02,Three types of nonlinear resonances,"We analyse different types of nonlinear resonances in a weakly damped Duffing
oscillator using bifurcation theory techniques. In addition to (i) odd
subharmonic resonances found on the primary branch of symmetric periodic
solutions with the forcing frequency and (ii) even subharmonic resonances due
to symmetry-broken periodic solutions that bifurcate off the primary branch and
also oscillate at the forcing frequency, we uncover (iii) novel resonance type
due to isolas of periodic solutions that are not connected to the primary
branch. These occur between odd and even resonances, oscillate at a fraction of
the forcing frequency, and give rise to a complicated resonance `curve' with
disconnected elements and high degree of multistability. We use bifurcation
continuation to compute resonance tongues in the plane of the forcing frequency
vs. the forcing amplitude for different but fixed values of the damping rate.
In this way, we demonstrate that identified here isolated resonances explain
the intriguing structure of ""patchy tongues"" observed for week damping and link
it to a seemingly unrelated phenomenon of ""bifurcation superstructure""
described for moderate damping.",1605.00858v2
2016-05-12,Resonance Beyond Frequency-Matching,"Resonance, defined as the oscillation of a system when the temporal frequency
of an external stimulus matches a natural frequency of the system, is important
in both fundamental physics and applied disciplines. However, the spatial
character of oscillation is not considered in the definition of resonance. In
this work, we reveal the creation of spatial resonance when the stimulus
matches the space pattern of a normal mode in an oscillating system. The
complete resonance, which we call multidimensional resonance, is a combination
of both the spatial and the conventionally defined (temporal) resonance and can
be several orders of magnitude stronger than the temporal resonance alone. We
further elucidate that the spin wave produced by multidimensional resonance
drives considerably faster reversal of the vortex core in a magnetic nanodisk.
Our findings provide insight into the nature of wave dynamics and open the door
to novel applications.",1605.03649v2
2016-08-03,Probing the resonance of Dirac particle by the application of complex momentum representation,"Resonance plays critical roles in the formation of many physical phenomena,
and several methods have been developed for the exploration of resonance. In
this work, we propose a new scheme for resonance by solving the Dirac equation
in complex momentum representation, in which the resonant states are exposed
clearly in complex momentum plane and the resonance parameters can be
determined precisely without imposing unphysical parameters. Combining with the
relativistic mean-field theory, this method is applied to probe the resonances
in $^{120}$Sn with the energies, widths, and wavefunctions being obtained.
Comparing with other methods, this method is not only very effective for narrow
resonances, but also can be reliably applied to broad resonances.",1608.01046v1
2016-08-17,Electron Spin Resonance at the Level of 10000 Spins Using Low Impedance Superconducting Resonators,"We report on electron spin resonance (ESR) measurements of phosphorus donors
localized in a 200 square micron area below the inductive wire of a lumped
element superconducting resonator. By combining quantum limited parametric
amplification with a low impedance microwave resonator design we are able to
detect around 20000 spins with a signal-to-noise ratio (SNR) of 1 in a single
shot. The 150 Hz coupling strength between the resonator field and individual
spins is significantly larger than the 1 - 10 Hz coupling rates obtained with
typical coplanar waveguide resonator designs. Due to the larger coupling rate,
we find that spin relaxation is dominated by radiative decay into the resonator
and dependent upon the spin-resonator detuning, as predicted by Purcell.",1608.05130v2
2016-08-27,"Fano resonances in dielectric, metallic and metamaterial photonic structures","We investigate numerically Fano resonances excited in periodic arrays of
dielectric, metallic and left-handed cylinders. Of particular interest are Fano
resonances excited in the linear array of cylin- ders. We analyze spatial
distribution and symmetry of electromagnetic field and discuss the relation
between observed Fano resonances and frequency spectra of two-dimensional
arrays of cylinders.",1608.07716v1
2016-12-02,Probing the resonance in the Dirac equation with quadruple-deformed potentials by complex momentum representation method,"Resonance plays critical roles in the formation of many physical phenomena,
and many techniques have been developed for the exploration of resonance. In a
recent letter [Phys. Rev. Lett. 117, 062502 (2016)], we proposed a new method
for probing single-particle resonances by solving the Dirac equation in complex
momentum representation for spherical nuclei. Here, we extend this method to
deformed nuclei with theoretical formalism presented. We elaborate numerical
details, and calculate the bound and resonant states in $^{37}$Mg. The results
are compared with those from the coordinate representation calculations with a
satisfactory agreement. In particular, the present method can expose clearly
the resonant states in complex momentum plane and determine precisely the
resonance parameters for not only narrow resonances but also broad resonances
that were difficult to obtain before.",1612.00527v1
2016-12-15,Testing universality of Efimov physics across broad and narrow Feshbach resonances,"Efimov physics is a universal phenomenon arising in quantum three-body
systems. For systems with resonant two-body interactions, Efimov predicted an
infinite series of three-body bound states with geometric scaling symmetry.
These Efimov states were first observed in cold Cs atoms and have since been
reported in a variety of atomic systems. While theories predict non-universal
behavior for narrow Feshbach resonances, experiments on Efimov resonances are
so far consistent with predictions based on universal theories. Here we
directly compare the Efimov spectra in a $^6$Li-$^{133}$Cs mixture near two
Feshbach resonances which are very different in their resonance strengths but
otherwise almost identical. Our result shows a clear dependence of the Efimov
resonance positions on Feshbach resonance strength and a clear departure from
the universal prediction for the narrow Feshbach resonance.",1612.05169v1
2017-07-25,Molecular predissociation resonances below an energy level crossing,"We study the resonances of $2\times 2$ systems of one dimensional
Schr\""odinger operators which are related to the mathematical theory of
molecular predissociation. We determine the precise positions of the resonances
with real parts below the energy where bonding and anti-bonding potentials
intersect transversally. In particular, we find that imaginary parts (widths)
of the resonances are exponentially small and that the indices are determined
by Agmon distances for the minimum of two potentials.",1707.07963v1
2017-10-24,Universal Feature in Optical Control of a p-wave Feshbach Resonance,"In this Letter we report the experimental results on optical control of a
p-wave Feshbach resonance, by utilizing a laser driven bound-to-bound
transition to shift the energy of closed channel molecule. The magnetic field
location for p-wave resonance as a function of laser detuning can be captured
by a simple formula with essentially one parameter, which describes how
sensitive the resonance depends on the laser detuning. The key result of this
work is to demonstrate, both experimentally and theoretically, that the ratio
between this parameter for $m=0$ resonance and that for $m=\pm 1$ resonance, to
large extent, is universal. We also show that this optical control can create
intriguing situations where interesting few- and many-body physics can occurs,
such as a p-wave resonance overlapping with an s-wave resonance or three p-wave
resonances being degenerate.",1710.08636v3
2018-09-13,Improving the read-out of the resonance frequency of nanotube mechanical resonators,"We report on an electrical detection method of ultrasensitive carbon nanotube
mechanical resonators. The noise floor of the detection method is reduced using
a RLC resonator and an amplifier based on a high electron mobility transistor
cooled at 4.2 K. This allows us to resolve the resonance frequency of nanotube
resonators with an unprecedented quality. We show that the noise of the
resonance frequency measured at 4.2 K is limited by the resonator itself, and
not by the imprecision of the measurement. The Allan deviation reaches ~10^-5
at 125 ms integration time. When comparing the integration time dependence of
the Allan deviation to a power law, the exponent approaches ~1/4. The Allan
deviation might be limited by the diffusion of particles over the surface of
the nanotube. Our work holds promise for mass spectrometry and surface science
experiments based on mechanical nano-resonators.",1809.04915v1
2019-06-30,Computing resonant modes of circular cylindrical resonators by vertical mode expansions,"Open subwavelength cylindrical resonators of finite height are widely used in
various photonics applications. Circular cylindrical resonators are
particularly important in nanophotonics, since they are relatively easy to
fabricate and can be designed to exhibit different resonance effects. In this
paper, an efficient and robust numerical method is developed for computing
resonant modes of circular cylinders which may have a few layers and may be
embedded in a layered background. The resonant modes are complex-frequency
outgoing solutions of the Maxwell's equations with no sources or incident
waves. The method uses field expansions in one-dimensional (1D) ``vertical''
modes to reduce the original three-dimensional eigenvalue problem to 1D
problems, and uses Chebyshev pseudospectral method to compute the 1D modes and
set up the discretized eigenvalue problem. In addition, a new iterative scheme
is developed so that the 1D nonlinear eigenvalue problems can be reliably
solved. For metallic cylinders, the resonant modes are calculated based on
analytic models for the dielectric functions of metals. The method is validated
by comparisons with existing numerical results, and it is also used to explore
subwavelength dielectric cylinders with high-$Q$ resonances and analyze gold
nanocylinders.",1907.00340v1
2019-06-30,Multi-resonant high-Q plasmonic metasurfaces,"Resonant metasurfaces are devices composed of nanostructured sub-wavelength
scatterers that generate narrow optical resonances, enabling applications in
filtering, nonlinear optics, and molecular fingerprinting. It is highly
desirable for these applications to incorporate such devices with multiple,
high-quality-factor resonances; however, it can be challenging to obtain more
than a pair of narrow resonances in a single plasmonic surface. Here, we
demonstrate a multi-resonant metasurface that operates by extending the
functionality of surface lattice resonances, which are the collective responses
of arrays of metallic nanoparticles. This device features a series of
resonances with high quality factors (Q ~ 40), an order of magnitude larger
than what is typically achievable with plasmonic nanoparticles, as well as a
narrow free spectral range. This design methodology can be used to better
tailor the transmission spectrum of resonant metasurfaces and represents an
important step towards the miniaturization of optical devices.",1907.00458v3
2019-07-17,Magneto-optical resonances in fluorescence from sodium D2 manifold,"We report on magneto-optical resonances observed in sodium fluorescence from
D2 manifold with an intensity modulated light. Fluorescence resonances are
measured in the perpendicular and backward directions to the light propagation,
in laboratory experiments using a sodium cell containing neon buffer gas.
Properties of these resonances are studied by varying the magnetic field at
fixed light modulation frequency, and vice-versa. Modulation with low-duty
cycle shows higher-harmonic resonances of the modulation frequency and
sub-harmonic resonances of the Larmor frequency. A dark resonance with maximum
amplitude for laser wavelength closer to the crossover peak is observed. The
origin of this dark resonance observed in Na D2 line is discussed using a
theoretical model. Present study is aimed towards improving the understanding
of magneto-optical resonances for remote magnetometry applications with
mesospheric sodium.",1907.07701v2
2019-07-22,Multiplanet systems in inviscid discs can avoid forming resonant chains,"Convergent migration involving multiple planets embedded in a viscous
protoplanetary disc is expected to produce a chain of planets in mean motion
resonances, but the multiplanet systems observed by the Kepler spacecraft are
generally not in resonance. We demonstrate that under equivalent conditions,
where in a viscous disc convergent migration will form a long-term stable
system of planets in a chain of mean motion resonances, migration in an
inviscid disc often produces a system which is highly dynamically unstable. In
particular, if planets are massive enough to significantly perturb the disc
surface density and drive vortex formation, the smooth capture of planets into
mean motion resonances is disrupted. As planets pile up in close orbits, not
protected by resonances, close encounters increase the probability of
planet-planet collisions, even while the gas disc is still present. While
inviscid discs often produce unstable non-resonant systems, stable, closely
packed, non-resonant systems can also be formed. Thus, when examining the
expectation for planet migration to produce planetary systems in mean motion
resonances, the effective turbulent viscosity of the protoplanetary disc is a
key parameter.",1907.09313v1
2019-09-18,Efficient Photonic Crystal Parametric Source harnessing high-Q resonances,"A new tuning mechanism is introduced in high-Q multimode photonic crystal
resonators allowing to harness the resonant enhancement of the parametric
resonance systematically. As a consequence, ultra-efficient stimulated and
spontaneous Four Wave Mixing at continuous microWatt pumping levels are
observed, and the scaling with Q is demonstrated. Experimental results are in
perfect agreement with an analytical model without fitting parameters.",1909.08717v1
2019-09-22,Some properties of threshold eigenstates and resonant states of discrete Schrödinger operators,"In this note, we study some properties of threshold resonant states or
threshold eigenfunctions for discrete Schr\""odinger operators. We mainly prove
two theorems. First, we prove that resonant states at the elliptic threshold
have the same asymptotic expansion as the continuous Schr\""odinger operator.
Second, we prove absence of resonant states at hyperbolic thresholds",1909.10014v1
2020-12-05,On Periodical Damping Ratio of a Controlled Dynamical System with Parametric Resonances,"This report provides an interpretation on the periodically varying damping
ratio of a dynamical system with direct control of oscillation or vibration
damping. The principal parametric resonance of the system and a new type of
parametric resonance, named ""zero-th order"" parametric resonance, are
investigated by using the method of multiple scales to find approximate,
analytical solutions of the system, which provide an interpretation on such
damping variations.",2012.02932v1
2012-05-22,Carbon nanotubes: Nonlinear high-Q resonators with strong coupling to single-electron tunneling,"Carbon nanotubes (CNTs) are nonlinear high-Q resonators with strong coupling
to single-electron tunneling. We begin by describing several methods to detect
the flexural motion of a CNT resonator. Next, we illustrate how single-electron
tunneling in quantum dot CNT resonators leads to sharp dips in the mechanical
resonance frequency and significant damping. We discuss four different
contributions to the nonlinear oscillation of a CNT resonator: beam-like
mechanical nonlinearity, nonlinearity due to gate-induced mechanical tension,
electrostatic nonlinearity, and nonlinearity due to single-electron tunneling,
and provide quantitative estimates of their strengths. Finally, we show how the
large response of the resonance frequency of a CNT resonator to a change in
gate voltage or tension makes CNT resonators ideally suited for parametric
excitation and for studying the coupling between different mechanical modes.",1205.4921v1
2017-05-16,Resonant lattice Kerker effect in metasurfaces with electric and magnetic optical responses,"To achieve efficient light control at subwavelength dimensions, plasmonic and
all-dielectric nanoparticles have been utilized both as a single element as
well as in the arrays. Here we study 2D periodic nanoparticle arrays
(metasurfaces) that support lattice resonances near the Rayleigh anomaly due to
the electric dipole (ED) and magnetic dipole (MD) resonant coupling between the
nanoparticles. Silicon and core-shell particles are considered. We demonstrate
for the first time that, choosing of lattice periods independently in each
mutual-perpendicular direction, it is possible to achieve a full overlap
between the ED-lattice resonance and MD resonances of nanoparticles in certain
spectral range and to realize the resonant lattice Kerker effect (resonant
suppression of the scattering or reflection). At the effect conditions, the
strong suppression of light reflectance in the structure is appeared due to
destructive interference between electromagnetic waves scattered by ED and MD
moments of every nanoparticle in the backward direction with respect to the
incident light wave. Influence of the array size on the revealed reflectance
and transmittance behavior is discussed. The resonant lattice Kerker effect
based on the overlap of both ED and MD lattice resonances is also demonstrated.",1705.05533v1
2018-07-17,Nature of isoscalar dipole resonances in heavy nuclei,"Isoscalar dipole nuclear response reveals the low- and high-energy
resonances. The nature of isoscalar dipole resonances in heavy spherical nuclei
is studied by using the translation-invariant kinetic model of small
oscillations of finite Fermi systems. Calculations of the velocity field at the
centroid energy show a pure vortex character of the low-energy isoscalar dipole
resonance in spherical nuclei and confirm the anisotropic compression character
of the high-energy one. The evolution of the velocity field in dependence on
the excitation energy of the nucleus within the resonance width is studied. It
is found that the low-energy isoscalar dipole resonance retains a vortex
character while with increasing energy this collective excitation also involves
compression. The high-energy resonance keeps the compression character with a
change in the excitation energy within the resonance width but the
compression-expansion region of the velocity field related to this resonance
shifts inside the nucleus.",1807.06407v1
2018-07-18,Coupled-Ring Resonance and Unitary Groups,"The group-theoretic content of photonic coupled microrings resonance
phenomena is shown, in particular, an interesting emergence of pseudo-unitary
group. The application to the resonance condition in a tri-microring
configuration is solved exactly. A practical application of this work will be
in the resonance frequency tuning based on the coupling coefficient, in
particular, the Mach-Zehnder interferometer approach was analyzed for the
coupling modulation.",1807.06773v1
2019-02-28,"A compact structure for realizing Lorentzian, Fano and EIT resonance lineshapes in a microring resonator","Microring resonators, as a fundamental building block of photonic integrated
circuits, have been well developed into numerous functional devices, whose
performances are strongly determined by microring's resonance lineshapes. We
propose a compact structure to reliably realize Lorentzian, Fano, and
electromagnetically induced transparency (EIT) resonance lineshapes in a
microring. By simply inserting two air-holes in the side-coupled waveguide of a
microring, a Fabry-Perot (FP) resonance is involved to couple with microring's
resonant modes, showing Lorentzian, Fano, and EIT lineshapes over one free
spectral range of the FP resonance. The quality factors, extinction ratios, and
slope rates in different lineshapes are discussed. At microring's specific
resonant wavelength, the lineshape could be tuned among these three types by
controlling the FP cavity's length. Experiment results verify the theoretical
analysis well and represent Fano lineshapes with extinction ratios of about 20
dB and slope rates over 280 dB/nm. The reliably and flexibly tunable lineshapes
in the compact structure have potentials to improve microring-based devices and
expand their application scopes.",1902.10902v1
2019-03-05,Efficient self-resonance instability from axions,"It was recently shown that a coherent oscillation of an axion can cause an
efficient parametric resonance, leading to a prominent emission of the
gravitational waves (GWs). In this paper, conducting the Floquet analysis, we
investigate the parametric resonance instability, which potentially triggers
the emission of the GWs from axions. Such a resonance instability takes place,
when the time evolution of the background field significantly deviates from the
harmonic oscillation. Therefore, the resonance instability cannot be described
by the Mathieu equation, whose stability/instability chart is well known. In
this paper, introducing an explicitly calculable parameter $\tilde{q}$, which
can be used to classify different types of the parametric resonance described
by the general Hill's equation, we investigate the stability/instability chart
for the general Hill's equation. This can also apply to the case where the
background oscillation is anharmonic. We show that the flapping resonance
instability, which takes place for $\tilde{q}=O(1)$, typically leads to the
most significant growth of the inhomogeneous modes among the self-resonance
instability. We also investigate whether the flapping resonance takes place for
the cosine potential or not.",1903.02119v2
2019-03-29,Structure of resonances in a square well potential,"We study the structure of resonances as derived from the exactly solvable
Lippmann-Schwinger equation for a one-dimensional square well potential. Within
this framework, we discuss the concept of resonance form factors, and the
relation of the corresponding spatial densities to ``resonance wave
functions''.",1904.00823v1
2019-11-16,Post- versus pre-resonance characteristics of axially excited chiral sculptured thin films,"Axially excited chiral sculptured thin films (STFs) are shown to exhibit the
circular Bragg phenomenon in the pre-resonant (long-wavelength) regime but not
in some parts of the post-resonant (short-wavelength) regime. Chiral STFs act
as very good polarization-independent reflectors in the vicinity of material
resonances in the latter regime.",1911.06984v1
2020-03-11,Mitigation of Resonances in Sinuous Antennas,"Sinuous antennas are capable of producing ultra-wideband radiation with
polarization diversity. Such a capability makes the sinuous antenna an
attractive candidate for wideband polarimetric radar applications.
Additionally, the ability of the sinuous antenna to be implemented as a planar
structure makes it a good fit for close in sensing applications such as ground
penetrating radar. However, recent literature has shown the sinuous antenna to
suffer from resonances which degrade performance. Such resonances produce late
time ringing which is particularly troubling for pulsed close in sensing
applications. The resonances occur in two forms: log-periodic resonances on the
arms, and a resonance due to the outer truncation of the sinuous antenna
geometry. A detailed investigation as to the correlation between the
log-periodic resonances and the sinuous antenna design parameters indicates the
resonances may be mitigated by selecting appropriate parameters. In addition,
the resonance due to truncation may be mitigated by moving the circular
truncation to the tip of the outermost cell which has advantages over the
clipping method proposed in the literature.",2003.05072v1
2020-06-11,Feshbach Resonances in an Erbium-Dysprosium Dipolar Mixture,"We report on the observation of heteronuclear magnetic Feshbach resonances in
several isotope mixtures of the highly magnetic elements erbium and dysprosium.
Among many narrow features, we identify two resonances with a width greater
than one Gauss. We characterize one of these resonances, in a mixture of
$^{168}$Er and $^{164}$Dy, in terms of loss rates and elastic cross section,
and observe a temperature dependence of the on-resonance loss rate suggestive
of a universal scaling associated with broad resonances. Our observations hold
promise for the use of such a resonance for tuning the interspecies scattering
properties in a dipolar mixture. We further compare the prevalence of narrow
resonances in an $^{168}$Er-$^{164}$Dy mixture to the single-species case, and
observe an increased density of resonances in the mixture.",2006.06456v1
2020-10-24,Octave-Tunable Magnetostatic Wave YIG Resonators on a Chip,"We have designed, fabricated, and characterized magnetostatic wave (MSW)
resonators on a chip. The resonators are fabricated by patterning
single-crystal yttrium iron garnet (YIG) film on a gadolinium gallium garnet
(GGG) substrate and excited by loop-inductor transducers. We achieved this
technology breakthrough by developing a YIG film etching process and
fabricating thick aluminum coplanar waveguide (CPW) inductor loop around each
resonator to individually address and excite MSWs. At 4.77 GHz, the 0.68 square
mm resonator achieves a quality factor Q > 5000 with a bias field of 987 Oe. We
also demonstrate YIG resonator tuning by more than one octave from 3.63 to 7.63
GHz by applying an in-plane external magnetic field. The measured quality
factor of the resonator is consistently over 3000 above 4 GHz. The
micromachining technology enables the fabrication of multiple single- and
two-port YIG resonators on the same chip with all resonators demonstrating
octave tunability and high Q .",2010.12732v1
2021-05-22,Fully symmetric controllable integrated three-resonator photonic molecule,"Photonic molecules can be used to realize complex optical energy states and
modes, analogous to those found in molecules, with properties useful for
applications like spectral engineering and quantum optics. It is desirable to
implement photonic molecules using high quality factor photonic integrated ring
resonators due to their narrow atom-like spectral resonance, tunability, and
the ability to scale the number of resonators on a photonic circuit. However,
to take full advantage of molecule spectral complexity and tuning degree of
freedom, resonator structures should have full symmetry in terms of
inter-resonator coupling and resonator-waveguide coupling as well as
independent resonance tuning, and low power dissipation operation, in a
scalable integration platform. To date, photonic molecule symmetry has been
limited to dual- and triple-cavity geometries coupled to single- or
dual-busses, and resonance tuning limited to dual resonator molecules. In this
paper, we demonstrate a three-resonator photonic molecule, consisting of
symmetrically coupled 8.11 million intrinsic Q silicon nitride rings, where
each ring is coupled to the other two rings. The resonance of each ring, and
that of the collective molecule, is controlled using low power dissipation,
monolithically integrated thin-film lead zirconate titanate (PZT) actuators
that are integrated with the ultra-low loss silicon nitride resonators. This
performance is achieved without undercut waveguides, yielding the highest Q to
date for a PZT controlled resonator. This advance leads to full control of
complex photonic molecule resonance spectra and splitting in a wafer-scale
integration platform. The resulting six tunable supermodes can be fully
controlled, including degeneracy, location and splitting as well as designed by
a model that can accurately predict the energy modes and transmission spectrum
and tunable resonance splitting.",2105.10815v1
2021-06-25,Resonance refraction and neutrino oscillations,"The refraction index and matter potential depend on neutrino energy and this
dependence has a resonance character associated to the production of the
mediator in the $s-$channel. For light mediators and light particles of medium
(background) the resonance can be realized at energies accessible to laboratory
experiments. We study properties of the energy dependence of the potential for
different C-asymmetries of background. Interplay of the background potential
and the vacuum term leads to (i) bump in the oscillation probability in the
resonance region, (ii) dip related to the MSW resonance in the background,
(iii) substantial deviation of the effective $\Delta m^2$ above the resonance
from the low energy value, etc. We considered generation of mixing in the
background. Interactions with background shifts the energy of usual MSW
resonance and produces new MSW resonances. Searches of the background effects
allow us to put bounds on new interactions of neutrinos and properties of the
background. We show that explanation of the MiniBooNE excess, as the bump due
to resonance refraction, is excluded.",2106.13829v1
2021-07-21,Spin-wave growth via Shapiro resonances in a spinor Bose-Einstein condensate,"We theoretically study the resonant phenomenon in a spin-1 Bose-Einstein
condensate periodically driven by a quadratic Zeeman coupling. This phenomenon
is closely related to the Shapiro steps in superconducting Josephson junctions,
and the previous experimental work [Evrard $et al.,$ Phys. Rev. A 100, 023604
(2019)] for a spin-1 bosonic system observed the resonant dynamics and then
called it Shapiro resonance. In this work, using the spin-1 Gross-Pitaevskii
equation, we study the Shapiro resonance beyond the single-mode approximation
used in the previous work, which assumes that all components of the spinor
wavefunction have the same spatial configuration. Considering resonant dynamics
starting from a polar state, we analytically calculate the Floquet-Lyapunov
exponents featuring an onset of the resonance under a linear analysis and find
that spin waves with finite wavenumbers can be excited. This kind of
non-uniform excitation cannot be described by the single-mode approximation.
Furthermore, to study the long-time resonant dynamics beyond the linear
analysis, we numerically solve the one-dimensional spin-1 Gross-Pitaevskii
equation, finding that the nonresonant hydrodynamic variables also grow at
wavelengths of even multiples of the resonant one due to the nonlinear effect.",2107.09924v1
2021-07-21,Parametric longitudinal coupling between a high-impedance superconducting resonator and a semiconductor quantum dot singlet-triplet spin qubit,"Long-distance two-qubit coupling, mediated by a superconducting resonator, is
a leading paradigm for performing entangling operations in a quantum computer
based on spins in semiconducting materials. Here, we demonstrate a novel,
controllable spin-photon coupling based on a longitudinal interaction between a
spin qubit and a resonator. We show that coupling a singlet-triplet qubit to a
high-impedance superconducting resonator can produce the desired longitudinal
coupling when the qubit is driven near the resonator's frequency. We measure
the energy splitting of the qubit as a function of the drive amplitude and
frequency of a microwave signal applied near the resonator antinode, revealing
pronounced effects close to the resonator frequency due to longitudinal
coupling. By tuning the amplitude of the drive, we reach a regime with
longitudinal coupling exceeding $1$ MHz. This demonstrates a new mechanism for
qubit-resonator coupling, and represents a stepping stone towards producing
high-fidelity two-qubit gates mediated by a superconducting resonator.",2107.10269v1
2021-09-03,Probing double hadron resonances by the complex scaling method,"Many newly discovered excited states are interpreted as bound states of
hadrons. Can these hadrons also form resonant states? In this paper, we extend
the complex scaling method (CSM) to calculate the bound state and resonant
state consistently for the $\Lambda_c D(\bar D)$ and $\Lambda_c \Lambda_c (\bar
\Lambda_c)$ systems. For these systems, the $\pi, \eta, \rho$ meson exchange
contributions are suppressed, the contributions of intermediate- and
short-range forces from $\sigma/\omega$ exchange are dominant. Our results
indicate that $\Lambda_c D$ system can not form bound state and resonant state.
There exist resonant states in a wide range of parameters for $\Lambda_c \bar
D$ and $\Lambda_c \Lambda_c (\bar \Lambda_c)$ systems. For these systems, the
larger bound state energy, the easier to form resonant states. Among all the
resonant states, the energies and widths of the P wave resonant states are
smaller and more stable, which is possible to be observed in the experiments.
The energies of D and F wave resonant states can reach dozens of MeV and the
widths can reach hundreds of MeV.",2109.01259v1
2021-12-09,Collective resonance of $D$ states in rubidium atoms probed by optical two-dimensional coherent spectroscopy,"Collective resonance of interacting particles has important implications in
many-body quantum systems and their applications. Strong interactions can lead
to a blockade that prohibits the excitation of a collective resonance of two or
more nearby atoms. However, a collective resonance can be excited with the
presence of weak interaction and has been observed for atoms in the first
excited state ($P$ states). Here, we report the observation of collective
resonance of rubidium atoms in a higher excited state ($D$ states) in addition
to the first excited state. The collective resonance is excited by a
double-quantum four-pulse excitation sequence. The resulting double-quantum
two-dimensional (2D) spectrum displays well-isolated peaks that can be
attributed to collective resonances of atoms in $P$ and $D$ states. The
experimental one-quantum and double-quantum 2D spectra can be reproduced by a
simulation based on the perturbative solutions to the optical Bloch equations,
confirming collective resonances as the origin of the measured spectra. The
experimental technique provides a new approach for preparing and probing
collective resonances of atoms in highly excited states.",2112.04642v1
2021-12-31,Microscopy of an ultranarrow Feshbach resonance using a laser-based atom collider: A quantum defect theory analysis,"We employ a quantum defect theory framework to provide a detailed analysis of
the interplay between a magnetic Feshbach resonance and a shape resonance in
cold collisions of ultracold $\rm ^{87}Rb$ atoms as captured in recent
experiments using a laser-based collider [Phys. Rev. Research 3, 033209
(2021)]. By exerting control over a parameter space spanned by both collision
energy and magnetic field, the width of a Feshbach resonance can be tuned over
several orders of magnitude. We apply a quantum defect theory specialized for
ultracold atomic collisions to fully describe of the experimental observations.
While the width of a Feshbach resonance generally increases with collision
energy, its coincidence with a shape resonance leads to a significant
additional boost. By conducting experiments at a collision energy matching the
shape resonance and using the shape resonance as a magnifying lens we
demonstrate a feature broadening to a magnetic width of 8 G compared to a
predicted Feshbach resonance width $\ll 0.1$~mG.",2112.15416v3
2022-03-16,Elastodynamical resonances and cloaking of negative material structures beyond quasistatic approximation,"Given the flexibility of choosing negative elastic parameters, we construct
material structures that can induce two resonance phenomena, referred to as the
elastodynamical resonances. They mimic the emerging plasmon/polariton resonance
and anomalous localized resonance in optics for subwavelength particles.
However, we study the peculiar resonance phenomena for linear elasticity beyond
the subwavelength regime. It is shown that the resonance behaviours possess
distinct characters, with some similar to the subwavelength resonances, but
some sharply different due to the frequency effect. It is particularly noted
that we construct a core-shell material structure that can induce anomalous
localized resonance as well as cloaking phenomena beyond the quasi-static
limit. The study is boiled down to analyzing the so-called elastic
Neumann-Poinc\'are (N-P) operator in the frequency regime. We provide an
in-depth analysis of the spectral properties of the N-P operator beyond the
quasi-static approximation,and these results are of independent interest to the
spectral theory of layer potential operators.",2203.08432v1
2022-05-02,Off-resonance artifact correction for magnetic resonance imaging: a review,"In magnetic resonance imaging (MRI), inhomogeneity in the main magnetic field
used for imaging, referred to as off-resonance, can lead to image artifacts
ranging from mild to severe depending on the application. Off-resonance
artifacts, such as signal loss, geometric distortions, and blurring, can
compromise the clinical and scientific utility of MR images. In this review, we
describe sources of off-resonance in MRI, how off-resonance affects images, and
strategies to prevent and correct for off-resonance. Given recent advances and
the great potential of low field and/or portable MRI, we also highlight the
advantages and challenges of imaging at low field with respect to
off-resonance.",2205.01028v2
2022-07-06,Spectral correlation between surface-enhanced resonant Raman and far field scattering destructed by dipole quadrupole coupled plasmon resonance,"The spectral relationships between surface enhanced resonant Raman scattering
(SERRS) and plasmon resonance observed in far field scattering cross are
investigated using single silver nanoparticle dimers with focusing on the
lowest energy (superradiant) plasmon resonance. We find that these
relationships can be classified into two types. The first is SERRS spectral
envelopes with spectral shapes similar to those of plasmon resonance spectra.
The second is SERRS envelopes exhibiting higher energy shifts from the plasmon
resonance spectra. These results are examined as an effect of degree of
morphological asymmetry in dimers based on an electromagnetic (EM) mechanism.
The analysis of the first and second types reveals that dipole-dipole and
dipole-quadrupole coupled plasmon resonance (subradiant Fano resonance)
respectively determine the EM enhancement. This mechanism is commonly important
for the development of plasmonic nanostructures for various surface enhanced
spectroscopies.",2207.02513v2
2022-09-25,ATLAS results on exotic hadronic resonances,"Recent results from the proton-proton collision data taken by the ATLAS
experiment on exotic resonances are presented. A search for $J/\psi p$
resonances in $\Lambda_{b}\rightarrow J/\psi p K$ decays with large $p K$
invariant masses is reported. A search for exotic resonances in the four-muon
final state is shown.",2209.12173v3
2022-12-17,Characteristics of partially filled Helmholtz resonators,"In this work we have developed a technique for the measurement of the
resonance curve of Helmholtz resonators as a function of filling with beads and
sands of different sizes, and water as the reference. Our measurements allowed
us to observe very different behaviors of resonance frequencies and resonance
half-widths as a function of the size of the sand grains and the beads. By
comparing results for beads and water we were able to prove that the sound
penetrates the interstitial space between the beads. This was confirmed by
measurements of the resonance properties in resonators filled with spherical
beads whose experimentally determined filling factor is close to the random
filling factor of about 0.54. The similar behavior of the frequency and
half-width of resonance of sand-filled resonators of three different sizes
allowed us to suggest that sound penetrates the sand in the same way as it does
the beads.",2212.08858v1
2022-12-22,Resonant contributions to polarized proton structure functions,"Nucleon resonance contributions to the polarized proton $g_1$ and $g_2$
structure functions are computed from resonance electroexcitation amplitudes
extracted from CLAS exclusive meson electroproduction data. Including
resonances in the mass range up to 1.75 GeV, and taking into account the
interference between excited states, we compare the resonant contributions with
the polarized proton structure function and polarization asymmetry data from
Jefferson Lab 6 GeV measurements. All resonance-like structure observed in the
polarized structure functions and asymmetries can be attributed to the resonant
contributions, confirming their essential role in the behavior of $g_1$ and
$g_2$ in the resonant region over the entire range $Q^2 < 7.5$ GeV$^2$ covered
by the measurements. Comparing the resonance contributions with the $g_1$ and
$g_2$ structure functions computed from parton distribution functions
extrapolated from the deep-inelastic region, we also quantify the degree to
which quark-hadron duality holds for $g_1$ and $g_2$ and their moments.",2212.11952v2
2023-06-13,Outerplane bipartite graphs with isomorphic resonance graphs,"We present novel results related to isomorphic resonance graphs of
2-connected outerplane bipartite graphs. As the main result, we provide a
structure characterization for 2-connected outerplane bipartite graphs with
isomorphic resonance graphs. Moreover, two additional characterizations are
expressed in terms of resonance digraphs and via local structures of inner
duals of 2-connected outerplane bipartite graphs, respectively.",2306.07611v1
2023-07-10,On the experimental description of neutron resonances,"We present a collection of simple derivations for the neutron-induced
resonance cross-sections. These formulae are commonly used to experimentally
describe the fundamental properties of resonances for neutron-rich nuclei far
from stability and to describe unbound nuclei. The main goal of this article is
to illustrate their dependencies with basic observables in order to discuss the
pertinence of experimental approaches in the derivation of their properties,
especially for ""N-body"" resonances.",2307.04560v1
2023-07-16,Controlling periodic Fano resonances of quantum acoustic waves with a giant atom coupled to microwave waveguide,"Nanoscale Fano resonances, with applications from telecommunications to
ultra-sensitive biosensing, have prompted extensive research. We demonstrate
that a superconducting qubit, jointly coupled to microwave waveguides and an
inter-digital transducer composite device, can exhibit acoustic Fano
resonances. Our analytical framework, leveraging the Taylor series
approximation, elucidates the origins of these quantum acoustic resonances with
periodic Fano-like interference. By analyzing the analytical Fano parameter, we
demonstrate that the Fano resonances and their corresponding Fano widths near
the resonance frequency of a giant atom can be precisely controlled and
manipulated by adjusting the time delay. Moreover, not just the near-resonant
Fano profiles, but the entire periodic Fano resonance features can be precisely
modulated from Lorentz, Fano to quasi-Lorentz shapes by tuning the coupling
strength of the microwave waveguide. Our analytical framework offers insights
into the control and manipulation of periodic Fano resonances in quantum
acoustic waves, thereby presenting significant potential for applications such
as quantum information processing, sensing, and communication.",2307.07949v1
2023-07-28,Bilayer Metasurface: Induced Transparency and Fabry Perot Resonance,"A Fabry-Perot resonator utilizes two solid, non-resonating, reflecting
mirrors to form resonant patterns when the separation between the mirrors
satisfies the resonance conditions. The resonant mode concentrates at the
middle of the cavity. In this study, we constructed a Fabry-Perot cavity with
nanostructured resonant metasurfaces as meta-mirrors. The individual
metasurfaces exhibit resonant transmission dips with a minimum transmission and
a quality factor of t0 and Qs, respectively. The coherent interference between
the two metasurfaces changes the behavior of the entire resonant system,
generating an induced transparency in the original spectrum. The sharpness of
the induced transparency peak is linearly related to the group delay of the
single metasurface. Assuming a Lorentzian lineshape, we show that for small t0,
the quality factor of the induced transparency peak is Qs/t0^3. The field
confines to the meta-mirrors region rather than at the middle of the
Fabry-Perot cavity. We provide examples of practical metasurfaces made from
dielectric scatters composed of silicon thin nanodisks and demonstrate high
quality factors and phase dispersion that are unattainable by any nano or
microscale flat optics systems.",2307.15414v1
2023-10-19,Mathematical theory on dipolar resonances of hard inclusions within a soft elastic material,"The current study is motivated by the paper [Z. Liu, et al., {\it Science},
289(5485), 2000], which investigates the incorporation of hard inclusions
within a soft elastic matrix (HISE). The objective is to attain a negative mass
density, which is caused by sub-wavelength dipolar resonances. This paper
offers a comprehensive and mathematically rigorous understanding of the dipolar
resonances within the HISE structure. Firstly, the original formula for the
resonant frequencies of arbitrarily shaped hard inclusions is derived
explicitly for the first time. Additionally, we demonstrate that the resonances
arise due to the high contrast in Lam\'e parameters between various materials,
while the sub-wavelength characteristics of the resonances are attributed to
the significant disparities in material densities. Furthermore, the dipolar
characterization of the resonances is rigorously justified. To validate our
findings, we investigate resonant phenomena within a spherical geometry,
offering both an alternative method for calculating resonant frequencies and a
confirmation of the results presented in this paper.",2310.12861v2
2023-10-24,On the degeneracy of whispering gallery modes in a high-Q sapphire microwave resonator,"Cylindrical WGM resonators machined in high-quality sapphire monocrystal
cooled down to liquid helium temperature offer exceptionally-high Q-factors in
the microwave frequency domain. Such a resonator constitutes the core of an
ultra-stable oscillator featuring fractional frequency stability better than
1e-15 at short integration times. As in any cylindrical resonant structure, the
WGM resonator presents a two fold degeneracy. When a defect breaks the
cylindrical symmetry of the resonator, the WGMs split and appear as doublets.
In the high-quality sapphire resonator, the frequency separation of these twin
modes varies from one mode order to another with a maximum value of a few tens
of kHz. While the mode splitting for a given mode was considered until now
unpredictable and intrinsic to each resonator since resulting a priori from
randomly distributed defects. we show here, at the contrary, that the observed
mode splitting found on all the sapphire resonators whatever their origin
mainly comes from a perfectly determined defect resulting from the
manufacturing processes.",2310.15573v1
2024-03-06,Resonant perturbation of a family of young asteroids associated with (5026) Martes,"The orbital dynamics of a very young asteroid pair (5026) Martes and 2005
WW113 is studied. We detect strong resonant perturbations of the larger member
of the pair (5026) Martes by the 3:11 mean motion resonance with the Earth. The
second asteroid of the pair (2005 WW113) has orbited far from the resonance and
is not perturbed. We provide a new estimation of the resonance structure and
found that, under the planetary perturbations, a single resonance splits into a
multiplet. The nominal position of the resonance is 2.37783 AU. However, the
center of the corresponding chaotic zone is detected at 2.37754 AU. As a
result, we noted a small but not negligible difference between the calculated
and observed position of resonance. The multiplet structure of the 3:11 Earth
resonance cannot explain this offset (the position of the main term of the
multiplet is 2.377698 AU).",2403.03559v1
2024-03-22,Closed-channel parameters of Feshbach resonances,"In the work of Phys. Rev. A 100, 042710 (2019), it was argued that the
general description of two-body Feshbach resonances requires ""closed-channel
parameters"" related to the bare bound state causing the resonance. The present
work shows that once the resonance theory is renormalised (i.e. its parameters
are expressed in terms of physical observables) the dependence of two-body
observables on the closed-channel parameters disappears when the inter-channel
coupling is localised in a region where the wave functions are energy
independent. In such a regime, the resulting quantum defect theory is
surprisingly independent of the bare bound state energy. This result highlights
a qualitative difference between resonances in this regime, such as magnetic
resonances in ultracold atoms, and other kinds of resonances, such as hadron
resonances. Although the closed-channel parameters of magnetic resonances do
not affect two-body observables, it is suggested that they could be evidenced
experimentally from short-distance probing and three-body observables.",2403.14962v1
2024-04-05,Resonant Raman signatures of exciton polarons in a transition metal oxide: BiVO$_4$,"In this work we investigate the delocalized excitons and excitons trapped by
a polaron formation in \BVO{} by means of resonant Raman spectroscopy. We
record Raman spectra with 16 laser lines between 1.9 and \SI{2.6}{\eV} and
analyze intensity variations of the Raman peaks for different vibrational
modes. The resonant Raman cross sections of the \Ag{} modes contain two types
of resonances. The first high-energy resonance near \SI{2.45}{\eV} belongs to a
transition between delocalized states; it is close to absorption edge measured
at \SI{2.3}{\eV} and exhibits a characteristic \SI{50}{\meV} anisotropy between
polarization parallel and perpendicular to the $c$ axis. The high energy Raman
resonance occurs inside the gap at \SI{1.94}{\eV} for all crystallographic
directions.
  The in-gap resonance can involve a localized transition. We attribute it to
an exciton-polaron, formed by a small localized electron polaron of Holstein
type and delocalized holes. It manifests in the vibrations of vanadium and
oxygen atoms where polaron localization occurs and the resonance energy matches
theoretical predictions. The vibrational modes couple to the polaron with
different efficiency determined from resonant Raman profiles.",2404.04112v1
2007-05-11,Electrical transport and optical studies of ferromagnetic Cobalt doped ZnO nanoparticles exhibiting a metal-insulator transition,"The observed correlation of oxygen vacancies and room temperature
ferromagnetic ordering in Co doped ZnO1-o nanoparticles reported earlier (Naeem
et al Nanotechnology 17, 2675-2680) has been further explored by transport and
optical measurements. In these particles room temperature ferromagnetic
ordering had been observed to occur only after annealing in forming gas. In the
current work the optical properties have been studied by diffuse reflection
spectroscopy in the UV-Vis region and the band gap of the Co doped compositions
has been found to decrease with Co addition. Reflections minima are observed at
the energies characteristic of Co+2 d-d (tethrahedral symmetry) crystal field
transitions, further establishing the presence of Co in substitutional sites.
Electrical transport measurements on palletized samples of the nanoparticles
show that the effect of a forming gas is to strongly decrease the resistivity
with increasing Co concentration. For the air annealed and non-ferromagnetic
samples the variation in the resistivity as a function of Co content are
opposite to those observed in the particles prepared in forming gas. The
ferromagnetic samples exhibit an apparent change from insulator to metal with
increasing temperatures for T>380K and this change becomes more pronounced with
increasing Co content. The magnetic and resistive behaviors are correlated by
considering the model by Calderon et al [M. J. Calderon and S. D. Sarma, Annals
of Physics 2007 (Accepted doi: 10.1016/j.aop.2007.01.010] where the
ferromagnetism changes from being mediated by polarons in the low temperature
insulating region to being mediated by the carriers released from the weakly
bound states in the higher temperature metallic region.",0705.1593v3
2011-05-18,"Influence of B - site Disorder in $La_{0.5}Ca_{0.5}Mn_{1-x}B_{x}O_{3}$ (B = Fe, Ru, Al and Ga) Manganites","We have investigated the influence of B - site doping on the crystal and
magnetic structure in $La_{0.5}Ca_{0.5}Mn_{1-x}B_{x}O_{3}$ (B= Fe, Ru, Al and
Ga) compounds using neutron diffraction, SANS, magnetization and resistivity
techniques. The B - site doped samples are isostructural and possess an
orthorhombic structure in \textit{Pnma} space group at 300K. A structural
transition from orthorhombic to monoclinic is found to precede the magnetic
transition to CE - type antiferromagnetic state in few of these samples. On
doping with Fe, charge and orbitally ordered CE - type antiferromagnetic state
is suppressed, followed by the growth in ferromagnetic insulating phase in
$0.02\leq x\leq0.06$ compounds. At higher Fe doping in $x>0.06$, the
ferromagnetic state is also suppressed and no evidence of long range magnetic
ordering is observed. In Ru doped samples $(0.01\leq x\leq0.05)$, the
ferromagnetic metallic state is favored at $T{}_{C}\approx200K$ and
$T_{MI}\approx125K$ and no significant change in $T_{C}$ and $T_{MI}$ as a
function of Ru doping is found. In contrast, with non magnetic Al substitution
for $0.01\leq x\leq0.03$, the charge ordered CE - type antiferromagnetic state
coexists with the ferromagnetic metallic phase. With further increase in Al
doping $(0.05\leq x\leq0.07)$, both CE - type antiferromagnetic and
ferromagnetic phases are gradually suppressed. This behavior is accompanied by
the evolution of A - type antiferromagnetic insulating state. Eventually, at
higher Al doping $(0.10\leq x\leq0.13)$, this phase is also suppressed and
signature of spin glass like transition are evident in M(T). Likewise,
substitution with Ga is observed to induce similar effects as described for Al
doped samples. The presence of short ranged ferromagnetic ordering has been
further explored using SANS measurements in few of the selected samples.",1105.3572v1
2011-07-08,Study of spin glass and cluster ferromagnetism in RuSr2Eu1.4Ce0.6Cu2O10-δ magneto Superconductor,"We report DC magnetization, detailed systematic linear and nonlinear AC
magnetic susceptibility and transport for a single phase
RuSr2Eu1.4Ce0.6Cu2O10-{\delta} (EuRu-1222) magneto-superconductor. The studied
sample is synthesized through standard solid state reaction route, which is
crystallized in single phase tetragonal structure with space group I4/mmm. DC
magnetic susceptibility measurements revealed that the studied EuRu-1222 is a
magneto-superconductor with Ru spins ordering at around 110 K and
superconductivity in the Cu-O2 planes below \approx 30 K. Temperature
dependence of AC susceptibility with different frequency and amplitude
variations confirms spin-glass behavior with cluster ferromagnetism of the
system. Change in the cusp position with frequency follows the Vogel-Fulcher
law, which is commonly accepted feature for a spin-glass (SG) system with
ferromagnetic clusters. The third harmonic of AC susceptibility (\c{hi}3) shows
that the system undergoes a spin glass transition below 80 K. Superconducting
transition temperature (Tc) onset and {\rho} = 0 are seen at around 30 and 18 K
without any applied field and the same decreases to 10 and 2 K under 130 kOe
applied field. Also low fields isothermal (MH) suggests that ferromagnetic
clusters are embedded in spin-glass (SG) matrix. The magnetization vs. applied
field (MH) loops exhibited ferromagnetic (FM) like behavior with rather small
coercive fields. Detailed AC magnetic susceptibility measurements are carried
out to unearth the short range magnetic correlations. These results support the
spin-glass (SG) formation followed by ferromagnetic clustering effects at low
temperatures. Our detailed magnetization and magneto transport results will
undoubtedly contribute to current understanding of the complex magnetism of the
EuRu-1222 system.",1107.1612v2
2012-06-13,"Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically doped topological insulator","The breaking of time-reversal symmetry by ferromagnetism is predicted to
yield profound changes to the electronic surface states of a topological
insulator. Here, we report on a concerted set of structural, magnetic,
electrical and spectroscopic measurements of \MBS thin films wherein
photoemission and x-ray magnetic circular dichroism studies have recently shown
surface ferromagnetism in the temperature range 15 K $\leq T \leq 100$ K,
accompanied by a suppressed density of surface states at the Dirac point.
Secondary ion mass spectroscopy and scanning tunneling microscopy reveal an
inhomogeneous distribution of Mn atoms, with a tendency to segregate towards
the sample surface. Magnetometry and anisotropic magnetoresistance measurements
are insensitive to the high temperature ferromagnetism seen in surface studies,
revealing instead a low temperature ferromagnetic phase at $T \lesssim 5$ K.
The absence of both a magneto-optical Kerr effect and anomalous Hall effect
suggests that this low temperature ferromagnetism is unlikely to be a
homogeneous bulk phase but likely originates in nanoscale near-surface regions
of the bulk where magnetic atoms segregate during sample growth. Although the
samples are not ideal, with both bulk and surface contributions to electron
transport, we measure a magnetoconductance whose behavior is qualitatively
consistent with predictions that the opening of a gap in the Dirac spectrum
drives quantum corrections to the conductance in topological insulators from
the symplectic to the orthogonal class.",1206.2908v2
2013-12-02,Double ellipsoidal Fermi surface model of the normal state of ferromagnetic superconductors,"We model the normal state of ferromagnetic superconductors with two general
ellipsoidal Fermi surfaces (FSs), one for each spin projection
$\sigma=\{\uparrow,\downarrow\}$, each with its ferromagnetically split
chemical potential $\mu_{\sigma}$ and its three distinct single particle
effective masses, $\{m_{i\sigma}\}$, the geometric mean of which is
$m_{\sigma}$. We study this model in the presence of an arbitrarily oriented
magnetic induction, ${\bf B}=\mu_{0}{\bf H}+{\bf M_{0}}$, where ${\bf M_{0}}$
includes the Ising-like spontaneous ferromagnetic order, which for URhGe is in
the $c$-axis direction above the superconducting transition temperature $T_c$.
We assume the low-$T$ total particle density $\Sigma_{\sigma} n_{\sigma}({\bf
B})$ to be independent of ${\bf B}$, and obtain a self-consistent asymptotic
expansion for $\sum_{\sigma}\Pi^{3/2}_{\sigma}({\bf B})$ in even powers of
${\bf B}$, where $\Pi_{\sigma}({\bf B})=m_{\sigma}({\bf B})\mu_{\sigma}({\bf
B})$. We assume that the $\mu_{\sigma}({\bf B})$ are linear in ${\bf B}$ for
both spins due to the Zeeman interaction and that the remaining even ${\bf B}$
dependence in the $\Pi_{\sigma}({\bf B})$ arises only from $m_{\downarrow}({\bf
B})$. Our analogous expression for the Sommerfeld constant $\gamma({\bf B})$
leads to good fits to the $\gamma({\bf H})$ data of Aoki and Flouquet [J. Phys.
Soc. Jpn. \textbf{81}, 011003 (2012)] obtained for the ferromagnetic
superconductor URhGe in the ferromagnetic, non-superconducting phase, with the
applied magnetic field ${\bf H}$ along each of the three crystallographic
directions. We discuss this model in terms of the reentrant superconducting
properties of URhGe and UCoGe. This model can be generalized to an arbitrary
number of ellipsoidal FSs.",1312.0644v2
2015-04-22,Gradual localization of 5f states in orthorhombic UTX ferromagnets - polarized neutron diffraction study of Ru substituted UCoGe,"We report on a microscopic study of the evolution of ferromagnetism in the Ru
substituted ferromagnetic superconductor (FM SC) UCoGe crystallizing in the
orthorhombic TiNiSi-type structure. For that purpose, two single crystals with
composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge have been prepared and
characterized by magnetization, AC susceptibility, specific heat and electrical
resistivity measurements. Both compounds have been found to order
ferromagnetically below TC = 6.5 K and 7.5 K, respectively, which is
considerably higher than the TC = 3 K of the parent compound UCoGe. The higher
values of TC are accompanied by enhanced values of the spontaneous moment
mspont. = 0.11 mB/f.u. and mspont. = 0.21 mB/f.u., respectively in comparison
to the tiny spontaneous moment of UCoGe (about 0.07mB/f.u.). No sign of
superconductivity was detected in either compound. The magnetic moments of the
samples were investigated on the microscopic scale using polarized neutron
diffraction (PND) and for UCo0.88Ru0.12Ge also by soft X-ray magnetic circular
dichroism (XMCD). The analysis of the PND results indicates that the observed
enhancement of ferromagnetism is mainly due to the growth of the orbital part
of the uranium 5f moment mL(U), reflecting a gradual localization of the 5f
electrons with Ru substitution. In addition, the parallel orientation of the U
and Co moments has been established in both substituted compounds. The results
are discussed and compared with related isostructural ferromagnetic UTX
compounds (T - transition metals, X - Si, Ge) in the context of a varying
degree of the 5f-ligand hybridization.",1504.05645v1
2016-10-03,Spiral order from orientationally correlated random bonds in classical XY models,"We discuss the stability of ferromagnetic long-range order in
three-dimensional classical XY ferromagnets upon substitution of a small subset
of equally oriented bonds by impurity bonds, on which the ferromagnetic
exchange J_perp > 0 is replaced by a strong antiferromagnetic coupling J_imp <
0. In the presence of a single impurity bond, once the absolute value of the
frustrating coupling J_imp < 0 exceeds a threshold J_c > 0, the ground state
becomes two-fold degenerate, corresponding to either clockwise or anticlockwise
canting of the spins in the vicinity of the impurity bond. In the presence of a
small concentration of impurity bonds, the effective low-energy Hamiltonian is
that of Ising variables encoding the sense of rotation of the local canting
around the impurities. Those degrees of freedom interact through a dipolar
interaction mediated by spin waves. A ferromagnetic Ising ground state
indicates the instability of the XY ferromagnet towards a spiral state with a
wave vector proportional to the concentration of impurity bonds. To analyze
under which circumstances such a ground state arises, we study first impurities
forming superlattices. For a subclass of those, we can rigorously establish the
existence of spiral order. For another class of superlattices, the Ising
variables order ferromagnetically in planes perpendicular to the orientation of
impurity bonds, but antiferromagnetically parallel to it, which results in a
fan-like XY ground state. Second, we consider the case when the impurity bonds
are randomly distributed on the three-dimensional host lattice according to a
Poisson process. We show the phenomenon of spiral order by disorder with an
ordering wave vector proportional to the impurity concentration. The analytical
predictions are confirmed by Monte Carlo simulations and are relevant for
magnetic materials such as YBaCuFeO_5.",1610.00784v4
2017-03-14,Thermodynamics of frustrated ferromagnetic spin-$1/2$ Heisenberg chains: The role of inter-chain coupling,"The thermodynamics of coupled frustrated ferromagnetic chains is studied
within a spin-rotation-invariant Green's function approach. We consider an
isotropic Heisenberg spin-half system with a ferromagnetic in-chain coupling
$J_1<0$ between nearest neighbors and a frustrating antiferromagnetic
next-nearest neighbor in-chain coupling $J_2>0$. We focus on moderate strength
of frustration $J_2 < |J_1|/4$ such that the in-chain spin-spin correlations
are predominantly ferromagnetic. We consider two inter-chain couplings (ICs)
$J_{\perp,y}$ and $J_{\perp,z}$, corresponding to the two axis perpendicular to
the chain, where ferromagnetic as well as antiferromagnetic ICs are taken into
account. We discuss the influence of frustration on the ground-state properties
for antiferromagnetic ICs, where the ground state is of quantum nature. The
major part of our study is devoted to the finite-temperature properties. We
calculate the critical temperature $T_{c}$ as a function of the competing
exchange couplings $J_{2},J_{\perp,y}, J_{\perp,z}$. We find that for fixed ICs
$T_c$ monotonically decreases with increasing frustration $J_2$, where as $J_2
\to |J_1|/4$ the $T_c(J_2)$-curve drops down rapidly. To characterize the
magnetic ordering below and above $T_c$ we calculate the spin-spin correlation
functions $\langle {\bf S}_0 {\bf S}_{\bf R} \rangle$, the magnetic order
parameter $M$, the uniform static susceptibility $\chi_0$ as well as the
correlation length $\xi$. Moreover, we discuss the specific heat $C_V$ and the
temperature dependence of the excitation spectrum $\omega_{\mathbf{q}}$. As
$J_2 \to |J_1|/4$ some unusual frustration-induced features were found, such as
an increase of the in-chain spin stiffness (in case of ferromagnetic ICs) or of
the in-chain spin-wave velocity (in case of antiferromagnetic ICs) with growing
temperature.",1703.04573v1
2018-02-22,Room Temperature Intrinsic Ferromagnetism in Epitaxial Manganese Selenide Films in the Monolayer Limit,"Monolayer van der Waals (vdW) magnets provide an exciting opportunity for
exploring two-dimensional (2D) magnetism for scientific and technological
advances, but the intrinsic ferromagnetism has only been observed at low
temperatures. Here, we report the observation of room temperature
ferromagnetism in manganese selenide (MnSe$_x$) films grown by molecular beam
epitaxy (MBE). Magnetic and structural characterization provides strong
evidence that in the monolayer limit, the ferromagnetism originates from a vdW
manganese diselenide (MnSe$_2$) monolayer, while for thicker films it could
originate from a combination of vdW MnSe$_2$ and/or interfacial magnetism of
$\alpha$-MnSe(111). Magnetization measurements of monolayer MnSe$_x$ films on
GaSe and SnSe$_2$ epilayers show ferromagnetic ordering with large saturation
magnetization of ~ 4 Bohr magnetons per Mn, which is consistent with density
functional theory calculations predicting ferromagnetism in monolayer
1T-MnSe$_2$. Growing MnSe$_x$ films on GaSe up to high thickness (~ 40 nm)
produces $\alpha$-MnSe(111), and an enhanced magnetic moment (~ 2x) compared to
the monolayer MnSe$_x$ samples. Detailed structural characterization by
scanning transmission electron microscopy (STEM), scanning tunneling microscopy
(STM), and reflection high energy electron diffraction (RHEED) reveal an abrupt
and clean interface between GaSe(0001) and $\alpha$-MnSe(111). In particular,
the structure measured by STEM is consistent with the presence of a MnSe$_2$
monolayer at the interface. These results hold promise for potential
applications in energy efficient information storage and processing.",1802.08152v1
2014-03-11,Spin-polaron band of heavy carriersin the heavy-fermion ferromagnetic superconductor UGe2,"In strongly correlated materials, cooperative behavior of the electrons
causes a variety of quantum ordered states that may, in some cases, coexist. It
has long been believed, however, that such coexistence among ferromagnetic
ordering, superconductivity and heavy-fermion behavior is impossible, as the
first supports parallel spin alignment while the conventional understanding of
the latter two phenomena assumes spin-singlet or anti-parallel spins. This
understanding has recently been challenged by an increasing number of
observations in uranium systems (UGe2, URhGe, UIr and UCoGe) in which
superconductivity is found within a ferromagnetic state and, more
fundamentally, both ordering phenomena are exhibited by the same set of heavy
5f electrons. Since the coexistence of superconductivity and ferromagnetism is
at odds with the standard theory of phonon-mediated spin-singlet
superconductivity, it requires an alternative pairing mechanism, in which
electrons are bound into spin-triplet pairs by spin fluctuations. Within the
heavy-fermion scenario, this alternative mechanism assumes that the magnetism
has a band character and that said band forms from heavy quasiparticles
composed of f electrons. This band is expected to be responsible for all three
phenomena although its nature and the nature of those heavy quasiparticles
still remains unclear. Here we report spectroscopic evidence for the formation
in UGe2 of subnanometer-sized spin polarons whose dynamics we follow into the
paramagnetic and ferromagnetic phases. These spin polarons behave as heavy
carriers and thus may serve as heavy quasiparticles made of 5f electrons; once
coherence is established, they form a narrow spin-polaron band which thus
provides a natural reconciliation of itinerant ferromagnetism with spin-triplet
superconductivity and heavy-fermion behavior.",1403.2597v1
2018-01-23,Current-driven domain wall dynamics in ferromagnetic layers synthetically exchange-coupled by a spacer: A micromagnetic study,"The current-driven domain wall motion along two exchange-coupled
ferromagnetic layers with perpendicular anisotropy is studied by means of
micromagnetic simulations and compared to the conventional case of a single
ferromagnetic layer. Our results, where only the lower ferromagnetic layer is
subjected to the interfacial Dzyaloshinskii-Moriya interaction and to the spin
Hall effect, indicate that the domain walls can be synchronously driven in the
presence of a strong interlayer exchange coupling, and that the velocity is
significantly enhanced due to the antiferromagnetic exchange coupling as
compared with the single-layer case. On the contrary, when the coupling is of
ferromagnetic nature, the velocity is reduced. We provide a full micromagnetic
characterization of the current-driven motion in these multilayers, both in the
absence and in the presence of longitudinal fields, and the results are
explained based on a one-dimensional model. The interfacial
Dzyaloshinskii-Moriya interaction, only necessary in this lower layer, gives
the required chirality to the magnetization textures, while the interlayer
exchange coupling favors the synchronous movement of the coupled walls by a
dragging mechanism, without significant tilting of the domain wall plane.
Finally, the domain wall dynamics along curved strips is also evaluated. These
results indicate that the antiferromagnetic coupling between the ferromagnetic
layers mitigates the tilting of the walls, which suggest these systems to
achieve efficient and highly packed displacement of trains of walls for
spintronics devices. A study, taking into account defects and thermal
fluctuations, allows to analyze the validity range of these claims.",1801.07432v1
2018-10-22,Tuning a binary ferromagnet into a multi-state synapse with spin-orbit torque induced plasticity,"Inspired by ion-dominated synaptic plasticity in human brain, artificial
synapses for neuromorphic computing adopt charge-related quantities as their
weights. Despite the existing charge derived synaptic emulations, schemes of
controlling electron spins in ferromagnetic devices have also attracted
considerable interest due to their advantages of low energy consumption,
unlimited endurance, and favorable CMOS compatibility. However, a generally
applicable method of tuning a binary ferromagnet into a multi-state memory with
pure spin-dominated synaptic plasticity in the absence of an external magnetic
field is still missing. Here, we show how synaptic plasticity of a
perpendicular ferromagnetic FM1 layer can be obtained when it is
interlayer-exchange-coupled by another in-plane ferromagnetic FM2 layer, where
a magnetic-field-free current-driven multi-state magnetization switching of FM1
in the Pt/FM1/Ta/FM2 structure is induced by spin-orbit torque. We use current
pulses to set the perpendicular magnetization state which acts as the synapse
weight, and demonstrate spintronic implementation of the excitatory/inhibitory
postsynaptic potentials and spike timing-dependent plasticity. This
functionality is made possible by the action of the in-plane interlayer
exchange coupling field which leads to broadened, multi-state magnetic reversal
characteristics. Numerical simulations, combined with investigations of a
reference sample with a single perpendicular magnetized Pt/FM1/Ta structure,
reveal that the broadening is due to the in-plane field component tuning the
efficiency of the spin-orbit-torque to drive domain walls across a landscape of
varying pinning potentials. The conventionally binary FM1 inside our
Pt/FM1/Ta/FM2 structure with inherent in-plane coupling field is therefore
tuned into a multi-state perpendicular ferromagnet and represents a synaptic
emulator for neuromorphic computing.",1810.09064v1
2018-10-24,Long spin coherence length and bulk-like spin-orbit torque in ferrimagnetic multilayers,"Ferromagnetic spintronics has been a main focus as it offers non-volatile
memory and logic applications through current-induced spin-transfer torques.
Enabling wider applications of such magnetic devices requires a lower switching
current for a smaller cell while keeping the thermal stability of magnetic
cells for non-volatility. As the cell size reduces, however, it becomes
extremely difficult to meet this requirement with ferromagnets because
spin-transfer torque for ferromagnets is a surface torque due to rapid spin
dephasing, leading to the 1/ferromagnet-thickness dependence of the spin-torque
efficiency. Requirement of a larger switching current for a thicker and thus
more thermally stable ferromagnetic cell is the fundamental obstacle for
high-density non-volatile applications with ferromagnets. Theories predicted
that antiferromagnets have a long spin coherence length due to the staggered
spin order on an atomic scale, thereby resolving the above fundamental
limitation. Despite several spin-torque experiments on antiferromagnets and
ferrimagnetic alloys, this prediction has remained unexplored. Here we report a
long spin coherence length and associated bulk-like-torque characteristic in an
antiferromagnetically coupled ferrimagnetic multilayer. We find that a
transverse spin current can pass through > 10 nm-thick ferrimagnetic Co/Tb
multilayers whereas it is entirely absorbed by 1 nm-thick ferromagnetic Co/Ni
multilayer. We also find that the switching efficiency of Co/Tb multilayers
partially reflects a bulk-like-torque characteristic as it increases with the
ferrimagnet-thickness up to 8 nm and then decreases, in clear contrast to
1/thickness-dependence of Co/Ni multilayers. Our results on
antiferromagnetically coupled systems will invigorate researches towards
energy-efficient spintronic technologies.",1810.10404v1
2020-02-19,Ion-Irradiation-Induced Cobalt/Cobalt Oxide Heterostructures: Printing 3D Interfaces,"Interfaces separating ferromagnetic (FM) layers from non-ferromagnetic layers
offer unique properties due to spin-orbit coupling and symmetry breaking,
yielding effects such as exchange bias, perpendicular magnetic anisotropy,
spin-pumping, spin-transfer torques, conversion between charge and spin
currents and vice-versa. These interfacial phenomena play crucial roles for
magnetic data storage and transfer applications, which require forming FM
nano-structures embedded in non-ferromagnetic matrices. Here, we investigate
the possiblity of creating such nano-structures by ion-irradiation. We study
the effect of lateral confinement on the ion-irradiation-induced reduction of
non-magnetic metal oxides (e.g., antiferro- or paramagnetic) to form
ferromagnetic metals. Our findings are later exploited to form 3-dimensional
magnetic interfaces between Co, CoO and Pt by spatially-selective irradiation
of CoO/Pt multilayers. We demonstrate that the mechanical displacement of the O
atoms plays a crucial role during the reduction from insulating,
non-ferromagnetic cobalt oxides to metallic cobalt. Metallic cobalt yields both
perpendicular magnetic anisotropy in the generated Co/Pt nano-structures, and,
at low temperatures, exchange bias at vertical interfaces between Co and CoO.
If pushed to the limit of ion-irradiation technology, this approach could, in
principle, enable the creation of densely-packed, atomic scale ferromagnetic
point-contact spin-torque oscillator (STO) networks, or conductive channels for
current-confined-path based current perpendicular-to-plane giant
magnetoresistance read-heads.",2002.08090v1
2019-01-02,Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures,"Recent theoretical and experimental work has demonstrated how the
superconducting critical temperature ($T_c$) can be modified by rotating the
magnetization of a single homogeneous ferromagnet proximity-coupled to the
superconducting layer. This occurs when the superconductor and ferromagnet are
separated by a thin heavy normal metal that provides an enhanced interfacial
Rashba spin-orbit interaction. We consider the reciprocal effect: magnetization
reorientation driven by the superconducting phase transition. We solve the
tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and
find that the relative angle between the spin-orbit field and the magnetization
gives rise to a contribution in the free energy even in the normal state due to
band-structure effects. For temperatures below $T_c$, superconductivity gives
rise to a competing contribution. By lowering the temperature, in addition to
reorientation of the favored magnetization direction from in-plane to
out-of-plane, a $\pi/4$ in-plane rotation for thicker ferromagnetic layers is
possible. Furthermore, computation of $T_c$ of the structure in the ballistic
limit shows a dependence on the in-plane orientation of the magnetization, in
contrast to our previous result on the diffusive limit. This finding is
relevant with respect to thin-film heterostructures since these are likely to
be in the ballistic regime of transport. Finally, we discuss the experimental
feasibility of observing the magnetic anisotropy induced by the superconducting
transition when other magnetic anisotropies, such as the shape anisotropy for a
ferromagnetic film, are taken into account. Our work suggests that the
superconducting condensation energy in principle can trigger a reorientation of
the magnetization of a thin-film ferromagnet upon lowering the temperature
below $T_c$, in particular for ferromagnets with weak magnetic anisotropies.",1901.00501v3
2019-03-08,The critical temperature of the 2D-Ising model through Deep Learning Autoencoders,"We investigate deep learning autoencoders for the unsupervised recognition of
phase transitions in physical systems formulated on a lattice. We focus our
investigation on the 2-dimensional ferromagnetic Ising model and then test the
application of the autoencoder on the anti-ferromagnetic Ising model. We use
spin configurations produced for the 2-dimensional ferromagnetic and
anti-ferromagnetic Ising model in zero external magnetic field. For the
ferromagnetic Ising model, we study numerically the relation between one latent
variable extracted from the autoencoder to the critical temperature $T_c$. The
proposed autoencoder reveals the two phases, one for which the spins are
ordered and the other for which spins are disordered, reflecting the
restoration of the $\mathbb{Z}_2$ symmetry as the temperature increases. We
provide a finite volume analysis for a sequence of increasing lattice sizes.
For the largest volume studied, the transition between the two phases occurs
very close to the theoretically extracted critical temperature. We define as a
quasi-order parameter the absolute average latent variable ${\tilde z}$, which
enables us to predict the critical temperature. One can define a latent
susceptibility and use it to quantify the value of the critical temperature
$T_c(L)$ at different lattice sizes and that these values suffer from only
small finite scaling effects. We demonstrate that $T_c(L)$ extrapolates to the
known theoretical value as $L \to \infty$ suggesting that the autoencoder can
also be used to extract the critical temperature of the phase transition to an
adequate precision. Subsequently, we test the application of the autoencoder on
the anti-ferromagnetic Ising model, demonstrating that the proposed network can
detect the phase transition successfully in a similar way.",1903.03506v2
2019-04-02,Relationship between charge redistribution and ferromagnetism at the heterointerface between perovskite oxides LaNiO$_3$ and LaMnO$_3$,"To investigate the relationship between the charge redistribution and
ferromagnetism at the heterointerface between perovskite transition-metal
oxides LaNiO$_3$ (LNO) and LaMnO$_3$ (LMO), we performed x-ray absorption
spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements. In the
LNO/LMO heterostructures with asymmetric charge redistribution, the electrons
donated from Mn to Ni ions are confined within one monolayer (ML) of LNO at the
interface, whereas holes are distributed over 3-4 ML on the LMO side. A
detailed analysis of the Ni-$L_{2,3}$ and Mn-$L_{2,3}$ XMCD spectra reveals
that Ni magnetization is induced only by the Ni$^{2+}$ ions in the 1 ML LNO
adjacent to the interface, while the magnetization of Mn ions is increased in
the 3-4 ML LMO of the interfacial region. The characteristic length scale of
the emergent (increased) interfacial ferromagnetism of the LNO (LMO) layers is
in good agreement with that of the charge distribution across the interface,
indicating a close relationship between the charge redistribution due to the
interfacial charge transfer and the ferromagnetism of the LNO/LMO interface.
Furthermore, the XMCD spectra clearly demonstrate that the vectors of induced
magnetization of both ions are aligned ferromagnetically, suggesting that the
delicate balance between the exchange interactions occurring inside each layer
and across the interface may induce the canted ferromagnetism of Ni$^{2+}$
ions, resulting in weak magnetization in the 1 ML LNO adjacent to the
interface.",1904.01335v1
2022-03-18,Quantum anomalous Hall effect and electric-field-induced topological phase transition in AB-stacked MoTe${}_2$/WSe${}_2$ moiré heterobilayers,"We propose a new mechanism to explain the quantum anomalous Hall (QAH) effect
and the electric-field-induced topological phase transition in AB-stacked
MoTe${}_2$/WSe${}_2$ moir\'e heterobilayers at $\nu=1$ hole filling. We suggest
that the Chern band of the QAH state is generated from an intrinsic band
inversion composed of the highest two moir\'e hole bands with opposite valley
numbers and a gap opening induced by two Coulomb-interaction-driven magnetic
orders. These magnetic orders, including an in-plane $120^{\circ}$-N\'eel order
and an in-plane ferromagnetic order, interact with moir\'e bands via
corresponding in-plane exchange fields. The N\'eel order ensures the insulating
gap, the ferromagnetic order induces the non-zero Chern number, and both orders
contribute to time-reversal symmetry breaking. The N\'eel order is acquired
from the Hartree-Fock exchange interaction, and the formation of ferromagnetic
order is attributed to interlayer-exciton condensation and exciton
ferromagnetism. The exciton ferromagnetism can be demonstrated by excitonic
Bose-Hubbard physics and Berezinskii-Kosterlitz-Thouless transition. In low
electric fields, the equilibrium state is a Mott-insulator state. At a certain
electric field, a correlated insulating state composed of the hole-occupied
band and the exciton condensate becomes a new thermodynamically stable phase,
and the topological phase transition occurs as the ferromagnetic order emerges.
The consistency between the present theory and experimental observations is
discussed. Experimental observations, including the
spin-polarized/valley-coherent nature of the QAH state, the absence of charge
gap closure at the topological phase transition, the canted spin texture, and
the insulator-to-metal transition, are interpreted by the mechanism.",2203.10088v4
2022-07-10,Quantum phase transition from a paramagnetic Anderson insulating state to a ferromagnetic many-body localized state via an intermediate ferromagnetic metallic phase,"Effects of electron correlations on Anderson insulators have been one of the
central themes for recent two decades, suggesting that the Anderson insulating
phase turns into a novel insulating state referred to as many body localization
(MBL). However, the role of spin degrees of freedom in this dynamical phase
transition still remains unclarified as a function of the interaction strength.
In this study, we perform real-space spin-resolved Hartree-Fock-Anderson
simulations to investigate metal-insulator transitions above a critical
disorder strength in three spatial dimensions, where all single-particle states
are Anderson-localized without interactions. Here, relatively weak correlations
below the Mott regime are taken into account in the mean-field fashion but
disorder effects are introduced essentially exactly. We find two types of
single-particle mobility edges, where the multifractal spectrum of the
interaction-driven low-energy mobility edge deviates from that of the
high-energy one smoothly connected with the multifractal spectrum of the
metal-insulator transition without interactions. We show that the weakly
interacting insulating phase remains to be a paramagnetic Anderson insulating
state up to the temperature of the order of the band width. On the other hand,
we uncover that the relatively strongly interacting insulating phase still
below the Mott regime is ferromagnetic, which turns into a ferromagnetic
metallic state at a critical temperature much lower than the order of the
bandwidth. Based on all these results, we propose a quantum phase transition
from a paramagnetic Anderson insulating state to a ferromagnetic MBL insulating
phase via an intermediate ferromagnetic metallic state, which intervenes
between these two insulators at the Fermi energy.",2207.04370v1
2022-11-03,Mn(Pt$_{1-x}$Pd$_{x}$)$_5$P: Isovalent Tuning of Mn Sublattice Magnetic Order,"We report the growth and characterization of MnPd$_5$P, a ferromagnet with
T$_C$ $\approx$ 295 K, and conduct a substitutional study with its
antiferromagnetic analogue MnPt$_5$P. We grow single crystals of MnPd$_5$P and
Mn(Pt$_{1-x}$Pd$_x$)$_5$P by adding Mn into (Pt$_{1-x}$Pd$_{x}$)-P based melts.
All compounds in the family adopt the layered anti-CeCoIn$_5$ structure with
space group P4/mmm, and EDS and XRD results indicate that MnPt$_5$P and
MnPd$_5$P form a solid solution. Based on magnetization and resistance data, we
construct a T-x phase diagram for Mn(Pt$_{1-x}$Pd$_x$)$_5$P and demonstrate the
antiferromagnetic order found in MnPt$_5$P is extraordinarily sensitive to Pd
substitution. At low Pd fractions (x $<$ 0.010), the single antiferromagnetic
transition in pure MnPt$_5$P splits into a higher temperature ferromagnetic
transition followed on cooling by a lower temperature ferromagnetic to
antiferromagnetic transition and then by a re-entrant antiferromagnetic to
ferromagnetic transition at lower temperatures. The antiferromagnetic region
makes up a bubble that persists to x $\approx$ 0.009 for T $\approx$ 150 K,
with all samples x $<$ 0.009 recovering their initial ferromagnetic state with
further cooling to base temperature. Over the same low x range we find a
non-monotonic change in the room temperature unit cell volume, further
suggesting that pure MnPt$_5$P is close to an instability. Once x $>$ 0.010,
Mn(Pt$_{1-x}$Pd$_x$)$_5$P undergoes a single ferromagnetic transition. The
Curie temperature increases rapidly with x, rising from T$_C$ $\approx$ 197 K
at x = 0.013 to a maximum of T$_C$ $\approx$ 312 K for x $\approx$ 0.62, and
then falls back to T$_C$ $\approx$ 295 K for pure MnPd$_5$P (x = 1). Given that
Pt and Pd are isoelectronic, this work raises questions as to the origin of the
extreme sensitivity of the magnetic ground state in MnPt$_5$P upon introducing
Pd.",2211.01818v1
2023-05-23,Nano-Patterned Magnetic Edges in CrGeTe3 for Quasi 1-D Spintronic Devices,"The synthesis of two-dimensional van der Waals magnets has paved the way for
both technological applications and fundamental research on magnetism confined
to ultra-small length scales. Edge magnetic moments in ferromagnets are
expected to be less magnetized than in the sample interior because of the
reduced amount of neighboring ferromagnetic spins at the sample edge. We
recently demonstrated that CrGeTe3 (CGT) flakes thinner than 10 nm are hard
ferromagnets; i.e., they exhibit an open hysteresis loop. In contrast, thicker
flakes exhibit zero net remnant field in the interior, with hard ferromagnetism
present only at the cleaved edges. This experimental observation suggests that
a nontrivial interaction exists between the sample edge and the interior. Here,
we demonstrate that artificial edges fabricated by focus ion beam etching also
display hard ferromagnetism. This enables us to write magnetic nanowires in CGT
directly and use this method to characterize the magnetic interaction between
the interior and edge. The results indicate that the interior saturation and
depolarization fields depend on the lateral dimensions of the sample. Most
notably, the interior region between the edges of a sample narrower than 300 nm
becomes a hard ferromagnet, suggesting an enhancement of the magnetic exchange
induced by the proximity of the edges. Last, we find that the CGT regions
amorphized by the gallium beam are nonmagnetic, which introduces a novel method
to tune the local magnetic properties of CGT films, potentially enabling
integration into spintronic devices.",2305.14431v1
2023-07-20,Observation of long-range ferromagnetism via anomalous supercurrents in a spin-orbit coupled superconductor,"Conventional superconductors naturally disfavor ferromagnetism because the
supercurrent-carrying electrons are paired into anti-parallel spin singlets. In
superconductors with strong Rashba spin-orbit coupling, impurity magnetic
moments induce supercurrents through the spin-galvanic effect. As a result,
long-range ferromagnetic interaction among the impurity moments may be mediated
through such anomalous supercurrents in a similar fashion as in itinerant
ferromagnets. Fe(Se,Te) is such a superconductor with topological surface
bands, previously shown to exhibit quantum anomalous vortices around impurity
spins. Here, we take advantage of the flux sensitivity of scanning
superconducting quantum interference devices to investigate superconducting
Fe(Se,Te) in the regime where supercurrents around impurities overlap. We find
homogeneous remanent flux patterns after applying a supercurrent through the
sample. The patterns are consistent with anomalous edge and bulk supercurrents
generated by in-plane magnetization, which occur above a current threshold and
follow hysteresis loops reminiscent of those of a ferromagnet. Similar
long-range magnetic orders can be generated by Meissner current under a small
out-of-plane magnetic field. The magnetization weakens with increasing
temperature and disappears after thermal cycling to above superconducting
critical temperature; further suggesting superconductivity is central to
establishing and maintaining the magnetic order. These observations demonstrate
surface anomalous supercurrents as a mediator for ferromagnetism in a
spin-orbit coupled superconductor, which may potentially be utilized for
low-power cryogenic memory.",2307.10722v2
2019-07-15,Resonance line in rotating accretion disc,"We study the resonance line emission from the rotating plane optically thick
accretion disc, consisting of free electrons and resonant atoms. We use the
standard assumption that the source of continuum radiation is located near
central plane of the accretion disc, where the temperature is the highest. This
corresponds to the Milne problem consideration for continuum. We shortly
discuss the impossibility of the Milne problem for the resonance radiation. We
assume that the resonant atoms are located in a thin layer of an accretion disc
near the surface. In this case the resonance line emission arises due to
scattering of a continuum on the resonant atoms. In thin layer we can neglect
the multiple scattering of the resonance radiation on the resonant atoms. We
consider the axially symmetric problems, where the Stokes parameter U =0. We
take into account the Doppler effect for the frequencies of the resonance line.
The three types of the resonant atom sources are considered (see Figs.1-3). The
first source is the axially symmetric continuous distribution of the resonant
atoms along the circular orbit. The second spot-like source rotates in the
orbit. The third type presents two spot-like sources located in the orbit
contrary one to another. In the first and third cases the shape of the emitting
resonance line is symmetric, i.e. the right and left wings have the similar
shapes. In the second case the resonance line has asymmetric shape. The shape
of the emerging line depends significantly on the ratio of the rotation
velocity value to the velocity, characterizing the Doppler width. It also
depends on the ratio of the electron number density to the number density of
resonant atoms. The results of the calculations characterize the different
observational effects of H$\alpha$ radiation in the accretion discs and can be
used for estimations of the parameters mentioned above.",1907.06416v1
2018-08-24,Capture into first-order resonances and long-term stability of pairs of equal-mass planets,"Massive planets form within the lifetime of protoplanetary disks and undergo
orbital migration due to planet-disk interactions. When the first planet
reaches the inner edge of the disk its migration stops and the second planet is
locked in resonance. We detail the resonant trapping comparing semi-analytical
formulae and numerical simulations in the case of two equal-mass coplanar
planets trapped in first order resonances. We describe the family of resonant
stable equilibrium points (zero-amplitude libration orbits) using expanded and
non-expanded Hamiltonians. We show that during convergent migration the planets
evolve along these families of equilibria. Eccentricity damping from the disk
leads to a final equilibrium configuration that we predict analytically. The
fact that observed multi-exoplanetary systems are rarely seen in resonances
suggests that the resonant configurations achieved by migration can become
unstable after the removal of the disk. We probe the stability of the
resonances as a function of planetary mass. To do this, we fictitiously
increase the masses of the planets, adiabatically maintaining the low-amplitude
libration regime until instability. We discuss two hypotheses for instability:
low-order secondary resonance of the libration frequency with a fast synodic
frequency, and minimal approach distance between planets. We show that
secondary resonances do not seem to impact resonant systems at low-amplitude of
libration. Resonant systems are more stable than non-resonant ones for a given
minimal distance at close encounters, but we show that the latter still play
the decisive role in the destabilisation of resonant pairs. We show that, as
the planetary mass increases and the minimal distance between planets gets
smaller in terms of mutual Hill radius, the region of stability around the
resonance center shrinks, until the equilibrium point itself becomes unstable.",1808.08059v1
1998-06-16,Ray and wave chaos in asymmetric resonant optical cavities,"Optical resonators are essential components of lasers and other
wavelength-sensitive optical devices. A resonator is characterized by a set of
modes, each with a resonant frequency omega and resonance width Delta
omega=1/tau, where tau is the lifetime of a photon in the mode. In a
cylindrical or spherical dielectric resonator, extremely long-lived resonances
are due to `whispering gallery' modes in which light circulates around the
perimeter trapped by total internal reflection. These resonators emit light
isotropically. Recently, a new category of asymmetric resonant cavities (ARCs)
has been proposed in which substantial shape deformation leads to partially
chaotic ray dynamics. This has been predicted to give rise to a universal,
frequency-independent broadening of the whispering-gallery resonances, and
highly anisotropic emission. Here we present solutions of the wave equation for
ARCs which confirm many aspects of the earlier ray-optics model, but also
reveal interesting frequency-dependent effects characteristic of quantum chaos.
For small deformations the lifetime is controlled by evanescent leakage, the
optical analogue of quantum tunneling. We find that the lifetime is much
shortened by a process known as `chaos-assisted tunneling'. In contrast, for
large deformations (~10%) some resonances are found to have longer lifetimes
than predicted by the ray chaos model due to `dynamical localization'.",9806017v1
2004-05-20,Strength of Higher-Order Spin-Orbit Resonances,"When polarized particles are accelerated in a synchrotron, the spin
precession can be periodically driven by Fourier components of the
electromagnetic fields through which the particles travel. This leads to
resonant perturbations when the spin-precession frequency is close to a linear
combination of the orbital frequencies. When such resonance conditions are
crossed, partial depolarization or spin flip can occur. The amount of
polarization that survives after resonance crossing is a function of the
resonance strength and the crossing speed. This function is commonly called the
Froissart-Stora formula. It is very useful for predicting the amount of
polarization after an acceleration cycle of a synchrotron or for computing the
required speed of the acceleration cycle to maintain a required amount of
polarization. However, the resonance strength could in general only be computed
for first-order resonances and for synchrotron sidebands. When Siberian Snakes
adjust the spin tune to be 1/2, as is required for high energy accelerators,
first-order resonances do not appear and higher-order resonances become
dominant. Here we will introduce the strength of a higher-order spin-orbit
resonance, and also present an efficient method of computing it. Several
tracking examples will show that the so computed resonance strength can indeed
be used in the Froissart-Stora formula. HERA-p is used for these examples which
demonstrate that our results are very relevant for existing accelerators.",0405108v1
2007-12-19,Destruction and Resurrection of Atomic Giant resonances in Endohedral Atoms A@C60,"It is demonstrated that in photoabsorption by endohedral atoms some atomic
Giant resonances are almost completely destroyed while the others are totally
preserved due to different action on it of the fullerenes shell. As the first
example we discuss the 4d10 Giant resonance in Xe@C60 whereas as the second
serves the Giant autoionization resonance in Eu@C60. The qualitative difference
comes from the fact that photoelectrons from the 4d Giant resonance has small
energies (tens of eV) and are strongly reflected by the C60 fullerenes shell.
As to the Eu@C60, Giant autoionization leads to fast photoelectrons (about
hundred eV) that go out almost untouched by the C60 shell. As a result of the
outgoing electrons energy difference the atomic Giant resonances will be
largely destroyed in A@C60 while the Giant autoionization resonance will be
almost completely preserved. Thus, on the way from Xe@C60 Giant resonance to
Eu@C60 Giant autoionization resonance the oscillation structure should
disappear. Similar will be the decrease of oscillations on the way from pure
Giant to pure Giant autoionization resonances for the angular anisotropy
parameters. At Giant resonance frequencies the role of polarization of the
fullerenes shell by the incoming photon beam is inessential. Quite different is
the situation for the outer electrons in Eu@C60, the photoionization of which
will be also considered.",0712.3253v1
2009-11-01,Transmission resonances in above-barrier reflection of ultra-cold atoms by the Rosen-Morse potential,"Quantum above-barrier reflection of ultra-cold atoms by the Rosen-Morse
potential is analytically considered within the mean field Gross-Pitaevskii
approximation. Reformulating the problem of reflectionless transmission as a
quasi-linear eigenvalue problem for the potential depth, an approximation for
the specific height of the potential that supports reflectionless transmission
of the incoming matter wave is derived via modification of the
Rayleigh-Schroedinger time-independent perturbation theory. The approximation
provides highly accurate description of the resonance position for all the
resonance orders if the nonlinearity parameter is small compared with the
incoming particles chemical potential. Notably, the result for the first
transmission resonance turns out to be exact, i.e., the derived formula for the
resonant potential height gives the exact value of the first nonlinear
resonances position for all the allowed variation range of the involved
parameters, the nonlinearity parameter and chemical potential. This has been
shown by constructing the exact solution of the problem for the first
resonance. Furthermore, the presented approximation reveals that, in contrast
to the linear case, in the nonlinear case reflectionless transmission may occur
not only for potential wells but also for potential barriers with positive
potential height. It also shows that the nonlinear shift of the resonance
position from the position of the corresponding linear resonance is
approximately described as a linear function of the resonance order. Finally, a
compact (yet, highly accurate) analytic formula for the n-th order resonance
position is constructed via combination of analytical and numerical methods.",0911.0158v1
2011-04-20,Asteroid families in the first order resonances with Jupiter,"Asteroids residing in the first-order mean motion resonances with Jupiter
hold important information about the processes that set the final architecture
of giant planets. Here we revise current populations of objects in the J2/1
(Hecuba-gap group), J3/2 (Hilda group) and J4/3 (Thule group) resonances. The
number of multi-opposition asteroids found is 274 for J2/1, 1197 for J3/2 and 3
for J4/3. Using both hierarchical clustering technique and colour
identification we characterise a collisionally-born asteroid family around the
object (1911) Schubart in the J3/2 resonance. There is also a looser cluster
around the largest asteroid (153) Hilda. Using N-body numerical simulations we
prove that the Yarkovsky effect (infrared thermal emission from the surface of
asteroids) causes a systematic drift in eccentricity for resonant asteroids,
while their semimajor axis is almost fixed due to the strong coupling with
Jupiter. This is a different mechanism from main belt families, where the
Yarkovsky drift affects basically the semimajor axis. We use the eccentricity
evolution to determine the following ages: (1.7+-0.7) Gyr for the Schubart
family and >~4 Gyr for the Hilda family. We also find that collisionally-born
clusters in the J2/1 resonance would efficiently dynamically disperse. The
steep size distribution of the stable population inside this resonance could
thus make sense if most of these bodies are fragments from an event older than
~1 Gyr. Finally, we test stability of resonant populations during Jupiter's and
Saturn's crossing of their mutual mean motion resonances. In particular we find
primordial objects in the J3/2 resonance were efficiently removed from their
orbits when Jupiter and Saturn crossed their 1:2 mean motion resonance.",1104.4004v1
2011-05-25,Origin and Sustainability of The Population of Asteroids Captured in the Exterior Resonance 1:2 with Mars,"At present, approximately 1500 asteroids are known to evolve inside or
sticked to the exterior 1:2 resonance with Mars at a = 2.418 AU, being (142)
Polana the largest member of this group. The effect of the forced secular modes
superposed to the resonance gives rise to a complex dynamical evolution.
Chaotic diffusion, collisions, close encounters with massive asteroids and
mainly orbital migration due to the Yarkovsky effect generate continuous
captures to and losses from the resonance, with a fraction of asteroids
remaining captured over long time scales and generating a concentration in the
semimajor axis distribution that exceeds by 20% the population of background
asteroids. The Yarkovsky effect induces different dynamics according to the
asteroid size, producing an excess of small asteroids inside the resonance. The
evolution in the resonance generates a signature on the orbits, mainly in
eccentricity, that depends on the time the asteroid remains captured inside the
resonance and on the magnitude of the Yarkovsky effect. The greater the
asteroids, the larger the time they remain captured in the resonance, allowing
greater diffusion in eccentricity and inclination. The resonance generates a
discontinuity and mixing in the space of proper elements producing
misidentification of dynamical family members, mainly for Vesta and Nysa-Polana
families. The half-life of resonant asteroids large enough for not being
affected by the Yarkovsky effect is about 1 Gyr. From the point of view of
taxonomic classes, the resonant population does not differ from the background
population and the excess of small asteroids is confirmed.",1105.5108v1
2012-06-01,Theoretical formalism for collective electromagnetic response of discrete metamaterial systems,"We develop a general formalism to describe the propagation of a near-resonant
electromagnetic field in a medium composed of magnetodielectric resonators. As
the size and the spatial separation of nanofabricated resonators in a
metamaterial array is frequently less than the wavelength, we describe them as
discrete scatterers, supporting a single mode of current oscillation
represented by a single dynamic variable. We derive a Lagrangian and
Hamiltonian formalism for the coupled electromagnetic fields and oscillating
currents in the length gauge, obtained by the Power-Zienau-Woolley
transformation. The response of each resonator to electromagnetic field is then
described by polarization and magnetization densities that, to the lowest order
in a multipole expansion, generate electric and magnetic dipole excitations. We
derive a closed set of equations for the coherently scattered field and normal
mode amplitudes of current oscillations of each resonator both within the
rotating wave approximation, in which case the radiative decay rate is much
smaller than the resonance frequency, and without such an assumption. The set
of equations includes the radiative couplings between a discrete set of
resonators mediated by the electromagnetic field, fully incorporating recurrent
scattering processes to all orders. By considering an example of a
two-dimensional split ring resonator metamaterial array, we show that the
system responds cooperatively to near-resonant field, exhibiting collective
eigenmodes, resonance frequencies, and radiative linewidths that result from
strong radiative interactions between closely-spaced resonators.",1206.0204v2
2013-12-17,Dynamical resonance locking in tidally interacting binary systems,"We examine the dynamics of resonance locking in detached, tidally interacting
binary systems. In a resonance lock, a given stellar or planetary mode is
trapped in a highly resonant state for an extended period of time, during which
the spin and orbital frequencies vary in concert to maintain the resonance.
This phenomenon is qualitatively similar to resonance capture in planetary
dynamics. We show that resonance locks can accelerate the course of tidal
evolution in eccentric systems and also efficiently couple spin and orbital
evolution in circular binaries. Previous analyses of resonance locking have not
treated the mode amplitude as a fully dynamical variable, but rather assumed
the adiabatic (i.e. Lorentzian) approximation valid only in the limit of
relatively strong mode damping. We relax this approximation, analytically
derive conditions under which the fixed point associated with resonance locking
is stable, and further check these analytic results using numerical
integrations of the coupled mode, spin, and orbital evolution equations. These
show that resonance locking can sometimes take the form of complex limit cycles
or even chaotic trajectories. We provide simple analytic formulae that define
the binary and mode parameter regimes in which resonance locks of some kind
occur (stable, limit cycle, or chaotic). We briefly discuss the astrophysical
implications of our results for white dwarf and neutron star binaries as well
as eccentric stellar binaries.",1312.4966v2
2014-02-17,An Analytic Model for Buoyancy Resonances in Protoplanetary Disks,"Zhu, Stone, and Rafikov (2012) found in 3D shearing box simulations a new
form of planet-disk interaction that they attributed to a vertical buoyancy
resonance in the disk. We describe an analytic linear model for this
interaction. We adopt a simplified model involving azimuthal forcing that
produces the resonance and permits an analytic description of its structure. We
derive an analytic expression for the buoyancy torque and show that the
vertical torque distribution agrees well with results of Athena simulations and
a Fourier method for linear numerical calculations carried out with the same
forcing. The buoyancy resonance differs from the classic Lindblad and
corotation resonances in that the resonance lies along tilted planes. Its width
depends on damping effects and is independent of the gas sound speed. The
resonance does not excite propagating waves. At a given large azimuthal
wavenumber k_y > 1/h (for disk thickness h), the buoyancy resonance exerts a
torque over a region that lies radially closer to the corotation radius than
the Lindblad resonance. Because the torque is localized to the region of
excitation, it is potentially subject to the effects of nonlinear saturation.
In addition, the torque can be reduced by the effects of radiative heat
transfer between the resonant region and its surroundings. For each azimuthal
wavenumber, the resonance establishes a large scale density wave pattern in a
plane within the disk.",1402.4162v1
2014-04-29,Fano resonance control in a photonic crystal structure and its application to ultrafast switching,"Fano resonances appear in quantum mechanical as well as classical systems as
a result of the interference between two paths: one involving a discrete
resonance and the other a continuum. Compared to a conventional resonance,
characterized by a Lorentzian spectral response, the characteristic asymmetric
and sharp spectral response of a Fano resonance is suggested to enable photonic
switches and sensors with superior characteristics. While experimental
demonstrations of the appearance of Fano resonances have been made in both
plasmonic and photonic-crystal structures, the control of these resonances is
experimentally challenging, often involving the coupling of near-resonant
cavities. Here, we experimentally demonstrate two simple structures that allow
surprisingly robust control of the Fano spectrum. One structure relies on
controlling the amplitude of one of the paths and the other uses symmetry
breaking. Short-pulse dynamic measurements show that besides drastically
increasing the switching contrast, the transmission dynamics itself is strongly
affected by the nature of the resonance. The influence of slow-recovery tails
implied by a long carrier lifetime can thus be reduced using a Fano resonance
due to a hitherto unrecognized reshaping effect of the nonlinear Fano transfer
function. For the first time, we present a system application of a Fano
structure, demonstrating its advantages by the experimental realization of 10
Gbit/s all-optical modulation with bit-error-ratios on the order of 10$^{-7}$
for input powers less than 1 mW. These results represent a significant
improvement compared to the use of a conventional Lorentzian resonance.",1404.7532v1
2014-08-05,Resonant Chains and Three-body Resonances in the Closely-Packed Inner Uranian Satellite System,"Numerical integrations of the closely-packed inner Uranian satellite system
show that variations in semi-major axes can take place simultaneously between
three or four consecutive satellites. We find that the three-body Laplace angle
values are distributed unevenly and have histograms showing structure, if the
angle is associated with a resonant chain, with both pairs of bodies near
first-order two-body resonances. Estimated three-body resonance libration
frequencies can be only an order of magnitude lower than those of first-order
resonances. Their strength arises from a small divisor from the distance to the
first-order resonances and insensitivity to eccentricity, which make up for
their dependence on moon mass. Three-body resonances associated with
low-integer Laplace angles can also be comparatively strong due to the many
multiples of the angle contributed from Fourier components of the interaction
terms. We attribute small coupled variations in semi-major axis, seen
throughout the simulation, to ubiquitous and weak three-body resonant
couplings. We show that a system with two pairs of bodies in first-order
mean-motion resonance can be transformed to resemble the well-studied
periodically-forced pendulum with the frequency of a Laplace angle serving as a
perturbation frequency. We identify trios of bodies and overlapping pairs of
two-body resonances in each trio that have particularly short estimated
Lyapunov timescales.",1408.1141v1
2014-09-11,Universal non-resonant absorption in carbon nanotubes,"Photoluminescence excitation measurements in semi-conducting carbon nanotubes
show a systematic non-resonant contribution between the well known excitonic
resonances. Using a global analysis method, we were able to delineate the
contribution of each chiral species including its tiny non-resonant component.
By comparison with the recently reported excitonic absorption cross-section on
the $S_{22}$ resonance, we found a universal non-resonant absorbance which
turns out to be of the order of one half of that of an equivalent graphene
sheet. This value as well as the absorption line-shape in the non-resonant
window is in excellent agreement with microscopic calculations based on the
density matrix formalism. This non-resonant absorption of semi-conducting
nanotubes is essentially frequency independent over 0.5~eV wide windows and
reaches approximately the same value betweeen the $S_{11}$ and $S_{22}$
resonances or between the $S_{22}$ and $S_{33}$ resonances. In addition, the
non-resonant absorption cross- section turns out to be the same for all the
chiral species we measured in this study. From a practical point of view, this
study puts firm basis on the sample content analysis based on photoluminescence
studies by targeting specific excitation wavelengths that lead to almost
uniform excitation of all the chiral species of a sample within a given
diameter range.",1409.3441v1
2015-02-23,Theoretical characterization of the collective resonance states underlying the xenon giant dipole resonance,"We present a detailed theoretical characterization of the two fundamental
collective resonances underlying the xenon giant dipole resonance (GDR). This
is achieved consistently by two complementary methods implemented within the
framework of the configuration-interaction singles (CIS) theory. The first
method accesses the resonance states by diagonalizing the many-electron
Hamiltonian using the smooth exterior complex scaling technique. The second
method involves a new application of the Gabor analysis to wave-packet
dynamics. We identify one resonance at an excitation energy of 74 eV with a
lifetime of 27 as, and the second at 107 eV with a lifetime of 11 as. Our work
provides a deeper understanding of the nature of the resonances associated with
the GDR: a group of close-lying intrachannel resonances splits into two
far-separated resonances through interchannel couplings involving the 4d
electrons. The CIS approach allows a transparent interpretation of the two
resonances as new collective modes. Due to the strong entanglement between the
excited electron and the ionic core, the resonance wave functions are not
dominated by any single particle-hole state. This gives rise to plasma-like
collective oscillations of the 4d shell as a whole.",1502.06462v1
2015-03-01,Magnetic-dipolar-mode Fano resonances for microwave spectroscopy of high absorption matter,"Study of interaction between high absorption matter and microwave radiated
energy is a subject of great importance. Especially, this concerns microwave
spectroscopic characterization of biological liquids. Use of effective testing
methods to obtain information about physical properties of different liquids on
the molecular level is one of the most important problems in biophysics.
However, the standard methods based on the microwave resonant techniques are
not sufficiently suitable for biological liquids because the resonance peak in
a resonator with high-loss liquids is so broad that the material parameters
cannot be measured correctly. Although molecular vibrations of biomolecules may
have microwave frequencies, it is not thought that such resonant coupling is
significant due to their low energy compared with thermal energy and the
strongly dampening aqueous environment. This paper presents an innovative
microwave sensing technique for different types of lossy materials, including
biological liquids. The technique is based on the combination of the microwave
perturbation method and the Fano-resonance effects observed recently in
microwave structures with embedded magnetic-dipolar quantum dots. When
frequency of the magnetic-dipolar-mode (MDM) resonance is not equal to the
cavity resonance frequency, one gets Fano transmission intensity. With tuning,
by a bias magnetic field, the MDM resonance frequency to the cavity resonance
frequency, one observes a Lorentz line shape. Use of an extremely narrow
Lorentzian peak allows exact probing the resonant frequency of a cavity loaded
by a high-lossy-material sample. For different kinds of samples, one has
different frequencies of Lorentzian peaks. This gives a picture for precise
spectroscopic characterization of high absorption matter in microwaves.",1503.00286v1
2016-12-22,Frequency control and coherent excitation transfer in a nanostring resonator network,"Coupling, synchronization, and non-linear dynamics of resonator modes are
omnipresent in nature and highly relevant for a multitude of applications
ranging from lasers to Josephson arrays and spin torque oscillators.
Nanomechanical resonators are ideal candidates to study these effects on a
fundamental level and to realize all-mechanical platforms for information
processing and storage. For larger resonator networks, however, this requires
the ability to tune the mode frequencies selectively and to operate the
resonators in the strong coupling regime. Here, we present a proof-of-principle
realization of a resonator network consisting of two high-quality nanostring
resonators, coupled mechanically by a shared support. First, we demonstrate
that we can control the fundamental mode frequencies of both nanostrings
independently by a strong drive tone resonant with one of the higher harmonics
of the network, rendering local control gates redundant. The tuning mechanism
relies on an effective increase of the pre-stress in a highly excited
nanostring, known as geometric nonlinearity. Using this selective frequency
control of the individual nanomechanical resonators, we investigate the
coherent dynamics of the resonator network, which is a classical model system
showing several of the characteristic features of strongly coupled quantum
systems. In particular, we demonstrate mode splitting, classical Rabi
oscillations, as well as adiabatic and diabatic transitions between the coupled
states representing the classical analog of Landau-Zener tunneling. Therefore,
this coupling and tuning concept opens the path to a selective phonon transfer
between two spatially separated mechanical resonators.",1612.07511v1
2018-09-24,Secular Resonance Between Iapetus and the Giant Planets,"Using numerical integrations, we find that the orbital eccentricity of
Saturn's moon Iapetus undergoes prominent multi-Myr oscillations. We identify
the responsible resonant argument to be
$\varpi-\varpi_{g5}+\Omega-\Omega_{eq}$, with the terms being the longitudes of
pericenter of Iapetus and planetary secular mode $g_5$, Iapetus's longitude of
the node and Saturn's equinox. We find that this argument currently (on a
$10^7$~yr timescale) appears to librate with a very large amplitude. On longer
timescales, the behavior of this resonant angle is strongly dependent on the
resonant interaction between Saturn's spin axis and the planetary mode $f_8$,
with long-term secular resonance being possible if Saturn's equinox is
librating relative to the node of the $f_8$ eigenmode. We present analytical
estimates of the dependence of the resonant argument on the orbital elements of
Iapetus. We find that this Iapetus-$g_5$ secular resonance could have been
established only after the passage of Iapetus through the 5:1 mean-motion
resonance with Titan, possibly in the last Gyr. Using numerical simulations, we
show that the capture into the secular resonance appears to be a
low-probability event. While the Iapetus-$g_5$ secular resonance can
potentially help us put new constraints on the past dynamics of the Saturnian
system, uncertainties in both the spin axis dynamics of Saturn and the tidal
evolution rate of Titan make it impossible to make any firm conclusions about
the resonance's longevity and origin.",1809.09072v1
2018-09-26,First-order mean motion resonances in two-planet systems: general analysis and observed systems,"This paper focuses on two-planet systems in a first-order $(q+1):q$ mean
motion resonance and undergoing type-I migration in a disc. We present a
detailed analysis of the resonance valid for any value of $q$. Expressions for
the equilibrium eccentricities, mean motions and departure from exact resonance
are derived in the case of smooth convergent migration. We show that this
departure, not assumed to be small, is such that period ratio normally exceeds,
but can also be less than, $ (q+1)/q.$ Departure from exact resonance as a
function of time for systems starting in resonance and undergoing divergent
migration is also calculated. We discuss observed systems in which two low mass
planets are close to a first-order resonance. We argue that the data are
consistent with only a small fraction of the systems having been captured in
resonance. Furthermore, when capture does happen, it is not in general during
smooth convergent migration through the disc but after the planets reach the
disc inner parts. We show that although resonances may be disrupted when the
inner planet enters a central cavity, this alone cannot explain the spread of
observed separations. Disruption is found to result in either the system moving
interior to the resonance by a few percent, or attaining another resonance. We
postulate two populations of low mass planets: a small one for which extensive
smooth migration has occurred, and a larger one that formed approximately
in-situ with very limited migration.",1809.10042v1
2020-04-05,Resonant high-energy bremsstrahlung of ultrarelativistic electrons in the field of a nucleus and a pulsed light wave,"The actual theoretical research investigates the resonant high-energy
spontaneous bremsstrahlung of ultrarelativistic electrons with considerable
energies in the field of a nucleus and a quasimonochromatic laser wave. Under
the resonant conditions within the laser field the intermediate virtual
electron transforms into the real particle. As a result, the accomplished
analysis defines that the polar emission angle characterizes the frequency of a
spontaneous photon. The study derives the expressions for the resonant
differential cross-sections of the represented processes that realize
simultaneous registration of the frequency and radiation angle in correlation
to the momentum of the initial electron (for the channel A) and of the final
electron (for the channel B) of the spontaneous photon with absorption of $r$
wave photons ($r = 1, 2, 3,... $ - the number of a resonance). Additionally,
the distribution of the resonant differential cross-section as a function of
the angle of the spontaneous photon emission for the higher numbers of
resonance ($r = 2, 3,... $) delineates a dependency with a sharp peak maximum
that coordinates to the particle radiation at the most probable frequency. To
summarize, the accomplished work represents that the resonant differential
cross-section acquires considerable magnitude. Thus, for the first resonance of
the channel A the resonant differential cross-section attains the $\sim
10^{12}$ order of a magnitude, and for the third resonance of the channel B
$\sim 10^5$ order of a magnitude (in the units of $\alpha Z^2 r_e^2$). Finally,
numerous scientific facilities with specialization in pulsed laser radiation
(SLAC, FAIR, XFEL, ELI, XCELS) may experimentally verify the constructed model
calculations.",2004.02247v1
2020-12-16,Perfectly-reflecting guided-mode-resonant photonic lattices possessing Mie modal memory,"Resonant periodic nanostructures provide perfect reflection across small or
large spectral bandwidths depending on the choice of materials and design
parameters. This effect has been known for decades, observed theoretically and
experimentally via one-dimensional and two-dimensional structures commonly
known as resonant gratings, metamaterials, and metasurfaces. The physical cause
of this extraordinary phenomenon is guided-mode resonance mediated by lateral
Bloch modes excited by evanescent diffraction orders in the subwavelength
regime. In recent years, hundreds of papers have declared Fabry-Perot or Mie
resonance to be basis of the perfect reflection possessed by periodic
metasurfaces. Treating a simple one-dimensional cylindrical-rod lattice, here
we show clearly and unambiguously that Mie resonance does not cause perfect
reflection. In fact, the spectral placement of the Bloch-mode-mediated
zero-order reflectance is primarily controlled by the lattice period by way of
its direct effect on the homogenized effective-medium refractive index of the
lattice. In general, perfect reflection appears away from Mie resonance.
However, when the lateral leaky-mode field profiles approach the
isolated-particle Mie field profiles, the resonance locus tends towards the Mie
resonance wavelength. The fact that the lattice fields remember the isolated
particle fields is referred here as Mie modal memory. On erasure of the Mie
memory by an index-matched sublayer, we show that perfect reflection survives
with the resonance locus approaching the homogenized effective-medium waveguide
locus. The results presented here will aid in clarifying the physical basis of
general resonant photonic lattices.",2012.09321v1
2020-12-23,Domino cooling of a coupled mechanical-resonator chain via cold-damping feedback,"We propose a domino-cooling method to realize simultaneous ground-state
cooling of a coupled mechanical-resonator chain through an optomechanical
cavity working in the unresolved-sideband regime. This domino-effect cooling is
realized by combining the cold-damping feedback on the first mechanical
resonator with nearest-neighbor couplings between other neighboring mechanical
resonators. We obtain analytical results for the effective susceptibilities,
noise spectra, final mean phonon numbers, and cooling rates of these mechanical
resonators, and find the optimal-cooling condition for these resonators.
Particularly, we analyze a two-mechanical-resonator case and find that by
appropriately engineering either the laser power or the feedback, a flexible
switch between symmetric and asymmetric ground-state cooling can be achieved.
This could be used for preparing symmetric quantum states in mechanical
systems. We also simulate the cooling performance of a coupled
$N$-mechanical-resonator chain and confirm that these resonators can be
simultaneously cooled to their quantum ground states in the unresolved-sideband
regime. Under proper parameter conditions, the cooling of the
mechanical-resonator chain shows a temperature gradient along the chain. This
study opens a route to quantum manipulation of multiple mechanical resonators
in the bad-cavity regime.",2012.12665v2
2012-05-07,Study of tunable resonances in laser beam divergence and beam deflection,"New, fundamental resonant properties of laser resonators are theoretically
predicted and experimentally demonstrated. These resonances occur either in the
time dependence of the beam width and that of beam radius of curvature of the
wavefront or in the time dependent pointing and position stability of the
output light beam of a laser resonator. The resonant frequency can be tuned
continuously from zero to the round-trip frequency in the first case; and from
zero to the half of the round-trip frequency in the second case, by for
example, moving one of the mirrors of the resonator. In both cases besides a
resonant frequency its complementary frequency to the round-trip frequency is
also resonant, and their shifted frequencies by multiples of the round-trip
frequency are also resonant. In our experimental demonstration we measured the
radiofrequency noise spectrum of the output laser beam, that was partially
blocked by a knife-edge. We observed increased noise at the theoretically
predicted frequencies. Similar resonances are predicted either in the time
dependent pulse-width and phase modulation or time jitter and the central
frequency of the ultrashort light pulses of the mode-locked lasers because of
the analogy between the space description of the light beams and the
time-description of the light pulses.",1205.1339v2
2018-08-30,Large scale changes in overtone resonances and resonant peak burning of HBAR with mass loading and its potential for applications,"This report presents the realization and characterization of a robust
composite resonator i.e. high overtone bulk acoustic wave resonator (HBAR) and
the changes happening to the resonance peaks once it undergoes mass loading
which has got the potential for application in material characterization,
communication system and sensing. Mass loading effect on a HBAR based on
BaxSr1-xTiO3 (BST) have been demonstrated by coating photoresist of various
thicknesses and characterization of resonance modes present in the frequency
spectrum of the resonator. Upon investigation, HBAR proves to be one of the
most promising and robust systems for gravimetric sensing. Burning effect in
the resonances occurs and it shifts significantly according to the amount of
mass loaded (increasing thickness of the photoresist coated) on the resonator
system. Some of the most important parameters like effective coupling
coefficient, spacing of parallel resonance frequency (SPRF) and quality factor
of the resonator and its numerous modes have been investigated meticulously.",1808.10118v2
2019-01-04,Permittivity and Conductivity Measured using a Novel Toroidal Split-Ring Resonator,"We describe and demonstrate the use of a novel toroidal split-ring resonator
to make accurate and precise measurements of the permittivity of liquids and
gases. We first analytically show how the resonance frequency and quality
factor of the resonator are related to the complex permittivity of the material
filling its gap. We then use the resonator to experimentally determine the
permittivity of a number of different materials. First, the compact and high-Q
resonator is used to measure both the real and imaginary parts of the complex
permittivity of methyl alcohol at 185 MHz. Second, the resonator was placed
inside a vacuum-tight Dewar. We measured the resonance frequency with the
resonator suspended in vacuum and then immersed in an atmosphere of air. From
these data, the dielectric constant of air was accurately determined. Next, the
resonator was submerged in liquid nitrogen and the boiling temperature of the
nitrogen bath was manipulated by regulating its vapor pressure. This system
allowed for a precise measurement of the dielectric constant of liquid nitrogen
over a temperature range of 64 to 77 K. Finally, we monitored the quality
factor of the copper resonator as its temperature drifted from 80 K to room
temperature. From these data, we extracted the linear temperature dependence of
copper's resistivity.",1901.00994v1
2019-08-30,Dynamical generation of resonances in the P33 partial wave,"We investigate the formation of resonances in the P33 partial wave with the
emphasis on possible emergence of dynamically generated quasi-bound states as a
consequence of a strong $p$-wave pion attractive interaction in this partial
wave, as well as their possible interaction with the genuine quark excited
states. By using the Laurent-Pietarinen expansion we follow the evolution of
the $S$-matrix poles in the complex energy plane as a function of the
interaction strength. Already without introducing a genuine quark resonant
state, two physically interesting resonances emerge with pole masses around
1200 MeV and 1400 MeV, with the dominant $\pi N$ and $\pi\Delta$ component,
respectively. The added genuine resonant state in the $(1s)^3$ quark
configuration mixes with the lower dynamically generated resonance forming the
physical $\Delta(1232)$ resonance, and pushes the second dynamical resonance to
around 1500 MeV, which allows it to be identified with the $\Delta(1600)$
resonance. Adding a second resonant state with one quark promoted to the $2s$
orbit generates another pole whose evolution remains well separated from the
lower two poles. We calculate the helicity amplitudes at the pole and suggest
that their $Q^2$ dependence could be a decisive test to discriminate between
different models of the $\Delta(1600)$ resonance.",1908.11750v1
2020-08-31,Dust distribution around low-mass planets on converging orbits,"Super-Earths can form at large orbital radii and migrate inward due to tidal
interactions with the circumstellar disk. In this scenario, convergent
migration may occur and lead to the formation of resonant pairs of planets. We
explore the conditions under which convergent migration and resonance capture
take place, and what dynamical consequences can be expected on the dust
distribution surrounding the resonant pair. We combine hydrodynamic
planet--disk interaction models with dust evolution calculations to investigate
the signatures produced in the dust distribution by a pair of planets in
mean-motion resonances. We find that convergent migration takes place when the
outer planet is the more massive. However, convergent migration also depends on
the local properties of the disk, and divergent migration may result as well.
For similar disk parameters, the capture in low degree resonances (e.g., 2:1 or
3:2) is preferred close to the star where the resonance strength can more
easily overcome the tidal torques exerted by the gaseous disk. Farther away
from the star, convergent migration may result in capture in high degree
resonances. The dust distribution shows potentially observable features
typically when the planets are trapped in a 2:1 resonance. In other cases, with
higher degree resonances (e.g., 5:4 or 6:5) dust features may not be
sufficiently pronounced to be easily observable. The degree of resonance
established by a pair of super-Earths may be indicative of the location in the
disk where capture occurred. There can be significant differences in the dust
distribution around a single super-Earth and a pair of super-Earths in
resonance.",2008.13464v1
2020-11-30,Resonances for Schrödinger operators on infinite cylinders and other products,"We study the resonances of Schr\""odinger operators on the infinite product
$X=\mathbb{R}^d\times \mathbb{S}^1$, where $d$ is odd, $\mathbb{S}^1$ is the
unit circle, and the potential $V\in L^\infty_c(X)$. This paper shows that at
high energy, resonances of the Schr\""odinger operator $-\Delta +V$ on
$X=\mathbb{R}^d\times \mathbb{S}^1$ which are near the continuous spectrum are
approximated by the resonances of $-\Delta +V_0$ on $X$, where the potential
$V_0$ given by averaging $V$ over the unit circle. These resonances are, in
turn, given in terms of the resonances of a Schr\""odinger operator on
$\mathbb{R}^d$ which lie in a bounded set. If the potential is smooth, we
obtain improved localization of the resonances, particularly in the case of
simple, rank one poles of the corresponding scattering resolvent on
$\mathbb{R}^d$. In that case, we obtain the leading order correction for the
location of the corresponding high energy resonances. In addition to direct
results about the location of resonances, we show that at high energies away
from the resonances, the resolvent of the model operator $-\Delta+V_0$ on $X$
approximates that of $-\Delta+V$ on $X$. If $d=1$, in certain cases this
implies the existence of an asymptotic expansion of solutions of the wave
equation. Again for the special case of $d=1$, we obtain a resonant rigidity
type result for the zero potential among all real-valued potentials.",2011.14513v2
2021-04-29,Resonant Chains of Exoplanets: Libration Centers for Three-body Angles,"Resonant planetary systems contain at least one planet pair with orbital
periods librating at a near-integer ratio (2/1, 3/2, 4/3, etc.) and are a
natural outcome of standard planetary formation theories. Systems with multiple
adjacent resonant pairs are known as resonant chains and can exhibit three-body
resonances -- characterized by a critical three-body angle. Here we study
three-body angles as a diagnostic of resonant chains through tidally-damped
N-body integrations. For each combination of the 2:1, 3:2, 4:3, and 5:4 mean
motion resonances (the most common resonances in the known resonant chains), we
characterize the three-body angle equilibria for several mass schemes,
migration timescales, and initial separations. We find that under our
formulation of the three-body angle, which does not reduce coefficients, 180
deg is the preferred libration center, and libration centers shifted away from
180 deg are associated with non-adjacent resonances. We then relate these
angles to observables, by applying our general results to two transiting
systems: Kepler-60 and Kepler-223. For these systems, we compare N-body models
of the three-body angle to the zeroth order in e approximation accessible via
transit phases, used in previous publications. In both cases, we find the
three-body angle during the Kepler observing window is not necessarily
indicative of the long-term oscillations and stress the role of dynamical
models in investigating three-body angles. We anticipate our results will
provide a useful diagnostic in the analysis of resonant chains.",2104.14665v1
2022-01-26,"Eviction-like resonances for satellite orbits. Application to Phobos, the main satellite of Mars","The motion of a satellite can experience secular resonances between the
precession frequencies of its orbit and the mean motion of the host planet
around the star. Some of these resonances can significantly modify the
eccentricity (evection resonance) and the inclination (eviction resonance) of
the satellite. In this paper, we study in detail the secular resonances that
can disturb the orbit of a satellite, in particular the eviction-like ones.
Although the inclination is always disturbed while crossing one eviction-like
resonance, capture can only occur when the semi-major axis is decreasing. This
is, for instance, the case of Phobos, the largest satellite of Mars, that will
cross some of these resonances in the future because its orbit is shrinking
owing to tidal effects. We estimate the impact of resonance crossing in the
orbit of the satellite, including the capture probabilities, as a function of
several parameters, such as the eccentricity and the inclination of the
satellite, and the obliquity of the planet. Finally, we use the method of the
frequency map analysis to study the resonant dynamics based on stability maps,
and we show that some of the secular resonances may overlap, which leads to
chaotic motion for the inclination of the satellite.",2201.10708v1
2022-04-06,Asymptotics of the meta-atom: plane wave scattering by a single Helmholtz resonator,"Using a combination of multipole methods and the method of matched
asymptotics, we present a solution procedure for acoustic plane wave scattering
by a single Helmholtz resonator in two dimensions. Closed-form representations
for the multipole scattering coefficients of the resonator are derived, valid
at low frequencies, with three fundamental configurations examined in detail:
the thin-walled, moderately thick-walled, and very thick-walled limits.
Additionally, we examine the impact of dissipation for very thick-walled
resonators, and also numerically evaluate the scattering, absorption, and
extinction cross sections (efficiencies) for representative resonators in all
three wall thickness regimes. In general, we observe strong enhancement in both
the scattered fields and cross sections at the Helmholtz resonance frequencies.
As expected, dissipation is shown to shift the resonance frequency, reduce the
amplitude of the field, and reduce the extinction efficiency at the fundamental
Helmholtz resonance. Finally, we confirm results in the literature on
Willis-like coupling effects for this resonator design, and crucially, connect
these findings to earlier works by the authors on two-dimensional arrays of
resonators, deducing that depolarisability effects (off-diagonal terms) for a
single resonator do not ensure the existence of Willis coupling effects
(bianisotropy) in bulk.",2204.02840v1
2022-05-23,Dynamical essence of the eccentric von Zeipel-Lidov-Kozai effect in restricted hierarchical planetary systems,"Aim. The eccentric von Zeipel-Lidov-Kozai (ZLK) effect is widely used to
explain dynamical phenomena in varieties of astrophysical systems. The purpose
of this work is to make clear the dynamical essence of the eccentric ZLK effect
by constructing an inherent connection between such an effect and dynamics of
secular resonance in restricted hierarchical planetary systems. Methods.
Dynamical structures of apsidal resonance are analytically studied by means of
perturbative treatments. The resonant model is formulated by averaging the
Hamiltonian (up to octupole order) over rotating ZLK cycles, producing an
additional motion integral. The phase portraits under the resonant model can be
used to analyse dynamical structures, including resonant centres, dynamical
separatrices and islands of libration. Results. By analysing phase portraits,
five branches of libration centres and eight libration zones are found in the
eccentricity--inclination space. There is an excellent agreement between
analytical results of libration zone and numerical distributions of resonant
orbit, indicating that the resonant model for apsidal resonances is valid and
applicable. Additionally, it is found that, in the test-particle limit,
distributions of flipping orbits are dominated by those apsidal resonances
centred at the inclination of i = 90 deg. Conclusions. The eccentric ZLK effect
is dynamically equivalent to the effect of apsidal resonance in restricted
hierarchical planetary systems. The dynamical response of the eccentric ZLK
effect (or effect of apsidal resonance) is to significantly excite
eccentricities and/or inclinations of test particles in the very long-term
evolution.",2205.11238v1
2022-06-02,Mechanical dissipation by substrate-mode coupling in SiN resonators,"State-of-the-art nanomechanical resonators are heralded as a central
component for next-generation clocks, filters, resonant sensors and quantum
technologies. To practically build these technologies will require monolithic
integration of microchips, resonators and readout systems. While it is widely
seen that mounting microchip substrates into a system can greatly impact the
performance of high-Q resonators, a systematic study has remained elusive,
owing to the variety of physical processes and factors that influence the
dissipation. Here, we analytically analyze a mechanism by which substrates
couple to resonators manufactured on them, and experimentally demonstrate that
this coupling can increase the mechanical dissipation of nanomechanical
resonators when the resonance frequencies of resonator and substrate coincide.
More generally, we then show a similar coupling mechanism can exist between two
adjacent resonators. Since the substrate-mode coupling mechanism strongly
depends on both the resonator position on the substrate and the mounting of the
substrate, this work provides key design guidelines for high-precision
nanomechanical technologies.",2206.00990v2
2023-05-19,Analytic evaluation of non-adiabatic couplings within the complex absorbing potential equation-of-motion coupled-cluster method,"We present the theory for the evaluation of non-adiabatic couplings (NACs)
involving resonance states within the complex absorbing potential
equation-of-motion coupled-cluster (CAP-EOM-CC) framework implemented within
the singles and doubles approximation. Resonance states are embedded in the
continuum and undergo rapid decay through autodetachment. In addition, nuclear
motions can facilitate transitions between different resonances and between
resonances and bound states. These non-adiabatic transitions affect the
chemical fate of resonances and have distinct spectroscopic signatures. The NAC
vector is a central quantity needed to model such effects.
  In the CAP-EOM-CC framework, resonance states are treated on the same footing
as bound states. Using the example of fumaronitrile, which supports a bound
radical anion and several anionic resonances, we analyze the non-adiabatic
coupling between bound states and pseudocontinuum states, between bound states
and resonances and between two resonances. We find that the NAC between a bound
state and a resonance is nearly independent of the CAP strength and thus
straightforward to evaluate whereas the NAC between two resonance states or
between a bound state and a pseudocontinuum state is more difficult to
evaluate.",2305.11724v2
2023-07-20,The loop-zag resonator: A loop-gap resonator design for improved sensitivity in electron-spin resonance experiments,"We present a novel design of loop-gap resonator, the loop-zag resonator, for
sub-X-band electron-spin resonance spectroscopy. The loop-zag design can
achieve improved coupling to small-sample spin systems through the improvement
of sample filling factor and RF $B_1$ field. By introducing ``zags'' to the
resonator's gap path, the capacitance is increased, accommodating a smaller
loop size and thereby a larger filling factor to maintain the requisite
resonant frequency. We present experimental spectra on five different
resonators, each with approximately the same resonant frequency of
$\sim2.9$~GHz, showing that an increase in the number of zags and reduction in
loop size gives rise to higher sensitivity. Finite-element simulations of these
resonators provide estimates of the improved filling factors obtained through
the addition of zags. The frequency range over which this loop-zag design is
practical enables a breadth of future applications in microwave engineering,
including ESR and ESR-like quantum information microwave techniques.",2307.11269v1
2023-08-15,Inner-scaled Helmholtz resonators with grazing turbulent boundary layer flow,"Response details are presented of small-scale Helmholtz resonators excited by
grazing turbulent boundary layer flow. A particular focus lies on scaling of
the resonance, in relation to the spatio-temporal characteristics of the
near-wall velocity and wall-pressure fluctuations. Resonators are tuned to
different portions of the inner-spectral peak of the boundary-layer
wall-pressure spectrum, at a spatial scale of $\lambda_x^+ \approx 250$ (or
temporal scale of $T^+ \approx 25$). Following this approach, small-scale
resonators can be designed with neck-orifice diameters of minimum intrusiveness
to the grazing flow. Here we inspect the TBL response by analysing velocity
data obtained with hot-wire anemometry and particle image velocimetry
measurements. This strategy follows the earlier work by Panton and Miller (J.
Acoust. Soc. Am. 526, 800, 1975) in which only the change in resonance
frequency, due to the grazing flow turbulence, was examined. Single resonators
are examined in a boundary layer flow at $Re_\tau \approx 2\,280$. Two
neck-orifice diameters of $d^+ \approx 68$ and 102 are considered, and for each
value of $d^+$ three different resonance frequencies are studied (targeting the
spatial scale of $\lambda_x^+ \approx 250$, as well as sub- and
super-wavelengths). Passive resonance only affects the streamwise velocity
fluctuations in the region $y^+ \lesssim 25$, while the vertical velocity
fluctuations are seen in a layer up to $y^+ \approx 100$. A narrow-band
increase in streamwise turbulence kinetic energy at the resonance scale
co-exists with a more than 20% attenuation of lower-frequency (larger scale)
energy. Current findings inspire further developments of passive surfaces that
utilize the concept of changing the local wall-impedance for boundary-layer
flow control, using miniature resonators as a meta-unit.",2308.07776v1
2024-01-16,Tracking Superharmonic Resonances for Nonlinear Vibration,"Many modern engineering structures exhibit nonlinear vibration.
Characterizing such vibrations efficiently is critical to optimizing designs
for reliability and performance. For linear systems, steady-state vibration
occurs only at the forcing frequencies. However, nonlinearities (e.g., contact,
friction, large deformation, etc.) can result in nonlinear vibration behavior
including superharmonics - responses at integer multiples of the forcing
frequency. When the forcing frequency is near an integer fraction of the
natural frequency, superharmonic resonance occurs, and the magnitude of the
superharmonics can exceed that of the fundamental harmonic that is externally
forced. Characterizing such superharmonic resonances is critical to improving
engineering designs. The present work extends the concept of phase resonance
nonlinear modes (PRNM) to be applicable to general nonlinearities, and is
demonstrated for eight different nonlinear forces. The considered forces
include stiffening, softening, contact, damping, and frictional nonlinearities
that have not been previously considered with PRNM. The proposed variable phase
resonance nonlinear modes (VPRNM) method can accurately track superharmonic
resonances for hysteretic nonlinearities that exhibit amplitude dependent phase
resonance conditions that cannot be captured by PRNM. The proposed method
allows for characterization of superharmonic resonances without constructing a
full frequency response curve at every force level with the harmonic balance
method. Thus, the present method allows for analysis of potential failures due
to large amplitudes near the superharmonic resonance with reduced computational
cost. The consideration of single degree of freedom systems in the present
paper provides insights into superharmonic resonances and a basis for
understanding internal resonances for multiple degree of freedom systems.",2401.08790v1
1998-05-27,Resonant relaxation in protoplanetary disks,"Resonant relaxation is a novel form of two-body relaxation that arises in
nearly Keplerian disks such as protoplanetary disks. Resonant relaxation does
not affect the semimajor axes of the particles, but enhances relaxation of
particle eccentricities and inclinations. The equilibrium state after resonant
relaxation is a Rayleigh distribution, with the mean-square eccentricity and
inclination inversely proportional to mass. The rate of resonant relaxation
depends strongly on the precession rate of the disk. If the precession due to
the disk's self-gravity is small compared to the total precession, then the
relaxation is concentrated near the secular resonance between each pair of
interacting bodies; on the other hand if the precession rate is dominated by
the disk's self-gravity then relaxation occurs through coupling to the
large-scale low-frequency m=1 normal modes of the disk. Depending on the disk
properties, resonant relaxation may be either stronger or weaker than the usual
non-resonant relaxation.",9805334v1
2001-12-19,A non-linear theory of vertical resonances in accretion discs,"An important and widely neglected aspect of the interaction between an
accretion disc and a massive companion with a coplanar orbit is the vertical
component of the tidal force. As shown by Lubow, the response of the disc to
vertical forcing is resonant at certain radii, at which a localized torque is
exerted, and from which a compressive wave (p mode) may be emitted. Although
these vertical resonances are weaker than the corresponding Lindblad
resonances, the m=2 inner vertical resonance in a binary star is typically
located within the tidal truncation radius of a circumstellar disc.
  In this paper I develop a general theory of vertical resonances, allowing for
non-linearity of the response, and dissipation by radiative damping and
turbulent viscosity. The problem is reduced to a universal, non-linear ordinary
differential equation with two real parameters. Solutions of the complex
non-linear Airy equation are presented to illustrate the non-linear saturation
of the resonance and the effects of dissipation. It is argued that the m=2
inner vertical resonance is unlikely to truncate the disc in cataclysmic
variable stars, but contributes to angular momentum transport and produces a
potentially observable non-axisymmetric structure.",0112443v1
2004-06-21,A search for cyclotron resonance features with INTEGRAL,"We present an INTEGRAL observation of the Cen-Crux region in order to search
the electron cyclotron resonance scattering features from the X-ray binary
pulsars. During the AO1 200ks observation, we clearly detected 4 bright X-ray
binaries, 1 Seyfert Galaxy, and 4 new sources in the field of view. Especially
from GX301-2, the cyclotron resonance feature is detected at about 37 keV, and
width of 3--4 keV. In addition, the depth of the resonance feature strongly
depends on the X-ray luminosity. This is the first detection of luminosity
dependence of the resonance depth. The cyclotron resonance feature is
marginally detected from 1E1145.1-6141. Cen X-3 was very dim during the
observation and poor statistics disable us to detect the resonance
features.These are first INTEGRAL results of searching for the cyclotron
resonance feature.",0406449v1
2004-10-19,The Drag Induced Resonant Capture for Kuiper Belt Objects,"It has been an interesting question that why there are one-third of Kuiper
Belt Objects (KBOs) trapped into the 3:2 resonance but, in contrast, only
several KBOs are claimed to be associated with the 2:1 resonance. In a model
proposed by Zhou et al. (2002), the stochastic outward migration of the Neptune
could reduce the number of particles in the 2:1 resonance and thus the objects
in the 3:2 resonance become more distinct. As a complementary study, we
investigate the effect of proto-stellar discs on the resonance capture. Our
results show that the gaseous drag of a proto-stellar disc can trap KBOs into
the 3:2 resonance rather easily. In addition, no objects are captured into the
2:1 resonance in our simulation.",0410426v2
2005-06-29,Neutron Catalysis of Resonance Fusion in Stellar Matter,"Within the framework of resonance fusion study in stellar matter the features
of system consisted of two alpha particles and one neutron have been
investigated at astrophysical energies. Consideration of three body scattering
has been carried out on base of well-known Faddeev's equations. It is found
that under certain conditions the series of resonance states appear in this
system at very low energies. The lifetimes of these three body resonances are
close to the lifetime of unstable nucleus 8Be. The simple forms of two body
repulsive potentials are taken into account to describe the parameters of the
alpha, alpha resonance and to satisfy n, alpha scattering data at very low
energies. The explanation of resonance phenomena in n, alpha, alpha system is
offered on base of physical model. The effect results from resonance quantum
phenomena in few body dynamics. In turn, the resonance fusion can give
influence on many astrophysical phenomena. The possibility of catalyzing this
new mode of fusion by free neutrons in alpha particle matter is considered too.",0506734v2
2006-04-27,"Resonance scattering, absorption and off-centre abundance peaks in clusters of galaxies","A possible explanation for the central abundance dips found from
spatially-resolved X-ray spectroscopy of several groups and clusters of
galaxies is resonance scattering. A number of the prominent iron emission lines
are resonance lines. We construct a unique spectral model which takes account
of resonance scattering for several thousand resonance lines, projection
effects, photoelectric absorption, and allows direct spectral fitting. We apply
our model to Chandra observations of two clusters with pronounced central
abundance dips, Centaurus and Abell 2199. The results show that the effect of
resonance scattering on emission from the centre of the cluster can be as much
as 30 per cent for the Fe-K resonance lines, and 10 per cent for several Fe-L
lines, if turbulence is low. The change to the metallicities obtained by
fitting low resolution CCD spectra is at most 10 per cent. Accounting for
resonance scattering does not remove the central dip. Allowing for internal
absorption within the Centaurus significantly improves the quality of the fits,
indicating the presence of absorbing material within the inner 40 kpc of NGC
4696.",0604575v1
2006-05-18,Resonant Relaxation near the Massive Black Hole in the Galactic Center,"The coherent torques between stars on orbits near massive black holes (MBHs)
lead to resonant angular momentum relaxation. Due to the fact that orbits are
Keplerian to good approximation, the torques efficiently change the magnitude
of the angular momenta and rotate the orbital inclinations. As a result the
stars are rapidly randomized. The galactic MBH is a good system for the
observational study of resonant relaxation. The age of the young B-stars at a
distance of $\sim0.01 pc$ from the MBH is comparable to the resonant relaxation
time, implying that resonant relaxation may have played an important role in
their dynamical structure. In contrast, the O-stars in the stellar disks at
$\sim0.1 pc$ are younger than the resonant relaxation time, as required by
their dynamical coherence. Resonant relaxation dynamics dominates the event
rate of gravitational wave (GW) emission from inspiraling stars into MBHs of
masses comparable to the Galactic MBH. Resonant relaxation leads to rates
$\lesssim 10$ times higher than those predicted by 2-body relaxation, which
would improve the prospects of detecting these events by future GW detectors,
such as LISA.",0605457v1
2001-07-26,Band structure approach to the resonant x-ray scattering,"We study the resonance behaviour of the forbidden 600 and 222 x-ray Bragg
peaks in Ge using LDA band structure methods. These Bragg peaks remain
forbidden in the resonant dipole scattering approximation even taking into
account the non local nature of the band states. However they become allowed at
resonance if the eigenstates of the unoccupied conduction band involve a
hybridization of p like and d like atomic states. We show that the energy
dependence of the resonant behaviour, including the phase of the scattering, is
a direct measure of this p-d hybridization.and obtain quantitative agreement
with experiment. A simple physical picture involving a product of dipole and
quadrupolar transition matrix elements explains this behaviour and shows that
it should be generally true for cases where the resonating atom is not at an
inversion center. This has strong implications for the description of the
resonance behavior of x-ray scattering in materials where the resonant atom is
not at an inversion center such as V2O3 and in ferro and antiferro electric and
piezo electric materials in general.",0107546v1
2002-09-18,Isolated resonances in conductance fluctuations in ballistic billiards,"We study numerically quantum transport through a billiard with a classically
mixed phase space. In particular, we calculate the conductance and Wigner delay
time by employing a recursive Green's function method. We find sharp, isolated
resonances with a broad distribution of resonance widths in both the
conductance and the Wigner time, in contrast to the well-known smooth
conductance fluctuations of completely chaotic billiards. In order to elucidate
the origin of the isolated resonances, we calculate the associated scattering
states as well as the eigenstates of the corresponding closed system. As a
result, we find a one-to-one correspondence between the resonant scattering
states and eigenstates of the closed system. The broad distribution of
resonance widths is traced to the structure of the classical phase space.
Husimi representations of the resonant scattering states show a strong overlap
either with the regular regions in phase space or with the hierarchical parts
surrounding the regular regions. We are thus lead to a classification of the
resonant states into regular and hierarchical, depending on their phase space
portrait.",0209433v1
2003-05-11,Feshbach resonances in a quasi-2D atomic gas,"Strongly confining an ultracold atomic gas in one direction to create a
quasi-2D system alters the scattering properties of this gas. We investigate
the effects of confinement on Feshbach scattering resonances and show that
strong confinement results in a shift in the position of the Feshbach resonance
as a function of the magnetic field. This shift, as well as the change of the
width of the resonance, are computed. We find that the resonance is strongly
damped in the thermal gas, but in the condensate the resonance remains sharp
due to many-body effects. We introduce a 2D model system, suited for the study
of resonant superfluidity, and having the same scattering properties as the
tightly confined real system near a Feshbach resonance. Exact relations are
derived between measurable quantities and the model parameters.",0305235v1
2003-07-15,Resonant and anti-resonant frequency dependence of the effective parameters of metamaterials,"We present a numerical study of the electromagnetic response of the
metamaterial elements that are usedto construct materials with negative
refractive index. For an array of split ring resonators (SRR) we find that the
resonant behavior of the effective magnetic permeability is accompanied by an
anti-resonant behavior of the effective permittivity. In addition, the
imaginary parts of the effective permittivity and permeability are opposite in
sign. We also observe an identical resonant versus anti-resonant frequency
dependence of the effective materials parameters for a periodic array of thin
metallic wires with cuts placed periodically along the length of the wire, with
roles of the permittivity and permeability reversed from the SRR case. We show
in a simple manner that the finite unit cell size is responsible for the
anti-resonant behavior.",0307361v1
2005-06-16,Noise properties of two single electron transistors coupled by a nanomechanical resonator,"We analyze the noise properties of two single electron transistors (SETs)
coupled via a shared voltage gate consisting of a nanomechanical resonator.
Working in the regime where the resonator can be treated as a classical system,
we find that the SETs act on the resonator like two independent heat baths. The
coupling to the resonator generates positive correlations in the currents
flowing through each of the SETs as well as between the two currents. In the
regime where the dynamics of the resonator is dominated by the back-action of
the SETs, these positive correlations can lead to parametrically large
enhancements of the low frequency current noise. These noise properties can be
understood in terms of the effects on the SET currents of fluctuations in the
state of a resonator in thermal equilibrium which persist for times of order
the resonator damping time.",0506397v2
2006-04-07,Optimal conversion of Bose condensed atoms into molecules via a Feshbach resonance,"In many experiments involving conversion of quantum degenerate atomic gases
into molecular dimers via a Feshbach resonance, an external magnetic field is
linearly swept from above the resonance to below resonance. In the adiabatic
limit, the fraction of atoms converted into molecules is independent of the
functional form of the sweep and is predicted to be 100%. However, for
non-adiabatic sweeps through resonance, Landau-Zener theory predicts that a
linear sweep will result in a negligible production of molecules. Here we
employ a genetic algorithm to determine the functional time dependence of the
magnetic field that produces the maximum number of molecules for sweep times
that are comparable to the period of resonant atom-molecule oscillations,
$2\pi\Omega_{Rabi}^{-1}$. The optimal sweep through resonance indicates that
more than 95% of the atoms can be converted into molecules for sweep times as
short as $2\pi\Omega_{Rabi}^{-1}$ while the linear sweep results in a
conversion of only a few percent. We also find that the qualitative form of the
optimal sweep is independent of the strength of the two-body interactions
between atoms and molecules and the width of the resonance.",0604216v2
2006-06-28,Dissipation in Single-Crystal 3C-SiC Ultra-High Frequency Nanomechanical Resonators,"The energy dissipation 1/Q (where Q is the quality factor) and resonance
frequency characteristics of single-crystal 3C-SiC ultrahigh frequency (UHF)
nanomechanical resonators are measured, for a family of UHF resonators with
resonance frequencies of 295MHz, 395MHz, 411MHz, 420MHz, 428MHz, and 482MHz. A
temperature dependence of dissipation, 1/Q ~ T^(0.3) has been identified in
these 3C-SiC devices. Possible mechanisms that contribute to dissipation in
typical doubly-clamped beam UHF resonators are analyzed. Device size and
dimensional effects on the dissipation are also examined. Clamping losses are
found to be particularly important in these UHF resonators. The resonance
frequency decreases as the temperature is increased, and the average frequency
temperature coefficient is about -45ppm/K.",0606711v1
2006-11-02,Signal amplification in a nanomechanical Duffing resonator via stochastic resonance,"We experimentally study stochastic resonance in a nonlinear bistable
nanomechanical resonator. The device consists of a PdAu doubly clamped beam
serving as a nanomechanical resonator excited capacitively by an adjacent gate
electrode and its vibrations are detected optically. The resonator is tuned to
its bistability region by an intense pump near a point of equal transition
rates between its two metastable states. The pump is amplitude modulated,
inducing modulation of the activation barrier between the states. When noise is
added to the excitation, the resonator's displacement exhibits noise dependent
amplification. We measure the resonator's response in the time and frequency
domains, the spectral amplification and the statistical distribution of the
jump time.",0611049v1
2001-10-11,Hadronic Regge Trajectories in the Resonance Energy Region,"Nonlinearity of hadronic Regge trajectories in the resonance energy region
has been proved.",0110160v1
2005-04-13,Sterile-active neutrino oscillations and shortcuts in the extra dimension,"We discuss a possible new resonance in active-sterile neutrino oscillations
arising in theories with large extra dimensions. Fluctuations in the brane
effectively increase the path-length of active neutrinos relative to the
path-length of sterile neutrinos through the extra-dimensional bulk. Well below
the resonance, the standard oscillation formulas apply. Well above the
resonance, active-sterile oscillations are suppressed. We show that a resonance
energy in the range of 30-400 MeV allows an explanation of all neutrino
oscillation data, including LSND data, in a consistent four-neutrino model. A
high resonance energy implies an enhanced signal in MiniBooNE. A low resonance
energy implies a distorted energy spectrum in LSND, and an enhanced v_mu
depletion from a stopped-pion source. The numerical value of the resonance
energy may be related back to the geometric aspects of the brane world. Some
astrophysical and cosmological consequences of the brane-bulk resonance are
briefly sketched.",0504096v3
2004-01-21,Resonance tongues and patterns in periodically forced reaction-diffusion systems,"Various resonant and near-resonant patterns form in a light-sensitive
Belousov-Zhabotinsky (BZ) reaction in response to a spatially-homogeneous
time-periodic perturbation with light. The regions (tongues) in the forcing
frequency and forcing amplitude parameter plane where resonant patterns form
are identified through analysis of the temporal response of the patterns.
Resonant and near-resonant responses are distinguished. The unforced BZ
reaction shows both spatially-uniform oscillations and rotating spiral waves,
while the forced system shows patterns such as standing-wave labyrinths and
rotating spiral waves. The patterns depend on the amplitude and frequency of
the perturbation, and also on whether the system responds to the forcing near
the uniform oscillation frequency or the spiral wave frequency. Numerical
simulations of a forced FitzHugh-Nagumo reaction-diffusion model show both
resonant and near-resonant patterns similar to the BZ chemical system.",0401031v1
2006-11-10,Vibrational and stochastic resonances in two coupled overdamped anharmonic oscillators,"We study the overdamped version of two coupled anharmonic oscillators under
the influence of both low- and high-frequency forces respectively and a
Gaussian noise term added to one of the two state variables of the system. The
dynamics of the system is first studied in the presence of both forces
separately without noise. In the presence of only one of the forces, no
resonance behaviour is observed, however, hysteresis happens there. Then the
influence of the high-frequency force in the presence of a low-frequency, i.e.
biharmonic forcing, is studied. Vibrational resonance is found to occur when
the amplitude of the high-frequency force is varied. The resonance curve
resembles a stochastic resonance-like curve. It is maximum at the value of $g$
at which the orbit lies in one well during one half of the drive cycle of the
low-frequency force and in the other for the remaining half cycle. Vibrational
resonance is characterized using the response amplitude and mean residence
time. We show the occurrence of stochastic resonance behaviour in the
overdamped system by replacing the high-frequency force by Gaussian noise.
Similarities and differences between both types of resonance are presented.",0611023v1
1995-12-13,Model for Resonance Enhancement of P- and T-noninvariant Effects in Neutron Reactions,"We consider a simplified model for resonant neutron-nucleus interaction with
coupled channels. An analytical solution is given for two coupled channels and
arbitrary neutron orbital momentum. A case of a week channel coupling,
corresponding to narrow Breit-Wigner resonance, is analyzed in details. As far
as the total width of a resonance coincides with the neutron width, the model
is directly appropriate only for light nuclei. We study a mixing of two narrow
s- and p-wave resonances by P- and P-,T-noninvariant potentials in the first
order of perturbation theory. As an example a close-lying pair of s- and p-wave
resonances of the $^{35}$Cl nucleus is considered. The favorable possibilities
are shown to exist on thick targets for measurements beyond the resonance
widths. In particular, an interference minimum near s-wave resonance is of
interest for P-odd neutron spin rotation on light spinless nuclei.",9512020v2
1998-01-03,Instanton tunneling and multiphonon giant resonances,"The sine-Gordon model is applied to describe the multiphonon giant
resonances.",9801002v1
1998-12-19,Photoproduction of the Lambda(1405) on the proton and nuclei,"We study the gamma p ---> K^+ Lambda(1405) reaction at energies close to
threshold using a chiral unitary model where the resonance is generated
dynamically from K^-p interaction with other channels constructed from the
octets of baryons and mesons. Predictions are made for cross sections into
several channels and it is shown that the detection of the K^+ is sufficient to
determine the shape and strength of the Lambda(1405) resonance. The
determination of the resonance properties in nuclei requires instead the
detection of the resonance decay channels. Pauli blocking effects on the
resonance, which have been shown to be very important for the resonance at rest
in the nucleus, are irrelevant here where the resonance is produced with a
large momentum. The nuclear modifications here would thus offer information on
the resonance and K^- nucleus dynamics complementary to the one offered so far
by K^- atoms.",9812055v1
2002-07-17,Exploration of Resonant Continuum and Giant Resonance in the Relativistic Approach,"Single-particle resonant-states in the continuum are determined by solving
scattering states of the Dirac equation with proper asymptotic conditions in
the relativistic mean field theory (RMF). The regular and irregular solutions
of the Dirac equation at a large radius where the nuclear potentials vanish are
relativistic Coulomb wave functions, which are calculated numerically.
Energies, widths and wave functions of single-particle resonance states in the
continuum for ^{120}Sn are studied in the RMF with the parameter set of NL3.
The isoscalar giant octupole resonance of ^{120}Sn is investigated in a fully
consistent relativistic random phase approximation. Comparing the results with
including full continuum states and only those single-particle resonances we
find that the contributions from those resonant-states dominate in the nuclear
giant resonant processes.",0207054v1
2004-06-16,The N(1710)P11 state is confirmed in the re-analysis of the pi N --> K Lambda production; it is a good candidate for a non-strange pentaquark,"Re-analyzing the old pi N --> K Lambda data, the additional proof is given
for the existence of the N(1710) P11 state, critically needed in light of
reported observations of exotic Theta(1539) and Xi(1862) pentaquarks. An
existing single-resonance model with S11, P11 and P13 Breit-Wiegner resonances
in the s-channel has been applied. It has been shown that the standard set of
resonant parameters fails to reproduce the shape of the differential cross
section. The new resonance parameter determination has been performed keeping
in mind the most recent knowledge about nucleon resonances. The extracted set
of parameters has confirmed the need for the strong contribution of a N(1710)
P11 resonance. The need for any significant contribution of the P13 resonance
has been eliminated. To reproduce the total cross section at the same time with
the linear dependence of the differential cross sections with the cos(theta) in
the energy range 1650 MeV < W < 1800 MeV the P11 resonance can not but be quite
narrow.",0406055v2
2005-05-17,Hadron production from resonance decay in relativistic collisions,"A statistical model for decay and formation of heavy hadronic resonances is
formulated. The resonance properties become increasingly uncertain with
increasing resonance mass. Drawing on analogy with the situation in low-energy
nuclear physics, we employ the Weisskopf approach to the resonance processes.
In the large-mass limit, the density of resonance states in mass is governed by
a universal Hagedorn-like temperature T_H. As resonances decay, progressively
more and more numerous lighter states get populated. For T_H \simeq 170 MeV,
the model describes data for the hadron yield ratios at the RHIC and SPS
energies under the extreme assumption of a single heavy resonance giving rise
to measured yields.",0505049v2
2004-09-06,Enzyme as a thermal resonance pump,"We found latent periodicity of 150 protein families now. We suppose that
latent periodicity can determine a spectrum of resonance oscillations in
proteins.",0409009v1
2000-10-01,Phase-space picture of resonance creation and avoided crossings,"Complex coordinate scaling (CCS) is used to calculate resonance eigenvalues
and eigenstates for a system consisting of an inverted Gaussian potential and a
monochromatic driving field. Floquet eigenvalues and Husimi distributions of
resonance eigenfunctions are calculated using two different versions of CCS.
The number of resonance states in this system increases as the strength of the
driving field is increased, indicating that this system might have increased
stability against ionization when the field strength is very high. We find that
the newly created resonance states are scarred on unstable periodic orbits of
the classical motion. The behavior of these periodic orbits as the field
strength is increased may explain why there are more resonance states at high
field strengths than at low field strengths. Close examination of an avoided
crossing between resonance states shows that this type of avoided crossing does
not delocalize the resonance states, although it may lead to interesting
effects at certain field strengths.",0010003v1
2003-09-23,Buffer-gas induced absorption resonances in Rb vapor,"We observe transformation of the electromagnetically induced transparency
(EIT) resonance into the absorption resonance in a $\Lambda$ interaction
configuration in a cell filled with $^{87}$Rb and a buffer gas. This
transformation occurs as a one-photon detuning of the coupling fields is varied
from the atomic transition. No such absorption resonance is found in the
absence of a buffer gas. The width of the absorption resonance is several times
smaller than the width of the EIT resonance, and the changes of absorption near
these resonances are about the same. Similar absorption resonances are detected
in the Hanle configuration in a buffered cell.",0309171v2
2006-11-25,Resonance phenomena in Macroscopic Quantum Tunneling: the small viscosity limit,"We present a new theoretical approach to describe the quantum behavior of a
macroscopic system interacting with an external irradiation field, close to the
resonant condition. Here we consider the extremely underdamped regime for a
system described by a double well potential. The theory includes both:
transitions from one well to the other and relaxation processes. We simulate
resonant phenomena in a rf-SQUID, whose parameters lie in the range typically
used in the experiments. The dependence of the transition probability W on the
external drive of the system $\phi_x$ shows three resonance peaks. One peak is
connected with the resonant tunneling and the two others with the resonant
pumping. The relative position of the two peaks correlated to the resonant
pumping depends on the pumping frequency $\nu$ and on the system parameters.
The preliminary measurements on our devices show a low dissipation level and
assure that they are good candidates in order to realize new experiments on the
resonant phenomena in the presence of an external microwave irradiation of
proper frequency.",0611255v1
2007-07-29,On dynamical tunneling and classical resonances,"This work establishes a firm relationship between classical nonlinear
resonances and the phenomenon of dynamical tunneling. It is shown that the
classical phase space with its hierarchy of resonance islands completely
characterizes dynamical tunneling and explicit forms of the dynamical barriers
can be obtained only by identifying the key resonances. Relationship between
the phase space viewpoint and the quantum mechanical superexchange approach is
discussed in near-integrable and mixed regular-chaotic situations. For
near-integrable systems with sufficient anharmonicity the effect of multiple
resonances {\it i.e.,} resonance-assisted tunneling can be incorporated
approximately. It is also argued that the, presumed, relation of avoided
crossings to nonlinear resonances does not have to be invoked in order to
understand dynamical tunneling. For molecules with low density of states the
resonance-assisted mechanism is expected to be dominant.",0707.4274v1
2007-07-30,Ultracold collisions in magnetic fields: reducing inelastic cross sections near Feshbach resonances,"We have carried out bound-state and low-energy quantum scattering
calculations on He + NH (triplet Sigma) in magnetic fields, with the NH
molecule in its n=1 rotationally excited states. We have explored the pattern
of levels as a function of magnetic field and identified the nearly good
quantum numbers in different regimes. We have used the bound-state calculations
to locate low-energy Feshbach resonances. When the magnetic field is used to
tune across such a resonance, the real and imaginary part of the scattering
length show asymmetric oscillations and peaks with amplitude between 1 and 3
Angstroms. The scattering length does not pass through a pole at resonance. The
resonant behavior is characterized by a complex resonant scattering length
a_res. The corresponding inelastic cross sections show troughs as well as peaks
near resonance. This may be important for efforts to achieve evaporative and
sympathetic cooling for molecules, because it offers the hope that inelastic
trap losses can be reduced by tuning close to a Feshbach resonance.",0707.4397v1
2007-11-11,Saturated absorption spectroscopy: elimination of crossover resonances by use of a nanocell,"It is demonstrated that velocity selective optical pumping/saturation
resonances of reduced absorption in a Rb vapor nanocell with thickness
\textit{L=} $\lambda $, 2$\lambda $, and 3$\lambda $ (resonant wavelength
$\lambda $ = 780 nm) allow the complete elimination of crossover (CO)
resonances. We observe well pronounced resonances corresponding to the
F$_{g}=3$ $\to $ F$_{e}=2,3,4$ hyperfine transitions of the $^{85}$Rb D$_{2}$
line with linewidths close to the natural width. A small CO resonance located
midway between F$_{g}=3$ $\to $ F$_{e}=3$ and F$_{g}=3$ $\to$ F$_{e}=4$
transitions appears only for \textit{L} = 4$\lambda $. The D$_{2}$ line
($\lambda $ = 852 nm) in a Cs nanocell exhibits a similar behavior. From the
amplitude ratio of the CO and VSOP resonances it is possible to determine the
thickness of the column of alkali vapor in the range of 1 - 1000 $\mu $m. The
absence of CO resonances for nanocells with $L \sim \lambda $ is attractive for
frequency reference application and for studying transitions between Zeeman
sublevels in external magnetic fields.",0711.1684v1
2007-12-11,Resonance production in heavy-ion collisions at STAR,"Hadronic resonances are sensitive to the properties of a hot and dense medium
created in a heavy ion collisions. During the hadronic phase, after
hadronization of quark and gluons into hadrons, resonances are useful to
determine the lifetime between chemical and thermal freeze-out, under the
assumption that the re-scattering of the decay particles and the probability of
regeneration of resonances from hadrons depends on the system properties and
the resonance lifetime. The system size and energy dependence of resonance
spectra and yields will be shown and discussed in the context of the lifetime
and size of the hadronic phase. Elliptic flow measurement will extend the
sensitivity of resonance yields to the partonic state through additional
information on constituent quark scaling. We also explore a possible new
technique to extract signals from the early, potentially chirally symmetric,
stage through the selection of resonances from jets.",0712.1838v1
2008-04-25,Coupled-resonator-induced reflection in photonic-crystal waveguide structures,"We study the resonant transmission of light in a coupled-resonator optical
waveguide interacting with two nearly identical side cavities. We reveal and
describe a novel effect of the coupled-resonator-induced reflection (CRIR)
characterized by a very high and easily tunable quality factor of the
reflection line, for the case of the inter-site coupling between the cavities
and the waveguide. This effect differs sharply from the
coupled-resonator-induced transparency (CRIT) -- an all-optical analogue of the
electromagnetically-induced transparency -- which has recently been studied
theoretically and observed experimentally for the structures based on
micro-ring resonators and photonic crystal cavities. Both CRIR and CRIT effects
have the same physical origin which can be attributed to the Fano-Feshbach
resonances in the systems exhibiting more than one resonance. We discuss the
applicability of the novel CRIR effect to the control of the slow-light
propagation and low-threshold all-optical switching.",0804.4140v1
2008-11-08,Ballistic Spin Resonance,"The phenomenon of spin resonance has had far reaching influence since its
discovery nearly 70 years ago. Electron spin resonance (ESR) driven by high
frequency magnetic fields has informed our understanding of quantum mechanics,
and finds application in fields as diverse as medicine and quantum information.
Spin resonance induced by high frequency electric fields, known as electric
dipole spin resonance (EDSR), has also been demonstrated recently. EDSR is
mediated by spin-orbit interaction (SOI), which couples the spin degree of
freedom and the momentum vector. Here, we report the observation of a novel
spin resonance due to SOI that does not require external driving fields.
Ballistic spin resonance (BSR) is driven by an internal spin-orbit field that
acts upon electrons bouncing at gigaHertz frequencies in narrow channels of
ultra-clean two-dimensional electron gas (2DEG). BSR is manifested in
electrical measurements of pure spin currents as a strong suppression of spin
relaxation length when the motion of electrons is in resonance with spin
precession. These findings point the way to gate-tunable coherent spin
rotations in ballistic nanostructures without external a.c. fields.",0811.1244v1
2009-02-15,Effects of Electric Fields on Heteronuclear Feshbach Resonances in Ultracold $^6\rm{Li}-^{87}\rm{Rb}$ Mixtures,"The effects of combined external electric and magnetic fields on elastic
collisions in ultracold Li--Rb mixtures is studied using recently obtained,
experimentally verified potentials. Our analysis provides both quantitative
predictions for and a detailed physical interpretation of the phenomena arising
from electric-field-induced interactions. It is shown that the electric field
shifts the positions of intrinsic magnetic Feshbach resonances, generates
copies of resonances previously restricted to a particular partial-wave
collision to other partial wave channels, and splits Feshbach resonances into
multiple resonances for states of non-zero angular momenta. It was recently
observed that the magnetic dipole-dipole interaction can also lift the
degeneracy of a p-wave state splitting the associated p-wave Feshbach resonance
into two distinct resonances at different magnetic fields. Our work shows that
the splitting of the resonances produced by an applied electric field is more
than an order of magnitude larger. This new phenomenon offers a complementary
way to produce and tune an anisotropic interaction and to study its effect on
the many-body physics of heteronuclear atomic gases.",0902.2505v1
2009-05-08,Exotic Grazing Resonances in Nanowires,"We investigate electromagnetic scattering from nanoscale wires and reveal for
the first time, the emergence of a family of exotic resonances, or enhanced
fields, for source waves close to grazing incidence. These grazing resonances
can have a much higher Q factor, broader bandwidth, and are much less
susceptible to material losses than the well known surface plasmon resonances
found in metal nanowires. Contrary to surface plasmon resonances however, these
grazing resonances can be excited in both dielectric and metallic nanowires and
are insensitive to the polarization state of the incident wave. This peculiar
resonance effect originates from the excitation of long range guided surface
waves through the interplay of coherently scattered continuum modes coupled
with the azimuthal first order propagating mode of the cylindrical nanowire.
The nanowire resonance phenomenon revealed here can be utilized in broad
scientific areas, including: metamaterial designs, nanophotonic integration,
nanoantennas, and nanosensors.",0905.1357v1
2009-05-31,The impact of local resonance on the enhanced transmission and dispersion of surface resonances,"We investigate the enhanced microwave transmission through the array of
metallic coaxial annular apertures (MCAAs) experimentally and theoretically.
The even-mode and the odd-mode surface resonances are clarified from the
spatial field distributions and the dispersion diagram. The impact of local
resonance is thoroughly embodied in the even-mode surface resonant states,
while the odd-mode surface resonances are scaled by periodicity, invariant to
different local geometry of the unit cell, and invisible in measurements. The
enhanced transmission is the collective selections on the interplay between the
local resonances and the evanescent Bloch wave channels on the surface.
Transmission measurements for different inner diameter of the apertures show
that the transmissivity extrema with respect to the specific angles precisely
correspond to the degenerate points in the dispersion diagram of surface
resonances.",0906.0128v1
2009-06-17,Resonances and bifurcations in axisymmetric scale-free potentials,"We investigate an analytical treatment of bifurcations of families of
resonant `thin' tubes in axisymmetric galactic potentials. We verify that the
most relevant bifurcations are due to the (1:1) resonance producing the
`inclined' orbits through two different mechanisms: from the disk orbit and
from the `thin' tube associated to the vertical oscillation. The closest
resonances occurring after these are the (4:3) resonance in the oblate case and
the (2:1) resonance in the prolate case. The (1:1) resonances are treated in a
straightforward way using a 2nd-order truncated normal form. The higher-order
resonances are instead cumbersome to investigate, because the normal form has
to be truncated to a high degree and the number of terms grows very rapidly. We
therefore adopt a further simplification giving analytic formulas for the
values of the parameters at which bifurcations ensue and compare them with
selected numerical results. Thanks to the asymptotic nature of the series
involved, the predictions are reliable well beyond the convergence radius of
the original series.",0906.3138v2
2010-09-01,Compact electric-LC resonators for metamaterials,"Alternative designs to an electric-LC (ELC) resonator, which is a type of
metamaterial inclusion, are presented in this article. Fitting the resonator
with an interdigital capacitor (IDC) helps to increase the total capacitance of
the structure. In effect, its resonance frequency is shifted downwards. This
implies a decreased overall resonator size with respect to its operating
wavelength. As a result, the metamaterial, composed of an array of IDC-loaded
ELC resonators with their collective electromagnetic response, possesses
improved homogeneity and hence is less influenced by diffraction effects of
individual cells. The impact of incorporating an IDC into ELC resonators in
terms of the electrical size at resonance and other relevant properties are
investigated through both simulation and experiment.",1009.0139v1
2010-09-08,Tuning the Resonance in High Temperature Superconducting Terahertz Metamaterials,"In this Letter we present resonance properties in terahertz metamaterials
consisting of a split-ring resonator array made from high temperature
superconducting films. By varying the temperature, we observed efficient
metamaterial resonance switching and frequency tuning with some features not
revealed before. The results were well reproduced by numerical simulations of
metamaterial resonance using the experimentally measured complex conductivity
of the superconducting film. We developed a theoretical model that explains the
tuning features, which takes into account the resistive resonance damping and
additional split-ring inductance contributed from both the real and imaginary
parts of the temperature-dependent complex conductivity. The theoretical model
further predicted more efficient resonance switching and frequency shifting in
metamaterials consisting of a thinner superconducting split-ring resonator
array, which were also verified in experiments.",1009.1640v1
2010-11-05,"Effects of Turbulence, Eccentricity Damping, and Migration Rate on the Capture of Planets into Mean Motion Resonance","Pairs of migrating extrasolar planets often lock into mean motion resonance
as they drift inward. This paper studies the convergent migration of giant
planets (driven by a circumstellar disk) and determines the probability that
they are captured into mean motion resonance. The probability that such planets
enter resonance depends on the type of resonance, the migration rate, the
eccentricity damping rate, and the amplitude of the turbulent fluctuations.
This problem is studied both through direct integrations of the full 3-body
problem, and via semi-analytic model equations. In general, the probability of
resonance decreases with increasing migration rate, and with increasing levels
of turbulence, but increases with eccentricity damping. Previous work has shown
that the distributions of orbital elements (eccentricity and semimajor axis)
for observed extrasolar planets can be reproduced by migration models with
multiple planets. However, these results depend on resonance locking, and this
study shows that entry into -- and maintenance of -- mean motion resonance
depends sensitively on migration rate, eccentricity damping, and turbulence.",1011.1486v1
2010-12-10,Quantum pumping in graphene nanoribbons at resonant transmission,"Adiabatic quantum charge pumping in graphene nanoribbon double barrier
structures with armchair and zigzag edges in the resonant transmission regime
is analyzed. Using recursive Green's function method we numerically calculate
the pumped charge for pumping contours encircling a resonance. We find that for
armchair ribbons the whole resonance line contributes to the pumping of a
single electron (ignoring double spin degeneracy) per cycle through the device.
The case of zigzag ribbons is more interesting due to zero-conductance
resonances. These resonances separate the whole resonance line into several
parts, each of which corresponds to the pumping of a single electron through
the device. Moreover, in contrast to armchair ribbons, one electron can be
pumped from the left lead to the right one or backwards. The current direction
depends on the particular part of the resonance line encircled by the pumping
contour.",1012.2221v1
2011-03-11,Observation and characterization of mode splitting in microsphere resonators in aquatic environment,"Whispering gallery mode (WGM) optical resonators utilizing resonance shift
(RS) and mode splitting (MS) techniques have emerged as highly sensitive
platforms for label-free detection of nano-scale objects. RS method has been
demonstrated in various resonators in air and liquid. MS in microsphere
resonators has not been achieved in aqueous environment up to date, despite its
demonstration in microtoroid resonators. Here, we demonstrate scatterer-induced
MS of WGMs in microsphere resonators in water. We determine the size range of
particles that induces MS in a microsphere in water as a function of resonator
mode volume and quality factor. The results are confirmed by the experimental
observations.",1103.2398v1
2011-05-05,Fano effect and nonuniversal phase lapses in mesoscopic regime of transport,"The transmission probability and phase through a few-electron quantum dot are
studied within a resonance theory for the strong coupling regime to the
conducting leads. We find that the interaction between overlapping resonances
leads to their separation in the complex energy plane and to the decoherent
dephasing of the resonant modes. The appearance of the Fano effect is
conditioned not only by the induced dephasing generally associated with a phase
lapse, but also by a favorable parity of the resonant modes. To identify the
contribution of each resonance to the transmission, we propose, in the case of
overlapping resonances, a decomposition of the scattering matrix in resonant
terms and a background. The resonant contributions are approximated by Fano
lines with complex asymmetry parameters and the background by a constant. The
conductance and the transmission phase calculated within this approach
reproduce the generic features of the experimental data.",1105.1167v1
2011-06-17,Sequential vibrational resonance in multistable systems,"The phenomenon of sequential vibrational resonance existed in a multistable
system that is excited by both high- and low-frequency signals is reported. By
the method of direct separation of motions, the theoretical investigation on
vibrational resonance is conducted in both cases of underdamped and overdamped,
and the analytical predictions are in good agreement with the numerical
simulations. In view of the theoretical results, the zero-order Bessel function
related to the high-frequency signal is included in the renormalized resonant
frequency, and which leads to the appearance of the sequential vibrational
resonance. In the case of underdamped system with small damping coefficient,
the resonance occurs in a series of discrete parameter regions. The sequential
vibrational resonance is different from the traditional multiple vibrational
resonance, because its appearance is much more regular. The results in this
work may be helpful in the field of signal processing electronics, especially
for dealing with the very-low-frequency signal.",1106.3431v1
2011-10-12,Giant red shift and enhancement of resonant light confinement in planar array of dielectric bars,"Results of research of resonant phenomena in planar periodic structures
consisted of dielectric elements are presented. A problem of plane wave
diffraction by a structure which a periodic cell is composed of two dielectric
bars with different lengths has been solved. For the first time an existence of
high Q-factor trapped mode resonances are revealed in these structures. The
main difference of studied structure in contrast to the planar structure with a
single dielectric bar in the unit cell is appearing of a great red shift of a
trapped mode resonant wavelength. The red shift is caused by strong coupling of
electromagnetic fields in neighbor dielectric bar resonators. This property is
very attractive to design resonant periodic planar structures by using moderate
refractive index materials like semiconductors within their transparency
window. In the near infrared band, the trapped mode resonances of periodic
planar structure with bars made of germanium have been studied. It is shown
that decreasing of structure asymmetry degree results in increasing of both red
shift and Q-factor of resonance.",1110.2699v2
2012-02-27,Magnetic hysteresis effects in superconducting coplanar microwave resonators,"We performed transmission spectroscopy experiments on coplanar half
wavelength niobium resonators at a temperature T=4.2 K. We observe not only a
strong dependence of the quality factor Q and the resonance frequency f_res on
an externally applied magnetic field but also on the magnetic history of our
resonators, i.e. on the spatial distribution of trapped Abrikosov vortices in
the device. We find these results to be valid for a broad range of frequencies
and angles between the resonator plane and the magnetic field direction as well
as for resonators with and without antidots near the edges of the center
conductor and the ground planes. In a detailed analysis we show, that
characteristic features of the experimental data can only be reproduced in
calculations, if a highly inhomogeneous rf-current density and a flux density
gradient with maxima at the edges of the superconductor is assumed. We
furthermore demonstrate, that the hysteretic behaviour of the resonator
properties can be used to considerably reduce the vortex induced losses and to
fine-tune the resonance frequency by the proper way of cycling to a desired
magnetic field.",1202.5963v1
2012-07-01,Observation of two new $N^*$ resonances in $ψ(3686) \rightarrow p\bar{p}π^0$,"Based on 106$\times10^6 \psi(3686)$ events collected with the BESIII detector
at the BEPCII facility, a partial wave analysis of $\psi(3686)\rightarrow
p\bar{p}\pi^0$ is performed. The branching fraction of this channel has been
determined to be $B(\psi(3686)\rightarrow p\bar{p}\pi^0) =
(1.65\pm0.03\pm0.15)\times 10^{-4}$. In this decay, 7 $N^*$ intermediate
resonances are observed. Among these $N^*$ resonances, two new resonances are
significant, one $1/2^+$ resonance with a mass of
$2300^{+40}_{-30}$$^{+109}_{-0}$ $\mathrm{MeV}/c^2$ and width of
$340^{+30}_{-30}$$^{+110}_{-58}$ $\mathrm{MeV}/c^2$, and one $5/2^-$ resonance
with a mass of $2570^{+19}_{-10}$$^{+34}_{-10}$ $\mathrm{MeV}/c^2$ and width of
$250^{+14}_{-24}$$^{+69}_{-21}$ $\mathrm{MeV}/c^2$. For the remaining 5 $N^*$
intermediate resonances, the analysis yields mass and width values which are
consistent with those from established resonances.",1207.0223v2
2012-07-04,Quantum dot admittance probed at microwave frequencies with an on-chip resonator,"We present microwave frequency measurements of the dynamic admittance of a
quantum dot tunnel coupled to a two-dimensional electron gas. The measurements
are made via a high-quality 6.75 GHz on-chip resonator capacitively coupled to
the dot. The resonator frequency is found to shift both down and up close to
conductance resonance of the dot corresponding to a change of sign of the
reactance of the system from capacitive to inductive. The observations are
consistent with a scattering matrix model. The sign of the reactance depends on
the detuning of the dot from conductance resonance and on the magnitude of the
tunnel rate to the lead with respect to the resonator frequency. Inductive
response is observed on a conductance resonance, when tunnel coupling and
temperature are sufficiently small compared to the resonator frequency.",1207.0945v2
2012-09-06,Magnetic Feshbach resonances in collisions of non-magnetic closed-shell $^1Σ$ molecules,"Magnetic Feshbach resonances play a central role in experimental research of
atomic gases at ultracold temperatures, as they allow one to control the
microscopic interactions between ultracold atoms by tuning an applied magnetic
field. These resonances arise due to strong hyperfine interactions between the
unpaired electron and the nuclear magnetic moment of the alkali metal atoms. A
major thrust of current research is to create an ultracold gas of diatomic
alkali-metal molecules in the ground rovibrational state of the ground
electronic $^1\Sigma$ state. Unlike alkali metal atoms, $^1\Sigma$ diatomic
molecules have no unpaired electrons. However, the hyperfine interactions of
molecules may give rise to magnetic Feshbach resonances. We use quantum
scattering calculations to study the possible width of these resonances. Our
results show that the widths of magnetic Feshbach resonances in ultracold
molecule-molecule collisions for $^1\Sigma$ molecules may exceed 1 milliGauss,
rendering such resonances experimentally detectable. We hope that this work
will stimulate the experimental search of these resonances.",1209.1418v2
2012-12-18,Resonance states in a cylindrical quantum dot with an external magnetic field,"Bound and resonance states of quantum dots play a significant role in
photo-absorption processes. In this work, we analyze a cylindrical quantum dot,
its spectrum and, in particular, the behaviour of the lowest resonance state
when a magnetic field is applied along the symmetry axis of the cylinder. To
obtain the energy and width of the resonance we use the complex rotation
method. As it is expected the structure of the spectrum is strongly influenced
by the Landau levels associated to the magnetic field. We show how this
structure affects the behaviour of the resonance state and that the binding of
the resonance has a clear interpretation in terms of the Landau levels and the
probability of localization of the resonance state. The localization
probability and the fidelity of the lowest energy state allows to identify two
different physical regimes, a large field-small quantum dot radius regime and a
small field-large quantum dot radius, where the binding of the resonance is
dominated by the field strength or the potential well, respectively.",1212.4323v2
2013-03-01,Unconventional Fano effect and off-resonance field enhancement in plasmonic coated spheres,"We investigate light scattering by coated spheres composed of a dispersive
plasmonic core and a dielectric shell. By writing the absorption cross-section
in terms of the internal electromagnetic fields, we demonstrate it is an
observable sensitive to interferences that ultimately lead to the Fano effect.
Specially, we show that unconventional Fano resonances, recently discovered for
homogeneous spheres with large dielectric permittivities, can also occur for
metallic spheres coated with single dielectric layers. These resonances arise
from the interference between two electromagnetic modes with the same multipole
moment inside the shell and not from interactions between various plasmon modes
of different layers of the particle. In contrast to the case of homogeneous
spheres, unconventional Fano resonances in coated spheres exist even in the
Rayleigh limit. These resonances can induce an off-resonance field enhancement,
which is approximately one order of magnitude larger than the one achieved with
conventional Fano resonances. We find that unconventional and conventional Fano
resonances can occur at the same input frequency provided the dispersive core
has a negative refraction index. This leads to an optimal field enhancement
inside the particle, a result that could be useful for potential applications
in plasmonics.",1303.0185v1
2013-04-01,Fano resonances and their control in optomechanics,"The Fano line profiles, originally discovered in the context of
photoionization, have been found to occur in a large class of systems like
resonators, metamaterials, plasmonics. We demonstrate the existence of such
resonances in cavity optomechanics by identifying the interfering contributions
to the fields generated at antiStokes and Stokes frequencies. Unlike the atomic
systems, the optomechanical systems provide great flexibility as the width of
the resonance is controlled by the coupling field. We further show how the
double cavities coupled by a single optomechanical mirror can lead to the
splitting of the Fano resonance and how the second cavity can be used to tune
the Fano resonances. The Fano resonances are quite sensitive to the decay
parameters associated with cavities and the mechanical mirror. Such resonances
can be studied by both pump probe experiments as well as via the spectrum of
the quantum fluctuations in the output fields.",1304.0389v2
2013-04-11,Experimental demonstrations of high-Q superconducting coplanar waveguide resonators,"We designed and successfully fabricated an absorption-type of superconducting
coplanar waveguide (CPW) resonators. The resonators are made from a Niobium
film (about 160 nm thick) on a high-resistance Si substrate, and each resonator
is fabricated as a meandered quarter-wavelength transmission line (one end
shorts to the ground and another end is capacitively coupled to a through
feedline). With a vector network analyzer we measured the transmissions of the
applied microwave through the resonators at ultra-low temperature (e.g., at 20
mK), and found that their loaded quality factors are significantly high, i.e.,
up to 10^6. With the temperature increases slowly from the base temperature
(i.e., 20 mK), we observed the resonance frequencies of the resonators are blue
shifted and the quality factors are lowered slightly. In principle, this type
of CPW-device can integrate a series of resonators with a common feedline,
making it a promising candidate of either the data bus for coupling the distant
solid-state qubits or the sensitive detector of single photons.",1304.3254v1
2013-04-15,Vibrational resonance in groundwater-dependent plant ecosystems,"We report the phenomenon of vibrational resonance in a single species and a
two species models of groundwater-dependent plant ecosystems with a biharmonic
oscillation (with two widely different frequencies \omega and \Omega, \Omega >>
\omega) of the water table depth. In these two systems, the response amplitude
of the species biomass shows multiple resonances with different mechanisms. The
resonance occurs at both low- and high-frequencies of the biharmonic force. In
the single species bistable system, the resonance occurs at discrete values of
the amplitude g of the high-frequency component of the water table.
Furthermore, the best synchronization of biomass and its carrying capacity with
the biharmonic force occurs at the resonance. In the two species excitable and
time-delay model, the response amplitude (Q) profile shows several plateau
regions of resonance, where the period of evolution of the species biomass
remains the same and the value of Q is inversely proportional to it. The
response amplitude is highly sensitive to the time-delay parameter \tau and
shows two distinct sequences of resonance intervals with a decreasing amplitude
with \tau.",1304.4170v1
2013-05-02,Finite element simulation of a perturbed axial-symmetric whispering-gallery mode and its use for intensity enhancement with a nanoparticle coupled to a microtoroid,"We present an optical mode solver for a whispering gallery resonator coupled
to an adjacent arbitrary shaped nano-particle that breaks the axial symmetry of
the resonator. Such a hybrid resonator-nanoparticle is similar to what was
recently used for bio-detection and for field enhancement. We demonstrate our
solver by parametrically studying a toroid-nanoplasmonic device and get the
optimal nano-plasmonic size for maximal enhancement. We investigate cases near
a plasmonic resonance as well as far from a plasmonic resonance. Unlike common
plasmons that typically benefit from working near their resonance, here working
far from plasmonic resonance provides comparable performance. This is because
the plasmonic resonance enhancement is accompanied by cavity quality
degradation through plasmonic absorption.",1305.0555v1
2013-11-05,Effect of magnetic field on resonant tunneling in 3D waveguides of variable cross-section,"We consider an infinite three-dimensional waveguide that far from the
coordinate origin coincides with a cylinder. The waveguide has two narrows of
diameter $\varepsilon$. The narrows play the role of effective potential
barriers for the longitudinal electron motion. The part of waveguide between
the narrows becomes a ""resonator""\, and there can arise conditions for electron
resonant tunneling. A magnetic field in the resonator can change the basic
characteristics of this phenomenon. In the presence of a magnetic field, the
tunneling phenomenon is feasible for producing spin-polarized electron flows
consisting of electrons with spins of the same direction.
  We assume that the whole domain occupied by a magnetic field is in the
resonator. An electron wave function satisfies the Pauli equation in the
waveguide and vanishes at its boundary. Taking $\varepsilon$ as a small
parameter, we derive asymptotics for the probability $T(E)$ of an electron with
energy $E$ to pass through the resonator, for the ""resonant energy""\,$E_{res}$,
where $T(E)$ takes its maximal value, and for some other resonant tunneling
characteristics.",1311.1126v1
2013-11-20,Formation and interaction of resonance chains in the open 3-disk system,"In ballistic open quantum systems one often observes that the resonances in
the complex-energy plane form a clear chain structure. Taking the open 3-disk
system as a paradigmatic model system, we investigate how this chain structure
is reflected in the resonance states and how it is connected to the underlying
classical dynamics. Using an efficient scattering approach we observe that
resonance states along one chain are clearly correlated while resonance states
of different chains show an anticorrelation. Studying the phase space
representations of the resonance states we find that their localization in
phase space oscillate between different regions of the classical trapped set as
one moves along the chains and that these oscillations are connected to a
modulation of the resonance spacing. A single resonance chain is thus no WKB
quantization of a single periodic orbits, but the structure of several
oscillating chains arises from the interaction of several periodic orbits. We
illuminate the physical mechanism behind these findings by combining the
semiclassical cycle expansion with a quantum graph model.",1311.5128v2
2014-04-03,Theoretical study of a $d^{*}$ resonance in $^{3}G_{3}$ partial wave of nucleon-nucleon scattering,"Inspired by the recent results of the WASA-at-COSY Collaboration, in which
they found a resonance pole in the coupled $^{3}D_{3}$ - $^{3}G_{3}$ partial
waves as expected from the $d^{*}$ resonance hypothesis, we calculated the
resonance structure in the coupled $^{3}D_{3}$ - $^{3}G_{3}$ partial wave phase
shifts of nucleon-nucleon scattering in the framework of two constituent quark
models: the quark delocalization color screening model and the chiral quark
model. Our results show that there is a resonance $^{7}S_{3}^{\Delta\Delta}$ in
the coupled $^{3}D_{3}^{NN}$ and $^{3}G_{3}^{NN}$ partial waves in both of
these two models, which is in accordance with the expectation from the $d^{*}$
resonance structure. The resonance shape in the $^{3}D_{3}^{NN}$ partial wave
is remarkable, whereas in the $^{3}G_{3}^{NN}$ phase shifts there is a small
rise around the resonance energy. This result is in agreement with the recent
experimental observations of WASA-at-COSY Collaboration.",1404.0947v2
2014-07-07,Dielectric Square Resonator Investigated with Microwave Experiments,"We present a detailed experimental study of the symmetry properties and the
momentum space representation of the field distributions of a dielectric square
resonator as well as the comparison with a semiclassical model. The experiments
have been performed with a flat ceramic microwave resonator. Both the resonance
spectra and the field distributions were measured. The momentum space
representations of the latter evidenced that the resonant states are each
related to a specific classical torus, leading to the regular structure of the
spectrum. Furthermore, they allow for a precise determination of the refractive
index. Measurements with different arrangements of the emitting and the
receiving antennas were performed and their influence on the symmetry
properties of the field distributions was investigated in detail, showing that
resonances with specific symmetries can be selected purposefully. In addition,
the length spectrum deduced from the measured resonance spectra and the trace
formula for the dielectric square resonator are discussed in the framework of
the semiclassical model.",1407.1802v2
2014-07-10,Ultrafast Switching in Terahertz Metamaterials using Ion Implanted Silicon on Sapphire,"We demonstrate ultrafast resonance switching of terahertz metamaterials
through optical excitation of radiation damaged silicon placed in the gap of
single split gap ring resonator. We observe the dynamic switching OFF of the
fundamental resonance mode on a time scale of 4 picoseconds (ps) followed by
the switching ON of the same resonance after 20 ps. Electric field
distributions in the metamaterials unit cell derived through numerical
simulations clearly support our experimental observations, showing that the
high electric field at the resonator gaps, responsible for inductive-capacitive
resonance (LC), completely disappears and switches OFF the resonance after
being optically excited. The ultrafast switching of the metamaterial resonance
is attributed to the generation of free carriers in ion-implanted silicon and
their recombination at an ultra-short time scale. Such silicon based active
control of metamaterials can lead to the ultrafast terahertz metadevices.",1407.2715v1
2014-08-06,On the dynamics of space debris: 1:1 and 2:1 resonances,"We study the dynamics of the space debris in the 1:1 and 2:1 resonances,
where geosynchronous and GPS satellites are located. By using Hamiltonian
formalism, we consider a model including the geopotential contribution for
which we compute the secular and resonant expansions of the Hamiltonian.
  Within such model we are able to detect the equilibria and to study the main
features of the resonances in a very effective way. In particular, we analyze
the regular and chaotic behavior of the 1:1 and 2:1 resonant regions by
analytical methods and by computing the Fast Lyapunov Indicators, which provide
a cartography of the resonances. This approach allows us to detect easily the
location of the equilibria, the amplitudes of the libration islands and the
main dynamical stability features of the resonances, thus providing an overview
of the 1:1 and 2:1 resonant domains under the effect of Earth's oblateness.
  The results are validated by a comparison with a model developed in Cartesian
coordinates, including the geopotential, the gravitational attraction of Sun
and Moon and the solar radiation pressure.",1408.1254v1
2014-08-10,Fast universal quantum gates on microwave photons with all-resonance operations in circuit QED,"Stark shift on a superconducting qubit in circuit quantum electrodynamics
(QED) has been used to construct universal quantum entangling gates on
superconducting resonators in previous works. It is a second-order coupling
effect between the resonator and the qubit in the dispersive regime, which
leads to a slow state-selective rotation on the qubit. Here, we present two
proposals to construct the fast universal quantum gates on superconducting
resonators in a microwave-photon quantum processor composed of multiple
superconducting resonators coupled to a superconducting transmon qutrit, that
is, the controlled-phase (c-phase) gate on two microwave-photon resonators and
the controlled-controlled phase (cc-phase) gates on three resonators, resorting
to quantum resonance operations, without any drive field. Compared with
previous works, our universal quantum gates have the higher fidelities and
shorter operation times in theory. The numerical simulation shows that the
fidelity of our c-phase gate is 99.57% within about 38.1 ns and that of our
cc-phase gate is 99.25% within about 73.3 ns.",1408.2168v2
2014-10-24,Bound and resonance states of the dipolar anion of hydrogen cyanide: competition between threshold effects and rotation in an open quantum system,"Bound and resonance states of the dipole-bound anion of hydrogen cyanide
HCN$^-$ are studied using a non-adiabatic pseudopotential method and the
Berggren expansion technique involving bound states, decaying resonant states,
and non-resonant scattering continuum. We devise an algorithm to identify the
resonant states in the complex energy plane. To characterize spatial
distributions of electronic wave functions, we introduce the body-fixed density
and use it to assign families of resonant states into collective rotational
bands. We find that the non-adiabatic coupling of electronic motion to
molecular rotation results in a transition from the strong-coupling to
weak-coupling regime. In the strong coupling limit, the electron moving in a
subthreshold, spatially extended halo state follows the rotational motion of
the molecule. Above the ionization threshold, electron's motion in a resonance
state becomes largely decoupled from molecular rotation. Widths of
resonance-band members depend primarily on the electron orbital angular
momentum.",1410.6660v1
2014-11-06,The nucleon resonances in the $J/ψ\to p\bar{p}η'$ decay,"We are aiming to study the $J/\psi \to p\bar{p}\eta'$ decay in an isobar
model and the effective Lagrangian approach. After a careful exploration of the
contributions of the $S_{11}(1535)$, $P_{11}(1710)$, $P_{13}(1900)$,
$S_{11}(2090)$ and $P_{11}(2100)$ resonances, we conclude that either a
subthreshold resonance or a broad $P$-wave state in the near threshold range
seems to be indispensable to describe present data of the $\pi N \to \eta'N$.
Furthermore, at least one broad resonance above $\eta'N$ threshold is
preferred. With this detailed analysis, we could give the invariant mass
spectrum and Dalitz plot of the $J/\psi \to p\bar{p}\eta'$ decay for the
purpose of assisting the future detailed partial wave analysis. It is found
that the $J/\psi \to p\bar{p}\eta'$ data are useful for disentangling the above
or below threshold resonant contribution, though it still further needs the
differential cross section data of $\pi N \to \eta'N$ to realize some of the
resonant and the non-resonant contribution. Our results are enlightening for
the $\eta'N$ production mechanism and the properties of the nucleon resonances
with the mass around 2.0~GeV.",1411.1493v1
2014-12-03,On bifurcations in degenerate resonance zones,"For Hamitonian systems with 3/2 degrees of freedom close to nonlinear
integrable and for symplectic maps of the cylinder, bifurcations in degenerate
resonance zones are discussed.",1412.1252v1
2014-12-18,Superconductive Ultra-compact Magnetically Coupled Resonator with Twin-spiral Structure,"We describe a practical design of an ultra-compact on-chip superconductive
micro-resonator as a potential magnetic element of metamaterial. The achieved
resonator size with respect to the wavelength in our experiment is about
{\lambda}/ 14400. The resonator consists of two superconducting Nb spirals,
sandwiched face to face, with a small gap filled with dielectric. The spirals
are turning in opposite directions: one clockwise, another counter-clockwise.
We study the resonator spectral response and its inner modes using numerical
simulation in HFSS. In experiment with a Laser Scanning Microscope (LSM) we
confirm the predictions for the resonance frequencies of Nb superconductive
resonator and its inner modes structures. Small size and the ease of
manufacturing make the two-spiral resonator an attractive solution for
superconductive filters, coupling circuits, and as a magnetic component of a
metamaterial.",1412.5750v2
2015-01-30,Dynamically tunable Fano resonance in periodically asymmetric graphene nanodisk pair,"We present a dynamically frequency tunable Fano resonance planar device
composed of periodically asymmetric graphene nanodisk pair for the mid-infrared
region. There are two kinds of modes in this structure, that is, the symmetric
mode and the antisymmetric mode. The resonance coupling between the symmetric
and antisymmetric modes creates a classical Fano resonance. Both of the Fano
resonance amplitude and frequency of the structure can be dynamically
controlled by varying the Fermi energy of graphene. Resonance transition in the
structure is studied to reveal the physical mechanism behind the dynamically
tunable Fano resonance. The features of the Fano resonant graphene
nanostructures should have promising applications in tunable THz filters,
switches, and modulators.",1501.07744v1
2015-08-24,Broadband architecture for galvanically accessible superconducting microwave resonators,"In many hybrid quantum systems, a superconducting circuit is required that
combines DC-control with a coplanar waveguide (CPW) microwave resonator. The
strategy thus far for applying a DC voltage or current bias to microwave
resonators has been to apply the bias through a symmetry point in such a way
that it appears as an open circuit for certain frequencies. Here, we introduce
a microwave coupler for superconducting CPW cavities in the form of a large
shunt capacitance to ground. Such a coupler acts as a broadband mirror for
microwaves while providing galvanic connection to the center conductor of the
resonator. We demonstrate this approach with a two-port
$\lambda/4$-transmission resonator with linewidths in the MHz regime
($Q\sim10^3$) that shows no spurious resonances and apply a voltage bias up to
$80$ V without affecting the quality factor of the resonator. This resonator
coupling architecture, which is simple to engineer, fabricate and analyse,
could have many potential applications in experiments involving superconducting
hybrid circuits.",1508.05770v2
2015-09-18,Theory of inelastic confinement-induced resonances due to the coupling of center-of-mass and relative motion,"A detailed study of the anharmonicity-induced resonances caused by the
coupling of center-of-mass and relative motion is presented for a system of two
ultracold atoms in single-well potentials. As has been confirmed
experimentally, these inelastic confinement-induced resonances are of interest,
since they can lead to coherent molecule formation, losses, and heating in
ultracold atomic gases. A perturbative model is introduced to describe the
resonance positions and the coupling strengths. The validity of the model and
the behavior of the resonances for different confinement geometries are
analyzed in comparison with exact numerical ab initio calculations. While such
resonances have so far only been detected for large positive values of the
$s$-wave scattering length, it is found that they are present also for negative
$s$-wave scattering lengths, i. e. for attractive interactions. The possibility
to coherently tune the resonances by a variation of the external confinement
geometry might pave the way for coherent molecule association where magnetic
Feshbach resonances are inaccessible.",1509.05799v1
2015-09-29,Second harmonic generation with plasmonic metasurfaces: direct comparison of electric and magnetic resonances,"Plasmonic resonances in metallic nanostructures have been shown to
drastically enhance local electromagnetic fields, and thereby increase the
efficiency of nonlinear optical phenomena, such as second harmonic generation
(SHG). While it has been experimentally observed that enhanced fields can
significantly boost SHG, to date it proved difficult to probe electrical and
magnetic resonances in one and the same nanostructure. This however is
necessary to directly compare relative contributions of electrical and magnetic
components of SHG enhancement. In this paper we report an experimental study of
a metasurface capable of providing electrical and magnetic resonant SHG
enhancement for TM polarization. Our metasurface could be engineered such that
the peak frequencies of electrical and magnetic resonances could be adjusted
independently. We used this feature to distinguish their relative
contributions. Experimentally it was observed that the magnetic resonance
provides only 50% as much enhancement to SHG as compared to the electric
resonance. In addition aligning both resonances in frequency results in
conversion efficiency of 1.32 x 10^(-10).",1509.08871v1
2015-10-19,Quasi-forbidden 2-body Förster resonances in cold Cs Rydberg gas,"Cold Rydberg atoms are known to display dipole-dipole interaction allowed
resonances, also called F\""orster resonances, which lead to an efficient energy
transfer when the proper electric field is used. This electric field also
enables resonances which do not respect the dipole-dipole selection rules under
zero field. A few of these quasi-forbidden resonances have been observed but
they are often overlooked. Here we show that in cold $^{133}$Cs atoms there is
a large number of these resonances that display a significant transfer
efficiency due to their strong interactions, even at low electric field. We
also develop a graphical method enabling to find all possible resonances
simultaneously. The resulting dramatic increase in the total number of
addressable resonant energy transfers at different electric fields could have
implications in the search for few-body interactions or macro-molecules built
from Rydberg atoms.",1510.05350v2
2016-03-05,Controlling the Characteristics of Nanomechanical Resonators,"The dynamics of nanomechanical resonators driven by both low- and
high-frequency signals is studied. Considering, as an example, resonators made
of a doubly-clamped beam with magnetomotive driving, it is shown that
three-frequency resonances arise due to the interaction of the above
frequencies. Properties and characteristics of these resonances are determined
analytically for linear and nonlinear modes of the resonator excitation. It is
shown that in opposite to the conventional two-frequency resonance, the central
frequency of these resonances, their linear dynamic range, and the critical
value for the bistability onset are easily controlled by changing the frequency
and the amplitude of the low-frequency driving current. The obtained results
can be used when developing NMRs for sensors, filters, memory elements, and
other applications.",1603.01732v1
2016-03-23,Dynamics and Transit Variations of Resonant Exoplanets,"The Transit Timing Variations (TTVs) are deviations of the measured
mid-transit times from the exact periodicity. One of the most interesting
causes of TTVs is the gravitational interaction between planets. Here we
consider a case of two planets in a mean motion resonance (orbital periods in a
ratio of small integers). This case is important because the resonant
interaction can amplify the TTV effect and allow planets to be detected more
easily. We develop an analytic model of the resonant dynamics valid for small
orbital eccentricities and use it to derive the principal TTV terms. We find
that a resonant system should show TTV terms with two basic periods (and their
harmonics). The resonant TTV period is proportional (m/M_*)^(-2/3), where m and
M_* are the planetary and stellar masses. For m=10^(-4) M_*, for example, the
TTV period exceeds the orbital period by ~2 orders of magnitude. The amplitude
of the resonant TTV terms scales linearly with the libration amplitude. The
ratio of the TTV amplitudes of two resonant planets is inversely proportional
to the ratio of their masses. These and other relationships discussed in the
main text can be used to aid the interpretation of TTV observations.",1603.07306v1
2016-09-12,Mathematical Study of Scattering Resonances,"We provide an introduction to mathematical theory of scattering resonances
and survey some recent results.",1609.03550v3
2017-03-04,On the Pollicott-Ruelle resonances,"The purpose of this survey is to present the recent advances about the
Pollicott-Ruelle resonances.",1703.01522v1
2017-08-10,Acoustic resonance in periodically sheared glass,"Using molecular dynamics simulation, we study acoustic resonance in
low-temperature glass by applying a small periodic shear at a boundary wall.
Shear wave resonance occurs as the frequency $\omega$ approaches $\omega_\ell=
\pi c_\perp\ell/L$ ($\ell=1, 2, 3,...)$. Here, $c_\perp$ is the transverse
sound speed and $L$ is the cell length. At resonance, large-amplitude sound
waves appear after many cycles even for very small applied strains. They then
induce plastic events, which are heterogeneous in space and intermittent on
time scales longer than the oscillation period $2\pi/\omega$. From these
irreversible particle motions, there arises strong dissipation suppressing the
growth of sounds. After many resonant cycles, we observe a phenomenon of forced
aging, where the shear modulus (measured after switching off the oscillation)
is increased significantly.Sometimes, exceptionally large plastic events and
system-size sliding motions induce a transition from resonant to off-resonant
states. At resonance, translational diffusion becomes appreciable as well as
aging due to enhanced configurational changes.",1708.03166v2
2017-08-15,Comment on arXiv:1612.01502 'Is the Trineutron Resonance Lower in Energy than a Tetraneutron Resonance ?',"Comment on the article by S. Gandolfi et al. Phys.Rev.Letters 118 (2017),
232501; arXiv:1612.01502 [nucl-th]",1708.04459v1
2017-08-15,The Dielectric Wakefield Resonator Accelerator,"We report preliminary studies of a three-channel, rectangular, high gradient
dielectric wakefield accelerator element, which, unlike the collinear
cylindrical dielectric wakefield device, does not suffer from low transformer
ratio and may offer relief from the beam breakup instability. When configured
as a resonator (DWR), it can be driven by a series of modest-charge drive
bunches. This rectangular 'mode-locked' resonator consists of three channels
lined with low-loss dielectric slabs: the central wider channel is the drive
bunch channel, whereas two adjacent narrow channels are used to accelerate
electron and/or positron bunches; this provides a favorable transformer ratio.
At the moment when, after reflecting from the resonator exit, the wakefield
returns to the resonator entrance, the next bunch is injected into the
resonator entrance. The length of the resonator is also chosen to be a multiple
of half the desired wakefield wavelength. The rectangular geometry permits
superposition of harmonics of wakefields in the resonator. The short length of
the device and its planar configuration should allow management of beam
breakup, and a lengthy drive bunch train can be dynamically stabilized by using
a series of DWR units rotated about the $z$-axis in $90^{\circ}$ increments.",1708.04599v1
2018-11-05,Design and characterization of a novel toroidal split-ring resonator,"The design and characterization of a novel toroidal split-ring resonator
(SRR) is described in detail. In conventional cylindrical SRRs, there is a
large magnetic flux within the bore of the resonator. However, there also
exists a non-negligible magnetic flux in the free space surrounding the
resonator. The energy losses associated with this radiated power diminish the
resonator's quality factor. In the toroidal SRR, on the other hand, the
magnetic field lines are strongly confined within the bore of the resonator
resulting in high intrinsic quality factors and stable resonance frequencies
without requiring additional electromagnetic shielding. This paper describes
the design and construction of a toroidal SRR as well as an experimental
investigation of its cw response in the frequency-domain and its time-domain
response to an rf pulse. Additionally, the dependence of the toroidal SRR's
resonant frequency and quality factor on the strength of inductive coupling to
external circuits is investigated both theoretically and experimentally.",1811.02630v1
2019-05-19,Effects of the Coulomb interaction on parameters of resonance states in mirror three-cluster nuclei,"We investigate how the Coulomb interaction affects the energy $E$ and width
$\Gamma$ of resonance states in mirror nuclei. We employ a three-cluster
microscopic model to determine position of resonance states in two- and
three-body continua. Two parameters are introduced to quantify effects of the
Coulomb interactions. As the energy and width of the corresponding resonance
states of mirror nuclei are displayed on an $E$-$\Gamma$ plane, these
parameters determine a rotation and a dilatation. With the help of these
parameters we found resonance states with strong, small and medium effects of
the Coulomb interaction. We also found two different scenarios of the motion of
resonance states due to the Coulomb interaction. The first standard (major)
scenario represent resonance states with the larger energy and larger width
than their counterparts have. The second rear scenario includes resonance
states with the larger energy but smaller width.",1905.07711v3
2019-05-24,Interaction between high intensity beam and structure resonances,"With the help of the linearized perturbation theory, the collective beam
instability due to the space charge, modelled by the Vlasov-Poisson equation,
is well studied in the former research theoretically in a general sense [Chao
Li and R. A. Jameson PRAB, 21, 024204 (2018)], where the related instability is
depicted by the ""structure resonance"". As an extension of the theoretical
study, this paper aims to verify the validity of the structure resonance with
numerical simulations and to show the basic principles which interpret the
interaction between structure resonance and beam in a general sense. It is
found that the reaction of beam to the structure resonance ($n\sigma\approx
180^\circ$) differs for the cases with $n= 0$ and $n\ne 0$ stop bands. The
non-resonant ""plasma oscillation"" is also revisited; the ""phase space mixing"",
lying in the transient plasma oscillation, is the mechanism that ties the
resonant effects, non-resonant effects and macroscopic beam phenomena together.",1905.10008v1
2020-07-18,Quenching effect of oscillating potential on anisotropic resonant transmission through a phosphorene electrostatic barrier,"The anisotropy in resonant tunneling transport through an electrostatic
barrier in mono layer black phosphorus either in presence or in absence of an
oscillating potential is studied. Non-perturbative Floquet theory is applied to
solve the time dependent problem and the results obtained are discussed
thoroughly. The resonance spectra in field free transmission are Lorentzian in
nature although the width of the resonance for the barrier along the zigzag
direction is too thinner than that for the armchair one. Resonant transmission
is suppressed for both the cases by the application of oscillating potential
that produces small oscillations in the transmission around the resonant energy
particularly at low frequency range. Sharp asymmetric Fano resonances are noted
in the transmission spectrum along the armchair direction while a distinct line
shape resonance is noted for the zigzag direction at higher frequency of the
oscillating potential. Even after the angular average, the conductance along
the armchair direction retains the characteristic Fano features that could be
observed experimentally. The present results are supposed to suggest that the
phosphorene electrostatic barrier could be used successfully as switching
devices and nano detectors.",2007.09356v2
2020-07-21,The Rayleigh-Lorentz Invariant and Optimal Adiabatic Qubit-Information Detection for Superconducting Qubit Resonators,"Dynamical properties of a resonator can be analyzed using the
Rayleigh-Lorentz invariant which is not an exact constant but varies more or
less over time. We investigate the time behavior of this invariant for a flux
qubit resonator in order for better understanding of qubit-information
detection with the resonator. Flux qubit resonators can be utilized in
implementing diverse next generation nano-optic and nano-electronic devices
such as quantum computing systems. Through the analyses of the temporal
evolution of the invariant, we derive a condition for optimal adiabatic
qubit-information detection with the resonator. This condition is helpful for
controlling the dynamics of qubit resonators over long periods of time. It is
necessary to consider it when designing a nano-resonator used for quantum
nondemolition readouts of qubit states, crucial in quantum computation.",2007.10671v1
2014-03-01,Universal quantum gates on microwave photons assisted by circuit quantum electrodynamics,"Based on a microwave-photon quantum processor with two superconducting
resonators coupled to one transmon qutrit, we construct the controlled-phase
(c-phase) gate on microwave-photon-resonator qudits, by combination of the
photon-number-dependent frequency-shift effect on the transmon qutrit by the
first resonator and the resonant operation between the qutrit and the second
resonator. This distinct feature provides us a useful way to achieve the
c-phase gate on the two resonator qudits with a higher fidelity and a shorter
operation time, compared with the previous proposals. The fidelity of our
c-phase gate can reach 99.51% within 93 ns. Moreover, our device can be
extended easily to construct the three-qudit gates on three resonator qudits,
far different from the existing proposals. Our controlled-controlled-phase gate
on three resonator qudits is accomplished with the assistance of a transmon
qutrit and its fidelity can reach 92.92% within 124.64 ns.",1403.0031v2
2014-03-10,Radiation-induced quantum Fano-type resonances in the transport of $N$-$P$-$N$ graphene based junctions,"We present a theoretical study of quantum resonances in the ballistic
transport of graphene based $N$-$P$-$N$ junction subject to an externally
applied electromagnetic field (EF). By making use of the Floquet analysis and
the quasi-classical approach we analyze the dynamics of electrons in the
presence of time and coordinate dependent potential $U(z,t)$. In the absence of
EF the resonant tunneling results in a set of sharp resonances in the
dependence of dc conductance $\sigma$ on the gate voltage $V_g$. In irradiated
$N$-$P$-$N$ junctions we obtain the Fano-type resonances in the dependence of
$\sigma(V_g)$. This \emph{coherent quantum-mechanical phenomenon} is due to the
interplay of two effects: the resonant tunneling through quasi-bound states and
the quantum-interference effect in the region between the ""resonant points"",
where the resonant absorption (emission) of photons occurs, and junction
interfaces.",1403.2206v2
2014-03-13,All-optical NMR in semiconductors provided by resonant cooling of nuclear spins interacting with electrons in the resonant spin amplification regime,"Resonant cooling of different nuclear isotopes manifested in
optically-induced nuclear magnetic resonances (NMR) is observed in n-doped
CdTe/(Cd,Mg)Te and ZnSe/(Zn,Mg)Se quantum wells and for donor-bound electrons
in ZnSe:F and GaAs epilayers. By time-resolved Kerr rotation used in the regime
of resonant spin amplification we can expand the range of magnetic fields where
the effect can be observed up to nuclear Larmor frequencies of 170 kHz. The
mechanism of the resonant cooling of the nuclear spin system is analyzed
theoretically. The developed approach allows us to model the resonant spin
amplification signals with NMR resonances.",1403.3288v1
2017-04-24,Above threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider,"Ultracold atomic gases have realised numerous paradigms of condensed matter
physics where control over interactions has crucially been afforded by tunable
Feshbach resonances. So far, the characterisation of these Feshbach resonances
has almost exclusively relied on experiments in the threshold regime near zero
energy. Here we use a laser-based collider to probe a narrow magnetic Feshbach
resonance of rubidium above threshold. By measuring the overall atomic loss
from colliding clouds as a function of magnetic field, we track the
energy-dependent resonance position. At higher energy, our collider scheme
broadens the loss feature, making the identification of the narrow resonance
challenging. However, we observe that the collisions give rise to shifts in the
centre-of-mass positions of outgoing clouds. The shifts cross zero at the
resonance and this allows us to accurately determine its location well above
threshold. Our inferred resonance positions are in excellent agreement with
theory.",1704.07109v2
2017-04-26,On novel elastic structures inducing plasmonic resonances with finite frequencies and cloaking due to anomalous localized resonances,"This paper is concerned with the theoretical study of plasmonic resonances
for linear elasticity governed by the Lam\'e system in $\mathbb{R}^3$, and
their application for cloaking due to anomalous localized resonances. We derive
a very general and novel class of elastic structures that can induce plasmonic
resonances. It is shown that if either one of the two convexity conditions on
the Lam\'e parameters is broken, then we can construct certain plasmon
structures that induce resonances. This significantly extends the relevant
existing studies in the literature where the violation of both convexity
conditions is required. Indeed, the existing plasmonic structures are a
particular case of the general structures constructed in our study.
Furthermore, we consider the plasmonic resonances within the finite frequency
regime, and rigorously verify the quasi-static approximation for diametrically
small plasmonic inclusions. Finally, as an application of the newly found
structures, we construct a plasmonic device of the core-shell-matrix form that
can induce cloaking due to anomalous localized resonance in the quasi-static
regime, which also includes the existing study as a special case.",1704.07981v1
2018-05-10,A bottle of tea as a universal Helmholtz resonator,"Resonance is an ubiquitous phenomenon present in many systems. In particular,
air resonance in cavities was studied by Hermann von Helmholtz in the 1850s.
Originally used as acoustic filters, Helmholtz resonators are rigid-wall
cavities which reverberate at given fixed frequencies. An adjustable type of
resonator is the so-called universal Helmholtz resonator, a device consisting
of two sliding cylinders capable of producing sounds over a continuous range of
frequencies. Here we propose a simple experiment using a smartphone and normal
bottle of tea, with a nearly uniform cylindrical section, which, filled with
water at different levels, mimics a universal Helmholtz resonator. Blowing over
the bottle, different sounds are produced. Taking advantage of the great
processing capacity of smartphones, sound spectra together with frequencies of
resonance are obtained in real time.",1805.04014v1
2009-12-22,Spectral properties of a resonator driven by a superconducting single-electron transistor,"We analyze the spectral properties of a resonator coupled to a
superconducting single electron transistor (SSET) close to the Josephson
quasiparticle resonance. Focussing on the regime where the resonator is driven
into a limit-cycle state by the SSET, we investigate the behavior of the
resonator linewidth and the energy relaxation rate which control the widths of
the main features in the resonator spectra. We find that the linewidth becomes
very narrow in the limit-cycle regime, where it is dominated by a slow phase
diffusion process, as in a laser. The overall phase diffusion rate is
determined by a combination of direct phase diffusion and the effect of
amplitude fluctuations which affect the phase because the resonator frequency
is amplitude dependent. For sufficiently strong couplings we find that a regime
emerges where the phase diffusion is no longer minimized when the average
resonator energy is maximized. Finally we show that the current noise of the
SSET provides a way of measuring both the linewidth and energy relaxation rate.",0912.4462v1
2012-04-20,Stability of prograde and retrograde planets in circular binary systems,"We investigate the stability of prograde versus retrograde planets in
circular binary systems using numerical simulations. We show that retrograde
planets are stable up to distances closer to the perturber than prograde
planets. We develop an analytical model to compute the prograde and retrograde
mean motion resonances' locations and separatrices. We show that instability is
due to single resonance forcing, or caused by nearby resonances' overlap. We
validate our results regarding the role of single resonances and resonances'
overlap on orbit stability, by computing surfaces of section of the CR3BP. We
conclude that the observed enhanced stability of retrograde planets with
respect to prograde planets is due to essential differences between the
phase-space topology of retrograde versus prograde resonances (at p/q mean
motion ratio, prograde resonance is of order p - q while retrograde resonance
is of order p + q).",1204.4718v2
2014-05-01,Trapping a single vortex and reducing quasiparticles in a superconducting resonator,"Vortices trapped in thin-film superconducting microwave resonators can have a
significant influence on the resonator performance. Using a variable-linewidth
geometry for a weakly coupled resonator we are able to observe the effects of a
single vortex trapped in the resonator through field cooling. For resonant
modes where the vortex is near a current antinode, the presence of even a
single vortex leads to a measurable decrease in the quality factor and a
dispersive shift of the resonant frequency. For modes with the vortex located
at a current node, the presence of the vortex results in no detectable excess
loss and, in fact, produces an increase in the quality factor. We attribute
this enhancement to a reduction in the density of nonequilibrium quasiparticles
in the resonator due to the suppressed gap from the vortex.",1405.0256v2
2014-06-20,Effective Medium Theory for Elastic Metamaterials in Thin Elastic Plates,"An effective medium theory for resonant and non-resonant metamaterials for
flexural waves in thin plates is presented. The theory provides closed-form
expressions for the effective parameters of arrangement of inclusions or
resonators in thin plates as a function of the filling fraction of the
inclusions, their physical properties and the frequency. It is shown that
positive or negative effective elastic parameters are possible depending on the
symmetry of the resonance but, unlike it happens for bulk elastic waves, the
responsible for the negative mass density behaviour is the monopolar term,
while the negative Young's modulus and Poisson's ratio is due to the
combination of monopolar and quadrupolar resonances, showing also that, at
least for the first order in the scattering coefficients, the dipolar resonance
plays no role in the description of the effective medium. Several examples are
given for both non-resonant and resonant effective parameters and the results
are verified by multiple scattering theory.",1406.5400v2
2015-12-23,Particle number scaling for diffusion-induced dissipation in graphene and carbon nanotube nanomechanical resonators,"When a contaminant diffuses on the surface of a nanomechanical resonator, the
motions of the two become correlated. Despite being a high-order effect in the
resonator-particle coupling, such correlations affect the system dynamics by
inducing dissipation of the resonator energy. Here, we consider this
diffusion-induced dissipation in the cases of multiple particles adsorbed on
carbon nanotube and graphene resonators. By solving the stochastic equations of
motion, we simulate the ringdown of the resonator, in order to determine the
resonator energy decay rate. We find two different scalings with the number of
adsorbed particles $K$ and particle mass $m$. In the regime where the
adsorbates are inertially trapped at an antinode of vibration, the dissipation
rate $\Gamma$ scales with the total adsorbed mass $\Gamma\propto Km$. In
contrast, in the regime where particles diffuse freely over the resonator, the
dissipation rate scales as the product of the total adsorbed mass and the
individual particle mass: $\Gamma\propto Km^2$.",1512.07543v2
2016-05-01,"Tailoring Rydberg interactions via Förster resonances: state combinations, hopping and angular dependence","F\""orster resonances provide a highly flexible tool to tune both the strength
and the angular shape of interactions between two Rydberg atoms. We give a
detailed explanation about how F\""orster resonances can be found by searching
through a large range of possible quantum number combinations. We apply our
search method to $SS$, $SD$ and $DD$ pair states of $^{87}$Rb with principal
quantum numbers from 30 to 100, taking into account the fine structure
splitting of the Rydberg states. We find various strong resonances between
atoms with a large difference in principal quantum numbers. We quantify the
strength of these resonances by introducing a figure of merit $\tilde C_3$
which is independent of the magnetic quantum numbers and geometry to classify
the resonances by interaction strength. We further predict to what extent
excitation exchange is possible on different resonances and point out
limitations of the coherent hopping process. Finally, we discuss the angular
dependence of the dipole-dipole interaction and its tunability near resonances.",1605.00259v3
2016-05-27,Quantifying resonant and near-resonant interactions in rotating turbulence,"Nonlinear triadic interactions are at the heart of our understanding of
turbulence. In flows where waves are present modes must not only be in a triad
to interact, but their frequencies must also satisfy an extra condition: the
interactions that dominate the energy transfer are expected to be resonant. We
derive equations that allow direct measurement of the actual degree of
resonance of each triad in a turbulent flow. We then apply the method to the
case of rotating turbulence, where eddies coexist with inertial waves. We show
that for a range of wave numbers, resonant and near-resonant triads are
dominant, the latter allowing a transfer of net energy towards two-dimensional
modes that would be inaccessible otherwise. The results are in good agreement
with approximations often done in theories of rotating turbulence, and with the
mechanism of parametric instability proposed to explain the development of
anisotropy in such flows. We also observe that, at least for the moderate
Rossby numbers studied here, marginally near-resonant and non-resonant triads
play a non-negligible role in the coupling of modes.",1605.08818v2
2016-08-04,Resonances and multistability in a Josephson junction connected to a resonator,"We study the dynamics of a Josephson junction connected to a dc current
supply via a distributed parameter capacitor, which serves as a resonator. We
reveal multistability in the current-voltage characteristic of the system; this
multistability is related to resonances between the generated frequency and the
resonator. The resonant pattern requires detailed consideration, in particular,
because its basic features may resemble those of patterns reported in
experiments with arrays of Josephson junctions demonstrating coherent
stimulated emission. From the viewpoint of nonlinear dynamics, the resonances
between a Josephson junction and a resonator are of interest because of
specificity of the former; its oscillation frequency is directly governed by
control parameters of the system and can vary in a wide range. Our analytical
results are in good agreement with the results of numerical simulations.",1608.01462v3
2016-08-15,Precession resonance in water waves,"We describe the theory and present numerical evidence for a new type of
nonlinear resonant interaction between gravity waves on the surface of deep
water. The resonance constitutes a generalisation of the usual 'exact'
resonance as we show that exchanges of energy between the waves can be enhanced
when the interaction is three-wave rather than four and the linear frequency
mismatch, or detuning, is non-zero i.e. $\omega_1\pm\omega_2\pm\omega_3 \neq0.$
This is possible because the resonance condition is now a match between the
so-called 'precession frequency' of a given $\textit{triad interaction}$ and an
existent nonlinear frequency in the system. In the limit of weak nonlinearity
this precession frequency is simply due to the linear 'drift' of the triad
phase; therefore, it tends toward the detuning. This means precession resonance
of this type can occur at finite amplitudes, with nonlinear corrections
contributing to the resonance. We report energy transfer efficiencies of up to
40%, depending on the model options. To the authors' knowledge this represents
the first new type of nonlinear resonance in surface gravity waves since the
seminal work of Benjamin & Feir (1967).",1608.04241v1
2016-08-22,Metallic coplanar resonators optimized for low-temperature measurements,"Metallic coplanar microwave resonators are widely employed at room
temperature, but their low-temperature performance has received little
attention so far. We characterize compact copper coplanar resonators with
multiple modes from 2.5 to 20 GHz at temperatures as low as 5 K. We investigate
the influence of center conductor width (20 to 100 {\mu}m) and coupling gap
size (10 to 50 {\mu}m), and we observe a strong increase of quality factor (Q)
for wider center conductors, reaching values up to 470. The magnetic-field
dependence of the resonators is weak, with a maximum change in Q of 3.5% for an
applied field of 7 T. This makes these metallic resonators well suitable for
magnetic resonance studies, as we document with electron spin resonance (ESR)
measurements at multiple resonance frequencies.",1608.06122v1
2016-12-15,Chaos in some young asteroid families,"Asteroid families are groups of minor planets that have a common origin in
breakup events. The very young compact asteroid clusters are the natural
laboratory to study resonance related chaotic and nonlinear dynamics. The
present dynamical configurations and evolution of asteroid associations
strongly depends on their ages. In present paper we allocate subclass of very
young asteroid families (younger than 1 Myr). We show that resonance-related
chaos can play a very important role in dynamics of very young asteroid
families. In case of Datura family chaos may be explained by high order mean
motion resonance 9:16 with Mars. In case Hobson family chaos is affected by
secular resonance. In other considered cases (Kapbos cluster and Lucascavin
cluster) origin of chaotic behavior is still unknown. The effect of resonance
is very selective in all cases: we see very stable orbits in the vicinity of
chaotic ones. In the high order resonance transfer from initial to final orbit
take place by temporary capture in exact resonance. The large asteroids (Ceres,
Vesta) can made significant effect on dynamic of small bodies in resonance. In
some cases (as for Datura and Lucascavin family), their perturbations can
extend area of chaotic motion.",1612.04951v1
2017-06-07,High-Q supercavity modes in subwavelength dielectric resonators,"Recent progress in nanoscale optical physics is associated with the
development of a new branch of nanophotonics exploring strong Mie resonances in
dielectric nanoparticles with high refractive index. The high-index resonant
dielectric nanostructures form building blocks for novel photonic metadevices
with low losses and advanced functionalities. However, unlike extensively
studied cavities in photonic crystals, such dielectric resonators demonstrate
low quality factors (Q-factors). Here, we uncover a novel mechanism for
achieving giant Q-factors of subwavelength nanoscale resonators by realizing
the regime of bound states in the continuum. We reveal strong mode coupling and
Fano resonances in high-index dielectric finite-length nanorods resulting in
high-Q factors at the nanoscale. Thus, high-index dielectric resonators
represent the simplest example of nanophotonic supercavities, expanding
substantially the range of applications of all-dielectric resonant
nanophotonics and meta-optics.",1706.02099v1
2017-07-11,Andreev reflection assisted lasing in an electromagnetic resonator coupled to a hybrid-quantum-dot,"A single mode electromagnetic resonator coupled to a two-level
hybrid-quantum-dot(hQD) is studied theoretically as a laser(maser), when the
hQD is driven out of equilibrium with external applied d.c. bias voltage. Using
the formalism of the non-equilibrium Green's functions for the hQD and the
semi-classical laser equations, we determine the relevant physical quantities
of the system. We find that due to the resonant Andreev reflections and the
formation of the Floquet-Andreev side-resonances in the sub-gap region, at
appropriate gate voltages and above a certain threshold bias voltage and
damping factor of the resonator, the two-level QD has non-zero gain spectrum
and lasing can happen in the system in the frequency range of superconducting
gap. Furthermore, our results show that depending on the damping factor of the
resonator and above a specific threshold bias voltages, the lasing can be
either due to single electron transitions or cascaded electron transitions
between the Andreev resonances and Floquet-Andreev side-resonances.",1707.03219v2
2017-10-09,Observation of Feshbach resonances between alkali and closed-shell atoms,"Magnetic Feshbach resonances are an invaluable tool for controlling ultracold
atoms and molecules. They can be used to tune atomic interactions and have been
used extensively to explore few- and many-body phenomena. They can also be used
for magnetoassociation, in which pairs of atoms are converted into molecules by
ramping an applied magnetic field across a resonance. Pairs of open-shell
atoms, such as the alkalis, chromium, and some lanthanides, exhibit broad
resonances because the corresponding molecule has multiple electronic states.
However, molecules formed between alkali and closed-shell atoms have only one
electronic state and no broad resonances. Narrow resonances have been predicted
in such systems, but until now have eluded observation. Here we present the
first observation of magnetic Feshbach resonances in a system containing a
closed-shell atom, Sr, interacting with an alkali atom, Rb. These resonances
pave the way to creating an ultracold gas of strongly polar, open-shell
molecules, which will open up new possibilities for designing quantum many-body
systems and for tests of fundamental symmetries.",1710.03093v1
2017-10-19,Tracking the resonant frequency of a micromechanical resonator using phononic frequency combs,"Micro and nanomechanical resonators have been extensively researched in
recent decades for applications to time and frequency references, as well as
highly sensitive sensors. Conventionally, the operation of these resonant
sensors is practically implemented using a feedback oscillator to dynamically
track variations in the resonant frequency. However, this approach places
limitations on the frequency stability of the output response, particularly
owing to near-carrier phase noise, potentially limiting measurements over long
integration times. Here, in this paper, utilizing the recent experimental
demonstration of phononic frequency combs, we demonstrate an alternative
resonant tracking approach with the potential to provide significant
improvements in near-carrier phase noise and long-term stability. In addition,
we also showcase comb dynamics mediated resonant frequency modulation which
indirectly points to the possible control of inevitable noise processes
including thermomechanical fluctuations. This resonant tracking approach may
also have general applicability to a number of other physical oscillators.",1710.07058v3
2018-01-26,Strong indirect coupling between graphene-based mechanical resonators via a phonon cavity,"Mechanical resonators are promising systems for storing and manipulating
information. To transfer information between mechanical modes, either direct
coupling or an interface between these modes is needed. In previous works,
strong coupling between different modes in a single mechanical resonator and
direct interaction between neighboring mechanical resonators have been
demonstrated. However, coupling between distant mechanical resonators, which is
a crucial request for long-distance classical and quantum information
processing using mechanical devices, remains an experimental challenge. Here,
we report the experimental observation of strong indirect coupling between
separated mechanical resonators in a graphene-based electromechanical system.
The coupling is mediated by a far-off-resonant phonon cavity through virtual
excitations via a Raman-like process. By controlling the resonant frequency of
the phonon cavity, the indirect coupling can be tuned in a wide range. Our
results may lead to the development of gate-controlled all-mechanical devices
and open up the possibility of long-distance quantum mechanical experiments.",1801.08752v1
2018-09-28,Towards the Minimal Spectrum of Excited Baryons,"In the light baryon sector resonances can be broad and overlapping and are in
most cases not directly visible in the cross section data. Automatized model
selection techniques that introduce penalties for resonances can be used to
determine the minimally needed set of resonances to describe the data. Several
possible penalization schemes are compared. As an application we perform a
blindfold identification of hyperon resonances in the $\bar{K} N \to K \Xi$
reaction based on the Least Absolute Shrinkage and Selection Operator (LASSO)
in combination with the Bayesian Information Criterion (BIC). We find ten
resonances --- out of the 21 above-threshold hyperon resonances with spin $J\le
7/2$ listed by the Particle Data Group. In traditional analyses, it is
practically impossible to test the relevance of all resonances and their
combinations that may potentially contribute to the reaction. By contrast, the
present method proves capable of determining the relevant resonances among a
large pool of candidates.",1810.00075v2
2018-10-05,Resonant spectra of multipole-bound anions,"In multipole-bound anions, the excess electron is attached by a short-range
multipole potential of a neutral molecule. Such anions are prototypical
marginally-bound open quantum systems. In particular, around the critical
multipole moment required to attach the valence electron, multipole-bound
anions exhibit critical behavior associated with a transition from bound states
dominated by low-$\ell$ partial waves to the electron continuum. In this work,
multipole-bound anions are described using a nonadiabatic electron-plus-rotor
model. The electron-molecule pseudo-potential is represented by a short-range
multipole field with a Gaussian form-factor. The resulting coupled-channel
Schr\""odinger equation is solved by means of the Berggren expansion method, in
which the electron's wave function is decomposed into bound states, narrow
resonances, and the non-resonant scattering continuum. We show that the
Gaussian model predicts the critical transition at the detachment threshold.
Resonant states, including bound states, decaying resonances, subthreshold
resonances, and antibound states are studied, and exceptional points where two
resonant states coalesce are predicted. We discuss the transition of rotational
band structures around the threshold and study the effects of channel coupling
on the decay width of resonant poles.",1810.02806v2
2018-10-25,Black resonators and geons in AdS$_5$,"We construct dynamical black hole solutions with a helical symmetry in
AdS$_5$, called black resonators, as well as their horizonless limits, called
geons. We introduce a cohomogeneity-1 metric describing a class of black
resonators and geons whose isometry group is $R\times SU(2)$. This allows us to
study them in a wide range of parameters. We obtain the phase diagram for the
black resonators, geons, and Myers-Perry-AdS$_5$, where the black resonators
emerge from the onset of a superradiant instability of the Myers-Perry-AdS$_5$
with equal angular momenta and are connected to the geons in the small horizon
limit. The angular velocities of the black resonators always satisfy $\Omega>1$
in units of the AdS radius. A black resonator is shown to have higher entropy
than a Myers-Perry-AdS$_5$ black hole with the same asymptotic charges. This
implies that the Myers-Perry-AdS$_5$ can dynamically evolve into the black
resonator under the exact $SU(2)$-symmetry although its endpoint will be
further unstable to $SU(2)$-violating perturbations.",1810.11089v2
2019-06-26,Chiral quantum optics using a topological resonator,"Topological photonic structures exhibit chiral edge states that are robust to
disorder and sharp bends. When coupled to quantum emitters, these edge states
generate directional light emission that enables unprecedented control of
interactions between light and matter in a nanophotonic device. While
directional light emission in one-dimensional topological, as well as
conventional, waveguides has been previously demonstrated, the extension of
these concepts to resonator structures that enhance light-matter coupling
remains challenging. Here we demonstrate chiral lightmatter interactions in a
topological resonator. We employ valley-Hall topological edge states to realize
a helical resonator at the interface of two topologically distinct regions.
Such a helical resonator has two counter-propagating modes with opposite
polarizations. We show chiral coupling of the resonator to a quantum emitter
resulting in a Purcell enhancement of 3.4 due to resonant coupling. Such chiral
resonators could enable designing complex nanophotonic circuits for quantum
information processing, and studying novel quantum many-body dynamics.",1906.11263v2
2019-09-24,Tuning high-Q superconducting resonators by magnetic field reorientation,"Superconducting resonators interfaced with paramagnetic spin ensembles are
used to increase the sensitivity of electron spin resonance experiments and are
key elements of microwave quantum memories. Certain spin systems that are
promising for such quantum memories possess 'sweet spots' at particular
combinations of magnetic fields and frequencies, where spin coherence times or
linewidths become particularly favorable. In order to be able to couple high-Q
superconducting resonators to such specific spin transitions, it is necessary
to be able to tune the resonator frequency under a constant magnetic field
amplitude. Here, we demonstrate a high quality, magnetic field resilient
superconducting resonator, using a 3D vector magnet to continuously tune its
resonance frequency by adjusting the orientation of the magnetic field. The
resonator maintains a quality factor of $> 10^5$ up to magnetic fields of 2.6
T, applied predominantly in the plane of the superconductor. We achieve a
continuous tuning of up to 30 MHz by rotating the magnetic field vector,
introducing a component of 5 mT perpendicular to the superconductor.",1909.11020v3
2020-02-24,Nuclear multipole responses from chiral effective field theory interaction,"We probe nuclear multipole resonances in the framework of the random-phase
approximation by using the interaction obtained from the chiral effective field
theory. The three-nucleon force is included in a form of the in-medium
two-nucleon interaction which was derived from the chiral three-nucleon force.
The isoscalar monopole, isoscalar dipole, isovector dipole and isoscalar
quadrupole resonances of the closed-shell $^{56,68,78}$Ni have been
investigated. The calculations reasonably reproduce the experimental multipole
resonances of $^{56,68}$Ni, and well describe the pygmy dipole resonance and
dipole polarizability measured in $^{68}$Ni. The multipole resonances of
$^{78}$Ni, including pygmy dipole resonance and dipole polarizability, are
predicted. The detailed effects of the tensor force and three-body force are
analyzed by dissecting the chiral interaction. We find that in general the
tensor force effect on electric giant resonances is not as significant as the
effect from the three-body force, although the tensor force provides more than
half of the binding energy. The effect from three-body force is strong in light
nuclei. Particularly, three-body force is crucial for the formation of the
pygmy resonance in calculations.",2002.10048v1
2020-02-26,Symmetry analysis and multipole classification of eigenmodes in electromagnetic resonators for engineering their optical properties,"The resonator is one of the main building blocks of a plethora of photonic
and microwave devices from nanolasers to compact biosensors and magnetic
resonance scanners. The symmetry of the resonators is tightly related to their
mode structure and multipole content which determines the linear and non-linear
response of the resonator. Here, we develop the algorithm for the
classification of eigenmodes in resonators of the simplest shapes depending on
their symmetry group. For each type of mode, we find its multipole content. As
an illustrative example, we apply the developed formalism to the analysis of
dielectric triangular prism and demonstrate the formation of high-Q resonances
originated due to suppression of the scattering through the main multipole
channel. The developed approach one to engineer, predict, and explain
scattering phenomena and optical properties of resonators and meta-atmos basing
only on their symmetry without the need for numerical simulations and it can be
used for the design of new photonic and microwave devices.",2002.11411v1
2020-04-24,Dynamics and multiqubit entanglement in distant resonators,"We consider the dynamics of the photon states in distant resonators coupled
to a common bus resonator at different positions. The frequencies of distant
resonators from a common bus resonator are equally detuned. These frequency
detunings are kept larger than the coupling strengths of each resonator to the
common bus resonator to satisfy the dispersive interaction regime. In the
dispersive regime, we show that the time dynamics of the system evolve to an
arbitrary W-type state in a single step at various interaction times. Our
results show that a one-step generation of arbitrary W-type states can be
achieved with high fidelity in a system of superconducting resonators.",2004.12008v1
2018-03-19,Sensorless Resonance Tracking of Resonant Electromagnetic Actuator through Back-EMF Estimation for Mobile Devices,"Resonant electromagnetic actuators have been broadly used as vibration motors
for mobile devices given their ability of generating relatively fast, strong,
and controllable vibration force at a given resonant frequency. Mechanism of
the actuators that is based on mechanical resonance, however, limits their use
to a situation where their resonant frequencies are known and unshifted. In
reality, there are many factors that alter the resonant frequency: for example,
manufacturing tolerances, worn mechanical components such as a spring,
nonlinearity in association with different input voltage levels. Here, we
describe a sensorless resonance tracking method that actuates the motor and
automatically detects its unknown damped natural frequency through the
estimation of back electromotive force (EMF) and inner mass movements. We
demonstrate the tracking performance of the proposed method through a series of
experiments. This approach has the potential to control residual vibrations and
then improve vibrotactile feedback, which can potentially be used for
human-computer interaction, cognitive and affective neuroscience research.",1803.07065v1
2018-03-30,Bloch-Floquet waves in optical ring resonators,"Modal coupling between frequency-degenerate resonances of an optical ring
resonator is a commonly observed phenomenon that results in adverse mode
splitting. Traditionally, this coupling is attributed to Rayleigh scattering of
a propagating electromagnetic wave into its associated degenerate
counter-propagating mode from small perturbations to the dielectric material of
the resonator. We have chosen to reframe the problem of intracavity Rayleigh
scattering by considering the optical ring resonator as an infinitely-long,
one-dimensional photonic crystal (PhC) that possesses a lattice constant equal
to the perimeter of the ring. Through application of Bloch-Floquet theory, we
show that modal coupling between degenerate resonances of a ring can
effectively be described as the formation of photonic frequency bands in the
dispersion relation of the resonator. We additionally demonstrate that the
Bragg planes of the PhC lattice coincide with the phase matching conditions for
constructive interference in the ring. Finally, we show that the magnitude of
frequency splitting of a particular resonance is proportional to its associated
coefficient in the Fourier expansion of the ring's periodic dielectric
function.",1803.11312v1
2018-06-05,A tunable quantum dissipator for active resonator reset in circuit QED,"We propose a method for fast, deterministic resonator reset based on tunable
dissipative modes. The dissipator is based on a Josephson junction with
relatively low quality factor. When the dissipator is tuned into resonance with
a high quality microwave resonator, resonator photons are absorbed by the
dissipator at a rate orders of magnitude faster than the resonator relaxation
rate. We determine the optimal parameters for realization of the tunable
dissipator, and examine application of the dissipator to removing spurious
photon population in the qubit readout resonator in circuit quantum
electrodynamics. We show that even in the nonlinear large photon occupation
regime, this enhanced resonator decay rate can be attained by appropriate
modulation of the dissipator frequency.",1806.01880v3
2018-07-20,"Strength, stability and three dimensional structure of mean motion resonances in the Solar System","In the framework of the circular restricted three body problem we show that
the numerically computed strength SR(e,i,w) is a good indicator of the strength
and width of the mean-motion resonances in the full space (e,i,w). We present a
survey of strengths in the space (e,i) for typical interior and exterior
resonances. The resonance strength is highly dependent on (e,i,w) except for
exterior resonances of the type 1:k for which the dependence with (i,w) is
softer. Such resonances are thus strong even for retrograde orbits. All other
resonances are weaker at very-high eccentricities for w ~ 90 or 270 and 60 < i
< 120. We explore the resonance structure in the space (a,i) by means of
dynamical maps and we find structures similar to those of space (a,e).",1807.07956v1
2018-08-24,Superconducting circuit quantum computing with nanomechanical resonators as storage,"We analyze the quantum information processing capability of a superconducting
transmon circuit used to mediate interactions between quantum information
stored in a collection of phononic crystal cavity resonators. Having only a
single processing element to be controlled externally makes this approach
significantly less hardware-intensive than traditional architectures with
individual control of each qubit. Moreover, when compared with the commonly
considered alternative approach using coplanar waveguide or 3d cavity microwave
resonators for storage, the nanomechanical resonators offer both very long
lifetime and small size -- two conflicting requirements for microwave
resonators. A detailed gate error analysis leads to an optimal value for the
qubit-resonator coupling rate as a function of the number of mechanical
resonators in the system. For a given set of system parameters, a specific
amount of coupling and number of resonators is found to optimize the quantum
volume, an approximate measure for the computational capacity of a system. We
see this volume is higher in the proposed hybrid nanomechanical architecture
than in the competing on-chip electromagnetic approach.",1808.08216v1
2018-12-20,Photoconductive Heaters Enable Control of Large-Scale Silicon Photonic Ring Resonator Circuits,"A multitude of large-scale silicon photonic systems based on ring resonators
have been envisioned for applications ranging from biomedical sensing to
quantum computing and machine learning. Yet, due to the lack of a scalable
solution for controlling ring resonators, practical demonstrations have been
limited to systems with only a few rings. Here, we demonstrate that large
systems can be controlled by using only doped waveguide elements inside their
ringswhile preserving their area and cost. We measure the large photoconductive
changes of the waveguides for monitoring the rings' resonance conditions across
high-dynamic ranges and leverage their thermo-optic effects for tuning. This
allows us to control ring resonators without requiring additional components,
complex tuning algorithms, or additional electrical I/Os. We demonstrate
automatic resonance alignment of 31 rings of a 16 x 16 switch and of a 14-ring
coupled resonator optical waveguide, making them the largest, yet most compact,
automatically controlled silicon ring resonator circuits to date, to the best
of our knowledge.",1812.09317v2
2018-12-22,Lattice effect on electric and magnetic resonance overlap in periodic array,"Designing the shape of silicon nanoparticles has been shown to be an
effective approach to increasing overlap between electric and magnetic dipole
resonances thereby achieving directional scattering and decrease of reflection.
Variations of disk diameter and/or height affect resonances differently and can
thus result in resonance overlap. In most of the studies, the disks are
arranged in a periodic array where the periodicity is varied together with disk
diameter, but the role of lattice effect is neglected. Here we theoretically
study a periodic array of disks and show that the contribution of the lattice
effect in shifting resonance positions is comparable to the effect of the
diameter change. We demonstrate that the lattice effect is important even when
the wavelength of diffraction remains on the blue side from electric and
magnetic dipole resonances and there are no additional lattice resonances are
excited. Period and disk dimensions are chosen so that the resonances overlap
in the proximity of the telecommunication wavelength which is of great
practical interest.",1812.09465v1
2019-03-14,Camera detection and modal fingerprinting of photonic crystal nanobeam resonances,"We demonstrate in simulation and experiment that the out-of-plane, far-field
scattering profile of resonance modes in photonic crystal nanobeam (PCN)
cavities can be used to identify resonance mode order. Through detection of
resonantly scattered light with an infrared camera, the overlap between optical
resonance modes and the leaky region of k-space can be measured experimentally.
Mode order dependent overlap with the leaky region enables usage of resonance
scattering as a ""fingerprint"" by which resonant modes in nanophotonic
structures can be identified via detection in the far-field. By selectively
observing emission near the PCN cavity region, the resonant scattering profile
of the device can be spatially isolated and the signal noise introduced by
other elements in the transmission line can be significantly reduced,
consequently improving the signal to noise ratio (SNR) of resonance detection.
This work demonstrates an increase in SNR of ~19 dB in out-of-plane scattering
measurements over in-plane transmission measurements. The capabilities
demonstrated here may be applied to improve characterization across
nanophotonic devices with mode-dependent spatial field profiles and enhance the
utility of these devices across a variety of applications.",1903.06244v1
2019-03-15,Root Cones and the Resonance Arrangement,"We study the connection between triangulations of a type $A$ root polytope
and the resonance arrangement, a hyperplane arrangement that shows up in a
surprising number of contexts. Despite an elementary definition for the
resonance arrangement, the number of resonance chambers has only been computed
up to the $n=8$ dimensional case. We focus on data structures for labeling
chambers, such as sign vectors and sets of alternating trees, with an aim at
better understanding the structure of the resonance arrangement, and, in
particular, enumerating its chambers. Along the way, we make connections with
similar (and similarly difficult) enumeration questions. With the root polytope
viewpoint, we relate resonance chambers to the chambers of polynomiality of the
Kostant partition function. With the hyperplane viewpoint, we clarify the
connections between resonance chambers and threshold functions. In particular,
we show that the base-2 logarithm of the number of resonance chambers is
asymptotically $n^2$.",1903.06595v2
2019-08-06,New islands of stability with double-trace deformations,"We assess the role of a resonant spectrum in the AdS instability, and
quantify the extent to which breaking the resonant spectrum of AdS can restore
stability. Specifically, we study non-collapsing `multi-oscillator' solutions
in AdS under various boundary conditions that allow for both resonant and
non-resonant spectra. We find non-collapsing two mode, equal amplitude
solutions in the non-resonant Robin case, and that these solutions vanish in
the fully resonant Dirichlet case. This is consistent with non-resonant
stability, and with the idea that stable solutions in the Dirichlet case are
all single-mode dominated. Surprisingly, when the boundary condition is
Neumann, we find non-collapsing solutions arbitrarily close to AdS that are not
single-mode dominated, despite the spectrum being fully resonant.",1908.02296v1
2019-08-19,Resonant excitation of whistler waves by a helical electron beam,"Chorus-like whistler-mode waves that are known to play a fundamental role in
driving radiation-belt dynamics are excited on the Large Plasma Device by the
injection of a helical electron beam into a cold plasma. The mode structure of
the excited whistler wave is identified using a phase-correlation technique
showing that the waves are excited through a combination of Landau resonance,
cyclotron resonance and anomalous cyclotron resonance. The dominant wave mode
excited through cyclotron resonance is quasi-parallel propagating, whereas wave
modes excited through Landau resonance and anomalous cyclotron resonance
propagate at oblique angles that are close to the resonance cone. An analysis
of the linear wave growth rates captures the major observations in the
experiment. The results have important implications for the generation process
of whistler waves in the Earth's inner magnetosphere.",1908.06952v1
2019-08-30,A case study about the mass exclusion limits for the BSM vector resonances with the direct couplings to the third quark generation,"The upper bounds that the LHC measurements searching for heavy resonances
beyond the Standard model set on the resonance production cross sections are
not universal. They depend on various characteristics of the resonance under
consideration, like its mass, spin, and its interaction pattern. Their validity
are also limited by the assumptions and approximations applied to their
calculations. The bounds are typically used to derive the mass exclusion limits
for the new resonances. In our work, we address some of the issues that emerge
when deriving the mass exclusion limits for the strongly coupled composite
$SU(2)_{L+R}$ vector resonance triplet which would interact directly to the
third quark generation only. We investigate the restrictions on the
applicability of the generally used limit-obtaining procedure to this
particular type of vector resonances. We demonstrate that, in this case, it is
necessary to consider the bottom quark partonic contents of the proton.
Eventually, we find the mass exclusion limits for this resonance triplet for
some representative subsets of the parameter space.",1908.11619v2
2019-11-27,"Spatial Resolution, Sensitivity and Surface Selectivity in Resonant Mode Photothermal Induced Resonance Spectroscopy","Photothermal-Induced Resonance (PTIR) is increasingly used in the measurement
of infrared absorption spectra of sub-micrometer objects. The technique
measures IR absorption spectra by relying on the photothermal effect induced by
a rapid pulse of light and the excitation of the resonance spectrum of an AFM
cantilever in contact with the sample. In this work we assess the spatial
resolution and depth response of PTIR in resonant mode while systematically
varying the pulsing frequency of the excitation laser and the cantilever
resonance. The spatial resolution shows a shallow linear dependence on the
inverse of the pulse frequency, which rules out tip size as a limiting factor
for resolution in the frequency range under investigation. Measured resolution
values are also one order of magnitude lower than in the thermal diffusion
limit, excluding thermal wave propagation as a limiting factor. We also show
that the pulsing frequency of the laser and choice of cantilever resonance
affect the intensity of the signal and the surface selectivity in PTIR images,
with higher frequencies providing increased surface selectivity. The results
confirm a difference in signal generation between resonant PTIR and other
photothermal techniques and indicate that photothermal induced heating and
expansion cannot fully account for observed intensity and resolution.",1911.12097v1
2019-12-10,Resonances in the Earth's Space Environment,"We study the presence of resonances in the region of space around the Earth.
We consider a massless body (e.g, a dust particle or a small space debris)
subject to different forces: the gravitational attraction of the geopotential,
the effects of Sun and Moon. We distinguish different types of resonances:
tesseral resonances are due to a commensurability involving the revolution of
the particle and the rotation of the Earth, semi-secular resonances include the
rates of variation of the mean anomalies of Moon and Sun, while secular
resonances just depend on the rates of variation of the arguments of perigee
and the longitudes of the ascending nodes of the perturbing bodies. We
characterize such resonances, giving precise statements on the regions where
the resonances can be found and provide examples of some specific
commensurability relations.",1912.04593v1
2020-03-04,Breaking Resonant Chains: Destabilization of Resonant Planets due to Long-term Mass Evolution,"Recent exoplanet observations reported a large number of multiple-planet
systems, in which some of the planets are in a chain of resonances. The
fraction of resonant systems to non-resonant systems provides clues about their
formation history. We investigated the orbital stability of planets in resonant
chains by considering the long-term evolution of planetary mass and stellar
mass and using orbital calculations. We found that while resonant chains were
stable, they can be destabilized by a change of $\sim$10% in planetary mass.
Such a mass evolution can occur by atmospheric escape due to photoevaporation.
We also found that resonant chains can be broken by a stellar mass loss of
$\lesssim1$%, which would be explained by stellar winds or coronal mass
ejections. The long-term mass change of planets and stars plays an important
role in the orbital evolutions of planetary systems including super-Earths.",2003.01965v1
2020-05-13,Identification and characterization of high order incoherent space charge driven structure resonances in the CERN Proton Synchrotron,"Space charge is typically one of the performance limitations for the
operation of high intensity and high brightness beams in circular accelerators.
In the Proton Synchrotron (PS) at CERN, losses are observed for vertical tunes
above $Q_y=6.25$, especially for beams with large space charge tune shift. The
work presented here shows that this behaviour is associated to structure
resonances excited by space charge due to the highly symmetric accelerator
lattice of the PS, typical for first generation alternating gradient
synchrotrons. Experimental studies demonstrate the dependency of the losses on
the beam brightness and the harmonic of the resonance, and simulation studies
reveal the incoherent nature of the resonance. Furthermore, the calculation of
the Resonance Driving Terms (RDT) generated by the space charge potential shows
that the operational working point of the PS is surrounded by multiple space
charge driven incoherent resonances. Finally, measurements and simulations on
both lattice driven and space charge driven resonances illustrate the different
behaviour of the beam loss depending on the source of the resonance excitation
and on the beam brightness.",2005.06575v1
2020-06-16,Enhancing nonlinear damping by parametric-direct internal resonance,"Mechanical sources of nonlinear damping play a central role in modern
physics, from solid-state physics to thermodynamics. The microscopic theory of
mechanical dissipation [M. I . Dykman, M. A. Krivoglaz, Physica Status Solidi
(b) 68, 111 (1975)] suggests that nonlinear damping of a resonant mode can be
strongly enhanced when it is coupled to a vibration mode that is close to twice
its resonance frequency. To date, no experimental evidence of this enhancement
has been realized. In this letter, we experimentally show that nanoresonators
driven into parametric-direct internal resonance provide supporting evidence
for the microscopic theory of nonlinear dissipation. By regulating the drive
level, we tune the parametric resonance of a graphene nanodrum over a range of
40-70 MHz to reach successive two-to-one internal resonances, leading to a
nearly two-fold increase of the nonlinear damping. Our study opens up an
exciting route towards utilizing modal interactions and parametric resonance to
realize resonators with engineered nonlinear dissipation over wide frequency
range.",2006.09364v3
2020-08-04,J/ψ-pair resonances by LHCb: a new revolution?,"A comment on the LHCb discovery of J/psi-pair resonances. To appear in
Science Bulletin as a NEWS and VIEWS Paper.",2008.01637v1
2020-09-04,Strong zero-field Förster resonances in K-Rb Rydberg systems,"We study resonant dipole-dipole coupling and the associated van der Waals
energy shifts in Rydberg excited atomic rubidium and potassium and investigate
F\""orster resonances between interspecies pair states. A comprehensive survey
over experimentally accessible pair state combinations reveals multiple
candidates with small F\""orster defects. We crucially identify the existence of
an ultrastrong, ""low"" electric field K-Rb F\""orster resonance with a extremely
large zero-field crossover distance exceeding 100 $\mu$m between the van der
Waals regime and the resonant regime. This resonance allows for a strong
interaction over a wide range of distances and by investigating its dependence
on the strength and orientation of external fields we show this to be largely
isotropic. As a result, the resonance offers a highly favorable setting for
studying long-range resonant excitation transfer and entanglement generation
between atomic ensembles in a flexible geometry. The two-species K-Rb system
establishes a unique way of realizing a Rydberg single-photon optical
transistor with a high-input photon rate and we specifically investigate an
experimental scheme with two separate ensembles.",2009.02004v1
2020-09-25,Lorentz Resonance in the Homogenization of Plasmonic Crystals,"We explain the Lorentz resonances in plasmonic crystals that consist of 2D
nano dielectric inclusions as the interaction between resonant material
properties and geometric resonances of electrostatic nature. One example of
such plasmonic crystals are graphene nanosheets that are periodically arranged
within a non-magnetic bulk dielectric. We identify local geometric resonances
on the length scale of the small scale period. From a materials perspective,
the graphene surface exhibits a dispersive surface conductance captured by the
Drude model. Together these phenomena conspire to generate Lorentz resonances
at frequencies controlled by the surface geometry and the surface conductance.
The Lorentz resonances found in the frequency response of the effective
dielectric tensor of the bulk metamaterial is shown to be given by an explicit
formula, in which material properties and geometric resonances are decoupled.
This formula is rigorous and obtained directly from corrector fields describing
local electrostatic fields inside the heterogeneous structure. Our analytical
findings can serve as an efficient computational tool to describe the general
frequency dependence of periodic optical devices. As a concrete example, we
investigate two prototypical geometries composed of nanotubes and nanoribbons.",2009.12166v2
2020-10-12,One- and two-dimensional correlation spectroscopy analyses for resonant and non-resonant coherent nonlinear optical processes,"Three-color coherent anti-Stokes Raman scattering represents non-degenerate
four wave mixing process that includes both a non-resonant and resonant
processes, the contributions of which depend on how the molecular vibrational
modes are being excited by the input laser pulses. Non-degenerate four wave
mixing processes are complex and understanding these processes requires
rigorous data analytical tools, which still lack in this research field. In
this work, we introduce one- and two-dimensional intensity-intensity
correlation functions in terms of a new variable (e.g., probe pulse delay) and
new perturbation parameter (e.g., probe pulse linewidth). In particular,
diagonal projections are defined here as a tool to reduce both synchronous and
asynchronous two-dimensional correlation spectroscopy analyses down to
one-dimensional analysis, revealing valuable analytical information. Detailed
analyses using the all Gaussian coherent Raman scattering closed-form solutions
and the representative experimental data for resonant and non-resonant
processes are presented and compared. This intensity-intensity correlation
analytical tool holds a promising potential in resolving and visualizing
resonant versus non-resonant four wave mixing processes for quantitative
label-free species-specific nonlinear spectroscopy and microscopy.",2010.06017v1
2020-10-31,Long-term dynamics driven by resonant wave-particle interactions: from Hamiltonian resonance theory to phase space mapping,"In this study we consider the Hamiltonian approach for the construction of a
map for a system with nonlinear resonant interaction, including phase trapping
and phase bunching effects. We derive basic equations for a single resonant
trajectory analysis and then generalize them into the map in the
energy/pitch-angle space. The main advances of this approach are the
possibility to consider effects of many resonances and to simulate the
evolution of the resonant particle ensemble on long time ranges. For
illustrative purposes we consider the system with resonant relativistic
electrons and field-aligned whistler-mode waves. The simulation results show
that the electron phase space density within the resonant region is flattened
with reduction of gradients. This evolution is much faster than the predictions
of quasi-linear theory. We discuss further applications of the proposed
approach and possible ways for its generalization.",2011.00208v1
2021-02-20,Effect of internal resonance on the dynamics of MoS2 resonator,"Nonlinear modal interactions and associated internal resonance phenomena have
recently been used to demonstrate improved oscillator performance and enhanced
sensing capabilities. Here, we show tunable modal interaction in a MoS2
resonator. We achieve the tunability of coupling between these initially
uncoupled modes by using electrostatic gate voltages. This tunable coupling
enables us to make the modes commensurate and observe energy exchange between
the modes. We attribute the strong energy exchange between the vibrational
modes to 2:1 internal resonance. This interaction strongly affects the dynamics
of the modal response of such resonators. We observe peak splitting, a
signature of energy exchange between the modes even when the modal response is
in the linear regime. We model our device to explain the observed effect of
excitation, detuning of modal frequencies, and intermodal coupling strength on
the resonator dynamics. MoS2 resonators explored in this work are ideal for
understanding the rich dynamics offered through the intermodal coupling.",2102.10384v1
2021-03-23,Cross sections of solar neutrino capture by 127I nuclei and Gamow Teller resonances,"Solar neutrino capture cross-section by 127I nucleus has been studied with
taking into account the influence of the resonance structure of the nuclear
strength function S(E). Three types of isobaric resonances: giant Gamow-Teller,
analog resonance and low-lying Gamow-Teller pigmy resonances has been
investigated on the framework of self-consistent theory of finite Fermi
systems. The calculations have been performed considering the resonance
structure of the charge-exchange strength function S(E). We analyze the effect
of each resonance on the energy dependence of the cross-section. It has been
shown that all high-lying resonances should be considered. Neutron emission
process for high energy nuclear excitation leads to formation 126Xe isotope. We
evaluate contribution from various sources of solar neutrinos to the
126Xe/127Xe isotopes ratio formed by energetic neutrinos. 126Xe/127Xe isotope
ratio could be an indicator of high-energy boron neutrinos in the solar
spectrum. We also discuss the uncertainties in the often used Fermi-functions
calculations.",2103.12325v1
2021-03-31,Investigation of multi-step effects for proton inelastic scattering to the $2^{+}_{1}$ state in $^6$He,"Multi-step effects between bound, resonant, and non-resonant states have been
investigated by the continuum-discretized coupled-channels method (CDCC). In
the CDCC, a resonant state is treated as multiple states fragmented in a
resonance energy region, although it is described as a single state in usual
coupled-channel calculations. For such the fragmented resonant states, one-step
and multi-step contributions to the cross sections should be carefully
discussed because the cross sections obtained by the one-step calculation
depend on the number of those states, which corresponds to the size of the
model space. To clarify the role of the multi-step effects, we propose the
one-step calculation without model-space dependence for the fragmented resonant
states. Furthermore, we also discuss the multi-step effects between the ground,
$2^{+}_{1}$ resonant, and non-resonant states in $^6$He for proton inelastic
scattering.",2103.16865v2
2021-05-12,Resonant contributions to inclusive nucleon structure functions from exclusive meson electroproduction data,"Nucleon resonance contributions to the inclusive proton $F_2$ and $F_L$
structure functions are computed from resonance electroexcitation amplitudes in
the mass range up to 1.75 GeV extracted from CLAS exclusive meson
electroproduction data. Taking into account for the first time quantum
interference effects, the resonance contributions are compared with inclusive
proton structure functions evaluated from $(e,e'X)$ cross section data and the
longitudinal to transverse cross section ratio. Contributions from isospin-1/2
and 3/2 resonances remain substantial over the entire range of photon
virtualities $Q^2 \lesssim 4$ GeV$^2$, where their electroexcitation amplitudes
have been obtained, and their $Q^2$ evolution displays pronounced differences
in the first, second and third resonance regions. We compare the structure
functions in the resonance region with those computed from parton distributions
fitted to deep-inelastic scattering data, and extrapolated to the resonance
region, providing new quantitative assessments of quark-hadron duality in
inclusive electron-proton scattering.",2105.05834v1
2021-06-21,Secular resonance of inner test particles in hierarchical planetary systems,"The present work studies the secular resonance associated with the critical
argument $\sigma = \varpi$ ($\varpi$ is the longitude of pericentre) for inner
test particles moving in low-eccentricity region with inclination $i$ smaller
than $39^{\circ}$. To formulate the dynamical model, the double-averaged
Hamiltonian is formulated up to an arbitrary order in the semimajor axis ratio,
and then those high-order periodic terms are removed from the double-averaged
Hamiltonian by means of Hori--Deprit transformation technique. The resulting
Hamiltonian determines a resonant model with a single degree of freedom. Based
on the resonant model, it becomes possible to explore the phase-space
structure, resonant centre, and resonant width in an analytical manner. In
particular, an excellent correspondence is found between the resonant width in
terms of the eccentricity variation and the maximum variation of eccentricity
($\Delta e$) for test particles initially placed on quasi-circular orbits. It
means that the secular dynamics in the low-eccentricity space with $i <
39^{\circ}$ is dominantly governed by the secular resonance associated with
$\sigma = \varpi$.",2106.10794v1
2021-08-06,Mitigating off-resonant error in the cross-resonance gate,"Off-resonant error for a driven quantum system refers to interactions due to
the input drives having non-zero spectral overlap with unwanted system
transitions. For the cross-resonance gate, this includes leakage as well as
off-diagonal computational interactions that lead to bit-flip error on the
control qubit. In this work, we quantify off-resonant error, with more focus on
the less studied off-diagonal control interactions, for a direct CNOT gate
implementation. Our results are based on numerical simulation of the dynamics,
while we demonstrate the connection to time-dependent Schrieffer-Wolff and
Magnus perturbation theories. We present two methods for suppressing such error
terms. First, pulse parameters need to be optimized so that off-resonant
transition frequencies coincide with the local minima due to the pulse spectrum
sidebands. Second, we show the advantage of a $Y$-DRAG pulse on the control
qubit in mitigating off-resonant error. Depending on qubit-qubit detuning, the
proposed methods can improve the average off-resonant error from approximately
$10^{-3}$ closer to the $10^{-4}$ level for a direct CNOT calibration.",2108.03223v1
2021-11-08,Resonance distribution in the quantum random Lorentz gas,"The multiple scattering model of a quantum particle in a random Lorentz gas
consisting of fixed point scatterers is considered in arbitrary dimension. An
efficient method is developed to numerically compute the map of the density of
scattering resonances in the complex plane of the wavenumber without finding
them one by one. The method is applied to two collision models for the
individual scatterers, namely a resonant model, and a non-resonant hard-sphere
model. The results obtained with the former are compared to the literature. In
particular, the spiral arms surrounding the single-scatterer resonance are
identified as proximity resonances. Moreover, the hard-sphere model is used to
reveal previously unknown structures in the resonance density. Finally, it is
shown how Anderson localization affects the distribution of resonance widths,
especially in the one-dimensional case.",2111.04410v3
2021-12-07,Plasmon resonances of nanorods in transverse electromagnetic scattering,"Plasmon resonance is the resonant oscillation of conduction electrons at the
interface between negative and positive permittivity material stimulated by
incident light, which forms the fundamental basis of many cutting-edge
industrial applications. We are concerned with the quantitative theoretical
understanding of this peculiar resonance phenomenon. It is known that the
occurrence of plasmon resonance as well as its quantitative behaviours
critically depend on the geometry of the material structure, the corresponding
material parameters and the operating wave frequency, which are delicately
coupled together. In this paper, we study the plasmon resonance for a 2D
nanorod structure, which presents an anisotropic geometry and arises in the
transverse electromagnetic scattering. We present delicate spectral and
asymptotic analysis to establish the accurate resonant conditions as well as
sharply characterize the quantitative behaviours of the resonant field.",2112.03697v2
2022-01-19,Observation of the P-wave Shape Resonance,"Partial wave resonances are quasi-bound states that are formed by tunneling
through the centrifugal barrier. Such states are important to collisions that
deviate from the Langevin limit where direct collision path is suppressed due
to quantum symmetry or a potential barrier. In such a case, quantum resonances
play a major role in the dynamics at low temperatures where scattering process
can be described mainly by the resonance contribution. Here we present the
first observation of the lowest-lying partial wave resonance in the Penning
ionization collisions between metastable neon and rovibrationally ground state
HD molecules. We observe the resonance at an energy of $k_B\times$22mK taking
advantage of the phase space correlation similar to atomic delta kick cooling.
We show that the $p$-wave resonance position is particularly sensitive to the
leading term of the van der Waals interaction. We also measure shape resonance
at a higher angular momentum state, $l=6$, allowing us to disentangle and probe
the short and the long parts of the intermolecular interaction.",2201.07716v2
2022-03-04,Post-Fabrication Trimming of Silicon Photonic Ring Resonators at Wafer-Scale,"Silicon ring resonator-based devices, such as modulators, detectors, filters,
and switches, play important roles in integrated photonic circuits for optical
communication, high-performance computing, and sensing applications. However,
the high sensitivity to fabrication variations has limited their volume
manufacturability and commercial adoption. Here, we report a low-cost
post-fabrication trimming method to tune the resonance wavelength of a silicon
ring resonator and correct for fabrication variations at wafer-scale. We use a
Ge implant to create an index trimmable section in the ring resonator and an
on-chip heater to apply a precise and localized thermal annealing to tune and
set its resonance to a desired wavelength. We demonstrate resonance wavelength
trimming of ring resonators fabricated across a 300 mm silicon-on-insulator
(SOI) wafer to within +/-32 pm of a target wavelength of 1310 nm, providing a
viable path to high-volume manufacturing and opening up new practical
applications for these devices.",2203.03503v1
2022-03-03,Intelligent resonance tracking of a microwave plasmonic resonator for compact wireless sensors,"Plasmonic sensing has been in the spotlight for decades, the concept and
applications of which have been generalized to spoof surface plasmons (SSPs) in
the microwave band. Here, we report a compact and wireless sensor within a
printed circuit board size of 18 mm * 12 mm, tracking the resonance frequency
shift of a microwave plasmonic resonator via a software-defined scheme. The
microwave plasmonic resonator yields a deep-subwavelength size, enhanced
sensitivity, and a good electromagnetic compatibility performance. The
software-defined resonance tracking scheme minimalizes the hardware circuit and
the consumed spectrum resources, and makes the detection intelligently adaptive
to the target resonance, with a signal-to-noise ratio of 69 dB and a data rate
of 2272 measuring points per second. The sensor has been validated via acetone
vapor concentration sensing, while its applications can be widely extended by
replacing the transducer materials. This approach provides compact, sensitive,
accurate and intelligent solutions for resonant sensors in the Internet of
things (IoT).",2203.04780v1
2022-03-18,Wire metamaterial filled metallic resonators,"In this work we study electromagnetic properties of a resonator recently
suggested for the search of axions - a hypothetical candidate to explain dark
matter. A wire medium loaded resonator (called a plasma haloscope when used to
search for dark matter) consists of a box filled with a dense array of parallel
wires electrically connected to top and bottom walls. We show that the
homogenization model of wire medium works for this resonator without mesoscopic
corrections, and that the resonator quality $Q$ at the frequency of our
interest drops versus the growth of the resonator volume $V$ until it is
dominated by resistive losses in the wires. We find that even at room
temperature metals like copper can give quality factors in the thousands, an
order of magnitude higher than originally assumed. Our theoretical results for
both loaded and unloaded resonator quality factors were confirmed by building
an experimental prototype. We discuss ways to further improve WM loaded
resonators.",2203.10083v2
2022-05-31,Spin-Acoustic Control of Silicon Vacancies in 4H Silicon Carbide,"We demonstrate direct, acoustically mediated spin control of naturally
occurring negatively charged silicon monovacancies (V$_{Si}^-$) in a high
quality factor Lateral Overtone Bulk Acoustic Resonator fabricated out of high
purity semi-insulating 4H-Silicon Carbide. We compare the frequency response of
silicon monovacancies to a radio-frequency magnetic drive via
optically-detected magnetic resonance and the resonator's own radio-frequency
acoustic drive via optically-detected spin acoustic resonance and observe a
narrowing of the spin transition to nearly the linewidth of the driving
acoustic resonance. We show that acoustic driving can be used at room
temperature to induce coherent population oscillations. Spin acoustic resonance
is then leveraged to perform stress metrology of the lateral overtone bulk
acoustic resonator, showing for the first time the stress distribution inside a
bulk acoustic wave resonator. Our work can be applied to the characterization
of high quality-factor micro-electro-mechanical systems and has the potential
to be extended to a mechanically addressable quantum memory.",2205.15488v1
2022-07-27,A Criterion for the Stability of Planets in Chains of Resonances,"Uncovering the formation process that reproduces the distinct properties of
compact super-Earth exoplanet systems is a major goal of planet formation
theory. The most successful model argues that non-resonant systems begin as
resonant chains of planets that later experience a dynamical instability.
However, both the boundary of stability in resonant chains and the mechanism of
the instability itself are poorly understood. Previous work postulated that a
secondary resonance between the fastest libration frequency and a difference in
synodic frequencies destabilizes the system. Here, we use that hypothesis to
produce a simple and general criterion for resonant chain stability that
depends only on planet orbital periods and masses. We show that the criterion
accurately predicts the maximum mass of planets in synthetic resonant chains up
to six planets. More complicated resonant chains produced in population
synthesis simulations are found to be less stable than expected, although our
criterion remains useful and superior to machine learning models.",2207.13833v1
2022-07-29,Coherent resonant transmission,"The reflectionless coherent light transport in the coupled resonator array is
investigated in the presence of intra-resonator intermodal coupling between the
clockwise and counterclockwise modes, which plays a constructive role for
modulating the light flow rather than inducing the unwanted backscattering. The
interplay between the intra-resonator intermodal coupling and the
inter-resonator couplings enables the coherent resonant transmission (CRT) of
the properly superposed injection constituted by the clockwise and
counterclockwise modes. The superposition coefficients of the initial
excitation determine the mode chirality of the resonant transmission.
Sequentially experiencing the time-reversal process of CRT and the CRT realizes
the perfect mode conversion that the mode chirality of the injection wave
switches into the opposite after resonant transmission. Our findings on the
coherent light transport provide insights for the control and manipulation of
light field in the integrated photonics, nanophotonics, chiral optics, and
beyond.",2207.14453v1
2022-09-03,Single photon controlled steady state electron transport through a resonance DQD-Cavity system in a strong coupling regime,"We perform theoretical calculations to study steady-state electron transport
in a double quantum dot, DQD, coupled to a quantized cavity photon field both
in resonance and off-resonance regimes considering weak and strong coupling. In
the resonant strong coupling regime, photon exchanges between the energy states
of the DQD and the cavity are found reflecting multiple Rabi-resonances. The
electron occupation of the states and the transport current can be smoothly
increased by tuning the cavity-environment coupling strength. Making the system
off-resonant, but still in the strong coupling regime, the photon exchange is
diminished and the electron occupation of the system and the transport current
through it are prominent for high cavity-environment coupling strength. In the
weak coupling regime between the DQD and the cavity, the system has almost the
same response in the resonant and the off-resonant regimes at high values of
the cavity-environment coupling strength.",2209.01495v1
2022-11-14,A mathematical design strategy for highly dispersive resonator systems,"Designing devices composed of many small resonators is a challenging problem
that can easily incur significant computational cost. Can asymptotic techniques
be used to overcome this often limiting factor? Integral methods and asymptotic
techniques have been used to derive concise characterisations for scattering by
resonators, but can these be generalised to systems of many dispersive
resonators whose material parameters have highly non-linear frequency
dependence? In this paper, we study halide perovskite resonators as a
demonstrative example. We extend previous work to show how a finite number of
coupled resonators can be modelled concisely in the limit of small radius. We
also show how these results can be used as the basis for an inverse design
strategy, to design resonator systems that resonate at specific frequencies.",2211.07223v1
2022-11-30,Fabrication and Characterization of Magnetic-Field-Resilient MoRe Superconducting Coplanar Waveguide Resonators,"Magnetic-field-resilient superconducting coplanar waveguide (SCPW) resonators
are essential for developing integrated quantum circuits of various qubits and
quantum memory devices. Molybdenum-Rhenium (MoRe), which is a disordered
superconducting alloy forming a highly transparent contact to the graphene and
carbon nanotubes (CNTs), would be a promising platform for realizing the
field-resilient SCPW resonators combined with graphene- and CNT-based
nano-hybrid qubits. We fabricated MoRe SCPW resonators and investigated their
microwave transmission characteristics with varying temperature and external
magnetic field. Our observations show that the thickness of MoRe film is a
critical parameter determining the lower critical field, kinetic inductance,
and characteristic impedance of the SCPW resonator, resulting in drastic
changes in the quality factor and the resonance frequency. As a result, we
obtained a maximum value of $Q_{i} > 10^{4}$ in parallel magnetic fields up to
$B_{||} = 0.15$ T for the 27-nm-thick MoRe resonator. Our experimental results
suggest that MoRe SCPW resonator would be useful for integrating nano-hybrid
spin or gatemon qubits and for developing spin-ensemble quantum memory devices.",2211.16948v1
2023-01-13,Possible interpretation of the complex expectation values associated with resonances,"We propose a possible scheme to interpret the complex expectation values
associated with resonances having the complex eigenenergies. Using the Green's
function for resonances, the expectation value is basically described by the
Breit-Wigner distribution as a function of the real excitation energy. In the
expression of the complex expectation values for resonances, the real part
brings the integral value of the distribution, while the imaginary part
produces the deviation from the Breit-Wigner distribution,which explains a
shift of the peak in the strength from the resonance energy. We apply the
present scheme to the several nuclear resonances of $^{12}$C including the
Hoyle state, and neutron/proton-rich nuclei of $^6$He, $^6$Be, $^8$He, and
$^8$C. In these nuclei, many-body resonances are obtained as the complex-energy
eigenstates under the correct boundary condition using the complex scaling
method, and their nuclear radii are uniquely evaluated. We discuss the peculiar
energy dependence of the strength function of the square radius for the
resonances in these nuclei.",2301.05355v1
2023-03-21,Correlated polarization dependences between surface-enhanced resonant Raman scattering and plasmon resonance elastic scattering showing spectral uncorrelation to each other,"We investigated the origin of the identical polarization angle dependences
between surface-enhanced resonant Raman scattering (SERRS) and plasmon
resonance for two types of single silver nanoparticle aggregates. The first
type (Type I), in which the SERRS spectral envelopes are similar to the plasmon
resonance elastic scattering spectra, shows the identical polarization
dependence between the SERRS and plasmon resonance. The second type (Type II),
in which the SERRS envelopes largely deviate from the plasmon resonance, also
exhibits identical polarization dependence. Scanning electron microscopy (SEM)
observations indicated that these aggregates were dimers. Thus, this
unintuitive result was examined by calculating the electromagnetic (EM)
enhancement by changing the morphology of the dimers. The calculation revealed
that Type I of dimer generates SERRS directly by superradiant plasmons. The
Type II of dimer generates SERRS indirectly by subradiant plasmons, which
receive light energy from the superradiant plasmons. This indirect SERRS
process clarifies that the interaction between the superradiant and subradiant
plasmons results in an identical polarization dependence between SERRS and
plasmon resonance for Type II of dimers.",2303.11608v1
2023-04-20,Control the qubit-qubit coupling in the superconducting circuit with double-resonator couplers,"We propose a scheme of using two fixed frequency resonator couplers to tune
the coupling strength between two Xmon qubits. The induced indirect qubit-qubit
interactions by two resonators could offset with each other, and the direct
coupling between two qubits are not necessarily for switching off. The small
direct qubit-quibt coupling could effectively suppress the frequency interval
between switching off and switching on, and globally suppress the second and
third-order static ZZ couplings. The frequencies differences between resonator
couplers and qubits readout resonators are very large, this might be helpful
for suppressing the qubits readout errors. The cross-kerr resonant processes
between a qubit and two resonators might induce pole and affect the crosstalks
between qubits. The double resonator couplers could unfreeze the restrictions
on capacitances and coupling strengths in the superconducting circuit, and it
can also reduce the flux noises and globally suppress the crosstalks.",2304.10047v2
2023-06-11,Resonant dynamics of extreme mass-ratio inspirals in a perturbed Kerr spacetime,"Extreme mass-ratio inspirals (EMRI) are one of the most sensitive probes of
black hole spacetimes with gravitational wave measurements. In this work, we
systematically analyze the dynamics of an EMRI system near orbital resonances,
assuming the background spacetime is weakly perturbed from Kerr. Using the
action-angle formalism, we have derived an effective resonant Hamiltonian that
describes the dynamics of the resonant degree of freedom, for the case that the
EMRI motion across the resonance regime. This effective resonant Hamiltonian
can also be used to derive the condition that the trajectory enters/exits a
resonant island and the permanent change of action variables across the
resonance with the gravitational wave radiation turned on. The orbital chaos,
on the other hand, generally leads to transitions between different branches of
rotational orbits with finite changes of the action variables. These findings
are demonstrated with numerical orbital evolutions that are mapped into
representations using action-angle variables. This study is one part of the
program of understanding EMRI dynamics in a generic perturbed Kerr spacetime,
which paves the way of using EMRIs to precisely measure the black hole
spacetime.",2306.06576v2
2023-06-16,Revised Hamiltonian near third-integer resonance and implications for transverse resonance island buckets in storage rings,"In storage rings, an accurate description of particle dynamics near
third-integer resonance is crucial for various applications. The conventional
approach is to extrapolate far-resonance dynamics to near-resonance, but
difficulty arises because the nonlinear detuning parameter diverges at this
critical point. Here we derive, via a suitable application of the canonical
perturbation theory, a revised detuning parameter that is well-behaved near
resonance. The resultant theory accurately describes the morphology of
transverse resonance island buckets (TRIBs) for a wide range of parameter
space. Our results have important implications for advanced applications of
storage rings, as well as for the underlying physics of resonant particle
dynamics.",2306.09587v1
2023-06-19,Resonance expansion for quantum walks and its applications to the long-time behavior,"In this paper, resonances are introduced to a class of quantum walks on
$\mathbb{Z}$. Resonances are defined as poles of the meromorphically extended
resolvent of the unitary time evolution operator. In particular, they appear
inside the unit circle. Some analogous properties to those of quantum
resonances for Schr\""odinger operators are shown. Especially, the resonance
expansion, an analogue of the eigenfunction expansion, indicates the long-time
behavior of quantum walks. The decaying rate, the asymptotic probability
distribution, and the weak limit of the probability density are described by
resonances and associated (generalized) resonant states. The generic simplicity
of resonances is also investigated.",2306.10719v1
2023-06-22,High Impedance Josephson Junction Resonators in the Transmission Line Geometry,"In this article we present an experimental study of microwave resonators made
out of Josephson junctions. The junctions are embedded in a transmission line
geometry so that they increase the inductance per length for the line. By
comparing two devices with different input/output coupling strengths, we show
that the coupling capacitors, however, add a significant amount to the total
capacitance of the resonator. This makes the resonators with high coupling
capacitance to act rather as lumped element resonators with inductance from the
junctions and capacitance from the end sections. Based on a circuit analysis,
we show that the input and output couplings of the resonator are limited to a
maximum value of $\omega_r Z_0 /4 Z_r$ where $\omega_r$ is the resonance
frequency and $Z_0$ and $Z_r$ are the characteristic impedances of the
input/output lines and the resonator respectively.",2306.12701v2
2023-09-08,Generative inverse design of multimodal resonant structures for locally resonant metamaterials,"In the development of locally resonant metamaterials, the physical resonator
design is often omitted and replaced by an idealized mass-spring system. This
paper presents a novel approach for designing multimodal resonant structures,
which give rise to multi-bandgap metamaterials with predefined band gaps. Our
method uses a conditional variational autoencoder to identify nontrivial
patterns between design variables of complex-shaped resonators and their modal
effective parameters. After training, the cost of generating designs satisfying
arbitrary criteria - frequency and mass of multiple modes - becomes negligible.
An example of a resonator family with six geometric variables and two targeted
modes is further elaborated. We find that the autoencoder performs well even
when trained with a limited dataset, resulting from a few hundred numerical
modal analyses. The method generates several designs that very closely
approximate the desired modal characteristics. The accuracy of the best
designs, proposed by the auto-encoder, is confirmed in tests of 3D-printed
resonator prototypes. Further experiments demonstrate the close agreement
between the measured and desired dispersion relation of a sample metamaterial
beam.",2309.04177v1
2023-09-12,4th Body-Induced Secondary Resonance Overlapping Inside Unstable Resonant Orbit Families: a Jupiter-Ganymede 4:3 + Europa Case Study,"The overlapping of mean-motion resonances is useful for low or
zero-propellant space mission design, but while most related prior work uses a
planar CRTBP model, tours of multi-moon systems require using resonances
affected by two moons. In this case study, we investigate Jupiter-Ganymede
unstable 4:3 resonant orbits in a concentric circular restricted 4-body
Jupiter-Europa-Ganymede model. We show that despite their high order, secondary
resonances between the 4:3 orbits and Europa have a large effect, including
11/34, 12/37, 23/71, and 25/77. Computing newly generated objects inside the
secondary resonances definitively confirms their overlap, which causes a
complete structural change of the higher-energy unstable 4:3 orbits whose
manifolds are most useful for low-TOF orbit transfers. We believe this
phenomenon is general, with major implications for resonant orbit use in tour
design.",2309.06073v2
2023-09-28,Quantum Resonance viewed as Weak Measurement,"Quantum resonance, i.e., amplification in transition probability available
under certain conditions, offers a powerful means for determining fundamental
quantities in physics, including the time duration of the second adopted in the
SI units and neutron's electric dipole moment which is directly linked to CP
violation. We revisit two of the typical examples, the Rabi resonance and the
Ramsey resonance, and show that both of these represent the weak value
amplification and that near the resonance points they share exactly the same
behavior of transition probabilities except for the measurement strength whose
difference leads to the known advantage of the Ramsey resonance in the
sensitivity. Conversely, as a by-product of the relationship, we may measure
the weak value through quantum resonance. In fact, we argue that previous
measurements of neutron electric dipole moment based on the Ramsey resonance
have potentially determined the weak value of neutron's spin with much higher
precision than the conventional weak value measurement.",2309.16281v2
2023-12-04,In-situ tuning of optomechanical crystals with nano-oxidation,"Optomechanical crystals are a promising device platform for quantum
transduction and sensing. Precise targeting of the optical and acoustic
resonance frequencies of these devices is crucial for future advances on these
fronts. However, fabrication disorder in these wavelength-scale nanoscale
devices typically leads to inhomogeneous resonance frequencies. Here we achieve
in-situ, selective frequency tuning of optical and acoustic resonances in
silicon optomechanical crystals via electric field-induced nano-oxidation using
an atomic-force microscope. Our method can achieve a tuning range >2 nm (0.13%)
for the optical resonance wavelength in the telecom C-band, and >60 MHz (1.2%)
for the acoustic resonance frequency at 5 GHz. The tuning resolution of 1.1 nm
for the optical wavelength, and $150$ kHz for the acoustic frequency allows us
to spectrally align multiple optomechanical crystal resonators using optimal
oxidation patterns determined via an inverse design protocol. Our results
establish a method for precise post-fabrication tuning of optomechancical
crystals. This technique can enable coupled optomechanical resonator arrays,
scalable resonant optomechanical circuits, and frequency matching of
microwave-optical quantum transducers.",2312.02123v1
2023-12-22,Dynamical structures associated with high-order and secondary resonances in the spin-orbit problem,"In our Solar system, spin-orbit resonances are common under Sun--planet,
planet--satellite and binary asteroid configurations. In this work, high-order
and secondary spin-orbit resonances are investigated by taking numerical and
analytical approaches. Poincar\'e sections as well as two types of dynamical
maps are produced, showing that there are complicated structures in the phase
space. To understand numerical structures, we adopt the theory of perturbative
treatments to formulate resonant Hamiltonian for describing spin-orbit
resonances. Results show that there is an excellent agreement between
analytical and numerical structures. It is concluded that the main V-shape
structure arising in the parameter space $(\dot\theta,\alpha)$ is sculpted by
the synchronous primary resonance, those minute structures inside the V-shape
region are dominated by secondary resonances and those structures outside the
V-shape region are governed by high-order resonances. At last, the analytical
approach is applied to binary asteroid systems (65803) Didymos and (4383)
Suruga to reveal their phase-space structures.",2312.14413v1
2012-10-01,The Color Differences of Kuiper Belt Objects in Resonance with Neptune,"(Abridged) New optical colors of 58 objects in mean motion resonances with
Neptune show the various resonant populations have significantly different
color distributions. The 5:3 and 7:4 resonances have semi-major axes near the
middle of the main Kuiper Belt and both are dominated by ultra-red material.
The 5:3 and 7:4 resonances have statistically the same color distribution as
the low inclination ""cold"" classical belt. The inner 4:3 and distant 5:2
resonances have objects with mostly moderately red colors, similar to the
scattered and detached disk populations. The 2:1 resonance, which is near the
outer edge of the main Kuiper Belt, has a large range of colors with similar
numbers of moderately red and ultra-red objects at all inclinations. The inner
3:2 resonance, like the outer 2:1, has a large range of objects from neutral to
ultra-red. The Neptune Trojans (1:1 resonance) are only slightly red, similar
to the Jupiter Trojans. The inner 5:4 resonance only has four objects with
measured colors but shows equal numbers of ultra-red and moderately red
objects. The 9:5, 12:5, 7:3, 3:1 and 11:3 resonances do not have reliable color
distribution statistics, though it appears noteworthy that all three of the
measured 3:1 objects have only moderately red colors, similar to the 4:3 and
5:2 resonances. The different color distributions are likely a result from the
disruption of the primordial Kuiper Belt from the scattering and migration of
the giant planets. The few low inclination objects known in the outer 2:1 and
5:2 resonances are mostly only moderately red. This suggests if the 2:1 and 5:2
have a cold low inclination component, the objects likely had a significantly
different origin than the ultra-red dominated cold components of the cold
classical belt and 5:3 and 7:4 resonances.",1210.0537v1
2016-04-25,Oblique internal-wave chain resonance over seabed corrugations,"We show that monochromatic long-crested corrugations on an otherwise flat
seafloor can coherently scatter the energy of an oblique incident internal wave
to multiple multi-directional higher-mode waves via a series of resonant
interactions. We demonstrate that a resonance between seabed corrugations and a
normally or slightly oblique incident internal wave results in a series of
follow-up resonant interactions, which take place between the same corrugations
and successively resonated shorter waves. A chain resonance of internal waves
that carries energy to small scales is thus obtained, and we find that the
Richardson number decreases by several orders of magnitude over the corrugated
patch. If the incidence angle is large, and the incident wave perfectly
satisfies a resonance condition with the topography, it turns out that not many
higher-mode resonance or near-resonance conditions can be satisfied, such that
energy stays confined within the first few modes. Nevertheless, if the incident
waves are sufficiently detuned from satisfying a perfect resonance condition
with the seabed corrugations, then we show that this frequency detuning may
balance off the large detuning due to oblique incidence, leading to a chain
resonance that again carries energy to small scales. The evolution of the
incident and resonated wave amplitudes is predicted from the envelope equation
for internal waves over resonant seabed topography in a three-dimensional
rotating fluid, which we derive considering the Boussinesq and $f$-plane
approximations with $f$ the Coriolis frequency, linear density stratification
and small-amplitude corrugations. Our results suggest that topographic features
on the ocean floor with a dominant wavenumber vector, through the chain
resonance mechanism elucidated here, may play a more important role than
previously thought in the enhancement of diapycnal mixing and energy
dissipation.",1604.07308v2
2018-10-25,Light-Quark Resonances at COMPASS,"The main goal of the spectroscopy program at COMPASS is to explore the
light-meson spectrum in the mass range below about $2\,\text{GeV}/c^2$ using
diffractive dissociation reactions. Our flagship channel is the production of
three charged pions in the reaction: $\pi^- + p \to \pi^-\pi^-\pi^+ +
p_\text{recoil}$, for which COMPASS has acquired the so far world's largest
dataset of roughly $50\,\text{M}$ exclusive events using an $190\,\text{GeV}/c$
$\pi^-$ beam.
  In order to extract the parameters of the $\pi_J$ and $a_J$ resonances that
appear in the $\pi^-\pi^-\pi^+$ system, we performed the so far most
comprehensive resonance-model fit, using Breit-Wigner parametrizations. This
method in combination with the high statistical precision of our data allows us
to study ground and excited states. We study the $a_4(2040)$ resonance in the
$\rho(770)\pi G$ and $f_2(1270)\pi F$ decays. In addition to the ground state
resonance $a_1(1260)$, we have found evidence for the $a_1(1640)$. We also
study the spectrum of $\pi_2$ states by simultaneously describing four
$J^{PC}=2^{-+}$ waves using three $\pi_2$ resonances, the $\pi_2(1670)$, the
$\pi_2(1880)$, and the $\pi_2(2005)$.
  Using a novel analysis approach, where the resonance-model fit is performed
simultaneously in narrow bins of the squared four-momentum transfer $t'$
between the beam pion and the target proton, allows us to study the $t'$
dependence of resonant and non-resonant components included in our model. We
observe that for most of the partial waves, the non-resonant components show a
steeper $t'$ spectrum compared to the resonances and that the $t'$ spectrum of
most of the resonances becomes shallower with increasing resonance mass. We
also study the $t'$ dependence of the relative phases between resonance
components. The pattern we observe is consistent with a common production
mechanism of these states.",1810.10805v1
1993-07-20,Thouless number and spin diffusion in quantum Heisenberg ferromagnets,"Using an analogy between the conductivity tensor of electronic systems and
the spin stiffness tensor of spin systems, we introduce the concept of the
Thouless number $g_0$ and the dimensionless frequency dependent conductance $g(
\omega )$ for quantum spin models. It is shown that spin diffusion implies the
vanishing of the Drude peak of $g ( \omega )$, and that the spin diffusion
coefficient $D_s$ is proportional to $g_0$. We develop a new method based on
the Thouless number to calculate $D_s$, and present results for $D_s$ in the
nearest-neighbor quantum Heisenberg ferromagnet at infinite temperatures for
arbitrary dimension $d$ and spin $S$.",9307042v1
1993-10-28,Quantum Ferromagnetism and Phase Transitions in Double-Layer Quantum Hall Systems,"Double layer quantum Hall systems have interesting properties associated with
interlayer correlations. At $\nu =1/m$ where $m$ is an odd integer they exhibit
spontaneous symmetry breaking equivalent to that of spin $1/2$ easy-plane
ferromagnets, with the layer degree of freedom playing the role of spin. We
explore the rich variety of quantum and finite temperature phase transitions in
these systems. In particular, we show that a magnetic field oriented parallel
to the layers induces a highly collective commensurate-incommensurate phase
transition in the magnetic order.",9310071v1
1993-11-15,Quantum Heisenberg Chain with Long-Range Ferromagnetic Interactions at Low Temperature,"A modified spin-wave theory is applied to the one-dimensional quantum
Heisenberg model with long-range ferromagnetic interactions. Low-temperature
properties of this model are investigated. The susceptibility and the specific
heat are calculated; the relation between their behaviors and strength of the
long-range interactions is obtained. This model includes both the
Haldane-Shastry model and the nearest-neighbor Heisenberg model; the
corresponding results in this paper are in agreement with the solutions of both
the models. It is shown that there exists an ordering transition in the region
where the model has longer-range interactions than the HS model. The critical
temperature is estimated.",9311034v1
1994-07-07,Scaling properties of the ferromagnetic state in the Hubbard model,"A numerical scaling analysis is used to show that Nagaoka's ferromagnetic
state in two-dimensional Hubbard model with one hole is supersede by an
antiferromagnetic (AF) state with a discontinuous jump in the total spin due to
the AF coupling as the Hubbard $U$ is made finite. The same applies to the
two-hole system, which has a spiral spin structure. We can show, via the
scaling, that the crossover to an AF state is a precursor of a pathological
coalescence of states having the minimum spin and Nagaoka's state at $U=\infty$
in the thermodynamic limit.",9407036v1
1994-08-19,Quantum description of spherical spins,"The spherical model for spins describes ferromagnetic phase transitions well,
but it fails at low temperatures. A quantum version of the spherical model is
proposed. It does not induce qualitative changes near the phase transition.
However, it produces a physical low temperature behavior. The entropy is
non-negative. Model parameters can be adapted to the description of real
quantum spins. Several applications are discussed. Zero-temperature quantum
phase transitions are analyzed for a ferromagnet and a spin glass in a
transversal field. Their crossover exponents are presented.",9408055v3
1994-10-19,Random Frustration in two-dimensional spin-1/2 Heisenberg antiferromagnet,"The square lattice spin-1/2 antiferromagnet containing a dilute
concentration, $\delta$, of randomly placed ferromagnetic nearest-neighbor
bonds is studied at low-temperature via non-linear $\sigma$-model techniques
and by exact diagonalization. We generally find that long-range N\' eel order
is destroyed above a critical strength in the defective ferromagnetic exchange
coupling-constant given by $|K_c|/J\sim \delta^{-1/2}$. We also observe large
statistical fluctuations both in the spin-stiffness and in the
antiferromagnetic structure-factor near this critical point, suggesting the
onset of a spin-glass phase.",9410075v2
1994-12-14,Robustness of a local Fermi Liquid against Ferromagnetism and Phase Separation,"We study the properties of Fermi Liquids with the microscopic constraint of a
local self-energy. In this case the forward scattering sum-rule imposes strong
limitations on the Fermi-Liquid parameters, which rule out any Pomeranchek
instabilities. For both attractive and repulsive interactions, ferromagnetism
and phase separation are suppressed. Superconductivity is possible in an s-wave
channel only. We also study the approach to the metal-insulator transition, and
find a Wilson ratio approaching 2. This ratio and other properties of
Sr_{1-x}La_xTiO_3 are all consistent with the local Fermi Liquid scenario.",9412068v1
1995-01-06,"Universal Finite-Size Scaling Function of the Ferromagnetic Heisenberg Chain in a Magnetic Field,","The finite-size scaling function of the magnetization of the ferromagnetic
Heisenberg chain is argued to be universal with respect to the magnitude of the
spin. The finite-size scaling function is given explicitly by an analytical
calculation in the classical limit $S=\infty.$ The universality is checked for
$S=1/2$ and $1$ by means of numerical calculations. Critical exponents are
obtained as well. It is concluded that this universal scaling function
originates in the universal behavior of the correlation function.",9501013v1
1995-01-20,Bounds on the mass gap of the ferromagnetic XXZ chain,"We prove rigorous lower and upper bounds for the mass gap of the
ferromagnetic spin 1/2 XXZ chain. The two bounds coincide asymptotically in the
Ising limit $\Delta\to\infty$. Near the isotropic point, $\Delta=1$, the
estimates are good enough to determine the critical behaviour of the mass gap
unambiguously. The derivation does not rely on exact solutions.",9501098v1
1995-02-13,Griffiths singularity in the two dimensional random bond disordered Ising ferromagnet,"For the two dimensional random bond disordered Ising ferromagnet, we measured
bulk data of the magnetic susceptibility ($\chi$) and correlation length
($\xi$) up to $\xi \simeq 536$, with the use of a novel finite size scaling
Monte Carlo technique. Our data are exclusively consistent with normal
power-law critical behaviors with only one singular point at criticality,
disproving the existence of Griffiths singularity even in an extremely deep
scaling region. The critical exponents of $\chi$ and $\xi$ increase
continuously with the strength of disorder.",9502053v2
1995-06-20,Universal Finite-Size Scaling Function of the Ferromagnetic Heisenberg Chain in a Magnetic Field. II,"The finite-size scaling function of the nonlinear susceptibility of the
ferromagnetic Heisenberg chain is given explicitly. It is conjectured that the
scaling function is universal for any values of $S$. The conjecture is based on
the exact solution of the nonlinear susceptibility for $S=\infty$, and
numerical calculations for $S=1/2$ and $S=1$.",9506087v1
1995-10-13,Density Matrix Renormalization Group Study of the Spin 1/2 Heisenberg Ladder with Antiferromagnetic Legs and Ferromagnetic Rungs,"The ground state and low lying excitation of the spin 1/2 Heisenberg ladder
with antiferromagnetic leg ($J$) and ferromagnetic rung ($-\lambda J, \lambda
>0$) interaction is studied by means of the density matrix renormalization
group method. It is found that the state remains in the Haldane phase even for
small $\lambda \sim 0.02$ suggesting the continuous transition to the gapless
phase at $\lambda = 0$. The critical behavior for small $\lambda$ is studied by
the finite size scaling analysis. The result is consistent with the recent
field theoretical prediction.",9510071v1
1995-10-18,Zero field muon spin lattice relaxation rate in a Heisenberg ferromagnet at low temperature,"We provide a theoretical framework to compute the zero field muon spin
relaxation rate of a Heisenberg ferromagnet at low temperature. We use the
linear spin wave approximation. The rate, which is a measure of the spin
lattice relaxation induced by the magnetic fluctuations along the easy axis,
allows one to estimate the magnon stiffness constant.",9510096v1
1995-12-02,The Magnus Force on Skyrmions in Ferromagnets and the Quantum Hall Effect,"The topological solitons, or ``skyrmions'', in a planar ferromagnet
experience a Magnus force proportional to the product of their velocity and the
surrounding magnetization. It has been suggested that the charged
quasiparticles near filling factor $\nu=1$ in the $GaAs$ quantum Hall effect
are skyrmions. If so we might expect this spin-induced Magnus force to act on
the quasiparticles in addition to the Lorentz force they experience because of
their charge. We show that this is not the case, and that the Magnus and
Lorentz forces are merely different descriptions of the same physical effect.",9512010v1
1995-12-08,Ferromagnetism in the Hubbard model on the square lattice: Improved instability criterion for the Nagaoka state,"The instability of the fully polarized ferromagnetic state (Nagaoka state)
with respect to single spin flips is re-examined for the Hubbard model on the
square lattice with a large family of variational wave functions which include
correlation effects of the majority spins in the vicinity of the flipped spin.
We find a critical hole density of $\delta_{cr} = 0.251$ for $U = \infty$ and a
critical coupling of $U_{cr} = 77.7 t$. Both values improve previous
variational results considerably.",9512060v1
1995-12-19,Finite-Size Scaling and Universality in the Spin 1 Quantum XY Chain,"The spin-1 XY chain in a transverse field is studied using finite-size
scaling. The ground state phase diagram displays a paramagnetic, an ordered
ferromagnetic and an ordered oscillatory phase. The paramagnetic-ferromagnetic
transition line belongs to the universality class of the 2D Ising model. Along
this line, universality is confirmed for the finite-size scaling functions of
several correlation lengths and for the conformal operator content.",9512137v1
1996-01-03,Quantum critical behavior of disordered itinerant ferromagnets,"The quantum ferromagnetic transition at zero temperature in disordered
itinerant electron systems is considered. Nonmagnetic quenched disorder leads
to diffusive electron dynamics that induces an effective long-range interaction
between the spin or order parameter fluctuations of the form r^{2-2d}, with d
the spatial dimension. This leads to unusual scaling behavior at the quantum
critical point, which is determined exactly. In three-dimensional systems the
quantum critical exponents are substantially different from their finite
temperature counterparts, a difference that should be easily observable.
Experiments to check these predictions are proposed.",9601008v2
1996-01-22,Finite size corrections on the boundary between the spin-glass and the ferromagnetic phases of Derrida's model,"The boundary line between the ferromagnetic and the spin-glass phases was
investigated. Finite size corrections to the free energy and magnetization were
calculated. The situation coincides with the case in the information theory,
when the transmission rate equals to the capacity of channel.",9601092v3
1996-02-01,Magnetic coupling in mesoscopic metal/ferromagnet layered systems,"We consider a mesoscopic mechanism of the exchange interaction in a system of
alternating ferromagnetic/nonmagnetic metallic layers. In the case of small
mesoscopic samples the sign and the amplitude of the exchange energy turn out
to be random sample specific quantities. They can be changed by applying an
external magnetic field, by attaching to the system superconducting electrodes
with different phases of the superconducting order parameter and by changing
the chemical potential of electrons in the matal with the help of a gate. In
the case of square or cubic geometries of the nonmagnetic layer at low
temperature the variance of the exchange energy turns out to be sample size
independent.",9602005v1
1996-02-21,Universal low-temperature properties of quantum and classical ferromagnetic chains,"We identify the critical theory controlling the universal, low temperature,
macroscopic properties of both quantum and classical ferromagnetic chains. The
theory is the quantum mechanics of a single rotor. The mapping leads to an
efficient method for computing scaling functions to high accuracy.",9602114v2
1996-03-26,Spin Diffusion in 2D XY Ferromagnet with Dipolar Interaction,"In the ordered phase of 2D XY ferromagnet the dipolar interaction between
spins induces a strong, relevant interaction between spin-waves. We study
quasi-excitations of the interacting spin-wave 'liquid' in the long wavelength
limit. We employ the Janssen-De-Dominicis method for classical Langevin
equation to find the transformation of the spin-wave excitation into a new
soft-mode excitation in the intermediate range of wavelengths; and into an
anomalous anisotropic diffusion mode excitation at long wavelengths. The
dissipation of a spin-wave at short wavelengths is found to be highly
anisotropic.",9603160v1
1996-03-26,Low density ferromagnetism in the Hubbard model,"A single-band Hubbard model with nearest and next-nearest neighbour hopping
is studied for $d=1$, 2, 3, using both analytical and numerical techniques. In
one dimension, saturated ferromagnetism is found above a critical value of $U$
for a band structure with two minima and for small and intermediate densities.
This is an extension of a scenario recently proposed by M\""uller--Hartmann. For
three dimensions and non-pathological band structures, it is proven that such a
scenario does not work.",9603163v1
1996-03-30,"Spectral Flow and Vortex Dynamics in Superfluids, Superconductors and Ferromagnets","We discuss the nondissipative Magnus-type force acting on linear defects in
Fermi systems, such as Abrikosov vortices in superconductors, singular and
continuous vortices in superfluid phases of $^3$He, magnetic vortices and
skyrmions in ferromagnets. Spectral flow of fermion zero modes in the vortex
core gives an essential contribution to the nondissipative force, which is
confirmed in Manchester experiments on rotating $^3$He-B. The spectral flow
effect is closely related to the angular momentum paradox.",9603197v1
1996-05-08,Many skyrmion wave functions and skyrmion statistics in quantum Hall ferromagnets,"We determine the charge and statistical angle of skyrmions in quantum Hall
ferromagnets by performing Berry phase calculations based on the microscopic
variational wave functions for many-skyrmion states. We find, in contradiction
to a recent claim by Dziarmaga, that both the charge and the statistical angle
of a skyrmion are independent of its spin (size), and are identical to those of
Laughlin quasiparticles at the same filling factor. We discuss some subtleties
in the use of these variational wave functions.",9605054v1
1996-06-20,Low Temperature Magnetic Properties of the Double Exchange Model,"We study the {\it ferromagnetic} (FM) Kondo lattice model in the strong
coupling limit (double exchange (DE) model). The DE mechanism proposed by Zener
to explain ferromagnetism has unexpected properties when there is more than one
itinerant electron. We find that, in general, the many-body ground state of the
DE model is {\it not} globally FM ordered (except for special filled-shell
cases). Also, the low energy excitations of this model are distinct from spin
wave excitations in usual Heisenberg ferromagnets, which will result in unusual
dynamic magnetic properties.",9606148v1
1996-07-22,The annealed positions of ferromagnetic bonds doped into a 2D antiferromagnet,"We determine where a given concentration of ferromagnetic (FM) bonds doped
into a square lattice antiferromagnet must go to minimize the system's total
magnetic energy. We find (i) an infinite degeneracy of ground--state
arrangements of FM bonds that correspond to completely unfrustrated
configurations for classical spins, and (ii) this degeneracy is lifted when
quantum fluctuations are included, and phase separated ground states, such as
periodic arrays of stripes of FM bonds, are found. A discussion of the
application of these ideas to doped cuprate high $T_c$ superconductors with
annealed disorder is presented.",9607154v1
1996-07-30,An extension of the characteristic angle method to the easy-plane spin-3/2 ferromagnet,"The Characteristic Angle (CA) method [Lei Zhou and Ruibao Tao, J. Phys. A,
{\bf 27} 5599] developed previously for the easy-plane spin-1 magnetic systems
has been successfully extended to the spin-3/2 case. A compact form of the CA
spin-3/2 operator transformation is given, then the ground state energy, the
magnon dispersion relation and the spontaneous magnetization are discussed for
an easy-plane spin-3/2 ferromagnet by using the CA method. Comparisons with the
old theoretical methods are made in the end.",9607218v1
1996-09-05,Magnetization switching in nanoscale ferromagnetic grains: simulations with heterogeneous nucleation,"We present results obtained with various types of heterogeneous nucleation in
a kinetic Ising model of magnetization switching in single-domain ferromagnetic
nanoparticles. We investigate the effect of the presence of the system boundary
and make comparison with simulations on periodic lattices. We also study
systems with bulk disorder and compare how two different types of disorder
influence the switching behavior.",9609056v1
1996-09-26,Ferromagnetism in the two dimensional t-t' Hubbard model at the Van Hove density,"Using an improved version of the projection quantum Monte Carlo technique, we
study the square-lattice Hubbard model with nearest-neighbor hopping t and
next-nearest-neighbor hopping t', by simulation of lattices with up to 20 X 20
sites. For a given R=2t'/t, we consider that filling which leads to a singular
density of states of the noninteracting problem. For repulsive interactions, we
find an itinerant ferromagnet (antiferromagnet) for R=0.94 (R=0.2). This is
consistent with the prediction of the T-matrix approximation, which sums the
most singular set of diagrams.",9609253v1
1996-10-25,Protracted Screening in the Periodic Anderson Model,"The asymmetric infinite-dimensional periodic Anderson model is examined with
a quantum Monte Carlo simulation. For small conduction band filling, we find a
severe reduction in the Kondo scale, compared to the impurity value, as well as
protracted spin screening consistent with some recent controversial
photoemission experiments. The Kondo screening drives a ferromagnetic
transition when the conduction band is quarter-filled and both the RKKY and
superexchange favor antiferromagnetism. We also find RKKY-driven ferromagnetic
and antiferromagnetic transitions.",9610188v1
1996-11-05,Chiral Metal as a Heisenberg Ferromagnet,"The two dimensional surface of an integer quantum hall multilayer is mapped
onto a Heisenberg spin-chain with ferromagnetic coupling. Using this mapping it
is shown non-perturbatively that the surface states constitute a very
anisotropic metal in the infinite size limit. For multilayers of finite size,
two diffusive mesoscopic regimes are identified and the conductance
fluctuations are calculated perturbatively for both. The Heisenberg spin-chain
representation is used to study the directed wave problem and the exact result
is obtained that the mean-square deflection of a directed wave grows as the
square root of the propagation of the distance.",9611035v1
1996-12-07,Resistivity due to a Domain Wall in Ferromagnetic Metal,"The resistivity due to a domain wall in ferromagnetic metallic wire is
calculated based on the linear response theory. The interaction between
conduction electrons and the wall is expressed in terms of a classical gauge
field which is introduced by the local gauge transformation in the electron
spin space. It is shown that the wall contributes to the decoherence of
electrons and that this quantum correction can dominate over the Boltzmann
resisitivity, leading to a decrease of resisitivity by nucleation of a wall.
The conductance fluctuation due to the motion of the wall is also investigated.
The results are compared with recent experiments.",9612067v1
1996-12-18,Interplay of Mott Transition and Ferromagnetism in the Orbitally Degenerate Hubbard Model,"A slave boson representation for the degenerate Hubbard model is introduced.
The location of the metal to insulator transition that occurs at commensurate
densities is shown to depend weakly on the band degeneracy M. The relative
weights of the Hubbard sub-bands depend strongly on M, as well as the magnetic
properties. It is also shown that a sizable Hund's rule coupling is required in
order to have a ferromagnetic instability appearing. The metal to insulator
transition driven by an increase in temperature is a strong function of it.",9612172v1
1997-02-12,Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors,"The flux-line lattice in the compound $ErNi_2B_2C$, which has a tendency to
ferromagnetic order in the a-b plane is studied with external magnetic field
direction close to the c-axis. We show the existence of an instability where
the direction of flux-lines spontaneously tilts away from that of the applied
field near the onset of ferromagnetic order. The enhanced fluctuations in the
flux lattice and the square flux lattice recently observed are explained and
further experiments suggested.",9702104v1
1997-02-25,Low-Temperature Scaling Regime of Random Ferromagnetic-Antiferromagnetic Spin Chains,"Using the Continuous Time Quantum Monte Carlo Loop algorithm, we calculate
the temperature dependence of the uniform susceptibility, and the specific heat
of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings,
down to very low temperatures. Our data show a consistent scaling behavior in
both quantities and support strongly the conjecture drawn from the
approximative real-space renormalization group treatment. A statistical
analysis scheme is developed which will be useful for the search scaling
behavior in numerical and experimental data of random spin chains.",9702215v1
1997-03-04,Magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9},"Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions,
we study the effect of iron disproportionation on the magnetic ordering, and
describe the first-order magnetic transition occurring in the perovskite
Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of
the exchange integrals for the antiferromagntic and ferromagnetic interactions,
in agreement with previous works on kindered compounds. Spin-wave theory yields
a magnon spectrum with a gapless antiferromagnetic mode together with two
gapped ferromagnetic ones.",9703044v1
1997-03-06,Ferromagnetic spin fluctuation induced superconductivity in Sr_2RuO_4,"We propose a quantitative model for triplet superconductivity in Sr_2RuO_4
based on first principles calculations for the electronic structure and
magnetic susceptibility. The superconductivity is due to ferromagnetic spin
fluctuations, that are strong at small wave vectors. The calculated effective
mass renormalization, renormalized susceptibility, and superconducting critical
temperature are all in good agreement with experiment. The most stable
superconducting solution has order parameters of comparable magnitude on all
three sheets of the Fermi surface. We also propose an explanation of the
discrepancy between the Fermi surface topology observed in the photoemission
and in de Haas-van Alphen experiments.",9703068v2
1997-03-07,Quantum Nucleation in a Ferromagnetic Film Placed in a Magnetic Field at an Arbitrary Angle,"We study the quantum nucleation in a thin ferromagnetic film placed in a
magnetic field at an arbitrary angle. The dependence of the quantum nucleation
and the temperature of the crossover from thermal to quantum regime on the
direction and the strength of the applied field are presented. It is found that
the maximal value of the rate and that of the crossover temperature are
obtained at a some angle with the magnetic field, not in the direction of the
applied field opposite to the initial easy axis.",9703069v1
1997-03-14,High Temperature Thermodynamics of the Ferromagnetic Kondo-Lattice Model,"We present a high temperature series expansion for the ferromagnetic Kondo
lattice model in the large coupling limit, which is used to model CMR
perovskites. Our results show the expected cross-over to Curie-Wei{\ss}
behavior at a temperature related to the bandwidth. Estimates for the magnetic
transition temperatures are in the experimentally observed range. The
compressibility shows that the high temperature charge excitations can be
modeled by spinless fermions. The CMR effect itself, however, warrants the
inclusion of dynamic effects and cannot be explained by a static calculation.",9703146v1
1997-03-24,A theoretical investigation of the specific heat of superlattices in a magnetic field,"We analyze the specific heat variations as a function of an external magnetic
field of a simple model of superlattice that includes (i) in--plane
ferromagnetic exchange, (ii) interplane ferromagnetic exchange, (iii) dipolar
interactions, (iv) magnetocristalline anisotropy. The calculations are carried
out at the spin wave level. The interplay between the existence of a canting
transition and the anisotropy of the structure generates non trivial behavior
for the spin wave contribution to the low temperature specific heat as a
function of an external magnetic field when dipolar interactions and
magnetocristalline anisotropy are taken into account.",9703202v1
1997-05-16,"Superconducting, ferromagnetic and antiferromagnetic phases in the t-t' Hubbard model","We apply a renormalization group approach to the determination of the phase
diagram of the t-t' Hubbard model at the Van Hove filling, as function of t'/t,
for small values of U/t. The model presents ferromagnetic, antiferromagnetic
and d-wave superconducting phases. Antiferromagnetism and d-wave
superconductivity arise from the same interactions, and compete in the same
region of parameter space.",9705165v1
1997-05-19,Nucleation Theory of Magnetization Switching in Nanoscale Ferromagnets,"A nucleation picture of magnetization switching in single-domain
ferromagnetic nanoparticles with high local anisotropy is discussed. Relevant
aspects of nucleation theory are presented, stressing the effects of the
particle size on the switching dynamics. The theory is illustrated by Monte
Carlo simulations and compared with experiments on single particles.",9705189v1
1997-06-02,Phase Separation in Electronic Models for Manganites,"The Kondo lattice Hamiltonian with ferromagnetic Hund's coupling as a model
for manganites is investigated. The classical limit for the spin of the
(localized) $t_{2g}$ electrons is analyzed on lattices of dimension 1,2,3 and
$\infty$ using several numerical methods. The phase diagram at low temperature
is presented. A regime is identified where phase separation occurs between hole
undoped antiferromagnetic and hole-rich ferromagnetic regions. Experimental
consequences of this novel regime are discussed. Regions of incommensurate spin
correlations have also been found. Estimations of the critical temperature in
3D are compatible with experiments.",9706014v2
1997-07-13,Stochastic Model and Equivalent Ferromagnetic Spin Chain with Alternation,"We investigate a non-equilibrium reaction-diffusion model and equivalent
ferromagnetic spin 1/2 XY spin chain with alternating coupling constant. The
exact energy spectrum and the n-point hole correlations are considered with the
help of the Jordan-Wigner fermionization and the inter-particle distribution
function method. Although the Hamiltonian has no explicit translational
symmetry, the translational invariance is recovered after long time due to the
diffusion. We see the scaling relations for the concentration and the two-point
function in finite size analysis.",9707137v1
1997-08-01,Double exchange magnets: Spin-dynamics in the paramagnetic phase,"The electronic structure of perovskite manganese oxides is investigated in
terms of a Kondo lattice model with ferromagnetic Hund coupling and
antiferromagnetic exchange between $t_{2g}$-spins using a finite temperature
diagonalization technique. Results for the dynamic structure factor are
consistent with recent neutron scattering experiments for the bilayer manganite
La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ . The susceptibility shows Curie-Weiss
behaviour and is used to derive a phase diagram. In the paramagnetic phase
carriers are characterized as ferromagnetic polarons in an antiferromagnetic
spin liquid.",9708007v1
1997-08-11,Stationary Properties of a Randomly Driven Ising Ferromagnet,"We consider the behavior of an Ising ferromagnet obeying the Glauber dynamics
under the influence of a fast switching, random external field. Analytic
results for the stationary state are presented in mean-field approximation,
exhibiting a novel type of first order phase transition related to dynamic
freezing. Monte Carlo simulations performed on a quadratic lattice indicate
that many features of the mean field theory may survive the presence of
fluctuations.",9708073v1
1997-10-21,Two-Dimensional Quantum Ferromagnets,"We present 1/N Schwinger boson and quantum Monte Carlo calculations of the
magnetization and NMR relaxation rate for the two-dimensional ferromagnetic
Heisenberg model representing a quantum Hall system at filling factor nu=1.
Comparing the analytic and numerical calculations, we find that the SU(N)
version of Schwinger boson theory gives accurate results for the magnetization
at low temperatures, whereas the O(N) model works well at higher temperatures.",9710220v2
1997-10-27,Thermodynamic Properties of Heisenberg Ferrimagnetic Spin Chains: Ferromagnetic-Antiferromagnetic Crossover,"We study thermodynamic properties of the one-dimensional Heisenberg
ferrimagnet with antiferromagnetically exchange-coupled two kinds of spins 1
and 1/2. The specific heat and the magnetic susceptibility are calculated
employing a modified spin-wave theory as well as a quantum Monte Carlo method.
The specific heat is in proportion to $T^{1/2}$ at low enough temperatures but
shows a Schottky-like peak at mid temperatures. The susceptibility diverges as
$T^{-2}$. We reveal that at low temperatures the model is regarded as a
ferromagnet, while at mid temperatures it behaves like a gapped
antiferromagnet.",9710291v2
1997-11-17,Suppressed Coherence due to Orbital Correlations in the Ferromagnetically Ordered Metallic Phase of Mn Compounds,"Small Drude weight $D$ together with small specific heat coefficient $\gamma$
observed in the ferromagnetic phase of R$_{1-x}$A$_x$MnO$_3$ (R=La, Pr, Nd, Sm;
A=Ca, Sr, Ba) are analyzed in terms of a proximity effect of the Mott
insulator. The scaling theory for the metal-insulator transition with the
critical enhancement of orbital correlations toward the staggered ordering of
two $e_g$ orbitals such as $3x^2-r^2$ and $3y^2-r^2$ symmetries may lead to the
critical exponents of $D \propto \delta^{u}$ and $\gamma \propto \delta^v$ with
$u=3/2$ and $v=0$. The result agrees with the experimental indications.",9711153v1
1997-12-25,Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain,"The low temperature magnetization process of the
ferromagnetic-antiferromagnetic Heisenberg chain is studied using the
interacting boson approximation. In the low field regime and near the
saturation field, the spin wave excitations are approximated by the $\delta$
function boson gas for which the Bethe ansatz solution is available. The finite
temperature properties are calculated by solving the integral equation
numerically. The comparison is made with Monte Carlo calculation and the limit
of the applicability of the present approximation is discussed.",9712289v1
1998-01-05,Shadow Bands and Tunneling Magnetoresistance in Itinerant Electron Ferromagnets,"In itinerant electron ferromagnets spectral weight is transferred at finite
temperatures from quasiparticle peaks located at majority and minority-spin
band energies to shadow-band peaks. For a given Bloch wavevector and band
index, the majority-spin shadow-band peak is located near the minority-spin
quasiparticle energy and the minority-spin shadow-band peak is located near the
majority-spin quasiparticle energy. This property can explain much of the
temperature dependence seen in the magnetoresistance of magnetic tunnel
junctions.",9801023v1
1998-01-13,Domain walls and the conductivity of mesoscopic ferromagnets,"Quantum interference phenomena in the conductivity of mesoscopic ferromagnets
are considered, particularly with regard to the effects of geometric phases
acquired by electrons propagating through regions of spatially varying
magnetization (due, e.g., to magnetic domain walls). Weak localization and
electron-electron interaction quantum corrections to the conductivity and
universal conductance fluctuations are discussed. Experiments are proposed for
multiply-connected geometries that should reveal conductance oscillations with
variations of the profile of the magnetization.",9801113v1
1998-01-20,1/N expansion for two-dimensional quantum ferromagnets,"The magnetization of a two-dimensional ferromagnetic Heisenberg model, which
represents a quantum Hall system at filling factor nu=1, is calculated
employing a large N Schwinger boson approach. Corrections of order 1/N to the
mean field (N=infinity) results for both the SU(N) and the O(N) generalization
of the bosonized model are presented. The calculations are discussed in detail
and the results are compared with quantum Monte Carlo simulations as well as
with recent experiments. The SU(N) model describes both Monte Carlo and
experimental data well at low temperatures, whereas the O(N) model is much
better at moderate and high temperatures.",9801203v1
1998-01-30,Thermally assisted macroscopic quantum tunneling of a ferromagnetic particle in a magnetic field at an arbitrary angle,"At finite temperature we study the quantum tunneling of magnetization for a
small ferromagnetic particle with the biaxial symmetry placed in a magnetic
field at an arbitrary angle. We present numerical WKB exponent below the
crossover temperature in which the quantum tunneling is affected by the thermal
activation, and the approximate form of the WKB exponent around the crossover
region. The effect of quantum fluctuations on the thermal activation rate
beyond the crossover regime are discussed.",9801319v1
1998-02-13,Antiferromagnetic interlayer exchange coupling across an amorphous metallic spacer layer,"By means of magneto-optical Kerr effect we observe for the first time
antiferromagnetic coupling between ferromagnetic layers across an amorphous
metallic spacer layer. Biquadratic coupling occurs at the transition from a
ferromagnetically to an antiferromagnetically coupled region. Scanning
tunneling microscopy images of all involved layers are used to extract
thickness fluctuations and to verify the amorphous state of the spacer. The
observed antiferromagnetic coupling behavior is explained by RKKY interaction
taking into account the amorphous structure of the spacer material.",9802148v1
1998-03-12,Improved Composite-Boson Theory of Quantum Hall Ferromagnets and Skyrmions without Sigma Models,"We propose an improved composite-boson theory of quantum Hall ferromagnets,
where the field operator describes solely the physical degrees of freedom
representing the deviation from the ground state. In this scheme skyrmions
appear merely as generic excitations confined in the lowest Landau level. We
evaluate the excitation energy of one skyrmion. Our theoretical estimation
accounts for the activation-energy data due to Schmeller et al. remarkably
well.",9803146v2
1998-04-03,Spherical Model for Anisotropic Ferromagnetic Films,"The corrections to the Curie temperature T_c of a ferromagnetic film
consisting of N layers are calculated for N \gg 1 for the model of D-component
classical spin vectors in the limit D \to \infty, which is exactly soluble and
close to the spherical model. The present approach accounts, however, for the
magnetic anisotropy playing the crucial role in the crossover from 3 to 2
dimensions in magnetic films. In the spatially inhomogeneous case with free
boundary conditions the D=\infty model is nonequivalent to the standard
spherical one and always leads to the diminishing of T_c(N) relative to the
bulk.",9804043v2
1998-04-06,Folding Transitions of the Square-Diagonal Lattice,"We address the problem of ""phantom"" folding of the tethered membrane modelled
by the two-dimensional square lattice, with bonds on the edges and diagonals of
each face. Introducing bending rigidities $K_1$ and $K_2$ for respectively long
and short bonds, we derive the complete phase diagram of the model, using
transfer matrix calculations. The latter displays two transition curves, one
corresponding to a first order (ferromagnetic) folding transition, and the
other to a continuous (anti-ferromagnetic) unfolding transition.",9804073v1
1998-04-21,"The randomly driven Ising ferromagnet, Part I: General formalism and mean field theory","We consider the behavior of an Ising ferromagnet obeying the Glauber dynamics
under the influence of a fast switching, random external field. After
introducing a general formalism for describing such systems, we consider here
the mean-field theory. A novel type of first order phase transition related to
spontaneous symmetry breaking and dynamic freezing is found. The
non-equilibrium stationary state has a complex structure, which changes as a
function of parameters from a singular-continuous distribution with Euclidean
or fractal support to an absolutely continuous one.",9804230v1
1998-04-21,"The randomly driven Ising ferromagnet, Part II: One and two dimensions","We consider the behavior of an Ising ferromagnet obeying the Glauber dynamics
under the influence of a fast switching, random external field. In Part I, we
introduced a general formalism for describing such systems and presented the
mean field theory. In this article we derive results for the one dimensional
case, which can be only partially solved. Monte Carlo simulations performed on
a square lattice indicate that the main features of the mean field theory
survive the presence of strong fluctuations.",9804233v1
1998-04-28,Interlayer Magnetic Coupling and the Quantum Hall Effect in Multilayer Electron Systems,"We study the effect that the electron-electron interaction has on the
properties of a multilayer electron system. We consider the case corresponding
to filling factor unity in each layer. We find that as a function of the sample
parameters the system has ferromagnetic, canted antiferromagnetic or
paramagnetic interlayer spin correlations. These three ground states are QHE
phases, because of the existence of a finite activation energy. In the
ferromagnetic phase the gap is due to the intrawell exchange energy, whereas in
the paramagnetic phase the gap appears due to the spatial modulation of the
interwell coherence.",9804298v1
1998-04-30,Manganites at Low Temperatures and Light Doping:Band Approach and Percolation,"A tight-band model is employed for the $e_{2g}$-orbitals in manganites. It is
shown that a large intraatomic Hund's coupling, $J_H$ and the resulting
double-exchange mechanism lead to antiferromagnetic ordering along one of the
cubic axis stabilized by the cooperative JT effect which further decreases the
band energy of electrons. As a result, LaMnO$_3$ is a band insulator built of
2D ferromagnetic layers. The critical concentration $x_c\simeq 0.16$, for onset
of ferromagnetic and metallic behavior at low temperatures in
La$_{1-x}$Sr$_x$MnO$_3$ and the phase transition are treated in the percolation
approach.",9804328v1
1998-05-05,Integral Relaxation Time of Single-Domain Ferromagnetic Particles,"The integral relaxation time \tau_{int} of thermoactivating noninteracting
single-domain ferromagnetic particles is calculated analytically in the
geometry with a magnetic field H applied parallel to the easy axis. It is shown
that the drastic deviation of \tau_{int}^{-1} from the lowest eigenvalue of the
Fokker-Planck equation \Lambda_1 at low temperatures, starting from some
critical value of H, is the consequence of the depletion of the upper potential
well. In these conditions the integral relaxation time consists of two
competing contributions corresponding to the overbarrier and intrawell
relaxation processes.",9805056v2
1998-05-12,The Two Dimensional XY Spin Glass with Ferromagnetic Next-Nearest-Neighbour Interactions,"The random-bond XY spin glass with ferromagnetic next-nearest-neighbour
interactions is studied on a square lattice by Monte Carlo simulations. We find
strong evidence for a finite-temperature spin glass transition at $T_c\approx
1.1$. We also give estimates for the spin glass critical exponents for
different values of the strength of the nearest-neighbour interaction. Our
results are consistent with universal behaviour.",9805141v1
1998-05-24,Thermally assisted domain walls quantum tunneling at the high temperature range,"A theoretical and numerical investigations of the quantum tunneling of the
domain walls in ferromagnets and weak ferromagnets was performed taking into
account the interaction between walls and thermal excitations of a crystal. The
numerical method for calculations of the probability of a thermally stimulated
quantum depinning as the function of temperature at the wide temperature range
has been evolved.",9805304v2
1998-06-06,Magnons and skyrmions in fractional Hall ferromagnets,"Recent experiments have established a qualitative difference between the
magnetization temperature-dependences $M(T)$ of quantum Hall ferromagnets at
integer and fractional filling factors. We explain this difference in terms of
the relative energies of collective magnon and particle-hole excitations in the
two cases. Analytic calculations for hard-core model systems are used to
demonstrate that, in the fractional case, interactions suppress the
magnetization at finite temperatures and that particle-hole excitations rather
than long-wavelength magnons control $M(T)$ at low $T$.",9806087v1
1998-06-28,Combination of Ferromagnetic and Antiferromagnetic Features in Heisenberg Ferrimagnets,"We investigate the thermodynamic properties of Heisenberg ferrimagnetic
mixed-spin chains both numerically and analytically with particular emphasis on
the combination of ferromagnetic and antiferromagnetic features. Employing a
new density-matrix renormalization-group technique as well as a quantum Monte
Carlo method, we reveal the overall thermal behavior: At very low temperatures,
the specific heat and the magnetic susceptibility times temperature behave like
$T^{1/2}$ and $T^{-1}$, respectively, whereas at intermediate temperatures,
they exhibit a Schottky-like peak and a minimum, respectively. Developing the
modified spin-wave theory, we complement the numerical findings and give a
precise estimate of the low-temperature behavior.",9806344v1
1998-07-09,Magnitoelastic interaction and long-range magnetic ordering in two-dimesional ferromagnetics,"The influence of magnitoelastic (ME) interaction on the stabilization of
long-range magnetic order (LMO) in the two-dimensional easy-plane ferromagnetic
is investigated in this work. The account of ME exchange results in the root
dispersion law of magnons and appearance of ME gap in the spectra of elementary
excitations. Such a behavior of the spectra testifies to the stabilization of
LMO and finite Curie's temperature.",9807129v1
1998-07-14,Spin-spin interaction and magnetic state of 2-D Wigner crystal,"It is demonstrated that there is anti-ferromagnetic spin-spin interaction
between nearest electrons in the 2D Wigner crystal. This is also valid for the
Wigner liquid - the state with destroyed long-range order but preserved
short-range one. We calculate the value of the anti-ferromagnetic interaction
(both analytically and numerically) and discuss a possible magnetic state of
the Wigner crystal. This state can be strongly influenced by the spin-Peierls
mechanism.",9807195v1
1998-08-03,Thermodynamics of Random Ferromagnetic Antiferromagnetic Spin-1/2 Chains,"Using the quantum Monte Carlo Loop algorithm, we calculate the temperature
dependence of the uniform susceptibility, the specific heat, the correlation
length, the generalized staggered susceptibility and magnetization of a
spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down
to very low temperatures. Our data show a consistent scaling behavior in all
the quantities and support strongly the conjecture drawn from the approximate
real-space renormalization group treatment.A statistical analysis scheme is
developed which will be useful for the search of scaling behavior in numerical
and experimental data of random spin chains.",9808027v1
1998-08-05,Magnetization bound for classical spin models on graphs,"In this paper we prove the existence of phase transitions at finite
temperature for O(n) classical ferromagnetic spin models on infrared finite
graphs. Infrared finite graphs are infinite graphs with $\lim {m\to 0^+} {\bar
Tr (L+m)^{-1} < \infty$, where $L$ is the Laplacian operator of the graph. The
ferromagnetic couplings are only requested to be bounded by two positive
constants. The proof, inspired by the classical result of Fr\""ohlich, Simon and
Spencer on lattices, is given through a rigorous bound on the average
magnetization. The result holds for $n\ge 1$ and it includes as a particular
case the Ising model.",9808046v1
1998-08-25,Spin polarized tunneling in ferromagnet/unconventional superconductor junctions,"We study tunneling in ferromagnet/unconventional superconductor (F/S)
junctions. We include the effects of spin polarization, interfacial resistance,
and Fermi wavevector mismatch (FWM) between the F and S regions. Andreev
reflection (AR) at the F/S interface, governing tunneling at low bias voltage,
is strongly modified by these parameters. The conductance exhibits a very wide
variety of features as a function of applied voltage.",9808285v2
1998-08-26,Orbital Ordering Induced Antiferromagnetic Spin Fluctuations in the Ferromagnetic State of 50 % Hole-doped Manganites: Pr{1/2}Sr{1/2}MnO3 and Nd{1/2}Sr{1/2}MnO3,"We report inelastic neutron scattering results on the spin dynamics in the 50
% hole-doped manganites, Pr{1/2}Sr{1/2}MnO3 and Nd{1/2}Sr{1/2}MnO3. In the
paramagnetic phase, these systems exhibit a ridge-type diffuse scattering,
indicating a two-dimensional ferromagnetic (FM) correlation. With decreasing
temperature, the systems enter the FM state, but simultaneously they develop
A-type antiferromagnetic spin fluctuations. The spin wave dispersion in the FM
state is strongly anisotropic. These behaviors can be consistently interpreted
from a viewpoint of the underlying orbital ordering.",9808286v1
1998-09-02,Anomalous ferromagnetic spin fluctuations in an antiferromagnetic insulator Pr_{1-x}Ca_{x}MnO_{3},"The high temperature paramagnetic state in an antiferromagnetic (AFM)
insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin
fluctuations with an anomalously small energy scale. The FM fluctuations show a
precipitous decrease of the intensity at the charge ordering temperature
T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature
T_{N}. These results demonstrate the importance of the spin ordering for the
complete switching of the FM fluctuation in doped manganites.",9809033v1
1998-09-18,Prediction of Ferromagnetic Ground State of NaCl-type FeN,"Ab-initio results for structural and electronic properties of NaCl-type FeN
are presented in a framework of plane-wave and ultrasoft pseudopotentials.
Competition among different magnetic ordering is examined. We find the
ferromagnetic phase stable overall. Stabilization over the unpolarized phase is
obtained by splitting one flat t_2g-type band crossing the Fermi energy. A
comparison with CrN is considered. We find large differences in the properties
of the two systems that can be addressed to the smaller ionicity and
magnetization of FeN.",9809256v2
1998-09-25,Theory of the Spin Reorientation Transition of Ultra-Thin Ferromagnetic Films,"The reorientation transition of the magnetization of ferromagnetic films is
studied on a microscopic basis within Heisenberg spin models. Analytic
expressions for the temperature dependent anisotropy are derived from which it
is seen that the reduced magnetization in the film surface at finite
temperatures plays a crucial role for this transition. Detailed phase diagrams
in the temperature-thickness plane are calculated.",9809347v1
1998-09-30,Localization of spinwaves in the quantum Hall ferromagnet,"The quantum Hall ferromagnet at filling fraction $\nu = 1$ has some unusual
properties due to the remarkable identity between the topological density of a
spin distortion and the associated electrical charge density. We investigate
the localization of spinwaves by coupling to a scalar disorder potential via
their topological density. A low energy description of the system in terms of a
non-linear sigma model of unitary supermatrices is derived. All states of this
model are localized in two dimensions. A possible experimental signature of
these effects in photo-luminescence is suggested.",9809406v1
1998-10-01,Improved Composite-Boson Theory of Monolayer and Bilayer Quantum Hall Ferromagnets,"An improved composite-boson theory of quantum Hall ferromagnets is formulated
both for the monolayer and bilayer systems. In this scheme the field operator
describes solely the physical degrees of freedom representing the deviation
from the ground state. Skyrmions are charged excitations confined to the lowest
Landau level. By evaluating the excitation energy of one skyrmion in the
interlayer-coherent phase it is shown that the bilayer QH state becomes stabler
as the interlayer density difference becomes larger.",9810003v1
1998-10-09,Zero Temperature Phases of the Electron Gas,"The stability of different phases of the three-dimensional non-relativistic
electron gas is analyzed using stochastic methods. With decreasing density, we
observe a {\it continuous} transition from the paramagnetic to the
ferromagnetic fluid, with an intermediate stability range ($25\pm 5 \leq
r_s\leq 35 \pm 5$) for the {\it partially} spin-polarized liquid. The freezing
transition into a ferromagnetic Wigner crystal occurs at $r_s=65 \pm 10$. We
discuss the relative stability of different magnetic structures in the solid
phase, as well as the possibility of disordered phases.",9810126v1
1998-11-11,Density of Zeros on the Lee-Yang circle obtained from magnetization data of a two-dimensional Ising ferromagnet,"In order to provide an experimental access to the statistical theory of Lee
and Yang (1952) the density function g(theta) of zeros on the Lee-Yang circle
has been determined for the first time by analyzing isothermal magnetization
data, m(H), of the Ising ferromagnet FeCl2 in axial magnetic fields, H, at
temperatures 34 < T < 99K. The validity of our approach is demonstrated by the
perfect agreement of magnetic specific heat data as calculated from g(theta)
and m(H) via Maxwells relation, respectively. Moreover, the correct in-plane
exchange constant of FeCl2 emerges from the series expansion of m(H) involved
in the analysis.",9811157v1
1998-11-13,Spin-accumulation in small ferromagnetic double barrier junctions,"The non-equilibrium spin accumulation in ferromagnetic double barrier
junctions is shown to govern the transport in small structures. Transport
properties of such systems are described by a generalization of the theory of
the Coulomb blockade. The spin accumulation enhances the magnetoresistance. The
transient non-linear transport properties are predicted to provide a unique
experimental evidence of the spin-accumulation in the form of a reversed
current on time scales of the order of the spin-flip relaxation time.",9811179v1
1998-12-08,Crossover properties from random percolation to frustrated percolation,"We investigate the crossover properties of the frustrated percolation model
on a two-dimensional square lattice, with asymmetric distribution of
ferromagnetic and antiferromagnetic interactions. We determine the critical
exponents nu, gamma and beta of the percolation transition of the model, for
various values of the density of antiferromagnetic interactions pi in the range
0<pi<0.5. Our data are consistent with the existence of a crossover from random
percolation behavior for pi=0, to frustrated percolation behavior,
characterized by the critical exponents of the ferromagnetic 1/2-state Potts
model, as soon as pi>0.",9812118v1
1998-12-11,Spin-Pseudospin Coherence and CP$^{3}$ Skyrmions in Bilayer Quantum Hall Ferromagnets,"We analyze bilayer quantum Hall ferromagnets, whose underlying symmetry group
is SU(4). Spin-pseudospin coherence develops spontaneously when the total
electron density is low enough. Quasiparticles are CP^3 skyrmions. One skyrmion
induces charge modulations on both of the two layers. At the filling factor$\nu
=2/m$ one elementary excitation consists of a pair of skyrmions and its charge
is $2e/m$. Recent experimental data due to Sawada et al. [Phys. Rev. Lett. {\bf
80}, 4534 (1998)] support this conclusion.",9812188v2
1998-12-14,Non-equilibrium spin accumulation in ferromagnetic single-electron transistors,"We study transport in ferromagnetic single-electron transistors. The non-
equilibrium spin accumulation on the island caused by a finite current through
the system is described by a generalized theory of the Coulomb blockade. It
enhances the tunnel magnetoresistance and has a drastic effect on the time-
dependent transport properties. A transient decay of the spin accumulation may
reverse the electric current on time scales of the order of the spin-flip
relaxation time. This can be used as an experimental signature of the non-
equilibrium spin accumulation.",9812224v1
1998-12-30,First order transitions and multicritical points in weak itinerant ferromagnets,"It is shown that the phase transition in low-T_c clean itinerant ferromagnets
is generically of first order, due to correlation effects that lead to a
nonanalytic term in the free energy. A tricritical point separates the line of
first order transitions from Heisenberg critical behavior at higher
temperatures. Sufficiently strong quenched disorder suppresses the first order
transition via the appearance of a critical endpoint. A semi-quantitative
discussion is given in terms of recent experiments on MnSi, and predictions for
other experiments are made.",9812420v2
1999-01-06,Thickness dependent Curie temperatures of ferromagnetic Heisenberg films,"We develop a procedure for calculating the magnetic properties of a
ferromagnetic Heisenberg film with single-ion anisotropy which is valid for
arbitrary spin and film thickness. Applied to sc(100) and fcc(100) films with
spin S=7/2 the theory yields the layer dependent magnetizations and Curie
temperatures of films of various thicknesses making it possible to investigate
magnetic properties of films at the interesting 2D-3D transition.",9901036v1
1999-01-18,Kondo effect in a quantum critical ferromagnet,"We study the Heisenberg ferromagnetic spin chain coupled with a boundary
impurity. Via Bethe ansatz solution, it is found that (i) for J>0, the impurity
spin behaves as a diamagnetic center and is completely screened by 2S bulk
spins in the ground state, no matter how large the impurity spin is; (ii) The
specific heat of the local composite (impurity plus 2S bulk spins which form
bound state with it) shows a simple power law $C_{loc}\sim T^{3/2}$. (iii)For
J<0, the impurity is locked into the critical behavior of the bulk. Possible
phenomena in higher dimensions are discussed.",9901167v2
1999-01-21,Possible Existence Of Topological Excitations In Quantum Spin Models In Low Dimensions,"The possibility of existence of topological excitations in the anisotropic
quantum Heisenberg model in one and two spatial dimensions is studied using
coherent state method. It is found that a part of the Wess-Zumino term
contributes to the partition function, as a topological term for ferromagnets
in the long wavelength limit in both one and two dimensions. In particular, the
XY limit of the two-dimensional anisotropic ferromagnet is shown to retain the
topological excitations, as expected from the quantum Kosterlitz-Thouless
scenario.",9901209v1
1999-01-22,Skyrmions and Quantum Hall Ferromagnets in Improved Composite-Boson Theory,"An improved composite-boson theory of quantum Hall ferromagnets is proposed.
It is tightly related with the microscopic wave-function theory. The
characteristic feature is that the field operator describes solely the physical
degrees of freedom representing the deviation from the ground state. It
presents a powerful tool to analyze excited states within the \LLLd.
Excitations include a Goldstone mode and nonlocal topological solitons.
Solitons are vortices and Skyrmions carrying the U(1) and SU(2) topological
charges, respectively. Their classical configurations are derived from their
microscopic wave functions. The activation energy of one Skyrmion is estimated,
which explains experimental data remarkably well.",9901236v1
1999-01-29,Theory of optical conductivity in doped manganites,"The frequency and temperature dependence of the optical conductivity of
ferromagnetic manganites is explained within the framework of the bipolaron
theory. As these materials are cooled below the Curie temperature, the colossal
magnetoressitance (CMR) is accompanied by a massive transfer of the spectral
weight of the optical conductivity to lower frequencies. As with the CMR
itself, this change in the optical conductivity is explained by the
dissociation of bipolarons into small polarons by exchange interaction with the
localized Mn spins during the transition to the low temperature ferromagnetic
phase.",9901340v2
1999-02-15,Ballistic and diffuse transport through a ferromagnetic domain wall,"We study transport through ballistic and diffuse ferromagnetic domain walls
in a two-band Stoner model with a rotating magnetization direction. For a
ballistic domain wall, the change in the conductance due to the domain wall
scattering is obtained from an adiabatic approximation valid when the length of
the domain wall is much longer than the Fermi wavelength. In diffuse systems,
the change in the resistivity is calculated using a diagrammatic technique to
the lowest order in the domain wall scattering and taking into account
spin-dependent scattering lifetimes and screening of the domain wall potential.",9902210v2
1999-02-18,Dephasing Effects by Ferromagnetic Boundary on Resistivity in Disordered Metallic Layer,"The resistivity of disordered metallic layer sandwiched by two ferromagnetic
layers at low-temperature is investigated theoretically. It is shown that the
magnetic field acting at the interface does not affect the classical Boltzmann
resistivity but causes a dephasing among electrons in the presence of the
spin-orbit interaction, suppressing the anti-localization due to the spin-orbit
interaction. The dephasing turns out to be stronger in the case where the
magnetization of the two layers is parallel, contributing to a positive
magnetoresistance close to a switching field at low temperature.",9902256v1
1999-02-19,Orbital Degree of Freedom and Phase Separation in Ferromagnetic Manganites at Finite Temperatures,"The spin and orbital phase diagram for perovskite manganites are investigated
as a function of temperature and hole concentration. The superexchange and
double exchange interactions dominate the ferromagnetic phases in the low and
high concentration regions of doped holes, respectively.The two interactions
favor different orbital states each other. Between the phases, two interactions
compete with each other and the phase separation appears in the wide range of
temperature and hole concentration. The anisotropy of the orbital space causes
discontinuous changes of the orbital state and promotes the phase separation.
The relation between the phase separation and the stripe- and sheet-type charge
segregation is discussed.",9902266v1
1999-03-02,Theory of the Josephson effect in superconductor / ferromagnet / superconductor junctions,"To reveal the influence of the exchange interaction on the Josephson effect,
the d.c. Josephson current in unconventional-superconductor / ferromagnet /
unconventional-superconductor junctions is studied. When the two
superconductors have d-wave symmetry, the Josephson current is drastically
suppressed with the increase of the exchange interaction. On the other hand,
when the two superconductors have different parities, e.g. s-wave and p-wave,
an enhancement of the Josephson current is obtained with the increment of the
exchange interaction due to the break-down of SU(2) symmetry in the spin space.",9903034v3
1999-03-05,Barkhausen avalanches in anisotropic ferromagnets with $180^\circ$ domain walls,"We show that Barkhausen noise in two-dimensional disordered ferromagnets with
extended domain walls is characterized by the avalanche size exponent $\tau_s
=1.54$ at low disorder. With increasing disorder the characteristic domain size
is reduced relative to the system size due to nucleation of new domains and a
dynamic phase transition occurs to the scaling behavior with $\tau_s=1.30$. The
exponents decrease at finite driving rate. The results agree with recently
observed behavior in amorphous Metglas and Fe-Co-B ribbons when the applied
anisotropic stress is varied.",9903090v2
1999-03-13,Colossal magnetooptical conductivity in doped manganites,"We show that the current carrier density collapse in doped manganites, which
results from bipolaron formation in the paramagnetic phase, leads to a colossal
change of the optical conductivity in an external magnetic field at
temperatures close to the ferromagnetic transition. As with the colossal
magnetoresistance (CMR) itself, the corresponding magnetooptical effect is
explained by the dissociation of localized bipolarons into mobile polarons
owing to the exchange interaction with the localized Mn spins in the
ferromagnetic phase. The effect is positive at low frequencies and negative in
the high-frequency region. The present results agree with available
experimental observations.",9903217v1
1999-03-15,Giant Mutual Proximity Effects in Ferromagnetic/Superconducting Nanostructures,"A strong mutual influence of superconductors (S) and ferromagnetic (F)
conductors in hybrid F/S (Ni/Al) nanostructures is observed. The magnitude of a
proximity-induced conductance on the F-side is more than two orders larger than
that predicted by theory. Re-entrance of the superconductors to the normal
state reciprocated by changes on the F-side has been found in low applied
magnetic fields with new peaks in the differential resistance as an effect of
the saturation magnetisation. An analysis has been developed providing a base
for a numerical description of the system. PACS numbers: 74.50.+r, 74.80.Fp,
85.30St",9903237v1
1999-03-20,Comparison of superconductivity in Sr_2RuO_4 and copper oxides,"To compare the superconductivity in strongly correlated electron systems with
the antiferromagnetic fluctuations in the copper oxides and with the
ferromagnetic fluctuations in Sr_2RuO_4 a t-J-I model is proposed. The
antiferromagnetic coupling J results in the superconducting state of
d_{x^2-y^2} symmetry and the ferromagnetic coupling constant I results in the
spin-triplet p-type state. The difference in the gap anisotropies provides the
large difference in T_c values, for the typical values of the coupling
constants: T_c of order of 1K for the ruthenate and T_c of order of 100K for
the cuprates.",9903314v1
1999-04-08,Magnetic and quadrupolar order in a one-dimensional ferromagnet with cubic crystal-field anisotropy,"The zero temperature phase diagram of a one-dimensional S=2 Heisenberg
ferromagnet with single-ion cubic anisotropy is studied numerically using the
density-matrix renormalization group method. Evidence is found that although
the model does not involve quadrupolar couplings, there is a purely quadrupolar
phase for large values of the anisotropy. The phase transition between the
magnetic and quadrupolar phases is continuous and it seems to be characterized
by Ising critical exponents.",9904109v1
1999-04-23,Shot noise in ferromagnetic single electron tunneling devices,"Frequency dependent current noise in ferromagnetic double junctions with
Coulomb blockade is studied theoretically in the limit of sequential tunneling.
Two different relaxation processes are found in the correlations between spin
polarized tunneling currents; low frequency spin fluctuations and high
frequency charge fluctuations. Spin accumulation in strongly asymmetric
junctions is shown to lead to a negative differential resistance. We also show
that large spin noise activated in the range of negative differential
resistance gives rise to a significant enhancement of the current noise.",9904341v1
1999-05-08,H_c_3 for a thin-film superconductor with a ferromagnetic dot,"We investigate the effect of a ferromagnetic dot on a thin-film
superconductor. We use a real-space method to solve the linearized
Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We
show that H_c_3 is crucially dependent on dot composition and geometry, and may
be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the
dot saturation magnetization is large, (2) the ratio of dot thickness to dot
diameter is of order one, and (3) the dot thickness is large.",9905107v1
1999-05-14,Scaling and finte-size-scaling in the two dimensional random-coupling Ising ferromagnet,"It is shown by Monte Carlo method that the finite size scaling (FSS) holds in
the two dimensional random-coupled Ising ferromagnet. It is also demonstrated
that the form of universal FSS function constructed via novel FSS scheme
depends on the strength of the random coupling for strongly disordered cases.
Monte Carlo measurements of thermodynamic (infinite volume limit) data of the
correlation length ($\xi$) up to $\xi \simeq 200$ along with measurements of
the fourth order cumulant ratio (Binder's ratio) at criticality are reported
and analyzed in view of two competing scenarios. It is demonstrated that the
data are almost exclusively consistent with the scenario of weak universality.",9905202v1
1999-05-24,Soliton-Magnon Scattering in Two-Dimensional Isotropic Ferromagnets,"It is studied the scattering of magnons by the 2d topological
Belavin-Polyakov soliton in isotropic ferromagnet. Analytical solutions of the
scattering problem are constructed: (i) exactly for any magnon wave vectors for
the partial wave with the azimuthal number m=1 (translational mode), and (ii)
in the long- and short-wave limits for the rest modes. The magnon mode
frequencies are found for the finite size magnets. An effective equation of the
soliton motion is constructed. The magnon density of states, connected with the
soliton-magnon interaction, is found in a long-wave approximation.",9905348v1
1999-05-27,Influence of spin-flip scattering on the stability of ferromagnetism in a two-band Hubbard model,"We investigate the influence of an interband exchange interaction on
magnetism in a two-band Hubbard model. Our main emphasis lies on spin-flip
scattering which is often neglected but is neccessary to retain the full
rotational symmetry of the Hamiltonian. We find a striking dependence of the
magnetization on the interband exchange coupling constant J and a substantial
suppression of ferromagnetic order for a large range of values of J. The onset
of an RKKY-like magnetic ordering mechanism is also observed.",9905396v1
1999-06-01,Two-dimensional behavior of the sublattice magnetization in three-dimensional Ising antiferromagnets,"A three-dimensional layered Ising-Antiferromagnet with a ferromagnetic
intra-layer coupling to z neighbors, zJ > 0, and an antiferromagnetic
interlayer coupling to z' neighbors, z'J' < 0, is investigated by Monte Carlo
simulations on a hexagonal lattice. The physical nature of the anomalous
temperature bahavior of the sublattice magnetizations, which is found for
certain values of r=zJ/z'J' and z' in magnetic fields is explained in terms of
successive phase transitions. They take place on the ferromagnetic
2-dimensional spin-down sublattice at T = T_c^{2d}, smeared by a finite
stabilizing molecular field, and on both antiferromagnetically coupled
sublattices at T_c^{3d} > T_c^{2d}.",9906003v1
1999-06-07,p-wave and d-wave superconductivity in quasi-two-dimensional metals,"We compare predictions of the mean-field theory of superconductivity for
nearly antiferromagnetic and nearly ferromagnetic metals in two dimensions. The
calculations are based on a parametrization of the effective interaction
arising from the exchange of magnetic fluctuations. The Eliashberg equations
for the transition temperature are solved including the full momentum
dependence of the self-energy. The results show that for comparable parameters
d-wave singlet pairing in nearly antiferromagnetic metals is generally much
stronger than p-wave triplet pairing in nearly ferromagnetic metals in quasi
two dimensions. The relevance to the layered materials, and in particular
Sr2RuO4 that exhibits p-wave triplet pairing, is discussed.",9906091v1
1999-06-09,The anomalous metallic ferromagnetic state of Sr doped manganites,"We deduce a model relevant for the anomalous metallic state of Sr doped
manganites at low temperatures within the ferromagnetic phase. It provides a
natural explanation to several anomalous features observed experimentally, such
as the vanishing Drude contribution in optical conductivity, the pseudo-gap in
the density of states, an the unusual dispersion observed in photoemission.",9906131v2
1999-06-26,Ferromagnetism and superstructure in Ca_{1-x}La_xB_6,"We critically investigate the model of a doped excitonic insulator, which
recently has been invoked to explain some experimental properties of the
ferromagnetic state in Ca_{1-x}La_xB_6. We demonstrate that the ground state of
this model is intrinsically unstable towards the appearance of a
superstructure. In addition, the model would lead to a phase separation regime
and the domain structure which may be prevented by the Coulomb forces only.
Recent experiments indicate that a superstructure may indeed show up in this
material.",9906401v1
1999-06-29,Quantitative Model of Large Magnetostrain Effect in Ferromagnetic Shape Memory Alloys,"A quantitative model describing large magnetostrain effect observed in
several ferromagnetic shape memory alloys such as Ni2MnGa is briefly
reported.The paper contains an exact thermodynamic consideration of the
mechanical and magnetic properties for a similar type materials. As a result,
the basic mechanical state equation including magnetic field effect is directly
derived from a general Poisson's rule. It is shown that the magnetic field
induced deformation effect is directly connected with the strain dependence of
magnetization. A simple model of magnetization and its dependence on the strain
is considered and applied to explain the results of experimental study of large
magnetostrain effects in Ni2MnGa.",9906433v1
1999-07-08,Diffusion Thermopower of Ferromagnetic Transition metals,"This paper discusses a simple calculation for the diffusion thermopower of a
transition metal ferromagnet. The main result of this calculation is that
unlike in the case of a free-electron model, the diffusion thermopower S and
its derivative with respect to temperature dS/dT have opposite signs. The
results of this calculation agree qualitatively with experimental results in
the high temperature region, where the diffusion thermopower is dominant.",9907116v3
1999-07-27,Triplet superconductivity in a one-dimensional ferromagnetic t-J model,"In this paper we study the ground state phase diagram of a one-dimensional
$t-U-J$ model, at half-filling. In the large-bandwidth limit and for
ferromagnetic exchange with easy-plane anisotropy, a phase with gapless charge
and massive spin excitations, characterized by the coexistence of triplet
superconducting ($TS$) and spin density wave ($SDW^{z}$) instabilities is
realized in the ground state. With reduction of the bandwidth, a transition
into an insulating phase showing properties of the spin-1/2 XY model takes
place. In the case of weakly anisotropic antiferromagnetic exchange the system
shows a long range dimerized (Peierls) ordering in the ground state. The
complete weak-coupling phase diagram of the model, including effects of the
on-site Hubbard interaction, is obtained.",9907415v1
1999-07-29,Calculation Method for the Three-Dimensional Ising Ferromagnet Thermodynamics within the Frames of $ρ^6$ Model,"Calculation of thermodynamic functions of the three-dimensional Ising
ferromagnet above and below critical temperature is performed in the
approximation of sixfold basis distribution ($\rho^6$ model). Comparison with
the results for the $\rho^4$ model indicates that dependence of the
thermodynamic functions on the renormalization group parameter $s$ becomes
weaker. The optimal interval of the renormalization group parameter values is
determined.",9907468v2
1999-08-03,Diffusion in disordered lattices and related Heisenberg ferromagnets,"We study the diffusion of classical hard-core particles in disordered
lattices within the formalism of a quantum spin representation. This analogy
enables an exact treatment of non-instantaneous correlation functions at finite
particle densities in terms of single spin excitations in disordered
ferromagnetic backgrounds. Applications to diluted chains and percolation
clusters are discussed. It is found that density fluctuations in the former
exhibit a stretched exponential decay while an anomalous power law asymptotic
decay is conjectured for the latter.",9908051v1
1999-08-04,Large Magnetoresistance Ratio in Ferromagnetic Single-Electron Transistors in the Strong Tunneling Regime,"We study transport through a ferromagnetic single-electron transistor. The
resistance is represented as a path integral, so that systems where the tunnel
resistances are smaller than the quantum resistance can be investigated. Beyond
the low order sequential tunneling and co-tunneling regimes, a large
magnetoresistance ratio at sufficiently low temperatures is found. In the
opposite limit, when the thermal energy is larger than the charging energy, the
magnetoresistance ratio is only slightly enhanced.",9908061v2
1999-08-31,Spin resolved Andreev reflection in ferromagnet-superconductor junctions with Zeeman splitting,"Andreev reflection in ferromagnet-superconductor junctions is derived in a
regime in which Zeeman splitting dominates the response of the superconductor
to an applied magnetic field. Spin-up and spin-down Andreev reflections are
shown to be resolved as voltage is increased. In the metallic limit, the
transition from Andreev to tunnel conductivity in the spin-up channels has a
non trivial behavior when spin polarization is increased. The conductance is
asymmetric in a voltage reversal.",9908465v1
1999-09-09,Application of the Projected Dynamics Method to an Anisotropic Heisenberg Model,"The Projected Dynamics method was originally developed to study metastable
decay in ferromagnetic discrete spin models. Here, we apply it to a classical,
continuous Heisenberg model with anisotropic ferromagnetic interactions, which
evolves under a Monte Carlo dynamic. The anisotropy is sufficiently large to
allow comparison with the Ising model. We describe the Projected Dynamics
method and how to apply it to this continuous-spin system. We also discuss how
to extract metastable lifetimes and how to extrapolate from small systems to
larger systems.",9909142v1
1999-09-10,Time Evolution of Spin Waves,"A rigorous derivation of macroscopic spin-wave equations is demonstrated. We
introduce a macroscopic mean-field limit and derive the so-called
Landau-Lifshitz equations for spin waves. We first discuss the ferromagnetic
Heisenberg model at T=0 and finally extend our analysis to general spin
hamiltonians for the same class of ferromagnetic ground states.",9909146v1
1999-09-14,Lro in Lattice Systems of Linear Classical and Quantum Oscillators. Strong N-N Pair Quadratic Interaction,"For systems of one-component interacting oscillators on the d-dimensional
lattice, d>1, whose potential energy besides a large nearest-neighbour (n-n)
ferromagnetic translation-invariant quadratic term contains small
non-nearest-neighbour translation invariant term, an existence of a
ferromagnetic long-range order for two valued lattice spins, equal to a sign of
oscillator variables, is established for sufficiently large magnitude g of the
n-n interaction with the help of the Peierls type contour bound. The Ruelle
superstability bound is used for a derivation of the contour bound.",9909207v1
1999-09-15,The magnetism of the t-t' Hubbard model,"The magnetic properties of the t-t' Hubbard Model in the two dimensional
square lattice are studied within an unrestricted Hartree-Fock approximation in
real space. The interplay between antiferromagnetism, ferromagnetism, phase
separation and inhomogeneous magnetic textures is studied. It is shown that, at
sufficiently large values of t'/t, a rich fenomenology is to be expected
between the antiferromagnetic phase at half filling and the ferromagnetic phase
a lower fillings.",9909224v1
1999-09-16,"Ferromagnetic, A-type, and Charge-Ordered CE-type States in Doped Manganites using Jahn-Teller Phonons","The two-orbital model for manganites with both non-cooperative and
cooperative Jahn-Teller phonons is studied at hole density x=0.5 using Monte
Carlo techniques. The phase diagram is obtained varying the electron-phonon
coupling and the $\rm t_{2g}$-spins exchange. The insulating CE-type charge-
and orbital-ordered state with the $z$-axis charge $stacking$ observed in
narrow-bandwidth manganites is stabilized in the simulations. Its charge gap
$\Delta_{\rm CO}$ is much larger than the critical temperature $\rm k_B
T_{CO}$. Metallic-like A-type and ferromagnetic states are also obtained in the
same framework, and the phase boundaries among them have first-order
characteristics.",9909254v1
1999-09-21,Electronic Correlations in Manganites,"The influence of local electronic correlations on the properties of colossal
magnetoresistance manganites is investigated. To this end, a ferromagnetic
two-band Kondo lattice model is supplemented with the local Coulomb repulsion
missing in this model, and is analyzed within dynamical mean-field theory.
Results for the spectral function, optical conductivity, and the
paramagnetic-to-ferromagnetic phase transition show that electronic
correlations have drastic effects and may explain some experimental
observations.",9909311v2
1999-10-12,Hysteresis in One-Dimensional Anti-Ferromagnetic Random-Field Ising Model at Zero-Temperature,"We analyse hysteresis in a one-dimensional anti-ferromagnetic random field
Ising model at zero-temperature. The random field is taken to have a
rectangular distribution of width $2 \Delta$ centered about the origin. A
uniform applied field is varied slowly from $-\infty$ to $+\infty$ and back.
Analytic expression for the hysteresis loop is obtained in the case $\Delta \le
|J|$, where $|J|$ is the strength of the nearest neighbor interaction.",9910169v1
1999-10-14,Giant 1/f noise in perovskite manganites: evidence of the percolation threshold,"We discovered an unprecedented magnitude of the 1/f noise near the Curie
temperature Tc in low-Tc manganites. The scaling behavior of the 1/f noise and
the resistance provides strong evidence of the percolation nature of the
ferromagnetic transition in the polycrystalline samples. The step-like changes
of the resistance with temperature, observed for single crystals, suggest that
the size of the ferromagnetic domains depends on the size of crystallites.",9910220v1
1999-11-23,First and second order ferromagnetic transition at T=0 in a 1D itinerant system,"We consider a modified version of the one-dimensional Hubbard model, the
t1-t2 Hubbard chain, which includes an additional next-nearest-neighbor
hopping. It has been shown that at weak coupling this model has a Luttinger
liquid phase or a spin liquid phase depending upon the ratio of t2 to t1.
Additionally if the on-site interaction U is large enough, the ground state is
fully polarized. Using exact diagonalization and the density-matrix
renormalization group, we show that the transition to the ferromagnetic phase
is either of first or second order depending on whether the Luttinger liquid or
spin liquid is being destabilized. Since we work at T=0, the second order
transition is a quantum magnetic critical point.",9911361v1
1999-11-24,Exactly solvable spin ladder model with degenerate ferromagnetic and singlet states,"We study the spin ladder model with interactions between spins on neighboring
rungs. The model Hamiltonian with the exact singlet ground state degenerated
with ferromagnetic state is obtained. The singlet ground state wave function
has a special recurrent form and depends on two parameters. Spin correlations
in the singlet ground state show double-spiral structure with period of spirals
equals to the system size. For special values of parameters they have
exponential decay. The spectrum of the model is gapless and there are
asymptotically degenerated excited states for special values of parameters in
the thermodynamic limit.",9911394v1
1999-12-02,Charge and orbital ordering in underdoped La1-xSrxMnO3,"We have explored spin, charge and orbitally ordered states in La1-xSrxMnO3 (0
< x < 1/2) using model Hartree-Fock calculations on d-p-type lattice models. At
x=1/8, several charge and orbitally modulated states are found to be stable and
almost degenerate in energy with a homogeneous ferromagnetic state. The present
calculation indicates that a ferromagnetic state with a charge modulation along
the c-axis which is consistent with the experiment by Yamada et al. might be
responsible for the anomalous behavior around x = 1/8.",9912021v1
1999-12-06,Finite-size scaling corrections in two-dimensional Ising and Potts ferromagnets,"Finite-size corrections to scaling of critical correlation lengths and free
energies of Ising and three-state Potts ferromagnets are analysed by numerical
methods, on strips of width $N$ sites of square, triangular and honeycomb
lattices. Strong evidence is given that the amplitudes of the ``analytical''
correction terms, $N^{-2}$, are identically zero for triangular-- and honeycomb
Ising systems. For Potts spins, our results are broadly consistent with this
lattice-dependent pattern of cancellations, though for correlation lengths
non-vanishing (albeit rather small) amplitudes cannot be entirely ruled out.",9912090v1
1999-12-07,Theory of Spin polarized Tunneling in Superconducting Sr2RuO4,"A theory of tunneling conductance in ferromagnetic metal/insulator/triplet -
supercondcutor junctions is presented for unitary and non-unitary spin triplet
pairing states which are promising candidates for the superconducting paring
symmetry of Sr2RuO4. As the magnitude of the exchange interaction in the
ferromagnetic metal is increased, the conductance for the unitary pairing state
below the energy gap is reduced in contrast to the case for the non-unitary
pairing state.",9912100v1
1999-12-20,Ferromagnetic Nanowires with Superconducting Electrodes,"The proximity effect in mesoscopic ferromagnet/superconductor ($FS$) Ni/Al
structures of various geometries was studied experimentally on both $F$- and
$S$-sides of the structures. Samples with a wide range of interface
transparency were fabricated. The dependence of the effect on $FS$ interface
transparency was investigated. The amplitude of this effect was found to be
larger than expected from classical theory of proximity effect. Preliminary
experiments showed no phase-sensitive oscillations in Andreev interferometer
geometry. Various theoretical models are discussed.",9912370v1
1999-12-22,Observation of domain wall resistivity in $\rm SrRuO_3$,"$\rm SrRuO_3$ is an itinerant ferromagnet with $T_c \sim 150 \rm K$. When
$\rm SrRuO_3$ is cooled through $T_c$ in zero applied magnetic field, a stripe
domain structure appears whose orientation is uniquely determined by the large
uniaxial magnetocrystalline anisotropy. We find that the ferromagnetic domain
walls clearly enhance the resisitivity of $\rm SrRuO_3$ and that the
enhancement has different temperature dependence for currents parallel and
perpendicular to the domain walls. We discuss possible interpretations of our
results.",9912404v1
2000-01-11,The temperature dependent behaviour of surface states in ferromagnetic semiconductors,"We present a model calculation for the temperature dependent behaviour of
surface states on a ferromagnetic local-moment film. The film is described
within the s-f model featuring local magnetic moments being exchange coupled to
the itinerant conduction electrons. The surface states are generated by
modifying the hopping in the vicinity of the surface of the film. In the
calculation for the temperature dependent behaviour of the surface states we
are able to reproduce both Stoner-like and spin-mixing behaviour in agreement
with recent (inverse) photoemission data on the temperature dependent behaviour
of a Gd(0001) surface state.",0001141v1
2000-01-13,"Comment on ""Observation of Spin Injection at a Ferromagnet-Semiconductor Interface, by P.R. Hammar et al","In a recent Letter Hammar et al. claim the observation of injection of a
spin-polarized current in a two-dimensional electron gas (2DEG). This is an
important observation, since, despite considerable effort of several groups,
all attempts to realize spin-injection into a 2DEG using purely electrical
measurements have failed sofar. However, in my opinion the claim made is not
correct, and the observed behaviour can be explained by a combination of a
magneto resistance (Hall) effect (e.g. generated by the fringe magnetic fields
present at the edges of the ferromagnetic electrode), with a {\it
spin-independent} rectification effect due to the presence of a metal-
semiconductor junction.",0001187v1
2000-01-13,Scaling exponents for Barkhausen avalanches in polycrystals and amorphous ferromagnets,"We investigate the scaling properties of the Barkhausen effect, recording the
noise in several soft ferromagnetic materials: polycrystals with different
grain sizes and amorphous alloys. We measure the Barkhausen avalanche
distributions and determine the scaling exponents. In the limit of vanishing
external field rate, we can group the samples in two distinct classes,
characterized by exponents \tau = 1.50 \pm 0.05 or \tau = 1.27 \pm 0.03, for
the avalanche size distributions. We interpret these results in terms of the
depinning transition of domain walls and obtain an expression relating the
cutoff of the distributions to the demagnetizing factor which is in
quantitative agreement with experiments.",0001191v1
2000-01-17,Anderson-Mott Transition in a Magnetic Field: Corrections to Scaling,"It is shown that the Anderson-Mott metal-insulator transition of
paramagnetic, interacting disordered electrons in an external magnetic field is
in the same universality class as the transition from a ferromagnetic metal to
a ferromagnetic insulator discussed recently. As a consequence, large
corrections to scaling exist in the magnetic-field universality class, which
have been neglected in previous theoretical descriptions. The nature and
consequences of these corrections to scaling are discussed.",0001232v2
2000-02-16,Ferromagnetism and Canted Spin Phase in AlAs/GaMnAs Single Quantum Wells: Monte Carlo Simulation,"The magnetic order resulting from a confinement-adapted
Ruderman-Kittel-Kasuya-Yosida indirect exchange between magnetic moments in the
metallic phase of a AlAs/Ga(1-x)Mn(x)As quantum well is studied by Monte Carlo
simulation. This coupling mechanism involves magnetic moments and carriers
(holes), both coming from the same Mn(2+) ions. It leads to a paramagnetic, a
ferromagnetic, or a canted spin phase, depending on the carrier concentration,
and on the magnetic layer width. It is shown that high transition temperatures
may be obtained.",0002254v1
2000-03-29,Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet : Sr_2FeMoO_6,"Ultrafast spin dynamics in ferromagnetic half-metallic compound Sr_2FeMoO_6
is investigated by pump-probe measurements of magneto-optical Kerr effect.
Half-metallic nature of this material gives rise to anomalous thermal
insulation between spins and electrons, and allows us to pursue the spin
dynamics from a few to several hundred picoseconds after the optical
excitation. The optically detected magnetization dynamics clearly shows the
crossover from microscopic photoinduced demagnetization to macroscopic critical
behavior with universal power law divergence of relaxation time for wide
dynamical critical region.",0003467v3
2000-03-30,Resistance Jumps and Hysteresis in Ferromagnetic Wires,"A phenomenological approach based on the principle of minimum heat generation
is proposed for understanding experiments for metallic wires with a
ferromagnetic domain wall controlled by a magnetic field. This approach
elucidates the origin of negative jump and of hysteresis in the
magnetoresistance experiments. To justify our approach, we computed the
transmission probability of a single electron through a wire. Under certain
conditions, the presence of a domain wall enhances the transmission through an
impurity potential. Combining this result with the principle of minimum heat
generation explains the counterintuitive negative resistance jump.",0003485v2
2000-05-02,Two-Dimensional Modeling of Soft Ferromagnetic Films,"We examine the response of a soft ferromagnetic film to an in-plane applied
magnetic field. Our theory, based on asymptotic analysis of the micromagnetic
energy in the thin-film limit, proceeds in two steps: first we determine the
magnetic charge density by solving a convex variational problem; then we
construct an associated magnetization field using a robust numerical method.
Experimental results show good agreement with the theory. Our analysis is
consistent with prior work by van den Berg and by Bryant and Suhl, but it goes
much further; in particular it applies even for large fields which penetrate
the sample.",0005057v1
2000-07-11,Spin diffusion in doped semiconductors: the role of Coulomb interactions,"We examine the effect of the Coulomb interaction on the mobility and
diffusion of spin packets in doped semiconductors. We find that the diffusion
constant is reduced, relative to its non-interacting value, by the combined
effect of Coulomb-enhanced spin susceptibility and spin Coulomb drag. In
ferromagnetic semiconductors, the spin diffusion constant vanishes at the
ferromagnetic transition temperature.",0007197v4
2000-07-25,Indication of the ferromagnetic instability in a dilute two-dimensional electron system,"The magnetic field B_c, in which the electrons become fully spin-polarized,
is found to be proportional to the deviation of the electron density from the
zero-field metal-insulator transition in a two-dimensional electron system in
silicon. The tendency of B_c to vanish at a finite electron density suggests a
ferromagnetic instability in this strongly correlated electron system.",0007402v2
2000-08-01,Fate of Zero-Temperature Ising Ferromagnets,"We investigate the relaxation of homogeneous Ising ferromagnets on finite
lattices with zero-temperature spin-flip dynamics. On the square lattice, a
frozen two-stripe state is apparently reached approximately 1/4 of the time,
while the ground state is reached otherwise. The asymptotic relaxation is
characterized by two distinct time scales, with the longer stemming from the
influence of a long-lived diagonal stripe ``defect''. In greater than two
dimensions, the probability to reach the ground state rapidly vanishes as the
size increases and the system typically ends up wandering forever within an
iso-energy set of stochastically ``blinking'' metastable states.",0008019v1
2000-08-07,Features of Hopping Integral and Unconventional Orbital Modes for Quantum Skyrmions in Heisenberg Ferromagnet,"We use the coherent state approximation for the skyrmion in the isotropic
quantum Heisenberg ferromagnet to obtain analytical expression for skyrmion
hopping integral as a function of distance. It appears the skyrmion hopping is
restricted by distances larger than its effective diameter. Some puzzling
properties of the orbital skyrmionic modes are discussed. Spin distribution in
these states is obtained and effect of quantum spin contraction is
demonstrated.The principal possibility of lowering the skyrmion energy due to a
bonding-like state formation is illustrated.",0008104v2
2000-08-16,Effects of Fe doping in La1/2Ca1/2MnO3,"The effect of Fe doping in the Mn site on the magnetic, transport and
structural properties of polycrystalline La1/2Ca1/2MnO3 was studied. Doping
with low Fe concentration (< 10%) strongly affects electrical transport and
magnetization. Long range charge order is disrupted even for the lowest doping
level studied (~2%). For Fe concentration up to 5% a ferromagnetic state
develops at low temperature with metallic like conduction and thermal
hysteresis. In this range, the Curie temperature decreases monotonously as a
function of Fe doping. Insulating behavior and a sudden depression of the
ferromagnetic state is observed by further Fe doping.",0008236v1
2000-08-18,Dynamic critical behavior of disordered 3D Heisenberg ferromagnets,"The influence of a strong disorder on the critical dynamics of 3D Heisenberg
ferromagnet was investigated by high-resolution quasielastic neutron
scattering. A new disorder-induced dynamical critical behavior was found,
characterized by its critical exponent z=2.3. The dynamical scaling function
appeared mainly unaffected by disorder but its description led to a new
parameterization of the Renormalization Group theory, as in the case of pure
Nickel.",0008267v1
2000-08-21,Bag Formation in Quantum Hall Ferromagnets,"Charged skyrmions or spin-textures in the quantum Hall ferromagnet at filling
factor nu=1 are reinvestigated using the Hartree-Fock method in the lowest
Landau level approximation. It is shown that the single Slater determinant with
the minimum energy in the unit charge sector is always of the hedgehog form. It
is observed that the magnetization vector's length deviates locally from unity,
i.e. a bag is formed which accommodates the excess charge. In terms of a
gradient expansion for extended spin-textures a novel O(3) type of effective
action is presented, which takes bag formation into account.",0008297v1
2000-08-29,Transport Anomalies and Marginal Fermi-Liquid Effects at a Quantum Critical Point,"The conductivity and the tunneling density of states of disordered itinerant
electrons in the vicinity of a ferromagnetic transition at low temperature are
discussed. Critical fluctuations lead to nonanalytic frequency and temperature
dependences that are distinct from the usual long-time tail effects in a
disordered Fermi liquid. The crossover between these two types of behavior is
proposed as an experimental check of recent theories of the quantum
ferromagnetic critical behavior. In addition, the quasiparticle properties at
criticality are shown to be those of a marginal Fermi liquid.",0008431v2
2000-09-04,Observation of anomalous single-magnon scattering in half-metallic ferromagnets by chemical pressure control,"Temperature variation of resistivity and specific heat have been measured for
prototypical half-metallic ferromagnets,
  R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have
found variation of the temperature scalings in the resistivity from
  T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in
terms of the anomalous single-magnon scattering (AMS) process in the
half-metallic system.",0009035v1
2000-10-05,Oscillations of Andreev states in clean ferromagnetic films,"We investigate the influence of the exchange field on the Andreev bound
states in a ferromagnetic (F) film backed on one side by a superconductor (S).
Our model accounts for diffusive reflection at the outer surface and possible
backscattering at the FS-interface. Phase shifting of the Andreev level by the
exchange field results in an oscillatory behaviour of the density of states of
F as a function of the layer thickness. We show that our results agree
quantitatively with recent experiments.",0010089v1
2000-10-06,Static critical behavior of the ferromagnetic transition in LaMnO3.14 manganite,"The ferromagnetic phase transition in LaMnO3.14 is investigated by measuring
the dc magnetization as a function of magnetic field and temperature. Modified
Arrott plot and Kouvel Fisher analysis yield estimates for the critical
exponents beta, and gama, with values between that predicted for the Heisenberg
model and mean field theory. At low fields we found an anomalous small value of
beta, indicating that the critical behavior is influenced by the range of
magnetic fields used.",0010108v1
2000-10-16,Spin waves in ultrathin ferromagnetic overlayers,"The influence of a non-magnetic metallic substrate on the spin wave
excitations in ultrathin ferromagnetic overlayers is investigated for different
crystalline orientations. We show that spin wave dumping in these systems occur
due to the tunneling of holes from the substrate into the overlayer, and that
the spin wave energies may be considerably affected by the exchange coupling
mediated by the substrate.",0010215v1
2000-10-28,Theory of Tunneling Spectroscopy in Ferromagnetic Nanoparticles,"We present a theory of the low-energy excitations of a ferromagnetic metal
nanoparticle. In addition to the particle-hole excitations, which occur in a
paramagnetic metal nanoparticle, we predict a branch of excitations involving
the magnetization-orientation collective coordinate. Tunneling matrix elements
are in general sizable for several different collective states associated with
the same band configuration. We point out that the average change in ground
state spin per added electron differs from non-interacting quasiparticle
expectations, and that the change in the spin-polarization, due to Zeeman
coupling, is strongly influenced by Coulomb blockade physics.",0010469v1
2000-11-03,Critical exponents of ferromagnetic Ising model on fractal lattices,"We review the value of the critical exponents $\nu^{-1}$, $\beta/\nu$, and
$\gamma/\nu$ of ferromagnetic Ising model on fractal lattices of Hausdorff
dimension between one and three. They are obtained by Monte Carlo simulation
with the help of Wolff algorithm. The results are accurate enough to show that
the hyperscaling law $d_f=2\beta/\nu+\gamma/\nu$ is satisfied in non-integer
dimension. Nevertheless, the discrepancy between the simulation results and the
$\epsilon$-expansion studies suggests that the strong universality should be
adapted for the fractal lattices.",0011060v1
2000-11-07,Electron Spin Flip Relaxation by One Magnon Processes: Application to the Gadolinium surface band,"The ""s-f model"", also known as the ferromagnetic Kondo lattice, contains a
description of band electrons coupled to localized spins which is an
appropriate description of the magnetic part of the low-energy physics of Gd
metal. Here the model is used to estimate the lifetime broadening of the
minority spin component of the surface electron band in ferromagnetic
gadolinium metal at temperatures below the Curie temperature. The low
temperature result 0.10 eV agrees nicely with a measurement by Fedorov et al.",0011121v2
2000-11-10,Electronic pressure on ferromagnetic domain wall,"The scattering of the eletron by a domain wall in a nano-wire is studied
perturbatively to the lowest order. The correction to the thermodaynamic
potential of the electron system due to the scattering is calculated from the
phase shift. The wall profile is determined by taking account of this
correction, and the result indicates that the wall in a ferromagnet with small
exchange coupling can be squeezed to be very thin to lower the electron energy.",0011177v1
2000-11-22,Coexistence of 0 and $π$ states in Josephson junctions,"New modes of the magnetic flux penetration in SQUIDs with ferromagnetic
junctions are predicted theoretically. Characteristic multinode anharmonicity
of the current-phase relation implies the coexistence of stable and metastable
0 and $\pi$ states for a large interval of strength of the ferromagnetic
barrier influence at low temperature. As a consequence, the coexistence of
integer and half-integer fluxoid configurations appears in both rf and dc
SQUIDs, and generates two flux jumps per one external flux quantum. In dc
SQUIDs, new flux jumps are manifested as two dips in the critical current
dependence on the external magnetic flux.",0011378v1
2000-11-24,"Jahn-Teller, Charge and Magnetic Ordering in half-doped Manganese Oxides","The phase diagram of half-doped manganite systems of formula
A_{0.5}A'_{0.5}MnO_3 is investigated within a single-orbital model
incorporating magnetic double-exchange and superexchange, together with
intersite Coulomb and electron-lattice interactions. Strong Jahn-Teller and
breathing mode deformations compete together and result in shear lattice
deformations. The latters stabilize the charge-ordered CE-type phase, which
undergo first-order transitions with temperature or magnetic field to either
Ferromagnetic metallic or Paramagnetic insulating phases. An essential feature
is the self-consistent screening of Coulomb and electron-phonon interactions in
the ferromagnetic phase.",0011419v1
2000-12-15,History Dependent Phenomena in the Transverse Ising Ferroglass: the Free Energy Landscape,"In this paper we investigate the relationship between glassy and
ferromagnetic phases in disordered Ising ferromagnets in the presence of
transverse magnetic fields, $\Gamma$. Iterative mean field simulations probe
the free energy landscape and suggest the existence of a glass transition as a
function of $\Gamma$ which is distinct from the Curie temperature. New
experimental field-cooled and zero-field-cooled data on LiHo$_x$Y$_{1-x}$F$_4$
provide support for our theoretical picture.",0012298v2
2000-12-18,The phase-separated states in antiferromagnetic semiconductors with polarizable lattice,"The possibility of the slab or stripe phase separation (alternating
ferromagnetic highly- conductive and insulating antiferromagnetic layers) is
proved for isotropic degenerate antiferromagnetic semiconductors. This type of
phase separation competes with the droplet phase separation (ferromagnetic
droplets in the antiferromagnetic host or vice versa). The interaction of
electrons with optical phonons alone cannot cause phase-separated state with
alternating highly-conductive and insulating regions but it stabilizes the
magnetic phase separation. The magnetostriction deformation of the lattice in
the phase-separated state is investigated.",0012321v1
2000-12-19,Material-specific spin filtering in ferromagnet/superconductor ballistic nanojunctions,"We study spin-dependent electronic transport across
ferromagnet/superconductor ballistic junctions modeled using tight-binding
Hamiltonians with s, p and d orbitals and material-specific parameters. We show
that by accurately modeling the band structure of the bulk materials, one can
reproduce the measured differential conductance of Cu/Pb nanocontacts. In
contrast the differential conductance of Co/Pb contacts can only be reproduced
if an enhanced magnetic moment is present at the interface.",0012352v1
2000-12-27,Test of Bell's Inequality using the Spin Filter Effect in Ferromagnetic Semiconductor Micro-structures,"A theoretical proposal for testing Bell's inequality in mesoscopic systems is
presented. We show that the entanglement of two electron spins can be detected
in the spin filter effect in the mesoscopic semiconductor / ferromagnetic
semiconductor / semiconductor junction. The current-current correlation
function is calculated by use of the quantum scattering theory and we compare
it with the local hidden variable theory. We also discuss the influence of an
imperfect spin filter and derive the condition to see the violation of Bell's
inequality experimentally.",0012475v2
2001-01-17,Negative Magnetoresistance Produced by Hall Fluctuations in a Ferromagnetic Domain Structure,"We present a model for a negative magnetoresistance (MR) that would develop
in a material with many ferromagnetic domains even if the individual domains
have no magnetoresistance and even if there is no boundary resistance. The
negative MR is due to a classical current-distortion effect arising from
spatial variations in the Hall conductivity, combined with a change in domain
structure due to an applied magnetic field. The negative MR can exceed 1000% if
the product of the carrier relaxation time and the internal magnetic field due
to spontaneous magnetization is sufficiently large.",0101268v2
2001-01-22,Orbital Correlations in the Ferromagnetic Half-Metal $CrO_{2},"We deduce a model relevant for the description of the ferromagnetic
half-metal Chromium dioxide ($CrO_{2}$), widely used in magnetic recording
technology. The model describes the effect of dynamical, local orbital
correlations arising from local quantum chemistry of the material. A finite
temperature solution of the model in $d=\infty$ provides a natural explanation
of the optical response, photoemission, resistivity and the large Woods-Saxon
ratio observed in experiments. Our study confirms the important role of many
body dynamical correlation effects for a proper understanding of the metallic
phase of $CrO_{2}$.",0101335v1
2001-02-11,Antiferromagnetic Interlayer Coupling in Ferromagnetic Semiconductor EuS/PbS(001) Superlattices,"Antiferromagnetic coupling between ferromagnetic layers has been observed for
the first time in all-semiconductor superlattice structure EuS/PbS(001), by
neutron scattering and magnetization measurements. Spin-dependent superlattice
band structure effects are invoked to explain the possible origin and the
strength of the observed coupling.",0102194v2
2001-02-14,Nagaoka ferromagnetism in the two-dimensional infinite-U Hubbard model,"We present different numerical calculations based on variational quantum
Monte Carlo simulations supporting a ferromagnetic ground-state for finite and
small hole densities in the two-dimensional infinite-$U$ Hubbard model.
Moreover, by studying the energies of different total spin sectors, these
calculations strongly suggest that the paramagnetic phase is unstable against a
phase with a partial polarization for large hole densities $\delta \sim 0.40$
with evidence for a second-order transition to the paramagnetic large doping
phase.",0102249v1
2001-02-26,Dynamical Properties in the Bilayer Quantum Hall Ferromagnet,"The spectral functions of the pseudospin correlation functions in the bilayer
quantum Hall system at \nu=1 are investigated numerically, where the pseudospin
describes the layer degrees of freedom. In the pseudospin-ferromagnetic phase,
the lowest-energy excitation branch is closely connected with the ground state
through the fluctuations of pseudospin S_y and S_z, and it plays a significant
role on the tunneling properties in this system. For the system with very small
tunneling amplitude and layer separation smaller than the critical one, the
system-size dependence of calculated spectral function A_{y z} suggests the
superfluidity on the tunneling current in the absence of impurities.",0102476v1
2001-03-05,"Theory of Magnetic Properties and Spin-Wave Dispersion for Ferromagnetic (Ga,Mn)As","We present a microscopic theory of the long-wavelength magnetic properties of
the ferromagnetic diluted magnetic semiconductor (Ga,Mn)As. Details of the host
semiconductor band structure, described by a six-band Kohn-Luttinger
Hamiltonian, are taken into account. We relate our quantum-mechanical
calculation to the classical micromagnetic energy functional and determine
anisotropy energies and exchange constants. We find that the exchange constant
is substantially enhanced compared to the case of a parabolic heavy-hole-band
model.",0103116v2
2001-03-06,Short-time dynamics of random-bond Potts ferromagnet with continuous self-dual quenched disorders,"We present Monte Carlo simulation results of random-bond Potts ferromagnet
with the Olson-Young self-dual distribution of quenched disorders in
two-dimensions. By exploring the short-time scaling dynamics, we find universal
power-law critical behavior of the magnetization and Binder cumulant at the
critical point, and thus obtain estimates of the dynamic exponent $z$ and
magnetic exponent $\eta$, as well as the exponent $\theta$. Our special
attention is paid to the dynamic process for the $q$=8 Potts model.",0103130v1
2001-03-16,Critical dynamics and universality of the random-bond Potts ferromagnet with tri-distributed quenched disorders,"Critical behavior in short-time dynamics is investigated by a Monte Carlo
study for the random-bond Potts ferromagnet with a trinary distribution of
quenched disorders on two-dimensional triangular lattices. The dynamic scaling
is verified and applied to estimate critical exponents $\theta$, $z$ and
$\beta/\nu$ for several realizations of the trinary distribution. Our critical
scaling analysis strongly indicates that the bond randomness influences the
critical universality.",0103355v2
2001-03-30,A Model for Ferromagnetic Nanograins with Discrete Electronic States,"We propose a simple phenomenological model for an ultrasmall ferromagnetic
grain, formulated in terms of the grain's discrete energy levels. We compare
the model's predictions with recent measurements of the discrete tunneling
spectrum through such a grain. The model can qualitatively account for the
observed features if we assume (i) that the anisotropy energy varies among
different eigenstates of one grain, and (ii) that nonequilibrium spin
accumulation occurs.",0103626v1
2001-04-18,Resistance spikes and domain wall loops in Ising quantum Hall ferromagnets,"We explain the recent observation of resistance spikes and hysteretic
transport properties in Ising quantum Hall ferromagnets in terms of the unique
physics of their domain walls. Self-consistent RPA/Hartree-Fock theory is
applied to microscopically determine properties of the ground state and
domain-wall excitations. In these systems domain wall loops support
one-dimensional electron systems with an effective mass comparable to the bare
electron mass and may carry charge. Our theory is able to account
quantitatively for the experimental Ising critical temperature and to explain
characteristics of the resistive hysteresis loops.",0104334v1
2001-05-01,Storage Capacity of Two-dimensional Neural Networks,"We investigate the maximum number of embedded patterns in the two-dimensional
Hopfield model. The grand state energies of two specific network states,
namely, the energies of the pure-ferromagnetic state and the state of specific
one stored pattern are calculated exactly in terms of the correlation function
of the ferromagnetic Ising model. We also investigate the energy landscape
around them by computer simulations. Taking into account the qualitative
features of the phase diagrams obtained by Nishimori, Whyte and Sherrington
[Phys. Rev. E {\bf 51}, 3628 (1995)], we conclude that the network cannot
retrieve more than three patterns.",0105008v2
2001-05-03,Freezing in random graph ferromagnets,"Using T=0 Monte Carlo and simulated annealing simulation, we study the energy
relaxation of ferromagnetic Ising and Potts models on random graphs. In
addition to the expected exponential decay to a zero energy ground state, a
range of connectivities for which there is power law relaxation and freezing to
a metastable state is found. For some connectivities this freezing persists
even using simulated annealing to find the ground state. The freezing is caused
by dynamic frustration in the graphs, and is a feature of the local
search-nature of the Monte Carlo dynamics used. The implications of the
freezing on agent-based complex systems models are briefly considered.",0105061v2
2001-05-09,Hot Electron Magnetotransport in a Spin-Valve Transistor at Finite temperatures,"The hot electron magnetotransport in a spin-valve transistor has been
theoretically explored at finite temperatures. We have explored the parallel
and anti-parallel collector current changing the relative spin orientation of
the ferromagnetic layers at finite temperatures. In this model calculations,
hot electron energy redistribution due to spatial inhomogeneity of Schottky
barrier heights and hot electron spin polarization in the ferromagnetic layer
at finite temperatures have been taken into account. The results of this model
calculations accord with the experimental data semi-quantitative manner. We
therefore suggest that both effects remarked above should be taken into account
substantially when one explores the hot electron magnetotransport in a
spin-valve system transistor at finite temperatures.",0105190v1
2001-05-12,Weak Ferromagnetism and Excitonic Condensates,"We investigate a model of excitonic ordering (i.e electron-hole pair
condensation) appropriate for the divalent hexaborides. We show that the
inclusion of imperfectly nested electron hole Fermi surfaces can lead to the
formation of an undoped excitonic metal phase. In addition, we find that weak
ferromagnetism with compensated moments arises as a result of gapless
excitations. We study the effect of the low lying excitations on the density of
states, Fermi surface topology and optical conductivity and compare to
available experimental data.",0105245v1
2001-05-17,Rhodium Doped Manganites : Ferromagnetism and Metallicity,"The possibility to induce ferromagnetism and insulator to metal transitions
in small A site cation manganites Ln_{1-x}Ca_xMnO_3 by rhodium doping is shown
for the first time. Colossal magnetoresistance (CMR) properties are evidenced
for a large compositional range (0.35 \leq x < 0.60). The ability of rhodium to
induce such properties is compared to the results obtained by chromium and
ruthenium doping. Models are proposed to explain this behavior.",0105347v1
2001-05-24,Shapes and textures of ferromagnetic liquid droplets,"Theoretical calculations, computer simulations and experiments indicate the
possible existence of a ferromagnetic liquid state. Should such a state exist,
demagnetization effects would force a nontrivial magnetization texture governed
by the shape of the liquid droplet. Since liquid droplets are deformable, the
droplet shape couples to the magnetization texture. This paper solves the joint
shape/texture problem subject to the assumption of cylindrical droplet
symmetry. The shape undergoes a change in topology from spherical to toroidal
as exchange energy grows or surface tension decreases.",0105467v2
2001-06-05,Emptiness Formation Probability for the One-Dimensional Isotropic XY Model,"We study a correlation function for the one-dimensional isotropic ${XY}$
model (${XX0}$ model), which is called the Emptiness Formation Probability
(EFP). It is the probability of the formation of a ferromagnetic string in the
anti-ferromagnetic ground state. Using the expression of the EFP as a Toeplitz
determinant, we discuss its asymptotic behaviors. We also compare the
analytical results with numerical calculations as the density-matrix
renormalization group and the quantum Monte-Carlo method.",0106062v2
2001-06-14,Non-equilibrium Relaxation Study of Ferromagnetic Transition in Double-Exchange Systems,"Ferromagnetic transition in double-exchange systems is studied by
non-equilibrium relaxation technique combined with Monte Carlo calculations.
Critical temperature and critical exponents are estimated from relaxation of
the magnetic moment. The results are consistent with the previous Monte Carlo
results in thermal equilibrium. The exponents estimated by these independent
techniques suggest that the universality class of this transition is the same
as that of short-range interaction models but is different from the mean-field
one.",0106266v1
2001-06-19,Crystallographic structure of ultrathin Fe films on Cu(100),"We report bcc-like crystal structures in 2-4 ML Fe films grown on fcc Cu(100)
using scanning tunneling microscopy. The local bcc structure provides a
straightforward explanation for their frequently reported outstanding magnetic
properties, i.e., ferromagnetic ordering in all layers with a Curie temperature
above 300 K. The non-pseudomorphic structure, which becomes pseudomorphic above
4 ML film thickness is unexpected in terms of conventional rules of thin film
growth and stresses the importance of finite thickness effects in ferromagnetic
ultrathin films.",0106370v1
2001-06-28,Superconductivity Near Ferromagnetism in MgCNi3,"An unusual quasi-two-dimensional heavy band mass van Hove singularity (vHs)
lies very near the Fermi energy in MgCNi3, recently reported to superconduct at
8.5 K. This compound is strongly exchange enhanced and is unstable to
ferromagnetism upon hole doping with 12% Mg --> Na or Li. The 1/4-depleted fcc
(frustrated) Ni sublattice and lack of Fermi surface nesting argues against
competing antiferromagnetic and charge density wave instabilities. We identify
an essentially infinite mass along the M-Gamma line, leading to
quasi-two-dimensionality of this vHs may promote unconventional p-wave pairing
that could coexist with superconductivity.",0106583v1
2001-07-03,Random phase approximation for multi-band Hubbard models,"We derive the random-phase approximation for spin excitations in general
multi-band Hubbard models, starting from a collinear ferromagnetic Hartree-Fock
ground state. The results are compared with those of a recently introduced
variational many-body approach to spin-waves in itinerant ferromagnets. As we
exemplify for Hubbard models with one and two bands, the two approaches lead to
qualitatively different results. The discrepancies can be traced back to the
fact that the Hartree-Fock theory fails to describe properly the local moments
which naturally arise in a correlated-electron theory.",0107050v1
2001-07-03,Persistence in One-dimensional Ising Models with Parallel Dynamics,"We study persistence in one-dimensional ferromagnetic and anti-ferromagnetic
nearest-neighbor Ising models with parallel dynamics. The probability P(t) that
a given spin has not flipped up to time t, when the system evolves from an
initial random configuration, decays as P(t) \sim 1/t^theta_p with theta_p
\simeq 0.75 numerically. A mapping to the dynamics of two decoupled A+A \to 0
models yields theta_p = 3/4 exactly. A finite size scaling analysis clarifies
the nature of dynamical scaling in the distribution of persistent sites
obtained under this dynamics.",0107053v1
2001-07-05,Magnetization in quasiperiodic magnetic multilayers with biquadratic exchange and uniaxial anisotropy,"A theoretical study is made of the magnetization versus applied field curves
of ferromagnetic/nonmagnetic multilayers constructed according to a Fibonacci
quasiperiodic sequence. The ferromagnetic films are assumed to have uniaxial
anisotropy and are coupled by both bilinear and biquadratic effective exchange.
The effects of quasiperiodicity in the magnetic phases are illustrated
numerically for Fe/Cr systems.",0107127v1
2001-07-12,Theory of Angular Magnetoresistance in CPP spin valves,"The resistance of CPP spin valve is a continuous function of the angle
$\theta $ between the magnetizations of both ferromagnets. We use the cicuit
theory for non-collinear magnetoelectronics to compute the angular
magnetoresistance of CPP spin valves taking the spin accumulation in the
ferromagnetic layers into account.",0107250v1
2001-07-27,"Noncollinear Ferromagnetism in (III,Mn)V Semiconductors","We investigate the stability of the collinear ferromagnetic state in kinetic
exchange models for (III,Mn)V semiconductors with randomly distributed Mn ions
>. Our results suggest that {\em noncollinear ferromagnetism} is commom to
these semiconductor systems. The instability of the collinear state is due to
long-ranged fluctuations invloving a large fraction of the localized magnetic
moments. We address conditions that favor the occurrence of noncollinear
groundstates and discuss unusual behavior that we predict for the temperature
and field dependence of its saturation magnetization.",0107573v2
2001-07-28,Ferromagnetic-spin glass transition in four-dimensional random-bond Ising model,"The four-dimensional +-J random-bond Ising model is studied using
ground-state calculations. System sizes up to N=6^4 spins are considered. Here
it is found that the ferromagnetic-spin glass transition occurs at a critical
concentration p_c=0.28(1) of the antiferromagnetic bonds, which is comparable
to values found previously by high-temperature series expansions. The
transition is characterized by a correlation-length exponent \nu=1.0(1) and an
order-parameter exponent \beta=0.4(1). Thus, this transition is in a different
universality class from four-dimensional bond percolation, where \nu=0.678(50)
and \beta=0.639(20).",0107583v1
2001-07-30,Spin Torques in Ferromagnetic/Normal Metal Structures,"Recent theories of spin-current-induced magnetization reversal are formulated
in terms of a spin-mixing conductance $G^{mix}$. We evaluate $G^{mix}$ from
first-principles for a number of (dis)ordered interfaces between magnetic and
non-magnetic materials. In multi-terminal devices, the magnetization direction
of a one side of a tunnel junction or a ferromagnetic insulator can ideally be
switched with negligible charge current dissipation.",0107589v1
2001-08-01,Correlation between magnetic and transport properties of phase separated La$_{0.5}$Ca$_{0.5}$MnO$_{3}$,"The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.",0108026v2
2001-08-07,Fictitious fluxes in doped antiferromagnets,"In a tight binding model of charged spin-1/2 electrons on a square lattice, a
fully polarized ferromagnetic spin configuration generates an apparent U(1)
flux given by $2\pi$ times the skyrmion charge density of the ferromagnetic
order parameter. We show here that for an antiferromagnet, there are two
``fictitious'' magnetic fields, one staggered and one unstaggered. The
staggered topological flux per unit cell can be varied between
$-\pi\le\Phi\le\pi$ with a negligible change in the value of the effective
nearest neighbor coupling constant whereas the magnitude of the unstaggered
flux is strongly coupled to the magnitude of the second neighbor effective
coupling.",0108113v1
2001-08-20,Magnetic Field Scaling of the Conductance of Epitaxial Cuprate-Manganite Bilayers,"Conductance-voltage characteristics of epitaxial interfaces between oxide
ferromagnets and oxide superconductors have been measured as a function of
temperature and magnetic field. Their functional form is similar to that
predicted by theories of transport across nearly transparent contacts between
highly spin-polarized ferromagnets and d-wave superconductors. However, their
magnetic field dependencies scale in striking and unusual ways, challenging our
current understanding. Existing theories fail to account for apparent
nonequilibium effects that are natural for spin injection in such geometries.",0108313v1
2001-08-29,Magnetic Semiconductors are Frustrated Ferromagnets,"Starting from microscopic and symmetry considerations, we derive the
Hamiltonian describing the exchange interaction between the localized Mn spins
and the valence band holes in $Ga_{1-x}Mn_x As$. We find that due to the strong
spin-orbit coupling in the valence band, this exchange interaction has a rather
complex structure and generates a highly anisotropic effective interaction
between the Mn spins. The corresponding ground state has a finite ferromagnetic
magnetization but is intrinsically spin-disordered even at zero temperature.",0108477v1
2001-09-04,Proteinlike behavior of a spin system near the transition between ferromagnet and spin glass,"A simple spin system is studied as an analog for proteins. We investigate how
the introduction of randomness and frustration into the system effects the
designability and stability of ground state configurations. We observe that the
spin system exhibits protein-like behavior in the vicinity of the transition
between ferromagnet and spin glass.
  Our results illuminate some guiding principles in protein evolution.",0109044v1
2001-09-12,Dynamic Monte Carlo Simulations for a Square-Lattice Ising Ferromagnet with a Phonon Heat Bath,"We derive a direct connection between Monte Carlo time and physical time in
terms of physical parameters, using a quantum Hamiltonian with a
$d$-dimensional phonon heat bath interacting with a square-lattice Ising
ferromagnet. Based on the calculated transition rates, we perform dynamic Monte
Carlo simulations using absorbing Markov chains to measure the lifetimes of the
metastable state at low temperatures. We also calculate the lifetimes
analytically using absorbing Markov chains. The phonon dynamic gives
field-dependent prefactors in the lifetimes at low temperatures, that are
different from the piecewise field-independent prefactors obtained from the
Glauber dynamic.",0109214v1
2001-09-14,Singular Effects of Impurities near the Ferromagnetic Quantum-Critical Point,"Systematic theoretical results for the effects of a dilute concentration of
magnetic impurities on the thermodynamic and transport properties in the region
around the quantum critical point of a ferromagnetic transition are obtained.
In the quasi-classical regime, the dynamical spin fluctuations enhance the
Kondo temperature. This energy scale decreases rapidly in the quantum
fluctuation regime, where the properties are those of a line of critical points
of the multichannel Kondo problem with the number of channels increasing as the
critical point is approached, except at unattainably low temperatures where a
single channel wins out.",0109276v2
2001-10-02,Global phase diagram of bilayer quantum Hall ferromagnets,"We present a microscopic study of the interlayer spacing d versus in-plane
magnetic field $B_\parallel$ phase diagram for bilayer quantum Hall (QH)
pseudo-ferromagnets. In addition to the interlayer charge balanced commensurate
and incommensurate states analyzed previously, we address the corresponding
interlayer charge unbalanced ""canted"" QH states. We predict a large anomaly in
the bilayer capacitance at the canting transition and the formation of dipole
stripe domains with periods exceeding 1 micron in the canted state.",0110049v1
2001-10-11,Electrical Spin Injection in a Ferromagnetic / Tunnel Barrier/ Semiconductor Heterostructure,"We demonstrate experimentally the electrical ballistic electron spin
injection from a ferromagnetic metal / tunnel barrier contact into a
semiconductor III-V heterostructure. We introduce the Oblique Hanle Effect
technique for reliable optical measurement of the degree of injected spin
polarization. In a CoFe / Al2O3 / GaAs / (Al,Ga)As heterostructure we observed
injected spin polarization in excess of 8 % at 80K.",0110240v1
2001-10-16,"Spin Waves, Phase Separation, and Interphase Boundaries in Double Exchange Magnets","We study a classical double exchange magnet with direct antiferromagnetic
superexchange coupling, J, between the localized spins. It is shown that the
de-stabilization of the ferromagnetic ground state with increasing J leads to
phase separation; the latter always preempts the spin-wave instability
(softening of the magnon spectrum). It is also found that the boundaries
separating the ferromagnetic and antiferromagnetic areas of the sample tend to
be abrupt.",0110322v2
2001-10-19,Magnetic properties of 3d-impurities substituted in GaAs,"We have calculated the magnetic properties of substituted 3d-impurities
(Cr-Ni) in a GaAs host by means of first principles electronic structure
calculations. We provide a novel model explaining the ferromagnetic long rang
order of III-V dilute magnetic semiconductors. The origin of the ferromagnetism
is shown to be due to delocalized spin-uncompensated As dangling bond
electrons. Besides the quantitative prediction of the magnetic moments, our
model provides an understanding of the halfmetallicity, and the raise of the
critical temperature with the impurity concentration.",0110405v1
2001-10-22,Anisotropic spin and charge transport in Rashba Hamiltonian,"We explore spin and charge transport phenomena in two dimensional electron
gas in presence of Rashba spin-orbit coupling connected to two ideal
Ferromagnetic leads. In particular we show through a combination of analytical
and numerical calculation that the spin polarization which is transported
depends on the Magnetization direction of ferromagnet even if the magnetization
of both FM's are parallel.Conductance is also shown to be anisotropic. These
anisotrpies present in spin and charge transport are a consequence of breaking
of rotational invariance due to Rashba spin-orbit interaction and are present
irrespective of the Hamiltonian considered being an effective mass Hamiltonian
or tight binding model Hamiltonian.",0110440v1
2001-10-22,Total Energy Studies for Ferromagnetic Nickel: What is the Optimum Combination of the Multi-band Gutzwiller Method and Density Functional Theory?,"The multi-band Gutzwiller method, combined with calculations based on density
functional theory, is employed to study total energy curves of the
ferromagnetic ground state of Ni. A new method is presented which allows flow
of charge between d and s, p type orbitals in an approximate way. Further it is
emphasized that the missing repulsive contribution to the total energy at large
magnetic moments can be estimated from an analysis of specific DFT
calculations.",0110450v1
2001-10-22,Dimensional crossover and driven interfaces in disordered ferromagnets,"We study the depinning transition of driven interfaces in thin ferromagnetic
films driven by external magnetic fields. Approaching the transition point the
correlation length increases with decreasing driving. If the correlation length
becomes of the order of the film thickness a crossover to two dimensional
behavior occurs. From the corresponding scaling analysis we determine the
exponents characterizing the transition of the three dimensional system.",0110456v1
2001-10-22,First-principles study of band offsets in ferromagnetic semiconductor heterojunctions,"We report valence and conduction band alignments and offsets for
heterojunctions between CdCr2Se4, an n-type ferromagnetic semiconductor, and
the non-magnetic materials Si and GaAs, evaluated using density functional
theory. We explore numerically the impact of different interface features on
the type of band alignment and the magnitude of the offsets. For example, we
find it is energetically favorable to deplete Cr atoms from the layers at the
interface; this also leads to band alignments smaller in magnitude compared to
those obtained for Cr-rich interfaces and ideal for electrical spin-injection
into either Si or Ga-terminated GaAs substrates.",0110474v1
2001-10-24,Topological Nature of Anomalous Hall Effect in Ferromagnet,"The anomalous Hall effect in two-dimensional ferromagnets is discussed to be
the physical realization of the parity anomaly in (2+1)D, and the band crossing
points behave as the topological singularity in the Brillouin zone. This
appears as the sharp peaks and the sign changes of the transverse conductance
$\sigma_{xy}$ as a function of the Fermi energy and/or the magnetization. The
relevance to the experiments including the three dimensional systems is also
discussed.",0110504v1
2001-11-03,"Mean-field approach to ferromagnetism in (III,Mn)V diluted magnetic semiconductors at low carrier densities","We present a detailed study, within the mean-field approximation, of an
impurity band model for III-V diluted magnetic semiconductors. Such a model
should be relevant at low carrier densities, below and near the metal-insulator
transition. Positional disorder of the magnetic impurities inside the host
semiconductor is shown to have observable consequences for the shape of the
magnetization curve. Below the critical temperature the magnetization is
spatially inhomogeneous, leading to very unusual temperature dependence of the
average magnetization as well as specific heat. Disorder is also found to
enhance the ferromagnetic transition temperature. Unusual spin and charge
transport is implied.",0111045v1
2001-11-26,Ferromagnetic transition in a double-exchange system containing impurities in the Dynamical Mean Field Approximation,"We formulate the Dynamical Mean Field Approximation equations for the
double-exchange system with quenched disorder for arbitrary relation between
Hund exchange coupling and electron band width. Close to the
ferromagnetic-paramagnetic transition point the DMFA equations can be reduced
to the ordinary mean field equation of Curie-Weiss type. We solve the equation
to find the transition temperature and present the magnetic phase diagram of
the system.",0111491v4
2001-11-29,Positive cross-correlations induced by ferromagnetic contacts,"Due to the Fermionic nature of carriers, correlations between electric
currents flowing through two different contacts attached to a conductor present
a negative sign. Possibility for positive cross-correlations has been
demonstrated in hybrid normal/superconductor structures under certain
conditions. In this paper we show that positive cross-correlations can be
induced, if not already present, in such structures by employing ferromagnetic
leads with magnetizations aligned anti-parallel to each other. We consider
three-terminal hybrid structures and calculate the mean-square correlations of
current fluctuations as a function of the bias voltage at finite temperature.",0111564v2
2001-12-11,Conductance of Rashba spin-split systems with ferromagnetic contacts,"We study theoretically the conductance of heterostructures with ferromagnetic
conductors (F) and a two dimensional electron gas with Rashba spin-orbit
interaction (R) using the Landauer-B\""{u}ttiker formalism. Assuming a
one-dimensional model, we first find the $S$-matrix for the FR interface. This
result is then applied to different devices such as a FRF structure, first
suggested by Datta and Das[Appl. Phys. Lett. 56, 665 (1990)]. We find analytic
results for the conductance for the case of collinear magnetization.",0112175v1
2001-12-13,Magnon softening and damping in the ferromagnetic manganites due to orbital correlations,"We present a theory for spin excitations in ferromagnetic metallic manganites
and demonstrate that orbital fluctuations have strong effects on the magnon
dynamics in the case these compounds are close to a transition to an orbital
ordered state. In particular we show that the scattering of the spin
excitations by low-lying orbital modes with cubic symmetry causes both the
magnon softening and damping observed experimentally.",0112252v2
2001-12-17,Ferromagnetic Phase Transition in Barabasi-Albert Networks,"Ising spins put onto a Barabasi-Albert scale-free network show an effective
phase transition from ferromagnetism to paramagnetism upon heating, with an
effective critical temperature increasing as the logarithm of the system size.
Starting with all spins up and upon equilibration pinning the few
most-connected spins down nucleates the phase with most of the spins down.",0112312v1
2001-12-18,"Spins, charges and currents at Domain Walls in a Quantum Hall Ising Ferromagnet","We study spin textures in a quantum Hall Ising ferromagnet. Domain walls
between ferro and unpolarized states at $\nu=2$ are analyzed with a functional
theory supported by a microscopic calculation. In a neutral wall, Hartree
repulsion prevents the appearance of a fan phase provoked by a negative
stiffness. For a charged system, electrons become trapped as solitons at the
domain wall. The size and energy of the solitons are determined by both Hartree
and spin-orbit interactions. Finally, we discuss how electrical transport takes
place through the domain wall.",0112334v3
2001-12-20,Ferromagnetic and antiferromagnetic spin fluctuations and superconductivity in the hcp-phase of Fe,"High purity iron, which transforms into the hcp phase under pressure, has
recently been reported to be superconducing in the pressure range 150-300 kBar
[shim]. The electronic structure and the electron-phonon coupling
($\lambda_{ph}$) are calculated for hcp iron at different volumes. A
parameter-free theory for calculating the coupling constants $\lambda_{sf}$
from ferromagnetic (FM) and antiferromagnetic (AFM) spin fluctuations is
developed. The calculated $\lambda_{sf}$ are sufficiently large to explain
superconductivity especially from FM fluctuations. The results indicate that
superconductivity mediated by spin fluctuations is more likely than from
electron-phonon interaction.",0112382v1
2001-12-21,Theory of Ferromagnetism in Doped Excitonic Condensates,"Nesting in a semimetal can lead to an excitonic insulator state with
spontaneous coherence between conduction and valence bands and a gap for
charged excitations. In this paper we present a theory of the ferromagnetic
state that occurs when the density of electrons in the conduction band and
holes in the valence band differ. We find an unexpectedly rich doping-field
phase diagram and an unusual collective excitation spectrum that includes two
gapless collective modes. We predict regions of doping and external field in
which phase-separated condensates of electrons and holes with parallel spins
and opposing spins coexist.",0112420v1
2001-12-26,Spin-polarized tunneling in ferromagnetic double barrier junctions,"Spin-polarized tunneling in FMS/M/FMS double tunnel junctions where FMSs are
ferromagnetic semiconductor layers and M is a metal spacer is studied
theoretically within the single-site coherent potential approximation (CPA).
The exchange interaction between a conduction electron and localized moment of
the magnetic ion is treated in the framework of the s-f model. The spin
polarization in the FMS layers is observed to oscillates as a function of the
number of atomic planes in the spacer layer. Amplitude of these oscillations
decreases with increasing the exchange interaction in FMS layers.",0112464v1
2002-01-09,Mean-field model of the ferromagnetic ordering in the superconducting phase of ErNi_2B_2C,"A mean-field model explaining most of the details in the magnetic phase
diagram of ErNi_2B_2C is presented. The low-temperature magnetic properties are
found to be dominated by the appearance of long-period commensurate structures.
The stable structure at low temperatures and zero field is found to have a
period of 40 layers along the a direction, and upon cooling it undergoes a
first-order transition at T_C = 2.3 K to a different 40-layered structure
having a net ferromagnetic component of about 0.4 mu_B/Er. The
neutron-diffraction patterns predicted by the two 40-layered structures, above
and below T_C, are in agreement with the observations of Choi et al.",0201133v1
2002-01-16,Why ferromagnetic semiconductors?,"Rapid development of information technologies originates from the exponential
increase in the density of information that can be processed, stored, and
transfer by the unit area of relevant devices. There is, however, a growing
amount of evidences that the progress achieved in this way approaches its
limits. Various novel ideas put forward to circumvent barriers ahead are
described. Particular attention is paid to those concepts which propose to
exploit electron or nuclear spins as the information carriers. Here,
ferromagnetic semiconductors of III-V or II-VI compounds containing a sizable
concentration of transition metals appear as outstanding spintronic materials.",0201279v1
2002-01-18,Electrons in a ferromagnetic metal with a domain wall,"We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.",0201338v1
2002-01-23,"Correlated defects, metal-insulator transition, and magnetic order in ferromagnetic semiconductors","The effect of disorder on transport and magnetization in ferromagnetic III-V
semiconductors, in particular (Ga,Mn)As, is studied theoretically. We show that
Coulomb-induced correlations of the defect positions are crucial for the
transport and magnetic properties of these highly compensated materials. We
employ Monte Carlo simulations to obtain the correlated defect distributions.
Exact diagonalization gives reasonable results for the spectrum of valence-band
holes and the metal-insulator transition only for correlated disorder. Finally,
we show that the mean-field magnetization also depends crucially on defect
correlations.",0201411v2
2002-02-01,Nonlinear spin-polarized transport through a ferromagnetic domain wall,"A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.",0202002v1
2002-02-04,Coexistence of spin-triplet superconductivity and ferromagnetism induced by the local Hund's rule exchange,"We characterize the coexistence of itinerant ferromagnetism and spin-triplet
superconductivity within a single mechanism involving local (Hund's rule)
exchange among $d$ electrons. The ratio of transition temperatures and the spin
anisotropy of the superconducting gap is estimated for $ZrZn_2$. The $A$ phase
is stable in very low applied and molecular fields, whereas the $A1$ phases
persists in higher fields. A small residual magnetic moment is present below
the Stoner threshold in the superconducting phase.",0202043v1
2002-02-14,Orbital Zeeman effect: Signature of a massive spin wave mode in ferromagnetism,"By deriving the quantum hydrodynamic equations for an isotropic single-band
ferromagnet in an arbitrary magnetic field, we find that a massive mode
recently predicted splits under the action of the field. The splitting is a
peculiarity of charged fermions and is linear in the field to leading order in
$q$ bearing resemblance to the Zeeman effect in this limit, and providing a
clear signature for the experimental observation of this mode.",0202225v1
2002-02-26,Enhanced Granular Magnetoresistance due to Ferromagnetic Layers,"Giant magnetoresistance (GMR) of sequentially evaporated Fe-Ag structures
have been investigated. Direct experimental evidence is given that inserting
ferromagnetic layers into a granular structure significantly enhances the
magnetoresistance. The increase of the GMR effect is attributed to spin
polarization effects. The large enhancement (up to more than a fourfold value)
and the linear variation of the GMR in low magnetic fields are explained by
scattering of the spin polarized conduction electrons on paramagnetic grains.",0202464v1
2002-02-28,Anisotropy of ultra-thin ferromagnetic films and the spin reorientation transition,"The influence of uniaxial anisotropy and the dipole interaction on the
direction of the magnetization of ultra-thin ferromagnetic films in the
ground-state is studied. The ground-state energy can be expressed in terms of
anisotropy constants which are calculated in detail as function of the system
parameters and the film thickness. In particular non-collinear spin
arrangements are taken into account. Conditions for the appearance of a spin
reorientation transition are given and analytic results for the width of the
canted phase and its shift in applied magnetic fields associated with this
transition are derived.",0202534v1
2002-03-12,Tunnel magnetoresistance and interfacial electronic state,"We study the relation between tunnel magnetoresistance (TMR) and interfacial
electronic states modified by magnetic impurities introduced at the interface
of the ferromagnetic tunnel junctions, by making use of the periodic Anderson
model and the linear response theory. It is indicated that the TMR ratio is
strongly reduced depending on the position of the $d$-levels of impurities,
based on reduction in the spin-dependent $s$-electron tunneling in the majority
spin state. The results are compared with experimental results for Cr-dusted
ferromagnetic tunnel junctions, and also with results for metallic multilayers
for which similar reduction in giant magnetoresistance has been reported.",0203247v1
2002-03-13,Ferromagnetic imprinting of spin polarization in a semiconductor,"We present a theory of the imprinting of the electron spin coherence and
population in an n-doped semiconductor which forms a junction with a
ferromagnet. The reflection of non-equilibrium semiconductor electrons at the
interface provides a mechanism to manipulate the spin polarization vector. In
the case of unpolarized excitation, this ballistic effect produces spontaneous
electron spin coherence and nuclear polarization in the semiconductor, as
recently observed by time-resolved Faraday rotation experiments. We investigate
the dependence of the spin reflection on the Schottky barrier height and the
doping concentration in the semiconductor and suggest control mechanisms for
possible device applications.",0203285v1
2002-03-18,Ultra-efficient Cooling in Ferromagnet-Superconductor Microrefrigerators,"A promising scheme for electron microrefrigeration based on
ferromagnet-superconductor contacts is presented. In this setup, cooling power
densities up to 600 nW/$\mu$m$^2$ can be achieved leading to electronic
temperature reductions largely exceeding those obtained with existing
superconductor-normal metal tunnel contacts. Half-metallic CrO$_2$/Al bilayers
are indicated as ideal candidates for the implementation of the device.",0203355v1
2002-04-05,Mesoscopic effects in superconductor-ferromagnet-superconductor junctions,"We show that at zero temperature the supercurrent through the superconductor
- ferromagnetic metal - superconductor junctions does not decay exponentially
with the thickness $L$ of the junction. At large $L$ it has a random
sample-specific sign which can change with a change in temperature. In the case
of mesoscopic junctions the phase of the order parameter in the ground state is
a random sample-specific quantity. In the case of junctions of large area the
ground state phase difference is $\pm \pi/2$.",0204123v1
2002-04-05,Atomic correlations in itinerant ferromagnets: quasi-particle bands of nickel,"We measure the band structure of nickel along various high-symmetry lines of
the bulk Brillouin zone with angle-resolved photoelectron spectroscopy. The
Gutzwiller theory for a nine-band Hubbard model whose tight-binding parameters
are obtained from non-magnetic density-functional theory resolves most of the
long-standing discrepancies between experiment and theory on nickel. Thereby we
support the view of itinerant ferromagnetism as induced by atomic correlations.",0204142v1
2002-04-21,Mean field solution of the Ising model on a Barabasi-Albert network,"The mean field solution of the Ising model on a Barabasi-Albert scale-free
network with ferromagnetic coupling between linked spins is presented. The
critical temperature $T_c$ for the ferromagnetic to paramagnetic phase
transition (Curie temperature) is infinite and the effective critical
temperature for a finite size system increases as the logarithm of the system
size in agreement with recent numerical results of Aleksiejuk, Holyst and
Stauffer.",0204455v4
2002-04-25,Nonsinusoidal current-phase relation in SFS Josephson junctions,"Various types of the current-phase relation I(phi) in
superconductor-ferromagnet-superconductor (SFS) point contacts and planar
double-barrier junctions are studied within the quasiclassical theory in the
limit of thin diffusive ferromagnetic interlayers. The physical mechanisms
leading to highly nontrivial I(phi) dependence are identified by studying the
spectral supercurrent density. These mechanisms are also responsible for the
0-pi transition in SFS Josephson junctions.",0204568v2
2002-05-13,Effect of Subband Landau Level Coupling to the Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet,"In a recent experiment (Phys. Rev. Lett. {\bf 87}, 036903 (2001)), Spielman
et al observed a linearly dispersing collective mode in quantum Hall
ferromagnet. While it qualitatively agrees with the Goldstone mode dispersion
at small wave vector, the experimental mode velocity is slower than that
calculated by previous theories by a factor about 0.55. A better agreement with
the experimental data may possibly be achieved by taking the subband Landau
level coupling into account due to the finiteness of the layer thickness. A
novel coupling of quantum fluctuation to the tunneling is briefly discussed.",0205250v2
2002-05-22,Universal angular magnetoresistance and spin torque in ferromagnetic/normal metal hybrids,"The electrical resistance of ferromagnetic/normal-metal (F/N)
heterostructures depends on the nature of the junctions which may be tunnel
barriers, point contacts, or intermetallic interfaces. For all junction types,
the resistance of disordered F/N/F perpendicular spin valves as a function of
the angle between magnetization vectors is shown to obey a simple universal
law. The spin-current induced magnetization torque can be measured by the
angular magnetoresistance of these spin valves. The results are generalized to
arbitrary magnetoelectronic circuits.",0205453v1
2002-05-23,Magnetic-domain-controlled vortex pinning in a superconductor/ferromagnet bilayer,"Vortex pinning in a type-II superconducting Pb film covering a Co/Pt
multilayer with perpendicular magnetic anisotropy is investigated. Different
stable magnetic domain patterns like band and bubble domains can be created in
the Co/Pt multilayer, clearly influencing the vortex pinning in the
superconducting Pb layer. Most effective pinning is observed for the bubble
domain state. We demonstrate that the pinning properties of the
superconductor/ferromagnet bilayer can be controlled by tuning the size,
density and magnetization direction of the bubbles.",0205470v1
2002-06-01,From classical to quantum spintronics: Theory of coherent spin injection and spin valve phenomena,"We present a theory of coherent quantum transport in ferromagnetic/
non-magnetic/ ferromagnetic heterojunctions. We predict quantum coherence to
give rise to a quantum spin valve effect that, unlike its familiar classical
analog, occurs even in the absence of a net spin current through the
heterostructure. Thus the relationship between spin and charge transport is
qualitatively different in the presence of quantum interference than in the
(semi)classical regime. This has important implications for the design of
quantum coherent spintronic devices and the interpretation of experiments.",0206009v1
2002-06-24,Derivatives and inequalities for order parameters in the Ising spin glass,"Identities and inequalities are proved for the order parameters, correlation
functions and their derivatives of the Ising spin glass. The results serve as
additional evidence that the ferromagnetic phase is composed of two regions,
one with strong ferromagnetic ordering and the other with the effects of
disorder dominant. The Nishimori line marks a crossover between these two
regions.",0206438v2
2002-06-24,Temperature-dependent quasiparticle band structure of the ferromagnetic semiconductor EuS,"We present calculations for the temperature-dependent electronic structure of
the ferromagnetic semiconductor EuS. A combination of a many-body evaluation of
a multiband Kondo-lattice model and a first-principles T=0--bandstructure
calculation (tight-binding linear muffin-tin orbital (TB-LMTO)) is used to get
realistic information about temperature- and correlation effects in the EuS
energy spectrum. The combined method strictly avoids double-counting of any
relevant interaction. Results for EuS are presented in terms of spectral
densities, quasiparticle band structures and quasiparticle densities of states,
and that over the entire temperature range.",0206449v1
2002-06-25,Order parameter symmetry in ferromagnetic superconductors,"We analyze the symmetry and the nodal structure of the superconducting order
parameter in a cubic ferromagnet, such as ZrZn$_2$. We demonstrate how the
order parameter symmetry evolves when the electromagnetic interaction of the
conduction electrons with the internal magnetic induction and the spin-orbit
coupling are taken into account. These interactions break the cubic symmetry
and lift the degeneracy of the order parameter. It is shown that the order
parameter which appears immediately below the critical temperature has two
components, and its symmetry is described by {\em co-representations} of the
magnetic point groups. This allows us to make predictions about the location of
the gap nodes.",0206487v1
2002-06-30,Spatially Resolved Dynamics of Localized Spin-Wave Modes in Ferromagnetic Wires,"We have observed localized spin-wave modes in individual thin-film
ferromagnetic wires using time-resolved Kerr microscopy as a micron-scale
spectroscopic probe. The localization is due to the partial demagnetization of
a wire when an external field is applied in the plane of the film and
perpendicular to the long axis of the wire. Spatially-resolved spectra
demonstrate the existence of distinct modes at the edges of a rectangular wire.
Spectral images clearly show the crossover of the two edge modes into a single
mode in low applied fields, in agreement with the results of micromagnetic
simulations.",0207022v1
2002-07-02,Unveiling Order behind Complexity: Coexistence of Ferromagnetism and Bose-Einstein Condensation,"We present an algebraic framework for identifying the order parameter and the
possible phases of quantum systems that is based on identifying the local
dimension $N$ of the quantum operators and using the SU(N) group representing
the generators of generalized spin-particle mappings. We illustrate this for
$N$=3 by presenting for any spatial dimension the exact solution of the
bilinear-biquadratic $S$=1 quantum Heisenberg model at a high symmetry point.
Through this solution we rigorously show that itinerant ferromagnetism and
Bose-Einstein condensation may coexist.",0207073v1
2002-07-11,Heavy quasiparticles in the ferromagnetic superconductor ZrZn2,"We report a study of the de Haas-van Alphen effect in the normal state of the
ferromagnetic superconductor ZrZn2. Our results are generally consistent with
an LMTO band structure calculation which predicts four exchange-split Fermi
surface sheets. Quasiparticle effective masses are enhanced by a factor of
about 4.9 implying a strong coupling to magnetic excitations or phonons. Our
measurements provide insight in to the mechanism for superconductivity and
unusual thermodynamic properties of ZrZn2.",0207285v1
2002-07-13,Using single quantum states as spin filters to study spin polarization in ferromagnets,"By measuring electron tunneling between a ferromagnet and individual energy
levels in an aluminum quantum dot, we show how spin-resolved quantum states can
be used as filters to determine spin-dependent tunneling rates. We also observe
magnetic-field-dependent shifts in the magnet's electrochemical potential
relative to the dot's energy levels. The shifts vary between samples and are
generally smaller than expected from the magnet's spin-polarized density of
states. We suggest that they are affected by field-dependent charge
redistribution at the magnetic interface.",0207333v1
2002-07-16,Ferromagnetic Luttinger Liquids,"We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.",0207383v1
2002-07-19,Fluctuation-Driven Quantum Phase Transitions in Clean Itinerant Ferromagnets,"The quantum phase transition in clean itinerant ferromagnets is analyzed. It
is shown that soft particle-hole modes invalidate Hertz's mean-field theory for
$d \leq 3$. A renormalized mean-field theory predicts a fluctuation-induced
first order transition for $1 < d \leq 3$, whose stability is analyzed by
renormalization group techniques. Depending on microscopic parameter values,
the first order transition can be stable, or be pre-empted by a
fluctuation-induced second order transition. The critical behavior at the
latter is determined. The results are in agreement with recent experiments.",0207470v2
2002-07-23,Magnetically mediated superconductivity: Crossover from cubic to tetragonal lattice,"We compare predictions of the mean-field theory of superconductivity for
nearly antiferromagnetic and nearly ferromagnetic metals for cubic and
tetragonal lattices. The calculations are based on the parametrization of an
effective interaction arising from the exchange of magnetic fluctuations and
assume that a single band is relevant for superconductivity. The results show
that for comparable model parameters, the robustness of magnetic pairing
increases gradually as one goes from a cubic structure to a more and more
anisotropic tetragonal structure either on the border of antiferromagnetism or
ferromagnetism.",0207556v1
2002-07-26,Ballistic versus diffusive magnetoresistance of a magnetic point contact,"The quasiclassical theory of a nanosize point contacts (PC) between two
ferromagnets is developed. The maximum available magnetoresistance values in PC
are calculated for ballistic versus diffusive transport through the area of a
contact. In the ballistic regime the magnetoresistance in excess of few
hundreds percents is obtained for the iron-group ferromagnets. The necessary
conditions for realization of so large magnetoresistance in PC, and the
experimental results by Garcia et al are discussed",0207648v1
2002-08-02,Axisymmetric versus Non-axisymmetric Vortices in Spinor Bose-Einstein Condensates,"The structure and stability of various vortices in F=1 spinor Bose-Einstein
condensates are investigated by solving the extended Gross-Pitaevskii equation
under rotation. We perform an extensive search for stable vortices, considering
both axisymmetric and non-axisymmetric vortices and covering a wide range of
ferromagnetic and antiferromagnetic interactions. The topological defect called
Mermin-Ho (Anderson-Toulouse) vortex is shown to be stable for ferromagnetic
case. The phase diagram is established in a plane of external rotation Omega vs
total magnetization M by comparing the free energies of possible vortices. It
is shown that there are qualitative differences between axisymmetric and
non-axisymmetric vortices which are manifested in the Omega- and M-dependences.",0208032v1
2002-08-08,Metallic Continuum Quantum Ferromagnets at Finite Temperature,"We study via renormalization group (RG) and large N methods the problem of
continuum SU(N) quantum Heisenberg ferromagnets (QHF) coupled to gapless
electrons. We establish the phase diagram of the dissipative problem and
investigate the changes in the Curie temperature, magnetization, and magnetic
correlation length due to dissipation and both thermal and quantum
fluctuations. We show that the interplay between the topological term (Berry's
phase) and dissipation leads to non-trivial effects for the finite temperature
critical behavior.",0208185v2
2002-08-13,Ferromagnetism in Cr-doped GaN: A First Principles Calculation,"Otherwise antiferromagnetic chromium is shown to couple ferromagnetically
when doped into GaN irrespective of whether the host is a crystal or a cluster.
The results on the doped clusters and crystals are obtained from density
functional theory based molecular orbital theory and linearized muffin tin
orbital tight binding supercell band structure method respectively. The
calculated half metallic behavior of Cr-doped GaN crystal combined with the
observed room temperature Curie point make it an ideal candidate for
spintronics applications.",0208258v1
2002-08-14,Plasticity of Ferromagnets near the Curie Point,"We propose an explanation of the anomalous growth of plasticity in
ferromagnets near the Curie point. We demonstrate that this effect is caused by
spin-dependent detachment of dislocations from obstacles under an influence of
the internal magnetic field. Magnetization fluctuations grow in the vicinity of
the Curie point, yield an increase of the detachment probability and, hence, an
increase of the plasticity. We apply this model for a description of the
temperature behaviour of the critical stress in nickel and of the microhardness
of gadolinium. An external magnetic field suppresses the magnetization
fluctuations and, hence may suppress the above singularities.",0208271v1
2002-08-16,Possible symmetries of the superconducting order parameter in a hexagonal ferromagnet,"We study the order parameter symmetry in a hexagonal crystal with co-existing
superconductivity and ferromagnetism. An experimental example is provided by
carbon-based materials, such as graphite-sulfur composites, in which an
evidence of such co-existence has been recently discovered. The presence of a
non-zero magnetization in the normal phase brings about considerable changes in
the symmetry classification of superconducting states, compared to the
non-magnetic case.",0208339v2
2002-08-27,Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets,"Using a model of nonmagnetic impurity potential, we have examined the
behavior of planar vortex solutions in the classical two-dimensional XY
ferromagnets in the presence of a spin vacancy localized out of the vortex
core. Our results show that a spinless atom impurity gives rise to an effective
potential that repels the vortex structure.",0208523v1
2002-08-30,Exact calculation of the skyrmion lifetime in a ferromagnetic Bose condensate,"The tunneling rate of a skyrmion in ferromagnetic spin-1/2 Bose condensates
through an off-centered potential barrier is calculated exactly with the
periodic instanton method. The prefactor is shown to depend on the chemical
potential of the core atoms, at which level the atom tunnels. Our results can
be readily extended to estimate the lifetime of other topological excitations
in the condensate, such as vortices and monopoles.",0208593v1
2002-08-30,Spin Waves in Random Spin Chains,"We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random
antiferromagnetic impurity bonds with modified spin-wave theory. By describing
thermal excitations in the language of spin waves, we successfully observe a
low-temperature Curie susceptibility due to formation of large spin clusters
first predicted by the real-space renormalization-group approach, as well as a
crossover to a pure ferromagnetic spin chain behavior at intermediate and high
temperatures. We compare our results of the modified spin-wave theory to
quantum Monte Carlo simulations.",0208607v1
2002-09-03,"Defect correlations, metal-insulator transition, and magnetic order in ferromagnetic semiconductors","Diluted ferromagnetic III-V semiconductors typically show a high degree of
compensation. Compensation is connected to the presence of comparable densities
of charged defects of either sign. This naturally leads to the development of
strong correlations between defect positions during growth and annealing. We
show that these correlations are required to understand the experimentally
observed transport and magnetic properties as well as the persistence of the
energy gap upon doping with magnetic ions.",0209055v1
2002-09-05,Orbital Kondo Effect in $CrO_{2}$: A LSDA+DMFT Study,"Motivated by a collection of experimental results indicating the strongly
correlated nature of the ferromagnetic metallic state of $CrO_{2}$, we present
results based on a combination of the actual bandstructure [3] with dynamical
mean-field theory (DMFT) for the multi-orbital case. In striking contrast with
LSDA(+U) [3] and model many-body approaches [14], much better semiquantitative
agreement with (i) recent photoemission results, (ii) domain of applicability
of the half-metal concept, and (iii) thermodynamic and dc transport data, is
obtained within a single picture. Our approach has broad applications for the
detailed first principles investigation of other transition metal oxide-based
half-metallic ferromagnets.",0209132v1
2002-09-10,Hidden Quantum Critical Point in a Ferromagnetic Superconductor,"We consider a coexistence phase of both Ferromagnetism and superconductivity
and solve the self-consistent mean-field equations at zero temperature. The
superconducting gap is shown to vanish at the Stoner point whereas the
magnetization doesn't. This indicates that the para-Ferro quantum critical
point becomes a hidden critical point. The effective mass in such a phase gets
enhanced whereas the spin wave stiffness is reduced as compared to the pure FM
phase. The spin wave stiffness remains finite even at the para-Ferro quantum
critical point.",0209237v1
2002-09-11,Current and Noise in a FM/quantum dot/FM System,"Using the Keldysh nonequilibrium technique we calculate current, noise and
Fano factor in a ferromagnetic(FM)-quantum dot-ferromagnetic(FM) system with
Coulomb interaction and spin-flip scattering in the dot. The lead polarizations
are considered in both parallel P and antiparallel AP alignments. We show that
spin-flip can increase both AP-current and AP-noise, while the P-current and
P-noise are almost insensible to it. This fact leads to a suppression of the
tunnelling magnetoresistance with increasing spin-flip rate.",0209263v1
2002-09-17,Possible phase separated bulk superconductivity in Ru0.9Sr2YCu2.1O7.9,"The Ru0.9Sr2YCu2.1O7.9 sample being synthesized by high-pressure
high-temperature solid-state reaction underwent (weak) ferromagnetic transition
at 150 K followed by superconducting transition at 30 K. It showed clear
Meissner signal in the field-cooled process up to external magnetic field of a
few hundred Oe (~300 Oe). The magnetic susceptibility data and magnetic
hysteresis data could be explained assuming that the sample was a macroscopic
mixture of a superconductor and a (weak) ferromagnet. Any anomalous behaviour
implying the coexistence of superconductivity and magnetism on a microscopic
scale was not observed.",0209376v1
2002-09-17,Magnetic Order and Dynamics in an Orbitally Degenerate Ferromagnetic Insulator,"Neutron scattering was used to determine the spin structure and the magnon
spectrum of the Mott--Hubbard insulator YTiO$_3$. The magnetic structure is
complex, comprising substantial G-type and A-type antiferromagnetic components
in addition to the predominant ferromagnetic component. The magnon spectrum, on
the other hand, is gapless and nearly isotropic. We show that these findings
are inconsistent with the orbitally ordered states thus far proposed for
YTiO$_3$ and discuss general implications for a theoretical description of
exchange interactions in orbitally degenerate systems.",0209400v1
2002-09-18,Microphase separation in Pr0.67Ca0.33MnO3 by small angle neutron scattering,"We have evidenced by small angle neutron scattering at low temperature the
coexistence of ferromagnetism (F) and antiferromagnetism (AF) in
Pr0.67Ca0.33MnO3. The results are compared to those obtained in
Pr0.80Ca0.20MnO3 and Pr0.63Ca0.37MnO3, which are F and AF respectively.
Quantitative analysis shows that the small angle scattering is not due to a
mesoscopic mixing but to a nanoscopic electronic and magnetic ''red cabbage''
structure, in which the ferromagnetic phase exists in form of thin layers in
the AF matrix (stripes or 2D ''sheets'').",0209426v1
2002-09-18,Quantum behavior of Orbitals in Ferromagnetic Titanates: Novel Orderings and Excitations,"We investigate the collective behavior of orbital angular momentum in the
spin ferromagnetic state of a Mott insulator with $t_{2g}$ orbital degeneracy.
The frustrated nature of the interactions leads to an infinite degeneracy of
classical states. Quantum effects select four distinct orbital orderings. Two
of them have a quadrupolar order, while the other states show in addition weak
orbital magnetism. Specific predictions are made for neutron scattering
experiments which might help to identify the orbital order in YTiO$_3$ and to
detect the elementary orbital excitations.",0209434v1
2002-09-20,Spontaneous spin polarized tunneling current through a quantum dot array,"We show theoretically that a strongly spin-polarized current can be generated
in semiconductors by taking advantage of the ferromagnetic phase of a quantum
dot array (QDA). A Hubbard model with coupling to leads is used to study the
tunneling current of the QDA system as a function of gate voltage. Due to the
weak interdot coupling and strong Coulomb repulsion, it is found that a
ferromagnetic phase exists in QDA within a window of gate voltage. Therefore
QDA can be used as a spin filter to detect and control spin states in quantum
information devices.",0209499v1
2002-09-23,Rigorous Proof of Pseudospin Ferromagnetism in Two-Component Bosonic Systems with Component-Independent Interactions,"For a two-component bosonic system, the components can be mapped onto a
pseudo-spin degree of freedom with spin quantum number S=1/2. We provide a
rigorous proof that for a wide-range of real Hamiltonians with component
independent mass and interaction, the ground state is a ferromagnetic state
with pseudospin fully polarized. The spin-wave excitations are studied and
found to have quadratic dispersion relations at long wave length.",0209529v1
2002-09-27,Local Density of States in the Antiferromagnetic and Ferromagnetic Kondo Models,"Based on a simple approximation scheme we have computed the local density of
states (LDOS) of the antiferromagnetic and ferromagnetic Kondo models for the
full range of band occupations and coupling strengths. For both models the LDOS
with its full energy dependence has not been calculated before. Arguments are
given for the results to be qualitatively trustworthy despite the simplicity of
the approximation scheme.",0209639v1
2002-10-29,First order superconducting transition near a ferromagnetic quantum critical point,"We address the issue of how triplet superconductivity emerges in an
electronic system near a ferromagnetic quantum critical point (FQCP). Previous
studies found that the superconducting transition is of second order, and Tc is
strongly reduced near the FQCP due to pair-breaking effects from thermal spin
fluctuations. In contrast, we demonstrate that near the FQCP, the system avoids
pair-breaking effects by undergoing a first order transition at a much larger
Tc. A second order superconducting transition emerges only at some distance
from the FQCP.",0210653v1
2002-11-08,Spin Motion in Electron Transmission through Ultrathin Ferromagnetic Films Accessed by Photoelectron Spectroscopy,"Ab initio and model calculations demonstrate that the spin motion of
electrons transmitted through ferromagnetic films can be analyzed in detail by
means of angle- and spin-resolved core-level photoelectron spectroscopy. The
spin motion appears as precession of the photoelectron spin polarization around
and as relaxation towards the magnetization direction. In a systematic study
for ultrathin Fe films on Pd(001) we elucidate its dependence on the Fe film
thickness and on the Fe electronic structure. In addition to elastic and
inelastic scattering, the effect of band gaps on the spin motion is addressed
in particular.",0211163v1
2002-11-11,Spin-dependent electron transport through a ferromagnetic domain wall,"We present a theoretical study of spin-dependent transport through a
ferromagnetic domain wall. With an increase of the number of components of the
exchange coupling, we have observed that the variance of the conductance
becomes half. As the strength of the domain wall magnetization is increased,
negative magnetoresistance is also observed.",0211203v1
2002-11-21,Parametric quantum spin pump,"We investigate a non-adiabatic parametric quantum pump consists of a
nonmagnetic scattering region connected by two ferromagnetic leads. The
presence of ferromagnetic leads allows electrons with different spins to
experience different potential landscape. Using this effect we propose a
quantum spin pump that drives spin-up electrons to flow in one direction and
spin-down electrons to flow in opposite direction. As a result, the spin pump
can deliver a spin current with vanishing charge current.",0211460v1
2002-12-05,Phenomenological theory of spinor Bose-Einstein condensates,"A phenomenological model is proposed to describe the behavior of spinor
Bose-Einstein condensates. In the absence of hyperfine spin-spin interactions,
Bose-Einstein condensation leads to a spontaneous magnetization at the same
transition temperature. This is the so-called Bose-Einstein ferromagnetism.
Including the hyperfine spin interactions, the phase diagram of the spinor
condensate in an optical trap is studied and the Gross-Pitaevskii equation is
extended. The possibility of checking for the existence of the Bose-Einstein
ferromagnetism experimentally is also discussed.",0212114v3
2002-12-18,Paramagnetic-ferromagnetic transition in a double-exchange model,"We study paramagnetic - ferromagnetic transition due to exchange interaction
between classical localized magnetic moments and conduction electrons. We
formulate the Dynamical Mean Field Approximation equations for arbitrary
electron dispersion law, concentration and relation between exchange coupling
and the electron band width. Solving these equations we find explicit formula
for the transition temperature $T_c$. We present the results of calculations of
the $T_c$ for the semi-circular electron density of states.",0212450v2
2003-01-07,Order parameter oscillations in Fe/Ag/Bi2Sr2CaCu2O{8+delta} tunnel junctions,"We have performed temperature dependent tunneling conductance spectroscopy on
Fe/Ag/Bi2Sr2CaCu2O8 (BSCCO) planar junctions. The multilayered Fe
counterelectrode was designed to probe the proximity region of the ab-plane of
BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude
and sign dependent on the energy, decaying with increasing distance from the
junction barrier, in conjunction with the theoretical predictions involving
d-wave superconductors coupled with ferromagnets. The conductance oscillates in
antiphase at E = 0 and E = +/-Delta. Spectral features characteristic to a
broken time-reversal pairing symmetry are detected and they do not depend on
the geometrical characteristics of the ferromagnetic film.",0301081v1
2003-01-16,Observation of soft magnetorotons in bilayer quantum Hall ferromagnets,"Inelastic light scattering measurements of low-lying collective excitations
of electron double layers in the quantum Hall state at total filling nu_T=1
reveal a deep magnetoroton in the dispersion of charge-density excitations
across the tunneling gap. The roton softens and sharpens markedly when the
phase boundary for transitions to highly correlated compressible states is
approached. The findings are interpreted with Hartree-Fock evaluations that
link soft magnetorotons to enhanced excitonic Coulomb interactions and to
quantum phase transitions in the ferromagnetic bilayers.",0301295v1
2003-01-24,Quantized Anomalous Hall Effect in Two-Dimensional Ferromagnets - Quantum Hall Effect from Metal -,"We study the effect of disorder on the anomalous Hall effect (AHE) in
two-dimensional ferromagnets. The topological nature of AHE leads to the
integer quantum Hall effect from a metal, i.e., the quantization of
$\sigma_{xy}$ induced by the localization except for the few extended states
carrying Chern number. Extensive numerical study on a model reveals that
Pruisken's two-parameter scaling theory holds even when the system has no gap
with the overlapping multibands and without the uniform magnetic field.
Therefore the condition for the quantized AHE is given only by the Hall
conductivity $\sigma_{xy}$ without the quantum correction, i.e., $|\sigma_{xy}|
> e^2/(2h)$.",0301482v1
2003-01-31,Non-collinear magnetism in iron at high pressures,"Using a first principles based, magnetic tight-binding total energy model,
the magnetization energy and moments are computed for various ordered spin
configurations in the high pressure polymorphs of iron (fcc, or $\gamma$-Fe,
and hcp, or $\epsilon$-Fe), as well ferromagnetic bcc iron ($\alpha$-Fe). For
hcp, a non-collinear, antiferromagnetic, spin configuration that minimizes
unfavorable ferromagnetic nearest neighbor ordering is the lowest energy state
and is more stable than non-magnetic $\epsilon$ iron up to about 75 GPa.
Accounting for non-collinear magnetism yields better agreement with the
experimental equation of state, in contrast to the non-magnetic equation of
state, which is in poor agreement with experiment below 50 GPa.",0301615v1
2003-02-13,Exact diagonalization study of domain structure in integer filling factor quantum Hall ferromagnets,"Opposite spin Landau levels in a quantum well can be brought into coincidence
by tilting the magnetic field away from normal orientation. We demonstrate that
the magnetotransport anomaly at integer filling factors that was recently
discovered by Pan {\it et al} is due to such a coincidence. By performing exact
diagonalization calculations using microscopically evaluated effective
electron-electron interactions, we are able to establish that the electronic
ground state at coincidence is an Ising quantum Hall ferromagnet and that the
low energy excitations correspond to the formation of a domain wall.",0302271v1
2003-02-24,First order transition from correlated electron semiconductor to ferromagnetic metal in single crystalline FeSi1-xGex,"The phase diagram of FeSi1-xGex, obtained from magnetic, thermal and
transport measurements on single crystals, shows a first-order transition from
a correlated electron semiconductor to a ferromagnetic metal at a critical
concentration, x ~ 0.25. The gap of the insulating phase strongly decreases
with x. The specific heat coefficient appears to track the density of states of
a Kondo insulator. The phase diagram is consistent with a correlation induced
insulator-metal transition in conjunction with disorder on the Si/Ge ligand
site.",0302497v1
2003-03-02,Andreev conductance of a domain wall,"At low temperatures, the transport through a superconductor-ferromagnet
tunnel interface is due to tunneling of electrons in pairs. Exchange field of a
monodomain ferromagnet aligns electron spins and suppresses the two electron
tunneling. The presence of the domain walls at the SF interface strongly
enhances the subgap current. The Andreev conductance is proven to be
proportional to the total length of domain walls at the SF interface.",0303014v1
2003-03-10,Critical Behavior of the Ferromagnetic Ising Model on a Sierpinski Carpet: Monte Carlo Renormalization Group Study,"We perform a Monte Carlo Renormalization Group analysis of the critical
behavior of the ferromagnetic Ising model on a Sierpi\'nski fractal with
Hausdorff dimension $d_f\simeq 1.8928$. This method is shown to be relevant to
the calculation of the critical temperature $T_c$ and the magnetic
eigen-exponent $y_h$ on such structures. On the other hand, scaling corrections
hinder the calculation of the temperature eigen-exponent $y_t$. At last, the
results are shown to be consistent with a finite size scaling analysis.",0303173v1
2003-03-19,Long Range Coherent Manipulation of Nuclear Spins in Quantum Hall Ferromagnet,"A coherent superposition of many nuclear spin states can be prepared and
manipulated via the hyperfine interaction with the electronic spins by varying
the Landau level filling factor through the gate voltage in appropriately
designed Quantum Hall Ferromagnet. During the manipulation periods the 2D
electron system forms spatially large Skyrmionic spin textures, where many
nuclear spins follow locally the electron spin polarization. It is shown that
the collective spin rotation of a single spin texture is gapless in the limit
of zero Zeeman splitting, and may dominate the nuclear spins relaxation and
decoherence processes in the quantum well.",0303394v1
2003-03-29,Modified self-consistent harmonic approximation and its application to two-dimensional easy-axis quantum ferromagnets,"In the paper we describe the modification of self-consistent harmonic
approximation for quantum S=1 systems. This method has a number of advantages
in comparison with usual SCHA. We apply the method to two-dimensional
ferromagnets with easy-axis exchange or single-site anisotropy. The results are
in good agreement with Monte-Carlo simulations and pure-quantum SCHA.",0303619v2
2003-04-04,Co-ordination between Rashba spin-orbital interaction and space charge effect and enhanced spin injection into semiconductors,"We consider the effect of the Rashba spin-orbital interaction and space
charge in a ferromagnet-insulator/semiconductor/insulator-ferromagnet junction
where the spin current is severely affected by the doping, band structure and
charge screening in the semiconductor. In diffusion region, if the the
resistance of the tunneling barriers is comparable to the semiconductor
resistance, the magnetoresistance of this junction can be greatly enhanced
under appropriate doping by the co-ordination between the Rashba effect and
screened Coulomb interaction in the nonequilibrium transport processes within
Hartree approximation.",0304117v1
2003-04-17,Competing Ground States in Triple-layered Sr4Ru3O10: Verging on Itinerant Ferromagnetism with Critical Fluctuations,"Sr4Ru3O10 is characterized by a sharp metamagnetic transition and
ferromagnetic behavior occurring within the basal plane and along the c-axis,
respectively. Resistivity at magnetic field, B, exhibits low-frequency quantum
oscillations when B||c-axis and large magnetoresistivity accompanied by
critical fluctuations driven by the metamagnetism when B^c-axis. The complex
behavior evidenced in resistivity, magnetization and specific heat presented is
not characteristic of any obvious ground states, and points to an exotic state
that shows a delicate balance between fluctuations and order.",0304411v1
2003-04-17,Spontaneous Pseudospin Spiral Order in Bilayer Quantum Hall Systems,"Using exact diagonalization of bilayer quantum Hall systems at total filling
factor $\nu_T=1$ in the torus geometry, we show that there is a new long-range
interlayer phase coherence due to spontaneous pseudospin spiral order at
interlayer distances larger than the critical value at which the pseudospin
ferromagnetic order is destroyed. We emphasize the distinction between the
interlayer phase coherence and the pseudospin ferromagnetic order.",0304417v2
2003-04-23,Critical Resistance of the Quantum Hall Ferromagnet in AlAs 2D Electrons,"Magnetic transitions in AlAs two-dimensional electrons give rise to sharp
resistance spikes within the quantum Hall effect. Such spikes are likely caused
by carrier scattering at magnetic domain walls below the Curie temperature. We
report a critical behavior in the temperature dependence of the spike width and
amplitude, from which we deduce the Curie temperature of the quantum Hall
ferromagnet. Our data also reveal that the Curie temperature increases
monotonically with carrier density.",0304507v2
2003-05-02,Monte Carlo Study of Doping Change and Disorder Effect on Double Exchange Ferromagnetism,"Phase diagram and critical properties are studied for three-dimensional
double exchange model with and without quenched disorder. Employing the Monte
Carlo method and the systematic analysis on the finite-size effect, we estimate
the Curie temperature and the critical exponent as functions of the doping
concentration and the strength of the random potential. The Curie temperature
well scales to the kinetic energy of electrons in the ground state as expected
for this kinetics-driven ferromagnetism. The universality class of this
transition is described by the short-range Heisenberg fixed point. The results
are compared with the experimental results in the colossal magnetoresistance
manganites.",0305029v1
2003-05-15,Inhomogeneous Ferromagnetism and Unconventional Charge Dynamics in Disordered Double Exchange Magnets,"We solve the double exchange model in the presence of arbitrary
substitutional disorder by using a self consistently generated effective
Hamiltonian for the spin degrees of freedom. The magnetic properties are
studied through classical Monte Carlo while the effective exchange, $D_{ij}$,
are calculated by solving the disordered fermion problem, and renormalised
self-consistently with increasing temperature. We present exact results on the
conductivity, magnetoresistance, optical response and `real space' structure of
the inhomogeneous ferromagnetic state, and compare our results with charge
dynamics in disordered La_{1-x}Sr_xMnO_3. The large sizes, ${\cal O} (10^3)$,
accessible within our method allows a complete, controlled calculation on the
disordered strongly interacting problem.",0305352v1
2003-05-20,Yang-Lee zeros of the one-dimensional Q-state Potts model,"The distributions of the Yang-Lee zeros of the ferromagnetic and
antiferromagnetic Q-state Potts models in one dimension are studied for
arbitrary Q and temperature. The Yang-Lee zeros of the Potts antiferromagnet
have been fully investigated for the first time. The distributions of the
Yang-Lee zeros show a variety of different shapes. Some of the Yang-Lee zeros
lie on the positive real axis even for T>0. For the ferromagnetic model this
happens only for Q<1, while there exist some zeros of the antiferromagnetic
model on the positive real axis both for Q<1 and for Q>1.",0305456v1
2003-05-21,From Bubble to Skyrmion: Dynamic Transformation Mediated by a Strong Magnetic Tip,"Skyrmions in thin metallic ferromagnetic films are stable due to competition
between the RKKY interaction and uniaxial magnetic anisotropy. We mimic the
RKKY interaction by the next-nearest-neighbors ferromagnetic and
antiferromagnetic exchange interactions. We demonstrate analytically and
numerically dissipative transformation of a bubble created by a strong
cylindrical magnetic tip into a stable Skyrmion.",0305487v1
2003-05-23,Little-Parks effect and multiquanta vortices in a hybrid superconductor--ferromagnet system,"Within the phenomenological Ginzburg-Landau theory we investigate the phase
diagram of a thin superconducting film with ferromagnetic nanoparticles. We
study the oscillatory dependence of the critical temperature on an external
magnetic field similar to the Little-Parks effect and formation of multiquantum
vortex structures. The structure of a superconducting state is studied both
analytically and numerically.",0305551v1
2003-06-02,Ferromagnetism in Fe-doped Ba6Ge25 Chiral Clathrate,"We have successfully synthesized a Ba6Ge25 clathrate, substituting 3 Fe per
formula unit by Ge. This chiral clathrate has Ge sites forming a framework of
closed cages and helical tunnel networks. Fe atoms randomly occupy these sites,
and exhibit high-spin magnetic moments. A ferromagnetic transition is observed
with Tc = 170 K, the highest observed Tc for a magnetic clathrate. However, the
magnetic phase is significantly disordered, and exhibits a transformation to a
re-entrant spin glass phase. This system has a number of features in common
with other dilute magnetic semiconductors.",0306044v1
2003-06-04,Competition of Orbital Antiferromagnetism With Q-Triplet-Pairing in the Ferromagnetic Superconductor UGe$_2$,"Within a multicomponent BCS-like framework we study the coexistence and
competition of various CDW and SC order parameters in the presence of a strong
ferromagnetic background. We find that the competition of unconventional CDW,
also called orbital antiferromagnet, with SC at finite momentum (${\bf
Q}$-triplet pairing) shows unique characteristics like an extreme sensitivity
on the deviations from nesting. We argue that pressure in UGe$_2$ creates
deviations from the nesting and report a phase diagram in qualitative agreement
with the observed behavior of UGe$_2$.",0306106v1
2003-06-10,Determining the current polarization in Al/Co nanostructured point contacts,"We present a study of the Andreev reflections in superconductor/ferromagnet
nanostructured point contacts. The experimental data are analyzed in the frame
of a model with two spin-dependent transmission coefficients for the majority
and minority charge carriers in the ferromagnet. This model consistently
describes the whole set of conductance measurements as a function of voltage,
temperature, and magnetic field. The ensemble of our results shows that the
degree of spin polarization of the current can be unambiguously determined
using Andreev physics.",0306241v1
2003-06-10,Anisotropic susceptibilities of thin ferromagnetic films within many-body Green's function theory,"Transverse and parallel static susceptibilities of in-plane uniaxial
anisotropic ferromagnetic films are calculated within many-body Green's
function theory on the basis of an Heisenberg model. The importance of
collective magnetic excitations in particular in the paramagnetic regime are
stressed by comparing with mean field calculations. The paper generalizes the
work of Jensen et al. [1] to the multilayer case and to spins with S>1/2.",0306243v2
2003-06-19,Griffiths phase in diluted magnetic semiconductors,"We study the effects of disorder in the vicinity of the ferromagnetic
transition in a diluted magnetic semiconductor in the strongly localized
regime. We derive an effective polaron Hamiltonian, which leads to the
Griffiths phase above the ferromagnetic transition point. The Griffiths-McCoy
effects yield non-perturbative contributions to the dynamic susceptibility. We
explicitly derive the long-time susceptibility, which has a pseudo-scaling
form, with the dynamic critical exponent being expressed through the
percolation indices.",0306488v2
2003-06-20,Quantum dynamics of tunneling between ferromagnets,"We study the Josephson-like spin currents between two ferromagnetic metals by
deriving the effective action of the junction. A DC spin Josephson current with
the full O(3) symmetry is obtained. By the analogy to the superconducting
junctions, we have shown that a time-independent uniform magnetic field can
serve as the source of the AC spin Josephson effect. That is, the spin current
becomes a periodic function of the time with the period proportional to the
inverse of the magnitude of the external magnetic field.",0306518v2
2003-06-20,Andreev bound states for superconducting-ferromagnetic box,"Within the microscopic Bogoliubov--de Gennes (BdG) formalism an exact
quantization condition for Andreev bound states of the
ferromagnetic-superconducting hybrid systems of box geometry is derived and a
semi-classical formula for the density of states is obtained. The
semi-classical formula is shown to agree with the exact result, even when the
exchange field $h$, is much larger than the superconductor order parameter,
provided $h$ is small compared with the Fermi energy.",0306523v1
2003-06-26,Thermodynamic properties of a classical d-dimensional spin-S Heisenberg ferromagnet with long-range interactions via the spectral density method,"The thermodynamic properties of a classical d-dimensional spin-S Heisenberg
ferromagnet, with long-range interactions decaying as $r^{-p}$ and in the
presence of an external magnetic field, is investigated by means of the
spectral density method in the framework of classical statistical mechanics. We
find that long-range order exists at finite temperature for $d<p<2d$ with
$d\leq 2$ and for $p>d$ with $d>2$, consistently with known theorems. Besides,
the related critical temperature is determined and a study of the critical
properties is performed.",0306673v1
2003-06-27,The coexistence of p-wave spin triplet superconductivity and itinerant ferromagnetism,"A model for coexistence of p-wave spin-triplet superconductivity (SC) and
itinerant ferromagnetism (FM) is presented. The Hamiltonian can be diagonalized
by using the so(5) algebraic coherent state. We obtain the coupling equations
of the magnetic exchange energy and superconducting gaps through the
double-time Green function. It is found that the ferromagnetisation gives rise
to the phase transitions of p-wave superconducting states or superfluid of
$^{3}He$.",0306691v1
2003-07-01,Spin clustering and ferromagnetic couplings in a dilute magnetic semiconductor,"Ferromagnetic couplings in spin clusters are shown to be strongly enhanced
compared to those for an ordered impurity arrangement, even for the same spin
separation and hole doping. The consequent energy-enhancement of the
cluster-localized spin-wave modes indicates a potentially significant role of
positional Mn disorder in enhancing $T_{\rm C}$. Within a simple model
involving two spin-excitation energy scales corresponding to weakly and
strongly coupled spins, the temperature dependence of magnetization is found to
be in good agreement with the SQUID magnetization data for Ga$_{1-x}$Mn$_x$As.",0307009v1
2003-07-14,First Principles Calculation of Anomalous Hall Conductivity in Ferromagnetic bcc Fe,"We perform a first principles calculation of the anomalous Hall effect in
ferromagnetic bcc Fe. Our theory identifies an intrinsic contribution to the
anomalous Hall conductivity and relates it to the k-space Berry phase of
occupied Bloch states. The theory is able to account for both dc and
magneto-optical Hall conductivities with no adjustable parameters.",0307337v2
2003-07-16,Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers,"A vector spin model is used to show how frustrations within a multisublattice
antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting
on an exchange coupled ferromagnetic film. Possibilities for the existence of
exchange bias are examined and shown to exist for the case of weak chemical
disorder at the interface in an otherwise perfect structure. A sensitive
dependence on interlayer exchange is found for anisotropies acting on the
ferromagnet through the exchange coupling, and we show that a wide range of
anisotropies can appear even for a perfect crystalline structure with an
ideally flat interface.",0307384v1
2003-07-29,Metamorphosis of the Quantum Hall Ferromagnet at $ν= 2/5$,"We report on the dramatic evolution of the quantum Hall ferromagnet in the
fractional quantum Hall regime at $\nu = 2/5$ filling. A large enhancement in
the characteristic timescale gives rise to a dynamical transition into a novel
quantized Hall state. The observed Hall state is determined to be a
zero-temperature phase distinct from the spin-polarized and spin-unpolarized
$\nu = 2/5$ fractional quantum Hall states. It is characterized by a strong
temperature dependence and puzzling correlation between temperature and time.",0307711v1
2003-07-31,Ferromagnetism in the Strong Hybridization Regime of the Periodic Anderson Model,"We determine exactly the ground state of the one-dimensional periodic
Anderson model (PAM) in the strong hybridization regime. In this regime, the
low energy sector of the PAM maps into an effective Hamiltonian that has a
ferromagnetic ground state for any electron density between half and three
quarters filling. This rigorous result proves the existence of a new magnetic
state that was excluded in the previous analysis of the mixed valence systems.",0308002v1
2003-08-08,Numerical Investigation on Asymmetric Bilayer System at Integer Filling Factor,"Deformation of the easy-axis ferromagnetic state in asymmetric bilayer
systems are investigated numerically. Using the exact diagonalization the
easy-axis to easy-plane ferromagnetic transition at total filling factor 3 or 4
is investigated. At still higher filling, novel stripe state in which stripes
are aligned in the vertical direction occurs. The Hartree-Fock energies of
relevant ordered states are calculated and compared.",0308158v2
2003-09-03,Superconducting Vortices and Elliptical Ferromagnetic Textures,"In this article an analytical and numerical study of superconducting thin
film with ferromagnetic textures of elliptical geometries in close proximity is
presented. The screening currents induced in the superconductor due to the
magnetic texture are calculated. Close to the superconducting transition
temperature $T_c$ the spontaneous creation of superconducting vortices becomes
energy favorable depending on the value of the magnetization and the
geometrical quantities of the magnetic texture. The creation of vortices by
elliptic dots is more energy favorable than those created by circular ones. The
superconductor covered by elliptic dots array exhibits anisotropic transport
properties.",0309090v1
2003-09-10,Non-monotonic angular magnetoresistance in asymmetric spin valves,"The electric resistance of ferromagnet/normal-metal/ferromagnet perpendicular
spin valves depends on the relative angle between the magnetization directions.
In contrast to common wisdom, this angular magnetoresistance is found to be not
necessarily a monotone function of the angle. The parameter dependence of the
global resistance minimum at finite angles is studied and the conditions for
experimental observation are specified.",0309252v2
2003-09-15,Spiral phase and phase separation of the double exchange model in the large-S limit,"The phase diagram of the double exchange model is studied in the large-S
limit at zero temperature in two and three dimensions. We find that the spiral
state has lower energy than the canted antiferromagnetic state in the region
between the antiferromagnetic phase and the ferromagnetic phase. At small
doping, the spiral phase is unstable against phase separation due to its
negative compressibility. When the Hund coupling is small, the system separates
into spiral regions and antiferromagnetic regions. When the Hund coupling is
large, the spiral phase disappears completely and the system separates into
ferromagnetic regions and antiferromagnetic regions.",0309346v1
2003-09-22,Spin textures in slowly rotating Bose-Einstein Condensates,"Slowly rotating spin-1 Bose-Einstein condensates are studied through a
variational approach based upon lowest Landau level calculus. The author finds
that in a gas with ferromagnetic interactions, such as $^{87}$Rb, angular
momentum is predominantly carried by clusters of two different types of
skyrmion textures in the spin-vector order parameter. Conversely, in a gas with
antiferromagnetic interactions, such as $^{23}$Na, angular momentum is carried
by $\pi$-disclinations in the nematic order parameter which arises from spin
fluctuations. For experimentally relevant parameters, the cores of these
$\pi$-disclinations are ferromagnetic, and can be imaged with polarized light.",0309511v1
2003-10-02,Nonquasiparticle states in half-metallic ferromagnet NiMnSb,"Nonquasiparticle states above the Fermi energy are studied by first-principle
dynamical mean field calculations for a prototype half-metallic ferromagnet,
NiMnSb. We present a quantitative evaluation of the spectral weight of this
characteristic feature and discuss the possible experimental investigation
(BIS, NMR, STM and Andreev reflection) to clarify the existence of these
states.",0310032v1
2003-10-07,One dimensional gapless magnons in a single anisotropic ferromagnetic nanolayer,"Gapless magnons in a plane ferromagnet with normal axis anisotropy are shown
to exist besides the usual gapped modes that affect spin dependent transport
properties only above a finite temperature. These magnons are one dimensional
objects, in the sense that they are localized inside the domain walls that form
in the film. They may play an essential role in the spin dependent scattering
processes even down to very low temperatures.",0310159v1
2003-10-08,Quantum phase transitions of magnetic rotons,"Due to weak spin-orbit coupling, the magnetic excitations of an itinerant
ferromagnet become magnetic rotons, excitations with degenerate minima on a
hypersphere at finite wavevector. Using self-consistent Hartree and
renormalization group calculations, we study weak fluctuation-driven
first-order quantum phase transitions, a quantum tricritical point controlled
by anisotropy and the non-Fermi liquid behavior associated with the large phase
volume of magnetic rotons. We propose that magnetic rotons are essential for
the description of the anomalous high-pressure behavior of the itinerant
helical ferromagnet MnSi.",0310186v2
2003-10-10,Magnetocrystalline anisotropy and orbital polarization in ferromagnetic transition metals,"The magnetocrystalline anisotropy energies (MAEs) of the ferromagnetic metals
bcc Fe, fcc and hcp Co, and fcc Ni have been calculated by using the {\it ab
initio} tight-binding method. Disentangling the strong correlation among the
$d$ orbitals with the Hamiltonian in the local spin-density approximation, we
have investigated the orbital polarizations induced by the Hubbard $U$ and
Racah $B$. The experimental MAE of fcc Ni is found with the value of $U$ close
to that determined from experiments and used in other theories. With the
optimized values of $U$ and $J$, both the MAEs and the orbital moments for Fe
and Co are in close agreement with experiment.",0310249v1
2003-11-04,Coexistence of ferromagnetism and singlet superconductivity via kinetic exchange,"We propose a novel mechanism for the coexistence of metallic ferromagnetism
and singlet superconductivity assuming that the magnetic instability is due to
kinetic exchange. Within this scenario, the unpaired electrons which contribute
to the magnetization have a positive feedback on the gain of the kinetic energy
in the coexisting phase by undressing the effective mass of the carriers
involved into the pairing. The evolution of the magnetization and pairing
amplitude, and the phase diagram are first analyzed for a generic kinetic
exchange model and then are determined within a specific case with spin
dependent bond-charge occupation.",0311063v1
2003-11-11,Massive Spin Collective Mode in Quantum Hall Ferromagnet,"It is shown that the collective spin rotation of a single Skyrmion in quantum
Hall ferromagnet can be regarded as precession of the entire spin texture in
the external magnetic field, with an effective moment of inertia which becomes
infinite in the zero g-factor limit. This low-lying spin excitation may
dramatically enhance the nuclear spin relaxation rate via the hyperfine
interaction in the quantum well slightly away from filling factor equal one.",0311239v1
2003-11-14,Large anisotropy in the paramagnetic susceptibility of SrRuO3 films,"By using the extraordinary Hall effect in SrRuO3 films we performed sensitive
measurements of the paramagnetic susceptibility in this itinerant ferromagnet,
from Tc (~ 150 K) to 300 K. These measurements, combined with measurements of
magnetoresistance, reveal that the susceptibility, which is almost isotropic at
300 K, becomes highly anisotropic as the temperature is lowered, diverging
along a single crystallographic direction in the vicinity of Tc. The results
provide a striking manifestation of the effect of exceptionally large
magnetocrystalline anisotropy in the paramagnetic state of a 4d itinerant
ferromagnet.",0311341v1
2003-11-18,Quantum-critical behavior of itinerant ferromagnets,"We study the stability of the Quantum Critical Point (QCP) for itinerant
ferromagnets commonly described by the Hertz-Millis-Moriya (HMM) theory. We
argue that in $D \leq 3$, long-range spatial correlations associated with the
Landau damping of the order parameter field generate a universal {\it
negative}, non-analytic $|q|^{(D+1)/2}$ contribution to the static magnetic
susceptibility $\chi_s (q, 0)$, which makes HMM theory unstable. We argue that
the actual transition is either towards incommensurate ordering, or first
order. We also show that singular corrections are specific to the spin problem,
while charge susceptibility remains analytic at criticality.",0311420v1
2003-11-24,A first principles study of wurtzite-structure MnO,"We present results of a density functional theory study of MnO in the
wurtzite structure. Our motivation is provided by recent experiments reporting
ferromagnetism in Mn-doped wurtzite structure ZnO. We find that wurtzite MnO a)
is not strongly energetically disfavored as compared with the ground state
rocksalt MnO, b) shows strong magnetostructural coupling and c) has a
piezoelectric response that is larger than that of ZnO. These predictions augur
well for the creation of ferromagnetic piezoelectric semiconductor based on
Mn-doped ZnO.",0311529v1
2003-12-09,Structural and magnetic properties of transition metal substituted ZnO,"Structural and magnetic properties have been studied for polycrystalline
Zn_{1-x}TM_xO, where TM (transition metal ions) = Mn, Fe, and Co. No bulk
ferromagnetism was observed for single-phase materials, contrary to the
existing theories. Single-phase samples demonstrate paramagnetic Curie-Weiss
behavior with antiferromagnetic interactions, similar to other diluted magnetic
semiconductors. Non-optimal synthesis conditions lead to formation of second
phases that are responsible for spin-glass behavior (ZnMnO_3 impurity for
Zn_{1-x}Mn_xO (S. Kolesnik et al., J. Supercond.: Incorp. Novel Magn. 15, 251
(2002)) or high-temperature ferromagnetic ordering (Co metal for Zn_{1-x}Co_xO
with the Curie temperature T_C > 800 K or (Zn,Fe)_3O_4 for Zn_{1-x}Fe_xO with
T_C = 440 K).",0312233v1
2003-12-15,Phonon Mechanism of the Ferromagnetic Transition in La1-xSrxMnO3,"Temperature dependence of longitudinal optical phonons with oxygen character
was measured in La1-xSrxMnO3 (x=0.2, 0.3) by inelastic neutron scattering in
the (1 0 0) cubic direction. The zone center mode intensity is consistent with
the Debye-Waller factor. However the intensity of the bond-stretching phonons
half way to the zone boundary and near the zone boundary decreases dramatically
as the temperature increases through the ferromagnetic (FM) transition. We
found evidence that the lost phonon spectral weight might shift into polaron
scattering at the same wavevectors. The temperature evolution starts well below
the onset of the FM transition suggesting that the transition is driven by
phonon renormalization rather than by magnetic fluctuations.",0312368v1
2003-12-31,Excitation of Spin Waves in Superconducting Ferromagnets,"This Letter presents a theoretical analysis of propagation of spin waves in a
superconducting ferromagnet. The surface impedance was calculated for the case
when the magnetization is normal to the sample surface. We found the
frequencies at which the impedance and the power absorption have singularities
related to the spin wave propagation, and determined the form of these
singularities. With a suitable choice of parameters, there is a frequency
interval in which two propagating spin waves of the same circular polarization
are generated, one of them having a negative group velocity.",0312720v1
2004-01-14,Origin of asymmetric reversal modes in ferromagnetic/antiferromagnetic multilayers,"Experimentally an asymmetry of the reversal modes has been found in certain
exchange bias systems. From a numerical investigation of the domain state model
evidence is gained that this effect depends on the angle between the easy axis
of the antiferromagnet and the applied magnetic field. Depending on this angle
the ferromagnet reverses either symmetrically, e. g. by a coherent rotation on
both sides of the loop, or the reversal is asymmetric with a non uniform
reversal mode for the ascending branch, which may even yield a zero
perpendicular magnetization.",0401232v1
2004-01-16,Magnetic field induced phase transitions in spin ladders with ferromagnetic legs,"We study the phase diagram of spin ladders with ferromagnetic legs under the
influence of a symmetry breaking magnetic field in the weak coupling effective
field theory by bosonization. For antiferromagnetic interleg coupling we
identify two phase transitions introduced by the external magnetic field. In
order to establish the universality of the phases we supplement the
bosonization approach by results from a strong coupling (rung) expansion and
from spin wave analysis.",0401301v1
2004-01-22,Asymptotically Exact Solution for Superconductivity near Ferromagnetic Criticality,"We analyze an asymptotically exact solution for the transition temperature of
p-wave superconductivity near ferromagnetic criticality on the basis of the
three-dimensional electron systems in which scattering processes are dominated
by exchange interactions with small momentum transfers. Taking into account all
Feynman diagrams in the gap equation, we show that vertex corrections neglected
in the conventional Eliashberg's formalism enhance the dynamical retarded
effect of the pairing interaction, and raise the superconducting transition
temperature significantly, though they just give subleading corrections to
properties of the normal state.",0401412v2
2004-01-29,Review on Giant Magnetoelectric effects in Oxide ferromagnetic/ferroelectric Layered Structures,"The synthesis of layered ferrite-lead titanate zirconate (PZT) and lanthanum
nanganite-PZT and the observation of giant magneto-electric interactions are
discussed. The ferrites used in our studies included pure and Zn substituted
cobalt-, nickel- and lithium ferrites. Ferromagnetic manganites used included
both calcium and strontium substituted systems. The samples were prepared from
10-40 mm thick films obtained by tape-casting. Our studies showed strong ME
coupling in manganite-PZT and cobalt zinc ferrite-PZT, and a giant ME effect in
nickel zinc ferrite-PZT. We found evidence for Zn assisted enhancement in ME
coefficients that were attributed to low anisotropy and high permeability that
resulted in favorable magneto-mechanical coupling in the composites.",0401607v1
2004-02-04,Ferromagnetism mediated by few electrons in a semimagnetic quantum dot,"A (II,Mn)VI diluted magnetic semiconductor quantum dot with an integer number
of electrons controlled with a gate voltage is considered. We show that a
single conduction band electron is able to induce a spontaneous collective
magnetization of the Mn spins, overcoming the short range antiferromagnetic
interactions. The carrier mediated ferromagnetism in the dot survives at
temperatures above 1 Kelvin, two orders of magnitude larger than the Curie
temperature for the same material in bulk. The magnetic behavior of the dot
depends dramatically on the parity of the number of injected electrons.",0402140v2
2004-02-12,Spin Dynamics of Double-Exchange Manganites with Magnetic Frustration,"This work examines the effects of magnetic frustration due to competing
ferromagnetic and antiferromagnetic Heisenberg interactions on the spin
dynamics of the double-exchange model. When the local moments are non-colinear,
a charge-density wave forms because the electrons prefer to sit on lines of
sites that are coupled ferromagnetically. With increasing hopping energy, the
local spins become aligned and the average spin-wave stiffness increases. Phase
separation is found only within a narrow range of hopping energies. Results of
this work are applied to the field-induced jump in the spin-wave stiffness
observed in the manganite Pr$_{1-x}$Ca$_x$MnO$_3$ with $0.3 \le x \le 0.4$.",0402344v1
2004-02-16,Triplet superconductivity vs. easy-plane ferromagnetism in a 1D itinerant electron system with transverse spin anisotropy,"In this paper we study the ground state phase diagram of a one-dimensional
$t-U-J$ model, at half-filling. In the large-bandwidth limit and for
ferromagnetic exchange with easy-plane anisotropy, a phase with gapless charge
and massive spin excitations, characterized by the coexistence of triplet
superconducting and spin density wave instabilities is realized in the ground
state. With reduction of the bandwidth, a transition into an insulating phase
showing properties of the spin-1/2 XY model takes place.",0402405v1
2004-02-16,Numerical simulations of two dimensional magnetic domain patterns,"I show that a model for the interaction of magnetic domains that includes a
short range ferromagnetic and a long range dipolar anti-ferromagnetic
interaction reproduces very well many characteristic features of
two-dimensional magnetic domain patterns. In particular bubble and stripe
phases are obtained, along with polygonal and labyrinthine morphologies. In
addition, two puzzling phenomena, namely the so called `memory effect' and the
`topological melting' observed experimentally are also qualitatively described.
Very similar phenomenology is found in the case in which the model is changed
to be represented by the Swift-Hohenberg equation driven by an external
orienting field.",0402406v2
2004-02-26,"Zinc-blende CaP, CaAs and CaSb as half-metals: A new route to magnetism in calcium compounds","Existence of ferromagnetism in bulk calcium compounds is discovered
theoretically. First-principles calculations of calcium phosphide, calcium
arsenide and calcium antimonide in the zinc-blende structure have been
performed to show the half-metallic ground state in each optimized stable
structure. Magnetism comes from spin-polarization of electrons in
  $p$-orbitals of P, As or Sb and $d$-orbitals of calcium atoms. The
half-metallicity is analogous to the half-metallic zinc-blende compounds, {\it
e.g.} CrAs or CrSb, but the predicted compounds become ferromagnetic without
transition metals. In (In$_{1-x}$Ca$_x$)Sb, the magnetism remains to be stable
in a range of the doping rate ($x>0.8$).",0402641v1
2004-02-28,Crossover in the Structure Between Bloch and Linear Domain Walls,"Near the Curie temperature of a ferromagnet the form of a domain wall changes
from the Bloch type to (asymptotically) the linear Zhirnov wall. Unlike the
simple 180 degree rotation of the magnetization vector in a Bloch wall, its
absolute value diminishes near the center of the wall. This leads to a decrease
of the total transverse component of the exchange field inside the wall and to
an increase of mistracking of the spins of the electrons traversing the wall.
This mechanism may help explain large magnetoresistance of domain walls in thin
nanowires, as the Curie temperatures of low-dimensional nanostructures are
known to be lower than in bulk ferromagnets while the anisotropy energy stays
virtually unchanged.",0403006v1
2004-03-02,"Ferromagnetic EuS films: Magnetic stability, electronic structure and magnetic surface states","We present the temperature and layer dependent electronic structure of a
20-layer EuS(100)-film using a combination of first-principles and model
calculation, the latter based on the ferromagnetic Kondo-lattice. The
calculated thickness-dependent Curie temperature agrees very well with
experimental data. The projected 5d-bandstructure is at finite temperatures
strongly influenced by damping effects due to spin exchange processes.
Spin-split unoccupied 5d-surfaces states are found with a Stoner-like
collapsing for increasing temperature towards the Curie point and with an
exponential decay of spectral weight with increasing distance from the surface.",0403075v1
2004-03-03,"Anti-ferromagnetism, spin-phonon interaction and the local-density approximation in high-T$_C$ superconductors","Results from different sets of band calculations for undoped and doped
HgBa$_2$CuO$_4$ show that small changes in localization can lead to very
different ground states.
  The normal LDA results are compared with 'modified' LDA results, in which
different linearization energies make the O-p band more localized. The ground
states in the normal calculations are far from the anti-ferromagnetic ones,
while nearly AFM states are found in the modified calculations. The proximity
of an AFM state in the doped system leads to increased $\lambda_{sf}$, and the
modified band structure has favorable conditions for spin-phonon coupling and
superconductivity mediated by spin fluctuations.",0403103v1
2004-03-03,Antiferromagnetism at the YBa2Cu3O7 / La2/3Ca1/3MnO3 interface,"The magnetic properties of a series of YBa2Cu3O7-x/La2/3Ca1/3MnO3
(YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures
(3.5 mbar) show the expected ferromagnetic behaviour. However, field cooled
hysteresis loops at low temperature show the unexpected existence of exchange
bias, effect associated with the existence of ferromagnetic/antiferromagnetic
(F/AF) interfaces. The blocking temperature (TB) is found thickness dependent
and the exchange bias field (HEB) is found inversely proportional to the FM
layer thickness, as expected. The presence of an AF material is probably
associated to interface disorder and Mn valence shift towards Mn4+.",0403113v1
2004-03-19,"Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction","Current-driven magnetization reversal in a ferromagnetic semiconductor based
(Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K.
Magnetoresistance measurements combined with current pulse application on a
rectangular 1.5 x 0.3 um^2 device revealed that magnetization switching occurs
at low critical current densities of 1.1 - 2.2 x 10^5 A/cm^2 despite the
presence of spin-orbit interaction in the p-type semiconductor system. Possible
mechanisms responsible for the effect are discussed.",0403500v3
2004-03-24,Direct evidence for ferromagnetic spin polarization in gold nanoparticles,"We report the first direct observation of ferromagnetic spin polarization of
Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular
dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold
magnetization is explored. Magnetization of gold atoms estimated by XMCD shows
a good agreement with the results obtained by conventional magnetometry. This
result is evidence of intrinsic spin polarization in nano-sized gold.",0403600v1
2004-04-01,Semiclassical dynamics of domain walls in the one-dimensional Ising ferromagnet in a transverse field,"We investigate analytically and numerically the dynamics of domain walls in a
spin chain with ferromagnetic Ising interaction and subject to an external
magnetic field perpendicular to the easy magnetization axis (transverse field
Ising model). The analytical results obtained within the continuum
approximation and numerical simulations performed for discrete classical model
are used to analyze the quantum properties of domain walls using the
semiclassical approximation. We show that the domain wall spectrum shows a band
structure consisting of 2$S$ non-intersecting zones.",0404014v1
2004-04-05,Nonequilibrium Superconductivity near Spin Active Interfaces,"The Riccati formulation of the quasiclassical theory of nonequilibrium
superconductors is developed for spin-dependent scattering near magnetic
interfaces. We derive boundary conditions for the Riccati distribution
functions at a spin-active interface that are applicable to a wide range of
nonequilibrium transport properties of hybrid systems of superconducting and
magnetic materials. We use these results to calculate spin, charge and heat
transport for normal metal-ferromagnet-superconductor (NFS) and
superconducting-ferromagnetic-superconducting (SFS) point contacts.",0404074v1
2004-04-07,Electric Field Effect in Diluted Magnetic Insulator Anatase Co:TiO2,"An external electric field induced reversible modulation of room temperature
magnetic moment is achieved in an epitaxial and insulating thin film of
dilutely cobalt-doped anatase TiO2. This first demonstration of electric field
effect in any oxide based diluted ferromagnet is realized in a high quality
epitaxial heterostructure of PbZr0.2Ti0.8O3/Co:TiO2/SrRuO3 grown on (001)
LaAlO3. The observed effect, which is about 15% in strength in a given
heterostructure, can be modulated over several cycles. Possible mechanisms for
electric field induced modulation of insulating ferromagnetism are discussed.",0404172v1
2004-04-14,Investigation of the field-treated magnetic state in Gd5Ge4,"At low temperatures, the intermetallic compound Gd$_5$Ge$_4$ shows a sharp
field-induced transition into a ferromagnetic state around 25 kOe of applied
field. The material remains in the field treated ferromagnetic state even when
the magnetic field is removed. We have investigated the character of this
field-treated state by magnetization and heat capacity measurements. The nature
of the magnetization and the heat capacity are found to be different above and
below a charactersitic temperature Tirr = 25 K.",0404302v1
2004-04-19,High Curie temperatures in ferromagnetic Cr-doped AlN thin films,"Al1-xCrxN thin films with $0.02\le x \le 0.1$ were deposited by reactive
co-sputtering onto c-plane (001) sapphire. Room-temperature ferromagnetism with
a coercive field of 85 Oe was observed in samples with chromium contents as low
as x = 0.027 (2.7%). With increasing Cr content the mean magnetic moment is
strongly suppressed, with a maximum saturation moment of 0.62 and 0.71 $\mu_B$
per Cr atom at 300 and 50 K respectively. We show that the Curie temperature of
Al1-xCrxN for x = 0.027 is greater than 900 K.",0404436v1
2004-04-21,Hund's rule and metallic ferromagnetism,"We study tight-binding models of itinerant electrons in two different bands,
with effective on-site interactions expressing Coulomb repulsion and Hund's
rule. We prove that, for sufficiently large on-site exchange anisotropy, all
ground states show metallic ferromagnetism: They exhibit a macroscopic
magnetization, a macroscopic fraction of the electrons is spatially
delocalized, and there is no energy gap for kinetic excitations.",0404483v2
2004-05-13,Precessional dynamics of elemental moments in a ferromagnetic alloy,"We demonstrate an element-specific measurement of magnetization precession in
a metallic ferromagnetic alloy, separating Ni and Fe moment motion in Ni81Fe19.
Pump-probe X-ray magnetic circular dichroism (XMCD), synchronized with short
magnetic field pulses, is used to measure free magnetization oscillations up to
2.6 GHz with elemental specificity and a rotational resolution of < 2 deg.
Magnetic moments residing on Ni sites and Fe sites in a Ni81Fe19(50nm) thin
film are found to precess together at all frequencies, coupled in phase within
instrumental resolution of 90 ps.",0405295v1
2004-05-14,Calculating the Curie Temperature reliably in diluted III-V ferromagnetic semiconductors,"We present a semi-analytic theory for the Curie temperature in diluted
magnetic semi-conductors that treats disorder effects exactly in the effective
Heisenberg Hamiltonian, and spin fluctuations within a local RPA. The exchange
couplings are taken from concentration dependent {\it ab initio} estimates. The
theory gives very good agreement with published data for well-annealed samples
of Mn$_x$Ga$_{1-x}$As. We predict the critical temperatures for
Mn$_x$Ga$_{1-x}$N lower than in doped GaAs, despite the stronger
nearest-neighbour ferromagnetic coupling. We also predict the dependence on the
hole concentration.",0405322v1
2004-05-22,"Oxygen stoichiometry, crystal structure, and magnetism in La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$","We have prepared a series of polycrystalline samples
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$} with $0 < \delta \le 0.21$ and
characterized their oxygen content, crystal structure, and magnetic properties.
While the fully oxygenated samples are good ferromagnets, samples with larger
$\delta$ values display increasingly broad magnetic transitions. The saturation
magnetization at 5 K falls rapidly as $\delta$ increases. First principles
electronic structure calculations provide insights into the magnetic behavior
of the fully oxygenated compound, and the manner in which ferromagnetic
ordering is affected by increasing oxygen non-stoichiometry.",0405535v2
2004-05-27,Excitation of magnetostatic spin waves in ferromagnetic films,"The torque equation of nonlinear spin dynamics is considered in the
magnetostatic approximation. In this framework, exact expressions for
propagator of linear magnetostatic waves in ferromagnetic film between two
antennas and corresponding mutual impedance of the antennas are derived, under
conditions of uniform but arbitrarily oriented static magnetization and
arbitrary anisotropy. The results imply also full description of spectrum of
the waves.",0405640v1
2004-06-22,Spiral Exchange Interaction in Diluted Magnetic Semiconductor Junction,"We studied the exchange interactions mediated by polarized itinerant carriers
in diluted magnetic semiconductor (DMS) junction. In contrast to the ordinary
RKKY oscillations, the induced moment possesses an interesting spiral motion,
accompanied with angular oscillations. The spiral motion remains robust in the
entire $T<T_{c}$ regime while the oscillatory motion gets enhanced as $T \to
T_{c}$. To explore the novel phenomena, we propose a
ferromagnet/DMS/ferromagnet junction would bring out interesting spin-dependent
transport properties and possible applications in spintronics.",0406499v1
2004-06-24,Electronic Structure and Magnetic Exchange Coupling in Ferromagnetic Full Heusler Alloys,"Density-functional studies of the electronic structures and exchange
interaction parameters have been performed for a series of ferromagnetic full
Heusler alloys of general formula Co$_2$MnZ (Z = Ga, Si, Ge, Sn), Rh$_2$MnZ (Z
= Ge, Sn, Pb), Ni$_2$MnSn, Cu$_2$MnSn and Pd$_2$MnSn, and the connection
between the electronic spectra and the magnetic interactions have been studied.
Different mechanisms contributing to the exchange coupling are revealed. The
band dependence of the exchange parameters, their dependence on volume and
valence electron concentration have been thoroughly analyzed within the Green
function technique.",0406588v1
2004-06-25,Single particle spectrum of the flux phase in the FM Kondo Model,"We investigate the 2D ferromagnetic Kondo lattice model for manganites with
classical corespins at Hund's rule coupling J_H=6, with antiferromagnetic
superexchange 0.03 < J' < 0.05. We employ canonical and grand canonical
unbiased Monte Carlo simulations and find paramagnetism, weak ferromagnetism
and the Flux phase, depending on doping and on J'. The observed single particle
spectrum in the flux phase differs from the idealized infinite lattice case,
but agrees well with an idealized finite lattice case with thermal
fluctuations.",0406635v1
2004-07-06,Effect of Spin Current on Uniform Ferromagnetism: Domain Nucleation,"Large spin current applied to a uniform ferromagnet leads to a spin-wave
instability as pointed out recently.
  In this paper, it is shown that such spin-wave instability is absent in a
state containing a domain wall, which indicates that nucleation of magnetic
domains occurs above a certain critical spin current.
  This scenario is supported also by an explicit energy comparison of the two
states under spin current.",0407116v2
2004-07-07,Roles of non-equilibrium conduction electrons on magnetization dynamics of ferromagnets,"The mutual dependence of spin-dependent conduction and magnetization dynamics
of ferromagnets provides the key mechanisms in various spin-dependent
phenomena. We compute the response of the conduction electron spins to a
spatial and time varying magnetization ${\bf M} ({\bf r},t)$ within the
time-dependent semiclassical transport theory. We show that the induced
non-equilibrium conduction spin density in turn generates four spin torques
acting on the magnetization--with each torque playing different roles in
magnetization dynamics. By comparing with recent theoretical models, we find
that one of these torques that has not been previously identified is crucial to
consistently interpret experimental data on domain wall motion.",0407174v2
2004-07-09,Superconductivity controlled by the magnetic state of ferromagnetic nanoparticles,"Novel hybrid superconductor/ferromagnetic particles structures are presented.
Arrays of Co submicron particles were fabricated on overlap, edge type
Josephson junctions and on a narrow Nb microbridge by means of high-resolution
e-beam lithography.We observed a strong dependence between the magnetic state
of the particles and the field-dependent critical $I_c(H)$ of these structures.",0407249v2
2004-07-14,Monte Carlo simulations of ferromagnetism in p-CdMnTe quantum wells,"Monte Carlo simulations, in which the Schrodinger equation is solved at each
Monte Carlo sweep, are employed to assess the influence of magnetization
fluctuations,short-range antiferromagnetic interactions, disorder, magnetic
polaron formation, and spin-Peierls instability on the carrier-mediated Ising
ferromagnetism in two-dimensional electronic systems. The determined critical
temperature and hysteresis are affected in a nontrivial way by the
antiferromagnetic interactions. The findings explain striking experimental
results for modulation-doped p-CdMnTe quantum wells.",0407356v2
2004-07-19,Voltage Dependence of Spin Polarized Tunneling,"A mesoscopic spin valve is used to determine the effective spin polarization
of electrons tunneling from and into ferromagnetic transition metals at finite
voltages. The tunneling spin polarization from the ferromagnet (FM) slowly
decreases with bias, but drops faster and even inverts with voltage when
electrons tunnel into it. A bias-dependent free electron model shows that in
the former case electrons originate near the Fermi level of the FM with large
polarization whereas in the latter, electrons tunnel into hot electron states
for which the polarization is significantly reduced. The change in sign is
ascribed to the detailed matching of the electron wave function through the
tunnel barrier.",0407489v1
2004-07-19,Highly polarized injection luminescence in forward-biased ferromagnetic-semiconductor junctions at low spin polarization of current,"We consider electron tunneling from a nonmagnetic $n$-type semiconductor
($n$-S) into a ferromagnet (FM) through a very thin forward-biased Schottky
barrier resulting in efficient extraction of electron spin from a thin $n$-S
layer near FM-S interface at low spin polarization of the current. We show that
this effect can be used for an efficient polarization radiation source in a
heterostructure where the accumulated spin polarized electrons are injected
from $n$-S and recombine with holes in a quantum well. The radiation
polarization depends on a bias voltage applied to the FM-S junction.",0407492v1
2004-08-04,Two-cycles in spin systems: multi-state Ising-type ferromagnets,"Hamiltonians for general multi-state spin-glass systems with Ising symmetry
are derived for both sequential and synchronous updating of the spins. The
possibly different behaviour caused by the way of updating is studied in detail
for the (anti)-ferromagnetic version of the models, which can be solved
analytically without any approximation, both thermodynamically via a
free-energy calculation and dynamically using the generating functional
approach. Phase diagrams are discussed and the appearance of two-cycles in the
case of synchronous updating is examined. A comparative study is made for the
Q-Ising and the Blume-Emery-Griffiths ferromagnets and some interesting
physical differences are found. Numerical simulations confirm the results
obtained.",0408086v1
2004-08-20,"Low temperature ferromagnetism in (Ga, Mn)N","The magnetic properties of dilute magnetic semiconductors (DMS) are
calculated from first-principles by mapping the ab initio results on a
classical Heisenberg model. It is found that the range of the exchange
interaction in (Ga, Mn)N is very short ranged due to the exponential decay of
the impurity wave function in the gap. Curie temperatures (Tc) of DMS are
calculated by using the Monte Carlo method. It is found that the Tc values of
(Ga, Mn)N are very low since, due to the short ranged interaction, percolation
of the ferromagnetic coupling is difficult to achieve for small concentrations.",0408450v1
2004-08-26,Spintronics and ferromagnetism in wide-band-gap semiconductors,"Recent progress in understanding and controlling spintronic properties of
(Ga,Mn)As and related compounds is contrasted to diverging experimental and
theoretical results concerning the origin of high temperature ferromagnetism
discovered in an ample class of magnetically doped wide-band-gap
semiconductors.",0408561v1
2004-09-01,Mesoscopic quantized properties of magnetic-dipolar-mode oscillations in disk ferromagnetic particles,"Magnetic dipolar mode or magnetostatic (MS) oscillations in ferrite samples
have the wavelength much smaller than the electromagnetic wavelength at the
same frequency and, at the same time, much larger than the exchange interaction
spin wavelength. This intermediate position between the electromagnetic and
spin wave (exchange interaction) processes reveals very special behaviors of
the geometrical effects. It was shown recently that magnetic dipolar mode
oscillations in a normally magnetized ferromagnetic disk are characterized by
discrete energy levels resulting from the structural confinement. In this
article we give results of the energy spectra in MS wave ferrite disks taking
into account nonhomogeneity of the internal DC magnetic field.",0409023v1
2004-09-12,Inhomogeneous magnetic behavior of Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3,"Unlike La0.7Ca0.3CoO2.97, Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO2.95 do not show
distinct ferromagnetic transitions, but instead they exhibit very low magnetic
moments down to 50 K. A detail study of magnetic properties of Pr0.7Ca0.3CoO3
and Nd0.7Ca0.3CoO2.95 shows that the materials are inhomogeneous, exhibiting
properties similar to those of frustrated magnetic systems. In both these
cobaltates, small ferromagnetic clusters seem to be present in an
antiferromagnetic host.",0409297v1
2004-09-22,"Interactions, disorder and local defects in graphite","Recent experiments report the existence of ferromagnetic and superconducting
fluctuations in graphite at unexpectedly high temperatures. The interplay of
disorder and interactions in a 2D graphene layer is shown to give rise to a
rich phase diagram where strong coupling phases can become stable. Local
defects can explain the ferromagnetic signals.",0409567v1
2004-09-30,Scaling theory of magneto-resistance in disordered local moment ferromagnets,"We present a scaling theory of magneto-transport in Anderson-localized
disordered ferromagnets. Within our framework a pronounced
magnetic-field-sensitive resistance peak emerges naturally for temperatures
near the magnetic phase transition. We find that the resistance anomaly is a
direct consequence of the change in localization length caused by the magnetic
transition. For increasing values of the external magnetic field, the
resistance peak is gradually depleted and pushed towards higher temperatures.
Our results are in good agreement with magneto-resistance measurements on a
variety of disordered magnets.",0410003v2
2004-10-01,"Mixed magnetic phases in (Ga,Mn)As epilayers","Two different ferromagnetic-paramagnetic transitions are detected in
(Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition
at a higher temperature results from (Ga,Mn)As cluster phases with [110]
uniaxial anisotropy and that at a lower temperature is associated with a
ferromagnetic (Ga,Mn)As matrix with <100> cubic anisotropy. A change in the
magnetic easy axis from [100] to [110] with increasing temperature can be
explained by the reduced contribution of <100> cubic anisotropy to the magnetic
properties above the transition temperature of the (Ga,Mn)As matrix.",0410022v1
2004-10-13,"Structure, Tranport and Magnetism of La(0.67)Ca(0.33)Mn(1-x)Ta(x)O(3)","For the first time,we report the effect of pentavalent subtitution at the Mn
site of La(0.67)Ca(0.33)MnO(3). The ferromagnetic -metallic ground state
modifies to a cluster-glass insulator beyond x=0.03. The observed suppression
in the transition temperatures (39K/at.%) is the largest reported for the Mn
site subtituted manganites. We argue that charge state(valence) of the
substituent has a dominant role in affecting the ferromagnetic - metallic
ground state of CMR manganites.",0410329v1
2004-10-13,Tricritical behavior in itinerant quantum ferromagnets,"It is shown that the peculiar features observed in the low-temperature phase
diagrams of ZrZn_2, UGe_2, and MnSi can be understood in terms of a simple
mean-field theory. The nature of the ferromagnetic transition changes from
second order to first order at a tricritical point, and in a small external
magnetic field surfaces of first-order transitions emerge which terminate in
quantum critical points. This field dependence of the phase diagram follows
directly from the existence of the tricritical point. The quantum critical
behavior in a nonzero field is calculated exactly.",0410344v1
2004-10-20,Static properties and spin dynamics of the ferromagnetic spin-1 Bose gas in magnetic field,"Properties of spin-1 Bose gases with ferromagnetic interaction in the
presence of a nonzero magnetic field are studied. The equation of state and
thermodynamic quantities are worked out with the help of a mean-field
approximation. The phase diagram besides Bose-Einstein condensation contains a
first order transition where two values of the magnetization coexist. The
dynamics is investigated with the help of the Random Phase Approximation. The
soft mode corresponding to the critical point of the magnetic phase transition
is found to behave like in conventional theory.",0410501v1
2004-10-26,Superconducting pi qubit with a ferromagnetic Josephson junction,"Solid-state qubits have the potential for the large-scale integration and for
the flexibility of layout for quantum computing. However, their short
decoherence time due to the coupling to the environment remains an important
problem to be overcome. We propose a new superconducting qubit which
incorporates a spin-electronic device: the qubit consists of a superconducting
ring with a ferromagnetic pi junction which has a metallic contact and a normal
Josephson junction with an insulating barrier. Thus, a quantum coherent
two-level state is formed without an external magnetic field. This feature and
the simple structure of the qubit make it possible to reduce its size leading
to a long decoherence time.",0410658v1
2004-10-31,Lateral length scales in exchange bias,"When a ferromagnet is in proximity with an antiferromagnet, lateral length
scales such as the respective magnetic domain sizes drastically affect the
exchange bias. Bilayers of FeF2 and either Ni, Co or Fe are studied using SQUID
and spatially resolved MOKE. When the antiferromagnetic domains are larger than
or comparable to the ferromagnetic domains, a local, non-averaging exchange
bias is observed. This gives rise to unusual and tunable magnetic hysteresis
curves.",0411014v1
2004-11-04,Localised magnetic excitations of coupled impurities in a transverse Ising ferromagnet,"A Green's function formalism is used to calculate the spectrum of excitations
of two neighboring impurities implanted in a semi-infinite ferromagnetic. The
equations of motion for the Green's functions are determined in the framework
of the Ising model in a transverse field and results are given for the effect
of the exchange coupling, position and orientation of the impurities on the
spectra of localized spin wave modes.",0411119v1
2004-11-11,Ferromagnetic-superconducting hybrid films and their possible applications: A direct study in a model combinatorial film,"Model combinatorial films (CFs) which host a pure superconductor adjacent to
a ferromagneticsuperconducting hybrid film (HF) are manufactured for the study
of the influence of ferromagnetic nanoparticles (FNs) on the nucleation of
superconductivity. Careful resistance measurements were performed
simultaneously on two different sites of the CFs. Enhancement of
superconductivity and magnetic memory effects were observed only on the hybrid
site of the CFs but were absent on their purely superconducting part. Our
results give direct proof that the FNs modulate the superconducting order
parameter in an efficient and controlled way giving us the possibility of
miscellaneous practical applications.",0411311v1
2004-11-18,Hanle Effect in Transport through Quantum Dots Coupled to Ferromagnetic Leads,"We suggest a series of transport experiments on spin precession in quantum
dots coupled to one or two ferromagnetic leads. Dot spin states are created by
spin injection and analyzed via the linear conductance through the dot, while
an applied magnetic field gives rise to the Hanle effect. Such a Hanle
experiment can be used to determine the spin lifetime in the quantum dot, to
measure the spin injection efficiency into the dot, as well as proving the
existence of intrinsic spin precession which is driven by the Coulomb
interaction.",0411477v2
2004-12-01,Magnetic phase separation in EuB6 detected by muon spin rotation,"We report results of the first muon-spin rotation measurements performed on
the low carrier density ferromagnet EuB$_6$. The ferromagnetic state is reached
via two magnetic transitions at $T_{\rm m}=16.5$ K and $T_{\rm c}=12.6$ K. Two
distinct components are resolved in the muon data, one oscillatory and one
non-oscillatory, which arise from different types of magnetic environment, and
we have followed the temperature dependence of these components in detail.
These results provide evidence for magnetic phase separation and can be
interpreted in terms of the gradual coalescing of magnetic polarons.",0412019v1
2004-12-02,Integrating Magnetism into Semiconductor Electronics,"Vision of ferromagnet/semiconductor hybrid as a strongly coupled but flexible
spin system is presented. We analyze the experiments and argue that contrary to
the common sense the nonmagnetic semiconductor plays a crucial role in
manipulating of ferromagnetism. The magnetism of the hybrid (magnetic
hysteresis loop and the orientation of magnetization vector in space) is tuned
both optically and electrically with the help of semiconductor. As a result the
hybrid represents an elementary magnetic storage with electronic record and
readout",0412054v2
2004-12-22,Ballistic anisotropic magnetoresistance,"Electronic transport in ferromagnetic ballistic conductors is predicted to
exhibit ballistic anisotropic magnetoresistance (BAMR) - a change in the
ballistic conductance with the direction of magnetization. This phenomenon
originates from the effect of the spin-orbit interaction on the electronic band
structure which leads to a change in the number of bands crossing the Fermi
energy when the magnetization direction changes. We illustrate the significance
of this phenomenon by performing ab-initio calculations of the ballistic
conductance in ferromagnetic Ni and Fe nanowires which display a sizable BAMR
when the magnetization changes direction from parallel to perpendicular to the
wire axis.",0412637v1
2005-01-07,Nonequilibrium quantum phase transition in itinerant electron systems,"We study the effect of the voltage bias on the ferromagnetic phase transition
in a one-dimensional itinerant electron system. The applied voltage drives the
system into a nonequilibrium steady state with a non-zero electric current. The
bias changes the universality class of the second order ferromagnetic
transition. While the equilibrium transition belongs to the universality class
of the uniaxial ferroelectric, we find the mean-field behavior near the
nonequilibrium critical point.",0501133v2
2005-01-19,Ferromagnetic 0-pi Junctions as Classical Spins,"The ground state of highly damped PdNi based 0-pi ferromagnetic Josephson
junctions shows a spontaneous half quantum vortex, sustained by a supercurrent
of undetermined sign. This supercurrent flows in the electrode of a Josephson
junction used as a detector and produces a phi(0)/4 shift in its magnetic
diffraction pattern. We have measured the statistics of the positive or
negative sign shift occurring at the superconducting transition of such a
junction. The randomness of the shift sign, the reproducibility of its
magnitude and the possibility of achieving exact flux compensation upon field
cooling: all these features show that 0-pi junctions behave as classical spins,
just as magnetic nanoparticles with uniaxial anisotropy.",0501459v1
2005-01-20,Observation of magnetoelectric behavior at room temperature in Pb(Fe1-xTix)O3,"The coexistence of ferroelectric and ferromagnetic properties at room
temperature is very rarely observed. We have been successful in converting
ferroelectric PbTiO3 into a magnetoelectric material by partly substituting Fe
at the Ti site. The Pb(Fe1-xTix)O3 system exhibits ferroelectric and
ferromagnetic ordering at room temperature. Even more remarkably, our results
demonstrate a coupling between the two order parameters. Hence it could be a
futuristic material to provide cost effective and simple path for designing
novel electromagnetic devices.",0501489v1
2005-01-20,Magnetoresistance of mesoscopic granular ferromagnets,"We have performed magnetoresistance (MR) measurements of granular
ferromagnets having lateral dimensions smaller than 0.5 $\mu$m and containing a
small number of grains (down to about 100). Compared to macroscopic samples,
these granular samples exhibit unusually large saturation fields and MR
amplitudes. In addition, the evolution of the magnetoresistance curve as the
intergrain distance decreases is qualitatively different than that of large
samples. We discuss these results and suggest that they reflect a transition
from percolation to quasi single-channel dominated transport.",0501508v1
2005-01-21,Density of states anomalies in hybrid superconductor-ferromagnet-normal metal structures,"The results of calculations of the spatially-resolved density of states (DoS)
in an S(F/N) bilayer are presented (S is a superconductor, F is a metallic
ferromagnet, N is a normal metal) within quasiclassical theory in the dirty
limit. Analytical solutions are obtained in the case of thin F, N layers which
demonstrate the peculiar features of DoS in this system. The dependencies of
the minigap and the DoS peak positions on the exchange energy and parameters of
the layers are studied numerically",0501514v1
2005-01-24,Spin transport and magnetoresistance in F/S/F spin valves,"We consider spin transport and spin relaxation in superconductors using the
quasiclassical theory of superconductivity. We include spin relaxation due to
spin-orbit interaction as well as magnetic impurities, and show that the energy
dependence of the spin-flip rate is different for these two mechanisms. In
ferromagnet-superconductor-ferromagnet systems made of Co and Al, interface
resistances can be small compared to bulk resistances. This simplifies the
description of transport in Co/Al/Co spin valves, for which we numerically
calculate the temperature and Al length dependence of the magnetoresistance.",0501566v1
2005-02-23,Quantum Monte Carlo Simulations on S=1/2 antiferromagnetic-Ferromagnetic Random Alternating spin chain,"The S=1/2 Heisenberg chain with bond alternation and randomness of
antiferromagnetic (AFM) and ferromagnetic (FM) interactions is investigated by
quantum Monte Carlo simulations of loop/cluster algorithm. Our results have
shown interesting finite temperature magnetic properties of this model. The
relevance of our study to the observed results of the material
(CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$ is discussed.",0502543v1
2005-02-24,Tailoring Fe/Ag Superparamagnetic Composites by Multilayer Deposition,"The magnetic properties of Fe/Ag granular multilayers were examined by SQUID
magnetization and Mossbauer spectroscopy measurements. Very thin (0.2 nm)
discontinuous Fe layers show superparamagnetic properties that can be tailored
by the thickness of both the magnetic and the spacer layers. The role of
magnetic interactions was studied in novel heterostructures of
superparamagnetic and ferromagnetic layers and the specific contribution of the
ferromagnetic layers to the low field magnetic susceptibility was identified.",0502578v1
2005-03-05,Pressure dependence of superconducting and magnetic critical temperatures in the ruthenocuprates,"We study the dependence on filling and pressure of the superconducting and
ferromagnetic critical temperatures of the ruthenocuprates, within the two-band
model. At zero pressure, we find separate regions of coexistence of
superconductivity and ferromagnetism as a function of filling, with contiguous
regions merging together as pressure increases. As a function of pressure, a
stronger enhancement of the magnetic phase results in a reduced pressure effect
on the superconducting critical temperature. Comparison with recent experiments
on the determination of the critical temperatures as a function of the pressure
is also discussed.",0503119v1
2005-03-13,Magnetism in C60 Films Induced by Proton Irradiation,"It is shown that polycrystalline fullerene thin films on hydrogen passivated
Si(111) substrates irradiated by 2 MeV protons displays ferromagnetic-like
behavior at 5 K. At 300 K both the pristine and the irradiated film show
diamagnetic behavior. Magnetization data in the temperature range 2 - 300 K, in
1 Tesla applied field, for the irradiated film shows much stronger temperature
dependence compared to the pristine film. Possible origin of ferromagnetic-like
signals in the irradiated films are discussed.",0503315v2
2005-03-14,Surface spin waves in superconducting and insulating ferromagnets,"Surface magnetization waves are studied on a semi-infinite magnetic medium in
the perpendicular geometry. Both superconducting and insulating ferromagnets
are considered. Exchange and dipole energies are taken into account, as well as
retardation effects. At large wave vectors, the spectrum for a superconductor
and insulator is the same, though for the former the branch is terminated much
earlier than for the latter due to excitation of plasmons. At small wave
vectors, the surface wave is more robust in the superconductor since it is
separated from the bulk continuum by a finite gap.",0503340v1
2005-03-17,High Temperature Ferromagnetism in GaAs-based Heterostructures with Mn Delta Doping,"We show that suitably-designed magnetic semiconductor heterostructures
consisting of Mn delta-doped GaAs and p-type AlGaAs layers, in which the
locally high concentration of magnetic moments of Mn atoms are controllably
overlapped with the 2-dimensional hole gas wavefunction, realized remarkably
high ferromagnetic transition temperatures (TC). Significant reduction of
compensative Mn interstitials by varying the growth sequence of the structures
followed by low temperature annealing led to high TC up to 250 K. The
heterostructure with high TC exhibited peculiar anomalous Hall effect behavior,
whose sign depends on temperature.",0503444v1
2005-04-04,Transition from Ferromagnetism to Antiferromagnetism in Ga$_{1-x}$Mn$_x$N,"Using density functional theory, we study the magnetic stability of the
Ga$_{1-x}$Mn$_x$N alloy system. We show that unlike Ga$_{1-x}$Mn$_x$As, which
shows only ferromagnetic (FM) phase, Ga$_{1-x}$Mn$_x$N can be stable in either
FM or antiferromagnetic phases depending on the alloy concentration. The
magnetic order can also be altered by applying pressure or with charge
compensation. A unified model is used to explain these behaviors.",0504083v1
2005-04-06,Non-collinear single-electron spin-valve transistors,"We study interaction effects on transport through a small metallic cluster
connected to two ferromagnetic leads (a single-electron spin-valve transistor)
in the ""orthodox model"" for the Coulomb blockade. The non-local exchange
between the spin accumulation on the island and the ferromagnetic leads is
shown to affect the transport properties such as the electric current and
spin-transfer torque as a function of the magnetic configuration, gate voltage,
and applied magnetic field.",0504137v1
2005-04-15,Tuning the ferromagnetic properties of hydrogenated GaMnAs,"Hydrogenation and posthydrogenation annealings have been used as a very
efficient tool to tune the hole density over a wide range, at fixed magnetic
moment concentration, in thin GaMnAs layers. Reduction of the hole density
resulted in strong modifications of their ferromagnetic properties. In
particular, we observed in magnetotransport experiments the decrease of the
Curie temperature, along with modifications of the magnetic anisotropy, a
behavior consistent with the mean-field theory.",0504387v2
2005-04-21,Sum rules for X-ray magnetic circular dichroism spectra in strongly correlated ferromagnets,"It is proven that the sum rules for X-ray magnetic dichroism (XMCD) spectra
that are used to separate spin and orbital contributions to the magnetic moment
are formally correct for an arbitrary strength of electron-electron
interactions. However, their practical application for strongly correlated
systems can become complicated due to the spectral density weight spreading
over a broad energy interval. Relevance of incoherent spectral density for the
XMCD sum rules is illustrated by a simple model of a ferromagnet with orbital
degrees of freedom.",0504549v2
2005-04-25,Reentrant spin-glass transition in a dilute magnet,"We have performed a large scale Monte Carlo simulation of a dilute classical
Heisenberg model with ferromagnetic nearest neighbor and antiferromagnetic
next-nearest neighbor interactions. We found that the model reproduces a
reentrant spin-glass transition. That is, as the temperature is decreased, the
magnetization increases rapidly below a certain temperature, reaches a maximum
value, then ceases at some lower temperature. The low temperature phase was
suggested to be a spin-glass phase that is characterized by ferromagnetic
clusters.",0504615v1
2005-04-26,Green's function theory of quasi-two-dimensional spin-half Heisenberg ferromagnets: stacked square versus stacked kagomé lattice,"We consider the thermodynamic properties of the quasi-two-dimensional
spin-half Heisenberg ferromagnet on the stacked square and the stacked kagom\'e
lattices by using the spin-rotation-invariant Green's function method. We
calculate the critical temperature $T_C$, the uniform static susceptibility
$\chi$, the correlation lengths $\xi_\nu$ and the magnetization $M$ and
investigate the short-range order above $T_C$. We find that $T_C$ and $M$ at
$T>0$ are smaller for the stacked kagom\'e lattice which we attribute to
frustration effects becoming relevant at finite temperatures.",0504662v2
2005-04-26,Spin-Polarized Standing Waves in the Fermi Surface of a Ferromagnetic Thin Film,"The spin-selective electron reflection at a ferromagnetic-paramagnetic
interface is investigated using Fe films on a W(110) substrate. Angle-resolved
photoemission of the majority and minority Fermi surfaces of the Fe film is
used to probe standing wave formation. Intense quantum well states resulting
from interfacial reflection are observed exclusively for majority states. Such
high spin polarization is explained by the Fermi surface topology of the
connecting substrate, and we argue that Fe/W is a particularly suitable
interface for that purpose.",0504670v1
2005-05-10,Griffiths singularity in the random Ising ferromagnet,"The explicit form of the Griffiths singularity in the random ferromagnetic
Ising model in external magnetic field is derived. In terms of the continuous
random temperature Ginzburg-Landau Hamiltonian it is shown that in the
paramagnetic phase away from the critical point the free energy as the function
of the external magnetic field h in the limit h -> 0 has the essential
singularity of the form $\exp[-(const)h^{-D/3}]$ (where 1<D<4 is the space
dimensionality). It is demonstrated that in terms of the replica formalism this
contribution to the free energy comes due to off-perturbative replica instanton
excitations.",0505233v1
2005-05-11,Surface spin-transfer torque and spin-injection effective field in ferromagnetic junctions: Unified theory,"We consider theoretically a current flowing perpendicular to interfaces of a
spin-valve type ferromagnetic metallic junction. For the first time an
effective approach is investigated to calculate a simultaneous action of the
two current effects, namely, the nonequilibrium longitudinal spin injection and
the transversal spin-transfer surface torque. Dispersion relation for
fluctuations is derived and solved. Nonlinear problem is solved about steady
state arising due to instability for a thick enough free layer.",0505268v2
2005-05-22,Dynamics of topological solitons in two-dimensional ferromagnets,"Dynamical topological solitons are studied in classical two-dimensional
Heisenberg easy-axis ferromagnets. The properties of such solitons are treated
both analytically in the continuum limit and numerically by spin dynamics
simulations of the discrete system. Excitation of internal mode causes orbital
motion. This is confirmed by simulations.",0505542v2
2005-05-23,Local defects and ferromagnetism in graphene layers,"We study the changes in the electronic structure induced by lattice defects
in graphene planes. In many cases, lattice distortions give rise to localized
states at the Fermi level. Electron-electron interactions lead to the existence
of local moments. The RKKY interaction between these moments is always
ferromagnetic, due to the semimetallic properties of graphene",0505557v1
2005-05-23,Phase diagrams of soluble multi-spin glass models,"We include p-spin interactions in a spherical version of a soluble mean-field
spin-glass model proposed by van Hemmen. Due to the simplicity of the
solutions, which do not require the use of the replica trick, we are able to
carry out a detailed investigation of a number of special situations. For p
larger or equal to 3, there appear first-order transitions between the
paramagnetic and the ordered phases. In the presence of additional
ferromagnetic interactions, we show that there is no stable mixed phase, with
both ferromagnetic and spin-glass properties.",0505566v1
2005-05-24,"Magnetic scattering of spin polarized carriers in (In,Mn)Sb dilute magnetic semiconductor","Magnetoresistance measurements on the magnetic semiconductor (In,Mn)Sb
suggest that magnetic scattering in this material is dominated by isolated
Mn$^{2+}$ ions located outside the ferromagnetically-ordered regions when the
system is below $T_{c}$. A model is proposed, based on the $p$-$d$ exchange
between spin-polarized charge carriers and localized Mn$^{2+}$ ions, which
accounts for the observed behavior both below and above the ferromagnetic phase
transition. The suggested picture is further verified by high-pressure
experiments, in which the degree of magnetic interaction can be varied in a
controlled way.",0505582v1
2005-05-25,Sharp magnetization step across the ferromagnetic to antiferromagnetic transition in doped-CeFe$_2$ alloys,"Very sharp magnetization step is observed across the field induced
antiferromagnetic to ferromagnetic transition in various doped-CeFe$_2$ alloys,
when the measurement is performed below 5K. In the higher temperature regime
(T$>$5K) this transition is quite smooth in nature. Comparing with the recently
observed similar behaviour in manganites showing colossal magnetoresistance and
magnetocaloric material Gd$_5$Ge$_4$ we argue that such magnetization step is a
generalized feature of a disorder influenced first order phase transition.",0505609v1
2005-05-31,Spontaneous currents and half-integer Shapiro steps in Superconductor-Ferromagnet-Superconductor 0-pi Josephson junctions,"We study Superconductor-Ferromagnet-Superconductor (Nb-Cu0.47 Ni0.53-Nb)
Josephson junctions with spatial variations in the barrier thickness. Critical
current vs. magnetic flux diffraction patterns indicate that the critical
current density changes sign along the width of the junctions, creating
interfaces between 0 and pi junction regions around which spontaneous currents
can circulate. Shapiro steps observed at half-integer Josephson voltages can be
explained by the phase-locking of the spontaneous circulating currents to the
applied rf modulation.",0506003v1
2005-06-03,Half-metallic ferromagnets for magnetic tunnel junctions,"Using theoretical arguments, we show that, in order to exploit half-metallic
ferromagnets in tunneling magnetoresistance (TMR) junctions, it is crucial to
eliminate interface states at the Fermi level within the half-metallic gap;
contrary to this, no such problem arises in giant magnetoresistance elements.
Moreover, based on an a priori understanding of the electronic structure, we
propose an antiferromagnetically coupled TMR element, in which interface states
are eliminated, as a paradigm of materials design from first principles. Our
conclusions are supported by ab-initio calculations.",0506079v1
2005-06-24,Complete spin extraction from semiconductors near ferromagnet-semiconductor interfaces,"We show that spin polarization of electrons in nonmagnetic semiconductors
near specially tailored ferromagnet-semiconductor junctions can achieve 100%.
This effect is realized even at moderate spin injection coefficients of the
contact when these coefficients only weakly depend on the current. The effect
of complete spin extraction occurs at relatively strong electric fields and
arises from a reduction of spin penetration length due to the drift of
electrons from a semiconductor towards the spin-selective tunnel junction.",0506625v1
2005-06-24,Off-perturbative states in disordered systems,"The systematic approach for the off-perturbative calculations in disordered
systems is developed. The proposed scheme is applied for the random temperature
and the random field ferromagnetic Ising models. It is shown that away from the
critical point, in the paramagnetic phase of the random temperature model, and
in the ferromagnetic phase of the random field one, the free energy contains
non-analytic contributions which have the form of essential singularities. It
is demonstrated that these contributions appear due to localized in space
instanton-like excitations.",0506633v2
2005-07-04,Appearance of an inhomogeneous superconducting state in La{0.67}Sr{0.33}MnO{3}-YBa{2}Cu{3}O{7}-La{0.67}Sr{0.33}MnO{3} trilayers,"An experimental study of proximity effect in La{0.67}Sr{0.33}MnO3 - YBa2Cu3O7
- La{0.67}Sr{0.33}MnO3 trilayers is reported. Transport measurements on these
samples show clear oscillations in critical current (I_c) as the thickness of
La{0.67}Sr{0.33}MnO3 layers (d_F) is scanned from ~ 50 A to ~ 1100 A. In the
light of existing theories of ferromagnet-superconductor (FM-SC)
heterostructures, this observation suggests a long range proximity effect in
the manganite, modulated by it's weak exchange energy (~ 2 meV). The observed
modulation of the magnetic coupling between the ferromagnetic LSMO layers as a
function of d_F, also suggests an oscillatory behavior of the SC order
parameter near the FM-SC interface.",0507073v1
2005-07-05,Critical aging of a ferromagnetic system from a completely ordered state,"We adapt the non-linear $\sigma$ model to study the nonequilibrium critical
dynamics of O(n) symmetric ferromagnetic system. Using the renormalization
group analysis in $d=2+\epsilon$ dimensions we investigate the pure relaxation
of the system starting from a completely ordered state. We find that the
average magnetization obeys the long-time scaling behavior almost immediately
after the system starts to evolve while the correlation and response functions
demonstrate scaling behavior which is typical for aging phenomena. The
corresponding fluctuation-dissipation ratio is computed to first order in
$\epsilon$ and the relation between transverse and longitudinal fluctuations is
discussed.",0507112v2
2005-07-08,Pairing symmetry signatures of T1 in superconducting ferromagnets,"We study the nuclear relaxation rate 1/T1 as a function of temperature for a
superconducting-ferromagnetic coexistent system using a p-wave triplet model
for the superconducting pairing symmetry. This calculation is contrasted with a
singlet s-wave one done previously, and we see for the s-wave case that there
is a Hebel-Slichter peak, albeit reduced due to the magnetization, and no peak
for the p-wave case. We then compare these results to a nuclear relaxation rate
experiment on UGe2 to determine the possible pairing symmetry signatures in
that material. It is seen that the experimental data is inconclusive to rule
out the possibility of s-wave pairing in $UGe_{2}$.",0507212v1
2005-07-11,Electron-induced stabilization of ferromagnetism in GaGdN,"Using {\it ab initio} band structure calculations and symmetry arguments, we
show that the magnetic property of Ga$_{1-x}$Gd$_x$N is drastically different
from TM-doped GaN. The coupling between Gd atoms in the alloy is
antiferromagnetic, but the ferromagnetic phase can be stabilized by introducing
electrons. Furthermore, we propose a model that may explain the recently
observed colossal magnetic moments in this system, based on the polarization of
donor electrons.",0507257v1
2005-07-28,Optical study of interactions in a d-electron Kondo lattice with ferromagnetism,"We report on a comprehensive optical, transport and thermodynamic study of
the Zintl compound Yb$_{14}$MnSb$_{11}$, demonstrating that it is the first
ferromagnetic Kondo lattice compound in the underscreened limit. We propose a
scenerio whereby the combination of Kondo and Jahn-Teller effects provides a
consistent explanation of both transport and optical data.",0507693v1
2005-08-01,The Ruthenocuprates - Natural Superconductor-Ferromagnet Multilayers,"The recently discovered ruthenocuprates have attracted great interest because
of the microscopic coexistence of superconducting and ferromagnetic order.
Typically, these materials become magnetically ordered at temperatures around
125-145 K and superconductivity sets in between 15 and 50 K. While
superconductivity arises in the CuO2 layers the RuO2 layers in between order
magnetically. In this paper we summarize some of the crystallographic, magnetic
and superconducting properties of the ruthenocuprates, as obtained from
investigations on polycrystalline samples as well as single crystals.",0508044v1
2005-08-02,Numerical simulation of magnetization process in antiferromagnetic ferromagnetic bilayer with compensated interface,"The properties of antiferromagnetic ferromagnetic bilayer have been studied
using self-consistent mean-field approximation for Heisenberg Hamiltonian. The
perpendicular exchange coupling has been revealed in a bilayer with a
compensated interface. For a uniform antiferromagnetic film a symmetrical
hysteresis loop has been calculated, because the transverse instability
develops within the antiferromagnetic film at certain critical value of
external magnetic field. On the other hand, shifted hysteresis loop with a
finite exchange bias field has been obtained for a non-uniform
antiferromagnetic film consisting of various domains with perpendicular
directions of the easy anisotropy axes.",0508069v1
2005-08-03,Electronic Mechanism for the Coexistence of Ferroelectricity and Ferromagnetism,"We study the strong coupling limit of a two-band Hubbard Hamiltonian that
also includes an inter-orbital on-site repulsive interaction $U_{ab}$. When the
two bands have opposite parity and are quarter filled, we prove that the ground
state is simultaneously ferromagnetic and ferroelectric for infinite
intra-orbital Coulomb interactions $U_{aa}$ and $U_{bb}$. We also show that
this coexistence leads to a singular magnetoelectric effect.",0508113v2
2005-08-04,Polar phonons and intrinsic dielectric response of the ferromagnetic insulating spinel CdCr$_2$S$_4$ from first principles,"We have studied the dielectric properties of the ferromagnetic spinel
CdCr$_2$S$_4$ from first principles. Zone-center phonons and Born effective
charges were calculated by frozen-phonon and Berry phase techniques within
LSDA+U. We find that all infrared-active phonons are quite stable within the
cubic space group. The calculated static dielectric constant agrees well with
previous measurements. These results suggest that the recently observed
anomalous dielectric behavior in CdCr$_2$S$_4$ is not due to the softening of a
polar mode. We suggest further experiments to clarify this point.",0508136v1
2005-08-07,Ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors,"We develop a theory of the magnetization dynamics triggered by ultrafast
optical excitation of ferromagnetic semiconductors. We describe the effects of
the strong carrier spin relaxation on the nonlinear optical response by using
the Lindblad semigroup method. We demonstrate magnetization control during
femtosecond timescales via the interplay between circularly polarized optical
excitation, hole-spin damping, polarization dephasing, and the Mn-hole spin
interactions. Our results show a light-induced magnetization precession and
relaxation for the duration of the optical pulse.",0508178v1
2005-08-19,Vortex-antivortex dynamics and field-polarity-dependent flux creep in hybrid superconductor/ferromagnet nanostructures,"Vortex-antivortex arrays that are created in a type-II superconducting film
by lattices of ferromagnetic dots with perpendicular anisotropy have been
investigated. The highest critical current is shifted to a nonzero value of the
applied field, and current-voltage characteristics show different regimes of
vortex motion even in zero-applied field due to the presence of the
vortex-antivortex arrays. Creep of interstitial vortices is observed at low
driving forces. This flux creep is strongly field-polarity dependent.",0508459v1
2005-08-23,Switching magnetization of nano-scale ferromagnetic particle using non-local spin injection,"We have performed non-local spin injection into a nano-scale ferromagnetic
particle configured in a lateral spin valve structure to switch its
magnetization only by spin current. The non-local spin injection aligns the
magnetization of the particle parallel to the magnetization of the spin
injector. The responsible spin current for switching is estimated from the
experiment to be about 200 $\mu$A, which is reasonable compared with the values
obtained for conventional pillar structures. Interestingly the switching always
occurs from anti-parallel to parallel in the particle/injector magnetic
configurations, whereas no opposite switching is observed. Possible reasons for
this discrepancy are discussed.",0508559v1
2005-08-23,Direct measurement of charge transfer phenomena at ferromagnetic/superconducting oxide interfaces,"YBa2Cu3O7-x/La0.67Ca0.33MnO3 ferromagnetic/superconducting interfaces are
analyzed by scanning transmission electron microscopy and electron energy loss
spectroscopy with monolayer resolution. We demonstrate that extensive charge
transfer occurs between the manganite and the superconductor, in a manner
similar to modulation-doped semiconductors, which explains the reduced critical
temperatures of heterostructures. This behavior is not seen with insulating
PrBa2Cu3O7 layers. Furthermore, we confirm directly that holes in the
YBa2Cu3O7-x are located on the CuO2 planes.",0508564v2
2005-08-26,Kinetic arrest of the first order ferromagnetic to antiferromagnetic transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$ : formation of a magnetic-glass,"We present results of dc magnetization and magnetic relaxation study showing
the kinetic arrest of a first order ferromagnetic to antiferromagnetic
transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$. This leads to the formation of a
non-ergodic glass-like magnetic state. The onset of the magnetic-glass
transformation is tracked through the slowing down of the magnetization
dynamics. This glassy state is formed with the assistance of an external
magnetic field and this is distinctly different from the well known
'spin-glass' state.",0508625v1
2005-08-29,Interlayer Transport in Bilayer Quantum Hall Systems,"Bilayer quantum Hall systems have a broken symmetry ground state at filling
factor $\nu=1$ which can be viewed either as an excitonic superfluid or as a
pseudospin ferromagnet. We present a theory of inter-layer transport in quantum
Hall bilayers that highlights remarkable similarities and critical differences
between transport in Josephson junction and ferromagnetic metal spin-transfer
devices. Our theory is able to explain the size of the large but finite low
bias interlayer conductance and the voltage width of this collective transport
anomaly.",0508702v2
2005-09-02,Phonon spectrum of the ferromagnetic superconductor UGe$_2$ : Consequences for the specific heat,"We report inelastic neutron scattering measurements of the phonon spectrum of
the pressure-induced ferromagnetic superconductor UGe$_{2}$. No changes of the
spectrum were found on cooling down to low temperature. The phonon contribution
to the specific heat was estimated from a fit to our data. The excess specific
heat previously noted at around $T_{x} \approx$ 30 K is not due to phonons but
is well described by the temperature dependence of the magnetic order parameter
at the molecular field level.",0509052v2
2005-09-10,Microscopic Theory of Skyrmions in Quantum Hall Ferromagnets,"We present a microscopic theory of skyrmions in the monolayer quantum Hall
ferromagnet. It is a peculiar feature of the system that the number density and
the spin density are entangled intrinsically as dictated by the W$%_{\infty}$
algebra. The skyrmion and antiskyrmion states are constructed as W$_{\infty
}$-rotated states of the hole-excited and electron-excited states,
respectively. They are spin textures accompanied with density modulation that
decreases the Coulomb energy. We calculate their excitation energy as a
function of the Zeeman gap and compared the result with experimental data.",0509262v1
2005-09-19,Spiral vortices in a 2D ferromagnet,"We present a study of a new class of exact solutions having a form of spiral
vortices for an isotropic two-dimensional Heisenberg ferromagnet using a
continuum theory and direct numerical simulations of the spin system on a
square lattice. We find their features issued from the conservation laws and
describe their interaction. Reasons behind the formation of the proper spin
configurations on a square lattice are investigated.",0509481v1
2005-10-03,Thermoelectric effects in strongly interacting quantum dot coupled to ferromagnetic leads,"We study thermoelectric effects in Kondo correlated quantum dot coupled to
ferromagnetic electrodes by calculating conductance, thermopower and thermal
conductance in the Kondo regime. We also study the effect of the asymmetry in
the coupling to the leads, which has important consequences for anti-parallel
magnetization configuration. We discuss the thermoelectric figure of merit,
tunnel magnetoresistance and violation of the Wiedemann-Franz law in this
system. The results agree with recently measured thermopower of the quantum dot
defined in a two dimensional electron gas.",0510036v1
2005-10-05,Gated Spin Transport through an Individual Single Wall Carbon Nanotube,"Hysteretic switching in the magnetoresistance of short-channel,
ferromagnetically contacted individual single wall carbon nanotubes is
observed, providing strong evidence for nanotube spin transport. By varying the
voltage on a capacitively coupled gate, the magnetoresistance can be
reproducibly modified between +10% and -15%. The results are explained in terms
of wave vector matching of the spin polarized electron states at the
ferromagnetic / nanotube interfaces.",0510112v1
2005-10-08,Slater-Pauling Rule and Curie-Temperature of Co$_2$-based Heusler compounds,"A concept is presented serving to guide in the search for new materials with
high spin polarization. It is shown that the magnetic moment of half-metallic
ferromagnets can be calculated from the generalized Slater-Pauling rule.
Further, it was found empirically that the Curie temperature of Co$_2$ based
Heusler compounds can be estimated from a seemingly linear dependence on the
magnetic moment. As a successful application of these simple rules, it was
found that Co$_2$FeSi is, actually, the half-metallic ferromagnet exhibiting
the highest magnetic moment and the highest Curie temperature measured for a
Heusler compound.",0510210v1
2005-10-11,Non-damping magnetization oscillations in a single-domain ferromagnet,"Non-damped oscillations of the magnetization vector of a ferromagnetic system
subject to a spin polarized current and an external magnetic field are studied
theoretically by solving the Landau-Lifshitz-Gilbert equation. It is shown that
the frequency and amplitude of such oscillations can be controlled by means of
an applied magnetic field and a spin current. The possibility of injection of
the oscillating spin current into a non-magnetic system is also discussed.",0510280v1
2005-10-15,From ballistic transport to tunneling in electromigrated ferromagnetic breakjunctions,"We fabricate ferromagnetic nanowires with constrictions whose cross section
can be reduced gradually from 100 nm to the atomic scale and eventually to the
tunneling regime by means of electromigration. These devices are mechanically
stable against magnetostriction and magnetostatic effects. We measure
magnetoresistances ~ 0.3% for 100*30 nm^2 constrictions, increasing to a
maximum of 80% for atomic-scale widths. These results are consistent with a
geometrically-constrained domain wall trapped at the constriction. For the
devices in the tunneling regime we observe large fluctuations in MR, between
-10 and 85%.",0510410v1
2005-10-18,Anomalous Hall effect in ferromagnetic disordered metals,"The anomalous Hall effect in disordered band ferromagnets is considered in
the framework of quantum transport theory. A microscopic model of electrons in
a random potential of identical impurities including spin-orbit coupling is
used. The Hall conductivity is calculated from the Kubo formula for both, the
skew scattering and the side-jump mechanisms. The recently discussed Berry
phase induced Hall current is also evaluated within the model. The effect of
strong impurity scattering is analyzed and it is found to affect the ratio of
the non-diagonal (Hall) and diagonal components of the conductivity as well as
the relative importance of different mechanisms.",0510481v1
2005-11-02,Biferroic YCrO3,"YCrO3 which has a monoclinic structure, shows weak ferromagnetism below 140 K
(TN) and a ferroelectric transition at 473 K accompanied by hysteresis. We have
determined the structure and energetics of YCrO3 with ferromagnetic and
antiferromagnetic ordering by means of first-principles density functional
theory calculations, based on pseudopotentials and a plane wave basis. The
non-centrosymmetric monoclinic structure is found to be lower in energy than
the orthorhombic structure, supporting the biferroic nature of YCrO3.",0511045v1
2005-11-07,Current-induced switching in single ferromagnetic layer nanopillar junctions,"Current induced magnetization dynamics in asymmetric Cu/Co/Cu single magnetic
layer nanopillars has been studied experimentally at room temperature and in
low magnetic fields applied perpendicular to the thin film plane. In sub-100 nm
junctions produced using a nanostencil process a bistable state with two
distinct resistance values is observed. Current sweeps at fixed applied fields
reveal hysteretic and abrupt transitions between these two resistance states.
The current induced resistance change is 0.5%, a factor of 5 greater than the
anisotropic magnetoresistance (AMR) effect. We present an experimentally
obtained low field phase diagram of current induced magnetization dynamics in
single ferromagnetic layer pillar junctions.",0511144v1
2005-11-21,Kondo effect in quantum dots coupled to ferromagnetic leads with noncollinear magnetizations,"Non-equilibrium Green's function technique has been used to calculate
spin-dependent electronic transport through a quantum dot in the Kondo regime.
The dot is described by the Anderson Hamiltonian and is coupled either
symmetrically or asymmetrically to ferromagnetic leads, whose magnetic moments
are noncollinear. It is shown that the splitting of the zero bias Kondo anomaly
in differential conductance decreases monotonically with increasing angle
between magnetizations, and for antiparallel configuration it vanishes in the
symmetrical case while remains finite in the asymmetrical one.",0511506v1
2005-11-23,Phase separation in the trapped spinor gases with anisotropic spin-spin interaction,"We investigate the effect of the anisotropic spin-spin interaction on the
ground state density distribution of the one dimensional spin-1 bosonic gases
within a modified Gross-Pitaevskii theory both in the weakly interaction regime
and in the Tonks-Girardeau (TG) regime. We find that for ferromagnetic spinor
gas the phase separation occurs even for weak anisotropy of the spin-spin
interaction, which becomes more and more obvious and the component of $m_F=0$
diminishes as the anisotropy increases. However, no phase separation is found
for anti-ferromagnetic spinor gas in both regimes.",0511581v2
2005-12-13,Thermal collapse of spin-polarization in half-metallic ferromagnets,"The temperature dependence of the magnetization and spin-polarization at the
Fermi level is investigated for half-metallic ferromagnets. We reveal a new
mechanism, where the hybridization of states forming the half-metallic gap
depends on thermal spin fluctuations and the polarization can drop abruptly at
temperatures much lower than the Curie point. We verify this for NiMnSb by
ab-initio calculations. The thermal properties are studied by mapping ab-initio
results to an extended Heisenberg model which includes longitudinal
fluctuations and is solved by a Monte Carlo method.",0512277v1
2005-12-13,First order phase transitions in Ferromagnet/Superconductor layered structures,"We study the thermodynamics of clean structures composed of superconductor
(S) and ferromagnet (F) layers and consisting of one or more SFS junctions. We
use fully self consistent numerical methods to compute the condensation free
energies of the possible order parameter configurations as a function of
temperature $T$. As $T$ varies, we find that there are phase transitions
between states characterized by different junction configurations (denoted as
``0'' or ``$\pi$'' according to the phase difference of the order parameter in
consecutive S layers). We show that these transitions are of first order. We
calculate the associated latent heats and find them to be measurable.",0512285v1
2005-12-19,Experimental Evidence for Crossed Andreev Reflection,"We report on electronic transport properties of mesoscopic
superconductor-ferromagnet spin-valve structures. Two ferromagnetic iron leads
form planar tunnel contacts to a superconducting aluminum wire, where the
distance of the two contacts is of the order of the coherence length of the
aluminum. We observe a negative non-local resistance which can be explained by
crossed Andreev reflection, a process where an electron incident from one of
the leads gets reflected as a hole into the other, thereby creating a pair of
spatially separated, entangled particles.",0512445v1
2005-12-19,Aspects of the FM Kondo Model: From Unbiased MC Simulations to Back-of-an-Envelope Explanations,"Effective models are derived from the ferromagnetic Kondo lattice model with
classical corespins, which greatly reduce the numerical effort. Results for
these models are presented. They indicate that double exchange gives the
correct order of magnitude and the correct doping dependence of the Curie
temperature. Furthermore, we find that the jump in the particle density
previously interpreted as phase separation is rather explained by ferromagnetic
polarons.",0512462v1
2005-12-19,Spin injection into a short DNA chain,"Quantun spin transport through a short DNA chain connected to ferromagnetic
electrodes has been investigated by the transfer matrix method. We describe the
system by a tight-binding model where the parameters are extracted from the
experimental data and realistic metal energy bands. For ferromagnetic iron
electrodes, the magnetoresistance of a 30-basepair Poly(G)-Poly(C) DNA is found
to be lower than 10% at a bias of < 4 V, but can rach up to 20% at a bias of 5
V. In the presence of the spin-flip mechanism, the magnetoresistance is
significantly enhanced when the spin-flip coupling is weak but as the coupling
becomes stronger the decreasing magnetoresistance develops an oscillatory
behavior.",0512473v1
2005-12-27,Electronic Structure and Bulk Spin Valve Behavior in Ca$_3$Ru$_2$O$_7$,"We report density functional calculations of the magnetic properties and
Fermiology of Ca$_3$Ru$_2$O$_7$. The ground state consists of ferromagnetic
bilayers, stacked antiferromagnetically. The bilayers are almost but not
exactly half-metallic. In the ferromagnetic state opposite spin polarizations
are found for in-plane and out-of-plane transport. Relatively high out of plane
conductivity is found for the majority spin, which is relatively weakly
conductive in-plane. In the ground state in-plane quantities are essentially
the same, but the out of plane transport is strongly reduced.",0512673v1
2005-12-28,Correlation effects in the valence bands of ferromagnetic semiconductor EuS,"We present a many body analysis of the multi-band Kondo lattice model. The
study is then combined with the first principles TB-LMTO band structure
calculations, in order to investigate the temperature dependent correlation
effects in the 3$\textit{p}$ valence bands of the ferromagnetic semiconductor
EuS. Some of the physical properties of interest like the quasi-particle
density of states (Q-DOS), spectral density (SD) and quasi-particle band
structure (Q-BS) are calculated and discussed. Therewith, we propose a spin
resolved ARPES of the valence bands of EuS to be performed.",0512688v1
2005-12-30,A Tunable Anomalous Hall Effect in a Non-Ferromagnetic System,"We measure the low-field Hall resistivity of a magnetically-doped
two-dimensional electron gas as a function of temperature and
electrically-gated carrier density. Comparing these results with the carrier
density extracted from Shubnikov-de Haas oscillations reveals an excess Hall
resistivity that increases with decreasing temperature. This excess Hall
resistivity qualitatively tracks the paramagnetic polarization of the sample,
in analogy to the ferromagnetic anomalous Hall effect. The data are consistent
with skew-scattering of carriers by disorder near the crossover to
localization.",0512730v1
2006-01-10,Short-time behavior of a classical ferromagnet with double-exchange interaction,"We investigate the critical dynamics of a classical ferromagnet on the simple
cubic lattice with double-exchange interaction. Estimates for the dynamic
critical exponents $z$ and $\theta$ are obtained using short-time Monte Carlo
simulations. We also estimate the static critical exponents $\nu$ and $\beta$
studying the behavior of the samples at an early time. Our results are in good
agreement with available estimates and support the assertion that this model
and the classical Heisenberg model belong to the same universality class.",0601208v1
2006-01-12,Random phase approximation for the 1D anti-ferromagnetic Heisenberg model,"The Hartree-Fock-RPA approach is applied to the 1D anti-ferromagnetic
Heisenberg model in the Jordan-Wigner representation. Somewhat contrary to
expectation, this leads to reasonable results for spectral functions and sum
rules in the symmetry unbroken phase. In a preliminary application of
Self-Consistent RPA to finite size chains strongly improved results are
obtained.",0601264v4
2006-01-17,Microwave Response and Spin Waves in Superconducting Ferromagnets,"Excitation of spin waves is considered in a superconducting ferromagnetic
slab with the equilibrium magnetization both perpendicular and parallel to the
surface. The surface impedance is calculated and its behavior near propagation
thresholds is analyzed. Influence of non-zero magnetic induction at the surface
is considered in various cases. The results provide a basis for investigation
of materials with coexisting superconductivity and magnetism by microwave
response measurements.",0601386v2
2006-01-24,Attractive electron-electron interaction induced by geometric phase in a Bloch band,"We investigate electron pairing in the presence of the Berry curvature field
that ubiquitously exists in ferromagnetic metals with spin-orbit coupling. We
show that a sufficiently strong Berry curvature field on the Fermi surface can
transform a repulsive interaction between electrons into an attractive one in
the p-wave channel. We also reveal a topological possibility for turning an
attractive s-wave interaction into one in the p-wave channel, even if the Berry
curvature field only exists inside the Fermi surface (circle). We speculate
that these novel mechanism might be relevant to the recently discovered
ferromagnetic superconductors such as UGe$_{2}$ and URhGe.",0601531v2
2006-02-06,Thermoelectric effects in a strongly interacting quantum dot coupled to ferromagnetic leads,"We study thermoelectric effects in Kondo correlated quantum dot coupled to
ferromagnetic electrodes by calculating thermopower S in the Kondo regime as
function of on-dot energy level and temperature. The system is represented by
the Anderson model and the results agree well with those recently measured for
a quantum dot coupled to nonmagnetic leads. For magnetic electrodes one
observes marked dependence of S on the degree of their polarization.",0602121v1
2006-02-06,Colossal magnetocapacitance and colossal magnetoresistance in HgCr2S4,"We present a detailed study of the dielectric and charge transport properties
of the antiferromagnetic cubic spinel HgCr2S4. Similar to the findings in
ferromagnetic CdCr2S4, the dielectric constant of HgCr2S4 becomes strongly
enhanced in the region below 60 - 80 K, which can be ascribed to polar
relaxational dynamics triggered by the onset of ferromagnetic correlations. In
addition, the observation of polarization hysteresis curves indicates the
development of ferroelectric order below about 70 K. Moreover, our
investigations in external magnetic fields up to 5 T reveal the simultaneous
occurrence of magnetocapacitance and magnetoresistance of truly colossal
magnitudes in this material.",0602126v1
2006-02-17,Ferromagnetic and superconducting instabilities in graphite,"We review our recent work on magnetic properties of graphite and related
carbon materials. The results demonstrate that a structural disorder,
topological defects, as well as adsorbed foreign atoms can be responsible for
the occurrence of both ferromagnetic and superconducting patches in graphitic
structures.",0602413v2
2006-02-28,On magnetic susceptibility of a spin-S impurity in nearly ferromagnetic Fermi liquid,"We present the renormalization group analysis for the problem of a spin-S
impurity in nearly ferromagnetic Fermi liquid. We evaluate the renormalization
group function that governs the temperature behavior of the invariant charge to
the second order of both weak and strong coupling expansions. It allows us to
determine behavior of the zero field magnetic susceptibility of impurity at low
and high temperatures. We predict that derivative of the susceptibility with
temperature should always have the maximum.",0602650v1
2006-03-06,Edge states generated by spin-orbit coupling at domain walls in magnetic semiconductors,"Electronic states localized at domain walls between ferromagnetically ordered
phases in two-dimensional electron systems are generated by moderate spin-orbit
coupling. The spin carried by these states depends on the slope of the magnetic
background at the domain wall. The number of localized states is determined by
a real space topological number, and spin perpendicular to the ferromagnetic
order accumulates in these localized states at domain walls. These trapped
states may be observed in experiments that probe either spin density or
conduction paths in quantum wells.",0603145v3
2006-03-13,Phase transitions in random magnetic bilayer,"The influence of random interlayer exchange on the phase states of the
simplest magnetic heterostructure consisting of two ferromagnetic Ising layers
with large interaction radius is studied. It is shown that such system can
exist in three magnetic phases: ferromagnetic, antiferromagnetic and
ferrimagnetic. The possible phase diagrams and temperature dependencies of
thermodynamic parameters are described. The regions of existence of the
magnetic phases in external magnetic field are determined at zero temperature.",0603347v3
2006-03-14,Fingerprints of the Magnetic Polaron in Nonequilibrium Electron Transport through a Quantum Wire Coupled to a Ferromagnetic Spin Chain,"We study nonequilibrium quantum transport through a mesoscopic wire coupled
via local exchange to a ferromagnetic spin chain. Using the Keldysh formalism
in the self-consistent Born approximation, we identify fingerprints of the
magnetic polaron state formed by hybridization of electronic and magnon states.
Because of its low decoherence rate, we find coherent transport signals. Both
elastic and inelastic peaks of the differential conductance are discussed as a
function of external magnetic fields, the polarization of the leads and the
electronic level spacing of the wire.",0603374v2
2006-03-15,Dynamic hysteresis from zigzag domain walls,"We investigate dynamic hysteresis in ferromagnetic thin films with zigzag
domain walls. We introduce a discrete model describing the motion of a wall in
a disordered ferromagnet with in-plane magnetization, driven by an external
magnetic field, considering the effects of dipolar interactions and anisotropy.
We analyze the effects of external field frequency and temperature on the
coercive field by Monte Carlo simulations, and find a good agreement with the
experimental data reported in literature for Fe/GaAs films. This implies that
dynamic hysteresis in this case can be explained by a single propagating domain
wall model without invoking domain nucleation.",0603406v2
2006-03-15,"Dephasing in (Ga,Mn)As nanowires and rings","To understand quantum mechanical transport in ferromagnetic semiconductor the
knowledge of basic material properties like phase coherence length and
corresponding dephasing mechanism are indispensable ingredients. The lack of
observable quantum phenomena prevented experimental access to these quantities
so far. Here we report about the observations of universal conductance
fluctuations in ferromagnetic (Ga,Mn)As. The analysis of the length and
temperature dependence of the fluctuations reveals a T^{-1} dependence of the
dephasing time.",0603418v1
2006-03-20,Triplet superconductivity in a 1D itinerant electron system with transverse spin anisotropy,"In this paper we study the ground state phase diagram of a one-dimensional
t-J-U model away from half-filling. In the large-bandwidth limit and for
ferromagnetic exchange with easy-plane anisotropy a phase with gapless charge
and massive spin excitations, characterized by the coexistence of triplet
superconducting and spin density wave instabilities is realized in the ground
state. With increasing ferromagnetic exchange transitions into a ferrometallic
and then a spin gapped triplet superconducting phase take place.",0603504v1
2006-03-21,Huge nonequilibrium magnetoresistance in hybrid superconducting spin valves,"A hybrid ferromagnet-superconductor spin valve is proposed. Its operation
relies on the interplay between nonequilibrium transport and proximity-induced
exchange coupling in superconductors. Huge tunnel magnetoresistance values as
large as some 10^6% can be achieved in suitable ferromagnet-superconductor
combinations under proper voltage biasing. The controllable spin-filter nature
of the structure combined with its intrinsic simplicity make this setup
attractive for low-temperature spintronic applications where reduced power
dissipation is an additional requirement.",0603555v1
2006-03-30,Dynamics of a quantum phase transition in the random Ising model,"A quantum phase transition from paramagnetic to ferromagnetic phase is driven
by a time-dependent external magnetic field. For any rate of the transition the
evolution is non-adiabatic and finite density of defects is excited in the
ferromagnetic state. The density of excitations has only logarithmic dependence
on the transition rate. This is much weaker than any usual power law scaling
predicted for pure systems by the Kibble-Zurek mechanism.",0603814v2
2006-04-13,Spin-wave instability for parallel pumping in ferromagnetic thin films under oblique field,"Spin-wave instability for parallel pumping is studied theoretically. The
spin-wave instability threshold is calculated in ferromagnetic thin films under
oblique field which has an oblique angle to the film plane. The butterfly curve
of the threshold usually has a cusp at a certain value of the static external
field. While the static field value of the cusp point varies as the oblique
angle changes, the general properties of the butterfly curve show little
noteworthy change. For very thin films, however, multiple cusps of the
butterfly curve can appear due to different standing spin-wave modes, which
indicate a novel feature for thin films under oblique field.",0604329v1
2006-04-13,Magnetic order and valency at La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ interfaces,"We report on first principles calculations of the electronic structure of
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ junction with two possible types of
interface terminations. We find that the La$_{0.7}$Sr$_{0.3}$O/TiO$_{2}$
interface preserves the interlayer ferromagnetic coupling between the interface
MnO$_{2}$ layer and the bulk. The other interface, MnO$_{2}$/SrO, favours
antiferromagnetic coupling with the bulk. By inserting two unit cells of
undoped LaMnO$_{3}$ at the interface the ferromagnetism is recovered. This is
understood in terms of the doping level and the mobility of carriers near the
interface.",0604343v1
2006-05-08,Microscopic Calculation of Spin Torques in Disordered Ferromagnets,"Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called $\beta$-term and the Gilbert damping, $\alpha$, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as $\alpha \ne \beta$
hold for localized as well as itinerant ferromagnetism.",0605186v1
2006-05-09,Influence of band structure effects on domain-wall resistance in diluted ferromagnetic semiconductors,"Intrinsic domain-wall resistance (DWR) in (Ga,Mn)As is studied theoretically
and compared to experimental results. The recently developed model of spin
transport in diluted ferromagnetic semiconductors [Van Dorpe et al., Phys. Rev.
B 72, 205322 (2005)] is employed. The model combines the disorder-free
Landauer-B\""uttiker formalism with the tight-binding description of the host
band structure. The obtained results show how much the spherical 4x4 kp model
[Nguyen, Shchelushkin, and Brataas, cond-mat/0601436] overestimates DWR in the
adiabatic limit, and reveal the dependence of DWR on the magnetization profile
and crystallographic orientation of the wall.",0605230v1
2006-05-10,Field-Induced Quantum Criticality of Systems with Ferromagnetically Coupled Structural Spin Units,"The field-induced quantum criticality of compounds with ferromagnetically
coupled structural spin units (as dimers and ladders) is explored by applying
Wilson's renormalization group framework to an appropriate effective action. We
determine the low-temperature phase boundary and the behavior of relevant
quantities decreasing the temperature with the applied magnetic field fixed at
its quantum critical point value. In this context, a plausible interpretation
of some recent experimental results is also suggested.",0605274v1
2006-05-12,The magnetic reorientation transition in thin ferromagnetic films treated by many-body Green's function theory,"This contribution describes the reorientation of the magnetization of thin
ferromagnetic Heisenberg films as function of the temperature and/or an
external field. Working in a rotating frame allows an exact treatment of the
single-ion anisotropy when going to higher-order Green's functions. Terms due
to the exchange interaction are treated by a generalized Tyablikov (RPA)
decoupling.",0605331v1
2006-05-12,Surfactant assisted synthesis of Co and Li doped ZnO nanocrystalline samples showing room temperature ferromagnetism,"We have developed a simple, surfactant assisted synthesis route for the
preparation, in gram quantities, of Co and Li doped ZnO nanocrystalline samples
showing robust room temperature ferromagnetism. Our studies show that RTF is
intrinsic to Zn0.85Co0.05Li0.10O and not due to any segregated secondary
phases. In addition, it has been shown that the defects play an important role
in activating RTF in these oxide systems. This also provide an explanation for
the widely varying results observed in the literature. The method can also be
extended for the synthesis of other transition metal doped ZnO.",0605332v1
2006-05-12,Large domain wall resistance in self-organised manganite film,"The electrical resistance of magnetic domain walls in ferromagnetic metallic
manganites can be enhanced to 10-12 Ohm.m2 by patterning nanoconstrictions [J.
Appl. Phys. 89, 6955 (2001)]. We show equally large enhancements in a phase
separated La0.60Ca0.40MnO3 manganite film without recourse to nanopatterning.
The domain walls were measured in the current-perpendicular-to-the-plane (CPP)
geometry between ferromagnetic metallic La0.70Ca0.30MnO3 electrodes patterned
like magnetic tunnel junctions.",0605341v2
2006-05-23,Intrinsic vs. extrinsic anomalous Hall effect in ferromagnets,"A unified theory of the anomalous Hall effect (AHE) is presented for
multi-band ferromagnetic metallic systems with dilute impurities. In the clean
limit, the AHE is mostly due to the extrinsic skew-scattering. When the Fermi
level is located around anti-crossing of band dispersions split by spin-orbit
interaction, the intrinsic AHE to be calculated ab initio is resonantly
enhanced by its non-perturbative nature, revealing the extrinsic-to-intrinsic
crossover which occurs when the relaxation rate is comparable to the spin-orbit
interaction energy.",0605580v2
2006-05-31,"Spin injection from perpendicular magnetized ferromagnetic $δ$-MnGa into (Al,Ga)As heterostructures","Electrical spin injection from ferromagnetic $\delta$-MnGa into an (Al,Ga)As
p-i-n light emitting diode (LED) is demonstrated. The $\delta$-MnGa layers show
strong perpendicular magnetocrystalline anisotropy, enabling detection of spin
injection at remanence without an applied magnetic field. The bias and
temperature dependence of the spin injection are found to be qualitatively
similar to Fe-based spin LED devices. A Hanle effect is observed and
demonstrates complete depolarization of spins in the semiconductor in a
transverse magnetic field.",0606013v1
2006-06-07,Detection of current-induced spins by ferromagnetic contacts,"Detection of current-induced spin accumulation via ferromagnetic contacts is
discussed. Onsager's relations forbid that in a two-probe configuration spins
excited by currents in time-reversal symmetric systems can be detected by
switching the magnetization of a ferromangetic detector contact. Nevertheless,
current-induced spins can be transferred as a torque to a contact magnetization
and affect the charge currents in many-terminal configurations. We demonstrate
the general concepts by solving the microscopic transport equations for the
diffuse Rashba system with magnetic contacts.",0606193v2
2006-06-13,Peculiar behavior of the electrical resistivity of MnSi at the ferromagnetic phase transition,"The electrical resistivity of a single crystal of MnSi was measured across
its ferromagnetic phase transition line at ambient and high pressures. Sharp
peaks of the temperature coefficient of resistivity characterize the transition
line. Analysis of these data shows that at pressures to ~0.35 GPa these peaks
have fine structure, revealing a shoulder at ~ 0.5 K above the peak. It is
symptomatic that this structure disappears at pressures higher than ~0.35 GPa,
which was identified earlier as a tricritical point",0606324v1
2006-06-21,Current-excited magnetization dynamics in narrow ferromagnetic wires,"We investigate the current-excited magnetization dynamics in a narrow
ferromagnetic Permalloy wire by means of Lorentz microscopy, together with the
results of simultaneous transport measurements. A detailed structural evolution
of the magnetization is presented as a function of the applied current density.
Local structural deformation, bidirectional displacement, and magnetization
reversal are found below the Curie temperature with increasing the current
density. We discuss probable mechanisms of observed features of the
current-excited magnetization dynamics.",0606547v1
2006-07-03,Magnetic effects on the phase transitions in unconventional superconductors,"A new critical behavior in unconventional superconductors and superfluids is
established and described by the Wilson-Fisher renormalization-group method.
For certain symmetries of order a new type of fluctuation-driven first order
phase transitions at finite and zero temperature are predicted. The results can
be applied to a wide class of ferromagnetic superconductive and superfluid
systems, in particular, to itinerant ferromagnets as UGe_2 and URhGe.",0607057v2
2006-07-23,Non-collinear Spin Valve Effect in Ferromagnetic Semiconductor Trilayers,"We report the observation of the spin valve effect in
(Ga,Mn)As/p-GaAs/(Ga,Mn)As trilayer devices. Magnetoresistance measurements
carried out in the current in plane geometry reveal positive magnetoresistance
peaks when the two ferromagnetic layers are magnetized orthogonal to each
other. Measurements carried out for different post-growth annealing conditions
and spacer layer thickness suggest that the positive magnetoresistance peaks
originate in a noncollinear spin valve effect due to spin-dependent scattering
that is believed to occur primarily at interfaces.",0607580v2
2006-08-01,"Structural and magnetic properties of ZnO:TM (TM: Co,Mn) nanopowders","We report on the structural and magnetic characterization of Co0.1Zn0.9O and
Mn0.1Zn0.9O nanopowders obtained by a soft chemistry route. We show that those
samples fired at low temperatures display a ferromagnetic interaction that can
not be attributed to the presence of impurities. A magnetic aging mechanism is
observed, reflecting the key role played by defects in the stabilization of
ferromagnetism in this kind of diluted magnetic semiconductors.",0608014v1
2006-08-19,Spin dynamics in molecular ring nanomagnets: Significant effect of acoustic phonons and magnetic anisotropies,"The nuclear spin-lattice relaxation rate 1/T_1_ is calculated for magnetic
ring clusters by fully diagonalizing their microscopic spin Hamiltonians.
Whether the nearest-neighbor exchange interaction J is ferromagnetic or
antiferromagnetic, 1/T_1_ versus temperature T in ring nanomagnets may be
peaked at around k_B_T=|J| provided the lifetime broadening of discrete energy
levels is in proportion to T^3^. Experimental findings for ferromagnetic and
antiferromagnetic Cu^II^ rings are reproduced with crucial contributions of
magnetic anisotropies as well as acoustic phonons.",0608438v1
2006-08-22,Clustering induced suppression of ferromagnetism in diluted magnets,"Ferromagnetism in diluted magnets in the compensated regime p << x is shown
to be suppressed by the formation of impurity spin clusters. The majority bulk
spin couplings are shown to be considerably weakened by the preferential
accumulation of holes in spin clusters, resulting in low-energy magnon
softening and enhanced low-temperature decay of magnetic order. A locally
self-consistent magnon renormalization analysis of spin dynamics shows that
although strong intra-cluster correlations tend to prolong global order, T_c is
still reduced compared to the ordered case.",0608474v2
2006-09-01,Thermally excited spin-current in metals with embedded ferromagnetic nanoclusters,"We show that a thermally excited spin-current naturally appears in metals
with embedded ferromagnetic nanoclusters. When such materials are subjected to
a magnetic field, a spin current can be generated by a temperature gradient
across the sample as a signature of electron-hole symmetry breaking in a metal
due to the electron spin-flip scattering from polarised magnetic moments. Such
a spin current can be observed via a giant magneto-thermopower which tracks the
polarisation state of the magnetic subsystem and is proportional to the
magnetoresistance. Our theory explains the recent experiment on Co clusters in
copper by S. Serrano-Guisan \textit{et al} [Nature Materials AOP,
doi:10.1038/nmat1713 (2006)]",0609012v1
2006-09-19,$π$-Electron Ferromagnetism in Metal Free Carbon Probed by Soft X-Ray Dichroism,"Elemental carbon represents a fundamental building block of matter and the
possibility of ferromagnetic order in carbon attracted widespread attention.
However, the origin of magnetic order in such a light element is only poorly
understood and has puzzled researchers. We present a spectromicroscopy study at
room temperature of proton irradiated metal free carbon using the elemental and
chemical specificity of x-ray magnetic circular dichroism (XMCD). We
demonstrate that the magnetic order in the investigated system originates only
from the carbon $\pi$-electron system.",0609478v3
2006-10-09,Single-domain versus two-domain configuration in thin ferromagnetic prisms,"Thin ferromagnetic elements in the form of rectangular prisms are
theoretically investigated in order to study the transition from single-domain
to two-domain state, with changing the in-plane aspect ratio p. We address two
main questions: first, how general is the transition; second, how the critical
value p_c depends on the physical parameters. We use two complementary methods:
discrete-lattice calculations and a micromagnetic continuum approach. Ultrathin
films do not appear to split in two domains. Instead, thicker films may undergo
the above transition. We have used the continuum approach to analyze recent
Magnetic Force Microscopy observations in 30 nm-thick patterned Permalloy
elements, finding a good agreement for p_c.",0610233v1
2006-10-11,0-pi transition in SFS junctions with strongly spin-dependent scattering,"We develop theory of proximity effect in a superconductor - GMR alloy -
superconductor trilayers, which takes into account strong spin dependence of
electron scattering of compositional disorder in a diluted ferromagnetic alloy.
We show that in such a system the critical current oscillations as the function
of the thickness of the ferromagnetic layer, with the period of $v_{F}/2I$,
decay exponentially with the characteristic length of the order of the mean
free path.",0610299v3
2006-10-19,"Magneto-resistive memory in ferromagnetic (Ga,Mn)As nanostructures","We show a novel magneto-resistive effect that appears in lithographically
shaped, three-arm nanostructure, fabricated from ferromagnetic (Ga,Mn)As
layers. The effect, related to a rearrangement of magnetic domain walls between
different pairs of arms in the structure, reveals as a dependence of zero-field
resistance on the direction of previously applied magnetic field. This effect
could allow designing devices with unique switching and memory properties.",0610535v1
2006-10-23,Scaling and universality in the aging kinetics of the two-dimensional clock model,"We study numerically the aging dynamics of the two-dimensional p-state clock
model after a quench from an infinite temperature to the ferromagnetic phase or
to the Kosterlitz-Thouless phase. The system exhibits the general scaling
behavior characteristic of non-disordered coarsening systems. For quenches to
the ferromagnetic phase, the value of the dynamical exponents, suggests that
the model belongs to the Ising-type universality class. Specifically, for the
integrated response function $\chi (t,s)\simeq s^{-a_\chi}f(t/s)$, we find
$a_\chi $ consistent with the value $a_\chi =0.28$ found in the two-dimensional
Ising model.",0610615v1
2006-10-24,Flux-flow induced giant magnetoresistance in all-amorphous superconductor-ferromagnet hybrids,"We present magnetoresistance measurements on all-amorphous ferromagnet (F) /
superconductor (S) heterostructures. The F/S/F trilayers show large
magnetoresistance peaks in a small field range around the coercive field of the
F layers, at temperatures within and below the superconducting transition. This
is interpreted as flux flow of weakly pinned vortices induced by the stray
field of Bloch magnetic domains in the F layers. Bilayers show much smaller
effects, implying that the Bloch walls of the F-layers in the trilayer line up
and focus the stray fields. The data are used to discuss the expected minimum
F-layer thickness needed to nucleate vortices.",0610667v1
2006-11-09,Super-Aging in two-dimensional random ferromagnets,"We study the aging properties, in particular the two-time autocorrelations,
of the two-dimensional randomly diluted Ising ferromagnet below the critical
temperature via Monte-Carlo simulations. We find that the autocorrelation
function displays additive aging $C(t,t_w)=C_{st}(t)+C_{ag}(t,t_w)$, where the
stationary part $C_{st}$ decays algebraically. The aging part shows anomalous
scaling $C_{ag}(t,t_w)={\cal C}(h(t)/h(t_w))$, where $h(u)$ is a
non-homogeneous function excluding a $t/t_w$ scaling.",0611246v1
2006-11-10,Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads,"We have fabricated a lateral double barrier magnetic tunnel junction (MTJ)
which consists of a single self-assembled InAs quantum dot (QD) with
ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance
(TMR) effect, which is evidence for spin transport through a single
semiconductor QD. The TMR ratio and the curve shapes are varied by changing the
gate voltage.",0611269v2
2006-11-10,Nuclear spin ferromagnetic phase transition in an interacting 2D electron gas,"Electrons in a two-dimensional semiconducting heterostructure interact with
nuclear spins via the hyperfine interaction. Using a a Kondo lattice
formulation of the electron-nuclear spin interaction, we show that the nuclear
spin system within an interacting two-dimensional electron gas undergoes a
ferromagnetic phase transition at finite temperatures. We find that
electron-electron interactions and non-Fermi liquid behavior substantially
enhance the nuclear spin Curie temperature into the $mK$ range with decreasing
electron density.",0611292v2
2006-11-22,Octupolar order in the multiple spin exchange model on a triangular lattice,"We show how a gapless spin liquid with hidden octupolar order arises in an
applied magnetic field, in a model applicable to thin films of 3He with
competing ferromagnetic and antiferromagnetic (cyclic) exchange interactions.
Evidence is also presented for nematic -- i.e., quadrupolar -- correlations
bordering on ferromagnetism in the absence of a magnetic field.",0611575v2
2006-11-26,Critical cooling rate for the glass formation of ferromagnetic Fe40Ni40P14B6 alloy,"Bulk ferromagnetic amorphous Fe-Ni-P-B alloys in rod shape were formed by a
rapid solidification technique. The largest amorphous specimen prepared had a
diameter of ~2.5 mm and the corresponding cooling rate for the glass formation
of this alloy system in our experiment can be estimate to be around 492.4 K/s
by the method of finite-difference numerical calculation. This value is on the
same order of magnitude as the critical cooling rate Rc of Fe40Ni40P14B6 alloy
estimated by the method of constructing the continuous-cooling-transformation
(CCT) curve. It is indicated that the heterophase impurities have been
eliminated well in our experiment.",0611651v2
2006-11-30,Theory of Brillouin Light Scattering from Ferromagnetic Nanospheres,"We develop the theory of Brillouin light scattering (BLS) from spin wave
modes in ferromagnetic nanospheres, within a framework that incorporates the
spatial variation of the optical fields within the sphere. Our recent theory of
exchange dipole spin wave modes of the sphere provides us with eigenvectors.
When properly normalized, these eigenvectors allow calculation of the absolute
cross section of various modes which contribute to BLS spectrum. We then
present explicit calculation of the BLS spectrum associated with the first few
dipole/exchange spin wave modes with emphasis on their relative intensity.",0611785v1
2006-12-02,Magneto-optical and magnetotransport properties of heavily Mn-doped GaMnAs,"We have studied the magneto-optical and magnetotrasnport properties of GaMnAs
thin films with high Mn concentrations (x= 12.2 - 21.3%) grown by
molecular-beam epitaxy. These heavily Mn-doped GaMnAs films were formed by
decreasing the growth temperature to as low as 150-190 degree C and by reducing
the film thickness to 10 nm in order to prevent precipitation of hexagonal MnAs
clusters. Magnetic circular dichroism (MCD) and anomalous Hall effect
measurements indicate that these GaMnAs films have the nature of intrinsic
ferromagnetic semiconductors with high ferromagnetic transition temperature up
to 170 K.",0612055v1
2006-12-19,Characteristic temperatures of exchange biased systems,"Characteristic temperatures in ferromagnetic - antiferromagnetic exchange
biased systems are analyzed. In addition to usual blocking temperature of
exchange bias $T_{B}$, and the N\'{e}el temperature of an antiferromagnet
$T_{N}$, the inducing temperature $T_{ind}$, i.e., the temperature, at which
the direction of exchange anisotropy is established, has been recently
proposed. We demonstrate that this temperature is in general case different
from $T_{B}$ and $T_{N}$. Physics and experimental approaches to measure the
inducing temperature are discussed. Measurements of $T_{ind}$, in addition to
$T_{B}$, and $T_{N}$, provide important information about exchange interactions
in ferromagnetic - antiferromagnetic heterostructures.",0612500v1
2006-12-30,Low relaxation rate in a low-Z alloy of iron,"The longest relaxation time and sharpest frequency content in ferromagnetic
precession is determined by the intrinsic (Gilbert) relaxation rate \emph{$G$}.
For many years, pure iron (Fe) has had the lowest known value of $G=\textrm{57
Mhz}$ for all pure ferromagnetic metals or binary alloys. We show that an
epitaxial iron alloy with vanadium (V) possesses values of $G$ which are
significantly reduced, to 35$\pm$5 Mhz at 27% V. The result can be understood
as the role of spin-orbit coupling in generating relaxation, reduced through
the atomic number $Z$.",0701004v1
2007-02-24,Quantum spin tunneling of magnetization in small ferromagnetic particles,"A new quantum approach is presented that can account for the description of
small ferromagnetic particles magnetization tunneling. An estimate of the
saturation value of an external applied magnetic field along the easy axis is
obtained. An analytic expression for the tunneling factor in the absence of an
external magnetic field is deduced from the present approach that also allows
to obtain the crossover temperature characterizing the regime where tunneling
is dominated by the quantum effects.",0702572v1
2007-03-05,Non--Heisenberg Spin Dynamics of Double-Exchange Ferromagnets with Coulomb Repulsion,"With a variational three--body calculation we study the role of the interplay
between the onsite Coulomb, Hund's rule, and superexchange interactions on the
spinwave excitation spectrum of itinerant ferromagnets. We show that
correlations between a Fermi sea electron--hole pair and a magnon result in a
very pronounced zone boundary softening and strong deviations from the
Heisenberg spinwave dispersion. We show that this spin dynamics depends
sensitively on the Coulomb and exchange interactions and discuss its possible
relevance to experiments in the manganites.",0703099v2
2007-03-09,"Crystal structure, magnetism, and bonding of the hexagonal compounds Pd$_{1.63}$Mn$_{0.37}$Si and Pd$_{1.82}$Mn$_{0.18}$Ge related to the Fe$_2$P structure","We have used single crystal X-ray diffraction methods to establish the
crystal structures of a compound in the Pd-Mn-Si system and in the Pd-Mn-Ge
system. The title compounds have structures related to the Fe$_2$P structure
type and are ferromagnetic with Curie temperatures above the room temperature.
Density functional electronic structure calculations help to understand the
nature of the local moment ferromagnetism in these compounds. However neither
the electronic structure calculations nor the magnetic measurements provide any
evidence of half-metallic behavior.",0703240v1
2007-03-27,Critical Scattering and Dynamical Scaling in an Heisenberg Ferromagnet Neutron Spin Echo versus Renormalization Group Theory,"High resolution Neutron Spin Echo (NSE) spectroscopy was used to investigate
the dynamics of an 3D Heisenberg ferromagnet in the exchange-controlled regime
over a broad range of temperatures and momentum transfer. These results allow
for the first time an extensive comparison between the experimental dynamical
critical behavior and the predictions of the Renormalization Group (RG) theory.
The agreement is exhaustive and surprising as the RG theory accounts not only
for the critical relaxation but also for the shape crossover towards an
exponential diffusive relaxation when moving from the critical to the
hydrodynamic regime above $T_C$.",0703702v1
2007-03-30,Multicomponent Bright Solitons in F = 2 Spinor Bose-Einstein Condensates,"We study soliton solutions for the Gross--Pitaevskii equation of the spinor
Bose--Einstein condensates with hyperfine spin F=2 in one-dimension. Analyses
are made in two ways: by assuming single-mode amplitudes and by generalizing
Hirota's direct method for multi-components. We obtain one-solitons of
single-peak type in the ferromagnetic, polar and cyclic states, respectively.
Moreover, twin-peak type solitons both in the ferromagnetic and the polar state
are found.",0703805v3
2006-03-28,Remote-control and clustering of physical computations using the XML-RPC protocol and the open-Mosix system,"The applications of the remote control of physical simulations performed in
clustered computers running under an open-Mosix system are presented. Results
from the simulation of a 2-dimensional ferromagnetic system of spins in the
Ising scheme are provided. Basic parameters of a simulated hysteresis loop like
coercivity and exchange bias due to pinning of ferromagnetic spins are given.
The paper describes in physicists terminology a cost effective solution which
utilizes an XML-RPC protocol (Extensible Markup Language - Remote Procedure
Calling) and standard C++ and Python languages.",0603111v1
1992-10-23,The Savvidy ``ferromagnetic vacuum'' in three-dimensional lattice gauge theory,"The vacuum effective potential of three-dimensional SU(2) lattice gauge
theory in an applied color-magnetic field is computed over a wide range of
field strengths. The background field is induced by an external current, as in
continuum field theory. Scaling and finite volume effects are analyzed
systematically. The first evidence from lattice simulations is obtained of the
existence of a nontrivial minimum in the effective potential. This supports a
``ferromagnetic'' picture of gluon condensation, proposed by Savvidy on the
basis of a one-loop calculation in (3+1)-dimensional QCD.",9210028v1
1996-02-05,Anti-Ferromagnetic Condensate in Yang-Mills Theory,"SU(2) gauge theory with competing interactions is shown to possess a rich
phase structure with anti-ferromagnetic vacua. It is argued that the phase
boundaries persist in the weak coupling limit suggesting the existence of
different renormalized continuum theories for QCD.",9602003v2
1996-11-02,Is trivial the antiferromagnetic RP(2) model in four dimensions?,"We study the antiferromagnetic RP(2) model in four dimensions. We find a
second order transition with two order parameters, one ferromagnetic and the
other antiferromagnetic. The antiferromagnetic sector has mean-field critical
exponents and a renormalized coupling which goes to zero in the continuum
limit. The exponents of the ferromagnetic channel are not the mean-field ones,
but the difference can be interpreted as logarithmic corrections. We perform a
detailed analysis of these corrections and conclude the triviality of the
continuum limit of this model.",9611003v1
1997-03-05,Ferromagnetism of Axion Domain Wall,"We show that axion domain wall is ferromagnetic in the universe with
nonvanishing baryon number or lepton number. It is caused by protons and
electrons bounded to the domain wall with their spins aligned. These bound
states arise due to attractive potentials generated through pseudo-vector
couplings between the fermions and the axion. Using a model of hadronic axions
we predict existence of a primordial magnetic field with strength $10^{-13}$
Gauss at recombination.",9703237v1
1999-10-25,Ferromagnetism of quark liquid,"Usually it is believed that the Hartree-Fock state of quark matter is a Fermi
gas state with no polarisation of spins. We examine the possibility of the
polarised quark liquid interacting with the one-gluon-exchange interaction. It
is suggested that the Hartree-Fock state shows a spontaneous magnetic
instability at low densities through the same mechanism as the appearance of
ferromagnetism in electron gas. Metastability of the polarised quark liquid is
also discussed.",9910470v1
2000-07-12,No Primordial Magnetic Field from Domain Walls,"It is pointed out that, contrary to some claims in the literature, the domain
walls cannot be a source of a correlated at large scales primordial magnetic
field, even if the fermionic modes bound on the wall had ferromagnetic
properties. In a particular model with massive (2+1) dimensional fermions bound
to a domain wall, previously claimed to exhibit a ferromagnetic behavior, it is
explicitly shown that the fermionic system in fact has properties of a normal
diamagnetic with the susceptibility vanishing at high temperature.",0007123v2
2005-08-20,Color Ferromagnetism of Quark Matter ; a Possible Origin of Strong Magnetic Field in Magnetars,"We show a possibility that strong ``magnetic field'' $\sim 10^{15} $G is
produced by color ferromagnetic quark matter in neutron stars. In the quark
matter a color magnetic field is generated spontaneously owing to Savvidy
mechanism and a gluon condensate arises for the stabilization of the field.
Since the quark matter is electrically charged in the neutron stars, the
rotation of the quarks around the color magnetic field produces the strong
``magnetic field''.",0508219v1
2006-09-06,Possible Ferromagnetism in the Large N(c) and N(f) limit of quark matter,"We consider high density quark matter in the large $\N_c$ and $\N_f$ limit
with $\N_f/\N_c$ fixed. In this limit, the color superconductivity disappears.
We discuss that the chiral density wave state is also absent in the limit, if
we assume the existence of the non-perturbative magnetic screening effect as
indicated by recent lattice study. We argue that ferromagnetism can become a
candidate for the ground state if quarks are massive.",0609060v4
1994-08-24,Equations for Correlation Functions of Eight-Vertex Model: Ferromagnetic and Disordered Phases,"The Kyoto group (Jimbo, Miwa, Nakayashikiet al.) showed that the partition
function and correlation funtions of the eight-vertex model in
antiferromagnetic phases can be calculated using simple analytical properties
of the $R$-matrix. We extend these methods to ferromagnetic and disordered
phases. We use Baxter's symmetries to obtain appropriate parametrizations of
the $R$-matrix and to substantiate the validity of the analytical approach for
these phases. These symmetries allow one to relate correlation functions in
different phases.",9408131v2
1996-06-25,Gauge Theory Model -- quark dynamics and anti-ferromagnets,"Two-dimensional QED with N-flavor fermions serves as a model of quark
dynamics in QCD as well as an effective theory of an anti-ferromagnetic spin
chain. It is reduced to N-degree quantum mechanics in which a potential is
self-consistently determined by the Schr\""odinger equation itself.",9606167v1
1996-12-06,Self-Dual Chern-Simons Solitons and Generalized Heisenberg Ferromagnet Models,"We consider the (2+1)-dimensional gauged Heisenberg ferromagnet model coupled
with the Chern-Simons gauge fields. Self-dual Chern-Simons solitons, the static
zero energy solution saturating Bogomol'nyi bounds, are shown to exist when the
generalized spin variable is valued in the Hermitian symmetric spaces G/H. By
gauging the maximal torus subgroup of H, we obtain self-dual solitons which
satisfy vortex-type nonlinear equations thereby extending the two dimensional
instantons in a nontrivial way. An explicit example for the CP(N) case is
given.",9612063v1
2001-04-03,Smirnov-type integral formulae for correlation functions of the bulk/boundary XXZ model in the anti-ferromagnetic regime,"Presented are the integral solutions to the quantum Knizhnik-Zamolodchikov
equations for the correlation functions of both the bulk and boundary XXZ
models in the anti-ferromagnetic regime. The difference equations can be
derived from Smirnov-type master equations for correlation functions on the
basis of the CTM bootstrap. Our integral solutions with an appropriate choice
of the integral kernel reproduce the formulae previously obtained by using the
bosonization of the vertex operators of the quantum affine algebra $U_q
(\hat{\mathfrak{sl}_2})$.",0104018v1
2003-09-09,Some topological issues for ferromagnets and fluids,"We analyze the canonical structure of a continuum model of ferromagnets and
clarify known difficulties in defining a momentum density. The moments of the
momentum density corresponding to volume-preserving coordinate transformations
can be defined, but a nonsingular definition of the other moments requires an
enlargement of the phase space which illuminates a close relation to fluid
mechanics. We also discuss the nontrivial connectivity of the phase space for
two and three dimensions and show how this feature can be incorporated in the
quantum theory, working out the two-dimensional case in some detail.",0309087v1
2005-04-01,Fifth-neighbor spin-spin correlator for the anti-ferromagnetic Heisenberg chain,"We study the generating function of the spin-spin correlation functions in
the ground state of the anti-ferromagnetic spin-1/2 Heisenberg chain without
magnetic field. We have found its fundamental functional relations from those
for general correlation functions, which originate in the quantum
Knizhink-Zamolodchikov equation. Using these relations, we have calculated the
explicit form of the generating functions up to n=6. Accordingly we could
obtain the spin-spin correlator <S_j^z S_{j+k}^z> up to k=5.",0504008v3
2005-09-06,A Bethe Ansatz Study of Free Energy and Excitation Spectrum for Even Spin Fateev Zamolodchikov Model,"A Bethe Ansatz study of a self dual Z_N spin model is undertaken for even
spin system. One has to solve a coupled system of Bethe Ansatz Equations (BAE)
involving zeroes of two families of transfer matrices. A numerical study on
finite size lattices is done for identification of elementary excitations over
the Ferromagnetic and Antiferromagnetic ground states. The free energies for
both Ferromagnetic and Antiferromagnetic ground states and dispersion relation
for elementary excitations are found.",0509045v1
2005-09-20,Large-n excitations in the ferromagnetic Ising field theory in a small magnetic field: mass spectrum and decay widths,"In presence of a small magnetic field h, the elementary excitations in the
scaling two-dimensional Ising model are studied perturbatively in h in the
ferromagnetic phase. For excitations with large numbers n, the mass spectrum is
obtained in the first order in h. The decay widths of excitations with energies
above the stability threshold are calculated in the leading h^3-order.",0509149v1
2001-01-22,Winterbottom Construction for Finite Range Ferromagnetic Models: An L_1 Approach,"We provide a rigorous microscopic derivation of the thermodynamic description
of equilibrium crystal shapes in the presence of a substrate, first studied by
Winterbottom. We consider finite range ferromagnetic Ising models with pair
interactions in dimensions greater or equal to 3, and model the substrate by a
finite-range boundary magnetic field acting on the spins close to the bottom
wall of the box.",0101174v1
2004-01-27,An efficient geometric integrator for thermostatted anti-/ferromagnetic models,"(Anti)-/ferromagnetic Heisenberg spin models arise from discretization of
Landau-Lifshitz models in micromagnetic modelling. In many applications it is
essential to study the behavior of the system at a fixed temperature. A
formulation for thermostatted spin dynamics was given by Bulgac and Kusnetsov
which incorporates a complicated nonlinear dissipation/driving term while
preserving spin length. It is essential to properly model this term in
simulation, and simplified schemes give poor numerical performance, e.g.
requiring an excessively small timestep for stable integration. In this paper
we present an efficient, structure-preserving method for thermostatted spin
dynamics.",0401369v1
2006-07-20,A preconditioning strategy for microwave susceptibility in ferromagnets,"3D numerical simulations of ferromagnetic materials can be compared with
experimental results via microwave susceptibility. In this paper, an optimised
computation of this microwave susceptibility for large meshes is proposed. The
microwave susceptibility is obtained by linearisation of the Landau and
Lifchitz equations near equilibrium states and the linear systems to be solved
are very ill-conditionned. Solutions are computed using the Conjugate Gradient
method for the Normal equation (CGN Method). An efficient preconditioner is
developed consisting of a projection and an approximation of an ``exact''
preconditioner in the set of circulant matrices. Control of the condition
number due to the preconditioning and evolution of the singular value
decomposition are shown in the results.",0607493v1
2006-09-08,Control of travelling walls in a ferromagnetic nanowire,"We investigate the problem of controlling the magnetic moment in a
ferromagnetic nanowire submitted to an external magnetic field in the direction
of the nanowire. The system is modeled with the one dimensional
Landau-Lifschitz equation. In the absence of control, there exist particular
solutions, which happen to be relevant for practical issues, called travelling
walls. In this paper, we prove that it is possible to move from a given
travelling wall profile to any other one, by acting on the external magnetic
field. The control laws are simple and explicit, and the resulting trajectories
are shown to be stable.",0609231v2
2003-02-28,A Polymer Expansion for the Quantum Heisenberg Ferromagnet Wave Function,"A polymer expansion is given for the Quantum Heisenberg Ferromagnet wave
function. Working on a finite lattice, one is dealing entirely with algebraic
identities; there is no question of convergence. The conjecture to be pursued
in further work is that effects of large polymers are small. This is relevant
to the question of the utility of the expansion and its possible extension to
the infinite volume. In themselves the constructions of the present paper are
neat and elegant and have surprising simplicity.",0302067v2
2003-03-13,A Polymer Expansion for the Random Walk on the Permutation Group Associated to the Quantum Heisenberg Ferromagnet,"For a long time one has associated to the Quantum Heisenberg Ferromagnet on a
lattice, a random walk on the permutation group of the lattice vertices. We
here present a polymer expansion for the solution of the heat equation coupled
to the random walk. We work on a finite lattice, there is no question of
convergence. We leave to future work bounding terms in the expansion necessary
to extend the result to an infinite lattice.",0303036v1
2003-07-24,The large-spin asymptotics of the ferromagnetic XXZ chain,"We present new results and give a concise review of recent previous results
on the asymptotics for large spin of the low-lying spectrum of the
ferromagnetic XXZ Heisenberg chain with kink boundary conditions. Our main
interest is to gain detailed information on the interface ground states of this
model and the low-lying excitations above them. The new and most detailed
results are obtained using a rigorous version of bosonization, which can be
interpreted as a quantum central limit theorem.",0307051v1
2001-07-25,Magnetization Reversal in Ferromagnetic Film Through Solitons by Electromagnetic Field,"We study the reversal of magnetization in an isotropic ferromagnetic film
free from charges by exposing it to a circularly polarized electromagnetic (EM)
field. The magnetization excitations obtained in the form of line and lump
solitons of the completely integrable modified KP-II equation which is derived
using a reductive perturbation method from the set of coupled Landau-Lifshitz
and Maxwell equations. It is observed that when the polarization of the
EM-field is reversed followed by a rotation, for every $ {\pi \over 2}
$-degrees, the magnetization is reversed.",0107058v1
2000-10-05,Ferromagnetism of Nuclear Matter in the Relativistic Approach,"We study the spin-polarization mechanism in the highly dense nuclear matter
with the relativistic mean-field approach. In the relativistic Hartree-Fock
framework we find that there are two kinds of spin-spin interaction channels,
which are the axial-vector and tensor exchange ones. If each interaction is
strong and different sign, the system loses the spherical symmetry and holds
the spin-polarization in the high-density region. When the axial-vector
interaction is negative enough, the system holds ferromagnetism.",0010018v2
2004-06-02,Ultra-cold Neutron Production in Anti-ferromagnetic Oxygen Solid,"Spin waves, or magnons, in the anti-ferromagnetic $\alpha$ phase of solid
oxygen provide a novel mechanism for ultra-cold neutron (UCN) production.
Magnons dominate the energy exchange mechanisms for cold neutrons and UCN in
solid $\alpha$-oxygen, much in the same way as do phonons in solid deuterium
superthermal UCN sources. We present calculations of UCN production and
upscattering rates in S-O$_2$. The results indicate that S-O$_2$ is potentially
a much more efficient UCN source material than solid deuterium.",0406004v1
2006-04-24,Ferromagnetic instabilities in neutron matter at finite temperature with the Gogny interaction,"The properties of spin polarized neutron matter are studied both at zero and
finite temperature using the D1 and the D1P parameterizations of the Gogny
interaction. The results show two different behaviors: whereas the D1P force
exhibits a ferromagnetic transition at a density of $\rho_c \sim 1.31$
fm$^{-3}$ whose onset increases with temperature, no sign of such a transition
is found for D1 at any density and temperature, in agreement with recent
microscopic calculations.",0604058v2
2003-02-14,"Retarded Electromagnetic Interaction and Origin of Non-linear Phenomena in Ferroelectrics, Ferromagnetics and Optics","The non-linear relations between polarization strength and electric field
strength for ferroelectrics, as well as magnetization strength and magnetic
field strength for ferromagnetics, can be achieved by introducing retarded
electromagnetic interactions. The electric and magnetic hysteretic loops, as
well as polarization and magnetization curves, can be described well based on
soft mode theory in the alternating electromagnetic fields of low and medium
frequencies. The fundamental phenomenological formula in non-linear optics can
also be obtained in high frequency fields. The results show that all of these
non-linear phenomena originate from retarded electromagnetic interaction.",0302048v1
2006-09-22,Application of atomic magnetometry in magnetic particle detection,"We demonstrate the detection of magnetic particles carried by water in a
continuous flow using an atomic magnetic gradiometer. Studies on three types of
magnetic particles are presented: a single cobalt particle (diameter ~150 um,
multi-domain), a suspension of superparamagnetic magnetite particles (diameter
\~1 um), and ferromagnetic cobalt nanoparticles (diameter ~10 nm, 120 kA/m
magnetization). Estimated detection limits are 20 um diameter for a single
cobalt particle at a water flow rate 30 ml/min, 5x10^3 magnetite particles at
160 ml/min, and 50 pl for the specific ferromagnetic fluid at 130 ml/min.
Possible applications of our method are discussed.",0609197v1
2004-04-05,Logarithmic divergence of the block entanglement entropy for the ferromagnetic Heisenberg model,"Recent studies have shown that logarithmic divergence of entanglement entropy
as function of size of a subsystem is a signature of criticality in quantum
models. We demonstrate that the ground state entanglement entropy of $ n$ sites
for ferromagnetic Heisenberg spin-1/2 chain of the length $L$ in a sector with
fixed magnetization $y$ per site grows as ${1/2}\log_{2} \frac{n(L-n)}{L}C(y)$,
where $C(y)=2\pi e({1/4}-y^{2})$",0404026v1
2004-07-09,Thermal entanglement of spins in a nonuniform magnetic field,"We study the effect of inhomogeneities in the magnetic field on the thermal
entanglement of a two spin system. We show that in the ferromagnetic case a
very small inhomogeneity is capable to produce large values of thermal
entanglement. This shows that the absence of entanglement in the ferromagnetic
Heisenberg system is highly unstable against inhomogeneoity of magnetic fields
which is inevitably present in any solid state realization of qubits.",0407073v3
2004-12-15,Thermal effects on quantum communication through spin chains,"We study the effect of thermal fluctuations in a recently proposed protocol
for transmission of unknown quantum states through quantum spin chains. We
develop a low temperature expansion for general spin chains. We then apply this
formalism to study exactly thermal effects on short spin chains of four spins.
We show that optimal times for extraction of output states are almost
independent of the temperature which lowers only the fidelity of the channel.
Moreover we show that thermal effects are smaller in the anti-ferromagnetic
chains than the ferromagnetic ones.",0412115v2
1999-07-22,Multi-Field Integrable Systems Related to WKI-Type Eigenvalue Problems,"Higher flows of the Heisenberg ferromagnet equation and the
Wadati-Konno-Ichikawa equation are generalized into multi-component systems on
the basis of the Lax formulation. It is shown that there is a correspondence
between the multi-component systems through a gauge transformation. An
integrable semi-discretization of the multi-component higher Heisenberg
ferromagnet system is obtained.",9907018v1
2007-04-05,Correlation functions and excitation spectrum of the frustrated ferromagnetic spin-1/2 chain in an external magnetic field,"Magnetic field effects on the one-dimensional frustrated ferromagnetic chain
are studied by means of effective field theory approaches in combination with
numerical calculations utilizing Lanczos diagonalization and the density matrix
renormalization group method. The nature of the ground state is shown to change
from a spin-density-wave region to a nematic-like one upon approaching the
saturation magnetization. The excitation spectrum is analyzed and the behavior
of the single spin-flip excitation gap is studied in detail, including the
emergent finite-size corrections.",0704.0764v2
2007-04-09,Electron Transport in Nanogranular Ferromagnets,"We study electronic transport properties of ferromagnetic nanoparticle arrays
and nanodomain materials near the Curie temperature in the limit of weak
coupling between the grains. We calculate the conductivity in the Ohmic and
non-Ohmic regimes and estimate the magnetoresistance jump in the resistivity at
the transition temperature. The results are applicable for many emerging
materials, including artificially self-assembled nanoparticle arrays and a
certain class of manganites, where localization effects within the clusters can
be neglected.",0704.1167v2
2007-04-22,Sm2Al: Another ferromagnet with spin-orbital compensation?,"We report the observation of a compensation point in the temperature
dependence of magnetization data of polycrystalline Sm2Al. Magnetization
measurements show that this compound magnetically orders at about 150 K. Below
this temperature, the magnetization data shows a compensation point, which
shifts with field. Hysteresis loops obtained below the compensation temperature
show that the compound possesses exchange anisotropy. Both the exchange
anisotropy field and the coercive field are found to be quite large and
comparable to those of the classical spin-orbit compensated ferromagnet
(Sm,Gd)Al2. The heat capacity data also suggest that there are similarities
between (Sm,Gd)Al2 and Sm2Al.",0704.2864v1
2007-05-04,Theory of a Magnetically-Controlled Quantum-Dot Spin Transistor,"We examine transport through a quantum dot coupled to three ferromagnetic
leads in the regime of weak tunnel coupling. A finite source-drain voltage
generates a nonequilibrium spin on the otherwise non-magnetic quantum dot. This
spin accumulation leads to magnetoresistance. A ferromagnetic but current-free
base electrode influences the quantum-dot spin via incoherent spin-flip
processes and coherent spin precession. As the dot spin determines the
conductance of the device, this allows for a purely magnetic transistor-like
operation. We analyze the effect of both types of processes on the electric
current in different geometries.",0705.0648v2
2007-05-25,Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys,"Half-metallic Heusler alloys are among the most promising materials for
future applications in spintronic devices. Although most Heusler alloys are
ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated
ferrimagnetic) alloys would be more desirable for applications due to the lower
external fields. Ferrimagnetism can be either found in perfect Heusler
compounds or achieved through the creation of defects in ferromagnetic Heusler
alloys.",0705.3731v1
2007-06-02,Thermodynamic Properties of Ferromagnetic Mott- Insulators GaV4S8,"We present the results of the magnetic and specific heat measurements on V4
tetrahedral-cluster compound GaV4S8 between 2 to 300K. We find two transitions
related to a structural change at 42K followed by ferromagnetic order at 12K on
cooling. Remarkably similar properties were previously reported for the cluster
compounds of Mo4. These compounds show an extremely high density of low energy
excitations in their electronic properties. We explain this behavior in a
cluster compound as due to the reduction of coulomb repulsion among electrons
that occupy highly degenerate orbits of different clusters.",0706.0265v1
2007-06-02,Giant magnetoresistance in nanoscale ferromagnetic heterocontacts,"A quasiclassical theory of giant magnetoresistance in nanoscale point
contacts between different ferromagnetic metals is developed. The contacts were
sorted by three types of mutual positions of the conduction spin-subband
bottoms which are shifted one against another by the exchange interaction. A
model of linear domain wall has been used to account for the finite contact
length. The magnetoresistance is plotted against the size of the nanocontact.
In heterocontacts the magnetoresistance effect turned out to be not only
negative, as usual, but can be positive as well. Relevance of the results to
existing experiments on GMR in point heterocontacts is discussed.",0706.0266v1
2007-06-14,"Magnetic patterning of (Ga,Mn)As by hydrogen passivation","We present an original method to magnetically pattern thin layers of
(Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the
hole density, and thereby locally suppress the carrier-mediated ferromagnetic
phase. The sample surface is thus maintained continuous, and the minimal
structure size is of about 200 nm. In micron-sized ferromagnetic dots
fabricated by hydrogen passivation on perpendicularly magnetized layers, the
switching fields can be maintained closer to the continuous film coercivity,
compared to dots made by usual dry etch techniques.",0706.2138v1
2007-07-12,Bistability in superconducting rings containing an inhomogeneous Josephson junction,"We investigate the magnetic response of a superconducting Nb ring containing
a ferromagnetic PdNi Josephson junction and a tunnel junction in parallel. A
doubling of the switching frequency is observed within certain intervals of the
external magnetic field. Assuming sinusoidal current-phase relations of both
junctions our model of a dc-SQUID embedded within a superconducting ring
explains this feature by a sequence of current reversals in the ferromagnetic
section of the junction in these field intervals. The switching anomalies are
induced by the coupling between the magnetic fluxes in the two superconducting
loops.",0707.1791v1
2007-07-16,Ferromagnetism of an all-carbon composite composed of a carbon nanowire nside a single-walled carbon nanotube,"Using the first-principles spin density functional approach, we have studied
magnetism of a new type of all-carbon nanomaterials, i.e., the carbon nanowires
inserted into the single-walled carbon nanotubes. It is found that if the 1D
carbon nanowire density is not too higher, the ferromagnetic ground state will
be more stable than the antiferromagnetic one, which is caused by weak coupling
between the 1D carbon nanowire and the single-walled carbon nanotube. Also,
both dimerization of the carbon nanowire and carbon vacancy on the tube-wall
are found to enhance the magnetic moment of the composite.",0707.2386v2
2007-07-17,Subnanosecond switching of local spin-exchange coupled to ferromagnets,"The dynamics of a single spin embedded in a the tunnel junction between
ferromagnetic contacts is strongly affected by the exchange coupling to the
tunneling electrons. Using time-dependent equation of motion for the spin under
influence of the spin-polarized tunneling current, it is shown that the
magnetic field induced by bias voltage pulses allows for sub-nanosecond
switching of the local spin and the possibility of spin reversal is
illustrated. Furthermore, it is shown that the time-evolution of the Larmor
frequency sharply peaks around the spin-flip event, and it is argued that this
feature can be used as an indicator for the spin-flip.",0707.2600v2
2007-07-25,Exchange shift of stripe domains in antiferromagnetically coupled multilayers,"Antiferromagnetically coupled multilayers with perpendicular anisotropy, as
[CoPt]/Ru, Co/Ir, Fe/Au, display ferromagnetic stripe phases as the ground
states. It is theoretically shown that the antiferromagnetic interlayer
exchange causes a relative shift of domains in adjacent layers. This ``exchange
shift'' is responsible for several recently observed effects: an anomalous
broadening of domain walls, the formation of so-called ``tiger-tail'' patterns,
and a ``mixed state'' of antiferromagnetic and ferromagnetic domains in
[CoPt]/Ru multilayers. The derived analitical relations between the values of
the shift and the strength of antiferromagnetic coupling provide an effective
method for a quantitative determination of the interlayer exchange
interactions.",0707.3765v1
2007-07-26,"Room temperature Ferromagnetism in Th1-xFexO2-d (x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) nanoparticles","Nanocrystalline (Th1-xFex)O2-d particles with different Fe concentrations (x
= 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been prepared by a gel combustion
method. Rietveld refinement analyses of X-ray diffraction data revealed the
formation of an impurity free cubic type Th1-xFexO2-d structure up to x = 0.20.
This observation is further confirmed from the detailed studies conducted on 10
at. percent Fe doped ThO2 using high-resolution transmission electron
microscopy (HRTEM) imaging and indexing of the selected-area electron
diffraction (SAED) patterns. DC Magnetization studies as a function field
indicate that they are ferromagnetic with Curie temperature (Tc) well above
room temperature.",0707.3883v1
2007-07-27,"Photo-induced precession of magnetization in ferromagnetic (Ga,Mn)As","Precession of magnetization induced by pulsed optical excitation is observed
in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical
measurements. It appears as complicated oscillations of polarization plane of
linearly-polarized probe pulses, but is reproduced by gyromagnetic theory
incorporating an impulsive change in an effective magnetic field due to changes
in magnetic anisotropy. It is inferred from the shape of the impulse that the
changes in anisotropy result from non-equilibrium carrier population: cooling
of hot photo-carriers and subsequent annihilation of photo-carriers.",0707.4055v2
2007-07-28,Performances of a Newly High Sensitive Trilayer F/Cu/F GMI Sensor,"We have selected stress-annealed nanocrystalline Fe-based ribbons for
ferromagnetic/copper/ferromagnetic sensors exhibiting high magneto-impedance
ratio. Longitudinal magneto-impedance reaches 400% at 60 kHz and longitudinal
magneto-resistance increases up to 1300% around 200 kHz.",0707.4232v2
2007-08-02,Simultaneous ferromagnetic metal-semiconductor transition in electron-doped EuO,"We present a general framework to describe the simultaneous
para-to-ferromagnetic and semiconductor-to-metal transition in electron-doped
EuO. The theory correctly describes detailed experimental features of the
conductivity and of the magnetization, in particular the doping dependence of
the Curie temperature. The existence of correlation-induced local moments on
the impurity sites is essential for this description.",0708.0416v2
2007-08-06,Multi-magnon bound states in the frustrated ferromagnetic 1D chain,"We study a one-dimensional Heisenberg chain with competing ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest neighbor interactions in
magnetic field. Starting from the fully polarized high-field state, we
calculate the dispersions of the lowest-lying $n$-magnon excitations and the
saturation field (n=2,3,4). We show that the lowest-lying excitations are
always bound multi-magnon states with a total momentum of $\pi$ except for a
small parameter range. We argue that bose condensation of the bound $n$ magnons
leads to novel Tomonaga-Luttinger liquids with multi-polar correlations;
nematic and triatic ordered liquids correspond to n=2 and n=3.",0708.0701v1
2007-08-14,"Random telegraph noise from magnetic nanoclusters in the ferromagnetic semiconductor (Ga,Mn)As","Measurements of the low frequency electrical noise in the ferromagnetic
semiconductor (Ga,Mn)As reveal an enhanced integrated noise at low temperature.
For moderate localization, we find a 1/f normalized power spectrum density over
the entire range of temperatures studied (4.2K < T < 70K). However, for
stronger localization and a high density of Mn interstitials, we observe
Lorentzian noise spectra accompanied by random telegraph noise. Magnetic field
dependence and annealing studies suggest that interstitial Mn defects couple
with substitutional Mn atoms to form nanoscale magnetic clusters characterized
by a net moment of about 20 Bohr magnetons whose fluctuations modulate hole
transport.",0708.1895v1
2007-08-15,Spin Valve Effect in Self-exchange Biased Ferromagnetic Metal/Semiconductor Bilayers,"We report magnetization and magetoresistance measurements in hybrid
ferromagnetic metal/semiconductor heterostructures comprised of MnAs/(Ga,Mn)As
bilayers. Our measurements show that the (metallic) MnAs and (semiconducting)
(Ga,Mn)As layers are exchange coupled, re- sulting in an exchange biasing of
the magnetically softer (Ga,Mn)As layer that weakens with layer thickness.
Magnetoresistance measurements in the current-perpendicular-to-the-plane
geometry show a spin valve effect in these self-exchange biased bilayers.
Similar measurements in MnAs/p- GaAs/(Ga,Mn)As trilayers show that the exchange
coupling diminishes with spatial separation between the layers.",0708.2092v1
2007-08-17,Observation of Ferromagnetic Clusters in Bi0.125Ca0.875MnO3,"The electron doped manganite system, Bi0.125Ca0.875MnO3, exhibits large bulk
magnetization of unknown origin. To select amongst possible magnetic ordering
models, we have conducted temperature and magnetic field dependent small-angle
neutron scattering measurements. Nontrivial spin structure has been revealed.
Ferromagnetic spin clusters form in the antiferromagnetic background when
temperature is decreased to Tc~108K. With a further reduction in temperature or
the application of external magnetic field, the clusters begin to form in
larger numbers, which gives an overall enhancement of magnetization below Tc.",0708.2300v1
2007-08-27,Weakly anisotropic frustrated zigzag spin chain,"The frustrated spin-1/2 model with weakly anisotropic ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest-neighbor exchanges is
studied with use of variational mean-field approach, scaling estimates of the
infrared divergencies in the perturbation theory and finite-size calculations.
The ground state phase diagram of this model contains three phases: the
ferromagnetic phase, the commensurate spin-liquid phase and the incommensurate
phase. The non-trivial behavior of the boundaries between these phases and the
character of the phase transitions in case of weak anisotropy are determined.",0708.3555v1
2007-08-30,Reentrant transitions of Ising-Heisenberg ferromagnet on a triangular lattice with diamond-like decorations,"The mixed spin-1/2 and spin-1 Ising-Heisenberg ferromagnet on the decorated
triangular lattice consisting of inter-connected diamonds is investigated
within the framework of an exact decoration-iteration mapping transformation.
It is shown that the diamond-like decoration by a couple of the Heisenberg
spins gives rise to a diverse critical behaviour including reentrant phase
transitions with two consecutive critical points.",0708.4103v1
2007-08-30,Quadratic operators used in deducing exact ground states for correlated systems: ferromagnetism at half filling provided by a dispersive band,"Quadratic operators are used in transforming the model Hamiltonian (H) of one
correlated and dispersive band in an unique positive semidefinite form coopting
both the kinetic and interacting part of H. The expression is used in deducing
exact ground states which are minimum energy eigenstates only of the full
Hamiltonian. It is shown in this frame that at half filling, also dispersive
bands can provide ferromagnetism in exact terms by correlation effects .",0708.4117v1
2007-09-19,Spin-dependent tunneling and Coulomb blockade in ferromagnetic nanoparticles,"We review studies on spin-dependent tunneling phenomena in systems containing
ferromagnetic nanoparticles. We discuss preparation methods of assembling
nanoparticles as well as the mechanisms and results of spin-dependent transport
properties. The emphasis of this review is on characteristic spin-dependent
tunneling phenomena such as enhanced tunnel magnetoresistance (TMR) due to
co-tunneling in the Coulomb blockade regime and sign changes of the TMR due to
spin accumulation in nanoparticles.",0709.2940v1
2007-09-22,Ferromagnetic behavior in magnetized plasmas,"We consider a low-temperature plasma within a newly developed MHD Fluid
model. In addition to the standard terms, the electron spin, quantum particle
dispersion and degeneracy effects are included. It turns out that the electron
spin properties can give rise to Ferromagnetic behavior in certain regimes. If
additional conditions are fulfilled, a homogenous magnetized plasma can even be
unstable. This happen in the low-temperature high-density regime, when the
magnetic properties associated with the spin can overcome the stabilizing
effects of the thermal and Fermi pressure, to cause a Jeans like instability.",0709.3575v1
2007-09-24,Magnetoresistance in an all-manganite heterostructure,"We study the magnetic and transport properties of all-manganite
heterostructures consisting of ferromagnetic metallic electrodes separated by
an antiferromagnetic barrier. We find that the magnetic ordering in the barrier
is influenced by the relative orientation of the electrodes magnetization
producing a large difference in resistance between the parallel and
antiparallel orientations of the ferromagnetic layers. The external application
of a magnetic field in a parallel configuration also leads to large
magnetoresistance.",0709.3720v1
2007-09-26,Single crystal growth and anisotropy of CeRuPO,"We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction.",0709.4144v2
2007-10-04,Time dilation of a bound half-fluxon pair in a long Josephson junction with a ferromagnetic insulator,"The fluxon dynamics in a long Josephson junction with a ferromagnetic
insulating layer is investigated. It is found that the Josephson phase obeys a
double sine-Gordon equation involving a bound pi fluxon solution, and the
internal oscillations of the bound pair acting as a clock exhibit Lorentz
reductions in their frequencies regarded as a relativistic effect in the time
domain, i.e., time dilation. This is the complement to the Lorentz contraction
of fluxons with no clock. A possible observation scheme is also discussed.",0710.0947v1
2007-10-06,Modulated phases in magnetic models frustrated by long-range interactions,"We study an Ising model in one dimension with short range ferromagnetic and
long range (power law) antiferromagnetic interactions. We show that the zero
temperature phase diagram in a (longitudinal) field H involves a sequence of up
and down domains whose size varies continuously with H, between -H_c and H_c
which represent the edge of the ferromagnetic up and down phases. The
implications of long range interaction in many body systems are discussed.",0710.1341v1
2007-10-13,Rotation of easy axis in training effect and recovery of exchange bias in ferromagnet/antiferromagnet bilayers,"For ferromagnet/antiferromagnet bilayers, rotation of the easy axis has been
\textit{for the first time} observed during measurements of training effect and
the recovery of exchange bias using FeNi/FeMn system. These salient phenomena
strongly suggest irreversible motion of antiferromagnet spins during subsequent
measurements of hysteresis loops. It is found that the rotation of the easy
axis can partly account for the training effect and the recovery of the
exchange bias.",0710.2594v1
2007-11-05,Magnetization easy-axis in martensitic Heusler alloys estimated by strain measurements under magnetic-field,"We study the temperature dependence of strain under constant magnetic-fields
in Ni-Mn based ferromagnetic Heusler alloys in the form Ni-Mn-$X$ ($X$: Ga, In,
Sn, Sb) which undergo a martensitic transformation. We discuss the influence of
the applied magnetic-field on the nucleation of ferromagnetic martensite and
extract information on the easy-axis of magnetization in the martensitic state.",0711.0639v1
2007-11-08,Ferroelectrically induced weak-ferromagnetism in a single-phase multiferroic by design,"We present a strategy to design structures for which a polar lattice
distortion induces weak ferromagnetism. We identify a large class of
multiferroic oxides as potential realizations and use density-functional theory
to screen several promising candidates. By elucidating the interplay between
the polarization and the Dzyaloshinskii-Moriya vector, we show how the
direction of the magnetization can be switched between 180$^{\circ}$ symmetry
equivalent states with an applied electric field.",0711.1331v2
2007-11-19,Diluted antiferromagnet in a ferromagnetic enviroment,"The question of robustness of a network under random ``attacks'' is treated
in the framework of critical phenomena. The persistence of spontaneous
magnetization of a ferromagnetic system to the random inclusion of
antiferromagnetic interactions is investigated. After examing the static
properties of the quenched version (in respect to the random antiferromagnetic
interactions) of the model, the persistence of the magnetization is analysed
also in the annealed approximation, and the difference in the results are
discussed.",0711.3016v1
2007-11-21,"Electron-electron interaction in 2D and 1D ferromagnetic (Ga,Mn)As","We investigated the magnetotransport in high quality ferromagnetic (Ga,Mn)As
films and wires. At low temperature the conductivity decreases with decreasing
temperature without saturation down to 20 mK. Here we show, that the
conductivity decrease follows a ln($T/T_0$) dependency in 2D films and a
$-1/\sqrt{T}$ dependency in 1D wires and is independent of an applied magnetic
field. This behavior can be explained by the theory of electron-electron
interaction.",0711.3278v2
2007-11-29,On the question of ferromagnetism in alkali metal thin films,"Electronic and magnetic structure of $(100)$ films of K and Cs are calculated
within the plane-wave projector augmented wave (PAW) formalism of the density
functional theory (DFT) using both local spin density approximation (LSDA) and
the PW91 generalized gradient approximation (GGA). Only a 6 layer Cs film is
found to have a ferromagnetic (FM) state which is degenerate with a
paramagnetic (PM) state within the accuracy of these calculations. This is at
variance with the results obtained from a finite thickness uniform jellium
model (UJM). Implications of these results for the experiments on transition
metal doped alkali metal thin films and bulk hosts are discussed.",0711.4744v1
2007-11-30,Large voltage from spin pumping in magnetic tunnel junctions,"We studied the response of a ferromagnet-insulator-normal metal tunnel
structure under an external oscillating radio frequency (R.F.) magnetic field.
The D. C. voltage across the junction is calculated and is found not to
decrease despite the high resistance of the junction; instead, it is of the
order of $\mu V$ to $100\mu V$, much larger than the experimentally observed
value (100 nano-V) in the ""strong coupled"" ohmic ferromagnet-normal metal
bilayers. This is consistent with recent experimental results in tunnel
structures, where the voltage is larger than $\mu V$s. The damping and loss of
an external RF field in this structure is calculated.",0711.4939v1
2007-12-06,Two-band ferromagnetic Kondo-lattice model for local-moment half-metals,"We introduce a two-band Kondo-lattice model to describe ferromagnetic
half-metals with local magnetic moments. In a model study, the electronic and
magnetic properties are presented by temperature dependent magnetization
curves, band-structures, spin polarizations and plasma frequencies. These are
obtained from numerically evaluated equations, based on the single-electron
Green functions. We show that the mutual influence between the itinerant
electrons and the local magnetic moments is responsible for several phase
transitions of the half-metals, namely first and second order magnetic phase
transitions, as well as half-metal to semiconductor and half-metal to semimetal
transitions.",0712.0905v1
2007-12-19,Energy spectrum of bound-spinons in the quantum Ising spin-chain ferromagnet,"We study the excitation energy spectrum in the S=1/2 ferromagnetic Ising spin
chain with the easy axis z in a magnetic field h={h_x,0,h_z}. According to Wu
and McCoy's scenario of weak confinement, the fermionic spinon excitations
(kinks), being free at h_z = 0 in the ordered phase, are coupled into bosonic
bound states at arbitrary small h_z. We calculate the energy spectrum of such
excitations in the leading order in small h_z, using different perturbative
methods developed for the similar problem in the Ising field theory.",0712.3189v1
2007-12-20,Spin-dependent diffraction at ferromagnetic/spin spiral interface,"Spin-dependent transport is investigated in ballistic regime through the
interface between a ferromagnet and a spin spiral. We show that spin-dependent
interferences lead to a new type of diffraction called ""spin-diffraction"". It
is shown that this spin-diffraction leads to local spin and electrical currents
along the interface. This study also shows that in highly non homogeneous
magnetic configuration (non adiabatic limit), the contribution of the
diffracted electrons is crucial to describe spin transport in such structures.",0712.3351v1
2008-01-14,The Transmission Property of the Discrete Heisenberg Ferromagnetic Spin Chain,"We present a mechanism for displaying the transmission property of the
discrete Heisenberg ferromagnetic spin chain (DHF) via a geometric approach. By
the aid of a discrete nonlinear Schr\""odinger-like equation which is the
discrete gauge equivalent to the DHF, we show that the determination of
transmitting coefficients in the transmission problem is always bistable. Thus
a definite algorithm and general stochastic algorithms are presented. A new
invariant periodic phenomenon of the non-transmitting behavior for the DHF,
with a large probability, is revealed by an adoption of various stochastic
algorithms.",0801.2060v1
2008-01-14,Weak Ferromagnetic Exchange and Anomalous Specific Heat in ZnCu3(OH)6Cl2,"Experimental evidence for a plethora of low energy spin excitations in the
spin-1/2 kagome antiferromagnet ZnCu3(OH)6Cl2 may be understandable in terms of
an extended Fermi surface of spinons coupled to a U(1) gauge field. We carry
out variational calculations to examine the possibility that such a state may
be energetically viable. A Gutzwiller-projected wavefunction reproduces the
dimerization of a kagome strip found previously by DMRG. Application to the
full kagome lattice shows that the inclusion of a small ferromagnetic
next-nearest-neighbor interaction favors a ground state with a spinon Fermi
surface.",0801.2138v2
2008-01-25,Ferromagnetism and Kondo Insulator Behavior in the Disordered Periodic Anderson Model,"The effect of binary alloy disorder on the ferromagnetic phases of f-electron
materials is studied within the periodic Anderson model. We find that disorder
in the conduction band can drastically enhance the Curie temperature due to an
increase of the local f-moment. The effect may be explained qualitatively and
even quantitatively by a simple theoretical ansatz. The emergence of an alloy
Kondo insulator at non-integer filling is also pointed out.",0801.3934v1
2008-01-25,"Optimization of parameters of nanostructure for study inverse proximity effects on ""superconductor-ferromagnetic"" interface using Polarized Neutron Reflectometry in enhanced standing wave regime","This work is devoted to experimental study of influence of superconductivity
(S) on ferromagnetism (FM) (inverse proximity effects) with the help of
Polarized Neutron Reflectivity. Combining meausurements of specular and diffuse
intensities it is possible to obtain full picture of magnetization change in
S/FM layered systems like magnetization rotation, domain state formation,
inducing of magnetization in S layer, etc. To increase weak magnetic signal we
propose to use enhanced neutron standing wave regime (e.g. waveguides). Choose
of materials, optimization of thicknesses of layers, estimation of roughnesses
influence is presented in this work.",0801.3967v1
2008-01-29,Comparative study of ordered and disordered Y1-xSrxCoO3-d,"We have succeeded in preparing A-site ordered- and disordered-Y1/4Sr3/4CoO3-d
with various oxygen deficiencies delta, and have made comparative study of
their structural and physical properties. In the A-site ordered structure,
oxygen vacancies order, and d = 0.34 sample shows a weak ferromagnetic
transition beyond 300 K. On the other hand, in the A-site disordered structure,
no oxygen vacancy ordering is observed, and d = 0.16 sample shows a
ferromagnetic metallic transition around 150 K. A-site disordering destroys the
orderings of oxygen-vacancies and orbitals, leading to the strong modification
of the electronic phases.",0801.4445v1
2008-02-08,Fractional periodicity and magnetism of extended quantum rings,"The magnetic properties and nature of the persistent current in small
flux-penetrated $t-t'-U$ rings are investigated. An effective rigid-rotator
description is formulated for this system, which coincides with a transition to
a ferromagnetic state in the model. The criteria for the onset of effective
rigid rotation is given. The model is used to understand continuum model
ground-state solutions for a 2D few-particle hard-wall quantum dot, where
ferromagnetic solutions are found even without the Zeeman coupling to spin.
After the onset of effective rigid rotation, a 97--98% correspondence can be
determined between the lattice model and continuum model eigenstate results.",0802.1108v1
2008-02-19,Small dimensional microstrips embedded with ferromagnetic layers: Numerical simulations and experimental results,"We use a numerical electromagnetic simulation software to investigate a
filtering device consisting of a small dimensional microstrips embedded with a
thin layer of ferromagnetic material and we compare our results to experimental
results. We are able to show good correlation of simulation versus experiment
for the magnitude of insertion loss and phase shift. The microstrips considered
have dimensions on the order of the skin depth of the conductor and hence the
field distribution is not easily calculated by analytic methods. We show that
numerical simulation methods provide an accurate means of characterizing these
structures.",0802.2599v1
2008-02-26,Electronic Transport Properties of the Ising Quantum Hall Ferromagnet in a Si Quantum Well,"Magnetotransport properties are investigated for a high mobility Si two
dimensional electron systems in the vicinity of a Landau level crossing point.
At low temperatures, the resistance peak having a strong anisotropy shows large
hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak
is split into two peaks in the paramagnetic regime. A mean field calculation
for the peak positions indicates that electron scattering is strong when the
pseudospin is partially polarized. We also study the current-voltage
characteristics which exhibit a wide voltage plateau.",0802.3756v2
2008-03-03,Laser-induced Precession of Magnetization in GaMnAs,"We report on the photo-induced precession of the ferromagnetically coupled Mn
spins in (Ga,Mn)As, which is observed even with no external magnetic field
applied. We concentrate on various experimental aspects of the time-resolved
magneto-optical Kerr effect (TR-MOKE) technique that can be used to clarify the
origin of the detected signals. We show that the measured data typically
consist of several different contributions, among which only the oscillatory
signal is directly connected with the ferromagnetic order in the sample.",0803.0320v1
2008-03-05,Distribution of magnetic domain pinning fields in GaMnAs ferromagnetic films,"Using the angular dependence of the planar Hall effect in GaMnAs
ferromagnetic films, we were able to determine the distribution of magnetic
domain pinning fields in this material. Interestingly, there is a major
difference between the pinning field distribution in as-grown and in annealed
films, the former showing a strikingly narrower distribution than the latter.
This conspicuous difference can be attributed to the degree of non-uniformity
of magnetic anisotropy in both types of films. This finding provides a better
understanding of the magnetic domain landscape in GaMnAs that has been the
subject of intense debate.",0803.0714v1
2008-03-06,Finite frequency noise of a superconductor/ferromagnet quantum point contact,"We have calculated the finite-frequency current noise of a
superconductor-ferromagnet quantum point contact (SF QPC). This signal is
qualitatively affected by the spin-dependence of interfacial phase shifts
(SDIPS) acquired by electrons upon reflection on the QPC. For a weakly
transparent QPC, noise steps appear at frequencies or voltages determined
directly by the SDIPS. These steps can occur at experimentally accessible
temperatures and frequencies. Finite frequency noise is thus a promising tool
to characterize the scattering properties of a SF QPC.",0803.0854v2
2008-03-14,Kondo effect in quantum dots coupled to ferromagnetic leads with noncollinear magnetizations: effects due to electron-phonon coupling,"Spin-polarized transport through a quantum dot strongly coupled to
ferromagnetic electrodes with non-collinear magnetic moments is analyzed
theoretically in terms of the non-equilibrium Green function formalism.
Electrons in the dot are assumed to be coupled to a phonon bath. The influence
of electron-phonon coupling on tunnelling current, linear and nonlinear
conductance, and on tunnel magnetoresistance is studied in detail. Variation of
the main Kondo peaks and phonon satellites with the angle between magnetic
moments of the leads is analyzed.",0803.2152v1
2008-03-15,Spin diode based on a single-wall carbon nanotube,"Electronic transport through a single-wall metallic carbon nanotube weakly
coupled to one ferromagnetic and one nonmagnetic lead is analyzed in the
sequential tunneling limit. It is shown that both the spin and charge currents
flowing through such systems are highly asymmetric with respect to the bias
reversal. As a consequence, nanotubes coupled to one nonmagnetic and one
ferromagnetic lead can be effectively used as spin diodes whose functionality
can be additionally controlled by a gate voltage.",0803.2279v1
2008-03-17,The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/superconductor contact,"The Andreev reflection probability for a ferromagnet/isolator/superconductor
(FIS) contact at the arbitrary spin-dependent amplitudes of the electron waves
transmitted through and reflected from the potential barrier is found. It is
shown that Andreev reflection probabilities of electron and hole excitations in
the FIS contact are different. The energy levels of Andreev bound states are
found. The ballistic conductance of the point FIS contact is calculated.",0803.2499v2
2008-03-18,The Blume-Emery-Griffiths Spin Glass and Inverted Tricritical Points,"The Blume-Emery-Griffiths spin glass is studied by renormalization-group
theory in d=3. The boundary between the ferromagnetic and paramagnetic phases
has first-order and two types of second-order segments. This topology includes
an inverted tricritical point, first-order transitions replacing second-order
transitions as temperature is lowered. The phase diagrams show disconnected
spin-glass regions, spin-glass and paramagnetic reentrances, and complete
reentrance, where the spin-glass phase replaces the ferromagnet as temperature
is lowered for all chemical potentials.",0803.2720v2
2008-03-26,Unusual spin-wave population in nickel after femtosecond laser pulse excitation,"The spin-wave relaxation mechanisms after intense laser excitation in
ferromagnetic nickel films are investigated with all-optical pump-probe
experiments. Uniform precession (Kittel mode), Damon-Eshbach surface modes and
perpendicular standing spin waves can be identified by their dispersion f(H).
However, different to other ferromagnets f(H) deviates from the expected
behavior. Namely, a mode discontinuity is observed, that can be attributed to a
non-linear process. Above a critical field the power spectrum reveals a
redistribution of the energy within the spin-wave spectrum populated.",0803.3686v2
2008-04-04,Inhomogeneous Gilbert damping from impurities and electron-electron interactions,"We present a unified theory of magnetic damping in itinerant electron
ferromagnets at order $q^2$ including electron-electron interactions and
disorder scattering. We show that the Gilbert damping coefficient can be
expressed in terms of the spin conductivity, leading to a Matthiessen-type
formula in which disorder and interaction contributions are additive. In a weak
ferromagnet regime, electron-electron interactions lead to a strong enhancement
of the Gilbert damping.",0804.0820v2
2008-04-05,Integrable Isotropic Geometrical Flows and Heisenberg Ferromagnets,"Geometrical flows (GF) play an important role in modern mathematics and
physics. In this letter we have considered some integrable isotropic GF --
Ricci flows (RF) and mean curvature flows (MCF) -- which are related with
integrable Heisenberg ferromagnets. In 2+1 dimensions, these GF have a
singularity at $t=t_{0}$.",0804.0837v1
2008-04-17,Non-analytic behavior of 2D itinerant ferromagnets,"We consider an ordered ferromagnet in the vicinity of a T=0 transition into a
paramagnet. We show that the free energy and the transverse and longitudinal
static susceptibilities contain non-analyticities which destroy a continuous
second-order transition. Depending on the parameters, the transition either
becomes first-order, or occurs via an intermediate spiral phase.",0804.2736v1
2008-04-17,Conductivity behavior of La$_{0.75}$Ca$_{0.25}$MnO$_{3}$ in vicinity of ferromagnetic-paramagnetic transition studied with single current pulses,"Temperature and current dependences of resistivity of bulk
La$_{0.75}$Ca$_{0.25}$MnO$_{3}$ sample grown by the floating-zone method were
studied using single ramp pulses of current. It is found that near the Curie
temperature $T_C$ the sample resistance depends substantially on current
magnitude. The observed features can be determined by inhomogeneous Joule
overheating due to mixed phase state of manganites near the
ferromagnetic-paramagnetic transition and percolation character of this
transition.",0804.2806v1
2008-04-28,Criticality in diluted ferromagnet,"We perform a detailed study of the critical behavior of the mean field
diluted Ising ferromagnet by analytical and numerical tools. We obtain
self-averaging for the magnetization and write down an expansion for the free
energy close to the critical line. The scaling of the magnetization is also
rigorously obtained and compared with extensive Monte Carlo simulations. We
explain the transition from an ergodic region to a non trivial phase by
commutativity breaking of the infinite volume limit and a suitable vanishing
field. We find full agreement among theory, simulations and previous results.",0804.4503v1
2008-05-08,Theory of huge tunneling magnetoresistance in graphene,"We investigate theoretically the spin-independent tunneling magnetoresistance
effect in a graphene monolayer modulated by two parallel ferromagnets deposited
on a dielectric layer. For the parallel magnetization configuration, Klein
tunneling can be observed in the transmission spectrum, but at specific oblique
incident angles. For the antiparallel magnetization configuration, the
transmission can be blocked by the magnetic-electric barrier provided by the
ferromagnets. Such a transmission discrepancy results in a tremendous
magnetoresistance ratio and can be tuned by the inclusion of an electric
barrier.",0805.1105v1
2008-05-08,"Electronic Structure, Phonons and Dielectric Anomaly in Ferromagnetic Insulating Double Perovskite La2NiMnO6","Using first-principles density functional calculations, we study the
electronic and magnetic properties of ferromagnetic insulating
double-perovskite compound La2NiMnO6, which has been reported to exhibit
interesting magnetic field sensitive dielectric anomaly as a function of
temperature. Our study reveals existence of very soft infra-red active phonons
that couple strongly with spins at the Ni and Mn sites through modification of
the super-exchange interaction. We suggest that these modes are the origin for
observed dielectric anomaly in La2NiMnO6.",0805.1112v1
2008-05-09,"Spin dynamics in (III,Mn)V ferromagnetic semiconductors: the role of correlations","We address the role of correlations between spin and charge degrees of
freedom on the dynamical properties of ferromagnetic systems governed by the
magnetic exchange interaction between itinerant and localized spins. For this
we introduce a general theory that treats quantum fluctuations beyond the
Random Phase Approximation based on a correlation expansion of the Green's
function equations of motion. We calculate the spin susceptibility, spin--wave
excitation spectrum, and magnetization precession damping. We find that
correlations strongly affect the magnitude and carrier concentration dependence
of the spin stiffness and magnetization Gilbert damping.",0805.1320v2
2008-06-10,Exact degenerate ground states for the F-AF spin chain with bond alternation,"We investigate the $J_1$-$J_2$ spin chain consisting of spins with magnitude
$\frac12$. The nearest-neighbor and the next-nearest-neighbor exchange
interactions are ferromagnetic and antiferromagnetic, respectively, and induce
strong frustration. Both these interactions involve the bond alternation. We
find exact solutions for all the degenerate ground states on the phase boundary
of the ferromagnetic phase. The degeneracy remains irrespective of two
parameters representing the bond alternation. The exact solutions are of closed
forms for no bond alternation and of recursion formulae in general. The exact
solutions are applicable to the $\Delta$ chain as a special case.",0806.1604v2
2008-06-17,Structural and angular dependence of coercivity and magnetic remanence of electrochemical ferromagnetic nanowires,"A novel method for controlling nanowire magnetic properties and growth from
filling time profile is presented.
  The wires are grown with an electrodeposition method (""Template synthesis"")
with a wide selection of pore diameters. We show that stray-fields presence in
ferromagnetic nanowires are entirely dependent on the nanowire diameter.
Besides a crossover effect in the reversal mechanism is observed with change in
diameter. In this work, theory and experiment agree and confirm that according
to the variety of hysteresis loop measured, about four ranges of values of pore
diameter control the orientation of nanowire magnetization easy axis with
respect to the geometrical axis.",0806.2826v1
2008-08-06,Surface Magnetoelectric Effect in Ferromagnetic Metal Films,"A surface magnetoelectric effect is revealed by density-functional
calculations that are applied to ferromagnetic Fe(001), Ni(001) and Co(0001)
films in the presence of external electric field. The effect originates from
spin-dependent screening of the electric field which leads to notable changes
in the surface magnetization and the surface magnetocrystalline anisotropy.
These results are of considerable interest in the area of
electrically-controlled magnetism and magnetoelectric phenomena.",0808.0841v1
2008-08-09,Gilbert Damping in Conducting Ferromagnets I: Kohn-Sham Theory and Atomic-Scale Inhomogeneity,"We derive an approximate expression for the Gilbert damping coefficient
\alpha_G of itinerant electron ferromagnets which is based on their description
in terms of spin-density-functional-theory (SDFT) and Kohn-Sham quasiparticle
orbitals. We argue for an expression in which the coupling of magnetization
fluctuations to particle-hole transitions is weighted by the spin-dependent
part of the theory's exchange-correlation potential, a quantity which has large
spatial variations on an atomic length scale. Our SDFT result for \alpha_G is
closely related to the previously proposed spin-torque correlation-function
expression.",0808.1373v1
2008-08-20,"Anharmonic effect on lattice distortion, orbital ordering and magnetic properties in Cs2AgF4","We develop the cluster self-consistent field method incorporating both
electronic and lattice degrees of freedom to study the origin of ferromagnetism
in Cs$_{2}$AgF$_{4}$. After self-consistently determining the harmonic and
anharmonic Jahn-Teller distortions, we show that the anharmonic distortion
stabilizes the staggered x$^{2}$-z$^{2}$/y$^{2}$-z$^{2}$ orbital and
ferromagnetic ground state, rather than the antiferromagnetic one. The
amplitudes of lattice distortions, Q$_{2}$ and Q$_{3}$, the magnetic coupling
strengthes, J$_{x,y}$, and the magnetic moment, are in good agreement with the
experimental observation.",0808.2759v1
2008-08-21,"GaMnAs: layers, wires and dots","Thin layers of GaMnAs ferromagnetic semiconductor grown by molecular beam
epitaxy on GaAs(001) substrates were studied. To improve their magnetic
properties the post-growth annealing procedures were applied, using the surface
passivation layers of amorphous arsenic. This post growth treatment effectively
increases the ferromagnetic-to-paramagnetic phase transition temperature in
GaMnAs, and provides surface-rich MnAs layer which can be used for formation of
low dimensional structures such as superlattices. If the surface rich MnAs
layer consists of MnAs dots, then it is possible to grow Mn-doped GaAs
nanowires",0808.2887v1
2008-08-27,"Coherent control of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As","We report single-color, time resolved magneto-optical measurements in
ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control
of the magnetization precession by applying two successive ultrashort laser
pulses. The magnetic field and temperature dependent experiments reveal the
collective Mn-moment nature of the oscillatory part of the time-dependent Kerr
rotation, as well as contributions to the magneto-optical signal that are not
connected with the magnetization dynamics.",0808.3738v2
2008-08-29,Spin-wave mediated quantum corrections to the conductivity in thin ferromagnetic gadolinium films,"We present a study of quantum corrections to the conductivity of thin
ferromagnetic gadolinium films. In situ magneto-transport measurements were
performed on a series of thin films with thickness d < 135A. For sheet
resistances R0 < 4011 Ohm and temperatures T < 30K, we observe a linear
temperature dependence of the conductivity in addition to the logarithmic
temperature dependence expected from well known quantum corrections in two
dimensions. We show that such a linear T-dependence can arise from a spin-wave
mediated Altshuler-Aronov type correction.",0808.4103v1
2008-09-07,Magnetic properties of Co-doped TiO2 anatase nanopowders,"This letter reports on the magnetic properties of Ti1-xCoxO2 anatase phase
nanopowders with different Co contents. It is shown that oxygen vacancies play
a fundamental role in promoting the long-range ferromagnetic order in the
material studied, in addition to the transition-metal doping. Furthermore, the
results allow ruling out the premise of a strict connection between Co
clustering and the ferromagnetism observed in the Co:TiO2 anatase system.",0809.1256v2
2008-09-08,Electronic inhomogeneity in EuO: Possibility of magnetic polaron states,"We have observed the spatial inhomogeneity of the electronic structure of a
single-crystalline electron-doped EuO thin film with ferromagnetic ordering by
employing infrared magneto-optical imaging with synchrotron radiation. The
uniform paramagnetic electronic structure changes to a uniform ferromagnetic
structure via an inhomogeneous state with decreasing temperature and increasing
magnetic field slightly above the ordering temperature. One possibility of the
origin of the inhomogeneity is the appearance of magnetic polaron states.",0809.1299v1
2008-09-09,Size Dependence of Current Spin Polarization Through Superconductor/Ferromagnet Nanocontacts,"The spin polarization P of the transport current through the interface
between superconducting Al and ferromagnetic Fe is determined by means of
Andreev reflection at nanostructured point contacts. We observe a systematic
decrease of P with decreasing contact resistance. Our data provide evidence for
the reduction of P by spin-orbit scattering and thus establish a link between
density-of-states and transport spin polarizations.",0809.1576v1
2008-09-11,Ferromagnetic ordering in dilute magnetic dielectrics with and without free carriers,"The state of art in the theoretical and experimental studies of transition
metal doped oxides (dilute magnetic dielectrics) is reviewed. The available
data show that the generic non-equilibrium state of oxide films doped with
magnetic impurities may either favor ferromagnetism with high Curie temperature
or result in highly inhomogeneous state without long-range magnetic order. In
both case concomitant defects (vacancies, interstitial ions play crucial part.",0809.2005v1
2008-09-18,The importance of local band effects for ferromagnetism in hole doped La$_2$CuO$_4$,"Band calculations for supercells of La$_{(2-x)}$Ba$_x$CuO$_4$ show that the
rigid band model for doping is less adequate than what is commonly assumed. In
particular, weak ferromagnetism (FM) can appear locally around clusters of high
Ba concentration. The clustering is important at large dilution and averaged
models for magnetism, such as the virtual crystal approximation, are unable to
stabilize magnetic moments. These results give a support to the idea that weak
FM can be the cause of the destruction of superconductivity at high hole
doping.",0809.3246v1
2008-09-26,Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models,"We study the magnetic interactions in Mott-Hubbard systems with partially
filled $t_{2g}$-levels and with strong spin-orbit coupling. The latter
entangles the spin and orbital spaces, and leads to a rich variety of the low
energy Hamiltonians that extrapolate from the Heisenberg to a quantum compass
model depending on the lattice geometry. This gives way to ""engineer"" in such
Mott insulators an exactly solvable spin model by Kitaev relevant for quantum
computation. We, finally, explain ""weak"" ferromagnetism, with an anomalously
large ferromagnetic moment, in Sr$_2$IrO$_4$.",0809.4658v2
2008-09-28,Coherent terahertz needle radiation emission mechanism from nanostructured ferromagnetic metal films excited by femtosecond laser pulses,"A coherent terahertz needle radiation emission mechanism is proposed. This
mechanism can be realized in the experiments on femtosecond laser pulses
interacting with surface of nanostructured ferromagnetic metal film. The
proposed mechanism is based on exciting of coupled coherent phonon-magnon modes
on a nanostructured metal surface by laser femtosecond pulse. The value of the
Poynting vector for the terahertz radiation is estimated.",0809.4868v1
2008-10-06,Spin polarized current and Andreev transmission in planar superconducting/ferromagnetic Nb/Ni junctions,"We have measured the tunnelling current in Nb/Nb$_x$O$_y$/Ni planar tunnel
junctions at different temperatures. The junctions are in the intermediate
transparency regime. We have extracted the current polarization of the
metal/ferromagnet junction without applying a magnetic field. We have used a
simple theoretical model, that provides consistent fitting parameters for the
whole range of temperatures analyzed. We have also been able to gain insight
into the microscopic structure of the oxide barriers of our junctions.%",0810.0929v1
2008-10-19,Spin-triplet f-wave pairing due to three-site cyclic-exchange ferromagnetic interactions,"Ferromagnetiam and superconductivity in a two-dimensional triangular-lattice
Hubbard model are studied using the density-matrix renormalization group
method. We propose a mechanism of the {\it f}-wave spin-triplet pairing derived
from the three-site cyclic-exchange ferromagnetic interactions. We point out
that a triangular network of hopping integrals, which is required for the
three-site cyclic hopping processes, is contained in the (possibly)
spin-triplet superconducting systems, such as Bechgaard salts (TMTSF)$_2$X,
cobalt oxide Na$_{0.35}$CoO$_2$$\cdot$1.3H$_2$O, and layered perovskite
Sr$_2$RuO$_4$.",0810.3387v1
2008-10-28,Ferromagnetism and increased ionicity in epitaxially grown TbMnO3 films,"Thin films of TbMnO3 have been grown on SrTiO3 substrates. The films grow
under compressive strain and are only partially clamped to the substrate. This
produces remarkable changes in the magnetic properties and, unlike the bulk
material, the films display ferromagnetic interactions below the ordering
temperature of ~40K. X-ray photoemission measurements in the films show that
the Mn-3s splitting is 0.3eV larger than that of the bulk. Ab initio embedded
cluster calculations yield Mn-3s splittings that are in agreement with the
experiment and reveal that the larger observed values are due to a larger
ionicity of the films.",0810.5137v1
2008-11-18,Quasiparticles in the Kondo lattice model at partial fillings of the conduction band,"We study the spectral properties of the one-dimensional Kondo lattice model
as function of the exchange coupling, the band filling, and the quasimomentum
in the ferromagnetic and paramagnetic phase. Using the density-matrix
renormalization group method, we compute the dispersion relation of the
quasiparticles, their lifetimes, and the Z-factor. As a main result, we provide
evidence for the existence of the spinpolaron at partial band fillings. We find
that the quasiparticle lifetime differs by orders of magnitude between the
ferromagnetic and paramagnetic phase and depends strongly on the quasimomentum.",0811.3000v1
2008-11-28,Bit storage by $360^\circ$ domain walls in ferromagnetic nanorings,"We propose a design for the magnetic memory cell which allows an efficient
storage, recording, and readout of information on the basis of thin film
ferromagnetic nanorings. The information bit is represented by the polarity of
a stable 360$^\circ$ domain wall introduced into the ring. Switching between
the two magnetization states is achieved by the current applied to a wire
passing through the ring, whereby the $360^\circ$ domain wall splits into two
charged $180^\circ$ walls, which then move to the opposite extreme of the ring
to recombine into a $360^\circ$ wall of the opposite polarity.",0811.4663v1
2008-12-02,Independent magnetization behavior of a ferromagnetic metal/semiconductor hybrid system,"We report the discovery of an effect where two ferromagnetic materials, one
semiconductor ((Ga,Mn)As) and one metal (permalloy), can be directly deposited
on each other and still switch their magnetization independently. We use this
independent magnetization behavior to create various resistance states
dependent on the magnetization direction of the individual layers. At zero
magnetic field a two layer device can reach up to four non-volatile resistance
states.",0812.0455v1
2008-12-12,Entanglement generation and perfect state transfer in ferromagnetic qubit chains,"We propose to use ferromagnetic systems for entanglement generation and
distribution together with perfect state transfer between distant parties in a
qubit chain. The scheme relies on an effective 2-qubit dynamics, realized by
leaving two empty sites in a uniformly filled chain. This allows long-range
interacting qubit chains to serve as quantum channels for both tasks with
optimal performances. Remarkably, the entanglement between sender and receiver
sites is independent of both the transmission distance and of system size. This
property opens new perspectives for short and mid-range quantum communication
with qubit chains.",0812.2404v2
2009-01-14,Interface coupling properties and reflection of bulk spin waves from biaxial multilayer ferromagnetic media,"The reflection coefficient of bulk spin waves from multilayer ferromagnetic
structure with periodically modulated parameters of exchange interaction,
uniaxial and rhombic magnetic anisotropy and saturation magnetization is
calculated with a non-ideal coupling between layers. The strong dependence of
spin-wave reflection coefficient on frequency, magnetic field and parameter of
interfacial coupling is revealed. It allows changing the reflection intensity
from 0 to 1 by changing either only external magnetic field value or frequency.
The proposed model of boundary conditions gives the opportunity to take into
account the quality of interfaces when studying the reflection processes of
spin waves in multilayer structures.",0901.2012v1
2009-01-15,Vortex stabilization in magnetic trilayer dots,"The magnetization reversal and spin structure in circular
Co/insulator/Ni80Fe20 trilayer dots has been investigated numerically. The
effect of dipolar coupling between a soft ferromagnetic Permalloy (Py=Ni80Fe20)
layer and a hard ferromagnetic Cobalt layer inside one stack is studied. We
find either a stabilization or even a triggering of the vortex state in the Py
layer due to the magnetic stray field of the Co layer, while the Co
magnetization remains in a single-domain state. Furthermore, for thin Py layers
a 360 deg-domain wall is observed. We construct a phase diagram, where regions
of vortex stabilization, triggering, and occurrence of a 360 deg domain wall
are marked.",0901.2209v1
2009-01-16,Cr-doping effect on the orbital fluctuation of heavily doped Nd1-xSrxMnO3 (x ~ 0.625),"We have investigated the Cr-doping effect of Nd0.375Sr0.625MnO3 near the
phase boundary between the x2-y2 and 3z2-r2 orbital ordered states, where a
ferromagnetic correlation and concomitant large magnetoresistance are observed
owing to orbital fluctuation. Cr-doping steeply suppresses the ferromagnetic
correlation and magnetoresistance in Nd0.375Sr0.625Mn1-yCryO3 with 0 < y <
0.05, while they reappear in 0.05 < y < 0.10. Such a reentrant behavior implies
that a phase boundary is located at y = 0.05, or a phase crossover occurs
across y = 0.05.",0901.2419v1
2009-01-19,Magnetism in Mn delta-doped cubic GaN: density-functional theory studies,"The magnetism in 12.5% and 25% Mn delta-doped cubic GaN has been investigated
using the density-functional theory calculations. The results show that the
single-layer delta-doping and half-delta-doping structures show robust ground
state half-metallic ferromagnetism (HMF), and the double-layer delta-doping
structure shows robust ground state antiferromagnetism (AFM) with large
spin-flip energy of 479.0 meV per Mn-Mn pair. The delta-doping structures show
enhanced two-dimensional magnetism. We discuss the origin of the HMF using a
simple crystal field model. Finally, we discuss the antiferromagnet/ferromagnet
heterostructure based on Mn doped GaN.",0901.2820v1
2009-01-19,The ground state magnetic phase diagram of the ferromagnetic Kondo-lattice model,"The magnetic ground state phase diagram of the ferromagnetic Kondo-lattice
model is constructed by calculating internal energies of all possible bipartite
magnetic configurations of the simple cubic lattice explicitly. This is done in
one dimension (1D), 2D and 3D for a local moment of S = 3/2. By assuming
saturation in the local moment system we are able to treat all appearing higher
local correlation functions within an equation of motion approach exactly. A
simple explanation for the obtained phase diagram in terms of bandwidth
reduction is given. Regions of phase separation are determined from the
internal energy curves by an explicit Maxwell construction.",0901.2855v1
2009-01-21,Frustrated Ising Model on a Diamond Hierarchical Lattice,"A frustrated Ising model on a diamond hierarchical lattice is studied. We
obtain the exact partition function of this model and calculate the transition
temperature, specific heat, entropy, magnetization, and ferromagnetic
correlation function. Depending on the magnitude of a parameter giving the
frustration, there exist three types of ground states: ferromagnetic, classical
spin-liquid with highly developed short-range order, and paramagnetic. The
dependence of the zero-temperature entropy on the frustration parameter has an
infinite number of steps. The temperature dependence of the specific heat
exhibits many peaks with decreasing temperature and entropy loss. The dominant
spin configurations at low temperatures are also specified.",0901.3181v2
2009-02-06,Spin torque from tunneling through impurities in a magnetic tunnel junction,"We calculate the contribution to the spin transfer torque from sequential
tunneling through impurities in a magnetic tunnel junction. For a junction with
weakly polarized ferromagnetic contacts, the torque is found to be in the plane
spanned by the magnetizations of the ferromagnetic contacts and proportional to
$\sin \theta$, where $\theta$ is the angle between the magnetic moments. If the
polarization is larger, the torque acquires a significant out-of-plane
component and a different dependence on $\theta$.",0902.1150v2
2009-02-07,Implementing Quantum Gates using the Ferromagnetic Spin-J XXZ Chain with Kink Boundary Conditions,"We demonstrate an implementation scheme for constructing quantum gates using
unitary evolutions of the one-dimensional spin-J ferromagnetic XXZ chain. We
present numerical results based on simulations of the chain using the
time-dependent DMRG method and techniques from optimal control theory. Using
only a few control parameters, we find that it is possible to implement one-
and two-qubit gates on a system of spin-3/2 XXZ chains, such as Not, Hadamard,
Pi-8, Phase, and C-Not, with fidelity levels exceeding 99%.",0902.1276v2
2009-02-11,A Blume-Capel Ising Ferromagnet with Annealed Vacancies on a Hierarchical Lattice,"A dilute Ising ferromagnet is considered in this study using renormalization
group techniques with a hierarchical lattice. A series of phase diagrams have
been produced that probe the effects of varying the temperature and
concentration of nonmagnetic impurities. Each phase diagram corresponds to a
different strength for the internal coupling coefficients on our lattice.
Phases have been interpreted and critical exponents calculated for the higher
order transitions.",0902.1971v2
2009-02-19,Effective mass suppression in a ferromagnetic two-dimensional electron liquid,"We present numerical calculations of the electron effective mass in an
interacting, ferromagnetic, two-dimensional electron system. We consider
quantum interaction effects associated with the charge-density fluctuation
induced many-body vertex corrections. Our theory, which is free of adjustable
parameters, reveals that the effective mass is suppressed (relative to its band
value) in the strong coupling limit, in good agreement with the results of
recent experimental measurements.",0902.3437v2
2009-02-25,"Tunneling magnetoresistance in (La,Pr,Ca)MnO3 nanobridges","The manganite (La,Pr,Ca)MnO3 is well known for its micrometer scale phase
separation into coexisting ferromagnetic metallic and antiferromagnetic
insulating (AFI) regions. Fabricating bridges with widths smaller than the
phase separation length scale has allowed us to probe the magnetic properties
of individual phase separated regions. We observe tunneling magnetoresistance
across naturally occurring AFI tunnel barriers separating adjacent
ferromagnetic regions spanning the width of the bridges. Further, near the
Curie temperature, a magnetic field induced metal-to-insulator transition among
a discrete number of regions within the narrow bridges gives rise to abrupt and
colossal low-field magnetoresistance steps at well defined switching fields.",0902.4386v1
2009-03-07,Shot noise of a ferromagnetic nanowire with a domain wall,"We study shot noise of the spin-polarized current in a diffusive
ferromagnetic nanowire which contains a ballistic domain wall. We find that the
existence of a short domain wall influences strongly the shot noise for
sufficiently high spin-polarization of the wire. Compared to the situation of
the absence of the domain wall, the shot noise can be reduced or enhanced
depending on the length of the domain wall and its relative conductance.",0903.1360v1
2009-03-17,Electronic transport in ferromagnetic conductors with inhomogeneous magnetic order parameter -- domain-wall resistance,"We microscopically derive transport equations for the conduction electrons in
ferromagnetic materials with an inhomogeneous magnetization profile. Our
quantum kinetic approach includes elastic scattering and anisotropic spin-flip
scattering at magnetic impurities. In the diffusive limit, we calculate the
resistance through a domain wall and find that the domain-wall resistance can
be positive or negative. In the limit of long domain walls we derive analytical
expressions and compare them with existing works, which used less general
models or different theoretical frameworks.",0903.3033v2
2009-03-23,Spatial distribution of Gaussian fluctuations of the molecular field and magnetization in the pyramid-like Ising nanoscopic system interacting with the substrate,"We study thermodynamic properties of an Ising model of a ferromagnetic
nanoscopic pyramid deposited onto a ferromagnetic bulk substrate. The influence
of the interaction between the pyramid and the substrate is calculated in terms
of the equilibrium reduced-state (density) operator used for description of
thermodynamic properties of nanoscopic systems. The spatial distribution of the
fluctuations of molecular field and magnetization in the nanoscopic pyramid is
obtained in the Gaussian fluctuations approximation. Experimental consequences
for the magnetic force measurements are briefly discussed.",0903.3659v1
2009-04-02,Spin-Fluctuation Drag Thermopower of Nearly Ferromagnetic Metals,"We investigate theoretically the Seebeck effect in materials close to a
ferromagnetic quantum critical point to explain anomalous behaviour at low
temperatures. It is found that the main effect of spin fluctuations is to
enhance the coefficient of the leading $T$-linear term, and a quantum critical
behaviour characterized by a spin-fluctuation temperature appears in the
temperature dependence of correction terms as in the specific heat.",0904.0287v2
2009-04-17,Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects,"Investigations of the magnetic properties of graphenes prepared by different
methods reveal that dominant ferromagnetic interactions coexist along with
antiferromagnetic interactions in all the samples. Thus, all the graphene
samples exhibit room-temperature magnetic hysteresis. The magnetic properties
depend on the number of layers and the sample area, small values of both
favoring larger magnetization. Molecular charge-transfer affects the magnetic
properties of graphene, interaction with a donor molecule such as
tetrathiafulvalene having greater effect than an electron-withdrawing molecule
such as tetracyanoethylene",0904.2739v1
2009-04-23,"Crystal growth, structure and ferromagnetic properties of a Ce3Pt23Si11 single crystal","A high-quality single crystal of Ce3Pt23Si11 has been grown using the
Czochralski method. The crystal structure is presented and the chemical
composition has been checked using an electron microprobe analyzer.
Measurements of the electrical resistivity and magnetic susceptibility
performed at low temperature show a ferromagnetic transition at Tc = 0.44 K.",0904.3720v1
2009-04-27,Surface magnetization in non-doped ZnO nanostructures,"We have investigated the magnetic properties of non-doped ZnO nanostructures
by using {\it ab initio} total energy calculations. Contrary to many proposals
that ferromagnetism in non-doped semiconductors should be induced by intrinsic
point defects, we show that ferromagnetism in nanostructured materials should
be mediated by extended defects such as surfaces and grain boundaries. This
kind of defects create delocalized, spin polarized states that should be able
to warrant long-range magnetic interactions.",0904.4147v1
2009-05-13,Orientation dependence of the Schottky barrier height for La$_0.6$Sr$_0.4$MnO$_3$/SrTiO$_3$ heterojunctions,"The authors report on the crystallographic orientation dependence of the
Schottky properties for heterojunctions between a half-metallic ferromagnet
La$_0.6$Sr$_0.4$MnO$_3$ (LSMO) and Nb-doped SrTiO3 semiconductor. The Schottky
barrier height determined by in situ photoemission measurements is independent
for the substrate orientations (001) and (110), while the magnetic properties
of LSMO (110) films are more enhanced than for (001) films. These results
suggest that the performance of magnetic devices based on ferromagnetic
manganite is improved by using (110)-oriented substrates.",0905.2018v1
2009-05-13,Itinerant ferromagnetism in an atomic Fermi gas: Influence of population imbalance,"We investigate ferromagnetic ordering in an itinerant ultracold atomic Fermi
gas with repulsive interactions and population imbalance. In a spatially
uniform system, we show that at zero temperature the transition to the
itinerant magnetic phase transforms from first to second order with increasing
population imbalance. Drawing on these results, we elucidate the phases present
in a trapped geometry, finding three characteristic types of behavior with
changing population imbalance. Finally, we outline the potential experimental
implications of the findings.",0905.2036v2
2009-05-13,Magnetic and transport properties of n-type Fe-doped In2O3 ferromagnetic thin films,"Room temperature ferromagnetism was observed in n-type Fe-doped In2O3 thin
films deposited on c-cut sapphire substrates by pulsed laser deposition.
Structure, magnetism, composition, and transport studies indicated that Fe
occupied the In sites of the In2O3 lattice rather than formed any metallic Fe
or other magnetic impurity phases. Magnetic moments of films were proved to be
intrinsic and showed to have a strong dependence on the carrier densities which
depended on the Fe concentration and its valance state as well as oxygen
pressure.",0905.2083v1
2009-05-21,Freezing into Stripe States in Two-Dimensional Ferromagnets and Crossing Probabilities in Critical Percolation,"When a two-dimensional Ising ferromagnet is quenched from above the critical
temperature to zero temperature, the system eventually converges to either a
ground state (all spins aligned) or an infinitely long-lived metastable stripe
state. By applying results from percolation theory, we analytically determine
the probability to reach the stripe state as a function of the aspect ratio and
the form of the boundary conditions. These predictions agree with simulation
results. Our approach generally applies to coarsening dynamics of non-conserved
scalar fields in two dimensions.",0905.3521v2
2009-05-26,Proximity effect in atomic-scaled hybrid superconductor/ferromagnet structures: crucial role of electron spectra,"We study the influence of the configuration of the majority and minority spin
subbands of electron spectra on the properties of atomic-scaled
superconductor-ferromagnet S-F-S and F-S-F hybrid structures. At low
temperatures, the S/F/S junction is either a 0 or junction depending on the
energy shift between S and F materials and the anisotropy of the Fermi
surfaces. We found that the spin switch effect in F/S/F system can be reversed
if the minority spin electron spectra in F metal is of the hole-like type.",0905.4212v1
2009-06-02,Effect of annealing on the magnetic and superconducting properties of single-crystalline UCoGe,"Single-crystals of the new ferromagnetic superconductor UCoGe have been
grown. The quality of as-grown samples can be significantly improved by a
heat-treatment procedure, which increases the residual resistance ratio (RRR)
from ~5 to ~30. Magnetization and resistivity measurements show the annealed
samples have a sharp ferromagnetic transition with a Curie temperature T_C is
2.8 K. The ordered moment of 0.06 mu_B is directed along the orthorhombic
c-axis. Superconductivity is found below a resistive transition temperature T_s
= 0.65 K.",0906.0497v1
2009-06-03,Effects of ferromagnetic fluctuations on the electric and thermal transport properties in NaxCoO2,"We investigate the electronic states and the transport properties of the CoO2
plane in NaxCoO2 on the basis of the two-dimensional triangular lattice 11-band
d-p model by using the fluctuation exchange approximation, where we consider
the Coulomb interaction between the t2g electrons on a Co site. It is found
that all of the effective mass of quasiparticles, the resistivity, the
thermoelectric power and the uniform spin susceptibility increase with
increasing x for x > 0.6. This implies that the ferromagnetic fluctuations play
significant roles on determining the electronic states. These results are
qualitatively consistent with the experiments.",0906.0618v1
2009-06-18,Metamagnetic phase transition in the Ising plus Dzyaloshinskii-Moriya model,"We study the 1D ferromagnetic Ising (spin-1/2) model with the
Dzyaloshinskii-Moriya (DM) interaction. We analyze the low energy excitation
spectrum and the ground state magnetic phase diagram using the Lanczos method.
The DM interaction-dependency is calculated for the low-energy excitation
spectrum, spiral order parameter and spin-spin correlation functions. We show
that a metamagnetic quantum phase transition occurs between the ferromagnetic
and spiral phases. The existence of the metamagnetic phase transition is
confirmed, using the variational matrix product states approach.",0906.3443v1
2009-06-18,Temperature-dependent resistivity of ferromagnetic GaMnAs: Interplay between impurity scattering and many-body effects,"The static conductivity of the dilute magnetic semiconductor GaMnAs is
calculated using the memory function formalism and time-dependent
density-functional theory to account for impurity scattering and to treat
Hartree and exchange interactions within the hole gas. We find that the Coulomb
scattering off the charged impurities alone is not sufficient to explain the
experimentally observed drop in resistivity below the ferromagnetic transition
temperature: the often overlooked scattering off the fluctuations of localized
spins is shown to play a significant role.",0906.3526v1
2009-06-22,Temperature dependent electrical resistivity of a single strand of ferromagnetic single crystalline nanowire,"We have measured the electrical resistivity of a single strand of a
ferromagnetic Ni nanowire of diameter 55 nm using a 4-probe method in the
temperature range 3 K-300 K. The wire used is chemically pure and is a high
quality oriented single crystalline sample in which the temperature independent
residual resistivity is determined predominantly by surface scattering. Precise
evaluation of the temperature dependent resistivity ($\rho$) allowed us to
identify quantitatively the electron-phonon contribution (characterized by a
Debye temperature $\theta_R$) as well as the spin-wave contribution which is
significantly suppressed upon size reduction.",0906.3903v1
2009-06-29,Clamping of ferroelectric and ferromagnetic domain walls in conical spiral magnets,"We study the structure of domain walls in multiferroic magnets with the
conical spiral ordering. We formulate a simple spin model which has a conical
spiral ground state in absence of magnetic anisotropies. We find a transition
from the regime where ferromagnetic and ferroelectric domain walls are clamped
to the regime where they are decoupled and derive a continuum model describing
rotation of the spiral plane at the domain wall. The importance of these
results for the switching phenomena observed in CoCr2O4 is discussed.",0906.5298v1
2009-06-30,Survival of short-range order in the Ising model on negatively curved surfaces,"We examine the ordering behavior of the ferromagnetic Ising lattice model
defined on a surface with a constant negative curvature. Small-sized
ferromagnetic domains are observed to exist at temperatures far greater than
the critical temperature, at which the inner core region of the lattice
undergoes a mean-field phase transition. The survival of short-range order at
such high temperatures can be attributed to strong boundary-spin contributions
to the ordering mechanism, as a result of which boundary effects remain active
even within the thermodynamic limit. Our results are consistent with the
previous finding of disorder-free Griffiths phase that is stable at
temperatures lower than the mean-field critical temperature.",0906.5523v1
2009-07-16,Anomalous magnetoresistance on the topological surface,"We investigate charge transport in two-dimensional ferromagnet/feromagnet
junction on a topological insulator. The conductance across the interface
depends sensitively on the directions of the magnetizations of the two
ferromagnets, showing anomalous behaviors compared with the conventional
spin-valve. It is found that the conductance depends strongly on the in-plane
direction of the magnetization. Moreover, in sharp contrast to the conventional
magnetoresistance effect, in the p-n junction, the conductance at the parallel
configuration is much smaller than that at the antiparallel configuration. This
stems from the way how the wavefunctions connect between both sides.",0907.2810v2
2009-07-27,Ferromagnetism in the Hubbard model with Topological/Non-Topological Flat Bands,"We introduce and study two classes of Hubbard models with magnetic flux or
with spin-orbit coupling, which have a flat lowest band separated from other
bands by a nonzero gap. We study the Chern number of the flat bands, and find
that it is zero for the first class but can be nontrivial in the second. We
also prove that the introduction of on-site Coulomb repulsion leads to
ferromagnetism in both the classes.",0907.4564v3
2009-08-05,"Femtosecond Coherent Control of Spin with Light in (Ga,Mn)As ferromagnets","Using density matrix equations of motion, we predict a femtosecond collective
spin tilt triggered by nonlinear, near--ultraviolet ($\sim$3eV), coherent
photoexcitation of (Ga,Mn)As ferromagnetic semiconductors with linearly
polarized light. This dynamics results from carrier coherences and nonthermal
populations excited in the \{111\} equivalent directions of the Brillouin zone
and triggers a subsequent uniform precession. We predict nonthermal
magnetization control by tuning the laser frequency and polarization direction.
Our mechanism explains recent ultrafast pump--probe experiments.",0908.0707v1
2009-08-10,Phase diagram of an anisotropic frustrated ferromagnetic spin-1/2 chain in a magnetic field: a density matrix renormalization group study,"We study the phase diagram of a frustrated spin-1/2 ferromagnetic chain with
anisotropic exchange interactions in an external magnetic field, using the
density matrix renormalization group method. We show that an easy-axis
anisotropy enhances the tendency towards multimagnon bound states, while an
easy-plane anisotropy favors chirally ordered phases. In particular, a moderate
easy-plane anisotropy gives rise to a quantum phase transition at intermediate
magnetization. We argue that this transition is related to the finite-field
phase transition experimentally observed in the spin-1/2 compound LiCuVO_4.",0908.1281v2
2009-08-25,The magnetism of wurtzite CoO nanoclusters,"The possibility that the apparent room temperature ferromagnetism, often
measured in Co-doped ZnO, is due to uncompensated spins at the surface of
wurtzite CoO nanoclusters is investigated by means of a combination of density
functional theory and Monte Carlo simulations. We find that the critical
temperature extracted from the specific heat systematically drops as the
cluster size is reduced, regardless of the particular cluster shape.
Furthermore the presence of defects, in the form of missing magnetic sites,
further reduces $T_\mathrm{C}$. This suggests that even a spinodal decomposed
phase is unlikely to sustain room temperature ferromagnetism in ZnO:Co.",0908.3632v1
2009-08-25,The Canted Spiral: An Exact Ground State of XXZ Zigzag Ladders,"We derive the exact ground states for a one dimensional family of $S=1/2$ XXZ
Hamiltonians on the zigzag ladder. These states exhibit true long range spiral
order that spontaneously breaks the U(1) invariance of the Hamiltonian. Besides
breaking a continuous symmetry in $d=1$, this spiral ordering has a
ferromagnetic component along the symmetry axis that can take any value between
zero and full saturation. In this sense, our canted spiral solutions are a
generalization of the SU(2) Heisenberg ferromagnet to non-zero ordering
wave-vectors of the transverse spin components. We extend this result to the
$d=2$ anisotropic triangular lattice.",0908.3639v1
2009-08-25,Non-equilibrium magnetization dynamics of ferromagnetically coupled Kondo spins,"An analytical description of non-equilibrium phenomena in interacting quantum
systems is rarely possible. Here we present one example where such a
description can be achieved, namely the ferromagnetic Kondo model. In
equilibrium, this model is tractable via perturbative renormalization-group
techniques. We employ a recently developed extension of the flow-equation
method to calculate the non-equilibrium decay of the local magnetization at
zero temperature. The flow equations admit analytical solutions which become
exact at short and long times, in the latter case revealing that the system
always retains a memory of its initial state.",0908.3647v1
2009-09-16,Magneto-Optical Modulation Ellipsometry,"The paper investigates the ellipsometric method of measuring the
magneto-optical parameter and optical constants in one experiment at affixed
angle of the light incidence in ferromagnetics. The influence of the
magnetization modulation on the change of ellipsometrical angles is shown. The
method is considered for the geometries of polar, meridional and equatorial
reflection Kerr effects. The formulae relating to the measured signals in
polarizer-subject-analyzer (PSA) circuit with four magneto-optical and optical
constants illustrated by the example of ferromagnetic Ni are given.",0909.2977v1
2009-09-16,Intrinsic ferromagnetic impurity phases in SmFeAsO1-xFx detected by muSR,"We report about muSR measurements on SmFeAsO1-xFx which helped us to identify
the signature of diluted ferromagnetic inclusions, ubiquitous in the iron
pnictides. These impurities are characterized by a Curie temperature close to
room temperature and they seem responsible for a non negligible magnetic
relaxation of the implanted muons, that should not be confused with intrinsic
pnictide properties.",0909.3004v1
2009-11-08,Nonequilibrium dynamical ferromagnetism of interacting Single-Molecule Magnets,"We propose a nonequilibrium Monte Carlo (MC) approach to explore
nonequilibrium dynamical ferromagnetism of interacting single molecule magnets
(SMMs). Both quantum spin tunneling and thermally activated spin reversal are
successfully implemented in the same MC simulation framework. Applied to a
typical example, this simulation method satisfactorily reproduces experimental
magnetization curves with experimental parameters. Our results show that both
quantum and classical effects are essential to determine the hysteresis
behaviors. This method is effective and reliable to gain deep insights into
SMMs.",0911.1539v1
2009-11-08,Elusive Glassy Phase in the Random Field Ising Model,"We consider the random field Ising model and show rigorously that the spin
glass susceptibility at equilibrium is always bounded by the ferromagnetic
susceptibility, and therefore that no spin glass phase can be present at
equilibrium out of the ferromagnet critical line. When the magnetization is,
however, fixed to values smaller than the equilibrium one, a glassy phase can
exist, as we show explicitly on the Bethe lattice.",0911.1551v2
2009-11-30,Ferromagnetism in the Blume-Emery-Griffiths model on finite-size Cayley tree,"The ferromagnetic properties of the spin-1 BEG model on finite-size Cayley
tree are investigated using the exact recursion method. The spontaneous
magnetization of the system is studied in detail for different values of the
reduced crystal-field interaction D/J, and it is found that there is an unusual
behavior (anti-Curie temperature) when D/J>2.0. We also obtain the Curie
temperature of this finite-size system. When the system size is large enough,
our results will fit well with that in the thermodynamic limit.",0911.5586v1
2010-01-05,Slow Cooling of an Ising Ferromagnet,"A ferromagnetic Ising chain which is endowed with a single-spin-flip Glauber
dynamics is investigated. For an arbitrary annealing protocol, we derive an
exact integral equation for the domain wall density. This integral equation
admits an asymptotic solution in the limit of extremely slow cooling. For
instance, we extract an asymptotic of the density of domain walls at the end of
the cooling procedure when the temperature vanishes. Slow annealing is usually
studied using a Kibble-Zurek argument; in our setting, this argument leads to
approximate predictions which are in good agreement with exact asymptotics.",1001.0741v1
2010-01-12,Dynamics of random dipoles : chaos {\it vs} ferromagnetism,"The microcanonical dynamics of an ensemble of random magnetic dipoles in a
needle has been investigated. Analyzing magnetic reversal times, a transition
between a chaotic paramagnetic phase and an integrable ferromagnetic phase has
been numerically found. In particular, a simple criterium for transition has
been formulated. Close to the transition point the statistics of average
magnetic reversal times and fluctuations have been studied and critical
exponents numerically given.",1001.1849v2
2010-01-30,Magnetoresistance of a spin MOSFET with ferromagnetic MnAs source and drain contacts,"Spin-dependent transport was investigated in a spin metal-oxide-semiconductor
field-effect transistors (spin MOSFET) with ferromagnetic MnAs source and drain
(S/D) contacts. The spin MOSFET of bottom-gate type was fabricated by
photolithography using an epitaxial MnAs film grown on a silicon-on-insulator
(SOI) substrate. In-plane magnetoresistance showed spin-valve-type hysteretic
behavior, when the measurements were performed with constant source-drain and
source-gate biases. By comparing with the magnetization-related resistance
change resulting from the MnAs contacts, we conclude that the spin-polarized
electrons are injected from the MnAs source into the Si MOS inversion channel,
and detected by the MnAs drain.",1002.0057v1
2010-02-01,Spin relaxation torque in metallic ferromagnets,"Spin relaxation torque ${\cal T}$ in uniform metallic ferromagnets with the
spin-orbit interaction arising from random impurities is calculated
microscopically. ${\cal T}$ is shown to be written by spatial derivatives of
the electric field, but is not always given as a divergence of a torque dipole
density. The result is due to the fast dissipation of the orbital angular
momentum, and thus a conserving spin current cannot be defined. It is discussed
that the $\beta$ term in the spin transfer torque can also be asymmetric.",1002.0207v2
2010-02-10,Phase Diagram of the Low-Density Two-Dimensional Homogeneous Electron Gas,"We have used quantum Monte Carlo methods to calculate the zero-temperature
phase diagram of the two-dimensional homogeneous electron gas. We find a
transition from a paramagnetic fluid to an antiferromagnetic triangular Wigner
crystal at density parameter r_s=31(1) a.u. and a transition to a ferromagnetic
crystal at r_s=38(5) a.u. The fully spin-polarized fluid is never stable. We
searched for, but did not find, the ferromagnetic hybrid phase proposed by H.
Falakshahi and X. Waintal [Phys. Rev. Lett. 94, 046801 (2005)].",1002.2101v1
2010-03-04,"The QCD string tension curve, the ferromagnetic magnetization, and the quark-antiquark confining potential at finite Temperature","We study the string tension as a function of temperature, fitting the SU(3)
lattice QCD finite temperature free energy potentials computed by the Bielefeld
group. We compare the string tension points with order parameter curves of
ferromagnets, superconductors or string models, all related to confinement. We
also compare the SU(3) string tension with the one of SU(2) Lattice QCD. With
the curve providing the best fit to the finite temperature string tensions, the
spontaneous magnetization curve, we then show how to include finite
temperature, in the state of the art confining and chiral invariant quark
models.",1003.0936v1
2010-03-06,Magnetoresistance studies of $La_{2/3} Sr_{1/3} MnO_3$ - $YBa_2 Cu_3 O_7$ - $La_{2/3} Sr_{1/3} Mn O_3$ trilayers with ferromagnetic coupling along the nodal direction of $YBa_2 Cu_3 O_7$,"I have successfully prepared (110) trilayers of \LSMO-\YBCO-\LSMO.
Magnetization measurements on these samples reveal a stronger coupling between
the ferromagnetic layers. The coupling is an order of magnitude higher than
that seen in the case of (001) trilayers. Magnetoresistance measurements show a
first order transition in the data coinciding with the antiferromagnetic regime
deduced from the magnetization measurements. I have also measured the
anisotropic magnetoresistance (AMR) of these samples revealing an unusually
high AMR ($\sim 72000%$). I attribute such a high AMR to the pair breaking
effects in these films.",1003.1414v1
2010-03-16,Macroscopic quantum state in a semiconductor device,"We show how nanostructuring of a metallic gate on a field-effect transistor
(FET) can lead to a macroscopic, robust and voltage controlled quantum state in
the electron channel of a FET. A chain of triple quantum dot molecules created
by gate structure realizes a spin-half Heisenberg chain with spin-spin
interactions alternating between ferromagnetic and anti-ferromagnetic. The
quantum state is a semiconductor implementation of an integer spin-one
antiferromagnetic Heisenberg chain with a unique correlated ground state and a
finite energy gap, originally conjectured by Haldane.",1003.3162v1
2010-03-16,Interference patterns of multifacet 20x(0-pi-) Josephson junctions with ferromagnetic barrier,"We have realized multifacet Josephson junctions with periodically alternating
critical current density (MJJs) using
superconductor-insulator-ferromagnet-superconductor heterostructures. We show
that anomalous features of critical current vs. applied magnetic field,
observed also for other types of MJJs, are caused by a non-uniform flux density
(parallel to the barrier) resulting from screening currents in the electrodes
in the presence of a (parasitic) off-plane field component.",1003.3216v1
2010-03-28,Conserved spin and orbital phase along carbon nanotubes connected with multiple ferromagnetic contacts,"We report on spin dependent transport measurements in carbon nanotubes based
multi-terminal circuits. We observe a gate-controlled spin signal in non-local
voltages and an anomalous conductance spin signal, which reveal that both the
spin and the orbital phase can be conserved along carbon nanotubes with
multiple ferromagnetic contacts. This paves the way for spintronics devices
exploiting both these quantum mechanical degrees of freedom on the same
footing.",1003.5387v1
2010-03-29,Quantum magnetism and counterflow supersolidity of up-down bosonic dipoles,"We study a gas of dipolar Bosons confined in a two-dimensional optical
lattice. Dipoles are considered to point freely in both up and down directions
perpendicular to the lattice plane. This results in a nearest neighbor
repulsive (attractive) interaction for aligned (anti-aligned) dipoles. We find
regions of parameters where the ground state of the system exhibits insulating
phases with ferromagnetic or anti-ferromagnetic ordering, as well as with
rational values of the average magnetization. Evidence for the existence of a
novel counterflow supersolid quantum phase is also presented.",1003.5591v2
2010-03-30,Colossal anisotropy in diluted magnetic topological insulators,"We consider dilute magnetic doping in the surface of a three dimensional
topological insulator where a two dimensional Dirac electron gas resides. We
find that exchange coupling between magnetic atoms and the Dirac electrons has
a strong and peculiar effect on both. First, the exchange-induced single ion
magnetic anisotropy is very large and favors off-plane orientation. In the case
of ferromagnetically ordered phase we find a colossal magnetic anisotropy
energy, of the order of the critical temperature. Second, a persistent
electronic current circulates around the magnetic atom and, in the case of a
ferromagnetic phase, around the edges of the surface.",1003.5931v1
2010-04-08,Spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites,"Correlation-induced spin-charge and spin-orbital coupling effects on spin
dynamics in ferromagnetic manganites are calculated with realistic parameters
in order to provide a quantitative comparison with experimental results for
spin stiffness, magnon dispersion, magnon damping, anomalous zone-boundary
magnon softening, and Curie temperature. The role of orbital degeneracy,
orbital ordering, and orbital correlations on spin dynamics in different doping
regimes is highlighted.",1004.1352v2
2010-04-26,Majorana fermion chain at the Quantum Spin Hall edge,"We study a realization of a 1d chain of Majorana bound states at the
interfaces between alternating ferromagnetic and superconducting regions at a
quantum spin Hall insulator edge. In the limit of well separated Majoranas, the
system can be mapped to the transverse field Ising model. The disordered
critical point can be reached by tuning the relative magnitude or phases of the
ferromagnetic and superconducting order parameters. We compute the voltage
dependence of the tunneling current from a metallic tip into the Majorana chain
as a direct probe of the random critical state.",1004.4585v2
2010-04-26,Ferromagnetism of cold fermions loaded into a decorated square lattice,"We investigate two-component ultracold fermions loaded into a decorated
square lattice, which are described by the Hubbard model with repulsive
interactions and nearest neighbor hoppings. By combining the real-space
dynamical mean-field theory with the numerical renormalization group method, we
discuss how a ferromagnetically ordered ground state in the weak coupling
regime, which originates from the existence of a dispersionless band, is
adiabatically connected to a Heisenberg ferrimagnetic state in the strong
coupling limit. The effects of level splitting and hopping imbalance are also
addressed.",1004.4650v1
2010-06-04,Scaling Behavior of Response Functions in the Coarsening Dynamics of Disordered Ferromagnets,"We study coarsening dynamics in the ferromagnetic random bond Ising model in
d = 1; 2. We focus on the validity of super-universality and the scaling
properties of the response functions. In the d = 1 case, we obtain a complete
understanding of the evolution, from pre- asymptotic to asymptotic behavior.
The corresponding response function shows a clear violation of
super-universality. Further, our results for d = 1; 2 settle the controversy
regarding the decay exponent which characterizes the response function.",1006.0934v1
2010-06-07,"Entanglement, fidelity, and quantum phase transition in antiferromagnetic-ferromagnetic alternating Heisenberg chain","The fidelity and entanglement entropy in an antiferromagnetic-ferromagnetic
alternating Heisenberg chain are investigated by using the method of
density-matrix renormalization-group. The effect of anisotropy on fidelity and
entanglement entropy are investigated. The relations between fidelity,
entanglement entropy and quantum phase transition are analyzed. It is found
that the quantum phase transition point can be well characterized by both the
ground-state entropy and fidelity for large system.",1006.1155v1
2010-06-09,Impurity effects and ferromagnetism in excitonic insulators,"Both nonmagnetic and magnetic impurity effects in spin singlet and triplet
excitonic insulators were investigated. The bound state energies caused by
single impurity were given. The different compositions of the bound states can
be used to detect the symmetry of the excitonic insulators. In finite
concentration problems, nonmagnetic impurities showed same pair-breaking effect
in singlet and triplet excitonic insulators while magnetic impurities showed
weaker pair-breaking effect in triplet excitonic insulators than in singlet
ones. The pair-breaking effects suppressed the ferromagnetic range via doping
and gave a natural explaination for experimental results.",1006.1687v1
2010-06-09,Analytical expression of the magneto-optical Kerr effect and Brillouin light scattering intensity arising from dynamic magnetization,"Time-resolved magneto-optical Kerr effect (MOKE) and Brillouin light
scattering (BLS) spectroscopy are important techniques for the investigation of
magnetization dynamics. Within this article, we calculate analytically the MOKE
and BLS signals from prototypical spin-wave modes in the ferromagnetic layer.
The reliability of the analytical expressions is confirmed by optically exact
numerical calculations. Finally, we discuss the dependence of the MOKE and BLS
signals on the ferromagnetic layer thickness.",1006.1906v1
2010-06-17,Spin Control of Drifting Electrons using Local Nuclear Polarization in Ferromagnet/Semiconductor Heterostructures,"We demonstrate methods to locally control the spin rotation of moving
electrons in a GaAs channel. The Larmor frequency of optically-injected spins
is modulated when the spins are dragged through a region of spin-polarized
nuclei created at a MnAs/GaAs interface. The effective field created by the
nuclei is controlled either optically or electrically using the ferromagnetic
proximity polarization effect. Spin rotation is also tuned by controlling the
carrier traverse time through the polarized region. We demonstrate coherent
spin rotations exceeding 4 pi radians during transport.",1006.3554v1
2010-06-24,Periodic solutions for the Landau-Lifshitz-Gilbert equation,"Ferromagnetic materials tend to develop very complex magnetization patterns
whose time evolution is modeled by the so-called Landau-Lifshitz-Gilbert
equation (LLG). In this paper, we construct time-periodic solutions for LLG in
the regime of soft and small ferromagnetic particles which satisfy a certain
shape condition. Roughly speaking, it is assumed that the length of the
particle is greater than its hight and its width. The approach is based on a
perturbation argument and the spectral analysis of the corresponding linearized
problem as well as the theory of sectorial operators.",1006.4765v1
2010-07-13,Magnetic-field control of the electric polarization in BiMnO3,"We present the microscopic theory of improper multiferroicity in BiMnO3,
which can be summarized as follows: (1) the ferroelectric polarization is
driven by the hidden antiferromagnetic order in the otherwise centrosymmetric
C2/c structure; (2) the relativistic spin-orbit interaction is responsible for
the canted spin ferromagnetism. Our analysis is supported by numerical
calculations of electronic polarization using Berry's phase formalism, which
was applied to the low-energy model of BiMnO3 derived from the first-principles
calculations. We explicitly show how the electric polarization can be
controlled by the magnetic field and argue that BiMnO3 is a rare and
potentially interesting material where ferroelectricity can indeed coexist and
interplay with the ferromagnetism.",1007.2039v1
2010-07-13,Tunable phase diagram and vortex pinning in a superconductor-ferromagnet bilayer,"We have observed the evolution of phase diagram and vortex pinning using a
single ferromagnet/superconductor bilayer of [Co/Pt]8/Nb through a special
demagnetization procedure. It induces a continuous and reversible change of the
domain width with equal positive/negative domains enabling the observation of
the predicted tunable phase diagram. The tunable domain pattern also
systematically affects vortex pinning. We have determined the dependence of the
activation energy of vortex pinning on domain width, temperature, and magnetic
field.",1007.2179v1
2010-07-14,Frustration-induced insulating chiral spin state in itinerant triangular-lattice magnets,"We study the double-exchange model at half-filling with competing
superexchange interactions on a triangular lattice, combining exact
diagonalization and Monte-Carlo methods. We find that in between the expected
itinerant ferromagnetic and $120^{\circ}$ Yafet-Kittel phases a robust
scalar-chiral, insulating spin state emerges. At finite temperatures the
ferromagnet - scalar-chiral quantum critical point is characterized by
anomalous bad-metal behavior in charge transport as observed in frustrated
itinerant magnets R$_2$Mo$_{2}$O$_7$.",1007.2278v2
2010-07-20,Finite-temperature magnetism in bcc Fe under compression,"We investigate the contributions of finite-temperature magnetic fluctuations
to the thermodynamic properties of bcc Fe as a function of pressure. First, we
apply a tight-binding total-energy model parameterized to first-principles
linearized augmented planewave computations to examine various ferromagnetic,
anti-ferromagnetic, and noncollinear spin spiral states at zero temperature.
The tight-binding data are fit to a generalized Heisenberg Hamiltonian to
describe the magnetic energy functional based on local moments. We then use
Monte Carlo simulations to compute the magnetic susceptibility, the Curie
temperature, heat capacity, and magnetic free energy. Including the
finite-temperature magnetism improves the agreement with experiment for the
calculated thermal expansion coefficients.",1007.3422v1
2010-07-26,"Spin fluctuations, susceptibility and the dipole oscillation of a nearly ferromagnetic Fermi gas","We discuss the spin fluctuations and the role played by the magnetic
susceptibility in an atomic Fermi gas interacting with positive scattering
length. Both thermal and quantum fluctuations are considered. Using a sum rule
approach and recent {\it ab initio} Monte Carlo results for the magnetic
susceptibility of uniform matter we provide explicit predictions for the
frequency of the spin dipole oscillation of a gas trapped by a harmonic
potential and discuss the deviations from the behaviour of an ideal gas when
the system approaches the ferromagnetic transition. The role of the Landau's
parameters in the characterization of the magnetic properties is also
discussed.",1007.4504v1
2010-07-28,Microwave response of a magnetic single-electron transistor,"We consider a single-electron transistor in the form of a ferromagnetic dot
in contact with normal-metal and pinned ferromagnetic leads. Microwave-driven
precession by the dot induces a pumped electric current. In open circuits, this
pumping produces a measurable reverse bias voltage, which can be enhanced and
made highly nonlinear by Coulomb blockade in the dot. The dependence of this
bias on the power and spectrum of microwave irradiation may be utilized to
develop nanoscale microwave detectors analogous to single-electron
transistor-based electrostatic sensors and nanoelectromechanical devices.",1007.4966v2
2010-07-28,Spin-dependent transport through quantum-dot Aharonov-Bohm interferometers,"We study the influence of spin polarization on the degree of coherence of
electron transport through interacting quantum dots. To this end, we identify
transport regimes in which the degree of coherence can be related to the
visibility of the Aharonov-Bohm oscillations in the current through a
quantum-dot Aharonov-Bohm interferometer with one normal and one ferromagnetic
lead. For these regimes, we calculate the visibility and, thus, the degree of
coherence, as a function of the degree of spin polarization of the
ferromagnetic lead.",1007.4988v2
2010-07-28,Current-induced torques in the presence of spin-orbit coupling,"In systems with strong spin-orbit coupling, the relationship between
spin-transfer torque and the divergence of the spin current is generalized to a
relation between spin transfer torques, total angular momentum current, and
mechanical torques. In ferromagnetic semiconductors, where the spin-orbit
coupling is large, these considerations modify the behavior of the spin
transfer torques. One example is a persistent spin transfer torque in a spin
valve: the spin transfer torque does not decay away from the interface, but
approaches a constant value. A second example is a mechanical torque at single
ferromagnetic-nonmagnetic interface.",1007.5037v1
2010-08-02,"Tipping without Flipping: A Novel Metastable ""Tilted"" State in Anisotropic Ferromagnets in External Fields","We show that in suitable anisotropic ferromagnets, both stable and metastable
``tilted'' phases occur, in which the magnetization ${\vec M}$ makes an angle
between zero and $180$ degrees with the externally applied ${\vec H}$. Tuning
either the magnitude of the external field or the temperature can lead to
continuous transitions between these states. A unique feature is that one of
these transitions is between two {\it metastable} states. Near the transitions
the longitudinal susceptibility becomes anomalous with an exponent which has an
{\it exact} scaling relation with the critical exponents.",1008.0215v1
2010-08-02,Tunneling spectroscopy probing magnetic and nonmagnetic electrodes in tunnel junctions,"Tunneling spectroscopy is applied to tunnel junctions with only one or no
ferromagnetic electrode to study the excitation of quasi particles in magnetic
tunnel junctions. The bias dependence is investigated with high accuracy by
inelastic electron tunneling spectroscopy. Both types of junctions show a zero
bias anomaly that is different in size and sign compared to magnetic tunnel
junctions, i.e. junctions with two ferromagnetic electrodes. A pronounced
difference is also found depending on the material that is probed by the
tunneling electrons, which might be attributed to the excitation of magnons.",1008.0326v1
2010-08-05,Anisotropic magnetocaloric effect in all-ferromagnetic (La0.7Sr0.3MnO3/SrRuO3) superlattices,"We exploit the magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3
superlattices to realize a crossover between inverse and conventional magnetic
entropy changes. Our data reveal a strong anisotropic nature of the
magnetocaloric effect due to the magnetic anisotropy of the superlattice.
Therefore, artificial superlattices built from ferromagnetic materials that can
be used to alter the magnetic structure as well as the magnetic anisotropy,
could also be utilized for tuning the magnetocaloric properties, which may open
a constructive approach for magnetic refrigeration applications.",1008.1041v1
2010-08-06,Ferromagnetic phases in spin-Fermion systems,"Spin-Fermion systems which obtain their magnetic properties from a system of
localized magnetic moments being coupled to conducting electrons are
considered. The dynamical degrees of freedom are spin-$s$ operators of
localized spins and spin-1/2 Fermi operators of itinerant electrons.
Renormalized spin-wave theory, which accounts for the magnon-magnon
interaction, and its extension are developed to describe the two ferrimagnetic
phases in the system: low temperature phase $0<T<T^{*}$, where all electrons
contribute the ordered ferromagnetic moment, and high temperature phase
$T^{*}<T<T_C$, where only localized spins form magnetic moment. The
magnetization as a function of temperature is calculated. The theoretical
predictions are utilize to interpret the experimentally measured
magnetization-temperature curves of $UGe_2$..",1008.1148v1
2010-08-16,Electronic phase separation in the pyrochlore double-exchange model,"Electronic phase separation and related inhomogeneity is ubiquitously seen in
strongly-correlated systems. A typical example is found between ferromagnetic
metal and antiferromagnetic insulator in CMR manganese oxides. Here we
demonstrate that the geometrical frustration brings distinctive aspects into
the phase separation phenomena. From Monte Carlo simulation and a simple energy
comparison for the pyrochlore double-exchange model, we show that such phase
separation takes place between ferromagnetic and paramagnetic metals. We
discuss the relevance of our results to a spin-glassy metallic phase found in
Mo pyrochlore oxides under external pressure.",1008.2786v1
2010-08-26,No spin glass phase in ferromagnetic random-field random-temperature scalar Ginzburg-Landau model,"Krzakala, Ricci-Tersenghi and Zdeborova have shown recently that the random
field Ising model with non-negative interactions and arbitrary external
magnetic field on an arbitrary lattice does not have a static spin glass phase.
In this paper we generalize the proof to a soft scalar spin version of the
Ising model: the Ginzburg-Landau model with random magnetic field and random
temperature-parameter. We do so by proving that the spin glass susceptibility
cannot diverge unless the ferromagnetic susceptibility does.",1008.4497v1
2010-09-01,Competing Superconducting States in Strong Ferromagnets,"We report results from a systematic study of the competition of exotic
triplet pair density wave (PDW) superconductivity (SC) with homogeneous (zero
pair momentum) SC in strongly polarized media such as half metallic systems.
From the two different PDW states allowed by symmetry in this background only
one may dominate or even coexist with homogeneous SC. We propose a direct
experimental identification of PDW SC in this context. Our results suggest that
these exotic states may plausibly emerge in heterostructures involving
proximity of SC with half-metallic CrO$_2$ where induced SC is established in
the half metallic region and in strongly ferromagnetic superconductors.",1009.0122v1
2010-09-01,Ferromagnetically coupled magnetic impurities in a quantum point contact,"We investigate the ground and excited states of interacting electrons in a
quantum point contact using exact diagonalization method. We find that strongly
localized states in the point contact appear when a new conductance channel
opens due to momentum mismatch. These localized states form magnetic impurity
states which are stable in a finite regime of chemical potential and excitation
energy. Interestingly, these magnetic impurities have ferromagnetic coupling,
which shed light on the experimentally observed puzzling coexistence of Kondo
correlation and spin filtering in a quantum point contact.",1009.0204v1
2010-09-04,Magnetization Reversal by Electric-Field Decoupling of Magnetic and Ferroelectric Domains Walls in Multiferroic-Based Heterostructures,"We demonstrate that the magnetization of a ferromagnet in contact with an
antiferromagnetic multiferroic (LuMnO3) can be speedily reversed by electric
field pulsing, and the sign of the magnetic exchange bias can switch and
recover isothermally. As LuMnO3 is not ferroelastic, our data conclusively show
that this switching is not mediated by strain effects but is a unique
electric-field driven decoupling of the ferroelectric and ferromagnetic domains
walls. Their distinct dynamics are essential for the observed magnetic
switching.",1009.0820v1
2010-09-24,Critical behavior of Ising spins in a tridimensional percolating nano system with noninteger fractal dimension,"In an artificial 3D percolation nano medium, the clusters filled by the Ising
magnets give rise to a topologically nontrivial magnetic structure, leading to
new features of the ferromagnetic phase transition without an external magnetic
field. In such an inhomogeneous system, the standard Ising model is strongly
modified by the spatial percolation cluster distribution. We found numerically
that at percolation occupation probability $p<1$ far from the percolation
threshold $p_{c3D}$, the magnetization shows ferromagnetic-paramagnetic phase
transition with the transition temperature $T_{c}$ depending considerably on
the probability $p$. We provide numerical evidence that in vicinity $p_{c3D}$\
the dependence $T_{c}(p)$ is affected by the noninteger fractal dimension
$D_{H}(p)$ of the incipient percolation spanning cluster.",1009.4897v1
2010-09-27,Graphene spintronics: the role of ferromagnetic electrodes,"We report a first principles study of spin-transport under finite bias
through a graphene-ferromagnet (FM) interface, where FM=Co(111), Ni(111). The
use of Co and Ni electrodes achieves spin efficiencies reaching 80% and 60%,
respectively. This large spin filtering results from the materials specific
interaction between graphene and the FM which destroys the linear dispersion
relation of the graphene bands and leads to an opening of spin-dependent energy
gaps of roughly 0.4-0.5 eV at the K points. The minority spin band gap resides
higher in energy than the majority spin band gap located near the Fermi level,
a feature that results in large minority spin dominated currents.",1009.5254v1
2010-10-12,Linear-response theory of spin Seebeck effect in ferromagnetic insulators,"We formulate a linear response theory of the spin Seebeck effect, i.e., a
spin voltage generation from heat current flowing in a ferromagnet. Our
approach focuses on the collective magnetic excitation of spins, i.e., magnons.
We show that the linear-response formulation provides us with a qualitative as
well as quantitative understanding of the spin Seebeck effect observed in a
prototypical magnet, yttrium iron garnet.",1010.2325v2
2010-10-29,The Structural and Magnetic ordering in $La{}_{0.5-x}Nd_{x}Ca_{0.5}MnO_{3}$ (0.1 \ensuremath{\le} x \ensuremath{\le} 0.5) Manganites,"The crystal and magnetic structure of polycrystalline
$La{}_{0.5-x}Nd{}_{x}Ca_{0.5}MnO{}_{3}$ (0.0 \ensuremath{\le} x
\ensuremath{\le} 0.5) samples have been investigated using magnetization,
resistivity, transmission electron microscope, and neutron diffraction
techniques. The samples are isostructural and possess orthorhombic structure in
\textit{Pnma} space group. On lowering of temperature, the samples exhibit CE -
type antiferromagnetic structure coexisting with a weak ferromagnetic ordering.
The charge and orbitally ordered antiferromagnetic phase is weakened by the
growth of ferromagnetic phase. The evolution of structural distortions and
magnetic structure at low temperature as a function of Nd doping exhibit a
strong correlation with A - site disorder ($\sigma{}^{2}$).",1010.6124v1
2010-11-18,Possibility of exchange switching ferromagnet - antiferromagnet junctions,"Current flowing is studied in magnetic junctions consisting of a
ferromagnetic metal (FM), antiferromagnetic conductor (AFM) and a nonmagnetic
metal closing the electric circuit. The FM layer with high anisotropy and
pinned spins of the magnetic atoms in the lattice acts as a spin injector
relative to the AFM layer. To obtain resulting magnetization in the AFM layer,
magnetic field is applied, which may be varied to control the magnetization.
The spin-polarized current from the FM layer creates a torque and makes it
possible to switch the magnetization. A possibility is shown to lower the
threshold current density by the orders of magnitude by means of the magnetic
field.",1011.4303v1
2010-11-22,Wang-Landau study of the triangular Blume-Capel ferromagnet,"We report on numerical simulations of the two-dimensional Blume-Capel
ferromagnet embedded in the triangular lattice. The model is studied in both
its first- and second-order phase transition regime for several values of the
crystal field via a sophisticated two-stage numerical strategy using the
Wang-Landau algorithm. Using classical finite-size scaling techniques we
estimate with high accuracy phase-transition temperatures, thermal, and
magnetic critical exponents and we give an approximation of the phase diagram
of the model.",1011.4780v2
2010-11-24,The competition between superconductivity and ferromagnetism in small metallic grains: thermodynamic properties,"We study the thermodynamic properties of a small superconducting metallic
grain using a quantum Monte Carlo method. The grain is described by the
universal Hamiltonian, containing pairing and ferromagnetic exchange
correlations. In particular, we study how the thermodynamic signatures of
pairing correlations are affected by the spin exchange interaction. We find the
exchange interaction effects to be qualitatively different in the BCS and
fluctuation-dominated regimes of pairing correlations.",1011.5421v1
2010-12-10,Active microcantilevers based on piezoresistive ferromagnetic thin films,"We report the piezoresisitivity in magnetic thin films of FeGa and their use
for fabricating self transducing microcantilevers. The actuation occurs as a
consequence of both the ferromagnetic and magnetostrictive property of FeGa
thin films, while the deflection readout is achieved by exploiting the
piezoresisitivity of these films. This self-sensing, self-actuating
micromechanical system involves a very simple bilayer structure, which
eliminates the need for the more complex piezoelectric stack that is commonly
used in active cantilevers. Thus, it potentially opens opportunities for
remotely actuated, cantilever-based sensors.",1012.2330v1
2010-12-20,Fully electrically read-write device out of a ferromagnetic semiconductor,"We report the realization of a read-write device out of the ferromagnetic
semiconductor (Ga,Mn)As as the first step to fundamentally new information
processing paradigm. Writing the magnetic state is achieved by current-induced
switching and read-out of the state is done by the means of the tunneling
anisotropic magneto resistance (TAMR) effect. This one bit demonstrator device
can be used to design a electrically programmable memory and logic device.",1012.4252v1
2010-12-21,Spin superconductor in ferromagnetic graphene,"We show a spin superconductor (SSC) in ferromagnetic graphene as the
counterpart to the charge superconductor, in which a spin-polarized
electron-hole pair plays the role of the spin $2 (\hbar/2)$ `Cooper pair' with
a neutral charge. We present a BCS-type theory for the SSC. With the
`London-type equations' of the super-spin-current density, we show the
existence of an electric `Meissner effect' against a spatial varying electric
field. We further study a SSC/normal conductor/SSC junction and predict a
spin-current Josephson effect.",1012.4528v2
2010-12-28,Weak ferromagnetism in cobalt oxalate crystals,"Microcrystals of diaquocobalt(II) oxalate have been synthesized by the
coprecipitation reaction of aqueous solutions of Cobalt (II) bromide and oxalic
acid. Chemical analysis and thermal experiments revealed that there is only one
phase present. X-ray powder diffraction studies show that this compound is
orthorhombic with space group Cccm. Molar susceptibility versus temperature
measurements show the existence of an antiferromagnetic ordering, however, the
hysteresis measured in magnetization measurements as a function of magnetic
field reveals a weak ferromagnetic behavior.",1012.5824v1
2011-01-07,Novel effects of localization due to `intrinsic disorder' in the `two-fluid' model for manganites,"We discuss the effects of a novel polaronic disorder in the recently proposed
two-fluid model for manganites. Using effective field theory as well as direct
numerical simulations, we show that this disorder can have dramatic effects in
terms of the transition from ferromagnetic insulator to ferromagnetic metal
upon hole-doping, including an Anderson localized regime where variable range
hopping may be observed.",1101.1370v1
2011-01-08,"Voids and Mn-rich inclusions in a (Ga,Mn)As ferromagnetic semiconductor investigated by transmission electron microscopy","Voids adjacent to both cubic (ZnS-type) and hexagonal (NiAs-type) Mn-rich
nanocrystals are characterized using aberration-corrected transmission electron
microscopy in annealed Ga0.995Mn0.005As magnetic semiconductor specimen grown
by molecular beam epitaxy. Nano-beam electron diffraction measurements suggest
that the nanocrystals exhibit deviations in lattice parameter from that of bulk
MnAs. In situ annealing inside the electron microscope is used to study the
nucleation, coalescence, and grain growth of individual nanocrystals. After
annealing at 903 K, the magnetic transition temperature of the specimen likely
to be dominated by the presence of cubic ferromagnetic nanocrystals.",1101.1600v1
2011-01-20,Tunneling Hamiltonian description of the atomic-scale 0-pi transition in superconductor/ferromagnetic-insulator junctions,"We show a perturbation theory of the Josephson transport through
ferromagnetic insulators (FIs). Recently we have found that the appearance of
the atomic scale 0-pi transition in such junctions based on numerical
calculations. In order to explore the mechanism of this anomalous transition,
we have analytically calculated the Josephson current using the tunneling
Hamiltonian theory and found that the spin dependent pi-phase shift in the FI
barrier gives the atomic scale 0-pi transition.",1101.3806v1
2011-01-20,Controllable manipulation of superconductivity using magnetic vortices,"The magneto-transport of a superconducting/ferromagnetic hybrid structure
consisting of a superconducting thin film in contact with an array of magnetic
nanodots in the so-called ""magnetic vortex-state"" exhibits interesting
properties. For certain magnetic states, the stray magnetic field from the
vortex array is intense enough to drive the superconducting film into the
normal state. In this fashion, the normal-to-superconducting phase transition
can be controlled by the magnetic history. The strong coupling between
superconducting and magnetic subsystems allows characteristically ferromagnetic
properties, such as hysteresis and remanence, to be dramatically transferred
into the transport properties of the superconductor.",1101.3846v1
2011-01-29,Spin-injection terahertz radiation in magnetic junctions,"Electromagnetic radiation of 1 - 10 THz range has been found at room
temperature in a structure with a point contact between a ferromagnetic rod and
a thin ferromagnetic film under electric current of high enough density. The
radiation is due to nonequilibrium spin injection between the structure
components. By estimates, the injection can lead to inverted population of the
spin subbands. The radiation power exceeds by orders of magnitude the thermal
background (with the Joule heating taking into account) and follows the current
without inertia.",1101.5683v1
2011-01-30,Spin-Charge Locking and Tunneling into a Helical Metal,"We derive a kinetic equation for the electrons moving on the surface of a
three-dimensional topological insulator. Due to the helical nature of the
excitations backward scattering is suppressed in the collision integral, and
the spin dynamics is entirely constrained by that of the charge. We further
analyze the tunneling between the helical and a conventional metal or
ferromagnet. We find that the tunnel resistance strongly depends on the angle
between the magnetization in the ferromagnet and the current in the helical
metal. A nonmagnetic layer on top of the helical metal amplifies the
current-induced spin polarization.",1101.5802v1
2011-02-11,Chiral spin states in polarized kagome spin systems with spin-orbit coupling,"We study quantum spin systems with a proper combination of geometric
frustration, spin-orbit coupling and ferromagnetism. We argue that such a
system is likely to be in a chiral spin state, a fractional quantum Hall (FQH)
state for bosonic spin degrees of freedom. The energy scale of the bosonic FQH
state is of the same order as the spin-orbit coupling and ferromagnetism ---
overall much higher than the energy scale of FQH states in semiconductors.",1102.2406v1
2011-02-17,Thermodynamics of the frustrated one-dimensional spin-1/2 Heisenberg ferromagnet in a magnetic field,"We calculate the low-temperature thermodynamic quantities (magnetization,
correlation functions, transverse and longitudinal correlation lengths, spin
susceptibility, and specific heat) of the frustrated one-dimensional spin-half
J1-J2 Heisenberg ferromagnet, i.e. for J2< 0.25|J1|, in an external magnetic
field using a second-order Green-function formalism and full diagonalization of
finite systems. We determine power-law relations for the field dependence of
the position and the height of the maximum of the uniform susceptibility.
Considering the specific heat at low magnetic fields, two maxima in its
temperature dependence are found.",1102.3581v2
2011-03-11,Atomic scale 0-pi transition in a high-Tc superconductor/ferromagnetic-insulator/high-T superconductor Josephson junction,"We study the Josephson transport in a high-Tc
superconductor/ferromagnetic-insulator(FI)/high-Tc superconductor numerically.
We found the formation of a pi-junction in such systems. More remarkably the
ground state of such junction alternates between 0- and pi-states when
thickness of FI is increasing by a single atomic layer. We propose an
experimental setup for observing the atomic-scale 0-pi transition. Such
FI-based pi-junctions can be used to implement highly-coherent quantum bits.",1103.2187v1
2011-03-12,Effective field theories and spin-wave excitations in helical magnets,"We consider two classes of helical magnets. The first one has magnetic
ordering close to antiferromagnet and the second one has magnetic ordering
close to ferromagnet. The first case is relevant to cuprate superconductors and
the second case is realized in FeSrO$_3$ and FeCaO$_3$. We derive the effective
field theories for these cases and calculate corresponding excitation spectra.
We demonstrate that the ""hourglass"" spin-wave dispersion observed
experimentally in cuprates is a fingerprint of the ""antiferromagnetic spin
spiral state"". We also show that quantum fluctuations are important for the
""ferromagnetic spin spiral"", they influence qualitative features of the
spin-wave dispersion.",1103.2422v1
2011-03-23,Critical scaling to infinite temperature,"Three dimensional Ising model ferromagnets on different lattices with nearest
neighbor interactions, and on simple cubic lattices with equivalent
interactions out to further neighbors, are studied numerically. The
susceptibility data for all these systems are analyzed using the critical
Renormalization Group Theory formalism over the entire temperature range above
Tc with an appropriate choice of scaling variable and scaling expressions.
Representative experimental data on a metallic ferromagnet (Ni) and an
elementary fluid (Xe) are interpreted in the same manner so as to estimate
effective coordination numbers.",1103.4491v1
2011-03-31,Electromagnetic propulsion and separation by chirality of nanoparticles in liquids,"We introduce a new mechanism for the propulsion and separation by chirality
of small ferromagnetic particles suspended in a liquid. Under the action of a
uniform d.c. magnetic field H and an a.c. electric field E isomers with
opposite chirality move in opposite directions. Such a mechanism could have a
significant impact on a wide range of emerging technologies. The component of
the chiral velocity that is odd in H is found to be proportional to the
intrinsic orbital and spin angular momentum of the magnetized electrons. This
effect arises because a ferromagnetic particle responds to the applied torque
as a small gyroscope.",1104.0026v1
2011-04-04,Hysteresis in Anti-Ferromagnetic Random-Field Ising Model at Zero Temperature,"We study hysteresis in anti-ferromagnetic random-field Ising model at zero
temperature. The external field is cycled adiabatically between -$\infty$ and
$\infty$. Two different distributions of the random-field are considered, (i) a
uniform distribution of width $2\Delta$ centered at the origin, and (ii) a
Gaussian distribution with average value zero and standard deviation $\sigma$.
In each case the hysteresis loop is determined exactly in one dimension and
compared with numerical simulations of the model.",1104.0586v1
2011-05-05,Spontaneous separation of two-component Fermi gases in a double-well trap,"The two-component Fermi gas in a double-well trap is studied using the
density functional theory and the density profile of each component is
calculated within the Thomas-Fermi approximation. We show that the two
components are spatially separate in the two wells once the repulsive
interaction exceeds the Stoner point, signaling the occurrence of the
ferromagnetic transition. Therefore, the double-well trap helps to explore
itinerant ferromagnetism in atomic Fermi gases, since the spontaneous
separation can be examined by measuring component populations in one well.",1105.0995v1
2011-05-09,Precessing ball solitons as dissipative structures during a phase transition in a ferromagnet,"Precessing ball solitons (PBS) in a ferromagnet during the first order phase
transition induced by a magnetic field directed along the axis of anisotropy,
while the action of the periodic field perpendicular to the main magnetic
field, have been analyzed. Under this condition, the characteristics of arising
equilibrium PBS's are uniquely determined by the frequency of the periodic
field, but the solitons with other frequencies are impossible. It is shown that
the equilibrium PBS's are essentially the ""dissipative structures"" that can
arise in a metastable state.",1105.1807v1
2011-05-24,Tunable anisotropic magnetism in trapped two-component Bose gases,"We theoretically address magnetic ordering at zero and finite temperature in
both homogeneous and trapped Bose-Bose mixtures in optical lattices. By using
Bosonic Dynamical Mean-Field Theory, we obtain the phase diagram of the
homogeneous two-component Bose-Hubbard model in a three-dimensional (3D) cubic
lattice, which features competing magnetic order of XY-ferromagnetic and
anti-ferromagnetic type in addition to the Mott and superfluid states. We show
that these magnetic phases persist also in the presence of a harmonic trap.",1105.4886v1
2011-05-25,Non-Gaussian resistance noise in the ferromagnetic insulating state of a hole doped manganite,"We report the observation of a large 1/f noise in the ferromagnetic
insulating state (FMI) of a hole doped manganite single crystal of
La0.80Ca0.20MnO3 which manifests hopping conductivity in presence of a Coulomb
gap. The temperature dependent noise magnitude shows a deep within the FMI
state, there is a sharp freeze out of the noise magnitude with temperature on
cooling. As the material enters the FMI state, the noise becomes non-Gaussian
as seen through probability density function and second spectra. It is proposed
to arise from charge fluctuations in a correlated glassy phase of the polaronic
carriers which develop in these systems as reported in recent simulation
studies.",1105.5079v1
2011-05-30,Dynamical spin-flip susceptibility for a strongly interacting ultracold Fermi gas,"The Stoner model predicts that a two-component Fermi gas at increasing
repulsive interactions undergoes a ferromagnetic transition. Using the
random-phase approximation we study the dynamical properties of the interacting
Fermi gas. For an atomic Fermi gas under harmonic confinement we show that the
transverse (spin-flip) dynamical susceptibility displays a clear signature of
the ferromagnetic phase in a magnon peak emerging from the Stoner particle-hole
continuum. The dynamical spin susceptibilities could be experimentally explored
via spin-dependent Bragg spectroscopy.",1105.5997v1
2011-06-01,Ferromagnetic and antiferromagnetic dimer splittings in LaMn0.1Ga0.9O3,"Inelastic neutron scattering was employed to study the magnetic excitations
of Mn3+ dimers in LaMn0.1Ga0.9O3. The nearest-neighbor interaction of Mn3+ ions
is ferromagnetic in the basal (a,b)-plane, but antiferromagnetic along the
c-direction, thus two different types of dimer excitations are simultaneously
present in the experiments. From the observed energy spectra we derive
Heisenberg-type exchange interactions Jab=0.210(4) meV and Jc=-0.285(5) meV as
well as an axial anisotropy parameter D=0.036(6) meV. These parameters
considerably differ from those derived for the isostructural parent compound
LaMnO3 due to structural effects.",1106.0161v1
2011-06-02,Cubic to hexagonal iron phase transition promoted by interstitial hydrogen,"Using ab-initio density functional theory we study the role of interstitial
hydrogen on the energetics of the phase transformation of iron from bcc to hcp
along Bain's pathway. The impurity creates an internal stress field that can be
released through a tetragonal distortion of the lattice, promoting the bcc
(ferromagnetic) $\rightarrow$ fcc (frustrated antiferromagnetic) $\rightarrow$
hcp (ferromagnetic) transition. The transformation between crystal systems is
accompanied by a drastic magnetic reorganization and sudden variations of the
unit cell volume, that can be one of the reasons for embrittlement and
mechanical failure of iron upon hydrogen adsorption.",1106.0386v1
2011-06-06,Rise and fall of defect induced ferromagnetism in SiC single crystals,"6H-SiC (silicon carbide) single crystals containing VSi-VC divacancies are
investigated with respect to magnetic and structural properties. We found that
an initial increase of structural disorder leads to pronounced ferromagnetic
properties at room temperature. Further introduction of disorder lowers the
saturation magnetization and is accompanied with the onset of lattice
amorphization. Close to the threshold of full amorphization, also divacancy
clusters are formed and the saturation magnetization nearly drops to zero.",1106.0966v1
2011-06-07,Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei,"Spin relaxation in quantum Hall ferromagnet regimes is studied. As the
initial non-equilibrium state, a coherent deviation of the spin system from the
${\vec B}$ direction is considered and the breakdown of this Goldstone-mode
state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring
non-exponentially with time is studied in terms of annihilation processes in
the ""Goldstone condensate"" formed by ""zero spin excitons"". The relaxation rate
is calculated analytically even if the initial deviation is not small. This
relaxation channel competes with the relaxation mechanisms due to spin-orbit
coupling, and at strong magnetic fields it becomes dominating.",1106.1386v1
2011-06-09,Majorana fermions in spin-orbit coupled ferromagnetic Josephson junctions,"We study all possible Majorana modes in two-dimensional spin-orbit coupled
ferromagnetic superconductor-normal state-superconductor (SNS) Josephson
junctions and propose experiments to detect them. With the S region in a
non-trivial topological phase and a superconducting phase difference $\phi =
\pi$ across the junction, two delocalized Majorana fermions with no excitation
gap appear in the N region. In addition, if S and N belong to different
topological phases and have well-separated the Fermi surfaces, localized
Majorana fermions with a finite excitation gap also emerge at both SN
interfaces for all $\phi$.",1106.1801v2
2011-06-16,Thermomagnonic spin transfer and Peltier effects in insulating magnets,"We study the coupled magnon energy transport and collective magnetization
dynamics in ferromagnets with magnetic textures. By constructing a
phenomenological theory based on irreversible thermodynamics, we describe
motion of domain walls by thermal gradients and generation of heat flows by
magnetization dynamics. From microscopic description based on magnon kinetics,
we estimate the transport coefficients and analyze the feasibility of
energy-related applications in insulating ferromagnets, such as yttrium iron
garnet and europium oxide.",1106.3135v2
2011-06-17,Gate-dependent spin-torque in a nanoconductor-based spin-valve,"This article discusses the spin-torque effect in a spin-valve made out of two
ferromagnetic leads connected through a coherent nanoconductor (NC), in the
limit where a single channel of the NC lies near the Fermi energy of the leads.
Due to quantum interferences inside the NC, the spin-torque presents clear
qualitative differences with respect to the case of a multichannel disordered
spin-valve. In particular, it can be modulated with the NC gate voltage. In
principle, this modulation can be observed experimentally, assuming that the
spin-torque affects a ferromagnetic nano-domain in direct contact with the NC.",1106.3540v1
2011-06-22,Magnetic excitations in iron pnictides,"Spin wave dispersion and damping are investigated in the metallic SDW state
of different itinerant electron models including a small interlayer hopping.
Magnetic excitations in iron pnictides are shown to be well understood in terms
of physical mechanisms characteristic of metallic magnets, such as
carrier-induced ferromagnetic spin couplings, intra-band particle-hole
excitations, and the spin-charge coupling mechanism, which is also important in
ferromagnetic manganites.",1106.4421v1
2011-06-28,Stability of precessing domain walls in ferromagnetic nanowires,"We show that recently reported precessing solution of Landau-Lifshitz-Gilbert
equations in ferromagnetic nanowires is stable under small perturbations of
initial data, applied field and anisotropy constant. Linear stability is
established analytically, while nonlinear stability is verified numerically.",1106.5808v2
2011-07-01,Current induced magnetization reversal on the surface of a topological insulator,"We study dynamics of the magnetization coupled to the surface Dirac fermions
of a three di- mensional topological insulator. By solving the
Landau-Lifshitz-Gilbert equation in the presence of charge current, we find
current induced magnetization dynamics and discuss the possibility of mag-
netization reversal. The torque from the current injection depends on the
transmission probability through the ferromagnet and shows nontrivial
dependence on the exchange coupling. The mag- netization dynamics is a direct
manifestation of the inverse spin-galvanic effect and hence another ferromagnet
is unnecessary to induce spin transfer torque in contrast to the conventional
setup.",1107.0116v1
2011-07-06,Hysteretic magnetic pinning and reversible resistance switching in High-Tc superconductor/ferromagnet multilayers,"We study a high-TC superconducting (YBa2Cu3O7-d) / ferromagnetic (Co/Pt
multilayer) hybrid which exhibits resistance switching driven by the magnetic
history: depending on the direction of the external field, a pronounced
decrease or increase of the mixed-state resistance is observed as magnetization
reversal occurs within the Co/Pt multilayer. We demonstrate that stray magnetic
fields cause these effects via i) creation of vortices/antivortices and ii)
magnetostatic pinning of vortices that are induced by the external field.",1107.1122v1
2011-07-08,Ferromagnetism in lead graphite-pencils and magnetic composite with CoFe2O4 particles,"This work has been initiated with a curiosity to investigate the elemental
composition and magnetic response of different grades of lead pencils (6B, 2B,
HB, 2H, 5H) that people use in daily life. Interestingly, experimental results
landed with a great achievement of observing soft magnetism in lead pencils,
indicating a wide scope of magnetic tuning for room temperature applications. A
novel magnetic composite has been synthesized by mixing different concentration
of CoFe2O4 (CF) nanoparticles in 5H and 6B pencils for studying the magnetic
tailoring aspects using pencils. Our results showed different possibilities of
controlling disorder induced ferromagnetic parameters and a simple approach of
producing sufficiently high coercive magnetic composite using pencils.",1107.1662v1
2011-07-20,Upper critical field of p-wave ferromagnetic superconductors with orthorhombic symmetry,"We extended the Scharnberg-Klemm theory of $H_{c2}(T)$ in p-wave
superconductors with broken symmetry to cases of partially broken symmetry in
an orthorhombic crystal, as is appropriate for the more exotic ferromagnetic
superconductor UCoGe in strong magnetic fields. For some partially broken
symmetry cases, $H_{c2}(T)$ can mimic upward curvature in all three crystal
axis directions, and reasonably good fits to some of the UCoGe data are
obtained.",1107.4071v1
2011-07-26,"Role of interface in ferromagnetism of (Zn,Co)O films","We demonstrate that room temperature ferromagnetic response (RT FR) of ZnCoO
films grown at low temperature by the Atomic layer Deposition (ALD) method is
due to Co metal accumulations at the ZnCoO/substrate interface region. The
accumulated experimental evi evidences allow us to reject several other
explanations of this effect in our samples, despite the fact that some of them
are likely to be responsible for the low temperature FM in this class of the
material.",1107.5188v1
2011-08-09,"Magnetic phases of a highly frustrated magnet, ZnCr2O4, up to an ultra-high magnetic field of 600 T","The Faraday rotation and magneto-optical absorption spectral measurements
were conducted to reveal the full-magnetization process and map out a magnetic
phase diagram of a typical geometrical frustrated magnet, ZnCr2O4, by using the
electromagnetic flux compression method in ultra-magnetic fields up to 600 T. A
fully polarized ferromagnetic phase is observed in which the absorption spectra
associated with an exciton-magnon-phonon transition disappears. Furthermore,
prior to the fully polarized ferromagnetic phase above 410 T, we found a novel
magnetic phase above 350 T followed by a canted 3:1 phase.",1108.1932v1
2011-08-16,"All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic semiconductors","Using density matrix equations of motion and a tight-binding band
calculation, we predict all-optical switching between four metastable magnetic
states of (III,Mn)As ferromagnets. This switching is initiated non-thermally
within 100fs, during nonlinear coherent photoexcitation. For a single optical
pulse, magnetization reversal is completed after $\sim$100 ps and controlled by
the coherent femtosecond photoexcitation. Our predicted switching comes from
magnetic nonlinearities triggered by a femtosecond magnetization tilt that is
sensitive to un--adiabatic light--induced spin interactions.",1108.3193v1
2011-08-19,"Hydrostatic pressure study of paramagnetic-ferromagnetic phase transition in (Ga,Mn)As","The effect of hydrostatic pressure on the paramagnetic - ferromagnetic phase
transition has been studied in (Ga,Mn)As. The variation of the Curie
temperature (TC) with pressure was monitored by two transport methods: (1) -
measurement of zero field resistivity versus temperature {\rho}(T), (2) -
dependence on temperature of the Hall voltage hysteresis loop. Two specimens of
different resistivity characteristics were examined. The measured
pressure-induced changes of TC were relatively small (of the order of 1K/GPa)
for both samples, however they were opposite for the two.",1108.3960v1
2011-08-22,Spin Density Wave in Insulating Ferromagnetic Frustrated Chain LiCuVO$_4$,"We study field induced quantum phase in weakly-coupled ferromagnetic
frustrated chain LiCuVO$_4$ by neutron diffraction technique. A new
incommensurate magnetic peak is observed at $H \ge 8.5$ T. The field dependent
propagation vector is identified with the spin density wave correlation in the
theoretically predicted magnetic quadrupole order. Quantum fluctuation,
geometrical frustration, and interchain interaction induce the exotic spin
density wave long-range order in the insulating magnet.",1108.4255v1
2011-09-06,Griffiths phase in solid-solution of ferromagnetic manganite and cobaltite,"We report the existence of Griffiths phase (GP) over a wide range of $x$ in
La$_{0.6}$Sr$_{0.4}$Mn$_{1-x}$Co$_x$O$_3$, the solid solution of ferromagnetic
(FM) La$_{0.6}$Sr$_{0.4}$MnO$_3$ and La$_{0.6}$Sr$_{0.4}$CoO$_3$, from
magnetization measurements. In this compound, GP arises due to the quenching of
randomly distributed Co-O-Mn antiferromagnetic bonds in the FM background. In
contrary to divalent doped manganites, GP in the present system can exist
entirely in the metallic state above $T_C$ (for $x$$<$0.10). Based on the
present study, a magnetoelectronic phase diagram is drawn.",1109.1090v1
2011-09-07,Ferromagnetic properties of charged vector bosons condensate in the early universe,"Bose-Einstein condensation in the early universe is considered. The magnetic
properties of a condensate of charged vector bosons are studied, showing that a
ferromagnetic state is formed. As a consequence, the primeval plasma may be
spontaneously magnetized inside macroscopically large domains and primordial
magnetic fields can be generated.",1109.1330v1
2011-09-24,Josephson effect between triplet superconductors through a ferromagnetic barrier of finite width,"Charge and spin transport in a junction involving two triplet superconductors
and a ferromagnetic barrier are studied. We use Bogoliubov-de Gennes
wavefunctions to construct the Green's function, from which we obtain the
Josephson currents in terms of the Andreev reflection coefficients. We focus on
the consequences of a finite barrier width for the occurrence of 0-\pi
transitions and for the spin currents, and examine the appropriateness of the
common \delta-function approximation for the tunneling region.",1109.5238v2
2011-09-29,Sources of negative tunneling magneto-resistance in multilevel quantum dots with ferromagnetic contacts,"We analyze distinct sources of spin-dependent energy level shifts and their
impact on the tunneling magnetoresistance (TMR) of interacting quantum dots
coupled to collinearly polarized ferromagnetic leads. Level shifts due to
virtual charge fluctuations can be quantitatively evaluated within a
diagrammatic representation of our transport theory. The theory is valid for
multilevel quantum dot systems and we exemplarily apply it to carbon nanotube
quantum dots, where we show that the presence of many levels can qualitatively
influence the TMR effect.",1109.6599v1
2011-09-30,Dephasing in ferromagnetic nanowires: The role of spin waves,"We present a calculation of the dephasing time of electrons in a ferromagnet
relevant for the conductance fluctuations. We focus on the contribution from
the interaction with spin waves. Explicit results are presented for a
quasi-one-dimensional systems. Going beyond previous calculations, we do not
restrict ourselves to the limit of a small exchange splitting compared to the
electronic elastic scattering time, nor does our calculation rely on the
diffusion approximation to describe electronic transport.",1109.6796v1
2011-10-18,Life times and chirality of spin-waves in antiferromagnetic and ferromagnetic FeRh: time depedent density functional theory perspective,"The study of the spin excitations in antiferromagnetic (AFM) and
ferromagnetic (FM) phases of FeRh is reported. We demonstrate that although the
Fe atomic moments are well defined there is a number of important phenomena
absent in the Heisenberg description: Landau damping of spin waves, large Rh
moments induced by the AFM magnons, the formation of the optical magnons
terminated by Stoner excitations. We relate the properties of the spin-wave
damping to the features of the Stoner continuum and compare the chirality of
the spin excitations in AFM, FM and paramagnetic (PM) systems.",1110.3913v1
2011-11-30,Non-Fraunhofer Interference Pattern in Inhomogeneous Ferromagnetic Josephson Junctions,"Generic conditions are established for producing a non-Fraunhofer response of
the critical supercurrent subject to an external magnetic field in
ferromagnetic Josephson junctions. Employing the quasiclassical Keldysh-Usadel
method, we demonstrate theoretically that an inhomogeneity in the magnitude of
the energy scales in the system, including Thouless energy, exchange field and
temperature gradient normal to the transport direction, influences drastically
the standard Fraunhofer pattern. The exotic non-Fraunhofer response, similar to
that observed in recent experiments, is described in terms of an intricate
interplay between multiple '0-pi'-states and is related to the appearance of
proximity vortices.",1112.0007v1
2011-12-12,Spin susceptibilities in zigzag graphene nanoribbons,"The simple Hubbard Hamiltonian with the mean field approximation is used to
know about the energy bands and spin susceptibilities of zigzag graphene
nanoribbons. Depending on the electron doping, antiferromagnetic or
ferromagnetic configurations are possible; in the former, an energy gap exits
which is proportional to the Hubbard parameter, while in the latter the up and
down spin bands intersect the Fermi level. Due to the two dimensional nature of
the system, a susceptibility square matrix is necessary to explain the
self-correlations and correlations between spins in the ribbon unit cell. The
transverse spin susceptibilities are computed and the static case for
ferromagnetic solutions is examined, as a function of the electron doping.",1112.2601v1
2011-12-28,Spectral signatures of magnetic Bloch oscillations in one-dimensional easy-axis ferromagnets,"Domain walls in a one-dimensional gapped easy-axis ferromagnet can exhibit
Bloch oscillations in an applied magnetic field. We investigate how exchange
couplings modify this behavior within an approximation based on noninteracting
domain-wall bound states. In particular, we obtain analytical results for the
spectrum and the dynamic structure factor, and show where in momentum space to
expect equidistant energy levels, the Wannier-Zeeman ladder, which is the
spectral signature of magnetic Bloch oscillations. We compare our results to
previous calculations employing a single domain-wall approximation, and make
predictions relevant for the material $CoCl2\cdot2H2O$.",1112.6195v2
2012-02-14,Magnon qubit on double Bose-Einstein condensate,"We have proposed a magnon qubit based on coupled configuration of
Bose-Einstein condensates (BEC) in two ferromagnetic samples placed closely to
each other. We have evaluated the magnon BEC qubit realization in the double
BEC scheme where we found a quantum synchronism condition providing an
effective Hamiltonian of magnon qubit. It has the form of well-known
superconducting Josephson qubit. The possibilities for coherent magnon BEC
qubit rotation are analyzed. Implementations of the magnon BEC qubit are
considered for small samples and thin ferromagnetic films. Advantages of the
proposed macroscopic qubit realization are discussed.",1202.3057v1
2012-02-22,Dynamic Critical Behavior in Models of Ferromagnetic Gadolinium,"A numerical technique combining Monte Carlo and molecular dynamics
simulations is used for the first time to examine the complex critical dynamics
of models of ferromagnetic gadolinium in which both strong exchange
interactions and relativistic effects of several different types are taken into
account. A finitesize scaling technique is used to calculate the corresponding
dynamic critical exponents. The role played by isotropic dipole-dipole
interaction in the critical behavior of gadolinium is evaluated. The results
obtained provide an explanation for the anomalous dynamic critical behavior of
gadolinium.",1202.4878v1
2012-02-29,Valence-band satellite in the ferromagnetic nickel: LDA+DMFT study with exact diagonalization,"The valence-band spectrum of the ferromagnetic nickel is calculated using the
LDA+DMFT method. The auxiliary impurity model emerging in the course of the
calculations is discretized and solved with the exact diagonalization, or, more
precisely, with the Lanczos method. Particular emphasis is given to spin
dependence of the valence-band satellite that is observed around 6 eV below the
Fermi level. The calculated satellite is strongly spin polarized in accord with
experimental findings.",1202.6595v1
2012-02-29,Epitaxial Ferromagnetic Nanoislands of Cubic GdN in Hexagonal GaN,"Periodic structures of GdN particles encapsulated in a single crystalline GaN
matrix were prepared by plasma assisted molecular beam epitaxy. High resolution
X-ray diffractometery shows that GdN islands, with rock salt structure are
epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron
microscopy combined with in-situ reflection high energy electron diffraction
allows for the study of island formation dynamics, which occurs after 1.2
monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one
due to GdN particles with Curie temperature of 70K and a second, anomalous room
temperature phase.",1203.0028v2
2012-03-03,Skyrmion Generation by Current,"Skyrmions, once a hypothesized field-theoretical object believed to describe
the nature of elementary particles, became common sightings in recent years
among several non-centrosymmetric metallic ferromagnets. For more practical
applications of Skyrmionic matter as carriers of information, thus realizing
the prospect of ""Skyrmionics"", it is necessary to have the means to create and
manipulate Skyrmions individually. We show through extensive simulation of the
Landau-Lifshitz-Gilbert equation that a circulating current imparted to the
metallic chiral ferromagnetic system can create isolated Skyrmionic spin
texture without the aid of external magnetic field.",1203.0638v1
2012-06-06,Magnon-driven quantum-dot heat engine,"We investigate a heat- to charge-current converter consisting of a
single-level quantum dot coupled to two ferromagnetic metals and one
ferromagnetic insulator held at different temperatures. We demonstrate that
this nano engine can act as an optimal heat to spin-polarized charge current
converter in an antiparallel geometry, while it acts as a heat to pure spin
current converter in the parallel case. We discuss the maximal output power of
the device and its efficiency.",1206.1259v2
2012-06-24,Vanishing Meissner effect as a hallmark of in-plane FFLO instability in superconductor - ferromagnet layered systems,"We demonstrate that in a wide class of multilayered superconductor -
ferromagnet structures (e.g., S/F, S/F/N and S/F/F') the vanishing Meissner
effect signals the appearance of the in-plane Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) modulated superconducting phase. In contrast to the bulk superconductors
the FFLO instability in these systems can emerge at temperatures close to the
critical one and is effectively controlled by the S layer thickness and the
angle between magnetization vectors in the F/F' bilayers. The predicted FFLO
state reveals through the critical temperature oscillations vs the
perpendicular magnetic field component.",1206.5488v2
2012-07-05,Evidence for the Presence of Spin Accumulation in Localized States at Ferromagnet-Silicon Interfaces,"We experimentally show evidence for the presence of spin accumulation in
localized states at ferromagnet-silicon interfaces, detected by electrical
Hanle effect measurements in CoFe/$n^{+}$-Si/$n$-Si lateral devices. By
controlling the measurement temperature, we can clearly observe marked changes
in the spin-accumulation signals at low temperatures, at which the electron
transport across the interface changes from the direct tunneling to the
two-step one via the localized states. We discuss in detail the difference in
the spin accumulation between in the Si channel and in the localized states.",1207.1154v1
2012-07-08,Non-monotonic behaviour of the superconducting order parameter in Nb/PdNi bilayers observed through point contact spectroscopy,"Point contact spectroscopy measurements have been performed on Nb/PdNi
bilayers in which the thickness of the Nb layer, dNb, was kept constant to 40
nm while the thickness of PdNi, dPdNi, was changed from 2 nm to 9 nm. Features
related to the superconducting gap induced in the ferromagnet have been
observed in the dV/dI versus V curves. These structures show a non-monotonic
behaviour as a function of dPdNi as a consequence of the damped oscillatory
behaviour of the superconducting order parameter in the ferromagnetic layer.",1207.1879v1
2012-07-13,Universality and itinerant ferromagnetism in rotating strongly interacting Fermi gases,"We analytically determine the properties of three interacting fermions in a
harmonic trap subject to an external rotation. Thermodynamic quantities such as
the entropy and energy are calculated from the third order quantum virial
expansion. By parameterizing the solutions in the rotating frame we find that
the energy and entropy are universal for all rotations in the strongly
interacting regime. Additionally, we find that rotation suppresses the onset of
itinerant ferromagnetism in strongly interacting repulsive three-body systems.",1207.3129v1
2012-07-17,Magnetic properties of Mn-doped Ge46 and Ba8Ge46 clathrates,"We present a detailed study of the magnetic properties of unique cluster
assembled solids namely Mn doped Ge46 and Ba8Ge46 clathrates using density
functional theory. We find that ferromagnetic (FM) ground states may be
realized in both the compounds when doped with Mn. In Mn2Ge44, ferromagnetism
is driven by hybridization induced negative exchange splitting, a generic
mechanism operating in many diluted magnetic semiconductors. However, for
Mn-doped Ba8Ge46 clathrates incorporation of conduction electrons via Ba
encapsulation results in RKKY-like magnetic interactions between the Mn ions.
We show that our results are consistent with the major experimental
observations for this system.",1207.3996v1
2012-08-03,Metal-insulator transition in Sr2-xLaxCoO4 driven by spin-state transition,"We sought the origin of the metal-insulator transition in Sr2-xLaxCoO4, using
electron-correlation corrected density functional calculations. Our results
show that Sr2CoO4 is in an intermediate-spin (IS) state and a strong Co4+ 3d-O
2p hybridization is responsible for its ferromagnetic metallicity. Upon La
doping, however, a spin-state transition occurs in Sr1.5La0.5CoO4: IS-Co4+ x 2
+ 1e --> LS-Co4+ + HS-Co3+ (LS: low spin; HS: high spin). Then the spin-state
transition suppresses an electron hopping via a spin-blockade and gives rise to
the insulating behavior of Sr1.5La0.5CoO4. A corresponding superexchange
accounts for its ferromagnetism. Thus, spin state could provide a way to tune
materials properties.",1208.0637v1
2012-08-15,Inertia and chiral edge modes of a skyrmion magnetic bubble,"The dynamics of a vortex in a thin-film ferromagnet resembles the motion of a
charged massless particle in a uniform magnetic field. Similar dynamics is
expected for other magnetic textures with a nonzero skyrmion number. However,
recent numerical simulations revealed that skyrmion magnetic bubbles show
significant deviations from this model. We show that a skyrmion bubble
possesses inertia and derive its mass from the standard theory of a thin-film
ferromagnet. Besides center-of-mass motion, other low energy modes are waves on
the edge of the bubble traveling with different speeds in opposite directions.",1208.3123v2
2012-08-28,Magnon Mediated Electric Current Drag Across a Ferromagnetic Insulator Layer,"In a semiconductor hererostructure, the Coulomb interaction is responsible
for the electric current drag between two 2D electron gases across an electron
impenetrable insulator. For two metallic layers separated by a ferromagnetic
insulator (FI) layer, the electric current drag can be mediated by a
nonequilibrium magnon current of the FI. We determine the drag current by using
the semiclassical Boltzmann approach with proper boundary conditions of
electrons and magnons at the metal-FI interface.",1208.5812v1
2012-09-09,Neutron Brillouin scattering with pulsed spallation neutron source - spin-wave excitations from ferromagnetic powder samples -,"Neutron Brillouin scattering (NBS) method was developed using a pulsed
spallation neutron source, and the feasibility of NBS was demonstrated by
observing ferromagnetic spin waves in La$_{0.8}$Sr$_{0.2}$MnO$_3$ and SrRuO$_3$
powders. Gapless spin-wave excitations were observed in
La$_{0.8}$Sr$_{0.2}$MnO$_3$, which were continuously extended to the lower
scattering vector $Q$ from previous results using single crystals. The novel
result is a well-defined quadratic $Q$ dependence in the spin-wave dispersion
curve with a large energy gap in SrRuO$_3$ indicating robust spin-orbit
coupling.",1209.1780v1
2012-09-13,Experimental verification of contact-size estimates in point-contact spectroscopy on superconductor/ferromagnet heterocontacts,"Nanostructured superconductor/ferromagnet heterocontacts are studied in the
different transport regimes of point-contact spectroscopy. Direct measurements
of the nanocontact size by scanning electron microscopy allow a comparison with
theoretical models for contact-size estimates of heterocontacts. Our
experimental data give evidence that size estimates yield reasonable values for
the point-contact diameter $d$ as long as the samples are carefully
characterized with respect to the local electronic parameters.",1209.2821v1
2012-09-21,"Ferromagnetic neutron stars: axial anomaly, dense neutron matter, and pionic wall","We show that a chiral nonlinear sigma model coupled to degenerate neutrons
exhibits a ferromagnetic phase at high density. The magnetization is due to the
axial anomaly acting on the parallel layers of neutral pion domain walls
spontaneously formed at high density. The emergent magnetic field would reach
the QCD scale ~ 10^19 [G], which suggests that the quantum anomaly can be a
microscopic origin of the magnetars (highly magnetized neutron stars).",1209.4814v1
2012-11-06,Study of planar Ising ferromagnet on the triangular lattice with selective dilution,"In the paper the Curie temperatures of selectively diluted planar Ising
ferromagnet on the triangular lattice are calculated vs. concentration of
magnetic atoms. Various analytical approaches are compared with the exact
numerical calculations for finite clusters, as well as with the exact
analytical solutions for the triangular and honeycomb lattices.",1211.1283v2
2012-11-26,Magneto-optical properties of La2/3Sr1/3MnO3 ultrathin films,"Pulse laser deposited La2/3Sr1/3MnO3 ultrathin films on SrTiO3 substrates
were characterized by polar and longitudinal Kerr magneto-optical spectroscopy.
An agreement between experimental and theoretical spectra was achieved for a
10.7 nm thick film, while a distinction in the Kerr effect amplitudes was
obtained for a 5 nm thick film. This points to the slight suppression of
ferromagnetism by interface effects. Nevertheless, the room temperature
ferromagnetism of the 5 nm thick film was clearly demonstrated. All the studied
films exhibit magneto-optical properties similar to single crystals and thick
films, which confirms a fully developed perovskite structure even at 5 nm.",1211.6025v1
2012-11-29,Possible Manipulation of Kondo Effect by Transition between Antiferromagnetic and Ferromagnetic s-d Coupling,"Kondo effect originates from antiferromagnetic (AFM) s-d coupling between
magnetic impurity and the conduction electron, while it will be totally
quenched in ferromagnetic (FM) regime due to malfunction of spin-flip. We
investigate the possibility of switching on/off Kondo effect by transition of
AFM/FM s-d coupling using 3d-metal phthalocyanine molecule (MPc) on Au(111) as
a model system. A Hamiltonian model is constructed based on the feature of MPc
molecule to show the condition for AFM/FM s-d coupling. The AFM s-d coupling
could transform to FM s-d coupling if the spin state of the lowest unoccupied
orbital changes.",1211.6955v1
2012-12-06,Growth and Characterization of Hybrid Insulating Ferromagnet-Topological Insulator Heterostructure Devices,"We report the integration of the insulating ferromagnet GdN with epitaxial
films of the topological insulator Bi2Se3 and present detailed structural,
magnetic and transport characterization of the heterostructures. Fabrication of
multi-channel Hall bars with bare and GdN-capped sections enables direct
comparison of magnetotransport properties. We show that the presence of the
magnetic overlayer results in suppression of weak anti-localization at the top
surface.",1212.1225v2
2012-12-19,Spin-Orbital Entanglement Emerging from Frustration in the Kugel-Khomskii Model,"We investigate the zero-temperature phase diagrams of the bilayer
square-lattice Kugel-Khomskii ($d^9$) model involving entangled and singlet
phases using mean-field cluster approach. This diagram includes interlayer
singlet phase observed in fluoride K$_3$Cu$_2$F$_7$ and exotic entangled
spin-orbital phases. For a monolayer case, realized in K$_2$CuF$_4$, we perform
similar calculations in finite temperature and show that the
alternating-orbital ferromagnet decays first to an entangled uniform
ferromagnet and then to a paramagnetic phase. Published in: J. Phys.: Conf.
Series 391, 012085 (2012).",1212.4612v1
2013-01-03,Nonequilibrium Rashba field driven domain wall motion in ferromagnetic nanowires,"We study the effects of spin-orbit interaction (SOI) on the current-induced
motion of a magnetic (Bloch) domain wall in ultrathin ferromagnetic nanowires.
The conspiracy of spin relaxation and SOI is shown to generate a novel strong
nonequilibrium Rashba field, which is dominant even for moderate SOI. This
field causes intricate spin precession and a transition from translatory to
oscillatory wall dynamics with increasing SOI. We show that current pulses of
different lengths can efficiently be used to control the domain wall motion.",1301.0389v2
2013-01-17,Imaging the antiferromagnetic to ferromagnetic first order phase transition of FeRh,"The antiferromagnetic (AFM) to ferromagnetic (FM) first order phase
transition of an epitaxial FeRh thin-film has been studied with x-ray magnetic
circular dichroism using photoemission electron microscopy. The FM phase is
magnetized in-plane due to shape anisotropy, but the magnetocrystalline
anisotropy is negligible and there is no preferred in-plane magnetization
direction. When heating through the AFM to FM phase transition the nucleation
of the FM phase occurs at many independent nucleation sites with random domain
orientation. The domains subsequently align to form the final FM domain
structure. We observe no pinning of the FM domain structure.",1301.4164v1
2013-01-21,Spin-Polarized Electrons in Bilayer Graphene Flakes,"We show that a bilayer graphene flake deposited above a ferromagnetic
insulator can behave as a spin-filtering device. The ferromagnetic material
induces exchange splitting in the graphene flake, and due to the Fano
antiresonances occurring in the transmission of the graphene flake as a
function of flake length and energy, it is possible to obtain a net spin
current. This happens when an antiresonance for one spin channel coincides with
a maximum transmission for the opposite spin. We propose these structures as a
means to obtain spin-polarized currents and spin filters in graphene-based
systems.",1301.4974v1
2013-01-23,Theoretical investigation of FeTe magnetic ordering under hydrostatic pressure,"We investigate the pressure phase diagram of FeTe, predicting structural and
magnetic properties in the normal state at zero temperature within density
functional theory (DFT). We carefully examined several possible different
crystal structures over a pressure range up to $\approx 30 $ GPa: simple
tetragonal (PbO type), simple monoclinic, orthorhombic (MnP type), hexagonal
(NiAs and wurzite type) and cubic (CsCl and NaCl type). We predict pressure to
drive the system through different magnetic ordering (notably also some
ferromagnetic phases) eventually suppressing magnetism at around 17GPa. We
speculate the ferromagnetic order to be the reason for the absence of a
superconducting phase in FeTe at variance with the case of FeSe.",1301.5517v1
2013-02-06,Penetration of a magnetic wall into thin ferromagnetic electrodes of a nano-contact spin valve,"We theoretically analyzed a magnetic wall confined in a nano-contact spin
valve paying special attention to the penetration of the magnetic wall into
thin ferromagnetic electrodes. We showed that, compared with the Bloch wall,
the penetration of the Neel wall is suppressed by increases of the
demagnetization energy. We found the optimal conditions of the radius and
height of the nano-contact to maximize the power of the current-induced
oscillation of the magnetic wall. We also found that the thermal stability of
the Bloch wall increases when the nano-contact's radius increases or height
decreases.",1302.1248v1
2013-02-27,Magnetic relaxation in uranium ferromagnetic superconductors,"There is proposed a phenomenological theory of quasi-elastic neutron
scattering in the itinerant ferromagnets UGe$_2$ and UCoGe based on their
property that magnetization supported by the moments located at uranium atoms
is not conserved quantity relaxing to equilibrium by the interaction with
itinerant electrons subsystem. As result the line width of quasi elastic
neutron scattering at $q\to 0$ acquires nonvanishing value at all temperatures
but the Curie temperature.",1302.6755v3
2013-02-27,Ferromagnetic to antiferromagnetic transition of one-dimensional spinor Bose gases with spin-orbit coupling,"We have analytically solved one-dimensional interacting two-component bosonic
gases with spin-orbit (SO) coupling by the Bethe-ansatz method. Through a gauge
transformation, the effect of SO coupling is incorporated into a spin-dependent
twisted boundary condition. Our result shows that the SO coupling can influence
the eigenenergy in a periodical pattern. The interplay between interaction and
SO coupling may induce the energy level crossing for the ground state, which
leads to a transition from the ferromagnetic to antiferromagnetic state.",1302.6901v2
2013-03-05,Phase diagram of the isotropic spin-3/2 model on the z=3 Bethe lattice,"We study an SU(2) symmetric spin-3/2 model on the z=3 Bethe lattice using the
infinite Time Evolving Block Decimation (iTEBD) method. This model is shown to
exhibit a rich phase diagram. We compute the expectation values of several
order parameters which allow us to identify a ferromagnetic, a ferrimagnetic, a
anti-ferromagnetic as well as a dimerized phase. We calculate the entanglement
spectra from which we conclude the existence of a symmetry protected
topological phase that is characterized by S=1/2 edge spins. Details of the
iTEBD algorithm used for the simulations are included.",1303.1110v1
2013-03-30,Features of amplification of dipole magnetic field with linear ferromagnetic concentrator,"Amplification of a low frequency magnetic field from a dipole source by means
of linear ferromagnetic concentrator of different dimensions (permalloy micro
wire) has been investigated experimentally. The results obtained strengthen the
validity of the analytical relation for amplification which allows for
nonlinear dependence of the magnetic permeability upon the value and
distribution of the dipole field over concentrator length.",1304.0111v1
2013-04-05,Magnetic properties of double exchange biased diluted magnetic alloy/ferromagnet/antiferromagnet trilayers,"The magnetic properties of trilayers consisting of a diluted magnetic alloy,
CuMn (Cu0.99Mn0.01), a soft ferromagnet, Py(Ni0.8Fe0.2), and an
antiferromagnet, alpha-Fe2O3, were investigated. The samples, grown by UHV
magnetron sputtering, were magnetically characterized in the temperature range
T = 3-100 K. Typical exchange bias features, namely clear hysteresis cycle
shifts and coercivity enhancements, were observed. Moreover the presence of an
inverse bias, which had been already reported for spin glass-based structures,
was also obtained in a well defined range of temperatures and CuMn thicknesses.",1304.1707v1
2013-04-11,Ferromagnetic spin correlations in a few-fermion system,"We study the spin correlations of a few fermions in a quasi one-dimensional
trap. Exact diagonalization calculations demonstrate that repulsive
interactions between the two species drives ferromagnetic correlations. The
ejection probability of an atom provides an experimental probe of the spin
correlations. With more than five atoms trapped, the system approaches the
itinerant Stoner limit. Losses to Feshbach molecules are suppressed by the
discretization of energy levels when fewer than seven atoms are trapped.",1304.3299v3
2013-04-21,Dynamic Magnetoelectric Effect in Ferromagnet-Superconductor Tunnel Junctions,"We study the magnetization dynamics in a ferromagnet-insulator-superconductor
tunnel junction and the associated buildup of the electrical polarization. We
show that for an open circuit, the induced voltage varies strongly and
nonmonotonically with the precessional frequency, and can be enhanced
significantly by the superconducting correlations. For frequencies much smaller
or much larger than the superconducting gap, the voltage drops to zero, while
when these two energy scales are comparable, the voltage is peaked at a value
determined by the driving frequency. We comment on the potential utilization of
the effect for the low-temperature spatially-resolved spectroscopy of magnetic
dynamics.",1304.5750v2
2013-04-25,Self-sustained Clusters and Ergodicity Breaking in Spin Models,"The emergence of self-sustained clusters and their role in ergodicity
breaking is investigated in fully connected Ising and Sherrington-Kirkpatick
(SK) models. The analysis reveals a clustering behavior at various parameter
regimes, as well as yet unobserved phenomena such as the absence of non-trivial
clusters in the Ising ferromagnetic and paramagnetic regimes, the formation of
restricted spin clusters in SK spin glass and a first order phase transition in
cluster sizes in the SK ferromagnet. The method could be adapted to investigate
other spin models.",1304.7010v1
2013-05-07,Determination of the Local Symmetry and the Multiferroic-ferromagnetic Crossover in Ni3-xCoxV2O8 by using Raman Scattering Spectroscopy,"Comprehensive vibrational studies on the multiferroic-to-normal-ferromagnetic
crossover in isostructural Ni3-xCoxV2O8 (NCVO, x = 0 - 3.0) are performed using
Raman scattering spectroscopy. The systematically red-shifted phonon modes are
discussed in terms of the mode Gr\""uneisen parameters, and are interpreted as a
chemical pressure effect. In addition, we present evidence that the local
symmetry is broken in the multiferroic phase.",1305.1377v1
2013-05-11,Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet Edwardsite,"We prepared a powder sample of edwardsite Cd2Cu3(SO4)2(OH)6 4H2O, which is a
new candidate compound for the spin-1/2 kagome antiferromagnet, and studied its
magnetic properties by magnetic susceptibility and heat capacity measurements.
Edwardsite has a deformed kagome lattice with an average antiferromagnetic
interaction of 51 K between nearby spins and shows an antiferromagnetic order
accompanied by a small ferromagnetic moment below 4.3 K. The weak
ferromagnetism is likely due to spin canting caused by sizable
Dzyaloshinsky-Moriya interactions, which may stabilize the long-range magnetic
order instead of a spin-liquid state expected for the kagome antiferromagnet.",1305.2477v1
2013-05-12,Effects of Density Conservation and Hydrodynamics on Aging in Nonequilibrium Processes,"Aging in kinetics of three different phase transitions, viz., magnetic,
binary solid and single component fluid, have been studied via Monte Carlo and
molecular dynamics simulations in three space dimensions with the objective of
identifying the effects of order-parameter conservation and hydrodynamics. We
observe that the relevant autocorrelations exhibit power-law decay in
ferromagnet and binary solid but with different exponents. At early time fluid
autocorrelation function nicely follows that of binary solid, the order
parameter being conserved for both of them, as opposed to a ferromagnet. At
late time the fluid data crosses over to an exponential decay which we identify
as a hydrodynamic effect and provide analytical justification for this
behavior.",1305.2557v1
2013-05-21,Switching of a single ferromagnetic layer driven by spin Hall effect,"The magnetization switching of a thin ferromagnetic layer placed on top of a
heavy metal (such as Pt, Ta or W) driven by an in-plane current has been
observed in recent experiments. The magnetization dynamics of these processes
is studied in a full micromagnetic framework which takes into account the
transfer-torque from spin Hall effect due to the spin-orbit coupling.
Simulations indicate that the reversal occurs via nucleation of complex
magnetization patterns. In particular, magnetic bubbles appear during the
reversal of the magnetization in the perpendicular configuration while for the
in-plane configuration, nucleation of vortexes are observed.",1305.4806v1
2013-05-28,Spin-charge disparity of polarons in organic ferromagnets,"Polaron formation in quasi-one-dimensional organic ferromagnets is studied
based on an extended Su-Schrieffer-Heeger model combined with a Kondo term. The
charge distribution of the polaron is found to be highly asymmetric under
spatial reflection, due to the spin radicals. On the contrary, the spin density
is nearly symmetric; the spin asymmetry introduced by the extra electron
inducing the polaron formation is nearly compensated by the spin polarization
of the lower-energy states. We discuss these results on the basis of real-space
mean-field calculations and symmetry arguments.",1305.6495v1
2013-06-19,Energetic stability of coreless vortices in spin-1 Bose-Einstein condensates with conserved magnetization,"We show that conservation of longitudinal magnetization in a spinor
condensate provides a stabilizing mechanism for a coreless vortex
phase-imprinted on a polar condensate. The stable vortex can form a composite
topological defect with distinct small- and large-distance topology: the inner
ferromagnetic coreless vortex continuously deforms toward an outer singular,
singly quantized polar vortex. A similar mechanism can also stabilize a
nonsingular nematic texture in the polar phase. A weak magnetization is shown
to destabilize a coreless vortex in the ferromagnetic phase.",1306.4700v2
2013-07-01,Spin-controlled superconductivity and tunable triplet correlations in graphene nanostructures,"We study graphene ferromagnet/superconductor/ferromagnet (F/S/F)
nanostructures via a microscopic self-consistent Dirac Bogoliubov-de Gennes
formalism. We show that as a result of proximity effects, experimentally
accessible spin switching phenomena can occur as one tunes the Fermi level
$\mu_F$ of the F regions or varies the angle $\theta$ between exchange field
orientations. Superconductivity can then be switched on and off by varying
either $\theta$ or $\mu_F$ (a spin-controlled superconducting graphene switch).
The induced equal-spin triplet correlations in S can be controlled by tuning
$\mu_F$, effectively making a graphene based two-dimensional spin-triplet
valve.",1307.0546v1
2013-07-02,Size Dependence of Domain Pattern Transfer in Multiferroic Heterostructures,"Magnetoelectric coupling in multiferroic heterostructures can produce large
lateral modulations of magnetic anisotropy enabling the imprinting of
ferroelectric domains into ferromagnetic films. Exchange and magnetostatic
interactions within ferromagnetic films oppose the formation of such domains.
Using micromagnetic simulations and a 1-D model, we demonstrate that competing
energies lead to the breakdown of domain pattern transfer below a critical
domain width. Moreover, rotation of the magnetic field results in abrupt
transitions between two scaling regimes with different magnetic anisotropy.",1307.0605v2
2013-07-02,Phase Field Crystal Model for Magneto-Elasticity in Isotropic Ferromagnetic Solids,"A new isotropic magneto-elastic phase field crystal (PFC) model to study the
relation between morphological structure and magnetic properties of pure
ferromagnetic solids is introduced. Analytic calculations were used to
determine the phase diagram and obtain the relationship between elastic strains
and magnetization. Time dependent numerical simulations were used to
demonstrate the effect of grain boundaries on the formation of magnetic
domains. It was shown that the grain boundaries act as nucleating sites for
domains of reverse magnetization. Finally, we derive a relation for coercivity
versus grain mis-orientation in the isotropic limit.",1307.0758v1
2013-07-16,Analysis of magnetic neutron-scattering data of two-phase ferromagnets,"We have analyzed magnetic-field-dependent small-angle neutron scattering
(SANS) data of soft magnetic two-phase nanocomposite ferromagnets in terms of a
recent micromagnetic theory for the magnetic SANS cross section [D. Honecker
and A. Michels, Phys. Rev. B $\mathbf{87}$, 224426 (2013)]. The approach yields
a value for the average exchange-stiffness constant and provides the Fourier
coefficients of the magnetic anisotropy field and magnetostatic field, which is
related to jumps of the magnetization at internal interfaces.",1307.4206v1
2013-07-17,Huge thermoelectric effects in ferromagnet-superconductor junctions in the presence of a spin-splitting field,"We show that a huge thermoelectric effect can be observed by contacting a
superconductor whose density of states is spin-split by a Zeeman field with a
ferromagnet with a non-zero polarization. The resulting thermopower exceeds
$k_B/e$ by a large factor, and the thermoelectric figure of merit $ZT$ can far
exceed unity, leading to heat engine efficiencies close to the Carnot limit. We
also show that spin-polarized currents can be generated in the superconductor
by applying a temperature bias.",1307.4672v2
2013-10-19,Superconductivity and magnetism on flux grown single crystals of NiBi3,"We present resistivity, magnetization and specific heat measurements on flux
grown single crystals of NiBi3. We find typical behavior of a type-II
superconductor, with, however, a sizable magnetic signal in the superconducting
phase. There is a hysteretic magnetization characteristic of a ferromagnetic
compound. By following the magnetization as a function of temperature, we find
a drop at temperatures corresponding to the Curie temperature of ferromagnetic
amorphous Ni. Thus, we assign the magnetism in NiBi$_3$ crystals to amorphous
Ni impurities.",1310.5247v1
2013-10-25,Giant coercivity enhancement and dimensional crossover of superconductivity in Co2FeSi-NbN nanoscale bilayers,"Proximity coupling and magnetic switching dynamics are shown to be correlated
in bilayers (B) of fully spin polarized ferromagnet (F) Co2FeSi and
superconductor (S) NbN. The upper critical field derived from resistivity
measurements shows a dimensional crossover with a reduced effective thickness
of the S layer. At temperatures (T) << superconducting Tc, the measured M-H
loops show two step switching; one at T-independent value ~ 7 Oe and other at
strongly T-dependent value becoming very large ~ 1 kOe at 2 K. These results
reveal induced ferromagnetism in S-layer at the S/F interface with vortex
pinning influenced dynamics.",1310.6818v1
2013-10-25,Domain wall motion in ferromagnetic nanotubes: Analytic results,"Dynamics of magnetization domain walls (DWs) in thin ferromagnetic nanotubes
subject to longitudinal external fields is addressed analytically in the
regimes of strong and weak penalization. Explicit functional forms of the DW
profiles and formulas for the DW propagation velocity are derived in both
regimes. In particular, the DW speed is shown to depend nonlinearly on the
nanotube radius.",1310.6883v1
2013-11-19,Anisotropic magneto-thermal transport and Spin-Seebeck effect,"The angular dependence of the thermal transport in insulating or conducting
ferromagnets is derived on the basis of the Onsager reciprocity relations
applied to a magnetic system. It is shown that the angular dependence of the
temperature gradient takes the same form as that of the anisotropic
magnetoresistance, including anomalous and planar Hall contributions. The
measured thermocouple generated between the extremities of the non-magnetic
electrode in thermal contact to the ferromagnet follows this same angular
dependence. The sign and amplitude of the magneto-voltaic signal is controlled
by the difference of the Seebeck coefficients of the thermocouple.",1311.4868v1
2013-11-24,Role of spin mixing conductance in spin pumping: enhancement of spin pumping efficiency in Ta/Cu/Py structures,"From spin pumping measurements in Ta/Py devices for different thicknesses of
Ta, we determine the spin Hall angle to be 0.021 - 0.033 and spin diffusion
length to be 8 nm in Ta. We have also studied the effect of changing the
properties of non-magnet/ferromagnet interface by adding a Cu interlayer. The
experimental results show that the effective spin mixing conductance increases
in the presence of Cu interlayer for Ta/Cu/Py devices, whereas it decreases in
Pt/Cu/Py devices. Our findings allow the tunability of the spin pumping
efficiency by adding a thin interlayer at the non-magnet/ferromagnet interface.",1311.6098v1
2013-12-05,Magnetic properties of ferromagnetic Pu2Pt3Si5,"The structural, magnetic, and thermodynamic properties of a new plutonium
based compound, Pu2Pt3Si5, are reported. Single crystals produced by a Sn-flux
technique have been analyzed showing a ferromagnetic behavior at 58 K.
Pu2Pt3Si5 crystallizes in the U2Co3Si5-type orthorhombic Iabm structure (72)
with atomic parameters a = 9.9226(2) \AA, b = 11.4436(2) \AA and c = 6.0148(1)
\AA. The effective (\mu_eff ~0.74 \mu_B) and saturated (\mu_sat ~0.32 B/Pu)
moments as well as the Sommerfeld coefficient (\gamma_e ~2 mJ.mol-1.K-2/Pu)
could point towards 5f localization in this material.",1312.1576v1
2013-12-06,First Principles Study of the Magnetic Properties of LaOMnAs,"Recent experiments reported giant magnetoresistance at room temperature in
LaOMnAs. Here a density functional theory calculation is performed to
investigate magnetic properties of LaOMnAs. The ground state is found to be the
G-type antiferromagnetic order within the $ab$ plane but coupled
ferromagnetically between planes, in agreement with recent neutron
investigations. The electronic band structures suggest an insulating state
which is driven by the particular G-type magnetic order, while a metallic state
accompanies the ferromagnetic order. This relation between magnetism and
conductance may be helpful to qualitatively understand the giant
magnetoresistance effects.",1312.1775v1
2013-12-13,A generalized magnetic refrigeration scheme,"We have investigated the magnetocaloric effects in antiferromagnets and
compared them with those in ferromagnets using Monte Carlo simulations. In
antiferromagnets, the magnetic entropy reaches a maximum value at a finite
magnetic field when the temperature is fixed below the N\'eel temperature.
Using the fact, we proposed a protocol for applying magnetic fields to achieve
the maximum efficiency for magnetic refrigeration in antiferromagnets. In
particular, we found that at low temperatures, antiferromagnets are more useful
for magnetic refrigeration than ferromagnets.",1312.3716v2
2013-12-31,Topological response in ferromagnets,"We present a theory of the intrinsic anomalous Hall effect in a model of a
doped Weyl semimetal, which serves here as the simplest toy model of a generic
three-dimensional metallic ferromagnet with Weyl nodes in the electronic
structure. We analytically evaluate the anomalous Hall conductivity as a
function of doping, which allows us to explicitly separate the Fermi surface
and non Fermi surface contributions to the Hall conductivity by carefully
evaluating the zero frequency and zero wavevector limits of the corresponding
response function. We show that this separation agrees with the one suggested a
long time ago in the context of the quantum Hall effect by Streda.",1401.0066v2
2014-01-02,Giant zero field cooled spontaneous exchange bias effect in phase separated La1.5Sr0.5CoMnO6,"We report a giant zero field cooled exchange bias (ZEB) effect (~0.65 T) in
La1.5Sr0.5CoMnO6 sample. Magnetic study has revealed a reentrant spin glass ~90
K, phase separation to spin glass and ferromagnetic phases below 50 K and
canted antiferromagnetic transition ~10 K. A small conventional exchange bias
(CEB) is established with the advent of spontaneous phase separation down to 10
K. Giant ZEB and enhanced CEB effects are found only below 10 K and are
attributed to the large unidirectional anisotropy at the interface of
isothermally field induced ferromagnetic phase and canted antiferromagnetic
background.",1401.0377v1
2014-01-03,Spin-superflow turbulence in spin-1 ferromagnetic spinor Bose-Einstein condensates,"Spin-superflow turbulence (SST) in spin-1 ferromagnetic spinor Bose-Einstein
condensates is theoretically and numerically studied by using the spinor
Gross-Pitaevskii (GP) equations. SST is turbulence in which the disturbed spin
and superfluid velocity fields are coupled. Applying the Kolmogorov-type
dimensional scaling analysis to the hydrodynamic equations of spin and velocity
fields, we theoretically find that the -5/3 and -7/3 power laws appear in
spectra of the superflow kinetic and the spin-dependent interaction energy,
respectively. Our numerical calculation of the GP equations confirms SST with
the coexistence of disturbed spin and superfluid velocity field with two power
laws.",1401.0599v2
2014-01-10,Intrinsic Localized Modes of a Classical Discrete Anisotropic Heisenberg Ferromagnetic Spin Chain,"We report several exact intrinsic localized mode solutions of the classical
spin evolution equation of a one-dimensional anisotropic Heisenberg
ferromagnetic spin chain in terms of Jacobian elliptic functions. These include
one, two and three spin excitations. All these solutions have smooth
anticontinuum limits. Their linear stability and semiclassical quantization are
also discussed briefly.",1401.2241v2
2014-01-13,Phase transitions in the domain structure of ferromagnetic superconductors,"Starting from the London - type model we study the domain structures in
ferromagnetic superconductors taking account of the nucleation of vortices and
antivortices coupled to the magnetic texture. We predict that the coupling
between domains and vortices results in the formation of two energetically
favorable domain configurations: (i) a Meissner - type vortex free
configuration with strong domain shrinking and (ii) a more rare domain
configuration with a dense vortex -- antivortex lattice. The switching between
these configurations is shown to result in the first order phase transitions
which could be observable in superconducting uranium based compounds.",1401.2806v1
2014-01-20,An Importance Sampling Scheme on Dual Factor Graphs. I. Models in a Strong External Field,"We propose an importance sampling scheme to estimate the partition function
of the two-dimensional ferromagnetic Ising model and the two-dimensional
ferromagnetic $q$-state Potts model, both in the presence of an external
magnetic field. The proposed scheme operates in the dual Forney factor graph
and is capable of efficiently computing an estimate of the partition function
under a wide range of model parameters. In particular, we consider models that
are in a strong external magnetic field.",1401.4912v5
2014-01-22,A quantum magnetic RC circuit,"We propose a setup that is the spin analog of the charge-based quantum RC
circuit. We define and compute the spin capacitance and the spin resistance of
the circuit for both ferromagnetic (FM) and antiferromagnetic (AF) systems. We
find that the antiferromagnetic setup has universal properties, but the
ferromagnetic setup does not. We discuss how to use the proposed setup as a
quantum source of spin excitations, and put forward a possible experimental
realization using ultracold atoms in optical lattices.",1401.5712v1
2014-01-29,Spin and charge ordering in three-leg ladders in oxyborates,"We study the spin ordering within the 3-leg ladders present in the oxyborate
Fe(3)O(2)BO(3) consisting of localized classical spins interacting with
conduction electrons (one electron per rung). We also consider the competition
with antiferromagnetic superexchange interactions to determine the magnetic
phase diagram. Beside a ferromagnetic phase we find (i) a phase with
ferromagnetic rungs ordered antiferromagnetically (ii) a zig-zag canted spin
ordering along the legs. We also determine the induced charge ordering within
the different phases and the interplay with lattice instability. Our model is
discussed in connection with the lattice dimerization transition observed in
this system, emphasizing on the role of the magnetic structure.",1401.7677v1
2014-02-12,Hydrostatic pressure to trigger and assist magnetic transitions: baromagnetic refrigeration,"The possible application of the barocaloric effect to produce solid state
refrigerators is a topic of interest in the field of applied physics. In this
work, we present experimental data about the influence of external pressure on
the magnetic properties of a manganite with phase separation. Using the Jahn
Teller effect associated with the presence of the charge ordering we were able
to follow the transition to the ferromagnetic state induced by pressure. We
also demonstrated that external pressure can assist the ferromagnetic state,
decreasing the magnetic field necessary to generate the magnetic transition.",1402.2824v1
2014-02-13,Giant magnetoresistance for ensembles of ferromagnetic granules in variable range hopping conductivity regime,"We study an effect of moderate magnetic field on variable range hopping
conductivity in arrays of ferromagnetic granules separated by tunnel barriers.
It is shown that the resulting magnetoresistance can be significantly larger
than the standard ""giant"" magnetoresistance in Fe-N-Fe-N... multilayers. The
effect is related to a gain in densities of states available for the virtual
processes within the intermediate granules due to magnetic-field induced
alignment of the granule magnetizations.",1402.3183v1
2014-02-15,Ferromagnetism and transport properties of the Kondo system Ce4Sb1.5Ge1.5,"Ferromagnetic ordering with a small magnetic moment is found below 14 K from
SQUID measurements for the compound Ce4Sb1.5Ge1.5. The transport
characteristics of a number of Ce4Sb3-xTx (T = Ge, Si, Sn, Pb, Al) systems were
measured at room temperature, Ce4Sb1.5Ge1.5 demonstrating the highest Seebeck
coefficient. Its transport properties (resistivity, thermal conductivity,
thermoelectric power) are experimentally investigated in detail up to low
temperatures. The Kondo-lattice behavior of resistivity and its anomaly at the
ordering point are found. A comparison with the Wiedemann-Franz law is
performed.",1402.3667v2
2014-02-28,"Standard, inverse and triplet spin-valve effects in F1/S/F2 systems","We demonstrate that contrary to the common belief the critical temperature Tc
of clean F1/S/F2 spin valves can depend non-monotonically on the angle between
the magnetic moments of the ferromagnetic F1 and F2 layers. Depending on the
system parameters the minimum of Tc may correspond to parallel, antiparallel or
non-collinear mutual orientation of magnetic moments. Such anomalous behavior
can reveal itself only provided the ferromagnetic layers differ from each other
and it completely disappears in the dirty limit.",1402.7259v1
2014-04-22,Approaching Pomeranchuk Instabilities from Ordered Phase: A Crossing-symmetric Equation Method,"We explore features of a 3D Fermi liquid near generalized Pomeranchuk
instabilities using a tractable crossing symmetric equation method. We approach
the instabilities from the ordered ferromagnetic phase. We find quantum
multi-criticality as approach to the ferromagnetic instability drives
instability in other channel(s). It is found that a charge nematic instability
precedes and is driven by Pomeranchuk instabilities in both the l = 0 spin and
density channels.",1404.5655v1
2014-07-14,Intrinsic magnetoresistance in metal films on ferromagnetic insulators,"We predict a magnetoresistance induced by the interfacial Rashba spin-orbit
coupling in normal metal|ferromagnetic insulator bilayer. It depends on the
angle between current and magnetization directions identically to the ""spin
Hall magnetoresistance"" mechanism caused by a combined action of spin Hall and
inverse spin Hall effects. Due to the identical phenomenology it is not obvious
whether the magnetoresistance reported by Nakayama et al. is a bulk metal or
interface effect. The interfacial Rashba induced magnetoresistance may be
distinguished from the bulk metal spin Hall magnetoresistance by its dependence
on the metal film thickness.",1407.3571v1
2014-07-18,Microwave-induced spin currents in ferromagnetic-insulator|normal-metal bilayer system,"A microwave technique is employed to simultaneously examine the spin pumping
and the spin Seebeck effect processes in a YIG|Pt bilayer system. The
experimental results show that for these two processes, the spin current flows
in opposite directions. The temporal dynamics of the longitudinal spin Seebeck
effect exhibits that the effect depends on the diffusion of bulk
thermal-magnons in the thermal gradient in the
ferromagnetic-insulator|normal-metal system.",1407.4957v2
2014-07-18,Structural and electronic properties of epitaxial YBaCuO/LaCaMnO bilayers grown on SrTiO$_3$ (110) substrates,"Epitaxial bilayers of the high-temperature-superconductor YBa2Cu3O7-d (YBCO)
and the ferromagnetic metal La0.67Ca0.33MnO3 (LCMO) were prepared by pulsed
laser deposition on (110)-oriented SrTiO3 substrates, such that the CuO2 planes
of YBCO are perpendicular to the YBCO-LCMO interface. X-ray diffraction and
Raman scattering demonstrate complete (110) orientation of both YBCO and LCMO
overlayers. The resistivity and magnetization of the bilayer films are highly
anisotropic. The critical temperatures for superconductivity and ferromagnetism
as well as the saturation magnetization exhibit modest reductions compared to
corresponding bulk values.",1407.5049v1
2014-07-25,Pre-asymptotic critical behavior and effective exponents in disordered metallic quantum ferromagnets,"We determine the pre-asymptotic critical behavior at the quantum
ferromagnetic transition in strongly disordered metals. We find that it is
given by effective power laws, in contrast to the previously analyzed
asymptotic critical behavior, which is valid only in an unobservably small
region. The consequences for analyzing experiments are discussed, in particular
ways to distinguish between critical behavior and Griffiths-phase effects.",1407.7068v1
2014-08-01,Spin-polarized quasiparticle transport in exchange-split superconducting aluminum on europium sulfide,"We report on nonlocal spin transport in mesoscopic superconducting aluminum
wires in contact with the ferromagnetic insulator europium sulfide. We find
spin injection and long-range spin transport in the regime of the exchange
splitting induced by europium sulfide. Our results demonstrate that spin
transport in superconductors can be manipulated by ferromagnetic insulators,
and opens a new path to control spin currents in superconductors.",1408.0176v1
2014-08-06,"Ground state, magnetization process and magnetocaloric effect of the exactly tractable spin-electron tetrahedral chain","A hybrid spin-electron system on one-dimensional tetrahedral chain, in which
the localized Ising spin regularly alternates with the mobile electron
delocalized over three lattice sites, is exactly investigated using the
generalized decoration-iteration transformation. The system exhibits either the
ferromagnetic or antiferromagnetic ground state depending on whether the
ferromagnetic or antiferromagnetic interaction between the Ising spins and
mobile electrons is considered. The enhanced magnetocaloric effect during the
adiabatic demagnetization suggests a potential use of the investigated system
for low-temperature magnetic refrigeration.",1408.1207v1
2014-08-13,Critical field theory for ferromagnetic quantum criticality in the strong coupling regime of Hertz-Moriya-Millis theory,"We develop U(1) slave spin-rotor theory, suggesting a metal-metal transition
from Landau's Fermi-liquid state to a bad metal phase, as U(1) slave
charge-rotor theory [Phys. Rev. B {\bf 70}, 035114 (2004)] describes a
metal-insulator transition from Landau's Fermi-liquid state to a spin-liquid
phase. U(1) slave spin-rotor formulation allows us to generalize
Hertz-Moriya-Millis theory for ferromagnetic quantum phase transitions,
replacing Landau's Fermi-liquid state with an incoherent metallic phase. As a
result, we argue that localized magnetic moments emerge to govern quantum
critical physics in bad metals.",1408.2993v2
2014-08-14,PT-symmetry in macroscopic magnetic structures,"We introduce the notion of PT-symmetry in magnetic nanostructures and show
that they can support a new type of non-Hermitian dynamics. Using the simplest
possible set-up consisting of two coupled ferromagnetic films, one with loss
and another one with a balanced amount of gain, we demonstrate the existence of
a spontaneous PT-symmetry breaking point where both the eigenfrequencies and
eigenvectors are degenerate. Below this point the frequency spectrum is real
indicating stable dynamics while above this point it is complex signaling
unstable dynamics.",1408.3285v1
2014-08-18,Metastable spin textures and Nambu-Goldstone modes of a ferromagnetic spin-1 Bose-Einstein condensate confined in a ring trap,"We investigate the metastability of a ferromagnetic spin-1 Bose-Einstein
condensate confined in a quasi-one-dimensional rotating ring trap by solving
the spin-1 Gross-Pitaevskii equation. We find analytical solutions that exhibit
spin textures. By performing linear stability analysis, it is shown that the
solutions can become metastable states. We also find that the number of
Nambu-Goldstone modes changes at a certain rotation velocity without changing
the continuous symmetry of the order parameter.",1408.4129v4
2014-09-14,Spin-polarized Andreev transport influenced by Coulomb repulsion through two quantum dot system,"Spin-polarized transport through a double quantum dot system attached to a
common superconducting lead and two ferromagnetic electrodes (fork geometry) is
investigated theoretically. The key objective of the analysis is to describe
the influence of electrodes' ferromagnetism on the Andreev tunneling. Both
direct and crossed Andreev tunneling processes are considered, in general. The
other objective is a detailed analysis of the role of Coulomb interaction and
its impact on the Andreev tunneling processes.",1409.4122v1
2014-09-16,"Magnetisms in $p$-type monolayer gallium chalcogenides (GaSe, GaS)","Magnetisms in $p$-type monolayer GaX (X=S,Se) is investigated by performing
density-functional calculations. Due to the large density of states near the
valence band edge, these monolayer semiconductors are ferromagnetic within a
small range of hole doping. The intrinsic Ga vacancies can promote local
magnetic moment while Se vacancies cannot. Magnetic coupling between
vacancy-induced local moments is ferromagnetic and surprisingly long-range. The
results indicate that magnetization can be induced by hole doping and can be
tuned by controlled defect generation.",1409.4733v2
2014-09-25,Interfacial Spin and Heat Transfer between Metals and Magnetic Insulators,"We study the role of thermal magnons in the spin and heat transport across a
normal-metal/insulating-ferromagnet interface, which is beyond an elastic
electronic spin transfer. Using an interfacial exchange Hamiltonian, which
couples spins of itinerant and localized orbitals, we calculate spin and energy
currents for an arbitrary interfacial temperature difference and misalignment
of spin accumulation in the normal metal relative to the ferromagnetic order.
The magnonic contribution to spin current leads to a temperature-dependent
torque on the magnetic order parameter; reciprocally, the coherent precession
of the magnetization pumps spin current into the normal metal, the magnitude of
which is affected by the presence of thermal magnons.",1409.7128v1
2014-10-03,Dynamics of a vortex dipole across a magnetic phase boundary in a spinor Bose-Einstein condensate,"Dynamics of a vortex dipole in a spin-1 Bose-Einstein condensate in which
magnetic phases are spatially distributed is investigated. When a vortex dipole
travels from the ferromagnetic phase to the polar phase, or vice versa, it
penetrates the phase boundary and transforms into one of the various spin
vortex dipoles, such as a leapfrogging ferromagnetic-core vortex dipole and a
half-quantum vortex dipole. Topological connections of spin wave functions
across the phase boundary are discussed.",1410.0743v1
2014-10-08,Uniqueness of zero-temperature metastate in disordered Ising ferromagnets,"We study ground states of Ising models with random ferromagnetic couplings,
proving the triviality of all zero-temperature metastates. This unexpected
result sheds a new light on the properties of these systems, putting strong
restrictions on their possible ground state structure. Open problems related to
existence of interface-supporting ground states are stated and an
interpretation of the main result in terms of first-passage and random surface
models in a random environment is presented.",1410.2283v1
2014-10-14,Skyrmion-like states in multilayer exchange coupled ferromagnetic nanostructures with distinct anisotropy directions,"We report the experimental observation of magnetic skyrmion-like states in
patterned ferromagnetic nanostructures consisting of perpendicular magnetized
Co/Pt multilayer film exchange coupled with Co nanodisks in vortex state. The
magnetic force microscopy and micromagnetic simulations show that depending on
the magnitude of Co/Pt perpendicular anisotropy in these systems two different
modes of skyrmion formation are realized.",1410.4174v1
2014-10-20,Phase diagram of exciton condensate in doped two-band Hubbard model,"Using the dynamical mean-field approximation we investigate formation of
excitonic condensate in the two-band Hubbard model in the vicinity of the
spin-state transition. With temperature and band filling as the control
parameters we realize all symmetry allowed spin-triplet excitonic phases, some
exhibiting a ferromagnetic polarization. While the transitions are first-order
at low temperatures, at elevated temperatures continuous transitions are found
that give rise to a multi-critical point. Rapid but continuous transition
between ferromagnetic and non-magnetic excitonic phases allows switching of
uniform magnetization by small changes of chemical potential.",1410.5198v1
2014-10-21,Magnetic switching dynamics in a ferrimagnetic two sub-lattice model including ultrafast exchange scattering,"We study the heat-induced magnetization dynamics in a toy model of a
ferrimagnetic alloy, which includes localized spins antiferromagnetically
coupled to an itinerant carrier system with a Stoner gap. We determine the
one-particle spin-density matrix including exchange scattering between
localized and itinerant bands as well as scattering with phonons. While a
transient ferromagnetic-like state can always be achieved by a sufficiently
strong excitation, this transient ferromagnetic-like state only leads to
magnetization switching for model parameters that also yield a compensation
point in the equilibrium M(T) curve.",1410.5745v2
2014-10-30,Superconducting Gap of UCoGe probed by Thermal Transport,"Thermal conductivity measurements in the superconducting state of the
ferromagnet UCoGe were performed at very low temperatures and under magnetic
field on samples of different qualities and with the heat current along the
three crystallographic axis. This allows to disentangle intrinsic and extrinsic
effects, confirm the situation of multigap superconductivity and shed new light
on the situation expected or claimed for the gap in these ferromagnetic
superconductors, like evidences of absence of ""partially gapped"" Fermi
surfaces.",1410.8361v1
2014-11-02,Universal free-energy distribution in the critical point of a random Ising ferromagnet,"We discuss the non-self-averaging phenomena in the critical point of weakly
disordered Ising ferromagnet. In terms of the renormalized replica
Ginzburg-Landau Hamiltonian in dimensions D <4, we derive an explicit
expression for the probability distribution function (PDF) of the critical free
energy fluctuations. In particular, using known fixed-point values for the
renormalized coupling parameters, we obtain the universal curve for such PDF in
the dimension D=3. It is demonstrated that this function is strongly
asymmetric: its left tail is much slower than the right one.",1411.0263v2
2014-11-06,Phenomenological description of anisotropy effects in some ferromagnetic superconductors,"We study phenomenologically by using the previously derived Landau free
energy, the role of anisotropy in ferromagnetic superconductors UGe2, URhGe,
and UCoGe. The three compounds are separately discussed with the special stress
on UGe2. The main effect comes from the strong uniaxial anisotropy of
magnetization while the anisotropy of Cooper pairs and crystal anisotropy only
slightly change the phase diagram in the vicinity of Curie temperature. The
limitations of this approach are also discussed.",1411.1748v1
2014-11-24,Flat band ferromagnetism without connectivity conditions in the flat band,"It is known that a system which exhibits a half filled lowest flat band and
the localized one-particle Wannier states on the flat band satisfy the
connectivity conditions, is always ferromagnetic. Without the connectivity
conditions on the flat band, the system is non-magnetic. We show that this is
not always true. The reason is connected to a peculiar behavior of the band
situated just above the flat band.",1411.6477v1
2014-11-27,Reverse magnetic vortex curling direction of ferromagnetic nanodisk,"We reverse the magnetic vortex curling direction of ferromagnetic nanodisk by
applying a circular Oersted field. The nanodisk is fabricated without breaking
its symmetry. The Oersted field is induced by passing current through an atomic
force microscope tip placed at the center of the disk. Micromagnetic simulation
indicates that compared to the uniformly distributed current throughout the
cross section of disk, the line current concentrated in the center can reverse
the chirality more easily, which is in accordance with our experimental
results.",1411.7444v1
2014-12-07,Asymmetric domain walls of small angle in soft ferromagnetic films,"We focus on a special type of domain walls appearing in the Landau-Lifshitz
theory for soft ferromagnetic films. These domain walls are divergence-free
$S^2$-valued transition layers that connect two directions in $S^2$ (differing
by an angle $2\theta$) and minimize the Dirichlet energy. Our main result is
the rigorous derivation of the asymptotic structure and energy of such
""asymmetric"" domain walls in the limit $\theta \to 0$. As an application, we
deduce that a supercritical bifurcation causes the transition from symmetric to
asymmetric walls in the full micromagnetic model.",1412.2382v1
2014-12-16,Charge and spin transport in a metal-semiconductor heterostructure with double Schottky barriers,"Taking into account the available experimental results, we model the
electronic properties and current-voltage characteristics of a
ferromagnet-semiconductor junction. The Fe/GaAs interface is considered as a
Fe/(i-GaAs)/n+-GaAs/n-GaAs multilayer structure with the Schottky barrier. We
also calculate numerically the current-voltage characteristics of a
double-Schottky-barrier structure Fe/GaAs/Fe, which are in agreement with
available experimental data. For this structure, we have estimated the spin
current in the GaAs layer, which characterizes spin injection from the
ferromagnet to the semiconductor.",1412.4932v1
2014-12-18,Coherent elastic excitation of spin waves,"We model the injection of elastic waves into a ferromagnetic film (F) by a
non-magnetic transducer (N). We compare the configurations in which the
magnetization is normal and parallel to the wave propagation. The lack of axial
symmetry in the former results in the emergence of evanescent interface states.
We compute the energy-flux transmission across the N$|$F interface and
sound-induced magnetization dynamics in the ferromagnet. We predict efficient
acoustically induced pumping of spin current into a metal contact attached to
F.",1412.5820v2
2014-12-18,Topological superconductivity and high Chern numbers in 2D ferromagnetic Shiba lattices,"Inspired by the recent experimental observation of topological
superconductivity in ferromagnetic chains, we consider a dilute 2D lattice of
magnetic atoms deposited on top of a superconducting surface with a Rashba
spin-orbit coupling. We show that the studied system supports a generalization
of $p_x+ip_y$ superconductivity and that its topological phase diagram contains
Chern numbers higher than $\xi/a$ $(\gg1)$, where $\xi$ is the superconducting
coherence length and $a$ is the distance between the magnetic atoms. The
signatures of nontrivial topology can be observed by STM spectroscopy in
finite-size islands.",1412.5834v1
2015-01-06,Critical behavior in lattice models with two symmetric absorbing state,"We analyze nonequilibrium lattice models with up-down symmetry and two
absorbing states by mean-field approximations and numerical simulations in two
and three dimensions. The phase diagram displays three phases: paramagnetic,
ferromagnetic and absorbing. The transition line between the first two phases
belongs to the Ising universality class and between the last two, to the direct
percolation universality class. The two lines meet at the point describing the
voter model and the size $\ell$ of the ferromagnetic phase vanishes with the
distance $\varepsilon$ to the voter point as $\ell\sim\varepsilon$, with
possible logarithm corrections in two dimensions.",1501.01116v1
2015-01-17,Magnetic and Magnetocaloric Study of the Ferromagnetically Coupled GdF3: The Best Cryogenic Magnetic Coolant Ever,"The magnetic susceptibility and isothermal magnetization for GdF3 were
measured, and the isothermal entropy change was evaluated up to 9 T. Combining
the large isotropic spin of Gd3+, the dense structure and the weak
ferromagnetic interaction, an extremely large -(delta)Sm for GdF3 was observed
up to 528 mJ cm-3 K-1 for (delta)H = 9 T, proving itself to be the best
cryogenic magnetic coolant ever.",1501.04180v1
2015-02-05,DFT calculations of magnetic anisotropy energy for GeMnTe ferromagnetic semiconductor,"Density functional theory (DFT) calculations of the energy of magnetic
anisotropy for diluted ferromagnetic semiconductor GeMnTe were performed using
using OpenMX package with fully relativistic pseudopotentials. The influence of
hole concentration and magnetic ion neighborhood on magnetic anisotropy energy
is presented. Analysis of microscopic mechanism of magnetic anisotropy is
provided, in particular the role of spin-orbit coupling, spin polarization and
spatial changes of electron density are discussed. The calculations are in
accordance with the experimental observation of perpendicular magnetic
anisotropy in rhombohedral GeMnTe (111) thin layers.",1502.01715v3
2015-02-06,Microscopic theory of Gilbert damping in metallic ferromagnets,"We present a microscopic theory for magnetization relaxation in metallic
ferromagnets of nanoscopic dimensions that is based on the dynamic spin
response matrix in the presence of spin-orbit coupling. Our approach allows the
calculation of the spin excitation damping rate even for perfectly crystalline
systems, where existing microscopic approaches fail. We demonstrate that the
relaxation properties are not completely determined by the transverse
susceptibility alone, and that the damping rate has a non-negligible frequency
dependence in experimentally relevant situations. Our results indicate that the
standard Landau-Lifshitz-Gilbert phenomenology is not always appropriate to
describe spin dynamics of metallic nanostructure in the presence of strong
spin-orbit coupling.",1502.02068v1
2015-02-14,Energy dissipation in single-domain ferromagnetic nanoparticles: Dynamical approach,"We study, both analytically and numerically, the phenomenon of energy
dissipation in single-domain ferromagnetic nanoparticles driven by an
alternating magnetic field. Our interest is focused on the power loss resulting
from the Landau-Lifshitz-Gilbert equation, which describes the precessional
motion of the nanoparticle magnetic moment. We determine the power loss as a
function of the field amplitude and frequency and analyze its dependence on
different regimes of forced precession induced by circularly and linearly
polarized magnetic fields. The conditions to maximize the nanoparticle heating
are also analyzed.",1502.04222v1
2015-03-05,Single-spin-flip dynamics of the Ising chain,"We consider the most general single-spin-flip dynamics for the ferromagnetic
Ising chain with nearest-neighbour influence and spin reversal symmetry. This
dynamics is a two-parameter extension of Glauber dynamics corresponding
respectively to non-linearity and irreversibility. The associated stationary
state measure is given by the usual Boltzmann-Gibbs distribution for the
ferromagnetic Hamiltonian of the chain. We study the properties of this
dynamics both at infinite and at finite temperature, all over its parameter
space, with particular emphasis on special lines and points.",1503.01661v3
2015-03-12,Dyson hierarchical quantum ferromagnetic Ising chain with pure or random transverse fields,"The Dyson hierarchical version of the quantum Ising chain with Long-Ranged
power-law ferromagnetic couplings $J(r) \propto r^{-1-\sigma}$ and pure or
random transverse fields is studied via real-space renormalization. For the
pure case, the critical exponents are explicitly obtained as a function of the
parameter $\sigma$, and are compared with previous results of other approaches.
For the random case, the RG rules are numerically applied and the critical
behaviors are compared with previous Strong Disorder Renormalization results.",1503.03727v2
2015-03-12,Control of current-induced spin-orbit effects in a ferromagnetic heterostructure by electric field,"We study the effects of electrostatic gating on the current-induced phenomena
in ultrathin ferromagnet/heavy metal heterostructures. We utilize heterodyne
detection and analysis of symmetry with respect to the direction of the
magnetic field to separate electric field contributions to the magnetic
anisotropy, current-induced field-like torque, and damping torque. Analysis of
the electric field effects allows us to estimate the Rashba and the spin Hall
contributions to the current-induced phenomena. Electrostatic gating can
provide insight into the spin-orbit phenomena, and enable new functionalities
in spintronic devices.",1503.03882v1
2015-03-13,Upper bound of one-magnon excitation and lower bound of effective mass for ferromagnetic spinor Bose and Fermi gases,"Using a variational method, we derive an exact upper bound for one-magnon
excitation energy in ferromagnetic spinor gases, which limits the quantum
corrections to the effective mass of a magnon to be positive. We also derive an
upper bound for one-magnon excitation energy in lattice systems. The results
hold for both Bose and Fermi systems in $d$ dimensions as long as the
interaction is local and invariant under spin rotation.",1503.03951v3
2015-03-16,Impact of Current on Static and Kinetic Depinning Fields of Domain Wall in Ferromagnetic Nanostrip,"The impact of current on static and kinetic depinning fields of a domain wall
in an one dimensional ferromagnetic nanostrip is investigated by solving the
Landau-Lifshitz-Gilbert equation with adiabatic and non-adiabatic spin-transfer
torques analytically and numerically. The results show that in the absence of
current, the static depinning field is greater than the kinetic depinning field
and both the depinning fields decrease by the increase of current applied in a
direction opposite to the direction of the applied field. Both the depinning
fields can also be tuned by the current to make them equal.",1503.04553v1
2015-03-18,Long-Range Triplet Supercurrents Induced by Singlet Supercurrents Parallel to Magnetic Interfaces,"Employing a spin-parameterized Kleldysh-Usadel technique for the diffusive
regime, we demonstrate that even in the low proximity limit, considerable
long-ranged triplet supercurrents can be effectively generated by spin-singlet
supercurrents flowing \textit{parallel} to the interfaces of uniform double
ferromagnet interlayers with noncollinear exchange fields ""{\it independent}""
of actual junction geometry. The triplet supercurrents are found to be most
pronounced when the thicknesses of the ferromagnet strips are unequal. To
experimentally verify this generic phenomenon, we propose an accessible and
well-controlled structure that can fully isolate the long-range triplet
effects.",1503.05584v1
2015-03-29,Cooperative Multiscale Aging in a Ferromagnet/Antiferromagnet Bilayer,"We utilize anisotropic magnetoresistance to study temporal evolution of the
magnetization state in epitaxial Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$
ferromagnet/antiferromagnet bilayers. The resistance exhibits power-law
evolution over a wide range of temperatures and magnetic fields, indicating
that aging is characterized by a wide range of activation time scales. We show
that aging is a cooperative process, i.e. the magnetic system is not a
superposition of weakly interacting subsystems characterized by simple
Arrhenius activation. The observed effects are reminiscent of avalanches in
granular materials, providing a conceptual link to a broad class of critical
phenomena in other complex condensed matter systems.",1503.08380v1
2015-04-16,Signatures of odd-frequency correlations in the Josephson current of superconductor/ferromagnet hybrid junctions,"Contacting a bilayer ferromagnet with a singlet even-frequency superconductor
allows for the realization of an effective triplet odd-frequency
superconductor. In this work, we investigate the Josephson effect between
superconductors with different symmetries (e.g. odd- versus even-frequency). In
particular, we study the supercurrent flowing between two triplet odd-frequency
superconducting leads through a weak singlet even-frequency superconductor. We
show that the peculiar temperature dependence of the critical current below the
superconducting transition of the weak superconductor is a signature of the
competition between odd/odd-frequency and odd/even-frequency Josephson
couplings.",1504.04400v1
2015-04-18,Dynamic phase transitions in a ferromagnetic thin film system: A Monte Carlo simulation study,"Dynamic phase transition properties of ferromagnetic thin film system under
the influence both bias and time dependent magnetic fields have been elucidated
by means of kinetic Monte Carlo simulation with local spin update Metropolis
algorithm. The obtained results after a detailed analysis suggest that bias
field is the conjugate field to dynamic order parameter, and it also appears to
define a phase line between two antiparallel dynamic ordered states depending
on the considered system parameters. Moreover, the data presented in this study
well qualitatively reproduce the recently published experimental findings where
time dependent magnetic behavior of a uniaxial cobalt films is studied in the
neighborhood of dynamic phase transition point.",1504.04749v1
2015-04-25,Layered systems at the mean field critical temperature,"We consider the Ising model on $\mathbb Z\times \mathbb Z$ where on each
horizontal line $\{(x,i), x\in \mathbb Z\}$, the interaction is given by a
ferromagnetic Kac potential with coupling strength $J_\gamma(x,y)\sim \gamma
J(\gamma (x-y))$ at the mean field critical temperature. We then add a nearest
neighbor ferromagnetic vertical interaction of strength $\epsilon$ and prove
that for every $\epsilon >0$ the systems exhibits phase transition provided
$\gamma>0$ is small enough.",1504.06767v1
2015-05-01,Anisotropic magneto-capacitance in ferromagnetic-plate capacitors,"The capacitance of a parallel plate capacitor can depend on applied magnetic
field. Previous studies have identified capacitance changes induced via
classical Lorentz force or spin-dependent Zeeman effects. Here we measure a
magnetization direction dependent capacitance in parallel-plate capacitors
where one plate is a ferromagnetic semiconductor, gallium manganese arsenide.
This anisotropic magneto-capacitance is due to the anisotropy in the density of
states dependent on the magnetization through the strong spin-orbit
interaction.",1505.00170v1
2015-05-04,Magnetomechanical effects in the elastic polymer composites containing different volume fraction of ferromagnetic powder particles,"In the present work a detailed thermodynamic consideration for the magnetic
free energy of the composite material consisting of the ferromagnetic powder
particles embedded into a polymer matrix is given. We estimate their
magnetostatic interaction energy and its dependence on the microscopic
distribution of the magnetization and the magnetic field in the composite
material. We also define the hydrostatic component of the mechanical force
developed and the volume change effect caused by the magnetostatic interactions
in such composites.",1505.00795v1
2015-05-20,Dipolar spin-misalignment correlations in inhomogeneous magnets: comparison between neutron scattering and micromagnetic approaches,"In inhomogeneous bulk ferromagnets, the dominating sources of spin disorder
are related to spatial variations of (i) the magnitude of the local saturation
magnetization and of (ii) the magnitude and/or direction of the magnetic
anisotropy field. For the particular example of a porous ferromagnet, where the
magnetization inhomogeneity is at maximum, we demonstrate, by means of
experimental neutron scattering data and micromagnetic simulations, the
anisotropic character of magnetization fluctuations induced by the dipolar
interaction.",1505.05337v1
2015-06-05,On the magnetization process of ferromagnetic materials,"The present article concludes that a ferromagnetic sample could be considered
like a paramagnetic system where the role of magnetic moments plays magnetic
domains. Based on this conclusion and taking into account presence of an
anisotropic field the formula which describes magnetization dependence on the
external magnetic field is derived. Expressions for a remanent magnetization
and a coercive force are presented. The new parameter to characterize a
magnetic stiffness of a material is introduced. A physical expression for a
dynamic magnetic susceptibility as a function of material's characteristics,
external magnetic field, and a temperature is given.",1506.01805v3
2015-06-23,Effects of magnetic anisotropy on spin dynamics of ferromagnetic frustrated chain,"By exploiting density-matrix renormalization group techniques, we investigate
the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing
ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied
magnetic fields. Numerical results of spin excitation spectra show that in the
field-induced spin quadrupole regime, the longitudinal component has a gapless
mode and the transverse component has a gapped mode irrespective of the
exchange anisotropy. The excitation gap of the transverse spin excitation
increases as the exchange anisotropy increases over the XY-like and Ising-like
regions, demonstrating that two-magnon bound states are stabilized due to the
easy-axis anisotropy.",1506.06883v1
2015-06-23,Magnetic Excitations of Spin Nematic State in Frustrated Ferromagnetic Chain,"By exploiting density-matrix renormalization group techniques, we investigate
the dynamical spin structure factor of a spin-1/2 Heisenberg chain with
ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor
exchange interactions in an applied magnetic field. In a field-induced spin
nematic regime, we find gapless longitudinal and gapped transverse spin
excitation spectra, in accordance with quasi-long-ranged longitudinal and
short-ranged transverse spin correlations, respectively. The gapless point
coincides with the dominant longitudinal spin correlation, whereas the gap
position exhibits a characteristic field dependence contradicting the dominant
transverse spin correlation.",1506.06891v1
2015-07-02,Piezo-Magnetoelectric Effect of Spin Origin in Dysprosium Orthoferrite,"Piezo-magnetoelectric effect, namely simultaneous induction of both the
ferromagnetic moment and electric polarization by an application of uniaxial
stress, was achieved in the non-ferroelectric and antiferromagnetic ground
state of DyFeO$_3$. The induced electric polarization and ferromagnetic moment
are coupled with each other, and monotonically increase with increasing
uniaxial stress. The present work provides a new way to design spin-driven
multiferroic states, that is, magnetic symmetry breaking forced by external
uniaxial stress.",1507.00449v1
2015-07-02,Spin-dependent tunneling in semiconductor heterostructures with a magnetic layer,"We present a theory that describes the appearance of circular polarization of
the photoluminescence (PL) in ferromagnet-semiconductor hybrid heterostructures
due to spin-dependent tunneling of photoexcited carriers from a quantum well
into a magnetic layer. The theory succeeds in explaining the experimental data
on time-resolved PL for heterostructures consisting of InGaAs-based quantum
well (QW) and a spatially separated Mn $\delta$-layer. We show that the
circular polarization of the PL originates from dynamic spin polarization of
electrons due to spin-dependent leakage from the QW onto Mn donor states split
by the exchange field of the ferromagnetic Mn delta-layer.",1507.00585v1
2015-08-07,A Holographic Realization of Ferromagnets,"A holographic realization for ferromagnetic systems has been constructed.
Owing to the holographic dictionary proposed on the basis of this realization,
we obtained relevant thermodynamic quantities such as magnetization, magnetic
susceptibility, and free energy. This holographic model reproduces the behavior
of the mean field theory near the critical temperature. At low temperatures,
the results automatically incorporate the contributions from spin wave
excitations and conduction electrons.",1508.01626v1
2015-08-23,Rotational properties of ferromagnetic nanoparticles driven by a precessing magnetic field in a viscous fluid,"We study the deterministic and stochastic rotational dynamics of
ferromagnetic nanoparticles in a precessing magnetic field. Our approach is
based on the system of effective Langevin equations and on the corresponding
Fokker-Planck equation. Two key characteristics of the rotational dynamics, the
average angular frequency of precession of nanoparticles and their average
magnetization, are of our interest. Using the Langevin and Fokker-Planck
equations, we calculate both analytically and numerically these characteristics
in the deterministic and stochastic cases, determine their dependence on the
model parameters, and analyze in detail the role of thermal fluctuations.",1508.05651v1
2015-08-25,Characterization of Topological Phases of Spin-1/2 Frustrated Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chains by Entanglement Spectrum,"The topological classification of a series of frustration-induced spin-gap
phases in the spin-1/2 ferromagnetic--antiferromagnetic alternating Heisenberg
chain with next-nearest-neighbour interaction reported in J. Phys. Soc. Jpn.
82, 064703 (2013) is confirmed using two kinds of entanglement spectra defined
by different divisions of the whole chain. For the numerical calculation, the
iDMRG method is used. The results are consistent with the valence bond solid
picture proposed in the previous paper.",1508.06129v2
2015-09-03,Asymptotic Ferromagnetic Ordering of Energy Levels for the Heisenberg Model on Large Boxes,"We prove a result for the spin-$1/2$ quantum Heisenberg ferromagnet on
$d$-dimensional boxes $\{1,\dots,L\}^d \subset \mathbb{Z}^d$. For any $n$, if
$L$ is large enough, the Hamiltonian satisfies: among all vectors whose total
spin is at most $(L^d/2)-n$, the minimum energy is attained by a vector whose
total spin is exactly $(L^d/2)-n$.",1509.00907v1
2015-09-15,Magnetic Nernst effect,"The thermodynamics of irreversible processes in continuous media predicts the
existence of a Magnetic Nernst effect that results from a magnetic analog to
the Seebeck effect in a ferromagnet and magnetophoresis occurring in a
paramagnetic electrode in contact with the ferromagnet. Thus, a voltage that
has DC and AC components is expected across a Pt electrode as a response to the
inhomogeneous magnetic induction field generated by magnetostatic waves of an
adjacent YIG slab subject to a temperature gradient. The voltage frequency and
dependence on the orientation of the applied magnetic induction field are quite
distinct from that of spin pumping.",1509.04440v1
2015-09-18,Observation of thermoelectric currents in high-field superconductor-ferromagnet tunnel junctions,"We report on the experimental observation of thermoelectric currents in
superconductor-ferromagnet tunnel junctions in high magnetic fields. The
thermoelectric signals are due to a spin-dependent lifting of particle-hole
symmetry, and are found to be in excellent agreement with recent theoretical
predictions. The maximum Seebeck coefficient inferred from the data is about
$-100~\mathrm{\mu V/K}$, much larger than commonly found in metallic
structures. Our results directly prove the coupling of spin and heat transport
in high-field superconductors.",1509.05568v1
2015-09-24,Nonadiabatic pure spin pumping in zigzag graphene nanoribbons with proximity induced ferromagnetism,"By combining Floquet theory with Green's function formalism, we present
non-adiabatic quantum spin and charge pumping through a zigzag ferromagnetic
graphene nanoribbon including a double-barriers structure driven weakly by two
local $ac$ gate voltages operating with a phase-lag. Over a wide range of Fermi
energies, interesting quantum pumping such as i) pure spin pumping with zero
net charge pumping, ii) pure charge pumping and iii) fully spin polarized
pumping can be achieved by tuning and manipulating driving frequency in the
non-adiabatic regime. Spin polarized pumping which is measurable using the
current technology depends on the competition between the energy level spacing
and driving frequency.",1509.07233v1
2015-09-27,Exchange Bias following Kinetic Arrest,"Exchange bias is often observed when anti-ferromagnetic and ferromagnetic
phases coexist. The coexistence of two competing magnetic phases can persist to
the lowest temperatures if the disorder-broadened 1st order transition
separating them is interrupted, as is proposed in the kinetic arrest
phenomenon. The fractions of coexisting phases can, in this phenomenon, be
tuned by following different cooling protocols. We discuss predicted behaviours
of exchange bias resulting from the kinetic arrest phenomenon. Specifically,
for appropriate values of cycling field Hmax and measuring temperature T0 there
will be no exchange bias under cooling in zero field, while it will manifest
with increasing cooling field, and then saturate.",1509.08052v1
2015-09-28,Superconductivity and Magnetism in Noncentrosymmetric RhGe,"RhGe synthesized at high pressure is crystallized in noncentrosymmetric cubic
structure of the B20 type. Measurements of the electrical resistivity and
magnetization demonstrate a superconducting state below T$_c$ ~ 4.5 K and a
weak ferromagnetism below T$_m$ ~ 140 K. Specific heat data confirm the bulk
nature of superconductivity in this ferromagnetic superconductor. The
superconducting region forms a dome on the P-T diagram with a maximum of T$_c$
near 4 GPa. Ab initio simulations suggest that the observed weak magnetization
emerges from the pronounced spin polarization with magnetic quadrupole and
toroidal moments located at Rh and Ge sites.",1509.08249v1
2015-10-22,Molecular Anisotropic Magnetoresistance,"Using density functional theory calculations, we demonstrate that the effect
of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude
with respect to conventional bulk ferromagnets in junctions containing
molecules sandwiched between ferromagnetic leads. We study ballistic transport
in metal-benzene complexes contacted by $3d$ transition-metal wires. We show
that the gigantic AMR can arise from spin-orbit coupling effects in the leads,
drastically enhanced by orbital-symmetry filtering properties of the molecules.
We further discuss how this molecular anisotropic magnetoresistance (MAMR) can
be tuned by proper choice of materials and their electronic properties.",1510.06632v1
2015-11-02,"Uniqueness, Spatial Mixing, and Approximation for Ferromagnetic 2-Spin Systems","We give fully polynomial-time approximation schemes (FPTAS) for the partition
function of ferromagnetic 2-spin systems in certain parameter regimes. The
threshold we obtain is almost tight up to an integrality gap. Our technique is
based on the correlation decay framework. The main technical contribution is a
new potential function, with which we establish a new kind of spatial mixing.",1511.00493v3
2015-11-04,Non-Convex Multipartite Ferromagnets,"We investigate a multipartite ferromagnetic model without self-interactions
between spins of the same party, so that the Hamiltonian is not a definite
quadratic form of the magnetisations. We find the free energy and study the
phase transition for all zero external fields. Moreover in the bipartite case
we analyse the fluctuations of the rescaled magnetisations, below and at the
critical point, and we study the phase transitions with non zero magnetic
fields.",1511.01307v2
2015-11-11,Spin Swapping Transport and Torques in Ultrathin Magnetic Bilayers,"Planar spin transport in disordered ultrathin magnetic bilayers comprising a
ferromagnet and a normal metal (typically used for spin pumping, spin Seebeck
and spin-orbit torque experiments) is investigated theoretically. Using a
tight-binding model that treats extrinsic spin Hall effect, spin swapping and
spin relaxation on equal footing, we show that the nature of spin-orbit coupled
transport dramatically depends on ratio between the layers thickness $d$ and
the mean free path $\lambda$. While spin Hall effect dominates in the diffusive
limit ($d\gg\lambda$), spin swapping dominates in Knudsen regime
($d\lesssim\lambda$). A remarkable consequence is that the symmetry of the
spin-orbit torque exerted on the ferromagnet is entirely different in these two
regimes.",1511.03454v1
2016-01-04,Ultrafast transient dynamics in composite multiferroics,"We investigate theoretically the dynamic multiferroic response of coupled
ferroelectric/ferromagnetic composites upon excitation by a photo-induced
acoustic strain pulse. Two magnetoelectric mechanisms are considered: interface
strain- and charge-mediated magnetoelectric couplings. The former results in
demagnetization, depolarization and repolarization within tens of picoseconds
via respectively magnetostriction and piezoelectricity. Charge magnetoelectric
interaction affects the ferroelectric/ferromagnetic feedback response leading
to magnetization recovery. Experimental realization based on time-resolved
x-ray diffraction is suggested. The findings indicate the potential of
composite multiferroics for photo-steered, high-speed, multi-state electronic
devices.",1601.00391v1
2016-01-04,Direct and inverse cascades of spin-wave turbulence in spin-1 ferromagnetic spinor Bose-Einstein condensates,"We theoretically and numerically study spin-wave turbulence in spin-1
ferromagnetic spinor Bose-Einstein condensates, finding direct and inverse
cascades with power-law behavior. To derive these power exponents analytically,
the conventional weak wave turbulence theory is applied to the spin-1 spinor
Gross-Pitaevskii equation. Thus, we obtain the $-7/3$ and $-5/3$ power laws in
the transverse spin correlation function for the direct and inverse cascades,
respectively. To confirm these power laws, numerical calculations are performed
that obtain results consistent with these power laws.",1601.00446v2
2016-01-12,U(1) Emergence versus Chiral Symmetry Restoration in the Ashkin Teller Model,"We show that suppression of vortices in the Ashkin Teller ferromagnet on a
square lattice splits the order-disorder transition and opens up an
intermediate phase where the macroscopic symmetry enhances to U(1). When we
selectively suppress the formation of non-chiral vortices, chiral vortices
proliferate and replace the U(1) phase with a new phase where chiral symmetry
is restored. This result demonstrates a fascinating phenomenon in which the
symmetry information encoded in topological defects manifests itself in the
symmetry of the phase where the defects proliferate. We also show that this
phenomenon can occur in all $\mathbb{Z}_n$ ferromagnets with even values of
$n$.",1601.02755v1
2016-01-24,Multiferroic Two-Dimensional Materials,"The relation between unusual Mexican-hat band dispersion, ferromagnetism and
ferroelasticity is investigated using a combination of analytical,
first-principles and phenomenological methods. The class of material with
Mexican-hat band edge is studied using the $\alpha$-SnO monolayer as a
prototype. Such band edge causes a van Hove singularity diverging with
$\frac{1}{\sqrt{E}}$, and in p-type material leads to spatial and/or
time-reversal spontaneous symmetry breaking. We show that an unexpected
multiferroic phase is obtained in a range of hole density for which the
material presents ferromagnetism and ferroelasticity simultaneously.",1601.06438v1
2016-01-30,Low-Temperature Spin-Wave Approximation for the Heisenberg Ferromagnet,"We study the low temperature thermodynamics of the quantum Heisenberg
ferromagnet in three dimension for any value of the spin $ S \geq 1/2 $. We
report on a rigorous proof of the validity of the spin-wave approximation for
the excitation spectrum, at the level of the first non-trivial contribution to
the free energy as the inverse temperature $ \beta \to \infty $.",1602.00155v1
2016-02-25,Uniaxial pressure induced half-metallic ferromagnetic phase transition in LaMnO$_3$,"We use first-principles theory to predict that the application of uniaxial
compressive strain leads to a transition from an antiferromagnetic insulator to
a ferromagnetic half-metal phase in LaMnO$_3$. We identify the Q2 Jahn-Teller
mode as the primary mechanism that drives the transition, indicating that this
mode can be used to tune the lattice, charge, and spin coupling. Applying
$\simeq$ 6 GPa of uniaxial pressure along the [010] direction activates the
transition to a half-metallic $\textit{pseudo-cubic}$ state. The
half-metallicity opens the possibility of producing colossal magnetoresistance
in the stoichiometric LaMnO$_3$ compound at significantly lower pressure
compared to recently observed investigations using hydrostatic pressure.",1602.07984v1
2016-03-23,Large Magnetoresistance at Room Temperature in Ferromagnet/Topological Insulator Contacts,"We report magnetoresistance for current flow through iron/topological
insulator (Fe/TI) and Fe/evaporated-oxide/TI contacts when a magnetic field is
used to initially orient the magnetic alignment of the incorporated
ferromagnetic Fe bar, at temperatures ranging from 100 K to room temperature.
This magnetoresistance is associated with the relative orientation of the Fe
bar magnetization and spin-polarization of electrons moving on the surface of
the TI with helical spin-momentum locking. The magnitude of the observed
magnetoresistance is relatively large compared to that observed in prior work.",1603.07283v1
2016-04-13,Dipolar Rings of Microscopic Ellipsoids: Magnetic Manipulation and Cell Entrapment,"We study the formation and dynamics of dipolar rings composed by microscopic
ferromagnetic ellipsoids, which self-assemble in water by switching the
direction of the applied field. We show how to manipulate these fragile
structures and control their shape via application of external static and
oscillating magnetic fields. We introduce a theoretical framework which
describes the ring deformation under an applied field, allowing to understand
the underlying physical mechanism. Our microscopic rings are finally used to
capture, entrap and later release a biological cell via magnetic command, i.e.
performing a simple operation which can be implemented in other microfluidic
devices which make use of ferromagnetic particles.",1604.03895v2
2016-04-20,Ultrafast and gigantic spin injection in semiconductors,"The injection of spin currents in semiconductors is one of the big challenges
of spintronics. Motivated by the ultrafast demagnetisation and spin injection
into metals, we propose an alternative femtosecond route based on the laser
excitation of superdiffusive spin currents in a ferromagnet such as Ni. Our
calculations show that even though only a fraction of the current crosses the
Ni-Si interface, the laser-induced creation of strong transient electrical
fields at a ferromagnet-semiconductor interface allows for the injection of
chargeless spin currents with a record spin polarisations of 80%. Beyond that
they are pulsed on the time scale of 100 femtoseconds which opens the door for
new experiments and ultrafast spintronics.",1604.05882v1
2016-04-22,Swift thermal steering of domain walls in ferromagnetic MnBi stripes,"We predict a fast domain wall (DW) motion induced by a thermal gradient
across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an
exchange torque fueled by magnon accumulation at the DWs. Depending on the
thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions
are possible. The finding unveils an energy efficient way to manipulate DWs as
an essential element in magnetic information processing such as racetrack
memory.",1604.06575v1
2016-04-28,Ferromagnetism and d+id superconductivity in 1/2 doped correlated systems on triangular lattice,"We investigate the quantum phase diagram of t-J model on triangular lattice
at 1/2 doping with various lattice sizes by using a combination of density
matrix renormalization group (DMRG), variational Monte Carlo and quantum field
theories. To sharply distinguish different phases, we calculated the symmetry
quantum numbers of the ground state wave functions, and the results are further
confirmed by studying correlation functions. Our results show there is a first
order phase transition from ferromagnetism to d+id superconductivity, with the
transition taking place at $J/t=0.4\pm0.2$.",1604.08615v1
2016-06-08,Magnetic energy of sc ferromagnetic films with three layers as described by third order perturbed Heisenberg Hamiltonian,"The solution of third order perturbed Heisenberg Hamiltonian of simple cubic
ferromagnetic ultra-thin films with three layers were found. All the magnetic
energy parameters such as spin exchange interaction, magnetic dipole
interaction, second order magnetic anisotropy, fourth order magnetic
anisotropy, applied magnetic field, demagnetization factor and stress induced
anisotropy were included in the third order perturbed Heisenberg Hamiltonian.
3-D plots of stress induced anisotropy, out of plane magnetic field,
demagnetization factor and spin exchange interaction are presented in this
manuscript. Magnetic easy and hard directions were determined using these 3-D
plots. MATLAB program was employed to solve the equation with seven parameters.",1606.02439v1
2016-06-27,Spin wave power flow and caustics in ultrathin ferromagnets with the Dzyaloshinskii-Moriya interaction,"The Dzyaloshinskii-Moriya interaction in ultrathin ferromagnets can result in
nonreciprocal propagation of spin waves. We examine theoretically how spin wave
power flow is influenced by this interaction. We show that the combination of
the dipole-dipole and Dzyaloshinskii-Moriya interactions can result in
unidirectional caustic beams in the Damon-Eshbach geometry. Morever,
self-generated interface patterns can also be induced from a point-source
excitation.",1606.08159v2
2016-07-05,Fluctuations of the free energy of the spherical Sherrington-Kirkpatrick model with ferromagnetic interaction,"We consider a spherical spin system with pure 2-spin spherical
Sherrington-Kirkpatrick Hamiltonian with ferromagnetic Curie-Weiss interaction.
The system shows a two-dimensional phase transition with respect to the
temperature and the coupling constant. We compute the limiting distributions of
the free energy for all parameters away from the critical values. The zero
temperature case corresponds to the well-known phase transition of the largest
eigenvalue of a rank 1 spiked random symmetric matrix. As an intermediate step,
we establish a central limit theorem for the linear statistics of rank 1 spiked
random symmetric matrices.",1607.01089v2
2016-07-13,Demagnetization factor dependence of energy of thick ferromagnetic films,"Second order perturbed Heisenberg Hamiltonian was employed to study the
variation of energy of ferromagnetic thick films with demagnetization factor.
Under the influence of demagnetization factor given by =6.6, the sc(001) film
with 10000 layers can be easily oriented in 0.6 radians direction for the
values of energy parameters used in this report. Easy direction of thick
fcc(001) film with 10000 layers was determined at 0.66 radians, when the
demagnetization factor is given by =2.6. The energy of sc(001) thick film is
larger than that of fcc(001) thick film. But the energy curve of fcc(001) thick
film is smoother than that of sc(001).",1607.03590v1
2016-07-29,Ferromagnetic detection of moduli dark matter,"We propose a scheme to detect light scalar moduli dark matter, based on
measuring the change of magnetization induced in a macroscopic hard
ferromagnet. Our method can probe moduli dark matter at the natural coupling to
the electron mass over several orders of magnitude in the moduli mass. The most
attracting feature of the proposed approach, compared to mechanical ones, is
that it relies on a nonresonant detection, allowing to probe a much wider
region of the parameter space. This is a crucial point, as long as the theory
is not able to predict the moduli mass.",1607.08824v1
2016-09-07,Magnetic decoupling of ferromagnetic metals through a graphene spacer,"We study the magnetic coupling between different ferromagnetic metals (FMs)
across a graphene (G) layer, and the role of graphene as a thin covalent
spacer. Starting with G grown on a FM substrate (Ni or Co), we deposit on top
at room temperature different FM metals (Fe, Ni, Co). By measuring the dichroic
effect of 3p photoemission lines we detect the magnetization of the substrate
and the sign of the exchange coupling in FM overlayer at room temperature. We
show that the G layer magnetically decouples the FM metals.",1609.01861v1
2016-09-27,Multiferroic Bi$_2$NiMnO$_6$ Thin Films: A Computational Prediction,"We report first-principles calculations for one of the few materials that is
believed to be a ferroelectric ferromagnet, Bi$_2$NiMnO$_6$. Our calculations
show that, contrary to what it has been reported so far, bulk Bi$_2$NiMnO$_6$
does not have a polarization. Instead, like BiMnO$_3$, it crystallizes into a
centrosymmetric structure with space group $C2/c$. We also predict that
Bi$_2$NiMnO$_6$ will indeed be a ferroelectric ferromagnet if it is grown as an
epitaxial film on a substrate with in-plane square symmetry and a lattice
constant around 4~\AA, such as BaTiO$_3$ or PbZr$_{1-x}$Ti$_{x}$O$_{3}$.",1609.08246v1
2016-10-03,Anomalous Thermal Hall Effect in a Disordered Weyl Ferromagnet,"We investigate the electric and thermal transport properties in a disordered
Weyl ferromagnet on an equal footing by using the Keldysh formalism in curved
spacetime. In particular, we calculate the anomalous thermal Hall conductivity,
which consists of the Kubo formula and the heat magnetization, without relying
on the Wiedemann-Franz law. We take nonmagnetic impurities into account within
the self-consistent $T$-matrix approximation and reproduce the Wiedemann-Franz
law for the extrinsic Fermi-surface and intrinsic Fermi-sea terms,
respectively. This is the first step towards a unified theory of the anomalous
Hall effect at finite temperature, where we should take into account both
disorder and interactions.",1610.00390v2
2016-10-18,Engineering Curvature Induced Anisotropy in Thin Ferromagnetic Films,"The large curvature effects on micromagnetic energy of a thin ferromagnetic
film with nonlocal dipolar energy are considered. We predict that the dipolar
interaction and surface curvature can produce perpendicular anisotropy which
can be controlled by engineering a special type of periodic surface shape
structure. Similar effects can be achieved by a significant surface roughness
in the film. We show that in general the anisotropy can point in an arbitrary
direction depending on the surface curvature. We provide simple examples of
these periodic surface structures to demonstrate how to engineer particular
anisotropies in the film.",1610.05574v1
2017-02-08,Annihilation of Domain Walls in a Ferromagnetic Wire,"We study the annihilation of topological solitons in the simplest setting: a
one-dimensional ferromagnet with an easy axis. We develop an effective theory
of the annihilation process in terms of four collective coordinates: two zero
modes of the translational and rotational symmetries $Z$ and $\Phi$,
representing the average position and azimuthal angle of the two solitons, and
two conserved momenta $\zeta$ and $\varphi$, representing the relative distance
and twist. Comparison with micromagnetic simulations shows that our approach
captures well the essential physics of the process.",1702.02248v1
2017-02-15,Pressure-induced insulator-metal transition in EuMnO3,"We study the influence of external pressure on the electronic and magnetic
structure of EuMnO3 from first-principles calculations. We find a
pressure-induced insulator-metal transition at which the magnetic order changes
from A-type antiferromagnetic to ferromagnetic with a strong interplay with
Jahn-Teller distortions. In addition, we find that the non-centrosymmetric
E*-type antiferromagnetic order can become nearly degenerate with the
ferromagnetic ground state in the high-pressure metallic state. This situation
can be exploited to promote a magnetically-driven realization of a
non-centrosymmetric (ferroelectric) metal.",1702.04607v2
2017-02-16,Domain wall nucleation in ferromagnetic nanowire with perpendicular magnetization stimulated by stray field of V-shaped magnetic particle,"We report the results of micromagnetic simulations of domain wall (DW)
nucleation and pinning/depinning processes in ferromagnetic planar structure
consisting of nanowire (NW) with perpendicular anisotropy and special V-shaped
nanoparticle (NP) with in-plane anisotropy located on top of NW. The
magnetization reversal features of this system in an external magnetic field
are investigated depending on the direction of particle magnetic moment.
Possible variants of magnetic logic cells (LCs) based on such system are
discussed.",1702.05416v1
2017-02-14,Exact and approximate analytical solutions of Weiss equation of ferromagnetism and their experimental relevance,"The recent progress in the theory of generalized Lambert functions makes
possible to solve exactly the Weiss equation of ferromagnetism. However, this
solution is quite inconvenient for practical purposes. Precise approximate
analytical solutions are obtained, giving the temperature dependence of the
spontaneous magnetization, and also the dependence of the magnetization on both
temperature and external magnetic field. The experimental relevance of these
results, mainly for the determination of the Curie temperature, is discussed.",1702.07225v1
2017-08-05,Magnetization reversal of thin ferromagnetic elements with surface anisotropy,"The magnetization reversal process in thin-film ferromagnetic elements with
surface anisotropy of various shapes and sizes is investigated by means of
numerical simulation. The dependence of the perpendicular and in-plane
hysteresis loops on the element thickness and the value of the surface
anisotropy constant is obtained. For sufficiently large values of the surface
anisotropy constant the magnetization reversal of thin-film elements is shown
to occur due to the nucleation of the buckling mode. For an elongated
rectangular element the nucleation field of the buckling mode is proportional
to the absolute value of the surface anisotropy constant, and inversely
proportional to the element thickness.",1708.01802v1
2017-08-07,Exact description of paramagnetic and ferromagnetic phases of an Ising model on a third-order Cayley tree,"In this paper we analytically study the recurrence equations of an Ising
model with three competing interactions on a Cayley tree of order three. We
exactly describe paramagnetic and ferromagnetic phases of the Ising model. We
obtain some rigorous results: critical temperatures and curves, number of
phases, partition function. Ganikhodjaev et al. [J. Concrete and Applicable
Mathematics, 9 (1), 26-34 (2011)] have numerically studied the Ising model on a
second-order Cayley tree. We compare the numerical results to exact solutions
of mentioned model.",1708.02585v1
2017-08-10,Electron transport in magnetic tunnel junctions -- a theoretical study of lattice and continuum models,"Magnetic tunnel junctions comprising of an insulator sandwiched between two
ferromagnetic films are the simplest spintronic devices. Theoretically, these
can be modeled by a metallic Hamiltonian in both the lattice and the continuum
with an addition of Zeeman field. We calculate conductance at arbitrary
orientations of the easy axes of the two ferromagnets. When mapped, the lattice
and the continuum models show a discrepancy in conductance in the limit of a
large Zeeman field. We resolve the discrepancy by modeling the continuum theory
in an appropriate way.",1708.03161v2
2017-08-28,Evidence for field induced proximity type behavior in ferromagnetic nanofluid,"We report some unusual magnetic properties observed in CoFe2O4 based
ferrofluid (with an average particle size of D = 6 nm). More precisely, in
addition to the low-field ferromagnetic (FM) phase transition with an intrinsic
Curie temperature T_Cb=350K, a second phase transition with an extrinsic Curie
temperature T_Cw = 266K emerges at higher (saturating) magnetic field. The
transitions meet at the crossover point T_cr = 210 K. The origin of the second
transition is attributed to magnetic field induced proximity type interaction
between FM particles through non-FM layers.",1708.08373v1
2018-02-01,Exploring the diluted ferromagnetic p-spin model with a Cavity Master Equation,"We introduce a new solution to Glauber multi-spin dynamics on random graphs.
The solution is based on the recently introduced Cavity Master Equation (CME),
a time-closure turning the in principle exact Dynamic Cavity Method into a
practical method of analysis and of fast simulation.
  Running CME once is of comparable computational complexity as one Monte Carlo
run on the same problem. We show that CME correctly models the ferromagnetic
$p$-spin Glauber dynamics from high temperatures down to and below the
spinoidal transition. We also show that CME allows a novel exploration of the
low-temperature spin-glass phase of the model.",1802.00298v1
2018-02-06,Nonlinear heat transport in ferromagnetic-quantum dot-superconducting systems,"We analyze the heat current traversing a quantum dot sandwiched between a
ferromagnetic and a superconducting electrode. The heat flow generated in
response to a voltage bias presents rectification as a function of the gate
potential applied to the quantum dot. Remarkably, in the thermally driven case
the heat shows a strong diode effect with large asymmetry ratios that can be
externally tuned with magnetic fields or spin-polarized tunneling. Our results
thus demonstrate the importance of hybrid systems as promising candidates for
thermal applications.",1802.02024v1
2018-04-12,Peculiar magnetic properties of NC6 and NC12 layered compounds from first principles,"In the context of characterizing nitrogen poor carbo-nitrides for different
applications, identification of an unusual onset of spin polarization of N(p)
states has been shown. A full saturation up to 3 Bohr magnetons is demonstrated
in extended two-dimensional carbon networks of C6N and C12N hexagonal
structures refined based on density functional theory calculations. From
establishing the energy-volume equations of states in both compounds assuming
spin degenerate (non spin polarized) and spin-polarized configurations, the
ground state is identified as ferromagnetic. The variation of magnetization
with volume points to strongly ferromagnetic behavior",1804.04441v1
2018-11-06,Quantized Josephson phase battery,"A ferromagnetic Josephson junction with a spin-flipper (magnetic impurity)
sandwiched in-between acts as a phase battery that can store quantized amounts
of superconducting phase difference $\Phi_0$ in the ground state of the
junction. Moreover, for such $\Phi_0$-Josephson junction anomalous Josephson
current appears at zero phase difference. We study the properties of this
quantum spin-flip scattering induced anomalous Josephson current, especially
its tun-ability via misorientation angle between two Ferromagnets.",1811.02484v2
2018-11-22,Studying of the interlayer interaction in magnetic multilayers (FM/I/FM) measuring the FMR peak asymmetry,"We experimentally study the interlayer interaction in a magnetic multilayer
system ferromagnet/insulator/ferromagnet with different spacer thickness. We
demonstrate that the sign and the magnitude of the interaction can be deduced
from the FMR peak shape rather than from the FMR peak shift. The proposed
technique allows studying the interlayer interaction using a single sample
(without a reference sample for comparison).",1811.09228v1
2019-05-23,Devil's staircase structures in $\varphi_{0}$ junction,"The superconductor-ferromagnet-superconductor $\varphi_{0}$ junction provides
a direct coupling between Josephson phase and magnetic moment of ferromagnetic
barrier. We demonstrate an appearance of additional fractional subharmonic
steps in the IV-characteristics of $\varphi_{0}$ junction under external
electromagnetic radiation due to spin-orbit coupling. An origin of subharmonic
steps is related to the locking of magnetic moment precession to the Josephson
oscillations. We prove that the positions of those steps follow a continued
fraction algorithm.",1905.09672v1
2020-07-06,Spin-flip excitations and Stoner ferromagnetism in a strongly correlated quantum Hall system,"Spin-flip excitations in a quantum Hall electron system at fixed filling
factor nu=2 are modelled and studied under conditions of a strong Coulomb
interaction when the `Landau level mixing' is a dominant factor determining the
excitation energy. The `one-exciton' approach used for the purely electronic
excitations in question allows us to describe the Stoner transition from the
unpolarized/paramgnet state to the polarized/ferromagnet one. The theoretical
results are compared with the available experimental data.",2007.02827v1
2020-07-27,Electric-Field-Induced Antiferromagnetic Insulating State in a Metallic Ferromagnet,"We show that a static electric field induces the transition from a
ferromagnetic metal to an antiferromagnetic insulator owing to the Bloch
oscillation of conduction electrons. In the steady state, the electric current
is inversely proportional to the applied electric field, implying the
nonperturbative insulating nature that is different from the Wannier-Stark
localization. Possible experimental realization based on recent terahertz pulse
sources is discussed.",2007.13720v1
2010-05-11,A spin quantum bit with ferromagnetic contacts for circuit QED,"We theoretically propose a scheme for a spin quantum bit based on a double
quantum dot contacted to ferromagnetic elements. Interface exchange effects
enable an all electric manipulation of the spin and a switchable strong
coupling to a superconducting coplanar waveguide cavity. Our setup does not
rely on any specific band structure and can in principle be realized with many
different types of nanoconductors. This allows to envision on-chip single spin
manipulation and read-out using cavity QED techniques.",1005.1901v2
2010-05-12,Kinetics of precessing ball solitons in ferromagnet at the first-order transition,"The fundamentals of precessing ball solitons (PBS) arising as a result of the
energy fluctuations at the first-order phase transition induced by a magnetic
field in ferromagnets with uniaxial anisotropy are presented. When external
magnetic field is anti-parallel to the magnetization direction of the crystal,
PBS states are possible in a wide range of amplitudes and energies, including
the positive and negative energy relative to an initial condition. PBS are born
with the greatest probability at near-zero energy, i.e. near the bifurcation
point. Evolution of the PBS, at which they transform into macroscopic domains
of a new magnetic phase or into quasi-equilibrium solitonic state, is analyzed.",1005.2054v1
2010-05-12,Ferromagnetism without flat bands in thin armchair nanoribbons,"Describing by a Hubbard type of model a thin armchair graphene ribbon in the
armchair hexagon chain limit, one shows in exact terms, that even if the system
does not have flat bands at all, at low concentration a mesoscopic sample can
have ferromagnetic ground state, being metallic in the same time. The mechanism
is connected to a common effect of correlations and confinement.",1005.2126v1
2010-05-13,Ferromagnetic spinel CuCr2Se4 studied by Raman spectroscopy and lattice dynamics calculations,"The lattice dynamics of the ferromagnetic spinel CuCr2Se4 (Tc = 430K) was
studied experimentally by measuring the Raman spectra and theoretically by
calculation of zone center phonon frequencies within a shell model. All Raman
allowed modes (A1g + E_g + 3F2g) were identified and assigned to specific
atomic motions. The relative intensity of the Raman lines varies strongly with
excitation photon energy between 1.58 and 2.71 eV, but no significant phonon
anomalies are observed near Tc.",1005.2245v1
2010-05-24,The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge,"In the present work, we have prepared Mn-doped Ge using different annealing
approaches after Mn ion implantation, and obtained samples with hole
concentrations ranging from 10^18 to 2.1x10^20 cm^-3, the latter being the
highest reported so far. Based on the magnetotransport properties of Mn doped
Ge, we argue that the hole concentration is a decisive parameter in
establishing carrier-mediated ferromagnetism in magnetic Ge.",1005.4325v1
2010-05-26,Ferromagnetism in the Highly-Correlated Hubbard Model,"The Hubbard model with strong correlations is treated in the many-electron
representation of Hubbard's operators. The regions of stability of saturated
and non-saturated ferromagnetism in the n-U plane for the square and simple
cubic lattices are calculated. The role of the bare density of states
singularities for the magnetic phase diagram is discussed. A comparison with
the results of previous works is performed.",1005.4795v1
2013-08-01,Topological States in Ferromagnetic CdO/EuO Superlattices and Quantum Wells,"Based on ab initio calculations, we demonstrate that the ferromagnetic
CdO/EuO superlattice is a simple Weyl semimetal with two linear Weyl nodes in
the Brillouin zone, and the corresponding CdO/EuO quantum well realizes the
stichometric quantum anomalous Hall state without random magnetic doping. In
addition, a simple effective model is presented to describe the basic mechanism
of spin polarized band inversion in this system.",1308.0349v3
2013-08-14,Ising models on the Regularized Apollonian Network,"We investigate the critical properties of Ising models on a Regularized
Apollonian Network (RAN), here defined as a kind of Apollonian Network (AN) in
which the connectivity asymmetry associated to its corners is removed.
Different choices for the coupling constants between nearest neighbors are
considered, and two different order parameters are used to detect the critical
behaviour. While ordinary ferromagnetic and anti-ferromagnetic models on RAN do
not undergo a phase transition, some anti-ferrimagnetic models show an
interesting infinite order transition. All results are obtained by an exact
analytical approach based on iterative partial tracing of the Boltzmann factor
as intermediate steps for the calculation of the partition function and the
order parameters.",1308.3259v1
2013-08-26,Ferromagnetic spin-orbital liquid of dipolar fermions in zigzag lattices,"Two-component dipolar fermions in zigzag optical lattices allow for the
engineering of spin-orbital models. We show that dipolar lattice fermions
permit the exploration of a regime typically unavailable in solid-state
compounds that is characterized by a novel spin-liquid phase with a finite
magnetization and spontaneously broken SU(2) symmetry. This peculiar spin
liquid may be understood as a Luttinger liquid of composite particles
consisting of bound states of spin waves and orbital domain walls moving in an
unsaturated ferromagnetic background. In addition, we show that the system
exhibits a boundary phase transitions involving non-local entanglement of edge
spins.",1308.5519v1
2013-08-29,Optimal interface doping at La_2/3Sr_1/3MnO_3/SrTiO_3(001) heterojunctions for spintronic applications,"We examine, by means of ab initio pseudopotential calculations,
La_2/3Sr_1/3MnO_3/SrTiO_3 (LSMO/STO) heterojunctions in which one unit layer of
La_(1-x)Sr_xMnO_3 (with 0<x<1) is inserted at the interface. The optimal
interlayer doping x for a robust interface ferromagnetism is investigated by
considering the energy differences between antiferromagnetic and ferromagnetic
alignment of the MnO_2-interface layer relative to bulk LSMO. The optimal
doping is found to be close to x=1/3, which corresponds to an abrupt TiO_2
(001)-layer termination of STO. This is also the composition which gives the
largest p-type Schottky barrier height in our calculations.",1308.6400v1
2014-03-03,Magnetic entropy change and critical exponents in double perovskite Y2NiMnO6,"We report on the magnetic entropy change and the critical exponents in the
double perovskite manganite Y2NiMnO6 with a ferromagnetic to paramagnetic
transition TC=85K. For a magnetic field change of 80kOe, a maximum magnetic
entropy change -6.57 J /kg K is recorded around TC. The corresponding relative
cooling power (134 J / kg) is appreciable towards potential application as a
magnetic refrigerant. The critical exponents, beta and gamma satisfy well to
values derived for a 3D Heisenberg ferromagnet.",1403.0453v1
2014-03-21,Electrical tuning of spin current in a boron nitride nanotube quantum dot,"Controlling spin current and magnetic exchange coupling by applying an
electric field and achieving high spin injection efficiency at the same time in
a nanostructure coupled to ferromagnetic electrodes have been the outstanding
challenges in nanoscale spintronics. A relentless quest is going on to find new
low dimensional materials with tunable spin dependent properties to address
these challenges. Herein, we predict, from first principles, the transverse
electric field induced switching in the sign of exchange coupling and tunnel
magnetoresistance in a boron nitride nanotube quantum dot attached to
ferromagnetic nickel contacts.",1403.5526v1
2014-03-23,"Spin-polarized electron transport in the high-pressure ferromagnetic phases (GaSb)$_2$M (M=Cr,Mn)","For the first time magnetrotransport of the ferromagnetic high-pressure
phases of (GaSb)$_2$M (M=Cr,Mn) was measured. It was found that the main
component of magnetotransport in these phases is negative and its amplitude is
increasing with temperature rising and approaching Curie temperature. Measuring
of magnetoresistance in the cycling magnetic fields demonstrated that the
Yosida component of magnetresistance is negligible and the main part of the
magnetoresistance can be attributed to the spin-polarized electron transport.",1403.5737v1
2014-03-26,Driving ferromagnets into a critical region of a magnetic phase diagram,"Exciting a ferromagnetic sample with an ultrashort laser pulse leads to a
quenching of the magne- tization on a subpicosecond timescale. On the basis of
the equilibration of intensive thermodynamic variables we establish a powerful
model to describe the demagnetization dynamics. We demonstrate that the
magnetization dynamics is mainly driven by the equilibration of chemical
potentials. The minimum of magnetization is revealed as a transient electronic
equilibrium state. Our method iden- tifies the slowing down of ultrafast
magnetization dynamics by a critical region within a magnetic phase diagram.",1403.6885v2
2014-03-31,Phase Transitions in Ferromagnetic Ising Models with spatially dependent magnetic fields,"In this paper we study the nearest neighbor Ising model with ferromagnetic
interactions in the presence of a space dependent magnetic field which vanishes
as $|x|^{-\alpha}$, $\alpha >0$, as $|x|\to \infty$. We prove that in
dimensions $d\ge 2$ for all $\beta$ large enough if $\alpha>1$ there is a phase
transition while if $\alpha<1$ there is a unique DLR state.",1403.7961v3
2016-07-17,Magnetic anisotropy dependence of the energy of oriented thick ferromagnetic films,"Heisenberg Hamiltonian was employed to describe the variation of energy of
thick ferromagnetic films with second and fourth order anisotropies. At angle
of 1.36 degrees and anisotropies of 1.25, energy is minimum for thick film of
sc(001) with 1000 layers. Energy becomes minimum at angle of 1.18 degrees and
fourth order anisotropy of 1.15 for thick film of bcc(001) with the same
thickness. According to these simulations, these lattices can be easily
oriented in some certain directions under the influence of some particular
values of anisotropies. Energy varies with second and fourth order anisotropies
in similar passion for both types of lattices. The energy gradually decreases
with second and fourth order anisotropy for both types of lattices in the range
described here.",1611.02227v1
2016-11-11,Incommensurate spiral order from double exchange interactions,"The double exchange model describing interactions of itinerant electrons with
localized spins is usually used to explain ferromagnetism in metals. We show
that for a variety of crystal lattices of different dimensionalities and for a
wide range of model parameters the ferromagnetic state is unstable against a
non-collinear spiral magnetic order. We revisit the phase diagram of the double
exchange model on a triangular lattice and show in a large part of the diagram
the incommensurate spiral state has a lower energy than the previously
discussed commensurate states. These results indicate that double exchange
systems are inherently frustrated and can host unconventional spin orders.",1611.03689v2
2016-11-15,Coarsening and percolation in a disordered ferromagnet,"By studying numerically the phase-ordering kinetics of a two-dimensional
ferromagnetic Ising model with quenched disorder -- either random bonds or
random fields -- we show that a critical percolation structure forms in an
early stage and is then progressively compactified by the ensuing coarsening
process. Results are compared with the non-disordered case, where a similar
phenomenon is observed, and interpreted within a dynamical scaling framework.",1611.04828v1
2016-11-26,Universal Depinning Transition of Domain Walls in Ultrathin Ferromagnets,"We present a quantitative and comparative study of magnetic field driven
domain wall depinning transition in different ferromagnetic ultrathin films
over a wide range of temperature. We reveal a universal scaling function
accounting for both drive and thermal effects on the depinning transition,
including critical exponents. The consistent description we obtain for both the
depinning and subthreshold thermally activated creep motion should shed light
on the universal glassy dynamics of thermally fluctuating elastic objects
pinned by disordered energy landscapes.",1611.08701v2
2017-01-16,Lateral ferromagnetic domain control in Cr2O3/Pt/Co positive exchange bias system,"We investigated the perpendicular exchange bias (PEB) switching from
negative- to positive-exchange bias state for Cr2O3/Pt/Co exchange coupling
thin film system exhibiting positive exchange bias phenomena. By changing Pt
spacer layer thickness or measurements temperature, we demonstrated the control
of two kind of intermediate state of the switching; the double hysteresis loop
indicating local, non-averaged PEB, and single hysteresis loop indicating
averaged PEB. We proposed the way to control the lateral ferromagnetic domain
though the control of PEB magnitude.",1701.04252v1
2017-01-16,Asymptotic behaviour of ground states for mixtures of ferromagnetic and antiferromagnetic interactions in a dilute regime,"We consider randomly distributed mixtures of bonds of ferromagnetic and
antiferromagnetic type in a two-dimensional square lattice with probability
$1-p$ and $p$, respectively, according to an i.i.d. random variable. We study
minimizers of the corresponding nearest-neighbour spin energy on large domains
in ${\mathbb Z}^2$. We prove that there exists $p_0$ such that for $p\le p_0$
such minimizers are characterized by a majority phase; i.e., they take
identically the value $1$ or $-1$ except for small disconnected sets. A
deterministic analogue is also proved.",1701.04482v1
2017-04-07,Realization of Quantum Anomalous Hall Effect in Graphene from \textit{n}-\textit{p} Codoping Induced Stable Atomic-Adsorption,"Using first-principles calculation methods, we study the possibility of
realizing quantum anomalous Hall effect in graphene from stable
3\textit{d}-atomic adsorption via charge-compensated \textit{n}-\textit{p}
codoping scheme. As concrete examples, we show that long-range ferromagnetism
can be established by codoping 3\textit{d} transition metal and boron atoms,
but only the Ni codopants can open up a global bulk gap to harbour the quantum
anomalous Hall effect. Our estimated ferromagnetic Curie transition temperature
can reach over 10 Kelvin for various codoping concentrations.",1704.02085v1
2017-04-14,How experimentally to detect a solitary superconductivity in dirty ferromagnet-superconductor trilayers?,"We theoretically study the proximity effect in the thin-film layered
ferromagnet (F) - superconductor (S) heterostructures in F$_1$F$_2$S design. We
consider the boundary value problem for the Usadel-like equations in the case
of so-called ""dirty"" limit. The ""latent"" superconducting pairing interaction in
F layers taken into account. The focus is on the recipe of experimental
preparation the state with so-called solitary superconductivity. We also
propose and discuss the model of the superconducting spin valve based on
F$_1$F$_2$S trilayers in solitary superconductivity regime.",1704.04453v1
2017-04-20,Domain percolation in a quenched ferromagnetic spinor condensate,"We show that the easy-axis (EA) magnetic domains formed in a quenched
ferromagnetic spinor condensate are described by percolation theory. We
introduce a generalized spin rotation to vary the proportion of positive and
negative EA domains, allowing us to explore domain percolation. Using
simulations we investigate the finite-size scaling behaviour to extract the
correlation length critical exponent and the transition point. We analyse the
sensitivity of our results to the early-time dynamics of the system, the
quadratic Zeeman energy, and the threshold condition used to define the
positive (percolating) domains.",1704.06332v2
2017-04-22,Boron Triangular Kagome Lattice with Half-Metallic Ferromagnetism,"Based on the first-principles evolutionary materials design, we report a
stable boron Kagome lattice composed of triangles in triangles on a
two-dimensional sheet. The Kagome lattice can be synthesized on a silver
substrate, with selecting Mg atoms as guest atoms. While the isolated Kagome
lattice is slightly twisted without strain, it turns into an ideal triangular
Kagome lattice under tensile strain. In the triangular Kagome lattice, we find
the exotic electronic properties, such as topologically non-trivial flat band
near the Fermi energy and half-metallic ferromagnetism, and predict the quantum
anomalous Hall effect in the presence of spin-orbit coupling.",1704.06842v2
2018-05-03,"Exact Intrinsic Localized Excitation of an Anisotropic Ferromagnetic Spin Chain in External Magnetic Field with Gilbert Damping, Spin Current and PT-Symmetry","We obtain the exact one-spin intrinsic localized excitation in an anisotropic
Heisenberg ferromagnetic spin chain in a constant/variable external magnetic
field with Gilbert damping included. We also point out how an appropriate
magnitude spin current term in a spin transfer nano-oscillator (STNO) can
stabilize the tendency towards damping. Further, we show how this excitation
can be sustained in a recently suggested PT-symmetric magnetic nanostructure.
We also briefly consider more general spin excitations.",1805.01230v1
2008-07-11,Breakdown of half-metallic ferromagnetism in zinc-blende II-V compounds,"We investigated the electronic and magnetic properties of a series of
zinc-blend II-V compounds by carrying out density-functional-theory
calculations including spin-orbit couplings. Contrary to the case of CaN and
CaP, the half-metallic characteristics of the II-V compounds such as CaSb and
CaBi were found to be destroyed. Our analysis of the valence band structures of
CaAs, CaSb, and CaBi revealed a critical role of the spin-orbit coupling
interactions on the exchange-split band structure, thereby leading to breakdown
of the half-metallic ferromagnetism for the systems with heavier group V
elements in the zinc-blend II-V compounds.",0807.1778v1
2008-07-29,Thermally activated Peierls dimerization in ferromagnetic spin chains,"We demonstrate that a Peierls dimerization can occur in ferromagnetic spin
chains activated by thermal fluctuations. The dimer order parameter and
entanglement measures are studied as functions of the modulation of the
magnetic exchange interaction and temperature, using a spin-wave theory and the
density-matrix renormalization group. We discuss the case where a periodic
modulation is caused by spin-phonon coupling and the case where electronic
states effectively induce such a modulation. The importance of the latter for a
number of transition metal oxides is highlighted.",0807.4693v1
2009-12-07,Thermoelectric spin diffusion in a ferromagnetic metal,"We present a semiclassical theory of spin-diffusion in a ferromagnetic metal
subject to a temperature gradient. Spin-flip scattering can generate pure
thermal spin currents by short-circuiting spin channels while suppressing spin
accumulations. A thermally induced spin density is locally generated when the
energy dependence of the density of states is spin polarized.",0912.1213v1
2009-12-09,Microscopic Theory of Current-Spin Interaction in Ferromagnets,"Interplay between magnetization dynamics and electric current in a conducting
ferromagnet is theoretically studied based on a microscopic model calculation.
First, the effects of the current on magnetization dynamics (spin torques) are
studied with special attention to the ""dissipative"" torques arising from
spin-relaxation processes of conduction electrons. Next, an analysis is given
of the ""spin motive force"", namely, a spin-dependent 'voltage' generation due
to magnetization dynamics, which is the reaction to spin torques. Finally, an
attempt is presented of a unified description of these effects.",0912.1676v1
2009-12-28,Notes on ferromagnetic diluted P-spin model,"In this paper we develop the interpolating cavity field technique for the
mean field ferromagnetic p-spin. The model we introduce is a natural extension
of the diluted Curie-Weiss model to p>2 spin interactions. Several properties
of the free energy are analyzed and, in particular, we show that it recovers
the expressions already known for p=2 models and for p>2 fully connected
models. Further, as the model lacks criticality, we present extensive numerical
simulations to evidence the presence of a first order phase transition and
deepen the behavior at the transition line. Overall, a good agreement is
obtained among analytical results, numerics and previous works.",0912.5173v1
2009-12-29,"Synthesis, characterization and magnetic properties of room-temperature nanofluid ferromagnetic graphite","We report the chemical synthesis route, structural characterization, and
physical properties of nanofluid magnetic graphite (NFMG) obtained from the
previously synthesized bulk organic magnetic graphite (MG) by stabilizing the
aqueous ferrofluid suspension with an addition of active cationic surfactant.
The measured magnetization-field hysteresis curves along with the temperature
dependence of magnetization confirmed room-temperature ferromagnetism in both
MG and NFMG samples.",0912.5344v1
2011-11-23,Dark solitons in ferromagnetic chains with first- and second-neighbor interactions,"We study the ferromagnetic spin chain with both first- and second-neighbor
interactions. We obtained the condition for the appearance and stability of
bright and dark solitons for arbitrary wave number inside the Brillouin zone.
The influence of the second-neighbor interaction and the anisotropy on the
soliton properties is considered. The scattering of dark solitons from point
defects in the discrete spin chain is investigated numerically.",1111.5477v1
2012-01-03,A universal scaling law of exchange bias training effect,"Exchange bias training effect in ferromagnetic/antiferromagnetic bilayers is
investigated. In some systems the evolution of the exchange bias field $H_E$
with the number of cycle $n$ cannot be fitted by the empirical $1/\sqrt{n}$
function. A unified expression is derived from a discretized Landau-Khalatnikov
equation in the framework of the thermodynamics model which is proposed by Ch.\
Binek. This generalized model describes well training effect independent of the
magnetization reversal mechanism in the ferromagnetic layers.",1201.0620v1
2012-01-10,Time reversal invariant topological superconductivity in correlated non-centrosymmetric systems,"Using functional renormalization group method, we study the favorable
condition for electronic correlation driven time reversal invariant topological
superconductivity in symmetry class DIII. For non-centrosymmetric systems we
argue that the proximity to ferromagnetic (or small wavevector magnetic)
instability can be used as a guideline for the search of this type of
superconductivity. This is analogous to the appearance of singlet
unconventional superconductivity in the neighborhood of antiferromagnetic
instability. We show three concrete examples where ferromagnetic-like
fluctuation leads to topological pairing.",1201.2003v1
2012-01-12,Ferromagnet/Insulator/Ferroelectric nanometer multilayer for multiferroictronics,"We have investigated the field-induced-changes in both the magnetization and
the polarization in ferromagnet/Insulator/ferroelectric (FM/I/FE) multilayer by
following both the Stoner-Wohlfarth (SW) model and the Landau theory. It has
been found that with the stresses introduced in the FM/I/FE structure by the
fields, both the magnetization and the polarization states can be significantly
modified and the combination of their states can be of multiple states. These
results demonstrate the feasibility of combining both the spintronics and the
ferroelectrics into the multiferroictronics.",1201.2527v1
2012-01-26,Thermal switching rate of a ferromagnetic material with uniaxial anisotropy,"The field dependence of the thermal switching rate of a ferromagnetic
material with uniaxial anisotropy was studied by solving the Fokker-Planck
equation. We derived the analytical expression of the thermal switching rate
using the mean first-passage time approach, and found that Brown's formula
[Phys. Rev. 130, 1677 (1963)] is applicable even in the low barrier limit by
replacing the attempt frequency with the proper factor which is expressed by
the error function.",1201.5460v2
2012-04-09,Graphene nanoring as a tunable source of polarized electrons,"We propose a novel spin filter based on a graphene nanoring fabricated above
a ferromagnetic strip. The exchange interaction between the magnetic moments of
the ions in the ferromagnet and the electron spin splits the electronic states,
and gives rise to spin polarization of the conductance and the total electric
current. We demonstrate that both the current and its polarization can be
controlled by a side-gate voltage. This opens the possibility to use the
proposed device as a tunable source of polarized electrons.",1204.1828v1
2012-04-10,Flat-Band Ferromagnetism as a Pauli-Correlated Percolation Problem,"We investigate the location and nature of the para-ferro transition of
interacting electrons in dispersionless bands using the example of the Hubbard
model on the Tasaki lattice. This case can be analyzed as a geometric
site-percolation problem where different configurations appear with nontrivial
weights. We provide a complete exact solution for the 1D case and develop a
numerical algorithm for the 2D case. In two dimensions the paramagnetic phase
persists beyond the uncorrelated percolation point, and the grand-canonical
transition is via a first-order jump to an unsaturated ferromagnetic phase.",1204.2110v2
2012-04-12,Metamagnetism and Weak Ferromagnetism in Nickel (II) oxalate crystals,"Microcrystals of orthorhombic nickel (II) oxalate dihydrate were synthesized
through a precipitation reaction of aqueous solutions of nickel chloride and
oxalic acid. Magnetic susceptibility exhibits a sharp peak at 3.3 K and a
broadrounded maximum near 43 K. We associated the lower maximum with a
metamagnetic transition that occurs when the magnetic field is about \geq 3.5
T. The maximum at 43 K is the typical of 1D antiferromagnets, whereas weak
ferromagnetism behavior was observed in the range of 3.3 to 43 K.",1204.2850v1
2012-04-18,Domain wall heat conductance in ferromagnetic wires,"We present a theoretical study of heat transport in electrically insulating
ferromagnetic wires containing a domain wall. In the regime of validity of
continuum micromagnetism a domain wall is found to have no effect on the heat
conductance. However, spin waves are found to be reflected by domain walls with
widths of a few lattice spacings, which is associated with emergence of an
additional spin wave bound state. The resulting domain wall heat conductance
should be significant for thin films of Yttrium Iron Garnet with sharply
defined magnetic domains.",1204.4008v2
2012-04-21,Ferromagnetism and Antiferromagnetism of Correlated Topological Insulator with Flat Band,"In this paper, based on the mean field approach and
random-phase-approximation, we study the magnetic properties of the spinful
Haldane model on honeycomb lattice of topological flat band with on-site
repulsive Coulomb interaction. We find that the antiferromagnetic (AF) order is
more stable than ferromagnetic (FM) order at (or near) half-filling; while away
from half-filling the phase diagram becomes complex: At large doping, FM order
is more stable than AF order due to the flatness of band structure. In
particular, we find that at quarter filling case, the system becomes a Q=1$
topological insulator which is induced by the FM order.",1204.4766v1
2012-04-21,Collapse of Skyrmions in 2d Ferro- and Antiferromagnets,"Collapse of a skyrmion due to the discreteness of a crystal lattice in
isotropic two-dimensional ferro- and antiferromagnets has been studied
analytically and by numerical solution of equations of motion for up to 2000 x
2000 classical spins on a square lattice coupled via Heisenberg exchange
interaction. Excellent agreement between analytical and numerical results has
been achieved. The lifetime of the skyrmion scales with its initial size,
lambda_0, as(lambda_0/a)^5 in ferromagnets and as (lambda_0/a)^2.15 in
antiferromagnets, with a being the lattice parameter. This makes
antiferromagnetic skyrmions significantly shorter lived than ferromagnetic
skyrmions.",1204.4848v1
2013-09-13,Skyrmion spin texture in ferromagnetic semiconductor-superconductor heterostructures,"We provide a derivation of a spin Skyrmion number classification for
two-dimensional topological superconductors constructed from ferromagnetic and
Rashba spin-orbit coupled semiconductor-superconductor heterostructures. We
show that in the non-trivial topological phase, characterized by a non-zero
Chern number, there is always a topological spin texture in the occupied bands
represented by a Skyrmion number. The Skyrmion number has the advantage of
being both physically intuitive and directly measurable using spin-sensitive
band structure imaging techniques. In addition, we show that the Skyrmion
classification can be extended to the equivalent one-dimensional topological
superconductors.",1309.3411v2
2013-09-13,Tunneling Anisotropic Thermopower and Seebeck Effects in Magnetic Tunnel Junctions,"The Tunneling Anisotropic Magneto-Thermopower (TAMT) and the Tunneling
Anisotropic Spin-Seebeck (TASS) effects are studied for a magnetic tunnel
junction (MTJ) composed of a ferromagnetic electrode, a zinc-blende
semiconductor and a normal metal. We develop a theoretical model for describing
the dependence of a thermally induced tunneling current across the MTJ on the
in-plane orientation of the magnetization in the ferromagnetic layer. The model
accounts for the specific Bychkov-Rashba and Dresselhaus spin-orbit
interactions present in these systems, which are responsible for the $C_{2v}$
symmetry we find in the TAMT and the TASS.",1309.3463v1
2013-09-14,Nonconventional Spin Glass Transition in a Chemically Ordered Pyrochlore,"We report on the study of unusual spin glass properties in the geometrically
frustrated pyrochlore Tb$_{2}$Mo$_{2}$O$_{7}$, $T$$_{g}$$\simeq$24 K. The
analysis of the nonlinear part of dc and complex susceptibilities, near the
glass transition regime, suggests the existence of a statistical distribution
of relaxation times in short-range ordered ferromagnetic clusters. In addition,
the magnetic spins are not sufficiently frozen below the glass transition
temperature; apparently, responsible for the non-equilibrium scaling behavior
of the static critical exponents of nonlinear susceptibilities. Our report is
expected to shed new light in understanding the freezing properties of
frustrated pyrochlores with short range ferromagnetic interactions.",1309.3617v1
2013-09-25,Band structure calculations of Ti\raisebox{-.2ex}{\scriptsize 2}FeSn: a new half-metallic compound,"Within the framework of density functional theory, the electronic structure
and magnetic properties have been studied for the
Ti\raisebox{-.2ex}{\scriptsize 2}FeSn full-Heusler compound. The ferromagnetic
state is found to be energetically more favorable than paramagnetic and
antiferromagnetic states. The spin-polarized results show that
Ti\raisebox{-.2ex}{\scriptsize 2}FeSn compound has half-metallic ferromagnetic
character with a total spin moment of $2 \mu_{B}$ and a band gap in the
minority spin channel of 0.489 eV, at the equilibrium lattice constant a=6.342
A.",1309.6442v1
2013-09-26,"Tuning the metamagnetic transition in the (Co,Fe)MnP system for magnetocaloric purposes","The inverse magnetocaloric effect taking place at the
antiferro-to-ferromagnetic transition of (Co,Fe)MnP phosphides has been
characterized by magnetic and direct {\Delta}Tad measurements. In
Co0.53Fe0.47MnP, entropy change of 1.5 Jkg-1K-1 and adiabatic temperature
change of 0.6 K are found at room temperature for an intermediate field change
({\Delta}B= 1 T). Several methods were used to control the metamagnetic
transition properties, in each case a peculiar splitting of the
antiferro-to-ferromagnetic transition is observed.",1309.6741v1
2013-09-27,Multiferroicity in V-doped PbTiO$_{3}$,"We report \emph{ab initio} predictions on the proper multiferroic
(ferromagnetic, insulating and ferroelectric) character of PbTiO$_{3}$ doped
with vanadium. V impurities coupled ferromagnetically carry a magnetization of
1 $\mu_{\rm B}$ each. The coupling is expected to be strong, since the
paramagnetic solution is higher by 150 meV/vanadium, and no stable
antiferromagnetic solution was found. The electronic gap in the doped system is
about 0.2-0.3 eV in GGA, hence the system is properly multiferroic. V doping
increases the spontaneous polarization in PbTiO$_{3}$, with an approximate
percentual rate of 0.7 $\mu$C/cm$^{2}$.",1309.7205v1
2013-09-28,Superfluid phases of spin-1 bosons in cubic optical lattice,"We analyze theoretically the emergence of different superfluid phases of
spin-1 bosons in a three-dimensional cubic optical lattice by generalizing the
recently developed Ginzburg-Landau theory for the Bose-Hubbard model to a
spinor Bose gas. In particular at zero temperature, our theory distinguishes
within its validity range between various superfluid phases for an
anti-ferromagnetic interaction with an external magnetic field. In addition, we
determine that the superfluid-Mott insulator phase transition is of second
order and that the transitions between the respective superfluid phases with
anti-ferromagnetic interaction can be both of first and second order.",1309.7449v2
2014-05-05,Multigap Superconductivity in the Ferromagnetic Superconductor UCoGe Revealed by Thermal Conductivity Measurements,"We performed thermal conductivity measurements on a single crystal of the
ferromagnetic superconductorUCoGe under magnetic field. Two different
temperature dependencies of the thermal conductivity are observed, for H//b
linear at low magnetic field and quadratic for magnetic field larger than 1
Tesla. At the same field value, a plateau appears in the field dependency of
the residual term of thermal conductivity. Such observations suggest a multigap
superconductivity with a line of nodes in the superconducting gap.",1405.0817v2
2014-05-11,Tuning perpendicular magnetic anisotropy in the MgO/CoFeB/Ta thin films,"Understanding the magnetic anisotropy at ferromagnetic metal/oxide interface
is a fundamental and intriguing subject. Here we propose an approach to
manipulate the strength of perpendicular magnetic anisotropy (PMA) by varying
MgO thickness in the MgO/CoFeB/Ta thin films. We identify that the PMA at the
MgO/CoFeB interface is tuned by the crystalline structure of bulk MgO layer and
decreases dramatically due to the onset of crystalline MgO forming with the
increase of MgO thickness. Our work opens an avenue to manipulate the magnetic
anisotropy by the modification of the ferromagnetic metal/oxide interface.",1405.2551v2
2014-05-18,Monte Carlo Studies of the Ising Antiferromagnet with a Ferromagnetic Mean-field Term,"The unusual thermodynamic properties of the Ising antiferromagnet
supplemented with a ferromagnetic, mean-field term are outlined. This simple
model is inspired by more realistic models of spin-crossover materials. The
phase diagram is estimated using Metropolis Monte Carlo methods, and
differences with preliminary Wang-Landau Monte Carlo results for small systems
are noted.",1405.4553v1
2014-06-16,In-situ microwave characterization of ferromagnetic microwires-filled polymer composites: a review,"This review describes the emerging research area and relevant physics of
polymer-based composites enabled by amorphous ferromagnetic microwires.
Fruitful results ranging from their tunable magnetic field and mechanical
stress properties and influences of direct current on their microwave behavior
are displayed in addition to the brief analysis on the underlying physics. The
multifunctionalities exhibited strongly imply a variety of potential
applications such as structural health monitoring and high-performance sensors.
This article underlines that the future challenge mainly lies in proper
microwire tailoring in expectation of a better microwave performance of
microwire composites",1406.3903v1
2014-06-24,Interaction created effective flat bands in conducting polymers,"For a general class of conducting polymers with arbitrary large unit cell and
different on-site Coulomb repulsion values on different type of sites, I
demonstrate in exact terms the emergence possibility of an upper, interaction
created ""effective"" flat band. This last appears as a consequence of a kinetic
energy quench accompanied by a strong interaction energy decrease, and leads to
a non-saturated ferromagnetic state. This ordered state clearly differs from
the known flat-band ferromagnetism. This is because it emerges in a system
without bare flat bands, requires inhomogeneous on-site Coulomb repulsions
values, and possesses non-zero lower interaction limits at the emergence of the
ordered phase.",1406.6293v1
2014-06-27,Spin-Ordered States in Multilayer Massless Dirac Fermion Systems,"We investigate the spin-ordered states in multilayer massless Dirac fermion
systems under magnetic fields, in which the intralayer interaction is
ferromagnetic owing to the exchange interaction, while the interlayer
interaction is antiferromagnetic arising from the interlayer hopping and the
on-site Coulomb repulsion. The possible spin-ordered states are examined within
the mean field theory, and we apply it to alpha-(BEDT-TTF)2I3, which is a
multilayer massless Dirac fermion system under pressure. In the weak interlayer
coupling regime the system exhibits a ferromagnetically spin-ordered state with
the effective Zeeman g-factor less than two contrasting to that observed in the
single-layer graphene.",1406.7109v1
2015-12-18,Existence of travelling-wave solutions representing domain wall motion in a thin ferromagnetic nanowire,"We study the dynamics of a domain wall under the influence of applied
magnetic fields in a one-dimensional ferromagnetic nanowire, governed by the
Landau--Lifshitz--Gilbert equation. Existence of travelling-wave solutions
close to two known static solutions is proven using
implicit-function-theorem-type arguments.",1512.06016v2
2016-05-02,Majorana fermions at odd junctions in a wire network of ferromagnetic impurities,"We consider a wire network of ferromagnetic impurities on the surface of an
$s$-wave superconductor with strong Rashba spin-orbit interaction. Within the
topological phase, zero-energy Majorana fermions appear at wire end-points as
well as at junctions between an odd number of wire segments, while no
low-energy states are present at junctions between an even number of wire
segments, providing strong experimentally accessible signatures for Majorana
fermions. We also investigate the quasiparticle energy gap with respect to
varying the Rashba spin-orbit coupling and magnetic impurity strength.",1605.00696v1
2016-05-05,Theory of magnon motive force in chiral ferromagnets,"We predict that magnon motive force can lead to temperature dependent,
nonlinear chiral damping in both conducting and insulating ferromagnets. We
estimate that this damping can significantly influence the motion of skyrmions
and domain walls at finite temperatures. We also find that in systems with low
Gilbert damping moving chiral magnetic textures and resulting magnon motive
forces can induce large spin and energy currents in the transverse direction.",1605.01694v2
2016-05-12,Transmission of spin waves in ordered FeRh epitaxial thin films,"We report on B2-ordering dependence of magnetostatic surface spin waves in
ferromagnetic FeRh at room temperature. Spin waves transmit over a distance
longer than 21 {\mu}m in highly ordered FeRh alloys even with relatively large
spin-orbit interaction. The long-range transmission likely arises from the
induced Rh moments of the ordered FeRh due to ferromagnetic exchange
interaction between Fe and Rh. The results indicate a potential of using FeRh
in spintronic and magnonic applications by integrating with other fascinating
magnetic characteristics of FeRh such as electric field induced magnetic phase
transition.",1605.03798v1
2016-08-02,Ferromagnetic Damping/Anti-damping in a Periodic 2D Helical surface; A Non-Equilibrium Keldysh Green Function Approach,"In this paper, we investigate theoretically the spin-orbit torque as well as
the Gilbert damping for a two band model of a 2D helical surface state with a
Ferromagnetic (FM) exchange coupling. We decompose the density matrix into the
Fermi sea and Fermi surface components and obtain their contributions to the
electronic transport as well as the spin-orbit torque (SOT). Furthermore, we
obtain the expression for the Gilbert damping due to the surface state of a 3D
Topological Insulator (TI) and predicted its dependence on the direction of the
magnetization precession axis.",1608.00984v2
2016-08-22,Spin transport in half-metallic ferromagnets,"We theoretically investigate spin transport in half-metallic ferromagnets at
finite temperatures. The side-jump and skew-scattering contributions to spin
Hall conductivity are derived using the Kubo formula. The electron-magnon
interaction causes a finite density of states in the energy gap of the
minority-spin band and induces spin Hall conductivity. We show that spin Hall
conductivity is proportional to $T^{3/2}$, with $T$ being temperature and is
sensitive to $T$. We propose that spin Hall conductivity may be a tool to study
the minority-spin state.",1608.06333v2
2016-12-06,Exceptional magneto-electric coupling and spontaneous electric polarization in anti-ferromagnet Co4Nb2O9,"Synthesis and extensive structural, pyroelectric, magnetic, dielectric and
magneto-electric characterizations are reported for polycrystalline Co4Nb2O9
towards unraveling the multiferroic state especially in reference to the
magnetic spin flop transition. Magnetic measurements confirm the Co4Nb2O9
becomes antiferromagnetic (AFM) at around 28 K but no clear evidence for
spin-flop effect was found. Associated with the magnetic phase transition, a
sharp peak in pyroelectric current indicates the appearance of the strong
magneto-electric coupling below Neel temperature (TN) with a large coupling
constant upto 17.8 uC/m^2T. Using temperature oscillation technique, we
establish Co4Nb2O9 to be a genuine multiferroic with spontaneous electric
polarization in the anti-ferromagnetic state.",1612.01970v1
2016-12-08,"First-principles study on the magnetic properties of ordered Nd$_{6}$(Fe,Ga)$_{14}$ alloys","We studied the stable magnetic structure of ordered Nd$_{6}$Fe$_{14-x}$Ga$_x$
($x = 0, 1)$ alloys, which appears in the grain-boundary (GB) phase of Nd-Fe-B
permanent magnets, using first-principles techniques. Slight Ga doping ($x =
1$) was shown to contribute to the stabilization of an anti-ferromagnetic (AF)
state, whereas the non-doped case ($x = 0$) was revealed to favor ferromagnetic
state rather than AF state with a slight energy difference.",1612.02633v3
2016-12-12,Breakdown of the Nagaoka phase at finite doping,"The Nagaoka ($U=\infty$) limit of the Hubbard model on a square lattice is
mapped onto the itinerant-localized Kondo model at infinitely strong coupling.
Such a model is well suited to perform quantum Monte Carlo (QMC) simulations to
compute spin correlation functions. This model is shown to exhibit no
short-range ferromagnetic (FM) spin correlations at any doping $\delta\ge 0.01$
and finite temperature, $T=0.1t$. Our simulations give no indication that there
is a tendency towards ferromagnetic ordering in the ground state.",1612.03646v2
2016-12-19,Electrically driven magnetic antenna based on multiferroic composites,"We suggest and demonstrate via large scale numerical simulations an
electrically operated spin- wave inducer based on composite multiferroic
junctions. Specifcally, we consider an interfacially coupled
ferromagnetic/ferroelectric structure that emits controllably spin waves in the
ferromagnets if the ferroelectric polarization is poled by an external electric
field. The roles of geometry and material properties are discussed.",1612.06326v1
2016-12-26,Large-scale calculation of ferromagnetic spin systems on the pyrochlore lattice,"We perform the high-performance computation of the ferromagnetic Ising model
on the pyrochlore lattice. We determine the critical temperature accurately
based on the finite-size scaling of the Binder ratio. Comparing with the data
on the simple cubic lattice, we argue the universal finite-size scaling. We
also calculate the classical XY model and the classical Heisenberg model on the
pyrochlore lattice.",1612.08312v1
2017-06-01,Superconductivity in the Ferromagnet URhGe under uniaxial pressure,"Uniaxial pressure applied in the b crystallographic direction perpendicular
to spontaneous magnetization in heavy fermion ferromagnet URhGe strongly
stimulates superconductivity in this compound. The phenomenological approach
allows point out two mechanisms of superconducting temperature raising. They
originates from stimulation by the uniaxial stress both intraband and interband
amplitudes of triplet Cooper pairing. The phenomenon of reentrant
superconductivity under magnetic field along b-axis is also strongly sensitive
to the uniaxial stress in the same direction. The uniaxial stress accelerates
suppression the Curie temperature by the transversal magnetic field. The
emergence of the first order transition to the paramagnetic state occurs at
much lower field than in the absence of uniaxial stress.",1706.00354v1
2017-06-17,The Ferromagnetism in the Vicinity of Lifshitz Topological Transitions,"We show that the critical temperature of a ferromagnetic phase transition in
a quasi-two-dimensional hole gas confined in a diluted magnetic semiconductor
quantum well strongly depends on the hole chemical potential and hole density.
The significant variations of the the Curie temperature occur close to the
Lifshitz topological transition points where the hole Fermi surface acquires
additional components of topological connectivity due to the filling of excited
size-quantization subbands. The model calculations demonstrate that the Curie
temperature can be doubled by a small variation of the gate voltage for the
CdMnTe/CdMgTe quantum well based device.",1706.05490v1
2017-06-20,Thermally induced antiferromagnetic exchange in magnetic multilayers,"We demonstrate sharp thermally-induced switching between ferromagnetic and
antiferromagnetic RKKY exchange in a spin-valve with the spacer incorporating a
thin diluted ferromagnetic layer as the core. We illustrate the mechanism
behind the effect as due to a change in the effective thickness of the spacer
induced by the Curie transition into its paramagnetic state.",1706.06325v1
2017-10-09,Model for Ferromagnetic Quantum Critical Point in a 1D Kondo Lattice,"Motivated by recent experiments, we study a quasi-one dimensional model of a
Kondo lattice with Ferromagnetic coupling between the spins. Using bosonization
and dynamical large-N techniques we establish the presence of a Fermi liquid
and a magnetic phase separated by a local quantum critical point, governed by
the Kondo breakdown picture. Thermodynamic properties are studied and a gapless
charged mode at the quantum critical point is highlighted.",1710.03345v3
2017-10-26,Fate of Ising ferromagnets and antiferromagnets by zero-temperature Glauber dynamics on the two-dimensional Archimedean and 2-uniform lattices,"The fate of the Ising ferromagnet and antiferromagnet by the zero-temperature
Glauber dynamics from random initial spin configuration is investigated in the
two-dimensional Archimedean and 2-uniform lattices. Blinker states are found in
addition to the ground state and metastable state. We show that an
even-coordinated lattice can arrive at a blinker state or a metastable state
without stripe structure, in contrast to common expectation. The universal
relationship between the critical percolation and the probability of stripe
final state is confirmed for six lattices. Results about the fate of the
antiferromagnetic Ising model show that the geometric frustration suppresses
ordering more and promotes blinker state.",1710.09946v1
2017-12-07,Microscopic mechanism for the unusual antiferromagnetic order and the pressure-induced transition to ferromagnetism in USb$_2$,"Uranium dipnictide USb$_2$ reflects enigmatic properties posing a substantial
challenge for a microscopic modeling. Among others, it develops a nonstandard
antiferromagnetic order of a $\uparrow\downarrow\downarrow\uparrow$-type along
[001] crystallographic direction, and under pressure it undergoes transition to
the ferromagnetic phase. Here we propose a minimal low-energy model of USb$_2$
which, as we demonstrate at the mean-field level, accommodates physical
mechanism for mentioned observations. Relying on the obtained results we also
comment on the features of magnetism observed in other U-based compounds:
UAs$_2$, UBi$_2$, UAsSe, URh$_x$Ir$_{1-x}$Ge and UGe$_2$.",1712.02534v1
2017-12-13,Viscous dynamics of vortices in a ferromagnetic film,"We derive viscous forces for vortices in a thin-film ferromagnet. The viscous
force acting on vortex $i$ is a linear superposition $\mathbf F_i = - \sum_{j}
\hat{D}_{ij} \mathbf V_j$, where $\mathbf V_j$ is the velocity of vortex $j$.
Thanks to the long-range nature of vortices, the mutual drag tensor
$\hat{D}_{ij}$ is comparable in magnitude to the coefficient of self-drag
$D_{ii}$.",1712.05052v1
2017-12-15,Stability of ferromagnetism in many-electron systems,"We construct a model-independent framework describing stabilities of
ferromagnetism in strongly correlated electron systems; Our description relies
on the operator theoretic correlation inequalities. Within the new framework,
we reinterpret the Marshall-Lieb-Mattis theorem and Lieb\rq{}s theorem; in
addition, from the new perspective, we prove that Lieb\rq{}s theorem still
holds true even if the electron-phonon and electron-photon interactions are
taken into account. We also examine the Nagaoka-Thouless theorem and its
stabilities. These examples verify the effectiveness of our new viewpoint.",1712.05529v3
2017-12-15,"Wurtzite (Ga,Mn)As nanowire shells with ferromagnetic properties","(Ga,Mn)As in wurtzite crystal structure, is coherently grown by molecular
beam epitaxy on the {1100} side facets of wurtizte (Ga,In)As nanowires and
further encapsulated by (Ga,Al)As and low temperature GaAs. For the first time
a true long-range ferromagnetic magnetic order is observed in non-planar
(Ga,Mn)As, which is attributed to a more effective hole confinement in the
shell containing Mn by a proper selection/choice of both the core and outer
shell materials.",1712.05713v1
2017-12-23,Theory of type-II superconductivity in ferromagnetic metals with triplet pairing,"The superconducting state in uranium compounds UGe2, URhGe and UCoGe is
formed at temperatures far below the Curie temperature pointing on
nonconventional nature of superconductivity in these materials - namely the
superconductivity with triplet pairing. The emergence of superconductivity is
accompanied by the slight magnetization expulsion typical for the type-II
superconductors. Following classic Abrikosov paper I develop the theory of
type-II superconductivity in application to two-band ferromagnetic metal with
equal spin triplet pairing.",1712.08750v4
2018-01-10,Bound states induced by the ferromagnetic dimer in a triangular lattice,"The ongoing efforts aiming at control and manipulation of novel topological
phases renewed the interest in bound states induced in superconducting
substrates by magnetic impurities. First described by Yu, Shiba and Rusinov,
those bound states are spin-polarized and exhibit a rather large spatial extent
in two dimensional (2D) materials. Here, using the Bogoliubov--de~Gennes
formalism, we study the Yu--Shiba--Rusinov bound states induced by a
ferromagnetic dimer in 2D triangular lattice. We describe various topographies
of the in-gap bound states, depending on the coupling between impurities and
superconducting host.",1801.03559v1
2018-09-27,Disordered flat bands on the kagome lattice,"We study two models of correlated bond- and site-disorder on the kagome
lattice considering both translationally invariant and completely disordered
systems. The models are shown to exhibit a perfectly flat ground state band in
the presence of disorder for which we provide exact analytic solutions. Whereas
in one model the flat band remains gapped and touches the dispersive band, the
other model has a finite gap, demonstrating that the band touching is not
protected by topology alone. Our model also displays fully saturated
ferromagnetic groundstates in the presence of repulsive interactions, an
example of disordered flat band ferromagnetism.",1809.10726v2
2018-10-19,Strong coupling phases of partially filled twisted bilayer graphene narrow bands,"We identify states favored by Coulomb interactions projected onto the Wannier
basis of the four narrow bands of the ""magic angle"" twisted bilayer graphene.
At the filling of two electrons/holes per moire unit cell, such interactions
favor an insulating SU(4) ferromagnet. The kinetic terms select the ground
state in which the two valleys with opposite spins are equally mixed, with
vanishing magnetic moment per particle. We also find extended excited states,
the gap to which decreases in magnetic field. An insulating stripe
ferromagnetic phase is favored at one electron/hole per unit cell.",1810.08642v1
2019-06-10,High Frequency Domain Wall Oscillations in Ferromagnetic Nanowire with a Nanoscale Dzyaloshinskii Moriya Interaction (DMI) Region,"The Dzyaloshinskii Moriya Interaction (DMI) has laid the foundation for many
novel chiral structures such as Skyrmions. In most of the studies so far, the
DMI is present in the whole of the magnetic layer. Here, we report our
investigations on a ferromagnetic nanowire where DMI is confined to a nanoscale
region. We observe that the local modulation of magnetic properties causes
oscillation of domain walls under the influence of spin-transfer torque. The
oscillation frequency is tunable within a few GHz, making this observation
potentially useful for applications in neuromorphic computing.",1906.03844v1
2019-07-11,Magnetization-density distribution in the metallic ferromagnet SrRuO3 determined by polarized neutron diffraction,"The magnetization-density distribution in the metallic ferromagnet SrRuO$_3$
was studied by means of polarized neutron diffraction. The analyzes by
multipole refinements and by the maximum entropy method consistently reveal a
strong polarization of all oxygen sites carrying 30\% of the total
magnetization. The spin-density distribution on the Ru site exhibits a nearly
cubic shape in agreement with an almost equal occupation of $t_{2g}$ orbitals
and $pd$ hybridization. The experimental analysis is well reproduced by density
functional calculations. There is no qualitative change in the magnetization
distribution between 2 and 200 K.",1907.05140v1
2019-07-14,Zeros of ferromagnetic 2-spin systems,"We study zeros of the partition functions of ferromagnetic 2-state spin
systems in terms of the external field, and obtain new zero-free regions of
these systems via a refinement of Asano's and Ruelle's contraction method. The
strength of our results is that they do not depend on the maximum degree of the
underlying graph. Via Barvinok's method, we also obtain new efficient and
deterministic approximate counting algorithms. In certain regimes, our
algorithm outperforms all other methods such as Markov chain Monte Carlo and
correlation decay.",1907.06156v1
2019-07-15,Exchange biased Anomalous Hall Effect driven by frustration in a magnetic Kagome lattice,"Co3Sn2S2 is a ferromagnetic Weyl semimetal that has been the subject of
intense scientific interest due to its large anomalous Hall effect. We show
that the coupling of this material's topological properties to its magnetic
texture leads to a strongly exchange biased anomalous Hall effect. We argue
that this is likely caused by the coexistence of ferromagnetism and spin glass
phases, the latter being driven by the geometric frustration intrinsic to the
Kagome network of magnetic ions.",1907.06651v1
2019-09-16,Experimental Confirmation of Quantum Hall Ferromagnetic State in an Organic Dirac Fermion System,"We have experimentally confirmed the quantum Hall ferromagnetic state with
Chern number \nu=0, characterized by the helical edge state, in a layered
organic Dirac fermion system \alpha-(BEDT-TTF)_2I_3. The interlayer resistance
saturates at low temperatures and high magnetic fields. It does not scale with
the sample cross-sectional area in the saturating region, and resonantly
depends on the magnetic field direction. These results strongly suggest that
the helical edge state dominates transport. This is the first observation of
the topological phase in organic molecular crystals.",1909.07006v1
2019-09-25,Magnetic Quantum Phase Transitions in a Clean Dirac Metal,"We consider clean Dirac metals where the linear band crossing is caused by a
strong spin-orbit interaction, and study the quantum phase transitions from the
paramagnetic phase to various magnetic phases, including homogeneous
ferromagnets, ferrimagnets, canted ferromagnets, and magnetic nematics. We show
that in all of these cases the coupling of fermionic soft modes to the order
parameter generically renders the quantum phase transition first order, with
certain gapless Dirac systems providing a possible exception. These results are
surprising since a strong spin-orbit scattering suppresses the mechanism that
causes the first order transition in ordinary metals. The important role of
chirality in generating a new mechanism for a first-order transition is
stressed.",1909.11642v1
2019-10-15,Itinerant-electron magnetism: the importance of many-body correlations,"Do electrons become ferromagnetic just because of their repulisve Coulomb
interaction? Our calculations on the three-dimensional electron gas imply that
itinerant ferromagnetim of delocalized electrons without lattice and band
structure, the most basic model considered by Stoner, is suppressed due to
many-body correlations as speculated already by Wigner, and a possible
ferromagnetic transition lowering the density is precluded by the formation of
the Wigner crystal.",1910.06554v2
2019-10-28,"Geometric Flows of Curves, Two-Component Camassa-Holm Equation and Generalized Heisenberg Ferromagnet Equation","In this paper, we study the generalized Heisenberg ferromagnet equation,
namely, the M-CVI equation. This equation is integrable. The integrable motion
of the space curves induced by the M-CVI equation is presented. Using this
result, the Lakshmanan (geometrical) equivalence between the M-CVI equation and
the two-component Camassa-Holm equation is established. Note that these
equations are gauge equivalent each to other.",1910.13281v1
2020-01-24,Homogenization of ferromagnetic energies on Poisson random sets in the plane,"We prove that by scaling nearest-neighbour ferromagnetic energies defined on
Poisson random sets in the plane we obtain an isotropic perimeter energy with a
surface tension characterised by an asymptotic formula. The result relies on
proving that cells with `very long' or `very short' edges of the corresponding
Voronoi tessellation can be neglected. In this way we may apply Geometry
Measure Theory tools to define a compact convergence, and a characterisation of
metric properties of clusters of Voronoi cells using limit theorems for
subadditive processes.",2001.08919v1
2020-02-02,Topological Valley Transport of Gapped Dirac Magnons in Bilayer Ferromagnetic Insulators,"Bilayer Heisenberg ferromagnetic insulators hold degenerate terahertz Dirac
magnon modes associated with two opposite valleys of the hexagonal Brillouin
zone. We show that this energy degeneracy can be removed by breaking of the
inversion symmetry (I), leading to a topological magnon valley current. We show
furthermore that this current leads to valley Seebeck effect for magnons and is
thereby detectable. We perform calculations in the specific example of bilayer
CrBr3, where I can be broken by electrostatic doping.",2002.00446v2
2020-02-24,Upper critical field in ferromagnetic metals with triplet pairing,"The theory of triplet superconductivity in ferromagnetic metals based on
electron-electron interaction by spin fluctuation exchange is developed. The
equations for the upper critical field temperature dependence are derived. In
contrast to the similar equations for the superconductivity in two band metals
they contain the pairing amplitudes and the Fermi velocities depending on
magnetic field. The critical field behaviour near the critical temperature and
at T = 0 is established analytically.",2002.10156v3
2020-02-21,"Generalized Heisenberg Ferromagnet type Equation and Modified Camassa-Holm Equation: Geometric Formulation, Soliton Solutions and Equivalence","We study the integrability and equivalence of a generalized Heisenberg
ferromagnet-type equation (GHFE). The different forms of this equation as well
as its reduction are presented. The Lax representation (LR) of the equation is
obtained. We observe that the geometrical and gauge equivalent counterpart of
the GHFE is the modified Camassa-Holm equation (mCHE) with an arbitrary
parameter $\kappa$. Finally, the 1-soliton solution of the GHFE is obtained.",2002.10969v1
2020-04-21,Anisotropic ferromagnet with two spins per site,"Green function diagrammatic technique is used to investigate a model
ferromagnet in the case, when the effective spin at a site is compounded of two
anisotropically interacting electron spins. The results are: the transverse
magnetic excitations and the longitudinal ones are obtained in the random phase
approximation, magnetization and critical temperature are calculated to the
first order in the reciprocal of the effective number z of ions interacting
with a given ion, and exchange interaction at the same site gives the contrary
effects in changes of the magnitudes mentioned above in dependence on the
exchange-isotropy parameter I and the exchange-anisotropy parameter D.",2004.09884v1
2020-04-25,Torque-induced dispersive readout in a weakly coupled hybrid system,"We propose a quantum state readout mechanism of a weakly coupled qubit in
dispersive regime. The hybrid system consists of ferromagnetic insulator and a
superconducting qubit in a microwave cavity. The enhancement of the measurement
sensitivity is achieved by exerting torque on the ferromagnetic insulator
magnetization, which compensates the damping of the system leading to an
exceptional point. The proposed machanism allows to measure the qubit state
either via the transmission of the cavity or the FMR signal of the magnetic
material.",2004.12114v1
2020-04-23,Zakharov-Ito equation and Generalized Heisenberg ferromagnet-type equation: equivalence and related geometric curve flows,"These results continue our studies of integrable generalized Heisenberg
ferromagnet-type equations (GHFE) and their equivalent counterparts. We
consider the GHFE which is the spin equivalent of the Zakharov-Ito equation
(ZIE). We have established that these equations are gauge and geometrical
equivalent to each other. The integrable motion of space curves induced by the
ZIE is constructed. The 1-soliton solution of the GHFE is obtained from the
seed solution of the ZIE.",2004.12816v1
2020-04-28,Magnetic Flux Pumping in Superconducting Loop Containing a Josephson $ψ$ Junction,"We demonstrate that a Josephson junction with a half-metallic weak link
integrated into the superconducting loop enables the pumping of magnetic flux
piercing the loop. In such junctions, the ground state phase $\psi$ is
determined by the mutual orientation of magnetic moments in two ferromagnets
surrounding the half-metal. Thus, the precession of magnetic moment in one of
two ferromagnets controlled, e.g., by the microwave radiation, results in the
accumulation of the phase $\psi$ and subsequent switching between the states
with different vorticities. The proposed flux pumping mechanism does not
require the application of voltage or external magnetic field which enables the
design of electrically decoupled memory cells in superconducting spintronics.",2004.13403v1
2020-12-13,Tunneling magnetoresistance in ensembles of ferromagnetic granules with exchange interaction and random easy axes of magnetic anisotropy,"We study the tunneling magnetoresistance in the ensembles of ferromagnetic
granules with random easy axes of magnetic anisotropy taking into account the
exchange interaction between granules. It is shown that due to the exchange
interaction magnetoresistance is effectively decoupled from magnetization, i.e.
the strongest negative magnetoresistance can be observed at the field where
magnetization is almost saturated. Under some conditions, the sign of
magnetoresistance can be reversed and tunneling magnetoresistance can become
positive at certain magnetic fields. Our theory agrees with measurements of
magnetoresistance in ensembles of Fe granules in SiCxNy matrix.",2012.07114v1
2021-01-11,Bose Einstein condensation and ferromagnetism of low density Bose gas of particles with arbitrary spin,"Properties of the ground state and the spectrum of elementary excitations are
investigated for the low density ultracold spinor 3D Bose gas of particles with
arbitrary nonzero spin. Gross-Pitaevskii equations are derived. Within the
framework of the considering interaction Hamiltonian it is shown that the
ground state spin structure and spin part of the chemical potential is
determined by the renormalized interaction, being defined by the contribution
of the virtual large momenta. The ferromagnetic structure of the ground state,
and the equation of the phase, density, and spin dynamics are obtained from
Gross-Pitaevskii equations.",2101.03744v2
2021-01-14,The magnetic field induced ferromagnetism in EuPd$_2$Sn$_4$ novel compound,"We report on crystal structure, magnetic and thermal physical properties of
EuPd$_2$Sn$_4$ stannide. From the magnetic susceptibility measurements a
divalent state of Eu rare earth element was determined together with an
antiferromagnetic (AFM) order at 11 K. By applying magnetic field, the magnetic
behavior variation reveals a complex magnetic structure. Above a critical field
Bc a ferromagnetic (FM)-like character starts to prevail. AFM and FM regimes
are separated by a metamagnetic region. Heat capacity measurements confirm this
behavior.",2101.05854v1
2021-01-19,Direct evidence of ferromagnetism in MnSb2Te4,"We report the magnetic imaging of ferromagnetic domains in the van der Waals
single crystal MnSb2Te4 from two different sources using cryogenic magnetic
force microscopy. The magnetic field dependence of the domains reveals very
weak pinning of domain walls in MnSb2Te4, resulting in a negligibly small
magnetic hysteresis loop. The temperature dependence of the domain contrast
reveals a mean field like behavior, in good agreement with that of bulk
magnetization measurements.",2101.07892v1
2021-01-21,Polarons in a ferromagnetic spinor Bose-Einstein condensates,"We investigate the polarons formed by immersing a spinor impurity in a
ferromagnetic state of $F=1$ spinor Bose-Einstein condensate. The ground state
energies and effective masses of the polarons are calculated in both
weak-coupling regime and strong-coupling regime. In the weakly interacting
regime the second order perturbation theory is performed. In the strong
coupling regime we use a simple variational treatment. The analytical
approximations to the energy and effective mass of the polarons are
constructed. Especially, a transition from the mobile state to the
self-trapping state of the polaron in the strong coupling regime is discussed.
We also estimate the signatures of polaron effects in spinor BEC for the future
experiments.",2101.08474v1
2021-01-25,Discovery of an insulating ferromagnetic phase of electrons in two dimensions,"This is a commentary on two papers (PNAS 117 (51) 32244-32250 (2020) and
arXiv:2011.06721), which observed a series of ordering transitions in a
strongly correlated two-dimensional electron system confined to a AlAs quantum
well. We summarize the main discoveries (electron nematicity, insulating
ferromagnetism, etc.) of them and speculate on $T-r_s$ phase diagram based on
theoretical considerations.",2101.10299v1
2000-06-05,Absence of overscreened Kondo effect in ferromagnetic host,"We study the low temperature behavior of a boundary magnetic impurity S'=1/2
in an open ferromagnetic Takhatajian-Babujian spin-S chain. For
antiferromagnetic Kondo coupling, it is show via Bethe ansatz solution that the
impurity spin is always locked into the critical behavior the bulk. At low
temperature, a local composite of spin S-1/2 forms near the impurity site and
its contribution to specific heat is of simple power law T^{1/2}. The absence
of overscreened Kondo effect is due to the large correlation length of host
spins which is divergent near the quantum critical point.",0006058v1
2000-06-27,Mesoscopic Tunneling Magnetoresistance,"We study spin-dependent transport through
ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic
Coulomb blockade regime. A general transport equation allows us to calculate
the conductance in the absence or presence of spin-orbit interaction and for
arbitrary orientation of the lead magnetizations. The tunneling
magnetoresistance (TMR), defined at the Coulomb blockade conductance peaks, is
calculated and its probability distribution presented. We show that mesoscopic
fluctuations can lead to the optimal value of the TMR.",0006429v3
2012-05-02,Strain and structure driven complex magnetic ordering of a CoO overlayer on Ir(100),"We have investigated the magnetic ordering in the ultrathin c(10$\times$2)
CoO(111) film supported on Ir(100) on the basis of ab-initio calculations. We
find a close relationship between the local structural properties of the oxide
film and the induced magnetic order, leading to alternating ferromagnetically
and anti-ferromagnetically ordered segments. While the local magnetic order is
directly related to the geometric position of the Co atoms, the mismatch
between the CoO film and the Ir substrate leads to a complex long-range order
of the oxide.",1205.0493v1
2012-05-04,Measurement of the gradient of the Casimir force between a nonmagnetic sphere and a magnetic plate,"We measured the gradient of the Casimir force between an Au sphere and a
plate made of ferromagnetic metal (Ni). It is demonstrated that the magnetic
properties influence the force magnitude. This opens prospective opportunities
for the control of the Casimir force in nanotechnology and for obtaining
Casimir repulsion by using ferromagnetic dielectrics.",1205.0872v1
2012-05-11,Effective Potential Approach to Quark Ferromagnetization in High Density Quark Matter,"A possibility of spontaneous magnetization in high density symmetric quark
matter is investigated using the NJL type effective model of QCD by means of an
effective potential with respect to an auxiliary field. It is shown that the
quark ferromagnetic condensate has non-vanishing value at high baryon density
due to the tensor-type four-point interaction between quarks.",1205.2409v2
2012-05-17,Tunneling anisotropic magnetoresistance in single-molecule magnet junctions,"We theoretically investigate quantum transport through single-molecule magnet
(SMM) junctions with ferromagnetic and normal-metal leads in the sequential
regime. The current obtained by means of the rate-equation gives rise to the
tunneling anisotropic magnetoresistance (TAMR), which varies with the angle
between the magnetization direction of ferromagnetic lead and the easy axis of
SMM. The angular dependence of TAMR can serve as a probe to determine
experimentally the easy axis of SMM. Moreover, it is demonstrated that both the
magnitude and sign of TAMR are tunable by the bias voltage, suggesting a
promising TAMR based spintronic molecule-device.",1205.3916v2
2017-04-29,Double-Exchange Interaction in Optically Induced Nonequilibrium State: A Conversion from Ferromagnetic to Antiferromagnetic Structure,"The double-exchange (DE) interaction, that is, a ferromagnetic (FM)
interaction due to a combination of electron motion and the Hund coupling, is a
well known source of a wide class of FM orders. Here, we show that the DE
interaction in highly photoexcited states is antiferromagnetic (AFM). Transient
dynamics of quantum electrons coupled with classical spins are analyzed. An ac
field applied to a metallic FM state results in an almost perfect N\'eel state.
A time characterizing the FM-to-AFM conversion is scaled by light amplitude and
frequency. This hidden AFM interaction is attributable to the electron-spin
coupling under nonequilibrium electron distribution.",1705.00240v1
2017-05-11,Bethe Ansatz for two-magnon scattering states in 2D and 3D Heisenberg-Ising ferromagnets,"Various versions of the Bethe ansatz are suggested for evaluation of
scattering two-magnon states in 2D and 3D Heisenberg-Ising ferromagnets. It is
shown that for 2D square (3D qubic) finite-periodic or infinite lattices about
a half (3/4) of states have a correctly 2D- (3D-) generalized Bethe form. The
remaining scattering states are treated (on the infinite lattices only) within
the degenerative discrete-diffractive modification of the Bethe ansatz
previously suggested by the author.",1705.04117v2
2017-05-29,"Part of a collection of reviews on antiferromagnetic spintronics. Antiferromagnetic dynamics, spin-texures, and nanostructures","Antiferromagnets as active elements of spintronics can be faster than their
ferromagnetic counterparts and more robust to magnetic noise. Owing to the
strongly exchange-coupled magnetic sublattice structure, antiferromagnetic
order parameter dynamics are qualitatively different and thus capable of
engendering novel device functionalities. In this review, we discuss
antiferromagnetic textures -- nanoparticles, domain walls, and skyrmions, --
under the action of different spin torques. We contrast the antiferromagnetic
and ferromagnetic dynamics, with a focus on the features that can be relevant
for applications.",1705.10377v1
2017-05-30,Synthetic Antiferromagnetic Spintronics: Part of a collection of reviews on antiferromagnetic spintronics,"Spintronic and nanomagnetic devices often derive their functionality from
layers of different materials and the interfaces between them. This is
especially true for synthetic antiferromagnets - two or more ferromagnetic
layers that are separated by metallic spacers or tunnel barriers and which have
antiparallel magnetizations. Here, we discuss the new opportunities that arise
from synthetic antiferromagnets, as compared to crystal antiferromagnets or
ferromagnets.",1705.10526v1
2017-09-05,Gate-controlled magnonic-assisted switching of magnetization in ferroelectric/ferromagnetic junctions,"Interfacing a ferromagnet with a polarized ferroelectric gate generates a
non-uniform, interfacial spin density coupled to the ferroelectric polarization
allowing so for an electric field control of effective transversal field to
magnetization. Here we study the dynamic magnetization switching behavior of
such a multilayer system based on the Landau-Lifshitz-Baryakhtar equation,
demonstrating that interfacial magnetoelectric coupling is utilizable as a
highly localized and efficient tool for manipulating magnetism.",1709.01286v1
2017-09-06,Edge states in a ferromagnetic honeycomb lattice with armchair boundaries,"We investigate the properties of magnon edge states in a ferromagnetic
honeycomb lattice with armchair boundaries. In contrast with fermionic
graphene, we find novel edge states due to the missing bonds along the boundary
sites. After introducing an external on-site potential at the outermost sites
we find that the energy spectra of the edge states are tunable. Additionally,
when a non-trivial gap is induced, we find that some of the edge states are
topologically protected and also tunable. Our results may explain the origin of
the novel edge states recently observed in photonic lattices. We also discuss
the behavior of these edge states for further experimental confirmations",1709.01855v1
2017-09-13,Ultrafast spin-lattice relaxation in ferromagnets including effective spin-orbit fields,"We investigate ultrafast demagnetization due to electron-phonon interaction
in a model band-ferromagnet. We show that the microscopic mechanism behind the
spin dynamics due to electron-phonon interaction is the interplay of scattering
and the precession around momentum-dependent effective internal spin-orbit
magnetic fields. The resulting magnetization dynamics can only be mimicked by
spin-flip transitions if the spin precession around the internal fields is
sufficiently fast (compared to the scattering time) so that it averages out the
transverse spin components.",1709.04253v1
2017-09-17,Magnetic shape-memory effect in SrRuO$_3$,"Like most perovskites, SrRuO$_3$ exhibits structural phase transitions
associated with rotations of the RuO$_6$ octahedra. The application of moderate
magnetic fields in the ferromagnetically ordered state allows one to fully
control these structural distortions, although the ferromagnetic order occurs
at six times lower temperature than the structural distortion. Our neutron
diffraction and macroscopic measurements unambiguously show that magnetic
fields rearrange structural domains, and that for the field along a cubic
[110]$_c$ direction a fully detwinned crystal is obtained. Subsequent heating
above the Curie temperature causes a magnetic shape-memory effect, where the
initial structural domains recover.",1709.05688v1
2017-09-25,Study of the non-linear eddy-current response in a ferromagnetic plate: theoretical analysis for the 2D case,"The non-linear induction problem in an infinite ferromagnetic pate is studied
theoretically by means of the truncated region eigenfunction expansion (TREE)
for the 2D case. The non-linear formulation is linearised using a fixed-point
iterative scheme, and the solution of the resulting linear problem is
constructed in the Fourier domain following the TREE formalism. The calculation
is carried out for the steady-state response under harmonic excitation and the
harmonic distortion is derived from the obtained spectrum. This article is
meant to be the theoretical part of a study, which will be complemented by the
corresponding experimental work in a future communication.",1709.08380v1
2017-09-26,Three-dimensional Bose-Einstein Condensation in the Spin-1/2 Ferromagnetic-leg Ladder 3-Br-4-F-V,"The critical exponent of the phase boundary has been examined on the
three-dimensional incommensurate ordering phase in the spin-1/2
ferromagnetic-leg ladder 3-Br-4-F-V
[=3-(3-bromo-4-fluorophenyl)-1,5-diphenylverdazyl]. Using the
temperature-window fitting technique, we obtained the critical exponents which
agreed with the three-dimensional (3D) Bose-Einstein condensation (BEC)
universality class at both sides of the lower critical field and the saturation
field. 3-Br-4-F-V thus becomes a new member of the quantum magnets which prove
the universality of the 3D BEC exponent.",1709.08849v1
2017-09-28,Switching of Co magnetization driven by antiferromagnetic-ferromagnetic phase transition of FeRh alloy in Co/FeRh bilayers,"We show that Co spins in Co/FeRh epitaxial bilayers grown on W(110) switch
reversibly between the two orthogonal in-plane directions as the FeRh layer
undergoes temperature driven antiferromagnetic-ferromagnetic (AFM-FM) phase
transition. Switching of Co magnetization is characterized by a hysteretic
behavior owing to a temperature hysteresis of the AFM-FM transition in FeRh.
The spin reorientation of Co is driven by the evolution interfacial exchange
coupling to FeRh system across the AFM-FM process. Our results provide a new
method of writing information purely by a local temperature change.",1709.09928v1
2018-03-13,Spin Seebeck effect in a simple ferromagnet near Tc: A Ginzburg-Landau approach,"A time-dependent Ginzburg-Landau theory is used to examine the longitudinal
spin Seebeck effect in a simple ferromagnet in the vicinity of the Curie
temperature Tc. It is shown analytically that the spin Seebeck effect is
proportional to the magnetization near Tc, whose result is in line with the
previous numerical finding. It is argued that the present result can be tested
experimentally using a simple magnetic system such as EuO/Pt or EuS/Pt.",1803.04602v1
2018-03-22,Vortex liquid phase in the p-wave ferromagnetic superconductor UCoGe,"The upper critical field for field along the b-axis of the p-wave
ferromagnetic superconductor UCoGe has a particular S-shape, akin to the
re-entrant superconducting phase of URhGe. To explore the evolution of the
superconducting phase under this transverse magnetic field, we report the
thermal conductivity and resistivity measurements, revealing a possible
field-induced vortex liquid phase, and supporting a field-induced change of the
superconducting order parameter.",1803.08468v3
2018-06-04,Dynamical quadrupole structure factor of frustrated ferromagnetic chain,"We investigate the dynamical quadrupole structure factor of a spin-1/2
$J_{1}$-$J_{2}$ Heisenberg chain with competing ferromagnetic $J_{1}$ and
antiferromagnetic $J_{2}$ in a magnetic field by exploiting density-matrix
renormalization group techniques. In a field-induced spin nematic regime, we
observe gapless excitations at $q=\pi$ according to quasi-long-range
antiferro-quadrupole correlations. The gapless excitation mode has a quadratic
form at the saturation, while it changes into a linear dispersion as the
magnetization decreases.",1806.01434v1
2018-06-06,Traveling domain walls in chiral ferromagnets,"We show that chiral symmetry breaking enables traveling domain wall solution
for the conservative Landau-Lifshitz equation of a uniaxial ferromagnet with
Dzyaloshinskii-Moriya interaction. In contrast to related domain wall models
including stray-field based anisotropy, traveling wave solutions are not found
in closed form. For the construction we follow a topological approach and
provide details of solutions by means of numerical calculations.",1806.02082v1
2018-06-30,Motion of discrete interfaces on the triangular lattice,"We study the motion of discrete interfaces driven by ferromagnetic
interactions on the two-dimensional triangular lattice by coupling the Almgren,
Taylor and Wang minimizing movements approach and a discrete-to-continuum
analysis, as introduced by Braides, Gelli and Novaga in the pioneering case of
the square lattice. We examine the motion of origin-symmetric convex
""Wulff-like"" hexagons, i.e. origin-symmetric convex hexagons with sides having
the same orientations as those of the hexagonal Wulff shape related to the
density of the anisotropic perimeter $\Gamma$-limit of the ferromagnetic
energies as the lattice spacing vanishes. We compare the resulting limit motion
with the corresponding evolution by crystalline curvature with natural
mobility.",1807.00195v2
2018-07-05,Coulomb blockade-tuned indirect exchange in ferromagnetic nanostructures,"We develop a theory of the reversible switching of the magnetic state of the
ferromagnet-insulator-normal metalferromagnet (FINF) nanostructure. The
switching is controlled by tuning the Coulomb blockade strength via the gate
voltage on the normal metal granule. The proposed mechanism allows for
realizing the switching without passing a dissipative current through the
structure.",1807.02051v1
2018-07-07,Theoretical investigation on the ferromagnetic two-dimensional scandium monochloride sheet that has a high Curie temperature and could be exfoliated from a known material,"A two-dimensional scandium monochloride sheet was investigated by using
density functional theory. It could be exfoliated from a known bulk material
with a cleavage energy slightly lower than that of graphene. The sheet has a
ferromagnetic ground state with a Curie temperature of 100 K. Moreover, the
sheet becomes a half-metal under hole doping. The Curie temperature increases
to 250 K with the doping amount of 0.4 per primitive cell, which is close to
the ice point. The two-dimensional scandium monochloride sheet should be a good
candidate for two-dimensional spintronics.",1807.02652v1
2018-07-15,"Anisotropy of Neel ""orange-peel"" coupling in magnetic multilayers","We calculate the energy of the magnetostatic interaction between two
ferromagnetic films with uniform magnetization and correlated interfaces (the
""orange-peel"" effect). The ""orange-peel"" coupling is anisotropic: the
interaction is ferromagnetic when the films are magnetized in-plane; and it is
antiferromagnetic when magnetization is out-of-plane. The interaction
anisotropy can be used to distinguish the ""orange-peel"" effect from the
interlayer exchange coupling.",1807.05590v1
2018-07-18,Banana and pizza-slice-shaped mesogens give a new constrained ferromagnet universality class,"It has been known that at high density, the local orientation of
banana-shaped molecules shows a spontaneously bent state, giving rise to
interesting liquid-crystalline phases such as splay-bend and twist-bend. This
spontaneous bend can be modelled theoretically by allowing the bend elastic
constant in the Frank elastic energy to become negative. Here we extend this
idea to polar banana and pizza-slice-shaped molecules which can also splay
spontaneously. By allowing both splay and bend elastic constants to be negative
we discovered two additional new liquid crystalline phases. In particular,
using renormalization group technique, we showed that the phase transition
belongs to a new constrained ferromagnet universality class.",1807.07039v1
2018-07-28,Ultrafast spin current generation in ferromagnetic thin films,"Spin currents have been shown to play a key role in the ultrafast
laser-driven demagnetization process in ferromagnetic thin films. Here, we show
that an oscillating spin current can be generated in the film via the
application of a femtosecond laser pulse in the visible range. In particular,
we prove that the spin current is due to ballistic electrons traveling back and
forth in the film. The dependence of the current intensity on the driving
electric field is also investigated.",1807.10946v1
2018-12-06,Ferromagnetic Mott State in Twisted Graphene Bilayers at the Magic Angle,"We address the effective tight-binding Hamiltonian that describes the
insulating Mott state of twisted graphene bilayers at a magic angle. In that
configuration, twisted bilayers form a honeycomb superlattice of localized
states, characterized by the appearance of flat bands with four-fold
degeneracy. After calculating the maximally localized superlattice Wannier
wavefunctions, we derive the effective spin model that describes the Mott
state. We suggest that the system is an exotic ferromagnetic Mott insulator,
with well defined experimental signatures.",1812.02550v2
2018-12-08,Magnetic properties of nanowires with ferromagnetic core and antiferromagnetic shell,"We present a Monte Carlo study of the magnetic properties of thin cylindrical
nanowires composed of a ferromagnetic core and an antiferromagnetic shell
implementing a classical spin Hamiltonian. We address systematically the impact
of interface exchange coupling on the loop characteristics and the
magnetization reversal mechanism. We study the effect of shell
polycrystallinity on the characteristic fields of the isothermal hysteresis
loop (coercivity, exchange-bias). We demonstrate that coupling to a
polycrystalline antiferromagnetic shell increases the critical core diameter
for transition from transverse to vortex domain walls.",1812.03339v1
2018-12-20,Non-local Spin-charge Conversion via Rashba Spin-Orbit Interaction,"We show theoretically that conversion between spin and charge by spin-orbit
interaction in metals occurs even in a non-local setup where magnetization and
spin-orbit interaction are spatially separated if electron diffusion is taken
into account. Calculation is carried out for the Rashba spin-orbit interaction
treating the coupling with a ferromagnet perturbatively. The results indicate
the validity of the concept of effective spin gauge field (spin motive force)
in the non-local configuration. The inverse Rashba-Edelstein effect observed
for a trilayer of a ferromagnet, a normal metal and a heavy metal can be
explained in terms of the non-local effective spin gauge field.",1812.08884v1
2019-01-05,Coupled Dispersionless and Generalized Heisenberg Ferromagnet Equations with Self-Consistent Sources: Geometry and Equivalence,"We propose a new integrable coupled dispersionless equation with
self-consistent sources (CDESCS). We obtain the Lax pair and the equivalent
generalized Heisenberg ferromagnet equation (GHFE), demonstrating its
integrability. Specifically, we explore the geometry of these equations. Last,
we consider the relation between the motion of curves/surfaces and the CDESCS
and the GHFE.",1901.01470v3
2019-01-31,"Anisotropic ferromagnetism and structure stability in $4f$-$3d$ intermetallics: ab initio structure optimization and magnetic anisotropy for RCo$_5$ (R=Ce, La, and Y)","Electronic mechanism in the interplay between ferromagnetism and structure
stability of $4f$-$3d$ intermetallics in the main phase of rare-earth permanent
magnets is investigated from first principles. We present a case study with an
archetypical materials family RCo$_5$ (R=Ce, La, Y), which was a part of the
earliest rare-earth permanent magnets and from which other representative
main-phase compounds can be regarded as a derived type. Comparison with the
champion magnet materials family R$_2$T$_{14}$B and recently revisited
materials family RT$_{12}$ (T=Co and Fe) points to a direction leading to a
mid-class magnet for the possible next generation materials.",1901.11498v1
2019-02-08,Magnetic excitations and transport properties in frustrated ferromagnetic chain,"To clarify the transport property mediated by bound magnons in a spin nematic
state, we investigate the spin Drude weight of a spin-1/2 $J_{1}$-$J_{2}$
Heisenberg chain with ferromagnetic $J_{1}$ and antiferromagnetic $J_{2}$ in a
magnetic field by numerical diagonalization. At zero magnetic field, numerical
results with up to 24 sites suggest that the spin Drude weight would be zero in
the thermodynamic limit, indicating diffusive spin transport. With increasing
the magnetic field, the spin Drude weight is enhanced at low temperatures,
indicating that bound magnons would contribute to the spin transport.",1902.02932v1
2019-02-24,Half-Metallic Ferromagnets and Spin Gapless Semiconductors,"A brief review of experimental and theoretical studies of half-metallic
ferromagnets (HMF) and spin gapless semiconductors (SGS) is given. The data on
resistivity and magnetoresistivity are presented. An important role of
non-quasiparticle states owing to electron-magnon scattering in transport
properties is discussed. The problem of low-temperature resistivity in HMF is
treated in terms of one-magnon and two-magnon scattering processes.",1902.08972v1
2019-03-05,Electronic structure and magnetism of transition metal dihalides: bulk to monolayer,"Based on first-principles calculations, the evolution of the electronic and
magnetic properties of transition metal dihalides MX$_2$ (M= V, Mn, Fe, Co, Ni;
X = Cl, Br, I) is analyzed from the bulk to the monolayer limit. A variety of
magnetic ground states is obtained as a result of the competition between
direct exchange and superexchange. The results predict that FeX$_2$, NiX$_2$,
CoCl$_2$ and CoBr$_2$ monolayers are ferromagnetic insulators with sizable
magnetocrystalline anisotropies. This makes them ideal candidates for robust
ferromagnetism at the single layer level. Our results also highlight the
importance of spin-orbit coupling to obtain the correct ground state.",1903.01789v1
2019-03-29,Nonlocal Reductions of a Generalized Heisenberg Ferromagnet Equation,"We study nonlocal reductions of coupled equations in $1+1$ dimensions of the
Heisenberg ferromagnet type. The equations under consideration are completely
integrable and have a Lax pair related to a linear bundle in pole gauge. We
describe the integrable hierarchy of nonlinear equations related to our system
in terms of generating operators. We present some special solutions associated
with four distinct discrete eigenvalues of the scattering operator. Using Lax
pair diagonalization method, we derive recurrence formulas for the conserved
densities and find the first two simplest conserved densities.",1904.00797v2
2019-04-26,Density Functional Methods for the Magnetism of Transition Metals: SCAN in Relation to Other Functionals,"We report tests of various density functionals for ferromagnetic, Fe, Co and
Ni with a focus on characterizing the behavior of the so-called strongly
constrained and appropriately normed (SCAN) functional. It is found that SCAN
is closer in behavior to functionals that yield localized behavior, such as
hybrid functionals, than other semilocal functionals that are tested. The
results are understood in terms of a tendency to differentiate orbitals,
favoring integer occupation, which is necessary for a correct description of
atomic systems, but inappropriate for the open shell metallic ferromagnetic
metals studied here.",1904.11825v1
2019-04-29,Melting of Ferromagnetic Order on a Trellis Ladder,"The ground state properties of a frustrated spin-1/2 system is studied on a
trellis ladder which is composed of two zigzag ladders interacting through rung
interactions. The presence of rung interaction between the zigzag ladders
induces a non-magnetic ground state, although, each of zigzag ladders has
ferromagnetic order in weak antiferromagnetic leg interaction limit. The rung
interaction also generates rung dimers and opens spin gap which increases
rapidly with rung interaction strength. The correlation between spins decreases
exponentially with the distance between them.",1904.12521v1
2019-08-22,Anomalous Hall effect at the spontaneously electron-doped polar surface of PdCoO2 ultrathin films,"We revealed the electrical transport through surface ferromagnetic states of
a nonmagnetic metal PdCoO2. Electronic reconstruction at the Pd-terminated
surface of PdCoO2 induces Stoner-like ferromagnetic states, which could lead to
spin-related phenomena among the highly conducting electrons in PdCoO2.
Fabricating a series of nanometer-thick PdCoO2 thin films, we detected a
surface-magnetization-driven anomalous Hall effect via systematic thickness-
and termination-dependent measurements. Besides, we discuss that finite
magnetic moments in electron doped CoO2 triangular lattices may have given rise
to additional unconventional Hall resistance.",1908.08173v1
2019-12-03,Ferromagnetic spin correlations in the two-dimensional Hubbard model,"We analyze the dynamical nearest-neighbor and next-nearest-neighbor spin
correlations in the 4-site and 8-site dynamical cluster approximation to the
two-dimensional Hubbard model. Focusing on the robustness of these correlations
at long imaginary times, we reveal enhanced ferromagnetic correlations on the
lattice diagonal, consistent with the emergence of composite spin-1 moments at
a temperature scale that essentially coincides with the pseudo-gap temperature
$T^*$. We discuss these results in the context of the spin-freezing theory of
unconventional superconductivity.",1912.01260v1
2019-12-11,Dynamical symmetry in quantum dissipative models,"We show that the dynamical symmetry exists in dissipative quantum many-body
systems. Under constraints on both Hamiltonian and dissipation parts, the time
evolution of particular observables can be symmetric between repulsive and
attractive interactions in the Hubbard model, or symmetric between
ferromagnetic and anti-ferromagnetic interactions in the Ising model with
external fields. We present a theorem to determine the existence of the
dynamical symmetry in dissipative systems. This theorem is also responsible for
the symmetry of steady states, even without the constraint on the initial
state. We demonstrate the applications of our theorem with numerical
simulations using tensor network algorithms.",1912.05495v1
2020-03-23,Nernst heat theorem for the Casimir-Polder interaction between a magnetizable atom and ferromagnetic dielectric plate,"We find the low-temperature behavior of the Casimir-Polder free energy for a
polarizable and magnetizable atom interacting with a plate made of
ferromagnetic dielectric material. It is shown that the corresponding
Casimir-Polder entropy goes to zero with vanishing temperature, i.e., the
Nernst heat theorem is satisfied, if the dc conductivity of the plate material
is disregarded in calculations. If the dc conductivity is taken into account,
the Nernst theorem is violated. These results are discussed in light of recent
experiments.",2003.10101v1
2020-03-31,Floquet Control of Indirect Exchange Interaction in Periodically Driven Two-Dimensional Electron Systems,"We present a theory for the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction
mediated by a two-dimensional (2D) electron system subjected to periodic
driving. This is demonstrated for a heterostructure consisting of two
ferromagnets laterally sandwiching the 2D metallic spacer. Our calculations
reveal new non-analytic features in the spin susceptibility. For weak
light-matter coupling, the RKKY interaction shows oscillations with a period
tunable by the light amplitude and frequency. For stronger light-matter
coupling, the interaction becomes non-oscillatory and remains purely
ferromagnetic.",2003.14383v1
2020-05-18,Tuning thermo-magnetic properties of dilute-ferromagnet multilayers using RKKY interaction,"We demonstrate a 20-fold enhancement in the strength of the RKKY interlayer
exchange in dilute-ferromagnet/normal-metal multilayers by incorporating
ultrathin Fe layers at the interfaces. Additionally, the resulting increase in
the interface magnetic polarization profoundly affects the finite-size effects,
sharpening the Curie transition of the multilayer, while allowing to separately
tune its Curie temperature via intralayer magnetic dilution. These results
should be useful for designing functional materials for applications in
magneto-caloric micro-refrigeration and thermally-assisted spin-electronics.",2005.08846v1
2020-05-26,Magnetorheological effect in elastomers containing uniaxial ferromagnetic particles,"The description of the collective magnetorheological effect induced by
magnetic field in magnetoactive elastomers is proposed. The condition of
consistency is used between magnetic and mechanic momenta of forces exerted on
magnetically uniaxial ferromagnetic particles in elastomer at their
magnetization. The study shows that even in the case of small concentration of
particles, the value of magnetically-induced shear can be anomalously large,
reaching up to tens of percent. The deformation of magnetoactive elastomer can
evolve critically, as a second-order phase transition, if magnetic field is
aligned along the easy axis of particles.",2005.12736v1
2020-06-19,Absence of renormalization group pathologies in some critical Dyson-Ising ferromagnets,"The Dyson-Ising ferromagnet is a one-dimensional Ising model with a power law
interaction. When the power is between -1 and -2, the model has a phase
transition. Van Enter and Le Ny proved that at sufficiently low temperatures
the decimation renormalization group transformation is not defined in the sense
that the renormalized measure is not a Gibbs measure. We consider a modified
model in which the nearest neighbor couplings are much larger than the other
couplings. For a family of Hamiltonians which includes critical cases, we prove
that the first step of the renormalization group transformation can be
rigorously defined for majority rule and decimation.",2006.11429v1
2020-06-22,Macroscale non-local transfer of superconducting signatures to a ferromagnet in a cavity,"Cavity spintronics recently heralded non-local magnonic signal transfer
between magnetic samples. Here we show that by including superconductors in the
cavity, we can make use of these principles to bring composite
superconductor--ferromagnet systems to the macroscale. We analyze how a
superconductor's a.c. conductivity influences the spin dynamics of a spatially
separated magnet, and we discuss the potential impact on spintronic
applications.",2006.12516v2
2020-06-27,Thermal Kosterlitz-Thouless transitions in the $1/r^2$ long-range ferromagnetic quantum Ising chain revisited,"For the inverse square long-range ferromagnetic Ising chain in a transverse
field, the thermal phase boundary of the floating Kosterlitz-Thouless phase is
obtained for several values of the transverse field down to the quantum
critical point. The sharp domain walls in the classical model are increasingly
smeared out by the transverse field, which is evidenced by a pronounced
broadening of the non-universal bump in the specific heat. The discernability
of KT critical scaling in finite-size simulations is discussed.",2006.15402v1
2020-10-16,Zero-magnon sound in quantum Heisenberg ferromagnets,"Using a functional renormalization group approach we show that at low
temperatures and in a certain range of magnetic fields the longitudinal dynamic
structure factor of quantum Heisenberg ferromagnets in dimensions $D\leq 2$
exhibits a well-defined quasi-particle peak with linear dispersion that we
identify as zero-magnon sound. In $D>2$ the larger phase space available for
the decay into transverse spin waves leads only to a broad hump centered at
zero frequency whose width scales linearly in momentum.",2010.08425v3
2020-10-21,Thermal gating of magnon exchange in magnetic multilayers with antiferromagnetic spacers,"We observe a strong thermally-controlled magnon-mediated interlayer coupling
of two ferromagnetic layers via an antiferromagnetic spacer in spin-valve type
trilayers. The effect manifests itself as a field-induced coherent switching of
the two ferromagnets, which can be controlled by varying temperature and the
spacer thickness. We explain the observed behavior as due to a strong
hybridization of the ferro- and antiferro-magnetic magnon modes in the trilayer
at temperatures just below the N\'eel temperature of the antiferromagnetic
spacer.",2010.11134v1
2021-03-10,On the mean-field equations for ferromagnetic spin systems,"We derive mean-field equations for a general class of ferromagnetic spin
systems with an explicit error bound in finite volumes. The proof is based on a
link between the mean-field equation and the free convolution formalism of
random matrix theory, which we exploit in terms of a dynamical method. We
present three sample applications of our results to Ka\'{c} interactions,
randomly diluted models, and models with an asymptotically vanishing external
field.",2103.06207v4
2021-03-25,p+ip-wave pairing symmetry at type-II van Hove singularities,"Based on the random phase approximation calculation in two-orbital honeycomb
lattice model, we investigate the pairing symmetry of Ni-based transition-metal
trichalcogenides by electron doping access to type-II van Hove singularities
(vHs). We find that chiral even-parity d+id-wave (Eg) state is suppressed by
odd-parity p+ip-wave (Eu) state when electron doping approaches the type-II
vHs. The type-II vHs peak in density of states (DOS) enables to strengthen the
ferromagnetic fluctuation, which is responsible for triplet pairing. The
competition between antiferromagnetic and ferromagnetic fluctuation results in
pairing phase transition from singlet to triplet pairing. The Ni-based
transition-metal trichalcogenides provide a promising platform to
unconventional superconductor emerging from electronic DOS.",2103.13753v1
2021-03-29,Determination of paramagnetic and ferromagnetic phases of an Ising model on a third-order Cayley tree,"In this present paper, the recurrence equations of an Ising model with three
coupling constants on a third-order Cayley tree are obtained. Paramagnetic and
ferromagnetic phases associated with the Ising model are characterized. Types
of phases and partition functions corresponding to the model are rigorously
studied. Exact solutions of the mentioned model are compared with the numerical
results given in Ganikhodjaev et al. [J. Concr. Appl. Math., 2011, 9, No. 1,
26-34].",2103.15473v1
2021-04-03,Evidence for spin-polarized bound states in semiconductor-superconductor-ferromagnetic insulator islands,"We report Coulomb blockade transport studies of semiconducting InAs nanowires
grown with epitaxial superconducting Al and ferromagnetic insulator EuS on
overlapping facets. Comparing experiment to a theoretical model, we associate
cotunneling features in even-odd bias spectra with spin-polarized Andreev
levels. Results are consistent with zero-field spin splitting exceeding the
induced superconducting gap. Energies of subgap states are tunable on either
side of zero via electrostatic gates.",2104.01463v2
2021-05-08,Conserved momenta of ferromagnetic solitons through the prism of differential geometry,"The relation between symmetries and conservation laws for solitons in a
ferromagnet is complicated by the presence of gyroscopic (precessional) forces,
whose description in the Lagrangian framework involves a background gauge
field. This makes canonical momenta gauge-dependent and requires a careful
application of Noether's theorem. We show that Cartan's theory of differential
forms is a natural language for this task. We use it to derive conserved
momenta of the Belavin--Polyakov skyrmion, whose symmetries include
translation, global spin rotation, and dilation.",2105.03553v2
2021-06-09,Einstein-de Haas Nanorotor,"We propose a nanoscale rotor embedded between two ferromagnetic electrodes
that is driven by spin injection. The spin-rotation coupling allows this
nanorotor to continuously receive angular momentum from an injected spin under
steady current flow between ferromagnetic electrodes in an antiparallel
magnetization configuration. We develop a quantum theory of this angular
momentum transfer and show that a relaxation process from a precession state
into a sleeping top state is crucial for the efficient driving of the nanorotor
by solving the master equation. Our work clarifies a general strategy for
efficient driving of a nanorotor.",2106.04861v3
2021-07-12,Spin wave driven domain wall motion in easy-plane ferromagnets: a particle perspective,"In easy-plane ferromagnets, we show that the interplay between a domain wall
and a spin wave packet can be formulated as the collision of two massive
particles with a gravity-like attraction. In the presence of magnetic
dissipation, the domain wall mimics a particle subject to viscous friction,
while the spin wave packet resembles a particle of variable mass. Due to
attractive nature of the interaction, the domain wall acquires a backward
displacement as a spin wave packet penetrating the domain wall, even though
there is no change in momentum of the wave packet before and after penetration.",2107.05401v2
2021-08-28,Background for the Self Consistent Renormalisation (SCR) Theory,"A detailed review is given on the evolution of the theory of itinerant
magnetism. The self-consistent renormalization (SCR) theory is quite successful
in addressing the phenomenon of itinerant magnetism in weakly and nearly
ferromagnetic and anti-ferromagnetic materials. It goes beyond the Stoner and
random phase approximation (RPA) theories in taking the correlation effects
into account. The Mathematical machinery of the SCR theory is rather
complicated. The aim of these notes is to provide the required background. The
problems with Stoner and RPA theory are discussed and the way in which the SCR
theory rectifies those problems is also discussed.",2108.12683v1
2021-09-03,Robust spin-transfer torque and magnetoresistance in non-collinear antiferromagnetic junctions,"Ferromagnetic spin-valves and tunneling junctions are crucial for spintronics
applications and are one of the most fundamental spintronics devices. Motivated
by the potential unique advantages of antiferromagnets for spintronics, we
theoretically study here junctions built out of non-collinear antiferromagnets.
We demonstrate a large and robust magnetoresistance and spin-transfer torque
capable of ultrafast switching between parallel and anti-parallel states of the
junction. In addition, we show that the non-collinear order results in a
spin-transfer torque that is in several key aspects different from the
spin-transfer torque in ferromagnetic junctions.",2109.01399v1
2021-09-17,Fabricacion de un magnetron sputtering para deposito de peliculas nanometricas magneticas,"This paper presents the development of scientific instrumentation for the
fabrication of ferromagnetic thin films, by sputtering technique, for the use
of 2-inch-diameter targets. Thin films were deposited using Permalloy alloy
(Ni80Fe20) as ferromagnetic material at room temperature on Si (001)
substrates. The film thicknesses were measured with profilometry and a
deposition rate for this alloy of 16.2 nm/min was calculated. Scanning electron
microscopy showed a continuous film formation and a chemical composition
similar to the target",2109.08649v1
2021-10-06,Sharp Signal Detection Under Ferromagnetic Ising Models,"In this paper we study the effect of dependence on detecting a class of
structured signals in Ferromagnetic Ising models. Natural examples of our class
include Ising Models on lattices, and Mean-Field type Ising Models such as
dense Erd\H{o}s-R\'{e}nyi, and dense random regular graphs. Our results not
only provide sharp constants of detection in each of these cases and thereby
pinpoint the precise relationship of the detection problem with the underlying
dependence, but also demonstrate how to be agnostic over the strength of
dependence present in the respective models.",2110.02949v1
2021-11-24,Spin Hall response at finite wave vector in ferromagnets,"Spin Hall effect at finite wave vector in a ferromagnetic conductor is
theoretically studied by calculating the spin density as the linear response to
an applied electric field. The cases of a spin-orbit interaction due to random
impurities and a localized Rashba interaction are considered. It is shown that
the spin Hall effect has a broad response for the wave vector $q\lesssim 2\kf$
where $\kf $ is the Fermi wave vector. This fact confirms the local nature of
the spin-charge conversion effects.",2111.12247v1
2021-12-21,Hyperscaling analysis of a disorder-induced ferromagnetic quantum critical point in Ni$_{1-x}$Rh$_{x}$ with $x = 0.375$,"Here we report on hyperscaling analysis on thermodynamic measurements as a
function of temperature and magnetic field for Ni$_{1-x}$Rh$_{x}$ with $x =
0.375$ where a ferromagnetic quantum critical point has been recently
identified [Phys. Rev. Lett. $\textbf{124}$, 117203 (2020)]. The obtained
critical exponents agree well with the theory proposed by Belitz, Kirkpatrick,
and Vojta for disorder tuned quantum critical point in the preasymptotic
region.",2112.10997v1
2021-12-26,Uniqueness result for a weighted pendulum equation modeling domain walls in notched ferromagnetic nanowires,"We prove an existence and uniqueness result for solutions $\varphi$ to a
weighted pendulum equation in $\mathbb{R}$ where the weight is non-smooth and
coercive. We also establish (in)stability results for $\varphi$ according to
the monotonicity of the weight. These results are applied in a reduced model
for thin ferromagnetic nanowires with notches to obtain existence, uniqueness
and stability of domain walls connecting two opposite directions of the
magnetization.",2112.13358v1
2022-01-07,Integrable negative flows of the Heisenberg ferromagnet equation hierarchy,"We study the negative flows of the hierarchy of the integrable Heisenberg
Ferromagnet model and their soliton solutions. The first negative flow is
related to the so-called short pulse equation. We provide a framework which
generates Lax pairs for the other members of the hierarchy. The Inverse
scattering, based on the dressing method is illustrated with the derivation of
the one-soliton solution.",2201.02655v1
2022-02-14,Optimizing the topological properties of stacking semiconductor-ferromagnet-superconductor heterostructures,"We study the electronic properties of a planar semiconductor-superconductor
heterostructure, in which a thin ferromagnetic insulator layer lies in between
and acts as a spin filtering barrier. We find that in such a system one can
simultaneously enhance the strengths of all the three important induced
physical quantities, i.e., Rashba spin-orbit coupling, exchange coupling, and
superconducting pairing potential, for the hybrid mode by external gating. Our
results show specific advantage of this stacked device geometry compared to
conventional devices. We further discuss how to optimize geometrical parameters
for the heterostructure and complement our numerical simulations with analytic
calculations.",2202.06604v1
2022-04-08,In situ controllable magnetic phases in doped twisted bilayer transition-metal dichalcogenides,"We study the electronic structure of hole-doped transition metal
dichalcogenides for small twist-angels, where the onsite repulsion is extremely
strong. Using unbiased diagrammatic Monte Carlo simulations, we find evidence
for magnetic correlations which are driven by delocalization and can be
controlled in situ via the dielectric environment. For weak spin-orbit
coupling, we find that the moderately doped system becomes anti-ferromagnetic,
whilst the regime of strong spin-orbit coupling features ferromagnetic
correlations. We show that this behavior is accurately predicted by an
analytical theory based on moment expansion of the Hamiltonian, and analysis of
corresponding particle trajectories.",2204.03917v1
2022-04-13,What Formulation Should One Choose for Modeling a 3D HTS Motor Pole with Ferromagnetic Materials?,"We discuss the relevance of several finite-element formulations for nonlinear
systems containing high-temperature superconductors (HTS) and ferromagnetic
materials (FM), in the context of a 3D motor pole model. The formulations are
evaluated in terms of their numerical robustness and efficiency. We propose a
coupled h-phi-a-formulation as an optimal choice, modeling the problem with an
a-formulation in the FM and an h-phi-formulation in the remaining domains.
While maintaining a low number of degrees of freedom, the h-phi-a-formulation
guarantees a robust resolution and strongly reduces the number of iterations
required for handling the nonlinearities of HTS and FM compared to standard
formulations.",2204.06499v1
2022-04-28,Graphene on a ferromagnetic substrate: instability of the electronic liquid,"We previously show [JETP Letters, {\bf 114}, 763 (2021)] that a graphene
sample placed on a ferromagnetic substrate demonstrates a cooperative
magnetoelectronic instability. The instability induces a gap in the electronic
spectrum and a canting deformation of the magnetization near the
graphene-substrate interface. In this paper we prove that the interaction
between the electrons in graphene strongly enhances the instability. Our
estimates suggest that in the presence of even a moderate interaction the
instability can be sufficiently pronounced to be detected experimentally in a
realistic setting.",2204.13434v1
2022-04-30,Piezoelectric ferromagnetism in two dimensional FeCl$_2$,"We predict that monolayer FeCl$_2$ is a two-dimensional piezoelectric
ferromagnet (PFM) with easy-axis magnetism and a Curie temperature of 260 K.
Our ab-initio calculations combined with data mining reveal 2H-FeCl$_2$ as the
only easy-axis 2D monolayer PFM, and that its magnetic anisotropy increases
many-fold with moderate hole doping. We develop an analysis based on magnetic
anisotropy energy densities that explain the magnetic and doping-dependent
behavior of FeCl$_2$, as well as VSe$_2$ and CrI$_3$, and can enable the design
of future 2D magnetically ordered materials.",2205.00300v1
2022-05-03,On multi-soliton solutions to a generalized inhomogeneous nonlinear Schrodinger equation for the Heisenberg ferromagnetic spin chain,"A generalized inhomogeneous higher-order nonlinear Schrodinger (GIHNLS)
equation for the Heisenberg ferromagnetic spin chain system in (1+1)-dimensions
under zero boundary condition at infinity is taken into account. The spectral
analysis is first performed to generate a related matrix Riemann-Hilbert
problem on the real axis. Then, through solving the resulting matrix
Riemann-Hilbert problem by taking the jump matrix to be the identity matrix,
the general bright multi-soliton solutions to the GIHNLS equation are attained.
Furthermore, the one- and two-soliton solutions are written out and analyzed by
figures.",2205.01318v2
2022-05-07,Current-driven Dynamics of Skyrmion Bubbles in Achiral Uniaxial Magnets,"We report dynamics of skyrmion bubbles driven by spin-transfer torque in
achiral ferromagnetic nanostripes using micromagnetic simulations. In a
three-dimensional uniaxial ferromagnet with a quality factor that is smaller
than 1, the skyrmion bubble is forced to stay at the central nanostripe by a
repulsive force from the geometry border. The coherent motion of skyrmion
bubbles in the nanostripe can be realized by increasing the quality factor to
~3.8. Our results should propel the design for future spintronic devices such
as artificial neural computing and racetrack memory based on dipole-stabilized
skyrmion bubbles.",2205.03641v1
2022-06-02,Itinerant spin polaron and metallic ferromagnetism in semiconductor moiré superlattices,"Itinerant spin polaron and metallic ferromagnetism are theoretically
predicted in the Mott insulator in semiconductor moir\'e superlattices doped
below and above half filling of the narrow moir\'e band, respectively. The
existence of spin polaron can be directly identified from the kink in the
dependence of the charge gap on the magnetic field.",2206.01221v3
2022-06-06,Analytical models for the pulse shape of a superconductor-ferromagnet tunnel junction thermoelectric microcalorimeter,"The superconductor-ferromagnet thermoelectric detector (SFTED) is a novel
ultrasensitive radiation detector based on the giant thermoelectric effect in
superconductorferromagnet tunnel junctions. We demonstrate analytical models
and solutions in the time domain for a SFTED operated as a microcalorimeter
(pulse excitation), in the linear smallsignal limit. Based on these solutions,
the signal current and temperature pulse response were studied for two
different electrical circuit models, providing design conditions for stable and
non-oscillatory response.",2206.02513v1
2022-06-10,Spin Pumping into Anisotropic Dirac Electrons,"We study spin pumping into an anisotropic Dirac electron system induced by
microwave irradiation to an adjacent ferromagnetic insulator theoretically. We
formulate the Gilbert damping enhancement due to the spin current flowing into
the Dirac electron system using second-order perturbation with respect to the
interfacial exchange coupling. As an illustration, we consider the anisotropic
Dirac system realized in bismuth to show that the Gilbert damping varies
according to the magnetization direction in the ferromagnetic insulator. Our
results indicate that this setup can provide helpful information on the
anisotropy of the Dirac electron system.",2206.04899v1
2022-07-30,Inertial spin waves in ferromagnets and antiferromagnets,"Inertial effects in spin dynamics are theoretically predicted to emerge at
ultrashort time scales, but their experimental signatures are often ambiguous.
Here, we calculate the spin-wave spectrum in ferromagnets and two-sublattice
antiferromagnets in the presence of inertial effects. It is shown how
precession and nutation spin waves hybridize with each other, leading to the
renormalization of the frequencies, the group velocities, the effective
gyromagnetic ratios and the effective damping parameters. Possible ways of
distinguishing between the signatures of inertial dynamics and similar effects
explainable within conventional models are discussed.",2208.00131v1
2022-08-01,Calculation of magnon drag force induced by an electric current in ferromagnetic metals,"Magnon drag effect induced by an applied electric field in ferromagnetic
metals is theoretically studied by a microscopic calculation of the force on
magnons arising from magnon emission/absorption and scattering due to driven
electrons. It is shown that magnon scattering contribution dominates over the
emission/absorption one in a wide temperature regime in good metals with long
elastic lifetime $\taue$, as the latter has a relative suppression factor of
$(\Deltasd\taue)^{-2}$ due to the electron spin flip by the magnon, where
$\Deltasd$ is the $sd$ exchange interaction energy. Spin-transfer efficiency is
discussed including the magnon drag effect.",2208.00622v1
2022-08-13,The Landau-Lifshitz-Bloch equation on the thin film,"We consider the initial boundary value problem of Landau-Lifshitz-Bloch
equation on three-dimensional ferromagnetic films, where the effective field
contains the stray field controlled by Maxwell equation and the exchange field
contains exchange constant. In this paper, we establish the existence of weak
solutions of the equation by using the Faedo-Galerkin approximation method. We
also derive its two-dimensional limit equation in a mathematically rigorous way
when the film thickness tends to zero under appropriate compactness conditions.
Moreover, we obtain an equation that can better describe the magnetic dynamic
behavior of ferromagnetic films with negligible thickness at high temperature.",2208.06558v1
2022-04-26,Functional nanostructures superconductor-ferromagnet for spintronics,"The work is devoted to the study of the processes of formation and analysis
of the parameters of a functional nanostructure -- a superconducting spin
valve, which is a multilayer structure consisting of ferromagnetic cobalt
nanofilms separated by niobium superconductor films. The studies were carried
out using molecular dynamics simulations. The atomic structure of individual
nanolayers of the system is considered.",2208.08364v1
2022-08-26,Unified theory of spin and charge in a ferromagnet,"We derive a unified theory of spin and charge degrees of freedom in a
ferromagnet. The spin-transfer torque and spin electromotive force are examined
from the coarse-grained perspective of collective coordinates. The resulting
equations of motion reflect a balance of conservative, gyroscopic
(Berry-phase), and dissipative forces. We then expand the space of collective
coordinates by adding the electric charge. The adiabatic spin-transfer torque
and spin emf turn out to be a gyroscopic force; their nonadiabatic counterparts
are a dissipative force.",2208.12800v2
2022-09-20,Possible origin of the interface field in spintronic experiments,"The effective field at the interface between ferromagnetic and metal layers
is often observed in spintronic experiments. It is common to ascribe it to
specific exchange interactions caused by spin-orbit coupling, namely, Rashba
field, Dzyaloshinskiy-Moriya interaction, spin currents, etc. Alternative view
involves the global magnetic field (Oersted field) generated by current both
inside and outside the conductor. It is shown here that the inhomogeneous stray
field surrounding ferromagnetic layers can produce significant contribution
into the observed interface field. This mechanism should be taken into account
for better understanding the current-induced phenomena in magnetic multilayers.",2209.09738v1
2022-09-20,Field-Induced Spin Nematic Liquid of the $S=1/2$ Bond-Alternating Chain with the Anisotropy,"The $S=1/2$ ferromagnetic-antiferromagnetic bond-alternating spin chain with
the anisotropy on the ferromagnetic exchange interaction in magnetic field is
investigated using the numerical diagonalization and the density matrix
renormalization group analyses. It is found that the nematic-spin-dominant
Tomonaga-Luttinger liquid phase is induced by the external magnetic field for
sufficiently large anisotropy. The phase diagram with respect to the anisotropy
and the magnetization is presented.",2209.09740v1
2022-09-28,Constructing Non-Abelian Quantum Spin Liquids Using Combinatorial Gauge Symmetry,"We construct Hamiltonians with only 1- and 2-body interactions that exhibit
an exact non-Abelian gauge symmetry (specifically, combinatiorial gauge
symmetry). Our spin Hamiltonian realizes the quantum double associated to the
group of quaternions. It contains only ferromagnetic and anti-ferromagnetic
$ZZ$ interactions, plus longitudinal and transverse fields, and therefore is an
explicit example of a spin Hamiltonian with no sign problem that realizes a
non-Abelian topological phase. In addition to the spin model, we propose a
superconducting quantum circuit version with the same symmetry.",2209.14333v2
2022-11-17,Boundary Ferromagnetism in Zigzag Edged Graphene,"The flat band of edge states which occur in the simple tight-binding lattice
model of graphene with a zig-zag edge have long been conjectured to take up a
ferromagnetic configuration. In this work we demonstrate that, for a large
class of interaction Hamiltonians which can be added to the tight-binding
model, and at the first order in perturbation theory, the degeneracy of the
edge states is resolved in such a way that the ground state is in the maximal,
spin j = N/2 representation of the spin symmetry where N is the number of edge
states.",2211.09282v1
2022-11-24,Avoided ferromagnetic quantum critical point in CeZn,"Cubic CeZn shows a structural phase transition under pressure, and it
modifies the ground state from an antiferromagnetic (AFM) state to a
ferromagnetic (FM) state. To investigate how the FM state terminates at a
quantum phase transition, we measured the electrical resistivity under pressure
for a single crystal CeZn. The transition temperature into the FM state
decreases monotonously with increasing pressure, accompanied by the pronounced
Kondo effect, but a drastic change in the field response occurs before the
ordered phase terminates. This result suggests that the FM quantum critical
point is avoided by the appearance of an AFM-like state.",2211.13401v1
2022-12-29,Localized Spin-Wave Modes and Microwave Absorption in Random-Anisotropy Ferromagnets,"The theory of localized spin-wave excitations in random-anisotropy magnets
has been developed. Starting with a pure Heisenberg ferromagnet, we study the
evolution of standing spin waves in a finite-size sample towards localized
modes on increasing the strength of random anisotropy. Profiles of the
localized modes and their phases are analyzed and visualized in a 2D sample.
Localization length is obtained by several methods and its dependence on random
anisotropy is computed. The connection between the localization of spin
excitations and the broadband nature of the absorption of microwave power by
random-anisotropy magnets is elucidated.",2212.14301v1
2023-02-15,Perfect Sampling of $q$-Spin Systems on $\mathbb Z^2$ via Weak Spatial Mixing,"We present a perfect marginal sampler of the unique Gibbs measure of a spin
system on $\mathbb Z^2$. The algorithm is an adaptation of a previous `lazy
depth-first' approach by the authors, but relaxes the requirement of strong
spatial mixing to weak. It exploits a classical result in statistical physics
relating weak spatial mixing on $\mathbb Z^2$ to strong spatial mixing on
squares. When the spin system exhibits weak spatial mixing, the run-time of our
sampler is linear in the size of sample. Applications of note are the
ferromagnetic Potts model at supercritical temperatures, and the ferromagnetic
Ising model with consistent non-zero external field at any non-zero
temperature.",2302.07821v1
2023-02-21,Efficient asymptotic models for axisymmetric eddy current problems in linear ferromagnetic materials,"The problem under consideration is that of time-harmonic eddy current
problems in linear ferromagnetic materials surrounded by a dielectric medium
with a smooth common interface. Assuming axisymmetric geometries and
orthoradial axisymmetric data, we construct an efficient multiscale expansion
for the orthoradial solution that provides reduced computational costs. We
investigate numerically the accuracy of the approach using an analytical
procedure and infinite cylinders as well. It results that the computation of
two asymptotics is sufficient to ensure accurate solutions in the case of low
frequencies.",2302.10457v1
2023-02-27,Ferromagnetism and Metal-Insulator transition in F-doped LaMnO3,"We present our studies on polycrystalline samples of fluorine doped LaMnO3
(LaMnO3-yFy). LaMnO2.5F0.5 exhibits remarkable magnetic and electrical
properties. It shows ferromagnetic and metallic behavior with a high Curie
temperature of ~ 239 K and a high magnetoresistance of -64. This drastic change
in magnetic properties in comparison to pure LaMnO3 is ascribed to the presence
of mixed-valence Mn ions driven by the F-doping at the O-sites, which enables
double exchange (DE) in LMOF. Furthermore, the resistivity data exhibits two
resistivity peaks at 239 K and 213 K, respectively. Our results point towards
the possibility of multiple double exchange hopping paths of two distinct
resistances existing simultaneously in the sample below 213 K.",2302.13845v1
2023-03-22,Even-odd effect for spin current through thin antiferromagnetic insulator,"Magnon spin transport in a metal-antiferromagnetic insulator-ferromagnetic
insulator heterostructure is considered. The spin current is generated via the
spin Seebeck effect and in the limit of clean sample where the effects of
interface imperfections and lattice defects are excluded. For NiO as an
antiferromagnetic insulator we have a magnetic order of antiferromagnetically
combined planes which are internally in ferromagnetic order. We find that the
sign of the spin current depends on the magnetization direction of the plane
next to the metal resulting in an even-odd effect for the spin current.
Moreover, as long as damping is excluded, this even-odd effect is the only
remaining dependence on the NiO thickness for high temperatures.",2303.12282v1
2023-03-27,Metastable ferromagnetic clusters in dissipative many-body systems of polar molecules,"We investigate the effect of two-body loss due to chemical reactions on
quantum magnetism of fermionic polar molecules in an optical lattice. We show
that an interplay between dissipation and strong long-range interactions leads
to formation of metastable ferromagnetic clusters. The spin states of clusters
are controlled by interaction parameters and reflect the symmetry of
interactions. The size of clusters strongly depends on the initial
configuration of molecules due to Hilbert-space fragmentation during
dissipative many-body dynamics. We construct an effective model to show the
emergence of metastable states as quasi-dark states. Application to quantum
simulation of the spin-$S$ Heisenberg model is discussed.",2303.14967v2
2023-04-12,Transport properties of very overdoped nonsuperconducting Bi2Sr2CuO6+d thin films,"The transport properties, resistance, Hall effect, and low T
magnetoresistance for very oxygen overdoped nonsuperconducting Bi2Sr2CuO6+d
(Bi2201) thin films are reported. From 20 to 300K, the temperature dependence
of the resistance is well described by a law of the form a+bT4/3, theoretically
predicted to occur in the presence of ferromagnetic fluctuations. In addition,
this prediction is reinforced by the analysis of the transverse and the
longitudinal low T magnetoresistance. Interestingly, the presence of a weak
disorder causing low T electronic localization allows us to evidence very short
diffusion lengths, as observed in other systems with ferromagnetic
fluctuations.",2304.05851v1
2023-06-08,A Macroscopic Theory of Saturated Ferromagnetic Conductors,"A phenomenological theory of rigid and saturated ferromagnetic conductors is
constructed from a four-continuum model consisting of a rigid lattice
continuum, a bound charge continuum for polarization, a circulating current
continuum for magnetization, and a free charge continuum for electrical
conduction. The basic laws of physics are applied to the four continua. Thermal
couplings and the related dissipative effects are also included. The theory
includes the Landau-Lifshitz-Gilbert equation as one of a system of
simultaneous equations.",2306.11525v1
2023-06-22,SPT extension of $Z_2$ quantum Ising model's ferromagnetic phase,"This paper focuses on the creation of a model with explicitly defined
symmetry-protected topological (SPT) phases on a triangular lattice as an
extension of $Z_2$ Ising model's ferromagnetic phase. Unlike in previously
known similar works, this model is based on an initially interacting system
which is known to describe experimentally realizable physical systems. The
Hamiltonian for these edge states contains four-point spin interactions between
next-to-next nearest neighbors. As an initially interacting A generic technique
for creating SPT models is developed, allowing for the construction of
translation-invariant edge models.",2306.13170v2
2023-09-08,Nonlinear Stability of Static Néel Walls in Ferromagnetic Thin Films,"In this paper, the nonlinear (orbital) stability of static 180^\circ N\'eel
walls in ferromagnetic films, under the reduced wave-type dynamics for the
in-plane magnetization proposed by Capella, Melcher and Otto [CMO07], is
established. It is proved that the spectrum of the linearized operator around
the static N\'eel wall lies in the stable complex half plane with non-positive
real part. This information is used to show that small perturbations of the
static N\'eel wall converge to a translated orbit belonging to the manifold
generated by the static wall.",2309.04432v2
2023-09-11,Reentrant Ferromagnetic Ordering of the Random-Field Heisenberg Model in d>2 Dimensions: Fourier-Legendre Renormalization-Group Theory,"The random-magnetic-field classical Heisenberg model is solved in spatial
dimensions d>=2 using the recently developed Fourier-Legendre
renormalization-group theory for $4\pi$ steradians continuously orientable
spins, with renormalization-group flows of 12,500 variables. The
random-magnetic-field Heisenberg model is exactly solved in 10 hierarchical
models, for d=2,2.26,2.46,2.58,2.63,2.77,2.89,3. For non-zero random fields,
ferromagnetic order is seen for d>2. This ordering shows, at d=3, reentrance as
a function of temperature.",2309.05576v1
2023-09-13,Multiscaling in the 3D critical site-diluted Ising ferromagnet,"We have studied numerically the appearance of multiscaling behavior in the
three-dimensional ferromagnetic Ising site diluted model, in the form of a
multifractal distribution of the decay exponents for the spatial correlation
functions at the critical temperature. We have computed the exponents of the
long-distance decay of higher moments of the correlation function, up to the
10th power, by studying three different quantities: global susceptibilities,
local susceptibilities and correlation functions. We have found very clear
evidences for multiscaling behavior.",2309.06752v2
2023-09-13,Symmetry transformation of nonlinear optical current of tilted Weyl nodes and application to ferromagnetic MnBi2Te4,"A Weyl node is characterized by its chirality and tilt. We develop a theory
of how $n$th-order nonlinear optical conductivity behaves under transformations
of anisotropic tensor and tilt, which clarify how chirality-dependent and
-independent parts of optical conductivity transform under the reversal of tilt
and chirality. Built on this theory, we propose ferromagnetic $\rm
MnBi_{2}Te_{4}$ as a magnetoelectrically regulated, terahertz optical device,
by magnetoelectrically switching the chirality-dependent and -independent dc
photocurrents. These results are useful for creating nonlinear optical devices
based on topological Weyl semimetals.",2309.06760v2
2023-10-06,Near optimal bounds for weak and strong spatial mixing for the anti-ferromagnetic Potts model on trees,"We show that the anti-ferromagnetic Potts model on trees exhibits strong
spatial mixing for a near-optimal range of parameters. Our work complements
recent results of Chen, Liu, Mani, and Moitra [arXiv.2304.01954] who showed
this to be true in the infinite temperature setting, corresponding to uniform
proper colorings. We furthermore prove weak spatial mixing results
complementing results in [arXiv.2304.01954].",2310.04338v1
2023-10-23,Gyromagnetic effects in dynamics of magnetic microparticles,"We derive equations of motion for paramagnetic and ferromagnetic particles
fully accounting for gyromagnetic effects. Considering the Einstein-de Haas
effect for an ellipsoidal paramagnetic particle we find that starting from a
quiescent non-magnetized state, after the field is switched on a rotation along
the short axis is established. This is confirmed by the stability analysis of
the fixed points of the corresponding ordinary differential equations. In the
case of a ferromagnetic particle we integrate the equations of motion in the
dissipationless case by finding the integrals of motion. We also reformulate
the equations in a Hamiltonian framework in this case and find a period of
small nutation oscillations.",2310.14674v1
2023-10-30,"Magnetic Stability, Fermi Surface Topology, and Spin-Correlated Dielectric Response in Monolayer 1T-CrTe2","We have carried out density-functional theory (DFT) calculations to study the
magnetic stability of both ferromagnetic (FM) and anti-ferromagnetic (AFM)
states in monolayer 1T-CrTe2. Our results show that the AFM order is lower in
energy and thus is the ground state. By tuning the lattice parameters, the AFM
order can transition to the FM order, in good agreement with experimental
observation. We observe a commensurate SDW alongside the previously predicted
CDW, and attribute the AFM order to the SDW. This results in distinct hole and
electron Fermi pockets and a pronounced optical anisotropy, suggesting
quasi-one-dimensional behavior in this material.",2310.19735v1
2023-11-02,The generation and detection of the spin-valley-polarization in semi-Dirac materials,"We investigated the transport properties in a normal metal/ferromagnet/normal
metal/superconductor junction based on semi-Dirac materials with inverted
energy gap. With a scattering matrix approach, we show that the electron
transport in the junction is spin-valley-polarized due to the ferromagnetic
exchange energy. It is also shown that the Andreev reflection is strongly
suppressed, which is a clear experimental signal for the
spin-valley-polarization in semi-Dirac materials.",2311.00948v1
2023-11-27,Positive magnetoresistance in anapole superconductor junctions,"The article presents a method to detect time-reversal symmetry breaking in
non-centrosymmetric superconductors using only transport measurements.
Specifically, if time-reversal symmetry is broken via a phase difference
between singlet and triplet correlations, as in anapole superconductors, the
conductance in SFN junctions is enhanced by increasing the exchange field
strength in the ferromagnet. This is in sharp contrast with the negative
magnetoresistance when using superconductors in which time reversal symmetry is
preserved. Moreover, results show a large quadrupolar component of the
magnetoresistance which is qualitatively different from the bipolar giant
magnetoresistance in strong ferromagnets.",2311.15708v1
2023-12-07,Oxidation tuning of ferroic transitions in Gd$_2$C monolayer,"Tuning of ferroic phases provides great opportunities for material
functionalities, especially in two-dimensional materials. Here, a $4f$
rare-earth carbide Gd$_2$C monolayer is predicted to be ferromagnetic metal
with large magnetization, inherited from its bulk property. Based on
first-principles calculations, we propose a strategy that the surface
passivation can effectively tune its ferroicity, namely switching among
ferromagnetic, antiferromagnetic, and ferroelectric phases. Metal-insulator
transition also occurs accompanying these ferroic transitions. Our calculation
also suggests that the magneto-optic Kerr effect and second harmonic generation
are effective methods to monitor these phase transitions.",2312.04011v1
2023-12-17,Symmetry breaking in zero-field two-dimensional electron bilayers,"We theoretically consider bilayers of two dimensional (2D) electron gases as
in semiconductor quantum wells, and investigate possible spontaneous symmetry
breaking transitions at low carrier densities driven by interlayer Coulomb
interactions. We use a self-consistent technique implementing mean field
truncations of the interacting four-fermion terms, and find a U(1) layer
symmetry breaking transition at low carrier densities where the individual
layer identities are lost leading to an effective pseudospin XY ferromagnet in
the 2D plane. Our results validate earlier theoretical works using simpler
restricted Hartree-Fock techniques, and establish the pseudospin XY ferromagnet
as a possible low-density symmetry broken phase of 2D bilayers.",2312.10791v2
2024-01-15,Optimization of thermo-spin voltage in vertical nanostructures by geometrical means,"The thermo-spin conversion provides new concepts for further developing the
green energy-harvesting technology because spin can be controlled with minimal
energy in nanostructures. Through theoretical analysis of thermo-spin
generation, transportation and conversion in ferromagnet/non-ferromagnet/heavy
metal (FM/NM/HM) vertical structures, we found that the output transverse
thermo-spin voltage is independent of the structure's width, but varies in a
linear function with the structure's length. To validate our predictions, we
fabricated the thermo-spin devices with a CoFeAl/Cu/Pt structure. Our results
indicate that FM/NM/HM structures can be utilized to design flexible
thermo-spin conversion devices.",2401.07755v1
2024-02-20,Electron-phonon coupling in ferromagnetic Fe-Co alloys from first principles,"We calculate from first principles the electron-phonon coupling strength in
ferromagnetic iron-cobalt Fe$_{1-x}$Co$_x$ alloys for compositions ranging from
$x=0$ to $x=0.75$. We find strong, spin-dependent variation of the
electron-phonon coupling strength with alloy composition. The minimum of the
electron-phonon interaction is found near the composition $x=0.25$. We analyze
the variation of the electron-phonon interaction with composition, as a
function of electron spin, density of states, electron-phonon matrix elements,
and phonon frequencies. Our results are in good qualitative agreement with
magnetization dynamics experiments.",2402.12650v1
2024-04-04,Interaction-induced nonlinear magnon transport in noncentrosymmetric ferromagnets,"We study the effect of the magnon-magnon interaction on the nonlinear magnon
transport. The magnon-magnon interaction induces nonreciprocal magnon decay
when the time-reversal symmetry is broken, and leads to nonlinear thermal
responses of magnons. We construct a theoretical framework to study the
nonlinear thermal responses due to the nonreciprocal magnon decay by using the
imaginary Dyson equation and quantum kinetic theory, which is then applied to a
model of honeycomb ferromagnets with Dzyaloshinskii-Moriya interactions. An
order estimate shows that the nonlinear thermal response from the present
mechanism is feasible for experimental measurement.",2404.03260v1
2024-04-08,Electrical control of superconducting spin valves using ferromagnetic helices,"The geometrical properties of a helical ferromagnet are shown theoretically
to control the critical temperature of a proximity-coupled superconductor.
Using the Usadel equation for diffusive spin transport, we provide
self-consistent analysis of how curvature and torsion modulate the proximity
effect. When the helix is attached to a piezoelectric actuator, the pitch of
the helix -- and hence the superconducting transition -- can be controlled
electrically.",2404.05798v1
1994-01-24,Theory of Spin-Split Cyclotron Resonance in the Extreme Quantum Limit,"We present an interpretation of recent cyclotron resonance experiments on the
two-dimensional electron gas in GaAs/AlGaAs heterostructures. We show that the
observed dependence of the resonance spectrum on Landau level occupancy and
temperature arises from the interplay of three factors: spin-splitting of the
cyclotron frequency; thermal population of the two spin states; and coupling of
the resonances for each spin orientation by Coulomb interactions. In addition,
we derive an $f$-sum rule which allows spin polarisation to be determined
directly from resonance spectra.",9401049v1
1996-09-03,Comment on ``New Class of Resonances at the Edge of the Two-Dimensional Electron Gas.'',"A reproducible resonance structure in the conductance through an
incompressible strip in the quantized Hall regime was recently reported by
Zhitenev {\it et al}. Although the authors disfavored the explanation of the
conductance resonances based on resonant tunneling (RT) through an impurity
state, I believe that it should not be dismissed and can explain a number of
experimental observations very well. In particular, I point out a new
characteristic signature of RT in the quantized Hall regime: the quantization
of the slopes of the resonance tracks on the magnetic field-gate voltage plot.",9609023v1
1998-03-17,Dielectric resonances of binary random networks,"We investigate the AC conductivity of binary random impedance networks, with
emphasis on its dependence on the ratio of the complex conductances of both
phases. We propose an algorithm to determine the conductance of a finite
network, in terms of its poles and of the associated residues. A numerical
implementation of the algorithm, on the example of the square lattice, allows a
detailed investigation of the resonant dielectric response of the binary model,
including the density of resonances, the spectral function, the distribution of
spacings between resonances. The distribution of local electric fields at
resonance is found to be multifractal.",9803209v1
1999-05-04,"Spectroscopy, Interactions and Level Splittings in Au Nanoparticles","We have measured the electronic energy spectra of nm-scale Au particles using
a new tunneling spectroscopy configuration. The particle diameters ranged from
5nm to 9nm, and at low energies the spectrum is discrete, as expected by the
electron-in-a-box model. The density of tunneling resonances increases rapidly
with energy, and at higher energies the resonances overlap forming broad
resonances. Near the Thouless energy, the broad resonances merge into a
continuum. The tunneling resonances display Zeeman splitting in a magnetic
field. Surprisingly, the g-factors (~0.3) of energy levels in Au nano-particles
are much smaller than the g-factor (2.1) in bulk gold.",9905043v1
1999-06-15,Internal Spatiotemporal Stochastic Resonance in a Microscopic Surface Reaction Model,"We show the existence of internal stochastic resonance in a microscopic
stochastic model for the oscillating CO oxidation on single crystal surfaces.
This stochastic resonance arises directly from the elementary reaction steps of
the system without any external input. The lattice gas model is investigated by
means of Monte Carlo simulations. It shows oscillation phenomena and mesoscopic
pattern formation. Stochastic resonance arises once homogeneous nucleation in
the individual surface phases (reconstructed and non-reconstructed) is added.
This nucleation is modelled as a noise process. As a result, synchronization of
the kinetic oscillations is obtained. Internal stochastic resonance may thus be
an internal regulation mechanism of extreme adaptability.",9906215v1
1999-07-08,Semiclassical theory of the emission properties of wave-chaotic resonant cavities,"We develop a perturbation theory for the lifetime and emission intensity for
isolated resonances in asymmetric resonant cavities. The inverse lifetime
$\Gamma$ and the emission intensity $I(\theta)$ in the open system are
expressed in terms of matrix elements of operators evaluated with eigenmodes of
the closed resonator. These matrix elements are calculated in a semiclassical
approximation which allows us to represent $\Gamma$ and $I(\theta)$ as sums
over the contributions of rays which escape the resonator by refraction.",9907109v1
1999-12-02,Nanomechanical vibrating wire resonator for phonon spectroscopy in Helium,"We demonstrate how to build a vibrating wire resonator for phonon excitation
in liquid helium. The resonator is designed as a nanoscopic mechanically
flexible beam machined out of a semiconductor/metal-hybrid. Quenching of the
mechanical resonance around 100 MHz by phonon excitation in liquid ^4He at 4.2
K is shown. First measurements operating the nano-resonator in a dilution of
^3He/^4He at 30 mK are presented.",9912039v1
1999-12-22,Fano Resonances in Electronic Transport through a Single Electron Transistor,"We have observed asymmetric Fano resonances in the conductance of a single
electron transistor resulting from interference between a resonant and a
nonresonant path through the system. The resonant component shows all the
features typical of quantum dots, but the origin of the non-resonant path is
unclear. A unique feature of this experimental system, compared to others that
show Fano line shapes, is that changing the voltages on various gates allows
one to alter the interference between the two paths.",9912419v2
2000-07-16,High frequency resonant experiments in Fe$_8$ molecular clusters,"Precise resonant experiments on Fe$_{8}$ magnetic clusters have been
conducted down to 1.2 K at various tranverse magnetic fields, using a
cylindrical resonator cavity with 40 different frequencies between 37 GHz and
110 GHz. All the observed resonances for both single crystal and oriented
powder, have been fitted by the eigenstates of the hamiltonian ${\cal
H}=-DS_z^2+ES_x^2-g\mu_B{\bf H}\cdot {\bf S}$. We have identified the
resonances corresponding to the coherent quantum oscillations for different
orientations of spin S = 10.",0007265v1
2000-08-23,Impurity induced resonant state in a pseudogap state of a high temperature superconductor,"We predict a resonance impurity state generated by the substitution of one Cu
atom with a nonmagnetic atom, such as Zn, in the pseudogap state of a high-T_c
superconductor. The precise microscopic origin of the pseudogap is not
important for this state to be formed, in particular this resonance will be
present even in the absence of superconducting fluctuations in the normal
state. In the presence of superconducting fluctuations, we predict the
existence of a counterpart impurity peak on a symmetric bias.
  The nature of impurity resonance is similar to the previously studied
resonance in the d-wave superconducting state.",0008349v1
2001-03-16,Dispersoin of the πresonance,"We study the dispersion of the $\pi$ resonance in the superconducting state
within the projected SO(5) model\cite{project}. Away from the the commensurate
momentum, the propagation of the $\pi$ resonance creates phase slips in the
superconducting order parameter. This frustration effect leads to a strong
dressing of the $\pi$ resonance and a downwards dispersion away from the
commensurate wave vector. Based on these results, we argue that the the
commensurate resonance and incommensurate magnetic fluctuations in the cuprates
are continuously connected.",0103363v1
2001-11-29,Resonant control of elastic collisions in an optically trapped Fermi gas of atoms,"We have loaded an ultracold gas of fermionic atoms into a far off resonance
optical dipole trap and precisely controlled the spin composition of the
trapped gas. We have measured a magnetic-field Feshbach resonance between atoms
in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The
resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a
width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the
elastic collision cross section in the gas by nearly 3 orders of magnitude.",0111571v1
2001-12-07,The neutron resonance in the cuprates and its effect on fermionic excitations,"We argue that the exciton scenario for the magnetic resonance in the cuprate
superconductors yields a small spectral weight of the resonance, in agreement
with experiment. We show that the small weight is related to its concentration
in a small region of momentum and energy. Despite this, we find that a large
fermionic self-energy can indeed be generated by a resonance with such
properties, i.e., the scattering from the resonance substantially affects the
electronic properties of the cuprates below $T_c$.",0112126v2
2002-11-14,Electron Spin Polarization in Resonant Interband Tunneling Devices,"We study spin-dependent interband resonant tunneling in double-barrier
InAs/AlSb/ GaMnSb heterostructures. We demonstrate that these structures can be
used as spin filters utilizing spin-selective tunneling of electrons through
the light-hole resonant channel. High densities of the spin polarized electrons
injected into bulk InAs make spin resonant tunneling devices a viable
alternative for injecting spins into a semiconductor. Another striking feature
of the proposed devices is the possibility of inducing additional resonant
channels corresponding to the heavy holes. This can be implemented by
saturating the in-plane magnetization in the quantum well.",0211300v1
2003-03-13,Crossing of two Coulomb-Blockade Resonances,"We investigate theoretically the transport of non--interacting electrons
through an Aharanov--Bohm (AB) interferometer with two quantum dots (QD)
embedded into its arms. In the Coulomb-blockade regime, transport through each
QD proceeds via a single resonance. The resonances are coupled through the arms
of the AB device but may also be coupled directly. In the framework of the
Landauer--Buttiker approach, we present expressions for the scattering matrix
which depend explicitly on the energies of the two resonances and on the AB
phase. We pay particular attention to the crossing of the two resonances.",0303254v1
2003-03-20,Bona fide Stochastic Resonance: A view point from stochastic energetics,"We investigate the resonance type behaviour of an overdamped Brownian
particle in a bistable potential driven by external periodic signal. It has
been shown previously that the input energy pumped into the system by the
external drive shows resonance type behaviour as function of noise strength. We
further extend this idea to study the behaviour as function of frequency of the
external driving force and show the occurrence of similar nonmonotonic
behaviour, which can be ascribed as a signature of bona fide stochastic
resonance. Both weak and strong driving limit has been explored indicating the
occurrence of marginal supra-threshold stochastic resonance in a bistable
potential system.",0303417v1
2003-05-16,Resonant formation of strongly correlated paired states in rotating Bose gases,"We propose increasing the fractional quantum Hall gap of a rapidly rotating
Bose gas by increasing the interatomic interactions via a Feshbach resonance.
The generation of molecules by the resonance causes pair correlations to grow
throughout the system effecting the ground state. By an extension of the usual
Chern-Simons theory, built of composite atoms and molecules, we are able to
account for these resonance effects. We find that the resulting ground state
evolves from a Laughlin wavefunction to a unique paired wavefunction as one
approaches the resonance.",0305399v2
2003-05-18,New Resonances Along with Cyclotron Resonance in Heterostructures,"The usual cyclotron resonance occurs at \omega_c=eB/m*c which is independent
of spin. The new resonances depend on spin. The new resonances occur at
\omega_{c\pm}=(1/2)g_{\pm}eB/m*c where (1/2)g_{\pm}= {\it l}+(1/2)\pm s/(2{\it
l}+1). The energy in the centre of two new frequencies varies as the square
root of the 2-dimensional electrons due to spin excess in the Gaussian model.
The frequencies \omega_{c\pm} are linearly proportional to the magnetic field
except near crossing point where the linear combination of wave functions must
be made.",0305415v1
2003-07-10,Quantum dots as scatterers in electronic transport : interference and correlations,"Conductance through a system consisting of a wire with side-attached quantum
dots is calculated. Such geometry of the device allows to study the coexistence
of quantum interference, electron correlations and their influence on
conductance. We underline the differences between ""classical"" Fano resonance in
which the resonant channel is of single-particle nature and ""many-body"" Fano
resonance with the resonant channel formed by Kondo effect. The influence of
electron-electron interactions on the Fano resonance shape is also analyzed.",0307230v1
2003-08-05,Coherent Resonance in Trapped Bose Condensates,"Coherent resonance is the effect of resonant excitation of nonlinear coherent
modes in trapped Bose condensates. This novel effect is shown to be feasible
for Bose-condensed trapped gases. Conditions for realizing this effect are
derived. A method of stabilizing Bose condensates with attractive interactions
is advanced. The origin of dynamic critical phenomena is elucidated.
Interference effects are studied. The existence of atomic squeezing and
multiparticle coherent entanglement is demonstrated. Coherent resonance is a
generalization of atomic resonance, involving internal states of an individual
atom, to collective states of a multiparticle system.",0308082v1
2003-11-01,Superconducting Qubit Storage and Entanglement with Nanomechanical Resonators,"We describe a quantum computational architecture based on integrating
nanomechanical resonators with Josephson junction phase qubits, with which we
implement single- and multi-qubit operations. The nanomechanical resonator is a
GHz-frequency, high-quality-factor dilatational resonator, coupled to the
Josephson phase through a piezoelectric interaction. This system is analogous
to one or more few-level atoms (the Josephson qubits) in a tunable
electromagnetic cavity (the nanomechanical resonator). Our architecture
combines the best features of solid-state and cavity-QED approaches, and may
make possible multi-qubit processing in a scalable, solid-state environment.",0311007v1
2004-02-18,Decoherence in Josephson Qubits from Junction Resonances,"Although Josephson junction qubits show great promise for quantum computing,
the origin of dominant decoherence mechanisms remains unknown. We report Rabi
oscillations for an improved phase qubit, and show that their coherence
amplitude is significantly degraded by spurious microwave resonators. These
resonators arise from changes in the junction critical current produced by
two-level states in the tunnel barrier. The discovery of these high frequency
resonators impacts the future of all Josephson qubits as well as existing
Josephson technologies. We predict that removing or reducing these resonators
through materials research will improve the coherence of all Josephson qubits.",0402470v1
2004-04-30,Nonequilibrium dynamics and thermodynamics of a degenerate Fermi gas across a Feshbach resonance,"We consider a two-species degenerate Fermi gas coupled by a diatomic Feshbach
resonance. We show that the resulting superfluid can exhibit a form of coherent
BEC-to-BCS oscillations in response to a nonadiabatic change in the system's
parameters, such as for example a sudden shift in the position of the Feshbach
resonance. In the narrow resonance limit, the resulting soliton-like
collisionless dynamics can be calculated analytically. In equilibrium the
thermodynamics can be accurately computed across the full range of BCS-BEC
crossover, with corrections controlled by the ratio of the resonance width to
the Fermi energy.",0404724v1
2004-05-26,Dissociation of ultracold molecules with Feshbach resonances,"Ultracold molecules are associated from an atomic Bose-Einstein condensate by
ramping a magnetic field across a Feshbach resonance. The reverse ramp
dissociates the molecules. The kinetic energy released in the dissociation
process is used to measure the widths of 4 Feshbach resonances in 87Rb. This
method to determine the width works remarkably well for narrow resonances even
in the presence of significant magnetic-field noise. In addition, a
quasi-mono-energetic atomic wave is created by jumping the magnetic field
across the Feshbach resonance.",0405606v2
2004-08-21,High Temperature Universal Properties of Atomic Gases Near Feshbach Resonance with Non-Zero Orbital Angular Momentum,"We show that the high temperature behavior of atomic gases near Feshbach
Resonance with non-zero orbital angular momentum $(\ell >0)$ belong to a
universality class different from that of s-wave resonances. The universal
interaction energy is $2(2\ell +1)$ times larger than that of the s-wave when
approaching the resonance from the atomic side, but is essentially zero on the
molecular side; contrary to s-wave resonances where interaction energies on
both sides are the same except for a sign change. The measurement of these
universality properties should be feasible in current experiments.",0408469v1
2005-01-06,Resonator design for surface electron lifetime studies using scanning tunneling spectroscopy,"We derive expressions for the lossy boundary-scattering contribution to the
linewidth of surface electronic states confined with atomic corrals and island
resonators. Correcting experimentally measured linewidths for these
contributions along with thermal and intrumental broadening enables intrinsic
many-body lifetimes due to electron-electron and electron-phonon scattering to
be determined. In small resonators lossy-scattering dominates linewidths whilst
different scaling of widths and separations cause levels to merge in large
resonators. Our results enable the design of resonators suitable for lifetime
studies.",0501102v1
2005-12-21,Resonant activation in a nonadiabatically driven optical lattice,"We demonstrate the phenomenon of resonant activation in a non-adiabatically
driven dissipative optical lattice with broken time-symmetry. The resonant
activation results in a resonance as function of the driving frequency in the
current of atoms through the periodic potential. We demonstrate that the
resonance is produced by the interplay between deterministic driving and
fluctuations, and we also show that by changing the frequency of the driving it
is possible to control the direction of the diffusion.",0512552v1
2006-01-09,Relaxation of the molecular state in atomic Fermi gases near a Feshbach resonance,"The relaxation processes in an ultra-cold degenerate atomic Fermi gas near a
Feshbach resonance are considered. It is shown that the relaxation rate of the
molecules being in a resonance with the atomic Fermi system is of the order of
the part of the chemical potential determined by the interaction between
resonance molecules. In this connection the lower part of the excitation
spectrum in the system of resonance molecules is not well-defined.",0601140v2
2006-06-21,Signal Amplification in NbN Superconducting Resonators via Stochastic Resonance,"We exploit nonlinearity in NbN superconducting stripline resonators, which is
originated by local thermal instability, for studying stochastic resonance. As
the resonators are driven into instability, small amplitude modulated (AM)
microwave signals are amplified with the aid of injected white noise. The
dependence of the signal amplification on the modulation amplitude and the
modulation frequency is examined and compared with theory.",0606555v1
2006-07-25,Escape rate of metastable states in a driven NbN superconducting microwave resonator,"We study thermal instability and formation of local hot spots in a driven
nonlinear NbN superconducting microwave resonator. White noise injected into
the resonator results in transitions between the metastable states via a
process consisting of two stages. In the first stage, the input noise entering
the system induces fluctuations in the resonator mode. While, in the second
one, these mode fluctuations result in phase transitions of the hot spot due to
induced temperature fluctuations. The associated noise-activated escape rate is
calculated theoretically, and also measured experimentally by means of driving
the system into stochastic resonance. A comparison between theory and
experiment yields a partial agreement.",0607628v1
2006-10-13,Figure of Merit of one-dimensional resonant transmission systems in the quantum regime,"The figure of merit, ZT, for a one-dimensional conductor displaying a
Lorentzian resonant transmission probability is calculated. The optimum working
conditions for largest ZT values are determined. It is found that, the
resonance energy has to be adjusted to be several resonance widths away from
the Fermi level. Similarly it is better for the temperature to be equal to
several resonance widths. The approximate relationships, which can be a fairly
good guide for designing devices, between different parameters under optimum
working conditions are given.",0610368v1
2007-03-08,High-Frequency Nanofluidics: An Experimental Study using Nanomechanical Resonators,"Here we apply nanomechanical resonators to the study of oscillatory fluid
dynamics. A high-resonance-frequency nanomechanical resonator generates a
rapidly oscillating flow in a surrounding gaseous environment; the nature of
the flow is studied through the flow-resonator interaction. Over the broad
frequency and pressure range explored, we observe signs of a transition from
Newtonian to non-Newtonian flow at $\omega\tau\approx 1$, where $\tau$ is a
properly defined fluid relaxation time. The obtained experimental data appears
to be in close quantitative agreement with a theory that predicts purely
elastic fluid response as $\omega\tau\to \infty$.",0703230v2
1999-05-17,Parametric resonant acceleration of particles by gravitational waves,"We study the resonant interaction of charged particles with a gravitational
wave propagating in the non-empty interstellar space in the presence of a
uniform magnetic field. It is found that this interaction can be cast in the
form of a parametric resonance problem which, besides the main resonance,
allows for the existence of many secondary ones. Each of them is associated
with a non-zero resonant width, depending on the amplitude of the wave and the
energy density of the interstellar plasma. Numerical estimates of the
particles' energisation and the ensuing damping of the wave are given.",9905054v1
1998-08-21,Electroproduction of the Delta Resonance at High Momentum Transfer,"We studied the electroproduction of the Delta(1232) resonance via the
reaction p(e,e'p)\pi0 at four-momentum transfers Qsq = 2.8 and 4.0 GeV^2. This
is the highest Qsq for which exclusive resonance electroproduction has ever
been observed. Decay angular distributions for Delta to p-pi0$ were measured
over a wide range of barycentric energies covering the resonance. The
$N-\Delta$ transition form factor G*_M and ratios of resonant multipoles
E{1+}/M{1+} and S{1+}/M{1+} were extracted from the decay angular
distributions. These ratios remain small, indicating that perturbative QCD is
not applicable for this reaction at these momentum transfers.",9808024v1
1993-01-06,Neutrinos with Mixing in Twisting Magnetic Fields,"Transitions in a system of neutrinos with vacuum mixing and magnetic moments,
propagating in matter and transverse magnetic field, are considered. It is
shown that in the realistic case of magnetic field direction varying along the
neutrino path qualitatively new phenomena become possible: permutation of
neutrino conversion resonances, appearance of resonances in the
neutrino-antineutrino ($\nu_{lL}\leftrightarrow\bar{\nu}_{lR}$) transition
channels, neutrino-antineutrino resonant conversion, large amplitude
$\nu_{lL}\leftrightarrow\bar{\nu}_{lR}$ oscillations, merging of different
resonances (triple resonances). Possible phenomenological implications of these
effects are briefly discussed.",9301211v1
1997-06-23,QCD Laplace Sum Rules and the $Π(1300)$ Resonance,"A global fit to the shape of the first QCD Laplace sum rule exhibiting
sensitivity to pion-resonance [$\Pi (1300)$] parameters is performed, leading
to predictions for the pion-resonance mass and decay constant. This fit leads
to predictions of $M_{\pi} = 1.15 \pm 0.15 GeV$ for the pion-resonance mass,
and $F_\pi^2=(4.5\pm 2.1).(f_\pi^2m_\pi^4/M_\pi^4)$ for the pion-resonance
decay constant.",9706473v1
1998-07-21,The 1.4 GeV J^PC = 1^-+ state as an interference of a non-resonant background and a resonance at 1.6 GeV,"We investigate theoretical interpretations of the 1.4 GeV J^PC exotic
resonance reported by the E852 collaboration. A K-matrix analysis shows that
the 1.4 GeV enhancement in the E852 eta pi data can be understood as an
interference of a non-resonant Deck-type background and a resonance at 1.6 GeV.",9807433v2
1999-07-20,Parametric resonance in neutrino oscillations in matter,"Neutrino oscillations in matter can exhibit a specific resonance enhancement
-- parametric resonance, which is different from the MSW resonance.
Oscillations of atmospheric and solar neutrinos inside the earth can undergo
parametric enhancement when neutrino trajectories cross the core of the earth.
In this paper we review the parametric resonance of neutrino oscillations in
matter. In particular, physical interpretation of the effect and the prospects
of its experimental observation in oscillations of solar and atmospheric
neutrinos in the earth are discussed.",9907435v1
2001-11-12,Chiral Perturbation Theory and the f2(1270) resonance,"Within Chiral Perturbation Theory, we study elastic pion scattering in the
I=0, J=2, channel, whose main features are the f2(1270) resonance and the
vanishing of the lowest order. By means of a chiral model that includes an
explicit resonance coupled to pions, we describe the data and calculate the
resonance contribution to the O(p^4) and O(p^6) chiral parameters. We also
generalize the Inverse Amplitude Method to higher orders, which allows us to
study channels with vanishing lowest order. In particular, we apply it to the
I=0,J=2 case, finding a good description of the f2(1270) resonance, as a pole
in the second Riemann sheet.",0111140v1
2001-12-19,Resonances from a Hadronic Fireball,"Production of $\phi(1020), \Lambda^*(1520)$ and $\bar{K^*}(892)$ resonances
at the final stage of a heavy-ion collision is considered. It is shown that
original momentum distributions and abundance of resonances formed during the
process of heavy ion collision may differ significantly from their measured
spectra and yields. Reconstruction probability of resonances decaying inside
the fireball can be strongly suppressed because of interactions of their
hadronic decay products in the fireball medium. We investigate dependence of
the degree of the suppression on the fireball size, dynamics, and the resonance
decay width in medium. Quantitative results are presented for lead-lead
collisions at 158 GeV SPS beam energy.",0112252v1
2002-05-13,The Behavior of Form Factors of Nucleon Resonances and Quark-Hadron Duality,"A behavior of the nucleon structure functions in the resonance region is
investigated. Expressions for resonance production form factors, dependent on
photon virtuality $Q^2$, which have correct threshold behavior and take into
account available data on resonance decays, are obtained. Contributions of
resonances to nucleon structure functions are calculated. Obtained expressions
are used to investigate the quark-hadron duality in the electron-nucleon
scattering processes with the structure function $F_2$ as an example.",0205130v1
2003-04-17,How to parameterize a light and broad resonance (the $σ$ meson),"We point out that a commonly used parameterization form to describe the
$\sigma$ resonance is problematic by introducing a spurious singularity below
two particle threshold, on the second sheet. The spurious singularity violates
chiral symmetry and leads to sizable contribution when the resonance is light
and broad -- as what happens to the $\sigma$ resonance, hence must be removed.",0304173v2
2004-11-24,The Use of the Scattering Phase Shift in Resonance Physics,"The scattering phase shift encodes a good amount of physical information
which can be used to study resonances from scattering data. Among others, it
can be used to calculate the continuum density of states and the collision time
in a resonant process. Whereas the first information can be employed to examine
the evolution of unstable states directly from scattering data, the second one
serves as a tool to detect resonances and their properties. We demonstrate both
methods concentrating in the latter case on 'exotic' resonances in pi-pi and
pi-K scattering.",0411317v2
2005-10-04,One-loop Renormalization of Resonance Chiral Theory: Scalar and Pseudoscalar Resonances,"We consider the Resonance Chiral Theory with one multiplet of scalar and
pseudoscalar resonances, up to bilinear couplings in the resonance fields, and
evaluate its beta-function at one-loop with the use of the background field
method. Thus we also provide the full set of operators that renormalize the
theory at one loop and render it finite.",0510041v1
2005-10-05,One-loop Renormalization of Resonance Chiral Theory with Scalar and Pseudoscalar Resonances,"The divergent part of the generating functional of the Resonance Chiral
Theory is evaluated up to one loop when one multiplet of scalar an pseudoscalar
resonances are included and interaction terms which couple up to two resonances
are considered. Hence we obtain the renormalization of the couplings of the
initial Lagrangian and, moreover, the complete list of operators that make this
theory finite, at this order.",0510056v1
1992-11-02,RG flows and resonance scattering amplitudes,"We review recent progresses in the study of factorized resonance scattering
S-matrices. The resonance amplitudes are introduced through a suitable
analytical continuation of the ADE Toda S-matrices. By using the thermodynamic
Bethe ansatz approach we are able to compute the ground state energy, which
describes a rich pattern of flows interpolating between the central charges of
the coset models based on the ADE Lie algebras. We also present the simplest
resonance ``$\phi^3$'' scattering model and discuss its relation with new flows
in non-unitary minimal models. Further generalizations are discussed in terms
of certain asymptotic conditions in a family of ``resonance'' functional
hierarchies.",9211010v1
2002-06-23,Review of Mathematical Techniques Applicable in Astrophysical Reaction Rate Theory,"An overview is presented on statistical techniques for the analytic
evaluation of integrals for non-resonant, non-resonant depleted, non-resonant
cut-off, non-resonant sccreened, and resonant thermonuclear reaction rates. The
techniques are based on statistical distribution theory and the theory of
Meijer's G-function and Fox's H-function. The implementation of Meijer's
G-function in Mathematica constituts an additional utility for analytic
manipulations and numerical computation of thermonuclear reaction rate
integrals. Recent results in the astrophysical literature related to the use of
analytic thermonuclear reaction rates are incorporated.",0206239v1
2003-05-09,Hamilton-Jacobi method for a simple resonance,"It is well known that a generic small perturbation of a Liouville-integrable
Hamiltonian system causes breakup of resonant and near-resonant invariant tori.
A general approach to the simple resonance case in the convex real-analytic
setting is developed, based on a new technique for solving the Hamilton-Jacobi
equation. It is shown that a generic perturbation creates in the core of a
resonance a partially hyperbolic lower-dimensional invariant torus, whose
Lagrangian stable and unstable manifolds, described as global solutions of the
Hamilton-Jacobi equation, split away from this torus at exponentially small
angles. Optimal upper bounds with best constants are obtained for exponentially
small splitting in the general case.",0305143v1
2005-11-07,Resonance Gyrons and Quantum Geometry,"We describe irreducible representations, coherent states and star-products
for algebras of integrals of motions (symmetries) of two-dimensional resonance
oscillators. We demonstrate how the quantum geometry (quantum K\""ahler form,
metric, quantum Ricci form, quantum reproducing measure) arises in this
problem. We specifically study the distinction between the isotropic resonance
$1:1$ and the general $l:m$ resonance for arbitrary coprime $l,m$. Quantum
gyron is a dynamical system in the resonance algebra. We derive its Hamiltonian
in irreducible representations and calculate the semiclassical asymptotics of
the gyron spectrum via the quantum geometrical objects.",0511161v1
2001-09-21,On the resonances of the Laplacian on waveguides,"The resonances for the Dirichlet and Neumann Laplacian are studied on
compactly perturbed waveguides. An upper bound on the number of resonances near
the physical plane is proven. In the absence of resonances, an upper bound is
proven for the localised resolvent. This is then used to prove that the
existence of a quasimode whose asymptotics is bounded away from the thresholds
implies the existence of resonances converging to the real axis.",0109022v1
2000-05-29,Coherence resonance near blowout bifurcation in nonlinear dynamical systems,"Previous studies have shown that noise can induce coherence resonance in some
nonlinear dynamical systems close to a bifurcation of a periodic motion, such
as in excitable systems. We demonstrate that coherence resonance can be
observed in systems close to a {\sl blowout bifurcation}. It is shown that for
dynamical systems with an invariant subspace in which there is a phase-coherent
chaotic attractor, the interplay among the oscillation of local transverse
stability, noise and nonlinearity can lead to coherence resonance phenomenon.
The mechanism of coherence resonance in this type of system is different from
that in previously studied systems.",0005060v1
2003-01-28,Quantization of Classical Maps with tunable Ruelle-Pollicott Resonances,"We investigate the correspondence between the decay of correlation in
classical system, governed by Ruelle--Pollicott resonances, and the properties
of the corresponding quantum system. For this purpose we construct classical
systems with controllable resonances together with their quantum counterpart.
As an application of such tailormade resonances we reveal the role of
Ruelle--Pollicott resonances for the localization properties of quantum energy
eigenstates.",0301041v2
2004-09-06,Resonance Patterns in a Stadium-shaped Microcavity,"We investigate resonance patterns in a stadium-shaped microcavity around
$n_ck R \simeq 10$, where $n_c$ is the refractive index, $k$ the vacuum
wavenumber, and $R$ the radius of the circular part of the cavity. We find that
the patterns of high $Q$ resonances can be classified, even though the
classical dynamics of the stadium system is chaotic. The patterns of the high
$Q$ resonances are consistent with the ray dynamical consideration, and appears
as the stationary lasing modes with low pumping rate in the nonlinear dynamical
model. All resonance patterns are presented in a finite range of $kR$.",0409011v1
2004-09-10,Resonant light scattering by optical solitons,"We consider the process of light scattering by optical solitons in a planar
waveguide with homogeneous and inhomogeneous refractive index core. We observe
resonant reflection (Fano resonances) as well as resonant transmission of light
by optical solitons. All resonant effects can be controlled in experiment by
changing the soliton intensity.",0409023v2
2005-10-12,Resonant light-light interaction in slab waveguides: angular filters and spectral hole burning,"We consider the process of low-power light scattering by optical solitons in
a slab waveguide with homogeneous and inhomogeneous refractive index core. We
observe resonant reflection (Fano resonance) as well as resonant transmission
of light by optical solitons at certain incident angles. The resonance position
can be controlled experimentally by changing the soliton intensity and the
relative frequency detuning between the soliton and the probe light beams.",0510023v1
1996-08-29,Coherent eta photoproduction on the deuteron in the $S_{11}$ resonance region,"Coherent eta photoproduction on the deuteron is studied in the $S_{11}$
resonance region neglecting eta rescattering and two-body processes. For the
elementary reaction on the nucleon, we have considered the dominant
$S_{11}(1535)$ resonance and as background the nucleon pole terms as well as
$\rho$ and $\omega$ meson exchange. We have studied the influence of different
choices for the neutron resonance amplitude, different prescriptions for fixing
the invariant mass of the resonance amplitude and different methods for
deriving the elementary production amplitude for an arbitrary reference frame.",9608064v1
1997-11-26,Multiphonon Giant Resonances,"A new class of giant resonances in nuclei is discussed, i.e., giant
resonances built on other giant resonances. These resonances are observed with
very large cross sections in relativistic heavy ion collisions. A great
experimental and theoretical effort is underway to understand the reaction
mechanism which leads to the excitation of these states in nuclei, as well as
the better microscopic understanding of their properties, e.g., strength,
energy centroids, widths, and anharmonicities.",9711057v1
1998-10-09,Rescattering effects in coherent eta-photoproduction on the deuteron,"Rescattering effects in coherent eta photoproduction on the deuteron are
studied in the region of the S_11(1535) resonance. For the elementary reaction
mechanism on the nucleon, an effective isobar model with inclusion of
resonances and Born terms is used. The resonance parameters are fixed by
considering pion photoproduction only. For the coherent eta production on the
deuteron we have considered the impulse approximation taking into account the
P_11(1440), D_13(1520), and S_11(1535) resonances, rescattering, and meson
exchange currents. For the rescattering mechanism a coupled channel model
including the dominant S_11(1535) resonance is used.",9810027v1
2000-05-16,Algebraic Model for scattering of three-s-cluster systems. II. Resonances in the three-cluster continuum of 6He and 6Be,"The resonance states embedded in the three-cluster continuum of 6He and 6Be
are obtained in the Algebraic Version of the Resonating Group Method. The model
accounts for a correct treatment of the Pauli principle. It also provides the
correct three-cluster continuum boundary conditions by using a Hyperspherical
Harmonics basis. The model reproduces the observed resonances well and achieves
good agreement with other models. A better understanding for the process of
formation and decay of the resonance states in six-nucleon systems is obtained.",0005047v1
2000-09-02,Quantum corrections for pion correlations involving resonance decays,"A method is presented to include quantum corrections into the calculation of
two-pion correlations for the case where particles originate from resonance
decays. The technique uses classical information regarding the space-time
points at which resonances are created. By evaluating a simple thermal model,
the method is compared to semiclassical techniques that assume exponential
decaying resonances moving along classical trajectories. Significant
improvements are noted when the resonance widths are broad as compared to the
temperature.",0009003v2
2001-07-09,Toroidal dipole resonances in the relativistic random phase approximation,"The isoscalar toroidal dipole strength distributions in spherical nuclei are
calculated in the framework of a fully consistent relativistic random phase
approximation. It is suggested that the recently observed ""low-lying component
of the isoscalar dipole mode"" might in fact correspond to the toroidal giant
dipole resonance. Although predicted by several theoretical models, the
existence of toroidal resonances has not yet been confirmed in experiment. The
strong mixing between the toroidal resonance and the dipole compression mode
might help to explain the large discrepancy between theory and experiment on
the position of isoscalar giant dipole resonances.",0107024v2
2002-02-14,Dilepton decays of baryon resonances,"Dalitz decay of baryon resonances is studied and expressions for the decay
width are derived for resonances with arbitrary spin and parity. Contributions
of the various terms in the transition matrix element are compared and
relevance of spin-parity and the resonance mass is discussed. Explicite
algebraic expressions are cited for spin$\le$5/2 resonances. The results can be
used in models of dielectron production in elementary reactions and heavy ion
collisions.",0202047v1
2002-10-02,Shell model in the complex energy plane and two-particle resonances,"An implementation of the shell-model to the complex energy plane is
presented. The representation used in the method consists of bound
single-particle states, Gamow resonances and scattering waves on the complex
energy plane. Two-particle resonances are evaluated and their structure in
terms of the single-particle degreees of freedom are analysed. It is found that
two-particle resonances are mainly built upon bound states and Gamow
resonances, but the contribution of the scattering states is also important.",0210006v1
2003-07-01,Complex scaling of the hyper-spheric coordinates and Faddeev equations,"We implement complex scaling of Faddeev equations using hyper-spheric
coordinates and adiabatic expansion. Complex scaling of coordinates allows
convenient calculations of three-body resonances. We derive the necessary
equations and investigate the adiabatic spectrum at large distances. We
illustrate the viability of the implementation by calculations of several
three-body resonances: a $0^+$ resonance in a model benchmark system of three
identical bosons; the $2^+$ resonance in the $^6$He nucleus within the
$\alpha+n+n$ model; and the two $0^+$ resonances in $^{12}$C within the
three-$\alpha$ model.",0307006v1
2003-10-24,Balance functions in a thermal model with resonances,"The pi+ pi- balance function in rapidity is computed in a thermal model with
resonances. It is found that the correlations from the neutral-resonance decays
are important, yielding about a half of the total contribution, which in
general consist of resonance and non-resonance parts. The model yields the
pionic balance function a few per cent wider that what follows from the recent
data for the Au+Au collisions at 130GeV.",0310062v2
2004-10-25,Hadron resonance probes of QGP,"We discuss the indirect and direct role of the short-lived resonances as
probes of QGP freeze-out process. The indirect effect is the distortion of
stable single particle yields and spectra by contributions of decaying
resonances, which alter significantly the parameters obtained in fits to
experimental data. We than discuss the direct observation of short-lived
resonances as a probe of post-hadronization dynamics allowing to distinguish
between different hadronization models.",0410101v1
2006-10-17,Roper + Pion decays as a test of the radial resonances wavefunction,"We calculate the decays of baryon resonances to the pion + Roper resonance
channel in the frame of the flux-tube breaking model. The baryon and meson
wavefunctions we use are obtained from a linear confinement semi-relativistic
constituent quark model. The results, in good agreement with the existing data,
provide a spectrum independant test on the radial form of the main component of
the Roper resonance. They shed light on a likely orbital nature for the second
delta resonance.",0610065v1
2006-10-27,Hadronic Decays and Baryon Structure,"Relativistic constituent quark models generally describe three-quark systems
with particular interactions. The corresponding invariant mass eigenvalue
spectra and pertinent eigenstates should exhibit the multiplet structure
anticipated for baryon resonances. Taking into account the flavour content,
spin structure, and spatial distribution of the baryon wave functions together
with mass relations of the eigenvalues and decay properties of the eigenstates,
we can link the theoretical mass eigenstates with the experimentally measured
resonances. The resulting classification of baryon resonances differs in some
respects from the one suggested by the Particle Data Group. With regard to the
hadronic decay widths of light and strange baryon resonances a consistent
picture emerges only, if the classification includes two-star resonances.",0610111v1
2002-05-08,Rotational Feshbach Resonances in Ultracold Molecular Collisions,"In collisions at ultralow temperatures, molecules will possess Feshbach
resonances, foreign to ultracold atoms, whose virtual excited states consist of
rotations of the molecules. We estimate the mean spacing and mean widths of
these resonant states, exploiting the fact the molecular collisions at low
energy display chaotic motion. As examples, we consider the experimentally
relevant molecules O_2, OH, and PbO. The density of s-wave resonant states for
these species is quite high, implying that a large number of narrow resonant
states will exist.",0205020v1
2003-10-24,Multiplet Structure of Feshbach Resonances in non-zero partial waves,"We report a unique feature of magnetic field Feshbach resonances in which
atoms collide with non-zero orbital angular momentum. P-wave ($l=1$) Feshbach
resonances are split into two components depending on the magnitude of the
resonant state's projection of orbital angular momentum onto the field axis.
This splitting is due to the magnetic dipole-dipole interaction between the
atoms and it offers a means to tune anisotropic interactions of an ultra-cold
gas of atoms. A parameterization of the resonance in terms of an effective
range expansion is given.",0310121v1
2005-02-04,Strong optical force induced by morphology dependent resonances,"We consider the resonant optical force acting on a pair of transparent
microspheres by the excitation of the Morphology Dependent Resonance (MDR). The
bonding and anti-bonding modes of the MDR correspond to strong attractions and
repulsions respectively. The dependence of the force on separation and the role
of absorption are discussed. At resonance, the force can be enhanced by orders
of magnitude so that it will dominate over other relevant forces. We find that
a stable binding configuration can be induced by the resonant optical force.",0502020v1
2005-09-30,Classification of electromagnetic resonances in finite inhomogeneous three-dimensional structures,"We present a simple and unified classification of macroscopic electromagnetic
resonances in finite arbitrarily inhomogeneous isotropic dielectric 3D
structures situated in free space. By observing the complex-plane dynamics of
the spatial spectrum of the volume integral operator as a function of angular
frequency and constitutive parameters we identify and generalize all the usual
resonances, including complex plasmons, real laser resonances in media with
gain, and real quasi-static resonances in media with negative permittivity and
gain.",0509259v1
2006-07-13,Resonant transparency of materials with negative permittivity,"It is shown that the transparency of opaque material with negative
permittivity exhibits resonant behavior. The resonance occurs as a result of
the excitation of the surface waves at slab boundaries. Dramatic field
amplification of the incident evanescent fields at the resonance improves the
resolution of the the sub-wavelength imaging system (superlens). A finite
thickness slab can be totally transparent to a \textit{p}-polarized obliquely
incident electromagnetic wave for certain values of the incidence angle and
wave frequency corresponding to the excitation of the surface modes. At the
resonance, two evanescent waves have a finite phase shift providing non-zero
energy flux through the non-transparent region.",0607130v1
2006-09-01,Simple Theoretical Models for Resonant Cold Atom Interactions,"Magnetically tunable scattering resonances have been used with great success
for precise control of s-wave scattering lengths in ultracold atomic
collisions. We describe relatively simple yet quite powerful analytic
treatments of such resonances based on the analytic properties of the van der
Waals long range potential. This theory can be used to characterize a number of
properties of specific resonances that have been used successfully in various
experiments with $^{87}$Rb, $^{85}$Rb, $^{40}$K, and $^{6}$Li. Optical Feshbach
resonances are also possible and may be practical with narrow intercombination
line photoassociative transitions in species like Sr and Yb.",0609013v1
1999-04-29,Quantum Computation as a Dynamical Process,"In this paper, we discuss the dynamical issues of quantum computation. We
demonstrate that fast wave function oscillations can affect the performance of
Shor's quantum algorithm by destroying required quantum interference. We also
show that this destructive effect can be routinely avoided by using
resonant-pulse techniques. We discuss the dynamics of resonant pulse
implementations of quantum logic gates in Ising spin systems. We also discuss
the influence of non-resonant excitations. We calculate the range of parameters
where undesirable non-resonant effects can be minimized. Finally, we describe
the ``$2\pi k$-method'' which avoids the detrimental deflection of non-resonant
qubits.",9904105v1
2000-05-19,Resonant radiative processes,"The frequency correlation properties of the radiation from an atom in a
strong field in resonance with neighboring transitions are considered. It is
shown that the difference in frequency correlation in two-photon and stepwise
processes decreases with increase of the external field. The spectral
compositions of the Doppler-broadened resonance scattering and fluorescence are
analyzed. It is shown that in these cases the Doppler line width is
anisotropic.",0005081v1
2001-02-11,Interference of resonances and the double-pole of the S-matrix in a double well system,"We discuss the interaction between two resonant states in a quantum
double-well structure. The behaviour of the resonant states depends on the
coupling between the wells, i.e. the height and width of the barrier that
separates them. We distinguish a region with resonant tunneling and a region
where the two resonances repel each other. The transition between the two
regions is marked by a double pole of the S-matrix.",0102057v1
2001-11-29,Field quantization for chaotic resonators with overlapping modes,"Feshbach's projector technique is employed to quantize the electromagnetic
field in optical resonators with an arbitray number of escape channels. We find
spectrally overlapping resonator modes coupled due to the damping and noise
inflicted by the external radiation field. For wave chaotic resonators the mode
dynamics is determined by a non--Hermitean random matrix. Upon including an
amplifying medium, our dynamics of open-resonator modes may serve as a starting
point for a quantum theory of random lasing.",0111156v2
2002-08-02,Trapping and cooling single atoms with far-off resonance intracavity doughnut modes,"We investigate cooling and trapping of single atoms inside an optical cavity
using a quasi-resonant field and a far-off resonant mode of the Laguerre-Gauss
type. The far-off resonant doughnut mode provides an efficient trapping in the
case when it shifts the atomic internal ground and excited state in the same
way, which is particularly useful for quantum information applications of
cavity quantum electrodynamics (QED) systems. Long trapping times can be
achieved, as shown by full 3-D simulations of the quasi-classical motion inside
the resonator.",0208016v2
2003-09-02,Quantum statistics of overlapping modes in open resonators,"We study the quantum dynamics of optical fields in weakly confining
resonators with overlapping modes. Employing a recently developed quantization
scheme involving a discrete set of resonator modes and continua of external
modes we derive Langevin equations and a master equation for the resonator
modes. Langevin dynamics and the master equation are proved to be equivalent in
the Markovian limit. Our open-resonator dynamics may be used as a starting
point for a quantum theory of random lasers.",0309028v2
2005-01-01,Tunable Whispering Gallery Mode Resonators for Cavity Quantum Electrodynamics,"We theoretically study the properties of highly prolate shaped dielectric
microresonators. Such resonators sustain whispering gallery modes that exhibit
two spatially well separated regions with enhanced field strength. The field
per photon on the resonator surface is significantly higher than e.g. for
equatorial whispering gallery modes in microsphere resonators with a comparable
mode volume. At the same time, the frequency spacing of these modes is much
more favorable, so that a tuning range of several free spectral ranges should
be attainable. We discuss the possible application of such resonators for
cavity quantum electrodynamics experiments with neutral atoms and reveal
distinct advantages with respect to existing concepts.",0501002v1
2006-05-01,Nonlinear coupling of nano mechanical resonators to Josephson quantum circuits,"We propose a technique to couple the position operator of a nano mechanical
resonator to a SQUID device by modulating its magnetic flux bias. By tuning the
magnetic field properly, either linear or quadratic couplings can be realized,
with a discretely adjustable coupling strength. This provides a way to realize
coherent nonlinear effects in a nano mechanical resonator by coupling it to a
Josephson quantum circuit. As an example, we show how squeezing of the nano
mechanical resonator state can be realized with this technique. We also propose
a simple method to measure the uncertainty in the position of the nano
mechanical resonator without quantum state tomography.",0605017v1
2006-06-23,Effective resonant transitions in quantum optical systems: kinematic and dynamic resonances,"We show that quantum optical systems preserving the total number of
excitations admit a simple classification of possible resonant transitions
(including effective), which can be classified by analizying the free
Hamiltonian and the corresponding integrals of motion. Quantum systems not
preserving the total number of excitations do not admit such a simple
classification, so that an explicit form of the effective Hamiltonian is needed
to specify the allowed resonances. The structure of the resonant transitions
essentially depends on the algebraic propereties of interacting subsystems.",0606200v1
2006-12-04,Approximate resonance states in the semigroup decomposition of resonance evolution,"The semigroup decomposition formalism makes use of the functional model for
$C_{.0}$ class contractive semigroups for the description of the time evolution
of resonances. For a given scattering problem the formalism allows for the
association of a definite Hilbert space state with a scattering resonance. This
state defines a decomposition of matrix elements of the evolution into a term
evolving according to a semigroup law and a background term. We discuss the
case of multiple resonances and give a bound on the size of the background
term. As an example we treat a simple problem of scattering from a square
barrier potential on the half-line.",0612027v1
2007-05-30,Strongly-resonant p-wave superfluids,"We study theoretically a dilute gas of identical fermions interacting via a
p-wave resonance. We show that, depending on the microscopic physics, there are
two distinct regimes of p-wave resonant superfluids, which we term ""weak"" and
""strong"". Although expected naively to form a BCS-BEC superfluid, a
strongly-resonant p-wave superfluid is in fact unstable towards the formation
of a gas of fermionic triplets. We examine this instability and estimate the
lifetime of the p-wave molecules due to the collisional relaxation into
triplets. We discuss consequences for the experimental achievement of p-wave
superfluids in both weakly- and strongly-resonant regimes.",0705.4460v1
2007-08-15,Evaluating the Signatures of the Mean Motion Resonances in the Solar System,"The characteristics of the resonant disturbing function for an asteroid
perturbed by a planet in circular orbit are discussed. The location of the
libration centers and their dependence with the orbital elements of the
resonant orbit are analyzed. A proposed numerical method (Gallardo 2006a) for
computing the strengths of the resonances is revised and applied to the region
of the main belt of asteroids showing the relevance of several mean motion
resonances (MMR) with several planets.",0708.2080v1
2007-12-23,Bidirectional wavelength tuning of semiconductor quantum dots as artificial atoms in an optical resonator,"We consider a pair of artificial atoms with different ground state energies.
By means of finite element calculations we predict that the ground state
energies can be tuned into resonance if the artificial atoms are placed into a
flexible ring structure, which is elastically deformed by an external force.
This concept is experimentally verified by embedding a low density of
self-assembled quantum dots into the wall of a rolled up micro tube ring
resonator. We demonstrate that quantum dots can elastically be tuned in- and
out of resonance with each other or with the ring resonator modes.",0712.3927v1
2008-02-25,Atomic hyperfine resonances in a magnetic quadrupole field,"The quantum resonances of an atom possessing a single valence electron which
shows hyperfine interaction with the nucleus is investigated in the presence of
a three dimensional magnetic quadrupole field. Particular emphasis is put on
the study of the interplay of the hyperfine and quadrupole forces. Analyzing
the underlying Hamiltonian a variety of symmetries are revealed which give rise
to a two-fold degeneracy of the resonance energies. Our numerical approach
employs the complex scaling method and a Sturmian basis set. Several regimes
and classes of short-lived and long-lived resonances are identified. The
energies and decay widths of the resonances are characterized by their
electronic and nuclear spin properties.",0802.3645v1
2008-03-08,Resonance Clustering in Globally Coupled Electrochemical Oscillators with External Forcing,"Experiments are carried out with a globally coupled, externally forced
population of limit-cycle electrochemical oscillators with an approximately
unimodal distribution of heterogeneities. Global coupling induces mutually
entrained (at frequency $\omega_{1}$) states; periodic forcing produces
forced-entrained ($\omega_{\mathrm{F}}$) states. As a result of the interaction
of mutual and forced entrainment, resonant cluster states occur with equal
spacing of frequencies that have discretized frequencies following a resonance
rule $\omega_{n}\cong n\omega_{1}-(n-1)\omega_{\mathrm{F}}$. Resonance
clustering requires an optimal, intermediate global coupling strength; at weak
coupling the clusters have smaller sizes and do not strictly follow the
resonance rule, while at strong coupling the population behaves similar to a
single, giant oscillator.",0803.1204v1
2008-04-28,Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes,"We show that when a microsphere is illuminated by an evanescent wave, the
optical forces on- and off- whispering gallery mode (WGM) resonance can differ
by several orders of magnitude. Such size selective force allows one to
selectively manipulate the resonating particles, while leaving those particles
at off-resonance untouched. As WGM resonances have very high-Q's, this kind of
force could be deployed for size-selective manipulation with a very high
accuracy (~1/Q), as well as simultaneous particle-sorting according to their
size or resonant frequency.",0804.4341v1
2008-06-18,The initial momentum dependence of the quantum resonance in the delta-kicked rotor,"The influence of an initial momentum on the appearance of ""quantum
resonances"" in the delta-kicked rotor system is explored experimentally. We
show that for certain initial momenta, a resonance can be negated entirely,
whereas at others a resonance can be made to appear. At a larger number of
kicks, all resonances are shown to narrow. We show that as a consequence, the
individual ""diffraction peaks"" may split. We compare our results to numerical
simulations as well as analytical theory.",0806.3107v3
2008-08-08,Resonant Excitation of Disk Oscillations in Deformed Disks III: Revision of Mathematical Treatment,"In previous studies, we have examined a resonant excitation of disk
oscillations in deformed disks. In these studies, however, mathematical
treatment around the resonant points was not rigorous. In this paper the
inadequate point is corrected, with no essential changes in the final results.
For this excitation process to work, disks must be general relativistic. That
is, the non-monotonic radial distribution of epicyclic frequency in
relativistic disks is essential for the presence of the resonance and for
trapping of oscillations. In this paper, the growth rate of resonant
oscillations is expressed in a form more suitable for numerical calculations.",0808.1218v1
2008-09-09,Unique resonant normal forms for area preserving maps at an elliptic fixed point,"We construct a resonant normal form for an area-preserving map near a generic
resonant elliptic fixed point. The normal form is obtained by a simplification
of a formal interpolating Hamiltonian. The resonant normal form is unique and
therefore provides the formal local classification for area-preserving maps
with the elliptic fixed point. The total number of formal invariants is
infinite. We consider the cases of weak (of order $n\ge5$) and strong (of order
$n=3,4$) resonances. We also construct unique normal forms for analytic
families of area-preserving maps.
  We note that our constructions involve non-linear grading functions.",0809.1614v1
2008-12-14,"Magnetic resonance in the cuprates -- exciton, plasmon, or π-mode","We re-analyzed the issue whether the resonance peak observed in neutron
scattering experiments on the cuprates is an exciton, a \pi-resonance, or a
magnetic plasmon. We considered a toy model with on-cite Hubbard U and
nearest-neighbor interactions in both charge and spin channels. We found that
the resonance is predominantly an exciton, even if magnetic interaction is
absent and d-wave pairing originates from attractive density-density
interaction. Our results indicate that one cannot distinguish between spin and
charge-mediated pairing interactions by just looking at the resonance peak in
the dynamic spin susceptibility.",0812.2697v1
2008-12-17,Baryon resonances in the mean field approach and a simple explanation of the Theta+ pentaquark,"We suggest to classify baryon resonances as single-quark states in a mean
field, and/or as its collective excitations. Identifying the Roper resonance
N(1440), the nucleon resonance N(1535), and the singlet hyperon Lambda(1405) as
single-quark excitations, we find that there must be an exotic S=+1 baryon
resonance Theta+ (the ""pentaquark"") with a mass about 1440+1535-1405=1570 MeV
and spin-parity one-half-plus. We argue that Theta+ is an analog of the
Gamov--Teller excitation long known in nuclear physics.",0812.3418v1
2008-12-18,Parametric resonances in electrostatically interacting carbon nanotube arrays,"We study, numerically and analytically, a model of a one-dimensional array of
carbon nanotube resonators in a two-terminal configuration. The system is
brought into resonance upon application of an AC-signal superimposed on a
DC-bias voltage. When the tubes in the array are close to each other,
electrostatic interactions between tubes become important for the array
dynamics. We show that both transverse and longitudinal parametric resonances
can be excited in addition to primary resonances. The intertube electrostatic
interactions couple modes in orthogonal directions and affect the mode
stability.",0812.3515v1
2009-01-06,Probing viscoelastic properties of a thin polymer film sheared between a beads layer and quartz crystal resonator,"We report measurements of viscoelastic properties of thin polymer films of
10-100 nm at the MHz range. These thin films are confined between a quartz
crystal resonator and a millimetric bead layer, producing an increase of both
resonance frequency and dissipation of the quartz resonator. The shear modulus
and dynamic viscosity of thin films extracted from these measurements are
consistent with the bulk values of the polymer. This modified quartz resonator
provides an easily realizable and effective tool for probing the rheological
properties of thin films at ambient environment.",0901.0630v1
2009-02-06,Calculating few-body resonances using an oscillator trap,"We investigate the possibility of calculating the parameters of few-body
resonances using the oscillator trap boundary conditions. We place the few-body
system in an oscillator trap and calculate the energy spectrum and the strength
function of a suitably chosen transition. Broader resonances are identified as
Lorentzian peaks in the strength function. Narrower resonances are identified
through the pattern of avoided crossings in the spectrum of the system as
function of the trap size. As an example we calculate 0+ resonances in 12C
within the 3-alpha model.",0902.1110v1
2009-02-24,A Primer on Resonances in Quantum Mechanics,"After a pedagogical introduction to the concept of resonance in classical and
quantum mechanics, some interesting applications are discussed. The subject
includes resonances occurring as one of the effects of radiative reaction, the
resonances involved in the refraction of electromagnetic waves by a medium with
a complex refractive index, and quantum decaying systems described in terms of
resonant states of the energy. Some useful mathematical approaches like the
Fourier transform, the complex scaling method and the Darboux transformation
are also reviewed.",0902.4061v1
2009-03-27,Effect of non-zero constant vorticity on the nonlinear resonances of capillary water waves,"The influence of an underlying current on 3-wave interactions of capillary
water waves is studied. The fact that in irrotational flow resonant 3-wave
interactions are not possible can be invalidated by the presence of an
underlying current of constant non-zero vorticity. We show that: 1) wave trains
in flows with constant non-zero vorticity are possible only for two-dimensional
flows; 2) only positive constant vorticities can trigger the appearance of
three-wave resonances; 3) the number of positive constant vorticities which do
trigger a resonance is countable; 4) the magnitude of a positive constant
vorticity triggering a resonance can not be too small.",0903.4813v1
2009-03-30,Radiative decay into $γ$-baryon decuplet of dynamically generated resonances,"We study the radiative decay into $\gamma$ and a baryon of the SU(3) decuplet
of ten resonances that are dynamically generated from the interaction of vector
mesons with baryons of the decuplet. We obtain quite different partial decay
widths for the various resonances, and for different charge states of the same
resonance, suggesting that the experimental investigation of these radiative
decays should bring much information on the nature of these resonances.",0903.5138v1
2009-05-20,Recursive T matrix algorithm for resonant multiple scattering: Applications to localized plasmon excitations,"A matrix balanced version of the Recursive Centered T Matrix Algorithm
(RCTMA) applicable to systems possessing resonant inter-particle couplings is
presented. Possible domains of application include systems containing
interacting localized plasmon resonances, surface resonances, and photonic jet
phenomena. This method is of particular interest when considering modifications
to complex systems. The numerical accuracy of this technique is demonstrated in
a study of particles with strongly interacting localized plasmon resonances.",0905.3307v1
2009-06-27,Ultracold three-body collisions near narrow Feshbach resonances,"We study ultracold three-body collisions of bosons and fermions when the
interatomic interaction is tuned near a narrow Feshbach resonance. We show that
the width of the resonance has a substantial impact on the collisional
properties of ultracold gases in the strongly interacting regime. We obtain
numerical and analytical results that allow us to identify universal features
related to the resonance width. For narrow resonances, we have found a
suppression of all inelastic processes in boson systems leading to deeply bound
states and an enhancement for fermion systems.",0906.5019v2
2009-07-19,Preparation and Detection of a Mechanical Resonator Near the Ground State of Motion,"We have cooled the motion of a radio-frequency nanomechanical resonator by
parametric coupling to a driven microwave frequency superconducting resonator.
Starting from a thermal occupation of 480 quanta, we have observed occupation
factors as low as 3.8$\pm$1.2 and expect the mechanical resonator to be found
with probability 0.21 in the quantum ground state of motion. Cooling is limited
by random excitation of the microwave resonator and heating of the dissipative
mechanical bath.",0907.3313v1
2009-08-26,High $p_T$ resonances as a possibility to explore hot and dense nuclear matter,"One of the fundamental objectives of experiments with ultrarelativistic heavy
ions is to explore strongly interacting matter at high density and high
temperature. In this investigation we study in particular the information which
can be obtained by analyzing baryonic and mesonic resonances. The decay
products of these resonances carry information on the resonances properties at
the space time point of their decay. We especially investigate the percentage
of reconstructable resonances as a function of density for heavy ion collisions
in the energy range between $E_{lab}$ = 30 AGeV and $\sqrt{s}$ = 200 AGeV, the
energy domain between the future FAIR facility and the present RHIC collider.",0908.3811v1
2009-09-24,Amplitude Noise Squeezing in Cavity-Driven Oscillations of a Mechanical Resonator,"We analyze the amplitude and phase noise of limit-cycle oscillations in a
mechanical resonator coupled parametrically to an optical cavity driven above
its resonant frequency. At a given temperature the limit-cycle oscillations
have lower amplitude noise than states of the same average amplitude excited by
a pure harmonic drive; for sufficiently low thermal noise a sub-Poissonian
resonator state can be produced. We also calculate the linewidth narrowing that
occurs in the limit-cycle states, and show that while the minimum is set by
direct phase diffusion, diffusion due to the optical spring effect can dominate
if the cavity is not driven exactly at a side-band resonance.",0909.4389v2
2010-01-18,Resonance induced by repulsive interactions in a model of globally-coupled bistable systems,"We show the existence of a competition-induced resonance effect for a generic
globally coupled bistable system. In particular, we demonstrate that the
response of the macroscopic variable to an external signal is optimal for a
particular proportion of repulsive links. Furthermore, we show that a resonance
also occurs for other system parameters, like the coupling strength and the
number of elements. We relate this resonance to the appearance of a multistable
region, and we predict the location of the resonance peaks, by a simple
spectral analysis of the Laplacian matrix.",1001.2993v1
2010-03-01,"Entropy, fidelity, and double orthogonality for resonance states in two-electron quantum dots","Resonance states of a two-electron quantum dot are studied using a
variational expansion with both real basis-set functions and complex scaling
methods. The two-electron entanglement (linear entropy) is calculated as a
function of the electron repulsion at both sides of the critical value, where
the ground (bound) state becomes a resonance (unbound) state. The linear
entropy and fidelity and double orthogonality functions are compared as methods
for the determination of the real part of the energy of a resonance. The
complex linear entropy of a resonance state is introduced using complex scaling
formalism.",1003.0468v1
2010-03-29,One More Tool for Understanding Resonance,"We propose the application of graphical convolution to the analysis of the
resonance phenomenon. This time-domain approach encompasses both the finally
attained periodic oscillations and the initial transient period. It also
provides interesting discussion concerning the analysis of non-sinusoidal
waves, based not on frequency analysis, but on direct consideration of
waveforms, and thus presenting an introduction to Fourier series. Further
developing the point of view of graphical convolution, we come to a new
definition of resonance in terms of time domain.",1003.5543v2
2010-04-04,Greatly enhanced absorption of non-resonant microwave fields by ultracold molecules near a Feshbach resonance,"We show that the probability of the collision-induced absorption of
non-resonant microwave photons by a gas of ultracold molecules is dramatically
enhanced near a Feshbach scattering resonance. This can be used for detecting
Feshbach resonances of ultracold molecules by measuring the microwave field
absorption and for tuning the elastic scattering cross sections of ultracold
molecules by varying the frequency and intensity of the microwave field in a
wide range of the field parameters.",1004.0481v2
2010-04-14,Super FSR tunable optical microbubble resonator,"An optical resonator is often called fully tunable if its tunable range
exceeds the spectral interval that contains the resonances at all the
characteristic modes of this resonator. For the high Q-factor spheroidal and
toroidal microresonators, this interval coincides with the azimuthal free
spectral range. In this Letter, we demonstrate the first mechanically fully
tunable spheroidal microresonator created of a silica microbubble having a 100
micron order radius and a micron order wall thickness. The tunable bandwidth of
this resonator is more than two times greater than its azimuthal free spectral
range.",1004.2405v1
2010-06-04,Resonant Metalenses for Breaking the Diffraction Barrier,"We introduce the resonant metalens, a cluster of coupled subwavelength
resonators. Dispersion allows the conversion of subwavelength wavefields into
temporal signatures while the Purcell effect permits an efficient radiation of
this information in the far-field. The study of an array of resonant wires
using microwaves provides a physical understanding of the underlying mechanism.
We experimentally demonstrate imaging and focusing from the far-field with
resolutions far below the diffraction limit. This concept is realizable at any
frequency where subwavelength resonators can be designed.",1006.0799v1
2010-06-04,Emission and Absorption quantum noise measurement with an on-chip resonant circuit,"Using a quantum detector, a superconductor-insulator-superconductor junction,
we probe separately the emission and absorption noise in the quantum regime of
a superconducting resonant circuit at equilibrium. At low temperature the
resonant circuit exhibits only absorption noise related to zero point
fluctuations whereas at higher temperature emission noise is also present. By
coupling a Josephson junction, biased above the superconducting gap, to the
same resonant circuit, we directly measure the noise power of quasiparticles
tunneling through the junction at two resonance frequencies. It exhibits a
strong frequency dependence, consistent with theoretical predictions.",1006.0892v2
2010-09-21,Momentum distributions from three-body decaying 9Be and 9B resonances,"The complex-rotated hyperspherical adiabatic method is used to study the
decay of low-lying $^9$Be and $^9$B resonances into $\alpha$, $\alpha$ and $n$
or $p$. We consider six low-lying resonances of $^9$Be ($1/2^\pm$, $3/2^\pm$
and $5/2^\pm$) and one resonance of $^9$B ($5/2^-$) to compare with. The
properties of the resonances at large distances are decisive for the momentum
distributions of the three decaying fragments. Systematic detailed energy
correlations of Dalitz plots are presented.",1009.4029v1
2010-09-22,Coupling Circuit Resonators Among Themselves and To Nitrogen-Vacancy Centers in Diamond,"We propose a scheme to couple NV centers in diamond through coplanar
waveguide resonators. The central conductor of the resonator is split into
several pieces which are coupled strongly with each other via simple capacitive
junctions or superconducting Josephson junctions. The NV centers are then put
at the junctions. The discontinuity at the junctions induces a large local
magnetic field, with which the NV centers are strongly coupled to the circuit
resonator. The coupling strength $g$ between the resonator and the NV center is
of order of $g/2\pi\sim 1$--$30\unit{MHz}$.",1009.4314v2
2010-11-17,Effect of electron-phonon coupling on transmission through Luttinger liquid hybridized with resonant level,"We show that electron-phonon coupling strongly affects transport properties
of the Luttinger liquid hybridized with a resonant level. Namely, this coupling
significantly modifies the effective energy-dependent width of the resonant
level in two different geometries, corresponding to the resonant or
antiresonant transmission in the Fermi gas. This leads to a rich phase diagram
for a metal-insulator transition induced by the hybridization with the resonant
level.",1011.3934v1
2010-11-26,Nonlinear effects in resonant layers in solar and space plasmas,"The present paper reviews recent advances in the theory of nonlinear driven
magnetohydrodynamic (MHD) waves in slow and Alfven resonant layers. Simple
estimations show that in the vicinity of resonant positions the amplitude of
variables can grow over the threshold where linear descriptions are valid.
Using the method of matched asymptotic expansions, governing equations of
dynamics inside the dissipative layer and jump conditions across the
dissipative layers are derived. These relations are essential when studying the
efficiency of resonant absorption. Nonlinearity in dissipative layers can
generate new effects, such as mean flows, which can have serious implications
on the stability and efficiency of the resonance.",1011.5786v1
2010-11-26,Scalar-Pseudoscalar scattering and pseudoscalar resonances,"The interactions between the f_0(980) and a_0(980) scalar resonances and the
lightest pseudoscalar mesons are studied. We first obtain the interacting
kernels, without including any ad hoc free parameter, because the lightest
scalar resonances are dynamically generated. These kernels are unitarized,
giving the final amplitudes, which generate pseudoscalar resonances, associated
with the K(1460), \pi(1300), \pi(1800), \eta(1475) and X(1835). We also
consider the exotic channels with I=3/2 and I^G=1^+ quantum numbers. The former
could be also resonant in agreement with a previous prediction.",1011.5843v1
2010-12-02,Hybrid metal-dielectric ring resonators for optical magnetic metamaterials down to ultraviolet range,"In this paper, we derive a model from Maxwell equations for the magnetic
resonance of split-ring resonators. Using this model we revisit the scaling of
split-ring resonators. Inspired by our model, we propose a new type of
split-hybrid metal-dielectric ring resonator, of which the ring is made
composed of moderately high index dielectric material (e.g. SiC, TiO2, ZnS)
(for the major portion), while and metal (e.g. Ag) fills the gap. Such a new
magnetic metamaterial is able to overcome the saturation problem of split-ring
resonatorssaturation-free and therefore is able to operate at short wavelength
down to ultraviolet range.",1012.0400v2
2010-12-14,Electromagnetic production of hyperon resonances,"The study of hyperon resonances has entered a new era of precision with
advent of high-statistics photoproduction data from the CLAS detector at
Jefferson Lab. These data have multi-particle final states, allowing clean
identification of exclusive reactions associated with strange mesons and
baryons. Examples of physics results are: evidence for isospin interference in
the decay of the $\Lambda(1405)$ resonance; a strong suggestion of meson cloud
effects in the structure of the $\Sigma(1385)$ resonance; data from $K^*$
photoproduction that will test the existence of the purported $K_0(800)$ meson.
Properties of other hyperon resonances will also be studied in the near future.",1012.3129v1
2010-12-27,Quantum behaviour of a flux qubit coupled to a resonator,"We present a detailed theoretical analysis for a system of a superconducting
flux qubit coupled to a transmission line resonator. The master equation,
accounting incoherent processes for a weakly populated resonator, is
analytically solved. An electromagnetic wave transmission coefficient through
the system, which provides a tool for probing dressed states of the qubit, is
derived. We also consider a general case for the resonator with more than one
photon population and compare the results with an experiment on the
qubit-resonator system in the intermediate coupling regime, when the coupling
energy is comparable with the qubit relaxation rate.",1012.5599v1
2011-01-16,Fano resonances in magnetic metamaterials,"We study the scattering of magnetoinductive plane waves by internal
(external) capacitive (inductive) defects coupled to a one-dimensional
split-ring resonator array. We examine a number of simple defect configurations
where Fano resonances occur and study the behavior of the transmission
coefficient as a function of the controllable external parameters. We find that
for embedded capacitive defects, the addition of a small amount of coupling to
second neighbors is necessary for the occurrence of Fano resonance. For
external inductive defects, Fano resonances are commonplace, and they can be
tuned by changing the relative orientation or distance between the defect and
the SSR array.",1101.3032v2
2011-02-21,Stable double-resonance optical spring in laser gravitational-wave detectors,"We analyze the optical spring characteristics of a double pumped Fabry-Perot
cavity. A double-resonance optical spring occurs when the optical spring
frequency and the detuning frequency of the cavity coincide. We formulate a
simple criterion for the stability of an optical spring and apply it to the
double resonance regime. Double resonance configurations are very promising for
future gravitational wave detectors as they allow us to surpass the Standard
Quantum Limit. We show that stable double resonance can be demonstrated in
middle scale prototype interferometers such as the Glasgow 10m-Prototype,
Gingin High Optical Power Test Facility or the AEI 10m Prototype Interferometer
before being implemented in future gravitational wave detectors.",1102.4266v1
2011-02-22,The n:m resonance dual pair,"In this paper we build dual pairs of Poisson maps \[
\RR\stackrel{R_\pm}{\longleftarrow}(D,\om_\pm)
\stackrel{\Pi_\pm}{\longrightarrow} B \] associated to $n:m$ resonance, as well
as to $n:-m$ resonance. Except for the above mentioned cases $1:\pm1$, these
are not pairs of momentum maps. Here $D$ is an open subset of $\CC^2$ with the
above mentioned symplectic forms $\om_\pm$, and $B$ an open subset of $\RR^3$.
The Poisson structure on $B$, which depends on the natural numbers $n$ and $m$,
is not Lie-Poisson. Instead, its symplectic leaves are the Kummer shapes:
bounded surfaces for $n:m$ resonance, and unbounded surfaces for $n:-m$
resonance",1102.4377v1
2011-04-18,Characterization of a microwave frequency resonator via a nearby quantum dot,"We present measurements of a hybrid system consisting of a microwave
transmission-line resonator and a lateral quantum dot defined on a GaAs
heterostructure. The two subsystems are separately characterized and their
interaction is studied by monitoring the electrical conductance through the
quantum dot. The presence of a strong microwave field in the resonator is found
to reduce the resonant conductance through the quantum dot, and is attributed
to electron heating and modulation of the dot potential. We use this
interaction to demonstrate a measurement of the resonator transmission spectrum
using the quantum dot.",1104.3535v1
2011-04-21,Coherent spectroscopy of rare-earth-ion doped whispering-gallery mode resonators,"We perform an investigation into the properties of Pr3+:Y2SiO5 whispering
gallery mode resonators as a first step towards achieving the strong coupling
regime of cavity QED with rare-earth-ion doped crystals. Direct measurement of
cavity QED parameters are made using photon echoes, giving good agreement with
theoretical predictions. By comparing the ions at the surface of the resonator
to those in the center it is determined that the physical process of making the
resonator does not negatively affect the properties of the ions. Coupling
between the ions and resonator is analyzed through the observation of optical
bistability and normal-mode splitting.",1104.4150v1
2011-05-20,Asymmetric resonance in selective reflection: Explanation via Fano-like mechanism,"Fano mechanism is the universal explanation of asymmetric resonance appearing
in different systems. We report the evidence of Fano-like resonance in
selective reflection from a resonant two-level medium. We draw an analogy with
the asymmetric resonance previously obtained for the coupled oscillators. We
also take into account the effects of dielectric background and local-field
correction and connect our results with optical bistability.",1105.4020v1
2011-06-22,Storing light as a mechanical excitation in a silica optomechanical resonator,"We report the experimental demonstration of optomechanical light storage in a
silica resonator. We use writing and readout laser pulses tuned to one
mechanical frequency below an optical cavity resonance to control the coupling
between the mechanical displacement and the optical field at the cavity
resonance. The writing pulse maps a signal pulse at the cavity resonance to a
mechanical excitation. The readout pulse later converts the mechanical
excitation back to an optical pulse. The light storage lifetime is determined
by the relatively long damping time of the mechanical excitation.",1106.4512v1
2011-06-28,The Friedrichs Model and its use in resonance phenomena,"We present here a relation of different types of Friedrichs models and their
use in the description and comprehension of resonance phenomena. We first
discuss the basic Friedrichs model and obtain its resonance in the case that
this is simple or doubly degenerated. Next, we discuss the model with $N$
levels and show how the probability amplitude has an oscillatory behavior. Two
generalizations of the Friedrichs model are suitable to introduce resonance
behavior in quantum field theory. We also discuss a discrete version of the
Friedrichs model and also a resonant interaction between two systems both with
continuous spectrum. In an Appendix, we review the mathematics of rigged
Hilbert spaces.",1106.5782v1
2011-07-29,Coupling constants of the $S_{11}$ resonances to pseudoscalar mesons and octet baryons,"Coupling constants of $S_{11}(1535)$ and $S_{11}(1650)$ resonances to
meson-baryon ($\pi N$, $\eta N$, $\eta^\prime N$, $KY$) are investigated in a
chiral quark model, complemented by inclusion of five-quark components in those
resonances. The known strong decay partial widths of both resonances are well
reproduced, provided sizeable strangeness components in the relevant wave
functions. %to excellent description for the strong decays of the above two
resonances, which %cannot be reproduced very well in the traditional chiral
quark model with or without %$SU(6)\otimes O(3)$ breaking. Finally, we find
that $S_{11}(1535)$ and $S_{11}(1650)$ %couple strongly to the channels with
strangeness.",1107.5991v2
2011-08-04,Higher-order optical resonance node detection of integrated disk microresonator,"We have demonstrated higher-order optical resonance node detection by using
an integrated disk microresonator from through port of the coupling bus
waveguide. In addition to the fundamental mode, the disk resonator has
higher-order whispering gallery modes. The excited second-order higher-order
mode has a node at the position where the electromagnetic energy of the
fundamental mode is close to a maximum. This high resolution measurement of
optical resonance mode profile has a variety of applications for optical
sensing and detection. The self-referencing characteristics of the two optical
resonance modes have potential to achieve optical detection independent of
external perturbation, such as temperature change.",1108.1082v1
2012-02-03,Magnetic resonance in the ordered phases of the 2D frustrated quantum magnet Cs2CuCl4,"The temperature evolution of the electron spin resonance is studied at
cooling the crystal samples of Cs2CuCl4 through the Neel point 0.62 K. A
coexistence of the high-frequency spinon type resonance developed in the
spin-liquid phase and of the low-frequency antiferromagnetic resonance was
found in the ordered phase. The low-frequency magnetic resonance spectrum in
the low field range has two gapped branches and corresponds well to the
spectrum of spin excitations of a planar spiral spin structure with two axes of
the anisotropy. The field induced phase transitions result in a more
complicated low-frequency spectra.",1202.0783v1
2012-02-14,Design and Fabrication of Micromachined Resonators,"Microelectromechanical system (MEMS) based on-chip resonators offer great
potential for sensing and high frequency signal processing applications due to
their exceptional features like small size, large frequency-quality factor
product, integrability with CMOS ICs, low power consumption etc. This work is
mainly aimed at the design, modeling, simulation, and fabrication of
micromachined polysilicon disk resonators exhibiting radial-contour mode
vibrations. A few other bulk mode modified resonator geometries are also being
explored. The resonator structures have been designed and simulated in
CoventorWare finite-element platform and fabricated by the PolyMUMPs surface
micromachining process.",1202.3048v1
2012-07-20,High-frequency nanotube mechanical resonators,"We report on a simple method to fabricate high-frequency nanotube mechanical
resonators reproducibly. We measure resonance frequencies as high as 4.2 GHz
for the fundamental eigenmode and 11 GHz for higher order eigenmodes. The
high-frequency resonances are achieved using short suspended nanotubes and by
introducing tensile stress in the nanotube. These devices allow us to determine
the coefficient of the thermal expansion of an individual nanotube, which is
negative and is about -0.7E-5 1/K at room temperature. High-frequency
resonators made of nanotubes hold promise for mass sensing and experiments in
the quantum limit.",1207.4874v1
2012-08-17,"Bayesian inference of the resonance content of p(gamma,K+)Lambda","A Bayesian analysis of the world's p(gamma,K+)Lambda data is presented. We
adopt a Regge-plus-resonance framework featuring consistent couplings for
nucleon resonances up to spin J=5/2, and evaluate 2048 model variants
considering all possible combinations of 11 candidate resonances. The best
model, labeled RPR-2011, is discussed with special emphasis on nucleon
resonances in the 1900-MeV mass region.",1208.3618v1
2012-09-27,Resonance linewidth and inhomogeneous broadening in a metamaterial array,"We examine the effect of inhomogeneous broadening on the collective response
of a planar metamaterial consisting of asymmetric split ring resonators. We
show that such a response leads to a transmission resonance that can persist
when the broadening of individual meta-atom resonance frequencies is roughly
one half the frequency characterizing the split ring asymmetry. We also find
that larger degrees of inhomogeneous broadening can drastically alter the
cooperative response, destroying this resonance. The reduced effect of
cooperative response due to inhomogeneous broadening may find applications in
producing metamaterial samples that more closely mimic homogeneous
magneto-dielectric medium with well-defined susceptibility and permittivity.",1209.6154v1
2012-11-05,Enhancement of four reflection shifts by a three-layer surface plasmon resonance,"We investigate the effect of a surface plasmon resonance on Goos-Hanchen and
Imbert-Fedorov spatial and angular shifts in the reflection of a light beam by
considering a three-layer system made of glass, gold and air. We calculate
these spatial and angular shifts as a function of the incidence angle showing
that they are strongly enhanced in correspondence of the resonant angle. In
particular, we find giant spatial and angular Goos-Hanchen shits for the p-wave
light close to the plasmon resonance. We also predict a similar, but less
pronounced, resonant effect on spatial and angular Imbert-Fedorov shifts for
both s-wave and p-wave light.",1211.1050v1
2012-11-26,Review of lattice studies of resonances,"I review recent progress in extracting resonance parameters using lattice
field theory, with an emphasis on determining hadron resonances from lattice
quantum chromodynamics. Until recently, the \rho-meson channel was the only one
considered, while, during the last year, several resonant channels have been
investigated for the first time. Recent lattice results for scattering phase
shifts in resonant channels are presented.",1211.6163v1
2013-01-03,Low-loss tunable metamaterials using superconducting circuits with Josephson junctions,"We report on experiments with superconducting metamaterials containing
Josephson junctions. In these structures, split-ring resonators used in
conventional metamaterials are replaced by superconducting loops that are
interrupted by Josephson junctions, so called rf-SQUIDs. Like the split-ring
resonators, these elements can be seen as LC-resonators that couple to the
magnetic field. The advantage of superconducting thin-film metamaterials is
that, due to the tunable intrinsic inductance of the Josephson junction, the
resonance frequency of the rf-SQUID can be changed by applying an external dc
magnetic field. We present experimental results that demonstrate the tunability
of the resonance frequency of these devices.",1301.0440v1
2013-01-08,Hadronic Resonances in Heavy-Ion Collisions at ALICE,"Modifications to the masses and widths of hadronic resonances in heavy-ion
collisions could be a sign of chiral symmetry restoration. Uncorrected spectra,
masses, and widths of the phi(1020) and K*(892)0 resonances have been measured
in Pb-Pb collisions at 2.76 TeV using the ALICE detector. These measurements
are presented and compared to resonances in other collision systems.",1301.1581v1
2013-01-28,Comparison of f-Q scaling in wineglass and radial modes in ring resonators,"Low phase noise MEMS oscillators necessitate resonators with high f-Q.
Resonators achieving high f-Q (mechanical frequency-quality factor product)
close to the thermo-elastic damping (TED) limit have been demonstrated at
expense of feed-through. Here we present a study comparing frequency scaling of
quality factors of wineglass and radial modes in a ring resonator using an
opto-mechanical two port transmission measurement. Higher harmonics of the
wineglass mode show an increasing trend in the f-Q product, as compared to a
saturation of f-Q for radial modes. The measured f-Q of 5.11e13Hz at 9.82GHz in
air at room temperature for a wineglass mode is close to the highest measured
values in silicon resonators.",1301.6564v1
2013-02-05,Metamaterial atom with multijunction superconducting structure,"We present results of numerical simulations of a metamaterial element
(meta-atom) for planar negative media based on cuprate Josephson junctions. The
proposed circuit consists of two coupled resonators: ""magnetic dipole"" and
""electric dipole"". The first one is a superconducting spiral resonator with
multijunction superconducting structure - SQIF (SQIF - superconducting quantum
interference filter), and the second one is a comb-shape resonator made from
normal metal film. We show, that in comparison with passive metal resonators,
the superconducting resonator with Josephson junctions (magnetic dipole) can be
tuned by external magnetic field due to magnetic dependence of Josephson
inductance. The simulated characteristics of one-dimensional planar negative
media are discussed.",1302.0997v1
2013-04-01,Orbital resonances around Black holes,"We compute the length and timescales associated with resonant orbits in the
Kerr Metric for all orbital and spin parameters. Resonance induced effects are
potentially observable when the Event Horizon telescope resolves the inner
structure of Sgr A*, space-based gravitational wave detectors record
phase-shifts in the waveform during the resonant passage of a neutron star as
it spirals in to the black hole and in the frequencies of quasi periodic
oscillations for accreting black holes. The onset of geodesic chaos for
non-Kerr spacetimes should occur at the resonance locations quantified here.",1304.0330v1
2013-05-16,Metamaterial transparency induced by cooperative electromagnetic interactions,"We propose a cooperative asymmetry-induced transparency, CAIT, formed by
collective excitations in metamaterial arrays of discrete resonators. CAIT can
display a sharp transmission resonance even when the constituent resonators
individually exhibit broad resonances. We further show how dynamically
reconfiguring the metamaterial allows one to actively control the transparency.
While reminiscent of electromagnetically induced transparency, which can be
described by independent emitters, CAIT relies on a cooperative response
resulting from strong radiative couplings between the resonators.",1305.3808v1
2013-05-21,Distribution of resonances for hyperbolic surfaces,"We study the distribution of resonances for geometrically finite hyperbolic
surfaces of infinite area by countting resonances numerically. The resonances
are computed as zeros of the Selberg zeta function, using an algorithm for
computation of the zeta function for Schottky groups. Our particular focus is
on three aspects of the resonance distribution that have attracted attention
recently: the fractal Weyl law, the spectral gap, and the concentration of
decay rates.",1305.4850v2
2013-06-04,Hadronic Resonance Production with ALICE Experiment at LHC,"The production of resonances in heavy-ion collisions is expected to be
sensitive to the properties of strongly interacting matter created in such
collisions. We report on the measurements of $\phi$ and $K^{*0}$ resonances in
Pb-Pb collisions at $\sqrt{s_{NN}} $ = 2.76 TeV. The masses, widths and yields
in Pb-Pb collisions as a function of centrality are compared to that in pp
collisions to understand the role of re-scattering and regeneration. The
resonance to non-resonance particle ratios are shown as a function of collision
centrality and compared with the results at lower energies.",1306.0673v1
2013-06-10,Spin Transfer of Quantum Information between Majorana Modes and a Resonator,"We show that resonant coupling and entanglement between a mechanical
resonator and majorana bound states can be achieved via spin currents in a 1D
quantum wire with strong spin-orbit interactions. The bound states induced by
vibrating and stationary magnets can hybridize thus resulting in spin-current
induced $4\pi$-periodic torque, as a function of the relative field angle,
acting on the resonator. We study the feasibility of detecting and manipulating
majorana bound states with the use of magnetic resonance force microscopy
techniques.",1306.2339v1
2013-06-12,Overcoming Si3N4 film stress limitations for High Quality factor ring resonators,"Silicon nitride (Si3N4) ring resonators are critical for a variety of
photonic devices. However the intrinsically high film stress of silicon nitride
has limited both the optical confinement and quality factor (Q) of ring
resonators. We show that stress in Si3N4 films can be overcome by introducing
mechanical trenches for isolating photonic devices from propagating cracks. We
demonstrate a Si3N4 ring resonator with an intrinsic quality factor of 7
million, corresponding to a propagation loss of 4.2 dB/m. This is the highest
quality factor reported to date for high confinement Si3N4 ring resonators in
the 1550 nm wavelength range.",1306.2994v1
2013-10-12,Resonant dynamics of chromium condensates,"We numerically study the dynamics of a spinor chromium condensate in low
magnetic fields. We show that the condensate evolution has a resonant character
revealing rich structure of resonances similar to that already discussed in the
case of alkali-atoms condensates. This indicates that dipolar resonances occur
commonly in the systems of cold atoms. In fact, they have been already observed
experimentally. We further simulate two recent experiments with chromium
condensates, in which the threshold in spin relaxation and the spontaneous
demagnetization phenomena were observed. We demonstrate that both these effects
originate in resonant dynamics of chromium condensate.",1310.3384v1
2013-10-21,Resonant state expansion applied to planar waveguides,"The resonant state expansion, a recently developed method in electrodynamics,
is generalized here to planar open optical systems with non-normal incidence of
light. The method is illustrated and verified on exactly solvable examples,
such as a dielectric slab and a Bragg reflector microcavity, for which explicit
analytic formulas are developed. This comparison demonstrates the accuracy and
convergence of the method. Interestingly, the spectral analysis of a dielectric
slab in terms of resonant states reveals an influence of waveguide modes in the
transmission. These modes, which on resonance do not couple to external light,
surprisingly do couple to external light for off-resonant excitation.",1310.5600v1
2013-11-13,Purely imaginary polar resonances of rapidly-rotating Kerr black holes,"We prove the existence of a unique family of non-oscillatory
(purely-imaginary) polar quasinormal resonances of rapidly-rotating Kerr black
holes. These purely imaginary resonances can be expressed in the compact form:
w_n=-i2*pi*T_{BH}*(l+1+n), where T_{BH} is the black-hole temperature, l is the
spheroidal harmonic index of the mode, and n=0,1,2,... is the resonance
parameter. It is shown that our analytical results for the black-hole resonance
spectrum agree with new numerical data that recently appeared in the
literature.",1311.3007v1
2013-12-03,Cyclotron-resonance-assisted photon drag effect in InSb/InAlSb quantum wells excited by terahertz radiation,"We report on the observation of the cyclotron-resonance-assisted photon drag
effect. Resonant photocurrent is detected in InSb/InAlSb quantum wells
structures subjected to a static magnetic field and excited by terahertz
radiation at oblique incidence. The developed theory based on Boltzmann's
kinetic equation is in a good agreement with the experimental findings. We show
that the resonant photocurrent originates from the transfer of photon momentum
to free electrons drastically enhanced at cyclotron resonance.",1312.0726v1
2014-01-23,Can new heavy gauge bosons be observed in ultra-high energy cosmic neutrino events?,"A wide range of models beyond the Standard Model predict charged and neutral
resonances, generically called $W'$- and $Z'$-bosons, respectively. In this
paper we study the impact of such resonances on the deep inelastic scattering
of ultra-high energy neutrinos as well as on the resonant charged current
$\bar\nu_e e^-$ scattering (Glashow resonance). We find that the effects of
such resonances can not be observed with the Pierre Auger Observatory or any
foreseeable upgrade of it.",1401.6012v1
2014-07-15,Molecular-absorption-induced thermal bistablity in PECVD silicon nitride microring resonators,"The wavelength selective linear absorption in communication C-band is
investigated in CMOS-processed PECVD silicon nitride rings. In the overcoupled
region, the linear absorption loss lowers the on-resonance transmission of a
ring resonator and increases its overall quality factor. Both the linear
absorption and ring quality factor are maximized near 1520 nm. The direct
heating by phonon absorption leads to thermal optical bistable switching in
PECVD silicon nitride based microring resonators. We calibrate the linear
absorption rate in the microring resonator by measuring its transmission
lineshape at different laser power levels, consistent with coupled mode theory
calculations.",1407.4146v1
2014-07-17,Logic-Memory Device of a Mechanical Resonator,"We report multifunctional operation based on the nonlinear dynamics in a
single microelectromechanical system (MEMS) resonator. This Letter focuses on a
logic-memory device that uses a closed loop control and a nonlinear MEMS
resonator in which multiple states coexist. To obtain both logic and memory
operations in a MEMS resonator, we examine the nonlinear dynamics with and
without control input. Based on both experiments and numerical simulations, we
develop a novel device that combines an OR gate and memory functions in a
single MEMS resonator.",1407.4858v1
2014-08-25,Coherent control of non-Markovian photon-resonator dynamics,"We study the unitary time evolution of photons interacting with a dielectric
resonator using coherent control pulses. We show that non-Markovianity of
transient photon dynamics in the resonator subsystem may be controlled to
within a photon-resonator transit time. In general, appropriate use of coherent
pulses and choice of spatial subregion may be used to create and control a wide
range of non-Markovian transient dynamics in photon resonator systems.",1408.5844v1
2014-10-31,Feshbach Resonances in Kerr Frequency Combs,"We show that both the power and repetition rate of a frequency comb generated
in a nonlinear ring resonator, pumped with continuous wave (cw) coherent light,
are modulated. The modulation is brought about by the interaction of the cw
background with optical pulses excited in the resonator, and occurs in
resonators with nonzero high-order chromatic dispersion and
wavelength-dependent quality factor. The modulation frequency corresponds to
the detuning of the pump frequency from the eigenfrequency of the pumped mode
in the resonator.",1410.8604v1
2014-12-12,Contribution of resonance tunneling of molecule to physical observables,"Probabilities of resonant tunneling through a potential barrier are compared
for a rigid molecule and an excited molecule. It is shown that the resonance
spectrum is mainly governed by the transmission resonance spectrum of the rigid
molecule. Analytical expressions for the probability for the tunneling of the
rigid molecule through a barrier allow resonance-spectrum-averaged observables,
including quantum diffusion, to be estimated.",1412.3905v1
2015-01-08,Dissociative electron attachment and electron-impact resonant dissociation of vibrationally excited O2 molecules,"State-by-state cross sections for dissociative electron attachment and
electron-impact dissociation for molecular oxygen are computed using ab initio
resonance curves calculated with the R-matrix method. When O2 is in its
vibrational ground state, the main contribution for both processes comes from
the $^2\Pi_u$ resonance state of $O_2^-$ but with a significant contribution
from the $^4\Sigma$ resonant state. Vibrational excitation leads to an
increased contribution from the low-lying $^2\Pi_{g}$ resonance, greatly
increased cross sections for both processes, and the threshold moving to lower
energies. These results provide important input for models of O2-containing
plasmas in nonequilibrium conditions.",1501.01771v1
2015-01-29,Purcell factor of Mie resonators featuring electric and magnetic modes,"We present a modal approach to compute the Purcell factor in Mie resonators
exhibiting both electric and magnetic resonances. The analytic expressions of
the normal modes are used to calculate the effective volumes. We show that
important features of the effective volume can be predicted thanks to the
translation-addition coefficients of a displaced dipole. Using our formalism,
it is easy to see that, in general, the Purcell factor of Mie resonators is not
dominated by a single mode, but rather by a large superposition. Finally we
consider a silicon resonator homogeneously doped with electric dipolar
emitters, and we show that the average electric Purcell factor dominates over
the magnetic one.",1501.07452v2
2015-03-13,Non-Schlesinger Isomonodromic Deformations of Fuchsian Systems and Middle Convolution,"The paper is devoted to non-Schlesinger isomonodromic deformations for
resonant Fuchsian systems. There are very few explicit examples of such
deformations in the literature. In this paper we construct a new example of the
non-Schlesinger isomonodromic deformation for a resonant Fuchsian system of
order 5 by using middle convolution for a resonant Fuchsian system of order 2.
Moreover, it is known that middle convolution is an operation that preserves
Schlesinger's deformation equations for non-resonant Fuchsian systems. In this
paper we show that Bolibruch's non-Schlesinger deformations of resonant
Fuchsian systems are, in general, not preserved by middle convolution.",1503.03959v1
2015-05-04,Does Geometric Coupling Generates Resonances?,"Geometrical coupling in a co-dimensional one Randall-Sundrum scenario (RS) is
used to study resonances of $p-$form fields. The resonances are calculated
using the transfer matrix method. The model studied consider the standard RS
with delta-like branes, and branes generated by kinks and domain-wall as well.
The parameters are changed to control the thickness of the smooth brane. With
this a very interesting pattern is found for the resonances. The geometrical
coupling does not generate resonances for the reduced $p-$form in all cases
considered.",1505.00689v2
2015-05-05,A Resonance Problem in Relaxation of Ground States of Nonlinear Schrodinger Equations,"In this paper we consider a resonance problem, in a generic regime, in the
consideration of relaxation of ground states of semilinear Schrodinger
equations. Different from previous results, our consideration includes the
presence of resonance, resulted by overlaps of frequencies of different states.
All the known key results, proved under non-resonance conditions, have been
recovered uniformly. These are achieved by better understandings of normal form
transformation and Fermi Golden rule. Especially, we find that if certain
denominators are zeros (or small), resulted by the presence of resonances (or
close to it), then cancellations between terms make the corresponding
numerators proportionally small.",1505.01107v1
2015-05-22,Counting function of magnetic resonances for exterior problems,"We study the asymptotic distribution of the resonances near the Landau levels
$\Lambda\_q =(2q+1)b$, $q \in \mathbb{N}$, of the Dirichlet (resp. Neumann,
resp. Robin) realization in the exterior of a compact domain of $\mathbb{R}^3$
of the 3D Schr{\""o}dinger operator with constant magnetic field of scalar
intensity $b\textgreater{}0$. We investigate the corresponding resonance
counting function and obtain the main asymptotic term. In particular, we prove
the accumulation of resonances at the Landau levels and the existence of
resonance free sectors. In some cases, it provides the discreteness of the set
of embedded eigenvalues near the Landau levels.",1505.06026v1
2015-06-08,Clear Identification of Previously Unresolved Overlapping Resonances in Dissociative Electron Attachment: A Case Study on Chlorine Molecule,"An observed broad resonance peak in dissociative electron attachment (DEA)
cross sections to a molecule might be due to either closely lying or
overlapping resonances involved in the process. We developed a state-of-the-art
experimental approach that enables us to identify unambiguously both the
closely lying and the overlapping resonances based on kinetic energy and/or
angular distribution measurements of fragment negative ion(s) generated from
DEA process. Experimental observations strongly supported by theoretical
potential energy curve calculations unambiguously identify previously
unresolved overlapping resonances in DEA to chlorine molecule.",1506.02524v1
2015-07-03,Unitarity implications of diboson resonance in the TeV region for Higgs physics,"We investigate the implications of a putative new resonance in the TeV region
coupled to the weak bosons. By studying perturbative unitarity in longitudinal
WW scattering, we find that a weakly coupled spin-1 resonance, that explains
the ATLAS diboson excesses, is allowed with a SM-like Higgs. On the other hand,
larger values of the resonance couplings, preferred in models of strong
dynamics, would imply either sizeable reduction of the Higgs couplings or new
physics, beyond the diboson resonance, at a few TeV.",1507.00900v1
2015-07-24,Pseudo orbit expansion for the resonance condition on quantum graphs and the resonance asymptotics,"In this note we explain the method how to find the resonance condition on
quantum graphs, which is called pseudo orbit expansion. In three examples with
standard coupling we show in detail how to obtain the resonance condition. We
focus on non-Weyl graphs, i.e. the graphs which have fewer resonances than
expected. For these graphs we explain benefits of the method of ""deleting
edges"" for simplifying the graph.",1507.06845v2
2015-08-05,Controlling carbon nanotube photoluminescence using silicon microring resonators,"We report on coupling between semiconducting single-wall carbon nanotubes
(s-SWNT) photoluminescence and silicon microring resonators. Polyfluorene
extracted s-SWNT deposited on such resonators exhibit sharp emission peaks, due
to interaction with the cavity modes of the microring resonators. Ring
resonators with radius of 5 {\mu}m and 10 {\mu}m were used, reaching quality
factors up to 4000 in emission. These are among the highest values reported for
carbon nanotubes coupled with an integrated cavity on silicon platform, which
open up the possibility to build s-SWNT based efficient light source on
silicon.",1508.01007v1
2015-09-06,Feshbach-Resonance-Enhanced Coherent Atom-Molecule Conversion with Ultra-Narrow Photoassociation Resonance,"We reveal the existence of high-density Feshbach resonances in the collision
between the ground and metastable states of $^{171}$Yb and coherently produce
the associated Feshbach molecules by photoassociation. The extremely small
transition rate is overcome by the enhanced Franck-Condon factor of the weakly
bound Feshbach molecule, allowing us to observe Rabi oscillations with long
decay time between an atom pair and a molecule in an optical lattice. We also
perform the precision measurement of the binding energies, which characterizes
the observed resonances. The ultra-narrow photoassociation will be a basis for
practical implementation of optical Feshbach resonances.",1509.01830v1
2015-09-27,Self-Assembled Graphene Plasmon Resonators,"The ability to fabricate dense small features over a large area is important
for graphene plasmonics. We present the first self-assembled graphene plasmonic
resonators operating in the mid-IR. The resonators are 35 nm in diameter with
20 nm spacing and cover a centimeter sized area. The resonators exhibit a very
broad resonance. We fit our data using a drude model and combine it with SEM
data to investigate the contribution to broadening from our process. We find
that the self-assembly does not contribute significantly to the broadening
observed.",1509.08118v1
2015-11-21,Mathematical analysis of plasmonic resonances for nanoparticles: the full Maxwell equations,"In this paper we use the full Maxwell equations for light propagation in
order to analyze plasmonic resonances for nanoparticles. We mathematically
define the notion of plasmonic resonance and analyze its shift and broadening
with respect to changes in size, shape, and arrangement of the nanoparticles,
using the layer potential techniques associated with the full Maxwell
equations. We present an effective medium theory for resonant plasmonic systems
and derive a condition on the volume fraction under which the Maxwell-Garnett
theory is valid at plasmonic resonances.",1511.06817v1
2016-01-13,Apex-angle-dependent resonances in triangular split ring resonators,"Along with other frequency selective structures [1] (circles and squares),
triangular split-ring resonators (TSRRs) only allow frequencies near the center
resonant frequency to propagate. Further, TSRRs are attractive due to their
small surface area [2], comparatively, and large quality factors (Q) factors as
previously investigated by Gay-Balmaz, et al. [3]. In this work we examine the
effects of varying the apex angle on the resonant frequency, the Q factor, and
the phase shift imparted by the TSRR element within the GHz frequency regime.",1601.03265v1
2016-03-02,Tilted excitation implies odd periodic resonances,"Our aim is to unveil how resonances of parametric systems are affected when
symmetry is broken. We showed numerically and experimentally that odd
resonances indeed come about when the pendulum is excited along a tilted
direction. Applying the Melnikov subharmonic function, we not only determined
analytically the loci of saddle-node bifurcations delimiting resonance regions
in parameter space, but also explained these observations by demonstrating
that, under the Melnikov method point of view, odd resonances arise due to an
extra torque that appears in the asymmetric case.",1603.00819v2
2016-06-16,Resonance interaction of two dipoles in optically active surroundings,"We study the resonance interaction between two quantum electric dipoles
immersed in optically active surroundings. Quantum electrodynamics is employed
to deal with dipole-vacuum interaction. Our results show that the optical
activity of surroundings will not change the single atom behaviors while it can
change the collective behaviors of the two dipoles, as well as greatly affect
the dipole-dipole resonance interaction. Especially, if the orientations of two
dipoles are orthogonal and respectively perpendicular to the interdipole axis,
the interdipole resonance interaction can be established with the help of
optically active surroundings while there is no resonance interaction in
vacuum.",1606.05149v1
2016-09-29,Complex-Path Prediction of Resonance-Assisted Tunneling in Mixed Systems,"We present a semiclassical prediction of regular-to-chaotic tunneling in
systems with a mixed phase space, including the effect of a nonlinear resonance
chain. We identify complex paths for direct and resonance-assisted tunneling in
the phase space of an integrable approximation with one nonlinear resonance
chain. We evaluate the resonance-assisted contribution analytically and give a
prediction based on just a few properties of the classical phase space. For the
standard map excellent agreement with numerically determined tunneling rates is
observed. The results should similarly apply to ionization rates and quality
factors.",1609.09276v2
2016-10-27,Negative refractive index induced by percolation in disordered metamaterials,"An effective medium model is developed for disordered metamaterials
containing a spatially random distribution of dielectric spheres. Similar to
effective medium models for ordered metamaterials, this model predicts
resonances in the effective permeability and permittivity arising from
electric- and magnetic-dipole Mie resonances in the spheres. In addition, the
model predicts a redshift of the electric resonance with increasing particle
loading. Interestingly, when the particle loading exceeds the percolation
threshold of 33\%, the model predicts that the electric resonance overlaps with
the magnetic resonance, resulting in a negative refractive index.",1610.08704v2
2017-02-13,Quantum dot resonant-fluorescence linewidth narrowing and enhanced intensity,"We study the processes in a quantum dot and its surrounds under resonant
excitation with the addition of weak non-resonant light. We observe a decrease
in inhomogeneous emission linewidth, as well as previously observed enhancement
of resonant fluorescence (RF). Scanning excitation and detection frequencies,
we distinguish between homogeneous and inhomogeneous broadening. Monte Carlo
simulations model the enhanced RF only if we include charge-carrier loss from
the quantum dot induced by the resonant laser. The cause of the linewidth
narrowing is predominantly independent of the enhanced RF.",1702.03947v1
2018-02-19,Spin-Orbit Coupling Induced Resonance in an Ultracold Bose Gas,"We study a two-component Bose gas with artificial spin-orbit coupling (SOC)
which couples the center-of-mass momentum of atom to its internal states. We
show that in this system resonance can be induced by tuning SOC strength. With
a two-dimensional SOC, resonances in two scattering channels can be induced by
tuning the aspect ratio of SOC strengths. With a three-dimensional SOC,
resonance in all scattering channels can be induced by tuning the appropriate
SOC strength. Similarly, we also find that in a Fermi gas with two- or
three-dimensional SOC resonance can be induced by tuning SOC strength.",1802.06522v2
2018-04-04,Wideband Bandpass Filters Based on Multipole Resonances of Spoof Localized Surface Plasmons,"We propose wideband bandpass filters based on multipole resonances of spoof
localized surface plasmons (SLSPs). The resonance characteristics and geometric
tunability of SLSPs are investigated under microstrip excitations. Strong
coupling with interlayer microstrip lines is proposed to join discrete
multipole resonances into a continuous and flat passband. The SLSP filters
exhibit wide passbands in compact sizes and well-balanced shapes, while holding
satisfactory spurious rejection bands, group delays, and geometric tunability.
This work exposes the SLSPs' application potential in filters as novel
resonators.",1804.01294v1
2018-11-03,Photonic crystal-Microring resonators for tunable delay lines,"In this paper, a new design of optical delay line based on coupled ring
resonators in photonic crystals is proposed and analyzed by means of numerical
simulation in CST Microwave Studio. The performance of the proposed photonic
crystal ring resonator (PhCRR) based coupled resonant optical waveguide (CROW)
is compared to: point-defect cavity based coupled cavity waveguides (CCW) in
photonic crystal. microring resonator (MRR) based CROW. The suggested design
addresses compactness issues of the MRR CROW while offering normalized delay
values better than CCW and comparable to MRR CROW. The PhCRR CROW also enhances
design flexibility as the PhCRRs support multiple modes and thereby supporting
multi-channel transfer/delay application on a single device.",1811.07828v1
2018-11-20,Reducing parasitic resonances in particle accelerators components by broadband Higher Order Mode couplers,"In particle accelerator components, parasitic resonances must be reduced
because they heat up the equipment and cause beam instabilities. In this paper,
a method for designing and characterizing Higher Order Mode (HOM) couplers for
reducing such resonances in a broad bandwidth is proposed. A case study is
considered for a specific component, called QuattroTank, showing geometrical
discontinuities and thus causing significant electro-magnetic resonances.
Results of numerical simulation and experimental emulation prove the capability
of the proposed method to reduce the peaks and the $Q-factor of the resonances.",1811.08154v1
2020-07-23,Complex scaling : physics of unbound light nuclei and perspective,"The complex scaling method (CSM) is one of the most powerful methods of
describing the resonances with complex energy eigenstates, based on
non-Hermitian quantum mechanics. We present the basic application of CSM to the
properties of the unbound phenomena of light nuclei. In particular, we focus on
many-body resonant and non-resonant continuum states observed in unstable
nuclei. We also investigate the continuum level density (CLD) in the scattering
problem in terms of the Green's function with CSM. We discuss the explicit
effects of resonant and non-resonant contributions in CLD and transition
strength functions.",2007.12172v1
2020-07-24,Optimal Resonant Asymptotics of Wakefield Excitation in Plasma by Non-resonant Sequence of Relativistic Electron Bunches,"Resonant asymptotics of wakefield excitation in plasma by non-resonant
sequence of relativistic electron bunches has been numerically simulated. It
has been shown that in resonant asymptotics at optimal parameters the wakefield
is excited with the maximum growth rate and the amplitude of the excited
wakefield is the largest.",2007.12745v1
2010-05-14,Double resonances in Borromean heteronuclear triatomic systems,"We investigate the occurrence of Borromean three-body continuum s-wave
resonances, in an $\alpha\alpha\beta$ system for large negative two-body
scattering lengths. The energy and width are determined by a scaling function
with arguments given by energy ratios of the two-body virtual state subsystem
energies with the shallowest three-body bound state. The Borromean continuum
resonances emerging from Efimov states present a peculiar behavior for trapped
ultracold atoms near a Feshbach resonance: two resonances with equal energies
at different values of the scattering length. The corresponding three-body
recombination peaks should merge as the temperature is raised, with one moving
towards lower values of the scattering length as the other moves to larger
values.",1005.2576v1
2014-03-05,Locally Resonant Granular Chain,"We report the design and testing of a tunable and nonlinear mechanical
metamaterial, called locally resonant granular chain. It consists of a
one-dimensional array of hollow spherical particles in contact, containing
local resonators. The resonant particles are made of an aluminium outer
spherical shell and a steel inner mass connected by a polymeric plastic
structure acting as a spring. We characterize the linear spectra of the
individual particles and of one-dimensional arrays of particles using theory,
numerical analysis, and experiments. A wide band gap is observed as well as
tunability of the dispersive spectrum by changing the applied static load.
Finally, we experimentally explore the nonlinear dynamics of the resonant
particles. By using nonlinear acoustical techniques, we reveal a complex,
nonclassical nonlinear dynamics.",1403.1052v1
2014-03-26,Improving Dark Matter Axion Searches with Active Resonators,"Axions are a well motivated candidate for dark matter. The most sensitive
experiments searching for dark matter axions rely on the coupling of axions to
the electromagnetic resonances of a microwave cavity immersed in a strong
magnetic field. The sensitivity of the experiment is proportional to the Q of
the resonance that is coupled to axions. To date, the resonators used in axion
searches have all been passive, with Qs limited by power loss in the cavity
walls. I propose the use of active feedback resonators to increase the Q of
microwave cavity axion dark matter experiments by several orders of magnitude.
This should allow experiments to significantly increase the rate at which they
can test potential axion masses and couplings.",1403.6720v1
2018-05-16,Thermometry and memcapacitance with qubit-resonator system,"We study theoretically dynamics of a driven-dissipative qubit-resonator
system. Specifically, a transmon qubit is coupled to a transmission-line
resonator; this system is considered to be probed via a resonator, by means of
either continuous or pulsed measurements. Analytical results obtained in the
semiclassical approximation are compared with calculations in the semi-quantum
theory as well as with the previous experiments. We demonstrate that the
temperature dependence of the resonator frequency shift can be used for the
system thermometry and that the dynamics, displaying pinched-hysteretic curve,
can be useful for realization of memory devices, the quantum memcapacitors.",1805.06154v1
2011-11-15,Fano-like interference of plasmon resonances at a single rod-shaped nanoantenna,"Single metallic nanorods acting as half-wave antennas in the optical range
exhibit an asymmetric, multi-resonant scattering spectrum that strongly depends
on both their length and dielectric properties. Here we show that such spectral
features can be easily understood in terms of Fano-like interference between
adjacent plasmon resonances. On the basis of analytical and numerical results
for different geometries, we demonstrate that Fano resonances may appear for
such single-particle nanoantennas provided that interacting resonances overlap
in both spatial and frequency domains.",1111.3551v2
2012-01-27,Study of nuclear giant resonances using a Fermi-liquid method,"The nuclear giant resonances are studied by using a Fermi-liquid method, and
the nuclear collective excitation energies of different values of $l$ are
obtained, which are fitted with the centroid energies of the giant resonances
of spherical nuclei, respectively. In addition, the relation between the
isovector giant resonance and the corresponding isoscalar giant resonance is
discussed.",1201.5723v1
2014-05-15,"Ultra-high energy neutrinos and $W^{\prime}$, $Z^{\prime}$ gauge bosons at the Pierre Auger Observatory","A wide range of models beyond the Standard Model predict charged and neutral
resonances, generically called $W'$- and $Z'$-bosons, respectively. We present
a study of the impact of such resonances on the deep inelastic scattering of
ultra-high energy neutrinos as well as on the resonant charged current
$\bar\nu_e e^-$ scattering (Glashow resonance). We find that the effects of
such resonances can not be observed with the Pierre Auger Observatory or any
foreseeable upgrade of it.",1405.3756v1
2016-05-09,Epitaxial rhenium microwave resonators,"We have fabricated rhenium microwave resonators from epitaxial films. We have
used thin films of different structural quality depending on their growth
conditions. The resonators were coupled to a microwave transmission line which
allows the measurement of their resonance frequencies and internal quality
factors. From the resonance frequency at low temperature , the effective
penetration depth and the London penetration depth of the rhenium film are
extracted.",1605.02513v1
2016-05-26,Quantum Communication Between Remote Mechanical Resonators,"Mechanical resonators represent one of the most promising candidates to
mediate the interaction between different quantum technologies, bridging the
gap between efficient quantum computation and long-distance quantum
communication. In this letter, we introduce a novel interferometric scheme
where the interaction of a mechanical resonator with input/output quantum
pulses is controlled by an independent classical drive. We design protocols for
state teleportation and direct quantum state transfer, between distant
mechanical resonators. The proposed device, feasible with state-of-the-art
technology, can serve as building block for the implementation of long-distance
quantum networks of mechanical resonators.",1605.08327v1
2016-08-09,Multi-resonance split ring resonator structures at sub-terahertz frequencies,"This paper reports on the computational development of novel architectures of
multi-resonance Split Ring Resonators (SRRs), for efficient manipulation of
Terahertz (THz) frequency beams. The conceived resonators are based on both a
capacitive and inductive scheme. Simulation results have been obtained for a 60
GHz to 240 GHz operational bandwidth.",1608.02729v2
2016-12-12,Observation of Fano resonance using a coupled resonator metamaterial composed of meta-atoms arranged by double periodicity,"We studied the transmission characteristics of a planar metamaterial
consisting of an array of electric split-ring resonators (eSRRs) with double
periodicity. Because of coupling between different resonant modes induced by
different lattice periods in metamaterials with double periodicity, the
appearance of Fano resonance can be expected in the same manner as that in the
case of coupled classical oscillators. We fabricated complementary eSRRs and
verified that a Fano-like spectral shape appeared in the transmission spectra
of eSRRs with double periodicity in the terahertz region.",1612.03552v1
2016-12-28,Theory of adiabatic fountain resonance,"The theory of ""Adiabatic Fountain Resonance"" with superfluid $^4$He is
clarified. In this geometry a film region between two silicon wafers bonded at
their outer edge opens up to a central region with a free surface. We find that
the resonance in this system is not a Helmholtz resonance as claimed by
Gasparini and co-workers, but in fact is a fourth sound resonance. We postulate
that it occurs at relatively low frequency because the thin silicon wafers flex
appreciably from the pressure oscillations of the sound wave.",1612.08797v1
2017-06-05,Generalized magnetic mirrors,"We propose generalized magnetic mirrors that can be achieved by excitations
of sole electric resonances. Conventional approaches to obtain magnetic mirrors
rely heavily on exciting the fundamental magnetic dipoles, whereas here we
reveal that besides magnetic resonances, electric resonances of higher orders
can be also employed to obtain highly efficient magnetic mirrors. Based on the
electromagnetic duality, it is also shown that electric mirrors can be achieved
by exciting magnetic resonances. We provide direct demonstrations of the
generalized mirrors proposed in a simple system of one-dimensional periodic
array of all-dielectric wires, which may shed new light to many advanced fields
of photonics related to resonant multipolar excitations and interferences.",1706.01398v2
2017-10-12,Kinetic equation for systems with resonant captures and scatterings,"We study a Hamiltonian system of type describing a charged particle resonant
interaction with an electromagnetic wave. We consider an ensemble of particles
that repeatedly pass through the resonance with the wave, and study evolution
of the distribution function due to multiple scatterings on the resonance and
trappings (captures) into the resonance. We derive the corresponding kinetic
equation. Particular cases of this problem has been studied in our recent
papers [1, 2].",1710.04489v1
2017-10-18,Studies of Single Component Fermi Gas near a $P$-wave Resonance with Lowest Order Constrained Variational Method,"We study single component Fermi gas near a $p$-wave resonance with the lowest
order constrained variational (LOCV) method. We obtain the energy per particle
for the ground state of single component Fermi gas near a $p$-wave resonance
with LOCV method. We also calculate compressibility of the single component
Fermi gas near a $p$-wave resonance and it shows that near the $p$-wave
resonance, the system would lose its stability and collapse. The two $p$-wave
contacts are also obtained and their variation tendencies with interaction
strength are consistent with recent experimental results.",1710.06581v2
2017-12-29,"Traps in hadron spectroscopy: Thresholds, triangle singularities, etc","The knowledge of hadron spectrum is based on experimental observations of
hadronic resonances. The resonances are normally observed as peaks in certain
invariant mass distributions. However, neither is a peak necessarily due to the
presence of a resonance, nor does a resonance necessarily lead to a peak.
Kinematic singularities can also produce peaks. Here, we discuss such
possibilities and methods distinguishing genuine resonances from kinematic
effects.",1712.10126v2
2018-09-16,Nanoparticle lattices with electric and magnetic resonances [Prospective],"Lattice resonances in nanoparticle arrays recently have gained a lot of
attention because of the possibility to produce spectrally narrow resonant
features in transmission and reflection as well as significantly increase
absorption in the structures. Most of the efforts so far have been put to study
these lattice resonances in dipole approximation. However, the recent research
shows that higher multipoles not only produce resonant feature but are also
involved in cross-coupling, affect each other, and induce a magnetoelectric
response. In this Prospective, we review the recent achievements in studying of
interplay and coupling of different multipoles in periodic nanoparticle arrays
and share our vision on further progress of the field.",1809.05787v1
2018-10-08,On the optical nonreciprocity and slow light propagation in coupled spinning optomechanical resonators,"We study the optical transmission characteristics of pump-probe driven
spinning optomechanical ring resonators coupled in a series configuration.
After performing the steady-state analysis valid for an arbitrary number of
resonators, as an example, we discuss the two-resonator problem in detail.
Therein, we focus on how changing the optical Sagnac effect due to same or
opposite spinning directions of resonators can lead to enhanced, non-reciprocal
and delayed probe light transmission. This work can help in devising spin
degree of freedom based novel devices of manipulating light propagation in
quantum networks and quantum communication technologies.",1810.03709v1
2018-10-30,Subwavelength resonances of encapsulated bubbles,"The aim of this paper is to derive a formula for the subwavelength resonance
frequency of an encapsulated bubble with arbitrary shape in two dimensions.
Using Gohberg-Sigal theory, we derive an asymptotic formula for this resonance
frequency, as a perturbation away from the resonance of the uncoated bubble, in
terms of the thickness of the coating. The formula is numerically verified in
the case of circular bubbles, where the resonance can be efficiently computed
using the multipole method.",1810.12756v1
2019-06-05,The collisional resonance function in discrete-resonance quasilinear plasma systems,"A method is developed to analytically determine the resonance broadening
function in quasilinear theory, due to either Krook or Fokker-Planck scattering
collisions of marginally unstable plasma systems where discrete resonance
instabilities are excited without any mode overlap. It is demonstrated that a
quasilinear system that employs the calculated broadening functions reported
here systematically recovers the nonlinear growth rate and mode saturation
levels for near-threshold plasmas previously calculated from kinetic theory.
The distribution function is also calculated, which enables precise
determination of the characteristic collisional resonance width.",1906.01780v1
2019-06-28,Fano-like spectral features in nanodiamond solutions for biometric applications,"Fano resonance is a unique feature of interacting quantum systems, exhibiting
resonance shapes distinctively different from conventional symmetric resonance
curves. Recently, Fano resonances have been found in plasmonic nanoparticles,
photonic crystals, and electromagnetic metamaterials. Here we report Fano-like
photoluminiscence curves in nanodiamond solutions as a result of incoherent
combination of two or more scattering and fluorescence processes. We argue
that, analogously to Fano resonances, the steep asymmetric dispersion of the
photoluminiscence profile in nanodiamond solutions, in combination with
biologically-compatible spectral features characterizing nanodiamond
fluorescence, can find promising biometric applications in several areas such
as bio-sensors, bio-switches and bio-filters.",1907.00059v1
2019-10-24,Stimulated Four-Wave Mixing in Linearly Uncoupled Resonators,"We experimentally demonstrate stimulated four-wave mixing in two linearly
uncoupled integrated Si$_3$N$_4$ micro-resonators. In our structure the
resonance combs of each resonator can be tuned independently, with the energy
transfer from one resonator to the other occurring in the presence of a
nonlinear interaction. This method allows flexible and efficient on-chip
control of the nonlinear interaction, and is readily applicable to other
third-order nonlinear phenomena.",1910.11426v1
2020-01-15,Magnetic Feshbach resonances in $^{7}\text{Li}-^{133}\text{Cs}$ mixtures,"Motivated by the prospect of observing Efimov and Bose polaron physics in
ultracold mixtures of bosonic atoms with large mass imbalance, this work
investigates the magnetic Feshbach resonances between $^{7}\text{Li}$ and
$^{133}\text{Cs}$. The resonances are predicted at the 1 gauss level using the
model of Pires et al. [Phys. Rev. A, 90, 012710] obtained from experimental
observations of resonances between $^{6}\text{Li}$ and $^{133}\text{Cs}$. It is
found that a few resonances in a practical range of magnetic field intensity
could be used to tune the scattering length between $^{7}\text{Li}$ and
$^{133}\text{Cs}$ atoms. Opportunities for observing Efimov and Bose polaron
physics are discussed.",2001.05329v1
2020-02-10,Electron Spin Resonance spectroscopy with femtoliter detection volume,"We report electron spin resonance measurements of donors in silicon at
millikelvin temperatures using a superconducting $LC$ planar micro-resonator
and a Josephson Parametric Amplifier. The resonator includes a nanowire
inductor, defining a femtoliter detection volume. Due to strain in the
substrate, the donor resonance lines are heavily broadened. Single-spin to
photon coupling strengths up to $\sim 3~\text{kHz}$ are observed. The single
shot sensitivity is $120 \pm 24~$spins/Hahn echo, corresponding to $\approx 12
\pm 3$~spins$/\sqrt{\text{Hz}}$ for repeated acquisition.",2002.03669v1
2020-12-01,Excited $J^{--}$ meson resonances at the SU(3) flavor point from lattice QCD,"We present the first calculation within lattice QCD of excited light meson
resonances with $J^{PC} = 1^{--}$, $2^{--}$ and $3^{--}$. Working with an exact
SU(3) flavor symmetry, for the singlet representation of pseudoscalar-vector
scattering, we find two $1^{--}$ resonances, a lighter broad state and a
heavier narrow state, a broad $2^{--}$ resonance decaying in both $P$- and
$F$-waves, and a narrow $3^{--}$ state. We present connections to experimental
$\omega^\star_J, \phi^\star_J$ resonances decaying into $\pi \rho$,
$K\bar{K}^*$, $\eta \omega$ and other final states.",2012.00518v1
2020-12-03,Frequency span optimization for asymmetric resonance curve fitting,"The wide application of the modern resonant measurement techniques makes all
the steps of the measuring process, including data acquisition more efficient
and reliable. Here we investigate the multidimensional space of the parameters
to determine the optimum span for resonant measurements. The study concentrated
on experimental systems with standard performance and capabilities. We
determine the range of the optimum span for the resonant frequency and quality
factor by simulating and fitting resonant curves with different levels of
asymmetry.",2012.01921v2
2017-05-12,Polarizability Expressions for Predicting Resonances in Plasmonic and Mie Scatterers,"Polarizability expressions are commonly used in optics and photonics to model
the light scattering by small particles. Models based on Taylor series of the
scattering coefficients of the particles fail to predict the morphologic
resonances hosted by dielectric particles. Here, we propose to use the
factorization of the special functions appearing in the expression of the Mie
scattering coefficients to derive point-like models. These models can be
applied to reproduce both Mie resonances of dielectric particles and plasmonic
resonances of metallic particles. They provide simple but robust tools to
predict accurately the electric and magnetic Mie resonances in dielectric
particles.",1705.04488v1
2017-05-15,Resonance control of graphene drum resonator in nonlinear regime by standing wave of light,"We demonstrate the control of resonance characteristics of a drum type
graphene mechanical resonator in nonlinear oscillation regime by the
photothermal effect, which is induced by a standing wave of light between a
graphene and a substrate. Unlike the conventional Duffing type nonlinearity,
the resonance characteristics in nonlinear oscillation regime is modulated by
the standing wave of light despite a small variation amplitude. From numerical
calculations with a combination of equations of heat and motion with Duffing
type nonlinearity, this can be explained that the photothermal effect causes
delayed modulation of stress or tension of the graphene.",1705.05056v1
2017-09-04,Azbel'-Kaner-Like Cyclotron Resonance in a Two-Dimensional Electron System,"Resonant microwave absorption of a two-dimensional electron system in an
AlGaAs/GaAs heterostructure excited by a near-field technique was investigated.
Along with collective magnetoplasmon modes, we observed resonance that
precisely follows the cyclotron resonance (CR) position and revealed no signs
of collective plasma depolarization shift. We show that the discovered CR mode
is absent in the Faraday geometry, and is localized at the edge of the exciting
metal electrode. Such behavior points in favor of the single-particle
Azbel'-Kaner nature of the discovered resonance.",1709.00840v1
2018-03-05,Zero resonances for localised potentials,"This paper considers Hamiltonians with localised potentials and gives a
variational characterisation of resonant coupling parameters, which allow to
provide estimates for the first resonant parameter and in turn also to provide
bounds for resonant free regions. As application we provide a constructive
approach to calculate the first resonant parameter for Yukawa type potentials
in $\mathbb R^3$.",1803.01813v3
2018-03-12,Probing unconventional superconductivity in proximitized graphene by impurity scattering,"We demonstrate how potential impurities are a very powerful tool for
determining the pairing symmetry in graphene proximity-coupled to a
spin-singlet superconductor. All d-wave states are characterized by subgap
resonances, with spatial patterns clearly distinguishing between nodal and
chiral d-wave symmetry, while s-wave states have no subgap resonances. We also
find strong supergap impurity resonances associated with the normal state Dirac
point. Sub- and supergap resonances only interact at very low doping levels,
then causing suppression of the supergap resonances.",1803.04455v2
2018-06-06,Detection of emitter-resonator coupling strength in quantum Rabi model via an auxiliary resonator,"In this paper, we propose a theoretical scheme to detect the
emitter-resonator coupling strength in the ultra-strong coupling regime in the
quantum Rabi model via introducing an auxiliary resonator. We demonstrate the
total system as a two-mode Rabi model and obtain the ground state by the
transformed rotating wave approximation, which is shown to be superior to the
usually applied rotating wave approximation. Here, the coupling strength is
detected by monitoring the average excitation number in the auxiliary resonator
and the sensitivity of the detection scheme is discussed analytically.",1806.01971v2
2018-06-06,Nonlinear resonances generate large-scale vortices in the phase space in plasma systems,"It is well-known that the resonance phenomena can destroy the adiabatic
invariance and cause chaos and mixing. In the present paper we show that the
nonlinear wave-particle resonant interaction may cause the emergence of
large-scale coherent structures in the phase space. The combined action of the
drift due to nonlinear scattering on resonance and trapping (capture) into
resonance create a vortex-like structure, where the areas of particle
acceleration and deceleration are macroscopically separated. At the same time,
nonlinear scattering also creates a diffusion that causes mixing and
uniformization in around the vortex.",1806.02240v1
2018-08-16,Arbitrary state preparation of a mechanical resonator via controlled pulse shaping and projective measurement in a qubit-resonator interaction,"We introduce a protocol capable of generating a general measurement operator
for a mechanical resonator. The technique requires a qubit-resonator
interaction and uses a coherent pulse to drive qubit transitions. This is
followed by projective measurement of the qubit's energy, constraining the
resonator in a state that depends on the pulse shape. The freedom to choose a
pulse shape for the coherent drive enables an arbitrary position-basis
measurement operator. Using this measurement operator, we outline a two pulse
protocol that probabilistically generates a pure mechanical state with a
desired wavefunction, with near unit fidelity for realizable parameters.",1808.05666v1
2018-12-01,Time Asymptotic expansions of solution for fourth-order Schrödinger equation with zero resonance or eigenvalue,"In this paper, we first deduce the asymptotic expansions of resolvent of
$H=(-\Delta)^2+V$ with the presence of resonance or eigenvalue at the
degenerate zero threshold for $d\geq5$. In particular, we identify these
resonance spaces for full kinds of zero resonances. As a consequence, we then
establish the {\it time asymptotic expansions} and {\it Kato-Jensen estimates}
for the solution of fourth-order Schr\""odinger equation under the presence of
zero resonance or eigenvalue.",1812.00223v2
2018-12-22,Lattice resonances under oblique light incidence on nanoparticle array,"Ultra-thin optical structures, known as metasurfaces, have shown promising
light controlling capability at the nanoscale. In this paper, we study their
particular case, a periodic array of high-refractive-index nanoparticles with
electric and magnetic resonances. The main result of the work is a numerical
demonstration that the lattice effect in the periodic arrangement of
nanoparticles changes the resonance position even if the resonances are above
the diffraction wavelength (Rayleigh anomaly). We show that the disk resonance
changes can be achieved not only by varying periods of the array under normal
light incidence but also by changing the incident angle.",1812.09456v1
2019-01-09,Resonance-assisted tunneling in 4D normal-form Hamiltonians,"Nonlinear resonances in the classical phase space lead to a significant
enhancement of tunneling. We demonstrate that the double resonance gives rise
to a complicated tunneling peak structure. Such double resonances occur in
Hamiltonian systems with an at least four-dimensional phase space. To explain
the tunneling peak structure, we use the universal description of single and
double resonances by 4D normal-form Hamiltonians. By applying perturbative
methods, we reveal the underlying mechanism of enhancement and suppression of
tunneling and obtain excellent quantitative agreement. Using a minimal matrix,
we obtain model an intuitive understanding.",1901.02692v2
2019-01-16,Phase modulated pulse interferometry for simultaneous multi-channel ultrasound detection,"In optical detection of ultrasound, resonators with high Q-factors are often
used to maximize sensitivity. However, in order to perform parallel
interrogation, conventional interferometric techniques require an overlap
between the resonator spectra, which is difficult to achieve with high Q-factor
resonators. In this paper, a new method is developed for parallel interrogation
of optical resonators with non-overlapping spectra. The method is based on a
phase modulation scheme for pulse interferometry (PM-PI) and requires only a
single photodetector and sampling channel per ultrasound detector. Using PM-PI,
parallel ultrasound detection is demonstrated with four high Q-factor
resonators.",1901.05163v1
2019-02-21,First-order perturbation theory for material changes in the surrounding of open optical resonators,"The single-mode approximation of the resonant state expansion has proven to
give accurate first-order approximations of resonance shifts and linewidth
changes when modifying the material properties inside open optical resonators.
Here, we extend this first-order perturbation theory to modifications of the
material properties in the surrounding medium. As a side product of our
derivations, we retrieve the already known analytical normalization condition
for resonant states. We apply our theory to two example systems: A metallic
nanosphere and a one-dimensional photonic crystal slab.",1902.08120v1
2019-03-05,Strong nonreciprocity in modulated resonator chains through synthetic electric and magnetic fields,"We study nonreciprocity in spatiotemporally modulated 1D resonator chains
from the perspective of equivalent 2D resonator arrays with a synthetic
dimension and transverse synthetic electric and magnetic fields. The synthetic
fields are respectively related to temporal and spatial modulation of the
resonator chain, and we show that their combination can break transmission
reciprocity without additional elements. This nonreciprocal effect is analogous
to the Hall effect for charged particles. We experimentally implement chains of
2 and 3 spatiotemporally modulated resonators and measure over 58 dB of
isolation contrast.",1903.07408v1
2019-04-18,Inverse resonance scattering for on rotationally symmetric manifolds,"We discuss inverse resonance scattering for the Laplacian on a rotationally
symmetric manifold $M = (0,\infty) \times Y$ whose rotation radius is constant
outside some compact interval. The Laplacian on $M$ is unitarily equivalent to
a direct sum of one-dimensional Schr\""odinger operators with compactly
supported potentials on the half-line. We prove
  o Asymptotics of counting function of resonances at large radius
  o Inverse problem: The rotation radius is uniquely determined by its
eigenvalues and resonances. Moreover, there exists an algorithm to recover the
rotation radius from its eigenvalues and resonances.
  The proof is based on some non-linear real analytic isomorphism between two
Hilbert spaces.",1904.08908v1
2019-12-15,Angle-action variables for orbits trapped at a Lindblad resonance,"The conventional approach to orbit trapping at Lindblad resonances via a
pendulum equation fails when the parent of the trapped orbits is too circular.
The problem is explained and resolved in the context of the Torus Mapper and a
realistic Galaxy model. Tori are computed for orbits trapped at both the inner
and outer Lindblad resonances of our Galaxy. At the outer Lindblad resonance,
orbits are quasiperiodic and can be accurately fitted by torus mapping. At the
inner Lindblad resonance, orbits are significantly chaotic although far from
ergodic, and each orbit explores a small range of tori obtained by torus
mapping.",1912.07026v1
2020-03-18,New Cyclotron Resonances,"The possibilities and conditions of effective interaction, in particular
acceleration, of charged particles by the field of plane electromagnetic wave
in the presence of an external constant mag-netic field are considered. It is
shown that the well-known conditions of cyclotron resonances require
generalization. New conditions for the resonant interaction of charged
particles are for-mulated, which contain not only the strength of the external
magnetic field (as the well-known conditions of cyclotron resonances) but also
the field strength of the wave. strengths. It is shown that new resonance
conditions open up new possibilities for effective particle acceleration.",2003.08110v1
2020-05-09,Resonance enhancement of neutrino oscillations due to transition magnetic moments,"We prove that a resonance enhancement of neutrino oscillations in magnetic
field is possible due to transition magnetic moments and demonstrate that this
resonance is strictly connected to the neutrino polarization. To study the main
properties of this resonance, we obtain the probabilities of transitions
between neutrino states with definite flavor and helicity in inhomogeneous
electromagnetic field in the adiabatic approximation. Since the resonance is
present only when the adiabaticity condition is fulfilled, we also obtain and
discuss this condition.",2005.04503v2
2020-06-08,Resonance structure of $^{8}$Be with the two-cluster resonating group method,"A two-cluster microscopic model is applied to study elastic alpha-alpha
scattering and resonance structure of $^{8}$Be. The model is an algebraic
version of the Resonating Group Method, which makes use complete set of
oscillator functions to expand wave function of two-cluster system. Interaction
between clusters is determined by well-known semi-realistic nucleon-nucleon
potentials of Hasegawa-Nagata, Minnesota and Volkov. Detail analysis of
resonance wave functions is carried out in oscillator, coordinate and momentum
spaces. Effects of the Pauli principle on wave functions of the $^{8}$Be
continuous spectrum states are thoroughly studied.",2006.04525v1
2020-09-17,Exploring the di-$J/ψ$ resonances based on {\it{ab initio}} perturbative QCD,"We extend the nonrelativistic QCD framework to explore the nature of the
newly discovered di-$J/\psi$ resonances. Assuming them as either molecule-like
states or tetraquarks, we calculated their hadroproduction cross sections at
the LHC. We find that the observed resonances are most likely spin-2 particles,
and there should exist their spin-0 counterparts near these resonances. The
ratio of production cross sections of the observed resonances to the latent
spin-0 ones are also presented, which might help to distinguish molecule-like
states from tetraquarks.",2009.08376v3
2020-10-04,Resonant Processing of Instrumental Sound Controlled by Spatial Position,"We present an acoustic musical instrument played through a resonance model of
another sound. The resonance model is controlled in real time as part of the
composite instrument. Our implementation uses an electric violin, whose spatial
position modifies filter parameters of the resonance model. Simplicial
interpolation defines the mapping from spatial position to filter parameters.
With some effort, pitch tracking can also control the filter parameters. The
individual technologies -- motion tracking, pitch tracking, resonance models --
are easily adapted to other instruments.",2010.01572v1
2020-10-21,High-Q dielectric Mie-resonant nanostructures (a mini-review),"Future technologies underpinning high-performance optical communications,
ultrafast computations and compact biosensing will rely on densely packed
reconfigurable optical circuitry based on nanophotonics. For many years,
plasmonics was considered as the only available platform for nanoscale optics,
but the recently emerged novel field of Mie resonant metaphotonics provides
more practical alternatives for nanoscale optics by employing resonances in
high-index dielectric nanoparticles and structures. In this mini-review we
highlight some recent trends in the physics of dielectric Mie-resonant
nanostructures with high quality factor (Q factor) for efficient spatial and
temporal control of light by employing multipolar resonances and the bound
states in the continuum. We discuss a few applications of these concepts to
nonlinear optics, nanolasers, subwavelength waveguiding, and sensing.",2010.10854v1
2021-04-06,Husimi Functions for Coupled Optical Resonators,"Phase-space analysis has been widely used in the past for the study of
optical resonant systems. While it is usually employed to analyze the far-field
behaviour of resonant systems we focus here on its applicability to coupling
problems. By looking at the phase-space description of both the resonant mode
and the exciting source it is possible to understand the coupling mechanisms as
well as to gain insights and approximate the coupling behaviour with reduced
computational efforts. In this work we develop the framework for this idea and
apply it to a system of an asymmetric dielectric resonator coupled to a
waveguide.",2104.02368v1
2021-12-09,Precession resonances in hierarchical triple systems,"We describe a new kind of resonance occuring in relativistic three-body
hierarchical systems: the precession resonance, occuring when the relativistic
precession timescale of a binary equals the period of a distant perturber. We
find that, contrary to what most previous studies assume, it can lead to an
exponential increase of eccentricity of the binary even when relativistic
precession dominates the quadrupolar perturbation. The resonance may happen in
the observation band of LISA or change the eccentricity distribution of
triples. We discuss the physics of the resonance, showing that it mainly
depends on three parameters.",2112.05167v2
2022-02-07,Convolutional Neural Networks for Mode On-Demand High Finesse Optical Resonator Design,"We demonstrate the use of machine learning through convolutional neural
networks to solve inverse design problems of optical resonator engineering. The
neural network finds a harmonic modulation of a spherical mirror to generate a
resonator mode with a given target topology (""mode on-demand""). The procedure
allows us to optimize the shape of mirrors to achieve a significantly enhanced
coupling strength and cooperativity between a resonator photon and a quantum
emitter located at the center of the resonator. In a second example, a
double-peak mode is designed which would enhance the interaction between two
quantum emitters, e.g., for quantum information processing.",2202.03359v1
2022-02-15,Asymptotic analysis of subwavelength halide perovskite resonators,"Halide perovskites are promising materials with many significant applications
in photovoltaics and optoelectronics. In this paper, we use integral methods to
quantify the resonant properties of halide perovskite nano-particles. We prove
that, for arbitrarily small particles, the subwavelength resonant frequencies
can be expressed in terms of the eigenvalues of the Newtonian potential
associated with its shape. We also characterize the hybridized subwavelength
resonant frequencies of a dimer of two halide perovskite particles. Finally, we
examine the specific case of spherical resonators and demonstrate that our new
results are consistent with previous works.",2202.07274v1
2022-06-24,Meridional composite pulses for low-field magnetic resonance,"We discuss procedures for error-tolerant spin control in environments that
permit transient, large-angle reorientation of magnetic bias field. Short
sequences of pulsed, non-resonant magnetic field pulses in a laboratory-frame
meridional plane are derived. These are shown to have band-pass excitation
properties comparable to established amplitude-modulated, resonant pulses used
in high, static-field magnetic resonance. Using these meridional pulses, we
demonstrate robust $z$ inversion in proton ($^{1}$H) nuclear magnetic resonance
near earth's field.",2206.12025v1
2022-08-04,A home-lab experiment: resonance and sound speed using telescopic vacuum cleaner pipes,"We propose a home laboratory in which a telescopic vacuum cleaner pipe and a
smartphone are used to investigate sound speed and acoustic resonance. When the
pipe is hit or the hands clapped near one end the sound produced is registered
by a smartphone. By means of an appropriate application the resonant frequency
is obtained. Varying the pipe's length and registering the corresponding
resonant frequency allows to obtain the sound speed. This home-lab, first
proposed during covid19 pandemic, has been incorporated as a home challenge to
experiment with acoustic resonance in new normal times.",2208.02671v1
2022-11-15,A note on separation conditions of resonance sets in the instability analysis for high-frequency oscillations in geometric optics,"In this paper, we study the instability of highly-oscillating solutions to
semi-linear hyperbolic systems. A instability criterion was given in \cite{Lu}
under rather strong separation conditions of resonance sets: coupled resonance
sets are pairwise disjoint. Here we show that such separation conditions in
\cite{Lu} can be relaxed: one of the coupled non-transparent resonance sets is
allowed to intersect with at most two others. We obtain the same instability
criterion as in \cite{Lu}. Finally, we give some applications to coupled
Klein-Gordon systems with equal masses and nonlinear terms specified
particularly, where on the intersections of resonance sets, the related
interaction coefficients are non-transparent.",2211.07929v1
2022-12-19,Depletion-limited Kerr solitons in singly-resonant optical parametric oscillators,"We analyze the impact of pump depletion in the generation of cavity solitons
in a singly-resonant parametrical oscillator that includes a $\chi^{(3)}$
nonlinear section. We find an analytical expression that provides the soliton
existence region using variational methods, study the efficiency of energy
conversion, and compare it to a driven Kerr resonator modeled by the
Lugiato-Lefever equation. At high walk-off, solitons in singly-resonant optical
parametric oscillators are more efficient than those formed in a Kerr resonator
driven through a linear coupler.",2212.09493v1
2023-05-29,LLC type galvanic isolated resonant converter,"Resonant converters are often being used for high power and high voltage
applications to achieve high efficiency, high power density and low EMI. In
this paper, we will use a resonant converter for a completely different
application. We will take advantage of the Zero Voltage Switching (ZVS) and
operating in the vicinity of the series resonance to design a low power and
ultra-low noise galvanic isolated half bridge resonant DC-DC converter for
powering a medical amplifier. Under lower power we consider up to 6W (500mA @
12V). The DC-DC converter must meet the safety requirements of the standard IEC
60601.",2305.18132v1
2023-07-03,Complex translation methods and its application to resonances for quantum walks,"In this paper, some properties of resonances for multi-dimensional quantum
walks are studied. Resonances for quantum walks are defined as eigenvalues of
complex translated time evolution operators in the pseudo momentum space. For
some typical cases, we show some results of existence or nonexistence of
resonances. One is a perturbation of an elastic scattering of a quantum walk
which is an analogue of classical mechanics. Another one is a shape resonance
model which is a perturbation of a quantum walk with a non-penetrable barrier.",2307.00962v3
2023-08-11,Manipulating the Quasi-Normal Modes of Radially Symmetric Resonators,"We derive two methods for simultaneously controlling the resonance frequency,
linewidth and multipolar nature of the resonances of radially symmetric
structures. Firstly, we formulate an eigenvalue problem for a global shift in
the permittivity of the structure to place a resonance at a particular complex
frequency. Next, we employ quasi-normal mode perturbation theory to design
radially graded structures with resonances at desired frequencies.",2308.06179v1
2023-10-31,Radiating Resonances for the Helmholtz Equation and Thin 2D Waveguide Detection,"We investigate the radiating resonances for the Helmholtz equation in the two
dimensional space in the presence of an unbounded waveguide with a high
contrast index of refraction. Using a suitable asymptotic analysis of the
Green's function of the problem, we describe when these radiating resonances
appear, and we exploit these resonances to identify the thickness, location,
and index of refraction of the waveguide. We propose a suitable numerical
reconstruction algorithm that requires observations in a multifrequency range
containing the first radiating resonance.",2311.00132v1
2023-11-22,A blueprint for truncation resonance placement in elastic periodic lattices with unit cell asymmetry,"Elastic periodic lattices act as mechanical filters of incident vibrational
loads. By and large, they forbid wave propagation within bandgaps and resonate
outside them. However, they often encounter `truncation resonances' inside
bandgaps when certain conditions are met. This study provides an
all-encompassing blueprint for the design and selective placement of truncation
resonances in elastic periodic lattices, integrating all factors that play a
role in the onset of truncation resonances and shaping the finite lattice's
response, from unit cell configuration, mass and stiffness contrasts, to types
and symmetry of boundary conditions.",2311.13698v1
2023-12-16,A Pairing Formula for Resonant States on Finite Regular Graphs,"On a finite regular graph, (co)resonant states are eigendistributions of the
transfer operator associated to the shift on one-sided infinite
non-backtracking paths. We introduce two pairings of resonant and coresonant
states, the vertex pairing which involves only the dependence on the
initial/terminal vertex of the path, and the geodesic pairing which is given by
integrating over all geodesics the evaluation of the coresonant state on the
first half of the geodesic times the resonant state on the second half. The
main result is that these two pairings coincide up to a constant which depends
on the resonance, i.e. the corresponding eigenvalue of the transfer operator.",2312.10509v1
2024-02-09,"Radiative neutron capture rate of $^{11}$B$(n,γ)^{12}$B reaction from the Coulomb dissociation of $^{12}$B","We calculate the $^{11}$B$(n,\gamma)^{12}$B reaction rate, an important
constituent in nucleosynthesis networks, contributed by resonant as well as
non-resonant capture. For the resonant rate, we use the narrow resonance
approximation whereas the non-resonant contribution is calculated with the
Coulomb dissociation method for which we use finite-range distorted wave Born
approximation theory. We then compare our calculated rate of
$^{11}$B$(n,\gamma)^{12}$B reaction with those reported earlier and with other
charged particle reactions on $^{11}$B.",2402.06755v1
1996-10-09,Normal Helium 3: a Mott-Stoner liquid,"A physical picture of normal liquid $^3$He, which accounts for both ``almost
localized'' and ``almost ferromagnetic'' aspects, is proposed and confronted to
experiments.",9610076v1
1997-11-24,Microscopic conditions favoring itinerant ferromagnetism,"A systematic investigation of the microscopic conditions stabilizing
itinerant ferromagnetism of correlated electrons in a single-band model is
presented. Quantitative results are obtained by quantum Monte Carlo simulations
for a model with Hubbard interaction U and direct Heisenberg exchange
interaction F within the dynamical mean-field theory. Special emphasis is
placed on the investigation of (i) the distribution of spectral weight in the
density of states, (ii) the importance of genuine correlations, and (iii) the
significance of the direct exchange, for the stability of itinerant
ferromagnetism at finite temperatures. We find that already a moderately strong
peak in the density of states near the band edge suffices to stabilize
ferromagnetism at intermediate U-values in a broad range of electron densities
n. Correlation effects prove to be essential: Slater--Hartree-Fock results for
the transition temperature are both qualitatively and quantitatively incorrect.
The nearest-neighbor Heisenberg exchange does not, in general, play a decisive
role. Detailed results for the magnetic phase diagram as a function of U, F, n,
temperature T, and the asymmetry of the density of states are presented and
discussed.",9711242v2
1998-08-25,"Comment on ""High-Temperature Series Analysis of the 2D Random-Bond Ising Ferromagnet""","A comment on PRL vol. 80, 4697 (1998) by Roder, Adler and Janke. Minior
correction included.",9808280v2
1998-11-19,Magnetism and Electronic States of Systems with Strong Hund Coupling,"This paper is a brief review of our recent studies concerning on magnetism
and electronic states of lattice systems with Hund coupling. First we examined
the effectiveness of the Hund coupling in realizing ferromagnetism in the
doubly degenerate Hubbard model. One- and infinite-dimensional systems were
studied and thereby dimensional dependence was discussed. In quarter-filled
systems the insulating ferromagnetic state accompanied by alternating orbital
order was found stable. In more-than-quarter filling cases metallic
ferromagnetism is stabilized by the ``double exchange mechanism''. These
results are common to one and infinite dimensions. In less-than-quarter filling
cases the ferromagnetic ground state is stable in one dimension but not in
infinite dimensions. Secondly we examined the electronic states and the
resistivity in the double exchange model by using the one-particle Green
function. The splitting and narrowing of the one-particle spectrum due to the
Hund coupling were clarified in the framework of a single-site approximation.
The resistivity due to the scattering by random localized spins was shown to be
too small to explain the experimental results of doped manganites.",9811286v1
1998-11-30,Landau theory of bi-criticality in a random quantum rotor system,"We consider here a generalization of the random quantum rotor model in which
each rotor is characterized by an M-component vector spin. We focus entirely on
the case not considered previously, namely when the distribution of exchange
interactions has non-zero mean. Inclusion of non-zero mean permits
ferromagnetic and superconducting phases for M=1 and M=2, respectively. We find
that quite generally, the Landau theory for this system can be recast as a
zero-mean problem in the presence of a magnetic field. Naturally then, we find
that a Gabay-Toulouse line exists for $M>1$ when the distribution of exchange
interactions has non-zero mean. The solution to the saddle point equations is
presented in the vicinity of the bi-critical point characterized by the
intersection of the ferromagnetic (M=1) or superconducting (M=2) phase with the
paramagnetic and spin glass phases. All transitions are observed to be second
order. At zero temperature, we find that the ferromagnetic order parameter is
non-analytic in the parameter that controls the paramagnet/ferromagnet
transition in the absence of disorder. Also for M=1, we find that replica
symmetry breaking is present but vanishes at low temperatures. In addition, at
finite temperature, we find that the qualitative features of the phase diagram,
for M=1, are {\it identical} to what is observed experimentally in the random
magnetic alloy $LiHo_xY_{1-x}F_4$.",9811418v1
1998-12-09,Ferromagnetism and the temperature-dependent electronic structure in thin Hubbard films,"The magnetic behavior of thin ferromagnetic itinerant-electron films is
investigated within the strongly correlated single-band Hubbard model. For its
approximate solution we apply a generalization of the modified alloy analogy
(MAA) to deal with the modifications due to the reduced translational symmetry.
The theory is based on exact results in the limit of strong Coulomb interaction
which are important for a reliable description of ferromagnetism. Within the
MAA the actual type of the alloy analogy is determined selfconsistently. The
MAA allows, in particular, the investigation of quasiparticle lifetime effects
in the paramagnetic as well as the ferromagnetic phase. For thin fcc(100) and
fcc(111) films the layer magnetizations are discussed as a function of
temperature as well as film thickness. The magnetization at the surface-layer
is found to be reduced compared to the inner layers. This reduction is stronger
in fcc(100) than in fcc(111) films. The magnetic behavior can be
microscopically understood by means of the layer-dependent spectral density and
the quasiparticle density of states. The quasiparticle lifetime that
corresponds to the width of the quasiparticle peaks in the spectral density is
found to be strongly spin- and temperature-dependent.",9812151v1
1999-01-21,Resistive Anomalies at Ferromagnetic Transitions Revisited: the case of SrRuO_3,"We show that recent resistivity data on SrRuO_3 for T->T_c are consistent
with conventional theory when corrections to scaling are included and a small
shift in T_c is allowed.",9901207v2
1999-06-12,Mesoscopic coherence effect in superconductor-metallic ferromagnet structures,The boundary condition in Eq.6 is invalid.,9906177v4
2000-02-24,Skyrmions in spinor Bose-Einstein condensates,"We show that spinor Bose-Einstein condensates not only have line-like vortex
excitations, but in general also allow for point-like topological excitations,
i.e., skyrmions. We discuss the static and dynamic properties of these
skyrmions for spin-1/2 and ferromagnetic spin-1 Bose gases.",0002375v1
2000-02-29,Ferromagnetism in III-V and II-VI semiconductor structures,"The current status of research on the carrier-mediated ferromagnetism in
tetrahedrally coordinated semiconductors is briefly reviewed. The experimental
results for III-V semiconductors, where Mn atoms introduce both spins and
holes, are compared to the case of II-VI compounds, in which the ferromagnetism
has been observed for the modulation-doped p-type Cd1-xMnxTe/Cd1-y-zMgyZnzTe:N
heterostructures, and more recently, in Zn1-xMnxTe:N epilayers. On the
theoretical side, a model is presented, which takes into account: (i) strong
spin-orbit and kp couplings in the valence band; (ii) the effect of confinement
and strain upon the hole density-of-states and response function, and (iii) the
influence of disorder and carrier-carrier interactions, particularly near the
metal-to-insulator transition. A comparison between experimental and
theoretical results demonstrates that the model can describe the magnetic
circular dichroism, the values of TC observed in the studied systems as well as
explain the directions of the easy axis and the magnitudes of the corresponding
anisotropy fields as a function of confinement and biaxial strain. Various
suggestions concerning design of novel ferromagnetic semiconductor systems are
described.",0002450v2
2001-02-05,"Comment on ``Specific heat of a Fermi system near ferromagnetic quantum phase transition'' by Grosu, Bodea, and Crisan (cond-mat/0101392)","We comment on various incorrect claims made in a recent paper by Grosu et al.
(cond-mat/0101392).",0102064v2
2001-05-16,A dynamical mean field theory for the magnetic transition temperature of ferromagnetic semiconductors,"This paper has been withdrawn by the authors due to a numerical error. A
revised version will be posted shortly.",0105331v2
2001-11-16,"Ferromagnetism in (III,Mn)V Semiconductors","In this review article we briefly summarize the main experimental properties
of (III,Mn)V ferromagnets and outline several different but related approaches
that have been explored in an effort to gain insight into these materials. The
main body of the paper deals with the development of the semi-phenomenological
model in which the low energy degrees of freedom are exchange-coupled
valence-band holes and $S=5/2$ Mn local moments. We discuss physical
predictions based on a mean-field treatment of the disorder-free model and
demonstrate that it successfully describes a number of non-trivial properties
of (Ga,Mn)As and (In,Mn)As ferromagnets. Study of collective excitations of
these ferromagnets shows that the simple mean-field-theory is reasonably
reliable for typical parameters of current samples but must fail at large
carrier densities and also in the limit of very strong exchange coupling.
Finally we discuss the results of Monte Carlo calculations that describe the
effect of collective fluctuations of Mn moment orientations. The method can
deal with some of the complications and additional physics, including the
possibility of non-collinear ground states, that enters when disorder is added
to the theoretical model.",0111314v1
2001-12-13,Kondo effect and STM spectra through ferromagnetic nanoclusters,"Motivated by recent scanning tunneling microscope (STM) experiments on cobalt
clusters adsorbed on single wall metallic nanotubes [Odom {\em et al.}, Science
{\bf 290}, 1549 (2000)], we study theoretically the size dependence of STM
spectra and spin-flip scattering of electrons from finite size ferromagnetic
clusters adsorbed on metallic surfaces. We study two models of nanometer size
ferromagnets: (i) An itinerant model with delocalized s, p and d electrons and
(ii) a local moment model with both localized d-level spins and delocalized
cluster electrons. The effective exchange coupling between the spin of the
cluster and the conduction electrons of the metallic substrate depends on the
specific details of the single particle density of states on the cluster. The
calculated Kondo coupling is inversely proportional to the total spin of the
ferromagnetic cluster in both models and thus the Kondo temperature is rapidly
suppressed as the size of the cluster increases. Mesoscopic fluctuations in the
charging energies and magnetization of nanoclusters can lead to large
fluctuations in the Kondo temperatures and a very asymmetric voltage dependence
of the STM spectra. We compare our results to the experiments.",0112258v2
2002-11-07,NMR evidence for an inhomogeneous transition between the ferromagnetic and antiferromagnetic ground states in Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ manganites,"The low temperature behavior of Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ manganites are
known to undergo a transition at $x\sim$0.3, from an insulating ferromagnetic
state, at low Ca concentration, to an insulating antiferromagnetic state. Above
the onset concentration for the charge-ordering effect ($x\sim 0.3$), a
metal-insulator transition induced by an external magnetic field is also
observed and related to the collapse of the charge-ordered state. In this paper
we show that the ferro-antiferromagnetic transition takes place in an
inhomogeneous way: around the critical concentration the sample is a mixture of
ferromagnetic and antiferromagnetic regions. The zero-field NMR measurements
show that a fraction of the ferromagnetic regions is in a fast hopping regime,
which suggests that a small fraction of the sample could be metallic, even in
zero field. This fraction of fast hopping regions is maximal at $x=$0.3, which
is also the concentration for which the insulator-metal transition has been
observed in the smallest field.",0211143v1
2002-11-25,Giant frequency dependence of dynamic freezing in nanocrystalline ferromagnetic LaCo0.5Mn0.5O3,"This paper is withdrawn now and soon will be replaced by a complete study on
LaCo0.5-MgxMn0.5O3.",0211524v2
2003-02-13,"Electronic phase separation in the rare earth manganates, (La1-xLnx)0.7Ca0.3MnO3 (Ln = Nd, Gd and Y)","All the three series of manganates showsaturation magnetization
characteristic of ferromagnetism, with the ferromagnetic Tc decreasing with
increasing in x up to a critical value of x, xc (xc = 0.6, 0.3, 0.2
respectively for Nd, Gd, Y). For x > xc, the magnetic moments are considerably
smaller showing a small increase around TM, the value of TM decreasing slightly
with increase in x or decrease in < rA >. The ferromagnetic compositions (x xc)
show insulator-metal (IM) transitions, while the compositions with x > xc are
insulating. The magnetic and electrical resistivity behavior of these
manganates is consistent with the occurrence of phase separation in the
compositions around xc, corresponding to a critical average radius of the
A-site cation, < rAc >, of 1.18 A. Both Tc and TIM increase linearly when < rA
> > < rAc > or x xc as expected of a homogenous ferromagnetic phase. Both Tc
and TM decrease linearly with the A-site cation size disorder at the A-site as
measured by the variance s2. Thus, an increase in s2 favors the insulating AFM
state. Percolative conduction is observed in the compositions with < rA > > <
rAc >. Electron transport properties in the insulating regime for x > xc
conforms to the variable range hopping mechanism. More interestingly, when x >
xc, the real part of dielectric constant (e') reaches a high value (104-106) at
ordinary temperatures dropping to a very small (~500) value below a certain
temperature, the value of which decreases with decreasing frequency.",0302268v1
2003-03-21,"Independent Electronic and Magnetic Doping in (Ga,Mn)As Based Digital Ferromagnetic Heterostructures","Ferromagnetic semiconductors promise the extension of metal-based spintronics
into a material system that combines widely tunable electronic, optical, and
magnetic properties. Here, we take steps towards realizing that promise by
achieving independent control of electronic doping in the ferromagnetic
semiconductor (Ga,Mn)As. Samples are comprised of superlattices of 0.5
monolayer (ML) MnAs alternating with 20 ML GaAs and are grown by low
temperature (230 C) atomic layer epitaxy (ALE). This allows for the reduction
of excess As incorporation and hence the number of charge-compensating
As-related defects. We grow a series of samples with either Be or Si doping in
the GaAs spacers (p- and n-type dopants, respectively), and verify their
structural quality by in situ reflection high-energy electron diffraction
(RHEED) and ex situ x-ray diffraction. Magnetization measurements reveal
ferromagnetic behavior over the entire doping range, and show no sign of MnAs
precipitates. Finally, magneto-transport shows the giant planar Hall effect and
strong (20%) resistance fluctuations that may be related to domain wall motion.",0303461v1
2003-06-20,Giant lasing effect in magnetic nanoconductors,"We propose a new principle for a compact solid-state laser in the 1-100 THz
regime. This is a frequency range where attempts to fabricate small size lasers
up till now have met severe technical problems. The proposed laser is based on
a new mechanism for creating spin-flip processes in ferromagnetic conductors.
The mechanism is due to the interaction of light with conduction electrons; the
interaction strength, being proportional to the large exchange energy, exceeds
the Zeeman interaction by orders of magnitude. On the basis of this
interaction, a giant lasing effect is predicted in a system where a population
inversion has been created by tunneling injection of spin-polarized electrons
from one ferromagnetic conductor to another -- the magnetization of the two
ferromagnets having different orientations. Using experimental data for
ferromagnetic manganese perovskites with nearly 100% spin polarization we show
the laser frequency to be in the range 1-100 THz. The optical gain is estimated
to be of order 10^7 cm^{-1}, which exceeds the gain of conventional
semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental
study is proposed and discussed.",0306522v1
2003-08-13,Nonlinear magnetic susceptibility and aging phenomena in reentrant ferromagnet: Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Linear and nonlinear dynamic properties of a reentrant ferromagnet
Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound are
studied using AC and DC magnetic susceptibility. This compound undergoes
successive phase transitions at the transition temperatures $T_{h}$ (= 16 K),
$T_{c}$ (= 9.7 K), and $T_{RSG}$ (= 3.5 K). The static and dynamic behaviors of
the reentrant spin glass phase below $T_{RSG}$ are characterized by those of
normal spin glass phase with critical exponent $\beta$ = 0.57 $\pm$ 0.10, a
dynamic critical exponent $x$ = 8.5 $\pm$ 1.8, and an exponent $p$ (= 1.55
$\pm$ 0.13) for the de Almeida -Thouless line. A prominent nonlinear
susceptibility is observed between $T_{RSG}$ and $T_{c}$ and around $T_{h}$,
suggesting a chaotic nature of the ferromagnetic phase ($T_{RSG} \leq T \leq
T_{c}$) and the helical spin ordered phase ($T_{c} \leq T \leq T_{h}$). The
aging phenomena are observed both in the RSG and FM phases, with the same
qualitative features as in normal spin glasses. The aging of zero-field cooled
magnetization indicates a drastic change of relaxation mechanism below and
above $T_{RSG}$. The time dependence of the absorption $\chi^{\prime \prime}$
is described by a power law form ($\approx t^{-b^{\prime \prime}}$) in the
ferromagnetic phase, where $b^{\prime \prime} \approx 0.074 \pm 0.016$ at $f$ =
0.05 Hz and $T$ = 7 K. No $\omega t$-scaling law for $\chi^{\prime \prime}$
[$\approx (\omega t)^{-b^{\prime \prime}}$] is observed.",0308247v1
2004-01-24,Dielectric and Pyroelectric Properties of Thick Film Ferromagnetic - Piezoelectric Structures,"Layered ferromagnetic-piezoelectric composites show mechanical strain
mediated electromagnetic coupling. Here we discuss dielectric and piezoelectric
properties of ferrite-lead zirconate titanate (PZT) and lanthanum manganite-PZT
samples. Results of our investigations on dielectric and pyroelectric
properties of multilayer ferromagnetic-piezoelectric are presented here. Lead
zircinate-titanate PbZrxTi1-xO3 (PZT) was used for the piezoelectric phase in
all the structures. The following materials were used for the ferromagnetic
component: nickel-zinc ferrites Ni0.9Zn 0.1Fe2O4 (NFO1) and Ni0.8Zn0.2Fe2O4
(NFO2), cobalt ferrite (CFO), lithium ferrite (LFO), lanthanum strontium
manganite La0.7Sr0.3MnO3 (LSM), and lanthanum-calcium manganite La0.7Ca0.3MnO3
(LCM). The pyroelectric effect was studied by measuring the current J flowing
through a closed loop containing the sample and an electrometer as the sample
temperature T was slowly varied at the rate 0.1 K/s. Polarized PZT layers
generate a pyroelectric current as the temperature changes. The main indicator
of pyroelectric nature of the current is the sign reversal when the thermal
cycle is switched from heating to cooling. Almost all of the multilayer
structures showed a pyroelectric current, but the pyroelectric coefficient
varied in a wide range. (i) For NFO1-PZT system the coefficient was in the
range 0.01 - 10 nC/(cm2 K), depending on the temperature. (ii) CFO-PZT and
LFO-PZT structures showed a large thermal current and a weak pyroelectric
effect. (iii) Thermal currents, however, were absent in LCM-PZT within the
temperature range from the room temperature to 400 K. (iv) In LSM-PZT, the
thermal current exceeded the pyroelectric current. A model is proposed for an
understanding of these results.",0401481v1
2004-01-28,Density Functional Calculations near Ferromagnetic Quantum Critical Points,"We discuss the application of the density functional theory in the local
density approximation (LDA) near a ferromagnetic quantum critical point. The
LDA fails to describe the critical fluctuations in this regime. This provides a
fingerprint of a materials near ferromagnetic quantum critical points:
overestimation of the tendency to magnetism in the local density approximation.
This is in contrast to the typical, but not universal, tendency of the LDA to
underestimate the tendency to magnetism in strongly Hubbard correlated
materials. We propose a method for correcting the local density calculations by
including critical spin fluctuations. This is based on (1) Landau expansion for
the free energy, evaluated within the LDA, (2) lowest order expansion of the
RPA susceptibility in LDA and (3) extraction of the amplitude of the relevant
(critical) fluctuations by applying the fluctuation-dissipation theorem to the
difference between a quantum-critical system and a reference system removed
from the quantum critical point. We illustrate some of the aspects of this by
the cases of Ni3Al and Ni3Ga, which are very similar metals on opposite sides
of a ferromagnetic quantum critical point. LDA calculations predict that Ni3Ga
is the more magnetic system, but we find that due to differences in the band
structure, fluctuation effects are larger in Ni3Ga, explaining the fact that
experimentally it is the less magnetic of the two materials.",0401563v1
2004-02-03,Observation of ferromagnetism above 900 K in Cr-GaN and Cr-AlN,"We report the observation of ferromagnetism at over 900K in Cr-GaN and Cr-AlN
thin films. The saturation magnetization moments in our best films of Cr-GaN
and Cr-AlN at low temperatures are 0.42 and 0.6 u_B/Cr atom, respectively,
indicating that 14% and 20%, of the Cr atoms, respectively, are magnetically
active. While Cr-AlN is highly resistive, Cr-GaN exhibits thermally activated
conduction that follows the exponential law expected for variable range hopping
between localized states. Hall measurements on a Cr-GaN sample indicate a
mobility of 0.06 cm^2/V.s, which falls in the range characteristic of hopping
conduction, and a free carrier density (1.4E20/cm^3), which is similar in
magnitude to the measured magnetically-active Cr concentration (4.9E19/cm^3). A
large negative magnetoresistance is attributed to scattering from loose spins
associated with non-ferromagnetic impurities. The results indicate that
ferromagnetism in Cr-GaN and Cr-AlN can be attributed to the double exchange
mechanism as a result of hopping between near-midgap substitutional Cr impurity
bands.",0402103v2
2004-04-12,Double Exchange in a Magnetically Frustrated System,"This work examines the magnetic order and spin dynamics of a double-exchange
model with competing ferromagnetic and antiferromagnetic Heisenberg
interactions between the local moments. The Heisenberg interactions are
periodically arranged in a Villain configuration in two dimensions with
nearest-neighbor, ferromagnetic coupling $J$ and antiferromagnetic coupling
$-\eta J$. This model is solved at zero temperature by performing a
$1/\sqrt{S}$ expansion in the rotated reference frame of each local moment.
When $\eta $ exceeds a critical value, the ground state is a magnetically
frustrated, canted antiferromagnet. With increasing hopping energy $t$ or
magnetic field $B$, the local moments become aligned and the ferromagnetic
phase is stabilized above critical values of $t$ or $B$. In the canted phase, a
charge-density wave forms because the electrons prefer to sit on lines of sites
that are coupled ferromagnetically. Due to a change in the topology of the
Fermi surface from closed to open, phase separation occurs in a narrow range of
parameters in the canted phase. In zero field, the long-wavelength spin waves
are isotropic in the region of phase separation. Whereas the average spin-wave
stiffness in the canted phase increases with $t$ or $\eta $, it exhibits a more
complicated dependence on field. This work strongly suggests that the jump in
the spin-wave stiffness observed in Pr$_{1-x}$Ca$_x$MnO$_3$ with $0.3 \le x \le
0.4$ at a field of 3 T is caused by the delocalization of the electrons rather
than by the alignment of the antiferromagnetic regions.",0404268v1
2004-06-17,"Effects of inter-site Coulomb interactions on ferromagnetism: Application to Fe, Co and Ni","We reanalyze the condition for metallic ferromagnetism in the framework of
the tight-binding approximation and investigate the consequences of the
inter-site Coulomb interactions using the Hartree-Fock approximation. We first
consider a non-degenerate $s$ band and we show that the inter-site interactions
modify the occurrence of ferromagnetism, and we derive a generalized Stoner
criterion. We analyze the main effects due to the renormalization of the
hopping integrals by the inter-site Coulomb interactions. These effects are
strongly dependent on the relative values of the inter-site electron-electron
interactions and on the shape of the density of states as illustrated by a
study of cubic crystals from which we establish general trends. We then
investigate a realistic $spd$ tight-binding model, including intra (Coulomb and
exchange) and inter-site charge-charge Coulomb integrals. This model is used to
study the electronic structure (band structure, densities of states, magnetic
moment) of bulk ferromagnetic 3d transition metals Fe(bcc), Co(hcp and fcc) and
Ni(fcc). An excellent agreement with local spin density functional calculations
is obtained for the three metals, in particular concerning the relative widths
of the majority and minority spin bands. Thus our tight-binding Hartree-Fock
model provides a consistent interpretation of this effect.",0406395v1
2004-09-02,Curie and Neel Temperatures of Quantum Magnets,"We estimate, using high-temperature series expansions, the transition
temperatures of the spin 1/2, 1 and 3/2 Heisenberg ferromagnet and
antiferromagnet in 3-dimensions. The manner in which the difference between
Curie and Neel temperatures vanishes with increasing spin quantum number is
investigated.",0409041v1
2004-09-17,Magnetism in Carbon Structures,"We discuss different magnetic phenomena observed in carbon-based structures,
in particular the diamagnetism, paramagnetism and ferromagnetism observed in
graphite, disordered carbon, fullerenes and irradiated carbon structures.",0409443v1
2004-10-21,A Note on Edwards' Hypothesis for Zero-Temperature Ising Dynamics,"We give a simple criterion for checking the so called Edwards' hypothesis in
certain zero-temperature, ferromagnetic spin-flip dynamics and use it to
invalidate the hypothesis in various examples in dimension one and higher.",0410543v1
2005-01-11,Ferromagnetic polarons in the one-dimensional ferromagnetic Kondo model with quantum mechanical S=3/2 core spins,"We present an extensive numerical study of the ferromagnetic Kondo lattice
model with quantum mechanical S=3/2 core spins. We treat one orbital per site
in one dimension using the density matrix renormalization group and include
on-site Coulomb repulsion between the electrons. We examine parameters relevant
to manganites, treating the range of low to intermediate doping, 0<x<0.5. In
particular, we investigate whether quantum fluctuations favor phase separation
over the ferromagnetic polarons observed in a model with classical core spins.
We obtain very good agreement of the quantum model with previous results for
the classical model, finding separated polarons which are repulsive at short
distance for finite t_2g superexchange J'. Taking on-site Coulomb repulsion
into account, we observe phase separation for small but finite superexchange
J', while for larger J' polarons are favored in accordance with simple energy
considerations previously applied to classical spins. We discuss the
interpretation of compressibilities and present a phase diagram with respect to
doping and the t_2g superexchange parameter J' with and without Coulomb
repulsion.",0501251v2
2005-05-08,Voltage-tunable ferromagnetism in semimagnetic quantum dots with few particles: magnetic polarons and electrical capacitance,"Magnetic semiconductor quantum dots with a few carriers represent an
interesting model system where ferromagnetic interactions can be tuned by
voltage. By designing the geometry of a doped quantum dot, one can tailor the
anisotropic quantum states of magnetic polarons. The strong anisotropy of
magnetic polaron states in disk-like quantum dots with holes comes from the
spin splitting in the valence band. The binding energy and spontaneous
magnetization of quantum dots oscillate with the number of particles and
reflect the shell structure. Due to the Coulomb interaction, the maximum
binding energy and spin polarization of magnetic polarons occur in the regime
of Hund's rule when the total spin of holes in a quantum dot is maximum. With
increasing number of particles in a quantum dot and for certain orbital
configurations, the ferromagnetic state becomes especially stable or may have
broken symmetry. In quantum dots with a strong ferromagnetic interaction, the
ground state can undergo a transition from a magnetic to a nonmagnetic state
with increasing temperature or decreasing exchange interaction. The
characteristic temperature and fluctuations of magnetic polarons depend on the
binding energy and degeneracy of the shell. The capacitance spectra of magnetic
quantum dots with few particles reveal the formation of polaron states.",0505195v2
2005-05-09,"Prospects of high temperature ferromagnetism in (Ga,Mn)As semiconductors","We report on a comprehensive combined experimental and theoretical study of
Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad
agreement between theoretical expectations and measured data allows us to
conclude that T_c in high-quality metallic samples increases linearly with the
number of uncompensated local moments on Mn_Ga acceptors, with no sign of
saturation. Room temperature ferromagnetism is expected for a 10% concentration
of these local moments. Our magnetotransport and magnetization data are
consistnent with the picture in which Mn impurities incorporated during growth
at interstitial Mn_I positions act as double-donors and compensate neighboring
Mn_Ga local moments because of strong near-neighbor Mn_Ga-Mn_I
antiferromagnetic coupling. These defects can be efficiently removed by
post-growth annealing. Our analysis suggests that there is no fundamental
obstacle to substitutional Mn_Ga doping in high-quality materials beyond our
current maximum level of 6.2%, although this achievement will require further
advances in growth condition control. Modest charge compensation does not limit
the maximum Curie temperature possible in ferromagnetic semiconductors based on
(Ga,Mn)As.",0505215v1
2005-06-14,"Orbital order, anisotropic spin couplings, and the spin-wave spectrum of the ferromagnetic Mott insulator YTiO3","Using a point-charge calculation of the electrostatic crystal field, we
determine the non-degenerate orbital ground state of the ferromagnetic Mott
insulator YTiO3, which is found to agree perfectly with experiment. Based on
the orbital order, we obtain by perturbation theory an effective spin
Hamiltonian that describes the magnetic superexchange between nearest-neighbor
Ti ions. The superexchange Hamiltonian includes, in addition to the isotropic
Heisenberg coupling, antisymmetric (Dzyaloshinskii-Moriya) and symmetric
anisotropy terms, caused by the spin-orbit interaction on the Ti ions. We find
ferromagnetic Heisenberg couplings for Ti-Ti bonds in the crystallographic ab
planes, but antiferromagnetic ones for Ti-Ti bonds between planes, in
contradiction with experiment (which gives ferromagnetic couplings for both).
Difficulties in calculating realistic values for the isotropic couplings of
YTiO3 have been already reported in the literature. We discuss possible origins
for these discrepancies. However, the much smaller values we obtain for the
symmetric and antisymmetric anisotropies may be expected to be reliable. We
therefore combine the experimentally-deduced isotropic coupling with the
calculated anisotropic ones to determine the magnetic order of the Ti ions,
which is found to be in satisfactory agreement with experiment. Based on this
magnetic order, we derive the spin-wave spectrum. We find an acoustic branch
with a very small zone-center gap and three optical spin-wave modes with
sizeable zone-center gaps. The acoustic branch reproduces the one reported in
experiment, and the optical ones are in a satisfactory agreement with
experiment, upon a proper folding of the magnetic Brillouin zone.",0506328v1
2005-06-27,Strong-coupling theory of high-temperature superconductivity and colossal magnetoresistance,"We argue that the extension of the BCS theory to the strong-coupling regime
describes the high-temperature superconductivity of cuprates and the colossal
magnetoresistance (CMR) of ferromagnetic oxides if the phonon dressing of
carriers and strong attractive correlations are taken into account. The
long-range Froehlich electron-phonon interaction has been identified as the
most essential in cuprates providing ""superlight"" lattice polarons and
bipolarons. Here some kinetic, magnetic, and more recent thermomagnetic normal
state measurements are interpreted in the framework of the strong-coupling
theory, including the Nernst effect and normal state diamagnetism. Remarkably,
a similar strong-coupling approach offers a simple explanation of CMR in
ferromagnetic oxides. The pairing of oxygen holes into heavy bipolarons in the
paramagnetic phase and their magnetic pair-breaking in the ferromagnetic phase
account for the first-order ferromagnetic phase transition, CMR, isotope
effects, and pseudogaps in doped manganites. Here we propose an explanation of
the phase coexistence and describe the shape of resistivity of manganites near
the transition in the framework of the strong-coupling approach.",0506706v3
2005-06-28,Spin dependent non-tunneling transport in granular ferromagnet,This paper is withdrawn.,0506739v3
2005-06-29,Spin-polarized electron transport in ferromagnet/semiconductor heterostructures: Unification of ballistic and diffusive transport,"A theory of spin-polarized electron transport in ferromagnet/semiconductor
heterostructures, based on a unified semiclassical description of ballistic and
diffusive transport in semiconductor structures, is developed. The aim is to
provide a framework for studying the interplay of spin relaxation and transport
mechanism in spintronic devices. A key element of the unified description of
transport inside a (nondegenerate) semiconductor is the thermoballistic current
consisting of electrons which move ballistically in the electric field arising
from internal and external electrostatic potentials, and which are thermalized
at randomly distributed equilibration points. The ballistic component in the
unified description gives rise to discontinuities in the chemical potential at
the boundaries of the semiconductor, which are related to the Sharvin interface
conductance. By allowing spin relaxation to occur during the ballistic motion
between the equilibration points, a thermoballistic spin-polarized current and
density are constructed in terms of a spin transport function. An integral
equation for this function is derived for arbitrary values of the momentum and
spin relaxation lengths. For field-driven transport in a homogeneous
semiconductor, the integral equation can be converted into a second-order
differential equation that generalizes the standard spin drift-diffusion
equation. The spin polarization in ferromagnet/semiconductor heterostructures
is obtained by invoking continuity of the current spin polarization and
matching the spin-resolved chemical potentials on the ferromagnet sides of the
interfaces. Allowance is made for spin-selective interface resistances.
Examples are considered which illustrate the effects of transport mechanism and
electric field.",0506755v2
2005-08-10,Half metallic digital ferromagnetic heterostructure composed of a $δ$-doped layer of Mn in Si,"We propose and investigate the properties of a digital ferromagnetic
heterostructure (DFH) consisting of a $\delta$-doped layer of Mn in Si, using
\textit{ab initio} electronic-structure methods. We find that (i) ferromagnetic
order of the Mn layer is energetically favorable relative to antiferromagnetic,
and (ii) the heterostructure is a two-dimensional half metallic system. The
metallic behavior is contributed by three majority-spin bands originating from
hybridized Mn-$d$ and nearest-neighbor Si-$p$ states, and the corresponding
carriers are responsible for the ferromagnetic order in the Mn layer. The
minority-spin channel has a calculated semiconducting gap of 0.25 eV. Analysis
of the total and partial densities of states, band structure, Fermi surfaces
and associated charge density reveals the marked two-dimensional nature of the
half metallicity. The band lineup is found to be favorable for retaining the
half metal character to near the Curie temperature ($T_{C}$). Being Si based
and possibly having a high $T_{C}$ as suggested by an experiment on dilutely
doped Mn in Si, the heterostructure may be of special interest for integration
into mature Si technologies for spintronic applications.",0508269v2
2005-12-05,Magnetic defects promote ferromagnetism in Zn1-xCoxO,"Experimental studies of Zn1-xCoxO as thin films or nanocrystals have found
ferromagnetism and Curie temperatures above room temperature and that p- or
n-type doping of Zn1-xCoxO can change its magnetic state. Bulk Zn1-xCoxO with a
low defect density and x in the range used in experimental thin film studies
exhibits ferromagnetism only at very low temperatures. Therefore defects in
thin film samples or nanocrystals may play an important role in promoting
magnetic interactions between Co ions in Zn1-xCoxO. The electronic structures
of Co substituted for Zn in ZnO, Zn and O vacancies, substituted N and
interstitial Zn in ZnO were calculated using the B3LYP hybrid density
functional in a supercell. The B3LYP functional predicts a band gap of 3.34 eV
for bulk ZnO, close to the experimental value of 3.47 eV. Occupied minority
spin Co 3d levels are at the top of the valence band and unoccupied levels lie
above the conduction band minimum. Majority spin Co 3d levels hybridize
strongly with bulk ZnO states. The neutral O vacancy and interstitial Zn are
deep and shallow donors, respectively. The Zn vacancy is a deep acceptor and
the acceptor level for substituted N is at mid gap. The possibility that p- or
n-type dopants promote exchange coupling of Co ions was investigated by
computing total energies of magnetic states of ZnO supercells containing two Co
ions and an oxygen vacancy, substituted N or interstitial Zn in various charge
states. The neutral N defect and the singly-positively charged O vacancy are
the only defects which strongly promote ferromagnetic exchange coupling of Co
ions at intermediate range.",0512101v1
2005-12-21,Interplay between itinerant and localized states in CaMn1-xRuxO3 (x =0 - 0.5) manganites,"Magnetic properties of polycrystalline CaMn1-xRuxO3 (x = 0 - 0.5) samples
were investigated in the temperature range 4.2 - 250 K, under external magnetic
field up to 15 kOe and under hydrostatic pressure up to 12 kbar. Transport
properties of the samples with x = 0.1, 0.2, 0.4, 0.5 were also investigated
under pressure up to 10 kbar. For x up to 0.4, the pressure was found to
suppress ferromagnetic correlations and to increase the resistivity, while for
x = 0.5 to act in the opposite way. While long ferromagnetic order is
completely suppressed, in small clusters ferromagnetic correlations probably
survive under pressure, as was revealed for CaMn0.9Ru0.1O3. The pressure effect
on the magnetic interactions and on the volume of ferromagnetic phase was found
to depend strongly on the Ru-content, and absolute value of the pressure
coefficient of spontaneous magnetization was found to decrease practically
linearly with increasing x in the range 0.1 < x < 0.5. The experimental data
are discussed in the frame of proposed energy-level diagram, which includes
magneto-impurity states at low and moderate Ru-doping and mixed-valence states
of Ru presented by a strongly-correlated t2g-like band at heavy Ru-doping. An
impact of disorder introduced by Ru-doping on the energy diagram and on derived
magnetic interactions is discussed. Predictions of the model regarding the
pressure effects on conductivity and temperature scales characteristic for
magnetic interactions are in reasonable agreement with experiment.",0512535v1
2005-12-29,"Ferromagnetism, paramagnetism and a Curie-Weiss metal in an electron doped Hubbard model on a triangular lattice","Motivated by the unconventional properties and rich phase diagram of NaxCoO2
we consider the electronic and magnetic properties of a two-dimensional Hubbard
model on an isotropic triangular lattice doped with electrons away from
half-filling. Dynamical mean-field theory (DMFT) calculations predict that for
negative inter-site hopping amplitudes (t<0) and an on-site Coulomb repulsion,
U, comparable to the bandwidth, the system displays properties typical of a
weakly correlated metal. In contrast, for t>0 a large enhancement of the
effective mass, ferromagnetism and a Curie-Weiss magnetic susceptibility are
found in a broad electron doping range. Our observation of Nagaoka
ferromagnetism is consistent with the A-type antiferromagnetism (i.e.
ferromagnetic layers stacked antiferromagnetically) observed in neutron
scattering experiments on NaxCoO2. We propose that `Curie-Weiss metal' phase
observed in NaxCoO2 is a consequence of the crossover from ``bad metal'' with
incoherent quasiparticles at temperatures T>T* and Fermi liquid behavior with
enhanced parameters below T*, where T* is a low energy coherence scale induced
by strong local Coulomb electron correlations. We propose a model which
contains the charge ordering phenomena observed in the system which, we
propose, drives the system close to the Mott insulating phase even at large
dopings.",0512696v2
2006-03-14,"Theory of ferromagnetic (III,Mn)V semiconductors","The body of research on (III,Mn)V diluted magnetic semiconductors initiated
during the 1990's has concentrated on three major fronts: i) the microscopic
origins and fundamental physics of the ferromagnetism that occurs in these
systems, ii) the materials science of growth and defects and iii) the
development of spintronic devices with new functionalities. This article
reviews the current status of the field, concentrating on the first two, more
mature research directions. From the fundamental point of view, (Ga,Mn)As and
several other (III,Mn)V DMSs are now regarded as textbook examples of a rare
class of robust ferromagnets with dilute magnetic moments coupled by
delocalized charge carriers. Both local moments and itinerant holes are
provided by Mn, which makes the systems particularly favorable for realizing
this unusual ordered state. Advances in growth and post-growth treatment
techniques have played a central role in the field, often pushing the limits of
dilute Mn moment densities and the uniformity and purity of materials far
beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds,
material quality and magnetic properties are intimately connected. In the
review we focus on the theoretical understanding of the origins of
ferromagnetism and basic structural, magnetic, magneto-transport, and
magneto-optical characteristics of simple (III,Mn)V epilayers, with the main
emphasis on (Ga,Mn)As. The conclusions we arrive at are based on an extensive
literature covering results of complementary ab initio and effective
Hamiltonian computational techniques, and on comparisons between theory and
experiment.",0603380v2
2006-03-15,"Anomalous Hall Effect in three ferromagnets: EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30","The Hall resistivity (Rho_xy), resistivity (Rho_xx), and magnetization of
three metallic ferromagnets are investigated as a function of magnetic field
and temperature. The three ferromagnets, EuFe4Sb12 (Tc = 84 K), Yb14MnSb11 (Tc
= 53 K), and Eu8Ga16Ge30 (Tc = 36 K) are Zintl compounds with carrier
concentrations between 1 x 10^21 cm^-3 and 3.5 x 10^21 cm^-3. The relative
decrease in Rho_xx below Tc [Rho_xx(Tc)/Rho_xx(2 K)] is 28, 6.5, and 1.3 for
EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30 respectively. The low carrier
concentrations coupled with low magnetic anisotropies allow a relatively clean
separation between the anomalous (Rho_'xy), and normal contributions to the
measured Hall resistivity. For each compound the anomalous contribution in the
zero field limit is fit to alpha Rho_xx + sigma_xy rho_xx^2 for temperatures T
< Tc. The anomalous Hall conductivity, sigma_xy, is -220 +- 5 (Ohm^-1 cm^-1),
-14.7 +- 1 (Ohm^-1 cm^-1), and 28 +- 3 (Ohm^-1 cm^-1) for EuFe4Sb12,
Yb14MnSb11, and Eu8Ga16Ge30 respectively and is independent of temperature for
T < Tc if the change in spontaneous magnetization (order parameter) with
temperature is taken into account. These data are consistent with recent
theories of the anomalous Hall effect that suggest that even for stochiometric
ferromagnetic crystals, such as those studied in this article, the intrinsic
Hall conductivity is finite at T = 0, and is a ground state property that can
be calculated from the electronic structure.",0603410v1
2006-04-11,A single layer of Mn in a GaAs quantum well: a ferromagnet with quantum fluctuations,"Some of the highest transition temperatures achieved for Mn-doped GaAs have
been in delta-doped heterostructures with well-separated planes of Mn. But in
the absence of magnetic anisotropy, the Mermin-Wagner theorem implies that a
single plane of magnetic ions cannot be ferromagnetic. Using a Heisenberg
model, we show that the same mechanism that produces magnetic frustration and
suppresses the transition temperature in bulk Mn-doped GaAs, due to the
difference between the light and heavy band masses, can stabilize ferromagnetic
order for a single layer of Mn in a GaAs quantum well. This comes at the price
of quantum fluctuations that suppress the ordered moment from that of a fully
saturated ferromagnet. By comparing the predictions of Heisenberg and
Kohn-Luttinger models, we conclude that the Heisenberg description of a
Mn-doped GaAs quantum well breaks down when the Mn concentration becomes large,
but works quite well in the weak-coupling limit of small Mn concentrations.
This comparison allows us to estimate the size of the quantum fluctuations in
the quantum well.",0604288v4
2006-05-11,Quantum critical behavior in itinerant electron systems -- Eliashberg theory and instability of a ferromagnetic quantum-critical point,"We consider the problem of fermions interacting with gapless long-wavelength
collective bosonic modes. The theory describes, among other cases, a
ferromagnetic quantum-critical point (QCP) and a QCP towards nematic ordering.
We construct a controllable expansion at the QCP in two steps: we first create
a new, non Fermi-liquid ``zero-order'' Eliashberg-type theory, and then
demonstrate that the residual interaction effects are small. We prove that this
approach is justified under two conditions: the interaction should be smaller
than the fermionic bandwidth, and either the band mass $m_B$ should be much
smaller than $m = p_F/v_F$, or the number of fermionic flavors $N$ should be
large. For an SU(2) symmetric ferromagnetic QCP, we find that the Eliashberg
theory itself includes a set of singular renormalizations which can be
understood as a consequence of an effective long-range dynamic interaction
between quasi-particles, generated by the Landau damping term. These singular
renormalizations give rise to a negative non-analytic $q^{3/2}$ correction to
the static spin susceptibility, and destroy a ferromagnetic QCP. We demonstrate
that this effect can be understood in the framework of the $\phi^4$ theory of
quantum criticality. We also show that the non-analytic $q^{3/2}$ correction to
the bosonic propagator is specific to the SU(2) symmetric case. For systems
with a scalar order parameter, the $q^{3/2}$ contributions from individual
diagrams cancel out in the full expression of the susceptibility, and the QCP
remains stable.",0605306v1
2006-05-19,"Magnetic unipolar features in con- ductivity of point contacts between normal and ferromagnetic d-metals (Co, Ni, Fe)","In nanocontacts between normal and ferromagnetic metals (N--F) abrupt changes
of the order of 1% are detected in differential resistance, dV/dI(V), versus
bias voltage, V, on achieving of high current densities, ~10^9 A/cm^2. These
features in dV/dI(V) are observed when the electron flow is directed from the
nonmagnetic metal into the ferromagnet and connected with magnetization
excitations in the ferromagnet induced by the current. Applying an external
magnetic field leads to a shift of the observed features to higher biasing
current, confirming the magnetic nature of the effect. Such effects are
observed for the non-ballistic (not spectral) regime of current flow in the
nanocontacts. Thus, the current induced magneto-conductance effects in
multilayered N--F structures (nanopillars) extensively studied in the recent
literature have much more general character and can be stimulated by elastic
electron scattering at single N--F interfaces.",0605485v1
2006-06-06,Infinite-range Ising ferromagnet in a time-dependent transverse field: quench and ac dynamics near the quantum critical point,"We study an infinite range ferromagnetic Ising model in the presence of a
transverse magnetic field which exhibits a quantum paramagnetic-ferromagnetic
phase transition at a critical value of the transverse field. In the
thermodynamic limit, the low-temperature properties of this model are dominated
by the behavior of a single large classical spin governed by an anisotropic
Hamiltonian. Using this property, we study the quench and AC dynamics of the
model both numerically and analytically, and develop a correspondence between
the classical phase space dynamics of a single spin and the quantum dynamics of
the infinite-range ferromagnetic Ising model. In particular, we compare the
behavior of the equal-time order parameter correlation function both near to
and away from the quantum critical point in the presence of a quench or AC
transverse field. We explicitly demonstrate that a clear signature of the
quantum critical point can be obtained by studying the AC dynamics of the
system even in the classical limit. We discuss possible realizations of our
model in experimental systems.",0606137v3
2006-06-15,Competing ferromagnetism in high temperature copper oxide superconductors,"The extreme variability of observables across the phase diagram of the
cuprate high temperature superconductors has remained a profound mystery, with
no convincing explanation of the superconducting dome. While much attention has
been paid to the underdoped regime of the hole-doped cuprates because of its
proximity to a complex Mott insulating phase, little attention has been paid to
the overdoped regime. Experiments are beginning to reveal that the
phenomenology of the overdoped regime is just as puzzling. For example, the
electrons appear to form a Landau Fermi liquid, but this interpretation is
problematic; any trace of Mott phenomena, as signified by incommensurate
antiferromagnetic fluctuations, is absent, and the uniform spin susceptibility
shows a ferromagnetic upturn. Here we show and justify that many of these
puzzles can be resolved if we assume that competing ferromagnetic fluctuations
are simultaneously present with superconductivity, and the termination of the
superconducting dome in the overdoped regime marks a quantum critical point
beyond which there should be a genuine ferromagnetic phase at zero temperature.
We propose new experiments, and make new predictions, to test our theory and
suggest that effort must be mounted to elucidate the nature of the overdoped
regime, if the problem of high temperature superconductivity is to be solved.
Our approach places competing order as the root of the complexity of the
cuprate phase diagram.",0606431v3
2006-06-21,Spin Glass and ferromagnetism in disordered Cerium compounds,"The competition between spin glass, ferromagnetism and Kondo effect is
analysed here in a Kondo lattice model with an inter-site random coupling
$J_{ij}$ between the localized magnetic moments given by a generalization of
the Mattis model which represents an interpolation between ferromagnetism and a
highly disordered spin glass. Functional integral techniques with Grassmann
fields have been used to obtain the partition function. The static
approximation and the replica symmetric ansatz have also been used. The
solution of the problem is presented as a phase diagram giving $T/{J}$ {\it
versus} $J_K/J$ where $T$ is the temperature, $J_{K}$ and ${J}$ are the
strengths of the intrasite Kondo and the intersite random couplings,
respectively. If $J_K/{J}$ is small, when temperature is decreased, there is a
second order transition from a paramagnetic to a spin glass phase. For lower
$T/{J}$, a first order transition appears between the spin glass phase and a
region where there are Mattis states which are thermodynamically equivalent to
the ferromagnetism. For very low ${T/{J}}$, the Mattis states become stable. On
the other hand, it is found as solution a Kondo state for large $J_{K}/{J}$
values. These results can improve the theoretical description of the well known
experimental phase diagram of $CeNi_{1-x}Cu_{x}$.",0606551v1
2006-06-23,"High temperature ferromagnetism in GdFe2Zn20: large, local moments embedded in the nearly ferromagnetic Fermi liquid compound YFe2Zn20","The RFe$_2$Zn$_{20}$ series manifests strongly correlated electron behavior
for the non-magnetic R = Y member and remarkably high temperature,
ferromagnetic ordering ($T_C$ = 86 K) for the local moment bearing R = Gd
member (a compound that is less than 5% atomic Gd). In contrast, the
isostructural RCo$_2$Zn$_{20}$ series manifests a more typical ordering
temperature ($T_N$ = 5.7 K for GdCo$_2$Zn$_{20}$) and YCo$_2$Zn$_{20}$ does not
show signs of correlated electron behavior. Studies of
R(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ (R = Gd, Y), combined with bandstructure
calculations for the end members, reveal that YFe$_2$Zn$_{20}$ is a nearly
ferromagnetic Fermi liquid and that the remarkably high $T_C$ associated with
GdFe$_2$Zn$_{20}$ is the result of submerging a large local moment into such a
highly polarizable matrix. These results indicate that the RFe$_2$Zn$_{20}$
series, and more broadly the RT$_2$Zn$_{20}$ (T = Fe, Co, Ni, Mn, Ru, Rh, Os,
Ir, Pt) isostructural family of compounds, offer an exceptionally promising
phase space for the study of the interaction between local moment and
correlated electron effects near the dilute R limit.",0606615v2
2006-10-24,"Synthesis, Structure, and Ferromagnetism of a New Oxygen Defect Pyrochlore System Lu2V2O_{7-x} (x = 0.40-0.65)","A new fcc oxygen defect pyrochlore structure system Lu2V2O_{7-x} with x =
0.40 to 0.65 was synthesized from the known fcc ferromagnetic semiconductor
pyrochlore compound Lu2V2O7 which can be written as Lu2V2O6O' with two
inequivalent oxygen sites O and O'. Rietveld x-ray diffraction refinements
showed significant Lu-V antisite disorder for x >= 0.5. The lattice parameter
versus x (including x = 0) shows a distinct maximum at x ~ 0.4. We propose that
these observations can be explained if the oxygen defects are on the O'
sublattice of the structure. The magnetic susceptibility versus temperature
exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C
that increases with x as expected in an ionic model. However, the magnetization
measurements also show that the (ferromagnetic) Weiss temperature theta and the
ferromagnetic ordering temperature T_C both strongly decrease with increasing x
instead of increasing as expected from C(x). The T_C decreases from 73 K for x
= 0 to 21 K for x = 0.65. Furthermore, the saturation moment at a field of 5.5
T at 5 K is nearly independent of x, with the value expected for a fixed spin
1/2 per V. The latter three observations suggest that Lu2V2O_{7-x} may contain
localized spin 1/2 vanadium moments in a metallic background that is induced by
oxygen defect doping, instead of being a semiconductor as suggested by the C(x)
dependence.",0610680v1
2006-11-09,"Ferromagnetism in the t-t' Hubbard model: interplay of lattice, band dispersion, and interaction effects studied within a Goldstone-mode preserving scheme","Ferromagnetism in the Hubbard model is investigated on sc, bcc, and fcc
lattices using a systematic inverse-degeneracy ($1/{\cal N}$) expansion which
incorporates self-energy and vertex corrections such that spin-rotation
symmetry and the Goldstone mode are explicitly preserved. First-order quantum
corrections to magnon energies are evaluated for several cases, providing a
comprehensive picture of the interplay of lattice, band dispersion, and
interaction effects on the stability of the ferromagnetic state with respect to
both long- and short-wavelength fluctuations. Our results support the belief
that ferromagnetism is a generic feature of the Hubbard model at intermediate
and strong coupling provided the DOS is sufficiently asymmetric and strongly
peaked near band edge, as for fcc lattice with finite $t'$. For
short-wavelength modes, behavior of a characteristic energy scale $\omega^*
\sim T_c$ (magnon-DOS-peak energy) is in excellent agreement with the $T_c$ vs.
$n$ behavior within DMFT, both with respect to the stable range of densities
($0.20 < n < 0.85$) as well as the optimal density $n=0.65$. However, our
finding of vanishing spin stiffness near optimal density highlights the role of
long-wavelength fluctuations in further reducing the stable range of densities.",0611238v1
2006-11-22,Magnetism and structure of magnetic multilayers based on the fully spin polarized Heusler alloys Co2MnGe and Co2MnSn,"Our Introduction starts with a short general review of the magnetic and
structural properties of the Heusler compounds which are under discussion in
this book. Then, more specifically, we come to the discussion of our
experimental results on multilayers composed of the Heusler alloys Co2MnGe and
Co2MnSn with V or Au as interlayers. The experimental methods we apply combine
magnetization and magneto-resistivity measurements, x-ray diffraction and
reflectivity, soft x-ray magnetic circular dichroism and spin polarized neutron
reflectivity. We find that below a critical thickness of the Heusler layers at
typically dcr = 1.5 nm the ferromagnetic order is lost and spin glass order
occurs instead. For very thin ferromagnetic Heusler layers there are
peculiarities in the magnetic order which are unusual when compared to
conventional ferromagnetic transition metal multilayer systems. In [Co2MnGe/Au]
multilayers there is an exchange bias shift at the ferromagnetic hysteresis
loops at low temperatures caused by spin glass ordering at the interface. In
[Co2MnGe/V] multilayers we observe an antiferromagnetic interlayer long range
ordering below a well defined Neel temperature originating from the dipolar
stray fields at the magnetically rough Heusler layer interfaces.",0611590v1
2006-12-24,Carrier induced ferromagnetism in diluted local-moment systems,"The electronic and magnetic properties of concentrated and diluted
ferromagnetic semiconductors are investigated by using the Kondo lattice model,
which describes an interband exchange coupling between itinerant conduction
electrons and localized magnetic moments. In our calculations, the electronic
problem and the local magnetic problem are solved separately. For the
electronic part an interpolating self-energy approach together with a coherent
potential approximation (CPA) treatment of a dynamical alloy analogy is used to
calculate temperature-dependent quasiparticle densities of states and the
electronic self-energy of the diluted local-moment system. For constructing the
magnetic phase diagram we use a modified RKKY theory by mapping the interband
exchange to an effective Heisenberg model. The exchange integrals appear as
functionals of the diluted electronic self-energy being therefore temperature-
and carrier-concentration-dependent and covering RKKY as well as double
exchange behavior. The disorder of the localized moments in the effective
Heisenberg model is solved by a generalized locator CPA approach. The main
results are: 1) extremely low carrier concentrations are sufficient to induce
ferromagnetism; 2) the Curie temperature exhibits a strikingly non-monotonic
behavior as a function of carrier concentration with a distinct maximum; 3)
$T_C$ curves break down at critical $n/x$ due to antiferromagnetic correlations
and 4) the dilution always lowers $T_C$ but broadens the ferromagnetic region
with respect to carrier concentration.",0612611v1
2007-01-14,Impact of the Fe Doping on Magnetism in Perovskite Cobaltites,"We systematically studied the magnetic and transport properties for the
polycrystalline samples of Fe-doped perovskite cobaltites:
Pr$_{1-y}$Ca$_{y}$Co$_{1-x}$Fe$_x$O$_3$ ($y$=0.3, $x$=0-0.15; $y$=0.45,
$x$=0-0.3) and Gd$_{0.55}$Sr$_{0.45}$Co$_{1-x}$Fe$_x$O$_{3}$ ($x$=0-0.3). Fe
doping leads to an enhancement of the ferromagnetism in the systems of
Pr$_{1-y}$Ca$_{y}$Co$_{1-x}$Fe$_x$O$_3$, while the ferromagnetism is suppressed
with further increasing Fe content and spin-glass behavior is observed at high
doping level of Fe. In contrast, the ferromagnetism is suppressed in the system
Gd$_{0.55}$Sr$_{0.45}$Co$_{1-x}$Fe$_x$O$_{3}$ as long as Fe is doped, and no
spin-glass behavior is observed in the sample with Fe doping up to 0.3. The
competition between ferromagnetic interactions through
Fe$^{3+}$-O-(LS)Co$^{4+}$ and antiferromagnetic interactions through
Fe$^{3+}$-O-Fe$^{3+}$ and Fe$^{3+}$-O-(IS)Co$^{3+}$ is considered to be
responsible for the behavior observed above. The average radius of the ions on
A sites plays the key role in determining what type of interactions Fe doping
mainly introduces.",0701302v1
2004-04-23,Quantum Hall States of Gluons in Quark Matter,"We have recently shown that dense quark matter possesses a color
ferromagnetic phase in which a stable color magnetic field arises
spontaneously. This ferromagnetic state has been known to be Savvidy vacuum in
the vacuum sector. Although the Savvidy vacuum is unstable, the state is
stabilized in the quark matter. The stabilization is achieved by the formation
of quantum Hall states of gluons, that is, by the condensation of the gluon's
color charges transmitted from the quark matter. The phase is realized between
the hadronic phase and the color superconducting phase. After a review of
quantum Hall states of electrons in semiconductors, we discuss the properties
of quantum Hall states of gluons in quark matter in detail. Especially, we
evaluate the energy of the states as a function of the coupling constant. We
also analyze solutions of vortex excitations in the states and evaluate their
energies. We find that the states become unstable as the gauge coupling
constant becomes large, or the chemical potential of the quarks becomes small,
as expected. On the other hand, with the increase of the chemical potential,
the color superconducting state arises instead of the ferromagnetic state. We
also show that the quark matter produced by heavy ion collisions generates
observable strong magnetic field $\sim 10^{15}$ Gauss when it enters the
ferromagnetic phase.",0404201v1
2001-11-02,Spiral-Logarithmic Structure in a Heisenberg Ferromagnet,"Spiral-logarithmic structure is suggested as a stationary solution of a
modified equation for the Heisenberg model, and the single- and N-soliton
solutions are constructed on this base.",0111004v1
2003-12-03,Magnetostatic Spin Waves,"In general, Maxwell's equations require that a wave of magnetic field be
accompanied by a wave of electric field, and vice versa. In magnetic media it
is possible to have waves of magnetization with negligible electric field. We
discuss an example of this based on ferromagnetic spin waves.",0312026v1
2007-04-09,Excitation Spectrum Gap and Spin-Wave Stiffness of XXZ Heisenberg Chains: Global Renormalization-Group Calculation,"The anisotropic XXZ spin-1/2 Heisenberg chain is studied using
renormalization-group theory. The specific heats and nearest-neighbor spin-spin
correlations are calculated thoughout the entire temperature and anisotropy
ranges in both ferromagnetic and antiferromagnetic regions, obtaining a global
description and quantitative results. We obtain, for all anisotropies, the
antiferromagnetic spin-liquid spin-wave velocity and the Isinglike
ferromagnetic excitation spectrum gap, exhibiting the spin-wave to spinon
crossover. A number of characteristics of purely quantum nature are found: The
in-plane interaction s_i^x s_j^x + s_i^y s_j^y induces an antiferromagnetic
correlation in the out-of-plane s_i^z component, at higher temperatures in the
antiferromagnetic XXZ chain, dominantly at low temperatures in the
ferromagnetic XXZ chain, and, in-between, at all temperatures in the XY chain.
We find that the converse effect also occurs in the antiferromagnetic XXZ
chain: an antiferromagnetic s_i^z s_j^z interaction induces a correlation in
the s_i^xy component. As another purely quantum effect, (i) in the
antiferromagnet, the value of the specific heat peak is insensitive to
anisotropy and the temperature of the specific heat peak decreases from the
isotropic (Heisenberg) with introduction of either type (Ising or XY)
anisotropy; (ii) in complete contrast, in the ferromagnet, the value and
temperature of the specific heat peak increase with either type of anisotropy.",0704.1064v2
2007-05-08,Precise measurements of radio-frequency magnetic susceptibility in (anti)ferromagnetic materials,"Dynamic magnetic susceptibility, $\chi$, was studied in several intermetallic
materials exhibiting ferromagnetic, antiferromagnetic and metamagnetic
transitions. Precise measurements by using a 14 MHz tunnel diode oscillator
(TDO) allow detailed insight into the field and temperature dependence of
$\chi$. In particular, local moment ferromagnets show a sharp peak in $\chi(T)$
near the Curie temperature, $T_c$. The peak amplitude decreases and shifts to
higher temperatures with very small applied dc fields. Anisotropic measurements
of CeVSb$_3$ show that this peak is present provided the magnetic easy axis is
aligned with the excitation field. In a striking contrast, small moment,
itinerant ferromagnets (i.e., ZrZn$_2$) show a broad maximum in $\chi(T)$ that
responds differently to applied field. We believe that TDO measurements provide
a very sensitive way to distinguish between local and itinerant moment magnetic
orders. Local moment antiferromagnets do not show a peak at the N\'eel
temperature, $T_N$, but only a sharp decrease of $\chi$ below $T_N$ due to the
loss of spin-disorder scattering changing the penetration depth of the ac
excitation field. Furthermore, we show that the TDO is capable of detecting
changes in spin order as well as metamagnetic transitions. Finally, critical
scaling of $\chi(T,H)$ in the vicinity of $T_C$ is discussed in CeVSb$_3$ and
CeAgSb$_2$.",0705.1072v2
2007-05-21,Ferromagnetic redshift of the optical gap in GdN,"We report measurements of the optical gap in a GdN film at temperatures from
300 to 6K, covering both the paramagnetic and ferromagnetic phases. The gap is
1.31eV in the paramagnetic phase and red-shifts to 0.9eV in the spin-split
bands below the Curie temperature. The paramagnetic gap is larger than was
suggested by very early experiments, and has permitted us to refine a
(LSDA+U)-computed band structure. The band structure was computed in the full
translation symmetry of the ferromagnetic ground state, assigning the
paramagnetic-state gap as the average of the majority- and minority-spin gaps
in the ferromagnetic state. That procedure has been further tested by a band
structure in a 32-atom supercell with randomly-oriented spins. After fitting
only the paramagnetic gap the refined band structure then reproduces our
measured gaps in both phases by direct transitions at the X point.",0705.2912v7
2007-08-09,Unusual heavy-mass nearly ferromagnetic state with a surprisingly large Wilson ratio in the double layered ruthenates (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ru$_{2}$O$_{7}$,"We report an unusual nearly ferromagnetic, heavy-mass state with a
surprisingly large Wilson ratio $R_{\textrm{w}}$ (e.g., $R_{\textrm{w}}\sim$
700 for $x =$ 0.2) in double layered ruthenates
(Sr$_{1-x}$Ca$_{x}$)$_{3}$Ru$_{2}$O$_{7}$ with 0.08 $< x <$ 0.4. This state
does not evolve into a long-range ferromagnetically ordered state despite
considerably strong ferromagnetic correlations, but freezes into a
cluster-spin-glass at low temperatures. In addition, evidence of non-Fermi
liquid behavior is observed as the spin freezing temperature of the
cluster-spin-glass approaches zero near $x \approx$ 0.1. We discuss the origin
of this unique magnetic state from the Fermi surface information probed by Hall
effect measurements.",0708.1291v5
2007-10-16,A generalization of Snoek's law to ferromagnetic films and composites,"The present paper establishes characteristics of the relative magnetic
permeability spectrum $\mu$(f) of magnetic materials at microwave frequencies.
The integral of the imaginary part of $\mu$(f) multiplied with the frequency f
gives remarkable properties. A generalisation of Snoek's law consists in this
quantity being bounded by the square of the saturation magnetization multiplied
with a constant. While previous results have been obtained in the case of
non-conductive materials, this work is a generalization to ferromagnetic
materials and ferromagnetic-based composites with significant skin effect. The
influence of truncating the summation to finite upper frequencies is
investigated, and estimates associated to the finite summation are provided. It
is established that, in practice, the integral does not depend on the damping
model under consideration. Numerical experiments are performed in the exactly
solvable case of ferromagnetic thin films with uniform magnetization, and these
numerical experiments are found to confirm our theoretical results. Microwave
permeability measurements on soft amorphous films are reported. The relation
between the integral and the saturation magnetization is verified
experimentally, and some practical applications of the theoretical results are
introduced. The integral can be used to determine the average magnetization
orientation in materials with complex configurations of the magnetization, and
furthermore to demonstrate the accuracy of microwave measurement systems. For
certain applications, such as electromagnetic compatibility or radar absorbing
materials, the relations established herein provide useful indications for the
design of efficient materials, and simple figures of merit to compare the
properties measured on various materials.",0710.2980v2
2008-01-15,Ferromagnet in a continuously tuneable random field,"The Random-Field Ising Model (RFIM) has been extensively studied as a model
system for understanding the effects of disorder in magnets. Since the late
1970s, there has been a particular focus on realizations of the RFIM in
site-diluted antiferromagnets. We observe random-field effects in the dilute
dipole-coupled ferromagnet $\mathrm{LiHo}_x\mathrm{Y}_{1-x}\mathrm{F}_4$. In
the presence of a magnetic field transverse to the Ising axis ($H_t$), the
behavior of $\mathrm{LiHo}_x\mathrm{Y}_{1-x}\mathrm{F}_4$ becomes increasingly
dominated by the influence of random-field terms in the effective Hamiltonian.
This is seen experimentally in the shape of the ferromagentic-paramagnetic
phase boundary and in changes to the critical exponents near the classical
critical point. We find that above the classical critical point the magnetic
susceptibility diverges as $H_t\to0$, and that the susceptibility both above
and below the classical critical point can be collapsed onto a single universal
curve using a modified Curie law which explicitly incorporates random-field
contributions. The discovery of a ferromagnetic realization of the RFIM opens
the door to investigation of the random-field problem with the wide variety of
techniques available for probing ferromagnets, including the ability to examine
both the statics and dynamics of the random-field problem. It also allows
studying the effects of controlled amounts of randomness on the dynamics of
domain pinning and the energetics of domain reversal.",0801.2335v1
2008-02-14,"Nonvolatile ferroelectric control of ferromagnetism in (Ga,Mn)As","There is currently much interest in materials and structures that provide
coupled ferroelectric and ferromagnetic responses, with a long-term goal of
developing new memories and spintronic logic elements. Within the field there
is a focus on composites coupled by magnetostrictive and piezoelectric strain
transmitted across ferromagnetic-ferroelectric interfaces, but substrate
clamping limits the response in the supported multilayer configuration favoured
for devices. This constraint is avoided in a ferroelectric-ferromagnetic
bilayer in which the magnetic response is modulated by the electric field of
the poled ferroelectric. Here, we report the realization of such a device using
a diluted magnetic semiconductor (DMS) channel and a polymer ferroelectric
gate. Polarization reversal of the gate by a single voltage pulse results in a
persistent modulation of the Curie temperature as large as 5%. The device
demonstrates direct and quantitatively understood electric-fieldmediated
coupling in a multiferroic bilayer and may provide new routes to nanostructured
DMS materials and devices via ferroelectric domain nanopatterning. The
successful implementation of a polymer-ferroelectric gate fieldeffect
transistor (FeFET) with a DMS channel adds a new functionality to semiconductor
spintronics and may be of importance for future low-voltage spintronics devices
and memory structures.",0802.2074v1
2008-02-22,Thermodynamics of Heisenberg ferromagnets with arbitrary spin in a magnetic field,"The thermodynamic properties (magnetization, magnetic susceptibility,
transverse and longitudinal correlation lengths, specific heat) of one- and
two-dimensional ferromagnets with arbitrary spin S in a magnetic field are
investigated by a second-order Green-function theory. In addition, quantum
Monte Carlo simulations for S= 1/2 and S=1 are performed using the stochastic
series expansion method. A good agreement between the results of both
approaches is found. The field dependence of the position of the maximum in the
temperature dependence of the susceptibility fits well to a power law at low
fields and to a linear increase at high fields. The maximum height decreases
according to a power law in the whole field region. The longitudinal
correlation length may show an anomalous temperature dependence: a minimum
followed by a maximum with increasing temperature. Considering the specific
heat in one dimension and at low magnetic fields, two maxima in its temperature
dependence for both the S= 1/2 and S = 1 ferromagnets are found. For S>1 only
one maximum occurs, as in the two-dimensional ferromagnets. Relating the theory
to experiments on the S= 1/2 quasi-one-dimensional copper salt TMCuC
[(CH_3)_4NCuCl_3], a fit to the magnetization as a function of the magnetic
field yields the value of the exchange energy which is used to make predictions
for the occurrence of two maxima in the temperature dependence of the specific
heat.",0802.3395v1
2008-04-10,Near-Zero Moment Ferromagnetism in the Semiconductor SmN,"The magnetic behaviour of SmN has been investigated in stoichiometric
polycrystalline films. All samples show ferromagnetic order with Curie
temperature (T_c) of 27 +/- 3 K, evidenced by the occurrence of hysteresis
below T_c. The ferromagnetic state is characterised by a very small moment and
a large coercive field, exceeding even the maximum applied field of 6 T below
about 15 K. The residual magnetisation at 2 K, measured after cooling in the
maximum field, is 0.035 mu_B per Sm. Such a remarkably small moment results
from a near cancellation of the spin and orbital contributions for Sm3+ in SmN.
Coupling to an applied field is therefore weak, explaining the huge coercive
field . The susceptibility in the paramagnetic phase shows
temperature-independent Van Vleck and Curie-Weiss contributions. The Van Vleck
contribution is in quantitative agreement with the field-induced admixture of
the J=7/2 excited state and the 5/2 ground state. The Curie-Weiss contribution
returns a Curie temperature that agrees with the onset of ferromagnetic
hysteresis, and a conventional paramagnetic moment with an effective moment of
0.4 mu_B per Sm ion, in agreement with expectations for the crystal-field
modified effective moment on the Sm3+ ions.",0804.1595v3
2008-05-03,Intrinsic room temperature ferromagnetism in Co-implanted ZnO,"We report on the structural and magnetic properties of a cobalt-implanted ZnO
film grown on a sapphire substrate. X-ray diffraction and transmission electron
microscopy reveal the presence of a (10-10)-oriented hexagonal Co phase in the
Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter
of is about 5-6 nm, form a Co rich layer in the substrate close to the
ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two
different magnetic phases in the implanted region. One originates from the Co
clusters in Al2O3, the other one belongs to a homogeneous ferromagnetic phase
with a ferromagnetic Curie temperature far above room temperature and can be
attributed to Co substitution on Zn sites in the ZnO layer. We have observed
magnetic dichroism at the Co L2,3 and O K edges at room temperature as well as
the multiplet structure in x-ray absorption spectra around the Co L3 edge,
supporting the intrinsic nature of the observed ferromagnetism in Co-implanted
ZnO film. The magnetic moment per substituted cobalt is found about 2.81 Bohr
magneton which is very close to the theoretical expected value of 3 Bohr
magneton per Co atom for Co 2+ in its high spin state.",0805.0361v2
2008-05-26,"Dopant-dependent impact of Mn-site doping on the critical-state manganites: R0.6Sr0.4MnO3 (R=La, Nd, Sm, and Gd)","Versatile features of impurity doping effects on perovskite manganites,
$R_{0.6}$Sr$_{0.4}$MnO$_{3}$, have been investigated with varying the doing
species as well as the $R$-dependent one-electron bandwidth. In
ferromagnetic-metallic manganites ($R$=La, Nd, and Sm), a few percent of Fe
substitution dramatically decreases the ferromagnetic transition temperature,
leading to a spin glass insulating state with short-range charge-orbital
correlation. For each $R$ species, the phase diagram as a function of Fe
concentration is closely similar to that for $R_{0.6}$Sr$_{0.4}$MnO$_{3}$
obtained by decreasing the ionic radius of $R$ site, indicating that Fe doping
in the phase-competing region weakens the ferromagnetic double-exchange
interaction, relatively to the charge-orbital ordering instability. We have
also found a contrastive impact of Cr (or Ru) doping on a spin-glass insulating
manganite ($R$=Gd). There, the impurity-induced ferromagnetic magnetization is
observed at low temperatures as a consequence of the collapse of the inherent
short-range charge-orbital ordering, while Fe doping plays only a minor role.
The observed opposite nature of impurity doping may be attributed to the
difference in magnitude of the antiferromagnetic interaction between the doped
ions.",0805.3966v1
2008-12-04,One-dimensional Ising ferromagnet frustrated by long-range interactions at finite temperatures,"We consider a one-dimensional lattice of Ising-type variables where the
ferromagnetic exchange interaction J between neighboring sites is frustrated by
a long-ranged anti-ferromagnetic interaction of strength g between the sites i
and j, decaying as |i-j|^-alpha, with alpha>1. For alpha smaller than a certain
threshold alpha_0, which is larger than 2 and depends on the ratio J/g, the
ground state consists of an ordered sequence of segments with equal length and
alternating magnetization. The width of the segments depends on both alpha and
the ratio J/g. Our Monte Carlo study shows that the on-site magnetization
vanishes at finite temperatures and finds no indication of any phase
transition. Yet, the modulation present in the ground state is recovered at
finite temperatures in the two-point correlation function, which oscillates in
space with a characteristic spatial period: The latter depends on alpha and J/g
and decreases smoothly from the ground-state value as the temperature is
increased. Such an oscillation of the correlation function is exponentially
damped over a characteristic spatial scale, the correlation length, which
asymptotically diverges roughly as the inverse of the temperature as T=0 is
approached. This suggests that the long-range interaction causes the Ising
chain to fall into a universality class consistent with an underlying
continuous symmetry. The e^(Delta/T)-temperature dependence of the correlation
length and the uniform ferromagnetic ground state, characteristic of the g=0
discrete Ising symmetry, are recovered for alpha > alpha_0.",0812.0907v2
2008-12-16,Evidence for reversible control of magnetization in a ferromagnetic material via spin-orbit magnetic field,"Conventional computer electronics creates a dichotomy between how information
is processed and how it is stored. Silicon chips process information by
controlling the flow of charge through a network of logic gates. This
information is then stored, most commonly, by encoding it in the orientation of
magnetic domains of a computer hard disk. The key obstacle to a more intimate
integration of magnetic materials into devices and circuit processing
information is a lack of efficient means to control their magnetization. This
is usually achieved with an external magnetic field or by the injection of
spin-polarized currents. The latter can be significantly enhanced in materials
whose ferromagnetic properties are mediated by charge carriers. Among these
materials, conductors lacking spatial inversion symmetry couple charge currents
to spin by intrinsic spin-orbit (SO) interactions, inducing nonequilibrium spin
polarization tunable by local electric fields. Here we show that magnetization
of a ferromagnet can be reversibly manipulated by the SO-induced polarization
of carrier spins generated by unpolarized currents. Specifically, we
demonstrate domain rotation and hysteretic switching of magnetization between
two orthogonal easy axes in a model ferromagnetic semiconductor.",0812.3160v2
2009-03-17,In search for the superconducting spin-switch: Magnetization induced resistance switching effects in La$_{0.67}$Sr$_{0.33}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ bi- and trilayers,"We have studied the influence of the magnetization on the superconducting
transition temperature ($T_c$) in bi- and trilayers consisting of the
half-metallic ferromagnet La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) and the
high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO). We have
made use of tilted epitaxial growth in order to achieve contacts between the
two materials that are partly in the crystallographic $ab$-plane of the YBCO.
As a result of uniaxial magnetic anisotropy in the tilted structures, we
observe sharp magnetization switching behavior. At temperatures close to $T_c$,
the magnetization switching induces resistance jumps in trilayers, resulting in
a magnetization dependence of $T_c$. In bilayers, this switching effect can be
observed as well, provided that the interface to the ferromagnetic layer is
considerably rough. Our results indicate that the switching behavior arises
from magnetic stray fields from the ferromagnetic layers that penetrate into
the superconductor. A simple model describes the observed behavior well. We
find no evidence that the switching behavior is caused by a so-called
superconducting spin-switch, nor by accumulation of spin-polarized electrons.
Observation of magnetic coupling of the ferromagnetic layers, through the
superconductor, supports the idea of field induced resistance switching.",0903.2993v1
2009-03-18,Superconductor-ferromagnet nanocomposites created by co-deposition of niobium and dysprosium,"We have created superconductor-ferromagnet composite films in order to test
the enhancement of critical current density, Jc, due to magnetic pinning. We
co-sputter the type-II superconductor niobium (Nb) and the low-temperature
ferromagnet dysprosium (Dy) onto a heated substrate; the immiscibility of the
two materials leads to a phase-separated composite of magnetic regions within a
superconducting matrix. Over a range of compositions and substrate
temperatures, we achieve phase separation on scales from 5 nm to 1 micron. The
composite films exhibit simultaneous superconductivity and ferromagnetism.
Transport measurements show that while the self-field Jc is reduced in the
composites, the in-field Jc is greatly enhanced up to the 3 T saturation field
of Dy. In one instance, the phase separation orders into stripes, leading to
in-plane anisotropy in Jc.",0903.3142v2
2009-05-19,Magnetism in Nb(1-y)Fe(2+y) - composition and magnetic field dependence,"We present a systematic study of transport and thermodynamic properties of
the Laves phase system Nb$_{1-y}$Fe$_{2+y}$. Our measurements confirm that
Fe-rich samples, as well as those rich in Nb (for $\mid y\mid\geq 0.02$), show
bulk ferromagnetism at low temperature. For stoichiometric NbFe$_2$, on the
other hand, magnetization, magnetic susceptibility and magnetoresistance
results point towards spin-density wave (SDW) order, possibly helical, with a
small ordering wavevector $Q \sim 0.05$ \AA$^{-1}$. Our results suggest that on
approaching the stoichiometric composition from the iron-rich side,
ferromagnetism changes into long-wavelength SDW order. In this scenario, $Q$
changes continuously from 0 to small, finite values at a Lifshitz point in the
phase diagram, which is located near $y=+0.02$. Further reducing the Fe content
suppresses the SDW transition temperature, which extrapolates to zero at
$y\approx -0.015$. Around this Fe content magnetic fluctuations dominate the
temperature dependence of the resistivity and of the heat capacity which
deviate from their conventional Fermi liquid forms, inferring the presence of a
quantum critical point. Because the critical point is located between the SDW
phase associated with stoichiometric NbFe$_2$ and the ferromagnetic order which
reemerges for very Nb-rich NbFe$_2$, the observed temperature dependences could
be attributed both to proximity to SDW order or to ferromagnetism.",0905.3051v1
2009-06-02,Correlation and confinement induced itinerant ferromagnetism in chain structures,"Using a positive semidefinite operator technique one deduces exact ground
states for a zig-zag hexagon chain described by a non-integrable Hubbard model
with on-site repulsion. Flat bands are not present in the bare band structure,
and the operators $\hat B^{\dagger}_{\mu,\sigma}$ introducing the electrons
into the ground state, are all extended operators and confined in the quasi 1D
chain structure of the system. Consequently, increasing the number of carriers,
the $\hat B^{\dagger}_{\mu,\sigma}$ operators become connected i.e. touch each
other on several lattice sites. Hence the spin projection of the carriers
becomes correlated in order to minimize the ground state energy by reducing as
much as possible the double occupancy leading to a ferromagnetic ground state.
This result demonstrates in exact terms in a many-body frame that the
conjecture made at two-particle level by G. Brocks et al.
[Phys.Rev.Lett.93,146405,(2004)] that the Coulomb interaction is expected to
stabilize correlated magnetic ground states in acenes is clearly viable, and
opens new directions in the search for routes in obtaining organic
ferromagnetism. Due to the itinerant nature of the obtained ferromagnetic
ground state, the systems under discussion may have also direct application
possibilities in spintronics.",0906.0520v1
2009-07-12,Odd triplet superconductivity in clean and moderately disordered SFFS junctions,"We study the Josephson effect and pairing correlations in SFFS junctions that
consist of conventional superconductors (S) connected through two metallic
monodomain ferromagnets (F) with transparent and spin inactive interfaces. We
solve the Eilenberger equations for arbitrary relative orientation of
magnetizations of the two F layers in the clean limit and for moderate disorder
in ferromagnets. Spatial variation of pair amplitudes, singlet $f_s$, and odd
in frequency triplet $f_{t0}$ and $f_{t1}$, with 0 and $\pm1$ spin projections,
as well as the Josephson current-phase relations are calculated for different
values of the ferromagnetic layers thickness and angle $\alpha$ between
in-plane magnetizations. In contrast to the dirty limit case, we find that for
$0<\alpha<\pi$ both spin singlet and triplet pair amplitudes in F layers
power-law decay in the same oscillatory manner with distance from the FS
interfaces. This decay gets faster as the impurity-scattering rate in
ferromagnets is increased. The computed triplet amplitude $f_{t1}$ has opposite
signs in the two magnet regions, penetrates into the superconductors and
monotonically decays over the same distance, which is the superconducting
coherence length, as the singlet amplitude $f_s$ saturates to the bulk value.
We point out that influence of misorientation of magnetizations on the
Josephson current can not be attributed directly to the appearance of odd
triplet correlations.",0907.2042v1
2009-09-13,"Unconventional ferromagnetism and transport properties of (In,Mn)Sb dilute magnetic semiconductor","Narrow-gap higher mobility semiconducting alloys In_{1-x}Mn_{x}Sb were
synthesized in polycrystalline form and their magnetic and transport properties
have been investigated. Ferromagnetic response in In_{0.98}Mn_{0.02}Sb was
detected by the observation of clear hysteresis loops up to room temperature in
direct magnetization measurements. An unconventional (reentrant) magnetization
versus temperature behavior has been found. We explained the observed
peculiarities within the frameworks of recent models which suggest that a
strong temperature dependence of the carrier density is a crucial parameter
determining carrier-mediated ferromagnetism of (III,Mn)V semiconductors. The
correlation between magnetic states and transport properties of the sample has
been discussed. The contact spectroscopy method is used to investigate a band
structure of (InMn)Sb near the Fermi level. Measurements of the degree of
charge current spin polarization have been carried out using the point contact
Andreev reflection (AR) spectroscopy. The AR data are analyzed by introducing a
quasiparticle spectrum broadening, which is likely to be related to magnetic
scattering in the contact. The AR spectroscopy data argued that at low
temperature the sample is decomposed on metallic ferromagnetic clusters with
relatively high spin polarization of charge carriers (up to 65% at 4.2K) within
a cluster.",0909.2407v2
2009-09-23,Phase-controlled proximity-effect in ferromagnetic Josephson junctions: calculation of DOS and electronic specific heat,"We study the thermodynamic properties of a dirty ferromagnetic
S$\mid$F$\mid$S Josephson junction with s-wave superconducting leads in the
low-temperature regime. We employ a full numerical solution with a set of
realistic parameters and boundary conditions, considering both a uniform and
non-uniform exchange field in the form of a Bloch domain wall ferromagnetic
layer. The influence of spin-active interfaces is incorporated via a
microscopic approach. We mainly focus on how the electronic specific heat and
density of states (DOS) of such a system is affected by the \textit{proximity
effect}, which may be tuned via the superconducting phase difference. Our main
result is that it is possible to \textit{strongly modify the electronic
specific heat} of the system by changing the phase difference between the two
superconducting leads from 0 up to nearly $\pi$ at low temperatures. An
enhancement of the specific heat will occur for small values $h\simeq\Delta$ of
the exchange field, while for large values of $h$ the specific heat is
suppressed by increasing the phase difference between the superconducting
leads. These results are all explained in terms of the proximity-altered DOS in
the ferromagnetic region, and we discuss possible methods for experimental
detection of the predicted effect.",0909.4323v1
2009-10-04,Quasi-Ferromagnet Spintronics in Graphene Nanodisk-Lead System,"A zigzag graphene nanodisk can be interpreted as a quantum dot with an
internal degree of freedom. It is well described by the infinite-range
Heisenberg model. We have investigated its thermodynamical properties. There
exists a quasi-phase transition between the quasi-ferromagnet and
quasi-paramagnet states, as signaled by a sharp peak in the specific heat and
in the susceptability. We have also analyzed how thermodynamical properties are
affected when two leads are attached to the nanodisk. It is shown that lead
effects are described by the many-spin Kondo Hamiltonian. There appears a new
peak in the specific heat, and the multiplicity of the ground state becomes
just one half of the system without leads. Another lead effect is to enhance
the ferromagnetic order. Being a ferromagnet, a nanodisk can be used as a spin
filter. Furthermore, since the relaxation time is finite, it is possible to
control the spin of the nanodisk by an external spin current. We then propose a
rich variety of spintronic devices made of nanodisks and leads, such as spin
memory, spin amplifier, spin valve, spin-field-effect transistor, spin diode
and spin logic gates such as spin-XNOR gate and spin-XOR gate. Graphene
nanodisks could well be basic components of future nanoelectronic and
spintronic devices.",0910.0593v1
2009-10-15,Spin Transfer from the point of view of the ferromagnetic degrees of freedom,"Spintronics is the generic term that describes magnetic systems coupled to an
electric generator, taking into account the spin attached to the charge
carriers. For this topical review of {\it Spin Caloritronics}, we focus our
attention on the study of {\it irreversible processes} occuring in spintronic
devices, that involve both the spins of the conduction electrons and the
ferromagnetic degrees of freedom. The aim of this report is to clarify the
nature of the different kinds of power dissipated in metallic ferromagnets
contacted to an electric generator, and to exploit it in the framework of the
theory of mesoscopic non-equilibrium thermodynamics. The expression of the
internal power (i.e. the internal entropy production multiplied by the
temperature) dissipated by a generic system connected to different reservoirs,
allows the corresponding kinetic equations to be derived with the introduction
of the relevant phenomenological kinetic coefficients. After derivation of the
kinetic equations for the ferromagnetic degrees of freedom (i.e. the
Landau-Lifshitz equation) and the derivation of the kinetic equations for the
spin-accumulation effects (within a two channel model), the kinetic equations
describing spin-transfer are obtained. Both spin-dependent relaxation (usual
spin-accumulation) and spin-precession in quasi-ballistic regime (transverse
spin-accumulation) are taken into account. The generalization of the
Landau-Lifshitz equation to spin-accumulation is then performed with the
introduction of two potential energy terms, that are experimentally accessible.",0910.2890v2
2009-10-17,Density functional study of the actinide nitrides,"The full potential all electron linearized augmented plane wave plus local
orbitals (FP-LAPW + lo) method, as implemented in the suite of software WIEN2K,
has been used to systematically investigate the structural, electronic, and
magnetic properties of the actinide compounds AnN (An = Ac, Th, Pa, U, Np, Pu,
Am). The theoretical formalism used is the generalized gradient approximation
to density functional theory (GGA-DFT) with the Perdew-Burke-Ernzerhof (PBE)
exchange-correlation functional. Each compound has been studied at six levels
of theory: non-magnetic (NM), non-magnetic with spin-orbit coupling (NM+SOC),
ferromagnetic (FM), ferromagnetic with spin-orbit coupling (FM+SOC),
anti-ferromagnetic (AFM), and anti-ferromagnetic with spin-orbit coupling
(AFM+SOC). The structural parameters, bulk moduli, densities of states, and
charge distributions have been computed and compared to available experimental
data and other theoretical calculations published in the literature. The total
energy calculations indicate that the lowest energy structures of AcN, ThN, and
PaN are degenerate at the NM+SOC, FM+SOC, and AFM+SOC levels of theory with
vanishing total magnetic moments in the FM+SOC and AFM+SOC cases, making the
ground states essentially non-magnetic with spin-orbit interaction. The ground
states of UN, NpN, PuN, and AmN are found to be FM+SOC at the level of theory
used in the present computations. The nature of the interactions between the
actinide metals and nitrogen atom, and the implications on 5f electron
delocalization and localization are discussed in detail.",0910.3337v1
2009-11-25,Visualizing supercurrents in ferromagnetic Josephson junctions with various arrangements of 0 and πsegments,"Josephson junctions with ferromagnetic barrier can have positive or negative
critical current depending on the thickness $d_F$ of the ferromagnetic layer.
Accordingly, the Josephson phase in the ground state is equal to 0 (a
conventional or 0 junction) or to $\pi$ ($\pi$ junction). When 0 and $\pi$
segments are joined to form a ""0-$\pi$ junction"", spontaneous supercurrents
around the 0-$\pi$ boundary can appear. Here we report on the visualization of
supercurrents in superconductor-insulator-ferromagnet-superconductor (SIFS)
junctions by low-temperature scanning electron microscopy (LTSEM). We discuss
data for rectangular 0, $\pi$, 0-$\pi$, 0-$\pi$-0 and 20 \times 0-$\pi$
junctions, disk-shaped junctions where the 0-$\pi$ boundary forms a ring, and
an annular junction with two 0-$\pi$ boundaries. Within each 0 or $\pi$ segment
the critical current density is fairly homogeneous, as indicated both by
measurements of the magnetic field dependence of the critical current and by
LTSEM. The $\pi$ parts have critical current densities $j_c^\pi$ up to
$35\units{A/cm^2}$ at $T = 4.2\units{K}$, which is a record value for SIFS
junctions with a NiCu F-layer so far. We also demonstrate that SIFS technology
is capable to produce Josephson devices with a unique topology of the 0-$\pi$
boundary.",0911.4831v1
2010-02-01,Spin Torques in Point Contacts to Exchange-Biased Ferromagnetic Films,"Hysteretic magneto-resistance of point contacts formed between non-magnetic
tips and single ferromagnetic films exchange-pinned by antiferromagnetic films
is investigated. The analysis of the measured current driven and field driven
hysteresis agrees with the recently proposed model of the surface spin-valve,
where the spin orientation at the interface can be different from that in the
bulk of the film. The switching in magneto-resistance at low fields is observed
to depend significantly on the direction of the exchange pinning, which allows
identifying this transition as a reversal of interior spins of the pinned
ferromagnetic films. The switching at higher fields is thus due to a spin
reversal in the point contact core, at the top surface of the ferromagnet, and
does not exhibit any clear field offset when the exchange-pinning direction or
the magnetic field direction is varied. This magnitude of the switching field
of the surface spins varies substantially from contact to contact and sometimes
from sweep to sweep, which suggests that the surface coercivity can change
under very high current densities and/or due to the particular microstructure
of the point contact. In contrast, no changes in the effect of the exchange
biasing on the interior spins are observed at high currents, possibly due to
the rapid drop in the current density away from nanometer sized point contact
cores.",1002.0209v1
2010-02-19,Electronic transport through a graphene-based ferromagnetic/normal/ferromagnetic junction,"Electronic transport in a graphene-based ferromagnetic/normal/ferromagnetic
junction is investigated by means of Landauer-B\""{u}ttiker formulism and the
nonequilibrium Green's function technique. For the zigzag edge case, the
results show that the conductance is always larger than $e^{2}/h$ for the
parallel configuration of lead magnetizations, but for the antiparallel
configuration the conductance becomes zero because of the band-selective rule.
So a magnetoresistance (MR) plateau emerges with the value 100% when the Fermi
energy is located around the Dirac point. Besides, choosing narrower graphene
ribbons can obtain the wider 100% MR plateaus and the length change of the
central graphene region does not affect the 100% MR plateaus. Although the
disorder will reduce the MR plateau, the plateau value can be still kept about
50% even in a large disorder strength case. In addition, when the
magnetizations of the left and right leads have a relative angle, the
conductance changes as a cosine function of the angle. What is more, for the
armchair edge case, the MR is usually small. So, it is more favorable to
fabricate the graphene-based spin valve device by using the zigzag edge
graphene ribbon.",1002.3665v1
2010-03-10,"Diffuse Neutron Scattering Study of Magnetic Correlations in half-doped La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) Manganites","The short range ordered magnetic correlations have been studied in half doped
La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) compounds by polarized neutron
scattering technique. On doping Sr2+ for Ca2+ ion, these compounds with x =
0.1, 0.3, and 0.4 exhibit CE-type, mixture of CE-type and A-type, and A-type
antiferromagnetic ordering, respectively. Magnetic diffuse scattering is
observed in all the compounds above and below their respective magnetic
ordering temperatures and is attributed to magnetic polarons. The correlations
are primarily ferromagnetic in nature above T\_N, although a small
antiferromagnetic contribution is also evident. Additionally, in samples x =
0.1 and 0.3 with CE-type antiferromagnetic ordering, superlattice diffuse
reflections are observed indicating correlations between magnetic polarons. On
lowering temperature below T\_N the diffuse scattering corresponding to
ferromagnetic correlations is suppressed and the long range ordered
antiferromagnetic state is established. However, the short range ordered
correlations indicated by enhanced spin flip scattering at low Q coexist with
long range ordered state down to 3K. In x = 0.4 sample with A-type
antiferromagnetic ordering, superlattice diffuse reflections are absent.
Additionally, in comparison to x = 0.1 and 0.3 sample, the enhanced spin flip
scattering at low Q is reduced at 310K, and as temperature is reduced below
200K, it becomes negligibly low. The variation of radial correlation function,
g(r) with temperature indicates rapid suppression of ferromagnetic correlations
at the first nearest neighbor on approaching TN. Sample x = 0.4 exhibits growth
of ferromagnetic phase at intermediate temperatures (~ 200K). This has been
further explored using SANS and neutron depolarization techniques.",1003.2026v1
2010-03-17,"Kondo behavior, ferromagnetic correlations, and crystal fields in the heavy Fermion compounds Ce3X (X=In, Sn)","We report measurements of inelastic neutron scattering, magnetic
susceptibility, magnetization, and the magnetic field dependence of the
specific heat for the heavy Fermion compounds Ce$_3$In and Ce$_3$Sn. The
neutron scattering results show that the excited crystal field levels have
energies $E_1$ = 13.2 meV, $E_2$ = 44.8 meV for Ce$_3$In and $E_1$ = 18.5 meV,
$E_2$ = 36.1 meV for Ce$_3$Sn. The Kondo temperature deduced from the
quasielastic linewidth is 17 K for Ce$_3$In and 40 K for Ce$_3$Sn. The low
temperature behavior of the specific heat, magnetization, and susceptibility
can not be well-described by J=1/2 Kondo physics alone, but require
calculations that include contributions from the Kondo effect, broadened
crystal fields, and ferromagnetic correlations, all of which are known to be
important in these compounds. We find that in Ce$_3$In the ferromagnetic
fluctuation makes a 10-15 % contribution to the ground state doublet entropy
and magnetization. The large specific heat coefficient $\gamma$ in this heavy
fermion system thus arises more from the ferromagnetic correlations than from
the Kondo behavior.",1003.3462v1
2010-04-09,Epitaxial ferromagnetic semiconductor GdN thin films on Si substrate,This paper has been withdrawn by the author,1004.1545v2
2010-04-22,Magnetic excitations in the metallic single-layer Ruthenates Ca(2-x)Sr(x)RuO(4) studied by inelastic neutron scattering,"By inelastic neutron scattering, we have analyzed the magnetic correlations
in the paramagnetic metallic region of the series Ca(2-x)Sr(x)RuO(4),
0.2<=x<=0.62. We find different contributions that correspond to 2D
ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors
(0.11,0,0), (0.26,0,0) and (0.3,0.3,0). These components constitute the
measured response as function of the Sr-concentration x, of the magnetic field
and of the temperature. A generic model is applicable to metallic
Ca(2-x)Sr(x)RuO(4) close to the Mott transition, in spite of their strongly
varying physical properties. The amplitude, characteristic energy and width of
the incommensurate components vary only little as function of x, but the
ferromagnetic component depends sensitively on concentration, temperature and
magnetic field. While ferromagnetic fluctuations are very strong in
Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T=1.5 K, they
are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of
a magnetic field and form a magnon mode above the metamagnetic transition. The
inelastic neutron scattering results document how the competition between
ferromagnetic and incommensurate antiferromagnetic instabilities governs the
physics of this system.",1004.3957v1
2010-06-18,Probing the magnetic state by linear and non linear ac magnetic susceptibility measurements in under doped manganite Nd0.8Sr0.2MnO3,"We have thoroughly investigated the entire magnetic states of under doped
ferromagnetic insulating manganite Nd0.8Sr0.2MnO3 through temperature dependent
linear and non linear complex ac magnetic susceptibility measurements. This
ferromagnetic insulating manganite is found to have frequency independent
ferromagnetic to paramagnetic transition temperature at around 140 K. At around
90 K (\approx T_f) the sample shows a second frequency dependent re - entrant
magnetic transition as explored through complex ac susceptibility measurements.
Non linear ac susceptibility measurements (higher harmonics of ac
susceptibility) have also been performed (with and without the superposition of
a dc magnetic field) to further investigate the origin of this frequency
dependence (dynamic behavior at this re-entrant magnetic transition).
Divergence of 3rd order susceptibility in the limit of zero exciting field
indicates a spin glass like freezing phenomena. However, large value of spin
relaxation time (?0= 10-8 s) and small value of coercivity (~22 Oe) obtained at
low temperature (below T_f) from critical slowing down model and dc magnetic
measurements, respectively, are in contrast with what generally observed in a
canonical spin glass (?0 = 10-12 - 10-14 s and very large value of coercivity
below freezing temperature). We have attributed our observation to the
formation of finite size ferromagnetic clusters which are formed as consequence
of intrinsic separation and undergo cluster glass like freezing below certain
temperature in this under doped manganite. The results are supported by the
electronic - and magneto - transport data.",1006.3733v1
2010-07-19,Magnetic properties of pseudomorphic epitaxial films of Pr_{0.7}Ca_{0.3}MnO_3 under different biaxial tensile stresses,"In order to analyse the effect of strain on the magnetic properties of
narrow-band manganites, the temperature and field dependent susceptibilities of
about 8.5 nm thick epitaxial Pr0.7Ca0.3MnO3 films, respectively grown on (001)
and (110) SrTiO3 substrates, have been compared. For ultrathin samples grown on
(001) SrTiO3, a bulk-like cluster-glass magnetic behaviour is found, indicative
of the possible coexistence of antiferromagnetic and ferromagnetic phases. On
the contrary, ultrathin films grown on (110) substrates show a robust
ferromagnetism, with a strong spontaneous magnetization of about 3.4 mB /Mn
atom along the easy axis. On the base of high resolution reciprocal space
mapping analyses performed by x-ray diffraction, the different behaviours are
discussed in terms of the crystallographic constraints imposed by the epitaxy
of Pr0.7Ca0.3MnO3 on SrTiO3. We suggest that for growth on (110) SrTiO3, the
tensile strain on the film c-axis, lying within the substrate plane, favours
the ferromagnetic phase, possibly by allowing a mixed occupancy and
hybridization of both in-plane and out-of-plane eg orbitals. Our data allow to
shed some physics of inhomogeneous states in manganites and on the nature of
their ferromagnetic insulating state.",1007.3078v1
2010-08-02,Spiral correlations in frustrated one-dimensional spin-1/2 Heisenberg J1-J2-J3 ferromagnets,"We use the coupled cluster method for infinite chains complemented by exact
diagonalization of finite periodic chains to discuss the influence of a
third-neighbor exchange J3 on the ground state of the spin-1/2 Heisenberg chain
with ferromagnetic nearest-neighbor interaction J1 and frustrating
antiferromagnetic next-nearest-neighbor interaction J2. A third-neighbor
exchange J3 might be relevant to describe the magnetic properties of the
quasi-one-dimensional edge-shared cuprates, such as LiVCuO4 or LiCu2O2. In
particular, we calculate the critical point J2^c as a function of J3, where the
ferromagnetic ground state gives way for a ground state with incommensurate
spiral correlations. For antiferromagnetic J3 the ferro-spiral transition is
always continuous and the critical values J2^c of the classical and the quantum
model coincide. On the other hand, for ferromagnetic J3 \lesssim
-(0.01...0.02)|J1| the critical value J2^c of the quantum model is smaller than
that of the classical model. Moreover, the transition becomes discontinuous,
i.e. the model exhibits a quantum tricritical point. We also calculate the
height of the jump of the spiral pitch angle at the discontinuous ferro-spiral
transition.",1008.0317v2
2010-08-30,"Intriguing complex magnetism of Co in RECoAsO (RE=La, Nd and Sm)","We synthesized bulk polycrystalline samples of RECoAsO (RE=La, Nd and Sm) by
solid state reaction route in an evacuated sealed quartz tube. All these
compounds are crystallized in a tetragonal structure with space group P4/nmm.
The Co, in these compounds is in itinerant ferromagnetic state with its
paramagnetic moment above 1.5 microB and the same orders ferromagnetically (FM)
with small saturation moment of around 0.20 microB below say 80K. This bulk
intrinsic magnetism of Co changes dramatically when nonmagnetic La is changed
by magnetic Sm and Nd. Although the itinerant ferromagnetism occurs below
80-100K with small saturation moment, typical anti-ferromagnetic (AFM)
transitions (TN1, TN2) are observed at 57K and 45K for Sm and at 69K and 14K
for Nd. The transition of Co spins from FM to AFM, for magnetic Sm and Nd in
RECoAsO is both field and temperature dependent. For applied fields below
100Oe, both TN1 and TN2 are seen, with intermediate fields below 1-2kOe only
TN1 and above say 5kOe the AFM transition is not observed. This is evidenced in
isothermal magnetization (MH) plots as well. It is clear that Sm/Nd magnetic
moments interact with the ordered Co spins in adjacent layer and thus
transforms the FM ordering to AFM. All the studied compounds are metallic in
nature, and their magneto-transport R(T)H follows the temperature and field
dependent FM-AFM transition of ordered Co spins.",1008.4999v3
2010-09-15,Magnetocaloric effect in manganites: metamagnetic transitions for magnetic refrigeration,"We present a study of the magnetocaloric effect in La5/8-yPryCa3/8MnO3
(y=0.3) and Pr0.5Ca0.09Sr0.41MnO3 manganites. The low temperature state of both
ystems is the result of a competition between the antiferromagnetic and
ferromagnetic phases. The samples display magnetocaloric effect evidenced in an
adiabatic temperature change during a metamagnetic transition from an
antiferromagnetic to a ferromagnetic phase . As additional features,
La5/8-yPryCa3/8MnO3 exhibits phase separation characterized by the coexistence
of antiferromagnetic and ferromagnetic phases and Pr0.5Ca0.09Sr0.41MnO3
displays inverse magnetocaloric effect in which temperature decreases while
applying an external magnetic field. In both cases, a significant part of the
magnetocaloric effect appears from non-reversible processes. As the traditional
thermodynamic description of the effect usually deals with reversible
transitions, we developed an alternative way to calculate the adiabatic
temperature change in terms of the change of the relative ferromagnetic
fraction induced by magnetic field. To evaluate our model, we performed direct
measurement of the sample's adiabatic temperature change by means of a
differential thermal analysis. An excellent agreement has been obtained between
experimental and calculated data. These results show that metamagnetic
transition in manganites play an important role in the study of magnetic
refrigeration.",1009.2914v1
2010-10-04,Defects induced ferromagnetism in Mn doped ZnO,"Single phase Mn doped (2 at %) ZnO samples have been synthesized by
solid-state reaction technique. Before the final sintering at 500 C, the mixed
powders have been milled for different milling periods (6, 24, 48 and 96
hours). The grain sizes of the samples are very close to each other (~ 32 \pm 4
nm). However, the defective state of the samples is different from each other
as manifested from the variation of magnetic properties and electrical
resistivity with milling time. All the samples have been found to be
ferromagnetic with clear hysteresis loops at room temperature. The maximum
value for saturation magnetization (0.11 {\mu}_B / Mn atom) was achieved for 96
hours milled sample. Electrical resistivity has been found to increase with
increasing milling time. The most resistive sample bears the largest saturation
magnetization. Variation of average positron lifetime with milling time bears a
close similarity with that of the saturation magnetization. This indicates the
key role played by open volume vacancy defects, presumably zinc vacancies near
grain surfaces, in inducing ferromagnetic order in Mn doped ZnO. To attain
optimum defect configuration favorable for ferromagnetism in this kind of
samples proper choice of milling period and annealing conditions is required.",1010.0547v1
2010-12-25,Charge inhomogeneities and transport in semiconductor heterostructures with a manganese $δ$-layer,"We study experimentally and theoretically the effects of disorder, nonlinear
screening, and magnetism in semiconductor heterostructures containing a
$\delta$-layer of Mn, where the charge carriers are confined within a quantum
well and hence both ferromagnetism and transport are two-dimensional (2D) and
differ qualitatively from their bulk counterparts. Anomalies in the electrical
resistance observed in both metallic and insulating structures can be
interpreted as a signature of significant ferromagnetic correlations. The
insulating samples turn out to be the most interesting as they can give us
valuable insights into the mechanisms of ferromagnetism in these
heterostructures. At low charge carrier densities, we show how the interplay of
disorder and nonlinear screening can result in the organization of the carriers
in the 2D transport channel into charge droplets separated by insulating
barriers. Based on such a droplet picture and including the effect of magnetic
correlations, we analyze the transport properties of this set of droplets,
compare it with experimental data, and find a good agreement between the model
calculations and experiment. Our analysis shows that the peak or shoulder-like
features observed in temperature dependence of resistance of 2D
heterostructures $\delta$-doped by Mn lie significantly below the Curie
temperature $T_{C}$ unlike the three-dimensional case, where it lies above and
close to $T_{C}$. We also discuss the consequences of our description for
understanding the mechanisms of ferromagnetism in the heterostructures under
study.",1012.5456v1
2011-01-20,Ensemble Inequivalence in the Ferromagnetic p-spin Model in Random Fields,"We study the effect that randomness has on long-range interacting systems by
using the ferromagnetic Ising model with $p$-body interactions in random
fields. The case with p=2 yields a phase diagram similar to that of previously
studied models and shows known features that inequivalence of the canonical and
microcanonical ensembles brings with it, for example negative specific heat in
a narrow region of the phase diagram. When p>2, however, the canonical phase
diagram is completely different from the microcanonical one. The temperature
does not necessarily determine the microcanonical phases uniquely, and thus the
ferromagnetic and paramagnetic phases are not separated in such a region of a
conventional phase diagram drawn with the temperature and field strength as the
axes. Below a certain value of the external field strength, part of the
ferromagnetic phase has negative specific heat. For large values of the
external field strength the ergodicity is broken before the phase transition
occurs for p>2. Moreover, for p>2, the Maxwell construction cannot be derived
in a consistent manner and therefore, in contrast to previous cases with
negative specific heat, the Maxwell construction does not bridge the gap
between the ensembles.",1101.3809v2
2011-01-21,Multiple spin state analysis applied to graphite-like carbon-based ferromagnetism,"Recent experiments indicate room-temperature ferromagnetism in graphite like
materials. This paper offers an multiple spin state analysis to find out the
origine of ferromagnetism in case of nano meter size graphene molecule.First
principle density function theory calculation (DFT-GGA with 631-G basis set) is
applied to nano meter size asymmetric graphene fifteen molecules. Major results
are,(1) Dihydrogenated zigzag edge molecule like C64H27 show that the most
stable (lowest molecular energy) spin state is the highest one as Sz=5/2.
Examples for spin density map of Sz=1/2,3/2 and 5/2 is shown in Fig.1. In other
molecules like C56H24, C64H25, C64H22 and C64H23 also show the highest spin
state most stable as shown in Fig.2. Energy difference between most stable spin
state and next one overcome temperature difference 1000K,which suggests a
stability of room temperature ferromagnetism. (2) Radical carbon zigzag edge
molecules are also analysed. As illustrated in Fig.3, in every five molecule,
also the highest spin state is most stable. (3) In contrast, nitrogen
substituted molecules like C59N5H22, C61N3H22 etc. show opposite result,that
is, the lowest spin state is most stable as shown in Fig.4. There are following
three key issues to bring those results. (A) Edge specified localized spin
arrangement. (B) Up-Up (also Down-Down) complex spin pairs inside of molecule.
(C) Optimized atom position rearrangement depend on the spin state. Detailed
mechanism will be discussed in the Symposium. Multiple spin state analysis is
very useful to design carbon based ferro-magnet and also to design new
spintronic devices.",1101.4082v1
2011-03-25,Effect of co-doping of donor and acceptor impurities in the ferromagnetic semiconductor Zn1-xCrxTe studied by soft x-ray magnetic circular dichroism,"We have performed x-ray absorption spectroscopy (XAS) and x-ray magnetic
circular dichroism (XMCD) studies of the diluted ferromagnetic semiconductor
Zn$_{1-\textit{x}}$Cr$_\textit{x}$Te doped with iodine (I) or nitrogen (N),
corresponding to electron or hole doping, respectively. From the shape of the
Cr $2p$ absorption peak in the XAS spectra, it was concluded that Cr ions in
the undoped, I-doped and lightly N-doped samples are divalent (Cr$^{2+}$),
while Cr$^{2+}$ and trivalent (Cr$^{3+}$) coexist in the heavily N-doped
sample. This result indicates that the doped nitrogen atoms act as acceptors
but that doped holes are located on the Cr ions. In the magnetic-field
dependence of the XMCD signal at the Cr $2p$ absorption edge, ferromagnetic
behaviors were observed in the undoped, I-doped, and lightly N-doped samples,
while ferromagnetism was considerably suppressed in heavily N-doped sample,
which is consistent with the results of magnetization measurements.",1103.4917v1
2011-04-24,Lambda- and Schottky-anomalies in solid-state phase transitions,"The origin of lambda and Schottky anomalies in solid-state phase transitions
are analyzed and illustrated. They are shown to be the latent heat of
nucleation-and-growth phase transitions.",1104.4637v1
2011-05-05,"Synthesis, magnetization and magneto transport study of RECoPO (RE = La, Nd & Sm)","We report the electrical, magneto transport and specific heat of the layered
polycrystalline RECoPO (RE = La, Nd and Sm) samples. These compounds are
iso-structural to recently discovered superconductor LaFeAs(O/F). Bulk
polycrystalline samples are synthesized by solid state reaction route in an
evacuated sealed quartz tube. All these compounds are crystallized in a
tetragonal structure with space group P4/nmm. The Cobalt in these compounds is
in itinerant state with its paramagnetic moment above 1.4\muB and the same
orders ferromagnetically (FM) with saturation moment of around 0.20\muB below
say 80K. Though, LaCoPO shows single paramagnetic (PM) to ferromagnetic (FM)
transition near 35K, the NdCoPO and SmCoPO exhibit successive PM-FM-AFM
transitions. Both FM and AFM transition temperatures vary with applied field.
Although the itinerant ferromagnetism occurs with small saturation moment,
typical anti-ferromagnetic (AFM) transitions (TN1, TN2) are observed at 69K and
14K for Nd and 57K and 45K for Sm. This FM-AFM transition of Co spins in NdCoPO
and SmCoPO is both field and temperature dependent. The Magneto-transport of
NdCoPO and SmCoPO distinctly follows their successive PM-FM-AFM transitions. It
is clear that Sm/Nd (4f) interacts with the Co (3d) in first time synthesized
Sm/NdCoPO.",1105.0971v2
2011-08-16,Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface,"LaAlO3 and SrTiO3 are insulating, nonmagnetic oxides, yet the interface
between them exhibits a two-dimensional electron system with high electron
mobility,1 superconductivity at low temperatures,2-6 and electric-field-tuned
metal-insulator and superconductorinsulator phase transitions.3,6-8 Bulk
magnetization and magnetoresistance measurements also suggest some form of
magnetism depending on preparation conditions5,9-11 and suggest a tendency
towards nanoscale electronic phase separation.10 Here we use local imaging of
the magnetization and magnetic susceptibility to directly observe a landscape
of ferromagnetism, paramagnetism, and superconductivity. We find submicron
patches of ferromagnetism in a uniform background of paramagnetism, with a
nonuniform, weak diamagnetic superconducting susceptibility at low temperature.
These results demonstrate the existence of nanoscale phase separation as
suggested by theoretical predictions based on nearly degenerate interface
sub-bands associated with the Ti orbitals.12,13 The magnitude and temperature
dependence of the paramagnetic response suggests that the vast majority of the
electrons at the interface are localized, and do not contribute to transport
measurements.3,6,7 In addition to the implications for magnetism, the existence
of a 2D superconductor at an interface with highly broken inversion symmetry
and a ferromagnetic landscape in the background suggests the potential for
exotic superconducting phenomena.",1108.3150v1
2011-08-24,Carrier-independent ferromagnetism and giant anomalous Hall effect in magnetic topological insulator,"Breaking the time-reversal symmetry of a topological insulator (TI) by
ferromagnetism can induce exotic magnetoelectric phenomena such as quantized
anomalous Hall (QAH) effect. Experimental observation of QAH effect in a
magnetically doped TI requires ferromagnetism not relying on the charge
carriers. We have realized the ferromagnetism independent of both polarity and
density of carriers in Cr-doped BixSb2-xTe3 thin films grown by molecular beam
epitaxy. Meanwhile, the anomalous Hall effect is found significantly enhanced
with decreasing carrier density, with the anomalous Hall angle reaching
unusually large value 0.2 and the zero field Hall resistance reaching one
quarter of the quantum resistance (h/e2), indicating the approaching of the QAH
regime. The work paves the way to ultimately realize QAH effect and other
unique magnetoelectric phenomena in TIs.",1108.4754v2
2011-10-11,Superposition of ferromagnetic and antiferromagnetic spin chains in the quantum magnet BaAg2Cu[VO4]2,"Based on density functional theory band structure calculations, quantum
Monte-Carlo simulations, and high-field magnetization measurements, we address
the microscopic magnetic model of BaAg2Cu[VO4]2 that was recently proposed as a
spin-1/2 anisotropic triangular lattice system. We show that the actual physics
of this compound is determined by a peculiar superposition of ferromagnetic and
antiferromagnetic uniform spin chains with nearest-neighbor exchange couplings
of Ja(1) ~ -19 K and Ja(2) ~ 9.5 K, respectively. The two chains featuring
different types of the magnetic exchange perfectly mimic the specific heat of a
triangular spin lattice, while leaving a clear imprint on the magnetization
curve that is incompatible with the triangular-lattice model. Both
ferromagnetic and antiferromagnetic spin chains run along the crystallographic
'a' direction, and slightly differ in the mutual arrangement of the magnetic
CuO4 plaquettes and non-magnetic VO4 tetrahedra. These subtle structural
details are, therefore, crucial for the ferromagnetic or antiferromagnetic
nature of the exchange couplings, and put forward the importance of
comprehensive microscopic modeling for a proper understanding of quantum spin
systems in transition-metal compounds.",1110.2329v2
2012-03-30,Electron cooling in diffusive normal metal - superconductor tunnel junctions with a spin-valve ferromagnetic interlayer,"We investigate heat and charge transport through a diffusive SIF1F2N tunnel
junction, where N (S) is a normal (superconducting) electrode, I is an
insulator layer and F1,2 are two ferromagnets with arbitrary direction of
magnetization. The flow of an electric current in such structures at subgap
bias is accompanied by a heat transfer from the normal metal into the
superconductor, which enables refrigeration of electrons in the normal metal.
We demonstrate that the refrigeration efficiency depends on the strength of the
ferromagnetic exchange field h and the angle {\alpha} between the
magnetizations of the two F layers. As expected, for values of h much larger
than the superconducting order parameter \Delta, the proximity effect is
suppressed and the efficiency of refrigeration increases with respect to a NIS
junction. However, for h \sim \Delta the cooling power (i.e. the heat flow out
of the normal metal reservoir) has a non-monotonic behavior as a function of h
showing a minimum at h \approx \Delta. We also determine the dependence of the
cooling power on the lengths of the ferromagnetic layers, the bias voltage, the
temperature, the transmission of the tunneling barrier and the magnetization
misalignment angle {\alpha}.",1203.6735v1
2012-10-18,Magnetocaloric effect and Magnetothermopower in the room temperature ferromagnet Pr0.6Sr0.4MnO3,"We have investigated magnetization(M), magnetocaloric effect(MCE) and
magnetothermopower(MTEP) in polycrystalline Pr0.6Sr0.4MnO3, which shows a
second-order paramagnetic to ferromagnetic transition near room temperature (TC
= 305 K). However, field-cooled M(T) within the long range ferromagnetic state
shows an abrupt decrease at TS = 86 K for H < 3 T. The low temperature
transition is first-order in nature as suggested by the hysteresis in M(T) and
exothermic/endothermic peaks in differential thermal analysis for cooling and
warming cycles. The anomaly at TS is attributed to a structural transition from
orthorhombic to monoclinic phase. The magnetic entropy change is negative at TC
but changes to positive at TS. Thermopower (Q) is negative from 350 K to 20 K,
shows a rapid decrease at TC and a small cusp around TS in zero field. The MTEP
reaches a maximum value of 25% for deltaH = 3 T around TC which is much higher
than 15% dc magnetoresistance for the same field change. A linear relation
between MTEP and magnetoresistance, and between delta Sm and Delta Q are found
near TC. Further, ac magnetotransport in low dc magnetic fields (H less than or
equal to 1 kOe), critical analysis of the paramagnetic to ferromagnetic
transition and scaling behavior of the magnetic entropy change versus a reduced
temperature under different magnetic fields are also reported.",1210.5216v1
2012-10-22,Large vortex state in ferromagnetic disks,"Magnetic vortices in soft ferromagnetic nano-disks have been extensively
studied for at least several decades both for their fundamental (as a ""live""
macroscopic realization of a field theory model of an elementary particle) as
well as applied value for high-speed high-density power-independent information
storage. Here it is shown that there is another stable vortex state with large
thickness-dependent core profile in nano-scale ferromagnetic disks of several
exchange lengths in size. Its energy is computed numerically (in the framework
of Magnetism@home distributed computing project) and its stability is studied
analytically, which allows to plot it on magnetic phase diagram. In cylinders
of certain geometries large vortices exist on par with classical ones, while
being separated by an energy barrier, controllable by tuning the geometry and
material of ferromagnetic disk. They can be an excellent candidate for magnetic
information storage not only because the resulting disk sizes are among the
smallest, able to support magnetic vortices, but also because it is the closest
to the classical vortex state of all other known metastable states of magnetic
nano-cylinder. It means that memory, based on switching between these two types
of magnetic vortices, may, potentially, achieve the highest possible rate of
switching.",1210.5960v3
2012-10-23,Numerical Simulations of Laser Induced Magnetic Bloch Oscillations,"We propose to use a laser to generate magnetic Bloch oscillations in one
dimensional easy-axis ferromagnets at low temperatures. This proposal is
investigated numerically in details for material parameters relevant for
CoCl2*2H2O.",1210.6200v1
2012-12-20,Macroscopic quantum tunneling and coherence of spins,"We present a review of suppression of tunneling rate (energy splitting) for
half-odd-integer spins in ferromagnetic and antiferromagnetic particles. We
also review the quenching of the tunneling rate in the presence of a magnetic
field.",1212.4904v1
2013-01-11,Spin polarization of electrons in quantum wires,"The total energy of a quasi-one-dimensional electron system is calculated
using density functional theory. It is shown that spontaneous ferromagnetic
state in quantum wire occurs at low one-dimensional electron density. The
critical electron density below which electrons are in spin-polarized state is
estimated analytically.",1301.2544v1
2013-03-28,New Diluted Ferromagnetic Semiconductor isostructural to 122 type iron pnictide superconductor with TC up to 180 K,"Diluted magnetic semiconductors (DMS) have received much attention due to its
potential applications to spintronics devices. A prototypical system (Ga,Mn)As
has been widely studied since 1990s. The simultaneous spin and charge doping
via hetero-valence (Ga3+,Mn2+) substitution, however, resulted in severely
limited solubility without availability of bulk specimens. Previously we
synthesized a new diluted ferromagnetic semiconductor of bulk Li(Zn,Mn)As with
Tc up to 50K, where isovalent (Zn,Mn) spin doping was separated from charge
control via Li concentrations. Here we report the synthesis of a new diluted
ferromagnetic semiconductor (Ba1-xKx)(Zn1-yMny)2As2, isostructural to iron 122
system, where holes are doped via (Ba2+, K1+), while spins via (Zn2+,Mn2+)
substitutions. Bulk samples with x=0.1-0.3 and y=0.05-0.15 exhibit
ferromagnetic order with TC up to 180K, comparable to that of record high Tc
for Ga(MnAs), significantly enhanced than Li(Zn,Mn)As. Moreover the
(Ba,K)(Zn,Mn)2As2 shares the same 122 crystal structure with semiconducting
BaZn2As2, antiferromagnetic BaMn2As2, and superconducting (Ba,K)Fe2As2, which
makes them promising to the development of multilayer functional devices.",1303.7157v1
2013-04-08,Dynamical barriers of pure and random ferromagnetic Ising models on fractal lattices,"We consider the stochastic dynamics of the pure and random ferromagnetic
Ising model on the hierarchical diamond lattice of branching ratio $K$ with
fractal dimension $d_f=(\ln (2K))/\ln 2$. We adapt the Real Space
Renormalization procedure introduced in our previous work [C. Monthus and T.
Garel, J. Stat. Mech. P02037 (2013)] to study the equilibrium time $t_{eq}(L)$
as a function of the system size $L$ near zero-temperature. For the pure Ising
model, we obtain the behavior $t_{eq}(L) \sim L^{\alpha} e^{\beta 2J L^{d_s}} $
where $d_s=d_f-1$ is the interface dimension, and we compute the prefactor
exponent $\alpha$. For the random ferromagnetic Ising model, we derive the
renormalization rules for dynamical barriers $B_{eq}(L) \equiv (\ln
t_{eq}/\beta)$ near zero temperature. For the fractal dimension $d_f=2$, we
obtain that the dynamical barrier scales as $ B_{eq}(L)= c L+L^{1/2} u$ where
$u$ is a Gaussian random variable of non-zero-mean. While the non-random term
scaling as $L$ corresponds to the energy-cost of the creation of a system-size
domain-wall, the fluctuation part scaling as $L^{1/2}$ characterizes the
barriers for the motion of the system-size domain-wall after its creation. This
scaling corresponds to the dynamical exponent $\psi=1/2$, in agreement with the
conjecture $\psi=d_s/2$ proposed in [C. Monthus and T. Garel, J. Phys. A 41,
115002 (2008)]. In particular, it is clearly different from the droplet
exponent $\theta \simeq 0.299$ involved in the statics of the random
ferromagnet on the same lattice.",1304.2134v1
2013-06-08,Observation of a Berry phase anti-damping spin-orbit torque,"Recent observations of current-induced magnetization switching at
ferromagnet/normal-conductor interfaces have important consequences for future
magnetic memory technology. In one interpretation, the switching originates
from carriers with spin-dependent scattering giving rise to a relativistic
anti-damping spin-orbit torque (SOT) in structures with broken space-inversion
symmetry. The alternative interpretation combines the relativistic spin Hall
effect (SHE), making the normal-conductor an injector of a spin-current, with
the non-relativistic spin-transfer torque (STT) in the ferromagnet. Remarkably,
the SHE in these experiments originates from the Berry phase effect in the band
structure of a clean crystal and the anti-damping STT is also based on a
disorder-independent transfer of spin from carriers to magnetization. Here we
report the observation of an anti-damping SOT stemming from an analogous Berry
phase effect to the SHE. The SOT alone can therefore induce magnetization
dynamics based on a scattering-independent principle. The ferromagnetic
semiconductor (Ga,Mn)As we use has a broken space-inversion symmetry in the
crystal. This allows us to consider a bare ferromagnetic element which
eliminates by design any SHE related contribution to the spin torque. We
provide an intuitive picture of the Berry phase origin of the anti-damping SOT
and a microscopic modeling of measured data.",1306.1893v1
2013-06-14,Magnetic structures of Mn3-xFexSn2: an experimental and theoretical study,"We investigate the magnetic structure of Mn3-xFexSn2 using neutron powder
diffraction experiments and electronic structure calculations. These alloys
crystallize in the orthorhombic Ni3Sn2 type of structure (Pnma) and comprise
two inequivalent sites for the transition metal atoms (4c and 8d) and two Sn
sites (4c and 4c). The neutron data show that the substituting Fe atoms
predominantly occupy the 4c transition metal site and carry a lower magnetic
moment than Mn atoms. Four kinds of magnetic structures are encountered as a
function of temperature and composition: two simple ferromagnetic structures
(with the magnetic moments pointing along the b or c axis) and two canted
ferromagnetic arrangements (with the ferromagnetic component pointing along the
b or c axis). Electronic structure calculations results agree well with the
low-temperature experimental magnetic moments and canting angles throughout the
series. Comparisons between collinear and non-collinear computations show that
the canted state is stabilized by a band mechanism through the opening of a
hybridization gap. Synchrotron powder diffraction experiments on Mn3Sn2 reveal
a weak monoclinic distortion at low temperature (90.08 deg at 175 K). This
lowering of symmetry could explain the stabilization of the c-axis canted
ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a
circumstance that would otherwise require unusually large high-order terms in
the spin Hamiltonian.",1306.3339v1
2013-07-12,Dilute ferromagnetic semiconductors: Physics and spintronic structures,"This review compiles results of experimental and theoretical studies on thin
films and quantum structures of semiconductors with randomly distributed Mn
ions, which exhibit spintronic functionalities associated with collective
ferromagnetic spin ordering. Properties of p-type Mn-containing III-V as well
as II-VI, V_2-VI_3, IV-VI, I-II-V, and elemental group IV semiconductors are
described paying particular attention to the most thoroughly investigated
system (Ga,Mn)As that supports the hole-mediated ferromagnetic order up to 190
K for the net concentration of Mn spins below 10%. Multilayer structures
showing efficient spin injection and spin-related magnetotransport properties
as well as enabling magnetization manipulation by strain, light, electric
fields, and spin currents are presented together with their impact on metal
spintronics. The challenging interplay between magnetic and electronic
properties in topologically trivial and non-trivial systems is described,
emphasizing the entangled roles of disorder and correlation at the carrier
localization boundary. Finally, the case of dilute magnetic insulators is
considered, such as (Ga,Mn)N, where low temperature spin ordering is driven by
short-ranged superexchange that is ferromagnetic for certain charge states of
magnetic impurities.",1307.3429v3
2013-11-03,Thickness-dependent ferromagnetic metal to paramagnetic insulator transition in La$_{0.6}$Sr$_{0.4}$MnO$_3$ thin films studied by x-ray magnetic circular dichroism,"Metallic transition-metal oxides undergo a metal-to-insulator transition
(MIT) as the film thickness decreases across a ritical thickness of several
monolayers (MLs), but its driving mechanism remains controversial. We have
studied the thickness-dependent MIT of the ferromagnetic metal
La$_{0.6}$Sr$_{0.4}$MnO$_3$ by x-ray absorption spectroscopy and x-ray magnetic
circular dichroism. As the film thickness was decreased across the critical
thickness of the MIT (6-8 ML), a gradual decrease of the ferromagnetic signals
and a concomitant increase of paramagnetic signals were observed, while the Mn
valence abruptly decreased towards Mn$^{3+}$. These observations suggest that
the ferromagnetic phase gradually and most likely inhomogeneously turns into
the paramagnetic phase and both phases abruptly become insulating at the
critical thickness.",1311.0520v4
2013-11-26,"Recent Progress in III-V based ferromagnetic semiconductors: Band structure, Fermi level, and tunneling transport","Spin-based electronics or spintronics is an emerging field, in which we try
to utilize spin degrees of freedom as well as charge transport in materials and
devices. While metal-based spin-devices, such as magnetic-field sensors and
magnetoresistive random access memory using giant magnetoresistance and
tunneling magnetoresistance, are already put to practical use,
semiconductor-based spintronics has greater potential for expansion because of
good compatibility with existing semiconductor technology. Many
semiconductor-based spintronics devices with useful functionalities have been
proposed and explored so far. To realize those devices and functionalities, we
definitely need appropriate materials which have both the properties of
semiconductors and ferromagnets. Ferromagnetic semiconductors (FMS), which are
alloy semiconductors containing magnetic atoms such as Mn and Fe, are one of
the most promising classes of materials for this purpose, and thus have been
intensively studied for the past two decades. Here, we review the recent
progress in the studies of the most prototypical III-V based FMS, p-type
(GaMn)As, and its heterostructures with focus on tunneling transport, Fermi
level, and bandstructure. Furthermore, we cover the properties of a new n-type
FMS, (InFe)As, which shows electron-induced ferromagnetism. These FMS materials
having zinc-blende crystal structure show excellent compatibility with
well-developed III-V heterostructures and devices.",1311.6616v1
2013-12-13,On Vortex Solutions of Landau-Lifshitz Equations,"We study the Landau-Lifshitz equation of ferromagnetism on $\mathbb{R}^2$
with an easy-axis anisotropy. We give the necessary condition for the existence
of the finite energy vortex solutions and show the behaviors of the solutions.",1312.3816v1
2014-02-26,Ferromagnetism of magnetic impurities coupled indirectly via conduction electrons: Insights from various theoretical approaches,"The magnetic ground-state properties of the periodic Anderson model with a
regular depletion of the correlated sites are analyzed within different
theoretical approaches. We consider the model on the one-dimensional chain and
on the two-dimensional square lattice with hopping between nearest neighbors.
At half-filling and with correlated impurities present at every second site,
the depleted Anderson lattice is the most simple system where the indirect
magnetic coupling mediated by the conduction electrons is ferromagnetic. We
discuss the underlying electronic structure and the possible mechanisms that
result in ferromagnetic long-range order. To this end, different numerical and
analytical concepts are applied to the depleted Anderson and also to the
related depleted Kondo lattice and are contrasted with each other. This
includes numerical approaches, i.e. Hartree-Fock theory, density-matrix
renormalization and dynamical mean-field theory, as well as analytical
concepts, namely a variant of the Lieb-Mattis theorem and the concept of
flat-band ferromagnetism, and finally perturbative approaches, i.e. the
effective RKKY exchange in the limit of weak and the ""inverse indirect magnetic
exchange"" in the limit of strong coupling between the conduction band and the
impurities.",1402.6657v2
2014-07-20,A walk in the statistical mechanical formulation of neural networks,"Neural networks are nowadays both powerful operational tools (e.g., for
pattern recognition, data mining, error correction codes) and complex
theoretical models on the focus of scientific investigation. As for the
research branch, neural networks are handled and studied by psychologists,
neurobiologists, engineers, mathematicians and theoretical physicists. In
particular, in theoretical physics, the key instrument for the quantitative
analysis of neural networks is statistical mechanics. From this perspective,
here, we first review attractor networks: starting from ferromagnets and
spin-glass models, we discuss the underlying philosophy and we recover the
strand paved by Hopfield, Amit-Gutfreund-Sompolinky. One step forward, we
highlight the structural equivalence between Hopfield networks (modeling
retrieval) and Boltzmann machines (modeling learning), hence realizing a deep
bridge linking two inseparable aspects of biological and robotic spontaneous
cognition. As a sideline, in this walk we derive two alternative (with respect
to the original Hebb proposal) ways to recover the Hebbian paradigm, stemming
from ferromagnets and from spin-glasses, respectively. Further, as these notes
are thought of for an Engineering audience, we highlight also the mappings
between ferromagnets and operational amplifiers and between antiferromagnets
and flip-flops (as neural networks -built by op-amp and flip-flops- are
particular spin-glasses and the latter are indeed combinations of ferromagnets
and antiferromagnets), hoping that such a bridge plays as a concrete
prescription to capture the beauty of robotics from the statistical mechanical
perspective.",1407.5300v1
2014-10-01,Evidence for magnetic clusters in Ni$_{1-x}$V$_{x}$ close to the quantum critical concentration,"The d-metal alloy Ni$_{1-x}$V$_{x}$ undergoes a quantum phase transition from
a ferromagnetic ground state to a paramagnetic ground state as the vanadium
concentration $x$ is increased. We present magnetization, ac-susceptibility and
muon-spin relaxation data at several vanadium concentrations near the critical
concentration $x_c \approx11.6%$ at which the onset of ferromagnetic order is
suppressed to zero temperature. Below $x_c$, the muon data reveal a broad
magnetic field distribution indicative of long-range ordered ferromagnetic
state with spatial disorder. We show evidence of magnetic clusters in the
ferromagnetic phase and close to the phase boundary in this disordered
itinerant system as an important generic ingredient of a disordered quantum
phase transition. In contrast, the temperature dependence of the magnetic
susceptibility above $x_c$ is best described in terms of a magnetic quantum
Griffiths phase with a power-law distribution of fluctuation rates of dynamic
magnetic clusters. At the lowest temperatures, the onset of a short-range
ordered cluster-glass phase is recognized by an increase in the muon
depolarization in transverse fields and maxima in ac-susceptibility.",1410.0094v1
2014-10-29,"(Ca,Na)(Zn,Mn)2As2: a new spin & charge doping decoupled diluted ferromagnetic semiconductor with hexagonal CaAl2Si2 structure","Here we report the successful synthesis of a spin- & charge-decoupled diluted
magnetic semiconductor (Ca,Na)(Zn,Mn)2As2, crystallizing into the hexagonal
CaAl2Si2 structure. The compound shows a ferromagnetic transition with a Curie
temperature up to 33 K with 10% Na doping, which gives rise to carrier density
of np~10^20 cm^-3. The new DMS is a soft magnetic material with HC<400 Oe. The
anomalous Hall effect is observed below the ferromagnetic ordering temperature.
With increasing Mn doping, ferromagnetic order is accompanied by an interaction
between the local spin and mobile charge, giving rise to a minimum in
resistivity at low temperatures and localizing the conduction electrons. The
system provides an ideal platform for studying the interaction of the local
spins and conduction electrons.",1410.8015v1
2014-12-02,Interplay of spin-orbit torque and thermoelectric effects in ferromagnet/normal metal bilayers,"We present harmonic transverse voltage measurements of current-induced
thermoelectric and spin-orbit torque (SOT) effects in ferromagnet/normal metal
bilayers, in which thermal gradients produced by Joule heating and SOT coexist
and give rise to ac transverse signals with comparable symmetry and magnitude.
Based on the symmetry and field-dependence of the transverse resistance, we
develop a consistent method to separate thermoelectric and SOT measurements. By
addressing first ferromagnet/light metal bilayers with negligible spin-orbit
coupling, we show that in-plane current injection induces a vertical thermal
gradient whose sign and magnitude are determined by the resistivity difference
and stacking order of the magnetic and nonmagnetic layers. We then study
ferromagnet/heavy metal bilayers with strong spin-orbit coupling, showing that
second harmonic thermoelectric contributions to the transverse voltage may lead
to a significant overestimation of the antidamping SOT. We find that
thermoelectric effects are very strong in Ta(6nm)/Co(2.5nm) and negligible in
Pt(6nm)/Co(2.5nm) bilayers. After including these effects in the analysis of
the transverse voltage, we find that the antidamping SOTs in these bilayers,
after normalization to the magnetization volume, are comparable to those found
in thinner Co layers with perpendicular magnetization, whereas the field-like
SOTs are about an order of magnitude smaller.",1412.0865v1
2015-02-26,Chiral anomaly and transport in Weyl metals,"We present an overview of our recent work on transport phenomena in Weyl
metals, which may be connected to their nontrivial topological properties,
particularly to chiral anomaly. We argue that there are two basic phenomena,
which are related to chiral anomaly in Weyl metals: Anomalous Hall Effect (AHE)
and Chiral Magnetic Effect (CME). While AHE is in principle present in any
ferromagnetic metal, we demonstrate that a magnetic Weyl metal is distinguished
from an ordinary ferromagnetic metal by the absence of the extrinsic and the
Fermi surface part of the intrinsic contributions to the AHE, as long as the
Fermi energy is sufficiently close to the Weyl nodes. The AHE in a Weyl metal
is thus shown to be a purely intrinsic, universal property, fully determined by
the location of the Weyl nodes in the first Brillouin zone. In other words, a
ferromagnetic Weyl metal may be thought of as the only example of a
ferromagnetic metal with a purely intrinsic AHE. We further develop a fully
microscopic theory of diffusive magnetotransport in Weyl metals. We derive
coupled diffusion equations for the total and axial (i.e. node-antisymmetric)
charge densities and show that chiral anomaly manifests as a
magnetic-field-induced coupling between them. We demonstrate that an
experimentally-observable consequence of CME in magnetotransport in Weyl metals
is a quadratic negative magnetoresistance, which will dominate all other
contributions to magnetoresistance under certain conditions and may be regarded
as a smoking-gun transport characteristic, unique to Weyl metals.",1502.07609v1
2015-03-24,Itinerant ferromagnetism in the As 4$p$ conduction band of Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ identified by x-ray magnetic circular dichroism,"X-ray magnetic circular dichroism (XMCD) measurements on single-crystal and
powder samples of Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ show that the
ferromagnetism below $T_{\textrm{C}}\approx$ 100 K arises in the As $4p$
conduction band. No XMCD signal is observed at the Mn x-ray absorption edges.
Below $T_{\textrm{C}}$, however, a clear XMCD signal is found at the As $K$
edge which increases with decreasing temperature. The XMCD signal is absent in
data taken with the beam directed parallel to the crystallographic $\textrm{c}$
axis indicating that the orbital magnetic moment lies in the basal plane of the
tetragonal lattice. These results show that the previously reported itinerant
ferromagnetism is associated with the As $4p$ conduction band and that distinct
local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular
easy axes coexist in this compound at low temperature.",1503.07197v2
2015-08-19,Independent tuning of electronic properties and induced ferromagnetism in topological insulators with heterostructure approach,"The quantum anomalous Hall effect (QAHE) has been recently demonstrated in
Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures
below 100 mK. In those materials, the spins of unfilled d-electrons in the
transition metal dopants are exchange coupled to develop a long-range
ferromagnetic order, which is essential for realizing QAHE. However, the
addition of random dopants does not only introduce excess charge carriers that
require readjusting the Bi/Sb ratio, but also unavoidably introduces
paramagnetic spins that can adversely affect the chiral edge transport in QAHE.
In this work, we show a heterostructure approach to independently tune the
electronic and magnetic properties of the topological surface states in
(BixSb1-x)2Te3 without resorting to random doping of transition metal elements.
In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium
iron garnet (YIG), a high Curie temperature (~ 550 K) magnetic insulator, we
find that the TI surface in contact with YIG becomes ferromagnetic via
proximity coupling which is revealed by the anomalous Hall effect (AHE). The
Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is
uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is
varied, the AHE resistivity scales with the longitudinal resistivity. In this
approach, we decouple the electronic properties from the induced ferromagnetism
in TI. The independent optimization provides a pathway for realizing QAHE at
higher temperatures, which is important for novel spintronic device
applications.",1508.04719v1
2015-09-07,Josephson current in a normal-metal nanowire coupled to superconductor/ferromagnet/superconductor junction,"We consider superconducting nanowire proximity coupled to superconductor /
ferromagnet / superconductor junction, where the magnetization penetrates into
superconducting segment in nanowire decaying as $\sim\exp[-\frac{\mid n
\mid}{\xi}]$ with site index $n$ and the decay length $\xi$. We tune chemical
potential and spin-orbit coupling so that topological superconducting regime
hosting Majorana fermion is realized for long $\xi$. We find that when $\xi$
becomes shorter, zero energy state at the interface between superconductor and
ferromagnet splits into two away from zero energy. Accordingly, the behavior of
Josephson current is drastically changed due to this ""zero mode-non-zero mode
crossover"". By tuning the model parameters, we find an almost second-harmonic
current-phase relation, $\sin2\varphi$, with phase difference $\varphi$. Based
on the analysis of Andreev bound state (ABS), we clarify that current-phase
relation is determined by coupling of the states within the energy gap. We find
that the emergence of crossing points of ABS is a key ingredient to generate
$\sin2\varphi$ dependence in current-phase relation. We further study both the
energy and $\varphi$ dependence of pair amplitudes in the ferromagnetic region.
For long $\xi$, odd-frequency spin-triplet $s$-wave component is dominant. The
magnitude of the odd-frequency pair amplitude is enhanced at the energy level
of ABS.",1509.01914v2
2016-01-21,Real-space renormalization for the finite temperature statics and dynamics of the Dyson Long-Ranged Ferromagnetic and Spin-Glass models,"The finite temperature dynamics of the Dyson hierarchical classical spins
models is studied via real-space renormalization rules concerning the couplings
and the relaxation times. For the ferromagnetic model involving Long-Ranged
coupling $J(r) \propto r^{-1-\sigma}$ in the region $1/2<\sigma<1$ where there
exists a non-mean-field-like thermal Ferromagnetic-Paramagnetic transition, the
RG flows are explicitly solved: the characteristic relaxation time $\tau(L)$
follows the critical power-law $\tau(L)\propto L^{z_c(\sigma)} $ at the phase
transition and the activated law $\ln \tau(L)\propto L^{\psi} $ with
$\psi=1-\sigma$ in the ferromagnetic phase. For the Spin-Glass model involving
random Long-Ranged couplings of variance $\overline{J^2(r)} \propto
r^{-2\sigma}$ in the region $2/3<\sigma<1$ where there exists a
non-mean-field-like thermal SpinGlass-Paramagnetic transition, the coupled RG
flows of the couplings and of the relaxation times are studied numerically :
the relaxation time $\tau(L)$ follows some power-law $\tau(L)\propto
L^{z_c(\sigma)} $ at criticality and the activated law $\ln \tau(L)\propto
L^{\psi} $ in the Spin-Glass phase with the dynamical exponent
$\psi=1-\sigma=\theta$ coinciding with the droplet exponent governing the flow
of the couplings $J(L) \propto L^{\theta} $.",1601.05643v2
2016-02-08,A Precessing Ferromagnetic Needle Magnetometer,"A ferromagnetic needle is predicted to precess about the magnetic field axis
at a Larmor frequency $\Omega$ under conditions where its intrinsic spin
dominates over its rotational angular momentum, $N\hbar \gg I\Omega$ ($I$ is
the moment of inertia of the needle about the precession axis and $N$ is the
number of polarized spins in the needle). In this regime the needle behaves as
a gyroscope with spin $N\hbar$ maintained along the easy axis of the needle by
the crystalline and shape anisotropy. A precessing ferromagnetic needle is a
correlated system of $N$ spins which can be used to measure magnetic fields for
long times. In principle, by taking advantage of rapid averaging of quantum
uncertainty, the sensitivity of a precessing needle magnetometer can far
surpass that of magnetometers based on spin precession of atoms in the gas
phase. Under conditions where noise from coupling to the environment is
subdominant, the scaling with measurement time $t$ of the quantum- and
detection-limited magnetometric sensitivity is $t^{-3/2}$. The phenomenon of
ferromagnetic needle precession may be of particular interest for precision
measurements testing fundamental physics.",1602.02818v2
2016-03-31,"Energetic, electronic and magnetic properties of Mn-dimers on reconstructed (001) GaAs surfaces","We study energetic, magnetic, and electronic properties of diluted
substitutional Mn-pairs on the reconstructed $(001)$ GaAs surfaces. The studies
are based on first-principles calculations in the framework of the density
functional theory. We demonstrate that the stability of the systems strongly
depends on the position, orientation, and the distance between the Mn-atoms
constituting the pair. Independently of the considered surface reconstruction
pattern, the Mn-pairs with Mn-atoms being the nearest neighbors (NN) on
cationic sublattice turn out to be energetically more favorable than the pairs
with the larger distance between the Mn-atoms. However, the preferential
build-up orientation of the Mn-NN-pair depends on the surface reconstruction
and is parallel either to $[110]$ or $[1\bar{1}0]$ crystallographic direction.
We reveal also the mechanisms of the magnetic ordering of Mn-NN-pairs. The
Mn-NN-pairs along the $[110]$ crystallographic direction exhibit always
ferromagnetic alignment of Mn spins, whereas the spins in the Mn-NN-pairs along
$[1\bar{1}0]$ direction are mostly anti-ferromagnetically aligned. In the
electronic structure of the systems containing Mn-pairs with ferromagnetically
aligned spins, we observe the valence band hole states in the neighborhood of
Fermi energy. This indicates that the surface ferromagnetism in this prototype
of dilute magnetic semiconductors can be explained in terms of the $p$-$d$
Zener model.",1603.09606v4
2016-04-12,An invisible non-volatile solid-state memory,"Information technologies require entangling data stability with encryption
for a next generation of secure data storage. Current magnetic memories,
ranging from low-density stripes up to high-density hard drives, can ultimately
be detected using routinely available probes or manipulated by external
magnetic perturbations. Antiferromagnetic resistors feature unrivalled
robustness but the stable resistive states reported scarcely differ by more
than a fraction of a percent at room temperature. Here we show that the
metamagnetic (ferromagnetic to antiferromagnetic) transition in intermetallic
Fe0.50Rh0.50 can be electrically controlled in a magnetoelectric
heterostructure to reveal or cloak a given ferromagnetic state. From an aligned
ferromagnetic phase, magnetic states are frozen into the antiferromagnetic
phase by the application of an electric field, thus eliminating the stray field
and likewise making it insensitive to external magnetic field. Application of a
reverse electric field reverts the antiferromagnetic state to the original
ferromagnetic state. Our work demonstrates the building blocks of a feasible,
extremely stable, non-volatile, electrically addressable, low-energy
dissipation, magnetoelectric multiferroic memory.",1604.03383v2
2016-06-28,Andreev bound states in superconductor/ferromagnet point contact Andreev reflection spectra,"As charge carriers traverse a single superconductor ferromagnet interface
they experience an additional spin-dependent phase angle which results in spin
mixing and the formation of a bound state called the Andreev Bound State. This
state is an essential component in the generation of long range spin triplet
proximity induced superconductivity and yet the factors controlling the degree
of spin mixing and the formation of the bound state remain elusive. Here we
demonstrate that point contact Andreev reflection can be used to detect the
bound state and extract the resulting spin mixing angle. By examining spectra
taken from La1.15Sr1.85Mn2O7 single crystal - Pb junctions, together with a
compilation of literature data on highly spin polarised systems, we show that
the existence of the Andreev Bound State both resolves a number of long
standing controversies in the Andreev literature as well as defining a route to
quantify the strength of spin mixing at superconductor-ferromagnet interfaces.
Intriguingly we find that for these high transparency junctions, the spin
mixing angle appears to take a relatively narrow range of values across all the
samples studied. The ferromagnets we have chosen to study share a common
property in terms of their spin arrangement, and our observations may point to
the importance of this property in determining the spin mixing angle under
these circumstances.",1606.08619v1
2016-07-13,Half-Metallic Superconducting Triplet Spin Valve,"We theoretically study a finite size $SF_1NF_2$ spin valve, where a normal
metal ($N$) insert separates a thin standard ferromagnet ($F_1$) and a thick
half-metallic ferromagnet ($F_2$). For sufficiently thin superconductor ($S$)
widths close to the coherence length $\xi_0$, we find that changes to the
relative magnetization orientations in the ferromagnets can result in
substantial variations in the transition temperature $T_c$, consistent with
experiment [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Our results
demonstrate that, in good agreement with the experiment, the variations are
largest in the case where $F_2$ is in a half-metallic phase and thus supports
only one spin direction. To pinpoint the origins of this strong spin-valve
effect, both the equal-spin $f_1$ and opposite-spin $f_0$ triplet correlations
are calculated using a self-consistent microscopic technique. We find that when
the magnetization in $F_1$ is tilted slightly out-of-plane, the $f_1$ component
can be the dominant triplet component in the superconductor. The coupling
between the two ferromagnets is discussed in terms of the underlying spin
currents present in the system. We go further and show that the zero energy
peaks of the local density of states probed on the $S$ side of the valve can be
another signature of the presence of superconducting triplet correlations. Our
findings reveal that for sufficiently thin $S$ layers, the zero energy peak at
the $S$ side can be larger than its counterpart in the $F_2$ side.",1607.03899v1
2016-07-25,On the Explanation of the Paramagnetic Meissner Effect in Superconductor/Ferromagnet Heterostructures,"An increase of the magnetic moment in superconductor/ferromagnet (S/F)
bilayers V(40nm)/F [F$=$Fe(1,3nm), Co(3nm), Ni(3nm)] was observed using SQUID
magnetometry upon cooling below the superconducting transition temperature Tc
in magnetic fields of 10 Oe to 50 Oe applied parallel to the sample surface. A
similar increase, often called the paramagnetic Meissner effect (PME), was
observed before in various superconductors and superconductor/ferromagnet
systems. To explain the PME effect in the presented S/F bilayers a model based
on a row of vortices located at the S/F interface is proposed. According to the
model the magnetic moment induced below Tc consists of the paramagnetic
contribution of the vortex cores and the diamagnetic contribution of the
vortex-free region of the S layer. Since the thickness of the S layer is found
to be 3-4 times less than the magnetic field penetration depth, this latter
diamagnetic contribution is negligible. The model correctly accounts for the
sign, the approximate magnitude and the field dependence of the paramagnetic
and the Meissner contributions of the induced magnetic moment upon passing the
superconducting transition of a ferromagnet/superconductor bilayer.",1607.07341v2
2016-09-15,Ferromagnetism and the Effect of Free Charge Carriers on Electric Polarization in Y_2NiMnO_6 Double Perovskite,"The double perovskite Y_2NiMnO_6 displays ferromagnetic transition at Tc = 81
K. The ferromagnetic order at low temperature is confirmed by the saturation
value of magnetization (M_s) and also, validated by the refined ordered
magnetic moment values extracted from neutron powder diffraction data at 10 K.
This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The
cation-ordered P 21/n nuclear structure is revealed by neutron powder
diffraction studies at 300 and 10 K. Analysis of frequency dependent dielectric
constant and equivalent circuit analysis of impedance data takes into account
the bulk contribution to total dielectric constant. This reveals an anomaly
which coincides with the ferromagnetic transition temperature (T_c).
Pyrocurrent measurements register a current flow with onset near Tc and a peak
at 57 K that shifts with temperature ramp rate. The extrinsic nature of the
observed pyrocurrent is established by employing a special protocol
measurement. It is realized that the origin is due to re-orientation of
electric dipoles created by the free charge carriers and not by spontaneous
electric polarization at variance with recently reported magnetism-driven
ferroelectricity in this material",1609.04511v1
2016-09-18,Correlation and transport phenomena in topological nodal-loop semimetals,"We study the unique physical properties of topological nodal-loop semimetals
protected by the coexistence of time-reversal and inversion symmetries with
negligible spin-orbit coupling. We argue that strong correlation effects occur
at the surface of such systems for relatively small Hubbard interaction $U$,
due to the narrow bandwidth of the ""drumhead"" surface states. In the
Hartree-Fock approximation, at small $U$ we obtain a surface ferromagnetic
phase through a continuous quantum phase transition characterized by the
surface-mode divergence of the spin susceptibility, while the bulk states
remain very robust against local interactions and remain non-ordered. At
slightly increased interaction strength, the system quickly changes from a
surface ferromagnetic phase to a surface charge-ordered phase through a
first-order transition. When Rashba-type spin-orbit coupling is applied to the
surface states, a canted ferromagnetic phase occurs at the surface for
intermediate values of $U$. The quantum critical behavior of the surface
ferromagnetic transition is nontrivial in the sense that the surface spin order
parameter couple to Fermi-surface excitations from both surface and bulk
states. This leads to unconventional Landau damping and consequently a na\""ive
dynamical critical exponent $z\!\approx\!1$ when the Fermi level is close to
the bulk nodal energy. We also show that, already without interactions, quantum
oscillations arise due to bulk states, despite the absence of a Fermi surface
when the chemical potential is tuned to the energy of the nodal loop. The bulk
magnetic susceptibility diverges logarithmically whenever the nodal loop
exactly overlaps with a quantized magnetic orbit in the bulk Brillouin zone.
These correlation and transport phenomena are unique signatures of nodal loop
states.",1609.05529v1
2016-10-13,Role of direct exchange and Dzyaloshinskii-Moriya interactions in magnetic properties of graphene derivatives: C$_2$F and C$_2$H,"According to the Lieb's theorem the ferromagnetic interaction in
graphene-based materials with bipartite lattice is a result of disbalance
between the number of sites available for $p_z$ electrons in different
sublattices. Here, we report on another mechanism of the ferromagnetism in
functionalized graphene that is the direct exchange interaction between spin
orbitals. By the example of the single-side semihydrogenated (C$_2$H) and
semifluorinated (C$_2$F) graphene we show that such a coupling can partially or
even fully compensate antiferromagnetic character of indirect exchange
interactions reported earlier [Phys. Rev. B {\bf 88}, 081405(R) (2013)]. As a
result, C$_2$H is found to be a two-dimensional material with the isotropic
ferromagnetic interaction and negligibly small magnetic anisotropy, which
prevents the formation of the long-range magnetic order at finite temperature
in accordance with the Mermin-Wagner theorem. This gives a rare example of a
system where direct exchange interactions play a crucial role in determining a
magnetic structure. In turn, C$_2$F is found to be at the threshold of the
antiferromagnetic-ferromagnetic instability, which in combination with the
Dzyaloshinskii-Moriya interaction can lead to a skyrmion state.",1610.04059v1
2017-07-31,Theoretical study of magnetism induced by proximity effect in a ferromagnetic Josephson junction with a normal metal,"We theoretically study the magnetism induced by the proximity effect in the
normal metal of ferromagnetic Josephson junction composed of two $s$-wave
superconductors separated by ferromagnetic metal/normal metal/ferromagnetic
metal junction (${S}/{F}/{N}/{F}/{S}$ junction). We calculate the magnetization
in the $N$ by solving the Eilenberger equation. We show that the magnetization
arises in the ${N}$ when the product of anomalous Green's functions of the
spin-triplet even-frequency odd-parity Cooper pair and spin-singlet
odd-frequency odd-parity Cooper pair in the ${N}$ has a finite value. The
induced magnetization $M(d,\theta)$ can be decomposed into two parts,
$M(d,\theta)=M^{\rm I}(d)+M^{\rm II}(d,\theta)$, where $d$ is the thickness of
$N$ and $\theta$ is superconducting phase difference between two ${S}$s.
Therefore, $\theta$ dependence of $M(d,\theta)$ allows us to control the
amplitude of magnetization by changing $\theta$. The variation of $M(d,\theta)$
with $\theta$ is indeed the good evidence of the magnetization induced by the
proximity effect, since some methods of magnetization measurement pick up total
magnetization in the ${S}/{F}/{N}/{F}/{S}$ junction.",1708.00782v1
2017-08-06,Electric-field-induced extremely large change in resistance in graphene ferromagnets,"A colossal magnetoresistance ($\sim 100\times10^3\%$) and an extremely large
magnetoresistance ($\sim 1\times10^6\%$) have been previously explored in
manganite perovskites and Dirac materials, respectively. However, the
requirement of an extremely strong magnetic field (and an extremely low
temperature) makes them not applicable for realistic devices. In this work, we
propose a device that can generate even larger changes in resistance in a
zero-magnetic field and at a high temperature. The device is composed of a
graphene under two strips of yttrium iron garnet (YIG), where two gate voltages
are applied to cancel the heavy charge doping in the YIG-induced half-metallic
ferromagnets. By calculations using the Landauer-B\""{u}ttiker formalism, we
demonstrate that, when a proper gate voltage is applied on the free
ferromagnet, changes in resistance up to $305\times10^6\%$ ($16\times10^3\%$)
can be achieved at the liquid helium (nitrogen) temperature and in a zero
magnetic field. We attribute such a remarkable effect to a gate-induced
full-polarization reversal in the free ferromagnet, which results in a
metal-state to insulator-state transition in the device. We also find that, the
proposed effect can be realized in devices using other magnetic insulators such
as EuO and EuS. Our work should be helpful for developing a realistic switching
device that is energy saving and CMOS-technology compatible.",1708.01858v2
2017-08-08,Nonlinear electric and thermoelectric Andreev transport through a hybrid quantum dot coupled to ferromagnetic and superconducting leads,"We discuss the nonlinear Andreev current of an interacting quantum dot
coupled to spin-polarized and superconducting reservoirs when voltage and
temperature biases are applied across the nanostructure. Due to the
particle-hole symmetry introduced by the superconducting (S) lead, the subgap
spin current vanishes identically. Nevertheless, the Andreev charge current
depends on the degree of polarization in the ferromagnetic (F) contact since
the shift of electrostatic internal potential of the conductor depends on spin
orientation of the charge carrier. This spin-dependent potential shift
characterizes nonlinear responses in our device. We show how the subgap current
versus the bias voltage or temperature difference depends on the lead
polarization in two cases, namely (i) S-dominant case, when the
dot-superconductor tunneling rate ($\Gamma_R$) is much higher than the
ferromagnet-dot tunnel coupling ($\Gamma_L$), and (ii) F-dominant case, when
$\Gamma_L\gg \Gamma_R$. For the ferromagnetic dominant case the spin-dependent
potential shows a nonmonotonic behavior as the dot level is detuned. Thus the
subgap current can also exhibit interesting behaviors such as current
rectification and the maximization of thermocurrents with smaller thermal
biases when the lead polarization and the quantum dot level are adjusted.",1708.02451v1
2018-02-11,Strongly suppressed superconducting proximity effect and ferromagnetism in trilayers of $\rm Bi_2Se_3$ / $\rm SrRuO_3$ / underdoped $\rm YBa_2Cu_3O_x$: A possible new platform for Majorana nano-electronics,"We report properties of topological insulator - ferromagnet - superconductor
trilayers comprised of thin films of 20 nm thick $\rm Bi_2Se_3$ on 10 nm $\rm
SrRuO_3$ on 30 nm $\rm YBa_2Cu_3O_x$. As deposited trilayers are underdoped and
have a superconductive transition with $\rm T_c$ onset at 75 K, zero resistance
at 65 K, $\rm T_{Cueri}$ at 150 K and $\rm T^*$ of about 200 K. Further
reannealing under vacuum yields the 60 K phase of $\rm YBa_2Cu_3O_x$ which
still has zero resistance below about 40 K. Only when $10\times 100$
micro-bridges were patterned in the trilayer, some of the bridges showed
resistive behavior all the way down to low temperatures. Magnetoresistance
versus temperature of the superconductive ones showed the typical peak due to
flux flow against pinning below $\rm T_c$, while the resistive ones showed only
the broad leading edge of such a peak. All this indicates clearly weak-link
superconductivity in the resistive bridges between superconductive $\rm
YBa_2Cu_3O_x$ grains via the topological and ferromagnetic cap layers.
Comparing our results to those of a reference trilayer with the topological
$\rm Bi_2Se_3$ layer substituted by a non-superconducting highly overdoped $\rm
La_{1.65}Sr_{0.35}CuO_4$, indicates that the superconductive proximity effect
as well as ferromagnetism in the topological trilayer are actually strongly
suppressed compared to the non-topological reference trilayer. This strong
suppression is likely to originate in strong proximity induced edge currents in
the SRO/YBCO layer that can lead to Majorana bound states, a possible signature
of which is observed in the present study as zero bias conductance peaks.",1802.03728v2
2018-02-19,Spin current and spin transfer torque in ferromagnet/superconductor spin valves,"Using fully self consistent methods, we study spin transport in realistic,
fabricable experimental spin valve systems consisting of two magnetic layers, a
superconducting layer, and a spacer normal layer between the ferromagnets. Our
methods ensure that the proper relations between spin current gradients and
spin transfer torques are satisfied. We present results as a function of
geometrical parameters, interfacial barrier values, misalignment angle between
the ferromagnets, and bias voltage. Our main results are for the spin current
and spin accumulation as functions of position within the spin valve structure.
We see precession of the spin current about the exchange fields within the
ferromagnets, and penetration of the spin current into the superconductor for
biases greater than the critical bias, defined in the text. The spin
accumulation exhibits oscillating behavior in the normal metal, with a strong
dependence on the physical parameters both as to the structure and formation of
the peaks. We also study the bias dependence of the spatially averaged spin
transfer torque and spin accumulation. We examine the critical bias effect of
these quantities, and their dependence on the physical parameters. Our results
are predictive of the outcome of future experiments, as they take into account
imperfect interfaces and a realistic geometry.",1802.06834v1
2018-04-02,"Anisotropic bulk and planar Heisenberg ferromagnets in uniform, arbitrarily oriented magnetic fields","Today, further downscaling of mobile electronic devices poses serious
problems, such as energy consumption and local heat dissipation. In this
context, spin wave majority gates made of very thin ferromagnetic films may
offer a viable alternative. However, similar downscaling of magnetic thin films
eventually enforces the latter to operate as quasi-two dimensional magnets, the
magnetic properties of which are not yet fully understood, especially those
related to anisotropies and external magnetic fields in arbitrary directions.
To this end, we have investigated the behaviour of an easy-plane and easy-axis
anisotropic ferromagnet -- both in two and three dimensions -- subjected to a
uniform magnetic field, applied along an arbitrary direction. In this paper, a
spin-1/2 Heisenberg Hamiltonian with anisotropic exchange interactions is
solved using double-time temperature-dependent Green's functions and the
Tyablikov decoupling approximation. We determine various magnetic properties
such as the Curie temperature and the magnetization as a function of
temperature and the applied magnetic field, discussing the impact of the
system's dimensionality and the type of anisotropy. The magnetic reorientation
transition taking place in anisotropic Heisenberg ferromagnets is studied in
detail. Importantly, spontaneous magnetization is found to be absent for
easy-plane two-dimensional spin systems with short range interactions.",1804.00436v1
2018-04-19,Chiral surface and edge plasmons in ferromagnetic conductors,"The recently introduced concept of ""surface Berry plasmons"" is studied in the
concrete instance of a ferromagnetic conductor in which the Berry curvature,
generated by spin-orbit (SO) interaction, has opposite signs for carriers
parallel or antiparallel to the magnetization. By using collisionless hy-
drodynamic equations with appropriate boundary conditions, we study both the
surface plasmons of a three-dimensional ferromagnetic conductor and the edge
plasmons of a two-dimensional one. The anomalous velocity and the broken
inversion symmetry at the surface or the edge of the conductor create a
""handedness"", whereby the plasmon frequency depends not only on the angle
between the wave vector and the magnetization, but also on the direction of
propagation along a given line. In particular, we find that the frequency of
the edge plasmon depends on the direction of propagation along the edge. These
Berry curvature effects are compared and contrasted with similar effects
induced in the plasmon dispersion by an external magnetic field in the absence
of Berry curvature. We argue that Berry curvature effects may be used to
control the direction of propagation of the surface plasmons via coupling with
the magnetization of ferromagnetic conductors, and thus create a link between
plasmonics and spintronics.",1804.06967v2
2018-11-02,Evidence for exchange Dirac gap in magneto-transport of topological insulator-magnetic insulator heterostructures,"Transport signatures of exchange gap opening because of magnetic proximity
effect (MPE) are reported for bilayer structures of Bi2Se3 thin films on
yttrium iron garnet (YIG) and thulium iron garnet (TmIG) of perpendicular
magnetic anisotropy (PMA). Pronounced negative magnetoresistance (MR) was
detected, and attributed to an emergent weak localization (WL) effect
superimposing on a weak antilocalization (WAL). Thickness-dependent study shows
that the WL originates from the time-reversal-symmetry breaking of topological
surface states by interfacial exchange coupling. The weight of WL declined when
the interfacial magnetization was aligned toward the in-plane direction, which
is understood as the effect of tuning the exchange gap size by varying the
perpendicular magnetization component. Importantly, magnetotransport study
revealed anomalous Hall effect (AHE) of square loops and anisotropic
magnetoresistance (AMR) characteristic, typifying a ferromagnetic conductor in
Bi2Se3/TmIG, and the presence of an interfacial ferromagnetism driven by MPE.
Coexistence of MPE-induced ferromagnetism and the finite exchange gap provides
an opportunity of realizing zero magnetic-field dissipation-less transport in
topological insulator/ferromagnetic insulator heterostructures.",1811.00689v1
2018-11-05,Evidence of long-range ferromagnetic order and spin frustration effects in the double perovskite $La_2CoMnO_6$,"We present a comprehensive study on the magnetic structure, dynamics, and
phase evolution in the single-phase double perovskite $La_2CoMnO_6$. The mixed
valence state due to oxygen deficiency is verified by X-ray photoelectron
spectroscopy, and confirms a double ferromagnetic transition observed in DC
magnetization. Neutron diffraction reveals that the magnetic structure is
dominated by long-range ferromagnetic ordering, which is further corroborated
by a critical exponents analysis of the paramagnetic to ferromagnetic phase
transition. An analysis of the magnetization dynamics by means of linear and
nonlinear ac magnetic susceptibilities marks the presence of two distinct
cluster glass-like states that emerge at low temperatures. The isothermal
entropy change as a function of temperature and magnetic field (H) is exploited
to investigate the mechanism of stabilization of the magnetic phases across the
H-T phase diagram. In the regime of the phase diagram where thermal energy is
sufficiently low, regions of competing interactions due to local disorder
become stabilized and display glass-like dynamics. The freezing mechanism of
clusters is illustrated using a unique probe of transverse susceptibility that
isolates the effects of the local anisotropy of the spin clusters. The results
are summarized in a new H-T phase diagram of $La_2CoMnO_6$ revealed for the
first time from these data.",1811.01835v1
2018-11-14,Interface-induced enhancement of the anomalous Nernst effect in ferromagnetic Mn$_5$Ge$_3$C$_{0.8}$ films,"The anomalous Nernst effect of thin bilayers comprising a thin normal metal
film and a ferromagnetic Mn$_5$Ge$_3$C$_{0.8}$ film has been investigated.
Epitaxial c-axis grown Mn$_5$Ge$_3$C$_{0.8}$ films have been obtained by e-beam
evaporation as well as by magnetron sputtering on Ge(111) substrates. The size
of the anomalous Nernst coefficient is independent of the growth method. Pt,
Ta, and Pt/Cu bilayers have been used as voltage leads on top of the
ferromagnetic film. We show that the interface between the normal metal
electrode and the ferromagnetic film contributes significantly to the anomalous
Nernst voltage which is suprisingly independent of the choice of the metal. The
interface-induced enhancement of the anomalous Nernst effect is verified for
samples with varying Mn content or undergoing an additional annealing step. The
results suggest that the interface quality has a strong impact on the size of
the anomalous Nernst effect.",1811.05857v2
2019-05-03,Effective spin-mixing conductance of topological-insulator/ferromagnet and heavy-metal/ferromagnet spin-orbit-coupled interfaces: A first-principles Floquet-nonequilibrium-Green-function approach,"The spin mixing conductance (SMC) is a key quantity determining efficiency of
spin transport across interfaces. Thus, knowledge of its precise value is
required for accurate measurement of parameters quantifying numerous effects in
spintronics, such as spin-orbit torque, spin Hall magnetoresistance, spin Hall
effect and spin pumping. However, the standard expression for SMC, provided by
the scattering theory in terms of the reflection probability amplitudes, is
inapplicable when strong spin-orbit coupling (SOC) is present directly at the
interface. This is the precisely the case of topological-insulator/ferromagnet
and heavy-metal/ferromagnet interfaces of great contemporary interest. We
introduce an approach where first-principles Hamiltonian of these interfaces,
obtained from noncollinear density functional theory (ncDFT) calculations, is
combined with charge conserving Floquet-nonequilibrium-Green-function formalism
to compute {\em directly} the pumped spin current $I^{S_z}$ into semi-infinite
left lead of two-terminal heterostructures Cu/X/Co/Cu or Y/Co/Cu---where
X=Bi$_2$Se$_3$ and Y=Pt or W---due to microwave-driven steadily precessing
magnetization of the Co layer. This allows us extract an effective SMC as a
prefactor in $I^{S_z}$ vs. precession cone angle $\theta$ dependence, as long
as it remains the same, $I^{S_z} \propto \sin^2 \theta$, as in the case where
SOC is absent. By comparing calculations where SOC in switched off vs. switched
on in ncDFT calculations, we find that SOC consistently reduces the pumped spin
current and, therefore, the effective SMC.",1905.01299v2
2019-05-03,Ferromagnetic Anomalous Hall Effect in Cr-doped Bi$_2$Se$_3$ Thin Films via Surface-State Engineering,"The anomalous Hall effect (AHE) is a non-linear Hall effect appearing in
magnetic conductors, boosted by internal magnetism beyond what is expected from
the ordinary Hall effect. With the recent discovery of the quantized version of
the AHE, the quantum anomalous Hall effect (QAHE), in Cr- or V-doped
topological insulator (TI) (Sb,Bi)$_2$Te$_3$ thin films, the AHE in magnetic
TIs has been attracting significant interest. However, one of the puzzles in
this system has been that while Cr- or V-doped (Sb,Bi)$_2$Te$_3$ and V-doped
Bi$_2$Se$_3$ exhibit AHE, Cr-doped Bi$_2$Se$_3$ has failed to exhibit even
ferromagnetic AHE, the expected predecessor to the QAHE, though it is the first
material predicted to exhibit the QAHE. Here, we have successfully implemented
ferromagnetic AHE in Cr-doped Bi$_2$Se$_3$ thin films by utilizing a surface
state engineering scheme. Surprisingly, the observed ferromagnetic AHE in the
Cr-doped Bi$_2$Se$_3$ thin films exhibited only positive slope regardless of
the carrier type. We show that this sign problem can be explained by the
intrinsic Berry curvature of the system as calculated from a tight-binding
model combined with a first-principles method.",1905.01300v1
2020-07-03,Transition between half-metal and ferromagnetic semiconductor induced by silicon vacancy in epitaxial silicene,"Since the inevitability in experimental synthesis, defects show great
importance to many materials. They will deeply regulate the properties of the
materials, and then affect the further applications. Thus, exploring the
effects of defects on the properties of materials is desired. Here, by using
first-principles calculations, we systematically studied the effect of silicon
vacancy defects on the properties of silicene generated on Nterminated cubic
boron nitride (111) surface. It is found that the introduction of silicon
vacancy would trigger transition between half-metal and ferromagnetic
semiconductor. With small vacancy ratios of 1/36 and 1/24, the ground-state of
the samples would behave as ferromagnetic semiconductors, and the band gaps are
about 1.25 and 0.95 eV, respectively. When the vacancy ratio is increased up to
1/6, the sample would turn into a ferromagnetic half-metal with a half-metallic
gap of around 0.15 eV. The change of the electronic structure of the samples is
driven by the different electron transfer between silicon layer and substrate,
i.e., there will be different amount of electrons transferred from the silicon
layer to the substrate when the vacancy ratio is altered. This work would open
a new way to regulate the properties of materials and extend applications in
nanoelectronic field.",2007.01646v1
2020-07-11,Magnon-bipolar carrier drag thermopower in antiferromagnetic/ferromagnetic semiconductors: theoretical formulation and experimental evidence,"Quantized spin-wave known as magnon, a bosonic quasiparticle, can drag
electrons or holes via sd exchange interaction and boost the thermopower over
the conventional diffusive thermopower. P-type magnon-drag thermopower has been
observed in both ferromagnetic and antiferromagnetic metallic and degenerate
semiconductors. However, it has been less reported for intrinsic or n-type
magnetic semiconductors; therefore, the impact of magnon-bipolar carrier drag
on thermopower has remained unexplored. Here, a theoretical model for
magnon-bipolar carrier drag thermopower is derived based on the magnon-carrier
interaction lifetimes. The model predicts that the bipolar carrier drag
thermopower becomes independent of both the carrier and magnon relaxation
times. A proof of concept experiment is presented that confirms this
prediction. We also report the observation of magnon-carrier drag thermopower
in n-type and intrinsic ferromagnetic semiconductors experimentally. The p-type
antiferromagnetic MnTe is doped with different amounts of Cr to produce
non-degenerate and n-type semiconductors of various carrier concentrations. Cr
dopants have a donor nature and create ferromagnetic-antiferromagnetic clusters
due to the Cr3+ oxidation state. Heat capacity measurements confirm the
presence of magnons in Cr-doped MnTe. It is shown that the magnon-drag
thermopower is significantly reduced for 3%-5% Cr-doped samples due to bipolar
drag effects and becomes negative for 14% and 20% Cr-doped MnTe due to dominant
magnon-electron drag thermopower.",2007.05682v1
2020-07-13,Molecule Oxygen Induced Ferromagnetism and Half-metallicity in α-BaNaO4: A First Principles Study,"Molecule oxygen resembles 3d and 4f metals in exhibiting long-range spin
ordering and electron strong correlated behaviors in compounds. The
ferromagnetic spin ordering and half-metallicity, however, are quite elusive
and have not been well acknowl-edged. In this article, we address this issue to
study how spins will interact each other if the oxygen dimers are arranged in a
dif-ferent way from that in the known super- and per-oxides by first principles
calculations. Based on the results of structure search, thermodynamic study and
lattice dynamics, we show that tetragonal {\alpha}-BaNaO4 is a stable
half-metal with a Curie temperature at 120 K, a first example in this class of
compounds. Like 3d and 4f metals, the O2 dimer carries a local magnetic moment
0.5 {\mu}B due to the unpaired electrons in its {\pi}* orbitals. This compound
can be regarded as forming from the O2 dimer layers stacking in a head to head
way. Different from that in AO2 (A=K, Rb, Cs), the spins are both
ferromagnetically coupled within and between the layers. Spin polarization
occurs in {\pi}* orbitals with spin-up electrons fully occupying the valence
band and spin-down electrons partially the conduction band, forming the
semiconducting and metallic channels, respectively. Our results highlight the
im-portance of geometric arrangement of O2 dimers in inducing ferromagnetism
and other novel properties in O2 dimer containing compounds.",2007.06433v1
2020-07-29,Impact of magnetic dopants on magnetic and topological phases in magnetic topological insulators,"A topological insulator doped with random magnetic impurities is studied. The
system is modelled by the Kane-Mele model with a random spin exchange between
conduction electrons and magnetic dopants. The dynamical mean field theory for
disordered systems is used to investigate the electron dynamics. The magnetic
long-range order and the topological invariant are calculated within the mean
field theory. They reveal a rich phase diagram, where different magnetic
long-range orders such as antiferromagnetic or ferromagnetic one can exist in
the metallic or insulating phases, depending on electron and magnetic impurity
fillings. It is found that insulator only occurs at electron half filling,
quarter filling and when electron filling is equal to magnetic impurity
filling. However, non-trivial topology is observed only in half-filling
antiferromagnetic insulator and quarter-filling ferromagnetic insulator. At
electron half filling, the spin Hall conductance is quantized and it is robust
against magnetic doping, while at electron quarter filling, magnetic dopants
drive the ferromagnetic topological insulator to ferromagnetic metal. The
quantum anomalous Hall effect is observed only at electron quarter filling and
dense magnetic doping.",2007.14687v1
2016-11-10,Pressure-induced quantum phase transition in the itinerant ferromagnet UCoGa,"In this paper, we report the results of a high pressure study of the
itinerant 5f-electron ferromagnet UCoGa. The work is focused on probing the
expected ferromagnet-to-paramagnet quantum phase transition induced by high
pressure and on the general features of the P-T(-H) phase diagram. Diamond
anvil cells were employed to measure the magnetization and electrical
resistivity under pressures up to ~ 10 GPa.At ambient pressure, UCoGa exhibits
collinear ferromagnetic ordering of uranium magnetic moments {\mu}U ~ 0.74
{\mu}B (at 2 K) aligned along the c-axis of the hexagonal crystal structure
below Curie temperature TC = 48K. With the application of pressure, gradual
decrease of both, TC and the saturated magnetic moment, has been observed up to
pressures ~ 6 GPa. This is followed by a sharp drop of magnetic moment and a
sudden disappearance of the magnetic order at the pressure of 6.5 GPa,
suggesting a first-order phase transition, as expected for a clean system. The
low temperature power law dependence of the electrical resistivity shows
distinct anomalies around the ~ 6 GPa, consistent with the pressure evolution
of the magnetic moment and the ordering temperature. The tricritical point of
the UCoGa phase diagram is located at approximately ~ 30 K and ~ 6 GPa.",1611.03276v1
2016-11-22,Uranium ferromagnet with negligible magnetocrystalline anisotropy - $\mathrm{U_{4}Ru_{7}Ge_{6}}$,"Strong magnetocrystalline anisotropy is a well-known property of uranium
compounds. The almost isotropic ferromagnetism in $\mathrm{U_{4}Ru_{7}Ge_{6}}$
reported in this paper represents a striking exception. We present results of
magnetization, AC susceptibility, thermal expansion, specific heat and
electrical resistivity measurements performed on a $\mathrm{U_{4}Ru_{7}Ge_{6}}$
single crystal at various temperatures and magnetic fields and discuss them in
conjunction with results of first-principles electronic-structure calculations.
$\mathrm{U_{4}Ru_{7}Ge_{6}}$ behaves as an itinerant 5$f$-electron ferromagnet
($T_{\mathrm{C}}= 10.7 K$, $\mu_{\mathrm{S}}= 0.85 \mu_{\mathrm{B}}/f.u.$ at
1.9 K. The ground-state easy-magnetization direction is along the [111] axis of
the cubic lattice. The anisotropy field $\mu_{0}H_{\mathrm{a}}$ along the [001]
direction is only of $\sim0.3 T$, which is at least 3 orders of magnitude
smaller value than in other U ferromagnets. At $T_{r}=5.9 K$ the easy
magnetization direction changes for [001] which holds at temperatures up to
$T_{\mathrm{C}}$. The magnetoelastic interaction induces a rhombohedral
(tetragonal) distortion of the paramagnetic cubic crystal lattice in case of
the [111]([001]) easy-magnetization direction. The rhombohedral distortion is
connected with two crystallographically inequivalent U sites. The ab initio
calculated ground-state magnetic moment of $1.01 \mu_{\mathrm{B}}/f.u.$ is
oriented along [111]. The two crystallographically inequivalent U sites are a
consequence of spin-orbit coupling of the U 5$f$-electrons. In the excited
state which is only 0.9 meV above the ground state the moment points to the
[001] direction in agreement with experiment.",1611.07335v1
2017-01-09,The Coprime Quantum Chain,"In this paper we introduce and study the coprime quantum chain, i.e. a
strongly correlated quantum system defined in terms of the integer eigenvalues
$n_i$ of the occupation number operators at each site of a chain of length $M$.
The $n_i$'s take value in the interval $[2,q]$ and may be regarded as $S_z$
eigenvalues in the spin representation $j = (q-2)/2$. The distinctive
interaction of the model is based on the coprimality matrix $\bf \Phi$: for the
ferromagnetic case, this matrix assigns lower energy to configurations where
occupation numbers $n_i$ and $n_{i+1}$ of neighbouring sites share a common
divisor, while for the anti-ferromagnetic case it assigns lower energy to
configurations where $n_i$ and $n_{i+1}$ are coprime. The coprime chain, both
in the ferro and anti-ferromagnetic cases, may present an exponential number of
ground states whose values can be exactly computed by means of graph
theoretical tools. In the ferromagnetic case there are generally also
frustration phenomena. A fine tuning of local operators may lift the
exponential ground state degeneracy and, according to which operators are
switched on, the system may be driven into different classes of universality,
among which the Ising or Potts universality class. The paper also contains an
appendix by Don Zagier on the exact eigenvalues and eigenvectors of the
coprimality matrix in the limit $q \rightarrow \infty$.",1701.02317v1
2017-01-11,Carrier driven coupling in ferromagnetic oxide heterostructures,"Transition metal oxides are well known for their complex magnetic and
electrical properties. When brought together in heterostructure geometries,
they show particular promise for spintronics and colossal magnetoresistance
applications. In this letter, we propose a new mechanism for the coupling
between layers of itinerant ferromagnetic materials in heterostructures. The
coupling is mediated by charge carriers that strive to maximally delocalize
through the heterostructure to gain kinetic energy. In doing so, they force a
ferromagnetic or antiferromagnetic coupling between the constituent layers. To
illustrate this, we focus on heterostructures composed of SrRuO$_3$ and
La$_{1-x}$A$_{x}$MnO$_3$ (A=Ca/Sr). Our mechanism is consistent with
antiferromagnetic alignment that is known to occur in multilayers of
SrRuO$_3$-La$_{1-x}$A$_{x}$MnO$_3$. To support our assertion, we present a
minimal Kondo-lattice model which reproduces the known magnetization properties
of such multilayers. In addition, we discuss a quantum well model for
heterostructures and argue that the spin-dependent density of states determines
the nature of the coupling. As a smoking gun signature, we propose that
bilayers with the same constituents will oscillate between ferromagnetic and
antiferromagnetic coupling upon tuning the relative thicknesses of the layers.",1701.03117v1
2017-01-18,Step Stone Effect: A sp anti-bonding Mediated Long-Range Ferromagnetism in Cr-doped Carrier-Free Bi2Te3,"Despite the recent success in the realization of the quantum anomalous Hall
effect, the underlying physical mechanism of the long range Ferromagnetism is
still unclear. Based on our density functional theory calculations, we
discovered an intriguing long-range ferromagnetic order in Cr-doped,
carrier-free Bi2Te3, with the separation between dopants more than 8 {\AA}. We
found that this magnetic coupling is facilitated by an anti-bonding state
originated from the lone pair of a Te 5p state and a Bi 6s state, despite this
anti-bonding state lies below the valence band maximum. Such a state serves as
a hidden step stone merged in the electron sea and mediates the long-range
magnetic order. An effective electron hopping model is proposed to explain this
mechanism. This novel mechanism sheds light on the understanding of long-range
ferromagnetism in insulators and may lead to the realization of the long-range
magnetic order in dilute magnetic semiconductors.",1701.04943v5
2017-01-02,Ferromagnetic films with three to twenty spin layers as described using second order perturbed Heisenberg Hamiltonian,"Modified second order perturbed Heisenberg Hamiltonian was employed to
describe the magnetic properties of ferromagnetic films with three to twenty
spin layers for the first time. Previously, the solution of second order
perturbed Heisenberg Hamiltonian was found for ferromagnetic films with two to
five layers under some assumptions by us. In this report, the exact solution is
presented without any assumptions by calculating the pseudo inverse of matrix
C. All eight magnetic parameters such as spin exchange interaction, second
order magnetic anisotropy, fourth order magnetic anisotropy, stress induced
magnetic anisotropy, demagnetization factor, in plane magnetic field, out of
plane magnetic field and magnetic dipole interaction were taken into account.
The easy and hard directions were found using 3-D and 2-D plots of total
magnetic energy versus these magnetic parameters. Angle between easy and hard
directions was nearly 107 degrees in many cases. The magnetic easy axis
gradually rotates from out of plane to in plane direction by indicating a
preferred in plane orientation of magnetic easy axis for films with higher
number of spin layers. These theoretical results agree with some experimental
research data of ferromagnetic thin films.",1701.07780v1
2017-04-28,Ferromagnetism and spin-dependent transport at a complex oxide interface,"Complex oxide interfaces are a promising platform for studying a wide array
of correlated electron phenomena in low-dimensions, including magnetism and
superconductivity. The microscopic origin of these phenomena in complex oxide
interfaces remains an open question. Here we investigate for the first time the
magnetic properties of semi-insulating NdTiO$_3$/SrTiO$_3$ (NTO/STO) interfaces
and present the first milli-Kelvin study of NTO/STO. The magnetoresistance (MR)
reveals signatures of local ferromagnetic order and of spin-dependent
thermally-activated transport, which are described quantitatively by a simple
phenomenological model. We discuss possible origins of the interfacial
ferromagnetism. In addition, the MR also shows transient hysteretic features on
a timescale of ~10-100 seconds. We demonstrate that these are consistent with
an extrinsic magneto-thermal origin, which may have been misinterpreted in
previous reports of magnetism in STO-based oxide interfaces. The existence of
these two MR regimes (steady-state and transient) highlights the importance of
time-dependent measurements for distinguishing signatures of ferromagnetism
from other effects that can produce hysteresis at low temperatures.",1704.08828v3
2018-05-07,Appearance of ferromagnetism property for Si nano-polycrystalline body and vanishing of electrical resistances at local high frequencies,"Reduction in the skin effect for the sintered Si nanopolycrystalline body as
an electricity conductor at a high frequency due to its nano-structure was
studied. Singular vanishing of electrical resistances near a local high
magnetic harmonic frequency of a few MHz was observed. This phenomenon has not
been observed for conventional ferromagnetic metals. The measured electrical
resistances changed to almost 0 m{\Omega} at room temperature. At the same
time, negative resistance of the sintered Si nano-polycrystalline body was
observed. It will be applicable to electronic transmittance lines or
semiconductors. Numerical calculation was also performed on the electrical
resistance with frequency dependency while considering the electric field and
magnetic field in the sintered Si nanopolycrystalline body. The calculation
could explain the variation of the relative permittivity of the Si
nanopolycrystalline and the phenomenon for vanishing the resistivity at
frequency of MHz theoretically. Reduced Si nanoparticles from SiO2 powder were
synthesized by laser ablation in liquid. A Si nano-polycrystalline body made of
the reduced Si nanoparticles was fabricated. It was found by measuring the
magnetization property of the body that the sintered Si nano-polycrystalline
body has ferromagnetism. High-density dangling bonds cause the sintered Si
nanopolycrystalline to have ferromagnetism. In this study, the density of the
unpaired electrons in the sintered Si nanopolycrystalline was observed using
ESR. It has been clarified that the Si nanopowder and the sintered Si
nanopolycrystalline have numerous dangling bonds. Both densities of the
dangling bonds were evaluated.",1805.02312v1
2018-05-07,Universality class of the nonequilibrium phase transition in two dimensional Ising ferromagnet driven by propagating magnetic field wave,"The finite size analysis of the nonequilibrium phase transition, in two
dimensional Ising ferromagnet driven by plane propagating magneticwave, is
studied by Monte Carlo simulation. It is observed that the system undergoes a
nonequilibrium dynamicphase transition from a high temperature dynamically
symmetric ({\it propagating}) phase to a low temperature dynamically
symmetry-broken ({\it pinned}) phase as the system is cooled below the
transition temperature. This transition temperature is determined precisely by
studying the fourth order Binder Cumulant of the dynamic order parameter as a
function of temperature for different system sizes ($L$). From the finite size
analysis of dynamic order parameter ($Q_L \sim L^{-{{\beta} \over {\nu}}}$) and
the dynamic susceptibility ($\chi^{Q}_{L} \sim L^{{\gamma} \over {\nu}}$), we
have estimated the critical exponents $\beta/\nu=0.146\pm0.025$ and
$\gamma/\nu=1.869\pm0.135$ (measured from the data read at the critical
temperature obtained from Binder cumulant), and $\gamma/\nu=1.746\pm0.017$
(measured from the peak positions of dynamic susceptibility). Our results
indicate that such driven Ising ferromagnet belongs to the same universality
class of the two-dimensional equilibrium Ising ferromagnet (where
$\beta/\nu=1/8$ and $\gamma/\nu=7/4$), within the limits of statistical errors.",1805.02389v2
2018-05-13,Pressure-induced spin reorientation transition in layered ferromagnetic insulator Cr2Ge2Te6,"Anisotropic magnetoresistance (AMR) of Cr2Ge2Te6 (CGT), a layered
ferromagnetic insulator, is investigated under an applied hydrostatic pressure
up to 2 GPa. The easy axis direction of the magnetization is inferred from the
AMR saturation feature in the presence and absence of the applied pressure. At
zero applied pressure, the easy axis is along the c-direction or perpendicular
to the layer. Upon application of a hydrostatic pressure>1 GPa, the uniaxial
anisotropy switches to easy-plane anisotropy which drives the equilibrium
magnetization from the c-axis to the ab-plane at zero magnetic field, which
amounts to a giant magnetic anisotropy energy change (>100%). As the
temperature is increased across the Curie temperature, the characteristic AMR
effect gradually decreases and disappears. Our first-principles calculations
confirm the giant magnetic anisotropy energy change with moderate pressure and
assign its origin to the increased off-site spin-orbit interaction of Te atoms
due to a shorter Cr-Te distance. Such a pressure-induced spin reorientation
transition is very rare in three-dimensional ferromagnets, but it may be common
to other layered ferromagnets with similar crystal structures to CGT, and
therefore offers a unique way to control magnetic anisotropy.",1805.04937v1
2018-05-25,Learning Restricted Boltzmann Machines via Influence Maximization,"Graphical models are a rich language for describing high-dimensional
distributions in terms of their dependence structure. While there are
algorithms with provable guarantees for learning undirected graphical models in
a variety of settings, there has been much less progress in the important
scenario when there are latent variables. Here we study Restricted Boltzmann
Machines (or RBMs), which are a popular model with wide-ranging applications in
dimensionality reduction, collaborative filtering, topic modeling, feature
extraction and deep learning.
  The main message of our paper is a strong dichotomy in the feasibility of
learning RBMs, depending on the nature of the interactions between variables:
ferromagnetic models can be learned efficiently, while general models cannot.
In particular, we give a simple greedy algorithm based on influence
maximization to learn ferromagnetic RBMs with bounded degree. In fact, we learn
a description of the distribution on the observed variables as a Markov Random
Field. Our analysis is based on tools from mathematical physics that were
developed to show the concavity of magnetization. Our algorithm extends
straighforwardly to general ferromagnetic Ising models with latent variables.
  Conversely, we show that even for a contant number of latent variables with
constant degree, without ferromagneticity the problem is as hard as sparse
parity with noise. This hardness result is based on a sharp and surprising
characterization of the representational power of bounded degree RBMs: the
distribution on their observed variables can simulate any bounded order MRF.
This result is of independent interest since RBMs are the building blocks of
deep belief networks.",1805.10262v2
2008-07-06,Low voltage control of ferromagnetism in a semiconductor p-n junction,"The concept of low-voltage depletion and accumulation of electron charge in
semiconductors, utilized in field-effect transistors (FETs), is one of the
cornerstones of current information processing technologies. Spintronics which
is based on manipulating the collective state of electron spins in a
ferromagnet provides complementary technologies for reading magnetic bits or
for the solid-state memories. The integration of these two distinct areas of
microelectronics in one physical element, with a potentially major impact on
the power consumption and scalability of future devices, requires to find
efficient means for controlling magnetization electrically. Current induced
magnetization switching phenomena represent a promising step towards this goal,
however, they relay on relatively large current densities. The direct approach
of controlling the magnetization by low-voltage charge depletion effects is
seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets
are separated by many orders of magnitude in their typical carrier
concentrations. Here we demonstrate that this concept is viable by reporting
persistent magnetization switchings induced by short electrical pulses of a few
volts in an all-semiconductor, ferromagnetic p-n junction.",0807.0906v1
2011-11-18,Nanoscale inhomogeneities: A new path toward high Curie temperature ferromagnetism in diluted materials,"Room temperature ferromagnetism has been one of the most sought after topics
in today's emerging field of spintronics. It is strongly believed that defect-
and inhomogeneity- free sample growth should be the optimal route for achieving
room-temperature ferromagnetism and huge efforts are made in order to grow
samples as ""clean"" as possible. However, until now, in the dilute regime it has
been difficult to obtain Curie temperatures larger than that measured in well
annealed samples of (Ga,Mn)As ($\sim$190 K for 12% doping). In the present
work, we propose an innovative path to room-temperature ferromagnetism in
diluted magnetic semiconductors. We theoretically show that even a very small
concentration of nanoscale inhomogeneities can lead to a tremendous boost of
the critical temperatures: up to a 1600% increase compared to the homogeneous
case. In addition to a very detailed analysis, we also give a plausible
explanation for the wide variation of the critical temperatures observed in
(Ga,Mn)N and provide a better understanding of the likely origin of very high
Curie temperatures measured occasionally in some cases. The colossal increase
of the ordering temperatures by nanoscale cluster inclusions should open up a
new direction toward the synthesis of materials relevant for spintronic
functionalities.",1111.4355v2
2011-11-23,Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb_2Ti_2O_7,"In a class of frustrated magnets known as spin ice, magnetic monopoles emerge
as classical defects and interact via the magnetic Coulomb law. With
quantum-mechanical interactions, these magnetic charges are carried by
fractionalised bosonic quasi-particles, spinons, which can undergo
Bose-Einstein condensation through a first-order transition via the Higgs
mechanism. Here, we report evidence of a Higgs transition from a magnetic
Coulomb liquid to a ferromagnet in single-crystal Yb2Ti2O7. Polarised
neutron-scattering experiments show that the diffuse [111]-rod scattering and
pinch-point features which develop on cooling are suddenly suppressed below T_C
~ 0.21 K, where magnetic Bragg peaks and a full depolarisation of the neutron
spins are observed with thermal hysteresis, indicating a first-order
ferromagnetic transition. Our results are explained on the basis of a quantum
spin-ice model, whose high-temperature phase is effectively described as a
magnetic Coulomb liquid, while the ground state shows a nearly collinear
ferromagnetism with gapped spin excitations.",1111.5406v2
2012-04-27,Energetically stable singular vortex cores in an atomic spin-1 Bose-Einstein condensate,"We analyze the structure and stability of singular singly quantized vortices
in a rotating spin-1 Bose-Einstein condensate. We show that the singular vortex
can be energetically stable in both the ferromagnetic and polar phases despite
the existence of a lower-energy nonsingular coreless vortex in the
ferromagnetic phase. The spin-1 system exhibits an energetic hierarchy of
length scales resulting from different interaction strengths and we find that
the vortex cores deform to a larger size determined by the characteristic
length scale of the spin-dependent interaction. We show that in the
ferromagnetic phase the resulting stable core structure, despite apparent
complexity, can be identified as a single polar core with axially symmetric
density profile which is nonvanishing everywhere. In the polar phase, the
energetically favored core deformation leads to a splitting of a singly
quantized vortex into a pair of half-quantum vortices that preserves the
topology of the vortex outside the extended core region, but breaks the axial
symmetry of the core. The resulting half-quantum vortices exhibit nonvanishing
ferromagnetic cores.",1204.6347v4
2013-09-19,Anomalous Hall effect in ferromagnets with Gaussian disorder,"Using the Kubo formalism we derived expressions and implemented the method
for calculating the anomalous Hall conductivity (AHC) in ferromagnets with
short-range Gaussian disorder directly from first-principles electronic
structure of the perfect crystal. We used this method to calculate the AHC in
bcc Fe, fcc Co, L1o-FePd, L1o-FePt as well as thin bcc Fe(001) films. Within
our approach we can transparently decompose the conductivity into intrinsic
(IC), side jump (SJ) and intrinsic skew-scattering (ISK) contributions. The
existence of ISK, which originates from asymmetric Mott scattering but is
clearly distinguishable from conventional skew-scattering in that it converges
to a finite value in clean limit, was pointed out by Sinitsyn et al. [Phys.
Rev. B 75, 045315 (2007)]. Here, we collect all contributions to the AHC in
ferromagnets which result in ""scattering-independent"" AHE in clean limit, and
analyze their relative magnitude from first principles calculations. By
comparing our results to existing experiments we show that the Gaussian
disorder is well suited to model various types of disorder present in real
materials, to some extent including the effect of temperature. In particular,
we show that in addition to intrinsic and side-jump AHE, the intrinsic
skew-scattering can be a major player in determining the magnitude of the AHE
in ferromagnets.",1309.4979v1
2014-05-19,Infrared electrodynamics and ferromagnetism in the topological semiconductors Bi$_2$Te$_3$ and Mn-doped Bi$_2$Te$_3$,"We report on infrared (IR) optical experiments on Bi$_2$Te$_3$ and Mn-doped
Bi$_2$Te$_3$ epitaxial thin films. In the latter film, dilute Mn doping (4.5\%)
of the topologically nontrivial semiconductor host results in
time-reversal-symmetry-breaking ferromagnetic order below $T_C$=15 K. Our
spectroscopic study shows both materials share the Bi$_2$Te$_3$ crystal
structure, as well as classification as bulk degenerate semiconductors. Hence
the Fermi energy is located in the Bi$_2$Te$_3$ conduction band in both
materials, and furthermore, there is no need to invoke topological surface
states to describe the conductivity spectra. We also demonstrate that the Drude
oscillator strength gives a simple metric with which to distinguish the
possibility of topological surface state origins of the low frequency
conductance, and conclude that in both the pristine and Mn-doped Bi$_2$Te$_3$
samples the electromagnetic response is indeed dominated by the bulk material
properties, rather than those of the surface. An encouraging aspect for taking
advantage of the interplay between nontrivial topology and magnetism, however,
is that the temperature dependence of the Mn-doped Bi$_2$Te$_3$ film suggests
bulk charge carriers do not play a significant role in mediating
ferromagnetism. Thus, a truly insulating bulk may still be suitable for the
formation of a ferromagnetic ground state in this dilute magnetic topological
semiconductor.",1405.4916v1
2014-05-26,Amorphous ferromagnetism and re-entrant magnetic glassiness in Sm$_{2}$Mo$_{2}$O$_{7}$: new insights into the electronic phase diagram of pyrochlore molybdates,"We discuss the magnetic properties of a Sm$_{2}$Mo$_{2}$O$_{7}$ single
crystal as investigated by means of different experimental techniques. In the
literature, a conventional itinerant ferromagnetic state is reported for the
Mo$^{4+}$ sublattice below $\sim 78$ K. However, our results of dc
magnetometry, muon spin spectroscopy ($\mu^{+}$SR) and high-harmonics magnetic
ac susceptibility unambiguously evidence highly disordered conditions in this
phase, in spite of the crystalline and chemical order. This disordered magnetic
state shares several common features with amorphous ferromagnetic alloys. This
scenario for Sm$_{2}$Mo$_{2}$O$_{7}$ is supported by the anomalously high
values of the critical exponents, as mainly deduced by a scaling analysis of
our dc magnetization data and confirmed by the other techniques. Moreover,
$\mu^{+}$SR detects a significant static magnetic disorder at the microscopic
scale. At the same time, the critical divergence of the third-harmonic
component of the ac magnetic susceptibility around $\sim 78$ K leads to
additional evidence towards the glassy nature of this magnetic phase. Finally,
the longitudinal relaxation of $\mu^{+}$ spin polarization (also supported by
results of ac susceptibility) evidences re-entrant glassy features similar to
amorphous ferromagnets.",1405.6608v1
2014-06-13,"{Effect of on-site Coulomb interaction (\textit{U}) on the electronic and magnetic properties of Fe$_{2}$MnSi, Fe$_{2}$MnAl and Co$_{2}$MnGe","The electronic band structures, density of states plots and magnetic moments
of Fe$_{2 }$MnSi, Fe$_{2 }$MnAl, and Co$_{2 }$MnGe are studied by using the
first principles calculations. The FM solutions using LSDA without \textit{U}
show the presence of half-metallic ferromagnetic (HFM) ground state in Fe$_{2
}$MnSi, whereas the ground state of Fe$_{2 }$MnAl is found to be metallic. In
both compounds the maximum contribution to the total magnetic moment is from
the Mn atom, while the Fe atom contributes very less. The electronic structures
and magnetic moments of Fe-based compounds affected significantly by
\textit{U}, whereas its effect is very less on Co$_{2}$MnGe. The magnetic
moment of Fe atom in Fe$_{2 }$MnSi (Fe$_{2 }$MnAl), increased by $\sim$ 70 %
($\sim$ 75 %) and in Mn atom it decreases by $\sim$ 50 % ($\sim$ 70 %) when the
value of \textit{U} is increased from 1 to 5 eV. The Hund's like exchange
interactions are increasing in Fe atom while decreasing in Mn atom with
increase in \textit{U}. The Fe and Mn moments are ferromagnetically coupled in
Fe$_{2 }$MnSi for all values of \textit{U}, whereas in Fe$_{2 }$MnAl they
coupled antiferromagnetically below \textit{U} = 2 eV and ferromagnetically
above it. Above \textit{U} = 2 eV the metallic ground state of Fe$_{2 }$MnAl
changes to semiconducting ground state and the ferromagnetic coupling between
Fe and Mn atoms appears to be responsible for this.",1406.3505v1
2014-06-27,Optimal bounds for periodic mixtures of ferromagnetic interactions,"In this paper we give optimal bounds for the homogenization of periodic Ising
systems when the coefficients may take two given values in given proportions.",1406.7152v1
2014-06-29,Trajectory of Anomalous Hall Effect toward the Quantized State in a Ferromagnetic Topological Insulator,"Topological insulators are bulk electronic insulators which possess symmetry
protected gapless modes on their surfaces. Breaking the symmetries that
underlie the gapless nature of the surface modes is predicted to give rise to
exotic new states of matter. In particular, it has recently been predicted and
shown that breaking of time reversal symmetry in the form of ferromagnetism can
give rise to a gapped state characterized by a zero magnetic field quantized
Hall response and dissipationless longitudinal transport known as the Quantum
Anomalous Hall (QAH) state. A key question that has thus far remained
experimentally unexplored is the relationship of this new type of quantum Hall
state with the previously known orbitally driven quantum Hall states. Here, we
show experimentally that a ferromagnetic topological insulator exhibiting the
QAH state is well described by the global phase diagram of the quantum Hall
effect. By mapping the behavior of the conductivity tensor in the parameter
space of temperature, magnetic field, and chemical potential in the vicinity of
the QAH phase, we find evidence for quantum criticality and delocalization
behavior that can quantitatively be described by the renormalization group
properties of the quantum Hall ground state. This result demonstrates that the
QAH state observed in ferromagnetic topological insulators can be understood
within the context of the law of corresponding states which governs the quantum
Hall state. This suggests a roadmap for studying the QAH effect including
transitions to possible adjacent topologically non-trivial states and a
possible universality class for the QAH transition.",1406.7450v1
2015-12-08,Density-matrix renormalization group study of Kitaev-Heisenberg model on the triangular lattice,"We study the Kitaev-Heisenberg model on the triangular lattice by using the
two-dimensional density-matrix renormalization group method. Calculating the
ground-state energy and spin structure factors, we obtain the ground state
phase diagram of the Kitaev-Heisenberg model. As suggested by previous studies,
we find a 120$^\circ$ antiferromagnetic (AFM) phase, a $\mathbb{Z}_2$-vortex
crystal phase, a nematic phase, a dual $\mathbb{Z}_2$-vortex crystal phase
(dual counterpart of $\mathbb{Z}_2$-vortex crystal phase), a $\mathbb{Z}_6$
ferromagnetic phase, and a dual ferromagnetic phase (dual counterpart of
$\mathbb{Z}_6 $ ferromagnetic phase). Spin correlations discontinuously change
at the phase boundaries because of first-order phase transitions. In the (dual)
$\mathbb{Z}_6$ ferromagnetic phase, we find that the dominant spin component of
the spin structure factors is different on either side of the SU(2) symmetric
point, although there is no phase transition. Furthermore, we study the
relation among von Neumann entanglement entropy, entanglement spectrum, and
phase transitions of the model. We find that the Schmidt gap closes at the
phase boundaries and thus the entanglement entropy clearly changes as well.
This is different from the Kitaev-Heisenberg model on the honeycomb lattice,
where the Schmidt gap and the entanglement entropy are not necessary a good
measure of phase transitions.",1512.02334v3
2016-05-03,Field-induced transition of the magnetic ground state from A-type antiferromagnetic to ferromagnetic order in CsCo2Se2,"We report on the magnetic properties of CsCo$_2$Se$_2$ with ThCr$_2$Si$_2$
structure, which we have characterized through a series of magnetization and
neutron diffraction measurements. We find that CsCo$_2$Se2$_2$ undergoes a
phase transition to an antiferromagnetically ordered state with a N\'eel
temperature of $T_{\rm N} \approx$ 66 K. The nearest neighbour interactions are
ferromagnetic as observed by the positive Curie-Weiss temperature of $\Theta
\approx$ 51.0 K. We find that the magnetic structure of CsCo$_2$Se$_2$ consists
of ferromagnetic sheets, which are stacked antiferromagnetically along the
tetragonal \textit{c}-axis, generally referred to as A-type antiferromagnetic
order. The observed magnitude of the ordered magnetic moment at $T$ = 1.5 K is
found to be only 0.20(1)$\mu_{\rm Bohr}$/Co. Already in comparably small
magnetic fields of $\mu_0 H_{MM}$(5K) $\approx$ 0.3 T, we observe a
metamagnetic transition that can be attributed to spin-rearrangements of
CsCo$_2$Se$_2$, with the moments fully ferromagnetically saturated in a
magnetic field of $\mu_0 H_{\rm FM}$(5K) $\approx$ 6.4 T. We discuss the entire
experimentally deduced magnetic phase diagram for CsCo$_2$Se$_2$ with respect
to its unconventionally weak magnetic coupling. Our study characterizes
CsCo$_2$Se$_2$, which is chemically and electronically posed closely to the
$A_xFe_{2-y}Se_2$ superconductors, as a host of versatile magnetic
interactions.",1605.01113v1
2016-05-13,Coarsening and thermalisation properties of a quenched ferromagnetic spin-1 condensate,"We examine the dynamics of a quasi-two-dimensional spin-1 condensate in which
the quadratic Zeeman energy q is suddenly quenched to a value where the system
has a ferromagnetic ground state. There are two distinct types of ferromagnetic
phases, i.e. a range of q values where the magnetization prefers to be in the
direction of the external field (easy-axis), and a range of q values where it
prefers to be transverse to the field (easy-plane). We study the quench
dynamics for a variety of q values and show that there is a single dynamical
critical exponent to characterize the scale invariant domain growth for each
ferromagnetic phase. For both quenches we give simple analytic models that
capture the essential scale invariant dynamics, and correctly predict the
exponents. Because the order parameter for each phase is different, the natures
of the domains and the relevant topological defects in each type of coarsening
is also different. To explore these differences we characterize the fractal
dimension of the domain walls, and the relationship of polar-core spin vortices
to the domains in the easy-plane phase. Finally, we consider how the energy
liberated from the quench thermalizes in the easy-axis quench. We show that
local equilibrium is established in the spin waves on moderate time scales, but
continues to evolve as the domains anneal.",1605.04016v2
2016-05-17,Electronic Structure of the Ferromagnetic Semiconductor Fe-doped Ge Revealed by Soft X-ray Angle-Resolved Photoemission Spectroscopy,"Ge$_{1-x}$Fe$_{x}$ (Ge:Fe) shows ferromagnetic behavior up to a relatively
high temperature of 210 K, and hence is a promising material for spintronic
applications compatible with Si technology. We have studied its electronic
structure by soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES)
measurements in order to elucidate the mechanism of the ferromagnetism. We
observed finite Fe 3$d$ components in the states at the Fermi level ($E_{F}$)
in a wide region in momentum space and $E_{F}$ was located above the
valence-band maximum (VBM). First-principles supercell calculation also
suggested that the $E_{F}$ is located above the VBM, within the narrow
spin-down $d$($e$) band and within the spin-up impurity band of the deep
acceptor-level origin derived from the strong $p$-$d$($t_{2}$) hybridization.
We conclude that the narrow $d$($e$) band is responsible for the ferromagnetic
coupling between Fe atoms while the acceptor-level-originated band is
responsible for the transport properties of Ge:Fe.",1605.05275v1
2016-08-09,Griffiths phase and critical behavior in layered Sr$_2$IrO$_4$ ferromagnet,"We report the existence of Griffiths phase (GP) and its influence on critical
phenomena in layered Sr$_2$IrO$_4$ ferromagnet (T$_C$ = 221.5 K). The power law
behavior of inverse magentic susceptibility, 1/$\chi$(T) with exponent $\lambda
= 0.18(2)$ confirm the GP in the regime T$_C$ $<$ T $\leq$ T$_G$ = 279.0(5) K.
Moreover, the detailed critical analysis via modified Arrott plot method
exhibits unrealistic critical exponents $\beta$ = 0.77(1), $\gamma$ = 1.59(2)
and $\delta = 3.06(4)$, in corroboration with magneto-caloric study. The
abnormal exponent values have been viewed in context of ferromagnetic-Griffiths
phase transition. The GP has been further analyzed using Bray model, which
yields a reliable value of $\beta$ = 0.19(2), belonging to the two-dimensional
(2D) XYh$_4$ universality class with strong anisotropy present in
Sr$_2$IrO$_4$. The present study proposes Bray model as a possible tool to
investigate the critical behavior for Griffiths ferromagnets in place of
conventional Arrott plot analysis. The possible origins of GP and its
correlation with insulating nature of Sr$_2$IrO$_4$ have been discussed.",1608.02726v1
2016-08-18,Phase diagram and spin correlations of the Kitaev-Heisenberg model: Importance of quantum effects,"We explore the phase diagram of the Kitaev-Heisenberg model with nearest
neighbor interactions on the honeycomb lattice using the exact diagonalization
of finite systems combined with the cluster mean field approximation, and
supplemented by the insights from the linear spin-wave and second--order
perturbation theories. This study confirms that by varying the balance between
the Heisenberg and Kitaev term, frustrated exchange interactions stabilize in
this model four phases with magnetic long range order: N\'eel phase,
ferromagnetic phase, and two other phases with coexisting antiferromagnetic and
ferromagnetic bonds, zigzag and stripy phases. They are separated by two
disordered quantum spin-liquid phases, and the one with ferromagnetic Kitaev
interactions has a substantially broader range of stability as the neighboring
competing ordered phases, ferromagnetic and stripy, have very weak quantum
fluctuations. Focusing on the quantum spin-liquid phases, we study spatial spin
correlations and dynamic spin structure factor of the model by the exact
diagonalization technique, and discuss the evolution of gapped low-energy spin
response across the quantum phase transitions between the disordered spin
liquid and magnetic phases with long range order.",1608.05333v1
2016-12-08,Two-dimensional ReN$_2$ materials from first principles,"The discovery of graphene makes it highly desirable to seek new
two-dimensional materials. Through first-principles investigation, we predict
two-dimensional materials of ReN$_{2}$: honeycomb and tetragonal structures.
The phonon spectra establish the dynamical stability for both of the two
structures, and the calculated in-plane stiffness constants proves their
mechanical stability. The energy bands near the Fermi level consist of N-p and
Re-d orbitals for the honeycomb structure, and are mainly from Re d orbitals
for the tetragonal structure. While the tetragonal structure is non-magnetic,
the honeycomb structure has N-based ferromagnetism, which will transit to
anti-ferromagnetism under 14$\%$ biaxial strain. The calculated electron
localization function and spin density indicate that direct N-N bond can occur
only in the honeycomb structure. The ferromagnetism allows us to distinguish
the two 2D phases easily. The tetragonal phase has lower energy than the
honeycomb one, which means that the tetragonal phase is more stable, but the
hexagonal phase has much larger bulk, shear, and Young's muduli than the
tetragonal phase. The tetragonal phase is a three-bands metal, and the
hexagonal phase is a ferromagnetic semi-metal. The special structural,
electronic, magnetic, and optical properties in the honeycomb and tetragonal
structures make them promising for novel applications.",1612.02748v2
2016-12-28,Robust Ferromagnetism in Silicene Nanoflakes through Patterned Hydrogenation,"Considerably different properties emerge in nanomaterials as a result of
quantum confinement and edge effects. In this study, the electronic and
magnetic properties of quasi zero dimensional silicene nanoflakes (SiNFs) are
investigated using first principles calculations. Whilst the zigzag edged
hexagonal SiNFs exhibit nonmagnetic semiconducting character, the zigzag edged
triangular SiNFs are magnetic semiconductors. One effective method of
harnessing the properties of silicene is hydrogenation owing to its
reversibility and controllability. From bare SiNFs to half hydrogenated and
then to fully hydrogenated, a triangular SiNF experiences a change from
ferrimagnetic to very strong ferromagnetic, and then to non-magnetic.
Nonetheless, a hexagonal SiNF undergoes a transfer from nonmagnetic to very
strong ferromagnetic, then to nonmagnetic. The half hydrogenated SiNFs produce
a large spin moment that is directly proportional to the square of the flakes
size. It has been revealed that the strong induced spin magnetizations align
parallel and demonstrates a collective character by large range ferromagnetic
exchange coupling, giving rise to its potential use in spintronic circuit
devices. Spin switch models are offered as an example of one of the potential
applications of SiNFs in tuning the transport properties by controlling the
hydrogen coverage.",1612.09005v4
2017-06-02,A new class of ferromagnetic semiconductors with high Curie temperatures,"Ferromagnetic semiconductors (FMSs), which have the properties and
functionalities of both semiconductors and ferromagnets, provide fascinating
opportunities for basic research in condensed matter physics and device
applications. Over the past two decades, however, intensive studies on various
FMS materials, inspired by the influential mean-field Zener (MFZ) model have
failed to realise reliable FMSs that have a high Curie temperature (Tc > 300
K), good compatibility with semiconductor electronics, and characteristics
superior to those of their non-magnetic host semiconductors. Here, we
demonstrate a new n type Fe-doped narrow-gap III-V FMS, (In,Fe)Sb, in which
ferromagnetic order is induced by electron carriers, and its Tc is unexpectedly
high, reaching ~335 K at a modest Fe concentration of 16%. Furthermore, we show
that by utilizing the large anomalous Hall effect of (In,Fe)Sb at room
temperature, it is possible to obtain a Hall sensor with a very high
sensitivity that surpasses that of the best commercially available InSb Hall
sensor devices. Our results reveal a new design rule of FMSs that is not
expected from the conventional MFZ model. (This work was presented at the JSAP
Spring meeting, presentation No. E15a-501-2:
https://confit.atlas.jp/guide/event/jsap2017s/subject/15a-501-2/advanced)",1706.00735v1
2017-06-10,Tricritical behavior of two-dimensional intrinsic ferromagnetic semiconducting CrGeTe3,"CrGeTe3 recently emerges as a new two-dimensional (2D) ferromagnetic
semiconductor that is promising for spintronic device applications. Unlike
CrSiTe3 whose magnetism can be understood using the 2D-Ising model, CrGeTe3
exhibits a smaller van der Waals gap and larger cleavage energy, which could
lead to a transition of magnetic mechanism from 2D to 3D. To confirm this
speculation, we investigate the critical behavior CrGeTe3 around the
second-order paramagnetic-ferromagnetic phase transition. We obtain the
critical exponents estimated by several common experimental techniques
including the modified Arrott plot, Kouvel-Fisher method and critical isotherm
analysis, which show that the magnetism of CrGeTe3 follows the tricritical
mean-field model with the critical exponents \b{eta}, {\gamma}, and {\delta} of
0.240, 1.000, and 5.070, respectively, at the Curie temperature of 67.9 K. We
therefore suggest that the magnetic phase transition from 2D to 3D for CrGeTe3
should locate near a tricritical point. Our experiment provides a direct
demonstration of the applicability of the tricritical mean-field model to a 2D
ferromagnetic semiconductor.",1706.03239v1
2017-06-11,Dirac magnons in honeycomb ferromagnets,"The discovery of the Dirac electron dispersion in graphene led to the
question of the Dirac cone stability with respect to interactions. Coulomb
interactions between electrons were shown to induce a logarithmic
renormalization of the Dirac dispersion. With a rapid expansion of the list of
compounds and quasiparticle bands with linear band touching, the concept of
bosonic Dirac materials has emerged. We consider a specific case of
ferromagnets consisting of the Van der Waals-bonded stacks of honeycomb layers,
e.g chromium trihalides CrX3 (X = F, Cl, Br and I), that display two spin wave
modes with energy dispersion similar to that for the electrons in graphene. At
the single particle level, these materials resemble their fermionic
counterparts. However, how different particle statistics and interactions
affect the stability of Dirac cones has yet to be determined. To address the
role of interacting Dirac magnons, we expand the theory of ferromagnets beyond
the standard Dyson theory to a case of non-Bravais honeycomb layers. We
demonstrate that magnon-magnon interactions lead to a significant
momentum-dependent renormalization of the bare band structure in addition to
strongly momentum-dependent magnon lifetimes. We show that our theory
qualitatively accounts for hitherto unexplained anomalies in a nearly half
century old magnetic neutron scattering data for CrBr3. We also show that
honeycomb ferromagnets display dispersive surface and edge states, unlike their
electronic analogs.",1706.03384v1
2017-06-14,Engineering the breaking of time-reversal symmetry in gate-tunable hybrid ferromagnet/topological insulator heterostructures,"Studying the influence of breaking time-reversal symmetry on topological
insulator surface states is an important problem of current interest in
condensed matter physics and could provide a route toward proof-of-concept
spintronic devices that exploit spin-textured surface states. Here, we develop
a new model system for studying the effect of breaking time-reversal symmetry:
a hybrid heterostructure wherein a ferromagnetic semiconductor Ga1-xMnxAs, with
an out-of-plane component of magnetization, is cleanly interfaced with a
three-dimensional topological insulator (Bi,Sb)2(Te,Se)3 by molecular beam
epitaxy. Lateral electrical transport in this bilayer is dominated by
conduction through the topological insulator whose conductivity is a few orders
of magnitude higher than that of the highly resistive ferromagnetic
semiconductor with a low Mn concentration. Electrical transport measurements of
a top-gated heterostructure device reveal a crossover from weak
anti-localization (negative magneto-conductance) to weak localization (positive
magneto-conductance) as the temperature is lowered or as the chemical potential
approaches the Dirac point. This is accompanied by a systematic emergence of an
anomalous Hall effect. These results are interpreted in terms of the opening of
a gap at the Dirac point as a result of the exchange coupling between the
topological insulator surface state and the ferromagnetic ordering in the
Ga1-xMnxAs layer. Our study shows that this hybrid system is well suited to
explore topological quantum phenomena and to realize proof-of-concept
demonstrations of topological spintronic devices at cryogenic temperatures.",1706.04661v1
2017-06-18,"Walls, Anomalies, and (De)Confinement in Quantum Anti-Ferromagnets","We consider the Abelian-Higgs model in 2+1 dimensions with instanton-monopole
defects. This model is closely related to the phases of quantum
anti-ferromagnets. In the presence of $\mathbb{Z}_2$ preserving monopole
operators, there are two confining ground states in the monopole phase,
corresponding to the Valence Bond Solid (VBS) phase of quantum magnets. We show
that the domain-wall carries a 't Hooft anomaly in this case. The anomaly can
be saturated by, e.g., charge-conjugation breaking on the wall or by the domain
wall theory becoming gapless (a gapless model that saturates the anomaly is
$SU(2)_1$ WZW). Either way the fundamental scalar particles (i.e. spinons)
which are confined in the bulk are deconfined on the domain-wall. This
$\mathbb{Z}_2$ phase can be realized either with spin-1/2 on a rectangular
lattice, or spin-1 on a square lattice. In both cases the domain wall contains
spin-1/2 particles (which are absent in the bulk). We discuss the possible
relation to recent lattice simulations of domain walls in VBS. We further
generalize the discussion to Abrikosov-Nielsen-Olsen (ANO) vortices in a dual
superconductor of the Abelian-Higgs model in 3+1 dimensions, and to the
easy-plane limit of anti-ferromagnets. In the latter case the wall can undergo
a variant of the BKT transition (consistent with the anomalies) while the bulk
is still gapped. The same is true for the easy-axis limit of anti-ferromagnets.
We also touch upon some analogies to Yang-Mills theory.",1706.05731v2
2017-06-29,Origin of Contact Resistance at Ferromagnetic Metal-Graphene Interfaces,"Edge contact geometries are thought to yield ultralow contact resistances in
most non-ferromagnetic metal-graphene interfaces owing to their large
metal-graphene coupling strengths. Here, we examine the contact resistance of
edge- versus surface-contacted ferromagnetic metal-graphene interfaces (i.e.
nickel- and cobalt-graphene interfaces) using both single-layer and few-layer
graphene. Good qualitative agreement is obtained between theory and experiment.
In particular, in both theory and experiment, we observe that the contact
resistance of edge-contacted ferromagnetic metal-graphene interfaces is much
lower than that of surface-contacted ones, for all devices studied and
especially for the single-layer graphene systems. We show that this difference
in resistance is not due to differences in the metal-graphene coupling
strength, which we quantify using Hamiltonian matrix elements. Instead, the
larger contact resistance in surface contacts results from spin filtering at
the interface, in contrast to the edge-contacted case where both spins are
transmitted. Temperature-dependent resistance measurements beyond the Curie
temperature TC show that the spin degree of freedom is indeed important for the
experimentally measured contact resistance. These results show that it is
possible to induce a large change in contact resistance by changing the
temperature in the vicinity of TC, thus paving the way for
temperature-controlled switches based on spin.",1706.09591v1
2017-07-14,Symmetry-broken dissipative exchange flows in thin-film ferromagnets with in-plane anisotropy,"Planar ferromagnetic channels have been shown to theoretically support a
long-range ordered and coherently precessing state where the balance between
local spin injection at one edge and damping along the channel establishes a
dissipative exchange flow, sometimes referred to as a spin superfluid. However,
realistic materials exhibit in-plane anisotropy, which breaks the axial
symmetry assumed in current theoretical models. Here, we study dissipative
exchange flows in a ferromagnet with in-plane anisotropy from a dispersive
hydrodynamic perspective. Through the analysis of a boundary value problem for
a damped sine-Gordon equation, dissipative exchange flows in a ferromagnetic
channel can be excited above a spin current threshold that depends on material
parameters and the length of the channel. Symmetry-broken dissipative exchange
flows display harmonic overtones that redshift the fundamental precessional
frequency and lead to a reduced spin pumping efficiency when compared to their
symmetric counterpart. Micromagnetic simulations are used to verify that the
analytical results are qualitatively accurate, even in the presence of nonlocal
dipole fields. Simulations also confirm that dissipative exchange flows can be
driven by spin transfer torque in a finite-sized region. These results
delineate the important material parameters that must be optimized for the
excitation of dissipative exchange flows in realistic systems.",1707.04664v3
2017-10-03,Temperature- dependence of anomalous Hall conductivity in Rashba-type ferromagnets,"The applicability and usefulness of Rashba model have been extended by recent
observations in the field of spintronics, such as the spin-orbit torque at the
junction interfaces between ferromagnetic (FM) metals and non-magnetic (NM)
metals and the perpendicular anomalous magnetoresistance (AMR) in
heterostructures such as FI/NM or FM/NI (I denotes an insulator). In
particular, the observations of the perpendicular AMR effect stimulate further
interest in the Rashba-type spin-orbit interaction (SOI) at interfaces. Thus,
the Rashba model with exchange splitting (EXS) is considered not only to play
as an effective model for the physical understanding but also to reflect actual
bi-layer systems in current spintronics devices. In the present work, we have
first investigated the temperature dependence of anomalous Hall conductivity
(AHC) of Rashba-type ferromagnets considered effects of spin fluctuations
within the disordered local moment (DLM) scheme. The most distinctive feature
that we observed is that intrinsic AHC increases with increasing temperature.
This can be understood from the aspect of spin chirality, which indicates that
the AHC increases with decreasing EXS when the SOI is much smaller than the
EXS. The extrinsic part of the Fermi surface term also increases with
increasing temperature and has a large contribution, comparable to that of the
intrinsic part. Although, such a behaviour has not yet been observed
experimentally, we suggest that the physical picture found in this work might
lurk in an anomalous Hall effects in Rashbe-type ferromagnets.",1710.00982v1
2017-10-31,Kitaev-Heisenberg Hamiltonian for High-Spin $d^7$ Mott Insulators,"In the search for quantum spin liquids, candidate materials for the Kitaev
model and its extensions have been intensively explored during the past decade,
as the models realize the exact quantum spin liquids in the ground state. Thus
far, insulating magnets in the low-spin $d^5$ electron configuration under the
strong spin-orbit coupling have been studied for realizing the Kitaev-type
bond-dependent anisotropic interactions between the spin-orbital entangled
Kramers doublets. To extend the candidates, here we investigate the systems in
a high-spin $d^7$ electron configuration, whose ground state is described by
the spin-orbital entangled Kramers doublet. By the second- order perturbation
in terms of the $t_{2g}$-$t_{2g}$ and $t_{2g}$-$e_g$ hoppings, we show that the
effective spin model possesses the anisotropic Kitaev interactions as well as
the isotropic Heisenberg ones. While the Kitaev interaction is always
ferromagnetic, the Heisenberg interaction can become either ferromagnetic or
antiferromagnetic depending on the Coulomb interactions and the crystalline
electric fields. We also derive the effective model for the low-spin $d^5$
electron configuration within the same perturbation scheme, in which the Kitaev
interaction becomes both ferromagnetic and antiferromagnetic, while the
Heisenberg one always ferromagnetic. Referring to the previous study for the
Kitaev-Heisenberg model, we find that the quantum spin liquid phase exists in
the reasonable parameter region in both $d^7$ and $d^5$ cases, while the former
has a richer structure of the phase diagram. We discuss the advantages of the
$d^7$ case in comparison with the $d^5$ case. Our results indicate that the
high-spin $d^7$ state provides another platform for the Kitaev-type quantum
spin liquid.",1710.11357v2
2017-12-17,"Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures","We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as
the function of pH at which the material was prepared by chemical route and
post annealing temperature. The material is a ferri or ferromagnet, but showed
magnetic blocking and random spin freezing process on lowering the measurement
temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C
showed a sharp magnetization peak at 105 K, the superparamagnetic blocking
temperature of the particles. The magnetization peak remained incomplete within
measurement temperature up to 350 K for rest of the samples, although peak
temperature was brought down by increasing applied dc field. The fitting of
temperature dependence of coercivity data according to Kneller law suggested
random orientation of ferromagnetic particles. The fitting of saturation
magnetization according to Bloch law provided the exponent that largely
deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt
increase of saturation magnetization below 50 K suggested the active role of
frozen surface spins in low temperature magnetic properties. AC susceptibility
data elucidated the low temperature spin freezing dynamics and exhibited the
characters of cluster spin glass in the samples depending on pH value and
annealing temperature.",1712.06114v1
2017-12-20,Optical Manipulation of Magnetic Vortex Visualized in situ by 4D Electron Microscopy,"Understanding the fundamental dynamics of topological vortex and antivortex
naturally formed in micro/nanoscale ferromagnetic building blocks under
external perturbations is crucial to magnetic vortex based information
processing and spintronic devices. All previous studies have focused on
magnetic vortex-core switching via external magnetic fields, spin-polarized
currents, or spin waves, which have largely prohibited the investigation of
novel spin configurations that could emerge from the ground states in
ferromagnetic disks and their underlying dynamics. Here, we report in situ
visualization of femtosecond laser quenching induced magnetic vortex change in
various symmetric ferromagnetic Permalloy disks by Lorentz phase imaging using
4D electron microscopy. Besides the switching of magnetic vortex chirality and
polarity, we observed with distinct occurrence frequencies a plenitude of
complex magnetic structures that have never been observed by magnetic field or
current assisted switching. These complex magnetic structures consist of a
number of newly created topological magnetic defects (vortex and antivortex)
strictly conserving the topological winding number, demonstrating the direct
impact of topological invariant on the magnetization dynamics in ferromagnetic
disks. Their spin configurations show mirror or rotation symmetry due to the
geometrical confinement of the disks. Combined micromagnetic simulations with
the experimental observations reveal the underlying magnetization dynamics and
formation mechanism of the optical quenching induced complex magnetic
structures. Their distinct occurrence rates are pertinent to their
formation-growth energetics and pinning effects at the disk edge. Based on
these findings, we propose a paradigm of optical-quenching-assisted fast
switching of vortex cores for the control of magnetic vortex based information
recording and spintronic devices.",1712.07280v1
2018-01-08,Observation of magnetic vortex pairs at room temperature in a planar α-Fe2O3/Co heterostructure,"Vortices are among the simplest topological structures, and occur whenever a
flow field `whirls' around a one-dimensional core. They are ubiquitous to many
branches of physics, from fluid dynamics to superconductivity and
superfluidity, and are even predicted by some unified theories of particle
interactions, where they might explain some of the largest-scale structures
seen in today's Universe. In the crystalline state, vortex formation is rare,
since it is generally hampered by long-range interactions: in ferroic materials
(ferromagnetic and ferroelectric), vortices are only observed when the effects
of the dipole-dipole interaction is modified by confinement at the nanoscale,
or when the parameter associated with the vorticity does not couple directly
with strain. Here, we present the discovery of a novel form of vortices in
antiferromagnetic (AFM) hematite ($\alpha$-Fe$_2$O$_3$) epitaxial films, in
which the primary whirling parameter is the staggered magnetisation.
Remarkably, ferromagnetic (FM) topological objects with the same vorticity and
winding number of the $\alpha$-Fe$_2$O$_3$ vortices are imprinted onto an
ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data
suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying
an out-of-plane core magnetisation), and indicate that the vortex/meron pairs
can be manipulated by the application of an in-plane magnetic field,
H$_{\parallel}$, giving rise to large-scale vortex-antivortex annihilation.",1801.02560v2
2018-01-30,Playing with universality classes of Barkhausen avalanches,"Many systems crackle, from earthquakes and financial market to Barkhausen
effect in ferromagnetic materials. Despite the diversity in essence, the noise
emitted in these dynamical systems consists of avalanche-like events with broad
range of sizes and durations, characterized by power-law avalanche
distributions and typical average avalanche shape that are signatures dependent
on the universality class of the underlying dynamics. Here we focus on the
crackling noise in ferromagnets and scrutinize the traditional statistics of
Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films
having different thicknesses. We show how scaling exponents and average shape
of the avalanches evolve with the structural character of the materials and
film thickness. We find quantitative agreement between experiment and
theoretical predictions of models for the magnetic domain wall dynamics, and
then elucidate the universality classes of Barkhausen avalanches in
ferromagnetic films. Thereby, we observe for the first time the dimensional
crossover in the domain wall dynamics, and the outcomes of the interplay
between system dimensionality and range of interactions governing the domain
wall dynamics on Barkhausen avalanches.",1801.09948v3
2018-10-03,Ferromagnetism-induced Phase Separation in a Two-dimensional Spin Fluid,"We study the liquid-gas phase separation observed in a system of repulsive
particles dressed with ferromagnetically aligning spins, a so-called `spin
fluid'. Microcanonical ensemble numerical simulations of finite-size systems
reveal that magnetization sets in and induces a liquid-gas phase separation
between a disordered gas and a ferromagnetic dense phase at low enough energies
and large enough densities. The dynamics after a quench into the coexistence
region show that the order parameter associated to the liquid-vapour phase
separation follows an algebraic law with an unusual exponent, as it is forced
to synchronize with the growth of the magnetization: this suggests that for
finite size systems the magnetization sets in along a Curie line, which is also
the gas-side spinodal line, and that the coexistence region ends at a
tricritical point. This picture is confirmed at the mean-field level with
different approximation schemes, namely a Bethe lattice resolution and a virial
expansion complemented by the introduction of a self-consistent Weiss-like
molecular field. However, a detailed finite-size scaling analysis shows that in
two dimensions the ferromagnetic phase escapes the
Berezinskii-Kosterlitz-Thouless scenario, and that the long-range order is not
destroyed by the unbinding of topological defects. The Curie line becomes thus
a magnetic crossover in the thermodynamic limit. Finally, the effects of the
magnetic interaction range and those of the interaction softness are
characterized within a mean-field semi-analytic low-density approach.",1810.01690v2
2018-10-23,Dynamics of Order Parameters of Non-stoquastic Hamiltonians in the Adaptive Quantum Monte Carlo Method,"We derive macroscopically deterministic flow equations with regard to the
order parameters of the ferromagnetic $p$-spin model with infinite-range
interactions. The $p$-spin model has a first-order phase transition for $p>2$.
In the case of $p\geq5$ ,the $p$-spin model with anti-ferromagnetic XX
interaction has a second-order phase transition in a certain region. In this
case, however, the model becomes a non-stoqustic Hamiltonian, resulting in a
negative sign problem. To simulate the $p$-spin model with anti-ferromagnetic
XX interaction, we utilize the adaptive quantum Monte Carlo method. By using
this method, we can regard the effect of the anti-ferromagnetic XX interaction
as fluctuations of the transverse magnetic field. A previous study derived
deterministic flow equations of the order parameters in the quantum Monte Carlo
method. In this study, we derive macroscopically deterministic flow equations
for the magnetization and transverse magnetization from the master equation in
the adaptive quantum Monte Carlo method. Under the Suzuki-Trotter
decomposition, we consider the Glauber-type stochastic process. We solve these
differential equations by using the Runge-Kutta method and verify that these
results are consistent with the saddle-point solution of mean-field theory.
Finally, we analyze the stability of the equilibrium solutions obtained by the
differential equations.",1810.09943v3
2019-06-06,Higher-Order Topological Superconductivity of Spin-Polarized Fermions,"We study the superconductivity of spin-polarized electrons in centrosymmetric
ferromagnetic metals. Due to the spin-polarization and the Fermi statistics of
electrons, the superconducting pairing function naturally has odd parity.
According to the parity formula proposed by Fu, Berg, and Sato, odd-parity
pairing leads to conventional first-order topological superconductivity when a
normal metal has an odd number of Fermi surfaces. Here, we derive generalized
parity formulae for the topological invariants characterizing higher-order
topology of centrosymmetric superconductors. Based on the formulae, we
systematically classify all possible band structures of ferromagnetic metals
that can induce inversion-protected higher-order topological superconductivity.
Among them, doped ferromagnetic nodal semimetals are identified as the most
promising normal state platform for higher-order topological superconductivity.
In two dimensions, we show that odd-parity pairing of doped Dirac semimetals
induces a second-order topological superconductor. In three dimensions,
odd-parity pairing of doped nodal line semimetals generates a nodal line
topological superconductor with monopole charges. On the other hand, odd-parity
pairing of doped monopole nodal line semimetals induces a three-dimensional
third-order topological superconductor. Our theory shows that the combination
of superconductivity and ferromagnetic nodal semimetals opens up a new avenue
for future topological quantum computations using Majorana zero modes.",1906.02709v3
2019-06-12,Spin transport and Spin Tunnelling Magneto-Resistance (STMR) of F$|$NCSC$|$F spin valve,"In this work, we study the spin transport at the
Ferromagnet$|$Noncentrosymmetric Superconductor (F$|$NCSC) junction of a
Ferromagnet$|$Noncentrosymmetric Superconductor$|$Ferromagnet (F$|$NCSC$|$F)
spin valve. We investigate the Tunnelling Spin-Conductance (TSC), spin current
and Spin Tunnelling Magneto-Resistance (STMR), and their dependence on various
important parameters like Rashba Spin-Orbit Coupling (RSOC), strength and
orientation of magnetization, an external in-plane magnetic field, barrier
strength and a significant Fermi Wavevector Mismatch (FWM) at the ferromagnetic
and superconducting regions. The study has been carried out for different
singlet-triplet mixing of the NCSC gap parameter. We develop Bogoliubov-de
Gennes (BdG) Hamiltonian and use the extended Blonder - Tinkham - Klapwijk
(BTK) approach along with the scattering matrix formalism to calculate the
scattering coefficients. Our results strongly suggest that the TSC is highly
dependent on RSOC, magnetization strength and its orientation, and
singlet-triplet mixing of the gap parameter. It is observed that NCSC with
moderate RSOC shows maximum conductance for a partially opaque barrier in
presence of low external magnetic field. For a strongly opaque barrier and a
nearly transparent barrier a moderate value and a low value of field
respectively are found to be suitable. Moreover, NCSC with large singlet
component is appeared to be useful. In addition, for NCSC with large RSOC and
low magnetization strength, a giant STMR ($\%$) is observed. We have also seen
that the spin current is strongly magnetization orientation dependent. With the
increase in bias voltage spin current increases in transverse direction, but
the component along the direction of flow is almost independent.",1906.05081v1
2019-07-11,Anomalous anisotropic behaviour of spin-triplet proximity effect in Au/SrRuO$_3$/Sr$_2$RuO$_4$ junctions,"Spin-polarized supercurrents can be generated with magnetic inhomogeneity at
a ferromagnet/spin-singlet-superconductor interface. In such systems, complex
magnetic inhomogeneity makes it difficult to functionalise the spin-polarized
supercurrents. However, spin-polarized supercurrents in
ferromagnet/spin-triplet-superconductor junctions can be controlled by angle
between magnetization and spin of Copper pairs ($d$-vector), that can
effectively be utilized in developing of a field of research known as
superconducting spintronics. Recently, we found induction of spin-triplet
correlation into a ferromagnet SrRuO$_3$ epitaxially deposited on a
spin-triplet superconductor Sr$_2$RuO$_4$, without any electronic spin-flip
scattering. Here, we present systematic magnetic field dependence of the
proximity effect in Au/SrRuO$_3$/ Sr$_2$RuO$_4$ junctions. It is found that
induced triplet correlations exhibit strong anisotropic field response. Such
behaviour attributes to the rotation of the $d$-vector of Sr$_2$RuO$_4$. This
anisotropic behaviour is in contrast with the vortex dynamic. Our results will
stimulate study of interaction between ferromagnetism and unconventional
superconductivity.",1907.05175v2
2019-07-07,"Spin-1 Dirac half-metal, spin-gapless semiconductor, and spin-polarized massive Dirac dispersion in transition metal dihalide monolayers","Spin-1 condensed matter systems characterized by the combination of a
Dirac-like dispersion and flat bands are ideal for realizing high-temperature
electronics and spintronic technologies in the absence of external magnetic
field. In this study, we propose a three-band tight binding model, with
spin-polarized Haldane-like next-nearest-neighbour tunnelling, on dice lattice
and show that spin-1 Dirac half-metal, spin-1 Dirac spin-gapless semiconductor,
and spin-polarized spin-1 massive Dirac dispersion with nontrivial topology can
exist in two-dimensional ferromagnetic condensed matter systems with electron
spin polarization P = 1. The proposed spin-polarized spin-1 phases can be
realized in ferromagnetic transition metal dihalides MX2 monolayers
effectively. By using first principle calculations, we show that a small
compressive strain leads MX2 monolayers to be spin-one Dirac half-metal for M =
Fe and X = Br, Cl while spin-one Dirac spin-gapless semiconductor for M = Co
and X = Br, Cl. Spin-one Dirac spin-gapless semiconductors CoBr2 and CoCl2
embeds flat band ferromagnetism where spin-orbit coupling opens a topologically
non-trivial Dirac gap between dispersing valance and conduction band while
leaving flat band unaffected. The intrinsic flat-band ferromagnetism in
spin-polarized spin-1 massive Dirac dispersion plays key role in materializing
quantum anomalous Hall state with Chern number C = -2.",1907.07756v1
2019-07-19,Multiple ferromagnetic transitions and structural distortion in the van-der-Waals ferromagnet VI$_3$ at ambient and finite pressures,"We present a combined study of zero-field $^{51}$V and $^{127}$I NMR at
ambient pressure and specific heat and magnetization measurements under
pressure up to 2.08 GPa on bulk single crystals of the van-der-Waals
ferromagnet VI$_3$. At ambient pressure, our results consistently demonstrate
that VI$_3$ undergoes a structural transition at $T_s \approx $78 K, followed
by two subsequent ferromagnetic transitions at $T_{FM1} \approx $50 K and
$T_{FM2} \approx $36 K upon cooling. At lowest temperature ($T < T_{FM2}$), two
magnetically-ordered V sites exist, whereas only one magnetically-ordered V
site is observed for $T_{FM1} < T\,< T_{FM2}$. Whereas $T_{FM1}$ is almost
unaffected by external pressure, $T_{FM2}$ is highly responsive to pressure and
merges with the $T_{FM1}$ line at $p \approx 0.6 $GPa. At even higher pressures
($p \approx $1.25\,GPa), the $T_{FM2}$ line merges with the structural
transition at $T_s$ which becomes moderately suppressed with $p$ for $p < 1.25$
GPa. Taken together, our data point towards a complex magnetic structure and an
interesting interplay of magnetic and structural degrees of freedom in VI$_3$.",1907.08550v2
2019-09-23,Skyrmion Brownian circuit implemented in a continuous ferromagnetic thin film,"The fabrication of a skyrmion circuit which stabilizes skyrmions is important
to realize micro- to nano-sized skyrmion devices. One example of promising
skyrmion-based device is Brownian computers, which have been theoretically
proposed, but not realized. It would require a skyrmion circuit in which the
skyrmion is stabilized and easily movable. However, the usual skyrmion circuits
fabricated by etching of the ferromagnetic film decrease the demagnetization
field stabilizing the skyrmions, and thus prevent their formation. In this
study, a skyrmion Brownian circuit implemented in a continuous ferromagnetic
film with patterned SiO$_2$ capping to stabilize the skyrmion formation. The
patterned SiO$_2$ capping controls the saturation field of the ferromagnetic
layer and forms a wire-shaped skyrmion potential well, which stabilizes
skyrmion formation in the circuit. Moreover, we implement a hub (Y-junction)
circuit without pinning sites at the junction by patterned SiO$_2$ capping.
This technique enables the efficient control of skyrmion-based memory and logic
devices, as well as Brownian computers.",1909.10130v2
2019-09-24,Unconventional Hund Metal in a Weak Itinerant Ferromagnet,"The physics of weak itinerant ferromagnets is challenging due to their small
magnetic moments and the ambiguous role of local interactions governing their
electronic properties, many of which violate Fermi liquid theory. While
magnetic fluctuations play an important role in the materials' unusual
electronic states, the nature of these fluctuations and the paradigms through
which they arise remain debated. Here we use inelastic neutron scattering to
study magnetic fluctuations in the canonical weak itinerant ferromagnet MnSi.
Data reveal that short-wavelength magnons continue to propagate until a mode
crossing predicted for strongly interacting quasiparticles is reached, and the
local susceptibility peaks at a coherence energy predicted for a correlated
Hund metal by first-principles many-body theory. Scattering between electrons
and orbital and spin fluctuations in MnSi can be understood at the local level
to generate non-Fermi liquid character. These results provide crucial insight
into the role of interorbital Hund's exchange within the broader class of
enigmatic multiband itinerant, weak ferromagnets.",1909.11195v2
2019-10-15,Superconducting Correlations in the One-Dimensional Kondo Lattice Models under Magnetic Fields,"We analyze superconducting correlations in the one-dimensional Kondo lattice
models with Ising anisotropy under transverse magnetic fields, using the
density matrix renormalization group. For the spin-1/2 local spin model, the
Ising anisotropy is introduced by the ferromagnetic Ising interaction between
the local spins, while for the spin-1 model, it is taken by the single-ion
anisotropy. The magnetic properties under the transverse fields for the
spin-1/2 model are very similar to those for the spin-1 model [K. Suzuki and K.
Hattori, J. Phys. Soc. Jpn. 88, 024707 (2019).]. For the superconducting
correlations, we analyze various Cooper pairs within nearest-neighbor pairs
including composite ones between the local spins and the electrons. We find
that, for the spin-1/2 model, the superconducting correlations are highly
enhanced in the Tomonaga-Luttinger liquid state near the Kondo-plateau phase,
where the conduction electrons and the local spins are strongly coupled with a
finite spin gap for the Ising axis. This is a clear contrast to the model under
the longitudinal magnetic fields, where there are no noticeable superconducting
correlations. Competitions between the transverse magnetic field and the Kondo
singlet formation lead to this enhanced superconducting correlations. For the
spin-1 model, the single-ion anisotropy suppresses the superconducting
correlation and there is no noticeable enhancement. We also examine the large
Kondo exchange coupling limit. For the moderate ferromagnetic Ising interaction
between the local spins, we find that another type of superconducting
correlation is enhanced inside the ferromagnetic phase. We discuss a possible
relation between our results and reentrant superconductivity in U-based
ferromagnetic superconductors under transverse magnetic fields.",1910.06545v2
2019-10-22,Magnetic topological insulator MnBi6Te10 with zero-field ferromagnetic state and gapped Dirac surface states,"Magnetic topological insulators (TIs) with nontrivial topological electronic
structure and broken time-reversal symmetry exhibit various exotic topological
quantum phenomena. The realization of such exotic phenomena at high temperature
is one of central topics in this area. We reveal that MnBi6Te10 is a magnetic
TI with an antiferromagnetic ground state below 10.8 K whose nontrivial
topology is manifested by Dirac-like surface states. The ferromagnetic axion
insulator state with Z4 = 2 emerges once spins polarized at field as low as 0.1
T, accompanied with saturated anomalous Hall resistivity up to 10 K. Such a
ferromagnetic state is preserved even external field down to zero at 2 K.
Theoretical calculations indicate that the few-layer ferromagnetic MnBi6Te10 is
also topologically nontrivial with a non-zero Chern number. Angle-resolved
photoemission spectroscopy experiments further reveal three types of Dirac
surface states arising from different terminations on the cleavage surfaces,
one of which has insulating behavior with an energy gap of ~ 28 meV at the
Dirac point. These outstanding features suggest that MnBi6Te10 is a promising
system to realize various topological quantum effects at zero field and high
temperature.",1910.10101v2
2019-10-24,Experimental evidence of inertial dynamics in ferromagnets,"The understanding of how spins move at pico- and femtosecond time scales is
the goal of much of modern research in condensed matter physics, with
implications for ultrafast and more energy-efficient data storage. However, the
limited comprehension of the physics behind this phenomenon has hampered the
possibility of realising a commercial technology based on it. Recently, it has
been suggested that inertial effects should be considered in the full
description of the spin dynamics at these ultrafast time scales, but a clear
observation of such effects in ferromagnets is still lacking. Here, we report
the first direct experimental evidence of inertial spin dynamics in
ferromagnetic thin films in the form of a nutation of the magnetisation at a
frequency of approximately 0.6 THz. This allows us to evince that the angular
momentum relaxation time in ferromagnets is on the order of 10 ps.",1910.11284v1
2020-01-19,Ultrafast kinetics of the antiferromagnetic-ferromagnetic phase transition in FeRh,"Understanding how fast short-range interactions build up long-range order is
one of the most intriguing topics in condensed matter physics. FeRh is a test
specimen for studying this problem in magnetism, where the microscopic
spin-spin exchange interaction is ultimately responsible for either ferro- or
antiferromagnetic macroscopic order. Femtosecond laser excitation can induce
ferromagnetism in antiferromagnetic FeRh, but the mechanism and dynamics of
this transition are topics of intense debates. Employing double-pump THz
emission spectroscopy has enabled us to dramatically increase the temporal
detection window of THz emission probes of transient states without sacrificing
any loss of resolution or sensitivity. It allows us to study the kinetics of
emergent ferromagnetism from the femtosecond up to the nanosecond timescales in
FeRh/Pt bilayers. Our results strongly suggest a latency period between the
initial pump-excitation and the emission of THz radiation by ferromagnetic
nuclei.",2001.06799v4
2020-02-23,Large anomalous Hall effect in a hexagonal ferromagnetic Fe5Sn3 single crystal,"In this paper, we report an experimental observation of the large anomalous
Hall effect (AHE) in a hexagonal ferromagnetic Fe5Sn3 single crystal with
current along the b axis and a magnetic field normal to the bc plane. The
intrinsic contribution of the anomalous Hall conductance sigma_AH^int was
approximately 613 {\Omega}-1 cm-1, which was more than 3 times the maximum
value in the frustrated kagome magnet Fe3Sn2 and nearly independent of the
temperature over a wide range between 5 and 350 K. The analysis results
revealed that the large AHE was dominated by a common, intrinsic term, while
the extrinsic contribution, i.e., the skew scattering and side jump, turned out
to be small. In addition to the large AHE, it was found the types of majority
carriers changed at approximately 275 and 30 K, consistent with the critical
temperatures of the spin reorientation. These findings suggest that the
hexagonal ferromagnetic Fe5Sn3 single crystal is an excellent candidate to use
for the study of the topological features in ferromagnets.",2002.09872v2
2020-04-22,Spectroscopic Signature for Local-moment Magnetism in van der Waals Ferromagnet Fe$_3$GeTe$_2$,"The van der Waals ferromagnet Fe$_3$GeTe$_2$ has recently attracted extensive
research attention due to its intertwined magnetic, electronic and topological
properties. Here, using high-resolution angle-resolved photoemission
spectroscopy, we systematically investigate the temperature evolution of the
electronic structure of bulk Fe$_3$GeTe$_2$. We observe largely dispersive
energy bands that are narrowed by a factor of 1.6 compared with ab-initio
calculation. Upon heating towards the ferromagnetic transition near 225 K, we
observe a massive reduction of quasiparticle coherence in a large energy range,
which is attributed to the enhanced magnetic fluctuation in the system.
Remarkably, the electron bands barely shift with increasing temperature, which
deviates from the exchange splitting picture within the itinerant Stoner model.
We argue that the local magnetic moments play a crucial role in the
ferromagnetism of Fe$_3$GeTe$_2$, despite its strongly itinerant nature. Our
results provide important insights into the electronic and magnetic properties
of Fe$_3$GeTe$_2$ and shed light on the generic understanding of itinerant
magnetism in correlated materials.",2004.10379v1
2020-12-06,Ultrafast ferromagnetic fluctuations preceding magnetoelastic first-order transitions,"First-order magnetic transitions are of both fundamental and technological
interest given that a number of emergent phases and functionalities are thereby
created. Of particular interest are giant magnetocaloric effects, which are
attributed to first-order magnetic transitions and have attracted broad
attention for solid-state refrigeration applications. While the conventional
wisdom is that atomic lattices play an important role in first-order magnetic
transitions, a coherent microscopic description of the lattice and spin degrees
of freedom is still lacking. Here, we study the magnetic phase transition
dynamics on the intermetallic LaFe13-xSix, which is one of the most classical
giant magnetocaloric systems, in both frequency and time domains utilizing
neutron scattering and ultrafast X-ray diffraction. We have observed a strong
magnetic diffuse scattering in the paramagnetic state preceding the first-order
magnetic transition, corresponding to picosecond ferromagnetic fluctuations.
Upon photon-excitation, the ferromagnetic state is completely suppressed in 0.9
ps and recovered in 20 ps. The ultrafast dynamics suggest that the magnetic
degree of freedom dominates this magnetoelastic transition and ferromagnetic
fluctuations might be universally relevant for this kind of compounds.",2012.03186v1
2020-12-22,Quantum Anomalous Hall Effect in Magnetic Doped Topological Insulators and Ferromagnetic Spin-Gapless Semiconductors -- A Perspective Review,"Quantum anomalous Hall effect, with a trademark of dissipationless chiral
edge states for electronics/spintronics transport applications, can be realized
in materials with large spin-orbit coupling and strong intrinsic magnetization.
After Haldane seminal proposal, several models have been presented to
control/enhance the spin-orbit coupling and intrinsic magnetic exchange
interaction. After brief introduction of Haldane model for spineless fermions,
following three fundamental quantum anomalous Hall models are discussed in this
perspective review: (i) low-energy effective four band model for magnetic-doped
topological insulator (Bi,Sb)2Te3 thin films, (ii) four band tight-binding
model for graphene with magnetic adatoms, and (iii) two (three) band spinfull
tight-binding model for ferromagnetic spin-gapless semiconductors with
honeycomb (kagome) lattice where ground state is intrinsically ferromagnetic.
These models cover two-dimensional Dirac materials hosting spinless, spinful
and spin-degenerate Dirac points where various mass terms open a band gap and
lead to quantum anomalous Hall effect. With emphasize on the topological phase
transition driven by ferromagnetic exchange interaction and its interplay with
spin-orbit-coupling, we discuss various symmetry constraints on the nature of
mass term and the materialization of these models. We hope this study will shed
light on the fundamental theoretical perspectives of quantum anomalous Hall
materials.",2101.01074v1
2021-01-05,Itinerant ferromagnetism mediated by giant spin polarization of metallic ligand band in van der Waals magnet Fe5GeTe2,"We investigate near-Fermi-energy (EF) element-specific electronic and spin
states of ferromagnetic van der Waals (vdW) metal Fe5GeTe2. The soft x-ray
angle-resolved photoemission spectroscopy (SX-ARPES) measurement provides
spectroscopic evidence of localized Fe 3d band. We also find prominent
hybridization between the localized Fe 3d band and the delocalized Ge/Te p
bands. This picture is strongly supported from direct observation of the
remarkable spin polarization of the ligand p bands near EF, using x-ray
magnetic circular dichroism (XMCD) measurements. The strength of XMCD signal
from ligand element Te shows the highest value, as far as we recognize, among
literature reporting finite XMCD signal for none-magnetic element in any
systems. Combining SX-ARPES and elemental selective XMCD measurements, we
collectively point an important role of giant spin polarization of the
delocalized ligand Te states for realizing itinerant long-range ferromagnetism
in Fe5GeTe2. Our finding provides a fundamental elemental selective view-point
for understanding mechanism of itinerant ferromagnetism in low dimensional
compounds, which also leads insight for designing exotic magnetic states by
interfacial band engineering in heterostructures.",2101.01324v1
2021-01-13,Spin pumping between noncollinear ferromagnetic insulators through thin superconductors,"Dynamical magnets can pump spin currents into superconductors. To understand
such a phenomenon, we develop a method utilizing the generalized Usadel
equation to describe time-dependent situations in superconductors in contact
with dynamical ferromagnets. Our proof-of-concept theory is valid when there is
sufficient dephasing at finite temperatures, and when the ferromagnetic
insulators are weakly polarized. We derive the effective equation of motion for
the Keldysh Green's function focusing on a thin film superconductor sandwiched
between two noncollinear ferromagnetic insulators of which one is dynamical. In
turn, we compute the spin currents in the system as a function of the
temperature and the magnetizations' relative orientations. When the induced
Zeeman splitting is weak, we find that the spin accumulation in the
superconducting state is smaller than in the normal states due to the lack of
quasiparticle states inside the gap. This feature gives a lower backflow spin
current from the superconductor as compared to a normal metal. Furthermore, in
superconductors, we find that the ratio between the backflow spin current in
the parallel and anti-parallel magnetization configuration depends strongly on
temperature, in contrast to the constant ratio in normal metals.",2101.05128v1
2017-09-06,"Tuning ferromagnetism and spin state in La$_{(1-x)}$$A_x$CoO$_3$ ($A=$ Sr, Ca) nanoparticles","We use the x-ray diffraction, magnetic susceptibility, isothermal
magnetization, and photoelectron spectroscopy to study the structural, magnetic
and electronic properties of La$_{(1-x)}$$A_x$CoO$_3$ ($A=$ Sr, Ca; $x=$ 0 --
0.2) nanoparticles. The Rietveld refinements of room temperature powder x-ray
diffraction data confirm the single phase and the rhombohedral crystal
structure with R$\bar{3}$C space group. We find drastic changes in the magnetic
properties and spin-states with Sr/Ca substitution (hole doping). For $x=$ 0
sample, the magnetic measurements show a ferromagnetic transition at T$_{\rm
C}$$\approx$85 K, which shifted significantly to higher temperatures with hole
doping; simultaneously a significant increase in the spontaneous magnetic
moment has been observed. Whereas, the coercive field H$_{\rm C}$ values are 7,
4.4 and 13.2~kOe for $x=$ 0, 0.2 (Sr), and 0.2(Ca) samples. Furthermore, the FC
magnetization shows a ferromagnetic Brillouin function like behavior at low
temperatures for Ca samples. We demonstrate that the Sr/Ca substitution
increases the population of IS (Co$^{3+}$) and LS (Co$^{4+}$) states and tune
the ferromagnetism in nanoparticles via double-exchange interactions between
Co$^{3+}$-- Co$^{4+}$. Our results suggest an important role of hole carriers
and nano-size effect in controlling the spin-state and magnetism in
La$_{(1-x)}$$A_x$CoO$_3$ nanoparticles.",1709.01745v1
2017-09-20,Property Testing in High Dimensional Ising models,"This paper explores the information-theoretic limitations of graph property
testing in zero-field Ising models. Instead of learning the entire graph
structure, sometimes testing a basic graph property such as connectivity, cycle
presence or maximum clique size is a more relevant and attainable objective.
Since property testing is more fundamental than graph recovery, any necessary
conditions for property testing imply corresponding conditions for graph
recovery, while custom property tests can be statistically and/or
computationally more efficient than graph recovery based algorithms.
Understanding the statistical complexity of property testing requires the
distinction of ferromagnetic (i.e., positive interactions only) and general
Ising models. Using combinatorial constructs such as graph packing and strong
monotonicity, we characterize how target properties affect the corresponding
minimax upper and lower bounds within the realm of ferromagnets. On the other
hand, by studying the detection of an antiferromagnetic (i.e., negative
interactions only) Curie-Weiss model buried in Rademacher noise, we show that
property testing is strictly more challenging over general Ising models. In
terms of methodological development, we propose two types of correlation based
tests: computationally efficient screening for ferromagnets, and score type
tests for general models, including a fast cycle presence test. Our correlation
screening tests match the information-theoretic bounds for property testing in
ferromagnets.",1709.06688v2
2017-09-20,Efficient and controlled domain wall nucleation for magnetic shift registers,"Ultrathin ferromagnetic strips with high perpendicular anisotropy have been
proposed for the development of memory devices where the information is coded
in tiny domains separated by domain walls. The design of practical devices
requires creating, manipulating and detecting domain walls in ferromagnetic
strips. Recent observations have shown highly efficient current-driven domain
wall dynamics in multilayers lacking structural symmetry, where the walls adopt
a chiral structure and can be driven at high velocities. However, putting such
a device into practice requires the continuous and synchronous injection of
domain walls as the first step. Here, we propose and demonstrate an efficient
and simple scheme for nucleating domain walls using the symmetry of the spin
orbit torques. Trains of short sub-nanosecond current pulses are injected in a
double bit line to generate a localized longitudinal Oersted field in the
ferromagnetic strip. Simultaneously, other current pulses are injected through
the heavy metal under the ferromagnetic strip. Notably, the Slonczewski-like
spin orbit torque assisted by the Oersted field allows the controlled injection
of a series of domain walls, giving rise to a controlled manner for writing
binary information and, consequently, to the design of a simple and efficient
domain wall shift register.",1709.06753v1
2017-09-28,Direct Evidence of Spontaneous Abrikosov Vortex State in Ferromagnetic Superconductor EuFe$_2$(As$_{1-x}$P$_x$)$_2$ with $x=0.21$,"Using low-temperature Magnetic Force Microscopy (MFM) we provide direct
experimental evidence for spontaneous vortex phase (SVP) formation in
EuFe$_2$(As$_{0.79}$P$_{0.21}$)$_2$ single crystal with the superconducting
$T^{\rm 0}_{\rm SC}=23.6$~K and ferromagnetic $T_{\rm FM}\sim17.7$~K transition
temperatures. Spontaneous vortex-antivortex (V-AV) pairs are imaged in the
vicinity of $T_{\rm FM}$. Also, upon cooling cycle near $T_{\rm FM}$ we observe
the first-order transition from the short period domain structure, which
appears in the Meissner state, into the long period domain structure with
spontaneous vortices. It is the first experimental observation of this scenario
in the ferromagnetic superconductors. Low-temperature phase is characterized by
much larger domains in V-AV state and peculiar branched striped structures at
the surface, which are typical for uniaxial ferromagnets with perpendicular
magnetic anisotropy (PMA). The domain wall parameters at various temperatures
are estimated.",1709.09802v2
2017-09-28,Massive Dirac fermions in a ferromagnetic kagome metal,"The kagome lattice is a two-dimensional network of corner-sharing triangles
known as a platform for exotic quantum magnetic states. Theoretical work has
predicted that the kagome lattice may also host Dirac electronic states that
could lead to topological and Chern insulating phases, but these have evaded
experimental detection to date. Here we study the d-electron kagome metal
Fe$_3$Sn$_2$ designed to support bulk massive Dirac fermions in the presence of
ferromagnetic order. We observe a temperature independent intrinsic anomalous
Hall conductivity persisting above room temperature suggestive of prominent
Berry curvature from the time-reversal breaking electronic bands of the kagome
plane. Using angle-resolved photoemission, we discover a pair of quasi-2D Dirac
cones near the Fermi level with a 30 meV mass gap that accounts for the Berry
curvature-induced Hall conductivity. We show this behavior is a consequence of
the underlying symmetry properties of the bilayer kagome lattice in the
ferromagnetic state with atomic spin-orbit coupling. This report provides the
first evidence for a ferromagnetic kagome metal and an example of emergent
topological electronic properties in a correlated electron system. This offers
insight into recent discoveries of exotic electronic behavior in kagome lattice
antiferromagnets and may provide a stepping stone toward lattice model
realizations of fractional topological quantum states.",1709.10007v1
2017-11-02,A Comparative Study on Spin-Orbit Torque Efficiencies from W/ferromagnetic and W/ferrimagnetic Heterostructures,"It has been shown that W in its resistive form possesses the largest
spin-Hall ratio among all heavy transition metals, which makes it a good
candidate for generating efficient dampinglike spin-orbit torque (DL-SOT)
acting upon adjacent ferromagnetic or ferrimagnetic (FM) layer. Here we provide
a systematic study on the spin transport properties of W/FM magnetic
heterostructures with the FM layer being ferromagnetic
Co$_{20}$Fe$_{60}$B$_{20}$ or ferrimagnetic Co$_{63}$Tb$_{37}$ with
perpendicular magnetic anisotropy. The DL-SOT efficiency $|\xi_{DL}|$, which is
characterized by a current-induced hysteresis loop shift method, is found to be
correlated to the microstructure of W buffer layer in both
W/Co$_{20}$Fe$_{60}$B$_{20}$ and W/Co$_{63}$Tb$_{37}$ systems. Maximum values
of $|\xi_{DL}|\approx 0.144$ and $|\xi_{DL}|\approx 0.116$ are achieved when
the W layer is partially amorphous in the W/Co$_{20}$Fe$_{60}$B$_{20}$ and
W/Co$_{63}$Tb$_{37}$ heterostructures, respectively. Our results suggest that
the spin Hall effect from resistive phase of W can be utilized to effectively
control both ferromagnetic and ferrimagnetic layers through a DL-SOT mechanism.",1711.00630v2
2017-11-12,Magnetic proximity effect of a topological insulator and a ferromagnet in thin film bilayers of $BiSbTe_3$ and $SrRuO_3$,"Magnetic proximity effect of a topological insulator in contact with a
ferromagnet is reported in thin film bilayers of 15 nm thick $BiSbTe_3$ on
either 15 or 40 nm thick $SrRuO_3$ on (100) $SrTiO_3$ wafers. Magneto transport
results of the bilayers were compared with those of reference films of 15 nm
$BiSbTe_3$ and 15 or 40 nm $SrRuO_3$. Comparison of the temperature coefficient
of resistance [(1/R)$\times$dR/dT which is qualitatively proportional to the
magnetization] of the bilayer and reference ferromagnetic film normalized above
$T_c$, shows a clear suppression in the bilayer by about 50% just below $T_c$,
indicating a weaker proximity magnetization in the bilayer. Resistance
hysteresis loops versus field at 1.85$\pm$0.05 K in the bilayer and reference
films show a clear magnetic proximity effect, where the peak resistance of the
bilayer at the coercive field shifts to lower fields by $\sim$30% compared to a
hypothetical bilayer of two resistors connected in parallel with no interaction
between the layers. Narrowing of the coercive peaks of the bilayers as compared
to those of the reference ferromagnetic films by 25-35% was also observed,
which represents another signature of the magnetic proximity effect.",1711.04275v2
2017-11-16,Spin-orbit torques and tunable Dzyaloshinskii-Moriya interaction in Co/Cu/Co trilayers,"We study the spin-orbit torques (SOTs) in Co/Cu/Co magnetic trilayers based
on first-principles density-functional theory calculations in the case where
the applied electric field lies in-plane, i.e., parallel to the interfaces. We
assume that the bottom Co layer has a fixed in-plane magnetization, while the
top Co layer can be switched. We find that the SOT on the top ferromagnet can
be controlled by the bottom ferromagnet because of the nonlocal character of
the SOT in this system. As a consequence the SOT is anisotropic, i.e., its
magnitude varies with the direction of the applied electric field. We show that
the Dzyaloshinskii-Moriya interaction (DMI) in the top layer is anisotropic as
well, i.e., the spin-spiral wavelength of spin-spirals in the top layer depends
on their in-plane propagation direction. This effect suggests that DMI can be
tuned easily in magnetic trilayers via the magnetization direction of the
bottom layer. In order to understand the influence of the bottom ferromagnet on
the SOTs and the DMI of the top ferromagnet we study these effects in Co/Cu
magnetic bilayers for comparison. We find the SOTs and the DMI to be
surprisingly large despite the small spin-orbit interaction of Cu.",1711.06102v2
2018-03-02,Broadband spectroscopy of thermodynamic magnetization fluctuations through a ferromagnetic spin-reorientation transition,"We use scanning optical magnetometry to study the broadband frequency spectra
of spontaneous magnetization fluctuations, or ""magnetization noise"", in an
archetypal ferromagnetic film that can be smoothly tuned through a spin
reorientation transition (SRT). The SRT is achieved by laterally varying the
magnetic anisotropy across an ultrathin Pt/Co/Pt trilayer, from the
perpendicular to in-plane direction, via graded Ar$^+$ irradiation. In regions
exhibiting perpendicular anisotropy, the power spectrum of the magnetization
noise, $S(\nu)$, exhibits a remarkably robust $\nu^{-3/2}$ power law over
frequencies $\nu$ from 1~kHz to 1~MHz. As the SRT region is traversed, however,
$S(\nu)$ spectra develop a steadily-increasing critical frequency, $\nu_0$,
below which the noise power is spectrally flat, indicating an evolving
low-frequency cutoff for magnetization fluctuations. The magnetization noise
depends strongly on applied in- and out-of-plane magnetic fields, revealing
local anisotropies and also a field-induced emergence of fluctuations in
otherwise stable ferromagnetic films. Finally, we demonstrate that higher-order
correlators can be computed from the noise. These results highlight broadband
spectroscopy of thermodynamic fluctuations as a powerful tool to characterize
the interplay between thermal and magnetic energy scales, and as a means of
characterizing phase transitions in ferromagnets.",1803.00962v1
2018-03-05,Electric-field modification of interfacial spin-orbit field-vector,"Current induced spin-orbit magnetic fields (iSOFs), arising either in
single-crystalline ferromagnets with broken inversion symmetry1,2 or in
non-magnetic metal/ferromagnetic metal bilayers3,4, can produce spin-orbit
torques which act on a ferromagnet's magnetization,thus offering an efficient
way for its manipulation.To further reduce power consumption in spin-orbit
torque devices, it is highly desirable to control iSOFs by the field-effect,
where power consumption is determined by charging/discharging a capacitor5,6.
In particular, efficient electric-field control of iSOFs acting on
ferromagnetic metals is of vital importance for practical applications. It is
known that in single crystalline Fe/GaAs (001) heterostructures with C2v
symmetry, interfacial SOFs emerge at the Fe/GaAs (001) interface due to the
lack of inversion symmetry7,8. Here, we show that by applying a gate-voltage
across the Fe/GaAs interface, interfacial SOFs acting on Fe can be robustly
modulated via the change of the magnitude of the interfacial spin-orbit
interaction. Our results show that, for the first time, the electric-field in a
Schottky barrier is capable of modifying SOFs, which can be exploited for the
development of low-power-consumption spin-orbit torque devices.",1803.01656v2
2018-03-20,Direct demonstration of the emergent magnetism resulting from the multivalence Mn in a LaMnO3 epitaxial thin film system,"Atomically engineered oxide heterostructures provide a fertile ground for
creating novel states. For example, a two-dimensional electron gas at the
interface between two oxide insulators, giant thermoelectric Seebeck
coefficient, emergent ferromagnetism from otherwise nonmagnetic components, and
colossal ionic conductivity. Extensive research efforts reveal that oxygen
deficiency or lattice strain play an important role in determining these
unexpected properties. Herein, by studying the abrupt presence of robust
ferromagnetism (up to 1.5 uB/Mn) in LaMnO3-based heterostructures, we find the
multivalence states of Mn that play a decisive role in the emergence of
ferromagnetism in the otherwise antiferromagnetic LaMnO3 thin films. Combining
spatially resolved electron energy-loss spectroscopy, X-ray absorption
spectroscopy and X-ray magnetic circular dichroism techniques, we determine
unambiguously that the ferromagnetism results from a conventional Mn3+-O-Mn4+
double-exchange mechanism rather than an interfacial effect. In contrast, the
magnetic dead layer of 5 unit cell in proximity to the interface is found to be
accompanied with the accumulation of Mn2+ induced by electronic reconstruction.
These findings provide a hitherto-unexplored multivalence state of Mn on the
emergent magnetism in undoped manganite epitaxial thin films, such as LaMnO3
and BiMnO3, and shed new light on all-oxide spintronic devices.",1803.07402v1
2018-07-29,"A family of high-temperature ferromagnetic monolayers with locked spin-dichroism-mobility anisotropy: MnNX and CrCX (X=Cl, Br, I; C=S, Se, Te)","Two-dimensional magnets have received increasing attention since Cr2Ge2Te6
and CrI3 were experimentally exfoliated and measured in 2017. Although layered
ferromagnetic metals were demonstrated at room temperature, a layered
ferromagnetic semiconductor with high Curie temperature (Tc) is yet to be
unveiled. Here, we theoretically predicted a family of high Tc ferromagnetic
monolayers, namely MnNX and CrCX (X=Cl, Br and I; C=S, Se and Te). Their Tc
values were predicted from over 100 K to near 500 K with Monte Carlo
simulations using an anisotropic Heisenberg model. Eight members among them
show semiconducting bandgaps varying from roughly 0.23 to 1.85 eV. These
semiconducting monolayers also show extremely large anisotropy, i.e. ~101 for
effective masses and ~102 for carrier mobilities, along the two in-plane
lattice directions of these layers. Additional orbital anisotropy leads to a
spin-locked linear dichroism, in different from previously known circular and
linear dichroisms in layered materials. Together with the mobility anisotropy,
it offers a spin-, dichroism- and mobility-anisotropy locking. These results
manifest the potential of this 2D family for both fundamental research and high
performance spin-dependent electronic and optoelectronic devices.",1807.11000v3
2018-08-20,Unconventional exchange bias coupling at perovskite/brownmillerite interface in spontaneously stabilized SrCoO3-δ/SrCoO2.5 bi-layer,"Interface effect in complex oxide thin film heterostructures lies at the
vanguard of current research to design technologically relevant functionality
and explore emergent physical phenomena. While most of the previous works focus
on the perovskite/perovskite heterostructures, the study on
perovskite/brownmillerite interfaces remain at its infancy. Here, we
investigate spontaneously stabilized perovskite-ferromagnet
(SrCoO3-{\delta})/brownmillertite-antiferromagnet (SrCoO2.5) bi-layer with TN >
TC and discover an unconventional interfacial magnetic exchange bias effect.
From magnetometry investigations, it is rationalized that the observed effect
stems from the interfacial ferromagnet/antiferromagnet coupling. The
possibility for coupled ferromagnet/spinglass interface engendering such effect
is ruled out. Strikingly, a finite coercive field persists in the paramagnetic
state of SrCoO3-{\delta} whereas the exchange bias field vanishes at TC. We
conjecture the observed effect to be due to the effective external quenched
staggered field provided by the antiferromagtic layer for the ferromagnetic
spins at the interface. Our results not only unveil a new paradigm to tailor
the interfacial magnetic properties in oxide heterostructures without altering
the cations at the interface, but also provide a purview to delve into the
fundamental aspects of exchange bias in such unusual systems paving a big step
forward in thin film magnetism.",1808.06321v1
2018-12-03,High-resolution neutron depolarization microscopy of the ferromagnetic transitions in Ni$_3$Al and HgCr$_2$Se$_4$ under pressure,"We performed neutron imaging of ferromagnetic transitions in Ni$_3$Al and
HgCr$_2$Se$_4$ crystals. These neutron depolarization measurements revealed
bulk magnetic inhomogeneities in the ferromagnetic transition temperature with
spatial resolution of about 100~$\mu$m. To obtain such spatial resolution, we
employed a novel neutron microscope equipped with Wolter mirrors as a neutron
image-forming lens and a focusing neutron guide as a neutron condenser lens.
The images of Ni$_3$Al show that the sample does not homogeneously go through
the ferromagnetic transition; the improved resolution allowed us to identify a
distribution of small grains with slightly off-stoichiometric composition.
Additionally, neutron depolarization imaging experiments on the chrome spinel,
HgCr$_2$Se$_4$, under pressures up to 15~kbar highlight the advantages of the
new technique especially for small samples or sample environments with
restricted sample space. The improved spatial resolution enables one to observe
domain formation in the sample while decreasing the acquisition time despite
having a bulky pressure cell in the beam.",1812.00864v1
2019-01-04,Cosmic Ferromagnetism of Magninos,"We study the physical conditions for the occurrence of ferromagnetic
instability in a neutral plasma of fermions. We consider a system of two
species $M$ and $Y$ which are oppositely charged under a local $U(1)_{X}$, with
$M$ much lighter than $Y$. The leading correction to free quasiparticle
behaviour for the lighter species arises from the exchange interaction, while
the heavier species remain spectators. This plasma, which is abelian,
asymmetric and idealised, is shown to be naturally susceptible to the formation
of a completely spin-imbalanced ferromagnetic state for the lighter species
(dubbed a magnino) in large parts of parameter space. It is shown that the
domain structure formed by this ferromagnetic state can mimic Dark Energy,
determining the masses of the two fermion species involved, depending on their
abundance relative to the standard photons. Incomplete cancellation of the
X-magnetic fields among the domains can give rise to residual long range
$X$-magnetic fields. Under the assumption that this $U(1)_{X}$ mixes with
Maxwell electromagnetism, this provides a mechanism for the seed for
cosmic-scale magnetic fields. An extended model with several flavours $M_a$ and
$Y_a$ of the species can incorporate Dark Matter. Thus the scenario shows the
potential for explaining the large scale magnetic fields, and what are arguably
the two most important outstanding puzzles of cosmology: Dark Matter and Dark
Energy.",1901.00995v2
2019-02-09,Antiferromagnetic phase transition in $Cr_{2}As$ via anisotropy of exchange interactions,"The electronic structure of anti-ferromagnetic $Cr_{2}As$ is investigated.
Anisotropy of exchange interactions between chrome sub-lattices is determined
($J^{X}(Cr_{I}-Cr_{II}) =4.77 meV,J^{Y}(Cr_{I}-Cr_{II}) =-6.36 meV$). The
behavior of exchange integrals from magnetic structure is analyzed.",1902.03337v1
2019-02-15,Interlayer RKKY Coupling in Bulk Rashba Semiconductors under Topological Phase Transition,"The bulk Rashba semiconductors BiTeX (X=I, Cl and Br) with intrinsically
enhanced Rashba spin-orbit coupling provide a new platform for investigation of
spintronic and magnetic phenomena in materials. We theoretically investigate
the interlayer exchange interaction between two ferromagnets deposited on
opposite surfaces of a bulk Rashba semiconductor BiTeI in its trivial and
topological insulator phases. In the trivial phase BiTeI, we find that for
ferromagnets with a magnetization orthogonal to the interface, the exchange
coupling is reminiscent of that of a conventional three-dimensional metal.
Remarkably, ferromagnets with a magnetization parallel to the interface display
a magnetic exchange qualitatively different from that of conventional
three-dimensional metal due to the spin-orbit coupling. In this case, the
interlayer exchange interaction acquires two periods of oscillations and decays
as the inverse of the thickness of the BiTeI layer. For topological BiTeI, the
magnetic exchange interaction becomes mediated only by the helical surface
states and acts between the one-dimensional spin chains at the edges of the
sample. The surface state-mediated interlayer exchange interaction allows for
the coupling of ferromagnets with non-collinear magnetization and displays a
decay power different from that of trivial BiTeI, allowing the detection of the
topological phase transition in this material. Our work provides insights into
the magnetic properties of these newly discovered materials and their possible
functionalization.",1902.06001v2
2019-03-27,High throughput computational screening for 2D ferromagnetic materials: the critical role of anisotropy and local correlations,"The recent observation of ferromagnetic order in two-dimensional (2D)
materials has initiated a booming interest in the subject of 2D magnetism. In
contrast to bulk materials, 2D materials can only exhibit magnetic order in the
presence of magnetic anisotropy. In the present work we have used the
Computational 2D Materials Database (C2DB) to search for new ferromagnetic 2D
materials using the spinwave gap as a simple descriptor that accounts for the
role of magnetic anisotropy. In addition to known compounds we find 12 novel
insulating materials that exhibit magnetic order at finite temperatures. For
these we evaluate the critical temperatures from classical Monte Carlo
simulations of a Heisenberg model with exchange and anisotropy parameters
obtained from first principles. Starting from 150 stable ferromagnetic 2D
materials we find five candidates that are predicted to have critical
temperatures exceeding that of CrI3. We also study the effect of Hubbard
corrections in the framework of DFT+U and find that the value of U can have a
crucial influence on the prediction of magnetic properties. Our work provides
new insight into 2D magnetism and identifies a new set of promising monolayers
for experimental investigation.",1903.11466v2
2019-04-16,Universal critical behavior in the ferromagnetic superconductor Eu(Fe$_{0.75}$Ru$_{0.25}$)$_{2}$As$_{2}$,"The study of universal critical behavior is a crucial issue in a continuous
phase transition, which groups various critical phenomena into universality
classes for revealing microscopic electronic behaviors. The understanding of
the nature of magnetism in Eu-based ferromagnetic superconductors is largely
impeded by the infeasibility of performing inelastic neutron scattering
measurements to deduce the microscopic magnetic behaviors and the effects on
the superconductivity, due to the significant neutron absorption effect of
natural $^{152}$Eu and unavailability of large single crystals. However, by
systematically combining the neutron diffraction experiment, the
first-principles calculations, and the quantum Monte Carlo simulations, we have
obtained a perfectly consistent universal critical exponent value of
$\beta=0.385(13)$ experimentally and theoretically for
Eu(Fe$_{0.75}$Ru$_{0.25}$)$_{2}$As$_{2}$, from which the magnetism in the
Eu-based ferromagnetic superconductors is identified as the universal class of
a three-dimensional anisotropic quantum Heisenberg model with long-range
magnetic exchange coupling. This study not only clarifies the nature of
microscopic magnetic behaviors in the Eu-based ferromagnetic superconductors,
but also opens a new avenue of systemic methodology for studying the universal
critical behaviors associated with magnetic phase transitions in the area of
magnetism and the spin fluctuations effects on the unconventional
superconductivity.",1904.07417v3
2019-04-18,Insight into the magnetic behavior of Sr$_2$IrO$_4$:A spontaneous magnetization study,"Sr$_2$IrO$_4$ is a weak ferromagnet where the spin arrangement is canted
anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays and
important role in magnetic behavior of Sr$_2$IrO$_4$. In this concern the
magnetization under zero applied field i.e. spontaneous magnetization would be
interesting to study and would give insight into the novel magnetic behavior of
Sr$_2$IrO$_4$. Sophisticated techniques like neutron diffraction, $\mu$
\textit{SR} etc has been used to understand the magnetic behavior of
Sr$_2$IrO$_4$ under zero applied field. To understand the magnetic behavior we
have performed detail field and temperature dependent magnetization study, the
measured field and temperature dependent magnetic data is analyzed rigorously.
We have attempted the understand the temperature dependance of spontaneous
magnetization, remanent magnetization and coercive force. We observe that the
spontaneous magnetization extracted from Arrott plot shows that the
Sr$_2$IrO$_4$ is not an ideal ferromagnet. The temperature dependent coercive
field is found to follows Guant's model of strong domain wall pinning. Our
investigation explicit the temperature dependence of various magnetic
properties shows the magnetic transitions from paramagnetic to ferromagnetic
phase with $T_c$ around 225 K and a low temperature evolution of magnetic
magnetic moment around $T_M$ $\sim$90 K.",1904.08792v1
2019-12-13,Frustration induced highly anisotropic magnetic patterns in classical $XY$ model on kagome lattice,"We predict and observed novel highly anisotropic magnetic patterns obtained
in the model of frustrated planar interacting magnetic moments (the classical
$X-Y$ model) on the regular kagome lattice. The frustration is provided by the
presence of both ferromagnetic and anti-ferromagnetic interactions between
adjacent magnetic moments defined on the lattice nodes. At the critical value
of the frustration $f=f_{cr}=3/4$ such a systems displays the phase transition
from the ordered ferromagnetic state to the disordered frustration regime
characterized by the highly-degenerated ground state. In the frustrated regime,
$f_{cr}< f \leq 1$, unexpected scaling of spatially averaged magnetization
$\langle \vec{M} \rangle $ on the total number of nodes,$N$, i.e. $\langle
\vec{M} \rangle \simeq N^{-1/4}$, has been obtained. Such scaling is provided
by highly anisotropic magnetic patterns displaying the ferromagnetic ordering
along the $y$-direction, and short-range correlations of magnetic moments along
the $x$-direction. We conjecture that all these intriguing features are
explained by the presence of the double-degenerated ground state in the basic
cell, i.e. single triangle, of the kagome lattice accompanying a large amount
of intrinsic constraints. We anticipate the implementation of the phase
transition and anisotropic magnetic patterns in various systems, e.g. natural
magnetic molecular clusters, artificially prepared Josephson junctions
networks, trapped-ions and/or photonic crystals.",1912.06397v1
2019-12-14,Spin-mediated charge-to-heat current conversion phenomena in ferromagnetic binary alloys,"Spin-mediated charge-to-heat current conversion phenomena, i.e., the
anomalous Ettingshausen effect (AEE) and the anisotropic magneto-Peltier effect
(AMPE), have been investigated in various ferromagnetic Ni-Fe, Ni-Pt, Ni-Pd,
and Fe-Pt binary alloys at room temperature. When a charge current is applied
to a ferromagnetic conductor, the AMPE modulates the Peltier coefficient
depending on the angle between the directions of the charge current and
magnetization, while the AEE generates a heat current in the direction
perpendicular to both the charge current and magnetization. We observed the
strong material dependence of the thermoelectric conversion coefficients and
figures of merit of these phenomena. Among the ferromagnetic alloys used in
this study, Ni$_{95}$Pt$_{5}$ exhibits the largest AMPE of which the anisotropy
of the Peltier coefficient is $\sim 12\%$. In contrast, the magnitude of the
AEE signals is moderate in Ni$_{95}$Pt$_{5}$ but largest in Ni$_{75}$Pt$_{25}$
and Ni$_{50}$Fe$_{50}$. We discuss these behaviors by exploring the relations
between these charge-to-heat current conversion phenomena and other transport
as well as magnetic properties. This systematic study will provide a clue for
clarifying the mechanisms of the AMPE and AEE and for enhancing the
thermoelectric conversion efficiency of these phenomena.",1912.06799v2
2019-12-16,High-Temperature Quantum Anomalous Hall Insulators in Lithium-Decorated Iron-Based Superconductor Materials,"Quantum anomalous Hall (QAH) insulator is the key material to study emergent
topological quantum effects, but its ultralow working temperature limits
experiments. Here, by first-principles calculations, we find a family of stable
two-dimensional (2D) structures generated by lithium decoration of layered
iron-based superconductor materials FeX (X = S, Se, Te), and predict
room-temperature ferromagnetic semiconductors together with large-gap
high-Chern-number QAH insulators in the 2D materials. The extremely robust
ferromagnetic order is induced by the electron injection from Li to Fe and
stabilized by strong ferromagnetic kinetic exchange in the 2D Fe layer. While
in the absence of spin-orbit coupling (SOC), the ferromagnetism polarizes the
system into a half Dirac semimetal state protected by mirror symmetry, the SOC
effect results in a spontaneous breaking of mirror symmetry and introduces a
Dirac mass term, which creates QAH states with sizable gaps (several tens of
meV) and multiple chiral edge modes. We also find a 3D QAH insulator phase
featured by macroscopic number of chiral conduction channels in bulk
LiOH-LiFeX. The findings open new opportunities to realize novel QAH physics
and applications at high temperatures.",1912.07461v4
2019-12-24,Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe$_3$,"We investigate the temperature-dependent electronic structure of the van der
Waals ferromagnet, CrGeTe$_3$. Using angle-resolved photoemission spectroscopy,
we identify atomic- and orbital-specific band shifts upon cooling through
${T_\mathrm{C}}$. From these, together with x-ray absorption spectroscopy and
x-ray magnetic circular dichroism measurements, we identify the states created
by a covalent bond between the Te ${5p}$ and the Cr ${e_g}$ orbitals as the
primary driver of the ferromagnetic ordering in this system, while it is the Cr
${t_{2g}}$ states that carry the majority of the spin moment. The ${t_{2g}}$
states furthermore exhibit a marked bandwidth increase and a remarkable
lifetime enhancement upon entering the ordered phase, pointing to a delicate
interplay between localized and itinerant states in this family of layered
ferromagnets.",1912.11314v1
2020-03-01,Roles of easy-plane and easy-axis XXZ anisotropy and bond alternation on a frustrated ferromagnetic spin-$1/2$ chain,"The spin-$1/2$ Heisenberg chain with a ferromagnetic first-neighbor exchange
coupling $J_1$ and an antiferromagnetic second-neighbor $J_2$ has a Haldane
dimer ground state with an extremely small spin gap. Thus, the ground state is
readily altered by perturbations. Here, we investigate the effects of XXZ
exchange magnetic anisotropy of both the easy-axis and easy-plane types and an
alternation in $J_1$ on the ground state, the spin gap, and magnetic properties
of the frustrated ferromagnetic spin-$1/2$ chain. It is found that there are
two distinct dimerized spin-gap phases, in one of which the spin gap and the
magnetic susceptibility are extremely small around the SU(2) symmetric case and
in the other they are moderately large far away from the SU(2) symmetric case.
A small alternation in the amplitude of $J_1$ rapidly shortens the pitch of
spin correlations towards the four-spin periodicity, as in the limit of
$J_1/J_2\to0$. These effects are not sufficient to quantitatively explain
overall experimentally observed magnetic properties in the
quasi-one-dimensional spin-gapped magnetoelectric cuprate
Rb$_2$Cu$_2$Mo$_3$O$_{12}$ that exhibits ferroelectricity stabilized by a
magnetic field. Our results are also relevant to Cs$_2$Cu$_2$Mo$_3$O$_{12}$,
where the ferromagnetic intrachain and antiferromagnetic interchain order has
recently been found, in a single chain level. We also reveal the nature of
symmetry-protected topological phase transitions in the model by mapping onto
effective spin-1 chain models.",2003.00554v2
2020-03-20,Current cross-correlations and waiting time distributions in Andreev transport through Cooper pair splitters based on triple quantum dots,"We study the spin-resolved subgap transport in a triple quantum-dot system
coupled to one superconducting and two ferromagnetic leads. We examine the
Andreev processes in the parallel and antiparallel alignments of ferromagnets
magnetic moments in both the linear and nonlinear response regimes. The
emphasis is put on the analysis of the current cross-correlations between the
currents flowing through the left and right arms of the device and relevant
electron waiting time distributions. We show that both quantities can give an
important insight into the subgap transport processes and their analysis can
help optimizing the system parameters for achieving the considerable Andreev
current and efficient Cooper pair splitting. Strong positive values of
cross-correlations are associated with the presence of tunneling processes
enhancing the Cooper pair splitting efficiency, while short waiting times for
electrons tunneling through distinct ferromagnetic contacts indicate fast
splitting of emitted Cooper pairs. In particular, we study two detuning schemes
and show that antisymmetric shift of side quantum dots energy levels is
favorable for efficient Cooper pair splitting. The analysis of spin-resolved
waiting time distributions supports the performance enhancement due to the
presence of ferromagnetic contacts, which is in particular revealed for short
times. Finally, we consider the effect of changing the inter-dot hopping
amplitude and predict that strong inter-dot correlations lead to a reduction of
Andreev transport properties in low-bias limit.",2003.09165v1
2020-03-23,Evolution of Griffiths Phase and Critical Behaviour of La1-xPbxMnO3+-y Solid Solutions,"Polycrystalline La1-xPbxMnO3+-y (x = 0.3, 0.35, 0.4) solid solutions were
prepared by solid state reaction method and their magnetic properties have been
investigated. Rietveld refinement of X-ray powder diffraction patterns showed
that all samples are single phase and crystallized with the rhombohedral
structure in the R-3c space group. A second order paramagnetic to ferromagnetic
phase transition was observed for all materials. The Griffiths phase (GP),
identified from the temperature dependence of the inverse susceptibility, was
suppressed by increasing magnetic field and showed a significant dependence on
A-site chemical substitution. The critical behaviour of the compounds was
investigated near to their Curie temperatures, using intrinsic magnetic field
data. The critical exponents (\b{eta}, {\gamma} and {\delta}) are close to the
mean-field approximation values for all three compounds. The observed
mean-field like behaviour is a consequence of the GP and the formation of
ferromagnetic clusters. Long-range ferromagnetic order is established as the
result of long-range interactions between ferromagnetic clusters. The
magnetocaloric effect was studied in terms of the isothermal entropy change.
Our study shows that the material with the lowest chemical substitution (x =
0.3) has the highest potential (among the three compounds) as magnetic
refrigerant, owing to its higher relative cooling power (258 J/kg at 5 T field)
and a magnetic phase transition near room temperature.",2003.10207v2
2020-05-01,Tunable Ferromagnetism and Thermally Induced Spin Flip in Vanadium-doped Tungsten Diselenide Monolayers at Room Temperature,"The outstanding optoelectronic and valleytronic properties of transition
metal dichalcogenides (TMDs) have triggered intense research efforts by the
scientific community. An alternative to induce long-range ferromagnetism (FM)
in TMDs is by introducing magnetic dopants to form a dilute magnetic
semiconductor. Enhancing ferromagnetism in these semiconductors not only
represents a key step towards modern TMD-based spintronics, but also enables
exploration of new and exciting dimensionality-driven magnetic phenomena. To
this end, we show tunable ferromagnetism at room temperature and a thermally
induced spin flip (TISF) in monolayers of V-doped WSe2. As vanadium
concentrations increase within the WSe2 monolayers the saturation magnetization
increases, and it is optimal at ~4at.% vanadium; the highest doping/alloying
level ever achieved for V-doped WSe2 monolayers. The TISF occurs at ~175 K and
becomes more pronounced upon increasing the temperature towards room
temperature. We demonstrate that TISF can be manipulated by changing the
vanadium concentration within the WSe2 monolayers. We attribute TISF to the
magnetic field and temperature dependent flipping of the nearest W-site
magnetic moments that are antiferromagnetically coupled to the V magnetic
moments in the ground state. This is fully supported by a recent spin-polarized
density functional theory calculation. Our findings pave the way for the
development of novel spintronic and valleytronic nanodevices based on
atomically thin magnetic semiconductors and stimulate further studies in this
rapidly expanding research field of 2D magnetism.",2005.00493v1
2020-06-01,Vortex-lattice formation in a spin-orbit coupled rotating spin-1 condensate,"We study the vortex-lattice formation in a rotating {Rashba} spin-orbit (SO)
coupled quasi-two-dimensional (quasi-2D) hyper-fine spin-1 spinor Bose-Einstein
condensate (BEC) in the $x-y$ plane using a numerical solution of the
underlying mean-field Gross-Pitaevskii equation. % The wave function for this
system %has three components corresponding to the three projections of
hyper-fine spin $F_z= +1,0,-1$. In this case, the non-rotating {Rashba}
SO-coupled spinor BEC can have topological excitation in the form of vortices
of different angular momenta in the three components, e.g. the $(0,+1,+2)$- and
$(-1,0,+1)$-type states in ferromagnetic and anti-ferromagnetic spinor BEC: the
numbers in the parenthesis denote the intrinsic angular momentum of the vortex
states of the three components with the negative sign denoting an anti-vortex.
The presence of these states with intrinsic vorticity breaks the symmetry
between rotation with vorticity along the $z$ and $-z$ axes and thus generates
a rich variety of vortex-lattice and anti-vortex-lattice states in a rotating
quasi-2D spin-1 spinor ferromagnetic and anti-ferromagnetic BEC, not possible
in a scalar BEC. {For weak SO coupling, } we find two types of symmetries of
these states $-$ hexagonal and ""square"". The hexagonal (square) symmetry state
has vortices arranged in closed concentric orbits with a maximum of $6, 12,
18...$ ($8,12,16...$) vortices in successive orbits. Of these two symmetries,
the square vortex-lattice state is found to have the smaller energy.",2006.00646v3
2020-06-04,Yu-Shiba-Rusinov bands in ferromagnetic superconducting diamond,"The combination of different exotic properties in materials paves the way for
the emergence of their new potential applications. An example is the recently
found coexistence of the mutually antagonistic ferromagnetism and
superconductivity in hydrogenated boron-doped diamond, which promises to be an
attractive system with which to explore unconventional physics. Here, we show
the emergence of Yu-Shiba-Rusinov (YSR) bands with a spatial extent of tens of
nanometers in ferromagnetic superconducting diamond using scanning tunneling
spectroscopy. We demonstrate theoretically how a two-dimensional (2D) spin
lattice at the surface of a three-dimensional (3D) superconductor gives rise to
the YSR bands, and how their density-of-states profile correlates with the spin
lattice structure. The established strategy to realize new forms of the
coexistence of ferromagnetism and superconductivity opens a way to engineer the
unusual electronic states and also to design better performing superconducting
devices.",2006.02853v1
2020-06-21,"Crystal Structure, Magnetism, and Electronic Properties of New Rare-Earth-Free Ferromagnetic MnPt5As","The design and synthesis of targeted functional materials have been a
long-term goal for material scientists. Although a universal design strategy is
difficult to generate for all types of materials, however, it is still helpful
for a typical family of materials to have such design rules. Herein, we
incorporated several significant chemical and physical factors regarding
magnetism, such as structure type, atom distance, spin-orbit coupling, and
successfully synthesized a new rare-earth-free ferromagnet, MnPt5As, for the
first time. MnPt5As can be prepared by using high-temperature pellet methods.
According to X-ray diffraction results, MnPt5As crystallizes in a tetragonal
unit cell with the space group P4/mmm (Pearson symbol tP7). Magnetic
measurements on MnPt5As confirm ferromagnetism in this phase with a Curie
temperature of ~301 K and a saturated moment of 3.5 uB per formula. Evaluation
by applying the Stoner Criterion also indicates that MnPt5As is susceptible to
ferromagnetism. Electronic structure calculations using the WIEN2k program with
local spin density approximation imply that the spontaneous magnetization of
this phase arises primarily from the hybridization of d orbitals on both Mn and
Pt atoms. The theoretical assessments are consistent with the experimental
results. Moreover, the spin-orbit coupling effects heavily influence on
magnetic moments in MnPt5As. MnPt5As is the first high-performance magnetic
material in this structure type. The discovery of MnPt5As offers a platform to
study the interplay between magnetism and structure.",2006.11897v1
2020-08-27,"Different universality classes of isostructural U$TX$ compounds ($T$ = Rh, Co, Co$_{0.98}$Ru$_{0.02}$; $X$ = Ga, Al)","Magnetization isotherms of the 5f-electron ferromagnets URhGa, UCoGa and
UCo0.98Ru0.02Al were measured at temperatures in the vicinity of their Curie
temperature in order to investigate the critical behavior near the
ferromagnetic phase transition. These compounds adopt the layered hexagonal
ZrNiAl-type structure and exhibit huge uniaxial magnetocrystalline anisotropy.
The critical \b{eta}, {\gamma} and {\delta} exponents were determined by
analyzing Arrott-Noakes plots, Kouvel-Fisher plots, critical isotherms, scaling
theory and Widom scaling relations. The values obtained for URhGa and UCoGa can
be explained by the results of the renormalization group theory for a 2D Ising
system with long-range interactions similar to URhAl reported by other
investigators. On the other hand, the critical exponents determined for
UCo0.98Ru0.02Al are characteristic of a 3D Ising ferromagnet with short-range
interactions suggested in previous studies also for the itinerant 5f-electron
paramagnet UCoAl situated near a ferromagnetic transition. The change from the
2D to the 3D Ising system is related to the gradual delocalization of 5f
electrons in the series of the URhGa, URhAl, UCoGa to UCo0.98Ru0.02Al and UCoAl
compounds and appears close to the strongly itinerant nonmagnetic limit. This
indicates possible new phenomena that may be induced by the change of
dimensionality in the vicinity of the quantum critical point.",2008.12061v1
2020-10-20,Pressure-induced huge increase of Curie temperature of the van der Waals ferromagnet VI3,"Evolution of magnetism in single crystals of the van der Waals compound VI3
in external pressure up to 7.3 GPa studied by measuring magnetization and ac
magnetic susceptibility is reported. Four magnetic phase transitions, at T1 =
54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed
at ambient pressure. The first two have been attributed to the onset of
ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is
characterized by the magnetic ordering transition at Curie temperature TC and
the transition between two different ferromagnetic phases TFM, accompanied by a
structure transition from monoclinic to triclinic symmetry upon cooling. The
pressure effects on magnetic parameters were studied with three independent
techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa
whereas TFM increases rapidly with increasing pressure and reaches TC at a
triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase
transition is observed moving to higher temperatures with increasing pressure
to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization
is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa)
suggesting a possible pressure-induced reduction of vanadium magnetic moment.
We discussed these results in light of recent theoretical studies to analyze
exchange interactions and provide how to increase the Curie temperature of VI3.",2010.10319v1
2020-10-26,Ultra-strong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers,"The critical step for future quantum industry demands realization of
efficient information exchange between different-platform hybrid systems,
including photonic and magnonic systems, that can harvest advantages of
distinct platforms. The major restraining factor for the progress in certain
hybrid systems is the fundamentally weak coupling parameter between the
elemental particles. This restriction impedes the entire field of hybrid
magnonics by making realization of scalable on-chip hybrid magnonic systems
unattainable. In this work, we propose a general flexible approach for
realization of on-chip hybrid magnonic systems with unprecedentedly strong
coupling parameters. The approach is based on multilayered micro-structures
containing superconducting, insulating and ferromagnetic layers with modified
both photon phase velocities and magnon eigen-frequencies. Phenomenologically,
the enhanced coupling strength is provided by the radically reduced photon mode
volume. The microscopic mechanism of the phonon-to-magnon coupling in studied
systems evidences formation of the long-range superconducting coherence via
thick strong ferromagnetic layers. This coherence is manifested by coherent
superconducting screening of microwave fields by the
superconductor/ferromagnet/superconductor three-layers in presence of
magnetization precession. This discovery offers new opportunities in microwave
superconducting spintronics for quantum technologies.",2010.13553v1
2020-11-01,"Tunable magneto-optical effect, anomalous Hall effect and anomalous Nernst effect in two-dimensional room-temperature ferromagnet $1T$-CrTe$_2$","Utilizing the first-principles density functional theory calculations
together with group theory analyses, we systematically investigate the spin
order-dependent magneto-optical effect (MOE), anomalous Hall effect (AHE), and
anomalous Nernst effect (ANE) in a recently discovered two-dimensional
room-temperature ferromagnet $1T$-CrTe$_2$. We find that the spin prefers an
in-plane direction by the magnetocrystalline anisotropy energy calculations.
The MOE, AHE, and ANE display a period of $2\pi/3$ when the spin rotates within
the atomic plane, and they are forbidden if there exists a mirror plane
perpendicular to the spin direction. By reorienting the spin from in-plane to
out-of-plane direction, the MOE, AHE, and ANE are enhanced by around one order
of magnitude. Moreover, we establish the layer-dependent magnetic properties
for multilayer $1T$-CrTe$_2$ and predict antiferromagnetism and ferromagnetism
for bilayer and trilayer $1T$-CrTe$_2$, respectively. The MOE, AHE, and ANE are
prohibited in antiferromagnetic bilayer $1T$-CrTe$_2$ due to the existence of
the spacetime inversion symmetry, whereas all of them are activated in
ferromagnetic trilayer $1T$-CrTe$_2$ and the MOE is significantly enhanced
compared to monolayer $1T$-CrTe$_2$. Our results show that the magneto-optical
and anomalous transports proprieties of $1T$-CrTe$_2$ can be effectively
modulated by altering spin direction and layer number.",2011.00394v1
2020-11-20,Phase diagram of vortices in the polar phase of spin-1 Bose-Einstein condensates,"The phase diagram of lowest-energy vortices in the polar phase of spin-1
Bose--Einstein condensates is investigated theoretically. Singly quantized
vortices are categorized by the local ordered state in the vortex core and
three types of vortices are found as lowest-energy vortices, which are elliptic
AF-core vortices, axisymmetric F-core vortices, and N-core vortices. These
vortices are named after the local ordered state, ferromagnetic (F),
antiferromagnetic (AF), broken-axisymmetry (BA), and normal (N) states apart
from the bulk polar (P) state. The N-core vortex is a conventional vortex, in
the core of which the superfluid order parameter vanishes. The other two types
of vortices are stabilized when the quadratic Zeeman energy is smaller than a
critical value. The axisymmetric F-core vortex is the lowest-energy vortex for
ferromagnetic interaction, and it has an F core surrounded by a BA skin that
forms a ferromagnetic-spin texture, as exemplified by the localized Mermin--Ho
texture. The elliptic AF-core vortex is stabilized for antiferromagnetic
interaction; the vortex core has both nematic-spin and ferromagnetic orders
locally and is composed of the AF-core soliton spanned between two BA edges.
The phase transition from the N-core vortex to the other two vortices is
continuous, whereas that between the AF-core and F-core vortices is
discontinuous. The critical point of the continuous vortex-core transition is
computed by the perturbation analysis of the Bogoliubov theory and the
Ginzburg--Landau formalism describes the critical behavior. The influence of
trapping potential on the core structure is also investigated.",2011.10342v3
2021-02-03,Low temperature ferromagnetism in perovskite SrIrO$_3$ films,"The 5$d$ based SrIrO$_3$ represents prototype example of nonmagnetic
correlated metal which mainly originates from a combined effect of spin-orbit
coupling, lattice dimensionality and crystal structure. Therefore, tuning of
these parameters results in diverse physical properties in this material. Here,
we study the structural, magnetic and electrical transport behavior in
epitaxial SrIrO$_3$ film ($\sim$ 40 nm) grown on SrTiO$_3$ substrate. Opposed
to bulk material, the SrIrO$_3$ film exhibits a ferromagnetic ordering at low
temperature below $\sim$ 20 K. The electrical transport data indicate an
insulating behavior where the nature of charge transport follows Mott's
variable-range-hopping model. A positive magnetoresistance is recorded at 2 K
which has correlation with magnetic moment. We further observe a nonlinear Hall
effect at low temperature ($<$ 20 K) which arises due to an anomalous component
of Hall effect. An anisotropic behavior of both magnetoresistance and Hall
effect has been evidenced at low temperature which coupled with anomalous Hall
effect indicate the development of ferromagnetic ordering. We believe that an
enhanced (local) structural distortion caused by lattice strain at low
temperatures induces ferromagnetic ordering, thus showing structural
instability plays vital role to tune the physical properties in SrIrO$_3$.",2102.02150v1
2021-02-22,High T$_C$ ferromagnetic inverse Heusler alloys: A comparative study of Fe$_2$RhSi and Fe$_2$RhGe,"We report the results of experimental investigations on structural, magnetic,
resistivity, caloric properties of Fe$_2$RhZ (Z=Si,Ge) along with
\textit{ab-initio} band structure calculations using first principle
simulations. Both these alloys are found to crystallize in inverse Heusler
structure but with disorder in tetrahedral sites between Fe and Rh. Fe$_2$RhSi
has saturation moment of 5.00 $\mu_B$ and while its counterpart has 5.19
$\mu_B$. Resistivity measurement reveals metallic nature in both of them.
Theoretical simulations using generalized gradient approximation(GGA) predict
inverse Heusler structure with ferromagnetic ordering as ground state for both
the alloys. However it underestimates the experimentally observed moments.
GGA+$U$ approach, with Hubbard $U$ values estimated from density functional
perturbation theory helps to improve the comparison of the experimental
results. Fe$_2$RhSi is found to be half metallic ferromagnet while Fe$_2$RhGe
is not. Varying $U$ values on Fe and Rh sites does not change the net moment
much in Fe$_2$RhSi, unlike in Fe$_2$RhGe. Relatively small exchange splitting
of orbitals in Fe$_2$RhGe compared to that of Fe$_2$RhSi is the reason for not
opening the band gap in the minority spin channel in the former. High ordering
temperature and moment make Fe$_2$RhSi useful for spintronics applications.",2102.10967v1
2021-02-27,Room temperature ferromagnetism of monolayer chromium telluride with perpendicular magnetic anisotropy,"The realization of long-range magnetic ordering in two-dimensional (2D)
systems can potentially revolutionize next-generation information technology.
Here, we report the successful fabrication of crystalline Cr3Te4 monolayers
with room temperature ferromagnetism. Using molecular beam epitaxy, the growth
of 2D Cr3Te4 films with monolayer thickness is demonstrated at low substrate
temperatures (~100C), compatible with Si CMOS technology. X-ray magnetic
circular dichroism measurements reveal a Curie temperature (Tc) of ~344 K for
the Cr3Te4 monolayer with an out-of-plane magnetic easy axis, which decreases
to ~240 K for the thicker film (~ 7 nm) with an in-plane easy axis. The
enhancement of ferromagnetic coupling and the magnetic anisotropy transition is
ascribed to interfacial effects, in particular the orbital overlap at the
monolayer Cr3Te4/graphite interface, supported by density-functional theory
calculations. This work sheds light on the low-temperature scalable growth of
2D nonlayered materials with room temperature ferromagnetism for new magnetic
and spintronic devices.",2103.00251v1
2021-03-16,Emergent Magnetic Phenomenon with Unconventional Structure in Epitaxial Manganate Thin Films,"A variety of emergent phenomena has been enabled by interface engineering in
the complex oxides heterostructures. While extensive attention has been
attracted to LaMnO3 (LMO) thin films for observing the control of
functionalities at its interface with substrate, the nature of the magnetic
phases in the thin film is, however,controversial. Here, it is reported that
the ferromagnetism in 2 and 5 unit cells thick LMO films epitaxially deposited
(001)-SrTiO3 substrates ferromagnetic/ferromagnetic coupling in 8 and
10-unit-cell ones, and a striking ferromagnetic/antiferromagnetic pinning
effect with apparent positive exchange bias in 15 and 20-unit-cell ones are
observed. This novel phenomenon in both 15 and 20-unit-cell films indicates a
coexistence of three magnetic orderings in a single LMO film.The
high-resolution scanning transmission electron microscopy suggests a P21/n to
Pbnm symmetry transition from interface to surface, with the spatial
stratification of MnO6 octahedral morphology, corresponding to different
magnetic orderings. These results should shed some new lights on manipulating
the functionality of oxides by interface engineering.",2103.09133v1
2021-03-30,Z2 topological order and first-order quantum phase transitions in systems with combinatorial gauge symmetry,"We study a generalization of the two-dimensional transverse-field Ising
model, combining both ferromagnetic and antiferromagnetic two-body
interactions, that hosts exact global and local Z2 gauge symmetries. Using
exact diagonalization and stochastic series expansion quantum Monte Carlo
methods, we confirm the existence of the topological phase in line with
previous theoretical predictions. Our simulation results show that the
transition between the confined topological phase and the deconfined
paramagnetic phase is of first-order, in contrast to the conventional Z2
lattice gauge model in which the transition maps onto that of the standard
Ising model and is continuous. We further generalize the model by replacing the
transverse field on the gauge spins with a ferromagnetic XX interaction while
keeping the local gauge symmetry intact. We find that the Z2 topological phase
remains stable, while the paramagnetic phase is replaced by a ferromagnetic
phase. The topological-ferromagnetic quantum phase transition is also of
first-order. For both models, we discuss the low-energy spinon and vison
excitations of the topological phase and their avoided level crossings
associated with the first-order quantum phase transitions.",2103.16625v1
2021-04-27,Observation of a phase transition within the domain walls of ferromagnetic Co3Sn2S2,"The ferromagnetic phase of Co$_3$Sn$_2$S$_2$ is widely considered to be a
topological Weyl semimetal, with evidence for momentum-space monopoles of Berry
curvature from transport and spectroscopic probes. As the bandstructure is
highly sensitive to the magnetic order, attention has focused on anomalies in
magnetization, susceptibility and transport measurements that are seen well
below the Curie temperature, leading to speculation that a ""hidden"" phase
coexists with ferromagnetism. Here we report spatially-resolved measurements by
Kerr effect microscopy that identify this phase. We find that the anomalies
coincide with a deep minimum in domain wall (DW) mobility, indicating a
crossover between two regimes of DW propagation. We demonstrate that this
crossover is a manifestation of a 2D phase transition that occurs within the
DW, in which the magnetization texture changes from continuous rotation to
unidirectional variation. We propose that the existence of this 2D transition
deep within the ferromagnetic state of the bulk is a consequence of a giant
quality factor for magnetocrystalline anisotropy unique to this compound. This
work broadens the horizon of the conventional binary classification of DWs into
Bloch and N\'eel walls, and suggests new strategies for manipulation of domain
walls and their role in electron and spin transport.",2104.13381v2
2021-06-03,Reentrant Bloch ferromagnetism,"An interacting electron liquid in two (2D) and three (3D) dimensions may
undergo a paramagnetic-to-ferromagnetic quantum spin polarization transition at
zero applied magnetic field, driven entirely by exchange interactions, as the
system density ($n$) is decreased. This is known as Bloch ferromagnetism. We
show theoretically that the application of an external magnetic field ($B$),
which directly spin polarizes the system through Zeeman spin splitting, has an
interesting effect on Bloch ferromagnetism if the applied field and carrier
density are both decreased (from some initial applied high magnetic field at a
high carrier density) in a power-law manner, $B\sim n^p$. For $p<p_c$, with
$p_c= 1 (2/3)$ in $2(3)$D, the system remains either fully spin-polarized or
undergoes a single transition from a partially spin-polarized (with two Fermi
surfaces corresponding to spin up and down electrons) to a fully spin-polarized
state (with a single Fermi surface of one spin) as the density and field
decrease, depending on whether the starting point is partially spin-polarized
or fully spin-polarized. However, for $p>p_c$, the system may undergo two
transitions if starting from the fully spin-polarized state: first, a weak
second order transition at high density and field from the field-induced fully
polarized phase to the partially polarized phase; and then, at a lower field
and density, a reentrant first order transition back to the fully
spin-polarized phase again with a single Fermi surface.",2106.02038v2
2021-06-04,Readout of a antiferromagnetic spintronics systems by strong exchange coupling of Mn2Au and Permalloy,"In antiferromagnetic spintronics, the read-out of the staggered magnetization
or Neel vector is the key obstacle to harnessing the ultra-fast dynamics and
stability of antiferromagnets for novel devices. Here, we demonstrate strong
exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits
Neel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows
us to benefit from the well-estabished read-out methods of ferromagnets, while
the essential advantages of antiferromagnetic spintronics are retained. We show
one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain
pattern. Conversely, alignment of the Permalloy magnetization reorients the
Mn2Au Neel vector, an effect, which can be restricted to large magnetic fields
by tuning the ferromagnetic layer thickness. To understand the origin of the
strong coupling, we carry out high resolution electron microscopy imaging and
we find that our growth yields an interface with a well-defined morphology that
leads to the strong exchange coupling.",2106.02333v1
2021-06-15,Phase separation of self-propelled disks with ferromagnetic and nematic alignment,"We present a comprehensive study of a model system of repulsive
self-propelled disks in two dimensions with ferromagnetic and nematic velocity
alignment interactions. We characterize the phase behavior of the system as a
function of the alignment and self-propulsion strength, featuring orientational
order for strong alignment and Motility-Induced Phase Separation (MIPS) at
moderate alignment but high enough self-propulsion. We derive a microscopic
theory for these systems yielding a close set of hydrodynamic equations from
which we perform a linear stability analysis of the homogenous disordered
state. This analysis predicts MIPS in the presence of aligning torques. The
nature of the continuum theory allows for an explicit quantitative comparison
with particle-based simulations, which consistently shows that ferromagnetic
alignment fosters phase separation, while nematic alignment does not alter
either the nature or the location of the instability responsible for it. In the
ferromagnetic case, such behavior is due to an increase of the imbalance of the
number of particle collisions along different orientations, giving rise to the
self-trapping of particles along their self-propulsion direction. On the
contrary, the anisotropy of the pair correlation function, which encodes this
self-trapping effect, is not significantly affected by nematic torques. Our
work shows the predictive power of such microscopic theories to describe
complex active matter systems with different interaction symmetries and sheds
light on the impact of velocity-alignment interactions in Motility-Induced
Phase Separation.",2106.08228v2
2021-06-29,Spin-orbit torques and magnetotransport properties of $α$-Sn and $β$-Sn heterostructures,"Topological insulators have emerged as an important material class for
efficient spin-charge interconversion. Most topological insulators considered
to date are binary or ternary compounds, with the exception of $\alpha$-Sn.
Here we report a comprehensive characterization of the growth, magnetotransport
properties, and current-induced spin-orbit torques of $\alpha$-Sn and
$\beta$-Sn-based ferromagnetic heterostructures. We show that $\alpha$-Sn grown
with a Bi surfactant on CdTe(001) promotes large spin-orbit torques in a
ferromagnetic FeCo layer at room temperature, comparable to Pt, whereas
$\alpha$-Sn grown without Bi surfactant and the non-topological phase,
$\beta$-Sn, induce lower torques. The dampinglike and fieldlike spin-orbit
torque efficiency in $\alpha$-Sn with Bi are 0.12 and 0.18, respectively.
Further, we show that $\alpha$-Sn grown with and without Bi presents a spin
Hall-like magnetoresistance comparable to that found in heavy metal/ferromagnet
bilayers. Our work demonstrates direct and efficient charge-to-spin conversion
in $\alpha$-Sn ferromagnetic heterostructures, showing that $\alpha$-Sn is a
promising material for current-induced magnetization control in spintronic
devices.",2106.15386v1
2021-07-07,"Coexistence of ferromagnetism, antiferromagnetism, and superconductivity in magnetically anisotropic (Eu,La)FeAs2","Materials with exceptional magnetism and superconductivity usually conceive
emergent physical phenomena. Here, we investigate the physical properties of
the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2
shows anisotropy-associated magnetic behaviors, such as Eu-related moment
canting and exchange bias. Through La doping, the magnetic anisotropy is
enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a
special exchange bias of the superposed ferromagnetic/superconducting loop
revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows
unusual robustness against La doping. Theoretical calculation and 57Fe
M\""ossbauer spectroscopy investigation reveal a doping-tunable dual
itinerant/localized nature of the Fe-related antiferromagnetism. Coexistence of
the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and
superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform
for further exploration of potential applications and emergent physics.
Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the
whole superconducting dome adjacent to the Fe-related antiferromagnetic phase,
which is of benefit for seeking underlying clues to high-temperature
superconductivity.",2107.03526v1
2021-09-02,Supercurrent-induced long-range triplet correlations and controllable Josephson effect in superconductor/ferromagnet hybrids with extrinsic SOC,"We predict that long-range triplet correlations (LRTC) in
superconductor/ferromagnet (S/F) hybrids with extrinsic impurity spin-orbit
coupling (SOC) can be generated and manipulated by supercurrent flowing in the
superconducting leads along the S/F interfaces. The LRTC appear via two basic
mechanisms. The essence of the first one is the generation of triplets by the
superconducting spin Hall effect. These pairs are long-range in the ferromagnet
under the appropriate mutual orientation of the condensate momentum and the
ferromagnet magnetization. The second mechanism is based on the singlet-triplet
conversion at the S/F interface followed by the rotation of the spin of the
obtained short-range opposite-spin pairs via the spin current swapping
mechanism. The structure of the supercurrent-induced LRTC is studied both for
S/F bilayers and S/F/S Josephson junctions. We demonstrate that in S/F/S
junctions, where the Josephson coupling is realized via the
supercurrent-induced LRTC, the ground state phase can be switched between $0$
and $\pi$ in a controllable manner. The switching is performed by reversing the
supercurrent in one of superconducting leads, thus realizing a new physical
principle of the $0-\pi$ shifter.",2109.00966v2
2021-09-08,Signature of half-metallicity in $\text{BiFeO}_\text{3}$,"$\text{BiFeO}_\text{3}$ has drawn a great attention over last several decades
due to its promising multiferroic character. In the ground state the bulk
$\text{BiFeO}_\text{3}$ is found to be in the rhombohedral phase. However, it
has been possible to stabilize $\text{BiFeO}_\text{3}$ with tetragonal
structure. The importance of tetragonal phase is due to its much larger value
of the electric polarization and the possible stabilization of ferromagnetism
as in the rhombohedral phase. Furthermore, the tetragonal structure of
$\text{BiFeO}_\text{3}$ has been reported with different $c/a$ ratio, opening
up the possibility of a much richer set of electronic phases. In this work, we
have used density functional theory based first-principle method to study the
ferromagnetic phase of the tetragonal $\text{BiFeO}_\text{3}$ structure as a
function of the $c/a$ ratio. We have found that as the $c/a$ ratio decreases
from $1.264$ to $1.016$, the tetragonal $\text{BiFeO}_\text{3}$ evolve from a
ferromagnetic semiconductor to a ferromagnetic metal, while passing through a
\emph{half-metallic} phase. This evolution of the electronic properties becomes
even more interesting when viewed with respect to the volume of each structure.
The most stable half-metallic phase initially counter-intuitively evolve to the
magnetic-semiconducting phase with a reduction in the volume, and after further
reduction in the volume it finally becomes a metal. So far, this type of metal
to insulator transition on compression was known to exist only in alkali
metals, especially in Lithium, in heavy alkaline earth metals, and in some
binary compound.",2109.03886v1
2021-09-17,Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet,"Electrons navigate more easily in a background of ordered magnetic moments
than around randomly oriented ones. This fundamental quantum mechanical
principle is due to their Bloch wave nature and also underlies ballistic
electronic motion in a perfect crystal. As a result, a paramagnetic metal that
develops ferromagnetic order often experiences a sharp drop in the resistivity.
Despite the universality of this phenomenon, a direct observation of the impact
of ferromagnetic order on the electronic quasiparticles in a magnetic metal is
still lacking. Here we demonstrate that quasiparticles experience a significant
enhancement of their lifetime in the ferromagnetic state of the low-density
magnetic semimetal EuCd2As2, but this occurs only in selected bands and
specific energy ranges. This is a direct consequence of the magnetically
induced band splitting and the multi-orbital nature of the material. Our
detailed study allows to disentangle different electronic scattering mechanisms
due to non-magnetic disorder and magnon exchange. Such high momentum and energy
dependence quasiparticle lifetime enhancement can lead to spin selective
transport and potential spintronic applications.",2109.08538v1
2021-10-11,Epitaxial growth of bilayer Bi(110) on two-dimensional ferromagnetic Fe3GeTe2,"Heterostructures of two-dimensional (2D) layered materials with selective
compositions play an important role in creating novel functionalities.
Effective interface coupling between 2D ferromagnet and electronic materials
would enable the generation of exotic physical phenomena caused by intrinsic
symmetry breaking and proximity effect at interfaces. Here, epitaxial growth of
bilayer Bi(110) on 2D ferromagnetic Fe3GeTe2 (FGT) with large magnetic
anisotropy has been reported. Bilayer Bi(110) islands are found to extend along
fixed lattice directions of FGT. The six preferred orientations could be
divided into two groups of three-fold symmetry axes with the difference
approximately to 26{\deg}. Moreover, dI/dV measurements confirm the existence
of interface coupling between bilayer Bi(110) and FGT. A variation of the
energy gap at the edges of bilayer Bi(110) is also observed which is modulated
by the interface coupling strengths associated with its buckled atomic
structure. This system provides a good platform for further study of the exotic
electronic properties of epitaxial Bi(110) on 2D ferromagnetic substrate and
promotes potential applications in the field of spin devices.",2110.05066v3
2021-11-01,Interface-enhanced ferromagnetism with long-distance effect in van der Waals semiconductor,"Ferromagnetic semiconductors discovered in two-dimensional (2D) materials
open an avenue for highly integrated and multifunctional spintronics. The Curie
temperature (TC) of existed 2D ferromagnetic semiconductors is extremely low
and the modulation effect of their magnetism is limited compared with their 2D
metallic counterparts. The interfacial effect was found to effectively
manipulate the three-dimensional magnetism, providing a unique opportunity for
tailoring the 2D magnetism. Here we demonstrate that the TC of 2D ferromagnetic
semiconductor Cr2Ge2Te6 can be enhanced by 130% (from ~65 K to above 150 K)
when adjacent to a tungsten layer. The interfacial W-Te bonding contributes to
the TC enhancement with a strong perpendicular magnetic anisotropy (PMA),
guaranteeing an efficient magnetization switching by the spin-orbit torque with
a low current density at 150 K. Distinct from the rapid attenuation in
conventional magnets, the interfacial effect exhibits a weak dependence on
Cr2Ge2Te6 thickness and a long-distance effect (more than 10 nanometers) due to
the weak interlayer coupling inherent to 2D magnets. Our work not only reveals
a unique interfacial behavior in 2D materials, but also advances the process
towards practical 2D spintronics.",2111.00645v1
2021-11-11,Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution,"In order to tune the magnetic properties of the cleavable high-Curie
temperature ferromagnet Fe$_{5-x}$GeTe$_2$, the effect of increasing the
electron count through arsenic substitution has been investigated. Small
additions of arsenic (2.5 and 5%) seemingly enhance ferromagnetic order in
polycrystalline samples by quenching fluctuations on one of the three magnetic
sublattices, whereas larger As concentrations decrease the ferromagnetic Curie
temperature ($T_{\rm C}$) and saturation magnetization. This work also
describes the growth and characterization of Fe$_{4.8}$AsTe$_2$ single crystals
that are structurally analogous to Fe$_{5-x}$GeTe$_2$ but with some phase
stability complications. Magnetization measurements reveal dominant
antiferromagnetic behavior in Fe$_{4.8}$AsTe$_2$ with a N\'{e}el temperature of
$T_{\rm N}$ $\approx$42K. A field-induced spin-flop below $T_{\rm N}$ results
in a switch from negative to positive magnetoresistance, with significant
hysteresis causing butterfly-shaped resistance loops. In addition to reporting
the properties of Fe$_{4.8}$AsTe$_2$, this work shows the importance of
manipulating the individual magnetic sublattices in Fe$_{5-x}$GeTe$_2$ and
motivates further efforts to control the magnetic properties in related
materials by fine tuning of the Fermi energy or crystal chemistry.",2111.06439v1
2021-11-18,Spin transport at finite temperatures: A first-principles study for ferromagnetic$|$nonmagnetic interfaces,"Symmetry lowering at an interface leads to an enhancement of the effect of
spin-orbit coupling and to a discontinuity of spin currents passing through the
interface. This discontinuity is characterized by a ""spin-memory loss"" (SML)
parameter $\delta$ that has only been determined directly at low temperatures.
Although $\delta$ is believed to be significant in experiments involving
interfaces between ferromagnetic and nonmagnetic metals, especially heavy
metals like Pt, it is more often than not neglected to avoid introducing too
many unknown interface parameters in addition to often poorly known bulk
parameters like the spin-flip diffusion length $l_{\rm sf}$. In this work, we
calculate $\delta$ along with the interface resistance $AR_{\rm I}$ and the
spin-asymmetry parameter $\gamma$ as a function of temperature for Co$|$Pt and
Py$|$Pt interfaces where Py is the ferromagnetic Ni$_{80}$Fe$_{20}$ alloy,
permalloy. We use first-principles scattering theory to calculate the
conductance as well as local charge and spin currents, modeling
temperature-induced disorder with frozen thermal lattice and, for ferromagnetic
materials, spin disorder within the adiabatic approximation. The bulk and
interface parameters are extracted from the spin currents using a Valet-Fert
model generalized to include SML.",2111.09731v1
2021-11-26,Optical Stabilization of Fluctuating High Temperature Ferromagnetism in YTiO$_3$,"In quantum materials, degeneracies and frustrated interactions can have a
profound impact on the emergence of long-range order, often driving strong
fluctuations that suppress functionally relevant electronic or magnetic phases.
Engineering the atomic structure in the bulk or at heterointerfaces has been an
important research strategy to lift these degeneracies, but these equilibrium
methods are limited by thermodynamic, elastic, and chemical constraints. Here,
we show that all-optical, mode-selective manipulation of the crystal lattice
can be used to enhance and stabilize high-temperature ferromagnetism in
YTiO$_3$, a material that exhibits only partial orbital polarization, an
unsaturated low-temperature magnetic moment, and a suppressed Curie
temperature, $T_c$ = 27 K. The enhancement is largest when exciting a 9 THz
oxygen rotation mode, for which complete magnetic saturation is achieved at low
temperatures and transient ferromagnetism is realized up to $T_{neq} >$ 80 K,
nearly three times the thermodynamic transition temperature. First-principles
and model calculations of the nonlinear phonon-orbital-spin coupling reveal
that these effects originate from dynamical changes to the orbital polarization
and the makeup of the lowest quasi-degenerate Ti $t_{2g}$ levels. Notably,
light-induced high temperature ferromagnetism in YTiO$_3$ is found to be
metastable over many nanoseconds, underscoring the ability to dynamically
engineer practically useful non-equilibrium functionalities.",2111.13622v1
2021-12-01,Inter-generational comparison of quantum annealers in solving hard scheduling problems,"We compare the performance of four quantum annealers, the D-Wave Two, 2X,
2000Q, and Advantage in solving an identical ensemble of a parametrized family
of scheduling problems. These problems are NP-complete and, in fact, equivalent
to vertex coloring problems. They are also practically motivated and closely
connected to planning problems from artificial intelligence. We examine factors
contributing to the performance differences while separating the contributions
from hardware upgrades, support for shorter anneal times, and possible
optimization of ferromagnetic couplings. While shorter anneal times can improve
the time to solution (TTS) at any given problem size, the scaling of TTS with
respect to the problem size worsens for shorter anneal times. In contrast,
optimizing the ferromagnetic coupling improves both the absolute TTS and the
scaling. There is a statistically significant improvement in performance
between D-Wave Two and 2X and from all older generation annealers to Advantage,
even when operated under identical anneal time and ferromagnetic couplings.
However, the performance improvement from 2X to 2000Q requires the anneal time
and ferromagnetic couplings to be optimized. Overall, owing to these
inter-generational hardware improvements and optimizations, the scaling
exponent reduces from $1.01 \pm 0.01$ on Two to $0.173 \pm 0.009$ on Advantage.",2112.00727v1
2021-12-06,First principles theory for the magnetic and charge instabilities in AV$_3$Sb$_5$ systems,"Vanadium-based materials AV$_3$Sb$_5$ (A=K, Rb, Cs) with layered kagome
lattice structures have drawn great attention recently due to the discoveries
of topologically nontrivial band structures, charge density wave states, giant
anomalous Hall effect, as well as unusual superconducting phase at low
temperatures. In this work, we theoretically study the magnetic and charge
instabilities for this class of materials based on first principles
calculations. We develop a method to calculate the generalized susceptibility
tensor defined in the sublattice-orbital-spin space, with the effects of
Coulomb interactions treated by generalized random phase approximation (RPA).
The RPA susceptibility calculations indicate that there are three leading
ferromagnetic instability modes at $\Gamma$ point, which are further verified
by unrestricted self-consistent Hartree-Fock calculations including both the
on-site and inter-site Coulomb interactions. The inclusion of inter-site
interactions tend to suppress the spin ferromagnetism due to charge transfer
from the V to Sb sites, leading to weak spin magnetic moments $\sim
0.1\mu_{\textrm{B}}$ per V atom with small intrinsic anomalous Hall
conductivity. Current loops can be generated in such weak spin ferromagnetic
states as a result of spin-orbit coupling effects. The electronic structures in
the ferromagnetic states are significantly reconstructed which have nearly
compensated electron and hole carriers from two bands. On the other hand, we do
not find any diverging instability mode at $M$ point driven by
electron-electron Coulomb interactions. First principles phonon calculations
indicate that there are unstable phonon modes which tend to drive the system
into an inverse star-of-David structure. Our results indicate that there may be
separate phase transitions in the magnetic and charge channels in the system.",2112.02808v1
2022-01-23,Van der Waals pi Josephson junctions,"Proximity-induced superconductivity in a ferromagnet can induce Cooper pairs
with a finite center-of-mass momentum. The resultant spatially modulated
superconducting order parameter is able to stabilize Josephson junctions (JJs)
with pi phase difference in superconductor-ferromagnet heterostructures and
realize 'quiet' phase qubits. The emergence of two-dimensional (2D) layered
superconducting and magnetic materials promises a new platform for realizing pi
JJs with atomically sharp interfaces by van der Waals stacking. Here we
demonstrate a thickness-driven 0-pi transition in JJs made of NbSe2 (an Ising
superconductor) with a Cr2Ge2Te6 (a ferromagnetic semiconductor) weak link. By
systematically varying the Cr2Ge2Te6 thickness, we observe a vanishing
supercurrent at a critical thickness around 8 nm, followed by a re-entrant
supercurrent upon further increase in thickness. Near the critical thickness,
we further observe unusual supercurrent interference patterns with vanishing
critical current around zero in-plane magnetic field. They signify the
formation of 0-pi JJs (with both 0 and pi regions) likely induced by the
nanoscale magnetic domains in Cr2Ge2Te6. Our work highlights the potential of
van der Waals superconductor-ferromagnet heterostructures for the explorations
of unconventional superconductivity and superconducting electronics.",2201.09185v3
2022-01-24,Direct observation of strong anomalous Hall effect and proximity-induced ferromagnetic state in SrIrO3,"The 5d iridium-based transition metal oxides have gained broad interest
because of their strong spin-orbit coupling which favors new or exotic quantum
electronic states. On the other hand, they rarely exhibit more mainstream
orders like ferromagnetism due to generally weak electron-electron correlation
strength. Here, we show a proximity-induced ferromagnetic (FM) state with TC =
100 K and strong magnetocrystalline anisotropy in a SrIrO3 (SIO)
heterostructure via interfacial charge transfer by using a ferromagnetic
insulator in contact with SIO. Electrical transport allows to selectively probe
the FM state of the SIO layer and the direct observation of a strong, intrinsic
and positive anomalous Hall effect (AHE). For T < 20 K, the AHE displays
unusually large coercive and saturation field, a fingerprint of a strong
pseudospin-lattice coupling. A Hall angle, sxyAHE/sxx, larger by an order of
magnitude than in typical 3d metals and a FM net moment of about 0.1 mB/Ir, is
reported. This emphasizes how efficiently the nontrivial topological band
properties of SIO can be manipulated by structural modifications and the
exchange interaction with 3d TMOs.",2201.09570v2
2022-02-28,Pervasive beyond room-temperature ferromagnetism in a doped van der Waals magnet: Ni doped Fe$_5$GeTe$_2$ with $T_{\text{C}}$ up to 478 K,"The existence of long range magnetic order in low dimensional magnetic
systems, such as the quasi-two-dimensional (2D) van der Waals (vdW) magnets,
has attracted intensive studies of new physical phenomena. The vdW
Fe$_N$GeTe$_2$ ($N$ = 3, 4, 5; FGT) family is exceptional owing to its vast
tunability of magnetic properties. Particularly, a ferromagnetic ordering
temperature ($T_{\text{C}}$) above room temperature at $N$ = 5 (F5GT) is
observed. Here, our study shows that, by nickel (Ni) substitution of iron (Fe)
in F5GT, a record high $T_{\text{C}}$ = 478(6) K is achieved. Importantly,
pervasive, beyond-room-temperature ferromagnetism exists in almost the entire
doping range of the phase diagram of Ni-F5GT. We argue that this striking
observation in Ni-F5GT can be possibly due to several contributing factors, in
which the structural alteration enhanced 3D magnetic couplings might be
critical for enhancing the ferromagnetic order.",2203.00125v2
2022-03-10,Prediction of single-atom-thick transition metal nitride CrN$_4$ with a square-planar network and high-temperature ferromagnetism,"Single-atom-thick two-dimensional materials such as graphene usually have a
hexagonal lattice while the square-planar lattice is uncommon in the family of
two-dimensional materials. Here, we demonstrate that single-atom-thick
transition metal nitride CrN$_4$ monolayer is a stable free-standing layer with
a square-planar network.
  The stability of square-planar geometry is ascribed to the combination of N=N
double bond, Cr-N coordination bond, and $\pi$-d conjugation, in which the
double $\pi$-d conjugation is rarely reported in previous studies.
  This mechanism is entirely different from that of the reported
two-dimensional materials, leading to lower formation energy and more robust
stability compared to the synthesized g-C$_3$N$_4$ monolayer.
  On the other hand, CrN$_4$ layer has a ferromagnetic ground state, in which
the ferromagnetic coupling between two Cr atoms is mediated by electrons of the
half-filled large $\pi$ orbitals from $\pi$-d conjugation.
  The high-temperature ferromagnetism in CrN$_4$ monolayer is confirmed by
solving the Heisenberg model with Monte Carlo method.",2203.05361v2
2022-03-24,Critical behavior in the Mn$_{5}$Ge$_{3}$ ferromagnet,"High-Curie-temperature ferromagnets are promising candidates for designing
new spintronic devices. Here we have successfully synthesized a single-crystal
sample of the itinerant ferromagnet Mn$ _{5}$Ge$_{3}$ used flux method and its
critical properties were investigated by means of bulk dc-magnetization at the
boundary between the ferromagnetic (FM) and paramagnetic (PM) phase. Critical
exponents $ \beta=0.336 \pm 0.001 $ with a critical temperature $ T_{c}=300.29
\pm 0.01 $ K and $ \gamma=1.193 \pm 0.003 $ with $ T_{c} = 300.15 \pm 0.05 $ K
are obtained by the modified Arrott plot, whereas $ \delta = 4.61 \pm 0.03 $ is
deduced by a critical isotherm analysis at $ T_{c} = 300 $ K. The
self-consistency and reliability of these critical exponents are verified by
the Widom scaling law and the scaling equations. Further analysis reveals that
the spin coupling in Mn$ _{5}$Ge$_{3}$ exhibits three-dimensional Ising-like
behavior. The magnetic exchange is found to decay as $ J(r)\approx r^{-4.855} $
and the spin interactions are extended beyond the nearest neighbors, which may
be related to different set of Mn--Mn interactions with unequal magnitude of
exchange strengths. Additionally, the existence of noncollinear spin
configurations in Mn$ _{5} $Ge$ _{3} $ results in a small deviation of obtained
critical exponents from those for standard 3D-Ising model.",2203.12778v1
2022-03-28,Theory-guided investigation on magnetic evolution of MnPt$_{5-x}$Pd$_x$P and discovery of anti-CeCoIn$_5$-type ferromagnetic MnPd$_5$P,"We report the magnetic changes from canted antiferromagnetic to ferromagnetic
orderings in anti-115-type MnPt$_{5-x}$Pd$_x$P ($x$ = 1, 2, 2.5, 3, 4, and 5)
and the discovery of a new rare-earth-free ferromagnet, MnPd$_5$P by both
theoretical prediction and experimental investigation. The family compounds
were synthesized using high temperature solid state method and characterized to
crystalize in the anti-CeCoIn$_5$ type with the space group P4/mmm exhibiting a
two-dimensional layered structural feature. The magnetic property measurements
indicate that the compounds ordered from canted A-type antiferromagnet in
MnPt$_5$P to ferromagnet above the room temperature with varying degrees of
coercivity and magnetic moments in MnPd$_5$P by reducing the spin orbital
coupling. The results of the MnPt$_{5-x}$Pd$_x$P have been analyzed in
comparison to the other candidates of the 151 family of Mn(Pt/Pd)$_5$(P/As) to
understand the complex structure-magnetism relationships.",2203.15016v1
2022-06-08,Macroscopic Quantum Tunneling of a Topological Ferromagnet,"The recent advent of topological states of matter spawned many significant
discoveries. The quantum anomalous Hall effect[1-3] is a prime example due to
its potential for applications in quantum metrology[4, 5] as well as its
influence on fundamental research into the underlying topological and magnetic
states[6-11] and axion electrodynamics[2, 12-14]. Here, we perform electronic
transport studies on a (V,Bi,Sb)2Te3 ferromagnetic topological insulator
nanostructure in the quantum anomalous Hall regime. This allows us access to
the dynamics of an individual ferromagnetic domain. The volume of the domain is
estimated to be about 85 000 nm3, containing some 50 000 vanadium atoms, spread
over a macroscopic distance of 115 nm. Telegraph noise resulting from the
magnetization fluctuations of this domain is observed in the Hall signal.
Careful analysis of the influence of temperature and external magnetic field on
the domain switching statistics provides evidence for quantum tunneling of
magnetization[15-22] in a macrospin state. This ferromagnetic macrospin is not
only the largest magnetic object in which quantum tunneling has been observed,
but also the first observation of the effect in a topological state of matter.",2206.03972v1
2022-06-27,Gate-tunable anomalous Hall effect in stacked van der Waals ferromagnetic insulator - topological insulator heterostructures,"The search of novel topological phases, such as the quantum anomalous Hall
insulator (QAHI) or the axion insulator, has motivated different schemes to
introduce magnetism into topological insulators. One scheme is to introduce
ferromagnetic dopants in topological insulators. However, it is generally
challenging and requires carefully engineered growth/heterostructures or
relatively low temperatures to observe the QAHI due to issues such as the added
disorder with ferromagnetic dopants. Another promising scheme is using the
magnetic proximity effect with a magnetic insulator to magnetize the
topological insulator. Most of these heterostructures are synthesized so far by
growth techniques such as molecular beam epitaxy and metallic organic chemical
vapor deposition. These are not readily applicable to allow mixing and matching
many of the available ferromagnetic and topological insulators due to
difference in growth conditions and lattice mismatch. Here, we demonstrate that
the magnetic proximity effect can still be obtained in stacked heterostructures
assembled via the dry transfer of exfoliated micrometer-sized thin flakes of
van der Waals topological insulator and magnetic insulator materials
(BiSbTeSe2/Cr2Ge2Te6), as evidenced in the observation of an anomalous Hall
effect (AHE). Furthermore, devices made from these heterostructures can allow
modulation of the AHE when controlling the carrier density via electrostatic
gating. These results show that simple mechanical transfer of magnetic van der
Waals materials provides another possible avenue to magnetize topological
insulators by magnetic proximity effect, a key step towards further realization
of novel topological phases such as QAHI and axion insulators.",2206.13045v1
2022-07-01,Light-induced giant and persistent changes in the converse magnetoelastic effects in Ni/BaTiO3 multiferroic heterostructure,"Magnetoelastic and magnetoelectric coupling in the artificial multiferroic
heterostructures facilitate valuable features for device applications such as
magnetic field sensors and electric write magnetic-read memory devices. In a
ferromagnetic/ferroelectric heterostructures, the strain mediated coupling
exploits piezoelectricity/electrostriction in ferroelectric phase and
magnetostriction/piezomagnetism in ferromagnetic phase. Such verity of these
combined effect can be manipulated by an external perturbation, such as
electric field, temperature or magnetic field. Here, we demonstrate the
remote-controlled tunability of these effects under the visible, coherent and
polarized light. The combined surface and bulk magnetic study of
domain-correlated Ni/BaTiO3 heterostructure reveals that the system is strong
sensitive about the light illumination via the combined effect of converse
piezoelectric, magnetoelastic coupling and converse magnetostriction.
Well-defined ferroelastic domain structure is fully transferred from a
tetragonal ferroelectric to magnetostrictive layer via interface strain
transfer during the film growth. The visible light illumination is used to
manipulate the original ferromagnetic microstructure by the light-induced
domain wall motion in ferroelectric, consequently the domain wall motion in the
ferromagnetic layer. Our findings mimic the attractive remote-controlled
ferroelectric random-access memory write and magnetic random-access memory read
application scenarios, hence, can be proven as a novel perspective for room
temperature device applications.",2207.00439v3
2022-07-29,Two-dimensional ferromagnetic extension of a topological insulator,"Inducing a magnetic gap at the Dirac point of the topological surface state
(TSS) in a 3D topological insulator (TI) is a route to dissipationless charge
and spin currents. Ideally, magnetic order is present only at the surface and
not in the bulk, e.g. through proximity of a ferromagnetic (FM) layer. However,
such a proximity-induced Dirac mass gap has not been observed, likely due to
insufficient overlap of TSS and the FM subsystem. Here, we take a different
approach, namely FM extension, using a thin film of the 3D TI Bi$_2$Te$_3$,
interfaced with a monolayer of the lattice-matched van der Waals ferromagnet
MnBi$_2$Te$_4$. Robust 2D ferromagnetism with out-of-plane anisotropy and a
critical temperature of $\text{T}_\text{c}\approx$~15 K is demonstrated by
X-ray magnetic dichroism and electrical transport measurements. Using
angle-resolved photoelectron spectroscopy, we observe the opening of a sizable
magnetic gap in the 2D FM phase, while the surface remains gapless in the
paramagnetic phase above T$_c$. This sizable gap indicates a relocation of the
TSS to the FM ordered Mn moments near the surface, which leads to a large
mutual overlap.",2207.14421v1
2022-08-07,Strain tunability of perpendicular magnetic anisotropy in van der Waals ferromagnets VI3,"Layered ferromagnets with high coercivity have special applications in
nanoscale memory elements in electronic circuits, such as data storage.
Therefore, searching for new hard ferromagnets and effectively tuning or
enhancing the coercivity are the hottest topics in layered magnets today. Here,
we report a strain tunability of perpendicular magnetic anisotropy in van der
Waals (vdW) ferromagnets VI3 using magnetic circular dichroism measurements.
For an unstrained flake, the M-H curve shows a rectangular-shaped hysteresis
loop with perpendicular magnetic anisotropy and a large coercivity (up to 1.775
T at 10 K). Furthermore, the coercivity can be enhanced to a maximum of 2.6 T
at 10 K under a 2.9% in-plane tensile strain. Our DFT calculations show that
the magnetic anisotropy energy (MAE) can be dramatically increased after
applying an in-plain tensile strain, which contributes to the enhancement of
coercivity in the VI3 flake. Meanwhile, the strain tunability on the coercivity
of CrI3, with a similar crystal structure, is limited. The main reason is the
strong spin-orbital coupling in V3+ in VI6 octahedra in comparison with that in
Cr3+. The strain tunability of coercivity in VI3 flakes highlights its
potential for integration into vdW heterostructures, paving the way toward
nanoscale spintronic devices and applications in the future.",2208.03678v1
2022-08-11,Flat-band based ferromagnetic semiconducting state in the graphitic C$_4$N$_3$ monolayer,"A new set of lattice-models based on the hexagonal $\sqrt{N}\times\sqrt{N}$
super-cells of the well-known honeycomb lattice with single-hole defect
(HL-D-1/2N) are proposed to realize the nontrivial isolated flat-bands. Through
performing both tight-binding and density functional theory calculations, we
demonstrate that the experimentally realized graphitic carbon nitride (Adv.
Mater., 22, 1004, 2010; Nat. Commun., 9, 3366, 2018), the HL-D-1/8 based
C$_4$N$_3$, is a perfect system to host such flat bands. For the flat
high-energy P-6m2 C$_4$N$_3$ structure, it displays the ferromagnetic
half-metallicity which is not related to the isolated flat bands. However, the
P-6m2 C$_4$N$_3$ structure is dynamically unstable. Using a structure searching
method based on group and graph theory, we find that a new corrugated Pca21
C4N3 structure has the lowest energy among all known C$_4$N$_3$ structures.
This Pca21 C$_4$N$_3$ structure is an intrinsic ferromagnetic
half-semiconductor (Tc$\approx$241 K) with one semiconducting spin-channel
(1.75 eV) and one insulating spin-channel (3.64 eV), which is quite rare in the
two-dimensional (2D) systems. Its ferromagnetic semiconducting property
originates from the isolated p$_z$-state flat-band as the corrugation shift the
flat band upward to the Fermi level. Interestingly, this Pca21 C$_4$N$_3$
structure is found to be piezoelectric and ferroelectric, which makes
C$_4$N$_3$ an unusual transition-metal-free 2D multiferroic.",2208.06065v1
2022-08-26,Quasiparticle characteristics of the weakly ferromagnetic Hund's metal MnSi,"Hund's metals are multi-orbital systems with $3d$ or $4d$ electrons
exhibiting both itinerant character and local moments, and they feature
Kondo-like screenings of local orbital and spin moments, with suppressed
coherence temperature driven by Hund's coupling $J_H$. They often exhibit
magnetic order at low temperature, but how the interaction between the
Kondo-like screening and long-range magnetic order is manifested in the
quasiparticle spectrum remains an open question. Here we present spectroscopic
signature of such interaction in a Hund's metal candidate MnSi exhibiting weak
ferromagnetism. Our photoemission measurements reveal renormalized
quasiparticle bands near the Fermi level with strong momentum dependence: the
ferromagnetism manifests through possibly exchange-split bands (Q1) below $T_C$
, while the spin/orbital screenings lead to gradual development of
quasiparticles (Q2) upon cooling. Our results demonstrate how the
characteristic spin/orbital coherence in a Hund's metal could coexist and
compete with the magnetic order to form a weak itinerant ferromagnet, via
quasiparticle bands that are well separated in momentum space and exhibit
distinct temperature dependence. Our results imply that the competition between
the spin/orbital screening and the magnetic order in a Hund's metal bears
intriguing similarity to the Kondo lattice systems.",2208.12456v2
2022-09-20,Tuning the hysteresis loop for the anomalous Hall effect in Pt ultrathin films on $\rm{CoFe_2O_4}$ by electrolyte gating,"Pt ultrathin films on ferromagnetic insulators have been widely studied for
spintronics applications, and magnetic moments of interface Pt atoms were
considered to be ferromagnetically ordered due to a magnetic proximity effect
(MPE). An anomalous Hall effect (AHE) is usually used to examine an
out-of-plane magnetic moments of the Pt layer. To tune ferromagnetic properties
of an Pt ultrathin film, we fabricated electric double layer transistors on Pt
thin films with thicknesses of 5.9 nm and 7.0 nm on a $\rm{CoFe_2O_4}$ (CFO)
ferrimagnetic insulator. For the Pt (7.0 nm)/CFO sample, a hysteresis loop was
observed in the anomalous Hall resistivity without the gate bias, and the
coercive field was tuned by applying the gate bias. For the Pt (5.9 nm)/CFO
sample, a hysteresis loop was not observed without a gate bias, but was opened
by applying a gate bias ($V\rm{_G} =$ $\pm$3 V). This indicated that the
long-range ferromagnetic ordering of magnetic moments in the Pt film was
switched on and off by the electric field effect. The hysteresis loop was
observed up to 19.5 K for a $V\rm{_G}$ of +3 V, while the AHE was observed up
to approximately room temperature.",2209.09797v2
2022-09-27,Ferromagnetism in an extended coherently-coupled atomic superfluid,"Ferromagnetism is an iconic example of a first-order phase transition taking
place in spatially extended systems and is characterized by hysteresis and the
formation of domain walls. In this paper we demonstrate that an extended atomic
superfluid in the presence of a coherent coupling between two internal states
exhibits a quantum phase transition from a para- to a ferromagnetic state. The
nature of the transition is experimentally assessed by looking at the phase
diagram as a function of the control parameters, at hysteresis phenomena, at
the magnetic susceptibility and the magnetization fluctuations around the
critical point. We show that the observed features are in good agreement with
mean-field calculations. Additionally, we develop experimental protocols to
deterministically generate domain walls that separate spatial regions of
opposite magnetization in the ferromagnetic state. Thanks to the enhanced
coherence properties of our atomic superfluid system compared to standard
condensed matter systems, our results open the way towards the study of
different aspects of the relaxation dynamics in isolated coherent many-body
quantum systems.",2209.13235v3
2022-09-30,Absence of magnetic interactions in Ni-Nb ferromagnet-superconductor bilayers,"Studies of ferromagnet-superconductor hybrid systems have uncovered magnetic
interactions between the competing electronic orderings. The electromagnetic
(EM) proximity effect predicts the formation of a spontaneous vector potential
inside a superconductor placed in proximity to a ferromagnet. In this work, we
use a Nb superconducting layer and Ni ferromagnetic layer to test for such
magnetic interactions. We use the complementary, but independent, techniques of
polarised neutron reflectometry and detection Josephson junctions to probe the
magnetic response inside the superconducting layer at close to zero applied
field. In this condition, Meissner screening is negligible, so our measurements
examine only additional magnetic and screening contributions from proximity
effects. We report the absence of any signals originating from EM proximity
effect in zero applied field. Our observations indicate that either EM
proximity effect is below the detection resolution of both of our experiments
or may indicate a new phenomenon that requires extension of current theory.
From our measurements, we estimate a limit of the size of the zero field EM
proximity effect in our Ni-Nb samples to be $\pm0.27$ mT.",2209.15366v2
2022-10-13,The Random-Bond Ising Model and its dual in Hyperbolic Spaces,"We analyze the thermodynamic properties of the random-bond Ising model (RBIM)
on closed hyperbolic surfaces using Monte Carlo and high-temperature series
expansion techniques. We also analyze the dual-RBIM, that is the model that in
the absence of disorder is related to the RBIM via the Kramers-Wannier duality.
Even on self-dual lattices this model is different from the RBIM, unlike in the
euclidean case. We explain this anomaly by a careful re-derivation of the
Kramers--Wannier duality. For the (dual-)RBIM, we compute the
paramagnet-to-ferromagnet phase transition as a function of both temperature
$T$ and the fraction of antiferromagnetic bonds $p$. We find that as
temperature is decreased in the RBIM, the paramagnet gives way to either a
ferromagnet or a spin-glass phase via a second-order transition compatible with
mean-field behavior. In contrast, the dual-RBIM undergoes a strongly first
order transition from the paramagnet to the ferromagnet both in the absence of
disorder and along the Nishimori line. We study both transitions for a variety
of hyperbolic tessellations and comment on the role of coordination number and
curvature. The extent of the ferromagnetic phase in the dual-RBIM corresponds
to the correctable phase of hyperbolic surface codes under independent bit- and
phase-flip noise.",2210.07227v2
2022-11-02,2D-Double transition metal MXenes for spintronics applications: surface functionalization induced ferromagnetic half-metallic complexes,"MXenes are rapidly emerging two-dimensional (2D) materials with thickness,
composition, and functionalization-dependent outstanding properties having
applications in diverse fields. To disclose nano-spintronic applications of
2D-double transition metal (DTM) carbide and nitride-based pristine and
surface-functionalized MXenes (M'2M""X2Tx, M' and M"" = Cr, Mo, W; X = C/N; T =
-F/-OH/=O), a systematic investigation has been performed on structural
stability, magnetic properties and electronic structure using spin-polarized
first-principles calculations. 36 stables functionalized MXenes were screened
from 144 explored DTM based MXenes. The explored materials exhibit striking
properties, having wide range of magnetic ground states, from non-magnetic to
ferromagnetic, and then to antiferromagnetic, accompanied by metallic to
half-metallic or gapless half-metallic properties, depending on transition
metal(s) and terminating group. Mo and W-based MXenes are found to be
nonmagnetic and metallic, whereas Cr-Mo and Cr-W-based MXenes are magnetic with
varying metallic behavior. W2CrN2O2 and Mo2CrN2O2 systems are found to be
ferromagnetic half-metallic 2D materials with a direct band gap of 1.35 eV and
0.77 eV respectively, in the minority spin channel. The comprehensive study on
DTM MXenes, provide intrinsic half-metallic properties along with robust
ferromagnetism, opens up a class of promising new 2D materials with tunable
magnetic and electronic properties for potential device applications in
nano-spintronics and electronics.",2211.00846v1
2022-11-02,Hydroxide-based magneto-ionics: electric-field control of reversible paramagnetic-to-ferromagnetic switch in $α$-Co(OH)$_{2}$ films,"Magneto-ionics has emerged as a promising approach to manipulate magnetic
properties, not only by drastically reducing power consumption associated with
electric current based devices but also by enabling novel functionalities. To
date, magneto-ionics have been mostly explored in oxygen-based systems, while
there is a surge of interests in alternative ionic systems. Here we demonstrate
highly effective hydroxide-based magneto-ionics in electrodeposited
${\alpha}$-Co(OH)$_{2}$ films. The ${\alpha}$-Co(OH)$_{2}$, which is a room
temperature paramagnet, is switched to ferromagnetic after electrolyte gating
with a negative voltage. The system is fully, magnetically reversible upon
positive voltage application. The origin of the reversible
paramagnetic-to-ferromagnetic transition is attributed to the ionic diffusion
of hydroxyl groups, promoting the formation of metallic cobalt ferromagnetic
regions. Our findings demonstrate one of the lowest turn-on voltages reported
for propylene carbonate gated experiments. By tuning the voltage magnitude and
sample area we demonstrate that the speed of the induced ionic effect can be
drastically enhanced.",2211.01191v1
2022-11-16,Continuous Electrical Manipulation of Magnetic Anisotropy and Spin Flopping in van der Waals Ferromagnetic Devices,"Controlling the magnetic anisotropy of ferromagnetic materials plays a key
role in magnetic switching devices and spintronic applications. Examples of
spin-orbit torque devices with different magnetic anisotropy geometries
(in-plane or out-of-plane directions) have been demonstrated with novel
magnetization switching mechanisms for extended device functionalities.
Normally, the intrinsic magnetic anisotropy in ferromagnetic materials is
unchanged within a fixed direction, and thus, it is difficult to realize
multifunctionality devices. Therefore, continuous modulation of magnetic
anisotropy in ferromagnetic materials is highly desired but remains
challenging. Here, we demonstrate a gate-tunable magnetic anisotropy transition
from out-of-plane to canted and finally to in-plane in layered Fe$_5$GeTe$_2$
by combining the measurements of the angle-dependent anomalous Hall effect and
magneto-optical Kerr effect with quantitative Stoner-Wohlfarth analysis. The
magnetic easy axis continuously rotates in a spin-flop pathway by gating or
temperature modulation. Such observations offer a new avenue for exploring
magnetization switching mechanisms and realizing new spintronic
functionalities.",2211.08909v1
2022-12-16,Transverse currents in spin transistors,"In many systems, planar Hall effect wherein transverse signal appears in
response to longitudinal stimulus is rooted in spin-orbit coupling. A spin
transistor put forward by Datta and Das on the other hand consists of
ferromagnetic leads connected to spin-orbit coupled central region and its
conductance can be controlled by tuning the strength of spin-orbit coupling. We
find that transverse currents also appear in Datta-Das transistors made by
connecting two two-dimensional ferromagnetic reservoirs to a central spin-orbit
coupled two-dimensional electron gas. We find that the spin transistor exhibits
a nonzero transverse conductivity which depends on the direction of
polarization in ferromagnets and the location where it is measured. We study
the conductivities for the system with finite and infinite widths. The
conductivities exhibit Fabry-P\'erot type oscillations as the length of the
spin-orbit coupled regions is varied. Interestingly, even in the limit when
longitudinal conductivity is made zero by cutting off the junction between the
central spin-orbit coupled region and the ferromagnetic lead on one side
(right), the transverse conductivities remain nonzero in the regions that are
on the left side of the cut-off junction.",2212.08301v4
2023-01-05,Two-dimensional Heisenberg models with materials-dependent superexchange interactions,"The two-dimensional (2D) van der Waals ferromagnetic semiconductors, such as
CrI$_3$ and Cr$_2$Ge$_2$Te$_6$, and the 2D ferromagnetic metals, such as
Fe$_3$GeTe$_2$ and MnSe$_2$, have been obtained in recent experiments and
attracted a lot of attentions. The superexchange interaction has been suggested
to dominate the magnetic interactions in these 2D magnetic systems. In the
usual theoretical studies, the expression of the 2D Heisenberg models were
fixed by hand due to experiences. Here, we propose a method to determine the
expression of the 2D Heisenberg models by counting the possible superexchange
paths with the density functional theory (DFT) and Wannier function
calculations. With this method, we obtain a 2D Heisenberg model with six
different nearest-neighbor exchange coupling constants for the 2D ferromagnetic
metal Cr$_3$Te$_6$, which is very different for the crystal structure of Cr
atoms in Cr$_3$Te$_6$. The calculated Curie temperature Tc = 328 K is close to
the Tc = 344 K of 2D Cr$_3$Te$_6$ reported in recent experiment. In addition,
we predict two stable 2D ferromagnetic semiconductors Cr$_3$O$_6$ and
Mn$_3$O$_6$ sharing the same crystal structure of Cr$_3$Te$_6$. The similar
Heisenberg models are obtained for 2D Cr$_3$O$_6$ and Mn$_3$O$_6$, where the
calculated Tc is 218 K and 208 K, respectively. Our method offers a general
approach to determine the expression of Heisenberg models for these 2D magnetic
semiconductors and metals, and builds up a solid basis for further studies.",2301.01923v1
2023-01-08,AdS/BCFT correspondence and Horndeski gravity in the presence of gauge fields: holographic paramagnetism/ferromagnetism phase transition,"This paper presents a dual gravity model for a (2+1)-dimensional system with
a limit on finite charge density and temperature, which will be used to study
the properties of the holographic phase transition to
paramagnetism-ferromagnetism in the presence of Horndeski gravity terms. In our
model, the non-zero charge density is supported by a magnetic field. As a
result, the radius $\rho/B$ indicates a localized condensate, as we increase
the Horndeski gravity parameter, that is represented by $\gamma$. Furthermore,
such condensate shows quantum Hall-type behavior. This radius is also inversely
related to the total action coefficients of our model. It was observed that
increasing the Horndeski parameter decreases the critical temperature of the
holographic model and leads to the harder formation of the magnetic moment at
the bottom of the black hole. However, when removing the magnetic field, the
ferromagnetic material presents a disorder of its magnetic moments, which is
observed through the entropy of the system. We also found that at low
temperatures, spontaneous magnetization and ferromagnetic phase transition.",2301.03121v3
2023-02-03,Signature of the coexistence of ferromagnetism and superconductivity at KTaO$_3$ heterointerfaces,"The coexistence of superconductivity and ferromagnetism is a long-standing
issue in the realm of unconventional superconductivity due to the antagonistic
nature of these two ordered states. Experimentally identifying and
characterizing novel heterointerface superconductors that coexist with
magnetism is challenging. Here, we report the experimental observation of
long-range ferromagnetic order at the verge of two-dimensional
superconductivity at KTaO$_3$ heterointerfaces. Remarkably, we observe in-plane
magnetization hysteresis loop persisting to above room temperature with direct
current superconducting quantum interference device measurements. Furthermore,
both the first-principles calculations and the x-ray magnetic circular
dichroism measurements reveal that the observed robust ferromagnetism is
attributed to the presence of oxygen vacancies that localize electrons in
nearby Ta 5$d$ states. Our findings not only indicate KTaO$_3$ heterointerfaces
as unconventional superconductors with time-reversal symmetry breaking, but
also inject a new momentum to the study of the delicate interplay between
superconductivity and magnetism boosted by strong spin-orbit coupling inherent
to the heavy Ta in 5$d$ orbitals of KTaO$_3$ heterointerfaces.",2302.01549v4
2023-02-25,Goldstone modes and the golden spiral in the ferromagnetic spin-1 biquadratic model,"Ferromagnetic ground states have often been overlooked in comparison to
seemingly more interesting antiferromagnetic ground states. However, both the
physical and mathematical structure of ferromagnetic ground states are
particularly rich. We show that the highly degenerate and highly entangled
ground states of the ferromagnetic spin-1 biquadratic model are scale
invariant, originating from spontaneous symmetry breaking from ${\rm SU}(3)$ to
${\rm U}(1)\times {\rm U}(1)$ with two type-B Goldstone modes. The ground state
degeneracies are characterized as the Fibonacci-Lucas sequences -- an ancient
mathematical gem, under open and periodic boundary conditions, with the
residual entropy being non-zero. This implies that the ground state
degeneracies for this model are asymptotically the golden spiral. In addition,
sequences of degenerate ground states generated from highest and generalized
highest weight states are constructed to establish that the entanglement
entropy scales logarithmically with the block size in the thermodynamic limit,
with the prefactor being half the number of type-B Goldstone modes. The latter
in turn is identified to be the fractal dimension.",2302.13126v3
2023-03-06,Magnetic domain depinning as possible evidence for two ferromagnetic phases in LaCrGe$_3$,"Two ferromagnetic phases, FM1 and FM2, were first proposed to exist in
LaCrGe$_3$ based on a broad maximum in the temperature derivative of
resistivity resembling that of the superconducting ferromagnet UGe$_2$ where
FM1 and FM2 are well-established. While evidence for two FM phases can be found
in certain additional probes, corresponding anomalies in magnetization have not
been recognized until now. Our spatially-resolved images of the magnetic
domains show a substantial change in the domain structure between the higher
temperature FM1 phase and the lower temperature FM2 phase. Furthermore, our
measurements of the coercive field and virgin magnetization curves reveal an
unconventional magnetic domain pinning region in the FM1 phase, followed by a
depinning region at lower temperatures where the system is reported to
crossover into the FM2 phase. We incorporate this discovery into a simple
domain magnetization model that demystifies the magnetization curve seen in all
previous studies. Finally, we find that the unusual domain behavior can be
explained by a change in the ferromagnetic exchange interaction and magnetic
moment, both of which are consistent with the existence of two FM phases. This
revelation may help explain a range of anomalous behaviors observed in
LaCrGe$_3$ and rekindles the discussion about the prevalence of multiple FM
phases in fragile FM systems.",2303.03447v2
2023-03-17,Chemically induced ferromagnetism near room temperature in single crystal (Zn$_{1-x}$Cr$_{x}$)Te half-metal,"Magnetic semiconductors are at the core of recent spintronics research
endeavors. Chemically doped II-VI diluted magnetic semiconductors, such as
(Zn$_{1-x}$Cr$_{x}$)Te, provide promising platform in this quest. However, a
detailed knowledge of the microscopic nature of magnetic ground state is
necessary for any practical application. Here, we report on the synergistic
study of (Zn$_{1-x}$Cr$_{x}$)Te single crystals using elastic neutron
scattering measurements and density functional calculations. For the first
time, our research unveils the intrinsic properties of ferromagnetic state in
macroscopic specimen of (Zn$_{0.8}$Cr$_{0.2}$)Te. The ferromagnetism is onset
at $T_c \sim$ 290 K and remains somewhat independent to modest change in the
substitution coefficient x. We show that magnetic moments on Zn/Cr site develop
ferromagnetic correlation in a-c plane with large ordered moment of $\mu$ =
3.08 $\mu_B$. Magnetic moment across the lattice is induced via the mediation
of Te site, uncoupled to the number of dopant carriers as inferred from the
density functional calculation. Additionally, the ab-initio calculations also
reveal half-metallicity in x = 0.2 composition. These properties are highly
desirable for future spintronic applications.",2303.09740v1
2023-03-17,Intrinsic and extrinsic anomalous transport properties of Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl from first principles,"Recently, Heusler ferromagnets have been found to exhibit unconventional
anomalous electric, thermal, and thermoelectric transport properties. In this
study, we employed first-principles density functional theory calculations to
systematically investigate both intrinsic and extrinsic contributions to the
anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and anomalous
thermal Hall effect (ATHE) in two Heusler ferromagnets: Fe$_2$CoAl and
Fe$_2$NiAl. Our analysis reveals that the extrinsic mechanism originating from
disorder dominates the AHE and ATHE in Fe$_2$CoAl , primarily due to the steep
band dispersions across the Fermi energy and corresponding high longitudinal
electronic conductivity. Conversely, the intrinsic Berry phase mechanism,
physically linked to nearly flat bands around the Fermi energy and gapped by
spin-orbit interaction band crossings, governs the AHE and ATHE in Fe$_2$NiAl.
With respect to ANE, both intrinsic and extrinsic mechanisms are competing in
Fe$_2$CoAl as well as in Fe$_2$NiAl. Furthermore, Fe$_2$CoAl and Fe$_2$NiAl
exhibit tunable and remarkably pronounced anomalous transport properties. For
instance, the anomalous Nernst and anomalous thermal Hall conductivities in
Fe$_2$NiAl attain giant values of 8.29 A/Km and 1.19 W/Km, respectively, at
room temperature. To provide a useful comparison, we also thoroughly
investigated the anomalous transport properties of Co$_2$MnGa. Our findings
suggest that Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl are promising
candidates for spintronics and spin-caloritronics applications.",2303.09812v2
2023-04-06,All-electrical operation of a Curie-switch at room temperature,"We present all-electrical operation of a Fe$_x$Cr$_{1-x}$-based Curie switch
at room temperature. More specifically, we study the current-induced
thermally-driven transition from ferromagnetic to antiferromagnetic
Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect coupling in a
Fe/Cr/Fe$_{17.5}$Cr$_{82.5}$/Cr/Fe multilayer. Magnetometry measurements at
different temperatures show that the transition from the ferromagnetic to the
antiferromagnetic coupling at zero field is observed at $\sim$325K. Analytical
modelling confirms that the observed temperature-dependent transition from
indirect ferromagnetic to indirect antiferromangetic interlayer exchange
coupling originates from the modification of the effective interlayer exchange
constant through the ferromagnetic-to-paramagnetic transition in the
Fe$_{17.5}$Cr$_{82.5}$ spacer with minor contributions from the
thermally-driven variations of the magnetization and magnetic anisotropy of the
Fe layers. Room-temperature current-in-plane magnetotransport measurements on
the patterned Fe/Cr/Fe$_{17.5}$Cr$_{82.5}$/Cr/Fe strips show the transition
from the 'low-resistance' parallel to the 'high-resistance' antiparallel
remanent magnetization configuration, upon increased probing current density.
Quantitative comparison of the switching fields, obtained by magnetometry and
magnetotransport, confirms that the Joule heating is the main mechanism
responsible for the observed current-induced resistive switching.",2304.03040v2
2023-04-11,Syntropic spin alignment at the interface between ferromagnetic and superconducting nitrides,"The magnetic correlations at the superconductor/ferromagnet (S/F) interfaces
play a crucial role in realizing dissipation-less spin-based logic and memory
technologies, such as triplet-supercurrent spin-valves and ""{\pi}"" Josephson
junctions. Here we report the coexistence of an induced large magnetic moment
and a crypto ferromagnetic state at high-quality nitride S/F interfaces. Using
polarized neutron reflectometry and d. c. SQUID measurements, we quantitatively
determined the magnetization profile of S/F bilayer and confirmed the induced
magnetic moment in the adjacent superconductor only exists below TC.
Interestingly, the direction of the induced moment in the superconductors was
unexpectedly parallel to that in the ferromagnet, which contrasts with earlier
findings in S/F heterostructures based on metals or oxides. The
first-principles calculations verify the observed unusual interfacial spin
texture is caused by the Heisenberg direct exchange coupling through d orbital
overlapping and severe charge transfer across the interfaces. Our work
establishes an incisive experimental probe for understanding the magnetic
proximity behavior at S/F interfaces and provides a prototype epitaxial
building block for superconducting spintronics.",2304.05234v1
2023-04-20,Pressure-induced transition from a Mott insulator to a ferromagnetic Weyl metal in La2O3Fe2Se2,"The insulator-metal transition in Mott insulators, known as the Mott
transition, is usually accompanied with various novel quantum phenomena, such
as unconventional superconductivity, non-Fermi liquid behavior and colossal
magnetoresistance. Here, based on high-pressure electrical transport and XRD
measurements, and first-principles calculations, we find that a unique
pressure-induced Mott transition from an antiferromagnetic Mott insulator to a
ferromagnetic Weyl metal in the iron oxychalcogenide La2O3Fe2Se2 occurs around
37 GPa without structural phase transition. Our theoretical calculations reveal
that such an insulator-metal transition is mainly due to the enlarged bandwidth
and diminishing of electron correlation at high pressure, fitting well with the
experimental data. Moreover, the high-pressure ferromagnetic Weyl metallic
phase possesses attractive electronic band structures with six pairs of Weyl
points close to the Fermi level, and its topological property can be easily
manipulated by the magnetic field. The emergence of Weyl fermions in
La2O3Fe2Se2 at high pressure may bridge the gap between nontrivial band
topology and Mott insulating states. Our findings not only realize
ferromagnetic Weyl fermions associated with the Mott transition, but also
suggest pressure as an effective controlling parameter to tune the emergent
phenomena in correlated electron systems.",2304.10222v1
2023-04-24,Observation of colossal topological Hall effect in noncoplanar ferromagnet Cr5Te6 thin films,"The topological Hall effect (THE) is critical to the exploration of the spin
chirality generated by the real-space Berry curvature, which has attracted
worldwide attention for its prospective applications in spintronic devices.
However, the prominent THE remains elusive at room temperature, which severely
restricts the practical integration of chiral spin textures. Here, we show a
colossal intrinsic THE in large-area ferromagnet Cr5Te6 thin films epitaxially
grown by pulsed laser deposition. Such a THE can be maintained until 270 K,
which is attributed to the field-stimulated noncoplanar spin textures induced
by the interaction of the in-plane ferromagnet and antiferromagnet
infrastructures. Our first-principles calculations further verify the
considerable Dzyaloshinskii-Moriya interaction in Cr5Te6. This work not only
paves the way for robust chiral spin textures near room temperature in
large-area low-dimensional ferromagnetic films for practical applications, but
also facilitates the development of high-density and dissipationless spintronic
devices.",2304.11778v1
2023-05-07,Effect of random antiferromagnetic exchange on the spin waves in a three-dimensional Heisenberg ferromagnet,"Neutron scattering is used to study spin waves in the three-dimensional
Heisenberg ferromagnet YTiO$_3$, with spin-spin exchange disorder introduced
$via$ La-substitution at the Y site. No significant changes are observed in the
spin-wave dispersion up to a La concentration of 20%. However, a strong
broadening of the spectrum is found, indicative of shortened spin-wave
lifetimes. Density-functional theory calculations predict minimal changes in
exchange constants as a result of average structural changes due to La
substitution, in agreement with the data. The absence of significant changes in
the spin-wave dispersion, the considerable lifetime effect, and the reduced
ordered magnetic moment previously observed in the La-substituted system are
qualitatively captured by an isotropic, nearest-neighbor, three-dimensional
Heisenberg ferromagnet model with random antiferromagnetic exchange. We
therefore establish Y$_{1-x}$La$_x$TiO$_3$ as a model system to study the
effect of antiferromagnetic spin-exchange disorder in a three-dimensional
Heisenberg ferromagnet.",2305.04280v1
2023-05-17,Potential-tuned magnetic switches and half-metallicity transition in zigzag graphene nanoribbons,"Realizing controllable room-temperature ferromagnetism in carbon-based
materials is one of recent prospects. The magnetism in graphene nanostructures
reported previously is mostly formed near the vacancies, zigzag edges, or
impurities by breaking the local sublattice imbalance, though a bulk chiral
spin-density-wave ground state is also reported at van Hove filling due to its
perfectly nested Fermi surface. Here, combining of the first-principles and
tight-binding model simulations, we predict a robust ferromagnetic domain lies
between the inter-chain carbon atoms inside the zigzag graphene nanoribbons by
applying a potential drop. We show that the effective zigzag edges provide the
strong correlation background through narrowing the band width, while the
internal Van Hove filling provides the strong ferromagnetic background
inherited from the bulk. The induced ferromagnetism exhibit interesting
switching effect when the nominal Van Hove filling crosses the intra- and
inter-chain region by tuning the potential drops. We further observe a robust
half-metallicity transition from one spin channel to another within the same
magnetic phase. These novel properties provide promising ways to manipulate the
spin degree of freedom in graphene nanostructures.",2305.10325v1
2023-05-25,Nonlinear spin dynamics of ferromagnetic ring in the vortex state and its application for spin-transfer nano-oscillator,"We study a nonlinear spin dynamics of a ferromagnetic ring in a vortex state
induced by the spin-polarized current. We also suggest to use the ferromagnetic
ring as a free layer of a coreless vortex spin-transfer nano-oscillator. The
calculated working frequency is about several GHz, that is much higher than the
gyromode frequency of the disk-based vortex oscillator. The response of the
vortex-state ring to the spin-polarized current has hysteretic behavior with
the reasonable values of the thresholds current densities: ignition threshold
is about $10^{8} \text{A}\text{cm}^{-2}$, and elimination current to maintain
the oscillations has much lower values about $10^{6} \text{A} \text{cm}^{-2}$.
The output signal can be extracted by the help of the inverse spin Hall effect
or by the giant magnetoresistance. The output electromotive force averaged over
all sample vanishes, and we suggest to use a ferromagnetic ring or disk in a
vortex state as a GMR analyzer. For an inverse spin Hall analyser we advise to
use two heavy metals with different signs of Spin-Hall angle. The ring-based
STNO is supposed to increase the areas of practical application of the STNOs.",2305.16019v2
2023-05-25,Observation of c-axis Magnetization at Low Temperatures in Weak Ferromagnet FeBO$_3$ Reveals a Spin-Reorientation Transition,"The weak ferromagnet FeBO$_3$ is well known for being a unique system for
modelling and testing magnetic dynamics primarily due to relatively simple and
localized magnetic structure and its interesting spin wave dynamics. At room
temperature, it has slightly canted iron moments lying in the a-b plane that
result in a strong antiferromagnetic moment and a weak ferromagnetic moment,
which results in pronounced ferromagnetic and antiferromagnetic spin modes.
However, some previous studies have shown unusual low-temperature behavior that
suggests a phase transition. By performing low-temperature magnetization
measurements, both in bulk and on the mesoscale, we have observed a low
temperature magnetic texture in this material in which a large c-axis
magnetization occurs. Magnetic fields along the c-axis as high as 1300 Oe were
observed close to the sample surface. This presents evidence for the onset of a
Morin transition or another type of spin-reorientation phase transition wherein
the Fe3+ moments would acquire a c-axis component to their canting below a
critical temperature. The observation of this c-axis magnetization suggests
that there is a different ground state in this material than has been
previously expected and could be due to as yet unexplored intricacies of the
Dzyaloshinskii-Moriya interaction.",2305.16082v1
2023-06-01,Constraints on proximity-induced ferromagnetism in a Dirac semimetal (Cd$_3$As$_2$)/ferromagnetic semiconductor (Ga$_{1-x}$Mn$_x$Sb) heterostructure,"Breaking time-reversal symmetry in a Dirac semimetal Cd$_3$As$_2$ through
doping with magnetic ions or by the magnetic proximity effect is expected to
cause a transition to other topological phases (such as a Weyl semimetal). To
this end, we investigate the possibility of proximity-induced ferromagnetic
ordering in epitaxial Dirac semimetal (Cd$_3$As$_2$)/ferromagnetic
semiconductor (Ga$_{1-x}$Mn$_x$Sb) heterostructures grown by molecular beam
epitaxy. We report the comprehensive characterization of these heterostructures
using structural probes (atomic force microscopy, x-ray diffraction, scanning
transmission electron microscopy), angle-resolved photoemission spectroscopy,
electrical magneto-transport, magnetometry, and polarized neutron
reflectometry. Measurements of the magnetoresistance and Hall effect in the
temperature range 2 K - 20 K show signatures that could be consistent with
either a proximity effect or spin-dependent scattering of charge carriers in
the Cd$_3$As$_2$ channel. Polarized neutron reflectometry sets constraints on
the interpretation of the magnetotransport studies by showing that (at least
for temperatures above 6 K) any induced magnetization in the Cd$_3$As$_2$
itself must be relatively small ($<$ 14 emu/cm$^3$).",2306.01167v1
2023-06-27,Interfacial-antiferromagnetic-coupling driven magneto-transport properties in ferromagnetic superlattices,"We explore the role of interfacial antiferromagnetic interaction in coupled
soft and hard ferromagnetic layers to ascribe the complex variety of
magneto-transport phenomena observed in $La_{0.7}Sr_{0.3}MnO_3/SrRuO_3$
(LSMO/SRO) superlattices (SLs) within a one-band double exchange model using
Monte-Carlo simulations. Our calculations incorporate the magneto-crystalline
anisotropy interactions and super-exchange interactions of the constituent
materials, and two types of antiferromagnetic interactions between Mn and Ru
ions at the interface: (i) carrier-driven and (ii) Mn-O-Ru bond super-exchange
in the model Hamiltonian to investigate the properties along the hysteresis
loop. We find that the antiferromagnetic coupling at the interface induces the
LSMO and SRO layers to align in anti-parallel orientation at low temperatures.
Our results reproduce the positive exchange bias of the minor loop and inverted
hysteresis loop of LSMO/SRO SL at low temperatures as reported in experiments.
In addition, conductivity calculations show that the carrier-driven
antiferromagnetic coupling between the two ferromagnetic layers steers the SL
towards a metallic (insulating) state when LSMO and SRO are aligned in
anti-parallel (parallel) configuration, in good agreement with the experimental
data. This demonstrate the necessity of carrier-driven antiferromagnetic
interactions at the interface to understand the one-to-one correlation between
the magnetic and transport properties observed in experiments. For high
temperature, just below the ferromagnetic $T_C$ of SRO, we unveiled the
unconventional three-step flipping process along the magnetic hysteresis loop.
We emphasize the key role of interfacial antiferromagnetic coupling between
LSMO and SRO to understand these multiple-step flipping processes along the
hysteresis loop.",2306.15143v1
2023-08-23,Enhancing the Capture of Magnetic Nanoparticles Inside of Ferromagnetic Nanostructures Using External Magnetic Fields,"The influence of an external magnetic field upon the capture of 130 nm
magnetic nanoparticles (MNPs) by ferromagnetic nanostructures was investigated.
The magnetophoretic forces acting upon a nanoparticle were simulated in
external magnetic fields parallel and perpendicular to ferromagnetic
nanostructures consisting of arrays of antidots and dots. Changing the
direction of the external field was found to dramatically alter the
magnetophoretic forces acting on the particle and the trajectories of the MNPs.
A field parallel to the nanostructures' surfaces generated magnetophoretic
forces that directed the nanoparticle into the nanostructures. A perpendicular
field produced forces directing particles onto the structures' surfaces.
Nanostructures were etched into the surfaces of Permalloy films using ion beam
lithography. MNPs were then deposited onto the films' surfaces under a parallel
or perpendicular magnetic field. The distributions of particles in the
nanostructures were analysed to obtain the capture efficiencies of each
structure which indicate the proportion of particles trapped inside. Without an
external field, the highest efficiency was displayed by arrays of circular
antidots with circular dot arrays displaying the lowest. Antidot arrays
displayed higher capture efficiencies than dot arrays. Addition of a field
parallel to the surface significantly increased the capture efficiencies and
addition of a field perpendicular to the surface decreased the efficiencies.
Under the perpendicular field, the particles were instead caught on the outer
edges of the nanostructures. These results suggest that application of a
parallel external magnetic field promotes the capture of MNPs within
ferromagnetic nanostructures and a perpendicular field increases the capture of
MNPs onto the outer surface and edges of nanostructures.",2308.12321v1
2023-10-23,Nonlinear Optical Effects Due to Magnetization Dynamics In a Ferromagnet,"We theoretically consider magnetization dynamics in a ferromagnetic slab
induced by the magnetic field of a strong femtosecond laser pulse. The
longitudinal geometry, in which the initial magnetization lies in both the
plane of incidence and the sample plane, is studied. The magnetization
oscillations at the optical wave frequency are calculated with the use of the
Kapitza pendulum approach taking into account that the optical frequency is
much greater than the magnetization oscillation eigenfrequency. We study the
reflection of the electromagnetic wave from a ferromagnet %with such a dynamics
and show that this laser-induced low-frequency magnetization dynamics leads to
the appearance of the second-order nonlinearity in the Maxwell's equations,
which in turn gives rise to both the second harmonic generation (SHG) and
rectification effect. Although the amplitude of the magnetization oscillations
is small, the considered effect may be responsible for the SHG with the
efficiency comparable to that of nonmagnetic SHG from metal surfaces. Our
estimations show that the suggested mechanism may explain the recent
experiments on magnetization induced modulation of the SHG intensity in a
``forbidden'' $P_{in}P_{out}$ combination of incident and reflected waves in
cobalt/heavy metal systems, where it can be even more pronounced due to the
spin current flow through the ferromagnet/ heavy metal interface.",2310.14967v1
2023-11-03,Robust room temperature ferromagnetism in an itinerant van der Waals antiferromagnet,"The coexistence of antiferromagnetic and ferromagnetic order at room
temperature in single-phase van der Waals materials, particularly within the
two-dimensional limit, has attracted significant research interest.
Nonetheless, such materials are rare. In this work, we introduce an itinerant
van der Waals antiferromagnet (Fe0.56Co0.44)5GeTe2, where the ferromagnetic
order of its exfoliated flakes remains discernible up to room temperature,
extending down to the monolayer limit. A notable phenomenon observed is the
evident odd-even layer-number effect at high temperature (e.g., T = 150 K).
Such behaviour can be expounded by a linear-chain model. Of particular interest
is the robust ferromagnetic order observed in even-layer flakes at low
temperature (e.g., T = 2 K), which could potentially be attributed to
spin-polarized defects. The intricate interplay among magnetic field strength,
layer number, and temperature gives rise to a diverse array of phenomena,
holding promise not only for new physics but also for practical applications.",2311.01735v1
2023-11-07,Revealing the ultra-fast domain wall motion in Manganese Gold through permalloy capping,"Antiferromagnets offer much faster dynamics compared to their ferromagnetic
counterparts but their order parameter is extremely difficult to detect and
control. So far, controlling the N\'eel order parameter electrically is limited
to only very few materials where N\'eel spin-orbit torques are allowed by
symmetry. In this work, we show that coupling a thin ferromagnet (permalloy)
layer on top of an antiferromagnet (Mn$_2$Au) solves a major roadblock -- the
controlled reading, writing, and manipulation of antiferromagnetic domains. We
confirm by atomistic spin dynamics simulations that the domain wall patterns in
the Mn$_2$Au are imprinted on the permalloy, therefore allowing for indirect
imaging of the N\'eel order parameter. Our simulations show that the coupled
domain wall structures in Mn$_2$Au-Py bilayers can be manipulated by either
acting on the N\'eel order parameter via N\'eel spin-orbit torques or by acting
on the magnetisation (the ferromagnetic order parameter) via magnetic fields.
In both cases, we predict ultra-high domain wall speeds on the order of 8.5
km/s. Thus, employing a thin ferromagnetic layer has the potential to easily
control the N\'eel order parameter in antiferromagnets even where N\'eel
spin-orbit torques are forbidden by symmetry. The controlled manipulation of
the antiferromagnetic order parameter provides a promising basis for the
development of high-density storage and efficient computing technologies
working in the THz regime.",2311.04305v1
2023-12-04,Survival of magnetic correlations above ordering temperature in a ferromagnetically ordered classical kagomé magnet: Li9Cr3(P2O7)3(PO4)2,"Motivated by the recent discovery of a semiclassical nematic spin liquid
state in a Heisenberg kagom\'e antiferromagnet Li9Fe3(P2O7)3(PO4)2 (LFPO) with
S=5/2 [Kermarrec et al. Phys. Rev. Lett. 127, 157202 (2021)], we now
investigate the impact of spin quantum number S on the ground state properties
by studying the isostructural kagom\'e magnet Li9Cr3(P2O7)3(PO4)2 (LCPO) with
active t2g orbitals and S = 3/2. Thermodynamic measurements reveal that the
ground state properties of LCPO is dominated by the ferromagnetic interactions
with a mean-field temperature $\theta \sim$ 3 K (J < 1 K) and the ordering
temperature, Tc ~ 2.7 K, and the size of the ordered moment $\sim 1.05 \pm 0.25
$ ~${\mu}_B$ is significantly reduced from that of a fully ordered moment. The
ab initio electronic structure calculations nicely corroborate the
thermodynamic results and suggest the presence of additional in and
out-of-plane further neighbor antiferromagnetic couplings, though significantly
weaker in comparison to the dominant first-nearest neighbor ferromagnetic
coupling. The spin-lattice relaxation rate measured with fields larger than the
saturation field shows a magnetic field induced gap ($\Delta \propto B$) in the
excitation spectrum, and in $B \rightarrow 0$ limit the gap has a finite
intercept ~ 3 K, equivalent to the mean-field scale. We interpret the origin of
this gap is associated with the magnetic interactions inherent to the material.
With our experimental results, we establish the stabilization of a
ferromagnetic like ground state and the persistence of magnetic-correlations
above the ordering temperature in LCPO.",2312.01731v1
2023-12-31,Magnetic properties at various fillings of the quasiflat band in a fermionic two-leg ladder model,"A recent study has demonstrated that a fermionic two-leg ladder model,
threaded by a flux and characterized by a spatially varying interleg hopping
term, gives rise to a quasiflat low-energy band. This band exhibits an unusual
ground state at half filling in the presence of interaction -- a ferromagnetic
Mott insulator. In this paper, we extend the study of this model to other
fillings of the quasiflat band and explore the magnetic properties of the
ground state at these fillings. In particular, we study four fillings:
one-quarter, three-quarters, slightly above half filling (half filling plus two
electrons), and slightly below half-filling (half filling minus two electrons).
Incorporating interaction within the Hubbard model and using the Density Matrix
Renormalization Group method to find the ground states, we find that the
spin-spin correlation is ferromagnetic at fillings less than half, similar to
that observed at half filling, but is antiferromagnetic beyond half filling.
Interestingly, these results hold only when mixing between the lowest quasiflat
band and the next-to-lowest dispersive band is negligible; once mixing between
the two bands is facilitated by increasing the interaction strength, the
correlation becomes ferromagnetic above half filling as well. Additionally, by
reducing the strength of the interaction in comparison to the bandwidth, a
transition from the ferromagnetic to the antiferromagnetic state is observed in
all the cases.",2401.00483v1
2024-01-24,Two-dimensional ferromagnetic semiconductor Cr2XP: First-principles calculations and Monte Carlo simulations,"According to the Mermin Wagner theorem, two-dimensional material is difficult
to have the Curie temperature above room temperature. By using the method of
band engineering, we design a promising two-dimensional ferromagnetic
semiconductor Cr2XP (X=P, As, Sb) with large magnetization, high Curie
temperature and sizable band gap. The formation of gap is discussed in terms of
the hybridizations, occupation and distribution of electronic states and charge
transfer. Large magnetic moments about 6.16~6.37uB origin from the occupation
of Cr-d electrons in crystal field.Competition and cooperation between d-d
(Cr-d~Cr-d) and d-p-d (Cr-d~X-p~Cr-d) exchange interactions lead to the
emergence of ferromagnetic ordering phase. Furthermore, Curie temperatures,
approaching to 269 K, 332 K and 400 K for Cr2P2, Cr2AsP and Cr2SbP, are
estimated by employing Monte Carlo simulation based on the Heisenberg model.
Magnetic anisotropy energy of Cr2XP is determined by calculating the total
energy dependence on the angle along different directions, and the origin is
also discussed by the second-order perturbation theory. In addition, the Cr2XP
possesses excellent thermodynamical, dynamical and mechanical stabilities, and
can overcome their own gravity to keep their planar structure without the
support of substrate. These above-mentioned advantages will offer some valuable
hints for two-dimensional ferromagnetic semiconductor Cr2XP in spintronic
devices.",2401.13425v1
2024-01-25,A promising candidate for ising ferromagnetism of two-dimensional kagome V$_2$O$_3$ honeycomb monolayer,"Due to the low dimensionality in the quantization of the electronic states
and degree of freedom for device modulation, two-dimensional (2D)
ferromagnetism plays a critical role in lots of fields. In this study, we
perform first-principles calculation to investigate the ising ferromagnetism
and half-metallicity of kagome V$_2$O$_3$ monolayer. Based on the calculations
using different functional, it is found that GGA-PBE gives a half-metallic band
gap while the GGA+U gives a semiconductor narrow band gap (~1.1 meV), which
shows quasi-half metallic nature. By studying the magnetic properties with LDA,
GGA-PBE, and GGA+U, we get a robust ferromagnetic ground state, where the giant
perpendicular magnetic anisotropy energy of ~0.544 meV is achieved by applying
the spin-orbit coupling (SOC) with GGA+U. Furthermore, by exploring the orbital
contribution to the electronic bands and the magnetic crystalline anisotropy,
it is uncovered that the 3d (V) orbitals contribute to the out-of-plane. The
electronic band structure shows two flat bands (F1 and F2) and Dirac points (D1
and D2) which further confirm that kagome V$_2$O$_3$ ML can also be used for
topological properties. Besides, the Curie temperature of the V$_2$O$_3$ ML is
calculated to be 640 K by Metropolis Monte Carlo (MC) simulations.",2401.14035v1
2024-02-06,"Ab initio calculation of the effective Coulomb interactions in MX2 (M=Ti, V, Cr, Mn, Fe, Co, Ni; X=S, Se, Te): intrinsic magnetic ordering and Mott insulating phase","Correlated phenomena such as magnetism and Mott phase are a very
controversial issue in two-dimensional transition metal dichalcogenides
(TMDCs). With the aim of finding the value of correlation strength and
understanding the origin of ferromagnetic order in TMDCs, we first identify
relevant low-energy degrees of freedom on both octahedral T and trigonal
prismatic H lattices in MX2 (M=Ti, V, Cr, Mn, Fe, Co, Ni; X=S, Se, Te) and then
determine the strength of the effective Coulomb interactions between localized
d electrons from the first principles using the constrained random-phase
approximation. The on-site Coulomb interaction (Hubbard U) values lie in the
range 1.4-3.7 eV (1.1-3.6 eV) and depend on the ground-state electronic
structure, d-electron number, and correlated subspace. For most of the TMDCs we
obtain 1 < U/W_b < 2 (the bandwidth W_b), which turn out to be larger than the
corresponding values in elementary transition metals. On the basis of the
calculated U and exchange J interaction, we have checked the condition to be
fulfilled for the formation of the ferromagnetic order by Stoner criterion. The
results indicate that experimentally observed MnX2 (X=S, Se) and VX2 (X=S, Se)
have an intrinsic ferromagnetic behavior in pristine form, although V-based
materials are close vicinity to the critical point separating ferromagnetic
from paramagnetic phase.",2402.04199v1
2024-02-10,Space-time shape optimization of rotating electric machines,"This article is devoted to the shape optimization of the internal structure
of an electric motor, and more precisely of the arrangement of air and
ferromagnetic material inside the rotor part with the aim to increase the
torque of the machine. The governing physical problem is the time-dependent,
non linear magneto-quasi-static version of Maxwell's equations. This multiphase
problem can be reformulated on a 2d section of the real cylindrical 3d
configuration; however, due to the rotation of the machine, the geometry of the
various material phases at play (the ferromagnetic material, the permanent
magnets, air, etc.) undergoes a prescribed motion over the considered time
period. This original setting raises a number of issues. From the theoretical
viewpoint, we prove the well-posedness of this unusual non linear evolution
problem featuring a moving geometry. We then calculate the shape derivative of
a performance criterion depending on the shape of the ferromagnetic phase via
the corresponding magneto-quasi-static potential. Our numerical framework to
address this problem is based on a shape gradient algorithm. The non linear
time periodic evolution problems for the magneto-quasi-static potential is
solved in the time domain, with a Newton-Raphson method. The discretization
features a space-time finite element method, applied on a precise, meshed
representation of the space-time region of interest, which encloses a
body-fitted representation of the various material phases of the motor at all
the considered stages of the time period. After appraising the efficiency of
our numerical framework on an academic problem, we present a quite realistic
example of optimal design of the ferromagnetic phase of the rotor of an
electric machine.",2402.07017v1
2024-02-22,Unexpected versatile electrical transport behaviors of ferromagnetic nickel films,"Perpendicular magnetic anisotropy (PMA) of magnets is paramount for
electrically controlled spintronics due to their intrinsic potentials for
higher memory density, scalability, thermal stability and endurance, surpassing
an in-plane magnetic anisotropy (IMA). Nickel film is a long-lived fundamental
element ferromagnet, yet its electrical transport behavior associated with
magnetism has not been comprehensively studied, hindering corresponding
spintronic applications exploiting nickel-based compounds. Here, we
systematically investigate the highly versatile magnetism and corresponding
transport behavior of nickel films. As the thickness reduces within the general
thickness regime of a magnet layer for a memory device, the hardness of nickel
films' ferromagnetic loop of anomalous Hall effect increases and then
decreases, reflecting the magnetic transitions from IMA to PMA and back to IMA.
Additionally, the square ferromagnetic loop changes from a hard to a soft one
at rising temperatures, indicating a shift from PMA to IMA. Furthermore, we
observe a butterfly magnetoresistance resulting from the anisotropic
magnetoresistance effect, which evolves in conjunction with the thickness and
temperature-dependent magnetic transformations as a complementary support. Our
findings unveil the rich magnetic dynamics and most importantly settle down the
most useful guiding information for current-driven spintronic applications
based on nickel film: The hysteresis loop is squarest for the ~8 nm-thick
nickel film, of highest hardness with Rxyr/Rxys~1 and minimum Hs-Hc, up to 125
K; otherwise, extra care should be taken for a different thickness or at a
higher temperature.",2402.14275v1
2024-02-22,On the origin of the above-room-temperature magnetism in the 2D van der Waals ferromagnet Fe$_3$GaTe$_2$,"Recent advancements in 2D magnetic materials have attracted a growing
interest driven by their unique properties and potential applications in
spintronic devices. However, the scarcity of systems that exhibit magnetism at
room-temperature has limited their practical implementation into functional
devices. In this work we focus on the recently synthetised van der Waals (vdW)
ferromagnet Fe$_3$GaTe$_2$, which exhibits above-room-temperature magnetism
(T$_{\mathrm{c}}$ = 350-380 K) and strong perpendicular magnetic anisotropy.
Through first-principles calculations, we examine the magnetic properties of
Fe$_3$GaTe$_2$ and compare them with the widely known Fe$_3$GeTe$_2$
ferromagnet. Our calculations unveil the complex microscopic mechanisms
governing their magnetic behaviour, emphasizing the pivotal role of the
ferromagnetic in-plane exchange interactions in the stabilization of the
elevated T$_{\mathrm{c}}$ in Fe$_3$GaTe$_2$. Additionally, we predict the
stability, strong perpendicular anisotropy and high T$_{\mathrm{c}}$ of
single-layer Fe$_3$GaTe$_2$. We also demonstrate the potential of strain
engineering and electrostatic doping to modulate its magnetic exchange
interactions and anisotropy. Our results incentivise the isolation of the
monolayer and pave the way for the future optimization of Fe$_3$GaTe$_2$ in
magnetic and spintronic nanodevices.",2402.14618v1
2024-03-06,"Crystal, ferromagnetism, and magnetoresistance with sign reversal in a EuAgP semiconductor","We synthesized the ferromagnetic EuAgP semiconductor and conducted a
comprehensive study of its crystalline, magnetic, heat capacity, band gap, and
magnetoresistance properties. Our investigation utilized a combination of X-ray
diffraction, optical, and PPMS DynaCool measurements. EuAgP adopts a hexagonal
structure with the $P6_3/mmc$ space group. As the temperature decreases, it
undergoes a magnetic phase transition from high-temperature paramagnetism to
low-temperature ferromagnetism. We determined the ferromagnetic transition
temperature to be $T_{\textrm{C}} =$ 16.45(1) K by fitting the measured
magnetic susceptibility using a Curie-Weiss law. Heat capacity analysis of
EuAgP considered contributions from electrons, phonons, and magnons, revealing
$\eta$ = 0.03 J/mol/$\textrm{K}^\textrm{2}$, indicative of semiconducting
behavior. Additionally, we calculated a band gap of $\sim$ 1.324(4) eV based on
absorption spectrum measurements. The resistivity versus temperature of EuAgP
measured in the absence of an applied magnetic field shows a pronounced peak
around $T_{\textrm{C}}$, which diminishes rapidly with increasing applied
magnetic fields, ranging from 1 to 14 T. An intriguing phenomenon emerges in
the form of a distinct magnetoresistance transition, shifting from positive
(e.g., 1.95\% at 300 K and 14 T) to negative (e.g., -30.73\% at 14.25 K and 14
T) as the temperature decreases. This behavior could be attributed to
spin-disordered scattering.",2403.03650v1
2024-03-21,Spin injection and detection in a Si-based ferromagnetic tunnel junction: A theoretical model based on the band diagram and experimental demonstration,"We have experimentally and theoretically investigated the spin
injection/detection polarization in a Si-based ferromagnetic tunnel junction
with an amorphous MgO layer, and demonstrated that the experimental features of
the spin polarization in a wide bias range can be well explained using our
theoretical model based on the band diagram of the junction and the direct
tunneling mechanism. It is shown that the spin polarization originates from the
band diagrams of the ferromagnetic Fe layer and n+-Si channel in the junction,
while the spin selectivity of the MgO tunnel barrier is not necessary. Besides,
we clarified the mechanism of the reduction in spin polarization when the bias
is high and nonlinear properties are prominent, where the widely-used spin
injection/detection model proposed by Valet and Fert is not applicable. The
dominant mechanism of such reduction is found to be spin accumulation
saturation (SAS) at the n+-Si interface in contact with the MgO layer as the
bias is increased in the spin extraction geometry, which is inevitable in
semiconductor-based ferromagnetic tunnel junctions. We performed numerical
calculations on a two-terminal spin transport device with a n+-Si channel using
the junction properties extracted from the experiments, and revealed that the
magnetoresistance (MR) ratio is suppressed mainly by SAS in a higher bias
range. Furthermore, we proposed methods for improving the MR ratio in
two-terminal spin transport devices. Our experiments and theoretical model
provide a deep understanding of the spin injection/detection phenomena in
semiconductor-based spin transport devices, toward the realization of high
performance under reasonably high bias conditions for practical use.",2403.14127v1
2001-06-14,Partial Averaging and Resonance Trapping in a Restricted Three-Body System,"Based on the value of the orbital eccentricity of a particle and also its
proximity to the exact resonant orbit in a three-body system, the Pendulum
Approximation (Dermott & Murray 1983) or the Second Fundamental Model of
Resonance (Andoyer 1903; Henrard & Lemaitre 1983) are commonly used to study
the motion of that particle near its resonance state. In this paper, we present
the method of partial averaging as an analytical approach to study the
dynamical evolution of a body near a resonance. To focus attention on the
capabilities of this technique, a restricted, circular and planar three-body
system is considered and the dynamics of its outer planet while captured in a
resonance with the inner body is studied. It is shown that the first-order
partially averaged system resembles a mathematical pendulum whose librational
motion can be viewed as a geometrical interpretation of the resonance capture
phenomenon. The driving force of this pendulum corresponds to the gravitational
attraction of the inner body and its contribution, at different resonant
states, is shown to be proportional to e^s, where s is the order of the
resonance and e is the orbital eccentricity of the outer planet. As examples of
such systems, the cases of (1:1), (1:2) and (1:3) resonances are discussed and
the results are compared with known planetary systems such as the
Sun-Jupiter-Trojan asteroids.",0106264v1
2005-03-31,The role of resonances in barred galaxies,"The dynamics of the inner disk of many galaxies is dominated by bars. As a
result, resonances between the bar and the disk become an important factor. In
order to detect resonances, we measure angular and radial frequencies of
individual orbits in N-body models of barred galaxies. In our simulations with
several million particles, stellar disks are immersed in live halos of dark
matter. A bar forms spontaneously and interacts with the disk through
resonances. We detect 9 of them. The corotation (CR) and the inner Lindblad
resonance (ILR) are the most significant. The spatial distributions of
particles trapped at these resonances show that ILR is not localized at a given
radius. Particles trapped at ILR lie along the bar spanning a wide range of
radii. On the other hand, particles at the corotation resonance form a ring
around the corotation radius. We study how orbits evolve near corotation and
how they are trapped. When an orbit is getting trapped, it evolves strongly,
but after that there is little evolution. Those trapped orbits circulate along
the corotation ring or librate around a stable lagragian point. The same
technique is applied to study resonances in the halo. The bar interacts
strongly with the halo particles that stay close to the disk. We find the
corotation resonance and the inner Lindblad resonance for halo particles.",0503710v2
1999-12-07,Quantum Resonances and Regularity Islands in Quantum Maps,"We study analytically as well as numerically the dynamics of a quantum map
near a quantum resonance of an order q. The map is embedded into a continuous
unitary transformation generated by a time-independent quasi-Hamiltonian. Such
a Hamiltonian generates at the very point of the resonance a local gauge
transformation described the unitary unimodular group SU(q). The resonant
energy growth of is attributed to the zero Liouville eigenmodes of the
generator in the adjoint representation of the group while the non-zero modes
yield saturating with time contribution. In a vicinity of a given resonance,
the quasi-Hamiltonian is then found in the form of power expansion with respect
to the detuning from the resonance. The problem is related in this way to the
motion along a circle in a (q^2-1)-component inhomogeneous ""magnetic"" field of
a quantum particle with $q$ intrinsic degrees of freedom described by the SU(q)
group. This motion is in parallel with the classical phase oscillations near a
non-linear resonance. The most important role is played by the resonances with
the orders much smaller than the typical localization length, q << l. Such
resonances master for exponentially long though finite times the motion in some
domains around them. Explicit analytical solution is possible for a few lowest
and strongest resonances.",9912009v1
2005-10-10,Quantum master equation descriptions of a nanomechanical resonator coupled to a single-electron transistor,"We analyse the quantum dynamics of a nanomechanical resonator coupled to a
normal-state single-electron transistor (SET). Starting from a microscopic
description of the system, we derive a master equation for the SET island
charge and resonator which is valid in the limit of weak electro-mechanical
coupling. Using this master equation we show that, apart from brief transients,
the resonator always behaves like a damped harmonic oscillator with a shifted
frequency and relaxes into a thermal-like steady state. Although the behaviour
remains qualitatively the same, we find that the magnitude of the resonator
damping rate and frequency shift depend very sensitively on the relative
magnitudes of the resonator period and the electron tunnelling time. Maximum
damping occurs when the electrical and mechanical time-scales are the same, but
the frequency shift is greatest when the resonator moves much more slowly than
the island charge. We then derive reduced master equations which describe just
the resonator dynamics. By making slightly different approximations, we obtain
two different reduced master equations for the resonator. Apart from minor
differences, the two reduced master equations give rise to a consistent picture
of the resonator dynamics which matches that obtained from the master equation
including the SET island charge.",0510236v1
2006-07-25,Adiabatic theorems for quantum resonances,"We study the adiabatic time evolution of quantum resonances over time scales
which are small compared to the lifetime of the resonances. We consider three
typical examples of resonances: The first one is that of shape resonances
corresponding, for example, to the state of a quantum-mechanical particle in a
potential well whose shape changes over time scales small compared to the
escape time of the particle from the well. Our approach to studying the
adiabatic evolution of shape resonances is based on a precise form of the
time-energy uncertainty relation and the usual adiabatic theorem in quantum
mechanics. The second example concerns resonances that appear as isolated
complex eigenvalues of spectrally deformed Hamiltonians, such as those
encountered in the N-body Stark effect. Our approach to study such resonances
is based on the Balslev-Combes theory of dilatation-analytic Hamiltonians and
an adiabatic theorem for nonnormal generators of time evolution. Our third
example concerns resonances arising from eigenvalues embedded in the continuous
spectrum when a perturbation is turned on, such as those encountered when a
small system is coupled to an infinitely extended, dispersive medium. Our
approach to this class of examples is based on an extension of adiabatic
theorems without a spectral gap condition. We finally comment on resonance
crossings, which can be studied using the last approach.",0607054v2
2007-08-20,Three-State Feshbach Resonances Mediated By Second-Order Couplings,"We present an analytical study of three-state Feshbach resonances induced by
second-order couplings. Such resonances arise when the scattering amplitude is
modified by the interaction with a bound state that is not directly coupled to
the scattering state containing incoming flux. Coupling occurs indirectly
through an intermediate state. We consider two problems: (i) the intermediate
state is a scattering state in a distinct open channel; (ii) the intermediate
state is an off-resonant bound state in a distinct closed channel. The first
problem is a model of electric-field-induced resonances in ultracold collisions
of alkali metal atoms [Phys. Rev. A 75, 032709 (2007)] and the second problem
is relevant for ultracold collisions of complex polyatomic molecules, chemical
reaction dynamics, photoassociation of ultracold atoms, and electron - molecule
scattering. Our analysis yields general expressions for the energy dependence
of the T-matrix elements modified by three-state resonances and the dependence
of the resonance positions and widths on coupling amplitudes for the
weak-coupling limit. We show that the second problem can be generalized to
describe resonances induced by indirect coupling through an arbitrary number of
sequentially coupled off-resonant bound states and analyze the dependence of
the resonance width on the number of the intermediate states.",0708.2638v2
2008-05-12,Turbulence in Extrasolar Planetary Systems Implies that Mean Motion Resonances are Rare,"This paper considers the effects of turbulence on mean motion resonances in
extrasolar planetary systems and predicts that systems rarely survive in a
resonant configuration. A growing number of systems are reported to be in
resonance, which is thought to arise from the planet migration process. If
planets are brought together and moved inward through torques produced by
circumstellar disks, then disk turbulence can act to prevent planets from
staying in a resonant configuration. This paper studies this process through
numerical simulations and via analytic model equations, where both approaches
include stochastic forcing terms due to turbulence. We explore how the
amplitude and forcing time intervals of the turbulence affect the maintenance
of mean motion resonances. If turbulence is common in circumstellar disks
during the epoch of planet migration, with the amplitudes indicated by current
MHD simulations, then planetary systems that remain deep in mean motion
resonance are predicted to be rare. More specifically, the fraction of resonant
systems that survive over a typical disk lifetime of 1 Myr is of order 0.01. If
mean motion resonances are found to be common, their existence would place
tight constraints on the amplitude and duty cycle of turbulent fluctuations in
circumstellar disks. These results can be combined by expressing the expected
fraction of surviving resonant systems in the approximate form P_b = C /
N_{orb}^{1/2}, where the dimensionless parameter C = 10 - 50 and where N_{orb}
is the number of orbits for which turbulence is active.",0805.1681v1
2008-06-03,Quark models of dibaryon resonances in nucleon-nucleon scattering,"We look for $\Delta\Delta$ and $N\Delta$ resonances by calculating $NN$
scattering phase shifts of two interacting baryon clusters of quarks with
explicit coupling to these dibaryon channels. Two phenomenological
nonrelativistic chiral quark models giving similar low-energy $NN$ properties
are found to give significantly different dibaryon resonance structures. In the
chiral quark model (ChQM), the dibaryon system does not resonate in the $NN$
$S$-waves, in agreement with the experimental SP07 $NN$ partial-wave scattering
amplitudes. In the quark delocalization and color screening model (QDCSM), the
$S$-wave NN resonances disappear when the nucleon size $b$ falls below 0.53 fm.
Both quark models give an $IJ^P = 03^+$ $\Delta\Delta$ resonance. At $b=0.52
$fm, the value favored by baryon spectrum, the resonance mass is 2390 (2420)
MeV for the ChQM with quadratic (linear) confinement, and 2360 MeV for the
QDCSM. Accessible from the $^3D_3^{NN}$ channel, this resonance is a promising
candidate for the known isoscalar ABC structure seen more clearly in the
$pn$$\to $$d\pi\pi$ production cross section at 2410 MeV in the recent
preliminary data reported by the CELSIUS-WASA Collaboration. In the isovector
dibaryon sector, our quark models give a bound or almost bound
$^5S_2^{\Delta\Delta}$ state that can give rise to a $^1D_2^{NN}$ resonance.
None of the quark models used has bound $N\Delta$ $P$-states that might
generate odd-parity resonances.",0806.0458v2
2010-11-22,Hamiltonian model of capture into mean motion resonance,"Mean motion resonances are a common feature of both our own Solar System and
of extrasolar planetary systems. Bodies can be trapped in resonance when their
orbital semi-major axes change, for instance when they migrate through a
protoplanetary disc. We use a Hamiltonian model to thoroughly investigate the
capture behaviour for first and second order resonances. Using this method, all
resonances of the same order can be described by one equation, with
applications to specific resonances by appropriate scaling. We focus on the
limit where one body is a massless test particle and the other a massive
planet. We quantify how the the probability of capture into a resonance depends
on the relative migration rate of the planet and particle, and the particle's
eccentricity. Resonant capture fails for high migration rates, and has
decreasing probability for higher eccentricities, although for certain
migration rates, capture probability peaks at a finite eccentricity. We also
calculate libration amplitudes and the offset of the libration centres for
captured particles, and the change in eccentricity if capture does not occur.
Libration amplitudes are higher for larger initial eccentricity. The model
allows for a complete description of a particle's behaviour as it successively
encounters several resonances. The model is applicable to many scenarios,
including (i) Planet migration through gas discs trapping other planets or
planetesimals in resonances; (ii) Planet migration through a debris disc; (iii)
Dust migration through PR drag. Full details can be found in
\cite{2010submitted}. (Abridged)",1011.4804v1
2011-01-12,Scattering by coupled resonating elements in air,"Scattering by (a) a single composite scatterer consisting of a concentric
arrangement of an outer N-slit rigid cylinder and an inner cylinder which is
either rigid or in the form of a thin elastic shell and (b) by a finite
periodic array of these scatterers in air has been investigated analytically
and through laboratory experiments. The composite scatterer forms a system of
coupled resonators and gives rise to multiple low frequency resonances. The
corresponding analytical model employs polar angle dependent boundary
conditions on the surface of the N-slit cylinder. The solution inside the slits
assumes plane waves. It is shown also that in the low-frequency range the
N-slit rigid cylinder can be replaced by an equivalent fluid layer. Further
approximations suggest a simple square root dependence of the resonant
frequencies on the number of slits and this is confirmed by data. The observed
resonant phenomena are associated with Helmholtz-like behaviour of the
resonator for which the radius and width of the openings are much smaller than
the wavelength. The problem of scattering by a finite periodic array of such
coupled resonators in air is solved using multiple scattering techniques. The
resulting model predicts band-gap effects resulting from the resonances of the
individual composite scatterers below the first Bragg frequency . Predictions
and data confirm that use of coupled resonators results in substantial
insertion loss peaks related to the resonances within the concentric
configuration. In addition, for both scattering problems experimental data,
predictions of the analytical approach and predictions of the equivalent fluid
layer approximations are compared in the low-frequency interval.",1101.2332v1
2012-09-21,Influence of external magnetic and laser radiation fields on Feshbach resonances in collision of atoms,"We study collision of two atoms with formation of Feshbach resonance at
combined interaction with the external magnetic field and laser radiation. In
cases of one- and two-photon resonances of laser radiation with two discrete
vibrational molecular levels, we show that Feshbach resonances appear at
interaction of external magnetic field with dressed states formed via
Autler-Townes effect. In addition, in case of one-photon resonance the lower
vibrational molecular state is coupled by laser radiation with the continuum of
the elastic channel and forms laser-induced Feshbach resonance via both
Autler-Townes effect and LICS mechanism. We study the combined process of
formation of Feshbach resonances; this enables the control of Feshbach
resonance by varying the magnetic field and intensity and frequency of laser
radiation. We obtain the cross-sections of elastic and inelastic scattering and
show that quenching of resonance occurs at the energy equal to that of the
systems ground state. Dependence of the cross-sections on the magnetic field
and laser intensity is examined in detail. In all considered cases, the
scattering length is obtained depending on the magnetic and laser fields are
studied. In the absence of magnetic interaction if the hyperfine substates of
the quasibound state in the closed channel and those of individual colliding
atoms in the open channel are the same, Feshbach resonances may arise via weak
interaction between nuclear and electronic motions, which leads to transitions
between electronic states. The obtained results can be employed in new studies
of collisions of cold atoms, e.g., of alkali metal atoms and for interpretation
of new experiments in BECs.",1209.4725v1
2012-12-12,Shape resonances in multi-condensate granular superconductors formed by networks of nanoscale-striped puddles,"A characteristic feature of a superconductor made of multiple condensates is
the possibility of the shape resonances in superconducting gaps. Shape
resonances belong to class of Fano resonances in configuration interaction
between open and closed scattering channels. The Shape resonances arise because
of the exchange interaction, a Josephson-like term, for transfer of pairs
between different condensates in different Fermi surface spots in the special
cases where at least one Fermi surface is near a 2.5 Lifshitz topological
transition. We show that tuning the shape resonances show first, the gap
suppression (like a Fano anti-resonance) driven by configuration interaction
between a BCS condensate and a BEC-like condensate, and second, the gap
amplification (like a Fano resonance) driven by configuration interaction
between BCS condensates in large and small Fermi surfaces. Shape resonances
usually occur in granular nanoscale complex matter (called superstripes)
because of the lattice instability near a 2.5 Lifshitz transition in presence
of interactions. Using a new imaging method, scanning nano-X-ray diffraction,
we have shown the generic formation in high temperature superconductors of a
granular superconducting networks made of striped puddles formed by ordered
oxygen interstitials or ordered local lattice distortions (like static short
range charge density waves). In the superconducting puddles the chemical
potential is tuned to a shape resonance in superconducting gaps and the maximum
Tc occurs where the puddles form scale free superconducting networks.",1212.2733v1
2012-12-21,Percolation transition in the kinematics of nonlinear resonance broadening in Charney-Hasegawa-Mima model of Rossby wave turbulence,"We study the kinematics of nonlinear resonance broadening of interacting
Rossby waves as modelled by the Charney-Hasegawa-Mima equation on a biperiodic
domain. We focus on the set of wave modes which can interact quasi-resonantly
at a particular level of resonance broadening and aim to characterise how the
structure of this set changes as the level of resonance broadening is varied.
The commonly held view that resonance broadening can be thought of as a
thickening of the resonant manifold is misleading. We show that in fact the set
of modes corresponding to a single quasi-resonant triad has a nontrivial
structure and that its area in fact diverges for a finite degree of broadening.
We also study the connectivity of the network of modes which is generated when
quasi-resonant triads share common modes. This network has been argued to form
the backbone for energy transfer in Rossby wave turbulence. We show that this
network undergoes a percolation transition when the level of resonance
broadening exceeds a critical value. Below this critical value, the largest
connected component of the quasi-resonant network contains a negligible
fraction of the total number of modes in the system whereas above this critical
value a finite fraction of the total number of modes in the system are
contained in the largest connected component. We argue that this percolation
transition should correspond to the transition to turbulence in the system.",1212.5336v1
2013-03-12,Resonant Behavior of Comet Halley and the Orionid Stream,"Comet 1P/Halley has the unique distinction of having a very comprehensive set
of observational records for almost every perihelion passage from 240 B.C. This
has helped to constrain theoretical models pertaining to its orbital evolution.
Many previous works have shown the active role of mean motion resonances in the
evolution of various meteoroid streams. Here we look at how various resonances,
especially the 1:6 and 2:13 mean motion resonances with Jupiter, affect comet
1P/Halley and thereby enhance the chances of meteoroid particles getting
trapped in resonance, leading to meteor outbursts in some particular years.
Comet Halley itself librated in the 2:13 resonance from 240 B.C. to 1700 A.D.
and in the 1:6 resonance from 1404 B.C. to 690 B.C., while stream particles can
survive for timescales of the order of 10,000 years and 1,000 years in the 1:6
and 2:13 resonances respectively. This determines the long term dynamical
evolution and stream structure, influencing the occurrence of Orionid
outbursts. Specifically we are able to correlate the occurrence of enhanced
meteor phenomena seen between 1436-1440, 1933-1938 & 2006-2010 with the 1:6
resonance and meteor outbursts in 1916 & 1993 with the 2:13 resonance. Ancient
as well as modern observational records agree with these theoretical
simulations to a very good degree.",1303.2928v2
2013-04-19,Periodicity of resonant tunneling current induced by the Stark resonances in semiconductor nanowire,"The modification of the electronic current resulting from Stark resonances
has been studied for the semiconductor nanowire with the double-barrier
structure. Based on the calculated current-voltage characteristics we have
shown that the resonant tunneling current is a periodic function of the width
of the spacer layer. We have also demonstrated that the simultaneous change of
the source-drain voltage and the voltage applied to the gate located near the
nanowire leads to almost periodic changes of the resonant tunneling current as
a function of the source-drain and gate voltages. The periodic properties of
the resonant tunneling current result from the formation of the Stark resonance
states. If we change the electric field acting in the nanowire, the Stark
states periodically acquire the energies from the transport window and enhance
the tunneling current in a periodic manner. We have found that the separations
between the resonant current peaks on the source-drain voltage scale can be
described by a slowly increasing linear function of the Stark state quantum
number. This allows us to identify the quantum states that are responsible for
the enhancement of the resonant tunneling. We have proposed a method of the
experimental observation of the Stark resonances in semiconductor
double-barrier heterostructures.",1304.5393v2
2013-05-28,Dynamical analysis of the Gliese-876 Laplace resonance,"The existence of multiple planetary systems involved in mean motion
conmensurabilities has increased significantly since the Kepler mission.
Although most correspond to 2-planet resonances, multiple resonances have also
been found. The Laplace resonance is a particular case of a three-body
resonance where the period ratio between consecutive pairs is n_1/n_2 near to
n_2/n_3 near to 2/1. It is not clear how this triple resonance can act in order
to stabilize (or not) the systems.
  The most reliable extrasolar system located in a Laplace resonance is GJ876
because it has two independent confirmations. However best-fit parameters were
obtained without previous knowledge of resonance structure and no exploration
of all the possible stable solutions for the system where done.
  In the present work we explored the different configurations allowed by the
Laplace resonance in the GJ876 system by varying the planetary parameters of
the third outer planet. We find that in this case the Laplace resonance is a
stabilization mechanism in itself, defined by a tiny island of regular motion
surrounded by (unstable) highly chaotic orbits. Low eccentric orbits and mutual
inclinations from -20 to 20 degrees are compatible with the observations. A
definite range of mass ratio must be assumed to maintain orbital stability.
Finally we give constrains for argument of pericenters and mean anomalies in
order to assure stability for this kind of systems.",1305.6768v1
2014-07-31,Effect of pairing fluctuations on the spin resonance in Fe-based superconductors,"The spin resonance observed in the inelastic neutron scattering data on
Fe-based superconductors has played a prominent role in the quest for
determining the symmetry of the order parameter in these compounds. Most
theoretical studies of the resonance employ an RPA-type approach in the
particle-hole channel and associate the resonance in the spin susceptibility
$\chi_S (\mathbf{q}, \omega)$ at momentum ${\bf Q} = (\pi,\pi)$ with the
spin-exciton of an $s^{+-}$ superconductor, pulled below $2\Delta$ by residual
attraction associated with the sign change of the gap between Fermi points
connected by ${\bf Q}$. Here we explore the effect of fluctuations in the
particle-particle channel on the spin resonance. Particle-particle and
particle-hole channels are coupled in a superconductor and to what extent the
spin resonance can be viewed as a particle-hole exciton needs to be addressed.
In the case of purely repulsive interactions we find that the particle-particle
channel at total momentum ${\bf Q}$ (the $\pi $channel) contributes little to
the resonance. However, if the interband density-density interaction is
attractive and the $\pi-$resonance is possible on its own, along with the
spin-exciton, we find a much stronger shift of the resonance frequency from the
position of the would-be spin-exciton resonance. We also show that the expected
double-peak structure in this situation does not appear because of the strong
coupling between particle-hole and particle-particle channels, and $\mathrm{Im}
\chi_S ({\bf Q}, \omega)$ displays only a single peak.",1408.0021v1
2014-11-14,Broadband resonances in ITO nanorod arrays,"In the nanophotonics community, there is an active discussion regarding the
origin of the selective absorption/scattering of light by the resonances with
nanorod arrays. Here we report a study of the resonances in ordered
indium-tin-oxide (ITO) nanorod arrays resulted from the waveguide modes. We
discover that with only 2.4% geometrical coverage, the micron-length nanorod
arrays strongly interact with light across an extra-wide band from visible to
mid-infrared resulting in less than 10% transmission. Simulations show
excellent agreement with our experimental observation. Near-field profile
obtained from simulation reveals the electric field is mainly localized on the
surfaces of the nanorods at all the resonances. Theoretical analysis is then
applied to explain the resonances and it was found that the resonances in the
visible are different from those in the infrared. When the light arrives at the
array, part of the light wave propagates through the free space in between the
nanorods and part of the wave is guided inside the nanorods and the phase
difference at the ends of the rod interactions forms the basis of the
resonances in the visible region; while the resonances in the infrared are
Fabry-Perot resonances of the surface guided waves between the two ends of the
nanorods. The simple analytical formulae developed predict the spectral
positions of these resonances well. This information can be used to design
devices like wavelength-selective photodetector, modulators, and nanorod-based
solar cells.",1411.3767v2
2015-01-14,Long-lived Chaotic Orbital Evolution of Exoplanets in Mean Motion Resonances with Mutual Inclinations,"We present N-body simulations of resonant planets with inclined orbits that
show chaotically evolving eccentricities and inclinations that can persist for
at least 10 Gyr. A wide range of behavior is possible, from fast, low amplitude
variations to systems in which eccentricities reach 0.9999 and inclinations
179.9 degrees. While the orbital elements evolve chaotically, at least one
resonant argument always librates. We show that the HD 73526, HD 45364 and HD
60532 systems may be in chaotically-evolving resonances. Chaotic evolution is
apparent in the 2:1, 3:1 and 3:2 resonances, and for planetary masses from
lunar- to Jupiter-mass. In some cases, orbital disruption occurs after several
Gyr, implying the mechanism is not rigorously stable, just long-lived relative
to the main sequence lifetimes of solar-type stars. Planet-planet scattering
appears to yield planets in inclined resonances that evolve chaotically in
about 0.5% of cases. These results suggest that 1) approximate methods for
identifying unstable orbital architectures may have limited applicability, 2)
the observed close-in exoplanets may be produced during the high eccentricity
phases induced by inclined resonances, 3) those exoplanets' orbital planes may
be misaligned with the host star's spin axis, 4) systems with resonances may be
systematically younger than those without, 5) the distribution of period ratios
of adjacent planets detected via transit may be skewed due to inclined
resonances, and 6) potentially habitable planets in resonances may have
dramatically different climatic evolution than the Earth. The GAIA spacecraft
is capable of discovering giant planets in these types of orbits.",1501.03231v1
2015-01-26,A study of the main resonances outside the geostationary ring,"We investigate the dynamics of satellites and space debris in external
resonances, namely in the region outside the geostationary ring. Precisely, we
focus on the 1:2, 1:3, 2:3 resonances, which are located at about 66 931.4 km,
87 705.0 km, 55 250.7 km, respectively. Some of these resonances have been
already exploited in space missions, like XMM-Newton and Integral.
  Our study is mainly based on a Hamiltonian approach, which allows us to get
fast and reliable information on the dynamics in the resonant regions.
Significative results are obtained even by considering just the effect of the
geopotential in the Hamiltonian formulation. For objects (typically space
debris) with high area-to-mass ratio the Hamiltonian includes also the effect
of the solar radiation pressure. In addition, we perform a comparison with the
numerical integration in Cartesian variables, including the geopotential, the
gravitational attraction of Sun and Moon, and the solar radiation pressure.
  We implement some simple mathematical tools that allows us to get information
on the terms which are dominant in the Fourier series expansion of the
Hamiltonian around a given resonance, on the amplitude of the resonant islands
and on the location of the equilibrium points. We also compute the Fast
Lyapunov Indicators, which provide a cartography of the resonant regions,
yielding the main dynamical features associated to the external resonances. We
apply these techniques to analyze the 1:2, 1:3, 2:3 resonances; we consider
also the case of objects with large area-to-mass ratio and we provide an
application to the case studies given by XMM-Newton and Integral.",1501.06273v1
2015-09-03,"Microspherical photonics: Giant resonant light forces, spectrally resolved optical manipulation, and coupled modes of microcavity arrays","In this dissertation novel resonant propulsion of dielectric microspheres is
studied with the goal of sorting spheres with identical resonances, which are
critical for developing microspherical photonics. First, evanescent field
couplers were developed by fixing tapered microfibers in mechanically robust
platforms. The tapers were obtained by chemical etching techniques. Using these
platforms, WGMs modal numbers, coupling regimes and quality factors were
determined for various spheres and compared with theory. Second, the
spectroscopic properties of photonic molecules formed by spheres with better
than 0.05% uniformity of WGM resonances were studied. It was shown that various
spatial configurations of coupled-cavities present relatively stable mode
splitting patterns in the fiber transmission spectra which can be used as
spectral signatures to distinguish such photonic molecules. The third part is
the study of giant resonant propulsion forces exerted on microspheres. This
effect was observed in suspensions of polystyrene spheres with sufficiently
large diameters. By integrating optical tweezers for individual sphere
manipulation, the wavelength detuning between a tunable laser and WGMs in each
of the spheres was precisely controlled. Resonant enhancement of optical forces
was directly demonstrated in experiments. The spectral shape, position and
magnitude of the observed propulsion force peaks were explained by efficient
transfer of light momentum to microspheres under resonant conditions. The peak
magnitude of the resonant force is shown to approach total absorption limit
imposed by the conservation of momentum. The transverse movement of the spheres
during the propulsion process was studied and the existence of a stable radial
trap was demonstrated. Giant resonant propulsion forces can be used for
large-scale sorting of microspheres with ultrahigh uniform resonant properties.",1509.01306v1
2015-09-28,Transit timing variations for planets near eccentricity-type mean motion resonances,"We derive the transit timing variations (TTVs) of two planets near a second
order mean motion resonance on nearly circular orbits. We show that the TTVs of
each planet are given by sinusoids with a frequency of $j n_2-(j-2)n_1$, where
$j \ge 3$ is an integer characterizing the resonance and $n_2$ and $n_1$ are
the mean motions of the outer and inner planets, respectively. The amplitude of
the TTV depends on the mass of the perturbing planet, relative to the mass of
the star, and on both the eccentricities and longitudes of pericenter of each
planet. The TTVs of the two planets are approximated anti-correlated, with
phases of $\phi$ and $\approx \phi+\pi$, where the phase $\phi$ also depends on
the eccentricities and longitudes of pericenter. Therefore, the TTVs caused by
proximity to a second order mean motion resonance do not in general uniquely
determine both planet masses, eccentricities, and pericenters. This is
completely analogous to the case of TTVs induced by two planets near a first
order mean motion resonance. We explore how other TTV signals, such as the
short-period synodic TTV or a first order resonant TTV, in combination with the
second order resonant TTV, can break degeneracies. Lastly, we derive
approximate formulae for the TTVs of planets near any order eccentricity-type
mean motion resonance; this shows that the same basic sinusoidal TTV structure
holds for all eccentricity-type resonances. Our general formula reduces to
previously derived results near first order mean motion resonances.",1509.08460v2
2015-10-19,On the Erigone family and the $z_2$ secular resonance,"The Erigone family is a C-type group in the inner main belt. Its age has been
estimated by several researchers to be less then 300 My, so it is a relatively
young cluster. Yarko-YORP Monte Carlo methods to study the chronology of the
Erigone family confirm results obtained by other groups. The Erigone family,
however, is also characterized by its interaction with the $z_2$ secular
resonance. While less than 15% of its members are currently in librating states
of this resonance, the number of objects, members of the dynamical group, in
resonant states is high enough to allow to use the study of dynamics inside the
$z_2$ resonance to set constraints on the family age.
  Like the ${\nu}_{6}$ and $z_1$ secular resonances, the $z_2$ resonance is
characterized by one stable equilibrium point at $\sigma = 180^{\circ}$ in the
$z_2$ resonance plane $(\sigma, \frac{d\sigma}{dt})$, where $\sigma$ is the
resonant angle of the $z_2$ resonance. Diffusion in this plane occurs on
timescales of $\simeq 12$ My, which sets a lower limit on the Erigone family
age. Finally, the minimum time needed to reach a steady-state population of
$z_2$ librators is about 90 My, which allows to impose another, independent
constraint on the group age.",1510.05551v1
2015-10-27,The influence of the Coulomb exchange term on nuclear single-proton resonances,"Nuclear single-proton resonances are sensitive to the Coulomb field, while
the exchange term of Coulomb field is usually neglected due to its nonlocality.
By combining the complex scaling method with the relativistic mean-field model,
the influence of the Coulomb exchange term on the single-proton resonances is
investigated by taking Sn isotopes and $N=82$ isotones as examples. It is found
that the Coulomb exchange term reduces the single-proton resonance energy
within the range of $0.4-0.6$ MeV, and lead to similar isotopic and isotonic
trends of the resonance energy as those without the Coulomb exchange term.
Moreover, the single-proton resonance width is also reduced by the Coulomb
exchange term, whose influence generally decreases with the increasing neutron
number and increases with the increasing proton number. However, the influence
of the Coulomb exchange term cannot change the trend of the resonance width
with respect to the neutron number and proton number. Furthermore, the
influence of the Coulomb exchange term on the resonance width is investigated
for the doubly magic nuclei $^{40}$Ca, $^{56,78}$Ni, $^{100,132}$Sn, and
$^{208}$Pb. It is found that the Coulomb exchange term reduces the proton
resonance width within $0.2$ MeV, whose magnitude depends on the specific
nucleus and the quantum numbers of resonant states.",1510.07857v1
2015-10-31,Nonlinear microwave photon-occupancy of a driven resonator strongly coupled to a transmon qubit,"We measure photon-occupancy in a thin-film superconducting lumped element
resonator coupled to a transmon qubit at 20$\,$mK and find a nonlinear
dependence on the applied microwave power. The transmon-resonator system was
operated in the strong dispersive regime, where the ac Stark shift ($2\chi$)
due to a single microwave photon present in the resonator was larger than the
linewidth ($\Gamma$) of the qubit transition. When the resonator was coherently
driven at $5.474325\,$GHz, the transition spectrum of the transmon at
$4.982\,$GHz revealed well-resolved peaks, each corresponding to an individual
photon number-state of the resonator. From the relative peak-heights we obtain
the occupancy of the photon-states and the average photon-occupancy $\bar{n}$
of the resonator. We observed a nonlinear variation of $\bar{n}$ with the
applied drive power $P_{rf}$ for $\bar{n} < 5$ and compare our results to
numerical simulations of the system-bath master equation in the steady state,
as well as to a semi-classical model for the resonator that includes the
Jaynes-Cummings interaction between the transmon and the resonator. We find
good quantitative agreement using both models and analysis reveals that the
nonlinear behavior is principally due to shifts in the resonant frequency
caused by a qubit-induced Jaynes-Cummings nonlinearity.",1511.00174v1
2015-11-04,"Compositeness of baryonic resonances: Applications to the Delta(1232), N(1535), and N(1650) resonances","We present a formulation of the compositeness for baryonic resonances in
order to discuss the meson-baryon molecular structure inside the resonances.
For this purpose, we derive a relation between the residue of the scattering
amplitude at the resonance pole position and the two-body wave function of the
resonance in a sophisticated way, and we define the compositeness as the norm
of the two-body wave functions. As applications, we investigate the
compositeness of the $\Delta (1232)$, $N (1535)$, and $N (1650)$ resonances
from precise $\pi N$ scattering amplitudes in a unitarized chiral framework
with the interaction up to the next-to-leading order in chiral perturbation
theory. The $\pi N$ compositeness for the $\Delta (1232)$ resonance is
evaluated in the $\pi N$ single-channel scattering, and we find that the $\pi
N$ component inside $\Delta (1232)$ in the present framework is nonnegligible,
which supports the previous work. On the other hand, the compositeness for the
$N (1535)$ and $N (1650)$ resonances is evaluated in a coupled-channels
approach, resulting that the $\pi N$, $\eta N$, $K \Lambda$ and $K \Sigma$
components are negligible for these resonances.",1511.01200v2
2016-01-30,Strongly-coupled nanotube electromechanical resonators,"Coupling an electromechanical resonator with carbon-nanotube quantum dots is
a significant method to control both the electronic charge and the spin quantum
states. By exploiting a novel micro-transfer technique, we fabricate two
strongly-coupled and electrically-tunable mechanical resonators on a single
carbon nanotube for the first time. The frequency of the two resonators can be
individually tuned by the bottom gates, and strong coupling is observed between
the electron charge and phonon modes of each resonator. Furthermore, the
conductance of either resonator can be nonlocally modulated by the phonon modes
in the other resonator. Strong coupling is observed between the phonon modes of
the two resonators, which provides an effective long distance electron-electron
interaction. The generation of phonon-mediated-spin entanglement is also
theoretically analyzed for the two resonators. This strongly-coupled nanotube
electromechanical resonator array provides an experimental platform for future
studies of the coherent electron-phonon interaction, the phonon mediated
long-distance electron interaction, and entanglement state generation.",1602.00082v1
2016-04-24,Spectral flow and resonance index,"It has been shown recently that spectral flow admits a natural integer-valued
extension to essential spectrum. This extension admits four different
interpretations; two of them are singular spectral shift function and total
resonance index. In this work we study resonance index outside essential
spectrum.
  Among results of this paper are the following.
  1. Total resonance index satisfies Robbin-Salamon axioms for spectral flow.
  2. Direct proof of equality ""total resonance index = intersection number"".
  3. Direct proof of equality ""total resonance index = total Fredholm index"".
  4. (a) Criteria for a perturbation~$V$ to be tangent to the~resonance set at
a point~$H,$ where the resonance set is the infinite-dimensional variety of
self-adjoint perturbations of the initial self-adjoint operator~$H_0$ which
have~$\lambda$ as an eigenvalue. (b) Criteria for the order of tangency of a
perturbation~$V$ to the resonance set.
  5. Investigation of the root space of the compact operator
$(H_0+sV-\lambda)^{-1}V$ corresponding to an eigenvalue $(s-r_\lambda)^{-1},$
where $H_0+r_\lambda V$ is a point of the resonance set.
  This analysis gives a finer information about behaviour of discrete spectrum
compared to spectral flow.
  Finally, many results of this paper are non-trivial even in finite
dimensions, in which case they can be and were tested in numerical experiments.",1604.07006v2
2016-07-21,Broken symmetry dielectric resonators for high quality-factor Fano metasurfaces,"We present a new approach to dielectric metasurface design that relies on a
single resonator per unit cell and produces robust, high quality-factor Fano
resonances. Our approach utilizes symmetry breaking of highly symmetric
resonator geoemetries, such as cubes, to induce couplings between the otherwise
orthogonal resonator modes. In particular, we design perturbations that couple
""bright"" dipole modes to ""dark"" dipole modes whose radiative decay is
suppressed by local field effects in the array. Our approach is widely scalable
from the near-infrared to radio frequencies. We first unravel the Fano
resonance behavior through numerical simulations of a germanium resonator-based
metasurface that achieved a quality-factor of ~1300 at ~10.8 um. Then, we
present two experimental demonstrations operating in the near-infrared (~1 um):
a silicon-based implementation that achieved a quality-factor of ~350; and a
gallium arsenide-based structure that achieves a quality-factor of ~600 - the
highest near-infrared quality-factor experimentally demonstrated to date with
this kind of metasurfaces. Importantly, large electromagnetic field
enhancements appear within the resonators at the Fano resonant frequencies. We
envision that combining high-quality factor, high field enhancement resonances
with nonlinear and active/gain materials such as gallium arsenide will lead to
new classes of active optical devices.",1607.06469v1
2017-02-01,Resonance capture at arbitrary inclination: II. Effect of the radial drift rate,"The effect of radial drift rate on mean motion resonance capture is studied
for prograde, polar and retrograde orbits. We employ the numerical framework of
our earlier exploration of resonance capture at arbitrary inclination. Randomly
constructed samples of massless particles are set to migrate radially from
outside the orbit of a Jupiter-mass planet at different drift rates totalling
more than $1.6\times 10^6$ numerical simulations. Slower drift rates reduce
overall capture probability especially for prograde orbits and enhance capture
at specific initial inclinations of high order resonances such as the outer
1:5, 1:4, 1:3, 2:5, 3:7 and 5:7. Global capture is reduced with increasing
eccentricity at all inclinations as high order resonances capture more
particles that are subsequently lost by disruptive close encounters with the
planet. The relative efficiency of retrograde resonances at long-lived capture
with respect to prograde resonances is explained by the reduced effect of
planet encounters as such events occur with a shorter duration and a higher
relative velocity for retrograde motion. Capture in the coorbital 1:1 resonance
is marginally affected by the radial drift rate except for nearly coplanar
retrograde eccentric orbits whose capture likelihood is increased significantly
with slower drift rates. An unexpected finding is the presence of a dynamical
corridor for capture in high order inner prograde resonances with initial
inclinations in the range [50$^\circ$,80$^\circ$] especially at the inner 5:2
resonance whose capture likelihood peaks at 80% to 90% depending on initial
eccentricity.",1702.00236v1
2019-05-15,A tunable ferroelectric based unreleased RF resonator,"This paper introduces the first tunable ferroelectric capacitor (FeCAP) based
unreleased RF MEMS resonator, integrated seamlessly in Texas Instruments' 130nm
Ferroelectric RAM (FeRAM) technology. An array of FeCAPs in this complementary
metal-oxide-semiconductor (CMOS) technology's back-end-of-line (BEOL) process
were used to define the acoustic resonance cavity as well as the
electromechanical transducers. To achieve high quality factor (Q) of the
resonator, acoustic waveguiding for vertical confinement within the CMOS stack
is studied and optimized. Additional design considerations are discussed to
obtain lateral confinement and suppression of spurious modes. An FeCAP
resonator is demonstrated with fundamental resonance at 703 MHz and Q of 1012.
This gives a frequency quality factor product fQ = 7.11$\times$10$^1$$^1$ which
is 1.6$\times$ higher than the most state-of-the-art Pb(Zr,Ti)O$_3$ (PZT)
resonators. Due to the ferroelectric characteristics of the FeCAPs,
transduction of the resonator can be switched on and off by adjusting the
electric polarization. In this case, the resonance can be turned off completely
at $\pm$0.3V corresponding to the coercive voltage of the constituent FeCAP
transducers. These novel switchable resonators may have promising applications
in on-chip timing, ad-hoc radio front ends, and chip-scale sensors.",1905.05903v1
2019-05-29,Resonant-State Expansion of the Fano Peak in Open Quantum Systems,"We describe the Fano asymmetry by expanding the transmission amplitude with
respect to states with point spectra (discrete eigenstates), including not only
bound states but also resonant states with complex eigenvalues. We first
introduce a novel complete set that spans the Hilbert space of the central part
of an open quantum-dot system. This complete set contains all states of point
spectra, but does not contain any states of continuous spectra. We thereby
analytically expand the conductance of the dot in terms of all discrete states
without any background integrals. This expansion implies that the resonant
states produce the main contributions to the electron transmission. We then
explain the Fano peak as an interference effect involving resonant states. We
find that there are three types of Fano asymmetry according to their origins:
the interference between a resonant state and an anti-resonant state, that
between a resonant state and a bound state, and that between two resonant
states. We derive microscopic expressions of the Fano parameters that describe
the three types of Fano asymmetry. We show that the last two types display the
asymmetric energy dependence given by Fano, but the first one shows a slightly
different form.",1905.12259v1
2020-07-04,Multiple Tunable Hyperbolic Resonances in Broadband Infrared Carbon-Nanotube Metamaterials,"Aligned, densely-packed carbon nanotube metamaterials prepared using vacuum
filtration are an emerging infrared nanophotonic material. We report multiple
hyperbolic plasmon resonances, together spanning the mid-infrared, in
individual resonators made from aligned and densely-packed carbon nanotubes. In
the first near-field scanning optical microscopy (NSOM) imaging study of
nanotube metamaterial resonators, we observe distinct deeply-subwavelength
field profiles at the fundamental and higher-order resonant frequencies. The
wafer-scale area of the nanotube metamaterials allows us to combine this
near-field imaging with a systematic far-field spectroscopic study of the
scaling properties of many resonator arrays. Thorough theoretical modeling
agrees with these measurements and identifies the resonances as higher-order
Fabry-P\'erot (FP) resonances of hyperbolic waveguide modes. Nanotube resonator
arrays show broadband extinction from 1.5-10 {\mu}m and reversibly switchable
extinction in the 3-5 {\mu}m atmospheric transparency window through the
coexistence of multiple modes in individual ribbons. Broadband carbon nanotube
metamaterials supporting multiple resonant modes are a promising candidate for
ultracompact absorbers, tunable thermal emitters, and broadband sensors in the
mid-infrared.",2007.01970v1
2018-05-21,Trans-Neptunian Objects Transiently Stuck in Neptune's Mean Motion Resonances: Numerical simulations of the current population,"A substantial fraction of our solar system's trans-Neptunian objects (TNOs)
are in mean motion resonance with Neptune. Many of these objects were likely
caught into resonances by planetary migration---either smooth or
stochastic---approximately 4 Gyr ago. Some, however, gravitationally scattered
off of Neptune and became transiently stuck in more recent events. Here, we use
numerical simulations to predict the number of transiently-stuck objects,
captured from the current actively scattering population, that occupy 111
resonances at semimajor axes $a=$30--100 au. Our source population is an
observationally constrained model of the currently-scattering TNOs. We predict
that, integrated across all resonances at these distances, the current
transient sticking population comprises 40\% of total
transiently-stuck+scattering TNOs, suggesting that these objects should be
treated as a single population. We compute the relative distribution of
transiently-stuck objects across all $p$:$q$ resonances with $1/6 \le q/p < 1$,
$p<40$, and $q<20$, providing predictions for the population of transient
objects with $H_r < 8.66$ in each resonance. We find that the relative
populations are approximately proportional to each resonance's libration period
and confirm that the importance of transient sticking increases with semimajor
axis in the studied range. We calculate the expected distribution of libration
amplitudes for stuck objects and demonstrate that observational constraints
indicate that both the total number and the amplitude-distribution of 5:2
resonant TNOs are inconsistent with a population dominated by transient
sticking from the current scattering disk. The 5:2 resonance hence poses a
challenge for leading theories of Kuiper belt sculpting.",1805.08228v1
2011-11-10,Resonances in sinh- and sine-Gordon models and higher equations of motion in Liouville theory,"The notion of operator resonances was introduced earlier by Al. Zamolodchikov
within the framework of the conformal perturbation theory. The resonances are
related to logarithmic divergences of integrals in the perturbation expansion,
and manifest themselves in poles of the correlation functions and form factors
of local operators considered as functions of conformal dimensions. The
residues of the poles can be computed by means of some operator identities.
Here we study the resonances in the Liouville, sinh- and sine-Gordon models,
considered as perturbations of a massless free boson. We show that the
well-known higher equations of motion discovered by Al. Zamolodchikov in the
Liouville field theory are nothing but resonance identities for some descendant
operators. The resonance expansion in the vicinity of a resonance point
provides a regularized version of the corresponding operators. We try to
construct the corresponding resonance identities and resonance expansions in
the sinh- and sine-Gordon theories. In some cases it can be done explicitly,
but in most cases we are only able to obtain a general form so far. We show
nevertheless that the resonances are perturbatively exact, which means that
each of them only appears in a single term of the perturbation theory.",1111.2547v5
2017-12-12,Shifting of the resonance location for planets embedded in circumstellar disks,"Context: In the early evolution of a planetary system, a pair of planets may
be captured in a mean motion resonance while still embedded in their nesting
circumstellar disk. Aims: The goal is to estimate the direction and amount of
shift in the semimajor axis of the resonance location due to the disk gravity
as a function of the gas density and mass of the planets. The stability of the
resonance lock when the disk dissipates is also tested. Methods: The orbital
evolution of a large number of systems is numerically integrated within a
three-body problem in which the disk potential is computed as a series of
expansion. This is a good approximation, at least over a limited amount of
time. Results: Two different resonances are studied: the 2:1 and the 3:2. In
both cases the shift is inwards, even if by a different amount, when the
planets are massive and carve a gap in the disk. For super--Earths, the shift
is instead outwards. Different disk densities, Sigma, are considered and the
resonance shift depends almost linearly on Sigma. The gas dissipation leads to
destabilization of a significant number of resonant systems, in particular if
it is fast. Conclusions: The presence of a massive circumstellar disk may
significantly affect the resonant behavior of a pair of planets by shifting the
resonant location and by decreasing the size of the stability region. The disk
dissipation may explain some systems found close to a resonance but not locked
in it.",1712.04178v1
2020-01-21,Effects of neighbouring planets on the formation of resonant dust rings in the inner Solar System,"Context. Findings by the Helios and STEREO mission have indicated the
presence of a resonant circumsolar ring of dust associated with Venus. Attempts
to model this phenomenon as an analogue to the resonant ring of Earth - as a
result of migrating dust trapped in external mean-motion resonances (MMRs) -
have so far been unable to reproduce the observed dust feature. Other theories
of origin have recently been put forward. However, the reason for the low
trapping efficiency of Venus's external MMRs remains unclear. Aims. Here we
look into the nature of the dust trapping resonant phenomena that arise from
the multi-planet configuration of the inner Solar System, aiming to add to the
existent understanding of resonant dust rings in single planet systems.
Methods. We numerically modelled resonant dust features associated with the
inner planets and specifically looked into the dependency of these structures
and the trapping efficiency of particular resonances on the configuration of
planets. Results. Besides Mercury showing no resonant interaction with the
migrating dust cloud, we find Venus, Earth, and Mars to considerably interfere
with each other's resonances, influencing their ability to form circumsolar
rings. We find that the single most important reason for the weakness of
Venus's external MMR ring is the perturbing influence of its outer neighbour -
Earth. In addition, we find Mercury and Mars to produce crescent-shaped density
features, caused by a directed apsidal precession occurring in particles
traversing their orbital region.",2001.07611v1
2021-01-12,Excitation of resonant surface plasmons for evanescent waves refocusing by a superlens,"The amplification of evanescent waves by flat superlens requires a
near-resonance coupling which has been linked to resonant surface plasmons. A
subtle interplay has been proposed to exist between the excitation of
well-defined resonant surface plasmons and the focusing capability of a
superlens. To gain insights into these resonant modes and their contributions
to the amplification and recovery of evanescent waves, we performed simple but
robust full-wave FDTD simulations on causal negative index Lorentz models. We
found that well-defined pair of resonant surface plasmons is excited whenever a
coupling of a diverging transmitted beam and a converging refracted beam occurs
at the second interface. The resonant coupling of these modes at the interface
led to the excitation of a single interface resonance predicted by the theory.
The physical consequence of this resonance is that incident wave energy is
pumped into the negative-index material medium and beyond it. These phenomena
contribute substantially to the amplification and recovery of the near-fields
in the image plane. It is noteworthy that, for evanescent wave refocusing to be
achieved in a flat superlens, its thickness, and the source-to-superlens
distance should be optimized. This optimization is critical in that an optimal
thickness alongside optimal source-to-superlens distance will allow evanescent
wave refocusing to dominate material lost. The FDTD simulated result showed an
image of the point source inside the superlens and beyond it when its thickness
was optimized. The resolution of the image beyond the superlens was
$\sim.58\lambda$ and this superlens behaves like a near-perfect lens. Overall,
these numerically simulated results could serve as useful approximations to the
degree of resonant amplification and refocusing of near-fields that can be
achieved by flat superlens in near-fields experimental imaging setups.",2101.04625v1
2017-11-01,Efficient quantum microwave-to-optical conversion using electro-optic nanophotonic coupled-resonators,"We propose a low noise, triply-resonant, electro-optic (EO) scheme for
quantum microwave-to-optical conversion based on coupled nanophotonics
resonators integrated with a superconducting qubit. Our optical system features
a split resonance - a doublet - with a tunable frequency splitting that matches
the microwave resonance frequency of the superconducting qubit. This is in
contrast to conventional approaches where large optical resonators with
free-spectral range comparable to the qubit microwave frequency are used. In
our system, EO mixing between the optical pump coupled into the low frequency
doublet mode and a resonance microwave photon results in an up-converted
optical photon on resonance with high frequency doublet mode. Importantly, the
down-conversion process, which is the source of noise, is suppressed in our
scheme as the coupled-resonator system does not support modes at that
frequency. Our device has at least an order of magnitude smaller footprint than
the conventional devices, resulting in large overlap between optical and
microwave fields and large photon conversion rate ($g/2\pi$) in the range of
$\sim$5-15 kHz. Owing to large $g$ factor and doubly-resonant nature of our
device, microwave-to-optical frequency conversion can be achieved with optical
pump powers in the range of tens of microwatts, even with moderate values for
optical $\it{Q}$ ($\sim 10^6$) and microwave $Q$ ($ \sim10^4$). The performance
metrics of our device, with substantial improvement over the previous EO-based
approaches, promise a scalable quantum microwave-to-optical conversion and
networking of superconducting processors via optical fiber communication.",1711.00346v1
2019-01-01,Triply-resonant coupled-cavity electro-optic modulators for on-chip RF photonic systems,"We propose a triply-resonant electro-optic modulator architecture which
maximizes modulation efficiency using simultaneous resonant enhancement of the
RF drive signal, the optical pump, and the generated optical sideband. Optical
enhancement of the optical pump and the sideband is achieved using resonant
supermodes of two coupled optical resonators, and the RF enhancement is
achieved with LC circuits formed by the capacitances of the optical resonators
and inductors which can be implemented using CMOS technology. In the proposed
configuration, the photon lifetime determines the bandwidth of the RF response
but not its center frequency, which is set by the coupling strength between the
two resonators and is not subject to the photon lifetime constraint inherent to
conventional single-mode resonant modulators. This enables efficient operation
at high RF carrier frequencies without a reduction in efficiency commonly
associated with the photon lifetime limit. Two optical configurations of the
modulator are proposed: a ""basic"" configuration with equal Q-factors in both
supermodes, most suitable for narrowband RF signals, and a ""generalized""
configuration with independently tailored Q-factors of the two supermodes,
which makes it possible to broaden the RF bandwidth without sacrificing the
resonant enhancement of the optical pump and paying a penalty in modulation
efficiency associated with doing so. Additionally, a significant gain in
modulation efficiency is expected from RF signal enhancement by LC resonant
matching. This results in a modulator which is compact, efficient, and capable
of modulation at high RF carrier frequencies. The proposed modulator
architecture optimally engineers the interaction of the device with each of the
three signals and between them, can be applied to any modulator cavity design
or modulation mechanism and promises to enable complex RF-photonic systems on
chip.",1901.00071v1
2019-04-24,A mathematical theory for Fano resonance in a periodic array of narrow slits,"This work concerns resonant scattering by a perfectly conducting slab with
periodically arranged subwavelength slits, with two slits per period. There are
two classes of resonances, corresponding to poles of a scattering problem. A
sequence of resonances has an imaginary part that is nonzero and on the order
of the width $\varepsilon$ of the slits; these are associated with Fabry-Perot
resonance, with field enhancement of order $1/\varepsilon$ in the slits. The
focus of this study is another class of resonances which become real valued at
normal incidence, when the Bloch wavenumber $\kappa$ is zero. These are
embedded eigenvalues of the scattering operator restricted to a period cell,
and the associated eigenfunctions extend to surface waves of the slab that lie
within the radiation continuum. When $0<|\kappa|\ll 1$, the real embedded
eigenvalues will be perturbed as complex-valued resonances, which induce the
Fano resonance phenomenon. We derive the asymptotic expansions of embedded
eigenvalues and their perturbations as resonances when the Bloch wavenumber
becomes nonzero. Based on the quantitative analysis of the diffracted field, we
prove that the Fano-type anomalies occurs for the transmission of energy
through the slab, and show that the field enhancement is of order
$1/(\kappa\varepsilon)$, which is stronger than Fabry-Perot resonance.",1904.11019v3
2019-12-02,Locally resonant metasurfaces for shear waves in granular media,"In this article the physics of horizontally polarized shear waves travelling
across a locally resonant metasurface in an unconsolidated granular medium is
experimentally and numerically explored. The metasurface is comprised of an
arrangement of sub-wavelength horizontal mechanical resonators embedded in
silica microbeads. The metasurface supports a frequency-tailorable attenuation
zone induced by the translational mode of the resonators. The experimental and
numerical findings reveal that the metasurface not only backscatters part of
the energy, but also redirects the wavefront underneath the resonators leading
to a considerable amplitude attenuation at the surface level, when all the
resonators have similar resonant frequency. A more complex picture emerges when
using resonators arranged in a so-called graded design, e.g., with a resonant
frequency increasing/decreasing throughout the metasurface. Unlike Love waves
propagating in a bi-layer medium, shear waves localized at the surface of our
metasurface are not converted into bulk waves. Although a detachment from the
surface occurs, the depth-dependent velocity profile of the granular medium
prevents the mode-conversion, steering again the horizontally polarized shear
waves towards the surface. The outcomes of our experimental and numerical
studies allow for understanding the dynamics of wave propagation in resonant
metamaterials embedded in vertically inhomogeneous soils and, therefore, are
essential for improving the design of engineered devices for ground vibration
and seismic wave containment.",1912.00617v1
2019-12-24,A study of the high-inclination population in the Kuiper belt -- III. The 4:7 mean motion resonance,"The high-inclination population in the 4:7 mean motion resonance (MMR) with
Neptune has also substantial eccentricities ($e\gtrsim0.1$), with more inclined
objects tending to occupy more eccentric orbits. For this high-order resonance,
there are two different resonant modes. The principal one is the
eccentricity-type mode, and we find that libration is permissible for orbits
with $e\ge e_c^0$, where the critical eccentricity $e_c^0$ increases as a
function of increasing inclination $i$. Correspondingly, we introduce a
limiting curve $e_c^0(i)$, which puts constraints on the $(e, i)$ distribution
of possible 4:7 resonators. We then perform numerical simulations on the
sweep-up capture and long-term stability of the 4:7 MMR, and the results show
that the simulated resonators are well-constrained by this theoretical limiting
curve. The other 4:7 resonant mode is the mixed-$(e, i)$-type, and we show that
stable resonators should exist at $i\gtrsim20^{\circ}$. We predict that the
intrinsic number of these mixed-$(e, i)$-type resonators may provide a new clue
into the Solar system's evolution, but, so far, only one real object has been
observed resonating in this mode.",1912.11174v1
2020-06-30,Nonclassicality of open circuit QED systems in the deep-strong coupling regime,"We investigate theoretically how the ground state of a qubit-resonator system
in the deep-strong coupling (DSC) regime is affected by the coupling to an
environment. We employ as a variational ansatz for the ground state of the
qubit-resonator-environment system a superposition of coherent states displaced
in qubit-state-dependent directions. We show that the reduced density matrix of
the qubit-resonator system strongly depends on how the system is coupled to the
environment, i.e., capacitive or inductive, because of the broken rotational
symmetry of the eigenstates of the DSC system in the resonator phase space.
When the resonator couples to the qubit and the environment in different ways
(for instance, one is inductive and the other is capacitive), the system is
almost unaffected by the resonator-waveguide coupling. In contrast, when the
two couplings are of the same type (for instance, both are inductive), by
increasing the resonator-waveguide coupling strength, the average number of
virtual photons increases and the quantum superposition realized in the
qubit-resonator entangled ground state is partially degraded. Since the
superposition becomes more fragile with increasing the qubit-resonator
coupling, there exists an optimal coupling strength to maximize the
nonclassicality of the qubit-resonator system.",2006.16769v2
2020-08-07,Tidal Evolution of the Evection Resonance/Quasi-Resonance and the Angular Momentum of the Earth-Moon System,"Forming the Moon by a high-angular momentum impact may explain the Earth-Moon
isotopic similarities, however, the post-impact angular momentum needs to be
reduced by a factor of 2 or more to the current value (1 L_EM) after the Moon
forms. Capture into the evection resonance, occurring when the lunar perigee
precession period equals one year, could remove the angular momentum excess.
However the appropriate angular momentum removal appears sensitive to the tidal
model and chosen tidal parameters. In this work, we use a constant-time delay
tidal model to explore the Moon's orbital evolution through evection. We find
that exit from formal evection occurs early and that subsequently, the Moon
enters a quasi-resonance regime, in which evection still regulates the lunar
eccentricity even though the resonance angle is no longer librating. Although
not in resonance proper, during quasi-resonance angular momentum is
continuously removed from the Earth-Moon system and transferred to Earth's
heliocentric orbit. The final angular momentum, set by the timing of
quasi-resonance escape, is a function of the ratio of tidal strength in the
Moon and Earth and the absolute rate of tidal dissipation in the Earth. We
consider a physically-motivated model for tidal dissipation in the Earth as the
mantle cools from a molten to a partially molten state. We find that as the
mantle solidifies, increased terrestrial dissipation drives the Moon out of
quasi-resonance. For post-impact systems that contain >2 L_EM, final angular
momentum values after quasi-resonance escape remain significantly higher than
the current Earth-Moon value.",2008.02968v1
2021-04-01,Dynamical structures of retrograde resonances: analytical and numerical studies,"In this work, retrograde mean motion resonances (MMRs) are investigated by
means of analytical and numerical approaches. Initially, we define a new
resonant angle to describe the retrograde MMRs and then perform a series of
canonical transformations to formulate the resonant model, in which the phase
portrait, resonant centre and resonant width can be analytically determined. To
validate the analytical developments, the non-perturbative analysis is made by
taking advantage of Poincar\'e surfaces of section. Some modifications are
introduced in the production of Poincar\'e sections and, in particular, it
becomes possible to make direct comparisons between the analytical and
numerical results. It is found that there exists an excellent correspondence
between the phase portraits and the associated Poincar\'e sections, and the
analytical results agree well with the numerical results in terms of the
resonant width and the location of resonant centre. Finally, the numerical
approach is utilized to determine the resonant widths and resonant centres over
the full range of eccentricity. In particular, seven known examples of
retrograde asteroids including 2015 BZ509, 2008 SO218, 1999 LE31, 2000 DG8,
2014 AT28, 2016 LS and 2016 JK24 are found inside the libration zones of
retrograde MMRs with Jupiter. The results obtained in this work may be helpful
for understanding the dynamical evolution for asteroids inside retrograde MMRs.",2104.00497v1
2021-04-14,On the role of resonances in polluting white dwarfs by asteroids,"Pollution of white dwarf atmospheres may be caused by asteroids that
originate from the locations of secular and mean-motion resonances in planetary
systems. Asteroids in these locations experience increased eccentricity,
leading to tidal disruption by the white dwarf. We examine how the $\nu_6$
secular resonance shifts outwards into a previously stable region of the
asteroid belt, as the star evolves to a white dwarf. Analytic secular models
require a planet to be engulfed in order to shift the resonance. We show with
numerical simulations that as a planet gets engulfed by the evolving star, the
secular resonance shifts and the rate of tidal disruption events increases with
the engulfed planet's mass and its orbital separation. We also investigate the
behaviour of mean-motion resonances. The width of a mean-motion resonance
increases as the star loses mass and becomes a white dwarf. The $\nu_6$ secular
resonance is more efficient at driving tidal disruptions than mean-motion
resonances with Jupiter. By examining 230 observed exoplanetary systems whose
central star will evolve into a white dwarf, we find that along with an Earth
mass planet at $1\,\rm au$, hot Jupiters at a semi--major axis $a\gtrsim
0.05\,\rm au$ and super--Earths of mass $10\,\rm M_\oplus$ at $a\gtrsim
0.3\,\rm au$ represent planet types whose engulfment shifts resonances enough
to cause pollution of the white dwarfs to a degree in agreement with
observations.",2104.06692v1
2021-05-10,Efimov scenario for overlapping narrow Feshbach resonances,"While Efimov physics in ultracold atoms is usually modeled with an isolated
Feshbach resonance many real world resonances appear in close vicinity to each
other and are therefore overlapping. Here we derive a realistic model based on
the mutual coupling of an open channel and two closed molecular channels while
neglecting short-range physics as permitted by the narrow character of the
considered resonances. The model is applied to three distinct scenarios with
experimental relevance. We show that the effect of overlapping resonances is
manifested most strikingly at a narrow resonance in whose vicinity there is a
slightly narrower one. In this system the Efimov ground state extends not only
over the scattering length zero crossing between the two resonances but also
over the pole of the second resonance to finally meet the dissociation
threshold below it. In the opposite scenario, when a narrow resonance is
considered in the vicinity of a slightly broader one, we observe that the
Efimov features are pushed to lower binding energies and smaller scattering
lengths by a significant factor facilitating their experimental investigation.
Both scenarios are referenced to the case of two narrow resonances which are
far enough away from each other to be effectively decoupled. In this case the
two-channel model results are recovered. Finally, we analyze the rich
excitation spectrum of the system and construct and explain its nodal pattern.",2105.04394v1
2021-07-02,Isovector giant monopole and quadrupole resonances in a Skyrme energy density functional approach with axial symmetry,"[Background] Giant resonance (GR) is a typical collective mode of vibration.
The deformation splitting of the isovector (IV) giant dipole resonance is well
established. However, the splitting of GRs with other multipolarities is not
well understood. [Purpose] I explore the IV monopole and quadrupole excitations
and attempt to obtain the generic features of IV giant resonances in deformed
nuclei by investigating the neutral and charge-exchange channels
simultaneously. [Method] I employ a nuclear energy-density functional (EDF)
method: the Skyrme-Kohn-Sham-Bogoliubov and the quasiparticle random-phase
approximation are used to describe the ground state and the transition to
excited states. [Results] I find the concentration of the monopole strengths in
the energy region of the isobaric analog or Gamow-Teller resonance irrespective
of nuclear deformation, and the appearance of a high-energy giant resonance
composed of the particle-hole configurations of $2\hbar \omega_0$ excitation.
Splitting of the distribution of the strength occurs in the giant monopole and
quadrupole resonances due to deformation. The lower $K$ states of quadrupole
resonances appear lower in energy and possess the enhanced strengths in the
prolate configuration, and vice versa in the oblate configuration, while the
energy ordering depending on $K$ is not clear for the $J=1$ and $J=2$
spin-quadrupole resonances. [Conclusions] The deformation splitting occurs
generously in the giant monopole and quadrupole resonances. The $K$-dependence
of the quadrupole transition strengths is largely understood by the anisotropy
of density distribution.",2107.00867v1
2021-09-24,Anomalous Loss Reduction Below Two-Level System Saturation in Aluminum Superconducting Resonators,"Superconducting resonators are widely used in many applications such as qubit
readout for quantum computing, and kinetic inductance detectors. These
resonators are susceptible to numerous loss and noise mechanisms, especially
the dissipation due to two-level systems (TLS) which become the dominant source
of loss in the few-photon and low temperature regime. In this study,
capacitively-coupled aluminum half-wavelength coplanar waveguide resonators are
investigated. Surprisingly, the loss of the resonators was observed to decrease
with a lowering temperature at low excitation powers and temperatures below the
TLS saturation. This behavior is attributed to the reduction of the TLS
resonant response bandwidth with decreasing temperature and power to below the
detuning between the TLS and the resonant photon frequency in a discrete
ensemble of TLS. When response bandwidths of TLS are smaller than their
detunings from the resonance, the resonant response and thus the loss is
reduced. At higher excitation powers, the loss follows a logarithmic power
dependence, consistent with predictions from the generalized tunneling model
(GTM). A model combining the discrete TLS ensemble with the GTM is proposed and
matches the temperature and power dependence of the measured internal loss of
the resonator with reasonable parameters.",2109.11742v6
2022-03-22,Strategies for reducing frequency scatter in large arrays of superconducting resonators,"Superconducting resonators are now found in a broad range of applications
that require high-fidelity measurement of low-energy signals. A common feature
across almost all of these applications is the need for increased numbers of
resonators to further improve sensitivity, and the ability to read out large
numbers of resonators without the need for additional cryogenic complexity is a
primary motivation. One of the major limitations of current resonator arrays is
the observed scatter in the resonator frequencies when compared to the initial
design. Here we present recent progress toward identifying one of the dominant
underlying causes of resonator scatter, inductor line width fluctuation. We
designed and fabricated an array of lumped-element resonators with inductor
line width changing from 1.8um to 2.2um in step of 0.1um defined with
electron-beam lithography to probe and quantify the systematic variation of
resonance frequency across a 6-inch wafer. The resonators showed a linear
frequency shift of 20MHz (140FWHM) and 30MHz (214FWHM), respectively, as they
are connected to two different capacitors. This linear relationship matches our
theoretical prediction. The widely used MLA photon lithography facility for
MKID fabrication has a resolution on the order of 600nm, which could cause
frequency fluctuation on the order of 100MHz or 710FWHM.",2203.17244v1
2022-05-11,Mathematical theory for electromagnetic scattering resonances and field enhancement in a subwavelength annular gap,"This work presents a mathematical theory for electromagnetic scattering
resonances in a subwavelength annular hole embedded in a metallic slab, with
the annulus width $h\ll1$. The model is representative among many 3D
subwavelength hole structures, which are able to induce resonant scattering of
electromagnetic wave and the so-called extraordinary optical transmission. We
develop a multiscale framework for the underlying scattering problem based upon
a combination of the integral equation in the exterior domain and the waveguide
mode expansion inside the tiny hole. The matching of the electromagnetic field
over the hole aperture leads to a sequence of decoupled infinite systems, which
are used to set up the resonance conditions for the scattering problem. By
performing rigorous analysis for the infinite systems and the resonance
conditions, we characterize all the resonances in a bounded domain over the
complex plane. It is shown that the resonances are associated with the TE and
TEM waveguide modes in the annular hole, and they are close to the real axis
with the imaginary parts of order ${\cal O}(h)$. We also investigate the
resonant scattering when an incident wave is present. It is proved that the
electromagnetic field is amplified with order ${\cal O}(1/h)$ at the resonant
frequencies that are associated with the TE modes in the annular hole. On the
other hand, one particular resonance associated with the TEM mode can not be
excited by a plane wave but can be excited with a near-field electric dipole
source, leading to field enhancement of order ${\cal O}(1/h)$.",2205.05377v1
2022-05-24,Resolution Limits of Resonant Sensors with Duffing Non-Linearity,"The resolution of resonant sensors is fundamentally limited by the presence
of noise. Thermomechanical noise, intrinsic to the resonator, sets the ultimate
sensor performance when all other noise sources have been eliminated. For
linear resonators, the sensing resolution can always be further improved by
increasing the driving power. However, this trend cannot continue indefinitely,
since at sufficiently high driving powers non-linear effects emerge and
influence the noise performance. As a consequence, the resonator's non-linear
characteristics play an inextricable role in determining its ultimate
resolution limits. Recently, several works have studied the characteristic
performance of non-linear resonators as sensors, with the counter intuitive
conclusion that increasing the quality factor of a resonator does not improve
its sensing resolution at the thermomechanical limit. In this work we further
analyze the ultimate resolution limits, and describe different regimes of
performance at integration times below and above the resonator's decay time. We
provide an analytical model to elucidate the effects of Duffing non-linearity
on the resolution of closed-loop sensors, and validate it using numerical
simulations. In contrast to previous works, our model and simulations show that
under certain conditions the ultimate sensing resolution of a Duffing resonator
can be improved by maximizing its quality factor. With measurements on a
nanomechanical membrane resonator, we experimentally verify the model and
demonstrate that frequency resolutions can be achieved that surpass the
previously known limits.",2205.11903v1
2022-07-12,Quadrupole and octupole order resonances in non-restricted hierarchical planetary systems,"Nonrestricted hierarchical three-body configurations are common in various
scales of astrophysical systems. Dynamical structures of the quadrupole-order
resonance (the von Zeipel-Lidov-Kozai resonance) and the octupole-order
resonance (the apsidal resonance) under the nonrestricted hierarchical
planetary systems are investigated in this work by taking advantage of
perturbative treatments. Under the quadrupole-order Hamiltonian model, the
distribution of libration and circulation regions as well as the distribution
of flipping region are analytically explored in the parameter space spanned by
the conserved quantities. The fundamental frequencies of system are produced
and then the nominal location of octupole-order resonance is identified. From
the viewpoint of perturbative theory, the quadrupole-order Hamiltonian
determines the unperturbed dynamical model and the octupole-order Hamiltonian
plays an role of perturbation to the quadrupole-order dynamics. The resonant
Hamiltonian for octupole-order resonances is formulated by means of averaging
theory, giving rise to a new constant of motion. Phase portraits are produced
to analyse dynamical structures of octupole-order resonance, including resonant
centres, saddle points, dynamical separatrices and islands of libration. By
analysing phase portraits, it is found that there are four branches of
libration centre and eight libration zones in the considered space.
Applications to orbit flips show that there are five flipping regions.",2207.05362v1
2022-07-26,Resonant tides in binary neutron star mergers: analytical-numerical relativity study,"Resonant excitations of $f$-modes in binary neutron star coalescences
influence the gravitational waves (GWs) emission in both quasicircular and
highly eccentric mergers and can deliver information on the star interior. Most
models of resonant tides are built using approximate, perturbative approaches
and thus require to be carefully validated against numerical relativity (NR)
simulations in the high-frequency regime. We perform detailed comparisons
between a set of high-resolution NR simulations and the state of the art
effective one body (EOB) model ${\tt TEOBResumS}$ with various tidal potentials
and including a model for resonant tides. For circular mergers, we find that
$f$-mode resonances can improve the agreement between EOB and NR, but there is
no clear evidence that the tidal enhancement after contact is due to a resonant
mechanism. Tidal models with $f$-mode resonances do not consistently reproduce,
at the same time, the NR waveforms and the energetics within the errors, and
their performances is comparable to resummed tidal models without resonances.
For highly eccentric mergers, we show for the first time that our EOB model
reproduces the bursty NR waveform to a high degree of accuracy. However, the
considered resonant model does not capture the $f$-mode oscillations excited
during the encounters and present in the NR waveform. Finally, we analyze
GW170817 with both adiabatic and dynamical tides models and find that the data
shows no evidence in favor of models including dynamical tides. This is in
agreement with the fact that resonant tides are measured at very high
frequencies, which are not available for GW170817 but might be tested with next
generation detectors.",2207.13106v1
2022-09-02,Modeling frequency shifts of collective bubble resonances with the boundary element method,"Increasing the number of closely-packed air bubbles immersed in water changes
the frequency of the Minnaert resonance. The collective interactions between
bubbles in a small ensemble are primarily in the same phase, causing them to
radiate a spherically-symmetric field that peaks at a frequency lower than the
Minnaert resonance for a single bubble. In contrast, large periodic arrays
include bubbles that are further apart than half the wavelength, so that
collective resonances have bubbles oscillating in opposite phases, ultimately
creating a fundamental resonance at a frequency higher than the single-bubble
Minnaert resonance. This work investigates the transition in resonance behavior
using a modal analysis of a mass-spring system and a boundary element method.
We significantly reduce the computational complexity of the full-wave solver to
a linear dependence on the number of bubbles in a rectangular array. The
simulated acoustic fields confirm the initial downshift in resonance frequency
and the strong influence of collective resonances when the array has hundreds
of bubbles covering more than half the wavelength. These results are essential
in understanding the low-frequency resonance characteristics of bubble
ensembles, which have important applications in diverse fields such as
underwater acoustics, quantum physics, and metamaterial design.",2209.01245v2
2022-09-28,A novel Machine-Learning method for spin classification of neutron resonances,"The performance of nuclear reactors and other nuclear systems depends on a
precise understanding of the neutron interaction cross sections for materials
used in these systems. These cross sections exhibit resonant structure whose
shape is determined in part by the angular momentum quantum numbers of the
resonances. The correct assignment of the quantum numbers of neutron resonances
is, therefore, paramount. In this project, we apply machine learning to
automate the quantum number assignments using only the resonances' energies and
widths and not relying on detailed transmission or capture measurements. The
classifier used for quantum number assignment is trained using stochastically
generated resonance sequences whose distributions mimic those of real data. We
explore the use of several physics-motivated features for training our
classifier. These features amount to out-of-distribution tests of a given
resonance's widths and resonance-pair spacings. We pay special attention to
situations where either capture widths cannot be trusted for classification
purposes or where there is insufficient information to classify resonances by
the total spin $J$. We demonstrate the efficacy of our classification approach
using simulated and actual $^{52}$Cr resonance data.",2209.14403v2
2022-10-02,Dynamical history of the Galilean satellites for a fast migration of Callisto,"The dynamics of the innermost Galilean satellites (Io, Europa and Ganymede)
is characterised by a chain of mean motion resonances, called Laplace
resonance, and by a strong tidal dissipation that causes wide variations of
their semi-major axes over large timescales. The precise history of energy
dissipation in the Jovian system is not known, but several theories have been
proposed. Tidal resonance locking states that big outer moons can also migrate
fast. If this is the case for Callisto, then it should have crossed the 2:1
mean motion resonance with Ganymede in the past, affecting the motion of all
four Galilean satellites. Therefore, we aim to determine whether a fast
migration for Callisto is compatible with the current orbital configuration of
the system. Due to the chaotic nature of the resonant crossing, different
outcomes are possible. A small portion of our simulations shows that Callisto
can cross the 2:1 resonance with Ganymede without being captured and preserving
the Laplace resonance. However, in most cases, we found that Callisto is
captured into resonance, despite its divergent migration. As Callisto continues
to migrate fast outwards, the moons depart substantially from the exact 8:4:2:1
commensurability, while still maintaining the resonant chain. Callisto can
eventually escape it by crossing a high-order mean motion resonance with
Ganymede. Afterwards, the moons' system is able to relax to its current
configuration for suitable dissipation parameters of the satellites. Therefore
it is possible, although challenging, to build a self-consistent picture of the
past history of the Galilean satellites for a fast migration of Callisto.",2210.00424v1
2022-11-23,Q-factor mediated quasi-BIC resonances coupling in asymmetric dimer lattices,"Resonance coupling in the regime of bound states in the continuum (BICs)
provides an efficient method for engineering nanostructure's optical response
with various lineshape while maintaining an ultra-narrow linewidth feature,
where the quality factor of resonances plays a crucial role. Independent
manipulation of the Q factors of BIC resonances enables full control of
interaction behavior as well as both near- and far-field light engineering. In
this paper, we harness reflection symmetry (RS) and translational symmetry (TS)
protected BIC resonances supported in an asymmetric dimer lattice and
investigate Q-factor-mediated resonance coupling behavior under controlled TS
and RS perturbations. We focus on in-plane electrical dipole BIC (EDi-BIC) and
magnetic dipole BIC (MD-BIC) which are protected by RS, and out-of-plane
electrical dipole BIC (EDo-BIC) protected by TS. The coupling between EDi-BIC
and EDo-BIC exhibits a resonance crossing behavior where the transmission
spectrum at the crossing could be tuned flexibly, showing an
electromagnetically induced transparency lineshape or satisfying the lattice
Kerker condition with pure phase modulation capability depending on TS and RS
perturbed Q factors. While the coupling between MD-BIC and EDo-BIC shows an
avoided resonance crossing behavior, where the strongly coupled resonances
would lead to the formation of a Friedrich-Wintgen BICs whose spectral position
could also be shifted by tuning the Q factors. Our results suggest an
intriguing platform to explore BIC resonance interactions with independent Q
factor manipulation capability for realizing multi-functional meta-devices.",2211.12659v1
2023-02-06,"When, where, and how many planets end up in first-order resonances?","The theory of Type~I migration has been widely used in many studies.
Transiting multi-planet systems offer us the opportunity to examine the
consistency between observation and theory, especially for those systems
harbouring planets in Mean Motion Resonance (MMR). The displacement these
resonant pairs show from exact commensurability provides us with information on
their migration and eccentricity-damping histories. Here, we adopt a
probabilistic approach, characterized by two distributions -- appropriate for
either the resonant or non-resonant planets -- to fit the observed planet
period ratio distribution. With the Markov chain Monte Carlo (MCMC) method, we
find that ${\approx}15\%$ of exoplanets are in first order ($j+1{:}j$) MMRs,
the ratio of eccentricity-to-semi-major axis damping is too high to allow
overstable librations and that the results are by-and-large consistent with
Type-I migration theory. In addition, our modeling finds that a small fraction
of resonant pairs is captured into resonance during migration, implying late
planet formation (gas-poor). Most of the resonant pairs park themselves at the
migration barrier, indicating early planet formation (gas-rich). Furthermore,
after improving the criterion on two-body resonant trapping, we obtain an upper
limit of the disc surface density at the time the planets are locked in
resonance.",2302.03070v2
2023-02-11,Resonance-facilitated three-channel p-wave scattering,"Feshbach resonances of arbitrary width are typically described in terms of
two-channel models. Within these models, one usually considers a single dressed
resonance, with the option to extend the analysis by including resonant
open-channel features that can drastically change the observed threshold
effects. For the strong $^{40}\mathrm{K}$ p-wave resonance studied in Ref.
\cite{ahmed2021}, the interplay between an open-channel shape resonance and the
Feshbach resonance could explain the unexpected nonlinear variation of the
binding energy with magnetic field. However, the presented two-channel
treatment relies on the introduction of two independent fitting parameters,
whereas the typical Breit-Wigner expression would only account for one. This
results in an effective magnetic moment that acquires a nonphysical value,
which is an indication of a major shortcoming of the two-channel model
treatment. In this study, we observe how the presence of a closed-channel shape
resonance explains the physical mechanism behind the observations and
demonstrates the need of a three-channel treatment. We introduce our novel
model as \textit{resonance facilitated}, where all coupling is mediated by the
Feshbach state, while there is no direct coupling between the additional
channel and the open channel. Notably, the resonance-facilitated structure
greatly reduces the complexity of the full three-channel model. The typical
Breit-Wigner form of the two-channel Feshbach formalism is retained and the
full effect of the added channel can be captured by a single resonance dressing
factor, which describes how the free propagation in the Feshbach state is
dressed by the added channel.",2302.05642v1
2023-04-24,Resonance frequency tracking schemes for micro- and nanomechanical resonators,"Nanomechanical resonators can serve as high performance detectors and have
potential to be widely used in the industry for a variety of applications. Most
nanomechanical sensing applications rely on detecting changes of resonance
frequency. In commonly used frequency tracking schemes, the resonator is driven
at or close to its resonance frequency. Closed-loop systems can continually
check whether the resonator is at resonance and accordingly adjust the
frequency of the driving signal. In this work, we study three resonance
frequency tracking schemes, a feedback-free (FF), a self-sustaining oscillator
(SSO), and a phase-locked loop oscillator (PLLO) scheme. We improve and extend
the theoretical models for the FF and the SSO tracking schemes, and test the
models experimentally with a nanoelectromechanical system (NEMS) resonator. We
employ a SSO architecture with a pulsed positive feedback topology and compare
it to the commonly used PLLO and FF schemes. We show that all tracking schemes
are theoretically equivalent and that they all are subject to the same speed
versus accuracy trade-off characteristics. In order to verify the theoretical
models, we present experimental steady-state measurements for all tracking
schemes. Frequency stability is characterized by computing the Allan deviation.
We obtain almost perfect correspondence between the theoretical models and the
experimental measurements. These results show that the choice of the tracking
scheme is dictated by cost, robustness and usability in practice as opposed to
fundamental theoretical differences in performance.",2304.11889v2
2023-06-01,"Nonlinear characteristics of Ti, Nb, and NbN superconducting resonators for parametric amplifiers","Superconducting resonators and parametric amplifiers are important components
in scientific systems such as kinetic inductance detector arrays,
frequency-domain multiplexers for other superconducting bolometers,
spin-ensemble based memories, and circuit quantum electrodynamics
demonstrators. In this paper, we report microwave measurements of
superconducting Ti, Nb, and NbN resonators and their use as parametric
amplifiers. These half-wave resonators were fabricated under near identical
sputtering and lithographic conditions to ensure a like-for-like comparison of
material properties. We report a wide range of properties and behaviours in
terms of transition temperatures, resistivities, rate-limiting nonlinear
response times, nonlinear dissipation, signs of the nonlinear inductances and
their dependences on temperature and resonance harmonic. We have successfully
operated Nb and NbN resonators as high gain parametric amplifiers, achieving
greater than $20\,\mathrm{dB}$ of power amplification. We have shown that for a
half-wave resonator, amplification can be realised not only in the fundamental
resonance but also in the higher harmonic resonances. Further, for materials
with high transition temperatures, e.g. Nb and NbN, amplification can be
achieved at $\sim4\,\mathrm{K}$, i.e. a temperature maintained by a pulse tube
cooler. Finally, in materials systems that have very fast response times, e.g.
NbN, we have found that a cross-harmonic type of amplification can be achieved
by placing pump tone in a different resonant mode as the signal and the idler.
This wide range of observations will have important implications on the design
and application of superconducting parametric amplifiers.",2306.00685v2
2023-10-25,Pauli resonance states in light nuclei: how they appear and how they can be eliminated,"Systematic analysis of parameters and properties of the Pauli resonance
states are performed for light nuclei $^{6}$Li, $^{7}$Li, $^{8}$Be, $^{9}$Be
and $^{10}$B, which are treated as two-cluster systems. The Pauli resonance
states are redundant solutions of the resonating group method appearing when
one try use more advanced description of the internal structure of interacting
clusters. Our calculations are performed in a standard and advanced versions of
the resonating group method. The standard version employs wave functions of
many-particle shell model to describe internal motion of nucleons within each
cluster. The advanced version is based on three-cluster resonating group
method. As in the standard version, the internal wave functions of three
clusters are approximated by wave functions of many-particle shell model model.
However, in advanced version one of pair of clusters forms a bound state, and
third cluster is considered to interact with such state. It is found that the
Pauli resonance states in nuclei under consideration have energy between 11 and
46 MeV, and their widths vary from 8 keV to 6.7 MeV. Analysis of wave functions
of Pauli resonance states and matrix elements of norm kernel allowed us to
formulate an effective method for eliminating Pauli resonance states. It is
demonstrated that this method effectively eliminate all determined the Pauli
resonance states.",2310.16373v3
2023-11-09,"The Propulsion Performance of Dual Heaving Foils in Tandem, with Spanwise Flexibility","The impact of spanwise flexibility on the propulsion performance of two foils
arranged in tandem and subjected to a prescribed sinusoidal heaving motion has
been studied at a Reynolds number of 100. This comprises a wide range of
natural frequencies of the flexible foil, covering pre-resonance, resonance,
and post-resonance regimes, with respect to the heaving frequency. The
propulsion performance of the foils under different Strouhal numbers, with
either fixed reduced frequency or fixed natural frequency, has also been
investigated. We observed that the propulsion efficiency, thrust, and power
consumption drop, but the tip deformation coefficient increases to its maximum
when operating at resonance. The propulsion efficiency of the flexible dual
foils increases significantly in the pre-resonance regime at small Strouhal
numbers. Both thrust force and power consumption increase with the reduced
frequency during the pre- and post-resonance regimes. An instability phenomenon
is observed in the instantaneous tip deformation coefficient of the flexible
dual foils in the post-resonance regimes. We also find that the dual heaving
foils, with a larger resonance Strouhal number, achieve a greater thrust
increment compared with that of rigid dual heaving foils when working at the
pre-resonance regimes. Meanwhile, dual heaving foils with a smaller resonance
Strouhal number can achieve a larger propulsion efficiency increment compared
with that of rigid dual heaving foils when working at small Strouhal numbers.",2311.05255v1
2005-01-17,Magnetic domain walls of relic fermions as Dark Energy,"We show that relic fermions of the Big Bang can enter a ferromagnetic state
if they possess a magnetic moment and satisfy the requirements of Stoner theory
of itinerant ferromagnetism. The domain walls of this ferromagnetism can
successfully simulate Dark Energy over the observable epoch spanning $\sim 10$
billion years. We obtain conditions on the anomalous magnetic moment of such
fermions and their masses. Known neutrinos fail to satisfy the requirements
thus pointing to the possibility of a new ultralight sector in Particle
Physics.",0501348v3
1994-01-31,The Free Energy and the Scaling Function of the Ferromagnetic Heisenberg Chain in a Magnetic Field,"A nonlinear susceptibilities (the third derivative of a magnetization $m_S$
by a magnetic field $h$ ) of the $S$=1/2 ferromagnetic Heisenberg chain and the
classical Heisenberg chain are calculated at low temperatures $T.$ In both
chains the nonlinear susceptibilities diverge as $T^{-6}$ and a linear
susceptibilities diverge as $T^{-2}.$ The arbitrary spin $S$ Heisenberg
ferromagnet $[$ ${\cal H} = \sum_{i=1}^{N} \{ - J{\bf S}_{i} {\bf S}_{i+1} -
(h/S) S_{i}^{z} \}$ $(J>0),$ $]$ has a scaling relation between $m_S,$ $h$ and
$T:$ $m_S(T,h) = F( S^2 Jh/T^2).$ The scaling function
$F(x)$=(2$x$/3)-(44$x^{3}$/135) + O($x^{5}$) is common to all values of spin
$S.$",9401074v1
1994-10-10,Monte Carlo Simulation of Ising Models with Dipole Interaction,"Recently, a new memory effect was found in the metamagnetic domain structure
of the diluted Ising antiferromagnet $Fe_x Mg_{1-x} Cl_2$ by domain imaging
with Faraday contrast. Essential for this effect is the dipole interaction. We
simulate the low temperature behavior of diluted Ising-antiferromagnets by a
Monte Carlo simulation considering long range interaction. The metamagnetic
domain structure occurring due to the dipole interaction is investigated by
graphical representation. In the model considered the antiferromagnetic state
is stable for an external magnetic field smaller than a lower boundary $B_{c1}$
while for fields larger than an upper boundary $B_{c2}$ the system is in the
saturated paramagnetic phase, where the spins are ferromagnetically polarized.
For magnetic fields in between these two boundaries a mixed phase occurs
consisting of ferromagnetic domains in an antiferromagnetic background. The
position of these ferromagnetic domains is stored in the system: after a cycle
in which the field is first removed and afterwards applied again the domains
reappear at their original positions. The reason for this effect can be found
in the frozen antiferromagnetic domain state which occurs after removing the
field.",9410028v1
1994-12-29,Magnetization switching in nanoscale ferromagnetic grains: description by a kinetic Ising model,"The magnetic relaxation of ferromagnetic powders has been studied for many
years, largely due to its importance to recording technologies. However, only
recently have experiments been performed that resolve the magnetic state of
individual sub-micron particles. Motivated by these experimental developments,
we use droplet theory and Monte Carlo simulations to study the time and field
dependence of some quantities that can be observed by magnetic force
microscopy. Particular emphasis is placed on the effects of finite particle
size. The qualitative agreement between experiments on switching and our
simulations in individual single-domain ferromagnets suggests that the
switching mechanism in such particles may involve local nucleation and
subsequent growth of droplets of the stable phase.",9412120v1
1995-01-26,Ground states of the infinite q-deformed Heisenberg ferromagnet,"We set up a general structure for the analysis of ``frustration-free ground
states'', or ``zero-energy states'', i.e., states minimizing each term in a
lattice interaction individually. The nesting of the finite volume ground state
spaces is described by a generalized inductive limit of observable algebras.
The limit space of this inductive system has a state space which is canonically
isomorphic (as a compact convex set) to the set of zero-energy states. We show
that for Heisenberg ferromagnets, and for generalized valence bond solid
states, the limit space is an abelian C*-algebra, and all zero-energy states
are translationally invariant or periodic. For the $q$-deformed spin-$1/2$
Heisenberg ferromagnet in one dimension (i.e., the XXZ-chain with
S$_q$U(2)-invariant boundary conditions) the limit space is an extension of the
non-commutative algebra of compact operators by two points, corresponding to
the ``all spins up'' and the ``all spins down'' states, respectively. These are
the only translationally invariant zero-energy states. The remaining ones are
parametrized by the density matrices on a Hilbert space, and converge weakly to
the ``all up'' (resp.\ ``all down'') state for shifts to $-\infty$ (resp.\
$+\infty$).",9501123v1
1995-05-03,Magnetic and Transport Properties of the Kondo Lattice Model with Ferromagnetic Exchange Coupling,"The Kondo lattice model with Hund's ferromagnetic spin coupling is
investigated as a microscopic model of the perovskite-type $3d$ manganese oxide
(R,A)MnO$_3$ where $R$ and $A$ are rare earth element and alkaline earth
element, respectively. We take the classical spin limit $S=\infty$ for the
simplicity of the calculation, since the quantum exchange process seems to be
irrelevant in the high temperature paramagnetic phase. Magnetic and transport
properties of the system are calculated. In the hole doped systems,
ferromagnetic instabilities are observed as the temperature is lowered. The
giant magnetoresistance of this model is in excellent agreement with the
experimental data of (La,Sr)MnO$_3$.",9505011v3
1995-08-09,Kinetic Ising Systems as Models of Magnetization Switching in Submicron Ferromagnets,"Recently experimental techniques, such as magnetic force microscopy (MFM),
have enabled the magnetic state of individual sub-micron particles to be
resolved. Motivated by these experimental developments, we use Monte Carlo
simulations of two-dimensional kinetic Ising ferromagnets to study the magnetic
relaxation in a negative applied field of a grain with an initial magnetization
$m_0 = +1$. The magnetostatic dipole-dipole interactions are treated to lowest
order by adding to the Hamiltonian a term proportional to the square of the
magnetization. We use droplet theory to predict the functional forms for some
quantities observed by MFM, such as the probability that the magnetization is
positive. Our simulations are in excellent agreement with droplet-theoretical
predictions. The qualitative agreement between experiments and our simulations
of switching in individual single-domain ferromagnets indicates that the
switching mechanism in such particles may involve local nucleation and
subsequent growth of droplets of the stable phase.",9508031v1
1995-10-13,Plateau of the Magnetization Curve of the S=1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic Spin Chain,"I analytically study the plateau of the magnetization curve at $M/M_{\rm S} =
1/3$ (where $M_{\rm S}$ is the saturation magnetization) of the one-dimensional
$S=1/2$ trimerized Heisenberg spin system with ferromagnetic ($J_{\rm
F}$)-ferromagnetic ($J_{\rm F}$)-antiferromagnetic ($J_{\rm A}$) interactions
at $T=0$. I use the bosonization technique for the fermion representation of
the spin Hamiltonian through the Jordan-Wigner transformation. The plateau
appears when $\gamma \equiv J_{\rm F}/J_{\rm A} \allowbreak < \gamma_{\rm C}$,
and vanishes when $\gamma > \gamma_{\rm C}$, where the critical value
$\gamma_{\rm C}$ is estimated as $\gamma_{\rm C} = 5 \sim 6$. The behavior of
the width of the plateau near $\gamma_{\rm C}$ is of the Kosterlitz-Thouless
type. The present theory well explains the numerical result by Hida.",9510070v1
1995-11-27,Topology and dynamics in ferromagnetic media,"A direct link between the topological complexity of ferromagnetic media and
their dynamics has recently been established through the construction of
unambiguous conservation laws as moments of a topological vorticity. In the
present paper we carry out this program under completely realistic conditions,
with due account of the long-range magnetostatic field and related boundary
effects. In particular, we derive unambiguous expressions for the linear and
angular momentum in a ferromagnetic film which are then used to study the
dynamics of magnetic bubbles under the influence of an applied magnetic-field
gradient. The semi-empirical golden rule of bubble dynamics is verified in its
gross features but not in its finer details. A byproduct of our analysis is a
set of virial theorems generalizing Derrick's scaling relation as well as a
detailed recalculation of the fundamental magnetic bubble.",9511126v2
1995-12-14,Polymerization in a Ferromagnetic Spin Model with Threshold,"We propose a spin model with a new kind of ferromagnetic interaction, which
may be called {\it ferromagnetic coupling with threshold}. In this model the
contribute of a given spin to the total energy has only two possible values and
depends on the number of parallel spins among its nearest and next to the
nearest neighbors. By mapping the model onto the Ising version of the isotropic
eight vertex model, we obtain some evidence of a low temperature phase made of
alternate parallel pluses and minuses polymers.",9512116v3
1996-03-06,Ferromagnetism in multi--band Hubbard models: From weak to strong Coulomb repulsion,"We propose a new mechanism which can lead to ferromagnetism in Hubbard models
containing triangles with different on-site energies. It is based on an
effective Hamiltonian that we derive in the strong coupling limit. Considering
a one-dimensional realization of the model, we show that in the quarter-filled,
insulating case the ground-state is actually ferromagnetic in a very large
parameter range going from Tasaki's flat-band limit to the strong coupling
limit of the effective Hamiltonian. This result has been obtained using a
variety of analytical and numerical techniques. Finally, the same results are
shown to apply away from quarter-filling, in the metallic case.",9603042v1
1996-06-05,Transport and magnetic properties in ferromagnetic manganese-oxide thin films,"The transport and magnetic properties in ferromagnetic manganese-oxide thin
films are studied based on the model of the coupling between the mobile
d-electrons and the core spins in Mn ions. The spontaneous magnetization and
the resistivity are obtained for various magnetic fields and temperature. The
resistivity in absence of magnetic field and the magnetoresistance exhibit
maxima near the Curie temperature, the applied magnetic field moves the
position of the resistivity peak to high temperature and suppresses the peak
value, which agree with the experimental results. The Hall resistivity is
predicted to exhibit maximum near the Curie point. The pressure effect of the
magnetoresistance can also be explained qualitatively in this mechanism. The
colossal magnetoresistance in ferromagnetic manganese-oxide thin films is
attributed to the spin-correlation fluctuation scattering and the low
dimensional effect.",9606029v1
1996-06-17,A note on ferromagnetism in the Hubbard model on the complete graph,"Recently there have appeared some papers which discuss the existence of
ferromagnetism in the Hubbard model defined on the complete graph. At least for
the special electron number N_e=N-1, where N denotes the number of sites in the
lattice, the existence of ferromagnetism in this model was established
rigorously some time ago, as special (and indeed the simplest) cases of more
general classes of models. Here we explain these implications to clarify the
situation, although we believe the implications are straightforward. We are
posting this note to the preprint archive to make it public, but we are not
planning to publish it in other forms. This is because we do not think the
problem warrants any extra publications, and we believe that the validity of
our explanation is evident to the readers.",9606115v1
1996-08-07,Power-law correlated phase in random-field XY models and randomly pinned charge-density waves,"Monte Carlo simulations have been used to study the Z6 ferromagnet in a
random field on simple cubic lattices, which is a simple model for randomly
pinned charge-density waves. The random field is chosen to have infinite
strength on a fraction x of the sites of the lattice, and to be zero on the
remaining sites. For x= 1/16 there are two phase transitions. At low
temperature there is a ferromagnetic phase, which is stabilized by the six-fold
nonrandom anisotropy. The intermediate temperature phase is characterized by a
|k|^(-3) decay of two-spin correlations, but no true ferromagnetic order. At
the transition between the power-law correlated phase and the paramagnetic
phase the magnetic susceptibility diverges, and the two-spin correlations decay
approximately as |k|^(-2.87).",9608036v1
1996-08-09,Chiral Metal as a Ferromagnetic Super Spin Chain,"The electrons on the surface of a disordered multi-layer integer quantum Hall
system constitute an unusual chiral metal with ballistic motion transverse to
the field, and diffusive motion parallel to it. We present a non-perturbative
analytic treatment of an appropriate model, consisting of disordered chiral
Fermions in two dimensions. A supersymmetric generating functional is set up
for the correlation functions of this system. The strong disorder limit is
mapped into a supersymmetric spin chain, with ferromagnetic exchange coupling,
reflecting the electron's chiral motion. The ferromagnetic ground state and the
spin wave excitations, corresponding to the diffusion modes of the chiral
metal, are found exactly. The parametric density of states correlator in the
ergodic limit is computed from a Boltzmann-weighted sum over low energy spin
states. The result is of a universal form and coincides with that for a
Hermitian random matrix.",9608049v2
1996-09-06,Quantum critical behavior of itinerant ferromagnets,"The quantum ferromagnetic transition of itinerant electrons is considered. We
give a pedagogical review of recent results which show that zero-temperature
soft modes that are commonly neglected, invalidate the standard
Landau-Ginzburg-Wilson description of this transition. If these modes are taken
into account, then the resulting order parameter field theory is nonlocal in
space and time. Nevertheless, for both disordered and clean systems the
critical behavior has been exactly determined for spatial dimensions d>2 and
d>1, respectively. The critical exponents characterizing the
paramagnetic-to-ferromagnetic transition are dimensionality dependent, and
substantially different from both mean-field critical exponents, and from the
classical Heisenberg exponents that characterize the transition at finite
temperatures. Our results should be easily observable, particularly those for
the disordered case, and experiments to check our predictions are proposed.",9609070v2
1996-12-24,Quantum critical behavior of clean itinerant ferromagnets,"We consider the quantum ferromagnetic transition at zero temperature in clean
itinerant electron systems. We find that the Landau-Ginzburg-Wilson order
parameter field theory breaks down since the electron-electron interaction
leads to singular coupling constants in the Landau-Ginzburg-Wilson functional.
These couplings generate an effective long-range interaction between the spin
or order parameter fluctuations of the form 1/r^{2d-1}, with d the spatial
dimension. This leads to unusual scaling behavior at the quantum critical point
in 1 < d\leq 3, which we determine exactly. We also discuss the
quantum-to-classical crossover at small but finite temperatures, which is
characterized by the appearance of multiple temperature scales. A comparison
with recent results on disordered itinerant ferromagnets is given.",9612224v2
1997-05-22,The field theory of Skyrme lattices in quantum Hall ferromagnets,"We report the application of the nonlinear $\sigma$ model to study the
multi-skyrmion problem in the quantum Hall ferromagnet system. We show that the
ground state of the system can be described by a ferromagnet triangular Skyrme
lattice near $\nu=1$ where skyrmions are extremely dilute. We find a transition
into antiferromagnet square lattice by increasing the skyrmion density and
therefore $|\nu-1|$. We investigate the possibility that the square Skyrme
lattice deforms to a single skyrmion with the same topological charge when the
Zeeman energy is extremely smaller than the Coulomb energy. We explicitly show
that the energy of a skyrmion with charge two is less than the energy of two
skyrmions each with charge one when $g \leq g_c$. By taking the quantum
fluctuations into account, we also argue the possibility of the existence of a
non-zero temperature Kosterlitz-Thouless and a superconductor-insulator phase
transition.",9705224v1
1997-05-27,Incommensurate phases in ferromagnetic spin-chains with weak antiferromagnetic interchain interaction,"We study planar ferromagnetic spin-chain systems with weak antiferromagnetic
inter-chain interaction and dipole-dipole interaction. The ground state depends
sensitively on the relative strengths of antiferromagnetic exchange and dipole
energies kappa=J'a^2c/(g_L\mu_B)^2. For increasing values of \kappa, the ground
state changes from a ferromagnetic via a collinear antiferromagnetic and an
incommensurate phase to a 120^o structure for very large antiferromagnetic
energy. Investigation of the magnetic phase diagram of the collinear phase, as
realized in CsNiF_3, shows that the structure of the spin order depends
sensitivly on the direction of the magnetic field in the hexagonal plane. For
certain angular domains of the field incommensurate phases appear which are
separated by commensurate phases. When rotating the field, the wave vector
characterizing the structure changes continuously in the incommensurate phase,
whereas in the commensurate phase the wave vector is locked to a fixed value
describing a two-sublattice structure. This is a result of the competition
between the exchange and the dipole-dipole interaction.",9705280v1
1997-05-30,Ferromagnetism in the Hubbard model: Influence of the lattice structure,"By use of the spectral density approach the influence of the lattice
structure on the possibility of ferromagnetism in the single band Hubbard model
is investigated. The d=\infty hypercubic lattice does not show magnetic phase
transitions of second order irrespective of the strength of the Coulomb
coupling. However, first order transitions to finite magnetic moments, not
visible as singularities of the paramagnetic susceptibility, may appear in the
very strong coupling regime. In d=3 second order transitions are found but only
for very strong couplings, where the non-locality of the electronic self-energy
acts in favour of the spontaneous magnetic moment. The influence of the
non-local part of the self-energy is particularly strong for lattices with
small coordination number. The non-bipartite fcc lattice exhibits saturated
ferromagnetism for all band occupations $1\le n\le 2$ while for less than half
filled bands ($0\le n\le 1$) the system remains in any case paramagnetic, and
that for d=3 as well as d=\infty. The Curie temperature runs through a maximum
at about $n=1.4$ and vanishes for $n\to 1$ and $n\to 2$.",9705305v1
1997-07-28,Lattice dependence of saturated ferromagnetism in the Hubbard model,"We investigate the instability of the saturated ferromagnetic ground state
(Nagaoka state) in the Hubbard model on various lattices in dimensions d=2 and
d=3. A variational resolvent approach is developed for the Nagaoka instability
both for U = infinity and for U < infinity which can easily be evaluated in the
thermodynamic limit on all common lattices. Our results significantly improve
former variational bounds for a possible Nagaoka regime in the ground state
phase diagram of the Hubbard model. We show that a pronounced particle-hole
asymmetry in the density of states and a diverging density of states at the
lower band edge are the most important features in order to stabilize Nagaoka
ferromagnetism, particularly in the low density limit.",9707286v2
1997-09-17,Theory of Hysteresis Loop in Ferromagnet,"A theory of the hysteresis loop in ferromagnets controlled by the domain wall
motion is presented. Domain walls are considered as plane or linear interfaces
moving in a random medium under the action of the external ac magnetic field
$H=H_0\sin\omega t$. We introduce important characteristics of the hysteresis
loop, such as dynamic threshold fields, reversal field etc. together with well
known characteristics as coercive field and hysteresis loop area (HLA) $\cal
A$. We show that all these characteristics are regulated by two dimensionless
combinations of the $H_0$ and $\omega$and intrinsic characteristics of the
ferromagnet. The moving domain wall can create magnetic bubbles playing the
role of pre-existing nuclei of the reversed magnetization. We discuss a simple
model of this process. For magnetization reversal determined by domain
inflation we predict that HLA scales as ${\cal A}\propto
\omega^{\beta}H_0^{\alpha}$ with $\alpha =1/2$ and $\beta =1/2$. Numerical
simulations confirmthis result.",9709194v2
1997-10-09,Enhancement of Quantum Tunneling for Excited States in Ferromagnetic Particles,"A formula suitable for a quantitative evaluation of the tunneling effect in a
ferromagnetic particle is derived with the help of the instanton method. The
tunneling between n-th degenerate states of neighboring wells is dominated by a
periodic pseudoparticle configuration. The low-lying level-splitting previously
obtained with the LSZ method in field theory in which the tunneling is viewed
as the transition of n bosons induced by the usual (vacuum) instanton is
recovered. The observation made with our new result is that the tunneling
effect increases at excited states. The results should be useful in analyzing
results of experimental tests of macroscopic quantum coherence in ferromagnetic
particles.",9710090v1
1997-10-16,"Hole doping and disorder effects on the one-dimensional Kondo lattice, for ferromagnetic Kondo couplings","We investigate the one-dimensional Kondo lattice model (1D KLM) for
ferromagnetic Kondo couplings. The so-called ferromagnetic 2-leg spin ladder
and the S=1 antiferromagnet occur as new one-dimensional Kondo insulators. Both
exhibit a spin gap. But, in contrast to the strong coupling limit, the Haldane
state which characterizes the 2-leg spin ladder Kondo insulator cannot fight
against very weak exterior perturbations. First, by using standard bosonization
techniques, we prove that an antiferromagnetic ground state occurs by doping
with few holes; it is characterized by a form factor of the spin-spin
correlation functions which exhibits two structures respectively at $q=\pi$ and
$q=2k_F$. Second, we prove precisely by using renormalization group methods
that the Anderson-localization inevitably takes place in that weak-coupling
Haldane system, by the introduction of quenched randomness; the spin-fixed
point rather corresponds to a ``glass'' state. Finally, a weak-coupling
``analogue'' of the S=1 antiferromagnet Kondo insulator is proposed; we show
that the transition into the Anderson-localization state may be avoided in that
unusual weak-coupling Haldane system.",9710166v1
1997-10-24,Magnetization Switching in Single-Domain Ferromagnets,"A model for single-domain uniaxial ferromagnetic particles with high
anisotropy, the Ising model, is studied. Recent experimental observations have
been made of the probability that the magnetization has not switched. Here an
approach is described in which it is emphasized that a ferromagnetic particle
in an unfavorable field is in fact a metastable system, and the switching is
accomplished through the nucleation and subsequent growth of localized
droplets. Nucleation theory is applied to finite systems to determine the
coercivity as a function of particle size and to calculate the probability of
not switching. Both of these quantities are modified by different boundary
conditions, magnetostatic interactions, and quenched disorder.",9710267v1
1997-12-29,Ferromagnetic transition and phase diagram of the one-dimensional Hubbard model with next-nearest-neighbor hopping,"We study the phase diagram of the one-dimensional Hubbard model with
next-nearest-neighbor hopping using exact diagonalization, the density-matrix
renormalization group, the Edwards variational ansatz, and an adaptation of
weak-coupling calculations on the two-chain Hubbard model. We find that a
substantial region of the strong-coupling phase diagram is ferromagnetic, and
that three physically different limiting cases are connected in one
ferromagnetic phase. At a point in the phase diagram at which there are two
Fermi points at weak coupling, we study carefully the phase transition from the
paramagnetic state to the fully polarized one as a function of the on-site
Coulomb repulsion. We present evidence that the transition is second order and
determine the critical exponents numerically. In this parameter regime, the
system can be described as a Luttinger liquid at weak coupling. We extract the
Luttinger-liquid parameters and show how their behavior differs from that of
the nearest-neighbor Hubbard model. The general weak-coupling phase diagram can
be mapped onto that of the two-chain Hubbard model. We exhibit explicitly the
adapted phase diagram and determine its validity by numerically calculating
spin and charge gaps using the density-matrix renormalization group.",9712310v1
1998-02-10,Ferromagnetism in a Hubbard model for an atomic quantum wire: a realization of flat-band magnetism from even-membered rings,"We have examined a Hubbard model on a chain of squares, which was proposed by
Yajima et al as a model of an atomic quantum wire As/Si(100), to show that the
flat-band ferromagnetism according to a kind of Mielke-Tasaki mechanism should
be realized for an appropriate band filling in such a non-frustrated lattice.
Reflecting the fact that the flat band is not a bottom one, the ferromagnetism
vanishes, rather than intensified, as the Hubbard U is increased. The exact
diagonalization method is used to show that the critical value of U is in a
realistic range. We also discussed the robustness of the magnetism against the
degradation of the flatness of the band.",9802101v2
1998-02-16,Ordering of localized moments in Kondo lattice models,"We describe the transition from a ferromagnetic phase, to a disordered para-
magnetic phase, which occurs in one-dimensional Kondo lattice models with
partial conduction band filling. The transition is the quantum order-disorder
transition of the transverse-field Ising chain, and reflects double-exchange
ordered regions of localized spins being gradually destroyed as the coupling to
the conduction electrons is reduced. For incommensurate conduction band
filling, the low-energy properties of the localized spins near the transition
are dominated by anomalous ordered (disordered) regions of localized spins
which survive into the paramagnetic (ferromagnetic) phase. Many interesting
properties follow, including a diverging susceptibility for a finite range of
couplings into the paramagnetic phase. Our critical line equation, together
with numerically determined transition points, are used to determine the range
of the double-exchange interaction. Models we consider are the spin 1/2 Kondo
lattices with antiferromagnetic (Kondo) coupling, with ferromagnetic (Hund's
rule) coupling, and the Kondo lattice with repulsive interactions between the
conduction electrons.",9802164v1
1998-04-20,Double-exchange model: phase separation versus canted spins,"We study the competition between different possible ground states of the
double-exchange model with strong ferromagnetic exchange interaction between
itinerant electrons and local spins. Both for classical and quantum treatment
of the local spins the homogeneous canted state is shown to be unstable against
a phase separation. The conditions for the phase separation into the mixture of
the antiferromagnetic and ferromagnetic/canted states are given. We also
discuss another possible realization of the phase-separated state:
ferromagnetic polarons embedded into an antiferromagnetic surrounding. The
general picture of a percolated state, which emerges from these considerations,
is discussed and compared with results of recent experiments on doped
manganaties.",9804213v3
1998-05-05,Fokker-Planck and Landau-Lifshitz-Bloch Equations for Classical Ferromagnets,"A macroscopic equation of motion for the magnetization of a ferromagnet at
elevated temperatures should contain both transverse and longitudinal
relaxation terms and interpolate between Landau-Lifshitz equation at low
temperatures and the Bloch equation at high temperatures. It is shown that for
the classical model where spin-bath interactions are described by stochastic
Langevin fields and spin-spin interactions are treated within the mean-field
approximation (MFA), such a ``Landau-Lifshitz-Bloch'' (LLB) equation can be
derived exactly from the Fokker-Planck equation, if the external conditions
change slowly enough. For weakly anisotropic ferromagnets within the MFA the
LLB equation can be written in a macroscopic form based on the free-energy
functional interpolating between the Landau free energy near T_C and the
``micromagnetic'' free energy, which neglects changes of the magnetization
magnitude |{\bf M}|, at low temperatures.",9805054v2
1998-06-01,Composite Polarons in Ferromagnetic Narrow-band Metallic Manganese Oxides,"A new mechanism is proposed to explain the colossal magnetoresistance and
related phenomena. Moving electrons accompanied by Jahn-Teller phonon and
spin-wave clouds may form composite polarons in ferromagnetic narrow-band
manganites. The ground-state and finite-temperature properties of such
composite polarons are studied in the present paper. By using a variational
method, it is shown that the energy of the system at zero temperature decreases
with the formation of composite polaron; the energy spectrum and effective mass
of the composite polaron at finite temperature is found to be strongly
renormalized by the temperature and the magnetic field. It is suggested that
the composite polaron contribute significantly to the transport and the
thermodynamic properties in ferromagnetic narrow-band metallic manganese
oxides.",9806017v1
1998-07-02,"Diamagnetic Effects, Spin Dependent Fermi Surfaces, and the Giant Magnetoresistance in Metallic Multilayers","We study the role of diamagnetic effects on the transport properties of
metallic magnetic multilayers to elucidate whether they can explain the Giant
Magnetoresistance (GMR) effect observed in those systems. Realistic Fermi
surface topologies in layered ferromagnets are taken into account, with the
possibilities of different types of orbits depending on the electron spin. Both
configurations, with ferromagnetic and anti-ferromagnetic couplings between
magnetic layers, are considered and the transmission coefficient for scattering
at the interface boundary is modelled to include magnetic and roughness
contributions. We assume that scattering processes conserve the electron spin,
due to large spin diffusion lengths in multilayer samples. Scattering from the
spacer mixes different orbit topologies in a way similar to magnetic
`breakdown' phenomena. For antiferromagnetic coupling, majority and minority
spins are interchanged from one magnetic layer to the next. Cyclotron orbits
are also traveled in opposite directions, producing a compensation-like effect
that yields a huge GMR, particularly for closed orbits. For open orbits, one
may get the `inverse' magnetoresistance effect along particular directions.",9807026v1
1998-07-16,Field Theory of Skyrme Lattices in Quantum Hall Ferromagnets,"We report the application of the nonlinear $\sigma$ model to study the
multi-skyrmion problem in the quantum Hall ferromagnet system. We make use of a
first-principle calculation to derive an analytical form for the
inter-skyrmionic interaction to show that the ground state of the system can be
described by a ferromagnet triangular Skyrme lattice near $\nu=1$ where
skyrmions are extremely dilute and a continuous transition into antiferromagnet
square lattice occurs by increasing the skyrmion density and therefore
$|\nu-1|$. Using these results we demonstrate that the transition for a
triangular to a square lattice which was previously derived, using the
Hartree-Fock method, can also be seen in the field theory picture. We
investigate the possibility that the skyrmions bound in pair to make a
bi-skyrmion triangular lattice when the Zeeman energy is extremely small. We
show that the energy of a skyrmion with charge $Q$ is less than the energy of
$Q$ skyrmions each with charge one when the short range interaction among them
is considered. By taking the quantum fluctuations into account, we also argue
the possibility of the existence of a %SMG superconductor-insulator and the
non-zero temperature phase transitions.",9807236v1
1998-07-17,Optical conductivity of colossal magnetorestistance compounds: Role of orbital degeneracy in the ferromagnetic phase,"Recent optical conductivity $\sigma(\omega)$ experiments have revealed an
anomalous spectral distribution in the ferromagnetic phase of the perovskite
system $La_{1-x}Sr_xMnO_3$. Using finite temperature diagonalization techniques
we investigate $\sigma(\omega)$ for a model that contains only the
$e_g$-orbital degrees of freedom. Due to strong correlations the orbital model
appears as a generalized t-J model with anisotopic interactions and 3-site
hopping. In the orbital t-J model $\sigma(\omega)$ is characterized by a broad
incoherent spectrum with increasing intensity as temperature is lowered, and a
Drude peak with small weight, consistent with experiment. Our calculations for
two-dimensional systems, which may have some particular relevance for the
double-layer manganites, show that the scattering from orbital fluctuations can
explain the order of magnitude of the incoherent part of $\sigma(\omega)$ in
the low temperature ferromagnetic phase. Moreover orbital correlation functions
are studied and it is shown that $x^2$-$y^2$ orbital order is prefered in the
doped planar model at low temperature.",9807255v1
1998-08-07,Electromagnetic Interactions in the Quantum Hall Ferromagnet,"The $\nu =1$ quantum Hall ground state in samples like GaAs is well known to
be ferromagnetic. The global SU(2) spin symmetry of the microscopic action is
broken down to a U(1) symmetry by the ground state. The Goldstone bosons
corresponding to this spontaneous breaking of symmetry are the ferromagnetic
magnons which are neutral spin waves. In addition, there are topologically
nontrivial, electrically charged spin excitations known as spin skyrmions,
which in these samples are the favoured charge carriers. In this letter, we
look into the electromagnetic coupling of these spin excitations. The discrete
symmetries P and T are also broken by the ground state and we find that to the
leading order, the electromagnetic interaction of the spin waves occurs through
a nonminimal coupling given by a Chern-Simons like term containing both the
electromagnetic potentials and the two Euler angles that specify the coset
SU(2)/U(1) and thereby, the Goldstone bosons.",9808081v1
1998-09-05,Griffith Singularities and the Replica Instantons in the Random Ferromagnet,"The problem of existence of non-analytic (Griffith-like) contributions to the
free energy of weakly disordered Ising ferromagnet is studied from the point of
view of the replica theory. The consideration is done in terms of the usual
random temperature Ginzburg-Landau Hamiltonian in space dimensions $D < 4$ in
the zero external magnetic field. It is shown that in the paramagnetic phase,
at temperatures not too close to $T_{c}$ (where the behaviour of the pure
system is correctly described by the Gaussian approximation), the free energy
of the system has additional non-perturbative contribution of the form
$\exp{-(const) \frac{\tau^{(4-D)/2}}{u}}$ (where $\tau = (T-T_{c})/T_{c}$),
which has essential singularity in the parameter $u \to 0$ which describes the
strength of the disorder. It is demonstrated that this contribution appears due
to non-linear localized (instanton-like) solutions of the mean-field stationary
equations which are characterized by the special type of the replica symmetry
breaking . It is argued that physically these replica instantons describe the
contribution from rare spatial ""ferromagnetic islands"" in which local (random)
temperature is below $T_{c}$",9809097v1
1998-10-06,Magnetoresistance of Granular Ferromagnets - Observation of a Magnetic Proximity Effect?,"We have observed a superparamagnetic to ferromagnetic transition in films of
isolated Ni grains covered by non-magnetic overlayers. The magnetoresistance
(MR) of the films was measured as a function of the overlayer thickness.
Initially, the granular Ni films exhibited negative MR curves peaked at H=0. As
different materials were deposited onto the grains hysteresis developed in the
MR. This behavior is ascribed to an increase of the typical domain size due to
magnetic coupling between grains. The strength of the inter-grain coupling is
found to correlate with the magnetic susceptibility of the overlayer material.
We discuss possible mechanisms for this coupling and suggest that the data may
reflect the existence of a magnetic proximity effect (analogous to the
well-known effect in superconductivity) in which a ferromagnetic moment is
induced in the metallic non-magnetic medium.",9810061v1
1998-11-17,The Anti-Jahn-Teller Polaron in LaMnO$_3$,"Distortions of the oxygen sublattice couple to $e_g$ orbitals of Mn$^{3+}$
and drive a cooperative Jahn-Teller (orbital ordering) transition in LaMnO$_3$.
A simple model for this transition is studied. Without further adjustment, the
model predicts the shape and stability of small (anti-Jahn-Teller) polarons
which form when holes are doped into the material. This leads to a new
description of the lightly doped insulator, the anti-ferromagnetic to
ferromagnetic transition, and the metal-insulator transition.",9811250v3
1998-12-27,Two Ferromagnetic States in Magnetoresistive Manganites - First Order Transition Driven by Orbitals -,"A systematic study of the electronic structure in perovskite manganites is
presented. The effective Hamiltonian is derived by taking into account the
degeneracy of $e_g$ orbitals and strong electron correlation in Mn ions. The
spin and orbital orderings are examined as functions of carrier concentration
in the mean-field approximation applied to the effective Hamiltonian. We obtain
the first order phase transition between ferromagnetic metallic and
ferromagnetic insulating states in the lightly doped region. The transition is
accompanied with the orbital order-disorder one which is directly observed in
the anomalous X-ray scattering experiments. The present investigation shows a
novel role of the orbital degree of freedom on metal-insulator transition in
manganites.",9812405v1
1999-01-06,``Smoke Rings'' in Ferromagnets,"It is shown that bulk ferromagnets support propagating non-linear modes that
are analogous to the vortex rings, or ``smoke rings'', of fluid dynamics. These
are circular loops of {\it magnetic} vorticity which travel at constant
velocity parallel to their axis of symmetry. The topological structure of the
continuum theory has important consequences for the properties of these
magnetic vortex rings. One finds that there exists a sequence of magnetic
vortex rings that are distinguished by a topological invariant (the Hopf
invariant). We present analytical and numerical results for the energies,
velocities and structures of propagating magnetic vortex rings in ferromagnetic
materials.",9901037v2
1999-01-07,Interplay between spin-relaxation and Andreev reflection in ferromagnetic wires with superconducting contacts,"We analyze the change in the resistance of a junction between a diffusive
ferromagnetic (F) wire and normal metal electrode, due to the onset of
superconductivity (S) in the latter and a double Andreev scattering process
leading to a complete internal reflection of a large fraction of the
spin-polarized electrons back into the ferromagnet. The superconducting
transition results in an additional contact resistance arising from the
necessity to match spin-polarized current in F-wire to spin-less current in
S-reservoir, which is comparable to the resistance of a piece of a F-wire with
the length equal to the spin-relaxation length.",9901051v1
1999-01-08,Quantum Ferrimagnets,"We study quantum ferrimagnets in one, two, and three dimensions by using a
variety of methods and approximations. These include: (i) a treatment based on
the spin coherent state path-integral formulation of quantum ferrimagnets by
taking into account the leading order quantum and thermal fluctuations (ii) a
field-theoretical (non-linear $\sigma$-model type) formulation of the special
case of one-dimensional quantum ferrimagnets at zero temperature (iii) an
effective description in terms of dimers and quantum rotors, and (iv) a quantum
renormalization group study of ferrimagnetic Heisenberg chains. Some of the
formalism discussed here can be used for a unified treatment of both
ferromagnets and antiferromagnets in the semiclassical limit. We show that the
low (high) energy effective Hamiltonian of a (S_1, S_2) Heisenberg ferrimagnet
is a ferromagnetic (antiferromagnetic) Heisenberg model. We also study the
phase diagram of quantum ferrimagnets in the presence of an external magnetic
field h ($h_{c1} < h < h_{c2}$) and show that the low- and the high-field
phases correspond respectively to the classical N\'eel and the fully polarized
ferromagnetic states. We also calculate the transition temperature for the
Berezinskii-Kosterlitz-Thouless phase transition in the special case of
two-dimensional quantum ferrimagnets.",9901063v2
1999-01-11,Temperature dependence of the resistivity in the double-exchange model,"The resistivity around the ferromagnetic transition temperature in the double
exchange model is studied by the Schwinger boson approach. The spatial spin
correlation responsible for scattering of conduction electrons are taken into
account by adopting the memory function formalism. Although the correlation
shows a peak lower than the transition temperature, the resistivity in the
ferromagnetic state monotonically increases with increasing temperature due to
a variation of the electronic state of the conduction electron. In the
paramagnetic state, the resistivity is dominated by the short range correlation
of scattering and is almost independent of the temperature. It is attributed to
a cancellation between the nearest-neighbor spin correlation, the fermion
bandwidth, and the fermion kinetic energy. This result implies the importance
of the temperature dependence of the electronic states of the conduction
electron as well as the localized spin states in both ferromagnetic and
paramagnetic phases.",9901078v1
1999-01-11,Coexistence of ferromagnetism and superconductivity in the hybrid ruthenate-cuprate compound RuSr_2GdCu_2O_8 studied by muon spin rotation (μ SR) and DC-magnetization,"We have investigated the magnetic and the superconducting properties of the
hybrid ruthenate-cuprate compound RuSr_{2}GdCu_{2}O_{8} by means of zero-field
muon spin rotation- (ZF-$\mu $SR) and DC magnetization measurements. The
DC-magnetisation data establish that this material exhibits ferromagnetic order
of the Ru-moments ($\mu (Ru) \approx 1 \mu_{B}$) below T_{Curie} = 133 K and
becomes superconducting at a much lower temperature T_c = 16 K. The ZF-$\mu $SR
experiments indicate that the ferromagnetic phase is homogeneous on a
microscopic scale and accounts for most of the sample volume. They also suggest
that the magnetic order is not significantly modified at the onset of
superconductivity.",9901084v2
1999-03-07,Correlation between Spin Polarization and Magnetic Moment in Ferromagnetic Alloys,"The correlation between the magnetic moment in ferromagnetic alloys and the
tunneling spin polarization in ferromagnet-insulator-superconductor tunneling
experiments has been a mystery. The measured spin polarization for Fe, Co, Ni,
and various Ni alloys is positive and roughly proportional to their magnetic
moments, which can not be explained by considering the net density of states.
Using a tight-binding coherent potential approximation (CPA) model, we show
that while the polarization of the net density of states is not correlated with
the magnetic moment, the polarization of the density of states of {\it s}
electrons is correlated with the magnetic moment in the same manner as observed
by the tunneling experiments.
  We also discuss the spin polarization measurements by Andreev reflection
experiments, some of which obtained different results from the tunneling
experiments and our calculations.",9903118v2
1999-03-09,Monte Carlo study of a two-dimensional quantum ferromagnet,"We present quantum Monte Carlo results for the field and temperature
dependence of the magnetization and the spin-lattice relaxation rate $1/T_1$ of
a two-dimensional $S=1/2$ quantum Heisenberg ferromagnet. The Monte Carlo
method, which yields results free of systematic errors, is described in detail.
The high accuracy of the calculated magnetization allows for stringent tests of
recent approximate analytical calculations. We also compare our results with
recent experimental data for a $\nu=1$ quantum Hall ferromagnet, which is
expected to be well described by the Heisenberg model. The dynamic response
function needed to extract $1/T_1$ is obtained using maximum-entropy analytic
continuation of the corresponding imaginary-time dependent correlation
function. We discuss the reliability of this approach.",9903148v1
1999-03-12,On the Coexistence in RuSr2GdCu2O8 of Superconductivity and Ferromagnetism,"We review the reasons that make superconductivity unlikely to arise in a
ferromagnet. Then, in light of the report by Tallon and collaborators that
RuSr2GdCu2O8 becomes superconducting at approximately 35 K which is well below
the Curie temperature of 132 K, we consider whether the objections really apply
to this compound. Our considerations are supported by local spin density
calculations for this compound, which indeed indicate a ferromagnetic RuO2
layer. The Ru moment resides in t_2g orbitals but is characteristic of
itinerant magnetism (and is sensitive to choice of exchange-correlation
potential and to the atomic positions). Based on the small exchange splitting
that is induced in the Cu-O layers, the system seems capable of supporting
singlet superconductivity an FFLO-type order parameter and possibly a pi-phase
alternation between layers. If instead the pairing is triplet in the RuO2
layers, it can be distinguished by a spin-polarized supercurrent. Either type
of superconductivity seems to imply a spontaneous vortex phase if the
magnetization is rotated out of the plane.",9903210v2
1999-04-29,Spin glass behavior upon diluting frustrated magnets and spin liquids: a Bethe-Peierls treatment,"A Bethe-Peierls treatment to dilution in frustrated magnets and spin liquids
is given. A spin glass phase is present at low temperatures and close to the
percolation point as soon as frustration takes a finite value in the dilute
magnet model; the spin glass phase is reentrant inside the ferromagnetic phase.
An extension of the model is given, in which the spin glass / ferromagnet phase
boundary is shown not to reenter inside the ferromagnetic phase asymptotically
close to the tricritical point whereas it has a turning point at lower
temperatures. We conjecture similar phase diagrams to exist in finite
dimensional models not constraint by a Nishimori's line. We increase
frustration to study the effect of dilution in a spin liquid state. This
provides a ``minimal'' ordering by disorder from an Ising paramagnet to an
Ising spin glass.",9904432v2
1999-05-18,From ferromagnetism to spin-density wave: Magnetism in the two channel periodic Anderson model,"The magnetic properties of the two-channel periodic Anderson model for
uranium ions, comprised of a quadrupolar and a magnetic doublet are
investigated through the crossover from the mixed-valent to the stable moment
regime using dynamical mean field theory. In the mixed-valent regime
ferromagnetism is found for low carrier concentration on a hyper-cubic lattice.
The Kondo regime is governed by band magnetism with small effective moments and
an ordering vector $\q$ close to the perfect nesting vector. In the stable
moment regime nearest neighbour anti-ferromagnetism dominates for less than
half band filling and a spin density wave transition for larger than half
filling. $T_m$ is governed by the renormalized RKKY energy scale $\mu_{eff}^2
<X_\sigma>^2 J^2\rho_0(\mu)$.",9905260v1
1999-06-23,Spin-orbit coupling effect on quantum Hall ferromagnets with vanishing Zeeman energy,"We present the phase diagram of a ferromagnetic quantum Hall effect liquid in
a narrow quantum well with vanishing single-particle Zeeman splitting,
$\epsilon_{{\rm Z}}$ and pronounced spin-orbit coupling. Upon decreasing
$\epsilon_{{\rm Z}}$, the spin-polarization field of a liquid takes, first, the
easy-axis configuration, followed by the formation of a helical state, which
affects the transport and NMR properties of a liquid and the form of
topological defects in it. The analysis is extended over high odd integer
filling factors.",9906354v2
1999-08-13,Theory of spin effect on Coulomb blockade of single-electron tunneling in ferromagnetic system,"Spin dependent single electron tunneling in a ferromagnetic double junction
is investigated theoretically in the limit of incoherent sequential tunneling.
The junction consists of a small nonmagnetic metallic grain with discrete
energy levels, which is connected to two ferromagnetic electrodes. We have
developed a new theoretical model taking into account charge as well as spin
degrees of freedom. The model allows us to investigate new phenomena such as
spin accumulation and spin fluctuations.",9908196v1
1999-08-13,On the magnetic stability at the surface in strongly correlated electron systems,"The stability of ferromagnetism at the surface at finite temperatures is
investigated within the strongly correlated Hubbard model on a semi-infinite
lattice. Due to the reduced surface coordination number the effective Coulomb
correlation is enhanced at the surface compared to the bulk. Therefore, within
the well-known Stoner-picture of band ferromagnetism one would expect the
magnetic stability at the surface to be enhanced as well. However, by taking
electron correlations into account well beyond the Hartree-Fock (Stoner) level
we find the opposite behavior: As a function of temperature the magnetization
of the surface layer decreases faster than in the bulk. By varying the hopping
integral within the surface layer this behavior becomes even more pronounced. A
reduced hopping integral at the surface tends to destabilize surface
ferromagnetism whereas the magnetic stability gets enhanced by an increased
hopping integral. This behavior represents a pure correlation effect and can be
understood in terms of general arguments which are based on exact results in
the limit of strong Coulomb interaction.",9908198v1
1999-08-13,Spin Wave Theory of Double Exchange Ferromagnets,"We construct the 1/S spin-wave expansion for double exchange ferromagnets at
T=0. It is assumed that the value of Hund's rule coupling, J_H, is sufficiently
large, resulting in a fully saturated, ferromagnetic half-metallic ground
state. We evaluate corrections to the magnon dispersion law, and we also find
that, in contrast to earlier statements in the literature, magnon-electron
scattering does give rise to spin wave damping. We analyse the momentum
dependence of these quantities and discuss the experimental implications for
colossal magnetoresistance compounds.",9908202v3
1999-08-13,Influence of uncorrelated overlayers on the magnetism in thin itinerant-electron films,"The influence of uncorrelated (nonmagnetic) overlayers on the magnetic
properties of thin itinerant-electron films is investigated within the
single-band Hubbard model. The Coulomb correlation between the electrons in the
ferromagnetic layers is treated by using the spectral density approach (SDA).
It is found that the presence of nonmagnetic layers has a strong effect on the
magnetic properties of thin films. The Curie temperatures of very thin films
are modified by the uncorrelated overlayers. The quasiparticle density of
states is used to analyze the results. In addition, the coupling between the
ferromagnetic layers and the nonmagnetic layers is discussed in detail. The
coupling depends on the band occupation of the nonmagnetic layers, while it is
almost independent of the number of the nonmagnetic layers. The induced
polarization in the nonmagnetic layers shows a long-range decreasing
oscillatory behavior and it depends on the coupling between ferromagnetic and
nonmagnetic layers.",9908203v2
1999-08-30,Spin-polarized tunneling of La0.67Sr0.33MnO3/YBa2Cu3O7-d junctions,"The transport properties between ferromagnets and high-Tc superconductors are
investigated in La0.67Sr0.33MnO3/YBa2Cu3O7-d (LSMO/YBCO)junctions in the
geometry of cross-strip lines. The conductance spectra show zero-bias
conductance peaks (ZBCP), reflecting the charge transport in the ab-plane. When
an external magnetic field is applied to the junctions, the conductance spectra
show two notable features, i.e., an increase of background conductance and an
asymmetric ZBCP splitting whose amplitude responds nonlinearly to the applied
field. It is shown that the magnetic field response are consistent with a
theoretical prediction of tunneling spectroscopy when the presence of a
ferromagnetic barrier between a spin-polarized ferromagnet and a d-wave
superconductor is assumed.",9908431v1
1999-10-21,Dynamics of Excited Electrons in Copper and Ferromagnetic Transition Metals: Theory and Experiment,"Both theoretical and experimental results for the dynamics of photoexcited
electrons at surfaces of Cu and the ferromagnetic transition metals Fe, Co, and
Ni are presented. A model for the dynamics of excited electrons is developed,
which is based on the Boltzmann equation and includes effects of
photoexcitation, electron-electron scattering, secondary electrons (cascade and
Auger electrons), and transport of excited carriers out of the detection
region. From this we determine the time-resolved two-photon photoemission
(TR-2PPE). Thus a direct comparison of calculated relaxation times with
experimental results by means of TR-2PPE becomes possible. The comparison
indicates that the magnitudes of the spin-averaged relaxation time \tau and of
the ratio \tau_\uparrow/\tau_\downarrow of majority and minority relaxation
times for the different ferromagnetic transition metals result not only from
density-of-states effects, but also from different Coulomb matrix elements M.
Taking M_Fe > M_Cu > M_Ni = M_Co we get reasonable agreement with experiments.",9910326v2
1999-10-26,Theory of Spin-Resolved Auger-Electron Spectroscopy from Ferromagnetic 3d-Transition Metals,"CVV Auger electron spectra are calculated for a multi-band Hubbard model
including correlations among the valence electrons as well as correlations
between core and valence electrons. The interest is focused on the
ferromagnetic 3d-transition metals. The Auger line shape is calculated from a
three-particle Green function. A realistic one-particle input is taken from
tight-binding band-structure calculations. Within a diagrammatic approach we
can distinguish between the \textit{direct} correlations among those electrons
participating in the Auger process and the \textit{indirect} correlations in
the rest system. The indirect correlations are treated within second-order
perturbation theory for the self-energy. The direct correlations are treated
using the valence-valence ladder approximation and the first-order perturbation
theory with respect to valence-valence and core-valence interactions. The
theory is evaluated numerically for ferromagnetic Ni. We discuss the
spin-resolved quasi-particle band structure and the Auger spectra and
investigate the influence of the core hole.",9910421v1
1999-11-05,Magnetic Order in the Double Exchange Model in Infinite Dimensions,"We studied magnetic properties of the double exchange (DE) model with S=1/2
localized spins at T=0, using exact diagonalization in the framework of the
dynamical mean field theory. Obtained phase diagram contains ferromagnetic,
antiferromagnetic and paramagnetic phases. Comparing the phase diagram with
that of the DE model with classical localized spins, we found that the quantum
fluctuations of localized spins partly destabilize the ferromagnetism and
expand the paramagnetic phase region. We found that phase separations occur
between the antiferromagnetic and paramagnetic phases as well as the
paramagnetic and ferromagnetic ones.",9911091v2
1999-11-12,Ferromagnetic Liquid Thin Films Under Applied Field,"Theoretical calculations, computer simulations and experiments indicate the
possible existence of a ferromagnetic liquid state, although definitive
experimental evidence is lacking. Should such a state exist, demagnetization
effects would force a nontrivial magnetization texture. Since liquid droplets
are deformable, the droplet shape is coupled with the magnetization texture. In
a thin-film geometry in zero applied field, the droplet has a circular shape
and a rotating magnetization texture with a point vortex at the center. We
calculate the elongation and magnetization texture of such ferromagnetic thin
film liquid droplet confined between two parallel plates under a weak applied
magnetic field. The vortex stretches into a domain wall and exchange forces
break the reflection symmetry. This behavior contrasts qualitatively and
quantitatively with the elongation of paramagnetic thin films.",9911202v1
1999-11-30,Two-dimensional frustrated Heisenberg model: Variational study,"The stability of the ferromagnetic phase of the 2D quantum spin-1/2 model
with nearest-neighbor ferro- and next-nearest neighbor antiferromagnetic
interactions is studied. It turns out that values of exchange integrals at
which the ferromagnetic state becomes unstable with respect to a creation of
one and two magnon are different. This difference shows that the classical
approximation is inapplicable to the study of the transition from the
ferromagnetic to the singlet state in contrast with 1D case. This problem is
investigated using a variational function of new type. It is based on the boson
representation of spin operators which is different from the Holstein-Primakoff
approximation. This allows us to obtain the accurate estimate of the transition
point and to study the character of the phase transition.",9911491v1
1999-12-02,Electrical transport in the ferromagnetic state of manganites: Small-polaron metallic conduction at low temperatures,"We report measurements of the resistivity in the ferromagnetic state of
epitaxial thin films of La_{1-x}Ca_{x}MnO_{3} and the low temperature specific
heat of a polycrystalline La_{0.8}Ca_{0.2}MnO_{3}. The resistivity below 100 K
can be well fitted by \rho - \rho_{o} = E \omega_{s}/sinh^{2}(\hbar
\omega_{s}/2k_{B}T) with \hbar \omega_{s}/k_{B} \simeq 100 K and E being a
constant. Such behavior is consistent with small-polaron coherent motion which
involves a relaxation due to a soft optical phonon mode. The specific heat data
also suggest the existence of such a phonon mode. The present results thus
provide evidence for small-polaron metallic conduction in the ferromagnetic
state of manganites.",9912037v1
1999-12-17,Ferromagnetic Semiconductor - Singlet (or Triplet) Superconductor - Ferromagnetic Semiconductor Systems as Possible Logic Circuits and Switches,"We consider thin superconducting (S) films of thickness d $\ll \xi_{0}$,
sandwiched between two ferromagnetic semiconducting insulators (FI) with
differently orientated magnetizations - the FI-S-FI system. We calculate the
dependence of the superconducting critical temperature on the orientation of
the magnetization in the insulators and on the thickness of the superconducting
film. The calculations are done for singlet as well as triplet superconductors.
In the singlet case T_{c} depends on the relative orientation of the left and
right magnetization only, while in the triplet case T_{c} depends on the
absolute orientation of magnetization. The latter property can serve as a kind
of spin-spectroscopy of triplet and unconventional superconductors, for
instance in resolving the structure of the triplet order parameter in the
recently discovered layered superconductor Sr_{2}RuO_{4}. The possibility of
logic circuits and switches, which are based on the FI-S-FI systems with
arbitrary orientation of magnetizations in FI films, is analyzed too.",9912315v1
2000-01-04,Itinerant ferromagnetism in half-metallic CoS_2,"We have investigated electronic and magnetic properties of the pyrite-type
CoS_2 using the linearized muffin-tin orbital (LMTO) band method. We have
obtained the ferromagnetic ground state with nearly half-metallic nature. The
half-metallic stability is studied by using the fixed spin moment method. The
non-negligible orbital magnetic moment of Co 3d electrons is obtained as $\mu_L
= 0.06 \mu_B$ in the local spin density approximation (LSDA). The calculated
ratio of the orbital to spin angular momenta <L_z >/< S_z > = 0.15 is
consistent with experiment. The effect of the Coulomb correlation between Co 3d
electrons is also explored with the LSDA + U method. The Coulomb correlation at
Co sites is not so large, $U \lesssim 1$ eV, and so CoS_2 is possibly
categorized as an itinerant ferromagnet. It is found that the observed
electronic and magnetic behaviors of CoS_2 can be described better by the LSDA
than by the LSDA + U.",0001028v1
2000-01-21,Superconductivity in a Ferromagnetic Layered Compound,"We examine superconductivity in layered systems with large Fermi-surface
splitting due to coexisting ferromagnetic layers. In particular, the hybrid
ruthenate-cuprate compound RuSr_2GdCu_2O_8 is examined on the coexistence of
the superconductivity and the ferromagnetism, which has been observed recently.
We calculate critical fields of the superconductivity taking into account the
Fulde-Ferrell-Larkin-Ovchinnikov state in a model with Fermi-surfaces which
shapes are similar to those obtained by a band calculation. It is shown that
the critical field is enhanced remarkably due to a Fermi-surface effect, and
can be high enough to make the coexistence possible in a microscopic scale. We
also clarify the direction of the spatial oscillation of the order parameter,
which may be observed by scanning tunneling microscope experiments.",0001318v2
2000-02-17,"Excitonic order at strong-coupling: pseudo-spins, doping, and ferromagnetism","A tight binding model is introduced to describe the strong interaction limit
of excitonic ordering. At stoichiometry, the model reduces in the strong
coupling limit to a pseudo-spin model with approximate U(4) symmetry. Excitonic
order appears in the pseudo-spin model as in-plane pseudo-magnetism. The U(4)
symmetry unifies all possible singlet and triplet order parameters describing
such states. Super-exchange, Hunds-rule coupling, and other perturbations act
as anisotropies splitting the U(4) manifold, ultimately stabilizing a
paramagnetic triplet state. The tendency to ferromagnetism with doping
(observed experimentally in the hexaborides) is explained as a spin-flop
transition to a different orientation of the U(4) order parameter. The physical
mechanism favoring such a reorientation is the enhanced coherence (and hence
lower kinetic energy) of the doped electrons in a ferromagnetic background
relative to the paramagnet. A discussion of the physical meaning of various
excitonic states and their experimental consequences is also provided.",0002259v1
2000-02-29,Magnetic properties of the Hubbard model on three-dimensional lattices: fluctuation-exchange and two-particle self-consistent studies,"The relation between three-dimensional lattice structure and magnetism in
correlated electron systems is explored for face centered cubic (FCC), body
centered cubic (BCC), and simple cubic (SC) lattices. In particular, we
question which lattice structure has the strongest tendency toward the
ferromagnetism or antiferromagnetism. We employ the Hubbard model to calculate
the spin susceptibility and the single-particle spectrum with the
fluctuation-exchange (FLEX) and the two-particle self-consistent (TPSC)
approximations in the weak coupling regime. We have shown that (i)
ferromagnetic spin fluctuations become dominant when the Fermi level lies
around a sharp peak (divergence) in the density of states (D(E)) near the
bottom of the band, which occurs for FCC with/without next nearest neighbor
hoppings (t') or BCC with an appropriate value of t'. Among the cases studied,
the ferromagnetic fluctuation is found to be the strongest for FCC with a
finite t'. (ii) When the peak in D(E) resides around the band center as in
bipartite SC or BCC, antiferromagnetic fluctuations become dominant when the
band is close to the half-filling, with the fluctuation being much stronger in
BCC.",0002441v1
2000-03-13,Electron - hole asymmetry and activation energy in quantum Hall ferromagnets,"We argue that the dissipative transport in ferromagnetic quantum Hall effect
liquids at $\nu=2N+1$ is dominated by the thermal activation of pairs
consisting of an electron and an antiskyrmion (topological texture which
represents a hole with 'screened' exchange interaction), thus manifesting the
lack of electron-hole symmetry in quantum Hall ferromagnets. We find that the
activation energy of such a pair is not the exchange energy, but is determined
by the interplay between the excess Zeeman energy of a skyrmion and the
charging energy of its topological texture: $${\cal E}=a\epsilon_{{\rm
Z}}^{1/3}E_{{\rm C}}^{2/3}\ln ^{1/3}(\frac{\Im_{i}}{E_{{\rm
C}}^{2/3}\epsilon_{{\rm Z}}^{1/3}}), E_{{\rm C}}=\frac{e^{2}}{\chi \lambda}, $$
with $ a\approx 1.75$.",0003224v2
2000-04-10,Weak localization correction to the FS interface resistance,"The classical resistance of a contact between a ferromagnet (F) and a
superconductor (S) acquires an additional contact term as compared to the
contact between a ferromagnet and a normal metal. The necessity to match
spin-polarized current in a ferromagnet to spin-less current in the
superconductor results in the accumulation of non-equilibrium polarization near
the F/S interface. In the present work, we show that the weak localization
correction to the classical diffusion coefficient, $\delta D$, is dependent on
the degree of polarization, with majority spins more likely to be reflected
from the interface than minority spins. Taking into account the change in the
spin polarized particle distribution in the F wire arising from $\delta D$, we
calculate the weak localization correction to the F/S contact resistance.",0004140v1
2000-04-10,T=0 Phase Diagram of the Double-Exchange Model,"We present the T=0 phase diagram of the double-exchange model (ferromagnetic
Kondo lattice model) for all values of the carrier concentration $n$ and Hund's
couplng $J$, within dynamical mean field theory. We find that depending on the
values of $n$ and $J$, the ground state is either a ferromagnet, a commensurate
antiferromagnet or some other incommensurate phase with intermediate wave
vectors . The antiferromagnetic phase is separated by first order phase
boundaries and wide regimes of phase separation. The transition from the
ferromagnetic phase to an incommensurate phase is second order.",0004151v2
2000-05-23,Spin tunneling of trigonal and hexagonal ferromagnets in an arbitrarily directed magnetic field,"The quantum tunneling of the magnetization vector are studied theoretically
in single-domain ferromagnetic nanoparticles placed in an external magnetic
field at an arbitrarily directed angle in the $ZX$ plane. We consider the
magnetocrystalline anisotropy with trigonal and hexagonal crystal symmetry,
respectively. By applying the instanton technique in the spin-coherent-state
path-integral representation, we calculate the tunnel splittings, the tunneling
rates and the crossover temperatures in the low barrier limit for different
angle ranges of the external magnetic field ($\theta_{H}=\pi/2$,
$\pi/2\ll\theta_{H}\ll\pi$, and $\theta_{H}=\pi$). Our results show that the
tunnel splittings, the tunneling rates and the crossover temperatures depend on
the orientation of the external magnetic field distinctly, which provides a
possible experimental test for magnetic quantum tunneling in nanometer-scale
single-domain ferromagnets.",0005373v1
2000-05-29,Quantum nucleation in ferromagnets with tetragonal and hexagonal symmetries,"The phenomenon of quantum nucleation is studied in a ferromagnet in the
presence of a magnetic field at an arbitrary angle. We consider the
magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal
symmetry, respectively. By applying the instanton method in the
spin-coherent-state path-integral representation, we calculate the dependence
of the rate of quantum nucleation and the crossover temperature on the
orientation and strength of the field for a thin film and for a bulk solid. Our
results show that the rate of quantum nucleation and the crossover temperature
depend on the orientation of the external magnetic field distinctly, which
provides a possible experimental test for quantum nucleation in nanometer-scale
ferromagnets.",0005491v2
2000-05-31,Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains,"The plateau-non-plateau transition in the
antiferromagnetic-(ferromagnetic)$_{n}$ polymerized $S=1/2$ XXZ chains under
the magnetic field is investigated. The universality class of this transition
belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points
are determined by level spectroscopy analysis of the numerical diagonalization
data for $4 \leq p \leq 13$ where $p(\equiv n+1)$ is the size of a unit cell.
It is found that the critical strength of ferromagnetic coupling decreases with
$p$ for small $p$ but increases for larger enough $p$. It is also found that
the plateau for large $p$ is wide enough for moderate values of exchange
coupling so that it should be easily observed experimentally. This is in
contrast to the plateaus for $p = 3$ chains which are narrow for a wide range
of exchange coupling even away from the critical point.",0005544v1
2000-07-04,Correlation Effects on the Double Exchange Model in a Ferromagnetic Metallic Phase,"The effect of the Hubbard interaction among conduction electrons on the
double exchange model is investigated in a ferromagnetic metallic phase.
Applying iterative perturbation theory to the Hubbard interaction within
dynamical mean field theory, we calculate the one-particle spectral function
and the optical conductivity, in which coherent-potential approximation is
further used to treat the ferromagnetic Hund coupling between conduction
electrons and localized spins. Identifying the decrease of the magnetization
for the localized spin with the increase of the temperature, we discuss the
temperature dependence of the one-particle spectrum and the optical
conductivity. It is found that the interplay between the Hund coupling and the
Hubbard interaction dramatically changes the spectral function, while it is
somehow obscured in the optical conductivity.",0007041v1
2000-07-07,"Origin and pressure dependence of ferromagnetism in A2Mn2O7 pyrochlores (A=Y, In, Lu, and Tl)","Non-conventional mechanisms have been recently invoked in order to explain
the ferromagnetic ground state of A2Mn2O7 pyrochlores (A=Y, In, Lu and Tl) and
the puzzling decrease of their Curie temperatures with applied pressure. Here
we show, using a perturbation expansion in the Mn-O hopping term, that both
features can be understood within the superexhange model, provided that the
intra-atomic oxygen interactions are properly taken into account. An additional
coupling between the Mn ions mediated by the In(5s)/Tl(6s) bands yields the
higher Tc's of these two compounds, this mechamism enhancing their
ferromagnetism for higher pressures.",0007124v3
2000-07-11,Hole-mediated ferromagnetism in tetrahedrally coordinated semiconductors,"A mean field model of ferromagnetism mediated by delocalized or weakly
localized holes in zinc-blende and wurzite diluted magnetic semiconductors is
presented. The model takes into account: (i) strong spin-orbit and kp couplings
in the valence band; (ii) the effect of strain upon the hole density-of-states,
and (iii) the influence of disorder and carrier-carrier interactions,
particularly near the metal-to-insulator transition. A quantitative comparison
between experimental and theoretical results for (Ga,Mn)As demonstrates that
theory describes the values of the Curie temperatures observed in the studied
systems as well as explain the directions of the easy axis and the magnitudes
of the corresponding anisotropy fields as a function of biaxial strain.
Furthermore, the model reproduces unusual sign, magnitude, and temperature
dependence of magnetic circular dichroism in the spectral region of the
fundamental absorption edge. Chemical trends and various suggestions concerning
design of novel ferromagnetic semiconductor systems are described.",0007190v2
2000-07-26,Critical Temperature of Ferromagnetic Transition in Three-Dimensional Double-Exchange Models,"Ferromagnetic transition in three-dimensional double-exchange models is
studied by the Monte Carlo method. Critical temperature $T_{\rm c}$ is
precisely determined by finite-size scaling analysis. Strong spin fluctuations
in this itinerant system significantly reduce $T_{\rm c}$ from mean-field
estimates. By choosing appropriate parameters, obtained values of $T_{\rm c}$
quantitatively agree with experiments for the ferromagnetic metal regime of
(La,Sr)MnO$_{3}$, which is a typical perovskite manganite showing colossal
magnetoresistance. This indicates that the double-exchange mechanism alone is
sufficient to explain $T_{\rm c}$ in this material. Critical exponents are also
discussed.",0007408v2
2000-07-31,Carrier-induced ferromagnetism in p-Zn1-xMnxTe,"We present a systematic study of the ferromagnetic transition induced by the
holes in nitrogen doped Zn1-xMnxTe epitaxial layers, with particular emphasis
on the values of the Curie-Weiss temperature as a function of the carrier and
spin concentrations. The data are obtained from thorough analyses of the
results of magnetization, magnetoresistance and spin-dependent Hall effect
measurements. The experimental findings compare favorably, without adjustable
parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY)
model or its continuous-medium limit, that is, the Zener model, provided that
the presence of the competing antiferromagnetic spin-spin superexchange
interaction is taken into account, and the complex structure of the valence
band is properly incorporated into the calculation of the spin susceptibility
of the hole liquid. In general terms, the findings demonstrate how the
interplay between the ferromagnetic RKKY interaction, carrier localization, and
intrinsic antiferromagnetic superexchange affects the ordering temperature and
the saturation value of magnetization in magnetically and electrostatically
disordered systems.",0007502v1
2000-08-10,Thermal properties of ferrimagnetic systems,"The heat capacity of some ferrimagnets has additional structures like a
shoulder in the Schottky-like peak, or emergence of a second peak when an
external magnetic field is applied. It is shown here that as long as spin
wave-spin wave interactions are ignored in a ferrimagnet, the ferromagnetic and
antiferromagnetic elementary excitation spectra give rise to two independent
heat capacity peaks, one enveloped by the other, which add up to give the peak
for the total system. Taking this into account helps understand the additional
structures in the peaks. Moreover, the classification of ferrimagnets into
predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is
shown to be validated by studying them under additional influences like
dimerization and frustration. Because these two are shown to influence the
ferromagnetic and antiferromagnetic dispersion relations - and hence the
quantities like heat capacity and magnetic susceptibility - by different
amounts, the characterisation of ferrimagnetic systems ($1,1/2$), ($3/2,1$) and
($3/2,1/2$) is brought out more clearly. Both these influences enhance
antiferromagnetic character.",0008167v1
2000-08-24,Coupling of two superconductors through a ferromagnet : evidence for a pi-junction,"We report measurements of the temperature dependence of the critical current
in Josephson junctions consisting of conventional superconducting banks of Nb
and a weakly ferromagnetic interlayer of a Cu$_x$Ni$_{1-x}$ alloy, with $x$
around 0.5. With decreasing temperature $I_c$ generally increases, but for
specific thicknesses of the ferromagnetic interlayer, a maximum is found
followed by a strong decrease down to zero, after which $I_c$ rises again. Such
a sharp cusp can only be explained by assuming that the junction changes from a
0-phase state at high temperatures to a $\pi$-phase state at low temperatures.",0008364v1
2000-08-24,Ferromagnetic Polarons in Manganites,"Using the Lanczos method in linear chains we study the double exchange model
in the low concentration limit, including an antiferromagnetic super-exchange
K. In the strong coupling limit we find that the ground state contains
ferromagnetic polarons whose length is very sensitive to the value of K/t. We
investigate the dispersion relation, the trapping by impurities, and the
interaction between these polarons. As the overlap between polarons increases,
by decreasing K/t, the effective interaction between them changes from
antiferromagnetic to ferromagnetic. The scaling to the thermodynamic limit
suggests an attractive interaction in the strong coupling regime (J_h > t) and
no binding in the weak limit (J_h \simeq t).",0008367v1
2000-08-30,Ferromagnetism in the Periodic Anderson Model - a Modified Alloy Analogy,"We introduce a new aproximation scheme for the periodic Anderson model (PAM).
The modified alloy approximation represents an optimum alloy approximation for
the strong coupling limit, which can be solved within the CPA-formalism.
Zero-temperature and finite-temperature phase diagrams are presented for the
PAM in the intermediate-valence regime. The diversity of magnetic properties
accessible by variation of the system parameters can be studied by means of
quasiparticle densities of states: The conduction band couples either ferro- or
antiferromagneticaly to the f-levels. A finite hybridization is a necessary
precondition for ferromagnetism. However, too strong hybridization generally
suppresses ferromagnetism, but can for certain system parameters also lead to a
semi-metallic state with unusual magnetic properties. By comparing with the
spectral density approximation, the influence of quasiparticle damping can be
examined.",0008441v1
2000-09-26,Soft tetragonal distortions in ferromagnetic Ni_2MnGa and related materials from first principles,"A detailed examination of the energy landscape, density of states and
magnetic moment of tetragonally distorted ferromagnetic Ni_2MnGa was performed
using first-principles local-spin-density (LSD) pseudopotential calculations,
varying V as well as c/a. The energy of tetragonal Ni_2MnGa is found to be
nearly constant for values of c/a over a wide range, with shallow minima near
c/a = 1 and 1.08 in addition to that near 1.2. This flat energy surface is
consistent with the wide range of observed values of c/a. It also explains the
observation of pseudomorphic growth of Ni_2MnGa on GaAs, despite a nominal 3%
lattice mismatch. The related materials Ni_2MnAl, Ni_2MnIn and ferromagnetic
NiMn were examined for similar behavior, but all are seen to have a single
well-defined minimum at c/a near 1, consistent with available experimental
information. For NiMn, the ground state antiferromagnetic ordering and
structural parameters are correctly predicted within the LSD approach.",0009406v1
2000-10-01,Critical exponents of the random-field O(N) model,"The critical behavior of the random-field Ising model has been a puzzle for a
long time. Different theoretical methods predict that the critical exponents of
the random-field ferromagnet in D dimensions are the same as in the pure
(D-2)-dimensional ferromagnet with the same number of the magnetization
components. This result contradicts the experiments and simulations. We
calculate the critical exponents of the random-field O(N) model with the
(4+\epsilon)-expansion and obtain values different from the critical exponents
of the pure ferromagnet in 2+\epsilon dimensions. In contrast to the previous
approaches we take into account an infinite set of relevant operators emerging
in the problem. We demonstrate how these previously missed relevant operators
lead to the breakdown of the (6-\epsilon)-expansion for the random-field Ising
model.",0010012v1
2000-10-02,"Limits on the Curie temperature of (III,Mn)V ferromagnetic semiconductors","Mean-field-theory predicts that the Curie temperature T_c of a (III,Mn)V
ferromagnet will be proportional to the valence band density-of-states of its
host (III,V) semiconductor, suggesting a route toward room-temperature
ferromagnetism in this materials class. In this Letter, we use theoretical
estimates of spin-wave energies and Monte-Carlo simulations to demonstrate that
long-wavelength collective fluctuations, neglected by mean-field theory, will
limit the critical temperature in large density-of-states materials. We discuss
implications for high T_c searches.",0010036v2
2000-10-04,Spin Injection from Ferromagnetic Metals into Gallium Nitride,"The injection of spin polarized electrons from ferromagnetic metals (Fe and
Co) into gallium nitride (GaN) via scanning tunneling microscopy (STM) is
demonstrated. Electrons from STM tips are injected into the semiconductor. Net
circular polarization of the emitted light is observed, which changes sign on
reversal of the magnetization of the tip. The polarization is found to be in
qualitative agreement with that expected from considerations based on the
splitting of the valence bands due to spin-orbit coupling and the crystal field
splitting corresponding to the wurtzite structure, and the magnitude of the
spin polarization from the ferromagnetic metal. We find a lower bound for the
spin injection efficiency of 25%, corresponding to a net spin polarization in
the semiconductor of 10%. This is the largest reported value for a room
temperature measurement of spin injection into semiconductors in air.",0010058v1
2000-10-11,Ideal Spin Filters: Theoretical Study of Electron Transmission Through Ordered and Disordered Interfaces Between Ferromagnetic Metals and Semiconductors,"It is predicted that certain atomically ordered interfaces between some
ferromagnetic metals (F) and semiconductors (S) should act as ideal spin
filters that transmit electrons only from the majority spin bands or only from
the minority spin bands of the F to the S at the Fermi energy, even for F with
both majority and minority bands at the Fermi level. Criteria for determining
which combinations of F, S and interface should be ideal spin filters are
formulated. The criteria depend only on the bulk band structures of the S and F
and on the translational symmetries of the S, F and interface. Several examples
of systems that meet these criteria to a high degree of precision are
identified. Disordered interfaces between F and S are also studied and it is
found that intermixing between the S and F can result in interfaces with spin
anti-filtering properties, the transmitted electrons being much less spin
polarized than those in the ferromagnetic metal at the Fermi energy. A patent
application based on this work has been commenced by Simon Fraser University.",0010153v1
2000-10-18,Current induced switching of magnetic domains to a perpendicular configuration,"In a ferromagnet--normal-metal--ferromagnet trilayer, a current flowing
perpendicularly to the layers creates a torque on the magnetic moments of the
ferromagnets. When one of the contacts is superconducting, the torque not only
favors parallel or antiparallel alignment of the magnetic moments, as is the
case for two normal contacts, but can also favor a configuration where the two
moments are perpendicular. In addition, whereas the conductance for parallel
and antiparallel magnetic moments is the same, signalling the absence of giant
magnetoresistance in the usual sense, the conductance is greater in the
perpendicular configuration. Thus, a negative magnetoconductance is predicted,
in contrast with the usual giant magnetoresistance.",0010255v2
2000-10-23,Vertical Boundary at x ~ 0.11 in the Structural Phase Diagram of the La1-xSrxMnO3 System (0.08 <= x <= 0.125),"The structural phase diagram of the La1-xSrxMnO3 system in the compositional
range 0.08 <= x <= 0.125 has been investigated by high-resolution synchrotron
x-ray powder diffraction techniques between 20-600 K. Recent studies have
reported that there is an unusual rentrant-type phase transition in this range
involving an abrupt change in lattice parameters but no change in the crystal
symmetry, which remains orthorhombic Pbnm. The transition to the reentrant
phase is from a ferromagnetic metallic to a ferromagnetic insulating phase with
some unusual properties. Our results demonstrate that for samples with x
=0.11-0.125 there exist two lower-symmetry structural regions having monoclinic
and triclinic symmetry respectively. There is a sharp first-order transition
from the monoclinic to the triclinic phase coinciding with the transition to
the ferromagnetic insulating phase, and an abrupt crossover from the
orthorhombic Pbnm region with a near-vertical phase boundary just below x =
0.11. The new phases indicate the presence of some novel type of orbital
ordering unlike that found in LaMnO3.",0010339v1
2000-10-29,Theory of Ferromagnetism in Diluted Magnetic Semiconductors,"Carrier-induced ferromagnetism has been observed in several (III,Mn)V
semiconductors. We review the theoretical picture of these ferromagnetic
semiconductors that emerges from a model with kinetic-exchange coupling between
localized Mn spins and valence-band carriers. We discuss the applicability of
this model, the validity of a mean-field approximation for its interaction term
widely used in the literature, and validity limits for the simpler RKKY model
in which only Mn spins appear explicitly. Our conclusions are based in part on
our analysis of the dependence of the system's elementary spin excitations on
carrier density and exchange-coupling strength. The analogy between this system
and spin-model ferrimagnets is explored. Finally, we list several extensions of
this model that can be important in realistic modeling of specific materials.",0010471v1
2000-11-06,Quantum Hall Ferromagnetism in a Two-Dimensional Electron System,"Experiments on a nearly spin degenerate two-dimensional electron system
reveals unusual hysteretic and relaxational transport in the fractional quantum
Hall effect regime. The transition between the spin-polarized (with fill
fraction $\nu = 1/3$) and spin-unpolarized ($\nu = 2/5$) states is accompanied
by a complicated series of hysteresis loops reminiscent of a classical
ferromagnet. In correlation with the hysteresis, magnetoresistance can either
grow or decay logarithmically in time with remarkable persistence and does not
saturate. In contrast to the established models of relaxation, the relaxation
rate exhibits an anomalous divergence as temperature is reduced. These results
indicate the presence of novel two-dimensional ferromagnetism with a
complicated magnetic domain dynamic.",0011081v1
2000-11-10,Triplet superconductivity induced by screened phonon interactions in ferromagnetic compounds,"We propose that screened pairing interactions mediated by phonons could give
rise to a spin triplet superconductivity in ferromagnetic compounds such as
UGe_2. It is pointed out that the pairing interactions include anisotropic
components such as those of p, d, f-waves in addition to dominant s-wave
component due to the momentum dependence. Since the ferromagnetic long-range
order coexists, there is a large splitting of the Fermi surfaces of up and down
spin electrons, which suppresses singlet pairing. Therefore, triplet pairing
occurs at last due to the sub-dominant anisotropic interactions, even in the
absence of magnetic contribution to the pairing interactions.",0011188v3
2000-12-19,Model study for the nonequlibrium magnetic domain structure during the growth of nanostructured ultrathin films,"The nonequilibrium magnetic domain structure of growing ultrathin
ferromagnetic films with a realistic atomic structure is studied as a function
of coverage and temperature. We apply a kinetic Monte Carlo method to a
micromagnetic model describing the transition from superparamagnetic islands at
low coverages to a closed ferromagnetic film. The magnetic relaxation and the
island growth happen simultaneously. Near the percolation threshold a
metastable magnetic domain structure is obtained with an average domain area
ranging between the area of individual magnetic islands and the area of the
large domains observed for thicker ferromagnetic films. We conclude that this
micro-domain structure is controlled and stabilized by the nonuniform atomic
nanostructure of the ultrathin film, causing a random interaction between
magnetic islands with varying sizes and shapes. The average domain area and
domain roughness are determined. A maximum of the domain area and a minimum of
the domain roughness are obtained as a function of the temperature.",0012355v3
2000-12-19,Resistance Spikes at Transitions between Quantum Hall Ferromagnets,"We report a new manifestation of first-order magnetic transitions in
two-dimensional electron systems. This phenomenon occurs in aluminum arsenide
quantum wells with sufficiently low carrier densities and appears as a set of
hysteretic spikes in the resistance of a sample placed in crossed parallel and
perpendicular magnetic fields, each spike occurring at the transition between
states with different partial magnetizations. Our experiments thus indicate
that the presence of magnetic domains at the transition starkly increases
dissipation, an effect also suspected in other ferromagnetic materials.
Analysis of the positions of the transition spikes allows us to deduce the
change in exchange-correlation energy across the magnetic transition, which in
turn will help improve our understanding of metallic ferromagnetism.",0012367v1
2001-01-10,Depairing currents in the superconductor/ferromagnet proximity system Nb/Fe,"We have investigated the behaviour of the depairing current J_{dp} in
ferromagnet/superconductor/ferromagnet (F/S/F) trilayers as function of the
thickness d_s of the superconducting layers. Theoretically, J_{dp} depends on
the superconducting order parameter or the pair density function, which is not
homogeneous across the film due to the proximity effect. We use a proximity
effect model with two parameters (proximity strength and interface
transparency), which can also describe the dependence of the superconducting
transition temperature T_c on d_s. We compare the computations with the
experimentally determined zero-field critical current J_{c0} of small strips
(typically 5~ \mu m wide) of Fe/Nb/Fe trilayers with varying thickness d_{Nb}
of the Nb layer. Near T_c the temperature dependence J_{c0}(T) is in good
agreement with the expected behaviour, which allows extrapolation to T = 0.
Both the absolute values of J_{c0}(0) and the dependence on d_{Nb} agree with
the expectations for the depairing current. We conclude that J_{dp} is
correctly determined, notwithstanding the fact that the strip width is larger
than both the superconducting penetration depth and the superconducting
coherence length, and that J_{dp}(d_s) is correctly described by the model.",0101138v1
2001-01-11,Internal Modes and Magnon Scattering on Topological Solitons in 2d Easy-Axis Ferromagnets,"We study the magnon modes in the presence of a topological soliton in a 2d
Heisenberg easy-axis ferromagnet. The problem of magnon scattering on the
soliton with arbitrary relation between the soliton radius R and the ""magnetic
length"" Delta_0 is investigated for partial modes with different values of the
azimuthal quantum numbers m. Truly local modes are shown to be present for all
values of m, when the soliton radius is enough large. The eigenfrequencies of
such internal modes are calculated analytically on limiting case of a large
soliton radius and numerically for arbitrary soliton radius. It is demonstrated
that the model of an isotropic magnet, which admits an exact analytical
investigation, is not adequate even for the limit of small radius solitons,
R<<Delta_0: there exists a local mode with nonzero frequency. We use the data
about local modes to derive the effective equation of soliton motion; this
equation has the usual Newtonian form in contrast to the case of the easy-plane
ferromagnet. The effective mass of the soliton is found.",0101150v1
2001-01-29,Nanoscale anisotropic structural correlations in the paramagnetic and ferromagnetic phases of Nd0.5Sr0.5 MnO3,"We report x-ray scattering studies of short-range structural correlations and
diffuse scattering in Nd0.5Sr0.5MnO3. On cooling, this material undergoes a
series of transitions, first from a paramagnetic insulating (PI) to a
ferromagnetic metallic (FM) phase, and then to a charge-ordered (CO) insulating
state. Highly anisotropic structural correlations were found in both the PI and
FM states. The correlations increase with decreasing temperature, reaching a
maximum at the CO transition temperature. Below this temperature, they abruptly
collapsed. Single-polaron diffuse scattering was also observed in both the PI
and FM states suggesting that substantial local lattice distortions are present
in these phases. We argue that our measurements indicate that nanoscale regions
exhibiting layered orbital order exist in the paramagnetic and ferromagnetic
phases of Nd0.5Sr0.5MnO3.",0101444v1
2001-01-31,Bulk and Edge excitations in a $ν=1$ quantum Hall ferromagnet,"In this article, we shall focus on the collective dynamics of the fermions in
a $\nu = 1$ quantum Hall droplet. Specifically, we propose to look at the
quantum Hall ferromagnet. In this system, the electron spins are ordered in the
ground state due to the exchange part of the Coulomb interaction and the Pauli
exclusion principle. The low energy excitations are ferromagnetic magnons. To
provide a means for describing these magnons, we shall discuss a method of
introducing collective coordinates in the Hilbert space of many-fermion
systems. These collective coordinates are bosonic in nature. They map a part of
the fermionic Hilbert space into a bosonic Hilbert space. Using this technique,
we shall interpret the magnons as bosonic collective ex citations in the
Hilbert space of the many-electron Hall system. By considering a Hall droplet
of finite extent, we shall also obtain the effective Lagrangian governing the
spin collective excitations at the edge of the sample.",0101475v1
2001-02-01,Enhancement of the Josephson current by an exchange field in superconductor-ferromagnet structures,"We calculate the dc Josephson current for two superconductor-ferromagnet
(S/F) bilayers separated by a thin insulating film. It is demonstrated that the
critical Josephson current $I_{c}$ in the junction strongly depends on the
relative orientation of the effective exchange field $h$ of the bilayers. We
found that in the case of an antiparallel orientation, $I_{c}$ increases at low
temperatures with increasing $h$ and at zero temperature has a singularity when
$h$ equals the superconducting gap $\Delta $. This striking behavior contrasts
suppression of the critical current by the magnetic moments aligned in parallel
and is an interesting new effect of the interplay between superconductors and
ferromagnets.",0102012v1
2001-03-16,Exciton trapping in magnetic wire structures,"The lateral magnetic confinement of quasi two-dimensional excitons into wire
like structures is studied. Spin effects are take into account and two
different magnetic field profiles are considered, which experimentally can be
created by the deposition of a ferromagnetic stripe on a semiconductor quantum
well with magnetization parallel or perpendicular to the grown direction of the
well. We find that it is possible to confine excitons into one-dimensional (1D)
traps. We show that the dependence of the confinement energy on the exciton
wave vector, which is related to its free direction of motion along the wire
direction, is very small. Through the application of a background magnetic
field it is possible to move the position of the trapping region towards the
edge of the ferromagnetic stripe or even underneath the stripe. The exact
position of this 1D exciton channel depends on the strength of the background
magnetic field and on the magnetic polarisation direction of the ferromagnetic
film.",0103362v1
2001-04-03,Magnetic field effects on two-dimensional Kagome lattices,"Magnetic field effects on single-particle energy bands (Hofstadter
butterfly), Hall conductance, flat-band ferromagnetism, and magnetoresistance
of two-dimensional Kagome lattices are studied. The flat-band ferromagnetism is
shown to be broken as the flat-band has finite dispersion in the magnetic
field. A metal-insulator transition induced by the magnetic field (giant
negative magnetoresistance) is predicted. In the half-filled flat band, the
ferromagnetic-paramagnetic transition and the metal-insulator one occur
simultaneously at a magnetic field for strongly interacting electrons. All of
the important magnetic fields effects should be observable in mesoscopic
systems such as quantum dot superlattices.",0104043v1
2001-04-06,Andreev reflection through a quantum dot coupled with two ferromagnets and a superconductor,"We study the Andreev reflection (AR) in a three terminal mesoscopic hybrid
system, in which two ferromagnets (F$_1$ and F$_2$) are coupled to a
superconductor (S) through a quantum dot (QD). By using non-equilibrium Green
function, we derive a general current formula which allows arbitrary spin
polarizations, magnetization orientations and bias voltages in F$_1$ and F$_2$.
The formula is applied to study both zero bias conductance and finite bias
current. The current conducted by crossed AR involving F$_1$, F$_2$ and S is
particularly unusual, in which an electron with spin $\sigma $ incident from
one of the ferromagnets picks up another electron with spin $\bar{\sigma}$ from
the other one, both enter S and form a Cooper pair. Several special cases are
investigated to reveal the properties of AR in this system.",0104103v1
2001-05-03,Magnetic phase separation in ordered alloys,"We present a lattice model to study the equilibrium phase diagram of ordered
alloys with one magnetic component that exhibits a low temperature phase
separation between paramagnetic and ferromagnetic phases. The model is
constructed from the experimental facts observed in Cu$_{3-x}$AlMn$_{x}$ and it
includes coupling between configurational and magnetic degrees of freedom which
are appropriated for reproducing the low temperature miscibility gap. The
essential ingredient for the occurrence of such a coexistence region is the
development of ferromagnetic order induced by the long-range atomic order of
the magnetic component. A comparative study of both mean-field and Monte Carlo
solutions is presented. Moreover, the model may enable the study of the
structure of the ferromagnetic domains embedded in the non-magnetic matrix.
This is relevant in relation to phenomena such as magnetoresistance and
paramagnetism.",0105055v1
2001-05-29,Ferromagnetic transition in a double-exchange system containing impurities,"We study ferromagnetic transition in three-dimensional double-exchange model
containing impurities. The influence of both spin fluctuations and impurity
potential on conduction electrons is described in coherent potential
approximation. In the framework of thermodynamic approach we construct Landau
functional for the system ""electrons (in disordered environment) + core spins"".
Analysing the Landau functional we calculate the temperature of ferromagnetic
transition $T_C$ and paramagnetic susceptibility $\chi$. For $T_C$, we thus
extend the result obtained by Furukawa in the framework of the Dynamical Mean
Field Approximation, with which our result coincides in the limit of zero
inpurity potential. We find, that the alloy disorder, able to produce a gap in
density of electron states, can substantially decrease $T_C$ with respect to
the case of no impurities.",0105550v2
2001-05-31,Microscopic Functional Integral Theory of Quantum Fluctuations in Double-Layer Quantum Hall Ferromagnets,"We present a microscopic theory of zero-temperature order parameter and
pseudospin stiffness reduction due to quantum fluctuations in the ground state
of double-layer quantum Hall ferromagnets. Collective excitations in this
systems are properly described only when interactions in both direct and
exchange particle-hole channels are included. We employ a functional integral
approach which is able to account for both, and comment on its relation to
diagrammatic perturbation theory. We also discuss its relation to Gaussian
fluctuation approximations based on Hubbard-Stratonovich-transformation
representations of interactions in ferromagnets and superconductors. We derive
remarkably simple analytical expressions for the correlation energy,
renormalized order parameter and renormalized pseudospin stiffness.",0105620v1
2001-05-31,Bulk and edge excitations of a $ν=1$ Hall ferromagnet,"In this article, we shall focus on the collective dynamics of the fermions in
a $\nu = 1$ quantum Hall droplet. Specifically, we propose to look at the
quantum Hall ferromagnet. In this system, the electron spins are ordered in the
ground state due to the exchange part of the Coulomb interaction and the Pauli
exclusion principle. The low energy excitations are ferromagnetic magnons. In
order to obtain an effective Lagrangian for these magnons, we shall introduce
bosonic collective coordinates in the Hilbert space of many-fermion systems.
These collective coordinates describe a part of the fermionic Hilbert space.
Using this technique, we shall interpret the magnons as bosonic collective
excitations in the Hilbert space of the many-electron Hall system. Furthermore,
by considering a Hall droplet of finite extent, we shall also obtain the
effective Lagrangian governing the spin collective excitations at the edge of
the sample.",0105626v1
2001-06-03,Ferromagnetic transition in a double-exchange system with alloy disorder,"We study ferromagnetic transition in three-dimensional double-exchange model
containing impurities. The influence of both spin fluctuations and impurity
potential on conduction electrons is described in coherent potential
approximation. In the framework of thermodynamic approach we construct Landau
functional for the system ""electrons (in disordered environment) + core spins"".
Analyzing the Landau functional we calculate the temperature of ferromagnetic
transition $T_C$ and paramagnetic susceptibility $\chi$. For $T_C$, we thus
extend the result obtained by Furukawa in the framework of the Dynamical Mean
Field Approximation, with which our result coincides in the limit of zero
impurity potential. We find, that the alloy disorder, able to produce a gap in
density of electron states, can substantially decrease $T_C$ with respect to
the case of no impurities. We also study the general relation between the
Coherent Potential Approximation and the Dynamical Mean Field Approximation.",0106032v1
2001-06-22,Phase Transitions in Non-extensive Spin Systems,"The spherical spin model with infinite-range ferromagnetic interactions is
investigated analytically in the framework of non-extensive thermostatics
generalizing the Boltzmann-Gibbs statistical mechanics. We show that for
repulsive correlations, a new weak-ferromagnetic phase develops. There is a
tricritical point separating para, weak-ferro and ferro regimes. The transition
from paramagnetic to weak-ferromagnetic phase is an unusual first order phase
transition in which a discontinuity of the averaged order parameter appears,
even for finite number of spins. This result puts in a new way the question of
the stability of critical phenomena with respect to the long-ranged
correlations.",0106460v2
2001-06-26,"A theory of ferromagnetism in planar heterostructures of (Mn,III)-V semiconductors","A density functional theory of ferromagnetism in heterostructures of compound
semiconductors doped with magnetic impurities is presented. The variable
functions in the density functional theory are the charge and spin densities of
the itinerant carriers and the charge and localized spins of the impurities.
The theory is applied to study the Curie temperature of planar heterostructures
of III-V semiconductors doped with manganese atoms. The mean-field,
virtual-crystal and effective-mass approximations are adopted to calculate the
electronic structure, including the spin-orbit interaction, and the magnetic
susceptibilities, leading to the Curie temperature. By means of these results,
we attempt to understand the observed dependence of the Curie temperature of
planar $\delta$-doped ferromagnetic structures on variation of their
properties. We predict a large increase of the Curie Temperature by additional
confinement of the holes in a $\delta$-doped layer of Mn by a quantum well.",0106548v2
2001-07-02,On the way to a Gutzwiller density functional theory,"Multi-band Gutzwiller-correlated wave functions reconcile the contrasting
concepts of itinerant band electrons versus electrons localized in partially
filled atomic shells. The exact evaluation of these variational ground states
in the limit of large coordination number allows the identification of
quasi-particle band structures, and the calculation of a variational spinwave
dispersion. The study of a generic two-band model elucidates the co-operation
of the Coulomb repulsion and the Hund's-rule exchange for itinerant
ferromagnetism. We present results of calculations for ferromagnetic nickel,
using a realistic 18 spin-orbital basis of $4s$, $4p$ and $3d$ valence
electrons. The quasi-particle energy bands agree much better with the
photo-emission and Fermi surface data than the band structure obtained from
spin-density functional theory (SDFT).",0107033v1
2001-08-01,Decorating Random Quadrangulations,"On various regular lattices (simple cubic, body centred cubic..) decorating
an edge with an Ising spin coupled by bonds of strength L to the original
vertex spins and competing with a direct anti-ferromagnetic bond of strength
alpha L can give rise to three transition temperatures for suitable alpha. The
system passes through ferromagnetic, paramagnetic, anti-ferromagnetic and
paramagnetic phases respectively as the temperature is increased.
  For the square lattice on the other hand multiple decoration is required to
see this effect. We note here that a single decoration suffices for the Ising
model on planar random quadrangulations (coupled to 2D quantum gravity). Other
random bipartite lattices such as the Penrose tiling are more akin to the
regular square lattice and require multiple decoration to have any affect.",0108010v1
2001-08-09,"Molecular Beam Epitaxy of Wurtzite (Ga,Mn)N Films on Sapphire(0001) Showing the Ferromagnetic Behaviour at Room Temperature","Wurtzite (Ga,Mn)N films showing ferromagnetic behaviour at room temperature
were successfully grown on sapphire(0001) substrates by molecular beam epitaxy
using ammonia as nitrogen source. Magnetization measurements were carried out
by a superconducting quantum interference device at the temperatures between
1.8K and 300K with magnetic field applied parallel to the film plane up to 7T.
The magnetic-field dependence of magnetization of a (Ga,Mn)N film at 300K were
ferromagnetic, while a GaN film showed Pauli paramagnetism like behaviour. The
Curie temperatures of a (Ga,Mn)N film was estimated as 940K.",0108159v1
2001-08-15,Evolution of the Magnetic Ground State in the Electron-Doped Antiferromagnet CaMnO$_3$,"Measurements of the specific heat on the system Ca$_{1-x}$La$_{x}$MnO$_{3}$
(% $x\leq 0.10$) are reported. Particular attention is paid to the effect that
doping the parent compound with electrons by substitution of La for Ca has on
the magnetic ground state. The high ($T>40$ K) temperature data reveals that
doping decreases $T_{N}$ from 122 K for the undoped sample to 103 K for
$x=0.10$. The low temperature ($T<20$ K) heat capacity data is consistent with
phase separation. The undoped sample displays a finite density of states and
typical antiferromagnetic behavior. The addition of electrons in the $x\leq
0.03$ samples creates local ferromagnetism as evidenced by a decreased
intermanl field and the need to add a ferromagnetic component to the heat
capacity data for $x=0.03$. Further substitution enhances the ferromagnetism as
evidenced by the formation of a long range spin density wave.",0108239v3
2001-08-23,Theory of High \tc Ferromagnetism in $SrB_6$ family: A case of Doped Spin-1 Mott insulator in a Valence Bond Solid Phase,"Doped divalent hexaborides such as $Sr_{1-x}La_xB_6$ exhibit high \tc
ferromagnetism. We isolate a degenerate pair of $2p$-orbitals of boron with two
valence electrons, invoke electron correlation and Hund coupling, to suggest
that the undoped state is better viewed as a spin-1 Mott insulator; it is
predicted to be a type of 3d Haldane gap phase with a spin gap $\sim 0.1 eV$,
much smaller than the charge gap of $ > 1.0 eV$ seen in ARPES. The
experimentally seen high \tc `ferromagnetism' is argued to be a complex
magnetic order in disguise - either a canted 6-sublattice AFM ($\approx 120^0$)
order or its quantum melted version, a chiral spin liquid state, arising from a
type of double exchange mechanism.",0108384v3
2001-08-27,Superconductivity and Quantum Phase Transitions in Weak Itinerant Ferromagnets,"It is argued that the phase transition in low-T_c clean itinerant
ferromagnets is generically of first order, due to correlation effects that
lead to a nonanalytic term in the free energy. A tricritical point separates
the line of first order transitions from Heisenberg critical behavior at higher
temperatures. Sufficiently strong quenched disorder suppresses the first order
transition via the appearance of a critical endpoint. A semi-quantitative
discussion is given in terms of recent experiments on MnSi and UGe_2. It is
then shown that the critical temperature for spin-triplet, p-wave
superconductivity mediated by spin fluctuations is generically much higher in a
Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling
of magnons to the longitudinal magnetic susceptibility. This qualitatively
explains the phase diagram recently observed in UGe_2 and ZrZn_2.",0108443v1
2001-09-18,"Spin textures, screening and excitations in dirty quantum Hall ferromagnets","We study quantum Hall ferromagnets in the presence of a random electrostatic
impurity potential. Describing these systems with a classical non-linear sigma
model and using analytical estimates supported by results from numerical
simulations, we examine the nature of the ground state as a function of
disorder strength, $\Delta$, and deviation, $\delta \nu$, of the average Landau
level filling factor from unity. Screening of an impurity potential requires
distortions of the spin configuration, and in the absence of Zeeman coupling
there is a disorder-driven, zero-temperature phase transition from a
ferromagnet at small $\Delta$ and $|\delta \nu|$ to a spin glass at larger
$\Delta$ or $|\delta \nu|$. We examine ground-state response functions and
excitations.",0109326v1
2001-10-22,Charge current in ferromagnet-superconductor junction with pairing state of broken time-reversal symmetry,"We calculate the tunneling conductance spectra of a ferromagnetic
metal/insulator/superconductor using the Blonder-Tinkham-Klapwijk (BTK)
formulation. Two possible states for the superconductor are considered with the
time reversal symmetry ($\cal{T}$) broken, i.e., $d_{x^2-y^2}+is$, or
$d_{x^2-y^2}+id_{xy}$. In both cases the tunneling conductance within the gap
is suppressed with the increase of the exchange interaction due to the
suppression of the Andreev reflection. In the $(d_{x^2-y^2}+is)$-wave case the
peaks that exist when the ferromagnet is a normal metal in the amplitude of the
s-wave component due to the bound state formation are reduced symmetrically,
with the increase of the exchange field, while in the
$(d_{x^2-y^2}+id_{xy})$-wave case the residual density of states within the gap
develops a dip around E=0 with the increase of the exchange field. These
results would be useful to discriminate between $\cal{T}$-broken pairing states
near the surface in high-$T_c$ superconductors",0110483v1
2001-11-09,Inhomogeneous superconductivity induced in a weak ferromagnet,"Under certain conditions, the order parameter induced by a superconductor (S)
in a ferromagnet (F) can be inhomogeneous and oscillating, which results e.g.
in the so-called pi-coupling in S/F/S junctions. In principle, the
inhomogeneous state can be induced at T_c as function of the F-layer thickness
d_F in S/F bilayers and multilayers, which should result in a dip-like
characteristic of T_c(d_F). We show the results of measurements on the S/F
system Nb/Cu_{1-x}Ni_x, for Ni-concentrations in the range x = 0.5-0.7, where
such effects might be expected. We find that the critical thickness for the
occurrence of superconductivity is still relatively high, even for these weak
ferromagnets. The resulting dip then is intrinsically shallow and difficult to
observe, which explains the lack of a clear signature in the T_c(d_F) data.",0111178v1
2001-11-14,Enhancement of magnetic ordering by the stress fields of grain boundaries in ferromagnets,"In the paper we predict a distinctive change of magnetic properties and
considerable increase of the Curie temperature caused by the strain fields of
grain boundaries in ferromagnetic films. It is shown that a sheet of
spontaneous magnetization may arise along a grain boundary at temperatures
greater than the bulk Curie temperature. The temperature dependence and space
distribution of magnetization in a ferromagnetic film with grain boundaries are
calculated. We found that $45^\circ$ grain boundaries can produce long-range
strain fields that results in the width of the magnetic sheet along the
boundary of the order of $ 0.5 \div 1 \mu m$ at temperatures grater than the
bulk Curie temperature by about $10^2$ K.",0111252v1
2001-11-24,"Influence of quantum confinement on the ferromagnetism of (Ga,Mn)As diluted magnetic semiconductor","We investigate the effect of quantum confinement on the ferromagnetism of
diluted magnetic semiconductor Ga$_{1-x}$Mn$_x$As using a combination of
tight-binding and density functional methods. We observe strong majority-spin
Mn $d$-As $p$ hybridization, as well as half metallic behavior, down to sizes
as small as 20 \AA in diameter. Below this critical size, the doped holes are
self-trapped by the Mn-sites, signalling both valence and electronic
transitions. Our results imply that magnetically doped III-V nanoparticles will
provide a medium for manipulating the electronic structure of dilute magnetic
semiconductors while conserving the ferromagnetic properties and even enhancing
it in certain size regime.",0111475v1
2001-11-26,Bound Magnetic Polaron Interactions in Insulating Doped Diluted Magnetic Semiconductors,"The magnetic behavior of insulating doped diluted magnetic semiconductors
(DMS) is characterized by the interaction of large collective spins known as
bound magnetic polarons. Experimental measurements of the susceptibility of
these materials have suggested that the polaron-polaron interaction is
ferromagnetic, in contrast to the antiferromagnetic carrier-carrier
interactions that are characteristic of nonmagnetic semiconductors. To explain
this behavior, a model has been developed in which polarons interact via both
the standard direct carrier-carrier exchange interaction (due to virtual
carrier hopping) and an indirect carrier-ion-carrier exchange interaction (due
to the interactions of polarons with magnetic ions in an interstitial region).
Using a variational procedure, the optimal values of the model parameters were
determined as a function of temperature. At temperatures of interest, the
parameters describing polaron-polaron interactions were found to be nearly
temperature-independent. For reasonable values of these constant parameters, we
find that indirect ferromagnetic interactions can dominate the direct
antiferromagnetic interactions and cause the polarons to align. This result
supports the experimental evidence for ferromagnetism in insulating doped DMS.",0111497v1
2001-11-27,Light and electric field control of ferromagnetism in magnetic quantum structures,"A strong influence of illumination and electric bias on the Curie temperature
and saturation value of the magnetization is demonstrated for semiconductor
structures containing a modulation-doped p-type Cd0.96Mn0.04Te quantum well
placed in various built-in electric fields. It is shown that both light beam
and bias voltage generate an isothermal and reversible cross-over between the
paramagnetic and ferromagnetic phases, in the way that is predetermined by the
structure design. The observed behavior is in quantitative agreement with the
expectations for systems, in which ferromagnetic interactions are mediated by
the weakly disordered two-dimensional hole liquid.",0111511v2
2001-12-07,Induced Ferromagnetism and Colossal Magnetoresistance by Ir-Doping in Pr1-xCaxMnO3,"The doping of the manganese site by iridium (up to 15%) in the small A cation
manganites Pr_{1-x}Ca_xMnO_3 (0.4 < x < 0.8), has been investigated as a new
method to suppress charge-ordering and induce CMR effects. Ir doping leads to
ferromagnetism and to insulator to metal transitions, with high transition
temperatures reaching 180K and CMR ratio in 7T as large as 10^4. The efficiency
with which iridium induces ferromagnetism and CMR is compared to previous
results obtained with other substitutions (Ru, Rh, Ni, Cr, ...). The ionic
radius of the foreign cations and their mixed-valencies are found to be the
main parameters governing the ability to collapse the charge-ordered state.",0112118v1
2001-12-10,Unusual magneto-elastic forces stabilize the insulating ferromagnetic state of manganites: the La(0.8)Ca(0.2)$MnO(3) case,"The ferromagnetic and insulating state observed in La$_{1-x}$Ca$_{x}$MnO$_3$,
0.125$<$x$<$0.2, is characterized by structural and magnetic anomalies below
T$_C$, similar to those observed in the x$_{Sr}$$\approx$1/8. A neutron
scattering study of the superlattice {\bf Q$_0$}= (0,0,1+/4)$_{cub}$ peak, and
of the magnetic excitations are reported in the x$_{Ca}$=0.2 sample. The
occurrence of this superstructure is associated with the observation of a gap
in the spin dynamics, at a {\bf q$_0$} wave-vector ({\bf q$_0$}={\bf
Q$_0$}-$\tau$) with the same modulus $|${\bf q$_0$}$|$ in all directions, which
divides the dispersion into two regimes. For $|${\bf q}$|$$<$$|${\bf q$_0$}$|$
the dispersion is splitted into two or three curves. For $|${\bf
q}$|$$>$$|${\bf q$_0$}$|$, magnetic excitations lock on acoustic and optic
phonon energies, revealing a new kind of magneto-vibrational coupling.
  We suggest an analysis in terms of two distinct magnetic couplings,
associated with two ferromagnetic media involved into a collective state.",0112159v1
2001-12-13,Ferromagnetism of $^3$He Films in the Low Field Limit,"We provide evidence for a finite temperature ferromagnetic transition in
2-dimensions as $H \to 0$ in thin films of $^3$He on graphite, a model system
for the study of two-dimensional magnetism. We perform pulsed and CW NMR
experiments at fields of 0.03 - 0.48 mT on $^3$He at areal densities of 20.5 -
24.2 atoms/nm$^2$. At these densities, the second layer of $^3$He has a
strongly ferromagnetic tendency. With decreasing temperature, we find a rapid
onset of magnetization that becomes independent of the applied field at
temperatures in the vicinity of 1 mK. Both the dipolar field and the NMR
linewidth grow rapidly as well, which is consistent with a large (order unity)
polarization of the $^3$He spins.",0112237v1
2001-12-14,Ferromagnetic GaMnAs/GaAs superlattices - MBE growth and magnetic properties,"We have studied the magnetic properties of (GaMnAs)m/(GaAs)n superlattices
with magnetic GaMnAs layers of thickness between 8 and 16 molecular layers (ML)
(23-45 \AA), and with nonmagnetic GaAs spacers from 4 ML to 10 ML (11-28 \AA).
While previous reports state that GaMnAs layers thinner than 50 \AA are
paramagnetic in the whole Mn composition range achievable using MBE growth (up
to 8% Mn), we have found that short period superlattices exhibit a
paramagnetic-to-ferromagnetic phase transition with a transition temperature
which depends on both the thickness of the magnetic GaMnAs layer and the
nonmagnetic GaAs spacer. The neutron scattering experiments have shown that the
magnetic layers in superlattices are ferromagnetically coupled for both thin
(below 50 \AA) and thick (above 50 \AA) GaMnAs layers.",0112264v1
2002-01-16,Ferromagnetic semiconductors,"The current status and prospects of research on ferromagnetism in
semiconductors are reviewed. The question of the origin of ferromagnetism in
europium chalcogenides, chromium spinels and, particularly, in diluted magnetic
semiconductors is addressed. The nature of electronic states derived from 3d of
magnetic impurities is discussed in some details. Results of a quantitative
comparison between experimental and theoretical results, notably for Mn-based
III-V and II-VI compounds, are presented. This comparison demonstrates that the
current theory of the exchange interactions mediated by holes in the valence
band describes correctly the values of Curie temperatures T_C magnetic
anisotropy, domain structure, and magnetic circular dichroism. On this basis,
chemical trends are examined and show to lead to the prediction of
semiconductor systems with T_C that may exceed room temperature, an expectation
that are being confirmed by recent findings. Results for materials containing
magnetic ions other than Mn are also presented emphasizing that the double
exchange involving hoping through d states may operate in those systems.",0201282v1
2002-01-26,"Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga, Mn)P:C","Ion implantation of Mn ions into hole-doped GaP has been used to induce
ferromagnetic behavior above room temperature for optimized Mn concentrations
near 3 at.%. The magnetism is suppressed when the Mn dose is increased or
decreased away from the 3 at.% value, or when n-type GaP substrates are used.
At low temperatures the saturated moment is on the order of one Bohr magneton,
and the spin wave stiffness inferred from the Bloch-law T^3/2 dependence of the
magnetization provides an estimate Tc = 385K of the Curie temperature that
exceeds the experimental value, Tc = 270K. The presence of ferromagnetic
clusters and hysteresis to temperatures of at least 330K is attributed to
disorder and proximity to a metal-insulating transition.",0201492v1
2002-02-05,Ferromagnetism and giant magnetoresistance in the rare earth fullerides Eu6-xSrxC60,"We have studied crystal structure, magnetism and electric transport
properties of a europium fulleride Eu6C60 and its Sr-substituted compounds,
Eu6-xSrxC60. They have a bcc structure, which is an isostructure of other M6C60
(M represents an alkali atom or an alkaline earth atom). Magnetic measurements
revealed that magnetic moment is ascribed to the divalent europium atom with S
= 7/2 spin, and a ferromagnetic transition was observed at TC = 10 - 14 K. In
Eu6C60, we also confirm the ferromagnetic transition by heat capacity
measurement. The striking feature in Eu6-xSrxC60} is very large negative
magnetoresistance at low temperature; the resistivity ratio \rho(H = 9
T)/\rho(H = 0 T) reaches almost 10^{-3} at 1 K in Eu6C60. Such large
magnetoresistance is the manifestation of a strong pi-f interaction between
conduction carriers on C60 and 4f electrons of Eu.",0202066v1
2002-03-06,"Aging, rejuvenation and memory effects in re-entrant ferromagnets","We have studied the slow dynamics of the ferromagnetic phases of the
re-entrant CdCr_{2x}In_{2-2x}S_4 system for 0.85<x<=1 by means of low frequency
ac susceptibility and magnetization measurements. Experimental procedures
widely used in the investigation of the out-of-equilibrium dynamics of spin
glasses (such as the x=0.85 compound) have been applied to search for aging,
rejuvenation and memory effects, and to test their dependence on the disorder
introduced by dilution of the magnetic ions. Whereas the rejuvenation effect is
found in all studied samples, the memory effect is clearly enhanced for
increasing dilutions. The results support a description of aging in both
ferromagnetic and re-entrant spin-glass phases in terms of hierarchical
reconformations of domain walls pinned by the disorder.",0203132v2
2002-03-10,Impurity Effect on Ferromagnetic Transition in Double-Exchange Systems,"Effect of randomness in the double-exchange model is studied. Large
fluctuations and spatial random distribution of impurities are taken into
account in an essentially exact manner by using the Monte Carlo calculation.
The randomness suppresses the ferromagnetism by reducing the coherence of
itinerant electrons. The suppression is significant in the critical region
where the fluctuations are dominant. Temperature dependences of the
magnetization are estimated for finite-size clusters. A characteristic
temperature for phase transition $T^{*}$ is estimated from the inflection
point, which is expected to give a good approximation for the critical
temperature in the thermodynamic limit. Our results suggest that the
ferromagnetism becomes unstable more rapidly than predicted in the previous
theoretical results by the coherent-potential approximation.",0203213v1
2002-03-12,Magnetoresistances observed by decomposition of the magnetic moment in La1-xCaxMnO3 films,"A ferromagnetic phase, characterized by electron carriers and a high
temperature colossal magnetoresistance (HTCMR) dependent on the magnetic
moment, and a semiconducting phase, characterized by hole carriers and a low
temperature CMR (LTCMR), are observed in La$_{1-x}$Ca$_{x}$MnO$_3$ thin films
by the van der Pauw method. The LTCMR is much more sensitive to the magnetic
field than the HTCMR. In the ferromagnetic phase for films with anisotropic
moments in two dimensions, a remnant resistivity of the order of 10$^{-8}
\~{\Omega}m$ is observed up to 100 K and increases exponentially with both a
temperature up to $T_c$ and a magnetic field above one Tesla (a positive
magnetoresistivity). We found that the ferromagnetic phase below $T_c$ is in a
polaronic state with a polaronic mobile conduction, and the carrier density
dips near $T_c$. For resistances measured by the four-probe method with line
electrodes, low temperature information of the HTCMR is not revealed. The van
der Pauw method is more effective for the resistance measurement of a magnetic
material than the four-probe method.",0203245v2
2002-03-14,Using a hybrid superconducting-ferromagnetic tip as a magnetic scanning tunneling microscope,"Approaching a two-component tip made of a superconductor (S) and a
ferromagnet (F) from a magnetic sample allows for two distinct tunneling
processes between the ferromagnets, through S: i) Charge and spin are
conserved; ii) Charge and spin are reversed, e.g. a Cooper pair flows from S,
one electron going into F, the other into the sample. At subgap voltages, this
allows two currents to flow from the tip : one is insensitive to the spin
polarizations and allows for surface topography, the other directly tracks the
relative spin polarizations of F and the sample. The whole device acts as a STM
sensitive to the spin polarization at the Fermi level (MSTM). Its sensitivity
is studied and optimized with respect to the tip geometry.",0203311v1
2002-03-24,Global versus Local Ferromagnetism in a Model for Diluted Magnetic Semiconductors Studied with Monte Carlo Techniques,"A model recently introduced for diluted magnetic semiconductors by Berciu and
Bhatt (PRL 87, 107203 (2001)) is studied with a Monte Carlo technique, and the
results are compared to Hartree-Fock calculations. For doping rates close to
the experimentally observed metal-insulator transition, a picture dominated by
ferromagnetic droplets formed below a T* scale emerges. The moments of these
droplets align as the temperature is lowered below a critical value Tc<T*. Our
Monte Carlo investigations provide critical temperatures considerably smaller
than Hartree-Fock predictions. Disorder does not seem to enhance ferromagnetism
substantially. The inhomogeneous droplet state should be strongly susceptible
to changes in doping and external fields.",0203493v2
2002-03-29,Coexistence of superconductivity and ferromagnetism in the graphite-sulfur system,"Superconducting characteristics such as the Meissner-Ochsenfeld state,
screening supercurrents and hysteresis loops of type-II superconductors were
observed from the temperature and magnetic field dependences of the magnetic
moment, m(T, H), in graphite powders reacted with sulfur for temperatures below
9.0 K. The temperature dependence of the lower critical field Hc1(T) was
determined and the zero-temperature penetration depth, lambda(0), was estimated
(lambda (0) = 227 nm). The superconductivity was observed to be highly
anisotropic and to coexist with a ferromagnetic state that has a Curie
temperature well above room temperature. A continuous transition from the
superconducting state to the ferromagnetic state could be achieved by simply
increasing the applied magnetic field.",0204006v1
2002-04-11,"Saturated Ferromagnetism and Magnetization Deficit in Optimally Annealed (Ga,Mn)As Epilayers","We examine the Mn concentration dependence of the electronic and magnetic
properties of optimally annealed Ga1-xMnxAs epilayers for 1.35% < x < 8.3%. The
Curie temperature (Tc), conductivity, and exchange energy increase with Mn
concentration up to x ~ 0.05, but are almost constant for larger x, with Tc ~
110 K. The ferromagnetic moment per Mn ion decreases monotonically with
increasing x, implying that an increasing fraction of the Mn spins do not
participate in the ferromagnetism. By contrast, the derived domain wall
thickness, an important parameter for device design, remains surprisingly
constant.",0204250v1
2002-05-06,Itinerant Ferromagnetism and Quantum Criticality in Sc$_3$In,"The electronic structure and magnetic properties of hexagonal Sc$_3$In are
calculated within density functional theory. We find that the Fermi energy lies
in a region of flat Sc $d$ derived bands leading to a peak in the density of
states and Stoner ferromagnetism. The calculated local spin density and
generalized gradient approximation spin magnetizations are both enhanced with
respect to experiment, which is an indication of significant quantum critical
fluctuations, neglected in these approximations. We find, as expected, that the
ferromagnetism is initially enhanced under pressure, meaning that the critical
point cannot be reached with modest pressure. However, we find that the density
of states peak around the Fermi energy and the calculated density functional
magnetic properties are sensitive to the $c/a$ ratio, so that the quantum
critical point may be reached under uniaxial strain.",0205103v1
2002-05-14,Ising Quantum Hall Ferromagnet in Magnetically Doped Quantum Wells,"We report on the observation of the Ising quantum Hall ferromagnet with Curie
temperature $T_C$ as high as 2 K in a modulation-doped (Cd,Mn)Te
heterostructure. In this system field-induced crossing of Landau levels occurs
due to the giant spin-splitting effect. Magnetoresistance data, collected over
a wide range of temperatures, magnetic fields, tilt angles, and electron
densities, are discussed taking into account both Coulomb electron-electron
interactions and s$-$d coupling to Mn spin fluctuations. The critical behavior
of the resistance ``spikes'' at $T \to T_C$ corroborates theoretical
suggestions that the ferromagnet is destroyed by domain excitations.",0205296v3
2002-05-15,Insulating Ferromagnetism in La$_{4}$Ba$_{2}$Cu$_{2}$O$_{10}$: an \textit{Ab Initio} Wannier Function Analysis,"Microscopic mechanisms of the puzzling insulating ferromagnetism of
half-filled La$_{4}$Ba$_{2}$Cu$_{2}$O$_{10}$ are elucidated with
energy-resolved Wannier states. The dominant magnetic coupling, revealed
through evaluated parameters ($t$, $U$, and $J$), turns out to be the intersite
direct exchange, a currently ignored mechanism that overwhelms the
antiferromagnetic superexchange. By contrast, the isostructural
Nd$_{4}$Ba$_{2}$Cu$_{2}$O$_{10}$ develops the observed antiferromagnetic order
via its characteristics of a 1D chain. Surprisingly, the in-plane order of both
cases is \textit{not} controlled by coupling between nearest neighbors. An
intriguing pressure-induced ferromagnetic to antiferromagnetic transition is
predicted.",0205300v1
2002-05-28,Magnetic properties of alpha-iron(II) phthalocyanine,"We report on the magnetic properties of the supra-molecular compound iron(II)
phthalocyanine in its alpha-form. dc- and ac-susceptometry measurements and
Mossbauer experiments show that the iron atoms are strongly magnetically
coupled into ferromagnetic Ising chains with very weak antiferromagnetic
interchain coupling. The transition to 3D magnetic ordering below 10 K is
hindered by the presence of impurities or other defects, by which the
domain-wall arrangements along individual chains become gradually
blocked/frozen, leading to a disordered 3D distribution of ferromagnetic chain
segments. Below 5 K, field-cooled and zero-field-cooled magnetization
measurements show strong irreversible behavior, attributed to pinning of the
domain-walls by the randomly distributed defects in combination with the
interchain coupling. High-field magnetization experiments reveal a canted
arrangement of the moments in adjacent ferromagnetic chains.",0205587v1
2002-05-28,"Ferromagnetism in (In,Mn)As Diluted Magnetic Semiconductor Thin Films Grown by Metalorganic Vapor Phase Epitaxy","In1-xMnxAs diluted magnetic semiconductor (DMS) thin films have been grown
using metalorganic vapor phase epitaxy (MOVPE).
Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source.
Nominally single-phase, epitaxial films were achieved with Mn content as high
as x=0.14 using growth temperatures Tg>475 C. For lower growth temperatures and
higher Mn concentrations, nanometer scale MnAs precipitates were detected
within the In1-xMnxAs matrix. Magnetic properties of the films were
investigated using a superconducting quantum interference device (SQUID)
magnetometer. Room-temperature ferromagnetic order was observed in a sample
with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K
and a room-temperature saturation magnetization of 49 emu/cm^3. The remnant
magnetization and the coercive field were small, with values of 10 emu/cm^3 and
400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is
discussed in light of the recent theory based on the formation of small
clusters of a few magnetic atoms.",0205602v1
2002-06-04,Magnetization plateaus in the ferromagnetic-ferromagnetic-antiferromagnetic Ising chain,"The Ising chain consisting of the antiferromagneticaly coupled ferromagnetic
trimer is considered in the external magnetic field. In the framework of the
transfer-matrix formalism the thermodynamics of the system is described. The
magnetization per site (m) is obtained as the explicit function of the external
magnetic field (H). The corresponding plots of m(H) are drawn. Two
qualitatively different regions of the values of coupling constants are
established: weak antiferromagnetic coupling (J_A<3J_F) and the strong
antiferromagnetic coupling $(J_A\geq3J_F)$. For the latter case the
magnetization curve with plateau at $m/m_{sat}=1/3$ is obtained. It is proven
that the plateau is caused by the stability of spatially modulated spin
structure <3111>. The values of magnetic field determining the width of the
plateau are obtained in the limit of zero temperature.",0206036v1
2002-06-19,"Ferromagnetism and interlayer exchange coupling in short period (Ga,Mn)As/GaAs superlattices","Magnetic properties of (Ga,Mn)As/GaAs superlattices are investigated. The
structures contain magnetic (Ga,Mn)As layers, separated by thin layers of
non-magnetic GaAs spacer. The short period Ga$_{0.93}$Mn$_{0.07}$As/GaAs
superlattices exhibit a paramagnetic-to-ferromagnetic phase transition close to
60K, for thicknesses of (Ga,Mn)As down to 23 \AA. For
Ga$_{0.96}$Mn$_{0.04}$As/GaAs superlattices of similar dimensions, the Curie
temperature associated with the ferromagnetic transition is found to oscillate
with the thickness of non magnetic spacer. The observed oscillations are
related to an interlayer exchange interaction mediated by the polarized holes
of the (Ga,Mn)As layers.",0206380v1
2002-07-04,Spin Polarized Current in the Ground State of Superconductor - Ferromagnet - Insulator Trilayers,"We study the ground state properties of a superconductor - ferromagnet -
insulator trilayer on the basis of a Hubbard Model featuring exchange splitting
in the ferromagnet and electron - electron attraction in the superconductor. We
solve the spin - polarized Hartree - Fock - Gorkov equations together with the
Maxwell's equation (Ampere's law) fully self-consistently. For certain values
of the exchange splitting we find that a spontaneous spin polarized current is
generated in the ground state and is intimately related to Andreev bound states
at the Fermi level. Moreover, the polarization of the current strongly depends
on the band filling.",0207135v1
2002-07-10,p-Type doping of II-VI heterostructures from surface states: application to ferromagnetic Cd$_{1-x}$Mn$_x$Te quantum wells,"We present a study of p-type doping of CdTe and Cd$_{1-x}$Mn$_x$Te quantum
wells from surface states. We show that this method is as efficient as usual
modulation doping with nitrogen acceptors, and leads to hole densities
exceeding $2 \times 10^{11}$ cm$^{-2}$. Surface doping was successfully applied
to obtain carrier-induced ferromagnetism in a Cd$_{1-x}$Mn$_x$Te quantum well.
The observed temperature dependence of photoluminescence spectra, and the
critical temperature, correspond well to those previously reported for
ferromagnetic quantum wells doped with nitrogen.",0207259v2
2002-07-19,"Crystal structure, superconductivity and magnetic properties of the superconducting ferromagnets Gd1.4-xDyxCe0.6Sr2RuCu2O10 (x=0 - 0.6)","The structural, electrical and magnetic properties of the superconducting
ferromagnets, Gd1.4-xDyxCe0.6Sr2RuCu2O10 (x=0-0.6) are systematically
investigated as a function of Dy doping and temperature. These compounds are
characterised by high temperature superconductivity (Tc ranging from 20-40 K
depending upon the Dy content) coexisting with weak ferromagnetism with two
magnetic transitions (TM2 ranging from 95-106 K and TM1 around 120 K). Doping
with Dy gives no significant structural changes except for a minor change in
the c/a ratio. However the superconducting transition temperature is
significantly suppressed and magnetic ordering temperature enhanced on Dy
doping. These effects are described and discussed.",0207478v1
2002-08-05,Coreless vortex ground state of the rotating spinor condensate,"We study the ground state of the rotating spinor condensate and show that for
slow rotation the ground state of the ferromagnetic spinor condensate is a
coreless vortex. While coreless vortex is not topologically stable, we show
that there is an energetic threshold for the creation of a coreless vortex.
This threshold corresponds to a critical rotation frequency that vanishes as
the system size increases. Also, we demonstrate the dramatically different
behavior of the spinor condensate with anti-ferromagnetic interactions. For
anti-ferromagnetic spinor condensate the angular momentum as a function of
rotation frequency exhibits the familiar staircase behavior, but in contrast to
an ordinary condensate the first step is to the state with angular momentum 1/2
per particle.",0208078v2
2002-08-06,Dipolar interaction between two-dimensional magnetic particles,"We determine the effective dipolar interaction between single domain
two-dimensional ferromagnetic particles (islands or dots), taking into account
their finite size. The first correction term decays as 1/D^5, where D is the
distance between particles. If the particles are arranged in a regular
two-dimensional array and are magnetized in plane, we show that the correction
term reinforces the antiferromagnetic character of the ground state in a square
lattice, and the ferromagnetic one in a triangular lattice. We also determine
the dipolar spin-wave spectrum and evaluate how the Curie temperature of an
ensemble of magnetic particles scales with the parameters defining the particle
array: height and size of each particle, and interparticle distance. Our
results show that dipolar coupling between particles might induce ferromagnetic
long range order at experimentally relevant temperatures. However, depending on
the size of the particles, such a collective phenomenon may be disguised by
superparamagnetism.",0208097v1
2002-08-06,Pressure dependence of the magnetization in the ferromagnetic superconductor UGe_2,"The recent discovery that superconductivity occurs in several clean itinerant
ferromagnets close to low temperature magnetic instabilities naturally invites
an interpretation based on a proximity to quantum criticality. Here we report
measurements of the pressure dependence of the low temperature magnetisation in
one of these materials, UGe_2. Our results show that both of the magnetic
transitions observed in this material as a function of pressure are first order
transitions and do not therefore correspond to quantum critical points. Further
we find that the known pressure dependence of the superconducting transition is
not reflected in the pressure dependence of the static susceptibility. This
demonstrates that the spectrum of excitations giving superconductivity is not
that normally associated with a proximity to quantum criticality in weak
itinerant ferromagnets. In contrast our data suggest that instead the pairing
spectrum might be related to a sharp spike in the electronic density of states
that also drives one of the magnetic transitions.",0208115v1
2002-08-16,In-plane dipole coupling anisotropy of a square ferromagnetic Heisenberg monolayer,"In this study we calculate the dipole-coupling-induced quartic in-plane
anisotropy of a square ferromagnetic Heisenberg monolayer. This anisotropy
increases with an increasing temperature, reaching its maximum value close to
the Curie temperature of the system. At T=0 the system is isotropic, besides a
small remaining anisotropy due to the zero-point motion of quantum mechanical
spins. The reason for the dipole-coupling-induced anisotropy is the disturbance
of the square spin lattice due to thermal fluctuations ('order-by-disorder'
effect). For usual ferromagnets its strength is small as compared to other
anisotropic contributions, and decreases by application of an external magnetic
field. The results are obtained from a Heisenberg Hamiltonian by application of
a mean field approach for a spin cluster, as well as from a many-body Green's
function theory within the Tyablikov-decoupling (RPA).",0208324v1
2002-08-30,Itinerant Ferromagnetism in the Periodic Anderson Model,"We introduce a novel mechanism for itinerant ferromagnetism, based on a
simple two-band model. The model includes an uncorrelated and dispersive band
hybridized with a second band which is narrow and correlated. The simplest
Hamiltonian containing these ingredients is the Periodic Anderson Model (PAM).
Using quantum Monte Carlo and analytical methods, we show that the PAM and an
extension of it contain the new mechanism and exhibit a non-saturated
ferromagnetic ground state in the intermediate valence regime. We propose that
the mechanism, which does not assume an intra atomic Hund's coupling, is
present in both the iron group and in some f electron compounds like
Ce(Rh_{1-x} Ru_x)_3 B_2, La_x Ce_{1-x} Rh_3 B_2 and the uranium
monochalcogenides US, USe, and UTe.",0208604v1
2002-09-08,"Nature of the Quantum Phase Transition in Clean, Itinerant Heisenberg Ferromagnets","A comprehensive theory of the quantum phase transition in clean, itinerant
Heisenberg ferromagnets is presented. It is shown that the standard mean-field
description of the transition is invalid in spatial dimensions $d\leq 3$ due to
the existence of soft particle-hole excitations that couple to the order
parameter fluctuations and lead to an upper critical dimension $d_c^+ = 3$. A
generalized mean-field theory that takes these additional modes into account
predicts a fluctuation-induced first-order transition. In a certain parameter
regime, this first-order transition in turn is unstable with respect to a
fluctuation-induced second-order transition. The quantum ferromagnetic
transition may thus be either of first or of second-order, in agreement with
experimental observations. A detailed discussion is given of the stability of
the first-order transition, and of the critical behavior at the
fluctuation-induced second-order transition. In $d=3$, the latter is mean
field-like with logarithmic corrections to scaling, and in $d<3$ it can be
controlled by means of a $3-\epsilon$ expansion.",0209190v3
2002-09-16,Phase Competition in Ln0.5a0.5mno3 Perovskites,"Single crystals of the systems Pr0.5(Ca1-xSrx)0.5MnO3,
(Pr1-yYy)0.5(Ca1-xSrx)0.5MnO3, and Sm0.5Sr0.5MnO3 were grown to provide a
series of samples with fixed ratio Mn(III)/Mn(IV)=1 having geometric tolerance
factors that span the transition from localized to itinerant electronic
behavior of the MnO3 array. A unique ferromagnetic phase appears at the
critical tolerance factor tc= 0.975 that separates charge ordering and
localized-electron behavior for t<tc from itinerant or molecular-orbital
behavior for t>tc. This ferromagnetic phase, which has to be distinguished from
the ferromagnetic metallic phase stabilized at tolerance factors t>tc,
separates two distinguishable Type-CE antiferromagnetic phases that are
metamagnetic. Measurements of the transport properties under hydrostatic
pressure were carried out on a compositions t a little below tc in order to
compare the effects of chemical vs. hydrostatic pressure on the phases that
compete with one another near t=tc.",0209370v1
2002-09-23,Spin injection into a ballistic semiconductor microstructure,"A theory of spin injection across a ballistic
ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann
regime. Spin injection coefficient $\gamma$ is suppressed by the Sharvin
resistance of the semiconductor $r_N^*=(h/e^2)(\pi^2/S_N)$, where $S_N$ is the
Fermi-surface cross-section. It competes with the diffusion resistances of the
ferromagnets $r_F$, and $\gamma\sim r_F/r_N^*\ll 1$ in the absence of contact
barriers. Efficient spin injection can be ensured by contact barriers. Explicit
formulae for the junction resistance and the spin-valve effect are presented.",0209539v2
2002-10-10,Spontaneous spin current near the interface between ferromagnets and unconventional superconductors,"Proximity effects between ferromagnets (F) and superconductors (S) with
broken time-reversal symmetry (T) are studied theoretically. For the S side we
consider a chiral (p_x \pm ip_y)-wave, and a d_{x^2-y^2}-wave superconductor,
the latter of which can form T-breaking surface state, i.e., (d_{x^2-y^2} \pm
is)-state. The Bogoliubov de Gennes equation which describes the spatial
variations of the superconducting order parameter and the magnetization is
derived and solved numerically. It is found that a spontaneous spin current
flows along the interface between the (p_x \pm ip_y)-wave superconductor and
the ferromagnet. On the contrary, in the case of a [110] interface of the
d_{x^2-y^2}-wave SC, the surface state has a (d \pm p_x \pm p_y)-wave (or
(d_{x^2-y^2} \pm is)-wave) symmetry, and thus no (only charge) spontaneous
current arises.",0210232v1
2002-10-10,"High temperature specific heat and magnetic measurements in Nd0.5Sr0.5MnO3 and R0.5Ca0.5MnO3 (R=Nd, Sm, Dy and Ho) samples","We have made a magnetic characterization of Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3,
Sm0.5Ca0.5MnO3, Dy0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 polycrystalline samples.
Ferromagnetic, antiferromagnetic and charge ordering transitions in our samples
agree with previous reports. We also report specific heat measurements with
applied magnetic fields between 0 and 9 T and temperatures between 2 and 300 K
in all cases. Each curve was successfully fitted at high temperatures by an
Einstein model with three optical phonon modes. Close to the charge ordering
and ferromagnetic transition temperatures the specific heat curves showed peaks
superposed to the characteristic response of the lattice oscillations. The
entropy variation corresponding to the charge ordering transition was higher
than the one corresponding to the ferromagnetic transition. The external
magnetic field seems to have no effect in specific heat of the CO phase
transition.",0210243v3
2002-10-15,Theoretical models of ferromagnetic III-V semiconductors,"Recent materials research has advanced the maximum ferromagnetic transition
temperature in semiconductors containing magnetic elements toward room
temperature. Reaching this goal would make information technology applications
of these materials likely. In this article we briefly review the status of work
over the past five years which has attempted to achieve a theoretical
understanding of these complex magnetic systems. The basic microscopic origins
of ferromagnetism in the (III,Mn)V compounds that have the highest transition
temperatures appear to be well understood, and efficient computation methods
have been developed which are able to model their magnetic, transport, and
optical properties. However many questions remain.",0210318v1
2002-10-17,Glass component induced hysteresis/memory effect in magnetoresistance of ferromagnetic Pr0.9Sr0.1CoO2.99,"Pr0.9Sr0.1CoO2.99 sample exhibits magnetoresistivity (MR) of up to 40 % at 5
K with a strong hysteresis/memory effect. Magnetisation measurements on
Pr0.9Sr0.1CoO2.99 in an applied field of 100 Oe show that, as temperature
decreases, the zero-field-cooled (ZFC) and field-cooled (FC) magnetisation
curves branch clearly at 50 K, and a cusp appears in the ZFC branch at Tcusp 20
K. Magnetisation measurements in various fields between 100 and 10,000 Oe show
that both the ZFC-FC branching temperature and, Tcusp, decrease with increasing
field. The magnetization-field isotherms at 5 and 10 K show hysteresis loops
typical of ferromagnets. No appreciable MR is seen in this compound at 50 K,
i.e. at a temperature close to ZFC-FC branching temperature. At 20 K, negative
MR of above 16% is observed without any hysteresis effect. We believe that the
appearance of a ferromagnetic component at 5 K and 10 K (i.e. at temperatures
below Tcusp) within the spin glass state of Co spins is responsible for both
large MR and the prominent hysteresis/memory effect in MR.",0210360v1
2002-10-19,Dirty quantum Hall ferromagnets and quantum Hall spin glasses,"We study quantum Hall ferromagnets in the presence of a random electrostatic
impurity potential, within the framework of a classical non-linear sigma model.
We discuss the behaviour of the system using a heuristic picture for the
competition between exchange and screening, and test our conclusions with
extensive numerical simulations. We obtain a phase diagram for the system as a
function of disorder strength and deviation of the average Landau level filling
factor from unity. Screening of an impurity potential requires distortions of
the spin configuration. In the absence of Zeeman coupling there is a
disorder-driven, zero-temperature phase transition from a ferromagnet at weak
disorder and small deviation from integer filling to a spin glass at stronger
disorder or large charge deviation. We characterise the spin glass phase in
terms of its magnetic and charge response, as well as its ac conductivity.",0210424v1
2002-10-24,Ferromagnetic superconductivity driven by changing Fermi surface topology,"We introduce a simple but powerful zero temperature Stoner model to explain
the unusual phase diagram of the ferromagnetic superconductor, UGe2. Triplet
superconductivity is driven in the ferromagnetic phase by tuning the majority
spin Fermi level through one of two peaks in the paramagnetic density of states
(DOS). Each peak is associated with a metamagnetic jump in magnetisation. The
twin peak DOS may be derived from a tight-binding, quasi-one-dimensional
bandstructure, inspired by previous bandstructure calculations.",0210552v2
2002-10-29,Ferromagnetism in diluted magnetic semiconductor quantum dot arrays embedded in semiconductors,"We present an Anderson-type model Hamiltonian with exchange coupling between
the localized spins and the confined holes in the quantum dots to study the
ferromagnetism in diluted magnetic semiconductor (DMS) quantum dot arrays
embedded in semiconductors. The hybridization between the quantum-confined
holes in the DMS quantum dots and the itinerant holes in the semiconductor
valence band makes hole transfer between quantum dots, which can induce the
long range ferromagnetic order of the localized spins. In addition, it makes
the carrier spins both in the DMS quantum dots and in the semiconductors
polarized. The spontaneous magnetization of the localized spins and the spin
polarization of the holes are calculated using both the Weiss mean field
approximation and the self-consistent spin wave approximation, which are
developed for the present model.",0210643v1
2002-11-05,Persistence in the Zero-Temperature Dynamics of the Random Ising Ferromagnet on a Voronoi-Delaunay lattice,"The zero-temperature Glauber dynamic is used to investigate the persistence
probability $P(t)$ in the randomic two-dimensional ferromagnetic Ising model on
a Voronoi-Delaunay tessellation. We consider the coupling factor $J$ varying
with the distance $r$ between the first neighbors to be $J(r) \propto
e^{-\alpha r}$, with $\alpha \ge 0$. The persistence probability of spins flip,
that does not depends on time $t$, is found to decay to a non-zero value
$P(\infty)$ depending on the parameter $\alpha$. Nevertheless, the quantity
$p(t)=P(t)-P(\infty)$ decays exponentially to zero over long times.
Furthermore, the fraction of spins that do not change at a time $t$ is a
monotonically increasing function of the parameter $\alpha$. Our results are
consistent with the ones obtained for the diluted ferromagnetic Ising model on
a square lattice.",0211097v1
2002-11-16,"Magnetic Transitions and Ferromagnetic Clusters in RuSr2(Eu,Ce)2Cu2O10+d","The macroscopic magnetizations of a RuSr2(Eu0.7Ce0.3)2Cu2O10+d sample were
investigated. A ferromagnet-like transition occurs around T_M in the low-field
magnetization. Highly nonlinear M(H), non-Curie-Weiss susceptibility, and slow
spin-dynamics, however, were observed up to T_1 approx 2-3 T_M. In addition, an
antiferromagnet-like differential-susceptibility maximum of Ru appears around a
separate temperature T_AM between T_1 and T_M. The data are therefore
consistent with a phase-separation model: superparamagnetic clusters (or
short-range spin-orders) are first precipitated from the paramagnetic matrix
below T_1, followed by an antiferromagnetic transition of the matrix at T_AM
and an apparent ferromagnetic (FM) transition around T_M, where the long-range
spin-order is established in the FM species imbedded in the matrix.",0211342v1
2002-11-20,Sensitivity of the Superconducting Transition Temperature to Changes in the Spin-Fluctuation Spectral Weight,"In the simplest model of magnetic pairing, the transition temperature to the
superconducting state depends on the dynamical susceptibility $\chi({\bf
q},\omega)$. We discuss how $T_c$ is affected by different momentum and
frequency parts of $\chi({\bf q},\omega)$ for nearly antiferromagnetic and
nearly ferromagnetic metals in two dimensions. While in the case of
phonon-mediated superconductivity any addition of spectral weight to
$\alpha^2F(\omega)$ at $\omega >0$ leads to an increase in $T_c$, we find that
adding magnetic spectral weight at any momentum ${\bf q}$ and low frequencies
($[0:3T_c]$ and $[0:(5-9)T_c]$ for nearly antiferromagnetic and ferromagnetic
metals respectively) leads to a suppression of $T_c$. The most effective
frequency and momentum range consists of large momenta ${\bf q} \sim (\pi,\pi)$
and frequencies around $10T_c$ for nearly antiferromagnetic metals and small
momenta ${\bf q} \sim 0$ and frequencies of approximately $(13-22)T_c$ for
nearly ferromagnetic metals.",0211436v1
2002-12-04,Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs,"The recently reported Rutherford backscattering and particle-induced X-ray
emission experiments have revealed that in low-temperature MBE grown GaMnAs a
significant part of the incorporated Mn atoms occupies tetrahedral interstitial
sites in the lattice. Here we study the magnetic properties of these
interstitial ions. We show that they do not participate in the hole-induced
ferromagnetism. Moreover, Mn interstitial double donors may form pairs with the
nearest substitutional Mn acceptors - our calculations evidence that the spins
in such pairs are antiferromagnetically coupled by the superexchange. We also
show that for the Mn ion in the other, hexagonal, interstitial position (which
seems to be the case in the GaMnBeAs samples) the p-d interactions with the
holes, responsible for the ferromagnetism, are very much suppressed.",0212093v1
2002-12-24,The specific heat of the rwo-dimensional +/-J Ising model,"The specific heat of the two-dimensional $\pm J$ Ising model has been
investigated by the numerical transfer matrix method and Monte Carlo
simulations from a new point of view. The region where a part of the specific
heat takes the negative value has been investigated, which is characteristic of
frustrated systems and reflects the non-trivial degeneracy of the ground state.
The region mentioned above is found to be fairly large in the $p-T$ plane ($p$
is the concentration of the ferromagnetic bond and $T$ is the temperature).
Moreover, it includes the Nishimori line. Namely, it includes a part of the
paramagnetic-ferromagnetic phase boundary, on which the specific heat cannot
diverge. The present result indicates that the specific heat does not diverge
at least on a part of the paramagnetic-ferromagnetic phase boundary above the
multicritical point, which is in conflict with previous results.",0212579v1
2002-12-24,Density-of-states picture and stability of ferromagnetism in the highly-correlated Hubbard model,"The problem of stability of saturated and non-saturated ferromagnetism in the
Hubbard model is considered in terms of the one-particle Green's functions.
Approximations by Edwards and Hertz and some versions of the self-consistent
approximations based on the 1/z-expansion are considered. The account of
longitudinal fluctuations turns out to be essential for description of the
non-saturated state. The corresponding pictures of density of states are
obtained. ""Kondo"" density-of-states singularities owing to spin-flip processes
are analyzed. The critical electron concentrations for instabilities of
saturated ferromagnetism and paramagnetic state are calculated for various
lattices. Drawbacks of various approximations are discussed. A comparison with
the results of previous works is performed.",0212586v2
2003-01-23,High Temperature Ferromagnetism with Giant Magnetic Moment in Transparent Co-doped SnO2-d,"Occurrence of room temperature ferromagnetism is demonstrated in pulsed laser
deposited thin films of Sn1-xCoxO2-d (x<0.3). Interestingly, films of
Sn0.95Co0.05O2-d grown on R-plane sapphire not only exhibit ferromagnetism with
a Curie temperature close to 650 K, but also a giant magnetic moment of about 7
Bohr-Magneton/Co, not yet reported in any diluted magnetic semiconductor
system. The films are semiconducting and optically highly transparent.",0301456v1
2003-02-04,Theory of Spin Orientation of Semiconductor Carriers at a Ferromagnetic Interface,"A quantum theory of the spin-dependent scattering of semiconductor electrons
by a Schottky barrier at an interface with a ferromagnet is presented. The
reflection of unpolarized non-equilibrium carriers produces spontaneous
spin-polarization in the semiconductor. If a net spin-polarization pre-exists
in the semiconductor, the combination of the ferromagnet magnetization and the
incident carrier polarization combine to tilt the reflected polarization in the
semiconductor. The spin reflection properties are investigated as functions of
the system characteristics: the Schottky barrier height, semiconductor doping
and applied bias. The effect on reflection due to the variation of the barrier
width with electron energy is contrasted for two means of excitation: optical
or electrical. Optically excited electrons have a wider energy spread than the
near-equilibrium excitation from non-magnetic ohmic contacts.",0302088v1
2003-02-06,Weak ferromagnetism with very large canting in a chiral lattice: (pyrimidine)2FeCl2,"The transition metal coordination compound (pyrimidine)2FeCl2 crystallizes in
a chiral lattice, space group I 4_1 2 2 (or I4_3 2 2). Combined magnetization,
Mossbauer spectroscopy and powder neutron diffraction studies reveal that it is
a canted antiferromagnet below T_N = 6.4 K with an unusually large canting of
the magnetic moments of 14 deg. from their general antiferromagnetic alignment,
one of the largest reported to date. This results in weak ferromagnetism with a
ferromagnetic component of 1 mu_B. The large canting is due to the interplay
between the antiferromagnetic exchange interaction and the local single-ion
anisotropy in the chiral lattice. The magnetically ordered structure of
(pyrimidine)2FeCl2, however, is not chiral. The implications of these findings
for the search of molecule based materials exhibiting chiral magnetic ordering
is discussed.",0302121v1
2003-02-12,Crossed Andreev reflection at ferromagnetic domain walls,"We investigate several factors controlling the physics of hybrid structures
involving ferromagnetic domain walls (DWs) and superconducting (S) metals. We
discuss the role of non collinear magnetizations in S/DW junctions in a spin
$\otimes$ Nambu $\otimes$ Keldysh formalism. We discuss transport in S/DW/N and
S/DW/S junctions in the presence of inelastic scattering in the domain wall. In
this case transport properties are similar for the S/DW/S and S/DW/N junctions
and are controlled by sequential tunneling of spatially separated Cooper pairs
across the domain wall. In the absence of inelastic scattering we find that a
Josephson current circulates only if the size of the ferromagnetic region is
smaller than the elastic mean free path meaning that the Josephson effect
associated to crossed Andreev reflection cannot be observed under usual
experimental conditions. Nevertheless a finite dc current can circulate across
the S/DW/S junction due to crossed Andreev reflection associated to sequential
tunneling.",0302236v4
2003-02-12,Temperature Dependence of the Dielectric Constant and Resistivity of Diluted Magnetic Semiconductors,"We study the effect that the ferromagnetic order has on the electrical
properties of Diluted Magnetic Semiconductors. We analyze the temperature
dependence of the dielectric constant and of the resistivity of
Ga$_{1-x}$Mn$_x$As. In our treatment the electronic structure of the
semiconductor is described by a six band Kohn-Luttinger Hamiltonian, the
thermal fluctuations of the Mn magnetic moments are treated in the mean field
approximation, the carrier-carrier interaction within the random phase
approximation, and the transport properties using the relaxation time
approximation. We find that the Thomas-Fermi length changes near 8% when going
from the ferromagnetic to the paramagnetic phase. We also find, in good
agreement with the experiments, that the resistivity changes near 20% when
going from zero to the Curie temperature. We explain this change in the
resistivity in terms of the variation of the Fermi surface and the transport
scattering time when going from the ferromagnetic phase to the paramagnetic
phase.",0302237v1
2003-02-12,Metastability and Avalanches in a Nonequilibrium Ferromagnetic System,"We present preliminary results on the metastable behavior of a nonequilibrium
ferromagnetic system. The metastable state mean lifetime is a non-monotonous
function of temperature; it shows a maximum at certain non-zero temperature
which depends on the strengh of the nonequilibrium perturbation. This is in
contrast with the equilibrium case in which lifetime increases monotonously as
the temperature is decreasesed. We also report on avalanches during the decay
from the metastable state. Assuming both free boundaries and nonequilibrium
impurities, the avalanches exhibit power-law size and lifetime distributions.
Such scale free behavior is very sensible. The chances are that our
observations may be observable in real (i.e. impure) ferromagnetic
nanoparticles.",0302241v1
2003-02-24,Magnetization study of RuSr2Y1.5Ce 0.5Cu2O10 (Ru-1222),"We have studied the magnetic properties of the non-superconducting
RuSr2Ln1.5Ce0.5Cu2O10 (Ln=Y, Dy and Ho, Ru-1222) compounds synthesized under
high pressure (6 Gpa) at elevated temperature. The materials become
magnetically ordered at TM =152(2) K regardless of Ln. The wide
ferromagnetic-like hysteresis loops which open at 5 K, close themselves around
Tirr= 90-100 K and the remanent magnetizations (Mrem) and the coercive fields
(HC) become zero. Surprisingly, at Tirr<T< TM a reappearance of the Mrem and HC
(with a peak at 120-130 K) is observed for all three samples studied. For the
non-magnetic Ln=Y compound, the extracted saturation moment at 5 K and the
effective paramagnetic moment are is 0.75 and 2.05 mB /Ru, values which are
close to the expected 1 mB and 1.73 mB respectively, for the low-spin state of
Ru5+. We argue that the Ru-1222 system becomes (i) anti-ferromagnetically (AFM)
ordered at TM. In this range a metamagnetic transition is induced by the
applied field (ii). At Tirr < TM, weak-ferromagnetism (W-FM) is induced by the
canting of the Ru moments.",0302475v1
2003-02-26,Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions,"We consider the tunnel spin current between two ferromagnetic metals from a
perspective similar to the one used in superconductor/superconductor tunnel
junctions. We use fundamental arguments to derive a Josephson-like spin tunnel
current $I_J^{\rm spin}\propto\sin(\theta_1-\theta_2)$. Here the phases are
associated with the planar contribution to the magnetization,
$<c_\uparrow^\dagger c_\downarrow>\sim e^{i\theta}$. The crucial step in our
analysis is the fact that the $z$-component of the spin is canonically
conjugate to the phase of the planar contribution: $[\theta,S^z]=i$. This is
analogous to the commutation relation $[\phi,N]=i$ in superconductors, where
$\phi$ is the phase associated to the superconducting order parameter and $N$
is the Cooper pair number operator. We briefly discuss the experimental
consequences of our theoretical analysis.",0302528v3
2003-02-28,Ferromagnetic Polarons in La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3,"Unrestricted Hartree-Fock calculations on La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3
in the full magnetic unit cell show that the magnetic ground states of these
compounds consist of 'ferromagnetic molecules' or polarons ordered in
herring-bone patterns. Each polaron consists of either three or five Mn ions
separated by O- ions with a magnetic moment opposed to those of the Mn ions.
Ferromagnetic coupling within the polarons is strong while coupling between
them is relatively weak. Magnetic moments on the Mn ions range between 3.8 and
3.9 Bohr magnetons in La0.5Ca0.5MnO3 and moments on the O- ions are -0.7 Bohr
magnetons. Each polaron has a net magnetic moment of 7.0 Bohr magnetons, in
good agreement with recently reported magnetisation measurements from electron
microscopy. The polaronic nature of the electronic structure reported here is
obviously related to the Zener polaron model recently proposed for
Pr0.6Ca0.4MnO3 on the basis of neutron scattering data.",0302622v2
2003-03-15,Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors,"Applying the dynamical coherent potential approximation to a simple model, we
have systematically studied the carrier states in $A_{1-x}$Mn$_xB$-type diluted
magnetic semiconductors (DMS's). The model calculation was performed for three
typical cases of DMS's: The cases with strong and moderate exchange
interactions in the absence of nonmagnetic potentials, and the case with strong
attractive nonmagnetic potentials in addition to moderate exchange interaction.
When the exchange interaction is sufficiently strong, magnetic impurity bands
split from the host band. Carriers in the magnetic impurity band mainly stay at
magnetic sites, and coupling between the carrier spin and the localized spin is
very strong. The hopping of the carriers among the magnetic sites causes
ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have
investigated the condition for the DE-like mechanism to operate in DMS's. The
result reveals that the nonmagnetic attractive potential at the magnetic site
assists the formation of the magnetic impurity band and makes the DE-like
mechanism operative by substantially enhancing the effect of the exchange
interaction. Using conventional parameters we have studied the carrier states
in Ga$_{1-x}$Mn$_x$As. The result shows that the ferromagnetism is caused
through the DE-like mechanism by the carriers in the bandtail originating from
the impurity states.",0303285v1
2003-04-15,Ferromagnetic Kondo-Lattice Model,"We present a many-body approach to the electronic and magnetic properties of
the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The
coupling between itinerant conduction electrons and localized magnetic moments
leads, on the one hand, to a distinct temperature-dependence of the electronic
quasiparticle spectrum and, on the other hand, to magnetic properties, as
e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly
influenced by the band electron selfenergy and therewith in particular by the
carrier density. We present results for the single-band Kondo-lattice model in
terms of quasiparticle densities of states and quasiparticle band structures
and demonstrate the density-dependence of the self-consistently derived Curie
temperature. The transition from weak-coupling (RKKY) to strong-coupling
(double exchange) behaviour is worked out.
  The multiband model is combined with a tight-binding-LMTO bandstructure
calculation to describe real magnetic materials. As an example we present
results for the archetypal ferromagnetic local-moment systems EuO and EuS. The
proposed method avoids the double counting of relevant interactions and takes
into account the correct symmetry of atomic orbitals.",0304338v1
2003-04-25,Ising-like Spin Anisotropy and Competing Antiferromagnetic - Ferromagnetic Orders in GdBaCo_{2}O_{5.5} Single Crystals,"In RBaCo_{2}O_{5+x} compounds (R is rare earth), a
ferromagnetic-antiferromagnetic competition is accompanied by a giant
magnetoresistance. We study the magnetization of detwinned GdBaCo_{2}O_{5.5}
single crystals, and find a remarkable uniaxial anisotropy of Co^{3+} spins
which is tightly linked with the chain oxygen ordering in GdO_{0.5} planes.
Reflecting the underlying oxygen order, CoO_2 planes also develop a spin-state
order consisting of Co^{3+} ions in alternating rows of S=1 and S=0 states. The
magnetic structure appears to be composed of weakly coupled ferromagnetic
ladders with Ising-like moments, which gives a simple picture for
magnetotransport phenomena.",0304578v1
2003-04-28,Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions,"We study a two-band Hubbard model using the dynamical mean-field theory
combined with the exact diagonalization method. At the electron density $n=2$,
a transition from a band-insulator to a correlated semimetal occurs when the
on-site Coulomb interaction $U$ is varied for a fixed value of the
charge-transfer energy $\Delta$. At low temperature, the correlated semimetal
shows ferromagnetism or superconductivity. With increasing doping $|n-2|$, the
ferromagnetic transition temperature rapidly decreases and finally becomes zero
at a critical value of $n$. The second-order phase transition occurs at high
temperature, while a phase separation of ferromagnetic and paramagnetic states
takes place at low temperature. The superconducting transition temperature
gradually decreases and finally becomes zero near $n=1$ ($n=3$) where the
system is Mott insulator which shows antiferromagnetism at low temperature.",0304624v1
2003-05-02,Enhancement of Curie temperature in Ga(1-x)Mn(x)As/Ga(1-y)Al(y)As ferromagnetic heterostructures by Be modulation doping,"The effect of modulation doping by Be on the ferromagnetic properties of
Ga(1-x)Mn(x)As is investigated in Ga(1-x)Mn(x)As/Ga(1-y)Al(y)As heterojunctions
and quantum wells. Introducing Be acceptors into the Ga(1-y)Al(y)As barriers
leads to an increase of the Curie temperature T_C of Ga(1-x)Mn(x)As, from 70 K
in undoped structures to over 100 K with the modulation doping. This increase
is qualitatively consistent with a multi-band mean field theory simulation of
carrier-mediated ferromagnetism. An important feature is that the increase of
T_C occurs only in those structures where the modulation doping is introduced
after the deposition of the magnetic layer, but not when the Be-doped layer is
grown first. This behavior is expected from the strong sensitivity of Mn
interstitial formation to the value of the Fermi energy during growth.",0305047v1
2003-05-06,Pressure induced transition from a spin glass to an itinerant ferromagnet in half doped manganite Ln0.5Ba0.5MnO3 (Ln=Sm and Nd) with quenched disorder,"The effect of quenched disorder on the multiphase competition has been
investigated by examining the pressure phase diagram of half doped manganite
Ln0.5B0.5MnO3 (Ln = Sm and Nd) with A-site disorders. Sm0.5Ba0.5MnO3, a spin
glass insulator at ambient pressure, switches to a ferromagnetic metal with
increasing pressure, followed by a rapid increase of the ferromagnetic
transition temperature Tc. The rapid increase of Tc was confirmed also for
Nd0.5Ba0.5MnO3. These observations indicate that the unusual suppression of the
multicritical phase boundary in the A-site disordered system, previously
observed as a function of the averaged A-site ionic radius, is essentially
controlled by the pressure and hence the band width. The effect of quenched
disorder is therefore much enhanced with approaching the multicritical region.",0305114v1
2003-05-19,Effects of local oxygen distortions on electronic structures of Na$_{x}$CoO$_{2}$,"By using pseudopotential method with local spin density functional
approximation, the electronic band structures of Na$_{x}$CoO$_{2}$ are
calculated for $x=0.25$, 0.5, 0.75, and $x=1$ in the presence of the structure
relaxations. As increasing Na content, the hybridization between cobalt and
oxygen orbitals is decreased, and a phase transition is predicted from a
wide-band ferromagnetic to a narrow band paramagnetic metals. The itinerant
ferromagnetism is strongly suppressed by the local distortions of the oxygens
around the cobalts. Moreover, straining the CoO$_{2}$ layers corresponding to
the hydrated superconductor Na$_{0.35}$CoO$_{2}\cdot $1.3H$%_{2}$O strongly
enhances both the hybridization and ferromagnetism.",0305423v2
2003-05-22,Domain wall superconductivity in hybrid superconductor -- ferromagnetic structures,"On the basis of phenomenological Ginzburg-Landau approach we investigate the
problem of order parameter nucleation in hybrid superconductor/ferromagnetic
systems with a domain structure in applied external magnetic field. Both the
isolated domain boundaries and periodic domain structures in ferromagnetic
layers are considered. We study the interplay between the superconductivity
localized at the domain walls and far from the walls and show that such
interplay determines a peculiar field dependence of the critical temperature
Tc. For a periodic domain structure the behavior of the upper critical field of
superconductivity nucleation near Tc is strongly influenced by the overlapping
of the superconducting nuclei localized over different domains.",0305520v1
2003-05-28,Giant frequency dependence of dynamic freezing in nanocrystalline ferromagnetic LaCo0.5Mn0.5O3,"We have investigated the magnetic properties of nanocrystalline
LaCo0.5Mn0.5O3. The temperature dependence of the imaginary part of the a.c.
susceptibility shows a strongly frequency dependent maximum at a temperature,
Tf, which is well below the ferromagnetic transition temperature (TC ~ 230 K).
The frequency dependence of Tf obeys the Arrhenius relation, f =
foexp(-Ea/kBT), with physically reasonable values of fo = 109 Hz and Ea/kB =
1518 K. The frequency shift of Tf per decade of frequency is one of the highest
values observed in any magnetic system, and a similarly large value is also
found in LaCo0.4Mg0.1Mn0.5O3, suggesting that such behavior is intrinsic
despite the apparent presence of long range ferromagnetic order.",0305653v1
2003-06-04,Magnetization reversal and two level fluctuations by spin-injection in a ferromagnetic metallic layer,"Slow magnetic relaxation and two level fluctuations measurements under high
current injection is performed in single-contacted ferromagnetic
nanostructures. The magnetic configurations of the samples are described by two
metastable states of the uniform magnetization. The current-dependent effective
energy barrier due to spin-transfer from the current to the magnetic layer is
measured. The comparison between the results obtained with Ni nanowires of 6
$\mu $m length and 60 nm diameter, and Co (10 nm)/Cu (10 nm)/Co(30 nm)
nanometric pillars of about 40 nm in diameter refined the characterization of
this effect. It is shown that all observed features cannot be reduced to the
action of a current dependent effective field. Instead, all measurements can be
described in terms of an effective temperature, which depends on the current
amplitude and direction. The system is then analogous to an unstable open
system. The effect of current induced magnetization reversal is interpreted as
the balance of spin injection between both interfaces of the ferromagnetic
layer.",0306103v1
2003-06-10,Magnetic Field Melting of the Charge-Ordered State of La0.5Ca0.5MnO3: A Local Structure Perspective,"The local structure about the Mn site in the half doped system La0.5Ca0.5MnO3
was measured in magnetic fields up 10 T to probe the melting of the charge
ordered state. Examination of the Mn-O and Mn-Mn correlations reveal three
distinct regions in the structure-field diagram. A broad region with weak field
dependence (mainly antiferromatnetic phase below 7.5 T), a narrow-mixed phase
region near ~ 8.5 T followed by a ferromagnetic phase region with strong
field-structure coupling. At high field the Mn-O radial distribution becomes
Gaussian and the Mn-Mn correlations are enhanced - consistent with the
dominance of a ferromagnetic phase. The exponential change in resistivity in
the first region (observed in transport measurements) is dominated by the
reordering of the moments on the Mn sites from CE type antiferromagnetic to
ferromagnetic order with only a weak change in the local distortions of the
MnO6 octahedra.",0306229v1
2003-06-11,Weak ferromagnetism and other instabilities of the two-dimensional t-t' Hubbard model at Van Hove fillings,"We investigate magnetic and superconducting instabilities of the
two-dimensional t-t' Hubbard model on a square lattice at Van Hove densities
from weak to intermediate coupling by means of the two-particle self-consistent
approach. We find that as the next-nearest-neighbor hopping |t'| increases from
zero, the leading instability is towards an incommensurate spin-density wave
whose wave vector moves slowly away from (pi, pi). For intermediate values of
|t'|, the leading instability is towards d_{x2-y2}-wave superconductivity. For
larger |t'|>0.33t, there are signs of a crossover to ferromagnetism at
extremely low temperatures. The suppression of the crossover temperature is
driven by Kanamori screening that strongly renormalizes the effective
interaction and also causes the crossover temperature to depend only weakly on
t'. Electronic self-energy effects for large |t'| lead to considerable
reduction of single-particle spectral weight at zero energy at temperatures as
high as T<0.1t, an effect that may be detrimental to the existence of a
ferromagnetic ground state at weak coupling.",0306296v2
2003-06-12,On Aharonov-Bohm oscillation in a ferromagnetic ring,"Aharonov-Bohm effect in a ferromagnetic thin ring in diffusive regime is
theoretically studied by calculating the Cooperon and Diffuson. In addition to
the spin-orbit interaction, we include the spin-wave excitation and the spin
splitting, which are expected to be dominant sources of dephasing in
ferromagnets at low temperatures. The spin splitting turns out to kill the
spin-flip channel of Cooperon but leaves the spin-conserving channel untouched.
For the experimental confirmation of interference effect (described by
Cooperons) such as weak localization and Aharonov-Bohm oscillation with period
$h/2e$, we need to suppress the dominant dephasing by orbital motion. To do
this we propose experiments on a thin film or thin ring with magnetization and
external field perpendicular to the film, in which case the effective field
inside the sample is equal to the external field (magnetization does not add
up). The field is first applied strong enough to saturate the magnetization and
then carrying out the measurement down to zero field keeping the magnetization
nearly saturated, in order to avoid domain formations (negative fields may also
be investigated if the coercive field is large enough).",0306309v1
2003-06-18,On the theory of superconductivity in ferromagnetic superconductors with triplet pairing,"We point out that ferromagnetic superconductors with triplet pairing and
strong spin-orbit coupling are even in the simplest case at least two-band
superconductors. The Gor'kov type formalism for such superconductors is
developed and the Ginzburg-Landau equations are derived. The dependence of the
critical temperature on the concentration of ordinary point-like impurities is
found. Its nonuniversality could serve as a qualitative measure of the two-band
character of ferromagnetic superconductors. The problem of the upper critical
field determination is also discussed.",0306471v3
2003-06-23,"Ferromagnetic transition temperature enhancement in (Ga,Mn)As semiconductor by carbon co-doping","We present a theoretical study of (Ga,Mn)(As,C) diluted magnetic
semiconductors with high C acceptor density that combines insights from
phenomenological model and microscopic approaches. A tight-binding coherent
potential approximation is used to describe the electronic structure in the
presence of Mn$_{\rm Ga}$ and C$_{\rm As}$ impurities. We find only a small
effect of C on the distribution and coherence of electronic states close to the
top of the valence band and on the coupling between Mn moments, even at doping
levels of several per cent. These results justify applying the model of
ferromagnetic Mn-Mn coupling mediated by itinerant holes in the valence band
also to C doped samples. The increase of ferromagnetic transition temperature
due to the presence of C acceptors is illustrated by calculations that use the
k.p Kohn-Luttinger description of the GaAs valence band and assume systems
where Mn local moment and itinerant hole densities can be varied independently.",0306557v1
2003-07-01,Growth and properties of ferromagnetic In(1-x)Mn(x)Sb alloys,"We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy,
In(1-x)Mn(x)Sb, and its growth by low-temperature molecular-beam epitaxy. The
magnetic properties were investigated by direct magnetization measurements,
electrical transport, magnetic circular dichroism, and the magneto-optical Kerr
effect. These data clearly indicate that In(1-x)Mn(x)Sb possesses all the
attributes of a system with carrier-mediated FM interactions, including
well-defined hysteresis loops, a cusp in the temperature dependence of the
resistivity, strong negative magnetoresistance, and a large anomalous Hall
effect. The Curie temperatures in samples investigated thus far range up to 8.5
K, which are consistent with a mean-field-theory simulation of the
carrier-induced ferromagnetism based on the 8-band effective band-orbital
method.",0307032v1
2003-07-07,"Mn Interstitial Diffusion in (Ga,Mn)As","We present a combined theoretical and experimental study of the ferromagnetic
semiconductor (Ga,Mn)As which explains the remarkably large changes observed on
low temperature annealing. Careful control of the annealing conditions allows
us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab
initio calculations, and resistivity measurements during annealing, show that
the observed changes are due to out-diffusion of Mn interstitials towards the
surface, governed by an energy barrier of about 0.7-0.8 eV. The Mn interstitial
is a double donor resulting in compensation of charge carriers and suppression
of ferromagnetism. Electric fields induced by high concentrations of
substitutional Mn acceptors have a significant effect on the diffusion.",0307140v1
2003-07-11,"Photo-induced spin dynamics in ferromagnetic semiconductor $p$-(Ga,Mn)As","Spin dynamics in ferromagnetic $p$-(Ga,Mn)As ($x$ = 0.011, $T_{C}$ = 30 K)
has been studied by carefully comparing the decay time of the photo-induced
reflectivity change with the transient behavior of polar Kerr rotation induced
by photo-generated carrier spins with a femtosecond light pulse of various
polarizations. As to the rising process, the rate of Kerr rotation is found
comparable to the generation rate of spin-polarized carriers. For the decay
process, the Kerr rotation and reflectivity signal both show the same decay
rate at above the $T_{C}$, whereas, below the $T_{C}$, the former becomes
slower than the latter. The magnitude of Kerr rotation suggests that 10$^{2}$
Mn spins are revolved by injecting one hole spin. On the basis of these
observations, collective rotation of ferromagnetically coupled Mn spins is
discussed in terms of $p$-$d$ exchange interaction and successive transverse
spin relaxation. Development of another long-lived behavior under external
perpendicular magnetic fields is also disclosed.",0307268v1
2003-07-28,Magnetic properties of Yb2Mo2O7 and Gd2Mo2O7 from rare earth Mossbauer measurements,"Using 170-Yb and 155-Gd Mossbauer measurements down to 0.03K, we have
examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice
interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where
this interaction is ferromagnetic. Additional information was obtained from
susceptibility, magnetisation and 172-Yb perturbed angular correlation
measurements. The microscopic measurements evidence lattice disorder which is
important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur
at 17K in Yb2Mo2O7 and at 75K in Gd2Mo2O7 and below these temperatures the rare
earths carry magnetic moments which are induced through couplings with the Mo
sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations
at 0.027K are out of thermal equilibrium, indicating that Gd and Mo spin
fluctuations persist at very low temperatures. Frustration is thus operative in
this essentially isotropic pyrochlore where the dominant Mo intra-sublattice
interaction is ferromagnetic.",0307677v1
2003-07-31,Thermodynamic properties of ferromagnetic mixed-spin chain systems,"Using a combination of high-temperature series expansion, exact
diagonalization and quantum Monte Carlo, we perform a complementary analysis of
the thermodynamic properties of quasi-one-dimensional mixed-spin systems with
alternating magnetic moments. In addition to explicit series expansions for
small spin quantum numbers, we present an expansion that allows a direct
evaluation of the series coefficients as a function of spin quantum numbers.
Due to the presence of excitations of both acoustic and optical nature, the
specific heat of a mixed-spin chain displays a double-peak-like structure,
which is more pronounced for ferromagnetic than for antiferromagnetic
intra-chain exchange. We link these results to an analytically solvable
half-classical limit. Finally, we extend our series expansion to incorporate
the single-ion anisotropies relevant for the molecular mixed-spin ferromagnetic
chain material MnNi(NO$_{2}$)$_{4}$(ethylenediamine)$_{2}$, with alternating
spins of magnitude 5/2 and 1. Including a weak inter-chain coupling, we show
that the observed susceptibility allows for an excellent fit, and the
extraction of microscopic exchange parameters.",0307761v2
2003-08-01,What is the value of the superconducting gap of a F/S/F trilayer ?,"Based on the model of F/S/F trilayer with atomic thickness [A. Buzdin and M.
Daumens, cond-mat/0305320] we discuss the relative roles of pair-breaking and
proximity effects, as a function of the exchange field, of disorder and of a
finite thickness in the superconducting layer. The exchange field can be small
(weak ferromagnets) or large (strong ferromagnets) compared to the
superconducting gap. With weak ferromagnets we show the existence of a
reentrant superconducting gap for the F/S/F trilayer with atomic thickness in
the parallel alignment (equivalent to the F/S bilayer). Qualitatively small
disorder is equivalent to reducing the value of the hopping parameters. In the
presence of a finite thickness in the superconducting layer the superconducting
gap in the antiparallel alignment is larger than in the parallel alignment,
meaning that pair breaking dominates over the proximity effect.",0308007v2
2003-08-25,Co distribution in ferromagnetic rutile Co-doped TiO$_2$ thin films grown by laser ablation on silicon substrates,"Pure rutile Co-doped TiO$_2$ films were fabricated successfully by the
conventional pulsed laser deposition technique on silicon substrates from a
ceramic target. Under the right fabrication conditions, Co concentration in the
films could be almost the same as in the synthesized target, and films under
various conditions all are ferromagnetic well above room temperature. Even
though Rutherford backscattering spectroscopy measurements show that Co atoms
seem to be mostly localized near the surface of the films and less exist in
deeper levels, other experimental evidences show that the ferromagnetism does
not come from Co segregations but from the Co-doped TiO$_2$ matrix. Rutile
Ti$_1-x$Co$_x$O$_2$ thin films grown by a very simple technique on low-price
silicon substrates showing Curie temperature (TC) above 400 K appear to be very
attractive to applications.",0308494v1
2003-08-28,External control of the direction of magnetization in ferromagnetic InMnAs/GaSb heterostructures,"In this paper, we demonstrate external control over the magnetization
direction in ferromagnetic (FM) In_{1-x}Mn_{x}As/GaSb heterostructures. FM
ordering with T_C as high as 50 K is confirmed by SQUID magnetization,
anomalous Hall effect (AHE), and magneto-optical Kerr effect (MOKE)
measurements. Even though tensile strain is known to favor an easy axis normal
to the layer plane, at low temperatures we observe that the magnetization
direction in several samples is intermediate between the normal and in-plane
axes. As the temperature increases, however, the easy axis rotates to the
direction normal to the plane. We further demonstrate that the easy
magnetization axis can be controlled by incident light through a bolometric
effect, which induces a pronounced increase in the amplitude of the AHE. A
mean-field-theory model for the carrier-mediated ferromagnetism reproduces the
tendency for dramatic reorientations of the magnetization axis, but not the
specific sensitivity to small temperature variations.",0308605v1
2003-09-02,The enhancement of phase separation aspect in electron doped manganite Ca0.8Sm0.16Nd0.04MnO3,"The complex lanthanide doping of electron manganites results in enhancement
of various phase separation effects in physical properties of these compounds.
Selecting Ca0.8Sm0.16Nd0.04MnO3 as a model case we show that the first order
structural phase transition from paramagnetic semi-metallic phase into
anti-ferromagnetic semi-metallic phase at TS ~ 158 +- 4 K is marked by an
abrupt decrease in magnetization, a step like anomaly DL/L = 10-4 in thermal
expansion and large latent heat DQ = 610 J/mol. In a certain temperature range
below TS, the high field magnetization exhibits hysteretic metamagnetic
behavior due to field-induced first order transformation. ac-susceptibility,
magnetization and resistivity data suggest rather a non-uniform state in
Ca0.8Sm0.16Nd0.04MnO3 at low temperatures. The metal - insulator transition
occurs at TMI ~112 +- 3 K, accompanied by a step-like increase in
magnetization. These features could be ascribed to ""sponging"" of electrons from
neighboring anti-ferromagnetic matrix by clusters undergoing the ferromagnetic
ordering.",0309065v1
2003-09-08,Local Ferromagnetism in Microporous Carbon with the Structural Regularity of Zeolite Y,"Magnetization M(H,T) measurements have been performed on microporous carbon
(MC) with a three-dimensional nano-array structure corresponding to that of a
zeolite Y supercage. The obtained results unambiguously demonstrate the
occurrence of high-temperature ferromagnetism in MC, probably originating from
a topological disorder associated with curved graphene sheets. The results
provide evidence that the ferromagnetic behavior of MC is governed by isolated
clusters in a broad temperature range, and suggest the occurrence of
percolative-type transition with the temperature lowering. A comparative
analysis of the results obtained on MC and related materials is given.",0309201v1
2003-09-19,Short-range spin- and pair-correlations: a variational wave-function,"A many-body wavefuction is postulated, which is sufficiently general to
describe superconducting pair-correlations, and/or spin-correlations, which can
occur either as long-range order or as finite-range correlations. The proposed
wave-function appears to summarize some of the more relevant aspects of the
rich phase-diagram of the high-Tc cuprates. Some of the states represented by
this wavefunction are reviewed: For superconductivity in the background of
robust anti-ferromagnetism, the Cooper-pairs are shown to be a superposition of
spinquantum numbers S=0 and S=1. If the anti-ferromagnetism is weak, a
continuous super-symmetric rotation is identified connecting s-wave
superconductivity to anti-ferromagnetism.",0309453v2
2003-09-19,High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins,"New mechanism of magnetoresistance, based on tunneling-emission of spin
polarized electrons from ferromagnets (FM) into semiconductors (S) and
precession of electron spin in the semiconductor layer under external magnetic
field, is described. The FM-S-FM structure is considered, which includes very
thin heavily doped (delta-doped) layers at FM-S interfaces. At certain
parameters the structure is highly sensitive at room-temperature to variations
of the field with frequencies up to 100 GHz. The current oscillates with the
field, and its relative amplitude is determined only by the spin polarizations
of FM-S junctions at relatively large bias voltage.",0309473v3
2003-09-29,Magnons in CMR pyrochlore Tl2Mn2O7,"Well defined spin waves were observed when the spin dynamics of Tl2Mn2O7, the
first pyrochlore compound found to exhibit colossal magnetoresistance, was
measured [J.W.Lynn et al., Phys.Rev.Lett. 80,4582(1998)], in stark contrast
with the experimental results on the larger family of magnetoresistive
manganites with perovskite structure. In this work, we present our calculation
for the spin waves in Tl2Mn2O7, which we described using the microscopic
generic model proposed recently for this compound [C.I.Ventura and M.A.Gusmao,
Phys.Rev.B 65, 14422(2002)]. We have employed a canonical transformation to
determine perturbatively the effective spin-wave Hamiltonian, obtaining
therefrom the renormalization of the ferromagnetic spin waves related to the
localized Mn$^{4+}$ spins, due to their coupling with the conduction electrons
present. We have calculated the magnon dispersion relations along different
paths in the first Brillouin zone, comparing them with those which are obtained
for an ideal isotropic ferromagnet. This comparison evidences an agreement
between the ferromagnetic magnons obtained from the generic model and the bare
spin waves, such as had been found in neutron scattering experiments.",0309684v1
2003-10-07,Phase diagram of a superconductor / ferromagnet bilayer,"The magnetic field (H) - temperature (T) phase diagram of a superconductor is
significantly altered when domains are present in an underlying ferromagnet
with perpendicular magnetic anisotropy. When the domains have a band-like
shape, the critical temperature Tc of the superconductor in zero field is
strongly reduced, and the slope of the upper critical field as a function of T
is increased by a factor of 2.4 due to the inhomogeneous stray fields of the
domains. Field compensation effects can cause an asymmetric phase boundary with
respect to H when the ferromagnet contains bubble domains. For a very
inhomogeneous domain structure, Tc~H^2 for low H and Tc~H for higher fields,
indicating a dimensional crossover from a one-dimensional network-like to a
two-dimensional behavior in the nucleation of superconductivity.",0310132v2
2003-10-27,Why Ni$_3$Al is an itinerant ferromagnet but Ni$_3$Ga is not,"Ni$_3$Al and Ni$_3$Ga are closely related materials on opposite sides of a
ferromagnetic quantum critical point. The Stoner factor of Ni is virtually the
same in both compounds and the density of states is larger in Ni$_3$Ga. So,
according to the Stoner theory, it should be more magnetic, and, in LDA
calculations, it is. However, experimentally, it is a paramagnet, while
Ni$_3$Al is an itinerant ferromagnet. We show that the critical spin
fluctuations are stronger than in Ni$_3$Ga, due to a weaker q-dependence of the
susceptibility, and this effect is strong enough to reverse the trend. The
approach combines LDA calculations with the Landau theory and the
fluctuation-dissipation theorem using the same momentum cut-off for both
materials. The calculations provide evidence for strong, beyond LDA, spin
fluctuations associated with the critical point in both materials, but stronger
in Ni$_3$Ga than in Ni$_3$Al.",0310629v2
2003-11-11,Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRu$_{1-x}$Rh$_x$O$_3$,"The solid-solution SrRu$_{1-x}$Rh$_x$O$_3$ ($0\le x \le1$) is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4$d^4$ to the enhanced paramagnetic
4$d^5$. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at $x \sim 0.6$.
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO$_3$. Furthermore, another
anomaly in the specific heat was observed at $x \sim 0.9$.",0311228v1
2003-11-22,Influence of a Uniform Current on Collective Magnetization Dynamics in a Ferromagnetic Metal,"We discuss the influence of a uniform current, $\vec{j} $, on the
magnetization dynamics of a ferromagnetic metal. We find that the magnon energy
$\epsilon(\vec{q})$ has a current-induced contribution proportional to
$\vec{q}\cdot \vec{\cal J}$, where $\vec{\cal J}$ is the spin-current, and
predict that collective dynamics will be more strongly damped at finite ${\vec
j}$. We obtain similar results for models with and without local moment
participation in the magnetic order. For transition metal ferromagnets, we
estimate that the uniform magnetic state will be destabilized for $j \gtrsim
10^{9} {\rm A} {\rm cm}^{-2}$. We discuss the relationship of this effect to
the spin-torque effects that alter magnetization dynamics in inhomogeneous
magnetic systems.",0311522v1
2003-12-10,Tunable spin polarization in III-V quantum wells with a ferromagnetic barrier,"We demonstrate the epitaxial growth of optical-quality electrically-gated
III-V ferromagnetic quantum structures. Photoluminescence spectroscopy reveals
that initially unpolarized photoexcited holes in a GaAs quantum well become
spin-polarized opposite to the magnetization of an adjacent digital
ferromagnetic layer in the AlGaAs barrier. A vertical bias is used to tune the
spin polarization from -0.4 to 6.3 percent at T = 5 K and B = 1 kG during which
the luminescence becomes quenched, indicating that the polarization is mediated
by wave function overlap between heavy holes in the quantum well and Mn-ions in
the barrier. Polarization is observed under negligible current flow and is
insensitive to the initial spin orientation of the carriers, differentiating
the effect from both electrical and optical spin injection.",0312240v1
2003-12-10,Exchange Biasing of the Ferromagnetic Semiconductor Ga1-xMnxAs,"We demonstrate the exchange coupling of a ferromagnetic semiconductor
(Ga1-xMnxAs) with an overgrown antiferromagnet (MnO). Unlike most conventional
exchange biased systems, the blocking temperature of the antiferromagnet (T_B =
48 +- 2 K) and the Curie temperature of the ferromagnet (T_C = 55.1 +- 0.2 K)
are comparable. The resulting exchange bias manifests itself as a clear shift
in the magnetization hysteresis loop when the bilayer is cooled in the presence
of an applied magnetic field and an enhancement of the coercive field.",0312259v2
2003-12-18,Anomalous Ferromagnetism of Monatomic Co Wire at the Pt(111) Surface Step Edge,"A first-principles investigation of the anomalous ferromagnetism of a
quasi-one-dimensional Co chain at the Pt(111) step edge is reported. Our
calculations show that the symmetry breaking at the step leads to an easy
magnetization axis at an odd angle of $\sim20^{\circ}$ {\em towards} the Pt
step, in agreement with experiment [P. Gambardella {\em et al.}, {\em Nature}
{\bf 416}, 301 (2002)]. Also, the Co spin and orbital moments become
noncollinear, even in the case of a collinear ferromagnetic spin arrangement. A
significant enhancement of the Co orbital magnetic moment is achieved when
modest electron correlations are treated within LSDA+$U$ calculations.",0312467v1
2003-12-25,Influence of Fe and Co on Phase Transitions in Ni-Mn-Ga Alloys,"Differential scanning calorimetry (DSC) and magnetic measurements were
performed to study the influence of ferromagnetic 3-d transition elements Fe
and Co on structural and magnetic properties of ferromagnetic shape memory
alloys Ni2MnGa. Addition of Fe or Co on the Ni sites decreases the temperature
of martensitic phase transition Tm, whereas addition of Co on the Mn sites
results in a considerable increase of Tm. Magnetic measurement revealed that
Curie temperature TC increases upon substitution of Fe or Co for Ni. This
observation is of importance for design of high temperature ferromagnetic shape
memory alloys.",0312639v1
2004-01-23,Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions,"The paper addresses inelastic spin-flip tunneling accompanied by surface spin
excitations (magnons) in ferromagnetic junctions. The inelastic tunneling
current is proportional to the magnon density of states which is
energy-independent for the surface waves and, for this reason, cannot account
for the bias-voltage dependence of the observed inelastic tunneling spectra.
This paper shows that the bias-voltage dependence of the tunneling spectra can
arise from the tunneling matrix elements of the electron-magnon interaction.
These matrix elements are derived from the Coulomb exchange interaction using
the itinerant-electron model of magnon-assisted tunneling. The results for the
inelastic tunneling spectra, based on the nonequilibrium Green's function
calculations, are presented for both parallel and antiparallel magnetizations
in the ferromagnetic leads.",0401460v6
2004-02-04,Magnetoresistance Effect in Spin-Polarized Junctions of Ferromagnetically Contacting Multiple Conductive Paths: Applications to Atomic Wires and Carbon Nanotubes,"For spin-polarized junctions of ferromagnetically contacting multiple
conductive paths, such as ferromagnet (FM)/atomic wires/FM and FM/carbon
nanotubes/FM junctions, we theoretically investigate spin-dependent transport
to elucidate the intrinsic relation between the number of paths and conduction,
and to enhance the magnetoresistance (MR) ratio. When many paths are randomly
located between the two FMs, electronic wave interference between the FMs
appears, and then the MR ratio increases with increasing number of paths.
Furthermore, at each number of paths, the MR ratio for carbon nanotubes becomes
larger than that for atomic wires, reflecting the characteristic shape of
points in contact with the FM.",0402119v1
2004-02-10,Magnetism in semiconductors: A dynamical mean field study of ferromagnetism in Ga_{1-x}Mn_xAs,"We employ the dynamical mean field approximation to perform a systematic
study of magnetism in Ga_{1-x}Mn_xAs. Our model incorporates the effects of the
strong spin-orbit coupling on the J=3/2 GaAs valence bands and of the exchange
interaction between the randomly distributed magnetic ions and the itinerant
holes. The ferromagnetic phase transition temperature T_c is obtained for
different values of the impurity-hole coupling J_c and of the hole
concentration n_h at the Mn doping of x=0.05. We also investigate the
temperature dependence of the local magnetization and spin polarization of the
holes. By comparing our results with those for a single band Hamiltonian in
which the spin-orbit coupling is switched off, we conclude that the spin-orbit
coupling in Ga_{1-x}Mn_xAs gives rise to frustration in the ferromagnetic
order, strengthening recent findings by Zarand and Janko (Phys. Rev. Lett. 89,
047201 (2002)).",0402289v1
2004-02-19,Fulde-Ferrell-Larkin-Ovchinnikov-like state in Ferromagnet-Superconductor Proximity System,"We discuss some properties of the ferromagnet-superconductor proximity
system. In particular, the emphasis is put on the physics of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state. In addition to Andreev
reflections it features a number of unusual thermodynamic and transport
properties, like: oscillatory behavior of the pairing amplitude, density of
states and superconducting transition temperature as a function of the
ferromagnet thickness. Surprisingly, under certain conditions spontaneous spin
polarized current is generated in the ground state of such a system. We provide
some informations regarding experimental observations of this exotic state.",0402492v1
2004-02-24,"Magneto-transport and magneto-optical properties of ferromagnetic (III,Mn)V semicondcutors: a review","Rapid developments in material research of metallic ferromagnetic (III,Mn)V
semiconductors over the past few years have brought a much better understanding
of these complex materials. We review here some of the main developments and
current understanding of the bulk properties of these systems within the
metallic regime, focusing principally on the magneto-transport and
magneto-optical properties. Although several theoretical approaches are
reviewed, the bulk of the review uses the effective Hamiltonian approach, which
has proven useful in describing many of these properties namely in (Ga,Mn)As
and (In,Mn)As. The model assumes a ferromagnetic coupling between Mn d-shell
local moments mediated by holes in the semiconductor valence band.",0402568v1
2004-02-26,"Optical properties of metallic (III,Mn)V ferromagnetic semiconductors in the infrared to visible range","We report on a study of the ac conductivity and magneto-optical properties of
metallic ferromagnetic (III,Mn)V semiconductors in the infrared to visible
spectrum. Our analysis is based on the successful kinetic exchange model for
(III,Mn)V ferromagnetic semiconductors. We perform the calculations within the
Kubo formalism and treat the disorder effects pertubatively within the Born
approximation, valid for the metallic regime. We consider an eight-band
Kohn-Luttinger model (six valence bands plus two conduction bands) as well as a
ten-band model with additional dispersionless bands simulating
phenomenologically the upper-mid-gap states induced by antisite and
interstitial impurities. These models qualitatively account for
optical-absorption experiments and predict new features in the mid-infrared
Kerr angle and magnetic-circular-dichroism properties as a function of Mn
concentration and free carrier density.",0402661v2
2004-03-01,Spin glass models with ferromagnetically biased couplings on the Bethe lattice: analytic solutions and numerical simulations,"We derive the zero-temperature phase diagram of spin glass models with a
generic fraction of ferromagnetic interactions on the Bethe lattice. We use the
cavity method at the level of one-step replica symmetry breaking (1RSB) and we
find three phases: A replica-symmetric (RS) ferromagnetic one, a magnetized
spin glass one (the so-called mixed phase), and an unmagnetized spin glass one.
We are able to give analytic expressions for the critical point where the RS
phase becomes unstable with respect to 1RSB solutions: we also clarify the
mechanism inducing such a phase transition. Finally we compare our analytical
results with the outcomes of a numerical algorithm especially designed for
finding ground states in an efficient way, stressing weak points in the use of
such numerical tools for discovering RSB effects. Some of the analytical
results are given for generic connectivity.",0403053v3
2004-03-01,Enhancing $T_c$ in ferromagnetic semiconductors,"We theoretically investigate disorder effects on the ferromagnetic transition
('Curie') temperature $T_c$ in dilute III$_{1-x}$Mn$_x$V magnetic
semiconductors (e.g. Ga$_{1-x}$Mn$_x$As) where a small fraction ($x \approx
0.01-0.1$) of the cation atoms (e.g. Ga) are randomly replaced by the magnetic
dopants (e.g. Mn), leading to long-range ferromagnetic ordering for $T<T_c$. We
find that $T_c$ is a complicated function of at least eight different
parameters including carrier density, magnetic dopant density, and carrier mean
free path; nominally macroscopically similar samples could have substantially
different Curie temperatures. We provide simple physically appealing
prescriptions for enhancing $T_c$ in diluted magnetic semiconductors, and
discuss the magnetic phase diagram in the system parameter space.",0403059v1
2004-03-02,Uniaxial-Pressure induced Ferromagnetism of Enhanced Paramagnetic Sr3Ru2O7,"We report a uniaxial pressure-dependence of magnetism in layered perovskite
strontium ruthenate Sr3Ru2O7. By applying a relatively small uniaxial pressure,
greater than 0.1 GPa normal to the RuO2 layer, ferromagnetic ordering manifests
below 80 K from the enhanced-paramagnet. Magnetization at 1 kOe and 2 K becomes
100 times larger than that under ambient condition. Uniaxial pressure
dependence of Curie temperature T_C suggests the first order magnetic
transition. Origin of this uniaxial-pressure induced ferromagnetism is
discussed in terms of the rotation of RuO6 octahedra within the RuO2 plane.",0403074v1
2004-03-17,Domain orbital state in ferromagnetic insulating La$_{0.825}$Ca$_{0.175}$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$ compound,"Using M\""ossbauer and EPR spectroscopy we have studied the insulating
ferromagnetic La$_{1-x}$Ca$_x$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$ ($x=0.175$)
compound prepared in air and reduced atmosphere. The average hyperfine field
follows a mean field approximation solution in contrast with the ferromagnetic
metallic regime where it significantly deviates from the order parameter
deduced from neutron diffraction data or mean field approximation. Although the
magnetic measurements show remarkable differences between air prepared and
reduced R samples the corresponding M\""ossbauer spectra are almost identical.
The strong temperature dependance of the hyperfine field distribution at the
$^{57}$Fe nucleus is related with the supertransferred magnetic field between
ferric ion and the oxygen bridged six nearest-neighbor manganese ions. The
sudden increasing of the width of the hyperfine field distribution above
$T_B\approx 100$ K has been attributed to the orbital disordering occurring for
$T>T_B$.",0403446v1
2004-03-18,Measurement of Spin Polarization by Andreev Reflection in Ferromagnetic In1-xMnxSb Epilayers,"We carried out Point Contact Andreev Reflection (PCAR) spin spectroscopy
measurements on epitaxially-grown ferromagnetic In1-xMnxSb epilayers with a
Curie temperature of ~9K. The spin sensitivity of PCAR in this material was
demonstrated by parallel control studies on its non-magnetic analog,
In1-yBeySb. We found the conductance curves of the Sn point contacts with
In1-yBeySb to be fairly conventional, with the possible presence of
proximity-induced superconductivity effects at the lowest temperatures. The
experimental Z-values of interfacial scattering agreed well with the estimates
based on the Fermi velocity mismatch between the semiconductor and the
superconductor. These measurements provided control data for subsequent PCAR
measurements on ferromagnetic In1-xMnxSb, which indicated spin polarization in
In1-xMnxSb to be 52 +- 3%.",0403451v1
2004-03-21,Phase diagram and magnetic properties of La$_{1-x}$Ca$_x$MnO$_3$ compound for $0\leq x \leq 0.23$,"In this article a detailed study of La$_{1-x}$Ca$_x$MnO$_3$ ($0\leq x \leq
0.23$) phase diagram using powder x-ray diffraction and magnetization
measurements is presented. Unfortunately, in the related literature no properly
characterized samples have been used, with consequence the smearing of the real
physics in this complicated system. As the present results reveal, there are
two families of samples. The first family concerns samples prepared in
atmosphere ($P({\rm O}_2)=0.2$ Atm) which are all ferromagnetic with Curie
temperature rising with $x$. The second family concerns samples, where a post
annealing in nearly zero oxygen partial pressure is applied. These samples show
a canted antiferromagnetic structure for $0\leq x \leq 0.1$ below $T_N$, while
for $0.125\leq x <0.23$ an unconventional ferromagnetic insulated phase is
present below $T_c$. The most important difference between nonstoichiometric
and stoichiometric samples concerning the magnetic behavior, is the anisotropy
in the exchange interactions, in the stoichiometric samples putting forward the
idea that a new orbital ordered phase is responsible for the ferromagnetic
insulating regime in the La$_{1-x}$Ca$_x$MnO$_3$ compound.",0403543v1
2004-03-24,Phase diagram and magnetic collective excitations of the Hubbard model in graphene sheets and layers,"We discuss the magnetic phases of the Hubbard model for the honeycomb lattice
both in two and three spatial dimensions. A ground state phase diagram is
obtained depending on the interaction strength
  U and electronic density n. We find a first order phase transition between
ferromagnetic regions where the spin is maximally polarized (Nagaoka
ferromagnetism) and regions with smaller magnetization (weak ferromagnetism).
When taking into account the possibility of spiral states, we find that the
lowest critical U is obtained for an ordering momentum different from zero. The
evolution of the ordering momentum with doping is discussed. The magnetic
excitations (spin waves) in the antiferromagnetic insulating phase are
calculated from the random-phase-approximation for the spin susceptibility. We
also compute the spin fluctuation correction to the mean field magnetization by
virtual emission/absorpion of spin waves. In the large $U$ limit, the
renormalized magnetization agrees qualitatively with the Holstein-Primakoff
theory of the Heisenberg antiferromagnet, although the latter approach produces
a larger renormalization.",0403605v2
2004-04-01,Cooperative dynamics in doped manganite films: phonon anomalies in the ferromagnetic state,"We present optical measurements of phononic excitations in
La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ (LCMO) and La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO)
thin films covering the full temperature range from the metallic ferromagnetic
to the insulating paramagnetic phase. All eight phonons expected for the
R$\bar{3}$c symmetry in LSMO and 17 out of the expected 25 phonons for the Pnma
symmetry in LCMO have been determined. Close to the
ferromagnetic-to-paramagnetic transition both compounds reveal an anomalous
behavior but with different characteristics. Anomalies in the phononic spectra
are a manifestation of the coupling of lattice degrees of freedom (DOF) to
electronic DOF. Specifically, the low-frequency external group proves to be an
indicator for lattice modifications induced by electronic correlations. The
enhanced electron-phonon coupling in LCMO is responsible for Fano-like
interference effects of distinct phonon modes with electronic continuum
excitations: we observe asymmetric phonon line shapes, mode splitting and
spectral weight transfer between modes.",0404024v1
2004-04-08,Exchange induced ordinary reflection in a single-channel superconductor-ferromagnet-superconductor junction,"The stationnary Josephson effect in a clean
Superconductor-Ferromagnet-Superconductor junction is revisited for arbitrarily
large spin polarizations. The quasiclassical calculation of the supercurrent
assumes that the Andreev reflection is complete for all channels. However, De
Jong and Beenakker have shown that the Andreev reflection at a clean FS
interface is incomplete, due to the exchange interaction in the ferromagnet.
Taking into account this incomplete Andreev reflection, we investigate the
quasiparticle spectrum, the Josephson current and the $0-\pi$ transition in a
ballistic single channel SFS junction. We find that energy gaps open in the
phase dependent spectrum. Although the spectrum is strongly modified when the
exchange energy increases, the Josephson current and the $0-\pi$ transition are
only weakly affected by the incomplete Andreev reflection, except when the
exchange energy is close to the Fermi energy.",0404190v3
2004-04-15,Evidence for crossed Andreev reflection in superconductor-ferromagnet hybrid structures,"We have measured the non-local resistance of aluminum-iron spin-valve
structures fabricated by e-beam lithography and shadow evaporation. The sample
geometry consists of an aluminum bar with two or more ferromagnetic wires
forming point contacts to the aluminum at varying distances from each other. In
the normal state of aluminum, we observe a spin-valve signal which allows us to
control the relative orientation of the magnetizations of the ferromagnetic
contacts. In the superconducting state, at low temperatures and excitation
voltages well below the gap, we observe a spin-dependent non-local resistance
which decays on a smaller length scale than the normal-state spin-valve signal.
The sign, magnitude and decay length of this signal is consistent with
predictions made for crossed Andreev reflection (CAR).",0404360v2
2004-04-20,Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in Rb${}_{2}$Cu${}_{2}$Mo${}_{3}$O${}_{12}$,"We have investigated magnetic properties of Rb$_2$Cu$_2$Mo$_3$O$_{12}$
powder. Temperature dependence of magnetic susceptibility and magnetic-field
dependence of magnetization have shown that this cuprate is a model compound of
a one-dimensional spin-1/2 Heisenberg system with ferromagnetic
first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor
(2NN) competing interactions (competing system). Values of the 1NN and 2NN
interactions are estimated as $J_1 = -138$ K and $J_2 = 51$ K ($\alpha \equiv
J_2 / J_1 = -0.37$). This value of $\alpha$ suggests that the ground state is a
spin-singlet incommensurate state. In spite of relatively large $J_1$ and
$J_2$, no magnetic phase transition appears down to 2 K, while an
antiferromagnetic transition occurs in other model compounds of the competing
system with ferromagnetic 1NN interaction. For that reason,
Rb$_2$Cu$_2$Mo$_3$O$_{12}$ is an ideal model compound to study properties of
the incommensurate ground state that are unconfirmed experimentally.",0404463v1
2004-04-20,Ferromagnetism and temperature-dependent Electronic Structure of hcp Gadolinium,"We use a combination of a many-body model analysis with an ab initio band
structure calculation to derive the temperature dependent electronic
quasiparticle structure of the rare-earth metal Gadolinium. As a local-moment
system Gd is properly represented by the ferromagnetic (multiband)
Kondo-lattice model (s-f (d-f) model). The single-particle part of the
model-Hamiltonian is taken from an augmented spherical wave (ASW) band
calculation. The proposed method avoids the double counting of relevant
interactions by exploiting an exact limiting case of the model and takes into
account the correct symmetry of atomic orbitals. The a priori only weakly
correlated 5d conduction bands get via interband exchange coupling to the
localized 4f levels a distinct temperature dependence which explains by a
Rudermann-Kittel-Kasuya-Yosida (RKKY) -type mechanism the ferromagnetism of Gd.
We get a self-consistently derived Curie temperature of 294.1 K and a
T=0-moment of 7.71 $\mu_{\rm B}$, surprisingly close to the experimental
values. The striking induced temperature-dependence of the 5d conduction bands
explains respective photoemission data. The only parameter of the theory
(interband exchange coupling J) is uniquely fixed by the band calculation.",0404472v1
2004-05-25,Dissipationless Anomalous Hall Current in the Ferromagnetic Spinel CuCr$_2$Se$_{4-x}$Br$_x$,"In a ferromagnet, an applied electric field $\bf E$ invariably produces an
anomalous Hall current ${\bf J}_H$ that flows perpendicular to the plane
defined by $\bf E$ and $\bf M$ (the magnetization). For decades, the question
whether ${\bf J}_H$ is dissipationless (independent of the scattering rate),
has been keenly debated without experimental resolution. In the ferromagnetic
spinel CuCr$_2$Se$_{4-x}$Br$_x$, the resistivity $\rho$ (at low temperature)
may be increased 1000 fold by varying $x$(Br), without degrading the $\bf M$.
We show that ${\bf J}_H/E$ (normalized per carrier, at 5 K) remains unchanged
throughout. In addition to resolving the controversy experimentally, our
finding has strong bearing on the generation and study of spin-Hall currents in
bulk samples.",0405584v1
2004-05-27,"Microphotoluminescence study of disorder in ferromagnetic (Cd,Mn)Te quantum well","Microphotoluminescence mapping experiments were performed on a modulation
doped (Cd,Mn)Te quantum well exhibiting carrier induced ferromagnetism. The
zero field splitting that reveals the presence of a spontaneous magnetization
in the low-temperature phase, is measured locally; its fluctuations are
compared to those of the spin content and of the carrier density, also measured
spectroscopically in the same run. We show that the fluctuations of the carrier
density are the main mechanism responsible for the fluctuations of the
spontaneous magnetization in the ferromagnetic phase, while those of the Mn
spin density have no detectable effect at this scale of observation.",0405657v2
2004-06-11,sin(2 phi) current-phase relation in SFS junctions with decoherence in the ferromagnet,"We propose a theoretical description of the sin(2 phi) current-phase relation
in SFS junctions at the 0-$\pi$ cross-over obtained in recent experiments by
Sellier et al. [Phys. Rev. Lett. 92, 257005 (2004)] where it was suggested that
a strong decoherence in the magnetic alloy can explain the magnitude of the
residual supercurrent at the 0-pi cross-over. To describe the interplay between
decoherence and elastic scattering in the ferromagnet we use an analogy with
crossed Andreev reflection in the presence of disorder. The supercurrent as a
function of the length R of the ferromagnet decays exponentially over a length
xi, larger than the elastic scattering length $l_d$ in the absence of
decoherence, and smaller than the coherence length $l_\phi$ in the absence of
elastic scattering on impurities. The best fit leads to $\xi \simeq
\xi_h^{({\rm diff})}/3$, where $\xi_h^{({\rm diff})}$ is exchange length of the
diffusive system without decoherence (also equal to $\xi$ in the absence of
decoherence). The fit of experiments works well for the amplitude of both the
sin(phi) and sin(2 phi) harmonics.",0406275v2
2004-06-21,Nonquasiparticle states in half-metallic ferromagnets,"Anomalous magnetic and electronic properties of the half-metallic
ferromagnets (HMF) have been discussed. The general conception of the HMF
electronic structure which take into account the most important correlation
effects from electron-magnon interactions, in particular, the spin-polaron
effects, is presented. Special attention is paid to the so called
non-quasiparticle (NQP) or incoherent states which are present in the gap near
the Fermi level and can give considerable contributions to thermodynamic and
transport properties. Prospects of experimental observation of the NQP states
in core-level spectroscopy is discussed. Special features of transport
properties of the HMF which are connected with the absence of one-magnon
spin-flip scattering processes are investigated. The temperature and magnetic
field dependences of resistivity in various regimes are calculated. It is shown
that the NQP states can give a dominate contribution to the temperature
dependence of the impurity-induced resistivity and in the tunnel junction
conductivity. First principle calculations of the NQP-states for the prototype
half-metallic material NiMnSb within the local-density approximation plus
dynamical mean field theory (LDA+DMFT) are presented.",0406487v1
2004-06-23,Weak itinerant ferromagnetism in YCo9Si4,"Weak itinerant ferromagnetism in YCo9Si4 below about 25 K is studied by means
of magnetisation, specific heat, and resistivity measurements. Single crystal
X-ray Rietveld refinements at room temperature reveal a fully ordered
distribution of Y, Co and Si atoms within the tetragonal space group I4/mcm
isostructural with LaCo9Si4. The latter exhibits itinerant electron
metamagnetism with an induced moment of about 1 mu_B/f.u. above 6 T, whereas
YCo9Si4 exhibits a spontaneous magnetisation M0~12 Am^2/kg at 2 K which
corresponds to an ordered moment of about 1.6 mu_B/f.u. indicating weak
itinerant ferromagnetism.",0406548v1
2004-06-23,Intermediate valence behavior in CeCo9Si4,"The novel ternary compound CeCo$_9$Si$_4$ has been studied by means of
specific heat, magnetisation, and transport measurements. Single crystal X-ray
Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms
with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The
smaller lattice constants of CeCo9Si4 in comparison with the trend established
by other RCo9Si4 is indicative for intermediate valence of cerium. While
RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly
ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large
as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is
of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic
YCo9Si4.",0406551v1
2004-07-12,Sign of the crossed conductances at a FSF double interface,"Crossed conductance in hybrid Ferromagnet / Superconductor / Ferromagnet
(FSF) structures results from the competition between normal transmission and
Andreev reflection channels. Crossed Andreev reflection (CAR) and elastic
cotunneling (EC) between the ferromagnets are dressed by local Andreev
reflections, which play an important role for transparent enough interfaces and
intermediate spin polarizations. This modifies the simple result previously
obtained at lowest order, and can explain the sign of the crossed resistances
in a recent experiment [D. Beckmann {\sl et al.}, cond-mat/0404360]. This holds
both in the multiterminal hybrid structure model (where phase averaging over
the Fermi oscillations is introduced ``by hand'' within the approximation of a
single non local process) and for infinite planar interfaces (where phase
averaging naturally results in the microscopic solution with multiple non local
processes).",0407283v2
2004-07-19,Anomalous self-energy and Fermi surface quasi-splitting in the vicinity of a ferromagnetic instability,"We discuss the low-temperature behavior of the electronic self-energy in the
vicinity of a ferromagnetic instability in two dimensions within the
two-particle self-consistent approximation, functional renormalization group
and Ward-identity approaches. Although the long-range magnetic order is absent
at T>0, the self-energy has a non-Fermi liquid form at low energies w<\Delta_0
near the Fermi level, where Delta_0 is the ground-state spin splitting. The
spectral function at temperatures T<Delta_0 has a two-peak structure with
finite spectral weight at the Fermi level. The simultaneous inclusion of
self-energy and vertex corrections shows that the above results remain
qualitatively unchanged down to very low temperatures T<<Delta_0. It is argued,
that this form of the spectral functions implies the quasi-splitting of the
Fermi surface in the paramagnetic phase in the presence of strong ferromagnetic
fluctuations.",0407473v1
2004-07-21,Boltzmann Test of Slonczewski's Theory of Spin Transfer Torque,"We use a matrix Boltzmann equation formalism to test the accuracy of
Slonczewski's theory of spin-transfer torque in thin-film heterostructures
where a non-magnetic spacer layer separates two non-collinear ferromagnetic
layers connected to non-magnetic leads. When applicable, the model predictions
for the torque as a function of the angle between the two ferromagnets agree
extremely well with the torques computed from a Boltzmann equation calculation.
We focus on asymmetric structures (where the two ferromagnets and two leads are
not identical) where the agreement pertains to a new analytic formula for the
torque derived by us using Slonczewski's theory. In almost all cases, we can
predict the correct value of the model parameters directly from the geometric
and transport properties of the multilayer. For some asymmetric geometries, we
predict a new mode of stable precession that does not occur for the symmetric
case studied by Slonczewski.",0407569v1
2004-07-28,Tunneling Anisotropic Magnetoresistance: A spin-valve like tunnel magnetoresistance using a single magnetic layer,"We introduce a new class of spintronics devices in which a spin-valve like
effect results from strong spin-orbit coupling in a single ferromagnetic layer
rather than from injection and detection of a spin-polarized current by two
coupled ferromagnets. The effect is observed in a
normal-metal/insulator/ferromagnetic-semiconductor tunneling device. This
behavior is caused by the interplay of the anisotropic density of states in
(Ga,Mn)As with respect to the magnetization direction, and the two-step
magnetization reversal process in this material.",0407735v1
2004-07-29,Anomalous-Hall heat current and Nernst effect in the ferromagnet CuCr_2Se_{4-x}Br_x,"In a ferromagnet, an anomalous-Hall heat current, given by the off-diagonal
Peltier term $\alpha_{xy}$, accompanies the anomalous Hall current. By
combining Nernst, thermopower and Hall experiments, we have measured how
$\alpha_{xy}$ varies with hole density and lifetime $\tau$ in $\rm
CuCr_2Se_{4-x}Br_x$. At low temperatures $T$, we find that $\alpha_{xy}$ is
independent of $\tau$, consistent with anomalous-velocity theories. Its
magnitude is fixed by a microscopic geometric area ${\cal A}\sim 34
\mathrm{\AA}^2$. Our results are incompatible with some models of the Nernst
effect in ferromagnets.",0407765v2
2004-08-02,Disorder in Diluted Spin Systems,"The influence of substitutional disorder on the magnetic properties of
diluted Heisenberg spin systems is studied with regard to the magnetic
stability of ferromagnetic diluted semiconductors (DMS). The equation of motion
for the magnon Green's function within Tyablikov approximation is solved
numerically for finite systems. The resulting spectral density is then used to
estimate the magnetization and Curie temperature of an infinite system. This
method is suitable for any form of a ferromagnetic exchange interaction.
Besides different lattices and spin magnitude $S$, exchange interactions of
different range are examined. The results show that, for short-range
interaction, no magnetic order exists below the critical percolation
concentration, whereas a linear dependence of the Curie temperature on the
concentration of spins is found for ferromagnetic long-range interaction.",0408039v1
2004-08-09,Charge and Lattice Dynamics of Ordered State in La$_{1/2}$Ca$_{1/2}$MnO$_3$: Infrared Reflection Spectroscopy Study,"We report an infrared reflection spectroscopy study of
La$_{1/2}$Ca$_{1/2}$MnO$_3$ over a broad frequency range and temperature
interval which covers the transitions from the high temperature paramagnetic to
ferromagnetic and, upon further cooling, to antiferromagnetic phase. The
structural phase transition, accompanied by a ferromagnetic ordering at
T$_C$=234 K, leads to enrichment of the phonon spectrum. A charge ordered
antiferromagnetic insulating ground state develops below the N\'eel transition
temperature T$_N$=163 K. This is evidenced by the formation of charge density
waves and opening of a gap with the magnitude of 2$\Delta_0$ = (320 $\pm$ 15)
cm$^{-1}$ in the excitation spectrum. Several of the infrared active phonons
are found to exhibit anomalous frequency softening. The experimental data
suggest coexistence of ferromagnetic and antiferromangetic phases at low
temperatures.",0408157v1
2004-08-12,High Temperature Ferromagnetism in Zn1-xMnxO semiconductor thin films,"Clear evidence of ferromagnetic behavior at temperatures >400 K as well as
spin polarization of the charge carriers have been observed in ZnMnO thin films
grown on Al2O3 and MgO substrates. The magnetic properties depended on the
exact Mn concentration and the growth parameters. In well-characterized
single-phase films, the magnetic moment is 4.8?B/Mn at 350 K, the highest
moment yet reported for any Mn doped magnetic semiconductor. Anomalous Hall
effect shows that the charge carriers (electrons) are spin polarized and
participate in the observed ferromagnetic behavior.",0408294v1
2004-08-27,"Confined spin waves reveal an assembly of nanosize domains in ferromagnetic La(1-x)CaxMnO3 (x=0.17,0.2)","We report a study of spin-waves in ferromagnetic La$_{1-x}$Ca$_{x}$MnO$_3$,
at concentrations x=0.17 and x=0.2 very close to the metallic transition
(x=0.225). Below T$_C$, in the quasi-metallic state (T=150K), nearly
q-independent energy levels are observed. They are characteristic of standing
spin waves confined into finite-size ferromagnetic domains, defined in {\bf a,
b) plane for x=0.17 and in all q-directions for x=0.2. They allow an estimation
of the domain size, a few lattice spacings, and of the magnetic coupling
constants inside the domains. These constants, anisotropic, are typical of an
orbital-ordered state, allowing to characterize the domains as ""hole-poor"". The
precursor state of the CMR metallic phase appears, therefore, as an assembly of
small orbital-ordered domains.",0408611v2
2004-09-06,Bubble domains in disc-shaped ferromagnetic particles,"We study the fundamental magnetic states of disc-shaped ferromagnetic
particles with a uniaxial anisotropy along the symmetry axis. Besides the
monodomain, a bidomain state is also identified and studied both numerically
and theoretically. This bidomain state consists of two coaxial oppositely
magnetized cylindrically symmetric domains and remains stable even at zero bias
field, unlike magnetic bubbles in ferromagnetic films. For a given disc
thickness we find the critical radius above which the magnetization
configuration falls into the bidomain bubble state. The critical radius depends
strongly on the film thickness especially for ultrathin films. The effect of an
external field is also studied and the bidomain state is found to remain stable
over a range of field strengths.",0409129v1
2004-09-07,From itinerant ferromagnetism to insulating antiferromagnetism: A magnetic and transport study of single crystal SrRu1-xMnxO3,"We report results of a magnetic and transport study of SrRu1-xMnxO3, i.e., Mn
doped SrRuO3. The Mn doping drives the system from the itinerant ferromagnetic
state (TC=165 K for x=0) through a quantum critical point at xc=0.39 to an
insulating antiferromagnetic state. The onset of antiferromagnetism is abrupt
with a Neel temperature increasing from 205 K for x=0.44 to 250 K for x=0.59.
Accompanying this quantum phase transition is a drastic change in resistivity
by as much as 8 orders of magnitude as a function of x at low temperatures. The
critical composition xc=0.39 sharply separates the two distinct ground states,
namely the ferromagnetic metal from the antiferromagnetic insulator.",0409157v1
2004-09-12,Unusual direction dependence of exchange energies in GaAs:Mn - Is the RKKY description relevant,"Ferromagnetism in Mn-doped GaAs, the prototypical dilute magnetic
semiconductor, has so far been attributed to hole mediated RKKY-type
interactions. First-principles calculations reveal a strong direction
dependence of the ferromagnetic (FM) stabilization energy of two magnetic ions,
a dependence that cannot be explained within RKKY. In the limit of host-like
hole (engineered here by an GGA+U approach with large U) where the RKKY model
is applicable, we find that the exchange energies are strongly reduced,
suggesting that this limit cannot explain the observed ferromagnetism. The
dominant contribution stabilizing the FM state is found to be maximal for
<110>-oriented pairs and minimal for <100> oriented pairs, providing an
alternate explanation for magnetism in such materials in terms of energy
lowering due to p-d hopping interactions, and offering a new design degree of
freedom to enhance FM.",0409295v1
2004-09-25,Bose-Einstein condensation of trapped interacting spin-1 atoms,"We investigate Bose-Einstein condensation of trapped spin-1 atoms with
ferromagnetic or antiferromagnetic two-body contact interactions. We adopt the
mean field theory and develop a Hartree-Fock-Popov type approximation in terms
of a semiclassical two-fluid model. For antiferromagnetic interactions, our
study reveals double condensations as atoms in the $|m_F=0>$ state never seem
to condense under the constraints of both the conservation of total atom number
$N$ and magnetization $M$. For ferromagnetic interactions, however, triple
condensations can occur. Our results can be conveniently understood in terms of
the interplay of three factors: (anti) ferromagnetic atom-atom interactions,
$M$ conservation, and the miscibilities between and among different condensed
components.",0409680v1
2004-10-04,Magnetotransport properties of ferromagnetic Pr0.85Ca0.15MnO3/ferroelectric Ba0.6Sr0.4TiO3 superlattice films,"Artificial superlattices designed with ferromagnetic Pr0.85Ca0.15MnO3
insulating layer and ferroelectric Ba0.6Sr0.4TiO3 layer were grown on (100)
SrTiO3 substrates. The magnetotransport properties were measured with the
current perpendicular to the plane geometry. An increase in magnetoresistance
(MR), with no significant low field effect, was observed as the number of
ferroelectric Ba0.6Sr0.4TiO3 layer thickness increases even up to 9 unit cells.
For example, the superlattice [(Pr0.85Ca0.15MnO3)10(Ba0.6Sr0.4TiO3)9]25 shows
35 % MR at 100 K, though the Pr0.85Ca0.15MnO3 film was a robust insulator with
negligible MR even at high applied magnetic field. This observed large MR
cannot be explained by simple interfacial ferromagnetism or by the tunneling
magnetoresistance. One possible explanation could be the effect due to the
ferroelectric spacer layer and the associated magnetoelectric coupling.",0410081v1
2004-10-09,Electronic Structure of Strained Manganite Thin Films with Room Temperature Ferromagnetism Investigated by Hard X-ray Photoemission Spectroscopy,"We report the bulk sensitive Hard X-ray (hv=5.95keV) core level photoemission
spectroscopy to investigate the intrinsic electronic structure of strained
(La0.85Ba0.15)MnO3 thin films. In a 20nm thick well-strained film with strongly
enhanced ferromagnetism, a new sharp satellite peak appeared at the low energy
site of the Mn 2p3/2 main peak, whereas a broader signal was observed for the
unstrained film with 300nm thickness. Cluster calculations revealed that the
intensity corresponded to the density of the state at the Fermi level relating
to the magnitude of the ferromagnetic order. The satellite intensity also
agreed quantitatively with the square of the magnetization.",0410223v1
2004-10-29,Weak ferromagnetism in antiferromagnets: Fe$_{2}$O$_{3}$ and La$_{2}$CuO$_{4}$,"The problem of weak ferromagnetism in antiferromagnets due to canting of
magnetic moments was treated using Green's function technique. At first the
eigenvalues and eigenfunctions of the electronic Hamiltonian corresponding to
collinear magnetic configuration are calculated which are then used to
determine first and second variations of the total energy as a function of the
magnetic moments canting angle. Spin-orbit coupling is taken into account via
perturbation theory. The results of calculations are used to determine an
effective spin Hamiltonian. This Hamiltonian can be mapped on conventional spin
Hamiltonian that allows to determine parameters of isotropic and anisotropic
(Dzyaloshinskii-Moriya) exchange interactions. The method was applied to the
typical antiferromagnets with weak ferromagnetism Fe$_{2}$O$_{3}$ and
La$_{2}$CuO$_{4}$. The obtained directions and values of the magnetic moments
canting angles are in a reasonable agreement with experimental data.",0410767v1
2004-10-30,Dynamics of Domain Wall in a Biaxial Ferromagnet With Spin-torque,"The dynamics of the domain wall (DW) in a biaxial ferromagnet interacting
with a spin-polarized current are described by sine-gordon (SG) equation
coupled with Gilbert damping term in this paper. Within our frame-work of this
model, we obtain a threshold of the current in the motion of a single DW with
the perturbation theory on kink soliton solution to the corresponding
ferromagnetic system, and the threshold is shown to be dependent on the Gilbert
damping term. Also, the motion properties of the DW are discussed for the zero-
and nonzero-damping cases, which shows that our theory to describe the dynamics
of the DW are self-consistent.",0411005v3
2004-11-08,Local Density of States and Order Parameter Configurations in Layered Ferromagnet-Superconductor Structures,"We analyze the local density of states (LDOS) of heterostructures consisting
of alternating ferromagnet, $F$, and superconductor, $S$, layers. We consider
structures of the $SFS$ and $SFSFSFS$ type, with thin nanometer scale $F$ and
$S$ layers, within the ballistic regime. The spin-splitting effects of the
ferromagnet and the mutual coupling between the $S$ regions, yield several
nontrivial stable and metastable pair amplitude configurations, and we find
that the details of the spatial behavior of the pair amplitude govern the
calculated electronic spectra. These are reflected in discernible signatures of
the LDOS. The roles that the magnetic exchange energy, interface scattering
strength, and the Fermi wavevector mismatch each have on the LDOS for the
different allowed junction configurations, are systematically investigated.",0411203v1
2004-11-09,Spin Glass and ferromagnetism in disordered Kondo lattice,"The competition among spin glass (SG), ferromagnetism and Kondo effect has
been analysed in a Kondo lattice model where the inter-site coupling $J_{ij}$
between the localized magnetic moments is given by a generalized Mattis model
\cite{Mattis} which represents an interpolation between ferromagnetism and a
highly disordered spin glass. Functional integral techniques with of Grassmann
fields has been used to obtain the partition function. The static approximation
and the replica symmetric ansatz has also been used. The solution of the
problem is presented as a phase diagram temperature $T$ {\it versus} $J_K$ (the
strength of the intra-site interaction). If $J_K$ is small, for decreasing
temperature there is a second order transition from a paramagnetic to a spin
glass phase For lower temperatures, a first order transition appears where
solutions for the spin glass order parameter and the local magnetizations are
simultaneously non zero. For very low temperatures, the local magnetizations
becomes thermodinamically stables. For high $J_K$, the Kondo state is
dominating. These results could be helpful to clarify the experimental
situation of $CeNi_{1-x}Cu_{x}$.",0411229v1
2004-11-14,"Transitions between ""$π$"" and ""0"" states in superconductor -- ferromagnet -- superconductor junctions","Experimental and theoretical study of superconductor (S) -- ferromagnet (F)
-- superconductor junctions showed that in certain range of parameters (e.g.,
the length of the ferromagnet $d_F$, the exchange field, $E_{\rm ex}$) the
ground state of a SFS junction corresponds to superconducting phase difference
$\pi$ or 0. The phase diagram of a SFS junction with the respect to $\pi$ and 0
states is investigated in this letter in $E_{\rm ex}, d_{F}, T$ space. It is
shown that the phase diagram is very sensitive to the geometry of the system,
in particular, to the amount of disorder.",0411367v2
2004-11-17,Spin-fluctuation dominated electrical transport of Ni3Al at high pressure,"We present the first study of a magnetic quantum phase transition in the
itinerant-electron ferromagnet Ni3Al at high pressures. Electrical resistivity
measurements in a diamond anvil cell at hydrostatic pressures up to 100 kbar
and temperatures as low as 50 mK indicate that the Curie temperature collapses
towards absolute zero at a critical pressure pc=82(2) kbar. Over wide ranges in
pressure and temperature, both in the ferromagnetic and paramagnetic states,
the temperature variation of the resistivity is found to deviate from the
conventional Fermi-liquid form. We consider the extent to which this deviation
can be understood in terms of a mean-field model of enhanced spin fluctuations
on the border of ferromagnetism in three dimensions.",0411451v1
2004-11-18,Ferromagnetic/DMS hybrid structures: one- and zero-dimensional magnetic traps for quasiparticles,"We investigated possibility of using local magnetic field originating from
ferromagnetic island deposited on the top of semiconductor quantum well to
produce zero- and one-dimensional traps for quasi-particles with spin. In
particular we considered two shapes of experimentally made magnets -
cylindrical and rectangular. In the case of ferromagnetic micro-disk the trap
can localize spin in three dimensions, contrary to the rectangular micro-magnet
which creates a trap that allows free propagation in one direction. We present
in detail prediction for absorption spectrum around the main absorption edge in
both type of micro-magnets.",0411482v1
2004-11-19,Phenomenological study of spin-triplet ferromagnetic superconductors,"Unconventional superconductivity with spin-triplet Cooper pairing is reviewed
on the basis of the quasi-phenomenological Ginzburg-Landau theory. The
superconductivity, in particular, the mixed phase of coexistence of
ferromagnetism and unconventional superconductivity is triggered by the
spontaneous magnetization. The mixed phase is stable whereas the other
superconducting phases that usually exist in unconventional superconductors are
either unstable, or, for particular values of the parameters of the theory,
some of these phases are metastable at relatively low temperatures in a quite
narrow domain of the phase diagram. The phase transitions from the normal phase
to the phase of coexistence is of first order while the phase transition from
the ferromagnetic phase to the coexistence phase can be either of first or
second order depending on the concrete substance. The Cooper pair and crystal
anisotropy are relevant to a more precise outline of the phase diagram shape
and reduce the degeneration of the ground states of the system but they do not
drastically influence the phase stability domains and the thermodynamic
properties of the respective phases.",0411503v1
2004-11-24,Electrical Spin Injection in Multi-Wall carbon NanoTubes with transparent ferromagnetic contacts,"We report on electrical spin injection measurements on MWNTs . We use a
ferromagnetic alloy Pd$_{1-x}$Ni$_{x}$ with x $\approx$ 0.7 which allows to
obtain devices with resistances as low as 5.6 $k\Omega$ at 300 $K$. The yield
of device resistances below 100 $k\Omega$, at 300 $K$, is around 50%. We
measure at 2 $K$ a hysteretic magneto-resistance due to the magnetization
reversal of the ferromagnetic leads. The relative difference between the
resistance in the antiparallel (AP) orientation and the parallel (P)
orientation is about 2%.",0411623v2
2004-12-03,Metastability in zero-temperature dynamics: Statistics of attractors,"The zero-temperature dynamics of simple models such as Ising ferromagnets
provides, as an alternative to the mean-field situation, interesting examples
of dynamical systems with many attractors (absorbing configurations, blocked
configurations, zero-temperature metastable states). After a brief review of
metastability in the mean-field ferromagnet and of the droplet picture, we
focus our attention onto zero-temperature single-spin-flip dynamics of
ferromagnetic Ising models. The situations leading to metastability are
characterized. The statistics and the spatial structure of the attractors thus
obtained are investigated, and put in perspective with uniform a priori
ensembles. We review the vast amount of exact results available in one
dimension, and present original results on the square and honeycomb lattices.",0412077v1
2004-12-10,Thermodynamic properties of tetrameric bond-alternating spin chains,"Thermodynamic properties of a tetrameric bond-alternating Heisenberg spin
chain with ferromagnetic-ferromagnetic-antiferromagnetic-antiferromagnetic
exchange interactions are studied using the transfer-matrix renormalization
group and compared to experimental measurements. The temperature dependence of
the uniform susceptibility exhibits typical ferrimagnetic features. Both the
uniform and staggered magnetic susceptibilities diverge in the limit $T\to 0$,
indicating that the ground state has both ferromagnetic and antiferromagnetic
long-range orders. A double-peak structure appears in the temperature
dependence of the specific heat. Our numerical calculation gives a good account
for the temperature and field dependence of the susceptibility, the
magnetization, and the specific heat for Cu(3-Clpy)$_{2}$(N$_{3}$)$_{2}$
(3-Clpy=3-Chloroyridine).",0412275v2
2004-12-13,"Quantitative Study of Magnetotransport through a (Ga,Mn)As Single Ferromagnetic Domain","We have performed a systematic investigation of the longitudinal and
transverse magnetoresistance of a single ferromagnetic domain in (Ga,Mn)As. We
find that, by taking into account the intrinsic dependence of the resistivity
on the magnetic induction, an excellent agreement between experimental results
and theoretical expectations is obtained. Our findings provide a detailed and
fully quantitative validation of the theoretical description of
magnetotransport through a single ferromagnetic domain. Our analysis
furthermore indicates the relevance of magneto-impurity scattering as a
mechanism for magnetoresistance in (Ga,Mn)As.",0412290v2
2004-12-14,Ising model in scale-free networks: A Monte Carlo simulation,"The Ising model in uncorrelated scale-free networks has been studied by means
of Monte Carlo simulations. These networks are characterized by a degree (or
connectivity) distribution $P(k) \sim k^{-\gamma}$. The
ferromagnetic-paramagnetic transition temperature has been studied as a
function of the parameter $\gamma$. For $\gamma > 3$ our results agree with
earlier analytical calculations, which found a phase transition at a
temperature $T_c(\gamma)$ in the thermodynamic limit. For $\gamma \leq 3$, a
ferromagnetic-paramagnetic crossover occurs at a size-dependent temperature
$T_{co}$, and the system is in the ordered ferromagnetic state at any
temperature for a system size $N \to \infty$. For $\gamma = 3$ and large enough
$N$, the crossover temperature is found to be $T_{co} \approx A \ln N$, with a
prefactor $A$ proportional to the mean degree. For $2 < \gamma < 3$, we obtain
$T_{co} \sim < k > N^z$, with an exponent $z$ that decreases as $\gamma$
increases. This exponent is found to be lower than predicted by earlier
calculations.",0412355v1
2004-12-21,GaN:Gd: A superdilute ferromagnetic semiconductor with a Curie temperature above 300 K,"We investigate the magnetic and magneto-optic properties of epitaxial GaN:Gd
layers as a function of the external magnetic field and temperature. An
unprecedented magnetic moment is observed in this diluted magnetic
semiconductor. The average value of the moment per Gd atom is found to be as
high as 4000 \mub as compared to its atomic moment of 8 \mub. The long-range
spin-polarization of the GaN matrix by Gd is also reflected in the circular
polarization of magneto-photoluminescence measurements. Moreover, the materials
system is found to be ferromagnetic above room temperature in the entire
concentration range under investigation (7$\times10^{15}$ to 2$\times10^{19}$
cm$^{-3}$). We propose a phenomenological model to understand the macroscopic
magnetic behavior of the system. Our study reveals a close connection between
the observed ferromagnetism and the colossal magnetic moment of Gd.",0412564v2
2004-12-27,Ferromagnetism and possible heavy fermion behavior in single crystals of NdOs$_4$Sb$_{12}$,"Single crystals of the filled-skutterudite compound NdOs$_4$Sb$_{12}$ have
been investigated by means of electrical resistivity, magnetization, and
specific heat measurements. The NdOs$_4$Sb$_{12}$ crystals have the
LaFe$_4$P$_{12}$-type cubic structure with a lattice parameter of 9.3 \AA.
Possible heavy-fermion behavior is inferred from specific heat measurements,
which reveal a large electronic specific heat coefficient $\gamma \approx 520$
mJ/mol-K$^2$, corresponding to an effective mass $m^* \sim$ 98 $m_e$. Features
related to a ferromagnetic transition at {$\sim$ 0.9 K} can be observed in
electrical resistivity, magnetization and specific heat. Conventional
Arrott-plot analysis indicates that NdOs$_4$Sb$_{12}$ conforms to mean-field
ferromagnetism.",0412713v3
2005-01-12,Ferromagnetism in Ga1-xMnxP: evidence for inter-Mn exchange mediated by localized holes within a detached impurity band,"We demonstrate that in ferromagnetic Ga1-xMnxP exchange is mediated by holes
localized in a Mn-derived band. For x<0.06, infrared absorption and
photoconductivity spectra indicate the presence of a Mn impurity band which is
not merged with the valence band. At temperatures above TC (<65 K) electrical
transport is dominated by excitation across this energy gap while nearest
neighbor hopping dominates below TC. Magnetization measurements reveal a moment
of 3.5 Bohr magnetons per substitutional Mn, while the large anomalous Hall
signal unambiguously demonstrates that the ferromagnetism is carrier-mediated.",0501275v3
2005-01-14,Electronic self-energy and triplet pairing fluctuations in the vicinity of a ferromagnetic instability in 2D systems: the quasistatic approach,"The self-energy, spectral functions and susceptibilities of 2D systems with
strong ferromagnetic fluctuations are considered within the quasistatic
approach. The self-energy at low temperatures T has a non-Fermi liquid form in
the energy window w<Delta near the Fermi level, where Delta is the ground-state
spin splitting for magnetically ordered ground state, and Delta ~ T^(1/2)
ln^(1/2)(vF/T) in the quantum critical regime (vF is the Fermi velocity).
Spectral functions have a two-peak structure at finite T above the magnetically
ordered ground state, which implies quasi-splitting of the Fermi surface in the
paramagnetic phase in the presence of strong ferromagnetic fluctuations. The
triplet pairing amplitude in the quasistatic approximation increases with
increasing correlation length; at low temperatures T<<Delta the vertex
corrections become important and the Eliashberg approach is not justified. The
results for the spectral properties and susceptibilities in the quantum
critical regime near charge- (spin-) instabilities with large enough
correlation length xi>>(T/vF)^(-1/3) are obtained.",0501331v2
2005-02-01,Orbital Ordering in ferromagnetic Lu2V2O7,"We have observed the orbital ordering in the ferromagnetic Mott-insulator
Lu2V2O7 by the polarized neutron diffraction technique. The orbital ordering
pattern determined from the observed magnetic form factors can be explained in
terms of a linear combination of wave functions |yz>, |zx> and |xy>; |0> =
(1/3)^(1/2) |xy> + (1/3)^(1/2)|yz> + (1/3)^(1/2) |zx> which is proportional to
|(x + y + z)^2 - r^2>; where each orbital is extended toward the center-of-mass
of the V tetrahedron. We discuss the stability of the ferromagnetic Lu2V2O7,
using a Hubbard Hamiltonian with these three orbitals.",0502020v1
2005-02-09,Weak ferromagnetism and spiral spin structures in honeycomb Hubbard planes,"Within the Hartree Fock- RPA analysis, we derive the spin wave spectrum for
the weak ferromagnetic phase of the Hubbard model on the honeycomb lattice.
Assuming a uniform magnetization, the polar (optical) and acoustic branches of
the spin wave excitations are determined. The bipartite lattice geometry
produces a q-dependent phase difference between the spin wave amplitudes on the
two sub-lattices. We also find an instability of the uniform weakly magnetized
configuration to a weak antiferromagnetic spiraling spin structure, in the
lattice plane, with wave vector Q along the Gamma-K direction, for electron
densities n>0.6. We discuss the effect of diagonal disorder on both the
creation of electron bound states, enhancement of the density of states, and
the possible relevance of these effects to disorder induced ferromagnetism, as
observed in proton irradiated graphite.",0502249v2
2005-02-11,Pt steps decorated by 3d nanowires calculated via an order-N method,"We present the magnetization energy and magnetic moments of 3d monowires
aligned along the step edges of Pt (533) and (322) vicinal substrates. We
employ an electronic structure method which scales linearly with the size of
the system. This allows us to treat with ease both ferromagnetic and
antiferromagnetic solutions, and in principle the method should allow for the
evaluation of more complex systems, such as wires deposited on rough step
edges. We find that Co, Fe, and Mn are almost perfect Heisenberg systems, with
almost no change in the moment between antiferromagnetic and ferromagnetic
solutions. A large polarisation of the Pt substrate is also observed. Our
results are in close agreement w ith recent experimental results obtained for
the case of a Co monowire. As expected the trend is for the late d series to be
stabalised by ferromagnetic long range order and the middle of the d series by
antiferromagnetic order. Since our method is only \emph{locally} self
consistent we discuss as some length the convergence of the results with
respect to the size of the region which is treated self-consistently.",0502295v1
2005-03-03,Transport properties of diluted magnetic semiconductors: Dynamical mean field theory and Boltzmann theory,"The transport properties of diluted magnetic semiconductors (DMS) are
calculated using dynamical mean field theory (DMFT) and Boltzmann transport
theory. Within DMFT we study the density of states and the dc-resistivity,
which are strongly parameter dependent such as temperature, doping, density of
the carriers, and the strength of the carrier-local impurity spin exchange
coupling. Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism. We find that spin-disorder scattering, formation of bound state, and
the population of the minority spin band are all operational in DMFT in
different parameter range. We also develop a complementary Boltzmann transport
theory for scattering by screened ionized impurities. The difference in the
screening properties between paramagnetic ($T>T_c$) and ferromagnetic ($T<T_c$)
states gives rise to the temperature dependence (increase or decrease) of
resistivity, depending on the carrier density, as the system goes from the
paramagnetic phase to the ferromagnetic phase. The metallic behavior below
$T_c$ for optimally doped DMS samples can be explained in the Boltzmann theory
by temperature dependent screening and thermal change of carrier spin
polarization.",0503077v1
2005-03-25,The role of ferroelectric-ferromagnetic layers on the properties of superlattice-based multiferroics,"A series of superlattices and trilayers composed of ferromagnetic and
ferroelectric or paraelectric layers were grown on (100) SrTiO3 by the pulsed
laser deposition technique. Their structural and magneto-electric properties
were examined. The superlattices made of ferromagnetic Pr0.85Ca0.15MnO3 (PCMO)
and a ferroelectric, namely Ba0.6Sr0.4TiO3 (BST) or BaTiO3, showed enhanced
magnetoresistance (MR) at high applied magnetic field, whereas such enhancement
was absent in Pr0.85Ca0.15MnO3/SrTiO3 superlattices, which clearly demonstrates
the preponderant role of the ferroelectric layers in this enhanced MR.
Furthermore, the absence of enhanced MR in trilayers of PCMO/BST indicates that
the magneto-electric coupling which is responsible for MR in these systems is
stronger in multilayers than in their trilayer counterparts.",0503609v1
2005-03-30,Stability of ferromagnetism in the half-metallic pnictides and similar compounds: A first-principles study,"Based on first-principles electron structure calculations and employing the
frozen-magnon approximation we study the exchange interactions in a series of
transition-metal binary alloys crystallizing in the zinc-blende structure and
calculate the Curie temperature within both the mean-field approximation (MFA)
and random-phase approximation (RPA). We study two Cr compounds, CrAs and CrSe,
and four Mn compounds: MnSi, MnGe, MnAs and MnC. MnC, MnSi and MnGe are
isovalent to CrAs and MnAs is isoelectronic with CrSe. Ferromagnetism is
particular stable for CrAs, MnSi and MnGe: All three compounds show Curie
temperatures around 1000 K. On the other hand, CrSe and MnAs show a tendency to
antiferromagnetism when compressing the lattice. In MnC the half-metallic gap
is located in the majority-spin channel contrary to the other five compounds.
The large half-metallic gaps, very high Curie temperatures, the stability of
the ferromagnetism with respect to the variation of the lattice parameter and a
coherent growth on semiconductors make MnSi and CrAs most promising candidates
for the use in spintronics devises.",0503713v1
2005-04-04,Theory of Spin-Wave Frequency Gaps in 3D Magnonic Crystals. Application to Manganites,"his study is an investigation of spin wave spectrum in macrostructures
composed of two ferromagnetic materials and showing a 3D periodicity: spherical
ferromagnetic grains disposed in the nodes of a 3D crystal lattice are embedded
in a matrix with different ferromagnetic properties. Frequency ranges forbidden
to spin wave propagation are found in the calculated magnonic spectra. Both the
position and the width of the gaps are found to depend on the magnetic
(exchange and magnetization) contrasts in the composite material, as well as on
its structural parameters (filling fraction, crystal lattice type). Having
applied our theory to interpretation of the existence of a spin wave gap in
doped manganites, recently revealed in neutron scattering experiments by S.
Hennion {\em et al.}, we obtained a good (though approximate) quantitative
agreement with the experimental results. A working hypothesis is proposed on
this basis, supposing that certain manganites can be treated as natural 3D
magnonic crystals.",0504073v1
2005-04-12,Spin and orbital ferromagnetism in strongly correlated itinerant electron systems,"Spectra of one-electron and collective excitations in narrow-band
ferromagnets with unquenched orbital moments are calculated in various
theoretical models. The interaction of spin and orbital excitations with
conduction electrons results in the damping of the former which, however, turns
out to be rather small; therefore, apart from usual spin waves, well-defined
orbitons can exist. Non-quasiparticle states occur in the electron energy
spectrum near the Fermi energy due to this interaction. The criteria of
stability of the saturated spin and orbital ferromagnetic ordering are
considered. Possible effects of orbital ordering in magnetite and in colossal
magnetoresistance manganites are discussed.",0504280v2
2005-04-19,Spin accumulation in degenerate semiconductors near modified Schottky contact with ferromagnets,"We study spin transport in forward and reverse biased junctions between a
ferromagnetic metal and a degenerate semiconductor with a delta-doped layer
near the interface at relatively low temperatures. We show that spin
polarization of electrons in the semiconductor, Pn, near the interface
increases both with the forward and reverse current and reaches saturation at
certain relatively large current while the spin injection coefficient, Gamma,
increases with reverse current and decreases with the forward current. We
analyze the condition for efficient spin polarization of electrons in
degenerate semiconductor near interface with ferromagnet. We compare the
accumulation of spin polarized electrons in degenerate semiconductors at low
temperatures with that in nondegenerate semiconductors at relatively high, room
temperatures.",0504494v2
2005-04-25,Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation,"Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs
reveals two distinct {\em demagnetization} processes -- fast ($<1$ ps) and slow
($\sim$100 ps). Both components diminish with increasing temperature and are
absent above the Curie temperature. The fast component rapidly grows with pump
power and saturates at high fluences ($>10$ mJ/cm$^2$); the saturation value
indicates a {\em complete quenching} of ferromagnetism on a sub-picosecond time
scale. We attribute this fast dynamics to spin heating through $p$-$d$ exchange
interaction between photo-carriers and Mn ions while the $\sim$100 ps component
is interpreted as spin-lattice relaxation.",0504611v2
2005-04-27,Perpendicular spin valves with ultra-thin ferromagnetic layers,"We address two finite size effects in perpendicular transport through
magnetic multilayers. When the magnetic layer thickness in spin valves becomes
of the order or smaller than the spin-flip diffusion length, structural
asymmetries affect the transport properties. A magnetic layer with thickness
approaching the magnetic coherence length becomes transparent for spin currents
polarized perpendicular to the magnetization. We use the generalized
magnetoelectronic circuit theory to investigate both effects on the angular
magnetoresistance (aMR) and spin transfer torque. We analyze recent aMR
experiments to determine the spin-flip diffusion length in the ferromagnet as
well as the interface spin-mixing conductance and propose a method to measure
the ferromagnetic coherence length.",0504705v2
2005-04-27,Tunneling density of states as a function of thickness in superconductor/ strong ferromagnet bilayers,"We have made an experimental study of the tunneling density of states (DOS)
in strong ferromagnetic thin films (CoFe) in proximity with a thick
superconducting film (Nb) as a function of $d_F$, the ferromagnetic thickness.
Remarkably, we find that as $d_F$ increases, the superconducting DOS exhibits a
scaling behavior in which the deviations from the normal-state conductance have
a universal shape that decreases exponentially in amplitude with characteristic
length $d^*\approx 0.4$ nm. We do not see oscillations in the DOS as a function
of $d_F$, as expected from predictions based on the Usadel equations, although
an oscillation in $T_c(d_F)$ has been seen in the same materials.",0504739v2
2005-04-28,Effect of electron interactions on the conductivity and exchange coupling energy of disordered metallic magnetic multilayer,"We consider the effect of electron-electron interactions on the
current-in-plane (CIP) conductivity and exchange coupling energy of a
disordered metallic magnetic multilayer. We analyze its dependence on the value
of ferromagnetic splitting of conducting electrons and ferromagnetic layers
relative magnetizations orientation. We show that contribution to the CIP
conductivity and exchange coupling energy as a periodic function of the angle
of magnetizations relative orientation experience $ 2\pi \to \pi $ transition
depending on the characteristic energies: ferromagnetic splitting of the
conducting electrons and the Thouless energy of paramagnetic layer.",0504754v3
2005-05-08,Unusual Exchange Bias Associated with Phase Separation in Perovskite Cobaltites,"We report the observation of unusual exchange bias phenomena in the doped
perovskite cobaltites La_{1-x}Sr_{x}CoO_{3} (x = 0.15, 0.18, and 0.30) in which
a spontaneous phase separation into ferromagnetic clusters embedded in a
non-ferromagnetic matrix occurs. When the La_{1-x}Sr_{x}CoO_{3} samples are
cooled in a static magnetic field through a freezing temperature, the
magnetization hysteresis loops exhibit exchange bias, i.e., the loops shift to
the negative field and the magnetization becomes asymmetric. Moreover, exchange
bias disappears when the measuring magnetic field is high enough. These results
suggest that the intrinsic phase inhomogeniety in a spontaneously
phase-separated system may induce an interfacial exchange anisotropy after a
field cooling. The diminution of exchange bias in high magnetic fields is
ascribed to the propagation of ferromagnetic regions with increasing magnetic
field.",0505189v1
2005-05-09,Long range statistical fluctuations of the crossed Josephson current,"We investigate the crossed Josephson effect in a geometry consisting of a
double ferromagnetic bridge between two superconductors, with tunnel
interfaces. The crossed Josephson current vanishes on average because the
Andreev reflected hole does not follow the same sequence of impurities as the
incoming electron. We show that i) the root mean square of the crossed
Josephson current distribution is proportional to the square root of the
junction area; and ii) the coherent coupling mediated by fluctuations is ``long
range'' since it decays over the ferromagnet phase coherence length $l_\phi$,
larger than the exchange length. We predict a crossed Josephson current due to
fluctuations if the length of the ferromagnets is smaller than $l_\phi$ and
larger than the exchange length $\xi_h$.",0505211v2
2005-05-10,Percolative Ferromagnetism in Anatase Co:TiO2,"We revisit the most widely investigated and controversial oxide diluted
magnetic semiconductor (DMS), Co:TiO2, with a new high temperature film growth,
and show that the corresponding material is not only an intrinsic DMS
ferromagnet, but also supports a percolative mechanism of ferromagnetism. We
establish the uniformity of dopant distribution across the film cross section
by Z-contrast imaging via scanning transmission electron microscopy (STEM) and
electron energy loss spectroscopy (EELS) at spatial resolution of 0.4 nm and
the oxidized 2+ valence state of cobalt by x-ray absorption spectroscopy (XAS).
The dependence of magnetic properties on cobalt concentration is consistent
with the defect polaron percolation model. The peculiar increase in the
transport activation energy above a specific cobalt concentration further
emphasizes the polaron contribution to magnetic order.",0505265v1
2005-05-16,Characterization of Magnetic Components in the Diluted Magnetic Semiconductor Zn$_{1-x}$Co$_x$O by X-ray Magnetic Circular Dichroism,"We report on the results of x-ray absorption (XAS), x-ray magnetic circular
dichroism (XMCD), and photoemission experiments on {\it n}-type
Zn$_{1-x}$Co$_x$O ($x=0.05$) thin film, which shows ferromagnetism at room
temperature. The XMCD spectra show a multiplet structure, characteristic of the
Co$^{2+}$ ion tetrahedrally coordinated by oxygen, suggesting that the
ferromagnetism comes from Co ions substituting the Zn site in ZnO. The magnetic
field and temperature dependences of the XMCD spectra imply that the
non-ferromagnetic Co ions are strongly coupled antiferromagnetically with each
other.",0505387v1
2005-05-17,Superconducting proximity effect in a diffusive ferromagnet with spin-active interfaces,"We reconsider the problem of the superconducting proximity effect in a
diffusive ferromagnet bounded by tunneling interfaces, using spin-dependent
boundary conditions. This introduces for each interface a phase-shifting
conductance Gphi which results from the spin dependence of the phase shifts
acquired by the electrons upon scattering on the interface. We show that Gphi
strongly affects the density of states and supercurrents predicted for
superconducting/ferromagnetic hybrid circuits. We show the relevance of this
effect by identifying clear signatures of Gphi in the data of T. Kontos et al
[Phys. Rev. Lett. 86, 304 (2001), ibid. 89, 137007 (2002)].",0505403v2
2005-05-25,Polar magneto-optical Kerr effect for low-symmetric ferromagnets,"The polar magneto-optical Kerr effect (MOKE) for low-symmetric ferromagnetic
crystals is investigated theoretically based on first-principle calculations of
optical conductivities and a transfer matrix approach for the electrodynamics
part of the problem. Exact average magneto-optical properties of polycrystals
are described, taking into account realistic models for the distribution of
domain orientations. It is shown that for low-symmetric ferromagnetic single
crystals the MOKE is determined by an interplay of crystallographic
birefringence and magnetic effects. Calculations for single and bi-crystal of
hcp 11-20 Co and for a polycrystal of CrO_2 are performed, with results being
in good agreement with experimental data.",0505614v1
2005-06-01,Ferromagnetism in one dimension: Critical Temperature,"Ferromagnetism in one dimension is a novel observation which has been
reported in a recent work (P. Gambardella et.al., Nature {\bf 416}, 301
(2002)), anisotropies are responsibles in that relevant effect. In the present
work, another approach is used to obtain transition between two different
magnetic ordering phases. Critical temperature has been estimated by Binder
method. Ferromagnetic long range interactions have been included in a special
Hamiltonian through a power law that decays at large inter-particle distance
$r$ as $r^{-\alpha}$, where $\alpha\geq0$. For the present model, we have found
that the trend of the critical temperature vanishes when the range of
interactions decreases ($\alpha\to\infty$) and close to mean field
approximation when the range of interactions increases ($\alpha\to0$). The
crossover between two these limit situations is discussed",0506033v2
2005-06-17,Theory of spin-polarized transport in ferromagnet-semiconductor structures: Unified description of ballistic and diffusive transport,"A theory of spin-polarized electron transport in ferromagnet-semiconductor
heterostructures, based on a unified semiclassical description of ballistic and
diffusive transport in semiconductors, is outlined. The aim is to provide a
framework for studying the interplay of spin relaxation and transport mechanism
in spintronic devices. Transport inside the (nondegenerate) semiconductor is
described in terms of a thermoballistic current, in which electrons move
ballistically in the electric field arising from internal and external
electrostatic potentials, and are thermalized at randomly distributed
equilibration points. Spin relaxation is allowed to take place during the
ballistic motion. For arbitrary potential profile and arbitrary values of the
momentum and spin relaxation lengths, an integral equation for a spin transport
function determining the spin polarization in the semiconductor is derived. For
field-driven transport in a homogeneous semiconductor, the integral equation
can be converted into a second-order differential equation that generalizes the
spin drift-diffusion equation. The spin-polarization in ferromagnet
semiconductor structures is obtained by matching the spin-resolved chemical
potentials at the interfaces, with allowance for spin-selective interface
resistances. Illustrative examples are considered.",0506441v1
2005-06-27,Ferromagnetism of the Hubbard Model at Strong Coupling in the Hartree-Fock Approximation,"As a contribution to the study of Hartree-Fock theory we prove rigorously
that the Hartree-Fock approximation to the ground state of the d-dimensional
Hubbard model leads to saturated ferromagnetism when the particle density (more
precisely, the chemical potential mu) is small and the coupling constant U is
large, but finite. This ferromagnetism contradicts the known fact that there is
no magnetization at low density, for any U, and thus shows that HF theory is
wrong in this case. As in the usual Hartree-Fock theory we restrict attention
to Slater determinants that are eigenvectors of the z-component of the total
spin, {S}_z = sum_x n_{x,\uparrow} - n_{x,\downarrow}, and we find that the
choice 2{S}_z = N = particle number gives the lowest energy at fixed 0 < mu <
4d.",0506695v2
2005-07-04,Suppression of ferromagnetism in URhGe doped with Ru,"In the correlated metal URhGe ferromagnetic order (T_C = 9.5 K) and
superconductivity (T_s= 0.25 K) coexist at ambient pressure. Here we report on
alloying URhGe by Ru, which enables one to tune the Curie temperature to 0 K.
URuGe has a paramagnetic ground state and is isostructural to URhGe. We have
prepared a series of polycrystalline URh_{1-x}Ru_{x}Ge samples over a wide
range of x values. Magnetization and electrical resistivity data (T > 2 K)
show, after an initial increase, a linear suppression of T_C with increasing x.
The critical Ru concentration for the suppression of ferromagnetic order is
x_cr ~ 0.38.",0507068v1
2005-07-11,Quantum Criticality in Ferromagnetic Single-Electron Transistors,"Considerable evidence exists for the failure of the traditional theory of
quantum critical points (QCPs), pointing to the need to incorporate novel
excitations. The destruction of Kondo entanglement and the concomitant critical
Kondo effect may underlie these emergent excitations in heavy fermion metals --
a prototype system for quantum criticality -- but the effect remains poorly
understood. Here, we show how ferromagnetic single-electron transistors can be
used to study this effect. We theoretically demonstrate a gate-voltage induced
quantum phase transition. The critical Kondo effect is manifested in a
fractional-power-law dependence of the conductance on temperature ($T$). The AC
conductance and thermal noise spectrum have related power-law dependences on
frequency ($\omega$) and, in addition, show an $\omega/T$ scaling. Our results
imply that the ferromagnetic nanostructure constitutes a realistic model system
to elucidate magnetic quantum criticality that is central to the heavy fermions
and other bulk materials with non-Fermi liquid behavior.",0507215v3
2005-07-13,Frustrated ferromagnetic spin-1/2 chain in the magnetic field,"We study the ground state properties of the Heisenberg spin-1/2 chain with
ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor
interactions using two approximate methods. One of them is the Jordan-Wigner
mean-field theory and another approach based on the transformation of spin
operators to bose-ones and on the variational treatment of bosonic Hamiltonian.
Both approaches give close results for the ground state energy and the T=0
magnetization curve. It is shown that quantum fluctuations change the classical
critical exponents in the vicinity of the transition point from the
ferromagnetic to the singlet ground state. The magnetization process displays
the different behavior in the regions near and far from the transition point.
The relation of the obtained results to experimental magnetization curve in
$Rb_{2}Cu_{2}Mo_{3}O_{12}$ is discussed.",0507301v2
2005-07-20,Superconducting Proximity Effect through a Magnetic Domain Wall,"We study the superconducting proximity effect in a
superconductor-ferromagnet-superconductor (SFS) heterostructure, containing a
domain wall in the ferromagnetic region. For the ferromagnet we assume an alloy
with an exchange splitting of the conduction bands comparable to the
superconducting gaps. We calculate the modification of the density of states in
the center of the domain wall as a result of the proximity effect. We show that
the density of states is sensitive to domain wall parameters due to
triplet-pairing correlations created in vicinity of the domain wall. We present
a theoretical tool which in a very effective way enables retaining the full
spatially dependent spin-space structure of the problem.",0507482v1
2005-07-21,Ferromagnetic semiconductor single wall carbon nanotube,"Possibility of a ferromagnetic semiconductor single wall carbon nanotube
(SWCNT), where ferromagnetism is due to coupling between doped magnetic
impurity on a zigzag SWCNT and electrons spin, is investigate. We found, in the
weak impurity-spin couplings, at low impurity concentrations the spin up
electrons density of states remain semiconductor while the spin down electrons
density of states shows a metallic behavior. By increasing impurity
concentrations the semiconducting gap of spin up electrons in the density of
states is closed, hence a semiconductor to metallic phase transition is take
place. In contrast, for the case of strong coupling, spin up electrons density
of states remain semiconductor and spin down electron has metallic behavior.
Also by increasing impurity spin magnitude, the semiconducting gap of spin up
electrons is increased.",0507503v1
2005-07-25,Interplay between magnetism and superconductivity in URhGe,"The magnetization rotation transition occurs in the itinerant ferromagnet
URhGe when the field about 12T is applied in direction perpendicular to
spontaneous magnetization in the plane of the smallest magnetic anisotropy
energy.The transition is accompanied by the maximum of resistivity in the
normal state and by reentrance of superconductivity at lower temperatures in
the field interval between 8 and 13 Tesla [F.Levy et al, Science, to be
published (2005)].
  We discuss the magnetization orientation transition and the modification of
triplet pairing superconducting state coexisting with ferromagnetism up to the
fields about 2 Tesla and then reappearing in the broad vicinity of the
transition.
  The nonsymmorphic space group crystal symmetry of ferromagnetic URhGe allows
existance of antiferromagnetic ordering of magnetic moments of pairs of uranium
atoms along a-axis. We show that the amplitude of this weak antiferromagnetic
ordering increases below the phase transition into superconducting state due to
Cooper pairs spontaneous magnetism.",0507572v1
2005-07-26,Transverse instability at a compensated interface of ferromagnetic antiferromagnetic bilayer,"The analytical theory for a ferromagnetic antiferromagnetic bilayer with a
compensated interface has been developed using an explicit expression for the
interfacial interaction energy density. A stability of a solution describing
domain walls within ferromagnetic and antiferromagnetic films has been
investigated. It is shown that even for high values of surface interaction
strength a transverse instability originates within the antiferromagnetic film,
because the deviation of the unit antiferromagnetic vector out of the interface
plane becomes energetically favorable in large enough external magnetic field.
However, it is possible to stabilize the spin distribution near the interface
assuming additional in-plane anisotropy within the antiferromagnetic layer. In
principle, this opens a way to control exchange bias just avoiding a
complicated problem of domain rearrangement within the antiferromagnetic film.",0507613v1
2005-07-28,Theory of transverse spin dynamics in a polarized Fermi liquid and an itinerant ferromagnet,"The linear equations for transverse spin dynamics in a weakly polarized
degenerate Fermi liquid with arbitrary relationship between temperature and
polarization are derived from Landau-Silin phenomenological kinetic equation
with general form of two-particle collision integral. Unlike the previous
treatment where Fermi velocity and density of states have been taken as
constants independent of polarization here we made derivation free from this
assumption. The obtained equations are applicable for description of spin
dynamics in paramagnetic Fermi liquid with finite polarization as well in an
itinerant ferromagnet. In both cases transverse spin wave frequency is found to
be proportional to the square of the wave vector with complex constant of
proportionality (diffusion coefficient) such that the damping has a finite
value at T=0. The polarization dependence of the diffusion coefficient is found
to be different for a polarized Fermi liquid and for an itinerant ferromagnet.
These conclusions are confirmed by derivation of transverse spin wave
dispersion law in frame of field theoretical methods from the integral equation
for the vortex function. It is shown that similar derivation taking into
consideration the divergency of static transverse susceptibility also leads to
the same attenuating spin wave spectrum.",0507675v1
2005-09-05,Magnetic behavior of EuCu2As2: Delicate balance between antiferromagnetic and ferromagnetic order,"The Eu-based compound, EuCu2As2, crystallizing in the ThCr2Si2-type
tetragonal structure, has been synthesized and its magnetic behavior has been
investigated by magnetization (M), heat-capacity (C) and electrical resistivity
(rho) measurements as a function of temperature (T) and magnetic field (H) as
well as by 151Eu Moessbauer measurements. The results reveal that Eu is
divalent ordering antiferromagnetically below 15 K in the absence of magnetic
field, apparently with the formation of magnetic Brillouin-zone boundary gaps.
A fascinating observation is made in a narrow temperature range before
antiferromagnetism sets in: That is, there is a remarkable upturn just below 20
K in the plot of magnetic susceptibility versus T even at low fields, as though
the compound actually tends to order ferromagnetically. There are corresponding
anomalies in the magnetocaloric effect data as well. In addition, a small
application of magnetic field (around 1 kOe at 1.8 K) in the antiferromagnetic
state causes spin-reorientation effect. These results suggest that there is a
close balance between antiferromagnetism and ferromagnetism in this compound",0509108v1
2005-09-06,"First- and Second-Order Phase Transitions, Fulde-Ferrel Inhomogeneous State and Quantum Criticality in Ferromagnet/Superconductor Double Tunnel Junctions","First- and second-order phase transitions, Fulde-Ferrel (FF) inhomogeneous
superconducting (SC) state and quantum criticality in
ferromagnet/superconductor/ferromagnet double tunnel junctions are
investigated. For the antiparallel alignment of magnetizations, it is shown
that a first-order phase transition from the homogeneous BCS state to the
inhomogeneous FF state occurs at a certain bias voltage $V^{\ast}$; while the
transitions from the BCS state and the FF state to the normal state at $%
V_{c}$ are of the second-order. A phase diagram for the central superconductor
is presented. In addition, a quantum critical point (QCP), $% V_{QCP}$, is
identified. It is uncovered that near the QCP, the SC gap, the chemical
potential shift induced by the spin accumulation, and the difference of free
energies between the SC and normal states vanish as $% |V-V_{QCP}|^{z\nu}$ with
the quantum critical exponents $z\nu =1/2$, 1 and 2, respectively. The tunnel
conductance and magnetoresistance are also discussed.",0509128v1
2005-09-19,Effect of random disorder and spin frustration on the reentrant spin glass phase and ferromagnetic phase in stage-2 Cu_{0.93}Co_{0.07}Cl_{2} graphite intercalation compound near the multicritical point,"Stage-2 Cu$_{0.93}$Co$_{0.07}$Cl$_{2}$ graphite intercalation compound
magnetically behaves like a reentrant ferromagnet near the multicritical point
($c_{MCP} \approx 0.96$). It undergoes two magnetic phase transitions at
$T_{RSG}$ ($= 6.64 \pm 0.05$ K) and $T_{c}$ ($= 8.62 \pm 0.05$ K). The static
and dynamic nature of the ferromagnetic and reentrant spin glass phase has been
studied using DC and AC magnetic susceptibility. Characteristic memory
phenomena of the DC susceptibility are observed at $T_{RSG}$ and $T_{c}$. The
nonlinear AC susceptibility $\chi_{3}^{\prime}$ has a positive local maximum at
$T_{RSG}$, and a negative local minimum at $T_{c}$. The relaxation time $\tau$
between $T_{RSG}$ and $T_{c}$ shows a critical slowing down: $\tau$ with $x =
13.1 \pm 0.4$ and $\tau_{0}^{*} = (2.5 \pm 0.5) \times 10^{-13}$ sec. The
influence of the random disorder on the critical behavior above $T_{c}$ is
clearly observed: $\alpha = -0.66$, $\beta = 0.63$, and $\gamma = 1.40$. The
exponent of $\alpha$ is far from that of 3D Heisenberg model.",0509494v1
2005-09-29,Vortex Lattices in Stripe Domains of Ferromagnet/Superconductor Bilayer,"The continuum theory of domain structures in ferromagnetic/superconducting
bilayers fails when the equilibrium domain size becomes comparable with
effective penetration depth $\Lambda$. Instead, a lattice of discrete vortices
must be considered. Here, we report our results on the discrete vortex lattices
in stripe domain structures of ferromagnetic/superconducting bilayers. The
vortices are assumed to be situated periodically on chains in stripe domains.
We study the configurations containing up to three chains per domain, and
calculate their equilibrium energies, equilibrium domain size and vortex
positions through a method based on London-Maxwell equations. In equilibrium,
the vortices in the neighbor domains are half-way shifted while they are next
to each other in the same domain. Additionally, more vortex chains per domain
appear spontaneously depending on magnetization and domain wall energy.",0509782v1
2005-10-06,Organometallic Benzene-Vanadium Wire: One-Dimensional Half-Metallic Ferromagnet,"Using density functional theory we have performed theoretical investigations
of the electronic properties of a free-standing one-dimensional organometallic
vanadium-benzene wire. This system represents the limiting case of multi-decker
V_n(C6H6)_{n+1} clusters which can be synthesized. We predict that the ground
state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its
density of states is metallic at the Fermi energy for the minority electrons
and shows a semiconductor gap for the majority electrons. We found that the
half-metallic behavior is conserved up to 12%, longitudinal elongation of the
wire. However, under further stretching, the system exhibits a transition to a
high-spin ferromagnetic state that is accompanied by an abrupt jump of the
magnetic moment and a gain of exchange energy.",0510144v1
2005-10-06,Magneto-optical evidence of double exchange in a percolating lattice,"Substituting $Eu$ by $Ca$ in ferromagnetic $EuB_6$ leads to a percolation
limited magnetic ordering. We present and discuss magneto-optical data of the
$Eu_{1-x}Ca_{x}B_6$ series, based on measurements of the reflectivity
$R(\omega)$ from the far infrared up to the ultraviolet, as a function of
temperature and magnetic field. Via the Kramers-Kronig transformation of
$R(\omega)$ we extract the complete absorption spectra of samples with
different values of $x$. The change of the spectral weight in the Drude
component by increasing the magnetic field agrees with a scenario based on the
double exchange model, and suggests a crossover from a ferromagnetic metal to a
ferromagnetic Anderson insulator upon increasing $Ca$-content at low
temperatures.",0510155v1
2005-10-12,Orbital ordering in the two-dimensional ferromagnetic semiconductor Rb_2CrCl_4,"We present the results of electronic structure calculations for the
two-dimensional ferromagnet Rb_2CrCl_4. They are obtained by the augmented
spherical wave method as based on density functional theory and the local
density approximation. In agreement with experimental data Rb_2CrCl_4 is found
to be semiconducting and displays long-range ferromagnetic order of the
localized Cr 3d moments. The magnetic properties are almost independent of the
structural modifications arising from the Jahn-Teller instability, which leads
from the parent body-centered tetragonal K_2NiF_4 structure to a side-centered
orthorhombic lattice. In contrast, our calculations give evidence for a strong
response of the optical band gap to the corresponding structural changes.",0510307v1
2005-10-27,High spin polarization in the ferromagnetic filled skutterudites KFe4Sb12 and NaFe4Sb12,"The spin polarization of ferromagnetic alkali-metal iron antimonides KFe4Sb12
and NaFe4Sb12 is studied by point-contact Andreev reflection using
superconducting Nb and Pb tips. From these measurements an intrinsic transport
spin polarization Pt of 67% and 60% for the K and Na compound, respectively, is
inferred which establishes these materials as a new class of highly spin
polarized ferromagnets. The results are in accord with band structure
calculations within the local spin density approximation (LSDA) that predict
nearly 100% spin polarization in the density of states. We discuss the impact
of calculated Fermi velocities and spin fluctuations on Pt.",0510736v1
2005-11-01,Spin-transfer mechanism of ferromagnetism in polymerized fullerenes: $Ab initio$ calculations,"A mechanism of the high temperature ferromagnetism in polymerized fullerenes
is suggested. It is assumed that some of the C$_{60}$ molecules in the crystal
become magnetically active due to spin and charge transfer from the
paramagnetic impurities (atoms or groups), such as hydrogen, fluorine, hydroxyl
group OH, amino group NH$_2$, or methyl group CH$_3$, dispersed in the
fullerene matrix. The exchange interaction between the spins localized on the
magnetically active fullerenes is evaluated using \textit{ab initio}
calculations. The nearest neighbour and next nearest neighbour exchange
interaction is found to be in the range $0.1\div 0.3 $ eV, that is, high enough
to account for the room temperature ferromagnetism.",0511025v2
2005-11-04,Weak ferromagnetic spin and charge stripe order in La[sub 5/3]Sr[sub 1/3]NiO[sub 4],"We present magnetization and specific heat data of a La5/3Sr1/3NiO4 single
crystal in high magnetic fields. From the charge and spin stripe ordering
temperatures, as well as a magnetic low temperature transition, we have
constructed the electronic phase diagram for fields up to 14 Tesla. While the
charge stripe ordering temperature TCO is independent of the magnetic field,
there is a significant shift of the spin stripe ordering temperature TSO of
about 1.5 K/ Tesla, if the magnetic fields are applied parallel to the
NiO2-planes. The specific heat measurements indicate a large anomalous entropy
change at TCO. In contrast, no significant entropy change is observed at the
spin stripe transition. The high field magnetization experiments reveal the
presence of in-plane weak ferromagnetic moments in the charge stripe ordered
phase. From a phenomenological analysis, the magnetic correlation length of
these moments is determined. We suggest that the weak ferromagnetism is due
either to the presence of bond-centered charge stripes or to double exchange
interactions across site-centered charge stripes.",0511105v2
2005-11-17,Effective ferromagnetic coupling between a superconductor and a ferromagnet in LaCaMnO/Nb hybrids,"In this work we present magnetization data on hybrids consisting of
multilayers (MLs) of man- ganites [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3]15 in
contact with a low-Tc Nb superconductor (SC). Although a pure SC should behave
diamagnetically in respect to the external magnetic field in our ML-SC hybrids
we observed that the magnetization of the SC follows that of the ML. Our
intriguing experimental results show that the SC below its TSC c becomes
ferromagnetically coupled to the ML. As a result in the regime where
diamagnetic behaviour of the SC was expected its bulk magne- tization switches
only whenever the coercive field of the ML is exceeded. By employing specific
experiments where the ML was selectively biased or not we demonstrate that the
ML inflicts its magnetic properties on the whole hybrid. Possible explanations
are discussed in connection to recent theoretical proposals and experimental
findings that were obtained in relative hybrids.",0511426v1
2005-11-24,Two-dimensional quantum spin-1/2 Heisenberg model with competing interactions,"We study the quantum spin-1/2 Heisenberg model in two dimensions, interacting
through a nearest-neighbor antiferromagnetic exchange ($J$) and a ferromagnetic
dipolar-like interaction ($J_d$), using double-time Green's function, decoupled
within the random phase approximation (RPA). We obtain the dependence of $k_B
T_c/J_d$ as a function of frustration parameter $\delta$, where $T_c$ is the
ferromagnetic (F) transition temperature and $\delta$ is the ratio between the
strengths of the exchange and dipolar interaction (i.e., $\delta = J/J_d$). The
transition temperature between the F and paramagnetic phases decreases with
$\delta$, as expected, but goes to zero at a finite value of this parameter,
namely $\delta = \delta_c = \pi /8$. At T=0 (quantum phase transition), we
analyze the critical parameter $\delta_c(p)$ for the general case of an
exchange interaction in the form $J_{ij}=J_d/r_{ij}^{p}$, where ferromagnetic
and antiferromagnetic phases are present.",0511606v1
2005-12-13,Fe implanted ferromagnetic ZnO,"Room-temperature ferromagnetism has been induced within ZnO single crystals
by implant-doping with Fe ions. For an implantation temperature of 620 K and an
ion fluence of 4x10^16 cm^-2, very tiny Fe particles, formed inside the host
matrix, are responsible for the ferromagnetic properties. They were identified
using synchrotron X-ray diffraction and Moessbauer spectroscopy. On the other
hand, Fe ions implanted at a temperature of 253 K and an ion fluence of 4x10^15
cm^-2 are incorporated into the host matrix and develop a room temperature
diluted magnetic semiconductor (DMS).",0512267v1
2005-12-20,Spin-dependent Quantum Interference in Single-Wall Carbon Nanotubes with Ferromagnetic Contacts,"We report the experimental observation of spin-induced magnetoresistance in
single-wall carbon nanotubes contacted with high-transparency ferromagnetic
electrodes. In the linear regime the spin-induced magnetoresistance oscillates
with gate voltage in quantitative agreement with calculations based on a
Landauer-Buttiker model for independent electrons. Consistent with this
interpretation, we find evidence for bias-induced oscillation in the
spin-induced magnetoresistance signal on the scale of the level spacing in the
nanotube. At higher bias, the spin-induced magnetoresistance disappears because
of a sharp decrease in the effective spin-polarization injected from the
ferromagnetic electrodes.",0512505v2
2005-12-22,Observation of Periodic pi-Phase Shifts in Ferromagnet-Superconductor Multilayers,"We report complementary studies of the critical temperature and the critical
current in ferromagnet (Ni) - superconductor (Nb) multilayers. The observed
oscillatory behavior of both quantities upon variation of the thickness of the
ferromagnetic layer is found to be in good agreement with theory. The length
scale of oscillations is identical for both quantities and is set by the
magnetic length corresponding to an exchange field of 200 meV in Ni. The
consistency between the behavior of the two quantities provides strong evidence
for periodic pi- phase shifts in these devices.",0512593v1
2005-12-23,Magnetization-dependent $T_c$ shift in F/S/F trilayers with a strong ferromagnet,"We have measured the superconducting transition temperature $T_c$ of Ni/Nb/Ni
trilayers when the magnetizations of the two outer Ni layers are parallel (P)
and antiparallel (AP). The largest difference in $T_c$ occurs when the Nb
thickness is just above the critical thickness at which superconductivity
disappears completely. We have observed a difference in $T_c$ between the P and
AP states as large as 41 mK - a significant increase over earlier results in
samples with higher $T_c$ and with a CuNi alloy in place of the Ni. Our result
also demonstrates that strong elemental ferromagnets are promising candidates
for future investigations of ferromagnet/superconductor heterostructures.",0512623v1
2006-01-23,Consequences of niobium doping for the ferromagnetism and microstructure of anatase Co: TiO2 films,"It is shown that dilute niobium doping has significant effect on the
ferromagnetism and microstructure of dilutely cobalt-doped anatase TiO2 films.
Epitaxial films of anatase TiO2 with 3% Co, without and with 1% niobium doping
were grown by pulsed-laser deposition at 875 C at different oxygen pressures.
For growth at 10^{-5} Torr niobium doping suppresses the ferromagnetism, while
it enhances the same in films grown at 10^{-4} Torr. High-resolution Z-contrast
Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy
show uniform surface segregation of cobalt-rich Ti_{1-x-y}Co_{x}Nb_{y}O_{2-d}
phase, but without cobalt metal clusters.",0601528v1
2006-01-25,Origin of Ferromagnetism and its pressure and doping dependence in Tl$_{2}$Mn$_{2}$O$_{7}$,"Using NMTO-{\it downfolding} technique, we explore and establish the origin
of ferromagnetism in the pyrochlore system, Tl$_{2}$Mn$_{2}$O$_{7}$. It is
found to be driven by hybridization induced spin-polarization of the
delocalized charge carriers derived from Tl-$s$ and O-$p$ states. The
mean-field estimate of the ferromagnetic transition temperature, T$_c$,
estimated using computed exchange integrals are found to be in good agreement
with the measurements. We find an enhancement of T$_{c}$ for moderate doping
with nonmagnetic Sb and a suppression of T$_{c}$ upon application of pressure,
both in agreement with experimental findings.",0601563v1
2006-01-30,"Magnetism of two-dimensional defects in Pd: stacking faults, twin boundaries and surfaces","Careful first-principles density functional calculations reveal the
importance of hexagonal versus cubic stacking of closed packed planes of Pd as
far as local magnetic properties are concerned. We find that, contrary to the
stable face centered cubic phase, which is paramagnetic, the hexagonal
close-packed phase of Pd is ferromagnetic with a magnetic moment of 0.35
$\mu_{B}$/atom. Our results show that two-dimensional defects with local hcp
stacking, like twin boundaries and stacking faults, in the otherwise fcc Pd
structure, increase the magnetic susceptibility. The (111) surface also
increases the magnetic susceptibility and it becomes ferromagnetic in
combination with an individual stacking fault or twin boundary close to it. On
the contrary, we find that the (100) surface decreases the tendency to
ferromagnetism. The results are consistent with the magnetic moment recently
observed in small Pd nanoparticles, with a large surface area and a high
concentration of two-dimensional stacking defects.",0601658v1
2006-01-31,Striking properties of Superconductor/Ferromagnet structures with spin-dependent scattering,"We investigate Superconductor/Ferromagnet (S/F) hybrid structures in the
dirty limit, described by the Usadel equations. More precisely, the
oscillations of the critical temperature and critical current with the
thickness of the ferromagnetic layers are studied. We show that spin-flip and
spin-orbit scattering lead to the decrease of the decay length and the increase
of the oscillations period. The critical current decay is more sensitive to
these pair-breaking mechanisms than that of the critical temperature. These two
scattering mechanisms should be taken into account to get a better agreement
between experimental results and theoretical description. We also study the
influence of the interface transparency on the properties of S/F structures.",0601707v2
2006-02-01,The metal-insulator transition of the ferromagnetic La7/8Sr1/8MnO3 probed by spin waves: a 2D stripe superstructure,"We report a study of spin waves in hole-doped ferromagnetic La7/8Sr1/8MnO3,
in the metallic state (165K) below TC (181K) and through the puzzling
metal-insulator transition which occurs at TO'O''=159K. They reveal very
unusual excitations. Propagating spin waves are observed in the small q-range
up to q=0.25 (lambda=4a), and, beyond, four dispersionless levels. Both types
of excitations have a quasi two-dimensional (2D) character. The transition is
revealed by a folding of the dispersed magnon branch at q=1/8. In the metallic
state, the dispersionless levels reveal ferromagnetic domains with 4 lattice
spacings for their size along a and b. They lead to a picture of charge
segregation with hole-poor domains surrounded with hole-rich paths. Within this
description, the transition appears as the ordering of domains, which can be
interpreted in terms of a 2D superstructure of orthogonal stripes.",0602026v1
2006-02-07,Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7: a ^{139}La NMR study,"In order to gain insights into the origin of colossal magneto-resistance
(CMR) in manganese oxides, we performed a ^{139}La NMR study in the
double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie
temperature T_C=126 K, applying a magnetic field induces a long-range
ferromagnetic order that persists up to T=330 K. The critical field at which
the induced magnetic moment is saturated coincides with the field at which the
CMR effect reaches to a maximum. Our results therefore indicate that the CMR
observed above T_C in this compound is due to the field-induced ferromagnetism
that produces a metallic state via the double exchange interaction.",0602161v1
2006-02-13,Magnetic properties of polymerized C$_{60}$ with Fe,"We provide evidence that high-pressure high-temperature (2.5 GPa and 1040 K)
treatment of mixtures of iron with fullerene powders leads to the complete
transformation of iron into iron carbide Fe$_3$C. The comparison of the
magnetic properties (Curie temperature and magnetic moment) of the here studied
samples and those for the ferromagnetic polymer Rh-C$_{60}$ indicates that the
main ferromagnetic signal reported in those samples is due to Fe$_3$C and not
related to the ferromagnetism of carbon as originally interpreted. Taking into
account the results obtained in this study the original paper on ``Magnetic
carbon"" (Nature {\bf 413}, 716 (2001)) was recently retracted.",0602306v3
2006-03-03,Dark solitons in F=1 spinor Bose--Einstein condensate,"We study dark soliton solutions of a multi-component Gross--Pitaevskii
equation for hyperfine spin F=1 spinor Bose--Einstein condensate. The
interactions are supposed to be inter-atomic repulsive and anti-ferromagnetic
ones of equal magnitude. The solutions are obtained from those of an integrable
$2\times 2$ matrix nonlinear Schr\""{o}dinger equation with nonvanishing
boundary conditions. We investigate the one-soliton and two-soliton solutions
in detail. One-soliton is classified into two kinds. The ferromagnetic state
has wavefunctions of domain-wall shape and its total spin is nonzero. The polar
state provides a hole soliton and its total spin is zero. These two states are
selected by choosing the type of the boundary conditions. In two-soliton
collisions, we observe the spin-mixing or spin-transfer. It is found that, as
""magnetic"" carriers, solitons in the ferromagnetic state are operative for the
spin-mixing while those in the polar are passive.",0603070v1
2006-03-07,Indication of intrinsic room-temperature ferromagnetism in Ti1-xCoxO2-d thin film: An x-ray magnetic circular dichroism study,"Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3
edges of Co doped rutile TiO2 at room temperature have revealed clear multiplet
features characteristic of ferromagnetic Co2+ ions coordinated by O2- ions,
being in sharp contrast to the featureless XMCD spectrum of Co metal or
metallic clusters. The absorption and XMCD spectra agree well with a full
atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry
crystal field at the Ti site in rutile TiO2. The results indicate that the
ferromagnetism arises from the Co2+ ions substituting the Ti4+ ions.",0603149v1
2006-03-17,Spin in fractional quantum Hall systems,"A system at filling factor 2/3 could be a candidate for a quantum Hall
ferromagnet at integer filling factor of composite fermions. Using exact
diagonalization with electrons on a torus we study the transition from the
singlet ground state to the polarized ground state at this filling and look for
signatures of quantum Hall ferromagnetism. Differences between the fractional
and corresponding integer systems are emphasised. Most interestingly, we find
around the transition a low excited half-polarized state which might become the
ground state in the thermodynamical limit. We study its structure and compare
it to the singlet and polarized ground states. A new interpretation of the
singlet state is suggested and comparison of the filling factors 2/3 and 2/5 is
presented. Adding magnetic inhomogeneities into the system we investigate the
stability of all the three involved states and the tendency to build up domains
like in conventional ferromagnets.",0603451v1
2006-03-17,An Extended Scaling Scheme for Critically Divergent Quantities in Ferromagnets and Spin Glasses,"From a consideration of high temperature series expansions in ferromagnets
and in spin glasses, we propose an extended scaling scaling scheme involving a
set of scaling formulae which express to leading order the temperature (T) and
the system size (L) dependences of thermodynamic observables over a much wider
range of T than the corresponding one in the conventional scaling scheme. The
extended scaling, illustrated by data on the canonical 2d ferromagnet and on
the 3d binomial Ising spin glass, leads to consistency for the estimates of
critical parameters obtained from scaling analyses for different observables.",0603453v3
2006-03-28,Ferromagnetic one dimensional Ti atomic chain,"Using the full potential linearized augmented plane wave (FLAPW) method, we
have explored the magnetic properties of one dimensional (1D) Ti atomic chain.
Astonishingly, we for the first time observed that the 1D Ti atomic chain has
ferromagnetic ground state even on NiAl(110) surface although the Ti has no
magnetic moment in bulk or macroscopic state. It was found that the physical
property of direct exchange interaction among Ti atoms occurred in free
standing state is well preserved on NiAl(110) surface and this feature has an
essential role in ferromagnetism of 1D Ti atomic chain. It was shown that the
m=$|2|$ state has the largest contribution to the magnetic moment of Ti atom
grown on NiAl(110) surface. In addition, we found that the magnetic dipole
interaction is a key factor in the study of magnetic anisotropy, not the
magnetocrystalline anisotropy arising from spin-orbit interaction.",0603740v1
2006-03-29,Electronic Structure and Optical Properties of the Co-doped Anatase TiO$_{2}$ Studied from First Principles,"The Co-doped anatase TiO$_{2}$, a recently discovered room-temperature
ferromagnetic insulator, has been studied by the first-principles calculations
in the pseudo-potential plane-wave formalism within the local-spin-density
approximation (LSDA), supplemented by the full-potential linear augmented plane
wave (FP-LAPW) method. Emphasis is placed on the dependence of its electronic
structures and linear optical properties on the Co-doping concentration and
oxygen vacancy in the system in order to pursue the origin of its
ferromagnetism. In the case of substitutional doping of Co for Ti, our
calculated results are well consistent with the experimental data, showing that
Co is in its low spin state. Also, it is shown that the oxygen vacancy enhances
the ferromagnetism and has larger effect on both the electronic structure and
optical properties than the Co-doping concentration only.",0603779v1
2006-04-02,The semiconductor-to-ferromagnetic-metal transition in FeSb2,"We propose FeSb2 to be a nearly ferromagnetic small gap semiconductor, hence
a direct analog of FeSi. We find that despite different compositions and
crystal structures, in the local density approximation with on-site Coulomb
repulsion correction (LDA+U) method magnetic and semiconducting solutions for
U=2.6 eV are energetically degenerate similar to the case of FeSi. For both
FeSb2 and FeSi (FeSi1-xGex alloys) the underlying transition mechanism allows
one to switch from a small gap semiconductor to a ferromagnetic metal with
magnetic moment 1 muB per Fe ion with external magnetic field.",0604020v2
2006-04-03,Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Fe(110) trilayers,"In order to clarify the influence of ferromagnetism on superconductivity
through a normal metal layer, the superconducting properties of epitaxial
Nb(110)/Au(111)/Fe(110) trilayers were studied as a function of the thickness
tAu of the intervening Au layer. Structural characterization of the samples
revealed sharp interfaces, almost free from roughness. A strong suppression of
the superconducting transition temperature Tc was observed for tAu<10 A,
implying a strong spin-polarization of the Au layer in the vicinity of the
Au/Fe interface. A periodic change of Tc with a period of ~21 A (~9 atomic
monolayer of Au) was observed for 20 A<tAu<104 A. Neither the Fermi surface
nesting of the normal metal layer, nor Fulde-Ferrel-Larkin-Ovchinnikov
oscillations induced by a superconducting proximity effect in the ferromagnet
can by themselves account for the observed period. These results suggest that a
new and more subtle form of quantum interference occurs in very clean trilayer
systems.",0604030v1
2006-04-03,Canted Ferromagnetism in Double Exchange Model with on-site Coulomb Repulsion,"The double exchange model with on-site Coulomb repulsion is considered.
Schwinger-bosons representation of the localized spins is used and two
spin-singlet Fermion operators are introduced. In terms of the new Fermi fields
the on-site Hund's interaction is in a diagonal form and the true magnons of
the system are identified. The singlet fermions can be understood as electrons
dressed by a cloud of repeatedly emitted and reabsorbed magnons. Rewritten in
terms of Schwinger-bosons and spin-singlet fermions the theory is U(1) gauge
invariant. We show that spontaneous breakdown of the gauge symmetry leads to
\emph{\textbf{canted ferromagnetism with on-site spins of localized and
delocalized electrons misaligned}}. On-site canted phase emerges in double
exchange model when Coulomb repulsion is large enough. The quantum phase
transition between ferromagnetism and canted phase is studied varying the
Coulomb repulsion for different values of parameters in the theory such as
Hund's coupling and chemical potential.",0604047v1
2006-04-04,High quality ferromagnetic 0 and pi Josephson tunnel junctions,"We fabricated high quality $\Nb/\Al_2\O_3/\Ni_{0.6}\Cu_{0.4}/\Nb$
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Depending on the thickness of the ferromagnetic $\Ni_{0.6}\Cu_{0.4}$ layer and
on the ambient temperature, the junctions were in the 0 or $\pi$ ground state.
All junctions have homogeneous interfaces showing almost perfect Fraunhofer
patterns. The $\Al_2\O_3$ tunnel barrier allows to achieve rather low damping,
which is desired for many experiments especially in the quantum domain. The
McCumber parameter $\beta_c$ increases exponentially with decreasing
temperature and reaches $\beta_c\approx700$ at $T=2.1 {\rm K}$. The critical
current density in the $\pi$ state was up to $5\:\rm{A/cm^2}$ at $T=2.1 {\rm
K}$, resulting in a Josephson penetration depth $\lambda_J$ as low as
$160\:\rm{\mu m}$. Experimentally determined junction parameters are well
described by theory taking into account spin-flip scattering in the
$\Ni_{0.6}\Cu_{0.4}$ layer and different transparencies of the interfaces.",0604097v3
2006-04-05,Shot noise in diffusive ferromagnetic metals,"We show that shot noise in a diffusive ferromagnetic wire connected by tunnel
contacts to two ferromagnetic electrodes can probe the intrinsic density of
states and the extrinsic impurity scattering spin-polarization contributions in
the polarization of the wire conductivity. The effect is more pronounced when
the electrodes are perfectly polarized in opposite directions. While in this
case the shot noise has a weak dependence on the impurity scattering
polarization, it is strongly affected by the polarization of the density of
states. For a finite spin-flip scattering rate the shot noise increases well
above the normal state value and can reach the full Poissonian value when the
density of states tends to be perfectly polarized. For the parallel
configuration we find that the shot noise depends on the relative sign of the
intrinsic and the extrinsic polarizations.",0604142v1
2006-04-06,Nonsinusoidal current-phase relations and the $0-π$ transition in diffusive ferromagnetic Josephson junctions,"We study the effect of the interfacial transparency on the Josephson current
in a diffusive ferromagnetic contact between two superconductors. In contrast
to the cases of the fully transparent and the low-transparency interfaces, the
current-phase relation is shown to be nonsinusoidal for a finite transparency.
It is demonstrated that even for the nearly fully transparent interfaces the
small corrections due to weak interfacial disorders contribute a small
second-harmonic component in the current-phase relation. For a certain
thicknesses of the ferromagnetic contact and the exchange field this can lead
to a tiny minimum supercurrent at the crossover between 0 and $\pi$ states of
the junction. Our theory has a satisfactory agreement with the recent
experiments in which a finite supercurrent was observed at the transition
temperature. We further explain the possibility for observation of a large
residual supercurrent if the interfaces have an intermediate transparency.",0604178v1
2006-04-11,Antiferromagnetic coupling and enhanced magnetization in all-ferromagnetic superlattices,"The structural and magnetic properties of a series of superlattices
consisting of two ferromagnetic metals La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) and
SrRuO$_3$ (SRO) grown on (001) oriented SrTiO$_3$ are studied. Superlattices
with a fixed LSMO layer thickness of 20 unit cells (u.c.) and varying SRO layer
thickness show a sudden drop in magnetization on cooling through temperature
where both LSMO and SRO layers are ferromagnetic. This behavior suggests an
antiferromagnetic coupling between the layers. In addition, the samples having
thinner SRO layers (n \TEXTsymbol{<} 6) exhibit enhanced saturation
magnetization at 10 K. These observations are attributed to the possible
modification in the stereochemistry of the Ru and Mn ions in the interfacial
region.",0604266v1
2006-04-12,Room temperature magneto-optics of ferromagnetic transition-metal doped ZnO thin films,"Magneto-optic studies of ZnO doped with transition metals Co, Mn, V and Ti
indicate a significant magnetic circular dichroism (MCD) at the ZnO band edge
at room temperature, together with an associated dispersive Faraday rotation.
Similar spectra occur for each dopant which implies that the ferromagnetism is
an intrinsic property of the bulk ZnO lattice. At 10 K additional paramagnetic
contributions to the MCD are observed, but above about 150K, the magnitude of
the MCD signal is dominated by the ferromagnetism and is almost temperature
independent. The MCD at the ZnO band edge shows room temperature hysteretic
behaviour.",0604307v1
2006-04-20,New Ferromagnetic Nitrides CaN and SrN and their synthesis process,"We introduce new type of ferromagnets, CaN and SrN, which were designed using
first-principles calculations. These are half-metallic ferromagnets and they
have magnetic moments of 1 $\mu_{\rm B}$ per chemical formula unit. Out of the
typical structures of binary compounds, the rock-salt structure is the most
stable form for both CaN and SrN. The majority of the magnetic moment of these
compound originates from the N sites since the $p$ states of N are
spin-polarized. Their formation energies were calculated and the results show
that it should be feasible to synthesize these materials. The structural
stability of CaN was confirmed by performing first-principles molecular
dynamics simulations. We propose a synthesis process for CaN basd on the
first-principles.",0604484v3
2006-05-05,Superconducting decay length in a ferromagnetic metal,"The complex decay length xi characterizing penetration of superconducting
correlations into a ferromagnet due to the proximity effect is studied
theoretically in the frame of the linearized Eilenberger equations. The real
part xi_1 and imaginary part xi_2 of the decay length are calculated as
functions of exchange energy and the rates of ordinary, spin flip and spin
orbit electronic scattering in a ferromagnet. The lengths xi_1,2 determine the
spatial scales of, respectively, decay and oscillation of a critical current in
SFS Josephson junctions in the limit of large distance between superconducting
electrodes. The developed theory provides the criteria of applicability of the
expressions for xi_1 and xi_2 in the dirty and the clean limits which are
commonly used in the analysis of SF hybrid structures.",0605137v1
2006-05-15,Spontaneous symmetry breaking in a quenched ferromagnetic spinor Bose condensate,"A central goal in condensed matter and modern atomic physics is the
exploration of many-body quantum phases and the universal characteristics of
quantum phase transitions in so far as they differ from those established for
thermal phase transitions. Compared with condensed-matter systems, atomic gases
are more precisely constructed and also provide the unique opportunity to
explore quantum dynamics far from equilibrium. Here we identify a second-order
quantum phase transition in a gaseous spinor Bose-Einstein condensate, a
quantum fluid in which superfluidity and magnetism, both associated with
symmetry breaking, are simultaneously realized. $^{87}$Rb spinor condensates
were rapidly quenched across this transition to a ferromagnetic state and
probed using in-situ magnetization imaging to observe spontaneous symmetry
breaking through the formation of spin textures, ferromagnetic domains and
domain walls. The observation of topological defects produced by this symmetry
breaking, identified as polar-core spin-vortices containing non-zero spin
current but no net mass current, represents the first phase-sensitive in-situ
detection of vortices in a gaseous superfluid.",0605351v1
2006-05-26,0-pi Josephson tunnel junctions with ferromagnetic barrier,"We fabricated high quality Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Using a ferromagnetic layer with a step-like thickness, we obtain a 0-pi
junction, with equal lengths and critical currents of 0 and pi parts. The
ground state of our 330 microns (1.3 lambda_J) long junction corresponds to a
spontaneous vortex of supercurrent pinned at the 0-pi step and carrying ~6.7%
of the magnetic flux quantum Phi_0. The dependence of the critical current on
the applied magnetic field shows a clear minimum in the vicinity of zero field.",0605656v3
2006-06-03,Nearly Ferromagnetic Superconductors,"The electromagnetic properties of superconductors near a ferromagnetic
instability are investigated by means of a generalized Ginzburg-Landau theory.
It is found that the magnetic flux expulsion capability of the superconductor
gets stronger, in a well-defined sense, as the normal-state magnetic
susceptibility increases. The temperature dependencies of the London
penetration depth, the critical fields, and the critical current are all
strongly affected by ferromagnetic fluctuations. In particular, for the
critical current we find a temperature exponent alpha ~ 2 over an appreciable
temperature range. The extent to which proximity to magnetic criticality may be
a viable explanation for recent observations in MgCNi microfibers, which find
alpha ~ 2, is discussed.",0606090v2
2006-06-13,Vortex Chain States in a Ferromagnet/Superconductor Bilayer,"The discrete vortex lattices in a ferromagnet/superconductor bilayer are
studied when the ferromagnet has periodic stripe domains with an out-of-plane
magnetization. The vortices are assumed to be situated periodically on chains
in the stripe domains. Only up to two vortex chains per domain configurations
are considered. When the domain period is fixed, the threshold magnetization is
calculated at which the transition from the Meissner state to the mixed state
occurs. When the domain period is not fixed, the equilibrium domain size and
vortex positions are calculated, depending on the domain's magnetization and
the domain wall energy. In equilibrium, the vortices in the neighbor domains
are half-way shifted, while they are next to each other in the same domain.",0606344v1
2006-06-20,"Compensation, interstitial defects and ferromagnetism in diluted semiconductors","We present a quantitative theory for ferromagnetism in diluted III-V
ferromagnetic semi-conductors in the presence of the two types of defects
commonly supposed to be responsible for compensation: As anti-sites and Mn
interstitials. In each case we reduce the description to that of an effective
random Heisenberg model with exchange integrals between active magnetic
impurities provided by ab initio calculation. The effective magnetic
Hamiltonian is then solved by a semi-analytical method (locally self-consistent
RPA), where disorder is treated exactly. Measured Curie temperatures are shown
to be inconsistent with the hypothesis that As anti-sites provide the dominant
mechanism for compensation. In contrast, if we assume that Mn interstitials are
the main source for compensation, we obtain a very good agreement between the
calculated Curie temperature and the measured values, in both as-grown and
annealed samples.",0606525v1
2006-07-07,"Partial localization of correlated electrons: spin dependent masses, saturated ferromagnetism, and effective s-d model","We determine the localization threshold in a partially filled and orbitally
degenerate model of correlated electrons. Particular emphasis is put on a
non-integer band filling, when the system decomposes into the localized and the
itinerant subsystems; this situation is described by an effective s-d model. A
simultaneous transition to the ferromagnetic state is discussed as driven by
the Hund's rule coupling. Dependence of the quasiparticle mass on the spin
direction appears naturally in the ferromagnetic phase and is attributed to the
electron correlation effects, as is also a metamagnetic transition in an
applied field. Although the main results have been obtained within the saddle
point slave-boson approach, their qualitative features are discussed in general
terms, i.e. as a transition from quantum-mechanical indistinguishability of
particles to the two-component situation. A comparison with the situation for
the orbitally nondegenerate band is also briefly mentioned.",0607188v1
2006-07-10,Boltzmann Equations for Spin and Charge Relaxations in Superconductors,"In a superconductor coupled with a ferromagnetic metal, spin and charge
imbalances can be induced by injecting spin-polarized electron current from the
ferromagnetic metal. We theoretically study a nonequilibrium distribution of
quasiparticles in the presence of spin and charge imbalances. We show that four
distribution functions are needed to characterize such a nonequilibrium
situation, and derive a set of linearized Boltzmann equations for them by
extending the argument by Schmid and Sch\""{o}n based on the quasiclassical
Green's function method. Using the Boltzmann equations, we analyze the spin
imbalance in a thin superconducting wire weakly coupled with a ferromagnetic
electrode. The spin imbalance induces a shift $\delta\mu$ ($- \delta \mu$) of
the chemical potential for up-spin (down-spin) quasiparticles. We discuss how
$\delta \mu$ is relaxed by spin-orbit impurity scattering.",0607227v1
2006-07-15,"Mn L3,2 X-ray Absorption Spectroscopy And Magnetic Circular Dichroism In Ferromagnetic (Ga,Mn)P","We have measured the X-ray absorption (XAS) and X-ray magnetic circular
dichroism (XMCD) at the Mn L3,2 edges in ferromagnetic Ga1-xMnxP films for
0.018<x<0.042. Large XMCD asymmetries at the L3 edge indicate significant
spin-polarization of the density of states at the Fermi energy. The spectral
shapes of the XAS and XMCD are nearly identical with those for Ga1-xMnxAs
indicating that the hybridization of Mn d states and anion p states is similar
in the two materials. Finally, compensation with sulfur donors not only lowers
the ferromagnetic Curie temperature but also reduces the spin polarization of
the hole states.",0607393v1
2006-08-04,Multiferroicity and colossal magneto-capacitance in Cr-thiospinels,"The sulfur based Cr-spinels RCr2S4 with R = Cd and Hg exhibit the coexistence
of ferromagnetic and ferroelectric properties together with a pronounced
magnetocapacitive coupling. While in CdCr2S4 purely ferromagnetic order is
established, in HgCr2S4 a bond-frustrated magnetic ground state is realized,
which, however, easily can be driven towards a ferromagnetic configuration in
weak magnetic fields. This paper shall review our recent investigation for both
compounds. Besides the characterization of the magnetic properties, the complex
dielectric permittivity was studied by means of broadband dielectric
spectroscopy as well as measurements of polarization hysteresis and
pyro-currents. The observed colossal magneto-capacitive effect at the magnetic
transition seems to be driven by an enormous variation of the relaxation
dynamics.",0608113v1
2006-08-15,Coexistence of Superconductivity and Ferromagnetism in Dilute Co-doped $La_{1.89} Ce_{0.11} Cu O_{4\pm\d}$ System,"Thin films of the optimally electron-doped $T'$-phase superconductor
La$_{1.89}$Ce$_{0.11}$CuO$_{4\pm \d}$ are investigated by dilute Co doping,
formed as La$_{1.89}$Ce$_{0.11}$(Cu$_{1-x}$Co$_{x}$)O$_{4\pm\d}$ (LCCCO) with
$x$ = 0.01 -- 0.05. The following results are obtained for the first time: for
the whole dilute Co doping range, LCCCO thin films show long-range
ferromagnetic ordering at the temperature range from 5 K to 300 K, which is
likely due to the RKKY interaction; in the very dilute Co doping, $x$ = 0.01
and 0.02, the superconductivity is maitained, the system shows the coexistence
of superconductivity and ferromagnetism in the CuO$_{2}$ plane. This may be
based on the nature of the charge carriers in electron-doped high-$T_{c}$
cuprate superconductors.",0608320v1
2006-08-30,Awaking of ferromagnetism in GaMnN through control of Mn valence,"Room temperature ferromagnetism of GaMnN thin films is awaked by a mild
hydrogenation treatment of samples synthesized by molecular beam epitaxy. Local
environment of Mn atoms is monitored by Mn-L2,3 near edge x-ray absorption fine
structure (NEXAFS) technique. Doped Mn ions are present at substitutional sites
of Ga both before and after the hydrogenation. No secondary phase can be
detected. Major valency of Mn changes from +3 to +2 by the hydrogenation. The
present result supports the model that the ferromagnetism occurs when Mn2+ and
Mn3+ are coexistent and holes in the mid- gap Mn band mediate the magnetic
coupling.",0608653v1
2006-09-06,Studies on the Weak Itinerant Ferromagnet SrRuO3 under High Pressure to 34 GPa,"The dependence of the Curie temperature Tc on nearly hydrostatic pressure has
been determined to 17.2 GPa for the weak itinerant ferromagnetic SrRuO3 in both
polycrystalline and single-crystalline form. Tc is found to decrease under
pressure from 162 K to 42.7 K at 17.2 GPa in nearly linear fashion at the rate
dTc/dP = -6.8 K/GPa. No superconductivity was found above 4 K in the pressure
range 17 to 34 GPa. Room-temperature X-ray diffraction studies to 25.3 GPa
reveal no structural phase transition but indicate that the average Ru-O-Ru
bond angle passes through a minimum near 15 GPa. The bulk modulus and its
pressure derivative were determined to be B =192(3) GPa and B' = 5.0(3),
respectively. Parallel ac susceptibility studies on polycrystalline CaRuO3 at 6
and 8 GPa pressure found no evidence for either ferromagnetism or
superconductivity above 4 K.",0609149v2
2006-09-07,Soft x-ray magnetic circular dichroism study of weakly ferromagnetic Zn$_{1-x}$V$_x$O thin film,"We performed a soft x-ray magnetic circular dichroism (XMCD) study of a
Zn$_{1-x}$V$_x$O thin film which showed small ferromagnetic moment. Field and
temperature dependences of V 2$p$ XMCD signals indicated the coexistence of
Curie-Weiss paramagnetic, antiferromagnetic, and possibly ferromagnetic V ions,
quantitatively consistent with the magnetization measurements. We attribute the
paramagnetic signal to V ions substituting Zn sites which are somewhat
elongated along the c-axis.",0609173v1
2006-09-08,Coexistence of ferromagnetism and Kondo effect in uranium compounds,"Coexistence between ferromagnetic order and Kondo behavior has been observed
in some uranium compounds. The underscreened Kondo lattice model can provide a
possible description of this coexistence. Here we present a model of a lattice
of S=1 spins coupled to the conduction electrons through an intra-site exchange
interaction $J_{K}$ and an inter-site ferromagnetic exchange $f-f$ interaction
$J_{H}$. Finite temperature results show that the Kondo temperature is larger
than the Curie ordering temperature, $T_{C}$, providing a possible scenario for
the coexistence of Kondo effect and magnetic order. Also, the Kondo behavior
disappears abruptly for low values of $J_{K}$ and smoothly when changing the
band occupation. These results are in qualitative agreement with the
experimental situation for the above mentioned uranium compounds.",0609199v1
2006-09-17,A Scattering method to the equilibrium spin current in a ferromagnet junction,"We extended McMillan's Green's function method to study the equilibrium spin
current (ESC) in a ferromagnet/ferromagnet (FM/FM) tunnelling junction, in
which the magnetic moments in both FM electrodes are not collinear. The
single-electron Green's function of the junction system is directly constructed
from the elements of the scattering matrix which can be obtained by matching
wavefunctions at boundaries. The ESC is found to be determined only by the
Andreev-type reflection amplitudes as in the Josephson effect. The obtained
expression of ESC is an exact result and at the strong barrier limit gives the
same explanation for the origin of ESC as the linear response theory, that is,
ESC comes from the exchange coupling between the magnetic moments of the two FM
electrodes, ${\mathbf{J}}\sim{\mathbf{h}}_{l}\times{\mathbf{h}}_{r}$. In the
weak barrier region, ESC cannot form spontaneously in a noncollinear FM/FM
junction when there is no tunneling barrier between the two FM electrodes.",0609407v1
2006-10-04,Zigzag spin-S chain near ferromagnet-antiferromagnet transition point,"The properties of the ferromagnetic frustrated spin-S one-dimensional
Heisenberg model in the vicinity of the transition point from the ferromagnetic
to the singlet ground state is studied using the perturbation theory (PT) in
small parameter characterizing the deviation from the transition point. The
critical exponents defining the behavior of the ground state energy and spin
correlation functions are determined using scaling estimates of infrared
divergencies of the PT. It is shown that the quantum fluctuations for $s=1/2$
are sufficiently strong to change the classical critical exponents, while for
spin systems with $s\geq 1$ the critical exponents remain classical. The
dimerization in the singlet phase near the transition point is discussed.",0610103v1
2006-10-06,Ferromagnetic phase transition for the spanning-forest model (q \to 0 limit of the Potts model) in three or more dimensions,"We present Monte Carlo simulations of the spanning-forest model (q \to 0
limit of the ferromagnetic Potts model) in spatial dimensions d=3,4,5. We show
that, in contrast to the two-dimensional case, the model has a ""ferromagnetic""
second-order phase transition at a finite positive value w_c. We present
numerical estimates of w_c and of the thermal and magnetic critical exponents.
We conjecture that the upper critical dimension is 6.",0610193v2
2006-10-08,Symmetries of Pairing Correlations in Superconductor-Ferromagnet Nanostructures,"Using selection rules imposed by the Pauli principle, we classify pairing
correlations according to their symmetry properties with respect to spin,
momentum, and energy. We observe that inhomogeneity always leads to mixing of
even- and odd-energy pairing components. We investigate the superconducting
pairing correlations present near interfaces between superconductors and
ferromagnets, with focus on clean systems consisting of singlet superconductors
and either weak or half-metallic ferromagnets. Spin-active scattering in the
interface region induces all of the possible symmetry components. In
particular, the long-range equal-spin pairing correlations have odd-frequency
s-wave and even-frequency p-wave components of comparable magnitudes. We also
analyze the Josephson current through a half-metal. We find analytic
expressions and an interesting universality in the temperature dependence of
the critical current in the tunneling limit.",0610212v2
2006-10-19,Bose-Einstein condensation of magnons in magnets with predominant ferromagnetic interaction,"We discuss Bose-Einstein condensation of magnons (BEC) in magnets with
predominant ferromagnetic (FM) interaction in magnetic field $H$ near
saturation ($H_c$). Because $H_c$ is independent of FM couplings, magnetic
materials of this type can have small $H_c$ that makes them promising
candidates for experimental investigation of BEC. Ferromagnets with easy-plane
anisotropy and antiferromagnets (AFs) containing weakly coupled FM planes or
chains are discussed in detail. We observe small effective interaction between
magnons near the QCP in such magnets, in contrast to AFs with strong AF
coupling previously discussed. In particular, this smallness allows us to find
crossovers in the critical temperature $T_c(H)\propto (H_c-H)^{1/\phi}$ from
$\phi=3/2$ to $\phi=1$ in quasi-1D magnets, and from $\phi=3/2$ to
$\phi\approx1$ ($T_c\ln T_c\propto H_c-H$) in quasi-2D ones.",0610536v4
2006-10-25,Proximity Effects in Ferromagnet/Superconductor Heterostructures,"We review the present status of the experimental and theoretical research on
the proximity effect in heterostructures composed of superconducting (S) and
ferromagnetic (F) thin films. First, we discuss traditional effects originating
from the oscillatory behavior of the superconducting pair wave function in the
F-layer. Then, we concentrate on recent theoretical predictions for S/F layer
systems. These are a) generation of odd triplet superconductivity in the
F-layer and b) ferromagnetism induced in the S-layer below the superconducting
transition temperature $T_{c}$ (inverse proximity effect). The second part of
the review is devoted to discussion of experiments relevant to the theoretical
predictions of the first part. In particular, we present results of
measurements of the critical temperature $T_{c}$ as a function of the thickness
of F-layers and we review experiments indicating existence of odd triplet
superconductivity, cryptoferromagnetism and inverse proximity effect.",0610708v2
2006-10-29,Calculations of spin induced transport in ferromagnets,"Based on first-principles density functional calculations, a general approach
for determining and analyzing the degree of spin polarization (P) in
ferromagnets is presented. The approach employs the so-called tetrahedron
method to evaluate the Fermi surface integrations of P in both ballistic and
diffusive regimes. The validity of the method is examined by comparing the
calculated P values for Fe and Ni with the experiment. The method is shown to
yield highly accurate results with minimal computational effort. Within our
approach, it is also possible to systematically analyze the contributions of
various types of electronic states to the spin induced transport. As a case
study, the transport properties of the soft-ferromagnet CeMnNi4 are
investigated in order to explain the origin of the existing difference between
the experimental and theoretical values of P in this intermetallic compound.",0610802v2
2006-11-13,Quantum Dot as a Spin--Current Diode,"We report a study of spin dependent transport in a system composed of a
quantum dot coupled to a normal metal lead and a ferromagnetic lead (NM-QD-FM).
We use the master equation approach to calculate the spin-resolved currents in
the presence of an external bias and an intra-dot Coulomb interaction. We find
that for a range of positive external biases (current flow from the normal
metal to the ferromagnet) the current polarization
$\wp=(I_\uparrow-I_\downarrow)/(I_\uparrow+I_\downarrow)$ is suppressed to
zero, while for the corresponding negative biases (current flow from the
ferromagnet to the normal metal) $\wp$ attains a relative maximum value. The
system thus operates as a rectifier for spin--current polarization. This effect
follows from an interplay between Coulomb interaction and nonequilibrium spin
accumulation in the dot. In the parameter range considered, we also show that
the above results can be obtained via nonequilibrium Green functions within a
Hartree-Fock type approximation.",0611336v2
2006-11-25,Long-range ferromagnetic correlations between Anderson impurities in a semiconductor host,"We study the two-impurity Anderson model for a semiconductor host using the
quantum Monte Carlo technique. We find that the impurity spins exhibit
ferromagnetic correlations with a range which can be much more enhanced than in
a half-filled metallic band. In particular, the range is longest when the Fermi
level is located above the top of the valence band and decreases as the
impurity bound state becomes occupied. Comparisons with the photoemission and
optical absorption experiments suggest that this model captures the basic
electronic structure of Ga_{1-x}Mn_xAs, the prototypical dilute magnetic
semiconductor (DMS). These numerical results might also be useful for
synthesizing DMS or dilute-oxide ferromagnets with higher Curie temperatures.",0611641v1
2006-12-06,Quantum effects for the 2D soliton in isotropic ferromagnets,"We evaluate a zero-point quantum correction to a Belavin-Polyakov soliton in
an isotropic 2D ferromagnet. By revising the scattering problem of
quasi-particles by a soliton we show that it leads to the Aharonov-Bohm type of
scattering, hence the scattering data can not be obtained by the Born
approximation. We proof that the soliton energy with account of quantum
corrections does not have a minimum as a function of its radius, which is
usually interpreted as a soliton instability. On the other hand, we show that
long lifetime solitons can exist in ferromagnets due to an additional integral
of motion, which is absent for the sigma-model.",0612152v2
2006-12-07,Paramagnetism of the Co sublattice in ferromagnetic Zn$_{1-x}$Co$_{x}$O films,"Using the spectroscopies based upon x-ray absorption, we have studied the
structural and magnetic properties of Zn$_{1-x}$Co$_{x}$O films ($x$ = 0.1 and
0.25) produced by reactive magnetron sputtering. These films show
ferromagnetism with a Curie temperature $T_{\mathrm{C}}$ above room temperature
in bulk magnetization measurements. Our results show that the Co atoms are in a
divalent state and in tetrahedral coordination, thus substituting Zn in the
wurtzite-type structure of ZnO. However, x-ray magnetic circular dichroism at
the Co \textit{L}$_{2,3}$ edges reveals that the Co 3\textit{d} sublattice is
paramagnetic at all temperatures down to 2 K, both at the surface and in the
bulk of the films. The Co 3\textit{d} magnetic moment at room temperature is
considerably smaller than that inferred from bulk magnetisation measurements,
suggesting that the Co 3\textit{d} electrons are not directly at the origin of
the observed ferromagnetism.",0612181v1
2006-12-07,Elementary Charge Transfer Processes in a Superconductor-Ferromagnet Entangler,"We study the production of spatially separated entangled electrons in
ferromagnetic leads from Cooper pairs in a superconducting lead. We give a
complete description of the elementary charge transfer processes, i) transfer
of Cooper pairs out of the superconductor by Andreev reflection and ii)
distribution of the entangled quasiparticles among the ferromagnetic leads, in
terms of their statistics. The probabilities that entangled electrons flow into
spatially separated leads are completely determined by experimentally
measurable conductances and polarizations. Finally, we investigate how
currents, noise and cross correlations are affected by transport of entangled
electrons.",0612197v2
2006-12-08,Electronic and magnetic properties of V-doped anatase TiO$_{2}$ from first principles,"We report a first-principles study on the geometric, electronic and magnetic
properties of V-doped anatase TiO$_{2}$. The DFT+U (Hubbard coefficient)
approach predicts semiconductor band structures for Ti$_{1-x}$V$_{x}$O$_{2}$
(x=6.25 and 12.5%), in good agreement with the poor conductivity of samples,
while the standard calculation within generalized gradient approximation fails.
Theoretical results show that V atoms tend to stay close and result in strong
ferromagnetism through superexchange interactions. Oxygen vacancy induced
magnetic polaron could produce long-range ferromagnetic interaction between
largely separated magnetic impurities. The experimentally observed
ferromagnetism in V-doped anatase TiO$_{2}$ at room temperature may originate
from a combination of short-range superexchange coupling and long-range bound
magnetic polaron percolation.",0612206v1
2006-12-28,Extended Scaling for Ferromagnets,"A simple systematic rule, inspired by high-temperature series expansion
(HTSE) results, is proposed for optimizing the expression for thermodynamic
observables of ferromagnets exhibiting critical behavior at $\Tc$. This
``extended scaling'' scheme leads to a protocol for the choice of scaling
variables, $\tau=(T-\Tc)/T$ or $(T^2 - \Tc^2)/T^2$ depending on the observable
instead of $(T-\Tc)/\Tc$, and more importantly to temperature dependent
non-critical prefactors for each observable. The rule corresponds to scaling of
the leading of the reduced susceptibility above $\Tc$ as $\chi_{\rm
c}^{*}(T)\sim \tau^{-\gamma}$ in agreement with standard practice with scaling
variable $\tau$, and for the leading term of the second-moment correlation
length as $\xi_{\rm c}^{*}(T)\sim T^{-1/2}\tau^{-\nu}$. For the specific heat
in bipartite lattices the rule gives $C_{\rm c}^{*}(T) \sim T^{-2}[(T^2
-\Tc^2)/T^2]^{-\alpha}$. The latter two expressions are not standard. The
scheme can allow for confluent and non-critical correction terms. A stringent
test of the extended scaling is made through analyses of high precision
numerical and HTSE data, or {\it real} data, on the three-dimensional canonical
Ising, XY, and Heisenberg ferromagnets.",0612665v2
2007-01-04,Spin-phonon coupling in antiferromagnetic chromium spinels,"The temperature dependence of eigenfrequencies and intensities of the IR
active modes has been investigated for the antiferromagnetic chromium spinel
compounds CdCr2O4, ZnCr2O4, ZnCr2S4, ZnCr2Se4, and HgCr2S4 by IR spectroscopy
for temperatures from 5 K to 300 K. At the transition into the magnetically
ordered phases, and driven by spin-phonon coupling, most compounds reveal
significant splittings of the phonon modes. This is true for geometrically
frustrated CdCr2O4, and ZnCr2O4, for bond frustrated ZnCr2S4 and for ZnCr2Se4,
which also is bond frustrated, but dominated by ferromagnetic exchange. The
pattern of splitting is different for the different compounds and crucially
depends on the nature of frustration and of the resulting spin order. HgCr2S4,
which is almost ferromagnetic, exhibits no splitting of the eigenfrequencies,
but shows significant shifts due to ferromagnetic spin fluctuations.",0701080v1
2007-01-30,Magnetic Impurity States and Ferromagnetic Interaction in Diluted Magnetic Semiconductors,"The electronic structure of diluted magnetic semiconductors is studied,
especially focusing on the hole character. The Haldane-Anderson model is extend
to a magnetic impurity, and is analyzed in the Hartree-Fock approximation. Due
to the strong hybridization of an impurity d-states with host p-states, it is
shown that holes are created in the valence band, at the same time the
localized magnetic moments are formed. These holes are weakly bound around the
impurity site with the characteristic length of several lattice constants. For
the case of the two impurities, it is found that when the separation of two
impurities is of the order of the length of holes, the overlap of these holes
favors the ferromagnetic interaction. The spatially extended holes play an
essential role for the ferromagnetic exchange interaction.",0701736v1
2007-02-05,Multiple magnetic transitions and magnetocaloric effect in Gd1-xSmxMn2Ge2 compounds,"Magnetic and magnetocaloric properties of polycrystalline samples of
Gd1-xSmxMn2Ge2 have been studied. All the compounds except GdMn2Ge2 show
re-entrant ferromagnetic behavior. Multiple magnetic transitions observed in
these compounds are explained on the basis of the temperature dependences of
the exchange strengths of the rare earth and Mn sublattices. Magnetocaloric
effect is found to be positive at the re-entrant ferromagnetic transition,
whereas it is negative at the antiferro-ferromagnetic transition. In SmMn2Ge2,
the magnetic entropy change associated with the re-entrant transition is found
to decrease with field, which is attributed to the admixture effect of the
crystal field levels. The isothermal magnetic entropy change is found to
decrease with increase in Sm concentration.",0702082v1
2007-02-19,Defects-driven appearance of half-metallic ferrimagnetism in Co-Mn--based Heusler alloys,"Half-metallic ferromagnetic full-Heusler alloys containing Co and Mn, having
the formula Co$_2$MnZ where Z a sp element, are among the most studied Heusler
alloys due to their stable ferromagnetism and the high Curie temperatures which
they present. Using state-of-the-art electronic structure calculations we show
that when Mn atoms migrate to sites occupied in the perfect alloys by Co, these
Mn atoms have spin moments antiparallel to the other transition metal atoms.
The ferrimagnetic compounds, which result from this procedure, keep the
half-metallic character of the parent compounds and the large
exchange-splitting of the Mn impurities atoms only marginally affects the width
of the gap in the minority-spin band. The case of [Co$_{1-x}$Mn$_x$]$_2$MnSi is
of particular interest since Mn$_3$Si is known to crystallize in the Heusler
$L2_1$ lattice structure of Co$_2$MnZ compounds. Robust half-metallic
ferrimagnets are highly desirable for realistic applications since they lead to
smaller energy losses due to the lower external magnetic fields created with
respect to their ferromagnetic counterparts.",0702437v1
2007-02-21,"Spin waves throughout the Brillouin zone and magnetic exchange coupling in ferromagnetic metallic manganites La$_{1-x}$Ca$_{x}$MnO$_3$ ($x=0.25,0.30$)","Using time-of-flight and triple-axis inelastic neutron spectroscopy, we
determine spin wave excitations throughout the Brillouin zone for ferromagnetic
manganites La$_{1-x}$Ca$_x$MnO$_3$ ($x=0.25,0.3$) in their low temperature
metallic states. While spin wave excitations in the long wavelength limit (spin
stiffness $D$) have similar values for both compounds, the excitations near the
Brillouin zone boundary of La$_{0.7}$Ca$_{0.3}$MnO$_3$ are considerable
softened in all symmetry directions compared to that of
La$_{0.75}$Ca$_{0.25}$MnO$_3$. A Heisenberg model with the nearest neighbor and
the fourth neighbor exchange interactions can describe the overall dispersion
curves fairly well. We compare the data with various theoretical models
describing the spin excitations of ferromagnetic manganites.",0702504v1
2007-02-27,Low-energy properties of the ferromagnetic metallic phase in manganites: Slave fermion approach to the quantum double exchange model,"We study the low energy properties of the one-orbital quantum double-exchange
model by using the slave fermion formulation. We construct a mean-field theory
which gives a simple explanation for the magnetic and thermodynamic properties
of the ferromagnetic metallic phase in manganites at low energy. The resulting
electron spectral function and tunneling density of states show an incoherent
asymmetric peak with weak temperature dependence, in addition to a
quasiparticle peak. We also show that the gauge fluctuations in the
ferromagnetic metallic phase are completely screened due to the Anderson-Higgs
mechanism. Therefore, the mean-field state is robust against gauge fluctuations
and exhibits spin-charge separation at low energy.",0702626v1
2007-03-13,Surface Spin-valve Effect,"We report an observation of spin-valve like hysteresis within a few atomic
layers at a ferromagnetic interface. We use phonon spectroscopy of nanometer
sized point contacts as an in-situ probe to study the mechanism of the effect.
Distinct in energy phonon peaks for contacts with dissimilar nonmagnetic outer
electrodes allow to localize the observed spin switching to the top or bottom
interfaces for nanometer thin ferromagnetic layers. The mechanism consistent
with our data is energetically distinct atomically thin surface spin layers
that can form current or field driven surface spin-valves within a single
ferromagnetic film.",0703341v1
2007-03-15,Mesoscopic Magnetic States in Metallic Alloys with Strong Electronic Correlations: A Percolative Scenario for CeNi$_{1-x}$Cu$_{x}$,"We present evidence for the existence of magnetic clusters of approximately
20 \AA in the strongly correlated alloy system CeNi$_{1-x}$Cu$_{x}$ (0.7 $\le$
x $\le$ 0.2) based on small angle neutron scattering experiments as well as the
occurrence of staircase-like hysteresis cycles during very low temperature (100
mK) magnetization measurements. An unusual feature is the observation of
long-range ferromagnetic order below the cluster-glass transition without any
indication of a sharp transition at a Curie temperature. These observations
strongly support a phenomenological model where a percolative process connects
the cluster-glass state observed at high temperatures with the long-range
ferromagnetic order observed by neutron diffraction experiments at very low
temperatures. The model can account for all the puzzling macroscopic and
microscopic data previously obtained in this system, providing a new
perspective with regard to the magnetic ground state of other alloyed compounds
with small magnetic moments or weak ferromagnetism with intrinsic disorder
effects.",0703399v1
1994-07-28,Ising Spins on Thin Graphs,"The Ising model on ``thin'' graphs (standard Feynman diagrams) displays
several interesting properties. For ferromagnetic couplings there is a mean
field phase transition at the corresponding Bethe lattice transition point. For
antiferromagnetic couplings the replica trick gives some evidence for a spin
glass phase. In this paper we investigate both the ferromagnetic and
antiferromagnetic models with the aid of simulations. We confirm the Bethe
lattice values of the critical points for the ferromagnetic model on $\phi^3$
and $\phi^4$ graphs and examine the putative spin glass phase in the
antiferromagnetic model by looking at the overlap between replicas in a
quenched ensemble of graphs. We also compare the Ising results with those for
higher state Potts models and Ising models on ``fat'' graphs, such as those
used in 2D gravity simulations.",9407024v1
2006-05-16,Phase Structure of Z(3)-Polyakov-Loop Models,"We study effective lattice actions describing the Polyakov loop dynamics
originating from finite-temperature Yang-Mills theory. Starting with a
strong-coupling expansion the effective action is obtained as a series of
Z(3)-invariant operators involving higher and higher powers of the Polyakov
loop, each with its own coupling. Truncating to a subclass with two couplings
we perform a detailed analysis of the statistical mechanics involved. To this
end we employ a modified mean field approximation and Monte Carlo simulations
based on a novel cluster algorithm. We find excellent agreement of both
approaches concerning the phase structure of the theories. The phase diagram
exhibits both first and second order transitions between symmetric,
ferromagnetic and anti-ferromagnetic phases with phase boundaries merging at
three tricritical points. The critical exponents nu and gamma at the continuous
transition between symmetric and anti-ferromagnetic phases are the same as for
the 3-state Potts model.",0605012v1
2001-10-19,Field theory of scaling lattice models. The Potts antiferromagnet,"In contrast to what happens for ferromagnets, the lattice structure
participates in a crucial way to determine existence and type of critical
behaviour in antiferromagnetic systems. It is an interesting question to
investigate how the memory of the lattice survives in the field theory
describing a scaling antiferromagnet. We discuss this issue for the square
lattice three-state Potts model, whose scaling limit as T->0 is argued to be
described exactly by the sine-Gordon field theory at a specific value of the
coupling. The solution of the scaling ferromagnetic case is recalled for
comparison. The field theory describing the crossover from antiferromagnetic to
ferromagnetic behaviour is also introduced.",0110181v1
2001-11-14,Approach to Fixation for Zero-Temperature Stochastic Ising Models on the Hexagonal Lattice,"We investigate zero-temperature dynamics on the hexagonal lattice H for the
homogeneous ferromagnetic Ising model with zero external magnetic field and a
disordered ferromagnetic Ising model with a positive external magnetic field h.
We consider both continuous time (asynchronous) processes and, in the
homogeneous case, also discrete time synchronous dynamics (i.e., a
deterministic cellular automaton), alternating between two sublattices of H.
The state space consists of assignments of -1 or +1 to each site of H, and the
processes are zero-temperature limits of stochastic Ising ferromagnets with
Glauber dynamics and a random (i.i.d. Bernoulli) spin configuration at time 0.
We study the speed of convergence of the configuration $\sigma^t$ at time t to
its limit $\sigma^{\infty}$ and related issues.",0111170v1
2006-08-03,On the absence of ferromagnetism in typical 2D ferromagnets,"We consider the Ising systems in $d$ dimensions with nearest-neighbor
ferromagnetic interactions and long-range repulsive (antiferromagnetic)
interactions which decay with a power, $s$, of the distance. The physical
context of such models is discussed; primarily this is $d=2$ and $s=3$ where,
at long distances, genuine magnetic interactions between genuine magnetic
dipoles are of this form. We prove that when the power of decay lies above $d$
and does not exceed $d+1$, then for all temperatures, the spontaneous
magnetization is zero. In contrast, we also show that for powers exceeding
$d+1$ (with $d\ge2$) magnetic order can occur.",0608009v3
2004-03-26,Numerical analysis of the existence and stability of nonlinear excitations in a parametric model of ferromagnetic chain,"A parametrized spin model was recently introduced and intended for
one-dimensional ferromagnets with a deformable Zeeman energy. This model is
revisited and given more realistic interpretation in terms of a model for
ferromagnetic systems with nonconvex anisotropies. A main virtue of the
improved form is its exact reduction to the discrete Remoissenet-Peyrard model,
i.e. a parametrized version of the Takeno-Homma's discrete sine-Gordon model.
The spin-wave phase of the improved parametrized spin model is investigated
assuming both harmonic and anharmonic excitations. Intrinsic-self-localized
modes, regarded as zone-boundary breather spin waves, are pointed out by
simulating the nonlinear difference equations describing the spin equilibrium
positions in the chain, and are shown to exist irrespective of values of the
model parameter. Domain-wall textures of the model are also numerically
examined in terms of kink solitons and with regard to the parametrization.",0403048v1
2004-03-20,Spin polarized states in nuclear matter with Skyrme effective interaction,"The possibility of appearance of spin polarized states in symmetric and
strongly asymmetric nuclear matter is analyzed within the framework of a Fermi
liquid theory with the Skyrme effective interaction. The zero temperature
dependence of the neutron and proton spin polarization parameters as functions
of density is found for SkM$^*$, SGII (symmetric case) and SLy4, SLy5 (strongly
asymmetric case) effective forces. By comparing free energy densities, it is
shown that in symmetric nuclear matter ferromagnetic spin state (parallel
orientation of neutron and proton spins) is more preferable than
antiferromagnetic one (antiparallel orientation of spins). Strongly asymmetric
nuclear matter undergoes at some critical density a phase transition to the
state with the oppositely directed spins of neutrons and protons while the
state with the same direction of spins does not appear. In comparison with
neutron matter, even small admixture of protons strongly decreases the
threshold density of spin instability. It is clarified that protons become
totally polarized within a very narrow density domain while the density profile
of the neutron spin polarization parameter is characterized by the appearance
of long tails near the transition density.",0403059v1
2004-08-26,Antiferromagnetic spin phase transition in nuclear matter with effective Gogny interaction,"The possibility of ferromagnetic and antiferromagnetic phase transitions in
symmetric nuclear matter is analyzed within the framework of a Fermi liquid
theory with the effective Gogny interaction. It is shown that at some critical
density nuclear matter with D1S effective force undergoes a phase transition to
the antiferromagnetic spin state (the opposite direction of neutron and proton
spins). The self--consistent equations of spin polarized nuclear matter with
D1S force have no solutions, corresponding to the ferromagnetic spin ordering
(the same direction of neutron and proton spins) and, hence, the ferromagnetic
transition does not appear. The dependence of antiferromagnetic spin
polarization parameter as a function of density is found at zero temperature.",0408064v2
2002-04-22,Giant Magnetic Moments of Nitrogen Stabilized Mn Clusters and Their Relevance to Ferromagnetism in Mn Doped GaN,"Using first principles calculations based on density functional theory, we
show that the stability and magnetic properties of small Mn clusters can be
fundamentally altered by the presence of nitrogen. Not only are their binding
energies substantially enhanced, but also the coupling between the magnetic
moments at Mn sites remains ferromagnetic irrespective of their size or shape.
In addition, these nitrogen stabilized Mn clusters carry giant magnetic moments
ranging from 4 Bohr magnetons in MnN to 22 Bohr magnetons in Mn_5N. It is
suggested that the giant magnetic moments of Mn_xN clusters may play a key role
in the ferromagnetism of Mn doped GaN which exhibit a wide range (10K - 940K)
of Curie temperatures.",0204064v1
2004-08-23,Ferromagnetic/superconducting bilayer structure: A model system for spin diffusion length estimation,"We report detailed studies on ferromagnet--superconductor bilayer structures.
Epitaxial bilayer structures of half metal--colossal magnetoresistive
La$_{\mathrm{2/3}}$Ca$_{\mathrm{1/3}}$MnO$_{\mathrm{3}}$ (HM--CMR) and
high--$T_{\mathrm{c}}$ superconducting
YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta}}$(HTSC) are grown on
SrTiO$_3$ (100) single--crystalline substrates using pulsed laser deposition.
Magnetization $M$(T) measurements show the coexistence of ferromagnetism and
superconductivity in these structures at low temperatures. Using the HM--CMR
layer as an electrode for spin polarized electrons, we discuss the role of spin
polarized self injection into the HTSC layer. The experimental results are in
good agreement with a presented theoretical estimation, where the spin
diffusion length $\xi_{\mathrm {FM}}$ is found to be in the range of
$\xi_{\mathrm{FM}} \approx$ 10 nm.",0408102v1
2006-05-09,Ising Ferromagnet: Zero-Temperature Dynamic Evolution,"The dynamic evolution at zero temperature of a uniform Ising ferromagnet on a
square lattice is followed by Monte Carlo computer simulations. The system
always eventually reaches a final, absorbing state, which sometimes coincides
with a ground state (all spins parallel), and sometimes does not (parallel
stripes of spins up and down). We initiate here the numerical study of
``Chaotic Time Dependence'' (CTD) by seeing how much information about the
final state is predictable from the randomly generated quenched initial state.
CTD was originally proposed to explain how nonequilibrium spin glasses could
manifest equilibrium pure state structure, but in simpler systems such as
homogeneous ferromagnets it is closely related to long-term predictability and
our results suggest that CTD might indeed occur in the infinite volume limit.",0605077v1
2003-12-03,Entanglement and Quantum Phases in the Anisotropic Ferromagnetic Heisenberg Chain in the Presence of Domain Walls,"We discuss entanglement in the spin-1/2 anisotropic ferromagnetic Heisenberg
chain in the presence of a boundary magnetic field generating domain walls. By
increasing the magnetic field, the model undergoes a first-order quantum phase
transition from a ferromagnetic to a kink-type phase, which is associated to a
jump in the content of entanglement available in the system. Above the critical
point, pairwise entanglement is shown to be non-vanishing and independent of
the boundary magnetic field for large chains. Based on this result, we provide
an analytical expression for the entanglement between arbitrary spins. Moreover
the effects of the quantum domains on the gapless region and for
antiferromagnetic anisotropy are numerically analysed. Finally multiparticle
entanglement properties are considered, from which we establish a
characterization of the critical anisotropy separating the gapless regime from
the kink-type phase.",0312039v3
2007-04-03,The 3D +-J Ising model at the ferromagnetic transition line,"We study the critical behavior of the three-dimensional $\pm J$ Ising model
[with a random-exchange probability $P(J_{xy}) = p \delta(J_{xy} - J) + (1-p)
\delta(J_{xy} + J)$] at the transition line between the paramagnetic and
ferromagnetic phase, which extends from $p=1$ to a multicritical (Nishimori)
point at $p=p_N\approx 0.767$. By a finite-size scaling analysis of Monte Carlo
simulations at various values of $p$ in the region $p_N<p<1$, we provide strong
numerical evidence that the critical behavior along the ferromagnetic
transition line belongs to the same universality class as the three-dimensional
randomly-dilute Ising model. We obtain the results $\nu=0.682(3)$ and
$\eta=0.036(2)$ for the critical exponents, which are consistent with the
estimates $\nu=0.683(2)$ and $\eta=0.036(1)$ at the transition of
randomly-dilute Ising models.",0704.0427v1
2007-04-05,Partially disordered state near ferromagnetic transition in MnSi,"The polarized neutron scattering in helimagnetic MnSi at low $T$ reveals
existence of a partially disordered chiral state at ambient pressure in the
magnetic field applied along $<111>$ axis below the first order transition to
the non-chiral ferromagnetic state. This unexpected phenomenon is explained by
the analysis of the spin-wave spectrum. We demonstrate that the square of the
spin-wave gap becomes negative under magnetic field applied along $<111>$ and
$<110>$ but not along the $<100>$ direction. It is a result of competition
between the spin-wave interaction and cubic anisotropy. This negative sign
means an instability of the spin wave spectrum for the helix and leads to a
destruction of the helical order, giving rise to the partially disordered state
below the first order ferromagnetic transition.",0704.0683v1
2007-04-17,Ferromagnetic quantum critical point in URhGe doped with Ru,"We have investigated the thermal, transport and magnetic properties of
URh$_{1-x}$Ru$_x$Ge alloys near the critical concentration $x_{cr} = 0.38$ for
the suppression of ferromagnetic order. The Curie temperature vanishes linearly
with $x$ and the ordered moment $m_0$ is suppressed in a continuous way. At
$x_{cr}$ the specific heat varies as $c \sim TlnT$, the $\gamma$-value
$c/T|_{0.5K}$ is maximum and the temperature exponent of the resistivity $\rho
\sim T^n$ attains a minimum value $n=1.2$. These observations provide evidence
for a ferromagnetic quantum phase transition. Interestingly, the coefficient of
thermal expansion and the Gr\""uneisen parameter $\Gamma$ remain finite at
$x_{cr}$ (down to $T = 1$ K), which is at odds with recent scaling results for
a metallic quantum critical point.",0704.2116v1
2007-04-18,Effect of a Zeeman field on the superconductor-ferromagnet transition in metallic grains,"We investigate the competition between pairing correlations and
ferromagnetism in small metallic grains in the presence of a Zeeman field. Our
analysis is based on the universal Hamiltonian, valid in the limit of large
Thouless conductance. We show that the coexistence regime of superconducting
and ferromagnetic correlations can be made experimentally accessible by tuning
an external Zeeman field. We compare the exact solution of the model with a
mean-field theory and find that the latter cannot describe pairing correlations
in the intermediate regime. We also study the occurrence of spin jumps across
the phase boundary separating the superconducting and coexistence regimes.",0704.2257v1
2007-04-19,Experimental studies on vacancy induced ferromagnetism in undoped TiO2,"Room temperature ferromagnetism is observed in undoped TiO2 films deposited
on Si substrates using pulsed laser deposition (PLD). The ferromagnetic
properties of the samples depend on the oxygen partial pressure during the PLD
synthesis. The appearance of higher binding energy component (HBEC) in the
oxygen 1s core peak from x-ray photoelectron spectroscopy (XPS) suggests the
presence of oxygen vacancies in these samples. The amount of oxygen during the
synthesis determines the vacancy concentration in the samples which is directly
related to the magnetic behavior of the samples. The magnetic moment decreases
with oxygen vacancy concentration in the samples. Valence band measurements
were performed to study the electronic structure of both stoichometric and
reduced TiO2. The analyses show the presence of Ti 3d band near the Fermi level
in reduced TiO2 samples. These bands are otherwise empty in stoichiometric TiO2
and reside in the conduction band which makes them unobservable by XPS. The
existence of this Ti 3d band near the Fermi level can possibly lead to Stoner
splitting of the band.",0704.2621v1
2007-05-03,"On the Dynamical Ferromagnetic, Quantum Hall, and Relativistic Effects on the Carbon Nanotubes Nucleation and Growth Mechanism","The mechanism of carbon nanotube (CNT) nucleation and growth has been a
mystery for over 15 years. Prior models have attempted the extension of older
classical transport mechanisms. In July 2000, a more detailed and accurate
nonclassical, relativistic mechanism was formulated considering the detailed
dynamics of the electronics of spin and orbital rehybridization between the
carbon and catalyst via novel mesoscopic phenomena and quantum dynamics.
Ferromagnetic carbon was demonstrated. Here, quantum (Hall) effects and
relativistic effects of intense many body spin-orbital interactions for novel
orbital rehybridization dynamics (Little Effect) are proposed in this new
dynamical magnetic mechanism. This dynamic ferromagnetic mechanism is proven by
imposing dynamic and static magnetic fields during CNT syntheses and observing
the different influence of these external magnetic environments on the
catalyzing spin currents and spin waves and the resulting CNT formation.",0705.0407v1
2007-05-23,Revelation of the role of impurities and conduction electron density in the high resolution photoemission study of ferromagnetic hexaborides,"We investigate the temperature evolution of the electronic structure of
ferromagnetic CaB$_6$ using ultra-high resolution photoemission spectroscopy;
electronic structure of paramagnetic LaB$_6$ is used as a reference. High
resolution spectra of CaB$_6$ reveal finite density of states at the Fermi
level, $\epsilon_F$ at all the temperatures and evidence of impurity induced
localized features in the vicinity of $\epsilon_F$, which are absent in the
spectra of LaB$_6$. Analysis of the high resolution spectra suggests that
disorder in B-sublattice inducing partial localization in the mobile electrons
and low electron density at $\epsilon_F$ is important to achieve ferromagnetism
in these systems.",0705.3327v1
2007-05-30,Spontaneous ferromagnetic spin ordering at the surface of La$_2$CuO$_4$,"Magnetic properties of high purity stoichiometric La$_2$CuO$_4$ nanoparticles
are systematically investigated as a function of particle size. Ferromagnetic
single-domain spin clusters are shown to spontaneously form at the surface of
fine grains as well as paramagnetic defects. Hysteresis loops and
thermomagnetic irreversibility are observed in a wide temperature range $5 -
350$ K with the remnant moment and coercivity gradually decreasing with
increasing temperature. Possible origins of the spontaneous surface
ferromagnetic clusters and the relation of our data to the appearance of
unusual magnetic phenomena and phase separation of doped cuprates are
discussed.",0705.4391v1
2007-06-05,Universal low-temperature behavior of the CePd_{1-x}Rh_x ferromagnet,"The heavy-fermion metal CePd_{1-x}Rh_x evolves from ferromagnetism at x=0 to
a non-magnetic state at some critical concentration x_c. Utilizing the
quasiparticle picture and the concept of fermion condensation quantum phase
transition (FCQPT), we address the question about non-Fermi liquid (NFL)
behavior of ferromagnet CePd_{1-x}Rh_x and show that it coincides with that of
both antiferromagnet YbRh_2(Si_{0.95}Ge_{0.05})_2 and paramagnet CeRu_2Si_2 and
CeNi_2Ge_2. We conclude that the NFL behavior being independent of the
peculiarities of specific alloy, is universal, while numerous quantum critical
points assumed to be responsible for the NFL behavior of different HF metals
can be well reduced to the only quantum critical point related to FCQPT.",0706.0742v2
2007-06-19,Spin gap and string order parameter in the ferromagnetic Spiral Staircase Heisenberg Ladder: a quantum Monte Carlo study,"We consider a spin-1/2 ladder with a ferromagnetic rung coupling J_\perp and
inequivalent chains. This model is obtained by a twist (\theta) deformation of
the ladder and interpolates between the isotropic ladder (\theta=0) and the
SU(2) ferromagnetic Kondo necklace model (\theta=\pi). We show that the ground
state in the (\theta,J_\perp) plane has a finite string order parameter
characterising the Haldane phase. Twisting the chain introduces a new energy
scale, which we interpret in terms of a Suhl-Nakamura interaction. As a
consequence we observe a crossover in the scaling of the spin gap at weak
coupling from \Delta/J_\| \propto J_\perp/J_\| for \theta < \theta_c \simeq
8\pi/9 to \Delta/J_\| \propto (J_\perp/J_\|)^2 for \theta > \theta_c. Those
results are obtained on the basis of large scale Quantum Monte Carlo
calculations.",0706.2769v2
2007-06-20,A scaling relation of anomalous Hall effect in ferromagnetic semiconductors and metals,"A scaling relation of the anomalous Hall effect recently found in a
ferromagnetic semiconductor (Ti,Co)O_2_ is compared with those of various
ferromagnetic semiconductors and metals. Many of these compounds with
relatively low conductivity sigma_xx_ < 10^4 ohm^-1 cm^-1 are also found to
exhibit similar relation: anomalous Hall conductivity sigma_AH_ approximately
scales as sigma_AH_ proportional to sigma_xx_^1.6, that is coincident with a
recent theory. This relation is valid over five decades of sigma_xx_
irrespective of metallic or hopping conduction.",0706.2924v1
2007-06-22,Orbital ordering in the ferromagnetic insulator Cs$_2$AgF$_4$ from first principles,"We found, using density-functional theory calculations within the generalized
gradient approximation, that Cs$_2$AgF$_4$ is stabilized in the insulating
orthorhombic phase rather than in the metallic tetragonal phase. The lattice
distortion present in the orthorhombic phase corresponds to the
$x^2-z^2$/$y^2-z^2$ hole-orbital ordering of the Ag$^{2+}$ $4d^9$ ions, and
this orbital ordering leads to the observed ferromagnetism, as confirmed by the
present total-energy calculations. This picture holds in the presence of
moderate 4d-electron correlation. The results are compared with the picture of
ferromagnetism based on the metallic tetragonal phase.",0706.3413v2
2007-07-11,Stripe width and non-local domain walls in the two-dimensional Dipolar Frustrated Ising Ferromagnet,"We describe a novel type of magnetic domain wall which, in contrast to Bloch
or Neel walls, is non-localized and, in a certain temperature range,
non-monotonic. The wall appears as the mean-field solution of the
two-dimensional ferromagnetic Ising model frustrated by the long-ranged dipolar
interaction. We provide experimental evidence of this wall delocalization in
the stripe-domain phase of perpendicularly magnetized ultrathin magnetic films.
In agreement with experimental results, we find that the stripe width decreases
with increasing temperature and approaches a finite value at the
Curie-temperature following a power law. The same kind of wall and a similar
temperature dependence of the stripe width is expected in the mean-field
approximation of the two-dimensional Coulomb frustrated Ising ferromagnet.",0707.1582v2
2007-07-18,Suppression of hole-mediated ferromagnetism in GaMnP by hydrogen,"We report the successful passivation of the Mn acceptors in GaMnP upon
exposure to a remote dc hydrogen plasma. The as-grown films are non-metallic
and ferromagnetic with a Curie temperature of T_C=55K. After hydrogenation the
sample resistivity increases by approximately three orders of magnitude at room
temperature and six orders of magnitude at 25 K. Furthermore, the hydrogenated
samples are paramagnetic, which is evidenced by a magnetization curve at 5 K
that is best described by a Brillouin function with g=2 and J=5/2 expected for
Mn atoms in the 3d^5 configuration. These observations unambiguously proof that
the ferromagnetism is carrier-mediated also in GaMnP.",0707.2777v1
2007-07-19,Magnetic-glassy multicritical behavior of the three-dimensional +- J Ising model,"We consider the three-dimensional $\pm J$ model defined on a simple cubic
lattice and study its behavior close to the multicritical Nishimori point where
the paramagnetic-ferromagnetic, the paramagnetic-glassy, and the
ferromagnetic-glassy transition lines meet in the T-p phase diagram (p
characterizes the disorder distribution and gives the fraction of ferromagnetic
bonds). For this purpose we perform Monte Carlo simulations on cubic lattices
of size $L\le 32$ and a finite-size scaling analysis of the numerical results.
The magnetic-glassy multicritical point is found at $p^*=0.76820(4)$, along the
Nishimori line given by $2p-1={\rm Tanh}(J/T)$. We determine the
renormalization-group dimensions of the operators that control the
renormalization-group flow close to the multicritical point, $y_1 = 1.02(5)$,
$y_2 = 0.61(2)$, and the susceptibility exponent $\eta = -0.114(3)$. The
temperature and crossover exponents are $\nu=1/y_2=1.64(5)$ and $\phi=y_1/y_2 =
1.67(10)$, respectively. We also investigate the model-A dynamics, obtaining
the dynamic critical exponent $z = 5.0(5)$.",0707.2866v1
2007-07-30,Tuning of ferromagnetism through anion substitution in Ga-Mn-pnictide ferromagnetic semiconductors,"We have synthesized Ga1-xMnxAs1-yPy and Ga1-xMnxP1-yNy by the combination of
ion implantation and pulsed-laser melting. We find that the incorporation of
isovalent impurities with smaller atomic radii leads to a realignment of the
magnetic easy axis in Ga1-xMnxP1-yNy/GaP and Ga1-xMnxAs1-yPy/GaAs thin films
from in-plane to out-of-plane. This tensile-strain-induced magnetic anisotropy
is reminiscent of that observed in Ga1-xMnxAs grown on larger lattice constant
(In,Ga)As buffer layers indicating that the role of strain in determining
magnetic anisotropy is fundamental to III-Mn-V materials. In addition, we
observe a decrease in the ferromagnetic Curie temperature in Ga1-xMnxAs1-yPy
with increasing y from 0 to 0.028. Such a decrease may result from localization
of holes as the P/As ratio on the Group V sublattice increases.",0707.4490v1
2007-08-02,Hydrogen patterning of Ga1-xMnxAs for planar spintronics,"We demonstrate two patterning techniques based on hydrogen passivation of
Ga1-xMnxAs to produce isolated ferromagnetically active regions embedded
uniformly in a paramagnetic, insulating host. The first method consists of
selective hydrogenation of Ga1-xMnxAs by lithographic masking. Magnetotransport
measurements of Hall-bars made in this manner display the characteristic
properties of the hole-mediated ferromagnetic phase, which result from good
pattern isolation. Arrays of Ga1-xMnxAs dots as small as 250 nm across have
been realized by this process. The second process consists of blanket
hydrogenation of Ga1-xMnxAs followed by local reactivation using confined
low-power pulsed-laser annealing. Conductance imaging reveals local electrical
reactivation of micrometer-sized regions that accompanies the restoration of
ferromagnetism. The spatial resolution achievable with this method can
potentially reach <100 nm by employing near-field laser processing. The high
spatial resolution attainable by hydrogenation patterning enables the
development of systems with novel functionalities such as lateral
spin-injection as well as the exploration of magnetization dynamics in
individual and coupled structures made from this novel class of semiconductors.",0708.0389v1
2007-08-08,Onset of ferromagnetism in low-doped GaMnAs,"We develop a quantitatively predictive theory for impurity-band
ferromagnetism in the low-doping regime of GaMnAs and compare with experimental
measurements of a series of samples whose compositions span the transition from
paramagnetic insulating to ferromagnetic conducting behavior. The theoretical
Curie temperatures depend sensitively on the local fluctuations in the Mn-hole
binding energy, which originates from disorder in the Mn distribution as well
as the presence of As antisite defects. The experimentally-determined hopping
energy at the Curie temperature is roughly constant over a series of samples
whose conductivities vary more than 10^4 and whose hole concentrations vary
more than 10^2. Thus in this regime the hopping energy is an excellent
predictor of the Curie temperature for a sample, in agreement with the theory.",0708.1063v1
2007-08-08,The anomalous Hall Effect and magnetoresistance in the layered ferromagnet Fe_{1/4}TaS_2: the inelastic regime,"The large magnetic anisotropy in the layered ferromagnet Fe_{1/4}TaS_2 leads
to very sharp reversals of the magnetization $\bf M$ at the coercive field. We
have exploited this feature to measure the anomalous Hall effect (AHE),
focussing on the AHE conductivity $\sigma^A_{xy}$ in the inelastic regime. At
low temperature T (5-50 K), $\sigma^A_{xy}$ is T-independent, consistent with
the Berry-phase/Karplus-Luttinger theory. Above 50 K, we extract an inelastic
AHE conductivity $\sigma^{in}_{xy}$ that scales as the square of $\Delta\rho$
(the T dependent part of the resistivity $\rho$). The term $\sigma^{in}_{xy}$
clarifies the T dependence and sign-reversal of the AHE coefficient R_s(T). We
discuss the possible ubiquity of $\sigma^{in}_{xy}$ in ferromagnets, and ideas
for interpreting its scaling with $(\Delta\rho)^2$. Measurements of the
magnetoresistance (MR) reveal a rich pattern of behavior vs. T and field
tilt-angle. We show that the 2 mechanisms, the anisotropic MR effect and
field-suppression of magnons, account for the intricate MR behavior, including
the bow-tie features caused by the sharp reversals in $\bf M$.",0708.1143v1
2007-08-17,Current-Induced Motion of Narrow Domain Walls and Dissipation in Ferromagnetic Metals,"Spin transport equations in a non-homogeneous ferromagnet are derived in the
limit where the sd exchange coupling between the electrons in the conduction
band and those in the d band is dominant. It is shown that spin diffusion in
ferromagnets assumes a tensor form. The diagonal terms are renormalized with
respect to that in normal metals and enhances the dissipation in the magnetic
system while the off-diagonal terms renormalize the precessional frequency of
the conduction electrons and enhances the non-adiabatic spin torque. To
demonstrate the new physics in our theory, we show that self-consistent
solutions of the spin diffusion equations and the Landau-Lifshitz equations in
the presence of a current lead to a an increase in the terminal velocity of a
domain wall which becomes strongly dependent on its width. We also provide a
simplified equation that predicts damping due to the conduction electrons.",0708.2412v1
2007-08-29,Separation of the strain and finite size effect on the ferromagnetic properties of La_{0.5}Sr_{0.5}CoO_3 thin films,"The ferromagnetic properties of epitaxial La$_{0.5}$Sr$_{0.5}$CoO$_3$ thin
films have been studied. The magnetic transition is affected by both strain and
finite thickness. We have used a series of films of different thickness and on
different substrates in order to quantitatively determine the change in Curie
temperature contributed by each effect. The phase diagram of T$_C$ versus
in-plane strain suggests that the ferromagnetic transition temperature is
suppressed by tensile strain and enhanced by compressive strain. The general
method of separating strain and finite thickness effects should be applicable
to any ordering phase transition in thin films.",0708.3964v1
2007-08-29,Spin-charge separation in a strongly correlated spin-polarized chain,"We combine the first-quantized path-integral formalism and bosonization to
develop a phenomenological theory for spin-charge coupled dynamics in
one-dimensional (1D) ferromagnetic systems with strong interparticle repulsion,
at low temperatures. We assume an effective spin-charge separation and retain
the standard Luttinger-liquid plasmon branch, which is explicitly coupled to a
ferromagnetic spin-wave texture with a quadratic dispersion. The dynamic spin
structure severely suppresses the plasmon peak in the single-particle
propagator, in both fermionic and bosonic systems. Our analysis provides an
effective theory for the new universality class of 1D ferromagnetic systems,
capturing both the trapped spin and propagating spin-wave regimes of the
long-time behavior.",0708.4012v4
2007-08-30,Origin of Ferromagnetism in nitrogen embedded ZnO:N thin films,"Nitrogen embedded ZnO:N films prepared by pulsed laser deposition exhibit
significant ferromagnetism. The nitrogen ions contained in ZnO confirmed by
Secondary Ion Microscopic Spectrum and Raman experiments and the embedded
nitrogen ions can be regarded as defects. According to the experiment results,
a mechanism is proposed based on one of the electrons in the completely filled
d-orbits of Zn that compensates the dangling bonds of nitrogen ions and leads
to a net spin of one half in the Zn orbits. These one half spins strongly
correlate with localized electrons that are captured by defects to form
ferromagnetism. Eventually, the magnetism of nitrogen embedded ZnO:N films
could be described by a bound magnetic polaron model.",0708.4053v1
2007-09-11,Magnetically asymmetric interfaces in a (LaMnO$_3$)/(SrMnO$_3$) superlattice due to structural asymmetries,"Polarized neutron reflectivity measurements of a ferromagnetic
[(LaMnO$_3$)$_{11.8}$/(SrMnO$_3$)$_{4.4}$]$_6$ superlattice reveal a modulated
magnetic structure with an enhanced magnetization at the interfaces where
LaMnO$_3$ was deposited on SrMnO$_3$ (LMO/SMO). However, the opposite
interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The
magnetic asymmetry arises from the difference in lateral structural roughness
of the two interfaces observed via electron microscopy, with strong
ferromagnetism present at the interfaces that are atomically smooth over tens
of nanometers. This result demonstrates that atomic-scale roughness can
destabilize interfacial phases in complex oxide heterostructures.",0709.1715v2
2007-09-19,Interplay of ferromagnetism and triplet superconductivity in a Josephson junction,"In this paper we extend our earlier analysis of the novel Josephson effect in
triplet superconductor--ferromagnet--triplet superconductor (TFT) junctions [B.
Kastening \emph{et al.}, Phys. Rev. Lett. {\bf{96}}, 047009 (2006)]. In our
more general formulation of the TFT junction we allow for potential scattering
at the barrier and an arbitrary orientation of the ferromagnetic moment.
Several new effects are found upon the inclusion of these extra terms: for
example, we find that a Josephson current can flow even when there is vanishing
phase difference between the superconducting condensates on either side of the
barrier. The critical current for a barrier with magnetization parallel to the
interface is calculated as a function of the junction parameters, and is found
to display strong non-analyticities. Furthermore, the Josephson current
switches first identified in our previous work are found to be robust features
of the junction, while the unconventional temperature-dependence of the current
is very sensitive to the extra terms in the barrier Hamiltonian.",0709.2918v1
2007-09-18,Theory of current-driven magnetization dynamics in inhomogeneous ferromagnets,"We give a brief account of recent developments in the theoretical
understanding of the interaction between electric currents and inhomogeneous
ferromagnetic order parameters. We start by discussing the physical origin of
the spin torques responsible for this interaction and construct a
phenomenological description. We then consider the electric current-induced
ferromagnetic instability and domain-wall motion. Finally, we present a
microscopic justification of the phenomenological description of current-driven
magnetization dynamics, with particular emphasis on the dissipative terms, the
so-called Gilbert damping $\alpha$ and the $\beta$ component of the adiabatic
current-driven torque.",0709.2937v2
2007-09-20,Magnetic fluctuations and itinerant ferromagnetism in two-dimensional systems with van Hove singularities,"We use the quasistatic approach to analyze the criterion of ferromagnetism
for two-dimensional (2D) systems with the Fermi level near Van Hove
singularities (VHS) of the electronic spectrum. It is shown that the spectrum
of spin excitations (paramagnons) is positively defined when the interaction I
between electrons and paramagnons, which corresponds to the Hubbard on-site
repulsion U, is sufficiently large. The critical interactions I_c and U_c
remain finite at Van Hove filling and exceed considerably their values obtained
from the Stoner criterion due to incommensurate spin fluctuations which are
important near the ferromagnetic quantum phase transition. Combining the
quasistatic approximation and the equation-of -motion method for the Green
functions we obtain the results for the electronic self-energy to first order
in the inverse number of spin components.",0709.3219v2
2007-10-11,X-ray magnetic circular dichroism and photoemission study of the diluted ferromagnetic semiconductor Zn$_{1-x}$Cr$_x$Te,"We have performed x-ray magnetic circular dichroism (XMCD) and valence-band
photoemission studies of the diluted ferromagnetic semiconductor
Zn$_{1-x}$Cr$_x$Te. XMCD signals due to ferromagnetism were observed at the Cr
2p absorption edge. Comparison with atomic multiplet calculations suggests that
the magnetically active component of the Cr ion was divalent under the
tetrahedral crystal field with tetragonal distortion along the crystalline a-,
b-, and c-axes. In the valence-band spectra, spectral weight near the Fermi
level was strongly suppressed, suggesting the importance of Jahn-Teller effect
and the strong Coulomb interaction between the Cr 3d electrons.",0710.2170v1
2007-10-15,Fermionic representation for the ferromagnetic Kondo lattice model -- diagrammatic study of spin-charge coupling effects on magnon excitations,"A purely fermionic representation is introduced for the ferromagnetic Kondo
lattice model which allows conventional diagrammatic tools to be employed to
study correlation effects. Quantum 1/S corrections to magnon excitations are
investigated using a systematic inverse-degeneracy expansion scheme which
incorporates correlation effects in the form of self-energy and vertex
corrections, while explicitly preserving the continuous spin-rotation symmetry.
Magnon self-energy is studied in the full range of interaction strength, and
shown to result in strong magnon damping and anomalous softening for zone
boundary modes, which accounts for several zone-boundary anomalies observed in
recent spin-wave measurements of ferromagnetic manganites.",0710.2828v1
2007-10-17,Superfluid density of superconductor-ferromagnet bilayers,"We report the first measurements of the effective superfluid density n_S(T)
\propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where
\lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers
were sputtered in ultrahigh vacuum in quick succession onto oxidized Si
substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses
vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as
Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at
d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several
times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni
thickness long after T_C has stopped changing. We argue that this indicates a
substantial superfluid density inside the ferromagnetic Ni films.",0710.3376v1
2007-10-29,Disorder and temperature dependence of the Anomalous Hall Effect in thin ferromagnetic films: Microscopic model,"We consider the Anomalous Hall Effect (AHE) in thin disordered ferromagnetic
films. Using a microscopic model of electrons in a random potential of
identical impurities including spin-orbit coupling, we develop a general
formulation for strong, finite range impurity scattering. Explicit calculations
are done within a short range but strong impurity scattering to obtain AH
conductivities for both the skew scattering and side jump mechanisms. We also
evaluate quantum corrections due to interactions and weak localization effects.
We show that for arbitrary strength of the impurity scattering, the
electron-electron interaction correction to the AH conductivity vanishes
exactly due to general symmetry reasons. On the other hand, we find that our
explicit evaluation of the weak localization corrections within the strong,
short range impurity scattering model can explain the experimentally observed
logarithmic temperature dependences in disordered ferromagnetic Fe films.",0710.5416v1
2007-11-01,Two magnetic regimes in doped ZnO corresponding to a dilute magnetic semiconductor and a dilute magnetic insulator,"Films of ZnO doped with magnetic ions, Mn and Co and, in some cases, with Al
have been fabricated with a very wide range of carrier densities. Ferromagnetic
behaviour is observed in both insulating and metallic films, but not when the
carrier density is intermediate. Insulating films exhibit variable range
hopping at low temperatures and are ferromagnetic at room temperature due to
the interaction of the localised spins with static localised states. The
magnetism is quenched when carriers in the localised states become mobile. In
the metallic (degenerate semiconductor) range, robust ferromagnetism reappears
together with very strong magneto-optic signals and room temperature anomalous
Hall data. This demonstrates the polarisation of the conduction bands and
indicates that, when ZnO is doped into the metallic regime, it behaves as a
genuine magnetic semiconductor.",0711.0172v2
2007-11-02,Phase space gaps and ergodicity breaking in systems with long range interactions,"We study a generalized isotropic XY-model which includes both two-spin and
four-spin mean-field interactions. This model can be solved in the
microcanonical ensemble. It is shown that in certain parameter regions the
model exhibits gaps in the magnetization at fixed energy, resulting in
ergodicity breaking. This phenomenon has previously been reported in
anisotropic and discrete spin models. The entropy of the model is calculated
and the microcanonical phase diagram is derived, showing the existence of first
order phase transitions from the ferromagnetic to a paramagnetic disordered
phase. It is found that ergodicity breaking takes place both in the
ferromagnetic and the paramagnetic phases. As a consequence, the system can
exhibit a stable ferromagnetic phase within the paramagnetic region, and
conversely a disordered phase within the magnetically ordered region.",0711.0268v1
2007-11-02,Effects of Ferromagnetic Magnetic Ordering and Phase Transition on the Resistivity of Spin Current,"It has been shown experimentally a long time ago that the magnetic ordering
causes an anomalous behavior of the electron resistivity in ferromagnetic
crystals. Phenomenological explanations based on the interaction between
itinerant electron spins and lattice spins have been suggested to explain these
observations. We show by extensive Monte Carlo simulation that this behavior is
also observed for the resistivity of the spin current calculated as a function
of temperature ($T$) from low-$T$ ordered phase to high-$T$ paramagnetic phase
in a ferromagnet. We show in particular that across the critical region, the
spin resistivity undergoes a huge peak. The origin of this peak is shown to
stem from the formation of magnetic domains near the phase transition. The
behavior of the resistivity obtained here is compared to experiments and
theories. A good agreement is observed.",0711.0298v1
2007-11-27,Nonequilibrium interacting electrons in a ferromagnet,"Dynamics of the magnetization in ferromagnets is examined in the presence of
transport electrons allowing the latter to interact. It is found that the
existence of inhomogeneities such as domain wall (DW) structures, leads to
changes that affect the dynamical structure of the equations of motion for the
magnetization. Only in the limit of uniform magnetizations or sufficiently wide
DW's, the equations of motion maintain the form they have in the noninteracting
case. In this limit, results like the spin torques, the Gilbert parameter, and
the DW velocities become renormalized. However the length scale that defines
such a limit depends on the strength of the interaction. It is shown that if
large ferromagnetic fluctuations exist in the metallic band then the range for
which conformity with the noninteracting case holds extends to the limit of
arbitrarily narrow DW's.",0711.4170v2
2007-12-14,Compensation of the Kondo effect in quantum dots coupled to ferromagnetic leads within equation of motion approach,"We propose a new approximation scheme within equation of motion approach
(EOM) to spin polarized transport through a quantum dot coupled to
ferromagnetic leads. It has some advantages over a widely used in the
literature standard EOM technique, in particular when we are interested in spin
polarized quantities. Namely, it gives the values of the dot spin polarization
which are closer to the ones obtained within numerical renormalization group
(NRG), than the standard EOM approach. While restoring the Kondo effect, the
spin polarization vanishes and the transport becomes unpolarized, in agreement
with NRG and a real time diagrammatic calculations. The standard EOM procedure
gives nonzero values of the spin polarization, and the transport is still spin
polarized. Both approximations give the same correct splitting of the Kondo
peaks due to ferromagnetism in the electrodes.",0712.2414v1
2007-12-14,The Spin Reorientation Transition and Phase Diagram of Ultrathin Ferromagnetic Films,"We show results from Monte Carlo simulations of a two dimensional Heisenberg
model for ultrathin films with perpendicular anisotropy. A complete phase
diagram is obtained as a function of anisotropy and temperature, spanning a
wide range of behavior. We discuss our results in relation with experimental
findings in different ultrathin films. We observe and characterize a line of
Spin Reorientation Transitions . This transition from out of plane stripe order
to in plane ferromagnetic order presents a paramagnetic gap in between in a
finite region in parameter space, as reported in experiments. For large
anisotropies direct transitions from a low temperature stripe phase to a
paramagnetic or tetragonal phase with dominant perpendicular magnetization is
observed, also in agreement with experiments.
  We also show the phase diagram for a system without exchange, i.e. with pure
dipolar and anisotropy interactions. It shows a similar behavior to the
ferromagnetic case with antiferromagnetic instead of stripe phases at low
temperatures. A Spin Reorientation Transition is also found in this case.",0712.2426v1
2008-01-08,Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures,"We report observations of tunneling anisotropic magnetoresitance (TAMR) in
vertical tunnel devices with a ferromagnetic multilayer-(Co/Pt) electrode and a
non-magnetic Pt counter-electrode separated by an AlOx barrier. In stacks with
the ferromagnetic electrode terminated by a Co film the TAMR magnitude
saturates at 0.15% beyond which it shows only weak dependence on the magnetic
field strength, bias voltage, and temperature. For ferromagnetic electrodes
terminated by two monolayers of Pt we observe order(s) of magnitude enhancement
of the TAMR and a strong dependence on field, temperature and bias. Discussion
of experiments is based on relativistic ab initio calculations of magnetization
orientation dependent densities of states of Co and Co/Pt model systems.",0801.1192v1
2008-01-15,"New High-$T_c$ Half-Heusler Ferromagnets NiMnZ (Z = Si, P, Ge, As)","Based on the first principle calculation, we propose a new class of
high-$T_c$ half-heusler ferromagnets NiMnZ (Z = Si, P, Ge, As). The structural
and magnetic properties are investigated through the calculation of the
electronic structure, phase stability, equilibrium lattice constant, magnetic
exchange interaction $J_{ij}$ and Curie temperature $T_c$. It is found that all
alloys show half-metallicity and ferromagnetism at temperatures much higher
than room temperature in a wide range of lattice expansion (compression). At
the equilibrium lattice constant, $T_c$ of 715K, 840K, 875K and 1050K are
predicted by Monte Carlo simulation for NiMnP, NiMnAs, NiMnGe and NiMnSi,
respectively. Following these results, these alloys are strongly expected to be
promising candidates for spintronic applications.",0801.2225v1
2008-01-22,"Phase coherent transport in (Ga,Mn)As","Quantum interference effects and resulting quantum corrections of the
conductivity have been intensively studied in disordered conductors over the
last decades. The knowledge of phase coherence lengths and underlying dephasing
mechanisms are crucial to understand quantum corrections to the resistivity in
the different material systems. Due to the internal magnetic field and the
associated breaking of time-reversal symmetry quantum interference effects in
ferromagnetic materials have been scarcely explored. Below we describe the
investigation of phase coherent transport phenomena in the newly discovered
ferromagnetic semiconductor (Ga,Mn)As. We explore universal conductance
fluctuations in mesoscopic (Ga,Mn)As wires and rings, the Aharonov-Bohm effect
in nanoscale rings and weak localization in arrays of wires, made of the
ferromagnetic semiconductor material. The experiments allow to probe the phase
coherence length L_phi and the spin flip length L_SO as well as the temperature
dependence of dephasing.",0801.3363v1
2008-01-29,Temperature Dependence of the Spin Resistivity in Ferromagnetic Thin Films,"The magnetic phase transition is experimentally known to give rise to an
anomalous temperature-dependence of the electron resistivity in ferromagnetic
crystals. Phenomenological theories based on the interaction between itinerant
electron spins and lattice spins have been suggested to explain these
observations. In this paper, we show by extensive Monte Carlo (MC) simulation
the behavior of the resistivity of the spin current calculated as a function of
temperature ($T$) from low-$T$ ordered phase to high-$T$ paramagnetic phase in
a ferromagnetic film. We analyze in particular effects of film thickness,
surface interactions and different kinds of impurities on the spin resistivity
across the critical region. The origin of the resistivity peak near the phase
transition is shown to stem from the existence of magnetic domains in the
critical region. We also formulate in this paper a theory based on the
Boltzmann's equation in the relaxation-time approximation. This equation can be
solved using numerical data obtained by our simulations. We show that our
theory is in a good agreement with our MC results. Comparison with experiments
is discussed.",0801.4444v1
2008-01-31,Impurity-Ion pair induced high-temperature ferromagnetism in Co-doped ZnO,"Magnetic 3d-ions doped into wide-gap oxides show signatures of room
temperature ferromagnetism, although their concentration is two orders of
magnitude smaller than that in conventional magnets. The prototype of these
exceptional materials is Co-doped ZnO, for which an explanation of the room
temperature ferromagnetism is still elusive. Here we demonstrate that magnetism
originates from Co2+ oxygen-vacancy pairs with a partially filled level close
to the ZnO conduction band minimum. The magnetic interaction between these
pairs is sufficiently long-ranged to cause percolation at moderate
concentrations. However, magnetically correlated clusters large enough to show
hysteresis at room temperature already form below the percolation threshold and
explain the current experimental findings. Our work demonstrates that the
magnetism in ZnO:Co is entirely governed by intrinsic defects and a phase
diagram is presented. This suggests a recipe for tailoring the magnetic
properties of spintronics materials by controlling their intrinsic defects.",0801.4945v1
2008-02-04,Adiabatic charge and spin pumping through quantum dots with ferromagnetic leads,"We study adiabatic pumping of electrons through quantum dots attached to
ferromagnetic leads. Hereby we make use of a real-time diagrammatic technique
in the adiabatic limit that takes into account strong Coulomb interaction in
the dot. We analyze the degree of spin polarization of electrons pumped from a
ferromagnet through the dot to a nonmagnetic lead (N-dot-F) as well as the
dependence of the pumped charge on the relative leads' magnetization
orientations for a spin-valve (F-dot-F) structure. For the former case, we find
that, depending on the relative coupling strength to the leads, spin and charge
can, on average, be pumped in opposite directions. For the latter case, we find
an angular dependence of the pumped charge, that becomes more and more
anharmonic for large spin polarization in the leads.",0802.0422v2
2008-02-10,Oxygen Vacancy Induced Ferromagnetism in V$_2$O$_{5-x}$,"{\it Ab initio} calculations within density functional theory with
generalized gradient approximation have been performed to study the effects of
oxygen vacancies on the electronic structure and magnetism in undoped
V$_2$O$_{5-x}$ ($0 < x < 0.5$). It is found that the introduction of oxygen
vacancies would induce ferromagnetism in V$_2$O$_{5-x}$ with the magnetization
being proportional to the O vacancy concentration $x$. The calculated
electronic structure reveals that the valence electrons released by the
introduction of oxygen vacancies would occupy mainly the neighboring V
$d_{xy}$-dominant band which then becomes spin-polarized due to intra-atomic
exchange interaction, thereby giving rise to the half-metallic ferromagnetism.",0802.1313v1
2008-02-26,Electron-mediated ferromagnetism and small spin-orbit interaction in a molecular-beam-epitaxy grown n-type $GaAs/Al_{0.3}Ga_{0.7}As$ heterostructure with Mn $δ$-doping,"We report the first evidence of electron-mediated ferromagnetism in a
molecular-beam-epitaxy (MBE) grown $GaAs/Al_{0.3}Ga_{0.7}As$ heterostructure
with Mn $\delta$-doping. The interaction between the magnetic dopants (Mn) and
the Two-Dimensional Electron Gas (2DEG) realizes magnetic ordering when the
temperature is below the Curie temperature ($T_{C} \sim 1.7K$) and the 2DEG is
brought in close proximity to the Mn layer by gating. The Anomalous Hall Effect
(AHE) contribution to the total Hall resistance is shown to be about three to
four orders of magnitude smaller than in the case of hole-mediated
ferromagnetism indicating the presence of small spin-orbit interaction.",0802.3871v3
2008-02-27,Cationic Ordering and Microstructural Effects in the Ferromagnetic Perovskite La0.5Ba0.5CoO3: Impact upon Magnetotransport Properties,"The synthesis and structural study of the stoichiometric perovskite
La0.5Ba0.5CoO3 have allowed three forms to be isolated. Besides the disordered
La0.5Ba0.5CoO3 and the perfectly ordered layered LaBaCo2O6, a third form called
nanoscale-ordered LaBaCo2O6, is obtained. As evidenced by transmission electron
microscopy investigations, the latter consists of 112-type 90 degree oriented
domains fitted into each other at a nanometer scale which induce large strains
and consequently local atomic scale lattice distortions. These three
ferromagnetic perovskites exhibit practically the same Tc (174-179 K), but
differently from the other phases, the nanoscale-ordered LaBaCo2O6 is a hard
ferromagnet, with Hc = 4.2 kOe, due to the strains which may pin domain walls,
preventing the reversal of the spins in a magnetic field. The magnetotransport
properties of these phases show that all of them exhibit a maximum intrinsic
magnetoresistance, close to 6-7 % around Tc under 70 kOe but that the ordered
phase exhibits a much higher tunnelling magnetoresistance effect at low
temperature of about 15 % against 4 % due to the grain boundary effects.",0802.3984v1
2008-03-03,Introduction to Monte Carlo methods for an Ising Model of a Ferromagnet,"This discussion serves as an introduction to the use of Monte Carlo
simulations as a useful way to evaluate the observables of a ferromagnet. Key
background is given about the relevance and effectiveness of this stochastic
approach and in particular the applicability of the Metropolis-Hastings
algorithm. Importantly the potentially devastating effects of spontaneous
magnetization are highlighted and a means to avert this is examined.
  An Ising model is introduced and used to investigate the properties of a two
dimensional ferromagnet with respect to its magnetization and energy at varying
temperatures. The observables are calculated and a phase transition at a
critical temperature is also illustrated and evaluated. Lastly a finite size
scaling analysis is undertaken to determine the critical exponents and the
Curie temperature is calculated using a ratio of cumulants with differing
lattice sizes. The results obtained from the simulation are compared to exact
calculations to endorse the validity of this numerical process. A copy of the
code used, written in C++, is enclosed and is freely available for use and
modification under the General Public License.",0803.0217v1
2008-03-04,Inhomogeneous vortex-state-driven enhancement of superconductivity in nanoengineered ferromagnet-superconductor heterostructures,"Thin film heterostructures provide a powerful means to study the antagonism
between superconductivity (SC) and ferromagnetism (FM). One interesting issue
in FM-SC hybrids which defies the notion of antagonistic orders is the
observation of magnetic field induced superconductivity (FIS). Here we show
that in systems where the FM domains/islands produce spatial inhomogeneities of
the SC order parameter, the FIS can derive significant contribution from
different mobilities of the magnetic flux identified by two distinct critical
states in the inhomogeneous superconductor. Our experiments on nanoengineered
bilayers of ferromagnetic CoPt and superconducting NbN where CoPt/NbN islands
are separated by a granular NbN, lend support to this alternative explanation
of FIS in certain class of FM-SC hybrids.",0803.0454v1
2008-03-08,Spin structure factors and valence-bond-solid states of the trimerized Heisenberg chains in a magnetic field,"By means of the density matrix renormalization group (DMRG) method, the
static spin structure factors and the magnetization plateaus of the trimerized
Heisenberg ferromagnet-ferromagnet-antiferromagnet and
antiferromagnet-antiferromagnet-ferromagnet spin chains in the presence of a
magnetic field are elaborately studied. It is found that in the plateau states,
the static structure factor with three peaks does not vary with the external
magnetic field as well as the exchange couplings; the spin correlation function
behaves as a perfect sequence and has a simple relation with the magnetization
per site. An approximate wave function for the plateau states is proposed, and
a picture based on the valence-bond-solid states is presented in order to
understand the origin and the total number of the magnetization plateaus, which
are shown to be in agreement with the DMRG results.",0803.1238v1
2008-03-26,Nanosized superparamagnetic precipitates in cobalt-doped ZnO,"The existence of semiconductors exhibiting long-range ferromagnetic ordering
at room temperature still is controversial. One particularly important issue is
the presence of secondary magnetic phases such as clusters, segregations,
etc... These are often tedious to detect, leading to contradictory
interpretations. We show that in our cobalt doped ZnO films grown
homoepitaxially on single crystalline ZnO substrates the magnetism
unambiguously stems from metallic cobalt nano-inclusions. The magnetic behavior
was investigated by SQUID magnetometry, x-ray magnetic circular dichroism, and
AC susceptibility measurements. The results were correlated to a detailed
microstructural analysis based on high resolution x-ray diffraction,
transmission electron microscopy, and electron-spectroscopic imaging. No
evidence for carrier mediated ferromagnetic exchange between diluted cobalt
moments was found. In contrast, the combined data provide clear evidence that
the observed room temperature ferromagnetic-like behavior originates from
nanometer sized superparamagnetic metallic cobalt precipitates.",0803.3774v2
2008-04-04,"Spin-charge coupling in a band ferromagnet: magnon-energy reduction, anomalous softening, and damping","The effects of correlation-induced coupling between spin and charge
fluctuations on spin-wave excitations in a band ferromagnet are investigated by
including self-energy and vertex corrections within a systematic
inverse-degeneracy expansion scheme which explicitly preserves the Goldstone
mode. Arising from the scattering of a magnon into intermediate spin-excitation
states (including both magnon and Stoner excitations) accompanied with charge
fluctuations in the majority spin band, this spin-charge coupling results not
only in a substantial reduction of magnon energies but also in anomalous
softening and significant magnon damping for zone-boundary modes lying within
the Stoner gap. Our results are in good qualitative agreement with recent
spin-wave excitation measurements in colossal magneto-resistive manganites and
ferromagnetic ultrathin films of transition metals.",0804.0680v1
2008-04-09,"Curie point singularity in the temperature derivative of resistivity in (Ga,Mn)As","We observe a singularity in the temperature derivative $d\rho/dT$ of
resistivity at the Curie point of high-quality (Ga,Mn)As ferromagnetic
semiconductors with $T_c$'s ranging from approximately 80 to 185 K. The
character of the anomaly is sharply distinct from the critical contribution to
transport in conventional dense-moment magnetic semiconductors and is
reminiscent of the $d\rho/dT$ singularity in transition metal ferromagnets.
Within the critical region accessible in our experiments, the temperature
dependence on the ferromagnetic side can be explained by dominant scattering
from uncorrelated spin fluctuations. The singular behavior of $d\rho/dT$ on the
paramagnetic side points to the important role of short-range correlated spin
fluctuations.",0804.1578v2
2008-04-17,Andreev-Klein reflection in graphene ferromagnet-superconductor junctions,"We show that Andreev reflection in a junction between ferromagnetic (F) and
superconducting (S) graphene regions is fundamentally different from the common
FS junctions. For a weakly doped F graphene with an exchange field $h$ larger
than its Fermi energy $E_{\rm F}$, Andreev reflection of massless Dirac
fermions is associated with a Klein tunneling through an exchange field p-n
barrier between two spin-split conduction and valence subbands. We find that
this Andreev-Klein process results in an enhancement of the subgap conductance
of a graphene FS junction by $h$ up to the point at which the conductance at
low voltages $eV\ll \Delta$ is greater than its value for the corresponding
non-ferromagnetic junction. We also demonstrate that the Andreev reflection can
be of retro or specular types in both convergent and divergent ways with the
reflection direction aligned, respectively, closer to and farther from the
normal to the junction as compared to the incidence direction.",0804.2774v1
2008-04-21,CeFePO: A Heavy Fermion Metal with Ferromagnetic Correlations,"The ground state properties of CeFePO, a homologue of the new high
temperature superconductors RFePnO(1-x)Fx, were studied by means of
susceptibility, specific heat, resistivity, and NMR measurements on
polycrystals. All the results demonstrate that this compound is a magnetically
non-ordered heavy Fermion metal with a Kondo temperature TK~10K, a Sommerfeld
coefficient gamma=700mJ/molK2 and a mass enhancement factor of the order of
200. The absence of a Fe-contribution to the effective moment at high
temperatures indicates that the magnetism in CeFePO is completely dominated by
the effect of Ce. Thus the strong electronic correlation effects originate from
the Ce-4f electrons rather than from the Fe-3d electrons. An enhanced
Sommerfeld-Wilson ratio R=5.5 as well as a Korringa product S0/T1TK2~0.065 well
below 1 indicate the presence of ferromagnetic correlations. Therefore, CeFePO
appears to be on the non-magnetic side of a ferromagnetic instability.",0804.3250v2
2008-04-22,Effects of the crystal structure on the ferromagnetic correlations in ZnO with magnetic impurities,"We study the ferromagnetism in the compound (Zn,Mn)O within the
Haldane-Anderson impurity model by using the quantum Monte Carlo technique and
the tight-binding approximation for determining the host band-structure and the
impurity-host hybridization. This computational approach allows us to determine
how the host crystal structure influences the impurity bound state, which plays
an important role in the development of the ferromagnetic (FM) correlations
between the impurities. We find that the FM correlations are strongly
influenced by the crystal structure. In particular, in p-type (Zn,Mn)O, we
observe the development of FM correlations with an extended range at low
temperatures for wurtzite and zincblende crystal structures. However, for the
rocksalt structure no FM correlations are observed between the impurities. In
addition, in n-type ZnO with magnetic impurities, the impurity bound state and
FM correlations are not found.",0804.3436v1
2008-04-23,Coexistence of itinerant ferromagnetism and a non-unitary superconducting state with line nodes: possible application to UGe$_2$,"We construct a mean-field theory for itinerant ferromagnetism coexisting with
a non-unitary superconducting state, where only the majority-spin band is
gapped and contains line nodes, while the minority-spin band is gapless at the
Fermi level. Our study is motivated by recent experimental results indicating
that this may be the physical situation realized in the heavy-fermion compound
UGe$_2$. We investigate the stability of the mean-field solution of the
magnetic and superconducting order parameters. Also, we provide theoretical
predictions for experimentally measurable properties of such a non-unitary
superconductor: the specific heat capacity, the Knight shift, and the tunneling
conductance spectra. Our study should be useful for direct comparison with
experimental results and also for further predictions of the physics that may
be expected in ferromagnetic superconductors.",0804.3803v1
2008-05-02,Domain-wall structure of a classical Heisenberg ferromagnet on a Mobius strip,"We study theoretically the structure of domain walls in ferromagnetic states
on Mobius strips. A two-dimensional classical Heisenberg ferromagnet with
single-site anisotropy is treated within a mean-field approximation by taking
into account the boundary condition to realize the Mobius geometry. It is found
that two types of domain walls can be formed, namely, parallel or perpendicular
to the circumference, and that the relative stability of these domain walls is
sensitive to the change in temperature and an applied magnetic field. The
magnetization has a discontinuity as a function of temperature and the external
field.",0805.0183v3
2008-05-10,Teleportation in the presence of common bath decoherence at the transmitting station,"We investigate the effect of common bath decoherence on the qubits of Alice
in the usual teleportation protocol. The system bath interaction is studied
under the central spin model, where the qubits are coupled to the bath spins
through isotropic Heisenberg interaction. We have given a more generalized
representation of the protocol in terms of density matrices and calculated the
average fidelity of the teleported state for different Bell state measurements
performed by Alice. The common bath interaction differentiates the outcome of
various Bell state measurements made by Alice. There will be a high fidelity
teleportation for a singlet measurement made by Alice when both the qubits of
Alice interact either ferromagnetically or antiferromagnetically with bath. In
contrast if one of the Alice's qubits interact ferromagnetically and the other
anti-ferromagnetically then measurement of Bell states belonging to the triplet
sector will give better fidelity. We have also evaluated the average fidelity
when Alice prefers non-maximally entangled states as her basis for measurement.",0805.1456v2
2008-06-01,"Itinerant Ferromagnetism in layered crystals LaCoOX (X = P, As)","The electronic and magnetic properties of cobalt-based layered oxypnictides,
LaCoOX (X = P, As), are investigated. LaCoOP and LaCoOAs show metallic type
conduction, and the Fermi edge is observed by hard x-ray photoelectron
spectroscopy. Ferromagnetic transitions occur at 43 K for LaCoOP and 66 K for
LaCoOAs. Above the transition temperatures, temperature dependence of the
magnetic susceptibility follows the Curie-Weiss law. X-ray magnetic circular
dichroism (XMCD) is observed at the Co L2,3-edge, but not at the other edges.
The calculated electronic structure shows a spin polarized ground state. These
results indicate that LaCoOX are itinerant ferromagnets and suggest that their
magnetic properties are governed by spin fluctuation.",0806.0123v1
2008-06-02,Voltage Dependence of Spin Transfer Torque in Magnetic Tunnel Junctions,"Theoretical investigations of spin transfer torque in magnetic tunnel
junctions using the tight-binding model in the framework of non-equilibrium
Green functions formalism are presented. We show that the behavior of the spin
transfer torque as a function of applied voltage can vary over a wide range
depending on the band parameters of the ferromagnetic electrodes and the
insulator that comprise the magnetic tunnel junction. The behavior of both the
parallel and perpendicular components of the spin torque is addressed. This
behavior is explained in terms of the spin and charge current dependence and on
the interplay between evanescent states in the insulator and the Fermi surfaces
of ferromagnetic electrodes comprising the junction. The origin of the
perpendicular (field-like) component of spin transfer torque at zero bias, i.e.
exchange coupling through the barrier between ferromagnetic electrodes is
discussed.",0806.0396v1
2008-06-10,Optical spectra of the heavy fermion uniaxial ferromagnet UGe$_2$,"We report a detailed study of UGe$_{2}$ single crystals using infrared
reflectivity and spectroscopic ellipsometry. The optical conductivity suggests
the presence of a low frequency interband transition and a narrow free-carrier
response with strong frequency dependence of the scattering rate and effective
mass. We observe sharp changes in the low frequency mass and scattering rate
below the upper ferromagnetic transition $T_C = 53 K$. The characteristic
changes are exhibited most strongly at an energy scale of around 12 meV (100
cm$^{-1}$). They recover their unrenormalized value above $T_C$ and for $\omega
>$ 40 meV. In contrast no sign of an anomaly is seen at the lower transition
temperature of unknown nature $T_x \sim$ 30 K, observed in transport and
thermodynamic experiments. In the ferromagnetic state we find signatures of a
strong coupling to the longitudinal magnetic excitations that have been
proposed to mediate unconventional superconductivity in this compound.",0806.1617v1
2008-06-20,Ferromagnetic spin fluctuation in LaFeAsO1-xFx,"The F doped LaFeAsO, a recently discovered superconductor with the high Tc of
26 K, has been studied by the resistivity, magnetic susceptibility, and heat
capacity measurements in the F doping range from 0 to 0.14 (x in LaFeAsO1-xFx).
In the low temperature region, a T3lnT term in the heat capacity and a T2 term
in the magnetic susceptibility, which are derived from the spin fluctuation,
are observed. The nearly ferromagnetic nature evidenced by a large Wilson ratio
(6.5 for x = 0, and 11.2 for x = 0.025) suggests that the superconductivity in
the LaFeAsO system is mediated by ferromagnetic spin fluctuation.",0806.3304v1
2008-06-20,Impurity bands and the character of the electronic states in ferromagnetic GaMnAs layers,"The interplay between disorder and spin polarization in a GaMnAs thin layer
results into spin-polarized impurity hole bands. A figure of merit is defined
to label the hole state as being extended or localized. The calculation leads
to a phase diagram determining the metallic or non-metallic character of the
sample. It is shown that samples with the highest figures of merit have a ratio
between the extended hole density and the Mn concentration near 0.2, in
agreement with the ratio of 0.1-0.25 known to occur among samples produced with
the highest Curie temperatures. Both the non-metal-to-metal and the
metal-to-non-metal transitions experimentally observed in the ferromagnetic
regime are obtained, as the Mn concentration increases. An explanation is given
for the occurrence of a maximal Curie temperature in ferromagnetic GaMnAs
samples.",0806.3423v2
2008-08-05,Evidence for the band broadening across the ferromagnetic transition in Cr$_{1/3}$NbSe$_2$,"The electronic structure of Cr$_{1/3}$NbSe$_2$ is studied via optical
spectroscopy. We observe two low-energy interband transitions in the
paramagnetic phase, which split into four peaks as the compound enters the
ferromagnetic state. The band structure calculation indicates the four peaks
are interband transitions to the spin up Cr e$_g$ states. We show that the peak
splitting below the Curie temperature is \emph{not} due to the exchange
splitting of spin up and down bands, but directly reflects a band broadening
effect in Cr-derived states upon the spontaneous ferromagnetic ordering.",0808.0678v1
2008-08-07,On the phase diagrams of the ferromagnetic superconductors ZrZn2 and UGe2,"A general phenomenological theory is presented for the phase behavior of
ferromagnetic superconductors with spin-triplet electron Cooper pairing. The
theory accounts in detail for the temperature-pressure phase diagram of
ZrZn$_2$, while the main features of the diagram for UGe$_2$ are also
described. Quantitative criteria are deduced for the U-type (type I) and
Zr-type (type II) unconventional ferromagnetic superconductors with
spin-triplet Cooper electron pairing. Some basic properties of quantum phase
transitions are also elucidated.",0808.0939v5
2008-08-13,"Spin Filter, Spin Amplifier and Other Spintronic Applications in Graphene Nanodisks","Graphene nanodisk is a graphene derivative with a closed edge. The trigonal
zigzag nanodisk with size $N$ has $N$-fold degenerated zero-energy states. A
nanodisk can be interpletted as a quantum dot with an internal degree of
freedom. The grand state of nanodisk has been argued to be a quasi-ferromagnet,
which is a ferromagnetic-like states with a finite but very long life time. We
investigate the spin-filter effects in the system made of nanodisks and leads
based on the master equation. The finite-size effect on spin filter is
intriguing due to a reaction from the polarization of incoming current to a
quasi-ferromagnet. Analyzing the relaxation process with the use of the
Landau-Lifshitz-Gilbert equation, we explore the response to four types of
incoming currents, namely, unpolarized current, perfectly polarized current,
partially polarized current and pulse polarized current. We propose some
applications for spintronics, such as spin memory, spin amplifier, spin valve,
spin-field-effect transistor and spin diode.",0808.1779v1
2008-08-16,All Oxide Ferromagnet/Semiconductor Epitaxial Heterostructures,"Oxide based ferromagnet/semiconductor heterostructures offer substantial
advantages for spin electronics. We have grown (111) oriented Fe3O4 thin films
and Fe3O4/ZnO heterostructures on ZnO(0001) and Al2O3(0001) substrates by
pulsed laser deposition. High quality crystalline films with mosaic spread as
small as 0.03 degree, sharp interfaces, and rms surface roughness of 0.3 nm
were achieved. Magnetization measurements show clear ferromagnetic behavior of
the magnetite layers with a saturation magnetization of 3.2 muB/f.u. at 300 K.
Our results demonstrate that the Fe3O4/ZnO system is an intriguing and
promising candidate for the realization of multi-functional heterostructures.",0808.2245v1
2008-08-25,Josephson tunnel junctions with strong ferromagnetic interlayer,"The dependence of the critical current density j_c on the ferromagnetic
interlayer thickness d_F was determined for Nb/Al_2O_3/Cu/Ni/Nb Josephson
tunnel junctions with ferromagnetic \Ni interlayer from very thin film
thicknesses (\sim 1 nm) upwards and classified into F-layer thickness regimes
showing a dead magnetic layer, exchange, exchange + anisotropy and total
suppression of j_c. The Josephson coupling changes from 0 to pi as function of
d_F, and -very close to the crossover thickness- as function of temperature.
The strong suppression of the supercurrent in comparison to non-magnetic
\Nb/Al_2O_3/Cu/Nb junctions indicated that the insertion of a F-layer leads to
additional interface scattering. The transport inside the dead magnetic layer
was in dirty limit. For the magnetically active regime fitting with both the
clean and the dirty limit theory were carried out, indicating dirty limit
condition, too. The results were discussed in the framework of literature",0808.3332v2
2008-08-26,Theoretical prediction and experimental study of a ferromagnetic shape memory alloy: Ga_2MnNi,"We predict the existence of a new ferromagnetic shape memory alloy Ga_2MnNi
using density functional theory. The martensitic start temperature (T_M) is
found to be approximately proportional to the stabilization energy of the
martensitic phase (deltaE_tot) for different shape memory alloys. Experimental
studies performed to verify the theoretical results show that Ga_2MnNi is
ferromagnetic at room temperature and the T_M and T_C are 780K and 330K,
respectively. Both from theory and experiment, the martensitic transition is
found to be volume conserving that is indicative of shape memory behavior.",0808.3469v1
2008-09-06,Extended scaling for ferromagnetic Ising models with zero-temperature transitions,"We study the second-moment correlation length and the reduced susceptibility
of two ferromagnetic Ising models with zero-temperature ordering. By
introducing a scaling variable motivated by high-temperature series expansions,
we are able to scale data for the one-dimensional Ising ferromagnet rigorously
over the entire temperature range. Analogous scaling expressions are then
applied to the two-dimensional fully frustrated Villain model where excellent
finite-size scaling over the entire temperature range is achieved. Thus we
broaden the applicability of the extended scaling method to Ising systems
having a zero-temperature critical point.",0809.1161v2
2008-09-06,Local Structure and It's Effect on The Ferromagnetic Properties of La$_{0.5}$Sr$_{0.5}$CoO$_3$ thin films},"We have used high-resolution Extended X-ray Absorption Fine-Structure and
diffraction techniques to measure the local structure of strained
La$_{0.5}$Sr$_{0.5}$CoO$_3$ films under compression and tension. The lattice
mismatch strain in these compounds affects both the bond lengths and the bond
angles, though the larger effect on the bandwidth is due to the bond length
changes. The popular double exchange model for ferromagnetism in these
compounds provides a correct qualitative description of the changes in Curie
temperature $T_C$, but quantitatively underestimates the changes. A microscopic
model for ferromagnetism that provides a much stronger dependence on the
structural distortions is needed.",0809.1178v2
2008-09-10,Multiferroic Properties of Nanocrystalline BaTiO3,"Some of the Multiferroics [1] form a rare class of materials that exhibit
magnetoelectric coupling arising from the coexistence of ferromagnetism and
ferroelectricity, with potential for many technological applications.[2,3] Over
the last decade, an active research on multiferroics has resulted in the
identification of a few routes that lead to multiferroicity in bulk
materials.[4-6] While ferroelectricity in a classic ferroelectric such as
BaTiO3 is expected to diminish with the reducing particle size,[7,8]
ferromagnetism cannot occur in its bulk form.[9] Here, we use a combination of
experiment and first-principles simulations to demonstrate that multiferroic
nature emerges in intermediate size nanocrystalline BaTiO3, ferromagnetism
arising from the oxygen vacancies at the surface and ferroelectricity from the
core. A strong coupling between a surface polar phonon and spin is shown to
result in a magnetocapacitance effect observed at room temperature, which can
open up possibilities of new electro-magneto-mechanical devices at the
nano-scale.",0809.1835v2
2008-09-12,Theory of electrical spin-detection at a ferromagnet/semiconductor interface,"We present a theoretical model that describes electrical spin-detection at a
ferromagnet/semiconductor interface. We show that the sensitivity of the spin
detector has strong bias dependence which, in the general case, is dramatically
different from that of the tunneling current spin polarization. We show that
this bias dependence originates from two distinct physical mechanisms: 1) the
bias dependence of tunneling current spin polarization, which is of microscopic
origin and depends on the specific properties of the interface, and 2) the
macroscopic electron spin transport properties in the semiconductor. Numerical
results show that the magnitude of the voltage signal can be tuned over a wide
range from the second effect which suggests a universal method for enhancing
electrical spin-detection sensitivity in ferromagnet/semiconductor tunnel
contacts. Using first-principles calculations we examine the particular case of
a Fe/GaAs Schottky tunnel barrier and find very good agreement with experiment.
We also predict the bias dependence of the voltage signal for a Fe/MgO/GaAs
tunnel structure spin detector.",0809.2278v1
2008-09-18,Spin fluctuations and ferromagnetic order in two-dimensional itinerant systems with Van Hove singularities,"The quasistatic approach is used to analyze the criterion of ferromagnetism
for two-dimensional (2D) systems with the Fermi level near Van Hove (VH)
singularities of the electron spectrum. It is shown that the spectrum of spin
excitations (paramagnons) is positively defined when the interaction between
electrons and paramagnons, determined by the Hubbard on-site repulsion U, is
sufficiently large. Due to incommensurate spin fluctuations near the
ferromagnetic quantum phase transition, the critical interaction Uc remains
finite at VH filling and exceeds considerably its value obtained from the
Stoner criterion. A comparison with the functional renormalization group
results and mean-field approximation which yields a phase separation is also
performed.",0809.3191v1
2008-10-06,Superconducting/ferromagnetic diffusive bilayer with a spin-active interface: a numerical study,"We calculate the density of states (DOS) in a diffusive
superconducting/ferromagnetic bilayer with a spin-active interface. We use a
self-consistent numerical treatment to make a systematic study of the effects
of the Spin-Dependence of Interfacial Phase Shifts (SDIPS) on the
self-consistent superconducting gap and the DOS. Strikingly, we find that the
SDIPS can induce a double gap structure (DGS) in the DOS of the ferromagnet,
even when the superconducing layer is much thicker than the superconducting
coherence lenght. We thus obtain DOS curves which have interesting similarities
with those of Phys. Rev. Lett. 100, 237002 (2008).",0810.0904v3
2008-10-20,Optical Properties of III-Mn-V Ferromagnetic Semiconductors,"We review the first decade of extensive optical studies of ferromagnetic,
III-Mn-V diluted magnetic semiconductors. Mn introduces holes and local moments
to the III-V host, which can result in carrier mediated ferromagnetism in these
disordered semiconductors. Spectroscopic experiments provide direct access to
the strength and nature of the exchange between holes and local moments; the
degree of itineracy of the carriers; and the evolution of the states at the
Fermi energy with doping. Taken together, diversity of optical methods reveal
that Mn is an unconventional dopant, in that the metal to insulator transition
is governed by the strength of the hybridization between Mn and its p-nictogen
neighbor. The interplay between the optical, electronic and magnetic properties
of III-Mn-V magnetic semiconductors is of fundamental interest and may enable
future spin-optoelectronic devices.",0810.3669v1
2008-10-22,Exchange bias effect in the phase separated Nd_{1-x}Sr_{x}CoO_3 at the spontaneous ferromagnetic/ferrimagnetic interface,"We report the new results of exchange bias effect in Nd_{1-x}Sr_{x}CoO_3 for
x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the
ferrimagnetic (FI) state in a spontaneously phase separated system. The
zero-field cooled magnetization exhibits the FI (T_{FI}) and ferromagnetic
(T_C) transitions at ~ 23 and \sim 70 K, respectively for x = 0.20. The
negative horizontal and positive vertical shifts of the magnetic hysteresis
loops are observed when the system is cooled through T_{FI} in presence of a
positive static magnetic field. Training effect is observed for x = 0.20, which
could be interpreted by a spin configurational relaxation model. The
unidirectional shifts of the hysteresis loops as a function of temperature
exhibit the absence of exchange bias above T_{FI} for x = 0.20. The analysis of
the cooling field dependence of exchange bias field and magnetization indicates
that the ferromagnetic (FM) clusters consist of single magnetic domain with
average size around \sim 20 and ~ 40 \AA ~ for x = 0.20 and 0.40, respectively.
The sizes of the FM clusters are close to the percolation threshold for x =
0.20, which grow and coalesce to form the bigger size for x = 0.40 resulting in
a weak exchange bias effect.",0810.4013v1
2008-10-30,Magnetoelectric Spin Wave Amplifier for Spin Wave Logic Circuits,"We propose and analyze a spin wave amplifier aimed to enhance the amplitude
of the propagating spin wave via the magnetoelectric effect. The amplifier is a
two-layer multiferroic structure, which comprises piezoelectric and
ferromagnetic materials. By applying electric field to the piezoelectric layer,
the stress is produced. In turn, the stress changes the direction of the easy
axis in the ferromagnetic layer and the direction of the anisotropy field. The
rotation frequency of the easy axis is the same as the frequency of the spin
wave propagating through the ferromagnetic layer. As a result of this two-stage
process, the amplitude of the spin wave can be amplified depending on the angle
of the easy axis rotation. We present results of numerical simulations
illustrating the operation of the proposed amplifier. According to numerical
estimates, the amplitude of the spin wave signal can be increased by several
orders of magnitude. The energy efficiency of the electric-to-magnetic power
conversion is discussed. The proposed amplifier preserves the phase of the
initial signal, which is important for application to logic circuits based on
spin waves.",0810.5586v1
2008-10-31,Quenched-Vacancy Induced Spin-Glass Order,"The ferromagnetic phase of an Ising model in d=3, with any amount of quenched
antiferromagnetic bond randomness, is shown to undergo a transition to a
spin-glass phase under sufficient quenched bond dilution. This general result,
demonstrated here with the numerically exact renormalization-group solution of
a d=3 hierarchical lattice, is expected to hold true generally, for the cubic
lattice and for quenched site dilution. Conversely, in the
ferromagnetic-spinglass-antiferromagnetic phase diagram, the spin-glass phase
expands under quenched dilution at the expense of the ferromagnetic and
antiferromagnetic phases. In the ferro-spinglass phase transition induced by
quenched dilution reentrance is seen, as previously found for the
ferro-spinglass transition induced by increasing the antiferromagnetic bond
concentration.",0811.0025v2
2008-11-03,Electronic transport driven spin-dynamics,"We propose a model to explore the dynamics of spin-systems coupled by
exchange interaction to the conduction band electrons of a semiconductor
material that forms the channel in a ferromagnet/semiconductor/ferromagnet
spin-valve structure. We show that recent observation of the novel transient
transport signature in a MnAs/GaAs/MnAs spin-valve structure with paramagnetic
Mn impurities [D. Saha et al., Phys. Rev. Lett., 100, 196603 (2008)] can be
quantitatively understood in terms of current driven dynamical polarization of
Mn spins. Using our model of spin polarized transport through Schottky barriers
at the two ferromagnet/semiconductor junctions in a spin-valve structure and a
dynamical equation describing the paramagnetic impurities coupled to conduction
band electrons we explain the scaling behaviour of observed transient features
such as the magnitude and time-scale with temperature.",0811.0204v1
2008-11-05,Ferromagnetism and orbital order in the two-orbital Hubbard model,"We investigate spin and orbital states of the two-orbital Hubbard model on a
square lattice by using a variational Monte Carlo method at quarter-filling,
i.e., the electron number per site is one. As a variational wave function, we
consider a Gutzwiller projected wave function of a mean-field type wave
function for a staggered spin and/or orbital ordered state. Then, we evaluate
expectation value of energy for the variational wave functions by using the
Monte Carlo method and determine the ground state. In the strong Coulomb
interaction region, the ground state is the perfect ferromagnetic state with
antiferro-orbital (AF-orbital) order. By decreasing the interaction, we find
that the disordered state becomes the ground state. Although we have also
considered the paramagnetic state with AF-orbital order, i.e., purely orbital
ordered state, and partial ferromagnetic states with and without AF-orbital
order, they do not become the ground state.",0811.0733v1
2008-11-06,Exchange coupling between two ferromagnetic electrodes separated by a graphene nanoribbon,"In this study, based on the self-energy method and the total energy
calculation, the indirect exchange coupling between two semi-infinite
ferromagnetic strips (FM electrodes) separated by metallic graphene nanoribbons
(GNRs) is investigated. In order to form a FM/GNR/FM junction, a graphitic
region of finite length is coupled to the FM electrodes along graphitic zigzag
or armchair interfaces of width $N$. The numerical results show that, the
exchange coupling strength which can be obtained from the difference between
the total energies of electrons in the ferromagnetic and antiferromagnetic
couplings, has an oscillatory behavior, and depends on the Fermi energy and the
length of the central region.",0811.0934v1
2008-11-07,Valence Bond States: Link models,"An isotropic anti-ferromagnetic quantum state on a square lattice is
characterized by symmetry arguments only. By construction, this quantum state
is the result of an underlying valence bond structure without breaking any
symmetry in the lattice or spin spaces. A detailed analysis of the correlations
of the quantum state is given (using a mapping to a 2D classical statistical
model and methods in field theory like mapping to the non-linear sigma model or
bosonization techniques) as well as the results of numerical treatments
(regarding exact diagonalization and variational methods). Finally, the
physical relevance of the model is motivated. A comparison of the model to
known anti-ferromagnetic Mott-Hubbard insulators is given by means of the
two-point equal-time correlation function obtained i) numerically from the
suggested state and ii) experimentally from neutron scattering on cuprates in
the anti-ferromagnetic insulator phase.",0811.1049v2
2008-11-14,Superconductivity induced by phosphorus doping and its coexistence with ferromagnetism in EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$,"We have studied EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ by the measurements of
x-ray diffraction, electrical resistivity, thermopower, magnetic
susceptibility, magnetoresistance and specific heat. Partial substitution of As
with P results in the shrinkage of lattice, which generates chemical pressure
to the system. It is found that EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ undergoes
a superconducting transition at 26 K, followed by ferromagnetic ordering of
Eu$^{2+}$ moments at 20 K. This finding is the first observation of
superconductivity stabilized by internal chemical pressure, and supplies a rare
example showing coexistence of superconductivity and ferromagnetism in the
ferro-arsenide family.",0811.2390v3
2008-11-17,Dynamical properties of the one-dimensional spin-1/2 Bose-Hubbard model near Mott-insulator to ferromagnetic liquid transition,"We investigate the dynamics of the one-dimensional strongly repulsive
spin-1/2 Bose-Hubbard model for filling $\nu\le1.$ While at $\nu=1$ the system
is a Hubbard-Mott insulator exhibiting dynamical properties of the Heisenberg
ferromagnet, at $\nu<1$ it is a ferromagnetic liquid with complex spin
dynamics. We find that close to the insulator-liquid transition the system
admits for a complete separation of spin and density degrees of freedom valid
at {\it all} energy and momentum scales within the $t-J$ approximation. This
allows us to derive the propagator of transverse spin waves and the shape of
the magnon peak in the dynamic spin structure factor.",0811.2676v2
2008-11-18,The phase diagram of the extended anisotropic ferromagnetic-antiferromagnetic Heisenberg chain,"By using Density Matrix Renormalization Group (DMRG) technique we study the
phase diagram of 1D extended anisotropic Heisenberg model with ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. We
analyze the static correlation functions for the spin operators both in- and
out-of-plane and classify the zero-temperature phases by the range of their
correlations. On clusters of $64,100,200,300$ sites with open boundary
conditions we isolate the boundary effects and make finite-size scaling of our
results. Apart from the ferromagnetic phase, we identify two gapless spin-fluid
phases and two ones with massive excitations. Based on our phase diagram and on
estimates for the coupling constants known from literature, we classify the
ground states of several edge-sharing materials.",0811.2973v3
2008-11-20,Thermo-spin effects in a quantum dot connected to ferromagnetic leads,"We study a system composed of a quantum dot in contact with ferromagnetic
leads, held at different temperatures. Spin analogues to the thermopower and
thermoelectric figures of merit are defined and studied as a function of
junction parameters. It is shown that in contrast to bulk ferromagnets, the
spin thermopower coefficient in a junction can be as large as the Seebeck
coefficient, resulting in a large spin figure of merit. In addition, it is
demonstrated that the junction can be tuned to supply only spin current but no
charge current. We also discuss experimental systems where our predictions can
be verified.",0811.3265v2
2008-11-21,Thermodynamics of the frustrated ferromagnetic spin-1/2 Heisenberg chain,"We studied the thermodynamics of the one-dimensional J1-J2 spin-1/2
Heisenberg chain for ferromagnetic nearest-neighbor bonds J1 < 0 and
frustrating antiferromagnetic next-nearest-neighbor bonds J1 > 0 using full
diagonalization of finite rings and a second-order Green-function formalism.
Thereby we focus on J2 < |J1|/4 where the ground state is still ferromagnetic,
but the frustration influences the thermodynamic properties. We found that
their critical indices are not changed by J2. The analysis of the
low-temperature behavior of the susceptibility chi leads to the conclusion that
this behavior changes from chi \propto T^{-2} at J2 < |J1|/4 to chi \propto
T^{-3/2} at the quantum-critical point J2=|J1|/4. Another effect of the
frustration is the appearance of an extra low-T maximum in the specific heat
C_v(T) for J2 \gtrsim |J1|/8, indicating its strong influence on the low-energy
spectrum.",0811.3549v1
2008-11-27,"Theory of Weak Localization in Ferromagnetic (Ga,Mn)As","We study quantum interference corrections to the conductivity in (Ga,Mn)As
ferromagnetic semiconductors using a model with disordered valence band holes
coupled to localized Mn moments through a p-d kinetic-exchange interaction. We
find that at Mn concentrations above 1% quantum interference corrections lead
to negative magnetoresistance, i.e. to weak localization (WL) rather than weak
antilocalization (WAL). Our work highlights key qualitative differences between
(Ga,Mn)As and previously studied toy model systems, and pinpoints the mechanism
by which exchange splitting in the ferromagnetic state converts valence band
WAL into WL. We comment on recent experimental studies and theoretical analyses
of low-temperature magnetoresistance in (Ga,Mn)As which have been variously
interpreted as implying both WL and WAL and as requiring an impurity-band
interpretation of transport in metallic (Ga,Mn)As.",0811.4585v1
2008-12-06,Voltage-Controlled Surface Magnetization of Itinerant Ferromagnet Ni_(1-x)Cu_x,"We argue that surface magnetization of a metallic ferromagnet can be turned
on and off isothermally by an applied voltage. For this, the material's
electron subsystem must be close enough to the boundary between para- and
ferromagnetic regions on the electron density scale. For the 3d series, the
boundary is between Ni and Cu, which makes their alloy a primary candidate.
Using Ginzburg-Landau functional, which we build from Ni_(1-x)Cu_x empirical
properties, ab-initio parameters of Ni and Cu, and orbital-free LSDA, we show
that the proposed effect is experimentally observable.",0812.1309v1
2008-12-08,Dilution Robustness for Mean Field Ferromagnets,"In this work we compare two different random dilution of a mean field
ferromagnet: the first model is built on a Bernoulli-diluted network while the
second lives on a Poisson-diluted network. While it is known that the two
models have in the thermodynamic limit the same free energy we investigate on
the structural constraints that the two models must fulfill. We rigorously
derive for each model the set of identities for the multi-overlaps distribution
using different methods for the two dilutions: constraints in the former model
are obtained by studying the consequences of the self-averaging of the internal
energy density, while in the latter are obtained by a stochastic-stability
technique. Finally we prove that the identities emerging in the two models are
the same, showing ""robustness"" of the ferromagnetic properties of diluted
networks with respect to the details of dilution.",0812.1568v2
2008-12-11,What drives the insulating state in ultrathin films of SrRuO3?,"Using density functional calculations we have examined the evolution of the
electronic structure of SrRuO3 films grown on SrTiO3 substrates as a function
of film thickness. At the ultrathin limit of two monolayers (RuO2-terminated
surface) the films are found to be at the brink of a spin-state transition
which drives the system to an antiferromagnetic and insulating state.
Increasing the film thickness to four monolayers, one finds the surprising
result that two entirely different solutions coexist. An antiferromagnetic
insulating solution coexists with a metallic solution corresponding to an
antiferromagnetic surface and a ferromagnetic bulk. The electronic structure
found at the ultrathin limit persists for thicker films and an unusual result
is predicted. Thicker films are found to be metallic as expected for the bulk,
but the magnetism does not directly evolve to the bulk ferromagnetic state. The
surface remains antiferromagnetic while the bulk exhibits ferromagnetic
ordering.",0812.2098v2
2008-12-29,Density matrix for the kink ground state of the ferromagnetic XXZ chain,"The exact expression for the density matrix of the kink ground state of the
ferromagnetic XXZ chain is obtained. Utilizing this, we exactly calculate
various correlation functions such as the longitudinal and transverse spin-spin
correlation functions, and the ferromagnetic and antiferromagnetic string
formation probabilities. The asymptotic behaviors of these correlation
functions are also analyzed. As a consequence, we find that the spin-spin
correlation functions decay exponentially for large distances, while the string
formation probabilities exhibit Gaussian decay for large strings. We also
evaluate the entanglement entropy, which shows interesting behaviors due to the
lack of the translational invariance of the state.",0812.4947v1
2009-01-19,Hysteresis and noise in ferromagnetic materials with parallel domain walls,"We investigate dynamic hysteresis and Barkhausen noise in ferromagnetic
materials with a huge number of parallel and rigid Bloch domain walls.
Considering a disordered ferromagnetic system with strong in-plane uniaxial
anisotropy and in-plane magnetization driven by an external magnetic field, we
calculate the equations of motion for a set of coupled domain walls,
considering the effects of the long-range dipolar interactions and disorder. We
derive analytically an expression for the magnetic susceptivity, related to the
effective demagnetizing factor, and show that it has a logarithmic dependence
on the number of domains. Next, we simulate the equations of motion and study
the effect of the external field frequency and the disorder on the hysteresis
and noise properties. The dynamic hysteresis is very well explained by means of
the loss separation theory.",0901.2918v1
2009-01-30,Theory of magnetism with temporal disorder applied to magnetically doped ZnO,"A dynamic model of the asymmetric Ising glass is presented: an Ising model
with antiferromagnet bonds with probabilities q arranged at random in a
ferromagnetic matrix. The dynamics is introduced by changing the arrangement of
the antiferromagnetic bonds after n Monte Carlo steps but keeping the same
value of q and spin configuration. In the region where there is a second order
transition between the ferromagnetic and paramagnetic states the dynamic
behaviour follows that expected for motional narrowing and reverts to the
static behaviour only for large n. There is a different dynamic behaviour where
there is a first order transition between the ferromagnetic and spin glass
states where it shows no effects of motional narrowing. The implications of
this are discussed. This model is devised to explain the properties of doped
ZnO where the magnetisation is reduced when the exchange interactions change
with time.",0901.4947v1
2009-02-27,Little-Parks Oscillations in Hybrid Ferromagnet-Superconductor Systems,"On the basis of of linearized Usadel equations we consider superconductivity
nucleation in multiply connected mesoscopic superconductor/ferromagnet hybrids
such as thin-walled superconducting cylinders placed in electrical contact with
a ferromagnetic metal. We study the interplay between the oscillations of $T_c$
due to the Little--Parks effect and the oscillations due to the exchange field.
We demonstrate that the exchange field provokes the switching between the
superconducting states with different vorticities and this may result in the
increase the critical temperature of the superconducting transition in the
magnetic field. Moreover we analyse the influence of the S/F transparency on
the realisation of the states with higher vorticities.",0902.4860v1
2009-03-05,"Escape Rate Measurements and Microwave Spectroscopy of 0, pi, and 0-pi ferromagnetic Josephson Tunnel Junctions","We present experimental studies of high quality underdamped 0, pi, and 0-pi
ferromagnetic Josephson tunnel junctions of intermediate length L (lambda_J < L
< 5 lambda_J, where lambda_J is the Josephson penetration depth). The junctions
are fabricated as Nb/Al_2O_3/Cu_40Ni_60/Nb
Superconductor-Insulator-Ferromagnet-Superconductor heterostructures. Using
microwave spectroscopy, we have investigated the eigenfrequencies of 0, pi, and
0-pi Josephson junctions in the temperature range 1.9K...320mK. Harmonic,
subharmonic and superharmonic pumping is observed in experiment, and the
experimental data are compared with numerical simulations. Escape rate
measurements without applied microwaves at temperatures T down to 20mK show
that the width of the switching current histogram decreases with temperature
and saturates below T=150mK. We analyze our data in the framework of the short
junction model. The differences between experimental data and theoretical
predictions are discussed.",0903.1046v1
2009-03-10,Spin-induced charge correlations in transport through interacting quantum dots with ferromagnetic leads,"We study the full counting statistics of electronic transport through a
single-level quantum dot weakly coupled to two leads, with either one or both
of them being ferromagnetic. The interplay of Coulomb interaction and finite
spin polarization implies spin-correlation induced charge correlations that
give rise to super-Poissonian transport behavior and positive cross
correlations of the currents of the two spin species. In the case of two
ferromagnetic leads, we analyze the nontrivial dependence of the cumulants on
the angle between the polarization directions of the leads. We find diverging
second and higher cumulants for spin polarizations approaching unity.",0903.1759v2
2009-03-16,Quantum phase transition and underscreened Kondo effect in electron transport through parallel double quantum dots,"We investigate electronic transport through parallel double quantum dot(DQD)
system with strong on-site Coulomb interaction and capacitive interdot
coupling. By applying numerical renormalization group(NRG) method, the ground
state of the system and the transmission probability at zero temperature have
been obtained. For a system of quantum dots with degenerate energy levels and
small interdot tunnel coupling, the spin correlations between the DQDs is
ferromagnetic, and the ground state of the system is a spin 1 triplet state.
The linear conductance will reach the unitary limit ($2e^2/h$) due to the
underscreened Kondo effect at low temperature. As the interdot tunnel coupling
increases, there is a quantum phase transition from ferromagnetic to
anti-ferromagnetic spin correlation in DQDs and the linear conductance is
strongly suppressed.",0903.2685v2
2009-03-30,Room-temperature ferromagnetism in the mixtures of the TiO2 and Co3O4 powders,"We report here the observation of ferromagnetism (FM) at 300 K in mixtures of
TiO2 and Co3O4 powders despite the antiferromagnetic and diamagnetic character
of both oxides respectively. The ferromagnetic behavior is found in the early
stages of reaction and only for TiO2 in anatase structure; no FM is found for
identical samples prepared with rutile-TiO2. Optical spectroscopy and X-ray
absorption spectra confirm a surface reduction of octahedral Co+3->Co+2 in the
mixtures which is in the origin of the observed magnetism",0903.5214v1
2009-04-03,Stabilization and functional properties of La3NiAlMnO9 and La3CoAlMnO9 magnetoelectric triple perovskites,"Ferromagnetic La3NiAlMnO9 (LNAMO) and La3CoAlMnO9 (LCAMO) triple-perovskite
thin films are stabilized in the 750-860 oC temperature range in 100 to 900
mTorr O2 pressure range using pulsed-laser deposition. The LCAMO and LNAMO
films exhibit ferromagnetism up to 190 K and 130 K respectively. The
structural, optical and magnetic properties of these films demonstrate that the
B-site 3d-cations, Al, Mn and Co or Ni ions, are structurally short-range
ordered. The strong spin-lattice-polarization coupling in LCAMO is evidenced by
the temperature dependence of the dielectric constant and the softening of the
phonon frequencies starting in the vicinity of the
ferromagnetic-to-paramagnetic phase transition mimicking the behaviours of
La2CoMnO6 double perovskite.",0904.0604v1
2009-05-06,Josephson tunnel junctions with ferromagnetic $\Fe_{0.75}\Co_{0.25}$ barriers,"Josephson tunnel junctions with the strong ferromagnetic alloy
$\Fe_{0.75}\Co_{0.25}$ as the barrier material were studied. The junctions were
prepared with high quality down to a thickness range of a few monolayers of
Fe-Co. An oscillation length of $\xi_{F2}\approx 0.79\:{\rm {nm}}$ between 0
and $\pi$-Josephson phase coupling and a very short decay length
$\xi_{F1}\approx 0.22\:{\rm {nm}}$ for the amplitude of the superconducting
pair wave function in the Fe-Co layer were determined. The rapid damping of the
pair wave function inside the Fe-Co layer is caused by the strong ferromagnetic
exchange field and additional magnetic pair breaking scattering. Josephson
junctions with Fe-Co barriers show a significantly increased tendency towards
magnetic remanence and flux trapping for larger thicknesses $d_{F}$.",0905.0761v1
2009-05-13,Correlation between Organic Magnetoresistance (OMAR) and Ferromagnetic ordering,"We report observation of ferromagnetic (FM) ordering in organic
semiconductors, namely regio-regular poly (3-hexyl thiophene) (RRP3HT) and
1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM), in the
temperature range of 5-300 K in addition to magnetoresistance (OMAR) observed
in the diodes made from the same materials. Particle induced x-ray emission
spectroscopy confirms the presence of dilute magnetic impurities in the
materials mainly as residues from the synthesis process. However, upon blending
these two materials with FM signal, the FM ordering is suppressed by a huge
paramagnetic (PM) signal indicating ground state charge transfer formation in
the blend. Together with the magneto-transport studies, these results indicate
that OMAR response is observed in a device only when the corresponding active
materials are FM. In the diodes with P3HT:PCBM complex, that as a blend shows
PM response, OMAR vanishes almost completely. We propose that ferromagnetism in
the active material can have important correlation with the OMAR response in
the diodes.",0905.2021v1
2009-05-16,Local-moment ferromagnetism and unusual magnetic domains in Fe$_{1/4}$TaS$_{2}$ crystals,"Single crystals of Fe$_{1/4}$TaS$_{2}$ have been studied by using
magneto-optical (MO) imaging and radio-frequency (rf) magnetic susceptibility,
$\chi$. Real time MO images reveal unusual, slow dynamics of dendritic domain
formation, the details of which are strongly dependent upon magnetic and
thermal history. Measurements of $\chi(T)$ show well-defined, local moment
ferromagnetic transition at $T\approx 155$ K as well as thermal hysteresis for
50 K$<T<$60 K. This temperature range corresponds to the domain formation
temperature as determined by MO. Together these observations provide strong
evidence for local moment ferromagnetism in Fe$_{1/4}$TaS$_{2}$ crystals with
large, temperature dependent magnetic anisotropy.",0905.2684v1
2009-05-22,Equilibrium properties of disordered spin models with two scale interactions,"Methods for understanding classical disordered spin systems with interactions
conforming to some idealized graphical structure are well developed. The
equilibrium properties of the Sherrington-Kirkpatrick model, which has a
densely connected structure, have become well understood. Many features
generalize to sparse Erdos-Renyi graph structures above the percolation
threshold, and to Bethe lattices when appropriate boundary conditions apply. In
this paper we consider spin states subject to a combination of sparse strong
interactions with weak dense interactions, which we term a composite model. The
equilibrium properties are examined through the replica method, with exact
analysis of the high temperature paramagnetic, spin glass and ferromagnetic
phases by perturbative schemes. We present results of a replica symmetric
variational approximations where perturbative approaches fail at lower
temperature. Results demonstrate novel reentrant behaviors from spin glass to
ferromagnetic phases as temperature is lowered, including transitions from
replica symmetry broken to replica symmetric phases. The nature of high
temperature transitions is found to be sensitive to the connectivity profile in
the sparse sub-graph, with regular connectivity a discontinuous transition from
the paramagnetic to ferromagnetic phases is apparent.",0905.3679v1
2009-05-25,Ultrafast photoinduced phase separation dynamics in Pr(0.6)Ca(0.4)MnO(3) thin films,"The time resolved Magnetooptical Kerr effect in the substrate-strain-induced
insulating ferromagnetic phase in (Pr$_{0.6}$Ca$_{0.4}$)MnO$_3$ thin films on
two different substrates was measured in a magnetic field up to 1.1T. The
photoinduced Kerr rotation and ellipticity show remarkably different
magnetic-field dependence. From the comparison of the magnetic field
dependencies of the photoinduced and static Kerr rotation and ellipticity we
conclude that a transient ferromagnetic metallic phase, embedded within the
insulating ferromagnetic phase, is created upon the photoexcitation at low
temperatures. A comparison of temporal dependence of the photoinduced Kerr
signals with the photoinduced reflectivity indicates the change of the
fractions of the phases takes place on a timescale of ten picoseconds
independent of the substrate.",0905.4016v1
2009-05-27,The role of hydrogen in room-temperature ferromagnetism at graphite surfaces,"We present a x-ray dichroism study of graphite surfaces that addresses the
origin and magnitude of ferromagnetism in metal-free carbon. We find that, in
addition to carbon $\pi$ states, also hydrogen-mediated electronic states
exhibit a net spin polarization with significant magnetic remanence at room
temperature. The observed magnetism is restricted to the top $\approx$10 nm of
the irradiated sample where the actual magnetization reaches $ \simeq 15$ emu/g
at room temperature. We prove that the ferromagnetism found in metal-free
untreated graphite is intrinsic and has a similar origin as the one found in
proton bombarded graphite.",0905.4315v2
2009-05-28,Kondo-Cluster-Glass State near a Ferromagnetic Quantum Phase Transition,"We report on a comprehensive study of CePd$_{1-x}$Rh$_x$ $(0.6 \leq x \leq
0.95)$ poly- and single crystals close to the ferromagnetic instability by
means of low-temperature ac susceptibility, magnetization and volume thermal
expansion. The signature of ferromagnetism in this heavy-fermion system can be
traced from 6.6 K in CePd down to 25 mK for $x=0.87$. Despite pronounced
non-Fermi-liquid (NFL) effects in both, specific heat and thermal expansion,
the Gr\""uneisen ratio {\it does not} diverge as $T\to 0$, providing evidence
for the absence of a quantum critical point. Instead, a peculiar
""Kondo-cluster-glass"" state is found for $x\geq 0.65$, and the NFL effects in
the specific heat, ac susceptibility and magnetization are compatible with the
quantum Griffiths phase scenario.",0905.4591v1
2009-05-29,Ferromagnetic quantum phase transition in Sr$_{1-x}$Ca$_x$RuO$_3$ thin films,"The ferromagnetic quantum phase transition in the perovskite ruthenate
Sr$_{1-x}$Ca$_x$RuO$_3$ is studied by low-temperature magnetization and
electrical resistivity measurements on thin films. The films were grown
epitaxially on SrTiO$_3$ substrates using metalorganic aerosol deposition and
characterized by X-ray diffraction and room temperature scanning tunneling
microscopy. High residual resistivity ratios of 29 and 16 for $x=0$ and $x=1$,
respectively, prove the high quality of the investigated samples. We observe a
continuous suppression of the ferromagnetic Curie temperature from $T_C=160$ K
at $x=0$ towards $T_C\to 0$ at $x_c\approx 0.8$. The analysis of the electrical
resistivity between 2 and 10 K reveals $T^2$ and $T^{3/2}$ behavior at $x\leq
0.6$ and $x\geq 0.7$, respectively. For undoped CaRuO$_3$, the measurement has
been extended down to 60 mK, revealing a crossover to $T^2$ behavior around 2
K, which suggests a Fermi-liquid ground state in this system.",0905.4885v1
2009-06-02,Structural and magnetic properties of E-Fe_{1-x}Co_xSi thin films deposited via pulsed laser deposition,"We report pulsed laser deposition synthesis and characterization of
polycrystalline Fe1-xCox Si thin films on Si (111). X-ray diffraction,
transmission electron, and atomic force microscopies reveal films to be dense,
very smooth, and single phase with a cubic B20 crystal structure.
Ferromagnetism with significant magnetic hysteresis is found for all films
including nominally pure FeSi films in contrast to the very weak paramagnetism
of bulk FeSi. For Fe1-xCoxSi this signifies a change from helimagnetism in
bulk, to ferromagnetism in thin films. These ferromagnetic thin films are
promising as a magnetic-silicide/silicon system for polarized current
production, manipulation, and detection.",0906.0433v1
2009-06-08,K$_2$Cr$_8$O$_{16}$ predicted as a half-metallic ferromagnet: Scenario for a metal-insulator transition,"Based on the first-principles electronic structure calculations, we predict
that a chromium oxide K$_2$Cr$_8$O$_{16}$ of hollandite type should be a
half-metallic ferromagnet where the Fermi level crosses only the majority-spin
band, whereas the minority-spin band has a semiconducting gap. We show that the
double-exchange mechanism is responsible for the observed saturated
ferromagnetism. We discuss possible scenarios of the metal-insulator transition
observed at low temperature and we argue that the formation of the
incommensurate, long-wavelength density wave of spinless fermions caused by the
Fermi-surface nesting may be the origin of the opening of the charge gap.",0906.1408v2
2009-06-09,Vortex description of quantum Hall ferromagnets,"We study particle states of quantum Hall ferromagnet from the viewpoint of
the incompressible fluid description. It is shown that phase space of
Chern-Simons matrix theory which is an effective theory for the incompressible
fluid is equivalent to moduli space of vortex theory. According to this
correspondence, elementary excitations in vortex theory are identified as
particle states in quantum Hall ferromagnet, and thus we propose that a pure
electron state is absent from the strong coupling region but only a composite
particle state is present.",0906.1764v3
2009-06-12,Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3,"The integration of ferromagnetic and ferroelectric materials into hybrid
heterostructures yields multifunctional systems with improved or novel
functionality. We here report on the structural, electronic and magnetic
properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial
thin film onto ferroelectric BaTiO3. As a function of temperature, the
crystal-structure of BaTiO3 undergoes phase transitions, which induce
qualitative changes in the magnetic anisotropy of the ferromagnet. We observe
abrupt changes in the coercive field of up to 1.2T along with resistance
changes of up to 6.5%. These results are attributed to the high sensitivity of
the double perovskites to mechanical deformation.",0906.2276v1
2009-06-26,Tuning odd triplet superconductivity by spin pumping,"We study proximity effect in diffusive
ferromagnet/normal-metal/superconductor junction with precessing magnetization
of the ferromagnet. We find that the odd-frequency pairing induced in the
normal metal is modified by spin pumping from the ferromagnet and hence can be
tuned by changing the precessional frequency. At the frequency corresponding to
twice the superconducting gap, the odd-frequency pairing is strongly enhanced.
We find a crossover from the even- to the odd-frequency superconductivity in
the normal metal by tuning the precessional frequency. This gives a clearcut
signature of the odd-frequency superconductivity observable by scanning
tunneling microscopy. According to the pairing symmetries in the normal metal,
we find a crossover from the gap to the peak structure in the tunneling
conductance between the normal metal and a scanning tunneling microscope tip.",0906.4895v1
2009-06-29,Mesoscopic interplay of superconductivity and ferromagnetism in ultra-small metallic grains,"We review the effects of electron-electron interactions on the ground-state
spin and the transport properties of ultra-small chaotic metallic grains. Our
studies are based on an effective Hamiltonian that combines a superconducting
BCS-like term and a ferromagnetic Stoner-like term. Such terms originate in
pairing and spin exchange correlations, respectively. This description is valid
in the limit of a large dimensionless Thouless conductance. We present the
ground-state phase diagram in the fluctuation-dominated regime where the
single-particle mean level spacing is comparable to the bulk BCS pairing gap.
This phase diagram contains a regime in which pairing and spin exchange
correlations coexist in the ground-state wave function. We discuss the
calculation of the tunneling conductance for an almost-isolated grain in the
Coulomb-blockade regime, and present measurable signatures of the competition
between superconductivity and ferromagnetism in the mesoscopic fluctuations of
the conductance.",0906.5210v1
2009-07-01,Electronic structure of ferromagnetic semiconductor Ga1-xMnxAs probed by sub-gap magneto-optical spectroscopy,"We employ Faraday and Kerr effect spectroscopy in the infrared range to
investigate the electronic structure of Ga1-xMnxAs near the Fermi energy. The
band structure of this archetypical dilute-moment ferromagnetic semiconductor
has been a matter of controversy, fueled partly by previous measurements of the
unpolarized infrared absorption and their phenomenological impurity-band
interpretation. The infrared magneto-optical effects we study arise directly
from the spin-splitting of the carrier bands and their chiral asymmetry due to
spin-orbit coupling. Unlike the unpolarized absorption, they are intimately
related to ferromagnetism and their interpretation is much more microscopically
constrained in terms of the orbital character of the relevant band states. We
show that the conventional theory of the disordered valence band with dominant
As p-orbital character and coupled by kinetic-exchange to Mn local moments
accounts semi-quantitatively for the overall characteristics of the measured
infrared magneto-optical spectra.",0907.0207v1
2009-07-17,"Phase diagram of CeFeAs$_{1-x}$P$_{x}$O obtained from electric resistivity, magnetization, and specific heat measurements","We performed a systematic study on the properties of CeFeAs$_{1-x}$P$_{x}$O
($0\leq x\leq 1$) by electrical resistivity, magnetization and specific heat
measurements. The c-axis lattice constant decreases significantly with
increasing P content, suggesting a remarkable chemical pressure. The Fe-3d
electrons show the enhanced metallic behavior upon P-doping and undergo a
magnetic quantum phase transition around $x \approx 0.4$. Meanwhile, the Ce-4f
electrons develop a ferromagnetic order near the same doping level. The
ferromagnetic order is vanishingly small around $x=0.9$. The data suggest a
heavy-fermion-like behavior as $x\geq 0.95$. No superconductivity is observed
down to 2 K. Our results show the ferromagnetic ordered state as an
intermediate phase intruding between the antiferromagnetic bad metal and the
nonmagnetic heavy fermion metal and support the cerium-containing iron
pnictides as a unique layered Kondo lattice system.",0907.2961v2
2009-08-01,"Phosphorous alloying: controlling the magnetic anisotropy in ferromagnetic (Ga,Mn)(As,P) Layers","Phosphorous alloying of GaMnAs thin films has been used for the manipulation
of the magnetic anisotropies in ferromagnetic Ga0.93Mn0.07As1-yPy layers. We
have determined the anisotropy constants as a function of temperature for
phosphorous alloying levels between 0 and 8.8 at % for a Mn doping level of ~
7at%. We show that it is possible to obtain layers with robust ferromagnetism
and either in-plane or out-of plane easy axes with small barriers for
magnetization reorientation by phosphorous alloying with y< 6at% or y> 6at%.
The critical temperatures are not significantly increased by the P alloying.",0908.0063v2
2009-08-01,Magnetic solitons in frustrated ferromagnetic spin chain,"We study the classical anisotropic ferromagnetic spin chain with frustration.
The behavior of soliton and kink solutions in the vicinity of the ground state
phase transition from the ferromagnetic to the spiral phase is studied. The
dependence of the soliton energy on small anisotropy parameter is established
using scaling estimates and numerical minimization of the energy functional.
Conditions of the existence of the solitons are determined. It is shown that
solitons survive in the spiral phase though with some restrictions on their
size. A comparison of the energies of the classical solitons and the bound
magnon complexes in the quantum model shows the functional similarity between
them. The influence of the finite-size effects on the soliton states is studied
and it is shown that the localized solitons originate from the uniform state
when the system size exceeds some critical value depending on the anisotropy.",0908.0068v1
2009-08-05,"Synthesis and characterization of ferromagnetic cobalt nanospheres, nanodiscs and nanocubes","We report the synthesis of cobalt nanoparticles with different shapes and
sizes by rapid pyrolysis of cobalt carbonyl in the presence of various
surfactants. The size and shape of the nanoparticles were influenced by
reaction conditions, such as type of the surfactant, molar ratio of surfactant
to precursor, reflux temperature and reaction time. The shapes that we have
achieved include spherical, nearly spherical, disc and cube. The presence of
linear amine yielded nanodiscs and they spontaneously self-assembled into long
ribbons. The effect of shape anisotropy on magnetic nanoparticles has been
investigated. Spherical nanoparticles of diameter 14.5 nm show strong
ferromagnetic behavior at low temperature and superparamagnetism at room
temperature. On the other hand the cubic nanoparticles of 45 nm sides showed
negligible coercive field at T = 10 K and ferromagnetism that persisted above T
= 300 K. The cobalt nanospheres were oxidized to grow cobalt oxide shell of
varying thickness to study exchange bias effect. A pronounced exchange bias and
a strong temperature dependant magnetization were observed in oxidized cobalt
nanospheres.",0908.0665v1
2009-08-18,AC- and DC-driven noise and I-V characteristics of magnetic nanostructures,"We study a structure consisting of a ferromagnetic (F) layer coupled to two
normal metal (N) leads. The system is driven out of equilibrium by the
simultaneous application of external dc and ac voltages across the N/F/N
structure. Using the Keldysh diagrammatic approach, and modeling the
ferromagnet as a classical spin of size S >> 1, we derive the Langevin equation
for the magnetization dynamics and calculate the noise correlator. We find that
the noise has an explicit frequency dependence in addition to depending on the
characteristics of the ac and dc drive. Further, we calculate the
current-voltage characteristics of the structure to O(1/S^2) and find that the
nonequilibrium dynamics of the ferromagnetic layer gives rise to corrections to
the current that are both linear and nonlinear in voltage.",0908.2483v2
2009-08-24,Interplay between antiferromagnetic order and spin polarization in ferromagnetic metal/electron-doped cuprate superconductor junctions,"Recently we proposed a theory of point-contact spectroscopy and argued that
the splitting of zero-bias conductance peak (ZBCP) in electron-doped cuprate
superconductor point-contact spectroscopy is due to the coexistence of
antiferromagnetic (AF) and d-wave superconducting orders [Phys. Rev. B {\bf
76}, 220504(R) (2007)]. Here we extend the theory to study the tunneling in the
ferromagnetic metal/electron-doped cuprate superconductor (FM/EDSC) junctions.
In addition to the AF order, the effects of spin polarization, Fermi-wave
vector mismatch (FWM) between the FM and EDSC regions, and effective barrier
are investigated. It is shown that there exits midgap surface state (MSS)
contribution to the conductance to which Andreev reflections are largely
modified due to the interplay between the exchange field of ferromagnetic metal
and the AF order in EDSC. Low-energy anomalous conductance enhancement can
occur which could further test the existence of AF order in EDSC. Finally, we
propose a more accurate formula in determining the spin polarization value in
combination with the point-contact conductance data.",0908.3366v1
2009-08-30,Spin conservation and Fermi liquid near a ferromagnetic quantum critical point,"We propose a new low-energy theory for itinerant fermions near a
ferromagnetic quantum critical point. We show that the full low-energy model
includes, in addition to conventional interaction via spin fluctuations,
another type of interaction, whose presence is crucial for the theory to
satisfy SU(2) spin conservation. We demonstrate the consistency between a
loop-wise expansion and a Fermi liquid description for the full model. We
further show that, prior to the ferromagnetic instability, the system develops
a Pomeranchuk-type instability into a state with zero magnetization but with
p-wave deformations of the Fermi surfaces of spin-up and -down electrons (a
spin nematic).",0908.4433v2
2009-09-02,Tunneling through ferromagnetic barriers on the surface of a topological insulator,"We study the transmission through single and double ferromagnetic barriers on
the surface of a topological insulator. By adjusting the gate voltage and
magnetization oreintation, the ferromagnetic barrier can be tuned into various
transmission regions, where the wavevector-dependent tunnelings are quite
different. We find that the Klein tunneling can be manipulated or even be
turned off. These special properties offer the possibility to control electron
beams on the ""topological metal"". Various novel devices, such as electronic
collimation, wavevector filter, magnetic and electric switchs, and
wavevector-based spin valve, may be constructed based on our observed
phenomena.",0909.0378v1
2009-09-07,$A$-site substitution effect on physical properties of Sr$_3$Fe$_{2-x}$Co$_x$O$_{7-δ}$,"We have investigated the $Ln^{3+}$-substitution ($Ln$ = lanthanoid) effect of
a quasi two-dimensional ferromagnet Sr$_3$Fe$_{2-x}$Co$_x$O$_{7-\delta}$ ($x$$
= $0.5). %$Ln^{3+}$-substitution creates antiferromagnetic insulating clusters
around $Ln^{3+}$. With increasing $Ln^{3+}$-concentration, the ferromagnetism
is gradually suppressed and the resistivity is increasing, which are ascribed
to an increase in antiferromagnetic (AFM) clusters created by
$Ln^{3+}$-substitution. In
Sr$_{2.7}$Gd$_{0.3}$Fe$_{1.5}$Co$_{0.5}$O$_{7-\delta}$, the magnetoresistance
(MR) is enhanced by about 20 % compared with that of
Sr$_3$Fe$_{1.5}$Co$_{0.5}$O$_{7-\delta}$. Coexistence of ferromagnetic (FM) and
AFM phases is essential for the enhancement of the MR\@. Applied magnetic
fields align the FM clusters in the same direction, resulting in a reduction in
the resistivity. A metamagnetic transition observed in the $Ln^{3+}$-doped
samples also contributes to the enhancement of the MR.",0909.1172v1
2009-09-11,Nagaoka ferromagnetism in large-spin systems -Fermion and Boson systems--,"We study magnetic properties of itinerant quantum magnetic particles
described by a generalized Hubbard model with large spin ($S>1/2$) which may be
realized in optical lattices of laser-cooled atom systems. In fermion systems
(half-integer spins), an extended form of Nagaoka ferromagnetism may be
realized. However, as novel aspects of the large spin cases, we found that the
condition on the lattice connectivity is more stringent than in the case of
$S=1/2$ particles, and that the system shows a peculiar degenerate structure of
the ground statein which the ferromagnetic state is included. In contrast, it
turns out that the ground state of itinerant bosonic systems (integer spins)
has a degenerate structure similar to that of fermion system with $S>1/2$
regardless of the shape, connectivity or filling of the lattice, and that the
state with the maximum total spin is always one of the ground states.",0909.2082v1
2009-09-21,"Experimental probing of the interplay between ferromagnetism and localisation in (Ga,Mn)As","The question whether the Anderson-Mott localisation enhances or reduces
magnetic correlations is central to the physics of magnetic alloys.
Particularly intriguing is the case of (Ga,Mn)As and related magnetic
semiconductors, for which diverging theoretical scenarios have been proposed.
Here, by direct magnetisation measurements we demonstrate how magnetism evolves
when the density of carriers mediating the spin-spin coupling is diminished by
the gate electric field in metal/insulator/semiconductor structures of
(Ga,Mn)As. Our findings show that the channel depletion results in a monotonic
decrease of the Curie temperature, with no evidence for the maximum expected
within the impurity-band models. We find that the transition from the
ferromagnetic to the paramagnetic state proceeds via the emergence of a
superparamagnetic-like spin arrangement. This implies that carrier localisation
leads to a phase separation into ferromagnetic and nonmagnetic regions, which
we attribute to critical fluctuations in the local density of states, specific
to the Anderson-Mott quantum transition.",0909.3694v1
2009-09-23,Magnetization Densities as Replica Parameters: The Dilute Ferromagnet,"In this paper we compute exactly the ground state energy and entropy of the
dilute ferromagnetic Ising model. The two thermodynamic quantities are also
computed when a magnetic field with random locations is present. The result is
reached in the replica approach frame by a class of replica order parameters
introduced by Monasson. The strategy is first illustrated considering the SK
model, for which we will show the complete equivalence with the standard
replica approach. Then, we apply to the diluted ferromagnetic Ising model with
a random located magnetic field, which is mapped into a Potts model. This
formalism can be, in principle, applied to all random systems, and we believe
that it could be of help in many other contexts.",0909.4215v3
2009-10-06,Magnetoelectric Coupling and Electric Control of Magnetization in Ferromagnet-Ferroelectric-Metal Superlattices,"Ferromagnet-ferroelectric-metal superlattices are proposed to realize the
large room-temperature magnetoelectric effect. Spin dependent electron
screening is the fundamental mechanism at the microscopic level. We also
predict an electric control of magnetization in this structure. The naturally
broken inversion symmetry in our tri-component structure introduces a
magnetoelectric coupling energy of $P M^2$. Such a magnetoelectric coupling
effect is general in ferromagnet-ferroelectric heterostructures, independent of
particular chemical or physical bonding, and will play an important role in the
field of multiferroics.",0910.1031v1
2009-10-09,Realization of random-field dipolar Ising ferromagnetism in a molecular magnet,"The longitudinal magnetic susceptibility of single crystals of the molecular
magnet Mn$_{12}$-acetate obeys a Curie-Weiss law, indicating a transition to a
ferromagnetic phase due to dipolar interactions. With increasing magnetic field
applied transverse to the easy axis, the transition temperature decreases
considerably more rapidly than predicted by mean field theory to a T=0 quantum
critical point. Our results are consistent with an effective Hamiltonian for a
random-field Ising ferromagnet in a transverse field, where the randomness is
induced by an external field applied to Mn$_{12}$-acetate crystals that are
known to have an intrinsic distribution of locally tilted magnetic easy axes.",0910.1754v1
2009-10-10,"Effect of inversion asymmetry on the intrinsic anomalous Hall effect in ferromagnetic (Ga,Mn)As","The relativistic nature of the electron motion underlies the intrinsic part
of the anomalous Hall effect, believed to dominate in ferromagnetic (Ga,Mn)As.
In this paper, we concentrate on the crystal band structure as an important
facet to the description of this phenomenon. Using different k.p and
tight-binding computational schemes, we capture the strong effect of the bulk
inversion asymmetry on the Berry curvature and the anomalous Hall conductivity.
At the same time, we find it not to affect other important characteristics of
(Ga,Mn)As, namely the Curie temperature and uniaxial anisotropy fields. Our
results extend the established theories of the anomalous Hall effect in
ferromagnetic semiconductors and shed new light on its puzzling nature.",0910.1907v4
2009-10-28,"Orbital fluctuations, spin-orbital coupling, and anomalous magnon softening in an orbitally degenerate ferromagnet","The correlated motion of electrons in the presence of strong orbital
fluctuations and correlations is investigated with respect to magnetic
couplings and excitations in an orbitally degenerate ferromagnet. Introduction
of the orbital degree of freedom results in a class of diagrams representing
spin-orbital coupling which become particularly important near the orbital
ordering instability. Low-energy staggered orbital fluctuation modes,
particularly with momentum near (\pi/2,\pi/2,0) (corresponding to CE-type
orbital correlations), are shown to generically yield strong intrinsically
non-Heisenberg (1-\cos q)^2 magnon self energy correction, resulting in no spin
stiffness reduction, but strongly suppressed zone-boundary magnon energies in
the Gamma-X direction. The zone-boundary magnon softening is found to be
strongly enhanced with increasing hole doping and for narrow-band materials,
which provides insight into the origin of zone-boundary anomalies observed in
ferromagnetic manganites.",0910.5321v2
2009-10-28,Ferromagnetism of electron gas,"In current work, we investigate the density and temperature dependence of
polarization parameter; using the relativistic formalism for the
electron-electron interaction within the Fermi liquid model. we calculate the
spin dependent scattering matrix elements in relativistic region, and then
obtain the non-relativistic behavior to study the magnetic properties of an
electron gas. By varying the polarization parameter, we minimized the free
energy and then obtain the polarization of the system as a function of density
and temperature. At zero temperature the exact results for polarization and
magnetic susceptibility have obtained. It has been shown that for a given
temperature (density) there is critical density (temperature) that the
ferromagnetic phase can appears in electron gas. Our results show that at
nonzero temperatures and in very low and very high densities the ferromagnetism
phase can not be exist.",0910.5332v4
2009-11-02,Effect of helical edge states on the tunneling conductance in ferromagnet/noncentrosymmetric superconductors junctions,"Helical edge states exist in the mixed spin-singlet and spin-triplet phase of
a noncentrosymmetric (NCS) superconductor. In this article we have considered a
planar ferromagnetic metal/NCS superconductor tunnel junction and have studied
the effect of these helical edge states which manifests itself through the
charge and spin tunneling conductance across the junction. We have shown the
behavior of conductances for the entire range of variation of $\gamma =
\Delta_-/\Delta_+$ where $\Delta_\pm$ are the order parameters in the positive
and negative helicity bands of the NCS superconductor.There exists a
competition between the Rashba parameter $\alpha$ and the exchange energy
$E_{ex}$ which is crucial for determining the variation of the conductance with
the applied bias voltage across the junction. We have found a nonzero spin
current across the junction which appears due to the exchange energy in the
Ferromagnet and modulates with the bias voltage. It also changes its profile
when the strength of the exchange energy is varied.",0911.0302v2
2009-11-04,Dissipative current in SIFS Josephson junctions,"We investigate superconductor/insulator/ferromagnet/superconductor (SIFS)
tunnel Josephson junctions in the dirty limit, using the quasiclassical theory.
We consider the case of a strong tunnel barrier such that the left S layer and
the right FS bilayer are decoupled. We calculate quantitatively the density of
states (DOS) in the FS bilayer for arbitrary length of the ferromagnetic layer,
using a self-consistent numerical method. We compare these results with a known
analytical DOS approximation, which is valid when the ferromagnetic layer is
long enough. Finally we calculate quantitatively the current-voltage
characteristics of a SIFS junction.",0911.0846v2
2009-11-17,Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XI: Stabilizing neutron stars against a ferromagnetic collapse,"We construct a new Hartree-Fock-Bogoliubov (HFB) mass model, labeled HFB-18,
with a generalized Skyrme force. The additional terms that we have introduced
into the force are density-dependent generalizations of the usual $t_1$ and
$t_2$ terms, and are chosen in such a way as to avoid the high-density
ferromagnetic instability of neutron stars that is a general feature of
conventional Skyrme forces, and in particular of the Skyrme forces underlying
all the HFB mass models that we have developed in the past. The remaining
parameters of the model are then fitted to essentially all the available mass
data, an rms deviation $\sigma$ of 0.585 MeV being obtained. The new model thus
gives almost as good a mass fit as our best-fit model HFB-17 ($\sigma$ = 0.581
MeV), and has the advantage of avoiding the ferromagnetic collapse of neutron
stars.",0911.3346v1
2009-11-27,Domain growth within the backbone of the three-dimensional $\pm J$ Edwards-Anderson spin glass,"The goal of this work is to show that a ferromagnetic-like domain growth
process takes place within the backbone of the three-dimensional $\pm J$
Edwards-Anderson (EA) spin glass model. To sustain this affirmation we study
the heterogeneities displayed in the out-of-equilibrium dynamics of the model.
We show that both correlation function and mean flipping time distribution
present features that have a direct relation with spatial heterogeneities, and
that they can be characterized by the backbone structure. In order to gain
intuition we analyze the pure ferromagnetic Ising model, where we show the
presence of dynamical heterogeneities in the mean flipping time distribution
that are directly associated to ferromagnetic growing domains. We extend a
method devised to detect domain walls in the Ising model to carry out a similar
analysis in the three-dimensional EA spin glass model. This allows us to show
that there exists a domain growth process within the backbone of this model.",0911.5264v1
2009-11-30,"Nonlocal Electronic Spin Detection, Spin Accumulation and the Spin Hall effect","In recent years, electrical spin injection and detection has grown into a
lively area of research in the field of spintronics. Spin injection into a
paramagnetic material is usually achieved by means of a ferromagnetic source,
whereas the induced spin accumulation or associated spin currents are detected
by means of a second ferromagnet or the reciprocal spin Hall effect,
respectively. This article reviews the current status of this subject,
describing both recent progress and well-established results. The emphasis is
on experimental techniques and accomplishments that brought about important
advances in spin phenomena and possible technological applications. These
advances include, amongst others, the characterization of spin diffusion and
precession in a variety of materials, such as metals, semiconductors and
graphene, the determination of the spin polarization of tunneling electrons as
a function of the bias voltage, and the implementation of magnetization
reversal in nanoscale ferromagnetic particles with pure spin currents.",0911.5619v1
2010-01-06,Sustained ferromagnetism induced by H-vacancies in graphane,"The electronic and magnetic properties of graphane with H-vacancies are
investigated with the help of quantum-chemistry methods. The hybridization of
the edges is found to be absolutely crucial in defining the size of the
bandgap, which is increased from 3.04 eV to 7.51 eV when the hybridization is
changed from the sp^2 to the sp^3 type. The H-vacancy defects also influence
the size of the gap depending on the number of defects and their distribution
between the two sides of the graphane plane. Further, the H-vacancy defects
induced on one side of the graphane plane and placed on the neighboring carbon
atoms are found to be the source of ferromagnetism which is distinguished by
the high stability of the state with a large spin number in comparison to that
of the singlet state and is expected to persist even at room temperatures.
However, the ferromagnetic ordering of the spins is obtained to be limited by
the concentration of H-vacancy defects and ordering would be preserved if
number of defects do not exceed eight.",1001.0919v2
2010-01-08,Thermodynamics of a two-dimensional frustrated spin-1/2 Heisenberg ferromagnet,"Using the spin-rotation-invariant Green's function method we calculate the
thermodynamic quantities (correlation functions <S_0 S_R>, uniform static spin
susceptibility \chi, correlation length \xi, and specific heat C_V) of the
two-dimensional spin-1/2 J1-J2 Heisenberg ferromagnet for J2 < J2^c \approx
0.44|J1|, where J2^c is the critical frustrating antiferromagnetic next-nearest
neighbor coupling at which the ferromagnetic ground state gives way for a
ground-state phase with zero magnetization. Examining the low-temperature
behavior of \chi and \xi, in the limit T \to 0 both quantities diverge
exponentially, i.e., \chi \propto \exp(b/T) and \xi \propto\exp(b/2T),
respectively. We find a linear decrease of the coefficient b with increasing
frustration according to b=-(\pi/2)(J1+2J2), i.e., the exponential divergence
of \chi and \xi is present up to J2^c. Furthermore, we find an additional
low-temperature maximum in the specific heat when approaching the critical
point, J2 \to J2^c.",1001.1222v2
2010-01-10,Underscreened Kondo effect in quantum dots coupled to ferromagnetic leads,"We analyze the equilibrium transport properties of underscreened Kondo effect
in the case of a two-level quantum dot coupled to ferromagnetic leads. Using
the numerical renormalization group (NRG) method, we have determined the gate
voltage dependence of the dot's spin and level-resolved spectral functions. We
have shown that the polarization of the dot is very susceptible to spin
imbalance in the leads and changes sign in the middle of the S=1 Coulomb
valley. Furthermore, we have also found that by fine-tuning an external
magnetic field one can compensate for the presence of ferromagnetic leads and
restore the Kondo effect in the case of $S=1/2$ Coulomb valley. However, the
underscreened Kondo effect cannot be fully recovered due to its extreme
sensitivity with respect to the magnetic field.",1001.1506v2
2010-01-14,Kondo effect in a quantum dot coupled to ferromagnetic leads and side-coupled to a nonmagnetic reservoir,"Equilibrium transport properties of a single-level quantum dot tunnel-coupled
to ferromagnetic leads and exchange-coupled to a side nonmagnetic reservoir are
analyzed theoretically in the Kondo regime. The equilibrium spectral functions
and conductance through the dot are calculated using the numerical
renormalization group (NRG) method. It is shown that in the antiparallel
magnetic configuration, the system undergoes a quantum phase transition with
increasing exchange coupling $J$, where the conductance drops from its maximum
value to zero. In the parallel configuration, on the other hand, the
conductance is generally suppressed due to an effective spin splitting of the
dot level caused by the presence of ferromagnetic leads, irrespective of the
strength of exchange constant. However, for $J$ ranging from J=0 up to the
corresponding critical value, the Kondo effect and quantum critical behavior
can be restored by applying properly tuned compensating magnetic field.",1001.2475v1
2010-02-03,Tailoring Interlayer Exchange Coupling of Ferromagnetic Films Across MgO with Fe Nanoclusters,"We investigate the interlayer exchange coupling in Fe/MgO/Fe and Fe/MgO/Co
systems with magnetic Fe nanoclusters embedded in the MgO spacer. Samples are
grown by molecular beam epitaxy (MBE) and utilize wedged MgO films to
independently vary the film thickness and the position of the Fe nanoclusters.
Depending on the position of the Fe nanoclusters, the bilinear coupling (J1)
exhibits strong variations in magnitude and can even switch between
antiferromagnetic and ferromagnetic. This effect is explained by the magnetic
coupling between the ferromagnetic films and the magnetic nanoclusters.
Interestingly, the coupling of Fe nanoclusters to a Co film is 160% stronger
than their coupling to a Fe film (at MgO spacing of 0.56 nm). This is much
greater than the coupling difference of 20% observed in the analogous thin film
systems (i.e. Fe/MgO/Co vs. Fe/MgO/Fe), identifying an interesting nano-scaling
effect related to the coupling between films and nanoclusters.",1002.0627v1
2010-02-07,Collective modes for an array of magnetic dots with perpendicular magnetization,"The dispersion relations of collective oscillations of the magnetic moment of
magnetic dots arranged in square-planar arrays and having magnetic moments
perpendicular to the array plane are calculated. The presence of the external
magnetic field perpendicular to the plane of array, as well as the uniaxial
anisotropy for single dot are taken into account. The ferromagnetic state with
all the magnetic moments parallel, and chessboard antiferromagnetic state are
considered. The dispersion relation yields information about the stability of
different states of the array. There is a critical magnetic field below which
the ferromagnetic state is unstable. The antiferromagnetic state is stable for
small enough magnetic fields. The dispersion relation is non-analytic as the
value of the wave vector approaches zero. Non-trivial Van Hove anomalies are
also found for both ferromagnetic and antiferromagnetic states.",1002.1477v1
2010-02-16,"Orbital Ordering and Unfrustrated $(π,0)$ Magnetism from Degenerate Double Exchange in the Iron Pnictides","The magnetic excitations of the iron pnictides are explained within a
degenerate double-exchange model. The local-moment spins are coupled by
superexchanges $J_1$ and $J_2$ between nearest and next-nearest neighbors,
respectively, and interact with the itinerant electrons of the degenerate
$d_{xz}$ and $d_{yz}$ orbitals via a ferromagnetic Hund exchange. The latter
stabilizes $(\pi,0)$ stripe antiferromagnetism due to emergent ferro-orbital
order and the resulting kinetic energy gain by hopping preferably along the
ferromagnetic spin direction. Taking the quantum nature of the spins into
account, we calculate the magnetic excitation spectra in the presence of both,
super- and double-exchange. A dramatic increase of the spin-wave energies at
the competing N\'eel ordering wave vector is found, in agreement with recent
neutron scattering data. The spectra are fitted to a spin-only model with a
strong spatial anisotropy and additional longer ranged couplings along the
ferromagnetic chains. Over a realistic parameter range, the effective couplings
along the chains are negative corresponding to unfrustrated stripe
antiferromagnetism.",1002.3165v3
2010-03-05,Finite size effects with variable range exchange coupling in thin-film Pd/Fe/Pd trilayers,"The magnetic properties of thin-film Pd/Fe/Pd trilayers in which an embedded
~1.5 A-thick ultrathin layer of Fe induces ferromagnetism in the surrounding Pd
have been investigated. The thickness of the ferromagnetic trilayer is
controlled by varying the thickness of the top Pd layer over a range from 8 A
to 56 A. As the thickness of the top Pd layer decreases, or equivalently as the
embedded Fe layer moves closer to the top surface, the saturated magnetization
normalized to area and the Curie temperature decrease whereas the coercivity
increases. These thickness-dependent observations for proximity-polarized
thin-film Pd are qualitatively consistent with finite size effects that are
well known for regular thin-film ferromagnets. The critical exponent $\beta$ of
the order parameter (magnetization) is found to approach the mean field value
of 0.5 as the thickness of the top Pd layer increases. The functional forms for
the thickness dependences, which are strongly modified by the nonuniform
exchange interaction in the polarized Pd, provide important new insights to
understanding nanomagnetism in two-dimensions.",1003.1305v1
2010-03-08,Stability of 2pi domain walls in ferromagnetic nanorings,"The stability of 2pi domain walls in ferromagnetic nanorings is investigated
via calculation of the minimum energy path that separates a 2pi domain wall
from the vortex state of a ferromagnetic nanoring. Trapped domains are stable
when they exist between certain types of transverse domain walls, i.e., walls
in which the edge defects on the same side of the magnetic strip have equal
sign and thus repel. Here the energy barriers between these configurations and
vortex magnetization states are obtained using the string method. Due to the
geometry of a ring, two types of 2pi walls must be distinguished that differ by
their overall topological index and exchange energy. The minimum energy path
corresponds to the expulsion of a vortex. The energy barrier for annihilation
of a 2pi wall is compared to the activation energy for transitions between the
two ring vortex states.",1003.1758v1
2010-03-09,Generation and Manipulation of Spin Current in Graphene Nanodisks: Robustness against Randomness and Lattice Defects,"Trigonal zigzag graphene nanodisk exhibits magnetism whose spin is
proportional to the edge length of the nanodisk. Its spin can be designed from
1/2 to a huge value. The spins form a quasiferromagnet, which has intermediate
properties between a single spin and a ferromagnet. In other words, the
ferromagnet order has a relatively long life time, and yet the nanodisk spin
can be rotated by external field or current. We consider a nanodisk connected
with two leads. This system acts as a spin filter just as in a
metal-ferromagnet-metal junction. In this way we can generate a spin current.
Furthermore we can manipulate spin current by spin valve, spin switch and other
spintronic devices made of graphene nanodisks. We also show that nanodisk spins
are robust against the effect of randomness in site energy, transfer energy and
lattice defects.",1003.1766v1
2010-03-09,Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes,"We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes
using thermal pyrolysis method and the effect of shape anisotropy on the static
and dynamic magnetic properties were studied. Shape anisotropy of approximately
10 % was introduced in nanocubes by making nanodiscs using a linear chain amine
surfactant during synthesis process. It has been observed that, ferromagnetism
persisted above room temperature and a sharp drop in magnetic moment at low
temperatures in zero-field cooled magnetization may be associated with the spin
disorder due to the effective anisotropy present in the system. Dynamic
magnetic properties were studied using RF transverse susceptibility
measurements at different temperatures and the singularities due to anisotropy
fields were probed at low temperatures. Symmetrically located broad peaks are
observed in the frozen state at the effective anisotropy fields and the peak
structure is strongly affected by shape anisotropy and temperature.
Irrespective of size the shape anisotropy gave rise to higher coercive fields
and larger transverse susceptibility ratio at all temperatures. The role of
shape anisotropy and the size of the particles on the observed magnetic
behaviour were discussed.",1003.1855v1
2010-03-10,Evidence for triplet superconductivity in Josephson junctions with ferromagnetic Cu$_{2}$MnAl-Heusler barriers,"We have studied Josephson junctions with barriers prepared from the Heusler
compound Cu$_2$MnAl. In the as-prepared state the Cu$_2$MnAl layers are non
ferromagnetic and the critical Josephson current density $j_{c}$ decreases
exponentially with the thickness of the Heusler layers $d_{F}$. On annealing
the junctions at 240\degree C the Heusler layers develop ferromagnetic order
and we observe a dependence $j_{c}(d_{F}$) with $j_{c}$ strongly enhanced and
weakly thickness dependent in the thickness range 7.0 nm < $d_{F}$ < 10.6 nm.
We attribute this feature to a triplet component in the superconducting pairing
function generated by the specific magnetization profile inside thin Cu$_2$MnAl
layers.",1003.2082v1
2010-03-11,"Magnetic and Electrical Properties of Ordered 112-type Perovskite LnBaCoMnO5+δ(Ln = Nd, Eu)","Investigation of the oxygen-deficient 112-type ordered oxides of the type
LnBaCoMnO5+\delta (Ln = Nd, Eu) evidences certain unusual magnetic behavior at
low temperatures, compared to the LnBaCo2O5+\delta cobaltites. One observes
that the substitution of manganese for cobalt suppresses the ferromagnetic
state and induces strong antiferromagnetic interactions. Importantly,
NdBaCoMnO5.9 depicts a clear paramagnetic to antiferromagnetic type transition
around 220 K, whereas for EuBaCoMnO5.7 one observes an unusual magnetic
behavior below 177 K which consists of ferromagnetic regions embedded in an
antiferromagnetic matrix. The existence of two sorts of crystallographic sites
for Co/Mn and their mixed valence states favor the ferromagnetic interaction
whereas antiferromagnetism originates from the Co3+-O-Co3+ and Mn4+-O-Mn4+
interactions. Unlike the parent compounds, the present Mn-substituted phases do
not exhibit prominent magnetoresistance effects in the temperature range
75-400K.",1003.2262v1
2010-03-12,Anomalous Hall Effect in Disordered Multiband Metals,"We present a microscopic theory of the anomalous Hall effect in metallic
multi-band ferromagnets, which accounts for all scattering-independent
contributions, i.e., both the intrinsic and the so-called side jump. For a
model of Gaussian disorder, the anomalous Hall effect is expressed solely in
terms of the electronic band structure of the host material. Our theory handles
systematically the interband-scattering coherence effects. We demonstrate the
method in the two-dimensional Rashba and three-dimensional ferromagnetic
(III,Mn)V semiconductor models. Our formalism is directly amenable to ab initio
treatments for a wide range of ferromagnetic metals.",1003.2626v2
2010-03-13,Ferromagnetic Clusters in the Brownmillerite Bilayered Compounds Ca2.5-xLaxSr0.5GaMn2O8: An Approach to Achieve Layered Spintronics Materials,"We report the effect of La-substitution on the magnetic and magnetotransport
properties of Brownmillerite-like bilayered compounds Ca2.5-xLaxSr0.5GaMn2O8 (x
= 0, 0.05, 0.075, and 0.1) by using dc-magnetization, resistivity and
magnetoresistance techniques. The Rietveld analysis of the room temperature
x-ray diffraction patterns confirms no observable change of average crystal
structure with the La-substitution. Both magnetic and magnetotransport
properties are found to be very sensitive to the La-substitution.
Interestingly, the La-substituted compounds show ferromagnetic-like behavior
(due to the occurrence of a double exchange mechanism) whereas, the parent
compound is an antiferromagnet (TN 150 K). All compounds show an insulating
behavior, in the measured temperature range of 100 - 300 K, with an overall
decrease in the resistivity with the substitution. A higher value of
magnetoresistance has been successfully achieved by the La-substitution. We
have proposed an electronic phase separation model, considering the formation
of ferromagnetic clusters in the antiferromagnetic matrix, to interpret the
observed magnetization and magnetotransport results for the La-substituted
samples. The present study demonstrates an approach to achieve new functional
materials, based on naturally occurring layered system like
Ca2.5-xLaxSr0.5GaMn2O8, for possible spintronics applications.",1003.2685v1
2010-03-26,Tunnel effect in ferromagnetic half-metal Co$_2$CrAl-superconductor heterostructures,"Ferromagnetic half-metal Co$_2$CrAl films and tunnel contacts Co$_2$CrAl -
insulator (I) - Pb are fabricated and investigated. It is found that the
normalized differential conductivity $\sigma ^{\rm FS} $ of such tunnel
junctions with low resistance is larger than the normalized differential
conductivity $\sigma ^{\rm NS} $ of known normal metal - I - superconductor
type tunnel junctions. It is shown that the observed increase in $\sigma ^{\rm
FS} $ is caused by the accumulation of spin polarized electrons in a
superconductor and can be used for estimating the spin polarization degree $P$
in ferromagnets. This method shows that $P$ of L2$_1$-type ordered Co$_2$CrAl
Heusler alloy films at $T = 4.2{\rm K}$ is close to 1.",1003.5093v1
2010-04-05,Hysteresis in the magneto-transport of Manganese-doped Germanium: evidence for carrier-mediated ferromagnetism,"We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion
implantation into Ge followed by pulsed laser annealing. Benefiting from the
short time annealing, the hole concentration in Mn-implanted Ge has been
increased by two orders of magnitude from 10$^{18}$ to over 10$^{20}$
cm$^{-3}$. Likely due to the high hole concentration, we observe that the
longitudinal and Hall resistances exhibit the same hysteresis as the
magnetization, which is usually considered as a sign of carrier-mediated
ferromagnetism.",1004.0568v1
2010-04-07,Itinerant ferromagnetism of a repulsive atomic Fermi gas: a quantum Monte Carlo study,"We investigate the phase diagram of a two-component repulsive Fermi gas at
T=0 by means of quantum Monte Carlo simulations. For a given value of the
positive s-wave scattering length, both purely repulsive and purely attractive
model potentials are considered in order to analyze the limits of the universal
regime where the details of interatomic forces can be neglected. The equation
of state of both balanced and unbalanced systems is calculated as a function of
the interaction strength and the critical density for the onset of
ferromagnetism is determined. The energy per particle of the strongly polarized
gas is calculated and parametrized in terms of the physical properties of
repulsive polarons, which are relevant for the stability of the fully
magnetized ferromagnetic state. Finally, we analyze the phase diagram in the
polarization/interaction plane under the assumption that only phases with
homogeneous magnetization can be produced.",1004.1169v1
2010-04-26,Spin transfer in a ferromagnet-quantum dot and tunnel barrier coupled Aharonov-Bohm ring system with Rashba spin-orbit interactions,"The spin transfer effect in ferromagnet-quantum dot (insulator)-ferromagnet
Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is
investigated by means of Keldysh nonequilibrium Green function method. It is
found that both the magnitude and direction of the spin transfer torque (STT)
acting on the right ferromagnet electrode can be effectively controlled by
changing the magnetic flux threading the AB ring or the gate voltage on the
quantum dot. The STT can be greatly augmented by matching a proper magnetic
flux and an SO interaction at a cost of low electrical current. The STT,
electrical current, and spin current are uncovered to oscillate with the
magnetic flux. The present results are expected to be useful for information
storage in nanospintronics.",1004.4507v1
2010-04-28,Is room temperature ferromagnetism possible in K-doped SnO2?,"Ab initio studies have theoretically predicted room temperature
ferromagnetism in crystalline SnO2, ZrO2 and TiO2 doped with non magnetic
element from the 1A column as K and Na. Our purpose is to address
experimentally the possibility of magnetism in both Sn1-xKxO2 and Sn1-xCaxO2
compounds. The samples have been prepared using equilibrium methods of standard
solid state route. Our study has shown that both Sn1-xCaxO2 and Sn1-xKxO2
structure is thermodynamically unstable and leads to a phase separation, as
shown by X-ray diffraction and detailed micro-structural analyses with high
resolution transmission electron microscopy (TEM). In particular, the
crystalline SnO2 grains are surrounded by K-based amorphous phase. In contrast
to Ca: SnO2 samples we have obtained a magnetic phase in K: SnO2 ones, but no
long range ferromagnetic order. The K: SnO2 samples exhibit a moments of the
order of 0.2 {\mu}B/K /ion, in contrast to ab-initio calculations which predict
3{\mu}B, where K atoms are on the Sn crystallographic site. The apparent
contradictions between our experiments and first principle studies are
discussed.",1004.5001v2
2010-04-30,Mean-field study of itinerant ferromagnetism in trapped ultracold Fermi gases: Beyond the local density approximation,"We theoretically investigate the itinerant ferromagnetic transition of a
spherically trapped ultracold Fermi gas with spin imbalance under strongly
repulsive interatomic interactions. Our study is based on a self-consistent
solution of the Hartree-Fock mean-field equations beyond the widely used local
density approximation. We demonstrate that, while the local density
approximation holds in the paramagnetic phase, after the ferromagnetic
transition it leads to a quantitative discrepancy in various thermodynamic
quantities even with large atom numbers. We determine the position of the phase
transition by monitoring the shape change of the free energy curve with
increasing the polarization at various interaction strengths.",1004.5443v2
2010-06-03,Ferromagnetically coupled Shastry-Sutherland quantum spin singlets in (CuCl)LaNb$_2$O$_7$,"Using inelastic neutron scattering, x-ray, neutron diffraction, and the
first-principle calculation techniques, we show that the crystal structure of
the two-dimensional quantum spin system (CuCl)LaNb$_2$O$_7$ is orthorhombic
with $Pbam$ symmetry in which CuCl$_4$O$_2$ octahedra are tilted from their
high symmetry positions and the Cu$^{2+} (s = 1/2)$ ions form a distorted
square lattice. The dominant magnetic interactions are the fourth nearest
neighbor antiferromagnetic interactions with a Cu-Cl--Cl-Cu exchange path,
which lead to the formation of spin singlets. The two strongest interactions
between the singlets are ferromagnetic, which makes (CuCl)LaNb$_2$O$_7$ the
first system of ferromagnetically coupled Shastry-Sutherland quantum spin
singlets.",1006.0755v1
2010-06-07,Interface ferromagnetism and orbital reconstruction in BiFeO3- La0.7Sr0.3MnO3 heterostructures,"We report the formation of a novel ferromagnetic state in the antiferromagnet
BiFeO3 at the interface with La0.7Sr0.3MnO3. Using x-ray magnetic circular
dichroism at Mn and Fe L2,3-edges, we discovered that the development of this
ferromagnetic spin structure is strongly associated with the onset of a
significant exchange bias. Our results demonstrate that the magnetic state is
directly related with an electronic orbital reconstruction at the interface,
which is supported by the linearly polarized x-ray absorption measurement at
oxygen K-edge.",1006.1194v1
2010-06-10,Probing the exchange field of a quantum-dot spin valve by a superconducting lead,"Electrons in a quantum-dot spin valve, consisting of a single-level quantum
dot coupled to two ferromagnetic leads with magnetizations pointing in
arbitrary directions, experience an exchange field that is induced on the dot
by the interplay of Coulomb interaction and quantum fluctuations. We show that
a third, superconducting lead with large superconducting gap attached to the
dot probes this exchange field very sensitively. In particular, we find
striking signatures of the exchange field in the symmetric component of the
supercurrent with respect to the bias voltage applied between the ferromagnets
already for small values of the ferromagnets' spin polarization.",1006.1976v2
2010-06-17,Nonlocal conductance via overlapping Andreev bound states in ferromagnet-superconductor heterostructures,"In a setup where two ferromagnetic electrodes are attached to a
superconductor, Andreev bound states are induced at both
ferromagnet/superconductor (FM/SC) interfaces. We study how these states
propagate through the SC and interact with each other. As a result of this
interaction, the energetic positions of the Andreev states are not anymore
determined solely by the magnetic properties of a single interface, but also
depend on the interface distance and the relative magnetization orientation of
the FM contacts. We discuss how these bound states show up as distinct peaks in
the nonlocal conductance signal, and lead to marked asymmetries with respect to
the applied voltage. We relate our results to nonlocal crossed Andreev and
elastic co-tunneling processes.",1006.3422v1
2010-06-18,Superfluid/ferromagnet/superfluid junction and $π$-phase in a superfluid Fermi gas,"We investigate the possibility of superfluid/ferromagnet/superfluid
(SFS)-junction in a superfluid Fermi gas. To examine this possibility in a
simple manner, we consider an attractive Hubbard model at $T=0$ within the
mean-field theory. When a potential barrier is embedded in a superfluid Fermi
gas with population imbalance ($N_\uparrow>N_\downarrow$, where $N_\sigma$ is
the number of atoms with pseudospin $\sigma=\uparrow,\downarrow$), this barrier
is shown to be {\it magnetized} in the sense that excess $\uparrow$-spin atoms
are localized around it. The resulting superfluid Fermi gas is spatially
divided into two by this {\it ferromagnet}, so that one obtains a junction
similar to the superconductor/ferromagnet/superconductor-junction discussed in
superconductivity. Indeed, we show that the so-called $\pi$-phase, which is a
typical phenomenon in the SFS-junction, is realized, where the superfluid order
parameter changes its sign across the junction. Our results would be useful for
the study of magnetic effects on fermion superfluidity using an ultracold Fermi
gas.",1006.3673v1
2010-06-26,Critical current diffraction pattern of SIFS Josephson junctions with step-like F-layer,"We present the latest generation of
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions
with a step-like thickness of the ferromagnetic (F) layer. The F-layer
thicknesses $d_1$ and $d_2$ in both halves were varied to obtain different
combinations of positive and negative critical current densities $j_{c,1}$ and
$j_{c,2}$. The measured dependences of the critical current on applied magnetic
field can be well described by a model which takes into account different
critical current densities (obtained from reference junctions) and different
net magnetization of the multidomain ferromagnetic layer in both halves.",1006.5109v2
2010-07-08,Observation of the Spin-Seebeck Effect in a Ferromagnetic Semiconductor,"The spin-Seebeck effect was recently discovered in a metallic ferromagnet and
consists of a thermally generated spin distribution that is electrically
measured utilizing the inverse spin Hall effect. Here this effect is reproduced
experimentally in a ferromagnetic semiconductor, GaMnAs, which allows for
flexible design of the magnetization directions, a larger spin polarization,
and measurements across the magnetic phase transition. The spin-Seebeck effect
in GaMnAs is observed even in the absence of longitudinal charge transport. The
spatial distribution of spin-currents is maintained across electrical breaks
highlighting the local nature of the effect, which is therefore ascribed to a
thermally induced spin redistribution.",1007.1364v1
2010-07-10,Dynamical instability of a spin spiral in an interacting Fermi gas as a probe of the Stoner transition,"We propose an experiment to probe ferromagnetic phenomena in an ultracold
Fermi gas, while alleviating the sensitivity to three-body loss and competing
many-body instabilities. The system is initialized in a small pitch spin
spiral, which becomes unstable in the presence of repulsive interactions. To
linear order the exponentially growing collective modes exhibit critical
slowing down close to the Stoner transition point. Also, to this order, the
dynamics are identical on the paramagnetic and ferromagnetic sides of the
transition. However, we show that scattering off the exponentially growing
modes qualitatively alters the collective mode structure. The critical slowing
down is eliminated and in its place a new unstable branch develops at large
wave vectors. Furthermore, long-wavelength instabilities are quenched on the
paramagnetic side of the transition. We study the experimental observation of
the instabilities, specifically addressing the trapping geometry and how
phase-contrast imaging will reveal the emerging domain structure. These probes
of the dynamical phenomena could allow experiments to detect the transition
point and distinguish between the paramagnetic and ferromagnetic regimes.",1007.1743v2
2010-07-12,The phases of deuterium at extreme densities,"We consider deuterium compressed to higher than atomic, but lower than
nuclear densities. At such densities deuterium is a superconducting quantum
liquid. Generically, two superconducting phases compete, a ""ferromagnetic"" and
a ""nematic"" one. We provide a power counting argument suggesting that the
dominant interactions in the deuteron liquid are perturbative (but screened)
Coulomb interactions. At very high densities the ground state is determined by
very small nuclear interaction effects that probably favor the ferromagnetic
phase. At lower densities the symmetry of the theory is effectively enhanced to
SU(3), and the quantum liquid enters a novel phase, neither ferromagnetic nor
nematic. Our results can serve as a starting point for investigations of the
phase dynamics of deuteron liquids, as well as exploration of the stability and
dynamics of the rich variety of topological objects that may occur in phases of
the deuteron quantum liquid, which range from Alice strings to spin skyrmions
to Z_2 vortices.",1007.1972v2
2010-07-19,Spin waves in zigzag graphene nanoribbons and the stability of edge ferromagnetism,"We study the low energy spin excitations of zigzag graphene nanoribbons of
varying width. We find their energy dispersion at small wave vector to be
dominated by antiferromagnetic correlations between the ribbon's edges, in
accrodance with previous calculations. We point out that spin wave lifetimes
are very long due to the semi-conducting nature of the electrically neutral
nanoribbons. However, application of very modest gate voltages cause a
discontinuous transition to a regime of finite spin wave lifetime. By further
increasing doping the ferromagnetic alignments along the edge become unstable
against transverse spin fluctuations. This makes the experimental detection of
ferromagnetism is this class of systems very delicate, and poses a difficult
challenge to the possible uses of these nanoribbons as basis for spintronic
devices.",1007.3285v2
2010-07-24,The itinerant ferromagnetic phase of the Hubbard model,"Using a newly developed quantum Monte Carlo technique, we provide strong
evidence for the stability of a saturated ferromagnetic phase in the
high-density regime of the two-dimensional infinite-U Hubbard model. By
decreasing the electron density, a discontinuous transition to a paramagnetic
phase is observed, accompanied by a divergence of the susceptibility on the
paramagnetic side. This behavior, resulting from a high degeneracy among
different spin sectors, is consistent with an infinite-order phase transition.
The remarkable stability of itinerant ferromagnetism renews the hope to
describe this phenomenon within a purely kinetic mechanism and will facilitate
the validation of experimental quantum simulators with cold atoms loaded in
optical lattices.",1007.4260v2
2010-07-27,Low-temperature properties of classical zigzag spin chain at the ferromagnet-helimagnet transition point,"Low-temperature thermodynamics of the classical frustrated ferromagnetic spin
chain near the ferromagnet-helimagnet transition point is studied by means of
mapping to the continuum limit. The calculation of the partition function and
spin correlation function is reduced to quantum problem of a particle in
potential well. It is shown that exactly at the transition point the
correlation length behaves as $T^{-1/3}$ and the magnetic susceptibility
diverges as $T^{-4/3}$ in the low-temperature limit. Corresponding numerical
factors for the correlation length and the susceptibility is calculated. It is
shown that the low-temperature susceptibility in the helical phase near the
transition point has a maximum at some temperature. Such behavior as well as
the location and the magnitude of the maximum as a function of deviation from
the transition point are in agreement with that observed in several materials
described by the quantum $s=1/2$ version of this model.",1007.4625v1
2010-07-30,Gapped Ferromagnetic Graphene Nanoribbons,"We theoretically design a graphene-based all-organic ferromagnetic
semiconductor by terminating zigzag graphene nanoribbons (ZGNRs) with organic
magnets. A large spin-split gap with 100% spin polarized density of states near
the Fermi energy is obtained, which is of potential application in spin
transistors. The interplays among electron, spin and lattice degrees of freedom
are studied using the first-principles calculations combined with fundamental
model analysis. All of the calculations consistently demonstrate that although
no d electrons existing, the antiferromagnetic \pi-\pi exchange together with
the strong spin-lattice interactions between organic magnets and ZGNRs make the
ground state ferromagnetic. The fundamental physics makes it possible to
optimally select the organic magnets towards practical applications.",1007.5416v2
2010-08-07,Disorder Induced Negative Magnetization in LaSrCoRuO6,"This paper reports effect of thermally induced disorder on the magnetic
properties of LaSrCoRuO6 double perovskite. While the ordered sample is
antiferromagnetic, the disordered sample exhibits negative values of
magnetization measured in low applied fields. Isothermal magnetization on this
sample shows hysteresis due to presence of ferromagnetic interactions. Based on
neutron diffraction and X-ray Absorption Fine Structure (XAFS) studies, these
results have been interpreted to be due disorder in site occupancy of Co and Ru
leading to octahedral distortions and formation of Ru-O-Ru ferromagnetic
linkages. Below 150K these ferromagnetic Ru spins polarize the Co spins in a
direction opposite to that of the applied field resulting in observed negative
magnetization.",1008.1314v1
2010-08-16,Thermal expansion of the superconducting ferromagnet UCoGe,"We report measurements of the coefficient of linear thermal expansion,
$\alpha (T)$, of the superconducting ferromagnet UCoGe. The data taken on a
single-crystalline sample along the orthorhombic crystal axes reveal a
pronounced anisotropy, with the largest length changes along the $b$ axis. The
large values of the step sizes $\Delta \alpha$ at the magnetic and
superconducting phase transitions provide solid evidence for bulk magnetism and
superconductivity. Specific-heat measurements corroborate bulk
superconductivity. Thermal-expansion measurements in magnetic fields $B
\parallel a,b$ show $\Delta \alpha$ at $T_C$ grows rapidly, which indicates the
character of the ferromagnetic transition becomes first-order-like.",1008.2635v1
2010-08-19,Limited influence of diluted ferromagnetic dimers on Curie temperature in complex magnetic systems,"In this work we investigate Ising and classical Heisenberg models for two and
three dimensional lattices in presence of diluted ferromagnetic dimers. For
such models the Curie temperature as a function of ratio of intra-dimer
exchange coupling constant I_A and other inter-site coupling constants I_B is
calculated. In case dimer is treated exactly and environment within the
mean-field approach it was found that even for I_A/I_B\to\infty T_C remains
finite. Similar analysis is proposed for rhombohedral phase of intermetallic
compound Gd2Fe17 where so-called Fe1-Fe1 ""dumbbell"" forms the diluted
ferromagnetic dimer. It was shown that for such complex magnetic systems T_C is
determined by all variety of exchange interactions and for the interval 0 <
I_A/I_B < \infty T_C changes are not more than +/-10%.",1008.3219v1
2010-09-07,Itinerant ferromagnetism in a Fermi gas with contact interaction: Magnetic properties in a dilute Hubbard model,"Ground state properties of the repulsive Hubbard model on a cubic lattice are
investigated by means of the auxiliary-field quantum Monte Carlo method. We
focus on low-density systems with varying on-site interaction $U/t$, as a model
relevant to recent experiments on itinerant ferromagnetism in a dilute Fermi
gas with contact interaction. Twist-average boundary conditions are used to
eliminate open-shell effects and large lattice sizes are studied to reduce
finite-size effects. The sign problem is controlled by a generalized
constrained path approximation. We find no ferromagnetic phase transition in
this model. The ground-state correlations are consistent with those of a
paramagnetic Fermi liquid.",1009.1409v1
2010-09-09,Antisite Domains in Double Perovskite Ferromagnets: Impact on Magnetotransport and Half-metallicity,"Several double perovskite materials of the form A_2BB'O_6 exhibit high
ferromagnetic T_c, and significant low field magnetoresistance. They are also a
candidate source of spin polarized electrons. The potential usefulness of these
materials is, however, frustrated by mislocation of the B and B' ions, which do
not organise themselves in the ideal alternating structure. The result is a
strong dependence of physical properties on preparative conditions, reducing
the magnetization and destroying the half-metallicity. We provide the first
results on the impact of spatially correlated antisite disorder, as observed
experimentally, on the ferromagnetic double perovskites. The antisite domains
suppress magnetism and half-metallicity, as expected, but lead to a dramatic
enhancement of the low field magnetoresistance.",1009.1702v1
2010-09-10,Improved half-metallic ferromagnetism of transition-metal pnictides and chalcogenides calculated with a modified Becke-Johnson exchange potential,"We use a density-functional-theory (DFT) approach with a modified
Becke-Johnson exchange plus local density approximation (LDA) correlation
potential (mBJLDA) [semi-local, orbital-independent, producing accurate
semiconductor gaps. see F. Tran and P. Blaha, Phys. Rev. Lett. 102, 226401
(2009)] to investigate the electronic structures of zincblende transition-metal
(TM) pnictides and chalcogenides akin to semiconductors. Our results show that
this potential does not yield visible changes in wide TM d-t_{2g} bands near
the Fermi level, but makes the occupied minority-spin p-bands lower by
0.25~0.35 eV and the empty (or nearly empty) minority-spin e_g bands across the
Fermi level higher by 0.33~0.73 eV. Consequently, mBJLDA, having no
atom-dependent parameters, makes zincblende MnAs become a truly half-metallic
(HM) ferromagnet with a HM gap (the key parameter) 0.318eV, being consistent
with experiment. For zincblende MnSb, CrAs, CrSb, CrSe, or CrTe, the HM gap is
enhanced by 19~56% compared to LDA and generalized gradient approximation
results. The improved HM ferromagnetism can be understood in terms of the
mBJLDA-enhanced spin exchange splitting.",1009.1920v1
2010-09-20,The cavity method for quantum disordered systems: from transverse random field ferromagnets to directed polymers in random media,"After reviewing the basics of the cavity method in classical systems, we show
how its quantum version, with some appropriate approximation scheme, can be
used to study a system of spins with random ferromagnetic interactions and a
random transverse field. The quantum cavity equations describing the
ferromagnetic-paramagnetic phase transition can be transformed into the
well-known problem of a classical directed polymer in a random medium. The
glass transition of this polymer problem translates ino the existence of a
`Griffith phase' close to the quantum phase transition of the quantum spin
problem, where the physics is dominated by rare events.",1009.3725v2
2010-09-22,Optimal control of magnetization dynamics in ferromagnetic heterostructures by spin--polarized currents,"We study the switching-process of the magnetization in a
ferromagnetic-normal-metal multilayer system by a spin polarized electrical
current via the spin transfer torque. We use a spin drift-diffusion equation
(SDDE) and the Landau-Lifshitz-Gilbert equation (LLGE) to capture the coupled
dynamics of the spin density and the magnetization dynamic of the
heterostructure. Deriving a fully analytic solution of the stationary SDDE we
obtain an accurate, robust, and fast self-consistent model for the
spin-distribution and spin transfer torque inside general ferromagnetic/normal
metal heterostructures. Using optimal control theory we explore the switching
and back-switching process of the analyzer magnetization in a seven-layer
system. Starting from a Gaussian, we identify a unified current pulse profile
which accomplishes both processes within a specified switching time.",1009.4296v2
2010-09-25,Micro-Structured Ferromagnetic Tubes for Spin Wave Excitation,"Micron scale ferromagnetic tubes placed on the ends of ferromagnetic CoTaZr
spin waveguides are explored in order to enhance the excitation of Backward
Volume Magnetostatic Spin Waves. The tubes produce a closed magnetic circuit
about the signal line of the coplanar waveguide and are, at the same time,
magnetically contiguous with the spin waveguide. This results in a 10 fold
increase in spin wave amplitude. However, the tube geometry distorts the
magnetic field near the spin waveguide and relatively high biasing magnetic
fields are required to establish well defined spin waves. Only the lowest
(uniform) spin wave mode is excited.",1009.4986v1
2010-09-28,Non-Collinear Ferromagnetic Luttinger Liquids,"The presence of electron-electron interactions in one dimension profoundly
changes the properties of a system. The separation of charge and spin degrees
of freedom is just one example. We consider what happens when a system
consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall,
is coupled to interacting electrons in one-dimension (more specifically a
Luttinger liquid). The ferromagnetism breaks spin charge separation and the
presence of the domain wall introduces a spin dependent scatterer into the
problem. The absence of spin charge separation and the effects of the electron
correlations results in very different behaviour for the excitations in the
system and for spin-transfer-torque effects in this model.",1009.5509v1
2010-10-20,Strain-driven non-collinear magnetic ordering in orthorhombic epitaxial YMnO3 thin films,"We show that using epitaxial strain and chemical pressure in orthorhombic
YMnO3 and Co-substituted (YMn0.95Co0.05O3) thin films, a ferromagnetic response
can be gradually introduced and tuned. These results, together with the
measured anisotropy of the magnetic response, indicate that the unexpected
observation of ferromagnetism in orthorhombic o-RMnO3 (R= Y, Ho, Tb, etc) films
originates from strain-driven breaking of the fully compensated magnetic
ordering by pushing magnetic moments away from the antiferromagnetic [010]
axis. We show that the resulting canting angle and the subsequent ferromagnetic
response, gradually increase (up to ~ 1.2\degree) by compression of the unit
cell. We will discuss the relevance of these findings, in connection to the
magnetoelectric response of orthorhombic manganites.",1010.4118v2
2010-10-26,Partial annealing of a coupled mean-field spin-glass model with an embedded pattern,"A partially annealed mean-field spin-glass model with a locally embedded
pattern is studied. The model consists of two dynamical variables, spins and
interactions, that are in contact with thermal baths at temperatures T_S and
T_J, respectively. Unlike the quenched system, characteristic correlations
among the interactions are induced by the partial annealing. The model exhibits
three phases, which are paramagnetic, ferromagnetic and spin-glass phases. In
the ferromagnetic phase, the embedded pattern is stably realized. The phase
diagram depends significantly on the ratio of two temperatures n=T_J/T_S. In
particular, a reentrant transition from the embedded ferromagnetic to the
spin-glass phases with T_S decreasing is found only below at a certain value of
n. This indicates that above the critical value n_c the embedded pattern is
supported by local field from a non-embedded region. Some equilibrium
properties of the interactions in the partial annealing are also discussed in
terms of frustration.",1010.5346v2
2010-10-27,Anomalous Josephson current through a ferromagnetic trilayer junction,"We studied the anomalous Josephson current appearing at zero phase difference
in junctions coupled with a ferromagnetic trilayer which has noncoplanar
magnetizations. A $\pi/2$ junction with an equilibrium phase difference $\pi/2$
is obtained under suitable conditions. The equilibrium phase difference and the
amplitude of the supercurrent are all tunable by the structure parameters. In
addition to calculating the anomalous current using the Bogoliubov-de Gennes
equation, we also developed a clear physical picture explaining the anomalous
Josephson effect in the structure. We show that the triplet proximity
correlation and the phase shift in the anomalous current-phase relation all
stem from the spin precession in the first and third ferromagnet layers.",1010.5554v2
2010-10-28,Density functional study of weak ferromagnetism in a thick BiCrO3 film,"Very thick films of BiCrO$_3$ have been grown on a SrTiO$_3$ substrate,
maintaining a tetragonal lattice up to thicknesses of 14,000\AA. Assuming we
can treat films of this thickness as bulk crystals, we first calculated the
experimentally undetermined atomic positions within the unit cell with the
measured lattice constant of the film, then relaxed the lattice constants along
with the atomic positions. All the calculations result in an antiferroelectric
crystal with the {\it Pnma} space group with noncollinear Bi displacements. We
find G-type antiferromagnetism with a spin-orbit induced weak ferromagnetic
component, however, the weak ferromagnetic component can cancel if the
antiferromagnetic spins are oriented along a particular one of the three 2-fold
rotation axes.",1010.6003v1
2010-11-25,Model for domain wall avalanches in ferromagnetic thin films,"The Barkhausen jumps or avalanches in magnetic domain-walls motion between
succesive pinned configurations, due the competition among magnetic external
driving force and substrum quenched disorder, appear in bulk materials and thin
films. We introduce a model based in rules for the domain wall evolution of
ferromagnetic media with exchange or short-range interactions, that include
disorder and driving force effects. We simulate in 2-dimensions with Monte
Carlo dynamics, calculate numerically distributions of sizes and durations of
the jumps and find power-law critical behavior. The avalanche-size exponent is
in excellent agreement with experimental results for thin films and is close to
predictions of the other models, such as like random-field and random-bond
disorder, or functional renormalization group. The model allows us to review
current issues in the study of avalanches motion of the magnetic domain walls
in thin films with ferromagnetic interactions and opens a new approach to
describe these materials with dipolar or long-range interactions.",1011.5643v3
2010-11-26,Weak itinerant ferromagnetism in Heusler type Fe2VAl0.95,"We report measurements of the magnetic, transport and thermal properties of
the Heusler type compound Fe2VAl0.95. We show that while stoichiometric Fe2VAl
is a non-magnetic semi-metal a 5% substitution on the Al-site with the 3d
elements Fe and V atoms leads to a ferromagnetic ground state with a Curie
temperature TC = 33+-3 K and a small ordered moment ms = 0.12 mB/Fe in
Fe2VAl0.95. The reduced value of the ratio ms/mp = 0.08, where mp = 1.4 mB/Fe
is the effective Curie-Weiss moment, together with the analysis of the
magnetization data M(H,T), show magnetism is of itinerant nature. The specific
heat shows an unusual temperature variation at low temperatures with an
enhanced Sommerfeld coefficient, g = 12 mJK-2mol-1. The resistivity, r(T), is
metallic and follows a power law behavior r(T) = r0+AT^n with n = 1.5 below TC.
With applying pressure, TC decreases with the rate of (1/TC)(dTC /dP) = -0.061
GPa-1. We conclude substitution on the Al-site with Fe and V atoms results in
itinerant ferromagnetism with a low carrier density.",1011.5704v1
2010-12-02,Electronic structure and magnetism of transition metal doped Zn12O12 clusters: Role of defects,"We present a comprehensive study of the energetics and magnetic properties of
ZnO clusters doped with 3d transition metals (TM) using ab initio density
functional calculations in the framework of generalized gradient approximation
+ Hubbard U (GGA+U) method. Our results within GGA+U for all 3d dopants except
Ti indicate that antiferromagnetic interaction dominates in a neutral,
defect-free cluster. Formation energies are calculated to identify the stable
defects in the ZnO cluster. We have analyzed in details the role of these
defects to stabilize ferromagnetism when the cluster is doped with Mn, Fe, and
Co. Our calculations reveal that in the presence of charged defects the
transition metal atoms residing at the surface of the cluster may have an
unusual oxidation state, that plays an important role to render the cluster
ferromagnetic. Defect induced magnetism in ZnO clusters without any TM dopants
is also analyzed. These results on ZnO clusters may have significant
contributions in the nanoengineering of defects to achieve desired
ferromagnetic properties for spintronic applications.",1012.0430v1
2010-12-03,Dissipationless mechanism of skyrmion Hall current in double-exchange ferromagnets,"We revisit a theory of skyrmion transport in ferromagnets. On a basis of an
effective U(1) gauge theory for spin-chirality fluctuations in double-exchange
ferromagnets, we derive an expression for the velocity of a skyrmion core
driven by the dc electric field. We find that mutual feedback effects between
conduction electrons and localized spins give rise to Chern-Simons terms,
suggesting a dissipationless mechanism for the skyrmion Hall current. A
conventional description of the current-induced skyrmion motion, appearing
through the spin transfer torque and scattering events, is reproduced in a
certain limit of our description, where the Chern-Simons terms are not fully
incorporated. Our theory is applicable to not only metallic but also insulating
systems, where the purely topological and dissipationless skyrmion Hall current
can be induced in the presence of an energy gap.",1012.0631v3
2010-12-09,Superconductivity Reinforced by Magnetic Field and the Magnetic Instability in Uranium Ferromagnets,"We review our recent results on ferromagnetic superconductors, URhGe and
UCoGe. High quality single crystals of both compounds were successfully grown.
The specific heat shows a clear jump related to the superconducting transition
in UCoGe. The finite values of C/T at 0K are discussed in terms of the
self-induced vortex state and the value of the ordered moment. With increasing
fields for H // b-axis in URhGe, the jump of thermal expansion increases and
shifts to lower temperature. The re-entrant and S-shaped superconducting phases
for URhGe and UCoGe respectively are explained by the unusual field dependence
of the effective mass, which is induced by the ferromagnetic instability when
the field is applied along the hard magnetization b-axis. The magnetic
fluctuations are very sensitive to the field orientation. This is reflected in
the Hc2 and the anisotropy of the effective mass.",1012.1987v1
2010-12-14,Scaling behavior of the spin pumping effect in ferromagnet/platinum bilayers,"We systematically measured the DC voltage V_ISH induced by spin pumping
together with the inverse spin Hall effect in ferromagnet/platinum bilayer
films. In all our samples, comprising ferromagnetic 3d transition metals,
Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V_ISH
invariably has the same polarity. V_ISH furthermore scales with the
magnetization precession cone angle with a universal prefactor, irrespective of
the magnetic properties, the charge carrier transport mechanism or type. These
findings quantitatively corroborate the present theoretical understanding of
spin pumping in combination with the inverse spin Hall effect.",1012.3017v2
2011-01-09,Semiconducting (Half-Metallic) Ferromagnetism in Mn(Fe) Substituted Pt and Pd Nitrides,"Using first principles calculations as based on density functional theory, we
propose a class of so far unexplored diluted ferromagnetic semiconductors and
half-metals. Here, we study the electronic properties of recently synthesized $
4d $ and $ 5d $ transition metal dinitrides. In particular, we address Mn- and
Fe-substitution in PtN$_2$ and PdN$_2$. Structural relaxation shows that the
resulting ordered compounds, Pt$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$ and
Pd$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$, maintain the cubic crystal symmetry of the
parent compounds. On substitution, all compounds exhibit long-range
ferromagnetic order. While both Pt$_{0.75}$Mn$_{0.25}$N$_2$ and
Pd$_{0.75}$Mn$_{0.25}$N$_2$ are semiconducting, Fe-substitution causes
half-metallic behavior for both parent materials.",1101.1635v1
2011-01-21,Multiple spin state analysis of magnetic nano graphene,"Recent experiments indicate room-temperature ferromagnetism in graphite-like
materials. This paper offers multiple spin state analysis applied to asymmetric
graphene molecule to find out mechanism of ferromagnetic nature. First
principle density functional theory is applied to calculate spin density,
energy and atom position depending on each spin state. Molecules with
dihydrogenated zigzag edges like C64H27, C56H24, C64H25, C56H22 and C64H23 show
that in every molecule the highest spin state is the most stable one with over
3000 K energy difference with next spin state. This result suggests a stability
of room temperature ferromagnetism in these molecules. In contrast, nitrogen
substituted molecules like C59N5H22, C52N4H20, C61N3H22, C54N2H20 and C63N1H22
show opposite result that the lowest spin state is the most stable. Magnetic
stability of graphene molecule can be explained by three key issues, that is,
edge specified localized spin density, parallel spins exchange interaction
inside of a molecule and atom position optimization depending on spin state.
Those results will be applied to design a carbon-base ferro-magnet, an ultra
high density 100 tera bit /inch2 class information storage and spintronic
devices.",1101.4080v1
2011-01-27,Asymmetric graphene model applied to graphite-like carbon-based ferromagnetism,"Several experiments have recently found room-temperature ferromagnetism in
graphite-like carbon based materials. This paper offers a model explaining such
ferromagnetism by using an asymmetric nano-graphene. Our first typical model is
C48H24 graphene molecule, which has three dihydrogenated (-CH2) zigzag edges.
There are several multiple spin states competing for stable minimum energy in
the same atomic topology. Both molecular orbital and density function theory
methods indicate that the quartet state(S=3/2) is more stable than that of
doublet (S=1/2), which means that larger saturation magnetization will be
achieved. We also enhanced this molecule to an infinite length ribbon having
many (-CH2) edges. Similar results were obtained where the highest spin state
was more stable than lower spin state. In contrast, a nitrogen substituted
(-NH) molecule C45N3H21 demonstrated opposite results. that is, the lowest spin
state(S=1/2) is more stable than that of highest one(S=3/2), which arises from
the slight change in atom position.",1101.5209v1
2011-01-27,Anomalous magnetic transport in ferromagnetic graphene junctions,"We investigate magnetotransport in a ferromagnetic/normal/ferromagnetic
graphene junction where a gate electrode is attached to the normal segment. It
is shown that the charge conductance can be maximal at an antiparallel
configuration of the magnetizations. Moreover, we demonstrate that both the
magnitude and the sign of the spin-transfer torque can be controlled by means
of the gate voltage in the normal segment. In this way, the present system
constitutes a spin-transfer torque transistor. These anomalous phenomena are
attributed to the combined effect of the exchange field and the Dirac
dispersion of graphene. Our prediction opens up the possibility of moving
domain walls parallel or antiparallel to the current in a controllable fashion
by means of a local gate voltage.",1101.5236v1
2011-01-31,Random-field p-spin glass model on regular random graphs,"We investigate in detail the phase diagrams of the p-body +/-J Ising model
with and without random fields on random graphs with fixed connectivity. One of
our most interesting findings is that a thermodynamic spin glass phase is
present in the three-body purely ferromagnetic model in random fields, unlike
for the canonical two-body interaction random-field Ising model. We also
discuss the location of the phase boundary between the paramagnetic and spin
glass phases that does not depend on the change of the ferromagnetic bias. This
behavior is explained by a gauge transformation, which shows that
gauge-invariant properties generically do not depend on the strength of the
ferromagnetic bias for the +/-J Ising model on regular random graphs.",1101.5863v1
2011-02-06,Microscopic model for the semiconductor-to-ferromagnetic-metal transition in FeSi$_{1-x}$Ge$_{x}$ Alloys,"The simplified bandstructure introduced by Mazurenko et al to model FeSi is
used to analyze the singlet semiconductor to ferromagnetic metal transition in
the isoelectronic isostructural alloys, FeSi$_{1-x}$Ge$_x$. The complex
bandstructure of the alloy is replaced by an alternating chain of doubly and
singly degenerate atoms to represent Fe and Si/Ge respectively. The
former(latter) form narrow(broad) bands with a substantial hybridization
between them. A substantial onsite repulsion including a Hund's rule coupling
is introduced on the Fe sites. The mean field phase diagram contains a first
order phase transition from the singlet semiconductor to a ferromagnetic metal
with increasing temperature and interaction strength similar to the alloys. The
analysis also reproduces the rapid rise of the spin susceptibility in the
semiconductor with a crossover to a Curie-Weiss form at higher temperatures.
Good agreement is found at zero temperature between the mean field and accurate
DMRG calculations.",1102.1190v1
2011-02-16,Magnetization dynamics and Majorana fermions in ferromagnetic Josephson junctions along the quantum spin Hall edge,"We investigate the interplay between ferromagnetic and superconducting order
at the edge of a quantum spin Hall insulator. Using complementary analytical
and self-consistent numerical approaches, we study a ferromagnetic Josephson
junction and show how the direct coupling between magnetism and the
superconducting U(1) phase gives rise to several unusual phenomena which
distinguishes the present system from its non-topological equivalent. In
particular, we demonstrate how the anomalous current-phase relation triggers
supercurrent-induced magnetization dynamics and also study the spatial
localization of the Majorana fermions appearing in the junction.",1102.3403v2
2011-02-18,Ground state properties of the one-dimensional electron liquid,"We present calculations of the energy, pair correlation function (PCF),
static structure factor (SSF), and momentum density (MD) for the
one-dimensional electron gas using the quantum Monte Carlo method. We are able
to resolve peaks in the SSF at even-integer-multiples of the Fermi wave vector,
which grow as the coupling is increased. Our MD results show an increase in the
effective Fermi wave vector as the interaction strength is raised in the
paramagnetic harmonic wire; this appears to be a result of the vanishing
difference between the wave functions of the paramagnetic and ferromagnetic
systems. We have extracted the Luttinger liquid exponent from our MDs by
fitting to data around the Fermi wave vector, finding good agreement between
the exponent of the ferromagnetic infinitely-thin wire and the ferromagnetic
harmonic wire.",1102.3854v2
2011-02-24,Noncoplanar spin canting in lightly-doped ferromagnetic Kondo lattice model on a triangular lattice,"Effect of the coupling to mobile carriers on the 120$^\circ$
antiferromagnetic state is investigated in a ferromagnetic Kondo lattice model
on a frustrated triangular lattice. Using a variational calculation for various
spin orderings up to a four-site unit cell, we identify the ground-state phase
diagram with focusing on the lightly-doped region. We find that an electron
doping from the band bottom immediately destabilizes a 120$^\circ$ coplanar
antiferromagnetic order and induces a noncoplanar three-sublattice ordering
accompanied by an intervening phase separation. This noncoplanar phase has an
umbrella-type spin configuration with a net magnetic moment and a finite spin
scalar chirality. This spin-canting state emerges in competition between the
antiferromagnetic superexchange interaction and the ferromagnetic
double-exchange interaction under geometrical frustration. In contrast, a hole
doping from the band top retains the 120$^\circ$-ordered state up to a finite
doping concentration and does not lead to a noncolpanar ordering.",1102.4940v1
2011-02-26,Electron scattering from domain walls in ferromagnetic Luttinger liquids,"We study the properties of interacting electrons in a one-dimensional
conduction band coupled to bulk non-collinear ferromagnetic order. The specific
form of non-collinearity we consider is that of an extended domain wall. The
presence of ferromagnetic order breaks spin-charge separation and the domain
wall introduces a spin-dependent scatterer active over the length of the wall
l. Both forward and backward scattering off the domain wall can be relevant
perturbations of the Luttinger liquid and we discuss the possible low
temperature phases. Our main finding is that backward scattering, while
determining the ultimate low temperature physics, only becomes important at
temperatures T/J < exp(-l/l_+) with J being the magnetic exchange and l_+ the
backward scattering length scale. In physical realizations, l >> l_+ and the
physics will be dominated by forward scattering which can lead to a charge
conducting but spin insulating phase. In a perturbative regime at higher
temperatures we furthermore calculate the spin and charge densities around the
domain wall and quantitatively discuss the interaction induced changes.",1102.5446v2
2011-03-02,Anomalous Hall effect in NiPt thin films,"We study Hall effect in sputtered NixPt1-x thin films with different Ni
concentrations. Temperature, magnetic field and angular dependencies are
analyzed and the phase diagram of NiPt thin films is obtained. It is found that
films with sub-critical Ni concentration exhibit cluster-glass behavior at low
temperatures with a perpendicular magnetic anisotropy below the freezing
temperature. Films with over-critical Ni concentration are ferromagnetic with
parallel anisotropy. At the critical concentration the state of the film is
strongly frustrated. Such films demonstrate canted magnetization with the easy
axis rotating as a function of temperature. The magnetism appears via
consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather
than a single second-order phase transition. But most remarkably, the
extraordinary Hall effect changes sign at the critical concentration. We
suggest that this is associated with a reconstruction of the electronic
structure of the alloy at the normal metal - ferromagnet quantum phase
transition.",1103.0367v2
2011-03-21,Coexistence of superconductivity and ferromagnetism in two dimensions,"Ferromagnetism is usually considered to be incompatible with conventional
superconductivity, as it destroys the singlet correlations responsible for the
pairing interaction. Superconductivity and ferromagnetism are known to coexist
in only a few bulk rare-earth materials. Here we report evidence for their
coexistence in a two-dimensional system: the interface between two bulk
insulators, LaAlO$_3$ (LAO) and SrTiO$_3$ (STO), a system that has been studied
intensively recently. Magnetoresistance, Hall and electric-field dependence
measurements suggest that there are two distinct bands of charge carriers that
contribute to the interface conductivity. The sensitivity of properties of the
interface to an electric field make this a fascinating system for the study of
the interplay between superconductivity and magnetism.",1103.4006v2
2011-03-23,"Ferromagnetism in Co-doped ZnO films grown by molecular beam epitaxy: magnetic, electrical and microstructural studies","We studied structural, optical and magnetic properties of high-quality 5 and
15% Co-doped ZnO films grown by plasma-assisted molecular beam epitaxy (MBE) on
(0001)-sapphire substrates. Magnetic force microscopy (MFM) and magnetic
measurements with SQUID magnetometer show clear ferromagnetic behavior of the
films up to room temperature whereas they are antiferromagnetic below 200 K
approximately. Temperature dependence of the carrier mobility was determined
using Raman line shape analysis of the longitudinal-optical-phonon-plasmon
coupled modes. It shows that the microscopic mechanism for ferromagnetic
ordering is coupling mediated by free electrons between spins of Co atoms.
These results bring insight into a subtle interplay between charge carriers and
magnetism in MBE-grown Zn(1-x)CoxO films.",1103.4463v1
2011-03-27,Measurements of Nanoscale Domain Wall Flexing in a Ferromagnetic Thin Film,"We use the high spatial sensitivity of the anomalous Hall effect in the
ferromagnetic semiconductor Ga1-xMnxAs, combined with the magneto-optical Kerr
effect, to probe the nanoscale elastic flexing behavior of a single magnetic
domain wall in a ferromagnetic thin film. Our technique allows position
sensitive characterization of the pinning site density, which we estimate to be
around 10^14 cm^{-3}. Analysis of single site depinning events and their
temperature dependence yields estimates of pinning site forces (10 pN range) as
well as the thermal deactivation energy. Finally, our data hints at a much
higher intrinsic domain wall mobility for flexing than previously observed in
optically-probed micron scale measurements.",1103.5240v1
2011-04-07,Finite-size effects on the magnetoelectric response of field-driven ferroelectric/ferromagnetic chains,"We study theoretically the coupled multiferroic dynamics of one-dimensional
ferroelectric/ferromagnet chains driven by harmonic magnetic and electric
fields as a function of the chain length. A linear magnetoelectric coupling is
dominated by the spin-polarized screening charge at the interface. We performed
Monte-Carlo simulations and calculations based on the coupled
Landau-Lifshitz-Gilbert and Landau-Khalatnikov equations showing that the net
magnetization and the total polarization of thin heterostructures, i.e. with up
to ten ferroelectric and ferromagnetic sites counted from the interface, can be
completely reversed by external electric and magnetic fields, respectively.
However, for larger system solely a certain magnetoelectrical control can be
achieved.",1104.1269v3
2011-04-08,Magnetization Dissipation in Ferromagnets from Scattering Theory,"The magnetization dynamics of ferromagnets are often formulated in terms of
the Landau-Lifshitz-Gilbert (LLG) equation. The reactive part of this equation
describes the response of the magnetization in terms of effective fields,
whereas the dissipative part is parameterized by the Gilbert damping tensor. We
formulate a scattering theory for the magnetization dynamics and map this
description on the linearized LLG equation by attaching electric contacts to
the ferromagnet. The reactive part can then be expressed in terms of the static
scattering matrix. The dissipative contribution to the low-frequency
magnetization dynamics can be described as an adiabatic energy pumping process
to the electronic subsystem by the time-dependent magnetization. The Gilbert
damping tensor depends on the time derivative of the scattering matrix as a
function of the magnetization direction. By the fluctuation-dissipation
theorem, the fluctuations of the effective fields can also be formulated in
terms of the quasistatic scattering matrix. The theory is formulated for
general magnetization textures and worked out for monodomain precessions and
domain wall motions. We prove that the Gilbert damping from scattering theory
is identical to the result obtained by the Kubo formalism.",1104.1625v1
2011-04-11,Synthesis and study of alpha-Fe1.4Ga0.6O3: An advanced Ferromagnetic Semiconductor,"We report the synthesis of alpha-Fe1.4Ga0.6O3 compound and present its
structural phase stability and interesting magnetic, dielectric and
photo-absorption properties. In our work Ga doped alpha-Fe2O3 samples are well
stabilized in alpha phase (rhombohedral crystal structure with space group
R3C). Properties of the present composition of Ga doped alpha-Fe2O3 system are
remarkably advanced in comparison with recently most studied FeGaO3
composition. At room temperature the samples are typical soft ferromagnet, as
well as direct band gap semiconductor. Dielectric study showed low dielectric
loss in the samples with large enhancement of ac conductivity at higher
frequencies. Optical absorption in the visible range has been enhanced by 4 to
5%. This composition has exhibited large scope of tailoring room temperature
ferromagnetic moment and optical band gap by varying grain size and non-ambient
(vacuum) heat treatment of the as prepared samples by mechanical alloying.",1104.1982v1
2011-04-12,Hybridization driven quantum critical behavior in weakly-itinerant ferromagnets,"We investigate the unusual magnetic properties of nearly-critical,
weakly-itinerant ferromagnets with general formula UTX, where T=Rh,Co and
X=Ge,Si. As a unique feature about these systems, we show that changes in the
V_{df} hybridization control their proximity to a ferromagnetic instability,
and determine the evolution of: the ground state magnetization, M_0, the Curie
Temperature, T_C, the density of states at the Fermi level, N(E_F), the T^2
resistivity coefficient, A, and the specific heat coefficient, \gamma. The
universal aspect of our findings comes from the dependence on only two
parameters: the T_d bandwidth, W_d, and the distance between T_d and U_f band
centers, C_{T_d}-C_{U_f}.",1104.2287v1
2011-04-15,Structural and Magnetic Phase Transitions in NdCoAsO under High Pressures,"We have investigated structural and magnetic phase transitions under high
pressures in a quaternary rare earth transition metal arsenide oxide NdCoAsO
compound that is isostructural to high temperature superconductor NdFeAsO.
Four-probe electrical resistance measurements carried out in a designer diamond
anvil cell show that the ferromagnetic Curie temperature and anti-ferromagnetic
Neel temperature increase with an increase in pressure. High pressure x-ray
diffraction studies using a synchrotron source show a structural phase
transition from a tetragonal phase to a new crystallographic phase at a
pressure of 23 GPa at 300 K. The NdCoAsO sample remained anti-ferromagnetic and
non-superconducting to temperatures down to 10 K and to the highest pressure
achieved in this experiment of 53 GPa. A P-T phase diagram for NdCoAsO is
presented to a pressure of 53 GPa and low temperatures of 10 K.",1104.3172v1
2011-04-18,Enhanced photon-assisted spin transport in a quantum dot attached to ferromagnetic leads,"We investigate real-time dynamics of spin-polarized current in a quantum dot
coupled to ferromagnetic leads in both parallel and antiparallel alignments.
While an external bias voltage is taken constant in time, a gate terminal,
capacitively coupled to the quantum dot, introduces a periodic modulation of
the dot level. Using non equilibrium Green's function technique we find that
spin polarized electrons can tunnel through the system via additional
photon-assisted transmission channels. Owing to a Zeeman splitting of the dot
level, it is possible to select a particular spin component to be
photon-transfered from the left to the right terminal, with spin dependent
current peaks arising at different gate frequencies. The ferromagnetic
electrodes enhance or suppress the spin transport depending upon the leads
magnetization alignment. The tunnel magnetoresistance also attains negative
values due to a photon-assisted inversion of the spin-valve effect.",1104.3483v2
2011-05-05,Magnetism and superconductivity at LAO/STO-interfaces: the role of Ti 3d interface electrons,"Ferromagnetism and superconductivity are in most cases adverse. However,
recent experiments reveal that they coexist at interfaces of LaAlO3 and SrTiO3.
We analyze the magnetic state within density functional theory and provide
evidence that magnetism is not an intrinsic property of the two-dimensional
electron liquid at the interface. We demonstrate that the robust ferromagnetic
state is induced by the oxygen vacancies in SrTiO3- or in the LaAlO3-layer.
This allows for the notion that areas with increased density of oxygen
vacancies produce ferromagnetic puddles and account for the previous
observation of a superparamagnetic behavior in the superconducting state.",1105.1163v2
2011-05-13,Room temperature p-induced surface ferromagnetism,"We prove a spontaneous magnetization of the oxygen-terminated ZnO (0001)
surface by utilizing a multi-code, SIESTA and KKR, first-principles approach,
involving both LSDA+U and selfinteraction corrections (SIC) to treat electron
correlation effects. Critical temperatures are estimated from Monte Carlo
simulations, showing that at and above 300 K the surface is thermodynamically
stable and ferromagnetic. The observed half-metallicity and long-range magnetic
order originate from the presence of p-holes in the valence band of the oxide.
The mechanism is universal in ionic oxides and points to a new route for the
design of ferromagnetic low dimensional systems.",1105.2777v1
2011-06-03,Origin of in-plane uniaxial magnetic anisotropy in CoFeB amorphous ferromagnetic thin-films,"Describing the origin of uniaxial magnetic anisotropy (UMA) is generally
problematic in systems other than single crystals. We demonstrate an in-plane
UMA in amorphous CoFeB films on GaAs(001) which has the expected symmetry of
the interface anisotropy in ferromagnetic films on GaAs(001), but strength
which is independent of, rather than in inverse proportion to, the film
thickness. We show that this volume UMA is consistent with a bond-orientational
anisotropy, which propagates the interface-induced UMA through the thickness of
the amorphous film. It is explained how, in general, this mechanism may
describe the origin of in-plane UMAs in amorphous ferromagnetic films.",1106.0606v1
2011-06-12,Critical Behavior of AC Antiferromagnetic and Ferromagnetic Susceptibilities of a Spin-1/2 Metamagnetic Ising System,"In this study, the temperature variations of the equilibrium and the
non-equilibrium antiferromagnetic and ferromagnetic susceptibilities of a
metamagnetic system are examined near the critical point. The kinetic equations
describing the time dependencies of the total and staggered magnetizations are
derived by utilizing linear response theory. In order to obtain dynamic
magnetic relaxation behavior of the system, the stationary solutions of the
kinetic equations in existence of sinusoidal staggered and physical external
magnetic fields are performed. In addition, the static and dynamical mean field
critical exponents are calculated in order to formulate the critical behavior
of antiferromagnetic and ferromagnetic magnetic response of a metamagnetic
system. Finally, a comparison of the findings of this study with previous
theoretical and experimental studies is represented and it is shown that a good
agreement is found with our results.",1106.2306v1
2011-06-17,Field-controlled domain wall pinning-depinning effects in ferromagnetic nanowire-nanoparticles system,"We represent the results of micromagnetic modeling and experimental magnetic
force microscopy investigations of domain wall (DW) pinning-depinning effects
in the hybrid systems consisting of ferromagnetic nanowire (NW) and two
ferromagnetic nanoparticles (NPs). It was demonstrated that the special NW-NPs
configuration including the NW with DW nucleating bulb at one end and two-NP
gate enables the realization of controlled DW pinning-depinning based on
switching of magnetization in NPs subsystem. The algorithm of external driving
field manipulation and independent NPs switching, which allow one to develop a
new type of magnetic logic cells, is proposed.",1106.3420v2
2011-06-24,Ferromagnetic frustrated spin systems on the square lattice: a Schwinger boson study,"We study a ferromagnetic Heisenberg spin system on the square lattice, with
nearest neighbors interaction J_1 frustrated by second J_2 and third J_3
neighbors antiferromagnetic interactions, using a mean field theory for the
Schwinger boson representation of spins. For J_3=0 we find that the boundary
between the ferromagnetic and the collinear classical phases shifts to smaller
values of J_2 when quantum fluctuations are included. Along the line J_2/|J_1|=
1 the boundaries between the collinear and incommensurate regions are strongly
shifted to larger values with respect to the classical case. We do not find
clear evidence for spin gapped phases within the present approximation.",1106.5018v2
2011-06-27,Projective studies of spin nematics in a quantum frustrated ferromagnet,"We study the ground state properties of the spin-1/2 frustrated ferromagnetic
J1-J2 Heisenberg model on the square lattice, employing projected BCS
wavefunctions with spin-triplet pairings of the spinon fields as trial
wavefunctions. Based on the variational Monte Carlo analysis, we argue that, in
the competing coupling regime, a certain type of the projected BCS
wavefunction, dubbed the projected Z2 planar state, achieves the best optimal
energy among the other competing states such as the ferromagnetic state and
collinear antiferromagnetic state. Like in quantum spin liquids, the projected
Z2 planar state preserves the translational symmetry of the square lattice.
However, it is also accompanied by a d-wave ordering of the quadrupole moments,
breaking the spin rotational symmetry. The state thus describes a quantum spin
analogue of the nematic liquid crystals. The calculated static correlation
functions also reveal that the projected Z2 planar state has a strong collinear
antiferromagnetic fluctuation.",1106.5333v2
2011-06-29,Hole mediated ferromagnetism in Cu-doped ZnO thin films,"We report the successful synthesis of ZnO:Cu thin films doped with holes,
resulting in room temperature ferromagnetism. Hole doping is achieved by
As-diffusion from the GaAs substrate into ZnO films, assisted by thermal
annealing. The As-diffusion is probed with the help of x-ray absorption spectra
collected at the As K-edge which show enhanced signature of diffusion in the
annealed samples. Introduction of holes, due to the As doping, in ZnO films is
further evidenced by the Cu L3,2-edge spectra. XMCD and magnetic measurements
show that the ferromagnetic interaction between doped Cu ions is enhanced after
hole doping.",1106.5831v1
2011-07-06,Counterexamples to Ferromagnetic Ordering of Energy Levels,"The Heisenberg ferromagnet has symmetry group ${\rm SU}(2)$. The property
known as ferromagnetic ordering of energy levels (FOEL) states that the minimum
energy eigenvalue among eigenvectors with total spin $s$ is monotone decreasing
as a function of $s$. While this property holds for certain graphs such as open
chains, in this note we demonstrate some counterexamples. We consider the spin
1/2 model on rings of length $2n$ for $n=2,3,...,8$, and show that the minimum
energy among all spin singlets is less than or equal to the minimum energy
among all spin triplets, which violates FOEL. This also shows some
counterexamples to the ""Aldous ordering"" for the symmetric exclusion process.
We also review some of the literature related to these examples.",1107.1266v2
2011-07-12,Spinmotive Force due to Intrinsic Energy of Ferromagnetic Nanowires,"We study, both analytically and numerically, a spinmotive force arising from
inherent magnetic energy of a domain wall in a wedged ferromagnetic nanowire.
In a spatially-nonuniform nanowire, domain walls are subjected to an effective
magnetic field, resulting in spontaneous motion of the walls. The spinmotive
force mechanism converts the ferromagnetic exchange and demagnetizing energy of
the nanowire into the electrical energy of the conduction electrons through the
domain wall motion. The calculations show that this spinmotive force can be
several microvolts, which is easily detectable by experiments.",1107.2209v2
2011-07-12,Magnetic interactions in iron superconductors studied with a five-orbital model within the Hartree-Fock and Heisenberg approximations,"We have analyzed the magnetic interactions of a five orbital model for iron
superconductors treated both within Hartree-Fock and Heisenberg approximations.
We have found that the exchange constants depend non-trivially on the Fe-As-Fe
angle and on the charge and orbital filling. Within the localized picture,
columnar ordering is found for intermediate Hund's coupling J_H. At smaller
J_H, an unusual orbital reorganization stabilizes checkerboard ordering.
Ferromagnetism appears at large J_H. Ferromagnetic correlations are enhanced
with electron doping while large hole doping stabilizes checkerboard
antiferromagnetism, explaining the change in magnetic interactions upon
substitution of Fe by Co or Mn. For intermediate and large values of U,
Hartree-Fock shows similar results as strong coupling though with a double
stripe phase instead of ferromagnetism. Itinerancy enhances the stability of
the columnar ordering. Comparison of the two approaches reveals a metallic
region of the phase diagram where strong coupling physics is determinant.",1107.2279v2
2011-07-14,The dimerized ferromagnetic Heisenberg chain,"Ferromagnetic, in contrast to antiferromagnetic, Heisenberg chains can
undergo a Spin-Peierls dimerization only at finite temperatures. They show
reentrant behavior as a function of temperature, which might play a role for
systems with small effective elastic constants as, for example, monatomic
chains on surfaces. We investigate the physical properties of the dimerized
ferromagnetic Heisenberg chain using a modified spin-wave theory. We calculate
the exponentially decaying spin and dimer correlation functions, analyze the
temperature dependence of the corresponding coherence lengths, the
susceptibility, as well as the static and dynamic spin structure factor. By
comparing with numerical data obtained by the density-matrix renormalization
group applied to transfer matrices, we find that the modified spin wave theory
yields excellent results for all these quantities for a wide range of
dimerizations and temperatures.",1107.2772v1
2011-07-15,On the Possibility of Ferromagnetism and Half-Metallicity in Local Moment Systems,"We use the Kondo lattice model to investigate the possibility of
ferromagnetism and half-metallicity in local moment systems. Using the spectral
density approach and making use of the fact that the spontaneous magnetization
of local moment and the itinerant electron polarization are coupled, we derive
an expression for the paramagnetic susceptibility. The magnetic ordering
temperature is determined from the singularities of the susceptibility. The
magnetic phase diagram is constructed in $T-n$(band filling) plane. It is found
that ferromagnetism is possible only for small values of $n$. It is also found
that the temperature drives the transition of the system from half-metal to
metal.",1107.3061v1
2011-07-19,Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization,"We use local and global magnetometry measurements to study the influence of
magnetic domain width w on the domain-induced vortex pinning in
superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic
Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating
layer to eliminate proximity effect. The quasi-periodic domain patterns with
different and systematically adjustable width w, as acquired by a special
demagnetization procedure, exert tunable vortex pinning on a superconducting
layer. The largest enhancement of vortex pinning, by a factor of more than 10,
occurs when w ~ 310 nm is close to the magnetic penetration depth.",1107.3743v1
2011-07-29,"Spin-wave excitations in the ferromagnetic-metallic and in the charge, orbital and spin ordered states in Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5","Inelastic neutron scattering experiments have been performed on single
crystals of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5. Colossal
magnetoresistance (CMR) in the manganites arises from the interplay between a
ferromagnetic metallic and antiferromagnetic charge and orbital ordered
insulating state. Therefore, it appears important to compare these phases
concerning their underlying magnetic interaction parameters. Our investigations
of the spin-wave disperion in the AFM ordered state of
Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ exhibits a strongly anisotropic stiffness. The
sign of the anisotropy is characteristic for the site-centered model for charge
and orbital ordering in half-doped manganites. Within this model, linear
spin-wave theory yields a perfect description of the experimental dispersion.
Furthermore, magnetic excitations in the ferromagnetic metallic state of
Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x=0.49 and x=0.50 exhibit nearly the same
magnon dispersion which can be described with a Heisenberg model including
nearest-neighbor interactions.",1107.5882v1
2011-08-14,Observation of non-conventional spin waves in composite fermion ferromagnets,"We find unexpected low energy excitations of fully spin-polarized
composite-fermion ferromagnets in the fractional quantum Hall liquid, resulting
from a complex interplay between a topological order manifesting through new
energy levels and a magnetic order due to spin polarization. The lowest energy
modes, which involve spin reversal, are remarkable in displaying unconventional
negative dispersion at small momenta followed by a deep roton minimum at larger
momenta. This behavior results from a nontrivial mixing of spin-wave and
spin-flip modes creating a spin-flip excitonic state of composite-fermion
particle-hole pairs. The striking properties of spin-flip excitons imply highly
tunable mode couplings that enable fine control of topological states of
itinerant two-dimensional ferromagnets.",1108.2901v1
2011-08-22,Electron-phonon-scattering dynamics in ferromagnetic metals and its influence on ultrafast demagnetization processes,"We theoretically investigate spin-dependent carrier dynamics due to the
electron-phonon interaction after ultrafast optical excitation in ferromagnetic
metals. We calculate the electron-phonon matrix elements including the
spin-orbit interaction in the electronic wave functions and the interaction
potential. Using the matrix elements in Boltzmann scattering integrals, the
momentum-resolved carrier distributions are obtained by solving their equation
of motion numerically. We find that the optical excitation with realistic laser
intensities alone leads to a negligible magnetization change, and that the
demagnetization due to electron-phonon interaction is mostly due to hole
scattering. Importantly, the calculated demagnetization quenching due to this
Elliot-Yafet type depolarization mechanism is not large enough to explain the
experimentally observed result. We argue that the ultrafast demagnetization of
ferromagnets does not occur exclusively via an Elliott-Yafet type process,
i.e., scattering in the presence of the spin-orbit interaction, but is
influenced to a large degree by a dynamical change of the band structure, i.e.,
the exchange splitting.",1108.4454v1
2011-08-25,Spin Accumulation at Ferromagnet/Non-magnetic Material Interfaces,"Many proposed and realized spintronic devices involve spin injection and
accumulation at an interface between a ferromagnet and a non-magnetic material.
We examine the electric field, voltage profile, charge distribution, spin
fluxes, and spin accumulation at such an interface. We include the effects of
both screening and spin scattering. We also include both the spin-dependent
chemical potentials {\mu}_{\uparrow,\downarrow} and the effective magnetic
field H* that is zero in equilibrium. For a Co/Cu interface, we find that the
spin accumulation in the copper is an order of magnitude larger when both
chemical potential and effective magnetic field are included. We also show that
screening contributes to the spin accumulation in the ferromagnet; this
contribution can be significant.",1108.4969v2
2011-08-31,Area-dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions,"In 2010, several experimental groups obtained compelling evidence for
spin-triplet supercurrent in Josephson junctions containing strong
ferromagnetic materials. Our own best results were obtained from large-area
junctions containing a thick central Co/Ru/Co ""synthetic antiferromagnet"" and
two thin outer layers made of Ni or PdNi alloy. Because the ferromagnetic
layers in our samples are multi-domain, one would expect the sign of the local
current-phase relation inside the junctions to vary randomly as a function of
lateral position. Here we report measurements of the area dependence of the
critical current in several samples, where we find some evidence for those
random sign variations. When the samples are magnetized, however, the critical
current becomes clearly proportional to the area, indicating that the
current-phase relation has the same sign across the entire area of the
junctions.",1108.6243v1
2011-09-05,"Carrier mediated interlayer exchange, ground state phase diagrams and transition temperatures of magnetic thin films","We investigate the influence of the carrier density and other parameters on
the interlayer exchange in magnetic thin film systems. The system consists of
ferromagnetic and non-magnetic layers where the carriers are allowed to move
from layer to layer. For the ferromagnetic layers we use the Kondo-lattice
model to describe interactions between itinerant electrons and local moments.
The electrons' properties are calculated by a Green's function's equation of
motion approach while the magnetization of the local moments is determined by a
minimization of the free energy. As results we present magnetic phase diagrams
and the interlayer exchange over a broad parameter range. Additionally we can
calculate the transition temperatures for different alignments of the
ferromagnetic layers' magnetizations.",1109.0830v1
2011-09-16,Elementary excitations and the phase transition in the bimodal Ising spin glass model,"We show how the nature of the the phase transition in the two-dimensional
bimodal Ising spin glass model can be understood in terms of elementary
excitations. Although the energy gap with the ground state is expected to be 4J
in the ferromagnetic phase, a gap 2J is in fact found if the finite lattice is
wound around a cylinder of odd circumference $L$. This 2J gap is really a
finite size effect that should not occur in the thermodynamic limit of the
ferromagnet. The spatial influence of the frustration must be limited and not
wrap around the system if $L$ is large enough. In essence, the absence of 2J
excitations defines the ferromagnetic phase without recourse to calculating
magnetisation or investigating the system response to domain wall defects. This
study directly investigates the response to temperature. We also estimate the
defect concentration where the phase transition to the spin glass glass state
occurs. The value $p_c = 0.1045(11)$ is in reasonable agreement with the
literature.",1109.3548v1
2011-09-16,Mesoscopic Current-In-Plane Giant Magneto-Resistance,"We develop a three dimensional semiclassical theory which generalizes the
Valet-Fert model in order to account for non-collinear systems with magnetic
texture, including e.g. domain walls or magnetic vortices. The theory allows
for spin transverse to the magnetization to penetrate inside the ferromagnet
over a finite length and properly accounts for the Sharvin resistances. For
ferromagnetic-normal-ferromagnetic multilayers where the current is injected in
the plane of the layers (CIP), we predict the existence of a non zero
mesoscopic CIP Giant Magneto-Resistance (GMR) at the diffusive level. This
mesoscopic CIP-GMR, which adds to the usual ballistic contributions, has a non
monotonic spatial variation and is reminiscent of conductance quantization in
the layers. Furthermore, we study the spin transfer torque in spin valve
nanopillars. We find that when the magnetization direction is non uniform
inside the free layer, the spin torque changes very significantly and simple
one-dimensional calculations cease to be reliable.",1109.3602v1
2011-09-16,Magnetic Proximity Effect as a Pathway to Spintronic Applications of Topological Insulators,"Spin-based electronics in topological insulators (TIs) is favored by the long
spin coherence1,2 and consequently fault-tolerant information storage.
Magnetically doped TIs are ferromagnetic up to 13 K,3 well below any practical
operating condition. Here we demonstrate that the long range ferromagnetism at
ambient temperature can be induced in Bi2-xMnxTe3 by the magnetic proximity
effect through deposited Fe overlayer. This result opens a new path to
interface-controlled ferromagnetism in TI-based spintronic devices.",1109.3609v2
2011-09-21,Anisotropic critical magnetic fluctuations in the ferromagnetic superconductor UCoGe,"We report neutron scattering measurements of critical magnetic excitations in
the weakly ferromagnetic superconductor UCoGe. The strong non-Landau damping of
the excitations we observe, although unusual has been found in another related
ferromagnet, UGe2 at zero pressure. However, we also find there is a
significant anisotropy of the magnetic correlation length in UCoGe that
contrasts with an almost isotropic length for UGe2. The values of the magnetic
correlation length and damping are found to be compatible with
superconductivity on small Fermi surface pockets. The anisotropy may be
important to explain why UCoGe is a superconductor at zero pressure while UGe2
is not.",1109.4541v1
2011-09-26,Electric-field control of magnetic domain wall motion and local magnetization reversal,"Spintronic devices currently rely on magnetic switching or controlled motion
of domain walls by an external magnetic field or spin-polarized current.
Achieving the same degree of magnetic controllability using an electric field
has potential advantages including enhanced functionality and low power
consumption. Here, we report on an approach to electrically control local
magnetic properties, including the writing and erasure of regular ferromagnetic
domain patterns and the motion of magnetic domain walls, in multiferroic
CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer
from ferroelastic domains in ferroelectric media to continuous magnetostrictive
films with negligible magnetocrystalline anisotropy. Optical polarization
microscopy of both ferromagnetic and ferroelectric domain structures reveals
that domain correlations and strong inter-ferroic domain wall pinning persist
in an applied electric field. This leads to an unprecedented electric
controllability over the ferromagnetic microstructure, an accomplishment that
produces giant magnetoelectric coupling effects and opens the way to
multiferroic spintronic devices.",1109.5514v1
2011-10-12,Spin supercurrent in Josephson contacts with noncollinear ferromagnets,"We present a theoretical study of the Josephson coupling of two s-wave
superconductors which are connected through a diffusive contact consisting of
noncollinear ferromagnetic domains. First, we consider a contact with two
domains with magnetization vectors misoriented by an angle $\theta$. Using the
quantum circuit theory, we find that in addition to the charge supercurrent, a
spin supercurrent, which is even in $\phi$ and odd in $\theta$, with a spin
polarization normal to the magnetization vectors flows between the domains.
Furthermore, with asymmetric insulating barriers at the interfaces of the
junction, the system may experience an antiferromagnetic-ferromagnetic phase
transition for $\phi=\pi$. Secondly, we discuss the spin supercurrent in an
extended magnetic texture with multiple domainwalls. We find the
position-dependent spin supercurrent. The magnitude of the spin supercurrent
strongly depends on the phase difference between the superconductors and the
number of domain walls. Our results demonstrate the possibility to couple the
superconducting phase to the magnetization dynamics.",1110.2568v1
2011-10-31,Thermal Transport Properties of Graphene-Based F/S/F Junctions,"We present an investigation of heat transport in gapless graphene-based
Ferromagnetic /singlet Superconductor/Ferromagnetic (FG$\mid$SG$\mid$FG)
junctions. We find that unlike uniform increase of thermal conductance vs
temperature, the thermal conductance exhibits intensive oscillatory behavior vs
width of the sandwiched s-wave superconducting region between the two
ferromagnetic layers. This oscillatory form is occurred by interference of the
massless Dirac fermions in graphene. Also we find that the thermal conductance
vs exchange field $h$ displays a minimal value at $h/E_F\simeq 1$ within the
low temperature regime where this finding demonstrates that propagating modes
of the Dirac fermions in this value reach at their minimum numbers and verifies
the previous results for electronic conductance. We find that for thin widths
of superconducting region, the thermal conductance vs temperature shows linear
increment i.e. $\Gamma\varpropto T$. At last we propose an experimental set-up
to detect our predicted effects.",1110.6719v1
2011-12-15,"Selective spin wave excitation in ferromagnetic (Ga,Mn)As layers by picosecond strain pulses","We demonstrate selective excitation of a spin wave mode in a ferromagnetic
(Ga,Mn)As film by picosecond strain pulses. For a certain range of magnetic
fields applied in the layer plane only a single frequency is detected for the
magnetization precession. We explain this selectivity of spin mode excitation
by the necessity of spatial matching of magnon and phonon eigenfunctions, which
represents a selection rule analogous to momentum conservation for
magnon-phonon interaction in bulk ferromagnetic materials.",1112.3394v1
2011-12-26,Thin-Film Magnetization Dynamics on the Surface of a Topological Insulator,"We theoretically study the magnetization dynamics of a thin ferromagnetic
film exchange-coupled with a surface of a strong three-dimensional topological
insulator. We focus on the role of electronic zero modes imprinted by domain
walls (DW's) or other topological textures in the magnetic film.
Thermodynamically reciprocal hydrodynamic equations of motion are derived for
the DW responding to electronic spin torques, on the one hand, and fictitious
electromotive forces in the electronic chiral mode fomented by the DW, on the
other. An experimental realization illustrating this physics is proposed based
on a ferromagnetic strip, which cuts the topological insulator surface into two
gapless regions. In the presence of a ferromagnetic DW, a chiral mode
transverse to the magnetic strip acts as a dissipative interconnect, which is
itself a dynamic object that controls (and, inversely, responds to) the
magnetization dynamics.",1112.5884v2
2012-02-01,Long-range proximity effect for opposite-spin pairs in S/F heterostructures under non-equilibrium quasiparticle distribution,"By now it is known that in a singlet superconductor/ferromagnet (S/F)
structure the superconducting correlations carried by opposite-spin pairs
penetrate into the ferromagnet over a short distance of the order of magnetic
coherence length. The long-range proximity effect (LRPE), taking place on the
length scale of the normal metal coherence length, can only be maintained by
equal-spin pairs, which can be generated by magnetic inhomogeneities in the
system. In this work we have predicted a new type of LRPE, which can take place
in S/F heterostructures under non-equilibrium conditions. The superconducting
correlations in the F region are generated by opposite-spin Cooper pairs and
equal-spin pairs are not involved. The possibility for an opposite-spin pair to
penetrate into the ferromagnet over a large distance is provided by creation of
the proper non-equilibrium quasiparticle distribution there. This leads to a
sharp increase (up to a few orders of magnitude) of the critical Josephson
current through a S/F/S junction at some values of the voltage controlling the
nonequilibrium distribution in the F interlayer.",1202.0165v1
2012-02-04,Non-equilibrium spatial distribution of Rashba spin torque in ferromagnetic metal layer,"We study the spatial distribution of spin torque induced by a strong Rashba
spin-orbit coupling (RSOC) in a ferromagnetic (FM) metal layer, using the
Keldysh non-equilibrium Green's function method. In the presence of the s-d
interaction between the non-equilibrium conduction electrons and the local
magnetic moments, the RSOC effect induces a torque on the moments, which we
term as the Rashba spin torque.
  A correlation between the Rashba spin torque and the spatial spin current is
presented in this work, clearly mapping the spatial distribution of Rashba Spin
torque in a nano-sized ferromagnetic device. When local magnetism is turned on,
the out-of-plane (Sz) Spin Hall effect (SHE) is disrupted, but rather
unexpectedly an in-plane (Sy) SHE is detected. We also study the effect of
Rashba strength (\alpha_R) and splitting exchange (\Delta) on the
non-equilibrium Rashba spin torque averaged over the device. Rashba spin torque
allows an efficient transfer of spin momentum such that a typical switching
field of 20 mT can be attained with a low current density of less than 10^6
A/cm^2.",1202.0890v2
2012-02-06,Critical Temperature Oscillations and Reentrant Superconductivity due to the FFLO like State in F/S/F Trilayers,"Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers, in which the
establishing of a Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state leads to
interference effects of the superconducting pairing wave function, form the
core of the superconducting spin valve. The realization of strong critical
temperature oscillations in such trilayers, as a function of the ferromagnetic
layer thicknesses or, even more efficient, reentrant superconductivity, are the
key condition to obtain a large spin valve effect, i.e. a large shift in the
critical temperature. Both phenomena have been realized experimentally in the
Cu 41 Ni 59 /Nb/Cu 41 Ni 59 trilayers investigated in the present work.",1202.1193v1
2012-02-17,Tuning the disorder of superglasses,"We study the interplay of superfluidity, glassy and magnetic orders of
hardcore bosons with random frustrating interactions. In the classical limit,
this model reduces to a $\pm J$ Edwards-Anderson Ising model with concentration
$p$ of the ferromagnetic bonds, which hosts a glassy-ferromagnetic transition
at a critical concentration $p_c^{\rm cl}\sim 0.77$ on a 3D cubic lattice. Our
quantum Monte Carlo simulation results using the worm algorithm show that
quantum fluctuations stabilize the coexistence of superfluidity and glassy
order (""superglass""), and shift the (super)glassy-ferromagnetic transition to
$p_c> p_c^{\rm cl}$. In contrast, antiferromagnetic order coexists with
superfluidity to form a supersolid, and the transition to the glassy phase
occurs at a higher $p$.",1202.3908v3
2012-02-22,Bulk Intergrowth of a Topological Insulator with a Room Temperature Ferromagnet,"We demonstrate that the layered room temperature ferromagnet Fe7Se8 and the
topological insulator Bi2Se3 form crystallographically oriented bulk composite
intergrowth crystals. The morphology of the intergrowth in real space and
reciprocal space is described. Critically, the basal planes of Bi2Se3 and
Fe7Se8 are parallel and hence the good cleavage inherent in the bulk phases is
retained. The intergrowth is on the micron scale. Both phases in the
intergrowth crystals display their intrinsic bulk properties: the
ferromagnetism of the Fe7Se8 is anisotropic, with magnetization easy axis in
the plane of the crystals, and ARPES characterization shows that the
topological surface states remain present on the Bi2Se3. Analogous behavior is
found for what has been called ""Fe-doped Bi2Se3.""",1202.4957v1
2012-02-23,Nodeless superconductivity in Ca3Ir4Sn13: evidence from quasiparticle heat transport,"We report resistivity $\rho$ and thermal conductivity $\kappa$ measurements
on Ca$_3$Ir$_4$Sn$_{13}$ single crystals, in which superconductivity with $T_c
\approx 7$ K was claimed to coexist with ferromagnetic spin-fluctuations. Among
three crystals, only one crystal shows a small hump in resistivity near 20 K,
which was previously attributed to the ferromagnetic spin-fluctuations. Other
two crystals show the $\rho \sim T^2$ Fermi-liquid behavior at low temperature.
For both single crystals with and without the resistivity anomaly, the residual
linear term $\kappa_0/T$ is negligible in zero magnetic field. In low fields,
$\kappa_0(H)/T$ shows a slow field dependence. These results demonstrate that
the superconducting gap of Ca$_3$Ir$_4$Sn$_{13}$ is nodeless, thus rule out
nodal gap caused by ferromagnetic spin-fluctuations.",1202.5164v2
2012-02-23,Spinons and helimagnons in the frustrated Heisenberg chain,"We investigate the dynamical spin structure factor S(q,w) for the Heisenberg
chain with ferromagnetic nearest (J1<0) and antiferromagnetic next-nearest
(J2>0) neighbor exchange using bosonization and a time-dependent density-matrix
renormalization group algorithm. For |J1|<< J2 and low energies we analytically
find and numerically confirm two spinon branches with different velocities and
different spectral weights. Following the evolution of S(q,w) with decreasing
J1/J2 we find that helimagnons develop at high energies just before entering
the ferromagnetic phase. Furthermore, we show that a recent interpretation of
neutron scattering data for LiCuVO4 in terms of two weakly coupled
antiferromagnetic chains (|J_1|<< J2) is not viable. We demonstrate that the
data are instead fully consistent with a dominant ferromagnetic coupling, J1/J2
~ -2.",1202.5225v1
2012-02-26,Quantum Anomalous Hall Effect in Flat Band Ferromagnet,"We proposed a theory of quantum anomalous Hall effect in a flat-band
ferromagnet on a two-dimensional (2D) decorated lattice with spin-orbit
coupling. Free electrons on the lattice have dispersionless flat bands, and the
ground state is highly degenerate when each lattice site is occupied averagely
by one electron, i.e., the system is at half filling. The on-site Coulomb
interaction can remove the degeneracy and give rise to the ferrimagnetism,
which is the coexistence of the ferromagnetic and antiferromagnetic long-range
orders. On the other hand the spin-orbit coupling makes the band structure
topologically non-trivial, and produces the quantum spin Hall effect with a
pair of helical edge states around the system boundary. Based on the rigorous
results for the Hubbard model, we found that the Coulomb interaction can
provide an effective staggered potential and turn the quantum spin Hall phase
into a quantum anomalous Hall phase.",1202.5747v1
2012-02-27,"Crystalline anisotropic magnetoresistance with two-fold and eight-fold symmetry in (In,Fe)As ferromagnetic semiconductor","We have investigated the anisotropic magnetoresistance (AMR) of (In,Fe)As
ferromagnetic semiconductor (FMS) layers grown on semi-insulating GaAs
substrates. In a 10 nm-thick (In,Fe)As layer which is insulating at low
temperature, we observed crystalline AMR with two-fold and eight-fold
symmetries. In a metallic 100 nm-thick (In,Fe)As layer with higher electron
concentration, only two-fold symmetric crystalline AMR was observed. Our
results demonstrate the macroscopic ferromagnetism in (In,Fe)As with magnetic
anisotropy that depends on the electron concentration. Non-crystalline AMR is
also observed in the 100 nm-thick layer, but its magnitude is as small as
10^-5, suggesting that there is no s-d scattering near the Fermi level of
(In,Fe)As. We propose the origin of the eight-fold symmetric crystalline
anisotropy in (In,Fe)As.",1202.5874v1
2012-03-08,Ferromagnetism and non-local correlations in the Hubbard model,"We study the possibility and stability of band-ferromagnetism in the
single-band Hubbard model for the simple cubic (SC) lattice. A non-local
self-energy is derived within a modified perturbation theory. Results for the
spectral density and quasiparticle density of states are shown with special
attention to the effects of k-dependence. The importance of non-local
correlations for the fulfillment of the Mermin-Wagner theorem is our main
result. A phase digram showing regions of ferromagnetic order is calculated for
the three dimensional lattice. Besides, we show results for the optical
conductivity and prove that already the renormalized one-loop contribution to
the conductivity cancels the Drude peak exactly in case of a local self-energy
which is not anymore true for a non-local self-energy.",1203.1726v1
2012-03-08,"Controlling Curie temperature in (Ga,Ms)As through location of the Fermi level within the impurity band","The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied
material for prototype applications in semiconductor spintronics. Because
ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has
direct and crucial bearing on its Curie temperature TC. It is vigorously
debated, however, whether holes in (Ga,Mn)As reside in the valence band or in
an impurity band. In this paper we combine results of channeling experiments,
which measure the concentrations both of Mn ions and of holes relevant to the
ferromagnetic order, with magnetization, transport, and magneto-optical data to
address this issue. Taken together, these measurements provide strong evidence
that it is the location of the Fermi level within the impurity band that
determines TC through determining the degree of hole localization. This finding
differs drastically from the often accepted view that TC is controlled by
valence band holes, thus opening new avenues for achieving higher values of TC.",1203.1852v1
2012-03-12,Ferromagnetic transition of a two-component Fermi gas of Hard Spheres,"We use microscopic many-body theory to analyze the problem of itinerant
ferromagnetism in a repulsive atomic Fermi gas of Hard Spheres. Using simple
arguments, we show that the available theoretical predictions for the onset of
the ferromagnetic transition predict a transition point at a density ($k_F a
\sim 1$) that is too large to be compatible with the universal low-density
expansion of the energy. We present new variational calculations for the
hard-sphere Fermi gas, in the framework of Fermi hypperneted chain theory, that
shift the transition to higher densities ($k_F a \sim 1.8$). Backflow
correlations, which are mainly active in the unpolarized system, are essential
for this shift.",1203.2521v1
2012-03-10,Room temperature ferromagnetism and giant permittivity in chemical routed Co1.5Fe1.5O4 ferrite particles and their composite with NaNO3,"We report structural, magnetic and dielectric properties of Co1.5Fe1.5O4
nanoparticles and their composites with non-magnetic NaNO3. The samples were
derived from metal nitrates solution at different pH values. The chemical
routed sample was air heated at 200 0C and 500 0C. Heating of the material
showed unusual decrease of crystallite size, but cubic spinel structure is seen
in all samples. The samples of Co1.5Fe1.5O4 showed substantially large room
temperature ferromagnetic moment, electrical conductivity, dielectric constant,
and low dielectric loss. The samples are soft ferromagnet and electrically
highly polarized. The interfaces of grains and grain boundaries are actively
participating to determine the magnetic and dielectric properties of the
ferrite grains. The effects of interfacial contribution are better realized
using the ferrite and NaNO3 composite samples. We have examined different
scopes of modifying the magnetic and dielectric parameters using same material
in pure and composite form.",1203.2944v1
2012-03-14,Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets,"A theoretical study has been carried out to analyse the available results
from the inelastic neutron scattering experiment performed on a quasi-two
dimensional spin-1/2 ferromagnetic material $K_2CuF_4$. Our formalism is based
on a conventional semi-classical like treatment involving a model of an ideal
gas of vortices/anti-vortices corresponding to an anisotropic XY Heisenberg
ferromagnet on a square lattice. The results for dynamical structure functions
for our model corresponding to spin-1/2, show occurrence of negative values in
a large range of energy transfer even encompassing the experimental range, when
convoluted with a realistic spectral window function. This result indicates
failure of the conventional theoretical framework to be applicable to the
experimental situation corresponding to low spin systems. A full quantum
formalism seems essential for treating such systems.",1203.3069v2
2012-03-19,Injection and detection of spin in a semiconductor by tunneling via interface states,"Injection and detection of spin accumulation in a semiconductor having
localized states at the interface is evaluated. Spin transport from a
ferromagnetic contact by sequential, two-step tunneling via interface states is
treated not in itself, but in parallel with direct tunneling. The spin
accumulation induced in the semiconductor channel is not suppressed, as
previously argued, but genuinely enhanced by the additional spin current via
interface states. Spin detection with a ferromagnetic contact yields a weighted
average of the spin accumulation in the channel and in the localized states. In
the regime where the spin accumulation in the localized states is much larger
than that in the channel, the detected spin signal is insensitive to the spin
accumulation in the localized states and the ferromagnet probes the spin
accumulation in the semiconductor channel.",1203.4034v1
2012-03-25,First Principles Calculation of Helical Spin Order in Iron Perovskite SrFeO3 and BaFeO3,"Motivated by recent discovery of ferromagnetism in cubic perovskite BaFeO3
under small magnetic field, we investigate spin order in BaFeO3 and
isostructual SrFeO3 by the first principles calculation. The on-site Coulomb
and exchange interactions are necessary for the helical spin order consistent
with experiments. SrFeO3 exhibits stable G-type helical order, while A- and
G-type helical orders in BaFeO3 are almost degenerate at short propagating
vector with tiny energetic barrier with respect to ferromagnetic spin order,
explaining ferromagnetism under small field. The results are consistent with
model calculation where negative charge-transfer energy is explicitly taken
into account.",1203.5470v1
2012-03-28,Theory of integer quantum Hall effect in insulating bilayer graphene,"A variational ground state for insulating bilayer graphene (BLG), subject to
quantizing magnetic fields, is proposed. Due to the Zeeman coupling, the layer
anti-ferromagnet (LAF) order parameter in fully gapped BLG gets projected onto
the spin easy plane, and simultaneously a ferromagnet order, which can further
be enhanced by exchange interaction, develops in the direction of the magnetic
field. The activation gap for the $\nu=0$ Hall state then displays a crossover
from quadratic to linear scaling with the magnetic field, as it gets stronger,
and I obtain excellent agreement with a number of recent experiments with
realistic strengths for the ferromagnetic interaction. A component of the LAF
order, parallel to the external magnetic field, gives birth to additional
incompressible Hall states at filling $\nu=\pm 2$, whereas the remote hopping
in BLG yields $\nu=\pm 1$ Hall states. Evolution of the LAF order in tilted
magnetic fields, scaling of the gap at $\nu=2$, the effect of external electric
fields on various Hall plateaus, and different possible hierarchies of
fractional quantum Hall states are highlighted.",1203.6340v3
2012-06-06,Fractional Spin Josephson Effect and Electrically Controlled Magnetization in Quantum Spin Hall Edges,"We explore a spin Josephson effect in a system of two ferromagnets coupled by
a tunnel junction formed of 2D time-reversal invariant topological insulators.
In analogy with the more commonly studied instance of the Josephson effect for
charge in superconductors, we investigate properties of the phase-coherent {\it
spin} current resulting from the misalignment of the in-plane magnetization
angles of the two ferromagnets. We show that the topological insulating barrier
offers the exciting prospect of hosting a {\it fractional} spin Josephson
effect mediated by bound states at the ferromagnet-topological insulator
interface. We provide multiple perspectives to understand the $4\pi$ periodic
nature of this effect. We discuss several measurable consequences, such as, the
generation of a transverse voltage signal which allows for purely electrical
measurements, an inverse of this effect where an applied voltage gives rise to
a transverse spin-current, and a fractional AC spin-Josephson effect.",1206.1295v2
2012-06-08,Spin-dependent Seebeck coefficients of Ni_{80}Fe_{20} and Co in nanopillar spin valves,"We have experimentally determined the spin-dependent Seebeck coefficient of
permalloy (Ni_{80}Fe_{20}) and cobalt (Co) using nanopillar spin valve devices.
The devices were specifically designed to completely separate heat related
effects from charge related effects. A pure heat current through the nanopillar
spin valve, a stack of two ferromagnetic layers (F) separated by a non-magnetic
layer (N), leads to a thermovoltage proportional to the spin-dependent Seebeck
coefficient S_{S}=S_{\uparrow}-S_{\downarrow} of the ferromagnet, where
S_{\uparrow} and S_{\downarrow} are the Seebeck coefficient for spin-up and
spin-down electrons. By using a three-dimensional finite-element model (3D-FEM)
based on spin-dependent thermoelectric theory, whose input material parameters
were measured in separate devices, we were able to accurately determine a
spin-dependent Seebeck coefficient of -1.8 microvolt/Kelvin and -4.5
microvolt/Kelvin for cobalt and permalloy, respectively corresponding to a
Seebeck coefficient polarization P_{S}=S_{S}/S_{F} of 0.08 and 0.25, where
S_{F} is the Seebeck coefficient of the ferromagnet. The results are in
agreement with earlier theoretical work in Co/Cu multilayers and spin-dependent
Seebeck and spin-dependent Peltier measurements in Ni_{80}Fe_{20}/Cu spin valve
structures.",1206.1659v1
2012-06-13,"The nature of 4f electron magnetism in the diluted ferromagnetic Kondo lattice, CeIr2B2","We report on the physical properties of the series Ce_(1-x)La_xIr_2B_2 (x D
0-0.9), obtained by means of magnetization, heat capacity and electrical
resistivity measurements as a function of temperature (down to 0.7 K for the
latter two measurements). The Curie temperature of CeIr2B2 (?5 K) is lowered
due to La substitution, as expected. However, no quantum critical point or
'non-Fermi liquid' behavior was observed even in the dilute limit of x D 0:9.
Interestingly, ferromagnetic ordering persists even for Ce0:1La0:9Ir2B2, below
0.8 K. Among the Ce systems, CeIr2B2 is one of the compounds in which direct
4f-4f interaction does not appear to play any role in the magnetism, which is
controlled by the indirect exchange interaction alone. In this compound, the
Kondo effect persists in the ferromagnetic ordered state, as inferred from the
entropy data.",1206.2737v1
2012-06-18,Competing ferromagnetic and nematic alignment in self-propelled polar particles,"We study a Vicsek-style model of self-propelled particles where ferromagnetic
and nematic alignment compete in both the usual ""metric"" version and in the
""metric-free"" case where a particle interacts with its Voronoi neighbors. We
show that the phase diagram of this out-of-equilibrium XY model is similar to
that of its equilibrium counterpart: the properties of the fully-nematic model,
studied before in [F. Ginelli, F. Peruani, M. Baer, and H. Chat\'e, Phys. Rev.
Lett. 104, 184502 (2010)], are thus robust to the introduction of a modest bias
of interactions towards ferromagnetic alignment. The direct transitions between
polar and nematic ordered phases are shown to be discontinuous in the metric
case, and continuous, belonging to the Ising universality class, in the
metric-free version.",1206.3811v1
2012-06-27,Nano-pattern induced ferromagnetism in strongly correlated electrons,"Band ferromagnetism in strongly correlated electron systems is one of the
most challenging issue in today's condensed-matter physics. In this theoretical
work, we study the competition between kinetic term, Coulomb repulsion, and
on-site correlated disorder for various lattice geometries. Unconventional and
complex ferromagnetic phase diagrams are obtained: wide region of stability,
cascade of transitions, re-entrance, high sensitivity to the carrier
concentration and strongly inhomogeneous ground states for relatively weak
on-site potential. The direct and systematic comparison with Exact
Diagonalization shows that the Unrestricted Hartree-Fock method is unexpectedly
accurate for such systems, which allows large size cluster calculations. A
match of the order of 99.9% for weak and intermediate couplings is found,
slightly reduced to about 95% in the large repulsion regime. Nano-patterned
lattices appear to be particularly promising candidates that could, with the
tremendous progress in growing and self-organized techniques, be synthesized in
a near future.",1206.6218v2
2012-07-06,Ferromagnetic Quantum critical behavior in three-dimensional Hubbard model with transverse anisotropy,"One-band Hubbard model with transverse anisotropy is considered at density of
electrons $n=0.4$. It is shown that when the anisotropy is appropriately
chosen, the ground state is ferromagnetic with magnetic order perpendicular to
the anisotropy. The increasing of the ratio $\frac tU$, where $t$ is the
hopping parameter and $U$ is the Coulomb repulsion, decreases the Curie
temperature, and the system arrives at the quantum critical point $(T_C=0)$.
The result is obtained introducing Schwinger bosons and slave Fermions
representation of the electron operators. Integrating out the spin-singlet
Fermi fields an effective Heisenberg model with ferromagnetic exchange constant
is obtained for vectors which identifies the local orientation of the spin of
the itinerant electrons. The amplitude of the spin vectors is an effective spin
of the itinerant electrons accounting for the fact that some sites, in the
ground state, are doubly occupied or empty. Owing to the anisotropy, the magnon
fluctuations drive the system to quantum criticality and when the effective
spin is critically small these fluctuations suppress the magnetic order.",1207.1674v1
2012-07-09,Collective Edge Modes of a Quantum Hall Ferromagnet in Graphene,"We derive an effective field-theoretical model for the one-dimensional
collective mode associated with a domain wall in a quantum Hall ferromagnetic
state, as realized in confined graphene systems at zero filling. To this end,
we consider the coupling of a quantum spin ladder forming near a kink in the
Zeeman field to the spin fluctuations of a neighboring spin polarized
two-dimensional environment. It is shown, in particular, that such coupling may
induce anisotropy of the exchange coupling in the legs of the ladder.
Furthermore, we demonstrate that the resulting ferromagnetic spin-1/2 ladder,
subject to a kinked magnetic field, can be mapped to an antiferromagnetic spin
chain at zero magnetic field.",1207.2069v1
2012-07-12,Griffiths singularity and magnetic phase diagram of La1-xCaxCoO3,"Magnetic properties of La$_{1-x}$Ca$_{x}$CoO$_{3}$ (0.10 $\leq x\leq$ 0.25)
are systemically studied in this work. All the samples exhibits the
ferromagnetic state at low temperatures. However, their inverse low-field
magnetic susceptibilities shows a sharply downward deviation from
high-temperature Curie-Weiss paramagnetic behavior well above the ferromagnetic
transition temperature ($T_C$), which indicates the presence of a ferromagnetic
clustered state above $T_C$. A detailed analysis on the susceptibilities
reveals that the short-range state in these Ca-doped samples can be well
described as the Griffiths phase. This characteristic is quite different from
those of the clustered states above $T_C$ recently reported in Sr- and Ba-doped
cobaltites, which are non-Griffith-like. It is proposed that this difference
possibly arises from the unique dependence of magnetic interactions among
Co$^{3+}$ ions on the size of the dopant in the doped cobaltites. Based on
these results, the magnetic diagram of the Ca-doped cobaltites is established.",1207.2818v1
2012-07-12,"Exchange interactions and Tc in rhenium doped silicon: DFT, DFT+U and Monte Carlo calculations","Interactions between rhenium impurities in silicon are investigated by means
of the density functional theory (DFT) and the DFT+U scheme. All couplings
between impurities are ferromagnetic except the Re-Re dimers which in the DFT
method are nonmagnetic, due to formation of the chemical bond supported by
substantial relaxation of the geometry. The critical temperature is calculated
by means of classical Monte Carlo (MC) simulations with the Heisenberg
hamiltonian. The uniform ferromagnetic phase is obtained with the DFT exchange
interactions at room temperature for the impurities concentration of 7%. With
the DFT+U exchange interactions, the ferromagnetic clusters form above room
temperature in MC samples containing only 3% Re.",1207.3059v1
2012-07-18,Temperature dependence of the electronic structure and Fermi-surface reconstruction of Eu(1-x)Gd(x)O through the ferromagnetic metal-insulator transition,"We present angle-resolved photoemission spectroscopy of Eu(1-x)Gd(x)O through
the ferromagnetic metal-insulator transition. In the ferromagnetic phase, we
observe Fermi surface pockets at the Brillouin zone boundary, consistent with
density functional theory, which predicts a half metal. Upon warming into the
paramagnetic state, our results reveal a strong momentum-dependent evolution of
the electronic structure, where the metallic states at the zone boundary are
replaced by pseudogapped states at the Brillouin zone center due to the absence
of magnetic long-range order of the Eu 4f moments.",1207.4490v1
2012-08-12,Enhanced Andreev reflection in gapped graphene,"We theoretically demonstrate unusual features of superconducting proximity
effect in gapped graphene which presents a pseudospin symmetry-broken
ferromagnet with a net pseudomagnetization. We find that the presence of a band
gap makes the Andreev conductance of graphene superconductor/pseudoferromagnet
(S/PF) junction to behave similar to that of a graphene
ferromagnet-superconductor junction. The energy gap $\Delta_N$ enhance the
pseudospin inverted Andreev conductance of S/PF junction to reach a limiting
maximum value for $\Delta_N\gg \mu$, which depending on the bias voltage can be
larger than the value for the corresponding junction with no energy gap. We
further demonstrate a damped-oscillatory behavior for the local density of
states of the PF region of S/PF junction and a long-range crossed Andreev
reflection process in PF/S/PF structure with antiparallel alignment of
pseudomagnetizations of PFs, which confirm that, in this respect, the gapped
normal graphene behaves like a ferromagnetic graphene.",1208.2461v1
2012-08-21,Dissipationless Spin Current between Two Coupled Ferromagnets,"We demonstrate the general principle which states that a dissipationless spin
current flows between two coupled ferromagnets if their magnetic orders are
misaligned. This principle applies regardless the two ferromagnets are metallic
or insulating, and also generally applies to bulk magnetic insulators. On a
phenomenological level, this principle is analogous to Josephson effect, and
yields a dissipationless spin current that is independent from scattering. The
microscopic mechanisms for the dissipationless spin current depend on the
systems, which are elaborated in details. A uniform, static magnetic field is
further proposed to be an efficient handle to create the misaligned
configuration and stabilize the dissipationless spin current.",1208.4274v2
2012-08-26,Analysis of the Kondo effect in ferromagnetic atomic-sized contacts,"Atomic contacts made of ferromagnetic metals present zero-bias anomalies in
the differential conductance due to the Kondo effect. These systems provide a
unique opportunity to perform a statistical analysis of the Kondo parameters in
nanostructures since a large number of contacts can be easily fabricated using
break-junction techniques. The details of the atomic structure differ from one
contact to another so a large number of different configurations can be
statistically analyzed. Here we present such a statistical analysis of the
Kondo effect in atomic contacts made from the ferromagnetic transition metals
Ni, Co and Fe. Our analysis shows clear differences between materials that can
be understood by fundamental theoretical considerations. This combination of
experiments and theory allow us to extract information about the origin and
nature of the Kondo effect in these systems and to explore the influence of
geometry and valence in the Kondo screening of atomic-sized nanostructures.",1208.5257v1
2012-08-29,Spin-orbital coupling in a triplet superconductor-ferromagnet junction,"We study a novel type of coupling between spin and orbital degrees of freedom
which appears at triplet superconductor-ferromagnet interfaces. Using a
self-consistent spatially-dependent mean-field theory, we show that increasing
the angle between the ferromagnetic moment and the triplet vector order
parameter enhances or suppresses the p-wave gap close to the interface,
according as the gap antinodes are parallel or perpendicular to the boundary,
respectively. The associated change in condensation energy establishes an
orbitally-dependent preferred orientation for the magnetization. When both gap
components are present, as in a chiral superconductor, we observe a first-order
transition between different moment orientations as a function of the exchange
field strength.",1208.5871v2
2012-09-20,Transport in multi-terminal superconductor/ferromagnet junctions having spin-dependent interfaces,"We study electronic transport in junctions consisting of a superconductor
electrode and two ferromagnet (F) leads in which crossed Andreev reflections
(CAR) and elastic cotunnelings are accommodated. We model the system using an
extended Blonder-Tinkham-Klapwijk treatment with a key modification that
accounts for spin-dependent interfacial barriers (SDIB). We compute
current-voltage relations as a function of parameters characterizing the SDIB,
magnetization in the F leads, geometry of the junction, and temperature. Our
results reveal a rich range of significantly altered physics due to a
combination of interfering spin-dependent scattering processes and population
imbalance in the ferromagnets, such as a significant enhancement in CAR current
and a sign change in the relative difference between resistance of two cases
having a antiparallel or parallel alignment of the magnetization in the F
leads, respectively. Our model accounts for the surprising experimental
findings of positive relative resistance by M. Colci et al. [Phys. Rev. B 85,
180512(R) (2012)] as well as previously measured negative relative resistance
results, both within sufficiently large parameter regions.",1209.4478v2
2012-09-21,Dominant itinerant ferromagnetism in Eu0.5Sr0.5CoO3: evidences from both critical analysis and Rhodes-Wohlfarth's criterion,"The critical behaviors of ferromagnet Eu0.5Sr0.5CoO3 arround TC=140.5K have
been comprehensively investigated by analyzing a series of isothermal
magnetization M(H) curves. Both Modified Arrott plot and Kouvel-Fisher methods
give nearly the same critical exponents, which scale nicely the M(H) curves
into two different branches below and above TC. The exponents {\gamma}=1.044
and {\delta}=3.06 demonstrate the relevance of mean-field characters for this
material. The conclusion of mean-field behavior proves a dominant itinerant
ferromagnetism (FM) due to a long range exchange interaction in the system.
Meanwhile, by using Rhodes-Wohlfarth's criterion [P. Rhodes and E. P.
Wohlfarth, Proc. R. Soc. Lond. A 273, 247 (1963)], it is further confirmed that
the itinerant FM dominates in the system.",1209.4790v2
2012-09-27,Theory of Strain-Controlled Magnetotransport and Stabilization of the Ferromagnetic Insulating Phase in Manganite Thin Films,"We show that applying strain on half-doped manganites makes it possible to
tune the system to the proximity of a metal-insulator transition and thereby
generate a colossal magnetoresistance (CMR) response. This phase competition
not only allows control of CMR in ferromagnetic metallic manganites but can be
used to generate CMR response in otherwise robust insulators at half-doping.
Further, from our realistic microscopic model of strain and magnetotransport
calculations within the Kubo formalism, we demonstrate a striking result of
strain engineering that, under tensile strain, a ferromagnetic charge-ordered
insulator, previously inaccessible to experiments, becomes stable.",1209.6174v2
2012-10-04,Ferromagnetic order in Yb(Rh$_{0.73}$Co$_{0.27}$)$_{2}$Si$_{2}$,"We present the discovery of ferromagnetism in single crystalline
Yb(Rh$_{0.73}$Co$_{0.27}$)$_{2}$Si$_{2}$ below $T_{C} = 1.30\,$K with a
spontaneous magnetic moment of $0.1\,\mu_{B}$/Yb along the crystallographic
c-axis. This is shown by the huge c-susceptibility peak, the hysteresis in
magnetization as well as by the field-dependent susceptibility and specific
heat data. This discovery motivates the reinvestigation of the magnetic order
in Yb(Rh$_{1-x}$Co$_{x}$)$_{2}$Si$_{2}$ with $x < 0.27$ and in pure
YbRh$_{2}$Si$_{2}$ under small pressures with field along the $c$-direction to
look for low-lying ferromagnetic order.",1210.1345v2
2012-10-12,Topological Magnon Insulator in Insulating Ferromagnet,"In the ferromagnetic insulator with Dzyaloshinskii-Moriya interaction, we
theoretically predict and numerically verify a topological magnon insulator,
where the charge-free magnon is topologically protected to transport along the
edge while it is insulating in the bulk. Within the bulk band gaps, edge states
form a connected loop as a $4\pi$- or $8\pi$-period M\""{o}bius strip in the
wave vector space. As a consequence, the chiral energy current traveling along
the corresponding edge is topologically protected from defects or disorders.
Using the nonequilibrium Green's function method, we demonstrate that the
energy current carried by magnons with energy in the bulk gap localizes at
edges and prefers to travel along one edge in only one direction at
nonequilibrium steady state. Our prediction about topological magnon insulator
could be observed at a wide energy range in the thin film of the insulating
ferromagnet, such as Lu$_2$V$_2$O$_7$.",1210.3487v2
2012-10-18,Measurement of Magnetic Exchange in Ferromagnet-Superconductor La2/3Ca1/3MnO3/YBa2Cu3O7 Bilayers,"The existence of coherent magnetic correlations in the normal phase of
cuprate high-temperature superconductors has proven difficult to measure
directly. Here we report on a study of ferromagnetic-superconductor bilayers of
La2/3Ca1/3MnO3/YBa2Cu3O7 (LCMO/YBCO) with varying YBCO layer thicknesses. Using
x-ray magnetic circular dichroism, we demonstrate that the ferromagnetic layer
induces a Cu magnetic moment in the adjacent high-temperature superconductor.
For thin samples, this moment exists at all temperatures below the Curie
temperature of the LCMO layer. However, for a YBCO layer thicker than 12 unit
cells, the Cu moment is suppressed for temperatures above the superconducting
transition, suggesting this to be a direct measurement of magnetic coherence in
the normal state of a superconducting oxide.",1210.5049v1
2012-10-18,Proximity effects in spin-triplet superconductor-ferromagnet heterostucture with spin-active interface,"We study the physical properties of a ballistic heterostructure made of a
ferromagnet (FM) and a spin-triplet superconductor (TSC) with a layered
structure stacking along the direction perpendicular to the planes where a
chiral px+ipy pairing occurs and assuming spin dependent processes at the
interface. We use a self-consistent Bogoliubov-de Gennes approach on a
three-dimensional lattice to obtain the spatial profiles of the pairing
amplitude and the magnetization. We find that, depending on the strength of the
ferromagnetic exchange field, the ground state of the system can have two
distinct configurations with a parallel or anti-parallel collinearity between
the magnetic moments in the bulk and at the interface. We demonstrate that a
magnetic state having non coplanar interface, bulk and Cooper pairs spins may
be stabilized if the bulk magnetization is assumed to be fixed along a given
direction. The study of the density of states reveals that the modification of
the electronic spectrum in the FM plays an important role in the setting of the
optimal magnetic configuration. Finally, we find the existence of induced
spin-polarized pair correlations in the FM-TSC system.",1210.5160v2
2012-10-31,Scattering-Independent Anomalous Nernst Effect in Ferromagnets,"Using the full-potential linearized augmented plane-wave method within the
density functional theory, we compute all contributions to the scattering
independent part of the thermoelectric conductivity tensor, namely the
intrinsic contribution and the side-jump contribution. For the ferromagnetic
materials bcc Fe, hcp Co, fcc Ni and L1_0 ordered alloys FePd and FePt, our
investigations of the energy and temperature dependence of the intrinsic and
side-jump contributions show that they are both of equal importance. Overall,
our calculations are able to correctly reproduce the order of magnitude and
sign of the experimentally measured signal, suggesting that the scattering
independent part plays an important role in the anomalous Nernst effect of
ferromagnets.",1210.8283v2
2012-11-07,Correlation-mediated processes for electron-induced switching between Neel states of Fe anti-ferromagnetic chains,"The controlled switching between two quasi-stable Neel states in adsorbed
anti-ferromagnetic Fe chains has recently been achieved by Loth et al [Science
335, 196 (2012)]. In order to rationalize their data, we evaluate the rate of
tunneling electron-induced switching between the N\'eel states. Good agreement
is found with the experiment permitting us to identify three switching
mechanisms: (i) low-bias direct electron-induced transitions, (ii)
intermediate-bias switching via spin-wave-like excitation, and (iii) high-bias
transitions mediated by domain wall formation. Spin correlations in the
anti-ferromagnetic chains are the switching driving force leading to a marked
chain-size dependence.",1211.1538v1
2012-11-13,Singlet-triplet conversion and the long-range proximity effect in superconductor-ferromagnet structures with generic spin dependent fields,"The long-range proximity effect in superconductor/ferromagnet (S/F) hybrid
nano-structures is observed if singlet Cooper pairs from the superconductor are
converted into triplet pairs which can diffuse into the fer- romagnet over
large distances. It is commonly believed that this happens only in the presence
of magnetic inhomogeneities. We show that there are other sources of the
long-range triplet component (LRTC) of the con- densate and establish general
conditions for their occurrence. As a prototypical example we consider first a
system where the exchange field and spin-orbit coupling can be treated as time
and space components of an effective SU(2) potential. We derive a SU(2)
covariant diffusive equation for the condensate and demonstrate that an
effective SU(2) electric field is responsible for the long-range proximity
effect. Finally, we extend our analysis to a generic ferromagnet and establish
a universal condition for the LRTC. Our results open a new avenue in the search
for such correlations in S/F structures and make a hitherto unknown connection
between the LRTC and Yang-Mills electrostatics.",1211.3084v2
2012-12-04,Dynamics of Ising models near zero temperature : Real Space Renormalization Approach,"We consider the stochastic dynamics of Ising ferromagnets (either pure or
random) near zero temperature. The master equation satisfying detailed balance
can be mapped onto a quantum Hamiltonian which has an exact zero-energy ground
state representing the thermal equilibrium. The largest relaxation time
$t_{eq}$ governing the convergence towards this Boltzmann equilibrium in
finite-size systems is determined by the lowest non-vanishing eigenvalue
$E_1=1/t_{eq}$ of the quantum Hamiltonian $H$. We introduce and study a
real-space renormalization procedure for the quantum Hamiltonian associated to
the single-spin-flip dynamics of Ising ferromagnets near zero temperature. We
solve explicitly the renormalization flow for two cases. (i) For the
one-dimensional random ferromagnetic chain with free boundary conditions, the
largest relaxation time $t_{eq}$ can be expressed in terms of the set of random
couplings for various choices of the dynamical transition rates. The validity
of these RG results in $d=1$ is checked by comparison with another approach.
(ii) For the pure Ising model on a Cayley tree of branching ratio $K$, we
compute the exponential growth of $t_{eq}(N)$ with the number $N$ of
generations.",1212.0643v2
2012-12-12,Strong fluctuations near the frustration point in cubic lattice ferromagnets with localized moments,"Thermodynamic properties of cubic Heisenberg ferromagnets with competing
exchange interactions are considered near the frustration point where the
coefficient $D$ in the spin-wave spectrum $E_{\mathbf{k}}\sim D k^{2}$
vanishes. Within the Dyson-Maleev formalism it is found that at low
temperatures thermal fluctuations stabilize ferromagnetism by increasing the
value of $D$. For not too strong frustration this leads to an unusual ""concave""
shape of the temperature dependence of magnetization, which is in agreement
with experimental data on the europium chalcogenides. The phase diagram is
constructed by means of Monte Carlo simulation, and suppression of
magnetization and Curie temperature is found in comparison with the results of
the spin-wave theory. This effect is explained by the the presence of
non-analytical corrections to the spin-wave spectrum which are represented in
the lowest order by the term $\sim (T/S)^{2} k^{2}\log{k}$.",1212.2773v2
2012-12-13,Spin injection from a normal metal into a mesoscopic superconductor,"We report on nonlocal transport in superconductor hybrid structures, with
ferromagnetic as well as normal-metal tunnel junctions attached to the
superconductor. In the presence of a strong Zeeman splitting of the density of
states, both charge and spin imbalance is injected into the superconductor.
While previous experiments demonstrated spin injection from ferromagnetic
electrodes, we show that spin imbalance is also created for normal-metal
injector contacts. Using the combination of ferromagnetic and normal-metal
detectors allows us to directly discriminate between charge and spin injection,
and demonstrate a complete separation of charge and spin imbalance. The
relaxation length of the spin imbalance is of the order of several $\mu$m and
is found to increase with a magnetic field, but is independent of temperature.
We further discuss possible relaxation mechanisms for the explanation of the
spin relaxation length.",1212.3164v1
2012-12-19,"Theory of the spin Hall effect, and its inverse, in a ferromagnetic metal near the Curie temperature","We give a theory of the inverse spin Hall effect (ISHE) in ferromagnetic
metals based on skew scattering via collective spin fluctuations. This extends
Kondo's theory of the anomalous Hall effect (AHE) to include short-range
spin-spin correlations. We find a relation between the ISHE and the four-spin
correlations near the Curie temperature TC. Such four-spin correlations do not
contribute to the AHE, which relates to the three-spin correlations. Thus our
theory shows an essential difference between the AHE and ISHE, providing an
essential complement to Kondo's classic theory of the AHE in metals. We note
the relation to skew-scattering mechanisms based on impurity scattering. Our
theory can be compared to recent experimental results byWei et al. [Nat.
Commun. 3, 1058 (2012)] for the ISHE in ferromagnetic alloys.",1212.4561v1
2012-12-20,Global phase diagram of a doped Kitaev-Heisenberg model,"The global phase diagram of a doped Kitaev-Heisenberg model is studied using
an SU(2) slave-boson mean-field method. Near the Kitaev limit, p-wave
superconducting states which break the time-reversal symmetry are stabilized as
reported by You {\it et al.} [Phys. Rev. B {\bf 86}, 085145 (2012)]
irrespective of the sign of the Kitaev interaction. By further doping, a d-wave
superconducting state appears when the Kitaev interaction is antiferromagnetic,
while another p-wave superconducting state appears when the Kitaev interaction
is ferromagnetic. This p-wave superconducting state does not break the
time-reversal symmetry as reported by Hyart {\it et al.} [Phys. Rev. B {\bf
85}, 140510 (2012)], and such a superconducting state also appears when the
antiferromagnetic Kitaev interaction and the ferromagnetic Heisenberg
interaction compete. This work, thus, demonstrates the clear difference between
the antiferromagnetic Kitaev model and the ferromagnetic Kitaev model when
carriers are doped while these models are equivalent in the undoped limit, and
how novel superconducting states emerge when the Kitaev interaction and the
Heisenberg interaction compete.",1212.5218v2
2012-12-21,Domain-wall-controlled transverse spin injection,"We propose an effect whereby an electric current along the interface between
a ferromagnetic and normal metal leads to injection of pure spin current into
the normal metal, if the magnetization-direction in the ferromagnet varies
along the direction of current. For the specific example of a ferromagnetic
domain wall, we compute the inverse spin-Hall effect voltage this spin current
gives rise to when injected into a Pt layer. Furthermore, we show that this
pure spin current leads to modification of the parameters that govern spin
transfer and current-driven domain-wall motion, which can be use to optimize
the latter in layered magnetic systems. This effect in principle enables
control over the location of spin-current injection in devices.",1212.5435v1
2013-01-01,Using x-ray diffraction to identify precipitates in transition metal doped semiconductors,"In the past decade, room temperature ferromagnetism was often observed in
transition metal doped semiconductors, which were claimed as diluted magnetic
semiconductors (DMS). Nowadays intensive activities are devoted to clarify
wether the observed ferromagnetism stems from carrier mediated magnetic
impurities, ferromagnetic precipitates, or spinodal decomposition. In this
paper, we have correlated the structural and magnetic properties of transition
metal doped ZnO, TiO2, and Si, prepared by ion implantation. Crystalline
precipitates, i.e., transition metal (Co, Ni) and Mn-silicide nanocrystals, are
responsible for the magnetism. Additionally due to their orientation nature
with respect to the host, these nanocrystals in some cases are not detectable
by conventional x-ray diffraction (XRD). This nature results in the pitfall of
using XRD to exclude magnetic precipitates in DMS materials.",1301.0100v1
2013-01-09,Nonlocal Thermoelectric Effects and Nonlocal Onsager Relations in a Three-Terminal Proximity-Coupled Superconductor-Ferromagnet Device,"We study thermal and charge transport in a three-terminal setup consisting of
one superconducting and two ferromagnetic contacts. We predict that the
simultaneous presence of spin filtering and of spin- dependent scattering phase
shifts at each of the two interfaces will lead to very large nonlocal thermo-
electric effects both in clean and in disordered systems. The symmetries of
thermal and electric transport coefficients are related to fundamental
thermodynamic principles by the Onsager reciprocity. Our results show that a
nonlocal version of the Onsager relations for thermoelectric currents holds in
a three-terminal quantum coherent ferromagnet-superconductor heterostructure
including a spin-dependent crossed Andreev reflection and coherent electron
transfer processes.",1301.1840v2
2013-01-14,Polarised Electromagnetic wave propagation through the ferromagnet: Phase boundary of dynamic phase transition,"The dynamical responses of ferromagnet to the propagating electromagnetic
field wave passing through it are modelled and studied here by Monte Carlo
simulation in two dimensional Ising ferromagnet. Here, the electromagnetic wave
is linearly polarised in such a way that the direction of magnetic field is
parallel to that of the magnetic momemts (spins). The coherent propagating mode
of spin-clusters is observed. The time average magnetisation over the full
cycle (time) of the field defines the order parameter of the dynamic
transition. Depending on the value of the temperature and the amplitude of the
propagating magnetic field wave, a dynamical phase transition is observed. The
dynamic transition was detected by studying the temperature dependences of the
dynamic order parameter, the variance of the dynamic order parameter, the
derivative of the dynamic order parameter and the dynamic specific heat. The
phase boundaries of the dynamic transitions were drawn for two different values
of the wave lengths of the propagating magnetic field wave. The phase boundary
was observed to shrink (inward) for lower speed of propagation of the EM wave.
The divergence of the releavant length scale was observed at the transition
point.",1301.3071v2
2013-01-14,Effect of Uniaxial Strain on Ferromagnetic Instability and Formation of Localized Magnetic States on Adatoms in Graphene,"We investigate the effect of an applied uniaxial strain on the ferromagnetic
instability due to long- range Coulomb interaction between Dirac fermions in
graphene. In case of undeformed graphene the ferromagnetic exchange instability
occurs at sufficiently strong interaction within the Hartree- Fock
approximation. In this work we show that using the same theoretical framework
but with an additional applied uniaxial strain, the transition can occur for
much weaker interaction, within the range in suspended graphene. We also study
the consequence of strain on the formation of localized magnetic states on
adatoms in graphene. We systematically analyze the interplay between the
anisotropic (strain- induced) nature of the Dirac fermions in graphene, on-
site Hubbard interaction at the impurity and the hybridization between the
graphene and impurity electrons. The polarization of the electrons in the
localized orbital is numerically calculated within the mean- field self-
consistent scheme. We obtain complete phase diagram containing non- magnetic as
well as magnetic regions and our results can find prospective application in
the field of carbon- based spintronics.",1301.3169v1
2013-01-16,Epitaxially Strained BiMnO3 Films: High-Temperature Robust Multiferroic Materials with Novel Magnetoelectric Coupling,"Multiferroics with the coexistence of ferroelectric and ferromagnetic orders
are ideal candidates for magnetoelectric applications. Unfortunately, only very
few ferroelectric-ferromagnetic multiferroics (with low magnetic critical
temperature) were discovered. Here we perform first principles calculations to
investigate the effects of the epitaxial strain on the properties of BiMnO3
films grown along the pseudocubic [001] direction. Unlike the ground state with
the centrosymmetric C2/c space group in bulk, we reveal that the tensile
epitaxial strain stabilizes the ferromagnetic and ferroelectric Cc state with a
large polarization (P > 80 {\mu}C/cm2) and high Curie temperature (Tc is
predicted to be between 169 K and 395 K). More importantly, there is a novel
intrinsic magnetoelectric coupling in the multiferroic Cc state with the easy
magnetization axis controllable by the external electric field.",1301.3660v2
2013-02-06,Ferromagnetic Kondo effect in a triple quantum dot system,"We propose that a simple device of three laterally-coupled quantum dots, the
central one contacted by metal leads, can realize the ferromagnetic Kondo
model, which is characterized by interesting properties like a non-analytic
inverted zero-bias anomaly and an extreme sensitivity to a magnetic field.
Furthermore, by tuning the gate voltages of the lateral dots, this device may
allow to study the transition from ferromagnetic to antiferromagnetic Kondo
effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model
the device by three coupled Anderson impurities that we study by numerical
renormalization group. We calculate the single-particle spectral function of
the central dot, which at zero frequency is proportional to the zero-bias
conductance, across the transition, both in the absence and in the presence of
a magnetic field.",1302.1499v2
2013-02-09,Current-driven dynamics of chiral ferromagnetic domain walls,"In most ferromagnets the magnetization rotates from one domain to the next
with no preferred handedness. However, broken inversion symmetry can lift the
chiral degeneracy, leading to topologically-rich spin textures such as
spin-spirals and skyrmions via the Dzyaloshinskii-Moriya interaction (DMI).
Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy
metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin
texture enables extremely efficient current-driven motion. We show that spin
torque from the spin Hall effect drives DWs in opposite directions in
Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a
N\'eel configuration with left-handed chirality. We directly confirm the DW
chirality and rigidity by examining current-driven DW dynamics with magnetic
fields applied perpendicular and parallel to the spin spiral. This work
resolves the origin of controversial experimental results and highlights a new
path towards interfacial design of spintronic devices.",1302.2257v1
2013-02-13,Ferromagnetism and the formation of interlayer As2-dimers in Ca(Fe1-xNix)2As2,"The compounds Ca(Fe1-xNix)2As2 with the tetragonal ThCr2Si2-type structure
(space group I4/mmm) show a continuous transition of the interlayer As-As
distances from a non-bonding state in CaFe2As2 (dAs-As = 313 pm) to
single-bonded As2-dimers in CaNi2As2 (dAs-As = 260 pm). Magnetic measurements
reveal weak ferromagnetism which develops near the composition
Ca(Fe0.5Ni0.5)2As2, while the compounds with lower and higher nickel
concentrations both are Pauli-paramagnetic. DFT band structure calculations
reveal that the As2-dimer formation is a consequence of weaker metal-metal in
MAs4-layers (M = Fe1-xNix) of Ni-richer compounds, and depends not on
depopulation or shift of As-As antibonding states as suggested earlier. Our
results also indicate that the ferromagnetism of Ca(Fe0.5Ni0.5)2As2 and related
compounds like SrCo2(Ge0.5P0.5)2 is probably not induced by dimer breaking as
recently suggested, but arises from the high density of states generated by the
transition metal 3d bands near the Fermi level without contribution of the
dimers.",1302.3046v1
2013-02-17,Long-Range Interaction of Spin-Qubits via Ferromagnets,"We propose a mechanism of coherent coupling between distant spin qubits
interacting dipolarly with a ferromagnet. We derive an effective two-spin
interaction Hamiltonian and estimate the coupling strength. We discuss the
mechanisms of decoherence induced solely by the coupling to the ferromagnet and
show that there is a regime where it is negligible. Finally, we present a
sequence for the implementation of the entangling CNOT gate and estimate the
corresponding operation time to be a few tens of nanoseconds. A particularly
promising application of our proposal is to atomistic spin-qubits such as
silicon-based qubits and NV-centers in diamond to which existing coupling
schemes do not apply.",1302.4017v2
2013-03-02,Super-magnetoresistance effect in triplet spin valves,"We study a triplet spin valve obtained by intercalating a triplet
superconductor spacer between two ferromagnetic regions with non-collinear
magnetizations. We demonstrate that the magnetoresitance of the triplet spin
valve depends on the relative orientations of the d-vector, characterizing the
superconducting state, and the magnetization directions of the ferromagnetic
layers. For devices characterized by a long superconductor, the Cooper pairs
spintronics regime is reached allowing to observe the properties of a polarized
current sustained by Cooper pairs only. In this regime a
super-magnetoresistance effect emerges, and the chiral symmetry of the order
parameter of the superconducting spacer is easily recognized. Our findings open
new perspectives in designing devices based on the cooperative nature of
ferromagnetic and triplet correlations in a spintronic framework.",1303.0375v1
2013-03-13,Ferromagnetic quantum critical point in UCo1-xFexGe,"We have carried out a comprehensive study of the UCo1-xFexGe series across
the entire range of compositions 0 <= x <= 1, and report the results of x-ray
diffraction, magnetization, specific heat, and electrical resistivity to
uncover the T-x phase diagram. Substitution of Fe into UCoGe initially results
in an increase in the Curie temperature and a rapid destruction of the
superconductivity. Near x = 0.22, the ferromagnetic transition is suppressed to
zero temperature at an apparent ferromagnetic itinerant electron quantum
critical point, where the temperature dependence of the electrical resistivity
and specific heat in this region reveal non-Fermi liquid behavior.",1303.3228v1
2013-03-18,Helical glasses near ferromagnetic quantum criticality,"We study the effects of quenched charge disorder on the phase reconstruction
near itinerant ferromagnetic quantum critical points in three spatial
dimensions. Combining a replica disorder average with a fermionic version of
the quantum order-by-disorder mechanism, we show that weak disorder
destabilizes the ferromagnetic state and enhances the susceptibility towards
incommensurate, spiral magnetic ordering. The Goldstone modes of the spiral
phase are governed by a 3d-XY model. The induced disorder in the pitch of the
spiral generates a random anisotropy for the Goldstone modes, inducing vortex
lines in the phase of the helical order and rendering the magnetic correlations
short ranged with a strongly anisotropic correlation length.",1303.4300v2
2013-04-02,Continuous- and discrete-time Glauber dynamics. First- and second-order phase transitions in mean-field Potts models,"As is known, at the Gibbs-Boltzmann equilibrium, the mean-field $q$-state
Potts model with a ferromagnetic coupling has only a first order phase
transition when $q\geq 3$, while there is no phase transition for an
antiferromagnetic coupling. The same equilibrium is asymptotically reached when
one considers the continuous time evolution according to a Glauber dynamics. In
this paper we show that, when we consider instead the Potts model evolving
according to a discrete-time dynamics, the Gibbs-Boltzmann equilibrium is
reached only when the coupling is ferromagnetic while, when the coupling is
anti-ferromagnetic, a period-2 orbit equilibrium is reached and a stable
second-order phase transition in the Ising mean-field universality class sets
in for each component of the orbit. We discuss the implications of this
scenario in real-world problems.",1304.0814v1
2013-04-19,Interfacial Coupling in Multiferroic-Ferromagnet Heterostructures,"We report local probe investigations of the magnetic interaction between
BiFeO3 films and a ferromagnetic Co0.9Fe0.1 layer. Within the constraints of
intralayer exchange coupling in the Co0.9Fe0.1, the multiferroic imprint in the
ferromagnet results in a collinear arrangement of the local magnetization and
the in-plane BiFeO3 ferroelectric polarization. The magnetic anisotropy is
uniaxial, and an in-plane effective coupling field of order 10 mT is derived.
Measurements as a function of multiferroic layer thickness show that the
influence of the multiferroic layer on the magnetic layer becomes negligible
for 3 nm thick BiFeO3 films. We ascribe this breakdown in the exchange coupling
to a weakening of the antiferromagnetic order in the ultrathin BiFeO3 film
based on our X-ray linear dichroism measurements. These observations are
consistent with an interfacial exchange coupling between the CoFe moments and a
canted antiferromagnetic moment in the BiFeO3.",1304.5394v1
2013-04-25,Critical behavior and magnetic relaxation dynamics of Nd0.4Sr0.6MnO3 nanoparticles,"Detailed dc and ac magnetic properties of chemically synthesized
Nd0.4Sr0.6MnO3 with different particle size (down to 27 nm) have been studied
in details. We have found ferromagnetic state in the nanoparticles, whereas,
the bulk Nd0.4Sr0.6MnO3 is known to be an A-type antiferromagnet. A
Griffiths-like phase has also been identified in the nanoparticles. Further,
critical behavior of the nanoparticles has been studied around the second order
ferromagnetic-paramagnetic transition region (|(T-TC)/TC|{\pounds} 0.04) in
terms of modified Arrott plot, Kouvel-Fisher plot and critical isotherm
analysis. The estimated critical exponents (b,g,d) are quite different from
those predicted according to three-dimensional mean-field, Heisenberg and Ising
models. This signifies a quite unusual nature of the size-induced ferromagnetic
state in Nd0.4Sr0.6MnO3. The nanoparticles are found to be interacting and do
not behave like ideal superparamagnet. Interestingly, we find spin glass like
slow relaxation of magnetization, aging and memory effect in the nanometric
samples. These phenomena have been attributed to very broad distribution of
relaxation time as well as to inter-particle interaction. Experimentally, we
have found out that the dynamics of the nanoparticle systems can be best
described by hierarchical model of spin glasses.",1304.6964v1
2013-04-26,Universality Aspects of Layering Transitions in Ferromagnetic Blume-Capel Thin Films,"Critical phenomena and universality behavior of ferromagnetic thin films
described by a spin-1 Blume-Capel Hamiltonian has been examined for various
thickness values ranging from 3 to 40 layers. Using effective field theory, we
have found that crystal field interactions significantly affects the critical
value of surface to bulk ratio of exchange interactions $R_{c}$ at which the
critical temperature becomes independent of film thickness $L$. Moreover, we
have extracted the shift exponent $\lambda$ from computed data. Based on the
results, we have shown that in the presence of surface exchange enhancement,
the system may exhibit a dimensional crossover. We have also found that
presence of crystal field interactions does not affect the value of $\lambda$.
Hence, a ferromagnetic spin-1/2 thin film is in the same universality class
with its spin-1 counterpart.",1304.7250v1
2013-04-26,Landau-Lifshitz theory of the longitudinal spin Seebeck effect,"Thermal-bias-induced spin angular momentum transfer between a paramagnetic
metal and ferromagnetic insulator is studied theoretically based on the
stochastic Landau-Lifshitz-Gilbert (LLG) phenomenology. Magnons in the
ferromagnet establish a nonequilibrium steady state by equilibrating with
phonons via bulk Gilbert damping and electrons in the paramagnet via spin
pumping, according to the fluctuation-dissipation theorem. Subthermal magnons
and the associated spin currents are treated classically, while the appropriate
quantum crossover is imposed on high-frequency magnetic fluctuations. We
identify several length scales in the ferromagnet, which govern qualitative
changes in the dependence of the thermally-induced spin current on the magnetic
film thickness.",1304.7295v2
2013-04-30,Spinmotive force with static and uniform magnetization induced by a time-varying electric field,"A new spinmotive force is predicted in ferromagnets with spin-orbit coupling.
By extending the theory of spinmotive force, we show that a time-varying
electric field can induce a spinmotive force with static and uniform
magnetization. This spinmotive has two advantages; it can be detected free from
the inductive voltage owing to the absence of dynamical magnetization and it
can be tuned by electric fields. To observe the effect, we propose two
experimental setups: electric voltage measurement in a single ferromagnet and
spin injection from a ferromagnet into an attached nonmagnetic conductor.",1304.7822v5
2013-05-01,Weyl fermions and the anomalous Hall effect in metallic ferromagnets,"We reconsider the problem of the anomalous Hall effect in ferromagnetic
SrRuO$_3$, incorporating insights from the recently developed theory of Weyl
semimetals. We demonstrate that SrRuO$_3$ possesses a large number of Weyl
nodes, separated in momentum space, in its bandstructure. While the nodes
normally do not coincide with the Fermi energy, unless the material is doped,
we show that even the nodes inside the Fermi sea have a significant effect on
the physical properties of the material. In particular, we show that the common
belief that (non-quantized part of) the intrinsic anomalous Hall conductivity
of a ferromagnetic metal is entirely a Fermi surface property, is incorrect:
there generally exists a contribution to the anomalous Hall conductivity that
arises from topological Fermi-arc surface states, associated with the Weyl
nodes, which is of the same order of magnitude as the Fermi surface
contribution.",1305.0183v2
2013-05-01,Charge and spin supercurrents in triplet superconductor--ferromagnet--singlet superconductor Josephson junctions,"We study the Josephson effect in a triplet
superconductor--ferromagnet--singlet superconductor junction. We show that the
interaction of tunneling Cooper pairs with the interface magnetization can
permit a Josephson current at the lowest order of a tunneling Hamiltonian
perturbation theory. Two conditions must be satisfied for this to occur: the
magnetization of the ferromagnet has a component parallel to the ${\bf
d}$-vector of the triplet superconductor, and the gaps of the superconductors
have the same parity with respect to the interface momentum. The resulting
charge current displays an unconventional dependence on the orientation of the
magnetic moment and the phase difference. This is accompanied by a
phase-dependent spin current in the triplet superconductor, while a
phase-independent spin current is always present. The tunneling perturbation
theory predictions are confirmed using a numerical Green's function method. An
analytical treatment of a one-dimensional junction demonstrates that our
conclusions are robust far away from the tunneling regime, and reveals
signatures of the unconventional Josephson effect in the critical currents.",1305.0211v2
2013-05-10,Long-Range Interaction of Singlet-Triplet Qubits via Ferromagnets,"We propose a mechanism of a long-range coherent interaction between two
singlet-triplet qubits dipolarly coupled to a dogbone-shaped ferromagnet. An
effective qubit-qubit interaction Hamiltonian is derived and the coupling
strength is estimated. Furthermore we derive the effective coupling between two
spin-1/2 qubits that are coupled via dipolar interaction to the ferromagnet and
that lie at arbitrary positions and deduce the optimal positioning. We consider
hybrid systems consisting of spin-1/2 and ST qubits and derive the effective
Hamiltonian for this case. We then show that operation times vary between 1MHz
and 100MHz and give explicit estimates for GaAs, Silicon, and NV-center based
spin qubits. Finally, we explicitly construct the required sequences to
implement a CNOT gate. The resulting quantum computing architecture retains all
the single qubit gates and measurement aspects of earlier approaches, but
allows qubit spacing at distances of order 1$\,\mu$m for two-qubit gates,
achievable with current semiconductor technology.",1305.2451v1
2013-05-15,Ab initio theory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets,"We report a computational theoretical investigation of electron spin-flip
scattering induced by the electron-phonon interaction in the transition-metal
ferromagnets bcc Fe, fcc Co and fcc Ni. The Elliott-Yafet electron-phonon
spin-flip scattering is computed from first-principles, employing a generalized
spin-flip Eliashberg function as well as ab initio computed phonon dispersions.
Aiming at investigating the amount of electron-phonon mediated demagnetization
in femtosecond laser-excited ferromagnets, the formalism is extended to treat
laser-created thermalized as well as nonequilibrium, nonthermal hot electron
distributions. Using the developed formalism we compute the phonon-induced spin
lifetimes of hot electrons in Fe, Co, and Ni. The electron-phonon mediated
demagnetization rate is evaluated for laser-created thermalized and
nonequilibrium electron distributions. Nonthermal distributions are found to
lead to a stronger demagnetization rate than hot, thermalized distributions,
yet their demagnetizing effect is not enough to explain the experimentally
observed demagnetization occurring in the subpicosecond regime.",1305.3511v1
2013-05-23,Spin pumping and interlayer exchange coupling through palladium,"The magnetic behaviour of ultrathin ferromagnetic films deposited on
substrates is strongly affected by the properties of the substrate. We
investigate the spin pumping rate, interlayer exchange coupling and dynamic
exchange coupling between ultrathin ferromagnetic films through palladium, a
non-magnetic substrate that displays strong Stoner enhancement. We find that
the interlayer exchange coupling, both in the static and dynamic versions, is
qualitatively affected by the substrate's Stoner enhancement. For instance, the
oscillatory behavior that is a hallmark property of the RKKY exchange coupling
is strongly suppressed by Stoner enhancement. Although the spin pumping rate of
ferromagnetic films atop palladium is only mildly changed by Stoner enhancement
the change is large enough to be detected experimentally. The qualitative
aspects of our results for palladium are expected to remain valid for any
non-magnetic substrate where Coulomb repulsion is large.",1305.5459v1
2013-05-29,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured antiferromagnets,"Antiferromagnets with vanishingly small (or zero) magnetization are
interesting candidates for spintronics applications. In the present paper we
propose two models for description of the current-induced phenomena in
antiferromagnetic textures. We show that the magnetization that originates from
rotation or oscillations of antiferromagnetic vector can, via $sd$-exchange
coupling, polarize the current and give rise to adiabatic and nonadiabatic spin
torques. Due to the Lorentz-type dynamics of antiferromagnetic moments (unlike
the Galilenian-like dynamics in ferromagnets), the adiabatic spin torque
affects the characteristic lengthscale of the moving texture. Nonadiabatic spin
torque contributes to the energy pumping and can induce the stable motion of
antiferromagnetic texture, but, in contrast to ferromagnets, has pure dynamic
origin. We also consider the current-induced phenomena in artificial
antiferromagnets where the current maps the staggered magnetization of the
structure. In this case the effect of nonadiabatic spin torque is similar to
that in ferromagnetic constituents of the structure. In particular, the current
can remove degeneracy of the translational antiferromagnetic domains
indistinguishable in the external magnetic field and thus can set into motion
the 180$^\circ$ domain wall.",1305.6734v2
2013-06-03,Thermodynamics of Ferromagnetic Spin Chains in a Magnetic Field: Impact of the Spin-Wave Interaction,"The thermodynamic properties of ferromagnetic spin chains have been the
subject of many publications. Still, the problem of how the spin-wave
interaction manifest itself in these low-temperature series has been neglected.
Using the method of effective Lagrangians, we explicitly evaluate the partition
function of ferromagnetic spin chains at low temperatures and in the presence
of a magnetic field up to three loops in the perturbative expansion where the
spin-wave interaction sets in. We discuss in detail the renormalization and
numerical evaluation of a particular three-loop graph and derive the
low-temperature series for the free energy density, energy density, heat
capacity, entropy density, as well as the magnetization and the susceptibility.
In the low-temperature expansion for the free energy density, the spin-wave
interaction starts manifesting itself at order $T^{5/2}$. In the pressure, the
coefficient of the $T^{5/2}$-term is positive, indicating that the spin-wave
interaction is repulsive. While it is straightforward to go up to three-loop
order in the effective loop expansion, the analogous calculation on the basis
of conventional condensed matter methods, such as spin-wave theory, appears to
be beyond reach.",1306.0600v1
2013-06-05,Ferromagnetism and Ferroelectricity in epitaxial ultra-thin BiMnO3 films,"We studied the ferroelectric and ferromagnetic properties of compressive
strained and unstrained BiMnO3 thin films grown by rf-magnetron sputtering.
BiMnO3 samples exhibit a 2D cube-on-cube growth mode and a pseudo-cubic
struc-ture up to a thickness of 15 nm and of 25 nm when deposited on (001)
SrTiO3 and (110) DyScO3, respectively. Above these thicknesses we observe a
switching to a 3D island growth and a simultaneous structural change to a
monoclinic structure characterized by a (00l) orientation of the monoclinic
unit cell. While ferromagnetism is observed below Tc = 100 K for all samples,
signatures of room temperature ferroelectricity were found only in the
pseudo-cubic ultra-thin films, indicating a correlation between electronic and
structural orders.",1306.1192v1
2013-06-09,Emerging Weak Localization Effects on Topological Insulator-Insulating Ferromagnet (Bi_2Se_3-EuS) Interface,"Thin films of topological insulator Bi_2Se_3 were deposited directly on
insulating ferromagnetic EuS. Unusual negative magnetoresistance was observed
near the zero field below the Curie temperature (T_C), resembling the weak
localization effect; whereas the usual positive magnetoresistance was recovered
above T_C. Such negative magnetoresistance was only observed for Bi_2Se_3
layers thinner than t~4nm, when its top and bottom surfaces are coupled. These
results provide evidence for a proximity effect between a topological insulator
and an insulating ferromagnet, laying the foundation for future realization of
the half-integer quantized anomalous Hall effect in three-dimensional
topological insulators.",1306.2038v2
2013-06-10,Ferromagnetism in neutron and charge neutral beta-equilibrated nuclear matter,"Ferromagnetism in infinite neutron matter as well as beta equilibrated,
charge neutral, dense, and infinite nuclear matter is investigated using a
model of interacting baryons and mesons. The standard minimal couplings between
the magnetic field and the particle charges as well as the baryon dipole
moments are included in the Lagrangian density. Minimizing the energy density
with respect to the magnetic field yields a self-consistent expression for the
ferromagnetic field. We calculate the phase boundary at a given density by
increasing the strength of the baryon dipole moments till the energy density of
magnetized matter is lower than that of unmagnetized matter. We find that,
depending on the density, it is crossed when the baryon dipole moments are
increased by a factor of 35. It is also sensitive to the details of the nuclear
matter parameterizations and crossing it induces a magnetic field of $\sim
10^{17}$ gauss.",1306.2175v5
2013-06-12,Magnon self energy in the correlated ferromagnetic Kondo lattice model: spin-charge coupling effects on magnon excitations in manganites,"Magnon self energy due to spin-charge coupling is calculated for the
correlated ferromagnetic Kondo lattice model using a diagrammatic expansion
scheme. Systematically incorporating correlation effects in the form of
self-energy and vertex corrections, the expansion scheme explicitly preserves
the continuous spin rotation symmetry and hence the Goldstone mode. Due to a
near cancellation of the correlation-induced quantum correction terms at
intermediate coupling and optimal band filling relevant for ferromagnetic
manganites, the renormalized magnon energies for the correlated FKLM are nearly
independent of correlation term. Even at higher band fillings, despite
exhibiting overall non-Heisenberg behavior, magnon dispersion in the \Gamma-X
direction retains nearly Heisenberg form. Therefore, the experimentally
observed doping dependent zone-boundary magnon softening must be ascribed to
spin-orbital coupling effects.",1306.2769v1
2013-06-13,"Investigation of the quaternary Fe2-xCoxMnSi alloys by structural, magnetic, resistivity and spin polarization measurements","Effects of the Co substitution have been observed on the structural, magnetic
and magneto-transport properties of Fe2-xCoxMnSi alloy. Curie temperature (TC)
and saturation magnetization (MS) of these alloys increased linearly with the
Co substitution. Competitive magnetic interaction between ferromagnetic (FM)
and anti-ferromagnetic (AFM) phases exists in Fe2-xCoxMnSi for x less than 0.2,
AFM phase is completely disappears for x greater than or equal to 0.2. The
value of Rhodes-Wohlfarth ratio pc/ps is greater than one for these alloys
which is the characteristics of iterant magnetism present in the system.
M\""ossbauer spectroscopic measurements have been done to investigate the atomic
disorder and local magnetic moment for some x values. Resistivity measurements
also confirm the stability of ferromagnetism with the concentration of Co and
also show a sign of half metallicity. Resistivity shows semiconducting
behaviour for x = 0.4 which is interesting in view of spin gapless
semiconductors.",1306.3086v3
2013-06-24,Magnon Energy Renormalization and Low-Temperature Thermodynamics of O(3) Heisenberg Ferromagnets,"We present the perturbation theory for lattice magnon fields of
$D$-dimensional O(3) Heisenberg ferromagnet. The effective Hamiltonian for the
lattice magnon fields is obtained starting from the effective Lagrangian, with
two dominant contributions that describe magnon-magnon interactions identified
as a usual gradient term for the unit vector field and a part originating in
the Wess-Zumino-Witten term of effective Lagrangian. Feynman diagrams for
lattice scalar fields with derivative couplings are introduced, on basis of
which we investigate the influence of magnon-magnon interactions on magnon
self-energy and ferromagnet free energy. We also comment appearance of spurious
terms in the low-temperature series for the free energy by examining
magnon-magnon interactions and internal symmetry of the effective Hamiltonian
(Lagrangian).",1306.5584v1
2013-06-25,Entanglement entropy scaling of the XXZ chain,"We study the entanglement entropy scaling of the XXZ chain. While in the
critical XY phase of the XXZ chain the entanglement entropy scales
logarithmically with a coefficient that is determined by the associated
conformal field theory, at the ferromagnetic point, however, the system is not
conformally invariant yet the entanglement entropy still scales logarithmically
albeit with a different coefficient. We investigate how such an nontrivial
scaling at the ferromagnetic point influences the estimation of the central
charge $c$ in the critical XY phase. In particular we use the entanglement
scaling of the finite or infinite system, as well as the finite-size scaling of
the ground state energy to estimate the value of $c$. In addition, the
spin-wave velocity and the scaling dimension are also estimated. We show that
in all methods the evaluations are influenced by the nearby ferromagnetic point
and result in crossover behavior. Finally we discuss how to determine whether
the central charge estimation is strongly influenced by the crossover behavior
and how to properly evaluate the central charge.",1306.5828v3
2013-07-05,Spin-orbit coupled fermions in ladder-like optical lattices at half-filling,"We study the ground-state phase diagram of two-component fermions loaded in a
ladder-like lattice at half filling in the presence of spin-orbit coupling. For
repulsive fermions with unidirectional spin-orbit coupling along the legs we
identify a N\'{e}el state which is separated from rung-singlet and
ferromagnetic states by Ising phase transition lines. These lines cross for
maximal spin-orbit coupling and a direct Gaussian phase transition between
rung-singlet and ferro phases is realized. For the case of Rashba-like
spin-orbit coupling, besides the rung singlet phases two distinct striped
ferromagnetic phases are formed. In case of attractive fermions with spin-orbit
coupling at half-filling for decoupled chains we identify a dimerized state
that separates a singlet superconductor and a ferromagnetic states.",1307.1607v1
2013-07-25,Bell inequality and nonlocality in a two-dimensional mixed spin systems,"In this paper, we use Bell inequality and nonlocality to study the bipartite
correlation in an exactly soluble two-dimensional mixed spin system. Bell
inequality turns out to be a valuable detector for phase transitions in this
model. It can detect not only the quantum phase transition, but also the
thermal phase transitions, of the system. The property of bipartite correlation
in the system is also analyzed. In the quantum anti-ferromagnetic phase, the
Bell inequality is violated thus nonlocality is present. It is interesting that
the nonlocality is enhanced by thermal fluctuation, and similar results have
not been observed in anti-ferromagnetic phase. In the ferromagnetic phase, the
quantum correlation turns out to be very novel, which cannot be captured by
entanglement or nonlocality.",1307.6680v1
2013-10-01,Temperature and Field Dependence of Magnetic Domains in La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$,"Colossal magnetoresistance and field-induced ferromagnetism are well
documented in manganite compounds. Since domain wall resistance contributes to
magnetoresistance, data on the temperature and magnetic field dependence of the
ferromagnetic domain structure are required for a full understanding of the
magnetoresistive effect. Here we show, using cryogenic Magnetic Force
Microscopy, domain structures for the layered manganite
La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ as a function of temperature and magnetic
field. Domain walls are suppressed close to the Curie temperature T$_C$, and
appear either via the application of a c-axis magnetic field, or by decreasing
the temperature further. At temperatures well below T$_C$, new domain walls,
stable at zero field, can be formed by the application of a c-axis field.
Magnetic structures are seen also at temperatures above T$_C$: these features
are attributed to inclusions of additional Ruddleston-Popper manganite phases.
Low-temperature domain walls are nucleated by these ferromagnetic inclusions.",1310.0258v5
2013-10-02,The effect of normal metal layers in ferromagnetic Josephson junctions,"Using the Usadel equation approach, we provide a compact formalism to
calculate the critical current density of 21 different types of ferromagnetic
(F) Josephson junctions containing insulating (I) and normal metal (N) layers
in the weak link regions. In particular, we obtain that even a thin additional
N layer may shift the 0-$\pi$ transitions to larger or smaller values of the
thickness $d_F$ of the ferromagnet, depending on its conducting properties. For
certain values of $d_F$, a 0-$\pi$ transition can even be achieved by changing
only the N layer thickness. We use our model to fit experimental data of SIFS
and SINFS tunnel junctions, where S is a superconducting electrode.",1310.0567v2
2013-10-07,Large in-plane deformation of RuO6 octahedron and ferromagnetism of bulk SrRuO3,"SrRuO3 is a ferromagnetic metal with several unusual physical properties such
as zero thermal expansion below Tc, so-called Invar behavior. Another anomalous
feature is that the a-axis lattice constant is larger than the b-axis lattice
constant, a clear deviation from the predictions of the Glazer structural
description with rigid RuO6 octahedron motion. Using high resolution neutron
diffraction techniques, we show how these two structural anomalies arise from
the irregular in-plane deformation, i.e. plastic behavior of the RuO6
octahedron, a weak band Jahn-Teller distortion. We further demonstrate that the
ferromagnetic instability of SrRuO3 is related to the temperature-induced
localization of Ru 4d bands.",1310.1686v2
2013-10-15,Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures,"The volume change and heat capacity at the ferromagnetic phase transition in
CoS2 were measured at high pressures using X-rays generated by the Argonne
synchrotron light source and by ac-calorimetry, respectively. The transition
entropy, calculated on the basis of these experimental data, drops along the
transition line due to quantum degradation, as required by Nernst law. The
volume change increases strongly along the transition line, which is explained
by specifics of the compressibility difference of coexisting phases that
results from nearly half metallic nature of the ferromagnetic phase of CoS2.",1310.3994v1
2013-10-18,Three `species' of Schrödinger cat states in an infinite-range spin model,"We explore a transverse-field Ising model that exhibits both spontaneous
symmetry-breaking and eigenstate thermalization. Within its ferromagnetic
phase, the exact eigenstates of the Hamiltonian of any large but finite-sized
system are all Schr\""odinger cat states: superpositions of states with `up' and
`down' spontaneous magnetization. This model exhibits two dynamical phase
transitions {\it within} its ferromagnetic phase: In the lowest-temperature
phase the magnetization can macroscopically oscillate between up and down. The
relaxation of the magnetization is always overdamped in the remainder of the
ferromagnetic phase, which is divided in to phases where the system thermally
activates itself {\it over} the barrier between the up and down states, and
where it quantum tunnels.",1310.4992v3
2013-10-24,Minority-spin $t_{2g}$ states and the degree of spin polarization in ferromagnetic metallic La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ ($x=0.38$),"Using angle-resolved photoemission spectroscopy (ARPES), we investigate the
electronic band structure and Fermi surface of ferromagnetic
La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ ($x=0.38$). Besides the expected two hole
pockets and one electron pocket of majority-spin $e_g$ electrons, we show an
extra electron pocket around the $\Gamma$ point. A comparison with
first-principles spin-polarized band-structure calculations shows that the
extra electron pocket arises from $t_{2g}$ electrons of minority-spin
character, indicating this compound is not a complete half-metallic
ferromagnet, with similar expectations for lightly-doped cubic manganites.
However, our data suggest that a complete half-metallic state is likely to be
reached as long as the bandwidth is mildly reduced. Moreover, the band-resolved
capability of ARPES enables us to investigate the band structure effects on
spin polarization for different experimental conditions.",1310.6476v1
2013-11-01,Superfluid Spin Transport through Easy-Plane Ferromagnetic Insulators,"Superfluid spin transport $-$ dissipationless transport of spin $-$ is
theoretically studied in a ferromagnetic insulator with easy-plane anisotropy.
We consider an open geometry where spin current is injected into the
ferromagnet from one side by a metallic reservoir with a nonequilibrium spin
accumulation, and ejected into another metallic reservoir located downstream.
Spin transport through the device is studied using a combination of
magnetoelectric circuit theory, Landau-Lifshitz-Gilbert phenomenology, and
microscopic linear-response theory. We discuss how spin superfluidity can be
probed using a magnetically-mediated electron-drag experiment.",1311.0288v4
2013-11-05,Quantum criticality and Lifshitz transition in the Ising system CeRu2Si2: Comparison with YbRh2Si2,"New thermoelectric power (TEP) measurements on prototype heavy-fermion
compounds close to magnetic quantum criticality are presented. The highly
sensitive technique of TEP is an unique tool to reveal Fermi surface
instabilities, referred here as Lifshitz transitions. The first focus is on the
Ising CeRu2Si2 series. Doping CeRu2Si2 with Rh produces a decoupling between
the first order metamagnetic transition and the pseudo-metamagnetism observed
in the pure compound. Comparison is made with the case of YbRh2Si2 which is
often considered as the archetype of local quantum criticality by contrast to
CeRu2Si2, taken as an example of spin-density wave criticality. Up to now for
ferromagnetic materials showing ferromagnetic wings, no simple case appears
where the Fermi surface is preserved between the ferromagnetic and paramagnetic
phases. An open issue is the consequence of Lifshitz transitions on
superconductivity in these multiband systems.",1311.1239v1
2013-11-11,The Vortex Signature of Discrete Ferromagnetic Dipoles at the LaAlO$_3$/SrTiO$_3$ Interface,"A hysteretic in-plane magnetoresistance develops below the superconducting
transition of LaAlO$_3$/SrTiO$_3$ interfaces for $\left|H_{/\!/}\right|<$ 0.15
T, independently of the carrier density or oxygen annealing. We show that this
hysteresis arises from vortex depinning within a thin superconducting layer, in
which the vortices are created by discrete ferromagnetic dipoles located solely
above the layer. We find no evidence for finite-momentum pairing or bulk
magnetism and hence conclude that ferromagnetism is strictly confined to the
interface, where it competes with superconductivity.",1311.2323v1
2013-11-11,Color Magnetism in Non-Abelian Vortex Matter,"We propose color magnetism as a generalization of the ordinary Heisenberg
(anti-)ferro magnets on a triangular lattice. Vortex matter consisting of an
Abrikosov lattice of non-Abelian vortices with color magnetic fluxes shows a
color ferro or anti-ferro magnetism, depending on the interaction among the
vortex sites. A prime example is a non-Abelian vortex lattice in rotating dense
quark matter, showing a color ferromagnetism. We show that the low-energy
effective theory for the vortex lattice system in the color ferromagnetic phase
is described by a 3+1 dimensional $CP^{N-1}$ nonlinear sigma model with
spatially anisotropic couplings. We identify gapless excitations independent
from Tkachenko modes as color magnons, that is, Nambu-Goldstone modes
propagating in the vortex lattice with an anisotropic linear dispersion
relation $\omega_p^2 = c_{xy}^2(p_x^2+p_y^2) + c_z^2 p_z^2$. We calculate the
transition temperature between the ordered and disordered phases, and apply it
to dense quark matter. We also identify the order parameter spaces for color
anti-ferromagnets.",1311.2399v2
2013-11-11,Ferromagnetic two-dimensional crystals: Single layers of K2CuF4,"The successful isolation of graphene ten years ago has evoked a rapidly
growing scientific interest in the nature of two-dimensional (2D) crystals. A
number of different 2D crystals has been produced since then, with properties
ranging from superconductivity to insulating behavior. Here, we predict the
possibility for realizing ferromagnetic 2D crystals by exfoliating atomically
thin films of K2CuF4. From a first-principles theoretical analysis, we find
that single layers of K2CuF4 form exactly 2D Kosterlitz-Thouless systems. The
2D crystal can form a free-standing membrane, and exhibits an experimentally
accessible transition temperature and robust magnetic moments of 1 Bohr
magneton per formula unit. 2D K2CuF4 unites ferromagnetic and insulating
properties and is a demonstration of principles for nanoelectronics such as
novel 2D-based heterostructures.",1311.2410v1
2013-11-21,Existence of Anisotropic Spin Fluctuations at Low Temperature in the Normal Phase of the Superconducting Ferromagnet UCoGe,"Thermal conductivity measurements have been performed on the superconducting
ferromagnet UCoGe down to very low temperature and under magnetic field. In
addition to the electronic quasiparticle thermal conductivity, additional
contributions to the thermal transport are detected: they are sensitive to the
amplitude and direction of the magnetic field, and at low temperature, they
display a strong anisotropy with the heat current direction. We identify these
contributions as arising from magnetic fluctuations. Detection of such
fluctuations on the thermal transport in 3D weak ferromagnets is very rare if
not unique, and pledges for a strongly itinerant character of the magnetism of
UCoGe.",1311.5468v1
2013-12-03,Tensor networks for frustrated systems: emergence of order from simplex entanglement,"We consider a frustrated anti-ferromagnetic triangular lattice Hamiltonian
and show that the properties of the manifold of its degenerated ground state
are represented by a novel type of tensor networks. These tensor networks are
not based on ancillary maximally entangled pairs, but rather on triangular
W-like simplices. Anti-ferromagnetic triangular frustration is then related to
ancillary W-states in contrast to ferromagnetic order which emerges from the
contraction of GHZ-like triangular simplices. We further discuss the outwards
entangling power of various simplices. This analysis suggests the emergence of
distinct macroscopic types of order from the classification of entanglement
residing on the simplices that define a tensor network.",1312.0952v1
2013-12-20,Cation-ordered A$'_{1/2}$A$''_{1/2}$B$_2$X$_4$ magnetic spinels as magnetoelectrics,"We show that 1:1 ordering of A$'$ and A$''$ cations in
A$'_{1/2}$A$''_{1/2}$B$_2$X$_4$ magnetic spinels results in appearance of
magnetoelectric properties. Possible value of magnetically induced electric
polarization is calculated using the recently proposed microscopic model, which
takes into account spin-dependent electric dipole moments of magnetic ions
located in noncentrosymmetric crystallographic positions. We build
phenomenological models of magnetic phase transitions in cation-ordered
spinels, which describe ferromagnetic and antiferromagnetic ordering patterns
of B cation spins, and calculate the respective magnetoelectric responses. We
find that magnetoelectric coefficients diverge at ferromagnetic or weak
ferromagnetic phase transitions in ordered spinels.",1312.5925v2
2014-01-09,Edge proximity-induced magnetoresistance and spin polarization in ferromagnetic gated bilayer graphene nanoribbon,"Coherent spin-dependent transport through a junction containing of
Normal/Ferromagnetic/Normal bilayer graphene nanoribbon with zigzag edges is
investigated by using Landauer formalism. In a more realistic set-up, the
exchange field is induced by two ferromagnetic insulator strips deposited on
the ribbon edges while a perpendicular electric field is applied by the top
gated electrodes. Our results show that, for antiparallel configuration, a band
gap is opened giving rise a semiconducting behavior, while for parallel
configuration, the band structure has no band gap. As a result, a giant
magnetoresistance is achievable by changing the alignment of induced
magnetization. Application of a perpendicular electric field on the parallel
configuration, results in a spin field-effect transistor where a fully spin
polarization occurs around the Dirac point. To be comparable our results with
the one for monolayer graphene, we demonstrate that the reflection symmetry and
so the parity conservation fails in bilayer graphene nanoribbons with the
zigzag edges.",1401.2171v1
2014-01-17,Layer Anti-Ferromagnetism on Bilayer Honeycomb Lattice,"Bilayer honeycomb lattice, with inter-layer tunneling energy, has a parabolic
dispersion relation, which causes the charge imbalance between two sublattices.
Here, we investigate the metal-insulator and magnetic phase transitions on the
strongly correlated bilayer honeycomb lattice by cellular dynamical mean-field
theory combined with continuous time quantum Monte Carlo method. We find that
different kinds of magnetic spontaneous symmetry breaking on dimer and
non-dimer sites, cause a novel phase transition between normal anti-ferromagnet
and layer anti-ferromagnet. We sketch the phase diagrams as the function of
temperature, interaction and inter-layer hopping. Finally, we set up an
experimental protocol for cold atoms in optical lattice to observe these
phenomena in future experiments.",1401.4249v1
2014-01-18,"Magnetic Moment and Band Structure Analysis of Fe, Co, Ni-modified Graphene-nano- ribbon","Magnetic properties and band characteristics of graphene-nano-ribbon (GNR)
modified by Fe, Co, and Ni were analyzed by the first principles DFT
calculation. Typical unit cell is [C32H2Fe1], [C32H2Co1] and [C32H2Ni1]
respectively. The most stable spin state was Sz=4/2 for Fe-modified GNR,
whereas Sz=3/2 for Co-case and Sz=2/2 for Ni-case. Atomic magnetic moment of
Fe, Co and Ni were 3.63, 2.49 and 1.26 {\mu}B, which were reduced values than
that of atomic Hund-rule due to magnetic coupling with graphene network. There
is a possibility for a ferromagnetic Fe, Co and Ni spin array through an
interaction with carbon pi-conjugated spin system. By expanding a unit cell of
Co-modified case as [C96H6Co3], ferromagnetic like spin state and ferrimagnetic
like one were compared. It was concluded that ferromagnetic state was more
stable magnetic state. Band calculations of Co-modified case show half-metal
like structure with relatively large band gap (0.55eV) for up-spin, whereas
small gap (0.05eV) for down-spin. This suggested a capability of spintronics
application like a spin fiter.",1401.4504v1
2014-01-24,Zero-temperature spinglass-ferromagnetic transition : scaling analysis of the domain-wall energy,"For the Ising model with Gaussian random coupling of average $J_0$ and unit
variance, the zero-temperature spinglass-ferromagnetic transition as a function
of the control parameter $J_0$ can be studied via the size-$L$ dependent
renormalized coupling defined as the domain-wall energy $J^R(L) \equiv
E_{GS}^{(AF)}(L)-E_{GS}^{(F)}(L)$ (i.e. the difference between the ground state
energies corresponding to AntiFerromagnetic and and Ferromagnetic boundary
conditions in one direction). We study numerically the critical exponents of
this zero-temperature transition within the Migdal-Kadanoff approximation as a
function of the dimension $d=2,3,4,5,6$. We then compare with the mean-field
spherical model. Our main conclusion is that in low dimensions, the critical
stiffness exponent $\theta^c$ is clearly bigger than the spin-glass stiffness
exponent $\theta^{SG}$, but that they turn out to coincide in high enough
dimension and in the mean-field spherical model. We also discuss the
finite-size scaling properties of the averaged value and of the width of the
distribution of the renormalized couplings.",1401.6342v2
2014-01-29,Magnetic polaron structures in the one-dimensional double and super-exchange model,"An analytical and numerical study of the one-dimensional double and
super-exchange model is presented. A phase separation between ferromagnetic and
anti-ferromagnetic phases occurs at low super-exchange interaction energy. When
the super-exchange interaction energy gets larger, the conduction electrons are
self-trapped within separate small magnetic polarons. These magnetic polarons
contain a single electron inside two or three sites depending on the conduction
electron density and form a Wigner crystallization. A new phase separation is
found between these small polarons and the anti-ferromagnetic phase. Our
results could explain the spin-glass-like behavior observed in the nickelate
one-dimensional compound Y(2-x)CaxBaNiO5.",1401.7656v1
2014-02-04,Exact Free Energies of Statistical Systems on Random Networks,"Statistical systems on random networks can be formulated in terms of
partition functions expressed with integrals by regarding Feynman diagrams as
random networks. We consider the cases of random networks with bounded but
generic degrees of vertices, and show that the free energies can be exactly
evaluated in the thermodynamic limit by the Laplace method, and that the exact
expressions can in principle be obtained by solving polynomial equations for
mean fields. As demonstrations, we apply our method to the ferromagnetic Ising
models on random networks. The free energy of the ferromagnetic Ising model on
random networks with trivalent vertices is shown to exactly reproduce that of
the ferromagnetic Ising model on the Bethe lattice. We also consider the cases
with heterogeneity with mixtures of orders of vertices, and derive the known
formula of the Curie temperature.",1402.0740v3
2014-02-10,Monte Carlo simulation of stoquastic Hamiltonians,"Stoquastic Hamiltonians are characterized by the property that their
off-diagonal matrix elements in the standard product basis are real and
non-positive. Many interesting quantum models fall into this class including
the Transverse field Ising Model (TIM), the Heisenberg model on bipartite
graphs, and the bosonic Hubbard model. Here we consider the problem of
estimating the ground state energy of a local stoquastic Hamiltonian $H$ with a
promise that the ground state of $H$ has a non-negligible correlation with some
`guiding' state that admits a concise classical description. A formalized
version of this problem called Guided Stoquastic Hamiltonian is shown to be
complete for the complexity class MA (a probabilistic analogue of NP). To prove
this result we employ the Projection Monte Carlo algorithm with a variable
number of walkers. Secondly, we show that the ground state and thermal
equilibrium properties of the ferromagnetic TIM can be simulated in polynomial
time on a classical probabilistic computer. This result is based on the
approximation algorithm for the classical ferromagnetic Ising model due to
Jerrrum and Sinclair (1993).",1402.2295v2
2014-02-12,Ferromagnetic barrier induced negative differential conductance on the surface of a topological insulator,"We theoretically investigate the effect of the negative differential
conductance of a ferromagnetic barrier on the surface of a topological
insulator. Due to the changes of the shape and position of the Fermi surfaces
in the ferromagnetic barrier, the transport processes can be divided into three
kinds: the total, partial and blockade transmission mechanisms. The bias
voltage can give rise to the transition of the transport processes from partial
to blockade transmission mechanisms, which results in a giant effect of
negative differential conductance. With appropriate structural parameters, the
current-voltage characteristics show that the minimum value of the current can
reach to zero in a wide range of the bias voltage, and a large peak-to-valley
current ratio can be obtained.",1402.2747v1
2014-02-14,Electronic relaxation rates in metallic ferromagnets,"We show that the single-particle and transport relaxation rates in
ferromagnetic metals, which determine the thermal and electrical conductivity,
respectively, at asymptotically low temperature do not obey a power law as
previously thought, but rather show an exponential temperature dependence. The
reason is the splitting of the conduction band that inevitably results from a
nonzero magnetization. At higher temperatures there is a sizable temperature
window where the transport rate shows a T^2 temperature dependence, in accord
with prior results. This window is separated from the asymptotic regime by a
temperature scale that is estimated to range from tens of mK to tens of K for
typical ferromagnets. We motivate and derive a very general effective theory
for metallic magnets that we then use to derive these results. Comparisons with
existing experiments are discussed, and predictions for future experiments at
low temperatures are made.",1402.3347v2
2014-02-25,Hysteretic ac loss in a coated superconductor subjected to oscillating magnetic field: ferromagnetic effect and frequency dependence,"Numerical simulations of the hysteretic ac loss in a coated superconductor
with a more realistic version of architecture were performed via finite-element
technique in the presence of an oscillating magnetic field. The coated
superconductor was electromagnetically modeled by resorting to the quasistatic
approximation of a vector potential approach in conjunction with the nonlinear
descriptions of the superconducting layer and ferromagnetic substrate therein
by a power law model and the Langevin equation respectively. A diverse effect
of the ferromagnetic substrate on the hysteretic ac loss, depending on the
strength of the applied magnetic field, was displayed and its underlying cause
was identified. The dependence of the hysteretic ac loss on the applied
frequency is found to be related to a critical amplitude of the applied
magnetic field, and the eddy-current loss dissipated in the metal coatings
becomes prominent as the frequency augments merely at high applied magnetic
fields.",1402.6071v1
2014-02-26,Raman spectra and Magnetization of all-ferromagnetic superlattices grown on (110) oriented SrTiO3,"Superlattices consist of two ferromagnets La0.7Sr0.3MnO3(LSMO)and SrRuO3(SRO)
were grown in (110)-orientation on SrTiO3(STO) substrates. The x-ray
diffraction and Raman spectra of these superlattices show the presence of
in-plane compressive strain and orthorhombic structure of less than 4 u.c.
thick LSMO spacer,respectively. Magnetic measurements reveal several features
including reduced magnetization, enhanced coercivity, antiferromagnetic
coupling, and switching from antiferromagnetic to ferromagnetic coupling with
magnetic field orientations. These magnetic properties are explained by the
observed orthorhombic structure of spacer LSMO in Raman scattering which occurs
due to the modification in the stereochemistry of Mn at the interfaces of SRO
and LSMO.",1402.6410v1
2014-02-26,Improved Domain Wall Dynamics and Magnonic Torques using Topological Insulators,"We investigate the magnetization dynamics that arise when a thin-film
ferromagnet is deposited on a topological insulator (TI), focusing in
particular on domain-wall motion via current and the possibility of a spin-wave
torque acting on the magnetization. We show analytically that the coupling
between the magnetic domain wall and the TI removes the degeneracy of the wall
profile with respect to its chirality and topological charge. Moreover, we find
that the threshold for Walker breakdown of domain wall motion is substantially
increased and determined by the interaction with the TI, allowing for higher
attainable wall velocities than in the conventional case where the hard axis
anisotropy determines the Walker threshold. Finally, we show that the allowed
modes of spin-wave excitations and the ensuing magnetization dynamics in the
presence of a TI coupling enable a magnonic torque acting even on homogeneous
magnetization textures. Our results indicate that the TI-ferromagnet
interaction has a similar effect on the magnetization dynamics as an intrinsic
Dzyaloshinskii-Moriya interaction in ferromagnets.",1402.6701v2
2014-02-27,On the longitudinal spin current induced by a temperature gradient in a ferromagnetic insulator,"Based on the solution of the stochastic Landau-Lifshitz-Gilbert equation
discretized for a ferromagnetic chain subject to a uniform temperature
gradient, we present a detailed numerical study of the spin dynamics with a
focus particularly on finite-size effects. We calculate and analyze the net
longitudinal spin current for various temperature gradients, chain lengths, and
external static magnetic fields. In addition, we model an interface formed by a
nonuniformly magnetized finite-size ferromagnetic insulator and a normal metal
and inspect the effects of enhanced Gilbert damping on the formation of the
space-dependent spin current within the chain. A particular aim of this study
is the inspection of the spin Seebeck effect beyond the linear response regime.
We find that within our model the microscopic mechanism of the spin Seebeck
current is the magnon accumulation effect quantified in terms of the exchange
spin torque. According to our results, this effect drives the spin Seebeck
current even in the absence of a deviation between the magnon and phonon
temperature profiles. Our theoretical findings are in line with the recently
observed experimental results by M. Agrawal et al., Phys. Rev. Lett. 111,
107204 (2013).",1402.6899v1
2014-04-02,Impurity-assisted tunneling magnetoresistance under weak magnetic field,"Injection of spins into semiconductors is essential for the integration of
the spin functionality into conventional electronics. Insulating layers are
often inserted between ferromagnetic metals and semiconductors for obtaining an
efficient spin injection, and it is therefore crucial to distinguish between
signatures of electrical spin injection and impurity-driven effects in the
tunnel barrier. Here we demonstrate an impurity-assisted tunneling
magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and
ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect
reflects on/off switching of the tunneling current through impurity channels by
the external magnetic field. The reported effect, which is universal for any
impurity-assisted tunneling process, finally clarifies the controversy of a
widely used technique that employs the same ferromagnetic electrode to inject
and detect spin accumulation.",1404.0633v2
2014-04-03,Anomalously Weak Cooper Pair-breaking by Exchange Energy in Ferromagnet/Superconductor Bilayers,"We report the superconducting transition temperature $T_c$ vs. thickness
$d_F$ of Ferromagnet/Superconductor (F/S) bilayers, where F is a strong $3d$
ferromagnet (Ni, Ni$_{0.81}$Fe$_{0.19}$ (Permalloy), Co$_{0.5}$Fe$_{0.5}$) and
S = Nb, taken from superfluid density measurements rather than resistivity. By
regrouping the many physical parameters that appear in theory, we show that the
effective exchange energy is determined from the F film thickness $d_F$ where
$T_c$ vs. $d_F$ begins to flatten out. Using this rearranged theory we
conclude: 1) the effective exchange energy, $E_{ex}$, is about 15 times smaller
than measured by ARPES and 5 times smaller than deduced in previous studies
similar to ours; 2) the dirty-limit coherence length, $\xi_{F}$, for Cooper
pairs in F is larger than the electron mean free path, $\ell_F$; and 3) the
$3d$-F/Nb interface is enough of a barrier that Cooper pairs typically must hit
it several times before getting through. The Py/Nb and CoFe/Nb interfaces are
more transparent than the Ni/Nb interface.",1404.1032v1
2014-04-03,Itinerant magnetism in URhGe revealed by angle resolved photoelectron spectroscopy,"The electronic structure of the ferromagnetic superconductor URhGe in the
paramagnetic phase has been studied by angle-resolved photoelectron
spectroscopy using soft x rays (hn=595-700 eV). Dispersive bands with large
contributions from U 5f states were observed in the ARPES spectra, and form
Fermi surfaces. The band structure in the paramagnetic phase is partly
explained by the band-structure calculation treating all U 5f electrons as
being itinerant, suggesting that an itinerant description of U 5f states is a
good starting point for this compound. On the other hand, there are qualitative
disagreements especially in the band structure near the Fermi level (E_B < 0.5
eV). The experimentally observed bands are less dispersive than the
calculation, and the shape of the Fermi surface is different from the
calculation. The changes in spectral functions due to the ferromagnetic
transition were observed in bands near the Fermi level, suggesting that the
ferromagnetism in this compound has an itinerant origin.",1404.1324v1
2014-04-07,Effect of carbon content on magnetostructural properties of Mn$_3$GaC,"Effect of carbon content on magnetostructural transformation in
antiperovskites of the type Mn$_3$GaC$_x$ ($x$ = 0.8, 1.0 and 1.05) has been
investigated. It is found that, increase in carbon content changes the ground
state from ferromagnetic metallic ($x$ = 0.8) to antiferromagnetic
semiconducting ($x$ = 1.05) type. This has been attributed to localization of
itinerant Mn $3d$ electrons due to increased Mn$3d$ - C$2p$ hybridization. Such
a hybridization strengthens Mn-C-Mn antiferromagnetic interactions over Mn-Mn
ferromagnetic interactions. Further, magnetic field can be used as a tool to
modulate the relative strengths of these ferromagnetic and antiferromagnetic
interactions thereby affecting the nature and strength of magnetocaloric
properties.",1404.1751v1
2014-04-08,Dispersion-driven ferromagnetism in a flat-band Hubbard system,"We investigate a mechanism to establish ground-state ferromagnetism in
flat-band Hubbard systems based on a kind of {\it order-from-disorder} effect
driven by dispersion. As a paradigm we consider a frustrated diamond chain,
where for ideal diamond geometry the lowest one-electron band is flat, but the
ground state remains paramagnetic for arbitrary on-site repulsion $U$. We focus
on half filling of the flat band. By using numerical and analytical arguments
we present the ground-state phase diagram for a distorted diamond chain, i.e.,
the former flat band becomes dispersive. Driven by the interplay of dispersion
and interaction the ground state is ferromagnetic if the interaction exceeds a
critical value $U_c$.",1404.2230v1
2014-04-18,Transport Properties of Dirac Ferromagnet,"We propose a model ferromagnet based on the Dirac Hamiltonian in three
spatial dimensions, and study its transport properties which include
anisotropic magnetoresistance (AMR) and anomalous Hall (AH) effect. This
relativistic extension allows two kinds of ferromagnetic order parameters,
denoted by $\bm{M}$ and $\bm{S}$, which are distinguished by the relative sign
between the positive- and negative-energy states (at zero momentum) and become
degenerate in the non-relativistic limit. Because of the relativistic coupling
between the spin and the orbital motion, both $\bm{M}$ and $\bm{S}$ induce
anisotropic deformations of the energy dispersion (and the Fermi surfaces) but
in mutually opposite ways. The AMR is determined primarily by the anisotropy of
the Fermi surface (group velocity), and secondarily by the anisotropy of the
damping; the latter becomes important for ${\bm M}=\pm{\bm S}$, where the Fermi
surfaces are isotropic. Even when the chemical potential lies in the gap, the
AH conductivity is found to take a finite non-quantized value, $\sigma_{ij} =
-(\alpha /3\pi^2 \hbar) \epsilon_{ijk} S_k $, where $\alpha$ is the (effective)
fine structure constant. This offers an example of Hall insulator in three
spatial dimensions.",1404.4741v2
2014-04-22,Spin-wave-induced correction to the conductivity of ferromagnets,"We calculate the correction to the conductivity of a disordered ferromagnetic
metal due to spin-wave-mediated electron--electron interactions. This
correction is the generalization of the Altshuler-Aronov correction to
spin-wave-mediated interactions. We derive a general expression for the
conductivity correction to lowest order in the spin-wave-mediated interaction
and for the limit that the exchange splitting $\Delta$ is much smaller than the
Fermi energy. For a ""clean"" ferromagnet with $\Delta\tau_{\rm el}/\hbar \gg 1$,
with $\tau_{\rm el}$ the mean time for impurity scattering, we find a
correction $\delta \sigma \propto -T^{5/2}$ at temperatures $T$ above the spin
wave gap. In the opposite, ""dirty"" limit, $\Delta\tau_{\rm el}/\hbar \ll 1$,
the correction is a non-monotonous function of temperature.",1404.5437v1
2014-07-03,A Poor Man's Derivation of Quantum Compass-Heisenberg Interaction: Superexchange Interaction in J-J Coupling Scheme,"The exchange interaction between 5d electrons in t$_{2g}$ orbitals is derived
in the J-J coupling scheme which is the appropriate basis in the case of strong
spin-orbit interaction. From simple calculations, it is found that
ferromagnetic Ising interaction (quantum compass model) occurs due to a
selection rule of hybridization between $\Gamma_7$ and $\Gamma_8$ orbitals,
while antiferromagnetic Heisenberg interaction appears from hybridization
between $\Gamma_7$ orbitals. It is also found that the ferromagnetic Ising
interaction becomes small as the spin-orbit interaction increases. Thus, the
sign of exchange interaction changes from ferromagnetic Ising to
antiferromagnetic Heisenberg interaction as the spin-orbit interaction
increases.",1407.0811v1
2014-07-22,Microscale Motion Control Through Ferromagnetic Films,"Actuation and control of motion in micro-mechanical systems are technological
challenges, since they are accompanied by mechanical friction and wear,
principal and well known sources of device lifetime reduction. In this
theoretical work we propose a non-contact motion control technique based on the
introduction of a tunable magnetic interaction. The latter is realized by
coating two non-touching sliding bodies with ferromagnetic films. The resulting
dynamics is determined by shape, size and ordering of magnetic domains arising
in the films below the Curie temperature. We demonstrate that the domain
behavior can be tailored by acting on handles like ferromagnetic coating
preparation, external magnetic fields and the finite distance between the
plates. In this way, motion control can be achieved without mechanical contact.
Moreover, we discuss how such handles can disclose a variety of sliding
regimes. Finally, we propose how to practically implement the proposed model
sliding system.",1407.6058v1
2014-07-25,Magnetic Proximity Effect and Interlayer Exchange Coupling of Ferromagnetic/Topological Insulator/Ferromagnetic Trilayer,"Magnetic proximity effect between topological insulator (TI) and
ferromagnetic insulator (FMI) is considered to have great potential in
spintronics. However, a complete determination of interfacial magnetic
structure has been highly challenging. We theoretically investigate the
interlayer exchange coupling of two FMIs separated by a TI thin film, and show
that the particular electronic states of the TI contributing to the proximity
effect can be directly identified through the coupling behavior between two
FMIs, together with a tunability of coupling constant. Such FMI/TI/FMI
structure not only serves as a platform to clarify the magnetic structure of
FMI/TI interface, but also provides insights into designing the magnetic
storage devices with ultrafast response.",1407.6900v1
2014-07-28,Majorana fermions in ferromagnetic chains on the surface of bulk spin-orbit coupled $s$-wave superconductors,"Majorana fermion (MF) excitations in solid state system have non-Abelian
statistics which is essential for topological quantum computation. Previous
proposals to realize MF, however, generally requires fine-tuning of parameters.
Here we explore a platform which avoids the fine-tuning problem, namely a
ferromagnetic chain deposited on the surface of a spin-orbit coupled $s$-wave
superconductor. We show that it generically supports zero-energy topological MF
excitations near the two ends of the chain with minimal fine-tuning. Depending
on the strength of the ferromagnetic moment in the chain, the number of MFs at
each end, $n$, can be either one or two, and should be revealed by a robust
zero-bias peak (ZBP) of height $2ne^2/h$ in scanning tunneling microscopy (STM)
measurements which would show strong (weak) signals at the ends (middle) of the
chain. The role of an approximate chiral symmetry which gives an integer
topological invariant to the system is discussed.",1407.7519v2
2014-08-07,Critical behavior and universality properties of uniaxial ferromagnetic thin films in the presence of random magnetic fields,"Critical phenomena in uniaxial ferromagnetic thin films in the presence of
random magnetic fields have been studied within the framework of effective
field theory. When the type of the random field distribution is bimodal, the
system exhibits tricritical behavior. Furthermore, the critical value of
surface to bulk ratio of exchange interactions at which the transition
temperature becomes independent of film thickness is insensitive to the
presence of disorder whether the distribution is bimodal or trimodal. Regarding
the universality properties, neither $p$, nor $h$ variations in the system can
affect the value of the shift exponent $\lambda$. In this regard, it can be
concluded that pure ferromagnetic thin films are in the same universality class
with those under the influence of random discrete magnetic fields.",1408.1513v1
2014-08-29,Spin-dependent ballistic transport properties and electronic structures of pristine and edge-doped zigzag silicene nanoribbons: large magnetoresistance,"The electronic structure and conductance of substitutionally edge-doped
zigzag silicene nanoribbons (ZSiNRs) are investigated using the nonequilibrium
Green's function method combined with the density functional theory. Two-probe
systems of ZSiNRs in both ferromagnetic and antiferromagnetic states are
considered. Doping effects of elements from groups III and V, in a parallel or
antiparallel magnetic configuration of the two electrodes, are discussed.
Switching on and off the external magnetic field, we may convert the metallic
ferromagnetic ZSiNRs into insulating antiferromagnetic ZSiNRs. In the
ferromagnetic state, even- or odd-width ZSiNRs exhibit a drastically different
magnetoresistance. In an odd-width edge-doped ZSiNR a large magnetoresistance
occurs compared to that in a pristine ZSiNR. The situation is reversed in
even-width ZSiNRs. These phenomena result from the drastic change of the
conductance in the antiparallel configuration.",1408.6899v1
2014-09-01,Proximity effect in superconductor/conical magnet heterostructures,"The presence of a spin-flip potential at the interface between a
superconductor and a ferromagnetic metal allows for the generation of
equal-spin spin-triplet Cooper pairs. These Cooper pairs are compatible with
the exchange interaction within the ferromagnetic region and hence allow for
the long-range proximity effect through a ferromagnet or half-metal. One
suitable spin-flip potential is provided by incorporating the conical magnet
Holmium (Ho) into the interface. The conical magnetic structure is
characterised by an opening angle $\alpha$ with respect to the crystal $c$-axis
and a turning (or pitch) angle $\beta$ measuring the rotation of magnetisation
with respect to the adjacent layers. Here, we present results showing the
influence of conical magnet interface layers with varying $\alpha$ and $\beta$
on the efficiency of the generation of equal-spin spin-triplet pairing. The
results are obtained by self-consistent solutions of the microscopic
Bogoliubov$-$de Gennes equations in the clean limit within a tight-binding
model of the heterostructure. In particular, the dependence of unequal-spin and
equal-spin spin-triplet pairing correlations on the conical magnetic angles
$\alpha$ and $\beta$ are discussed in detail.",1409.0366v1
2014-09-01,Imaging and Control of Ferromagnetism in a Polar Antiferromagnet,"Atomically sharp oxide heterostructures often exhibit unusual physical
properties that are absent in the constituent bulk materials. The interplay
between electrostatic boundary conditions, strain and dimensionality in
ultrathin epitaxial films can result in monolayer-scale transitions in
electronic or magnetic properties. Here we report an atomically sharp
antiferromagnetic-to-ferromagnetic phase transition when atomically growing
polar antiferromagnetic LaMnO3 (001) films on SrTiO3 substrates. For a
thickness of five unit cells or less, the films are antiferromagnetic, but for
six unit cells or more, the LaMnO3 film undergoes a phase transition to a
ferromagnetic state over its entire area, which is visualized by scanning
superconducting quantum interference device microscopy. The transition is
explained in terms of electronic reconstruction originating from the polar
nature of the LaMnO3 (001) films. Our results demonstrate how new emergent
functionalities can be visualized and engineered in atomically thick oxide
films at the atomic level.",1409.0520v1
2014-09-08,Strain induced edge magnetism at zigzag edge in graphene quantum dot,"We study the temperature dependent magnetic susceptibility of a strained
graphene quantum dot by using the determinant quantum Monte Carlo method.
Within the Hubbard model on a honeycomb lattice, our unbiased numerical results
show that a relative small interaction $U$ may lead to a edge ferromagnetic
like behavior in the strained graphene quantum dot, and a possible room
temperature transition is suggested. Around half filling, the ferromagnetic
fluctuations at the zigzag edge is strengthened both markedly by the on-site
Coulomb interaction and the strain, especially in low temperature region. The
resultant strongly enhanced ferromagnetic like behavior may be important for
the development of many applications.",1409.2341v2
2014-09-12,Reversal-mechanism of in-plane current induced perpendicular switching in a single ferromagnetic layer,"We propose a magnetization reversal model to explain the perpendicular
switching of a single ferromagnetic layer induced by an in-plane current.
Contrary to previously proposed reversal mechanisms that such magnetic
switching is directly from the Rashba or spin Hall effects, we suggest that
this type of switching arises from the current-induced chirality dependent
domain wall motion. By measuring the field dependent switching behaviors, we
show that such switching can also be achieved between any two multidomain
states, and all of these switching behaviors can be well explained by this
model. This model indicates that the spin Hall angle in such structures may be
overestimated and also predicts similar switching behaviors in other
ferromagnetic structures with chiral domain walls or skyrmions.",1409.3652v1
2014-09-22,Phase separation in a spin-orbit coupled Bose-Einstein condensate,"We study a spin-orbit (SO) coupled hyperfine spin-1 Bose-Einstein condensate
(BEC) in a quasi-one-dimensional trap. For a SO-coupled BEC in a
one-dimensional box, we show that in the absence of the Rabi term, any non-zero
value of SO coupling will result in a phase separation among the components for
a ferromagnetic BEC, like $^{87}$Rb. On the other hand, SO coupling favors
miscibility in a polar BEC, like $^{23}$Na. In the presence of a harmonic trap,
which favors miscibility, a ferromagnetic BEC phase separates, provided the
SO-coupling strength and number of atoms are greater than some critical value.
The Rabi term favors miscibility irrespective of the nature of the spin
interaction: ferromagnetic or polar.",1409.6211v2
2014-10-02,Observation of Majorana Fermions in Ferromagnetic Atomic Chains on a Superconductor,"Majorana fermions are predicted to localize at the edge of a topological
superconductor, a state of matter that can form when a ferromagnetic system is
placed in proximity to a conventional superconductor with strong spin-orbit
interaction. With the goal of realizing a one-dimensional topological
superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the
surface of superconducting lead (Pb). Using high-resolution spectroscopic
imaging techniques, we show that the onset of superconductivity, which gaps the
electronic density of states in the bulk of the Fe chains, is accompanied by
the appearance of zero energy end states. This spatially resolved signature
provides strong evidence, corroborated by other observations, for the formation
of a topological phase and edge-bound Majorana fermions in our atomic chains.",1410.0682v1
2014-10-08,Flat-band ferromagnetism in the multilayer Lieb optical lattice,"We theoretically study magnetic properties of two-component cold fermions in
half-filled multilayer Lieb optical lattices, i.e., two, three, and several
layers, using the dynamical mean-field theory. We clarify that the magnetic
properties of this system become quite different depending on whether the
number of layers is odd or even. In odd-number-th layers in an odd-number-layer
system, finite magnetization emerges even with an infinitesimal interaction.
This is a striking feature of the flatband ferromagnetic state in multilayer
systems as a consequence of the Lieb theorem. In contrast, in even-number
layers, magnetization develops from zero on a finite interaction. These
different magnetic behaviours are triggered by the flat bands in the local
density of states and become identical in the limit of the infinite-layer
(i.e., three-dimensional) system. We also address how interlayer hopping
affects the magnetization process. Further, we point out that layer
magnetization, which is a population imbalance between up and down atoms on a
layer, can be employed to detect the emergence of the flat-band ferromagnetic
state without addressing sublattice magnetization.",1410.2166v1
2014-10-13,Anomalous temperature and field behaviors of magnetization in cubic lattice frustrated ferromagnets,"Thermodynamic properties of cubic Heisenberg ferromagnets with competing
exchange interactions are considered near the frustration point where the
coefficient $D$ in the spin-wave spectrum $E_{\mathbf{k}}\sim D k^{2}$
vanishes. Within the Dyson-Maleev formalism it is found that at low
temperatures thermal fluctuations stabilize ferromagnetism by increasing the
value of $D$. For not too strong frustration this leads to an unusual ""concave""
shape of the temperature dependence of magnetization, which is in agreement
with experimental data on the europium chalcogenides. Anomalous temperature
behavior of magnetization is confirmed by Monte Carlo simulation. Strong field
dependence of magnetization (paraprocess) at finite temperature is found near
the frustration point.",1410.3264v2
2014-10-15,Equivalence of a mixing condition and the LSI in spin systems with infinite range interaction,"We investigate unbounded continuous spin-systems with infinite-range
interactions. We develop a new technique for deducing decay of correlations
from a uniform Poincar\'e inequality based on a directional Poincar\'e
inequality, which we derive through an averaging procedure. We show that this
decay of correlations is equivalent to the Dobrushin-Shlosman mixing condition.
With this, we also state and provide a partial answer to a conjecture regarding
the relationship between the relaxation rates of non-ferromagnetic and
ferromagnetic systems. Finally, we show that for a symmetric, ferromagnetic
system with zero boundary conditions, a weaker decay of correlations can be
bootstrapped.",1410.3924v3
2014-10-15,Non-linear spin transport in a rectifying ferromagnet/semiconductor Schottky contact,"The electrical creation and detection of spin accumulation in
ferromagnet/semiconductor Schottky contacts that exhibit highly non-linear and
rectifying electrical transport is evaluated. If the spin accumulation in the
semiconductor is small, the expression for the spin voltage is identical to
that of linear transport. However, if the spin accumulation is comparable to
the characteristic energy scale that governs the degree of non-linearity, the
spin detection sensitivity and the spin voltage are notably reduced. Moreover,
the non-linearity enhances the back-flow of spins into the ferromagnet and its
detrimental effect on the injected spin current, and the contact resistance
required to avoid back-flow is larger than for linear transport. It is also
shown that by virtue of the non-linearity, a non-magnetic metal contact can be
used to electrically detect spin accumulation in a semiconductor.",1410.3994v2
2014-10-15,Transport gap and hysteretic behavior of the Ising quantum Hall ferromagnets in Landau levels $\left\vert N\right\vert >0$ of bilayer graphene,"The chiral two-dimensional electron gas in Landau levels $\left\vert
N\right\vert >0$ of a Bernal-stacked graphene bilayer has a valley-pseudospin
Ising quantum Hall ferromagnetic behavior at odd filling factors $\nu _{N}=1,3$
of these fourfold degenerate states. At zero interlayer electrical bias, the
ground state at these fillings is spin polarized and electrons occupy one
valley or the other while a finite electrical bias produces a series of valley
pseudospin-flip transitions. In this work, we extend the Ising behavior to
chirally-stacked multilayer graphene and discuss the hysteretic behavior of the
Ising quantum Hall ferromagnets. We compute the transport gap due to different
excitations: bulk electron-hole pairs, electron-hole pairs confined to the
coherent region of a valley-pseudospin domain wall, and spin or
valley-pseudospin skyrmion-antiskyrmion pairs. We determine which of these
excitations has the lowest energy at a given value of the Zeeman coupling,
bias, and magnetic field.",1410.4232v1
2014-10-24,Phenomenological theory of magneto-electric coupling in granular multiferroics,"We study coupling between the ferroelectric polarization and magnetization of
granular ferromagnetic film using a phenomenological model of combined
multiferroic system consisting of granular ferromagnetic film placed above the
ferroelectric (FE) layer. The coupling is due to screening of Coulomb
interaction in the granular film by the FE layer. Below the FE Curie
temperature the magnetization has hysteresis as a function of electric field.
Below the magnetic ordering temperature the polarization has hysteresis as a
function of magnetic field. We study the magneto-electric coupling for weak and
strong spatial dispersion of the FE layer. The effect of mutual influence
decreases with increasing the spatial dispersion of the FE layer. For weak
dispersion the strongest coupling occurs in the vicinity of the
ferroelectric-paraelectric phase transition. For strong dispersion the
situation is the opposite. We study the magneto-electric coupling as a function
of distance between the FE layer and the granular film. For large distances the
coupling decays exponentially due to the exponential decrease of electric field
produced by the oscillating charges in the granular ferromagnetic film.",1410.6536v1
2014-10-24,Non-Fermi Liquid Behavior Close to a Quantum Critical Point in a Ferromagnetic State without Local Moments,"A quantum critical point (QCP) occurs upon chemical doping of the weak
itinerant ferromagnet Sc_{3.1}In. Remarkable for a system with no local
moments, the QCP is accompanied by non-Fermi liquid (NFL) behavior, manifested
in the logarithmic divergence of the specific heat both in the ferro- and the
paramagnetic states. Sc_{3.1}In displays critical scaling and NFL behavior in
the ferromagnetic state, akin to what had been observed only in f-electron,
local moment systems. With doping, critical scaling is observed close to the
QCP, as the critical exponents, and delta, gamma and beta have weak composition
dependence, with delta nearly twice, and beta almost half of their respective
mean-field values. The unusually large paramagnetic moment mu_PM~1.3 mu_B/F.U.
is nearly composition-independent. Evidence for strong spin fluctuations,
accompanying the QCP at x_c = 0.035 +- 0.005, may be ascribed to the reduced
dimensionality of Sc_{3.1}In, associated with the nearly one-dimensional Sc-In
chains.",1410.6850v1
2014-10-30,Intrinsic synchronization of an array of spin-torque oscillators driven by the spin-Hall effect,"This paper micromagnetically studies the magnetization dynamics driven by the
spin-Hall effect in a Platinum/Permalloy bi-layer. For a certain field and
current range, the excitation of a uniform mode, characterized by a power with
a spatial distribution in the whole ferromagnetic cross section, is observed.
We suggest to use the ferromagnet of the bi-layer as basis for the realization
of an array of spin-torque oscillators (STOs): the Permalloy ferromagnet will
act as shared free layer, whereas the spacers and the polarizers are built on
top of it. Following this strategy, the frequency of the uniform mode will be
the same for the whole device, creating an intrinsic synchronization. The
synchronization of an array of parallely connected STOs will allow to increase
the output power, as necessary for technological applications.",1410.8342v1
2014-11-01,Ferromagnetic interactions and martensitic transformation in Fe doped Ni-Mn-In shape memory alloys,"The structure, magnetic and martensitic properties of Fe doped Ni-Mn-In
magnetic shape memory alloys have been studied by differential scanning
calorimetry, magnetization, resistivity, X-ray diffraction (XRD) and EXAFS.
While Ni$_{2}$MnIn$_{1-x}$Fe$_{x}$ ($0 \le x \le 0.6$) alloys are ferromagnetic
and non martensitic, the martensitic transformation temperature in
Ni$_{2}$Mn$_{1.5} $In$_{1-y}$Fe$_{y}$ and Ni$_{2}$Mn$ _{1.6}
$In$_{1-y}$Fe$_{y}$ increases for lower Fe concentrations ($y \le 0.05$) before
decreasing sharply for higher Fe concentrations. XRD analysis reveals presence
of cubic and tetragonal structural phases in Ni$_{2}$MnIn$_{1-x}$Fe$_{x}$ at
room temperature with tetragonal phase content increasing with Fe doping. Even
though the local structure around Mn and Ni in these Fe doped alloys is similar
to martensitic Mn rich Ni-Mn-In alloys, presence of ferromagnetic interactions
and structural disorder induced by Fe affect Mn-Ni-Mn antiferromagnetic
interactions resulting in suppression of martensitic transformation in these Fe
doped alloys.",1411.0058v1
2014-11-03,Strain dependence of antiferromagnetic interface coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices,"We have investigated the magnetic response of La0.7Sr0.3MnO3/SrRuO3
superlattices to biaxial in-plane strain applied in-situ. Superlattices grown
on piezoelectric substrates of 0.72PbMg1/3Nb2/3O3-0.28PbTiO3(001) (PMN-PT) show
strong antiferromagnetic coupling of the two ferromagnetic components. The
coupling field of mu0HAF = 2.8 T is found to decrease by deltaHAF/delta epsilon
~ -520 mT %-1 under reversible biaxial strain mu0HAF at 80 K in a
[La0.7Sr0.3MnO3(22)/SrRuO3(55)]15 superlattice. This reveals a significant
strain effect on interfacial coupling. The applied in-plane compression
enhances the ferromagnetic order in the manganite layers which are under
as-grown tensile strain. It is thus difficult to disentangle the contributions
from strain-dependent antiferromagnetic Mn-O-Ru interface coupling and Mn-O-Mn
ferromagnetic double exchange near the interface, since the enhanced magnetic
order of Mn spins leads to a larger net coupling of SrRuO3 layers at the
interface. Strain-dependent orbital occupation in a single-ion picture cannot
explain the sign of the observed strain dependence, whereas the enhanced Mn
order at the interface is qualitatively in line with it.",1411.0411v2
2014-11-11,Striped Ferronematic ground states in a spin-orbit coupled $S=1$ Bose gas,"We theoretically establish the mean-field phase diagram of a homogeneous
spin-$1$, spin-orbit coupled Bose gas as a function of the spin-dependent
interaction parameter, the Raman coupling strength and the quadratic Zeeman
shift. We find that the interplay between spin-orbit coupling and
spin-dependent interactions leads to the occurrence of ferromagnetic or
ferronematic phases which also break translational symmetry. For weak Raman
coupling, increasing attractive spin-dependent interactions (as in $^{87}$Rb or
$^7$Li) induces a transition from a uniform to a stripe XY ferromagnet (with no
nematic order). For repulsive spin-dependent interactions however (as in
$^{23}$Na), we find a transition from an $XY$ spin spiral phase ($<S_{z} >= 0$
and uniform total density) with uniaxial nematic order, to a biaxial
ferronematic, where the total density, spin vector and nematic director
oscillate in real space. We investigate the stability of these phases against
the quadratic Zeeman effect, which generally tends to favor uniform phases with
either ferromagnetic or nematic order but not both. We discuss the relevance of
our results to ongoing experiments on spin-orbit coupled, spinor Bose gases.",1411.2990v1
2014-11-13,Tunnel Magnetoresistance with Atomically Thin Two-Dimensional Hexagonal Boron Nitride Barriers,"The two-dimensional atomically thin insulator hexagonal boron nitride (h-BN)
constitutes a new paradigm in tunnel based devices. A large band gap along with
its atomically flat nature without dangling bonds or interface trap states
makes it an ideal candidate for tunnel spin transport in spintronic devices.
Here, we demonstrate the tunneling of spin-polarized electrons through large
area monolayer h-BN prepared by chemical vapor deposition in magnetic tunnel
junctions. In ferromagnet/h-BN/ferromagnet heterostructures fabricated over a
chip scale, we show tunnel magneto resistance at room temperature. Measurements
at different bias voltages and on multiple devices with different ferromagnetic
electrodes establish the spin polarized tunneling using h-BN barriers. These
results open the way for integration of 2D monolayer insulating barriers in
active spintronic devices and circuits operating at ambient temperature, and
for further exploration of their properties and prospects.",1411.3524v1
2014-11-14,Lifetimes of Magnons in Two-Dimensional Diluted Ferromagnetic Systems,"Spin dynamics in low dimensional magnetic systems has been of fundamental
importance for a long time and has currently received an impetus owing to the
emerging field of nanoelectronics. Knowledge of the spin wave lifetimes, in
particular, can be favorable for future potential applications. We investigate
the low-temperature spin wave excitations in two-dimensional disordered
ferromagnetic systems, with a particular focus on the long wavelength magnon
lifetimes. A semi-analytical Green's functions based approach is used to
determine the dynamical spectral functions, for different magnetic impurity
concentrations, from which the intrinsic linewidth is extracted. We obtain an
unambiguous $q^4$ scaling of the magnon linewidth which is ascribed to the
disorder induced damping of the spin waves, thereby settling a longstanding
unresolved issue on the wave-vector dependence. Our findings are also in good
agreement with previous theoretical studies on Heisenberg ferromagnets.
Additionally, we demonstrate the futility of using the low moments associated
with the spectral densities to evaluate the magnon dispersions and lifetimes.",1411.3876v2
2014-11-22,On the origin of CE-type orbital fluctuations in the ferromagnetic metallic La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$,"We investigate the orbital fluctuations in the ferromagnetic-metallic phase
of La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ by considering a two orbital model within a
tight-binding description which reproduces the ARPES Fermi surface. We find
strong antisymmetric transverse orbital fluctuations at wavevector ($ 0.5 \pi,
0.5 \pi$) resulting from the Fermi-surface nesting between the portions of
bonding and antibonding bands instead of the widely believed nesting between
the portions of bonding band despite their flat segments, which provide an
insight into the origin of so called CE-type orbital fluctuations in the
ferromagnetic-metallic phase. Subsequent renormalization of the phonons near
wavevector ($0.5 \pi,0.5 \pi$) and the behavior of the phonon linewidth as a
function of momentum are in agreement with the inelastic neutron scattering
experiments.",1411.6088v1
2014-12-23,Temperature controlled motion of an antiferromagnet-ferromagnet interface within a dopant-graded FeRh epilayer,"Chemically ordered B2 FeRh exhibits a remarkable
antiferromagnetic-ferromagnetic phase transition that is first order. It thus
shows phase coexistence, usually by proceeding though nucleation at random
defect sites followed by propagation of phase boundary domain walls. The
transition occurs at a temperature that can be varied by doping other metals
onto the Rh site. We have taken advantage of this to yield control over the
transition process by preparing an epilayer with oppositely directed doping
gradients of Pd and Ir throughout its height, yielding a gradual transition
that occurs between 350~K and 500~K. As the sample is heated, a horizontal
antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up
through the layer, its position controlled by the temperature. This mobile
magnetic domain wall affects the magnetisation and resistivity of the layer in
a way that can be controlled, and hence exploited, for novel device
applications.",1412.7346v1
2014-12-24,Direct experimental evidence of multiferroicity in a nanocrystalline Zener polaron ordered manganite,"We discuss the particle size driven tunability of the coexistence of
ferromagnetism and ferroelectricity in Pr0.67Ca0.33MnO3(PCMO) with the help of
x ray diffraction, magnetization, impedance spectroscopy, and remanent
polarization measurements. The remanent polarization measurements using the
positive up negative down method clearly prove the existence of
ferroelectricity in PCMO with phase separation between Zener polaron(ZP)
ordered P21nm and disordered Pbnm structures. We also find that the
ferroelectric response is enhanced in nanocrystalline samples so long as ZP
ordering is not destroyed while the long-range antiferromagnetic ordering at
low temperature in bulk system is replaced by ferromagnetic correlations in
nanoparticles. The conclusion that by reducing the crystallite size it might be
possible to make ferromagnetism and ferroelectricity coexist near room
temperature should be generally applicable to all ZP ordered manganites.",1412.7723v1
2014-12-26,Domain wall of a ferromagnet on a three-dimensional topological insulator,"Topological insulators (TIs) show rich phenomena and functions which can
never be realized in ordinary insulators. Most of them come from the peculiar
surface or edge states. Especially, the quantized anomalous Hall effect (QAHE)
without an external magnetic field is realized in the two-dimensional
ferromagnet on a three-dimensional TI which supports the dissipationless edge
current. Here we demonstrate theoretically that the domain wall of this
ferromagnet, which carries edge current, is charged and can be controlled by
the external electric field. The chirality and relative stability of the Neel
wall and Bloch wall depend on the position of the Fermi energy as well as the
form of the coupling between the magnetic moments and orbital of the host TI.
These findings will pave a path to utilize the magnets on TI for the
spintronics applications.",1412.7910v2
2014-12-29,Electrically Tunable Magnetism in Magnetic Topological Insulators,"The external controllability of the magnetic properties in topological
insulators would be important both for fundamental and practical interests.
Here we predict the electric-field control of ferromagnetism in a thin film of
insulating magnetic topological insulators. The decrease of band inversion by
the application of electric fields results in a reduction of magnetic
susceptibility, and hence in the modification of magnetism. Remarkably, the
electric field could even induce the magnetic quantum phase transition from
ferromagnetism to paramagnetism. We further propose a topological transistor
device in which the dissipationless charge transport of chiral edge states is
controlled by an electric field. In particular, the field-controlled
ferromagnetism in magnetic topological insulator can be used for voltage based
writing of magnetic random access memories in magnetic tunnel junctions. The
simultaneous electrical control of magnetic order and chiral edge transport in
such devices may lead to electronic and spintronic applications for topological
insulators.",1412.8237v5
2015-01-05,A novel platform for two-dimensional chiral topological superconductivity,"We show that the surface of an $s$-wave superconductor decorated with a
two-dimensional lattice of magnetic impurities can exhibit chiral topological
superconductivity. If impurities order ferromagnetically and the
superconducting surface supports a sufficiently strong Rashba-type spin-orbit
coupling, Shiba sub-gap states at impurity locations can hybridize into
Bogoliubov bands with non-vanishing, sometimes large, Chern number $C$. This
topological superconductor supports $C$ chiral Majorana edge modes. We
construct phase diagrams for model two-dimensional superconductors, accessing
the dilute and dense magnetic impurity limits analytically and the intermediate
regime numerically. To address potential experimental systems, we identify
stable configurations of ferromagnetic iron atoms on the Pb (111) surface and
conclude that ferromagnetic adatoms on Pb surfaces can provide a versatile
platform for two-dimensional topological superconductivity.",1501.00999v1
2015-01-09,"Collective magnetization dynamics in ferromagnetic (Ga,Mn)As mediated by photo-excited carriers","We present a study of photo-excited magnetization dynamics in ferromagnetic
(Ga,Mn)As films observed by time-resolved magneto-optical measurements. The
magnetization precession triggered by linearly polarized optical pulses in the
absence of an external field shows a strong dependence on photon frequency when
the photo-excitation energy approaches the band-edge of (Ga,Mn)As. This can be
understood in terms of magnetic anisotropy modulation by both laser heating of
the sample and by hole-induced non-thermal paths. Our findings provide a means
for identifying the transition of laser-triggered magnetization dynamics from
thermal to non-thermal mechanisms, a result that is of importance for ultrafast
optical spin manipulation in ferromagnetic materials via non-thermal paths.",1501.02083v1
2015-01-12,Electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation,"The two-photon momentum distribution of annihilating electron-positron pairs
in ferromagnetic nickel (Ni) was determined by measuring the spin-polarized
two-dimensional angular correlation of annihilation radiation (ACAR). The
spectra were compared with theoretical results obtained within LDA+DMFT, a
combination of the local density approximation (LDA) and the many-body
dynamical mean-field theory (DMFT). The self-energy describing the electronic
correlations in Ni is found to make important anisotropic contributions to the
momentum distribution which are not present in LDA. Based on a detailed
comparison of the theoretical and experimental results the strength of the
local electronic interaction U in ferromagnetic Ni is determined as 2.0 +- 0.1
eV.",1501.02584v2
2015-01-13,Bound states of a ferromagnetic wire in a superconductor,"We consider the problem of bound states in strongly anisotropic ferromagnetic
impurities in a superconductor, motivated by recent experiments that claim to
observe Majorana modes at the ends of ferromagnetic wires on a superconducting
substrate [S. Nadj-Perge et al., Science 346, 602 (2014)]. Generalizing the
successful theory of bound states of spherically symmetric impurities, we
consider a wire-like potential using both analytical and numerical approaches.
We find that away from the ends of the wire the bound states form bands with
pronounced van Hove singularities, giving rise to subgap peaks in the local
density of states. For sufficiently strong magnetization of the wire, we show
that this process generically produces a sharp peak at zero energy in the local
density of states near the ends of the wire. This zero-energy peak has
qualitative similarities to the claimed signature of a Majorana mode observed
in the aforementioned experiment.",1501.03149v3
2015-01-17,Kondo dynamics in one-dimensional doped ferromagnetic insulators,"Some well-established examples of itinerant-electron ferromagnetism in one
dimension occur in a Mott-insulating phase. We examine the consequences of
doping a ferromagnetic insulator and cou- pling magnons to gapless charge
fluctuations. Using a bosonization scheme for strongly interacting electrons,
we derive an effective field theory for the magnon-holon interaction. When the
magnon momentum matches the Fermi momentum of the holons, the backscattering of
the magnon at low energies gives rise to a Kondo effect of a pseudospin defined
from the chirality degree of freedom (right- or left-moving particles). The
crossover between weak-coupling and strong-coupling fixed points of the
effective mobile-impurity model is then investigated using a numerical
renormalization group approach.",1501.04220v1
2015-01-20,"Structural, electronic, and magnetic properties of tris(8-hydroxyquinoline)iron(III) molecules and its magnetic coupling with ferromagnetic surface: first-principles study","Using first-principles calculations, we have systematically investigated the
structural, electronic, and magnetic properties of facial (fac-) and meridional
(mer-) tris(8-hydroxyquinoline)iron(III) (Feq3) molecules and their interaction
with ferromagnetic substrate. Our calculation results show that for the
isolated Feq3, mer-Feq3 is more stable than the fac-Feq3; and both Feq3 isomers
have a high spin-state of 5 {\mu}B as the ground state when an on-site
Hubbard-U term is included to treat the highly localized Fe 3d electrons; while
the standard DFT calculations produce a low spin-state of 1 {\mu}B. These
magnetic behaviors can be understood by the octahedral ligand field splitting
theory. Furthermore, we found that fac-Feq3 has a stronger bonding to the Co
surface than mer-Feq3 and an anti-ferromagnetic coupling was discovered between
Fe and Co substrate, originating from the superexchange coupling between Fe and
Co mediated by the interface oxygen and nitrogen atoms. These findings suggest
that Feq3 molecular films may serve as a promising spin-filter material in
spintronic devices.",1501.04926v1
2015-01-22,Coexistence and interconvertibility of ferromagnetic and antiferromagnetic phases in the single crystal of Mn$_3$ single-molecule magnet,"We report the coexistence of ferromagnetic and antiferromagnetic phases in
the single crystal of Mn$_3$ single-molecule magnet. The coexistent state
appears within a certain period of time in the progress of either oxidation or
reduction during a reversible oxidation-reduction process, when the sample is
exposed in the air (oxygen) or the methyl vapor. We noticed an apparent change
in the molecular structure, which is also reversible in terms of that the
methyl group is dropped or added to the molecules during the oxidation or
reduction. The absence or presence of the methyl group in the molecules exert
an essential impact upon the intermolecular exchange interaction, and the
ferromagnetic phase comes from the heterogenous intermolecular bonds between
pairs of molecules of which one molecule has a methyl group whereas the other
has lost the methyl group. The reversible change in molecular structure
suggests the magnetic structure of Mn$_3$ might be designed and modulated at
molecular scale, which implies Mn$_3$ has a great application potential.",1501.05484v1
2015-01-27,Spontaneous PT symmetry breaking of a ferromagnetic superfluid in a gradient field,"We consider the interaction of a ferromagnetic spinor Bose-Einstein
condensate with a magnetic field gradient. The magnetic field gradient realizes
a spin-position coupling that explicitly breaks time-reversal symmetry T and
space parity P, but preserves the combined PT symmetry. We observe using
numerical simulations, a first-order phase transition spontaneously breaking
this re-maining symmetry. The transition to a low-gradient phase, in which
gradient effects are frozen out by the ferromagnetic interaction, suggests the
possibility of high-coherence magnetic sensors unaffected by gradient
dephasing.",1501.06830v3
2015-01-28,Spin Amplification by Controlled Symmetry Breaking for Spin-Based Logic,"Spin amplification is one of the most critical challenges for spintronics and
spin-based logic in order to achieve spintronic circuits with fan-out. We
propose a new concept for spin amplification that will allow a small spin
current in a non-magnetic spin channel to control the magnetization of an
attached ferromagnet. The key step is to bring the ferromagnet into an unstable
symmetric state (USS), so that a small spin transfer torque from a small spin
current can provide a magnetic bias to control the spontaneous symmetry
breaking and select the final magnetization direction of the ferromagnet. Two
proposed methods for achieving the USS configuration are voltage-controlled
Curie temperature (VC-TC) and voltage-controlled magnetic anisotropy (VC-MA).
We believe the development of new 2D magnetic materials with greater tunability
of VC-TC and VC-MA will be needed for practical applications. A successful
realization of spin amplification by controlled symmetry breaking will be
important for the implementation of existing spin-logic proposals (e.g. ""All
Spin Logic"") and could inspire alternative ideas for spintronic circuits and
devices.",1501.07125v2
2015-02-16,Effect of non-uniform exchange field in ferromagnetic graphene,"We have presented here the consequences of the non-uniform exchange field on
the spin transport issues in spin chiral configuration of ferromagnetic
graphene. Taking resort to the spin orbit coupling (SOC) term and non-uniform
exchange coupling term we are successful to express the expression of Hall
conductivity in terms of the exchange field and SOC parameters through the Kubo
formula approach. However, for a specific configuration of the exchange
parameter we have evaluated the Berry curvature of the system. We also have
paid attention to the study of SU(2) gauge theory of ferromagnetic graphene.
The generation of anti damping spin orbit torque in spin chiral magnetic
graphene is also briefly discussed.",1502.04453v1
2015-02-18,Strain-induced magnetic phase transition in SrCoO$_{3-δ}$ thin films,"It has been well established that both in bulk at ambient pressure and for
films under modest strains, cubic SrCoO$_{3-\delta}$ ($\delta < 0.2$) is a
ferromagnetic metal. Recent theoretical work, however, indicates that a
magnetic phase transition to an antiferromagnetic structure could occur under
large strain accompanied by a metal-insulator transition. We have observed a
strain-induced ferromagnetic to antiferromagnetic phase transition in
SrCoO$_{3-\delta}$ films grown on DyScO$_3$ substrates, which provide a large
tensile epitaxial strain, as compared to ferromagnetic films under lower
tensile strain on SrTiO$_3$ substrates. Magnetometry results demonstrate the
existence of antiferromagnetic spin correlations and neutron diffraction
experiments provide a direct evidence for a G-type antiferromagnetic structure
with Ne\'el temperatures between $T_N \sim 135\,\pm\,10\,K$ and $\sim
325\,\pm\,10\,K$ depending on the oxygen content of the samples. Therefore, our
data experimentally confirm the predicted strain-induced magnetic phase
transition to an antiferromagnetic state for SrCoO$_{3-\delta}$ thin films
under large epitaxial strain.",1502.05192v1
2015-02-18,Ferromagnetism of Pd(001) substrate induced by Antiferromagnetic CoO,"Our first-principles study has revealed unexpected spin polarization of the
Pd(001) substrate in contact with antiferromagnetic CoO overlayers. We give an
evidence that the ferromagnetism of Pd is caused by the zigzag positions of Co
atoms with respect to the Pd interface, resulted from the lattice-mismatch
driven structural relaxation. Thanks to the itinerant nature of its 4d
electrons, we see that the ferromagnetic properties of Pd are highly sensitive
to the local environment and can be enhanced further by increasing the
thickness of CoO overlayer film or/and by applying an additional uniaxial
pressure along c-axis exerted externally on the bottom layers of the Pd
substrate. Our finding provides new functionality for the interfacial moments
of the CoO/Pd system, which can be accessed experimentally, e.g., by the
magneto-optical Kerr effect (MOKE) or/and by element-resolved X-ray magnetic
circular dichroism (XMCD) measurement.",1502.05208v1
2015-01-18,Theoretical Exploration on the Magnetic Properties of Ferromagnetic Metallic Glass: An Ising Model on Random Recursive Lattice,"The ferromagnetic Ising spins are modeled on a recursive lattice constructed
from random-angled rhombus units with stochastic configurations, to study the
magnetic properties of the bulk Fe-based metallic glass. The integration of
spins on the structural glass model well represents the magnetic moments in the
glassy metal. The model is exactly solved by the recursive calculation
technique. The magnetization of the amorphous Ising spins, i.e. the glassy
metallic magnet is investigated by our modeling and calculation on a
theoretical base. The results show that the glassy metallic magnets has a lower
Curie temperature, weaker magnetization, and higher entropy comparing to the
regular ferromagnet in crystal form. These findings can be understood with the
randomness of the amorphous system, and agrees well with others' experimental
observations.",1502.06561v2
2015-02-27,Magnetoanisotropic Andreev Reflection in Ferromagnet/Superconductor Junctions,"Andreev reflection spectroscopy of ferromagnet/superconductor (FS) junctions
is an important probe of spin polarization. We theoretically investigate
spin-polarized transport in FS junctions in the presence of Rashba and
Dresselhaus interfacial spin-orbit fields and show that Andreev reflection can
be controlled by changing the magnetization orientation. We predict a giant in-
and out-of-plane magnetoanisotropy of the junction conductance. If the
ferromagnet is highly spin polarized---in the half-metal limit---the
magnetoanisotropic Andreev reflection depends universally on the spin-orbit
fields only. Our results show that Andreev reflection spectroscopy can be used
for sensitive probing of interfacial spin-orbit fields in FS junction.",1502.08022v2
2015-03-02,Measuring the magnetic moment density in patterned ultrathin ferromagnets with submicron resolution,"We present a new approach to infer the surface density of magnetic moments
$I_s$ in ultrathin ferromagnetic films with perpendicular anisotropy. It relies
on quantitative stray field measurements with an atomic-size magnetometer based
on the nitrogen-vacancy center in diamond. The method is applied to
microstructures patterned in a 1-nm-thick film of CoFeB. We report measurements
of $I_s$ with a few percent uncertainty and a spatial resolution in the range
of $(100$ nm)$^2$, an improvement by several orders of magnitude over existing
methods. As an example of application, we measure the modifications of $I_s$
induced by local irradiation with He$^+$ ions in an ultrathin ferromagnetic
wire. This method offers a new route to study variations of magnetic properties
at the nanoscale.",1503.00705v1
2015-03-07,"Modulation of ferromagnetism in (In,Fe)As quantum wells via electrically controlled deformation of the electron wavefunctions","We demonstrate electrical control of ferromagnetism in field-effect
transistors with a trilayer quantum well (QW) channel containing an ultrathin
n-type ferromagnetic semiconductor (In,Fe)As layer. A gate voltage is applied
to control the electron wavefunctions {\phi}i in the QW, such that the overlap
of {\phi}i and the (In,Fe)As layer is modified. The Curie temperature is
largely changed by 42%, whereas the change in sheet carrier concentration is 2
- 3 orders of magnitude smaller than that of previous gating experiments. This
result provides a new approach for versatile, low power, and ultrafast
manipulation of magnetization.",1503.02174v2
2015-03-12,Current induced torques in structures with ultra-thin IrMn antiferromagnet,"Relativistic current induced torques and devices utilizing antiferromagnets
have been independently considered as two promising new directions in
spintronics research. Here we report electrical measurements of the torques in
structures comprising a $\sim1$~nm thick layer of an antiferromagnet IrMn. The
reduced N\'eel temperature and the thickness comparable to the spin-diffusion
length allow us to investigate the role of the antiferromagnetic order in the
ultra-thin IrMn films in the observed torques. In a Ta/IrMn/CoFeB structure,
IrMn in the high-temperature phase diminishes the torque in the CoFeB
ferromagnet. At low temperatures, the antidamping torque in CoFeB flips sign as
compared to the reference Ta/CoFeB structure, suggesting that IrMn in the
antiferromagnetic phase governs the net torque acting on the ferromagnet. At
low temperatures, current induced torque signatures are observed also in a
Ta/IrMn structure comprising no ferromagnetic layer.",1503.03729v2
2015-03-23,Ferromagnetic Mn doped InSb studied at the atomic scale by cross-sectional STM,"We present an atomically resolved study of metal-organic vapor epitaxy grown
Mn doped InSb that is ferromagnetic at room-temperature. Both topographic and
spectroscopic measurements have been performed by cross-sectional scanning
tunneling microscopy. The measurements show a perfect crystal structure without
any precipitates and reveal that Mn acts as a shallow acceptor. The Mn
concentration obtained from the cross-sectional STM data compares well with the
intended doping concentration. No second phase material or (nano)clustering of
the Mn was observed. While the pair correlation function of the Mn atoms showed
that their local distribution is uncorrelated beyond the STM resolution for
observing individual dopants, disorder in the Mn ion location is clearly noted.
We discuss the implications of the observed disorder for a number of suggested
explanations of the room-temperature ferromagnetism in Mn doped InSb grown by
metal-organic vapor epitaxy.",1503.06825v1
2015-03-30,Van Hove singularity and ferromagnetic instability in phosphorene,"Using Wannier function-based interpolation techniques, we present compelling
numerical evidence for the presence of a saddle-point van Hove singularity at
the $\Gamma $ point near the phosphorene Fermi energy. We show that in
proximity of the van Hove singularity the spin susceptibility presents the
logarithmic temperature dependence typical of Liftshitz phase transitions.
Furthermore, we demonstrate that the critical temperature for the ferromagnetic
transition can be greatly increased (up to 0.05 K) if strain along the zigzag
ridges is applied. Although the ferromagnetic state would be very difficult to
experimentally reach, the logarithmic temperature behaviour of the spin
susceptibility due to the van Hove singularity is found to persist at much
higher temperatures (up to $\sim$97 K).",1503.08649v2
2015-04-02,Avoided ferromagnetic quantum critical point in CeRuPO,"CeRuPO is a rare example of a ferromagnetic (FM) Kondo-lattice system.
External pressure suppresses the ordering temperature to zero at about
$p_c\approx3$ GPa. Our ac-susceptibility and electrical-resistivity
investigations evidence that the type of magnetic ordering changes from FM to
antiferromagnetic (AFM) at about $p^*\approx0.87$ GPa. Studies in applied
magnetic fields suggest that ferromagnetic and antiferromagnetic correlations
compete for the ground state at $p>p^*$, but finally the AFM correlations win.
The change in the magnetic ground-state properties is closely related to the
pressure evolution of the crystalline-electric-field level (CEF) scheme and the
magnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. The
N\'{e}el temperature disappears abruptly in a first-order-like fashion at
$p_c$, hinting at the absence of a quantum critical point. This is consistent
with the low-temperature transport properties exhibiting Landau-Fermi-liquid
(LFL) behavior in the whole investigated pressure range up to 7.5 GPa.",1504.00612v1
2015-04-20,A-site driven ferroelectricity in strained ferromagnetic L2NiMnO6 thin films,"We report on theoretical and experimental investigation of A-site driven
ferroelectricity in ferromagnetic La2NiMnO6 thin films grown on SrTiO3
substrates. Structural analysis and density functional theory calculations show
that epitaxial strain stretches the rhombohedral La2NiMnO6 crystal lattice
along the [111]cubic direction, triggering a displacement of the A-site La ions
in the double perovskite lattice. The lattice distortion and the A-site
displacements stabilize a ferroelectric polar state in ferromagnetic La2NiMnO6
crystals. The ferroelectric state only appears in the rhombohedral La2NiMnO6
phase, where MnO6 and NiO6 octahedral tilting is inhibited by the 3-fold
crystal symmetry. Electron localization mapping showed that covalent bonding
with oxygen and 6s orbital lone pair formation are negligible in this material.",1504.04905v1
2015-04-23,Spin-Reorientation and Weak Ferromagnetism in Antiferromagnetic TbMn_{0.5}Fe_{0.5}O_3,"Orthorhombic single crystals of TbMn0.5Fe0.5O3 are found to exhibit
spin-reorientation, magnetization reversal and weak ferromagnetism. Strong
anisotropy effects are evident in the temperature dependent magnetization
measurements along the three crystallographic axes a, b and c. A broad magnetic
transition is visible at T_N (Fe/Mn) = 286 K due to paramagnetic to AxGyCz
ordering. A sharp transition is observed at T_SR (Fe/Mn) = 28 K, which is
pronounced along c axis in the form of a sharp jump in magnetization where the
spins reorient to GxAyFz configuration. The negative magnetization observed
below TSR Fe/Mn along c axis is explained in terms of domain wall pinning. A
component of weak ferromagnetism is observed in field-scans along c-axis but
below 28 K. Field-induced steps-like transitions are observed in hysteresis
measurement along b axis below 28 K. It is noted that no sign of Tb-order is
discernible down to 2 K. TbMn0.5Fe0.5O3 could be highlighted as a potential
candidate to evaluate its magneto-dielectric effects across the magnetic
transitions.",1504.06060v1
2015-04-28,CaMn$_2$Al$_{10}$: itinerant Mn magnetism on the verge of ferromagnetic order,"We report the discovery of \CMA, a metal with strong magnetic anisotropy and
moderate electronic correlations. Magnetization measurements find a Curie-Weiss
moment of $0.83\,\mathrm{\mu_B}$/Mn, significantly reduced from the Hund's rule
value, and the magnetic entropy obtained from specific heat measurements is
correspondingly small, only $\approx 9$ \% of $R \mathrm{ln}\,2$. These results
imply that the Mn magnetism is highly itinerant, a conclusion supported by
density functional theory calculations that find strong Mn-Al hybridization.
Consistent with the layered nature of the crystal structure, the magnetic
susceptibility $\chi$ is anisotropic below 20 K, with a maximum ratio of
$\chi_{[010]}/\chi_{[001]}\approx 3.5$. A strong power-law divergence
$\chi(T)\sim T^{-1.2}$ below 20 K implies incipient ferromagnetic order, and an
Arrott plot analysis of the magnetization suggests a vanishingly low Curie
temperature $T_C\sim 0$. Our experiments indicate that \CMA~is a rare example
of a Mn-based weak itinerant magnet that is poised on the verge of
ferromagnetic order.",1504.07649v1
2015-04-29,Half-metallic ferromagnetism in the RbSe and CsTe compounds with CsCl structure: A first-principles study,"We investigate the electronic structures and magnetic properties of RbSe and
CsTe compounds in CsCl, RS and ZB structures by using first-principles
calculation. It is shown that these two compounds exhibit half-metallic
ferromagnetism with an integer magnetic moment of 1.00 $\mu_B$ per formula in
all the three structures. Total energy calculations indicate the CsCl phase is
more stable than the other two phases. We investigate these two compounds with
CsCl structure in detail. The ferromagnetism results mainly from the
spin-polarization of p states of anion Se (Te) for the two compounds. The
half-metallicities of RbSe and CsTe compounds can be preserved up to 2.5\% and
0.8\% compression of lattice constants with respect to their equilibrium
lattices, respectively.",1504.07705v1
2015-05-12,Nonreciprocal spin wave propagation in chiral-lattice ferromagnets,"Spin current, i.e. the flow of spin angular momentum or magnetic moment, has
recently attracted much attention as the promising alternative for charge
current with better energy efficiency. Genuine spin current is generally
carried by the spin wave (propagating spin precession) in insulating
ferromagnets, and should hold the chiral symmetry when it propagates along the
spin direction. Here, we experimentally demonstrate that such a spin wave spin
current (SWSC) shows nonreciprocal propagation characters in a chiral-lattice
ferromagnet. This phenomenon originates from the interference of chirality
between the SWSC and crystal-lattice, which is mediated by the relativistic
spin-orbit interaction. The present finding enables the design of perfect spin
current diode, and highlights the importance of the chiral aspect in SWSC.",1505.02868v1
2015-05-24,Coexistence of superconductivity and complex 4$f$ magnetism in Eu$_{0.5}$Ce$_{0.5}$BiS$_{2}$F,"EuBiS$_{2}$F is a self-doped superconductor due to the mixed valence of Eu.
Here we report that, with the Ce substitution for Eu by 50 at.\%, the material
exhibits ferromagnetic ordering at 8 K for the Ce-4$f$ moment,
superconductivity at 2.2 K in the BiS$_2$ layers, and possibly
antiferromagnetic ordering at 2.1 K for the Eu-4$f$ spins. The Eu valence is
essentially divalent with the Ce incorporation. We tentatively interpret the
coexistence of ferromagnetism and superconductivity by considering different
Bi-6$p$ orbitals that are responsible for superconductivity itself and for
mediating the ferromagnetic interaction, respectively. We argue that the
antiferromagnetic ordering of the Eu-4$f$ spins is most likely due to a
magnetic dipole-dipole interaction.",1505.06447v1
2015-05-26,Observation of pure inverse spin Hall effect in ferromagnetic metals by FM/AFM exchange bias structures,"We report that the spin current generated by spin Seebeck effect (SSE) in
yttrium iron garnet (YIG) can be detected by a ferromagnetic metal (NiFe). By
using the FM/AFM exchange bias structure (NiFe/IrMn), inverse spin Hall effect
(ISHE) and planar Nernst effect (PNE) of NiFe can be unambiguously separated,
allowing us to observe a pure ISHE signal. After eliminating the in plane
temperature gradient in NiFe, we can even observe a pure ISHE signal without
PNE from NiFe itself. It is worth noting that a large spin Hall angle (0.098)
of NiFe is obtained, which is comparable with Pt. This work provides a kind of
FM/AFM exchange bias structures to detect the spin current by charge signals,
and highlights ISHE in ferromagnetic metals can be used in spintronic research
and applications.",1505.06911v2
2015-05-27,Proximity-free enhancement of anomalous Nernst effects in metallic multilayers,"The anomalous Nernst effect (ANE) has been investigated in
alternately-stacked multilayer films comprising paramagnetic and ferromagnetic
metals. We found that the ANE is enhanced with increasing the number of the
paramagnet/ferromagnet interfaces with keeping the total thickness of the films
constant, and that the enhancement appears even in the absence of magnetic
proximity effects; similar behavior was observed not only in Pt/Fe multilayers
but also in Au/Fe and Cu/Fe multilayers free from proximity ferromagnetism.
This universal enhancement of the ANE in the metallic multilayers suggests the
presence of unconventional interface-induced thermoelectric conversion in the
Fe films attached to the paramagnets.",1505.07183v1
2015-05-28,Determining Spin Polarization of Seebeck Coefficients via Anomalous Nernst Effect,"Recently, Seebeck coefficients of ferromagnetic conductors are found to be
spin-dependent. However straightforward method of accurately determining its
spin polarization is still to be developed. Here, we have derived a linear
dependence of anomalous Nernst coefficient on anomalous Hall angle with scaling
factor related to spin polarization of Seebeck coefficient, which has been
experimentally verified in [Co/Pt]n superlattices. Based on the dependence, we
have also evaluated spin polarization of Seebeck coefficient of some
ferromagnetic conductors. Besides, we have also found a new mechanism to
generate pure spin current from temperature gradient in
ferromagnetic/nonmagnetic hybrid system, which could improve efficiency from
thermal energy to spin current.",1505.07662v1
2015-05-28,On the dynamical stability of ferromagnetic Ru and Os in the bct structure: a first-principles study,"Recent theoretical studies have predicted magnetic states for Ru and Os in
the body centered tetragonal structure (bct) with c/a < 1. In this study, we
present first principles calculations of the phonon dispersion for
ferromagnetic Ru- and Os-bct along the epitaxial and uniaxial Bain paths, to
evaluate their dynamical stability. The phonon dispersions were computed using
the density function perturbation theory, including the gradient corrections to
the exchange-correlation functional within the plane-waves
ultrasoft-pseudopotential approximation. The phonon dispersion for the local
minimum in the Bain path with c/a < 1 as well as the uniaxial and epitaxial
strained structures are analyzed. We find imaginary frequencies along different
directions of the Brillouin zone, which indicates that both systems are
dynamically unstable. Consequently, ferromagnetic Ru and Os in the body
centered tetragonal structure with c/a < 1 are not truly metastable phases.",1505.07869v2
2015-06-01,Electrical detection of magnetization reversal without auxiliary magnets,"First-generation magnetic random access memories based on anisotropic
magnetoresistance required magnetic fields for both writing and reading. Modern
all-electrical read/write memories use instead non-relativistic spin-transport
connecting the storing magnetic layer with a reference ferromagnet. Recent
studies have focused on electrical manipulation of magnetic moments by
relativistic spin-torques requiring no reference ferromagnet. Here we report
the observation of a counterpart magnetoresistance effect in such a
relativistic system which allows us to electrically detect the sign of the
magnetization without an auxiliary magnetic field or ferromagnet. We observe
the effect in a geometry in which the magnetization of a uniaxial (Ga,Mn)As
epilayer is set either parallel or antiparallel to a current-induced
non-equilibrium spin polarization of carriers. In our structure, this
linear-in-current magnetoresistance reaches 0.2\% at current density of $10^6$
A cm$^{-2}$.",1506.00400v1
2015-06-04,Electronic structure and weak itinerant magnetism in metallic Y2Ni7,"We report a density functional study of the electronic structure and
magnetism of Y2Ni7. The results show itinerant magnetism very similar to that
in the weak itinerant ferromagnet Ni3Al. The electropositive Y atoms in Y2Ni7
serves to donate charge to the Ni host mostly in the form of $s$ electrons. The
non-spin-polarized state shows a high density of states at the Fermi level,
N(EF) due to flat bands. This leads to the ferromagnetic instability. However,
there are also several much more dispersive bands crossing E(F), which should
promote the conductivity. Spin fluctuation effects appear to be comparable to
or weaker than Ni3Al, based on comparison with experimental data. Y2Ni7
provides a uniaxial analogue to cubic Ni3Al for studying weak itinerant
ferromagnetism, suggesting detailed measurements of its low temperature
physical properties and spin fluctuations, as well experiments under pressure.",1506.01553v2
2015-06-06,Spin filter and spin valve in ferromagnetic graphene,"We propose and demonstrate that a EuO-induced and top-gated graphene
ferromagnetic junction can be simultaneously operated as a spin filter as well
as a spin valve. We attribute such a remarkable result to a coexistence of a
half-metal band and a common energy gap for opposite spins in ferromagnetic
graphene. We show that, both the spin filter and the spin valve can be
effectively controlled by a back gate voltage, and they survive for practical
metal contacts and finite temperature. Specifically, larger single spin
currents and on-state currents can be reached with contacts with work functions
similar to graphene, and the spin filter can operate at higher temperature than
the spin valve.",1506.02127v1
2015-06-11,A continuous family of equilibria in ferromagnetic media are ground states,"We show that a foliation of equilibria (a continuous family of equilibria
whose graph covers all the configuration space) in ferromagnetic models are
ground states.
  The result we prove is very general, and it applies to models with long range
interactions and many body. As an application, we consider several models of
networks of interacting particles including models of Frenkel-Kontorova type on
$\mathbb{Z}^d$ and one-dimensional quasi-periodic media.
  The result above is an analogue of several results in the calculus variations
(fields of extremals) and in PDE's. Since the models we consider are discrete
and long range, new proofs need to be given. We also note that the main
hypothesis of our result (the existence of foliations of equilibria) is the
conclusion (using KAM theory) of several recent papers. Hence, we obtain that
the KAM solutions recently established are minimizers when the interaction is
ferromagnetic (and transitive).",1506.03582v1
2015-06-19,Inverse spin Hall effect in a complex ferromagnetic oxide heterostructure,"Complex oxide heterostructures are hot candidates for post CMOS
multi-functional devices. Especially in spintronics applications ferromagnetic
oxides may play a key role because they can exhibit extraordinary high spin
polarization. Indeed, there are already plenty of examples in spintronics,
notably in the area of spin pumping and inverse spin Hall effect (ISHE)
\cite{Azevedo2011, Czeschka2011, Hahn2013, Obstbaum2014}. Although complex
oxides have been used in these experiments as a source of spin currents, they
have never been demonstrated to act as a spin sink that exhibits ISHE. Here we
show that in a heterostructure consisting of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$
(LSMO) and SrRuO$_{3}$ (SRO) the low temperature ferromagnet SRO can act as a
spin sink and exhibit a sizeable ISHE which persists even below its Curie
temperature. This result opens up new possibilities for application of all
oxide heterostructures in spintronics and may significantly extend the research
on spin Hall effect and related phenomena.",1506.05921v1
2015-06-20,"Common effect of chemical and external pressures on the magnetic properties of $R$CoPO ($R$ = La, Pr, Nd, Sm). II","The direct correspondence between Co band ferromagnetism and structural
parameters is investigated in the pnictide oxides $R$CoPO for different
rare-earth ions ($R$ = La, Pr, Nd, Sm) by means of muon-spin spectroscopy and
{\it ab-initio} calculations, complementing our results published previously
[G. Prando {\it et al.}, {\it Phys. Rev. B} {\bf 87}, 064401 (2013)]. Both the
transition temperature to the ferromagnetic phase $T_{_{\textrm{C}}}$ and the
volume of the crystallographic unit cell $V$ are found to be conveniently tuned
by the $R$ ionic radius and/or external pressure. A linear correlation between
$T_{_{\textrm{C}}}$ and $V$ is reported and {\it ab-initio} calculations
unambiguously demonstrate a full equivalence of chemical and external
pressures. As such, $R$ ions are shown to be influencing the ferromagnetic
phase only via the induced structural shrinkage without involving any active
role from the electronic $f$ degrees of freedom, which are only giving a
sizeable magnetic contribution at much lower temperatures.",1506.06211v1
2015-06-26,Macroscopic quantum tunneling in spin filter ferromagnetic Josephson junctions,"The interfacial coupling of two materials with different ordered phases, such
as a superconductor (S) and a ferromagnet (F) is driving new fundamental
physics and innovative applications. For example, the creation of spin-filter
Josephson junctions and the demonstration of triplet supercurrents have
suggested the potential of a dissipationless version of spintronics based on
unconventional superconductivity. Here we demonstrate evidence for active
quantum applications of S-F-S junctions, through the observation of macroscopic
quantum tunneling in Josephson junctions with GdN ferromagnetic insulator
barriers. We prove a clear transition from thermal to quantum regime at a
crossover temperature of about 100 mK at zero magnetic field in junctions which
demonstrate a clear signature of unconventional superconductivity. Following
previous demonstration of passive S-F-S phase shifters in a phase qubit, our
result paves the way to the active use of spin filter Josephson systems in
quantum hybrid circuits.",1506.08108v1
2015-07-06,Delta chain with anisotropic ferromagnetic and antiferromagnetic interactions,"We consider analytically and numerically an anisotropic spin-$\frac{1}{2}$
delta-chain (sawtooth chain) with nearest-neighbor ferromagnetic and
next-nearest-neighbor antiferromagnetic interactions. For certain values of the
interactions a lowest one-particle band becomes flat and there is a class of
localized-magnon eigenstates which form a ground state with a macroscopic
degeneracy. In this case the model depends on a single parameter which can be
chosen as the anisotropy of the exchange interactions. When this parameter
changes from zero to infinity the model interpolates between the
one-dimensional isotropic ferromagnet and the frustrated Ising model on the
delta-chain. It is shown that the low-temperature thermodynamic properties in
these limiting cases are governed by the specific structure of the excitation
spectrum. In particular, the specific heat has one or infinite number of
low-temperature maxima for the small or the large anisotropy parameter,
correspondingly. Numerical calculations of finite chains demonstrate that this
behavior is generic for definite values of the anisotropy parameter.",1507.01389v1
2015-07-13,Direct surface charging and alkali-metal doping for tuning the interlayer magnetic order in planar nanostructures,"The continuous reduction of magnetic units to ultra small length scales
inspires efforts to look for a suitable means of controlling magnetic states.
In this study we show two surface charge alteration techniques for tuning the
interlayer exchange coupling (IEC) of ferromagnetic layers separated by
paramagnetic spacers. Our study reveals that already a modest amount of extra
charge can switch the mutual alignment of the magnetization from
anti-ferromagnetic to ferromagnetic or vice verse. We also propose adsorption
of alkali metals as an alternative way of varying the electronic and chemical
properties of magnetic surfaces. Clear evidence is found that the interlayer
magnetic order can be reversed by adsorbing alkali metals on the magnetic
layer. Moreover, alkali metal overlayers strongly enhance the perpendicular
magnetic anisotropy in FePt thin films. These findings combined with atomistic
spin model calculations suggest that electronic or ionic way of surface
charging can have a crucial role for magnetic hardening and spin state control.",1507.03365v1
2015-07-30,"First-order ferromagnetic transition in single-crystalline (Mn,Fe)2(P,Si)","(Mn,Fe)2(P,Si) single crystals have been successfully grown by flux method.
Single crystal diffraction demonstrates that Mn0.83Fe1.17P0.72Si0.28
crystallizes in a hexagonal crystal structure (space group P-62m) at both 100
and 280 K, in the ferromagnetic and paramagnetic states, respectively. The
magnetization measurements show that the crystals display a first-order
ferromagnetic phase transition at their Curie temperature (TC). The preferred
magnetization direction in is along the c axis. A weak magnetic anisotropy of
K1 = 0.25x106 J/m3 and K2 = 0.19x106 J/m3 is found at 5 K. These values
indicate a soft magnetic behaviour favourable for magnetic refrigeration. A
series of discontinuous magnetization jumps is observed far below TC by
increasing the field at a constant temperature. These magnetization jumps are
irreversible, occur spontaneously at constant temperature and magnetic field,
but can be restored by cycling across the first-order phase transition.",1507.08655v1
2015-07-31,Topological spin transport by Brownian diffusion of domain walls,"We propose thermally-populated domain walls (DWs) in an easy-plane
ferromagnetic insulator as robust spin carriers between two metals. The
chirality of a DW, which serves as a topological charge, couples to the metal
spin accumulation via spin-transfer torque and results in the
chirality-dependent thermal nucleation rates of DWs at the interface. After
overpopulated DWs of a particular (net) chirality diffuse and leave the
ferromagnet at the other interface, they reemit the spin current by spin
pumping. The conservation of the topological charge supports an algebraic decay
of spin transport as the length of the ferromagnet increases; this is analogous
to the decaying behavior of superfluid spin transport but contrasts with the
exponential decay of magnon spin transport. We envision that similar spin
transport with algebraic decay may be implemented in materials with exotic spin
phases by exploiting topological characteristics and the associated conserved
quantities of their excitations.",1507.08767v2
2015-08-01,Defect induced d0 ferromagnetism in a ZnO grain boundary,"Several experimental studies have referred to the grain boundary (GB) defect
as the origin of the ferromagnetism in ZnO. However, the mechanism of this
hypothesis has never been confirmed. Present study investigates the atomic
structure and the effect of point defects in a ZnO GB using the GGA+U
approximation. The relaxed GB possesses large periodicity and channels with 8
and 10 numbered atoms having 4 and 3 fold coordination. Unlike O vacancy (VO),
Zn vacancy (VZn) is preferentially aggregated at the GB, relative to the
bulk-like region, indicating the possibility of obtaining p-type conductivity
in polycrystalline ZnO. Although no magnetization is obtained from point
defect-free GB, VZn induces spin polarization as large as 0.68 {\mu}B/atom to
the O sites at the GB. Ferromagnetic exchange energy > 150 eV is obtained by
increasing the concentration of VZn and by the injection of holes into the
system. Electronic structure analysis indicates that the spin polarization
without external dopants originates from the O 2p orbitals, a common feature of
d0 semiconductors.",1508.00100v1
2015-08-04,Phase diagram of a frustrated asymmetric ferromagnetic spin ladder,"We perform a systematic investigation on the ground state of an asymmetric
two-leg spin ladder (where exchange couplings of the legs are unequal) with
ferromagnetic (FM) nearest-neighbor interaction and diagonal anti-ferromagnetic
frustration using the Density Matrix Renormalization Group (DMRG) method. When
the ladder is strongly asymmetric with moderate frustration, a magnetic canted
state is observed between a FM state and a singlet dimerized state. The phase
boundaries are dependent on the asymmetric strength $\alpha_{a}$. On the other
hand, when the asymmetric strength is intermediate, a so-called spin-stripe
state (spins align parallel on same legs, but antiparallel on rungs) is
discovered, and the system experiences a first-order phase transition from the
FM state to the spin-stripe state upon increasing frustration. We present
numerical evidence to interpret the phase diagram in terms of frustration and
the asymmetric strength.",1508.00723v2
2015-08-07,Ferromagnetic properties of SrRuO3 thin films deposited on the spin-triplet superconductor Sr2RuO4,"We report magnetic properties of epitaxial thin films of the itinerant
ferromagnet SrRuO3 deposited on the cleaved ab surface of the spin-triplet
superconductor Sr2RuO4. The films exhibit ferromagnetic transition near 160 K
as in the bulk SrRuO3, although the films are under 1.7% compressive strain.
The observed magnetization is even higher than that of the bulk SrRuO3. In
addition, we newly found that the magnetization relaxation after field removal
is strongly anisotropic: two relaxation processes are involved when magnetic
domains are aligned along the ab-plane.",1508.01628v1
2015-06-03,Stable room-temperature ferromagnetic phase at the FeRh(100) surface,"Interfaces and low dimensionality are sources of strong modifications of
electronic, structural, and magnetic properties of materials. FeRh alloys are
an excellent example because of the first-order phase transition taking place
at $\sim$400 K from an antiferromagnetic phase at room temperature to a high
temperature ferromagnetic one. It is accompanied by a resistance change and
volume expansion of about 1\%. We have investigated the electronic and magnetic
properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies
characterized by different probing depths, namely X-ray magnetic circular
dichroism and photoelectron spectroscopy. We thus reveal that the symmetry
breaking induced at the Rh-terminated surface stabilizes a surface
ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally
antiferromagnetic phase at room temperature. First-principles calculations
provide a microscopic description of the structural relaxation and the electron
spin-density distribution that fully support the experimental findings.",1508.01777v1
2015-08-09,Magnon-Magnon Interactions in O(3) Ferromagnets and Equations of Motion for Spin Operators,"The method of equations of motion for spin operators in the case of O(3)
Heisenberg ferromagnet is systematically analyzed starting from the effective
Lagrangian. It is shown that the random phase approximation and the Callen
approximation can be understood in terms of perturbation theory for type B
magnons. Also, the second order approximation of Kondo and Yamaji for one
dimensional ferromagnet is reduced to the perturbation theory for type A
magnons. An emphasis is put on the physical picture, i.e. on magnon-magnon
interactions and symmetries of the Heisenberg model. Calculations demonstrate
that all three approximations differ in manner in which the magnon-magnon
interactions arising from the Wess-Zumino term are treated, from where specific
features and limitations of each of them can be deduced.",1508.01974v1
2015-08-10,The role of dimensionality in the Kondo Ce$TX_{2}$ family: the case of CeCd$_{1-δ}$Sb$_{2}$,"Motivated by the presence of competing magnetic interactions in the heavy
fermion family Ce$TX_2$ ($T$ = transition metal, $X$ = pnictogen), here we
study the novel parent compound CeCd$_{1-\delta}$Sb$_{2}$ by combining
magnetization, electrical resistivity, and heat-capacity measurements. Contrary
to the antiferromagnetic (AFM) ground state observed in most members of this
family, the magnetic properties of our CeCd$_{1-\delta}$Sb$_{2}$ single
crystals revealed a ferromagnetic (FM) ordering at $T_{\rm c}$ = 3 K with an
unusual soft behavior. By using a mean field model including anisotropic
nearest-neighbors interactions and the tetragonal crystalline electric field
(CEF) Hamiltonian, a systematic analysis of our macroscopic data was obtained.
Our fits allowed us to extract a simple but very distinct CEF scheme, as
compared to the AFM counterparts. As in the previously studied ferromagnet
CeAgSb$_{2}$, a pure $|\pm 1/2 \rangle$ ground state is realized, hinting at a
general trend within the ferromagnetic members. We propose a general scenario
for the understanding of the magnetism in this family of compounds based on the
subtle changes of dimensionality in the crystal structure.",1508.02116v1
2015-08-17,Universality of the mean-field for the Potts model,"We consider the Potts model with $q$ colors on a sequence of weighted graphs
with adjacency matrices $A_n$, allowing for both positive and negative weights.
Under a mild regularity condition the mean-field prediction for the log
partition function of the Potts model on a sequence of matrices $A_n$ is
asymptotically correct, whenever $\text{tr}(A_n^2)=o(n)$. In particular, our
results are applicable for the Ising and the Potts models on any sequence of
graphs with average degree going to $+\infty$. Using this, we establish the
universality of the limiting log partition function of the ferromagnetic Potts
model for a sequence of asymptotically regular graphs, and that of the Ising
model for bi-regular bipartite graphs in both ferromagnetic and
anti-ferromagnetic domain. We also derive a large deviation principle for the
empirical measure of the colors for the Potts model on asymptotically regular
graphs.",1508.03949v2
2015-08-24,Magneto-Electric Effect for Multiferroic Thin Film by Monte Carlo Simulation,"Magneto-electric effect in a multiferroic heterostructure film, i.e. a
coupled ferromagnetic-ferroelectric thin film, has been investigated through
the use of the Metropolis algorithm in Monte Carlo simulations. A classical
Heisenberg model describes the energy stored in the ferromagnetic film, and we
use a pseudo-spin model with a transverse Ising Hamiltonian to characterise the
energy of electric dipoles in the ferroelectric film. The purpose of this
article is to demonstrate the dynamic response of polarisation is driven by an
external magnetic field, when there is a linear magneto-electric coupling at
the interface between the ferromagnetic and ferroelectric components.",1508.05701v2
2015-08-27,Magnetic structure and phase stability of the van der Waals bonded ferromagnet Fe3-xGeTe2,"The magnetic structure and phase diagram of the layered ferromagnetic
compound Fe$_3$GeTe$_2$ has been investigated by a combination of synthesis,
x-ray and neutron diffraction, high resolution microscopy, and magnetization
measurements. Single crystals were synthesized by self-flux reactions, and
single crystal neutron diffraction finds ferromagnetic order with moments of
1.11(5)$\mu_B$/Fe aligned along the $c$-axis at 4K. These flux-grown crystals
have a lower Curie temperature $T_{\textrm{c}}\approx$150K compared to crystals
previously grown by vapor transport ($T_{\textrm{c}}$=220K). The difference is
a reduced Fe content in the flux grown crystals, as illustrated by the behavior
observed in a series of polycrystalline samples. As Fe-content decreases, so
does the Curie temperature, magnetic anisotropy, and net magnetization. In
addition, Hall effect and thermoelectric measurements on flux-grown crystals
suggest multiple carrier types contribute to electrical transport in
Fe$_{3-x}$GeTe$_2$ and structurally-similar Ni$_{3-x}$GeTe$_2$.",1508.06959v3
2015-09-04,Stoner Magnetism in an Inversion Layer,"Motivated by recent experimental work on magnetic properties of Si-MOSFETs,
we report a calculation of magnetisation and susceptibility of electrons in an
inversion layer, taking into account the co-ordinate dependence of electron
wave function in the direction perpendicular to the plane. It is assumed that
the inversion-layer carriers interact via a contact repulsive potential, which
is treated at a mean-field level, resulting in a self-consistent change of
profile of the wave functions. We find that the results differ significantly
from those obtained in the pure 2DEG case (where no provision is made for a
quantum motion in the transverse direction). Specifically, the critical value
of interaction needed to attain the ferromagnetic (Stoner) instability is
decreased and the Stoner criterion is therefore relaxed. This leads to an
increased susceptibility and ultimately to a ferromagnetic transition deep in
the high-density metallic regime. In the opposite limit of low carrier
densities, a phenomenological treatment of the in-plane correlation effects
suggests a ferromagnetic instability above the metal-insulator transition.
Results are discussed in the context of the available experimental data.",1509.01320v1
2015-09-07,Spin-polarized edge currents and Majorana fermions in one- and two-dimensional topological superconductors,"We investigate the persistent currents, spin-polarized local density of
states, and spectral functions of topological superconductors constructed by
placing ferromagnetic impurities on top of an s-wave superconductor with Rashba
spin-orbit interaction. We solve self-consistently for the superconducting
order parameter and investigate both two-dimensional blocks and one-dimensional
wires of ferromagnetic impurities, with the magnetic moments pointing both
perpendicular and parallel to the surface. We find that the topologically
protected edge states of ferromagnetic blocks give rise to spin-polarized edge
currents, but that the total persistent current flows in opposite direction to
what is expected from the dispersion relation of the edge states. We also show
that the Majorana fermions at the end points of one-dimensional wires are
spin-polarized, which can be directly related to the spin-polarization of the
edge currents of two-dimensional blocks. Connections are also made to the
physics of the Yu-Shiba-Rusinov states for zero-dimensional impurities.",1509.02080v1
2015-09-08,Magnetic and structural properties of ferromagnetic Fe5PB2 and Fe5SiB2 and effects of Co and Mn substitutions,"Crystallographic and magnetic properties of Fe5PB2, Fe4CoPB2, Fe4MnPB2,
Fe5SiB2, Fe4CoSiB2, and Fe4MnSiB2 are reported. All adopt the tetragonal Cr5B3
structure-type and are ferromagnetic at room temperature with easy axis of
magnetization along the c-axis. The spin reorientation in Fe5SiB2 is observed
as an anomaly in the magnetization near 170 K, and is suppressed by
substitution of Co or Mn for Fe. The silicides are found to generally have
larger magnetic moments than the phosphides, but the data suggests smaller
magnetic anisotropy in the silicides. Cobalt substitution reduces the Curie
temperatures by more than 100 K and ordered magnetic moments by 16-20%, while
manganese substitution has a much smaller effect. This suggests Mn moments
align ferromagnetically with the Fe and that Co does not have an ordered moment
in these structures. Anisotropic thermal expansion is observed in Fe5PB2 and
Fe5SiB2, with negative thermal expansion seen along the c-axis of Fe5SiB2.
First principles calculations of the magnetic properties of Fe5SiB2 and
Fe4MnSiB2 are reported. The results, including the magnetic moment and
anisotropy, and are in good agreement with experiment.",1509.02544v1
2015-09-14,Ground-state phases of rung-alternated spin-1/2 Heisenberg ladder,"The ground-state phase diagram of Heisenberg spin-1/2 system on a two-leg
ladder with rung alternation is studied by combining analytical approaches with
numerical simulations. For the case of ferromagnetic leg exchanges a unique
ferrimagnetic ground state emerges, whereas for the case of antiferromagnetic
leg exchanges several different ground states are stabilized depending on the
ratio between exchanges along legs and rungs. For the more general case of a
honeycomb-ladder model for the case of ferromagnetic leg exchanges besides
usual rung-singlet and saturated ferromagnetic states we obtain a ferrimagnetic
Luttinger liquid phase with both linear and quadratic low energy dispersions
and ground state magnetization continuously changing with system parameters.
For the case of antiferromagnetic exchanges along legs, different dimerized
states including states with additional topological order are suggested to be
realized.",1509.04062v1
2015-09-16,Microwave excitation of spin wave beams in thin ferromagnetic films,"We present an approach enabling generation of narrow spin wave beams in thin
homogeneous ferromagnetic films. The main idea is to match the wave vector of
the spin wave with that corresponding to the spectral maximum of the exciting
microwave magnetic field only locally, in the region of space from which the
beam should be launched. We show that this can be achieved with the aid of a
properly designed coplanar waveguide transducer generating a nonuniform
microwave magnetic field. The resulting two-dimensional spin wave beams
obtained in micromagnetic simulations propagate over distances of several
micrometers. The proposed approach requires neither inhomogeneity of the
ferromagnetic film nor nonuniformity of the biasing magnetic field, and it can
be generalized to yield multiple spin wave beams of different width at the same
frequency. Other possible excitation scenarios and applications of spin wave
beam magnonics are also discussed.",1509.05061v2
2015-09-18,FPTAS for Hardcore and Ising Models on Hypergraphs,"Hardcore and Ising models are two most important families of two state spin
systems in statistic physics. Partition function of spin systems is the center
concept in statistic physics which connects microscopic particles and their
interactions with their macroscopic and statistical properties of materials
such as energy, entropy, ferromagnetism, etc. If each local interaction of the
system involves only two particles, the system can be described by a graph. In
this case, fully polynomial-time approximation scheme (FPTAS) for computing the
partition function of both hardcore and anti-ferromagnetic Ising model was
designed up to the uniqueness condition of the system. These result are the
best possible since approximately computing the partition function beyond this
threshold is NP-hard. In this paper, we generalize these results to general
physics systems, where each local interaction may involves multiple particles.
Such systems are described by hypergraphs. For hardcore model, we also provide
FPTAS up to the uniqueness condition, and for anti-ferromagnetic Ising model,
we obtain FPTAS where a slightly stronger condition holds.",1509.05494v1
2015-09-26,Spin relaxation near a ferromagnetic transition,"We study spin relaxation in dilute magnetic semiconductors near a
ferromagnetic transition, where spin fluctuations become strong. An enhancement
in the scattering rate of itinerant carriers from the spin fluctuations of
localized impurities leads to a change in the dominant spin relaxation
mechanism from Dyakonov-Perel to spin flips in scattering. On the ferromagnetic
side of the transition, we show that due to the presence of two magnetic
components -- the itinerant carriers and the magnetic impurities -- with
different gyromagnetic ratios, the relaxation rate of the total magnetization
can be quite different from the relaxation rate of the spin. Following a
disturbance of the equilibrium magnetization, the spin is initially
redistributed between the two components to restore the equilibrium
magnetization. It is only on a longer time scale, controlled by the spin-orbit
interaction, that the total spin itself relaxes to its equilibrium state.",1509.07926v1
2015-09-29,Field-free magnetization reversal by spin-Hall effect and exchange bias,"Magnetic random-access memory (MRAM) driven by spin-transfer torque (STT) is
a major contender for future memory applications. The energy dissipation
involved in writing remains problematic, even with the advent of more efficient
perpendicular magnetic anisotropy (PMA) devices. A promising alternative
switching mechanism employs spin-orbit torques and the spin-Hall effect (SHE)
in particular, but additional symmetry breaking is required to achieve
deterministic switching in PMA devices. Currently used methods rely on in-plane
magnetic fields or anisotropy gradients, which are not suitable for practical
applications. Here, we interface the magnetic layer with an anti-ferromagnetic
material. An in-plane exchange bias (EB) is created, and shown to enable
field-free SHE-driven magnetization reversal of a perpendicularly magnetized
Pt/Co/IrMn structure. Aside from the potential technological implications, our
experiment provides additional insight into the local spin structure at the
ferromagnetic/anti-ferromagnetic interface.",1509.08752v2
2015-10-07,Controllable intrinsic DC spin/valley Hall conductivity in ferromagnetic silicene: Exploring a fully spin/valley polarized transport,"We study intrinsic DC spin and valley Hall conductivity in doped
ferromagnetic silicene in the presence of an electric filed applied
perpendicular to silicene sheet. By calculating its energy spectrum and
wavefunction and by making use of Kubo formalism, we obtain a general relation
for the transverse Hall conductivity which can be used to obtain spin- and
valley-Hall conductivity. Our results, in the zero limit of the exchange field,
reduces to the previous results. Furthermore we discuss electrically tunable
spin and valley polarized transport in ferromagnetic silicene and obtain the
necessary conditions for observing a fully spin or valley polarized transport.",1510.02109v1
2015-10-13,Transportation of Static Magnetic Fields by a practically realizable Magnetic Hose,"A practically realizable magnetic hose, constructed by wrapping a
ferromagnetic cylinder with alternate superconductor-ferromagnet
heterostructure, was developed and its capability to transfer the static
magnetic fields, e.g., generated by an Nd-Fe-B magnet, was examined in this
letter. A diverse dependence of the transfer efficiency on the diameter of the
inner cylinder was found in the magnetic hose demonstrators and the underlying
cause was clarified by the finite-element simulations. Transfer efficiency of
over 50% in terms of a moderate field has been achieved in the best
demonstrator of this study, even with a thin sheet merely having moderate
magnetism to embody the ferromagnet in the heterostructure. This work links the
theoretically derived model with a physical reality and may also conceive
fantastic solutions to form a magnetic circuit with minimum leakage or to
create a magnetically shielded space, both of which are deemed promising in
most electromagnetic devices.",1510.03559v1
2015-10-15,Disorder-induced stabilization of the quantum Hall ferromagnet,"We report on an absolute measurement of the electronic spin polarization of
the $\nu=1$ integer quantum Hall state. The spin polarization is extracted in
the vicinity of $\nu=1$ (including at exactly $\nu=1$) via resistive NMR
experiments performed at different magnetic fields (electron densities), and
Zeeman energy configurations. At the lowest magnetic fields, the polarization
is found to be complete in a narrow region around $\nu=1$. Increasing the
magnetic field (electron density) induces a significant depolarization of the
system, which we attribute to a transition between the quantum Hall ferromagnet
and the Skyrmion glass phase theoretically expected as the ratio between
Coulomb interactions and disorder is increased. These observations account for
the fragility of the polarization previously observed in high mobility 2D
electron gas, and experimentally demonstrate the existence of an optimal amount
of disorder to stabilize the ferromagnetic state.",1510.04448v1
2015-10-19,Critical behavior of a triangular lattice Ising AF/FM bilayer,"We study a bilayer Ising spin system consisting of antiferromagnetic (AF) and
ferromagnetic (FM) triangular planes, coupled by ferromagnetic exchange
interaction, by standard Monte Carlo and parallel tempering methods. The AF/FM
bilayer is found to display the critical behavior completely different from
both the single FM and AF constituents as well as the FM/FM and AF/AF bilayers.
Namely, by finite-size scaling (FSS) analysis we identify at the same
temperature a standard Ising transition from the paramagnetic to FM state in
the FM plane that induces a ferrimagnetic state with a finite net magnetic
moment in the AF plane. At lower temperatures there is another phase
transition, that takes place only in the AF plane, to different ferrimagnetic
state with spins on two sublattices pointing parallel and on one sublattice
antiparallel to the spins on the FM plane. FSS indicates that the corresponding
critical exponents are close to the two-dimensional three-state ferromagnetic
Potts model values.",1510.05383v1
2015-10-21,"Equilibrium, Metastability, and Hysteresis in a Model Spin-crossover Material with Nearest-neighbor Antiferromagnetic-like and Long-range Ferromagnetic-like Interactions","Phase diagrams and hysteresis loops were obtained by Monte Carlo simulations
and a mean-field method for a simplified model of a spin-crossover material
with a two-step transition between the high-spin and low-spin states. This
model is a mapping onto a square-lattice $S=1/2$ Ising model with
antiferromagnetic nearest-neighbor and ferromagnetic Husimi-Temperley
(equivalent-neighbor) long-range interactions. Phase diagrams obtained by the
two methods for weak and strong long-range interactions are found to be
similar. However, for intermediate-strength long-range interactions, the Monte
Carlo simulations show that tricritical points decompose into pairs of critical
endpoints and mean-field critical points surrounded by horn-shaped regions of
metastability. Hysteresis loops along paths traversing the horn regions are
strongly reminiscent of thermal two-step transition loops with hysteresis,
recently observed experimentally in several spin-crossover materials. We
believe analogous phenomena should be observable in experiments and simulations
for many systems that exhibit competition between local antiferromagnetic-like
interactions and long-range ferromagnetic-like interactions caused by elastic
distortions.",1510.06357v2
2015-10-23,Goldstone mode stochastization in quantum Hall ferromagnet,"Experimental and theoretical studies of the coherent spin dynamics of
two-dimensional GaAs/AlGaAs electron gas were performed. The system in the
quantum Hall ferromagnet state exhibits a spin relaxation mechanism that is
determined by many-particle Coulomb interactions. In addition to the spin
exciton with changes in the spin quantum numbers of $\delta S\!=\!\delta S_z
\!=\!-1$, the quantum Hall ferromagnet supports a Goldstone spin exciton that
changes the spin quantum numbers to $\delta S\!=\!0$ and $\delta S_z\!=\!-1$,
which corresponds to a coherent spin rotation of the entire electron system to
a certain angle. The Goldstone spin exciton decays through a specific
relaxation mechanism that is unlike any other collective spin state.",1510.06900v1
2015-10-23,Mapping the domain wall pinning landscape in ferromagnetic films,"The propagation of domain walls in a ferromagnetic film is largely determined
by domain wall pinning at defects in the material. In this letter we map the
effective potential landscape for domain wall pinning in Permalloy films by
raster scanning a single ferromagnetic vortex and monitoring the hysteretic
vortex displacement vs. applied magnetic field. The measurement is carried out
using a differential magneto-optical microscopy technique which yields spatial
sensitivity $\sim 10$ nm. We present a simple algorithm for extracting an
effective pinning potential from the measurement of vortex displacement vs.
applied field. The resulting maps of the pinning potential reveal distinct
types of pinning sites, which we attribute to quasi-zero-, one-, and
two-dimensional defects in the Permalloy film.",1510.07059v2
2015-10-23,"Fast, nanoscale addressability of nitrogen-vacancy spins via coupling to a dynamic ferromagnetic vortex","The core of a ferromagnetic vortex domain creates a strong, localized
magnetic field which can be manipulated on nanosecond timescales, providing a
platform for addressing and controlling individual nitrogen-vacancy center
spins in diamond at room temperature, with nanometer-scale resolution. First,
we show that the ferromagnetic vortex can be driven into proximity with a
nitrogen-vacancy defect using small applied magnetic fields, inducing
significant nitrogen-vacancy spin splitting. Second, we find that the magnetic
field gradient produced by the vortex is sufficient to address spins separated
by nanometer length scales. By applying a microwave-frequency magnetic field,
we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced
coherent rotation of the spin state. Finally we demonstrate that by driving the
vortex on fast timescales, sequential addressing and coherent manipulation of
spins is possible on $\sim100$ ns timescales.",1510.07073v2
2015-10-26,Spatial evolution of the ferromagnetic phase transition in an exchange graded film,"A combination of experiments and numerical modeling was used to study the
spatial evolution of the ferromagnetic phase transition in a thin film
engineered to have a smooth gradient in exchange strength. Mean-field
simulations predict, and experiments confirm that a 100 nm Ni[x]Cu[1-x] alloy
film with Ni concentration that varies by 9 % as a function of depth behaves
predominantly as if comprised of a continuum of uncoupled ferromagnetic layers
with continuously varying Curie temperatures. A mobile boundary separating
ordered and disordered regions emerges as temperature is increased. We
demonstrate continuous control of the boundary position with temperature, and
reversible control of the magnetically ordered sample volume with magnetic
field.",1510.07535v1
2015-10-26,A Panoply of Orders from a Quantum Lifshitz Field Theory,"We propose a universal non-linear sigma model field theory for one
dimensional frustrated ferromagnets, which applies in the vicinity of a
""quantum Lifshitz point"", at which the ferromagnetic state develops a spin wave
instability. We investigate the phase diagram resulting from perturbations of
the exchange and of magnetic field away from the Lifshitz point, and uncover a
rich structure with two distinct regimes of different properties, depending
upon the value of a marginal, dimensionless, parameter of the theory. In the
regime relevant for one dimensional systems with low spin, we find a
metamagnetic transition line to a vector chiral phase. This line terminates in
a critical endpoint from which emerges a cascade of multipolar phases. We show
that the field theory has the property of ""asymptotic solubility"", so that a
particular saddle point approximation becomes asymptotically exact near the
Lifshitz point. Our results provide an analytic framework for prior numerical
results on frustrated ferromagnets, and can be applied much more broadly.",1510.07640v1
2015-10-27,Gate-Tunable Spin Transport and Giant Electroresistance in Ferromagnetic Graphene Vertical Heterostructures,"We investigate spin transport through ferromagnetic graphene vertical
heterostructures where a sandwiched tunneling layer is either a normal or
ferroelectric insulator. We show that the spin-polarization of the tunneling
current is electronically controlled via gate voltages. We also demonstrate
that the tunneling current of Dirac fermions can be prohibited when the spin
configuration of ferromagnetic graphene sheets is opposite. The giant
electroresistance can thus be developed by using the proposed heterostructure
in this study. The effects of temperature on the spin transport and the giant
electroresistance ratio are also investigated. Our findings discover the
prospect of manipulating the spin transport properties in vertical
heterostructures through an electric fields via gate and bias electrodes.",1510.07858v1
2015-10-28,Spin-$1$ $J_1-J_2-J_3$ ferromagnetic Heisenberg model with an easy-plane crystal field on the cubic lattice: A bosonic approach,"We examine the phase diagram of the spin-$1$ $J_1-J_2-J_3$ ferromagnetic
Heisenberg model with an easy-plane crystal field on the cubic lattice, in
which $J_1$ is the ferromagnetic exchange interaction between nearest
neighbors, $J_2$ is the antiferromagnetic exchange interaction between
next-nearest neighbors and $J_3$ is the antiferromagnetic exchange interaction
between next-next-nearest neighbors. Using the bond-operator formalism, we
investigate the phase transitions between the disordered paramagnetic phase and
the ordered ones.
  We show that the nature of the quantum phase transitions change as the
frustration parameters ($\frac{J_2}{J_1}$, $\frac{J_3}{J_1}$) are varied. The
zero-temperature phase diagram exhibits second- and first-order transitions,
depending on the energy gap behavior. Remarkably, we find a disordered
nonmagnetic phase, even in the absence of a crystal field, which is suggested
to be a quantum spin liquid candidate. We also depict the phase diagram at
finite temperature for some values of crystal field and frustration parameters.",1510.08412v1
2015-10-20,Exact asymmetric Skyrmion in anisotropic ferromagnet and its helimagnetic application,"Topological Skyrmions as intricate spin textures were observed experimentally
in helimagnets on 2d plane. Theoretical foundation of such solitonic states to
appear in pure ferromagnetic model, as exact solutions expressed through any
analytic function, was made long ago by Belavin and Polyakov (BP). We propose
an innovative generalization of the BP solution for an anisotropic ferromagnet,
based on a physically motivated geometric (in-)equality, which takes the exact
Skyrmion to a new class of functions beyond analyticity. The possibility of
stabilizing such metastable states in helimagnets is discussed with the
construction of individual Skyrmion and Skyrmion crystal with asymmetry, likely
to be detected in precision experiments.",1511.00712v2
2015-11-05,"Structural, Magnetic and Magneto-caloric studies of Ni50Mn30Sn20Shape Memory Alloy","We have synthesized a nominal composition of Ni50Mn30Sn20 alloy using arc
melting technique. Rietveld refinement confirms the austenite L21 structure in
Fm-3m space group. Electrical resistivity has been found to clearly exhibiting
two different phenomena viz. a magnetic transition from paramagnetic to
ferromagnetic and a structural transition from austenite to martensitic phase.
Thermo-magnetization measurements M(T) confirms ferromagnetic transition
temperature TC at 222 K and martensitic transition starting at 127 K(MS).
Magnetization measurement M(H) at 10 K confirms the ferromagnetic state.
Frequency dependence of ac susceptibility \c{hi}' at low temperature suggests
spin glass behavior in the system. The isothermal magnetic entropy change
values have been found to be 1.14 J/Kg.K, 2.69 J/Kg.K and 3.9 J/Kg.K, with
refrigeration capacities of 19.6 J/kg, 37.8 J/kg and 54.6 J/kg for the field
change of 1, 2 and 3 Tesla respectively at 227 K.",1511.01632v1
2015-11-16,On the ferromagnetic ground state of SmN,"SmN is a ferromagnetic semiconductor with the unusual property of an
orbital-dominant magnetic moment that is largely cancelled by an antiparallel
spin contribution, resulting in a near-zero net moment. However, there is a
basic gap in the understanding of the ferromagnetic ground state, with existing
density functional theory calculations providing values of the $4f$ magnetic
moments at odds with experimental data. To clarify the situation, we employ an
effective $4f$ Hamiltonian incorporating spin-orbit coupling, exchange, the
crystal field, and $J$-mixing to calculate the ground state $4f$ moments. Our
results are in excellent agreement with experimental data, revealing moderate
quenching of both spin and orbital moments to magnitudes of $\sim 2~\mu_B$ in
bulk SmN, enhanced to an average of $\sim 3~\mu_B$ in SmN layers within a
SmN/GdN superlattice. These calculations provide insight into recent studies of
SmN showing that it is an unconventional superconductor at low temperatures and
displays twisted magnetization phases in magnetic heterostructures.",1511.04820v1
2015-11-28,Andreev reflection and subgap conductance in monolayer $MoS_2$ ferromagnet/$s$ and $d$-wave superconductor junction,"The accurate and proper form of electron-hole excitations and corresponding
Dirac-like spinors of monolayer molybdenum disulfide superconductor are exactly
obtained. Andreev reflection and resulting subgap conductance in a
$MoS_2$-based ferromagnetic superconducting (F/S) junction is accurately
investigated in terms of dynamical characteristics of system. Due to
spin-splitting energy gap in the valence band and nondegenerate $K$ and $K'$
valleys, the ferromagnetic exchange energy $\sigma h$ can cause a distinct
behavior of Andreev process between spin-up and spin-down charge carriers
belonging to different valleys. The chemical potential is necessarily fixed by
a determined range in order to occur the retro Andreev reflection. Given
one-particle superconducting bispinors enable us to explicitly involve the
anisotropic superconducting gap $\Delta_S$ under electron-hole conversion,
i.e., taking place in $d$-wave pair coupling. The effect of such gap is exactly
explained in terms of the dependence of the Andreev process on the electron
incidence angle at the interface.",1511.08872v2
2016-01-22,Long-range supercurrents induced by the interference effect of opposite-spin triplet state in clean superconductor-ferromagnet structures,"By now it is known that in an s-wave
superconductor-ferromagnet-superconductor ($SFS$) structure the supercurrent
induced by spin singlet pairs can only transmit a short distance of the order
of magnetic coherence length. The long-range supercurrent, taking place on the
length scale of the normal metal coherence length, will be maintained by
equal-spin triplet pairs, which can be generated by magnetic inhomogeneities in
the system. In this paper, we show an unusual long-range supercurrent, which
can take place in clean $SF_1F_2S$ junction with non-parallel orientation of
magnetic moments. The mechanism behind the enhancement of Josephson current is
provided by the interference of the opposite-spin triplet states derived from
$S/F_1$ and $F_2/S$ interfaces when both ferromagnetic layers have the same
values of the length and exchange field. This finds can provide a natural
explanation for recent experiment [Robinson et al., Phys. Rev. Lett. 104,
207001 (2010)].",1601.06045v1
2016-02-04,Magnetic anisotropy of the single-crystalline ferromagnetic insulator Cr2Ge2Te6,"Cr2Ge2Te6 (CGT), a layered ferromagnetic insulator, has attracted a great
deal of interest recently owing to its potential for integration with Dirac
materials to realize the quantum anomalous Hall effect (QAHE) and to develop
novel spintronics devices. Here, we study the uniaxial magnetic anisotropy
energy of single-crystalline CGT and determine that the magnetic easy axis is
directed along the c-axis in its ferromagnetic phase. In addition, CGT is an
insulator below the Curie temperature. These properties make CGT a potentially
promising candidate substrate for integration with topological insulators for
the realization of the high-temperature QAHE.",1602.01556v1
2016-02-05,A novel type of splayed ferromagnetic order observed in Yb2Ti2O7,"The pyrochlore insulator Yb2Ti2O7 has attracted the attention of
experimentalists and theoreticians alike for about 15 years. Conflicting
neutron diffraction data on the possible existence of magnetic Bragg
reflections at low temperature have been published. Here we report the
observation of magnetic Bragg reflections by neutron powder diffraction at 60
mK. The magnetic diffraction pattern is analyzed using representation theory.
We find Yb2Ti2O7 to be a splayed ferromagnet as reported for Yb2Sn2O7, a
sibling compound with also dominating ferromagnetic interactions as inferred
from the positive Curie-Weiss temperature. However, the configuration of the
magnetic moment components perpendicular to the easy axis is of the
all-in--all-out type in Yb2Ti2O7 while it is two-in--two-out in Yb2Sn2O7. An
overall experimental picture of the magnetic properties emerges.",1602.02025v2
2016-02-11,Exact diagonalization study of double quantum dots in parallel geometry in zero-bandwidth limit,"Exact eigenstates of the parallel coupled double quantum dots attached to the
non-interacting leads taken in zero-bandwidth limit are analytically obtained
in each particle and spin sector. The ground state of the half-filled system is
identified from a four dimensional subspace of the twenty dimensional Hilbert
space for different values of tunable parameters of the system viz. the energy
levels of the quantum dots, the interdot tunneling matrix-element, the ondot
and interdot Coulomb interactions and quantities like spin-spin correlation
between the dots, occupancies of the dots are calculated. In the parameter
space of the interdot tunneling matrix-element and ondot Coulomb interaction,
the dots exhibit both ferromagnetic and antiferromagnetic correlation. There is
a critical dependency of the interdot tunneling matrix-element on the ondot
Coulomb interaction which leads to transition from the ferromagnetic
correlation to the antiferromagnetic correlation as the interdot tunneling
matrix-element is increased. The ferromagnetic and antiferromagnetic
correlations also exist in the absence of interdot tunneling matrix-element
through indirect exchange via the leads. The interdot Coulomb interaction is
found to affect this dependency considerably.",1602.03900v1
2016-02-15,Ferromagnetic Cluster Glass Phase Embedded in a Paramagnetic and Metallic Host in Non-uniform Magnetic System CaRu_{1-x}Sc_{x}O_{3},"We have investigated both static and dynamic magnetic properties of
polycrystalline CaRu$_{1-x}$Sc$_{x}$O$_{3}$ system in order to clarify the role
of Sc ions as a disorder for magnetic ordering. We have observed typical
features of a ferromagnetic cluster glass state below around 40 K: (i) a broad,
frequency-dependent peak in the ac magnetic susceptibility, (ii) a slow
relaxation of the magnetization, and (iii) a continuous increase in the dc
magnetic susceptibility in field cooling process. The composition dependence of
characteristic parameters for the cluster glass state suggests that chemical
segregation can hardly explain the clustering mechanism. We propose a possible
picture that the ferromagnetic clusters are distributed uniformly and form the
glassy state embedded in the paramagnetic and metallic host of CaRuO$_{3}$.",1602.04647v1
2016-02-23,Ferromagnetism and superconductivity with possible $p+ip$ pairing symmetry in partially hydrogenated graphene,"By means of first-principles calculations, we predict two new types of
partially hydrogenated graphene systems: C$_{6}$H$_{1}$ and C$_{6}$H$_{5}$,
which are shown to be ferromagnetic (FM) semimetal and FM narrow-gap
semiconductor, respectively. When properly doped, the Fermi surface of the two
systems consists of an electron pocket or six hole patches in the first
Brillouin zone with completely spin-polarized charge carries. If
superconductivity exists in these systems, the stable pairing symmetries are
shown to be $p+ip$ for electron doped case, and anisotropic $p+ip$ for hole
doped case. The predicted systems may provide fascinating platforms for
studying the novel properties of ferromagnetism and triplet-pairing
superconductivity as well as two-dimensional spintronics.",1602.07329v3
2016-03-03,Direct penetration of spin-triplet superconductivity into a ferromagnet in Au/SrRuO3/Sr2RuO4 junctions,"Efforts have been ongoing to establish superconducting spintronics utilizing
ferromagnet/superconductor heterostructures1. Previously reported devices are
based on spin-singlet superconductors (SSCs), where the spin degree of freedom
is lost. Spin-polarized supercurrent induction in ferromagnetic metals (FMs) is
achieved even with SSCs, but only with the aid of interfacial complex magnetic
structures, which severely affect information imprinted to the electron spin.
Use of spin-triplet superconductors (TSCs) with active spins potentially
overcomes this difficulty and further leads to novel functionalities. Here, we
report spin-triplet superconductivity induction into a FM SrRuO3 from a leading
TSC candidate Sr2RuO4, by fabricating microscopic devices using an epitaxial
SrRuO3/Sr2RuO4 hybrid. The differential conductance, exhibiting
Andreev-reflection features with multiple energy scales up to around half
tesla, indicates the penetration of superconductivity over a considerable
distance of 15 nm across the SrRuO3 layer without help of interfacial complex
magnetism. This demonstrates the first FM/TSC device exhibiting the
spin-triplet proximity effect.",1603.00971v2
2016-03-03,Observation of Quantum Griffiths Singularity and Ferromagnetism at Superconducting LaAlO3/SrTiO3(110) Interface,"Diverse phenomena emerge at the interface between band insulators LaAlO3 and
SrTiO3, such as superconductivity and ferromagnetism, showing an opportunity
for potential applications as well as bringing fundamental research interests.
Particularly, the two-dimensional electron gas formed at LaAlO3/SrTiO3
interface offers an appealing platform for quantum phase transition from a
superconductor to a weakly localized metal. Here we report the
superconductor-metal transition in superconducting two-dimensional electron gas
formed at LaAlO3/SrTiO3(110) interface driven by a perpendicular magnetic
field. Interestingly, when approaching the quantum critical point, the dynamic
critical exponent is not a constant but a diverging value, which is a direct
evidence of quantum Griffiths singularity raised from quenched disorder at
ultralow temperatures. Furthermore, the hysteretic property of
magnetoresistance was firstly observed at LaAlO3/SrTiO3(110) interfaces, which
suggests potential coexistence of superconductivity and ferromagnetism.",1603.01011v2
2016-03-07,Muon Spin Relaxation and Neutron Diffraction Studies of Cluster-Glass States in Sr1-xLaxRuO3,"To clarify the magnetic properties of cluster-glass states in Sr1-xLaxRuO3
(0.3 <= x <= 0.5), we report herein the results of muon spin relaxation (muSR)
and neutron powder diffraction measurements. The muSR experiments showed that
magnetic clusters start developing well above the peak temperature T^* in the
ac susceptibility. The volume fraction of the magnetically ordered region
increases continuously with decreasing temperature, showing no anomaly at T^*,
and reaches nearly 100% at the lowest temperature. The temperature variation of
the volume fraction is essentially independent of the La concentration in the x
range presently investigated, although the dc magnetization is significantly
suppressed with increasing x. Neutron powder diffraction experiments revealed
that the ground state for x = 0.3 is a long-range ferromagnetic ordered state.
These results indicate that, with decreasing temperature, cluster-glass states
in Sr1-xLaxRuO3 gradually develop into long-range ferromagnetic ordered states
with decreasing temperature, and that the magnetic ordering process differs
strikingly from that expected for a conventional second-order ferromagnetic
transition.",1603.01962v1
2016-03-11,Critical temperature of two-dimensional hydrogenated multilayer graphene-based diluted ferromagnet,"In the paper a theoretical study of critical (Curie) temperature of diluted
ferromagnet based on multilayer graphene (or graphite) with hydrogen adatoms
deposited over carbon atoms belonging to single sublattice is presented. The
calculations are performed within Pair Approximation (PA) for diluted
ferromagnetic system with long-range interactions. The method is able to take
into account the spin-space anisotropy of coupling. The results obtained within
Mean Field Approximation (MFA) are also presented for comparison. The assumed
interaction between hydrogen adatom spins is inversely proportional to their
mutual distance, with the additional exponential attenuation reflecting the
presence of disorder in the system. The results obtained for a wide range of
impurity concentrations and interaction decay length are discussed. The
strongly non-linear behaviour of critical temperature as a function of dilution
is predicted, at variance with MFA predictions. Moreover, MFA tends to
overestimate heavily the critical temperature values compared to PA. An
universal dependence of critical temperature on impurity concentration and
interaction decay length is found for strong dilution regime.",1603.03810v3
2016-03-23,Thermoelectric power quantum oscillations in the ferromagnet UGe$_2$,"We present thermoelectric power and resistivity measurements in the
ferromagnet UGe$_2$ as a function of temperature and magnetic field. At low
temperature, huge quantum oscillations are observed in the thermoelectric power
as a function of the magnetic field applied along the $a$ axis. The frequencies
of the extreme orbits are determined and an analysis of the cyclotron masses is
performed following different theoretical approaches for quantum oscillations
detected in the thermoelectric power. They are compared to those obtained by
Shubnikov-de Haas experiments on the same crystal and previous de Haas-van
Alphen experiments. The agreement of the different probes confirms
thermoelectric power as an excellent probe to extract simultaneously both
microscopic and macroscopic information on the Fermi-surface properties.
Band-structure calculations of UGe$_2$ in the ferromagnetic state are compared
to the experiment.",1603.07121v1
2016-03-24,Voltage induced switching dynamics of a coupled spin pair in a molecular junction,"Molecular spintronics is made possible by the coupling between electronic
configuration and magnetic po- larization of the molecules. For control and
application of the individual molecular states it is necessary to both read and
write their spin states. Conventionally, this is achieved by means of external
magnetic fields or ferromagnetic contacts, which may change the intentional
spin state and may present additional challenges when downsizing devices. Here,
we predict that coupling magnetic molecules together opens up possibilities for
all electrical control of both the molecular spin states as well as the current
flow through the system. Tuning between the regimes of ferromagnetic and
anti-ferromagnetic exchange interaction, the current can be, at least, an order
of magnitude enhanced or reduced. The effect is susceptible to the tunnel
coupling and molecular level alignment which can be used to achieve current
rectification.",1603.07652v1
2016-03-24,Role of Berry phase theory for describing orbital magnetism: From magnetic heterostructures to topological orbital ferromagnets,"We address the importance of the modern theory of orbital magnetization for
spintronics. Based on an all-electron first-principles approach, we demonstrate
that the predictive power of the routinely employed ""atom-centered""
approximation is limited to materials like elemental bulk ferromagnets, while
the application of the modern theory of orbital magnetization is crucial in
chemically or structurally inhomogeneous systems such as magnetic thin films,
and materials exhibiting non-trivial topology in reciprocal and real
space,~e.g.,~Chern insulators or non-collinear systems. We find that the modern
theory is particularly crucial for describing magnetism in a class of materials
that we suggest here $-$ topological orbital ferromagnets.",1603.07683v2
2016-03-30,Coexistence of charge and ferromagnetic order in fcc Fe,"Phase coexistence phenomena have been intensively studied in strongly
correlated materials where several ordered states simultaneously occur or
compete. Material properties critically depend on external parameters and
boundary conditions, where tiny changes result in qualitatively different
ground states. However, up to date, phase coexistence phenomena have
exclusively been reported for complex compounds composed of multiple elements.
Here we show that charge- and magnetically ordered states coexist in
double-layer Fe on Rh(001). Scanning tunneling microscopy and spectroscopy
measurements reveal periodic charge order stripes below a temperature of 130 K.
Close to liquid helium temperature, they are superimposed by ferromagnetic
domains as observed by spin-polarized scanning tunneling microscopy.
Temperature-dependent measurements reveal a pronounced cross-talk between
charge and spin order at the ferromagnetic ordering temperature about 70 K,
which is successfully modeled within an effective Landau theory including
sixth-order terms. Our results show that subtle balance between structural
modifications can lead to competing ordering phenomena.",1603.09100v1
2016-04-05,Micromagnetic simulation of exchange coupled ferri-/ferromagnetic composite in bit patterned media,"Ferri-/ferromagnetic exchange coupled composites are promising candidates for
bit patterned media because of the ability to control the magnetic properties
of the ferrimagnet by its composition. A micromagnetic model for the bilayer
system is presented where we also incorporate the microstructural features of
both layers. Micromagnetic finite element simulations are performed to
investigate the magnetization reversal behaviour of such media. By adding the
exchange coupled ferrimagnet to the ferromagnet, the switching field could be
reduced by up to $40\,\%$ and also the switching field distribution is
narrowed. To reach these significant improvements, an interface exchange
coupling strength of $2\,\mathrm{mJ/m^2}$ is required.",1604.01180v1
2016-04-06,Temperature Dependence of Angular Momentum Transport Across Interfaces,"Angular momentum transport in magnetic multilayered structures plays a
central role in spintronic physics and devices. The angular momentum currents
or spin currents are carried by either quasi-particles such as electrons and
magnons, or by macroscopic order parameters such as local magnetization of
ferromagnets. Based on the generic interface exchange interaction, we develop a
microscopic theory that describes interfacial spin conductance for various
interfaces among non-magnetic metals, ferromagnetic and antiferromagnetic
insulators. Spin conductance and its temperature dependence are obtained for
different spin batteries including spin pumping, temperature gradient and spin
Hall effect. As an application of our theory, we calculate the spin current in
a trilayer made of a ferromagnetic insulator, an antiferromagnetic insulator
and a non-magnetic heavy metal. The calculated results on the temperature
dependence of spin conductance quantitatively agree with the existing
experiments.",1604.01714v2
2016-04-07,Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions,"Thermoelectric effects result from the coupling of charge and heat transport,
and can be used for thermometry, cooling and harvesting of thermal energy. The
microscopic origin of thermoelectric effects is a broken electron-hole
symmetry, which is usually quite small in metal structures, and vanishes at low
temperatures. We report on a combined experimental and theoretical
investigation of thermoelectric effects in superconductor/ferromagnet hybrid
structures. We investigate the depencence of thermoelectric currents on the
thermal excitation, as well as on the presence of a dc bias voltage across the
junction. Large thermoelectric effects are observed in
superconductor/ferromagnet and superconductor/normal-metal hybrid structures.
The spin-independent signals observed under finite voltage bias are shown to be
reciprocal to the physics of superconductor/normal-metal microrefrigerators.
The spin-dependent thermoelectric signals in the linear regime are due to the
coupling of spin and heat transport, and can be used to design more efficient
refrigerators",1604.01940v1
2016-04-10,Interfacial Dzyaloshinskii-Moriya interaction in Pt/CoFeB films: effect of the heavy-metal thickness,"We report the observation of a Pt layer thickness dependence on the induced
interfacial Dzyaloshinskii-Moriya interaction in ultra-thin
Pt($d_{\text{Pt}}$)/CoFeB films. Taking advantage of the large spin-orbit
coupling of the heavy metal, the interfacial Dzyaloshinskii-Moriya interaction
is quantified by Brillouin light scattering measurements of the frequency
non-reciprocity of spin-waves in the ferromagnet. The magnitude of the induced
Dzyaloshinskii-Moriya coupling is found to saturate to a value $0.45$
mJ$/$m${}^2$ for Pt thicknesses larger than $\sim 2$ nm. The experimental
results are explained by analytical calculations based on the 3-site indirect
exchange mechanism that predicts a Dzyaloshinskii-Moriya interaction at the
interface between a ferromagnetic thin layer and a heavy metal. Our findings
open up a way to control and optimize chiral effects in ferromagnetic thin
films through the thickness of the heavy metal layer.",1604.02626v2
2016-04-14,Quantum Nucleation of Skyrmions in Magnetic Films by Inhomogeneous Fields,"Recent experiments have reported on controlled nucleation of individual
skyrmions in chiral magnets. Here we show that in magnetic ultra-thin films
with interfacial Dzyaloshinskii-Moriya interaction, single skyrmions of
different radii can be nucleated by creating a local distortion in the magnetic
field. In our study, we have considered zero temperature quantum nucleation of
a single skyrmion from a ferromagnetic phase. The physical scenario we model is
one where a uniform field stabilizes the ferromagnet, and an opposing local
magnetic field over a circular spot, generated by the tip of a local probe,
drives the skyrmion nucleation. Using spin path integrals and a collective
coordinate approximation, the tunneling rate from the ferromagnetic to the
single skyrmion state is computed as a function of the tip's magnetic field and
the circular spot radius. Suitable parameters for the observation of the
quantum nucleation of single skyrmions are identified.",1604.04010v1
2016-04-20,Competition between Kondo effect and RKKY physics in graphene magnetism,"The cooperative behavior of quantum impurities on 2D materials, such as
graphene and bilayer graphene, is characterized by a non-trivial competition
between screening (Kondo effect), and Ruderman-Kittel-Kasuya-Yosida (RKKY)
magnetism. In addition, due to the small density of states at the Fermi level,
impurities may not couple to the conduction electrons at all, behaving as free
moments. Employing a recently developed {\em{exact}} numerical method to study
multi-impurity lattice systems, we obtain non-perturbative results that
dramatically depart from expectations based on the conventional RKKY theory. At
half-filling and for weak coupling, impurities remain in the local moment
regime when they are on opposite sublattices, up to a critical value of the
interactions when they start coupling anti-ferromagnetically with correlations
that decay very slowly with inter-impurity distance. At finite doping, away
from half-filling, ferromagnetism is completely absent and the physics is
dominated by a competition between anti-ferromagnetism and Kondo effect. In
bilayer graphene, impurities on opposite layers behave as free moments, unless
the interaction is of the order of the hopping or larger.",1604.06109v2
2016-04-26,Intrinsic spin orbit torque in a single domain nanomagnet,"We present theoretical studies of the intrinsic spin orbit torque (SOT) in a
single domain ferromagnetic layer with Rashba spin-orbit coupling (SOC) using
the non-equilibrium Green's function formalism for a model Hamiltonian. We find
that, to the first order in SOC, the intrinsic SOT has only the field-like
torque symmetry and can be interpreted as the longitudinal spin current induced
by the charge current and Rashba field. We analyze the results in terms of the
material related parameters of the electronic structure, such as band filling,
band width, exchange splitting, as well as the Rashba SOC strength. On the
basis of these numerical and analytical results, we discuss the magnitude and
sign of SOT. Our results show that the different sign of SOT in identical
ferromagnetic layers with different supporting layers, e.g. Co/Pt and Co/Ta,
could be attributed to electrostatic doping of the ferromagnetic layer by the
support.",1604.07885v2
2016-04-29,Current induced magnetization dynamics and magnetization switching in superconducting ferromagnetic hybrid (F$|$S$|$F) structures,"We investigate the current induced magnetization dynamics and magnetization
switching in an unconventional p-wave superconductor sandwiched between two
misaligned ferromagnetic layers by numerically solving Landau-Lifshitz-Gilbert
equation modified with current induced Slonczewski's spin torque term. A
modified form of Ginzburg-Landau free energy functional has been used for this
purpose. We demonstrated the possibility of current induced magnetization
switching in the spin-triplet ferromagnetic superconducting hybrid structures
with strong easy axis anisotropy and the condition for magnetization reversal.
The switching time for such arrangement is calculated and is found to be highly
dependent on the magnetic configuration along with the biasing current. This
study would be useful in designing practical superconducting-spintronic
devices.",1604.08704v3
2016-04-29,Ferromagnetic Mott-Insulating State in Double Perovskites Gd2MgIrO6,"We have studied the electronic and magnetic properties of double perovskites
Gd2MgIrO6 by first-principles density functional theory (DFT). Based on the DFT
calculations, Gd2MgIrO6 is found to have a ferromagnetic (FM) ground state. The
material undergo half-metallic ferromagnets to Mott-Hubbard insulator
transition which happens due to strong correlation in Gd-4f and Ir-5d states.
Our results shows that the 5d electrons of Ir hybridize strongly with O-2p
states near the Fermi level giving rise to the insulating state of Gd2MgIrO6.
Our study suggests that the enhanced magnetic moment is a result of itinerant
exchange rather than the exchange interaction involving individual ions of Gd
and Ir atoms. The total magnetic moment calculated in the present studies is 15
{\mu}B per formula unit for Gd2MgIrO6.",1604.08931v1
2016-06-06,Switching field distribution of exchange coupled ferri-/ferromagnetic composite bit patterned media,"We investigate the switching field distribution and the resulting bit error
rate of exchange coupled ferri-/ferromagnetic bilayer island arrays by
micromagnetic simulations. Using islands with varying microstructure and
anisotropic properties, the intrinsic switching field distribution is computed.
The dipolar contribution to the switching field distribution is obtained
separately by using a model of a triangular patterned island array resembling
$1.4\,\mathrm{Tb/in}^2$ bit patterned media. Both contributions are computed
for different thickness of the soft exchange coupled ferrimagnet and also for
ferromagnetic single phase FePt islands. A bit patterned media with a bilayer
structure of FeGd($5\,\mathrm{nm}$)/FePt($5\,\mathrm{nm}$) shows a bit error
rate of $10^{-4}$ with a write field of $1.16\,\mathrm{T}$.",1606.01874v2
2016-07-08,Mott lobes of the $S=1$ Bose-Hubbard model with three-body interactions,"Using the density matrix renormalization group method, we studied the ground
state of the one-dimensional $S=1$ Bose-Hubbard model with local three-body
interactions, which can be a superfluid or a Mott insulator state. We drew the
phase diagram of this model for both ferromagnetic and antiferromagnetic
interaction. Regardless of the sign of the spin-dependent coupling, we obtained
that the Mott lobes area decreases as the spin-dependent strength increases,
which means that the even-odd asymmetry of the two-body antiferromagnetic chain
is absent for local three-body interactions. For antiferromagnetic coupling, we
found that the density drives first-order superfluid-Mott insulator transitions
for even and odd lobes. Ferromagnetic Mott insulator and superfluid states were
obtained with a ferromagnetic coupling, and a tendency to a ""long-range"" order
was observed.",1607.02302v2
2016-07-08,Effect of demagnetization factor dependence on energy of ultra-thin ferromagnetic films with four layers,"Simple cubic and body centered cubic ferromagnetic lattices with four layers
were studied using Heisenberg Hamiltonian. According to 3-D plots, the films
with four layers can be easily oriented in certain directions under the
influence of particular demagnetization factor and angles for both sc(001) and
bcc(001) ferromagnetic lattice structures. A flat part can be seen in the
middle of 3-D plots in addition to periodic variations. When the
demagnetization factor is given by =6, sc(001) film with four layers can be
easily oriented in 0.6 radians direction for the energy parameter values used
in this simulation. Under the influence of demagnetization factor given by =5.2
, thin film of bcc(001) lattice with four layers can be easily oriented along
0.63 radians direction.",1607.02313v1
2016-07-12,Current-driven periodic domain wall creation in ferromagnetic nano-wires,"We predict the electrical generation and injection of domain walls into a
ferromagnetic nano-wire without the need of an assisting magnetic field. Our
analytical and numerical results show that above a critical current $j_{c}$
domain walls are injected into the nano-wire with a period $T \sim
(j-j_{c})^{-1/2}$. Importantly, domain walls can be produced periodically even
in a simple exchange ferromagnet with uniaxial anisotropy, without requiring
any standard ""twisting"" interaction like Dzyaloshinskii-Moriya or dipole-dipole
interactions. We show analytically that this process and the period exponents
are universal and do not depend on the peculiarities of the microscopic
Hamiltonian. Finally we give a specific proposal for an experimental
realization.",1607.03336v1
2016-07-12,Effect of Quantum Tunneling on Spin Hall Magnetoresistance,"We present a formalism that simultaneously incorporates the effect of quantum
tunneling and spin diffusion on spin Hall magnetoresistance observed in normal
metal/ferromagnetic insulator bilayers (such as Pt/YIG) and normal
metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of
magnetization influences the magnetoresistance of the normal metal. In the
normal metal side the spin diffusion is known to affect the landscape of the
spin accumulation caused by spin Hall effect and subsequently the
magnetoresistance, while on the ferromagnet side the quantum tunneling effect
is detrimental to the interface spin current which also affects the spin
accumulation. The influence of generic material properties such as spin
diffusion length, layer thickness, interface coupling, and insulating gap can
be quantified in a unified manner, and experiments that reveal the quantum
feature of the magnetoresistance are suggested.",1607.03409v1
2016-07-28,"Tunneling magnetoresistance in trilayer structures composed of group-IV ferromagnetic semiconductor Ge1-xFex, MgO, and Fe","Group-IV-based ferromagnetic semiconductor Ge1-xFex (GeFe) is one of the most
promising materials for efficient spin injectors and detectors for Si and Ge.
Recent first principles calculations (Sakamoto et al., Ref. 9) suggested that
the Fermi level is located in two overlapping largely spin-polarized bands
formed in the bandgap of GeFe; spin-down d(e) band and spin-up p-d(t2) band.
Thus, it is important to clarify how these bands contribute to spin injection
and detection. In this study, we show the first successful observation of the
tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs)
containing a group-IV ferromagnetic semiconductor, that is, in MTJs composed of
epitaxially grown Fe/MgO/Ge0.935Fe0.065. We find that the p-d(t2) band in GeFe
is mainly responsible for the tunneling transport. Although the obtained TMR
ratio is small (0.3%), the TMR ratio is expected to be enhanced by suppressing
leak current through amorphous-like crystal domains observed in MgO.",1607.08298v1
2016-09-08,Evolution of an isolated monopole in a spin-1 Bose-Einstein condensate,"We simulate the decay dynamics of an isolated monopole defect in the nematic
vector of a spin-1 Bose-Einstein condensate during the polar-to-ferromagnetic
phase transition of the system. Importantly, the decay of the monopole occurs
in the absence of external magnetic fields and is driven principally by the
dynamical instability due to the ferromagnetic spin-exchange interactions. An
initial isolated monopole is observed to relax into a polar-core spin vortex,
thus demonstrating the spontaneous transformation of a point defect of the
polar order parameter manifold to a line defect of the ferromagnetic manifold.
We also investigate the dynamics of an isolated monopole pierced by a quantum
vortex line with winding number k. It is shown to decay into a coreless
Anderson-Toulouse vortex if k = 1 and into a singular vortex with an empty core
if k = 2. In both cases, the resulting vortex is also encircled by a polar-core
vortex ring.",1609.02506v2
2016-09-09,Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces,"The theory of superconductivity developed by Bardeen, Cooper and Schrieffer
(BCS) explains the stabilization of electron pairs into a spin-singlet, even
frequency, state by the formation of an energy gap within which the density of
states is zero. At a superconductor interface with an inhomogeneous
ferromagnet, a gapless odd frequency superconducting state is predicted, in
which the Cooper pairs are in a spin-triplet state. Although indirect evidence
for such a state has been obtained, the gap structure and pairing symmetry have
not so far been determined. Here we report scanning tunnelling spectroscopy of
Nb superconducting films proximity coupled to epitaxial Ho. These measurements
reveal pronounced changes to the Nb subgap superconducting density of states on
driving the Ho through a metamagnetic transition from a helical
antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap
is recovered. The results prove odd frequency spin-triplet superconductivity at
superconductor/inhomogeneous magnet interfaces.",1609.02905v1
2016-09-12,Estimation of spin relaxation lengths in spin valves of In and In2O3 nanostructures,"We report the electrical injection and detection of spin polarized current in
lateral ferromagnet-nonmagnet-ferromagnet spin valve devices, ferromagnet being
cobalt and nonmagnet being indium (In) or indium oxide (In2O3) nanostructures.
The In nanostructures were grown by depositing pure In on lithographically
pre-patterned structures. In2O3 nanostructures were obtained by oxidation of In
nanostructures. Spin valve devices were fabricated by depositing micro magnets
over the nanostructures with connecting nonmagnetic electrodes via two steps of
e-beam lithography. Clear spin switching behavior was observed in the both
types of spin valve devices measured at 10 K. From the measured spin signal,
the spin relaxation length ({\lambda}N) of In and In2O3 nanostructures were
estimated to be 449.6 nm and 788.6 nm respectively.",1609.03609v1
2016-09-15,Magnetoelectric Response in Multiferroic SrFe12O19 Ceramics,"We report here the realization of ferroelectricity, ferromagnetism and
magnetocapacitance effect in SrFe12O19 ceramics at room temperature. The
ceramics demonstrate a saturated polarization hysteresis loop, two I-V peaks
and large anomaly of dielectric constant near Curie temperature. These
evidences confirmed the ferroelectricity of SrFe12O19 ceramics after annealing
in O2 atmosphere. The remnant polarization of the SrFe12O19 ceramic is 103
{\mu}C/cm2. The material also exhibits strong ferromagnetic characterization,
the coercive field and remnant magnetic moment are 6192Oe and 35.8emu/g,
respectively. Subsequent annealing SrFe12O19 ceramics in O2 not only reveals
its innate ferroelectricity but also improves the ferromagnetic properties
through transforming Fe2+ into Fe3+. By applying a magnetic field, the
capacitance demonstrates remarkable change along with B field, the maximum
relative change of dielectric constant is 1174%, which reflects a giant
magnetocapacitance effect in SrFe12O19. These combined functional responses in
SrFe12O19 ceramics opens substantial possibilities for applications in novel
electric devices.",1609.04483v1
2016-09-20,Magnon nodal-line semimetals and drumhead surface states in anisotropic pyrochlore ferromagnets,"We introduce a new type of topological magnon matter: the magnonic pendant to
electronic nodal-line semimetals. Magnon spectra of anisotropic pyrochlore
ferromagnets feature twofold degeneracies of magnon bands along a closed loop
in reciprocal space. These magnon nodal lines are topologically protected by
the coexistence of inversion and time-reversal symmetry; they require the
absence of spin-orbit interaction (no Dzyaloshinskii-Moriya interaction). We
calculate the topological invariants of the nodal lines and show that details
of the associated magnon drumhead surface states depend strongly on the
termination of the surface. Magnon nodal-line semimetals complete the family of
topological magnons in three-dimensional ferromagnetic materials.",1609.06131v1
2016-09-28,Ferromagnetism and conductivity in atomically thin SrRuO3,"Atomically thin ferromagnetic and conducting electron systems are highly
desired for spintronics, because they can be controlled with both magnetic and
electric fields. We present (SrRuO3)1-(SrTiO3)5 superlattices and
single-unit-cell-thick SrRuO3 samples that are capped with SrTiO3. We achieve
samples of exceptional quality. In these samples, the electron systems comprise
only a single RuO2 plane. We observe conductivity down to 50 mK, a
ferromagnetic state with a Curie temperature of 25 K, and signals of magnetism
persisting up to approximately 100 K.",1609.08901v2
2016-10-02,Spin-transfer torque in ferromagnetic bilayers generated by anomalous Hall effect and anisotropic magnetoresistance,"We propose an experimental scheme to determine the spin-transfer torque
efficiency excited by the spin-orbit interaction in ferromagnetic bilayers from
the measurement of the longitudinal magnetoresistace. Solving a diffusive
spin-transport theory with appropriate boundary conditions gives an analytical
formula of the longitudinal charge current density. The longitudinal charge
current has a term that is proportional to the square of the spin-transfer
torque efficiency and that also depends on the ratio of the film thickness to
the spin diffusion length of the ferromagnet. Extracting this contribution from
measurements of the longitudinal resistivity as a function of the thickness can
give the spin-transfer torque efficiency.",1610.00222v1
2016-10-03,Magnetic microscopy and simulation of strain-mediated control of magnetization in Ni/PMN-PT nanostructures,"Strain-mediated thin film multiferroics comprising
piezoelectric/ferromagnetic heterostructures enable the electrical manipulation
of magnetization with much greater efficiency than other methods; however, the
investigation of nanostructures fabricated from these materials is limited.
Here we characterize ferromagnetic Ni nanostructures grown on a ferroelectric
PMN-PT substrate using scanning electron microscopy with polarization analysis
(SEMPA) and micromagnetic simulations. The magnetization of the Ni
nanostructures can be controlled with a combination of sample geometry and
applied electric field, which strains the ferroelectric substrate and changes
the magnetization via magnetoelastic coupling. We evaluate two types of
simulations of ferromagnetic nanostructures on strained ferroelectric
substrates: conventional micromagnetic simulations including a simple uniaxial
strain, and coupled micromagnetic-elastodynamic simulations. Both simulations
qualitatively capture the response of the magnetization changes produced by the
applied strain, with the coupled solution providing more accurate
representation.",1610.00746v1
2016-10-04,Resolving magnon number states in quantum magnonics,"Collective excitation modes in solid state systems play a central role in
circuit quantum electrodynamics, cavity optomechanics, and quantum magnonics.
In the latter, quanta of collective excitation modes in a ferromagnet, called
magnons, interact with qubits to provide the nonlinearity necessary to access
quantum phenomena in magnonics. A key ingredient for future quantum magnonics
systems is the ability to probe magnon states. Here we observe individual
magnons in a millimeter-sized ferromagnet coherently coupled to a
superconducting qubit. Specifically, we resolve magnon number states in
spectroscopic measurements of a transmon qubit with the hybrid system in the
strong dispersive regime. This enables us to detect a change in the magnetic
dipole of the ferromagnet equivalent to a single spin flipped among more than
$10^{19}$ spins. The strong dispersive regime of quantum magnonics opens up the
possibility of encoding superconducting qubits into non-classical magnon
states, potentially providing a coherent interface between a superconducting
quantum processor and optical photons.",1610.00839v1
2016-10-06,Giant Mesoscopic Fluctuations and Long Range Superconducting Correlations in Superconductor--Ferromagnet structures,"The fluctuating superconducting correlations emerging in dirty hybrid
structures in conditions of the strong proximity effect are demonstrated to
affect the validity range of the widely used formalism of Usadel equations at
mesoscopic scales. In superconductor -- ferromagnet (SF) structures these giant
mesoscopic fluctuations originating from the interference effects for the
Cooper pair wave function in the presence of the exchange field can be
responsible for an anomalously slow decay of superconducting correlations in a
ferromagnet even when the non-collinear and spin-orbit effects are negligible.
The resulting sample-to-sample fluctuations of the Josephson current in SFS
junctions and local density of states in SF hybrid structures can provide an
explanation of the long range proximity phenomena observed in mesoscopic
samples with collinear magnetization.",1610.01775v1
2016-10-06,Quantum Anomalous Hall State in Ferromagnetic SrRuO$_3$ (111) Bilayers,"SrRuO$_3$ heterostructures grown in the (111) direction are a rare example of
thin film ferromagnets. By means of density functional theory plus dynamical
mean field theory we show that the half-metallic ferromagnetic state with an
ordered magnetic moment of 2$\mu_{B}$/Ru survives the ultimate dimensional
confinement down to a bilayer, even at elevated temperatures of 500$\,$K. In
the minority channel, the spin-orbit coupling opens a gap at the linear band
crossing corresponding to $\frac34$ filling of the $t_{2g}$ shell. We
demonstrate that the respective state is Haldane's quantum anomalous Hall state
with Chern number $C$=1, without an external magnetic field or magnetic
impurities.",1610.01948v2
2016-10-14,Anisotropy of a Cubic Ferromagnet at Criticality,"Critical fluctuations change the effective anisotropy of cubic ferromagnet
near the Curie point. If the crystal undergoes phase transition into
orthorhombic phase and the initial anisotropy is not too strong, reduced
anisotropy of nonlinear susceptibility acquires at $T_c$ the universal value
$\delta_4^* = {{2v^*} \over {3(u^* + v^*)}}$ where $u^*$ and $v^*$ --
coordinates of the cubic fixed point on the flow diagram of renormalization
group equations. In the paper, the critical value of the reduced anisotropy is
estimated within the pseudo-$\epsilon$ expansion approach. The six-loop
pseudo-$\epsilon$ expansions for $u^*$, $v^*$, and $\delta_4^*$ are derived for
the arbitrary spin dimensionality $n$. For cubic crystals ($n = 3$)
higher-order coefficients of the pseudo-$\epsilon$ expansions obtained turn out
to be so small that use of simple Pad\'e approximants yields reliable numerical
results. Pad\'e resummation of the pseudo-$\epsilon$ series for $u^*$, $v^*$,
and $\delta_4^*$ leads to the estimate $\delta_4^* = 0.079 \pm 0.006$
indicating that detection of the anisotropic critical behavior of cubic
ferromagnets in physical and computer experiments is certainly possible.",1610.04332v1
2017-01-31,Anomalous current in diffusive ferromagnetic Josephson junctions,"We demonstrate that in diffusive superconductor/ferromagnet/superconductor
(S/F/S) junctions a finite, {\it anomalous}, Josephson current can flow even at
zero phase difference between the S electrodes. The conditions for the
observation of this effect are non-coplanar magnetization distribution and a
broken magnetization inversion symmetry of the superconducting current. The
latter symmetry is intrinsic for the widely used quasiclassical approximation
and prevent previous works, based on this approximation, from obtaining the
Josephson anomalous current. We show that this symmetry can be removed by
introducing spin-dependent boundary conditions for the quasiclassical equations
at the superconducting/ferromagnet interfaces in diffusive systems. Using this
recipe we considered generic multilayer magnetic systems and determine the
ideal experimental conditions in order to maximize the anomalous current.",1702.00056v2
2017-02-06,Magnetic phases of spin-1 lattice gases with random interactions,"A spin-1 atomic gas in an optical lattice, in the unit-filling Mott Insulator
(MI) phase and in the presence of disordered spin-dependent interaction, is
considered. In this regime, at zero temperature, the system is well described
by a disordered rotationally-invariant spin-1 bilinear-biquadratic model. We
study, via the density matrix renormalization group algorithm, a bounded
disorder model such that the spin interactions can be locally either
ferromagnetic or antiferromagnetic. Random interactions induce the appearance
of a disordered ferromagnetic phase characterized by a non-vanishing value of
spin-glass order parameter across the boundary between a ferromagnetic phase
and a dimer phase exhibiting random singlet order. The study of the
distribution of the block entanglement entropy reveals that in this region
there is no random singlet order.",1702.01765v2
2017-02-07,Ferromagnetism in chiral multilayer 2D semimetals,"We calculate the temperature dependent long-range magnetic coupling in the
presence of dilute concentrations of random magnetic impurities in chiral
multilayer two-dimensional semimetals, i.e., undoped intrinsic multilayer
graphene. Assuming a carrier-mediated indirect RKKY exchange interaction among
the well-separated magnetic impurities with the itinerant carriers mediating
the magnetic interaction between the impurities, we investigate the magnetic
properties of intrinsic multilayer graphene using an effective chiral
Hamiltonian model. We find that due to the enhanced density of states in the
rhombohedral stacking sequence of graphene layers, the magnetic ordering of
multilayer graphene is ferromagnetic in the continuum limit. The ferromagnetic
transition temperature is calculated using a finite-temperature self-consistent
field approximation and found to be within the experimentally accessible range
for reasonable values of the impurity-carrier coupling.",1702.01859v1
2017-02-09,Monte Carlo simulation of quantum Potts model,"Using Monte Carlo simulations in the frame of stochastic series expansion
(SSE), we study the three-state quantum Potts model. The cluster algorithm we
used is a direct generalization of that for the quantum Ising model. The
simulations include the one dimensional and two dimensional ferromagnetic
three-state quantum Potts model and the two dimensional antiferromagnetic
three-state quantum Potts model. Our results show that the phase transition of
the one dimensional ferromagnetic quantum Potts model belongs to the same
universality class of the two dimensional classical Potts model, the two
dimensional ferromagnetic quantum Potts model undergoes a first order
transition, which is also in analogy to its classical correspondence. The phase
transition of the antiferromagnetic quantum Potts model is continuous, whose
universality class belongs to the three-dimensional classical XY model, owing
to an `emergent' O(2) symmetry at the critical point, although its ordered
phase breaks the Z_6 symmetry.",1702.02675v1
2017-02-09,Long-range proximity effect in Nb-based heterostructures induced by a magnetically inhomogeneous permalloy layer,"Odd-frequency triplet Cooper pairs are believed to be the carriers of
long-range superconducting correlations in ferromagnets. Such triplet pairs are
generated by inhomogeneous magnetism at the interface between a superconductor
(S) and a ferromagnet (F). So far, reproducible long-range effects were
reported only in complex layered structures designed to provide the magnetic
inhomogeneity. Here we show that spin triplet pair formation can be found in
simple unstructured Nb/Permalloy (Py = Ni_0.8Fe_0.2)/Nb trilayers and Nb/Py
bilayers, but only when the thickness of the ferromagnetic layer ranges between
140 and 250 nm. The effect is related to the emergence of an intrinsically
inhomogeneous magnetic state, which is a precursor of the well-known stripe
regime in Py that in our samples sets in at thickness larger than 300 nm.",1702.02765v1
2017-03-13,Artificial control of the bias-voltage dependence of tunnelling anisotropic magnetoresistance using quantization in a single-crystal ferromagnet,"A major issue in the development of spintronic memory devices is the
reduction of the power consumption for the magnetization reversal. For this
purpose, the artificial control of the magnetic anisotropy of ferromagnetic
materials is of great importance. Here, we demonstrate the control of the
carrier-energy dependence of the magnetic anisotropy of the density of states
(DOS) using the quantum size effect in a single-crystal ferromagnetic material,
GaMnAs. We show that the mainly two-fold symmetry of the magnetic anisotropy of
DOS, which is attributed to the impurity band, is changed to a four-fold
symmetry by enhancing the quantum size effect in the valence band of the GaMnAs
quantum wells. By combination with the gate-electric field control technique,
our concept of the usage of the quantum size effect for the control of the
magnetism will pave the way for the ultra-low-power manipulation of
magnetization in future spintronic devices.",1703.04294v1
2017-03-23,Magnon activation by hot electrons via non-quasiparticle states,"We consider the situation when a femtosecond laser pulse creates a hot
electron state in half-metallic ferromagnet (e. g. ferromagnetic semiconductor)
on a picosecond timescale but do not act directly on localized spin system. We
show that the energy and magnetic moment transfer from hot itinerant electrons
to localized spins is facilitated by the so-called non-quasiparticle states,
which are the scattering states of a magnon and spin-majority electron. The
magnon distribution is described by a quantum kinetic equation that we derive
using the Keldysh diagram technique. In a typical ferromagnetic semiconductor
such as EuO magnons remain essentially in non-equilibrium on a scale of the
order of microsecond after the laser pulse.",1703.08106v1
2017-03-27,Dipolar ferromagnetism in three-dimensional superlattices of nanoparticles,"A series of atomistic finite temperature simulations on a model of an FCC
lattice of maghemite nanoparticles using the stochastic Landau-Lifshitz-Gilbert
(sLLG) equation are presented. The model exhibits a ferromagnetic transition
that is in good agreement with theoretical expectations. The simulations also
reveal an orientational disorder in the orientational order parameter for $T <
0.5 T_c$ due to pinning of the surface domain walls of the nanoparticles by
surface vacancies. The extent of the competition between surface pinning and
dipolar interactions provides support for the conjecture that recent
measurements on systems of FCC superlattices of iron-oxide nanoparticles
provide evidence for dipolar ferromagnetism is discussed.",1703.09290v1
2017-03-29,Current cross-correlations in double quantum dot based Cooper pair splitters with ferromagnetic leads,"We investigate the current cross-correlations in a double quantum dot based
Cooper pair splitter coupled to one superconducting and two ferromagnetic
electrodes. The analysis is performed by assuming a weak coupling between the
double dot and ferromagnetic leads, while the coupling to the superconductor is
arbitrary. Employing the perturbative real-time diagrammatic technique, we
study the Andreev transport properties of the device, focusing on the Andreev
current cross-correlations, for various parameters of the model, both in the
linear and nonlinear response regimes. Depending on parameters and transport
regime, we find both positive and negative current cross-correlations.
Enhancement of the former type of cross-correlations indicates transport
regimes, in which the device works with high Cooper pair splitting efficiency,
contrary to the latter type of correlations, which imply negative influence on
the splitting. The processes and mechanisms leading to both types of current
cross-correlations are thoroughly examined and discussed, giving a detailed
insight into the Andreev transport properties of the considered device.",1703.09957v1
2017-08-05,Spin Injection and Detection via the Anomalous Spin Hall Effect in a Ferromagnetic Metal,"We report a novel spin injection and detection mechanism via the anomalous
Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE)
refers to the transverse spin current generated within the ferromagnet. We
utilize the ASHE and its reciprocal effect to electrically inject and detect
magnons in a magnetic insulator in a non-local geometry. Our experiments reveal
that permalloy can have a higher spin injection and detection efficiency to
that of platinum, owing to the ASHE. We also demonstrate the tunability of the
ASHE via the orientation of the permalloy magnetization, thus creating new
possibilities for spintronic applications.",1708.01752v1
2017-08-06,Bias induced ferromagnetism and half-metallicity in graphene nano-ribbons,"Towards spin selective electronics made of three coordinated carbon atoms,
here we computationally propose robust and reversibly bias driven evolution of
pristine undoped graphene nano-ribbons(GNR) into ferromagnetic-semiconductor,
metal or a half metal, irrespective of their edge configurations. The evolution
is a result of a rare ferromagnetic(FM) order emerging among nearest
neighbouring(n-n) sites, in positively biased regions in their in-homogeneous
bias unit-cells, in attempt to cooperatively minimise on-site Coulomb repulsion
and kinetic energy, while maximising localization of electrons at the
positively biased sites. The phenomenon appears to be a general property of
in-homogeneously biased Coulomb correlated bipartite systems. Consequences are
particularly rich in zigzag edged graphene nano-ribbons(ZGNR) due to the
contest of bias driven n-n FM order and the inter-edge antiferromagnetic order
inherent to ZGNRs, leading to systematic closing of gap for one of the spins,
amounting to bias controlled unmissable opening of window for FM-semiconducting
and half-metallic transport.",1708.01860v1
2017-08-10,Spin Hall magnetoresistance and spin Nernst magnetothermopower: role of the inverse spin galvanic effect,"In ferromagnet/normal-metal bilayers, the sensitivity of the spin Hall
magnetoresistance and the spin Nernst magnetothermopower to the boundary
conditions at the interface is of central importance. In general, such boundary
conditions can be substantially affected by current-induced spin polarizations.
In order to quantify the role of the latter, we consider a Rashba
two-dimensional electron gas with a ferromagnet attached to one side of the
system. The geometry of such a system maximizes the effect of current-induced
spin polarization on the boundary conditions, and the spin Hall
magnetoresistance is shown to acquire a non-trivial and asymmetric dependence
on the magnetization direction of the ferromagnet.",1708.03165v1
2017-08-21,Transport Coefficients of Dirac Ferromagnet: Effects of Vertex Corrections,"As a strongly spin-orbit coupled metallic model with ferromagnetism, we have
considered an extended Stoner model to the relativistic regime, named Dirac
ferromagnet in three dimensions.
  In the previous paper~[Phys. Rev. B 90, 214418 (2014)], we studied the
transport properties giving rise to the anisotropic magnetoresistance~(AMR) and
the anomalous Hall effect~(AHE) with the impurity potential being taken into
account only as the self-energy.
  The effects of the vertex corrections~(VCs) to AMR and AHE are reported in
this paper.
  AMR is found not to change quantitatively when the VCs is considered,
although the transport lifetime is different from the one-electron lifetime and
the charge current includes additional contributions from the correlation with
spin currents.
  The side-jump and the skew-scattering contributions to AHE are also
calculated.
  The skew-scattering contribution is dominant in the clean case as can be seen
in the spin Hall effect in the non-magnetic Dirac electron system.",1708.06105v1
2017-08-21,"On the origin of magnetism in (Ga,Mn)As: from paramagnetic through superparamagnetic to ferromagnetic phase","The high-spectral-resolution spectroscopic studies of the energy gap
evolution, supplemented with electronic, magnetic and structural
characterization, show that the modification of the GaAs valence band caused by
Mn incorporation occurs already for a very low Mn content, much lower than that
required to support ferromagnetic spin - spin coupling in (Ga,Mn)As. Only for
n-type (Ga,Mn)As with the Mn content below about 0.3% the Mn-related extended
states are visible as a feature detached from the valence-band edge and partly
occupied with electrons. The combined magnetic and low-temperature
photoreflectance studies presented here indicate that the paramagnetic -
ferromagnetic transformation in p-type (Ga,Mn)As takes place without imposing
changes of the unitary character of the valence band with the Fermi level
located therein. The whole process is rooted in the nanoscale fluctuations of
the local (hole) density of states and the formation of a
superparamagnetic-like state. The Fermi level in (Ga,Mn)As is coarsened by the
carrier concentration of the itinerant valence band holes and further
fine-tuned by the many-body interactions.",1708.06435v1
2017-08-26,Magneto-thermopower in the Weak Ferromagnetic Oxide CaRu0.8Sc0.2O3: An Experimental Test for the Kelvin Formula in a Magnetic Material,"We have measured the resistivity, the thermopower, and the specific heat of
the weak ferromagnetic oxide CaRu0.8Sc0.2O3 in external magnetic fields up to
140 kOe below 80 K. We have observed that the thermopower Q is significantly
suppressed by magnetic fields at around the ferromagnetic transition
temperature of 30 K, and have further found that the magneto-thermopower
{\Delta}Q(H, T) = Q(H, T) - Q(0, T) is roughly proportional to the
magneto-entropy {\Delta}S(H, T) = S(H, T)-S(0, T).We discuss this relationship
between the two quantities in terms of the Kelvin formula, and find that the
observed {\Delta}Q is quantitatively consistent with the values expected from
the Kelvin formula, a possible physical meaning of which is discussed.",1708.07992v1
2018-02-07,"Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy","Future spintronics requires the realization of thin film of half-metallic
ferromagnets having high Curie temperature and 100\% spin polarization at the
Fermi level for potential spintronics applications. In this paper, we report
the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO
(001) substrate using pulsed laser deposition system, along with the study of
structural, magnetic and transport properties. The magnetic property
measurements of the thin film suggest a soft ferromagnetic state at room
temperature with an in-plane magnetic anisotropy and a Curie temperature well
above the room temperature. Anisotropic magnetoresistance (AMR) ratio and
temperature dependent electrical resistivity measurements of the thin film
indicate the compound to be half-metallic in nature and therefore suitable for
the fabrications of spintronics devices.",1802.02413v1
2018-02-13,Inducing ferromagnetism and Kondo effect in platinum by paramagnetic ionic gating,"Electrically controllable magnetism, which requires the field-effect
manipulation of both charge and spin degrees of freedom, has attracted growing
interests since the emergence of spintronics. In this work, we report the
reversible electrical switching of ferromagnetic (FM) states in platinum (Pt)
thin films by introducing paramagnetic ionic liquid (PIL) as the gating media.
The paramagnetic ionic gating controls the movement of ions with magnetic
moments, which induces itinerant ferromagnetism on the surface of Pt films with
large coercivity and perpendicular anisotropy mimicking the ideal
two-dimensional Ising-type FM state. The electrical transport of the induced FM
state shows Kondo effect at low temperature suggesting spatially separated
coexistence of Kondo scattering beneath the FM interface. The tunable FM state
indicates that paramagnetic ionic gating could serve as a versatile method to
induce rich transport phenomena combining field effect and magnetism at
PIL-gated interfaces.",1802.04448v2
2018-02-19,Strong enhancement of the spin Hall effect by spin fluctuations near the Curie point of FexPt1-x alloys,"Robust spin Hall effects (SHE) have recently been observed in non-magnetic
heavy metal systems with strong spin-orbit interactions. These SHE are either
attributed to an intrinsic band-structure effect or to extrinsic spin-dependent
scattering from impurities, namely side-jump or skew scattering. Here we report
on an extraordinarily strong spin Hall effect, attributable to spin
fluctuations, in ferromagnetic FexPt1-x alloys near their Curie point, tunable
with x. This results in a damping-like spin-orbit torque being exerted on an
adjacent ferromagnetic layer that is strongly temperature dependent in this
transition region, with a peak value that indicates a lower bound 0.34 (+-)
0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced
peak in the effective spin-mixing conductance of the FM/FePt interface, and
determine the spin diffusion length in these FexPt1-x alloys. These results
establish new opportunities for fundamental studies of spin dynamics and
transport in ferromagnetic systems with strong spin fluctuations, and a new
pathway for efficiently generating strong spin currents for applications.",1802.06911v1
2018-02-21,Magnonic Spin-Transfer Torque in Ferromagnet/Antiferromagnet/Ferromagnet Trilayer,"In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down
magnons coexist and form an intrinsic degree of freedom resembling electrons.
When polarized by an adjacent ferromagnet (F), a magnonic pure spin current can
be thermally generated in an AF. We explore thermal magnon transport in an
insulating F/AF/F trilayer where propagating magnons inside the AF spacer can
transfer angular momenta between the two Fs. We find that a sufficiently large
temperature gradient can switch the downstream F via magnonic spin-transfer
torque if it is initially antiparallel with the upstream F. A reciprocal
switching is achievable by reversing the temperature gradient. Using typical
material parameters, we estimate the threshold to be less than 1 K/nm at room
temperature, which can be reduced by raising temperature and enhancing the
interfacial exchange coupling.",1802.07709v2
2018-04-05,Two-Stage Proximity-Induced Gap-Opening in Topological Insulator - Insulating Ferromagnet (Bi$_x$Sb$_{1-x}$)$_2$Te$_3$ - EuS Bilayers,"To further investigate the interplay between ferromagnetism and topological
insulators, thin films of the low-carrier topological insulator
(Bi$_x$Sb$_{1-x}$)$_2$Te$_3$ were deposited on the insulating ferromagnet EuS
(100) in situ. AC susceptibility indicates magnetic anomalies between
$T\approx30~\mathrm{K}$ and $T\approx60~\mathrm{K}$, well above the Curie
temperature $T_C \approx 15~\mathrm{K}$ of EuS. When the Fermi level is close
to the Dirac point and the surface state dominates the electric conduction,
sharp increases in resistance with decreasing temperatures were observed
concurrently with the magnetic anomalies. Positive-negative magnetoresistance
crossovers were observed at the Curie temperature, which seem only to appear
when the sheet resistance exceeds the Mott-Ioffe-Regel limit $h/e^2$. A
two-stage gap-opening process due to magnetic proximity is proposed.",1804.02061v2
2018-04-06,Exact Results on Itinerant Ferromagnetism and the 15-puzzle Problem,"We apply a result from graph theory to prove exact results about itinerant
ferromagnetism. Nagaoka's theorem of ferromagnetism is extended to all
non-separable graphs except single polygons with more than four vertices by
applying the solution to the generalized 15-puzzle problem, which studies
whether the hole's motion can connect all possible tile configurations. This
proves that the ground state of a $U\to\infty$ Hubbard model with one hole away
from the half filling on a 2D honeycomb lattice or a 3D diamond lattice is
fully spin-polarized. Furthermore, the condition of connectivity for
$N$-component fermions is presented, and Nagaoka's theorem is also generalized
to $SU(N)$-symmetric fermion systems on non-separable graphs.",1804.02347v1
2018-04-09,Genuine multipartite nonlocality in the one-dimensional ferromagnetic spin-1/2 chain,"Genuine multipartite entanglement has been found in some spin chain systems.
However, genuine multipartite nonlocality, which is much rarer than genuine
multipartite entanglement, has never been found in any spin chain system. Here
we present genuine multipartite nonlocality in a spin chain system. After
introducing the definition of genuine multipartite nonlocality and a
multipartite Bell-type inequality, we construct a group of joint measurements
for the inequality in a one-dimensional ferromagnetic $N$-qubit chain with
nearest-neighbor XXZ interaction, and many violations to the inequality have
been found. The violations do indicate that genuine multipartite nonlocality
exists in this ferromagnetic spin-1/2 chain system. Last but not least, we also
calculate genuine multipartite entanglement concurrence in the same spin chain
to demonstrate the difference and relationship between genuine multipartite
nonlocality and genuine multipartite entanglement.",1804.02901v1
2018-04-09,Van der Waals spin valves,"We propose spin valves where a 2D non-magnetic conductor is intercalated
between two ferromagnetic insulating layers. In this setup, the relative
orientation of the magnetizations of the insulating layers can have a strong
impact on the in-plane conductivity of the 2D conductor. We first show this for
a graphene bilayer, described with a tight-binding model, placed between two
ferromagnetic insulators. In the anti-parallel configuration, a band gap opens
at the Dirac point, whereas in the parallel configuration, the graphene bilayer
remains conducting. We then compute the electronic structure of graphene
bilayer placed between two monolayers of the ferromagnetic insulator CrI$_3$,
using density functional theory. Consistent with the model, we find that a gap
opens at the Dirac point only in the antiparallel configuration.",1804.03021v1
2018-04-17,Emergent Magnetism at the 3$d$-5$d$ Interface: SrMnO$_3/$SrIrO$_3$,"Recent experiments have found new magnetic behaviors, which are different
from the parent bulk materials, at the interfaces between 3$d$ and 5$d$ oxides
such as SrMnO$_3$ (SMO) and SrIrO$_3$ (SIO). The system is of considerable
interest due to the strong spin-orbit coupling in the 5$d$ materials on one
hand and the double exchange physics in SMO on the other, which belongs to the
class of the colossal magnetoresistive (CMR) manganites. In order to gain
insight into the physics of the system, we have performed density-functional
studies on a selected interface structure, viz., the (SMO)$_1$(SIO)$_1$
superlattice, which has been experimentally grown and studied. Our
density-functional results show that the interfacial magnetism is controlled by
a net charge transfer at the interface from the SIO to the SMO side, turning
both of them into ferromagnetic metal from the original antiferromagnetic
insulating state in the bulk. The transferred electrons to the SMO side make it
ferromagnetic through the Anderson-Hasegawa double exchange interaction, while
the SIO part becomes ferromagnetic due to the doping of the half-filled
Mott-Hubbard insulator as suggested by the Nagaoka Theorem. Our results are
discussed in the context of the experiments for the same structure.",1804.06381v1
2018-04-17,Anomalous Hall effect in van der Waals bonded ferromagnet Fe$_{3-x}$GeTe$_2$,"We report anomalous Hall effect (AHE) in single crystals of
quasi-two-dimensional Fe$_{3-x}$GeTe$_2$ ($x \approx 0.36$) ferromagnet grown
by the flux method which induces defects on Fe site and bad metallic
resistivity. Fe K-edge x-ray absorption spectroscopy was measured to provide
information on local atomic environment in such crystals. The dc and ac
magnetic susceptibility measurements indicate a second-stage transition below
119 K in addition to the paramagnetic to ferromagnetic transition at 153 K. A
linear scaling behavior between the modified anomalous Hall resistivity
$\rho_{xy}/\mu_0H_{eff}$ and longitudinal resistivity
$\rho_{xx}^2M/\mu_0H_{eff}$ implies that the AHE in Fe$_{3-x}$GeTe$_2$ should
be dominated by the intrinsic Karplus-Luttinger mechanism rather than the
extrinsic skew-scattering and side-jump mechanisms. The observed deviation in
the linear-M Hall conductivity $\sigma_{xy}^A$ below 30 K is in line with its
transport characteristic at low temperatures, implying the scattering of
conduction electrons due to magnetic disorder and the evolution of the Fermi
surface induced by possible spin-reorientation transition.",1804.06392v1
2018-04-20,The nature of transport and ferromagnetic properties of the GaAs structures with the Mn δ-doped layer,"We reveal the nature of transport and ferromagnetic properties of the GaAs
structure with the single Mn {\delta}-doped layer. To modify the properties of
the structure the electrically active radiation defects are created by
irradiation with helium ions. The investigations show that the transport
properties of the structure are determined by two parallel conduction channels
(the channel associated with hole transport in the valence band and the channel
associated with electron transport in the Mn impurity band) and that the
ferromagnetic properties are determined by the electrons localized at the
allowed states within the Mn impurity band. The results also help to understand
the features of structures with the Mn {\delta}-layer nearby the quantum well.",1804.07650v3
2018-04-20,Fluctuation-induced Néel and Bloch skyrmions at topological insulator surfaces,"Ferromagnets in contact with a topological insulator have become appealing
candidates for spintronics due to the presence of Dirac surface states with
spin-momentum locking. Because of this bilayer Bi$_2$Se$_3$-EuS structures, for
instance, show a finite magnetization at the interface at temperatures well
exceeding the Curie temperature of bulk EuS. Here we determine theoretically
the effective magnetic interactions at a topological insulator-ferromagnet
interface {\it above} the magnetic ordering temperature. We show that by
integrating out the Dirac fermion fluctuations an effective
Dzyaloshinskii-Moriya interaction and magnetic charging interaction emerge. As
a result individual magnetic skyrmions and extended skyrmion lattices can form
at interfaces of ferromagnets and topological insulators, the first indications
of which have been very recently observed experimentally.",1804.07684v3
2018-04-29,Diluted magnetic Dirac-Weyl materials: Susceptibility and ferromagnetism in three-dimensional chiral gapless semimetals,"We theoretically investigate the temperature-dependent static susceptibility
and long-range magnetic coupling of three-dimensional (3D) chiral gapless
electron-hole systems (semimetals) with arbitrary band dispersion [i.e.,
$\varepsilon(k) \sim k^N$, where $k$ is the wave vector and $N$ is a positive
integer]. We study the magnetic properties of these systems in the presence of
dilute random magnetic impurities. Assuming carrier-mediated
Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction, we find that the
magnetic ordering of intrinsic 3D chiral semimetals in the presence of dilute
magnetic impurities is ferromagnetic for all values of $N$. Using
finite-temperature self-consistent field approximation, we calculate the
ferromagnetic transition temperature ($T_{\rm c}$). We find that $T_{\rm c}$
increases with increasing $N$ due to the enhanced density of states, and the
calculated $T_{\rm c}$ is experimentally accessible assuming reasonable
coupling between the magnetic impurities and itinerant carriers.",1804.10867v2
2018-11-04,Coexistence of exchange bias training effect and spin-orbit torque in IrMn-layer/ferromagnetic-ribbon heterostructures via magnetoimpedance effect,"We investigate a possible correlation between spin orbit torque (SOT) and
exchange-bias (EB) in IrMn-layer/ferromagnetic-ribbon heterostructure by
performing magnetoimpedance (MI) measurements. To uncover this correlation, we
benefit from EB training effect probed by MI effect at room temperature. A
damping-like SOT driven by ac current through the antiferromagnetic IrMn
applies to the ferromagnetic ribbon layer, determined by MI magnetic field and
frequency sweeps. Importantly, magnitude of the SOT is observed to remain
intact against EB training and decrease of EB through alternative magnetic
field sweep cycles. Our results pave the way to better elucidate the EB effect,
EB training and the SOT, useful for future spintronic elements.",1811.01352v4
2018-11-14,Relation between spin Hall effect and anomalous Hall effect in 3$d$ ferromagnetic metals,"We study the mechanisms of the spin Hall effect (SHE) and anomalous Hall
effect (AHE) in 3$d$ ferromagnetic metals (Fe, Co, permalloy
(Ni$_{81}$Fe$_{19}$; Py), and Ni) by varying their resistivities and
temperature. At low temperatures where the phonon scattering is negligible, the
skew scattering coefficients of the SHE and AHE in Py are related to its spin
polarization. However, this simple relation breaks down for Py at higher
temperatures as well as for the other ferromagnetic metals at any temperature.
We find that, in general, the relation between the SHE and AHE is more complex,
with the temperature dependence of the SHE being much stronger than that of
AHE.",1811.05589v2
2018-11-22,Magnetoelectric effects in superconductor/ferromagnet bilayers,"We demonstrate that the hybrid structures consisting of a superconducting
layer with an adjacent spin-textured ferromagnet demonstrate the variety of
equilibrium magnetoelectric effects originating from coupling between the
conduction electron spin and superconducting current. By deriving and solving
the generalized Usadel equation which takes into account the spin-filtering
effect we find that a supercurrent generates spin polarization in the
superconducting film which is non-coplanar with the local ferromagnetic moment.
The inverse magnetoelectric effect in such structures is shown to result in the
spontaneous phase difference across the magnetic topological defects such as a
domain wall and helical spin texture. The possibilities to obtain
dissipationless spin torques and detect domain wall motion through the
superconducting phase difference are discussed.",1811.09304v2
2018-11-25,Temperature-Dependent Magnetization Reversal in Exchange Bias NiFe/IrMn/NiFe Structures,"We demonstrate the magnetization reversal features in NiFe/IrMn/NiFe
thin-film structures with 40% and 75% relative content of Ni in Permalloy in
the temperature range from 80 K to 300 K. At the descending branches of the
hysteresis loops, the magnetization reversal sequence of the two ferromagnetic
layers is found to depend on the type of NiFe alloy. In the samples with 75%
relative content of Ni, the bottom ferromagnetic layer reverses prior to the
top one. On the contrary, in the samples with 40% of Ni, the top ferromagnetic
layer reverses prior to the bottom one. These tendencies of magnetization
reversal are preserved in the entire range of temperatures. These distinctions
can be explained by the morphological and structural differences of interfaces
in the samples based on two types of Permalloy.",1811.09963v1
2019-04-30,Ferromagnetism and Spin-Valley liquid states in Moiré Correlated Insulators,"Motivated by the recent observation of evidences of ferromagnetism in
correlated insulating states in systems with Moir\'{e} superlattices, we study
a two-orbital quantum antiferromagnetic model on the triangular lattice, where
the two orbitals physically correspond to the two valleys of the original
graphene sheet. For simplicity this model has a SU(2)$^s$$\otimes$SU(2)$^v$
symmetry, where the two SU(2) symmetries correspond to the rotation within the
spin and valley space respectively. Through analytical argument, Schwinger
boson analysis and also DMRG simulation, we find that even though all the
couplings in the Hamiltonian are antiferromagnetic, there is still a region in
the phase diagram with fully polarized ferromagnetic order. We argue that a
Zeeman field can drive a metal-insulator transition in our picture, as was
observed experimentally. We also construct spin liquids and topological ordered
phases at various limits of this model. Then after doping this model with extra
charge carriers, the system most likely becomes spin-triplet/valley-singlet
$d+id$ topological superconductor as was predicted previously.",1905.00033v2
2019-05-04,Theoretical Study on Four-fold Symmetric Anisotropic Magnetoresistance Effect in Cubic Single-crystal Ferromagnetic Model,"In this study, we present a theoretical interpretation of the experimental
results that the anisotropic magnetoresistance (AMR) effect has a four-fold
symmetric component, $c_4$, in cubic ferromagnetic metals. The theoretical
model that we employ is based on the Anderson impurity model that includes a
four-fold symmetric crystalline electric field, and we assume that the
impurities have 3d electron orbitals and spin--orbit interaction (SOI). We
describe the DC conductivity on the basis of the Kubo formula, and we
investigate $c_4$ by analyzing the magnetization direction dependence of the
resultant AMR ratio. Analytical and numerical calculations are performed; the
analytical calculation reveals that $c_4$ arises from the fourth-order
contribution of the SOI, and the numerical calculation provides the parameter
dependencies of $c_{4}$ in our model. From the calculation results, we observe
that the splitting of impurity 3d levels due to SOI is responsible for the
existence of $c_{4}$ in cubic ferromagnetic metals.",1905.01424v2
2019-05-07,Atomic scale electronic structure of the ferromagnetic semiconductor Cr2Ge2Te6,"Cr2Ge2Te6 is an intrinsic ferromagnetic semiconductor with van der Waals type
layered structure, thus represents a promising material for novel electronic
and spintronic devices. Here we combine scanning tunneling microscopy and
first-principles calculations to investigate the electronic structure of
Cr2Ge2Te6. Tunneling spectroscopy reveals a surprising large energy level shift
and change of energy gap size across the ferromagnetic to paramagnetic phase
transition, as well as a peculiar double-peak electronic state on the Cr-site
defect. These features can be quantitatively explained by density functional
theory calculations, which uncover a close relationship between the electronic
structure and magnetic order. These findings shed important new lights on the
microscopic electronic structure and origin of magnetic order in Cr2Ge2Te6.",1905.02444v1
2019-05-19,Magnetic Vortex induced by Nonmagnetic Impurity in Ferromagnets: Magnetic Multipole and Toroidal around the Vacancy,"We report our theoretical study on nucleation of a magnetic vortex around a
nonmagnetic impurity doped into ferromagnets. The mechanism lies in the
asymmetric Dzyaloshinskii-Moriya interaction arising from the breaking of
spatial inversion symmetry by the impurity. By using the spin-wave analysis and
Monte Carlo simulations, we show that the asymmetric interaction induces a
magnetic vortex with nonzero vorticity $l=+1$. The vortex is stabilized even
for less frustration in exchange interactions and in the absence of an external
magnetic field. We also find that the magnetic vortex is characterized by
magnetic multipoles according to its vorticity and helicity. We demonstrate a
potential realization of such a magnetic vortex by considering a monolayer
ferromagnet on a nonmagnetic substrate, which results in the magnetic monopole
and toroidal dipole.",1905.07669v1
2019-05-19,Long-range triplet proximity effect in multiply connected ferromagnet-superconductor hybrids,"Applying the linearized Usadel equations, we consider the nucleation of
superconductivity in multiply connected mesoscopic superconductor/ferromagnet
(S/F) hybrids such as a thin superconducting ring on a ferromagnet with a
uniform in-plane magnetization M and a spin-active S/F interface. We
demonstrate that the exchange field in F provokes a switching between
superconducting states with different vorticities which may increase the
critical temperature ( Tc ) of the superconductor in a magnetic field. We study
the interplay between oscillations in Tc due to the Little--Parks effect and
oscillations in Tc induced by the exchange field. Furthermore, we analyse the
influence of long-range spin-triplet correlations on the switching between
different vorticities.",1905.07683v1
2019-05-22,Competitive 0 and π states in S/F multilayers: multimode approach,"We have investigated the critical temperature behavior in periodic
superconductor/ ferromagnet (S/F) multilayers as a function of the
ferromagnetic layer thickness $d_f$ and the interface transparency. The
critical temperature $T_c(d_f)$ exhibits a damped oscillatory behavior in these
systems due to an exchange field in the ferromagnetic material. In this work we
have performed $T_c$ calculations using the self-consistent multimode approach,
which is considered to be exact solving method. Using this approach we have
derived the conditions of 0 or $\pi$ state realization in periodic S/F
multilayers. Moreover, we have presented the comparison between the single-mode
and multimode approaches and established the limits of applicability of the
single-mode approximation, frequently used by experimentalists.",1905.09193v2
2019-05-29,Skew Andreev reflection in ferromagnet/superconductor junctions,"Andreev reflection (AR) in ferromagnet/superconductor junctions is an
indispensable spectroscopic tool for measuring spin polarization. We study
theoretically how the presence of a thin semiconducting interface in such
junctions, inducing Rashba and Dresselhaus spin-orbit coupling, modifies AR
processes. The interface gives rise to an effective momentum- and
spin-dependent scattering potential, making the probability of AR strongly
asymmetric with respect to the sign of the incident electrons' transverse
momenta. This skew AR creates spatial charge carrier imbalances and transverse
Hall currents flow in the ferromagnet. We show that the effect is giant, as
compared to the normal regime. We provide a quantitative analysis and a
qualitative picture of this phenomenon, and finally show that skew AR also
leads to a widely tunable transverse supercurrent response in the
superconductor.",1905.12525v2
2020-07-03,Dynamic spin-triplet order induced by alternating electric fields in superconductor-ferromagnet-superconductor Josephson junctions,"Dynamic states offer extended possibilities to control the properties of
quantum matter. Recent efforts are focused on studying the ordered states which
appear exclusively under the time-dependent drives. Here we demonstrate a class
of systems which feature dynamic spin-triplet superconducting order stimulated
by the alternating electric field. The effect is based on the interplay of
ferromagnetism, interfacial spin-orbital coupling (SOC) and the condensate
motion driven by the field, which converts hidden static p-wave order, produced
by the joint action of the ferromagnetism and the SOC, into dynamical s-wave
equal-spin triplet correlations. We demonstrate that the critical current of
Josephson junctions hosting these states is proportional to the electromagnetic
power, supplied either by the external irradiation or by the ac current source.
Based on these unusual properties we propose the scheme of a Josephson
transistor which can be switched by the ac voltage and demonstrates an
even-numbered sequence of Shapiro steps. Combining the photo-active Josephson
junctions with recently discovered Josephson phase batteries we find
photo-magnetic SQUID devices which can generate spontaneous magnetic fields
while being exposed to irradiation.",2007.01805v2
2020-07-07,Magnetization control by angular momentum transfer from surface acoustic wave to ferromagnetic spin moments,"The angular momentum interconversion between electron spin and other type of
angular momenta is useful to develop new spintronic functionalities. The
conversions from the angular momentum of photon and mechanical rotation to
ferromagnetic spin moment have been well studied. While the recent studies
theoretically suggested circular vibration of atoms works as angular momentum
of phonon, the direct experimental demonstration of conversion to spin moments
remains to be performed. Here we demonstrate that the phonon angular momentum
of surface acoustic wave can control the magnetization of a ferromagnetic Ni
film by means of the phononic-to-electronic conversion of angular momentum in
Ni/LiNbO$_3$ hybrid device. This result clearly shows the phonon angular
momentum is useful to further fictionalize spintronic devices.",2007.03192v1
2010-05-07,Effect of ferromagnetic film thickness on magnetoresistance of thin-film superconductor-ferromagnet hybrids,"We study the influence of the thickness Df of the plain ferromagnetic (F)
film on the electrical resistance of the flux-coupled hybrids, consisting of
superconducting (S) Al film and multilayer [Co/Pt] F film with out-of-plain
magnetization. The behavior of such hybrids at high and low temperatures is
found to be different: the nucleation of superconductivity at high temperatures
is governed mainly by the typical lateral dimensions of the magnetic domains,
while low temperature properties are determined by topology of the magnetic
template. We show that an increase in the Df value leads to a broadening of the
field- and temperature intervals where non-monotonous dependence of the
superconducting critical temperature Tc on the applied magnetic field H is
observed (for demagnetized F films). Further increase in the Df value results
in a global suppression of superconductivity. Thus, we determined an optimal
thickness, when the non-monotonous dependence Tc(H) can be observed in rather
broad T and H range, what can be interesting for further studies of the
localized superconductivity in planar Al-based S/F hybrids and for development
of the devices which can exploit the localized superconductivity.",1005.1246v1
2010-05-13,Anomalous spin distribution in the superconducting ferromagnet UCoGe studied by polarized neutron diffraction,"We report a polarized neutron diffraction study conducted to reveal the
nature of the weak ferromagnetic moment in the superconducting ferromagnet
UCoGe. We find that the ordered moment in the normal phase in low magnetic
fields (B // c) is predominantly located at the U atom and has a magnitude of
about 0.1 muB at 3 T, in agreement with bulk magnetization data. By increasing
the magnetic field the U moment grows to about 0.3 muB in 12 T and most
remarkably, induces a substantial moment (about 0.2 muB) on the Co atom
directed antiparallel to the U moment. The anomalous polarizability of the Co
3d orbitals is unique among uranium intermetallics and might reflect the
proximity to a magnetic quantum critical point of UCoGe in zero field.",1005.2390v1
2010-05-14,Spin State Transfer in Laterally Coupled Quantum Dot Chains with Disorders,"Quantum dot arrays are a promising media for transferring quantum information
between two distant points without resorting to mobile qubits. Here we study
two most common disorders namely, hyperfine interaction and exchange coupling
fluctuations, in quantum dot arrays and their effects on quantum communication
through these chains. Our results show that the hyperfine interaction is more
destructive than the exchange coupling fluctuations. The average optimal time
for communication is not affected by any disorder in the system and our
simulations show that anti-ferromagnetic chains are much more resistive than
the ferromagnetic ones against both kind of disorders. Even when time
modulation of a coupling and optimal control is employed to improve the
transmission, the anti-ferromagnetic chain performs much better. We have
assumed the quasi-static approximation for hyperfine interaction and time
dependent fluctuations in the exchange couplings. Particularly, for studying
exchange coupling fluctuations we have considered the static disorder, white
noise and $1/f$ noise.",1005.2571v2
2013-08-05,Controlling the Polarity of the Transient Ferromagnetic-Like State in Ferrimagnets,"After the application of an ultrashort laser pulse, the antiferromagnetic
alignment in rare earth-transition metal alloys can temporarily become
ferromagnetic with the rare-earth polarity.
  Proposed models merely describe this effect, without showing the route for
its manipulation. Here we use extensive atomistic spin model simulations and
micromagnetic theory for ferrimagnets at elevated temperatures to predict that
the polarity of this transient ferromagnetic-like state can be controlled by
initial temperature. We show that this arises because the magnetic response of
each lattice has a different temperature dependence, at low temperatures the
transition metal responds faster than the rare earth, while at high
temperatures this role is interchanged. Our findings contribute to the physical
understanding and control of this state and thus open new perspectives for its
use in ultrafast magnetic devices.",1308.0993v2
2013-08-15,Spin heat accumulation induced by tunneling from a ferromagnet,"An electric current from a ferromagnet into a non-magnetic material can
induce a spin-dependent electron temperature. Here it is shown that this spin
heat accumulation, when created by tunneling from a ferromagnet, produces a
non-negligible voltage signal that is comparable to that due to the coexisting
electrical spin accumulation and can give a different Hanle spin precession
signature. The effect is governed by the spin polarization of the Peltier
coefficient of the tunnel contact, its Seebeck coefficient, and the spin heat
resistance of the non-magnetic material, which is related to the electrical
spin resistance by a spin-Wiedemann-Franz law. Moreover, spin heat injection is
subject to a heat conductivity mismatch that is overcome if the tunnel
interface has a sufficiently large resistance.",1308.3365v2
2013-08-21,"Reducing influence of antiferromagnetic interactions on ferromagnetic properties of p-(Cd,Mn)Te quantum wells","In order to explain the absence of hysteresis in ferromagnetic p-type
(Cd,Mn)Te quantum wells (QWs), spin dynamics was previously investigated by
Monte Carlo simulations combining the Metropolis algorithm with the
determination of hole eigenfunctions at each Monte Carlo sweep. Short-range
antiferromagnetic superexchange interactions between Mn spins - which compete
with the hole-mediated long-range ferromagnetic coupling - were found to
accelerate magnetization dynamics if the the layer containing Mn spins is wider
than the vertical range of the hole wave function. Employing this approach it
is shown here that appreciate magnitudes of remanence and coercivity can be
obtained if Mn ions are introduced to the quantum well in a delta-like fashion.",1308.4525v1
2013-08-22,"New Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping","We report the discovery of a new diluted magnetic semiconductor, Li(Zn,Mn)P,
in which charge and spin are introduced independently via lithium
off-stoichiometry and the isovalent substitution of Mn2+ for Zn2+,
respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a p-type
ferromagnetic semiconductor with excess Lithium providing charge doping. First
principles calculations indicate that excess Li is favored to partially occupy
the Zn site, leading to hole doping. Ferromagnetism is mediated in
semiconducting samples of relative low mobile carriers with a small coercive
force, indicating an easy spin flip.",1308.4929v1
2013-08-27,Experimental realization of magnetic energy concentration and transmission at a distance by metamaterials,"Controlling electromagnetic energy is essential for an efficient and
sustainable society. A key requirement is concentrating magnetic energy in a
desired volume of space in order to either extract the energy to produce work
or store it. Metamaterials have opened new possibilities for controlling
electromagnetic energy. Recently, a superconductor-ferromagnetic metamaterial
that allows unprecedented concentration and amplification of magnetic energy,
and also its transmission at distance through free space, has been devised
theoretically. Here we design and build an actual version of the
superconductor-ferromagnetic metamaterial and experimentally confirm these
properties. We show that also a ferromagnetic metamaterial, without
superconducting parts, can achieve concentration and transmission of energy
with only a slight decrease in the performance. Transmission of magnetic energy
at a distance by magnetic metamaterials may provide new ways of enhancing
wireless power transmission, where efficiency depends critically on the
magnetic coupling strength between source and receiver.",1308.5878v1
2014-03-04,All-optical control of ferromagnetic thin films and nanostructures,"The interplay of light and magnetism has been a topic of interest since the
original observations of Faraday and Kerr where magnetic materials affect the
light polarization. While these effects have historically been exploited to use
light as a probe of magnetic materials there is increasing research on using
polarized light to alter or manipulate magnetism. For instance deterministic
magnetic switching without any applied magnetic fields using laser pulses of
the circular polarized light has been observed for specific ferrimagnetic
materials. Here we demonstrate, for the first time, optical control of
ferromagnetic materials ranging from magnetic thin films to multilayers and
even granular films being explored for ultra-high-density magnetic recording.
Our finding shows that optical control of magnetic materials is a much more
general phenomenon than previously assumed. These results challenge the current
theoretical understanding and will have a major impact on data memory and
storage industries via the integration of optical control of ferromagnetic
bits.",1403.0784v1
2014-03-08,Ab initio study of CrNF: the first half-metallic ferromagnet nitride fluoride mimicking CrO2,"Based on the different covalent versus ionic chemical bonding and
isoelectronic rutile CrO2, CrNF is proposed starting from ordered rutile
derivative structures subjected to full geometry optimizations. The ground
state structure defined from cohesive energies is of MgUO4-type, characterized
by short covalent Cr-N and long ionic Cr-F distances. Like CrO2 it is a
half-metallic ferromagnet with M = 2 Bohr Magnetons integer magnetization per
formula unit with reduced band gap at minority spins. Major differences of
magnetic response to pressure characterize CrNF as a soft ferromagnet versus
hard magnetic CrO2. The chemical bonding properties point to prevailing
covalent Cr-N versus ionic Cr-F bonding. Synthesis routes with two different
protocols are proposed and analyzed.",1403.1961v1
2014-03-17,Ba(Zn1-2xMnxCox)2As2: A Bulk Form Diluted Magnetic Semiconductor with n-type Carriers,"We report the synthesis and characterization of bulk form diluted magnetic
semiconductors Ba(Zn1-2xMnxCox)2As2 (0 <= x <= 0.15) with a crystal structure
identical to that of 122-type Fe-based superconductors. Mn and Co co-doping
into the parent compound BaZn2As2 results in a ferromagnetic ordering below TC
~ 80 K. Hall effect measurements indicate that the carrier are n-type with the
density of ~10^17/cm3. The common crystal structure and excellent lattice
matching between the p-type ferromagnetic (Ba1-yKy)(Zn1-xMnx)2As2, the n-type
ferromagnetic Ba(Zn1-2xMnxCox)2As2, the antiferrmagnetic BaMn2As2 and the
superconducting Ba(Fe1-xCox)2As2 systems make it possible to make various
junctions between these systems through the As layer.",1403.4019v1
2014-03-17,Magnetic phase transition in coherently coupled Bose gases in optical lattices,"We describe the ground state of a gas of bosonic atoms with two coherently
coupled internal levels in a deep optical lattice in a one dimensional
geometry. In the single-band approximation this system is described by a
Bose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating
phase which can be either paramagnetic or ferromagnetic. We characterize the
quantum phase transitions at unit filling by means of a density matrix
renormalization group technique and compare it with a mean-field approach. The
presence of the ferromagnetic Ising-like transition modifies the Mott lobes. In
the Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ
model in a transverse field and the numerical results compare very well with
the analytical results obtained from the spin model. In the superfluid regime
quantum fluctuations strongly modify the phase transition with respect to the
well established mean-field three dimensional classical bifurcation.",1403.4185v2
2014-03-21,Interface boundary conditions for dynamic magnetization and spin wave dynamics in a ferromagnetic layer with the interface Dzyaloshinskii-Moriya interaction,"In this work we derive the interface exchange boundary conditions for the
classical linear dynamics of magnetization in ferromagnetic layers with the
interface Dzyaloshinskii-Moriya interaction (IDMI). We show that IDMI leads to
pinning of dynamic magnetization at the interface. An unusual peculiarity of
the IDMI-based pinning is that its scales as the spin-wave wave number. We
incorporate these boundary conditions into an existing numerical model for the
dynamics of the Damon-Eshbach spin wave in ferromagnetic films. IDMI affects
the dispersion and the frequency non-reciprocity of the traveling Damon-Eshbach
spin wave. For a broad range of film thicknesses L and wave numbers the results
of the numerical simulations of the spin wave dispersion are in a good
agreement with a simple analytical expression which shows that the contribution
of IDMI to the dispersion scales as 1/L, similarly to the effect of other types
of interfacial anisotropy. Suggestions to experimentalists how to detect the
presence of IDMI in a spin wave experiment are given.",1403.5385v4
2014-03-21,Quantum Monte Carlo study of one-dimensional transition metal organometallic cluster systems and their suitability as spin filters,"We present calculations of electronic and magnetic structures of
vanadium-benzene multidecker clusters V$_{n}$Bz$_{n+1}$ ($n$ = 1 - 3) using
advanced quantum Monte Carlo methods. These and related systems have been
identified as prospective spin filters in spintronic applications, assuming
that their ground states are half-metallic ferromagnets. Although we find that
magnetic properties of these multideckers are consistent with ferromagnetic
coupling, their electronic structures do not appear to be half-metallic as
previously assumed. In fact, they are ferromagnetic insulators with large and
broadly similar $\uparrow$-/$\downarrow$-spin gaps. This makes the potential of
these and related materials as spin filtering devices very limited, unless they
are further modified or functionalized.",1403.5411v1
2014-03-25,Critical temperature of site-diluted spin-1/2 systems with long-range ferromagnetic interactions,"In the paper the Pair Approximation (PA) method for studies of the
site-diluted spin-1/2 systems of arbitrary dimensionality with the long-range
ferromagnetic interactions is adopted. The method allows to take into account
arbitrary anisotropy of the interactions in the spin space, so it is not
limited to purely Ising couplings. Within this approach, the Gibbs free energy
is obtained, which allows to derive all the further interesting thermodynamic
properties. In particular, we obtain an equation for the critical temperature
of the second-order phase transitions for the model in question. In the study
we focus our attention on the systems with ferromagnetic interactions decaying
with the distance according to the power law $J(r)\propto r^{-n}$. We discuss
the dependence of the critical temperature on the concentration of magnetic
component and the index $n$ for selected one-, two- and three-dimensional
lattices.We confirm the absence of the critical concentration for a diluted
magnet with infinite interaction range. In the regime of the low concentrations
of magnetic component, we find a non-linear increase of the critical
temperature with the concentration in the form of $T_{c}\propto p^{n/d}$,
depending on the system dimensionality $d$ and the index $n$, whereas $n > d$.",1403.6283v1
2014-03-26,Parity violation in ferromagnet-superconductor heterostructures with strong spin-orbit coupling,"We study spectroscopic properties of ferromagnetic-superconductor
heterostructures with strong spin-orbit coupling of the Rashba type and in the
presence of exchange fields. The superconducting layer (film) experiences both
an intrinsic spin-orbit field and an exchange field due to the proximity to
ferromagnetic layers (films). We analyse the temperature dependence of the
order parameter for superconductivity at various values of exchange field and
spin-orbit coupling, and describe momentum-dependent properties that exhibit
parity violation. Furthermore, we show that parity violation can be probed in
tunneling experiments of the single-particle density of states and in
photoemission experiments of the momentum distribution.",1403.6858v1
2016-11-04,Quantum critical scaling in the disordered itinerant ferromagnet UCo$_{1-x}$Fe$_x$Ge,"Belitz-Kirkpatrick-Vojta (BKV) theory shows in excellent agreement with
experiment that ferromagnetic quantum phase transitions (QPTs) in clean metals
are generally first-order due to the coupling of the magnetization to
electronic soft modes, in contrast to the classical analogue that is an
archetypical second-order phase transition. For disordered metals BKV theory
predicts that the second order nature of the QPT is restored because the
electronic soft modes change their nature from ballistic to diffusive. Our
low-temperature magnetization study identifies the ferromagnetic QPT in the
disordered metal UCo$_{1-x}$Fe$_x$Ge as the first clear example that exhibits
the associated critical exponents predicted by BKV theory.",1611.01539v2
2016-07-17,Thick ferromagnetic films and their anisotropies as described by second order perturbed Heisenberg Hamiltonian,"Second and fourth order anisotropy dependence of energy of thick simple cubic
ferromagnetic films with 10000 layers is explained using Heisenberg Hamiltonian
with second order perturbation in this manuscript. The second and fourth order
anisotropy constants were assumed to be constants through out the film. When
the fourth order anisotropy is given by fourth order anisotropy of 6, the
sc(001) ferromagnetic thick films with 10000 layers can be easily oriented in
0.6 radians direction for the energy parameters given this report. Under the
influence of the second order anisotropy given by second order anisotropy of
6.3, the easy direction of sc(001) film with 10000 layers is given by 0.66
radians. Although the energy varies periodically in all cases, the maximum
energy considerably decreases with fourth order anisotropy constant. According
to 3-D plots, energy under influence of second order anisotropy is larger than
energy under influence of fourth order anisotropy.",1611.02228v1
2016-11-09,Possible Weyl fermions in the magnetic Kondo system CeSb,"Materials where the electronic bands have unusual topologies allow for the
realization of novel physics and have a wide range of potential applications.
When two electronic bands with linear dispersions intersect at a point, the
excitations could be described as Weyl fermions which are massless particles
with a particular chirality. Here we report evidence for the presence of Weyl
fermions in the ferromagnetic state of the low-carrier density, strongly
correlated Kondo lattice system CeSb, from electronic structure calculations
and angle-dependent magnetoresistance measurements. When the applied magnetic
field is parallel to the electric current, a pronounced negative
magnetoresistance is observed within the ferromagnetic state, which is
destroyed upon slightly rotating the field away. These results give evidence
for CeSb belonging to a new class of Kondo lattice materials with Weyl fermions
in the ferromagnetic state.",1611.02927v2
2016-11-10,Laser-induced ultrafast demagnetization time and spin moment in ferromagnets: First-principles calculation,"When a laser pulse excites a ferromagnet, its spin undergoes a dramatic
change. The initial demagnetization process is very fast. Experimentally, it is
found that the demagnetization time is related to the spin moment in the
sample. In this study, we employ the first-principles method to directly
simulate such a process. We use the fixed spin moment method to change the spin
moment in ferromagnetic nickel, and then we employ the Liouville equation to
couple the laser pulse to the system. We find that in general the dependence of
demagnetization time on the spin moment is nonlinear: It decreases with the
spin moment up to a point, after which an increase with the spin moment is
observed, followed by a second decrease. To understand this, we employ an
extended Heisenberg model, which includes both the exchange interaction and
spin-orbit coupling. The model directly links the demagnetization rate to the
spin moment itself and demonstrates analytically that the spin relaxes more
slowly with a small spin moment. A future experimental test of our predictions
is needed.",1611.03154v1
2016-11-21,Coherence and stiffness of spin waves in diluted ferromagnets,"We present results of a numerical analysis of magnon spectra in supercells
simulating two-dimensional and bulk random diluted ferromagnets with
long-ranged pair exchange interactions. We show that low-energy spectral
regions for these strongly disordered systems contain a coherent component
leading to interference phenomena manifested by a pronounced sensitivity of the
lowest excitation energies to the adopted boundary conditions. The dependence
of configuration averages of these excitation energies on the supercell size
can be used for an efficient determination of the spin-wave stiffness D. The
developed formalism is applied to the ferromagnetic Mn-doped GaAs semiconductor
with optional incorporation of phosphorus; the obtained concentration trends of
D are found in reasonable agreement with recent experiments. Moreover, a
relation of the spin stiffness to the Curie temperature Tc has been studied for
Mn-doped GaAs and GaN semiconductors. It is found that the ratio Tc/D exhibits
qualitatively the same dependence on Mn concentration in both systems.",1611.06691v1
2016-11-21,Effect of surface hybridization on RKKY coupling in ferromagnet/topological insulator/ferromagnet trilayer system,"We theoretically investigate the RKKY exchange coupling between two
ferromagnets (FM) separated by a thin topological insulator film (TI). We find
an unusual dependence of the RKKY exchange coupling on the TI thickness
($t_{TI}$). First, when $t_{TI}$ decreases, the coupling amplitude increases at
first and reaches its maximum value at some critical thickness, below which the
amplitude turns to diminish. This trend is attributed to the hybridization
between surfaces of the TI film, which opens a gap below critical thickness and
thus turns the surfaces into insulating state from semi-metal state. In
insulating phase, diamagnetism induced by the gap-opening compensates
paramagnetism of Dirac state, resulting in a diminishing magnetic
susceptibility and RKKY coupling. For typical parameters, the critical
thickness in Bi2Se3 thin film is estimated to be in the range of 3-5 nm.",1611.06710v2
2017-01-23,Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures,"The large spin orbit coupling in topological insulators results in helical
spin-textured Dirac surface states that are attractive for topological
spintronics. These states generate an efficient spin-orbit torque on proximal
magnetic moments at room temperature. However, memory or logic spin devices
based upon such switching require a non-optimal three terminal geometry, with
two terminals for the writing current and one for reading the state of the
device. An alternative two terminal device geometry is now possible by
exploiting the recent discovery of a unidirectional spin Hall magnetoresistance
in heavy metal/ferromagnet bilayers and (at low temperature) in magnetically
doped topological insulator heterostructures. We report the observation of
unidirectional spin Hall magnetoresistance in a technologically relevant device
geometry that combines a topological insulator with a conventional
ferromagnetic metal. Our devices show a figure-of-merit (magnetoresistance per
current density per total resistance) that is comparable to the highest
reported values in all-metal Ta/Co bilayers.",1701.06505v1
2017-01-24,Pumping of magnons in a Dzyaloshinskii-Moriya ferromagnet,"We formulate a microscopic linear response theory of nonequilibrium magnonic
torques and magnon pumping applicable to multiple-magnonic-band uniform
ferromagnets with Dzyaloshinskii-Moriya interactions. From the linear response
theory, we identify the extrinsic and intrinsic contributions where the latter
is expressed via the Berry curvature of magnonic bands. We observe that in the
presence of a time-dependent magnetization Dzyaloshinskii-Moriya interactions
can act as fictitious electric fields acting on magnons. We study various
current responses to this fictitious field and analyze the role of Berry
curvature. After identifying the magnon-mediated contribution to the
equilibrium Dzyaloshinskii-Moriya interaction, we also establish the Onsager
reciprocity between the magnon-mediated torques and heat pumping. We apply our
theory to the magnonic heat pumping and torque responses in honeycomb and
kagome lattice ferromagnets.",1701.06990v3
2017-01-28,Novel Majorana mode and magnetoresistance in ferromagnetic superconducting topological insulator,"Among the potential applications of topological insulators, we investigate
theoretically the effect of coexistence of proximity-induced ferromagnetism and
superconductivity on the surface states of 3-dimensional topological insulator,
where the superconducting electron-hole excitations can be significantly
affected by the magnetization of ferromagnetic order. We find that, Majorana
mode energy, as a verified feature of TI F/S structure, along the interface
sensitively depends on the magnitude of magnetization $m_{zfs}$ in FS region,
while its slope in perpendicular incidence presents steep and no change. Since
the superconducting gap is renormalized by a factor $\eta(m_{zfs})$, hence
Andreev reflection is more or less suppressed, and, in particular, resulting
subgap tunneling conductance is more sensitive to the magnitude of
magnetizations in FS and F regions. Furthermore, an interesting scenario
happens at the antiparallel configuration of magnetizations $m_{zf}$ and
$m_{zfs}$ resulting in magnetoresistance in N/F/FS junction, which can be
controlled and decreased by tuning the magnetization magnitude in FS region.",1701.08275v1
2017-04-03,Itinerant ferromagnetism of two-dimensional repulsive fermions with Rabi coupling,"We study a two-dimensional fermionic cloud of repulsive alkali-metal atoms
characterized by two hyperfine states which are Rabi coupled. Within a
variational Hartree-Fock scheme, we calculate analytically the ground-state
energy of the system. Then we determine the conditions under which there is a
quantum phase transition with spontaneous symmetry breaking from a
spin-balanced configuration to a spin-polarized one, an effect known as
itinerant ferromagnetism. Interestingly, we find that the transition appears
when the interaction energy per particle exceedes both the kinetic energy per
particle and the Rabi coupling energy. The itinerant ferromagnetism of the
polarized phase is analyzed, obtaining the population imbalance as a function
of interaction strength, Rabi coupling, and number density. Finally, the
inclusion of a external harmonic confinement is investigated by adopting the
local density approximation. We predict that a single atomic cloud can display
population imbalance near the center of the trap and a fully balanced
configuration at the periphery.",1704.00483v1
2017-04-12,Cycloidally modulated magnetic order stabilized by thermal fluctuations in the Néel-type skyrmion host GaV$_4$S$_8$,"We report small-angle neutron scattering studies of the lacunar spinel
GaV$_4$S$_8$, which reveal the long-wavelength magnetic states to be
cycloidally modulated. This provides direct support for the formation of
N\'eel-type skyrmions recently claimed to exist in this compound. In striking
contrast with all other bulk skyrmion host materials, upon cooling the
modulated magnetic states transform into a ferromagnetic state. These results
indicate all of the modulated states in GaV$_4$S$_8$, including the skyrmion
state, gain their stability from thermal fluctuations, while at lower
temperature the ferromagnetic state emerges in accord with the strong easy-axis
magnetic anisotropy. In the vicinity of the transition between the
ferromagnetic and modulated states, both a phase coexistence and a soliton-like
state are also evidenced by our study.",1704.03621v1
2017-04-22,Spin Density wave instability in a ferromagnet,"Ferromagnetic (FM) and incommensurate spin-density wave (ISDW) states are an
unusual set of competing magnetic orders that are seldom observed in the same
material without application of a polarizing magnetic field. We report, for the
first time, the discovery of an ISDW state that is derived from a FM ground
state through a Fermi surface (FS) instability in Fe$_3$Ga$_4$. This was
achieved by combining neutron scattering experiments with first principles
simulations. Neutron diffraction demonstrates that Fe$_3$Ga$_4$ is in an ISDW
state at intermediate temperatures and that there is a conspicuous re-emergence
of ferromagnetism above 360 K. First principles calculations show that the ISDW
ordering wavevector is in excellent agreement with a prominent nesting
condition in the spin-majority FS demonstrating the discovery of a novel
instability for FM metals; ISDW formation due to Fermi surface nesting in a
spin-polarized Fermi surface.",1704.06727v2
2017-04-25,Unified description of dynamics of a repulsive two-component Fermi gas,"We study a binary spin-mixture of a zero-temperature repulsively interacting
$^6$Li atoms using both the atomic-orbital and the density functional
approaches. The gas is initially prepared in a configuration of two magnetic
domains and we determine the frequency of the spin-dipole oscillations which
are emerging after the repulsive barrier, initially separating the domains, is
removed. We find, in agreement with recent experiment (G. Valtolina et al.,
arXiv:1605.07850 (2016)), the occurrence of a ferromagnetic instability in an
atomic gas while the interaction strength between different spin states is
increased, after which the system becomes ferromagnetic. The ferromagnetic
instability is preceded by the softening of the spin-dipole mode.",1704.07707v2
2017-04-27,Edge-controlled half-metallic ferromagnetism and direct gap in ZrS2 nanoribbons,"The electronic and magnetic properties of ZrS2 nanoribbons (NRs) are
investigated based on the first-principles calculations. It is found that the
ZrS2 NRs with armchair edges are all indirect-band-gap semiconductors without
magnetism and the band-gap exhibits odd-even oscillation behavior with the
increase of the ribbon width. For the NRs with zigzag edges, those with both
edges S-terminated are nonmagnetic direct-band-gap semiconductors and the gap
decreases monotonically as a function of the ribbon width. However, the NRs
with one edge S-terminated and the other edge Zr-terminated are ferromagnetic
half-metal, while those with both edges Zr-terminated tend to be ferromagnetic
half-metal when the width $N\geq9$. The magnetism of both systems mainly
originates from the unsaturated edge Zr atoms. Depending on the different edge
configurations and ribbon widths, the ZrS2 NRs exhibit versatile electronic and
magnetic properties, making them promising candidates for the applications of
electronics and spintronics.",1704.08459v1
2018-05-07,Mixed topological semimetals driven by orbital complexity in two-dimensional ferromagnets,"The concepts of Weyl fermions and topological semimetals emerging in
three-dimensional momentum space are extensively explored owing to the vast
variety of exotic properties that they give rise to. On the other hand, very
little is known about semimetallic states emerging in two-dimensional magnetic
materials, which present the foundation for both present and future information
technology. Here, we demonstrate that including the magnetization direction
into the topological analysis allows for a natural classification of
topological semimetallic states that manifest in two-dimensional ferromagnets
as a result of the interplay between spin-orbit and exchange interactions. We
explore the emergence and stability of such mixed topological semimetals in
realistic materials, and point out the perspectives of mixed topological states
for current-induced orbital magnetism and current-induced domain wall motion.
Our findings pave the way to understanding, engineering and utilizing
topological semimetallic states in two-dimensional spin-orbit ferromagnets.",1805.02549v3
2018-05-08,Effects of Lifshitz transitions in ferromagnetic superconductors: the case of URhGe,"In ferromagnetic superconductors, like URhGe, superconductivity co-exists
with magnetism near zero field, but then re-appears again in a finite field
range, where the system also displays mass enhancement in the normal state. We
present theoretical understanding of this non-monotonic behavior. We explore
the multi-band nature of URhGe and associate re-entrant superconductivity and
mass enhancement with the finite field Lifshitz transition in one of the bands.
We found good agreement between our theory and a number of experimental results
for URhGe, such as weakly first order reentrant transition, the dependence of
superconducting $T_c$ on a magnetic field, and the field dependence of the
effective mass, the specific heat and the resistivity in the normal state. Our
theory can be applied to other ferromagnetic multi-band superconductors.",1805.02949v1
2018-05-22,Spin-orbit torque in completely compensated synthetic antiferromagnet,"Synthetic antiferromagnets (SAF) have been proposed to replace ferromagnets
in magnetic memory devices to reduce the stray field, increase the storage
density and improve the thermal stability. Here we investigate the spin-orbit
torque in a perpendicularly magnetized Pt/[Co/Pd]/Ru/[Co/Pd] SAF structure,
which exhibits completely compensated magnetization and an exchange coupling
field up to 2100 Oe. The magnetizations of two Co/Pd layers can be switched
between two antiparallel states simultaneously by spin-orbit torque. The
magnetization switching can be read out due to much stronger spin-orbit
coupling at bottom Pt/[Co/Pd] interface compared to its upper counterpart
without Pt. Both experimental and theoretical analyses unravel that the torque
efficiency of antiferromagnetic coupled stacks is significantly higher than the
ferromagnetic counterpart, making the critical switching current of SAF
comparable to the conventional single ferromagnet. Besides adding an important
dimension to spin-orbit torque, the efficient switching of completely
compensated SAF might advance magnetic memory devices with high density, high
speed and low power consumption.",1805.08486v2
2018-05-23,Special temperatures in frustrated ferromagnets,"The description and detection of unconventional magnetic states such as spin
liquids is a recurring topic in condensed matter physics. While much of the
efforts have traditionally been directed at geometrically frustrated
antiferromagnets, recent studies reveal that systems featuring competing
antiferromagnetic and ferromagnetic interactions are also promising candidate
materials. We find that this competition leads to the notion of special
temperatures, analogous to those of gases, at which the competing interactions
balance, and the system is quasi-ideal. Although induced by weak perturbing
interactions, these special temperatures are surprisingly high and constitute
an accessible experimental diagnostic of eventual order or spin liquid
properties. The well characterised Hamiltonian and extended low-temperature
susceptibility measurement of the canonical frustrated ferromagnet
Dy$_2$Ti$_2$O$_7$ enables us to formulate both a phenomenological and
microscopic theory of special temperatures for magnets. Other members of this
new class of magnets include kapellasite Cu$_3$Zn(OH)$_6$Cl$_2$ and the spinel
GeCo$_2$O$_4$.",1805.09332v1
2018-05-31,Second-harmonic current-phase relation in Josephson junctions with ferromagnetic barriers,"We report the observation of a current-phase relation dominated by the second
Josephson harmonic in superconductor-ferromagnet-superconductor junctions. The
exotic current-phase relation is realized in the vicinity of a
temperature-controlled 0-to-$\pi$ junction transition, at which the first
Josephson harmonic vanishes. Direct current-phase relation measurements, as
well as Josephson interferometry, non-vanishing supercurrent and half-integer
Shapiro steps at the 0-$\pi$ transition self-consistently point to an intrinsic
second harmonic term, making it possible to rule out common alternative origins
of half-periodic behavior. While surprising for diffusive multimode junctions,
the large second harmonic is in agreement with theory predictions for thin
ferromagnetic interlayers.",1805.12546v2
2008-07-11,"Structural Disorder, Octahedral Coordination, and 2-Dimensional Ferromagnetism in Anhydrous Alums","The crystal structures of the triangular lattice, layered anhydrous alums
KCr(SO4)2, RbCr(SO4)2 and KAl(SO4)2 are characterized by X-ray and neutron
powder diffraction at temperatures between 1.4 and 773 K. The compounds all
crystallize in the space group P-3, with octahedral coordination of the
trivalent cations. In all cases, small amounts of disorder in the stacking of
the triangular layers of corner sharing MO6 octahedra and SO4 tetrahedra is
seen, with the MO6-SO4 network rotated in opposite directions between layers.
The electron diffraction study of KCr(SO4)2 supports this model, which on
average can be taken to imply trigonal prismatic coordination for the M3+ ions;
as was previously reported for the prototype anhydrous alum KAl(SO4)2. The
temperature dependent magnetic susceptibilities for ACr(SO4)2 (A = K,Rb,Cs)
indicate the presence of predominantly ferromagnetic interactions. Low
temperature powder neutron diffraction reveals that the magnetic ordering is
ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3
K.",0807.1895v1
2008-07-15,Physical realization and possible identification of topological excitations in quantum Heisenberg anti-ferromagnet on a two dimensional lattice,"Physical spin configurations corresponding to topological excitations,
expected to be present in the XY limit of a quantum spin 1/2 Heisenberg
anti-ferromagnet, are probed on a two dimensional square lattice . Quantum
vortices (anti-vortices) are constructed in terms of coherent staggered spin
field components, as limiting case of meronic (anti-meronic) configurations .
The crucial role of the associated Wess-Zumino-like (WZ-like) term is
highlighted in our procedure . The time evolution equation of coherent spin
fields used in this analysis is obtained by applying variational principle on
the quantum Euclidean action corresponding to the Heisenberg anti-ferromagnet
on lattice . It is shown that the WZ-like term can distinguish between vortices
and anti-vortices only in a charge sector with odd topological charges. Our
formalism is distinctly different from the conventional approach for the
construction of quantum vortices (anti-vortices) .",0807.2359v2
2008-07-23,Metal-insulator transition by isovalent anion substitution in Ga1-xMnxAs: Implications to ferromagnetism,"We have investigated the effect of partial isovalent anion substitution in
Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only
2.4% of As by P induces a metal-insulator transition at a constant Mn doping of
x=0.046 while the replacement of 0.4 % As with N results in the crossover from
metal to insulator for x=0.037. This remarkable behavior is consistent with a
scenario in which holes located within an impurity band are scattered by alloy
disorder in the anion sublattice. The shorter mean free path of holes, which
mediate ferromagnetism, reduces the Curie temperature TC from 113 K to 60 K
(100 K to 65 K) upon the introduction of 3.1 % P (1% N) into the As sublattice.",0807.3722v1
2008-07-28,Critical Scaling of the Magnetization and Magnetostriction in the Weak Itinerant Ferromagnet UIr,"The weak itinerant ferromagnet UIr is studied by magnetization and
magnetostriction measurements. Critical behavior, which surprisingly extends up
to several Tesla, is observed at the Curie temperature $T_C\simeq45$ K and is
analyzed using Arrott and Maxwell relations. Critical exponents are found that
do not match with any of the well-known universality classes. The
low-temperature magnetization $M_s\simeq0.5$ $\mu_B \cong const.$ below 3 T
rises towards higher fields and converges asymptotically around 50 T with the
magnetization at $T_C$. From the magnetostriction and magnetization data, we
extract the uniaxial pressure dependences of $T_C$, using a new method
presented here, and of $M_s$. These results should serve as a basis for
understanding spin fluctuations in anisotropic itinerant ferromagnets.",0807.4411v1
2009-12-01,Observation of spin-triplet superconductivity in Co-based Josephson Junctions,"We have measured a long-range supercurrent in Josephson junctions containing
Co (a strong ferromagnetic material) when we insert thin layers of either PdNi
or CuNi weakly-ferromagnetic alloys between the Co and the two superconducting
Nb electrodes. The critical current in such junctions hardly decays for Co
thicknesses in the range of 12-28 nm, whereas it decays very steeply in similar
junctions without the alloy layers. The long-range supercurrent is controllable
by the thickness of the alloy layer, reaching a maximum for a thickness of a
few nm. These experimental observations provide strong evidence for induced
spin-triplet pair correlations, which have been predicted to occur in
superconducting/ferromagnetic hybrid systems in the presence of certain types
of magnetic inhomogeneity.",0912.0205v1
2009-12-06,The Correlation Functions of the XXZ Heisenberg Chain for Zero or Infinite Anisotropy and Random Walks of Vicious Walkers,"The XXZ Heisenberg chain is considered for two specific limits of the
anisotropy parameter: $\Dl\to 0$ and $\Dl\to -\infty$. The corresponding wave
functions are expressed by means of the symmetric Schur functions. Certain
expectation values and thermal correlation functions of the ferromagnetic
string operators are calculated over the base of N-particle Bethe states. The
thermal correlator of the ferromagnetic string is expressed through the
generating function of the lattice paths of random walks of vicious walkers. A
relationship between the expectation values obtained and the generating
functions of strict plane partitions in a box is discussed. Asymptotic estimate
of the thermal correlator of the ferromagnetic string is obtained in the limit
of zero temperature. It is shown that its amplitude is related to the number of
plane partitions.",0912.1138v2
2009-12-08,Evidence of superconductivity on the border of quasi-2D ferromagnetism in Ca2RuO4 at high pressure,"The layered perovskite Ca2RuO4 is a spin-one Mott insulator at ambient
pressure and exhibits metallic ferromagnetism at least up to ~ 80 kbar with a
maximum Curie temperature of 28 K. Above ~ 90 kbar and up to 140 kbar, the
highest pressure reached, the resistivity and ac susceptibility show pronounced
downturns below ~ 0.4 K in applied magnetic fields of up to ~10 mT. This
indicates that our specimens of Ca2RuO4 are weakly superconducting on the
border of a quasi-2D ferromagnetic state.",0912.1513v1
2009-12-17,Surface magnetism in ZnO/Co3O4 mixtures,"We recently reported the observation of room temperature ferromagnetism in
mixtures of ZnO and Co3O4 despite the diamagnetic and antiferromagnetic
character of these oxides respectively. Here we present a detailed study on the
electronic structure of this material in order to account for this unexpected
ferromagnetism. Electrostatic interactions between both oxides lead to a
dispersion of Co3O4 particles over the surface of ZnO larger ones. As a
consequence, the reduction of Co+3 to Co2+ at the particle surface takes place
as evidenced by XAS measurements and optical spectrocopy. This reduction allows
to xplain the observed ferromagnetic signal within the well established
theories of magnetism.",0912.3458v1
2011-11-09,A dynamical phase transition in ferromagnetic granular materials,"We study, using simulations the dynamical properties of complex ferromagnetic
granular materials. The system of grains is modeled by a disordered
two-dimensional lattice in which the grains are embedded, while the magnitude
and direction of the easy axis are random. Using the monte-carlo method we
track the dynamics of the magnetic moments of the grains. We observe a
transition of the system from a macroscopic blocked (ferromagnetic) phase at
low temperature in which the grain's magnetic moment do not flip to the other
direction to an unblocked (superparamagnetic) phase at high temperature in
which the magnetic moment is free to rotate. Our results suggest that this
transition exhibits the characteristics of a second order phase transition such
as the appearance of a giant cluster of unblocked grains which is fractal at
the critical temperature, a peak in the size of the second largest cluster at
the same temperature and a power law distribution of cluster sizes near the
criticality.",1111.2130v1
2011-11-14,Callen-like method for the classical Heisenberg ferromagnet,"A study of the d-dimensional classical Heisenberg ferromagnetic model in the
presence of a magnetic field is performed within the two-time Green function's
framework in classical statistical physics. We extend the well known quantum
Callen method to derive analytically a new formula for magnetization. Although
this formula is valid for any dimensionality, we focus on one- and three-
dimensional models and compare the predictions with those arising from a
different expression suggested many years ago in the context of the classical
spectral density method. Both frameworks give results in good agreement with
the exact numerical transfer-matrix data for the one-dimensional case and with
the exact high-temperature-series results for the three-dimensional one. In
particular, for the ferromagnetic chain, the zero-field susceptibility results
are found to be consistent with the exact analytical ones obtained by M.E.
Fisher. However, the formula derived in the present paper provides more
accurate predictions in a wide range of temperatures of experimental and
numerical interest.",1111.3177v1
2011-11-14,Nambu-Goldstone dynamics and generalized coherent-state functional integrals,"The present paper gives a new method of attack on the Nambu-Goldstone
dynamics in spontaneously broken theories. Since the target space of the
Nambu-Goldstone fields is a group coset space, their effective quantum dynamics
can be naturally phrased in terms of generalized coherent-state functional
integrals. As an explicit example of this line of reasoning we construct a
low-energy effective Lagrangian for the Heisenberg ferromagnet in broken phase.
The leading field configuration in the WKB approximation leads to the
Landau-Lifshitz equation for quantum ferromagnet. The corresponding linearized
equations allow to identify the Nambu-Goldstone boson with ferromagnetic
magnon.",1111.3228v2
2011-11-21,Electron-phonon scattering dynamics in ferromagnets on ultrafast timescales: Influence of the phonon temperature,"The magnetization response of bulk ferromagnets after excitation by an
ultrashort optical pulse is calculated using a dynamical model of the
Elliott-Yafet type that includes the effects of the spin-orbit interaction in
the ab-initio ferromagnetic band structure, the electron-phonon interaction at
the level of Boltzmann scattering integrals, and dynamical changes in the
temperature of the phonon bath. Using realistic parameters for the ultrashort
optical pulse, the computed maximum magnetization quenching achievable with
electron-phonon scattering in a fixed band structure is much smaller than the
quenching observed in experiments. Heating of the phonon bath is found to not
appreciably change the magnetization dynamics on ultrashort timescales.",1111.4783v1
2011-11-21,Ab initio theory of galvanomagnetic phenomena in ferromagnetic metals and disordered alloys,"We present an ab initio theory of transport quantities of metallic
ferromagnets developed in the framework of the fully relativistic tight-binding
linear muffin-tin orbital method. The approach is based on the Kubo-Streda
formula for the conductivity tensor, on the coherent potential approximation
for random alloys, and on the concept of interatomic electron transport. The
developed formalism is applied to pure 3d transition metals (Fe, Co, Ni) and to
random Ni-based ferromagnetic alloys (Ni-Fe, Ni-Co, Ni-Mn). High values of the
anisotropic magnetoresistance (AMR), found for Ni-rich alloys, are explained by
a negligible disorder in the majority spin channel while a change of the sign
of the anomalous Hall effect (AHE) on alloying is interpreted as a band-filling
effect without a direct relation to the high AMR. The influence of disorder on
the AHE in concentrated alloys is investigated as well.",1111.4793v2
2011-11-23,Anomalous polarization-dependent transport in nanoscale double-barrier superconductor/ferromagnet/superconductor junctions,"We study the transport properties of nanoscale superconducting (S) devices in
which two superconducting electrodes are bridged by two parallel ferromagnetic
(F) wires, forming an SFFS junction with a separation between the two wires
less than the superconducting coherence length. This allows crossed Andreev
reflection to take place. We find that the resistance as a function of
temperature exhibits behavior reminiscent of the re-entrant effect and, at low
temperatures and excitation energies below the superconducting gap, the
resistance corresponding to antiparallel alignment of the magnetization of the
ferromagnetic wires is higher than that of parallel alignment, in contrast to
the behavior expected from crossed Andreev reflection. We present a model based
on spin-dependent interface scattering that explains this surprising result and
demonstrates the sensitivity of the junction transport properties to
interfacial parameters.",1111.5415v3
2011-11-28,Investigation of weak itinerant ferromagnetism and critical behavior of Y$_2$Ni$_7$,"The weak itinerant ferromagnetic behavior of Y$_2$Ni$_7$ is investigated
through magnetic, transport and calorimetric measurements. The low value of
saturation moment, large Rhodes-Wohlfarth ratio, large value of the linear term
in heat capacity and Fermi liquid like resistivity behavior with enhanced
electron-electron scattering contribution establish firmly the weak itinerant
ferromagetic nature of the sample. The critical exponents associated with the
paramagnetic to ferromagnetic transition are also investigated from
magnetization isotherms using modified Arrott plot, Kouvel-Fisher plot and
critical isotherm technique. The more accurate Kouvel-Fisher plot provides the
critical exponents to be $\beta$ = 0.306, $\gamma$ = 1.401 and $\delta$ =
5.578. These values are markedly different from the mean field values and
correspond closely to the two dimensional Ising spin system with long range
spin spin interaction.",1111.6343v1
2012-01-16,^31P NMR investigations on the ferromagnetic quantum critical system YbNi_4P_2,"We studied the new heavy-fermion system YbNi$_{4}$P$_{2}$, which presents
strong ferromagnetic correlations, using the local $^{31}$P NMR probe over a
wide field (0.2-8.6 \textsf{T}) and temperature (1.8-200 K) range. $^{31}$P NMR
Knight shift provides the static spin susceptibility which tracks the bulk
susceptibility whereas the spin-lattice relaxation rate $^{31}(1/T_{1}$)
provide information about the fluctuations of the Yb 4f moment. The Korringa
law is valid over a wide range in temperature and field. The Korringa product
$^{31}(1/T_{1}TK^{2}$S$_{0}$) $\ll$ 1 gives evidence for the presence of strong
ferromagnetic correlations. Over two decades in temperature a $^{31}(1/T_{1}T)
\sim T^{-3/4}$ behaviour was found.",1201.3260v1
2012-01-18,Quantum order-by-disorder driven phase reconstruction in the vicinity of ferromagnetic quantum critical points,"The formation of new phases close to itinerant electron quantum critical
points has been observed experimentally in many compounds. We present a unified
analytical model that explains the emergence of new types of order around
itinerant ferromagnetic quantum critical points. The central idea of our
analysis is that certain Fermi-surface deformations associated with the onset
of the competing order enhance the phase-space available for low-energy quantum
fluctuations and so self-consistently lower the free energy. We demonstrate
that this quantum order-by-disorder mechanism leads to instabilities towards
the formation of spiral and d-wave spin nematic phases close to itinerant
ferromagnetic quantum critical points in three spatial dimensions.",1201.3916v2
2012-01-19,Spin and valley quantum Hall ferromagnetism in graphene,"In a graphene Landau level (LL), strong Coulomb interactions and the fourfold
spin/valley degeneracy lead to an approximate SU(4) isospin symmetry. At
partial filling, exchange interactions can spontaneously break this symmetry,
manifesting as additional integer quantum Hall plateaus outside the normal
sequence. Here we report the observation of a large number of these quantum
Hall isospin ferromagnetic (QHIFM) states, which we classify according to their
real spin structure using temperature-dependent tilted field magnetotransport.
The large measured activation gaps confirm the Coulomb origin of the broken
symmetry states, but the order is strongly dependent on LL index. In the high
energy LLs, the Zeeman effect is the dominant aligning field, leading to real
spin ferromagnets with Skyrmionic excitations at half filling, whereas in the
`relativistic' zero energy LL, lattice scale anisotropies drive the system to a
spin unpolarized state, likely a charge- or spin-density wave.",1201.4167v1
2012-04-02,On the influence of nanometer-thin antiferromagnetic surface layer on ferromagnetic CrO$_2$,"We present magnetic stray field measurements performed on a single
micro-crystal of the half metallic ferromagnet CrO$_2$, covered by a naturally
grown 2\,-\,5\,nm surface layer of antiferromagnetic (AFM) Cr$_2$O$_3$. The
temperature variation of the stray field of the micro-crystal measured by
micro-Hall magnetometry shows an anomalous increase below $\sim$\,60\,K. We
find clear evidence that this behavior is due to the influence of the AFM
surface layer, which could not be isolated in the corresponding bulk
magnetization data measured using SQUID magnetometry. The distribution of
pinning potentials, analyzed from Barkhausen jumps, exhibits a similar
temperature dependence. Overall, the results indicate that the surface layer
plays a role in defining the potential landscape seen by the domain
configuration in the ferromagnetic grain.",1204.0531v1
2012-04-04,Theory of ferromagnetic unconventional superconductors with spin-triplet electron pairing,"A general phenomenological theory is presented for the phase behavior of
ferromagnetic superconductors with spin-triplet electron Cooper pairing. The
theory describes in details the temperature-pressure phase diagrams of real
inter-metallic compounds exhibiting the remarkable phenomenon of coexistence of
spontaneous magnetic moment of the itinerant electrons and spin-triplet
superconductivity. The quantum phase transitions which may occur in these
systems are also described. The theory allows for a classification of these
itinerant ferromagnetic superconductors in two types: type I and type II. The
classification is based on quantitative criteria.The comparison of theory and
experiment is performed and outstanding problems are discussed.",1204.1007v2
2012-04-04,Carrier-controlled ferromagnetism in SrTiO3,"Magnetotransport and superconducting properties are investigated for
uniformly La-doped SrTiO3 films and GdTiO3/SrTiO3 heterostructures,
respectively. GdTiO3/SrTiO3 interfaces exhibit a high-density two-dimensional
electron gas on the SrTiO3-side of the interface, while for the SrTiO3 films
carriers are provided by the dopant atoms. Both types of samples exhibit
ferromagnetism at low temperatures, as evidenced by a hysteresis in the
magnetoresistance. For the uniformly doped SrTiO3 films, the Curie temperature
is found to increase with doping and to coexist with superconductivity for
carrier concentrations on the high-density side of the superconducting dome.
The Curie temperature of the GdTiO3/SrTiO3 heterostructures scales with the
thickness of the SrTiO3 quantum well. The results are used to construct a
stability diagram for the ferromagnetic and superconducting phases of SrTiO3.",1204.1081v2
2012-04-13,"Comment on: ""Revealing common artifacts due to ferromagnetic inclusions in highly oriented pyrolytic graphite"", by M. Sepioni, R.R. Nair, I.-Ling Tsai, A.K. Geim and I.V. Grigorieva, EPL 97 (2012) 47001","This comment addresses several issues in the paper by Sepioni et al., where
it is stated that the ferromagnetism in pristine highly oriented pyrolytic
graphite (HOPG) reported by several groups in the previous years is most likely
due to impurity contamination. In this comment, clear arguments are given why
this statement is not justified. Furthermore, it is pointed out, that there are
already measurements using element-sensitive microscopic techniques, e.g. X-ray
Magnetic Circular Dichroism (XMCD) that directly proved the intrinsic origin of
the ferromagnetism in graphite, also in pristine HOPG.",1204.2992v1
2012-04-22,Spin Hall effect versus Rashba torque: a Diffusive Approach,"Current-driven magnetization dynamics of single ferromagnets in heavy
metal/ferromagnet bilayers has been recently realized. In this work, spin
torque induced by so-called Rashba spin-orbit coupling and spin Hall effect are
considered within a diffusive model. The dependence of the resulting torque as
a function of the thicknesses of the ferromagnet and heavy metal is analyzed.
We show that (i) both torques are on the form ${\bf T}=T_{||}{\bf m}\times{\bf
y}+T_\bot{\bf m}\times({\bf y}\times{\bf m})$, (ii) the ratio $T_{||}/T_\bot$
strongly depends on the thickness of the layers and (iii) the thickness
dependence of the spin torque provides an indication of the origin of the
(Rashba- or spin Hall effect-induced) spin torque .",1204.4869v1
2012-04-22,Anomalous ferromagnetism and non-Fermi-liquid behavior in the Kondo lattice CeRuSi2,"The structural, electronic and magnetic properties of the Kondo-lattice
system CeRuSi2 are experimentally investigated and analyzed in the series of
other ternary cerium compounds. This system is shown to be an excellent model
system demonstrating coexistence of the Kondo effect and anomalous
ferromagnetism with a small magnetic moment which is confirmed by magnetic and
\mu SR measurements. Data on specific heat, resistivity and Seebeck coefficient
are presented. Being deduced from the resistivity and specific heat data, the
non-Fermi-liquid behavior is observed at low temperatures, which is unusual for
a ferromagnetic Kondo system. A comparison with other magnetic Kondo lattices
is performed.",1204.4903v3
2012-04-25,Interface Metallic States between a Topological Insulator and a Ferromagnetic Insulator,"We study electronic structures at an interface between a topological
insulator and a ferromagnetic insulator by using three-dimensional two-band
model. In usual ferromagnetic insulators, the exchange potential is much larger
than the bulk gap size in the topological insulators and electronic structures
are asymmetric with respect to the fermi level. In such situation, we show that
unusual metallic states appear under the magnetic moment pointing the
perpendicular direction to the junction plane, which cannot be described by the
two-dimensional effective model around the Dirac point.
  When the magnetic moment is in the parallel direction to the plane, the
number of Dirac cones becomes even integers. The conclusions obtained in
analytical calculations are confirmed by numerical simulations on tight-binding
lattice.",1204.5562v1
2012-04-27,Magnetically-driven electronic phase separation in the semimetallic ferromagnet EuB$_6$,"From measurements of fluctuation spectroscopy and weak nonlinear transport on
the semimetallic ferromagnet EuB$_6$ we find direct evidence for
magnetically-driven electronic phase separation consistent with the picture of
percolation of magnetic polarons (MP), which form highly conducting
magnetically-ordered clusters in a paramagnetic and 'poorly conducting'
background. These different parts of the conducting network are probed
separately by the noise spectroscopy/nonlinear transport and the conventional
linear resistivity. We suggest a comprehensive and 'universal' scenario for the
MP percolation, which occurs at a critical magnetization either induced by
ferromagnetic order at zero field or externally applied magnetic fields in the
paramagentic region.",1204.6222v1
2013-09-12,Cosmic Neutrino Background as a Ferromagnet,"If cosmic background neutrinos interact very weakly with each other, through
spin-spin interactions, then they may have experienced a phase transition,
leading to a ferromagnetic ordering. The small magnetic field resulting from
ferromagnetic ordering -- if present before galaxy formation -- could act as a
primordial seed of the magnetic fields observed in several galaxies. Our
findings suggest that the magnetization could occur in the right epoch, if the
exchange boson of neutrino-neutrino interaction is a massless boson beyond the
Standard Model, with a coupling constant of $2.2\times 10^{-13}
\left(\frac{m_\nu}{10^{-4}\,\rm{eV}}\right)^2<g<2.3\times 10^{-7}$. The
estimation of the magnetic seed is $2.3 \times 10^{-27}\,\rm{G}\lesssim B_{\rm
CNB}\lesssim 6.8\times 10^{-10}G$.",1309.3244v2
2013-09-25,Ab-initio calculation of the effective on-site Coulomb interaction parameters for half-metallic magnets,"Correlation effects play an important role in the electronic structure of
half-metallic (HM) magnets. In particular, they give rise to non-quasiparticle
states above (or below) the Fermi energy at finite temperatures that reduce the
spin polarization and, as a consequence, the efficiency of spintronics devices.
Employing the constrained random-phase approximation (cRPA) within the
full-potential linearized augmented-plane-wave (FLAPW) method using maximally
localized Wannier functions, we calculate the strength of the effective on-site
Coulomb interaction (Hubbard $U$ and Hund exchange $J$) between localized
electrons in different classes of HM magnets considering: (i)
\emph{sp}-electron ferromagnets in rock-salt structure, (ii) zincblende
3\emph{d} binary ferromagnets, as well as (iii) ferromagnetic and ferrimagnetic
semi- and full-Heusler compounds.",1309.6657v1
2014-05-06,Magnetic and transport signatures of Rashba spin-orbit coupling on the ferromagnetic Kondo lattice model in two dimensions,"Motivated by emergent phenomena at oxide surfaces and interfaces,
particularly those involving transition metal oxides with perovskite crystal
structure such as LaTiO3/SrTiO3, we examine the ferromagnetic Kondo lattice
model (FKLM) in the presence of a Rashba spin-orbit coupling (RSOC). Using
numerical techniques, under the assumption that the electrons on localized
orbitals may be treated as classical continuum spins, we compute various
charge, spin and transport properties on square clusters at zero temperature.
We find that the main effect of the RSOC is the destruction of the
ferromagnetic state present in the FKLM at low electron fillings, with the
consequent suppression of conductivity. In addition, near half-filling the RSOC
leads to a departure of the antiferromagnetic state of the FKLM with a
consequent reduction to the intrinsic tendency to electronic phase separation.
The interplay between phase separation on one side, and magnetic and transport
properties on the other, is carefully analyzed as a function of the
RSOC/hopping ratio.",1405.1240v2
2014-05-12,Mapping the first order magnetic transition in Yb$_2$Ti$_2$O$_7$,"The very nature of the ground state of the pyrochlore compound
Yb$_2$Ti$_2$O$_7$ is much debated, as experimental results demonstrate evidence
for both a disordered or a long-range ordered ground state. Indeed, the
delicate balance of exchange interactions and anisotropy is believed to lead to
competing states, such as a Quantum Spin Liquid state or a ferromagnetic state
which may originate from an Anderson-Higgs transition. We present a detailed
magnetization study demonstrating a first order ferromagnetic transition at 245
mK and 150 mK in a powder and a single crystal sample respectively. Its
first-order character is preserved up to applied fields of $\sim$ 200 Oe. The
transition stabilizes a ferromagnetic component and involves slow dynamics in
the magnetization. Residual fluctuations are also evidenced, the presence of
which might explain some of the discrepancies between previously published data
for Yb$_2$Ti$_2$O$_7$.",1405.2704v1
2014-05-16,Damping of Confined Modes in a Ferromagnetic Thin Insulating Film: Angular Momentum Transfer Across a Nanoscale Field-defined Interface,"We observe a dependence of the damping of a confined mode of precessing
ferromagnetic magnetization on the size of the mode. The micron-scale mode is
created within an extended, unpatterned YIG film by means of the intense local
dipolar field of a micromagnetic tip. We find that damping of the confined mode
scales like the surface-to-volume ratio of the mode, indicating an interfacial
damping effect (similar to spin pumping) due to the transfer of angular
momentum from the confined mode to the spin sink of ferromagnetic material in
the surrounding film. Though unexpected for insulating systems, the measured
intralayer spin-mixing conductance $g_{\uparrow \downarrow} = 5.3 \times
10^{19} {\rm m}^{-2}$ demonstrates efficient intralayer angular momentum
transfer.",1405.4203v2
2014-05-19,"Josephson effect in normal and ferromagnetic topological insulator planar, step and edge junctions","We investigate Josephson junctions on the surface of a three-dimensional
topological insulator in planar, step, and edge geometries. The elliptical
nature of the Dirac cone representing the side surface states of the
topological insulator results in a scaling factor in the Josephson current in a
step junction as compared to the planar junction. In edge junctions, the
contribution of the Andreev bound states to the Josephson current vanishes due
to spin-momentum locking of the surface states. Furthermore, we consider a
junction with a ferromagnetic insulator between the superconducting regions. In
these ferromagnetic junctions, we find an anomalous finite Josephson current at
zero phase difference if the magnetization is pointing along the junction (and
perpendicular to the Josephson current). An out-of-plane magnetization with
respect to the central region of the junction opens up an exchange gap and
leads to a non-monotonic behavior of the critical Josephson current for
sufficiently large magnetization as the chemical potential increases.",1405.4695v1
2014-05-20,"Spin and orbital magnetic moments of Fe in the $n$-type ferromagnetic semiconductor (In,Fe)As","The electronic and magnetic properties of Fe atoms in the ferromagnetic
semiconductor (In,Fe)As codoped with Be have been studied by x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe
$L_{2,3}$ edge. The XAS and XMCD spectra showed simple spectral line shapes
similar to Fe metal, but the ratio of the orbital and spin magnetic moments
($M_\mathrm{orb}$/$M_\mathrm{spin}$) estimated using the XMCD sum rules was
significantly larger than that of Fe metal, indicating a significant orbital
moment of Fe $3d$ electrons in (In,Fe)As:Be. The positive value of
$M_\mathrm{orb}$/$M_\mathrm{spin}$ implies that the Fe $3d$ shell is more than
half-filled, which arises from the hybridization of the Fe$^{3+}$ ($d^5$) state
with the charge-transfer $d^6\underline{L}$ states, where $\underline{L}$ is a
ligand hole in the host valence band. The XMCD intensity as a function of
magnetic field indicated hysteretic behavior of the superparamagnetic-like
component due to discrete ferromagnetic domains.",1405.5130v1
2014-06-04,Magnetic hard-axis ordering near ferromagnetic quantum criticality,"We investigate the interplay of quantum fluctuations and magnetic
anisotropies in metallic ferromagnets. Our central result is that fluctuations
close to a quantum critical point can drive the moments to point along a
magnetic hard axis. As a proof of concept, we show this behavior explicitly for
a generic two-band model with local Coulomb and Hund's interactions, and a
spin-orbit-induced easy plane anisotropy. The phase diagram is calculated
within the fermionic quantum order-by-disorder approach, which is based on a
self-consistent free energy expansion around a magnetically ordered state with
unspecified orientation. Quantum fluctuations render the transition of the
easy-plane ferromagnet first-order below a tricritical point. At even lower
temperatures, directionally dependent transverse fluctuations dominate the
magnetic anisotropy and the moments flip to lie along the magnetic hard axis.
We discuss our findings in the context of recent experiments that show this
unusual ordering along the magnetic hard direction.",1406.1173v2
2014-06-09,"Properties of group-IV-based ferromagnetic semiconductor GeFe: Growth temperature dependence, lattice constant, location of Fe atoms, and their relevance to the magnetic properties","We report the growth temperature dependence of the properties of the
group-IV-based ferromagnetic semiconductor Ge1-xFex films (x = 6.5% and 10.5%),
including the lattice constant, Curie temperature (TC), and Fe-atom locations.
While TC strongly depends on the growth temperature, we find a universal
relationship between TC and the lattice constant, which does not depend on the
Fe content x. By using the channeling Rutherford backscattering and
particle-induced X-ray emission measurements, it is clarified that about 15% of
the Fe atoms exist in the tetrahedral interstitial sites in the Ge0.935Fe0.065
lattice and that the substitutional Fe concentration is not correlated with TC.
Considering these results, we suggest that the non-uniformity of the Fe
concentration plays an important role in determining the ferromagnetic
properties of GeFe.",1406.2202v1
2014-06-17,Frustration induced noncollinear magnetic order phase in one-dimensional Heisenberg chain with alternating antiferromagnetic and ferromagnetic next nearest neighbor interactions,"By using the coupled cluster method, the numerical exact diagonalization
method, and the numerical density matrix renormalization group method, we
investigated the properties of the one-dimensional Heisenberg chain with
alternating antiferromagnetic and ferromagnetic next nearest neighbor
interactions. In the classical limit, the ground state is in the collinear Neel
state if a<1/2, while for a>1/2, there is an noncollinear canted state. For the
quantum case, we found that, although the classical Neel state is absent, the
canted state exists if the frustration parameter a exceeds a critical point
ac1. The precise critical point ac1 can be determined by using the coupled
cluster method and the numerical exact diagonalization method separately. The
results of the coupled cluster method and the exact diagonalization method both
disclose that the type of phase transition occurring at ac1 changes from a
classical second-order transition to a quantum first-order transition due to
quantum fluctuation. Although there is another critical point ac2 in a finite
system at which the ground state evolves from the canted state to the collinear
Neel plus ferromagnetic state, that state is absent because ac2 tends to
infinity in the thermodynamic limit.",1406.4317v1
2014-06-17,Paramagnetic to ferromagnetic phase transition in lightly Fe-doped Cr$_2$B,"Cr$_2$B displays temperature independent paramagnetism. We induce
ferromagnetism by replacing less than $3\,\%$ of the Cr atoms by Fe. By the
lowest Fe doping level made, Curie-Weiss behavior is observed; $\Theta_{CW}$
changes from $-20\,$K for $0.5\,\%$ Fe-doped Cr$_2$B to positive values of
about 50 K by $5\,\%$ Fe doping. The ferromagnetic T$_C$ is 8 K for $2.5\,\%$
Fe doping and increases linearly to 46 K by $5\,\%$ doping; we infer that a
quantum phase transition occurs near the $2.0\,\%$ Fe level. Magnetic
fluctuations at the intermediate doping levels are reflected in the linear
resistance and an anomalous heat capacity at low temperatures. Imaging and
chemical analysis down to the atomic scale show that the Fe dopant is randomly
distributed.",1406.4527v1
2014-06-25,Magnetic structure of GdBiPt: A candidate antiferromagnetic topological insulator,"A topological insulator is a state of matter which does not break any
symmetry and is characterized by topological invariants, the integer
expectation values of non-local operators. Antiferromagnetism on the other hand
is a broken symmetry state in which the translation symmetry is reduced and
time reversal symmetry is broken. Can these two phenomena coexist in the same
material? A proposal by Mong {\it et al.}\cite{Mong2010} asserts that the
answer is yes. Moreover, it is theoretically possible that the onset of
antiferromagnetism enables the non-trivial topology since it may create
spin-orbit coupling effects which are absent in the non-magnetic phase. The
current work examines a real system, half-Heusler GdBiPt, as a candidate for
topological anti ferromagnetism. We find that the magnetic moments of the
gadolinium atoms form ferromagnetic sheets which are stacked
antiferromagnetically along the body diagonal. This magnetic structure may
induce spin orbit coupling on band electrons as they hop perpendicular to the
ferromagnetic sheets.",1406.6663v1
2015-12-04,Suppression of the ferromagnetic order in the Heusler alloy Ni50Mn35In15 by hydrostatic pressure,"We report the effect of hydrostatic pressure on the magnetic and structural
properties of the shape-memory Heusler alloy Ni50Mn35In15. Magnetization and
x-ray diffraction experiments were performed at hydrostatic pressures up to 5
GPa using diamond anvil cells. Pressure stabilizes the martensitic phase,
shifting the martensitic transition to higher temperatures and suppresses the
ferromagnetic austenitic phase. Above ~3 GPa, where the martensitic-transition
temperature approaches the Curie temperature in the austenite, the
magnetization shows no indication of ferromagnetic ordering anymore. We further
find an extremely large temperatureregion with a mixture of martensite and
austenite phases, which directly relates to the magnetic properties.",1512.01407v1
2015-12-17,Spatially resolved detection of complex ferromagnetic dynamics using optically detected NV spins,"We demonstrate optical detection of a broad spectrum of ferromagnetic
excitations using nitrogen-vacancy (NV) centers in an ensemble of nanodiamonds.
Our recently developed approach exploits a straightforward CW detection scheme
using readily available diamond detectors, making it easily implementable. The
NV center is a local detector, giving the technique spatial resolution, which
here is defined by our laser spot, but in principle can be extended far into
the nanoscale. Among the excitations we observe are propagating dipolar and
dipolar-exchange spinwaves, as well as dynamics associated with the
multi-domain state of the ferromagnet at low fields. These results offer an
approach, distinct from commonly used ODMR techniques, for spatially resolved
spectroscopic study of magnetization dynamics at the nanoscale.",1512.05418v2
2015-12-19,Large thermoelectric power and figure of merit in a ferromagnetic-quantum dot-superconducting device,"We investigate the thermoelectric properties of a quantum dot coupled to
ferromagnetic and superconducting electrodes. The combination of spin polarized
tunneling at the ferromagnetic-quantum dot interface and the application of an
external magnetic field that Zeeman splits the dot energy level leads to large
values of the thermopower (Seebeck coefficient). Importantly, the thermopower
can be tuned with an external gate voltage connected to the dot. We compute the
figure of merit that measures the efficiency of thermoelectric conversion and
find that it attains high values. We discuss the different contributions from
Andreev reflection processes and quasiparticle tunneling into and out of the
superconducting contact. Furthermore, we obtain dramatic variations of both the
magnetothermopower and the spin Seebeck effect, which suggest that in our
device spin currents can be controlled with temperature gradients only.",1512.06242v2
2016-05-11,Avoided ferromagnetic quantum critical point: Antiferromagnetic ground state in substituted CeFePO,"We have investigated single crystals of two substitution series
Ce(Ru$_{1-x}$Fe$_{x}$)PO and CeFe(As$_{1-y}$P$_{y}$)O in the vicinity to the
quantum critical material CeFePO by means of magnetic-susceptibility and
specific-heat measurements. We observe an antiferromagnetic ground state in the
vicinity of the quantum critical point, with pronounced metamagnetic
transitions for $H\parallel c$, which is the magnetically hard direction. Our
results verify that a ferromagnetic quantum critical point is avoided in
substituted CeFePO, because we clearly demonstrate that the ferromagnetic
ground state changes into an antiferromagnetic one, when approaching the
quantum critical point.",1605.03515v1
2016-05-13,Ferromagnetism in orthorhombic RAgAl3 (R = Ce and Pr) compounds,"We present a detailed study on magnetic, thermodynamic and transport
properties of polycrystalline RAgAl3(R = Ce and Pr) compounds. Both compounds
crystallize in orthorhombic structure, which is distorted from the tetragonal
BaAl4 structure with the space group Cmcm. Heat capacity measurement indicates
the bulk magnetic ordering of the compounds. CeAgAl3 and PrAgAl3 order
ferromagnetically at TC = 3.8 K and 5.8 K, respectively as it was confirmed
from magnetic measurements. CeAgAl3 exhibits heavy Fermion behaviour. The
Schottky behaviour in heat capacity data was observed in both compounds. The
crystalline electric field (CEF) analysis of the magnetic parts of heat
capacity of CeAgAl3 and PrAgAl3 yielded to a CEF level scheme with three
doublets and nine singlets and with an overall splitting of 51 K and 180 K,
respectively. Fit yielded a magnetic doublet state for CeAgAl3, whereas for
PrAgAl3 a pseudo-doublet ground-state with an energy difference of 15 K has
been obtained. The resistivity measurements display a low temperature drop at
the magnetic ordering temperature of the compounds. Negative magnetoresistance
(MR) due to the ferromagnetic ordering has been observed for both Ce and Pr
compounds.",1605.04261v3
2016-05-14,Observation of orbital two-channel Kondo effect in a ferromagnetic L10-MnGa film,"The experimental existence and stability of the quantum criticality point of
the two-channel Kondo (2CK) effect displaying exotic non-Fermi liquid physics
has been buried in persistent confusion despite the intensive theoretical and
experimental efforts in past three decades. Here we report an experimental
realization of the two-level system scattering-induced orbital 2CK effect in a
ferromagnetic L10-MnGa film, which is signified by a magnetic field-independent
resistivity upturn that has a logarithmic and square-root temperature
dependence beyond and below the Kondo temperature of ~14.5 K, respectively. Our
result not only evidences the robust existence of orbital 2CK effect even in
the presence of strong magnetic fields and long-range ferromagnetic ordering
but also extends the scope of 2CK host materials from nonmagnetic nanoscale
point contacts to diffusive conductors of disordered alloys.",1605.04366v4
2016-04-26,"Conductivity of weakly disordered metals close to a ""ferromagnetic"" quantum critical point","We calculate analytically the conductivity of weakly disordered metals close
to a ""ferromagnetic"" quantum critical point in the low temperature regime.
Ferromagnetic in the sense that the effective carrier potential $V(q,\omega)$,
due to critical fluctuations, is peaked at zero momentum $q=0$. Vertex
corrections, due to both critical fluctuations and impurity scattering, are
explicitly considered. We find that only the vertex corrections due to impurity
scattering, combined with the self-energy, generate appreciable effects as a
function of the temperature $T$ and the control parameter $a$, which measures
the proximity to the critical point. Our results are consistent with
resistivity experiments in several materials displaying typical Fermi liquid
behavior, but with a diverging prefactor of the $T^2$ term for small $a$.",1605.06129v3
2016-05-25,Chirality-induced magnon transport in AA-stacked bilayer honeycomb chiral magnets,"In this Letter, we study the magnetic transport in AA-stacked bilayer
honeycomb chiral magnets coupled either ferromagnetically or
antiferromagnetically. For both couplings, we observe chirality-induced gaps,
chiral protected edge states, magnon Hall and magnon spin Nernst effects of
magnetic spin excitations. For ferromagnetically coupled layers, thermal Hall
and spin Nernst conductivities do not change sign as function of magnetic field
or temperature similar to single-layer honeycomb ferromagnetic insulator. In
contrast, for antiferromagnetically coupled layers, we observe a sign change in
the thermal Hall and spin Nernst conductivities as the magnetic field is
reversed. We discuss possible experimental accessible honeycomb bilayer quantum
materials in which these effects can be observed.",1605.07971v5
2016-05-26,Direct measurement of proximity-induced magnetism at the interface between a topological insulator and a ferromagnet,"When a topological insulator (TI) is in contact with a ferromagnet, both time
reversal and inversion symmetries are broken at the interface. An energy gap is
formed at the TI surface, and its electrons gain a net magnetic moment through
short-range exchange interactions. Magnetic TIs can host various exotic quantum
phenomena, such as massive Dirac fermions, Majorana fermions, the quantum
anomalous Hall effect and chiral edge currents along the domain boundaries.
However, selective measurement of induced magnetism at the buried interface has
remained a challenge. Using magnetic second harmonic generation, we directly
probe both the in-plane and out-of-plane magnetizations induced at the
interface between the ferromagnetic insulator (FMI) EuS and the
three-dimensional TI Bi2Se3. Our findings not only allow characterizing
magnetism at the TI-FMI interface but also lay the groundwork for imaging
magnetic domains and domain boundaries at the magnetic TI surfaces.",1605.08137v2
2016-08-02,Topological Phases of Spin-1/2 Ferromagnetic--Antiferromagnetic Alternating Heisenberg Chains with Alternating Next-Nearest-Neighbour Interaction,"A series of symmetry-protected topological(SPT) and trivial spin-gap phases
in the spin-1/2 ferromagnetic--antiferromagnetic alternating Heisenberg chain
with alternating next-nearest-neighbour interaction are investigated using two
kinds of entanglement spectra defined by different divisions of the whole
chain. In the case one of the next-nearest-neighbor interaction vanishes, the
model reduces to the $\Delta$-chain in which a series of spin-gap phases are
found in J. Phys. Soc. Jpn. 77, 044707 (2008). From the degeneracy of the
entanglement spectra, these phases are identified as the SPT and trivial
phases. It is found that the ground state phases boundaries are insensitive to
the strength of the alternation in next-nearest neighbor interaction. These
results are consistent with the analysis based on the nonlinear $\sigma$ model
and exact solution on the ferromagnetic-nonmagnetic phase boundary.",1608.00837v2
2016-08-06,Zero-temperature study of a tetrameric spin-$1/2$ chain in a transverse magnetic field,"We consider an alternating Heisenberg spin-$1/2$
antiferromagnetic-ferromagnetic ($AF-F$) chain with the space modulated
dominant antiferromagnetic exchange and anisotropic ferromagnetic coupling
(tetrameric spin-$1/2$ chain). The zero-temperature effect of a symmetry
breaking transverse magnetic field on the model is studied numerically. It is
found that the anisotropy effect on the ferromagnetic coupling induces two new
gapped phases. We identified their orderings as a kind of the
stripe-antiferromagnetic phase. As a result, the magnetic phase diagram of the
tetrameric chain shows five gapped quantum phases and the system is
characterized by four critical fields which mark quantum phase transitions in
the ground state of the system with the changing transverse magnetic field. We
have also exploited the well known bipartite entanglement (name as concurrence)
and global entanglement tools to verify the occurrence of quantum phase
transitions and the corresponding critical points.",1608.02145v5
2016-08-10,Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3,"We report a detailed investigation of magnetization, magnetocaloric effect
and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to
perovskite family. Our results reveal that the compound is in canted magnetic
state (CMS) where ferromagnetic correlations are present in an
antiferromagnetic state. Magnetic entropy change of this compound follows a
power law (deltaS_M ~ H^m) dependence of magnetic field. In this compound,
inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional
magnetocaloric effect (CMCE) above it. The exponent m is found to be
independent of temperature and field only in the IMCE region. Investigation of
temperature and magnetic field dependence studies of exchange bias, reveal a
competition between effective Zeeman energy of the ferromagnetic regions and
anisotropic exchange energy at the interface between ferromagnetic and
antiferromagnetic regions. Variation of exchange bias due to temperature and
field cycling is also investigated.",1608.03223v1
2016-08-12,Intertwined nematic orders in a frustrated ferromagnet,"We investigate the quantum phases of the frustrated spin-$\frac{1}{2}$
$J_1$-$J_2$-$J_3$ Heisenberg model on the square lattice with ferromagnetic
$J_1$ and antiferromagnetic $J_2$ and $J_3$ interactions. Using the
pseudo-fermion functional renormalization group technique, we find an
intermediate paramagnetic phase located between classically ordered
ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We
observe that quantum fluctuations lead to significant shifts of the spiral
pitch angles compared to the classical limit. By computing the response of the
system with respect to various spin rotation and lattice symmetry-breaking
perturbations, we identify a complex interplay between different nematic spin
states in the paramagnetic phase. While retaining time-reversal invariance,
these phases either break spin-rotation symmetry, lattice-rotation symmetry, or
a combination of both. We therefore propose the $J_1$-$J_2$-$J_3$ Heisenberg
model on the square lattice as a paradigmatic example where different
intimately connected types of nematic orders emerge in the same model.",1608.03751v2
2016-08-18,Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains,"We predict very large changes in the room-temperature electroluminescence of
thermally-activated delayed fluorescence organic light emitting diodes near
patterned ferromagnetic films. These effects exceed the changes in a uniform
magnetic field by as much as a factor of two. We describe optimal ferromagnetic
film patterns for enhancing the electroluminescence. A full theory of the
spin-mixing processes in exciplex recombination, and how they are affected by
hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is
introduced, and is used to describe the effect of magnetic domain structures on
the luminescence in various regimes. This provides a method of enhancing light
emission rates from exciplexes and also a means of efficiently coupling
information encoded in magnetic domains to organic light emitting diode
emission.",1608.05242v1
2016-08-19,Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity,"We report a study of the structural and magnetic behavior of the topmost
magnetic layer in a ferromagnet-nonmagnet (Co-Au) multilayer system. Glancing
angle X-ray diffraction measurements performed on a series of multilayers
showed a gradually increasing degree of amorphization of the topmost magnetic
layer with increasing number of bilayers. Concurrently, the magnetic hardness
and magneto-crystalline anisotropy of the top Co layer were found to decrease,
as observed by magneto-optical Kerr effect measurements. This magnetic
softening has been discussed in the light of Herzer's random anisotropy model.
Micromagnetic simulations of the multilayer system also corroborated these
observations.",1608.05568v5
2016-08-24,Magnetic Phases in Periodically Rippled Graphene,"We study the effects that ripples induce on the electrical and magnetic
properties of graphene. The variation of the interatomic distance created by
the ripples translates in a modulation of the hopping parameter between carbon
atoms. A tight binding Hamiltonian including a Hubbard interaction term is
solved self consistently for ripples with different amplitudes and periods. We
find that, for values of the Hubbard interaction $U$ above a critical value
$U_C$, the system displays a superposition of local ferromagnetic and
antiferromagnetic ordered states. Nonetheless the global ferromagnetic order
parameter is zero. The $U_C$ depends only on the product of the period and
hopping amplitude modulation. When the Hubbard interaction is close to the
critical value of the antiferromagnetic transition in pristine graphene, the
antiferromagnetic order parameter becomes much larger than the ferromagnetic
one, being the ground state similar to that of flat graphene.",1608.06803v1
2016-12-05,The 2D percolation transition at finite temperature: The phase boundary for in-plane ferromagnetism in $\approx$2 ML Fe/W(110) films,"A two dimensional (2D) percolation transition in Fe/W(110) ultrathin magnetic
films occurs when islands in the second atomic layer percolate and resolve a
frustrated magnetic state to produce long-range in-plane ferromagnetic order.
Novel measurements of the magnetic susceptibility $\chi(\theta)$ as the films
are deposited at a constant temperature, allow the long-range percolation
transition to be observed as a sharp peak consistent with a critical phase
transition. The measurements are used to trace the
paramagnetic-to-ferromagnetic phase boundary between the $T=0$ percolation
magnetic transition and the thermal Curie magnetic transition of the undiluted
film. A quantitative comparison to critical scaling theory is made by fitting
the functional form of the phase boundary. The fitted parameters are then used
in theoretical expressions for $\chi(T)$ in the critical region of the
paramagnetic state to provide an excellent, independent representation of the
experimental measurements.",1612.01460v1
2016-12-07,Intrinsic Ferromagnetism in the Diluted Magnetic Semiconductor Co:TiO$_2$,"Here we present a study of magnetism in \CTO\ anatase films grown by pulsed
laser deposition under a variety of oxygen partial pressures and deposition
rates. Energy-dispersive spectrometry and transition electron microscopy
analyses indicate that a high deposition rate leads to a homogeneous
microstructure, while very low rate or postannealing results in cobalt
clustering. Depth resolved low-energy muon spin rotation experiments show that
films grown at a low oxygen partial pressure ($\approx 10^{-6}$ torr) with a
uniform structure are fully magnetic, indicating intrinsic ferromagnetism.
First principles calculations identify the beneficial role of low oxygen
partial pressure in the realization of uniform carrier-mediated ferromagnetism.
This work demonstrates that Co:TiO$_2$ is an intrinsic diluted magnetic
semiconductor.",1612.02235v1
2016-12-08,Synthesis and pressure and field dependent magnetic properties of the Kagome-bilayer spin liquid Ca$_{10}$Cr$_7$O$_{28}$,"We report synthesis of polycrystalline samples of the recently discovered
spin liquid material Ca$_{10}$Cr$_7$O$_{28}$ and present measurements of the
ambient and high pressure magnetic susceptibility $\chi$ versus temperature
$T$, magnetization $M$ versus magnetic field $H$ at various $T$, and heat
capacity $C$ versus $T$ at various $H$. The ambient pressure magnetic
measurements indicate the presence of both ferromagnetic and antiferromagnetic
exchange interactions with dominant ferromagnetic interactions and with the
largest magnetic energy scale $\sim 10$~K\@. The $\chi(T)$ measurements under
externally applied pressure of up to $P \approx 1$~GPa indicate the robust
nature of the spin-liquid state despite relative increase in the ferromagnetic
exchanges. $C(T)$ shows a broad anomaly at $T\approx 2.5$~K which moves to
higher temperatures in a magnetic field. The evolution of the low temperature
$C(T,H)$ and the magnetic entropy is consistent with frustrated magnetism in
Ca$_{10}$Cr$_7$O$_{28}$.",1612.02692v2
2016-12-14,Transport in Ferromagnet/Superconductor spin valves,"We consider charge transport properties in realistic, fabricable,
Ferromagnet/Superconductor spin valves having a layered structure
$F_1/N/F_2/S$, where $F_1$ and $F_2$ denote the ferromagnets, $S$ the
superconductor, and $N$ the normal metal spacer usually inserted in actual
devices. Our calculation is fully self-consistent, as required to ensure that
conservation laws are satisfied. We include the effects of scattering at all
the interfaces. We obtain results for the device conductance $G$, as a function
of bias voltage, for all values of the angle $\phi$ between the magnetizations
of the $F_1$ and $F_2$ layers and a range of realistic values for the material
and geometrical parameters in the sample. We discuss, in the context of our
results for $G$, the relative influence of all parameters on the spin valve
properties. We study also the spin current and the corresponding spin transfer
torque in $F_1/F_2/S$ structures.",1612.04696v1
2016-12-16,Polynomial-time classical simulation of quantum ferromagnets,"We consider a family of quantum spin systems which includes as special cases
the ferromagnetic XY model and ferromagnetic Ising model on any graph, with or
without a transverse magnetic field. We prove that the partition function of
any model in this family can be efficiently approximated to a given relative
error E using a classical randomized algorithm with runtime polynomial in 1/E,
system size, and inverse temperature. As a consequence we obtain a polynomial
time algorithm which approximates the free energy or ground energy to a given
additive error. We first show how to approximate the partition function by the
perfect matching sum of a finite graph with positive edge weights. Although the
perfect matching sum is not known to be efficiently approximable in general,
the graphs obtained by our method have a special structure which facilitates
efficient approximation via a randomized algorithm due to Jerrum and Sinclair.",1612.05602v1
2016-12-29,Chiral Majorana Fermion Modes on the Surface of Superconducting Topological Insulators,"The surface of superconducting topological insulators (STIs) has been
recognized as an effective $p\pm ip$ superconductivity platform for realizing
elusive Majorana fermions. Chiral Majorana modes (CMMs), which are different
from Majorana bound states localized at points, can be achieved readily in
experiments by depositing a ferromagnetic overlayer on top of the STI surface.
Here we simulate this heterostructure by employing a realistic tight-binding
model and show that the CMM appears on the edge of the ferromagnetic islands
only after the superconducting gap is inverted by the exchange coupling between
the ferromagnet and the STI. In addition, multiple CMMs can be generated by
tuning the chemical potential of the topological insulator. These results can
be applied to both proximity-effect induced superconductivity in topological
insulators and intrinsic STI compounds such as PbTaSe$_2$, BiPd and their
chemical analogues, providing a route to engineering CMMs in those materials.",1612.09276v1
2017-06-07,Coupled multiferroic domain switching in the canted conical spin spiral system Mn$_{2}$GeO$_{4}$,"Despite remarkable progress in developing multifunctional materials,
spin-driven ferroelectrics featuring both spontaneous magnetization and
electric polarization are still rare. Among such ferromagnetic ferroelectrics
are conical spin spiral magnets with a simultaneous reversal of magnetization
and electric polarization that is still little understood. Such materials can
feature various multiferroic domains that complicates their study. Here we
study the multiferroic domains in ferromagnetic ferroelectric Mn$_{2}$GeO$_{4}$
using neutron diffraction, and show that it features a double-Q conical
magnetic structure that, apart from trivial 180 degree commensurate magnetic
domains, can be described by ferromagnetic and ferroelectric domains only. We
show unconventional magnetoelectric couplings such as the magnetic-field-driven
reversal of ferroelectric polarization with no change of spin-helicity, and
present a phenomenological theory that successfully explains the
magnetoelectric coupling. Our measurements establish Mn$_{2}$GeO$_{4}$ as a
conceptually simple multiferroic in which the magnetic-field-driven flop of
conical spin spirals leads to the simultaneous reversal of magnetization and
electric polarization.",1706.02363v1
2017-06-21,Uniform magnetization dynamics of a submicron ferromagnetic coin driven by the spin-orbit coupled spin torque,"A simple model of magnetization dynamics in a ferromagnet/doped semiconductor
hybrid structure with Rashba spin-orbit interaction (SOI) driven by an applied
pulse of the electric field is proposed. The electric current excited by the
applied field is spin-polarized due to the SOI and therefore it induces the
magnetization rotation in the ferromagnetic layer via s-d exchange coupling.
Magnetization dynamics dependence on the electric pulse shape and magnitude is
analyzed for realistic values of parameters. We show that it is similar to the
dynamics of a damped nonlinear oscillator with the time-dependent frequency
proportional to the square root of the applied electric field. The
magnetization switching properties of an elliptic magnetic element are examined
as a function of the applied field magnitude and direction.",1706.06909v1
2017-06-22,Critical behavior of quasi-two-dimensional semiconducting ferromagnet CrGeTe$_3$,"The critical properties of the single-crystalline semiconducting ferromagnet
CrGeTe$_3$ were investigated by bulk dc magnetization around the paramagnetic
to ferromagnetic phase transition. Critical exponents $\beta = 0.200\pm0.003$
with critical temperature $T_c = 62.65\pm0.07$ K and $\gamma = 1.28\pm0.03$
with $T_c = 62.75\pm0.06$ K are obtained by the Kouvel-Fisher method whereas
$\delta = 7.96\pm0.01$ is obtained by the critical isotherm analysis at $T_c =
62.7$ K. These critical exponents obey the Widom scaling relation $\delta =
1+\gamma/\beta$, indicating self-consistency of the obtained values. With these
critical exponents the isotherm $M(H)$ curves below and above the critical
temperatures collapse into two independent universal branches, obeying the
single scaling equation $m = f_\pm(h)$, where $m$ and $h$ are renormalized
magnetization and field, respectively. The determined exponents match well with
those calculated from the results of renormalization group approach for a
two-dimensional Ising system coupled with long-range interaction between spins
decaying as $J(r)\approx r^{-(d+\sigma)}$ with $\sigma=1.52$.",1706.07324v1
2017-06-22,Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO$_3$,"The combination of ferromagnets with topological superconductors or
insulators allows for new phases of matter that support excitations such as
chiral edge modes and Majorana fermions. EuS, a wide-band-gap ferromagnetic
insulator with a Curie temperature around 16 K, and SrTiO$_3$ (STO), an
important substrate for engineering heterostructures, may support these phases.
We present scanning superconducting quantum interference device (SQUID)
measurements of EuS grown epitaxially on STO that reveal micron-scale
variations in ferromagnetism and paramagnetism. These variations are oriented
along the STO crystal axes and only change their configuration upon thermal
cycling above the STO cubic-to-tetragonal structural transition temperature at
105 K, indicating that the observed magnetic features are due to coupling
between EuS and the STO tetragonal structure. We speculate that the STO
tetragonal distortions may strain the EuS, altering the magnetic anisotropy on
a micron-scale. This result demonstrates that local variation in the induced
magnetic order from EuS grown on STO needs to be considered when engineering
new phases of matter that require spatially homogeneous exchange.",1706.07374v1
2017-06-27,Analytical and numerical $K_u - B$ phase diagrams for cobalt nanostructures: stability region for a Bloch skyrmion,"In this letter we calculate the energies corresponding to the different
magnetic phases present in a ferromagnetic cylinder by means of analytical
calculations. From the comparison of these energies, it is possible to
construct magnetic phase diagrams as a function of the uniaxial anisotropy of
the sample and the external magnetic field applied. As proof of concept, we
analyzed the magnetic phase diagrams for a cobalt dot of 240 nm in diameter and
70 nm in length, with an easy axis parallel to the dot axis, and with a
magnetic field applied towards or perpendicular to this axis. From these
diagrams we have obtained the stability regions for a Bloch skyrmion (Sk), a
vortex core (VC) and a ferromagnetic (F) configuration, which can point in any
$\psi$ direction. Our results provide a pathway to engineer the formation and
controllability of a skyrmion in a ferromagnetic dot to different anisotropy
constants and magnetic fields.",1706.08876v2
2017-06-27,"Intrinsic 2D ferromagnetism, quantum anomalous Hall conductivity, and fully-spin-polarized edge states of FeBr3 monolayer","It is of great interest to explore intrinsic two-dimensional ferromagnetism
and seek better two-dimensional quantum anomalous Hall insulator materials.
Here, we show that the FeBr$_3$ monolayer is an intrinsic two-dimensional
ferromagnetic material whose Curie temperature is 140 K thanks to its strong
spin exchange interaction and giant uniaxial magnetic anisotropy. Our phonon
spectra and mechanical analysis indicate that the FeBr$_3$ monolayer is
dynamically and mechanically stable. Our electronic structure calculation shows
that there is one Dirac cone at K point in the Brillouin zone and the
spin-orbit coupling opens a semiconductor gap of 33.5 meV. Further
tight-binding analysis reveals that the Chern number is equivalent to 1 and
there is a quantum anomalous Hall conductivity $\sigma _{xy} = e^2/h$, and the
chiral edge states are fully spin-polarized when an edge is created.
Furthermore, it is shown that the main results are not affected by electron
correlation effects and biaxial strain. Therefore, this FeBr$_3$ monolayer as
2D material would be useful for spintronic applications.",1706.08943v2
2017-07-05,Thermodynamics of the pyrochlore Heisenberg ferromagnet with arbitrary spin $S$,"We use the rotation-invariant Green's function method (RGM) and the
high-temperature expansion (HTE) to study the thermodynamic properties of the
spin-$S$ Heisenberg ferromagnet on the pyrochlore lattice. We examine the
excitation spectra as well as various thermodynamic quantities, such as the
order parameter (magnetization), the uniform static susceptibility, the
correlation length, the spin-spin correlations, and the specific heat, as well
as the static and dynamic structure factors. We discuss the influence of the
spin quantum number $S$ on the temperature dependence of these quantities. We
compare our results for the pyrochlore ferromagnet with the corresponding ones
for the simple-cubic lattice both having the same coordination number $z=6$. We
find a significant suppression of magnetic ordering for the pyrochlore lattice
due to its geometry with corner-sharing tetrahedra.",1707.01529v1
2017-07-19,Stability of skyrmion textures and the role of thermal fluctuations in cubic helimagnets: a new intermediate phase at low temperature,"The stability of the four known stationary points of the cubic helimagnet
energy functional: the ferromagnetic state, the conical helix, the conical
helicoid, and the skyrmion lattice, is studied by solving the corresponding
spectral problem. The only stable points are the ferromagnetic state at high
magnetic field and the conical helix at low field, and there is no metastable
state. Thermal fluctuations around the stationary point, included to quadratic
order in the saddle point expansion, destabilize the conical helix in a region
where the ferromagnetic state is unstable. Thus, a new intermediate phase
appears which, in a region of the phase diagram, is a skyrmion lattice
stabilized by thermal fluctuations. The skyrmion lattice lost the stability by
lowering temperature, and a new intermediate phase of unknown type, presumably
with three dimensional modulations, appears in the lower temperature region.",1707.06016v2
2017-07-31,Spin wave beam propagation in ferromagnetic thin film with graded refractive index: mirage effect and prospective applications,"Using analysis of iso-frequency contours of the spin-wave dispersion
relation, supported by micromagnetic simulations, we study the propagation of
spin-wave (SW) beams in thin ferromagnetic films through the areas of the
inhomogeneous refractive index. We compare the transmission and reflection of
SWs in areas with gradual and step variation of the SW refractive index. In
particular, we show the mirage effect for SWs with narrowing SW beam width, and
an application of the gradual modulation of the SWs refractive index as a
diverging lens. Furthermore, we study the propagation of SWs in ferromagnetic
stripe with modulated refractive index. We demonstrate that the system can be
considered as the graded-index waveguide, which preserves the width of the SW
beam for a long distance-the property essential for prospective applications of
magnonics.",1707.09768v4
2017-10-04,Ferromagnetic order in dipolar systems with anisotropy: application to magnetic nanoparticle supracrystals,"Single domain magnetic nanoparticles (MNP) interacting through dipolar
interactions (DDI) in addition to the magnetocrystalline energy may present a
low temperature ferromagnetic (SFM) or spin glass (SSG) phase according to the
underlying structure and the degree of order of the assembly. We study, from
Monte Carlo simulations in the framework of the effective one-spin or macrospin
models, the case of a monodisperse assembly of single domain MNP fixed on the
sites of a perfect lattice with fcc symmetry and randomly distributed easy
axes. We limit ourselves to the case of a low anisotropy, namely the onset of
the disappearance of the dipolar long-range ferromagnetic (FM) phase obtained
in the absence of anisotropy due to the disorder introduced by the latter.",1710.01532v2
2017-10-06,Work probability distribution for a ferromagnet with long-ranged and short-ranged correlations,"Work fluctuations and work probability distributions are fundamentally
different in systems with short- ranged versus long-ranged correlations.
Specifically, in systems with long-ranged correlations the work distribution is
extraordinarily broad compared to systems with shortranged correlations. This
difference profoundly affects the possible applicability of fluctuation
theorems like the Jarzynski fluctuation theorem. The Heisenberg ferromagnet ,
well below its Curie temperature, is a system with long-ranged correlations in
very low magnetic fields due to the presence of Goldstone modes. As the
magnetic field is increased the correlations gradually become short-ranged.
Hence, such a ferromagnet is an ideal system for elucidating the changes of the
work probability distribution as one goes from a domain with long-ranged
correlations to a domain with short-ranged correlations by tuning the magnetic
field. A quantitative analysis of this crossover behaviour of the work
probability distribution and the associated fluctuations is presented.",1710.02361v1
2017-10-15,Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO$_2$,"We study the electronic structure of the Pd-terminated surface of the
non-magnetic delafossite oxide metal PdCoO$_2$. Combining angle-resolved
photoemission spectroscopy and density-functional theory, we show how an
electronic reconstruction driven by surface polarity mediates a Stoner-like
magnetic instability towards itinerant surface ferromagnetism. Our results
reveal how this leads to a rich multi-band surface electronic structure, and
provide spectroscopic evidence for an intriguing sample-dependent coupling of
the surface electrons to a bosonic mode which we attribute to electron-magnon
interactions. Moreover, we find similar surface state dispersions in PdCrO$_2$,
suggesting surface ferromagnetism persists in this sister compound despite its
bulk antiferromagnetic order.",1710.05392v1
2017-10-23,"Electrically tunable exchange splitting in bilayer graphene on monolayer Cr$_2$X$_2$Te$_6$ with X=Ge, Si, and Sn","We investigate the electronic band structure and the proximity exchange
effect in bilayer graphene on a family of ferromagnetic multilayers
Cr$_2$X$_2$Te$_6$, X=Ge, Si, and Sn, with first principles methods. In each
case the intrinsic electric field of the heterostructure induces an orbital gap
on the order of 10 meV in the graphene bilayer. The proximity exchange is
strongly band dependent. For example, in the case of Cr$_2$Ge$_2$Te$_6$, the
low-energy valence band of bilayer graphene has exchange splitting of 8 meV,
while the low energy conduction band's splitting is 30 times less (0.3 meV).
This striking discrepancy stems from the layer-dependent hybridization with the
ferromagnetic substrate. Remarkably, applying a vertical electric field of a
few V/nm reverses the exchange, allowing us to effectively turn ON and OFF
proximity magnetism in bilayer graphene. Such a field-effect should be generic
for van der Waals bilayers on ferromagnetic insulators, opening new
possibilities for spin-based devices.",1710.08117v2
2017-10-25,Josephson Effect in Singlet Superconductor-Ferromagnet-Triplet Superconductor Junction,"We study the current-phase relation of a ballistic SIFIT junction, consisting
of a spin-singlet superconductor (S), a weak ferromagnetic metal (F), a
spin-triplet superconductor (T), and insulating ferromagnetic interfaces (I).
We use the generalized quasiclassical formalism developed by A. Millis et al.
to compute the current density and the free energy of the junction for
arbitrary orientation of the magnetizations of the junction barrier. We
investigate in detail the effect of the distribution of magnetization on the
various harmonics of the current-phase relation and the transition of the
ground state of the junction. The $\phi$-state junction can be realized for a
noncollinear orientation of the barrier magnetizations in the plane
perpendicular to the d-vector of the triplet superconductor.",1710.09082v1
2017-10-27,Single shot all optical switching of intrinsic micron size magnetic domains of a Pt/Co/Pt ferromagnetic stack,"We demonstrate that the magnetization reversal in a ferromagnetic Pt/Co/Pt
stack can be induced by a single femtosecond laser pulse. We find that the size
of the switched spot is comparable to the size of the intrinsic magnetic
domains. It requires an absorbed energy density of $\sim$4 mJ.cm$^{-2}$, beyond
which the excited spot fragments into a multidomain structure. The switching
process occurs back and forth with subsequent laser pulses and it is
helicity-independent. Furthermore, the dynamics of the magnetization reversal
occurs in a timescale less than one microsecond. These results suggest that all
optical switching in ferromagnetic films requires to match the laser spot with
the specific domain sizes.",1710.10341v1
2017-12-05,Majorana bound states in hybrid 2D Josephson junctions with ferromagnetic insulators,"We consider a Josephson junction consisting of superconductor/ferromagnetic
insulator (S/FI) bilayers as electrodes which proximizes a nearby 2D electron
gas. By starting from a generic Josephson hybrid planar setup we present an
exhaustive analysis of the the interplay between the superconducting and
magnetic proximity effects and the conditions under which the structure
undergoes transitions to a non-trivial topological phase. We address the 2D
bound state problem using a general transfer matrix approach that reduces the
problem to an effective 1D Hamiltonian. This allows for straightforward study
of topological properties in different symmetry classes. As an example we
consider a narrow channel coupled with multiple ferromagnetic superconducting
fingers, and discuss how the Majorana bound states can be spatially controlled
by tuning the superconducting phases. Following our approach we also show the
energy spectrum, the free energy and finally the multiterminal Josephson
current of the setup.",1712.01684v2
2017-12-05,Third order perturbed modified Heisenberg Hamiltonian of fcc structured ferromagnetic films with seventy spin layers,"Magnetic properties of fcc structured ferromagnetic films with the number of
spin layers up to seventy was described using third order perturbed Heisenberg
Hamiltonian. The variation of magnetic easy direction, magnetic energies in
easy and hard directions, magnetic anisotropy energy and the angle between easy
and hard directions was investigated by varying the number of spin layers. Spin
exchange interaction, magnetic dipole interaction, second and fourth order
magnetic anisotropies, in and out of plane applied magnetic fields,
demagnetization factor and stress induced anisotropy were considered in the
model. Because magnetic dipole interaction and demagnetization factor represent
microscopic and macroscopic properties of the sample, respectively, both these
terms were incorporated in our theoretical model. Although our model is a
semi-classical model, some discrete variations of angle of easy axis were
observed. Our theoretical data qualitatively agree with experimental data of Fe
and Ni ferromagnetic films.",1712.02636v1
2017-12-08,Spin Hall and spin swapping torques in diffusive ferromagnets,"A complete set of the generalized drift-diffusion equations for a coupled
charge and spin dynamics in ferromagnets in the presence of extrinsic
spin-orbit coupling is derived from the quantum kinetic approach, covering
major transport phenomena, such as the spin and anomalous Hall effects, spin
swapping, spin precession and relaxation processes. We argue that the spin
swapping effect in ferromagnets is enhanced due to spin polarization, while the
overall spin texture induced by the interplay of spin-orbital and spin
precessional effects displays a complex spatial dependence that can be
exploited to generate torques and nucleate/propagate domain walls in
centrosymmetric geometries without use of external polarizers, as opposed to
the conventional understanding of spin-orbit mediated torques.",1712.03009v1
2017-12-14,Quantum simulation of ferromagnetic Heisenberg model,"Large quantum simulators, with sufficiently many qubits to be impossible to
simulate classically, become hard to experimentally validate. We propose two
tests of a quantum simulator with Heisenberg interaction in a linear chain of
spins. In the first, we propagate half of a singlet state through a chain of
spin with a ferromagnetic interaction and subsequently recover the state with
an antiferromagnetic interaction. The antiferromagnetic interaction is
intrinsic to the system while the ferromagnetic one can be simulated by a
sequence of time-dependent controls of the antiferromagnetic interaction and
Suzuki-Trotter approximations. In the second test, we use the same technique to
transfer a spin singlet state from one end of a spin chain to the other. We
show that the tests are robust against parametric errors in operation of the
simulator and may be applicable even without error correction.",1712.05282v1
2017-12-20,Planar Hall torque,"Spin-orbit torques in bilayers of ferromagnetic and nonmagnetic materials
hold promise for energy efficient switching of magnetization in nonvolatile
magnetic memories. Previously studied spin Hall and Rashba torques originate
from spin-orbit interactions within the nonmagnetic material and at the bilayer
interface, respectively. Here we report a spin-orbit torque that arises from
planar Hall current in the ferromagnetic material of the bilayer and acts as
either positive or negative magnetic damping. This planar Hall torque exhibits
unusual biaxial symmetry in the plane defined by the applied electric field and
the bilayer normal. The magnitude of the planar Hall torque is similar to that
of the giant spin Hall torque and is large enough to excite auto-oscillations
of the ferromagnetic layer magnetization.",1712.07335v1
2017-12-21,Spin-triplet paired phases inside ferromagnet induced by Hund's rule coupling and electronic correlations: Application to $\mathrm{UGe}_2$,"We discuss a mechanism of real-space spin-triplet pairing, alternative to
that due to quantum paramagnon excitations, and demonstrate its applicability
to $\mathrm{UGe_2}$. Both the Hund's rule ferromagnetic exchange and
inter-electronic correlations contribute to the same extent to the equal-spin
pairing, particularly in the regime in which the weak-coupling solution does
not provide any. The theoretical results, obtained within the
orbitally-degenerate Anderson lattice model, match excellently the observed
phase diagram for $\mathrm{UGe_2}$ with the coexistent ferromagnetic (FM1) and
superconducting ($A_1$-type) phase. Additionally, weak $A_2$- and $A$-type
paired phases appear in very narrow regions near the metamaganetic (FM2
$\rightarrow$ FM1) and FM1 $\rightarrow$ paramagnetic first-order
phase-transition borders, respectively. The values of magnetic moments in the
FM2 and FM1 states are also reproduced correctly in a semiquantitative manner.
The Hund's metal regime is also singled out as appearing near FM1-FM2 boundary.",1712.08028v2
2018-01-23,Magnetic and Structural Properties of A-Site Ordered Chromium Spinel Sulfides: Alternating Antiferromagnetic and Ferromagnetic Interactions in the Breathing Pyrochlore Lattice,"We report a comprehensive study on the magnetic and structural properties of
the spinel sulfides LiInCr4S8, LiGaCr4S8, and CuInCr4S8, where Li+/Cu+ and
Ga3+/In3+ ions form a zinc-blende-type order. On the basis of synchrotron X-ray
diffraction and magnetization data obtained using polycrystalline samples,
these three sulfides are suggested to be breathing pyrochlore magnets with
alternating antiferromagnetic and ferromagnetic interactions on the small and
large tetrahedra, respectively. The measured magnetization processes of the
three sulfides up to 72 T are significantly different. The magnetization curves
of LiInCr4S8 and CuInCr4S8 have large hysteresis loops with different shapes,
while there is no hysteresis in that of LiGaCr4S8. Geometrical frustration of
the small tetrahedron is likely to give rise to a wide variety of ground
states, indicating the rich physics in these antiferromagnetic-ferromagnetic
breathing pyrochlore magnets.",1801.07354v1
2018-01-24,Critical behaviors of half-metallic ferromagnet Co3Sn2S2,"We have investigated the critical behavior of a shandite-type half-metal
ferromagnet Co3Sn2S2. It exhibits a second-order paramagnetic-ferromagnetic
phase transition with TC = 174 K. To investigate the nature of the magnetic
phase transition, a detailed critical exponent study has been performed. The
critical components beta, gamma, and delta determined using the modified Arrott
plot, the Kouvel-Fisher method as well as the critical isotherm analysis are
match reasonably well and follow the scaling equation, confirming that the
exponents are unambiguous and intrinsic to the material. The determined
exponents of Co3Sn2S2 deviates from theoretical estimated short-range universal
models. Instead, Co3Sn2S2 exhibits long-range order in the nature of magnetic
interaction with the spin decay as J(r) ~ 1/r^[-(d + sigma)] with sigma = 1.28.",1801.08048v1
2018-01-25,Electrical generation and detection of spin waves in a quantum Hall ferromagnet,"Spin waves are collective excitations of magnetic systems. An attractive
setting for studying long-lived spin-wave physics is the quantum Hall (QH)
ferromagnet, which forms spontaneously in clean two-dimensional electron
systems at low temperature and in a perpendicular magnetic field. We used
out-of-equilibrium occupation of QH edge channels in graphene to excite and
detect spin waves in magnetically ordered QH states. Our experiments provide
direct evidence for long distance spin wave propagation through different
ferromagnetic phases in the N=0 Landau level, as well as across the insulating
canted antiferromagnetic phase. Our results will enable experimental
investigation of the fundamental magnetic properties of these exotic
two-dimensional electron systems.",1801.08534v2
2018-09-05,Microscopic understanding of magnetic interactions in bilayer CrI$_3$,"We performed the detailed microscopic analysis of the inter-layer magnetic
couplings for bilayer CrI$_3$. As the first step toward understanding the
recent experimental observations and utilizing them for device applications, we
estimated magnetic force response as well as total energy. Various van der
Waals functionals equivocally point to the ferromagnetic ground state for the
low-temperature structured bilayer CrI$_3$ which is further confirmed
independently by magnetic force response calculations. The calculated
orbital-dependent magnetic forces clearly show that $e_g$-$t_{2g}$ interaction
is the key to stabilize this ferromagnetic order. By suppressing this
ferromagnetic interaction and enhancing antiferromagnetic orbital channels of
$e_g$-$e_g$ and $t_{2g}$-$t_{2g}$, one can realize the desirable
antiferromagnetic order. We showed that high-temperature monoclinic stacking
can be the case. Our results provide unique information and insight to
understand the magnetism of multi-layer CrI$_3$ paving the way to utilize it
for applications.",1809.01388v3
2018-09-09,Spin transfer torques and spin-dependent transport in a metallic F/AF/N tunneling junction,"We study spin-dependent electron transport through a
ferromagnetic-antiferromagnetic-normal metal tunneling junction subject to a
voltage or temperature bias, in the absence of spin-orbit coupling. We derive
microscopic formulas for various types of spin torque acting on the
antiferromagnet as well as for charge and spin currents flowing through the
junction. The obtained results are applicable in the limit of slow
magnetization dynamics. We identify a parameter regime in which an
unconventional damping-like torque can become comparable in magnitude to the
equivalent of the conventional Slonczewski's torque generalized to
antiferromagnets. Moreover, we show that the antiferromagnetic sublattice
structure opens up a channel of electron transport which does not have a
ferromagnetic analogue and that this mechanism leads to a pronounced field-like
torque. Both charge conductance and spin current transmission through the
junction depend on the relative orientation of the ferromagnetic and the
antiferromagnetic vectors (order parameters). The obtained formulas for charge
and spin currents allow us to identify the microscopic mechanisms responsible
for this angular dependence and to assess the efficiency of an
antiferromagnetic metal acting as a spin current polarizer.",1809.02950v1
2018-09-22,Global Memory from Local Hysteresis in an Amorphous Solid,"A disordered material that cannot relax to equilibrium, such as an amorphous
or glassy solid, responds to deformation in a way that depends on its past. In
experiments we train a 2D athermal amorphous solid with oscillatory shear, and
show that a suitable readout protocol reveals the shearing amplitude. When
shearing alternates between two amplitudes, signatures of both values are
retained only if the smaller one is applied last. We show that these behaviors
arise because individual clusters of rearrangements are hysteretic and
dissipative, and because different clusters respond differently to shear. These
roles for hysteresis and disorder are reminiscent of the return-point memory
seen in ferromagnets and many other systems. Accordingly, we show how a simple
model of a ferromagnet can reproduce key results of our experiments and of
previous simulations. Unlike ferromagnets, amorphous solids' disorder is
unquenched; they require ""training"" to develop this behavior.",1809.08505v3
2018-09-25,Axion Insulator State in a Ferromagnet/Topological Insulator/Antiferromagnet Heterostructure,"We propose to use ferromagnetic insulator MnBi2Se4/Bi2Se3/antiferromagnetic
insulator Mn2Bi2Se5 heterostructures for the realization of the axion insulator
state. Importantly, the axion insulator state in such heterostructures only
depends on the magnetization of the ferromagnetic insulator and hence can be
observed in a wide range of external magnetic field. Using density functional
calculations and model Hamiltonian simulations, we find that the top and bottom
surfaces have opposite half-quantum Hall conductance, with a sizable global
spin gap of 5.1 meV opened for the topological surface states of Bi2Se3. Our
work provides a new strategy for the search of axion insulators by using van
der Waals antiferromagnetic insulators along with three-dimensional topological
insulators.",1809.09265v2
2018-09-26,The spin-$\frac{1}{2}$ Heisenberg ferromagnet on the pyrochlore lattice: A Green's function study,"We consider the pyrochlore-lattice quantum Heisenberg ferromagnet and discuss
the properties of this spin model at arbitrary temperatures. To this end, we
use the Green's function technique within the random-phase (or Tyablikov)
approximation as well as the linear spin-wave theory and quantum Monte Carlo
simulations. We compare our results to the ones obtained recently by other
methods to corroborate our findings. Finally, we contrast our results with the
ones for the simple-cubic-lattice case: both lattices are identical at the
mean-field level. We demonstrate that thermal fluctuations are more efficient
in the pyrochlore case (finite-temperature frustration effects). Our results
may be of use for interpreting experimental data for ferromagnetic pyrochlore
materials.",1809.09951v1
2018-09-27,Magnetization induced shape transformations in flexible ferromagnetic rings,"Flexible ferromagnetic rings are spin-chain magnets, in which the magnetic
and mechanical subsystems are coupled. The coupling is achieved through the
tangentially oriented anisotropy axis. The possibility to operate the mechanics
of the nanomagnets by controlling their magnetization is an important issue for
the nanorobotics applications. A minimal model for the deformable curved
anisotropic Heisenberg ferromagnetic wire is proposed. An equilibrium phase
diagram is constructed for the closed loop geometry: (i) A vortex state with
vanishing total magnetic moment is typical for relatively large systems; in
this case the wire has the form of a regular circle. (ii) A topologically
trivial onion state with the planar magnetization distribution is realized in
small enough systems; magnetic loop is elliptically deformed. By varying
geometrical and elastic parameters a phase transition between the vortex and
onion states takes place. The detailed analytical description of the phase
diagram is well confirmed by numerical simulations.",1809.10622v1
2018-10-01,Energy-momentum tensor of a ferromagnet,"The energy-momentum tensor of a ferromagnet derived according to the standard
prescription of Noether's theorem has a major flaw: the term originating from
the spin Berry phase is gauge-dependent. As a consequence, some physical
quantities computed from the tensor show unphysical behavior. For example, the
presence of a spin-polarized current does not affect the energy of the domain
wall in the commonly accepted gauge, which implies-incorrectly-the absence of
the adiabatic spin torque. In other gauges, the spin torque shows unphysical
glitches occurring when the plane of magnetization crosses the Dirac string
associated with a magnetic monopole in spin space. We derive a gauge-invariant
energy-momentum tensor that is free from these artifacts but requires the
addition of an extra spatial dimension, with the ferromagnet living on its
boundary. It can be obtained most directly from the Wess-Zumino action for
spins, which relies on the same extra dimension.",1810.01006v2
2018-10-02,Switchable Weyl nodes in topological Kagome ferromagnet Fe3Sn2,"The control of topological quantum materials is the prerequisite for novel
devices exploiting these materials. Here we propose that the room temperature
ferromagnet Fe3Sn2, whose fundamental building blocks are Kagome bilayers of
iron, hosts Weyl nodes at the Fermi level which can move in momentum space
depending on the direction of the magnetization, itself readily controlled
either by modest external fields or temperature. The proposal is derived from
density functional calculations, including a mean field treatment of Hubbard
repulsion U, which have been validated by comparison with angle-resolved
photoemission data. Ferromagnetism with magnetization along certain directions
is shown to lift the Weyl degeneracies, while at the same time inducing texture
in the quasiparticle spin polarizations mapped in reciprocal space. In
particular, the polarization is attenuated and then rotated from parallel to
perpendicular to antiparallel to the magnetization as Weyl points derived from
crossing of majority and minority spin bands are traversed.",1810.01514v1
2018-10-03,Location of zeros for the partition function of the Ising model on bounded degree graphs,"The seminal Lee-Yang theorem states that for any graph the zeros of the
partition function of the ferromagnetic Ising model lie on the unit circle in
$\mathbb C$. In fact the union of the zeros of all graphs is dense on the unit
circle. In this paper we study the location of the zeros for the class of
graphs of bounded maximum degree $d\geq 3$, both in the ferromagnetic and the
anti-ferromagnetic case. We determine the location exactly as a function of the
inverse temperature and the degree $d$. An important step in our approach is to
translate to the setting of complex dynamics and analyze a dynamical system
that is naturally associated to the partition function.",1810.01699v3
2018-10-15,Ferromagnetic and Antiferromagnetic Coupling of Spin Molecular Interfaces with High Thermal Stability,"We report an advanced organic spin-interface architecture with magnetic
remanence at room temperature, constituted by metal phthalocyanine molecules
magnetically coupled with Co layer(s), mediated by graphene. Fe- and
Cu-phthalocyanines assembled on graphene/Co have identical structural
configurations, but FePc couples antiferromagnetically with Co up to room
temperature, while CuPc couples ferromagnetically with weaker coupling and
thermal stability, as deduced by element-selective X-ray magnetic circular
dichroic signals. The robust antiferromagnetic coupling is stabilized by a
superexchange interaction, driven by the out-of-plane molecular orbitals
responsible of the magnetic ground state and electronically decoupled from the
underlying metal via the graphene layer, as confirmed by ab initio theoretical
predictions. These archetypal spin interfaces can be prototypes to demonstrate
how antiferromagnetic and/or ferromagnetic coupling can be optimized by
selecting the molecular orbital symmetry.",1810.06317v1
2018-10-17,Role of Tin and Carbon in the magnetic interactions in Mn$_3$SnC,"In this paper we attempt to understand the role of tin and carbon in magnetic
interactions in Mn$_3$SnC. Mn$_3$SnC exhibits a time dependent magnetic
configuration and a complex magnetic ground state with both ferromagnetic and
antiferromagnetic orders. Such a magnetic state is attributed to presence of
distorted Mn$_6$C octahedra with long and short Mn--Mn bonds. Our studies show
that C deficiency increases the tensile strain on the Mn$_6$C octahedra which
elongates Mn--Mn bonds and strengthens ferromagnetic interactions while Sn
deficiency tends to ease out the strain resulting in shorter as well as longer
Mn--Mn bond distances in comparison with stoichiometric Mn$_3$SnC. Such a
variation strengthens both, ferromagnetic and antiferromagnetic interactions.
Thus the structural strain caused by both Sn and C is responsible for complex
magnetic ground state of Mn$_3$SnC.",1810.07482v1
2018-10-18,A novel chiral spin texture: Antiferromagnetic Skyrmionium,"Exotic spin textures viz. chiral domain wall, vortices, skyrmion,
skyrmionium, etc. have recently emerged as active field of research because of
their potential applications in high density data storage technology and logic
gate computing. Magnetic skyrmionium is a skyrmion like soliton, which carries
zero topological quantum number. Skyrmioniums are superior to conventional
skyrmions in ferromagnets due to their negligible skyrmion hall effect and
higher velocity. The physical properties of both skyrmion and skyrmionium have
been investigated rigorously in ferromagnetic systems. Recent observations hint
that such chiral spin structures in antiferromagnetic (AFM) systems are more
promising in comparison to the ferromagnetic ones because of their robustness
towards external perturbation, absence of Skyrmion hall effect, etc. However
skyrmionium in AFM materials are not reported in literature so far. In this
work, we demonstrate that skyrmionium can be created and stabilized in AFM
materials by application of spin polarized current in an experimentally
feasible geometry. We have further studied the dynamics of AFM skyrmionium by
applying spin polarized current.",1810.08262v2
2018-10-24,Photoinduced topological spin texture in a metallic ferromagnet,"Photoinduced nonequilibrium spin structure is examined in the double-exchange
model, in which itinerant electrons couple with localized spins through the
ferromagnetic Hund coupling. In particular, we focus on the transient spin
structure from the initial ferromagnetic metallic state to the steady
antiferromagnetic ordered state reported in [Phys. Rev. Lett. 119, 207202
(2017)]. By solving the Schr\""odinger equation combined with the
Landau-Lifshitz-Gilbert equation, we find finite winding number and chirality,
which implies emergence of topological chiral spin textures. These observations
are reproduced by a calculation where spin dynamics after sudden quench of the
chemical potential are examined in larger clusters. A possible mechanism of the
topological spin texture in the transient dynamics is discussed.",1810.10244v1
2018-10-26,Trajectory Generation for Millimeter Scale Ferromagnetic Swimmers: Theory and Experiments,"Microrobots have the potential to impact many areas such as microsurgery,
micromanipulation and minimally invasive sensing. Due to their small size,
microrobots swim in a regime that is governed by low Reynolds number
hydrodynamics. In this paper, we consider small scale artificial swimmers that
are fabricated using ferromagnetic filaments and locomote in response to time
varying external magnetic fields. We motivate the design of previously proposed
control laws using tools from geometric mechanics and also demonstrate how new
control laws can be synthesized to generate net translation in such swimmers.
We further describe how to modify these control inputs to make the swimmers
track rich trajectories in the workspace by investigating stability properties
of their limit cycles in the orientation angles phase space. Following a
systematic design optimization, we develop a principled approach to encode
internal magnetization distributions in millimeter scale ferromagnetic
filaments. We verify and demonstrate this procedure experimentally and finally
show translation, trajectory tracking and turning in place locomotion in these
optimal swimmers using a Helmholtz coils setup.",1810.11191v1
2018-10-29,Hydrodynamic sound modes and Galilean symmetry breaking in a magnon fluid,"The non-interacting magnon gas description in ferromagnets breaks down at
finite magnon density where momentum-conserving collisions between magnons
become important. Observation of the collision-dominated regime, however, has
been hampered by the lack of probes to access the energy and lengthscales
characteristic of this regime. Here we identify a key signature of the
collision-dominated hydrodynamic regime---a magnon sound mode---which governs
dynamics at low frequencies and can be detected with recently-introduced spin
qubit magnetometers. The magnon sound mode is an excitation of the longitudinal
spin component with frequencies below the spin wave continuum in gapped
ferromagnets. We also show that, in the presence of exchange interactions with
SU(2) symmetry, the ferromagnet hosts an usual hydrodynamic regime that lacks
Galilean symmetry at all energy and lengthscales. The hydrodynamic sound mode,
if detected, can lead to a new platform to explore hydrodynamic behavior in
quantum materials.",1810.12333v2
2019-06-05,Large Anomalous Hall Effect in Topological Insulators with Proximitized Ferromagnetic Insulators,"We report a proximity-driven large anomalous Hall effect in all-telluride
heterostructures consisting of ferromagnetic insulator Cr2Ge2Te6 and
topological insulator (Bi,Sb)2Te3. Despite small magnetization in the
(Bi,Sb)2Te3 layer, the anomalous Hall conductivity reaches a large value of
0.2e2/h in accord with a ferromagnetic response of the Cr2Ge2Te6. The results
show that the exchange coupling between the surface state of the topological
insulator and the proximitized Cr2Ge2Te6 layer is effective and strong enough
to open the sizable exchange gap in the surface state.",1906.02159v1
2019-06-05,Uncovering A Two-Dimensional Semiconductor with Intrinsic Ferromagnetism at Room Temperature,"Two-dimensional materials have been gaining great attention as they displayed
a broad series of electronic properties that ranging from superconductivity to
topology. Among them, those which possess magnetism are most desirable,
enabling us to manipulate charge and spin simultaneously. Here, based on
first-principles calculation, we demonstrate monolayer chromium iodide arsenide
(CrIAs), an undiscovered stable two-dimensional material, is an intrinsic
ferromagnetic semiconductor with out-of-plane spin magnetization. The indirect
bandgaps are predicted to be 0.32 eV for majority spin and 3.31 eV for minority
spin, large enough to preserve semiconducting features at room temperature. Its
Curie temperature, estimated by Heisenberg model with magnetic anisotropic
energy using Monte Carlo method, is as high as 655 K that well above the room
temperature, owing to strong direct exchange interaction between chromium d and
iodine p orbitals. This work offers the affirmative answer of whether there
exists two-dimensional ferromagnetic semiconductor at room temperature. And the
practical realization of quantum spintronic devices, which have been suppressed
because of lacking suitable room temperature magnetic materials, would embrace
a great opportunity.",1906.05444v1
2019-06-17,Local Photothermal Control of Phase Transitions for On-demand Room-temperature Rewritable Magnetic Patterning,"The ability to make controlled patterns of magnetic structures within a
nonmagnetic background is essential for several types of existing and proposed
technologies. Such patterns provide the foundation of magnetic memory and logic
devices, allow the creation of artificial spin-ice lattices and enable the
study of magnon propagation. Here, we report a novel approach for magnetic
patterning that allows repeated creation and erasure of arbitrary shapes of
thin-film ferromagnetic structures. This strategy is enabled by epitaxial
Fe$_{0.52}$Rh$_{0.48}$ thin films designed so that both ferromagnetic and
antiferromagnetic phases are bistable at room temperature. Starting with the
film in a uniform antiferromagnetic state, we demonstrate the ability to write
arbitrary patterns of the ferromagnetic phase by local heating with a focused
laser. If desired, the results can then be erased by cooling with a
thermoelectric cooler and the material repeatedly re-patterned.",1906.07239v1